ORCID Profile
0000-0002-2941-7577
Current Organisation
University of Tasmania
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
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.
Oceanography | Physical Oceanography | Climate Change Processes | Biological Oceanography | Chemical Oceanography | Glaciology
Climate Variability (excl. Social Impacts) | Expanding Knowledge in the Earth Sciences | Effects of Climate Change and Variability on Antarctic and Sub-Antarctic Environments (excl. Social Impacts) | Climate Change Models | Expanding Knowledge in the Environmental Sciences | Antarctic and Sub-Antarctic Oceanography | Marine Oceanic Processes (excl. climate related) |
Publisher: American Meteorological Society
Date: 08-2020
Abstract: The long-term trend of sea surface salinity (SSS) reveals an intensification of the global hydrological cycle due to human-induced climate change. This study demonstrates that SSS variability can also be used as a measure of terrestrial precipitation on interseasonal to interannual time scales, and to locate the source of moisture. Seasonal composites during El Niño–Southern Oscillation/Indian Ocean dipole (ENSO/IOD) events are used to understand the variations of moisture transport and precipitation over Australia, and their association with SSS variability. As ENSO/IOD events evolve, patterns of positive or negative SSS anomaly emerge in the Indo-Pacific warm pool region and are accompanied by atmospheric moisture transport anomalies toward Australia. During co-occurring La Niña and negative IOD events, salty anomalies around the Maritime Continent (north of Australia) indicate freshwater export and are associated with a significant moisture transport that converges over Australia to create anomalous wet conditions. In contrast, during co-occurring El Niño and positive IOD events, a moisture transport ergence anomaly over Australia results in anomalous dry conditions. The relationship between SSS and atmospheric moisture transport also holds for pure ENSO/IOD events but varies in magnitude and spatial pattern. The significant pattern correlation between the moisture flux ergence and SSS anomaly during the ENSO/IOD events highlights the associated ocean–atmosphere coupling. A case study of the extreme hydroclimatic events of Australia (e.g., the 2010/11 Brisbane flood) demonstrates that the changes in SSS occur before the peak of ENSO/IOD events. This raises the prospect that tracking of SSS variability could aid the prediction of Australian rainfall.
Publisher: Elsevier BV
Date: 1991
Publisher: Frontiers Media SA
Date: 24-07-2019
Publisher: Copernicus GmbH
Date: 29-04-2014
Publisher: American Geophysical Union (AGU)
Date: 02-2019
DOI: 10.1029/2018JC014655
Publisher: American Geophysical Union (AGU)
Date: 08-11-2013
DOI: 10.1002/2013GL057887
Publisher: Elsevier BV
Date: 09-2013
Publisher: American Meteorological Society
Date: 05-2018
Publisher: American Geophysical Union (AGU)
Date: 09-2017
DOI: 10.1002/2017GB005669
Publisher: Springer Science and Business Media LLC
Date: 24-04-2020
DOI: 10.1038/S41467-020-15754-3
Abstract: Recent research shows that 90% of the net global ocean heat gain during 2005–2015 was confined to the southern hemisphere with little corresponding heat gain in the northern hemisphere ocean. We propose that this heating pattern of the ocean is driven by anthropogenic climate change and an asymmetric climate variation between the two hemispheres. This asymmetric variation is found in the pre-industrial control simulations from 11 climate models. While both layers (0–700 m and 700–2000 m) experience steady anthropogenic warming, the 0–700 m layer experiences large internal variability, which primarily drives the observed hemispheric asymmetry of global ocean heat gain in 0–2000 m layer. We infer that the rate of global ocean warming is consistent with the climate simulations for this period. However, the observed hemispheric asymmetry in heat gain can be explained by the Earth’s internal climate variability without invoking alternate hypotheses, such as asymmetric aerosol loading.
Publisher: American Meteorological Society
Date: 11-2004
DOI: 10.1175/JPO2640.1
Abstract: The equatorial SST dipole represents a mode of climate variability in the tropical Atlantic Ocean that is closely tied to cross-equatorial flow in the atmosphere, from the cold to the warm hemisphere. It has been suggested that this mode is sustained by a positive feedback of the tropical winds on the cross-equatorial SST gradient. The role, if any, of the tropical ocean is the focus of this investigation, which shows that at the latitudes of the SST signal (centered on 10°N/S) there is a weak positive feedback suggested in data from the last half century, that the cross-equatorial wind stress is closely coupled to this SST gradient on monthly time scales with no discernable lag, and that the period from January to June is the most active period for coupling. Northward (southward) anomalies of cross-equatorial wind stress are associated with a substantial negative (positive) wind stress curl. This wind system can thus drive a cross-equatorial Sverdrup transport in the ocean from the warm to the cold side of the equator (opposite the winds) with a temporal lag of only a few months. The oceanic observations of subsurface temperature and a numerical model hindcast also indicate a clear relationship between this mode of wind-driven variability and changes in the zonal transport of the North Equatorial Countercurrent. It is estimated that the time-dependent oceanic flow is capable of providing a significant contribution to the d ing of the SST dipole but that external forcing is essential to sustaining the coupled variability.
Publisher: American Geophysical Union (AGU)
Date: 30-03-2023
DOI: 10.1029/2022JC018984
Abstract: Eddies modulate open ocean productivity, and this influence depends on both eddy source and evolution. Southeast Indian Ocean eddies are important pathways for the westward transport of biogeochemical anomalies from the Leeuwin current into the central oligotrophic South Indian Ocean (SIO). Eddy processes at the base of the mixed layer may stimulate and sustain phytoplankton, allowing these eddy impacts to persist over thousands of kilometers. We present 4 months of high‐frequency profiles from autonomous floats in one anticyclonic and one cyclonic eddy in the SIO. At the start of observations, from September to October, particulate organic carbon (POC) and especially chlorophyll were higher in the cyclone, and evenly distributed throughout the mixed layers in both eddies. As spring progressed and the eddies were transported westward, chlorophyll and POC concentrated at the base of the mixed layer at depths invisible to satellites, likely reflecting nutrient depletion in overlying waters. In the anticyclone, the increased chlorophyll at depth occurred as POC decreased, suggesting photo‐acclimation and thus both light and nutrient stress. In contrast, in the cyclone chlorophyll to POC ratios remained close to constant as their subsurface maxima formed. In both eddies, the subsurface biomass maxima exhibited no significant change in oxygen saturation state over several months suggesting these communities are sustained by low ongoing productivity in balance with community respiration. Thus, deep biomass layers may represent a mechanism for long‐distance transfer of eddy plankton communities which is not reflected in satellite remote sensing.
Publisher: American Geophysical Union (AGU)
Date: 10-2014
DOI: 10.1002/2014JC010076
Publisher: American Geophysical Union (AGU)
Date: 09-2019
DOI: 10.1029/2018JC014559
Publisher: American Geophysical Union (AGU)
Date: 31-05-2022
DOI: 10.1029/2021JC017863
Abstract: The Southern Ocean plays a vital role in global ocean circulation, and the Polar Front (PF) is one of its most important physical features. The PF meander south of Tasmania, around 153°E, 55°S, is a very dynamic region which spawns mesoscale eddies, and influences local biogeochemistry and sea‐air interaction. By using voyage and ancillary data, we investigated the unusually strong spring bloom in the vicinity of the PF meander in 2018. We infer that the upwelling of deep water at the front and in eddies, brings macronutrients and dissolved iron (dFe) to the surface. Chlorophyll concentration peaked at over 0.6 mg m −3 , which is anomalously high for this area. With reduced iron limitation, the physiological characteristics of phytoplankton in the northern, downstream part of the study area also changed. The photochemical efficiency was improved and released this area from its usual high‐nutrient low‐chlorophyll (HNLC) status. This was mainly indicated by the increase in the dawn Fv/Fm maximum (indictor of photochemical efficiency) from 0.2 to over 0.5. With the biomass increase and healthier community status, we observed consumption of surface dissolved inorganic carbon and increased particulate organic carbon production to about 40 μmol L −1 , forming a weak local carbon sink. Through the investigation of multiple years, a weak positive correlation between mixed layer depth shoaling and phytoplankton growth was found, but there was significant interannual variability in this relationship, likely caused by variable eddy conditions and dFe delivery.
Publisher: Copernicus GmbH
Date: 23-04-2015
Abstract: Abstract. In this paper we examine time-series measurements of near-surface chlorophyll concentration from a mooring that was deployed at 80.5°E on the equator in the Indian Ocean in 2010. These data reveal at least six striking spikes in chlorophyll from October through December, at approximately 2-week intervals, that coincide with the development of the fall Wyrtki jets during the transition between the summer and winter monsoons. Concurrent meteorological and in situ physical measurements from the mooring reveal that the chlorophyll pulses are associated with the intensification of eastward winds at the surface and eastward currents in the mixed layer. These observations are inconsistent with upwelling dynamics as they occur in the Atlantic and Pacific oceans, since eastward winds that force Wyrtki jet intensification should drive downwelling. The chlorophyll spikes could be explained by two alternative mechanisms: (1) turbulent entrainment of nutrients and/or chlorophyll from across the base of the mixed layer by wind stirring or Wyrtki jet-induced shear instability or (2) enhanced southward advection of high chlorophyll concentrations into the equatorial zone. The first mechanism is supported by the phasing and litude of the relationship between wind stress and chlorophyll, which suggests that the chlorophyll spikes are the result of turbulent entrainment driven by synoptic zonal wind events. The second mechanism is supported by the observation of eastward flows over the Chagos–Lacca e Ridge, generating high chlorophyll to the north of the equator. Occasional southward advection can then produce the chlorophyll spikes that are observed in the mooring record. Wind-forced biweekly mixed Rossby gravity waves are a ubiquitous feature of the ocean circulation in this region, and we examine the possibility that they may play a role in chlorophyll variability. Statistical analyses and results from the OFAM3 (Ocean Forecasting Australia Model, version 3) eddy-resolving model provide support for both mechanisms. However, the model does not reproduce the observed spikes in chlorophyll. Climatological satellite chlorophyll data show that the elevated chlorophyll concentrations in this region are consistently observed year after year and so are reflective of recurring large-scale wind- and circulation-induced productivity enhancement in the central equatorial Indian Ocean.
Publisher: American Meteorological Society
Date: 03-2017
Abstract: The Leeuwin Current System (LCS) along the coast of Western Australia consists of the poleward-flowing Leeuwin Current (LC), the equatorward-flowing Leeuwin Undercurrent (LUC), and neighboring flows in the south Indian Ocean (SIO). Using geostrophic currents obtained from a highly resolved (⅛°) hydrographic climatology [CSIRO Atlas of Regional Seas (CARS)], this study describes the spatial structure and annual variability of the LC, LUC, and SIO zonal currents, estimates their transports, and identifies linkages among them. In CARS, the LC is supplied partly by water from the tropics (an annual mean of 0.3 Sv 1 Sv ≡ 10 6 m 3 s −1 ) but mostly by shallow ( 200 m) eastward flows in the SIO (4.7 Sv), and it loses water by downwelling across the bottom of this layer (3.4 Sv). The downwelling is so strong that, despite the large SIO inflow, the horizontal transport of the LC does not much increase to the south (from 0.3 Sv at 22°S to 1.5 Sv at 34°S). This LC transport is significantly smaller than previously reported. The LUC is supplied by water from south of Australia (0.2 Sv), by eastward inflow from the SIO south of 28°S (1.6 Sv), and by the downwelling from the LC (1.6 Sv) and in response strengthens northward, reaching a maximum near 28°S (3.4 Sv). North of 28°S it loses water by outflow into subsurface westward flow (−3.6 Sv between 28° and 22°S) and despite an additional downwelling from the LC (1.9 Sv), it decreases to the north (1.7 Sv at 22°S). The seasonality of the LUC is described for the first time.
Publisher: American Geophysical Union (AGU)
Date: 08-2020
DOI: 10.1029/2020JC016115
Publisher: Copernicus GmbH
Date: 15-09-2016
DOI: 10.5194/CP-2016-72
Abstract: Abstract. A 120 m ice core was drilled on Mill Island, East Antarctica (65°30’ S, 100°40’ E) during the 2009/2010 Australian Antarctic field season. Contiguous discrete 5 cm s les were measured for hydrogen peroxide, water stable isotopes and trace ion chemistry. The ice core was annually dated using a combination of chemical species and water stable isotopes. The Mill Island ice core preserves a climate record covering 97 years from 1913 to 2009 C.E., with a mean snow accumulation of 1.35 m (ice-equivalent) per year (mIE yr−1). This northernmost East Antarctic coastal ice core site displays trace ion concentrations that are generally higher than other Antarctic ice core sites (e.g., mean sodium levels were 254 μEq L−1). The trace ion record at Mill Island is characterised by a unique and complex chemistry record with three distinct regimes identified. The trace ion record in Regime A displays clear seasonality from 2000 to 2009 C.E. Regime B displays elevated concentrations with no seasonality from 1934 to 2000 C.E. and Regime C displays relatively low concentrations with seasonality from 1913 to 1934 C.E. Sea salts were compared with instrumental data, including atmospheric models and satellite-derived sea ice concentration, to investigate influences on the Mill Island ice core record. The mean annual sea salt record does not correlate with wind speed. Instead, sea ice concentration to the east of Mill Island likely influences the annual mean sea salt record. A mechanism involving formation of frost flowers on sea ice is proposed to explain the extremely high sea salt concentration. The Mill Island ice core records are unexpectedly complex, with strong modulation of the trace chemistry on long timescales.
Publisher: Copernicus GmbH
Date: 09-05-2017
Abstract: Abstract. A 120 m ice core was drilled on Mill Island, East Antarctica (65°30′ S, 100°40′ E) during the 2009/2010 Australian Antarctic field season. Contiguous discrete 5 cm s les were measured for hydrogen peroxide, water stable isotopes, and trace ion chemistry. The ice core was annually dated using a combination of chemical species and water stable isotopes. The Mill Island ice core preserves a climate record covering 97 years from 1913 to 2009 CE, with a mean snow accumulation of 1.35 m (ice-equivalent) per year (mIE yr−1). This northernmost East Antarctic coastal ice core site displays trace ion concentrations that are generally higher than other Antarctic ice core sites (e.g. mean sodium levels were 254 µEq L−1). The trace ion record at Mill Island is characterised by a unique and complex chemistry record with three distinct regimes identified. The trace ion record in regime A displays clear seasonality from 2000 to 2009 CE regime B displays elevated concentrations with no seasonality from 1934 to 2000 CE and regime C displays relatively low concentrations with seasonality from 1913 to 1934 CE. Sea salts were compared with instrumental data, including atmospheric models and satellite-derived sea-ice concentration, to investigate influences on the Mill Island ice core record. The mean annual sea salt record does not correlate with wind speed. Instead, sea-ice concentration to the east of Mill Island likely influences the annual mean sea salt record. A mechanism involving formation of frost flowers on sea ice is proposed to explain the extremely high sea salt concentration. The Mill Island ice core records are unexpectedly complex, with strong modulation of the trace chemistry on long timescales.
Publisher: Frontiers Media SA
Date: 08-08-2019
Publisher: American Meteorological Society
Date: 03-2007
DOI: 10.1175/JPO2997.1
Abstract: This paper describes the oceanic variability at Bermuda between 1989 and 1999, recorded in two overlapping hydrographic time series. Station S and Bermuda Atlantic Time Series Study (BATS), which are 60 km apart, both show that a multidecadal trend of deep warming has reversed, likely as a result of the increased production of Labrador Sea Water since the early 1980s. In addition to recording similar changes in watermass properties, the two time series show similar mean vertical structure and variance as a function of pressure for temperature, salinity, and density above 1500 dbar. The seasonal cycles of these water properties at the two sites are statistically indistinguishable. The time series differ in the in idual eddy events they record and in their variability below 1500 dbar. The two time series are used to investigate the propagation of eddy features. Coherence and phase calculated from the low-mode variability of density show westward propagation at ∼3 cm s−1 of wavelengths around 300–500 km. Satellite altimeter data are used to provide a broader spatial view of the eddy (or wave) field near Bermuda.
Publisher: American Geophysical Union (AGU)
Date: 05-08-2022
DOI: 10.1029/2021GL097372
Abstract: Using an expanding Southern Ocean fleet of biogeochemical Argo (BGC‐Argo) floats, we developed a novel approach to estimate annual net community production (ANCP) by integrating subsurface oxygen drawdown from all available BGC‐Argo oxygen profiles. Our results suggest that, on average, 14% of remineralization occurs between 500 and 1,000 m and 15% occurs between the euphotic depth and 100 m. Using the improved methodology, we estimated total basin‐integrated ANCP in the Southern Ocean to be 3.89 GT C year −1 suggesting a more important role for the Southern Ocean in regulating oceanic carbon storage, atmospheric CO 2 exchange and climate than previously assumed.
Publisher: American Meteorological Society
Date: 05-2015
Abstract: This study presents a unique array of velocity profiles from Electromagnetic Autonomous Profiling Explorer (EM-APEX) profiling floats in the Antarctic Circumpolar Current (ACC) north of Kerguelen. The authors use these profiles to examine the nature of Ekman spirals, formed by the action of the wind on the ocean’s surface, in light of Ekman’s classical linear theory and more recent enhancements. Vertical decay scales of the Ekman spirals were estimated independently from current litude and rotation. Assuming a vertically uniform geostrophic current, decay scales from the Ekman current heading were twice as large as those from the current speed decay, indicating a compressed spiral, consistent with prior observations and violating the classical theory. However, if geostrophic shear is accurately removed, the observed Ekman spiral is as predicted by classical theory and decay scales estimated from litude decay and rotation converge toward a common value. No statistically robust relationship is found between stratification and Ekman decay scales. The results indicate that compressed spirals observed in the Southern Ocean arise from aliasing of depth-varying geostrophic currents into the Ekman spiral, as opposed to surface trapping of Ekman currents associated with stratification, and extends the geographical area of similar results from Drake Passage (Polton et al. 2013). Accounting for this effect, the authors find that constant viscosity Ekman models offer a reasonable description of momentum mixing into the upper ocean in the ACC north of Kerguelen. These results demonstrate the effectiveness of a new method and provide additional evidence that the same processes are active for the entire Southern Ocean.
Publisher: American Geophysical Union (AGU)
Date: 05-2016
DOI: 10.1002/2015JC011417
Abstract: In the present work, we investigate the interannual variability of the South Indian Countercurrent (SICC), a major and still understudied current of the Indian Ocean circulation. To characterize the interannual variability of the SICC, four different data sets (altimetry, GLORYS, OFAM3, and SODA) are analyzed using multiple tools, which include Singular Spectrum Analysis and wavelet methods. The quasi‐biennial band dominates the SICC low‐frequency variance, with the main peak in the 1.5–1.8 year interval. A secondary peak (2.1–2.5 year) is only found in the western basin. Interannual and decadal‐type modulations of the quasi‐biennial signal are also identified. In addition, limitations of SODA before the 1960s in the SICC region are revealed. Within the quasi‐biennial band, the SICC system presents two main patterns with a multiple jet structure. One pattern is characterized by a robust northern jet, while in the other the central jet is well developed and northern jet is weaker. In both patterns, the southern jet has always a strong signature. When the northern SICC jet is stronger, the northern cell of the subtropical gyre has a triangular shape, with its southern limb having a strong equatorward slant. The quasi‐biennial variability of the SICC is probably related to the Indian Ocean tropical climate modes that are known to have a strong biennial characteristic.
Publisher: Australian Antarctic Data Centre
Date: 2008
Publisher: American Geophysical Union (AGU)
Date: 02-2021
DOI: 10.1029/2020JC016708
Abstract: Major marine heatwave (MHW) events have caused catastrophic impacts on coastal marine ecosystems. However, to date there has not been a global assessment of MHWs in coastal areas where rich marine ecosystems are at risk. Here, we combine four satellite Sea Surface Temperature (SST) products to quantify the distribution, characteristics, and decadal trend of coastal MHWs, using an ensemble approach. Hotspots of MHW stress, defined as yearly cumulative intensity, were found to be concentrated in mid latitude coasts like the Mediterranean Sea, Japan Sea, and Tasman Sea, as well as the north‐eastern coast of the United States. We found a global increase in coastal MHW frequency and duration during the past 25 years by 1–2 events per decade and 5–10 days per decade, respectively, with regional distribution closely related to decadal climate variability. Increases in frequency and duration of MHWs has led to large increases of cumulative intensity and yearly cumulative intensity, particularly in mid‐latitudes and hotspot regions. Long‐term changes in mean SST were the main driver of the observed trends of coastal MHWs, while internal variability was important for explaining local decreases in MHW metrics such as along the south‐eastern Pacific coast. MHW average metrics and trends were consistent across all four products used in this analysis, giving high confidence in the results. However, important differences between products were observed for MHW mean intensity, which was well correlated to SST variability, suggesting sensitivity of this metric to the specific SST data set and demonstrating a need for an ensemble approach to MHW analysis.
Publisher: American Meteorological Society
Date: 04-2015
Abstract: A key remaining challenge in oceanography is the understanding and parameterization of small-scale mixing. Evidence suggests that topographic features play a significant role in enhancing mixing in the Southern Ocean. This study uses 914 high-resolution hydrographic profiles from novel EM-APEX profiling floats to investigate turbulent mixing north of the Kerguelen Plateau, a major topographic feature in the Southern Ocean. A shear–strain finescale parameterization is applied to estimate diapycnal diffusivity in the upper 1600 m of the ocean. The indirect estimates of mixing match direct microstructure profiler observations made simultaneously. It is found that mixing intensities have strong spatial and temporal variability, ranging from O (10 −6 ) to O (10 −3 ) m 2 s −1 . This study identifies topographic roughness, current speed, and wind speed as the main factors controlling mixing intensity. Additionally, the authors find strong regional variability in mixing dynamics and enhanced mixing in the Antarctic Circumpolar Current frontal region. This enhanced mixing is attributed to dissipating internal waves generated by the interaction of the Antarctic Circumpolar Current and the topography of the Kerguelen Plateau. Extending the mixing observations from the Kerguelen region to the entire Southern Ocean, this study infers a large water mass transformation rate of 17 Sverdrups (Sv 1 Sv ≡ 10 6 m 3 s −1 ) across the boundary of Antarctic Intermediate Water and Upper Circumpolar Deep Water in the Antarctic Circumpolar Current. This work suggests that the contribution of mixing to the Southern Ocean overturning circulation budget is particularly significant in fronts.
Publisher: Frontiers Media SA
Date: 06-09-2019
Publisher: European Space Agency
Date: 31-12-2010
Publisher: Copernicus GmbH
Date: 26-11-2021
Abstract: Abstract. Over the past decade, our understanding of the Indian Ocean has advanced through concerted efforts toward measuring the ocean circulation and air–sea exchanges, detecting changes in water masses, and linking physical processes to ecologically important variables. New circulation pathways and mechanisms have been discovered that control atmospheric and oceanic mean state and variability. This review brings together new understanding of the ocean–atmosphere system in the Indian Ocean since the last comprehensive review, describing the Indian Ocean circulation patterns, air–sea interactions, and climate variability. Coordinated international focus on the Indian Ocean has motivated the application of new technologies to deliver higher-resolution observations and models of Indian Ocean processes. As a result we are discovering the importance of small-scale processes in setting the large-scale gradients and circulation, interactions between physical and biogeochemical processes, interactions between boundary currents and the interior, and interactions between the surface and the deep ocean. A newly discovered regional climate mode in the southeast Indian Ocean, the Ningaloo Niño, has instigated more regional air–sea coupling and marine heatwave research in the global oceans. In the last decade, we have seen rapid warming of the Indian Ocean overlaid with extremes in the form of marine heatwaves. These events have motivated studies that have delivered new insight into the variability in ocean heat content and exchanges in the Indian Ocean and have highlighted the critical role of the Indian Ocean as a clearing house for anthropogenic heat. This synthesis paper reviews the advances in these areas in the last decade.
Publisher: Elsevier BV
Date: 06-1993
Publisher: Copernicus GmbH
Date: 29-04-2014
Abstract: Abstract. In this paper we examine time-series measurements of near-surface chlorophyll concentration from a mooring that was deployed at 80.5° E on the equator in the Indian Ocean in 2010. These data reveal at least six striking spikes in chlorophyll in October through December, with approximately 2 week periodicity, that coincide with the development of the fall Wyrtki jets during the transition between the summer and winter monsoons. Concurrent meteorological and in situ physical measurements from the mooring reveal that the chlorophyll pulses are associated with intensification of eastward winds at the surface and eastward currents in the mixed layer. These observations are inconsistent with upwelling dynamics as occurs in the Atlantic and Pacific Oceans, since eastward winds that force Wyrtki jet intensification should drive downwelling. The chlorophyll spikes could be explained by two alternative mechanisms: (1) turbulent entrainment of nutrients and/or chlorophyll from across the base of the mixed layer by wind stirring or Wyrtki jet-induced shear instability or (2) enhanced horizontal advection of high chlorophyll concentrations into the convergent equatorial zone. The first mechanism is supported by the phasing and litude of the relationship between wind stress and chlorophyll, which suggests that the chlorophyll spikes are the result of turbulent entrainment driven by synoptic zonal wind events. The second mechanism is supported by satellite chlorophyll observations that reveal a clear connection between the increased chlorophyll concentrations at the mooring location and larger-scale topographic wake effects from the Chagos–Laca e Ridge upstream. The biweekly periodicity of the chlorophyll spikes appears to be related to the presence of mixed Rossby-gravity waves, also known as Yanai waves, which can be seen throughout the time-series as a biweekly periodicity in the meridional velocities with upward phase propagation. Consistent with hypothesis 2, eastward flows over the Chagos–Laca e Ridge generate high chlorophyll concentrations to the north of the equator and periodic southward advection in the meridional flows associated with Yanai waves produces the chlorophyll spikes that are observed in the mooring record. Yanai waves may also contribute to vertical shear across the base of the mixed layer that could help support entrainment. The OFAM3 eddy-resolving model suggests that both of our proposed mechanisms may be important. Climatological satellite chlorophyll data show that the elevated chlorophyll concentrations in this region are consistently observed year after year and so are reflective of recurring large-scale wind and circulation-induced productivity enhancement in the central equatorial Indian Ocean.
Publisher: Elsevier BV
Date: 03-2014
Publisher: American Meteorological Society
Date: 02-2016
Abstract: In the stratified ocean, turbulent mixing is primarily attributed to the breaking of internal waves. As such, internal waves provide a link between large-scale forcing and small-scale mixing. The internal wave field north of the Kerguelen Plateau is characterized using 914 high-resolution hydrographic profiles from novel Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats. Altogether, 46 coherent features are identified in the EM-APEX velocity profiles and interpreted in terms of internal wave kinematics. The large number of internal waves analyzed provides a quantitative framework for characterizing spatial variations in the internal wave field and for resolving generation versus propagation dynamics. Internal waves observed near the Kerguelen Plateau have a mean vertical wavelength of 200 m, a mean horizontal wavelength of 15 km, a mean period of 16 h, and a mean horizontal group velocity of 3 cm s −1 . The internal wave characteristics are dependent on regional dynamics, suggesting that different generation mechanisms of internal waves dominate in different dynamical zones. The wave fields in the Subantarctic/Subtropical Front and the Polar Front Zone are influenced by the local small-scale topography and flow strength. The eddy-wave field is influenced by the large-scale flow structure, while the internal wave field in the Subantarctic Zone is controlled by atmospheric forcing. More importantly, the local generation of internal waves not only drives large-scale dissipation in the frontal region but also downstream from the plateau. Some internal waves in the frontal region are advected away from the plateau, contributing to mixing and stratification budgets elsewhere.
Publisher: Copernicus GmbH
Date: 29-03-2019
DOI: 10.5194/OS-2021-1
Abstract: Abstract. Over the past decade, our understanding of the Indian Ocean has advanced through concerted efforts toward measuring the ocean circulation and its water properties, detecting changes in water masses, and linking physical processes to ecologically important variables. New circulation pathways and mechanisms have been discovered, which control atmospheric and oceanic mean state and variability. This review brings together new understanding of the ocean-atmosphere system in the Indian Ocean since the last comprehensive review, describing the Indian Ocean circulation patterns, air-sea interactions and climate variability. The second International Indian Ocean Expedition (IIOE-2) and related efforts have motivated the application of new technologies to deliver higher-resolution observations and models of Indian Ocean processes. As a result we are discovering the importance of small scale processes in setting the large-scale gradients and circulation, interactions between physical and biogeochemical processes, interactions between boundary currents and the interior, and between the surface and the deep ocean. In the last decade we have seen rapid warming of the Indian Ocean overlaid with extremes in the form of marine heatwaves. These events have motivated studies that have delivered new insight into the variability in ocean heat content and exchanges in the Indian Ocean, and climate variability on interannual to decadal timescales.This synthesis paper reviews the advances in these areas in the last decade.
Publisher: American Geophysical Union (AGU)
Date: 11-2021
DOI: 10.1029/2021JC017930
Abstract: Long‐term temperature changes drive coastal Marine Heatwave (MHW) trends globally. Here, we provide a more comprehensive global analysis of cross‐shore gradients of MHW and Sea Surface Temperatures (SST) changes using an ensemble of three satellite SST products during recent decades. Our analysis reveals depressed onshore SST trends in more than 2/3 of coastal pixels, including both eastern and western boundary current systems. These were well correlated with depressed trends of MHW exposure and severity, ranging from a −2 to −10 decrease in MHW days per decade and from a −2.5°C to −15°C.days per decade decrease in cumulative intensity. Results were consistent across all satellite products, indicating that these cross‐shore gradients are a robust feature of observations. ERA reanalysis data show that neither air‐sea heat fluxes nor wind driven upwelling were found to be consistent drivers. Global ocean circulation models (OFAM3 and ACCESS‐OM2) have limited ability to simulate the depressed onshore trends. A heat budget analysis performed in the Chilean coast region, where models agree with observations, showed that the gradient of temperature change was controlled by an onshore increase of longwave radiative cooling, despite an increase in upwelling. This highlights the complexity of small‐scale coastal ocean‐atmosphere feedbacks, which coarser resolution climate models do not resolve. Here, we show that global coastal regions may act as thermal refugia for marine ecosystems from aspects of climate change and pulsative (MHW) changes. Contrary to the literature, our results suggest that driving mechanisms are region dependant, stressing the necessity to improve climate models resolution.
Publisher: American Geophysical Union (AGU)
Date: 08-2014
DOI: 10.1002/2013JC009516
Publisher: Wiley
Date: 27-08-2021
Publisher: Elsevier BV
Date: 03-2019
Publisher: American Meteorological Society
Date: 04-2015
Abstract: As demand for flight operations in Antarctica grows, accurate weather forecasting of cloud properties such as extent, cloud base, and cloud-top altitude becomes essential. The primary aims of this work are to ascertain relationships between numerical weather prediction (NWP) model output variables and surface-observed cloud properties and to develop low-cloud-base (& m) height prediction algorithms for use across Antarctica to assist in low-cloud forecasting for aircraft operations. NWP output and radiosonde data are assessed against surface observations, and the relationship between the relative humidity RH profile and the height of the observed low-cloud base is investigated. The ability of NWP-derived RH and ice–water cloud optical depth profiles to represent the observed low-cloud conditions around each of the three Australian stations in East Antarctica is assessed. NWP-derived RH is drier than that reported by radiosonde from ground level up to ~2000 m. This trend reverses in the higher troposphere, and the largest positive difference is observed at ~10 000 m. A consequence is very low RH thresholds are needed for low-cloud-base height prediction using NWP RH profiles. RH and optical depth–based threshold techniques all show skill in reproducing the observed cloud-base height at all Australian Antarctic stations, but the radiosonde-derived RH technique is superior in all cases. This comparison of three low-cloud-base height retrieval techniques provides the first documented assessment of the relative efficacy of each technique in Antarctica.
Publisher: American Geophysical Union (AGU)
Date: 06-2014
DOI: 10.1002/2014JC009935
Publisher: American Geophysical Union (AGU)
Date: 22-06-2018
DOI: 10.1029/2018GL078265
Publisher: Frontiers Media SA
Date: 04-06-2019
Publisher: American Geophysical Union (AGU)
Date: 02-2005
DOI: 10.1029/2004GL021755
Publisher: Elsevier BV
Date: 02-2020
Location: United States of America
Start Date: 2018
End Date: 2021
Funder: Marsden Fund
View Funded ActivityStart Date: 2016
End Date: 12-2020
Amount: $269,900.00
Funder: Australian Research Council
View Funded ActivityStart Date: 07-2017
End Date: 12-2022
Amount: $783,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 09-2021
End Date: 08-2025
Amount: $764,194.00
Funder: Australian Research Council
View Funded ActivityStart Date: 08-2021
End Date: 12-2027
Amount: $20,000,000.00
Funder: Australian Research Council
View Funded Activity