ORCID Profile
0000-0003-2041-0704
Current Organisation
Utrecht University
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Publisher: Copernicus GmbH
Date: 25-11-2013
Abstract: Abstract. A maximum in the strength of Agulhas leakage has been registered at the interface between the Indian and South Atlantic oceans during glacial Termination II (T-II). This presumably transported the salt and heat necessary for maintaining the Atlantic circulation at rates similar to the present day. However, it was never shown whether these waters were effectively incorporated into the South Atlantic gyre, or whether they retroflected into the Indian and/or Southern oceans. To resolve this question, we investigate the presence of paleo Agulhas rings from a sediment core on the central Walvis Ridge, almost 1800 km farther into the Atlantic Basin than previously studied. Analysis of a 60 yr data set from the global-nested INALT01 model allows us to relate density perturbations at the depth of the thermocline to the passage of in idual rings over the core site. Using this relation from the numerical model as the basis for a proxy, we generate a time series of variability of in idual Globorotalia truncatulinoides δ18O. We reveal high levels of pycnocline depth variability at the site, suggesting enhanced numbers of Agulhas rings moving into the South Atlantic Gyre around T-II. Our record closely follows the published quantifications of Agulhas leakage from the east of the Cape Basin, and thus shows that Indian Ocean waters entered the South Atlantic circulation. This provides crucial support for the view of a prominent role of the Agulhas leakage in the shift from a glacial to an interglacial mode of the Atlantic circulation.
Publisher: Copernicus GmbH
Date: 24-08-2021
Publisher: American Geophysical Union (AGU)
Date: 29-01-2020
DOI: 10.1029/2019JC015583
Abstract: Floating plastic debris is an increasing source of pollution in the world's oceans. Numerical simulations using models of ocean currents give insight into the transport and distribution of microplastics in the oceans, but most simulations do not account for the oscillating flow caused by global barotropic tides. Here, we investigate the influence of barotropic tidal currents on the transport and accumulation of floating microplastics, by numerically simulating the advection of virtual plastic particles released all over the world's oceans and tracking these for 13 years. We use geostrophic and surface Ekman currents from GlobCurrent and the currents caused by the four main tidal constituents (M , S , K , and O ) from the FES model. We analyze the differences between the simulations with and without the barotropic tidal currents included, focusing on the open ocean. In each of the simulations, we see that microplastic accumulates in regions in the subtropical gyres, which is in agreement with observations. The formation and location of these accumulation regions remain unaffected by the barotropic tidal currents. However, there are a number of coastal regions where we see differences when the barotropic tidal currents are included. Due to uncertainties of the model in coastal regions, further investigation is required in order to draw conclusions in these areas. Our results suggest that, in the global open ocean, barotropic tidal currents have little impact on the transport and accumulation of floating microplastic and can thus be neglected in simulations aimed at studying microplastic transport in the open ocean.
Publisher: American Geophysical Union (AGU)
Date: 10-2015
DOI: 10.1002/2015JC010972
Publisher: Wiley
Date: 13-03-2020
DOI: 10.1111/EVO.13946
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-853
Abstract: & & Understanding the pathways of floating material (e.g. larvae, plastics, oil) at the surface ocean is important to improve our knowledge on the surface circulation and for its ecological and environmental impacts.& For ex le, knowing where floating plastic and oil spills accumulate in the surface ocean can help ocean clean-up strategies.& One of the main methods of research is virtual particle simulations, which simulate the dispersion of floating material in the Ocean.& & & & & & & & & & & Previous studies have tried to understand the surface dispersion and accumulation via these numerical simulations. To define the circulation, the velocity outputs of ocean general circulation models are needed. Oceanic models have improved in the past years, but many still do not fully represent the ocean dynamics at the fine-scales (below 100 km).& The spatial resolution of ocean models and whether they include a tidal-forcing are two important model parameterizations that can determine how well the ocean dynamics are represented at the fine-scales. In this study we try to answer: How do these model characteristics affect the dispersion and accumulation of virtual particles at the ocean surface?& & & & & & & & & To answer this, we use the ocean surface velocity outputs of different NEMO simulations to simulate the trajectories of virtual particles, and we evaluate the impact of different NEMO simulations& #8217 spatial resolution and the presence or not of a tidal-forcing. As tidal-forcing has a big impact on the ocean model& #8217 s representation of internal tides and waves, we focus on a region where there is a high internal-tide signal: the Azores Islands.& We evaluate these impacts by looking at whether there is a difference in particles& #8217 accumulation and dispersion in the different model scenarios.& &
Publisher: American Geophysical Union (AGU)
Date: 23-02-2022
DOI: 10.1029/2021GL096859
Abstract: Some lipid‐biomarker‐based sea surface temperature (SST) proxies applied in the modern Mediterranean Sea exhibit large offsets from expected values, generating uncertainties in climate reconstructions. Lateral transport of proxy carriers along ocean currents prior to burial can contribute to this offset between reconstructed and expected SSTs. We perform virtual particle tracking experiments to simulate transport prior to and during sinking and derive a quantitative estimate of transport bias for alkenones and glycerol dibiphytanyl glycerol tetraethers (GDGTs), which form the basis of the U K’ 37 and TEX 86 paleothermometers, respectively. We use a simple 30‐day surface advection scenario and sinking speeds appropriate for the export of various proxy carriers (6, 12, 25, 50, 100, 250, 500, and 1000 md −1 ). For the assessed scenarios, lateral transport bias is generally small (always .85°C) within the Mediterranean Sea and does not substantially contribute to uncertainties in U K’ 37 ‐ or TEX 86 ‐based SSTs.
Publisher: Copernicus GmbH
Date: 14-10-2019
Abstract: Abstract. The Galápagos Archipelago and Galápagos Marine Reserve lie 1000 km off the coast of Ecuador and are among the world's most iconic wildlife refuges. However, plastic litter is now found even in this remote island archipelago. Prior to this study, the sources of this plastic litter on Galápagos coastlines were unidentified. Local sources are widely expected to be small, given the limited population and environmentally conscious tourism industry. Here, we show that remote sources of plastic pollution are also fairly localised and limited to nearby fishing regions and South American and Central American coastlines, in particular northern Peru and southern Ecuador. Using virtual floating plastic particles transported in high-resolution ocean surface currents, we analysed the plastic origin and fate using pathways and connectivity between the Galápagos region and the coastlines as well as known fishery locations around the east Pacific Ocean. We also analysed how incorporation of wave-driven currents (Stokes drift) affects these pathways and connectivity. We found that only virtual particles that enter the ocean from Peru, Ecuador, and (when waves are not taken into account) Colombia can reach the Galápagos region. It takes these particles a few months to travel from their coastal sources on the American continent to the Galápagos region. The connectivity does not seem to vary substantially between El Niño and La Niña years. Identifying these sources and the timing and patterns of the transport can be useful for identifying integrated management opportunities to reduce plastic pollution from reaching the Galápagos Archipelago.
Publisher: American Geophysical Union (AGU)
Date: 2021
DOI: 10.1029/2020JC016416
Publisher: Frontiers Media SA
Date: 31-03-2017
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7DT02930F
Abstract: The distribution of Fe( ii ) and Ni( ii ) over two distinct metal sites in [Fe 9−x Ni x ] clusters is studied by X-ray crystallography, Mössbauer and XRF spectroscopies, and DFT calculations.
Publisher: American Geophysical Union (AGU)
Date: 04-2015
DOI: 10.1002/2014JC010549
Abstract: The Pacific Equatorial Undercurrent (EUC) transports water originating from a number of distinct source regions, eastward across the Pacific Ocean. It is responsible for supplying nutrients to the productive eastern Equatorial Pacific Ocean. Of particular importance is the transport of iron by the EUC the limiting nutrient in that region. Although the mean circulation and sources of EUC water are reasonably well understood, it is unclear how the contribution of water from these sources to the EUC vary on seasonal to interannual timescales. Here a Lagrangian analysis is applied to the eddy‐resolving OFAM3 ocean simulation in order to identity variability in the makeup of the EUC over an 18 year period (1993–2010). While ENSO has an influence on the variability of source transport contributions to the EUC, the signal of increased (decreased) transport of water from the LLWBCs during El Niño (La Niña) periods does not translate to substantial changes in the makeup of the EUC between 165°E and 140°W. It is hypothesized that this is due to the large spread in travel times of water parcels as they travel from the source regions into the EUC. The consequent erosion of transport anomalies generated at the different western boundary source regions associated with ENSO may help explain why previous studies found little relationship between variability in iron fluxes off Papua New Guinea shelves and the chlorophyll response in the eastern tropical Pacific.
Publisher: Copernicus GmbH
Date: 29-05-2020
DOI: 10.5194/NPG-2020-18
Abstract: Abstract. The basinwide surface transport of tracers such as heat, nutrients and plastic in the North Atlantic Ocean is organized into large scale flow structures such as the Western Boundary Current and the Subtropical and Subpolar Gyres. Being able to identify these features from drifter data is important for studying tracer dispersal, but also to detect changes in the large scale surface flow due to climate change. We propose a new and conceptually simple method to detect groups of trajectories with similar dynamical behaviour from drifter data using network theory and normalized cut spectral clustering. Our network is constructed from conditional bin-drifter probability distributions and naturally handles drifter trajectories with data gaps and different lifetimes. The eigenvalue problem of the respective Laplacian can be replaced by a singular value decomposition of a related sparse data matrix. The construction of this matrix scales with O(NM + Nτ), where N is the number of particles, M the number of bins and τ the number of time steps. The concept behind our network construction is rooted in a particle's symbolic itinerary derived from its trajectory and a state space partition, which we incorporate in its most basic form by replacing a particle's itinerary by a probability distribution over symbols. We represent these distributions as the links of a bipartite graph, connecting particles and symbols. We apply our method to the periodically driven double-gyre flow and successfully identify well-known features. Exploiting the duality between particles and symbols defined by the bipartite graph, we demonstrate how a direct low-dimensional coarse definition of the clustering problem can still lead to relatively accurate results for the most dominant structures, and resolve features down to scales much below the coarse graining scale. Our method also performs well in detecting structures with incomplete trajectory data, which we demonstrate for the double-gyre flow by randomly removing data points. We finally apply our method to a set of ocean drifter trajectories and present the first network-based clustering of the North Atlantic surface transport based on surface drifters, successfully detecting well-known regions such as the Subpolar and Subtropical Gyres, the Western Boundary Current region and the Carribean Sea.
Publisher: Copernicus GmbH
Date: 14-11-2020
Abstract: Abstract. The basin-wide surface transport of tracers such as heat, nutrients and plastic in the North Atlantic Ocean is organized into large-scale flow structures such as the Western Boundary Current and the Subtropical and Subpolar gyres. Being able to identify these features from drifter data is important for studying tracer dispersal but also for detecting changes in the large-scale surface flow due to climate change. We propose a new and conceptually simple method to detect groups of trajectories with similar dynamical behaviour from drifter data using network theory and normalized cut spectral clustering. Our network is constructed from conditional bin-drifter probability distributions and naturally handles drifter trajectories with data gaps and different lifetimes. The eigenvalue problem of the respective Laplacian can be replaced by a singular value decomposition of a related sparse data matrix. The construction of this matrix scales with O(NM+Nτ), where N is the number of particles, M the number of bins and τ the number of time steps. The concept behind our network construction is rooted in a particle's symbolic itinerary derived from its trajectory and a state space partition, which we incorporate in its most basic form by replacing a particle's itinerary by a probability distribution over symbols. We represent these distributions as the links of a bipartite graph, connecting particles and symbols. We apply our method to the periodically driven double-gyre flow and successfully identify well-known features. Exploiting the duality between particles and symbols defined by the bipartite graph, we demonstrate how a direct low-dimensional coarse definition of the clustering problem can still lead to relatively accurate results for the most dominant structures and resolve features down to scales much below the coarse graining scale. Our method also performs well in detecting structures with incomplete trajectory data, which we demonstrate for the double-gyre flow by randomly removing data points. We finally apply our method to a set of ocean drifter trajectories and present the first network-based clustering of the North Atlantic surface transport based on surface drifters, successfully detecting well-known regions such as the Subpolar and Subtropical gyres, the Western Boundary Current region and the Caribbean Sea.
Publisher: The Royal Society
Date: 22-08-2014
Abstract: Climate-driven changes in biotic interactions can profoundly alter ecological communities, particularly when they impact foundation species. In marine systems, changes in herbivory and the consequent loss of dominant habitat forming species can result in dramatic community phase shifts, such as from coral to macroalgal dominance when tropical fish herbivory decreases, and from algal forests to ‘barrens’ when temperate urchin grazing increases. Here, we propose a novel phase-shift away from macroalgal dominance caused by tropical herbivores extending their range into temperate regions. We argue that this phase shift is facilitated by poleward-flowing boundary currents that are creating ocean warming hotspots around the globe, enabling the range expansion of tropical species and increasing their grazing rates in temperate areas. Overgrazing of temperate macroalgae by tropical herbivorous fishes has already occurred in Japan and the Mediterranean. Emerging evidence suggests similar phenomena are occurring in other temperate regions, with increasing occurrence of tropical fishes on temperate reefs.
Publisher: Springer Science and Business Media LLC
Date: 16-07-2018
Publisher: Inter-Research Science Center
Date: 21-07-2015
DOI: 10.3354/MEPS11362
Publisher: American Meteorological Society
Date: 02-2014
Abstract: The strongly eddying version of the Parallel Ocean Program (POP) is used in two 45-yr simulations to investigate the response of the Atlantic meridional overturning circulation (AMOC) to strongly enhanced freshwater input due to Greenland melting, with an integrated flux of 0.5 Sverdrups (Sv 1 Sv ≡ 106 m3 s−1). For comparison, a similar set of experiments is performed using a noneddying version of POP. The aim is to identify the signature of the salt advection feedback in the two configurations. For this reason, surface salinity is not restored in these experiments. The freshwater input leads to a quantitatively comparable reduction of the overturning strength in the two models. To examine the importance of transient effects in the relation between AMOC strength and density distribution, the results of the eddy-resolving model are related to water mass transformation theory. The freshwater forcing leads to a reduction of the rate of light to dense water conversion in the North Atlantic, but there is no change in dense to light transformation elsewhere, implying that high density layers are continuously deflating. The main focus of the paper is on the effect of the AMOC reduction on the basinwide advection of freshwater. The low-resolution model results show a change of the net freshwater advection that is consistent with the salt advection feedback. However, for the eddy-resolving model, the net freshwater advection into the Atlantic basin appears to be unaffected, despite the significant change in the large-scale velocity structure.
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-1203
Abstract: & & We study the vertical dispersion and distribution of negatively buoyant rigid microplastics within a realistic circulation model of the Mediterranean sea. We first propose an equation describing their idealized dynamics. In that framework, we evaluate the importance of some relevant physical effects: inertia, Coriolis force, small-scale turbulence and variable seawater density, and bound the relative error of simplifying the dynamics to a constant sinking velocity added to a large-scale velocity field. We then calculate the amount and vertical distribution of microplastic particles on the water column of the open ocean if their release from the sea surface is continuous at rates compatible with observations in the Mediterranean. The vertical distribution is found to be almost uniform with depth for the majority of our parameter range. Transient distributions from flash releases reveal a non-Gaussian character of the dispersion and various diffusion laws, both normal and anomalous. The origin of these behaviors is explored in terms of horizontal and vertical flow organization.& &
Publisher: American Geophysical Union (AGU)
Date: 02-03-2020
DOI: 10.1029/2019GL086768
Publisher: American Chemical Society (ACS)
Date: 27-08-2020
Publisher: UCL Press
Date: 08-11-2022
DOI: 10.14324/RFA.06.1.23
Abstract: How is public engagement perceived to contribute to open science? This commentary highlights common reflections on this question from interviews with 12 public engagement fellows in Utrecht University’s Open Science Programme in the Netherlands. We identify four reasons why public engagement is an essential enabler of open science. Interaction between academics and society can: (1) better align science with the needs of society (2) secure a relationship of trust between science and society (3) increase the quality and impact of science and (4) support the impact of open access and FAIR data practices (data which meet principles of findability, accessibility, interoperability and reusability). To be successful and sustainable, such public engagement requires support in skills training and a form of institutionalisation in a university-wide system, but, most of all, the fellows express the importance of a formal and informal recognition and rewards system. Our findings suggest that in order to make public engagement an integral part of open science, universities should invest in institutional support, create awareness, and stimulate dialogue among staff members on how to ‘do’ good public engagement.
Publisher: Copernicus GmbH
Date: 10-12-2020
DOI: 10.5194/ESSD-12-3341-2020
Abstract: Abstract. A valuable analogue for assessing Earth's sensitivity to warming is the Last Interglacial (LIG 129–116 ka), when global temperatures (0 to +2 ∘C) and mean sea level (+6 to 11 m) were higher than today. The direct contribution of warmer conditions to global sea level (thermosteric) is uncertain. We report here a global network of LIG sea surface temperatures (SST) obtained from various published temperature proxies (e.g. faunal and floral plankton assemblages, Mg ∕ Ca ratios of calcareous organisms, and alkenone U37K′). We summarize the current limitations of SST reconstructions for the LIG and the spatial temperature features of a naturally warmer world. Because of local δ18O seawater changes, uncertainty in the age models of marine cores, and differences in s ling resolution and/or sedimentation rates, the reconstructions are restricted to mean conditions. To avoid bias towards in idual LIG SSTs based on only a single (and potentially erroneous) measurement or a single interpolated data point, here we report average values across the entire LIG. Each site reconstruction is given as an anomaly relative to 1981–2010, corrected for ocean drift, and where available seasonal estimates are provided (189 annual, 99 December–February, and 92 June–August records). To investigate the sensitivity of the reconstruction to high temperatures, we also report maximum values during the first 5 millennia of the LIG (129–124 ka). We find mean global annual SST anomalies of 0.2 ± 0.1 ∘C averaged across the LIG and an early maximum peak of 0.9 ± 0.1 ∘C, respectively. The global dataset provides a remarkably coherent pattern of higher SST increases at polar latitudes than in the tropics (demonstrating the polar lification of surface temperatures during the LIG), with comparable estimates between different proxies. Polewards of 45∘ latitude, we observe annual SST anomalies averaged across the full LIG of 0.8 ± 0.3 ∘C in both hemispheres with an early maximum peak of 2.1 ± 0.3 ∘C. Using the reconstructed SSTs suggests a mean LIG global thermosteric sea level rise of 0.08 ± 0.1 m and a peak contribution of 0.39 ± 0.1 m, respectively (assuming warming penetrated to 2000 m depth). The data provide an important natural baseline for a warmer world, constraining the contributions of Greenland and Antarctic ice sheets to global sea level during a geographically widespread expression of high sea level, and can be used to test the next inter-comparison of models for projecting future climate change. The dataset described in this paper, including summary temperature and thermosteric sea level reconstructions, is available at 0.1594/PANGAEA.904381 (Turney et al., 2019).
Publisher: Wiley
Date: 16-09-2021
Publisher: Copernicus GmbH
Date: 07-03-2016
DOI: 10.5194/TC-2016-19
Abstract: Abstract. The dramatic calving of the Mertz Glacier Tongue in 2010, triggered by the impact of iceberg B09B, reshaped the oceanographic regime across the Mertz Polynya and Commonwealth Bay, regions where high salinity shelf water (HSSW) is formed, the precursor to Antarctic bottom water (AABW). Here we compare post-calving observations with high-resolution ocean modelling which suggest that this reconfiguration has led to the development of a new polynya off Commonwealth Bay, where HSSW production continues by the grounding of B09B. Our findings demonstrate how local changes in icescape can impact formation of AABW, with implications for large-scale ocean circulation and climate.
Publisher: Springer Science and Business Media LLC
Date: 10-06-2021
Publisher: Copernicus GmbH
Date: 19-08-2019
Abstract: Abstract. With the increasing number of data produced by numerical ocean models, so increases the need for efficient tools to analyse these data. One of these tools is Lagrangian ocean analysis, where a set of virtual particles is released and their dynamics are integrated in time based on fields defining the ocean state, including the hydrodynamics and biogeochemistry if available. This popular methodology needs to adapt to the large variety of models producing these fields at different formats. This is precisely the aim of Parcels, a Lagrangian ocean analysis framework designed to combine (1) a wide flexibility to model particles of different natures and (2) an efficient implementation in accordance with modern computing infrastructure. In the new Parcels v2.0, we implement a set of interpolation schemes to read various types of discretized fields, from rectilinear to curvilinear grids in the horizontal direction, from z to s levels in the vertical direction and using grid staggering with the Arakawa A, B and C grids. In particular, we develop a new interpolation scheme for a three-dimensional curvilinear C grid and analyse its properties. Parcels v2.0 capabilities, including a suite of meta-field objects, are then illustrated in a brief study of the distribution of floating microplastic in the northwest European continental shelf and its sensitivity to various physical processes.
Publisher: Springer Science and Business Media LLC
Date: 04-03-2015
DOI: 10.1038/NCOMMS7521
Abstract: Fossils of marine microorganisms such as planktic foraminifera are among the cornerstones of palaeoclimatological studies. It is often assumed that the proxies derived from their shells represent ocean conditions above the location where they were deposited. Planktic foraminifera, however, are carried by ocean currents and, depending on the life traits of the species, potentially incorporate distant ocean conditions. Here we use high-resolution ocean models to assess the footprint of planktic foraminifera and validate our method with proxy analyses from two locations. Results show that foraminifera, and thus recorded palaeoclimatic conditions, may originate from areas up to several thousands of kilometres away, reflecting an ocean state significantly different from the core site. In the eastern equatorial regions and the western boundary current extensions, the offset may reach 1.5 °C for species living for a month and 3.0 °C for longer-living species. Oceanic transport hence appears to be a crucial aspect in the interpretation of proxy signals.
Publisher: American Geophysical Union (AGU)
Date: 05-2012
DOI: 10.1029/2011JC007684
Publisher: Copernicus GmbH
Date: 14-09-2021
DOI: 10.5194/OS-2021-83
Abstract: Abstract. Coastlines potentially harbor a large part of litter entering the oceans such as plastic waste. The relative importance of the physical processes that influence the beaching of litter is still relatively unknown. Here, we investigate the beaching of litter by analyzing a data set of litter gathered along the Dutch North Sea coast during extensive beach cleanup efforts between the years 2014–2019. This data set is unique in the sense that data is gathered consistently over various years by many volunteers (a total of 14,000), on beaches which are quite similar in substrate (sandy). This makes the data set valuable to identify what environmental variables might play an important role in the beaching process, and to explore the variability of beach litter. We investigate this by fitting a random forest machine learning regression model to the observed litter concentrations. We find that especially tides play an important role, where an increasing tidal variability and tidal height lead to less litter found on beaches. Relatively straight and exposed coastlines appear to accumulate more litter. The regression model indicates that transport of litter through the marine environment is also important in explaining beach litter variability. By understanding what processes cause the accumulation of litter on the coast, recommendations can be given for more effective removal of litter from the marine environment. We estimate that 16,000–31,400 kilograms (95 % confidence interval) of litter are located on the 365 kilometers of Dutch North Sea coastline.
Publisher: Research Square Platform LLC
Date: 02-12-2021
DOI: 10.21203/RS.3.RS-955379/V1
Abstract: Millimeter- and micrometer-sized plastics are well-documented in aquatic ecosystems, but little is known about sub-micrometer particles because conventional analytical techniques lack sufficient spatial resolution or the spectroscopic means to unambiguously identify in idual nanometer-sized plastic particles. We combined the spatial resolution of atomic force microscopy with chemical information from infrared spectroscopy to detect, identify, and count nanoplastics down to 20 nm in diameter in s les from different depths in the South Atlantic Ocean. We present evidence for the presence of polyethylene terephthalate (PET) nanoplastics in different states of degradation at 5000 m. Using lab-based ageing of PET, we demonstrate that nanoplastics can form even without light or interaction with the plastisphere, and that macroscopic PET items are a plausible source of PET nanoplastics in the ocean.
Publisher: Wiley
Date: 12-2021
Publisher: Wiley
Date: 16-09-2022
Publisher: Springer Science and Business Media LLC
Date: 30-09-2016
DOI: 10.1038/SREP34205
Abstract: The application of high-resolution genetic data has revealed that oceanographic connectivity in marine species with planktonic larvae can be surprisingly limited, even in the absence of major barriers to dispersal. Australia’s southern coast represents a particularly interesting system for studying planktonic larval dispersal, as the hydrodynamic regime of the wide continental shelf has potential to facilitate onshore retention of larvae. We used a seascape genetics approach (the joint analysis of genetic data and oceanographic connectivity simulations) to assess population genetic structure and self-recruitment in a broadcast-spawning marine gastropod that exists as a single meta-population throughout its temperate Australian range. Levels of self-recruitment were surprisingly high and oceanographic connectivity simulations indicated that this was a result of low-velocity nearshore currents promoting the retention of planktonic larvae in the vicinity of natal sites. Even though the model applied here is comparatively simple and assumes that the dispersal of planktonic larvae is passive, we find that oceanography alone is sufficient to explain the high levels of genetic structure and self-recruitment. Our study contributes to growing evidence that sophisticated larval behaviour is not a prerequisite for larval retention in the nearshore region in planktonic-developing species.
Publisher: Elsevier BV
Date: 09-2015
Publisher: Copernicus GmbH
Date: 16-06-2022
DOI: 10.5194/EGUSPHERE-2022-426
Abstract: Abstract. The Galapagos Marine Reserve was established in 1986 to ensure protection of the islands' unique bio ersity. Unfortunately, the islands are polluted by marine plastic debris and the island authorities face the challenge to effectively remove plastic from its shorelines due to limited resources. To optimise efforts, we have identified the most effective cleanup locations on the Galapagos Islands using network theory. A network is constructed from a Lagrangian simulation describing the flow of macroplastic between the various islands within the Galapagos Marine Reserve, where the nodes represent locations along the coastline and the edges the likelihood for plastic to travel from one location and beach at another. We have found four network centralities that provide the best coastline ranking to optimise the cleanup effort based on various impact metrics. In particular locations with a high retention rate are favourable for cleanup. The results indicate that using the most effective centrality for finding cleanup locations is a good strategy for heavily polluted regions if the distribution of marine plastic debris on the coastlines is unknown and limited cleanup resources are available.
Publisher: Elsevier BV
Date: 11-2017
Publisher: American Geophysical Union (AGU)
Date: 02-2009
DOI: 10.1029/2008GL036614
Publisher: American Geophysical Union (AGU)
Date: 28-02-2016
DOI: 10.1002/2016GL067757
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-5705
Abstract: & & & & & span& When faced with a question, scientists and scholars are trained to& search& academic and informal& literature to find& the answer.& But where& can& the public& find reliable& answers to& questions about the climate crisis?& After all,& the climate crisis& is a topic about which our understanding& rapidly& evolves& across a wide array of disciplines.& The validity& and reliability& of& offered& information is difficult to& assess& for non-specialists, while scientific consensus is& sometimes deliberately undermined& in popular articles. Moreover,& civil& questions about& the& climate& crisis& can be very specific, pragmatic or locally applicable, so not all answers can be found on popular sources& that& commonly& rovide only the theoretical principles or general background.& This raises the question how we can connect citizens with climate-related questions to understandable scientific expert& & /span& & span& knowledge& /span& & span& .& /span& & & & / & & & & & & span& KlimaatHelpdesk.org& is meant to become the go-to place in the Netherlands for& citizens& with climate-related questions. It is a unique,& independent,& and accessible c& /span& & span& ommunications& /span& & span& & latform that connects the& ublic& with scientists and experts, run by a volunteer group& of students and academics. People who ask& a& question on this platform will receive& a& eer-reviewed answer to their question from a network of affiliated scholars and experts. KlimaatHelpdesk& archives& the& & /span& & span& question and& & /span& & span& corresponding& & /span& & span& answer& /span& & span& & on the website and thereby& rovides an& expanding,& easily accessible source of reliable and evidence-based information. Since the official launch in November 2020, more than& & enthusiastic experts& have& answered and/or reviewed& over& & questions& in a variety of disciplines:& from& meteorology, oceanography and biology to psychology,& law,& and philosophy.& /span& & & & / & & & & & & span& KlimaatHelpdesk& also serves as& a platform for students and young academics to get involved in science outreach and public engagement, and for scientists to explain their& research& to a targeted audience.& While& KlimaatHelpdesk& is further& expanding its& reach in& the Netherlands,& & /span& & span& we also work to make& the& latform portable to other& countries and disciplines. We are& eager and& ready to share our gained experience& with the wider& Science Communication, Engagement & Outreach& community.& /span& & & & / &
Publisher: Wiley
Date: 11-11-2021
Publisher: Proceedings of the National Academy of Sciences
Date: 02-05-2016
Abstract: Our current understanding of how marine biota are adapted to magnitudes, trends, and temporal patterns of variability in sea-surface temperature has arisen from examining long-term records at key ocean locations. However, floating plankton have a different perception of their habitat because they drift in ocean currents. Here we show that upper ocean microbes can be advected up to 3,500 km in latitude in 500 d, and that their operational temperatures exceed the in situ Eulerian temperature range by up to 10 °C, even in locations with strong seasonality. This result revises the present view of thermal exposure in the upper ocean, and provides a new framework for investigating climate change impacts on planktonic organisms.
Publisher: American Geophysical Union (AGU)
Date: 05-2015
DOI: 10.1002/2014JC010557
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-10993
Abstract: The knowledge of how seawater moves around in the global ocean and transports tracers and particulates, is crucial for solving many outstanding issues in physical oceanography and climate science. Due to limited available observations, seawater pathways are often estimated by evaluating virtual particle trajectories inferred from velocity fields computed with ocean models. The quality of these Lagrangian analyses strongly depends on how well the underlying ocean model represents the ocean circulation features of interest.Here, we investigate how simulated surface particle dispersal changes, if the & #8211 often omitted or only approximated & #8211 impact of surface waves is considered. Specifically, we test the impact of new representations of wave-current interactions for the ocean model NEMO in a case study for the Mediterranean Sea. We are using velocity output from a high-resolution (1/24& #176 ) ocean-only model simulation as well as a complementary coupled ocean-wave model simulation, to answer the following questions: How do waves impact the simulated surface particle dispersal, and what is the relative impact of Stokes drift and wave-driven Eulerian currents? How well can the wave impact be approximated by the superposition of Eulerian mean and Stokes drift velocity fields obtained from independently run ocean and wave models?We find that the wave coupling leads to a decrease in the mean surface current speed in summer dominated by wave-driven Eulerian currents, and an increase in the mean surface current speed in winter dominated by Stokes drift. We further show that Lagrangian simulations with superimposed Eulerian currents and Stokes drift from independent ocean-only and wave models do not necessarily yield more realistic results for surface dispersal patterns than simulations that do not include any wave effect. This implies that & #8211 whenever possible & #8211 velocity fields from a coupled ocean-wave model should be used for surface particle dispersal simulations.
Publisher: American Geophysical Union (AGU)
Date: 2018
DOI: 10.1002/2017JC013363
Publisher: American Geophysical Union (AGU)
Date: 20-12-2011
DOI: 10.1029/2011JC007171
Publisher: American Meteorological Society
Date: 2014
DOI: 10.1175/JCLI-D-12-00714.1
Abstract: The impact of Agulhas leakage variability on the strength of the Atlantic meridional overturning circulation (AMOC) in the Community Climate System Model, version 4 (CCSM4) is investigated. In this model an advective connection exists that transports salinity anomalies from the Agulhas region into the North Atlantic on decadal (30–40 yr) time scales. However, there is no identifiable impact of Agulhas leakage on the strength of the AMOC, suggesting that the salinity variations are too weak to significantly modify the stratification in the North Atlantic. It is argued that this study is inconclusive with respect to an impact of Agulhas leakage on the AMOC. Salinity biases leave the South Atlantic and Indian Oceans too homogeneous, in particular erasing the observed salinity front in the Agulhas retroflection region. Consequently, salinity variability in the southeastern South Atlantic is found to be much weaker than observed.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 07-04-2017
Abstract: Atlantic surface circulation transports high loads of plastic debris to remote Arctic waters.
Publisher: Springer Science and Business Media LLC
Date: 16-09-2013
DOI: 10.1038/NCOMMS3457
Abstract: Although environmental selection and spatial separation have been shown to shape the distribution and abundance of marine microorganisms, the effects of advection (physical transport) have not been directly tested. Here we examine 25 s les covering all major water masses of the Southern Ocean to determine the effects of advection on microbial biogeography. Even when environmental factors and spatial separation are controlled for, there is a positive correlation between advection distance and taxonomic dissimilarity, indicating that an 'advection effect' has a role in shaping marine microbial community composition. This effect is likely due to the advection of cells increasing the probability that upstream microorganisms will colonize downstream sites. Our study shows that in addition to distance and environmental selection, advection shapes the composition of marine microbial communities.
Publisher: Copernicus GmbH
Date: 15-02-2022
Abstract: Abstract. Having descended through the water column, microplankton in ocean sediments is representative of the ocean surface environment, where it originated. Sedimentary microplankton is therefore used as an archive of past and present surface oceanographic conditions. However, these particles are advected by turbulent ocean currents during their sinking journey. So far, it is unknown to what extent this particle advection shapes the microplankton composition in sediments. Here we use global simulations of sinking particles in a strongly eddying global ocean model, and define ocean bottom provinces based on the particle surface origin locations. We find that these provinces can be detected in global datasets of sedimentary microplankton assemblages, demonstrating the effect provincialism has on the composition of sedimentary remains of surface plankton. These provinces explain the microplankton composition, in addition to, e.g., the ocean surface environment. Connected provinces have implications for the optimal spatial extent of microplankton sediment s le datasets that are used for palaeoceanographic reconstruction, and for the optimal spatial averaging of sediment s les over global datasets.
Publisher: American Chemical Society (ACS)
Date: 21-10-2022
Publisher: American Geophysical Union (AGU)
Date: 06-03-2010
DOI: 10.1029/2009JC005585
Publisher: Copernicus GmbH
Date: 26-09-2017
Publisher: Elsevier BV
Date: 2018
DOI: 10.1016/J.MARPOLBUL.2017.11.011
Abstract: There is growing global concern over the chemical, biological and ecological impact of plastics in the ocean. Remote sensing has the potential to provide long-term, global monitoring but for marine plastics it is still in its early stages. Some progress has been made in hyperspectral remote sensing of marine macroplastics in the visible (VIS) to short wave infrared (SWIR) spectrum. We present a reflectance model of sunlight interacting with a sea surface littered with macro plastics, based on geometrical optics and the spectral signatures of plastic and seawater. This is a first step towards the development of a remote sensing algorithm for marine plastic using light reflectance measurements in air. Our model takes the colour, transparency, reflectivity and shape of plastic litter into account. This concept model can aid the design of laboratory, field and Earth observation measurements in the VIS-SWIR spectrum and explain the results.
Publisher: Copernicus GmbH
Date: 24-08-2021
DOI: 10.5194/ESD-2021-48
Abstract: Abstract. Having descended through the water column, microplankton in ocean sediments are representative for the ocean surface environment, where they originated from. Sedimentary microplankton is therefore used as an archive of past and present surface oceanographic conditions. However, these particles are advected by turbulent ocean currents during their sinking journey. So far, it is unknown to what extent this particle advection shapes the microplankton composition in sediments. Here we use global simulations of sinking particles in a strongly eddying global ocean model, and define ocean bottom provinces based on the particle surface origin locations. We find that these provinces can be detected in global datasets of sedimentary microplankton assemblages, demonstrating the effect provincialism has on the composition of sedimentary remains of surface plankton. These provinces explain the microplankton composition, together with e.g. ocean surface environment. Connected provinces have implications on the optimal spatial extent of microplankton sediment s le datasets that are used for palaeoceanographic reconstructions, and on the optimal spatial averaging of sediment s les over global datasets.
Publisher: Copernicus GmbH
Date: 26-09-2017
Publisher: American Geophysical Union (AGU)
Date: 2011
DOI: 10.1029/2010GL046267
Publisher: Elsevier BV
Date: 10-2013
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-13045
Abstract: & & The northward flow in the western tropical Atlantic Ocean is carried mainly by North Brazil Current (NBC), hence playing a major role in the cross-equatorial exchange of properties. As thermocline waters reach the equator, they largely retroflect to feed the Equatorial Undercurrent (EUC), a quasi-permanent zonal current that brings salty and highly-oxygenated waters to the eastern side of the basin. This retroflection system is governed by the zonal pressure gradient, which is driven by the trade winds. Hence, the wind fluctuations represent the major source of variability at seasonal and interannual scales. However, at shorter time scales, the variability of the retroflection system may be associated with both interior and coastal waves. In the present study we describe the water mass balance at the NBC-EUC retroflection area using a combination of shipboard observations and numerical reanalysis. The observations, from an oceanographic c aign in April 2010, provide a synoptic view of the retroflection region and allow assessing the goodness of the numerical data. We then use the ocean reanalysis GLORYS2v4 to analyse the temporal variability of this region, from intra-seasonal to seasonal scales, and use Lagrangian simulations to identify the principal water mass pathways feeding the retroflection. We find a substantial seasonal cycle in the boundary and interior (southern and northern) origins of those waters that feed the EUC. Our results also show the propagation of high-frequency waves (16-30 days) along the coast from the south, probably as coastal trapped waves, while waves with 30-60 days period come from the northern hemisphere, probably as westward Rossby waves reach the coast of America and follow south as Kelvin waves. These short-term fluctuations have a high impact on the water mass pathways that feed the EUC and the retroflection structure itself.& &
Publisher: Copernicus GmbH
Date: 04-10-2021
DOI: 10.5194/GMD-2021-195
Abstract: Abstract. Turbulent mixing is a vital component of vertical particulate transport, but ocean global circulation models (OGCMs) generally have low resolution representations of near-surface mixing. Furthermore, turbulence data is often not provided in reanalysis products. We present 1D parametrizations of wind-driven turbulent mixing in the ocean surface mixed layer, which are designed to be easily included in 3D Lagrangian model experiments. Stochastic transport is computed by Markov-0 or Markov-1 models, and we discuss the advantages/disadvantages of two vertical profiles for the vertical diffusion coefficient Kz. All vertical diffusion profiles and stochastic transport models lead to stable concentration profiles for buoyant particles, which for particles with rise velocities of 0.03 and 0.003 m s−1 agree relatively well with concentration profiles from field measurements of microplastics. Markov-0 models provide good model performance for integration timesteps of Δt ≈ 30 seconds, and can be readily applied in studying the behaviour of buoyant particulates in the ocean. Markov-1 models do not consistently improve model performance relative to Markov-0 models, and require an additional parameter that is poorly constrained.
Publisher: Wiley
Date: 07-2019
DOI: 10.1002/IEAM.4147
Abstract: Plastic pollution in the marine environment is well documented. What remains less recognized and understood are the chemicals associated with it. Plastics enter the ocean with unreacted monomers, oligomers, and additives, which can leach over time. Moreover, plastics sorb organic and inorganic chemicals from surrounding seawater, for ex le, polychlorinated biphenyls (PCBs) and metals. Thus, interception and cleanup of plastics reduces the amount of chemical contaminants entering or reentering the oceans and removes those already present. Here, we estimate 1) the mass of selected chemical additives entering the global oceans with common plastic debris items, and 2) the mass of sorbed chemicals (using PCBs as a case study) associated with microplastics in selected locations. We estimate the mass of additives that entered the oceans in 2015 as constituents of 7 common plastic debris items (bottles, bottle caps, expanded polystyrene (EPS) containers, cutlery, grocery bags, food wrappers, and straws or stirrers). We calculate that approximately 190 tonnes (t) of 20 chemical additives entered the oceans with these items in 2015. We also estimate the mass of PCBs associated with microplastics in 2 coastal (Hong Kong and Hawaii) and 2 open ocean (North Pacific and South Atlantic gyres) locations, as comparative case studies. We find that the mass of chemicals is related to the mass of plastics in a location, with greater mass of PCBs closer to the source (i.e., land), where there is more plastic per unit area compared to the open ocean. We estimate approximately 85 000 times more PCBs associated with plastics in an average 4.5-km stretch of beach in Hong Kong than from the same size transect in the North Pacific gyre. In conclusion, continuing efforts for plastic interception and cleanup on shorelines effectively reduces the amount of plastic-related chemicals entering and/or reentering the marine environment. Integr Environ Assess Manag 2019 :596-606. © 2019 SETAC.
Publisher: Copernicus GmbH
Date: 19-09-2023
Publisher: American Geophysical Union (AGU)
Date: 05-2022
DOI: 10.1029/2021JC018150
Abstract: The equatorial retroflection of the North Brazil Current (NBC) into the Equatorial Undercurrent (EUC) and its posterior tropical recirculation is a major regulator for the returning limb of the Atlantic Meridional Overturning Circulation. Indeed, most surface and thermocline NBC waters retroflect at the equator all the way into the central and eastern Atlantic Ocean, before they recirculate back through the tropics to the western boundary. Here, we use cruise data in the western equatorial Atlantic during April 2010 and reanalysis time series for the equatorial and tropical waters in both hemispheres in order to explore the recirculation pathways and transport variability. During the 1998–2016 period, the annual‐mean EUC transports 15.1 ± 1.3 Sv at 32°W, with 2.8 ± 0.4 Sv from the North Atlantic and 11.4 ± 1.3 Sv from the South Atlantic. At 32°W most of the total EUC transport comes from the western boundary retroflection south of 3°N (7.2 ± 0.9 Sv), a substantial fraction retroflects north of 3°N (5.6 ± 0.4 Sv), and the remaining flow (2.3 Sv) joins through the interior basin. The South Atlantic subtropical waters feed the EUC at all thermocline depths while the North Atlantic and South Atlantic tropical waters do so at the surface and upper‐thermocline levels. The EUC transport at 32°W has a pronounced seasonality, with spring and fall maxima and a range of 8.8 Sv. The 18 yr of reanalysis data shows a weak yet significant correlation with an Atlantic Niño index, and also suggests an enhanced contribution from the South Atlantic tropical waters during 2008–2016 as compared with 1997–2007.
Publisher: Springer Science and Business Media LLC
Date: 10-12-2015
DOI: 10.1038/NCOMMS10082
Abstract: The interoceanic transfer of seawater between the Indian Ocean and the Atlantic, ‘Agulhas leakage’, forms a choke point for the overturning circulation in the global ocean. Here, by combining output from a series of high-resolution ocean and climate models with in situ and satellite observations, we construct a time series of Agulhas leakage for the period 1870–2014. The time series demonstrates the impact of Southern Hemisphere westerlies on decadal timescales. Agulhas leakage shows a correlation with the Atlantic Multi-decadal Oscillation on multi-decadal timescales the former leading by 15 years. This is relevant for climate in the North Atlantic.
Publisher: American Geophysical Union (AGU)
Date: 28-09-2016
DOI: 10.1002/2016GL070501
Publisher: Copernicus GmbH
Date: 04-11-2016
Abstract: Abstract. The dramatic calving of the Mertz Glacier tongue in 2010, precipitated by the movement of iceberg B09B, reshaped the oceanographic regime across the Mertz Polynya and Commonwealth Bay, regions where high-salinity shelf water (HSSW) – the precursor to Antarctic bottom water (AABW) – is formed. Here we present post-calving observations that suggest that this reconfiguration and subsequent grounding of B09B have driven the development of a new polynya and associated HSSW production off Commonwealth Bay. Supported by satellite observations and modelling, our findings demonstrate how local icescape changes may impact the formation of HSSW, with potential implications for large-scale ocean circulation.
Publisher: American Geophysical Union (AGU)
Date: 02-2014
DOI: 10.1002/2013JC009525
Publisher: Wiley
Date: 30-09-2021
Publisher: Springer Science and Business Media LLC
Date: 05-04-2022
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-4342
Abstract: & & Field studies have shown that plastic fragments make up the majority of plastic pollution in the oceans in terms of abundance. How quickly environmental plastics fragment is not well understood, however. Here, we study this process by considering a model which captures continuous fragmentation of particles over time in a cascading fashion. With this cascading fragmentation model, we simulate particle size distributions (PSDs), specifying the abundance or mass of particles for different size classes.& & & & & & & & & The fragmentation model is coupled to an environmental box model, simulating the distributions of plastic particles in the ocean, coastal waters, and on the beach. Transport in the box model is based on a previous study regarding a previous study regarding sources and sinks of marine plastics in the Mediterranean Sea. We compare the modelled PSDs to available observations, and use the results to illustrate the effect of size-selective processes such as vertical mixing in the water column and resuspension of particles from the beach into coastal waters.& & & & & & & & & Using the coupled fragmentation and environmental box model, we quantify the role of fragmentation on the marine plastic mass budget. While fragmentation is a major source of (secondary) plastic particles in terms of abundance, it seems to have a minor effect on the total mass of particles larger than 0.1 mm. Future comparison to observed PSD data should allow us to understand size-selective plastic transport in the environment, and potentially inform us on plastic longevity.& &
Publisher: Wiley
Date: 23-12-2021
Publisher: Elsevier BV
Date: 08-2014
Publisher: American Geophysical Union (AGU)
Date: 05-2010
DOI: 10.1029/2010GL042847
Publisher: Elsevier BV
Date: 2013
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-8383
Abstract: & & Simulations of the geological past using General Circulation Models (GCMs) are computationally expensive. Mainly because of the long equilibration time scales, most of these GCMs have ocean components with a horizontal resolution of 1& #176 or coarser. Such models are non-eddying and the effects of mesoscale ocean eddies on the transport of heat and salt are parameterized. However, from present-day ocean modeling studies, it is known that eddying ocean models better represent regional and time-mean ocean flows compared to non-eddying models. At the same time, proxy data from sediment s le sites represent climate at specific locations. Hence, the coarse ocean resolution of typical palaeo-GCMs lead to a challenge for model-data comparison in past climates.& & & & Here we present the first simulations of a global eddying Eocene ocean with a 0.1& #176 (horizontal) resolution model, which are initialized and forced with data from a coarser resolution (1& #176 horizontally) equilibrated coupled ocean-atmosphere GCM. We investigate the response of the model equilibrium state to the change in ocean resolution and the consequences this has for model-data comparison in the middle-late Eocene (38Ma). We find that, compared to the non-eddying model, the eddying ocean resolution of palaeomodels reduce the biases in both sea surface temperatures and biogeographic patterns which are derived from proxy data.& &
Publisher: Proceedings of the National Academy of Sciences
Date: 31-08-2015
Abstract: Plastic pollution in the ocean is a rapidly emerging global environmental concern, with high concentrations (up to 580,000 pieces per km 2 ) and a global distribution, driven by exponentially increasing production. Seabirds are particularly vulnerable to this type of pollution and are widely observed to ingest floating plastic. We used a mixture of literature surveys, oceanographic modeling, and ecological models to predict the risk of plastic ingestion to 186 seabird species globally. Impacts are greatest at the southern boundary of the Indian, Pacific, and Atlantic Oceans, a region thought to be relatively pristine. Although evidence of population level impacts from plastic pollution is still emerging, our results suggest that this threat is geographically widespread, pervasive, and rapidly increasing.
Publisher: Wiley
Date: 06-03-2023
DOI: 10.1002/LNO.12330
Abstract: Marine microplastics can be colonized by biofouling microbial organisms, leading to a decrease in microplastics' buoyancy. The sinking of biofouled microplastics could therefore represent a novel carbon export pathway within the ocean carbon cycle. Here, we model how microplastics are biofouled by diatoms, their consequent vertical motion due to buoyancy changes, and the interactions between particle‐attached diatoms and carbon pools within the water column. We initialize our Lagrangian framework with biogeochemical data from NEMO‐MEDUSA‐2.0 and estimate the amount of organic carbon exported below 100 m depth starting from different surface concentrations of 1‐mm microplastics. We focus on the Mediterranean Sea that is characterized by some of the world's highest microplastics concentrations and is a hotspot for biogeochemical changes induced by rising atmospheric carbon dioxide levels. Our results show that the carbon export caused by sinking biofouled microplastics is proportional to the concentration of microplastics in the sea surface layer, at least at modeled concentrations. We estimate that, while current concentrations of microplastics can modify the natural biological carbon export by 1%, future concentrations projected under business‐as‐usual pollution scenarios may lead to carbon exports up to 5% larger than the baseline (1998–2012) by 2050. Areas characterized by high primary productivity, that is, the Western and Central Mediterranean, are those where microplastics‐mediated carbon export results to be the highest. While highlighting the potential and quantitatively limited occurrence of this phenomenon in the Mediterranean Sea, our results call for further investigation of a microplastics‐related carbon export pathway in the global ocean.
Publisher: American Geophysical Union (AGU)
Date: 02-2022
DOI: 10.1029/2021MS002850
Abstract: To capture the effects of mesoscale turbulent eddies, coarse‐resolution Eulerian ocean models resort to tracer diffusion parameterizations. Likewise, the effect of eddy dispersion needs to be parameterized when computing Lagrangian pathways using coarse flow fields. Dispersion in Lagrangian simulations is traditionally parameterized by random walks, equivalent to diffusion in Eulerian models. Beyond random walks, there is a hierarchy of stochastic parameterizations, where stochastic perturbations are added to Lagrangian particle velocities, accelerations, or hyper‐accelerations. These parameterizations are referred to as the first, second and third order “Markov models” (Markov‐N), respectively. Most previous studies investigate these parameterizations in two‐dimensional setups, often restricted to the ocean surface. On the other hand, the few studies that investigated Lagrangian dispersion parameterizations in three dimensions, where dispersion is largely restricted to neutrally buoyant surfaces, have focused only on random walk (Markov‐0) dispersion. Here, we present a three‐dimensional isoneutral formulation of the Markov‐1 model. We also implement an anisotropic, shear‐dependent formulation of random walk dispersion, originally formulated as a Eulerian diffusion parameterization. Random walk dispersion and Markov‐1 are compared using an idealized setup as well as more realistic coarse and coarsened (50 km) ocean model output. While random walk dispersion and Markov‐1 produce similar particle distributions over time when using our ocean model output, Markov‐1 yields Lagrangian trajectories that better resemble trajectories from eddy‐resolving simulations. Markov‐1 also yields a smaller spurious dianeutral flux.
Publisher: Copernicus GmbH
Date: 15-05-2018
Abstract: Abstract. We propose a satellite mission that uses a near-nadir Ka-band Doppler radar to measure surface currents, ice drift and ocean waves at spatial scales of 40 km and more, with snapshots at least every day for latitudes 75 to 82°, and every few days for other latitudes. The use of incidence angles of 6 and 12° allows for measurement of the directional wave spectrum, which yields accurate corrections of the wave-induced bias in the current measurements. The instrument's design, an algorithm for current vector retrieval and the expected mission performance are presented here. The instrument proposed can reveal features of tropical ocean and marginal ice zone (MIZ) dynamics that are inaccessible to other measurement systems, and providing global monitoring of the ocean mesoscale that surpasses the capability of today's nadir altimeters. Measuring ocean wave properties has many applications, including examining wave–current interactions, air–sea fluxes, the transport and convergence of marine plastic debris and assessment of marine and coastal hazards.
Publisher: Copernicus GmbH
Date: 19-10-2020
DOI: 10.5194/OS-2020-95
Abstract: Abstract. We study the vertical dispersion and distribution of negatively buoyant rigid microplastics within a realistic circulation model of the Mediterranean sea. We first propose an equation describing their idealized dynamics. In that framework, we evaluate the importance of some relevant physical effects: inertia, Coriolis force, small-scale turbulence and variable seawater density, and bound the relative error of simplifying the dynamics to a constant sinking velocity added to a large-scale velocity field. We then calculate the amount and vertical distribution of microplastic particles on the water column of the open ocean if their release from the sea surface is continuous at rates compatible with observations in the Mediterranean. The vertical distribution is found to be almost uniform with depth for the majority of our parameter range. Transient distributions from flash releases reveal a non-Gaussian character of the dispersion and various diffusion laws, both normal and anomalous. The origin of these behaviors is explored in terms of horizontal and vertical flow organization.
Publisher: IOP Publishing
Date: 11-2017
Publisher: Elsevier BV
Date: 03-2010
Publisher: American Association for the Advancement of Science (AAAS)
Date: 12-09-2014
Abstract: The open ocean is not uniform. The seas teem with unseen life that has evolved distinctive patterns of species distribution, much as the land-bound world contains a spectrum of biological provinces. Taking data from genome studies, Hellweger et al. devised a model showing how marine bacteria ersified throughout the world's oceans into stable geographic provinces independently of natural selection (see the Perspective by Giovannoni and Nemergut). All that is needed to create these distributions are mutations and ocean currents. Science , this issue p. 1346 see also p. 1246
Publisher: Copernicus GmbH
Date: 09-03-2021
Abstract: Abstract. We study the vertical dispersion and distribution of negatively buoyant rigid microplastics within a realistic circulation model of the Mediterranean sea. We first propose an equation describing their idealized dynamics. In that framework, we evaluate the importance of some relevant physical effects (inertia, Coriolis force, small-scale turbulence and variable seawater density), and we bound the relative error of simplifying the dynamics to a constant sinking velocity added to a large-scale velocity field. We then calculate the amount and vertical distribution of microplastic particles on the water column of the open ocean if their release from the sea surface is continuous at rates compatible with observations in the Mediterranean. The vertical distribution is found to be almost uniform with depth for the majority of our parameter range. Transient distributions from flash releases reveal a non-Gaussian character of the dispersion and various diffusion laws, both normal and anomalous. The origin of these behaviors is explored in terms of horizontal and vertical flow organization.
Publisher: American Geophysical Union (AGU)
Date: 04-2021
DOI: 10.1029/2020JC017098
Abstract: Microplastic debris ending up at the sea surface has become a known major environmental issue. However, how microplastic particles move and when they sink in the ocean remains largely unknown. Here, we model microplastic subject to biofouling (algal growth on a substrate) to estimate sinking timescales and the time to reach the depth where particles stop sinking. We combine NEMO‐MEDUSA 2.0 output, that represents hydrodynamic and biological properties of seawater, with a particle‐tracking framework. Different sizes and densities of particles (for different types of plastic) are simulated, showing that the global distribution of sinking timescales is largely size‐dependent as opposed to density‐dependent. The smallest particles we simulate (0.1 μm) start sinking almost immediately around the globe and their trajectories take the longest time to reach their first sinking depth (relative to larger particles). In oligotrophic subtropical gyres with low algal concentrations, particles between 1 and 0.01 mm do not sink within the simulation time of 90 days. This suggests that in addition to the comparatively well‐known physical processes, biological processes might also contribute to the accumulation of floating plastic (of 1–0.01 mm) in subtropical gyres. Particles of 1 μm in the gyres start sinking largely due to vertical advection, whereas in the equatorial Pacific they are more dependent on biofouling. The qualitative impacts of seasonality on sinking timescales are small, however, localized sooner sinking due to spring algal blooms is seen. This study maps processes that affect the sinking of virtual microplastic globally, which could ultimately impact the ocean plastic budget.
Publisher: American Geophysical Union (AGU)
Date: 28-05-2013
DOI: 10.1002/GRL.50483
Publisher: Copernicus GmbH
Date: 29-06-2020
DOI: 10.5194/NPG-2020-28
Abstract: Abstract. The detection of finite-time coherent particle sets in Lagrangian trajectory data using data clustering techniques is an active research field at the moment. Yet, the clustering methods mostly employed so far have been based on graph partitioning, which assigns each trajectory to a cluster, i.e. there is no concept of noisy, incoherent trajectories. This is problematic for applications to the ocean, where many small coherent eddies are present in a large fluid domain. In addition, to our knowledge none of the existing methods to detect finite-time coherent sets has an intrinsic notion of coherence hierarchy, i.e. the detection of finite-time coherent sets at different spatial scales. Such coherence hierarchies are present in the ocean, where basin scale coherence coexists with smaller coherent structures such as jets and mesoscale eddies. Here, for the first time in this context, we use the density-based clustering algorithm OPTICS (Ankerst et al., 1999) to detect finite-time coherent particle sets in Lagrangian trajectory data. Different from partition based clustering methods, OPTICS does not require to fix the number of clusters beforehand. Derived clustering results contain a concept of noise, such that not every trajectory needs to be part of a cluster. OPTICS also has a major advantage compared to the previously used DBSCAN method, as it can detect clusters of varying density. Further, clusters can also be detected based on density changes instead of absolute density. Finally, OPTICS based clusters have an intrinsically hierarchical structure, which allows to detect coherent trajectory sets at different spatial scales at once. We apply OPTICS directly to Lagrangian trajectory data in the Bickley jet model flow and successfully detect the expected vortices and the jet. The resulting clustering separates the vortices and the jet from background noise, with an imprint of the hierarchical clustering structure of coherent, small scale vortices in a coherent, large-scale, background flow. We then apply our method to a set of virtual trajectories released in the eastern South Atlantic Ocean in an eddying ocean model and successfully detect Agulhas rings. At larger scale, our method also separates the eastward and westward moving parts of the subtropical gyre. We illustrate the difference between our approach and partition based k-Means clustering using a 2-dimensional embedding of the trajectories derived from classical multidimensional scaling. We also show how OPTICS can be applied to the spectral embedding of a trajectory based network to overcome the problems of k-Means spectral clustering in detecting Agulhas rings.
Publisher: Copernicus GmbH
Date: 03-03-2022
Abstract: Abstract. Coastlines potentially harbor a large part of litter entering the oceans, such as plastic waste. The relative importance of the physical processes that influence the beaching of litter is still relatively unknown. Here, we investigate the beaching of litter by analyzing a data set of litter gathered along the Dutch North Sea coast during extensive beach cleanup efforts between the years 2014 and 2019. This data set is unique in the sense that data are gathered consistently over various years by many volunteers (a total of 14 000) on beaches that are quite similar in substrate (sandy). This makes the data set valuable to identify which environmental variables play an important role in the beaching process and to explore the variability of beach litter concentrations. We investigate this by fitting a random forest machine learning regression model to the observed litter concentrations. We find that tides play an especially important role, where an increasing tidal variability and tidal height leads to less litter found on beaches. Relatively straight and exposed coastlines appear to accumulate more litter. The regression model indicates that transport of litter through the marine environment is also important in explaining beach litter variability. By understanding which processes cause the accumulation of litter on the coast, recommendations can be given for more effective removal of litter from the marine environment, such as organizing beach cleanups during low tides at exposed coastlines. We estimate that 16 500–31 200 kg (95 % confidence interval) of litter is located along the 365 km of Dutch North Sea coastline.
Publisher: American Meteorological Society
Date: 02-2014
Abstract: This study uses a global ocean eddy-permitting climate model to explore the export of abyssal water from the Southern Ocean and its sensitivity to projected twenty-first-century poleward-intensifying Southern Ocean wind stress. The abyssal flow pathways and transport are investigated using a combination of Lagrangian and Eulerian techniques. In an Eulerian format, the equator- and poleward flows within similar abyssal density classes are increased by the wind stress changes, making it difficult to explicitly diagnose changes in the abyssal export in a meridional overturning circulation framework. Lagrangian particle analyses are used to identify the major export pathways of Southern Ocean abyssal waters and reveal an increase in the number of particles exported to the subtropics from source regions around Antarctica in response to the wind forcing. Both the Lagrangian particle and Eulerian analyses identify transients as playing a key role in the abyssal export of water from the Southern Ocean. Wind-driven modifications to the potential energy component of the vorticity balance in the abyss are also found to impact the Southern Ocean barotropic circulation.
Publisher: Copernicus GmbH
Date: 05-08-2019
Publisher: Copernicus GmbH
Date: 05-08-2019
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-3902
Abstract: & & The biogeographic distribution of marine planktonic communities in the global ocean and its drivers has been a topic of great interest in the scientific community. Some of these drivers can be abiotic: ocean currents, temperature, salinity, nutrients, and others biotic: presence of predators and competitive species. In our study, we focus on the distribution mediated by ocean currents and temperature. Combining Lagrangian modeling and network theory approaches, we estimate the pathways and timescales that establish the surface connectivity for passive i.e., freely floating plankton between stations in the Atlantic Ocean where plankton have been s led during & em& Tara Oceans & Tara Oceans Polar Circle& /em& (2009-2013) and & em& Tara Pacific& /em& (2016-2018) expeditions.& & & & We obtain these estimates using a transition matrix approach derived from surface ocean simulations. Given the high rates of reproduction of many planktonic species and that only a few organisms are needed to establish connectivity, we make use of the minimum time path between different stations. To obtain plankton connectivity, two types of constraints are applied on the passive connectivity model: & em& thermal niche& /em& and & em& thermal adaptation rate& /em& , based on data for a given planktonic species from the literature. From the preliminary analysis, we find that, using minimum time paths, passive particles representative of foraminifera can connect all the stations in less than 3 years. Application of thermal niche constraints increases the minimum connectivity time between stations by approximately 10%, suggesting that plankton can keep to within their favorable thermal conditions by advecting via slightly longer paths. Main pathways of connectivity between these stations are also highlighted in this study. The developed approach can be applied for other plankton species, for any location in the Atlantic and can also be further expanded to derive seasonal connectivity.& &
Publisher: Copernicus GmbH
Date: 29-01-2020
Abstract: Abstract. A valuable analogue for assessing Earth’s sensitivity to warming is the Last Interglacial (LIG 129–116 kyr), when global temperatures (0−+2 °C) and mean sea level (+6–11 m) were higher than today. The direct contribution of warmer conditions to global sea level (thermosteric) are uncertain. We report here a global network of LIG sea surface temperatures (SST) obtained from various published temperature proxies (e.g. faunal/floral assemblages, Mg/Ca ratios of calcareous plankton, alkenone UK’37). Each reconstruction is averaged across the LIG (anomalies relative to 1981–2010), corrected for ocean drift and with varying seasonality (189 annual, 99 December-February, and 92 June–August records). We summarise the current limitations of SST reconstructions for the LIG and the spatial temperature features of a naturally warmer world. Because of local δ18O seawater changes, uncertainty in the age models of marine cores, and differences in s ling resolution and/or sedimentation rates, the reconstructions are restricted to mean conditions. To avoid bias towards in idual LIG SSTs based on only a single (and potentially erroneous) measurement or a single interpolated data point, here we average across the entire LIG. To investigate the sensitivity of the reconstruction to high temperatures, we also report maximum values during the first 5 ka of the LIG (129–124 kyr). The global dataset provides a remarkably coherent pattern of higher SST increases at polar latitudes than in the tropics, with comparable estimates between different SST proxies. We report mean global annual SST anomalies of 0.2 ± 0.1 °C and a maximum of 0.9 ± 0.2 °C respectively. Using the reconstructed SSTs suggests a mean thermosteric sea level rise of 0.01 ± 0.1 m and a maximum of 0.13 ± 0.1 m respectively. The data provide an important natural baseline for a warmer world, constraining the contributions of Greenland and Antarctic ice sheets to global sea level during a geographically widespread expression of high sea level, and can be used to test the next inter-comparison of models for projecting future climate change. The dataset described in this paper, including summary temperature and thermosteric sea-level reconstructions, are available at 0.1594/PANGAEA.904381 (Turney et al., 2019).
Publisher: Springer Science and Business Media LLC
Date: 06-05-2022
Publisher: Copernicus GmbH
Date: 02-05-2019
DOI: 10.5194/OS-2019-37
Abstract: Abstract. The Galápagos Archipelago and Marine Reserve lies 1000 km off the coast of Ecuador and is among the world's most iconic wildlife refuges. However, plastic litter is now found even in this remote and iconic island archipelago. Prior to this study, the sources of this plastic litter on Galápagos coastlines were unidentified. Local sources are widely expected to be small, given the limited population and environmentally-conscious tourism industry. Here, we show that remote coastal sources of plastic pollution are also fairly localized and limited to South and Central American coastlines, in particular Northern Peru and Southern Ecuador. Using virtual floating plastic particles transported in high-resolution ocean surface currents, we analysed the backward-in-time and forward-in-time pathways and connectivity between the Galápagos region and the coastlines around the East Pacific Ocean. We also analysed how incorporation of wave-driven currents (Stokes drift) affects these pathways and connectivity. We found that only virtual particles that enter the ocean from Peru, Ecuador and (when waves are not taken into account) Colombia can reach the Galápagos. It takes these particles a few months to travel from their coastal sources on the American continent to the Galápagos region. The connectivity does not seem to vary substantially between El Niño and La Niña years. Identifying these sources and the timing and patterns of the transport can be useful for identifying integrated management opportunities to reduce plastic pollution from reaching the Galápagos Archipelago.
Publisher: Copernicus GmbH
Date: 17-03-2016
Publisher: Wiley
Date: 16-11-2021
Publisher: Wiley
Date: 17-11-2021
Publisher: Elsevier BV
Date: 03-3000
Publisher: Copernicus GmbH
Date: 08-03-2023
DOI: 10.5194/EGUSPHERE-2023-315
Abstract: Abstract. The Tropical Pacific Ocean is characterized by its dominant zonal flow, strong climate dependence on the El Niño Southern Oscillation (ENSO) and abundant tuna stocks. Tuna fisheries in the West and Central Pacific Ocean accounted for 55 % of world-wide tuna catch in 2019 and are one of the main sources of income in many Pacific island nations. One of the dominant fishing methods in this region relies on the use of drifting Fish Aggregating Devices (dFADs): rafts with long underwater appendages (on average 50 m deep) that attract and aggregate fish. Although currents such as the North Equatorial Countercurrent (NECC) and South Equatorial Current (SEC) in the tropical Pacific Ocean vary strongly with ENSO, little is known about the impact of this variability in flow on dFAD dispersion. In this study, virtual Lagrangian particles are tracked for the period 2006 to 2021 over the domain in a 3D hydrodynamic model and are advected in simulations with only surface flow as well as simulations using a depth-averaged horizontal flow over the upper 50 meters. The particle trajectories are used to determine zonal displacements, eddy-like behaviour and ENSO variability for drifters that are subjected to either surface or depth-averaged currents. It was found that virtual particles that are advected by only surface flow are displaced up to 35 % farther than those subjected to a depth-averaged flow, but no other major differences are found in dispersion patterns. Strongest correlations between ENSO and dFAD dispersion for the assessed variables were found in the West Pacific Ocean, with Pearson correlation coefficients up to 0.59 for dFAD displacement. Connections between ENSO and eddy-like behaviour were found in the western part of the SEC, indicating more circulation and meandering during el Niño. These findings may be useful for improving sustainable deployment strategies during ENSO events, and understanding the ocean processes driving the distribution of dFADs.
Publisher: Wiley
Date: 06-11-2015
DOI: 10.1111/GCB.13063
Publisher: American Geophysical Union (AGU)
Date: 07-2014
DOI: 10.1002/2014JC010071
Publisher: Copernicus GmbH
Date: 27-09-2021
DOI: 10.5194/BG-2021-236
Abstract: Abstract. The fate of (micro)plastic particles in the open ocean is controlled by physical and biological processes. Here, we model the effects of biofouling on the subsurface vertical distribution of spherical, virtual plastic particles with radii of 0.01–1 mm. For the physics, four vertical velocity terms are included: advection, wind-driven mixing, tidally induced mixing, and the sinking velocity of the biofouled particle. For the biology, we simulate the attachment, growth and loss of algae on particles. We track 10,000 particles for one year in three different regions with distinct biological and physical properties: the low productivity region of the North Pacific Subtropical Gyre, the high productivity region of the Equatorial Pacific and the high mixing region of the Southern Ocean. The growth of biofilm mass in the euphotic zone and loss of mass below the euphotic zone result in the oscillatory behaviour of particles, where the larger (0.1–1.0 mm) particles have much shorter average oscillation lengths ( 10 days 90th percentile) than the smaller (0.01–0.1 mm) particles (up to 130 days 90th percentile). A subsurface maximum concentration occurs just below the mixed layer depth (around 30 m) in the Equatorial Pacific, which is most pronounced for larger particles (0.1–1.0 mm). This occurs since particles become neutrally buoyant when the processes affecting the settling velocity of the particle and the motion of the ocean are in equilibrium. Seasonal effects in the subtropical gyre result in particles sinking below the mixed layer depth only during spring blooms, but otherwise remaining within the mixed layer. The strong winds and deepest average mixed layer depth in the Southern Ocean (400 m) result in the deepest redistribution of particles ( 5000 m). Our results show that the vertical movement of particles is mainly affected by physical (wind-induced mixing) processes within the mixed layer and biological (biofilm) dynamics below the mixed layer. Furthermore, positively buoyant particles with radii of 0.01–1.0 mm can sink far below the euphotic zone and mixed layer in regions with high near-surface mixing or high biological activity. This work can easily be coupled to other models to simulate open-ocean biofouling dynamics, in order to reach a better understanding of where ocean (micro)plastic ends up.
Publisher: Elsevier BV
Date: 04-2013
Publisher: Cold Spring Harbor Laboratory
Date: 25-10-2018
DOI: 10.1101/452250
Abstract: To better predict how populations and communities respond to climatic temperature variation, it is necessary to understand how the shape of the response of fitness-related traits to temperature evolves (the thermal performance curve). Currently, there is disagreement about the extent to which the evolution of thermal performance curves is constrained. One school of thought has argued for the prevalence of thermodynamic constraints through enzyme kinetics, whereas another argues that adaptation can—at least partly—overcome such constraints. To shed further light on this debate, we perform a phylogenetic meta-analysis of the thermal performance curves of growth rate of phytoplankton—a globally important functional group—, controlling for environmental effects (habitat type and thermal regime). We find that thermodynamic constraints have a minor influence on the shape of the curve. In particular, we detect a very weak increase of maximum performance with the temperature at which the curve peaks, suggesting a weak “hotter-is-better” constraint. Also, instead of a constant thermal sensitivity of growth across species, as might be expected from strong constraints, we find that all aspects of the thermal performance curve evolve along the phylogeny. Our results suggest that phytoplankton thermal performance curves adapt to thermal environments largely in the absence of hard thermodynamic constraints.
Publisher: Copernicus GmbH
Date: 17-03-2016
DOI: 10.5194/BG-2016-53
Abstract: Abstract. Phytoplankton growth is the foundation for energy transfer into higher trophic levels, influences climate by the uptake of atmospheric CO2, and plays an important role in nutrient cycling. Here we use a novel lagrangian approach to characterize the nitrate supply to the Great Australian Bight, identify episodes of extreme phytoplankton blooms and ascertain the origin of the nitrate sources that fuel them. We find that 55 % of nitrate used by phytoplankton enters the GAB in the upper 100 m and that 88 % originates locally from a region between the GAB and the Sub Antarctic Front, rather than from more remote oceans thus, most of the nitrate is recycled locally. Our results show extreme phytoplankton blooms have an annual periodicity, peaking in the Austral autumn when the mixed layer deepens. This suggests that stratification erosion is key supplying nutrients into the euphotic zone and triggering these episodes.
Publisher: Copernicus GmbH
Date: 15-03-2017
Abstract: Abstract. Occupying about 14 % of the world's surface, the Southern Ocean plays a fundamental role in ocean and atmosphere circulation, carbon cycling and Antarctic ice-sheet dynamics. Unfortunately, high interannual variability and a dearth of instrumental observations before the 1950s limits our understanding of how marine–atmosphere–ice domains interact on multi-decadal timescales and the impact of anthropogenic forcing. Here we integrate climate-sensitive tree growth with ocean and atmospheric observations on southwest Pacific subantarctic islands that lie at the boundary of polar and subtropical climates (52–54° S). Our annually resolved temperature reconstruction captures regional change since the 1870s and demonstrates a significant increase in variability from the 1940s, a phenomenon predating the observational record. Climate reanalysis and modelling show a parallel change in tropical Pacific sea surface temperatures that generate an atmospheric Rossby wave train which propagates across a large part of the Southern Hemisphere during the austral spring and summer. Our results suggest that modern observed high interannual variability was established across the mid-twentieth century, and that the influence of contemporary equatorial Pacific temperatures may now be a permanent feature across the mid- to high latitudes.
Publisher: Elsevier BV
Date: 10-2015
Publisher: Elsevier BV
Date: 09-2015
Publisher: Public Library of Science (PLoS)
Date: 12-2016
Publisher: Copernicus GmbH
Date: 07-03-2016
Publisher: Copernicus GmbH
Date: 28-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-13468
Abstract: & & The state of coral reef ecosystems is highly dependent on the availability and ratio of essential resources such as oxygen, minerals and nutrients, and the presence of pollutants, pathogens and other possible stressors. The distribution of these inputs is dynamic and depends on many factors, including the nearshore hydrodynamic processes. These are unique processes, consisting of tidal pumping, nearshore circulation, and wave action. Furthermore, these processes are highly influenced by complex reef bathymetry and the physical roughness of the reef. The latter has a crucial role in the boundary layer characteristics, which influences uptake by reef organisms at smaller spatial scales.& & & & The understanding of distribution and transport of particulate and dissolved substances is challenging as field surveys are difficult to perform and there is a large variety of coral shapes. However, assessing the hydrodynamic processes is a necessary first step in order to link the sources and sinks of substances with the coral health and growth. Within the interdisciplinary research program SEALINK, we aim to assess the distribution and pathways of substances around the island of Cura& #231 ao. Field observations on selected sites along the coast of Cura& #231 ao include current and wave measurements with Acoustic Doppler Current Profilers and flow visualization with fluorescent dye.& & & & We will present preliminary results from the field c aign showing velocity fields and wave transformation on different stations along the cross-shore transects on the reef platform. Using a combination of field observations and 3D non-hydrostatic Computational Fluid Dynamics models, we investigate the mixing mechanisms and local energy balance at scales of O(10 m) on the selected reef quadrants. This serves as a basis for a further analysis with Lagrangian Particle Tracking methods to track the selected substances identified with other field c aigns within the SEALINK program.& &
Publisher: IOP Publishing
Date: 12-2012
Publisher: Copernicus GmbH
Date: 02-05-2019
Publisher: American Geophysical Union (AGU)
Date: 2018
DOI: 10.1002/2017PA003181
Publisher: Copernicus GmbH
Date: 19-01-2021
Abstract: Abstract. The detection of finite-time coherent particle sets in Lagrangian trajectory data, using data-clustering techniques, is an active research field at the moment. Yet, the clustering methods mostly employed so far have been based on graph partitioning, which assigns each trajectory to a cluster, i.e. there is no concept of noisy, incoherent trajectories. This is problematic for applications in the ocean, where many small, coherent eddies are present in a large, mostly noisy fluid flow. Here, for the first time in this context, we use the density-based clustering algorithm of OPTICS (ordering points to identify the clustering structure Ankerst et al., 1999) to detect finite-time coherent particle sets in Lagrangian trajectory data. Different from partition-based clustering methods, derived clustering results contain a concept of noise, such that not every trajectory needs to be part of a cluster. OPTICS also has a major advantage compared to the previously used density-based spatial clustering of applications with noise (DBSCAN) method, as it can detect clusters of varying density. The resulting clusters have an intrinsically hierarchical structure, which allows one to detect coherent trajectory sets at different spatial scales at once. We apply OPTICS directly to Lagrangian trajectory data in the Bickley jet model flow and successfully detect the expected vortices and the jet. The resulting clustering separates the vortices and the jet from background noise, with an imprint of the hierarchical clustering structure of coherent, small-scale vortices in a coherent, large-scale background flow. We then apply our method to a set of virtual trajectories released in the eastern South Atlantic Ocean in an eddying ocean model and successfully detect Agulhas rings. We illustrate the difference between our approach and partition-based k-means clustering using a 2D embedding of the trajectories derived from classical multidimensional scaling. We also show how OPTICS can be applied to the spectral embedding of a trajectory-based network to overcome the problems of k-means spectral clustering in detecting Agulhas rings.
Publisher: Springer Science and Business Media LLC
Date: 05-09-2015
Publisher: Copernicus GmbH
Date: 29-01-2020
Publisher: American Geophysical Union (AGU)
Date: 12-2020
DOI: 10.1029/2020JC016294
Abstract: The transport of plastic particles from inland sources to the oceans garbage patches occurs trough coastal regions where the transport processes depend highly on wave‐induced motions. In this study, experimental measurements of the plastic particles wave‐induced Lagrangian drift in intermediate water depth are presented investigating the influence of the wave conditions, particle size and density on the motion of relatively large plastic particles. A large influence of the particle density is observed causing particles to float or sink for relative densities lower and larger than water respectively. The measured net drift of the floating particles correlates well with theoretical solutions for particle Stokes drift, where the net drift is proportional to the square of the wave steepness. Floating particles remain at the free water surface because of buoyancy and no evidence of any other influence of particle inertia on the net drift is observed. Nonfloating particles move close to the bed with lower velocity magnitudes than the floating particles’ motion at the free surface. The drift of nonfloating particles reduces with decreasing wave number, and therefore wave steepness.
Publisher: AIP Publishing
Date: 09-2014
DOI: 10.1063/1.4892530
Abstract: The Ekman dynamics of the ocean surface circulation is known to contain attracting regions such as the great oceanic gyres and the associated garbage patches. Less well-known are the extents of the basins of attractions of these regions and how strongly attracting they are. Understanding the shape and extent of the basins of attraction sheds light on the question of the strength of connectivity of different regions of the ocean, which helps in understanding the flow of buoyant material like plastic litter. Using short flow time trajectory data from a global ocean model, we create a Markov chain model of the surface ocean dynamics. The surface ocean is not a conservative dynamical system as water in the ocean follows three-dimensional pathways, with upwelling and downwelling in certain regions. Using our Markov chain model, we easily compute net surface upwelling and downwelling, and verify that it matches observed patterns of upwelling and downwelling in the real ocean. We analyze the Markov chain to determine multiple attracting regions. Finally, using an eigenvector approach, we (i) identify the five major ocean garbage patches, (ii) partition the ocean into basins of attraction for each of the garbage patches, and (iii) partition the ocean into regions that demonstrate transient dynamics modulo the attracting garbage patches.
Publisher: American Geophysical Union (AGU)
Date: 24-03-2012
DOI: 10.1029/2012GL051004
Publisher: American Geophysical Union (AGU)
Date: 08-2022
DOI: 10.1029/2021PA004405
Abstract: Model simulations of past climates are increasingly found to compare well with proxy data at a global scale, but regional discrepancies remain. A persistent issue in modeling past greenhouse climates has been the temperature difference between equatorial and (sub‐)polar regions, which is typically much larger in simulations than proxy data suggest. Particularly in the Eocene, multiple temperature proxies suggest extreme warmth in the southwest Pacific Ocean, where model simulations consistently suggest temperate conditions. Here, we present new global ocean model simulations at 0.1° horizontal resolution for the middle‐late Eocene. The eddies in the high‐resolution model affect poleward heat transport and local time‐mean flow in critical regions compared to the noneddying flow in the standard low‐resolution simulations. As a result, the high‐resolution simulations produce higher surface temperatures near Antarctica and lower surface temperatures near the equator compared to the low‐resolution simulations, leading to better correspondence with proxy reconstructions. Crucially, the high‐resolution simulations are also much more consistent with biogeographic patterns in endemic‐Antarctic and low‐latitude‐derived plankton, and thus resolve the long‐standing discrepancy of warm subpolar ocean temperatures and isolating polar gyre circulation. The results imply that strongly eddying model simulations are required to reconcile discrepancies between regional proxy data and models, and demonstrate the importance of accurate regional paleobathymetry for proxy‐model comparisons.
Publisher: Copernicus GmbH
Date: 09-03-2022
Abstract: Abstract. Turbulent mixing is a vital component of vertical particulate transport, but ocean global circulation models (OGCMs) generally have low-resolution representations of near-surface mixing. Furthermore, turbulence data are often not provided in OGCM model output. We present 1D parametrizations of wind-driven turbulent mixing in the ocean surface mixed layer that are designed to be easily included in 3D Lagrangian model experiments. Stochastic transport is computed by Markov-0 or Markov-1 models, and we discuss the advantages and disadvantages of two vertical profiles for the vertical diffusion coefficient Kz. All vertical diffusion profiles and stochastic transport models lead to stable concentration profiles for buoyant particles, which for particles with rise velocities of 0.03 and 0.003 m s−1 agree relatively well with concentration profiles from field measurements of microplastics when Langmuir-circulation-driven turbulence is accounted for. Markov-0 models provide good model performance for integration time steps of Δt≈30 s and can be readily applied when studying the behavior of buoyant particulates in the ocean. Markov-1 models do not consistently improve model performance relative to Markov-0 models and require an additional parameter that is poorly constrained.
Publisher: Oxford University Press (OUP)
Date: 06-07-2023
Abstract: Catch per unit of fishing effort (CPUE) is often used as an indicator of tuna abundance, where it is assumed that the two are proportional to each other. Tuna catch is therefore typically simplified in tuna population dynamics models and depends linearly on their abundance. In this paper, we use an in idual-based model of tuna and their interactions with drifting Fish Aggregating Devices (dFADs) to identify which behavioural, ocean flow, and fishing strategy scenarios lead to an emergent, non-linear dependency between catch, and both tuna and dFAD density at the ∼1○ grid scale. We apply a series of catch response equations to evaluate their ability to model associated catch rate, using tuna and dFAD density as terms. Our results indicate that, regardless of ocean flow, behavioural, or fisher strategy scenario, simulated catch is best modelled with a non-linear dependence on both tuna and dFAD abundance. We discuss how estimators of CPUE at the population scale are potentially biased when assuming a linear catch response.
Publisher: IOP Publishing
Date: 06-2021
Abstract: Global coastlines potentially contain significant amounts of plastic debris, with harmful implications for marine and coastal ecosystems, fisheries and tourism. However, the global amount, distribution and origin of plastic debris on beaches and in coastal waters is currently unknown. Here we analyze beaching and resuspension scenarios using a Lagrangian particle transport model. Throughout the first 5 years after entering the ocean, the model indicates that at least 77% of positively buoyant marine plastic debris (PBMPD) released from land-based sources is either beached or floating in coastal waters, assuming no further plastic removal from beaches or the ocean surface. The highest concentrations of beached PBMPD are found in Southeast Asia, caused by high plastic inputs from land and limited offshore transport, although the absolute concentrations are generally overestimates compared to field measurements. The modeled distribution on a global scale is only weakly influenced by local variations in resuspension rates due to coastal geomorphology. Furthermore, there are striking differences regarding the origin of the beached plastic debris. In some exclusive economic zones (EEZ), such as the Indonesian Archipelago, plastic originates almost entirely from within the EEZ while in other EEZs, particularly remote islands, almost all beached plastic debris arrives from remote sources. Our results highlight coastlines and coastal waters as important reservoirs of marine plastic debris and limited transport of PBMPD between the coastal zone and the open ocean.
Publisher: American Geophysical Union (AGU)
Date: 03-2019
DOI: 10.1029/2018JC014547
Publisher: Cold Spring Harbor Laboratory
Date: 22-09-2022
DOI: 10.1101/2022.09.20.508652
Abstract: Catch and distribution of tuna in the ocean are typically investigated with ocean basin-scale models. Due to their large scale, such models must greatly simplify tuna behaviour occurring at a scale below ∼100 km, despite interactions at this level potentially being important to both catch and distribution of tuna. For ex le, the associative behaviour of tuna with man-made floating objects, that are deployed by fishers to improve their catch rates (Fish Aggregating Devices FADs), are usually ignored or simplified. Here we present a model that can be used to investigate the influence of tuna dynamics below the ∼100 km scale on larger scales. It is an Agent-Based Model (ABM) of a hypothetical, tuna-like species, that includes their interactions with each other, free-floating FADs and prey. In this ABM, both tuna and FADs are represented by Lagrangian particles that are advected by an ocean flow field, with tuna also exhibiting active swimming based on internal states such as stomach fullness. We apply the ABM in multiple configurations of idealised flow and prey fields, alongside differing interaction strengths between agents. When tuna swimming behaviour is influenced equally by prey and FADs, we find that the model simulations compare well with observations at the ≲ 100 km scale. For instance, compared to observations, tuna particles have a similar stomach fullness when associated or non-associated to a FAD, tuna colonize at similar timescales at FADs after their deployment and tuna particles exhibit similar variations in continuous residence times. However, we find large differences in emergent dynamics such as residence and catch among different flow configurations, because the flow determines the time scale at which tuna encounter FADs. These findings are discussed in the context of directing future research, and an improved interpretation of tuna catch and other data for the sustainable management of these economically important species.
Publisher: Elsevier BV
Date: 12-2014
Publisher: Copernicus GmbH
Date: 24-04-2023
DOI: 10.5194/GMD-2023-49
Abstract: Abstract. A common task in oceanography is to model the vertical movement of particles such as microplastics, nanoparticles, mineral particles, gas bubbles, oil droplets, fish eggs, plankton, or algae. In some cases, the distribution of vertical rise or settling velocities of the particles in question can span a wide range, covering several orders of magnitude, often due to a broad particle size distribution or differences in density. This requires numerical methods that are able to adequately resolve a wide and possibly multi-modal velocity distribution. Lagrangian particle methods are commonly used for these applications. strength of such methods is that each particle can have its own rise or settling speed, which makes it easy to achieve a good representation of a continuous distribution of speeds. An alternative approach is to use Eulerian methods, where the partial differential equations describing the transport problem are solved directly with numerical methods. In Eulerian methods, different rise or settling speeds must be represented as discrete classes, and in practice only a limited number of classes can be included. Here, we consider three different ex les of applications for a water-column model: positively buoyant fish eggs, a mixture of positively and negatively buoyant microplastics, and positively buoyant oil droplets being entrained by waves. For each of the three cases we formulate a model for the vertical transport, based on the advection-diffusion equation with suitable boundary conditions and in one case a reaction term. We give a detailed description of an Eulerian and a Lagrangian implementation of these models, and we demonstrate that they give equivalent results for selected ex le cases. We also pay special attention to the convergence of the model results with increasing number of classes in the Eulerian scheme, and the number of particles in the Lagrangian scheme. For the Lagrangian scheme, we see the 1/√Np convergence as expected for a Monte Carlo method, while for the Eulerian implementation, we see a second order (1/N2k) convergence with the number of classes.
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-274
Abstract: & & The Galapagos Archipelago and the Galapagos Marine Reserve host one of the world& #8217 s most unique ecosystems. Although being a UNESCO world heritage site and being isolated from any dense population, over 8 tonnes of plastic are collected on the islands each year. To decrease the impact of plastic waste in the region, scientific evidence is needed on the sources and fate of the marine debris. Here, we will assess the skill of machine learning techniques to predict beaching events on these islands. In order to do so, we combine various hydrodynamic fields from ocean-, wave-, wind- and tide-models using the OceanParcels particle tracking framework to track virtual particles through the marine reserve. In addition, a beaching parameterization has been developed and implemented to quantify where and when virtual particles wash ashore. The results show that the particle pathways and beaching probabilities strongly depend on the dry and wet seasons characteristic for the Galapagos Islands.& & & & & Therefore, it is expected that the beaching events can to some extent be predicted from the forecasts of currents, tides and waves - without performing a Lagrangian simulation. To test this hypothesis, PCA analysis and random forests are applied to a set of over 100 variables and their skill to explain the beaching variability given by the particle model is determined. In addition, the results are compared to a timeseries of observed beached litter on one of the Island of San Cristobal to apply the models in a realistic case study. This work, in combination with a growing observational data set, will form the basis of a predictive model that will support the Galapagos National Park in their efforts to free the Galapagos Archipelago from marine debris.& &
Publisher: Elsevier BV
Date: 2018
DOI: 10.1016/J.MARPOLBUL.2017.10.077
Abstract: There are fundamental gaps in our understanding of the fates of microplastics in the ocean, which must be overcome if the severity of this pollution is to be fully assessed. The predominant pattern is high accumulation of microplastic in subtropical gyres. Using in situ measurements from the 7th Continent expedition in the North Atlantic subtropical gyre, data from satellite observations and models, we show how microplastic concentrations were up to 9.4 times higher in an anticyclonic eddy explored, compared to the cyclonic eddy. Although our s le size is small, this is the first suggestive evidence that mesoscale eddies might trap, concentrate and potentially transport microplastics. As eddies are known to congregate nutrients and organisms, this phenomenon should be considered with regards to the potential impact of plastic pollution on the ecosystem in the open ocean.
Publisher: Copernicus GmbH
Date: 30-10-2020
Abstract: Abstract. A large percentage of global ocean plastic waste enters the Northern Hemisphere Indian Ocean (NIO). Despite this, it is unclear what happens to buoyant plastics in the NIO. Because the subtropics in the NIO are blocked by landmass, there is no subtropical gyre and no associated subtropical garbage patch in this region. We therefore hypothesize that plastics “beach” and end up on coastlines along the Indian Ocean rim. In this paper, we determine the influence of beaching plastics by applying different beaching conditions to Lagrangian particle-tracking simulation results. Our results show that a large amount of plastic likely ends up on coastlines in the NIO, while some crosses the Equator into the Southern Hemisphere Indian Ocean (SIO). In the NIO, the transport of plastics is dominated by seasonally reversing monsoonal currents, which transport plastics back and forth between the Arabian Sea and the Bay of Bengal. All buoyant plastic material in this region beaches within a few years in our simulations. Countries bordering the Bay of Bengal are particularly heavily affected by plastics beaching on coastlines. This is a result of both the large sources of plastic waste in the region and the ocean dynamics that concentrate plastics in the Bay of Bengal. During the intermonsoon period following the southwest monsoon season (September, October, November), plastics can cross the Equator on the eastern side of the NIO basin into the SIO. Plastics that escape from the NIO into the SIO beach on eastern African coastlines and islands in the SIO or enter the subtropical SIO garbage patch.
Publisher: American Meteorological Society
Date: 10-04-2012
DOI: 10.1175/JCLI-D-11-00302.1
Abstract: The new Community Climate System Model, version 4 (CCSM4), provides a powerful tool to understand and predict the earth’s climate system. Several aspects of the Southern Ocean in the CCSM4 are explored, including the surface climatology and interannual variability, simulation of key climate water masses (Antarctic Bottom Water, Subantarctic Mode Water, and Antarctic Intermediate Water), the transport and structure of the Antarctic Circumpolar Current, and interbasin exchange via the Agulhas and Tasman leakages and at the Brazil–Malvinas Confluence. It is found that the CCSM4 has varying degrees of accuracy in the simulation of the climate of the Southern Ocean when compared with observations. This study has identified aspects of the model that warrant further analysis that will result in a more comprehensive understanding of ocean–atmosphere–ice dynamics and interactions that control the earth’s climate and its variability.
Publisher: Copernicus GmbH
Date: 15-01-2019
DOI: 10.5194/GMD-2018-339
Abstract: Abstract. With the increasing amount of data produced by numerical ocean models, so increases the need for efficient tools to analyse these data. One of these tools is Lagrangian ocean analysis, where a set of virtual particles are released and their dynamics is integrated in time based on fields defining the ocean state, including the hydrodynamics and biogeochemistry if available. This popular methodology needs to adapt to the large variety of models producing these fields at different formats. This is precisely the aim of Parcels, a Lagrangian ocean analysis framework designed to combine (1) a wide flexibility to model particles of different natures and (2) an efficient implementation in accordance with modern computing infrastructure. In the new Parcels v2.0, we implement a set of interpolation schemes to read various types of discretised fields, from rectilinear to curvilinear grids in the horizontal direction, from z- to s- levels in the vertical and different variable distributions such as the Arakawa's A-, B- and C- grids. In particular, we develop a new interpolation scheme for a three-dimensional curvilinear C-grid and analyse its properties. Parcels v2.0 capabilities, including a suite of meta-field objects, are then illustrated in a brief study of the distribution of floating microplastic in the North West European continental shelf and its sensitivity to different physical processes.
Publisher: Copernicus GmbH
Date: 20-10-2022
Abstract: Abstract. The Galapagos Marine Reserve was established in 1986 to ensure protection of the islands' unique bio ersity. Unfortunately, the islands are polluted by marine plastic debris and the island authorities face the challenge to effectively remove plastic from its shorelines owing to limited resources. To optimize efforts, we have developed a methodology to identify the most effective cleanup locations on the Galapagos Islands using network theory. A network is constructed from a Lagrangian simulation describing the flow of macroplastic between the various islands within the Galapagos Marine Reserve, where the nodes represent locations along the coastline and the edges the likelihood of plastic leaving one location and beaching at another. We have found four network centralities that provide the best coastline ranking to optimize the cleanup effort based on various impact metrics. Locations with a high retention rate are particularly favorable for cleanup. The results indicate that using the most effective centrality for finding cleanup locations is a good strategy for heavily polluted regions if the distribution of marine plastic debris on the coastlines is unknown and limited cleanup resources are available.
Publisher: Elsevier BV
Date: 10-2018
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-2725
Abstract: Mode waters are defined as thick, weakly stratified layers with homogeneous properties. They have the ability to store these properties, such as heat, carbon and nutrients, and exchange these with the surface or atmosphere during outcropping events or with other layers via mixing processes. Eighteen Degree Water (EDW) is the subtropical mode water of the western North Atlantic. Its yearly outcropping events in late winter makes it an important regulator of ocean heat, nutrients and carbon in the North Atlantic on annual timescales.Previous studies have given insight into the formation and destruction of Eighteen Degree Water. These have largely focused on physical aspects such as EDW formation rates. Due to the importance of EDW formation in setting the biogeochemical environment in the North Atlantic, it is instructive to investigate how biogeochemical tracers are altered along EDW formation routes. This study investigates in particular how dissolved inorganic carbon (DIC) is altered along ocean water parcel trajectories as EDW is formed. To do so, we compute Lagrangian trajectories of subducted EDW backwards in time using a coupled hydrodynamic and biogeochemical model. By s ling biogeochemical tracer values along Lagrangian pathways, we construct timeseries which we use to map the dominant locations at which DIC concentrations are altered in space and time to identify the Lagrangian fingerprint of DIC in Eighteen Degree Water.
Publisher: Elsevier BV
Date: 06-2023
Publisher: Public Library of Science (PLoS)
Date: 27-07-2022
DOI: 10.1371/JOURNAL.PCBI.1010291
Abstract: Microbes play a primary role in aquatic ecosystems and biogeochemical cycles. Spatial patchiness is a critical factor underlying these activities, influencing biological productivity, nutrient cycling and dynamics across trophic levels. Incorporating spatial dynamics into microbial models is a long-standing challenge, particularly where small-scale turbulence is involved. Here, we combine a fully 3D direct numerical simulation of convective mixed layer turbulence, with an in idual-based microbial model to test the key hypothesis that the coupling of gyrotactic motility and turbulence drives intense microscale patchiness. The fluid model simulates turbulent convection caused by heat loss through the fluid surface, for ex le during the night, during autumnal or winter cooling or during a cold-air outbreak. We find that under such conditions, turbulence-driven patchiness is depth-structured and requires high motility: Near the fluid surface, intense convective turbulence overpowers motility, homogenising motile and non-motile microbes approximately equally. At greater depth, in conditions analogous to a thermocline, highly motile microbes can be over twice as patch-concentrated as non-motile microbes, and can substantially lify their swimming velocity by efficiently exploiting fast-moving packets of fluid. Our results substantiate the predictions of earlier studies, and demonstrate that turbulence-driven patchiness is not a ubiquitous consequence of motility but rather a delicate balance of motility and turbulent intensity.
Publisher: Elsevier BV
Date: 04-2014
Publisher: American Meteorological Society
Date: 09-2007
DOI: 10.1175/JPO3108.1
Abstract: The adiabatic transit time of wave energy radiated by an Agulhas ring released in the South Atlantic Ocean to the North Atlantic Ocean is investigated in a two-layer ocean model. Of particular interest is the arrival time of baroclinic energy in the northern part of the Atlantic, because it is related to variations in the meridional overturning circulation. The influence of the Mid-Atlantic Ridge is also studied, because it allows for the conversion from barotropic to baroclinic wave energy and the generation of topographic waves. Barotropic energy from the ring is present in the northern part of the model basin within 10 days. From that time, the barotropic energy keeps rising to attain a maximum 500 days after initiation. This is independent of the presence or absence of a ridge in the model basin. Without a ridge in the model, the travel time of the baroclinic signal is 1300 days. This time is similar to the transit time of the ring from the eastern to the western coast of the model basin. In the presence of the ridge, the baroclinic signal arrives in the northern part of the model basin after approximately 10 days, which is the same time scale as that of the barotropic signal. It is apparent that the ridge can facilitate the energy conversion from barotropic to baroclinic waves and the slow baroclinic adjustment can be bypassed. The meridional overturning circulation, parameterized in two ways as either a purely barotropic or a purely baroclinic phenomenon, also responds after 1300 days. The ring temporarily increases the overturning strength. The presence of the ridge does not alter the time scales.
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-7881
Abstract: & & Ocean currents can transport sinking particles hundreds of kilometers from their origin at the ocean surface to their burial location, resulting in an offset between sea surface temperatures (SSTs) above the burial site and the particle& #8217 s origin. Quantifying this offset in particles carrying molecules used in SST proxies can reduce uncertainty in paleoclimate reconstructions. In the Mediterranean Sea, where & #948 & sup& & /sup& O& sub& foraminifera& /sub& , U& sup& K& #8217 & /sup& & sub& & /sub& - and TEX& sub& & /sub& -based SSTs can exhibit large offsets from surface conditions, understanding the possible contribution of lateral transport to proxy bias can provide additional insight when interpreting paleoclimate records.& & & & In this study, Lagrangian particle tracking experiments are performed using the NEMO flow field to simulate transport and allow for a quantitative estimate of transport bias. The model determines the ocean surface origin locations of foraminifera and sedimentary particles that carry alkenones or GDGTs to compare with surface sediment datasets for & #948 & sup& & /sup& O& sub& foraminifera& /sub& , U& sup& K& #8217 & /sup& & sub& & /sub& and TEX& sub& & /sub& , respectively. A range of sinking speeds appropriate for the export of organic matter (6, 12, 25, 50, 100, 250, and 500 m/d) is used in the model to represent different export modes (i.e., in idual coccoliths, coccospheres, aggregates), where the three fastest sinking speeds can also represent sinking foraminifera. Results show that lateral transport bias is generally small within the Mediterranean Sea and cannot explain the large offsets in proxy-based SST reconstructions in this basin.& &
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-11162
Abstract: During an expedition in January 2020, nanoplastics were s led at a depth of -5170m over Cape Basin in the South Atlantic Ocean. Using photo-induced force microscopy, it was identified that these were polyethylene terephthalate (PET) particles with an approximate diameter of 50 nm at different stages of degradation. Using a state-of-the-art Lagrangian 3D simulation that includes an idealized fragmentation scheme, we backtracked virtual particles from the s ling location to establish the possible origins of the PET nanoplastics. We performed several simulations with different fragmenting timescales, for 13 years from the date of s ling, using the GLO12V3R1 hydrodynamic data from Copernicus Marine Environment Monitoring Service. We found that the nanoparticles (smaller than 1& #956 m) could not have fragmented into nanoplastics at the surface and reached the s ling location within 13 years. The most likely scenario is that these particles started to sink from the surface as microplastics (larger than 1& #956 m) and then fragmented in the water column far from the surface. This suggests that the fragmentation happened through processes like slow thermal oxidative degradation or hydrolysis and not photodegradation. We also found that less than 0.2% of the virtual particles came from the coast and that the fragmentation timescale prescribed to the modelled particles, affects how they drift in the ocean by controlling the time they drift at different depths. This study contributes to understanding the fate and sources of nanoplastics suspended deep in the ocean.
Publisher: Copernicus GmbH
Date: 19-07-2017
DOI: 10.5194/GMD-2017-167
Abstract: Abstract. As Ocean General Circulation Models (OGCMs) move into the petascale age, where the output from global high-resolution model runs can be of the order of hundreds of terabytes in size, tools to analyse the output of these models will need to scale up too. Lagrangian Ocean Analysis, where virtual particles are tracked through hydrodynamic fields, is an increasingly popular way to analyse OGCM output, by mapping pathways and connectivity of biotic and abiotic particulates. However, the current software stack of Lagrangian Ocean Analysis codes is not dynamic enough to cope with the increasing complexity, scale and need for customisation of use-cases. Furthermore, most community codes are developed for stand-alone use, making it a nontrivial task to integrate virtual particles at runtime of the OGCM. Here, we introduce the new Parcels code, which was designed from the ground up to be sufficiently scalable to cope with petascale computing. We highlight its API design that combines flexibility and customisation with the ability to optimise for HPC workflows, following the paradigm of domain-specific languages. Parcels is primarily written in Python, utilising the wide range of tools available in the scientific Python ecosystem, while generating low-level C-code and using Just-In-Time compilation for performance-critical computation. We show a worked-out ex le of its API, and validate the accuracy of the code against seven idealised test cases. This version 0.9 of Parcels is focussed on laying out the API, with future work concentrating on optimisation, efficiency and at-runtime coupling with OGCMs.
Publisher: IOP Publishing
Date: 29-10-2019
Abstract: The tracking of virtual particles is one of the main numerical tools to understand the global dispersion of marine plastic debris and has been successful in explaining the global-scale accumulation patterns of surface microplastic, often called ‘garbage patches’. Yet, the inherent inaccuracies in plastic input scenarios and ocean circulation model results produce uncertainties in particle trajectories, which lify due to the chaotic property of the surface ocean flow. Within this chaotic system, the subtropical ‘garbage patches’ correspond to the attractor. These facts make the large scale surface ocean circulation a mixing dynamical system, which means that the information of a particle’s initial location is lost over time. We use mixing entropy and Markov chain mixing of the transfer operator associated with surface ocean transport to quantify the time scales of mixing for the global surface ocean in each subtropical basin. In the largest parts of all basins we find mixing times in the order of or below 10 years, which is lower than typical simulation times for surface plastic transport simulations. Maximum mixing times of more than 10 years are found in some parts of the North and South Pacific. Our results have important implications for global dispersion modelling of floating materials on the basin scale: precise initial information has little relevance for long term simulations, and there is a temporal limit after which the backtracking of particles is not meaningful any more.
Publisher: American Geophysical Union (AGU)
Date: 08-2019
DOI: 10.1029/2019JC015328
Publisher: Elsevier BV
Date: 02-2014
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-4092
Abstract: & & The distribution of plastic in the ocean is poorly constrained, with the mass of floating plastic at the ocean surface being orders of magnitude smaller than estimated plastic inputs. Coastlines likely contain significant amounts of plastic, but inconsistent methodologies between beached plastic observations prevent determining the mass and distribution of globally beached plastic. We present Lagrangian model sensitivity experiments to estimate the beached fraction of marine plastic and to investigate the global distribution of beached plastic on coastlines.& & & & We perform simulations where particles, representing masses of floating plastic, are inserted at the ocean coasts. The particles are then advected by surface currents (HYCOM/NCODA global reanalysis and surface Stokes drift from the WaveWatch III global reanalysis) for 5 years. Beaching is parametrized stochastically using exponentional probability. Here, we test the sensitivity to e-folding time scales between 1 and 100 days, applied when plastic is within the coastal zone, within 10km of the nearest coastline. Resuspension of beached plastic is parameterised exponentially with an e-folding timescale between 69 and 273 days. No other loss processes are implemented.& & & & Between 39-95% of floating plastic mass is beached after 5 years, with the beached fraction depending on the ratio between the beaching and resuspension timescales. In all simulations, at least 77% of floating plastic mass is found either beached or within the coastal zone, indicating coastal regions are a significant reservoir of mismanaged terrestrial plastic. However, plastic entering the ocean from islands or near energetic boundary currents is more likely to reach the open ocean. The distribution of beached plastic is closely related to the input distribution, with the highest concentrations found in Southeast Asia and the Mediterranean.& & & & Our results highlight coastlines and coastal waters as important reservoirs of marine plastic debris and indicate a need for greater understanding of plastic transport near and at the coastlines. Furthermore, improved representation of plastic beaching can help study marine plastic fragmentation, as mechanical stress during the transitions between coastlines and coastal waters and the increased UV exposure of beached plastic likely contribute to the fragmentation.& &
Publisher: Copernicus GmbH
Date: 21-11-2016
Publisher: AIP Publishing
Date: 08-2015
DOI: 10.1063/1.4927830
Abstract: Coherent sets in dynamical systems are regions in phase space that optimally “carry mass” with them under the system's evolution, so that these regions experience minimal leakage. The dominant tool for determining coherent sets is the transfer operator, which provides a complete description of Lagrangian mass transport. In this work, we combine existing transfer operator methods with a windowing scheme to study the spatial and temporal evolution of a so-called Agulhas ring: a large anticyclonic mesoscale eddy playing a key role in inter-ocean exchange of climate-relevant properties. Our focus is on ring decay over time and the windowing scheme enables us to study how the most coherent region (our estimate of the ring) varies in position and size over a period of more than two years. We compare the eddy-like structure and its spatio-temporal changes as revealed by our method and by a classical Eulerian approach.
Publisher: American Geophysical Union (AGU)
Date: 04-2019
DOI: 10.1029/2018JC014806
Publisher: Copernicus GmbH
Date: 21-11-2016
DOI: 10.5194/CP-2016-114
Abstract: Abstract. Occupying 14% of the world’s surface, the Southern Ocean plays a fundamental role in global climate, ocean circulation, carbon cycling and Antarctic ice-sheet stability. Unfortunately, high interannual variability and a dearth of instrumental observations before the 1950s limits our understanding of how marine-atmosphere-ice domains interact on multi-decadal timescales and the impact of anthropogenic forcing. Here we integrate climate-sensitive tree growth with ocean and atmospheric observations on southwest Pacific subantarctic islands that lie at the boundary of polar and subtropical climates (52–54˚S). Our annually-resolved temperature reconstruction captures regional change since the 1870s and demonstrates a significant increase in variability from the mid-twentieth century, a phenomenon predating the observational record. Climate reanalysis and modelling shows a parallel change in tropical Pacific sea surface temperatures that generate an atmospheric Rossby wave train which propagates across a large part of the Southern Hemisphere during the austral spring and summer.
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-280
Abstract: & & Microplastic debris ending up at the sea surface has become a known major environmental issue. However, how microplastic particles move and when they sink in the ocean remains largely unknown. Here, we model microplastic subject to biofouling (algal growth on a substrate) to estimate sinking timescales and the time to reach the depth where particles stops sinking. We combine NEMO-MEDUSA 2.0 output, that represents hydrodynamic and biological properties of seawater, with a particle-tracking framework. Different sizes and densities of particles (for different types of plastic) are simulated, showing that the global distribution of sinking timescales is largely size-dependent as opposed to density-dependent. The smallest particles we simulate (0.1 & #956 m) start sinking almost immediately around the globe and their trajectories produce the longest time to reach their first sinking depth (almost 40 days as a global median). In oligotrophic subtropical gyres with low algal concentrations, particles between 1 mm and 10 & #956 m do not sink within the 90-day simulation time. This suggests that in addition to the comparatively well-known physical processes, biological processes might also contribute to the accumulation of floating plastic (of 1 mm to 10 & #956 m) in subtropical gyres. Particles of 1 & #956 m in the gyres start sinking largely due to vertical advection, whereas 0.1 & #956 m particles sink both due to biofouling and advection. The qualitative impacts of seasonality on sinking timescales are small, however, localised sooner sinking due to spring algal blooms is seen. This study maps processes that affect the sinking of virtual microplastic globally, which could ultimately impact the ocean plastic budget.& &
Publisher: IOP Publishing
Date: 06-2019
Abstract: The increased use of drifting Fish Aggregating Devices (dFADs) by tuna purse seine fleets in recent years has supported considerable catches of these species. A greater understanding of the spatiotemporal dynamics of these objects as they drift with ocean currents is critical for understanding historical changes in fishing power, spatial management, and examining the effect of ambient dFAD density on catch and effort. Here, dFAD dynamics were estimated for all floating object sets made by purse seiners in the Western and Central Pacific Ocean during 2016 and 2017. The drift trajectories of these floating objects prior to the observed fishing events were estimated by seeding virtual Lagrangian particles within a state-of-the-art hydrodynamics model, and simulating their movements backwards in time. Resulting trajectory distributions are similar to observed dFAD trajectories from the same period. The approach provides spatial density estimates in areas where observed dFAD data are incomplete, particularly in the exclusive economic zone (EEZ) of Howland and Baker Islands, and certain high seas areas. We provide estimates of inter-EEZ connectivity of dFADs, which highlight the fact that dFADs set upon in small EEZs such as Nauru and Howland and Baker Islands are likely to have drifted from neighbouring EEZs less than one month prior to fishing. dFADs typically transited multiple EEZs, with a median of 4 and a maximum of 14, when assuming a drift-time of six months. Moreover, between 4 and 22% of dFAD sets made in the WCPO were estimated to have originated from the Eastern Pacific Ocean, depending on drift-time. We examine our results in the context of the improved management and assessment of dFAD fisheries, providing a methodology to estimated relative dFAD density over historical periods to support analyses of catch and effort. The sensitivity of these estimates to hydrodynamic models, including the proposed SKIM doppler radar altimetry method, is discussed.
Publisher: IOP Publishing
Date: 2016
Publisher: American Geophysical Union (AGU)
Date: 07-2019
DOI: 10.1029/2019PA003606
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-3350
Abstract: & & Any type of non-buoyant material in the ocean is transported by currents during its sinking journey. This transport can be far from negligible for typical (plankton) particles with a low sinking velocity. To estimate the lateral transport, the material can be modelled as a set of Lagrangian particles advected by currents that are obtained from Ocean General Circulation Models (OGCMs). State-of-the-art OGCMs are often strongly eddying, providing flow fields with a horizontal resolution of& 10km on a daily basis. However, many long term climate modelling studies (e.g. in palaeoclimate) rely on low resolution models that cannot capture mesoscale features. The lower model resolution could influence data-model comparisons using Lagrangian techniques, but this is not properly evaluated yet through a direct comparison.& & & & In this study, we simulate the transport of sinking Lagrangian particles using low (1& #176 non-eddying) & and high (0.1& #176 eddying) horizontal resolution OGCMs of the present-day ocean, and evaluate the effect of the two resolutions on particle transport. We find major differences between the transport in the non-eddying versus the eddying OGCM (in terms of the ergence of particle trajectories and their mean trajectory). Addition of stochastic noise to the particle trajectory parameterizes the effect of eddies well in some regions (e.g. in the North Pacific gyre).& & & & We recommend to apply sinking Lagrangian particles only in velocity fields with eddying OGCMs, which basically excludes all paleo-simulations. We are currently simulating the equilibrium Eocene (38Ma) climate using an eddying OGCM, to be able to apply these Lagrangian techniques in an eddying ocean of the past. We expect this to lead towards a better agreement between the OGCM and sedimentary fossil microplankton.& &
Publisher: Copernicus GmbH
Date: 30-11-2020
Abstract: Abstract. The Mediterranean Sea is characterized by a relatively strong west to east salinity gradient, which makes it an area suitable for testing the effect of salinity on foraminiferal shell geochemistry. We collected living specimens of the planktonic foraminifer Globigerinoides ruber albus to analyse the relation between element ∕ Ca ratios, stable oxygen isotopes of their shells, and surface seawater salinity, isotopic composition and temperature. The oxygen isotopes of sea surface water also correlate with salinity in the Mediterranean during winter, which is when s ling for this study took place. Seawater oxygen and hydrogen isotopes are positively correlated in both the eastern and western Mediterranean Sea, although the relationship differs from previously reported values, especially in the eastern region. The slope between salinity and seawater oxygen isotopes is lower than previously published results. Still, despite the rather modest slope, seawater and foraminiferal carbonate oxygen isotopes are correlated in our dataset, albeit with large residuals and high residual variability. This scatter could be due to either biological variability in vital effects or environmental variability. Numerical models backtracking particles show that ocean-current-driven mixing of particles of different origins might d en sensitivity and could result in an offset caused by horizontal transport. Results show that Na ∕ Ca is positively correlated with salinity and independent of temperature. As expected, foraminiferal Mg ∕ Ca increases with temperature, which is in line with earlier calibrations, and in the high salinity environment. By using living foraminifera during winter, the previously established Mg ∕ Ca–temperature calibration is extended to temperatures below 18 ∘C, which is a fundamental prerequisite of using single foraminifera for reconstructing past seasonality.
Publisher: IOP Publishing
Date: 05-2021
Abstract: Field studies in the global ocean have shown that plastic fragments make up the majority of plastic pollution in terms of abundance. It is not well understood how quickly plastics in the marine environmental fragment, however. Here, we study the fragmentation process in the oceanic environment by considering a model which captures continuous fragmentation of particles over time in a cascading fashion. With this cascading fragmentation model we simulate particle size distributions (PSDs), specifying the abundance or mass of particles for different size classes. The fragmentation model is coupled to an environmental box model, simulating the distributions of plastic particles in the ocean, coastal waters, and on the beach. We demonstrate the capabilities of the model by calibrating it to estimated plastic transport in the Mediterranean Sea, and compare the modelled PSDs to available observations in this region. Results are used to illustrate the effect of size-selective processes such as vertical mixing in the water column and resuspension of particles from the beach into coastal waters. The model quantifies the role of fragmentation on the marine plastic mass budget: while fragmentation is a major source of secondary plastic particles in terms of abundance, it seems to have a minor effect on the total mass of particles larger than 0.1 mm. Future comparison to observed PSD data allow us to understand size-selective plastic transport in the environment, and potentially inform us on plastic longevity.
Publisher: Copernicus GmbH
Date: 10-03-2020
DOI: 10.5194/CP-2020-26
Abstract: Abstract. The Mediterranean Sea is characterized by a relatively strong west to east salinity gradient, which makes it an area suitable to test the effect of salinity on foraminiferal shell geochemistry. We collected living specimens of the planktonic foraminifer Globigerinoides ruber (white) to analyse the relation between element/Ca ratios, stable oxygen isotopes of their shells and surface seawater salinity, isotopic composition and temperature. The oxygen isotopes of sea surface water correlate with salinity in the Mediterranean also during winter, when s led for this study. Sea water oxygen and hydrogen isotopes are positively correlated in both the eastern and western Mediterranean Sea, though especially in the eastern part the relationship differs from values reported previously for that area. The slope between salinity and seawater oxygen isotopes is lower than previously published. Still, despite the rather modest slope, seawater and foraminiferal carbonate oxygen isotopes are correlated in our dataset although with large residuals and high residual variability. This scatter can be due to either biological variability in vital effects or environmental variability. Numerical models backtracking particles show ocean current driven mixing of particles of different origin might d en sensitivity and could result in an offset caused by horizontal transport. Results show that Na/Ca is positively correlated to salinity and independent of temperature. Foraminiferal Mg/Ca increases with temperature, as expected, and in line with earlier calibrations, also in the high salinity environment. By using living foraminifera during winter, the previously established Mg/Ca-temperature calibration is extended to temperatures below 18 °C, which is a fundamental prerequisite of using single foraminifera for reconstructing past seasonality.
Publisher: Copernicus GmbH
Date: 31-07-2017
DOI: 10.5194/OS-2017-65
Abstract: Abstract. We propose a new satellite mission that uses a near-nadir Ka-band Doppler radar to measure surface currents, ice drift and ocean waves at spatial scales of 40 km and more, with snapshots at least every day for latitudes 75 to 82, and every few days otherwise. The use of incidence angles at 6 and 12 degrees allows a measurement of the directional wave spectrum which yields accurate corrections of the wave-induced bias in the current measurements. The instrument principle, algorithm for current velocity and mission performance are presented here. The proposed instrument can reveal features on tropical ocean and marginal ice zone dynamics that are inaccessible to other measurement systems, as well as a global monitoring of the ocean mesoscale that surpasses the capability of today’s nadir altimeters. Measuring ocean wave properties facilitates many applications, from wave-current interactions and air-sea fluxes to the transport and convergence of marine plastic debris and assessment of marine and coastal hazards.
Publisher: IOP Publishing
Date: 02-2020
Abstract: Marine plastic debris floating on the ocean surface is a major environmental problem. However, its distribution in the ocean is poorly mapped, and most of the plastic waste estimated to have entered the ocean from land is unaccounted for. Better understanding of how plastic debris is transported from coastal and marine sources is crucial to quantify and close the global inventory of marine plastics, which in turn represents critical information for mitigation or policy strategies. At the same time, plastic is a unique tracer that provides an opportunity to learn more about the physics and dynamics of our ocean across multiple scales, from the Ekman convergence in basin-scale gyres to in idual waves in the surfzone. In this review, we comprehensively discuss what is known about the different processes that govern the transport of floating marine plastic debris in both the open ocean and the coastal zones, based on the published literature and referring to insights from neighbouring fields such as oil spill dispersion, marine safety recovery, plankton connectivity, and others. We discuss how measurements of marine plastics (both in situ and in the laboratory), remote sensing, and numerical simulations can elucidate these processes and their interactions across spatio-temporal scales.
Publisher: American Geophysical Union (AGU)
Date: 15-02-2022
DOI: 10.1029/2021GL097214
Abstract: Beaches are thought to be a large reservoir for marine plastics. To protect vulnerable beaches, it is advantageous to have information on the sources of this plastic. Here, we develop a universally applicable Bayesian framework to map sources of plastic arriving on a specific beach. In this framework, we combine Lagrangian backtracking simulations of drifting particles with estimates of plastic input from coastlines, rivers and fisheries. The advantage over traditional Lagrangian simulations is that the Bayesian framework can consider information on known sources, and thus facilitates spatiotemporal source attribution for plastic arriving at the specified beach. We show that the main sources for our target beach in southwest Netherlands are the east coast of the UK, the Dutch coast, the English Channel (fisheries) and the Thames, Seine, Rhine and Trieux (rivers). We also show that floating time is a major uncertainty in source attribution using backtracking.
Publisher: American Geophysical Union (AGU)
Date: 04-2019
DOI: 10.1029/2018JC014482
Publisher: American Geophysical Union (AGU)
Date: 20-02-2014
DOI: 10.1002/2014GL059278
Publisher: Wiley
Date: 14-09-2016
DOI: 10.1111/GCB.13078
Abstract: Plastic marine debris pollution is rapidly becoming one of the critical environmental concerns facing wildlife in the 21st century. Here we present a risk analysis for plastic ingestion by sea turtles on a global scale. We combined global marine plastic distributions based on ocean drifter data with sea turtle habitat maps to predict exposure levels to plastic pollution. Empirical data from necropsies of deceased animals were then utilised to assess the consequence of exposure to plastics. We modelled the risk (probability of debris ingestion) by incorporating exposure to debris and consequence of exposure, and included life history stage, species of sea turtle and date of stranding observation as possible additional explanatory factors. Life history stage is the best predictor of debris ingestion, but the best-fit model also incorporates encounter rates within a limited distance from stranding location, marine debris predictions specific to the date of the stranding study and turtle species. There is no difference in ingestion rates between stranded turtles vs. those caught as bycatch from fishing activity, suggesting that stranded animals are not a biased representation of debris ingestion rates in the background population. Oceanic life-stage sea turtles are at the highest risk of debris ingestion, and olive ridley turtles are the most at-risk species. The regions of highest risk to global sea turtle populations are off of the east coasts of the USA, Australia and South Africa the east Indian Ocean, and Southeast Asia. Model results can be used to predict the number of sea turtles globally at risk of debris ingestion. Based on currently available data, initial calculations indicate that up to 52% of sea turtles may have ingested debris.
Publisher: American Meteorological Society
Date: 05-2011
Publisher: Copernicus GmbH
Date: 17-06-2021
DOI: 10.5194/ISPRS-ANNALS-V-4-2021-217-2021
Abstract: Abstract. The Lagrangian analysis of particulate matter, biota and drifters, which are dispersed by turbulent fluid currents, is a cornerstone of oceanographic studies, covering erse study objectives. The results of Lagrangian simulations and observations is predominantly visualised by means of easy-access plotting interfaces and simple presentation techniques. We analysed over 50 publications from the years 2010–2020 with respect to their visual design to deduce common visualisation practices in the domain. In idual figures are analysed towards adherence to visualisation best-practices, algebraic visualisation guidelines and the IPCC visual style guide. In this article, we present the resulting best-practices and common pitfalls in the design of Lagrangian ocean visualisations. Based on this visual study, we highlight that raising awareness of established visual guidelines may have a higher impact on improving the visual quality of publications in oceanography than the vigorous development of more general-purpose visualisation tools.
Publisher: Elsevier BV
Date: 2009
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-5680
Abstract: & & Estimates of plastic quantities entering our oceans are not yet consistent with observed concentrations in the marine environment. This has led to the often-quoted statement that 99% of the marine plastics are missing. Here, we present a framework where the global transport of marine plastics is modelled over long time scales, in which the effects of different sources and sinks is investigated. Data assimilation techniques are used to inform unknown parameters regarding these sources and sinks, enabling us to quantify their role on the global plastic mass budget.& & & & State-of-the-art numerical models are included in the framework to capture for the first time the combined effect of marine plastic beaching, resuspension, biofouling, turbulent mixing, and fragmentation. The relative importance of different marine plastic sources is investigated, such as mismanaged coastal plastic waste, riverine outflow, and fishing activity. Unknown parameters are found by means of calibration to a large set of observational data of plastic concentrations in the ocean surface water, water column, ocean floor, and on coastlines.& & & & We show that with this framework, the global marine plastic mass budget can be closed. An overview is given of which environmental reservoirs are likely to contain most of the plastic mass, which sources are contributing to most of the pollution, and what the residence times of litter in the marine environment is. With the model calibration approach, we additionally get a better insight in the physics governing the transport of marine litter.& & &
Publisher: Wiley
Date: 29-10-2021
Publisher: Copernicus GmbH
Date: 15-06-2020
DOI: 10.5194/OS-2020-50
Abstract: Abstract. A large percentage of global ocean plastic waste enters the northern hemisphere Indian Ocean (NIO). Despite this, it is unclear what happens to buoyant plastics in the NIO. Because the subtropics in the NIO is blocked by landmass, there is no subtropical gyre and no associated subtropical garbage patch in this region. We therefore hypothesise that plastics "beach" and end up on coastlines along the Indian Ocean rim. In this paper, we determine the influence of beaching plastics by applying different beaching conditions to Lagrangian particle tracking simulation results. Our results show that a large amount of plastic likely ends up on coastlines in the NIO, while some crosses the equator into the southern hemisphere Indian Ocean (SIO). In the NIO, the transport of plastics is dominated by seasonally reversing monsoonal currents, which transport plastics back and forth between the Arabian Sea and the Bay of Bengal. All buoyant plastic material in this region beaches within a few years in our simulations. Countries bordering the Bay of Bengal are particularly heavily affected by plastics beaching on coastlines. This is a result of both the large sources of plastic waste in the region, as well as ocean dynamics which concentrate plastics in the Bay of Bengal. During the intermonsoon period following the southwest monsoon season (September, October, November), plastics can cross the equator on the eastern side of the NIO basin into the SIO. Plastics that escape from the NIO into the SIO beach on eastern African coastlines and islands in the SIO or enter the subtropical SIO garbage patch.
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-201
Abstract: & & & span& To identify barriers to transport in a fluid domain, community detection algorithms from network science have been used to ide the domain into clusters that are sparsely connected with each other. In a previous application to the closed domain of the Mediterranean Sea, communities detected by the & em& Infomap& /em& algorithm have barriers that often coincide with well-known oceanographic features. We apply this clustering method to the surface of the Arctic and subarctic oceans and thereby show that it can also be applied to open domains. First, we construct a Lagrangian flow network by simulating the exchange of Lagrangian particles between different bins in an icosahedral-hexagonal grid. Then, & em& Infomap & /em& is applied to identify groups of well-connected bins. The resolved transport barriers include naturally occurring structures, such as the major currents. As expected, clusters in the Arctic are affected by seasonal and annual variations in sea-ice concentration. An important caveat of community detection algorithms is that many different isions into clusters may qualify as good solutions. Moreover, while certain cluster boundaries lie consistently at the same location between different good solutions, other boundary locations vary significantly, making it difficult to assess the physical meaning of a single solution. We therefore consider an ensemble of solutions to find persistent boundaries, trends and correlations with surface velocities and sea-ice cover.& /span& & / &
Publisher: Wiley
Date: 24-09-2021
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-5288
Abstract: & & Over 8 tonnes of plastic are removed from the coastlines of the Galapagos Islands each year. Although the Galapagos Marine Reserve is expanding to ensure an even larger protection of its unique bio ersity, the island authorities face the challenge to effectively remove plastic from its shorelines due to limited resources. We are developing a clean-up efficacy model that will optimize for most cost-effective and least-invasive clean-up locations. Network (connectivity) theory is widely applied in ecology to study the interaction of species between spatially separated habitats. Here, we use a similar approach to discern the most effective removal hubs on the Galapagos Islands. A connectivity matrix is constructed from a Lagrangian simulation describing the flow of macroplastic between the various islands within the Galapagos Marine Reserve, where the nodes represent locations along the coastline and the edges the likelihood that plastic travels from one location and beaches at another. To measure the impact of removal, various centralities are determined, such as degree centrality, betweenness centrality (using the most likely path) and eigenvector centrality. Combining the results with other metrics such as the distance to the nearest port or tourist attractions, recommendations are made for& & & ul& & li& most effective & em& intervention& /em& removal hubs that would prevent further spread of plastic throughout the marine reserve& /li& & li& most effective & em& accumulation& /em& removal hubs that would negate the impact of plastic on wildlife& /li& & li& most suited regions for protection resulting from the existence of clusters (e.g. regions of limited connectivity)& /li& & /ul& & & Though we focus on the Galapagos Islands, the methods we present are directly applicable to archipelagos worldwide that face marine plastic pollution issues.& &
Publisher: Copernicus GmbH
Date: 17-11-2017
Abstract: Abstract. As ocean general circulation models (OGCMs) move into the petascale age, where the output of single simulations exceeds petabytes of storage space, tools to analyse the output of these models will need to scale up too. Lagrangian ocean analysis, where virtual particles are tracked through hydrodynamic fields, is an increasingly popular way to analyse OGCM output, by mapping pathways and connectivity of biotic and abiotic particulates. However, the current software stack of Lagrangian ocean analysis codes is not dynamic enough to cope with the increasing complexity, scale and need for customization of use-cases. Furthermore, most community codes are developed for stand-alone use, making it a nontrivial task to integrate virtual particles at runtime of the OGCM. Here, we introduce the new Parcels code, which was designed from the ground up to be sufficiently scalable to cope with petascale computing. We highlight its API design that combines flexibility and customization with the ability to optimize for HPC workflows, following the paradigm of domain-specific languages. Parcels is primarily written in Python, utilizing the wide range of tools available in the scientific Python ecosystem, while generating low-level C code and using just-in-time compilation for performance-critical computation. We show a worked-out ex le of its API, and validate the accuracy of the code against seven idealized test cases. This version 0.9 of Parcels is focused on laying out the API, with future work concentrating on support for curvilinear grids, optimization, efficiency and at-runtime coupling with OGCMs.
Publisher: Copernicus GmbH
Date: 26-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-926
Abstract: & & Mesoscale eddies play a major role in ocean ventilation by stirring ocean tracers, such as carbon, along sloping surfaces of neutral buoyancy. To capture the effects of these turbulent eddies, coarse resolution ocean models resort to tracer diffusion parameterizations that take into account neutral surface slopes. Likewise, when studying tracer pathways in a Lagrangian framework, the effect of eddy dispersion needs to be parameterized when coarse models are used.& & & & Dispersion in Lagrangian simulations is traditionally parameterized by random walks, equivalent to diffusion in Eulerian models. Beyond random walks, there is a hierarchy of stochastic parameterizations, where stochastic perturbations are added to Lagrangian particle velocities, accelerations, or hyper-accelerations. These parameterizations are referred to as the 1& sup& st& /sup& , 2& sup& nd& /sup& and 3& sup& rd& /sup& order & #8216 Markov models& #8217 (Markov-N& em& )& /em& respectively. Most previous studies investigate these parameterizations in two-dimensional setups, often restricted to the ocean surface. The few studies that investigated Lagrangian dispersion parameterizations on three-dimensional neutral surfaces have focused only on random walk (Markov-0) dispersion.& & & & Here, we present a three-dimensional isoneutral formulation of the Markov-1 model. We also implement an anisotropic, shear-dependent formulation of Lagrangian random walk dispersion, originally formulated as a Eulerian diffusion parameterization by Le Sommer et al (2011). Random walk dispersion and Markov-1 are compared using an idealized setup as well as more realistic coarse and coarsened (50 km) ocean model output. While random walk dispersion and Markov-1 produce similar particle distributions over time, Markov-1 yields more realistic Lagrangian trajectories and leads to a smaller spurious dianeutral flux.& &
Publisher: American Geophysical Union (AGU)
Date: 02-2018
DOI: 10.1002/2017JC013542
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-1033
Abstract: & & Lagrangian simulations contribute to the study and comprehension of particulate-matter transport, its dissolution and dispersion in the oceans. Parcels is an open-source, Python-based module for Lagrangian ocean simulations. It is a known tool in the oceanographic community that has been applied to a variety of case studies, such as the tracing of microplastics, the backtracking of ocean floor plankton, and the migration of fish. In this module, particles are advected over time according to a selected flow field, where those particles can represent particulate-matter, biota or other objects with physical, hydrodynamic or biogeochemical properties. In this contribution, we present the substantial extensions of Parcels with respect to usability, physics modelling aspects of particle advection, and computational aspects of versatile, scalable and efficient simulations.& & & & Specifically, a suite of simple, concise notebook tutorials are tailored to novice user, covering step-by-step simulation setup instructions, whereas self-contained special-issue tutorials address advanced- and proficient user requirements. The considerable expansion of supported OGCM flow field input formats (e.g. MITgcm, POP and MOM5, among others) is a major interest in Parcels v2.2 for our steadily-growing user base.& & & & The new version further integrates previously-published physics methods into practical lagrangian particle simulations. As such, we implement an analytical advection scheme in addition to existing Runge-Kutta advection schemes. Furthermore, two-dimensional advection-diffusion is upgraded with the Milstein stochastic integration scheme and improved documentation. Those capabilities enable a more consistent modelling of diffusion- and uncertainty-dominated fluid transport processes.& & & & The case studies performed with previous versions indicate increased computational demands. Simulations are run over long decadal time scales as well as over day-periods with sub-second temporal increments, involving multiple basins and global scenarios, while also modelling increasingly complex particle processes. Overall, our developments respond to the big-data requirements of modern oceanographic studies, which include the aspects of (i) high record volume (i.e. large number of particles), (ii) high dimensionality in multi-variate records, (iii) high spatial resolution, (iv) high temporal resolution, (v) high scenario (i.e. case study) variability and (vi) the prevention of numerical error accumulation over long simulation time scales.& & & & The novel features of Parcels v2.2 are illustrated on distinct case studies within our contribution, in order to connect the technical features to their impact on particulate-matter ocean transport studies.& &
Publisher: AIP Publishing
Date: 02-2015
DOI: 10.1063/PT.3.2697
Abstract: A piece of plastic discarded into the sea travels far and wide, carried by complex currents. Eventually, the material settles into one of five distinct garbage patches in the subtropical oceans.
Publisher: Copernicus GmbH
Date: 25-04-2022
Abstract: Abstract. The fate of (micro)plastic particles in the open ocean is controlled by biological and physical processes. Here, we model the effects of biofouling on the subsurface vertical distribution of spherical, virtual plastic particles with radii of 0.01–1 mm. The biological specifications include the attachment, growth and loss of algae on particles. The physical specifications include four vertical velocity terms: advection, wind-driven mixing, tidally induced mixing and the sinking velocity of the biofouled particle. We track 10 000 particles for 1 year in three different regions with distinct biological and physical properties: the low-productivity region of the North Pacific Subtropical Gyre, the high-productivity region of the equatorial Pacific and the high mixing region of the Southern Ocean. The growth of biofilm mass in the euphotic zone and loss of mass below the euphotic zone result in the oscillatory behaviour of particles, where the larger (0.1–1.0 mm) particles have much shorter average oscillation lengths ( d 90th percentile) than the smaller (0.01–0.1 mm) particles (up to 130 d 90th percentile). A subsurface maximum particle concentration occurs just below the mixed-layer depth (around 30 m) in the equatorial Pacific, which is most pronounced for larger particles (0.1–1.0 mm). This occurs because particles become neutrally buoyant when the processes affecting the settling velocity of a particle and the seawater's vertical movement are in equilibrium. Seasonal effects in the subtropical gyre result in particles sinking below the mixed-layer depth only during spring blooms but otherwise remaining within the mixed layer. The strong winds and deepest average mixed-layer depth in the Southern Ocean (400 m) result in the deepest redistribution of particles ( m). Our results show that the vertical movement of particles is mainly affected by physical (wind-induced mixing) processes within the mixed-layer and biological (biofilm) dynamics below the mixed layer. Furthermore, positively buoyant particles with radii of 0.01–1.0 mm can sink far below the euphotic zone and mixed layer in regions with high near-surface mixing or high biological activity. This work can easily be coupled to other models to simulate open-ocean biofouling dynamics, in order to reach a better understanding of where ocean (micro)plastic ends up.
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2013
End Date: 2015
Funder: Australian Research Council
View Funded ActivityStart Date: 2014
End Date: 2016
Funder: Australian Research Council
View Funded ActivityStart Date: 2017
End Date: 2020
Funder: Australian Research Council
View Funded ActivityStart Date: 2020
End Date: 2024
Funder: Nederlandse Organisatie voor Wetenschappelijk Onderzoek
View Funded ActivityStart Date: 2017
End Date: 2022
Funder: H2020 European Research Council
View Funded ActivityStart Date: 2017
End Date: 2021
Funder: Nederlandse Organisatie voor Wetenschappelijk Onderzoek
View Funded Activity