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Papers by Bruce Huber

Frontiers in Marine Science

Warming along the Antarctic Peninsula has led to an increase in the export of glacial meltwater t... more Warming along the Antarctic Peninsula has led to an increase in the export of glacial meltwater to the coastal ocean. While observations to date suggest that this freshwater export acts as an important forcing on the marine ecosystem, the processes linking iceocean interactions to lower trophic-level growth, particularly in coastal bays and fjords, are poorly understood. Here, we identify salient hydrographic features in Barilari Bay, a west Antarctic Peninsula fjord influenced by warm modified Upper Circumpolar Deep Water. In this fjord, interactions between the glaciers and ocean act as a control on coastal circulation, contributing to the redistribution of water masses in an upwelling plume and a vertical flux of nutrients toward the euphotic zone. This nutrient-rich plume, containing glacial meltwater but primarily composed of ambient ocean waters including modified Upper Circumpolar Deep Water, spreads through the fjord as a 150-m thick layer in the upper water column. The combination of meltwater-driven stratification, long residence time of the surface plume owing to weak circulation, and nutrient enrichment promotes phytoplankton growth within the fjord, as evidenced by shallow phytoplankton blooms and concomitant nutrient drawdown at the fjord mouth in late February. Gradients in meltwater distributions are further paralleled by gradients in phytoplankton and benthic community composition. While glacial meltwater export and upwelling of ambient waters in this way contribute to elevated primary and secondary productivity, subsurface nutrient enhancement of glacially modified ocean waters suggests that a portion of these macronutrients, as well any iron upwelled or input in meltwater, are exported to the continental shelf. Sustained atmospheric warming in the coming decades, contributing to greater runoff, would invigorate the marine circulation with consequences for glacier dynamics and biogeochemical cycling within the fjord. We conclude that ice-ocean interactions along the Antarctic Peninsula margins act as an important control on coastal marine ecosystems, with repercussions for carbon cycling along the west Antarctic Peninsula shelf as a whole.

GSA Today

Climatic, cryospheric, and biologic changes taking place in the northern Antarctic Peninsula prov... more Climatic, cryospheric, and biologic changes taking place in the northern Antarctic Peninsula provide examples for how ongoing systemic change may progress through the entire Antarctic system. A large, interdisciplinary research project focused on the Larsen Ice Shelf system, synthesized here, has documented dramatic ice cover, oceanographic, and ecosystem changes in the Antarctic Peninsula during the Holocene and the present period of rapid regional warming. The responsiveness of the region results from its position in the climate and ocean system, in which a narrow continental block extends across zonal atmospheric and ocean flow, creating high snow accumulation, strong gradients and gyres, dynamic oceanography, outlet glaciers feeding into many fjords and bays having steep topography, and a continental shelf that contains many glacially carved troughs separated by areas of glacial sediment accumulation. The microcosm of the northern Antarctic Peninsula has a tendency to change rapidly-rapid relative not just to Antarctica's mainland but compared to the rest of the planet as well-and it is generally warmer than the rest of Antarctica. Both its Holocene and modern glaciological retreats offer a picture of how larger areas of Antarctica farther south might change under future warming.

Deep Sea Research Part Ii Topical Studies in Oceanography, Jun 1, 2009

Antarctic Bottom Water of the world ocean is derived from dense Shelf Water that is carried downs... more Antarctic Bottom Water of the world ocean is derived from dense Shelf Water that is carried downslope by gravity currents at specific sites along the Antarctic margins. Data gathered by the AnSlope and CLIMA programs reveal the presence of energetic gravity currents that ...

Journal of Geophysical Research: Oceans, 2013

The importance of cross-shelf transport across the Ross Sea on local and remote processes has bee... more The importance of cross-shelf transport across the Ross Sea on local and remote processes has been well documented. In the Ross Sea, mid-water intrusions of Circumpolar Deep Water (CDW) are modified by shelf water near the shelf break to form Modified Circumpolar Deep Water (MCDW). In 2010-2011, we deployed multi-platform technologies focused on this MCDW intrusion in the vicinity of Mawson and Pennell Banks to better understand its role in ecosystem processes across the shelf. The high-resolution time and space sampling provided by an underwater glider, a short-term mooring, and a ship-based survey highlight the scales over which these critical cross-shelf transport processes occur. MCDW cores were observed as small-scale well-defined features over the western slopes of Pennell and Mawson Banks. The mean transport along Pennell Bank was estimated to be about 0.24 Sv but was highly variable in time (hours to days). The observations suggest that the core of MCDW is transported by a predominately barotropic flow that follows topography around the banks toward the south until the slope of the bank flattens and the warmer water moves up and over the bank. This pathway is shown to link the source MCDW with an area of high productivity over the shallows of Pennell Bank.

Eos, Transactions American Geophysical Union, 2005

The first living chemotrophic ecosystem in the Southern Ocean was discovered in a region of the s... more The first living chemotrophic ecosystem in the Southern Ocean was discovered in a region of the seafloor previously occupied by the Larsen-B Ice Shelf. A towed video survey documents an ecosystem characterized by a bottom-draping white mat that appears similar to mats of Begiattoa, hydrogen sulfide oxidizing bacteria, and bivalves, 20-30 cm large, similar to vesicomyid clams commonly found at

Extraordinary weather conditions this past Austral field season in the NW Weddell Sea allowed a m... more Extraordinary weather conditions this past Austral field season in the NW Weddell Sea allowed a marine geologic expedition to enter the formerly ice shelf bound coastal regions of the Oscar II Coast located along the eastern northern side of the Antarctic Peninsula. In February to March (2005) the US Antarctic Program Research Vessel L. M Gould conducted high resolution seismic

Science, 1993

Oceanographic observations from the Ice Station Weddell 1 show that the western rim of the Weddel... more Oceanographic observations from the Ice Station Weddell 1 show that the western rim of the Weddell Gyre contributes to Weddell Sea Bottom Water. A thin (<300 meters), highly oxygenated benthic layer is composed of a low-salinity type of bottom water overlying a high-salinity component. This complex layering disappears near 66°S because of vertical mixing and further inflow from the continental margin. The bottom water flowing out of the western rim is a blend of the two types. Additionally, the data show that a narrow band of warmer Weddell Deep Water hugged the continental margin as it flowed into the western rim, providing the continental margin with the salt required for bottom-water production.

Proceedings of the Royal Society B: Biological Sciences, 2012

Lithodid crabs (and other skeleton-crushing predators) may have been excluded from cold Antarctic... more Lithodid crabs (and other skeleton-crushing predators) may have been excluded from cold Antarctic continental shelf waters for more than 14 Myr. The west Antarctic Peninsula shelf is warming rapidly and has been hypothesized to be soon invaded by lithodids. A remotely operated vehicle survey in Palmer Deep, a basin 120 km onto the Antarctic shelf, revealed a large, reproductive population of lithodids, providing the first evidence that king crabs have crossed the Antarctic shelf. DNA sequencing and morphology indicate the lithodid is Neolithodes yaldwyni Ahyong & Dawson, previously reported only from Ross Sea waters. We estimate a N. yaldwyni population density of 10 600 km −2 and a population size of 1.55 × 10 6 in Palmer Deep, a density similar to lithodid populations of commercial interest around Alaska and South Georgia. The lithodid occurred at depths of more than 850 m and temperatures of more than 1.4°C in Palmer Deep, and was not found in extensive surveys of the colder shel...

Nature Geoscience, 2010

Dense water formed over the Antarctic continental shelf rapidly descends into the deep ocean to s... more Dense water formed over the Antarctic continental shelf rapidly descends into the deep ocean to spread as Antarctic Bottom Water, ventilating the global ocean 1,2. The coldest and most voluminous component is Weddell Sea Bottom Water 1,3,4,5,6,7. Here we present an 8-year observational record (3 April 1999 to 29 January 2007) of the benthic layer stratification within the Weddell Sea Bottom Water export path southeast of the South Orkney Islands. A pronounced bottom temperature seasonal cycle is apparent, with the coldest pulse in May/June, warmest in October/November, though the timing of these phases vary with year. The cold pulse thermohaline characteristics and mean bottom current of 0.1 m/s indicate an origin in the southwest Weddell Sea, with shelf water discharge during the prior austral summer. The coldest bottom occurred in 1999 and 2002; in 2000 the cold phase was absent. We propose that the Weddell Sea Bottom Water seasonal fluctuation is governed by the wind seasonal cycle over the Weddell Sea western margin, with the interannual fluctuations linked to variability of the wind-driven Weddell Gyre. The observations suggest a link of Weddell Sea Bottom Water generation to the Southern Annular Mode and El Niño Southern Oscillation. The ratio of Antarctic Bottom Water (AABW) to North Atlantic Deep Water (NADW) volume within the deep ocean is estimated as 1.7, with AABW covering more than twice the sea floor area than NADW 8. Observations within

Journal of Geophysical Research, 1984

The end of winter stratification within the cold cyclonic trough of the Weddell gyre near 60øS be... more The end of winter stratification within the cold cyclonic trough of the Weddell gyre near 60øS between 5øE and the Greenwich meridian is resolved with the Mikhail Somov data set. The temperature maximum of the Weddell Deep Water (WDW) is, for the most part, less than 0.5øC, but warmer cells of WDW are found. These warm WDW cells have temperature, salinity, and oxygen properties similar to the WDW characteristic of the Weddell gyre inflow, which is situated to the southeast of the Mikhail Somov study region. The warm WDW cells are accompanied by domes in the pycnocline of 40 m amplitude over the surrounding pycnocline, while deeper isopycnals are depressed. Anticyclonic shear below the 27.83 a-0 isopycnal within the warm WDW cells is compensated by the cyclonic shear associated with the pycnocline dome. The pycnocline domes are exposed to about 50% greater entrainment by the turbulently active winter mixed layer, relative to the regional entrainment rate. This entrainment can significantly erode the warm cells in a single winter season, introducing excess heat and salt into the mixed layer. While the heat is lost to the atmosphere, the excess salt is not necessarily compensated by increased fresh water introduction. It is hypothesized that the warm WDW cells within the Weddell gyre trough are derived from instability within the frontal zone which extends from Maud Rise to the northeast, separating the Weddell warm regime from the cold regime. Greater than normal injection of warm WDW cells into the Weddell gyre trough would increase the surface salinity, which would tend to destabilize the pycnocline, increasing the probability of deep convection and polynya events.

Journal of Geophysical Research, 1989

At depths below 200 m, relatively warm, salty water spreads poleward from the Antarctic Circumpol... more At depths below 200 m, relatively warm, salty water spreads poleward from the Antarctic Circumpolar Current (ACC). This deep water mass is cooled, through interaction with the atmosphere, feeding the formation of dense bottom water which in turn influences much of the world ocean. Significant poleward spreading is accomplished within the Weddell gyre of the Atlantic sector of the southern ocean. An extensive data set obtained in the 1980s within the Weddell gyre provides a detailed view of the subsurface temperature maximum (T-max) stratum defining the top of the deep water mass. The seasonal sea ice growth and retreat pattern reflects the T-max distribution. There is evidence for subdivision of the T-max into two cold centers, which may reflect secondary circulation features within the gyre. The primary inflow of warm deep water is derived from the southern edge of the ACC near 20ø-30øE. The inflow spreads to the west along 65øS and is divided into smaller "pools" of relatively warm water west of Maud Rise with a cold feature directly over the rise, in a manner shown by models of topographically generated eddies. Variability of the T-max stratum in the vicinity of Maud Rise arising from changes in the vigor of the large-scale circulation may influence the regional vertical heat fluxes and be related to interannual variability of the sea ice cover and to the recurring polynya feature typical of the region. 413-428, 1976. Roden, G., Effect of seamounts and seamount chains on ocean circulation and thermohaline structure in Seamounts, Islands and

Journal of Geophysical Research, 1990

Austral winter 1986 observations from the Polarstern along the Greenwich meridian from the ice ed... more Austral winter 1986 observations from the Polarstern along the Greenwich meridian from the ice edge to the Antarctic margin show the mixed layer beneath the winter sea ice cover to be significantly depressed in oxygen saturation. Incorporation of Weddell Deep Water (WDW) into the winter mixed layer, responsible for this undersaturation, also introduces heat and salinity into the surface layer which strongly influences the mixed layer, sea-air exchanges and sea ice formation processes. The l total WDW transfer into the mixed layer averages 45 myr-, iml•lying a residence time for the surface water of 2.5 years. The associated winter heat flux is 41 W m-•, which limits ice thickness to about 0.55 m, agreeing quite well with observations. The air temperatures during the cruise are just sufficient to remove the WDW heat input in the presence of observed ice thickness and concentration. This suggests that the sea ice cover and WDW heat input into the mixed layer are in approximate balance by midwinter. The annual heat flux from WDW to the surface layer, and hence into the atmosphere, is estimated as 16 W m-2. Extrapolation of the Greenwich meridian WDW entrainment value to the full circumpolar 60ø-70øS belt yields total upwelling of 24 x 10 6 m 3 s-1. Similar extrapolation of the heat flux value gives a circumpolar total of 2.8 x 1014 W. As a consequence of circulation/topography interaction, the Maud Rise water column stands out as an anomaly relative to the surrounding region, with a significantly more saline and dense mixed layer. Below the mixed layer the water column over the crest of the rise is identical to that over the flanks if the latter water column is upwelled by 400 m. This uplifting is believed to be a response of the upstream flow encountering the rise. Increased upstream flow would be expected to increase Maud Rise upwelling and the dependent salinity (density) of the mixed layer. Slight increases in the mixed layer density could trigger a convective mode and generation of a polynya. It is hypothesized that spin-up of the Weddell Gyre's barotropic circulation induced by an increase of the regional wind stress curl would enhance the probability of polynya development over Maud Rise. 2. LARGE-SCALE FEATURES To provide background, the large-scale thermohaline field as viewed with the Ant V/2 data set is briefly presented. 2.1. Temperature and Salinity Sections The full depth temperature, salinity, and sigma-zero sections reveal the nearly homogeneous nature of the thermohaline structure characteristic of the zone poleward of the Antarctic Circumpolar Current (Figures 2a-2c; the complete set of sections are included in the Ant V/2 data report 11,655 11,656 GORDON AND HUBER: SOUTHERN OCEAN WINTER MIXED LAYER 60 ø 0.29 60 ø IOøE 55oS 65 ø 65 ø 0 o 70ø3 GORDON AND HUBER.' SOUTHERN OCEAN WINTER MIXED LAYER 5 ø Oø 60 ø ß • 60 ø • ß \ .

Journal of Geophysical Research, 1987

We collected data on temperature, salinity, nutrient concentrations (nitrate, nitrite, phosphate,... more We collected data on temperature, salinity, nutrient concentrations (nitrate, nitrite, phosphate, and silicic acid), and phytoplankton biomass (chlorophyll a, particulate carbon, nitrogen, and biogenic silica) in the upper 150 m in the marginal ice zone of the eastern Scotia Sea and northwestern Weddell Sea during November and early December of 1983. A distinct hydrographic front separating Drake Passage water from Weddell and Scotia sea surface waters was located at approximately 59øS and was the site of a consistent maximum in phytoplankton biomass. In addition, there was a pronounced phytoplankton biomass maximum associated with a surface salinity minimum near the northern limit of pack ice in the waters of the Weddell-Scotia confluence that characterized the western portion of the study area. In the eastern half of the study area, characterized by largely unmodified Weddell Sea surface water, the phytoplankton biomass near the ice edge was 2-5 times lower than that in the Weddell-Scotia confluence but was increasing with time. The water column structure, nutrient fields, and phytoplankton biomass distribution all suggest that the high phytoplankton biomass in the ice edge zone of the Weddell-Scotia confluence and the lower but temporally increasing biomass near the ice edge in unmodified Weddell Sea water reflect ice edge phytoplankton blooms in different stages of their seasonal development. A bloom had become well established in the waters of the Weddell-Scotia confluence by mid-November, but the ice-free, vertically stable near-surface water column necessary for enhanced phytoplankton growth had apparently not been present long enough for high biomass levels to develop within the Weddell Sea proper. INTRODUCTION Intense phytoplankton blooms near the edge of the seasonally retreating pack ice are quite common in polar oceans of both the northern and southern hemispheres [e.g., McRoy and

Journal of Geophysical Research, 1995

Journal of Geophysical Research, 2001

An oceanographic field program called the Antarctic Zone Flux experiment was carried out in the e... more An oceanographic field program called the Antarctic Zone Flux experiment was carried out in the eastern Weddell Sea during austral winter (July-September) 1994. Data from a drift buoy array were used in concert with shipboard observations to provide exceptionally high horizontal resolution of upper ocean hydrographic parameters near Maud Rise. Chemical and tracer data were obtained from the ship. We identify a "warm pool" southwest of the rise as a dynamically necessary region of positive (cyclonic) vorticity that is associated with a Taylor column over the rise. Both a warm "halo" surrounding the Taylor column and the warm pool are associated with thermocline shoaling that is a necessary condition for high upward heat fluxes to occur. These features extend the influence of Maud Rise bottom topography on upper ocean heat flux over a region that is larger, by a factor of at least 2, than the area directly overlying the rise. Areal mean upward heat fluxes of about 25 W m Ϫ2 are derived using both upper ocean T ("instantaneous") values and tracer data ("integrated") values. Fluxes derived over the warm halo and pool regions using only upper ocean T exceeded 100 W m Ϫ2 at specific sites. Elsewhere in the region, the T-derived heat fluxes varied widely from Ͻ10 to Ͼ50 W m Ϫ2 , whereas the tracer-derived heat fluxes showed a considerably more uniform distribution. Our mean values are similar to those that have been previously reported. Historical ice cover data have shown that the geographical region encompassed by Maud Rise and the warm pool area to the southwest is a preferred site for polynya formation, consistent with these findings. Time series analyses of the historical upper ocean data set suggest that conditions conducive to polynya formation are correlated with climate processes remote from the Southern Ocean.

Journal of Geophysical Research, 2001

An extensive set of conductivity-temperature-depth (CTD)/lowered acoustic Doppler current profile... more An extensive set of conductivity-temperature-depth (CTD)/lowered acoustic Doppler current profiler (LADCP) data obtained within the northwestern Weddell Sea in August 1997 characterizes the dense water outflow from the Weddell Sea and overflow into the Scotia Sea. Along the outer rim of the Weddell Gyre, there is a stream of relatively low salinity, high oxygen Weddell Sea Deep Water (defined as water between 0 ø and-0.7øC), constituting a more ventilated form of this water mass than that found farther within the gyre. Its enhanced ventilation is due to injection of relatively low salinity shelf water found near the northern extreme of Antarctic Peninsula's Weddell Sea shelf, shelf water too buoyant to descend to the deep-sea floor. The more ventilated form of Weddell Sea Deep Water flows northward along the eastern side of the South Orkney Plateau, passing into the Scotia Sea rather than continuing along an eastward path in the northern Weddell Sea. Weddell Sea Bottom Water also exhibits two forms: a low-salinity, better oxygenated component confined to the outer rim of the Weddell Gyre, and a more saline, less oxygenated component observed farther into the gyre. The more saline Weddell Sea Bottom Water is derived from the southwestern Weddell Sea, where highsalinity shelf water is abundant. The less saline Weddell Sea Bottom Water, like the more ventilated Weddell Sea Deep Water, is derived from lower-salinity shelf water at a point farther north along the Antarctic Peninsula. Transports of Weddell Sea Deep and Bottom Water masses crossing 44øW estimated from one LADCP survey are 25 x 106 and 5 x 106 m 3 s-1, respectively. The low-salinity, better ventilated forms of Weddell Sea Deep and Bottom Water flowing along the outer rim of the Weddell Gyre have the position and depth range that would lead to overflow of the topographic confines of the Weddell Basin, whereas the more saline forms may be forced to recirculate within the Weddell Gyre. 1. Gordon, 1998]. Streams of newly formed Weddell Sea Deep Water (WSDW, defined as deep water with potential temperatures between 0 ø and-0.7øC [Fahrbach et al., 1995]) and Weddell Sea Bottom Water (WSBW, defined as water colder than-0.7øC [Carmack and Foster, 1975]) are carried by the western boundary current of the Weddell Sea into the northwest corner of the Weddell Gyre [Deacon, 1979; Orsi et al., 1993]. From there these water masses flow eastward, either within the northern limb of the Weddell Gyre or reaching northward into the Scotia Sea [Gordon, 1966; Locarnini et al., 1993], eventually cooling the lower 2 km of the world ocean as Antarctic Bottom Water. The objective of this study is to describe the characteristics of Weddell Sea Deep Water (WSDW) and Weddell Sea Bottom Water (WSBW) within the northwest Weddell Sea and their overflow into the southern Scotia Sea. 2. DOVETAIL Data The data set used in this study was collected during cruise 97-5 of the polar research vessel Nathaniel B. Palmer from July

Frontiers in Marine Science

Warming along the Antarctic Peninsula has led to an increase in the export of glacial meltwater t... more Warming along the Antarctic Peninsula has led to an increase in the export of glacial meltwater to the coastal ocean. While observations to date suggest that this freshwater export acts as an important forcing on the marine ecosystem, the processes linking iceocean interactions to lower trophic-level growth, particularly in coastal bays and fjords, are poorly understood. Here, we identify salient hydrographic features in Barilari Bay, a west Antarctic Peninsula fjord influenced by warm modified Upper Circumpolar Deep Water. In this fjord, interactions between the glaciers and ocean act as a control on coastal circulation, contributing to the redistribution of water masses in an upwelling plume and a vertical flux of nutrients toward the euphotic zone. This nutrient-rich plume, containing glacial meltwater but primarily composed of ambient ocean waters including modified Upper Circumpolar Deep Water, spreads through the fjord as a 150-m thick layer in the upper water column. The combination of meltwater-driven stratification, long residence time of the surface plume owing to weak circulation, and nutrient enrichment promotes phytoplankton growth within the fjord, as evidenced by shallow phytoplankton blooms and concomitant nutrient drawdown at the fjord mouth in late February. Gradients in meltwater distributions are further paralleled by gradients in phytoplankton and benthic community composition. While glacial meltwater export and upwelling of ambient waters in this way contribute to elevated primary and secondary productivity, subsurface nutrient enhancement of glacially modified ocean waters suggests that a portion of these macronutrients, as well any iron upwelled or input in meltwater, are exported to the continental shelf. Sustained atmospheric warming in the coming decades, contributing to greater runoff, would invigorate the marine circulation with consequences for glacier dynamics and biogeochemical cycling within the fjord. We conclude that ice-ocean interactions along the Antarctic Peninsula margins act as an important control on coastal marine ecosystems, with repercussions for carbon cycling along the west Antarctic Peninsula shelf as a whole.

GSA Today

Climatic, cryospheric, and biologic changes taking place in the northern Antarctic Peninsula prov... more Climatic, cryospheric, and biologic changes taking place in the northern Antarctic Peninsula provide examples for how ongoing systemic change may progress through the entire Antarctic system. A large, interdisciplinary research project focused on the Larsen Ice Shelf system, synthesized here, has documented dramatic ice cover, oceanographic, and ecosystem changes in the Antarctic Peninsula during the Holocene and the present period of rapid regional warming. The responsiveness of the region results from its position in the climate and ocean system, in which a narrow continental block extends across zonal atmospheric and ocean flow, creating high snow accumulation, strong gradients and gyres, dynamic oceanography, outlet glaciers feeding into many fjords and bays having steep topography, and a continental shelf that contains many glacially carved troughs separated by areas of glacial sediment accumulation. The microcosm of the northern Antarctic Peninsula has a tendency to change rapidly-rapid relative not just to Antarctica's mainland but compared to the rest of the planet as well-and it is generally warmer than the rest of Antarctica. Both its Holocene and modern glaciological retreats offer a picture of how larger areas of Antarctica farther south might change under future warming.

Deep Sea Research Part Ii Topical Studies in Oceanography, Jun 1, 2009

Antarctic Bottom Water of the world ocean is derived from dense Shelf Water that is carried downs... more Antarctic Bottom Water of the world ocean is derived from dense Shelf Water that is carried downslope by gravity currents at specific sites along the Antarctic margins. Data gathered by the AnSlope and CLIMA programs reveal the presence of energetic gravity currents that ...

Journal of Geophysical Research: Oceans, 2013

The importance of cross-shelf transport across the Ross Sea on local and remote processes has bee... more The importance of cross-shelf transport across the Ross Sea on local and remote processes has been well documented. In the Ross Sea, mid-water intrusions of Circumpolar Deep Water (CDW) are modified by shelf water near the shelf break to form Modified Circumpolar Deep Water (MCDW). In 2010-2011, we deployed multi-platform technologies focused on this MCDW intrusion in the vicinity of Mawson and Pennell Banks to better understand its role in ecosystem processes across the shelf. The high-resolution time and space sampling provided by an underwater glider, a short-term mooring, and a ship-based survey highlight the scales over which these critical cross-shelf transport processes occur. MCDW cores were observed as small-scale well-defined features over the western slopes of Pennell and Mawson Banks. The mean transport along Pennell Bank was estimated to be about 0.24 Sv but was highly variable in time (hours to days). The observations suggest that the core of MCDW is transported by a predominately barotropic flow that follows topography around the banks toward the south until the slope of the bank flattens and the warmer water moves up and over the bank. This pathway is shown to link the source MCDW with an area of high productivity over the shallows of Pennell Bank.

Eos, Transactions American Geophysical Union, 2005

The first living chemotrophic ecosystem in the Southern Ocean was discovered in a region of the s... more The first living chemotrophic ecosystem in the Southern Ocean was discovered in a region of the seafloor previously occupied by the Larsen-B Ice Shelf. A towed video survey documents an ecosystem characterized by a bottom-draping white mat that appears similar to mats of Begiattoa, hydrogen sulfide oxidizing bacteria, and bivalves, 20-30 cm large, similar to vesicomyid clams commonly found at

Extraordinary weather conditions this past Austral field season in the NW Weddell Sea allowed a m... more Extraordinary weather conditions this past Austral field season in the NW Weddell Sea allowed a marine geologic expedition to enter the formerly ice shelf bound coastal regions of the Oscar II Coast located along the eastern northern side of the Antarctic Peninsula. In February to March (2005) the US Antarctic Program Research Vessel L. M Gould conducted high resolution seismic

Science, 1993

Oceanographic observations from the Ice Station Weddell 1 show that the western rim of the Weddel... more Oceanographic observations from the Ice Station Weddell 1 show that the western rim of the Weddell Gyre contributes to Weddell Sea Bottom Water. A thin (<300 meters), highly oxygenated benthic layer is composed of a low-salinity type of bottom water overlying a high-salinity component. This complex layering disappears near 66°S because of vertical mixing and further inflow from the continental margin. The bottom water flowing out of the western rim is a blend of the two types. Additionally, the data show that a narrow band of warmer Weddell Deep Water hugged the continental margin as it flowed into the western rim, providing the continental margin with the salt required for bottom-water production.

Proceedings of the Royal Society B: Biological Sciences, 2012

Lithodid crabs (and other skeleton-crushing predators) may have been excluded from cold Antarctic... more Lithodid crabs (and other skeleton-crushing predators) may have been excluded from cold Antarctic continental shelf waters for more than 14 Myr. The west Antarctic Peninsula shelf is warming rapidly and has been hypothesized to be soon invaded by lithodids. A remotely operated vehicle survey in Palmer Deep, a basin 120 km onto the Antarctic shelf, revealed a large, reproductive population of lithodids, providing the first evidence that king crabs have crossed the Antarctic shelf. DNA sequencing and morphology indicate the lithodid is Neolithodes yaldwyni Ahyong & Dawson, previously reported only from Ross Sea waters. We estimate a N. yaldwyni population density of 10 600 km −2 and a population size of 1.55 × 10 6 in Palmer Deep, a density similar to lithodid populations of commercial interest around Alaska and South Georgia. The lithodid occurred at depths of more than 850 m and temperatures of more than 1.4°C in Palmer Deep, and was not found in extensive surveys of the colder shel...

Nature Geoscience, 2010

Dense water formed over the Antarctic continental shelf rapidly descends into the deep ocean to s... more Dense water formed over the Antarctic continental shelf rapidly descends into the deep ocean to spread as Antarctic Bottom Water, ventilating the global ocean 1,2. The coldest and most voluminous component is Weddell Sea Bottom Water 1,3,4,5,6,7. Here we present an 8-year observational record (3 April 1999 to 29 January 2007) of the benthic layer stratification within the Weddell Sea Bottom Water export path southeast of the South Orkney Islands. A pronounced bottom temperature seasonal cycle is apparent, with the coldest pulse in May/June, warmest in October/November, though the timing of these phases vary with year. The cold pulse thermohaline characteristics and mean bottom current of 0.1 m/s indicate an origin in the southwest Weddell Sea, with shelf water discharge during the prior austral summer. The coldest bottom occurred in 1999 and 2002; in 2000 the cold phase was absent. We propose that the Weddell Sea Bottom Water seasonal fluctuation is governed by the wind seasonal cycle over the Weddell Sea western margin, with the interannual fluctuations linked to variability of the wind-driven Weddell Gyre. The observations suggest a link of Weddell Sea Bottom Water generation to the Southern Annular Mode and El Niño Southern Oscillation. The ratio of Antarctic Bottom Water (AABW) to North Atlantic Deep Water (NADW) volume within the deep ocean is estimated as 1.7, with AABW covering more than twice the sea floor area than NADW 8. Observations within

Journal of Geophysical Research, 1984

The end of winter stratification within the cold cyclonic trough of the Weddell gyre near 60øS be... more The end of winter stratification within the cold cyclonic trough of the Weddell gyre near 60øS between 5øE and the Greenwich meridian is resolved with the Mikhail Somov data set. The temperature maximum of the Weddell Deep Water (WDW) is, for the most part, less than 0.5øC, but warmer cells of WDW are found. These warm WDW cells have temperature, salinity, and oxygen properties similar to the WDW characteristic of the Weddell gyre inflow, which is situated to the southeast of the Mikhail Somov study region. The warm WDW cells are accompanied by domes in the pycnocline of 40 m amplitude over the surrounding pycnocline, while deeper isopycnals are depressed. Anticyclonic shear below the 27.83 a-0 isopycnal within the warm WDW cells is compensated by the cyclonic shear associated with the pycnocline dome. The pycnocline domes are exposed to about 50% greater entrainment by the turbulently active winter mixed layer, relative to the regional entrainment rate. This entrainment can significantly erode the warm cells in a single winter season, introducing excess heat and salt into the mixed layer. While the heat is lost to the atmosphere, the excess salt is not necessarily compensated by increased fresh water introduction. It is hypothesized that the warm WDW cells within the Weddell gyre trough are derived from instability within the frontal zone which extends from Maud Rise to the northeast, separating the Weddell warm regime from the cold regime. Greater than normal injection of warm WDW cells into the Weddell gyre trough would increase the surface salinity, which would tend to destabilize the pycnocline, increasing the probability of deep convection and polynya events.

Journal of Geophysical Research, 1989

At depths below 200 m, relatively warm, salty water spreads poleward from the Antarctic Circumpol... more At depths below 200 m, relatively warm, salty water spreads poleward from the Antarctic Circumpolar Current (ACC). This deep water mass is cooled, through interaction with the atmosphere, feeding the formation of dense bottom water which in turn influences much of the world ocean. Significant poleward spreading is accomplished within the Weddell gyre of the Atlantic sector of the southern ocean. An extensive data set obtained in the 1980s within the Weddell gyre provides a detailed view of the subsurface temperature maximum (T-max) stratum defining the top of the deep water mass. The seasonal sea ice growth and retreat pattern reflects the T-max distribution. There is evidence for subdivision of the T-max into two cold centers, which may reflect secondary circulation features within the gyre. The primary inflow of warm deep water is derived from the southern edge of the ACC near 20ø-30øE. The inflow spreads to the west along 65øS and is divided into smaller "pools" of relatively warm water west of Maud Rise with a cold feature directly over the rise, in a manner shown by models of topographically generated eddies. Variability of the T-max stratum in the vicinity of Maud Rise arising from changes in the vigor of the large-scale circulation may influence the regional vertical heat fluxes and be related to interannual variability of the sea ice cover and to the recurring polynya feature typical of the region. 413-428, 1976. Roden, G., Effect of seamounts and seamount chains on ocean circulation and thermohaline structure in Seamounts, Islands and

Journal of Geophysical Research, 1990

Austral winter 1986 observations from the Polarstern along the Greenwich meridian from the ice ed... more Austral winter 1986 observations from the Polarstern along the Greenwich meridian from the ice edge to the Antarctic margin show the mixed layer beneath the winter sea ice cover to be significantly depressed in oxygen saturation. Incorporation of Weddell Deep Water (WDW) into the winter mixed layer, responsible for this undersaturation, also introduces heat and salinity into the surface layer which strongly influences the mixed layer, sea-air exchanges and sea ice formation processes. The l total WDW transfer into the mixed layer averages 45 myr-, iml•lying a residence time for the surface water of 2.5 years. The associated winter heat flux is 41 W m-•, which limits ice thickness to about 0.55 m, agreeing quite well with observations. The air temperatures during the cruise are just sufficient to remove the WDW heat input in the presence of observed ice thickness and concentration. This suggests that the sea ice cover and WDW heat input into the mixed layer are in approximate balance by midwinter. The annual heat flux from WDW to the surface layer, and hence into the atmosphere, is estimated as 16 W m-2. Extrapolation of the Greenwich meridian WDW entrainment value to the full circumpolar 60ø-70øS belt yields total upwelling of 24 x 10 6 m 3 s-1. Similar extrapolation of the heat flux value gives a circumpolar total of 2.8 x 1014 W. As a consequence of circulation/topography interaction, the Maud Rise water column stands out as an anomaly relative to the surrounding region, with a significantly more saline and dense mixed layer. Below the mixed layer the water column over the crest of the rise is identical to that over the flanks if the latter water column is upwelled by 400 m. This uplifting is believed to be a response of the upstream flow encountering the rise. Increased upstream flow would be expected to increase Maud Rise upwelling and the dependent salinity (density) of the mixed layer. Slight increases in the mixed layer density could trigger a convective mode and generation of a polynya. It is hypothesized that spin-up of the Weddell Gyre's barotropic circulation induced by an increase of the regional wind stress curl would enhance the probability of polynya development over Maud Rise. 2. LARGE-SCALE FEATURES To provide background, the large-scale thermohaline field as viewed with the Ant V/2 data set is briefly presented. 2.1. Temperature and Salinity Sections The full depth temperature, salinity, and sigma-zero sections reveal the nearly homogeneous nature of the thermohaline structure characteristic of the zone poleward of the Antarctic Circumpolar Current (Figures 2a-2c; the complete set of sections are included in the Ant V/2 data report 11,655 11,656 GORDON AND HUBER: SOUTHERN OCEAN WINTER MIXED LAYER 60 ø 0.29 60 ø IOøE 55oS 65 ø 65 ø 0 o 70ø3 GORDON AND HUBER.' SOUTHERN OCEAN WINTER MIXED LAYER 5 ø Oø 60 ø ß • 60 ø • ß \ .

Journal of Geophysical Research, 1987

We collected data on temperature, salinity, nutrient concentrations (nitrate, nitrite, phosphate,... more We collected data on temperature, salinity, nutrient concentrations (nitrate, nitrite, phosphate, and silicic acid), and phytoplankton biomass (chlorophyll a, particulate carbon, nitrogen, and biogenic silica) in the upper 150 m in the marginal ice zone of the eastern Scotia Sea and northwestern Weddell Sea during November and early December of 1983. A distinct hydrographic front separating Drake Passage water from Weddell and Scotia sea surface waters was located at approximately 59øS and was the site of a consistent maximum in phytoplankton biomass. In addition, there was a pronounced phytoplankton biomass maximum associated with a surface salinity minimum near the northern limit of pack ice in the waters of the Weddell-Scotia confluence that characterized the western portion of the study area. In the eastern half of the study area, characterized by largely unmodified Weddell Sea surface water, the phytoplankton biomass near the ice edge was 2-5 times lower than that in the Weddell-Scotia confluence but was increasing with time. The water column structure, nutrient fields, and phytoplankton biomass distribution all suggest that the high phytoplankton biomass in the ice edge zone of the Weddell-Scotia confluence and the lower but temporally increasing biomass near the ice edge in unmodified Weddell Sea water reflect ice edge phytoplankton blooms in different stages of their seasonal development. A bloom had become well established in the waters of the Weddell-Scotia confluence by mid-November, but the ice-free, vertically stable near-surface water column necessary for enhanced phytoplankton growth had apparently not been present long enough for high biomass levels to develop within the Weddell Sea proper. INTRODUCTION Intense phytoplankton blooms near the edge of the seasonally retreating pack ice are quite common in polar oceans of both the northern and southern hemispheres [e.g., McRoy and

Journal of Geophysical Research, 1995

Journal of Geophysical Research, 2001

An oceanographic field program called the Antarctic Zone Flux experiment was carried out in the e... more An oceanographic field program called the Antarctic Zone Flux experiment was carried out in the eastern Weddell Sea during austral winter (July-September) 1994. Data from a drift buoy array were used in concert with shipboard observations to provide exceptionally high horizontal resolution of upper ocean hydrographic parameters near Maud Rise. Chemical and tracer data were obtained from the ship. We identify a "warm pool" southwest of the rise as a dynamically necessary region of positive (cyclonic) vorticity that is associated with a Taylor column over the rise. Both a warm "halo" surrounding the Taylor column and the warm pool are associated with thermocline shoaling that is a necessary condition for high upward heat fluxes to occur. These features extend the influence of Maud Rise bottom topography on upper ocean heat flux over a region that is larger, by a factor of at least 2, than the area directly overlying the rise. Areal mean upward heat fluxes of about 25 W m Ϫ2 are derived using both upper ocean T ("instantaneous") values and tracer data ("integrated") values. Fluxes derived over the warm halo and pool regions using only upper ocean T exceeded 100 W m Ϫ2 at specific sites. Elsewhere in the region, the T-derived heat fluxes varied widely from Ͻ10 to Ͼ50 W m Ϫ2 , whereas the tracer-derived heat fluxes showed a considerably more uniform distribution. Our mean values are similar to those that have been previously reported. Historical ice cover data have shown that the geographical region encompassed by Maud Rise and the warm pool area to the southwest is a preferred site for polynya formation, consistent with these findings. Time series analyses of the historical upper ocean data set suggest that conditions conducive to polynya formation are correlated with climate processes remote from the Southern Ocean.

Journal of Geophysical Research, 2001

An extensive set of conductivity-temperature-depth (CTD)/lowered acoustic Doppler current profile... more An extensive set of conductivity-temperature-depth (CTD)/lowered acoustic Doppler current profiler (LADCP) data obtained within the northwestern Weddell Sea in August 1997 characterizes the dense water outflow from the Weddell Sea and overflow into the Scotia Sea. Along the outer rim of the Weddell Gyre, there is a stream of relatively low salinity, high oxygen Weddell Sea Deep Water (defined as water between 0 ø and-0.7øC), constituting a more ventilated form of this water mass than that found farther within the gyre. Its enhanced ventilation is due to injection of relatively low salinity shelf water found near the northern extreme of Antarctic Peninsula's Weddell Sea shelf, shelf water too buoyant to descend to the deep-sea floor. The more ventilated form of Weddell Sea Deep Water flows northward along the eastern side of the South Orkney Plateau, passing into the Scotia Sea rather than continuing along an eastward path in the northern Weddell Sea. Weddell Sea Bottom Water also exhibits two forms: a low-salinity, better oxygenated component confined to the outer rim of the Weddell Gyre, and a more saline, less oxygenated component observed farther into the gyre. The more saline Weddell Sea Bottom Water is derived from the southwestern Weddell Sea, where highsalinity shelf water is abundant. The less saline Weddell Sea Bottom Water, like the more ventilated Weddell Sea Deep Water, is derived from lower-salinity shelf water at a point farther north along the Antarctic Peninsula. Transports of Weddell Sea Deep and Bottom Water masses crossing 44øW estimated from one LADCP survey are 25 x 106 and 5 x 106 m 3 s-1, respectively. The low-salinity, better ventilated forms of Weddell Sea Deep and Bottom Water flowing along the outer rim of the Weddell Gyre have the position and depth range that would lead to overflow of the topographic confines of the Weddell Basin, whereas the more saline forms may be forced to recirculate within the Weddell Gyre. 1. Gordon, 1998]. Streams of newly formed Weddell Sea Deep Water (WSDW, defined as deep water with potential temperatures between 0 ø and-0.7øC [Fahrbach et al., 1995]) and Weddell Sea Bottom Water (WSBW, defined as water colder than-0.7øC [Carmack and Foster, 1975]) are carried by the western boundary current of the Weddell Sea into the northwest corner of the Weddell Gyre [Deacon, 1979; Orsi et al., 1993]. From there these water masses flow eastward, either within the northern limb of the Weddell Gyre or reaching northward into the Scotia Sea [Gordon, 1966; Locarnini et al., 1993], eventually cooling the lower 2 km of the world ocean as Antarctic Bottom Water. The objective of this study is to describe the characteristics of Weddell Sea Deep Water (WSDW) and Weddell Sea Bottom Water (WSBW) within the northwest Weddell Sea and their overflow into the southern Scotia Sea. 2. DOVETAIL Data The data set used in this study was collected during cruise 97-5 of the polar research vessel Nathaniel B. Palmer from July