ORCID Profile
0000-0002-2038-7922
Current Organisation
NORCE Norwegian Research Centre AS
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Geophysics | Physical Oceanography | Geophysical Fluid Dynamics | Climate Change Processes
ANZSRC Socio-Economic Objective (SEO)
Marine Oceanic Processes (excl. climate related) | Climate Change Models |
Related Links
Publications
Deep-reaching global ocean overturning circulation generated by surface buoyancy forcing
Publisher: Authorea, Inc.
Date: 11-09-2023
Differentiating purging and nonpurging bulimia nervosa and binge eating disorder
Publisher: Wiley
Date: 24-09-2010
DOI: 10.1002/EAT.20823
Abstract: To explore similarities and differences in clinical and personality variables across three groups: binge eating disorder (BED), bulimia nervosa-purging type (BN-P), and bulimia nervosa-non purging type (BN-NP). The participants were 102 female eating disorders patients (34 BED, 34 BN-P, and 34 BN-NP) consecutively admitted to the eating disorders unit, at the University Hospital of Bellvitge, and diagnosed according to DSM-IV criteria. BED patients were older, and more likely to have personal and family history of obesity. A gradient in psychopathological scores emerged with BN-P patients having higher pathological scores on the SCL-90-R, followed by BN-NP and BED patients. No statistically significant differences were observed in personality traits. Our data supported that eating disorders (namely BED, BN-NP, and BN-P) followed a linear trend in general psychopathology. Whereas personality may represent a shared vulnerability factor, differences in clinical severity suggest there to be a continuum with BN-P being the most severe and BED being the least severe.
Influence of the Nonlinear Equation of State on Global Estimates of Dianeutral Advection and Diffusion
Publisher: American Meteorological Society
Date: 08-2010
Abstract: Recent work on the global overturning circulation and its energetics assumes that processes caused by nonlinearities of the equation of state of seawater are negligible. Nonlinear processes such as cabbeling and thermobaricity cause diapycnal motion as a consequence of isopycnal mixing. The nonlinear equation of state also causes the helical nature of neutral trajectories as a consequence of this helical nature, it is not possible to define a continuous “density” surface that aligns with neutral tangent planes. The result is an additional diapycnal advection, which needs to be accounted for in water-mass analysis. In this paper, the authors take advantage of new techniques in constructing very accurate continuous density surfaces to more precisely estimate isopycnal and diapycnal processes caused by the nonlinear equation of state. They then quantify the diapycnal advection due to each of these nonlinear processes and show that they lead in total to a significant downward diapycnal advection, particularly in the Southern Ocean. The nonlinear processes are therefore another source of dense water formation in addition to high-latitude convection. To maintain the abyssal stratification in the global ocean, these dense water masses have to be brought back toward surface layers, and this can occur by either diabatic or adiabatic processes. Including these nonlinear processes into the advection–diffusion balance, the authors show that observed diapycnal diffusivities are unlikely to be able to support the amount of dense water produced in the global ocean, thus placing more importance on the adiabatic way of bringing the deep waters back to the surface.
Ocean‐Sea Ice Processes and Their Role in Multi‐Month Predictability of Antarctic Sea Ice
Publisher: American Geophysical Union (AGU)
Date: 25-04-2022
DOI: 10.1029/2021GL097047
Abstract: Antarctic sea ice is a critical component of the climate system and a vital habitat for Southern Ocean ecosystems. Understanding the underlying physical processes and improving Antarctic sea ice prediction is of broad interest. Using the model data, we investigate sea ice and upper ocean predictability at interannual timescales in the Weddell Sea region. We find that oceanic predictability is largely confined to the Winter Water layer and responds to seasonal modifications of the water column, mainly driven by sea ice processes. Predictability depends not only on the depth of the Winter Water layer, but also on how strongly stratified its base is. Predictability is lost when warm Circumpolar Deep Water with no sea ice‐related memory entrains into the mixed layer. We show the strong dependence of sea ice predictability on the local upper ocean vertical structure, which suggests that both are likely to change in a warming climate.
The circulation and water masses of the Antarctic shelf and continental slope between 30 and
Publisher: Elsevier BV
Date: 05-2010
Direct Estimate of Lateral Eddy Diffusivity Upstream of Drake Passage
Publisher: American Meteorological Society
Date: 10-2014
Abstract: The first direct estimate of the rate at which geostrophic turbulence mixes tracers across the Antarctic Circumpolar Current is presented. The estimate is computed from the spreading of a tracer released upstream of Drake Passage as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). The meridional eddy diffusivity, a measure of the rate at which the area of the tracer spreads along an isopycnal across the Antarctic Circumpolar Current, is 710 ± 260 m2 s−1 at 1500-m depth. The estimate is based on an extrapolation of the tracer-based diffusivity using output from numerical tracers released in a one-twentieth of a degree model simulation of the circulation and turbulence in the Drake Passage region. The model is shown to reproduce the observed spreading rate of the DIMES tracer and suggests that the meridional eddy diffusivity is weak in the upper kilometer of the water column with values below 500 m2 s−1 and peaks at the steering level, near 2 km, where the eddy phase speed is equal to the mean flow speed. These vertical variations are not captured by ocean models presently used for climate studies, but they significantly affect the ventilation of different water masses.
Supplementary material to "ACCESS-OM2: A Global Ocean-Sea Ice Model at Three Resolutions"
Publisher: Copernicus GmbH
Date: 30-04-2019
Southern Ocean biogenic blooms freezing-in Oligocene colder climates
Publisher: Springer Science and Business Media LLC
Date: 09-11-2022
DOI: 10.1038/S41467-022-34623-9
Abstract: Crossing a key atmospheric CO 2 threshold triggered a fundamental global climate reorganisation ~34 million years ago (Ma) establishing permanent Antarctic ice sheets. Curiously, a more dramatic CO 2 decline (~800–400 ppm by the Early Oligocene(~27 Ma)), postdates initial ice sheet expansion but the mechanisms driving this later, rapid drop in atmospheric carbon during the early Oligocene remains elusive and controversial. Here we use marine seismic reflection and borehole data to reveal an unprecedented accumulation of early Oligocene strata (up to 2.2 km thick over 1500 × 500 km) with a major biogenic component in the Australian Southern Ocean. High-resolution ocean simulations demonstrate that a tectonically-driven, one-off reorganisation of ocean currents, caused a unique period where current instability coincided with high nutrient input from the Antarctic continent. This unrepeated and short-lived environment favoured extreme bioproductivity and enhanced sediment burial. The size and rapid accumulation of this sediment package potentially holds ~1.067 × 10 15 kg of the ‘missing carbon’ sequestered during the decline from an Eocene high CO 2 -world to a mid-Oligocene medium CO 2 -world, highlighting the exceptional role of the Southern Ocean in modulating long-term climate.
Using satellite altimetry to inform hypotheses of transport of early life stage of Patagonian toothfish on the Kerguelen Plateau
Publisher: Elsevier BV
Date: 11-2016
Diagnostics of isopycnal mixing in a circumpolar channel
Publisher: Elsevier BV
Date: 12-2013
ACCESS-OM2 v1.0: a global ocean–sea ice model at three resolutions
Publisher: Copernicus GmbH
Date: 05-02-2020
Abstract: Abstract. We introduce ACCESS-OM2, a new version of the ocean–sea ice model of the Australian Community Climate and Earth System Simulator. ACCESS-OM2 is driven by a prescribed atmosphere (JRA55-do) but has been designed to form the ocean–sea ice component of the fully coupled (atmosphere–land–ocean–sea ice) ACCESS-CM2 model. Importantly, the model is available at three different horizontal resolutions: a coarse resolution (nominally 1∘ horizontal grid spacing), an eddy-permitting resolution (nominally 0.25∘), and an eddy-rich resolution (0.1∘ with 75 vertical levels) the eddy-rich model is designed to be incorporated into the Bluelink operational ocean prediction and reanalysis system. The different resolutions have been developed simultaneously, both to allow for testing at lower resolutions and to permit comparison across resolutions. In this paper, the model is introduced and the in idual components are documented. The model performance is evaluated across the three different resolutions, highlighting the relative advantages and disadvantages of running ocean–sea ice models at higher resolution. We find that higher resolution is an advantage in resolving flow through small straits, the structure of western boundary currents, and the abyssal overturning cell but that there is scope for improvements in sub-grid-scale parameterizations at the highest resolution.
The sensitivity of the Eocene-Oligocene Southern Ocean to strength and position of wind stress
Publisher: Copernicus GmbH
Date: 24-02-2022
DOI: 10.5194/CP-2022-7
Abstract: Abstract. The early Cenozoic opening of the Tasmanian Gateway (TG) and Drake Passage (DP), alongside the synergistic action of the westerly winds, led to a Southern Ocean transition from large, subpolar gyres to the onset of the Antarctic Circumpolar Current (ACC). However, the impact of changing latitudinal position and strength of the wind stress in altering the early Southern Ocean circulation have been poorly addressed. Here, we use an eddy-permitting ocean model (0.25°) with realistic Late Eocene paleo-bathymetry to investigate the sensitivity of the Southern Ocean to paleo-latitudinal migrations (relative to the gateways) and strengthening of the wind stress. We find that southward wind stress shifts of 5 or 10°, with a shallow TG (300 m), lead to dominance of subtropical waters in the high latitudes and further warming of the Antarctic coast (increase by 2 °C). Southward migrations of wind stress with a deep TG (1500 m) cause the shrinking of the subpolar gyres and cooling of the surface waters in the Southern Ocean (decrease by 3–4 °C). With a 1500 m deep TG, and maximum westerly winds aligning with both the TG and DP, we observe a proto-ACC with a transport of ~47.9 Sv. This impedes the meridional transport of warm subtropical waters to Antarctic coast, thus laying a foundation for thermal isolation of the Antarctic. Intriguingly, proto-ACC flow through the TG is much more sensitive to strengthened wind stress compared to the DP. We suggest that topographic form stress can balance surface wind stress at depth to support the proto-ACC while the sensitivity of the transport is likely associated with the momentum budget between wind stress and near-surface topographic form stress driven by the subtropical gyres. In summary, this study proposes that the thermal isolation of Antarctica is a consequence of a combination of gateway deepening and the alignment of maximum wind stress with both gateways.
Deep Bottom Mixed Layer Drives Intrinsic Variability of the Antarctic Slope Front
Publisher: American Meteorological Society
Date: 12-2019
Abstract: The Antarctic Slope Front (ASF) is located along much of the Antarctic continental shelf break and helps to maintain a barrier to the movement of Circumpolar Deep Water (CDW) onto the continental shelf. The stability of the ASF has a major control on cross-shelf heat transport and ocean-driven basal melting of Antarctic ice shelves. Here, the ASF dynamics are investigated for continental shelves with weak dense shelf water (DSW) formation, which are thought to have a stable ASF, common for regions in East Antarctica. Using an ocean process model, this study demonstrates how offshore bottom Ekman transport of shelf waters leads to the development of a deep bottom mixed layer at the lower continental slope, and subsequently determines an intrinsic variability of the ASF. The ASF variability is characterized by instability events that affect the entire water column and occur every 5–10 years and last for approximately half a year. During these instability events, the cross-shelf density gradient weakens and CDW moves closer to the continent. Stronger winds increase the formation rate of the bottom mixed layer, which causes a subsequent increase of instability events. If the observed freshening trend of continental shelf waters leads to weaker DSW formation, more regions might be vulnerable for the ASF variability to develop in the future.
Supplementary material to The sensitivity of the Eocene-Oligocene Southern Ocean to strength and position of wind stress
Publisher: Copernicus GmbH
Date: 24-02-2022
Estimating Suppression of Eddy Mixing by Mean Flows
Publisher: American Meteorological Society
Date: 18-04-2012
Abstract: Particle- and tracer-based estimates of lateral diffusivities are used to estimate the suppression of eddy mixing across strong currents. Particles and tracers are advected using a velocity field derived from sea surface height measurements from the South Pacific, in a region west of Drake Passage. This velocity field has been used in a companion paper to show that both particle- and tracer-based estimates of eddy diffusivities are equivalent, despite recent claims to the contrary. These estimates of eddy diffusivities are here analyzed to show 1) that the degree of suppression of mixing across the strong Antarctic Circumpolar Current is correctly predicted by mixing length theory modified to include eddy propagation along the mean flow and 2) that the suppression can be inferred from particle trajectories by studying the structure of the autocorrelation function of the particle velocities beyond the first zero crossing. These results are then used to discuss how to compute lateral and vertical variations in eddy diffusivities using floats and drifters in the real ocean.
Generation of the Internal Pycnocline in the Subpolar Southern Ocean by Wintertime Sea Ice Melting
Publisher: American Geophysical Union (AGU)
Date: 03-2023
DOI: 10.1029/2022JC019113
Abstract: The ocean's internal pycnocline is a layer of elevated stratification that separates the well‐ventilated upper ocean from the more slowly renewed deep ocean. Despite its pivotal role in organizing ocean circulation, the processes governing the formation of the internal pycnocline remain little understood. Classical theories on pycnocline formation have been couched in terms of temperature and it is not clear how the theory applies in the high‐latitude Southern Ocean, where stratification is dominated by salinity. Here we assess the mechanisms generating the internal pycnocline at southern high latitudes through the analysis of a high‐resolution, realistic, global sea ice–ocean model. We show evidence suggesting that the internal pycnocline's formation is associated with sea ice‐ocean interactions in two distinct ice‐covered regions, fringing the Antarctic continental slope and the winter sea‐ice edge. In both areas, winter‐persistent sea‐ice melt creates strong, salinity‐based stratification at the base of the winter mixed layer. The resulting sheets of high stratification subsequently descend into the ocean interior at fronts of the Antarctic Circumpolar Current, and connect seamlessly to the internal pycnocline in areas further north in which pycnocline stratification is determined by temperature. Our findings thus suggest an important role of localized sea ice‐ocean interactions in configuring the vertical structure of the Southern Ocean.
Testing the influence of the Central American Seaway on orbitally forced Northern Hemisphere glaciation
Publisher: American Geophysical Union (AGU)
Date: 2005
DOI: 10.1029/2004GL021564
Ocean-sea ice processes and their role on multi-month predictability of Antarctic sea ice
Publisher: Wiley
Date: 12-2021
Interaction of Jets and Submesoscale Dynamics Leads to Rapid Ocean Ventilation
Publisher: American Meteorological Society
Date: 10-2020
Abstract: Ocean ventilation is the process by which climatically important tracers such as heat and carbon are exchanged between the atmosphere and ocean interior. In this paper a series of numerical simulations are used to study the interaction of submesoscales and a topographically steered jet in driving rapid ventilation. The ventilation is found to increase both as a function of wind stress and model resolution, with a submesoscale-resolving 1/120° model exhibiting the largest ventilation rate. The jet in this simulation is found to be persistently unstable to submesoscale instabilities, which are known to feature intense vertical circulations. The vertical tracer transport is found to scale as a function of the eddy kinetic energy and mean isopycnal slope, whose behaviors change as a function of the wind stress and due to the emergence of a strong potential vorticity gradient due to the lateral shear of the jet. These results highlight the importance of jet–submesoscale interaction as a bridge between the atmosphere and the ocean interior.
Deep convection as the key to the transition from Eocene to modern Antarctic Circumpolar Current
Publisher: Authorea, Inc.
Date: 08-07-2023
DOI: 10.22541/ESSOAR.168881813.35699121/V1
Abstract: From the Eocene (~50 million years ago) to today, Southern Ocean circulation has evolved from the existence of two ocean gyres to the dominance of the Antarctic Circumpolar Current (ACC). It has generally been thought that the opening of Southern Ocean gateways in the late Eocene, in addition to the alignment of westerly winds with these gateways or the presence of Antarctic ice sheet, was a sufficient requirement for the transition to an ACC of similar strength to its modern equivalent. Nevertheless, models representing these changes produce only a much weaker ACC. Here we show, using an eddying ocean model, that the missing ingredient in the transition to a modern ACC is deep convection around the Antarctic continent. This deep convection is caused by cold temperatures and high salinities due to sea-ice production around the Antarctic continent, leading to both the formation of Antarctic Bottom Water and a modern-strength ACC.
Water mass transformation by cabbeling and thermobaricity
Publisher: American Geophysical Union (AGU)
Date: 18-10-2016
DOI: 10.1002/2016GL070860
Global Patterns of Mesoscale Eddy Properties and Diffusivities
Publisher: American Meteorological Society
Date: 03-2014
Abstract: Mesoscale eddies play a major role in the transport of tracers in the ocean. Focusing on a sector in the east Pacific, the authors present estimates of eddy diffusivities derived from kinematic tracer simulations using satellite-observed velocity fields. Meridional diffusivities are diagnosed, and how they are related to eddy properties through the mixing length formulation of Ferrari and Nikurashin, which accounts for the suppression of diffusivity due to eddy propagation relative to the mean flow, is shown. The uniqueness of this study is that, through systematically varying the zonal-mean flow, a hypothetical “unsuppressed” diffusivity is diagnosed. At a given latitude, the unsuppressed diffusivity occurs when the zonal-mean flow equals the eddy phase speed. This provides an independent estimate of eddy phase propagation, which agrees well with theoretical arguments. It is also shown that the unsuppressed diffusivity is predicted very well by classical mixing length theory, that is, that it is proportional to the rms eddy velocity times the observed eddy size, with a spatially constant mixing efficiency of 0.35. Then, the suppression factor is estimated and it is shown that it too can be understood quantitatively in terms of easily observed mean flow properties. The authors then extrapolate from these sector experiments to the global scale, making predictions for the global surface eddy diffusivity. Together with a prognostic equation for eddy kinetic energy and a theory explaining observed eddy sizes, these concepts could potentially be used in a closure for eddy diffusivities in coarse-resolution ocean climate models.
An approximate geostrophic streamfunction for use in density surfaces
Publisher: Elsevier BV
Date: 2010
Reconciling float-based and tracer-based estimates of lateral diffusivities
Publisher: Journal of Marine Research/Yale
Date: 04-07-2012
Deepening of Southern Ocean gateway leads to abrupt onset of a deep-reaching meridional overturning circulation
Publisher: Authorea, Inc.
Date: 09-02-2023
DOI: 10.22541/ESSOAR.167590830.09227890/V1
Abstract: During the Eocene-Oligocene transition, the meridional overturning circulation underwent large changes, associated with the geological evolution of Southern Ocean gateways. These are crucial for the Cenozoic climate transition from Greenhouse to Icehouse, but their dynamics still remain elusive. We demonstrate, using an idealised eddying ocean model, that the opening of a gateway leads to an abrupt onset of a vigorous, deep-reaching, meridional overturning circulation. This meridional overturning circulation has a maximum transport for a shallow gateway, and decreases with further deepening of the gateway. This abrupt change in the meridional overturning circulation can be explained through the ability with which standing meanders – turbulent features located downstream of the gateway – can induce deep vertical heat transport at high latitudes where bottom waters are produced. Our results demonstrate the crucial role of turbulent processes, associated with tectonic evolution, in setting the strength of the global ocean’s deep-reaching meridional overturning circulation.
Circum‐Antarctic Shoreward Heat Transport Derived From an Eddy‐ and Tide‐Resolving Simulation
Publisher: American Geophysical Union (AGU)
Date: 19-01-2018
DOI: 10.1002/2017GL075677
A biologically relevant method for considering patterns of oceanic retention in the Southern Ocean
Publisher: Elsevier BV
Date: 12-2017
Vertical transport in the ocean due to sub-mesoscale structures: Impacts in the Kerguelen region
Publisher: Elsevier BV
Date: 08-2014
A regime diagram for ocean geostrophic turbulence
Publisher: Wiley
Date: 15-06-2016
DOI: 10.1002/QJ.2833
ACCESS-OM2: A Global Ocean-Sea Ice Model at Three Resolutions
Publisher: Copernicus GmbH
Date: 30-04-2019
DOI: 10.5194/GMD-2019-106
Abstract: Abstract. We introduce a new version of the ocean-sea ice implementation of the Australian Community Climate and Earth System Simulator, ACCESS-OM2. The model has been developed with the aim of being aligned as closely as possible with the fully coupled (atmosphere-land-ocean-sea ice) ACCESS-CM2. Importantly, the model is available at three different horizontal resolutions: a coarse resolution (nominally 1° horizontal grid spacing), an eddy-permitting resolution (nominally 0.25°) and an eddy-rich resolution (0.1° with 75 vertical levels), where the eddy-rich model is designed to be incorporated into the Bluelink operational ocean prediction and reanalysis system. The different resolutions have been developed simultaneously, both to allow testing at lower resolutions and to permit comparison across resolutions. In this manuscript, the model is introduced and the in idual components are documented. The model performance is evaluated across the three different resolutions, highlighting the relative advantages and disadvantages of running ocean-sea ice models at higher resolution. We find that higher resolution is an advantage in resolving flow through small straits, the structure of western boundary currents and the abyssal overturning cell, but that there is scope for improvements in sub-grid scale parameterisations at the highest resolution.
Mesoscale and Submesoscale Effects on Mixed Layer Depth in the Southern Ocean
Publisher: American Meteorological Society
Date: 09-2017
Abstract: Submesoscale dynamics play a key role in setting the stratification of the ocean surface mixed layer and mediating air–sea exchange, making them especially relevant to anthropogenic carbon uptake and primary productivity in the Southern Ocean. In this paper, a series of offline-nested numerical simulations is used to study submesoscale flow in the Drake Passage and Scotia Sea regions of the Southern Ocean. These simulations are initialized from an ocean state estimate for late April 2015, with the intent to simulate features observed during the Surface Mixed Layer at Submesoscales (SMILES) research cruise, which occurred at that time and location. The nested models are downscaled from the original state estimate resolution of 1/12° and grid spacing of about 8 km, culminating in a submesoscale-resolving model with a resolution of 1/192° and grid spacing of about 500 m. The submesoscale eddy field is found to be highly spatially variable, with pronounced hot spots of submesoscale activity. These areas of high submesoscale activity correspond to a significant difference in the 30-day average mixed layer depth between the 1/12° and 1/192° simulations. Regions of large vertical velocities in the mixed layer correspond with high mesoscale strain rather than large . It is found that is well correlated with the mesoscale density gradient but weakly correlated with both the mesoscale kinetic energy and strain. This has implications for the development of submesoscale eddy parameterizations that are sensitive to the character of the large-scale flow.
Planetary–Geometric Constraints on Isopycnal Slope in the Southern Ocean
Publisher: American Meteorological Society
Date: 12-2015
Abstract: On planetary scales, surface wind stress and differential buoyancy forcing act together to produce isopycnal surfaces that are relatively flat in the tropics/subtropics and steep near the poles, where they tend to outcrop. Tilted isopycnals in a rapidly rotating fluid are subject to baroclinic instability. The turbulent, mesoscale eddies generated by this instability have a tendency to homogenize potential vorticity (PV) along density surfaces. In the Southern Ocean (SO), the tilt of isopycnals is largely maintained by competition between the steepening effect of surface forcing and the flattening effect of turbulent, spatially inhomogeneous eddy fluxes of PV. Here quasigeostrophic theory is used to investigate the influence of a planetary–geometric constraint on the equilibrium slope of tilted density/buoyancy surfaces in the SO. If the meridional gradients of relative vorticity and PV are small relative to β , then quasigeostrophic theory predicts ds / dz = β / f 0 = cot( ϕ 0 )/ a , or equivalently r ≡ |∂ z s /( β / f 0 )| = 1, where f is the Coriolis parameter, β is the meridional gradient of f , s is the isopycnal slope, ϕ 0 is a reference latitude, a is the planetary radius, and r is the depth-averaged criticality parameter. It is found that the strict r = 1 condition holds over specific averaging volumes in a large-scale climatology. A weaker r = O (1) condition for depth-averaged quantities is generally satisfied away from large bathymetric features. The r = O (1) constraint is employed to derive a depth scale to characterize large-scale interior stratification, and an idealized sector model is used to test the sensitivity of this relationship to surface wind forcing. Finally, the possible implications for eddy flux parameterization and for the sensitivity of SO circulation/stratification to changes in forcing are discussed.
Sustained Upwelling of Subsurface Iron Supplies Seasonally Persistent Phytoplankton Blooms Around the Southern Kerguelen Plateau, Southern Ocean
Publisher: American Geophysical Union (AGU)
Date: 08-2018
DOI: 10.1029/2018JC013932
Opening the window to the Southern Ocean: The role of jet dynamics
Publisher: American Association for the Advancement of Science (AAAS)
Date: 05-10-2018
Abstract: Jet dynamics play a crucial role in Southern Ocean ventilation.
Quantifying the Consequences of the Ill-Defined Nature of Neutral Surfaces
Publisher: American Meteorological Society
Date: 08-2010
Abstract: In the absence of diapycnal mixing processes, fluid parcels move in directions along which they do not encounter buoyant forces. These directions define the local neutral tangent plane. Because of the nonlinear nature of the equation of state of seawater, these neutral tangent planes cannot be connected globally to form a well-defined surface in three-dimensional space that is, continuous “neutral surfaces” do not exist. This inability to form well-defined neutral surfaces implies that neutral trajectories are helical. Consequently, even in the absence of diapycnal mixing processes, fluid trajectories penetrate through any “density” surface. This process amounts to an extra mechanism that achieves mean vertical advection through any continuous surface such as surfaces of constant potential density or neutral density. That is, the helical nature of neutral trajectories causes this additional diasurface velocity. A water-mass analysis performed with respect to continuous density surfaces will have part of its diapycnal advection due to this diasurface advection process. Hence, this additional diasurface advection should be accounted for when attributing observed water-mass changes to mixing processes. Here, the authors quantify this component of the total diasurface velocity and show that locally it can be the same order of magnitude as diasurface velocities produced by other mixing processes, particularly in the Southern Ocean. The magnitude of this diasurface advection is proportional to the ocean’s neutral helicity, which is observed to be quite small in today’s ocean. The authors also use a perturbation experiment to show that the ocean rapidly readjusts to its present state of small neutral helicity, even if perturbed significantly. Additionally, the authors show how seasonal (rather than spatial) changes in the ocean’s hydrography can generate a similar vertical advection process. This process is described here for the first time although the vertical advection due to this process is small, it helps to understand water-mass transformation on density surfaces.
Acceleration and Overturning of the Antarctic Slope Current by Winds, Eddies, and Tides
Publisher: American Meteorological Society
Date: 08-2019
Abstract: All exchanges between the open ocean and the Antarctic continental shelf must cross the Antarctic Slope Current (ASC). Previous studies indicate that these exchanges are strongly influenced by mesoscale and tidal variability, yet the mechanisms responsible for setting the ASC’s transport and structure have received relatively little attention. In this study the roles of winds, eddies, and tides in accelerating the ASC are investigated using a global ocean–sea ice simulation with very high resolution (1/48° grid spacing). It is found that the circulation along the continental slope is accelerated both by surface stresses, ultimately sourced from the easterly winds, and by mesoscale eddy vorticity fluxes. At the continental shelf break, the ASC exhibits a narrow (~30–50 km), swift ( .2 m s −1 ) jet, consistent with in situ observations. In this jet the surface stress is substantially reduced, and may even vanish or be directed eastward, because the ocean surface speed matches or exceeds that of the sea ice. The shelfbreak jet is shown to be accelerated by tidal momentum advection, consistent with the phenomenon of tidal rectification. Consequently, the shoreward Ekman transport vanishes and thus the mean overturning circulation that steepens the Antarctic Slope Front (ASF) is primarily due to tidal acceleration. These findings imply that the circulation and mean overturning of the ASC are not only determined by near-Antarctic winds, but also depend crucially on sea ice cover, regionally-dependent mesoscale eddy activity over the continental slope, and the litude of tidal flows across the continental shelf break.
Deepening of Southern Ocean Gateway Leads to Abrupt Onset of a Deep‐Reaching Meridional Overturning Circulation
Publisher: American Geophysical Union (AGU)
Date: 04-10-2023
DOI: 10.1029/2023GL104382
Generation of the Southern Ocean pycnocline by sea ice-ocean interactions
Publisher: Wiley
Date: 14-02-2022
Modelling dispersal of juvenile krill released from the Antarctic ice edge: Ecosystem implications of ocean movement
Publisher: Elsevier BV
Date: 2019
Abrupt transitions in dynamics of a NPZD model across Southern Ocean fronts
Publisher: Elsevier BV
Date: 09-2017
Surface oceanography of BROKE-West, along the Antarctic margin of the south-west Indian Ocean (30
Publisher: Elsevier BV
Date: 05-2010
The Deep Ocean Buoyancy Budget and Its Temporal Variability
Publisher: American Meteorological Society
Date: 15-01-2014
DOI: 10.1175/JCLI-D-13-00016.1
Abstract: Despite slow rates of ocean mixing, observational and modeling studies suggest that buoyancy is redistributed to all depths of the ocean on surprisingly short interannual to decadal time scales. The mechanisms responsible for this redistribution remain poorly understood. This work uses an Earth system model to evaluate the global steady-state ocean buoyancy (and related steric sea level) budget, its interannual variability, and its transient response to a doubling of CO2 over 70 years, with a focus on the deep ocean. At steady state, the simple view of vertical advective–diffusive balance for the deep ocean holds at low to midlatitudes. At higher latitudes, the balance depends on a myriad of additional terms, namely mesoscale and submesoscale advection, convection and overflows from marginal seas, and terms related to the nonlinear equation of state. These high-latitude processes rapidly communicate anomalies in surface buoyancy forcing to the deep ocean locally the deep, high-latitude changes then influence the large-scale advection of buoyancy to create transient deep buoyancy anomalies at lower latitudes. Following a doubling of atmospheric carbon dioxide concentrations, the high-latitude buoyancy sinks are suppressed by a slowdown in convection and reduced dense water formation. This change is accompanied by a slowing of both upper and lower cells of the global meridional overturning circulation, reducing the supply of dense water to low latitudes beneath the pycnocline and the commensurate flow of light waters to high latitudes above the pycnocline. By this mechanism, changes in high-latitude buoyancy are communicated to the global deep ocean on relatively fast advective time scales.
Advection of baroclinic eddies by depth mean flow
Publisher: American Geophysical Union (AGU)
Date: 23-05-2014
DOI: 10.1002/2014GL060001
Gateway-driven weakening of ocean gyres leads to Southern Ocean cooling
Publisher: Springer Science and Business Media LLC
Date: 09-11-2021
DOI: 10.1038/S41467-021-26658-1
Abstract: Declining atmospheric CO 2 concentrations are considered the primary driver for the Cenozoic Greenhouse-Icehouse transition, ~34 million years ago. A role for tectonically opening Southern Ocean gateways, initiating the onset of a thermally isolating Antarctic Circumpolar Current, has been disputed as ocean models have not reproduced expected heat transport to the Antarctic coast. Here we use high-resolution ocean simulations with detailed paleobathymetry to demonstrate that tectonics did play a fundamental role in reorganising Southern Ocean circulation patterns and heat transport, consistent with available proxy data. When at least one gateway (Tasmanian or Drake) is shallow (300 m), gyres transport warm waters towards Antarctica. When the second gateway subsides below 300 m, these gyres weaken and cause a dramatic cooling (average of 2–4 °C, up to 5 °C) of Antarctic surface waters whilst the ACC remains weak. Our results demonstrate that tectonic changes are crucial for Southern Ocean climate change and should be carefully considered in constraining long-term climate sensitivity to CO 2 .
Late winter oceanography off the Sabrina and BANZARE coast (117–128°E), East Antarctica
Publisher: Elsevier BV
Date: 05-2011
Impact of Deep Water Formation on Antarctic Circumpolar Transport During Gateway Opening
Publisher: Authorea, Inc.
Date: 21-12-2022
DOI: 10.22541/ESSOAR.167160849.98375746/V1
Abstract: Ambiguity over the Eocene opening times of the Tasman Gateway and Drake Passage makes it difficult to determine the initiation time of the Antarctic Circumpolar Current (ACC). If the Tasman Gateway opened later than Drake Passage, then Australia may have prevented the proto-ACC from forming. Recent modelling results have shown that only a relatively weak circumpolar transport results under Eocene surface forcing. This leads to warm and buoyant coastal water around Antarctica, which may impede the formation of deep waters and convective processes. This suggests that a change in deep water formation might be required to increase the density contrast across the Southern Ocean and increase circumpolar transport.Here we use a simple reduced gravity model with two basins, to represent the Atlantic and the Pacific. This fixes the density difference between surface and deep water and allows us to isolate the impact of deep water formation on circumpolar transport. With no obstacle on the southern boundary the circumpolar current increases its transport from 82.3 to 270.0 Sv with deep water formation. Placing an Antipodean landmass on the southern boundary reduces this transport as the landmass increases in size. However, circumpolar flow north of this landmass remains a possibility even without deep water formation. Weak circumpolar transport continues until the basin is completely blocked by the Antipodes. When the Antipodes is instead allowed to split from the southern boundary, circumpolar transport recovers to its unobstructed value. Flow rapidly switches to south of the Antipodes when the gateway is narrow.
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Massachusetts Institute Of Technology
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