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  • 1
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    On the superposition of mean advective and eddy-induced transports in global ocean heat and salt budgets (2019)
    American Meteorological Society (AMS)
    Details
    Publication Date: 2019
    Description: Journal of Climate, Ahead of Print. 〈br/〉
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geosciences , Physics
    Published by American Meteorological Society (AMS)
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  • 2
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    Controls on circulation, cross-shelf exchange and dense water formation in an Antarctic polynya (2016)
    Wiley
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    Publication Date: 2016-06-17
    Description: Circulation on the Antarctic continental shelf influence cross-shelf exchange, Antarctic Bottom Water formation, and ocean heat flux to floating ice shelves. The physical processes driving the shelf circulation and its seasonal and interannual variability remain poorly understood. We use a unique time series of repeat hydrographic observations from the Adélie Land continental shelf and a box inverse model to explore the relationship between surface forcing, shelf circulation, cross-shelf exchange, and dense water formation. A wind-driven northwestward coastal current, set up by onshore Ekman transport, dominates the summer circulation. During winter, strong buoyancy loss creates dense shelf water. This dense water flows off the shelf, with a compensating on-shelf flow that is an order of magnitude larger in winter than in summer. The results demonstrate the importance of winter buoyancy loss in driving the shelf circulation and cross-shelf exchange, as well as dense water mass formation.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Direct observations of the Antarctic Slope Current transport at 113°E (2016)
    Wiley
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    Publication Date: 2016-09-22
    Description: The Antarctic Slope Current (ASC), defined here as the region of westward flow along the continental slope off Antarctica, forms the southern limb of the subpolar gyres. It regulates the exchange of water across the shelf break, and provides a path for interbasin westward transport. Despite its significance, the ASC remains largely unobserved around most of the Antarctic continent. Here we present direct velocity observations from a 17-month current meter moored array deployed across the continental slope between the 1000 and the 4200 m isobaths, in the southeastern Indian Ocean near 113°E. The observed time-mean flow consists of a surface intensified jet associated with the Antarctic Slope Front (ASF) and a broader bottom intensified westward flow that extends out to approximately the 4000 m isobath and is strongest along the upper slope. The time-mean transport of the ASC is -29.2 Sv. Fluctuations in the transport are large, typically exceeding the mean by a factor of 2. They are mainly due to changes in the northward extent of the current over the lower slope. However, seasonal changes in the wind also drive variations in the transport of the ASF and the flow in the upper slope. Both mean and variability are largely barotropic, thus invisible to traditional geostrophic methods. This article is protected by copyright. All rights reserved.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Decadal changes in the South Pacific western boundary current system revealed in observations and ocean state estimates (2011)
    Wiley
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    Publication Date: 2011-01-20
    Description: Observations and ocean state estimates are used to investigate the nature and mechanism of decadal variability in the East Australian Current (EAC) system and South Pacific subtropical gyre. A 62 year record on the Tasmanian continental shelf shows decadal variations of temperature and salinity, as well as a long-term trend, which has been related to wind-driven variations in the poleward extension of the EAC. Repeat expendable bathythermograph lines spanning the last 15 years suggest that low-frequency variations in the transport of the EAC extension and Tasman Front are anticorrelated, but the time series are too short to draw firm conclusions. Here we use two ocean state estimates spanning the past 50 years to diagnose the physical mechanisms and spatial structure of the decadal variability of the South Pacific subtropical gyre. The observations and state estimates paint a consistent picture of the decadal variability of the gyre and EAC system. Strengthening of the basin-wide wind stress curl drives a southward expansion of the subtropical gyre. As the gyre shifts south, the EAC extension pathway is favored at the expense of the Tasman Front, resulting in the observed anticorrelation of the these two major currents. The results suggest that the subtropical gyre and western boundary current respond to decadal variability in basin-scale wind stress curl, consistent with Island Rule dynamics; that strong decadal variability of the South Pacific gyre complicates efforts to infer trends from short-term records; and that wind stress curl changes over the South Pacific basin drive changes in the EAC system that are likely to have implications for marine ecosystems and regional climate.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Barotropic and baroclinic contributions to along- and across-stream transport in the Antarctic Circumpolar Current (2014)
    Wiley
    Details
    Publication Date: 2014-11-01
    Description: The Southern Ocean's ability to store and transport heat and tracers as well as to dissipate momentum and energy are intimately related to the vertical structure of the Antarctic Circumpolar Current (ACC). Here the partition between barotropic and baroclinic flow in the time-mean ACC is investigated in a Southern Ocean state estimate. The zonal geostrophic transport is predominantly baroclinic, with at most 25% of the transport at any longitude carried by the barotropic component. Following surface streamlines, changes in vertical shear and near-bottom velocity are large, and result in changes in the local partition of barotropic/baroclinic vertically integrated transport from 10/90% in the center of the basins, to 50/50% near complex topography. The velocity at depth is not aligned with the surface velocity. This non-equivalent barotropic flow supports significant cross-stream transports. Barotropic and baroclinic mass transport across the ACC is, on average, in opposite directions, with the net barotropic cross-stream transport being poleward and the net baroclinic equatorward. The sum partially cancels out, leaving a net geostrophic poleward transport across the different fronts between -5 and -20 Sv. Temperature is also transported across the fronts by the non-equivalent barotropic part of the ACC, with maximum values across the northern ACC fronts equivalent to -0.2 PW. The sign and magnitude of these transports is not sensitive to the choice of stream-coordinate. These cross-stream volume and temperature transports are variable in space, and dependent on the interactions between deep flow and bathymetry, thus difficult to infer from surface and hydrographic observations alone.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Frontal movements and property fluxes: Contributions to heat and freshwater trends in the Southern Ocean (2011)
    Wiley
    Details
    Publication Date: 2011-08-23
    Description: We examine the synoptic variability of temperature and salinity in the Southern Ocean using a static gravest empirical mode (GEM) mapping based on historical hydrography and a time-evolving projection of the GEM created using satellite altimetry (satGEM). The GEM and satGEM projections allow the separation of observed trends into a component due to a shift of the circumpolar fronts (adiabatic) using the satGEM and a component due to changes in water masses (diabatic) expressed as a temporal trend in residual between historical hydrography and the static GEM. The mean southward movement of the Antarctic Circumpolar Current (ACC) fronts drives an adiabatic warming of 1.196 ± 0.090 W m−2 distributed over most of the ACC and at all depths. This is strongest where the meridional temperature gradient is largest, such as in the upper 1000 dbar of the Subantarctic Front (SAF). There is a weak adiabatic freshening of 6.57 ± 0.18 mm yr−1 m−2, concentrated mainly below the Antarctic Intermediate Water and south of the SAF. Residuals between historical hydrography and the static GEM field, driven by diabatic changes in the water mass structure, have temporal trends in temperature and salinity. When these trends are integrated over the whole ACC there is a net cooling of −0.628 ± 0.129 W m−2 and strong freshening of 30.27 ± 0.70 mm yr−1 m−2. By combining the diabatic and adiabatic components and integrating over the ACC the net increase in heat and freshwater in the region is 0.570 ± 0.099 W m−2 and 36.91 ± 0.72 mm yr−1 m−2, respectively. The sum of the adiabatic and diabatic changes are consistent with previous trends inferred from observations.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Polar research: Six priorities for Antarctic science (2014)
    Nature Publishing Group (NPG)
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    Publication Date: 2014-08-08
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kennicutt, Mahlon C 2nd -- Chown, Steven L -- Cassano, John J -- Liggett, Daniela -- Massom, Rob -- Peck, Lloyd S -- Rintoul, Steve R -- Storey, John W V -- Vaughan, David G -- Wilson, Terry J -- Sutherland, William J -- England -- Nature. 2014 Aug 7;512(7512):23-5. doi: 10.1038/512023a.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Texas A&M University, College Station, Texas, USA, and past-president of the Scientific Committee on Antarctic Research. ; Monash University, Victoria, Australia. ; Cooperative Institute for Research in Environmental Sciences, Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado, USA. ; Gateway Antarctica, University of Canterbury, Christchurch, New Zealand. ; Australian Antarctic Division, and Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, Australia. ; British Antarctic Survey, Cambridge, UK. ; Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, Tasmania, Australia. ; School of Physics, University of New South Wales, Sydney, Australia. ; School of Earth Sciences, Ohio State University, Columbus, Ohio, USA. ; Conservation Science Group, Department of Zoology, University of Cambridge, Cambridge, UK.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25100467" target="_blank"〉PubMed〈/a〉
    Keywords: Antarctic Regions ; Astronomy ; Atmosphere/chemistry ; Biological Evolution ; Budgets ; *Climate Change ; Conservation of Natural Resources/methods ; Ecology ; Exobiology ; Ice Cover ; International Cooperation ; Oceans and Seas ; *Policy Making ; Research/economics/*trends
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 8
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    Changes in water properties and flow regime on the continental shelf off the Adélie/George V Land coast, East Antarctica, after glacier tongue calving (2017)
    Wiley
    Details
    Publication Date: 2017-07-23
    Description: Oceanic changes before and after the relocation of iceberg B9B and calving of the Mertz Glacier Tongue (MGT) in February 2010 are examined on the continental shelf off the Adélie Land/George V Land coast, East Antarctica. Summer hydrographic observations, including stable oxygen isotope ratio (δ 18 O), in 2001/08 and 2011/15 and results of a numerical model are used. Along the western flank of the MGT, temperature decreased between 2001 and 2015 for most of the water column in the Adélie Depression. δ 18 O generally decreased, especially at the MGT draft depths on the northern side. West of the MGT, temperature, salinity, and δ 18 O decreased in the intermediate layer. East of the MGT, in contrast, temperature increased between 2001 and 2011 at intermediate depths, salinity increased in the intermediate and deep layers, and δ 18 O slightly decreased in the deep layer but did not change much around 300 dbar. The numerical experiment exhibits a change in ocean circulation, revealing an increase in modified Circumpolar Deep Water (mCDW) inflow in the east and a decrease in the west. The contrasting changes in mCDW intrusion are consistent between the observations and numerical model, and are indicative of the effect of removal of the ice barriers. The contrast is overlain by overall decreases in salinity and δ 18 O, which suggests an increase in the continental meltwater fraction of 5–20% and might reveal a wide-ranging influence from West Antarctica. The oxygen isotope ratio is, hence, effective in monitoring the increase in continental melt over the Antarctic shelf.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Regional changes in icescape impact shelf circulation and basal melting (2017)
    Wiley
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    Publication Date: 2017-11-03
    Description: Ice shelf basal melt is the dominant contribution to mass loss from Antarctic ice shelves. However, the sensitivity of basal melt to changes in icescape (grounded icebergs, ice shelves and sea ice) and related ocean circulation is poorly understood. Here, we simulate the impact of the major 2010 calving event of the Mertz Glacier Tongue (MGT), East Antarctica, and related redistribution of sea ice and icebergs on the basal melt rate of the local ice shelves. We find that the position of the grounded tabular iceberg B9B controls the water masses that reach the nearby ice shelf cavities. After the calving of the MGT and the removal of B9B, warmer water is present both within the MGT cavity and on the continental shelf driving a 57% increase of the deep MGT basal melting. Major changes in icescape influence the oceanic heat flux responsible for basal ice shelf melting.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
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    Glacier tongue calving reduced dense water formation and enhanced carbon uptake (2013)
    Wiley
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    Publication Date: 2013-01-27
    Description: [1]  Dense shelf water formed in the Mertz Polynya supplies the lower limb of the global overturning circulation, ventilating the abyssal Indian and Pacific Oceans. Calving of the Mertz Glacier Tongue (MGT) in February 2010 altered the regional distribution of ice and reduced the size and activity of the polynya. The salinity and density of dense shelf water declined abruptly post-calving, consistent with a reduction of sea ice formation in the polynya. Break-out and melt of thick multi-year sea ice released by the movement of iceberg B9B and the MGT freshened near-surface waters. The input of meltwater likely enhanced the availability of light and iron, supporting a diatom bloom that doubled carbon uptake relative to pre-calving conditions. The enhanced biological carbon drawdown increased the carbonate saturation state, outweighing dilution by meltwater input. These observations highlight the sensitivity of dense water formation, biological productivity, and carbon export to changes in the Antarctic icescape.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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