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Stephen R Rintoul - One of the best experts on this subject based on the ideXlab platform.
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spatial variability of Antarctic Bottom Water in the australian Antarctic basin from 2018 2020 captured by deep argo
Geophysical Research Letters, 2020Co-Authors: George Z Thomas, Sarah G Purkey, Dean Roemmich, Annie Foppert, Stephen R RintoulAbstract:Author(s): Thomas, George | Advisor(s): Purkey, Sarah | Abstract: There are two varieties of Antarctic Bottom Water present in the Australian Antarctic Basin (AAB): locally-produced Adelie Land Bottom Water (ALBW) and distantly-produced Ross Sea Bottom Water (RSBW). Between 2014 and 2018, RSBW has rebounded from a multi-decade 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% 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.
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Recent recovery of Antarctic Bottom Water formation in the Ross Sea driven by climate anomalies
Nature Geoscience, 2020Co-Authors: Alessandro Silvano, Takeshi Tamura, Stephen R Rintoul, Pasquale Castagno, Giorgio Budillon, Paul R Holland, Annie Foppert, Noriaki Kimura, Pierpaolo Falco, F. Alexander HaumannAbstract: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 2018–2019 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 Niño 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. Interacting atmospheric circulation patterns are responsible for a recent reversal of a decades-long decline in deepWater formation on the Antarctic shelf, according to an analysis of in situ and remote sensing data from the Ross Sea.
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change in dense shelf Water and adelie land Bottom Water precipitated by iceberg calving
Geophysical Research Letters, 2018Co-Authors: Stephen R Rintoul, Kate Snow, Bernadette M Sloyan, Mcc A HoggAbstract:Antarctic Bottom Water supplies the deep limb of the global overturning circulation and ventilates the abyssal ocean. Antarctic Bottom Water has warmed, freshened, and contracted in recent decades, but the causes remain poorly understood. We use unique multiyear observations from the continental shelf and deep ocean near the Mertz Polynya to examine the sensitivity of this Bottom Water formation region to changes on the continental shelf, including the calving of a large iceberg. Postcalving, the seasonal cycle of Dense Shelf Water (DSW) density almost halved in amplitude and the volume of DSW available for export reduced. In the deep ocean, the density and volume of Adelie Land Bottom Water decreased sharply after calving, while oxygen concentrations remained high, indicating continued ventilation by DSW. This natural experiment illustrates how local changes in forcing over the Antarctic continental shelf can drive large and rapid changes in the abyssal ocean.
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freshening drives contraction of Antarctic Bottom Water in the australian Antarctic basin
Geophysical Research Letters, 2014Co-Authors: Esmee Van Wijk, Stephen R RintoulAbstract:Antarctic Bottom Water (AABW) in the Australian Antarctic Basin has become fresher and lighter since the late 1960s, with largest changes observed near the sources of AABW. The volume of AABW with neutral density (γn) > 28.30 kg m-3 decreased by ≥50% between 1969-1971 and 2008-2012, thinning at a rate of >100 m per decade. Contraction of dense AABW was balanced primarily by expansion of Water lighter than γn = 28.15 kg m-3 prior to 1995 and by inflation of less dense classes of AABW after 1995. Oxygen concentrations remained unchanged in the densest AABW and increased on neutral surfaces for AABW with γn > 28.31 kg m-3, between 1995 and 2011-2012, consistent with continued ventilation over this time period. The observed changes in potential temperature, salinity, density, volume, and oxygen of AABW can be accounted for by freshening of the source Waters but cannot be explained by changes in formation rate alone. Key Points Freshening drives contraction of Antarctic Bottom Water (AABW) AABW has contracted by about 50% and thinned more than 100 m per decade since 1970 Small increase in oxygen on isopycnals suggests continued ventilation of AABW ©2014. American Geophysical Union. All Rights Reserved.
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abyssal connections of Antarctic Bottom Water in a southern ocean state estimate
Geophysical Research Letters, 2013Co-Authors: Erik Van Sebille, Matthew H England, Stephen R Rintoul, Paul Spence, Matthew R Mazloff, Oleg A SaenkoAbstract:Antarctic Bottom Water (AABW) is formed in a few locations around the Antarctic continent, each source with distinct temperature and salinity. After formation, the different AABW varieties cross the Southern Ocean and flow into the subtropical abyssal basins. It is shown here, using the analysis of Lagrangian trajectories within the Southern Ocean State Estimate (SOSE) model, that the pathways of the different sources of AABW have to a large extent amalgamated into one pathway by the time it reaches 31°S in the deep subtropical basins. The Antarctic Circumpolar Current appears to play an important role in the amalgamation, as 70% of the AABW completes at least one circumpolar loop before reaching the subtropical basins. This amalgamation of AABW pathways suggests that on decadal to centennial time scales, changes to properties and formation rates in any of the AABW source regions will be conveyed to all three subtropical abyssal basins. © 2013 American Geophysical Union. All Rights Reserved.
Takeshi Tamura - One of the best experts on this subject based on the ideXlab platform.
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Recent recovery of Antarctic Bottom Water formation in the Ross Sea driven by climate anomalies
Nature Geoscience, 2020Co-Authors: Alessandro Silvano, Takeshi Tamura, Stephen R Rintoul, Pasquale Castagno, Giorgio Budillon, Paul R Holland, Annie Foppert, Noriaki Kimura, Pierpaolo Falco, F. Alexander HaumannAbstract: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 2018–2019 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 Niño 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. Interacting atmospheric circulation patterns are responsible for a recent reversal of a decades-long decline in deepWater formation on the Antarctic shelf, according to an analysis of in situ and remote sensing data from the Ross Sea.
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the suppression of Antarctic Bottom Water formation by melting ice shelves in prydz bay
Nature Communications, 2016Co-Authors: G D Williams, Laura Herraizborreguero, Fabien Roquet, Takeshi Tamura, Kay I Ohshima, Yasushi Fukamachi, Alexander D FraserAbstract:A fourth production region for the globally important Antarctic Bottom Water has been attributed to dense shelf Water formation in the Cape Darnley Polynya, adjoining Prydz Bay in East Antarctica. Here we show new observations from CTD-instrumented elephant seals in 2011–2013 that provide the first complete assessment of dense shelf Water formation in Prydz Bay. After a complex evolution involving opposing contributions from three polynyas (positive) and two ice shelves (negative), dense shelf Water (salinity 34.65–34.7) is exported through Prydz Channel. This provides a distinct, relatively fresh contribution to Cape Darnley Bottom Water. Elsewhere, dense Water formation is hindered by the freshWater input from the Amery and West Ice Shelves into the Prydz Bay Gyre. This study highlights the susceptibility of Antarctic Bottom Water to increased freshWater input from the enhanced melting of ice shelves, and ultimately the potential collapse of Antarctic Bottom Water formation in a warming climate.
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Antarctic Bottom Water production from the vincennes bay polynya east Antarctica
Geophysical Research Letters, 2014Co-Authors: Yujiro Kitade, G D Williams, Fabien Roquet, Takeshi Tamura, Yasushi Fukamachi, Shigeru Aoki, Keishi Shimada, Mark A Hindell, Shuki UshioAbstract:One year moorings at depths greater than 3000m on the continental slope off Vincennes Bay, East Antarctica, reveal the cold (<-0.5 degrees C) and fresh (<34.64) signals of newly formed Antarc ...
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Antarctic Bottom Water production by intense sea ice formation in the cape darnley polynya
Nature Geoscience, 2013Co-Authors: Kay I Ohshima, G D Williams, Laura Herraizborreguero, Fabien Roquet, Takeshi Tamura, Yasushi Fukamachi, Sohey Nihashi, Yujiro Kitade, Daisuke Hirano, Iain C FieldAbstract:Antarctic Bottom Water fills much of the global abyssal ocean, and is known to form in three main sites in the Southern Ocean. Data from instrumented elephant seals and moorings suggest an additional source of Bottom-Water formation in the Cape Darnley polynya that is driven by sea-ice production.
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Antarctic Bottom Water from the adelie and george v land coast east Antarctica 140 149 e
Journal of Geophysical Research, 2010Co-Authors: G D Williams, Takeshi Tamura, Stephen R Rintoul, Shigeru Aoki, Stan Jacobs, N L BindoffAbstract:[1] We report on observations of dense shelf Water overflows and Antarctic Bottom Water (AABW) formation along the continental margin of the Adelie and George V Land coast between 140°E and 149°E. Vertical sections and Bottom layer Water mass properties sampled during two RVIB Nathaniel B Palmer hydrographic surveys (NBP00–08, December 2000/January 2001 and NBP04–08, October 2004) describe the spreading of cold, dense shelf Water on the continental slope and rise from two independent source regions. The primary source region is the Adelie Depression, exporting high-salinity dense shelf Water through the Adelie Sill at 143°E. An additional eastern source region of lower-salinity dense shelf Water from the Mertz Depression is identified for the first time from Bottom layer properties northwest of the Mertz Sill and Mertz Bank (146°E–148°E) that extend as far as the Buffon Channel (144.75°E) in summer. Regional analysis of satellite-derived ice production estimates over the entire region from 1992 to 2005 suggests that up to 40% of the total ice production for the region occurs over the Mertz Depression and therefore this area is likely to make a significant contribution to the total dense shelf Water export. Concurrent time series from Bottom-mounted Microcats and ADCP instruments from the Mertz Polynya Experiment (April 1998 to May 1999) near the Adelie Sill and on the upper continental slope (1150 m) and lower continental rise (3250 m) to the north describe the seasonal variability in downslope events and their interaction with the ambient Water masses. The critical density for shelf Water to produce AABW is examined and found to be 27.85 kg m−3 from the Adelie Depression and as low as 27.80 kg m−3 from the Mertz Depression. This study suggests previous dense shelf Water export estimates based on the flow through the Adelie Sill alone are conservative and that other regions around East Antarctica with similar ice production to the Mertz Depression could be contributing to the total AABW in the Australian-Antarctic Basin.
G D Williams - One of the best experts on this subject based on the ideXlab platform.
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Freshening by glacial meltWater enhances melting of ice shelves and reduces formation of Antarctic Bottom Water
'American Association for the Advancement of Science (AAAS)', 2018Co-Authors: Silvano A, Pena-molino B, Wr Hobbs, Van Wijk E, Aoki S, Tamura T, G D WilliamsAbstract:Strong heat loss and brine release during sea ice formation in coastal polynyas act to cool and salinify Waters on the Antarctic continental shelf. Polynya activity thus both limits the ocean heat flux to the Antarctic Ice Sheet and promotes formation of Dense Shelf Water (DSW), the precursor to Antarctic Bottom Water. However, despite the presence of strong polynyas, DSW is not formed on the Sabrina Coast in East Antarctica and in the Amundsen Sea in West Antarctica. Using a simple ocean model driven by observed forcing, we show that freshWater input from basal melt of ice shelves partially offsets the salt flux by sea ice formation in polynyas found in both regions, preventing full-depth convection and formation of DSW. In the absence of deep convection, warm Water that reaches the continental shelf in the Bottom layer does not lose much heat to the atmosphere and is thus available to drive the rapid basal melt observed at the Totten Ice Shelf on the Sabrina Coast and at the Dotson and Getz ice shelves in the Amundsen Sea. Our results suggest that increased glacial meltWater input in a warming climate will both reduce Antarctic Bottom Water formation and trigger increased mass loss from the Antarctic Ice Sheet, with consequences for the global overturning circulation and sea level rise
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the suppression of Antarctic Bottom Water formation by melting ice shelves in prydz bay
Nature Communications, 2016Co-Authors: G D Williams, Laura Herraizborreguero, Fabien Roquet, Takeshi Tamura, Kay I Ohshima, Yasushi Fukamachi, Alexander D FraserAbstract:A fourth production region for the globally important Antarctic Bottom Water has been attributed to dense shelf Water formation in the Cape Darnley Polynya, adjoining Prydz Bay in East Antarctica. Here we show new observations from CTD-instrumented elephant seals in 2011–2013 that provide the first complete assessment of dense shelf Water formation in Prydz Bay. After a complex evolution involving opposing contributions from three polynyas (positive) and two ice shelves (negative), dense shelf Water (salinity 34.65–34.7) is exported through Prydz Channel. This provides a distinct, relatively fresh contribution to Cape Darnley Bottom Water. Elsewhere, dense Water formation is hindered by the freshWater input from the Amery and West Ice Shelves into the Prydz Bay Gyre. This study highlights the susceptibility of Antarctic Bottom Water to increased freshWater input from the enhanced melting of ice shelves, and ultimately the potential collapse of Antarctic Bottom Water formation in a warming climate.
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Antarctic Bottom Water production from the vincennes bay polynya east Antarctica
Geophysical Research Letters, 2014Co-Authors: Yujiro Kitade, G D Williams, Fabien Roquet, Takeshi Tamura, Yasushi Fukamachi, Shigeru Aoki, Keishi Shimada, Mark A Hindell, Shuki UshioAbstract:One year moorings at depths greater than 3000m on the continental slope off Vincennes Bay, East Antarctica, reveal the cold (<-0.5 degrees C) and fresh (<34.64) signals of newly formed Antarc ...
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Antarctic Bottom Water production by intense sea ice formation in the cape darnley polynya
Nature Geoscience, 2013Co-Authors: Kay I Ohshima, G D Williams, Laura Herraizborreguero, Fabien Roquet, Takeshi Tamura, Yasushi Fukamachi, Sohey Nihashi, Yujiro Kitade, Daisuke Hirano, Iain C FieldAbstract:Antarctic Bottom Water fills much of the global abyssal ocean, and is known to form in three main sites in the Southern Ocean. Data from instrumented elephant seals and moorings suggest an additional source of Bottom-Water formation in the Cape Darnley polynya that is driven by sea-ice production.
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Antarctic Bottom Water from the adelie and george v land coast east Antarctica 140 149 e
Journal of Geophysical Research, 2010Co-Authors: G D Williams, Takeshi Tamura, Stephen R Rintoul, Shigeru Aoki, Stan Jacobs, N L BindoffAbstract:[1] We report on observations of dense shelf Water overflows and Antarctic Bottom Water (AABW) formation along the continental margin of the Adelie and George V Land coast between 140°E and 149°E. Vertical sections and Bottom layer Water mass properties sampled during two RVIB Nathaniel B Palmer hydrographic surveys (NBP00–08, December 2000/January 2001 and NBP04–08, October 2004) describe the spreading of cold, dense shelf Water on the continental slope and rise from two independent source regions. The primary source region is the Adelie Depression, exporting high-salinity dense shelf Water through the Adelie Sill at 143°E. An additional eastern source region of lower-salinity dense shelf Water from the Mertz Depression is identified for the first time from Bottom layer properties northwest of the Mertz Sill and Mertz Bank (146°E–148°E) that extend as far as the Buffon Channel (144.75°E) in summer. Regional analysis of satellite-derived ice production estimates over the entire region from 1992 to 2005 suggests that up to 40% of the total ice production for the region occurs over the Mertz Depression and therefore this area is likely to make a significant contribution to the total dense shelf Water export. Concurrent time series from Bottom-mounted Microcats and ADCP instruments from the Mertz Polynya Experiment (April 1998 to May 1999) near the Adelie Sill and on the upper continental slope (1150 m) and lower continental rise (3250 m) to the north describe the seasonal variability in downslope events and their interaction with the ambient Water masses. The critical density for shelf Water to produce AABW is examined and found to be 27.85 kg m−3 from the Adelie Depression and as low as 27.80 kg m−3 from the Mertz Depression. This study suggests previous dense shelf Water export estimates based on the flow through the Adelie Sill alone are conservative and that other regions around East Antarctica with similar ice production to the Mertz Depression could be contributing to the total AABW in the Australian-Antarctic Basin.
Michael P Meredith - One of the best experts on this subject based on the ideXlab platform.
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decadal freshening of the Antarctic Bottom Water exported from the weddell sea
Journal of Climate, 2013Co-Authors: Loic Jullion, Michael P Meredith, Alberto Naveira C Garabato, Paul R Holland, Peggy Courtois, Brian A. KingAbstract:Recent decadal changes in Southern Hemisphere climate have driven strong responses from the cryosphere. Concurrently, there has been a marked freshening of the shelf and Bottom Waters across a wide sector of the Southern Ocean, hypothesised to be caused by accelerated glacial melt in response to a greater flux of warm Waters from the Antarctic Circumpolar Current onto the shelves of West Antarctica. However, the circumpolar pattern of changes has been incomplete: no decadal freshening in the deep layers of the Atlantic sector had been observed. In this study, we document a significant freshening of the Antarctic Bottom Water exported from the Weddell Sea, which is the source for the abyssal layer of the Atlantic overturning circulation, and we trace its possible origin to atmospheric-forced changes in the ice shelves and sea ice on the eastern flank of the Antarctic Peninsula that include an anthropogenic component. These findings suggest that the expansive and relatively cool Weddell gyre does not insulate the Bottom Water formation regions in the Atlantic sector from the ongoing changes in climatic forcing over the Antarctic region.
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remotely induced warming of Antarctic Bottom Water in the eastern weddell gyre
Geophysical Research Letters, 2013Co-Authors: Matthew P Couldrey, Laura Herraizborreguero, Michael P Meredith, Alberto Naveira C Garabato, Loic Jullion, Craig D Rye, P BrownAbstract:[1] Four repeat hydrographic sections across the eastern Weddell gyre at 30°E reveal a warming (by ~0.1°C) and lightening (by ~0.02–0.03 kg m−3) of the Antarctic Bottom Water (AABW) entering the gyre from the Indian sector of the Southern Ocean between the mid-1990s and late 2000s. Historical hydrographic and altimetric measurements in the region suggest that the most likely explanation for the change is increased entrainment of warmer mid-depth Circumpolar Deep Water by cascading shelf Water plumes close to Cape Darnley, where the Indian-sourced AABW entering the Weddell gyre from the east is ventilated. This change in entrainment is associated with a concurrent southward shift of the Antarctic Circumpolar Current's (ACC) southern boundary in the region. This mechanism of AABW warming may affect wherever the ACC flows close to Antarctica.
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synchronous intensification and warming of Antarctic Bottom Water outflow from the weddell gyre
Geophysical Research Letters, 2011Co-Authors: Michael P Meredith, Arnold L Gordon, Alberto Naveira C Garabato, Povl E Abrahamsen, Bruce A Huber, Loic Jullion, Hugh J VenablesAbstract:[1] Antarctic Bottom Water (AABW), the densest Water in the global overturning circulation, has warmed in recent decades, most notably in the Atlantic. Time series recorded within the boundary currents immediately upstream and downstream of the most significant outflow of AABW from the Weddell Sea indicate that raised outflow temperatures are synchronous with stronger boundary current flows. These changes occur rapidly in response to changes in wind forcing, suggesting that barotropic dynamics and the response of the Bottom Ekman layer are significant. The observed synchronicity indicates that the previously‐detected weakening of the export of the colder forms of AABW from the Weddell Sea need not be associated with a reduction in the total flux of AABW exported via this route. These points need careful consideration when attributing the observed AABW warming in the Atlantic, and when determining its contribution to global heat budgets and sea level rise. Citation: Meredith, M. P., A. L. Gordon, A. C. Naveira Garabato, E. P. Abrahamsen, B. A. Huber, L. Jullion, and H. J. Venables (2011), Synchronous intensification and warming of Antarctic Bottom Water outflow from the Weddell Gyre, Geophys. Res. Lett., 38, L03603, doi:10.1029/2010GL046265.
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wind controlled export of Antarctic Bottom Water from the weddell sea
Geophysical Research Letters, 2010Co-Authors: Loic Jullion, Alberto Naveira C Garabato, S Jones, Michael P MeredithAbstract:Recent studies suggest that the variability in Antarctic Bottom Water (AABW) properties in the Scotia Sea on time scales up to decadal may be linked to changes in the baroclinicity of the Weddell gyre, with vertical variations in the density structure at the gyre's northern edge acting to control the export of AABW over the South Scotia Ridge and toward the mid-latitude South Atlantic. We test this hypothesis by analysing the AABW properties in fifteen occupations of the SR1b hydrographic section (1993-2009) in eastern Drake Passage alongside possible forcings as derived from atmospheric reanalysis data. We show that variability in the wind stress over the Weddell gyre leads changes in AABW properties in the SR1b section by approximately five months. The sign of the lagged correlation is consistent with the notion of the AABW export from the Weddell Sea being controlled by the gyre's baroclinic adjustment to wind forcing on time scales of several months. Variability in the regional winds is found to be closely linked to the Southern Annular Mode (SAM). These results suggest that there may be a causal relationship between the SAM's positive tendency observed in recent decades and the subsequent warming of AABW detected across much of the Atlantic Ocean. Citation: Jullion, L., S. C. Jones, A. C. Naveira Garabato, and M. P. Meredith (2010), Wind-controlled export of Antarctic Bottom Water from the Weddell Sea, Geophys. Res. Lett., 37, L09609, doi: 10.1029/2010GL042822.
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On the Sources of Weddell Gyre Antarctic Bottom Water
Journal of Geophysical Research: Oceans, 2000Co-Authors: Michael P Meredith, Ricardo A. Locarnini, Kim A. Van Scoy, Andrew J. Watson, Karen J. Heywood, Brian A. KingAbstract:In March–April 1995, as part of the World Ocean Circulation Experiment section A23, we completed 49 hydrographic stations across the Weddell Gyre and southern Antarctic Circumpolar Current, from the Antarctic continental shelf (72.5°S, 16.5°W) to South Georgia (55°S, 34.5°W). Chlorofluorocarbon (CFC-11, CFC-12, and CFC-113) data collected at these stations reveal that distinct sources renew the Antarctic Bottom Water (defined as Waters with potential temperatures less than 0°C) of the Weddell Gyre. Weddell Sea Bottom Water (defined as Waters with potential temperatures less than −0.7°C) formed in the western Weddell Sea has CFC concentrations about 5 to 6 times higher in the eastward flowing northern Weddell Gyre than in the westward flowing southern limb. Our CFC measurements suggest that distinct sources of Weddell Sea Bottom Water exist in the western Weddell Sea, in agreement with previous descriptions based on potential temperature and salinity signals. In the northern Weddell Gyre, high CFC concentrations in Weddell Sea Deep Water, potential temperatures between 0°C and −0.7°C, confirm the long-recognized sources for this Water mass in the western and southwestern Weddell Sea. In the southern Weddell Gyre at about 20°W and along the Antarctic continental slope, Weddell Sea Deep Water with potential temperatures around −0.45°C shows a deep CFC maximum about 1000 m above the seafloor. CFC concentrations in this deep southern core are about 80% of those of new Weddell Sea Deep Water in the northern Weddell Gyre near 30°W. The A23 CFC and hydrographic data are not consistent with the hypothesis that Weddell Sea Deep Waters are derived from a single source in the western Weddell Sea. Instead, these tracers suggest that an important portion of the Weddell Sea Deep Water in the southern Weddell Gyre originates outside the western Weddell Sea, probably near the Amery Basin and environs, around 75°E. These features of the circulation and renewal of the deep Weddell Gyre should be carefully considered in simulations dealing with fluxes, pathways, and formation rates of Antarctic Bottom Water.
Yasushi Fukamachi - One of the best experts on this subject based on the ideXlab platform.
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the suppression of Antarctic Bottom Water formation by melting ice shelves in prydz bay
Nature Communications, 2016Co-Authors: G D Williams, Laura Herraizborreguero, Fabien Roquet, Takeshi Tamura, Kay I Ohshima, Yasushi Fukamachi, Alexander D FraserAbstract:A fourth production region for the globally important Antarctic Bottom Water has been attributed to dense shelf Water formation in the Cape Darnley Polynya, adjoining Prydz Bay in East Antarctica. Here we show new observations from CTD-instrumented elephant seals in 2011–2013 that provide the first complete assessment of dense shelf Water formation in Prydz Bay. After a complex evolution involving opposing contributions from three polynyas (positive) and two ice shelves (negative), dense shelf Water (salinity 34.65–34.7) is exported through Prydz Channel. This provides a distinct, relatively fresh contribution to Cape Darnley Bottom Water. Elsewhere, dense Water formation is hindered by the freshWater input from the Amery and West Ice Shelves into the Prydz Bay Gyre. This study highlights the susceptibility of Antarctic Bottom Water to increased freshWater input from the enhanced melting of ice shelves, and ultimately the potential collapse of Antarctic Bottom Water formation in a warming climate.
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a numerical investigation of formation and variability of Antarctic Bottom Water off cape darnley east Antarctica
Journal of Physical Oceanography, 2014Co-Authors: Yoshihiro Nakayama, Kay I Ohshima, Yasushi Fukamachi, Yoshimasa Matsumura, Hiroyasu HasumiAbstract:AbstractAt several locations around Antarctica, dense Water is formed as a result of intense sea ice formation. When this dense Water becomes sufficiently denser than the surrounding Water, it descends the continental slope and forms Antarctic Bottom Water (AABW). This study presents the AABW formation off the coast of Cape Darnley [Cape Darnley Bottom Water (CDBW)] in East Antarctica, using a nonhydrostatic model. The model is forced for 8 months by a temporally uniform surface salt flux (because of sea ice formation) estimated from Advanced Microwave Scanning Radiometer for Earth Observing System (EOS; AMSR-E) data and a heat budget calculation. The authors reproduce AABW formation and associated periodic downslope flows of dense Water. Descending pathways of dense Water are largely determined by the topography; most dense Water flows into depressions on the continental shelf, advects onto the continental slope, and is steered downslope to greater depths by the canyons. Intense sea ice formation is the ...
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Antarctic Bottom Water production from the vincennes bay polynya east Antarctica
Geophysical Research Letters, 2014Co-Authors: Yujiro Kitade, G D Williams, Fabien Roquet, Takeshi Tamura, Yasushi Fukamachi, Shigeru Aoki, Keishi Shimada, Mark A Hindell, Shuki UshioAbstract:One year moorings at depths greater than 3000m on the continental slope off Vincennes Bay, East Antarctica, reveal the cold (<-0.5 degrees C) and fresh (<34.64) signals of newly formed Antarc ...
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Antarctic Bottom Water production by intense sea ice formation in the cape darnley polynya
Nature Geoscience, 2013Co-Authors: Kay I Ohshima, G D Williams, Laura Herraizborreguero, Fabien Roquet, Takeshi Tamura, Yasushi Fukamachi, Sohey Nihashi, Yujiro Kitade, Daisuke Hirano, Iain C FieldAbstract:Antarctic Bottom Water fills much of the global abyssal ocean, and is known to form in three main sites in the Southern Ocean. Data from instrumented elephant seals and moorings suggest an additional source of Bottom-Water formation in the Cape Darnley polynya that is driven by sea-ice production.
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strong export of Antarctic Bottom Water east of the kerguelen plateau
Nature Geoscience, 2010Co-Authors: Yasushi Fukamachi, Stephen R Rintoul, John A Church, Shigeru Aoki, S Sokolov, Mark Rosenberg, Masaaki WakatsuchiAbstract:Deep western boundary currents east of the Antarctic Peninsula and the Kerguelen plateau are important pathways for transporting deep Antarctic Water masses to the global ocean. An array of moored current meters, used to quantify the Water transport in this system, reveals a flow that is stronger than any measured in a deep western boundary current at similar depths so far. The primary paths for the transport of Antarctic Bottom Water from the Southern Ocean into the global ocean are the deep western boundary currents east of the Antarctic Peninsula and the Kerguelen plateau1. Previous ship-based observations documented distinct Water properties and velocities associated with a deep western boundary current in the Kerguelen region2,3,4,5,6,7, but the mean flow is as yet unconstrained. Here we report measurements from a coherent array of eight current-meter moorings that reveal a narrow and intense equatorward flow extending throughout the Water column just east of the Kerguelen plateau. Velocities averaged over two years exceed 20 cm s−1 at depths of about 3,500 m, the strongest mean deep western boundary current flow yet observed at similar depths. We estimate the mean equatorward transport of Water colder than 0 ∘C at 12.3±1.2×106 m3 s−1, partially compensated by poleward flow. We also estimate the net equatorward flow of Water colder than 0.2 ∘C at about 8×106 m3 s−1, substantially higher than the 1.9×106 m3 s−1 reported from the boundary current that carries dense Water from the Weddell Sea into the Atlantic Ocean north of the Falkland plateau8. We conclude that the Kerguelen deep western boundary current is a significant pathway of the global ocean’s deep overturning circulation.