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Sample records for antarctic southern ocean

  1. Antarctic warming driven by internal Southern Ocean deep convection oscillations

    NASA Astrophysics Data System (ADS)

    Martin, Torge; Pedro, Joel B.; Steig, Eric J.; Jochum, Markus; Park, Wonsun; Rasmussen, Sune O.

    2016-04-01

    Simulations with the free-running, complex coupled Kiel Climate Model (KCM) show that heat release associated with recurring Southern Ocean deep convection can drive centennial-scale Antarctic temperature variations of 0.5-2.0 °C. We propose a mechanism connecting the intrinsic ocean variability with Antarctic warming that involves the following three steps: Preconditioning: heat supplied by the lower branch of the Atlantic Meridional Overturning Circulation (AMOC) accumulates at depth in the Southern Ocean, trapped by the Weddell Gyre circulation; Convection onset: wind and/or sea-ice changes tip the preconditioned, thermally unstable system into the convective state; Antarctic warming: fast sea-ice-albedo feedbacks (on annual to decadal timescales) and slower Southern Ocean frontal and sea-surface temperature adjustments to the convective heat release (on multi-decadal to centennial timescales), drive an increase in atmospheric heat and moisture transport towards Antarctica resulting in warming over the continent. Further, we discuss the potential role of this mechanism to explain climate variability observed in Antarctic ice-core records.

  2. Antarctic and Southern Ocean influences on Late Pliocene global cooling

    PubMed Central

    McKay, Robert; Naish, Tim; Carter, Lionel; Riesselman, Christina; Dunbar, Robert; Sjunneskog, Charlotte; Winter, Diane; Sangiorgi, Francesca; Warren, Courtney; Pagani, Mark; Schouten, Stefan; Willmott, Veronica; Levy, Richard; DeConto, Robert; Powell, Ross D.

    2012-01-01

    The influence of Antarctica and the Southern Ocean on Late Pliocene global climate reconstructions has remained ambiguous due to a lack of well-dated Antarctic-proximal, paleoenvironmental records. Here we present ice sheet, sea-surface temperature, and sea ice reconstructions from the ANDRILL AND-1B sediment core recovered from beneath the Ross Ice Shelf. We provide evidence for a major expansion of an ice sheet in the Ross Sea that began at ∼3.3 Ma, followed by a coastal sea surface temperature cooling of ∼2.5 °C, a stepwise expansion of sea ice, and polynya-style deep mixing in the Ross Sea between 3.3 and 2.5 Ma. The intensification of Antarctic cooling resulted in strengthened westerly winds and invigorated ocean circulation. The associated northward migration of Southern Ocean fronts has been linked with reduced Atlantic Meridional Overturning Circulation by restricting surface water connectivity between the ocean basins, with implications for heat transport to the high latitudes of the North Atlantic. While our results do not exclude low-latitude mechanisms as drivers for Pliocene cooling, they indicate an additional role played by southern high-latitude cooling during development of the bipolar world. PMID:22496594

  3. Antarctic and Southern Ocean influences on Late Pliocene global cooling

    USGS Publications Warehouse

    McKay, Robert; Naish, Tim; Carter, Lionel; Riesselman, Christina; Dunbar, Robert; Sjunneskog, Charlotte; Winter, Diane; Sangiorgi, Francesca; Warren, Courtney; Pagani, Mark; Schouten, Stefan; Willmott, Veronica; Levy, Richard; DeConto, Robert; Powell, Ross D.

    2012-01-01

    The influence of Antarctica and the Southern Ocean on Late Pliocene global climate reconstructions has remained ambiguous due to a lack of well-dated Antarctic-proximal, paleoenvironmental records. Here we present ice sheet, sea-surface temperature, and sea ice reconstructions from the ANDRILL AND-1B sediment core recovered from beneath the Ross Ice Shelf. We provide evidence for a major expansion of an ice sheet in the Ross Sea that began at ~3.3 Ma, followed by a coastal sea surface temperature cooling of ~2.5 °C, a stepwise expansion of sea ice, and polynya-style deep mixing in the Ross Sea between 3.3 and 2.5 Ma. The intensification of Antarctic cooling resulted in strengthened westerly winds and invigorated ocean circulation. The associated northward migration of Southern Ocean fronts has been linked with reduced Atlantic Meridional Overturning Circulation by restricting surface water connectivity between the ocean basins, with implications for heat transport to the high latitudes of the North Atlantic. While our results do not exclude low-latitude mechanisms as drivers for Pliocene cooling, they indicate an additional role played by southern high-latitude cooling during development of the bipolar world.

  4. Antarctic and Southern Ocean influences on Late Pliocene global cooling.

    PubMed

    McKay, Robert; Naish, Tim; Carter, Lionel; Riesselman, Christina; Dunbar, Robert; Sjunneskog, Charlotte; Winter, Diane; Sangiorgi, Francesca; Warren, Courtney; Pagani, Mark; Schouten, Stefan; Willmott, Veronica; Levy, Richard; DeConto, Robert; Powell, Ross D

    2012-04-24

    The influence of Antarctica and the Southern Ocean on Late Pliocene global climate reconstructions has remained ambiguous due to a lack of well-dated Antarctic-proximal, paleoenvironmental records. Here we present ice sheet, sea-surface temperature, and sea ice reconstructions from the ANDRILL AND-1B sediment core recovered from beneath the Ross Ice Shelf. We provide evidence for a major expansion of an ice sheet in the Ross Sea that began at ∼3.3 Ma, followed by a coastal sea surface temperature cooling of ∼2.5 °C, a stepwise expansion of sea ice, and polynya-style deep mixing in the Ross Sea between 3.3 and 2.5 Ma. The intensification of Antarctic cooling resulted in strengthened westerly winds and invigorated ocean circulation. The associated northward migration of Southern Ocean fronts has been linked with reduced Atlantic Meridional Overturning Circulation by restricting surface water connectivity between the ocean basins, with implications for heat transport to the high latitudes of the North Atlantic. While our results do not exclude low-latitude mechanisms as drivers for Pliocene cooling, they indicate an additional role played by southern high-latitude cooling during development of the bipolar world. PMID:22496594

  5. Risk maps for Antarctic krill under projected Southern Ocean acidification

    NASA Astrophysics Data System (ADS)

    Kawaguchi, S.; Ishida, A.; King, R.; Raymond, B.; Waller, N.; Constable, A.; Nicol, S.; Wakita, M.; Ishimatsu, A.

    2013-09-01

    Marine ecosystems of the Southern Ocean are particularly vulnerable to ocean acidification. Antarctic krill (Euphausia superba; hereafter krill) is the key pelagic species of the region and its largest fishery resource. There is therefore concern about the combined effects of climate change, ocean acidification and an expanding fishery on krill and ultimately, their dependent predators--whales, seals and penguins. However, little is known about the sensitivity of krill to ocean acidification. Juvenile and adult krill are already exposed to variable seawater carbonate chemistry because they occupy a range of habitats and migrate both vertically and horizontally on a daily and seasonal basis. Moreover, krill eggs sink from the surface to hatch at 700-1,000m (ref. ), where the carbon dioxide partial pressure (pCO2) in sea water is already greater than it is in the atmosphere. Krill eggs sink passively and so cannot avoid these conditions. Here we describe the sensitivity of krill egg hatch rates to increased CO2, and present a circumpolar risk map of krill hatching success under projected pCO2 levels. We find that important krill habitats of the Weddell Sea and the Haakon VII Sea to the east are likely to become high-risk areas for krill recruitment within a century. Furthermore, unless CO2 emissions are mitigated, the Southern Ocean krill population could collapse by 2300 with dire consequences for the entire ecosystem.

  6. The Effects of Interactive Stratospheric Chemistry on Antarctic and Southern Ocean Climate Change in an AOGCM

    NASA Technical Reports Server (NTRS)

    Li, Feng; Newman, Paul; Pawson, Steven; Waugh, Darryn

    2014-01-01

    Stratospheric ozone depletion has played a dominant role in driving Antarctic climate change in the last decades. In order to capture the stratospheric ozone forcing, many coupled atmosphere-ocean general circulation models (AOGCMs) prescribe the Antarctic ozone hole using monthly and zonally averaged ozone field. However, the prescribed ozone hole has a high ozone bias and lacks zonal asymmetry. The impacts of these biases on model simulations, particularly on Southern Ocean and the Antarctic sea ice, are not well understood. The purpose of this study is to determine the effects of using interactive stratospheric chemistry instead of prescribed ozone on Antarctic and Southern Ocean climate change in an AOGCM. We compare two sets of ensemble simulations for the 1960-2010 period using different versions of the Goddard Earth Observing System 5 - AOGCM: one with interactive stratospheric chemistry, and the other with prescribed monthly and zonally averaged ozone and 6 other stratospheric radiative species calculated from the interactive chemistry simulations. Consistent with previous studies using prescribed sea surface temperatures and sea ice concentrations, the interactive chemistry runs simulate a deeper Antarctic ozone hole and consistently larger changes in surface pressure and winds than the prescribed ozone runs. The use of a coupled atmosphere-ocean model in this study enables us to determine the impact of these surface changes on Southern Ocean circulation and Antarctic sea ice. The larger surface wind trends in the interactive chemistry case lead to larger Southern Ocean circulation trends with stronger changes in northerly and westerly surface flow near the Antarctica continent and stronger upwelling near 60S. Using interactive chemistry also simulates a larger decrease of sea ice concentrations. Our results highlight the importance of using interactive chemistry in order to correctly capture the influences of stratospheric ozone depletion on climate

  7. Reorganization of Southern Ocean plankton ecosystem at the onset of Antarctic glaciation.

    PubMed

    Houben, Alexander J P; Bijl, Peter K; Pross, Jörg; Bohaty, Steven M; Passchier, Sandra; Stickley, Catherine E; Röhl, Ursula; Sugisaki, Saiko; Tauxe, Lisa; van de Flierdt, Tina; Olney, Matthew; Sangiorgi, Francesca; Sluijs, Appy; Escutia, Carlota; Brinkhuis, Henk; Dotti, Carlota Escutia; Klaus, Adam; Fehr, Annick; Williams, Trevor; Bendle, James A P; Carr, Stephanie A; Dunbar, Robert B; Flores, José-Abel; Gonzàlez, Jhon J; Hayden, Travis G; Iwai, Masao; Jimenez-Espejo, Francisco J; Katsuki, Kota; Kong, Gee Soo; McKay, Robert M; Nakai, Mutsumi; Pekar, Stephen F; Riesselman, Christina; Sakai, Toyosaburo; Salzmann, Ulrich; Shrivastava, Prakash K; Tuo, Shouting; Welsh, Kevin; Yamane, Masako

    2013-04-19

    The circum-Antarctic Southern Ocean is an important region for global marine food webs and carbon cycling because of sea-ice formation and its unique plankton ecosystem. However, the mechanisms underlying the installation of this distinct ecosystem and the geological timing of its development remain unknown. Here, we show, on the basis of fossil marine dinoflagellate cyst records, that a major restructuring of the Southern Ocean plankton ecosystem occurred abruptly and concomitant with the first major Antarctic glaciation in the earliest Oligocene (~33.6 million years ago). This turnover marks a regime shift in zooplankton-phytoplankton interactions and community structure, which indicates the appearance of eutrophic and seasonally productive environments on the Antarctic margin. We conclude that earliest Oligocene cooling, ice-sheet expansion, and subsequent sea-ice formation were important drivers of biotic evolution in the Southern Ocean. PMID:23599491

  8. Southern Ocean frontal system changes precede Antarctic ice sheet growth during the middle Miocene

    NASA Astrophysics Data System (ADS)

    Kuhnert, Henning; Bickert, Torsten; Paulsen, Harald

    2009-07-01

    The middle Miocene climate approximately 14 Ma ago was characterized by the glaciation of Antarctica, deep-ocean cooling and variations in the global carbon cycle. Although the Southern Ocean underwent significant oceanographic changes, there is limited information on their spatial extent and timing. However, such knowledge is crucial for understanding the role of the Southern Ocean and the Antarctic Circumpolar Current (ACC) for Antarctic glaciation and the coupling between the ocean and continental climate. We have reconstructed surface temperatures and seawater oxygen isotopes at Ocean Drilling Program (ODP) Site 1092 in the Polar Frontal Zone of the Atlantic sector of the Southern Ocean from foraminiferal oxygen isotopes ( δ18O) and magnesium to calcium ratios (Mg/Ca). Sea surface cooling by ~ 4 °C and freshening indicated by the ~ 1‰ reduction of seawater δ18O ( δ18O sw) at 14.2 Ma precede the major step in Antarctic ice sheet growth at 13.8-13.9 Ma. This pattern qualitatively mirrors previous findings from the Pacific sector, and we interpret the surface hydrographic changes to reflect the circum-Antarctic northward shift of the Southern Ocean fronts and specifically at Site 1092 the passage of the Subantarctic Front. The magnitude of change in reconstructed δ18O sw requires a δ18O sw: salinity gradient significantly higher than the modern value (~ 0.52‰) and it possibly exceeded 1.1‰. This implies the Polar Frontal Zone was influenced by freshwater derived from Antarctica, which in turn confirms higher than modern continental precipitation. The latter has previously been suggested to have contributed to Antarctic glaciation.

  9. Antarctic icebergs melt over the Southern Ocean : Climatology and impact on sea ice

    NASA Astrophysics Data System (ADS)

    Merino, Nacho; Le Sommer, Julien; Durand, Gael; Jourdain, Nicolas C.; Madec, Gurvan; Mathiot, Pierre; Tournadre, Jean

    2016-08-01

    Recent increase in Antarctic freshwater release to the Southern Ocean is suggested to contribute to change in water masses and sea ice. However, climate models differ in their representation of the freshwater sources. Recent improvements in altimetry-based detection of small icebergs and in estimates of the mass loss of Antarctica may help better constrain the values of Antarctic freshwater releases. We propose a model-based seasonal climatology of iceberg melt over the Southern Ocean using state-of-the-art observed glaciological estimates of the Antarctic mass loss. An improved version of a Lagrangian iceberg model is coupled with a global, eddy-permitting ocean/sea ice model and compared to small icebergs observations. Iceberg melt increases sea ice cover, about 10% in annual mean sea ice volume, and decreases sea surface temperature over most of the Southern Ocean, but with distinctive regional patterns. Our results underline the importance of improving the representation of Antarctic freshwater sources. This can be achieved by forcing ocean/sea ice models with a climatological iceberg fresh-water flux.

  10. Holocene Southern Ocean surface temperature variability west of the Antarctic Peninsula.

    PubMed

    Shevenell, A E; Ingalls, A E; Domack, E W; Kelly, C

    2011-02-10

    The disintegration of ice shelves, reduced sea-ice and glacier extent, and shifting ecological zones observed around Antarctica highlight the impact of recent atmospheric and oceanic warming on the cryosphere. Observations and models suggest that oceanic and atmospheric temperature variations at Antarctica's margins affect global cryosphere stability, ocean circulation, sea levels and carbon cycling. In particular, recent climate changes on the Antarctic Peninsula have been dramatic, yet the Holocene climate variability of this region is largely unknown, limiting our ability to evaluate ongoing changes within the context of historical variability and underlying forcing mechanisms. Here we show that surface ocean temperatures at the continental margin of the western Antarctic Peninsula cooled by 3-4 °C over the past 12,000 years, tracking the Holocene decline of local (65° S) spring insolation. Our results, based on TEX(86) sea surface temperature (SST) proxy evidence from a marine sediment core, indicate the importance of regional summer duration as a driver of Antarctic seasonal sea-ice fluctuations. On millennial timescales, abrupt SST fluctuations of 2-4 °C coincide with globally recognized climate variability. Similarities between our SSTs, Southern Hemisphere westerly wind reconstructions and El Niño/Southern Oscillation variability indicate that present climate teleconnections between the tropical Pacific Ocean and the western Antarctic Peninsula strengthened late in the Holocene epoch. We conclude that during the Holocene, Southern Ocean temperatures at the western Antarctic Peninsula margin were tied to changes in the position of the westerlies, which have a critical role in global carbon cycling. PMID:21307939

  11. A Roadmap for Antarctic and Southern Ocean Science for the Next Two Decades and Beyond

    NASA Astrophysics Data System (ADS)

    Kennicutt, M. C., II

    2015-12-01

    Abstract: Antarctic and Southern Ocean science is vital to understanding natural variability, the processes that govern global change and the role of humans in the Earth and climate system. The potential for new knowledge to be gained from future Antarctic science is substantial. Therefore, the international Antarctic community came together to 'scan the horizon' to identify the highest priority scientific questions that researchers should aspire to answer in the next two decades and beyond. Wide consultation was a fundamental principle for the development of a collective, international view of the most important future directions in Antarctic science. From the many possibilities, the horizon scan identified 80 key scientific questions through structured debate, discussion, revision and voting. Questions were clustered into seven topics: i) Antarctic atmosphere and global connections, ii) Southern Ocean and sea ice in a warming world, iii) ice sheet and sea level, iv) the dynamic Earth, v) life on the precipice, vi) near-Earth space and beyond, and vii) human presence in Antarctica. Answering the questions identified by the horizon scan will require innovative experimental designs, novel applications of technology, invention of next-generation field and laboratory approaches, and expanded observing systems and networks. Unbiased, non-contaminating procedures will be required to retrieve the requisite air, biota, sediment, rock, ice and water samples. Sustained year-round access to Antarctica and the Southern Ocean will be essential to increase winter-time measurements. Improved models are needed that represent Antarctica and the Southern Ocean in the Earth System, and provide predictions at spatial and temporal resolutions useful for decision making. A co-ordinated portfolio of cross-disciplinary science, based on new models of international collaboration, will be essential as no scientist, programme or nation can realize these aspirations alone.

  12. Southern Ocean phytoplankton turnover in response to stepwise Antarctic cooling over the past 15 million years

    NASA Astrophysics Data System (ADS)

    Crampton, James S.; Cody, Rosie D.; Levy, Richard; Harwood, David; McKay, Robert; Naish, Tim R.

    2016-06-01

    It is not clear how Southern Ocean phytoplankton communities, which form the base of the marine food web and are a crucial element of the carbon cycle, respond to major environmental disturbance. Here, we use a new model ensemble reconstruction of diatom speciation and extinction rates to examine phytoplankton response to climate change in the southern high latitudes over the past 15 My. We identify five major episodes of species turnover (origination rate plus extinction rate) that were coincident with times of cooling in southern high-latitude climate, Antarctic ice sheet growth across the continental shelves, and associated seasonal sea-ice expansion across the Southern Ocean. We infer that past plankton turnover occurred when a warmer-than-present climate was terminated by a major period of glaciation that resulted in loss of open-ocean habitat south of the polar front, driving non-ice adapted diatoms to regional or global extinction. These findings suggest, therefore, that Southern Ocean phytoplankton communities tolerate “baseline” variability on glacial–interglacial timescales but are sensitive to large-scale changes in mean climate state driven by a combination of long-period variations in orbital forcing and atmospheric carbon dioxide perturbations.

  13. Southern Ocean phytoplankton turnover in response to stepwise Antarctic cooling over the past 15 million years.

    PubMed

    Crampton, James S; Cody, Rosie D; Levy, Richard; Harwood, David; McKay, Robert; Naish, Tim R

    2016-06-21

    It is not clear how Southern Ocean phytoplankton communities, which form the base of the marine food web and are a crucial element of the carbon cycle, respond to major environmental disturbance. Here, we use a new model ensemble reconstruction of diatom speciation and extinction rates to examine phytoplankton response to climate change in the southern high latitudes over the past 15 My. We identify five major episodes of species turnover (origination rate plus extinction rate) that were coincident with times of cooling in southern high-latitude climate, Antarctic ice sheet growth across the continental shelves, and associated seasonal sea-ice expansion across the Southern Ocean. We infer that past plankton turnover occurred when a warmer-than-present climate was terminated by a major period of glaciation that resulted in loss of open-ocean habitat south of the polar front, driving non-ice adapted diatoms to regional or global extinction. These findings suggest, therefore, that Southern Ocean phytoplankton communities tolerate "baseline" variability on glacial-interglacial timescales but are sensitive to large-scale changes in mean climate state driven by a combination of long-period variations in orbital forcing and atmospheric carbon dioxide perturbations. PMID:27274061

  14. Characterising Antarctic and Southern Ocean Lithosphere with Magnetic and Gravity Imaging of East Antarctic Rift Systems

    NASA Astrophysics Data System (ADS)

    Vaughan, A. P.; Kusznir, N. J.; Ferraccioli, F.; Jordan, T. A.; Purucker, M. E.; Golynsky, A. V.; Rogozhina, I.

    2012-12-01

    Since the International Geophysical Year (1957), a view has prevailed that the lithospheric structure of East Antarctica is relatively homogeneous, forming a geological block of largely cratonic nature, consisting of a mosaic of Precambrian terranes, stable since the Pan-African orogeny ~500 million years ago. Recent recognition of a continental-scale rift system cutting the East Antarctic interior indicates that this is incorrect, and has crystallised an alternative view of much more recent geological activity with important implications for tectonic reconstructions and controls on ice sheet formation and stability. The newly defined East Antarctic Rift System appears to extend from at least the South Pole to the continental margin at the Lambert Rift, a distance of 2500 km. This is comparable in scale to the well-studied East African rift system. New analysis of RadarSat data pioneered by Golynsky & Golynsky indicates that further rift zones may extend the East Antarctic Rift System into widely distributed extension zones within the continent. We have carried out a pilot study, using a newly developed gravity inversion technique with existing public domain satellite data, which shows that East Antarctica consists of distinct crustal thickness provinces with anomalously thick areas separated by thin, possibly rifted crust and overall high average thickness. Understanding the nature of crustal thickness in East Antarctica is critical because: 1) Better understanding of crustal thickness in Antarctica, especially along the ocean-continent transition (OCT), will make it possible to improve the plate reconstruction fit between Antarctica, Australia and India in Gondwana and also refine constraints on how and when these continents separated; 2) crustal thickness provinces can be used to aid supercontinent reconstructions and provide new assessments of the influence of basement architecture and mechanical properties on rifting processes; 3) tracking rift zones through

  15. Sensitivity of the Southern Ocean to enhanced regional Antarctic ice sheet meltwater input

    NASA Astrophysics Data System (ADS)

    Fogwill, C. J.; Phipps, S. J.; Turney, C. S. M.; Golledge, N. R.

    2015-10-01

    Despite advances in our understanding of the processes driving contemporary sea level rise, the stability of the Antarctic ice sheets and their contribution to sea level under projected future warming remains uncertain due to the influence of strong ice-climate feedbacks. Disentangling these feedbacks is key to reducing uncertainty. Here we present a series of climate system model simulations that explore the potential effects of increased West Antarctic Ice Sheet (WAIS) meltwater flux on Southern Ocean dynamics. We project future changes driven by sectors of the WAIS, delivering spatially and temporally variable meltwater flux into the Amundsen, Ross, and Weddell embayments over future centuries. Focusing on the Amundsen Sea sector of the WAIS over the next 200 years, we demonstrate that the enhanced meltwater flux rapidly stratifies surface waters, resulting in a significant decrease in the rate of Antarctic Bottom Water (AABW) formation. This triggers rapid pervasive ocean warming (>1°C) at depth due to advection from the original site(s) of meltwater input. The greatest warming is predicted along sectors of the ice sheet that are highly sensitized to ocean forcing, creating a feedback loop that could enhance basal ice shelf melting and grounding line retreat. Given that we do not include the effects of rising CO2—predicted to further reduce AABW formation—our experiments highlight the urgent need to develop a new generation of fully coupled ice sheet climate models, which include feedback mechanisms such as this, to reduce uncertainty in climate and sea level projections.

  16. The Biogeochemical Role of Antarctic Krill and Baleen Whales in Southern Ocean Nutrient Cycling.

    NASA Astrophysics Data System (ADS)

    Ratnarajah, L.

    2015-12-01

    Iron limits primary productivity in large areas of the Southern Ocean. It has been suggested that baleen whales form a crucial part of biogeochemical cycling processes through the consumption of nutrient-rich krill and subsequent defecation, but evidence on their contribution is scarce. We analysed the concentration of iron in Antarctic krill and baleen whale faeces and muscle. Iron concentrations in Antarctic krill were over 1 million times higher, and whale faecal matter were almost 10 million times higher than typical Southern Ocean High Nutrient Low Chlorophyll seawater concentrations. This suggests that Antarctic krill act as a reservoir of in in Southern Ocean surface waters, and that baleen whales play an important role in converting this fixed iron into a liquid form in their faeces. We developed an exploratory model to examine potential contribution of blue, fin and humpback whales to the Southern Ocean iron cycle to explore the effect of the recovery of great whales to historical levels. Our results suggest that pre-exploitation populations of blue whales and, to a lesser extent fin and humpback whales, could have contributed to the more effective recycling of iron in surface waters, resulting in enhanced phytoplankton production. This enhanced primary productivity is estimated to be: 8.3 x 10-5 to 15 g C m-2 yr-1 (blue whales), 7 x 10-5 to 9 g C m-2 yr-1 (fin whales), and 10-5 to 1.7 g C m-2 yr-1 (humpback whales). To put these into perspective, current estimates of primary production in the Southern Ocean from remotely sensed ocean colour are in the order of 57 g C m-2 yr-1 (south of 50°). The high degree of uncertainty around the magnitude of these increases in primary productivity is mainly due to our limited quantitative understanding of key biogeochemical processes including iron content in krill, krill consumption rates by whales, persistence of iron in the photic zone, bioavailability of retained iron, and carbon-to-iron ratio of phytoplankton

  17. Antarctic ice dynamics and southern ocean surface hydrology during the last glacial maximum

    SciTech Connect

    Labeyrie, L.D.; Burckle, L.; Labracherie, M.; Pichon, J.J.; Ippolito, P.; Grojean, M.C.; Duplessy, J.C.

    1985-01-01

    Eight high sedimentation rate cores located between 61/sup 0/S and 43/sup 0/S in the Atlantic and Indian sectors of the Southern Ocean have been studied in detail for foraminifera and diatom /sup 18/O//sup 16/O ratios, and changes in radiolarian and diatom specific abundance. Comparison of these different parameters permits a detailed description of the surface water hydrology during the last glacial maximum. The authors demonstrate that from 25 kyr BP to 15 kyr BP a large number of icebergs formed around the Antarctic continent. Melting along the Polar Front decreased surface salinity by approximately 1.5 per thousand between 43/sup 0/S and 50/sup 0/S. They propose that an increase of snow accumulation at the Antarctic periphery and downdraw during maximum ice extension are primary causes for this major discharge of icebergs.

  18. Antarctic contribution to meltwater pulse 1A from reduced Southern Ocean overturning

    NASA Astrophysics Data System (ADS)

    Fogwill, C. J.; Golledge, N. R.; Menviel, L.; Carter, L.; England, M. H.; Cortese, G.; Levy, R. H.

    2014-12-01

    During the last glacial termination, the upwelling strength of the southern polar limb of the Atlantic Meridional Overturning Circulation varied, changing the ventilation and stratification of the high-latitude Southern Ocean. During the same period, at least two phases of abrupt global sea-level rise - `meltwater pulses' - took place. Although the timing and magnitude of these events have become better-constrained, a causal link between ocean stratification, the meltwater pulses, and accelerated ice loss from Antarctica has not been proven. Here we simulate Antarctic ice sheet evolution over the last 25 kyr using a data-constrained ice-sheet model forced by changes in Southern Ocean temperature from an Earth system model. Results reveal several episodes of accelerated ice-sheet recession, the largest being coincident with meltwater pulse 1A. This resulted from reduced Southern Ocean overturning following Heinrich Event 1, when warmer subsurface water thermally eroded grounded marine-based ice and instigated a positive feedback that further accelerated ice-sheet retreat.

  19. Antarctic contribution to meltwater pulse 1A from reduced Southern Ocean overturning

    NASA Astrophysics Data System (ADS)

    Golledge, N. R.; Menviel, L.; Carter, L.; Fogwill, C. J.; England, M. H.; Cortese, G.; Levy, R. H.

    2014-09-01

    During the last glacial termination, the upwelling strength of the southern polar limb of the Atlantic Meridional Overturning Circulation varied, changing the ventilation and stratification of the high-latitude Southern Ocean. During the same period, at least two phases of abrupt global sea-level rise—meltwater pulses—took place. Although the timing and magnitude of these events have become better constrained, a causal link between ocean stratification, the meltwater pulses and accelerated ice loss from Antarctica has not been proven. Here we simulate Antarctic ice sheet evolution over the last 25 kyr using a data-constrained ice-sheet model forced by changes in Southern Ocean temperature from an Earth system model. Results reveal several episodes of accelerated ice-sheet recession, the largest being coincident with meltwater pulse 1A. This resulted from reduced Southern Ocean overturning following Heinrich Event 1, when warmer subsurface water thermally eroded grounded marine-based ice and instigated a positive feedback that further accelerated ice-sheet retreat.

  20. Antarctic contribution to meltwater pulse 1A from reduced Southern Ocean overturning.

    PubMed

    Golledge, N R; Menviel, L; Carter, L; Fogwill, C J; England, M H; Cortese, G; Levy, R H

    2014-01-01

    During the last glacial termination, the upwelling strength of the southern polar limb of the Atlantic Meridional Overturning Circulation varied, changing the ventilation and stratification of the high-latitude Southern Ocean. During the same period, at least two phases of abrupt global sea-level rise--meltwater pulses--took place. Although the timing and magnitude of these events have become better constrained, a causal link between ocean stratification, the meltwater pulses and accelerated ice loss from Antarctica has not been proven. Here we simulate Antarctic ice sheet evolution over the last 25 kyr using a data-constrained ice-sheet model forced by changes in Southern Ocean temperature from an Earth system model. Results reveal several episodes of accelerated ice-sheet recession, the largest being coincident with meltwater pulse 1A. This resulted from reduced Southern Ocean overturning following Heinrich Event 1, when warmer subsurface water thermally eroded grounded marine-based ice and instigated a positive feedback that further accelerated ice-sheet retreat. PMID:25263015

  1. Southern Ocean Asteroidea: a proposed update for the Register of Antarctic Marine Species

    PubMed Central

    Aguera, Antonio; Jossart, Quentin; Danis, Bruno

    2015-01-01

    Abstract Background The Register of Antarctic Marine Species (RAMS, De Broyer et al. 2015) is the regional component of the World Register of Marine Species (WoRMS Editorial Board 2015) in the Southern Ocean. It has been operating for the last ten years, with a special effort devoted towards its completion after the International Polar Year (IPY) in 2007-2008, in the framework of the Census of Antarctic Marine Life (CAML, 2005 - 2010). Its objective is to offer free and open access to a complete register of all known species living in the Southern Ocean, building a workbench of the present taxonomic knowledge for that region. The Antarctic zone defined by this dynamic and community-based tool has been investigated with a particular interest. The Sub-Antarctic zone was a secondary objective during the establishment of the RAMS and is still lacking the impulse of the scientific community for some taxa. New information In the present study, more than 13,000 occurrences records of Asteroidea (Echinodermata) have been compiled within the RAMS area of interest and checked against the RAMS species list of sea stars, using WoRMS Taxon Match tool. Few mismatches (basionym mistakes : i.e. original name misspelled or incorrect) were found within the existing list and 97 unregistered species are actually occurring within the RAMS boundaries. After this update, the number of Asteroidea species was increased by around 50%, now reaching 295 accepted species. PMID:26696769

  2. Ocean export production and foraminiferal stable isotopes in the Antarctic Southern Ocean across the mid-Pleistocene transition

    NASA Astrophysics Data System (ADS)

    Hasenfratz, A. P.; Martinez-Garcia, A.; Jaccard, S.; Hodell, D. A.; Vance, D.; Bernasconi, S. M.; Greaves, M.; Haug, G. H.

    2014-12-01

    Changes in buoyancy forcing in the Antarctic Zone (AZ) of the Southern Ocean are believed to play an instrumental role in modulating atmospheric CO2 concentrations during glacial cycles by regulating the transfer of carbon between the ocean interior and the atmosphere. Indeed, a million-year-spanning high-resolution excess Barium record from the AZ of the South Atlantic (ODP 1094), which traces changes in export production, shows decreased export production during cold periods suggesting decreased overturning. Here, we extend this AZ export production record back to 1.6 Myr. In addition, we present new carbon and oxygen isotope records of benthic and planktic foraminifera from the same site, complemented by Mg/Ca measurements in some intervals. The interpretation of these new data in the context of other South Atlantic records contributes to a better understanding of Southern Ocean hydrography and its role in modulating glacial/interglacial cycles over the past 1.6 Myr.

  3. Atmospheric occurrence and deposition of hexachlorobenzene and hexachlorocyclohexanes in the Southern Ocean and Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Galbán-Malagón, Cristóbal; Cabrerizo, Ana; Caballero, Gemma; Dachs, Jordi

    2013-12-01

    Despite the distance of Antarctica and the Southern Ocean to primary source regions of organochlorine pesticides, such as hexachlorobenzene (HCB) and hexachlorocyclohexanes (HCHs), these organic pollutants are found in this remote region due to long range atmospheric transport and deposition. This study reports the gas- and aerosol-phase concentrations of α-HCH, γ-HCH, and HCB in the atmosphere from the Weddell, South Scotia and Bellingshausen Seas. The atmospheric samples were obtained in two sampling cruises in 2008 and 2009, and in a third sampling campaign at Livingston Island (2009) in order to quantify the potential secondary sources of HCHs and HCB due to volatilization from Antarctic soils and snow. The gas phase concentrations of HCHs and HCB are low, and in the order of very few pg m-3 α-HCH and γ-HCH concentrations were higher when the air mass back trajectory was coming from the Antarctic continent, consistent with net volatilization fluxes of γ-HCH measured at Livingston Island being a significant secondary source to the regional atmosphere. In addition, the Southern ocean is an important net sink of HCHs, and to minor extent of HCB, due to high diffusive air-to-water fluxes. These net absorption fluxes for HCHs are presumably due to the role of bacterial degradation, depleting the water column concentrations of HCHs in surface waters and driving an air-water disequilibrium. This is the first field study that has investigated the coupling between the atmospheric occurrence of HCHs and HCB, the simultaneous air-water exchange, soil/snow-air exchange, and long range transport of organic pollutants in Antarctica and the Southern Ocean.

  4. Air-sea exchange of carbon dioxide in the Southern Ocean and Antarctic marginal ice zone

    NASA Astrophysics Data System (ADS)

    Butterworth, Brian J.; Miller, Scott D.

    2016-07-01

    Direct carbon dioxide flux measurements using eddy covariance from an icebreaker in the high-latitude Southern Ocean and Antarctic marginal ice zone are reported. Fluxes were combined with the measured water-air carbon dioxide partial pressure difference (ΔpCO2) to compute the air-sea gas transfer velocity (k, normalized to Schmidt number 660). The open water data showed a quadratic relationship between k (cm h-1) and the neutral 10 m wind speed (U10n, m s-1), kopen = 0.245 U10n2 + 1.3, in close agreement with decades old tracer-based results and much lower than cubic relationships inferred from previous open ocean eddy covariance studies. In the marginal ice zone, the effective gas transfer velocity decreased in proportion to sea ice cover, in contrast with predictions of enhanced gas exchange in the presence of sea ice. The combined open water and marginal ice zone results affect the calculated magnitude and spatial distribution of Southern Ocean carbon flux.

  5. A review of Tertiary climate changes in southern South America and the Antarctic Peninsula. Part 1: Oceanic conditions

    NASA Astrophysics Data System (ADS)

    Le Roux, J. P.

    2012-03-01

    Oceanic conditions around southern South America and the Antarctic Peninsula have a major influence on climate patterns in these subcontinents. During the Tertiary, changes in ocean water temperatures and currents also strongly affected the continental climates and seem to have been controlled in turn by global tectonic events and sea-level changes. During periods of accelerated sea-floor spreading, an increase in the mid-ocean ridge volumes and the outpouring of basaltic lavas caused a rise in sea-level and mean ocean temperature, accompanied by the large-scale release of CO2. The precursor of the South Equatorial Current would have crossed the East Pacific Rise twice before reaching the coast of southern South America, thus heating up considerably during periods of ridge activity. The absence of the Antarctic Circumpolar Current before the opening of the Drake Passage suggests that the current flowing north along the present western seaboard of southern South American could have been temperate even during periods of ridge inactivity, which might explain the generally warm temperatures recorded in the Southeast Pacific from the early Oligocene to middle Miocene. Along the east coast of southern South America, water temperatures also fluctuated between temperate-cool and warm until the early Miocene, when the first incursion of temperate-cold to cold Antarctic waters is recorded. The cold Falkland/Malvinas Current initiated only after the middle Miocene. After the opening of the Drake Passage, the South Equatorial Current would have joined the newly developed, cold Antarctic Circumpolar Current on its way to Southern South America. During periods of increased sea-floor spreading, it would have contributed heat to the Antarctic Circumpolar Current that caused a poleward shift in climatic belts. However, periods of decreased sea-floor spreading would have been accompanied by diminishing ridge volumes and older, cooler and denser oceanic plates, causing global sea

  6. Antarctic Marine Biodiversity – What Do We Know About the Distribution of Life in the Southern Ocean?

    PubMed Central

    Griffiths, Huw J.

    2010-01-01

    The remote and hostile Southern Ocean is home to a diverse and rich community of life that thrives in an environment dominated by glaciations and strong currents. Marine biological studies in the region date back to the nineteenth century, but despite this long history of research, relatively little is known about the complex interactions between the highly seasonal physical environment and the species that inhabit the Southern Ocean. Oceanographically, the Southern Ocean is a major driver of global ocean circulation and plays a vital role in interacting with the deep water circulation in each of the Pacific, Atlantic, and Indian oceans. The Census of Antarctic Marine Life and the Scientific Committee on Antarctic Research Marine Biodiversity Information Network (SCAR-MarBIN) have strived to coordinate and unify the available scientific expertise and biodiversity data to improve our understanding of Southern Ocean biodiversity. Taxonomic lists for all marine species have been compiled to form the Register of Antarctic Marine Species, which currently includes over 8,200 species. SCAR-MarBIN has brought together over 1 million distribution records for Southern Ocean species, forming a baseline against which future change can be judged. The sample locations and numbers of known species from different regions were mapped and the depth distributions of benthic samples plotted. Our knowledge of the biodiversity of the Southern Ocean is largely determined by the relative inaccessibility of the region. Benthic sampling is largely restricted to the shelf; little is known about the fauna of the deep sea. The location of scientific bases heavily influences the distribution pattern of sample and observation data, and the logistical supply routes are the focus of much of the at-sea and pelagic work. Taxa such as mollusks and echinoderms are well represented within existing datasets with high numbers of georeferenced records. Other taxa, including the species-rich nematodes, are

  7. Particulate export vs lateral advection in the Antarctic Polar Front (Southern Pacific Ocean)

    NASA Astrophysics Data System (ADS)

    Tesi, T.; Langone, L.; Ravaioli, M.; Capotondi, L.; Giglio, F.

    2012-04-01

    The overarching goal of our study was to describe and quantify the influence of lateral advection relative to the vertical export in the Antarctic Polar Front (Southern Pacific Ocean). In areas where lateral advection of particulate material is significant, budgets of bioactive elements can be inaccurate if fluxes through the water column and to the seabed are exclusively interpreted as passive sinking of particles. However, detailed information on the influence of lateral advection in the water column in the southern ocean is lacking. With this in mind, our study focused between the twilight zone (i.e. mesopelagic) and the benthic nepheloid layer to understand the relative importance of lateral flux with increasing water depth. Measurements were performed south of the Antarctic Polar Front for 1 year (January 10th 1999-January 3rd 2000) at 900, 1300, 2400, and 3700 m from the sea surface. The study was carried out using a 3.5 km long mooring line instrumented with sediment traps, current meters and sensors of temperature and conductivity. Sediment trap samples were characterized via several parameters including total mass flux, elemental composition (organic carbon, total nitrogen, biogenic silica, and calcium carbonate), concentration of metals (aluminum, iron, barium, and manganese), 210Pb activity, and foraminifera taxonomy. High fluxes of biogenic particles were observed in both summer 1999 and 2000 as a result of seasonal algal blooms associated with sea ice retreat and water column stratification. During no-productive periods, several high energy events occurred and resulted in advecting resuspended biogenic particles from flat-topped summits of the Pacific Antarctic Ridge. Whereas the distance between seabed and uppermost sediment traps was sufficient to avoid lateral advection processes, resuspension was significant in the lowermost sediment traps accounting for ~60 and ~90% of the material caught at 2400 and 3700 m, respectively. Samples collected during

  8. Response of the Southern Ocean dynamics to the changes in the Antarctic glacial runoff and icebergs discharge

    NASA Astrophysics Data System (ADS)

    Aksenov, Yevgeny; Nurser, George; Bacon, Sheldon; Rye, Craig; Megann, Alex; Kjellsson, Joakim; Holland, Paul; Ridley, Jeff; Coward, Andrew; Marshall, Gareth; Marsh, Bob; Mathiot, Pierre

    2016-04-01

    This study examines how changes in the freshwater discharge from the Antarctic (liquid runoff and icebergs) affect stratification and ocean circulation in the Southern Ocean. The changes in the ocean circulation could potentially modify transports of the warm subsurface waters onto the continental shelves and increase ice sheet melting. We investigate impacts of the increased freshwater discharge in the 1990s-2000s on the subsurface waters in the Southern Ocean in the NEMO 1° global sea ice-ocean model. In the simulations the warming signal is largely circum-Antarctic, with "hot spots" in the Bellingshausen-Amundsen and Ross seas. The warming of the subsurface waters in the Bellingshausen-Amundsen Sea exceeds 0.5°C/decade. Differences in spreading of the liquid freshwater and icebergs in the Southern Ocean are investigated. Hindcasts and forward projections with the eddy-admitting global NEMO 1/4° model are diagnosed to examine regional trends in the ocean and sea ice states and to attribute these to the changes in the freshwater forcing and wind. The study contributes to the "Poles Apart" research project and is funded by the Natural Environment Research Council UK.

  9. Potential climate change effects on the habitat of antarctic krill in the weddell quadrant of the southern ocean.

    PubMed

    Hill, Simeon L; Phillips, Tony; Atkinson, Angus

    2013-01-01

    Antarctic krill is a cold water species, an increasingly important fishery resource and a major prey item for many fish, birds and mammals in the Southern Ocean. The fishery and the summer foraging sites of many of these predators are concentrated between 0° and 90°W. Parts of this quadrant have experienced recent localised sea surface warming of up to 0.2°C per decade, and projections suggest that further widespread warming of 0.27° to 1.08°C will occur by the late 21(st) century. We assessed the potential influence of this projected warming on Antarctic krill habitat with a statistical model that links growth to temperature and chlorophyll concentration. The results divide the quadrant into two zones: a band around the Antarctic Circumpolar Current in which habitat quality is particularly vulnerable to warming, and a southern area which is relatively insensitive. Our analysis suggests that the direct effects of warming could reduce the area of growth habitat by up to 20%. The reduction in growth habitat within the range of predators, such as Antarctic fur seals, that forage from breeding sites on South Georgia could be up to 55%, and the habitat's ability to support Antarctic krill biomass production within this range could be reduced by up to 68%. Sensitivity analysis suggests that the effects of a 50% change in summer chlorophyll concentration could be more significant than the direct effects of warming. A reduction in primary production could lead to further habitat degradation but, even if chlorophyll increased by 50%, projected warming would still cause some degradation of the habitat accessible to predators. While there is considerable uncertainty in these projections, they suggest that future climate change could have a significant negative effect on Antarctic krill growth habitat and, consequently, on Southern Ocean biodiversity and ecosystem services. PMID:23991072

  10. Potential Climate Change Effects on the Habitat of Antarctic Krill in the Weddell Quadrant of the Southern Ocean

    PubMed Central

    Hill, Simeon L.; Phillips, Tony; Atkinson, Angus

    2013-01-01

    Antarctic krill is a cold water species, an increasingly important fishery resource and a major prey item for many fish, birds and mammals in the Southern Ocean. The fishery and the summer foraging sites of many of these predators are concentrated between 0° and 90°W. Parts of this quadrant have experienced recent localised sea surface warming of up to 0.2°C per decade, and projections suggest that further widespread warming of 0.27° to 1.08°C will occur by the late 21st century. We assessed the potential influence of this projected warming on Antarctic krill habitat with a statistical model that links growth to temperature and chlorophyll concentration. The results divide the quadrant into two zones: a band around the Antarctic Circumpolar Current in which habitat quality is particularly vulnerable to warming, and a southern area which is relatively insensitive. Our analysis suggests that the direct effects of warming could reduce the area of growth habitat by up to 20%. The reduction in growth habitat within the range of predators, such as Antarctic fur seals, that forage from breeding sites on South Georgia could be up to 55%, and the habitat’s ability to support Antarctic krill biomass production within this range could be reduced by up to 68%. Sensitivity analysis suggests that the effects of a 50% change in summer chlorophyll concentration could be more significant than the direct effects of warming. A reduction in primary production could lead to further habitat degradation but, even if chlorophyll increased by 50%, projected warming would still cause some degradation of the habitat accessible to predators. While there is considerable uncertainty in these projections, they suggest that future climate change could have a significant negative effect on Antarctic krill growth habitat and, consequently, on Southern Ocean biodiversity and ecosystem services. PMID:23991072

  11. The impact of changes in the Antarctic wind field on the Southern Ocean sea ice

    NASA Astrophysics Data System (ADS)

    Haid, Verena; Iovino, Dorotea; Masina, Simona

    2016-04-01

    Satellite observations show an enlargement of the sea ice extent of the Southern Ocean in the last decades. A possible trigger for the increase is a change in the atmospheric circulation, which leads to a southward shift and intensification of the westerlies around Antarctica. We performed a sensitivity study with an eddy-permitting sea ice-ocean model forced by ERA-Interim data. We compare a set of numerical simulations with simple manipulations of the wind velocities in the forcing data and investigate the response of sea ice and on-shelf water properties. In our results, increases of the zonal wind component lead to the onset of deep convection in the Weddell Sea within 10 years (with one exception) and a reduction of sea ice. Manipulations of the meridional wind component can lead to an increase of ice extent and volume, but only if regions of strengthened northward wind alternate with regions of increased southward wind. The convergent drift against the shoreline is necessary to thicken the sea ice. Without it, enhanced northward drift leads to an exhanced ice extent during winter but combined with a loss of sea ice thickness which entails a strongly reduced ice extent during summer. For increases of the westward/eastward wind component at the Antarctic coastline, the on-shelf water temperatures increase/decrease due to Ekman pumping. Except for regions with more southerly winds, the manipulated forcing in all cases increases the sea ice production at the coastline and therefore the on-shelf waters are more saline. After a period of 10 years in all the experiments the increased wind results in a higher density of the on-shelf water column.

  12. Dinoflagellate cyst assemblages from the Southern Ocean during the Oligocene Icehouse: tracers for Antarctic Sea ice, productivity and oceanic frontal systems?

    NASA Astrophysics Data System (ADS)

    Bijl, Peter; Houben, Alexander J. P.; Sangiorgi, Francesca

    2013-04-01

    The Oligocene Epoch (33.9-23 Ma) is the time interval in the Cenozoic that saw the establishment of a continental-scale Antarctic ice-sheet. Numerical modelling studies suggest that alongside, first sea-ice conditions may have started along the East Antarctic Margin. Integrated Ocean Drilling Expedition 318 drilled the Antarctic Margin in 2010, and recovered sediments from this early phase of Antarctic glaciation. With this record, we can now evaluate the robustness of the results of these numerical models with field data. Particularly the sediments recovered from Site U1356 yield a thick and relatively complete (albeit compromised by core gaps) Oligocene succession that is chronostratigraphically well-calibrated with use of nannoplankton- dinocyst- and magnetostratigraphy. Notably, this record yields well-preserved dinoflagellate cysts (dinocysts). Dinocysts are the fossilizable remains of dinoflagellates, some of which are today specifically linked to the high (seasonal) productivity of the ecosystems associated with sea-ice and oceanic fronts. Up to now, well-calibrated and complete records of dinocyst assemblages beyond the Pleistocene become progressively scarcer going further back in time. In the earliest Oligocene, just after the onset of Antarctic glaciation, we document the installation of dinoflagellate cyst assemblages that bear remarkable similarity with those of the present-day Southern Ocean. We interpret this as a regime-shift in plankton communities in response to the installation of the seasonally highly productive sea-ice ecosystem. Following this initial installation, we document variable dinocyst assemblages during the remainder of the Oligocene. These patterns argue that changes in sea-ice extent, and/or the intensity of the vertical mixing of the water column occurred in response to the waxing and waning of the Antarctic ice sheet and feedbacks. I will present a paleo-environmental reconstruction of the Oligocene Southern Ocean surface waters

  13. Global sediment thickness data set updated for the Australian-Antarctic Southern Ocean

    NASA Astrophysics Data System (ADS)

    Whittaker, Joanne M.; Goncharov, Alexey; Williams, Simon E.; Müller, R. Dietmar; Leitchenkov, German

    2013-08-01

    We present a new, 5 min sediment thickness grid for the Australian-Antarctic region (60°E-155°E, 30°S-70°S). New seismic reflection and refraction data have been used to add detail to the conjugate Australian and Antarctic margins and intervening ocean floor where regional sediment thickness patterns were poorly known previously. On the margins, sediment thickness estimates were computed from velocity-depth functions from sonobuoy/refraction velocity solutions ground-truthed against seismic reflection data. For the Southeast Indian Ridge abyssal plains, sediment thickness contours from Geli et al. (2007) were used. The new regional minimum sediment thickness grid was combined with the global National Geophysical Data Center (NGDC) sediment grid to create an updated global grid. Even using the minimum estimates, sediment accumulations on the extended Australian and Antarctic continental margins are 2 km thicker across large regions and up to 9 km thicker in the Ceduna Basin compared to the global NGDC compilation of sediment thickness data.

  14. Evolution of aerosol and CCN properties on the Antarctic Peninsula and Southern Ocean during the spring and summer seasons.

    NASA Astrophysics Data System (ADS)

    Corrigan, C.; Roberts, G.; Grant, G.

    2014-12-01

    The Southern Ocean has been identified as one of the key regions that need aerosol measurements to improve our models of global climate change. The Portable AERosol Observing System (PAEROS) was deployed in an extended field campaign to measure CCN and aerosols in Antarctica and the Southern Ocean from October 2013 to mid-March 2014. PAEROS is a lightweight, man-portable instrument package developed at the Scripps Institution of Oceanography for the purpose of collecting autonomous measurements of aerosol and cloud condensation nuclei (CCN) properties in remote and challenging environments. The initial phase involved the PAEROS package sampling onboard the R/V Gould during the five-day transit of the Drake Passage between Punta Arenas, Chile and Palmer Station on the Antarctic Peninsula. Upon arrival at Palmer Station, PAEROS was transferred to land and installed on top of a hill about 500 m from the main buildings. For five months, aerosol and CCN number concentrations, size distributions, black carbon concentrations, solar fluxes, and meteorological parameters were continuously measured at Palmer Station. The experiment covered most of an austral spring and summer cycle, during which time the sea ice retreated and biological activity flourished along the Antarctic Peninsula. While crossing the Drake Passage, a distinct gradient in aerosol concentrations was observed with increasing distance from South America. At Palmer Station, the total aerosol concentrations showed a seasonal cycle with lowest concentration in air masses originating from the Antarctic continent and highest number concentrations coming from the ocean during the peak of biological activity. Chlorophyll concentrations are routinely measured at Palmer Station and showed peak activity in the month of January 2014. Total aerosol and CCN concentrations increased in late spring (November) as the sea ice recedes from Palmer Station, probably a result of being closer to sea spray and biological activity

  15. Southern Ocean and Antarctic Peninsula Temperatures During Critical Climate Transitions of the Cenozoic Constrained by Clumped Isotope Thermometry

    NASA Astrophysics Data System (ADS)

    Dill, R.; Eagle, R.; Henry, D.; Praskin, S.; Mering, J. A.; Petryshyn, V. A.; Priyadarshi, A.; Rycroft, L.; Vollmer, T.; Chea, Y.; Dix, J.; Aguilar, A.; Supakkul, K.; Tran, B.; Lipel, Z.; Flores, S.; Riesselman, C. R.; Taviani, M.; Marenssi, S.; Harwood, D. M.; Lunt, D. J.; Valdes, P. J.; Meckler, A. N.; Tripati, A.

    2014-12-01

    The Southern Ocean and Antarctica play fundamental roles in the global climate system. These polar regions are a major area for the net loss of heat to space. Ice storage on Antarctica also influences the global water cycle. Through upwelling of deep waters, the Southern Ocean is an important regulator of atmospheric CO2. To better constrain the evolution of paleoclimate in this region over major climate transitions of the Cenozoic, we estimated ocean temperatures using clumped isotope thermometry. Clumped isotope thermometry is a thermodynamically-based stable isotope thermometer that can be used to constrain temperatures previously estimated using other paleothermometers (which in turn leads to constraints on ice volume), as it allows the exclusion of water isotope composition from temperature estimates (unlike the δ18O thermometer). We previously have published calibrations for foraminifera and mollusks, two of the major archives used in this study. Critical transitions investigated include the Eocene-Oligocene boundary and the Middle Miocene Climate Transition. Study sites include Seymour Island (Antarctic Peninsula), ANDRILL (Southern McMurdo Sounds), Ocean Drilling Program (ODP) Sites 689/690 (Weddell Sea), and ODP 744 (Kerguelen Plateau). Results will be compared to GCM output.

  16. The Effect of Ice Shelf Meltwater on Antarctic Sea Ice and the Southern Ocean in an Earth System Model

    NASA Astrophysics Data System (ADS)

    Pauling, A.; Bitz, C. M.; Smith, I.; Langhorne, P.

    2015-12-01

    It has been suggested that recent Antarctic sea ice expansion resulted from an increase in fresh water reaching the Southern Ocean. This presentation investigates this conjecture in an Earth System Model. The freshwater flux from ice sheet and ice shelf mass imbalance is largely missing in models that participated in the Fifth Coupled Model Intercomparison Project (CMIP5). However, CMIP5 models do account for the fresh water from precipitation minus evaporation (P-E). On average in CMIP5 models P- E reaching the Southern Ocean has increased to a present value of about 2600 Gt yr-1 greater than pre-industrial times and 3-8 times larger than estimates of the mass imbalance of Antarctic ice sheets and shelves. Two sets of model experiments were conducted from 1980-2013 in CESM1-CAM5 artificially distributing fresh water either at the ocean surface according to an estimate of iceberg melt, or at the ice shelf fronts at depth. An anomalous reduction in vertical advection of heat into the surface mixed layer resulted in sea surface cooling at high southern latitudes, and an associated increase in sea ice area. A freshwater enhancement of 1780 Gt yr-1 (approximately 1.3 times either present day basal melt or iceberg calving freshwater fluxes) raised the sea ice total area by 1×106 km2. Yet, even a freshwater enhancement up to 2670 Gt yr-1 was insufficient to offset the sea ice decline due to anthropogenic forcing for any period of 20 years or longer. Further, the sea ice response was found to be insensitive to the depth of fresh water injection.

  17. Marine gravity of the Southern Ocean and Antarctic margin from Geosat

    NASA Technical Reports Server (NTRS)

    Sandwell, David T.; Mcadoo, David C.

    1988-01-01

    Geosat altimeter data, collected from an orbit with a ground rack that repeated every 17 days and overlayed one of the 17-day Seasat ground tracks, were used to map the gravity field of the Southern Ocean and the continental margin of Antarctica. The combination of ascending an descending profiles produced a typical Geosat ground track spacing of 70 km at the equator, with the best coverage occurring between the latitudes of 60 and 72 deg in both the Northern and Southern hemispheres. The new data reveal many previously uncharted seamounts and fracture zones in the extreme Southern Ocean areas adjacent to Antarctica, showing the detailed gravity signatures of the passive and active continental margins of Antarctica. Seven large age-offset fracture zones apparent in the Geosat data record the early breakup of Gondwana.

  18. Antarctic lakes suggest millennial reorganizations of Southern Hemisphere atmospheric and oceanic circulation

    PubMed Central

    Hall, Brenda L.; Denton, George H.; Fountain, Andrew G.; Hendy, Chris H.; Henderson, Gideon M.

    2010-01-01

    The phasing of millennial-scale oscillations in Antarctica relative to those elsewhere in the world is important for discriminating among models for abrupt climate change, particularly those involving the Southern Ocean. However, records of millennial-scale variability from Antarctica dating to the last glacial maximum are rare and rely heavily on data from widely spaced ice cores, some of which show little variability through that time. Here, we present new data from closed-basin lakes in the Dry Valleys region of East Antarctica that show high-magnitude, high-frequency oscillations in surface level during the late Pleistocene synchronous with climate fluctuations elsewhere in the Southern Hemisphere. These data suggest a coherent Southern Hemisphere pattern of climate change on millennial time scales, at least in the Pacific sector, and indicate that any hypothesis concerning the origin of these events must account for synchronous changes in both high and temperate latitudes. PMID:21115838

  19. Antarctic lakes suggest millennial reorganizations of Southern Hemisphere atmospheric and oceanic circulation.

    PubMed

    Hall, Brenda L; Denton, George H; Fountain, Andrew G; Hendy, Chris H; Henderson, Gideon M

    2010-12-14

    The phasing of millennial-scale oscillations in Antarctica relative to those elsewhere in the world is important for discriminating among models for abrupt climate change, particularly those involving the Southern Ocean. However, records of millennial-scale variability from Antarctica dating to the last glacial maximum are rare and rely heavily on data from widely spaced ice cores, some of which show little variability through that time. Here, we present new data from closed-basin lakes in the Dry Valleys region of East Antarctica that show high-magnitude, high-frequency oscillations in surface level during the late Pleistocene synchronous with climate fluctuations elsewhere in the Southern Hemisphere. These data suggest a coherent Southern Hemisphere pattern of climate change on millennial time scales, at least in the Pacific sector, and indicate that any hypothesis concerning the origin of these events must account for synchronous changes in both high and temperate latitudes. PMID:21115838

  20. Subglacial biochemical weathering and transport drove fertilization in the Southern Ocean during Antarctic temperature maxima and NH Heinrich events

    NASA Astrophysics Data System (ADS)

    Frisia, S.; Augustinus, P. M.; Hellstrom, J.; Borsato, A.; Drysdale, R.; Weyrich, L.; Cooper, A.; Johnston, V. E.; Cotte, M.

    2013-12-01

    Changes in bioproductivity in the subantarctic region have been observed to coincide with episodes of significant iceberg discharge in the North Atlantic (Heinrich events), thus linking iron delivery to the Southern Ocean (SO) with abrupt climate changes in the Northern Hemisphere. Whilst upwelling has been proposed as a likely source of bioavailable iron during Heinrich events, it is well known that, today, subglacial metabolic pathways under limited carbon supply may accumulate divalent iron, which could have been mobilized and delivered to the SO during full glacial conditions. This alternative hypothesis remains largely untested for the SO because of the difficulties in accessing palaeoenvironmental archives from beneath the Antarctic ice sheets. We present a record of the subglacial production and fate of nutrients from calcite crusts formed beneath a tributary of the Rennick outlet glacier (East Antarctic Ice Sheet, EAIS) during the Last Glacial Maximum. Chemistry, stratigraphy and preliminary ancient DNA characterization of the microbial consortium of 27- to 17-kyr-old calcites suggest that bioweathering released iron in hypoxic pools of local basal meltwater. Anaerobic methane oxidising microbes released bicarbonate and sulfuric acid in the isolated pockets, which facilitated local weathering of the amphibolite rock. During episodes of channelized flow, identified by clast-rich microsparites, and which have ages near-commensurate with Antarctic Isotope Maximum2 (AIM2) and Heinrich event 2, ferrous iron may have been mobilized and transported subglacially to the ice shelf. The calcites formed during this phase preserve evidence of microbes using sulfite dehydrogenase, which explains the accumulation of sulfate in the calcite. Our data thus indicate that subglacial processes contributed to SO productivity increases at the time of Heinrich event 2, ultimately leading to drawdawn of atmospheric carbon dioxide at millennial scale.

  1. On the development of Antarctic katabatic winds and their impact on ocean and ice processes in the coastal Southern Ocean with implications for primary productivity

    NASA Astrophysics Data System (ADS)

    Goodrick, Scott Lawrence

    1997-10-01

    As a first step toward improving the present understanding of the physics that control air-sea CO2 exchange in the Southern Ocean, a coupled mesoscale atmosphere-ocean-sea ice model is described and used to examine the interaction of Antarctic katabatic winds with coastal ocean and sea ice processes. These winds are a dominant factor in shaping the climatology of Antarctica, particularly during the austral winter. Simulations are presented for winter and early spring conditions. For the spring case a simple primary productivity model is used to examine the early stages of phytoplankton bloom development. Latent heat polynyas are a common feature along the Antarctic coast. These ice-free regions are maintained by a balance between wind driven ice divergence and ice production. For the winter simulation the coupled model creates an initial polynya that closes after 4 days of simulation. The closing of the polynya is linked to the adjustment of the katabatic winds to the alongshore direction which forces shoreward Ekman transport of the sea ice, closing the polynya. Seasonal variations in the magnitude of the katabatic flows are linked to variations in the strength of the East Wind Drift. During the winter, the offshore directed katabtic winds adjust geostrophically, contributing to the strong polar easterlies of high southern latitudes. Shoreward Ekman transport associated with these easterlies supports a barotropic coastal current, the East Wind Drift. During spring the adjustment process is interrupted by the diurnal cycle, weakening the Ekman transport and the coastal current. Phytoplankton blooms in the Southern Ocean are typically linked to the retreat of the seasonal ice cover. As the sea ice melts the associated input of fresh water stabilizes the surface layer of the ocean limiting the depth of turbulent mixing. In early spring, sea ice coverage, incoming solar irradiance and wind stress are shown to be the major factors contributing to early bloom

  2. Postmiocene geodynamic evolution of the drake passage, Western Antarctic Region, southern ocean

    NASA Astrophysics Data System (ADS)

    Teterin, D. E.

    2011-08-01

    In 1994-2006, the German research vessel, Polarstern, and the Russian research vessel, Akademik Boris Petrov, carried out marine geologic and geophysical explorations in the Western Antarctic Region within the Bellingshausen, Amundsen, and Scotia marginal Seas and the Drake Passage. In these expeditions, new unique data on submarine topography have been collected by a multibeam echosounder, gravity and magnetic measurements have been carried out, multichannel seismic profiling has been performed, and the collections of rock samples have been acquired. The analysis and interpretation of new evidence together with previous geologic and geophysical data for the Drake Passage region have shown that end of spreading in the Aluk Ridge three million years ago resulted in the redistribution of stresses associated with the relative motion of the Antarctic, Scotia, and Phoenix Plates, which, in turn, caused significant tectonic reconstruction of the entire transition zone of the Drake Passage.

  3. Is there a linkage between the tropical cyclone activity in the southern Indian Ocean and the Antarctic Oscillation?

    NASA Astrophysics Data System (ADS)

    Mao, Rui; Gong, Dao-Yi; Yang, Jing; Zhang, Zi-Yin; Kim, Seong-Joong; He, Hao-Zhe

    2013-08-01

    this article, the relationship between the Antarctic Oscillation (AAO) and the tropical cyclone (TC) activity in the southern Indian Ocean (SIO) was examined. It was found that on the interannual time scale, the AAO is well linked with the TC activity in the SIO during TC season (December-March). The rank correlation coefficient between the AAO index and the TC frequency (TCF) in the SIO is 0.37, which is significant at the 95% confidence level. When the AAO is in a positive phase, TC passage in the northwestern coast of Australia (100E°-120°E and 10°S-30°S) increases by approximately 50%-100% from the climatology. The increase in the TC passage is primarily the result of more frequent TCs originating in this region due to enhanced water vapor convergence and ascending motions, which are caused by a cyclonic height anomaly over the western coast of Australia associated with the positive AAO phases. In addition, the AAO-height covariations, which are essential to the formation of the AAO-TC links in the SIO, were investigated through a historical climate simulation using the Community Climate System Model 4 from the Coupled Model Intercomparison Project Phase 5. The AAO-height links were well reproduced in the simulation. The similarity in the AAO-height links between the observation and the simulation supports the physical robustness of the AAO-TC links in the SIO.

  4. Satellite remote sensing of the island mass effect on the Sub-Antarctic Kerguelen Plateau, Southern Ocean

    NASA Astrophysics Data System (ADS)

    Jena, Babula

    2016-04-01

    The presence of the Kerguelen Plateau and surrounding bathymetric features has a strong influence on the persistently eastward flowing Antarctic Circumpolar Current (ACC), resulting in enhancement of surface chlorophyll-a (Chl-a) in the downstream section of the plateau along the polar front (PF). The phenomenon is reported in this paper as the island mass effect (IME). Analysis of climatological Chl-a datasets from Aqua- Moderate Resolution Imaging Spectroradiometer (Aqua- MODIS) and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) shows distinct bloomy plumes (Chl-a>0.5 mg/m3) during austral spring-summer spreading as far as ~1800 km offshore up to 98°E along the downstream of the north Kerguelen Plateau (NKP). Similar IME phenomena is apparent over the south Kerguelen Plateau (SKP) with the phytoplankton bloom extending up to 96.7°E, along the southern boundary of ACC. The IME phenomena are pronounced only during austral spring-summer period with the availability of light and sedimentary source of iron from shallow plateau to sea surface that fertilizes the mixed layer. The NKP bloom peaks with a maximum areal extent of 1.315 million km2 during December, and the SKP bloom peaks during January with a time lag of one month. The blooms exist for at least 4 months of a year and are significant both as the base of regional food web and for regulating the biogeochemical cycle in the Southern Ocean. Even though the surface water above the Kerguelen Plateau is rich in Chl-a, an exception of an oligotrophic condition dominated between NKP and SKP due to apparent intrusion of iron limited low phytoplankton regime waters from the Enderby basin through the northeastward Fawn Trough Current.

  5. Satellite remote sensing of the island mass effect on the Sub-Antarctic Kerguelen Plateau, Southern Ocean

    NASA Astrophysics Data System (ADS)

    Jena, Babula

    2016-09-01

    The presence of the Kerguelen Plateau and surrounding bathymetric features has a strong influence on the persistently eastward flowing Antarctic Circumpolar Current (ACC), resulting in enhancement of surface chlorophyll-a (Chl- a) in the downstream section of the plateau along the polar front (PF). The phenomenon is reported in this paper as the island mass effect (IME). Analysis of climatological Chl- a datasets from Aqua- Moderate Resolution Imaging Spectroradiometer (Aqua- MODIS) and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) shows distinct bloomy plumes (Chl- a>0.5 mg/m3) during austral spring-summer spreading as far as ~1800 km offshore up to 98°E along the downstream of the north Kerguelen Plateau (NKP). Similar IME phenomena is apparent over the south Kerguelen Plateau (SKP) with the phytoplankton bloom extending up to 96.7°E, along the southern boundary of ACC. The IME phenomena are pronounced only during austral spring-summer period with the availability of light and sedimentary source of iron from shallow plateau to sea surface that fertilizes the mixed layer. The NKP bloom peaks with a maximum areal extent of 1.315 million km2 during December, and the SKP bloom peaks during January with a time lag of one month. The blooms exist for at least 4 months of a year and are significant both as the base of regional food web and for regulating the biogeochemical cycle in the Southern Ocean. Even though the surface water above the Kerguelen Plateau is rich in Chl- a, an exception of an oligotrophic condition dominated between NKP and SKP due to apparent intrusion of iron limited low phytoplankton regime waters from the Enderby basin through the northeastward Fawn Trough Current.

  6. Simulations of Antarctic ice shelves and the Southern Ocean in the POP2x ocean model coupled with the BISICLES ice-sheet model

    NASA Astrophysics Data System (ADS)

    Asay-Davis, Xylar; Martin, Daniel; Price, Stephen; Maltrud, Mathew

    2014-05-01

    We present initial results from Antarctic, ice-ocean coupled simulations using large-scale ocean circulation and ice-sheet evolution models. This presentation focuses on the ocean model, POP2x, which is a modified version of POP, a fully eddying, global-scale ocean model (Smith and Gent, 2002). POP2x allows for circulation beneath ice shelf cavities using the method of partial top cells (Losch, 2008). Boundary layer physics, which control fresh water and salt exchange at the ice-ocean interface, are implemented following Holland and Jenkins (1999), Jenkins (2001), and Jenkins et al. (2010). Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP; Losch, 2008) and other continental-scale simulations and melt-rate observations (Kimura et al., 2013; Rignot et al., 2013) and with results from other idealized ice-ocean coupling test cases (e.g., Goldberg et al., 2012). A companion presentation, 'Fully resolved whole-continent Antarctica simulations using the BISICLES AMR ice sheet model coupled with the POP2x Ocean Model', concentrates more on the ice-sheet model, BISICLES (Cornford et al., 2012), which includes a 1st-order accurate momentum balance (L1L2) and uses block structured, adaptive-mesh refinement to more accurately model regions of dynamic complexity, such as ice streams, outlet glaciers, and grounding lines. For idealized test cases focused on marine-ice sheet dynamics, BISICLES output compares very favorably relative to simulations based on the full, nonlinear Stokes momentum balance (MISMIP-3d; Pattyn et al., 2013). Here, we present large-scale (Southern Ocean) simulations using POP2x at 0.1 degree resolution with fixed ice shelf geometries, which are used to obtain and validate modeled submarine melt rates against observations. These melt rates are, in turn, used to force evolution of the BISICLES model. An offline-coupling scheme, which we compare with the ice-ocean coupling work of Goldberg et al. (2012), is then used to

  7. Distributions of dissolved and particulate iron in the sub-Antarctic and Polar Frontal Southern Ocean (Australian sector)

    NASA Astrophysics Data System (ADS)

    Lannuzel, Delphine; Bowie, Andrew R.; Remenyi, Tomas; Lam, Phoebe; Townsend, Ashley; Ibisanmi, Enitan; Butler, Edward; Wagener, Thibaut; Schoemann, Véronique

    2011-11-01

    This paper presents iron (Fe) profiles in the upper 1000 m from nine short-term (transect) stations and three long-term (process) stations occupied in the Australian sector of the Southern Ocean during the SAZ-Sense expedition in austral summer (January-February) 2007. Strong vertical and horizontal gradients in Fe concentrations were observed between the 18 sampled profiles (i.e. 0.09-0.63 nmol/l dissolved Fe (dFe)). Average dFe concentrations in surface gggwaters in the northern Sub-Antarctic Zone (SAZ-N) West (station P1) were 0.27±0.04 nmol/l. This is lower in the SAZ-N East region (station P3 and around) where average dFe values in the mixed layer were 0.48±0.10 nmol/l. The Polar Front (PF) station (P2) exhibited the lowest average surface Fe values (i.e., 0.22±0.02 nmol/l). Iron concentrations in deep waters down to 1000 m were more uniform (0.25-0.37 nmol/l dFe), which is in accordance with values reported elsewhere in remote waters of the Southern Ocean, but lower than those observed in the North Atlantic and North Pacific basins. A strong decoupling was observed between dFe and nutrient cycles at all stations. Particulate Fe levels were generally very low for all SAZ stations (<0.08-1.38 nmol/l), with higher values observed at stations collected near Tasmania and in the SAZ-N East region. The intrusion of subtropical waters, enriched with Fe from sediments or dust further north, is thought to mediate Fe input to the SAZ-N and STZ areas, while input from below would be the main source of Fe in the PF region. We applied the tracer Fe * (Fe *= [dFe]- RFe:P×[PO 43-], where RFe:P is the algal uptake ratio) to estimate the degree to which the water masses were Fe limited. In this study, Fe * tended to be negative and decreased with increasing depths and latitude. Positive Fe * values, indicating Fe sufficiency, were observed in the (near-)surface waters collected in the SAZ-N East and near continental sources, where primary production was higher and

  8. Ocean processes at the Antarctic continental slope.

    PubMed

    Heywood, Karen J; Schmidtko, Sunke; Heuzé, Céline; Kaiser, Jan; Jickells, Timothy D; Queste, Bastien Y; Stevens, David P; Wadley, Martin; Thompson, Andrew F; Fielding, Sophie; Guihen, Damien; Creed, Elizabeth; Ridley, Jeff K; Smith, Walker

    2014-07-13

    The Antarctic continental shelves and slopes occupy relatively small areas, but, nevertheless, are important for global climate, biogeochemical cycling and ecosystem functioning. Processes of water mass transformation through sea ice formation/melting and ocean-atmosphere interaction are key to the formation of deep and bottom waters as well as determining the heat flux beneath ice shelves. Climate models, however, struggle to capture these physical processes and are unable to reproduce water mass properties of the region. Dynamics at the continental slope are key for correctly modelling climate, yet their small spatial scale presents challenges both for ocean modelling and for observational studies. Cross-slope exchange processes are also vital for the flux of nutrients such as iron from the continental shelf into the mixed layer of the Southern Ocean. An iron-cycling model embedded in an eddy-permitting ocean model reveals the importance of sedimentary iron in fertilizing parts of the Southern Ocean. Ocean gliders play a key role in improving our ability to observe and understand these small-scale processes at the continental shelf break. The Gliders: Excellent New Tools for Observing the Ocean (GENTOO) project deployed three Seagliders for up to two months in early 2012 to sample the water to the east of the Antarctic Peninsula in unprecedented temporal and spatial detail. The glider data resolve small-scale exchange processes across the shelf-break front (the Antarctic Slope Front) and the front's biogeochemical signature. GENTOO demonstrated the capability of ocean gliders to play a key role in a future multi-disciplinary Southern Ocean observing system. PMID:24891389

  9. Wide range of metallic and organic contaminants in various tissues of the Antarctic prion, a planktonophagous seabird from the Southern Ocean.

    PubMed

    Fromant, Aymeric; Carravieri, Alice; Bustamante, Paco; Labadie, Pierre; Budzinski, Hélène; Peluhet, Laurent; Churlaud, Carine; Chastel, Olivier; Cherel, Yves

    2016-02-15

    Trace elements (n=14) and persistent organic pollutants (POPs, n=30) were measured in blood, liver, kidney, muscle and feathers of 10 Antarctic prions (Pachyptila desolata) from Kerguelen Islands, southern Indian Ocean, in order to assess their concentrations, tissue distribution, and inter-tissue and inter-contaminant relationships. Liver, kidney and feathers presented the highest burdens of arsenic, cadmium and mercury, respectively. Concentrations of cadmium, copper, iron, and zinc correlated in liver and muscle, suggesting that uptake and pathways of metabolism and storage were similar for these elements. The major POPs were 4,4'-DDE, mirex, PCB-153 and PCB-138. The concentrations and tissue distribution patterns of environmental contaminants were overall in accordance with previous results in other seabirds. Conversely, some Antarctic prions showed surprisingly high concentrations of BDE-209. This compound has been rarely observed in seabirds before, and its presence in Antarctic prions could be due to the species feeding habits or to the ingestion of plastic debris. Overall, the study shows that relatively lower trophic level seabirds (zooplankton-eaters) breeding in the remote southern Indian Ocean are exposed to a wide range of environmental contaminants, in particular cadmium, selenium and some emerging-POPs, which merits further toxicological investigations. PMID:26674704

  10. Ocean processes at the Antarctic continental slope

    PubMed Central

    Heywood, Karen J.; Schmidtko, Sunke; Heuzé, Céline; Kaiser, Jan; Jickells, Timothy D.; Queste, Bastien Y.; Stevens, David P.; Wadley, Martin; Thompson, Andrew F.; Fielding, Sophie; Guihen, Damien; Creed, Elizabeth; Ridley, Jeff K.; Smith, Walker

    2014-01-01

    The Antarctic continental shelves and slopes occupy relatively small areas, but, nevertheless, are important for global climate, biogeochemical cycling and ecosystem functioning. Processes of water mass transformation through sea ice formation/melting and ocean–atmosphere interaction are key to the formation of deep and bottom waters as well as determining the heat flux beneath ice shelves. Climate models, however, struggle to capture these physical processes and are unable to reproduce water mass properties of the region. Dynamics at the continental slope are key for correctly modelling climate, yet their small spatial scale presents challenges both for ocean modelling and for observational studies. Cross-slope exchange processes are also vital for the flux of nutrients such as iron from the continental shelf into the mixed layer of the Southern Ocean. An iron-cycling model embedded in an eddy-permitting ocean model reveals the importance of sedimentary iron in fertilizing parts of the Southern Ocean. Ocean gliders play a key role in improving our ability to observe and understand these small-scale processes at the continental shelf break. The Gliders: Excellent New Tools for Observing the Ocean (GENTOO) project deployed three Seagliders for up to two months in early 2012 to sample the water to the east of the Antarctic Peninsula in unprecedented temporal and spatial detail. The glider data resolve small-scale exchange processes across the shelf-break front (the Antarctic Slope Front) and the front's biogeochemical signature. GENTOO demonstrated the capability of ocean gliders to play a key role in a future multi-disciplinary Southern Ocean observing system. PMID:24891389

  11. Bone-eating worms from the Antarctic: the contrasting fate of whale and wood remains on the Southern Ocean seafloor

    PubMed Central

    Glover, Adrian G.; Wiklund, Helena; Taboada, Sergio; Avila, Conxita; Cristobo, Javier; Smith, Craig R.; Kemp, Kirsty M.; Jamieson, Alan J.; Dahlgren, Thomas G.

    2013-01-01

    We report the results from the first experimental study of the fate of whale and wood remains on the Antarctic seafloor. Using a baited free-vehicle lander design, we show that whale-falls in the Antarctic are heavily infested by at least two new species of bone-eating worm, Osedax antarcticus sp. nov. and Osedax deceptionensis sp. nov. In stark contrast, wood remains are remarkably well preserved with the absence of typical wood-eating fauna such as the xylophagainid bivalves. The combined whale-fall and wood-fall experiment provides support to the hypothesis that the Antarctic circumpolar current is a barrier to the larvae of deep-water species that are broadly distributed in other ocean basins. Since humans first started exploring the Antarctic, wood has been deposited on the seafloor in the form of shipwrecks and waste; our data suggest that this anthropogenic wood may be exceptionally well preserved. Alongside the new species descriptions, we conducted a comprehensive phylogenetic analyses of Osedax, suggesting the clade is most closely related to the frenulate tubeworms, not the vestimentiferans as previous reported. PMID:23945684

  12. A Strategic Vision for NSF Investments in Antarctic and Southern Ocean Research: Recommendations of a New Study from the National Academes of Sciences, Engineering, and Medicine.

    NASA Astrophysics Data System (ADS)

    Weller, R. A.; Bell, R. E.; Geller, L.

    2015-12-01

    A Committee convened by the National Academies of Sciences, Engineering, and Medicine carried out a study (at the request of NSF's Division of Polar Programs) to develop a strategic vision for the coming decade of NSF's investments in Antarctic and Southern Ocean research. The study was informed by extensive efforts to gather ideas from researchers across the United States. This presentation will provide an overview of the Committee's recommendations—regarding an overall strategic framework for a robust U.S. Antarctic program, regarding the specific areas of research recommended as highest priority for NSF support, and regarding the types of infrastructure, logistical support, data management, and other critical foundations for enabling and adding lasting value to the proposed research .

  13. Vertical distribution of pelagic ostracods (Myodocopa) in the Subantarctic and Antarctic zones of the Australian-New Zealand sector in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Chavtur, V. G.; Mazdygan, E. R.

    2015-03-01

    Materials from the Russian expeditions in the Australia-New Zealand sector of the Southern Ocean during the period from 1956 until 1983 have been studied. In the Subantarctic zone, the fauna of pelagic ostracods is formed mainly by the allochthonic complex tropical-subtropical and antarctic species. The number of ostracod species, as well as their density and biomass, increase with depth, reaching a maximum at the 400-500-m layer and decreasing closer to the bottom. The vertical distribution of pelagic ostracods is similar in the Antarctic and Subantarctic zones. Nevertheless, the maximum number of species here is determined mainly by the aboriginal complex of widespread and cold-water ostracods, which moves deeper when moving to higher latitudes. There are regular changes in the vertical distribution of dominant species with latitude. They are determined by the specific structure and dynamics of water masses in separate subzones of the study region.

  14. A new source of Southern Ocean and Antarctic aerosol from tropospheric polar cell chemistry of sea ice emissions

    NASA Astrophysics Data System (ADS)

    Humphries, R. S.; Klekociuk, A. R.; Schofield, R.; Robinson, A. D.; Harris, N. R. P.; Keywood, M.; Ward, J.; Galbally, I.; Molloy, S.; Thomas, A.; Wilson, S. R.

    2014-12-01

    The Antarctic region is a pristine environment with minimal anthropogenic influence. Aerosol measurements in this environment allow the study of natural aerosols and polar atmospheric dynamics. Measurements in this region have been limited primarily to continental and coastal locations where permanent stations exist, with a handful of measurements in the sea ice region. The MAPS campaign (Measurements of Aerosols and Precursors during SIPEXII) occurred as part of SIPEX II (Sea Ice Physics and Ecosystems eXperiment II) voyage in Spring, 2012, and produced the first Antarctic pack-ice focused aerosol dataset aimed at characterizing new particle formation processes off the coast of East Antarctica (~65°S, 120°E). Numerous atmospheric parameters and species were measured, including the number of aerosol particles in the 3-10 nm size range, the range associated with nucleating particle formation. A latitudinal transect through the sea ice identified the Polar Front from sudden changes in nucleating particle concentrations, averaging 51cm-3 north of the front in the Ferrel cell, and 766 cm-3 south of the front, in the Polar cell region. The Polar Front location was also confirmed by meteorological and back-trajectory data. Background aerosol populations in the Polar cell fluctuated significantly but displayed no growth indicators, suggesting transport. Back-trajectories revealed that air parcels often descended from the free-troposphere within the previous 24-48 hrs. It is proposed that particle formation occurs in the free troposphere from precursors uplifted at the polar front region which, being a sea-ice/ocean region, is a significant precursor source. After tropospheric formation, populations descending at the poles are transported northward and reach the sea ice surface, missing continental stations. Current measurements of Antarctic aerosol suggest very low loading which may be explained by these circulation patterns and may underestimate total regional loading

  15. Linkages between East Antarctic Ice Sheet extent and Southern Ocean temperatures based on a Pliocene high-resolution record of ice-rafted debris off Prydz Bay, East Antarctica

    NASA Astrophysics Data System (ADS)

    Passchier, S.

    2011-12-01

    Ice-rafted debris mass accumulation rates (IRD MAR) at a drill site on the Antarctic continental margin are investigated to evaluate the linkages between East Antarctic Ice Sheet extent and Southern Ocean temperatures in the early to mid-Pliocene. ODP Site 1165 is within 400 km of the Antarctic coastline and in the direct pathway of icebergs released by the Amery Ice Shelf. The Amery Ice Shelf is the largest ice shelf in East Antarctica and it buttresses the Lambert Glacier drainage system, which accounts for 14% of the outflow from the East Antarctic Ice Sheet. IRD MAR were low during peak Southern Ocean warming in the early Pliocene. After a brief precursor, a tenfold increase in IRD MAR at 3.3 Ma marks the termination of the early Pliocene ice sheet minimum, coincident with the M2 glacial. For the mid-Pliocene, a strong correlation exists between the high-amplitude signal in the LR04 benthic stack and IRD MAR, suggesting linkages between East Antarctic ice extent, global ice volume and deep-water temperatures. The IRD record at Site 1165 provides evidence of greater sensitivity of the Lambert Glacier-Amery Ice Shelf system to Southern Ocean warming than is currently predicted by ice sheet models, which may relate to uncertainties in the understanding of ocean heat uptake, poleward heat transport and ice sheet-ocean interactions.

  16. Oceanographic changes in the Southern Ocean and Antarctic cryosphere dynamics during the Oligocene and Miocene: a view from offshore Wilkes Land

    NASA Astrophysics Data System (ADS)

    Sangiorgi, Francesca; Bijl, Peter K.; Hartman, Julian D.; Schouten, Stefan; Brinkhuis, Henk

    2016-04-01

    With the ongoing increase in atmospheric CO2 and global temperatures, a fundamental scientific and societal question arises concerning the stability of the Antarctic cryosphere. Modern observational data indicate the Southern Ocean has experienced significant warming, with oceanic fronts being pushed several tenth of km closer to the continent. Moreover, basal melt of ice shelves from warming oceans is causing accelerated grounding line retreat of the Antarctic ice sheets and shelves. However, monitoring data are available for the last few decades only, which prevents the evaluation of long-term changes in ice mass balance. Studying intervals in Earth's past history, which represent the best possible analogues of (near) future conditions, becomes thus essential. The Oligocene and Miocene Epochs encompass periods with CO2 concentrations between today's and those expected for the (near) future. It has also become clear that ice-proximal oceanographic regime is a critical factor for the stability and mass balance of ice sheets. Integrated Ocean Drilling Program (IODP) Expedition 318 offshore Wilkes Land (East Antarctica) Site U1356 satisfies both requirements of being ice-proximal and having a relative complete, stratigraphically well-resolved Oligocene-Miocene sequence (albeit with a possible 5-Myrs gap between Late Oligocene and Early Miocene). This allows for the first time studying oceanographic changes and cryosphere dynamics in the interval ~34-13 Myrs. Thus far, ice-proximal reconstructions were hindered by the paucity of suitable sedimentary archives around Antarctica and/or poor stratigraphic constraints. We reconstructed changes in surface oceanography and seawater temperatures by means of dinoflagellate cyst assemblages and TEX86 paleothermometry. The dinocyst data suggest (summer) sea-ice occurrence at Site U1356 only for the first 1.5 Ma following the onset of full Antarctic glaciation and after the Mid-Miocene Climatic Optimum. In between, both dinocysts

  17. Predictive habitat modelling of humpback (Megaptera novaeangliae) and Antarctic minke (Balaenoptera bonaerensis) whales in the Southern Ocean as a planning tool for seismic surveys

    NASA Astrophysics Data System (ADS)

    Bombosch, Annette; Zitterbart, Daniel P.; Van Opzeeland, Ilse; Frickenhaus, Stephan; Burkhardt, Elke; Wisz, Mary S.; Boebel, Olaf

    2014-09-01

    Seismic surveys are frequently a matter of concern regarding their potentially negative impacts on marine mammals. In the Southern Ocean, which provides a critical habitat for several endangered cetacean species, seismic research activities are undertaken at a circumpolar scale. In order to minimize impacts of these surveys, pre-cruise planning requires detailed, spatio-temporally resolved knowledge on the likelihood of encountering these species in the survey area. In this publication we present predictive habitat modelling as a potential tool to support decisions for survey planning. We associated opportunistic sightings (2005-2011) of humpback (Megaptera novaeangliae, N=93) and Antarctic minke whales (Balaenoptera bonaerensis, N=139) with a range of static and dynamic environmental variables. A maximum entropy algorithm (Maxent) was used to develop habitat models and to calculate daily basinwide/circumpolar prediction maps to evaluate how species-specific habitat conditions evolved throughout the spring and summer months. For both species, prediction maps revealed considerable changes in habitat suitability throughout the season. Suitable humpback whale habitat occurred predominantly in ice-free areas, expanding southwards with the retreating sea ice edge, whereas suitable Antarctic minke whale habitat was consistently predicted within sea ice covered areas. Daily, large-scale prediction maps provide a valuable tool to design layout and timing of seismic surveys as they allow the identification and consideration of potential spatio-temporal hotspots to minimize potential impacts of seismic surveys on Antarctic cetacean species.

  18. Antarctic and Southern Ocean Mineral Dust Aerosol Transport Pathways: Forward-Trajectory Modeling and Source Constraints Derived from the RICE Ice Core

    NASA Astrophysics Data System (ADS)

    Neff, P. D.; Tuohy, A.; Bertler, N. A. N.; Edwards, R.

    2014-12-01

    Mineral dust fertilization of Southern Ocean surface waters, and mixing with Antarctic deep-water, influences oceanic uptake of atmospheric carbon dioxide and draws down global atmospheric CO2concentration during glacial periods. Quantifying modern variability in dust source and transport strength, especially with respect to high- and low-latitude climate phenomena (e.g. SAM, ENSO), will improve understanding of this important aspect of the global carbon cycle. Here we present data from a new intermediate-depth, coastal ice core drilled at Roosevelt Island, Antarctica as part of the Roosevelt Island Climate Evolution (RICE) project. Using HySPLIT forward trajectories, climate reanalysis and geochemistry data, this work explores variability in atmospheric transport for modern Southern Hemisphere dust source areas (primarily Australia, southern South America and southern Africa). While New Zealand represents a relatively small dust source at present, it is strongly-connected to the Antarctic due to its position within the circumpolar westerly winds and was a major dust source during the last glacial period. Geochemical data from the RICE ice core (79.36ºS, 161.71ºW, 550 m a.s.l.) are used to constrain sources of dust in this sector. The lanthanide elements—common in crustal material and not susceptible to fractionation—can preserve the signature of their original source material, allowing for characterisation of dust provenance. Initial results suggest that only air trajectories originating in New Zealand regularly reach the Ross Sea, Marie Byrd Land and Roosevelt Island within 3 to 5 days (see Figure 1), a characteristic travel time of suspended dust particles. We discuss estimates of the relative source strength of New Zealand compared with other dust source areas to evaluate its overall contribution. Figure 1: Daily 96-hour forward trajectories for Southern Hemisphere dust source areas, 2010-2013 (NOAA HySPLIT, NCEP reanalysis). NCEP reanalysis 1980

  19. Ecology and biogeochemistry of the antarctic circumpolar current during austral spring: a summary of southern ocean JGOFS cruise ANT X/6 of R.V. Polarstern

    NASA Astrophysics Data System (ADS)

    Smetacek, V.; De Baar, H. J. W.; Bathmann, U. V.; Lochte, K.; Rutgers Van Der Loeff, M. M.

    The R.V. Polarstern cruise ANT X/6, part of the international Southern Ocean JGOFS programme, investigated phytoplankton spring bloom development and its biogeochemical effects in different water masses of the Atlantic sector of the Southern Ocean: the Polar Frontal region (PFr), the southern Antarctic Circumpolar Current zone (sACC), its boundary with the Weddell Gyre (AWB) and the marginal ice zone (MIZ). The relative roles of physical stability, iron limitation and grazing pressure in enhancing or constraining phytoplankton biomass accumulation were examined. Three sections were carried out between the PFr and the ice edge along the 6°W meridian from early October to late November 1992. This paper summarises the major findings of the cruise and discusses their implications for our understanding of Southern Ocean ecology and biogeochemistry. A major finding was the negligible build-up of plankton biomass and concomitant absence of CO 2 drawdown associated with seasonal retreat of the ice cover. In striking contrast to this unexpected poverty of both the MIZ and the frontal region of the AWB, distinct phytoplankton blooms, dominated by different diatom species, accumulated in the PFr. Chlorophyll stocks in the sACC remained monotonously low throughout the study. Our findings confirm those of other studies that frontal regions are the major productive sites in the Southern Ocean and that input of meltwater and associated ice algae to the surface layer from a retreating ice edge is by itself an insufficient condition for induction of phytoplankton blooms. The blooms in the PFr developed under conditions of shallow mixing layers, high iron concentrations and relatively low grazing pressure. However, in all three blooms, high biomass extended to deeper than 70 m, which cannot be explained by either in situ growth or sinking out of a part of the population from the upper euphotic zone. Subduction of adjoining, shallower layers to explain depth distribution is invoked

  20. Middle Eocene to early Miocene environmental changes in the sub-Antarctic Southern Ocean: evidence from biogenic and terrigenous depositional patterns at ODP Site 1090

    NASA Astrophysics Data System (ADS)

    Diekmann, Bernhard; Kuhn, Gerhard; Gersonde, Rainer; Mackensen, Andreas

    2004-02-01

    During Leg 177 of the Ocean Drilling Program (ODP), a well-preserved middle Eocene to lower Miocene sediment record was recovered at Site 1090 on the Agulhas Ridge in the Atlantic sector of the Southern Ocean. This new sediment record shows evidence of a hitherto unknown late Eocene opal pulse. Lithological variations, compositional data, mass-accumulation rates of biogenic and lithogenic sediment constituents, grain-size distributions, geochemistry, and clay mineralogy are used to gain insights into mid-Cenozoic environmental changes and to explore the circumstances of the late Eocene opal pulse in terms of reorganizations in ocean circulation. The base of the section is composed of middle Eocene nannofossil oozes mixed with red clays enriched in authigenic clinoptilolite and smectite, deposited at low sedimentation rates (≤2 cm ka -1). It indicates reduced terrigenous sediment input and moderate biological productivity during this preglacial warm climatic stage. The basal strata are overlain by an extended succession (100 m, 4 cm ka -1) of biosiliceous oozes and muds, comprising the upper middle Eocene, the entire late Eocene, and the lowermost early Oligocene. The opal pulse occurred between 37.5 and 33.5 Ma and documents the development of upwelling cells along topographic highs, and the utilization of a marine nutrient- and silica reservoir established during the pre-late Eocene through enhanced submarine hydrothermal activity and the introduction of terrigenous solutions from chemical weathering on adjacent continents. This palaeoceanographic overturn probably was initiated through the onset of increased meridional ocean circulation, caused by the diversion of the Indian equatorial current to the south. The opal pulse was accompanied by increased influxes of terrigenous detritus from southern African sources (illite), mediated by enhanced ocean particle advection in response to modified ocean circulation. The opal pulse ended because of frontal shifts to

  1. Population-Level Transcriptomic Responses of the Southern Ocean Salp Salpa thompsoni to Environment Variability of the Western Antarctic Peninsula Region

    NASA Astrophysics Data System (ADS)

    Bucklin, A. C.; Batta Lona, P. G.; Maas, A. E.; O'Neill, R. J.; Wiebe, P. H.

    2015-12-01

    In response to the changing Antarctic climate, the Southern Ocean salp Salpa thompsoni has shown altered patterns of distribution and abundance that are anticipated to have profound impacts on pelagic food webs and ecosystem dynamics. The physiological and molecular processes that underlay ecological function and biogeographical distribution are key to understanding present-day dynamics and predicting future trajectories. This study examined transcriptome-wide patterns of gene expression in relation to biological and physical oceanographic conditions in coastal, shelf and offshore waters of the Western Antarctic Peninsula (WAP) region during austral spring and summer 2011. Based on field observations and collections, seasonal changes in the distribution and abundance of salps of different life stages were associated with differences in water mass structure of the WAP. Our observations are consistent with previous suggestions that bathymetry and currents in Bransfield Strait could generate a retentive cell for an overwintering population of S. thompsoni, which may generate the characteristic salp blooms found throughout the region later in summer. The statistical analysis of transcriptome-wide patterns of gene expression revealed differences among salps collected in different seasons and from different habitats (i.e., coastal versus offshore) in the WAP. Gene expression patterns also clustered by station in austral spring - but not summer - collections, suggesting stronger heterogeneity of environmental conditions. During the summer, differentially expressed genes covered a wider range of functions, including those associated with stress responses. Future research using novel molecular transcriptomic / genomic characterization of S. thompsoni will allow more complete understanding of individual-, population-, and species-level responses to environmental variability and prediction of future dynamics of Southern Ocean food webs and ecosystems.

  2. An Investigation of Biogenic Trace Gas Emissions from the Southern Ocean: Impact on Boundary Layer Marine Composition and on the Distant Antarctic Plateau Atmosphere

    NASA Astrophysics Data System (ADS)

    Davis, D. D.; Neff, W.; Wang, Y.; Zeng, T.; Slusher, D.; Bradshaw, J.; Stickel, R.; Nicovitch, M.

    2008-12-01

    During the last ten years chemical measurements at the South Pole as well as over extended regions of the larger plateau have revealed the presences of a chemically unique boundary layer (BL) atmosphere. Unique in that it has been shown to have a very large chemical oxidizing capacity. This has been reflected in summertime concentration measurements of the hydroxyl radical that average between 2 to 3 x 10(6) molec/cm(3). These new findings make quite evident that the Antarctic plateau (geographically the size of continental USA) must now be viewed as much more than a chemical graveyard where species transported to its surface from a multitude of SH sources are simply buried in ice. In fact, during the Austral spring, summer, and fall months, chemical elements arriving at the plateau may in many cases be further oxidized before burial and in still other cases oxidized even after burial. To be presented are several previously unreported observations of biogenic gases measured both over the Southern Ocean and on the plateau, some of which span all seasons of the year. Of particular significance will be regional modeling results that suggest that the concentration levels and chemical forms that these biogenic gases appear upon reaching the plateau depend not only on the productivity of the Southern Ocean and the seas surrounding Antarctica, but also on at least two additional factors. These include the efficiency of the transport process (e.g., as influenced by the sea ice extent) and the chemical oxidizing capacity of the Antarctic plateau's BL atmosphere.

  3. Seasonal study of carbon dioxide in the southern extreme of the pacific sector, Antarctic Ocean. Progress report

    SciTech Connect

    Takahashi, Taro; Goddard, J.G.; Rubin, S.I.; Breger, D.

    1994-05-05

    This report describes the progress made during the six-month period between December 1, 1993, when this grant was awarded, and May 1, 1994. The major aim of this investigation is to measure the distribution of the total CO{sub 2} concentration and pCO{sub 2} in seawater in the Pacific sector of the extreme Southern Ocean as far south as 78{degrees}S. The areas investigated include the continental shelf areas in the Ross, Amundsen and Bellingshausen Seas ad the off-shore deep water areas as far north as 67{degrees}S. The measurements were made aboard the R/VIB Nathaniel B. Palmer between February 14, 1994 and April 5, 1994, and the preliminary results are briefly described in this report. This expedition constitutes the first of a pair expeditions. The first is designed investigate oceanic CO{sub 2} sink/source conditions during the austral summer The second expedition, which is designed for the following winter, has been scheduled for September, 1994.

  4. First evidence of widespread active methane seepage in the Southern Ocean, off the sub-Antarctic island of South Georgia

    NASA Astrophysics Data System (ADS)

    Römer, M.; Torres, M.; Kasten, S.; Kuhn, G.; Graham, A. G. C.; Mau, S.; Little, C. T. S.; Linse, K.; Pape, T.; Geprägs, P.; Fischer, D.; Wintersteller, P.; Marcon, Y.; Rethemeyer, J.; Bohrmann, G.

    2014-10-01

    An extensive submarine cold-seep area was discovered on the northern shelf of South Georgia during R/V Polarstern cruise ANT-XXIX/4 in spring 2013. Hydroacoustic surveys documented the presence of 133 gas bubble emissions, which were restricted to glacially-formed fjords and troughs. Video-based sea floor observations confirmed the sea floor origin of the gas emissions and spatially related microbial mats. Effective methane transport from these emissions into the hydrosphere was proven by relative enrichments of dissolved methane in near-bottom waters. Stable carbon isotopic signatures pointed to a predominant microbial methane formation, presumably based on high organic matter sedimentation in this region. Although known from many continental margins in the world's oceans, this is the first report of an active area of methane seepage in the Southern Ocean. Our finding of substantial methane emission related to a trough and fjord system, a topographical setting that exists commonly in glacially-affected areas, opens up the possibility that methane seepage is a more widespread phenomenon in polar and sub-polar regions than previously thought.

  5. Southern Ocean eddy phenomenology

    NASA Astrophysics Data System (ADS)

    Frenger, I.; Münnich, M.; Gruber, N.; Knutti, R.

    2015-11-01

    Mesoscale eddies are ubiquitous features in the Southern Ocean, yet their phenomenology is not well quantified. To tackle this task, we use satellite observations of sea level anomalies and sea surface temperature (SST) as well as in situ temperature and salinity measurements from profiling floats. Over the period 1997-2010, we identified over a million mesoscale eddy instances and were able to track about 105 of them over 1 month or more. The Antarctic Circumpolar Current (ACC), the boundary current systems, and the regions where they interact are hot spots of eddy presence, representing also the birth places and graveyards of most eddies. These hot spots contrast strongly to areas shallower than about 2000 m, where mesoscale eddies are essentially absent, likely due to topographical steering. Anticyclones tend to dominate the southern subtropical gyres, and cyclones the northern flank of the ACC. Major causes of regional polarity dominance are larger formation numbers and lifespans, with a contribution of differential propagation pathways of long-lived eddies. Areas of dominance of one polarity are generally congruent with the same polarity being longer-lived, bigger, of larger amplitude, and more intense. Eddies extend down to at least 2000 m. In the ACC, eddies show near surface temperature and salinity maxima, whereas eddies in the subtropical areas generally have deeper anomaly maxima, presumably inherited from their origin in the boundary currents. The temperature and salinity signatures of the average eddy suggest that their tracer anomalies are a result of both trapping in the eddy core and stirring.

  6. The seasonal succession of zooplankton in the Southern Ocean south of Australia, part II: The Sub-Antarctic to Polar Frontal Zones

    NASA Astrophysics Data System (ADS)

    Hunt, Brian P. V.; Hosie, Graham W.

    2006-07-01

    Between October 2001 and March 2002 six transects were completed at monthly intervals in the Sub-Antarctic Zone (SAZ) and Inter-Sub-Antarctic Front Zone (ISAFZ)/Polar Frontal Zone (PFZ) in the Southern Ocean south of Australia. Zooplankton were collected with a Continuous Plankton Recorder and NORPAC net and multivariate analysis was used to analyse the seasonal succession of communities. Despite strong, seasonally consistent, biogeographic differences between the SAZ and ISAFZ/PFZ, community structure in all zones was dominated by a suite of common taxa. These included the ubiquitous Oithona similis, foraminiferans and appendicularians (Core taxa), occurring in >97% of samples and contributing an average of 75% to total sample abundance, and Calanus simillimus, Rhincalanus gigas, Ctenocalanus citer, Clausocalanus brevipes, Clausocalanus laticeps, Oithona frigida, Limacina spp. and chaetognaths (Summer taxa), present in >57% of samples and occurring at seasonally high densities. Because of the dominance of the Core and Summer taxa, the seasonal succession was most clearly evident as a change in zooplankton densities. In October densities averaged <15 ind m -3, rising to 52 ind m -3 (max=92 ind m -3) in November, and subsequently increasing slowly through to January (ave=115 ind m -3; max=255 ind m -3). Densities peaked abruptly in February (ave=634 ind m -3; max=1593 ind m -3), and remained relatively high in March (ave=193 ind m -3; max=789 ind m -3). A latitudinal lag in seasonal development was observed with peak densities occurring first in the SAZ (February) and then in the ISAFZ/PFZ (March). The seasonal community succession was strongly influenced by species population cycles. The role of zooplankton in biogeochemical cycling in the SAZ and ISAFZ/PFZ was discussed in the light of past sediment trap data collected from the study area.

  7. Particulate export and lateral advection in the Antarctic Polar Front (Southern Pacific Ocean): One-year mooring deployment

    NASA Astrophysics Data System (ADS)

    Tesi, T.; Langone, L.; Ravaioli., M.; Giglio, F.; Capotondi, L.

    2012-12-01

    An instrumented mooring line with sediment traps, current meters and recorders of temperature and conductivity was deployed just south of the Antarctic Polar Front (63° 26‧ S, 178° 03‧E; water depth 4400 m) from January 9th 1999 to January 10th 2000. Sediment traps at 900 and 3700 m had a single large cup to collect particulate material throughout the 1-year study whereas time-series sediment traps were used to characterize the temporal variability at 1300 and 2400 m. Samples were characterized via several parameters including total mass flux, elemental composition (organic carbon, total nitrogen, biogenic silica, and calcium carbonate), concentration of metals (aluminum, iron, barium, and manganese), 210Pb activity, and foraminifera identification. High vertical fluxes of biogenic particles were observed in both summer 1999 and 2000 as a result of seasonal algal blooms associated with sea ice retreat and water column stratification. During autumn and winter, several high energy events occurred and resulted in advecting resuspended biogenic particles from flat-topped summits of the Pacific Antarctic Ridge. Whereas the distance between seabed and uppermost sediment traps was sufficient to avoid lateral advection processes, resuspension was significant in the lowermost sediment traps accounting for ~ 60 and ~ 90% of the material caught at 2400 and 3700 m, respectively. Although resuspended material showed an elemental composition relatively similar to vertical summer fluxes, samples collected during high energy events contained benthic foraminifera and exhibited significantly higher 210Pb activity indicating a longer residence time in the water column. In addition, during quiescent periods characterized by low mass fluxes, the content of lithogenic particles increased at the expense of phytodetritus indicating the influence of material advected through the benthic nepheloid layer. Organic matter content was particularly high during these periods and showed

  8. Migration of the Antarctic Circumpolar Current in the Late Neogene: reconstruction from sediment wave on the Conrad Rise, Indian Sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Oiwane, H.; Ikehara, M.; Suganuma, Y.; Nakamura, Y.; Nogi, Y.; Miura, H.; Sato, T.

    2012-12-01

    ACC is the largest and strongest ocean current in the world. It is important for the interoceanic exchange of water, exchange of gases to the atmosphere, and thermal isolation of the Antarctic continent. Fluctuation of the ACC has been reconstructed from several methods such as microfossils, anisotropy of magnetic susceptibilities, and statistical analysis of Ice-Rafted Debris. On the other hand, sediment waves are investigated and interpreted to reconstruct the fluctuation of the bottom- and contour currents. In this study, we tried reconstructing the ACC using sediment waves based on multidisciplinary survey on the Conrad Rise in the Indian sector of the Southern Ocean. The Conrad Rise is a topographic high that is elevated ca. 3000 m from the ocean floor. We conducted multibeam bathymetry, seismic reflection, and sediment coring on the southwestern slope of the rise. Seismic units on the Conrad Rise are divided into three units, A, B, and C in descending order. Unit A shows transparent to low amplitude with sediment wave structure. Sediment waves don't show systematic changes of its dimension and thickness. Sedimentary core showed that the surface sediment is composed of diatom ooze. Unit B shows higher amplitude than that of unit A, and shows planar, parallel configuration. Unit C has high-amplitude reflectors at its top and shows chaotic facies below. Based on morphological characteristics of the sediment waves, oceanographic setting of the Conrad Rise, and components of the surface sediment, it is most likely that the sedimentary structure and component of the Unit A is significantly constrained by the ACC. On the other hand, the Unit B shows planar configuration suggesting deposition without current effect. Additionally, higher amplitude suggests different component form that of the Unit A. These a series of evidence represent difference of sedimentary environment between units A and B, especially on the point of the influence of the ACC. Accordingly, onset

  9. The Southern Ocean: Source and sink?

    NASA Astrophysics Data System (ADS)

    Strugnell, J. M.; Cherel, Y.; Cooke, I. R.; Gleadall, I. G.; Hochberg, F. G.; Ibáñez, C. M.; Jorgensen, E.; Laptikhovsky, V. V.; Linse, K.; Norman, M.; Vecchione, M.; Voight, J. R.; Allcock, A. L.

    2011-03-01

    Many members of the benthic fauna of the Antarctic continental shelf share close phylogenetic relationships to the deep-sea fauna adjacent to Antarctica and in other ocean basins. It has been suggested that connections between the Southern Ocean and the deep sea have been facilitated by the presence of a deep Antarctic continental shelf coupled with submerging Antarctic bottom water and emerging circumpolar deep water. These conditions may have allowed 'polar submergence', whereby shallow Southern Ocean fauna have colonised the deep sea and 'polar emergence', whereby deep-sea fauna colonised the shallow Southern Ocean. A recent molecular study showed that a lineage of deep-sea and Southern Ocean octopuses with a uniserial sucker arrangement on their arms appear to have arisen via polar submergence. A distantly related clade of octopuses with a biserial sucker arrangement on their arms (historically placed in the genus Benthoctopus) is also present in the deep-sea basins of the world and the Southern Ocean. To date their evolutionary history has not been examined. The present study investigated the origins of this group using 3133 base pairs (bp) of nucleotide data from five mitochondrial genes (12S rRNA, 16S rRNA, cytochrome c oxidase subunit I, cytochrome c oxidase subunit III, cytochrome b) and the nuclear gene rhodopsin from at least 18 species (and 7 outgroup taxa). Bayesian relaxed clock analyses showed that Benthoctopus species with a high-latitude distribution in the Southern Hemisphere represent a paraphyletic group comprised of three independent clades. The results suggest that the Benthoctopus clade originated in relatively shallow Northern Hemisphere waters. Benthoctopus species distributed in the Southern Ocean are representative of polar emergence and occur at shallower depths than non-polar Benthoctopus species.

  10. Pteropods in Southern Ocean ecosystems

    NASA Astrophysics Data System (ADS)

    Hunt, B. P. V.; Pakhomov, E. A.; Hosie, G. W.; Siegel, V.; Ward, P.; Bernard, K.

    2008-09-01

    To date, little research has been carried out on pelagic gastropod molluscs (pteropods) in Southern Ocean ecosystems. However, recent predictions are that, due to acidification resulting from a business as usual approach to CO 2 emissions (IS92a), Southern Ocean surface waters may begin to become uninhabitable for aragonite shelled thecosome pteropods by 2050. To gain insight into the potential impact that this would have on Southern Ocean ecosystems, we have here synthesized available data on pteropod distributions and densities, assessed current knowledge of pteropod ecology, and highlighted knowledge gaps and directions for future research on this zooplankton group. Six species of pteropod are typical of the Southern Ocean south of the Sub-Tropical Convergence, including the four Thecosomes Limacina helicina antarctica, Limacina retroversa australis, Clio pyramidata, and Clio piatkowskii, and two Gymnosomes Clione limacina antarctica and Spongiobranchaea australis. Limacina retroversa australis dominated pteropod densities north of the Polar Front (PF), averaging 60 ind m -3 (max = 800 ind m -3) and 11% of total zooplankton at the Prince Edward Islands. South of the PF L. helicina antarctica predominated, averaging 165 ind m -3 (max = 2681 ind m -3) and up to >35% of total zooplankton at South Georgia, and up to 1397 ind m -3 and 63% of total zooplankton in the Ross Sea. Combined pteropods contributed <5% to total zooplankton in the Lazarev Sea, but 15% (max = 93%) to macrozooplankton in the East Antarctic. In addition to regional density distributions we have synthesized data on vertical distributions, seasonal cycles, and inter-annual density variation. Trophically, gymnosome are specialist predators on thecosomes, while thecosomes are considered predominantly herbivorous, capturing food with a mucous web. The ingestion rates of L. retroversa australis are in the upper range for sub-Antarctic mesozooplankton (31.2-4196.9 ng pig ind -1 d -1), while those of L

  11. Population genetic variation of the Southern Ocean krill, Euphausia superba, in the Western Antarctic Peninsula region based on mitochondrial single nucleotide polymorphisms (SNPs)

    NASA Astrophysics Data System (ADS)

    Batta-Lona, Paola G.; Bucklin, Ann; Wiebe, Peter H.; Patarnello, Tomaso; Copley, Nancy J.

    2011-07-01

    The Southern Ocean krill, Euphausia superba, is one of the best-studied marine zooplankton species in terms of population genetic diversity and structure; with few exceptions, previous studies have shown the species to be genetically homogeneous at larger spatial scales. The goals of this study are to examine sub-regional scale population genetic diversity and structure of E. superba using molecular characters selected with this goal in mind, and to thereby examine hypotheses of the source(s) of recruitment for krill populations of the Western Antarctic Peninsula (WAP). Collections were made throughout the WAP region during US GLOBEC cruises in austral fall, 2001 and 2002. A total of 585 E. superba (including all 6 furcilia larval stages, juveniles, and adults) was analyzed after confirmation of species identification using a competitive multiplexed species-specific PCR (SS-PCR) reaction based on mitochondrial cytochrome oxidase I (mtCOI) sequences. The molecular markers used were allele frequencies at single nucleotide polymorphism (SNP) sites in the gene encoding mitochondrial Cytochrome b (cyt b). Four SNP sites that showed desirable patterns of allelic variation were selected; alleles were detected using a multiplexed single-base extension PCR protocol. A total of 22 SNP haplotypes (i.e., strings of polymorphisms at the four SNP sites) was observed; haplotype diversity (Hd)=0.811 (s.d.=0.008). Analysis of molecular variation within and among samples, areas (i.e., Marguerite Bay, Crystal Sound, shelf, and offshore) and collection years revealed no difference between 2001 and 2002 collections overall, although differences between 2001 and 2002 collections from Marguerite Bay explained 7.4% of the variance ( FST=0.072; p=0.002±0.001). Most of the variation (96.3%) occurred within samples each year, with no significant differentiation among areas. There was small, but significant differentiation among samples within areas in 2001 (4.6%; FST=0.045; p=0.015±0

  12. Benthic Epiphytic Diatoms in Deep-sea Southern Ocean Sediments as a New Tool for Reconstructing Antarctic Paleoclimatic and Paleoceanographic History: Implications of Floating 'Macroalgal Biotic Oases'

    NASA Astrophysics Data System (ADS)

    Harwood, D. M.; Porter, N.; OConnell, S.

    2014-12-01

    A new paleobiological proxy for Antarctic paleoclimate history provides insight into past extent of open marine shelves on Wilkes Land margin, and calls for reassessment of IRD interpretations in the deep-sea. Marine, epiphytic benthic diatoms that grow attached to macroalgae (seaweed) are recovered in Miocene sediment from DSDP Site 269. They suggest periodic presence of floating rafts or 'biotic oases' in the Southern Ocean comprising buoyant macroalgae, attached benthic diatoms, and biota associated with this displaced coastal community. Macroalgae attach to the substrate with a holdfast, a multi-fingered structure that serves as an anchor. Uprooted holdfasts attached to buoyant macroalgae can raft sedimentary particles, some large (>50 kg), into the deep-sea. In addition, a rich biota of associated invertebrates live in cavities within the holdfast, the dispersal of which may explain the biogeographic distribution of organisms on Subantarctic islands. The stratigraphic occurrence of large, benthic epiphytic diatoms of genera Arachnoidiscus, Isthmia, Rhabdonema, Gephyra, Trigonium, and smaller Achnanthes, Cocconeis, Grammatophora, and Rhaphoneis in sediment cores from DSDP Site 269 reflect a rich, productive epiphytic diatom flora that maintained its position in the photic zone attached to their buoyant seaweed hosts. Amphipods and other herbivores grazed the benthic diatoms and produced diatom-rich fecal pellets that were delivered to the sea-floor. The discontinuous stratigraphic occurrence of the epiphytic diatoms, amongst the background of planktonic diatoms in Core 9 of DSDP Site 269, suggests environmental changes induced by either warm or cold events may have controlled the production and/or release of the macroalgae into the deep-sea. Warm events led to increased shelf areas, and cold events led to formation of ice on the macroalgae to increase their buoyancy and lift-off. Complicating the distinction between warm and cold events is the potential for the

  13. Antarctic glaciation caused ocean circulation changes at the Eocene-Oligocene transition.

    PubMed

    Goldner, A; Herold, N; Huber, M

    2014-07-31

    Two main hypotheses compete to explain global cooling and the abrupt growth of the Antarctic ice sheet across the Eocene-Oligocene transition about 34 million years ago: thermal isolation of Antarctica due to southern ocean gateway opening, and declining atmospheric CO2 (refs 5, 6). Increases in ocean thermal stratification and circulation in proxies across the Eocene-Oligocene transition have been interpreted as a unique signature of gateway opening, but at present both mechanisms remain possible. Here, using a coupled ocean-atmosphere model, we show that the rise of Antarctic glaciation, rather than altered palaeogeography, is best able to explain the observed oceanographic changes. We find that growth of the Antarctic ice sheet caused enhanced northward transport of Antarctic intermediate water and invigorated the formation of Antarctic bottom water, fundamentally reorganizing ocean circulation. Conversely, gateway openings had much less impact on ocean thermal stratification and circulation. Our results support available evidence that CO2 drawdown--not gateway opening--caused Antarctic ice sheet growth, and further show that these feedbacks in turn altered ocean circulation. The precise timing and rate of glaciation, and thus its impacts on ocean circulation, reflect the balance between potentially positive feedbacks (increases in sea ice extent and enhanced primary productivity) and negative feedbacks (stronger southward heat transport and localized high-latitude warming). The Antarctic ice sheet had a complex, dynamic role in ocean circulation and heat fluxes during its initiation, and these processes are likely to operate in the future. PMID:25079555

  14. The Future of Southern Ocean Observing Systems

    NASA Astrophysics Data System (ADS)

    Talley, L. D.

    2015-12-01

    Knowledge of the Southern Ocean's role in global climate from seasonal to millennial timescales is evolving, with rapidly increasing recognition of the centrality of the Southern Ocean to Earth's heat, carbon, nutrient, and freshwater budgets, and of the impact of interactions between the ocean and the major ice shelves and grounded ice sheets of Antarctica, which have been decreasing in mass. Observations in this data-sparse and logistically remote region have never been so important, and many nations are rising to the challenge of supporting both experiments and long-term sustained observations. As illustrated in the figure from Meredith et al. (Current Op. Env. Sustain. 2013), autonomous in situ technologies are at the fore because of the difficulty and expense of sending ships year-round and because the crucial satellite remote sensing must be accompanied by in situ observations, including beneath sea ice and ice shelves. The Southern Ocean Observing System (SOOS) has grown out of this recognized need for coordinated observations from the Antarctic coastline northward to the subtropics, from the bottom water production regions in coastal polynyas over the continental shelves, to the regions of interaction of warm ocean waters with Antarctic ice shelves, beneath the vast seasonal sea ice region, and in the hot spots of air-sea fluxes and cross-Antarctic Circumpolar Current (ACC) mixing where the ACC interacts with topography and continental boundaries. The future includes international coordination and collaboration and strengthening of new and existing technologies, which include satellite observing, ice-enabled profiling floats, profiling from marine mammals, moored measurements in many strategic locations, glider and other autonomous operations in all regions, and drilling through floating ice shelves to measure the ocean waters below. Improved and consistent weather observations around the Antarctic coastlines will improve forecasting and reanalysis. Ice

  15. Fate of Polycyclic Aromatic Hydrocarbons in Seawater from the Western Pacific to the Southern Ocean (17.5°N to 69.2°S) and Their Inventories on the Antarctic Shelf.

    PubMed

    Cai, Minggang; Liu, Mengyang; Hong, Qingquan; Lin, Jing; Huang, Peng; Hong, Jiajun; Wang, Jun; Zhao, Wenlu; Chen, Meng; Cai, Minghong; Ye, Jun

    2016-09-01

    Semivolatile organic compounds such as polycyclic aromatic hydrocarbons (PAHs) have the potential to reach pristine environments through long-range transport. To investigate the long-range transport of the PAHs and their fate in Antarctic seawater, dissolved PAHs in the surface waters from the western Pacific to the Southern Ocean (17.5°N to 69.2°S), as well as down to 3500 m PAH profiles in Prydz Bay and the adjacent Southern Ocean, were observed during the 27th Chinese National Antarctic Research Expedition in 2010. The concentrations of Σ9PAH in the surface seawater ranged from not detected (ND) to 21 ng L(-1), with a mean of 4.3 ng L(-1); and three-ring PAHs were the most abundant compounds. Samples close to the Australian mainland displayed the highest levels across the cruise. PAHs originated mainly from pyrogenic sources, such as grass, wood, and coal combustion. Vertical profiles of PAHs in Prydz Bay showed a maximum at a depth of 50 m and less variance with depth. In general, we inferred that the water masses as well as the phytoplankton were possible influencing factors on PAH surface-enrichment depth-depletion distribution. Inventory estimation highlighted the contribution of intermediate and deep seawater on storing PAHs in seawater from Prydz Bay, and suggested that climate change rarely shows the rapid release of the PAHs currently stored in the major reservoirs (intermediate and deep seawater). PMID:27509536

  16. Southern Ocean Response to NADW Changes

    NASA Technical Reports Server (NTRS)

    Rind, David; Schmidt, G.; Russell, G.; deMenocal, P.; Hansen, James E. (Technical Monitor)

    2000-01-01

    The possibility of North Atlantic Deep Water (NADW) changes in both past and future climates has raised the issue of how the Southern Ocean would respond. Recent experiments with the GISS coupled atmosphere-ocean model have shown that a "bipolar see-saw" between NADW production and Antarctic Bottom Water (AABW) production in the Weddell Sea can occur in conjunction with freshening of the North Atlantic. However, this effect operates not through a slow ocean response but via a rapid atmospheric mechanism. As NADW reduces, colder temperatures in the North Atlantic, and Northern Hemisphere in general, are associated with higher surface pressure (increased atmospheric mass). Reduced mass in the Southern Hemisphere occurs in response, with lower pressure over the South Pole (an EOF #1 effect, the "high phase" of the Antarctic Oscillation).The lower pressure is associated with stronger west winds that generate an intensified Antarctic Circumpolar Current (ACC), which leads to longitudinal heat divergence in the South Atlantic (and heat convergence in the Southern Indian Ocean). Colder temperatures in the Weddell Sea region lead to sea ice growth, increased salinity and surface water density, and greater Weddell Sea Bottom Water production. Increased poleward transport of heat occurs in the South Atlantic in conjunction with increased bottom water production, but its convergence at high latitudes is not sufficient to offset the longitudinal heat divergence due to the intensified ACC. The colder temperatures at high latitudes in the South Atlantic increase the latitudinal temperature gradient, baroclinic instability, eddy energy and eddy poleward transport of momentum, helping to maintain the lower pressure over the pole in an interactive manner. The heat flux convergence in the Indian Ocean provides a warming tendency in that region, and overall global production of AABW remains unchanged. These results have implications for the interpretation of the ice core records of

  17. Warming of the Southern Ocean since the 1950s.

    PubMed

    Gille, Sarah T

    2002-02-15

    Autonomous Lagrangian Circulation Explorer floats recorded temperatures in depths between 700 and 1100 meters in the Southern Ocean throughout the 1990s. These temperature records are systematically warmer than earlier hydrographic temperature measurements from the region, suggesting that mid-depth Southern Ocean temperatures have risen 0.17 degrees C between the 1950s and the 1980s. This warming is faster than that of the global ocean and is concentrated within the Antarctic Circumpolar Current, where temperature rates of change are comparable to Southern Ocean atmospheric temperature increases. PMID:11847337

  18. Abundant Hydrothermal Venting in the Southern Ocean Near 62°S/159°E on the Australian-Antarctic Ridge

    NASA Astrophysics Data System (ADS)

    Baker, E. T.; Hahm, D.; Rhee, T. S.; Park, S. H.; Lupton, J. E.; Walker, S. L.; Choi, H.

    2014-12-01

    Circum-Antarctic Ridges (CARs) comprise almost one-third of the global Mid-Ocean Ridge, yet remain terra incognita for hydrothermal activity and chemosynthetic ecosystems. The InterRidge Vents Database lists only 3 confirmed (visualized) and 35 inferred (plume evidence) active sites along the ~21,000 km of CARs. Here, we report on a multi-year effort to locate and characterize hydrothermal activity on two 1st-order segments of the Australian-Antarctic Ridge that are perhaps more isolated from other known vent fields than any other vent site on the Mid-Ocean Ridge. KR1 is a 300-km-long segment near 62°S/159°E, and KR2 a 90-km-long segment near 60°S/152.5°E. We used profiles collected by Miniature Autonomous Plume Recorders (MAPRs) on rock corers in March and December of 2011 to survey each segment, and an intensive CTD survey in Jan/Feb 2013 to pinpoint sites and sample plumes on KR1. Optical and oxidation-reduction potential (ORP, aka Eh) anomalies indicate multiple active sites on both segments. Seven profiles on KR2 found 3 sites, each separated by ~25 km. Forty profiles on KR1 identified 13 sites, some within a few km of each other. The densest site concentration on KR1 occurred along a relatively inflated, 90-km-long section near the segment center. CTD tows covered 20 km of the eastern, most inflated portion of this area, finding two 6-km-long zones centered near 158.6°E and 158.8°E with multiple plume anomalies. Three ORP anomalies within 50 m of the seafloor indicate precise venting locations. We call this area the Mujin "Misty Harbor" vent field. Vent frequency sharply decreases away from Mujin. 3He/heat ratios determined from 20 plume samples in the Mujin field were mostly <0.015 fM/J, indicative of chronic venting, but 3 samples, 0.021-0.034 fM/J, are ratios typical of a recent eruption. The spatial density of hydrothermal activity along KR1 and KR2 is similar to other intermediate-rate spreading ridges. We calculate the plume incidence (ph) along

  19. Ecological importance of the Southern Boundary of the Antarctic Circumpolar Current

    NASA Astrophysics Data System (ADS)

    Tynan, Cynthia T.

    1998-04-01

    The Southern Ocean surrounds the Antarctic continent and supports one of the most productive marine ecosystems. Migratory and endemic species of whales, seals and birds benefit from the high biomass of their principal prey, krill (Euphausia superba) and cephalopods, in this area. Most species of baleen whales and male sperm whales in the Southern Hemisphere migrate between low-latitude breeding grounds in winter and highly productive Antarctic feeding grounds in summer. Here I show the importance of the southernmost reaches of the strongest ocean current, the Antarctic Circumpolar Current (ACC), to a complex and predictable food web of the Southern Ocean. The circumpolar distributions of blue, fin and humpback whales from spring to midsummer trace the non-uniform high-latitude penetration of shoaled, nutrient-rich Upper Circumpolar Deep Water, which is carried eastward by the ACC. The poleward extent of this water mass delineates the Southern Boundary of the ACC and corresponds not only to the circumpolar distributions of baleen whales, but also to distributions of krill and to regions of high, seasonally averaged, phytoplankton biomass. Sperm whales, which feed on cephalopods, also congregate in highest densities near the Southern Boundary. The association of primary production, Krill, and whales with the Southern Boundary, suggests that it provides predictably productive foraging for many species, and is of critical importance to the function of the Southern Ocean ecosystem.

  20. Primary production in Southern Ocean waters

    NASA Astrophysics Data System (ADS)

    Arrigo, Kevin R.; Worthen, Denise; Schnell, Anthony; Lizotte, Michael P.

    1998-07-01

    The Southern Ocean forms a link between major ocean basins, is the site of deep and intermediate water ventilation, and is one of the few areas where macronutrients are underutilized by phytoplankton. Paradoxically, prior estimates of annual primary production are insufficient to support the Antarctic food web. Here we present results from a primary production algorithm based upon monthly climatological phytoplankton pigment concentrations from the coastal zone color scanner (CZCS). Phytoplankton production was forced using monthly temperature profiles and a radiative transfer model that computed changes in photosynthetically usable radiation at each CZCS pixel location. Average daily productivity (g C m-2 d-1) and total monthly production (Tg C month-1) were calculated for each of five geographic sectors (defined by longitude) and three ecological provinces (defined by sea ice coverage and bathymetry as the pelagic province, the marginal ice zone, and the shelf). Annual primary production in the Southern Ocean (south of 50°S) was calculated to be 4414 Tg C yr-1, 4-5 times higher than previous estimates made from in situ data. Primary production was greatest in the month of December (816 Tg C month-1) and in the pelagic province (contributing 88.6% of the annual primary production). Because of their small size the marginal ice zone (MIZ) and the shelf contributed only 9.5% and 1.8%, respectively, despite exhibiting higher daily production rates. The Ross Sea was the most productive region, accounting for 28% of annual production. The fourfold increase in the estimate of primary production for the Southern Ocean likely makes the notion of an "Antarctic paradox" (primary production insufficient to support the populations of Southern Ocean grazers, including krill, copepods, microzooplankton, etc.) obsolete.

  1. Recent Changes in the Ventilation of the Southern Oceans

    NASA Astrophysics Data System (ADS)

    Waugh, Darryn W.; Primeau, Francois; DeVries, Tim; Holzer, Mark

    2013-02-01

    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, and there is intense debate on the impact of this on the ocean's circulation and uptake and redistribution of atmospheric gases. We used measurements of chlorofluorocarbon-12 (CFC-12) made in the southern oceans in the early 1990s and mid- to late 2000s to examine changes in ocean ventilation. Our analysis of the CFC-12 data reveals a decrease in the age of subtropical subantarctic mode waters and an increase in the age of circumpolar deep waters, suggesting that the formation of the Antarctic ozone hole has caused large-scale coherent changes in the ventilation of the southern oceans.

  2. Recent changes in the ventilation of the southern oceans.

    PubMed

    Waugh, Darryn W; Primeau, Francois; Devries, Tim; Holzer, Mark

    2013-02-01

    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, and there is intense debate on the impact of this on the ocean's circulation and uptake and redistribution of atmospheric gases. We used measurements of chlorofluorocarbon-12 (CFC-12) made in the southern oceans in the early 1990s and mid- to late 2000s to examine changes in ocean ventilation. Our analysis of the CFC-12 data reveals a decrease in the age of subtropical subantarctic mode waters and an increase in the age of circumpolar deep waters, suggesting that the formation of the Antarctic ozone hole has caused large-scale coherent changes in the ventilation of the southern oceans. PMID:23372011

  3. On the birth of near-modern Southern Ocean ecosystems

    NASA Astrophysics Data System (ADS)

    Houben, A.; Bohaty, S. M.; Passchier, S.; Roehl, U.; Bijl, P.; Pross, J.; Stickley, C. E.; van de Flierdt, T.; Escutia, C.; Klaus, A.; Brinkhuis, H.

    2011-12-01

    It has become widely appreciated that the initiation of major Antarctic glaciation occurred around Eocene - Oligocene boundary times (~34-33 Ma). Some studies suggest that this greenhouse-icehouse transition (GIT) invoked a more productive Southern Ocean and therefore circum-Antarctic marine systems as a result of e.g., increased wind-stress and upwelling after ice-sheet arrival and related atmospheric reorganization. Yet, actual documentation of such presumed major reorganization among plankton communities in the Southern Ocean is quite limited. This is partly due to scarce and incomplete records, and/or lack of suitable plankton remains for various reasons. Principally on the basis of the recent Integrated Ocean Drilling Program Expedition 318, drilling of the Wilkes Land margin, and in context with studies into e.g., XRF-geochemistry, ice rafted debris, and clay mineralogy, we here discuss late Eocene to early Oligocene dinoflagellate cyst assemblage changes related to the GIT, and compare results with several other circum-Antarctic sites. Conspicuously, the earliest Oligocene circum-Antarctic dinoflagellate cyst assemblages are consistently dominated by protoperidinioid taxa, in sharp contrast to the Eocene assemblages. Extant protoperidinioid dinoflagellates have a heterotrophic feeding strategy, are therefore found in association with high productivity ecosystems, and particularly dominate modern southern ocean settings. Combined results indicate the birth of near modern circum-Antarctic marine ecosystems to coincide with the GIT.

  4. Dynamic thinning of glaciers on the Southern Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Wouters, B.; Martin-Español, A.; Helm, V.; Flament, T.; van Wessem, J. M.; Ligtenberg, S. R. M.; van den Broeke, M. R.; Bamber, J. L.

    2015-05-01

    Growing evidence has demonstrated the importance of ice shelf buttressing on the inland grounded ice, especially if it is resting on bedrock below sea level. Much of the Southern Antarctic Peninsula satisfies this condition and also possesses a bed slope that deepens inland. Such ice sheet geometry is potentially unstable. We use satellite altimetry and gravity observations to show that a major portion of the region has, since 2009, destabilized. Ice mass loss of the marine-terminating glaciers has rapidly accelerated from close to balance in the 2000s to a sustained rate of -56 ± 8 gigatons per year, constituting a major fraction of Antarctica’s contribution to rising sea level. The widespread, simultaneous nature of the acceleration, in the absence of a persistent atmospheric forcing, points to an oceanic driving mechanism.

  5. Spatial Patterns of Variability in Antarctic Surface Temperature: Connections to the Southern Hemisphere Annular Mode and the Southern Oscillation

    NASA Technical Reports Server (NTRS)

    Kwok, Ron; Comiso, Josefino C.; Koblinsky, Chester J. (Technical Monitor)

    2002-01-01

    The 17-year (1982-1998) trend in surface temperature shows a general cooling over the Antarctic continent, warming of the sea ice zone, with moderate changes over the oceans. Warming of the peripheral seas is associated with negative trends in the regional sea ice extent. Effects of the Southern Hemisphere Annular Mode (SAM) and the extrapolar Southern Oscillation (SO) on surface temperature are quantified through regression analysis. Positive polarities of the SAM are associated with cold anomalies over most of Antarctica, with the most notable exception of the Antarctic Peninsula. Positive temperature anomalies and ice edge retreat in the Pacific sector are associated with El Nino episodes. Over the past two decades, the drift towards high polarity in the SAM and negative polarity in the SO indices couple to produce a spatial pattern with warmer temperatures in the Antarctic Peninsula and peripheral seas, and cooler temperatures over much of East Antarctica.

  6. Observations of change in the Southern Ocean.

    PubMed

    Jacobs, Stan

    2006-07-15

    The Southern Ocean has been in a state of disequilibrium with its atmosphere and cryosphere during recent decades. Ocean station and drifting float observations have revealed rising temperatures in the upper 3000m. Salinity has declined in intermediate waters and more rapidly in the sparsely sampled high latitudes. Dissolved oxygen levels may also have decreased, but measurement accuracy is inconsistent. Sea ice area increased from 1979 to 1998, particularly in the Ross Sea, while a decline in ice extent since the early 1970s has been led by the Amundsen-Bellingshausen sector. Fresher waters with lower oxygen isotope content on the Pacific-Antarctic continental shelf are consistent with increased melting of continental ice. Newly forming bottom water has become colder and less salty downstream from that region, but generally warmer in the Weddell Sea. Many ice shelves have retreated or thinned, but others have grown and no trend is apparent in the large iceberg calving rate. Warming and isotherm shoaling within the polar gyres may result in part from changes in the Southern Annular Mode, which could facilitate deep-water access to the continental shelves. Sea-level rise over the past half century has a strong eustatic component and has recently accelerated. Observations over longer periods and with better spatial coverage are needed to better understand the processes causing these changes and their links to the Antarctic ice sheet. PMID:16782605

  7. The Southern Ocean CIRCLE initiative

    NASA Astrophysics Data System (ADS)

    Murphy, E. J.; Ellis-Evans, J. C.

    2003-04-01

    The circumpolar Southern Ocean is the principal ocean connection between the Atlantic, Pacific and Indian Oceans, and exerts a profound influence on world climate through ocean circulation and its major role in the global carbon cycle. It is a major repository of biodiversity and also the only ocean system where significant marine living resources are yet to be fully exploited. However, this key component of the Earth System is still poorly understood, in part due to the logistical problems of a harsh, remote location and the circumpolar nature of the environment. Circumpolar patterns of variability have now been recognized and the current challenge is to understand how, at a circumpolar scale, this variability is generated, its impact on the regional biogeochemical cycles, its interaction with ecosystem processes and the links to global scale processes. Many of these scientific issues can only be addressed by Southern Ocean scale studies, and although a range of national and international research programmes are already targeting particular aspects, the research effort is largely uncoordinated. The European Polar Board is sponsoring a pan-European initiative (Southern Ocean CIRCLE) to coordinate the currently disparate Southern Ocean research effort and this initiative aims to address climate variability, biogeochemical cycling and ecosystem dynamics with particular reference to the links between these aspects in the circumpolar Southern Ocean. This poster outlines the development of the SO CIRCLE initiative, the major areas of science and proposals for implementation. It also outlines how SO CIRCLE will link to other programmes with a Southern Ocean component (e.g. CLIVAR, CliC, GLOBEC, SOLAS). A key aspect of the initiative will be to coordinate European scientific effort in the Southern Ocean with that of the wider international community.

  8. Southern Ocean warming delayed by circumpolar upwelling and equatorward transport

    NASA Astrophysics Data System (ADS)

    Armour, Kyle C.; Marshall, John; Scott, Jeffery R.; Donohoe, Aaron; Newsom, Emily R.

    2016-07-01

    The Southern Ocean has shown little warming over recent decades, in stark contrast to the rapid warming observed in the Arctic. Along the northern flank of the Antarctic Circumpolar Current, however, the upper ocean has warmed substantially. Here we present analyses of oceanographic observations and general circulation model simulations showing that these patterns--of delayed warming south of the Antarctic Circumpolar Current and enhanced warming to the north--are fundamentally shaped by the Southern Ocean's meridional overturning circulation: wind-driven upwelling of unmodified water from depth damps warming around Antarctica; greenhouse gas-induced surface heat uptake is largely balanced by anomalous northward heat transport associated with the equatorward flow of surface waters; and heat is preferentially stored where surface waters are subducted to the north. Further, these processes are primarily due to passive advection of the anomalous warming signal by climatological ocean currents; changes in ocean circulation are secondary. These findings suggest the Southern Ocean responds to greenhouse gas forcing on the centennial, or longer, timescale over which the deep ocean waters that are upwelled to the surface are warmed themselves. It is against this background of gradual warming that multidecadal Southern Ocean temperature trends must be understood.

  9. Water masses, ocean fronts, and the structure of Antarctic seabird communities: putting the eastern Bellingshausen Sea in perspective

    USGS Publications Warehouse

    Ribic, Christine A.; Ainley, David G.; Ford, R. Glenn; Fraser, William R.; Tynan, Cynthia T.; Woehler, Eric J.

    2015-01-01

    Waters off the western Antarctic Peninsula (i.e., the eastern Bellingshausen Sea) are unusually complex owing to the convergence of several major fronts. Determining the relative influence of fronts on occurrence patterns of top-trophic species in that area, therefore, has been challenging. In one of the few ocean-wide seabird data syntheses, in this case for the Southern Ocean, we analyzed ample, previously collected cruise data, Antarctic-wide, to determine seabird species assemblages and quantitative relationships to fronts as a way to provide context to the long-term Palmer LTER and the winter Southern Ocean GLOBEC studies in the eastern Bellingshausen Sea. Fronts investigated during both winter (April–September) and summer (October–March) were the southern boundary of the Antarctic Circumpolar Current (ACC), which separates the High Antarctic from the Low Antarctic water mass, and within which are embedded the marginal ice zone and Antarctic Shelf Break Front; and the Antarctic Polar Front, which separates the Low Antarctic and the Subantarctic water masses. We used clustering to determine species' groupings with water masses, and generalized additive models to relate species' densities, biomass and diversity to distance to respective fronts. Antarctic-wide, in both periods, highest seabird densities and lowest species diversity were found in the High Antarctic water mass. In the eastern Bellingshausen, seabird density in the High Antarctic water mass was lower (as low as half that of winter) than found in other Antarctic regions. During winter, Antarctic-wide, two significant species groups were evident: one dominated by Adélie penguins (Pygoscelis adeliae) (High Antarctic water mass) and the other by petrels and prions (no differentiation among water masses); in eastern Bellingshausen waters during winter, the one significant species group was composed of species from both Antarctic-wide groups. In summer, Antarctic-wide, a High Antarctic group

  10. Water masses, ocean fronts, and the structure of Antarctic seabird communities: putting the eastern Bellingshausen Sea in perspective

    USGS Publications Warehouse

    Ribic, Christine A.; Ainley, David G.; Ford, R. Glenn; Fraser, William R.; Tynan, Cynthia T.; Woehler, Eric J.

    2011-01-01

    Waters off the western Antarctic Peninsula (i.e., the eastern Bellingshausen Sea) are unusually complex owing to the convergence of several major fronts. Determining the relative influence of fronts on occurrence patterns of top-trophic species in that area, therefore, has been challenging. In one of the few ocean-wide seabird data syntheses, in this case for the Southern Ocean, we analyzed ample, previously collected cruise data, Antarctic-wide, to determine seabird species assemblages and quantitative relationships to fronts as a way to provide context to the long-term Palmer LTER and the winter Southern Ocean GLOBEC studies in the eastern Bellingshausen Sea. Fronts investigated during both winter (April–September) and summer (October–March) were the southern boundary of the Antarctic Circumpolar Current (ACC), which separates the High Antarctic from the Low Antarctic water mass, and within which are embedded the marginal ice zone and Antarctic Shelf Break Front; and the Antarctic Polar Front, which separates the Low Antarctic and the Subantarctic water masses. We used clustering to determine species' groupings with water masses, and generalized additive models to relate species' densities, biomass and diversity to distance to respective fronts. Antarctic-wide, in both periods, highest seabird densities and lowest species diversity were found in the High Antarctic water mass. In the eastern Bellingshausen, seabird density in the High Antarctic water mass was lower (as low as half that of winter) than found in other Antarctic regions. During winter, Antarctic-wide, two significant species groups were evident: one dominated by Adélie penguins (Pygoscelis adeliae) (High Antarctic water mass) and the other by petrels and prions (no differentiation among water masses); in eastern Bellingshausen waters during winter, the one significant species group was composed of species from both Antarctic-wide groups. In summer, Antarctic-wide, a High Antarctic group

  11. Water masses, ocean fronts, and the structure of Antarctic seabird communities: Putting the eastern Bellingshausen Sea in perspective

    NASA Astrophysics Data System (ADS)

    Ribic, Christine A.; Ainley, David G.; Glenn Ford, R.; Fraser, William R.; Tynan, Cynthia T.; Woehler, Eric J.

    2011-07-01

    Waters off the western Antarctic Peninsula (i.e., the eastern Bellingshausen Sea) are unusually complex owing to the convergence of several major fronts. Determining the relative influence of fronts on occurrence patterns of top-trophic species in that area, therefore, has been challenging. In one of the few ocean-wide seabird data syntheses, in this case for the Southern Ocean, we analyzed ample, previously collected cruise data, Antarctic-wide, to determine seabird species assemblages and quantitative relationships to fronts as a way to provide context to the long-term Palmer LTER and the winter Southern Ocean GLOBEC studies in the eastern Bellingshausen Sea. Fronts investigated during both winter (April-September) and summer (October-March) were the southern boundary of the Antarctic Circumpolar Current (ACC), which separates the High Antarctic from the Low Antarctic water mass, and within which are embedded the marginal ice zone and Antarctic Shelf Break Front; and the Antarctic Polar Front, which separates the Low Antarctic and the Subantarctic water masses. We used clustering to determine species' groupings with water masses, and generalized additive models to relate species' densities, biomass and diversity to distance to respective fronts. Antarctic-wide, in both periods, highest seabird densities and lowest species diversity were found in the High Antarctic water mass. In the eastern Bellingshausen, seabird density in the High Antarctic water mass was lower (as low as half that of winter) than found in other Antarctic regions. During winter, Antarctic-wide, two significant species groups were evident: one dominated by Adélie penguins ( Pygoscelis adeliae) (High Antarctic water mass) and the other by petrels and prions (no differentiation among water masses); in eastern Bellingshausen waters during winter, the one significant species group was composed of species from both Antarctic-wide groups. In summer, Antarctic-wide, a High Antarctic group dominated

  12. Southern Ocean Iron Experiment (SOFex)

    SciTech Connect

    Coale, Kenneth H.

    2005-07-28

    The Southern Ocean Iron Experiment (SOFeX) was an experiment decades in the planning. It's implementation was among the most complex ship operations that SIO has been involved in. The SOFeX field expedition was successful in creating and tracking two experimentally enriched areas of the Southern Ocean, one characterized by low silicic acid, one characterized by high silicic acid. Both experimental sites were replete with abundant nitrate. About 100 scientists were involved overall. The major findings of this study were significant in several ways: (1) The productivity of the southern ocean is limited by iron availability. (2) Carbon uptake and flux is therefore controlled by iron availability (3) In spite of low silicic acid, iron promotes non-silicious phytoplankton growth and the uptake of carbon dioxide. (4) The transport of fixed carbon from the surface layers proceeds with a C:N ratio that would indicate differential remineralization of nitrogen at shallow depths. (5) These finding have major implications for modeling of carbon export based on nitrate utilization. (6) The general results of the experiment indicate that, beyond other southern ocean enrichment experiments, iron inputs have a much wider impact of productivity and carbon cycling than previously demonstrated. Scientific presentations: Coale, K., Johnson, K, Buesseler, K., 2002. The SOFeX Group. Eos. Trans. AGU 83(47) OS11A-0199. Coale, K., Johnson, K. Buesseler, K., 2002. SOFeX: Southern Ocean Iron Experiments. Overview and Experimental Design. Eos. Trans. AGU 83 (47) OS22D-01. Buesseler, K.,et al. 2002. Does Iron Fertilization Enhance Carbon Sequestration? Particle flux results from the Southern Ocean Iron Experiment. Eos. Trans. AGU 83 (47), OS22D-09. Johnson, K. et al. 2002. Open Ocean Iron Fertilization Experiments From IronEx-I through SOFeX: What We Know and What We Still Need to Understand. Eos. Trans. AGU 83 (47), OS22D-12. Coale, K. H., 2003. Carbon and Nutrient Cycling During the Southern

  13. Modeling the coupled ocean-katabatic wind systems of the Antarctic

    SciTech Connect

    McNider, R.T.; Goodrick, S.L.

    1994-12-31

    The wind stress distribution along the periphery of the antarctic continent is like no other place on Earth. A large easterly component near the coast is evidently attributable to the geostrophic adjustment of the katabatic winds driven by the cold antarctic plateau. The large curl between these topographically driven easterlies and the strong Southern Hemispheric westerlies may have a significant role in the upwelling and associated biological productivity of the southern oceans. The direct downslope databatic flows and their alongshore adjustment may have also have significance to polynya development, bottom-water formation, and the maintenance of the coastal currents including the East Wind Drift. This paper reports on preliminary model studies of the coupling between antarctic katabatic flows and the coastal ocean. Although considerable past work in coupling large-scale and low-order ocean/atmosphere models has been done, relatively less work on coupling true mesoscale multidimensional models containing high-resolution boundary layers has been under taken. The following describes a coupled atmosphere/ocean model which has been developed by McNider from the frameworks of a mesoscale atmospheric model and a coastal ocean model. 9 refs., 3 figs.

  14. Impacts of Atmosphere-Ocean Coupling on Southern Hemisphere Climate Change

    NASA Technical Reports Server (NTRS)

    Li, Feng; Newman, Paul; Pawson, Steven

    2013-01-01

    Climate in the Southern Hemisphere (SH) has undergone significant changes in recent decades. These changes are closely linked to the shift of the Southern Annular Mode (SAM) towards its positive polarity, which is driven primarily by Antarctic ozone depletion. There is growing evidence that Antarctic ozone depletion has significant impacts on Southern Ocean circulation change. However, it is poorly understood whether and how ocean feedback might impact the SAM and climate change in the SH atmosphere. This outstanding science question is investigated using the Goddard Earth Observing System Coupled Atmosphere-Ocean-Chemistry Climate Model(GEOS-AOCCM).We perform ensemble simulations of the recent past (1960-2010) with and without the interactive ocean. For simulations without the interactive ocean, we use sea surface temperatures and sea ice concentrations produced by the interactive ocean simulations. The differences between these two ensemble simulations quantify the effects of atmosphere-ocean coupling. We will investigate the impacts of atmosphere-ocean coupling on stratospheric processes such as Antarctic ozone depletion and Antarctic polar vortex breakup. We will address whether ocean feedback affects Rossby wave generation in the troposphere and wave propagation into the stratosphere. Another focuson this study is to assess how ocean feedback might affect the tropospheric SAM response to Antarctic ozone depletion

  15. Cadmium isotope variations in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Xue, Zichen; Rehkämper, Mark; Horner, Tristan J.; Abouchami, Wafa; Middag, Rob; van de Flierd, Tina; de Baar, Hein J. W.

    2013-11-01

    Cadmium concentrations and isotope compositions were determined for 47 seawater samples from the high nutrient low chlorophyll (HNLC) zone of the Atlantic sector of the Southern Ocean. The samples include 13 surface waters from a transect of the Weddell Gyre and 3 depth profiles from the Weddell Sea and Drake Passage. The Southern Ocean mixed layer samples from this study and Abouchami et al. (2011) define a clear but broad ‘HNLC trend’ in a plot of εCd114/110 versus [Cd], which is primarily a consequence of isotopic fractionation associated with biological uptake (εCd114/110 is the deviation of the 114Cd/110Cd ratio of a sample from NIST SRM 3108 Cd in parts per 10,000). The trend is especially apparent in comparison to the large range of values shown by a global set of seawater Cd data for shallow depths. The Southern Ocean samples are also distinguished by their relatively high Cd concentrations (typically 0.2 to 0.6 nmol/kg) and moderately fractionated εCd114/110 (generally between +4 and +8) that reflect the limited biological productivity of this region. Detailed assessment reveals fine structure within the ‘HNLC trend’, which may record differences in the biological fractionation factor, different scenarios of closed and open system isotope fractionation, and/or distinct source water compositions. Southern Ocean seawater from depths ⩾1000 m has an average εCd114/110 of +2.5±0.2 (2se, n=16), and together with previous results this establishes a relatively constant εCd114/110 value of +3.0±0.3 (2se, n=27) for global deep waters. Significant isotopic variability was observed at intermediate depths in the Southern Ocean. Seawater from 200 m to 400 m in Weddell Sea has high Cd concentrations and εCd114/110 as low as +1, presumably due to remineralization of Cd from biomass that records incomplete nutrient utilization. Antarctic Intermediate Water, which was sampled at 150 to 750 m depth in the Drake Passage, features a distinct Cd isotope

  16. Atmosphere-ocean interactions in the Pacific Southern Ocean

    NASA Astrophysics Data System (ADS)

    Lamy, F.; Gersonde, R.; Purcell, C.; Winckler, G.; Tiedemann, R.; Knorr, G.

    2014-12-01

    Atmosphere-ocean interactions play an important role for understanding processes and feedbacks in the Southern Ocean (SO) that play a key role for explaining the variability in atmospheric CO2 concentrations. The most important atmospheric forcing at high and mid-latitudes of the Southern Hemisphere is the westerly wind belt which strongly impacts the strength and extension of the Antarctic Circumpolar Current (ACC), upwelling of deep-water masses, and also controls the back-flow of intermediate waters to the tropics. We combine sea surface temperature, current strength, and mineral dust proxy data from the Pacific SO including Drake Passage with climate model results. Our data show that Drake Passage throughflow was reduced and the ACC generally weakened during the last glacial. The reduced Drake Passage throughflow was accompanied by a pronounced northward extension of the Antarctic cold-water sphere in the Southeast Pacific sector and stronger export of surface and intermediate water into the South Pacific gyre. These oceanographic changes are consistent with reduced westerly winds within the modern maximum wind strength zone over the subantarctic ACC and reduced wind forcing due to extended sea-ice further south. Despite of reduced winds in the core of the westerlies, we observe 3-fold higher dust deposition during glacial periods in the Pacific SO. This observation may be explained by a combination of factors including more expanded arid dust source areas in Australia and a northward extent or enhancement of the westerlies over Southeast Australia during glacials that would plausibly increase the dust uptake and export into the Pacific SO. Such scenario would imply stronger westerlies at the present northernmost margin of the wind belt coeval with weaker core westerlies and reduced ACC strength including Drake Passage throughflow during glacials. These results have strong implications for the global meridional overturning circulation and the interbasin

  17. Ocean temperature thresholds for Last Interglacial West Antarctic Ice Sheet collapse

    NASA Astrophysics Data System (ADS)

    Sutter, Johannes; Gierz, Paul; Grosfeld, Klaus; Thoma, Malte; Lohmann, Gerrit

    2016-03-01

    The West Antarctic Ice Sheet (WAIS) is considered the major contributor to global sea level rise in the Last Interglacial (LIG) and potentially in the future. Exposed fossil reef terraces suggest sea levels in excess of 7 m in the last warm era, of which probably not much more than 2 m are considered to originate from melting of the Greenland Ice Sheet. We simulate the evolution of the Antarctic Ice Sheet during the LIG with a 3-D thermomechanical ice sheet model forced by an atmosphere-ocean general circulation model (AOGCM). Our results show that high LIG sea levels cannot be reproduced with the atmosphere-ocean forcing delivered by current AOGCMs. However, when taking reconstructed Southern Ocean temperature anomalies of several degrees, sensitivity studies indicate a Southern Ocean temperature anomaly threshold for total WAIS collapse of 2-3°C, accounting for a sea level rise of 3-4 m during the LIG. Potential future Antarctic Ice Sheet dynamics range from a moderate retreat to a complete collapse, depending on rate and amplitude of warming.

  18. Icecolors `93: Beginnings of an antarctic phytoplankton and bacterial DNA library from southern ocean natural communities exposed to ultraviolet-B

    SciTech Connect

    Jovine, R.V.M.; Prezelin, B.

    1994-12-31

    Springtime ozone depletion and the resultant increase in ultraviolet-B (UV-B) radiation [280-320 nanometers (nm)] have deleterious effects on primary productivity. To assess damage to cellular components other than the photosynthetic apparatus, we isolated total community DNA from samples in the field before, during, and after the 1993 springtime depletion in stratospheric ozone. The effort was motivated by the concern that the ozone-dependent increases in UV-B radiation may increase DNA damage within primary producers. This increase in damage could result in changes of species composition as well as hereditary changes within species that can influence the competitiveness of these organisms in their natural community. Previous studies have focused on DNA damage in isolated cultures of antarctic phytoplankton that were irradiated with UV-B under lab conditions. These studies clearly indicate variable species sensitivities to the increase in UV-B flux. These studies, however, did not resolve the question of whether such damage occurred in field samples collected from actively mixing, polyphyletic phytoplankton communities. Potential species composition changes and the resultant changes in the trophic dynamics cannot be interpreted in terms of DNA damage unless this damage can be documented in samples isolated under these dynamic natural conditions. 7 refs., 2 figs.

  19. Microwave remote sensing of the Southern Ocean ice cover

    NASA Astrophysics Data System (ADS)

    Comiso, Josefino C.; Grenfell, Thomas C.; Lange, Manfred; Lohanick, Alan W.; Moore, Richard K.; Wadhams, Peter

    The Southern Ocean sea ice cover grows dramatically to about 20 × 106 km2 in the spring and breaks up abruptly to about 4 × 106 km2 in the summer (e.g., Zwally et al. [1983b]). This makes it one of the most seasonally variable climate parameters on the surface of the globe. Compared to the Northern Hemisphere, the ice cover in the Southern Ocean is about 20% greater at its maximum extent [Comiso and Zwally, 1984; Gloersen and Campbell, 1988]. By virtue of its size alone, the impact of the Southern Ocean ice cover on the regional and global climate can be considerable, since sea ice drastically changes surface albedo and roughness and insulates the ocean from the atmosphere. Seasonal and interannual variations in the spatial distribution of sea ice also cause the redistribution of salts, which, in turn, cause changes in the vertical stratification of the ocean. Compared to the Arctic, the environmental geographical background for sea ice in the Antarctic is also very different. Land surrounds most of the southern limits of the Arctic ice cover, whereas in the Antarctic, there is no corresponding land boundary in the north. The Southern Ocean ice cover is more divergent since it is more vulnerable to dynamic forcing than its Arctic counterpart. Accurate estimation of the percentage of open water is important because heat and salinity fluxes increase considerably even with just small increases in the fraction of open water or new ice [Maykut, 1978; Allison, 1981]. These fluxes are, in turn, closely linked with bottom water formation, ocean circulation, and momentum exchange between the ocean and the atmosphere. Oceanic heat flux is also believed to be a major determinant of ice growth rate [Bagriantsev et. al., 1989].

  20. Volcanic time-markers for Marine Isotopic Stages 6 and 5 in Southern Ocean sediments and Antarctic ice cores: implications for tephra correlations between palaeoclimatic records

    NASA Astrophysics Data System (ADS)

    Hillenbrand, C.-D.; Moreton, S. G.; Caburlotto, A.; Pudsey, C. J.; Lucchi, R. G.; Smellie, J. L.; Benetti, S.; Grobe, H.; Hunt, J. B.; Larter, R. D.

    2008-03-01

    Three megascopic and disseminated tephra layers (which we refer to as layers A, B, and C) occur in late Quaternary glaciomarine sediments deposited on the West Antarctic continental margin. The stratigraphical positions of the distal tephra layers in 28 of the 32 studied sediment cores suggest their deposition during latest Marine Isotopic Stage (MIS) 6 and MIS 5. One prominent tephra layer (layer B), which was deposited subsequent to the penultimate deglaciation (Termination II), is present in almost all of the cores. Geochemical analyses carried out on the glass shards of the layers reveal a uniform trachytic composition and indicate Marie Byrd Land (MBL), West Antarctica, as the common volcanic source. The geochemical composition of the marine tephra is compared to that of ash layers of similar age described from Mount Moulton and Mount Takahe in MBL and from ice cores drilled at Dome Fuji, Vostok and EPICA Dome C in East Antarctica. The three tephra layers in the marine sediments are chemically indistinguishable. Also five englacial ash layers from Mt. Moulton, which originated from highly explosive Plinian eruptions of the Mt. Berlin volcano in MBL between 142 and 92 ka ago, are chemically very similar, as are two tephra layers erupted from Mt. Takahe at ca 102 ka and ca 93 ka. Statistical analysis of the chemical composition of the glass shards indicates that the youngest tephra (layer A) in the marine cores matches the ash layer that erupted from Mt. Berlin at 92 ka, which was previously correlated with tephra layers in the EPICA Dome C and the Dome Fuji ice cores. A tephra erupted from Mt. Berlin at 136 ka seems to correspond to a tephra layer deposited at 1733 m in the EPICA Dome C ice core. Additionally, the oldest tephra (layer C) in the marine sediments resembles an ash layer deposited at Vostok around 142 ka, but statistical evidence for the validity of this correlation is inconclusive. Although our results underscore the potential of

  1. STS-48 ESC Earth observation of Antarctic sea ice and clouds over Indian Ocean

    NASA Technical Reports Server (NTRS)

    1991-01-01

    STS-48 Earth observation taken aboard Discovery, Orbiter Vehicle (OV) 103, is of Antarctic sea ice and clouds over the southern Indian Ocean. Considerable detail can be seen in the ice field. The distribution of the ice field as seen through the breaks in the clouds is complex, and according to NASA scientists studying the STS-48 imagery, it likely contains information about ocean currents. The image was captured using an electronic still camera (ESC), was stored on a removable hard disk or small optical disk, and was converted to a format suitable for downlink transmission. The ESC documentation was part of Development Test Objective (DTO) 648, Electronic Still Photography.

  2. The Southern Hemisphere quasi-stationary eddies and their relationship with Antarctic sea ice

    NASA Astrophysics Data System (ADS)

    Hobbs, William Richard

    The west Antarctic region shows one of the strongest warming trends globally over the late 20th century, whilst much of the Antarctic continent shows little trend or even cooling. Additionally, sea ice reductions in the Antarctic Peninsula region have been balanced by sea ice increases in the Ross Sea region. Despite this heterogeneity, much recent research in the Southern Hemisphere has focused on the approximately zonally-symmetric Southern Annular Mode. In this research, reanalysis and satellite data are analyzed to show that at monthly and annual timescales the zonally asymmetric circulation over the Southern Ocean is dominated by two quasi-stationary anticyclones; a stable western anticyclone approximately located south of New Zealand, and a more variable eastern anticyclone located over the Drake Passage region. Time series describing each anticyclone's strength and longitude, and these time series are used to investigate the physical nature and influence of the anticyclones. The anticyclones are found to have some covariance, and in particular they tend to shift in phase, but their strengths are negatively correlated. Quasi-geostrophic diagnosis indicates that the west anticyclone is maintained by meridional vorticity advection by poleward airflow south of Australia, whereas the east anticyclone is forced by zonal convergence over the Pacific Ocean. The differences in variability and dynamic nature between the anticyclones bring into question the utility of the zonal wave decomposition, which is commonly used in analysis of the Southern Hemisphere zonally asymmetric circulation. It is shown that the quasi-stationary anticyclones influence west Antarctic sea ice in a pattern that resembles the 1st and 3rd principal components of ice variability. The anticyclones have some effect on wind-driven sea ice motion, but the primary mechanism explaining their link to sea ice appears to be meridional thermal advection.

  3. A Southern Ocean mode of multidecadal variability

    NASA Astrophysics Data System (ADS)

    Le Bars, D.; Viebahn, J. P.; Dijkstra, H. A.

    2016-03-01

    A 250 year simulation of a strongly eddying global version of the Parallel Ocean Program (POP) model reveals a new mode of intrinsic multidecadal variability, the Southern Ocean Mode (SOM), with a period of 40-50 year. The peak-to-peak difference in the global ocean heat content within a multidecadal cycle is up to 60 ZJ. This change results from surface heat flux variations in the South Atlantic and propagation of temperature anomalies along the Antarctic Circumpolar Current and into the Weddell gyre around 30°E. The temperature anomalies propagate as deep as 5000 m along the isopycnals between 50°S and 30°S and induce multidecadal changes in the Atlantic Meridional Overturning Circulation. A positive feedback loop between the generation of eddies through baroclinic instability and the dynamics of the mean circulation is essential for the existence of the SOM. The dominant physics appears similar to that responsible for variability found in a three-layer quasi-geostrophic eddy-resolving model. This combined with the fact that the SOM is not found in a noneddying version of the same global POP model further suggests that eddy processes are crucial for its existence and/or excitation.

  4. Eddy stirring in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Naveira Garabato, A. C.; Ferrari, R.; Polzin, K. L.

    2011-09-01

    There is an ongoing debate concerning the distribution of eddy stirring across the Antarctic Circumpolar Current (ACC) and the nature of its controlling processes. The problem is addressed here by estimating the isentropic eddy diffusivity κ from a collection of hydrographic and altimetric observations, analyzed in a mixing length theoretical framework. It is shown that, typically, κ is suppressed by an order of magnitude in the upper kilometer of the ACC frontal jets relative to their surroundings, primarily as a result of a local reduction of the mixing length. This observation is reproduced by a quasi-geostrophic theory of eddy stirring across a broad barotropic jet based on the scaling law derived by Ferrari and Nikurashin (2010). The theory interprets the observed widespread suppression of the mixing length and κ in the upper layers of frontal jets as the kinematic consequence of eddy propagation relative to the mean flow within jet cores. Deviations from the prevalent regime of mixing suppression in the core of upper-ocean jets are encountered in a few special sites. Such `leaky jet' segments appear to be associated with sharp stationary meanders of the mean flow that are generated by the interaction of the ACC with major topographic features. It is contended that the characteristic thermohaline structure of the Southern Ocean, consisting of multiple upper-ocean thermohaline fronts separated and underlaid by regions of homogenized properties, is largely a result of the widespread suppression of eddy stirring by parallel jets.

  5. Sea Ice on the Southern Ocean

    NASA Technical Reports Server (NTRS)

    Jacobs, Stanley S.

    1998-01-01

    Year-round satellite records of sea ice distribution now extend over more than two decades, providing a valuable tool to investigate related characteristics and circulations in the Southern Ocean. We have studied a variety of features indicative of oceanic and atmospheric interactions with Antarctic sea ice. In the Amundsen & Bellingshausen Seas, sea ice extent was found to have decreased by approximately 20% from 1973 through the early 1990's. This change coincided with and probably contributed to recently warmer surface conditions on the west side of the Antarctic Peninsula, where air temperatures have increased by approximately 0.5 C/decade since the mid-1940's. The sea ice decline included multiyear cycles of several years in length superimposed on high interannual variability. The retreat was strongest in summer, and would have lowered the regional mean ice thickness, with attendant impacts upon vertical heat flux and the formation of snow ice and brine. The cause of the regional warming and loss of sea ice is believed to be linked to large-scale circulation changes in the atmosphere and ocean. At the eastern end of the Weddell Gyre, the Cosmonaut Polyna revealed greater activity since 1986, a recurrence pattern during recent winters and two possible modes of formation. Persistence in polynya location was noted off Cape Ann, where the coastal current can interact more strongly with the Antarctic Circumpolar Current. As a result of vorticity conservation, locally enhanced upwelling brings warmer deep water into the mixed layer, causing divergence and melting. In the Ross Sea, ice extent fluctuates over periods of several years, with summer minima and winter maxima roughly in phase. This leads to large interannual cycles of sea ice range, which correlate positively with meridinal winds, regional air temperatures and subsequent shelf water salinities. Deep shelf waters display considerable interannual variability, but have freshened by approximately 0.03/decade

  6. Ceilometer measurements in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    McDonald, Adrian; Alexander, Simon; French, John; Harvey, Mike; Ichoja, Andrew; Klekociuk, Andrew; Plank, Graeme; Katurji, Marwan

    2016-04-01

    Current climate models display a consistent deficit of reflected shortwave radiation over the Southern Ocean which is mainly due to the poor representation of clouds. Recent work has also shown that reanalysis also perform poorly relative to satellite observations in terms of cloud fraction. In particular, satellite observations have shown that low-level clouds (with tops below 3 km) are ubiquitous over the Southern Ocean. But, most satellite instruments, even the current generation of active satellite instruments, have difficulties in sampling low level clouds. As part of the New Zealand Deep South challenge project focussed on improving the representation of clouds in the Southern Ocean, we have begun to deploy autonomous instruments on 'ships of opportunity'. This study discusses measurements from a Väisälä CL51 laser ceilometer and ancillary instruments on the first two research voyages in the Southern Ocean and initial results. The route of the first voyage covers a return trip from Wellington (New Zealand) to Terra Nova Bay (Antarctica) onboard the R/V Tangaroa and occurred in January to mid-February 2015. The second deployment is onboard the Aurora Australis Australian Antarctic Division supply ship and began in October 2015 and is planned to finish at Macquarie Island in March 2016. The sampling provided by the ships route allows the ceilometer measurements of the height of the cloud base in a region where limited data apart from, potentially biased, satellite measurements of low-level cloud exist. Analysis of the boundary layer height derived from the ceilometer is also presented. The climatological structure derived from the ceilometer measurements is first detailed. We then compare these measurements with satellite and ground-based observations. We then examine variations in these measurements relative to their meteorological context. Details of plans for future voyages are also detailed. We will also present a preliminary analysis of a case study of

  7. Late Pleistocene variations in Antarctic sea ice II: effect of interhemispheric deep-ocean heat exchange

    NASA Astrophysics Data System (ADS)

    Crowley, Thomas J.; Parkinson, Claire L.

    1988-10-01

    Variations in production rates of warm North Atlantic Deep Water (NADW) have been proposed as a mechanism for linking climate fluctuations in the northern and southern hemispheres during the Pleistocene. We have tested this hypothesis by examining the sensitivity of a thermodynamic/dynamic model for Antarctic sea ice to changes in vertical ocean heat flux and comparing the simulations with modified CLIMAP sea-ice maps for 18 000 B.P. Results suggest that changes in NADW production rates, and the consequent changes in the vertical ocean heat flux in the Antarctic, can only account for about 20% 30% of the overall variance in Antarctic sea-ice extent. This conclusion has been validated against an independent geological data set involving a time series of sea-surface temperatures from the subantarctic. The latter comparison suggests that, although the overall influence of NADW is relatively minor, the linkage may be much more significant at the 41 000-year obliquity period. Despite some limitations in the models and geological data, we conclude that NADW variations may have played only a modest role in causing late Pleistocene climate change in the high latitudes of the southern hemisphere. Our conclusion is consistent with calculations by Manabe and Broccoli (1985) suggesting that atmospheric CO2 changes may be more important for linking the two hemispheres.

  8. Secondary organic aerosols over oceans via oxidation of isoprene and monoterpenes from Arctic to Antarctic

    PubMed Central

    Hu, Qi-Hou; Xie, Zhou-Qing; Wang, Xin-Ming; Kang, Hui; He, Quan-Fu; Zhang, Pengfei

    2013-01-01

    Isoprene and monoterpenes are important precursors of secondary organic aerosols (SOA) in continents. However, their contributions to aerosols over oceans are still inconclusive. Here we analyzed SOA tracers from isoprene and monoterpenes in aerosol samples collected over oceans during the Chinese Arctic and Antarctic Research Expeditions. Combined with literature reports elsewhere, we found that the dominant tracers are the oxidation products of isoprene. The concentrations of tracers varied considerably. The mean average values were approximately one order of magnitude higher in the Northern Hemisphere than in the Southern Hemisphere. High values were generally observed in coastal regions. This phenomenon was ascribed to the outflow influence from continental sources. High levels of isoprene could emit from oceans and consequently have a significant impact on marine SOA as inferred from isoprene SOA during phytoplankton blooms, which may abruptly increase up to 95 ng/m3 in the boundary layer over remote oceans. PMID:23880782

  9. Improved representation of Southern Ocean fronts in a finite element ocean model

    NASA Astrophysics Data System (ADS)

    Janjic, T.; Timmerman, R.; Schroeter, J.

    2012-04-01

    Orsi et al. 1995 determined the positions of fronts in Southern Ocean based on the water mass criteria from hydrographic sections data. Following Orsi et al. 1995 three main Southern Ocean fronts are distinguished, the subantarctic front (SAF), the polar front (PF) and the southern Antarctic Circumpolar current (sACC) front. All three fronts are continuous features of the ACC, and extend from the sea surface to the deep ocean. Several studies used satellite observations (gradients of sea surface height and sea surface temperature) to locate ACC fronts. In recent work by Sokolov and Rintoul 2009, the authors introduced south, north and middle branches of each of the three major fronts. The position of the branches are determined based on the contour lines of absolute SSH, where the absolute SSH values were calculated by adding the SSH anomalies to the mean surface dynamic height (relative to 2500 dbar) derived from the World Ocean Circulation Experiment climatology. In this work, we estimate the locations of the Southern Ocean fronts using the finite element ocean model and the same criteria as specified in Orsi et al. 1995. The ocean model representation of the locations of fronts is improved by assimilating dynamical ocean topography (DOT) data. In our study, the DOT is generated using the satellite altimetry and our knowledge of the geoid as given by the GOCO2S model which combines GRACE and GOCE gravity data. In addition, front locations determined in such a way are compared to the streamline approach of Sokolov and Rintoul 2009.

  10. Metagenomic Analysis of a Southern Maritime Antarctic Soil

    PubMed Central

    Pearce, David A.; Newsham, Kevin K.; Thorne, Michael A. S.; Calvo-Bado, Leo; Krsek, Martin; Laskaris, Paris; Hodson, Andy; Wellington, Elizabeth M.

    2012-01-01

    Our current understanding of Antarctic soils is derived from direct culture on selective media, biodiversity studies based on clone library construction and analysis, quantitative PCR amplification of specific gene sequences and the application of generic microarrays for microbial community analysis. Here, we investigated the biodiversity and functional potential of a soil community at Mars Oasis on Alexander Island in the southern Maritime Antarctic, by applying 454 pyrosequencing technology to a metagenomic library constructed from soil genomic DNA. The results suggest that the commonly cited range of phylotypes used in clone library construction and analysis of 78–730 OTUs (de-replicated to 30–140) provides low coverage of the major groups present (∼5%). The vast majority of functional genes (>77%) were for structure, carbohydrate metabolism, and DNA/RNA processing and modification. This study suggests that prokaryotic diversity in Antarctic terrestrial environments appears to be limited at the generic level, with Proteobacteria, Actinobacteria being common. Cyanobacteria were surprisingly under-represented at 3.4% of sequences, although ∼1% of the genes identified were involved in CO2 fixation. At the sequence level there appeared to be much greater heterogeneity, and this might be due to high divergence within the relatively restricted lineages which have successfully colonized Antarctic terrestrial environments. PMID:23227023

  11. Southern Ocean buoyancy forcing of ocean ventilation and glacial atmospheric CO2

    NASA Astrophysics Data System (ADS)

    Watson, Andrew J.; Vallis, Geoffrey K.; Nikurashin, Maxim

    2015-11-01

    Atmospheric CO2 concentrations over glacial-interglacial cycles closely correspond to Antarctic temperature patterns. These are distinct from temperature variations in the mid to northern latitudes, so this suggests that the Southern Ocean is pivotal in controlling natural CO2 concentrations. Here we assess the sensitivity of atmospheric CO2 concentrations to glacial-interglacial changes in the ocean's meridional overturning circulation using a circulation model for upwelling and eddy transport in the Southern Ocean coupled with a simple biogeochemical description. Under glacial conditions, a broader region of surface buoyancy loss results in upwelling farther to the north, relative to interglacials. The northern location of upwelling results in reduced CO2 outgassing and stronger carbon sequestration in the deep ocean: we calculate that the shift to this glacial-style circulation can draw down 30 to 60 ppm of atmospheric CO2. We therefore suggest that the direct effect of temperatures on Southern Ocean buoyancy forcing, and hence the residual overturning circulation, explains much of the strong correlation between Antarctic temperature variations and atmospheric CO2 concentrations over glacial-interglacial cycles.

  12. Habitat Selection and Foraging Behavior of Southern Elephant Seals in the Western Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Huckstadt, L.; Costa, D. P.; McDonald, B. I.; Tremblay, Y.; Crocker, D. E.; Goebel, M. E.; Fedak, M. E.

    2006-12-01

    We examined the foraging behavior of 18 southern elephant seals foraging over two seasons in the Western Antarctic Peninsula. The foraging behavior and habitat utilization of 7 females in 2005 and 12 in 2006 were followed using satellite linked Satellite Relay Data Loggers that measured diving behavior as well collected salinity and temperature profiles as the animals dove. Animals were tagged after the annual molt during February at Cape Shirreff Livngston Island, South Shetland Islands. There was significant interannual variation in the regions of the Southern Ocean used by seals from Livingston Island. In 2005 of the 7 animals tagged one foraged 4700 km due west of the Antarctic Peninsula going as far as 150 W. The remaining females headed south along the Western Antarctic Peninsula bypassing Marguerite Bay moving south along Alexander Island. Three of these animals continued to forage in the pack ice as it developed. On their return trip all females swam past Livingston Island, continuing on to South Georgia Island where they apparently bred in the austral spring. One animal returned to Cape Shirreff to molt and her tag was recovered. During 2006 animals initially followed a similar migratory pattern going south along the Antarctic Peninsula, but unlike 2005 where the majority of the animals remained in the immediate vicinity of the Western Antarctic Peninsula, most of the animals in 2006 moved well to the west foraging as far as the Amundsen Sea. We compared the area restricted search (focal foraging areas) areas of these animals using a newly developed fractal landscape technique that identifies and quantifies areas of intensive search. The fractal analysis of area restricted search shows that the area, distance and coverage (Fractal D) searched were not different between years, while the time spent in the search areas was higher in 2005. Further analysis will examine how the physical properties of the water column as determined from the CTD data derived from

  13. Fisheries in the Southern Ocean: an ecosystem approach.

    PubMed

    Kock, Karl-Hermann; Reid, Keith; Croxall, John; Nicol, Stephen

    2007-12-29

    The Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) is bound by its Article II, 3 to follow an ecosystem approach to management. This approach has been extended to the application of a precautionary approach in the late 1980s. In our review, we deal primarily with the science-related aspects of CCAMLR and its development towards an ecosystem approach to the management of the living resources of the Southern Ocean. To assist the Commission in meeting its objectives, as set out in Article II, 3, the Scientific Committee established the CCAMLR Ecosystem Monitoring Programme to detect possible effects of krill fishing on the performance of top-level predators, such as albatrosses, penguins, petrels and fur seals. Fisheries in the Southern Ocean followed the fate of other fisheries worldwide in which target species were depleted to low level one after the other. Currently, two types of fisheries are open: the longline fisheries on Patagonian toothfish (Dissostichus eleginoides) and Antarctic toothfish (Dissostichus mawsoni) and the trawl fisheries on mackerel icefish (Champsocephalus gunnari). Both fisheries are managed in a single-species context, however, with conservation measures in place to protect by-catch species, such as rattails (Macrouridae) and skates and rays (Rajidae). Two major problems still exist in fisheries in the Southern Ocean: the by-catch of birds in longline fisheries primarily in the Indian Ocean and the high level of IUU fishing again in the Indian Ocean. Both, the by-catch of birds and high IUU catches undermine the credibility of CCAMLR to safeguard the marine living resources in the Southern Ocean. PMID:17553767

  14. Salp/krill interactions in the Southern Ocean: spatial segregation and implications for the carbon flux

    NASA Astrophysics Data System (ADS)

    Pakhomov, E. A.; Froneman, P. W.; Perissinotto, R.

    Available data on the spatial distribution and feeding ecophysiology of Antarctic krill, Euphausia superba, and the tunicate, Salpa thompsoni, in the Southern Ocean are summarized in this study. Antarctic krill and salps generally display pronounced spatial segregation at all spatial scales. This appears to be the result of a clear biotopical separation of these key species in the Antarctic pelagic food web. Krill and salps are found in different water masses or water mass modifications, which are separated by primary or secondary frontal features. On the small-scale (<100 km), Antarctic krill and salps are usually restricted to the specific water parcels, or are well segregated vertically. Krill and salp grazing rates estimated using the in situ gut fluorescence technique are among the highest recorded in the Antarctic pelagic food web. Although krill and salps at times may remove the entire daily primary production, generally their grazing impact is moderate (⩽50% of primary production). The regional ecological consequences of years of high salp densities may be dramatic. If the warming trend, which is observed around the Antarctic Peninsula and in the Southern Ocean, continues, salps may become a more prominent player in the trophic structure of the Antarctic marine ecosystem. This likely would be coupled with a dramatic decrease in krill productivity, because of a parallel decrease in the spatial extension of the krill biotope. The high Antarctic regions, particularly the Marginal Ice Zone, have, however, effective physiological mechanisms that may provide protection against the salp invasion.

  15. Antarctic ice-rafted detritus (IRD) in the South Atlantic: Indicators of iceshelf dynamics or ocean surface conditions?

    USGS Publications Warehouse

    Nielsen, Simon H.H.; Hodell, D.A.

    2007-01-01

    Ocean sediment core TN057-13PC4/ODP1094, from the Atlantic sector of the Southern Ocean, contains elevated lithogenic material in sections representing the last glacial period compared to the Holocene. This ice-rafted detritus is mainly comprised of volcanic glass and ash, but has a significant input of what was previously interpreted as quartz during peak intervals (Kanfoush et al., 2000, 2002). Our analysis of these clear mineral grains indicates that most are plagioclase, and that South Sandwich Islands is the predominant source, similar to that inferred for the volcanic glass (Nielsen et al., in review). In addition, quartz and feldspar with possible Antarctic origin occur in conjunction with postulated episodes of Antarctic deglaciation. We conclude that while sea ice was the dominant ice rafting agent in the Polar Frontal Zone of the South Atlantic during the last glacial period, the Holocene IRD variability may reflect Antarctic ice sheet dynamics.

  16. Oceanic an climatic consequences of a sudden large-scale West Antarctic Ice Sheet collapse

    NASA Astrophysics Data System (ADS)

    Scarff, Katie; Green, Mattias; Schmittner, Andreas

    2015-04-01

    Atmospheric warming is progressing to the point where the West Antarctic Ice Sheet (WAIS) will experience an elevated rate of discharge. The current discharge rate of WAIS is around 0.005Sv, but this rate will most likely accelerate over this century. The input of freshwater, in the form of ice, may have a profound effect on oceanic circulation systems, including potentially reducing the formation of deep water in the Southern Ocean and thus triggering or enhancing the bipolar seesaw. Using UVic - an intermediate complexity ocean-climate model - we investigate how various hosing rates from the WAIS will impact of the present and future ocean circulation and climate. These scenarios range from observed hosing rates (~0.005Sv) being applied for 100 years, to a total collapse of the WAIS over the next 100 years (the equivalent to a0.7Sv hosing). We show that even the present day observed rates can have a significant impact on the ocean and atmospheric temperatures, and that the bipolar seesaw may indeed be enhanced by the Southern Ocean hosing. Consequently, there is a speed-up of the Meridional Overturning Circulation (MOC) early on during the hosing, which leads to a warming over the North Atlantic, and a subsequent reduction in the MOC on centennial scales. The larger hosing cases show more dramatic effects with near-complete shutdowns of the MOC during the hosing. Furthermore, global warming scenarios based on the IPCC "business as usual" scenario show that the atmospheric warming will change the response of the ocean to Southern Ocean hosing and that the warming will dominate the perturbation. The potential feedback between changes in the ocean stratification in the scenarios and tidally driven abyssal mixing via tidal conversion is also explored.

  17. Deciphering the role of southern gateways and carbon dioxide on the onset of the Antarctic Circumpolar Current

    NASA Astrophysics Data System (ADS)

    Lefebvre, Vincent; Donnadieu, Yannick; Sepulchre, Pierre; Swingedouw, Didier; Zhang, Zhong-Shi

    2012-12-01

    Growth of Antarctic ice sheet during the Cenozoic 34 million years ago appears as a potential tipping point in the long term cooling trend that began 50 Ma ago. For decades, the onset of the Antarctic Circumpolar Current (ACC) following the opening of the Drake Passage and of the Tasman Seaway has been suggested as the main driver of the continental-scale Antarctic glaciation. However, recent modeling works emphasized that the Eocene/Oligocene atmospheric carbon dioxide (CO2) lowering could be the primary forcing of the Antarctic glaciation, questioning the ACC theory. Here, we investigate the response of the ACC to changes in CO2concentrations occurring from the late Eocene to the late Oligocene. We used a fully coupled atmosphere-ocean model (FOAM) with a mid-Oligocene geography. We find that the opening of southern oceanic gateways does not trigger the onset of the ACC for CO2typical of the late Eocene (>840 ppm). A cooler background climatic state such as the one prevalent at the end of the Oligocene is required to simulate a well-developed ACC. In this cold configuration, the intensified sea-ice development around Antarctica and the resulting brine formation lead to a strong latitudinal density gradient in the Southern Ocean favoring the compensation of the Ekman transport, and consequently the ACC. Our results imply that the ACC has acted as a feedback rather than as a driver of the global cooling.

  18. Ocean forcing of glacier retreat in the western Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Cook, A. J.; Holland, P. R.; Meredith, M. P.; Murray, T.; Luckman, A.; Vaughan, D. G.

    2016-07-01

    In recent decades, hundreds of glaciers draining the Antarctic Peninsula (63° to 70°S) have undergone systematic and progressive change. These changes are widely attributed to rapid increases in regional surface air temperature, but it is now clear that this cannot be the sole driver. Here, we identify a strong correspondence between mid-depth ocean temperatures and glacier-front changes along the ~1000-kilometer western coastline. In the south, glaciers that terminate in warm Circumpolar Deep Water have undergone considerable retreat, whereas those in the far northwest, which terminate in cooler waters, have not. Furthermore, a mid-ocean warming since the 1990s in the south is coincident with widespread acceleration of glacier retreat. We conclude that changes in ocean-induced melting are the primary cause of retreat for glaciers in this region.

  19. Ocean forcing of glacier retreat in the western Antarctic Peninsula.

    PubMed

    Cook, A J; Holland, P R; Meredith, M P; Murray, T; Luckman, A; Vaughan, D G

    2016-07-15

    In recent decades, hundreds of glaciers draining the Antarctic Peninsula (63° to 70°S) have undergone systematic and progressive change. These changes are widely attributed to rapid increases in regional surface air temperature, but it is now clear that this cannot be the sole driver. Here, we identify a strong correspondence between mid-depth ocean temperatures and glacier-front changes along the ~1000-kilometer western coastline. In the south, glaciers that terminate in warm Circumpolar Deep Water have undergone considerable retreat, whereas those in the far northwest, which terminate in cooler waters, have not. Furthermore, a mid-ocean warming since the 1990s in the south is coincident with widespread acceleration of glacier retreat. We conclude that changes in ocean-induced melting are the primary cause of retreat for glaciers in this region. PMID:27418507

  20. Open-ocean barriers to dispersal: a test case with the Antarctic Polar Front and the ribbon worm Parborlasia corrugatus (Nemertea: Lineidae).

    PubMed

    Thornhill, Daniel J; Mahon, Andrew R; Norenburg, Jon L; Halanych, Kenneth M

    2008-12-01

    Open-ocean environments provide few obvious barriers to the dispersal of marine organisms. Major currents and/or environmental gradients potentially impede gene flow. One system hypothesized to form an open-ocean dispersal barrier is the Antarctic Polar Front, an area characterized by marked temperature change, deep water, and the high-flow Antarctic Circumpolar current. Despite these potential isolating factors, several invertebrate species occur in both regions, including the broadcast-spawning nemertean worm Parborlasia corrugatus. To empirically test for the presence of an open-ocean dispersal barrier, we sampled P. corrugatus and other nemerteans from southern South America, Antarctica, and the sub-Antarctic islands. Diversity was assessed by analyzing mitochondrial 16S rRNA and cytochrome c oxidase subunit I sequence data with Bayesian inference and tcs haplotype network analysis. Appropriate neutrality tests were also employed. Although our results indicate a single well-mixed lineage in Antarctica and the sub-Antarctic, no evidence for recent gene flow was detected between this population and South American P. corrugatus. Thus, even though P. corrugatus can disperse over large geographical distances, physical oceanographic barriers (i.e. Antarctic Polar Front and Antarctic Circumpolar Current) between continents have likely restricted dispersal over evolutionary time. Genetic distances and haplotype network analysis between South American and Antarctic/sub-Antarctic P. corrugatus suggest that these two populations are possibly two cryptic species. PMID:18992005

  1. Sensitivity of the recent increase in Antarctic sea ice in ocean models

    NASA Astrophysics Data System (ADS)

    Kjellsson, Joakim; Holland, Paul; Marshall, Gareth; Coward, Andrew; Aksenov, Yevgeny; Bacon, Sheldon; Megann, Alexis; Ridley, Jeff

    2015-04-01

    We study the recent increase in Antarctic sea ice using a coupled ocean--sea ice model forced by atmospheric reanalysis. We investigate the impact on sea ice from both model parameters (e.g. vertical mixing and eddy parameterisation) as well as external forcing (e.g. precipitation and melt water from the Antarctic continent). We use the NEMO ocean model coupled to the CICE sea-ice model at 1 degree horizontal resolution forced with ERA-Interim reanalysis. The results will have impacts for our understanding of the Southern Ocean, its sea ice and their representation in future coupled climate-model studies, e.g. CMIP6. Since the dawn of the satellite era there has been a slow increase in Antarctic sea ice with pronounced spatial structure. The reason for this increase is not yet fully understood and very few climate-model simulations reproduce the observed mean state and/or increase. By varying model parameters and external forcing, we determine that obtaining a realistic sea ice cover requires a complex balance of horizontal and vertical mixing as well as fresh water input. The surface fresh water balance impacts the vertical salinity gradient and thus vertical fluxes of heat and salt. Underestimation of precipitation or melt water results in deep convection in the open ocean and the opening of large polynyas in the Weddell and Ross sea. The presence of polynyas reduces the sea ice extent. The depth of the mixed layer has a large impact on the sea ice seasonal cycle. The summer mixed layer must be sufficiently deep to prevent SST from becoming too high but not so deep as to mix up heat and salt from below. In winter, a deep mixed layer lets brine rejected from sea ice mix down to depths below that of the summer mixed layer thus maintaining a necessary stratification.

  2. Productivity and linkages of the food web of the southern region of the western Antarctic Peninsula continental shelf

    NASA Astrophysics Data System (ADS)

    Ballerini, Tosca; Hofmann, Eileen E.; Ainley, David G.; Daly, Kendra; Marrari, Marina; Ribic, Christine A.; Smith, Walker O.; Steele, John H.

    2014-03-01

    The productivity and linkages in the food web of the southern region of the west Antarctic Peninsula continental shelf were investigated using a multi-trophic level mass balance model. Data collected during the Southern Ocean Global Ocean Ecosystem Dynamics field program were combined with data from the literature on the abundance and diet composition of zooplankton, fish, seabirds and marine mammals to calculate energy flows in the food web and to infer the overall food web structure at the annual level. Sensitivity analyses investigated the effects of variability in growth and biomass of Antarctic krill (Euphausia superba) and in the biomass of Antarctic krill predators on the structure and energy fluxes in the food web. Scenario simulations provided insights into the potential responses of the food web to a reduced contribution of large phytoplankton (diatom) production to total primary production, and to reduced consumption of primary production by Antarctic krill and mesozooplankton coincident with increased consumption by microzooplankton and salps. Model-derived estimates of primary production were 187-207 g C m-2 y-1, which are consistent with observed values (47-351 g C m-2 y-1). Simulations showed that Antarctic krill provide the majority of energy needed to sustain seabird and marine mammal production, thereby exerting a bottom-up control on higher trophic level predators. Energy transfer to top predators via mesozooplanton was a less efficient pathway, and salps were a production loss pathway because little of the primary production they consumed was passed to higher trophic levels. Increased predominance of small phytoplankton (nanoflagellates and cryptophytes) reduced the production of Antarctic krill and of its predators, including seabirds and seals.

  3. Platelet ice distribution in Antarctic sea ice and its implications for ocean - ice shelf interaction

    NASA Astrophysics Data System (ADS)

    Langhorne, P.; Hughes, K. G.; Gough, A. J.; Smith, I.; Williams, M.; Robinson, N. J.; Stevens, C. L.; Rack, W.; Price, D.; Leonard, G. H.; Mohoney, A. R.; Haas, C.; Haskell, T. G.

    2015-12-01

    Ice shelf basal melting freshens and cools the fluid in the ice shelf-ocean boundary layer, producing Ice Shelf Water (ISW). The potential temperature of ISW is below the surface freezing point. Antarctic sea ice that has been affected by supercooled Ice Shelf Water (ISW) has a unique crystallographic structure and is called platelet ice. We have synthesized platelet ice observations to construct a continent-wide map of the winter presence of ISW at the ocean surface. Where suitable observations exist, oceanic heat fluxes are derived from sub-ice platelet layer measurements and these are shown in the figure. They demonstrate that in some regions of coastal Antarctica, supercooled ISW drives a negative oceanic heat flux of approximately -30 Wm-2 that persists for several months during winter. This heat flux from the sea ice to the ocean significantly increases the sea ice thickness close to an ice shelf. In other regions, particularly where the thinning of ice shelves is believed to be greatest, platelet ice is not observed. The most extensive dataset, which includes our new results, dates back to 1902 and extends north of the combined Ross and McMurdo Ice Shelf front in the southern Ross Sea. Here the surface water is held just below its freezing point as it enters McMurdo Sound from beneath the McMurdo Ice Shelf. Despite a more recent decrease in ocean salinity consistent with observations in the south-western Ross Sea, there has been no detectable change in the volume or temperature of this supercooled ISW under sea ice since the early twentieth century. The inclusion of platelet ice into first year sea ice is an annual process. Hence it will respond immediately to changes in the sub-ice shelf circulation pattern and its export of supercooled water, emphasizing the urgent need for careful, Antarctic-wide monitoring.

  4. Controlling high-latitude Southern Ocean convection in climate models

    NASA Astrophysics Data System (ADS)

    Stössel, Achim; Notz, Dirk; Haumann, F. Alexander; Haak, Helmuth; Jungclaus, Johann; Mikolajewicz, Uwe

    2015-02-01

    Earth System Models (ESMs) generally suffer from a poor simulation of the High-Latitude Southern Ocean (HLSO). Here we aim at a better understanding of the shortcomings by investigating the sensitivity of the HLSO to the external freshwater flux and the horizontal resolution in forced and coupled simulations with the Max-Planck-Institute Ocean Model (MPIOM). Forced experiments reveal an immediate reduction of open-ocean convection with additional freshwater input. The latter leads to a remarkably realistic simulation of the distinct water-mass structure in the central Weddell Sea featuring a temperature maximum of +0.5 °C at 250 m depth. Similar, but more modest improvements occur over a time span of 40 years after switching from a forced to a coupled simulation with an eddy-resolving version of MPIOM. The switch is accompanied with pronounced changes of the external freshwater flux and the wind field, as well as a more realistic heat flux due to coupling. Similar to the forced freshwater-flux experiments, a heat reservoir develops at depth, which in turn decreases the vertically integrated density of the HLSO and reduces the Antarctic Circumpolar Current to rather realistic values. Coupling with a higher resolution version of the atmosphere model (ECHAM6) yields distinct improvements of the HLSO water-mass structure and sea-ice cover. While the coupled simulations reveal a realistic amount of Antarctic runoff, its distribution appears too concentrated along the coast. Spreading the runoff over a wider region, as suggested in earlier studies to mimic the effect of freshwater transport through icebergs, also leads to noticeable improvements of the HLSO water-mass properties, predominantly along the coast. This suggests that the spread of the runoff improves the representation of Antarctic Bottom Water formation through enhanced near-boundary convection rather than weakened open-ocean convection.

  5. Southern Ocean Deep-Convection as a Driver of Centennial-to-Millennial-Scale Climate Variability at Southern High Latitudes

    NASA Astrophysics Data System (ADS)

    Pedro, J. B.; Martin, T.; Steig, E. J.; Jochum, M.; Park, W.; Rasmussen, S.

    2014-12-01

    Antarctic Isotope Maxima (AIM) are centennial-to-millennial scale warming events observed in Antarctic ice core records from the last glacial period and deglaciation. Mounting evidence links AIM events to parallel variations in atmospheric CO2, Southern Ocean (SO) sea surface temperatures and Antarctic Bottom Water production. According to the prevailing view, AIM events are forced from the North Atlantic by melt-water discharge from ice sheets suppressing the production of North Atlantic Deep Water and associated northward heat transport in the Atlantic. However observations and model studies increasingly suggest that melt-water fluxes have the wrong timing to be invoked as such a trigger. Here, drawing on results form the Kiel Climate Model, we present an alternative hypothesis in which AIM events are forced via internal oscillations in SO deep-convection. The quasi-periodic timescale of deep-convection events is set by heat (buoyancy) accumulation at SO intermediate depths and stochastic variability in sea ice conditions and freshening at the surface. Massive heat release from the SO convective zone drives Antarctic and large-scale southern hemisphere warming via a two-stage process involving changes in the location of Southern Ocean fronts, in the strength and intensity of the Westerlies and in meridional ocean and atmospheric heat flux anomalies. The potential for AIM events to be driven by internal Southern Ocean processes and the identification of time-lags internal to the southern high latitudes challenges conventional views on the North Atlantic as the pacemaker of millennial-scale climate variability.

  6. Topographic form stress in the Southern Ocean State Estimate

    NASA Astrophysics Data System (ADS)

    Masich, Jessica; Chereskin, Teresa K.; Mazloff, Matthew R.

    2015-12-01

    We diagnose the Southern Ocean momentum balance in a 6 year, eddy-permitting state estimate of the Southern Ocean. We find that 95% of the zonal momentum input via wind stress at the surface is balanced by topographic form stress across ocean ridges, while the remaining 5% is balanced via bottom friction and momentum flux divergences at the northern and southern boundaries of the analysis domain. While the time-mean zonal wind stress field exhibits a relatively uniform spatial distribution, time-mean topographic form stress concentrates at shallow ridges and across the continents that lie within the Antarctic Circumpolar Current (ACC) latitudes; nearly 40% of topographic form stress occurs across South America, while the remaining 60% occurs across the major submerged ridges that underlie the ACC. Topographic form stress can be divided into shallow and deep regimes: the shallow regime contributes most of the westward form stress that serves as a momentum sink for the ACC system, while the deep regime consists of strong eastward and westward form stresses that largely cancel in the zonal integral. The time-varying form stress signal, integrated longitudinally and over the ACC latitudes, tracks closely with the wind stress signal integrated over the same domain; at zero lag, 88% of the variance in the 6 year form stress time series can be explained by the wind stress signal, suggesting that changes in the integrated wind stress signal are communicated via rapid barotropic response down to the level of bottom topography.

  7. Levoglucosan indicates high levels of biomass burning aerosols over oceans from the Arctic to Antarctic

    NASA Astrophysics Data System (ADS)

    Hu, Q.; Xie, Z.; Wang, X.; Kang, H.; Zhang, P.

    2015-12-01

    Biomass burning discharges numerous kinds of gases and aerosols, such as carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), black carbon (BC), alcohols, organic acids and persistent organic pollutants (POPs), and is known to affect air quality, global carbon cycle, and climate. However, the extent to which biomass burning gases/aerosols are present on a global scale, especially in the marine atmosphere, is poorly understood. Here we measure levoglucosan, a superior molecular tracer of biomass burning aerosols because of its single source, in marine air from the Arctic Ocean through the North and South Pacific Ocean to coastal Antarctica during burning season. Levoglucosan was found to be present in all regions at ng/m3 levels. As a whole, levoglucosan concentrations in the Southern Hemisphere were comparable to those in the Northern Hemisphere. Marine air in the mid-latitudes (30°-60° N and S) has the highest levoglucosan loading due to the emission from adjacent lands. Air over the Arctic Ocean which affected by biomass burning in the east Siberia has intermediate loading. Equatorial latitudes is the main source of biomass burning emissions, however, levoglucosan is in relatively low level. Large amount of precipitation and high hydroxyl radical concentration in this region cause more deposition and degradation of levoglucosan during transport. Previous studies were debatable on the influence of biomass burning on the Antarctic because of uncertain source of BC. Here via levoglucosan, it is proved that although far away from emission sources, the Antarctic is still affected by biomass burning aerosols which may be derived from South America. Biomass burning has a significant impact on mercury (Hg) and water-soluble organic carbon (WSOC) in marine aerosols from pole to pole, with more contribution to WSOC in the Northern Hemisphere than in the Southern Hemisphere.

  8. Simulations of coupled, Antarctic ice-ocean evolution using POP2x and BISICLES (Invited)

    NASA Astrophysics Data System (ADS)

    Price, S. F.; Asay-Davis, X.; Martin, D. F.; Maltrud, M. E.; Hoffman, M. J.

    2013-12-01

    We present initial results from Antarctic, ice-ocean coupled simulations using large-scale ocean circulation and land ice evolution models. The ocean model, POP2x is a modified version of POP, a fully eddying, global-scale ocean model (Smith and Gent, 2002). POP2x allows for circulation beneath ice shelf cavities using the method of partial top cells (Losch, 2008). Boundary layer physics, which control fresh water and salt exchange at the ice-ocean interface, are implemented following Holland and Jenkins (1999), Jenkins (1999), and Jenkins et al. (2010). Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP; Losch, 2008; Kimura et al., 2013) and with results from other idealized ice-ocean coupling test cases (e.g., Goldberg et al., 2012). The land ice model, BISICLES (Cornford et al., 2012), includes a 1st-order accurate momentum balance (L1L2) and uses block structured, adaptive-mesh refinement to more accurately model regions of dynamic complexity, such as ice streams, outlet glaciers, and grounding lines. For idealized test cases focused on marine-ice sheet dynamics, BISICLES output compares very favorably relative to simulations based on the full, nonlinear Stokes momentum balance (MISMIP-3d; Pattyn et al., 2013). Here, we present large-scale (southern ocean) simulations using POP2x with fixed ice shelf geometries, which are used to obtain and validate modeled submarine melt rates against observations. These melt rates are, in turn, used to force evolution of the BISICLES model. An offline-coupling scheme, which we compare with the ice-ocean coupling work of Goldberg et al. (2012), is then used to sequentially update the sub-shelf cavity geometry seen by POP2x.

  9. Source of the Magnetic Susceptibility Variations in Southern Ocean Sediments Over the Last Glacial Cycle

    NASA Astrophysics Data System (ADS)

    Maher, B.; Thompson, R.

    2014-12-01

    Changes in the sources, mineralogy and rates of iron supply to the Southern Ocean may have global impact and significance, by influencing plankton growth rates and nutrient take-up in this, the largest of the high nutrient low chlorophyll (HNLC) regions of the world ocean. Iron 'fertilization' in the Southern Ocean may increase rates of carbon export production and thus the ocean uptake flux of atmospheric CO2, and also diminish the northward flow of residual nutrients to the extra-polar ocean, especially the HNLC regions of the Pacific. Changes in Southern Ocean export production may contribute to global climate change over glacial-interglacial timescales. The key sources of iron for the Southern Ocean are reported to be windblown dust and sedimentary supply; their relative significance an issue of much long-standing debate. Links between aeolian dust fluxes to the Southern Ocean and to the Antarctic ice cores have been proposed for the Scotia Sea region of the Southern Ocean, downwind from the South American land mass. Regional downcore variations in the magnetic susceptibility of sediments from the Scotia Sea show remarkable similarity to variations in dust concentration and flux in East Antarctic ice cores (with glacial stages characterised by increases in ice dust and sediment magnetic susceptibility). Indeed, the strength of the ice dust/sediment magnetism correlations (r ~ 0.7) provides a pragmatic basis for use of the sedimentary magnetic susceptibility records as a chronostratigraphic proxy, a boon in the carbonate-free deep-sea sediments of the Southern Ocean. However, the source and causal basis of the sediment magnetism/ice dust co-variations remain controversial; aeolian dust, bacterial magnetite and wind-driven current transport of marine sediment have all been invoked as possible key sources. Here, we use magnetic and isotopic methods to resolve this debate, and identify and quantify the sources of magnetic material to the Scotia Sea for the last

  10. Circulation of Antarctic intermediate water in the South Indian Ocean

    NASA Astrophysics Data System (ADS)

    Fine, Rana A.

    1993-10-01

    Chlorofluorocarbon (CFC) and hydrographic data collected on the R.R.S. Charles Darwin Cruise 29 along 32°S during November-December 1987, are used to examine the circulation in the South Indian Ocean. The emphasis is on Antarctic Intermediate Water (AAIW); bottom waters and mode waters are also examined. Bottom waters entering in the western boundary of the Crozet Basin (about 60°E) and in the Mozambique Basin (about 40°E) have low concentrations of anthropogenic CFCs. The rest of the bottom and deep waters up to about 2000 m have concentrations that are below blank levels. Above the intermediate waters there are injections of mode waters, which are progressively denser in the eastward direction. They form a broad subsurface CFC maximum between 200 and 400 m. The injections of recently ventilated (with respect to CFCs and oxygen) Subantarctic Mode Waters (SAMWs) at different densities indicate that there is considerable exchange between the subtropical and subantarctic regions. The tracer data presented show that the circulation of AAIW in the South Indian Ocean is different from that in the South Atlantic and South Pacific oceans in several ways. (1) The most recently ventilated AAIW is observed in a compact anticyclonic gyre west of 72°E. The shallow topography (e.g. that extending northeastward from the Kerguelen Plateau) may deflect and limit the eastward extent of the most recently ventilated AAIW. As a consequence, there is a zonal offset in the South Indian Ocean of the location of the most recently ventilated SAMW and AAIW, which does not occur in the other two oceans. The strongest component of SAMW is in the east, while the AAIW is strongest in the western-central South Indian Ocean. The offset results in a higher vertical gradient in CFCs in the east. (2) The Agulhas Current may impede input of AAIW along the western boundary. (3) Tracers are consistent with an inter-ocean flow from the South Pacific into the Eastern Indian Ocean, similar to the

  11. Glacier mass loss. Dynamic thinning of glaciers on the Southern Antarctic Peninsula.

    PubMed

    Wouters, B; Martin-Español, A; Helm, V; Flament, T; van Wessem, J M; Ligtenberg, S R M; van den Broeke, M R; Bamber, J L

    2015-05-22

    Growing evidence has demonstrated the importance of ice shelf buttressing on the inland grounded ice, especially if it is resting on bedrock below sea level. Much of the Southern Antarctic Peninsula satisfies this condition and also possesses a bed slope that deepens inland. Such ice sheet geometry is potentially unstable. We use satellite altimetry and gravity observations to show that a major portion of the region has, since 2009, destabilized. Ice mass loss of the marine-terminating glaciers has rapidly accelerated from close to balance in the 2000s to a sustained rate of -56 ± 8 gigatons per year, constituting a major fraction of Antarctica's contribution to rising sea level. The widespread, simultaneous nature of the acceleration, in the absence of a persistent atmospheric forcing, points to an oceanic driving mechanism. PMID:25999505

  12. Sustained growth of the Southern Ocean carbon storage in a warming climate

    NASA Astrophysics Data System (ADS)

    Ito, Takamitsu; Bracco, Annalisa; Deutsch, Curtis; Frenzel, Hartmut; Long, Matthew; Takano, Yohei

    2015-06-01

    We investigate the mechanisms controlling the evolution of Southern Ocean carbon storage under a future climate warming scenario. A subset of Coupled Model Intercomparison Project Phase 5 models predicts that the inventory of biologically sequestered carbon south of 40°S increases about 18-34 Pg C by 2100 relative to the preindustrial condition. Sensitivity experiments with an ocean circulation and biogeochemistry model illustrates the impacts of the wind and buoyancy forcings under a warming climate. Intensified and poleward shifted westerly wind strengthens the upper overturning circulation, not only leading to an increased uptake of anthropogenic CO2 but also releasing biologically regenerated carbon to the atmosphere. Freshening of Antarctic Surface Water causes a slowdown of the lower overturning circulation, leading to an increased Southern Ocean biological carbon storage. The rectified effect of these processes operating together is the sustained growth of the carbon storage in the Southern Ocean, even under the warming climate with a weaker global ocean carbon uptake.

  13. Dissolved organic carbon in the deep Southern Ocean: Local versus distant controls

    NASA Astrophysics Data System (ADS)

    Bercovici, Sarah K.; Hansell, Dennis A.

    2016-02-01

    The global ocean contains a massive reservoir (662 ± 32 Pg C) of dissolved organic carbon (DOC), and its dynamics, particularly in the deepest zones, are only slowly being understood. DOC in the deep ocean is ubiquitously low in concentration (~35 to 48 µmol kg-1) and aged (4000 to 6000 years), persisting for multiple meridional overturning circulations. Deep waters relatively enriched in DOC form in the North Atlantic, migrate to the Southern Ocean to mix with waters from Antarctic shelves and the deep Pacific and Indian Oceans, in turn forming the voluminous waters of the Circumpolar Deep Water. Here we seek evidence for local (autochthonous) versus distant (allochthonous) processes in determining the distribution of DOC in the deep Southern Ocean. Prior analyses on DOC in the deep Southern Ocean have conflicted, describing both conservative and nonconservative traits: the deep DOC field has been reported as uniform in distribution, yet local inputs have been suggested as quantitatively important. We use multiple approaches (multiple linear regression, mass transport, and mass balance calculations) with data from Climate Variability and Predictability Repeat Hydrography sections to evaluate the system. We find that DOC concentrations in the deep Southern Ocean largely reflect the conservative mixing of the several deep waters entering the system from the north. Mass balance suggests that the relatively depleted DOC radiocarbon content in the deep Southern Ocean is a conserved property as well. These analyses advance our understanding of the controls on the DOC reservoir of the Southern Ocean.

  14. Atmospheric and oceanic impacts of Antarctic glaciation across the Eocene-Oligocene transition.

    PubMed

    Kennedy, A T; Farnsworth, A; Lunt, D J; Lear, C H; Markwick, P J

    2015-11-13

    The glaciation of Antarctica at the Eocene-Oligocene transition (approx. 34 million years ago) was a major shift in the Earth's climate system, but the mechanisms that caused the glaciation, and its effects, remain highly debated. A number of recent studies have used coupled atmosphere-ocean climate models to assess the climatic effects of Antarctic glacial inception, with often contrasting results. Here, using the HadCM3L model, we show that the global atmosphere and ocean response to growth of the Antarctic ice sheet is sensitive to subtle variations in palaeogeography, using two reconstructions representing Eocene and Oligocene geological stages. The earlier stage (Eocene; Priabonian), which has a relatively constricted Tasman Seaway, shows a major increase in sea surface temperature over the Pacific sector of the Southern Ocean in response to the ice sheet. This response does not occur for the later stage (Oligocene; Rupelian), which has a more open Tasman Seaway. This difference in temperature response is attributed to reorganization of ocean currents between the stages. Following ice sheet expansion in the earlier stage, the large Ross Sea gyre circulation decreases in size. Stronger zonal flow through the Tasman Seaway allows salinities to increase in the Ross Sea, deep-water formation initiates and multiple feedbacks then occur amplifying the temperature response. This is potentially a model-dependent result, but it highlights the sensitive nature of model simulations to subtle variations in palaeogeography, and highlights the need for coupled ice sheet-climate simulations to properly represent and investigate feedback processes acting on these time scales. PMID:26438285

  15. Shearwater Foraging in the Southern Ocean: The Roles of Prey Availability and Winds

    PubMed Central

    Raymond, Ben; Shaffer, Scott A.; Sokolov, Serguei; Woehler, Eric J.; Costa, Daniel P.; Einoder, Luke; Hindell, Mark; Hosie, Graham; Pinkerton, Matt; Sagar, Paul M.; Scott, Darren; Smith, Adam; Thompson, David R.; Vertigan, Caitlin; Weimerskirch, Henri

    2010-01-01

    Background Sooty (Puffinus griseus) and short-tailed (P. tenuirostris) shearwaters are abundant seabirds that range widely across global oceans. Understanding the foraging ecology of these species in the Southern Ocean is important for monitoring and ecosystem conservation and management. Methodology/Principal Findings Tracking data from sooty and short-tailed shearwaters from three regions of New Zealand and Australia were combined with at-sea observations of shearwaters in the Southern Ocean, physical oceanography, near-surface copepod distributions, pelagic trawl data, and synoptic near-surface winds. Shearwaters from all three regions foraged in the Polar Front zone, and showed particular overlap in the region around 140°E. Short-tailed shearwaters from South Australia also foraged in Antarctic waters south of the Polar Front. The spatial distribution of shearwater foraging effort in the Polar Front zone was matched by patterns in large-scale upwelling, primary production, and abundances of copepods and myctophid fish. Oceanic winds were found to be broad determinants of foraging distribution, and of the flight paths taken by the birds on long foraging trips to Antarctic waters. Conclusions/Significance The shearwaters displayed foraging site fidelity and overlap of foraging habitat between species and populations that may enhance their utility as indicators of Southern Ocean ecosystems. The results highlight the importance of upwellings due to interactions of the Antarctic Circumpolar Current with large-scale bottom topography, and the corresponding localised increases in the productivity of the Polar Front ecosystem. PMID:20532034

  16. Feedbacks between ice and ocean dynamics at the West Antarctic Filchner-Ronne Ice Shelf in future global warming scenarios

    NASA Astrophysics Data System (ADS)

    Goeller, Sebastian; Timmermann, Ralph

    2016-04-01

    The ice flow at the margins of the West Antarctic Ice Sheet is moderated by large ice shelves. Their buttressing effect substantially controls the mass balance of the WAIS and thus its contribution to sea level rise. The stability of these ice shelves results from the balance of mass gain by accumulation and ice flow from the adjacent ice sheet and mass loss by calving and basal melting due to the ocean heat flux. Recent results of ocean circulation models indicate that warm circumpolar water of the Southern Ocean may override the submarine slope front of the Antarctic Continent and boost basal ice shelf melting. In particular, ocean simulations for several of the IPCC's future climate scenarios demonstrate the redirection of a warm coastal current into the Filchner Trough and underneath the Filchner-Ronne Ice Shelf within the next decades. In this study, we couple the finite elements ocean circulation model FESOM and the three-dimensional thermomechanical ice flow model RIMBAY to investigate the complex interactions between ocean and ice dynamics at the Filchner-Ronne Ice Shelf. We focus on the impact of a changing ice shelf cavity on ocean dynamics as well as the feedback of the resulting sub-shelf melting rates on the ice shelf geometry and implications for the dynamics of the adjacent marine-based Westantarctic Ice Sheet. Our simulations reveal the high sensitivity of grounding line migration to ice-ocean interactions within the Filchner-Ronne Ice Shelf and emphasize the importance of coupled model studies for realistic assessments of the Antarctic mass balance in future global warming scenarios.

  17. Performance of a Southern Ocean sea ice forecast model

    NASA Astrophysics Data System (ADS)

    Heil, P.; Roberts, A.; Budd, W.

    2003-12-01

    The presentation examines the forecast peformance of an oriented fracture sea ice model applied to the Southern Ocean to predict sea ice state up to five days in advance. The model includes a modified Coulombic elastic-viscous-plastic rheology, enthalpy conserving thermodynamics and a new method of parameterising thickness distribution mechanics. 15 ice thickness classes are employed within each grid cell with a horizontal resolution of 50km. The model provides considerable insight into the thickness evolution and climatology of Antarctic sea ice. To date, thickness evolution of the Southern Ocean sea ice zone has mostly been assessed using course two-category models in climate simulations and results presented in this talk provide much greater detail over some existing model output. Simulations are presented from the model driven with NCEP-2 atmospheric analyses, NOAA sea surface temperatures, and mean climatogological currents generated using an eddy resolving ocean model. Analyses are generated by nudging ice concentrations with daily satellite derived open water fractions, and simulations using this method are compared to those without. There are important considerations in assimilating passive microwave ice concentration data into thickness distribution models, and particular attention is given to the treatment of lead ice and the impact this has on estimated total Southern Ocean sea ice volume. It is shown that nudging the model with satellite derived concentrations has an impact on ice mechanics as judged from simulated buoy tracks. A comparison with sonar soundings of sea ice draft is also favourable but shows variation with location. Whilst 5 day forecasts are reasonably skilled, predictive performance changes with season. Application of this research to operational ocean data assimilation systems is discussed in the final stages of the talk.

  18. Multi-year record of atmospheric mercury at Dumont d'Urville, East Antarctic coast: continental outflow and oceanic influences

    NASA Astrophysics Data System (ADS)

    Angot, Hélène; Dion, Iris; Vogel, Nicolas; Legrand, Michel; Magand, Olivier; Dommergue, Aurélien

    2016-07-01

    Under the framework of the Global Mercury Observation System (GMOS) project, a 3.5-year record of atmospheric gaseous elemental mercury (Hg(0)) has been gathered at Dumont d'Urville (DDU, 66°40' S, 140°01' E, 43 m above sea level) on the East Antarctic coast. Additionally, surface snow samples were collected in February 2009 during a traverse between Concordia Station located on the East Antarctic plateau and DDU. The record of atmospheric Hg(0) at DDU reveals particularities that are not seen at other coastal sites: a gradual decrease of concentrations over the course of winter, and a daily maximum concentration around midday in summer. Additionally, total mercury concentrations in surface snow samples were particularly elevated near DDU (up to 194.4 ng L-1) as compared to measurements at other coastal Antarctic sites. These differences can be explained by the more frequent arrival of inland air masses at DDU than at other coastal sites. This confirms the influence of processes observed on the Antarctic plateau on the cycle of atmospheric mercury at a continental scale, especially in areas subject to recurrent katabatic winds. DDU is also influenced by oceanic air masses and our data suggest that the ocean plays a dual role on Hg(0) concentrations. The open ocean may represent a source of atmospheric Hg(0) in summer whereas the sea-ice surface may provide reactive halogens in spring that can oxidize Hg(0). This paper also discusses implications for coastal Antarctic ecosystems and for the cycle of atmospheric mercury in high southern latitudes.

  19. Mercury depletion events over Antarctic and Arctic oceans

    NASA Astrophysics Data System (ADS)

    Nerentorp Mastromonaco, M. G.; Gardfeldt, K.; Wangberg, I.; Jourdain, B.; Dommergue, A.; Kuronen, P.; Pirrone, N.; Jacobi, H.

    2013-12-01

    Mercury is a global pollutant and in its elemental form it is spread by air to remote areas far away from point sources. In Antarctic and Arctic regions the airborne mercury may be oxidized, followed by deposition of the metal on land and sea surfaces. It is previously known that during early spring in these regions, processes involving halogen radical photochemistry induce an oxidation of gaseous elemental mercury (GEM) in air. This phenomenon is known as an atmospheric mercury depletion event (AMDE) and is characterized by sudden and remarkable decreases in GEM that occurs within hours or days. All or most part of the GEM in air is transformed into gaseous oxidized mercury (GOM) and particulate mercury (HgP). Equivalent ozone depletion events (ODE) do also occur in Antarctic and Arctic regions and the halogen radical photolytic processes involved for AMDEs and ODEs are interrelated. During two oceanographic campaigns at the Weddell Sea onboard RV Polarstern, ANTXXIX/6 (130608-130812) and ANTXXIX/7 (130814-131016), continuous measurements of GEM, GOM and HgP in air were performed using the Tekran mercury speciation system 1130/35. This is the first time such long time series of GEM-, GOM- and HgP data has been achieved over water in the Antarctic during winter and spring. Several mercury depletion events were detected as early as in the middle of July and are correlated and verified with ozone measurements onboard the ship. The observed depletion events were characterised by sudden major decreases in both GEM and ozone concentrations and highly elevated values of HgP. A depletion event is a local phenomenon but evidences show that traces of such events can be detected far away from its origin. During a spring campaign at the Pallas-Matorova station in northern Finland (68o00'N, 24o14'E), GEM, GOM and HgP were measured during three weeks in April 2012 using the Tekran mercury speciation system 1130/35. Traces of remote AMDEs were observed by sudden decreases of GEM

  20. Variability and trends in Southern Ocean eddy activity in 1/12° ocean model simulations

    NASA Astrophysics Data System (ADS)

    Patara, Lavinia; Böning, Claus W.; Biastoch, Arne

    2016-05-01

    The response of eddy kinetic energy (EKE) to the strengthening of Southern Hemisphere winds occurring since the 1950s is investigated with a global ocean model having a resolution of 1/12° in the Antarctic Circumpolar Current domain. The simulations expose regional differences in the relative importance of stochastic and wind-related contributions to interannual EKE changes. In the Pacific and Indian sectors the model captures the EKE variability observed since 1993 and confirms previous hypotheses of a lagged response to regional wind stress anomalies. Here the multidecadal trend in wind stress is reflected in an increase in EKE typically exceeding 5 cm2 s-2 decade-1. In the western Atlantic, EKE variability is mostly stochastic, is weakly correlated with wind fluctuations, and its multidecadal trends are close to zero. The nonuniform distribution of wind-related changes in the eddy activity could affect the regional patterns of ocean circulation and biogeochemical responses to future climate change.

  1. Observations of frozen skin of southern ocean from multifrequency scanning microwave radiometer (MSMR) onboard oceansat - 1

    NASA Astrophysics Data System (ADS)

    Vyas, N.; Bhandari, S.; Dash, M.; Pandey, P.; Khare, N.

    Encircling the Antarctic, Southern Ocean connects all the three oceans of the world with fastest current system found anywhere in the world. The region is thermally very stable and is covered with ice, which has a strong seasonal variability. The sea ice pulsates annually with seasonal migration varying from 4 million square kilometer to 20 million square kilometer during summer and winter respectively. This has strong influence on energy balance of the ocean-ice-atmosphere system, and hence on atmospheric general circulation affecting weather and climate. Sea ice also works as an insulator thus inhibiting the energy flux between ocean and atmosphere. It also influences the ecosystem of the southern ocean, which has rich fish resources with global economic values such as krill and tooth fish. During winter Krill survives on algae found at the under side of the sea ice. The southern ocean is known to have high nutrition but low concentration of chlorophyll-a, which is a proxy of the phytoplankton. It is now understood that iron is the limiting factor as has been shown by various iron fertilization experiments. Passive microwave radiometry from space has been extensively used for the study of sea ice types and concentration in the Arctic and the Antarctic regions. Since late 1970s, data from SMMR and SSM/I have been used to study trends in sea ice extent and area. We have further extended the above studies by using data from OCEANSAT - 1 MSMR. The data, acquired at 18 GHz (H) with 50 kilometer resolution and having a swath of 1360 kilometer and a repeat cycle of 2 days, was processed to generate the brightness temperature maps over the Antarctica for a period of 2 years and the results were analyzed in conjunction with those obtained earlier (since 1978) through the study of SMMR and SSM/I data. Besides strong seasonal variability, our analysis shows an increasing trend in the sea ice extent during the recent years and the rate appears to be accelerating contrary to

  2. Levoglucosan indicates high levels of biomass burning aerosols over oceans from the Arctic to Antarctic

    PubMed Central

    Hu, Qi-Hou; Xie, Zhou-Qing; Wang, Xin-Ming; Kang, Hui; Zhang, Pengfei

    2013-01-01

    Biomass burning is known to affect air quality, global carbon cycle, and climate. However, the extent to which biomass burning gases/aerosols are present on a global scale, especially in the marine atmosphere, is poorly understood. Here we report the molecular tracer levoglucosan concentrations in marine air from the Arctic Ocean through the North and South Pacific Ocean to Antarctica during burning season. Levoglucosan was found to be present in all regions at ng/m3 levels with the highest atmospheric loadings present in the mid-latitudes (30°–60° N and S), intermediate loadings in the Arctic, and lowest loadings in the Antarctic and equatorial latitudes. As a whole, levoglucosan concentrations in the Southern Hemisphere were comparable to those in the Northern Hemisphere. Biomass burning has a significant impact on atmospheric Hg and water-soluble organic carbon (WSOC) from pole-to-pole, with more contribution to WSOC in the Northern Hemisphere than in the Southern Hemisphere. PMID:24176935

  3. Foraging habitats of southern elephant seals, Mirounga leonina, from the Northern Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Muelbert, Monica M. C.; de Souza, Ronald B.; Lewis, Mirtha N.; Hindell, Mark A.

    2013-04-01

    Elephant Island (EI) is uniquely placed to provide southern elephant seals (SES) breeding there with potential access to foraging grounds in the Weddell Sea, the frontal zones of the South Atlantic Ocean, the Patagonian shelf and the Western Antarctic Peninsula (WAP). Quantifying where seals from EI forage therefore provides insights into the types of important habitats available, and which are of particular importance to elephant seals. Twenty nine SES (5 sub-adult males—SAM and 24 adult females—AF) were equipped with SMRU CTD-SLDRs during the post-breeding (PB 2008, 2009) and post-moulting (PM 2007, 2008, 2009, 2010) trips to sea. There were striking intra-annual and inter-sex differences in foraging areas, with most of the PB females remaining within 150 km of EI. One PB AF travelled down the WAP as did 16 out of the 20 PM females and foraged near the winter ice-edge. Most PM sub-adult males remained close to EI, in areas similar to those used by adult females several months earlier, although one SAM spent the early part of the winter foraging on the Patagonian Shelf. The waters of the Northern Antarctic Peninsula (NAP) contain abundant resources to support the majority of the Islands' SES for the summer and early winter, such that the animals from this population have shorter migrations than those from most other populations. Sub-adult males and PB females are certainly taking advantage of these resources. However, PM females did not remain there over the winter months, instead they used the same waters at the ice-edge in the southern WAP that females from both King George Island and South Georgia used. Females made more benthic dives than sub-adult males—again this contrasts with other sites where SAMs do more benthic diving. Unlike most other populations studied to date EI is a relatively southerly breeding colony located on the Antarctic continental shelf. EI seals are using shelf habitats more than other SES populations but some individuals still

  4. Biodiversity and biogeography of Antarctic and sub-Antarctic mollusca

    NASA Astrophysics Data System (ADS)

    Linse, Katrin; Griffiths, Huw J.; Barnes, David K. A.; Clarke, Andrew

    2006-04-01

    For many decades molluscan data have been critical to the establishment of the concept of a global-scale increase in species richness from the poles to the equator. Low polar diversity is key to this latitudinal cline in diversity. Here we investigate richness patterns in the two largest classes of molluscs at both local and regional scales throughout the Southern Ocean. We show that biodiversity is very patchy in the Southern Ocean (at the 1000-km scale) and test the validity of historical biogeographic sub-regions and provinces. We used multivariate analysis of biodiversity patterns at species, genus and family levels to define richness hotspots within the Southern Ocean and transition areas. This process identified the following distinct sub-regions in the Southern Ocean: Antarctic Peninsula, Weddell Sea, East Antarctic—Dronning Maud Land, East Antarctic—Enderby Land, East Antarctic—Wilkes Land, Ross Sea, and the independent Scotia arc and sub Antarctic islands. Patterns of endemism were very different between the bivalves and gastropods. On the basis of distributional ranges and radiation centres of evolutionarily successful families and genera we define three biogeographic provinces in the Southern Ocean: (1) the continental high Antarctic province excluding the Antarctic Peninsula, (2) the Scotia Sea province including the Antarctic Peninsula, and (3) the sub Antarctic province comprising the islands in the vicinity of the Antarctic Circumpolar Current.

  5. Benthic myodocopid Ostracoda (Philomedidae) from the Southern Ocean.

    PubMed

    Chavtur, Vladimir G; Keyser, Dietmar

    2016-01-01

    This study is based on the material of myodocopid ostracodes of the family Philomedidae collected by the Russian Antarctic Polar Expeditions (1963-2007) and the Germany Expeditions on R/V "Polarstern" (1990-2002) from the continental shelf and upper slope near the Mawson and Davis stations, the Weddell Seas, the region of the South Shetland Islands near the Russian Polar station "Molodezhnaya" and adjacent waters. Eight philomedid species belonging to two genera were identified in these collections. Scleroconcha tuberculata sp. nov. is described and figured as a new species. Additional descriptions and figures for the species S. gallardoi Kornicker, 1971, Philomedes assimilis Brady, 1907, P. charcoti Daday, 1908, P. heptatrix Kornicker, 1975, P. rotunda Skogsberg, 1920, P. orbicularis Brady, 1907 and P. tetrathrix Kornicker, 1975 are given. Keys for all species of the mentioned genera known from the Southern Ocean are presented. A list of sampling stations and species collected is provided in the Appendix 1. PMID:27470832

  6. Extraordinarily high biomass benthic community on Southern Ocean seamounts.

    PubMed

    Thresher, R E; Adkins, J; Fallon, S J; Gowlett-Holmes, K; Althaus, F; Williams, A

    2011-01-01

    We describe a previously unknown assemblage of seamount-associated megabenthos that has by far the highest peak biomass reported in the deep-sea outside of vent communities. The assemblage was found at depths of 2-2.5 km on rocky geomorphic features off the southeast coast of Australia, in an area near the Sub-Antarctic Zone characterised by high rates of surface productivity and carbon export to the deep-ocean. These conditions, and the taxa in the assemblage, are widely distributed around the Southern mid-latitudes, suggesting the high-biomass assemblage is also likely to be widespread. The role of this assemblage in regional ecosystem and carbon dynamics and its sensitivities to anthropogenic impacts are unknown. The discovery highlights the lack of information on deep-sea biota worldwide and the potential for unanticipated impacts of deep-sea exploitation. PMID:22355636

  7. Extraordinarily high biomass benthic community on Southern Ocean seamounts

    PubMed Central

    Thresher, R. E.; Adkins, J.; Fallon, S. J.; Gowlett-Holmes, K.; Althaus, F.; Williams, A.

    2011-01-01

    We describe a previously unknown assemblage of seamount-associated megabenthos that has by far the highest peak biomass reported in the deep-sea outside of vent communities. The assemblage was found at depths of 2–2.5 km on rocky geomorphic features off the southeast coast of Australia, in an area near the Sub-Antarctic Zone characterised by high rates of surface productivity and carbon export to the deep-ocean. These conditions, and the taxa in the assemblage, are widely distributed around the Southern mid-latitudes, suggesting the high-biomass assemblage is also likely to be widespread. The role of this assemblage in regional ecosystem and carbon dynamics and its sensitivities to anthropogenic impacts are unknown. The discovery highlights the lack of information on deep-sea biota worldwide and the potential for unanticipated impacts of deep-sea exploitation. PMID:22355636

  8. Southern Ocean Eddies as Weather Makers

    NASA Astrophysics Data System (ADS)

    Frenger, Ivy; Byrne, David; Gruber, Nicolas; Knutti, Reto; Münnich, Matthias; Papritz, Lukas

    2013-04-01

    Several hundred mesoscale eddies populate the Southern Ocean south of 30°S at any time, however, little is known about their effect on the overlying atmosphere. As these eddies feature sea surface temperature (SST) anomalies one can expect them to play a role in the coupling of the atmosphere and the ocean. Here we show based on satellite observations of about 600,000 eddies occurring between 1997 and 2010, that these ocean eddies significantly alter near surface wind, cloud properties and rainfall by several percent. Relative to the atmospheric variability, the magnitude of the anomalies related to ocean eddies represents ±13-15 % (wind, cloud fraction), ±6-10 % (cloud water content) and ±2-6 % (rain). This impact on the atmosphere is striking given the fact that oceanic eddies constitute non-stationary SST fronts of moderate size relative to the much larger atmospheric low pressure systems which are constantly passing by at these latitudes. The spatial pattern of these changes is consistent with a mechanism labeled downward momentum mechanism in which the SST anomalies related to eddies modify the stability and thus turbulence of the atmospheric boundary layer. We will investigate the mechanisms and impact of the atmospheric modifications associated with ocean eddies in a regional high-resolution coupled atmosphere-ocean model (COSMO-ROMS) over the Southern Ocean.

  9. Does the sensitivity of Southern Ocean circulation depend upon bathymetric details?

    PubMed

    Hogg, Andrew McC; Munday, David R

    2014-07-13

    The response of the major ocean currents to changes in wind stress forcing is investigated with a series of idealized, but eddy-permitting, model simulations. Previously, ostensibly similar models have shown considerable variation in the oceanic response to changing wind stress forcing. Here, it is shown that a major reason for these differences in model sensitivity is subtle modification of the idealized bathymetry. The key bathymetric parameter is the extent to which the strong eddy field generated in the circumpolar current can interact with the bottom water formation process. The addition of an embayment, which insulates bottom water formation from meridional eddy fluxes, acts to stabilize the deep ocean density and enhances the sensitivity of the circumpolar current. The degree of interaction between Southern Ocean eddies and Antarctic shelf processes may thereby control the sensitivity of the Southern Ocean to change. PMID:24891390

  10. Covariation of deep Southern Ocean oxygenation and atmospheric CO2 through the last ice age.

    PubMed

    Jaccard, Samuel L; Galbraith, Eric D; Martínez-García, Alfredo; Anderson, Robert F

    2016-02-11

    No single mechanism can account for the full amplitude of past atmospheric carbon dioxide (CO2) concentration variability over glacial-interglacial cycles. A build-up of carbon in the deep ocean has been shown to have occurred during the Last Glacial Maximum. However, the mechanisms responsible for the release of the deeply sequestered carbon to the atmosphere at deglaciation, and the relative importance of deep ocean sequestration in regulating millennial-timescale variations in atmospheric CO2 concentration before the Last Glacial Maximum, have remained unclear. Here we present sedimentary redox-sensitive trace-metal records from the Antarctic Zone of the Southern Ocean that provide a reconstruction of transient changes in deep ocean oxygenation and, by inference, respired carbon storage throughout the last glacial cycle. Our data suggest that respired carbon was removed from the abyssal Southern Ocean during the Northern Hemisphere cold phases of the deglaciation, when atmospheric CO2 concentration increased rapidly, reflecting--at least in part--a combination of dwindling iron fertilization by dust and enhanced deep ocean ventilation. Furthermore, our records show that the observed covariation between atmospheric CO2 concentration and abyssal Southern Ocean oxygenation was maintained throughout most of the past 80,000 years. This suggests that on millennial timescales deep ocean circulation and iron fertilization in the Southern Ocean played a consistent role in modifying atmospheric CO2 concentration. PMID:26840491

  11. Southern elephant seals from Kerguelen Islands confronted by Antarctic Sea ice. Changes in movements and in diving behaviour

    NASA Astrophysics Data System (ADS)

    Bailleul, Frédéric; Charrassin, Jean-Benoıˆt; Ezraty, Robert; Girard-Ardhuin, Fanny; McMahon, Clive R.; Field, Iain C.; Guinet, Christophe

    2007-02-01

    The behaviour of southern elephant seals from Kerguelen Island ( 49∘50'S, 70∘30'E) was investigated in relation to the oceanographic regions of the Southern Ocean. The oceanographic and the seal behaviour data, including location and diving activity, were collected using a new generation of satellite-relayed devices measuring and transmitting pressure, temperature, and salinity along with locations. Dive duration, maximum diving depth, time spent at the bottom of the dives, and shape of dive profiles were compared between male and female seals, and were related to the oceanographic characteristics of areas prospected by the seals. Most animals travelled to the Antarctic shelf. However, during winter, adult females travelled away from the continent, remained and foraged within the marginal sea-ice zone, while juvenile males remained within the pack ice to forage mainly on the Antarctic shelf. Therefore, as the ice expanded females appeared to shift from benthic to pelagic foraging farther north, while males continued to forage almost exclusively benthically on the continental shelf. This difference is likely related to the different energetic requirements between the two sexes, but also may be related to pregnant females having to return to Kerguelen in early spring in order to give birth and successfully raise their pups, while males can remain in the ice. Our results show an important link between elephant seals and Antarctic sea ice and suggest that changes in sea-ice conditions could strongly affect the behaviour of this species.

  12. Southern Ocean biological impacts on global ocean oxygen

    NASA Astrophysics Data System (ADS)

    Keller, David P.; Kriest, Iris; Koeve, Wolfgang; Oschlies, Andreas

    2016-06-01

    Southern Ocean (SO) physical and biological processes are known to have a large impact on global biogeochemistry. However, the role that SO biology plays in determining ocean oxygen concentrations is not completely understood. These dynamics are investigated here by shutting off SO biology in two marine biogeochemical models. The results suggest that SO biological processes reduce the ocean's oxygen content, mainly in the deep ocean, by 14 to 19%. However, since these processes also trap nutrients that would otherwise be transported northward to fuel productivity and subsequent organic matter export, consumption, and the accompanying oxygen consumption in midlatitude to low-latitude waters, SO biology helps to maintain higher oxygen concentrations in these subsurface waters. Thereby, SO biology can influence the size of the tropical oxygen minimum zones. As a result of ocean circulation the link between SO biological processes and remote oxygen changes operates on decadal to centennial time scales.

  13. Community structure across a large-scale ocean productivity gradient: Marine bird assemblages of the Southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Hyrenbach, K. David; Veit, Richard R.; Weimerskirch, Henri; Metzl, Nicolas; Hunt, George L., Jr.

    2007-07-01

    Our objective was to understand how marine birds respond to oceanographic variability across the Southern Indian Ocean using data collected during an 16-day cruise (4-21 January 2003). We quantified concurrent water mass distributions, ocean productivity patterns, and seabird distributions across a heterogeneous pelagic ecosystem from subtropical to sub-Antarctic waters. We surveyed 5155 km and sighted 15,606 birds from 51 species, and used these data to investigate how seabirds respond to spatial variability in the structure and productivity of the ocean. We addressed two spatial scales: the structure of seabird communities across macro-mega scale (1000 s km) biogeographic domains, and their coarse-scale (10 s km) aggregation at hydrographic and bathymetric gradients. Both seabird density and species composition changed with latitudinal and onshore-offshore gradients in depth, water temperature, and chlorophyll-a concentration. The average seabird density increased across the subtropical convergence (STC) from 2.4 birds km -2 in subtropical waters to 23.8 birds km -2 in sub-Antarctic waters. The composition of the avifauna also differed across biogeographic domains. Prions ( Pachyptila spp.) accounted for 57% of all sub-Antarctic birds, wedge-tailed shearwaters ( Puffinus pacificus) accounted for 46% of all subtropical birds, and Indian Ocean yellow-nosed albatross ( Thallasarche carteri) accounted for 32% of all birds in the STC. While surface feeders were the most abundant foraging guild across the study area, divers were disproportionately more numerous in the sub-Antarctic domain, and plungers were disproportionately more abundant in subtropical waters. Seabird densities were also higher within shallow shelf-slope regions, especially in sub-Antarctic waters, where large numbers of breeding seabirds concentrated. However, we did not find elevated seabird densities along the STC, suggesting that this broad frontal region is not a site of enhanced aggregation.

  14. Southern Ocean isopycnal mixing and ventilation changes driven by winds

    NASA Astrophysics Data System (ADS)

    Abernathey, Ryan; Ferreira, David

    2015-12-01

    Observed and predicted changes in the strength of the westerly winds blowing over the Southern Ocean have motivated a number of studies on the response of the Antarctic Circumpolar Current and Southern Ocean meridional overturning circulation (MOC) to wind perturbations and led to the hypothesis of the "eddy compensation" regime, wherein the MOC becomes insensitive to wind changes. In addition to the MOC, tracer transport also depends on mixing processes. Here we show, in a high-resolution process model, that isopycnal mixing by mesoscale eddies is strongly dependent on the wind strength. This dependence can be explained by mixing length theory and is driven by increases in eddy kinetic energy; the mixing length does not change strongly in our simulation. Simulation of a passive ventilation tracer (analogous to CFCs or anthropogenic CO2) demonstrates that variations in tracer uptake across experiments are dominated by changes in isopycnal mixing, rather than changes in the MOC. We argue that to properly understand tracer uptake under different wind-forcing scenarios, the sensitivity of isopycnal mixing to winds must be accounted for.

  15. Southern Ocean heat and carbon uptake: mechanisms, recent trends, and future changes

    NASA Astrophysics Data System (ADS)

    Froelicher, T. L.

    2015-12-01

    The Southern Ocean's dominant influence on the global heat balance and nutrient and carbon cycles stems from the fact that it is the primary gateway through which Earth's cold, centuries old and nutrient rich deep and bottom waters interact with the atmosphere. The westerly winds in the Southern Hemisphere drive a strongly divergent surface flow that draws up water from below in a wide ring circling the Antarctic continent. In the first part of the talk, we assess the uptake, transport, and storage of oceanic anthropogenic carbon and heat in the Southern Ocean over the period 1861-2005 in a new set of carbon-climate Earth System Models. Simulations show that the Southern Ocean south of 30°S, covering only 30% of the global surface ocean area, accounts for more than 40% of global anthropogenic carbon uptake. Furthermore, the Southern Ocean takes up three quarters of the total excess heat generated by the increasing levels of greenhouse gases in the atmosphere. Anthropogenic carbon and heat storage show a common broad-scale pattern of change, but ocean heat storage is more structured than ocean carbon storage suggesting that different mechanisms are important. The Southern Ocean, however, remains the region where models differ the most in the representation of anthropogenic carbon and, in particular, heat uptake. While the Southern Ocean carbon uptake has increased considerably in recent decades, as expected based on the substantial increase in atmospheric CO2, there is considerable concern that this sink will saturate or even reverse in response to warming, changing ocean circulation and chemistry. In the second part of the talk, novel multi-millennial global warming simulations with a comprehensive Earth System Model under a 1% yr-1 atmospheric CO2 increase to 2xCO2 and constant forcing thereafter scenario will be used to explore future long-term changes in the Southern Ocean carbon uptake. We show that after full equilibration of the model with doubling of

  16. The International Bathymetric Chart of the Southern Ocean - A new Map of Antarctica

    NASA Astrophysics Data System (ADS)

    Arndt, J.; Schenke, H. W.

    2012-12-01

    The International Bathymetric Chart of the Southern Ocean (IBCSO) is an expert group of the Scientific Committee on Antarctic Research (SCAR) since the XXVIII SCAR Conference held on 30th July 2004 in Bremen Germany and a regional Mapping project of the General Bathymetric Chart of the Ocean (GEBCO) operated under the joint auspices of the Intergovernmental Oceanographic Commission (IOC) (of UNESCO) and the International Hydrographic Organization (IHO). The objective of IBCSO was to produce a first seamless bathymetric grid for the area south of latitude 60° S covering the area of the Antarctic Treaty. The IBCSO is going to be a benefit for scientific purposes. These include (a) interpretation of seabed geology, (b) the building of habitat models and maps, and (c) mapping and tracing of deep ocean current pathways. In addition the IBCSO is going to serve as database for the development of new Electronic Nautical Charts (ENC) in the Southern Ocean to improve the safety of navigation in Antarctic waters. As the first version of the IBCSO grid is close to be released, so is the corresponding map. It is proposed to present the latest draft version, or even the final version, of the new IBCSO map. Besides the map itself, the process to achieve the first version of the IBCSO grid and map is going to be presented. This includes a description of the datasets used to create the map and a rough explanation of the working steps to generate the first grid version of the IBCSO.

  17. Low densities of drifting litter in the African sector of the Southern Ocean.

    PubMed

    Ryan, Peter G; Musker, Seth; Rink, Ariella

    2014-12-15

    Only 52 litter items (>1cm diameter) were observed in 10,467 km of at-sea transects in the African sector of the Southern Ocean. Litter density north of the Subtropical Front (0.58 items km(-2)) was less than in the adjacent South Atlantic Ocean (1-6 items km(-2)), but has increased compared to the mid-1980s. Litter density south of the Subtropical Front was an order of magnitude less than in temperate waters (0.032 items km(-2)). There was no difference in litter density between sub-Antarctic and Antarctic waters either side of the Antarctic Polar Front. Most litter was made of plastic (96%). Fishery-related debris comprised a greater proportion of litter south of the Subtropical Front (33%) than in temperate waters (13%), where packaging dominated litter items (68%). The results confirm that the Southern Ocean is the least polluted ocean in terms of drifting debris and suggest that most debris comes from local sources. PMID:25455366

  18. Pronounced warming in the Indian and Pacific sectors of the Southern Ocean during the 1970s

    NASA Astrophysics Data System (ADS)

    Turney, Chris; Fogwill, Chris; Palmer, Jonathan; van Sebille, Erik; Thomas, Zoë; McGlone, Matt; Richardson, Sarah; Wilmshurst, Janet; Fenwick, Pavla; Carter, Lionel; Jones, Richard; Harsch, Melanie; Wilson, Kerry-Jayne; Clark, Graeme; Marzinelli, Ezequiel; Rogers, Tracey; Rainsley, Eleanor; Ciasto, Laura; Waterman, Stephanie; Antarctic Expedition 2013-2014 Members, Australasian

    2015-04-01

    Occupying some 20% of the world's ocean surface, the Southern Ocean is home to a diverse and unique biota and plays a fundamental role in global oceanic circulation, climate variability, Antarctic ice sheet stability and carbon cycling. Significant warming has been observed over recent decades, most prominently in the Antarctic Circumpolar Current (ACC). The mechanism(s) behind this warming, however, remain uncertain. Here, we integrate historic ocean and atmospheric observations and climate-sensitive tree growth on subantarctic islands from the northern limit of the ACC to extend historic and satellite measurements to produce a unique proxy record of temperature across 4˚ of latitude in the southwest Pacific. We demonstrate a hitherto unobserved abrupt warming during the 1970s that is unprecedented over the past 130 years, coincident with a significant decline in marine vertebrate populations and wider warming across the Indian Ocean. Comparison between our reconstruction and high-resolution ocean modelling provides a possible mechanism, suggesting warmer waters resulted from a poleward migration of the subtropical and ACC fronts. Projected increases in the strength of westerly winds are likely to continue the fronts' migration, driving warming in the Southern Ocean (>50˚S), with significant impacts on biota.

  19. Observed and Modeled Trends in Southern Ocean Sea Ice

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.

    2003-01-01

    Conceptual models and global climate model (GCM) simulations have both indicated the likelihood of an enhanced sensitivity to climate change in the polar regions, derived from the positive feedbacks brought about by the polar abundance of snow and ice surfaces. Some models further indicate that the changes in the polar regions can have a significant impact globally. For instance, 37% of the temperature sensitivity to a doubling of atmospheric CO2 in simulations with the GCM of the Goddard Institute for Space Studies (GISS) is attributable exclusively to inclusion of sea ice variations in the model calculations. Both sea ice thickness and sea ice extent decrease markedly in the doubled CO, case, thereby allowing the ice feedbacks to occur. Stand-alone sea ice models have shown Southern Ocean hemispherically averaged winter ice-edge retreats of 1.4 deg latitude for each 1 K increase in atmospheric temperatures. Observations, however, show a much more varied Southern Ocean ice cover, both spatially and temporally, than many of the modeled expectations. In fact, the satellite passive-microwave record of Southern Ocean sea ice since late 1978 has revealed overall increases rather than decreases in ice extents, with ice extent trends on the order of 11,000 sq km/year. When broken down spatially, the positive trends are strongest in the Ross Sea, while the trends are negative in the Bellingshausen/Amundsen Seas. Greater spatial detail can be obtained by examining trends in the length of the sea ice season, and those trends show a coherent picture of shortening sea ice seasons throughout almost the entire Bellingshausen and Amundsen Seas to the west of the Antarctic Peninsula and in the far western Weddell Sea immediately to the east of the Peninsula, with lengthening sea ice seasons around much of the rest of the continent. This pattern corresponds well with the spatial pattern of temperature trends, as the Peninsula region is the one region in the Antarctic with a strong

  20. Satellite-Derived Dynamics of Southern Ocean Sea Ice

    NASA Technical Reports Server (NTRS)

    Drinkwater, Mark R.; Liu, Xiang

    2000-01-01

    Antarctic ERS-2, RADARSAT Synthetic Aperture Radar and ERS-1/2 Scatterometer images were analyzed with SMMI radiometer image time-series data to investigate seasonal variability in satellite-tracked sea-ice dynamics in the Southern Ocean during 1992. Supporting field data were acquired during 'in-situ' experiments including the winter 1992 Ice Station Weddell and Winter Weddell Gyre studies. A variety of surface measurements were made during these experiments including Argos-buoy deployment and GPS drift measurements. These are used in conjunction with International Program for Antarctic Buoys drift trajectories for ice-motion tracking validation. Comparisons between gridded Special Sensor Microwave Imager (SSMI) ice-motion vectors and European Center for Medium Range Weather Forecasts/National Centers for Environmental Prediction (ECMWF/NCEP) analyses indicate that large-scale drift is forced predominantly by the long-term mean, large-scale synoptic pressure field. Only sub-daily SAR sea-ice tracking can capture high-frequency fluctuations, driven by polar lows or tidal forcing. In these cases, sea-ice drift can respond rapidly to changes in forcing on semi-diurnal time scales depending on the location with respect to the coastline. Seasonality of ice drift, particularly in the Weddell and Ross Seas, is linked to ice extent and compactness, and internal ice stresses transmitted through the pack ice from the coast. Three-monthly seasonal climatologies are presented of austral winter of ice drift in the Southern Ocean. The large Weddell and Ross Sea gyres are clearly resolved along with key seasonal and spatial attributes of their cyclonic circulation. Regional time series of ice dynamics parameters are used to illustrate correlations with meteorological forcing. Persistent divergence such as that occurring in the Ronne-Filchner polynya system results in large fractions of new ice. Similarly, convergence zones produce large fractions of deformed ice and characterize

  1. Marine introductions in the Southern Ocean: an unrecognised hazard to biodiversity.

    PubMed

    Lewis, Patrick N; Hewitt, Chad L; Riddle, Martin; McMinn, Andrew

    2003-02-01

    This study investigated the potential for transport of organisms between Hobart, Macquarie Island and the Antarctic continent by ships used in support of Antarctic science and tourism. Northward transport of plankton in ballast water is more likely than southward transport because ballast is normally loaded in the Antarctic and unloaded at the home port. Culturing of ballast water samples revealed that high-latitude hitchhikers were able to reach greater diversities when cultured at temperate thermal conditions than at typical Southern Ocean temperatures, suggesting the potential for establishment in the Tasmanian coastal environment. Several known invasive species were identified among fouling communities on the hulls of vessels that travel between Hobart and the Southern Ocean. Southward transport of hull fouling species is more likely than northward transport due to the accumulation of assemblages during the winter period spent in the home port of Hobart. This study does not prove that non-indigenous marine species have, or will be, transported and established as a consequence of Antarctic shipping but illustrates that the potential exists. Awareness of the potential risk and simple changes to operating procedures may reduce the chance of introductions in the future. PMID:12586117

  2. Southern Ocean biogeochemical control of glacial/interglacial carbon dioxide change

    NASA Astrophysics Data System (ADS)

    Sigman, D. M.

    2014-12-01

    In the effort to explain the lower atmospheric CO2 concentrations observed during ice ages, two of the first hypotheses involved redistributing dissolved inorganic carbon (DIC) within the ocean. Broecker (1982) proposed a strengthening of the ocean's biological pump during ice ages, which increased the dissolved inorganic carbon gradient between the dark, voluminous ocean interior and the surface ocean's sun-lit, wind-mixed layer. Boyle (1988) proposed a deepening in the ocean interior's pool of DIC associated with organic carbon regeneration, with its concentration maximum shifting from intermediate to abyssal depths. While not irrefutable, evidence has arisen that these mechanisms can explain much of the ice age CO2 reduction and that both were activated by changes in the Southern Ocean. In the Antarctic Zone, reduced exchange of water between the surface and the underlying ocean sequestered more DIC in the ocean interior (the biological pump mechanism). Dust-borne iron fertilization of the Subantarctic surface lowered CO2 partly by the biological pump mechanism and partly by Boyle's carbon deepening. Each mechanism owes a part of its CO2 effect to a transient increase in seafloor calcium carbonate dissolution, which raised the ice age ocean's alkalinity, causing it to absorb more CO2. However, calcium carbonate cycling also sets limits on these mechanisms and their CO2 effects, such that the combination of Antarctic and Subantarctic changes is needed to achieve the full (80-100 ppm) ice age CO2 decline. Data suggest that these changes began at different phases in the development of the last ice age, 110 and 70 ka, respectively, explaining a 40 ppm CO2 drop at each time. We lack a robust understanding of the potential causes for both the implied reduction in Antarctic surface/deep exchange and the increase in Subantarctic dust supply during ice ages. Thus, even if the evidence for these Southern Ocean changes were to become incontrovertible, conceptual gaps stand

  3. East Antarctic land-ice/ocean networks: progress and questions

    NASA Astrophysics Data System (ADS)

    Blankenship, D. D.; Young, D. A.; Greenbaum, J. S.; Roberts, J. L.; van Ommen, T. D.; Aitken, A.; Siegert, M. J.

    2014-12-01

    International collaborative exploration over the last decade has revealed East Antarctica as a geologically diverse continent underlying an ice sheet with significant sea level potential, parts of which are currently undergoing rapid change. The Wilkes and Aurora Subglacial Basins (WSB and ASB), two of the largest reservoirs of sea level potential in Antarctica, are broader, deeper, and more susceptible to marine ice sheet instability than previously known. The morphology and coastal connections of the ASB indicate a dynamic early ice sheet with a significant erosional history and multiple ice sheet configurations. Recent results imply significant retreat into the WSB during the Pliocene while today irreversible discharge there is halted by only a small ridge. We have unveiled complex contemporary subglacial landscapes beneath both basins providing new challenges and opportunities to ice sheet modelers. For instance, geothermal heat flow varies spatially on multiple scales in the continental crust assumed to be homogeneous. A large, active, subglacial hydrological system flows through the ASB along pathways that likely predate large-scale glaciation. Proxies indicate four to eight meters of global sea level rise during the last interglacial period. Ice core results constrain the amount of sea level rise to one to three meters from contributed by East Antarctica. Going forward, new altimetry data along the East Antarctic coast reveal extensive lowering of the Totten and Denman Glaciers while satellite gravity indicate a variable but persistent record of negative regional mass loss. These discoveries provide a new baseline as the international community increases its focus on the region through ongoing airborne and marine exploration to address the many outstanding questions: What is the character and distribution of subglacial boundary conditions and water systems upstream of the grounding line in areas of significant potential sea level impact? How much subglacial

  4. Insolation-induced mid-Brunhes transition in Southern Ocean ventilation and deep-ocean temperature.

    PubMed

    Yin, Qiuzhen

    2013-02-14

    Glacial-interglacial cycles characterized by long cold periods interrupted by short periods of warmth are the dominant feature of Pleistocene climate, with the relative intensity and duration of past and future interglacials being of particular interest for civilization. The interglacials after 430,000 years ago were characterized by warmer climates and higher atmospheric concentrations of carbon dioxide than the interglacials before, but the cause of this climatic transition (the so-called mid-Brunhes event (MBE)) is unknown. Here I show, on the basis of model simulations, that in response to insolation changes only, feedbacks between sea ice, temperature, evaporation and salinity caused vigorous pre-MBE Antarctic bottom water formation and Southern Ocean ventilation. My results also show that strong westerlies increased the pre-MBE overturning in the Southern Ocean via an increased latitudinal insolation gradient created by changes in eccentricity during austral winter and by changes in obliquity during austral summer. The stronger bottom water formation led to a cooler deep ocean during the older interglacials. These insolation-induced differences in the deep-sea temperature and in the Southern Ocean ventilation between the more recent interglacials and the older ones were not expected, because there is no straightforward systematic difference in the astronomical parameters between the interglacials before and after 430,000 years ago. Rather than being a real 'event', the apparent MBE seems to have resulted from a series of individual interglacial responses--including notable exceptions to the general pattern--to various combinations of insolation conditions. Consequently, assuming no anthropogenic interference, future interglacials may have pre- or post-MBE characteristics without there being a systematic change in forcings. These findings are a first step towards understanding the magnitude change of the interglacial carbon dioxide concentration around 430

  5. Glacial-interglacial variability in diatom abundance and valve size: Implications for Southern Ocean paleoceanography

    NASA Astrophysics Data System (ADS)

    Nair, Abhilash; Mohan, Rahul; Manoj, M. C.; Thamban, Meloth

    2015-10-01

    Antarctic sea ice extent along with Southern Ocean biological productivity varied considerably during glacial-interglacial periods, and both are known to have played a considerable role in regulating atmospheric CO2 variations in the past. Here we present data on diatom absolute abundance (valves/g of sediment) and size over the past ~ 42 ka B.P. and how they link to glacial-interglacial changes in Antarctic sea ice extent, Southern Ocean frontal systems, and aeolian dust flux. Our records of sea ice and permanent open ocean zone diatom abundances suggest a shift in the Antarctic winter sea ice limit and Polar Front respectively up to the modern-day Polar Frontal Zone during marine isotopic stages (MIS) 2 and late MIS 3. In addition to glacial shifts in the Polar Front, diatom assemblages also recorded a plausible northward shifts in Polar Front during few intervals of MIS 1. Glacial periods north of the Polar Front in the Indian sector of the Southern Ocean were characterized by higher total diatom abundance, larger Fragilariopsis kerguelensis apical length, and Thalassiosira lentiginosa radius. This is probably a consequence of (1) a northward expansion of the opal belt, a region characterized by high production and export of biogenic silica; (2) an increase in terrigenous input, via erosion of Crozet Islands; and (3) the alleviation of iron deficit by high input of Fe-bearing dust. The larger and highly silicified diatoms such as F. kerguelensis and T. lentiginosa may have mainly contributed in transporting biogenic silica and organic carbon to the seabed for the last 42 ka, in the northern Polar Frontal Zone of the Indian sector of the Southern Ocean.

  6. Deglacial Atlantic Radiocarbon: A Southern Ocean Perspective

    NASA Astrophysics Data System (ADS)

    Robinson, L. F.; Burke, A.; Adkins, J. F.; Chen, T.; Spooner, P.

    2014-12-01

    It is widely accepted that the Southern Ocean is an important component of the climate system, acting as a key site for carbon and heat exchange between the atmosphere and oceans. The deglaciation with its associated millenial climate changes is a key time period for testing the mechanisms behind these exchanges. Ascertaining the precise timing of these events is a challenge given complications from variable and largely unconstrained reservoir ages, dissolution of carbonate hard parts and sediment redistribution by strong currents. Nevertheless improvements to our understanding of Southern Ocean dynamics in the past requires accurately-dated proxy records that can be embedded in GCM models. Radiocarbon measured in deep-sea corals offers just such an archive and proxy. Using the skeletons of deep-sea corals we are now able to reconstruct aspects of the history of three distinct water masses in the Drake Passage on a precise timescale, allowing direct comparison to U-series dated speleothem terrestrial records and polar ice cores. We present here a new deglacial radiocarbon record from the Drake Passage which more than doubles the resolution of published records. We focus on the deglacial, as well as providing insights from the contrasting period leading up to the LGM. Together with new data from far-field sites we interpret our results as evidence for a Southern Ocean control on atmospheric carbon dioxide and radiocarbon evolution during the deglaciation, and a northern hemisphere control during the run up to the LGM.

  7. Methyl iodine over oceans from the Arctic Ocean to the maritime Antarctic

    PubMed Central

    Hu, Qihou; Xie, Zhouqing; Wang, Xinming; Yu, Juan; Zhang, Yanli

    2016-01-01

    Studies about methyl iodide (CH3I), an important atmospheric iodine species over oceans, had been conducted in some maritime regions, but the understanding of the spatial distribution of CH3I on a global scale is still limited. In this study, we reports atmospheric CH3I over oceans during the Chinese Arctic and Antarctic Research Expeditions. CH3I varied considerably with the range of 0.17 to 2.9 pptv with absent of ship emission. The concentration of CH3I generally decreased with increasing latitudes, except for higher levels in the middle latitudes of the Northern Hemisphere than in the low latitudes. For sea areas, the Norwegian Sea had the highest CH3I concentrations with a median of 0.91 pptv, while the Central Arctic Ocean had the lowest concentrations with all values below 0.5 pptv. CH3I concentration over oceans was affected by many parameters, including sea surface temperature, salinity, dissolved organic carbon, biogenic emissions and input from continents, with distinctive dominant factor in different regions, indicating complex biogeochemical processes of CH3I on a global scale. PMID:27184471

  8. Methyl iodine over oceans from the Arctic Ocean to the maritime Antarctic

    NASA Astrophysics Data System (ADS)

    Hu, Qihou; Xie, Zhouqing; Wang, Xinming; Yu, Juan; Zhang, Yanli

    2016-05-01

    Studies about methyl iodide (CH3I), an important atmospheric iodine species over oceans, had been conducted in some maritime regions, but the understanding of the spatial distribution of CH3I on a global scale is still limited. In this study, we reports atmospheric CH3I over oceans during the Chinese Arctic and Antarctic Research Expeditions. CH3I varied considerably with the range of 0.17 to 2.9 pptv with absent of ship emission. The concentration of CH3I generally decreased with increasing latitudes, except for higher levels in the middle latitudes of the Northern Hemisphere than in the low latitudes. For sea areas, the Norwegian Sea had the highest CH3I concentrations with a median of 0.91 pptv, while the Central Arctic Ocean had the lowest concentrations with all values below 0.5 pptv. CH3I concentration over oceans was affected by many parameters, including sea surface temperature, salinity, dissolved organic carbon, biogenic emissions and input from continents, with distinctive dominant factor in different regions, indicating complex biogeochemical processes of CH3I on a global scale.

  9. Methyl iodine over oceans from the Arctic Ocean to the maritime Antarctic.

    PubMed

    Hu, Qihou; Xie, Zhouqing; Wang, Xinming; Yu, Juan; Zhang, Yanli

    2016-01-01

    Studies about methyl iodide (CH3I), an important atmospheric iodine species over oceans, had been conducted in some maritime regions, but the understanding of the spatial distribution of CH3I on a global scale is still limited. In this study, we reports atmospheric CH3I over oceans during the Chinese Arctic and Antarctic Research Expeditions. CH3I varied considerably with the range of 0.17 to 2.9 pptv with absent of ship emission. The concentration of CH3I generally decreased with increasing latitudes, except for higher levels in the middle latitudes of the Northern Hemisphere than in the low latitudes. For sea areas, the Norwegian Sea had the highest CH3I concentrations with a median of 0.91 pptv, while the Central Arctic Ocean had the lowest concentrations with all values below 0.5 pptv. CH3I concentration over oceans was affected by many parameters, including sea surface temperature, salinity, dissolved organic carbon, biogenic emissions and input from continents, with distinctive dominant factor in different regions, indicating complex biogeochemical processes of CH3I on a global scale. PMID:27184471

  10. Sources and Levels of Ambient Ocean Sound near the Antarctic Peninsula

    PubMed Central

    Dziak, Robert P.; Bohnenstiehl, DelWayne R.; Stafford, Kathleen M.; Matsumoto, Haruyoshi; Park, Minkyu; Lee, Won Sang; Fowler, Matt J.; Lau, Tai-Kwan; Haxel, Joseph H.; Mellinger, David K.

    2015-01-01

    Arrays of hydrophones were deployed within the Bransfield Strait and Scotia Sea (Antarctic Peninsula region) from 2005 to 2009 to record ambient ocean sound at frequencies of up to 125 and 500 Hz. Icequakes, which are broadband, short duration signals derived from fracturing of large free-floating icebergs, are a prominent feature of the ocean soundscape. Icequake activity peaks during austral summer and is minimum during winter, likely following freeze-thaw cycles. Iceberg grounding and rapid disintegration also releases significant acoustic energy, equivalent to large-scale geophysical events. Overall ambient sound levels can be as much as ~10–20 dB higher in the open, deep ocean of the Scotia Sea compared to the relatively shallow Bransfield Strait. Noise levels become lowest during the austral winter, as sea-ice cover suppresses wind and wave noise. Ambient noise levels are highest during austral spring and summer, as surface noise, ice cracking and biological activity intensifies. Vocalizations of blue (Balaenoptera musculus) and fin (B. physalus) whales also dominate the long-term spectra records in the 15–28 and 89 Hz bands. Blue whale call energy is a maximum during austral summer-fall in the Drake Passage and Bransfield Strait when ambient noise levels are a maximum and sea-ice cover is a minimum. Fin whale vocalizations were also most common during austral summer-early fall months in both the Bransfield Strait and Scotia Sea. The hydrophone data overall do not show sustained anthropogenic sources (ships and airguns), likely due to low coastal traffic and the typically rough weather and sea conditions of the Southern Ocean. PMID:25875205

  11. Sources and levels of ambient ocean sound near the Antarctic Peninsula.

    PubMed

    Dziak, Robert P; Bohnenstiehl, DelWayne R; Stafford, Kathleen M; Matsumoto, Haruyoshi; Park, Minkyu; Lee, Won Sang; Fowler, Matt J; Lau, Tai-Kwan; Haxel, Joseph H; Mellinger, David K

    2015-01-01

    Arrays of hydrophones were deployed within the Bransfield Strait and Scotia Sea (Antarctic Peninsula region) from 2005 to 2009 to record ambient ocean sound at frequencies of up to 125 and 500 Hz. Icequakes, which are broadband, short duration signals derived from fracturing of large free-floating icebergs, are a prominent feature of the ocean soundscape. Icequake activity peaks during austral summer and is minimum during winter, likely following freeze-thaw cycles. Iceberg grounding and rapid disintegration also releases significant acoustic energy, equivalent to large-scale geophysical events. Overall ambient sound levels can be as much as ~10-20 dB higher in the open, deep ocean of the Scotia Sea compared to the relatively shallow Bransfield Strait. Noise levels become lowest during the austral winter, as sea-ice cover suppresses wind and wave noise. Ambient noise levels are highest during austral spring and summer, as surface noise, ice cracking and biological activity intensifies. Vocalizations of blue (Balaenoptera musculus) and fin (B. physalus) whales also dominate the long-term spectra records in the 15-28 and 89 Hz bands. Blue whale call energy is a maximum during austral summer-fall in the Drake Passage and Bransfield Strait when ambient noise levels are a maximum and sea-ice cover is a minimum. Fin whale vocalizations were also most common during austral summer-early fall months in both the Bransfield Strait and Scotia Sea. The hydrophone data overall do not show sustained anthropogenic sources (ships and airguns), likely due to low coastal traffic and the typically rough weather and sea conditions of the Southern Ocean. PMID:25875205

  12. Sources and levels of ambient ocean sound near the antarctic peninsula

    DOE PAGESBeta

    Dziak, Robert P.; Bohnenstiehl, DelWayne R.; Stafford, Kathleen M.; Matsumoto, Haruyoshi; Park, Minkyu; Lee, Won Sang; Fowler, Matt J.; Lau, Tai-Kwan; Haxel, Joseph H.; Mellinger, David K.; et al

    2015-04-14

    Arrays of hydrophones were deployed within the Bransfield Strait and Scotia Sea (Antarctic Peninsula region) from 2005 to 2009 to record ambient ocean sound at frequencies of up to 125 and 500 Hz. Icequakes, which are broadband, short duration signals derived from fracturing of large free-floating icebergs, are a prominent feature of the ocean soundscape. Icequake activity peaks during austral summer and is minimum during winter, likely following freeze-thaw cycles. Iceberg grounding and rapid disintegration also releases significant acoustic energy, equivalent to large-scale geophysical events. Overall ambient sound levels can be as much as ~10–20 dB higher in the open,more » deep ocean of the Scotia Sea compared to the relatively shallow Bransfield Strait. Noise levels become lowest during the austral winter, as sea-ice cover suppresses wind and wave noise. Ambient noise levels are highest during austral spring and summer, as surface noise, ice cracking and biological activity intensifies. Vocalizations of blue (Balaenoptera musculus) and fin (B. physalus) whales also dominate the long-term spectra records in the 15–28 and 89 Hz bands. Blue whale call energy is a maximum during austral summer-fall in the Drake Passage and Bransfield Strait when ambient noise levels are a maximum and sea-ice cover is a minimum. Fin whale vocalizations were also most common during austral summer-early fall months in both the Bransfield Strait and Scotia Sea. The hydrophone data overall do not show sustained anthropogenic sources (ships and airguns), likely due to low coastal traffic and the typically rough weather and sea conditions of the Southern Ocean.« less

  13. Sources and levels of ambient ocean sound near the antarctic peninsula

    SciTech Connect

    Dziak, Robert P.; Stafford, Kathleen M.; Matsumoto, Haruyoshi; Lee, Won Sang; Fowler, Matt J.

    2015-04-14

    Arrays of hydrophones were deployed within the Bransfield Strait and Scotia Sea (Antarctic Peninsula region) from 2005 to 2009 to record ambient ocean sound at frequencies of up to 125 and 500 Hz. Icequakes, which are broadband, short duration signals derived from fracturing of large free-floating icebergs, are a prominent feature of the ocean soundscape. Icequake activity peaks during austral summer and is minimum during winter, likely following freeze-thaw cycles. Iceberg grounding and rapid disintegration also releases significant acoustic energy, equivalent to large-scale geophysical events. Overall ambient sound levels can be as much as ~10–20 dB higher in the open, deep ocean of the Scotia Sea compared to the relatively shallow Bransfield Strait. Noise levels become lowest during the austral winter, as sea-ice cover suppresses wind and wave noise. Ambient noise levels are highest during austral spring and summer, as surface noise, ice cracking and biological activity intensifies. Vocalizations of blue (Balaenoptera musculus) and fin (B. physalus) whales also dominate the long-term spectra records in the 15–28 and 89 Hz bands. Blue whale call energy is a maximum during austral summer-fall in the Drake Passage and Bransfield Strait when ambient noise levels are a maximum and sea-ice cover is a minimum. Fin whale vocalizations were also most common during austral summer-early fall months in both the Bransfield Strait and Scotia Sea. The hydrophone data overall do not show sustained anthropogenic sources (ships and airguns), likely due to low coastal traffic and the typically rough weather and sea conditions of the Southern Ocean.

  14. How deep is deep enough? Ocean iron fertilization and carbon sequestration in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Robinson, J.; Popova, E. E.; Yool, A.; Srokosz, M.; Lampitt, R. S.; Blundell, J. R.

    2014-04-01

    Artificial ocean iron fertilization (OIF) enhances phytoplankton productivity and is being explored as a means of sequestering anthropogenic carbon within the deep ocean. To be considered successful, carbon should be exported from the surface ocean and isolated from the atmosphere for an extended period (e.g., the Intergovernmental Panel on Climate Change's standard 100 year time horizon). This study assesses the impact of deep circulation on carbon sequestered by OIF in the Southern Ocean, a high-nutrient low-chlorophyll region known to be iron stressed. A Lagrangian particle-tracking approach is employed to analyze water mass trajectories over a 100 year simulation. By the end of the experiment, for a sequestration depth of 1000 m, 66% of the carbon had been reexposed to the atmosphere, taking an average of 37.8 years. Upwelling occurs predominately within the Antarctic Circumpolar Current due to Ekman suction and topography. These results emphasize that successful OIF is dependent on the physical circulation, as well as the biogeochemistry.

  15. Last Glacial - Holocene climate variability in the Atlantic sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Xiao, Wenshen; Esper, Oliver; Gersonde, Rainer

    2016-03-01

    The Southern Ocean plays a major role in the glacial/interglacial global carbon cycle. However, there is a substantial lack of information from its Antarctic Zone south of the Polar Front (PF) to understand key climate processes (e.g., sea ice variability, productivity changes, CO2 source region, shifts of the Southern Westerly Wind) active in this region during the glacial/interglacial transition, due to the limited high-resolution sediment records from this area. To close this gap, we investigated high resolution diatom records from a series of sediment cores from the Atlantic and Western Indian sectors of the Southern Ocean between the modern PF and the Winter Sea Ice (WSI) edge. Summer Sea Surface Temperature (SSST) and sea ice information spanning the past 30 thousand years were derived from diatom transfer functions and indicators, which augment comprehensive information on past surface ocean conditions and related ocean and atmospheric circulation, as well as opal deposition. These complementary lines of evidences also provide important environmental boundary conditions for climate simulations understanding the past climate development in the high latitudes Southern Ocean. Our reconstructions show that the Last Glacial (LG) SSSTs south of the modern PF are 1-3 °C colder than modern conditions, WSI expanded to the modern PF. Our data suggests effective carbon export in the Antarctic Zone during the LG. Deglacial two steps of warming support the bipolar seesaw mechanism. Antarctic Zone is an important source region for the CO2 deglacial increase. The warming was more suppressed towards south, due to continuous ice discharge from Antarctica. The SSSTs exceeded modern values during the early Holocene optimum, when WSI extent probably retreated south of its modern position. The southern boundary of maximum opal deposition zone may have shifted to south of 55°S in the Bouvet Island area at this time. The mid-late Holocene cooling with WSI re-expanding to the

  16. Bicarbonate uptake by Southern Ocean phytoplankton

    NASA Astrophysics Data System (ADS)

    Cassar, Nicolas; Laws, Edward A.; Bidigare, Robert R.; Popp, Brian N.

    2004-06-01

    Marine phytoplankton have the potential to significantly buffer future increases in atmospheric carbon dioxide levels. However, in order for CO2 fertilization to have an effect on carbon sequestration to the deep ocean, the increase in dissolved CO2 must stimulate primary productivity; that is, marine phototrophs must be CO2 limited [, 1993]. Estimation of the extent of bicarbonate (HCO3-) uptake in the oceans is therefore required to determine whether the anthropogenic carbon sources will enhance carbon flux to the deep ocean. Using short-term 14CO2-disequilibrium experiments during the Southern Ocean Iron Experiment (SOFeX), we show that HCO3- uptake by Southern Ocean phytoplankton is significant. Since the majority of dissolved inorganic carbon (DIC) in the ocean is in the form of bicarbonate, the biological pump may therefore be insensitive to anthropogenic CO2. Approximately half of the DIC uptake observed was attributable to direct HCO3- uptake, the other half being direct CO2 uptake mediated either by passive diffusion or active uptake mechanisms. The increase in growth rates and decrease in CO2 concentration associated with the iron fertilization did not trigger any noticeable changes in the mode of DIC acquisition, indicating that under most environmental conditions the carbon concentrating mechanism (CCM) is constitutive. A low-CO2 treatment induced an increase in uptake of CO2, which we attributed to increased extracellular carbonic anhydrase activity, at the expense of direct HCO3- transport across the plasmalemma. Isotopic disequilibrium experimental results are consistent with Southern Ocean carbon stable isotope fractionation data from this and other studies. Although iron fertilization has been shown to significantly enhance phytoplankton growth and may potentially increase carbon flux to the deep ocean, an important source of the inorganic carbon taken up by phytoplankton in this study was HCO3-, whose concentration is negligibly affected by the

  17. The Evolutionary Origins of the Southern Ocean Philobryid Bivalves: Hidden Biodiversity, Ancient Persistence

    PubMed Central

    Jackson, Jennifer A.; Linse, Katrin; Whittle, Rowan; Griffiths, Huw J.

    2015-01-01

    Philobryids (Bivalvia: Arcoida) are one of the most speciose marine bivalve families in the Southern Ocean and are common throughout the Southern Hemisphere. Considering this diversity and their brooding reproductive mode (limiting long-distance dispersal), this family may have been present in the Southern Ocean since its inception. However Philobrya and Adacnarca appear only in the Quaternary fossil record of the Antarctic, suggesting a much more recent incursion. Molecular dating provides an independent means of measuring the time of origin and radiation of this poorly known group. Here we present the first combined molecular and morphological investigation of the Philobryidae in the Southern Ocean. Two nuclear loci (18S and 28S) were amplified from 35 Southern Ocean Adacnarca and Philobrya specimens, with a combined sequence length of 2,282 base pairs (bp). Adacnarca specimens (A. nitens and A. limopsoides) were resolved as a strongly supported monophyletic group. Genus Philobrya fell into two strongly supported groups (‘sublaevis’ and ‘magellanica/wandelensis’), paraphyletic with Adacnarca. The A. nitens species complex is identified as at least seven morpho-species through morphological and genetic analysis of taxon clustering. Phylogenetic analyses resolve Philobryidae as a strongly supported monophyletic clade and sister taxon to the Limopsidae, as anticipated by their classification into the superfamily Limopsoidea. Bayesian relaxed clock analyses of divergence times suggest that genus Adacnarca radiated in the Southern Ocean from the Early Paleogene, while P. sublaevis and P. wandelensis clades radiated in the late Miocene, following the formation of the Antarctic Circumpolar Current. PMID:25853413

  18. Strong coupling among Antarctic ice shelves, ocean circulation and sea ice in a global sea-ice - ocean circulation model

    NASA Astrophysics Data System (ADS)

    Sergienko, Olga

    2016-04-01

    The thermodynamic effects of Antarctic ice shelf interaction with ocean circulation are investigated using a global, high-resolution, isopycnal ocean-circulation model coupled to a sea-ice model. The model uses NASA MERRA Reanalysis from 1992 to 2011 as atmospheric forcing. The simulated long-period variability of ice-shelf melting/freezing rates differ across geographic locations. The ice shelves in Antarctic Peninsula, Amundsen and Bellingshausen sea embayments and the Amery Ice Shelf experience an increase in melting starting from 2005. This increase in melting is due to an increase in the subsurface (100-500 m) ocean heat content in the embayments of these ice shelves, which is caused by an increase in sea-ice concentration after 2005, and consequent reduction of the heat loss to the atmosphere. Our simulations provide a strong evidence for a coupling between ocean circulation, sea ice and ice shelves.

  19. The Influence of Sea Ice on Primary Production in the Southern Ocean: A Satellite Perspective

    NASA Technical Reports Server (NTRS)

    Smith, Walker O., Jr.; Comiso, Josefino C.

    2007-01-01

    Sea ice in the Southern Ocean is a major controlling factor on phytoplankton productivity and growth, but the relationship is modified by regional differences in atmospheric and oceanographic conditions. We used the phytoplankton biomass (binned at 7-day intervals), PAR and cloud cover data from SeaWiFS, ice concentrations data from SSM/I and AMSR-E, and sea-surface temperature data from AVHRR, in combination with a vertically integrated model to estimate primary productivity throughout the Southern Ocean (south of 60"s). We also selected six areas within the Southern Ocean and analyzed the variability of the primary productivity and trends through time, as well as the relationship of sea ice to productivity. We found substantial interannual variability in productivity from 1997 - 2005 in all regions of the Southern Ocean, and this variability appeared to be driven in large part by ice dynamics. The most productive regions of Antarctic waters were the continental shelves, which showed the earliest growth, the maximum biomass, and the greatest areal specific productivity. In contrast, no large, sustained blooms occurred in waters of greater depth (> 1,000 m). We suggest that this is due to the slightly greater mixed layer depths found in waters off the continental shelf, and that the interactive effects of iron and irradiance (that is, increased iron requirements in low irradiance environments) result in the limitation of phytoplankton biomass over large regions of the Southern Ocean.

  20. Role of squid in the Southern Ocean pelagic ecosystem and the possible consequences of climate change

    NASA Astrophysics Data System (ADS)

    Rodhouse, Paul G. K.

    2013-10-01

    Southern Ocean squid are important predators and prey and are a potential fishery resource. Their future under climate change is analysed from predictions of change by 2100 and assessments of the effects on squid biology. There are ˜18 Antarctic species of squid. Young feed primarily on crustaceans and switch later to fishes. They are preyed on by odontocetes, seals and seabirds - which together consume ˜34×106tyr-1 - and fish. As predators, squid are second to fish as biomass producers but recent evidence suggests predator consumption of squid needs to be reassessed. Fatty acid composition and stable nitrogen isotope ratios indicate some predators consume less squid in their diet than gut contents data suggest. Southern Ocean oceanography is unique in having circumpolar circulation and frontal systems and at high latitudes it is heavily influenced by sea ice. The Antarctic Peninsula is among the fastest warming regions worldwide but elsewhere the Southern Ocean is warming more slowly and the Ross Sea is probably cooling. Sea ice is receding in the Peninsula region and increasing elsewhere. Modelled predictions for 2100 suggest although the Southern Ocean will warm less than other oceans and sea ice will reduce. The Antarctic Circumpolar Current may shift slightly southwards with intensification of westerly winds but resolution of the models is insufficient to predict mesoscale change. Globally, pH of seawater has decreased by 0.1 units since the mid-1900s and is predicted to decrease by another 0.5 units by 2100. Impact on calcifying organisms will be high in the cold Southern Ocean where solubility of calcium carbonate is high. Predicted temperature increases are unlikely to have major effects on squid other than changes in distribution near the limits of their range; acidification may have greater impact. Small changes in large scale circulation are unlikely to affect squid but changes in mesoscale oceanography may have high impact. Change in sea ice extent

  1. Extensive lake sediment coring survey on Sub-Antarctic Indian Ocean Kerguelen Archipelago (French Austral and Antarctic Lands)

    NASA Astrophysics Data System (ADS)

    Arnaud, Fabien; Fanget, Bernard; Malet, Emmanuel; Poulenard, Jérôme; Støren, Eivind; Leloup, Anouk; Bakke, Jostein; Sabatier, Pierre

    2016-04-01

    Recent paleo-studies revealed climatic southern high latitude climate evolution patterns that are crucial to understand the global climate evolution(1,2). Among others the strength and north-south shifts of westerlies wind appeared to be a key parameter(3). However, virtually no lands are located south of the 45th South parallel between Southern Georgia (60°W) and New Zealand (170°E) precluding the establishment of paleoclimate records of past westerlies dynamics. Located around 50°S and 70°E, lost in the middle of the sub-Antarctic Indian Ocean, Kerguelen archipelago is a major, geomorphologically complex, land-mass that is covered by hundreds lakes of various sizes. It hence offers a unique opportunity to reconstruct past climate and environment dynamics in a region where virtually nothing is known about it, except the remarkable recent reconstructions based on a Lateglacial peatbog sequence(4). During the 2014-2015 austral summer, a French-Norwegian team led the very first extensive lake sediment coring survey on Kerguelen Archipelago under the umbrella of the PALAS program supported by the French Polar Institute (IPEV). Two main areas were investigated: i) the southwest of the mainland, so-called Golfe du Morbihan, where glaciers are currently absent and ii) the northernmost Kerguelen mainland peninsula so-called Loranchet, where cirque glaciers are still present. This double-target strategy aims at reconstructing various independent indirect records of precipitation (glacier advance, flood dynamics) and wind speed (marine spray chemical species, wind-borne terrigenous input) to tackle the Holocene climate variability. Despite particularly harsh climate conditions and difficult logistics matters, we were able to core 6 lake sediment sites: 5 in Golfe du Morbihan and one in Loranchet peninsula. Among them two sequences taken in the 4km-long Lake Armor using a UWITEC re-entry piston coring system by 20 and 100m water-depth (6 and 7m-long, respectively). One

  2. Paleoceanography and Paleoclimatology of the Southern Ocean: A Synthesis of Three Decades of Scientific Ocean Drilling

    NASA Astrophysics Data System (ADS)

    Warnke, D. A.; Filippelli, G.; Flores, J.; Marchitto, T. M.

    2004-12-01

    A Workshop on " Paleoceanography and Paleoclimatology of the Southern Ocean: A Synthesis of Three Decades of Scientific Ocean Drilling" Jan. 21-23, 2005 Boulder, CO Co-Convenors: D. Warnke, G. Filippelli, J.-A. Flores, T. Marchitto One of the greatest successes of the Ocean Drilling Program has been the concerted drilling efforts and exciting results recovered from the Southern Ocean (SO), which has been the focus of ten DSDP/ODP drilling legs. The SO is a critical component in the development and persistence of Antarctic glaciation, is a sensitive mixing pool of global water masses, a locus of high biological sedimentation, and contains high resolution records of climate forcing and response. As such, it is one of the most important oceanographic regions in the world. It is now an important time to mine the rich results from scientific ocean drilling over the past several decades and develop a scientific framework for future ocean drilling in this region. The focus of this Synthesis Workshop will be on the biogeochemical history of the SO, including: · Productivity proxies, rates, records, variations, and role of climate · Sedimentary records of organic carbon, calcium, silica, nutrients, and biogenic proxies: The role of the SO as a biogeochemical sink · Development and dynamics of the APFZ · Thermal structure and evolution of the SO · The role of limiting nutrients The overall goal to integrate the various proxies into a coherent paleoceanographic picture. Such a goal will help to synthesize several decades of scientific ocean drilling in the SO, and will likely bring to the forefront the as-yet-unanswered questions about the biogeochemical history of this important oceanic system. With this goal in mind, workshop participants will submit of a short (~250 word) abstract as the Workshop application, commit to presenting a poster at the workshop based on this abstract, and contribute to one or more manuscripts that will be published after the workshop, likely

  3. Southern Ocean circulation changes across the last deglaciation: contribution from Marion-Dufresne cruises

    NASA Astrophysics Data System (ADS)

    Michel, Elisabeth; Siani, Giuseppe; Mazaud, Alain; Paterne, Martine; deVries, Tim; Jaccard, Samuel; Waelbroeck, Claire; Crosta, Xavier; Isguder, Gulay; Dewilde, Fabien; De Pol-Holz, Ricardo; Skinner, Luke; Kissel, Catherine

    2015-04-01

    The last deglaciation is marked by rapid climatic events linked to large reorganizations of the deep ocean circulation. To decipher the role of the Southern Ocean in these deep circulation changes requires reconstructing the evolution of its stratification and its zonal behavior during the last deglaciation from high resolution, well dated records. Furthermore, nowadays the connection between atmosphere and the deep ocean occurs through the Southern Ocean, and it might had a leading role in the evolution of atmospheric CO2 concentrations across the deglaciation. However, establishing a precise chronology for marine sediment records in high latitudes is a difficult task, as it requires the determination of radiocarbon surface water age changes. It has been possible to retrieve high sedimentation rate cores during Indian and Pacific oceanographic cruises, particularly PACHIDERME and INDIEN SUD expeditions. We pre. We aim at tying these marine records to terrestrial records, using tephra deposited in marine and terrestrial region in the different sector of the Southern Ocean when it is possible. This work is in progress within a French-Swedish project. We will present results at different depth from South West Pacific sector of the Southern Ocean and from the Indian sector. A precise chronology in the Indian sector requires to first establish the tephrochronology of Kerguelen Islands that is under progress. We compare these new records with previously published records of the Atlantic and Pacific sectors. It indicates that upwelling events drive radiocarbon changes in waters above 2500 m depth and increases in atmospheric CO2. Oceanic circulation changes are not synchroneous at deeper depth between 2500 and 4000 m depth. Southern Ocean temperature and vertical mixing increases occurs synchroneously with temperature increase above the Antarctic and atmospheric CO2 increases within error of marine and Ice chronologies, while the ACC current intensity decrease (or

  4. Transient tracer applications in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Stöven, T.; Tanhua, T.; Hoppema, M.

    2014-10-01

    Transient tracers can be used to constrain the Inverse-Gaussian transit time distribution (IG-TTD) and thus provide information about ocean ventilation. Individual transient tracers have different time and application ranges which are defined by their atmospheric history (chronological transient tracers) or their decay rate (radioactive transient tracers). The classification ranges from tracers for highly ventilated water masses, e.g. sulfur hexafluoride (SF6), the decay of Tritium (δ3H) and to some extent also dichlorodifluoromethane (CFC-12) to tracers for less ventilated deep ocean basins, e.g. CFC-12, Argon-39 (39Ar) and radiocarbon (14C). The IG-TTD can be empirically constrained by using transient tracer couples with sufficiently different input functions. Each tracer couple has specific characteristics which influence the application limit of the IG-TTD. Here we provide an overview of commonly used transient tracer couples and their validity areas within the IG-TTD by using the concept of tracer age differences (TAD). New measured CFC-12 and SF6 data from a section along 10° E in the Southern Ocean in 2012 are presented. These are combined with a similar data set of 1998 along 6° E in the Southern Ocean as well as with 39Ar data from the early 1980s in the western Atlantic Ocean and the Weddell Sea for investigating the application limit of the IG-TTD and to analyze changes in ventilation in the Southern Ocean. We found that the IG-TTD can be constrained south to 46° S which corresponds to the Subantarctic Front (SAF) denoting the application limit. The constrained IG-TTD north of the SAF shows a slight increase in mean ages between 1998 and 2012 in the upper 1200 m between 42-46° S. The absence of SF6 inhibits ventilation analyses below this depth. The time lag analysis between the 1998 and 2012 data shows an increase in ventilation down to 1000 m and a steady ventilation between 2000 m-bottom south of the SAF between 51-55° S.

  5. A review of Tertiary climate changes in southern South America and the Antarctic Peninsula. Part 2: continental conditions

    NASA Astrophysics Data System (ADS)

    Le Roux, J. P.

    2012-03-01

    Climate changes in southern South America and the Antarctic Peninsula during the Tertiary show a strong correlation with ocean warming and cooling events, which are in turn related to tectonic processes. During periods of accelerated sea-floor spreading and mid-ocean ridge activity, sea-levels rose so that parts of the continents were flooded and forests were destroyed. However, this was balanced by the large-scale release of CO2 during volcanic outgassing and carbonate precipitation on the continental shelves, which caused rising air temperatures and the poleward expansion of (sub)tropical and temperate forests. Cooling episodes generally caused an increase in the north-south thermal gradient because of an equatorward shift in climate belts, so that the Westerly Winds intensified and brought higher rainfall to the lower latitudes. An increase in wind-blown dust caused temperatures to drop further by reflecting sunlight back into space. The rising Andes Range had a marked influence on climate patterns. Up to the middle Miocene it was still low enough to allow summer rainfall to reach central and north-central Chile, but after about 14 Ma it rose rapidly and effectively blocked the spill-over of moisture from the Atlantic Ocean and Amazon Basin. At this time, the cold Humboldt Current was also established, which together with the Andes helped to create the "Arid Diagonal" of southern South America stretching from the Atacama Desert to the dry steppes of Patagonia. This caused the withdrawal of subtropical forests to south-central Chile and the expansion of sclerophytic vegetation to central Chile. However, at the same time it intercepted more rain from the northeast, causing the effect of the South American monsoon to intensify in northwestern Argentina and southern Bolivia, where forest communities presently occur. In Patagonia, glaciation started as early as 10.5 Ma, but by 7 Ma had become a prominent feature of the landscape and continued apparently

  6. Bipolar Atlantic deepwater circulation in the middle-late Eocene: Effects of Southern Ocean gateway openings

    NASA Astrophysics Data System (ADS)

    Borrelli, Chiara; Cramer, Benjamin S.; Katz, Miriam E.

    2014-04-01

    We present evidence for Antarctic Circumpolar Current (ACC)-like effects on Atlantic deepwater circulation beginning in the late-middle Eocene. Modern ocean circulation is characterized by a thermal differentiation between Southern Ocean and North Atlantic deepwater formation regions. In order to better constrain the timing and nature of the initial thermal differentiation between Northern Component Water (NCW) and Southern Component Water (SCW), we analyze benthic foraminiferal stable isotope (δ18Obf and δ13Cbf) records from Ocean Drilling Program Site 1053 (upper deep water, western North Atlantic). Our data, compared with published records and interpreted in the context of ocean circulation models, indicate that progressive opening of Southern Ocean gateways and initiation of a circum-Antarctic current caused a transition to a modern-like deep ocean circulation characterized by thermal differentiation between SCW and NCW beginning ~38.5 Ma, in the initial stages of Drake Passage opening. In addition, the relatively low δ18Obf values recorded at Site 1053 show that the cooling trend of the middle-late Eocene was not global, because it was not recorded in the North Atlantic. The timing of thermal differentiation shows that NCW contributed to ocean circulation by the late-middle Eocene, ~1-4 Myr earlier than previously thought. We propose that early NCW originated in the Labrador Sea, based on tectonic reconstructions and changes in foraminiferal assemblages in this basin. Finally, we link further development of meridional isotopic gradients in the Atlantic and Pacific in the late Eocene with the Tasman Gateway deepening (~34 Ma) and the consequent development of a circumpolar proto-ACC.

  7. Modelling Antarctic ice shelf melting under LGM and doubled CO2 climate using ice shelf-ocean model and climate model

    NASA Astrophysics Data System (ADS)

    Obase, T.; Abe-Ouchi, A.; Kusahara, K.; Hasumi, H.

    2014-12-01

    Ice-ocean interaction is thought to be a responsible process on long-term Antarctic ice sheet variations, such as retreat of West Antarctic Ice Sheet during Eemian interglacial. Numerical simulation of Antarctic ice sheet require melt rate at ice shelf base as a boundary condition, but the relation between climate and melt rate is unclear. We calculate Antarctic ocean and basal melting of Antarctic ice shelves under Last Glacial Maximum(LGM) and doubled CO2(2xCO2) climate at equilibrium as well as present-day(CTL). We use circumpolar ice shelf-ocean general circulation model(OGCM, based on COCO) and outputs of climate model(MIROC). For the CTL case, we drive OGCM with surface atmospheric climatology based on reanalysis(OMIP) and present-day ocean temperature and salinity for restoration at northern boundary, placed at around latitude of 40S. The surface boundary conditions for LGM(or 2xCO2) is computed from the outputs from climate model simulations. Annual mean marine 2m air temperature anomaly averaged for south of 60S is -7.3℃ for LGM and +6.0℃ for 2xCO2. LGM (or 2xCO2) anomalies of surface atmospheric variables are superimposed to OMIP to make LGM (or 2xCO2) atmospheric boundary conditions. We modify the ocean temperature and salinity column for restoration at northern boundary by superimposing anomaly to present-day ocean climatology. Present-day geometry of ice sheet and ice shelf is used in all experiments to test the sensitivity to climate. We show that melting amount of Antarctic ice shelves show 23% reduction for the LGM and 3.5 times increase for the 2xCO2 compared to the CTL case. We perform a series of additional sensitivity experiments to investigate the role of surface change in sea surface atmospheric variables (temperature, wind) and ocean structures in the Southern Ocean on melt rate of ice shelves. Water mass, ocean circulation and sea ice production on continental shelf are analyzed.

  8. Phytoplankton and cloudiness in the Southern Ocean.

    PubMed

    Meskhidze, Nicholas; Nenes, Athanasios

    2006-12-01

    The effect of ocean biological productivity on marine clouds is explored over a large phytoplankton bloom in the Southern Ocean with the use of remotely sensed data. Cloud droplet number concentration over the bloom was twice what it was away from the bloom, and cloud effective radius was reduced by 30%. The resulting change in the short-wave radiative flux at the top of the atmosphere was -15 watts per square meter, comparable to the aerosol indirect effect over highly polluted regions. This observed impact of phytoplankton on clouds is attributed to changes in the size distribution and chemical composition of cloud condensation nuclei. We propose that secondary organic aerosol, formed from the oxidation of phytoplankton-produced isoprene, can affect chemical composition of marine cloud condensation nuclei and influence cloud droplet number. Model simulations support this hypothesis, indicating that 100% of the observed changes in cloud properties can be attributed to the isoprene secondary organic aerosol. PMID:17082422

  9. Bioavailable iron in the Southern Ocean: the significance of the iceberg conveyor belt

    PubMed Central

    Raiswell, Rob; Benning, Liane G; Tranter, Martyn; Tulaczyk, Slawek

    2008-01-01

    Productivity in the Southern Oceans is iron-limited, and the supply of iron dissolved from aeolian dust is believed to be the main source from outside the marine reservoir. Glacial sediment sources of iron have rarely been considered, as the iron has been assumed to be inert and non-bioavailable. This study demonstrates the presence of potentially bioavailable Fe as ferrihydrite and goethite in nanoparticulate clusters, in sediments collected from icebergs in the Southern Ocean and glaciers on the Antarctic landmass. Nanoparticles in ice can be transported by icebergs away from coastal regions in the Southern Ocean, enabling melting to release bioavailable Fe to the open ocean. The abundance of nanoparticulate iron has been measured by an ascorbate extraction. This data indicates that the fluxes of bioavailable iron supplied to the Southern Ocean from aeolian dust (0.01–0.13 Tg yr-1) and icebergs (0.06–0.12 Tg yr-1) are comparable. Increases in iceberg production thus have the capacity to increase productivity and this newly identified negative feedback may help to mitigate fossil fuel emissions. PMID:18513396

  10. Detection and characterization of a Cryptosporidium isolate from a southern elephant seal (Mirounga leonina) from the Antarctic peninsula.

    PubMed

    Rengifo-Herrera, C; Ortega-Mora, L M; Gómez-Bautista, M; García-Moreno, F T; García-Párraga, D; Castro-Urda, J; Pedraza-Díaz, S

    2011-02-01

    The presence of Cryptosporidium and Giardia in 221 fecal samples from different species of Antarctic pinnipeds was investigated by immunofluorescence microscopy and PCR. Cryptosporidium, a skunk-like genotype, was detected only in a southern elephant seal. Giardia was not detected. This is the first report of a Cryptosporidium sp. in Antarctic marine mammals. PMID:21169427

  11. The past, present and future distribution of a deep-sea shrimp in the Southern Ocean.

    PubMed

    Basher, Zeenatul; Costello, Mark J

    2016-01-01

    Shrimps have a widespread distribution across the shelf, slope and seamount regions of the Southern Ocean. Studies of Antarctic organisms have shown that individual species and higher taxa display different degrees of sensitivity and adaptability in response to environmental change. We use species distribution models to predict changes in the geographic range of the deep-sea Antarctic shrimp Nematocarcinus lanceopes under changing climatic conditions from the Last Glacial Maximum to the present and to the year 2100. The present distribution range indicates a pole-ward shift of the shrimp population since the last glaciation. This occurred by colonization of slopes from nearby refugia located around the northern part of Scotia Arc, southern tip of South America, South Georgia, Bouvet Island, southern tip of the Campbell plateau and Kerguelen plateau. By 2100, the shrimp are likely to expand their distribution in east Antarctica but have a continued pole-ward contraction in west Antarctica. The range extension and contraction process followed by the deep-sea shrimp provide a geographic context of how other deep-sea Antarctic species may have survived during the last glaciation and may endure with projected changing climatic conditions in the future. PMID:26925334

  12. The past, present and future distribution of a deep-sea shrimp in the Southern Ocean

    PubMed Central

    Costello, Mark J.

    2016-01-01

    Shrimps have a widespread distribution across the shelf, slope and seamount regions of the Southern Ocean. Studies of Antarctic organisms have shown that individual species and higher taxa display different degrees of sensitivity and adaptability in response to environmental change. We use species distribution models to predict changes in the geographic range of the deep-sea Antarctic shrimp Nematocarcinus lanceopes under changing climatic conditions from the Last Glacial Maximum to the present and to the year 2100. The present distribution range indicates a pole-ward shift of the shrimp population since the last glaciation. This occurred by colonization of slopes from nearby refugia located around the northern part of Scotia Arc, southern tip of South America, South Georgia, Bouvet Island, southern tip of the Campbell plateau and Kerguelen plateau. By 2100, the shrimp are likely to expand their distribution in east Antarctica but have a continued pole-ward contraction in west Antarctica. The range extension and contraction process followed by the deep-sea shrimp provide a geographic context of how other deep-sea Antarctic species may have survived during the last glaciation and may endure with projected changing climatic conditions in the future. PMID:26925334

  13. The de-correlation of westerly winds and westerly-wind stress over the Southern Ocean during the Last Glacial Maximum

    SciTech Connect

    Liu, Wei; Lu, Jian; Leung, Lai-Yung R.; Xie, Shang-Ping; Liu, Zhengyu; Zhu, Jiang

    2015-02-22

    This paper investigates the changes of the Southern Westerly Winds (SWW) and Southern Ocean (SO) upwelling between the Last Glacial Maximum (LGM) and preindustrial (PI) in the PMIP3/CMIP5 simulations, highlighting the role of the Antarctic sea ice in modulating the wind stress effect on the ocean. Particularly, a discrepancy may occur between the changes in SWW and westerly wind stress, caused primarily by an equatorward expansion of winter Antarctic sea ice that undermines the wind stress in driving the liquid ocean. Such discrepancy may reflect the LGM condition in reality, in view of that the model simulates this condition has most credible simulation of modern SWW and Antarctic sea ice. The effect of wind stress on the SO upwelling is further explored via the wind-induced Ekman pumping, which is reduced under the LGM condition in all models, in part by the sea-ice “capping” effect present in the models.

  14. Last Glacial Maximum sea surface temperature and sea-ice extent in the Pacific sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Benz, Verena; Esper, Oliver; Gersonde, Rainer; Lamy, Frank; Tiedemann, Ralf

    2016-08-01

    Sea surface temperatures and sea-ice extent are most critical variables to evaluate the Southern Ocean paleoceanographic evolution in relation to the development of the global carbon cycle, atmospheric CO2 and ocean-atmosphere circulation. Here we present diatom transfer function-based summer sea surface temperature (SSST) and winter sea-ice (WSI) estimates from the Pacific sector of the Southern Ocean to bridge a gap in information that has to date hampered a well-established reconstruction of the last glacial Southern Ocean at circum-Antarctic scale. We studied the Last Glacial Maximum (LGM) at the EPILOG time slice (19,000-23,000 calendar years before present) in 17 cores and consolidated our LGM picture of the Pacific sector taking into account published data from its warmer regions. Our data display a distinct east-west differentiation with a rather stable WSI edge north of the Pacific-Antarctic Ridge in the Ross Sea sector and a more variable WSI extent over the Amundsen Abyssal Plain. The zone of maximum cooling (>4 K) during the LGM is in the present Subantarctic Zone and bounded to its south by the 4 °C isotherm. The isotherm is in the SSST range prevailing at the modern Antarctic Polar Front, representing a circum-Antarctic feature, and marks the northern edge of the glacial Antarctic Circumpolar Current (ACC). The northward deflection of colder than modern surface waters along the South American continent led to a significant cooling of the glacial Humboldt Current surface waters (4-8 K), which affected the temperature regimes as far north as tropical latitudes. The glacial reduction of ACC temperatures may also have resulted in significant cooling in the Atlantic and Indian Southern Ocean, thus enhancing thermal differentiation of the Southern Ocean and Antarctic continental cooling. The comparison with numerical temperature and sea-ice simulations yields discrepancies, especially concerning the estimates of the sea-ice fields, but some simulations

  15. Final Report. Coupled simulations of Antarctic Ice-sheet/ocean interactions using POP and CISM

    SciTech Connect

    Asay-Davis, Xylar Storm

    2015-12-30

    The project performed under this award, referred to from here on as CLARION (CoupLed simulations of Antarctic Ice-sheet/Ocean iNteractions), included important advances in two models of ice sheet and ocean interactions. Despite its short duration (one year), the project made significant progress on its three major foci. First, together with collaborator Daniel Martin at Lawrence Berkeley National Laboratory (LBNL), I developed the POPSICLES coupled ice sheet-ocean model to the point where it could perform a number of pan-Antarctic simulations under various forcing conditions. The results were presented at a number of major conferences and workshops worldwide, and are currently being incorporated into two manuscripts in preparation.

  16. Effect of Atmospheric Forcing Resolution on Delivery of Ocean Heat to the Antarctic Floating Ice Shelves

    NASA Astrophysics Data System (ADS)

    Klinck, J. M., II; Dinniman, M. S.; Bromwich, D. H.; Holland, D. M.

    2014-12-01

    Oceanic melting of the base of the floating Antarctic ice shelves is now thought to be a more significant cause of mass loss for the Antarctic ice sheet than iceberg calving. In this study, we use a 10 km horizontal resolution circum-Antarctic ocean/sea ice/ice shelf model (based on ROMS) to study the delivery of ocean heat to the base of the ice shelves. The atmospheric forcing comes from the ERA-Interim reanalysis (~80 km resolution) and from simulations using the Polar-optimized WRF model (30 km resolution) where the upper atmosphere was relaxed to the ERA-Interim reanalysis. Total basal ice shelf melt increases by 14% with the higher resolution winds but only 3% with both the higher resolution winds and atmospheric surface temperatures. The higher resolution winds lead to more heat being delivered to the ice shelf cavities from the adjacent ocean and an increase in the efficiency of heat transfer between the water and the ice. The higher resolution winds also lead to changes in the heat delivered from the open ocean to the continental shelves as well as changes in the heat lost to the atmosphere over the shelves and the sign of these changes varies regionally. Addition of the higher resolution temperatures to the winds results in lowering, primarily during summer, the wind driven increase in heat advected into the ice shelf cavities due to colder summer air temperatures near the coast.

  17. Southern Ocean overturning, export production and climate variability over the past 1 Myr

    NASA Astrophysics Data System (ADS)

    Jaccard, S.; Hayes, C. T.; Martinez Garcia, A.; Galbraith, E. D.; Anderson, R. F.; Sigman, D. M.; Haug, G. H.

    2011-12-01

    of ODP site 1094. New evidence from ODP site 1090 (42°S, 9°E, 3700 m) shows that iron fertilization in the SAZ would have permitted to sequester additional remineralized carbon in the ocean interior, forcing the climate system to reach full glacial conditions. This mechanism was only effective when the Southern Ocean lid was already sealed, precluding the sequestered CO2 to evade through the Antarctic valve. The threshold persisted throughout the lukewarm interval, suggesting that processes taking place in the Antarctic Zone of the Southern Ocean were responsible for the observed reduced interglacial pCO2 levels.

  18. Holocene polar front migrations over the Conrad Rise in the Indian sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Ikehara, M.; Katsuki, K.; Yokoyama, Y.; Yamane, M.; Khim, B.

    2011-12-01

    The Southern Ocean has played a significant role in the global climate system during the geologic past. In order to understand the paleoceanographic variations with the polar front system and Antarctic Circumpolar Current (ACC), we conducted two cruises KH-07-4 and KH-10-7 in the Indian sector of the Southern Ocean. Two piston cores were collected from the Conrad Rise. We examined centennial-scale changes of diatom assemblages and stable isotopic ratios in planktic foraminifera during the Holocene in a high-accumulation-rate sediment core from the Conrad Rise. Although abundances of dominant diatom taxa (Fragilariopsis kerguelensis and Thalassiothrix antarctica) are comparatively constant, relative abundances of secondary taxa fluctuate. Before ca 9900 cal. yr BP, winter sea-ice and cold water covered the Conrad Rise. Following deglaciation the sea-ice retreated from the Conrad Rise. The Polar Front moved southward during the early Holocene optimum and north Antarctic Zone waters covered the Conrad Rise for about 650 yr. After 9300 cal. yr BP, solar insolation strongly influenced sea surface temperature and primary productivity in the Southern Ocean. In the high-latitude Indian Sector, productivity increased 1500 yr after the onset of late Holocene neoglaciation. Periodic δ18O and cold-water diatom taxa spikes (at intervals of 200 and 300-500 yr, respectively) occurred after 9300 cal. yr BP, probably associated with solar activity. Fluctuations in short-term sea surface temperature and cold-water taxa are synchronous with changes in dD observed in an east Antarctic ice core.

  19. High Biomass Low Export Regimes in the Southern Ocean

    SciTech Connect

    Lam, Phoebe J.; Bishop, James K.B.

    2006-01-27

    This paper investigates ballasting and remineralization controls of carbon sedimentation in the twilight zone (100-1000 m) of the Southern Ocean. Size-fractionated (<1 {micro}m, 1-51 {micro}m, >51 {micro}m) suspended particulate matter was collected by large volume in-situ filtration from the upper 1000 m in the Subantarctic (55 S, 172 W) and Antarctic (66 S, 172 W) zones of the Southern Ocean during the Southern Ocean Iron Experiment (SOFeX) in January-February 2002. Particles were analyzed for major chemical constituents (POC, P, biogenic Si, CaCO3), and digital and SEM image analyses of particles were used to aid in the interpretation of the chemical profiles. Twilight zone waters at 66 S in the Antarctic had a steeper decrease in POC with depth than at 55 S in the Subantarctic, with lower POC concentrations in all size fractions at 66 S than at 55 S, despite up to an order of magnitude higher POC in surface waters at 66 S. The decay length scale of >51 {micro}m POC was significantly shorter in the upper twilight zone at 66 S ({delta}{sub e}=26 m) compared to 55 S ({delta}{sub e}=81 m). Particles in the carbonate-producing 55 S did not have higher excess densities than particles from the diatom-dominated 66 S, indicating that there was no direct ballast effect that accounted for deeper POC penetration at 55 S. An indirect ballast effect due to differences in particle packaging and porosities cannot be ruled out, however, as aggregate porosities were high ({approx}97%) and variable. Image analyses point to the importance of particle loss rates from zooplankton grazing and remineralization as determining factors for the difference in twilight zone POC concentrations at 55 S and 66 S, with stronger and more focused shallow remineralization at 66 S. At 66 S, an abundance of large (several mm long) fecal pellets from the surface to 150 m, and almost total removal of large aggregates by 200 m, reflected the actions of a single or few zooplankton species capable of

  20. Mitochondrial acclimation capacities to ocean warming and acidification are limited in the antarctic Nototheniid Fish, Notothenia rossii and Lepidonotothen squamifrons.

    PubMed

    Strobel, Anneli; Graeve, Martin; Poertner, Hans O; Mark, Felix C

    2013-01-01

    Antarctic notothenioid fish are characterized by their evolutionary adaptation to the cold, thermostable Southern Ocean, which is associated with unique physiological adaptations to withstand the cold and reduce energetic requirements but also entails limited compensation capacities to environmental change. This study compares the capacities of mitochondrial acclimation to ocean warming and acidification between the Antarctic nototheniid Notothenia rossii and the sub-Antarctic Lepidonotothen squamifrons, which share a similar ecology, but different habitat temperatures. After acclimation of L. squamifrons to 9°C and N. rossii to 7°C (normocapnic/hypercapnic, 0.2 kPa CO2/2000 ppm CO2) for 4-6 weeks, we compared the capacities of their mitochondrial respiratory complexes I (CI) and II (CII), their P/O ratios (phosphorylation efficiency), proton leak capacities and mitochondrial membrane fatty acid compositions. Our results reveal reduced CII respiration rates in warm-acclimated L. squamifrons and cold hypercapnia-acclimated N. rossii. Generally, L. squamifrons displayed a greater ability to increase CI contribution during acute warming and after warm-acclimation than N. rossii. Membrane unsaturation was not altered by warm or hypercapnia-acclimation in both species, but membrane fatty acids of warm-acclimated L. squamifrons were less saturated than in warm normocapnia-/hypercapnia-acclimated N. rossii. Proton leak capacities were not affected by warm or hypercapnia-acclimation of N. rossii. We conclude that an acclimatory response of mitochondrial capacities may include higher thermal plasticity of CI supported by enhanced utilization of anaplerotic substrates (via oxidative decarboxylation reactions) feeding into the citrate cycle. L. squamifrons possesses higher relative CI plasticities than N. rossii, which may facilitate the usage of energy efficient NADH-related substrates under conditions of elevated energy demand, possibly induced by ocean warming and

  1. Regional variation in lytic and lysogenic viral infection in the Southern Ocean and its contribution to biogeochemical cycling.

    PubMed

    Evans, Claire; Brussaard, Corina P D

    2012-09-01

    Lytic and lysogenic viral infection was investigated throughout the Southern Ocean at sites spanning the sub-Antarctic zone, the Antarctic Circumpolar Current, and an Antarctic continental sea. Higher lytic virus activity was recorded in the more productive sub-Antarctic zone than in the iron-limited waters of the Antarctic Circumpolar Current during two transects. Reduced lytic viral activity in the Antarctic Circumpolar Current was combined with a shift toward lysogenic infection, probably resulting from the lower concentration of potential prokaryotic hosts. Superimposed on this variation, lytic viral production was lower in a transect completed in the Drake Passage in autumn (1.8 × 10(8) to 1.5 × 10(9) liter(-1) day(-1)) than over the Greenwich Meridian during summer (5.1 × 10(8) to 2.0 × 10(10) cells liter(-1) day(-1)), indicating that viral activity is linked to the overall seasonal fluctuations in biotic activity. Interestingly, while prokaryotic abundance was lowest in the coastal Weddell Sea, levels of bacterial and lytic viral production (4.3 × 10(8) to 1.7 × 10(10) cells liter(-1) day(-1)) in this area were similar to those of the other zones. This may explain the weak relationship between the distribution of prokaryotes and chlorophyll in the Weddell Sea, as a high turnover of prokaryotic biomass may have been stimulated by the availability of substrates in the form of viral lysate. With estimated carbon and iron releases of 0.02 to 7.5 μg liter(-1) day(-1) and 1.5 to 175.7 pg liter(-1) day(-1), respectively, viral activity in the Southern Ocean is shown to be a major contributor to satisfying the elemental requirements of microbes, notably prokaryotes in the Weddell Sea and phytoplankton in the sub-Antarctic zone. PMID:22798377

  2. Coastal zone color scanner pigment concentrations in the southern ocean and relationships to geophysical surface features

    NASA Technical Reports Server (NTRS)

    Comiso, J. C.; Mcclain, C. R.; Sullivan, C. W.; Ryan, J. P.; Leonard, C. L.

    1993-01-01

    Climatological data on the distribution of surface pigment fields in the entire southern ocean over a seasonal cycle are examined. The occurrence of intense phytoplankton blooms during austral summer months and during other seasons in different regions is identified and analyzed. The highest pigment concentrations are observed at high latitudes and over regions with water depths usually less than 600 m. Basin-scale pigment distribution shows a slightly asymmetric pattern of enhanced pigment concentrations about Antarctica, with enhanced concentrations extending to lower latitudes in the Atlantic and Indian sectors than in the Pacific sector. A general increase in pigment concentrations is evident from the low latitudes toward the Antarctic circumpolar region. Spatial relationships between pigment and archived geophysical data reveal significant correlation between pigment distributions and both bathymetry and wind stress, while general hemispheric scale patterns of pigment distributions are most coherent with the geostrophic flow of the Antarctic Circumpolar Current.

  3. On the interannual variability of ocean temperatures around South Georgia, Southern Ocean: Forcing by El Niño/Southern Oscillation and the Southern Annular Mode

    NASA Astrophysics Data System (ADS)

    Meredith, Michael P.; Murphy, Eugene J.; Hawker, Elizabeth J.; King, John C.; Wallace, Margaret I.

    2008-09-01

    The ocean around South Georgia, in the southwest Atlantic sector of the Southern Ocean, is highly productive, with large stocks of Antarctic krill supporting extensive colonies of marine- and land-based predators. The operation of this ecosystem is strongly influenced by physical forcings, and the role of the El Niño/Southern Oscillation (ENSO) phenomenon has been highlighted previously. Here we examine in detail the transmission of ENSO signals to South Georgia, and investigate other sources of interannual variability. ENSO variability generates anomalies in sea-surface temperature (SST) across the South Pacific via atmospheric teleconnections. These anomalies are advected toward South Georgia within the Antarctic Circumpolar Current (ACC), and previous studies have focussed on long-period advection (order of 2-3 years) from the southwest Pacific. We observe here, however, that the region close to the Antarctic Peninsula in the southeast Pacific is especially susceptible to ENSO forcing via anomalous meridional winds; this induces SST anomalies that are advected to South Georgia on a much more rapid timescale (order 5-6 months). The phasing of these teleconnections is such that anomalies that reach the southeast Pacific from farther west tend to be reinforced here by air-sea-ice interaction. We also find an important role for the Southern Annular Mode (SAM) in determining SST variability at South Georgia. This is a circumpolar mode of climate variability, and thus can readily influence local SST at South Georgia directly. The SAM is, however, not perfectly zonally symmetric, and (like ENSO) has a particular impact on meridional winds in the southeast Pacific. The average timescale for SAM influence on South Georgia SST is shorter than that of ENSO, since it includes a stronger component of direct local forcing. The South Georgia ecosystem is not self-sustaining, with import of krill from breeding and nursery grounds upstream in the ACC being important. We

  4. Dynamics of the Oligocene Southern Ocean: dinocysts as surface paleoceanographic tracers

    NASA Astrophysics Data System (ADS)

    Bijl, Peter; Houben, Alexander; Brinkhuis, Henk; Sangiorgi, Francesca

    2015-04-01

    The Oligocene Epoch (33.9-23 Ma) is the time interval in the Cenozoic that saw the establishment of a continental-scale Antarctic ice-sheet. There remains a controversy about whether this early episode of a glaciated Antarctica was stable, or whether dynamic ice conditions prevailed. Most of this controversy persists due to the absence of chronostratigraphically well-dated sedimentary archives from close to the east Antarctic ice sheet, which has recorded a direct signal of glacial dynamics. Another major question is how the Oligocene Southern Ocean responded to the glaciation and subsequent evolution of the ice sheet, as the Southern ocean is a major player in global ocean circulation. Numerical modelling studies suggest that alongside the buildup of continental ice on Antarctica, first sea-ice conditions may have started along the East Antarctic Margin, but this conclusion lacks support from field evidence. Other numerical models predict that hysteresis effects within the ice sheet will make a continental-size Antarctic ice sheet rather insensitive to warming. In contrast, deep-water benthic foraminiferal oxygen isotope records across the Oligocene suggest dramatic waxing and waning of Antarctic ice sheets. This paradox is as yet not solved Integrated Ocean Drilling Expedition 318 drilled the Antarctic Margin in 2010, and recovered sediments from the early phase of Antarctic glaciation. With this record, we can now evaluate the robustness of the results of the numerical models and the oceanographic changes with field data. Sediments recovered from Site U1356 yield a thick and relatively complete (albeit compromised by core gaps) Oligocene succession both of which are chrono-stratigraphically well-calibrated with use of nannoplankton- dinocyst- and magnetostratigraphy. Notably, this record yields well-preserved dinoflagellate cysts (dinocysts), which we can use to investigate surface-water condition changes across the Eocene-Oligocene to provide answers to these

  5. The reinvigoration of the Southern Ocean carbon sink.

    PubMed

    Landschützer, Peter; Gruber, Nicolas; Haumann, F Alexander; Rödenbeck, Christian; Bakker, Dorothee C E; van Heuven, Steven; Hoppema, Mario; Metzl, Nicolas; Sweeney, Colm; Takahashi, Taro; Tilbrook, Bronte; Wanninkhof, Rik

    2015-09-11

    Several studies have suggested that the carbon sink in the Southern Ocean-the ocean's strongest region for the uptake of anthropogenic CO2 -has weakened in recent decades. We demonstrated, on the basis of multidecadal analyses of surface ocean CO2 observations, that this weakening trend stopped around 2002, and by 2012, the Southern Ocean had regained its expected strength based on the growth of atmospheric CO2. All three Southern Ocean sectors have contributed to this reinvigoration of the carbon sink, yet differences in the processes between sectors exist, related to a tendency toward a zonally more asymmetric atmospheric circulation. The large decadal variations in the Southern Ocean carbon sink suggest a rather dynamic ocean carbon cycle that varies more in time than previously recognized. PMID:26359401

  6. Impacts of the north and tropical Atlantic Ocean on the Antarctic Peninsula and sea ice.

    PubMed

    Li, Xichen; Holland, David M; Gerber, Edwin P; Yoo, Changhyun

    2014-01-23

    In recent decades, Antarctica has experienced pronounced climate changes. The Antarctic Peninsula exhibited the strongest warming of any region on the planet, causing rapid changes in land ice. Additionally, in contrast to the sea-ice decline over the Arctic, Antarctic sea ice has not declined, but has instead undergone a perplexing redistribution. Antarctic climate is influenced by, among other factors, changes in radiative forcing and remote Pacific climate variability, but none explains the observed Antarctic Peninsula warming or the sea-ice redistribution in austral winter. However, in the north and tropical Atlantic Ocean, the Atlantic Multidecadal Oscillation (a leading mode of sea surface temperature variability) has been overlooked in this context. Here we show that sea surface warming related to the Atlantic Multidecadal Oscillation reduces the surface pressure in the Amundsen Sea and contributes to the observed dipole-like sea-ice redistribution between the Ross and Amundsen-Bellingshausen-Weddell seas and to the Antarctic Peninsula warming. Support for these findings comes from analysis of observational and reanalysis data, and independently from both comprehensive and idealized atmospheric model simulations. We suggest that the north and tropical Atlantic is important for projections of future climate change in Antarctica, and has the potential to affect the global thermohaline circulation and sea-level change. PMID:24451542

  7. The biodiversity of the deep Southern Ocean benthos

    PubMed Central

    Brandt, A; De Broyer, C; De Mesel, I; Ellingsen, K.E; Gooday, A.J; Hilbig, B; Linse, K; Thomson, M.R.A; Tyler, P.A

    2006-01-01

    Our knowledge of the biodiversity of the Southern Ocean (SO) deep benthos is scarce. In this review, we describe the general biodiversity patterns of meio-, macro- and megafaunal taxa, based on historical and recent expeditions, and against the background of the geological events and phylogenetic relationships that have influenced the biodiversity and evolution of the investigated taxa. The relationship of the fauna to environmental parameters, such as water depth, sediment type, food availability and carbonate solubility, as well as species interrelationships, probably have shaped present-day biodiversity patterns as much as evolution. However, different taxa exhibit different large-scale biodiversity and biogeographic patterns. Moreover, there is rarely any clear relationship of biodiversity pattern with depth, latitude or environmental parameters, such as sediment composition or grain size. Similarities and differences between the SO biodiversity and biodiversity of global oceans are outlined. The high percentage (often more than 90%) of new species in almost all taxa, as well as the high degree of endemism of many groups, may reflect undersampling of the area, and it is likely to decrease as more information is gathered about SO deep-sea biodiversity by future expeditions. Indeed, among certain taxa such as the Foraminifera, close links at the species level are already apparent between deep Weddell Sea faunas and those from similar depths in the North Atlantic and Arctic. With regard to the vertical zonation from the shelf edge into deep water, biodiversity patterns among some taxa in the SO might differ from those in other deep-sea areas, due to the deep Antarctic shelf and the evolution of eurybathy in many species, as well as to deep-water production that can fuel the SO deep sea with freshly produced organic matter derived not only from phytoplankton, but also from ice algae. PMID:17405207

  8. Antarctic-type blue whale calls recorded at low latitudes in the Indian and eastern Pacific Oceans

    NASA Astrophysics Data System (ADS)

    Stafford, Kathleen M.; Bohnenstiehl, DelWayne R.; Tolstoy, Maya; Chapp, Emily; Mellinger, David K.; Moore, Sue E.

    2004-10-01

    Blue whales, Balaenoptera musculus, were once abundant around the Antarctic during the austral summer, but intensive whaling during the first half of the 20th century reduced their numbers by over 99%. Although interannual variability of blue whale occurrence on the Antarctic feeding grounds was documented by whalers, little was known about where the whales spent the winter months. Antarctic blue whales produce calls that are distinct from those produced by blue whales elsewhere in the world. To investigate potential winter migratory destinations of Antarctic blue whales, we examined acoustic data for these signals from two low-latitude locales: the eastern tropical Pacific Ocean and the Indian Ocean. Antarctic-type blue whale calls were detected on hydrophones in both regions during the austral autumn and winter (May-September), with peak detections in July. Calls occurred over relatively brief periods in both oceans, suggesting that there may be only a few animals migrating so far north and/or producing calls. Antarctic blue whales appear to use both the Indian and eastern Pacific Oceans concurrently, indicating that there is not a single migratory destination. Acoustic data from the South Atlantic and from mid-latitudes in the Indian or Pacific Oceans are needed for a more global understanding of migratory patterns and destinations of Antarctic blue whales.

  9. Trends and variability of the atmosphere-ocean turbulent heat flux in the extratropical Southern Hemisphere

    NASA Astrophysics Data System (ADS)

    Herman, Agnieszka

    2015-10-01

    Ocean-atmosphere interactions are complex and extend over a wide range of temporal and spatial scales. Among the key components of these interactions is the ocean-atmosphere (latent and sensible) turbulent heat flux (THF). Here, based on daily optimally-interpolated data from the extratropical Southern Hemisphere (south of 30°S) from a period 1985-2013, we analyze short-term variability and trends in THF and variables influencing it. It is shown that, in spite of climate-change-related positive trends in surface wind speeds over large parts of the Southern Ocean, the range of the THF variability has been decreasing due to decreasing air-water temperature and humidity differences. Occurrence frequency of very large heat flux events decreased accordingly. Remarkably, spectral analysis of the THF data reveals, in certain regions, robust periodicity at frequencies 0.03-0.04 day-1, corresponding exactly to frequencies of the baroclinic annular mode (BAM). Finally, it is shown that the THF is correlated with the position of the major fronts in sections of the Antarctic Circumpolar Current where the fronts are not constrained by the bottom topography and can adjust their position to the atmospheric and oceanic forcing, suggesting differential response of various sections of the Southern Ocean to the changing atmospheric forcing.

  10. Sea ice, winter convection, and the temperature minimum layer in the Southern Ocean

    SciTech Connect

    Toole, J.M.

    1981-09-20

    The structure of the near surface waters in the Southern Ocean, poleward of the Antarctic Polar Front but away from continental margins, is investigated with a three-dimensional time-dependent numerical model which resolves the annual sea ice cycle. The growth and decay of the ice field is predicted, using one of Semtner's (1976) thermodynamic ice models, in terms of specified atmospheric data and computed thermohaline characteristics of the ocean layers. The ice field is found to be sensitive to the lateral advection of heat by the oceanic circulation as well as vertical heat transports due to deep winter convection. The model treats the temperature minimum layer in the Southern Ocean as the remnant of a deep winter mixed layer which becomes capped by surface heating and precipitation in summer. The predicted thermohaline characteristics of the temperature minimum layer and the surface mixed layer are in good agreement with observations. Finally, the annual air-sea heat exchange predicted by the model is discussed. The model's predicted area averaged heat loss experienced by the ocean south of the Atlantic Polar Front is much smaller than was previously estimated. This is attributed to errors in the southern region of the model domain. It is suggested that models, which include the interactions between sea ice and surface, deep, and bottom waters along the continental margins, are needed to investigate this region.

  11. Southern Ocean Climate and Sea Ice Anomalies Associated with the Southern Oscillation

    NASA Technical Reports Server (NTRS)

    Kwok, R.; Comiso, J. C.

    2001-01-01

    The anomalies in the climate and sea ice cover of the Southern Ocean and their relationships with the Southern Oscillation (SO) are investigated using a 17-year of data set from 1982 through 1998. We correlate the polar climate anomalies with the Southern Oscillation index (SOI) and examine the composites of these anomalies under the positive (SOI > 0), neutral (0 > SOI > -1), and negative (SOI < -1) phases of SOL The climate data set consists of sea-level pressure, wind, surface air temperature, and sea surface temperature fields, while the sea ice data set describes its extent, concentration, motion, and surface temperature. The analysis depicts, for the first time, the spatial variability in the relationship of the above variables and the SOL The strongest correlation between the SOI and the polar climate anomalies are found in the Bellingshausen, Amundsen and Ross sea sectors. The composite fields reveal anomalies that are organized in distinct large-scale spatial patterns with opposing polarities at the two extremes of SOI, and suggest oscillating climate anomalies that are closely linked to the SO. Within these sectors, positive (negative) phases of the SOI are generally associated with lower (higher) sea-level pressure, cooler (warmer) surface air temperature, and cooler (warmer) sea surface temperature in these sectors. Associations between these climate anomalies and the behavior of the Antarctic sea ice cover are clearly evident. Recent anomalies in the sea ice cover that are apparently associated with the SOI include: the record decrease in the sea ice extent in the Bellingshausen Sea from mid- 1988 through early 199 1; the relationship between Ross Sea SST and ENSO signal, and reduced sea ice concentration in the Ross Sea; and, the shortening of the ice season in the eastern Ross Sea, Amundsen Sea, far western Weddell Sea, and the lengthening of the ice season in the western Ross Sea, Bellingshausen Sea and central Weddell Sea gyre over the period 1988

  12. The interdisciplinary marine system of the Amundsen Sea, Southern Ocean: Recent advances and the need for sustained observations

    NASA Astrophysics Data System (ADS)

    Meredith, Michael P.; Ducklow, Hugh W.; Schofield, Oscar; Wåhlin, Anna; Newman, Louise; Lee, SangHoon

    2016-01-01

    The Southern Ocean exerts a profound influence on the functioning of the Earth System, in part because its location and unique bathymetric configuration enable direct linkages to the other major ocean basins (Ganachaud and Wunsch, 2000; Lumpkin and Speer, 2007). It is the site of the world's largest current system, the Antarctic Circumpolar Current (ACC), which transfers waters and climatically/ecologically-important tracers between the Atlantic, Indian and Pacific Oceans (Rintoul et al., 2001). In addition to the strong horizontal connectivity, the ACC is also characterized by a vigorous overturning circulation, which upwells warm, nutrient-rich waters from intermediate depth to the surface, where they are modified by interactions with the atmosphere and cryosphere to form new water masses, some of which are lighter and others more dense (Marshall and Speer, 2012). This overturning circulation structures the Southern Ocean both horizontally and vertically, dictates the levels of its communication with the rest of the global ocean, and is a fundamental control on the sequestration of carbon from the atmosphere into the ocean interior (Sallée et al., 2012). In some locations, the upwelled waters can intrude onto the Antarctic shelves, supplying heat and nutrients to the shallower regions. This is believed to be especially effective in west Antarctica, where the southern edge of the ACC moves close to the shelf break (Martinson, 2011; Orsi et al., 1995; Thoma et al., 2008).

  13. The Effects of Snow Depth Forcing on Southern Ocean Sea Ice Simulations

    NASA Technical Reports Server (NTRS)

    Powel, Dylan C.; Markus, Thorsten; Stoessel, Achim

    2003-01-01

    The spatial and temporal distribution of snow on sea ice is an important factor for sea ice and climate models. First, it acts as an efficient insulator between the ocean and the atmosphere, and second, snow is a source of fresh water for altering the already weak Southern Ocean stratification. For the Antarctic, where the ice thickness is relatively thin, snow can impact the ice thickness in two ways: a) As mentioned above snow on sea ice reduces the ocean-atmosphere heat flux and thus reduces freezing at the base of the ice flows; b) a heavy snow load can suppress the ice below sea level which causes flooding and, with subsequent freezing, a thickening of the sea ice (snow-to-ice conversion). In this paper, we compare different snow fall paramterizations (incl. the incorporation of satellite-derived snow depth) and study the effect on the sea ice using a sea ice model.

  14. On the role of the Antarctic continent in forcing large-scale circulations in the high southern latitudes

    NASA Technical Reports Server (NTRS)

    Parish, Thomas R.; Bromwich, David H.; Tzeng, Ren-Yow

    1994-01-01

    The Antarctic topography and attendant katabatic wind regime appear to play a key role in the climate of the high southern latitudes. During the nonsummer months, persistent and often times intense katabatic winds occur in the lowest few hundred meters of the Antarctic atmosphere. These slope flows transport significant amounts of cold air northward and thereby modify the horizontal pressure field over the high southern latitudes. Three-year seasonal cycle numerical simulations using the NCAR Community Climate Model Version 1 (CCM1) with and without representation of the Antarctic orography were performed to explore the role of the elevated terrain and drainage flows on the distribution and evolution of the horizontal pressure field. The katabatic wind regime is an important part of a clearly defined mean meridional circulation in the high southern latitudes. The position and intensity of the attendant sea level low pressure belt appears to be tied to the Antarctic orography. The seasonal movement of mass in the high southern latitudes is therefore constrained by the presence of the Antarctic ice sheet. The semiannual oscillation of pressure over Antarctica and the high southern latitutdes is well depicted in the CCM1 only when the Antarctic orography is included.

  15. Decadal Changes in Hydrography of the Southern Pacific Ocean and Ross Sea

    NASA Astrophysics Data System (ADS)

    Talley, L. D.; Carter, B.; Warner, M. J.; Swift, J. H.; Orsi, A. H.; Sloyan, B.

    2014-12-01

    Quasi-decadal hydrographic sections of the GO-SHIP program cross the world's oceans with the highest accuracy measurements, documenting temporal variability in physical and chemical properties. The central southern Pacific and Ross Sea have been surveyed regularly along GO-SHIP sections P16S (150W) and S4P (67S) since the first occupation in WOCE in 1992. Observed changes are consistent with anthropogenic forcing. The central Ross Sea gyre's bottom 1000 m is nearly adiabatic (well mixed), and well-ventilated based on chlorofluorocarbon (CFC) and sulfur hexafluoride observations (see Figure), and can be easily compared from one survey to the next. This Ross Sea bottom layer observed in March, 2014, on P16S continued to warm, with a monotonic increase over the 4 WOCE/GO-SHIP surveys thus far: 1992, 2005, 2011, and now 2014 (see Figure). Deep temperature has increased by 0.1°C since 1992, continuing the trend of enhanced global ocean deep warming in the Southern Ocean documented by Purkey/Johnson (2010) and IPCC AR5 WG1. The abyssal central Ross Sea waters also continued to freshen slightly. The upper ocean in the Ross Sea warmed, became more stratified, had higher nutrients and total carbon, and was less ventilated in terms of apparent oxygen utilization than in 2005. North of the Antarctic Circumpolar Current along 150W, the upper ocean's Subantarctic Mode Water became saltier, also continuing the subtropical trend of the past several decades (Durack/Wijffels 2010), with an apparently stronger incursion of saline subtropical waters that render it more salt and temperature stratified, ruling out a local deep mixed layer formation mechanism, with an increasing tendency towards double diffusive processes. The Antarctic Intermediate Water salinity minimum continued to freshen. The arrival in 2014 of CFC's at the ocean bottom between 32S and 40S indicates that the Antarctic Bottom Water there is about 40-50 years old. CFCs in the ocean's surface layer decreased, in

  16. Dynamics of the Atlantic meridional overturning circulation and Southern Ocean in an ocean model of intermediate complexity

    NASA Astrophysics Data System (ADS)

    McCreary, Julian P.; Furue, Ryo; Schloesser, Fabian; Burkhardt, Theodore W.; Nonaka, Masami

    2016-04-01

    A steady-state, variable-density, 2-layer, ocean model (VLOM) is used to investigate basic dynamics of the Atlantic meridional overturning circulation and Southern Ocean. The domain consists of idealized (rectangular) representations of the Atlantic, Southern, and Pacific Oceans. The model equations represent the depth-averaged, layer-1 response (except for one solution in which they represent the depth-integrated flow over both layers). To allow for overturning, water can cross the bottom of layer 1 at the velocity we =wd +wm +wn , the three parts representing: interior diffusion wd that increases the layer-1 thickness h throughout the basin, mixed-layer entrainment wm that ensures h is never less than a minimum value hm , and diapycnal (cooling) processes external to the basin wn that adjust h to hn . For most solutions, horizontal mixing has the form of Rayleigh damping with coefficient ν , which we interpret to result from baroclinic instability through the closure, V∗ = - (ν /f2) ∇P , where ∇P = ∇(1/2 g‧h2) is the depth-integrated pressure gradient, g‧ is the reduced-gravity coefficient, and ν is a mixing coefficient; with this interpretation, the layer-1 flow corresponds to the sum of the Eulerian-mean and eddy-mean (V∗) transport/widths, that is, the "residual" circulation. Finally, layer-1 temperature cools polewards in response to a surface heat flux Q, and the cooling can be strong enough in the Southern Ocean for g‧ = 0 south of a latitude y0 , in which case layer 1 vanishes and the model reduces to a single layer 2. Solutions are obtained both numerically and analytically. The analytic approach splits fields into interior and boundary-layer parts, from which a coupled set of integral constraints can be derived. The set allows properties of the circulation (upwelling-driven transport out of the Southern Ocean M , downwelling transport in the North Atlantic, transport of the Antarctic Circumpolar Current) and stratification (Atlantic

  17. Astronomically-induced Mid-Brunhes Transition in the Southern and Deep Oceans

    NASA Astrophysics Data System (ADS)

    Yin, Qiuzhen

    2013-04-01

    The interglacials after 430 ka (ka: 1000 years) ago were characterized by warmer climates and higher atmospheric CO2 concentrations than the interglacials before, but the cause of this climatic transition (the so-called Mid-Brunhes Event, MBE) is unknown. Based on model simulations, my results show that, in response to insolation changes only, feedbacks between sea ice, temperature, evaporation and salinity caused vigorous pre-MBE Antarctic Bottom Water formation and Southern Ocean ventilation. My results also show that strong Westerlies increased the pre-MBE overturning in the Southern Ocean via an increased latitudinal insolation gradient created by changes in eccentricity during austral winter and in obliquity during austral summer. The stronger bottom water formation led to a cooler deep ocean during the older interglacials. These insolation-induced differences in the deep-sea temperature and in the Southern Ocean ventilation between the more recent interglacials and the older ones were not expected, because there is no straightforward visible systematic difference in the astronomical parameters between the interglacials before and after 430 ka ago. Rather than being a real "event", the apparent MBE (i.e. the difference in the interglacial intensity before and after 430 ka BP) appears in my results to come from the complex response of the climate system to the astronomical and insolation forcings prevailing before and after 430 ka BP. This does not mean that nothing could have happened between MIS-13 and MIS-11 which might have amplified such difference. Given the important roles of the Southern and Deep Oceans on the carbon cycle, these findings are a first step towards understanding the magnitude change of the interglacial CO2 concentration around 430 ka. Reference: Yin Q.Z., 2013. Insolation-induced Mid-Brunhes Transition in the Southern and Deep Oceans. Nature, DOI 10.1038/nature11790. Acknowledgement: This work is supported by the European Research Council

  18. The ocean's role in polar climate change: asymmetric Arctic and Antarctic responses to greenhouse gas and ozone forcing.

    PubMed

    Marshall, John; Armour, Kyle C; Scott, Jeffery R; Kostov, Yavor; Hausmann, Ute; Ferreira, David; Shepherd, Theodore G; Bitz, Cecilia M

    2014-07-13

    In recent decades, the Arctic has been warming and sea ice disappearing. By contrast, the Southern Ocean around Antarctica has been (mainly) cooling and sea-ice extent growing. We argue here that interhemispheric asymmetries in the mean ocean circulation, with sinking in the northern North Atlantic and upwelling around Antarctica, strongly influence the sea-surface temperature (SST) response to anthropogenic greenhouse gas (GHG) forcing, accelerating warming in the Arctic while delaying it in the Antarctic. Furthermore, while the amplitude of GHG forcing has been similar at the poles, significant ozone depletion only occurs over Antarctica. We suggest that the initial response of SST around Antarctica to ozone depletion is one of cooling and only later adds to the GHG-induced warming trend as upwelling of sub-surface warm water associated with stronger surface westerlies impacts surface properties. We organize our discussion around 'climate response functions' (CRFs), i.e. the response of the climate to 'step' changes in anthropogenic forcing in which GHG and/or ozone-hole forcing is abruptly turned on and the transient response of the climate revealed and studied. Convolutions of known or postulated GHG and ozone-hole forcing functions with their respective CRFs then yield the transient forced SST response (implied by linear response theory), providing a context for discussion of the differing warming/cooling trends in the Arctic and Antarctic. We speculate that the period through which we are now passing may be one in which the delayed warming of SST associated with GHG forcing around Antarctica is largely cancelled by the cooling effects associated with the ozone hole. By mid-century, however, ozone-hole effects may instead be adding to GHG warming around Antarctica but with diminished amplitude as the ozone hole heals. The Arctic, meanwhile, responding to GHG forcing but in a manner amplified by ocean heat transport, may continue to warm at an accelerating rate

  19. The ocean's role in polar climate change: asymmetric Arctic and Antarctic responses to greenhouse gas and ozone forcing

    PubMed Central

    Marshall, John; Armour, Kyle C.; Scott, Jeffery R.; Kostov, Yavor; Hausmann, Ute; Ferreira, David; Shepherd, Theodore G.; Bitz, Cecilia M.

    2014-01-01

    In recent decades, the Arctic has been warming and sea ice disappearing. By contrast, the Southern Ocean around Antarctica has been (mainly) cooling and sea-ice extent growing. We argue here that interhemispheric asymmetries in the mean ocean circulation, with sinking in the northern North Atlantic and upwelling around Antarctica, strongly influence the sea-surface temperature (SST) response to anthropogenic greenhouse gas (GHG) forcing, accelerating warming in the Arctic while delaying it in the Antarctic. Furthermore, while the amplitude of GHG forcing has been similar at the poles, significant ozone depletion only occurs over Antarctica. We suggest that the initial response of SST around Antarctica to ozone depletion is one of cooling and only later adds to the GHG-induced warming trend as upwelling of sub-surface warm water associated with stronger surface westerlies impacts surface properties. We organize our discussion around ‘climate response functions’ (CRFs), i.e. the response of the climate to ‘step’ changes in anthropogenic forcing in which GHG and/or ozone-hole forcing is abruptly turned on and the transient response of the climate revealed and studied. Convolutions of known or postulated GHG and ozone-hole forcing functions with their respective CRFs then yield the transient forced SST response (implied by linear response theory), providing a context for discussion of the differing warming/cooling trends in the Arctic and Antarctic. We speculate that the period through which we are now passing may be one in which the delayed warming of SST associated with GHG forcing around Antarctica is largely cancelled by the cooling effects associated with the ozone hole. By mid-century, however, ozone-hole effects may instead be adding to GHG warming around Antarctica but with diminished amplitude as the ozone hole heals. The Arctic, meanwhile, responding to GHG forcing but in a manner amplified by ocean heat transport, may continue to warm at an

  20. Antarctic science

    NASA Astrophysics Data System (ADS)

    Summerhayes, Colin

    Once upon a time, dinosaurs roamed Antarctica and swam in its seas. Since then, life evolved as the climate cooled into the ice ages. Life will no doubt continue to evolve there as the globe now warms. But nowadays, humans are having a profound and direct effect on life in Antarctica, the sub-Antarctic islands, and the surrounding Southern Ocean, which are being invaded by a wide range of alien species including microbes, algae, fungi, bryophytes, land plants, invertebrates, fish, birds, and mammals.

  1. Seasonal and geographic variation of southern blue whale subspecies in the Indian Ocean.

    PubMed

    Samaran, Flore; Stafford, Kathleen M; Branch, Trevor A; Gedamke, Jason; Royer, Jean-Yves; Dziak, Robert P; Guinet, Christophe

    2013-01-01

    Understanding the seasonal movements and distribution patterns of migratory species over ocean basin scales is vital for appropriate conservation and management measures. However, assessing populations over remote regions is challenging, particularly if they are rare. Blue whales (Balaenoptera musculus spp) are an endangered species found in the Southern and Indian Oceans. Here two recognized subspecies of blue whales and, based on passive acoustic monitoring, four "acoustic populations" occur. Three of these are pygmy blue whale (B.m. brevicauda) populations while the fourth is the Antarctic blue whale (B.m. intermedia). Past whaling catches have dramatically reduced their numbers but recent acoustic recordings show that these oceans are still important habitat for blue whales. Presently little is known about the seasonal movements and degree of overlap of these four populations, particularly in the central Indian Ocean. We examined the geographic and seasonal occurrence of different blue whale acoustic populations using one year of passive acoustic recording from three sites located at different latitudes in the Indian Ocean. The vocalizations of the different blue whale subspecies and acoustic populations were recorded seasonally in different regions. For some call types and locations, there was spatial and temporal overlap, particularly between Antarctic and different pygmy blue whale acoustic populations. Except on the southernmost hydrophone, all three pygmy blue whale acoustic populations were found at different sites or during different seasons, which further suggests that these populations are generally geographically distinct. This unusual blue whale diversity in sub-Antarctic and sub-tropical waters indicates the importance of the area for blue whales in these former whaling grounds. PMID:23967221

  2. Effects of Drake Passage widening during the Eocene-Oligocene Transition on Southern Ocean bulk sediment trace element geochemistry

    NASA Astrophysics Data System (ADS)

    Elsworth, G.; Galbraith, E. D.; Halverson, G. P.

    2013-12-01

    Presently, the Southern Ocean provides three-quarters of the global nutrient supply to the low latitude surface ocean (Sarmiento et al. 2004; Palter et al. 2010). In this region the removal of nutrients by sinking organic matter is exceeded by wind-driven upwelling of remineralized nutrients along the Antarctic Circumpolar Current (ACC). The excess nutrients are then advected across the ACC into Subantarctic Mode Water (SAMW), a water mass that transfers the unutilized Southern Ocean nutrients to low-latitude upwelling regions (Toggweiler et al. 1991). However, prior to the opening of the Drake Passage near the Eocene-Oligocene Transition (EOT) the ACC did not exist, suggesting a change in nutrient dynamics of the Southern Ocean. Earth system model simulations by Yang et al. 2013 suggest that as the Drake Passage opened, the supply of southern nutrients would have increased, possibly amplifying iron limitation and increasing oxygenation of the deep Southern Ocean. These results indicate that different surface nutrient return pathways in the pre- and post-Drake Passage Southern Ocean may have changed nutrients available to phytoplankton. To assess geological records of these model predictions, Integrated Ocean Drilling Program (IODP) Sites 689 and 1090 have been sampled at 15 to 50 kyr intervals from 31 to 37 Ma. Site 689, located on Maud Rise in the Weddell Sea, and Site 1090, located on Agulhas Ridge in the Southern Atlantic, provide a crucial transect across the Atlantic Sector of the Southern Ocean to examine the influence of the developing ACC on ocean circulation. Bulk sediment trace element analyses using inductively coupled plasma optical emission spectrometry (ICP OES) provide indications of biological surface export (Ca, Ba), deep-water oxygenation (U, Mo, Mn), and dust influx (Th, Rb). Results will be presented at the meeting.

  3. Biogeochemical cycling of cadmium isotopes in the Southern Ocean along the Zero Meridian

    NASA Astrophysics Data System (ADS)

    Abouchami, W.; Galer, S. J. G.; de Baar, H. J. W.; Middag, R.; Vance, D.; Zhao, Y.; Klunder, M.; Mezger, K.; Feldmann, H.; Andreae, M. O.

    2014-02-01

    We present depth profiles of Cd isotopes and concentrations from the Southern Ocean at four stations in the Atlantic sector along the Greenwich Meridian (47°S to 68°S) located across the main Antarctic frontal zones and productivity belt. The vertical profiles of Cd concentration typically show low values in surface waters, elevated values at intermediate depths, reflecting remineralization of sinking particulate organic matter, and constant values in deep waters. The surface-to-deep isotopic gradient shows “heavy” Cd isotope signatures in the mixed surface layer, becoming more pronounced northward, with values up to ɛ112/110Cd of around +4.1 in the Subantarctic sector of the Southern Ocean. Deep Antarctic waters display a uniform and “light” ɛ112/110Cd of +1.18 ± 0.38 and Cd concentrations of 0.761 ± 0.101 nmol/kg (n = 23, 2SD). Intermediate waters are characterized by ɛ112/110Cd lying between those of surface and deep waters, with a constant value of about +0.8 in the High Nutrient Low Chlorophyll sector and a notably higher value of +2.3 in the Subantarctic sector. The Cd isotope fractionation in the Southern Ocean closely follows a simple closed-system Rayleigh model, in which biological uptake of Cd imparts the ɛ112/110Cd signature to the surface layer while that of deep waters is determined by the flux of regenerated isotopically-light Cd from sinking organic matter from the surface ocean and the degree of mixing of distinct water masses. The vertical gradient documented for Cd isotopes and nutrient ratios, along with the meridional gradient in surface waters, highlights the important role played by upwelling in the Southern Ocean in closing the meridional overturning circulation via the export of Antarctic intermediate and mode waters which have a distinctive chemical (low Cd:P) and Cd isotope (“heavy”) signature. The combined Cd-Zn isotope systematics provide evidence for a strong link between the magnitude of biological Cd stable

  4. Planktonic foraminiferal biogeography in the Indian sector of the Southern Ocean: Contribution from CPR data

    NASA Astrophysics Data System (ADS)

    Meilland, Julie; Fabri-Ruiz, Salomé; Koubbi, Philippe; Monaco, Claire Lo; Cotte, Cédric; Hosie, Graham W.; Sanchez, Sophie; Howa, Hélène

    2016-04-01

    Within the framework of the Scientific Committee on Antarctic Research (SCAR) Southern Ocean-Continuous Plankton Recorder (SO-CPR) Survey, the oceanic regions around Crozet and Kerguelen Islands were investigated in February-March 2013. Living planktonic Foraminifera (LPF) were collected in the upper mixed layer with a CPR along a 2160 nautical mile sea transect that crossed main hydrological fronts in the Indian sector of the Southern Ocean. In the SO-CPR database, mean total abundances of Foraminifera occurring during late austral summer are highly variable at an inter-annual scale, from 10 to 250 ind.m-3, representing 10-40% of the total zooplankton abundance, respectively. In the Southern Ocean, major inter-annual changes in zooplankton community structure were already reported. In this study, we describe the large scale distributional pattern of individual planktonic foraminiferal species living in near-surface waters of the Indian sector of the Southern Ocean, and we attempt to explain why major spatial variability in relative species abundances occurs during a late austral summer. In February-March 2013, LPF total abundances recorded between 42.86°S and 56.42°S ranged from 0 to a maximum of 258 ind.m-3. In the Open Ocean Zone, the LPF community was composed of four major species (Globigerinita uvula, Neogloboquadrina pachyderma, Neogloboquadrina incompta, Globigerina bulloides). Generally, LPF total abundances are supposed to mirror primary production induced by hydrological fronts or induced by topography near Crozet and Kerguelen Islands. However, during late austral summer 2013, high foraminiferal abundances in the upper mixed layer did not always match the pattern of near-surface primary production (high Chl-a concentration areas delineated from satellite imagery). Low LPF standing stocks in late austral summer in the Southern Ocean contrasted with the presence of high densities of heavily silicified diatoms. This suggests that the late bloom

  5. Subduction of SAMW/AAIW in the Upper Cell of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Sallee, J.; Speer, K.; Rintoul, S.; Wijffels, S.

    2008-12-01

    The intensity and location of the upper overturning cell in the Southern Ocean is uncertain, for instance if the cell is associated with subduction centered on the Subantarctic Front or the Polar Front. Argo data provide a new view of the Southern Ocean interior and allow for the first time to resolve the seasonal cycle of the upper ocean. This new dataset is used to revisit the role of the mean flow in subducting water masses in the vicinity of the Antarctic Circumpolar Current. New eddy diffusivity estimates are also used to revise the main balances of the 2-d overturning cell, and it is found that horizontal buoyancy mixing plays an important role near the main fronts of the ACC. The new estimate of kappa allows us to also revisit the estimate of the eddy induced advection through the parameterization of Gent and McWilliam (1990). Eddy diffusivity in the Southern Ocean has been estimated from several approaches in order to quantify the role of eddies on mixed layer heat and mass budgets, and to revisit the role of eddies on the upper cell of the meridional overturning circulation. We find 2 main convergences of the 2-d upper cell in the ACC, associated with AAIW and SAMW subduction. The eddy induced advection tends to balance the subduction induced by Ekman and lateral geostrophic induction. We also investigate the regional patterns of the subduction along the circumpolar belt.

  6. Effects of whaling on the structure of the Southern Ocean food web: insights on the "krill surplus" from ecosystem modelling.

    PubMed

    Surma, Szymon; Pakhomov, Evgeny A; Pitcher, Tony J

    2014-01-01

    The aim of this study was to examine the ecological plausibility of the "krill surplus" hypothesis and the effects of whaling on the Southern Ocean food web using mass-balance ecosystem modelling. The depletion trajectory and unexploited biomass of each rorqual population in the Antarctic was reconstructed using yearly catch records and a set of species-specific surplus production models. The resulting estimates of the unexploited biomass of Antarctic rorquals were used to construct an Ecopath model of the Southern Ocean food web existing in 1900. The rorqual depletion trajectory was then used in an Ecosim scenario to drive rorqual biomasses and examine the "krill surplus" phenomenon and whaling effects on the food web in the years 1900-2008. An additional suite of Ecosim scenarios reflecting several hypothetical trends in Southern Ocean primary productivity were employed to examine the effect of bottom-up forcing on the documented krill biomass trend. The output of the Ecosim scenarios indicated that while the "krill surplus" hypothesis is a plausible explanation of the biomass trends observed in some penguin and pinniped species in the mid-20th century, the excess krill biomass was most likely eliminated by a rapid decline in primary productivity in the years 1975-1995. Our findings suggest that changes in physical conditions in the Southern Ocean during this time period could have eliminated the ecological effects of rorqual depletion, although the mechanism responsible is currently unknown. Furthermore, a decline in iron bioavailability due to rorqual depletion may have contributed to the rapid decline in overall Southern Ocean productivity during the last quarter of the 20th century. The results of this study underscore the need for further research on historical changes in the roles of top-down and bottom-up forcing in structuring the Southern Ocean food web. PMID:25517505

  7. Comparisons of The Habitat Utilization Of Top Predators In The Southern Ocean And The North Pacific

    NASA Astrophysics Data System (ADS)

    Costa, D. P.; Robinson, P.; Huckstadt, L. E.; Crocker, D. E.; Goebel, M. E.

    2010-12-01

    Northern and Southern elephant seals (Mirounga angustirostris, M. leonina) separated some 4 MYA. While these congeners are physiologically very similar and thus have the potential to forage in similar ways they inhabit very different habitats. While southern elephant seals (SES) are distributed throughout the southern ocean, northern elephant seals (NES) are limited to the Northeast Pacific Ocean and range over lower latitudes than SES. In order to compare and contrast the physiological capability and response to different habitats we compared the foraging behavior of 167 adult female northern elephant seals (Año Nuevo and San Benitos Islands) and 55 southern elephant seals (Livingston Island, Antarctic Peninsula) using satellite telemetry and dive recorders. As expected both species carried out very similar dive depths (NES 509m ± 166 vs SES 345m±79) and dive durations (NES 23.0 min ± 6.7; SES 22.5 min ± 5.0). However, there were significant differences in their foraging pattern that we attribute to differences in the availability of continental shelf and suitable foraging habitat. While 85% of NES females foraged offshore, the dominant strategy for SES was benthic foraging on the continental shelf. Even with the differences in habitat, the fundamental components of their foraging patterns remained the same as when they foraged pelagically they both species relied on persistent large scale oceanographic features where mixing enhances productivity such as the North Pacific Transition zone (NES) and the Southern Antarctic Circumpolar Current Front (SES). Given the very different habitats and prey species consumed by these two species their overall foraging behavior is surprisingly similar suggesting that as a mesopelagic predator the elephant seal design is rather robust.

  8. The development of Antarctic katabatic winds and implications for the coastal ocean

    SciTech Connect

    Davis, A.M.J.; McNider, R.T.

    1997-05-01

    The influence of katabatic winds on the Antarctic coastal waters is examined by using simple models of the ocean and atmosphere. A katabatic flow model incorporating Coriolis dynamics is solved analytically and another with nonlinear friction is solved numerically to provide wind stress to a two-layer coastal ocean model. The resulting solutions are evidently the first to incorporate Coriolis terms with a thermodynamic equation that includes compressional warming effects. The emphasis in this paper is on delineating the parameters that control the relative adjustment of the katabatic wind into alongshore and offshore components. By including nonlinear friction, it is shown that steeper slopes and weaker stratification tend to direct the wind more toward the ocean. It is further demonstrated that the katabatic forcing supports the strong polar easterlies (winds from the east) along the periphery of the continent and that the offshore extent should be dependent on the atmospheric Rossby deformation radius. The ocean model shows that significant downwelling occurs at the coast, while upwelling is predicted at a distance of the order of the ocean Rossby radius. An alongshore coastal jet from the east is found in the model and is evidently the manifestation of the east wind drift. The upwelling offshore may be a significant aspect of polynya formation and maintenance of the Antarctic divergence zone and contribute to the biological productivity of the region. 19 refs., 6 figs., 2 tabs.

  9. Bathymetric distribution patterns of Southern Ocean macrofaunal taxa: Bivalvia, Gastropoda, Isopoda and Polychaeta

    NASA Astrophysics Data System (ADS)

    Brandt, Angelika; Linse, Katrin; Schüller, Myriam

    2009-11-01

    The aim of this study is to compare the depth distributions of four major Southern Ocean macrobenthic epi- and infaunal taxa, the Bivalvia, Gastropoda, Isopoda, and Polychaeta, from subtidal to abyssal depth. All literature data up to summer 2008, as well as the unpublished data from the most recent ANDEEP I-III (Antarctic benthic deep-sea biodiversity: colonisation history and recent community patterns) expeditions to the Southern Ocean deep sea are included in the analysis. Benthic invertebrates in the Southern Ocean are known for their wide bathymetric ranges. We analysed the distributions of four of the most abundant and species-rich taxa from intertidal to abyssal (5200 m) depths in depth zones of 100 m. The depth distributions of three macrofaunal classes (Bivalvia, Gastropoda, Polychaeta) and one order (Isopoda) showed distinct differences. In the case of bivalves, gastropods and polychaetes, the number of species per depth zone decreased from the shelf to the slope at around 1000 m depth and then showed stable low numbers. The isopods showed the opposite trend; they were less species rich in the upper 1000 m but increased in species numbers from the slope to bathyal and abyssal depths. Depth ranges of families of the studied taxa (Bivalvia: 31 families, Gastropoda: 60, Isopoda: 32, and Polychaeta: 46 families) were compiled and illustrated. At present vast areas of the deep sea in the Southern Ocean remain unexplored and species accumulation curves showed that only a fraction of the species have been discovered to date. We anticipate that further investigations will greatly increase the number of species known in the Southern Ocean deep sea.

  10. Sea ice and the ocean mixed layer over the Antarctic shelf seas

    NASA Astrophysics Data System (ADS)

    Petty, A. A.; Holland, P. R.; Feltham, D. L.

    2013-08-01

    An ocean mixed layer model has been incorporated into the Los Alamos sea ice model CICE to investigate regional variations in the surface-driven formation of Antarctic shelf waters. This model captures well the expected sea ice thickness distribution, and produces deep (> 500 m) mixed layers in the Weddell and Ross shelf seas each winter. This results in the complete destratification of the water column in deep southern coastal regions (leading to HSSW formation) and also in some shallower regions (no HSSW formation) of these seas. Shallower mixed layers are produced in the Amundsen and Bellingshausen seas. By deconstructing the surface power input to the mixed layer, we show that the freshwater flux from sea ice growth/melt dominates the evolution of the mixed layer in all seas, with a smaller contribution from the surface heat flux. The Weddell and Ross shelf seas receive an annual surplus of energy at the surface, the Amundsen shelf sea energy input in autumn/winter is balanced by energy extraction in spring/summer, and the Bellingshausen shelf sea experiences an annual surface energy deficit, through both a low energy input in autumn/winter and the highest energy loss in spring/summer. An analysis of the sea ice mass balance demonstrates the contrasting mean ice growth, melt and export in each region. The Weddell and Ross shelf seas have the highest annual ice growth, with a large fraction exported northwards each year, whereas the Bellingshausen shelf sea experiences the highest annual ice melt, driven by the advection of ice from the northeast. A linear regression analysis is performed to determine the temporal and spatial correlations between the autumn/winter mixed layer power input and several atmospheric variables. The temporal mean Weddell and Ross autumn/winter power input shows stronger spatial correlation to several atmospheric variables compared to the Amundsen and Bellingshausen. In contrast the spatial mean autumn/winter power input shows stronger

  11. The reinvigoration of the Southern Ocean carbon sink

    NASA Astrophysics Data System (ADS)

    Landschützer, Peter; Gruber, Nicolas; Haumann, F. Alexander; Rödenbeck, Christian; Bakker, Dorothee C. E.; van Heuven, Steven; Hoppema, Mario; Metzl, Nicolas; Sweeney, Colm; Takahashi, Taro; Tilbrook, Bronte; Wanninkhof, Rik

    2015-09-01

    Several studies have suggested that the carbon sink in the Southern Ocean—the ocean’s strongest region for the uptake of anthropogenic CO2 —has weakened in recent decades. We demonstrated, on the basis of multidecadal analyses of surface ocean CO2 observations, that this weakening trend stopped around 2002, and by 2012, the Southern Ocean had regained its expected strength based on the growth of atmospheric CO2. All three Southern Ocean sectors have contributed to this reinvigoration of the carbon sink, yet differences in the processes between sectors exist, related to a tendency toward a zonally more asymmetric atmospheric circulation. The large decadal variations in the Southern Ocean carbon sink suggest a rather dynamic ocean carbon cycle that varies more in time than previously recognized.

  12. Vulnerability of polar oceans to anthropogenic acidification: comparison of arctic and antarctic seasonal cycles.

    PubMed

    Shadwick, E H; Trull, T W; Thomas, H; Gibson, J A E

    2013-01-01

    Polar oceans are chemically sensitive to anthropogenic acidification due to their relatively low alkalinity and correspondingly weak carbonate buffering capacity. Here, we compare unique CO2 system observations covering complete annual cycles at an Arctic (Amundsen Gulf) and Antarctic site (Prydz Bay). The Arctic site experiences greater seasonal warming (10 vs 3°C), and freshening (3 vs 2), has lower alkalinity (2220 vs 2320 μmol/kg), and lower summer pH (8.15 vs 8.5), than the Antarctic site. Despite a larger uptake of inorganic carbon by summer photosynthesis, the Arctic carbon system exhibits smaller seasonal changes than the more alkaline Antarctic system. In addition, the excess surface nutrients in the Antarctic may allow mitigation of acidification, via CO2 removal by enhanced summer production driven by iron inputs from glacial and sea-ice melting. These differences suggest that the Arctic system is more vulnerable to anthropogenic change due to lower alkalinity, enhanced warming, and nutrient limitation. PMID:23903871

  13. Vulnerability of Polar Oceans to Anthropogenic Acidification: Comparison of Arctic and Antarctic Seasonal Cycles

    PubMed Central

    Shadwick, E. H.; Trull, T. W.; Thomas, H.; Gibson, J. A. E.

    2013-01-01

    Polar oceans are chemically sensitive to anthropogenic acidification due to their relatively low alkalinity and correspondingly weak carbonate buffering capacity. Here, we compare unique CO2 system observations covering complete annual cycles at an Arctic (Amundsen Gulf) and Antarctic site (Prydz Bay). The Arctic site experiences greater seasonal warming (10 vs 3°C), and freshening (3 vs 2), has lower alkalinity (2220 vs 2320 μmol/kg), and lower summer pH (8.15 vs 8.5), than the Antarctic site. Despite a larger uptake of inorganic carbon by summer photosynthesis, the Arctic carbon system exhibits smaller seasonal changes than the more alkaline Antarctic system. In addition, the excess surface nutrients in the Antarctic may allow mitigation of acidification, via CO2 removal by enhanced summer production driven by iron inputs from glacial and sea-ice melting. These differences suggest that the Arctic system is more vulnerable to anthropogenic change due to lower alkalinity, enhanced warming, and nutrient limitation. PMID:23903871

  14. Extratropical Cyclone in the Southern Ocean

    NASA Technical Reports Server (NTRS)

    2001-01-01

    These images from the Multi-angle Imaging SpectroRadiometer portray an occluded extratropical cyclone situated in the Southern Ocean, about 650 kilometers south of the Eyre Peninsula, South Australia.

    Parts of the Yorke Peninsula and a portion of the Murray-Darling River basin are visible between the clouds near the top of the left-hand image, a true-color view from MISR's nadir(vertical-viewing) camera. Retrieved cloud-tracked wind velocities are indicated by the superimposed arrows. The image on the right displays cloud-top heights. Areas where cloud heights could not be retrieved are shown in black. Both the wind vectors and the cloud heights were derived using data from multiple MISR cameras within automated computer processing algorithms. The stereoscopic algorithms used to generate these results are still being refined, and future versions of these products may show modest changes.

    Extratropical cyclones are the dominant weather system at midlatitudes, and the term is used generically for region allow-pressure systems in the mid- to high-latitudes. In the southern hemisphere, cyclonic rotation is clockwise. These storms obtain their energy from temperature differences between air masses on either side of warm and cold fronts, and their characteristic pattern is of warm and cold fronts radiating out from a migrating low pressure center which forms, deepens, and dissipates as the fronts fold and collapse on each other. The center of this cyclone has started to decay, with the band of cloud to the south most likely representing the main front that was originally connected with the cyclonic circulation.

    These views were acquired on October 11, 2001 during Terra orbit 9650, and represent an area of about 380 kilometers x 1900 kilometers.

  15. Extratropical Cyclone in the Southern Ocean

    NASA Technical Reports Server (NTRS)

    2002-01-01

    These images from the Multi-angle Imaging SpectroRadiometer (MISR) portray an occluded extratropical cyclone situated in the Southern Ocean, about 650 kilometers south of the Eyre Peninsula, South Australia. The left-hand image, a true-color view from MISR's nadir (vertical-viewing) camera, shows clouds just south of the Yorke Peninsula and the Murray-Darling river basin in Australia. Retrieved cloud-tracked wind velocities are indicated by the superimposed arrows. The image on the right displays cloud-top heights. Areas where cloud heights could not be retrieved are shown in black. Both the wind vectors and the cloud heights were derived using data from multiple MISR cameras within automated computer processing algorithms. The stereoscopic algorithms used to generate these results are still being refined, and future versions of these products may show modest changes. Extratropical cyclones are the dominant weather system at midlatitudes, and the term is used generically for regional low-pressure systems in the mid- to high-latitudes. In the southern hemisphere, cyclonic rotation is clockwise. These storms obtain their energy from temperature differences between air masses on either side of warm and cold fronts, and their characteristic pattern is of warm and cold fronts radiating out from a migrating low pressure center which forms, deepens, and dissipates as the fronts fold and collapse on each other. The center of this cyclone has started to decay, with the band of cloud to the south most likely representing the main front that was originally connected with the cyclonic circulation. These views were acquired on October 11, 2001, and the large view represents an area of about 380 kilometers x 1900 kilometers. Image courtesy NASA/GSFC/LaRC/JPL, MISR Team.

  16. Pairwise surface drifter separation in the western Pacific sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    van Sebille, Erik; Waterman, Stephanie; Barthel, Alice; Lumpkin, Rick; Keating, Shane R.; Fogwill, Chris; Turney, Chris

    2015-10-01

    The Southern Ocean plays a critical role in global climate, yet the mixing properties of the circulation in this part of the ocean remain poorly understood. Here dispersion in the vicinity of the Southern Antarctic Circumpolar Current Front, one of the branches of the Antarctic Circumpolar Current, is studied using 10 pairs of surface drifters deployed systematically across the frontal jet and its flanks. Drifter pairs were deployed with an initial separation of 13 m and report their position every hour. The separation of the pairs over 7 months, in terms of their Finite-Scale Lyapunov Exponents (FSLE), dispersion, and diffusivity, is characterized and related to expected behavior from Quasi-Geostrophic (QG) and Surface Quasi-Geostrophic (SQG) theories. The FSLE analysis reveals two submesoscale regimes, with SQG-like behavior at scales below 3.2 km and mixed QG/SQG behavior at scales between 3.2 and 73 km. The dispersion analysis, however, suggests QG-like behavior for the smallest scales. Both dispersion and diffusivity appear isotropic for scales up to 500 km. Finally, there is no clear indication of a cross-jet variation of drifter dispersion.

  17. Biomass and energy transfer to baleen whales in the South Atlantic sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Reilly, S.; Hedley, S.; Borberg, J.; Hewitt, R.; Thiele, D.; Watkins, J.; Naganobu, M.

    2004-06-01

    Baleen whales are an important group of predators on Antarctic krill in the Southern Ocean. During the CCAMLR 2000 Survey to estimate the biomass and distribution of Antarctic krill, International Whaling Commission observers carried out a visual line transect survey to estimate the number of baleen whales occurring in the survey area. This paper reviews techniques used to estimate krill consumption by baleen whales and in combination with estimates of whale abundance estimates of krill consumption are generated for the South Atlantic sector of the Southern Ocean. This survey estimates that the present populations of whales feeding in this region are likely to consume approximately 1.6 million tonnes, but possibly up to as much as 2.7 million tonnes of krill within the summer season. Although this only represents 4-6% of the estimated krill biomass in the region (and probably less than this percentage of the total annual krill production), the depleted numbers of baleen whales resulting from past or current whaling activities should be taken into account when setting quotas for the commercial exploitation of krill if there is to be a recovery to pre-exploitation biomass levels of baleen whales.

  18. Exploring the southern ocean response to climate change

    NASA Technical Reports Server (NTRS)

    Martinson, Douglas G.; Rind, David; Parkinson, Claire

    1993-01-01

    The purpose of this project was to couple a regional (Southern Ocean) ocean/sea ice model to the existing Goddard Institute for Space Science (GISS) atmospheric general circulation model (GCM). This modification recognizes: the relative isolation of the Southern Ocean; the need to account, prognostically, for the significant air/sea/ice interaction through all involved components; and the advantage of translating the atmospheric lower boundary (typically the rapidly changing ocean surface) to a level that is consistent with the physical response times governing the system evolution (that is, to the base of the fast responding ocean surface layer). The deeper ocean beneath this layer varies on time scales several orders of magnitude slower than the atmosphere and surface ocean, and therefore the boundary between the upper and deep ocean represents a more reasonable fixed boundary condition.

  19. Water-mass transformation by sea ice in the upper branch of the Southern Ocean overturning

    NASA Astrophysics Data System (ADS)

    Abernathey, Ryan P.; Cerovecki, Ivana; Holland, Paul R.; Newsom, Emily; Mazloff, Matt; Talley, Lynne D.

    2016-08-01

    Ocean overturning circulation requires a continuous thermodynamic transformation of the buoyancy of seawater. The steeply sloping isopycnals of the Southern Ocean provide a pathway for Circumpolar Deep Water to upwell from mid depth without strong diapycnal mixing, where it is transformed directly by surface fluxes of heat and freshwater and splits into an upper and lower branch. While brine rejection from sea ice is thought to contribute to the lower branch, the role of sea ice in the upper branch is less well understood, partly due to a paucity of observations of sea-ice thickness and transport. Here we quantify the sea-ice freshwater flux using the Southern Ocean State Estimate, a state-of-the-art data assimilation that incorporates millions of ocean and ice observations. We then use the water-mass transformation framework to compare the relative roles of atmospheric, sea-ice, and glacial freshwater fluxes, heat fluxes, and upper-ocean mixing in transforming buoyancy within the upper branch. We find that sea ice is a dominant term, with differential brine rejection and ice melt transforming upwelled Circumpolar Deep Water at a rate of ~22 × 106 m3 s-1. These results imply a prominent role for Antarctic sea ice in the upper branch and suggest that residual overturning and wind-driven sea-ice transport are tightly coupled.

  20. Life cycle strategies of epipelagic copepods in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Atkinson, Angus

    1998-06-01

    Twelve epipelagic copepod species were reviewed to compare their adaptations to the short primary production season and low temperatures which characterise the Southern Ocean. The species show a spectrum of adaptations, but three broad life cycle strategies were defined: (1) herbivorous in summer, a short reproductive period and winter diapause at depth ( Calanoides acutus and possibly Ctenocalanus citer); (2) predominantly omnivorous/detritivorous diet, an extended period of feeding, growth and reproduction and less reliance on diapause at depth ( Metridia gerlachei, Calanus propinquus, Calanus simillimus, Oithona similis, Microcalanus pygmaeus, and possibly Oncaea curvata and Oithona frigida); (3) overwintering and feeding within sea ice as early nauplii or copepodids ( Stephos longipes and Paralabidocera antarctica). The large species Rhincalanus gigas appears to be intermediate between strategies (1) and (2). Contrasting species from groups (1) and (2), namely C. acutus and O. similis, were selected for more detailed comparison. For C. acutus, maximum (probably food saturated) feeding and egg production rates are well below equivalent values for Calanus spp. at lower latitudes. Likewise, summer growth and moulting rates are slower, and the growth season of this herbivore is only 2-4 months. Therefore, both the low summer temperatures and short primary production season seem to dictate a long (˜1 year) life cycle for C. acutus. A collation of data on O. similis revealed that its abundance increases about tenfold from the Antarctic shelf northwards to the Polar Frontal Zone, where abundances are similar to those in temperate and tropical shelf seas. In contrast to C. acutus, O. similis appears to remain in the epipelagic and reproduce there year-round, although the food sources which sustain this are still uncertain.

  1. Latitudinal exposure to DDTs, HCB, PCBs, PBDEs and DP in giant petrels (Macronectes spp.) across the Southern Ocean.

    PubMed

    Roscales, Jose L; González-Solís, Jacob; Zango, Laura; Ryan, Peter G; Jiménez, Begoña

    2016-07-01

    Studies on Persistent Organic Pollutants (POPs) in Antarctic wildlife are scarce, and usually limited to a single locality. As a result, wildlife exposure to POPs across the Southern Ocean is poorly understood. In this study, we report the differential exposure of the major southern ocean scavengers, the giant petrels, to POPs across a wide latitudinal gradient. Selected POPs (PCBs, HCB, DDTs, PBDEs) and related compounds, such as Dechlorane Plus (DP), were analyzed in plasma of southern giant petrels (Macronectes giganteus) breeding on Livingston (62°S 61°W, Antarctica), Marion (46°S 37°E, sub-Antarctic), and Gough (40°S 10°W, cool temperate) islands. Northern giant petrels (Macronectes halli) from Marion Island were also studied. Stable isotope ratios of C and N (δ(13)C and δ(15)N) were used as dietary tracers of the marine habitat and trophic level, respectively. Breeding locality was a major factor explaining petrel exposure to POPs compared with species and sex. Significant relationships between δ(13)C values and POP burdens, at both inter- and intra-population levels, support latitudinal variations in feeding grounds as a key factor in explaining petrel pollutant burdens. Overall, pollutant levels in giant petrels decreased significantly with latitude, but the relative abundance (%) of the more volatile POPs increased towards Antarctica. DP was found at negligible levels compared with legacy POPs in Antarctic seabirds. Spatial POP patterns found in giant petrels match those predicted by global distribution models, and reinforce the hypothesis of atmospheric long-range transport as the main source of POPs in Antarctica. Our results confirm that wildlife movements out of the polar region markedly increase their exposure to POPs. Therefore, strategies for Antarctic wildlife conservation should consider spatial heterogeneity in exposure to marine pollution. Of particular relevance is the need to clarify the exposure of Antarctic predators to emerging

  2. Hafnium and neodymium isotope composition of seawater and filtered particles from the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Stichel, T.; Frank, M.; Haley, B. A.; Rickli, J.; Venchiarutti, C.

    2009-12-01

    Radiogenic hafnium (Hf) and neodymium (Nd) isotopes have been used as tracers for past continental weathering regimes and ocean circulation. To date, however, there are only very few data available on dissolved Hf isotope compositions in present-day seawater and there is a complete lack of particulate data. During expedition ANTXXIV/3 (February to April 2008) we collected particulate samples (> 0.8 µm), which were obtained by filtrations of 270-700 liters of water. The samples were separated from the filters, completely dissolved, and purified for Nd and Hf isotope determination by TIMS and MC-ICPMS, respectively. In addition, we collected filtered (0.45 µm) seawater samples (20-120 liters) to determine the dissolved isotopic composition of Hf and Nd. The Hf isotope composition of the particulate fraction in the Drake Passage ranged from 0 to -28 ɛHf and is thus similar to that observed in core top sediments from the entire Southern Ocean in a previous study. The most unradiogenic and isotopically homogenous Hf isotope compositions in our study were found near the Antarctic Peninsula. Most of the stations north of the Southern Antarctic Circumpolar Front (SACC) show a large variation in ɛHf between 0 and -23 within the water column of one station and between the stations. The locations at which these Hf isotope compositions were measured are mostly far away from the potential source areas. Nd, in contrast, was nearly absent throughout the entire sample set and the only measurable ɛNd data ranged from 0 to -7, which is in good agreement with the sediment data in that area. The dissolved seawater isotopic compositions of both Hf and Nd show only minor variance (ɛHf = 4.2 to 4.7 and ɛNd = -8.8 to -7.6, respectively). These patterns in Hf isotopes and the nearly complete absence of Nd indicates that the particulate fraction does not contain a lot of terrigeneous material but is almost entirely dominated by biogenic opal. The homogenous and relatively radiogenic

  3. The Southern Ocean FINEstructure project: Turbulent dissipation and mixing rates and mechanisms in a Southern Ocean mixing hotspot.

    NASA Astrophysics Data System (ADS)

    Waterman, S.; Naveira Garabato, A. C.; Polzin, K. L.

    2012-04-01

    The Southern Ocean FINE structure project is an observational field study designed to investigate various mechanisms of ocean mixing and the roles that they play in the larger-scale circulation in a standing meander of the Antarctic Circumpolar Current (ACC) north of the Kerguelen Plateau. The region is potentially of special significance to closing both the Southern Ocean overturning circulation and the momentum budget of ACC. By presenting both a large-scale topographic obstacle and small-scale topographic roughness in the path of multiple ACC jets, it is a likely site for both enhanced adiabatic and diabatic mixing processes. We present the first results of the project which relate to the rates and mechanisms of turbulent energy dissipation and turbulent mixing in the region. From the first-ever full-depth microstructure measurements in the Southern Ocean, we map the observed turbulent kinetic energy dissipation and diapycnal mixing rates in this mixing hotspot. We next explore some of the physical mechanisms that observations and theory suggest may underpin the observed distributions. This exploration leads us to a characterization of the internal wave field in the region, and a study of some of the processes related to its generation, evolution and eventual dissipation. Results show that the observed turbulent energy dissipation and mixing rates are highly spatially variable. Systematic structure with depth and proximity to rough topography suggest a link with the local internal wave field, which can be characterized as consisting of near-inertial waves propagating from the surface downwards and higher frequency internal waves potentially sourced at the bottom propagating upwards, both being modified by a background shear as they propagate. Turbulent dissipation is high in regions where internal wave energy is high, however, the rates of turbulent dissipation and mixing are, in key places, generally lower than anticipated from the observed internal wave energy

  4. Eocene/Oligocene ocean de-acidification linked to Antarctic glaciation by sea-level fall.

    PubMed

    Merico, Agostino; Tyrrell, Toby; Wilson, Paul A

    2008-04-24

    One of the most dramatic perturbations to the Earth system during the past 100 million years was the rapid onset of Antarctic glaciation near the Eocene/Oligocene epoch boundary (approximately 34 million years ago). This climate transition was accompanied by a deepening of the calcite compensation depth--the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution. Changes in the global carbon cycle, rather than changes in continental configuration, have recently been proposed as the most likely root cause of Antarctic glaciation, but the mechanism linking glaciation to the deepening of calcite compensation depth remains unclear. Here we use a global biogeochemical box model to test competing hypotheses put forward to explain the Eocene/Oligocene transition. We find that, of the candidate hypotheses, only shelf to deep sea carbonate partitioning is capable of explaining the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor. In our simulations, glacioeustatic sea-level fall associated with the growth of Antarctic ice sheets permanently reduces global calcium carbonate accumulation on the continental shelves, leading to an increase in pelagic burial via permanent deepening of the calcite compensation depth. At the same time, fresh limestones are exposed to erosion, thus temporarily increasing global river inputs of dissolved carbonate and increasing seawater delta13C. Our work sheds new light on the mechanisms linking glaciation and ocean acidity change across arguably the most important climate transition of the Cenozoic era. PMID:18432242

  5. Warm ocean is eroding West Antarctic Ice Sheet

    NASA Astrophysics Data System (ADS)

    Shepherd, Andrew; Wingham, Duncan; Rignot, Eric

    2004-12-01

    Satellite radar measurements show that ice shelves in Pine Island Bay have thinned by up to 5.5 m yr-1 over the past decade. The pattern of shelf thinning mirrors that of their grounded tributaries - the Pine Island, Thwaites and Smith glaciers - and ocean currents on average 0.5°C warmer than freezing appear to be the source. The synchronised imbalance of the inland glaciers is the result of reduced lateral and basal tractions at their termini, and the drawdown of grounded ice shows that Antarctica is more sensitive to changing climates than was previously considered.

  6. The Leading Modes of Decadal SST Variability in the Southern Ocean in CMIP5 Simulations

    NASA Astrophysics Data System (ADS)

    Wang, Gang; Dommenget, Dietmar

    2016-04-01

    The leading modes of Sea Surface Temperature (SST) variability in the Southern Ocean on decadal and even larger time scales are analysed using Coupled Model Intercomparison Project 5 (CMIP5) model simulations and observations. We compare the modes from the CMIP5 super ensemble against several simple null hypotheses, such as isotropic diffusion (red noise) and a Slab Ocean model, to investigate the sources of decadal variability and the physical processes affecting the characteristics of the modes. The results show three main modes in the Southern Ocean: the first and most dominant mode on interannual to decadal time scales is an annular mode with largest amplitudes in the Pacific, which is strongly related to atmospheric forcing by the Southern Annular Mode (SAM) and El Nino Southern Oscillation (ENSO). The second mode is an almost basin wide monopole pattern, which has pronounced multi-decadal and longer time scales variability. It is firstly inducted by the Wave-3 patterns in the atmosphere and further developed via ocean dynamics. The third mode is a dipole pattern in the southern Pacific that has a pronounced peak in the power spectrum at multi-decadal time scales. All three leading modes found in the CMIP5 super model have distinct patterns and time scale behaviour that can not be explained by simple stochastic null hypothesis, thus all three leading modes are ocean-atmospheric coupled modes and are likely to be substantially influenced or driven by ocean dynamical processes. The mechanism of the basin-wide mode is further analysed based on a series of idealized experiments. The results show that the monopole mode has a two-step power spectrum, with a first spectral increase on interannual time scale and a second higher up level on the multi-decadal to centennial time scales. Ocean dynamics, especially the ocean advection, transport the anomalous signals, connect the entire ocean and lead to the homogeneous-like spatial pattern even under stochastic

  7. The response of the West Antarctic Ice Sheet to ocean warming beneath the Filchner Ronne Ice Shelf

    NASA Astrophysics Data System (ADS)

    Goeller, Sebastian; Timmermann, Ralph; Thoma, Malte

    2015-04-01

    The ice flow at the margins of the West Antarctic Ice Sheet (WAIS) is moderated by large ice shelves. Their buttressing effect substantially controls the mass balance of the WAIS and thus its contribution to sea level rise. The stability of these ice shelves results from the balance of mass gain by accumulation and ice flow from the adjacent ice sheet and mass loss by calving and basal melting due to the ocean heat flux. Recent results of ocean circulation models indicate that warm circumpolar water of the Southern Ocean may override the submarine slope front of the Antarctic Continent and boost basal ice shelf melting. In particular, ocean simulations for several of the IPCC's future climate scenarios demonstrate the redirection of a warm coastal current into the Filchner Trough and underneath the Filchner-Ronne Ice Shelf (FRIS) within the next decades. In this study, we couple the finite elements ocean circulation model FESOM and the three-dimensional thermomechanical ice flow model RIMBAY to investigate the sensitivity of the ice dynamics within the entire FRIS catchment to simulated future basal shelf melt rates. Our simulations indicate a high sensitivity of the ice dynamics for the Möller and the Institute Ice Stream but only very little response of other ice streams like Rutford, Foundation and Recovery Ice Stream to enhanced basal shelf melting. The grounding line between the Möller and Institute Ice Streams is located on a submarine ridge in front of a deep trough further inland. In this area, basal shelf melting causes a local thinning of the FRIS. The consequent initial retreat of the grounding line continues once it reaches the adjacent reverse-sloped bedrock. We state, that a possible 'point of no return' for a vast grounding line retreat along this steep reverse bedrock slope might have been crossed already even for simulated present-day melt rates, indicating that the WAIS is currently not in equlibrium. Furthermore, our simulations show an

  8. Dynamics of the last glacial maximum Antarctic ice-sheet and its response to ocean forcing.

    PubMed

    Golledge, Nicholas R; Fogwill, Christopher J; Mackintosh, Andrew N; Buckley, Kevin M

    2012-10-01

    Retreat of the Last Glacial Maximum (LGM) Antarctic ice sheet is thought to have been initiated by changes in ocean heat and eustatic sea level propagated from the Northern Hemisphere (NH) as northern ice sheets melted under rising atmospheric temperatures. The extent to which spatial variability in ice dynamics may have modulated the resultant pattern and timing of decay of the Antarctic ice sheet has so far received little attention, however, despite the growing recognition that dynamic effects account for a sizeable proportion of mass-balance changes observed in modern ice sheets. Here we use a 5-km resolution whole-continent numerical ice-sheet model to assess whether differences in the mechanisms governing ice sheet flow could account for discrepancies between geochronological studies in different parts of the continent. We first simulate the geometry and flow characteristics of an equilibrium LGM ice sheet, using pan-Antarctic terrestrial and marine geological data for constraint, then perturb the system with sea level and ocean heat flux increases to investigate ice-sheet vulnerability. Our results identify that fast-flowing glaciers in the eastern Weddell Sea, the Amundsen Sea, central Ross Sea, and in the Amery Trough respond most rapidly to ocean forcings, in agreement with empirical data. Most significantly, we find that although ocean warming and sea-level rise bring about mainly localized glacier acceleration, concomitant drawdown of ice from neighboring areas leads to widespread thinning of entire glacier catchments-a discovery that has important ramifications for the dynamic changes presently being observed in modern ice sheets. PMID:22988078

  9. Effects of changing continuous iron input rates on a Southern Ocean algal assemblage

    NASA Astrophysics Data System (ADS)

    Hare, C. E.; DiTullio, G. R.; Riseman, S. F.; Crossley, A. C.; Popels, L. C.; Sedwick, P. N.; Hutchins, D. A.

    2007-05-01

    The upwelling of nutrients and iron (Fe) sustains biological production in much of the Southern Ocean. Using a shipboard natural community continuous culture system (Ecostat), we supplied a single added Fe concentration at two dilution rates chosen to examine the effects of variations in realistic growth and loss rates on an Fe-limited algal community in the Antarctic Zone south of Australia. A parallel growout experiment provided "no-dilution" +Fe and -Fe controls. In the continuous flow experiment, phytoplankton biomass was lower and more constant throughout the incubation and major nutrients were never depleted. Nanophytoplankton abundance remained similar in both growout treatments, and therefore, growth of this group did not appear to be Fe-limited. The addition of Fe in a continuous fashion resulted in a community co-dominated by both small diatoms and nanophytoplankton. Increases in dilution rate favored diatom species that were smaller and faster-growing, as well as non-silicified algal groups. Particulate carbon (PC) to particulate nitrogen (PN) ratios increased above the Redfield ratio when Fe was added in a continuous fashion, while biogenic silica (BSi) to PC and PN ratios decreased 2-3 fold in the continuous flow experiment compared to the initial conditions and the parallel growout control experiment. Photosynthetic efficiency increased in the continuous flow treatments above the control but remained significantly lower than in the 1.4 nM Fe addition. The results of our shipboard continuous flow experiments are compared and contrasted with those of the mesoscale Southern Ocean Iron RElease Experiment (SOIREE) carried out at the same site. Our results suggest that increases in natural dilution rates (i.e. vertical turbulent diffusion) in polar Antarctic waters could shift the algal community towards smaller, faster-growing algal species, thus having a major effect on nutrient cycling and carbon export in the Southern Ocean.

  10. An observing system simulation for Southern Ocean carbon dioxide uptake.

    PubMed

    Majkut, Joseph D; Carter, Brendan R; Frölicher, Thomas L; Dufour, Carolina O; Rodgers, Keith B; Sarmiento, Jorge L

    2014-07-13

    The Southern Ocean is critically important to the oceanic uptake of anthropogenic CO2. Up to half of the excess CO2 currently in the ocean entered through the Southern Ocean. That uptake helps to maintain the global carbon balance and buffers transient climate change from fossil fuel emissions. However, the future evolution of the uptake is uncertain, because our understanding of the dynamics that govern the Southern Ocean CO2 uptake is incomplete. Sparse observations and incomplete model formulations limit our ability to constrain the monthly and annual uptake, interannual variability and long-term trends. Float-based sampling of ocean biogeochemistry provides an opportunity for transforming our understanding of the Southern Ocean CO2 flux. In this work, we review current estimates of the CO2 uptake in the Southern Ocean and projections of its response to climate change. We then show, via an observational system simulation experiment, that float-based sampling provides a significant opportunity for measuring the mean fluxes and monitoring the mean uptake over decadal scales. PMID:24891388

  11. The atmospheric hydrologic cycle over the Southern Ocean and Antarctica from operational numerical analyses

    SciTech Connect

    Bromwich, D.H.; Robasky, F.M.; Cullather, R.I.; Van Woert, M.L.

    1995-12-01

    Moisture budget calculations for Antarctica and the Southern Ocean are performed using operational numerical analyses from several sources. The analyses are compared for an 8-yr period and evaluated against rawinsonde sites. The comparisons to East Antarctic and Macquarie Island rawinsondes show the European Centre for Medium-Range Weather Forecasts (ECMWF) analyses to be superior in reproducing sounding values at each level. While results are highly variable, agreement of the ECMWF analyses to zonally averaged sounding moisture flux values along the East Antarctic coast is very close. The National Meteorological Center (NMC) and Australian Bureau of Meteorology analyses generally underestimate transport at each level; error cancellation occurs during vertical integration however. A comparison of moisture convergence for East Antarctica with values calculated from rawinsonde data indicates the ECMWF analysis is within 5 mm per yr of the observed value, while the NMC result is severely deficient. Comparison of the moisture transport convergence derived from the numerical analyses with previous moisture flux studies over the Southern Ocean reveals general agreement in the location of the boundary between the moisture source and sink. The ECMWF and NMC analyses place the convergence maximum slightly farther south than has been previously found. It is inferred that this results from the blocking effect of the Antarctic coastal topography. At full resolution this point is at approximately 64{degree}S. Long-term net precipitation derived from analyses is somewhat smaller than values determined by glaciological methods. Net precipitation varies interannually by 25%, with most of the variation concentrated in the South Pacific sector. The results offer a positive outlook for determining continental-scale precipitation trends in Antarctica through atmospheric methods and demonstrate that the ECMWF analyses provide generally good estimates. 56 refs., 21 figs., 3 tabs.

  12. Modeling UV-B Effects on Primary Production Throughout the Southern Ocean Using Multi-Sensor Satellite Data

    NASA Technical Reports Server (NTRS)

    Lubin, Dan

    2001-01-01

    This study has used a combination of ocean color, backscattered ultraviolet, and passive microwave satellite data to investigate the impact of the springtime Antarctic ozone depletion on the base of the Antarctic marine food web - primary production by phytoplankton. Spectral ultraviolet (UV) radiation fields derived from the satellite data are propagated into the water column where they force physiologically-based numerical models of phytoplankton growth. This large-scale study has been divided into two components: (1) the use of Total Ozone Mapping Spectrometer (TOMS) and Special Sensor Microwave Imager (SSM/I) data in conjunction with radiative transfer theory to derive the surface spectral UV irradiance throughout the Southern Ocean; and (2) the merging of these UV irradiances with the climatology of chlorophyll derived from SeaWiFS data to specify the input data for the physiological models.

  13. Sea level trends in the Southern Ocean over the last century from historical data

    NASA Astrophysics Data System (ADS)

    Testut, Laurent; Martin-Miguez, Belén.; Watson, Christopher; Wöppelmann, Guy; Coleman, Richard; Creach, Ronan; Brolsma, Henk; Handsworth, Roger; Pouvreau, Nicolas; Legrésy, Benoit

    2010-05-01

    It is well known that the spatial distribution of sea level measurements throughout the Southern Ocean is sparse and mostly consists of datasets with short records. The PSMSL (Permanent Service for Mean Sea Level) has only a few sea level time series below 45° South and most of them are shorter than twenty years. The lack of observations constrains the ability to determine or reconstruct global estimates of mean sea level change over the past century. For this reason, any available historical information becomes invaluable for deriving long-term estimates of sea level change in this part of the world. The aim of this presentation is to describe the way we have recovered and analysed the available historic sea level observations made in few sites of the Southern Ocean and to propose new reliable long term sea level trend estimates in this region. The first site is Saint-Paul, a small island of the Southern Indian Ocean where historical measurements were done in 1874 and connected to the permanent GLOSS tide gauge. The two other historical observations were recorded by the Australasian Antarctic Expedition lead by Sir Douglas Mawson in 1912 at Maquarie Island and Cap Denison (Antarctica). The last site concerned by this presentation is the Dumont d'Urville (Antarctica) where historical information from the beginning of the 1950's were found and analysed.

  14. Seasonal time bombs: dominant temperate viruses affect Southern Ocean microbial dynamics

    PubMed Central

    Brum, Jennifer R; Hurwitz, Bonnie L; Schofield, Oscar; Ducklow, Hugh W; Sullivan, Matthew B

    2016-01-01

    Rapid warming in the highly productive western Antarctic Peninsula (WAP) region of the Southern Ocean has affected multiple trophic levels, yet viral influences on microbial processes and ecosystem function remain understudied in the Southern Ocean. Here we use cultivation-independent quantitative ecological and metagenomic assays, combined with new comparative bioinformatic techniques, to investigate double-stranded DNA viruses during the WAP spring–summer transition. This study demonstrates that (i) temperate viruses dominate this region, switching from lysogeny to lytic replication as bacterial production increases, and (ii) Southern Ocean viral assemblages are genetically distinct from lower-latitude assemblages, primarily driven by this temperate viral dominance. This new information suggests fundamentally different virus–host interactions in polar environments, where intense seasonal changes in bacterial production select for temperate viruses because of increased fitness imparted by the ability to switch replication strategies in response to resource availability. Further, temperate viral dominance may provide mechanisms (for example, bacterial mortality resulting from prophage induction) that help explain observed temporal delays between, and lower ratios of, bacterial and primary production in polar versus lower-latitude marine ecosystems. Together these results suggest that temperate virus–host interactions are critical to predicting changes in microbial dynamics brought on by warming in polar marine systems. PMID:26296067

  15. Trends and variability of the atmosphere–ocean turbulent heat flux in the extratropical Southern Hemisphere

    PubMed Central

    Herman, Agnieszka

    2015-01-01

    Ocean–atmosphere interactions are complex and extend over a wide range of temporal and spatial scales. Among the key components of these interactions is the ocean–atmosphere (latent and sensible) turbulent heat flux (THF). Here, based on daily optimally-interpolated data from the extratropical Southern Hemisphere (south of 30°S) from a period 1985–2013, we analyze short-term variability and trends in THF and variables influencing it. It is shown that, in spite of climate-change-related positive trends in surface wind speeds over large parts of the Southern Ocean, the range of the THF variability has been decreasing due to decreasing air–water temperature and humidity differences. Occurrence frequency of very large heat flux events decreased accordingly. Remarkably, spectral analysis of the THF data reveals, in certain regions, robust periodicity at frequencies 0.03–0.04 day−1, corresponding exactly to frequencies of the baroclinic annular mode (BAM). Finally, it is shown that the THF is correlated with the position of the major fronts in sections of the Antarctic Circumpolar Current where the fronts are not constrained by the bottom topography and can adjust their position to the atmospheric and oceanic forcing, suggesting differential response of various sections of the Southern Ocean to the changing atmospheric forcing. PMID:26449323

  16. Seasonal time bombs: dominant temperate viruses affect Southern Ocean microbial dynamics.

    PubMed

    Brum, Jennifer R; Hurwitz, Bonnie L; Schofield, Oscar; Ducklow, Hugh W; Sullivan, Matthew B

    2016-02-01

    Rapid warming in the highly productive western Antarctic Peninsula (WAP) region of the Southern Ocean has affected multiple trophic levels, yet viral influences on microbial processes and ecosystem function remain understudied in the Southern Ocean. Here we use cultivation-independent quantitative ecological and metagenomic assays, combined with new comparative bioinformatic techniques, to investigate double-stranded DNA viruses during the WAP spring-summer transition. This study demonstrates that (i) temperate viruses dominate this region, switching from lysogeny to lytic replication as bacterial production increases, and (ii) Southern Ocean viral assemblages are genetically distinct from lower-latitude assemblages, primarily driven by this temperate viral dominance. This new information suggests fundamentally different virus-host interactions in polar environments, where intense seasonal changes in bacterial production select for temperate viruses because of increased fitness imparted by the ability to switch replication strategies in response to resource availability. Further, temperate viral dominance may provide mechanisms (for example, bacterial mortality resulting from prophage induction) that help explain observed temporal delays between, and lower ratios of, bacterial and primary production in polar versus lower-latitude marine ecosystems. Together these results suggest that temperate virus-host interactions are critical to predicting changes in microbial dynamics brought on by warming in polar marine systems. PMID:26296067

  17. The Southern Ocean biological response to aeolian iron deposition.

    PubMed

    Cassar, Nicolas; Bender, Michael L; Barnett, Bruce A; Fan, Songmiao; Moxim, Walter J; Levy, Hiram; Tilbrook, Bronte

    2007-08-24

    Biogeochemical rate processes in the Southern Ocean have an important impact on the global environment. Here, we summarize an extensive set of published and new data that establishes the pattern of gross primary production and net community production over large areas of the Southern Ocean. We compare these rates with model estimates of dissolved iron that is added to surface waters by aerosols. This comparison shows that net community production, which is comparable to export production, is proportional to modeled input of soluble iron in aerosols. Our results strengthen the evidence that the addition of aerosol iron fertilizes export production in the Southern Ocean. The data also show that aerosol iron input particularly enhances gross primary production over the large area of the Southern Ocean downwind of dry continental areas. PMID:17717181

  18. The ocean's role in polar climate change: asymmetric Arctic and Antarctic responses to greenhouse gas and ozone forcing. (Invited)

    NASA Astrophysics Data System (ADS)

    Marshall, J.; Ferreira, D.; Bitz, C. M.

    2013-12-01

    In recent decades the Arctic has been warming with sea ice disappearing. But the Antarctic has been (mainly) cooling and sea ice is growing. We argue here that inter-hemispheric asymmetries in the mean ocean circulation, with sinking in the northern north Atlantic and upwelling around Antarctica, strongly influences the surface response to GHG forcing, accelerating warming in the Arctic and delaying it in the Antarctic. Moreover, while GHG forcing has been qualitatively similar at the poles, ozone depletion only occurs in the Antarctic. The coupled atmosphere-ocean response to ozone depletion may further help to explain the Antarctic trends. A framework is presented to quantify the processes at work built around `Climate Response Functions' for GHG and Ozone-hole forcing.

  19. Mean Upper-Ocean Circulation of the Southern Hemisphere Oceans Based on Goce Data

    NASA Astrophysics Data System (ADS)

    Menezes, V. V.; Bingham, R. J.; Vianna, M. L.; Phillips, H. E.

    2012-12-01

    One of the main goals of the Gravity and steady-state Ocean Circulation Explorer (GOCE) satellite mission launched in 2009 is to improve the previous estimates of the global ocean circulation structures determined from Mean Dynamic Topographies (MDTs). Recently published studies suggest that the GOCE-based MDTs and their respective mean geostrophic circulation fields (MGCs) are superior to those obtained from GRACE (Gravity Recovery and Climate Experiment)-only data. These studies focus mostly on the circulation of the North Atlantic and North Pacific oceans with emphasis on the strong western boundary current systems. In contrast, no detailed assessment has yet been made to determine the impact of the GOCE models in the southern hemisphere (SH) upper-ocean circulation especially in the subtropical region. It is generally recognized that the SH circulation is still not well established even at large scales, and the new GOCE and GRACE products can contribute to increase our understanding of the dominant currents in these regions, which may have even greater impact on the global climate than the NH counterparts. In the present work, we compute five global GOCE-derived MDTs with a 0.25 x 0.25 degree spatial grid based on three GOCE geoid models (TIM3, GOCO02S, GOCO3S) and three mean sea surfaces (CLS01, CLS11, DTU10) using the standard spectral approach (MSS minus Geoid). These MDTs do not have the well-known large-amplitude striation-type noise that plagued all of the GRACE-only MDTs with he same resolution, but still present commission errors which are filptered out with Singular Spectrum Analysis methods. Additionally, the MGCs were calculated by use of a Anderssen-Hegland averaging scheme for estimation of derivatives, which is able to filter out the well-known high amplitude noise caused by standard finite-difference methods. Comparisons with previous GRACE-only MGCs show that GOCE permits retrieval of currents with much higher intensities (e.g. the Agulhas

  20. Environmental contamination in Antarctic ecosystems.

    PubMed

    Bargagli, R

    2008-08-01

    Although the remote continent of Antarctica is perceived as the symbol of the last great wilderness, the human presence in the Southern Ocean and the continent began in the early 1900s for hunting, fishing and exploration, and many invasive plant and animal species have been deliberately introduced in several sub-Antarctic islands. Over the last 50 years, the development of research and tourism have locally affected terrestrial and marine coastal ecosystems through fuel combustion (for transportation and energy production), accidental oil spills, waste incineration and sewage. Although natural "barriers" such as oceanic and atmospheric circulation protect Antarctica from lower latitude water and air masses, available data on concentrations of metals, pesticides and other persistent pollutants in air, snow, mosses, lichens and marine organisms show that most persistent contaminants in the Antarctic environment are transported from other continents in the Southern Hemisphere. At present, levels of most contaminants in Antarctic organisms are lower than those in related species from other remote regions, except for the natural accumulation of Cd and Hg in several marine organisms and especially in albatrosses and petrels. The concentrations of organic pollutants in the eggs of an opportunistic top predator such as the south polar skua are close to those that may cause adverse health effects. Population growth and industrial development in several countries of the Southern Hemisphere are changing the global pattern of persistent anthropogenic contaminants and new classes of chemicals have already been detected in the Antarctic environment. Although the Protocol on Environmental Protection to the Antarctic Treaty provides strict guidelines for the protection of the Antarctic environment and establishes obligations for all human activity in the continent and the Southern Ocean, global warming, population growth and industrial development in countries of the Southern

  1. The Deep South Clouds & Aerosols project: Improving the modelling of clouds in the Southern Ocean region

    NASA Astrophysics Data System (ADS)

    Morgenstern, Olaf; McDonald, Adrian; Harvey, Mike; Davies, Roger; Katurji, Marwan; Varma, Vidya; Williams, Jonny

    2016-04-01

    Southern-Hemisphere climate projections are subject to persistent climate model biases affecting the large majority of contemporary climate models, which degrade the reliability of these projections, particularly at the regional scale. Southern-Hemisphere specific problems include the fact that satellite-based observations comparisons with model output indicate that cloud occurrence above the Southern Ocean is substantially underestimated, with consequences for the radiation balance, sea surface temperatures, sea ice, and the position of storm tracks. The Southern-Ocean and Antarctic region is generally characterized by an acute paucity of surface-based and airborne observations, further complicating the situation. In recognition of this and other Southern-Hemisphere specific problems with climate modelling, the New Zealand Government has launched the Deep South National Science Challenge, whose purpose is to develop a new Earth System Model which reduces these very large radiative forcing problems associated with erroneous clouds. The plan is to conduct a campaign of targeted observations in the Southern Ocean region, leveraging off international measurement campaigns in this area, and using these and existing measurements of cloud and aerosol properties to improve the representation of clouds in the nascent New Zealand Earth System Model. Observations and model development will target aerosol physics and chemistry, particularly sulphate, sea salt, and non-sulphate organic aerosol, its interactions with clouds, and cloud microphysics. The hypothesis is that the cloud schemes in most GCMs are trained on Northern-Hemisphere data characterized by substantial anthropogenic or terrestrial aerosol-related influences which are almost completely absent in the Deep South.

  2. Decreased calcification in the Southern Ocean over the satellite record

    NASA Astrophysics Data System (ADS)

    Freeman, Natalie M.; Lovenduski, Nicole S.

    2015-03-01

    Widespread ocean acidification is occurring as the ocean absorbs anthropogenic carbon dioxide from the atmosphere, threatening marine ecosystems, particularly the calcifying plankton that provide the base of the marine food chain and play a key role within the global carbon cycle. We use satellite estimates of particulate inorganic carbon (PIC), surface chlorophyll, and sea surface temperature to provide a first estimate of changing calcification rates throughout the Southern Ocean. From 1998 to 2014 we observe a 4% basin-wide reduction in summer calcification, with ˜9% reductions in large regions (˜1 × 106 km2) of the Pacific and Indian sectors. Southern Ocean trends are spatially heterogeneous and primarily driven by changes in PIC concentration (suspended calcite), which has declined by ˜24% in these regions. The observed decline in Southern Ocean calcification and PIC is suggestive of large-scale changes in the carbon cycle and provides insight into organism vulnerability in a changing environment.

  3. Elevated East Antarctic outlet glaciers during warmer-than-present climates in southern Victoria Land

    NASA Astrophysics Data System (ADS)

    Swanger, Kate M.; Marchant, David R.; Schaefer, Joerg M.; Winckler, Gisela; Head, James W.

    2011-10-01

    We document Plio-Pleistocene changes in the level of Taylor Glacier, an outlet glacier in southern Victoria Land that drains Taylor Dome on the periphery of the East Antarctic Ice Sheet (EAIS). Chronologic control comes from 3He cosmogenic-nuclide analyses of 27 boulders sampled from drifts and moraines in Kennar Valley, a small hanging valley that opens onto a peripheral lobe of Taylor Glacier in the Quartermain Mountains. Assuming a constant boulder-erosion rate of 10 cm Myr -1, our preferred age model spans the last 3.1 Myr and calls for stepped ice recession from a local highstand ~ 200 m above the present base of Taylor Glacier at the mouth of Kennar Valley. The texture and sedimentology of all mapped moraines and drifts indicate deposition from cold-based ice, analogous with the modern Taylor Glacier at the mouth of Kennar Valley. The Kennar Valley glacial record shows an uncharacteristic relationship with average global temperatures, exhibiting higher-than-present ice levels during globally warm periods, including the Pliocene climatic optimum (~ 3.1 Ma) and Marine Oxygen Isotope Stage (MIS) 31 (~ 1.07 Ma). The Kennar Valley record also suggests that the rate of ice-surface lowering accelerated after the mid-Pleistocene transition at ~ 0.9 Ma. Correlation of our moraine record with published reports for fluctuations of Taylor Glacier elsewhere in the Quartermain Mountains, and with a dated moraine record from Ferrar Glacier (a second outlet for Taylor Dome), reveals similar ice-surface changes, highlighting minor, but widespread ice recession in southern Victoria Land since the mid- to late-Pliocene. Our record for minimal variability in the East Antarctic Ice Sheet contrasts with recent data from nearby marine cores that call for dynamic fluctuations in the volume of grounded ice in the Ross Embayment, and significant reduction of the West Antarctic Ice Sheet (WAIS) during warmer-than-present intervals. Taken together, these records from the Ross Embayment

  4. The Southern Ocean in the Coupled Model Intercomparison Project phase 5

    PubMed Central

    Meijers, A. J. S.

    2014-01-01

    The Southern Ocean is an important part of the global climate system, but its complex coupled nature makes both its present state and its response to projected future climate forcing difficult to model. Clear trends in wind, sea-ice extent and ocean properties emerged from multi-model intercomparison in the Coupled Model Intercomparison Project phase 3 (CMIP3). Here, we review recent analyses of the historical and projected wind, sea ice, circulation and bulk properties of the Southern Ocean in the updated Coupled Model Intercomparison Project phase 5 (CMIP5) ensemble. Improvements to the models include higher resolutions, more complex and better-tuned parametrizations of ocean mixing, and improved biogeochemical cycles and atmospheric chemistry. CMIP5 largely reproduces the findings of CMIP3, but with smaller inter-model spreads and biases. By the end of the twenty-first century, mid-latitude wind stresses increase and shift polewards. All water masses warm, and intermediate waters freshen, while bottom waters increase in salinity. Surface mixed layers shallow, warm and freshen, whereas sea ice decreases. The upper overturning circulation intensifies, whereas bottom water formation is reduced. Significant disagreement exists between models for the response of the Antarctic Circumpolar Current strength, for reasons that are as yet unclear. PMID:24891395

  5. The Southern Ocean in the Coupled Model Intercomparison Project phase 5.

    PubMed

    Meijers, A J S

    2014-07-13

    The Southern Ocean is an important part of the global climate system, but its complex coupled nature makes both its present state and its response to projected future climate forcing difficult to model. Clear trends in wind, sea-ice extent and ocean properties emerged from multi-model intercomparison in the Coupled Model Intercomparison Project phase 3 (CMIP3). Here, we review recent analyses of the historical and projected wind, sea ice, circulation and bulk properties of the Southern Ocean in the updated Coupled Model Intercomparison Project phase 5 (CMIP5) ensemble. Improvements to the models include higher resolutions, more complex and better-tuned parametrizations of ocean mixing, and improved biogeochemical cycles and atmospheric chemistry. CMIP5 largely reproduces the findings of CMIP3, but with smaller inter-model spreads and biases. By the end of the twenty-first century, mid-latitude wind stresses increase and shift polewards. All water masses warm, and intermediate waters freshen, while bottom waters increase in salinity. Surface mixed layers shallow, warm and freshen, whereas sea ice decreases. The upper overturning circulation intensifies, whereas bottom water formation is reduced. Significant disagreement exists between models for the response of the Antarctic Circumpolar Current strength, for reasons that are as yet unclear. PMID:24891395

  6. Sea ice and the ocean mixed layer over the Antarctic shelf seas

    NASA Astrophysics Data System (ADS)

    Petty, A. A.; Holland, P. R.; Feltham, D. L.

    2014-04-01

    An ocean mixed-layer model has been incorporated into the Los Alamos sea ice model CICE to investigate regional variations in the surface-driven formation of Antarctic shelf waters. This model captures well the expected sea ice thickness distribution, and produces deep (> 500 m) mixed layers in the Weddell and Ross shelf seas each winter. This results in the complete destratification of the water column in deep southern coastal regions leading to high-salinity shelf water (HSSW) formation, and also in some shallower regions (no HSSW formation) of these seas. Shallower mixed layers are produced in the Amundsen and Bellingshausen seas. By deconstructing the surface processes driving the mixed-layer depth evolution, we show that the net salt flux from sea ice growth/melt dominates the evolution of the mixed layer in all regions, with a smaller contribution from the surface heat flux and a negligible input from wind stress. The Weddell and Ross shelf seas receive an annual surplus of mixing energy at the surface; the Amundsen shelf sea energy input in autumn/winter is balanced by energy extraction in spring/summer; and the Bellingshausen shelf sea experiences an annual surface energy deficit, through both a low energy input in autumn/winter and the highest energy loss in spring/summer. An analysis of the sea ice mass balance demonstrates the contrasting mean ice growth, melt and export in each region. The Weddell and Ross shelf seas have the highest annual ice growth, with a large fraction exported northwards each year, whereas the Bellingshausen shelf sea experiences the highest annual ice melt, driven by the advection of ice from the northeast. A linear regression analysis is performed to determine the link between the autumn/winter mixed-layer deepening and several atmospheric variables. The Weddell and Ross shelf seas show stronger spatial correlations (temporal mean - intra-regional variability) between the autumn/winter mixed-layer deepening and several

  7. Rapid variability of Antarctic Bottom Water transport into the Pacific Ocean inferred from GRACE

    NASA Astrophysics Data System (ADS)

    Mazloff, Matthew R.; Boening, Carmen

    2016-04-01

    Air-ice-ocean interactions in the Antarctic lead to formation of the densest waters on Earth. These waters convect and spread to fill the global abyssal oceans. The heat and carbon storage capacity of these water masses, combined with their abyssal residence times that often exceed centuries, makes this circulation pathway the most efficient sequestering mechanism on Earth. Yet monitoring this pathway has proven challenging due to the nature of the formation processes and the depth of the circulation. The Gravity Recovery and Climate Experiment (GRACE) gravity mission is providing a time series of ocean mass redistribution and offers a transformative view of the abyssal circulation. Here we use the GRACE measurements to infer, for the first time, a 2003-2014 time series of Antarctic Bottom Water export into the South Pacific. We find this export highly variable, with a standard deviation of 1.87 sverdrup (Sv) and a decorrelation timescale of less than 1 month. A significant trend is undetectable.

  8. RTOPO-1: A consistent dataset for Antarctic ice shelf topography and global ocean bathymetry

    NASA Astrophysics Data System (ADS)

    Timmermann, Ralph

    2010-05-01

    Sub-ice shelf circulation and freezing/melting rates depend critically on an accurate and consistent representation of cavity geometry (i.e. ice-shelf draft and ocean bathymetry). Existing global or pan-Antarctic data sets have turned out to contain various inconsistencies and inaccuracies. The goal of this work is to compile independent regional fields into a global data set. We use the S-2004 global 1-minute bathymetry as the backbone and add an improved version of the BEDMAP topography for an area that roughly coincides with the Antarctic continental shelf. Locations of the merging line have been carefully adjusted in order to get the best out of each data set. High-resolution gridded data for the Amery, Fimbul, Filchner-Ronne, Larsen C and George VI Ice Shelves and for Pine Island Glacier have been carefully merged into the ambient ice and ocean topographies. Multibeam ship survey data for bathymetry in the former Larsen B cavity and the southeastern Bellingshausen Sea have been obtained from the data centers of Alfred Wegener Institute (AWI), British Antarctic Survey (BAS) and Lamont-Doherty Earth Observatory (LDEO), gridded, and again carefully merged into the existing bathymetry map. The resulting global 1-minute data set contains consistent masks for open ocean, grounded ice, floating ice, and bare land surface. The Ice Shelf Cavern Geometry Team: Anne Le Brocq, Tara Deen, Eugene Domack, Pierre Dutrieux, Ben Galton-Fenzi, Dorothea Graffe, Hartmut Hellmer, Angelika Humbert, Daniela Jansen, Adrian Jenkins, Astrid Lambrecht, Keith Makinson, Fred Niederjasper, Frank Nitsche, Ole Anders Nøst, Lars Henrik Smedsrud, and Walter Smith

  9. Acid rock drainage and rock weathering in Antarctica: important sources for iron cycling in the Southern Ocean.

    PubMed

    Dold, B; Gonzalez-Toril, E; Aguilera, A; Lopez-Pamo, E; Cisternas, M E; Bucchi, F; Amils, R

    2013-06-18

    Here we describe biogeochemical processes that lead to the generation of acid rock drainage (ARD) and rock weathering on the Antarctic landmass and describe why they are important sources of iron into the Antarctic Ocean. During three expeditions, 2009-2011, we examined three sites on the South Shetland Islands in Antarctica. Two of them displayed intensive sulfide mineralization and generated acidic (pH 3.2-4.5), iron-rich drainage waters (up to 1.78 mM Fe), which infiltrated as groundwater (as Fe(2+)) and as superficial runoff (as Fe(3+)) into the sea, the latter with the formation of schwertmannite in the sea-ice. The formation of ARD in the Antarctic was catalyzed by acid mine drainage microorganisms found in cold climates, including Acidithiobacillus ferrivorans and Thiobacillus plumbophilus. The dissolved iron (DFe) flux from rock weathering (nonmineralized control site) was calculated to be 0.45 × 10(9) g DFe yr(-1) for the nowadays 5468 km of ice-free Antarctic rock coastline which is of the same order of magnitude as glacial or aeolian input to the Southern Ocean. Additionally, the two ARD sites alone liberate 0.026 and 0.057 × 10(9) g DFe yr(-1) as point sources to the sea. The increased iron input correlates with increased phytoplankton production close to the source. This might even be enhanced in the future by a global warming scenario, and could be a process counterbalancing global warming. PMID:23682976

  10. The oceanographic and climatic evolution of the Paleogene Southern Ocean (Arne Richter Award for Outstanding Young Scientists Lecture)

    NASA Astrophysics Data System (ADS)

    Bijl, Peter; Houben, Alexander J. P.

    2014-05-01

    Continental-scale ice sheets first appeared in Antarctica following long-term cooling through the Eocene Epoch (56-34 Ma) within the Paleogene Period (65.5-23 Ma). Both the long-term cooling following early Eocene hothouse climates and the onset of large-scale glaciation itself has been related to the gradual decline of atmospheric greenhouse gas concentrations. Although much work is now centered in improving techniques for reconstructing past atmospheric pCO2, at present proxy-based reconstructions of atmospheric greenhouse gases for the Paleogene are of low temporal resolution and subject to a large degree of uncertainty. Furthermore, long-term mid-Eocene surface water cooling appears to have been confined to high- and mid-latitudes only, with little to no cooling in the tropical regions. This observation questions the role of atmospheric greenhouse gas (notably CO2) decline as a primary cause of Eocene climate cooling. Furthermore, the greenhouse-gas hypothesis has now superceded long-held hypothesis that the opening of southern ocean tectonic gateways cooled Antarctica. A direct relationship between the deepening of the Tasmanian Gateway and Antarctic glaciation has been refuted by accurate dating of this tectonic event, indicating that the Tasmanian Gateway deepened 2 million years prior to Antarctic glaciation. However, the precise secondary role of gateway evolution on Antarctic climate change is not well constrained. On the other hand, it is increasingly apparent that the Southern Ocean was the main region for intermediate-deep water formation in the Paleogene, which implies that even environmental change with regional effects may have had direct implications for global climate change. While the forcing mechanism that pushed Antarctica towards fully glaciated conditions is likely atmospheric pCO2 decline across a critical threshold, the regional environmental responses are not well constrained. Numerical modeling studies suggest that in conjunction with the

  11. Controls on the Southern Ocean mixed layer salinity budget in CMIP5 models

    NASA Astrophysics Data System (ADS)

    Close, Sally; Goosse, Hugues

    2013-04-01

    Global-scale changes in upper ocean salinity, driven by changes in freshwater forcing, are both predicted by climate models as a feature of the climatic response to anthropogenic climate change and reported by a number of recent observation-based studies. In the extrapolar regions, such change has been predominantly attributed to changes in the hydrological cycle. However, in the high latitudes, changes in sea ice coverage may also provide a significant source of freshwater forcing. Variations in mixed layer properties have wide-reaching influence, affecting, for example, oceanic heat storage and the rates of exchange between the atmosphere and deeper ocean. It has further been suggested that heat supplied by the deep ocean may have a significant influence on the cryosphere, indicating that a good understanding of the behaviour of the Southern Ocean mixed layer is crucial to describing the climate of this region. Our aims in this work are to assess the dominant mechanisms that drive salinity variability in the Southern Ocean mixed layer using model data and to further examine the relationship between mixed layer and sea ice variability. In this study, the evolution of the upper Southern Ocean hydrographic structure in response to the RCP4.5 forcing scenario is analyzed using model data drawn from the Coupled Model Intercomparison Project Phase 5 archive. A robust freshening trend is evident, associated with an increase in stratification and decoupling of the upper ocean as the mixed layer gains buoyancy at a faster rate than the underlying ocean. The magnitudes of the individual terms of the salinity budget are evaluated, and significant discrepancy noted amongst the models analysed here. Motivated by the important role of entrainment suggested by this analysis, we examine the relationship between the weakening entrainment rate, decreasing sea ice coverage and increases in heat storage at depth that are evident in the model data. Our analysis suggests that the

  12. Environmental forcing and Southern Ocean marine predator populations: effects of climate change and variability.

    PubMed

    Trathan, P N; Forcada, J; Murphy, E J

    2007-12-29

    The Southern Ocean is a major component within the global ocean and climate system and potentially the location where the most rapid climate change is most likely to happen, particularly in the high-latitude polar regions. In these regions, even small temperature changes can potentially lead to major environmental perturbations. Climate change is likely to be regional and may be expressed in various ways, including alterations to climate and weather patterns across a variety of time-scales that include changes to the long interdecadal background signals such as the development of the El Niño-Southern Oscillation (ENSO). Oscillating climate signals such as ENSO potentially provide a unique opportunity to explore how biological communities respond to change. This approach is based on the premise that biological responses to shorter-term sub-decadal climate variability signals are potentially the best predictor of biological responses over longer time-scales. Around the Southern Ocean, marine predator populations show periodicity in breeding performance and productivity, with relationships with the environment driven by physical forcing from the ENSO region in the Pacific. Wherever examined, these relationships are congruent with mid-trophic-level processes that are also correlated with environmental variability. The short-term changes to ecosystem structure and function observed during ENSO events herald potential long-term changes that may ensue following regional climate change. For example, in the South Atlantic, failure of Antarctic krill recruitment will inevitably foreshadow recruitment failures in a range of higher trophic-level marine predators. Where predator species are not able to accommodate by switching to other prey species, population-level changes will follow. The Southern Ocean, though oceanographically interconnected, is not a single ecosystem and different areas are dominated by different food webs. Where species occupy different positions in

  13. Southern Ocean control of glacial AMOC stability and Dansgaard-Oeschger interstadial duration

    NASA Astrophysics Data System (ADS)

    Buizert, Christo; Schmittner, Andreas

    2015-12-01

    Glacial periods exhibit abrupt Dansgaard-Oeschger (DO) climatic oscillations that are thought to be linked to instabilities in the Atlantic meridional overturning circulation (AMOC). Great uncertainty remains regarding the dynamics of the DO cycle, as well as controls on the timing and duration of individual events. Using ice core data we show that the duration of warm (interstadial) periods is strongly correlated with Antarctic climate, and presumably with Southern Ocean (SO) temperature and the position of the Southern Hemisphere (SH) westerlies. We propose a SO control on AMOC stability and interstadial duration via the rate of Antarctic bottom water formation, meridional density/pressure gradients, Agulhas Leakage, and SO adiabatic upwelling. This hypothesis is supported by climate model experiments that demonstrate SO warming leads to a stronger AMOC that is less susceptible to freshwater perturbations. In the AMOC stability diagram, SO warming and strengthening of the SH westerlies both shift the vigorous AMOC branch toward higher freshwater values, thus raising the threshold for AMOC collapse. The proposed mechanism could provide a consistent explanation for several diverse observations, including maximum DO activity during intermediate ice volume/SH temperature, and successively shorter DO durations within each Bond cycle. It may further have implications for the fate of the AMOC under future global warming.

  14. Microphysics and Southern Ocean Cloud Feedback

    NASA Astrophysics Data System (ADS)

    McCoy, Daniel T.

    Global climate models (GCMs) change their cloud properties in the Southern Ocean (SO) with warming in a qualitatively consistent fashion. Cloud albedo increases in the mid-latitudes and cloud fraction decreases in the subtropics. This creates a distinctive 'dipole' structure in the SW cloud feedback. However, the shape of the dipole varies from model to model. In this thesis we discuss the microphysical mechanisms underlying the SW cloud feedback over the mid-latitude SO. We will focus on the negative lobe of the dipole. The negative SW cloud feedback in the mid-latitudes is created by transitions from ice to liquid in models. If ice transitions to liquid in mixed-phase clouds the cloud albedo increases because ice crystals are larger than liquid droplets and therefore more reflective for a constant mass of water. Decreases in precipitation efficiency further enhance this effect by decreasing sinks of cloud water. This transition is dependent on the mixed-phase cloud parameterization. Parameterizations vary wildly between models and GCMs disagree by up to 35 K on the temperature where ice and liquid are equally prevalent. This results in a wide spread in the model predictions of the increase in liquid water path (LWP, where the path is the vertically integrated mass of water) with warming that drives the negative optical depth cloud feedback. It is found that this disagreement also results in a wide array of climate mean-states as models that create liquid at lower temperatures have a higher mean-state LWP, lower ice water path (IWP), and higher condensed (ice and liquid) water path (CWP). This presents a problem in climate models. GCMs need to have a reasonable planetary albedo in their climate mean-state. We show evidence that GCMs have tuned cloud fraction to compensate for the variation in mid-latitude cloud albedo driven by the mixed-phase cloud parameterization. This tuning results in mid-latitude clouds that are both too few and too bright as well as a

  15. Penguins as bioindicators of mercury contamination in the southern Indian Ocean: geographical and temporal trends.

    PubMed

    Carravieri, Alice; Cherel, Yves; Jaeger, Audrey; Churlaud, Carine; Bustamante, Paco

    2016-06-01

    Penguins have been recently identified as useful bioindicators of mercury (Hg) transfer to food webs in the Southern Ocean over different spatial and temporal scales. Here, feather Hg concentrations were measured in adults and chicks of all the seven penguin species breeding in the southern Indian Ocean, over a large latitudinal gradient spanning Antarctic, subantarctic and subtropical sites. Hg was also measured in feathers of museum specimens of penguins collected at the same sites in the 1950s and 1970s. Our aim was to evaluate geographical and historical variations in Hg transfer to penguins, while accounting for feeding habits by using the stable isotope technique (δ(13)C, habitat; δ(15)N, diet/trophic level). Adult feather Hg concentrations in contemporary individuals ranged from 0.7 ± 0.2 to 5.9 ± 1.9 μg g(-1) dw in Adélie and gentoo penguins, respectively. Inter-specific differences in Hg accumulation were strong among both adults and chicks, and mainly linked to feeding habits. Overall, penguin species that feed in Antarctic waters had lower feather Hg concentrations than those that feed in subantarctic and subtropical waters, irrespective of age class and dietary group, suggesting different Hg incorporation into food webs depending on the water mass. While accounting for feeding habits, we detected different temporal variations in feather Hg concentrations depending on species. Notably, the subantarctic gentoo and macaroni penguins had higher Hg burdens in the contemporary rather than in the historical sample, despite similar or lower trophic levels, respectively. Whereas increases in Hg deposition have been recently documented in the Southern Hemisphere, future monitoring is highly needed to confirm or not this temporal trend in penguins, especially in the context of actual changing Hg emission patterns and global warming. PMID:26896669

  16. Macrofauna under sea ice and in the open surface layer of the Lazarev Sea, Southern Ocean

    NASA Astrophysics Data System (ADS)

    Flores, Hauke; van Franeker, Jan-Andries; Cisewski, Boris; Leach, Harry; Van de Putte, Anton P.; Meesters, Erik (H. W. G.); Bathmann, Ulrich; Wolff, Wim J.

    2011-10-01

    A new fishing gear was used to sample the macrozooplankton and micronekton community in the surface layer (0-2 m) under ice and in open water, the Surface and Under Ice Trawl (SUIT). In total, 57 quantitative hauls were conducted in the Lazarev Sea (Southern Ocean) during 3 different seasons (autumn 2004, winter 2006, summer 2007/2008). At least 46 species from eight phyla were caught in all 3 seasons combined. Biomass density was dominated by Antarctic krill Euphausia superba. The average biomass density was highest under the winter sea ice and lowest under the young ice in autumn. In summer, macrozooplankton biomass was dominated by ctenophores in open water and by Antarctic krill under ice. The community composition varied significantly among seasons, and according to the presence of sea ice. The response of the community composition to the presence of sea ice was influenced by species that were significantly more abundant in open water than under ice ( Cyllopus lucasii, Hyperiella dilatata), only seasonally abundant under ice ( Clione antarctica), or significantly associated with sea ice ( Eusirus laticarpus). A number of abundant species showed distinct diel patterns in the surface occurrence both under ice and in open water, indicating that the surface layer serves as a foraging ground predominantly at night. Our results emphasize the potential of a number of non-euphausiid macrozooplankton and micronekton species to act as energy transmitters between the production of sea ice biota and the pelagic food web. By providing a regional-scale quantitative record of macrofauna under Antarctic sea ice covering 3 seasons, this study adds new and direct evidence that the ice-water interface layer is a major functional node in the ecosystem of the Antarctic seasonal sea ice zone.

  17. Ocean acidification exerts negative effects during warming conditions in a developing Antarctic fish

    PubMed Central

    Flynn, Erin E.; Bjelde, Brittany E.; Miller, Nathan A.; Todgham, Anne E.

    2015-01-01

    Anthropogenic CO2 is rapidly causing oceans to become warmer and more acidic, challenging marine ectotherms to respond to simultaneous changes in their environment. While recent work has highlighted that marine fishes, particularly during early development, can be vulnerable to ocean acidification, we lack an understanding of how life-history strategies, ecosystems and concurrent ocean warming interplay with interspecific susceptibility. To address the effects of multiple ocean changes on cold-adapted, slowly developing fishes, we investigated the interactive effects of elevated partial pressure of carbon dioxide (pCO2) and temperature on the embryonic physiology of an Antarctic dragonfish (Gymnodraco acuticeps), with protracted embryogenesis (∼10 months). Using an integrative, experimental approach, our research examined the impacts of near-future warming [−1 (ambient) and 2°C (+3°C)] and ocean acidification [420 (ambient), 650 (moderate) and 1000 μatm pCO2 (high)] on survival, development and metabolic processes over the course of 3 weeks in early development. In the presence of increased pCO2 alone, embryonic mortality did not increase, with greatest overall survival at the highest pCO2. Furthermore, embryos were significantly more likely to be at a later developmental stage at high pCO2 by 3 weeks relative to ambient pCO2. However, in combined warming and ocean acidification scenarios, dragonfish embryos experienced a dose-dependent, synergistic decrease in survival and developed more slowly. We also found significant interactions between temperature, pCO2 and time in aerobic enzyme activity (citrate synthase). Increased temperature alone increased whole-organism metabolic rate (O2 consumption) and developmental rate and slightly decreased osmolality at the cost of increased mortality. Our findings suggest that developing dragonfish are more sensitive to ocean warming and may experience negative physiological effects of ocean acidification only

  18. Ocean acidification exerts negative effects during warming conditions in a developing Antarctic fish.

    PubMed

    Flynn, Erin E; Bjelde, Brittany E; Miller, Nathan A; Todgham, Anne E

    2015-01-01

    Anthropogenic CO2 is rapidly causing oceans to become warmer and more acidic, challenging marine ectotherms to respond to simultaneous changes in their environment. While recent work has highlighted that marine fishes, particularly during early development, can be vulnerable to ocean acidification, we lack an understanding of how life-history strategies, ecosystems and concurrent ocean warming interplay with interspecific susceptibility. To address the effects of multiple ocean changes on cold-adapted, slowly developing fishes, we investigated the interactive effects of elevated partial pressure of carbon dioxide (pCO2) and temperature on the embryonic physiology of an Antarctic dragonfish (Gymnodraco acuticeps), with protracted embryogenesis (∼10 months). Using an integrative, experimental approach, our research examined the impacts of near-future warming [-1 (ambient) and 2°C (+3°C)] and ocean acidification [420 (ambient), 650 (moderate) and 1000 μatm pCO2 (high)] on survival, development and metabolic processes over the course of 3 weeks in early development. In the presence of increased pCO2 alone, embryonic mortality did not increase, with greatest overall survival at the highest pCO2. Furthermore, embryos were significantly more likely to be at a later developmental stage at high pCO2 by 3 weeks relative to ambient pCO2. However, in combined warming and ocean acidification scenarios, dragonfish embryos experienced a dose-dependent, synergistic decrease in survival and developed more slowly. We also found significant interactions between temperature, pCO2 and time in aerobic enzyme activity (citrate synthase). Increased temperature alone increased whole-organism metabolic rate (O2 consumption) and developmental rate and slightly decreased osmolality at the cost of increased mortality. Our findings suggest that developing dragonfish are more sensitive to ocean warming and may experience negative physiological effects of ocean acidification only in

  19. The discovery of new deep-sea hydrothermal vent communities in the southern ocean and implications for biogeography.

    PubMed

    Rogers, Alex D; Tyler, Paul A; Connelly, Douglas P; Copley, Jon T; James, Rachael; Larter, Robert D; Linse, Katrin; Mills, Rachel A; Garabato, Alfredo Naveira; Pancost, Richard D; Pearce, David A; Polunin, Nicholas V C; German, Christopher R; Shank, Timothy; Boersch-Supan, Philipp H; Alker, Belinda J; Aquilina, Alfred; Bennett, Sarah A; Clarke, Andrew; Dinley, Robert J J; Graham, Alastair G C; Green, Darryl R H; Hawkes, Jeffrey A; Hepburn, Laura; Hilario, Ana; Huvenne, Veerle A I; Marsh, Leigh; Ramirez-Llodra, Eva; Reid, William D K; Roterman, Christopher N; Sweeting, Christopher J; Thatje, Sven; Zwirglmaier, Katrin

    2012-01-01

    Since the first discovery of deep-sea hydrothermal vents along the Galápagos Rift in 1977, numerous vent sites and endemic faunal assemblages have been found along mid-ocean ridges and back-arc basins at low to mid latitudes. These discoveries have suggested the existence of separate biogeographic provinces in the Atlantic and the North West Pacific, the existence of a province including the South West Pacific and Indian Ocean, and a separation of the North East Pacific, North East Pacific Rise, and South East Pacific Rise. The Southern Ocean is known to be a region of high deep-sea species diversity and centre of origin for the global deep-sea fauna. It has also been proposed as a gateway connecting hydrothermal vents in different oceans but is little explored because of extreme conditions. Since 2009 we have explored two segments of the East Scotia Ridge (ESR) in the Southern Ocean using a remotely operated vehicle. In each segment we located deep-sea hydrothermal vents hosting high-temperature black smokers up to 382.8°C and diffuse venting. The chemosynthetic ecosystems hosted by these vents are dominated by a new yeti crab (Kiwa n. sp.), stalked barnacles, limpets, peltospiroid gastropods, anemones, and a predatory sea star. Taxa abundant in vent ecosystems in other oceans, including polychaete worms (Siboglinidae), bathymodiolid mussels, and alvinocaridid shrimps, are absent from the ESR vents. These groups, except the Siboglinidae, possess planktotrophic larvae, rare in Antarctic marine invertebrates, suggesting that the environmental conditions of the Southern Ocean may act as a dispersal filter for vent taxa. Evidence from the distinctive fauna, the unique community structure, and multivariate analyses suggest that the Antarctic vent ecosystems represent a new vent biogeographic province. However, multivariate analyses of species present at the ESR and at other deep-sea hydrothermal vents globally indicate that vent biogeography is more complex than

  20. The Discovery of New Deep-Sea Hydrothermal Vent Communities in the Southern Ocean and Implications for Biogeography

    PubMed Central

    Rogers, Alex D.; Tyler, Paul A.; Connelly, Douglas P.; Copley, Jon T.; James, Rachael; Larter, Robert D.; Linse, Katrin; Mills, Rachel A.; Garabato, Alfredo Naveira; Pancost, Richard D.; Pearce, David A.; Polunin, Nicholas V. C.; German, Christopher R.; Shank, Timothy; Boersch-Supan, Philipp H.; Alker, Belinda J.; Aquilina, Alfred; Bennett, Sarah A.; Clarke, Andrew; Dinley, Robert J. J.; Graham, Alastair G. C.; Green, Darryl R. H.; Hawkes, Jeffrey A.; Hepburn, Laura; Hilario, Ana; Huvenne, Veerle A. I.; Marsh, Leigh; Ramirez-Llodra, Eva; Reid, William D. K.; Roterman, Christopher N.; Sweeting, Christopher J.; Thatje, Sven; Zwirglmaier, Katrin

    2012-01-01

    Since the first discovery of deep-sea hydrothermal vents along the Galápagos Rift in 1977, numerous vent sites and endemic faunal assemblages have been found along mid-ocean ridges and back-arc basins at low to mid latitudes. These discoveries have suggested the existence of separate biogeographic provinces in the Atlantic and the North West Pacific, the existence of a province including the South West Pacific and Indian Ocean, and a separation of the North East Pacific, North East Pacific Rise, and South East Pacific Rise. The Southern Ocean is known to be a region of high deep-sea species diversity and centre of origin for the global deep-sea fauna. It has also been proposed as a gateway connecting hydrothermal vents in different oceans but is little explored because of extreme conditions. Since 2009 we have explored two segments of the East Scotia Ridge (ESR) in the Southern Ocean using a remotely operated vehicle. In each segment we located deep-sea hydrothermal vents hosting high-temperature black smokers up to 382.8°C and diffuse venting. The chemosynthetic ecosystems hosted by these vents are dominated by a new yeti crab (Kiwa n. sp.), stalked barnacles, limpets, peltospiroid gastropods, anemones, and a predatory sea star. Taxa abundant in vent ecosystems in other oceans, including polychaete worms (Siboglinidae), bathymodiolid mussels, and alvinocaridid shrimps, are absent from the ESR vents. These groups, except the Siboglinidae, possess planktotrophic larvae, rare in Antarctic marine invertebrates, suggesting that the environmental conditions of the Southern Ocean may act as a dispersal filter for vent taxa. Evidence from the distinctive fauna, the unique community structure, and multivariate analyses suggest that the Antarctic vent ecosystems represent a new vent biogeographic province. However, multivariate analyses of species present at the ESR and at other deep-sea hydrothermal vents globally indicate that vent biogeography is more complex than

  1. The impact of multidecadal Atlantic meridional overturning circulation variations on the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Zhang, Liping; Delworth, Thomas L.; Zeng, Fanrong

    2016-05-01

    The impact of multidecadal variations of the Atlantic meridional overturning circulation (AMOC) on the Southern Ocean (SO) is investigated in the current paper using a coupled ocean-atmosphere model. We find that the AMOC can influence the SO via fast atmosphere teleconnections and subsequent ocean adjustments. A stronger than normal AMOC induces an anomalous warm SST over the North Atlantic, which leads to a warming of the Northern Hemisphere troposphere extending into the tropics. This induces an increased equator-to-pole temperature gradient in the Southern Hemisphere (SH) upper troposphere and lower stratosphere due to an amplified tropical upper tropospheric warming as a result of increased latent heat release. This altered gradients leads to a poleward displacement of the SH westerly jet. The wind change over the SO then cools the SST at high latitudes by anomalous northward Ekman transports. The wind change also weakens the Antarctic bottom water (AABW) cell through changes in surface heat flux forcing. The poleward shifted westerly wind decreases the long term mean easterly winds over the Weddell Sea, thereby reducing the turbulent heat flux loss, decreasing surface density and therefore leading to a weakening of the AABW cell. The weakened AABW cell produces a temperature dipole in the SO, with a warm anomaly in the subsurface and a cold anomaly in the surface that corresponds to an increase of Antarctic sea ice. Opposite conditions occur for a weaker than normal AMOC. Our study here suggests that efforts to attribute the recent observed SO variability to various factors should take into consideration not only local process but also remote forcing from the North Atlantic.

  2. Antarctic Peninsula and Weddell Sea

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Numerous icebergs are breaking out of the sea ice in the Southern Ocean surrounding the Antarctic Peninsula. This true-color MODIS image from November 13, 2001, shows several icebergs drifting out of the Weddell Sea. The Antarctic Peninsula (left) reaches out into the Drake Passage, which separates the southern tip of South America from Antarctica. Warmer temperatures have cleared a tiny patch of bare ground at the Peninsula's tip. The predominant ocean current in the area is the Antarctic Circumpolar Current ('circum' meaning 'around'), which is also the 'West Wind Drift.' The current is the largest permanent current in the world, and water is moved eastward by westerly winds. Icebergs leaving the Weddell Sea are likely to be moved north and east by the current. Credit: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC

  3. Controls on biogenic silica burial in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Chase, Zanna; Kohfeld, Karen E.; Matsumoto, Katsumi

    2015-10-01

    Understanding the controls on opal export in the Southern Ocean can inform both the prediction of how the leakage of silicic acid from the Southern Ocean responds to climate and the interpretation of paleo-proxies. We have compiled a database of 185 230Thorium-normalized opal burial rates and 493 opal concentration measurements in Southern Ocean sediments and matched these with environmental climatologies. By subdividing the Southern Ocean on the basis of oceanographic regions and interpolating the opal burial rates, we estimate a total biogenic Si burial south of 40°S of 2.3 ± 1.0 Tmol Si yr-1. In both the seasonally ice-covered and permanently ice-free regions we can explain 73% of opal burial variability from surface ocean properties. Where sea ice is present for at least part of the year, the length of the ice-free season determines the upper limit of opal burial in the underlying sediments. In the ice-free regions of the Southern Ocean, the supply of silicic acid through winter mixing is the most important factor. Our results do not support a strong role of iron in controlling opal burial. We do however find that satellite-derived net primary production increases with increasing (modeled) dust delivery. These findings support the decoupling between carbon and opal fluxes in the Southern Ocean. When corrected for opal dissolution, the observed opal fluxes are in reasonable agreement with fluxes simulated using an ocean biogeochemical model. However, the results suggest current preservation algorithms for opal could be improved by incorporating the composition of particle flux, not only its magnitude.

  4. An oceanic teleconnection between the equatorial and southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Schouten, M. W.; de Ruijter, W. P. M.; van Leeuwen, P. J.; Dijkstra, H. A.

    2002-08-01

    Sequences of Kelvin and Rossby waves are found to rapidly carry sea surface height anomalies across the Indian Ocean, and have an impact on Indian to Atlantic interocean exchange. Satellite altimeter data reveal an oceanic teleconnection between equatorial winds and variability of the interocean exchange. Four times per year, we observe an equatorial Kelvin wave to hit Indonesia, forced by monsoon variability. The signal then propagates southward along the Indonesian coast and triggers Rossby waves that propagate westward across the subtropical Indian Ocean. On reaching the Madagascar and Mozambique Channel regions, large rings form at the same four per year frequency. These drift towards the Agulhas retroflection where they control the shedding of Agulhas rings. Disturbances of this pin-ball-like propagating signal can be traced from Indian Ocean Dipole/El Niño events in 1994 and 1997/1998, to decreases of Indian-Atlantic ocean exchange by Agulhas rings over two years later.

  5. Late Pleistocene evolution of Scott Glacier, southern Transantarctic Mountains: implications for the Antarctic contribution to deglacial sea level

    NASA Astrophysics Data System (ADS)

    Bromley, Gordon R. M.; Hall, Brenda L.; Stone, John O.; Conway, Howard

    2012-09-01

    Glacial deposits preserved adjacent to Scott Glacier, southern Transantarctic Mountains, provide a record of past fluctuations in the thickness of the West Antarctic Ice Sheet. Geologic mapping of these deposits, in conjunction with emerging 10Be surface-exposure data, indicate that the most recent expansion of Scott Glacier occurred during the last glacial maximum in response to grounding of ice in the Ross Sea Embayment. At that time, the ice surface at the confluence of Scott Glacier and the West Antarctic Ice Sheet lay at ˜1100 m elevation. While this ice-surface reconstruction is in accord with other geologic estimates from throughout the Ross Sea Embayment, it contrasts with most computer-based simulations, which tend to overestimate former ice thickness in the southern Ross Sea. Together with recently modelled estimates of Antarctica's contribution to sea level, this finding calls into question an Antarctic source for meltwater pulse 1A.

  6. Temporal variability of transformation, formation, and subduction rates of upper Southern Ocean waters

    NASA Astrophysics Data System (ADS)

    Kwon, Eun Young

    2013-11-01

    Kinematic and thermodynamic approaches are employed to diagnose the time-dependent transformation, formation, and subduction rates of upper Southern Ocean waters in a multidecadal simulation within an eddy-permitting coupled climate model. In the Subantarctic Mode Water (SAMW) density class, a convergence of diapycnal volume fluxes leads to the formation and inflation of mixed layer waters during winter. A portion of this water is detrained into the pycnocline during early spring, when surface heating restratifies the deep winter mixed layer. The annually averaged subduction rate of SAMW shows pronounced interannual variability, partly controlled by the temporal tendency of the winter mixed layer depth from one year to the next. No significant correlation between the Southern Annular Mode (SAM) and the isopycnally integrated SAMW subduction rate is apparent. However, Ekman downwelling/upwelling intensities modulated by the SAM influence interannual variations in the subduction rates of water masses lighter and heavier than SAMW with an opposing sign: during positive phases of the SAM, more pycnocline waters are entrained into the mixed layer and transformed into lighter densities within the Antarctic Intermediate Water density class, whereas more mixed layer waters are subducted into the pycnocline within the Subtropical Mode Water density class. Such distinct responses of upper Southern Ocean water masses to the SAM are qualitatively consistent with observational constraints. Based on a comparison between offline kinematic and thermodynamic diagnostics, we infer that diapycnal mixing within the mixed layer may contribute up to 50% of the formation rate of SAMW on interannual timescales.

  7. Ocean-driven thinning enhances iceberg calving and retreat of Antarctic ice shelves

    PubMed Central

    Liu, Yan; Moore, John C.; Cheng, Xiao; Gladstone, Rupert M.; Bassis, Jeremy N.; Liu, Hongxing; Wen, Jiahong; Hui, Fengming

    2015-01-01

    Iceberg calving from all Antarctic ice shelves has never been directly measured, despite playing a crucial role in ice sheet mass balance. Rapid changes to iceberg calving naturally arise from the sporadic detachment of large tabular bergs but can also be triggered by climate forcing. Here we provide a direct empirical estimate of mass loss due to iceberg calving and melting from Antarctic ice shelves. We find that between 2005 and 2011, the total mass loss due to iceberg calving of 755 ± 24 gigatonnes per year (Gt/y) is only half the total loss due to basal melt of 1516 ± 106 Gt/y. However, we observe widespread retreat of ice shelves that are currently thinning. Net mass loss due to iceberg calving for these ice shelves (302 ± 27 Gt/y) is comparable in magnitude to net mass loss due to basal melt (312 ± 14 Gt/y). Moreover, we find that iceberg calving from these decaying ice shelves is dominated by frequent calving events, which are distinct from the less frequent detachment of isolated tabular icebergs associated with ice shelves in neutral or positive mass balance regimes. Our results suggest that thinning associated with ocean-driven increased basal melt can trigger increased iceberg calving, implying that iceberg calving may play an overlooked role in the demise of shrinking ice shelves, and is more sensitive to ocean forcing than expected from steady state calving estimates. PMID:25733856

  8. Ocean-driven thinning enhances iceberg calving and retreat of Antarctic ice shelves.

    PubMed

    Liu, Yan; Moore, John C; Cheng, Xiao; Gladstone, Rupert M; Bassis, Jeremy N; Liu, Hongxing; Wen, Jiahong; Hui, Fengming

    2015-03-17

    Iceberg calving from all Antarctic ice shelves has never been directly measured, despite playing a crucial role in ice sheet mass balance. Rapid changes to iceberg calving naturally arise from the sporadic detachment of large tabular bergs but can also be triggered by climate forcing. Here we provide a direct empirical estimate of mass loss due to iceberg calving and melting from Antarctic ice shelves. We find that between 2005 and 2011, the total mass loss due to iceberg calving of 755 ± 24 gigatonnes per year (Gt/y) is only half the total loss due to basal melt of 1516 ± 106 Gt/y. However, we observe widespread retreat of ice shelves that are currently thinning. Net mass loss due to iceberg calving for these ice shelves (302 ± 27 Gt/y) is comparable in magnitude to net mass loss due to basal melt (312 ± 14 Gt/y). Moreover, we find that iceberg calving from these decaying ice shelves is dominated by frequent calving events, which are distinct from the less frequent detachment of isolated tabular icebergs associated with ice shelves in neutral or positive mass balance regimes. Our results suggest that thinning associated with ocean-driven increased basal melt can trigger increased iceberg calving, implying that iceberg calving may play an overlooked role in the demise of shrinking ice shelves, and is more sensitive to ocean forcing than expected from steady state calving estimates. PMID:25733856

  9. On the role of sea ice for Southern Ocean stratification

    NASA Astrophysics Data System (ADS)

    Haumann, F. Alexander; Münnich, Matthias; Gruber, Nicolas

    2013-04-01

    The formation, subsequent lateral transport, and melt of sea ice represents a key process for the determination of upper ocean stratification in the Southern Ocean. Sea ice is transported northward in large parts of the Southern Ocean by strong near-surface winds and melts along the ice edge south of the polar front, an important upwelling region. Here, it adds freshwater to the surface ocean, lowers the sea-water density, and possibly reduces upwelling by increasing the stratification. Consequently, this redistribution of freshwater in time and space affects the vertical overturning circulation which is an important determinant of the ocean-atmosphere CO2 exchange and, thus, of the global climate. We investigate the Southern Ocean sea-ice ocean system using satellite observations together with simulations with a newly developed regional ocean sea-ice model on the basis of ROMS. As it is not possible yet to derive sea-ice volume transport from remote sensing data due to a lack of ice thickness data, we quantify the freshwater flux exerted by the sea ice from the model and compare it to the observed sea-ice area transport. This shows that the transport is large in the Weddell and Ross Seas where sea ice extends to its lowest latitudes. We assess the importance of sea-ice freshwater transport on the stratification and circulation by comparing this flux to the net atmospheric freshwater flux from reanalysis data and by perturbing our model simulations.

  10. Humpback Whale Song on the Southern Ocean Feeding Grounds: Implications for Cultural Transmission

    PubMed Central

    Garland, Ellen C.; Gedamke, Jason; Rekdahl, Melinda L.; Noad, Michael J.; Garrigue, Claire; Gales, Nick

    2013-01-01

    Male humpback whales produce a long, complex, and stereotyped song on low-latitude breeding grounds; they also sing while migrating to and from these locations, and occasionally in high-latitude summer feeding areas. All males in a population sing the current version of the constantly evolving display and, within an ocean basin, populations sing similar songs; however, this sharing can be complex. In the western and central South Pacific region there is repeated cultural transmission of song types from eastern Australia to other populations eastward. Song sharing is hypothesized to occur through several possible mechanisms. Here, we present the first example of feeding ground song from the Southern Ocean Antarctic Area V and compare it to song from the two closest breeding populations. The early 2010 song contained at least four distinct themes; these matched four themes from the eastern Australian 2009 song, and the same four themes from the New Caledonian 2010 song recorded later in the year. This provides evidence for at least one of the hypothesized mechanisms of song transmission between these two populations, singing while on shared summer feeding grounds. In addition, the feeding grounds may provide a point of acoustic contact to allow the rapid horizontal cultural transmission of song within the western and central South Pacific region and the wider Southern Ocean. PMID:24278134

  11. Southern ocean controls on the extent of denitrification in the southeast Pacific (ODP Site 1234)

    NASA Astrophysics Data System (ADS)

    Robinson, R. S.; Mix, A.; Martinez, P.

    2005-12-01

    A mechanistic understanding of the observed temporal changes in oceanic denitrification, the bacterial reduction of nitrate under suboxic conditions, has been sought due to the potential importance of N inventory changes and the production of N2O on the climate system. High-resolution oxygen isotope and bulk sediment δ15N records from ODP Site 1234 on the Chile Margin are presented as a record of denitrification changes within the Peru-Chile Upwelling system over the last 65ky. The character of the Site 1234 δ15N record is quite similar to that of its northern hemisphere counterparts with the exception of timing. Denitrification changes in the southeast Pacific show coherent variation with Antarctic climate, as indicated by the Byrd ice core δ18O record, rather than with northern hemisphere climate change. The high latitude polar oceans play a fundamental role in setting the physical and biological controls on subsurface oxygen supply and demand. The southern hemisphere character of the Chile margin record suggests that episodes of reduced denitrification in the SE Pacific likely represent times when more oxygen was supplied as the result of changes in the chemical composition of Subantarctic Mode Water (SAMW), which forms in the Subantarctic zone of the Southern Ocean and ventilates the low latitude thermocline. An increase in oxygen can be achieved through (1) lower temperatures/ higher ventilation rates and/or (2) reduced oxygen demand in the low latitude subsurface due to reduction in the preformed nutrient content of SAMW.

  12. Investigating the Biases in the Antarctic Sea Ice - Ocean System of Climate Models using Process-oriented Diagnostics

    NASA Astrophysics Data System (ADS)

    Lecomte, O.; Goosse, H.; Fichefet, T.; Holland, P.; Uotila, P.; Zunz, V.

    2015-12-01

    Most analyses of Antarctic sea ice in simulations of the CMIP5 archive have so far been oriented towards the quantification of the disagreement between model results and sea ice observations only. Since the decomposition of those biases into distinct physical components is necessary to understand their origins, we propose here an ocean-sea ice-atmosphere integrated and process-oriented approach. Not only the biases in variables essential to the sea ice seasonal evolution are estimated regionally with regard to observations, but their contributions to the sea ice concentration budget are estimated. Following a previously developed method, the sea ice concentration balance over the autumn-winter seasons is decomposed into four terms, including the sea ice concentration change during the period of interest, advection, divergence and a residual accounting for the net contribution of thermodynamics and ice deformation. Concurrently, correlations between trends in ocean temperature at depth and trends in ice concentration are calculated directly from various model output fields (including CMIP5 models) to disentangle the role of ice-ocean interactions. Results show that the geographical patterns of all mean sea ice concentration budget terms over 1992-2005 are in qualitative agreement with the observed ones. Sea ice thermodynamic growth is maintained by horizontal divergence near the continent and in the central ice pack, whereas melting close to the ice edge is led by sea ice advection. However, significant errors in all budget terms are observed due to ice velocities that tend to be overestimated all around Antarctica in several models, leading to a relatively weak divergence in the inner ice pack and to an excessive advection in the marginal ice zone. Biases in ice drift speed and direction are ultimately related to biases in winds in all models. This method paves the way for a systematic assessment of forthcoming CMIP6 sea ice model outputs in the Southern Hemisphere.

  13. Sources and sinks of momentum in the Southern Ocean State Estimate

    NASA Astrophysics Data System (ADS)

    Masich, J.; Chereskin, T. K.; Mazloff, M. R.

    2015-12-01

    Strong, persistent winds over the Southern Ocean drive the Antarctic Circumpolar Current (ACC) on an unblocked eastward path around Antarctica. Observations and reanalyses have shown that Southern Ocean winds have increased over the past 60 years [Thompson, 2002; Swart and Fyfe, 2012]. ACC baroclinic transport appears to remain stable [Böning et al., 2008], however, suggesting that the interior mechanisms that output momentum from the Antarctic Circumpolar Current (ACC) system are counterbalancing changes in the input wind stress. Here we describe where and how momentum exits the ACC system in a six-year, eddy permitting state estimate of the Southern Ocean. We find that 95% of the zonal momentum input via wind stress at the surface is balanced by topographic form stress across ocean ridges, while the remaining 5% is balanced via bottom friction and momentum flux divergences at the northern and southern boundaries of the analysis domain. While the time-mean zonal wind stress field exhibits a relatively uniform spatial distribution, time-mean topographic form stress concentrates at shallow ridges and across the continents that lie within the ACC latitudes -- primarily Kerguelen Plateau, the Macquarie Ridge region, and South America and the Drake Passage fracture zones -- as well as across deep basins separated by basin-scale plains. Topographic form stress can be divided into shallow and deep regimes: the shallow regime contributes most of the westward form stress that serves as a momentum sink for the ACC system, while the deep regime consists of strong eastward and westward form stresses that largely cancel in the zonal integral. The time-varying form stress signal, integrated longitudinally and over the ACC latitudes, tracks closely with the wind stress signal integrated over the same domain; at zero lag, 88% of the variance in the six-year form stress time series can be explained by the wind stress signal, indicating that changes in the integrated wind stress

  14. THE CD ISOTOPE SIGNATURE OF THE SOUTHERN OCEAN

    NASA Astrophysics Data System (ADS)

    Abouchami, W.; Galer, S. J.; Middag, R.; de Baar, H.; Andreae, M. O.; Feldmann, H.; Raczek, I.

    2009-12-01

    The availability of micronutrients can limit and control plankton ecosystems, notably in the Southern Ocean which plays a major role in regulating the CO2 biological pump. Cadmium has a nutrient-like distribution in seawater - it is directly incorporated into living plankton in the upper water column and re-mineralised at depth. The nutritional role of Cd (Price and Morel, 1990) makes it a potentially useful tracer of biological productivity. We report Cd concentration and Cd stable isotope data obtained using a double-spike TIMS method on seawater samples collected during the Zero and Drake Passage cruise (ANTXXIV-III, IPY-GEOTRACES 2008). Four vertical profiles were collected from 40 to 70°S across the Polar Front using the ultra-clean Titan frame (De Baar et al., 2008), providing a record of changes in biological productivity from the Subantarctic to the Antarctic region. Data from two profiles from the SE Atlantic (47.66°S, 4.28W) and Drake Passage (55.13°S, 65.53°W) obtained on 1 litre-sized samples are presented. Both profiles show a increase in Cd concentration with depth, with noticeably higher concentrations in the SE Atlantic. Cd and PO4 are positively correlated with distinct slopes for the two profiles. The Cd isotope data are expressed as ɛ112/110Cd relative to our JMC Mainz standard (± 8ppm, 2SD, N=17). ɛ112/110Cd values show a continuous decrease with increasing depth and a significant shift towards heavier values in the upper 400m at both stations resolvable outside analytical error (2SE ≤ 20ppm). The sense of Cd isotope fractionation confirms previous findings of uptake of “light” Cd by phytoplankton in the upper water column (Lacan et al., 2006; Ripperger et al., 2007; Schmidt et al., 2009). Most important is the evidence for a distinctive heavier Cd isotope signature in AASW relative to AAIW. This result demonstrates that different water masses carry distinct Cd isotopic compositions reflecting changes in Cd uptake by phytoplankton

  15. Climate variability and spatiotemporal dynamics of five Southern Ocean krill species

    NASA Astrophysics Data System (ADS)

    Loeb, Valerie J.; Santora, Jarrod A.

    2015-05-01

    Understanding the ecological response of marine organisms to future climate change will benefit from quantifying spatiotemporal aspects of their distribution and abundance as well as the influence of ocean-atmospheric climate modes on their population cycles. Our study provides a synthesis of 18 years of data (1992-2009) for 5 krill (euphausiid) species monitored near the North Antarctic Peninsula (NAP) during austral summer. Distribution and abundance data are presented for postlarval stages of Euphausia crystallorophias, E. frigida, E. superba, E. triacantha and Thysanoessa macrura and larval E. superba and T. macrura. Intraseasonal, interannual and longer-term distribution and abundance patterns are quantified relative to climate modes driving ecosystem variability off the Antarctic Peninsula: El Niño-Southern Oscillation (ENSO), Southern Annual Mode (SAM) and associated zonal and meridional winds. Interannual abundance variations of all 5 species are significantly correlated with seasonally averaged ENSO indices and, with the exception of E. triacantha, elevated population sizes are associated with the higher productivity La Niña phase. Time-lagged responses of each species to ENSO indices approximate their generation times and suggest evolution of their life histories and reproductive efforts in accordance with the ENSO cycle. Postlarval E. crystallorophias and E. frigida and larval T. macrura demonstrate significant abundance increases after 1998 associated with a shift from an El Niño dominated period to predominantly La Niña and "Nino-neutral" conditions. Seasonal changes in species distributions and co-occurrence indicate portions of the southernmost E. frigida, E. triacantha and T. macrura populations move poleward with E. superba during late-summer, suggesting that environmental conditions associated with sea ice development (e.g., food, retention) may be more favorable than within the Antarctic Circumpolar Current during low productivity seasons

  16. Sea-ice transport driving Southern Ocean salinity and its recent trends.

    PubMed

    Haumann, F Alexander; Gruber, Nicolas; Münnich, Matthias; Frenger, Ivy; Kern, Stefan

    2016-01-01

    Recent salinity changes in the Southern Ocean are among the most prominent signals of climate change in the global ocean, yet their underlying causes have not been firmly established. Here we propose that trends in the northward transport of Antarctic sea ice are a major contributor to these changes. Using satellite observations supplemented by sea-ice reconstructions, we estimate that wind-driven northward freshwater transport by sea ice increased by 20 ± 10 per cent between 1982 and 2008. The strongest and most robust increase occurred in the Pacific sector, coinciding with the largest observed salinity changes. We estimate that the additional freshwater for the entire northern sea-ice edge entails a freshening rate of -0.02 ± 0.01 grams per kilogram per decade in the surface and intermediate waters of the open ocean, similar to the observed freshening. The enhanced rejection of salt near the coast of Antarctica associated with stronger sea-ice export counteracts the freshening of both continental shelf and newly formed bottom waters due to increases in glacial meltwater. Although the data sources underlying our results have substantial uncertainties, regional analyses and independent data from an atmospheric reanalysis support our conclusions. Our finding that northward sea-ice freshwater transport is also a key determinant of the mean salinity distribution in the Southern Ocean further underpins the importance of the sea-ice-induced freshwater flux. Through its influence on the density structure of the ocean, this process has critical consequences for the global climate by affecting the exchange of heat, carbon and nutrients between the deep ocean and surface waters. PMID:27582222

  17. Contribution of glacial melt water to the recent Southern Ocean sea ice increase

    NASA Astrophysics Data System (ADS)

    Haid, Verena; Iovino, Dorotea

    2015-04-01

    In recent years climate change and global warming are topics that are discussed everywhere. Big concerns are the melting of land ice, the reduced summer sea ice cover in the Arctic Ocean, and the general decline of the cryosphere. In contrast to those scenarios, the response of Antarctic sea ice to a warming climate is elaborate and puzzling: sea ice extent has been slightly increasing on a circumpolar scale during the last decades. Atmospheric data analysis ascribed this expansion to changes in the wind dynamics; simulations with climate-scale ocean model suggest that accelerated basal melting of ice shelves plays a major role. We investigate the influence of the glacial melt water on the sea ice of the Southern Ocean on the circumpolar and regional scales employing the ocean/sea ice NEMO-LIM coupled system at eddy-permitting resolution. The forcing of the sea ice-ocean model is supplied from the ERA-Interim data set. After a 25-year spin-up period the reference run supplies a realistic simulation of the period 2004-2013. Different volumes and distributions of melt water are applied in individual model runs spanning the same period and results are compared with the reference run. The results of this study will increase our understanding of the effect of climate change on the Southern Ocean at present and thus also of the future development. Questions like how long the increasing trend in sea ice will last or how fast it will be reversed once the tipping point is reached will be able to be addressed with more accuracy.

  18. IBCSO v1 - The first release of the International Bathymetric Chart of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Schenke, H. W.; Arndt, J.

    2012-12-01

    The International Bathymetric Chart of the Southern Ocean (IBCSO) is an expert group of the Scientific Committee on Antarctic Research (SCAR) since the XXVIII SCAR Conference held on 30th July 2004 in Bremen Germany and a regional mapping project of the General Bathymetric Chart of the Ocean (GEBCO) operated under the joint auspices of the Intergovernmental Oceanographic Commission (IOC) (of UNESCO) and the International Hydrographic Organization (IHO). The objective of IBCSO was to produce the first seamless bathymetric grid for the area south of latitude 60° S surrounding Antarctica. The IBCSO is going to be highly beneficial many scientific investigations. These include (a) interpretation of seabed geology, (b) the building of habitat models and maps, and (c) mapping and tracing of deep ocean current pathways. In addition the IBCSO is going to serve as an indispensable database for new nautical Charts in the Southern Ocean to improve the safety of navigation in Antarctic waters. After the inaugural meeting in 2004, the Editorial Board was then established at the 1st IBCSO Meeting at Santa Barbara in 2007 including representatives from several SCAR member countries. Since then, plenty of institutions holding bathymetric data in the Southern Ocean have been asked for a contribution to the IBCSO dataset. After the time consuming gathering, compilation and analyses of bathymetric data, finally the first version of the IBCSO is close to be released. Besides the grid an adjacent map has been developed, which is also going to be released in the near future. It is proposed to give an overview in what has been done in the IBCSO project in the last years for the creation of IBCSO v1. This will include acknowledgements to the data contributors and a short explanation of the working steps data acquisition, homogenization, cleaning and gridding. Previews of the new grid are going to demonstrate the improvement that has been achieved by IBCSO v1 compared to other bathymetric

  19. Thick-shelled, grazer-protected diatoms decouple ocean carbon and silicon cycles in the iron-limited Antarctic Circumpolar Current.

    PubMed

    Assmy, Philipp; Smetacek, Victor; Montresor, Marina; Klaas, Christine; Henjes, Joachim; Strass, Volker H; Arrieta, Jesús M; Bathmann, Ulrich; Berg, Gry M; Breitbarth, Eike; Cisewski, Boris; Friedrichs, Lars; Fuchs, Nike; Herndl, Gerhard J; Jansen, Sandra; Krägefsky, Sören; Latasa, Mikel; Peeken, Ilka; Röttgers, Rüdiger; Scharek, Renate; Schüller, Susanne E; Steigenberger, Sebastian; Webb, Adrian; Wolf-Gladrow, Dieter

    2013-12-17

    Diatoms of the iron-replete continental margins and North Atlantic are key exporters of organic carbon. In contrast, diatoms of the iron-limited Antarctic Circumpolar Current sequester silicon, but comparatively little carbon, in the underlying deep ocean and sediments. Because the Southern Ocean is the major hub of oceanic nutrient distribution, selective silicon sequestration there limits diatom blooms elsewhere and consequently the biotic carbon sequestration potential of the entire ocean. We investigated this paradox in an in situ iron fertilization experiment by comparing accumulation and sinking of diatom populations inside and outside the iron-fertilized patch over 5 wk. A bloom comprising various thin- and thick-shelled diatom species developed inside the patch despite the presence of large grazer populations. After the third week, most of the thinner-shelled diatom species underwent mass mortality, formed large, mucous aggregates, and sank out en masse (carbon sinkers). In contrast, thicker-shelled species, in particular Fragilariopsis kerguelensis, persisted in the surface layers, sank mainly empty shells continuously, and reduced silicate concentrations to similar levels both inside and outside the patch (silica sinkers). These patterns imply that thick-shelled, hence grazer-protected, diatom species evolved in response to heavy copepod grazing pressure in the presence of an abundant silicate supply. The ecology of these silica-sinking species decouples silicon and carbon cycles in the iron-limited Southern Ocean, whereas carbon-sinking species, when stimulated by iron fertilization, export more carbon per silicon. Our results suggest that large-scale iron fertilization of the silicate-rich Southern Ocean will not change silicon sequestration but will add carbon to the sinking silica flux. PMID:24248337

  20. Thick-shelled, grazer-protected diatoms decouple ocean carbon and silicon cycles in the iron-limited Antarctic Circumpolar Current

    PubMed Central

    Assmy, Philipp; Smetacek, Victor; Montresor, Marina; Klaas, Christine; Henjes, Joachim; Strass, Volker H.; Arrieta, Jesús M.; Bathmann, Ulrich; Berg, Gry M.; Breitbarth, Eike; Cisewski, Boris; Friedrichs, Lars; Fuchs, Nike; Herndl, Gerhard J.; Jansen, Sandra; Krägefsky, Sören; Latasa, Mikel; Peeken, Ilka; Röttgers, Rüdiger; Scharek, Renate; Schüller, Susanne E.; Steigenberger, Sebastian; Webb, Adrian; Wolf-Gladrow, Dieter

    2013-01-01

    Diatoms of the iron-replete continental margins and North Atlantic are key exporters of organic carbon. In contrast, diatoms of the iron-limited Antarctic Circumpolar Current sequester silicon, but comparatively little carbon, in the underlying deep ocean and sediments. Because the Southern Ocean is the major hub of oceanic nutrient distribution, selective silicon sequestration there limits diatom blooms elsewhere and consequently the biotic carbon sequestration potential of the entire ocean. We investigated this paradox in an in situ iron fertilization experiment by comparing accumulation and sinking of diatom populations inside and outside the iron-fertilized patch over 5 wk. A bloom comprising various thin- and thick-shelled diatom species developed inside the patch despite the presence of large grazer populations. After the third week, most of the thinner-shelled diatom species underwent mass mortality, formed large, mucous aggregates, and sank out en masse (carbon sinkers). In contrast, thicker-shelled species, in particular Fragilariopsis kerguelensis, persisted in the surface layers, sank mainly empty shells continuously, and reduced silicate concentrations to similar levels both inside and outside the patch (silica sinkers). These patterns imply that thick-shelled, hence grazer-protected, diatom species evolved in response to heavy copepod grazing pressure in the presence of an abundant silicate supply. The ecology of these silica-sinking species decouples silicon and carbon cycles in the iron-limited Southern Ocean, whereas carbon-sinking species, when stimulated by iron fertilization, export more carbon per silicon. Our results suggest that large-scale iron fertilization of the silicate-rich Southern Ocean will not change silicon sequestration but will add carbon to the sinking silica flux. PMID:24248337

  1. Reduced calcification in modern Southern Ocean planktonic foraminifera

    NASA Astrophysics Data System (ADS)

    Moy, Andrew D.; Howard, William R.; Bray, Stephen G.; Trull, Thomas W.

    2009-04-01

    Anthropogenic carbon dioxide has been accumulating in the oceans, lowering both the concentration of carbonate ions and the pH (ref. 1), resulting in the acidification of sea water. Previous laboratory experiments have shown that decreased carbonate ion concentrations cause many marine calcareous organisms to show reduced calcification rates. If these results are widely applicable to ocean settings, ocean acidification could lead to ecosystem shifts. Planktonic foraminifera are single-celled calcite-secreting organisms that represent between 25 and 50% of the total open-ocean marine carbonate flux and influence the transport of organic carbon to the ocean interior. Here we compare the shell weights of the modern foraminifer Globigerina bulloides collected from sediment traps in the Southern Ocean with the weights of shells preserved in the underlying Holocene-aged sediments. We find that modern shell weights are 30-35% lower than those from the sediments, consistent with reduced calcification today induced by ocean acidification. We also find a link between higher atmospheric carbon dioxide and low shell weights in a 50,000-year-long record obtained from a Southern Ocean marine sediment core. It is unclear whether reduced calcification will affect the survival of this and other species, but a decline in the abundance of foraminifera caused by acidification could affect both marine ecosystems and the oceanic uptake of atmospheric carbon dioxide.

  2. Sea-level response to abrupt ocean warming of Antarctic ice shelves

    NASA Astrophysics Data System (ADS)

    Pattyn, Frank

    2016-04-01

    Antarctica's contribution to global sea-level rise increases steadily. A fundamental question remains whether the ice discharge will lead to marine ice sheet instability (MISI) and collapse of certain sectors of the ice sheet or whether ice loss will increase linearly with the warming trends. Therefore, we employ a newly developed ice sheet model of the Antarctic ice sheet, called f.ETISh (fast Elementary Thermomechanical Ice Sheet model) to simulate ice sheet response to abrupt perturbations in ocean and atmospheric temperature. The f.ETISh model is a vertically integrated hybrid (SSA/SIA) ice sheet model including ice shelves. Although vertically integrated, thermomechanical coupling is ensured through a simplified representation of ice sheet thermodynamics based on an analytical solution of the vertical temperature profile, including strain heating and horizontal advection. The marine boundary is represented by a flux condition either coherent with power-law basal sliding (Pollard & Deconto (2012) based on Schoof (2007)) or according to Coulomb basal friction (Tsai et al., 2015), both taking into account ice-shelf buttressing. Model initialization is based on optimization of the basal friction field. Besides the traditional MISMIP tests, new tests with respect to MISI in plan-view models have been devised. The model is forced with stepwise ocean and atmosphere temperature perturbations. The former is based on a parametrised sub-shelf melt (limited to ice shelves), while the latter is based on present-day mass balance/surface temperature and corrected for elevation changes. Surface melting is introduced using a PDD model. Results show a general linear response in mass loss to ocean warming. Nonlinear response due to MISI occurs under specific conditions and is highly sensitive to the basal conditions near the grounding line, governed by both the initial conditions and the basal sliding/deformation model. The Coulomb friction model leads to significantly higher

  3. Seasonal dynamics in diatom and particulate export fluxes to the deep sea in the Australian sector of the southern Antarctic Zone

    NASA Astrophysics Data System (ADS)

    Rigual-Hernández, Andrés S.; Trull, Thomas W.; Bray, Stephen G.; Closset, Ivia; Armand, Leanne K.

    2015-02-01

    Particle fluxes were recorded over a one-year period (2001-02) in the southern Antarctic Zone in the Australian Sector of the Southern Ocean. Here, we present the results on the seasonal and vertical variability of biogenic particle and diatom valve fluxes. Total mass and diatom fluxes were highly seasonal, with maxima registered during the austral summer and minima during winter. Biogenic opal dominated sedimentation, followed by carbonate, and very low levels of organic carbon (annual average 1.4%). The strong correlation between opal and organic carbon at both depth levels suggests that a significant fraction of organic matter exported to the deep sea was associated with diatom sedimentation events. Seasonal diatom fluxes appear driven principally by changes in the flux of Fragilariopsis kerguelensis. The occurrence of the sea-ice affiliated diatoms Fragilariopsis cylindrus and Fragilariopsis curta in both sediment traps is considered to correspond to the sedimentation of a diatom bloom advected from an area under the influence of sea ice. Highest fluxes of the subsurface-dwelling species Thalassiothrix antarctica registered at the end of the summer bloom were linked to a drop of the light levels during the summer-autumn transition. This study provides the first annual observation on seasonal succession of diatom species in the Australian sector of the Antarctic Zone, and corresponds, in terms of magnitude and seasonality of diatom fluxes, to those in neighbouring sectors (Pacific and eastern Atlantic).

  4. Teleconnected influence of the boreal winter Antarctic Oscillation on the Somali Jet: Bridging role of sea surface temperature in southern high and middle latitudes

    NASA Astrophysics Data System (ADS)

    Shi, Wenjing; Xiao, Ziniu; Xue, Jianjun

    2016-01-01

    The teleconnection impact of the boreal winter Antarctic Oscillation (AAO) on the Somali Jet (SMJ) intensity in the following spring and summer is examined in this paper. The variability of the boreal winter AAO is positively related to the SMJ intensity in both spring and summer. The analyses show that the SST in southern high and middle latitudes seems to serve as a bridge linking these two systems. When the AAO is in strong positive phase, SST over the Southern Ocean cools in the high latitudes and warms in the middle latitudes, which persists into summer; however, the variability of SST in southern high and middle latitudes is also closely correlated to SMJ intensity. A possible mechanism that links SST variability with the AAO-SMJ relationship is also discussed. The AAO in boreal winter produces an SST anomaly pattern in southern high and middle latitudes through the air-sea coupling. This AAOrelated SST anomaly pattern modulates the local Ferrel cell anomaly in summer, followed by the regional Hadley cell anomaly in tropics. The anomalous vertical motion in tropics then changes the land-sea thermal contrast between the tropical Indian Ocean and the Asian continent through the variability of low cloud cover and downward surface longwave radiation flux. Finally, the land-sea thermal contrast anomaly between the tropical Indian Ocean and the Asian continent changes the SMJ intensity. The results from Community Atmosphere Model experiments forced by the SST anomaly in southern high and middle latitudes also confirm this diagnostic physical process to some extent.

  5. Oxygen depletion recorded in upper waters of the glacial Southern Ocean

    PubMed Central

    Lu, Zunli; Hoogakker, Babette A. A.; Hillenbrand, Claus-Dieter; Zhou, Xiaoli; Thomas, Ellen; Gutchess, Kristina M.; Lu, Wanyi; Jones, Luke; Rickaby, Rosalind E. M.

    2016-01-01

    Oxygen depletion in the upper ocean is commonly associated with poor ventilation and storage of respired carbon, potentially linked to atmospheric CO2 levels. Iodine to calcium ratios (I/Ca) in recent planktonic foraminifera suggest that values less than ∼2.5 μmol mol−1 indicate the presence of O2-depleted water. Here we apply this proxy to estimate past dissolved oxygen concentrations in the near surface waters of the currently well-oxygenated Southern Ocean, which played a critical role in carbon sequestration during glacial times. A down-core planktonic I/Ca record from south of the Antarctic Polar Front (APF) suggests that minimum O2 concentrations in the upper ocean fell below 70 μmol kg−1 during the last two glacial periods, indicating persistent glacial O2 depletion at the heart of the carbon engine of the Earth's climate system. These new estimates of past ocean oxygenation variability may assist in resolving mechanisms responsible for the much-debated ice-age atmospheric CO2 decline. PMID:27029225

  6. Oxygen depletion recorded in upper waters of the glacial Southern Ocean.

    PubMed

    Lu, Zunli; Hoogakker, Babette A A; Hillenbrand, Claus-Dieter; Zhou, Xiaoli; Thomas, Ellen; Gutchess, Kristina M; Lu, Wanyi; Jones, Luke; Rickaby, Rosalind E M

    2016-01-01

    Oxygen depletion in the upper ocean is commonly associated with poor ventilation and storage of respired carbon, potentially linked to atmospheric CO2 levels. Iodine to calcium ratios (I/Ca) in recent planktonic foraminifera suggest that values less than ∼2.5 μmol mol(-1) indicate the presence of O2-depleted water. Here we apply this proxy to estimate past dissolved oxygen concentrations in the near surface waters of the currently well-oxygenated Southern Ocean, which played a critical role in carbon sequestration during glacial times. A down-core planktonic I/Ca record from south of the Antarctic Polar Front (APF) suggests that minimum O2 concentrations in the upper ocean fell below 70 μmol kg(-1) during the last two glacial periods, indicating persistent glacial O2 depletion at the heart of the carbon engine of the Earth's climate system. These new estimates of past ocean oxygenation variability may assist in resolving mechanisms responsible for the much-debated ice-age atmospheric CO2 decline. PMID:27029225

  7. Oxygen depletion recorded in upper waters of the glacial Southern Ocean

    NASA Astrophysics Data System (ADS)

    Lu, Zunli; Hoogakker, Babette A. A.; Hillenbrand, Claus-Dieter; Zhou, Xiaoli; Thomas, Ellen; Gutchess, Kristina M.; Lu, Wanyi; Jones, Luke; Rickaby, Rosalind E. M.

    2016-03-01

    Oxygen depletion in the upper ocean is commonly associated with poor ventilation and storage of respired carbon, potentially linked to atmospheric CO2 levels. Iodine to calcium ratios (I/Ca) in recent planktonic foraminifera suggest that values less than ~2.5 μmol mol-1 indicate the presence of O2-depleted water. Here we apply this proxy to estimate past dissolved oxygen concentrations in the near surface waters of the currently well-oxygenated Southern Ocean, which played a critical role in carbon sequestration during glacial times. A down-core planktonic I/Ca record from south of the Antarctic Polar Front (APF) suggests that minimum O2 concentrations in the upper ocean fell below 70 μmol kg-1 during the last two glacial periods, indicating persistent glacial O2 depletion at the heart of the carbon engine of the Earth's climate system. These new estimates of past ocean oxygenation variability may assist in resolving mechanisms responsible for the much-debated ice-age atmospheric CO2 decline.

  8. Coastal zone color scanner pigment concentrations in the southern ocean and relationships to geophysical surface features

    SciTech Connect

    Comiso, J.C.; McClain, C.R. ); Sullivan, C.W. ); Ryan, J.P. ); Leonard, C.L. )

    1993-02-15

    The spatial and seasonal distributions of phytoplankton pigment concentration over the entire southern ocean have been studied for the first time using the coastal zone color scanner historical data set (from October 1978 through June 1986). Enhanced pigment concentrations are observed between 35[degrees]S and 55[degrees]S throughout the year, with such enhanced regions being more confined to the south in the austral summer and extending further north in the winter. North and south of the polar front, phytoplankton blooms (>1 mg/m[sup 3]) are not uniformly distributed around the circumpolar region. Instead, blooms appear to be located in regions of ice retreat (or high melt areas) such as the Scotia Sea and the Ross Sea, in relatively shallow areas (e.g., the Patagonian and the New Zealand shelves), in some regions of Ekman upwelling like the Tasman Sea, and near areas of high eddy kinetic such as the Agulhas retroflection. Among all features examined by regression analysis, bathymetry appears to be the one most consistently correlated with pigments (correlation coefficient being about [minus]0.3 for the entire region). The cause of negative correlation with bathymetry is unknown but is consistent with the observed abundance of iron in shallow areas in the Antarctic region. It is also consistent with resuspension of phytoplankton cells by wind-induced mixing, especially in shallow waters. Nutrients (phosphate, nitrate, and silicate) are found to correlate significantly with pigments when the entire southern ocean is considered, but south of 55[degrees]S the correlation is poor, probably because the Antarctic waters are not nutrient limited. Large interannual variability (>30%) in average pigment concentration over the entire region during different seasons indicates possible influence of time dependent parameters. 66 refs., 13 figs., 6 tabs.

  9. Sedimentary sequences of the Pacific-Indian Ocean sector of the Antarctic continental margin

    SciTech Connect

    Cooper, A.; Eittreim, S. ); Anderson, J. ); Stagg, H. )

    1990-06-01

    Seismic-reflection data across the Pacific-Indian Ocean sector of the Antarctic continental margin commonly reveal preglacial and glacial sedimentary sections up to 14 km thick. In this sector, diverse tectonic regimes have controlled the locations of preglacial rift deposits as well as glacial-till deltas. These regimes include major rift embayments, passive margins, formerly active and presently active margins, and active rifts. The sedimentary sections are principally of Mesozoic and Cenozoic age, although Paleozoic strata may exist at great depth. The upper parts of these sections commonly comprise prograding and aggrading sigmoidal sequences that are separated by unconformities and are up to 6 km thick. Where drilled in Prydz Bay and the Ross Sea, these upper sequences are solely glacial marine rocks of early Oligocene and younger age. The lower portions of the sections are commonly well-layered sequences that infill structural basins. The evolution of these sedimentary sequences is strongly controlled by extensional tectonic processes. Depocenters are located primarily within rift structures that formed initially during Gondwana breakup and later during magmatic-arc development. Rift-related deposits fill the basement grabens and are unconformably covered by glacial-till deltas. The till deltas apparently have been deposited beneath and at the front of former grounded ice sheets that selectively moved through rift embayments and over thermally subsiding margins. Since initial Cenozoic glaciation, these thick till deltas have prograded the continental shelf edge up to 70 km seaward to its present location. The sedimentary sequences underlying the Antarctic margin hold a record of Antarctic (Gondwana) rifting and glaciation - a record that would, if drilled, greatly improve their understanding of global climate and sea-level changes.

  10. Using Satellite-derived Ice Concentration to Represent Antarctic Coastal Polynyas in Ocean Climate Models

    NASA Technical Reports Server (NTRS)

    Stoessel, Achim; Markus, Thorsten

    2003-01-01

    The focus of this paper is on the representation of Antarctic coastal polynyas in global ice-ocean general circulation models (OGCMs), in particular their local, regional, and high-frequency behavior. This is verified with the aid of daily ice concentration derived from satellite passive microwave data using the NASATeam 2 (NT2) and the bootstrap (BS) algorithms. Large systematic regional and temporal discrepancies arise, some of which are related to the type of convection parameterization used in the model. An attempt is made to improve the fresh-water flux associated with melting and freezing in Antarctic coastal polynyas by ingesting (assimilating) satellite ice concentration where it comes to determining the thermodynamics of the open-water fraction of a model grid cell. Since the NT2 coastal open-water fraction (polynyas) tends to be less extensive than the simulated one in the decisive season and region, assimilating NT2 coastal ice concentration yields overall reduced net freezing rates, smaller formation rates of Antarctic Bottom Water, and a stronger southward flow of North Atlantic Deep Water across 30 S. Enhanced net freezing rates occur regionally when NT2 coastal ice concentration is assimilated, concomitant with a more realistic ice thickness distribution and accumulation of High-Salinity Shelf Water. Assimilating BS rather than NT2 coastal ice concentration, the differences to the non-assimilated simulation are generally smaller and of opposite sign. This suggests that the model reproduces coastal ice concentration in closer agreement with the BS data than with the NT2 data, while more realistic features emerge when NT2 data are assimilated.

  11. Large-amplitude gravity waves above the southern Andes, the Drake Passage, and the Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    de la Torre, A.; Alexander, P.; Hierro, R.; Llamedo, P.; Rolla, A.; Schmidt, T.; Wickert, J.

    2012-01-01

    Above the southern Andes range and its prolongation in the Antarctic Peninsula, large-amplitude mountain and shear gravity waves observed with Weather Research and Forecasting (WRF) mesoscale model simulations during winter 2009 are analyzed. Two specific reasons motivated this study: (1) a decade of satellite observations of temperature fluctuations in the stratosphere, allowing us to infer that this region may be launching the largest-amplitude gravity waves into the upper atmosphere, and (2) the recent design of a research program to investigate these features in detail, the Southern Andes Antarctic Gravity wave Initiative (SAANGRIA). The simulations are forced with ERA-Interim data from the European Centre for Medium-Range Weather Forecasts. The approach selected for the regional downscaling is based on consecutive integrations with weekly reinitialization with 24 h of spin-up, and the outputs during this period are excluded from the analysis. From 1 June to 31 August 2009, five case studies were selected on the basis of their outstanding characteristics and large wave amplitudes. In general, one or two prevailing modes of oscillation are identified after applying continuous wavelet transforms at constant pressure levels and perpendicularly to the nominal orientation of the dominant wave crests. In all cases, the dominant modes are characterized by horizontal wavelengths around 50 km. Their vertical wavelengths, depending on a usually strong background wind shear, are estimated to be between 2 and 11 km. The corresponding intrinsic periods range between 10 and 140 min. In general, the estimated vertical wavelength (intrinsic period) maximizes (minimizes) around 250-300 hPa. The synoptic circulation for each case is described. Zonal and meridional components of the vertical flux of horizontal momentum are shown in detail for each case, including possible horizontal wavelengths between 12 and 400 km. Large values of this flux are observed at higher pressure

  12. Biological and physical controls in the Southern Ocean on past millennial-scale atmospheric CO2 changes.

    PubMed

    Gottschalk, Julia; Skinner, Luke C; Lippold, Jörg; Vogel, Hendrik; Frank, Norbert; Jaccard, Samuel L; Waelbroeck, Claire

    2016-01-01

    Millennial-scale climate changes during the last glacial period and deglaciation were accompanied by rapid changes in atmospheric CO2 that remain unexplained. While the role of the Southern Ocean as a 'control valve' on ocean-atmosphere CO2 exchange has been emphasized, the exact nature of this role, in particular the relative contributions of physical (for example, ocean dynamics and air-sea gas exchange) versus biological processes (for example, export productivity), remains poorly constrained. Here we combine reconstructions of bottom-water [O2], export production and (14)C ventilation ages in the sub-Antarctic Atlantic, and show that atmospheric CO2 pulses during the last glacial- and deglacial periods were consistently accompanied by decreases in the biological export of carbon and increases in deep-ocean ventilation via southern-sourced water masses. These findings demonstrate how the Southern Ocean's 'organic carbon pump' has exerted a tight control on atmospheric CO2, and thus global climate, specifically via a synergy of both physical and biological processes. PMID:27187527

  13. Biological and physical controls in the Southern Ocean on past millennial-scale atmospheric CO2 changes

    NASA Astrophysics Data System (ADS)

    Gottschalk, Julia; Skinner, Luke C.; Lippold, Jörg; Vogel, Hendrik; Frank, Norbert; Jaccard, Samuel L.; Waelbroeck, Claire

    2016-05-01

    Millennial-scale climate changes during the last glacial period and deglaciation were accompanied by rapid changes in atmospheric CO2 that remain unexplained. While the role of the Southern Ocean as a 'control valve' on ocean-atmosphere CO2 exchange has been emphasized, the exact nature of this role, in particular the relative contributions of physical (for example, ocean dynamics and air-sea gas exchange) versus biological processes (for example, export productivity), remains poorly constrained. Here we combine reconstructions of bottom-water [O2], export production and 14C ventilation ages in the sub-Antarctic Atlantic, and show that atmospheric CO2 pulses during the last glacial- and deglacial periods were consistently accompanied by decreases in the biological export of carbon and increases in deep-ocean ventilation via southern-sourced water masses. These findings demonstrate how the Southern Ocean's 'organic carbon pump' has exerted a tight control on atmospheric CO2, and thus global climate, specifically via a synergy of both physical and biological processes.

  14. 2015 Antarctic Maximum Sea Ice Extent Breaks Streak of Record Highs

    NASA Video Gallery

    Antarctic sea ice likely reached its annual maximum extent on Oct. 6, barring a late season surge. This video shows the evolution of the sea ice cover of the Southern Ocean from its minimum yearly ...

  15. Southern Ocean nutrient trapping and the efficiency of the biological pump

    NASA Astrophysics Data System (ADS)

    Primeau, FrançOis W.; Holzer, Mark; Devries, Timothy

    2013-05-01

    We present a data-assimilated model of the ocean's phosphorus cycle that is constrained by climatological phosphate, temperature, salinity, sea-surface height, surface heat and freshwater fluxes, as well as chlorofluorocarbon-11(CFC-11) and natural Δ14C. Export production is estimated to be 5.8±2.0×1012 mol P/yr of which (26±6)% originates in the Southern Ocean (SO) south of 40°S. The biological pump efficiency, defined as the proportion of the ocean's phosphate inventory that is regenerated, is (39±7)%. Dividing the SO south of 40°S into a sub-Antarctic zone (SANTZ) and an Antarctic zone (ANTZ) separated by the latitude of maximum Ekman divergence, we estimate that the SANTZ and ANTZ account, respectively, for (23±5)% and (3±1)% of global export production, (17±4)% and (3±1)% of the regenerated nutrient inventory, and (31±1)% and (43±5)% of the preformed nutrient inventory. Idealized SO nutrient depletion experiments reveal a large-scale transfer of nutrients into circumpolar and deep waters and from the preformed to the regenerated pool. In accord with the concept of the biogeochemical divide, we find that nutrient drawdown in the ANTZ is more effective than in the SANTZ for increasing the efficiency of the biological pump, while having a smaller impact on production in regions north of 40°S. Complete SO nutrient drawdown would allow the biological pump to operate at 94% efficiency by short circuiting the transport of nutrients in northward Ekman currents, leading to a trapping of nutrients in circumpolar and deep waters that would decrease production outside the SO by approximately 44% while increasing it in the SO by more than 725%.

  16. Antarctic, Sub-Antarctic and cold temperate echinoid database

    PubMed Central

    Pierrat, Benjamin; Saucède, Thomas; Festeau, Alain; David, Bruno

    2012-01-01

    Abstract This database includes spatial data of Antarctic, Sub-Antarctic and cold temperate echinoid distribution (Echinodermata: Echinoidea) collected during many oceanographic campaigns led in the Southern Hemisphere from 1872 to 2010. The dataset lists occurrence data of echinoid distribution south of 35°S latitude, together with information on taxonomy (from species to genus level), sampling sources (cruise ID, sampling dates, ship names) and sampling sites (geographic coordinates and depth). Echinoid occurrence data were compiled from the Antarctic Echinoid Database (David et al. 2005a), which integrates records from oceanographic cruises led in the Southern Ocean until 2003. This database has been upgraded to take into account data from oceanographic cruises led after 2003. The dataset now reaches a total of 6160 occurrence data that have been checked for systematics reliability and consistency. It constitutes today the most complete database on Antarctic and Sub-Antarctic echinoids. PMID:22787419

  17. Bacterial community dynamics during polysaccharide degradation at contrasting sites in the Southern and Atlantic Oceans.

    PubMed

    Wietz, Matthias; Wemheuer, Bernd; Simon, Heike; Giebel, Helge-Ansgar; Seibt, Maren A; Daniel, Rolf; Brinkhoff, Thorsten; Simon, Meinhard

    2015-10-01

    The bacterial degradation of polysaccharides is central to marine carbon cycling, but little is known about the bacterial taxa that degrade specific marine polysaccharides. Here, bacterial growth and community dynamics were studied during the degradation of the polysaccharides chitin, alginate and agarose in microcosm experiments at four contrasting locations in the Southern and Atlantic Oceans. At the Southern polar front, chitin-supplemented microcosms were characterized by higher fractions of actively growing cells and a community shift from Alphaproteobacteria to Gammaproteobacteria and Bacteroidetes. At the Antarctic ice shelf, chitin degradation was associated with growth of Bacteroidetes, with 24% higher cell numbers compared with the control. At the Patagonian continental shelf, alginate and agarose degradation covaried with growth of different Alteromonadaceae populations, each with specific temporal growth patterns. At the Mauritanian upwelling, only the alginate hydrolysis product guluronate was consumed, coincident with increasing abundances of Alteromonadaceae and possibly cross-feeding SAR11. 16S rRNA gene amplicon libraries indicated that growth of the Bacteroidetes-affiliated genus Reichenbachiella was stimulated by chitin at all cold and temperate water stations, suggesting comparable ecological roles over wide geographical scales. Overall, the predominance of location-specific patterns showed that bacterial communities from contrasting oceanic biomes have members with different potentials to hydrolyse polysaccharides. PMID:25753990

  18. A Southern Indian Ocean database of hydrographic profiles obtained with instrumented elephant seals.

    PubMed

    Roquet, Fabien; Williams, Guy; Hindell, Mark A; Harcourt, Rob; McMahon, Clive; Guinet, Christophe; Charrassin, Jean-Benoit; Reverdin, Gilles; Boehme, Lars; Lovell, Phil; Fedak, Mike

    2014-01-01

    The instrumentation of southern elephant seals with satellite-linked CTD tags has offered unique temporal and spatial coverage of the Southern Indian Ocean since 2004. This includes extensive data from the Antarctic continental slope and shelf regions during the winter months, which is outside the conventional areas of Argo autonomous floats and ship-based studies. This landmark dataset of around 75,000 temperature and salinity profiles from 20-140 °E, concentrated on the sector between the Kerguelen Islands and Prydz Bay, continues to grow through the coordinated efforts of French and Australian marine research teams. The seal data are quality controlled and calibrated using delayed-mode techniques involving comparisons with other existing profiles as well as cross-comparisons similar to established protocols within the Argo community, with a resulting accuracy of ±0.03 °C in temperature and ±0.05 in salinity or better. The data offer invaluable new insights into the water masses, oceanographic processes and provides a vital tool for oceanographers seeking to advance our understanding of this key component of the global ocean climate. PMID:25977785

  19. A Southern Indian Ocean database of hydrographic profiles obtained with instrumented elephant seals

    PubMed Central

    Roquet, Fabien; Williams, Guy; Hindell, Mark A.; Harcourt, Rob; McMahon, Clive; Guinet, Christophe; Charrassin, Jean-Benoit; Reverdin, Gilles; Boehme, Lars; Lovell, Phil; Fedak, Mike

    2014-01-01

    The instrumentation of southern elephant seals with satellite-linked CTD tags has offered unique temporal and spatial coverage of the Southern Indian Ocean since 2004. This includes extensive data from the Antarctic continental slope and shelf regions during the winter months, which is outside the conventional areas of Argo autonomous floats and ship-based studies. This landmark dataset of around 75,000 temperature and salinity profiles from 20–140 °E, concentrated on the sector between the Kerguelen Islands and Prydz Bay, continues to grow through the coordinated efforts of French and Australian marine research teams. The seal data are quality controlled and calibrated using delayed-mode techniques involving comparisons with other existing profiles as well as cross-comparisons similar to established protocols within the Argo community, with a resulting accuracy of ±0.03 °C in temperature and ±0.05 in salinity or better. The data offer invaluable new insights into the water masses, oceanographic processes and provides a vital tool for oceanographers seeking to advance our understanding of this key component of the global ocean climate. PMID:25977785

  20. Patterns of marine bacterioplankton biodiversity in the surface waters of the Scotia Arc, Southern Ocean.

    PubMed

    Jamieson, Rachel E; Rogers, Alex D; Billett, David S M; Smale, Dan A; Pearce, David A

    2012-05-01

    Spatial patchiness in marine surface bacterioplankton populations was investigated in the Southern Ocean, where the Antarctic Circumpolar Current meets the islands of the Scotia Arc and is subjected to terrestrial input, upwelling of nutrients and seasonal phytoplankton blooms. Total bacterioplankton population density, group-specific taxonomic distribution and six of eight dominant members of the bacterioplankton community were found to be consistent across 18 nearshore sites at eight locations around the Scotia Arc. Results from seven independent 16S rRNA gene clone libraries (1223 sequences in total) and fluorescent in situ hybridization suggested that microbial assemblages were predominantly homogeneous between Scotia Arc sites, where the Alphaproteobacteria, Gammaproteobacteria and the Cytophaga-Flavobacterium-Bacteroidetes cluster were the dominant bacterial groups. Of the 1223 useable sequences generated, 1087 (89%) shared ≥ 97% similarity with marine microorganisms and 331 (27%) matched published sequences previously detected in permanently cold Arctic and Antarctic marine environments. Taken together, results suggest that the dominant bacterioplankton groups are consistent between locations, but significant differences may be detected across the rare biodiversity. PMID:22273466

  1. The impact of Southern Ocean gateways on the Cenozoic climate evolution

    NASA Astrophysics Data System (ADS)

    von der Heydt, Anna; Viebahn, Jan; Dijkstra, Henk

    2016-04-01

    During the Cenozoic period, which covers the last 65 Million (Ma) years, Earth's climate has undergone a major long-term transition from warm "greenhouse" to colder "icehouse" conditions with extensive ice sheets in the polar regions of both hemispheres. On the very long term the gradual cooling may be seen as response to the overall slowly decreasing atmospheric CO2-concentration due to weathering processes in the Earth System, however, continental geometry has changed considerably over this period and the long-term gradual trend was interrupted, by several rapid transitions as well as periods where temperature and greenhouse gas concentrations seem to be decoupled. The Eocene-Oligocene boundary (˜34 Ma, E/O) and mid-Miocene climatic transition (˜13 Ma, MCT) reflect major phases of Antarctic ice sheet build-up and global climate cooling, while Northern Hemisphere ice sheets developed much later, most likely at the Pliocene-Pleistocene transition (˜2.7Ma). Thresholds in atmospheric CO2-concentration together with feedback mechanisms related to land ice formation are now among the favoured mechanisms of these climatic transitions, while the long-proposed ocean circulation changes caused by opening of tectonic gateways seem to play a less direct role. The opening of the Southern Ocean gateways, notably the Drake Passage and the Tasman Gateway as well as the northward movement of Australia over this long time period, however, has eventually led to the development of today's strongest ocean current, the Antarctic Circumpolar Current (ACC), playing a major role in the transport properties of the global ocean circulation. The overall state of the global ocean circulation, therefore, preconditions the climate system to dramatic events such as major ice sheet formation. Here, we present results of a state-of-the art global climate model (CESM) under various continental configurations: (i) present day geometry, (ii) present day geometry with a closed Drake Passage and

  2. Antarctic sea ice control on ocean circulation in present and glacial climates.

    PubMed

    Ferrari, Raffaele; Jansen, Malte F; Adkins, Jess F; Burke, Andrea; Stewart, Andrew L; Thompson, Andrew F

    2014-06-17

    In the modern climate, the ocean below 2 km is mainly filled by waters sinking into the abyss around Antarctica and in the North Atlantic. Paleoproxies indicate that waters of North Atlantic origin were instead absent below 2 km at the Last Glacial Maximum, resulting in an expansion of the volume occupied by Antarctic origin waters. In this study we show that this rearrangement of deep water masses is dynamically linked to the expansion of summer sea ice around Antarctica. A simple theory further suggests that these deep waters only came to the surface under sea ice, which insulated them from atmospheric forcing, and were weakly mixed with overlying waters, thus being able to store carbon for long times. This unappreciated link between the expansion of sea ice and the appearance of a voluminous and insulated water mass may help quantify the ocean's role in regulating atmospheric carbon dioxide on glacial-interglacial timescales. Previous studies pointed to many independent changes in ocean physics to account for the observed swings in atmospheric carbon dioxide. Here it is shown that many of these changes are dynamically linked and therefore must co-occur. PMID:24889624

  3. Adaptations of phytoplankton in the Indian Ocean sector of the Southern Ocean during austral summer of 1998—2014

    NASA Astrophysics Data System (ADS)

    Mishra, R. K.; Naik, R. K.; Anil Kumar, N.

    2015-12-01

    This study investigates the effects of light and temperature on the surface water diatoms and chlorophytes, phytoplankton in the Indian Ocean sector of the Southern Ocean (SO) during the austral summer of 1998‒2014. Significant longitudinal variations in hydrographic and biological parameters were observed at the Sub tropical front (STF), Sub Antarctic front (SAF) and Polar front (PF) along 56°E‒58°E. The concentrations of total surface chlorophyll a ( Chl a), diatoms, and chlorophytes measured by the National Aeronautics Space Agency (NASA) estimated by the Sea-Viewing Wide Field-of-View Sensors (SeaWiFS), the Moderate Resolution Imaging Spectro Radiometer (MODIS), and the NASA Ocean Biological Model (NOBM) were used in the study. Variations in the concentration of total Chl a was remarkable amongst the fronts during the study period. The contribution of diatoms to the total concentration of surface Chl a increased towards south from the STF to the PF while it decreased in the case of chlorophytes. The maximum photosynthetically active radiation (PAR) was observed at the STF and it progressively decreased to the PF through the SAF. At the PF region the contribution of diatoms to the total Chl a biomass was ≥80%. On the other hand, the chlorophytes showed a contrary distribution pattern with ≥70% of the total Chl a biomass recorded at the STF which gradually decreased towards the PF, mainly attributed to the temperate adaptation. This clearly reveals that the trend of diatoms increased at the STF and decreased at the SAF and the PF. Further, the trend of chlorophytes was increased at the STF, SAF and PF with a shift in the community in the frontal system of the Indian Ocean sector of the SO.

  4. The Antarctic sea ice concentration budget of an ocean-sea ice coupled model

    NASA Astrophysics Data System (ADS)

    Lecomte, Olivier; Goosse, Hugues; Fichefet, Thierry; Holland, Paul R.; Uotila, Petteri

    2015-04-01

    The Antarctic sea ice concentration budget of the NEMO-LIM ocean-sea ice coupled model is computed and analyzed. Following a previously developed method, the sea ice concentration balance over the autumn-winter seasons is decomposed into four terms, including the sea ice concentration change during the period of interest, advection, divergence and a residual accounting for the net contribution of thermodynamics and ice deformation. Preliminary results from this analysis show that the geographical patterns of all budget terms over 1992-2010 are in qualitative agreement with the observed ones. Sea ice thermodynamic growth is maintained by horizontal divergence near the continent and in the central ice pack, while melting close to the ice edge is led by sea ice advection. Quantitatively however, the inner ice pack divergence and associated sea ice freezing are much stronger, as compared to observations. The advection of sea ice in both the central pack and the marginal areas are likewise stronger, which corroborates the findings of a previous study in which the same methods were applied to a fully coupled climate model. Nonetheless, the seasonal evolution of sea ice area and total extent are reasonably well simulated, since enhanced sea ice freezing due to larger divergence in the central pack is compensated by intensified melting in the outer pack owing to faster advection. Those strong dynamic components in the sea ice concentration budget are due to ice velocities that tend to be biased high all around Antarctica and particularly near the ice edge. The obtained results show that the applied method is particularly well suited for assessing the skills of an ocean-sea ice coupled model in simulating the seasonal and regional evolution of Antarctic sea ice for the proper physical reasons.

  5. Interannual and Regional Variability of Southern Ocean Snow on Sea Ice and its Correspondence with Sea Ice Cover and Atmospheric Circulation Patterns

    NASA Technical Reports Server (NTRS)

    Markus, T.; Cavalieri, D. J.

    2006-01-01

    Snow depth on sea ice plays a critical role in the heat exchange between ocean and atmosphere because of its thermal insulation property. Furthermore, a heavy snow load on the relatively thin Southern Ocean sea-ice cover submerges the ice floes below sea level, causing snow-to-ice conversion. Snowfall is also an important freshwater source into the weakly stratified ocean. Snow depth on sea-ice information can be used as an indirect measure of solid precipitation. Satellite passive microwave data are used to investigate the interannual and regional variability of the snow cover on sea ice. In this study we make use of 12 years (1992-2003) of Special Sensor Microwave/Imager (SSM/I) radiances to calculate average monthly snow depth on the Antarctic sea-ice cover. The results show a slight increase in snow depth and a partial eastward propagation of maximum snow depths, which may be related to the Antarctic Circumpolar Wave.

  6. Biogeochemical cycling of zinc and its isotopes in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Zhao, Y.; Vance, D.; Abouchami, W.; de Baar, H. J. W.

    2014-01-01

    We report Zn concentration and isotope data for seawater samples from the Atlantic sector of the Southern Ocean, collected during the IPY/GEOTRACES ANT-XXIV/III cruise along the Greenwich Zero Meridian. Data are reported for the full depth range of the water column at three stations, as well as a transect of surface samples, using a new analytical approach that is presented in detail here. Zn concentrations increase with depth, though due to proximity to upwelling sites, surface concentrations are not as low as in some parts of the ocean such as further northward into the Sub-Antarctic Zone. For two depth profiles south of the Polar Front Zone, the physical stratification of the upper water column is reflected in sudden near-surface changes in Zn concentration with depth. In contrast, beneath 100-300 m Zn concentrations barely change with depth. Zn isotopic data beneath 1000 m, for the Southern Ocean data presented here as well as published data from the North Atlantic and North Pacific, are strikingly homogeneous, with an average δ66Zn = +0.53 ± 0.14‰ (2SD, 2SE = 0.03, n = 21). The surface Southern Ocean is more variable, with δ66Zn ranging from 0.07‰ to 0.80‰. Between the two is a thin horizon at 40-80 m which, in the Southern Ocean as well as the North Atlantic and North Pacific, is characterised by distinctly light isotopic signatures, with δ66Zn about 0.3‰ lower than surface waters. Strong correlations between Si and Zn concentrations seen here and elsewhere, coupled to the lack of any systematic relationship between Si and Zn isotopes in the Southern Ocean, suggest that the removal of Zn associated with diatom opal involves little or no isotopic fractionation. Regeneration of this Zn also explains the homogeneous Zn isotopic composition of the global deep ocean so far sampled. However, the low Zn content of opal requires that deep ocean Zn does not directly come from the opal phase itself, but rather from associated organic material external to

  7. Iron Fertilization in the Southern Ocean Deduced From Environmental Magnetism of Sediment Cores

    NASA Astrophysics Data System (ADS)

    Yamazaki, T.; Ikehara, M.

    2012-12-01

    With rock-magnetic technique, biogenic magnetites in sediments can be detected utilizing the characteristics of almost no magnetostatic interactions and narrow coercivity distribution, reflecting occurrence of single-domain magnetites in a chain (e.g., Egli et al., 2010; Roberts et al., 2011). Magnetic mineral assemblages in pelagic sediments of Pacific and Indian Oceans often have two distinctive constituents; the first is characterized by non-interacting on first-order reversal curve (FORC) diagrams and low-coercivity (~40 mT) with small dispersion on isothermal remanent magnetization (IRM) component analyses, and the second is characterized by interacting and middle-coercivity (~100 mT). The former is interpreted as biogenic magnetites and the latter is terrigenous maghemites (Yamazaki, 2009; 2012). The ratio of anhysteretic remanent magnetization susceptibility to saturation IRM reflects relative abundance of the biogenic and terrigenous components. In the Southern Ocean, magnetic mineral concentration increases in glacial periods. The variation pattern closely resembles eolian dust flux records from Antarctic ice cores, but the cause of the linkage was unclear, as the dust flux is too small for the source of terrigenous materials in the Southern Ocean. Our environmental magnetic study of late Pleistocene sediments from the south Indian Ocean revealed that biogenic magnetites are a dominant constituent of the magnetic minerals. In glacials, the abundance of both biogenic and terrigenous components increased with increased proportions of the latter. Increased ocean productivity in glacials is suggested from increased proportions of biogenic magnetites with elongated morphologies, indicative of less-oxic conditions, and increased sedimentation rates. These observations suggest that the increased magnetic concentration in glacials in the Southern Ocean may be explained by iron fertilization; the production of biogenic magnetites was enhanced associated with

  8. Temporal variations and trends of CFC11 and CFC12 surface-water saturations in Antarctic marginal seas: Results of a regional ocean circulation model

    NASA Astrophysics Data System (ADS)

    Rodehacke, Christian B.; Roether, Wolfgang; Hellmer, Hartmut H.; Hall, Timothy

    2010-02-01

    The knowledge of chlorofluorocarbon (CFC11, CFC12) concentrations in ocean surface waters is a prerequisite for deriving formation rates of, and water mass ages in, deep and bottom waters on the basis of CFC data. In the Antarctic coastal region, surface-layer data are sparse in time and space, primarily due to the limited accessibility of the region. To help filling this gap, we carried out CFC simulations using a regional ocean general circulation model (OGCM) for the Southern Ocean, which includes the ocean-ice shelf interaction. The simulated surface layer saturations, i.e. the actual surface concentrations relative to solubility-equilibrium values, are verified against available observations. The CFC surface saturations driven by concentration gradients between atmosphere and ocean are controlled mainly by the sea ice cover, sea surface temperature, and salinity. However, no uniform explanation exists for the controlling mechanisms. Here, we present simulated long-term trends and seasonal variations of surface-layer saturation at Southern Ocean deep and bottom water formation sites and other key regions, and we discuss differences between these regions. The amplitudes of the seasonal saturation cycle vary from 22% to 66% and their long-term trends range from 0.1%/year to 0.9%/year. The seasonal surface saturation maximum lags the ice cover minimum by two months. By utilizing observed bottle data the full seasonal CFC saturation cycle can be determined offering the possibility to predict long-term trends in the future. We show that ignoring the trends and using instead the saturations actually observed can lead to systematic errors in deduced inventory-based formation rates by up to 10% and suggest an erroneous decline with time.

  9. Influence of the Southern Ocean on the Global deep ocean stratification

    NASA Astrophysics Data System (ADS)

    Sun, S.; Eisenman, I.; Stewart, A.

    2015-12-01

    The stratification of the deep ocean plays a key role in the climate system by influencing the ocean circulation and regulating the outgassing of CO2. Previous studies have suggested that Southern Ocean processes control the global ocean stratification below the main thermocline (i.e., below ~500m). In this study, three ocean-only simulations are carried out with the Community Earth System Model (CESM1): one control simulation forced with Pre-industrial (PI) surface conditions, a second control simulation forced with Last Glacial Maximum (LGM) surface conditions, and a test simulation forced with LGM surface conditions in southern high latitudes and PI surface conditions elsewhere. We find that the test simulation does broadly reproduce the LGM density stratification of the global ocean below 2000m, but not at intermediate depths between 500m and 1500m. We propose a mechanism whereby the stratification of the intermediate-depth waters is influenced by the differing effects on the surface buoyancy distribution of fixed versus restoring aspects of the surface buoyancy forcing. This implies the Southern Ocean exerts less influence over the global deep ocean stratification than has been previously suggested, at least when considering the difference between LGM and PI climates in CESM1.

  10. Tropical inter-annual SST oscillations and Southern Ocean swells

    NASA Astrophysics Data System (ADS)

    Fan, Yalin; Rogers, Erick; Jensen, Tommy

    2016-04-01

    The possibility of teleconnections between Southern Ocean swells and sea surface temperature (SST) anomalies on inter-annual time scales in the Eastern Pacific Niño3 region and southeastern Indian Ocean is investigated using numerical wave models. Two alternative parameterizations for swell dissipation are used. It is found that swell dissipation in the models is not directly correlated with large inter-annual variations such as the El Nino - Southern Oscillation (ENSO) or Indian Ocean Dipole (IOD). However, using one of the two swell dissipation parameterizations, a correlation is found between observed SST anomalies and the modification of turbulent kinetic energy flux (TKEF) by Southern Ocean swells due to the damping of short wind waves: modeled reduction of TKEF is in opposite phase with the SST anomalies in the Niño-3 region, indicating a potential positive feedback. The modeled bi-monthly averaged TKEF reduction in the southeastern Indian Ocean is also well correlated with the IOD mode.

  11. Southern Ocean air-sea heat flux, SST spatial anomalies, and implications for multi-decadal upper ocean heat content trends.

    NASA Astrophysics Data System (ADS)

    Tamsitt, V. M.; Talley, L. D.; Mazloff, M. R.

    2014-12-01

    The Southern Ocean displays a zonal dipole (wavenumber one) pattern in sea surface temperature (SST), with a cool zonal anomaly in the Atlantic and Indian sectors and a warm zonal anomaly in the Pacific sector, associated with the large northward excursion of the Malvinas and southeastward flow of the Antarctic Circumpolar Current (ACC). To the north of the cool Indian sector is the warm, narrow Agulhas Return Current (ARC). Air-sea heat flux is largely the inverse of this SST pattern, with ocean heat gain in the Atlantic/Indian, cooling in the southeastward-flowing ARC, and cooling in the Pacific, based on adjusted fluxes from the Southern Ocean State Estimate (SOSE), a ⅙° eddy permitting model constrained to all available in situ data. This heat flux pattern is dominated by turbulent heat loss from the ocean (latent and sensible), proportional to perturbations in the difference between SST and surface air temperature, which are maintained by ocean advection. Locally in the Indian sector, intense heat loss along the ARC is contrasted by ocean heat gain of 0.11 PW south of the ARC. The IPCC AR5 50 year depth-averaged 0-700 m temperature trend shows surprising similarities in its spatial pattern, with upper ocean warming in the ARC contrasted by cooling to the south. Using diagnosed heat budget terms from the most recent (June 2014) 6-year run of the SOSE we find that surface cooling in the ARC is balanced by heating from south-eastward advection by the current whereas heat gain in the ACC is balanced by cooling due to northward Ekman transport driven by strong westerly winds. These results suggest that spatial patterns in multi-decadal upper ocean temperature trends depend on regional variations in upper ocean dynamics.

  12. Intense summer Si-recycling in the surface Southern Ocean

    NASA Astrophysics Data System (ADS)

    Beucher, Charlotte; Tréguer, Paul; Hapette, Ana-Maria; Corvaisier, Rudolph; Metzl, Nicolas; Pichon, Jean-Jacques

    2004-05-01

    Si-cycle in surface waters was investigated in summer 2003 during a transect conducted from south-Australia to Antarctica. Diatoms dominated the microphytoplankton. Silicic acid was depleted up to 60°S a subsurface maximum of biogenic silica (= biosilica) was observed in the Permanent Open Ocean Zone. In the 100-0.01% light zone, the ratio of depth-integrated biosilica dissolution rate (D) to depth-integrated biosilica production rate (P) ranged between 0 to 3.1, being >1 for 5 of our 6 stations. The biosilica dissolution was related to the percentage of dead diatoms but not to the temperature and might be, at least partially, under bacteria mediation. This study shows that during summer the Southern Ocean silicate pump can be much less efficient than usually expected. Existence of scenarios with intense surface Si-recycling in the Southern Ocean has major consequences both for modelers and paleoceanographers.

  13. Microbial ecology of Antarctic aquatic systems.

    PubMed

    Cavicchioli, Ricardo

    2015-11-01

    The Earth's biosphere is dominated by cold environments, and the cold biosphere is dominated by microorganisms. Microorganisms in cold Southern Ocean waters are recognized for having crucial roles in global biogeochemical cycles, including carbon sequestration, whereas microorganisms in other Antarctic aquatic biomes are not as well understood. In this Review, I consider what has been learned about Antarctic aquatic microbial ecology from 'omic' studies. I assess the factors that shape the biogeography of Antarctic microorganisms, reflect on some of the unusual biogeochemical cycles that they are associated with and discuss the important roles that viruses have in controlling ecosystem function. PMID:26456925

  14. Biological and physical controls in the Southern Ocean on past millennial-scale atmospheric CO2 changes

    PubMed Central

    Gottschalk, Julia; Skinner, Luke C.; Lippold, Jörg; Vogel, Hendrik; Frank, Norbert; Jaccard, Samuel L.; Waelbroeck, Claire

    2016-01-01

    Millennial-scale climate changes during the last glacial period and deglaciation were accompanied by rapid changes in atmospheric CO2 that remain unexplained. While the role of the Southern Ocean as a 'control valve' on ocean–atmosphere CO2 exchange has been emphasized, the exact nature of this role, in particular the relative contributions of physical (for example, ocean dynamics and air–sea gas exchange) versus biological processes (for example, export productivity), remains poorly constrained. Here we combine reconstructions of bottom-water [O2], export production and 14C ventilation ages in the sub-Antarctic Atlantic, and show that atmospheric CO2 pulses during the last glacial- and deglacial periods were consistently accompanied by decreases in the biological export of carbon and increases in deep-ocean ventilation via southern-sourced water masses. These findings demonstrate how the Southern Ocean's 'organic carbon pump' has exerted a tight control on atmospheric CO2, and thus global climate, specifically via a synergy of both physical and biological processes. PMID:27187527

  15. Effects of Whaling on the Structure of the Southern Ocean Food Web: Insights on the “Krill Surplus” from Ecosystem Modelling

    PubMed Central

    Surma, Szymon; Pakhomov, Evgeny A.; Pitcher, Tony J.

    2014-01-01

    The aim of this study was to examine the ecological plausibility of the “krill surplus” hypothesis and the effects of whaling on the Southern Ocean food web using mass-balance ecosystem modelling. The depletion trajectory and unexploited biomass of each rorqual population in the Antarctic was reconstructed using yearly catch records and a set of species-specific surplus production models. The resulting estimates of the unexploited biomass of Antarctic rorquals were used to construct an Ecopath model of the Southern Ocean food web existing in 1900. The rorqual depletion trajectory was then used in an Ecosim scenario to drive rorqual biomasses and examine the “krill surplus” phenomenon and whaling effects on the food web in the years 1900–2008. An additional suite of Ecosim scenarios reflecting several hypothetical trends in Southern Ocean primary productivity were employed to examine the effect of bottom-up forcing on the documented krill biomass trend. The output of the Ecosim scenarios indicated that while the “krill surplus” hypothesis is a plausible explanation of the biomass trends observed in some penguin and pinniped species in the mid-20th century, the excess krill biomass was most likely eliminated by a rapid decline in primary productivity in the years 1975–1995. Our findings suggest that changes in physical conditions in the Southern Ocean during this time period could have eliminated the ecological effects of rorqual depletion, although the mechanism responsible is currently unknown. Furthermore, a decline in iron bioavailability due to rorqual depletion may have contributed to the rapid decline in overall Southern Ocean productivity during the last quarter of the 20th century. The results of this study underscore the need for further research on historical changes in the roles of top-down and bottom-up forcing in structuring the Southern Ocean food web. PMID:25517505

  16. Three Plate Reconstruction in the Eastern Indian Ocean: New Constraints on Wharton and Australian-Antarctic basins

    NASA Astrophysics Data System (ADS)

    Jacob, J.; Dyment, J.

    2012-12-01

    Understanding the continuous seismicity and repeated occurrence of major earthquakes in Sumatra and the neighboring area requires detailed constrains on the subducting plate. In this study we analyze the past plate kinematics evolution of the Wharton basin, eastern Indian Ocean through a three plate reconstruction involving Australia (AUS), Antarctica (ANT), and India (IND). We compile marine magnetic identifications in the Australian-Antarctic Basin [1,2], the Crozet and Central Indian basins (Yatheesh et al, in prep.) and the Wharton Basin [3]. The Wharton Basin is characterized by an extinct spreading center dated by anomaly 18 (38 Ma). The southern flank of the basin exhibits a continuous sequence of anomalies 20n (42 Ma) to 34n (84 Ma), whereas the northern flank lacks some of the older anomalies because a significant part has been subducted in the Sunda Trench. The three-plate reconstructions have provided set of rotation parameters describing the evolution of IND-AUS. Using these parameters, we have reconstructed the missing isochrons of the northern flank and the detailed geometry of the subducted part of the Wharton basin. Such an exercise provides useful constraints on the age and structure of the plate in subduction under Indonesia. As a byproduct, the three plate reconstruction provided set of rotation parameters for AUS-ANT as well, which constrains the conjugate fit between the basins. Previous studies [1,2,4,5] have achieved such a fit on the base of ill-defined fracture zones. We consider the well-defined fracture zones from the Crozet, Central Indian, and Wharton basins, but avoid using the poor fracture zone imprints from the Australian-Antarctic Basin. As a result from this approach, we conclude that the relative motion of AUS with respect to ANT initially followed a north-south direction, then changed to northwest-southeast at anomaly 32ny, and reverted to northeast southwest at anomaly 24no prior to the establishment of the Southeast Indian

  17. A subwaveform threshold retracker for ERS-1 altimetry: A case study in the Antarctic Ocean

    NASA Astrophysics Data System (ADS)

    Yang, Yuande; Hwang, Cheinway; Hsu, Hung-Jui; Dongchen, E.; Wang, Haihong

    2012-04-01

    Based on a correlation analysis method, a subwaveform threshold retracker is developed and coded in FORTRAN for satellite altimetry to determine the leading edge and retracking gate, and to improve the precision of sea surface heights (SSHs) and gravity anomalies (GAs). Using ERS-1/ERM waveforms, the subwaveform threshold retracker outperforms full-waveform threshold retrackers at the tide gage Port Station. A direct comparison between retracked SSHs and in situ SSHs is made at tide gage Port Station. Here the subwaveform retracking improves SSH precision from 0.241 to 0.193 m, yielding an improvement percentage (IMP) of 20%. Using ERS-1/GM waveforms, the subwaveform threshold retracker outperforms the Beta-5 and full-waveform threshold retrackers over the Bellingshausen and Amundsen Seas (BAS) in the Antarctic Ocean. The standard deviations of raw and retracked SSHs are 0.157 and 0.070 and 1.836 and 0.220 m over the ice-free and ice-covered oceans, corresponding to IMPs of 54.4% and 88%, respectively. Use of retracking improves the precision of GAs by up to 46.6% when comparing altimeter-derived and shipborne GAs.

  18. How North Atlantic cooling alters Southern Ocean wind

    NASA Astrophysics Data System (ADS)

    Schultz, Colin

    2011-07-01

    At least seven times during the last ice age, large portions of the polar glaciers crumbled, sending rafts of ice floating into the North Atlantic Ocean. When these icebergs melted, the resultant injection of cold freshwater was enough to drive down ocean temperatures by as much as 12°C. These so-called Heinrich events are associated with rising atmospheric carbon dioxide (CO2) levels, but a mechanism to explain the connection convincingly has yet to arise. One proposed explanation sees the melting-iceberg-triggered North Atlantic cooling tied to increases in CO2 venting from the Southern Ocean, which surrounds Antarctica, through increased wind-driven upwelling. To test this hypothesis, which was initially proposed by researchers in 2009 based on paleoclimate evidence, Lee et al. ran ocean-atmosphere coupled climate simulations to determine the physical mechanism that could support this cross-hemisphere connection. (Paleoceanography, doi:10.1029/ 2010PA002004, 2011)

  19. Genetic affinities between trans-oceanic populations of non-buoyant macroalgae in the high latitudes of the Southern Hemisphere.

    PubMed

    Fraser, Ceridwen I; Zuccarello, Giuseppe C; Spencer, Hamish G; Salvatore, Laura C; Garcia, Gabriella R; Waters, Jonathan M

    2013-01-01

    Marine biologists and biogeographers have long been puzzled by apparently non-dispersive coastal taxa that nonetheless have extensive transoceanic distributions. We here carried out a broad-scale phylogeographic study to test whether two widespread Southern Hemisphere species of non-buoyant littoral macroalgae are capable of long-distance dispersal. Samples were collected from along the coasts of southern Chile, New Zealand and several subAntarctic islands, with the focus on high latitude populations in the path of the Antarctic Circumpolar Current or West Wind Drift. We targeted two widespread littoral macroalgal species: the brown alga Adenocystisutricularis (Ectocarpales, Heterokontophyta) and the red alga Bostrychiaintricata (Ceramiales, Rhodophyta). Phylogenetic analyses were performed using partial mitochondrial (COI), chloroplast (rbcL) and ribosomal nuclear (LSU / 28S) DNA sequence data. Numerous deeply-divergent clades were resolved across all markers in each of the target species, but close phylogenetic relationships - even shared haplotypes - were observed among some populations separated by large oceanic distances. Despite not being particularly buoyant, both Adenocystisutricularis and Bostrychiaintricata thus show genetic signatures of recent dispersal across vast oceanic distances, presumably by attachment to floating substrata such as wood or buoyant macroalgae. PMID:23894421

  20. Genetic Affinities between Trans-Oceanic Populations of Non-Buoyant Macroalgae in the High Latitudes of the Southern Hemisphere

    PubMed Central

    Fraser, Ceridwen I.; Zuccarello, Giuseppe C.; Spencer, Hamish G.; Salvatore, Laura C.; Garcia, Gabriella R.; Waters, Jonathan M.

    2013-01-01

    Marine biologists and biogeographers have long been puzzled by apparently non-dispersive coastal taxa that nonetheless have extensive transoceanic distributions. We here carried out a broad-scale phylogeographic study to test whether two widespread Southern Hemisphere species of non-buoyant littoral macroalgae are capable of long-distance dispersal. Samples were collected from along the coasts of southern Chile, New Zealand and several subAntarctic islands, with the focus on high latitude populations in the path of the Antarctic Circumpolar Current or West Wind Drift. We targeted two widespread littoral macroalgal species: the brown alga Adenocystisutricularis (Ectocarpales, Heterokontophyta) and the red alga Bostrychiaintricata (Ceramiales, Rhodophyta). Phylogenetic analyses were performed using partial mitochondrial (COI), chloroplast (rbcL) and ribosomal nuclear (LSU / 28S) DNA sequence data. Numerous deeply-divergent clades were resolved across all markers in each of the target species, but close phylogenetic relationships – even shared haplotypes – were observed among some populations separated by large oceanic distances. Despite not being particularly buoyant, both Adenocystisutricularis and Bostrychiaintricata thus show genetic signatures of recent dispersal across vast oceanic distances, presumably by attachment to floating substrata such as wood or buoyant macroalgae. PMID:23894421

  1. First records of winter sea ice concentration in the southwest Pacific sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Ferry, Alexander J.; Crosta, Xavier; Quilty, Patrick G.; Fink, David; Howard, William; Armand, Leanne K.

    2015-11-01

    We use a Generalized Additive Model (GAM) to provide the first winter sea ice concentration record from two cores located within the southwest Pacific sector of the Southern Ocean. To compliment the application of GAM, a time series analysis on satellite records of sea ice concentration data was used to extend the standard 13.25 year time series used for paleoceanography. After comparing GAM sea ice estimates with previously published paleo sea ice data we then focus on a new paleo winter sea ice record for marine sediment core E27-23 (59°37.1'S, 155°14.3'E), allowing us to provide a more comprehensive view of winter sea ice dynamics for the southwest Pacific Ocean. The paleo winter sea ice concentration estimates provide the first suggestion that winter sea ice within the southwestern Pacific might have expanded during the Antarctic Cold Reversal. Throughout the Holocene, core E27-23 documents millennial scale variability in paleo winter sea ice coverage within the southwest Pacific. Holocene winter sea ice expansion may have resulted from the Laurentide Ice Sheet deglaciation, increased intensity of the westerly winds, as well as a northern migration of the Subtropical and/or Sub-Antarctic Fronts. Brief consideration is given to the development of a paleo summer sea ice proxy. We conclude that there is no evidence that summer sea ice ever existed at core sites SO136-111 and E27-23 over the last 220 and 52,000 years, respectively.

  2. ERS-1 scatterometer measurements over the Southern Ocean

    NASA Technical Reports Server (NTRS)

    Freilich, M. H.

    1994-01-01

    Backscatter cross section measurements from the ERS-1 Active Microwave Instrument (AMI) scatterometer were reprocessed to vector winds using the Freilich-Dunbar model function and a meteorologically aided ambiguity removal scheme. This consistent data set was used to examine the wind field over the Southern Ocean from 20 to 60 deg South. The large number of ERS-1 measurements allows relatively accurate calculation of annual mean wind, stress, and curl fields as well as overall statistics of the winds at mid to high southern latitudes. The long duration of the data time series allows preliminary examination of low frequency (semi annual) wind variability.

  3. Inferring source regions and supply mechanisms of iron in the Southern Ocean from satellite data

    NASA Astrophysics Data System (ADS)

    Graham, Robert M.; de Boer, Agatha M.; van Sebille, Erik; kohfeld, Karen E.; Schlosser, Christian

    2016-04-01

    In many biogeochemical models a large shelf sediment iron flux is prescribed through the seafloor over all areas of bathymetry shallower than 1000 m. Here we infer the likely location of shelf sediment iron sources by identifying where mean annual satellite chlorophyll concentrations are enhanced over shallow bathymetry ( > 1000 m). We show that mean annual chlorophyll concentrations are not visibly enhanced over areas of shallow bathymetry located more than 500 km from a coastline. Chlorophyll concentrations > 2 mg m-3 are only found within 50 km of a continental or island coastline. These results suggest that large sedimentary iron fluxes only exist on continental or island shelves. Large sedimentary iron fluxes are unlikely to be found on isolated seamounts and submerged plateaus. We further compare satellite chlorophyll concentrations to the position of ocean fronts to assess the relative role of horizontal advection and upwelling for supplying iron to the ocean surface. Sharp gradients in chlorophyll concentrations are observed across western boundary currents. Large chlorophyll blooms develop where western boundary currents detach from the continental shelves and turn eastwards into the Southern Ocean. Chlorophyll concentrations are enhanced along contours of sea surface height extending off continental and island shelves. These observations support the hypothesis that bioavailable iron from continental shelves is entrained into western boundary currents and advected into the Sub-Antarctic Zone along the Dynamical Subtropical Front. Likewise, iron from island shelves is entrained into nearby fronts and advected downstream. Mean annual chlorophyll concentrations are very low in open ocean regions with large modelled upwelling velocities, where fronts cross over topographic ridges. These results suggests that open ocean upwelling is unlikely to deliver iron to the surface from deep sources such as hydrothermal vents.

  4. Extensive dissolution of live pteropods in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Bednaršek, N.; Tarling, G. A.; Bakker, D. C. E.; Fielding, S.; Jones, E. M.; Venables, H. J.; Ward, P.; Kuzirian, A.; Lézé, B.; Feely, R. A.; Murphy, E. J.

    2012-12-01

    The carbonate chemistry of the surface ocean is rapidly changing with ocean acidification, a result of human activities. In the upper layers of the Southern Ocean, aragonite--a metastable form of calcium carbonate with rapid dissolution kinetics--may become undersaturated by 2050 (ref. ). Aragonite undersaturation is likely to affect aragonite-shelled organisms, which can dominate surface water communities in polar regions. Here we present analyses of specimens of the pteropod Limacina helicina antarctica that were extracted live from the Southern Ocean early in 2008. We sampled from the top 200m of the water column, where aragonite saturation levels were around 1, as upwelled deep water is mixed with surface water containing anthropogenic CO2. Comparing the shell structure with samples from aragonite-supersaturated regions elsewhere under a scanning electron microscope, we found severe levels of shell dissolution in the undersaturated region alone. According to laboratory incubations of intact samples with a range of aragonite saturation levels, eight days of incubation in aragonite saturation levels of 0.94-1.12 produces equivalent levels of dissolution. As deep-water upwelling and CO2 absorption by surface waters is likely to increase as a result of human activities, we conclude that upper ocean regions where aragonite-shelled organisms are affected by dissolution are likely to expand.

  5. Isotopic evidence for reduced productivity in the glacial Southern Ocean

    SciTech Connect

    Shemesh, A. ); Macko, S.A. ); Charles, C.D. ); Rau, G.H. )

    1993-10-15

    Records of carbon and nitrogen isotopes in biogenic silica and carbon isotopes in planktonic foraminifera from deep-sea sediment cores from the Southern Ocean reveal that the primary production during the last glacial maximum was lower than Holocene productivity. These observations conflict with the hypothesis that the low atmospheric carbon dioxide concentrations were introduced by an increase in the efficiency of the high-latitude biological pump. Instead, different oceanic sectors may have had high glacial productivity, or alternative mechanisms that do not involve the biological pump must be considered as the primary cause of the low glacial atmospheric carbon dioxide concentrations.

  6. Development of the circum-antarctic current.

    PubMed

    Kennett, J P; Houtz, R E; Andrews, P B; Edwards, A R; Gostin, V A; Hajos, M; Hampton, M A; Jenkins, D G; Margolis, S V; Ovenshine, A T; Perch-Nielsen, K

    1974-10-11

    Deep-sea drilling in the Southern Ocean south of Australia and New Zealand shows that the Circum-Antarctic Current developed about 30 million years ago in the middle to late Oligocene when final separation occurred between Antarctica and the continental South Tasman Rise. Australia had commenced drifting northward from Antarctica 20 million years before this. PMID:17744222

  7. Late Quaternary Variability in the Deep Water Exchange Between South Atlantic, Southern and Indian Oceans

    NASA Astrophysics Data System (ADS)

    Leuschner, D. C.; Krueger, S.; Ehrmann, W.; Schmiedl, G.; Kuhn, G.; Mackensen, A.; Diekmann, B.

    2005-12-01

    The Southern Ocean, south of Africa, is an important mixing region for northern and southern derived deep-water masses. In this region, the North Atlantic Deep Water (NADW) extends southward into the Circumpolar Deep Water (CDW) dividing it into an upper (UCDW) and a lower (LCDW) layer. Thus, marine sediments from this area are a sensitive recorder for changes of the paleocirculation and relative variations in the deep-water formation in both, the northern Atlantic and Antarctic regions. Here we present results from the EXCHANGE Project which is located in this transition zone of the South Atlantic, the Southern Ocean and the Indian Ocean. In this project we investigate six sediment cores taken along a transect from continental slope at the southern tip of Africa towards the Conrad Rise. Pronounced glacial/interglacial variations in the dominance of NADW and LCDW across the transect are reflected in the clay mineral assemblage and carbon isotope composition of benthic foraminifera. High kaolinite/chlorite-ratios associated with high stable carbon isotope ratios indicate stronger influence of NADW during interglacials. In contrast, glacials are dominated by southern-derived LCDW. Our results suggest a fast southward advance of NADW-dominance during the last two terminations while the northward retreat of NADW, with the onset of glacial conditions, is more gradual. In general, interglacial sediments are also characterized by higher mean grain size diameters in the terrigenous silt fraction (10 to 63 microns), thus indicating stronger bottom currents. However, maximum grain size and sortable silt values are reached at the early stages of the last two glacial periods. Due to the generally weakened bottom current strength, as a result of reduced deep water formation, we would expect smaller values when compared with interglacial conditions. We therefore assume that eolian dust input from the Patagonian region plays a significant role especially in the early glacial

  8. Interannual variability of monthly Southern Ocean sea ice distributions

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.

    1992-01-01

    The interannual variability of the Southern-Ocean sea-ice distributions was mapped and analyzed using data from Nimbus-5 ESMR and Nimbus-7 SMMR, collected from 1973 to 1987. The set of 12 monthly maps obtained reveals many details on spatial variability that are unobtainable from time series of ice extents. These maps can be used as baseline maps for comparisons against future Southern Ocean sea ice distributions. The maps are supplemented by more detailed maps of the frequency of ice coverage, presented in this paper for one month within each of the four seasons, and by the breakdown of these results to the periods covered individually by each of the two passive-microwave imagers.

  9. Strong responses of Southern Ocean phytoplankton communities to volcanic ash

    NASA Astrophysics Data System (ADS)

    Browning, T. J.; Bouman, H. A.; Henderson, G. M.; Mather, T. A.; Pyle, D. M.; Schlosser, C.; Woodward, E. M. S.; Moore, C. M.

    2014-04-01

    Volcanic eruptions have been hypothesized as an iron supply mechanism for phytoplankton blooms; however, little direct evidence of stimulatory responses has been obtained in the field. Here we present the results of twenty-one 1-2 day bottle enrichment experiments from cruises in the South Atlantic and Southern Ocean which conclusively demonstrated a photophysiological and biomass stimulation of phytoplankton communities following supply of basaltic or rhyolitic volcanic ash. Furthermore, experiments in the Southern Ocean demonstrated significant phytoplankton community responses to volcanic ash supply in the absence of responses to addition of dissolved iron alone. At these sites, dissolved manganese concentrations were among the lowest ever measured in seawater, and we therefore suggest that the enhanced response to ash may have been a result of the relief of manganese (co)limitation. Our results imply that volcanic ash deposition events could trigger extensive phytoplankton blooms, potentially capable of significant impacts on regional carbon cycling.

  10. Elevated East Antarctic outlet glaciers during warmer-than-present climates in southern Victoria Land

    NASA Astrophysics Data System (ADS)

    Swanger, K.; Marchant, D. R.; Schaefer, J. M.; Winckler, G.; Head, J. W.

    2010-12-01

    We document Plio-Pleistocene changes in the level of Taylor Glacier, an outlet glacier in southern Victoria Land that drains Taylor Dome on the periphery of the East Antarctic Ice Sheet (EAIS). Chronologic control comes from 3He cosmogenic-nuclide analyses of 27 boulders sampled from drifts and moraines in Kennar Valley, a small hanging valley that opens onto a peripheral lobe of Taylor Glacier in the Quartermain Mountains. Assuming a constant boulder-erosion rate of 10 cm Myr-1, our preferred age model spans the last 3.1 Myr and calls for stepped ice recession from a local highstand ~200 m above the present Taylor Glacier at the mouth of Kennar Valley. The texture and sedimentology of all mapped moraines and drifts indicate deposition from cold-based ice, analogous with the situation for the modern Taylor Glacier. Correlation of our moraine record with published reports for fluctuations of Taylor Glacier elsewhere in the Quartermain Mountains, and with a dated moraine record for Ferrar Glacier (a second outlet for Taylor Dome) in the nearby Wilkness Mountains, reveals consistent ice-surface changes, highlighting minor, but widespread ice recession in southern Victoria Land since the mid to late Pliocene. The combined records show an atypical relationship with average global temperatures, with higher-than-present ice levels occurring during globally warm periods, including the Pliocene climatic optimum (˜3.1 Ma), Marine Oxygen Isotope Stage (MIS) 31 (~1.1 Ma), and the penultimate interglacial, MIS 5.5 (~120 ka). The combined records also suggest that the rate of ice-surface lowering for both outlet glaciers accelerated after the Mid-Pleistocene transition at ~0.9 Myr.

  11. Isotopic Investigation of Contemporary and Historic Changes in Penguin Trophic Niches and Carrying Capacity of the Southern Indian Ocean

    PubMed Central

    Jaeger, Audrey; Cherel, Yves

    2011-01-01

    A temperature-defined regime shift occurred in the 1970s in the southern Indian Ocean, with simultaneous severe decreases in many predator populations. We tested a possible biological link between the regime shift and predator declines by measuring historic and contemporary feather isotopic signatures of seven penguin species with contrasted foraging strategies and inhabiting a large latitudinal range. We first showed that contemporary penguin isotopic variations and chlorophyll a concentration were positively correlated, suggesting the usefulness of predator δ13C values to track temporal changes in the ecosystem carrying capacity and its associated coupling to consumers. Having controlled for the Suess effect and for increase CO2 in seawater, δ13C values of Antarctic penguins and of king penguins did not change over time, while δ13C of other subantarctic and subtropical species were lower in the 1970s. The data therefore suggest a decrease in ecosystem carrying capacity of the southern Indian Ocean during the temperature regime-shift in subtropical and subantarctic waters but not in the vicinity of the Polar Front and in southward high-Antarctic waters. The resulting lower secondary productivity could be the main driving force explaining the decline of subtropical and subantarctic (but not Antarctic) penguins that occurred in the 1970s. Feather δ15N values did not show a consistent temporal trend among species, suggesting no major change in penguins’ diet. This study highlights the usefulness of developing long-term tissue sampling and data bases on isotopic signature of key marine organisms to track potential changes in their isotopic niches and in the carrying capacity of the environment. PMID:21311756

  12. Changes in the ventilation of the southern oceans.

    PubMed

    Waugh, Darryn W

    2014-07-13

    Changes in the ventilation of the southern oceans over the past few decades are examined using ocean measurements of CFC-12 and model simulations. Analysis of CFC-12 measurements made between the late 1980s and late 2000s reveal large-scale coherent changes in the ventilation, with a decrease in the age of subtropical Subantarctic Mode Waters (SAMW) and an increase in the age of Circumpolar Deep Waters. The decrease in SAMW age is consistent with the observed increase in wind stress curl and strength of the subtropical gyres over the same period. A decrease in the age of SAMW is also found in Community Climate System Model version 4 perturbation experiments where the zonal wind stress is increased. This decrease is due to both more rapid transport along isopycnals and the movement of the isopycnals. These results indicate that the intensification of surface winds in the Southern Hemisphere has caused large-scale coherent changes in the ventilation of the southern oceans. PMID:24891397

  13. 10Be application to soil development on Marion Island, southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Haussmann, N.; Aldahan, A.; Boelhouwers, J.; Possnert, G.

    2010-04-01

    Marion Island, located in the southern Indian Ocean, constitutes the summit of an active shield volcano. It is a small terrestrial environment where glacially abraded bedrock became exposed c × 10 kyr ago. These conditions provide an interesting possibility for the assessment of 10Be accumulation rates and their application to soil erosion studies on the island. 10Be concentrations were measured in precipitation, soil profiles and an Azorella selago cushion plant. The data reveal a 10Be precipitation flux several times higher than model prediction. Estimation of the 10Be accumulation based on the soil inventory suggests a span between 2000 and 7000 yr. This time span is not in accordance with the accepted notion that the island was covered with ice about 10,000 yr ago and suggests either removal of 10Be from the soil profile, an overestimated Holocene 10Be-flux or a delayed soil development history. Our results provide new data on 10Be concentrations from the sub-Antarctic islands and contribute towards enlarging the southern-hemisphere 10Be database.

  14. Southern Ocean forcing of the North Atlantic at multi-centennial time scales in the Kiel Climate Model

    NASA Astrophysics Data System (ADS)

    Martin, Torge; Park, Wonsun; Latif, Mojib

    2015-04-01

    Internal multi-centennial variability of open ocean deep convection in the Atlantic sector of the Southern Ocean impacts the strength of the Atlantic Meridional Overturning Circulation (AMOC) in the Kiel Climate Model. The northward extent of Antarctic Bottom Water (AABW) strongly depends on the state of Weddell Sea deep convection. The retreat of AABW results in an enhanced meridional density gradient that drives an increase in the strength and vertical extent of the North Atlantic Deep Water (NADW) cell. This shows, for instance, as a peak in AMOC strength at 30°N about a century after Weddell Sea deep convection has ceased. The stronger southward flow of NADW is compensated by an expansion of the North Atlantic subpolar gyre and an acceleration of the North Atlantic Current, indicating greater deep water formation. Contractions of the North Atlantic subpolar gyre enable warm water anomalies, which evolved in response to deep convection events in the Southern Ocean, to penetrate farther to the north, eventually weakening the AMOC and closing a quasi-centennial cycle. Gyre contractions are accompanied by increases in sea level of up to 20 cm/century in some areas of the North Atlantic. In the Southern Ocean itself, the heat loss during the convective regime results in a sea surface height decrease on the order of 10 cm/century, with a maximum of 30 cm/century in the Weddell Sea. Hence, the impact of the Southern Ocean Centennial Variability (SOCV) on regional as well as North Atlantic sea level is of the same order of magnitude as the rise of global average sea level during the 20th century, which amounts to about 15-20 cm. This suggests that internal variability on a centennial time scale cannot be neglected a priori in assessments of 20th and 21st century AMOC and regional sea level change.

  15. Antarctic Crabs: Invasion or Endurance?

    PubMed Central

    Griffiths, Huw J.; Whittle, Rowan J.; Roberts, Stephen J.; Belchier, Mark; Linse, Katrin

    2013-01-01

    Recent scientific interest following the “discovery” of lithodid crabs around Antarctica has centred on a hypothesis that these crabs might be poised to invade the Antarctic shelf if the recent warming trend continues, potentially decimating its native fauna. This “invasion hypothesis” suggests that decapod crabs were driven out of Antarctica 40–15 million years ago and are only now returning as “warm” enough habitats become available. The hypothesis is based on a geographically and spatially poor fossil record of a different group of crabs (Brachyura), and examination of relatively few Recent lithodid samples from the Antarctic slope. In this paper, we examine the existing lithodid fossil record and present the distribution and biogeographic patterns derived from over 16,000 records of Recent Southern Hemisphere crabs and lobsters. Globally, the lithodid fossil record consists of only two known specimens, neither of which comes from the Antarctic. Recent records show that 22 species of crabs and lobsters have been reported from the Southern Ocean, with 12 species found south of 60°S. All are restricted to waters warmer than 0°C, with their Antarctic distribution limited to the areas of seafloor dominated by Circumpolar Deep Water (CDW). Currently, CDW extends further and shallower onto the West Antarctic shelf than the known distribution ranges of most lithodid species examined. Geological evidence suggests that West Antarctic shelf could have been available for colonisation during the last 9,000 years. Distribution patterns, species richness, and levels of endemism all suggest that, rather than becoming extinct and recently re-invading from outside Antarctica, the lithodid crabs have likely persisted, and even radiated, on or near to Antarctic slope. We conclude there is no evidence for a modern-day “crab invasion”. We recommend a repeated targeted lithodid sampling program along the West Antarctic shelf to fully test the validity of the

  16. The Southern Ocean ecosystem under multiple climate change stresses--an integrated circumpolar assessment.

    PubMed

    Gutt, Julian; Bertler, Nancy; Bracegirdle, Thomas J; Buschmann, Alexander; Comiso, Josefino; Hosie, Graham; Isla, Enrique; Schloss, Irene R; Smith, Craig R; Tournadre, Jean; Xavier, José C

    2015-04-01

    A quantitative assessment of observed and projected environmental changes in the Southern Ocean (SO) with a potential impact on the marine ecosystem shows: (i) large proportions of the SO are and will be affected by one or more climate change processes; areas projected to be affected in the future are larger than areas that are already under environmental stress, (ii) areas affected by changes in sea-ice in the past and likely in the future are much larger than areas affected by ocean warming. The smallest areas (<1% area of the SO) are affected by glacier retreat and warming in the deeper euphotic layer. In the future, decrease in the sea-ice is expected to be widespread. Changes in iceberg impact resulting from further collapse of ice-shelves can potentially affect large parts of shelf and ephemerally in the off-shore regions. However, aragonite undersaturation (acidification) might become one of the biggest problems for the Antarctic marine ecosystem by affecting almost the entire SO. Direct and indirect impacts of various environmental changes to the three major habitats, sea-ice, pelagic and benthos and their biota are complex. The areas affected by environmental stressors range from 33% of the SO for a single stressor, 11% for two and 2% for three, to <1% for four and five overlapping factors. In the future, areas expected to be affected by 2 and 3 overlapping factors are equally large, including potential iceberg changes, and together cover almost 86% of the SO ecosystem. PMID:25369312

  17. Sea ice trends and cyclone activity in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Coggins, Jack; McDonald, Adrian; Rack, Wolfgang; Dale, Ethan

    2015-04-01

    Significant trends in the extent of Southern Hemisphere sea ice have been noted over the course of the satellite record, with highly variable trends between different seasons and regions. In this presentation, we describe efforts to assess the impact of cyclones on these trends. Employing a maximum cross-correlation method, we derive Southern Ocean ice-motion vectors from daily gridded SSMI 85.5 GHz brightness temperatures. We then derive a sea ice budget from the NASA-Team 25 km square daily sea ice concentrations. The budget quantifies the total daily change in sea ice area, and includes terms representing the effects of ice advection and divergence. A residual term represents the processes of rafting, ridging, freezing and thawing. We employ a cyclone tracking algorithm developed at the University of Canterbury to determine the timing, location, size and strength of Southern Hemisphere cyclones from mean sea-level pressure fields of the ERA-Interim reanalysis. We then form composites of the of sea ice budget below the location of cyclones. Unsurprisingly, we find that clockwise atmospheric flow around Southern Hemisphere cyclones exerts a strong influence on the movement of sea ice, an effect which is visible in the advection and divergence terms. Further, we assess the climatological importance of cyclones by comparing seasons of sea ice advance for periods with varying numbers of cyclones. This analysis is performed independently for each sea ice concentration pixel, thus affording us insight into the geographical importance of storm systems. We find that Southern Hemisphere sea ice extent is highly sensitive to the presence of cyclones in the periphery of the pack in the advance season. Notably, the sensitivity is particularly high in the northern Ross Sea, an area with a marked positive trend in sea ice extent. We discuss whether trends in cyclone activity in the Southern Ocean may have contributed to sea ice extent trends in this region.

  18. Imprint of Southern Ocean eddies on winds, clouds and rainfall

    NASA Astrophysics Data System (ADS)

    Frenger, I.; Gruber, N.; Knutti, R.; Münnich, M.

    2013-08-01

    Owing to the turbulent nature of the ocean, mesoscale eddies are omnipresent. The impact of these transitory and approximately circular sea surface temperature fronts on the overlying atmosphere is not well known. Stationary fronts such as the Gulf Stream have been reported to lead to pronounced atmospheric changes. However, the impact of transient ocean eddies on the atmosphere has not been determined systematically, except on winds and to some extent clouds. Here, we examine the atmospheric conditions associated with over 600,000 individual eddies in the Southern Ocean, using satellite data. We show that ocean eddies locally affect near-surface wind, cloud properties and rainfall. The observed pattern of atmospheric change is consistent with a mechanism in which sea surface temperature anomalies associated with the oceanic eddies modify turbulence in the atmospheric boundary layer. In the case of cyclonic eddies, this modification triggers a slackening of near-surface winds, a decline in cloud fraction and water content, and a reduction in rainfall. We conclude that transient mesoscale ocean structures can significantly affect much larger atmospheric low-pressure systems that swiftly pass by at the latitudes investigated.

  19. Possible impacts of ozone depletion on trophic interactions and biogenic vertical carbon flux in the Southern Ocean

    SciTech Connect

    Marchant, H.J.; Davidson, A.

    1992-03-01

    Among the most productive region of the Southern Ocean is the marginal ice edge zone that trails the retreating ice edge in spring and early summer. The timing of this near-surface phytoplankton bloom coincides with seasonal stratospheric ozone depletion when UV irradiance is reportedly as high as in mid-summer. Recent investigations indicate that antarctic marine phytoplankton are presently UV stressed. The extent to which increasing UV radiation diminishes the ability of phytoplankton to fix C02 and/or leads to changes in their species composition is equivocal. The colonial stage in the life cycle of the alga Phaeocystis pouchetii is one of the major components of the bloom. The authors have found that this alga produces extracellular products which are strongly UV-B absorbing. When exposed to increasing levels of UV-B radiation, survival of antarctic colonial Phaeocystis was significantly greater than colonies of this species from temperate waters and of the single-celled stage of its life cycle which produces no UV-B-absorbing compounds. Phaeocystis is apparently a minor dietary component of Antarctic krill, Euphausia superba, and its nutritional value to crustacea is reportedly low. Phytoplankton, principally diatoms, together with fecal pellets and molted exoskeletons of grazers contribute most of the particulate carbon flux from the euphotic zone to deep water.

  20. An investigation of Bjerknes Compensation in the Southern Ocean in the CCSM4

    SciTech Connect

    Weijer, Wilbert; Kinstle, Caroline M.

    2012-08-28

    This project aims to understand the relationship between poleward oceanic and atmospheric heat transport in the Southern Ocean by analyzing output from the community Climate System Model Version 4 (CCSM4). In particular, time series of meridional heat transport in both the atmosphere and the ocean are used to study whether variability in ocean heat transport is balanced by opposing changes in atmospheric heat transport, called Bjerknes Compensation. It is shown that the heat storage term in the Southern Ocean has a significant impact on the oceanic heat budget; as a result, no robust coherences between oceanic and atmospheric heat transports could be found at these southern latitudes.

  1. Spatial distribution of atmospheric aerosol optical depth over Atlantic Ocean along the route of Russian Antarctic expeditions

    NASA Astrophysics Data System (ADS)

    Kabanov, Dmitry M.; Radionov, Vladimir F.; Sakerin, Sergey M.; Smirnov, Alexander

    2015-11-01

    During recent decade, Microtops and SPM portable sun photometers are used to perform annual measurements of aerosol optical depth (AOD) and water vapor content of the atmosphere over Atlantic Ocean along the route of the Russian Antarctic expeditions (RAE). The data accumulation has made it possible to analyze the specific features of the spatial distribution of spectral AOD of the atmosphere along eastern RAE route and identify six basic regions (latitudinal zones). The statistical characteristics of AOD in the identified oceanic regions in winter and spring periods are discussed. The estimates of finely and coarsely dispersed AOD components in different regions, as well as the interannual atmospheric AOD variations, are presented.

  2. Two new species of family Neotanaidae (Peracarida: Tanaidacea) from the Antarctic and Mid-Pacific Oceans.

    PubMed

    Araújo-Silva, Catarina L; Froufe, Elsa; Larsen, Kim

    2015-01-01

    Samples collected from the Antarctic (ANDEEP/2002) and Mid-Pacific (BIONOD/2012) Oceans allowed analyses of several specimens of the family Neotanaidae. From these surveys two new species are described: Neotanais bicornutus and Venusticrus thor. The new material led to a re-diagnosis of Venusticrus, and N. rotermundiae is now assigned to this genus. The male of N. bicornutus shares a number of characters with the "robustus" species group, but differs by having a pleotelson about 1.5 times as wide as long, cheliped carpus about 1.5 times as long as cephalothorax, cheliped propodus with two long dorsal projections, and uropod endopod article 1 with 8-10 fine setae proximal to mid-length on outer margin. The N. bicornutus preparatory female differs from all species by a combination of characters including the number of setae on dorsal margin of cheliped carpus (about 15 setae), the uropod attachment slightly posterior to mid-length, uropod basal article about 2.7 times as long as endopod article 1. The female of V. thor differs from those of V. insolitus, V. glandurus and V. rotermundiae by the body proportions, the pleon having three lateral setae on epimera, pleon with a blunt ventral keel, pereopodal setation, number of setae on maxilliped endite and basis as well as other characters. Total genomic DNA was extracted from two specimens of V. thor and sequences of two genes, i.e., cytochrome oxidase 1 (COI) and ribosomal (28S) were obtained. PMID:26624054

  3. Upper ocean variability in west Antarctic Peninsula continental shelf waters as measured using instrumented seals

    NASA Astrophysics Data System (ADS)

    Costa, Daniel P.; Klinck, John M.; Hofmann, Eileen E.; Dinniman, Michael S.; Burns, Jennifer M.

    2008-02-01

    Temperature profile data for the west Antarctic Peninsula (WAP) continental shelf waters, collected from freely ranging instrumented seals (crabeater, Lobodon carcinophagus and leopard, Hydrurga leptonyx), were used to demonstrate that these platforms can be used to supplement traditional oceanographic sampling methods to investigate the physical properties of the upper water column. The seal-derived profiles were combined with temperature profiles obtained from ship-based CTD measurements and from a numerical circulation model developed for the WAP to describe changes in temperature structure, heat content, and heat flux in the upper ocean waters of the WAP continental shelf. The seal-derived data documented the fall-to-winter transition of the surface waters and the shelf-wide presence of modified Circumpolar Deep Water (CDW) below 150-200 m on the WAP continental shelf. The heat content of the upper 200 m calculated from the seal-derived temperature profiles ranged between 1000 and 1500 MJ m -2; similar estimates were obtained from simulated temperature distributions. The seal-derived temperature measurements provided broader space and time resolution than was possible using any other currently available oceanographic sampling method. As such, the seal-derived measurements provided a valuable dataset for evaluation of temperature fields obtained from a numerical circulation model.

  4. Observational Evidence of a Hemispheric-wide Ice-ocean Albedo Feedback Effect on Antarctic Sea-ice Decay

    NASA Technical Reports Server (NTRS)

    Nihashi, Sohey; Cavalieri, Donald J.

    2007-01-01

    The effect of ice-ocean albedo feedback (a kind of ice-albedo feedback) on sea-ice decay is demonstrated over the Antarctic sea-ice zone from an analysis of satellite-derived hemispheric sea ice concentration and European Centre for Medium-Range Weather Forecasts (ERA-40) atmospheric data for the period 1979-2001. Sea ice concentration in December (time of most active melt) correlates better with the meridional component of the wind-forced ice drift (MID) in November (beginning of the melt season) than the MID in December. This 1 month lagged correlation is observed in most of the Antarctic sea-ice covered ocean. Daily time series of ice , concentration show that the ice concentration anomaly increases toward the time of maximum sea-ice melt. These findings can be explained by the following positive feedback effect: once ice concentration decreases (increases) at the beginning of the melt season, solar heating of the upper ocean through the increased (decreased) open water fraction is enhanced (reduced), leading to (suppressing) a further decrease in ice concentration by the oceanic heat. Results obtained fi-om a simple ice-ocean coupled model also support our interpretation of the observational results. This positive feedback mechanism explains in part the large interannual variability of the sea-ice cover in summer.

  5. Rethinking the Ocean's Role in the Southern Oscillation

    NASA Astrophysics Data System (ADS)

    Clement, A. C.; di Nezio, P. N.; Deser, C.

    2010-12-01

    The usual explanation for variability in the Southern Oscillation (SO), a shift of atmospheric mass between the Indo-Pacific warm pool region and the eastern Pacific reflected in opposite sign changes in sea level pressure, involves dynamical coupling between the atmosphere and ocean via the ‘Bjerknes feedback’ mechanism. Here we revisit this explanation using a collection of simulations with atmospheric general circulation models that have varying degrees of coupling to the ocean. The main finding is that the SO emerges as a dominant mode of tropical Pacific variability without dynamical coupling to the ocean. Atmospheric models coupled to a mixed layer ocean (i.e. with no coupled ocean dynamics) simulate what is refered to here as an ‘Atmospheric Walker Mode’ (AWM). This mode of variability has patterns in sea level pressure, sea surface temperature, and precipitation which strongly resemble observed patterns associated with the SO. The spectrum of the AWM is red out to about a decadal timescale, consistent with a stochastically forced, weakly damped process, and our analysis suggests that variability in the AWM is related to variability in the NE and SE trade winds and associated surface wind divergence in the warm pool. The main influence of ocean dynamics on the SO in fully coupled climate models is the addition power primarily at interannual timescales, as expected from the positive Bjerknes feedback. On decadal and longer timescales, ocean dynamics enhance the damping of (or act as a negative feedback on) SO variability. However, interactive ocean dynamics do not appear to be required to set the first-order spatial structure of the SO or associated patterns in SST, precipitation, or atmospheric circulation. Implications for Pacific climate variability on interannual, decadal, and century timescales are discussed.

  6. Sea ice and the ocean mixed layer over the Antarctic shelf seas

    NASA Astrophysics Data System (ADS)

    Petty, A.; Holland, P.; Feltham, D. L.

    2013-12-01

    An ocean mixed layer model has been incorporated into the Los Alamos sea ice model CICE, to investigate regional variations in the surface-driven formation of Antarctic shelf sea waters. The model captures well the expected sea ice thickness distribution and produces deep (>500 m) mixed layers in the Weddell and Ross shelf seas each winter. By deconstructing the surface power input to the mixed layer, we have shown that the salt/fresh water flux from sea ice growth/melt dominates the evolution of the mixed layer in all shelf sea regions, with a smaller contribution from the mixed layer-surface heat flux. The Weddell and Ross shelf seas have the highest annual ice growth, with a large fraction exported northwards each year, whereas the Bellingshausen shelf sea experiences the highest annual ice melt, driven by the advection of ice from the northeast. Forcing the model with ERA-Interim (1980-2011) and hadGEM2-ES (1980-2099) atmospheric data allows us to look at the impact of atmospheric trends on the sea ice and ocean mixed layer. Both simulations show a shallowing of the wintertime mixed layer in the Amundsen & Bellingshausen seas, potentially increasing the access of warm CDW to ice shelves in both regions. The ERA-I hindcast simulation shows a significant freshening in the Ross and salinification in the Weddell due to surface driven trends (primarily through changes in the sea ice). The Ross freshening is smaller than observed however, highlighting the important role of ice shelf melt in the Amundsen Sea.

  7. The de-correlation of westerly winds and westerly-wind stress over the Southern Ocean during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Lu, Jian; Leung, L. Ruby; Xie, Shang-Ping; Liu, Zhengyu; Zhu, Jiang

    2015-12-01

    Motivated by indications from paleo-evidence, this paper investigates the changes of the Southern Westerly Winds (SWW) and westerly-wind stress between the Last Glacial Maximum (LGM) and pre-industrial in the PMIP3/CMIP5 simulations, highlighting the role of Antarctic sea ice in modulating the wind effect on ocean. Particularly, a de-correlation occurs between the changes in SWW and westerly-wind stress, caused primarily by an equatorward expansion of winter Antarctic sea ice that undermines the efficacy of wind in generating stress over the liquid ocean. Such de-correlation may reflect the LGM condition in reality, in view of the fact that the model which simulates this condition has most fidelity in simulating modern SWW and Antarctic sea ice. Therein two models stand out for their agreements with paleo-evidence regarding the change of SWW and the westerly-wind stress. They simulate strengthened and poleward-migrated LGM SWW in the atmosphere, consistent with the indications from dust records. Whilst in the ocean, they well capture an equatorward-shifted pattern of the observed oceanic front shift, with most pronounced equatorward-shifted westerly wind stress during the LGM.

  8. Iron supply to the Southern Ocean mixed layer from below; the ocean model effect

    NASA Astrophysics Data System (ADS)

    Schourup-Kristensen, Vibe; Hauck, Judith; Losch, Martin; Wolf-Gladrow, Dieter A.; Völker, Christoph

    2015-04-01

    In the iron limited Southern Ocean, the biogeochemical results of commonly used ocean general circulation biogeochemical models differ greatly dependent on the ocean model used. This is largely due to the difficulties in reproducing a realistic mixed layer depth (MLD), which leads to different degrees of light limitation and nutrient supply from below. Regarding the iron sources to the Southern Ocean, research has traditionally focused on the input from dust and the sediment, but recent studies have highlighted the importance of the vertical supply to the mixed layer from the nutrient rich deeper water. This latter supply mechanism may also be affected by the large inter-model differences in the MLD and thereby influence the total net primary production and export production in the models. We have performed a model study in which the biogeochemical model REcoM2 was coupled to two different ocean models, the Finite Element Sea-ice Ocean Model (FESOM) and the MIT general circulation model (MITgcm). The effect of the ocean mixed layer on the magnitude of the iron sources from below in the two models was analyzed, as was the effect on the export and net primary production. Our results revealed a remarkable difference in terms of mode and magnitude of transport dependent on the mixed layer depth in the two models; the mean iron supply from below in the Southern Ocean was on average four times higher in MITgcm than in FESOM. The dominant pathway was entrainment in MITgcm, whereas diffusion dominated in FESOM. We discuss how the difference in the depth and seasonal amplitude of the mixed layer between the models has a major effect on the vertical iron profile and thereby also on the iron fluxes. A further effect of the difference in supply is that the fraction of exported net primary production is higher in MITgcm than in FESOM, showing that the choice of ocean model has a significant impact on the modeled carbon cycle in the Southern Ocean, with possible implications for

  9. Canterbury Drifts, SW Pacific Ocean: Record of Antarctic Intermediate Water Flow Since 24 Ma

    NASA Astrophysics Data System (ADS)

    Carter, R. M.

    2005-12-01

    .37 Ma, this record closely mirrors the climate history of Antarctica, as manifested in the Vostok ice core, at 0.1-0.6 ky resolution. Beyond, and back to 3.9 Ma, the gamma record reflects southern mid-latitude ice-volumes and perhaps Antarctic polar plateau temperature at a resolution of 1.3 ky.

  10. Small iceberg bursts: melting breakwaters in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Ardhuin, F.; Tournadre, J.; Queffeulou, P.; Girard-Ardhuin, F.

    2010-12-01

    The variability of small-size iceberg distributions is revealed from a novel analysis of satellite altimeter data. The yearly cycle is modulated by pulse-like events confined to single ocean basins. A strong iceberg population is found in the South Atlantic in 2003-2005, and in the South Pacific in 2008. Anomalies of the order of 1°C in sea surface temperatures may be related to the iceberg distribution. Icebergs are very strongly associated with anomalies in the heights of ocean waves, with far-reaching consequences for the global wave climate. A preliminary numerical modelling of wave blocking by icebergs, including partial wave reflection, reduces model errors on the significant wave height by 26% in the region south of 45° South. Observed changes in small iceberg populations thus have profound impacts on Southern ocean dynamics and beyond. Latitude-time Hovmöller diagrams of the small iceberg ice volume cumulated over each 2° band of latitude for (a) the South Atlantic 50°W to 30°E, (b) the Indian Ocean 50°E to 130°, (c) the South Pacific 130°E to 100°, for each 2° band of latitude. (d), (e), and (f) significant wave heigth model bias against satellite altimeters for the same three sectors of the Southern Ocean, for a model without iceberg effects. In the left panels (a,b,c) the black line marks the maximum extend of the sea ice, and in the right panels (c,d,e) the white areas give the minimum extent of the 80% sea ice coverage, used as a mask in the model.

  11. Inventory of ocean monitoring in the Southern California Bight.

    PubMed

    Schiff, Kenneth C; Weisberg, Stephen B; Raco-Rands, Valerie

    2002-06-01

    Monitoring of the ocean environment in southern California, USA, has been conducted by a diverse array of public and private organizations with different motivations, working on a variety of spatial and temporal scales. To create a basis from which to integrate information from these diverse programs, we conducted an inventory of ocean monitoring activities in the Southern California Bight to address the following questions: (1) How much money is being expended annually on marine monitoring programs? (2) Which organizations are conducting the most monitoring? (3) How are resources allocated among the different types of monitoring programs? This inventory focused on programs existing, or those expected to be in existence, for at least 10 years and that were active at any time between 1994 and 1997. For each program identified for inclusion in this study, information was collected on the number of sites, sampling intensity, parameters measured, and methods used. Levels of effort were translated into cost estimates based upon a market survey of local consulting firms. One hundred fourteen marine monitoring programs, conducted by 65 organizations and costing US $31 million annually, were identified. Most of the effort (81 programs, 65% of samples, 70% of costs) was expended by ocean dischargers as part of their compliance with National Pollutant Discharge Elimination System (NPDES) permit requirements. Federal programs (11 programs, 25% of samples, 10% of total expenditures) expended more than state or local government programs. More than one quarter of monitoring expenditures were conducted to measure concentrations and mass of effluent inputs to the ocean. The largest effort expended on receiving water monitoring was for measuring bacteria, followed by sediments, fish/shellfish, water quality, and intertidal habitats. The large level of expenditures by individual agencies has presented opportunities for integrating small, site-specific ocean monitoring programs into

  12. The SOOS Data Portal, providing access to Southern Oceans data

    NASA Astrophysics Data System (ADS)

    Proctor, Roger; Finney, Kim; Blain, Peter; Taylor, Fiona; Newman, Louise; Meredith, Mike; Schofield, Oscar

    2013-04-01

    The Southern Ocean Observing System (SOOS) is an international initiative to enhance, coordinate and expand the strategic observations of the Southern Oceans that are required to address key scientific and societal challenges. A key component of SOOS will be the creation and maintenance of a Southern Ocean Data Portal to provide improved access to historical and ongoing data (Schofield et al., 2012, Eos, Vol. 93, No. 26, pp 241-243). The scale of this effort will require strong leveraging of existing data centres, new cyberinfrastructure development efforts, and defined data collection, quality control, and archiving procedures across the international community. The task of assembling the SOOS data portal is assigned to the SOOS Data Management Sub-Committee. The information infrastructure chosen for the SOOS data portal is based on the Australian Ocean Data Network (AODN, http://portal.aodn.org.au). The AODN infrastructure is built on open-source tools and the use of international standards ensures efficiency of data exchange and interoperability between contributing systems. OGC standard web services protocols are used for serving of data via the internet. These include Web Map Service (WMS) for visualisation, Web Feature Service (WFS) for data download, and Catalogue Service for Web (CSW) for catalogue exchange. The portal offers a number of tools to access and visualize data: - a Search link to the metadata catalogue enables search and discovery by simple text search, by geographic area, temporal extent, keyword, parameter, organisation, or by any combination of these, allowing users to gain access to further information and/or the data for download. Also, searches can be restricted to items which have either data to download, or attached map layers, or both - a Map interface for discovery and display of data, with the ability to change the style and opacity of layers, add additional data layers via OGC Web Map Services, view animated timeseries datastreams

  13. Low-frequency sound level in the Southern Indian Ocean.

    PubMed

    Tsang-Hin-Sun, Eve; Royer, Jean-Yves; Leroy, Emmanuelle C

    2015-12-01

    This study presents long-term statistics on the ambient sound in the Southern Indian Ocean basin based on 2 years of data collected on six widely distributed autonomous hydrophones from 47°S to 4°S and 53°E to 83°E. Daily mean power spectra (10-100 Hz) were analyzed in order to identify the main sound sources and their space and time variability. Periodic signals are principally associated with the seasonal presence of three types of blue whales and fin whales whose signatures are easily identified at specific frequencies. In the low frequencies, occurrence of winter lows and summer highs in the ambient noise levels are well correlated with iceberg volume variations at the southern latitudes, suggesting that icebergs are a major sound source, seasonally contributing to the ambient noise, even at tropical latitudes (26°S). The anthropogenic contribution to the noise spectrum is limited. Shipping sounds are only present north and west of the study area in the vicinity of major traffic lanes. Acoustic recordings from the southern sites may thus be representative of the pristine ambient noise in the Indian Ocean. PMID:26723301

  14. The Last Termination in the South Indian Ocean: A unique terrestrial record from Kerguelen Islands (49°S) situated within the Southern Hemisphere westerly belt

    NASA Astrophysics Data System (ADS)

    Van der Putten, Nathalie; Verbruggen, Cyriel; Björck, Svante; Michel, Elisabeth; Disnar, Jean-Robert; Chapron, Emmanuel; Moine, Bertrand N.; de Beaulieu, Jacques-Louis

    2015-08-01

    The awareness of the significance of the Southern Ocean in the Earth's climate system has become increasingly obvious. The deglacial atmospheric CO2 rise during warming periods in Antarctica has been attributed to CO2 ventilation from the deep ocean caused by enhanced upwelling around the Antarctic Divergence. It has been hypothesized that, more intense Southern Hemisphere westerly winds aligned with the Antarctic Circumpolar Current due to a southward shift of the wind belt from its Last Glacial Maximum equator-ward position, are the main drivers. Reconstructions of past changes in atmospheric circulation in the Southern Hemisphere are still scarce and the overall picture is patchy with sometimes contradictory results. For obvious reasons, most terrestrial records originate from southern South America and New Zealand. Here we present a terrestrial record from the Indian sector of the Southern Ocean, from Kerguelen Islands located at 49°S. A peat record is investigated using a multi-proxy approach (pollen and plant macrofossils, magnetic susceptibility, XRF analyses, biogenic silica content, Rock-Eval6 analysis and humification degree). Peat accumulation starts at about 16,000 cal yr BP with relatively warm and dry conditions. The most prominent change in our proxy data occurs at 13,600 cal yr BP, when peat ponds were established on the peat surface, resulting in lacustrine-type deposits, as a result of very high humidity, and with proxies implying very windy conditions. Within chronological uncertainties, this onset coincides with the onset of the so-called Oceanic Cold Reversal, based on the deuterium excess data in the EPICA Dome C ice core record. Kerguelen Islands are located in the moisture source area of Dome C and a change in atmospheric circulation at that time could explain both records. Around 12,900 cal yr BP, at the end of the Antarctic Cold Reversal, pond/lake sediments give way to more peaty deposits, with proxies suggesting slightly drier

  15. Environmental forcings of Paleogene Southern Ocean dinoflagellate biogeography

    NASA Astrophysics Data System (ADS)

    Bijl, Peter K.; Pross, Jörg; Warnaar, Jeroen; Stickley, Catherine E.; Huber, Matthew; Guerstein, Raquel; Houben, Alexander J. P.; Sluijs, Appy; Visscher, Henk; Brinkhuis, Henk

    2011-02-01

    Despite warm polar climates and low meridional temperature gradients, a number of different high-latitude plankton assemblages were, to varying extents, dominated by endemic species during most of the Paleogene. To better understand the evolution of Paleogene plankton endemism in the high southern latitudes, we investigate the spatiotemporal distribution of the fossil remains of dinoflagellates, i.e., organic-walled cysts (dinocysts), and their response to changes in regional sea surface temperature (SST). We show that Paleocene and early Eocene (˜65-50 Ma) Southern Ocean dinocyst assemblages were largely cosmopolitan in nature but that a distinct switch from cosmopolitan-dominated to endemic-dominated assemblages (the so-called “transantarctic flora”) occurred around the early-middle Eocene boundary (˜50 Ma). The spatial distribution and relative abundance patterns of this transantarctic flora correspond well with surface water circulation patterns as reconstructed through general circulation model experiments throughout the Eocene. We quantitatively compare dinocyst assemblages with previously published TEX86-based SST reconstructions through the early and middle Eocene from a key locality in the southwest Pacific Ocean, ODP Leg 189 Site 1172 on the East Tasman Plateau. We conclude that the middle Eocene onset of the proliferation of the transantarctic flora is not linearly correlated with regional SST records and that only after the transantarctic flora became fully established later in the middle Eocene, possibly triggered by large-scale changes in surface-ocean nutrient availability, were abundances of endemic dinocysts modulated by regional SST variations.

  16. Decadal-scale thermohaline variability in the Atlantic sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Hutchinson, K.; Swart, S.; Meijers, A.; Ansorge, I.; Speich, S.

    2016-05-01

    An enhanced Altimetry Gravest Empirical Mode (AGEM), including both adiabatic and diabatic trends, is developed for the Antarctic Circumpolar Current (ACC) south of Africa using updated hydrographic CTD sections, Argo data, and satellite altimetry. This AGEM has improved accuracy compared to traditional climatologies and other proxy methods. The AGEM for the Atlantic Southern Ocean offers an ideal technique to investigate the thermohaline variability over the past two decades in a key region for water mass exchanges and transformation. In order to assess and attribute changes in the hydrography of the region, we separate the changes into adiabatic and diabatic components. Integrated over the upper 2000 dbar of the ACC south of Africa, results show mean adiabatic changes of 0.16 ± 0.11°C decade-1 and 0.006 ± 0.014 decade-1, and diabatic differences of -0.044 ± 0.13°C decade-1 and -0.01 ± 0.017 decade-1 for temperature and salinity, respectively. The trends of the resultant AGEM, that include both adiabatic and diabatic variability (termed AD-AGEM), show a significant increase in the heat content of the upper 2000 dbar of the ACC with a mean warming of 0.12 ± 0.087°C decade-1. This study focuses on the Antarctic Intermediate Water (AAIW) mass where negative diabatic trends dominate positive adiabatic differences in the Subantarctic Zone (SAZ), with results indicating a cooling (-0.17°C decade-1) and freshening (-0.032 decade-1) of AAIW in this area, whereas south of the SAZ positive adiabatic and diabatic trends together create a cumulative warming (0.31°C decade-1) and salinification (0.014 decade-1) of AAIW.

  17. Nineteen-year changes in surface salinity in the Southern Ocean south of Australia

    NASA Astrophysics Data System (ADS)

    Morrow, Rosemary; Kestenare, Elodie

    2014-01-01

    A 19-year time series of underway sea surface salinity (SSS) data from the SURVOSTRAL line between Hobart, Australia and Adelie Land, Antarctica has revealed the distinct patterns of seasonal and interannual variability in two key zones of the Southern Ocean: in the Subantarctic Zone and in the Antarctic Zone. Both regions show a weak seasonal freshening of the surface waters over the summer months, with surface waters becoming shallower, warmer and fresher during the summer heating cycle. In the region north of the Subantarctic Front, interannual variations in the summer SSS signature are linked to the latitudinal movements of the Subtropical Front. When this front shifts southward, more high salinity subtropical waters are brought into the domain. Rather than responding to local wind stress forcing, the interannual SSS variability is strongly linked to southward flow from eastern Tasmania (the Tasman outflow), whose decadal variability responds with a 2-3 year delay to remote wind forcing in the South Pacific (Hill et al., 2008). Over this period, variations in the local surface freshwater forcing make a minor contribution to the SURVOSTRAL SSS signature. There appears to be a regime shift in the surface forcing and the SSS response, before and after the large perturbation in 2001-2002. In the Antarctic Zone, the summer SSS signature shows distinct biannual variations that are correlated with upstream sea-ice coverage in the preceding spring. There is no significant correlation between local precipitation changes and the SURVOSTRAL SSS time series. Rather, the integrated effects of upstream sea-ice melt dominate the interannual variations in SSS at the SURVOSTRAL line. Finally, a simple 2D Lagrangian particle analysis shows that in some years the surface waters circulate for a longer time in the northern part of the domain, where their freshwater content may be reduced by mixing with the surrounding waters.

  18. Effects of variability associated with the Antarctic circumpolar current on sound propagation in the ocean

    NASA Astrophysics Data System (ADS)

    de Groot-Hedlin, C.; Blackman, Donna K.; Jenkins, C. Scott

    2009-02-01

    A series of small depth charges was detonated along a transect from New Zealand to Antarctica over a period of 3 days in late December of 2006. The hydroacoustic signals were recorded by a hydrophone deployed near the source and at a sparse network of permanent hydrophone stations operated by the International Monitoring System (IMS), at distances up to 9600 km. Our purpose was to determine how well signal characteristics could be predicted by the World Ocean Atlas 2005 (WOA05) climatological database for sources within the Antarctic circumpolar current (ACC). Waveforms were examined in the 1-100 Hz frequency band, and it was found that for clear transmission paths, the shot signals exceeded the noise only at frequencies above 20-30 Hz. Comparisons of signal spectra for recordings near the source and at the IMS stations show that transmission loss is nearly uniform as a function of frequency. Where recorded signal-to-noise ratios are high, observed and predicted traveltimes and signal dispersion agree to within 2 s under the assumption that propagation is adiabatic and follows a geodesic path. The deflection of the transmission path by abrupt spatial variations in sound speed at the northern ACC boundary is predicted to decrease traveltimes to the IMS stations by several seconds, depending on the path. Acoustic velocities within the ACC are predicted to vary monthly, hence the accuracy of source location estimates based only on arrival times at IMS stations depends on the monthly or seasonal database used to predict traveltimes and on whether we account for path deflection. However, estimates of source locations within the ACC that are based only on observed waveforms at IMS hydrophones are highly dependent on the configuration of the IMS network; a set of shots observed only at an IMS station in the Indian Ocean and another in the South Pacific was located to within 10 km in longitude, but was poorly constrained in latitude. Several sets of shots observed only at

  19. Contribution of enhanced Antarctic Bottom Water formation to Antarctic warm events and millennial-scale atmospheric CO2 increase

    NASA Astrophysics Data System (ADS)

    Menviel, L.; Spence, P.; England, M. H.

    2015-03-01

    During Marine Isotope Stage 3, the Atlantic Meridional Overturning Circulation (AMOC) weakened significantly on a millennial time-scale leading to Greenland stadials. Ice core records reveal that each Greenland stadial is associated with a warming over Antarctica, so-called Antarctic Isotope Maximum (AIM), and that atmospheric CO2 increases with Antarctic temperature during the long Greenland stadials. Here we perform transient simulations spanning the period 50-34 ka B.P. with two Earth System Models (LOVECLIM and the UVic ESCM) to understand the possible link between changes in the AMOC, changes in high latitude Southern Hemispheric climate and evolution of atmospheric CO2. We find that oceanic carbon releases due to the AMOC resumption during stadial/interstadial transitions lead to an atmospheric CO2 increase. However, the atmospheric CO2 increases observed during the first parts of AIM12 (∼47.6 ka B.P.) and AIM8 (∼39.8 ka B.P.) occur during periods of weak AMOC (HS5 and HS4 respectively) and could instead be explained by enhanced Antarctic Bottom Water transport. Enhanced Antarctic Bottom Water formation is shown to effectively ventilate the deep Pacific carbon and lead to CO2 outgassing into the atmosphere. In addition, changes in the AMOC alone are not sufficient to explain the largest Antarctic Isotope Maxima (namely AIM12 and AIM8). Stronger formation of Antarctic Bottom Water during AIM12 and AIM8 would enhance the southern high latitude warming and lead to a better agreement with high southern latitude paleoproxy records. The robustness of this southern warming response is tested using an eddy-permitting coupled ocean sea-ice model. We show that stronger Antarctic Bottom Water formation contributes to Southern Ocean surface warming by increasing the Southern Ocean meridional heat transport.

  20. Deep and bottom water export from the Southern Ocean to the Pacific over the past 38 million years

    USGS Publications Warehouse

    van de Flierdt, T.; Frank, M.; Halliday, A.N.; Hein, J.R.; Hattendorf, B.; Gunther, D.; Kubik, P.W.

    2004-01-01

    The application of radiogenic isotopes to the study of Cenozoic circulation patterns in the South Pacific Ocean has been hampered by the fact that records from only equatorial Pacific deep water have been available. We present new Pb and Nd isotope time series for two ferromanganese crusts that grew from equatorial Pacific bottom water (D137-01, "Nova," 7219 m water depth) and southwest Pacific deep water (63KD, "Tasman," 1700 m water depth). The crusts were dated using 10Be/9Be ratios combined with constant Co-flux dating and yield time series for the past 38 and 23 Myr, respectively. The surface Nd and Pb isotope distributions are consistent with the present-day circulation pattern, and therefore the new records are considered suitable to reconstruct Eocene through Miocene paleoceanography for the South Pacific. The isotope time series of crusts Nova and Tasman suggest that equatorial Pacific deep water and waters from the Southern Ocean supplied the dissolved trace metals to both sites over the past 38 Myr. Changes in the isotopic composition of crust Nova are interpreted to reflect development of the Antarctic Circumpolar Current and changes in Pacific deep water circulation caused by the build up of the East Antarctic Ice Sheet. The Nd isotopic composition of the shallower water site in the southwest Pacific appears to have been more sensitive to circulation changes resulting from closure of the Indonesian seaway. Copyright 2004 by the American Geophysical Union.

  1. Southern-ocean and glaciogenic nutrients control diatom export production on the Chile margin

    NASA Astrophysics Data System (ADS)

    Chase, Zanna; McManus, James; Mix, Alan C.; Muratli, Jesse

    2014-09-01

    Biogenic particle flux was reconstructed using 230-Thorium normalization at two sites on the southern Chile margin. ODP Site 1233 at 41°S, 838 m depth, is at the southern limit of the Peru-Chile upwelling system, where the northern extent of the Antarctic Circumpolar Current impinges on the South American continental margin. ODP Site 1234, at 36°S, 1014 m depth, is located within the core of the coastal upwelling system near the mouths of the Bio Bio and Itata Rivers. At 41°S, opal, lithogenic and carbonate fluxes are greatest during the Last Glacial interval (26-20 ka), carbonate has a secondary peak during the mid Holocene (˜8 ka) and organic carbon fluxes increase slightly from 17 ka to the present. At 36°S, large lithogenic fluxes are observed both during the Last Glacial interval and the Holocene, and a maximum in organic carbon flux is observed during the late Holocene (˜5 ka) without an accompanying peak in opal flux. These reconstructed fluxes at 36°S and 41°S fit within a larger latitudinal pattern of a poleward increase in the magnitude of opal flux during the glacial period. The pattern of normalized opal flux, opal mass accumulation rate and opal:carbonate ratios is consistent with either i) enhanced supply of Si from the Southern Ocean, as proposed by the Silicic Acid Leakage Hypothesis or ii) enhanced Si and Fe delivery from land, driven by glacial erosion. The pattern of reconstructed export production supports our view that the appearance of more reducing conditions in the sediments upon deglaciation was most likely driven by decreased ventilation, rather than increased local productivity.

  2. Southern Ocean Sea Ice Development Since the Last Glacial, a Combined Proxy Data-Modeling Approach

    NASA Astrophysics Data System (ADS)

    Gersonde, R.; Benz, V.; Esper, O.; Lohmann, G.; Xiao, W.; Zhang, X.

    2014-12-01

    Southern Ocean (SO) sea ice plays a critical role in climate at global and regional scales. To advance our understanding of processes that drive and regulate sea ice there is a strong need to further extend sea ice records into the past covering a broad range of boundary conditions and time scales. We present the SO sea ice development since the last glacial using a new diatom-based transfer function (Esper and Gersonde 2014). We have enhanced a previous circumpolar reconstruction of the Last Glacial Maximum (LGM) (Gersonde et al. 2005) by new estimates from the hitherto not well-explored Pacific sector. This corroborates earlier results that LGM winter sea ice was expanded by ca. 100% compared to present. Time-series documenting the past 30,000 yrs are available from 29 sites from the western Indian, the Atlantic and the Pacific sectors. In general, the records suggest a post-glacial sea ice retreat between 18,000-15,000 yrs followed by a slight expansion during the Antarctic Cold Reversal. Minimum sea ice extent was reached in the early Holocene. Around 8.000 yrs ago we observe a re-expansion of sea ice, primarily in the Ross and the Weddell/Scotia Sea sectors. This general pattern is also mirrored by sea ice proxy records (ssNa flux) obtained from Antarctic ice cores. However, the marine records show that the sea ice development is subject to spatial heterogeneity related to SO circulation systems and bottom topography, and to land/ocean distribution. This may lead to area-specific expansions and latitudinal gradients in sea ice concentration with implications on climate-relevant factors e.g. albedo, ocean/atmosphere exchange, moisture distribution, water mass generation and biological productivity. The obtained proxy data are compared with scenarios from Earth system modelling (e.g. Zhang et al., 2013) to verify the outcome of numerical modeling, to test the potential of models to bridge gaps in the proxy-based record (e.g. summer sea ice extent, areas lacking

  3. Deep Ocean Heat Uptake and the Influence of Sea Ice in the Southern Ocean

    SciTech Connect

    Cecilia M. Bitz

    2011-11-22

    Climate sensitivity defines the equilibrium response to climate forcing, but ocean heat uptake is equally important at controlling the transient, response. Heat stored beneath the mixed layer is not in close thermal contact with the atmosphere, and therefore warming below the mixed layer sequesters heat that would otherwise be available to warm the surface, slowing the rate of surface warming. In this study, we investigate mechanisms that control heat uptake, primarily in the Southern Ocean, where roughly 40% of the global heat uptake occurs.

  4. Subtropical Indian Ocean SST dipole events and southern African rainfall

    NASA Astrophysics Data System (ADS)

    Reason, C. J. C.

    An atmospheric general circulation model (AGCM) is used to examine how the regional atmospheric circulation and rainfall over southern Africa respond to a recently observed dipole in subtropical sea surface temperature (SST) over the South Indian Ocean. Observations suggest that when SST is warm to the south of Madagascar and cool off Western Australia, increased summer rains occur over large areas of southeastern Africa. The model results suggest that this SST pattern leads to increased rainfall via enhanced convergence of moister than average air over the region. Increased evaporation occurs over the warm pole in the South West Indian Ocean and this moist air is advected towards Mozambique and eastern South Africa as a result of the low pressure anomaly generated over this pole which strengthens the onshore flow.

  5. Anthropogenic CO2 estimates in the Southern Ocean: Storage partitioning in the different water masses

    NASA Astrophysics Data System (ADS)

    Pardo, Paula C.; Pérez, F. F.; Khatiwala, S.; Ríos, A. F.

    2014-01-01

    The role of the Southern Ocean (SO) remains a key issue in our understanding of the global carbon cycle and for predicting future climate change. A number of recent studies suggest that 30 to 40% of ocean uptake of anthropogenic carbon (CANT) occurs in the SO, accompanied by highly efficient transport of CANT by intermediate-depth waters out of that region. In contrast, storage of CANT in deep and bottom layers is still an open question. Significant discrepancies can be found between results from several indirect techniques and ocean models. Even though reference methodologies state that CANT concentrations in deep and bottom layers of the SO are negligible, recent results from tracer-based methods and ocean models as well as accurate measurements of 39Ar, CCl4 and CFCs along the continental slope and in the Antarctic deep and bottom waters contradict this conclusion. The role of the SO in the uptake, storage and transport of CANT has proved to be really important for the global ocean and there is a need for agreement between the different techniques. A CO2-data-based ("back-calculation") method, the CT0 method, was developed with the aim of obtaining more accurate CANT concentration and inventory estimates in the SO region (south of 45°S). Data from the GLODAP (Global Ocean Data Analysis Project) and CARINA databases were used. The CT0 method tries to reduce at least two of the main caveats attributed to the back-calculation methods: the need for a better definition of water mass mixing and, most importantly, the unsteady state of the air-sea CO2 disequilibrium (ΔCdis) term. Water mass mixing was computed on the basis of results from an extended Optimum Multi-Parametric (eOMP) analysis applied to the main water masses of the SO. Recently published parameterizations were used to obtain more reliable values of ΔCdis and also of preformed alkalinity. The variability of the ΔCdis term (δCdis) was approximated using results from an ocean carbon cycle model

  6. Russian deep-sea investigations of Antarctic fauna

    NASA Astrophysics Data System (ADS)

    Malyutina, Marina

    2004-07-01

    A review of the Russian deep-sea investigation of Antarctic fauna beginning from the first scientific collection of Soviet whaling fleet expeditions 1946-1952 is presented. The paper deals with the following expeditions, their main tasks and results. These expeditions include three cruises of research vessel (R.V.) Ob in the Indian sector of the Antarctic and in the Southern Pacific (1955-1958); 11 cruises of the R.V. Akademik Kurchatov in the southern Atlantic (November-December 1971); 16 cruises of the R.V. Dmitriy Mendeleev in the Australia-New Zealand area and adjacent water of the Antarctic (December 1975-March 1976); 43 cruises of the R.V. Akademik Kurchatov in the southern Atlantic (October 1985-February 1986); and 43 cruises of the R.V. Dmitriy Mendeleev in the Atlantic sector of the South Ocean (January-May 1989). A list of the main publications on the benthic taxa collected during these expeditions with data of their distribution is presented. The results of Russian explorations of the Antarctic fauna are presented as theoretical conclusions in the following topics: (1) Vertical zonation in the distribution of the Antarctic deep-sea fauna; (2) Biogeographic division of the abyssal and hadal zones; (3) Origin of the Antarctic deep-sea fauna; (4) Distributional pathways of the Antarctic abyssal fauna through the World Ocean.

  7. Observed platelet ice distributions in Antarctic sea ice: An index for ocean-ice shelf heat flux

    NASA Astrophysics Data System (ADS)

    Langhorne, P. J.; Hughes, K. G.; Gough, A. J.; Smith, I. J.; Williams, M. J. M.; Robinson, N. J.; Stevens, C. L.; Rack, W.; Price, D.; Leonard, G. H.; Mahoney, A. R.; Haas, C.; Haskell, T. G.

    2015-07-01

    Antarctic sea ice that has been affected by supercooled Ice Shelf Water (ISW) has a unique crystallographic structure and is called platelet ice. In this paper we synthesize platelet ice observations to construct a continent-wide map of the winter presence of ISW at the ocean surface. The observations demonstrate that, in some regions of coastal Antarctica, supercooled ISW drives a negative oceanic heat flux of -30 Wm-2 that persists for several months during winter, significantly affecting sea ice thickness. In other regions, particularly where the thinning of ice shelves is believed to be greatest, platelet ice is not observed. Our new data set includes the longest ice-ocean record for Antarctica, which dates back to 1902 near the McMurdo Ice Shelf. These historical data indicate that, over the past 100 years, any change in the volume of very cold surface outflow from this ice shelf is less than the uncertainties in the measurements.

  8. Southern Ocean deep convection in global climate models: A driver for variability of subpolar gyres and Drake Passage transport on decadal timescales

    NASA Astrophysics Data System (ADS)

    Behrens, Erik; Rickard, Graham; Morgenstern, Olaf; Martin, Torge; Osprey, Annette; Joshi, Manoj

    2016-06-01

    We investigate the individual and joint decadal variability of Southern Ocean state quantities, such as the strength of the Ross and Weddell Gyres, Drake Passage transport, and sea ice area, using the National Institute of Water and Atmospheric Research UK Chemistry and Aerosols (NIWA-UKCA) model and CMIP5 models. Variability in these quantities is stimulated by strong deep reaching convective events in the Southern Ocean, which produce an Antarctic Bottom Water-like water mass and affect the large-scale meridional density structure in the Southern Ocean. An increase in the (near) surface stratification, due to freshwater forcing, can be a precondition for subsequent strong convection activity. The combination of enhanced-gyre driven sea ice and freshwater export, as well as ongoing subsurface heat accumulation, lead to a time lag between changes in oceanic freshwater and heat content. This causes an ongoing weakening of the stratification until sudden strong mixing events emerge and the heat is released to the atmosphere. We find that strong convection reduces sea ice cover, weakens the subpolar gyres, increases the meridional density gradient and subsequently results in a positive Drake Passage transport anomaly. Results of available CMIP5 models confirm that variability in sea ice, Drake Passage transport, and the Weddell Gyre strength is enhanced if models show strong open ocean convective events. Consistent relationships between convection, sea ice, Drake Passage transport, and Ross Gyre strength variability are evident in most models, whether or not they host open ocean convection.

  9. Ocean acidification state in western Antarctic surface waters: controls and interannual variability

    NASA Astrophysics Data System (ADS)

    Mattsdotter Björk, M.; Fransson, A.; Torstensson, A.; Chierici, M.

    2014-01-01

    During four austral summers (December to January) from 2006 to 2010, we investigated the surface-water carbonate system and its controls in the western Antarctic Ocean. Measurements of total alkalinity (AT), pH and total inorganic carbon (CT) were investigated in combination with high-frequency measurements on sea-surface temperature (SST), salinity and Chl a. In all parameters we found large interannual variability due to differences in sea-ice concentration, physical processes and primary production. The main result from our observations suggests that primary production was the major control on the calcium carbonate saturation state (Ω) in austral summer for all years. This was mainly reflected in the covariance of pH and Chl a. In the sea-ice-covered parts of the study area, pH and Ω were generally low, coinciding with low Chl a concentrations. The lowest pH in situ and lowest aragonite saturation (ΩAr ~ 1.0) were observed in December 2007 in the coastal Amundsen and Ross seas near marine outflowing glaciers. These low Ω and high pH values were likely influenced by freshwater dilution. Comparing 2007 and 2010, the largest ΩAr difference was found in the eastern Ross Sea, where ΩAr was about 1.2 units lower in 2007 than in 2010. This was mainly explained by differences in Chl a (i.e primary production). In 2010 the surface water along the Ross Sea shelf was the warmest and most saline, indicating upwelling of nutrient and CO2-rich sub-surface water, likely promoting primary production leading to high Ω and pH. Results from multivariate analysis agree with our observations showing that changes in Chl a had the largest influence on the ΩAr variability. The future changes of ΩAr were estimated using reported rates of the oceanic uptake of anthropogenic CO2, combined with our data on total alkalinity, SST and salinity (summer situation). Our study suggests that the Amundsen Sea will become undersaturated with regard to aragonite about 40 yr sooner than

  10. Silicon dynamics within an intense open-ocean diatom bloom in the Pacific sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Brzezinski, Mark A.; Nelson, David M.; Franck, Valerie M.; Sigmon, Daniel E.

    An intense diatom bloom developed within a strong meridional silicic acid gradient across the Antarctic Polar Front at 61°S, 170°W following stratification of the water column in late October/early November 1997. The region of high diatom biomass and the silicic acid gradient propogated southward across the Seasonal Ice Zone through time, with the maximum diatom biomass tracking the center of the silicic acid gradient. High diatom biomass and high rates of silica production persisted within the silicic acid gradient until the end of January 1998 (ca. 70 d) driving the gradient over 500 km to the south of its original position at the Polar Front. The bloom consumed 30 to >40 μM Si(OH) 4 in the euphotic zone between about 60 and 66°S leaving near surface concentrations <2.5 μM and occasionally <1.0 μM in its wake. Integrated biogenic silica concentrations within the bloom averaged 410 mmol Si m -2 (range 162-793 mmol Si m -2). Average integrated silica production on two consecutive cruises in December 1997 and January 1998 that sampled the bloom while it was well developed were 27.5±6.9 and 22.6±20 mmol Si m -2 d -1, respectively. Those levels of siliceous biomass and silica production are similar in magnitude to those reported for ice-edge diatom blooms in the Ross Sea, Antarctica, which is considered to be among the most productive regions in the Southern Ocean. Net silica production (production minus dissolution) in surface waters during the bloom was 16-21 mmol Si m -2 d -1, which is sufficient for diatom growth to be the cause of the southward displacement of the silicic acid gradient. A strong seasonal change in silica dissolution : silica production rate ratios was observed. Integrated silica dissolution rates in the upper 100-150 m during the low biomass period before stratification averaged 64% of integrated production. During the bloom integrated dissolution rates averaged only 23% of integrated silica production, making 77% of the opal produced

  11. Antarctic Entomology.

    PubMed

    Chown, Steven L; Convey, Peter

    2016-03-11

    The Antarctic region comprises the continent, the Maritime Antarctic, the sub-Antarctic islands, and the southern cold temperate islands. Continental Antarctica is devoid of insects, but elsewhere diversity varies from 2 to more than 200 species, of which flies and beetles constitute the majority. Much is known about the drivers of this diversity at local and regional scales; current climate and glacial history play important roles. Investigations of responses to low temperatures, dry conditions, and varying salinity have spanned the ecological to the genomic, revealing new insights into how insects respond to stressful conditions. Biological invasions are common across much of the region and are expected to increase as climates become warmer. The drivers of invasion are reasonably well understood, although less is known about the impacts of invasion. Antarctic entomology has advanced considerably over the past 50 years, but key areas, such as interspecific interactions, remain underexplored. PMID:26982437

  12. Development of a southern oceanic air standard reference material.

    PubMed

    Rhoderick, George C; Kelley, Michael E; Miller, Walter R; Brailsford, Gordon; Possolo, Antonio

    2016-02-01

    In 2009, the United States Congress charged the National Institute of Standards and Technology (NIST) with supporting climate change research. As part of this effort, the Gas Sensing Metrology Group at NIST began developing new gas standard mixtures for greenhouse gas mixtures relevant to atmospheric measurements. Suites of gravimetrically prepared primary standard mixtures (PSMs) were prepared at ambient concentration levels for carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in a dry-air balance. In parallel, 30 gas cylinders were filled, by the National Institute of Water and Atmospheric Research (NIWA) in Wellington, New Zealand, to high pressure from pristine southern oceanic air at Baring Head, New Zealand, and shipped to NIST. Using spectroscopic instrumentation, NIST analyzed the 30 cylinder samples for mole fractions of CO2, CH4, and N2O. Certified values were assigned to these mixtures by calibrating the instrumentation with the PSM suites that were recently developed at NIST. These mixtures became NIST Standard Reference Material (SRM) 1721 Southern Oceanic Air and are certified for ambient mole fraction, the first of their kind for NIST. The relative expanded uncertainties corresponding to coverage intervals with 95% probability are no larger than 0.06% of the certified values, representing the smallest uncertainties to date ever assigned to an NIST gas SRM. PMID:26650733

  13. Recent Precipitation Trends Over the Southern Ocean in Relation to Oceanic Freshening Near Antarctica

    NASA Astrophysics Data System (ADS)

    Cullather, R. I.; Jacobs, S. S.; Giulivi, C. F.; Leonard, K. C.; Stammerjohn, S. E.

    2008-12-01

    Quantitative assessments of large-scale precipitation over the world's oceanic regions are problematic, particularly for significant regions of the data-sparse Southern Hemisphere. Available data sets are based on the assimilation of land-based measurements, satellite radiance values, numerical weather forecast models, or some combination of the three. In this study we examine several products that cover most or all of the satellite era 1979-2007 over the Southern Ocean and surrounding mid-latitudes to 45°S. These include CMAP, the NCEP Reanalysis II, ERA-40, GPCP version 2, and the Japanese Re-analysis. Averaged fields from these data show large discrepancies in the mean spatial depiction and the annual cycle. Comparisons with unique in situ snowfall measurements and satellite-derived accumulation on sea ice are presented. The available record of oceanographic measurements in the Ross Sea indicates that salinity below 200 m in the Ross Sea has decreased by 0.03 per decade since 1958, with the highest (lowest) values in 1967 (2000). The fields examined here suggest that precipitation is likely not directly influencing the oceanic freshening observed in the Ross Sea, or in other coastal seas adjacent to Antarctica. The salinity anomaly is consistent with increasing attrition of continental ice, but places a heavy demand on the melt rate. Potential contributions to oceanic freshening from changes in sea ice extent, transport, and thickness are discussed.

  14. Seafloor seismicity, Antarctic ice-sounds, cetacean vocalizations and long-term ambient sound in the Indian Ocean basin

    NASA Astrophysics Data System (ADS)

    Royer, J.-Y.; Chateau, R.; Dziak, R. P.; Bohnenstiehl, D. R.

    2015-08-01

    This paper presents the results from the Deflo-hydroacoustic experiment in the Southern Indian Ocean using three autonomous underwater hydrophones, complemented by two permanent hydroacoustic stations. The array monitored for 14 months, from November 2006 to December 2007, a 3000 × 3000 km wide area, encompassing large segments of the three Indian spreading ridges that meet at the Indian Triple Junction. A catalogue of 11 105 acoustic events is derived from the recorded data, of which 55 per cent are located from three hydrophones, 38 per cent from 4, 6 per cent from five and less than 1 per cent by six hydrophones. From a comparison with land-based seismic catalogues, the smallest detected earthquakes are mb 2.6 in size, the range of recorded magnitudes is about twice that of land-based networks and the number of detected events is 5-16 times larger. Seismicity patterns vary between the three spreading ridges, with activity mainly focused on transform faults along the fast spreading Southeast Indian Ridge and more evenly distributed along spreading segments and transforms on the slow spreading Central and ultra-slow spreading Southwest Indian ridges; the Central Indian Ridge is the most active of the three with an average of 1.9 events/100 km/month. Along the Sunda Trench, acoustic events mostly radiate from the inner wall of the trench and show a 200-km-long seismic gap between 2 °S and the Equator. The array also detected more than 3600 cryogenic events, with different seasonal trends observed for events from the Antarctic margin, compared to those from drifting icebergs at lower (up to 50°S) latitudes. Vocalizations of five species and subspecies of large baleen whales were also observed and exhibit clear seasonal variability. On the three autonomous hydrophones, whale vocalizations dominate sound levels in the 20-30 and 100 Hz frequency bands, whereas earthquakes and ice tremor are a dominant source of ambient sound at frequencies <20 Hz.

  15. Bacterioplankton in antarctic ocean waters during late austral winter: abundance, frequency of dividing cells, and estimates of production.

    PubMed

    Hanson, R B; Shafer, D; Ryan, T; Pope, D H; Lowery, H K

    1983-05-01

    Bacterioplankton productivity in Antarctic waters of the eastern South Pacific Ocean and Drake Passage was estimated by direct counts and frequency of dividing cells (FDC). Total bacterioplankton assemblages were enumerated by epifluorescent microscopy. The experimentally determined relationship between in situ FDC and the potential instantaneous growth rate constant (mu) is best described by the regression equation ln mu = 0.081 FDC - 3.73. In the eastern South Pacific Ocean, bacterioplankton abundance (2 x 10 to 3.5 x 10 cells per ml) and FDC (11%) were highest at the Polar Front (Antarctic Convergence). North of the Subantarctic Front, abundance and FDC were between 1 x 10 to 2 x 10 cells per ml and 3 to 5%, respectively, and were vertically homogeneous to a depth of 600 m. In Drake Passage, abundance (10 x 10 cells per ml) and FDC (16%) were highest in waters south of the Polar Front and near the sea ice. Subantarctic waters in Drake Passage contained 4 x 10 cells per ml with 4 to 5% FDC. Instantaneous growth rate constants ranged between 0.029 and 0.088 h. Using estimates of potential mu and measured standing stocks, we estimated productivity to range from 0.62 mug of C per liter . day in the eastern South Pacific Ocean to 17.1 mug of C per liter . day in the Drake Passage near the sea ice. PMID:16346297

  16. Salp distribution and size composition in the Atlantic sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Kawaguchi, S.; Siegel, V.; Litvinov, F.; Loeb, V.; Watkins, J.

    2004-06-01

    Salp abundance and length frequency were measured during the large-scale CCAMLR 2000 Survey conducted in the Atlantic Sector of the Southern Ocean in the 1999/2000 season. Results from regional surveys around Elephant Island in 1994/95 and 1996/97 seasons also were examined. During the CCAMLR 2000 Survey, salp abundance was higher in the Antarctic Peninsula and South Sandwich Island areas than in the central Scotia Sea. The probable reason for this pattern is a negative relationship with phytoplankton abundance; the central Scotia Sea having greater phytoplankton concentrations than required for optimal salp filter-feeding performance. Cluster analysis of salp size composition resulted in three cluster groups for each of the three surveys. Clusters comprising large salps occurred in warmer waters in all three surveys. The size composition of the salp populations suggests that the timing of intense asexual reproductive budding was earlier in warmer waters. As surface water temperatures generally decrease from north to south, and increase from spring to summer, the general spatio-temporal pattern of asexual reproduction by budding is likely to proceed from north to south as the summer season progresses.

  17. Bacterioplankton community shifts associated with epipelagic and mesopelagic waters in the Southern Ocean.

    PubMed

    Yu, Zheng; Yang, Jun; Liu, Lemian; Zhang, Wenjing; Amalfitano, Stefano

    2015-01-01

    The Southern Ocean is among the least explored marine environments on Earth, and still little is known about regional and vertical variability in the diversity of Antarctic marine prokaryotes. In this study, the bacterioplankton community in both epipelagic and mesopelagic waters was assessed at two adjacent stations by high-throughput sequencing and quantitative PCR. Water temperature was significantly higher in the superficial photic zone, while higher salinity and dissolved oxygen were recorded in the deeper water layers. The highest abundance of the bacterioplankton was found at a depth of 75 m, corresponding to the deep chlorophyll maximum layer. Both Alphaproteobacteria and Gammaproteobacteria were the most abundant taxa throughout the water column, while more sequences affiliated to Cyanobacteria and unclassified bacteria were identified from surface and the deepest waters, respectively. Temperature was the most significant environmental variable affecting the bacterial community structure. The bacterial community composition displayed significant differences at the epipelagic layers between two stations, whereas those in the mesopelagic waters were more similar to each other. Our results indicated that the epipelagic bacterioplankton might be dominated by short-term environmental variable conditions, whereas the mesopelagic communities appeared to be structured by longer water-mass residence time and relative stable environmental factors. PMID:26256889

  18. The leading role of ammonium in the nitrogen uptake regime of Southern Ocean marginal ice zones

    NASA Astrophysics Data System (ADS)

    Goeyens, L.; Tréguer, P.; Baumann, M. E. M.; Baeyens, W.; Dehairs, F.

    1995-06-01

    The nitrogen signature of marginal ice zones in the Southern Ocean often departs from the "classical" Antarctic nutrient profiles with high nitrate and low ammonium values in the surface layer. Weddell Sea marginal ice zones e.g. show enhanced nitrate depletions, amounting to ~ 500 mmol N m -2. Additionally, ammonium stocks in the upper layer can be up to 7% of the inorganic nitrogen pool. The corresponding nitrogen uptake regime suggests elevated nitrate assimilation during the early phase of the productive season and significantly reduced nitrate assimilation at a later stage. Absolute as well as specific nitrate uptake rates decrease by an order of magnitude when ammonium stocks exceed 1.7% of the total inorganic nitrogen. The variability in nitrogen utilisation reflects physiological changes in the phytoplankton assemblage. In response to increased ammonium stocks phytoplankton show a reduction in their capacity to take up nitrate and following an initial diatom bloom non-siliceous phytoplankton become predominant in a regenerated production regime.

  19. Blue and fin whale call source levels and propagation range in the Southern Ocean.

    PubMed

    Sirović, Ana; Hildebrand, John A; Wiggins, Sean M

    2007-08-01

    Blue (Balaenoptera musculus) and fin whales (B. physalus) produce high-intensity, low-frequency calls, which probably function for communication during mating and feeding. The source levels of blue and fin whale calls off the Western Antarctic Peninsula were calculated using recordings made with calibrated, bottom-moored hydrophones. Blue whales were located up to a range of 200 km using hyperbolic localization and time difference of arrival. The distance to fin whales, estimated using multipath arrivals of their calls, was up to 56 km. The error in range measurements was 3.8 km using hyperbolic localization, and 3.4 km using multipath arrivals. Both species produced high-intensity calls; the average blue whale call source level was 189+/-3 dB re:1 microPa-1 m over 25-29 Hz, and the average fin whale call source level was 189+/-4 dB re:1 microPa-1 m over 15-28 Hz. Blue and fin whale populations in the Southern Ocean have remained at low numbers for decades since they became protected; using source level and detection range from passive acoustic recordings can help in calculating the relative density of calling whales. PMID:17672667

  20. Light limitation of phytoplankton biomass and macronutrient utilization in the Southern Ocean

    SciTech Connect

    Mitchell, B.G.; Brody, E.A.; Holm-Hansen, O. ); McClain, C. ); Bishop, J. )

    1991-12-01

    The Antarctic Circumpolar Current (ACC) is unique in that it has continually high concentrations of major plant nutrients but low phytoplankton biomass. This enigmatic phenomenon is the focus of significant speculation that trace nutrients, including Fe, may limit phytoplankton crop size. Global climatologies indicate that the ACC is a region with low surface temperatures, weak density stratification, little summertime surface solar irradiance, and strong wind stress. These physical phenomena act to limit growth rates of the phytoplankton community. Using a photo-physiological description of phytoplankton growth in a simple one-dimensional ecosystem model forced by observations or climatologies of mixing depth and surface irradiance, the authors make an evaluation of the potential for massive, nutrient-exhausting, phytoplankton blooms forming in the ACC. The ACC has persistent mixed layers in excess of 50 m. Literature values and model optimization indicate that the minimal aggregate specific loss rate and typical physical conditions of stratification and surface irradiance, the model predicts that phytoplankton in the ACC would not utilize >10% of the available macronutrients. Without a mechanism for increasing the strength of stratification, the authors predict that massive Fe additions to the Southern Ocean would fail to significantly mitigate the atmospheric CO{sub 2} derived from fossil fuel.

  1. Bacterioplankton community shifts associated with epipelagic and mesopelagic waters in the Southern Ocean

    PubMed Central

    Yu, Zheng; Yang, Jun; Liu, Lemian; Zhang, Wenjing; Amalfitano, Stefano

    2015-01-01

    The Southern Ocean is among the least explored marine environments on Earth, and still little is known about regional and vertical variability in the diversity of Antarctic marine prokaryotes. In this study, the bacterioplankton community in both epipelagic and mesopelagic waters was assessed at two adjacent stations by high-throughput sequencing and quantitative PCR. Water temperature was significantly higher in the superficial photic zone, while higher salinity and dissolved oxygen were recorded in the deeper water layers. The highest abundance of the bacterioplankton was found at a depth of 75 m, corresponding to the deep chlorophyll maximum layer. Both Alphaproteobacteria and Gammaproteobacteria were the most abundant taxa throughout the water column, while more sequences affiliated to Cyanobacteria and unclassified bacteria were identified from surface and the deepest waters, respectively. Temperature was the most significant environmental variable affecting the bacterial community structure. The bacterial community composition displayed significant differences at the epipelagic layers between two stations, whereas those in the mesopelagic waters were more similar to each other. Our results indicated that the epipelagic bacterioplankton might be dominated by short-term environmental variable conditions, whereas the mesopelagic communities appeared to be structured by longer water-mass residence time and relative stable environmental factors. PMID:26256889

  2. Particle Size Distributions of Water Soluble Species and Nutrient Elements in Aerosols over the Southern Ocean and Coastal East Antarctica

    NASA Astrophysics Data System (ADS)

    Xu, G.; Gao, Y.

    2012-12-01

    The particle size is an important parameter to determin the chemical and physical properties of aerosols of marine origin, especially the fine mode particles that may act as cloud condenstation neuclei (CCN), affecting cloud microphysics and consequently climate. The air-to-sea deposition of aerosol particles are also dependent on particle sizes, which are important for the calculation of atmospheric nutrient fluxes to the ocean. To characterize the size distributions of water-soluble inorganic, organic aerosol species (including Na+, non-sea-salt (nss) sulfate, methane sulfonate (MSA), oxalate and succinate) of marine origin and nutrient elements (inlcuding Cu, Fe, Mn, Ni and Zn and Cd) over the Southern Ocean and coastal East Antarctica, size-segregated aerosols were collected from 40°S, 100°E to 69°S, 76°E and between 69°S, 76°E and 66°S, 110°E during a cruise from November 2010 to March 2011. Results indicate that sea salt particles, a major aerosol component and generated by strong westerly winds, existed mainly in the coarse mode with a concentration peak at >3.0 μm over the Southern Ocean. However, the nss-sulfate, a secondary aerosol species, existed mainly in the fine mode, with a single peak at <0.49 μm over the Southern Ocean, and in a bimodal distribution, peaking at 0.10 - 0.18 μm and 0.32 - 0.56 μm over coastal East Antarctic seas. Over the Southern Ocean, MSA showed a bimodal distribution, a large peak at 0.32-0.56 μm and a small peak at 3.0-7.2 μm, while over coastal East Antarctica, MSA was enriched in particles of 0.32-0.56 μm. Oxalate and formate existed in the fine mode, while succinate showed a bimodal distribution. Nutrient elements including Fe, Mn and Cd showed a bimodal distribution, at both submicron and supermicron size ranges. While Zn was mainly accumulated at 1.0-3.2 μm over coastal East Antarctica, both Zn and Cd mainly existed in the fine mode with a concentration peak at <0.49 μm over the Southern Ocean. Different

  3. The distinct roles of the Antarctic and Subantarctic Zones in ocean productivity and atmospheric CO2 across the Mid-Pleistocene transition

    NASA Astrophysics Data System (ADS)

    Jaccard, S.; Martinez-Garcia, A.; Hasenfratz, A.; Sigman, D. M.; Haug, G. H.

    2012-12-01

    The emergence of low frequency, high-amplitude, quasi-periodic (100-kyr) glacial variability during the middle Pleistocene in the absence of any significant change in orbital forcing indicates a fundamental change internal to the climate system. The mid-Pleistocene transition (MPT), which occurred between 1.2 and 0.7 Myr, has variably been attributed to either global cooling possibly associated with a long-term decrease in greenhouse gas concentrations or changes in internal ice-sheet dynamics independent of changes in atmospheric pCO2. The available low-resolution pCO2 estimates indicate that atmospheric CO2 concentrations were 30 ppm higher during glacial stages before the MPT, but also that interglacial values were similar to those of the late Pleistocene. This resulted in no significant change in the atmospheric CO2 trend. However, the higher atmospheric CO2 concentrations during glacial stages resulted in an increase in glacial temperatures in the tropics, and a 30% decrease in glacial/interglacial amplitude before 450 kyr. During this period Southern Ocean dust fluxes doubled and reached values that are comparable to those of the LGM. Thus, an increase in Fe availability may have potentially contributed, in combination with other mechanisms to explain part of the 30 ppm decrease in glacial atmospheric CO2 observed across the MPT. This observation is coherent with a progressive increase in glacial carbon sequestration due to Fe fertilization in the Southern Ocean as Northern Hemisphere glaciations intensify. Here, we investigate how the combined changes in Fe supply and in the strength of vertical convection have affected the sequestration of remineralized carbon in the ocean interior over the last 1.6 Myrs. We will show highly-resolved, continuous records from two South Atlantic ODP sedimentary archives located on either side of the Antarctic polar front highlighting the existence of a strong positive feedback mechanism between ice volume, Southern Ocean dust

  4. Graviry fields of the southern ocean from Geosat data

    NASA Astrophysics Data System (ADS)

    McAdoo, David C.; Marks, Karen M.

    1992-03-01

    In August 1990, the U.S. Navy declassified all Geodetic Mission (GM) radar altimeter data acquired by the Geosat satellite over oceanic regions south of 60°S. We have used these GM data in conjunction with the unclassified, lower-resolution Geosat Exact Repeat Mission (ERM) altimeter data to construct high-resolution gravity fields on a 5-km grid covering the annular region of the southern ocean, which lies between 60°S and 72°S and encircles Antarctica. During the GM a complete mapping of the marine geoid (between 72°S and 72°N) was accomplished. The GM produce more densely spaced ground tracks (typically 2 or 3 km at 60°S) than those of either the ERM or Seasat. Consequently, we were able to use the GM data to map the marine gravity field at a higher resolution than was previously possible using satellite altimeter data. This paper describes the techniques we used to derive these gravity fields and image them. These techniques involve (1) computing along-track sea surface height slopes, (2) gridding of these ascending and descending slopes, (3) converting the slopes to conventional deflections of the vertical, (4) transforming the deflections to gravity anomalies in the frequency domain, and (5) imaging. The resulting images of the marine gravity field reveal much that is new about the seafloor and the tectonic fabric of the southern ocean: a region which includes large expanses of seafloor that have never been surveyed by ships.

  5. Characteristics of regional aerosols: Southern Arizona and eastern Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Prabhakar, Gouri

    Atmospheric aerosols impact the quality of our life in many direct and indirect ways. Inhalation of aerosols can have harmful effects on human health. Aerosols also have climatic impacts by absorbing or scattering solar radiation, or more indirectly through their interactions with clouds. Despite a better understanding of several relevant aerosol properties and processes in the past years, they remain the largest uncertainty in the estimate of global radiative forcing. The uncertainties arise because although aerosols are ubiquitous in the Earth's atmosphere they are highly variable in space, time and their physicochemical properties. This makes in-situ measurements of aerosols vital in our effort towards reducing uncertainties in the estimate of global radiative forcing due to aerosols. This study is an effort to characterize atmospheric aerosols at a regional scale, in southern Arizona and eastern Pacific Ocean, based on ground and airborne observations of aerosols. Metals and metalloids in particles with aerodynamic diameter (Dp) smaller than 2.5 μm are found to be ubiquitous in southern Arizona. The major sources of the elements considered in the study are identified to be crustal dust, smelting/mining activities and fuel combustion. The spatial and temporal variability in the mass concentrations of these elements depend both on the source strength and meteorological conditions. Aircraft measurements of aerosol and cloud properties collected during various field campaigns over the eastern Pacific Ocean are used to study the sources of nitrate in stratocumulus cloud water and the relevant processes. The major sources of nitrate in cloud water in the region are emissions from ships and wildfires. Different pathways for nitrate to enter cloud water and the role of meteorology in these processes are examined. Observations of microphysical properties of ambient aerosols in ship plumes are examined. The study shows that there is an enhancement in the number

  6. Effects of Southern Hemisphere Wind Changes on the Meridional Overturning Circulation in Ocean Models.

    PubMed

    Gent, Peter R

    2016-01-01

    Observations show that the Southern Hemisphere zonal wind stress maximum has increased significantly over the past 30 years. Eddy-resolving ocean models show that the resulting increase in the Southern Ocean mean flow meridional overturning circulation (MOC) is partially compensated by an increase in the eddy MOC. This effect can be reproduced in the non-eddy-resolving ocean component of a climate model, providing the eddy parameterization coefficient is variable and not a constant. If the coefficient is a constant, then the Southern Ocean mean MOC change is balanced by an unrealistically large change in the Atlantic Ocean MOC. Southern Ocean eddy compensation means that Southern Hemisphere winds cannot be the dominant mechanism driving midlatitude North Atlantic MOC variability. PMID:26163010

  7. Changes of carbon dioxide in surface waters during spring in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Bakker, D. C. E.; De Baar, H. J. W.; Bathmann, U. V.

    The fugacity of C0 2 (fCO 2) and the content of chlorophyll a in surface-water were determined during consecutive sections between 47° and 60°S along 6°W in austral spring, October- November 1992. In the Polar Frontal region, the fCO 2 of surface-water decreased from slightly below the atmospheric value to 50 μatm below it. This was accompanied by the development of diatom blooms. Seasonal warming of 1.2°C and air-sea exchange partly compensated the decrease of fCO 2 by biological activity. Meanders of the Polar Frontal jet and a mesoscale eddy were reflected in spatial variability of fCO 2 and chlorophyll a. Systematic observations indicated relationships between fCO 2 and chlorophyll a, albeit changing with time. The combination of biological CO 2- uptake with formation of Antarctic Intermediate Water (AAIW) makes the Polar Front a site of combined biological/physical CO 2-drawdown from the atmosphere. In the southern part of the Antarctic Circumpolar Current (sACC) and the Southern Frontal region, fCO 2 increased 7-8 μatm due to surface-water warming of 0.5°C. A sharp rise of surface water fCO 2 of 13 μatm occurred south of the southern Frontal jet. As the ice-cover disappeared, the Boundary between the ACC and the Weddell Gyre released significant amounts of CO 2. The Weddell Gyre would become a strong CO 2-source after the imminent retreat of the ice. Clearly mechanisms behind changes of fCO 2 in surface waters differ for the hydrographic regions. Interstitial brines of sea-ice had fCO 2 as low as 100 μatm and had been depleted in nutrients. The summation of significant sources and sinks in the different regions indicates an overall minor oceanic CO 2-sink of 0.3 mmol m -2 day -1 throughout the cruise, on the basis of the Wanninkhof relationship at in situ wind speed without skin effect. Uptake of C0 2 increased to 1.0 mmol m -2 day -1, when a uniform cold skin temperature difference of 0.2°C was assumed. The skin temperature difference derived from

  8. The Southern Antarctic Circumpolar Current Front: physical and biological coupling at South Georgia

    NASA Astrophysics Data System (ADS)

    Ward, Peter; Whitehouse, Mick; Meredith, Mike; Murphy, Eugene; Shreeve, Rachael; Korb, Rebecca; Watkins, Jon; Thorpe, Sally; Woodd-Walker, Rachel; Brierley, Andrew; Cunningham, Nathan; Grant, Sharon; Bone, Doug

    2002-12-01

    The coupling of physics and biology was examined along a 160 km long transect running out from the north coast of South Georgia Island and crossing the Southern Antarctic Circumpolar Current Front (SACCF) during late December 2000. Surface and near surface potential TS properties indicated the presence of three water types: a near-shore group of stations characterised by water which became progressively warmer and fresher closer to South Georgia, an offshore grouping in which sea surface temperatures and those at the winter water level were relatively warm (1.8°C and 0.5°C, respectively), and a third in which surface and winter water temperatures were cooler and reflected the presence of the SACCF. The transect bisected the SACCF twice, revealing that it was flowing in opposite directions, north-westward closest to South Georgia and south-eastwards at its furthest point from the island. The innermost limb was a narrow intense feature located just off the shelf break in 2000-3500 m of water and in which rapid surface baroclinic velocities (up to 35 cm s -1) were encountered. Offshore in the outermost limb, shown subsequently to be a mesoscale eddy that had meandered south from the retroflected limb of the SACCF, flow was broader and slower with peak velocities around 20 cm s -1. Chlorophyll a biomass was generally low (<1 mg m -3) over much of the transect but increased dramatically in the region of the innermost limb of the SACCF, where a deepening of the surface mixed layer was coincident with a subsurface chlorophyll maximum (7.4 mg m -3) and elevated concentrations down to 100 m. The bloom was coincident with depleted nutrient concentrations, particularly silicate, nitrate and phosphate, and although ammonium concentrations were locally depleted the bloom lay within an elevated band (up to 1.5 mmol m -3) associated with the frontal jet. Increased zooplankton abundance, higher copepod body carbon mass and egg production rates all showed a strong spatial

  9. Subtropical forest expansion in the middle Miocene Europe: pCO2, Antarctic ice volume and oceanic changes

    NASA Astrophysics Data System (ADS)

    Hamon, N.; Sepulchre, P.; Donnadieu, Y.; Ramstein, G.

    2012-04-01

    The middle Miocene is a crucial period for ape's evolution and corresponds to their appearance in Europe. The dispersion of apes was made possible by tectonic changes and the expansion of their habitat, which is tropical to subtropical forest, in Europe. The context in which the Middle Miocene Climatic Optimum occurred still lacks constraints in terms of atmospheric pCO2 and Antarctic ice sheet volume and extent. Using the coupled atmosphere - ocean GCM FOAM and the dynamic vegetation model CARAIB, we investigate the sensitivity of Miocene climate and vegetation to pCO2 levels and Antarctic ice sheet configurations. We performed sensitivity experiments to test the impact of varying pCO2 (280 ppmv, 560 ppmv and 700 ppmv) and Antarctic albedo (ice and tundra) on the European vegetation during the Middle Miocene Climatic Optimum. Our results indicate that higher than present pCO2 is necessary to simulate subtropical forest in Western and Central Europe during the middle Miocene. However, a threshold between 560 and 700 ppmv makes subtropical forest partly collapse, which is due to colder and slightly dryer conditions in Europe. This can be explained by the fact that CO2-induced warming of the high latitudes strongly reduces North Atlantic Deep Water formation, therefore reducing the heat transport in this region. Moreover, the albedo change over Antarctica, which is directly linked to the ice surface, leads to further warming in Europe, and the expansion of subtropical forest. These results suggest that a small East Antarctic Ice Sheet (25% of present-day ice volume) together with higher than present pCO2 are in better agreement with available European middle Miocene data.

  10. The Southern Ocean as a constraint to reduce uncertainty in future ocean carbon sinks

    NASA Astrophysics Data System (ADS)

    Kessler, A.; Tjiputra, J.

    2016-04-01

    Earth system model (ESM) simulations exhibit large biases compares to observation-based estimates of the present ocean CO2 sink. The inter-model spread in projections increases nearly 2-fold by the end of the 21st century and therefore contributes significantly to the uncertainty of future climate projections. In this study, the Southern Ocean (SO) is shown to be one of the hot-spot regions for future uptake of anthropogenic CO2, characterized by both the solubility pump and biologically mediated carbon drawdown in the spring and summer. We show, by analyzing a suite of fully interactive ESMs simulations from the Coupled Model Intercomparison Project phase 5 (CMIP5) over the 21st century under the high-CO2 Representative Concentration Pathway (RCP) 8.5 scenario, that the SO is the only region where the atmospheric CO2 uptake rate continues to increase toward the end of the 21st century. Furthermore, our study discovers a strong inter-model link between the contemporary CO2 uptake in the Southern Ocean and the projected global cumulated uptake over the 21st century. This strong correlation suggests that models with low (high) carbon uptake rate in the contemporary SO tend to simulate low (high) uptake rate in the future. Nevertheless, our analysis also shows that none of the models fully capture the observed biophysical mechanisms governing the CO2 fluxes in the SO. The inter-model spread for the contemporary CO2 uptake in the Southern Ocean is attributed to the variations in the simulated seasonal cycle of surface pCO2. Two groups of model behavior have been identified. The first one simulates anomalously strong SO carbon uptake, generally due to both too strong a net primary production and too low a surface pCO2 in December-January. The second group simulates an opposite CO2 flux seasonal phase, which is driven mainly by the bias in the sea surface temperature variability. We show that these biases are persistent throughout the 21st century, which highlights the

  11. Production regime and associated N cycling in the vicinity of Kerguelen Island, Southern Ocean

    NASA Astrophysics Data System (ADS)

    Cavagna, A. J.; Fripiat, F.; Elskens, M.; Mangion, P.; Chirurgien, L.; Closset, I.; Lasbleiz, M.; Florez-Leiva, L.; Cardinal, D.; Leblanc, K.; Fernandez, C.; Lefèvre, D.; Oriol, L.; Blain, S.; Quéguiner, B.; Dehairs, F.

    2015-11-01

    Although the Southern Ocean is considered a high-nutrient, low-chlorophyll (HNLC) area, massive and recurrent blooms are observed over and downstream of the Kerguelen Plateau. This mosaic of blooms is triggered by a higher iron supply resulting from the interaction between the Antarctic Circumpolar Current and the local bathymetry. Net primary production, N uptake (NO3- and NH4+), and nitrification rates were measured at eight stations in austral spring 2011 (October-November) during the KEOPS 2 cruise in the Kerguelen Plateau area. Natural iron fertilization stimulated primary production, with mixed layer integrated net primary production and growth rates much higher in the fertilized areas (up to 315 mmol C m-2 d-1 and up to 0.31 d-1 respectively) compared to the HNLC reference site (12 mmol C m-2 d-1 and 0.06 d-1 respectively). Primary production was mainly sustained by nitrate uptake, with f ratios (corresponding to NO3--uptake / (NO3--uptake + NH4+-uptake)) lying at the upper end of the observations for the Southern Ocean (up to 0.9). We report high rates of nitrification (up to ~ 3 μmol N L-1 d-1, with ~ 90 % of them < 1 μmol N L-1 d-1) typically occurring below the euphotic zone, as classically observed in the global ocean. The specificity of the studied area is that at most of the stations, the euphotic layer was shallower than the mixed layer, implying that nitrifiers can efficiently compete with phytoplankton for the ammonium produced by remineralization at low-light intensities. Nitrate produced by nitrification in the mixed layer below the euphotic zone is easily supplied to the euphotic zone waters above, and nitrification sustained 70 ± 30 % of the nitrate uptake in the productive area above the Kerguelen Plateau. This complicates estimations of new production as potentially exportable production. We conclude that high productivity in deep mixing system stimulates the N cycle by increasing both assimilation and regeneration.

  12. Upper Miocene-Pliocene diatoms in the Southern Ocean: IODP Site U1361 on the continental rise off Wilkes Land, Antarctica

    NASA Astrophysics Data System (ADS)

    Kobayashi, M.; Iwai, M.

    2012-04-01

    During the Integrated Ocean Drilling Program (IODP) Expedition 318, a total three sites has been drilled at the continental rise along the Antarctic margin off Wilkes Land. Sedimentary sections obtained at those three sites provide continuous sequence of Miocene through Pleistocene to access siliceous biochronology and paleoceanography in the Southern Ocean. Systematic offset of diatom biostratigraphic events and geomagnetic polarity in uppermost Miocene to lowermost Pliocene section observed at Site 1095 in the Antarctic Peninsula (Iwai et al., 2002, Acton et al., 2002; Leg 178SR) and it was critical to access the timing of overdeepening of continental shelf topograhhy and Ice dinamics (Bart and Iwai, 2011, PPP). The offset has been reconfirmed at Sites U1359 and U1361 (Escutia et al., 2011; 318 Expedition Reports). We conclude that the most probable reason for the discrepancy between the biostratigraphic and magnetostratigraphic data from Sites 1095, U1359, and U1361 is previous miscalibration of Southern Ocean biostratigraphic events to the GPTS in the late Miocene to basal Pliocene time interval. Here we will present the result of counted diatom biostratigraphy at Site U1361 as an example.

  13. Coastal ocean transport patterns in the central Southern California Bight

    USGS Publications Warehouse

    Noble, M.A.; Rosenberger, K.J.; Hamilton, P.; Xu, J. P.

    2009-01-01

    In the past decade, several large programs that monitor currents and transport patterns for periods from a few months to a few years were conducted by a consortium of university, federal, state, and municipal agencies in the central Southern California Bight, a heavily urbanized section of the coastal ocean off the west coast of the United States encompassing Santa Monica Bay, San Pedro Bay, and the Palos Verdes shelf. These programs were designed in part to determine how alongshelf and cross-shelf currents move sediments, pollutants, and suspended material through the region. Analysis of the data sets showed that the current patterns in this portion of the Bight have distinct changes in frequency and amplitude with location, in part because the topography of the shelf and upper slope varies rapidly over small spatial scales. However, because the mean, subtidal, and tidal-current patterns in any particular location were reasonably stable with time, one could determine a regional pattern for these current fields in the central Southern California Bight even though measurements at the various locations were obtained at different times. In particular, because the mean near-surface flows over the San Pedro and Palos Verdes shelves are divergent, near-surface waters from the upper slope tend to carry suspended material onto the shelf in the northwestern portion of San Pedro Bay. Water and suspended material are also carried off the shelf by the mean and subtidal flow fields in places where the orientation of the shelf break changes abruptly. The barotropic tidal currents in the central Southern California Bight flow primarily alongshore, but they have pronounced amplitude variations over relatively small changes in alongshelf location that are not totally predicted by numerical tidal models. Nonlinear internal tides and internal bores at tidal frequencies are oriented more across the shelf. They do not have a uniform transport direction, since they move fine sediment

  14. Application of the TEX86-L temperature proxy in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Kim, Jung-Hyun; Willmott, Veronica; Etourneau, Johan; Crosta, Xavier; Massé, Guillaume; Bonnin, Jérôme; Schouten, Stefan; Sinninghe Damsté, Jaap S.

    2013-04-01

    . Cosmochim. Acta, 74, 4639-4654, 2010. Kim, J.-H., Crosta, X., Willmott, V., Renssen, H., Massé, G., Bonnin, J., Helmke, P., Schouten, S., and Sinninghe Damsté, J.S.: Increase in Late Holocene subsurface temperature variability in East Antarctica, Geophys. Res. Lett., 39, L06705, doi:10.1029/2012GL051157, 2012. Schouten, S., Hopmans, E.C., Schefuß, E., and Sinninghe Damsté, J.S.: Distributional variations in marine crenarchaeotal membrane lipids: A new organic proxy for reconstructing ancient sea water temperatures? Earth Planet. Sci. Lett., 204, 265-274, 2002. Shevenell, A.E., Ingalls, A.E., Domack, E.W., and Kelly, C.: Holocene Southern Ocean surface temperature variability west of the Antarctic Peninsula, Nature, 470, 250-254, 2011.

  15. Sequence stratigraphy of the ANDRILL Southern McMurdo Sound (SMS) project drillcore, Antarctica: an expanded, near-field record of Antarctic Early to Middle Miocene climate and relative sea-level change

    NASA Astrophysics Data System (ADS)

    Fielding, C. R.; Browne, G. H.; Field, B.; Florindo, F.; Harwood, D. M.; Krissek, L. A.; Levy, R. H.; Panter, K.; Passchier, S.; Pekar, S. F.; SMS Science Team

    2008-12-01

    Present understanding of Antarctic climate change during the Early to Middle Miocene, including definition of major cycles of glacial expansion and contraction, relies in large part on stable isotope proxy records from Ocean Drilling Program cores. Here, we present a sequence stratigraphic analysis of the Southern McMurdo Sound drillcore (AND-2A), which was acquired during the Austral Spring of 2007. This core offers a hitherto unavailable ice-proximal stratigraphic archive of the Early to Middle Miocene from a high-accommodation Antarctic continental margin setting, and provides clear evidence of repeated fluctuations in climate, ice expansion/contraction and attendant sea-level change over the period 20-14 Ma, with a more fragmentary record of the post-14 Ma period. A succession of seventy sequences is recognized, each bounded by a significant facies dislocation (sequence boundary), composed internally of deposits of glacimarine to open shallow marine environments, and each typically dominated by the transgressive systems tract. From changes in facies abundances and sequence character, a series of long-term (m.y.) changes in climate and relative sea-level is identified. The lithostratigraphy can be correlated confidently to glacial events Mi1b and Mi2, to the Miocene Climatic Optimum, and to the global eustatic sea-level curve. SMS provides a detailed, direct, ice-proximal reference point from which to evaluate stable isotope proxy records for Neogene Antarctic paleoclimate.

  16. Automated ocean color product validation for the Southern California Bight

    NASA Astrophysics Data System (ADS)

    Davis, Curtiss O.; Tufillaro, Nicholas; Jones, Burt; Arnone, Robert

    2012-06-01

    Automated match ups allow us to maintain and improve the products of current satellite ocean color sensors (MODIS, MERIS), and new sensors (VIIRS). As part of the VIIRS mission preparation, we have created a web based automated match up tool that provides access to searchable fields for date, site, and products, and creates match-ups between satellite (MODIS, MERIS, VIIRS), and in-situ measurements (HyperPRO and SeaPRISM). The back end of the system is a 'mySQL' database, and the front end is a `php' web portal with pull down menus for searchable fields. Based on selections, graphics are generated showing match-ups and statistics, and ascii files are created for downloads for the matchup data. Examples are shown for matching the satellite data with the data from Platform Eureka SeaPRISM off L.A. Harbor in the Southern California Bight.

  17. A Deep-Sea Coral Clumped Isotope Record From Southern Ocean Intermediate Water Spanning the Most Recent Glacial Termination

    NASA Astrophysics Data System (ADS)

    Hines, S.; Eiler, J. M.; Adkins, J. F.

    2015-12-01

    Movement of intermediate waters plays an important role in global heat and carbon transport in the ocean and changes in their distribution are closely tied to glacial-interglacial climate change. Ocean temperature is necessarily linked to circulation because density is a function of temperature and salinity. In the modern ocean, stratification is dominated by differences in temperature, but this may not have been the case in the past. Coupled radiocarbon and U/Th dates on deep-sea Desmophyllum dianthus corals allow for the reconstruction of past intermediate water circulation rates. The addition of temperature measurements further aids in understanding of the mechanisms driving the observed signals, since there are different boundary conditions for resetting these two properties at the surface. In the modern Southern Ocean, temperature and radiocarbon are broadly correlated. At the surface there are meridional gradients of these properties, with colder, more radiocarbon-depleted water closer to the Antarctic continent. We present a high-resolution time series of clumped isotope temperature measurements on 30 corals spanning the Last Glacial Maximum through the end of the Antarctic Cold Reversal (ACR). These samples have previously been U/Th and radiocarbon dated. Corals were collected south of Tasmania from depths of between ~1450 - 1900 m, with 70% between 1500 and 1700 m. Uranium and thorium measurements were made by MC-ICP-MS on a ThermoFinnigan Neptune, radiocarbon was measured by AMS at the KCCAMS Laboratory at UC Irvine, and clumped isotope temperatures were measured on a MAT 253 attached to an automated carbonate preparation line. Preliminary results show constant temperature between ~20 - 18 ka, a gradual rise of ~6 ºC through Heinrich Stadial 1 (~18 - 15 ka), an abrupt drop of ~7 ºC directly preceeding the start of the Bølling at 14.7 ka, and another slight rise of ~4 ºC through the ACR (14.7 - 12.8 ka). The addition of clumped isotope temperatures to

  18. The influence of Southern Ocean winds on the North Atlantic carbon sink

    NASA Astrophysics Data System (ADS)

    Bronselaer, Ben; Zanna, Laure; Munday, David R.; Lowe, Jason

    2016-06-01

    Observed and predicted increases in Southern Ocean winds are thought to upwell deep ocean carbon and increase atmospheric CO2. However, Southern Ocean dynamics affect biogeochemistry and circulation pathways on a global scale. Using idealized Massachusetts Institute of Technology General Circulation Model (MITgcm) simulations, we demonstrate that an increase in Southern Ocean winds reduces the carbon sink in the North Atlantic subpolar gyre. The increase in atmospheric CO2 due to the reduction of the North Atlantic carbon sink is shown to be of the same magnitude as the increase in atmospheric CO2 due to Southern Ocean outgassing. The mechanism can be described as follows: The increase in Southern Ocean winds leads to an increase in upper ocean northward nutrient transport. Biological productivity is therefore enhanced in the tropics, which alters the chemistry of the subthermocline waters that are ultimately upwelled in the subpolar gyre. The results demonstrate the influence of Southern Ocean winds on the North Atlantic carbon sink and show that the effect of Southern Ocean winds on atmospheric CO2 is likely twice as large as previously thought in past, present, and future climates.

  19. Influence of frontal zones on the distribution of particulate matter and organic compounds in surface waters of the Atlantic and Southern Oceans

    NASA Astrophysics Data System (ADS)

    Nemirovskaya, I. A.; Lisitzin, A. P.; Kravchishina, M. D.; Redzhepova, Z. Yu.

    2015-10-01

    Particulate matter and organic compounds (chlorophyll, lipids, and hydrocarbons) were analyzed in surface waters along the routes of R/Vs Akademik Fedorov (cruise 32) and Akademik Treshnikov (cruise 2) in February-May of 2012 and 2014, respectively, in the course of the 57th and 59th Russian Antarctic expeditions. It was found that the frontal zones exert the primary influence on the concentrations of the mentioned components in the Southern Ocean and in the western part of the Atlantic Ocean. The supply of pollutants into the Eastern Atlantic Ocean on the shelf of the Iberian peninsula results in a pronounced increase in the concentrations of lipids and hydrocarbons causing local anthropogenic pollution zones.

  20. Southern Ocean control on the extent of denitrification in the southeast Pacific over the last 70 ka

    NASA Astrophysics Data System (ADS)

    Robinson, Rebecca S.; Mix, Alan; Martinez, Philippe

    2007-01-01

    Temporal changes in oceanic denitrification, the bacterial reduction of nitrate under suboxic conditions, highlight the potential importance of N inventory changes and the production of N 2O on the climate system. At the same time, the cause of the globally observed variation in denitrification remains unclear. High-resolution benthic foraminiferal oxygen isotope and bulk sediment nitrogen isotope records from ODP Site 1234 on the Chile Margin record integrated denitrification changes within the Peru-Chile Upwelling system over the last ˜70 ka. Denitrification changes in the southeast Pacific are coherent with Antarctic climate changes recorded by the Byrd ice core δ 18O record, and lead northern hemisphere climate events. The southern-hemisphere character of the Chile margin δ 15N record suggests that episodes of reduced denitrification in the SE Pacific represent times when more oxygen was supplied as the result of changes in the ventilation and preformed nutrient content of Subantarctic Mode Water (SAMW), which forms in the Subantarctic zone of the Southern Ocean and feeds into the low-latitude thermocline.