ORCID Profile
0000-0003-2958-1454
Current Organisation
University of Tasmania
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Publisher: American Meteorological Society
Date: 08-2021
Publisher: Springer Science and Business Media LLC
Date: 16-11-2020
Publisher: Springer Science and Business Media LLC
Date: 10-08-2022
DOI: 10.1038/S41586-022-04946-0
Abstract: The East Antarctic Ice Sheet contains the vast majority of Earth's glacier ice (about 52 metres sea-level equivalent), but is often viewed as less vulnerable to global warming than the West Antarctic or Greenland ice sheets. However, some regions of the East Antarctic Ice Sheet have lost mass over recent decades, prompting the need to re-evaluate its sensitivity to climate change. Here we review the response of the East Antarctic Ice Sheet to past warm periods, synthesize current observations of change and evaluate future projections. Some marine-based catchments that underwent notable mass loss during past warm periods are losing mass at present but most projections indicate increased accumulation across the East Antarctic Ice Sheet over the twenty-first century, keeping the ice sheet broadly in balance. Beyond 2100, high-emissions scenarios generate increased ice discharge and potentially several metres of sea-level rise within just a few centuries, but substantial mass loss could be averted if the Paris Agreement to limit warming below 2 degrees Celsius is satisfied.
Publisher: American Geophysical Union (AGU)
Date: 08-2017
DOI: 10.1002/2017JC012837
Publisher: American Meteorological Society
Date: 03-2019
Abstract: The dynamics of an oceanic storm track—where energy and enstrophy transfer between the mean flow and eddies—are investigated using observations from an eddy-rich region of the Antarctic Circumpolar Current downstream of the Shackleton Fracture Zone (SFZ) in Drake Passage. Four years of measurements by an array of current- and pressure-recording inverted echo sounders deployed between November 2007 and November 2011 are used to diagnose eddy–mean flow interactions and provide insight into physical mechanisms for these transfers. Averaged within the upper to mid-water column (400–1000-m depth) and over the 4-yr-record mean field, eddy potential energy is highest in the western part of the storm track and maximum eddy kinetic energy occurs farther away from the SFZ, shifting the proportion of eddy energies from to about 1 along the storm track. There are enhanced mean 3D wave activity fluxes immediately downstream of SFZ with strong horizontal flux vectors emanating northeast from this region. Similar patterns across composites of Polar Front and Subantarctic Front meander intrusions suggest the dynamics are set more so by the presence of the SFZ than by the eddy’s sign. A case study showing the evolution of a single eddy event, from 15 to 23 July 2010, highlights the storm-track dynamics in a series of snapshots. Consistently, explaining the eddy energetics pattern requires both horizontal and vertical components of W , implying the importance of barotropic and baroclinic processes and instabilities in controlling storm-track dynamics in Drake Passage.
Publisher: American Geophysical Union (AGU)
Date: 03-2016
DOI: 10.1002/2015JC011333
Publisher: American Meteorological Society
Date: 06-2022
Abstract: Meanders formed where the Antarctic Circumpolar Current (ACC) interacts with topography have been identified as dynamical hot spots, characterized by enhanced eddy energy, momentum transfer, and cross-front exchange. However, few studies have used observations to diagnose the dynamics of ACC standing meanders. We use a synoptic hydrographic survey and satellite altimetry to explore the momentum and vorticity balance of a Subantarctic Front standing meander, downstream of the Southeast Indian Ridge. Along-stream anomalies of temperature in the upper ocean (150–600 m) show along-stream cooling entering the surface trough and along-stream warming entering the surface crest, while warming is observed from trough to crest in the deeper ocean (600–1500 m). Advection of relative vorticity is balanced by vortex stretching, as found in model studies of meandering currents. Meander curvature is sufficiently large that the flow is in gradient wind balance, resulting in ageostrophic horizontal ergence. This drives downwelling of cooler water along isopycnals entering the surface trough and upwelling of warmer water entering the surface crest, consistent with the observed evolution of temperature anomalies in the upper ocean. Progressive along-stream warming observed between 600 and 1500 m likely reflects cyclogenesis in the deep ocean. Vortex stretching couples the upper and lower water column, producing a low pressure at depth between surface trough and crest and cyclonic flow that carries cold water equatorward in the surface trough and warm water poleward in the surface crest (poleward heat flux). The results highlight gradient–wind balance and cyclogenesis as central to dynamics of standing meanders and their critical role in the ACC momentum and vorticity balance. The Antarctic Circumpolar Current (ACC) in the Southern Ocean is a nearly zonal current that encircles Antarctica. It acts as a barrier between warmer water equatorward and colder water poleward. In a few regions where the current encounters strong topographic changes, the current meanders and opens a pathway for heat to travel across the ACC toward Antarctica. We surveyed a meander in the ACC and examined the along-stream change of temperature. In the upper ocean, temperature changes are caused by a vertical circulation, bringing cool water down when entering the surface trough (the part of the meander closest to the equator), and warm water up when exiting the surface trough and entering the surface crest. At depth, cold water is transported equatorward in the surface trough and warm water poleward in the surface crest, leading to a net transport of heat poleward. This study highlights the importance of the secondary circulation within a meander for generating cross-ACC flows and moving heat toward Antarctica.
Publisher: American Meteorological Society
Date: 02-2020
Abstract: An unusual double-thermostad warm-core ring of the Gulf Stream was discovered in the Slope Sea, south of Georges Bank, during the R/V Endeavor cruise 578 in May 2016. The ring’s stratification was peculiar as it included two thermostads at, respectively, 100–200 m (core T = 18.14°C, S = 36.52) and 250–500 m (core T = 16.70°C, S = 36.35). Extensive use of satellite data (SST imagery and SSH maps) allowed the life history of this ring to be reconstructed, with independent SST and SSH data mutually corroborating each other. The double-thermostad ring was formed by vertical alignment of two preexisting warm-core anticyclonic rings of the Gulf Stream. The first ring spawned by the Gulf Stream in February has cooled by ~2°C before merging in April with the second ring spawned by the Gulf Stream in March. During vertical alignment of these rings, the warmer ring overrode the colder ring, thereby forming the double-thermostad ring surveyed in May 2016. From ADCP sections through the ring, the upper and lower thermostads had different core relative vorticities of −0.65 f and −0.77 f , respectively, where f is the local Coriolis parameter. An in-depth literature survey has confirmed that this is the first report of a double-thermostad warm-core ring of the Gulf Stream and one of the best-documented cases of vertical alignment of two eddies ever observed in the World Ocean.
Publisher: American Geophysical Union (AGU)
Date: 24-07-2019
DOI: 10.1029/2019GL082999
Abstract: Circumpolar Deep Water (CDW) transport across the Antarctic continental slope regulates the delivery of heat to the shelf and its availability to melt floating ice shelves. The cross‐slope density field, calculated from profiles collected by conductivity‐temperature‐depth‐tagged marine mammals on the East Antarctic slope (0–160°E, above 1,000‐ to 3,000‐m isobaths), indicates eddy‐driven overturning: onshore transport of CDW and offshore transport of shallower Antarctic Surface Water. Enhanced eddy activity, determined by a spice standard deviation threshold in the CDW layer, is present over about a third of the East Antarctic slope analyzed. Significantly stronger CDW transport in regions of elevated spice variability produces subsurface temperature anomalies of 0.2–0.25 °C relative to the East Antarctic average. Estimating eddy diffusivity from the hydrography yields about 0.8 m 2 /s of warm CDW transport to the shelf break in high‐variability regions. Variability of eddy‐induced CDW transport influences the reservoir of heat available for transport across the shelf break.
Publisher: American Geophysical Union (AGU)
Date: 12-2021
DOI: 10.1029/2021JC017935
Abstract: Changes in properties and quantity of Antarctic Bottom Water (AABW) have major implications for the climate system, through sequestration of heat and carbon into, and ventilation of, the abyssal ocean. Yet, it remains one of the most difficult water masses to observe. An array of 12 Deep Argo floats, capable of profiling from the surface to the seafloor and under sea ice, provides a new perspective on AABW in the Australian‐Antarctic Basin. Over 2 years of data from the floats illuminate AABW properties with unprecedented detail, simultaneously s ling AABW at multiple locations, year‐round, throughout the basin. Calibrating each float in idually with nearby, quasi‐simultaneous shipboard profiles ensures the highest quality salinity data, with estimated accuracy of ±0.005 or better. Pathways of Ross Sea and Adélie Land Bottom Water (RSBW and ALBW), defined by their unique temperature and salinity characteristics, are mapped along the continental slope from their respective sources. The main pathway of RSBW, identified by its characteristic deep salinity maximum, is inferred to be inshore of the 3,700 m isobath, where it cools and freshens westward along the slope before interacting with ALBW near 140°E. A pulse of very cold and very fresh (nearly −0.6°C, 34.82 g kg −1 ) ALBW appears in February 2019, highlighting temporal variability on daily scales near its source. Deep Argo has greatly enhanced our view of AABW in the Australian‐Antarctic Basin and will prove to be an essential tool for monitoring future changes in the deep ocean by drastically increasing observations in a cost‐effective way.
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-8371
Abstract: & & & & & & & & Antarctic Bottom Water (AABW) supplies the lower limb of the global overturning circulation, ventilates the abyssal ocean and sequesters heat and carbon on multidecadal to millennial timescales. AABW originates on the Antarctic continental shelf, where strong winter cooling and brine released during sea ice formation produce Dense Shelf Water, which sinks to the deep ocean. The salinity, density and volume of AABW have decreased over the last 50 years, with the most marked changes observed in the Ross Sea. These changes have been attributed to increased melting of the Antarctic Ice Sheet. Here we use in situ observations to document a recovery in the salinity, density and thickness (that is, depth range) of AABW formed in the Ross Sea, with properties in 2018& #8211 similar to those observed in the 1990s. The recovery was caused by increased sea ice formation on the continental shelf. Increased sea ice formation was triggered by anomalous wind forcing associated with the unusual combination of positive Southern Annular Mode and extreme El Ni& #241 o conditions between 2015 and 2018. Our study highlights the sensitivity of AABW formation to remote forcing and shows that climate anomalies can drive episodic increases in local sea ice formation that counter the tendency for increased ice-sheet melt to reduce AABW formation.& & & / & & / & & / &
Publisher: American Geophysical Union (AGU)
Date: 02-12-2020
DOI: 10.1029/2020GL089467
Abstract: There are two varieties of Antarctic Bottom Water present in the Australian Antarctic Basin (AAB): locally produced Adélie Land Bottom Water (ALBW) and distantly produced Ross Sea Bottom Water (RSBW). Between 2014 and 2018, RSBW has rebounded from a multidecade freshening trend. The return of the salty RSBW to the AAB is revealed by six Deep Argo floats that have occupied the region from January of 2018 to March of 2020. The floats depict a zonal variation in temperature and salinity in the bottom waters of the AAB, driven by the inflow of RSBW. A simple Optimum Multiparameter Analysis based on potential temperature and salinity gives a sense of scale to the composition of the bottom waters, which are nearly 80% of the new, salty RSBW in the south‐east corner of the basin by 2019 and generally less than 40% to the west closer to the ALBW outflow region and the abyssal plain.
Start Date: 2012
End Date: 2017
Funder: Directorate for Geosciences
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