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Image courtesy of Professor Mike Meredith, British Antarctic Survey, Cambridge, UK
Theo Murphy international scientific meeting organised by Professor Andrew Watson FRS, Professor John Marshall FRS and Professor Mike Meredith.
The Southern Ocean is the most remote and the least understood of the world’s oceans, but plays a crucial role in past and present climate change. Currently it is the focus of intense physical and biogeochemical research. This meeting will bring together observationalists and modellers to exchange their latest insights, and will reach across the disciplines to bring together physical oceanographers, climatologists and carbon cycle scientists.
Biographies of the key contributors and recorded audio files of the presentations are available below and you can also download the programme (PDF).
Enquiries: Contact the events team
Professor Andrew Watson FRS, University of East Anglia, UK
Biography not yet available
Professor John Marshall FRS, MIT, USA
Professor Mike Meredith, British Antarctic Survey, UK
Michael Meredith leads the Polar Oceans strategic research programme at the British Antarctic Survey. Dr. Meredith is Chair of the Southern Ocean Observing System (SOOS), and serves on the Scientific Advisory Board of the Alfred Wegener Institute (AWI). Amongst other activities, he is a member of POGO (the Partnership for Observations of the Global Ocean), and an invited PI on the United States Palmer Long-Term Ecological Research (LTER) program. Following completion of his doctorate, he conducted physical oceanographic research at UEA, where he was awarded a NERC Fellowship. He has also previously worked at the Proudman Oceanographic Laboratory, Liverpool, where he led a project concerned with understanding the time-dependency of high-latitude ocean circulation. Dr. Meredith has worked in both Arctic and Antarctic regions, with particular expertise in understanding the role of the ocean in climate change and variability using combinations of direct measurements, remote sensing and numerical modelling. He has conducted numerous field campaigns in the polar regions, and has authored or co-authored more than 80 journal papers on the the imoprtance of these environments.
Dr Stephen Rintoul, CSIRO and Antarctic Climate and Ecosystems Cooperative Research Centre, AustraliaSouthern Ocean circulation, variability and links to climate
Dr Stephen Rintoul is a physical oceanographer and climate scientist with a long-standing interest in the Southern Ocean and its role in the earth system. Born and educated in the USA, he has worked for the CSIRO in Australia since 1990. Primarily an observationalist, he uses a variety of tools to measure the Southern Ocean and has led a dozen oceanographic expeditions to the region. Dr Rintoul is a Coordinating Lead Author of the Oceans chapter in the 5th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). His scientific achievements have been recognised by a number of honours, including the Georg Wüst Prize of the German Society for Marine Research, the Martha T Muse Prize for Antarctic Science and Policy, the Australian Antarctic Medal, and election to the Australian Academy of Science.
The Southern Ocean circulation connects the ocean basins, providing the dominant oceanic teleconnection and allowing a global-scale overturning to exist. But the region is much more than a pipe: water mass transformations driven by air-sea fluxes and diapycnal mixing in the Southern Ocean link the deep and upper ocean and close the global overturning. By returning deep waters to the upper ocean, and thereby countering the relentless export of organic material from the upper ocean, the Southern Ocean overturning is central to global budgets of carbon, nutrients and other properties. The downward limbs of the various Southern Ocean overturning cells ventilate the ocean interior and set the capacity of the ocean to store heat and anthropogenic carbon dioxide and thereby regulate climate. Given the imprint of the Southern Ocean on global ocean circulation, climate, and biogeochemical cycles, change in the Southern Ocean would have widespread consequences. New measurements reveal aspects of the Southern Ocean circulation that are changing rapidly (eg the volume of Antarctic Bottom Water), while others are more resilient (eg the transport of the Antarctic Circumpolar Current). These observations provide insight into the sensitivity of the Southern Ocean circulation to changes in forcing, whether natural or anthropogenic.
Dr Sarah Gille, University of California San Diego, USAPoleward heat transport in the Southern Ocean: identifying roles of winds and fronts
Professor Gille earned a BS in physics at Yale and a PhD in physical oceanography from the Massachusetts Institute of Technology/Woods Hole Oceanographic Institution Joint Program. She did postdoctoral research at Scripps Institution of Oceanography and at the University of East Anglia, and was a faculty member at the University of California, Irvine. She joined the UCSD faculty in 2000. Her research interests include:
Observed long-term warming trends in the Southern Ocean have been interpreted as a sign of increased poleward eddy heat transport or of a poleward displacement of the entire Antarctic Circumpolar Current (ACC), possibly in response to a decadal-scale intensification of the Southern Annular Mode (SAM). The two-decade-long record from satellite altimetry is an important source of information for evaluating the mechanisms governing these trends. Satellite altimeter data indicate that short-term meandering of the ACC tracks the SAM on monthly to seasonal scales and is closely linked to El Nino variability on seasonal to interannual timescales, but the signal is not yet long enough to intrepret decadal-scale trends in the ACC. The long-term warming trend suggests the possibility that more (or warmer) Upper Circumpolar Deep Water may be coming into contact with the Antarctic Ice Shelves, particularly in regions where the southern edge of the ACC is closest to the Antarctic continent (such as in the Amundsen Sea Embayment, near Pine Island Glacier.) The Southern Ocean State Estimate (an assimilating model that is constrained both by altimetry and Argo observations) allows us to evaluate the relative contributions of air-sea fluxes, horizontal advection, and diffusion for the Amundsen Sea region.
Professor Mike Meredith, British Antarctic Survey, UKDense water export in the Atlantic sector of the Southern Ocean: mechanisms, changes and consequences
Michael Meredith leads the Polar Oceans strategic research programme at the British Antarctic Survey. Dr Meredith is Chair of the Southern Ocean Observing System (SOOS), and serves on the Scientific Advisory Board of the Alfred Wegener Institute (AWI). Amongst other activities, he is a member of POGO (the Partnership for Observations of the Global Ocean), and an invited PI on the United States Palmer Long-Term Ecological Research (LTER) program. Following completion of his doctorate, he conducted physical oceanographic research at UEA, where he was awarded a NERC Fellowship. He has also previously worked at the Proudman Oceanographic Laboratory, Liverpool, where he led a project concerned with understanding the time-dependency of high-latitude ocean circulation. Dr Meredith has worked in both Arctic and Antarctic regions, with particular expertise in understanding the role of the ocean in climate change and variability using combinations of direct measurements, remote sensing and numerical modelling. He has conducted numerous field campaigns in the polar regions, and has authored or co-authored more than 80 journal papers on the the imoprtance of these environments.
The waters that form around the periphery of the Antarctic continent include the densest components of the global overturning circulation. These flow northward to flood the abyss of the global ocean by navigating various topographical obstacles, including complex ridge systems, narrow passages and deep trenches. These dense waters are undergoing significant changes in climate, with a circumpolar freshening now recognized, and a marked warming along the major outflow routes. Determining the causes of the latter is important, since the rate of warming is believed to be significant for assessments of sea level rise, the global heat budget, and benthic biodiversity. The rate of warming is strongest in the Atlantic, into which deep waters are fed from the Weddell Sea. This presentation will present a synopsis of recent advances in our understanding of the processes and controls that lead to variability in the properties and flux of the dense waters that exit the Weddell Sea northward, including wind-forced controls, topographic interactions, and abyssal mixing. Priorities for future research effort will be highlighted.
Professor I Nick McCave, University of Cambridge, UKGlacial versus Holocene Antarctic Circumpolar Current flow speeds through the Scotia Sea
Nick McCave was Woodwardian Professor of Geology at the University of Cambridge since 1985 (now Emeritus). He was brought up in Guernsey, impressed by a 10 m tidal range, and educated there, at Oxford and Brown Universities. He has been investigating marine sedimentation since he was a NATO post-doc at the Netherlands Institute for Sea Research in the late 1960s working on tides, sand waves and banks, following a classical geological upbringing. He was then a founding member of the School of Environmental Sciences at the University of East Anglia and also spent 10 years (1977-87) as an Adjunct Scientist at Woods Hole Oceanographic Institution (USA) working on deep sea boundary layers, sediment dynamics and nepheloid layers in the Western Boundary Undercurrent. Since then he has specialised in properties of deep ocean sediments, especially grainsize, for understanding past behaviour of ocean currents in the climate system. This has involved work under deeep western boundary currents in the southwestern Pacific and Indian Oceans, and all over the North Atlantic. Present work is on calibration of the ‘mud current meter’. He has been President of SCOR (The Scientific Committee on Oceanic Research of ICSU).
There are differences of opinion as to whether during the last glacial maximum (LGM) ACC flow speed was faster than present or unchanged, under either stronger or weaker winds, and whether the whole current shifted to the north or not. We have examined whether the ACC flow speed and transport was greater or less at a past climate extreme with sediment data on the LGM to Holocene difference of ACC flow through the Drake Passage/Scotia Sea flow constriction. We find essentially no change in the average flow of the ACC through the region. However, ACC flow at the LGM was significantly slower in the southern ice-covered portion of the area (south of 56° S), and only slightly (insignificantly) faster in the north, which implicates shielding from wind stress by fast-ice in the flow’s spatial variability. Slower flow over rough topography in the south implies reduced diapycnal mixing in this key region, consistent with a reduced overturning circulation. Added to the most probable scenarios that LGM winter sea-ice extent was ~5° further north and the frontal system was likely 5°-7° further north, some models can now be further constrained.
Professor Karen J Heywood, University of East Anglia, UKProcesses at the Antarctic continental slope important for climate and the carbon cycle
Karen Heywood is a Professor of Physical Oceanography in the School of Environmental Sciences at the University of East Anglia. She has been at UEA since 1989, where she teaches and undertakes research in ocean physics. She originally did a physics degree followed by a PhD in physical oceanography. She is particularly interested in observing the polar oceans, and the interaction of the oceans with ice. She has led many research cruises to the polar regions. She is the leader of the UEA Seaglider group which owns and operates a fleet of four Seagliders used to investigate multidisciplinary ocean processes worldwide. She enjoys interacting with the public and is leading an exhibit entitled 'A Pinch of Salt' for the Royal Society Summer Science Exhibition in 2013.
Acceleration of Antarctic ice sheet loss is mainly driven by basal ice shelf melt, in turn determined by ocean-ice interaction and related to the heat transport onto the Antarctic continental shelf. Processes of water mass transformation through sea-ice formation/melting and ocean-atmosphere interaction on the Antarctic continental shelf are key to the formation of deep and bottom waters as well as determining the heat flux beneath ice shelves. Climate models however cannot include such small-scale processes and struggle to reproduce the water mass properties of the region.
Changes in temperature and salinity of Southern Ocean water masses have been identified regionally. Here we discuss recent changes in water mass properties on the Antarctic continental shelf. Some of the mechanisms through which the warm waters offshore in the Southern Ocean may penetrate onshore are discussed, including eddies and along-slope waves.
In early 2012 the GENTOO project deployed three Seagliders for up to two months to sample the water to the east of the Antarctic Peninsula in unprecedented temporal and spatial detail. We discuss evidence in the Seaglider data of exchanges across the shelf-break front (the Antarctic Slope Front), including observations of dense water spilling off the continental shelf, and of a subsurface lens of Warm Deep Water on the shelf emanating from offshore. GENTOO demonstrated the capability of ocean gliders to play a key role in a future Southern Ocean Observing System.
Dr James R Ledwell, Woods Hole Oceanographic Institution, USADiapycnal mixing from coordinated tracer and turbulence measurements
Dr Ledwell studied physics at Boston College and the University of Massachusetts before moving to Harvard University to study atmospheric science with Profs. Michael McElroy, Steven Wofsy, Richard Goody and Richard Lindzen. Finishing his PhD in 1982, he moved to Goddard Institute of Space Studies, to work with James Hansen and Inez Fung, and to Lamont Doherty Earth Observatory, encouraged and guided by Wallace S. Broecker. That was also the start of an ongoing collaboration with Professor Andrew Watson, to develop and exploit perfluorinated compounds as ocean tracers to study mixing processes in the ocean. Since then, a series of mulit-year experiments have been performed by Ledwell, Watson, and their colleagues in a variety of oceanic environments. Dr Ledwell, who moved to Woods Hole in 1990, has also developed and led a series of short-term mixing experiments in the upper ocean with fluorescent dyes. Dr Ledwell was a recipient of the Alexander Agassiz Award of the National Academy of Sciences in 2007, and was elected a fellow of the American Geophysical Union in 2011.
Measurements of the dissipation rate of turbulent kinetic energy in the southeast Pacific sector of the Antarctic Circumpolar Current (ACC) imply a diapycnal diffusivity of order 10-5 m2/s at nearly all depths. A tracer released in this same region agreed with this result in the lower part of the Upper Circumpolar Deep Water. Both the tracer and dissipation profiles give diffusivities more than an order of magnitude greater in the topographically rough Scotia Sea than in the relatively smooth southeast Pacific, although it presently appears that integration of the dissipation-based diffusivity falls short of the diffusivity measured by the tracer. The leading hypothesis for enhanced mixing in the Scotia Sea is that lee waves, generated by geostrophic flows over the topography, propagate upward and become unstable and break, to generate turbulent mixing well above the bottom. Extrapolation of the measurements to all of the area of the ACC suggests an average diffusivity of nearly 10-4 m2/s. An effort will be made to estimate from the diffusivity measurements the convergence of buoyancy in various water masses of the ACC, and therefore of the role played by diapycnal mixing in the ACC in the Meridional Overturning Circulation of the ocean.
Professor Raffaele Ferrari, MIT, USARecent observations of Southern Ocean mixing and their implications
Raffaele Ferrari, Breene M Kerr Professor of Physical Oceanography at the Massachusetts Institute of Technology, studies the dynamics of the ocean circulation and its role in shaping climate and climate change. A major thrust of his research is to understand how ocean turbulence affects the circulation and biological productivity of the oceans. He is a leading PI of three observational programs, one in the Southern Ocean and two in the North Atlantic, focused on measuring the rate at which mesoscale eddies mix through the oceans heat, salt, carbon and other climatologically important tracers. From 2003 to 2008, he lead a multi-institution US Climate Process Team to improve the representation of ocean turbulence in climate models. He is the Director of the MIT Program in Atmospheres, Oceans, and Climate.
The Meridional Overturning Circulation (MOC) of the ocean is a critical regulator of the Earth's climate processes. Climate models have been shown to be highly sensitive to the representation of lateral eddy mixing in the southern limb of the MOC, within the Antarctic Circumpolar Current latitudes, although the lack of extensive in situ observations of Southern Ocean mixing processes has made evaluation of mixing somewhat difficult. We present the first direct estimate of the rate of lateral eddy mixing across the Antarctic Circumpolar Current is presented. The estimate is computed from the spreading of a tracer released upstream of Drake Passage as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). The meridional eddy diffusivity, a measure of the rate at which the area of the tracer spreads along an isopycnal across the Antarctic Circumpolar Current, is approximately 700 m^2/s at 1500 m depth. The estimate is based on an extrapolation of the tracer based diffusivity using output from numerical tracers released in a 1/20th of a degree model simulation of the circulation and turbulence in the Drake Passage region. The model is shown to reproduce the observed spreading rate of the DIMES tracer and suggests that the meridional eddy diffusivity is weak in the upper kilometer of the water column with values below 500 m^2/s and peaks at the steering level, near 2 km, where the eddy phase speed is equal to the mean flow speed. The implications of these results for the ventilation of deep water masses and for the representation of oceanic turbulence in ocean models used for climate studies will be discussed.
Dr Andrew Meijers, British Antarctic Survey, UK
Dr Jan Zika, University of Southampton, UK
Professor John Marshall FRS, MIT, USAWhat's happening at the poles?
John Marshall is the Cecil and Ida Green Professor of Oceanography at MIT. His research is directed at understanding the cause of the general circulation of the oceans, its interaction with the atmosphere and its role in the global climate and climate change.
The Arctic is warming and sea ice is disappearing. But the Antarctic is (mainly) cooling and sea ice is growing. Why? We discuss the role of the ocean in the asymmetric response of the poles to Greenhouse Gas and Ozone Hole forcing and suggest that part of the answer might lay in inter-hemispheric asymmetries in the mean ocean circulation.
Dr Andy Hogg, ANU, AustraliaCirculation in the Southern Ocean: a conspiracy between wind, buoyancy, eddies and geometry
Dr Andy Hogg is a physical oceanographer who has contributed to our understanding of the dynamics of global-scale ocean circulation, particularly in the Southern Ocean. He was the primary developer of a high-resolution model used for the investigation of the role of eddy processes in ocean circulation, and has demonstrated that these smaller-scale processes (not simulated by most ocean-climate models) can have controlling influences on the global scale flow. He has also helped to formulate the mechanical energy budget and driving forces for the oceans and contributed to a new understanding of the way the Southern Ocean will respond to variations in wind stress and climate change. Dr Hogg holds a position as an Associate Professor and ARC Future Fellow at the Australian National University, and is a founding Chief Investigator of the ARC Centre of Excellence for Climate System Science.
Disentangling the individual contributions of surface wind stress and surface buoyancy forcing to the Southern Ocean circulation is complicated by the dynamical role played by eddies, as well as interactions between flow and topography in this region. Here we show a suite of recent results from idealised (but high resolution) ocean models, which are helping to unravel the governing dynamics of the Southern Ocean. It is now clear that eddies may partially moderate the Southern Ocean response to future changes in wind stress, but that the sensitivity of the overturning circulation and the circumpolar transport differ considerably. Surface buoyancy forcing (both local and remote) plays a strong role in controlling the system response, and is likely to dominate Southern Ocean change on long timescales. Idealised model have the twin advantages of complete equilibration and model efficiency; however, an important caveat on the application of idealised model results is that details of the model topography can dominate the behaviour of the system.
Professor Darryn Waugh, John Hopkins University, USAChanges in the ventilation of the southern oceans
Darryn Waugh is a Professor in the Department of Earth and Planetary Sciences at the Johns Hopkins University. His research interests are large-scale dynamics and transport in the atmosphere and oceans. A recent focus has been on determining / understanding the time scales for transport from the surface into the stratosphere and into the oceans, and the connection with stratospheric ozone depletion and oceanic uptake of carbon, respectively. He has authored over 110 peer-reviewed articles and participated in several international assessments, including being lead chapter author of the 2006 WMO/UNEP ``Scientific Assessment of Ozone Depletion''.
Darryn Waugh was born in New Zealand, and obtained Bachelor and Masters degrees in Mathematics from the University of Waikato, NZ in 1985 and 1987, respectively. He earned his PhD in Applied Mathematics at Cambridge University, UK in 1991. He was a post-doctoral fellow at MIT and a research scientist at Monash University, Australia, before joining the Hopkins faculty in 1998.
Surface westerly winds in the Southern Hemisphere have intensified over the past few decades, primarily in response to the formation of the Antarctic ozone hole. I will discuss the impact of this intensification on the transport of surface waters into the interior (“ventilation”) of the southern oceans. Measurements of CFC-12 made in the southern oceans in the early 1990s and mid- to late-2000s will be used to show large-scale coherent changes in the ventilation, with a decrease in the age of subtropical subantarctic mode waters and an increase in the age of circumpolar deep waters. Model simulations will be used to examine the possible mechanisms involved with these changes in ventilation, and the possible impact on the oceanic uptake of heat.
Professor Jorge Sarmiento, Princeton University, USAA proposal for a Southern Ocean biogeochemical observations and modeling program (SOBOM)
Dr Jorge L Sarmiento is the George J Magee Professor of Geosciences and Geological Engineering at Princeton University. He has published 177 papers on the global carbon cycle, on the use of chemical tracers to study ocean circulation, and on the impact of climate change on ocean biology and biogeochemistry. He has participated in the scientific planning and execution of many of the large-scale multi-institutional and international oceanographic biogeochemical and tracer programs of the last three decades. He was Director of Princeton's Atmospheric and Oceanic Sciences Program from 1980 to 1990 and 2006 to the present, and is Director of the Cooperative Institute for Climate Science. He has served on the editorial board of multiple journals and as editor of Global Biogeochemical Cycles. He is a Fellow of the American Geophysical Union, a Fellow of the American Association for the Advancement of Science, and the American Geophysical Union’s 2009 Roger Revelle Medalist.
Because the Southern Ocean surrounding the Antarctic is the primary window through which the vast volume of the intermediate, deep, and bottom waters of the ocean interact with the surface layer of the ocean and thus the atmosphere, this region has a profound influence on the Earth’s climate and ecosystems. Indeed, prior modeling and observational studies suggest that, despite occupying just over a quarter of the surface ocean area,
Furthermore, model simulations of the future project that climate change will have a profound impact on vertical exchange of deep and surface waters in the Southern Ocean, with corresponding changes in the ocean carbon cycle, heat uptake, and ecosystems; and that, due to acidification, the Southern Ocean will become undersaturated in aragonitic calcium carbonate by 2030, with potentially major impacts on calcifying organisms and Antarctic ecosystems. Despite its disproportionate importance, the Southern Ocean is the least observed and least understood region of the world ocean, and the studies underlying these results are thus highly controversial. The two most critical issues are that models of the Southern Ocean are too coarse to resolve critical features of the ocean circulation; and that we have only limited observations to assess the models due to the great difficulty of obtaining data in this region. We propose taking advantage of recent advances in computational capacity and biogeochemical sensors to develop a research program consisting of a strategic and optimal mix of innovative and sustained observations of the carbon cycle, ultra-high resolution modeling, and focused process studies.
Professor Andrew Watson FRS, University of East Anglia, UKGlacial – interglacial changes in CO2 and the links to Southern Ocean dynamics
Andrew Watson was appointed a Royal Society Research Professor as part of the Royal Society's 350th anniversary celebrations, in 2009. He researches the global carbon cycle, and the processes that affect atmospheric carbon dioxide, both through earth history and on the modern, human-disturbed planet. He studied planetary atmospheres at the University of Michigan, before returning to the UK and working at the Plymouth Marine Laboratory, where he developed tracer techniques that have enabled large scale ocean experiments. He has used these techniques to study diverse properties of the ocean, including gas exchange, the role of iron as a limiting nutrient, and most recently, mixing in the Southern Ocean. He is a Fellow of the Royal Society, a member of NERC council, and recipient of the European Geophysical Union's Nansen medal for achievements in marine science. He has recently moved from the University of East Anglia to the University of Exeter.
The causes of reduced atmospheric CO2 in the Quaternary glaciations remain imperfectly understood, and difficult to model from first principles. It is clear however, from the correlation observed in Antarctic ice cores between temperatures and CO2, that Southern Ocean processes play key roles in driving these changes. Among these, there is good reason to believe that changes in the overturning and bottom water formation processes are very important. We discuss here some aspects of these processes in the modern ocean, and highlight differences in glacial time that we believe would have contributed to decreasing atmospheric CO2. We concentrate on (1) decreased Southern Ocean upwelling due to a weaker residual circulation, (2) a greater remoteness of the upwelling sites from those of bottom water formation, (3) a seasonal rectification effect due to the proximity of winter sea ice formation to the polar front, resulting in greater salinity stratification of the oceans, (4) Decreased air-sea equilibration of newly densified surface water, due to the intense and rapid cooling that occurs in coastal polynas which would have been the main formation region for bottom waters in glacial time.
Dr Mario Hoppema, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, GermanyPenetration of anthropogenic carbon into the deep Southern Ocean with special emphasis on the Weddell Sea
Dr Mario Hoppema is a senior scientist at the Alfred Wegener Institute (AWI) for Polar and Marine Research in Bremerhaven, Germany. By training he is a chemist, having studied at the University of Leiden in his home country the Netherlands. Ph.D. research on the carbon and oxygen cycles of the nearby Wadden Sea and coastal North Sea was conducted at the Royal Netherlands Institute for Sea Research at Texel. Since 1992 he has worked on the carbon cycle and biogeochemistry of the Atlantic sector of the Southern Ocean at AWI and the University of Bremen. Data have been collected at several long cruises with RV “Polarstern” (and once with RRS “James Cook”) and results were published in some 50 peer-reviewed publications. Hoppema has participated in several EU projects, the actual one being CARBOCHANGE IP. He is topic editor of the journal Ocean Science and has been guest editor of some special issues. He was involved in the major data rescue and quality control effort CARINA where he was leading the Southern Ocean part.
Using 10 cruises spanning 1984 to 2011, we investigate the time rate of change of TCO2 in the Weddell Gyre (i) along the Prime Meridian, (ii) on the continental slope near the tip of the Antarctic Peninsula, and (iii) at the bottom of the Weddell Sea interior. In the Weddell Sea Bottom Water at the Prime Meridian, the spatial distribution of the increase in DIC bears a high resemblance to that of CFCs, suggesting that the changes in Cant are propagated from the surface. However, other variables like dissolved oxygen and silicate also show trends through time, pointing to non-steady state conditions which might also affect the derived CO2 increase. Near the tip of the Peninsula, the coldest and most recently ventilated waters, hugging the continental slope, exhibit increasing DIC over time in clear dependence of temperature. In the bottom layer of the Weddell Sea interior, no relationship is found between DIC and potential temperature. The mean values of DIC in these waters are observed to have remained essentially constant, suggesting that no significant ventilation of these waters has taken place over the time scale of observations. This finding is in line with the low levels of CFCs at this location.
Co-authors:Steven van Heuven, Centre for Isotope Research, University of Groningen, The NetherlandsElizabeth Jones, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, GermanyHein J W de Baar, Royal Netherlands Institute for Sea Research, The Netherlands
Professor Corinne Le Quéré, Tyndall Centre for Climate Change Research, University of East Anglia, UKRecent trends in the Southern Ocean CO2 sink
Corinne Le Quéré is Professor of Climate Change Science and Policy at the University of East Anglia and Director of the Tyndall Centre for Climate Change Research. She conducts research on the interactions between climate change and the carbon cycle. She developed and used models to understand and quantify the effectiveness of the oceans to take up anthropogenic CO2, and how that changes through time. Her work suggests that the recent strenghtening of Southern Ocean winds has slowed down the increase in the ocean CO2 sink. Prof Le Quéré was author of the 3rd, 4th and 5th (ongoing) Assessments of the Intergovernmental Panel on Climate Change (IPCC) and co-Chairs the Global Carbon Project. She is originally from Canada, and conducted research in Princeton, Paris, and Jena, Germany. She received an Award from the French Academy of Sciences in 2012.
Dr Peter Brown, University of East Anglia, UKSouthern Ocean carbon: accumulation, fluxes and transport from the Weddell Gyre to the global ocean
Peter Brown is a Senior Research Associate at the University of East Anglia and the British Antarctic Survey. After a MChem in Chemistry at the University of Leicester, he had a spell in the Pharmaceutical industry before pursuing a PhD at UEA investigating natural and anthropogenic carbon fluxes in the North Atlantic. Since 2008 Peter has been investigating the freshwater and carbon budgets of the Weddell Gyre in the Southern Ocean. His main interests are in Southern Ocean ventilation, and the dynamics and biogeochemical processes affecting the marine carbon and freshwater cycles, principally through the analysis of the inorganic carbon system, transient tracer proxies and oxygen isotopes. He also studies the variability in the air-sea flux of natural, modern and anthropogenic carbon and their accumulation, storage and transport in the water column in shelf seas and the open ocean. He was a contributor to the International CarboOcean CARINA Carbon Synthesis, SOCAT and EU-CarboChange Projects.
In the Southern Ocean, the Weddell Gyre (WG) is regarded as the primary location for the formation of deep and bottom waters and is potentially a significant area for the sequestration of carbon, nutrients and atmospheric gases. Here, measurements of the inorganic carbon system and transient tracers from four cruises that cross and enclose the Weddell Gyre combined with velocity fields from a box inverse model are used to investigate the accumulation, fluxes and transports of contemporary and anthropogenic carbon into/out of the gyre. The gyre is found to be a sink for both Canth and contemporary carbon dioxide for the summer/fall period under investigation; substantial undersaturation of pCO2 (up to 80 μatm) of the surface layer down to the depth of the Winter Water temperature minimum is found, possibly related to the recent retreat of sea-ice in the area. Little accumulation of carbon is found to occur in the WG, although elevated concentrations associated with sea-ice production/anthropogenic uptake are observed to be exported through the gaps in the South Scotia Ridge, primarily as transports of Antarctic Bottom Water. These results highlight the role of the region in injecting human-derived carbon into the global abyss.
Dr Robert Anderson, LDEO, USABiological response to variable dust supply in the South Atlantic sediment record
Robert F Anderson is a Ewing-Lamont Research Professor at the Lamont-Doherty Earth Observatory and an Adjunct Professor in the Department of Earth and Environmental Sciences, Columbia University, New York. He studies the ocean carbon cycle and its sensitivity to global change. His interests span a range of topics and time scales, from climate-related changes in the ocean's carbon budget across late-Pleistocene glacial cycles to predicting the ocean's response to global warming, and the implications for the ocean's uptake of fossil fuel CO2. Of particular interest are changes in ocean and atmospheric circulation associated with abrupt climate variability during the last glacial period. These events are thought to hold clues to the interhemispheric teleconnections that influence the Southern Ocean where deep waters exchange carbon dioxide and other gases with the atmosphere, and where ecosystems are particularly sensitive to environmental perturbations in ways that may impact the ocean's carbon cycle. He received the A G Huntsman Award for Excellence in Marine Science, is a fellow of the American Geophysical Union, and has published more than 130 peer reviewed papers.
Iron, which can be supplied by mineral aerosols (dust), is thought to limit phytoplankton growth in most of the Southern Ocean. However, paleo records of Southern Ocean biological productivity generally show little to no response to enhanced flux of dust. The Subantarctic South Atlantic (SASA, roughly 40°-50°S) is anomalous in this regard. The greater biological response seen in the SASA than elsewhere in the Southern Ocean may reflect the upwind proximity of the principal dust source for high southern latitudes, which is located in Patagonia. Previous studies have shown a tight coupling between dust and biological productivity in the SASA at the glacial-interglacial time scale. Here, by analyzing cores at higher temporal resolution, we demonstrate coupling at millennial time scales as well. Specifically, we show that 230Th-normalized fluxes in SASA sediments of lithogenic minerals (primarily dust) and of C37-alkenones (produced by coccolithophorids) and of other biogenic tracers are clearly correlated with the dust flux records from two ice cores in Antarctica over the past 100,000 years. As the correlation is now evident in three high-resolution sediment cores spanning a large portion of the SASA, we conclude that a widespread biological response to variable dust supply. The lack of response in other regions of the Southern Ocean demonstrates that other processes may be at play.
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