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Sample records for antarctic ocean

  1. Seeking the True Antarctic Ocean

    NASA Astrophysics Data System (ADS)

    Miller, R. G.

    2007-12-01

    With World Ocean warming a corrected name use is recommend with a universal adoption of the name, "Antarctic Ocean. This one large body of circumpolar water lies adjacent to - and south of - the Antarctic Convergence, on its northern perimeter, and is bordered to the south by the shoreline of the Antarctic continent. The Antarctic Ocean has a distinct water mass, with a true perimeter, and with a homogeneity, comprizing a unique environment for a specialized flora and fauna. It is recognized generally by its surface waters, ranging from 3.5 - 4.5 degrees Celsius (summer) and one degree C (winter).While its northern boundary, ' The Antarctic Convergence', has a water quality and thermal difference, this polar front is continuous and circumpolar, and it abuts -- and streams along with -- the ultimate southern extremities of the Atlantic, Pacific and Indian Ocean waters. Parameters, characteristics and dynamics of water exchange are considered, here, with some water exchanges, with Intermediate and Antarctic Bottom water noted. It maintains its own forceful 'West Wind Drift', a current driven and emboldened by Earth's Geostrophic West Wind. Features defining the Antarctic Ocean: (1)Washing all shores of the continent named Antarctica; it is .the only ocean reaching this Antarctic Continent.; (2) it is one of Earth's two Polar (and coldest) oceans, the other, named Arctic Ocean, of which it is the opposite (the Anti); (3) its distinctive cold waters of the Antarctic Ocean and its peripheral seas, floating ice tongues, the frigid stamp of Antarctica's continental glaciers and ice fields; (4) the Antarctic Continent is the source of continual replenishment from her ice cap and melt-water derived from the great mountains, valleys and the massive polar dome of ice. Further, in the literature the present usage, 'Southern Ocean', by some authors, confuses the true Antarctic environmental waters (i.e. south of - and within the South Polar Front - Convergence) with southern

  2. 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.

  3. 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

  4. Antarctic Ice Sheet fertilises the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Wadham, J. L.; Death, R.; Monteiro, F. M.; Le Brocq, A. M.; Tranter, M.; Ridgwell, A. J.; Raiswell, R.; Hawkings, J.

    2012-12-01

    Southern Ocean (SO) marine primary productivity (PP) is limited by the availability of iron in surface waters, such that variations in iron supply to the SO are thought to exert a major control upon atmospheric CO2 concentrations on glacial/interglacial timescales. The zone bordering the Antarctic Ice Sheet exhibits high PP, exhibiting seasonal plankton blooms in response to elevated dissolved iron concentrations. The source of iron stimulating these PP increases is in debate, traditionally ascribed contributors being aeolian dust, coastal sediments/upwelling and sea ice. More recently, icebergs and glacial meltwater have been suggested as sources. Data from glacial meltwaters worldwide indicate that sub-Antarctic meltwaters are likely to be anoxic, as a result of long flow paths and little surface input of oxygenated meltwaters. Hence, it is probable that they are rich in dissolved iron (as Fe(II)), acquired via the oxidation of sulphide minerals in sediments. In contrast, iron in iceberg rafted debris is dominated by iron oxyhydroxides, generated in oxic sectors of the ice sheet bed by regelation processes or entrained in icebergs as they pass over shelf sediments. The potential for iron from both these ice sheet sources to impact PP has not yet been quantified. Here we apply the MIT marine ecosystem model to determine the potential impact of ice sheet iron export on SO PP. Fluxes of iceberg and meltwater-derived iron are focused along major ice stream corridors, and enhance iron concentrations in surface ocean waters. The impact on SO PP is greatest in coastal regions, including the Ross Sea, Weddell Sea and Amundsen Sea, all of which are areas of high observed marine PP. Inclusion of ice sheet iron sources in modelled scenarios raises SO PP by 10-30%, and provides a plausible explanation for very high seasonally observed PP around the coastal zone. These results highlight Antarctic runoff and icebergs as previously neglected sources of bioavailable iron to the

  5. Meltwater Pathways and Iron Delivery to the Antarctic Coastal Ocean

    NASA Astrophysics Data System (ADS)

    Null, K. A.; Corbett, D. R.; Crenshaw, J.; Peterson, R. N.; Peterson, L.; Buck, C. S.; Lyons, W. B.

    2016-02-01

    Freshwater inputs to the Antarctic coastal ocean can occur through multiple pathways including calving, streams, and groundwater discharge. The impacts of submarine groundwater discharge on polar ecosystems are generally poorly understood and, until recently, had not been considered as an important physical process along the coast of the Antarctic continent. Here, we present a study utilizing multiple tracers (radium, radon, and stable water isotopes) to quantify freshwater inputs and chemical constituent fluxes associated with multiple discharge pathways, including submarine groundwater discharge, along the Western Antarctic Peninsula. Previous research has shown that primary production in iron-limited waters offshore of the Antarctic Peninsula is fueled in part by continentally-derived sediments, and our work demonstrates that subglacial/submarine groundwater discharge (SSGD) to continental shelf waters in the region is also an important source of dissolved iron (6.4 Gg yr-1; dFe). For reference, this flux equates to approximately 25 times the iron flux from calving in the study area. SSGD also contributed a significantly higher macronutrient flux than calving, although calving contributed more than twice as much freshwater. Thus, SSGD is likely a much more important source of macronutrients and dFe to the nearshore coastal ocean along the Western Antarctic Peninsula, and potentially to the continental shelf and offshore waters of the entire continent than previously recognized. If we assume similar discharge rates along the entire Antarctic coastline ( 45,000 km), the delivery of dFe via SSGD ( 216 Gg yr-1) is comparable to the other fluxes of Fe to the Southern Ocean via dust, icebergs, and glacial runoff from the Antarctic Ice Sheet, and should be considered in future geochemical budgets.

  6. 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.

  7. Rationale for future Antarctic and Southern Ocean drilling

    NASA Astrophysics Data System (ADS)

    De Santis, Laura; Gohl, Karsten; Larter, Rob; Escutia, Carlota; Ikehara, Minoru; Hong, JongKuk; Naish, Tim; Barrett, Peter; Rack, Frank; Wellner, Julia

    2013-04-01

    Valuable insights into future sensitivity of the Antarctic cryosphere to atmospheric and oceanic warming can be gained from the geologic record of past climatic warm intervals. Continental to deep ocean sediments provide records of contemporaneous changes in ice sheet extent and oceanographic conditions that extend back in time, including periods with atmospheric CO2 levels and temperatures similar to those likely to be reached in the next 100 years. The Circum-Antarctic region is under-sampled respect to scientific ocean drilling. However, recovery from glacially-influenced, continental shelf and rise sediments (expeditions ODP178, 188 and IODP 318), provided excellent records of Cenozoic climate and ice sheet evolution. The ANtarctic DRILLing program achieved >98% recovery on the Ross Sea shelf with a stable platform on fast ice with riser drilling technology. Newer technologies, such as the MeBo shallow drilling rig will further improve Antarctic margin drilling. Drilling around Antarctica in the past decades revealed cooling and regional ice growth during the Cenozoic, coupled with paleogeographic, CO2 atmosphere concentration and global temperature changes. Substantial progress has been made in dating sediments and in the interpretation of paleoclimate/paleoenvironmental proxies in Antarctic margin sediments (e.g. orbital scale variations in Antarctica's cryosphere during the Miocene and Pliocene). Holocene ultra-high resolution shelf sections recently recovered can be correlated to the ice core record, to detect local mechanisms versus inter-hemispheric connections. While the potential for reconstructing past ice sheet history has been demonstrated through a careful integration of geological and geophysical data with numerical ice sheet modelling, uncertainties remain high due to the sparse geographic distribution of the records and the regional variability in the ice sheet's response. Projects developed using a multi-leg, multi-platform approach (e

  8. Ocean Circulation and Dynamics on the West Antarctic Peninsula Continental Shelf

    DTIC Science & Technology

    2007-09-01

    Antarctic krill ( Euphausia superba ) across the Scotia...ity in the distribution of antarctic krill , euphausia superba , west of the antarctic peninsula. Deep Sea Research I 46 (6), 951-984. Lawson, G., 2006... krill (Euphasia superba ). The region has been hypothesized to act as a source for krill populations elsewhere in the Southern Ocean (Murphy et al.,

  9. 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.

  10. 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.

  11. 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.

  12. Large Scale Eocene Ocean Circulation Transition Could Help Antarctic Glaciation.

    NASA Astrophysics Data System (ADS)

    Baatsen, M.

    2016-12-01

    The global climate underwent major changes going from the Eocene into the Oligocene, including the formation of a continental-scale Antarctic ice sheet. In addition to a gradual drawdown of CO2 since the Early Eocene, the changing background geography of the earth may also have played a crucial role in setting the background oceanic circulation pattern favorable to ice growth. On the other hand, the ocean circulation may have changed only after the ice sheet started growing, with a similar climatic imprint. It is, therefore, still under debate what the primary forcing or trigger of this transition was. Using an ocean general circulation model (POP) and two different geography reconstruc-tions for the middle-late Eocene, we find two distinctly different patterns of the oceanic circulation to be possible under the same forcing. The first one features deep-water formation and warmer SSTs in the Southern Pacific while in the second, deep water forms in the North Pacific Ocean and Southern Ocean SSTs are colder. The presence of a double equilibrium shows that the ocean circulation was highly susceptible to large scale transitions during the middle-late Eocene. Additionally, changes in benthic oxygen and Neodymium isotopes depict significant changes during the same period. We suggest that a transition in the global meridional overturing circulation can explain the observed changes and preconditions the global climate for the two-step transition into an Icehouse state at the Eocene-Oligocene boundary.

  13. Ocean Heat Delivery Mechanisms Beneath Antarctic Ice Shelves

    NASA Astrophysics Data System (ADS)

    Stern, Alon

    Ocean currents around Antarctica are responsible for transporting heat under the Antarctic ice shelves and exporting cold melt-water out into the open ocean. These ocean currents are important for the determining the melt rates beneath the Antarctica ice shelves. This thesis explores the three modes of melting beneath Antarctic ice shelves using laboratory experiments, analysis of field observations, and both of complex and simple numerical models. In Chapter 1, we construct a laboratory experiment to simulate the density driven circulation under an idealized Antarctic ice shelf (mode 1). Results confirm that the ice front can act as a dynamic barrier that partially inhibits fluid from entering or exiting the ice shelf cavity, away from two wall-trapped boundary currents. The strength of the dynamic barrier is sensitive to changes in the ice shelf geometry and changes in the buoyancy fluxes which drive the flow. Chapter 2 explores how instabilities in topographically steered jets could be responsible for the exchange of warm Circumpolar Deep Water across the continental shelf break in West Antarctica (mode 2). Results show that the majority of mixing occurs in discrete mixing events which coincide with the shelf break jet becoming baroclinically unstable. The largest instability events display a intermittent low frequency variability with instabilities occurring up to 50 years apart. Chapter 3 uses observational data to study the summer intrusion of surface waters below McMurdo Ice Shelf (mode 3). A six month temperature record collected below the ice shelf in 2011-2012 shows the temporal and spatial structure of the summertime warm water signal that penetrates beneath the ice shelf. A Ross Sea numerical model demonstrates a seasonal warm water pathway leading from the west side of the Ross Sea Polynya (RSP) towards McMurdo Sound.

  14. 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.

  15. 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.

  16. Connecting Antarctic sea ice to deep-ocean circulation in modern and glacial climate simulations

    NASA Astrophysics Data System (ADS)

    Marzocchi, Alice; Jansen, Malte F.

    2017-06-01

    Antarctic sea-ice formation plays a key role in shaping the abyssal overturning circulation and stratification in all ocean basins, by driving surface buoyancy loss through the associated brine rejection. Changes in Antarctic sea ice have therefore been suggested as drivers of major glacial-interglacial ocean circulation rearrangements. Here, the relationship between Antarctic sea ice, buoyancy loss, deep-ocean stratification, and overturning circulation is investigated in Last Glacial Maximum and preindustrial simulations from the Paleoclimate Modelling Intercomparison Project (PMIP). The simulations show substantial intermodel differences in their representation of the glacial deep-ocean state and circulation, which is often at odds with the geological evidence. We argue that these apparent inconsistencies can largely be attributed to differing (and likely insufficient) Antarctic sea-ice formation. Discrepancies can be further amplified by short integration times. Deep-ocean equilibration and sea-ice representation should, therefore, be carefully evaluated in the forthcoming PMIP4 simulations.

  17. History of Antarctic glaciation: An Indian Ocean perspective

    NASA Astrophysics Data System (ADS)

    Ehrmann, W. U.; Hambrey, M. J.; Baldauf, J. G.; Barron, J.; Larsen, B.; Mackensen, A.; Wise, S. W., Jr.; Zachos, J. C.

    Legs 119 and 120 of the Ocean Drilling Program cored 16 sites on a S-N transect from the Antarctic continental shelf of Prydz Bay to the northern Kerguelen Plateau in the Indian Ocean. Thick sequences of glacigenic sediments were recovered in Prydz Bay, whereas the record on Kerguelen Plateau consists mainly of pelagic and, in part, glaciomarine sediments. This paper is a summary of the principle scientific results from the two legs that were concerned with the Cenozoic glacial and climatic history of Antarctica. It integrates a wide range of investigations, such as sedimentological studies including clay sedimentology and ice-rafted debris, studies of the oxygen isotopic composition of planktonic and benthic foraminifers, and paleontological investigations. The scientific data obtained from these cruises indicate that a long-term cooling trend started at about 52 Ma, after the thermal maximum in early Eocene time. All parameters under review indicate that there has been continental-scale ice in East Antarctica at least since earliest Oligocene time. However, the ice probably was temperate in character, whereas that of the present day is polar with the bulk of ice below the pressure melting point. The question of ice extent, specifically, whether ice had reached the Antarctic coast as early as middle and late Eocene time, is still a matter of dispute. Evidence for that is suggested by the occurrence of isolated middle Eocene sand and gravel grains and by a poorly dated, possibly upper Eocene sequence of thick massive diamictites in Prydz Bay. From Oligocene to recent time, the ice sheet experienced several major advance and retreat phases, some of them being quite rapid and short-term. However, although we did not find any clear evidence for a disappearance of the ice as postulated from other parts of Antarctica, the fragmentary nature of the stratigraphic record may hide major recessions of the ice sheet from the coast. Major increases of ice volume occurred in

  18. 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

  19. Perfluorinated compounds in the Antarctic region: ocean circulation provides prolonged protection from distant sources.

    PubMed

    Bengtson Nash, Susan; Rintoul, Stephen R; Kawaguchi, So; Staniland, Iain; van den Hoff, John; Tierney, Megan; Bossi, Rossana

    2010-09-01

    In order to investigate the extent to which Perfluorinated Contaminants (PFCs) have permeated the Southern Ocean food web to date, a range of Antarctic, sub-Antarctic and Antarctic-migratory biota were analysed for key ionic PFCs. Based upon the geographical distribution pattern and ecology of biota with detectable vs. non-detectable PFC burdens, an evaluation of the potential contributory roles of alternative system input pathways is made. Our analytical findings, together with previous reports, reveal only the occasional occurrence of PFCs in migratory biota and vertebrate predators with foraging ranges extending into or north of the Antarctic Circumpolar Current (ACC). Geographical contamination patterns observed correspond most strongly with those expected from delivery via hydrospheric transport as governed by the unique oceanographic features of the Southern Ocean. We suggest that hydrospheric transport will form a slow, but primary, input pathway of PFCs to the Antarctic region.

  20. 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

  1. Impact of un-modelled oceanic mass variations on Antarctic ice mass changes derived from GRACE

    NASA Astrophysics Data System (ADS)

    Groh, Andreas; Horwath, Martin; Gutknecht, Benjamin D.

    2017-04-01

    The estimation of regional mass changes from GRACE satellite gravimetry data is affected by leakage-in from mass signals outside the region of interest. In the case of Antarctica, oceanic mass variations, e.g. due to variations of the Antarctic Circumpolar Current (ACC), are a distinct source of leakage. Based on the Atmosphere and Ocean De-aliasing Level-1b (AOD1B) products, high-frequency mass changes in the ocean and the atmosphere are reduced from the GRACE monthly solutions. However, residual mass signals due to errors and limitations of the utilised models may still bias regional mass change estimates of the entire Antarctic Ice sheet and of individual drainage basins. While the present AOD1B RL05 product incorporates non-tidal oceanic mass variations modelled by OMCT (Ocean Model for Circulation and Tides), the upcoming AOD1B RL06 products will use simulated bottom pressure fields from the Max-Planck-Institute for Meteorology Ocean Model (MPIOM). One difference between both models is their spatial coverage. In contrast to the OMCT, the model domain of the MPIOM does not include the ocean areas beneath the Antarctic ice shelves. These un-modelled ocean mass changes close to the coastline are an additional source of signal leakage requiring particular attention when deriving Antarctic ice mass changes. In the present study we assess the impact of residual oceanic mass change on Antarctic mass balance estimates based on analyses using AOD1B products of different releases. We then focus on the quantification of ocean mass changes beneath the two largest ice shelves in Antarctica, namely the Filchner-Ronne Ice Shelf and the Ross Ice Shelf. By using AOD1B RL05 products signal leakage stemming from the un-modelled ocean mass variations beneath these ice shelves is assessed. Finally, we demonstrate how sensitivity kernels used in a regional integration approach may be adapted to account for this additional source of leakage.

  2. 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.

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

    PubMed

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

    2016-05-17

    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.

  4. 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

  5. Classification of Physico-Chemical Vertical Profiles in the Antarctic Ocean Using Elephant Seals as Samplers

    NASA Astrophysics Data System (ADS)

    Nerini, D.; Guinet, C.; Bailleul, F.; Pauthenet, E.

    2016-02-01

    Since a decade, marine mammals constitute valuable auxiliaries for operational oceanography. Starting with a collection of TSO profiles sampled along trajectories of equipped elephant seals cruising around Kerguelen Island (Antarctic Ocean), we propose a statistical method to construct a classification of the water masses. The originality of the proposed approach lies on the fact that the functional aspect of the data is included in the analysis as well as the multivariate aspect : each observation is a sampled profile of both temperature, salinity and oxygen. We highlight the importance of the oxygen profiles in the analysis especially when an animal crosses the Antarctic Polar Front. It is then possible to compare the vertical structure of the ocean to AVHRR images and the classification provides an interesting way to access meso-scale vertical structures of the Antarctic Ocean.

  6. Southern Ocean deep convection as a driver of Antarctic warming events

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    Simulations with a free-running coupled climate model show that heat release associated with Southern Ocean deep convection variability can drive centennial-scale Antarctic temperature variations of up to 2.0°C. The mechanism involves three steps: Preconditioning: heat accumulates at depth in the Southern Ocean; Convection onset: wind and/or sea ice changes tip the buoyantly unstable system into the convective state; and Antarctic warming: fast sea ice-albedo feedbacks (on annual-decadal time scales) and slow Southern Ocean frontal and sea surface temperature adjustments to convective heat release (on multidecadal-century time scales) drive an increase in atmospheric heat and moisture transport toward Antarctica. We discuss the potential of this mechanism to help drive and amplify climate variability as observed in Antarctic ice core records.

  7. 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.

  8. 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.

  9. Impacts of marine instability across the East Antarctic Ice Sheet on Southern Ocean dynamics

    NASA Astrophysics Data System (ADS)

    Phipps, Steven J.; Fogwill, Christopher J.; Turney, Christian S. M.

    2016-09-01

    Recent observations and modelling studies have demonstrated the potential for rapid and substantial retreat of large sectors of the East Antarctic Ice Sheet (EAIS). This has major implications for ocean circulation and global sea level. Here we examine the effects of increasing meltwater from the Wilkes Basin, one of the major marine-based sectors of the EAIS, on Southern Ocean dynamics. Climate model simulations reveal that the meltwater flux rapidly stratifies surface waters, leading to a dramatic decrease in the rate of Antarctic Bottom Water (AABW) formation. The surface ocean cools but, critically, the Southern Ocean warms by more than 1 °C at depth. This warming is accompanied by a Southern Ocean-wide "domino effect", whereby the warming signal propagates westward with depth. Our results suggest that melting of one sector of the EAIS could result in accelerated warming across other sectors, including the Weddell Sea sector of the West Antarctic Ice Sheet. Thus, localised melting of the EAIS could potentially destabilise the wider Antarctic Ice Sheet.

  10. 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.

  11. 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.

  12. Impacts of marine instability across the East Antarctic Ice Sheet on Southern Ocean dynamics

    NASA Astrophysics Data System (ADS)

    Phipps, Steven; Fogwill, Christopher; Turney, Christian

    2017-04-01

    Recent observations and modelling studies have demonstrated the potential for rapid and substantial retreat of large sectors of the East Antarctic Ice Sheet (EAIS). This has major implications for ocean circulation and global sea level. Here we examine the effects of increasing meltwater from the Wilkes Basin, one of the major marine-based sectors of the EAIS, on Southern Ocean dynamics. Climate model simulations reveal that the meltwater flux rapidly stratifies surface waters, leading to a dramatic decrease in the rate of Antarctic Bottom Water formation. The surface ocean cools but, critically, the Southern Ocean warms by more than 1oC at depth. This warming is accompanied by a Southern Oceanwide "domino effect", whereby the warming signal propagates westward with depth. Our results suggest that melting of one sector of the EAIS could result in accelerated warming across other sectors, including the Weddell Sea sector of the West Antarctic Ice Sheet. Thus, localised melting of the EAIS could potentially destabilise the wider Antarctic Ice Sheet.

  13. Preconditioning of Antarctic maximum sea ice extent by upper ocean stratification on a seasonal timescale

    NASA Astrophysics Data System (ADS)

    Su, Zhan

    2017-06-01

    This study uses an observationally constrained and dynamically consistent ocean and sea ice state estimate. The author presents a remarkable agreement between the location of the edge of Antarctic maximum sea ice extent, reached in September, and the narrow transition band for the upper ocean (0-100 m depths) stratification, as early as April to June. To the south of this edge, the upper ocean has high stratification, which forbids convective fluxes to cross through; consequently, the ocean heat loss to the atmosphere is an efficient way to cool the surface ocean to the freezing point during April to September. To the north, the upper ocean has low stratification such that the ocean heat loss to the atmosphere is not efficient to cool the upper ocean. The upper ocean is instead cooled mainly through mixing with the colder inflow carried by northward Ekman transport but cannot reach the freezing point due to the nature of mixing. Therefore, upper ocean stratification, dominated by salinity here, provides an important constraint on the northward expansion of Antarctic sea ice to its maximum.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Restricted regions of enhanced growth of Antarctic krill in the circumpolar Southern Ocean.

    PubMed

    Murphy, Eugene J; Thorpe, Sally E; Tarling, Geraint A; Watkins, Jonathan L; Fielding, Sophie; Underwood, Philip

    2017-07-31

    Food webs in high-latitude oceans are dominated by relatively few species. Future ocean and sea-ice changes affecting the distribution of such species will impact the structure and functioning of whole ecosystems. Antarctic krill (Euphausia superba) is a key species in Southern Ocean food webs, but there is little understanding of the factors influencing its success throughout much of the ocean. The capacity of a habitat to maintain growth will be crucial and here we use an empirical relationship of growth rate to assess seasonal spatial variability. Over much of the ocean, potential for growth is limited, with three restricted oceanic regions where seasonal conditions permit high growth rates, and only a few areas around the Scotia Sea and Antarctic Peninsula suitable for growth of the largest krill (>60 mm). Our study demonstrates that projections of impacts of future change need to account for spatial and seasonal variability of key ecological processes within ocean ecosystems.

  20. 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.

  1. Sensitivity of the Southern Ocean circulation to enhanced regional Antarctic meltwater input

    NASA Astrophysics Data System (ADS)

    Phipps, Steven; Fogwill, Christopher; Turney, Christopher

    2015-04-01

    Recent observational and modelling evidence suggests that Antarctica may be a larger source of meltwater than previously supposed. In this presentation, we use a fully coupled climate system model to assess the sensitivity of the Southern Ocean circulation to meltwater input. We present the results of a series of idealised simulations which explore the effects of increased meltwater flux from specific sectors of the West Antarctic Ice Sheet. In particular, we assess the response to physically-plausible scenarios which involve spatially and temporally variable meltwater inputs into the Ross, Weddell and Amundsen embayments. Our simulations reveal that increased freshwater input results in a rapid increase in the stratification of the upper ocean. This causes a reduction in the mixing of the cold surface waters with the underlying warmer waters, including a reduction of up to 50% in the rate of Antarctic Bottom Water formation. The reduced mixing leads to cooling at the surface, but a rapid and pervasive warming at depth. This warming is strongest at depths of between 200 and 700m, and is focused along sectors of the Antarctic ice sheets that are known to be sensitive to ocean forcing. In the Ross and Amundsen sectors, the water temperature increases by up to 1.6°C at the depth of the grounding lines. This provides an additional feedback mechanism that may further enhance the basal melting and thermally-driven grounding line retreat of the Antarctic ice sheets during the 21st century. The rapid nature of the feedback also strengthens recent hypotheses that attribute rapid sea level rise scenarios to Antarctic sources.

  2. Antarctic ice sheet discharge driven by atmosphere-ocean feedbacks at the Last Glacial Termination

    NASA Astrophysics Data System (ADS)

    Fogwill, C. J.; Turney, C. S. M.; Golledge, N. R.; Etheridge, D. M.; Rubino, M.; Thornton, D. P.; Baker, A.; Woodward, J.; Winter, K.; van Ommen, T. D.; Moy, A. D.; Curran, M. A. J.; Davies, S. M.; Weber, M. E.; Bird, M. I.; Munksgaard, N. C.; Menviel, L.; Rootes, C. M.; Ellis, B.; Millman, H.; Vohra, J.; Rivera, A.; Cooper, A.

    2017-01-01

    Reconstructing the dynamic response of the Antarctic ice sheets to warming during the Last Glacial Termination (LGT; 18,000-11,650 yrs ago) allows us to disentangle ice-climate feedbacks that are key to improving future projections. Whilst the sequence of events during this period is reasonably well-known, relatively poor chronological control has precluded precise alignment of ice, atmospheric and marine records, making it difficult to assess relationships between Antarctic ice-sheet (AIS) dynamics, climate change and sea level. Here we present results from a highly-resolved ‘horizontal ice core’ from the Weddell Sea Embayment, which records millennial-scale AIS dynamics across this extensive region. Counterintuitively, we find AIS mass-loss across the full duration of the Antarctic Cold Reversal (ACR; 14,600-12,700 yrs ago), with stabilisation during the subsequent millennia of atmospheric warming. Earth-system and ice-sheet modelling suggests these contrasting trends were likely Antarctic-wide, sustained by feedbacks amplified by the delivery of Circumpolar Deep Water onto the continental shelf. Given the anti-phase relationship between inter-hemispheric climate trends across the LGT our findings demonstrate that Southern Ocean-AIS feedbacks were controlled by global atmospheric teleconnections. With increasing stratification of the Southern Ocean and intensification of mid-latitude westerly winds today, such teleconnections could amplify AIS mass loss and accelerate global sea-level rise.

  3. Antarctic ice sheet discharge driven by atmosphere-ocean feedbacks at the Last Glacial Termination

    PubMed Central

    Fogwill, C. J.; Turney, C. S. M.; Golledge, N. R.; Etheridge, D. M.; Rubino, M.; Thornton, D. P.; Baker, A.; Woodward, J.; Winter, K.; van Ommen, T. D.; Moy, A. D.; Curran, M. A. J.; Davies, S. M.; Weber, M. E.; Bird, M. I.; Munksgaard, N. C.; Menviel, L.; Rootes, C. M.; Ellis, B.; Millman, H.; Vohra, J.; Rivera, A.; Cooper, A.

    2017-01-01

    Reconstructing the dynamic response of the Antarctic ice sheets to warming during the Last Glacial Termination (LGT; 18,000–11,650 yrs ago) allows us to disentangle ice-climate feedbacks that are key to improving future projections. Whilst the sequence of events during this period is reasonably well-known, relatively poor chronological control has precluded precise alignment of ice, atmospheric and marine records, making it difficult to assess relationships between Antarctic ice-sheet (AIS) dynamics, climate change and sea level. Here we present results from a highly-resolved ‘horizontal ice core’ from the Weddell Sea Embayment, which records millennial-scale AIS dynamics across this extensive region. Counterintuitively, we find AIS mass-loss across the full duration of the Antarctic Cold Reversal (ACR; 14,600–12,700 yrs ago), with stabilisation during the subsequent millennia of atmospheric warming. Earth-system and ice-sheet modelling suggests these contrasting trends were likely Antarctic-wide, sustained by feedbacks amplified by the delivery of Circumpolar Deep Water onto the continental shelf. Given the anti-phase relationship between inter-hemispheric climate trends across the LGT our findings demonstrate that Southern Ocean-AIS feedbacks were controlled by global atmospheric teleconnections. With increasing stratification of the Southern Ocean and intensification of mid-latitude westerly winds today, such teleconnections could amplify AIS mass loss and accelerate global sea-level rise. PMID:28054598

  4. Antarctic ice sheet discharge driven by atmosphere-ocean feedbacks at the Last Glacial Termination.

    PubMed

    Fogwill, C J; Turney, C S M; Golledge, N R; Etheridge, D M; Rubino, M; Thornton, D P; Baker, A; Woodward, J; Winter, K; van Ommen, T D; Moy, A D; Curran, M A J; Davies, S M; Weber, M E; Bird, M I; Munksgaard, N C; Menviel, L; Rootes, C M; Ellis, B; Millman, H; Vohra, J; Rivera, A; Cooper, A

    2017-01-05

    Reconstructing the dynamic response of the Antarctic ice sheets to warming during the Last Glacial Termination (LGT; 18,000-11,650 yrs ago) allows us to disentangle ice-climate feedbacks that are key to improving future projections. Whilst the sequence of events during this period is reasonably well-known, relatively poor chronological control has precluded precise alignment of ice, atmospheric and marine records, making it difficult to assess relationships between Antarctic ice-sheet (AIS) dynamics, climate change and sea level. Here we present results from a highly-resolved 'horizontal ice core' from the Weddell Sea Embayment, which records millennial-scale AIS dynamics across this extensive region. Counterintuitively, we find AIS mass-loss across the full duration of the Antarctic Cold Reversal (ACR; 14,600-12,700 yrs ago), with stabilisation during the subsequent millennia of atmospheric warming. Earth-system and ice-sheet modelling suggests these contrasting trends were likely Antarctic-wide, sustained by feedbacks amplified by the delivery of Circumpolar Deep Water onto the continental shelf. Given the anti-phase relationship between inter-hemispheric climate trends across the LGT our findings demonstrate that Southern Ocean-AIS feedbacks were controlled by global atmospheric teleconnections. With increasing stratification of the Southern Ocean and intensification of mid-latitude westerly winds today, such teleconnections could amplify AIS mass loss and accelerate global sea-level rise.

  5. Antarctic ice sheet discharge driven by atmosphere-ocean feedbacks across the Last Glacial Termination

    NASA Astrophysics Data System (ADS)

    Fogwill, Christopher

    2017-04-01

    Reconstructing the dynamic response of the Antarctic ice sheets to warming during the Last Glacial Termination (LGT; 18,000-11,650 yrs ago) allows us to disentangle ice-climate feedbacks that are key to improving future projections. Whilst the sequence of events during this period is reasonably well known, relatively poor chronological control has precluded precise alignment of ice, atmospheric and marine records, making it difficult to assess relationships between Antarctic ice-sheet (AIS) dynamics, climate change and sea level. Here we present results from a highly-resolved 'horizontal ice core' from the Weddell Sea Embayment, which records millennial-scale AIS dynamics across this extensive region. Counterintuitively, we find AIS mass-loss across the full duration of the Antarctic Cold Reversal (ACR; 14,600-12,700 yrs ago), with stabilisation during the subsequent millennia of atmospheric warming. Earth-system and ice-sheet modelling suggests these contrasting trends were likely Antarctic-wide, sustained by feedbacks amplified by the delivery of Circumpolar Deep Water onto the continental shelf. Given the anti-phase relationship between inter-hemispheric climate trends across the LGT our findings demonstrate that Southern Ocean-AIS feedbacks were controlled by global atmospheric teleconnections. With increasing stratification of the Southern Ocean and intensification of mid-latitude westerly winds today, such teleconnections could amplify AIS mass loss and accelerate global sea-level rise.

  6. Response of the Antarctic ice sheet to ocean forcing using the POPSICLES coupled ice sheet-ocean model

    NASA Astrophysics Data System (ADS)

    Martin, D. F.; Asay-Davis, X.; Price, S. F.; Cornford, S. L.; Maltrud, M. E.; Ng, E. G.; Collins, W.

    2014-12-01

    We present the response of the continental Antarctic ice sheet to sub-shelf-melt forcing derived from POPSICLES simulation results covering the full Antarctic Ice Sheet and the Southern Ocean spanning the period 1990 to 2010. Simulations are performed at 0.1 degree (~5 km) ocean resolution and ice sheet resolution as fine as 500 m using adaptive mesh refinement. A comparison of fully-coupled and comparable standalone ice-sheet model results demonstrates the importance of two-way coupling between the ice sheet and the ocean. The POPSICLES model couples the POP2x ocean model, a modified version of the Parallel Ocean Program (Smith and Gent, 2002), and the BISICLES ice-sheet model (Cornford et al., 2012). BISICLES makes use of adaptive mesh refinement to fully resolve dynamically-important regions like grounding lines and employs a momentum balance similar to the vertically-integrated formulation of Schoof and Hindmarsh (2009). Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests like MISMIP3D (Pattyn et al., 2013) and realistic configurations (Favier et al. 2014). POP2x includes sub-ice-shelf circulation using partial top cells (Losch, 2008) and boundary layer physics 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). A companion presentation, "Present-day circum-Antarctic simulations using the POPSICLES coupled land ice-ocean model" in session C027 describes the ocean-model perspective of this work, while we focus on the response of the ice sheet and on details of the model. The figure shows the BISICLES-computed vertically-integrated ice velocity field about 1 month into a 20-year coupled Antarctic run. Groundling lines are shown in green.

  7. Antarctic climate, Southern Ocean circulation patterns, and deep water formation during the Eocene

    NASA Astrophysics Data System (ADS)

    Huck, Claire E.; van de Flierdt, Tina; Bohaty, Steven M.; Hammond, Samantha J.

    2017-07-01

    We assess early-to-middle Eocene seawater neodymium (Nd) isotope records from seven Southern Ocean deep-sea drill sites to evaluate the role of Southern Ocean circulation in long-term Cenozoic climate change. Our study sites are strategically located on either side of the Tasman Gateway and are positioned at a range of shallow (<500 m) to intermediate/deep ( 1000-2500 m) paleowater depths. Unradiogenic seawater Nd isotopic compositions, reconstructed from fish teeth at intermediate/deep Indian Ocean pelagic sites (Ocean Drilling Program (ODP) Sites 738 and 757 and Deep Sea Drilling Project (DSDP) Site 264), indicate a dominant Southern Ocean-sourced contribution to regional deep waters (ɛNd(t) = -9.3 ± 1.5). IODP Site U1356 off the coast of Adélie Land, a locus of modern-day Antarctic Bottom Water production, is identified as a site of persistent deep water formation from the early Eocene to the Oligocene. East of the Tasman Gateway an additional local source of intermediate/deep water formation is inferred at ODP Site 277 in the SW Pacific Ocean (ɛNd(t) = -8.7 ± 1.5). Antarctic-proximal shelf sites (ODP Site 1171 and Site U1356) reveal a pronounced erosional event between 49 and 48 Ma, manifested by 2 ɛNd unit negative excursions in seawater chemistry toward the composition of bulk sediments at these sites. This erosional event coincides with the termination of peak global warmth following the Early Eocene Climatic Optimum and is associated with documented cooling across the study region and increased export of Antarctic deep waters, highlighting the complexity and importance of Southern Ocean circulation in the greenhouse climate of the Eocene.

  8. 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

  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. Links between atmosphere, ocean, and cryosphere from two decades of microseism observations on the Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Anthony, Robert E.; Aster, Richard C.; McGrath, Daniel

    2017-01-01

    The lack of landmasses, climatological low pressure, and strong circumpolar westerly winds between the latitudes of 50°S to 65°S produce exceptional storm-driven wave conditions in the Southern Ocean. This combination makes the Antarctic Peninsula one of Earth's most notable regions of high-amplitude wave activity and thus, ocean-swell-driven microseism noise in both the primary (direct wave-coastal region interactions) and secondary (direct ocean floor forcing due to interacting wave trains) period bands. Microseism observations are examined across 23 years (1993-2015) from Palmer Station (PMSA), on the west coast of the Antarctic Peninsula, and from East Falkland Island (EFI). These records provide a spatially integrative measure of both Southern Ocean wave amplitudes and the interactions between ocean waves and the solid Earth in the presence of sea ice, which can reduce wave coupling with the continental shelf. We utilize a spatiotemporal correlation-based approach to illuminate how the distribution of sea ice influences seasonal microseism power. We characterize primary and secondary microseism power due to variations in sea ice and find that primary microseism energy is both more sensitive to sea ice and more capable of propagating across ocean basins than secondary microseism energy. During positive phases of the Southern Annular Mode, sea ice is reduced in the Bellingshausen Sea and overall storm activity in the Drake Passage increases, thus strongly increasing microseism power levels.

  11. 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.

  12. Ammonia-oxidizing Archaea in the Arctic Ocean and Antarctic coastal waters.

    PubMed

    Kalanetra, Karen M; Bano, Nasreen; Hollibaugh, James T

    2009-09-01

    We compared abundance, distributions and phylogenetic composition of Crenarchaeota and ammonia-oxidizing Archaea (AOA) in samples collected from coastal waters west of the Antarctic Peninsula during the summers of 2005 and 2006, with samples from the central Arctic Ocean collected during the summer of 1997. Ammonia-oxidizing Archaea and Crenarchaeota abundances were estimated from quantitative PCR measurements of amoA and 16S rRNA gene abundances. Crenarchaeota and AOA were approximately fivefold more abundant at comparable depths in the Antarctic versus the Arctic Ocean. Crenarchaeota and AOA were essentially absent from the Antarctic Summer Surface Water (SSW) water mass (0-45 m depth). The ratio of Crenarchaeota 16S rRNA to archaeal amoA gene abundance in the Winter Water (WW) water mass (45-105 m depth) of the Southern Ocean was much lower (0.15) than expected and in sharp contrast to the ratio (2.0) in the Circumpolar Deep Water (CDW) water mass (105-3500 m depth) immediately below it. We did not observe comparable segregation of this ratio by depth or water mass in Arctic Ocean samples. A ubiquitous, abundant and polar-specific crenarchaeote was the dominant ribotype in the WW and important in the upper halocline of the Arctic Ocean. Our data suggest that this organism does not contain an ammonia monooxygenase gene. In contrast to other studies where Crenarchaeota populations apparently lacking amoA genes are found in bathypelagic waters, this organism appears to dominate in well-defined, ammonium-rich, near-surface water masses in polar oceans.

  13. Recent dramatic thinning of largest West Antarctic ice stream triggered by oceans

    NASA Astrophysics Data System (ADS)

    Payne, Antony J.; Vieli, Andreas; Shepherd, Andrew P.; Wingham, Duncan J.; Rignot, Eric

    2004-12-01

    A growing body of observational data suggests that Pine Island Glacier (PIG) is changing on decadal or shorter timescales. These changes may have far-reaching consequences for the future of the West Antarctic ice sheet (WAIS) and global sea levels because of PIG's role as the ice sheet's primary drainage portal. We test the hypothesis that these changes are triggered by the adjoining ocean. Specifically, we employ an advanced numerical ice-flow model to simulate the effects of perturbations at the grounding line on PIG's dynamics. The speed at which these changes are propagated upstream implies a tight coupling between ice-sheet interior and surrounding ocean.

  14. Rapid stepwise onset of Antarctic glaciation and deeper calcite compensation in the Pacific Ocean.

    PubMed

    Coxall, Helen K; Wilson, Paul A; Pälike, Heiko; Lear, Caroline H; Backman, Jan

    2005-01-06

    The ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth. At present, this depth is approximately 4,500 m, with some variation between and within ocean basins. The calcite compensation depth is linked to ocean acidity, which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate. Geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the Eocene/Oligocene boundary (approximately 34 million years ago) when significant permanent ice sheets first appeared on Antarctica, but the relationship between these two events is poorly understood. Here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical Pacific Ocean that cover the Eocene/Oligocene boundary. We find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40,000 years each, synchronous with the stepwise onset of Antarctic ice-sheet growth. The glaciation was initiated, after climatic preconditioning, by an interval when the Earth's orbit of the Sun favoured cool summers. The changes in oxygen-isotope composition across the Eocene/Oligocene boundary are too large to be explained by Antarctic ice-sheet growth alone and must therefore also indicate contemporaneous global cooling and/or Northern Hemisphere glaciation.

  15. 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.

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

    PubMed

    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.

  17. 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

  18. Present-day Circum-Antarctic Simulations using the POPSICLES Coupled Ice Sheet-Ocean Model

    NASA Astrophysics Data System (ADS)

    Asay-Davis, X.; Martin, D. F.; Price, S. F.; Maltrud, M. E.; Collins, W.

    2014-12-01

    We present POPSICLES simulation results covering the full Antarctic Ice Sheet and the Southern Ocean spanning the period 1990 to 2010. Simulations are performed at 0.1o (~5 km) ocean resolution and with adaptive ice-sheet model resolution as fine as 500 m. We compare time-averaged melt rates below a number of major ice shelves with those reported by Rignot et al. (2013) as well as other recent studies. We also present seasonal variability and decadal trends in submarine melting from several Antarctic regions. Finally, we explore the influence on basal melting and system dynamics resulting from two different choices of climate forcing: a "normal-year" climatology and the CORE v. 2 forcing data (Large and Yeager 2008).POPSICLES couples the POP2x ocean model, a modified version of the Parallel Ocean Program (Smith and Gent, 2002), and the BISICLES ice-sheet model (Cornford et al., 2012). POP2x includes sub-ice-shelf circulation using partial top cells (Losch, 2008) and boundary layer physics 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). BISICLES makes use of adaptive mesh refinement and a 1st-order accurate momentum balance similar to the L1L2 model of Schoof and Hindmarsh (2009) to accurately model regions of dynamic complexity, such as ice streams, outlet glaciers, and grounding lines. Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests (MISMIP-3D; Pattyn et al., 2013) and realistic configurations (Favier et al. 2014).A companion presentation, "Response of the Antarctic Ice Sheet to ocean forcing using the POPSICLES coupled ice sheet-ocean model" in session C024 covers the ice-sheet response to these melt rates in the coupled simulation

  19. 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.

  20. 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.

  1. 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.

  2. How many species in the Southern Ocean? Towards a dynamic inventory of the Antarctic marine species

    NASA Astrophysics Data System (ADS)

    De Broyer, Claude; Danis, Bruno; with 64 SCAR-MarBIN Taxonomic Editors

    2011-03-01

    The IPY sister-projects CAML and SCAR-MarBIN provided a timely opportunity, a strong collaborative framework and an appropriate momentum to attempt assessing the "Known, Unknown and Unknowable" of Antarctic marine biodiversity. To allow assessing the known biodiversity, SCAR-MarBIN "Register of Antarctic Marine Species (RAMS)" was compiled and published by a panel of 64 taxonomic experts. Thanks to this outstanding expertise mobilized for the first time, an accurate list of more than 8100 valid species was compiled and an up-to-date systematic classification comprising more than 16,800 taxon names was established. This taxonomic information is progressively and systematically completed by species occurrence data, provided by literature, taxonomic and biogeographic databases, new data from CAML and other cruises, and museum collections. RAMS primary role was to establish a benchmark of the present taxonomic knowledge of the Southern Ocean biodiversity, particularly important in the context of the growing realization of potential impacts of the global change on Antarctic ecosystems. This, in turn, allowed detecting gaps in knowledge, taxonomic treatment and coverage, and estimating the importance of the taxonomic impediment, as well as the needs for more complete and efficient taxonomic tools. A second, but not less important, role of RAMS was to contribute to the "taxonomic backbone" of the SCAR-MarBIN, OBIS and GBIF networks, to establish a dynamic information system on Antarctic marine biodiversity for the future. The unknown part of the Southern Ocean biodiversity was approached by pointing out what remains to be explored and described in terms of geographical locations and bathymetric zones, habitats, or size classes of organisms. The growing importance of cryptic species is stressed, as they are more and more often detected by molecular studies in several taxa. Relying on RAMS results and on some case studies of particular model groups, the question of the

  3. 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.

  4. 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

    2012-10-02

    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.

  5. 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.

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

    PubMed Central

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

    2012-01-01

    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

  7. 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.

  8. Air-sea carbon dioxide exchange in the Southern Ocean and Antarctic Sea ice zone

    NASA Astrophysics Data System (ADS)

    Butterworth, Brian J.

    The Southern Ocean is an important part of the global carbon cycle, responsible for roughly half of the carbon dioxide (CO2) absorbed by the global ocean. The air-sea CO2 flux (Fc) can be expressed as the product of the water-air CO2 partial pressure difference (DeltapCO2) and the gas transfer velocity ( k), an exchange coefficient which represents the efficiency of gas exchange. Generally, Fc is negative (a sink) throughout the Southern Ocean and Antarctic sea ice zone (SIZ), but uncertainty in k has made it difficult to develop an accurate regional carbon budget. Constraining the functional dependence of k on wind speed in open water environments, and quantifying the effect of sea ice on k, will reduce uncertainty in the estimated contribution of the Southern Ocean and Antarctic SIZ to the global carbon cycle. To investigate Fc in the Southern Ocean, a ruggedized, unattended, closed-path eddy covariance (EC) system was deployed on the Antarctic research vessel Nathaniel B. Palmer for nine cruises during 18 months from January 2013 to June 2014 in the Southern Ocean and coastal Antarctica. The methods are described and results are shown for two cruises chosen for their latitudinal range, inclusion of open water and sea ice cover, and large DeltapCO2. The results indicated that ship-based unattended EC measurements in high latitudes are feasible, and recommendations for deployments in such environments were provided. Measurements of Fc and DeltapCO2 were used to compute k. The open water data showed a quadratic relationship between k (cm hr-1) and the neutral 10-m wind speed (U10n, m s -1), k=0.245 U10n 2+1.3, in close agreement with tracer-based results and much lower than previous EC studies. In the SIZ, it was found that k decreased in proportion to sea ice cover. This contrasted findings of enhanced Fc in the SIZ by previous open-path EC campaigns. Using the NBP results a net annual Southern Ocean (ocean south of 30°S) carbon flux of -1.1 PgC yr-1 was

  9. Evolution of surface and deep water conditions in the Antarctic Southern Ocean across the MPT

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    The mid-Pleistocene transition (MPT; 1.25-0.7 Myr) marked a fundamental change in the periodicity of the climate cycles, shifting from a 41-kyr to a high-amplitude, asymmetric 100-kyr cycle without any noticeable change in orbital forcing. Hypotheses to explain the MPT involve non-linear responses to orbital forcing, changes in glacial dynamics and internal changes in the carbon cycle. Specifically, a decrease in pCO2 during peak ice age conditions and the associated global cooling has been proposed as one of the possible triggers for the MPT. Previous results have indicated that the Southern Ocean provides a coherent two-part mechanism for the timing and amplitude of the glacial/interglacial pCO2 variations. However, there is still much uncertainty and debate regarding the response of the Antarctic Southern Ocean biogeochemistry to changes invoked for the MPT, and its contribution to the proposed pCO2 variations. Here, we show 1.5 Myr-long records of export production, and planktonic (Neogloboquadrina pachyderma) and benthic (Melonis pompilioides) foraminiferal stable isotopes and trace metals from ODP Site 1094 retrieved from the Atlantic sector of the Antarctic Southern Ocean (53.2°S, 5.1°E, 2807m). While glacial planktonic δ18O increases across the MPT, glacial Mg/Ca-derived SST decrease later, around 700 ka, when glacial atmospheric pCO2 has already dropped. As glacial export production that is crucially related to micronutrients upwelled from the subsurface ocean remains unchanged across the past 1.5 Myr, it seems that cooling of the glacial surface ocean did not significantly alter the stability of the water column. Furthermore, paired measurements of benthic δ18O and Mg/Ca enables the determination of seawater δ18O of the deep ocean, which allows us to estimate changes in the density gradient and the salinity of the deep water.

  10. A dynamical process study of intense precipitation events over the East Antarctic ice sheet and Southern Ocean

    NASA Astrophysics Data System (ADS)

    Terpstra, Annick; Gorodetskaya, Irina

    2017-04-01

    Extreme precipitation events over the Antarctic coastal and escarpment zones strongly influences regional accumulation patterns and thereby the Antarctic ice-sheet mass balance. Several recent intense precipitation events in Dronning Maud Land (leading to anomalous regional snow accumulation in 2009 and 2011) were preceded by episodes of intense poleward moisture transport organised in narrow, elongated bands. These so-called atmospheric rivers, linking moisture uptake in tropical regions and the deposition at high-latitudes, provide favourable conditions for intense precipitation events over the ice sheet. However, the poleward extent of such moisture plumes is not always sufficient for precipitation formation over the continent, resulting in precipitation over the ocean thus failing to contribute to the surface mass balance of the Antarctic ice sheet. In this study we compare and contrast moisture transport events resulting in either precipitation over the Southern Ocean at the sea-ice/ice-shelf margin or over the Antarctic continent. Identification of the ocean precipitation cases is based on atmospheric river events during the Antarctic Circumnavigation Expedition (ACE, austral summer 2016-2017). We combine ECMWF products analysis with high-resolution regional numerical simulations using Polar-WRF, to gain insight in factors influencing the ability for moisture to reach the Antarctic ice sheet. In particular we focus on (1) moisture sources for precipitation, separating between the transport of moisture originating from lower-latitudes and local moisture recycling, (2) underlying dynamical mechanism for moisture transport, and (3) the production of precipitation.

  11. Winter habitat predictions of a key Southern Ocean predator, the Antarctic fur seal (Arctocephalus gazella)

    NASA Astrophysics Data System (ADS)

    Arthur, Benjamin; Hindell, Mark; Bester, Marthan; De Bruyn, P. J. Nico; Trathan, Phil; Goebel, Michael; Lea, Mary-Anne

    2017-06-01

    Quantification of the physical and biological environmental factors that influence the spatial distribution of higher trophic species is central to inform management and develop ecosystem models, particularly in light of ocean changes. We used tracking data from 184 female Antarctic fur seals (Arctocephalus gazella) to develop habitat models for three breeding colonies for the poorly studied Southern Ocean winter period. Models were used to identify and predict the broadly important winter foraging habitat and to elucidate the environmental factors influencing these areas. Model predictions closely matched observations and several core areas of foraging habitat were identified for each colony, with notable areas of inter-colony overlap suggesting shared productive foraging grounds. Seals displayed clear choice of foraging habitat, travelling through areas of presumably poorer quality to access habitats that likely offer an energetic advantage in terms of prey intake. The relationships between environmental predictors and foraging habitat varied between colonies, with the principal predictors being wind speed, sea surface temperature, chlorophyll a concentration, bathymetry and distance to the colony. The availability of core foraging areas was not consistent throughout the winter period. The habitat models developed in this study not only reveal the core foraging habitats of Antarctic fur seals from multiple colonies, but can facilitate the hindcasting of historical foraging habitats as well as novel predictions of important habitat for other major colonies currently lacking information of the at-sea distribution of this major Southern Ocean consumer.

  12. 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.

  13. 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

  14. Accelerated freshening of Antarctic Bottom Water over the last decade in the Southern Indian Ocean.

    PubMed

    Menezes, Viviane V; Macdonald, Alison M; Schatzman, Courtney

    2017-01-01

    Southern Ocean abyssal waters, in contact with the atmosphere at their formation sites around Antarctica, not only bring signals of a changing climate with them as they move around the globe but also contribute to that change through heat uptake and sea level rise. A repeat hydrographic line in the Indian sector of the Southern Ocean, occupied three times in the last two decades (1994, 2007, and, most recently, 2016), reveals that Antarctic Bottom Water (AABW) continues to become fresher (0.004 ± 0.001 kg/g decade(-1)), warmer (0.06° ± 0.01°C decade(-1)), and less dense (0.011 ± 0.002 kg/m(3) decade(-1)). The most recent observations in the Australian-Antarctic Basin show a particularly striking acceleration in AABW freshening between 2007 and 2016 (0.008 ± 0.001 kg/g decade(-1)) compared to the 0.002 ± 0.001 kg/g decade(-1) seen between 1994 and 2007. Freshening is, in part, responsible for an overall shift of the mean temperature-salinity curve toward lower densities. The marked freshening may be linked to an abrupt iceberg-glacier collision and calving event that occurred in 2010 on the George V/Adélie Land Coast, the main source region of bottom waters for the Australian-Antarctic Basin. Because AABW is a key component of the global overturning circulation, the persistent decrease in bottom water density and the associated increase in steric height that result from continued warming and freshening have important consequences beyond the Southern Indian Ocean.

  15. Accelerated freshening of Antarctic Bottom Water over the last decade in the Southern Indian Ocean

    PubMed Central

    Menezes, Viviane V.; Macdonald, Alison M.; Schatzman, Courtney

    2017-01-01

    Southern Ocean abyssal waters, in contact with the atmosphere at their formation sites around Antarctica, not only bring signals of a changing climate with them as they move around the globe but also contribute to that change through heat uptake and sea level rise. A repeat hydrographic line in the Indian sector of the Southern Ocean, occupied three times in the last two decades (1994, 2007, and, most recently, 2016), reveals that Antarctic Bottom Water (AABW) continues to become fresher (0.004 ± 0.001 kg/g decade−1), warmer (0.06° ± 0.01°C decade−1), and less dense (0.011 ± 0.002 kg/m3 decade−1). The most recent observations in the Australian-Antarctic Basin show a particularly striking acceleration in AABW freshening between 2007 and 2016 (0.008 ± 0.001 kg/g decade−1) compared to the 0.002 ± 0.001 kg/g decade−1 seen between 1994 and 2007. Freshening is, in part, responsible for an overall shift of the mean temperature-salinity curve toward lower densities. The marked freshening may be linked to an abrupt iceberg-glacier collision and calving event that occurred in 2010 on the George V/Adélie Land Coast, the main source region of bottom waters for the Australian-Antarctic Basin. Because AABW is a key component of the global overturning circulation, the persistent decrease in bottom water density and the associated increase in steric height that result from continued warming and freshening have important consequences beyond the Southern Indian Ocean. PMID:28138548

  16. Natural iron fertilization of the Atlantic sector of the Southern Ocean by continental shelf sources of the Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    de Jong, Jeroen; Schoemann, Véronique; Lannuzel, Delphine; Croot, Peter; de Baar, Hein; Tison, Jean-Louis

    2012-03-01

    In large parts of the Southern Ocean, primary production is limited due to shortage of iron (Fe). We measured vertical Fe profiles in the western Weddell Sea, Weddell-Scotia Confluence, and Antarctic Circumpolar Current (ACC), showing that Fe is derived from benthic Fe diffusion and sediment resuspension in areas characterized by high turbulence due to rugged bottom topography. Our data together with literature data reveal an exponential decrease of dissolved Fe (DFe) concentrations with increasing distance from the continental shelves of the Antarctic Peninsula and the western Weddell Sea. This decrease can be observed 3500 km eastward of the Antarctic Peninsula area, downstream the ACC. We estimated DFe summer fluxes into the upper mixed layer of the Atlantic sector of the Southern Ocean and found that horizontal advection dominates DFe supply, representing 54 ± 15% of the total flux, with significant vertical advection second most important at 29 ± 13%. Horizontal and vertical diffusion are weak with 1 ± 2% and 1 ± 1%, respectively. The atmospheric contribution is insignificant close to the Antarctic continent but increases to 15 ± 10% in the remotest waters (>1500 km offshore) of the ACC. Translating Southern Ocean carbon fixation by primary producers into biogenic Fe fixation shows a twofold excess of new DFe input close to the Antarctic continent and a one-third shortage in the open ocean. Fe recycling, with an estimated “fe” ratio of 0.59, is the likely pathway to balance new DFe supply and Fe fixation.

  17. Natural iron fertilization of the Atlantic sector of the Southern Ocean by continental shelf sources of the Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Jong, Jeroen; Schoemann, VéRonique; Lannuzel, Delphine; Croot, Peter; Baar, Hein; Tison, Jean-Louis

    2012-03-01

    In large parts of the Southern Ocean, primary production is limited due to shortage of iron (Fe). We measured vertical Fe profiles in the western Weddell Sea, Weddell-Scotia Confluence, and Antarctic Circumpolar Current (ACC), showing that Fe is derived from benthic Fe diffusion and sediment resuspension in areas characterized by high turbulence due to rugged bottom topography. Our data together with literature data reveal an exponential decrease of dissolved Fe (DFe) concentrations with increasing distance from the continental shelves of the Antarctic Peninsula and the western Weddell Sea. This decrease can be observed 3500 km eastward of the Antarctic Peninsula area, downstream the ACC. We estimated DFe summer fluxes into the upper mixed layer of the Atlantic sector of the Southern Ocean and found that horizontal advection dominates DFe supply, representing 54 ± 15% of the total flux, with significant vertical advection second most important at 29 ± 13%. Horizontal and vertical diffusion are weak with 1 ± 2% and 1 ± 1%, respectively. The atmospheric contribution is insignificant close to the Antarctic continent but increases to 15 ± 10% in the remotest waters (>1500 km offshore) of the ACC. Translating Southern Ocean carbon fixation by primary producers into biogenic Fe fixation shows a twofold excess of new DFe input close to the Antarctic continent and a one-third shortage in the open ocean. Fe recycling, with an estimated "fe" ratio of 0.59, is the likely pathway to balance new DFe supply and Fe fixation.

  18. 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

  19. Ocean acidification and calcium carbonate saturation states in the coastal zone of the West Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Jones, Elizabeth M.; Fenton, Mairi; Meredith, Michael P.; Clargo, Nicola M.; Ossebaar, Sharyn; Ducklow, Hugh W.; Venables, Hugh J.; de Baar, Hein J. W.

    2017-05-01

    The polar oceans are particularly vulnerable to ocean acidification; the lowering of seawater pH and carbonate mineral saturation states due to uptake of atmospheric carbon dioxide (CO2). High spatial variability in surface water pH and saturation states (Ω) for two biologically-important calcium carbonate minerals calcite and aragonite was observed in Ryder Bay, in the coastal sea-ice zone of the West Antarctic Peninsula. Glacial meltwater and melting sea ice stratified the water column and facilitated the development of large phytoplankton blooms and subsequent strong uptake of atmospheric CO2 of up to 55 mmol m-2 day-1 during austral summer. Concurrent high pH (8.48) and calcium carbonate mineral supersaturation (Ωaragonite 3.1) occurred in the meltwater-influenced surface ocean. Biologically-induced increases in calcium carbonate mineral saturation states counteracted any effects of carbonate ion dilution. Accumulation of CO2 through remineralisation of additional organic matter from productive coastal waters lowered the pH (7.84) and caused deep-water corrosivity (Ωaragonite 0.9) in regions impacted by Circumpolar Deep Water. Episodic mixing events enabled CO2-rich subsurface water to become entrained into the surface and eroded seasonal stratification to lower surface water pH (8.21) and saturation states (Ωaragonite 1.8) relative to all surface waters across Ryder Bay. Uptake of atmospheric CO2 of 28 mmol m-2 day-1 in regions of vertical mixing may enhance the susceptibility of the surface layer to future ocean acidification in dynamic coastal environments. Spatially-resolved studies are essential to elucidate the natural variability in carbonate chemistry in order to better understand and predict carbon cycling and the response of marine organisms to future ocean acidification in the Antarctic coastal zone.

  20. Macronutrient supply, uptake and recycling in the coastal ocean of the west Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Henley, Sian F.; Tuerena, Robyn E.; Annett, Amber L.; Fallick, Anthony E.; Meredith, Michael P.; Venables, Hugh J.; Clarke, Andrew; Ganeshram, Raja S.

    2017-05-01

    Nutrient supply, uptake and cycling underpin high primary productivity over the continental shelf of the west Antarctic Peninsula (WAP). Here we use a suite of biogeochemical and isotopic data collected over five years in northern Marguerite Bay to examine these macronutrient dynamics and their controlling biological and physical processes in the WAP coastal ocean. We show pronounced nutrient drawdown over the summer months by primary production which drives a net seasonal nitrate uptake of 1.83 mol N m-2 yr-1, equivalent to net carbon uptake of 146 g C m-2 yr-1. High primary production fuelled primarily by deep-sourced macronutrients is diatom-dominated, but non-siliceous phytoplankton also play a role. Strong nutrient drawdown in the uppermost surface ocean has the potential to cause transient nitrogen limitation before nutrient resupply and/or regeneration. Interannual variability in nutrient utilisation corresponds to winter sea ice duration and the degree of upper ocean mixing, implying susceptibility to physical climate change. The nitrogen isotope composition of nitrate (δ15NNO3) shows a utilisation signal during the growing seasons with a community-level net isotope effect of 4.19 ± 0.29‰. We also observe significant deviation of our data from modelled and observed utilisation trends, and argue that this is driven primarily by water column nitrification and meltwater dilution of surface nitrate. This study is important because it provides a detailed description of the nutrient biogeochemistry underlying high primary productivity at the WAP, and shows that surface ocean nutrient inventories in the Antarctic sea ice zone can be affected by intense recycling in the water column, meltwater dilution and sea ice processes, in addition to utilisation in the upper ocean.

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. Brief communication: Increasing shortwave absorption over the Arctic Ocean is not balanced by trends in the Antarctic

    NASA Astrophysics Data System (ADS)

    Katlein, Christian; Hendricks, Stefan; Key, Jeffrey

    2017-09-01

    On the basis of a new, consistent, long-term observational satellite dataset we show that, despite the observed increase of sea ice extent in the Antarctic, absorption of solar shortwave radiation in the Southern Ocean poleward of 60° latitude is not decreasing. The observations hence show that the small increase in Antarctic sea ice extent does not compensate for the combined effect of retreating Arctic sea ice and changes in cloud cover, which both result in a total increase in solar shortwave energy deposited into the polar oceans.

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

    PubMed

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

    2013-11-01

    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/m(3) 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.

  7. The atmospheric ocean: eddies and jets in the Antarctic Circumpolar Current.

    PubMed

    Thompson, Andrew F

    2008-12-28

    Although the Antarctic Circumpolar Current (ACC) is the longest and the strongest oceanic current on the Earth and is the primary means of inter-basin exchange, it remains one of the most poorly represented components of global climate models. Accurately describing the circulation of the ACC is made difficult owing to the prominent role that mesoscale eddies and jets, oceanic equivalents of atmospheric storms and storm tracks, have in setting the density structure and transport properties of the current. The successes and limitations of different representations of eddy processes in models of the ACC are considered, with particular attention given to how the circulation responds to changes in wind forcing. The dynamics of energetic eddies and topographically steered jets may both temper and enhance the sensitivity of different aspects of the ACC's circulation to changes in climate.

  8. 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

  9. 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.

  10. 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.

  11. Antarctic Circumpolar Wave dynamics in a simplified ocean- atmosphere coupled model

    NASA Astrophysics Data System (ADS)

    Maze, G.; D'Andrea, F.; Colin de Verdiere, A.

    2004-12-01

    The Antarctic Circumpolar Wave (ACW) is one of the main pattern of variability in the Ocean-Atmosphere system in the southern Hemisphere extratropics. It involves sea surface temperature (SST), sea level pressure (SLP) and other variables, and consists of a wave train of zonal number 2, travelling around Antarctica at the speed of 6-8 cm s-1, hence taking around 8 years to complete a circle. A fundamental feature of this observed pattern is that anomalies are eastward propagating and seem to be phase locked: for example SST and SLP are in quadrature (high downstream of warm SST). Nevertheless the atmospheric part of the wave has been questioned by some observational studies. Different analytical and numerical studies have veen proposed, but a convincing theoretical explanation for the ACW is still missing. In this work we study the ACW as simulated by a simple dynamical model, in order to determine the basic physical processes that characterize it. The model used is an atmospheric quasi-geostrophic tridimensional model coupled to an ocean "slab" mixed layer, which includes mean geostrophic advection by the antarctic circumpolar current (ACC). The atmosphere-ocean coupling is obtained via surface sensible heat fluxes. We analyse three configuration of the model, a "passive ocean" one, where the ocean responds to the atmopheric forcing but does not feeds back to the atmosphere; a "passive atmosphere" one, where the stationary reponse of the atmosphere to prescribed SST anomalies; and a fully coupled one. The two forced experiment show separately a positive feedback in the coupled system.The passive ocean experiment shows an ACW-type low frequency variability in the ocean, ie a propagating SST anomaly with 4 years period. SSTa amplitude created were around 0.5C wich is less than observed anomalies (1.5oC). This means that the stochastic focing of the atmosphere is sufficient to substain a variability of the SST whose periodicity is set by the mean advection

  12. 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.

  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.

  14. 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.

  15. 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.

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

    PubMed Central

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

    2016-01-01

    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. PMID:27274061

  17. The impact of long-term oceanic warming on the Antarctic Oscillation in austral winter.

    PubMed

    Hao, Xin; He, Shengping; Wang, Huijun; Han, Tingting

    2017-09-26

    Increasing greenhouse gas concentration and ozone depletion are generally considered two important factors that affect the variability of the Antarctic Oscillation (AAO). Here, we find that the first leading mode of sea surface temperature (SST) variability (rotated empirical orthogonal functions) shows a long-term upward trend from 1901 to 2004 and is closely related to the AAO index that is obtained using the observationally constrained reanalysis data. Further, regressions of the sea level pressure and the 500-hPa geopotential height anomalies, against the principle component associated with the long-term SST anomalies, display a seesaw behavior between the middle and high latitudes of the Southern Hemisphere in austral winter, which is similar to the high polarity of the AAO. The circulation responses to the long-term oceanic warming in three numerical models are consistent with the observed results. This finding suggests that the long-term oceanic warming is partly responsible for the upward trend of the AAO in austral winter. The thermal wind response to the oceanic warming in South Indian and South Atlantic Ocean may be a possible mechanism for this process.

  18. 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.

  19. 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

    2014-09-29

    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. 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.

  1. Ocean acidification and fertilization in the antarctic sea urchin Sterechinus neumayeri: the importance of polyspermy.

    PubMed

    Sewell, Mary A; Millar, Russell B; Yu, Pauline C; Kapsenberg, Lydia; Hofmann, Gretchen E

    2014-01-01

    Ocean acidification (OA), the reduction of the seawater pH as a result of increasing levels of atmospheric CO2, is an important climate change stressor in the Southern Ocean and Antarctic. We examined the impact of OA on fertilization success in the Antarctic sea urchin Sterechinus neumayeri using pH treatment conditions reflective of the current and near-future "pH seascape" for this species: current (control: pH 8.052, 384.1 μatm of pCO2), a high CO2 treatment approximating the 0.2-0.3 unit decrease in pH predicted for 2100 (high CO2: pH 7.830, 666.0 μatm of pCO2), and an intermediate medium CO2 (pH 7.967, 473.4 μatm of pCO2). Using a fertilization kinetics approach and mixed-effect models, we observed significant variation in the OA response between individual male/female pairs (N = 7) and a significant population-level increase (70-100%) in tb (time for a complete block to polyspermy) at medium and high CO2, a mechanism that potentially explains the higher levels of abnormal development seen in OA conditions. However, two pairs showed higher fertilization success with CO2 treatment and a nonsignificant effect. Future studies should focus on the mechanisms and levels of interindividual variability in OA response, so that we can consider the potential for selection and adaptation of organisms to a future ocean.

  2. 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.

  3. 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

  4. Sensitivity of ocean circulation and sea-ice conditions to loss of West Antarctic ice shelves and ice sheet

    NASA Astrophysics Data System (ADS)

    Bougamont, Marion; Hunke, Elizabeth C.; Tulaczyk, Slawek

    We use a global coupled ocean-sea ice model to test the hypothesis that the disintegration of the West Antarctic ice sheet (WAIS), or just its ice shelves, may modify ocean circulation and sea-ice conditions in the Southern Ocean. We compare the results of three model runs: (1) a control run with a standard (modern) configuration of landmask in West Antarctica, (2) a no-shelves run with West Antarctic ice shelves removed and (3) a no-WAIS run. In the latter two runs, up to a few million square kilometres of new sea surface area opens to sea-ice formation, causing the volume and extent of Antarctic sea-ice cover to increase compared with the control run. In general, near-surface waters are cooler around Antarctica in the no-shelves and no-WAIS model runs than in the control run, while warm intermediate and deep waters penetrate further south, increasing poleward heat transport. Varying regional responses to the imposed changes in landmask configuration are determined by the fact that Antarctic polynyas and fast ice develop in different parts of the model domain in each run. Model results suggest that changes in the extent of WAIS may modify oceanographic conditions in the Southern Ocean.

  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. 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.

  7. 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.

  8. Drivers of Antarctic sea-ice expansion and Southern Ocean surface cooling over the past four decades

    NASA Astrophysics Data System (ADS)

    Purich, Ariaan; England, Matthew

    2017-04-01

    Despite global warming, total Antarctic sea-ice coverage has increased overall during the past four decades. In contrast, the majority of CMIP5 models simulate a decline. In addition, Southern Ocean surface waters have largely cooled, in stark contrast to almost all historical CMIP5 simulations. Subantarctic Surface Waters have cooled and freshened while waters to the north of the Antarctic Circumpolar Current have warmed and increased in salinity. It remains unclear as to what extent the cooling and Antarctic sea-ice expansion is due to natural variability versus anthropogenic forcing; due for example to changes in the Southern Annular Mode (SAM). It is also unclear what the respective role of surface buoyancy fluxes is compared to internal ocean circulation changes, and what the implications are for longer-term climate change in the region. In this presentation we will outline three distinct drivers of recent Southern Ocean surface trends that have each made a significant contribution to regional cooling: (1) wind-driven surface cooling and sea-ice expansion due to shifted westerly winds, (2) teleconnections of decadal variability from the tropical Pacific, and (3) surface cooling and ice expansion due to large-scale Southern Ocean freshening, most likely driven by SAM-related precipitation trends over the open ocean. We will also outline the main reasons why climate models for the most part miss these Southern Ocean cooling trends, despite capturing overall trends in the SAM.

  9. Rapid ocean wave teleconnections linking Antarctic salinity anomalies to the equatorial ocean-atmosphere system

    NASA Astrophysics Data System (ADS)

    Atkinson, C. P.; Wells, N. C.; Blaker, A. T.; Sinha, B.; Ivchenko, V. O.

    2009-04-01

    The coupled climate model FORTE is used to investigate rapid ocean teleconnections between the Southern Ocean and equatorial Pacific Ocean. Salinity anomalies located throughout the Southern Ocean generate barotropic signals that propagate along submerged topographic features and result in the growth of baroclinic energy anomalies around Indonesia and the tropical Pacific. Anomalies in the Ross, Bellingshausen and Amundsen Seas exchange the most barotropic kinetic energy between high and low latitudes. In the equatorial Pacific, baroclinic Kelvin waves are excited which propagate eastwards along the thermocline, resulting in SST anomalies in the central and eastern Pacific. SST anomalies are subsequently amplified to magnitudes of 1.25°C by air-sea interaction, which could potentially influence other coupled Pacific phenomena.

  10. 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.

  11. 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.

  12. The not-so-silent world: Measuring Arctic, Equatorial, and Antarctic soundscapes in the Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Haver, Samara M.; Klinck, Holger; Nieukirk, Sharon L.; Matsumoto, Haru; Dziak, Robert P.; Miksis-Olds, Jennifer L.

    2017-04-01

    Anthropogenic noise in the ocean has been shown, under certain conditions, to influence the behavior and health of marine mammals. Noise from human activities may interfere with the low-frequency acoustic communication of many Mysticete species, including blue (Balaenoptera musculus) and fin whales (B. physalus). This study analyzed three soundscapes in the Atlantic Ocean, from the Arctic to the Antarctic, to document ambient sound. For 16 months beginning in August 2009, acoustic data (15-100 Hz) were collected in the Fram Strait (79°N, 5.5°E), near Ascension Island (8°S, 14.4°W) and in the Bransfield Strait (62°S, 55.5°W). Results indicate (1) the highest overall sound levels were measured in the equatorial Atlantic, in association with high levels of seismic oil and gas exploration, (2) compared to the tropics, ambient sound levels in polar regions are more seasonally variable, and (3) individual elements beget the seasonal and annual variability of ambient sound levels in high latitudes. Understanding how the variability of natural and man-made contributors to sound may elicit differences in ocean soundscapes is essential to developing strategies to manage and conserve marine ecosystems and animals.

  13. Measurement of ocean temperatures using instruments carried by Antarctic fur seals

    NASA Astrophysics Data System (ADS)

    Boyd, I. L.; Hawker, E. J.; Brandon, M. A.; Staniland, I. J.

    2001-01-01

    The study aimed to test the utility of instruments deployed on marine mammals for measuring physical oceanographic variation and, using this method, to examine temperature variation in the coastal waters around South Georgia. There was a significant correlation between temperature measurements made using a towed undulating oceanographic recorder (UOR) and concurrent measurements from time-depth recorders (TDRs) fitted to lactating Antarctic fur seals foraging from the coast of South Georgia. Congruence was found at horizontal spatial scales from 0.01°×0.01° to 0.5°×0.5° (degrees of latitude and longitude), and at a vertical scale of 10 m. However, there was no significant correlation between temperature measured by TDRs in the top 5 m and sea surface temperature (SST) measured by satellite remote sensing. TDR data provided information about temperature variation vertically through the water column, and through time. The UOR data were used to recalibrate the TDR data in order to correct for the slow response time of the TDR thermistor relative to the speed of seal movements through the water column. Seasonal temperature variation was apparent, and temperatures also varied between regions, and with bathymetry. These results were consistent with the current interpretation of the coastal oceanography around South Georgia. In particular, the relationship between on- and off-shelf waters showed larger amounts of warmer surface water in a region in which more run-off was to be expected. The study also showed that Antarctic fur seals concentrate their activity in regions of colder, and presumably oceanic, water. Such instrumented animals could provide near real time data for assimilation into ocean models.

  14. Why does Antarctic sea-ice and Southern Ocean surface water appear to be oblivious to global warming?

    NASA Astrophysics Data System (ADS)

    England, M. H.; Purich, A.

    2016-12-01

    Despite global warming, total Antarctic sea-ice coverage has overall increased during the past three-four decades. In contrast, the majority of CMIP5 models simulate a decline. In addition, Southern Ocean surface waters have largely cooled over the past 50 years, in stark contrast to almost all historical CMIP5 simulations. For the most part Subantarctic Surface Waters have cooled and freshened while waters to the north of the ACC have warmed and increased in salinity. It remains unclear (1) to what extent Antarctic sea-ice expansion is due to natural variability vs. anthropogenic forcing of the Southern Annular Mode (via increasing greenhouse gases and/or ozone depleting substances), (2) what the respective role of surface buoyancy fluxes is compared to internal ocean circulation changes, (3) how much of the cooling trends might have been mitigated by ocean eddy fluxes, and (4) what the implications are for interior water masses, carbon uptake, and the global ocean thermohaline circulation. In this talk I will discuss possible causes for the observed trends in surface hydrographic properties over the Southern Ocean, with a focus on both Antarctic sea-ice expansion and sea surface cooling. I will also outline the main reasons why climate models for the most part miss these trends.

  15. 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

  16. Ammonium in coastal Antarctic aerosol and snow: Role of polar ocean and penguin emissions

    NASA Astrophysics Data System (ADS)

    Legrand, Michel; Ducroz, FrançOis; Wagenbach, Dietmar; Mulvaney, Robert; Hall, Julie

    1998-05-01

    Year-round aerosol samples collected in the boundary layer at coastal Antarctic sites (Dumont D'Urville, Neumayer, and Halley) indicate a seasonal cycle of ammonium concentrations with a minimum in winter (April-September). A large intersite difference appears in the summer (November-February) maxima values, from ˜12.5 ng m-3 at Neumayer to 140-230 ng m-3 at Dumont D'Urville. At Dumont D'Urville, ammonium concentrations are the largest ever reported from Antarctic sites, and the large summer maxima are associated with large enrichments with respect to sea salt for potassium and calcium. In addition, seasonal ammonium variations at Dumont D'Urville are in phase with a well-marked seasonal cycle of oxalate concentrations which exhibit maxima of 5-10 ng m-3 in spring and summer and minima of less than 0.5 ng m-3 in winter. Such a composition of aerosols present in the boundary layer at Dumont D'Urville in summer is linked to the presence of a large Adélie penguin population from the end of October to March at the site. Ornithogenic soils (defined as guano-enriched soils), together with the bacterial decomposition of uric acid, are a source of ammonium, oxalate, and cation (such as potassium and calcium) aerosol, in addition to a subsequent large ammonia loss from ornithogenic soils to the atmosphere. The total breeding population of 5 million Adélie penguins widely distributed around the Antarctic continent may emit, at most, some 2.5 × 10-4 Mt of NH3-N during the summer months. In contrast, Halley and Neumayer Stations are far less exposed to penguin colony emissions. At Neumayer, ammonium concentrations peak from January to March and are in phase with the increase of biogenic sulfur species. Here the NH4+/(MSA + nss SO4-) molar ratio is close to 13% in summer aerosol and to 40% in winter aerosol. Using this summer ratio, which may be related to ammonia and sulfur oceanic emissions occurring south of 50°S in summer and estimated DMS emissions in these regions at

  17. Poles apart: the "bipolar" pteropod species Limacina helicina is genetically distinct between the Arctic and Antarctic oceans.

    PubMed

    Hunt, Brian; Strugnell, Jan; Bednarsek, Nina; Linse, Katrin; Nelson, R John; Pakhomov, Evgeny; Seibel, Brad; Steinke, Dirk; Würzberg, Laura

    2010-03-23

    The shelled pteropod (sea butterfly) Limacina helicina is currently recognised as a species complex comprising two sub-species and at least five "forma". However, at the species level it is considered to be bipolar, occurring in both the Arctic and Antarctic oceans. Due to its aragonite shell and polar distribution L. helicina is particularly vulnerable to ocean acidification. As a key indicator of the acidification process, and a major component of polar ecosystems, L. helicina has become a focus for acidification research. New observations that taxonomic groups may respond quite differently to acidification prompted us to reassess the taxonomic status of this important species. We found a 33.56% (+/-0.09) difference in cytochrome c oxidase subunit I (COI) gene sequences between L. helicina collected from the Arctic and Antarctic oceans. This degree of separation is sufficient for ordinal level taxonomic separation in other organisms and provides strong evidence for the Arctic and Antarctic populations of L. helicina differing at least at the species level. Recent research has highlighted substantial physiological differences between the poles for another supposedly bipolar pteropod species, Clione limacina. Given the large genetic divergence between Arctic and Antarctic L. helicina populations shown here, similarly large physiological differences may exist between the poles for the L. helicina species group. Therefore, in addition to indicating that L. helicina is in fact not bipolar, our study demonstrates the need for acidification research to take into account the possibility that the L. helicina species group may not respond in the same way to ocean acidification in Arctic and Antarctic ecosystems.

  18. Poles Apart: The “Bipolar” Pteropod Species Limacina helicina Is Genetically Distinct Between the Arctic and Antarctic Oceans

    PubMed Central

    Bednarsek, Nina; Linse, Katrin; Nelson, R. John; Pakhomov, Evgeny; Seibel, Brad; Steinke, Dirk; Würzberg, Laura

    2010-01-01

    The shelled pteropod (sea butterfly) Limacina helicina is currently recognised as a species complex comprising two sub-species and at least five “forma”. However, at the species level it is considered to be bipolar, occurring in both the Arctic and Antarctic oceans. Due to its aragonite shell and polar distribution L. helicina is particularly vulnerable to ocean acidification. As a key indicator of the acidification process, and a major component of polar ecosystems, L. helicina has become a focus for acidification research. New observations that taxonomic groups may respond quite differently to acidification prompted us to reassess the taxonomic status of this important species. We found a 33.56% (±0.09) difference in cytochrome c oxidase subunit I (COI) gene sequences between L. helicina collected from the Arctic and Antarctic oceans. This degree of separation is sufficient for ordinal level taxonomic separation in other organisms and provides strong evidence for the Arctic and Antarctic populations of L. helicina differing at least at the species level. Recent research has highlighted substantial physiological differences between the poles for another supposedly bipolar pteropod species, Clione limacina. Given the large genetic divergence between Arctic and Antarctic L. helicina populations shown here, similarly large physiological differences may exist between the poles for the L. helicina species group. Therefore, in addition to indicating that L. helicina is in fact not bipolar, our study demonstrates the need for acidification research to take into account the possibility that the L. helicina species group may not respond in the same way to ocean acidification in Arctic and Antarctic ecosystems. PMID:20360985

  19. 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

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. Freshening of Antarctic Intermediate Water in the South Atlantic Ocean in 2005-2014

    NASA Astrophysics Data System (ADS)

    Yao, Wenjun; Shi, Jiuxin; Zhao, Xiaolong

    2017-07-01

    Basin-scale freshening of Antarctic Intermediate Water (AAIW) is reported to have occurred in the South Atlantic Ocean during the period from 2005 to 2014, as shown by the gridded monthly means of the Array for Real-time Geostrophic Oceanography (Argo) data. This phenomenon was also revealed by two repeated transects along a section at 30° S, performed during the World Ocean Circulation Experiment Hydrographic Program. Freshening of the AAIW was compensated for by a salinity increase of thermocline water, indicating a hydrological cycle intensification. This was supported by the precipitation-minus-evaporation change in the Southern Hemisphere from 2000 to 2014. Freshwater input from atmosphere to ocean surface increased in the subpolar high-precipitation region and vice versa in the subtropical high-evaporation region. Against the background of hydrological cycle changes, a decrease in the transport of Agulhas Leakage (AL), which was revealed by the simulated velocity field, was proposed to be a contributor to the associated freshening of AAIW. Further calculation showed that such a decrease could account for approximately 53 % of the observed freshening (mean salinity reduction of about 0.012 over the AAIW layer). The estimated variability of AL was inferred from a weakening of wind stress over the South Indian Ocean since the beginning of the 2000s, which would facilitate freshwater input from the source region. The mechanical analysis of wind data here was qualitative, but it is contended that this study would be helpful to validate and test predictably coupled sea-air model simulations.

  5. Statistical modeling of a former Arctic Ocean ice shelf complex using Antarctic analogies

    NASA Astrophysics Data System (ADS)

    Kirchner, N.; Furrer, R.; Jakobsson, M.; Zwally, H. J.; Robbins, J. W.

    2013-06-01

    Geophysical mapping and coring of the central Arctic Ocean seafloor provide evidence for repeated occurrences of ice sheet/ice shelf complexes during previous glacial periods. Several ridges and bathymetric highs shallower than present water depths of ˜1000m show signs of erosion from deep-drafting (armadas of) icebergs, which originated from thick outlet glaciers and ice shelves. Mapped glacigenic landforms and dates of cored sediments suggest that the largest ice shelf complex was confined to the Amerasian sector of the Arctic Ocean during Marine Isotope Stage (MIS) 6. However, the spatial extent of ice shelves can not be well reconstructed from occasional groundings on bathymetric highs. Therefore, we apply a statistical approach to provide independent support for an extensive MIS 6 ice shelf complex, which previously was inferred only from interpretation of geophysical and geological data. Specifically, we assess whether this ice shelf complex comprises a likely source of the deep-draft icebergs responsible for the mapped scour marks. The statistical modeling is based on exploiting relations between contemporary Antarctic ice shelves and their local physical environments and the assumption that Arctic Ocean MIS6 ice shelves scale similarly. Analyzing ice thickness data along the calving front of contemporary ice shelves, a peak over threshold method is applied to determine sources of deep-drafting icebergs in the Arctic Ocean MIS6 ice shelf complex. This approach is novel to modeling Arctic paleoglacial configurations. Predicted extreme calving front drafts match observed deep-draft iceberg scours if the ice shelf complex is sufficiently large.

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

    DOE PAGES

    Dziak, Robert P.; Bohnenstiehl, DelWayne R.; Stafford, Kathleen M.; ...

    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

  7. Sources and fate of polycyclic aromatic hydrocarbons in the Antarctic and Southern Ocean atmosphere

    NASA Astrophysics Data System (ADS)

    Cabrerizo, Ana; Galbán-Malagón, Cristóbal; Del Vento, Sabino; Dachs, Jordi

    2014-12-01

    Polycyclic aromatic hydrocarbons (PAHs) are a geochemically relevant family of semivolatile compounds originating from fossil fuels, biomass burning, and their incomplete combustion, as well as biogenic sources. Even though PAHs are ubiquitous in the environment, there are no previous studies of their occurrence in the Southern Ocean and Antarctic atmosphere. Here we show the gas and aerosol phase PAHs concentrations obtained from three sampling cruises in the Southern Ocean (Weddell, Bellingshausen, and South Scotia Seas), and two sampling campaigns at Livingston Island (Southern Shetlands). This study shows an important variability of the atmospheric concentrations with higher concentrations in the South Scotia and northern Weddell Seas than in the Bellingshausen Sea. The assessment of the gas-particle partitioning of PAHs suggests that aerosol elemental carbon contribution is modest due to its low concentrations. Over the ocean, the atmospheric concentrations do not show a temperature dependence, which is consistent with an important role of long-range atmospheric transport of PAHs. Conversely, over land at Livingston Island, the PAHs gas phase concentrations increase when the temperature increases, consistently with the presence of local diffusive sources. The use of fugacity samplers allowed the determination of the air-soil and air-snow fugacity ratios of PAHs showing that there is a significant volatilization of lighter molecular weight PAHs from soil and snow during the austral summer. The higher volatilization, observed in correspondence of sites where the organic matter content in soil is higher, suggests that there may be a biogenic source of some PAHs. The volatilization of PAHs from soil and snow is sufficient to support the atmospheric occurrence of PAHs over land but may have a modest regional influence on the atmospheric occurrence of PAHs over the Southern Ocean.

  8. 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

  9. Antarctic marine biodiversity--what do we know about the distribution of life in the Southern Ocean?

    PubMed

    Griffiths, Huw J

    2010-08-02

    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

  10. 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

  11. 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.

  12. 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.

  13. Antarctic sea ice control on ocean circulation in present and glacial climates

    PubMed Central

    Ferrari, Raffaele; Jansen, Malte F.; Adkins, Jess F.; Burke, Andrea; Stewart, Andrew L.; Thompson, Andrew F.

    2014-01-01

    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

  14. 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

  15. 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.

  16. Dianeutral mixing and transformation of Antarctic Intermediate Water in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    You, Yuzhu

    1998-12-01

    Transformation of Antarctic Intermediate Water (AAIW) is achieved through one or more processes of epineutral advection, epineutral diffusion, dianeutral advection, and dianeutral diffusion. This paper points to the importance of dianeutral mixing in achieving the AAIW water-mass transformation in the Indian Ocean. Six neutral surfaces were mapped to span the intermediate water of the Indian Ocean between 580 and 1500 m at the reference cast. South of the Antarctic frontal zone, AAIW shows a diffusive tongue in the meridional Turner angle (after J. Stewart Turner) sections. On its equatorward transition, the transformed AAIW is characterized by a tongue of doubly stable conditions extending a great distance to as far as about 5°S. A maximum downwelling dianeutral velocity of -2×10-7 m s-1 due to cabbeling is found in the Antarctic frontal zone, which is 3 orders larger than that in the subtropical gyre. Thermobaricity acts similarly to cabbeling in the Antarctic frontal zone and contributes a maximum downwelling dianeutral velocity of -1×10-7 m s-1 but mainly arises in upwelling north of the frontal zone. A strong downwelling dianeutral velocity of -2×10-7 m s-1 contributed by vertical turbulent mixing occurs on the upper two neutral surfaces south of the frontal zone. With assumed constant epineutral diffusivity K of 103 m2 s-1 and dianeutral diffusivity D of 10-5 m2 s-1, an area-mean net dianeutral upwelling velocity of 0.11×10-7 m s-1 is found north of 32°S across the lowermost neutral surface σθ=27.66. It means a net upward volume transport of 0.6 Sv (1 Sv=106 m3 s-1). This weak but net upwelling transport roughly corresponds to a net 0.5 Sv transported downward, with a downwelling dianeutral velocity of -0.25×10-7 m s-1 across the same neutral surface south of 45°S. Toward the core of AAIW, the net dianeutral velocity increases to 0.15×10-7 m s-1 across the"27.37" neutral surface. The corresponding net dianeutral transport increases to 0.8 Sv. You

  17. Decadal-Scale Response of the Antarctic Ice sheet to a Warming Ocean using the POPSICLES Coupled Ice Sheet-Ocean model

    NASA Astrophysics Data System (ADS)

    Martin, D. F.; Asay-Davis, X.; Cornford, S. L.; Price, S. F.; Ng, E. G.; Collins, W.

    2015-12-01

    We present POPSICLES simulation results covering the full Antarctic Ice Sheet and the Southern Ocean spanning the period from 1990 to 2010. We use the CORE v. 2 interannual forcing data to force the ocean model. Simulations are performed at 0.1o(~5 km) ocean resolution with adaptive ice sheet resolution as fine as 500 m to adequately resolve the grounding line dynamics. We discuss the effect of improved ocean mixing and subshelf bathymetry (vs. the standard Bedmap2 bathymetry) on the behavior of the coupled system, comparing time-averaged melt rates below a number of major ice shelves with those reported in the literature. We also present seasonal variability and decadal melting trends from several Antarctic regions, along with the response of the ice shelves and the consequent dynamic response of the grounded ice sheet.POPSICLES couples the POP2x ocean model, a modified version of the Parallel Ocean Program, and the BISICLES ice-sheet model. POP2x includes sub-ice-shelf circulation using partial top cells and the commonly used three-equation boundary layer physics. Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP) and other continental-scale simulations and melt-rate observations. BISICLES makes use of adaptive mesh refinement and a 1st-order accurate momentum balance similar to the L1L2 model of Schoof and Hindmarsh to accurately model regions of dynamic complexity, such as ice streams, outlet glaciers, and grounding lines. Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests (MISMIP-3d) and realistic configurations.The figure shows the BISICLES-computed vertically-integrated grounded ice velocity field 5 years into a 20-year coupled full-continent Antarctic-Southern-Ocean simulation. Submarine melt rates are painted onto the surface of the floating ice shelves. Grounding lines are shown in green.

  18. Ocean Drilling Program Leg 178 (Antarctic Peninsula): Sedimentology of glacially influenced continental margin topsets and foresets

    USGS Publications Warehouse

    Eyles, N.; Daniels, J.; Osterman, L.E.; Januszczak, N.

    2001-01-01

    Ocean Drilling Program Leg 178 (February-April 1998) drilled two sites (Sites 1097 and 1103) on the outer Antarctic Peninsula Pacific continental shelf. Recovered strata are no older than late Miocene or early Pliocene (<4.6 Ma). Recovery at shallow depths in loosely consolidated and iceberg-turbated bouldery sediment was poor but improved with increasing depth and consolidation to allow description of lithofacies and biofacies and interpretation of depositional environment. Site 1097 lies on the outer shelf within Marguerite Trough which is a major outlet for ice expanding seaward from the Antarctic Peninsula and reached a maximum depth drilled of 436.6 m below the sea floor (mbsf). Seismic stratigraphic data show flat-lying upper strata resting on strata that dip gently seaward. Uppermost strata, to a depth of 150 mbsf, were poorly recovered, but data suggest they consist of diamictites containing reworked and abraded marine microfauna. This interval is interpreted as having been deposited largely as till produced by subglacial cannibalization of marine sediments (deformation till) recording ice sheet expansion across the shelf. Underlying gently dipping strata show massive, stratified and graded diamictite facies with common bioturbation and slump stuctures that are interbedded with laminated and massive mudstones with dropstones. The succession contains a well-preserved in situ marine microfauna typical of open marine and proglacial marine environments. The lower gently dipping succession at Site 1097 is interpreted as a complex of sediment gravity flows formed of poorly sorted glacial debris. Site 1103 was drilled in that part of the continental margin that shows uppermost flat-lying continental shelf topsets overlying steeper dipping slope foresets seaward of a structural mid-shelf high. Drilling reached a depth of 363 mbsf with good recovery in steeply dipping continental slope foreset strata. Foreset strata are dominated by massive and chaotically

  19. 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.

  20. Observations of upper ocean stability and heat fluxes in the Antarctic from under-ice Argo float profile data.

    NASA Astrophysics Data System (ADS)

    Wilson, E. A.; Riser, S.

    2016-12-01

    Sea ice growth around Antarctica is intimately linked to the stability and thermohaline structure of the underlying ocean. As sea ice grows, the resulting brine triggers convective instabilities that deepen the mixed layer and entrain warm water from the weakly stratified pycnocline. The heat released from this process acts as a strong negative feedback to ice growth which, under the right scenarios, can exceed the initial atmospheric heat loss. Much of our current understanding of this ice-ocean interaction comes from a handful of relatively short field campaigns in the Weddell Sea. Here, we supplement those observations with an analysis of over 9000 under-ice Argo float profiles, collected between 2006-2015. These profiles provide an unprecedented view of the temporal and spatial variability of the upper ocean structure throughout the Antarctic region. With these observations and a theoretical understanding of the coupled ice-ocean system, we assess the ocean's potential to limit thermodynamic ice growth as well as its susceptibility to deep convection in different regions. Using these results, we infer how recent climatic changes may influence Antarctic sea ice growth and deep ocean ventilation in the near future.

  1. Antarctic Ice Sheet variability in the Plio-Pleistocene, its impact on the Southern Ocean and teleconnections to distant latitudes

    NASA Astrophysics Data System (ADS)

    DeConto, R.; Pollard, D.; Naish, T.

    2012-12-01

    In recent years, geological records and numerical modeling have begun to paint a picture of a highly dynamic West Antarctic Ice Sheet (WAIS) through the Pliocene and during some Pleistocene interglacials. However, the primary mechanisms driving that variability remain poorly constrained, as does the impact of substantial changes in Antarctic ice volume on global climate and the evolution of the Northern Hemispheric cryosphere over the last ~3.5 million years. Here, we take an integrated data-model view of the past variability of WAIS and the potential for substantial changes in East Antarctic Ice Sheet volume over the last ~5 million years, using a newly improved ice sheet-shelf model coupled to atmospheric and ocean model components. Recent findings support 1) the notion of a dynamic WAIS over the last 5 million years, highly sensitive to modest changes in sub-ice shelf ocean temperatures but relatively insensitive to changes in surface mass balance, 2) the potential for substantial WAIS retreat as recently as Marine Isotope Stage (MIS) 7 and the last interglacial, 3) a relatively stable EAIS through the Pliocene and Pleistocene, making some estimates of past sea level (particularly in the Pliocene) difficult to justify without invoking some unknown ice sheet dynamical processes and/or exceptional climate sensitivity and polar amplification of warming. Correlations between new Antarctic and Arctic climate records spanning the last several million years imply strong interhemispheric connectivity operating on a range of timescales,from sub-millennial to orbital. Possible teleconnection mechanisms are discussed here in the context of new climate model simulations that test the potential for Antarctic ice sheet variability to impact the global system from the warm Pliocene to present.

  2. 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.

  3. Impacts of Interactive Stratospheric Chemistry on Antarctic and Southern Ocean Climate Change in the Goddard Earth Observing System Version 5 (GEOS-5)

    NASA Technical Reports Server (NTRS)

    Li, Feng; Vikhliaev, Yury V.; Newman, Paul A.; Pawson, Steven; Perlwitz, Judith; Waugh, Darryn W.; Douglass, Anne R.

    2016-01-01

    Stratospheric ozone depletion plays a major role in driving climate change in the Southern Hemisphere. To date, many climate models prescribe the stratospheric ozone layer's evolution using monthly and zonally averaged ozone fields. However, the prescribed ozone underestimates Antarctic ozone depletion and lacks zonal asymmetries. In this study we investigate the impact of using interactive stratospheric chemistry instead of prescribed ozone on climate change simulations of the Antarctic and Southern Ocean. Two sets of 1960-2010 ensemble transient simulations are conducted with the coupled ocean version of the Goddard Earth Observing System Model, version 5: one with interactive stratospheric chemistry and the other with prescribed ozone derived from the same interactive simulations. The model's climatology is evaluated using observations and reanalysis. Comparison of the 1979-2010 climate trends between these two simulations reveals that interactive chemistry has important effects on climate change not only in the Antarctic stratosphere, troposphere, and surface, but also in the Southern Ocean and Antarctic sea ice. Interactive chemistry causes stronger Antarctic lower stratosphere cooling and circumpolar westerly acceleration during November-December-January. It enhances stratosphere-troposphere coupling and leads to significantly larger tropospheric and surface westerly changes. The significantly stronger surface wind stress trends cause larger increases of the Southern Ocean Meridional Overturning Circulation, leading to year-round stronger ocean warming near the surface and enhanced Antarctic sea ice decrease.

  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. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. Upper ocean nitrogen fluxes in the Polar Antarctic Zone: Constraints from the nitrogen and oxygen isotopes of nitrate

    NASA Astrophysics Data System (ADS)

    Difiore, Peter J.; Sigman, Daniel M.; Dunbar, Robert B.

    2009-11-01

    We report nitrate nitrogen (N) and oxygen (O) isotope measurements from the seasonally sea ice covered Polar Antarctic Zone (PAZ) south of the Southern Antarctic Circumpolar Front. The 15N/14N and 18O/16O ratios of nitrate both increase into the summertime surface mixed layer, in strong correlation with the upward decrease in nitrate concentration, the expected result of nitrate assimilation by phytoplankton. Culture studies indicate that algal assimilation of nitrate fractionates the nitrate N and O isotopes equally, while previous field studies suggest that nitrate N and O isotope behavior can be decoupled by euphotic zone nitrification. Our data for the PAZ show strong coupling of the dual isotopes of nitrate, and a numerical model of Antarctic summertime surface layer N cycling fits our observations (including isotopic compositions of both nitrate and suspended particulate N) if the nitrification rate is no more than 6% of the nitrate assimilation rate by phytoplankton. The model estimates that the N isotope effect of nitrate assimilation is 5.0 ± 0.7‰. This estimate lacks some of the uncertainties associated with previous studies within the Antarctic Circumpolar Current, and it is at the low end of most recent estimates from the Southern Ocean, the range of which we speculatively attribute to an effect of mixed layer depth on the amplitude of isotope discrimination.

  11. Circumpolar connections between Antarctic krill ( Euphausia superba Dana) populations: Investigating the roles of ocean and sea ice transport

    NASA Astrophysics Data System (ADS)

    Thorpe, S. E.; Murphy, E. J.; Watkins, J. L.

    2007-05-01

    Antarctic krill, Euphausia superba Dana, has a heterogeneous circumpolar distribution in the Southern Ocean. Krill have a close association with sea ice which provides access to a critical food source and shelter, particularly in the early life stages. Advective modelling of transport pathways of krill have until now been on regional scales and have not taken explicit account of sea ice. Here we present Lagrangian modelling studies at the circumpolar scale that include interaction with sea ice. The advection scheme uses ocean velocity output from the Ocean Circulation and Climate Advanced Modelling (OCCAM) project model together with satellite-derived sea ice motion vectors to examine the potential roles of the ocean and sea ice in maintaining the observed circumpolar krill distribution. We show that the Antarctic Coastal Current is likely to be important in generating the large-scale distribution and that sea ice motion can substantially modify the ocean transport pathways, enhancing retention or dispersal depending upon location. Within the major krill region of the Scotia Sea, the effect of temporal variability in both the ocean and sea ice velocity fields is examined. Variability in sea ice motion increases variability of influx to South Georgia, at times concentrating the influx into pulses of arrival. This variability has implications for the ecosystem around the island. The inclusion of sea ice motion leads to the identification of source regions for the South Georgia krill populations additional to those identified when only ocean motion is considered. This study indicates that the circumpolar oceanic circulation and interaction with sea ice is important in determining the large-scale distribution of krill and its associated variability.

  12. 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

  13. Estimating the biodiversity of the East Antarctic shelf and oceanic zone for ecoregionalisation: Example of the ichthyofauna of the CEAMARC (Collaborative East Antarctic Marine Census) CAML surveys

    NASA Astrophysics Data System (ADS)

    Koubbi, Philippe; Ozouf-Costaz, Catherine; Goarant, Anne; Moteki, Masato; Hulley, Percy-Alexander; Causse, Romain; Dettai, Agnès; Duhamel, Guy; Pruvost, Patrice; Tavernier, Eric; Post, Alexandra L.; Beaman, Robin J.; Rintoul, Stephen R.; Hirawake, Toru; Hirano, Daisuke; Ishimaru, Takashi; Riddle, Martin; Hosie, Graham

    2010-08-01

    Ecoregions are defined in terms of community structure as a function of abiotic or even anthropogenic forcing. They are meso-scale structures defined as the potential habitat of a species or the predicted communities geographic extent. We assume that they can be more easily defined for long-lived species, such as benthos or neritic fish, in the marine environment. Uncertainties exist for the pelagic realm because of its higher variability, plus little is known about the meso- and bathypelagic zones. A changing environment and modification of habitats will probably drive new communities from plankton to fish or top predators. We need baseline studies, such as those of the Census of Antarctic Marine Life, and databases like SCAR-MarBIN as tools for integrating all of these observations. Our objective is to understand the biodiversity patterns in the Southern Ocean and how these might change through time.

  14. Eddy-Pump: Pelagic carbon pump processes along the eddying Antarctic Polar Front in the Atlantic Sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Strass, Volker H.; Wolf-Gladrow, Dieter; Pakhomov, Evgeny A.; Klaas, Christine

    2017-04-01

    The Southern Ocean influences earth's climate in many ways. It hosts the largest upwelling region of the world oceans where 80% of deep waters resurface (Morrison et al., 2015). A prominent feature is the broad ring of cold water, the Antarctic Circumpolar Current (ACC), which encircles the Antarctic continent and connects all other oceans. The ACC plays a major role in the global heat and freshwater transports and ocean-wide cycles of chemical and biogenic elements, and harbours a series of unique and distinct ecosystems. Due to the upwelling of deep-water masses in the Antarctic Divergence, there is high supply of natural CO2 as well as macronutrients, leading to the worldwide highest surface nutrient concentrations. Despite the ample macronutrients supply, phytoplankton concentration is generally low, limited either by low micronutrient (iron) availability, insufficient light due to deep wind-mixed layers or grazing by zooplankton, or by the combination of all, varying temporally and regionally.

  15. Decadal-Scale Response of the Antarctic Ice sheet to a Warming Ocean using the POPSICLES Coupled Ice Sheet-Ocean model

    NASA Astrophysics Data System (ADS)

    Martin, Daniel; Asay-Davis, Xylar; Cornford, Stephen; Price, Stephen; Ng, Esmond; Collins, William

    2016-04-01

    We present POPSICLES simulation results covering the full Antarctic Ice Sheet and the Southern Ocean spanning the period from 1990 to 2010. We use the CORE v. 2 interannual forcing data to force the ocean model. Simulations are performed at 0.1 degree (~5 km) ocean resolution with adaptive ice sheet resolution as fine as 500 m to adequately resolve the grounding line dynamics. We discuss the effect of improved ocean mixing and subshelf bathymetry (vs. the standard Bedmap2 bathymetry) on the behavior of the coupled system, comparing time-averaged melt rates below a number of major ice shelves with those reported in the literature. We also present seasonal variability and decadal melting trends from several Antarctic regions, along with the response of the ice shelves and the consequent dynamic response of the grounded ice sheet. POPSICLES couples the POP2x ocean model, a modified version of the Parallel Ocean Program, and the BISICLES ice-sheet model. POP2x includes sub-ice-shelf circulation using partial top cells and the commonly used three-equation boundary layer physics. Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP) and other continental-scale simulations and melt-rate observations. BISICLES makes use of adaptive mesh refinement and a 1st-order accurate momentum balance similar to the L1L2 model of Schoof and Hindmarsh to accurately model regions of dynamic complexity, such as ice streams, outlet glaciers, and grounding lines. Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests (MISMIP-3d) and realistic configurations.

  16. Influence of Antarctic Intermediate Water on the deoxygenation of the Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Santos, Guilherme Cordova; Kerr, Rodrigo; Azevedo, José Luiz Lima; Mendes, Carlos Rafael Borges; da Cunha, Letícia Cotrim

    2016-12-01

    Hydrographic trends in the Antarctic Intermediate Water (AAIW) layer that may be associated with changes in the thickness and oxygen content of oxygen minimum zones (OMZs) in the eastern tropical South Atlantic (ETSA) and eastern tropical North Atlantic (ETNA) are investigated by using historical data (1960 to 2015). Our results reveal that the thickness of these OMZs has continually increased (2.58 ± 0.67 m yr-1 for the ETSA and 3.37 ± 0.73 m yr-1 for the ETNA), the mean oxygen concentration has decreased (- 0.12 ± 0.03 μmol kg-1 yr-1 for the ETSA and - 0.17 ± 0.05 μmol kg-1 yr-1 for the ETNA), and the mean temperature has increased. The optimum multiparameter analysis method is used to track modifications in the AAIW along its path through the South Atlantic Subtropical Gyre. We observe an AAIW layer vertical expansion rate of 1.67 ± 0.71 m yr-1, a decrease in the mean oxygen concentration of - 0.18 ± 0.04 μmol kg-1 yr-1 and an increase in the mean temperature of 0.010 ± 0.005 °C yr-1. Moreover, a similar decrease in oxygen concentrations is observed in the AAIW layer of the studied OMZ regions compared to those in the non-AAIW portions of these OMZs, which indicates strong deoxygenation in this water mass over time. Our results suggest that warming in the AAIW source region and in its extensive temporal displacement through the SASG to the eastern tropical Atlantic Ocean appreciably shifted this water mass toward lower densities with depleted oxygen (increases in ventilation age and oxygen consumption). The warming trend that is reported here suggests that global warming is one of the factors that influence oxygen solubility changes during the deoxygenation and expansion of OMZs.

  17. 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

  18. Neutral Poly/Per-Fluoroalkyl Substances in Air from the Atlantic to the Southern Ocean and in Antarctic Snow.

    PubMed

    Wang, Zhen; Xie, Zhiyong; Mi, Wenying; Möller, Axel; Wolschke, Hendrik; Ebinghaus, Ralf

    2015-07-07

    The oceanic scale occurrences of typical neutral poly/per-fluoroalkyl substances (PFASs) in the atmosphere across the Atlantic, as well as their air-snow exchange at the Antarctic Peninsula, were investigated. Total concentrations of the 12 PFASs (∑PFASs) in gas phase ranged from 2.8 to 68.8 pg m(-3) (mean: 23.5 pg m(-3)), and the levels in snow were from 125 to 303 pg L(-1) (mean: 209 pg L(-1)). Fluorotelomer alcohols (FTOHs) were dominant in both air and snow. The differences of specific compounds to ∑PFASs were not significant between air and snow. ∑PFASs were higher above the northern Atlantic compared to the southern Atlantic, and the levels above the southern Atlantic <30°S was the lowest. High atmospheric PFAS levels around the Antarctic Peninsula were the results of a combination of air mass, weak elimination processes and air-snow exchange of PFASs. Higher ratios of 8:2 to 10:2 to 6:2 FTOH were observed in the southern hemisphere, especially around the Antarctic Peninsula, suggesting that PFASs in the region were mainly from the long-range atmospheric transport. No obvious decrease of PFASs was observed in the background marine atmosphere after 2005.

  19. A Tale of Two Forcings: Present-Day Coupled Antarctic Ice-sheet/Southern Ocean dynamics using the POPSICLES model.

    NASA Astrophysics Data System (ADS)

    Martin, Daniel; Asay-Davis, Xylar; Cornford, Stephen; Price, Stephen; Ng, Esmond; Collins, William

    2015-04-01

    We present POPSICLES simulation results covering the full Antarctic Ice Sheet and the Southern Ocean spanning the period 1990 to 2010 resulting from two different choices of climate forcing: a 'normal-year' climatology and the CORE v. 2 interannual forcing data (Large and Yeager 2008). Simulations are performed at 0.1o (~5 km) ocean resolution and adaptive ice sheet resolution as fine as 500 m. We compare time-averaged melt rates below a number of major ice shelves with those reported by Rignot et al. (2013) as well as other recent studies. We also present seasonal variability and decadal melting trends from several Antarctic regions, along with the response of the ice shelves and consequent dynamics of the grounded ice sheet. POPSICLES couples the POP2x ocean model, a modified version of the Parallel Ocean Program (Smith and Gent, 2002), and the BISICLES ice-sheet model (Cornford et al., 2012). POP2x includes sub-ice-shelf circulation using partial top cells (Losch, 2008) and boundary layer physics 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). BISICLES makes use of adaptive mesh refinement and a 1st-order accurate momentum balance similar to the L1L2 model of Schoof and Hindmarsh (2009) to accurately model regions of dynamic complexity, such as ice streams, outlet glaciers, and grounding lines. Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests (MISMIP-3d; Pattyn et al., 2013) and realistic configurations (Favier et al. 2014).

  20. 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.

  1. Seabed images from Southern Ocean shelf regions off the northern Antarctic Peninsula and in the southeastern Weddell Sea

    NASA Astrophysics Data System (ADS)

    Piepenburg, Dieter; Buschmann, Alexander; Driemel, Amelie; Grobe, Hannes; Gutt, Julian; Schumacher, Stefanie; Segelken-Voigt, Alexandra; Sieger, Rainer

    2017-07-01

    Recent advances in underwater imaging technology allow for the gathering of invaluable scientific information on seafloor ecosystems, such as direct in situ views of seabed habitats and quantitative data on the composition, diversity, abundance, and distribution of epibenthic fauna. The imaging approach has been extensively used within the research project DynAMo (Dynamics of Antarctic Marine Shelf Ecosystems) at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research Bremerhaven (AWI), which aimed to comparatively assess the pace and quality of the dynamics of Southern Ocean benthos. Within this framework, epibenthic spatial distribution patterns have been comparatively investigated in two regions in the Atlantic sector of the Southern Ocean: the shelf areas off the northern tip of the Antarctic Peninsula, representing a region with above-average warming of surface waters and sea-ice reduction, and the shelves of the eastern Weddell Sea as an example of a stable high-Antarctic marine environment that is not (yet) affected by climate change. The AWI Ocean Floor Observation System (OFOS) was used to collect seabed imagery during two cruises of the German research vessel Polarstern, ANT-XXIX/3 (PS81) to the Antarctic Peninsula from January to March 2013 and ANT-XXXI/2 (PS96) to the Weddell Sea from December 2015 to February 2016. Here, we report on the image and data collections gathered during these cruises. During PS81, OFOS was successfully deployed at a total of 31 stations at water depths between 29 and 784 m. At most stations, series of 500 to 530 pictures ( > 15 000 in total, each depicting a seabed area of approximately 3.45 m2 or 2.3 × 1.5 m) were taken along transects approximately 3.7 km in length. During PS96, OFOS was used at a total of 13 stations at water depths between 200 and 754 m, yielding series of 110 to 293 photos (2670 in total) along transects 0.9 to 2.6 km in length. All seabed images taken during the two cruises

  2. Mitochondrial Acclimation Capacities to Ocean Warming and Acidification Are Limited in the Antarctic Nototheniid Fish, Notothenia rossii and Lepidonotothen squamifrons

    PubMed Central

    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

  3. 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

  4. Access of warm Southern Ocean water along the East Antarctic Margin - first results from the NBP1503 cruise

    NASA Astrophysics Data System (ADS)

    Nitsche, F. O.; Guerrero, R.; Williams, G. D.; Porter, D. F.; Cougnon, E.; Fraser, A. D.; Correia, R.; Richardson, D.

    2015-12-01

    The future of the Antarctic Ice Sheet is one of the critical questions in assessing the effects of climate change. The East Antarctic Ice Sheet (EAIS) was regarded as relatively stable, and only recently has become the subject of a series of studies to determine if parts of the EAIS might be susceptible to melting if warm ocean masses reach the ice sheet. We are presenting new oceanographic and bathymetry observations from the East Antarctic continental margin between 115° E and 135° E that have been collected as part of the scientific cruise NBP1503 onboard the NB Palmer in early 2015. The goal of the scientific cruise was to determine to what extent warmer ocean water could reach (or is reaching) the inner shelf. Sea ice conditions prevented access to most inner continental shelf areas. Instead, we collected detailed multibeam bathymetry and Conductivity-Temperature-Depth (CTD) data from the continental slope, rise and the outer shelf north of the Dibble Glacier, Frost Glacier, Dalton Iceberg Tongue and Totten Glacier. An oceanographic section of 19 CTD stations on the continental slope parallel to the margin shows that modified Circumpolar Deep Water (mCDW) with higher salinity and temperatures is present near the shelf break over large sections of the investigated margin, but is absent in other sections. The shelf break depth varies significantly along the margin between ~300 and ~500 m. The shallower depths are potentially an obstacle for access of mCDW to the shelf. As a result, a ~100 m thick layer of mCDW resides on the ~500 m deep outer shelf north of the Totten Glacier, but there is no indication of mCDW in the Dibble Polynya because the shelf break is shallower. The access and presence of warmer mCDW water, especially north of Totten Glacier and the Moscow University Ice Shelf, has important implications in understanding the observed thinning of this ice stream.

  5. Behavioural sensitivity of a key Southern Ocean species (Antarctic krill, Euphausia superba) to p,p'-DDE exposure.

    PubMed

    Poulsen, Anita H; Kawaguchi, So; King, Catherine K; King, Robert A; Bengtson Nash, Susan M

    2012-01-01

    Persistent organic pollutants (POPs) have been frequently measured throughout the Southern Ocean food web for which little information is available to assess the potential risks of POP exposure. The current study evaluated the toxicological sensitivity of a key Southern Ocean species, Antarctic krill, to aqueous exposure of p,p'-dichlorodiphenyl dichloroethylene (p,p'-DDE). Behavioural endpoints were used as indicators of sublethal toxicity. Immediate behavioural responses (partial immobility and tail flicking) most likely reflect neurotoxicity, while the p,p'-DDE body residue causing a median level of sublethal toxicity in Antarctic krill following 96h exposure (IEC50(sublethal toxicity)=3.9±0.21mmol/kg lipid weight) is comparable to those known to cause sublethal narcosis in temperate aquatic species. Critical body residues (CBRs) were more reproducible across tests than effective seawater concentrations. These findings support the concept of the CBR approach, that effective tissue residues are comparable across species and geographical ranges despite differences in environmental factors. Copyright © 2011 Elsevier Inc. All rights reserved.

  6. Impacts of freshwater changes on Antarctic sea ice in an eddy-permitting sea-ice-ocean model

    NASA Astrophysics Data System (ADS)

    Haid, Verena; Iovino, Doroteaciro; Masina, Simona

    2017-06-01

    In a warming climate, satellite data indicate that the sea ice extent around Antarctica has increased over the last decades. One of the suggested explanations is the stabilizing effect of increased mass loss of the Antarctic ice sheet. Here, we investigate the sea ice response to changes in both the amount and the spatial distribution of freshwater input to the ocean by comparing a set of numerical sensitivity simulations with additional supply of water at the Antarctic ocean surface. We analyze the short-term response of the sea ice cover and the on-shelf water column to variations in the amount and distribution of the prescribed surface freshwater flux.Our results confirm that enhancing the freshwater input can increase the sea ice extent. Our experiments show a negative development of the sea ice extent only for extreme freshwater additions. We find that the spatial distribution of freshwater is of great influence on sea ice concentration and thickness as it affects sea ice dynamics and thermodynamics. For strong regional contrasts in the freshwater addition the dynamic response dominates the local change in sea ice, which generally opposes the thermodynamic response. Furthermore, we find that additional coastal runoff generally leads to fresher and warmer dense shelf waters.

  7. Dominant covarying climate signals in the Southern Ocean and Antarctic Sea Ice influence during last three decades

    NASA Astrophysics Data System (ADS)

    Cerrone, Dario; Fusco, Giannetta; Simmonds, Ian; Aulicino, Giuseppe; Budillon, Giorgio

    2017-04-01

    A composite dataset (comprising geopotential height, sea surface temperature, zonal and meridional surface winds, precipitation, cloud cover, surface air temperature, latent plus sensible heat fluxes , and sea ice concentration) has been investigated with the aim of revealing the dominant timescales of variability from 1982 to 2013. Three covarying climate signals associated with variations in the sea ice distribution around Antarctica have been detected through the application of the Multiple-Taper Method with Singular Value Decomposition (MTM-SVD). Features of the established patterns of variation over the Southern Hemisphere (SH) extratropics have been identified in each of these three climate signals in the form of coupled or individual oscillations. The climate patterns considered here are the Southern Annular Mode (SAM), the Pacific-South America (PSA) teleconnection, the Semi-Annual Oscillation (SAO) and Zonal Wavenumber-3 (ZW3) mode. It is shown that most of the sea ice temporal variance is concentrated at the quasi-triennial scale resulting from the constructive superposition of the PSA and ZW3 patterns. In addition the combination of the SAM and SAO patterns is found to promote the interannual sea ice variations underlying a general change in the Southern Ocean atmospheric and oceanic circulations. These two modes of variability are also found consistent with the occurrence of the SAM+/PSA- or SAM-/PSA+ combinations, which could have favored the cooling of the sub-Antarctic and important changes in the Antarctic sea ice distribution since 2000.

  8. Glacial diatom-bound 15N/14N records from the Antarctic Zone of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Robinson, R. S.; Sigman, D. M.

    2005-12-01

    The potential role of Southern Ocean surface conditions in glacial/interglacial atmospheric CO{_2} changes was noted several decades ago, but a consensus view of their importance has yet to be reached. The overturning and deep ocean ventilation that occurs in the currently macronutrient-rich Antarctic Zone releases deeply sequestered CO{_2} to the atmosphere, making it of particular interest with regard to glacial/interglacial carbon cycle changes. Here we present three downcore records of diatom-bound δ15N as a proxy for nutrient consumption in the Antarctic surface, one each from the Atlantic, Indian, and Pacific sectors. In the Indian sector (MD84-552), glacial diatom-bound δ15N is slightly (1-2 ‰) elevated relative to the Holocene. In the Atlantic (RC13-259) and Pacific (NP9802-5GC) sectors, diatom-bound δ15N is significantly elevated (4-10 ‰) during the coldest episodes of the glacial periods (MIS 2 and 4) relative to the Holocene and the warmer stages of the glacial. At face value, these data suggest significant yet spatially variable degrees of enhanced nutrient consumption during the last ice age. As opal accumulation and other indicators suggest that export production was reduced at each of these sites during glacial times, these data appear to support previous suggestions of reduced macronutrient supply to the glacial Antarctic surface, through stratification of the upper water column. The large zonal differences in the degree and of δ{15}N change may be related to surface ocean hydrography. Both the Atlantic and Pacific core locations lie within the seasonal sea ice zone, whereas the Indian Sector core is within the modern permanently open ocean zone. While the seasonal ice zone provides an ideal location for extensive drawdown of nutrients (e.g., stable surface layer, micronutrients from summertime sea ice melt), these δ15N changes cannot yet be attributed uniquely to nutrient consumption changes, especially because of their large amplitude

  9. The role of ocean gateways in the dynamics and sensitivity to wind stress of the early Antarctic Circumpolar Current

    NASA Astrophysics Data System (ADS)

    Munday, D. R.; Johnson, H. L.; Marshall, D. P.

    2015-03-01

    The date of inception of the Antarctic Circumpolar Current is debated due to uncertainty in the relative opening times of Drake Passage and the Tasman Seaway. Using an idealized eddy-resolving numerical ocean model, we investigate whether both ocean gateways have to be open to allow for a substantial circumpolar current. We find that overlapping continental barriers do not impede a circumpolar transport in excess of 50Sv, as long as a circumpolar path can be traced around the barriers. However, the presence of overlapping barriers does lead to an increased sensitivity of the current's volume transport to changes in wind stress. This change in sensitivity is interpreted in terms of the role of pressure drops across continental barriers and submerged bathymetry in balancing the momentum input by the surface wind stress. Specifically, when the pressure drop across continents is the main balancing sink of momentum, the zonal volume transport is sensitive to changes in wind stress. Changes in zonal volume transport take place via altering the depth-independent part of the circumpolar transport rather than that arising from thermal wind shear. In such a scenario, isopycnals continue to slope steeply across the model Southern Ocean, implying a strong connection between the deep and surface oceans. This may have consequences for the meridional overturning circulation and its sensitivity to wind stress.

  10. 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

  11. Using Seismic Noise Generated by Ocean Waves to Monitor Seasonal and Secular Changes in Antarctic Sea Ice

    NASA Astrophysics Data System (ADS)

    Anthony, R. E.; Aster, R. C.; Thompson, D. W. J.; Reusch, D. B.

    2015-12-01

    The Earth's background seismic noise between ~1-30 seconds period is commonly dominated by microseisms that arise when oceanic wave energy and swell are converted to ground displacement as the waves crash and interact with the continental shelf. Peak power in the microseism bands at high-latitude stations typically coincides with large-scale extratropical cyclonic winter storm activity. However, due to the seasonal formation of sea ice around the continental shelves of polar regions, oceanic waves are impeded from efficiently exciting seismic energy, and annual peak microseism power thus occurs prior to the midwinter storm peak. We utilize recently collected seismic data from across the continent to show that power in three distinct microseism bands is found to be strongly anti-correlated with sea ice extent, with the shorter period signals being exceptionally sensitive to local conditions. Particular focus is given to the Antarctic Peninsula, the strongest source of microseism energy on the continent, where we note a significant increase in primary microseism power attributable to near coastal sources from 1993-2012. This increase correlates with regional sea ice loss driven by large-scale wind changes associated with strengthening of the Southern Annular Mode. Additionally, we use microseism analysis to explore changes in sea ice strength and extent relative to wave state and storminess in the Southern Oceans. Investigation of microseism seasonality, power, and decadal-scale trends in the Antarctic shows promise as a spatially integrated tool for monitoring and interpreting such sea ice strength and extent metrics through time.

  12. 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.

  13. 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.

  14. Transport of nutrients and contaminants from ocean to island by emperor penguins from Amanda Bay, East Antarctic.

    PubMed

    Huang, Tao; Sun, Liguang; Wang, Yuhong; Chu, Zhuding; Qin, Xianyan; Yang, Lianjiao

    2014-01-15

    Penguins play important roles in the biogeochemical cycle between Antarctic Ocean and land ecosystems. The roles of emperor penguin Aptenodytes forsteri, however, are usually ignored because emperor penguin breeds in fast sea ice. In this study, we collected two sediment profiles (EPI and PI) from the N island near a large emperor penguin colony at Amanda Bay, East Antarctic and performed stable isotope and element analyses. The organic C/N ratios and carbon and nitrogen isotopes suggested an autochthonous source of organic materials for the sediments of EPI (C/N = 10.21 ± 0.28, n = 17; δ(13)C = -13.48 ± 0.50‰, δ(15)N = 8.35 ± 0.55‰, n = 4) and an allochthonous source of marine-derived organic materials for the sediments of PI (C/N = 6.15 ± 0.08, δ(13)C = -26.85 ± 0.11‰, δ(15)N = 21.21 ± 2.02‰, n = 20). The concentrations of total phosphorus (TP), selenium (Se), mercury (Hg) and zinc (Zn) in PI sediments were much higher than those in EPI, the concentration of copper (Cu) in PI was a little lower, and the concentration of element lead (Pb) showed no difference. As measured by the geoaccumulation indexes, Zn, TP, Hg and Se were from moderately to very strongly enriched in PI, relative to local mother rock, due to the guano input from juvenile emperor penguins. Because of its high trophic level and transfer efficiency, emperor penguin can transport a large amount of nutrients and contaminants from ocean to land even with a relatively small population, and its roles in the biogeochemical cycle between ocean and terrestrial environment should not be ignored. © 2013.

  15. COMMENTS ON "MEASUREMENTS OF ATMOSPHERIC MERCURY SPECIES AT A COASTAL SITE IN THE ANTARCTIC AND OVER THE SOUTH ATLANTIC OCEAN DURING POLAR SUMMER"

    EPA Science Inventory

    Attached comment submitted to Environmental Science and Technology entitled, Comments on "Measurements of Atmospheric Mercury Species at a Costal Site in the Antarctic and over the South Atlantic Ocean during Polar Summer" by Temme et al. Environmental Science and Technology 37 (...

  16. COMMENTS ON "MEASUREMENTS OF ATMOSPHERIC MERCURY SPECIES AT A COASTAL SITE IN THE ANTARCTIC AND OVER THE SOUTH ATLANTIC OCEAN DURING POLAR SUMMER"

    EPA Science Inventory

    Attached comment submitted to Environmental Science and Technology entitled, Comments on "Measurements of Atmospheric Mercury Species at a Costal Site in the Antarctic and over the South Atlantic Ocean during Polar Summer" by Temme et al. Environmental Science and Technology 37 (...

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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

  2. Investigation into the impact of storms on sustaining summer primary productivity in the Sub-Antarctic Ocean

    NASA Astrophysics Data System (ADS)

    Nicholson, Sarah-Anne; Lévy, Marina; Llort, Joan; Swart, Sebastiaan; Monteiro, Pedro M. S.

    2016-09-01

    In the Sub-Antarctic Ocean elevated phytoplankton biomass persists through summer at a time when productivity is expected to be low due to iron limitation. Biological iron recycling has been shown to support summer biomass. In addition, we investigate an iron supply mechanism previously unaccounted for in iron budget studies. Using a 1-D biogeochemical model, we show how storm-driven mixing provides relief from phytoplankton iron limitation through the entrainment of iron beneath the productive layer. This effect is significant when a mixing transition layer of strong diffusivities (kz > 10-4 m2 s-1) is present beneath the surface-mixing layer. Such subsurface mixing has been shown to arise from interactions between turbulent ocean dynamics and storm-driven inertial motions. The addition of intraseasonal mixing yielded increases of up to 60% in summer primary production. These results stress the need to acquire observations of subsurface mixing and to develop the appropriate parameterizations of such phenomena for ocean-biogeochemical models.

  3. The changing climate of the Southern Ocean: influence of the meandering pathway of the Antarctic Circumpolar Current (Fridtjof Nansen Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Talley, Lynne

    2017-04-01

    The Southern Ocean is a region of potentially dramatic climate change impacts, due to the large amount of freshwater tied up in the Antarctic ice sheet and the potential for sea level rise accompanying loss of that ice. It is the region of the largest deep ocean heat gains of the global ocean, likely due to changes in production of dense waters in coastal regions of Antarctica. It is also a region of climate change surprises, where sea ice cover is slightly advancing rather than retreating, surface waters are not necessarily warming, and carbon may be outgassing from the deep ocean at greater rates than hitherto expected. These effects can largely be attributed to strengthened winds, which enhance upwelling of deep waters to the sea surface. Southeastward and upward spiraling of northern deep waters into the Southern Ocean and through the Antarctic Circumpolar Current (ACC) brings the cool, but not freezing, deep waters to the Antarctic margin in the regions where the overlying ice shelves are losing the most mass. This spiraling pathway is not uniformly southeastward nor is upwelling along the pathway uniform: the location of the fronts where carbon-rich upwelled water reaches the surface is strongly steered by topography and by the subpolar Ross and Weddell gyres, while upwelling itself is enhanced by strongly localized eddy fields where the ACC crosses major topography. The pattern of topographically-steered meanders of the ACC dictates the regions where winter sea ice is expanding versus contracting in response to stronger winds.

  4. Halogen and trace element geochemistry in Mid-Ocean Ridge basalts from the Australian-Antarctic Ridge (AAR)

    NASA Astrophysics Data System (ADS)

    Yang, Y. S.; Seo, J. H.; Park, S. H.; Kim, T.

    2015-12-01

    Australian-Antarctic Ridge (AAR) is an extension of easternmost SE Indian Mid-Ocean Ridge (MOR).We collected volcanic glasses from the "in-axis" of the KR1 and KR2 MOR, and the overlapping zones of the KR1 MOR and the nearby seamounts ("KR1 mixing"). We determined trace and halogen elements in the glasses. Halogen concentrations and its ratios in the glasses are important to understand the mantle metasomatism and volatile recycling. 52 of the collected glasses are "primitive" (higher than 6 wt% MgO), while 3 of them have rather "evolved" composition (MgO wt% of 1.72, 2.95 and 4.15). K2O concentrations and Th/Sc ratios in the glasses show a negative correlation with its MgO concentration. Incompatible element ratios such as La/Sm are rather immobile during a magma differentiation so the ratios are important to understand mantle composition (Hofmann et al. 2003). La/Sm ratios in the glasses are 0.95 ~ 3.28 suggesting that the AAR basalts can be classified into T-MORB and E-MORB (Schilling et al., 1983). La/Sm ratios are well-correlated with incompatible elements such as U, Ba, Nb, and negatively correlated with compatible elements such as Sc, Eu2+, Mg. The AAR glasses contain detectable halogen elements. The "KR1 mixing" glasses in halogen elements are more abundant than "in-axis" the glasses. Cl is the least variable element compared to the other halogens such as Br and I in the AAR. The "KR1 mixing" glasses have the largest variations of Br/Cl ratios compared to the "in-axis" glasses. The Cl/Br and Th/Sc ratios in the "in-axis" glasses and in the "KR1 mixing" glasses show positive and negative correlations, respectively. The Br-rich glasses in the "KR1 mixing" zone might be explained by a recycled Br-rich oceanic slab of paleo-subduction or by a hydrothermal alteration in the AAR. I composition in the glasses does not show a correlation other trace elements. The K/Cl and K/Ti ratios in the AAR glasses are similar to the basalts from the Galapagos Spreading Center

  5. Could the acid-base status of Antarctic sea urchins indicate a better-than-expected resilience to near-future ocean acidification?

    PubMed

    Collard, Marie; De Ridder, Chantal; David, Bruno; Dehairs, Frank; Dubois, Philippe

    2015-02-01

    Increasing atmospheric carbon dioxide concentration alters the chemistry of the oceans towards more acidic conditions. Polar oceans are particularly affected due to their low temperature, low carbonate content and mixing patterns, for instance upwellings. Calcifying organisms are expected to be highly impacted by the decrease in the oceans' pH and carbonate ions concentration. In particular, sea urchins, members of the phylum Echinodermata, are hypothesized to be at risk due to their high-magnesium calcite skeleton. However, tolerance to ocean acidification in metazoans is first linked to acid-base regulation capacities of the extracellular fluids. No information on this is available to date for Antarctic echinoderms and inference from temperate and tropical studies needs support. In this study, we investigated the acid-base status of 9 species of sea urchins (3 cidaroids, 2 regular euechinoids and 4 irregular echinoids). It appears that Antarctic regular euechinoids seem equipped with similar acid-base regulation systems as tropical and temperate regular euechinoids but could rely on more passive ion transfer systems, minimizing energy requirements. Cidaroids have an acid-base status similar to that of tropical cidaroids. Therefore Antarctic cidaroids will most probably not be affected by decreasing seawater pH, the pH drop linked to ocean acidification being negligible in comparison of the naturally low pH of the coelomic fluid. Irregular echinoids might not suffer from reduced seawater pH if acidosis of the coelomic fluid pH does not occur but more data on their acid-base regulation are needed. Combining these results with the resilience of Antarctic sea urchin larvae strongly suggests that these organisms might not be the expected victims of ocean acidification. However, data on the impact of other global stressors such as temperature and of the combination of the different stressors needs to be acquired to assess the sensitivity of these organisms to global

  6. Wind, Sea Ice, Inertial Oscillations and Upper Ocean Mixing in Marguerite Bay, Western Antarctic Peninsula: Observations and Modeling

    DTIC Science & Technology

    2006-09-01

    Antarctic krill , Euphausia superba . American Zoologist 31, 49-63... Antarctic krill Euphausia superba and possible causes for its variability. Marine Ecology Progress Series 123, 45-56. Shirasawa, K. and Ingram, R.G., 1991...Peninsula (wAP) for study due to its unusually high concentration of Antarctic Krill (Euphasia superba ) and krill predators such as penguins, seals and

  7. Paleoproductivity changes off Lützow-Holm Bay in the Antarctic Ocean during the past 650 kyrs

    NASA Astrophysics Data System (ADS)

    Ikehara, M.; Okamoto, S.; Khim, B.; Suganuma, Y.; Katsuki, K.; Itaki, T.; Miura, H.

    2009-12-01

    The Southern Ocean has played a significant role in the global climate system during the geologic past, even in the present-day. For example, it has been proposed that primary production was higher and nutrient utilization in surface waters was more efficient in the glacial Southern Ocean than today, effectively lowering the glacial atmospheric CO2 concentration. In order to resolve the causes and processes of atmospheric CO2 change, important is to understand mechanisms and processes of sub-systems in the Antarctic Cryosphere such as a change of biological productivity, sea surface temperature, surface water frontal system, sea-ice distribution, and East Antarctic ice sheet during the glacial-interglacial climate cycle. We collected a piston core off Lützow-Holm Bay (LHB-3PC, 66.0S, 40.0E, WD 4469 m) in the Indian Sector of the Southern Ocean during the R/V Hakuho-maru cruise KH07-4 Leg 3. Sediments of core LHB-3PC are mainly composed of diatomaceous clay. Age model of core LHB-3PC was established by diatom and radiolarian biostratigraphy and a graphic correlation between grain size variation of magnetic minerals and Marine Isotope Stage (MIS). Based on the lithology and non-destructive measurements, relative higher density and silty clay sediments were deposited during the glacial period. The silty clay layers are characterized by clearly upward fining sequence, and the base of each layer is clearly defined as a sharp boundary over lighter-colored pelagic sediments. These lithologic features indicate that the silty clay layers were deposited as a result of down-slope turbidity transport from the continental margin of Antarctica. Thus, the turbidites were formed during the glacial periods due to glacial advances on the continental shelf edge. Concentrations of total organic carbon (TOC) ranged from 0.1 to 0.4 wt% at core LHB-3PC, except for each turbidite layers. TOC increased at the interglacials. High biogenic opal contents also occurred during the

  8. Ocean acidification decreases the light-use efficiency in an Antarctic diatom under dynamic but not constant light.

    PubMed

    Hoppe, Clara J M; Holtz, Lena-Maria; Trimborn, Scarlett; Rost, Björn

    2015-07-01

    There is increasing evidence that different light intensities strongly modulate the effects of ocean acidification (OA) on marine phytoplankton. The aim of the present study was to investigate interactive effects of OA and dynamic light, mimicking natural mixing regimes. The Antarctic diatom Chaetoceros debilis was grown under two pCO2 (390 and 1000 μatm) and light conditions (constant and dynamic), the latter yielding the same integrated irradiance over the day. To characterize interactive effects between treatments, growth, elemental composition, primary production and photophysiology were investigated. Dynamic light reduced growth and strongly altered the effects of OA on primary production, being unaffected by elevated pCO2 under constant light, yet significantly reduced under dynamic light. Interactive effects between OA and light were also observed for Chl production and particulate organic carbon quotas. Response patterns can be explained by changes in the cellular energetic balance. While the energy transfer efficiency from photochemistry to biomass production (Φe,C ) was not affected by OA under constant light, it was drastically reduced under dynamic light. Contrasting responses under different light conditions need to be considered when making predictions regarding a more stratified and acidified future ocean. © 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.

  9. Enzyme-level interconversion of nitrate and nitrite in the fall mixed layer of the Antarctic Ocean

    NASA Astrophysics Data System (ADS)

    Kemeny, P. C.; Weigand, M. A.; Zhang, R.; Carter, B. R.; Karsh, K. L.; Fawcett, S. E.; Sigman, D. M.

    2016-07-01

    In the Southern Ocean, the nitrogen (N) isotopes of organic matter and the N and oxygen (O) isotopes of nitrate (NO3-) have been used to investigate NO3- assimilation and N cycling in the summertime period of phytoplankton growth, both today and in the past. However, recent studies indicate the significance of processes in other seasons for producing the annual cycle of N isotope changes. This study explores the impact of fall conditions on the 15N/14N (δ15N) and 18O/16O (δ18O) of NO3- and nitrite (NO2-) in the Pacific Antarctic Zone using depth profiles from late summer/fall of 2014. In the mixed layer, the δ15N and δ18O of NO3- + NO2- increase roughly equally, as expected for NO3- assimilation; however, the δ15N of NO3--only (measured after NO2- removal) increases more than does NO3--only δ18O. Differencing indicates that NO2- has an extremely low δ15N, often < -70‰ versus air. These observations are consistent with the expression of an equilibrium N isotope effect between NO3- and NO2-, likely due to enzymatic NO3--NO2- interconversion. Specifically, we propose reversibility of the nitrite oxidoreductase (NXR) enzyme of nitrite oxidizers that, having been entrained from the subsurface during late summer mixed layer deepening, are inhibited by light. Our interpretation suggests a role for NO3--NO2- interconversion where nitrifiers are transported into environments that discourage NO2- oxidation. This may apply to surface regions with upwelling, such as the summertime Antarctic. It may also apply to oxygen-deficient zones, where NXR-catalyzed interconversion may explain previously reported evidence of NO2- oxidation.

  10. 77 FR 60677 - Proposed Information Collection; Comment Request; Antarctic Marine Living Resources Conservation...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-10-04

    ... National Oceanic and Atmospheric Administration Proposed Information Collection; Comment Request; Antarctic... Antarctic Marine Living Resources (Convention) established the Commission for the Conservation of Antarctic... Convention and a member of CCAMLR and its Scientific Committee. The Antarctic Marine Living...

  11. Dense Outflows and Deep Convection in the Antarctic Zone of the Southern Ocean

    DTIC Science & Technology

    2009-09-30

    project, and from the eastern Weddell Sea as part of MaudNESS ( Maud Rise Nonlinear Equation of State Study). Data include seawater temperature...ocean of the Maud Rise region of the Weddell Sea were presented at the July 2009 IAPSO (International Association for Physical Sciences of the...contributes to the AABW. Second, it has carried out preliminary analyses of data that detail upper ocean conditions in the Maud Rise region of the eastern

  12. Marine bacteria in deep Arctic and Antarctic ice cores: a proxy for evolution in oceans over 300 million generations

    NASA Astrophysics Data System (ADS)

    Price, P. B.; Bay, R. C.

    2012-06-01

    Using fluorescence spectrometry to map autofluorescence of chlorophyll (Chl) and tryptophan (Trp) versus depth in polar ice cores in the US National Ice Core Laboratory, we found that the Chl and Trp concentrations often showed an annual modulation of up to 25%, with peaks at depths corresponding to local summers. Using epifluorescence microscopy (EFM) and flow cytometry (FCM) triggered on 670 nm fluorescence (red) to study microbes from unstained melts of the polar ice, we inferred that picocyanobacteria may have been responsible for the red fluorescence in the cores. Micron-size bacteria in all ice melts from 2 Arctic and 6 Antarctic sites showed FCM patterns of scattering and of red vs. orange fluorescence (interpreted as due to Chl vs. phycoerythrin (PE)) that bore similarities to patterns of cultures of unstained picocyanobacteria Prochlorococcus and Synechococcus. Concentrations in ice from all sites were low but measurable at ~1 to ~103 cells cm-3. Calibrations showed that FCM patterns of mineral grains and volcanic ash could be distinguished from microbes with high efficiency by triggering on scattering instead of by red fluorescence. Average Chl and PE autofluorescence intensities showed no decrease per cell with time during up to 150 000 yr of storage in glacial ice. Taking into account the annual modulation of ~25% and seasonal changes of ocean temperatures and winds, we suggest that picocyanobacteria are wind-transported year-round from warmer ocean waters onto polar ice. Ice cores offer the opportunity to study evolution of marine microbes over ~300 million generations by analyzing their genomes vs. depth in glacial ice over the last 700 000 yr as frozen proxies for changes in their genomes in oceans.

  13. Marine bacteria in deep Arctic and Antarctic ice cores: a proxy for evolution in oceans over 300 million generations

    NASA Astrophysics Data System (ADS)

    Price, P. B.; Bay, R. C.

    2012-10-01

    Using fluorescence spectrometry to map autofluorescence of chlorophyll (Chl) and tryptophan (Trp) versus depth in polar ice cores in the US National Ice Core Laboratory, we found that the Chl and Trp concentrations often showed an annual modulation of up to 25%, with peaks at depths corresponding to local summers. Using epifluorescence microscopy (EFM) and flow cytometry (FCM) triggered on red fluorescence at 670 nm to study microbes from unstained melts of the polar ice, we inferred that picocyanobacteria may have been responsible for the red fluorescence in the cores. Micron-size bacteria in all ice melts from Arctic and Antarctic sites showed FCM patterns of scattering and of red vs. orange fluorescence (interpreted as due to Chl vs. phycoerythrin (PE)) that bore similarities to patterns of cultures of unstained picocyanobacteria Prochlorococcus and Synechococcus. Concentrations in ice from all sites were low, but measurable at ~ 1 to ~ 103 cells cm-3. Calibrations showed that FCM patterns of mineral grains and volcanic ash could be distinguished from microbes with high efficiency by triggering on scattering instead of by red fluorescence. Average Chl and PE autofluorescence intensities showed no decrease per cell with time during up to 150 000 yr of storage in glacial ice. Taking into account the annual modulation of ~ 25% and seasonal changes of ocean temperatures and winds, we suggest that picocyanobacteria are wind-transported year-round from warmer ocean waters onto polar ice. Ice cores offer the opportunity to study evolution of marine microbes over ~ 300 million generations by analysing their genomes vs. depth in glacial ice over the last 700 000 yr as frozen proxies for changes in their genomes in oceans.

  14. Effects of ocean warming and acidification on fertilization in the Antarctic echinoid Sterechinus neumayeri across a range of sperm concentrations.

    PubMed

    Ho, M A; Price, C; King, C K; Virtue, P; Byrne, M

    2013-09-01

    The gametes of marine invertebrates are being spawned into an ocean that is simultaneously warming and decreasing in pH. Predicting the potential for interactive effects of these stressors on fertilization is difficult, especially for stenothermal polar invertebrates adapted to fertilization in cold, viscous water and, when decreased sperm availability may be an additional stressor. The impact of increased temperature (2-4 °C above ambient) and decreased pH (0.2-0.4 pH units below ambient) on fertilization in the Antarctic echinoid Sterechinus neumayeri across a range of sperm concentrations was investigated in cross-factorial experiments in context with near future ocean change projections. The high temperature treatment (+4 °C) was also used to assess thermal tolerance. Gametes from multiple males and females in replicate experiments were used to reflect the multiple spawner scenario in nature. For fertilization at low sperm density we tested three hypotheses, 1) increased temperature enhances fertilization success, 2) low pH reduces fertilization and, 3) due to the cold stenothermal physiology of S. neumayeri, temperature would be the more significant stressor. Temperature and sperm levels had a significant effect on fertilization, but decreased pH did not affect fertilization. Warming enhanced fertilization at the lowest sperm concentration tested likely through stimulation of sperm motility and reduced water viscosity. Our results indicate that fertilization in S. neumayeri, even at low sperm levels potentially found in nature, is resilient to near-future ocean warming and acidification. Copyright © 2013 Elsevier Ltd. All rights reserved.

  15. Bimodal pattern of seismicity detected at the ocean margin of an Antarctic ice shelf

    NASA Astrophysics Data System (ADS)

    Lombardi, Denis; Benoit, Lionel; Camelbeeck, Thierry; Martin, Olivier; Meynard, Christophe; Thom, Christian

    2016-08-01

    In Antarctica, locally grounded ice, such as ice rises bordering floating ice shelves, plays a major role in the ice mass balance as it stabilizes the ice sheet flow from the hinterland. When in direct contact with the ocean, the ice rise buttressing effect may be altered in response of changing ocean forcing. To investigate this vulnerable zone, four sites near the boundary of an ice shelf with an ice rise promontory in Dronning Maud Land, East-Antarctica were monitored for a month in early 2014 with new instruments that include both seismic and GPS sensors. Our study indicated that this transition zone experiences periodic seismic activity resulting from surface crevassing during oceanic tide-induced flexure of the ice shelf. The most significant finding is the observation of apparent fortnightly tide-modulated low-frequency, long-duration seismic events at the seaward front of the ice rise promontory. A basal origin of these events is postulated with the ocean water surge at each new spring tide triggering basal crevassing or basal slip on a local bedrock asperity. Detection and monitoring of such seismicity may help identifying ice rise zones vulnerable to intensified ocean forcing.

  16. Measurements of atmospheric mercury species at a coastal site in the Antarctic and over the south Atlantic Ocean during polar summer.

    PubMed

    Temme, Christian; Einax, Jürgen W; Ebinghaus, Ralf; Schroeder, William H

    2003-01-01

    Mercury and many of its compounds behave exceptionally in the environment because of their volatility, capability for methylation, and subsequent biomagnification in contrast with most of the other heavy metals. Long-range atmospheric transport of elemental mercury, its transformation to more toxic methylmercury compounds, the ability of some to undergo photochemical reactions, and their bioaccumulation in the aquatic food chain have made it a subject of global research activities, even in polar regions. The first continuous high-time-resolution measurements of total gaseous mercury in the Antarctic covering a 12-month period were carried out at the German Antarctic research station Neumayer (70 degrees 39' S, 8 degrees 15' W) between January 2000 and February 2001. We recently reported that mercury depletion events (MDEs) occur in the Antarctic after polar sunrise, as was previously shown for Arctic sites. These events (MDEs) end suddenly during Antarctic summer. A possible explanation of this phenomenon is presented in this paper, showing that air masses originating from the sea-ice surface were a necessary prerequisite for the observations of depletion of atmospheric mercury at polar spring. Our extensive measurements at Neumayer of atmospheric mercury species during December 2000-February 2001 show that fast oxidation of gaseous elemental mercury leads to variable Hg0 concentrations during Antarctic summer, accompanied by elevated concentrations, up to more than 300 pg/m3, of reactive gaseous mercury. For the first time in the Southern Hemisphere, atmospheric mercury species measurements were also performed onboard of a research vessel, indicating the existence of homogeneous background concentrations over the south Atlantic Ocean. These new findings contain evidence for an enhanced oxidizing potential of the Antarctic atmosphere over the continent that needs to be considered for the interpretation of dynamic transformations of mercury during summertime.

  17. Modelled ocean changes at the Plio-Pleistocene transition driven by Antarctic ice advance

    NASA Astrophysics Data System (ADS)

    Hill, Daniel J.; Bolton, Kevin P.; Haywood, Alan M.

    2017-03-01

    The Earth underwent a major transition from the warm climates of the Pliocene to the Pleistocene ice ages between 3.2 and 2.6 million years ago. The intensification of Northern Hemisphere Glaciation is the most obvious result of the Plio-Pleistocene transition. However, recent data show that the ocean also underwent a significant change, with the convergence of deep water mass properties in the North Pacific and North Atlantic Ocean. Here we show that the lack of coastal ice in the Pacific sector of Antarctica leads to major reductions in Pacific Ocean overturning and the loss of the modern North Pacific Deep Water (NPDW) mass in climate models of the warmest periods of the Pliocene. These results potentially explain the convergence of global deep water mass properties at the Plio-Pleistocene transition, as Circumpolar Deep Water (CDW) became the common source.

  18. Modelled ocean changes at the Plio-Pleistocene transition driven by Antarctic ice advance

    PubMed Central

    Hill, Daniel J.; Bolton, Kevin P.; Haywood, Alan M.

    2017-01-01

    The Earth underwent a major transition from the warm climates of the Pliocene to the Pleistocene ice ages between 3.2 and 2.6 million years ago. The intensification of Northern Hemisphere Glaciation is the most obvious result of the Plio-Pleistocene transition. However, recent data show that the ocean also underwent a significant change, with the convergence of deep water mass properties in the North Pacific and North Atlantic Ocean. Here we show that the lack of coastal ice in the Pacific sector of Antarctica leads to major reductions in Pacific Ocean overturning and the loss of the modern North Pacific Deep Water (NPDW) mass in climate models of the warmest periods of the Pliocene. These results potentially explain the convergence of global deep water mass properties at the Plio-Pleistocene transition, as Circumpolar Deep Water (CDW) became the common source. PMID:28252023

  19. Modelled ocean changes at the Plio-Pleistocene transition driven by Antarctic ice advance.

    PubMed

    Hill, Daniel J; Bolton, Kevin P; Haywood, Alan M

    2017-03-02

    The Earth underwent a major transition from the warm climates of the Pliocene to the Pleistocene ice ages between 3.2 and 2.6 million years ago. The intensification of Northern Hemisphere Glaciation is the most obvious result of the Plio-Pleistocene transition. However, recent data show that the ocean also underwent a significant change, with the convergence of deep water mass properties in the North Pacific and North Atlantic Ocean. Here we show that the lack of coastal ice in the Pacific sector of Antarctica leads to major reductions in Pacific Ocean overturning and the loss of the modern North Pacific Deep Water (NPDW) mass in climate models of the warmest periods of the Pliocene. These results potentially explain the convergence of global deep water mass properties at the Plio-Pleistocene transition, as Circumpolar Deep Water (CDW) became the common source.

  20. Bathymetric control of warm ocean water access along the East Antarctic Margin

    NASA Astrophysics Data System (ADS)

    Nitsche, F. O.; Porter, D.; Williams, G.; Cougnon, E. A.; Fraser, A. D.; Correia, R.; Guerrero, R.

    2017-09-01

    Observed thinning of the Totten Glacier in East Antarctica has cast doubt upon the stability of the East Antarctic Ice Sheet. Recent oceanographic observations at the front of the Totten Ice Shelf have confirmed the presence of modified Circumpolar Deep Water (mCDW), which likely promotes enhanced melting. Details of how this water accesses the shelf remain uncertain. Here we present new bathymetry and autumnal oceanographic data from the outer continental shelf, north of the Totten Glacier, that show up to 0.7°C mCDW in a >100 km wide and >500 m deep depression within the shelf break. In other parts of East Antarctica, a shelf break bathymetry shallower than 400 m prevents these warmer waters from entering the shelf environment. Our observations demonstrate that detailed knowledge of the bathymetry is critical to correctly model the across-shelf exchange of warm water to the various glaciers/ice shelves of Antarctica for future sea level prediction.

  1. Important role for ocean warming and increased ice-shelf melt in Antarctic sea-ice expansion

    NASA Astrophysics Data System (ADS)

    Bintanja, R.; Oldenborgh, G. V.; Drijhout, S.; Wouters, B.; Katsman, C. A.

    2013-12-01

    Changes in sea ice significantly modulate climate change because of its high reflective and strong insulating nature. In contrast to Arctic sea ice, sea ice surrounding Antarctica has expanded, with record extent in 2010. This ice expansion has previously been attributed to dynamical atmospheric changes that induce atmospheric cooling. Here we show that accelerated basal melting of Antarctic ice shelves is likely to have contributed significantly to sea-ice expansion. Specifically, we present observations indicating that melt water from Antarctica's ice shelves accumulates in a cool and fresh surface layer that shields the surface ocean from the warmer deeper waters that are melting the ice shelves. Simulating these processes in a coupled climate model we find that cool and fresh surface water from ice-shelf melt indeed leads to expanding sea ice in austral autumn and winter. This powerful negative feedback counteracts Southern Hemispheric atmospheric warming. Although changes in atmospheric dynamics most likely govern regional sea-ice trends, our analyses indicate that the overall sea-ice trend is dominated by increased ice-shelf melt. We suggest that cool sea surface temperatures around Antarctica could offset projected snowfall increases in Antarctica, with implications for estimates of future sea-level rise.

  2. Important role for ocean warming and increased ice-shelf melt in Antarctic sea-ice expansion

    NASA Astrophysics Data System (ADS)

    Bintanja, R.; van Oldenborgh, G. J.; Drijfhout, S. S.; Wouters, B.; Katsman, C. A.

    2013-05-01

    Changes in sea ice significantly modulate climate change because of its high reflective and strong insulating nature. In contrast to Arctic sea ice, sea ice surrounding Antarctica has expanded, with record extent in 2010. This ice expansion has previously been attributed to dynamical atmospheric changes that induce atmospheric cooling. Here we show that accelerated basal melting of Antarctic ice shelves is likely to have contributed significantly to sea-ice expansion. Specifically, we present observations indicating that melt water from Antarctica's ice shelves accumulates in a cool and fresh surface layer that shields the surface ocean from the warmer deeper waters that are melting the ice shelves. Simulating these processes in a coupled climate model we find that cool and fresh surface water from ice-shelf melt indeed leads to expanding sea ice in austral autumn and winter. This powerful negative feedback counteracts Southern Hemispheric atmospheric warming. Although changes in atmospheric dynamics most likely govern regional sea-ice trends, our analyses indicate that the overall sea-ice trend is dominated by increased ice-shelf melt. We suggest that cool sea surface temperatures around Antarctica could offset projected snowfall increases in Antarctica, with implications for estimates of future sea-level rise.

  3. 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.

  4. The ice thickness distribution across the Atlantic sector of the Antarctic Ocean in midwinter

    NASA Astrophysics Data System (ADS)

    Wadhams, Peter; Lange, Manfred A.; Ackley, Stephen F.

    1987-12-01

    During the first leg of the Winter Weddell Sea Project (Antarktis V/2) cruise of F.S. Polarstern the entire width of the Antarctic sea ice zone was traversed in the vicinity of 0° longitude in the period July 18 to September 10, 1986. Ice thicknesses were measured by direct drilling and by helicopter profiling using an Exstar 100-MHz impulse radar system. In addition, aerial photography of the ice cover was done from 100- to 2000-m altitude using a 70-mm aerial camera mounted in the helicopter. The results of the point measurements (drilling) are reported in this paper together with an indication of how the radar and photography data will be used to extend them so as to yield area-averaged ice thickness distributions. It was found that the main ice type across the entire width of the ice cover was consolidated pancake ice occurring in vast floes; this formed out of a 250-km-wide band at the advancing ice edge which comprised a concentrated field of individual pancakes in a matrix of frazil ice. Preferred thicknesses of undeformed floes were 40-60 cm of ice covered with 5-15 cm of snow. The individual pancakes attained almost all of this thickness before consolidation; subsequent congelation growth was slow, estimated at 0.4 cm d-1. The floes contained much small-scale roughness on the upper and lower surfaces due to rafting of pancakes at the time of consolidation, but pressure ridging was modest except in the far south. A few very thick (8-11 m) multiyear floes were observed embedded in the pack at latitudes beyond 66° S.

  5. Linear sea-level response to abrupt ocean warming of major West Antarctic ice basin

    NASA Astrophysics Data System (ADS)

    Mengel, M.; Feldmann, J.; Levermann, A.

    2016-01-01

    Antarctica's contribution to global sea-level rise has recently been increasing. Whether its ice discharge will become unstable and decouple from anthropogenic forcing or increase linearly with the warming of the surrounding ocean is of fundamental importance. Under unabated greenhouse-gas emissions, ocean models indicate an abrupt intrusion of warm circumpolar deep water into the cavity below West Antarctica's Filchner-Ronne ice shelf within the next two centuries. The ice basin's retrograde bed slope would allow for an unstable ice-sheet retreat, but the buttressing of the large ice shelf and the narrow glacier troughs tend to inhibit such instability. It is unclear whether future ice loss will be dominated by ice instability or anthropogenic forcing. Here we show in regional and continental-scale ice-sheet simulations, which are capable of resolving unstable grounding-line retreat, that the sea-level response of the Filchner-Ronne ice basin is not dominated by ice instability and follows the strength of the forcing quasi-linearly. We find that the ice loss reduces after each pulse of projected warm water intrusion. The long-term sea-level contribution is approximately proportional to the total shelf-ice melt. Although the local instabilities might dominate the ice loss for weak oceanic warming, we find that the upper limit of ice discharge from the region is determined by the forcing and not by the marine ice-sheet instability.

  6. 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.

  7. 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.

  8. 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 .

  9. Ocean Acidification at High Latitudes: Potential Effects on Functioning of the Antarctic Bivalve Laternula elliptica

    PubMed Central

    Cummings, Vonda; Hewitt, Judi; Van Rooyen, Anthony; Currie, Kim; Beard, Samuel; Thrush, Simon; Norkko, Joanna; Barr, Neill; Heath, Philip; Halliday, N. Jane; Sedcole, Richard; Gomez, Antony; McGraw, Christina; Metcalf, Victoria

    2011-01-01

    Ocean acidification is a well recognised threat to marine ecosystems. High latitude regions are predicted to be particularly affected due to cold waters and naturally low carbonate saturation levels. This is of concern for organisms utilising calcium carbonate (CaCO3) to generate shells or skeletons. Studies of potential effects of future levels of pCO2 on high latitude calcifiers are at present limited, and there is little understanding of their potential to acclimate to these changes. We describe a laboratory experiment to compare physiological and metabolic responses of a key benthic bivalve, Laternula elliptica, at pCO2 levels of their natural environment (430 µatm, pH 7.99; based on field measurements) with those predicted for 2100 (735 µatm, pH 7.78) and glacial levels (187 µatm, pH 8.32). Adult L. elliptica basal metabolism (oxygen consumption rates) and heat shock protein HSP70 gene expression levels increased in response both to lowering and elevation of pH. Expression of chitin synthase (CHS), a key enzyme involved in synthesis of bivalve shells, was significantly up-regulated in individuals at pH 7.78, indicating L. elliptica were working harder to calcify in seawater undersaturated in aragonite (ΩAr = 0.71), the CaCO3 polymorph of which their shells are comprised. The different response variables were influenced by pH in differing ways, highlighting the importance of assessing a variety of factors to determine the likely impact of pH change. In combination, the results indicate a negative effect of ocean acidification on whole-organism functioning of L. elliptica over relatively short terms (weeks-months) that may be energetically difficult to maintain over longer time periods. Importantly, however, the observed changes in L. elliptica CHS gene expression provides evidence for biological control over the shell formation process, which may enable some degree of adaptation or acclimation to future ocean acidification scenarios. PMID:21245932

  10. Ocean acidification at high latitudes: potential effects on functioning of the Antarctic bivalve Laternula elliptica.

    PubMed

    Cummings, Vonda; Hewitt, Judi; Van Rooyen, Anthony; Currie, Kim; Beard, Samuel; Thrush, Simon; Norkko, Joanna; Barr, Neill; Heath, Philip; Halliday, N Jane; Sedcole, Richard; Gomez, Antony; McGraw, Christina; Metcalf, Victoria

    2011-01-05

    Ocean acidification is a well recognised threat to marine ecosystems. High latitude regions are predicted to be particularly affected due to cold waters and naturally low carbonate saturation levels. This is of concern for organisms utilising calcium carbonate (CaCO(3)) to generate shells or skeletons. Studies of potential effects of future levels of pCO(2) on high latitude calcifiers are at present limited, and there is little understanding of their potential to acclimate to these changes. We describe a laboratory experiment to compare physiological and metabolic responses of a key benthic bivalve, Laternula elliptica, at pCO(2) levels of their natural environment (430 µatm, pH 7.99; based on field measurements) with those predicted for 2100 (735 µatm, pH 7.78) and glacial levels (187 µatm, pH 8.32). Adult L. elliptica basal metabolism (oxygen consumption rates) and heat shock protein HSP70 gene expression levels increased in response both to lowering and elevation of pH. Expression of chitin synthase (CHS), a key enzyme involved in synthesis of bivalve shells, was significantly up-regulated in individuals at pH 7.78, indicating L. elliptica were working harder to calcify in seawater undersaturated in aragonite (Ω(Ar) = 0.71), the CaCO(3) polymorph of which their shells are comprised. The different response variables were influenced by pH in differing ways, highlighting the importance of assessing a variety of factors to determine the likely impact of pH change. In combination, the results indicate a negative effect of ocean acidification on whole-organism functioning of L. elliptica over relatively short terms (weeks-months) that may be energetically difficult to maintain over longer time periods. Importantly, however, the observed changes in L. elliptica CHS gene expression provides evidence for biological control over the shell formation process, which may enable some degree of adaptation or acclimation to future ocean acidification scenarios.

  11. 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.

  12. Quantitative estimate of Antarctic Intermediate Water contributions from the Drake Passage and the southwest Indian Ocean to the South Atlantic

    NASA Astrophysics Data System (ADS)

    You, Yuzhu

    2002-04-01

    Recently obtained World Ocean Circulation Experiment (WOCE) bottle sections and a pre-WOCE bottle data set are used in a water mass mixing model. The mixing scheme comprises three intermediate water sources: Antarctic Intermediate Water (AAIW) from the northern Drake Passage, a combination source of the Indian Ocean intermediate waters entering from south of Africa, and a transformed end-member of the former two sources. I call them dAAIW, iAAIW, and aAAIW, respectively. The dAAIW originates from the southeast South Pacific, enters the South Atlantic in the northern Drake Passage, and is modified in the Falkland Current loop. The iAAIW is a combination of the Indian Ocean sources including Red Sea Intermediate Water, Indonesian Intermediate Water, and AAIW formed locally in the south central Indian Ocean and transformed dAAIW that has returned following a loop through the Indian Ocean. The aAAIW is a transformed end-member of a mixture of dAAIW and iAAIW located in the eastern tropical South Atlantic, characterized by an oxygen minimum and nutrient maxima. Although aAAIW is not an import source like dAAIW and iAAIW, it spans property fields to extrema as a result of water mass mixing and transformation processes and therefore must be included in the basin-wide water mass mixing scheme. The study is performed on five neutral surfaces that encompass the AAIW layer from 700 to 1200 dbar in the subtropical latitudes with a distance of about 100 dbar between a pair of surfaces. Four conservative variables of potential temperature, salinity, initial phosphate (PO4o), and NO and one conservative dynamical tracer fN2 (where f is the Coriolis frequency and N2 is the squared buoyancy frequency) are used as input information to the mixing model. The model-derived mixing fraction gives a quantitative description of AAIW sources when they are mapped onto neutral surfaces. The contoured pattern of mixing fraction shows water mass spreading paths, thus implying circulation and

  13. 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.

  14. Antarctic Meteorology and Climatology

    NASA Astrophysics Data System (ADS)

    King, J. C.; Turner, J.

    1997-07-01

    This book is a comprehensive survey of the climatology and meteorology of Antarctica. The first section of the book reviews the methods by which we can observe the Antarctic atmosphere and presents a synthesis of climatological measurements. In the second section, the authors consider the processes that maintain the observed climate, from large-scale atmospheric circulation to small-scale processes. The final section reviews our current knowledge of the variability of Antarctic climate and the possible effects of "greenhouse" warming. The authors stress links among the Antarctic atmosphere, other elements of the Antarctic climate system (oceans, sea ice and ice sheets), and the global climate system. This volume will be of greatest interest to meteorologists and climatologists with a specialized interest in Antarctica, but it will also appeal to researchers in Antarctic glaciology, oceanography and biology. Graduates and undergraduates studying physical geography, and the earth, atmospheric and environmental sciences will find much useful background material in the book.

  15. Ocean acidification state in western Antarctic surface waters: drivers and interannual variability

    NASA Astrophysics Data System (ADS)

    Mattsdotter Björk, M.; Fransson, A.; Chierici, M.

    2013-05-01

    Each December during four years from 2006 to 2010, the surface water carbonate system was measured and investigated in the Amundsen Sea and Ross Sea, western Antarctica as part of the Oden Southern Ocean expeditions (OSO). The I/B Oden started in Punta Arenas in Chile and sailed southwest, passing through different regimes such as, the marginal/seasonal ice zone, fronts, coastal shelves, and polynyas. Discrete surface water was sampled underway for analysis of total alkalinity (AT), total dissolved inorganic carbon (CT) and pH. Two of these parameters were used together with sea-surface temperature (SST), and salinity to obtain a full description of the surface water carbonate system, including pH in situ and calcium carbonate saturation state of aragonite (ΩAr) and calcite (ΩCa). Multivariate analysis was used to investigate interannual variability and the major controls (sea-ice concentration, SST, salinity and chlorophyll a) on the variability in the carbonate system and Ω. This analysis showed that SST and chlorophyll a were the major drivers of the Ω variability in both the Amundsen and Ross seas. In 2007, the sea-ice edge was located further south and the area of the open polynya was relatively small compared to 2010. We found the lowest pH in situ (7.932) and Ω = 1 values in the sea-ice zone and in the coastal Amundsen Sea, nearby marine out flowing glaciers. In 2010, the sea-ice coverage was the largest and the areas of the open polynyas were the largest for the whole period. This year we found the lowest salinity and AT, coinciding with highest chl a. This implies that the highest ΩAr in 2010 was likely an effect of biological CO2 drawdown, which out-competed the dilution of carbonate ion concentration due to large melt water volumes. We predict and discuss future Ω values, using our data and reported rates of oceanic uptake of anthropogenic CO2, suggesting that the Amundsen Sea will become undersaturated with regard to aragonite about 20 yr sooner

  16. 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.

  17. Seasonal and Diel Vocalization Patterns of Antarctic Blue Whale (Balaenoptera musculus intermedia) in the Southern Indian Ocean: A Multi-Year and Multi-Site Study

    PubMed Central

    Leroy, Emmanuelle C.; Samaran, Flore; Bonnel, Julien; Royer, Jean-Yves

    2016-01-01

    Passive acoustic monitoring is an efficient way to provide insights on the ecology of large whales. This approach allows for long-term and species-specific monitoring over large areas. In this study, we examined six years (2010 to 2015) of continuous acoustic recordings at up to seven different locations in the Central and Southern Indian Basin to assess the peak periods of presence, seasonality and migration movements of Antarctic blue whales (Balaenoptera musculus intermedia). An automated method is used to detect the Antarctic blue whale stereotyped call, known as Z-call. Detection results are analyzed in terms of distribution, seasonal presence and diel pattern of emission at each site. Z-calls are detected year-round at each site, except for one located in the equatorial Indian Ocean, and display highly seasonal distribution. This seasonality is stable across years for every site, but varies between sites. Z-calls are mainly detected during autumn and spring at the subantarctic locations, suggesting that these sites are on the Antarctic blue whale migration routes, and mostly during winter at the subtropical sites. In addition to these seasonal trends, there is a significant diel pattern in Z-call emission, with more Z-calls in daytime than in nighttime. This diel pattern may be related to the blue whale feeding ecology. PMID:27828976

  18. Seasonal and Diel Vocalization Patterns of Antarctic Blue Whale (Balaenoptera musculus intermedia) in the Southern Indian Ocean: A Multi-Year and Multi-Site Study.

    PubMed

    Leroy, Emmanuelle C; Samaran, Flore; Bonnel, Julien; Royer, Jean-Yves

    2016-01-01

    Passive acoustic monitoring is an efficient way to provide insights on the ecology of large whales. This approach allows for long-term and species-specific monitoring over large areas. In this study, we examined six years (2010 to 2015) of continuous acoustic recordings at up to seven different locations in the Central and Southern Indian Basin to assess the peak periods of presence, seasonality and migration movements of Antarctic blue whales (Balaenoptera musculus intermedia). An automated method is used to detect the Antarctic blue whale stereotyped call, known as Z-call. Detection results are analyzed in terms of distribution, seasonal presence and diel pattern of emission at each site. Z-calls are detected year-round at each site, except for one located in the equatorial Indian Ocean, and display highly seasonal distribution. This seasonality is stable across years for every site, but varies between sites. Z-calls are mainly detected during autumn and spring at the subantarctic locations, suggesting that these sites are on the Antarctic blue whale migration routes, and mostly during winter at the subtropical sites. In addition to these seasonal trends, there is a significant diel pattern in Z-call emission, with more Z-calls in daytime than in nighttime. This diel pattern may be related to the blue whale feeding ecology.

  19. 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

  20. Antarctic ice sheet response to combined surface and oceanic sub-ice shelf melt during past interglacials and in the future

    NASA Astrophysics Data System (ADS)

    DeConto, R.; Pollard, D.; Kowalewski, D.

    2012-04-01

    New sediment core records from the Ross Embayment (ANDRILL; Naish et al., Nature, 2009) and time-continuous modeling of the Antarctic ice sheet-shelf system (Pollard and DeConto, Nature, 2009) imply dramatic, orbitally paced variability of the West Antarctic Ice Sheet (WAIS) through the Plio-Pleistocene. Model-simulated episodes of WAIS retreat are common during the warm Pliocene, but they also occur during some interglacials in the colder Pleistocene. The relatively modest forcing of these simulated past retreats hints at the future vulnerability of the ice sheet. In our previous long-term simulations, the ice-sheet model was driven by parameterized climatologies (surface temperature, precipitation, sea level, and oceanic sub-ice shelf melt) scaled mainly to deep-sea benthic oxygen isotope records. In the model, WAIS was found to be highly sensitive to sub-ice-shelf melt rates, with modest increases (~2 m/yr) capable of triggering sudden grounding-line retreat and dynamic thinning in the Ross, Weddell and Amundsen Sea sectors- largely in response to reduced ice-shelf buttressing. Here we present new ice sheet-shelf simulations of specific past interglacials and future scenarios with elevated greenhouse gasses. The model is driven by atmospheric climatologies from a new high-resolution Regional Climate Model adapted to the South Polar region and modest increases in circum-Antarctic ocean temperatures. The model (accounting for past greenhouse gas and orbital forcing) shows that melt on ice-shelf surfaces played a contributing role in prior Pleistocene WAIS retreats, but increased oceanic sub ice-shelf melt was likely the dominant mechanism driving those past retreats. At levels of atmospheric CO2 exceeding 2x preindustrial levels (560 ppmv), surface melt on ice-shelf surfaces becomes increasingly important. As CO2 levels approach 4x preindustrial levels, surface melt on ice shelves and the low-elevation flanks of WAIS is sufficient to cause near complete WAIS

  1. How do long-offset oceanic transforms adapt to plate motion changes? The example of the Western Pacific-Antarctic plate boundary

    NASA Astrophysics Data System (ADS)

    Lodolo, Emanuele; Coren, Franco; Ben-Avraham, Zvi

    2013-03-01

    Oceanic transform faults respond to changes in the direction of relative plate motion. Studies have shown that short-offset transforms generally adjust with slight bends near the ridge axis, while long-offset ones have a remarkably different behavior. The western Pacific-Antarctic plate boundary highlights these differences. A set of previously unpublished seismic profiles, in combination with magnetic anomaly identifications, shows how across a former, ~1250 km long transform (the Emerald Fracture Zone), plate motion changes have produced a complex geometric readjustment. Three distinct sections are recognized along this plate boundary: an eastern section, characterized by parallel, multiple fault strand lineaments; a central section, shallower than the rest of the ridge system, overprinted by a mantle plume track; and a western section, organized in a cascade of short spreading axes/transform lineaments. This configuration was produced by changes that occurred since 30 Ma in the Australia-Pacific relative plate motion, combined with a gradual clockwise change in Pacific-Antarctic plate motion. These events caused extension along the former Emerald Fracture Zone, originally linking the Pacific-Antarctic spreading ridge system with the Southeast Indian ridge. Then an intra-transform propagating ridge started to develop in response to a ~6 Ma change in the Pacific-Antarctic spreading direction. The close proximity of the Euler poles of rotation amplified the effects of the geometric readjustments that occurred along the transform system. This analysis shows that when a long-offset transform older than 20 Ma is pulled apart by changes in spreading velocity vectors, it responds with the development of multiple discrete, parallel fault strands, whereas in younger lithosphere, locally modified by thermal anisotropies, tensional stresses generate an array of spreading axes offset by closely spaced transforms.

  2. Horizontal and vertical distribution of euphausiid species on the Western Antarctic Peninsula U.S. GLOBEC Southern Ocean study site

    NASA Astrophysics Data System (ADS)

    Wiebe, Peter H.; Ashjian, Carin J.; Lawson, Gareth L.; Piñones, Andrea; Copley, Nancy J.

    2011-07-01

    The Western Antarctic Peninsula (WAP) is a site of high krill abundance and a likely source region for krill populations found to the north and east of the area. The U.S. GLOBEC Southern Ocean program studied factors that contribute to the overwintering success of krill in the region of Marguerite Bay, WAP. A MOCNESS net system was used to sample the vertical distribution and abundance of zooplankton relative to physical features (hydrography and circulation) during four broad-scale survey cruises in the fall and winter of 2001 and 2002. Four species were found throughout the study area on all four cruises: Euphausia superba, Euphausia crystallorophias, Euphausia triacantha, and Thysanoessa macrura. The species had significantly different horizontal and vertical distributions. Both E. superba and T. macrura were broadly distributed throughout the area, but the central 50% of their vertical distributions were distinct with E. superba most abundant in the upper 100 m in the coldest, freshest water (average temperature and salinity: -1.13 °C; 33.80) and T. macrura occurring between 100 and 250 m (at 0.01 °C; 34.228). E. crystallorophias had a more coastal distribution and was usually found deeper in slightly warmer and saltier water (-0.44 °C; 33.9982) than E. superba and either overlapped or was above T. macrura in depth. E. triacantha was much rarer and sporadically distributed in the study area and was found substantially deeper (center of distribution about 300 m) in the warmest saltiest water (1.40 °C; 34.65) than the other three euphausiid species. Larval distributions for E. superba indicated that at least some proportion of the populations resulted from reproduction and development on the continental shelf, and not solely from offshore reproduction and transport onto the shelf. A neutral particle tracking model was used to gain insight into the relative importance of shelf versus off-shelf origins for the larvae. The results suggest that a combination of

  3. 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.

  4. Ocean-Atmosphere Environments of Antarctic-Region Cold-Air Mesocyclones: Evaluation of Reanalyses for Contrasting Adjacent 10-Day Periods ("Macro-Weather") in Winter.

    NASA Astrophysics Data System (ADS)

    Carleton, A. M.; Auger, J.; Birkel, S. D.; Maasch, K. A.; Mayewski, P. A.; Claud, C.

    2015-12-01

    Mesoscale cyclones in cold-air outbreaks (mesocyclones) feature in the weather and climate of the Antarctic (e.g., Ross Sea) and sub-antarctic (Drake Passage). They adversely impact field operations, and influence snowfall, the ice-sheet mass balance, and sea-air energy fluxes. Although individual mesocyclones are poorly represented on reanalyses, these datasets robustly depict the upper-ocean and troposphere environments in which multiple mesocyclones typically form. A spatial metric of mesocyclone activity—the Meso-Cyclogenesis Potential (MCP)—used ERA-40 anomaly fields of: sea surface temperature (SST) minus marine air temperature (MAT), near-surface winds, 500 hPa air temperature, and the sea-ice edge location. MCP maps composited by teleconnection phases for 1979-2001, broadly correspond to short-period satellite "climatologies" of mesocyclones. Here, we assess 3 reanalysis datasets (CFSR, ERA-I and MERRA) for their reliably to depict MCP patterns on weekly to sub-monthly periods marked by strong regional shifts in mesocyclone activity (frequencies, track densities) occurring during a La Niña winter: June 21-30, 1999 (SE Indian Ocean) and September 1-10, 1999 (Ross Sea sector). All reanalyses depict the marked variations in upper ocean and atmosphere variables between adjacent 10-day periods. Slight differences may owe to model resolution or internal components (land surface, coupled ocean models), and/or how the observations are assimilated. For June 21-30, positive SST-MAT, southerly winds, proximity to the ice edge, and negative T500, accompany increased meso-cyclogenesis. However, for September 1-10, surface forcing does not explain frequent comma cloud "polar lows" north-east of the Ross Sea. Inclusion of the upper-level diffluence (e.g., from Z300 field) in the MCP metric, better depicts the observed mesocyclone activity. MCP patterns on these "macro-weather" time scales appear relatively insensitive to the choice of reanalysis.

  5. Surface oceanography of BROKE-West, along the Antarctic margin of the south-west Indian Ocean ( 30-80∘E)

    NASA Astrophysics Data System (ADS)

    Williams, G. D.; Nicol, S.; Aoki, S.; Meijers, A. J. S.; Bindoff, N. L.; Iijima, Y.; Marsland, S. J.; Klocker, A.

    2010-05-01

    Hydrographic CTD and ADCP data were collected during the BROKE-West research voyage (January-March 2006) in the south-west Indian Ocean sector of the Antarctic margin. These data describe the large-scale circulation, water masses, fronts and summertime stratification in the surface layer over the continental shelf, slope and rise region between 30 and 80∘E that forms CCAMLR Statistical Area 58.4.2. The surface circulation matched the full-depth circulation and consisted of the eastward flowing southern Antarctic Circumpolar Current front to the north, and the westward flowing Antarctic Slope Current associated with the Antarctic Slope Front along the continental slope to the south. Two sub-polar gyres were detected south of the Southern Boundary of the Antarctic Circumpolar Current: the eastern Weddell Gyre in the Cosmonaut Sea ( 30-50∘E) and the greater Prydz Bay Gyre in the Cooperation Sea ( 60-80∘E). In the eastern Weddell Gyre, the seasonal mixed layer depths were shallower, warmer and fresher relative to the regions to the east which were deeper, cooler and more saline. This spatial variability is found to be strongly correlated to the large-scale pattern of sea ice melt/retreat in the months preceding the voyage and the accumulated wind stress thereafter. Areas of upwelling warm deep waters into the surface layer are presented from positive anomalies of potential temperature and nutrient concentrations (nitrate and silicate). These anomalies were strongest in the eastern Weddell Gyre in the vicinity of the Cosmonaut Polynya/Embayment, north of Cape Anne and near the Southern Boundary of the Antarctic Circumpolar Current in the eastern sector of the survey. The summertime stratification (seasonal mixed layer, seasonal pycnocline and Tmin layer) are discussed relative to the distributions of chl a and acoustically determined Antarctic Krill ( Euphausia superba) densities. Elevated chl a concentrations were found in the surface layer of the marginal ice

  6. 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.

  7. Long-term and large-scale epidemiology of Brucella infection in baleen whales and sperm whales in the western North Pacific and Antarctic Oceans

    PubMed Central

    OHISHI, Kazue; BANDO, Takeharu; ABE, Erika; KAWAI, Yasushi; FUJISE, Yoshihiro; MARUYAMA, Tadashi

    2016-01-01

    In a long-term, large-scale serologic study in the western North Pacific Ocean, anti-Brucella antibodies were detected in common minke whales (Balaenoptera acutorostrata) in the 1994–2010 offshore surveys (21%, 285/1353) and in the 2006–2010 Japanese coastal surveys (20%, 86/436), in Bryde’s whales (B. edeni brydei) in the 2000–2010 offshore surveys (9%, 49/542), in sei whales (B. borealis) in the 2002–2010 offshore surveys (5%, 40/788) and in sperm whales (Physeter macrocephalus) in the 2000–2010 offshore surveys (8%, 4/50). Anti-Brucella antibodies were not detected in 739 Antarctic minke whales (B. bonaerensis) in the 2000–2010 Antarctic surveys. This suggests that Brucella was present in the four large whale populations inhabiting the western North Pacific, but not in the Antarctic minke whale population. By PCR targeting for genes of outer membrane protein 2, the Brucella infection was confirmed in tissue DNA samples from Bryde’s whales (14%, 2/14), sei whales (11%, 1/9) and sperm whales (50%, 2/4). A placental tissue and an apparently healthy fetus from a sperm whale were found to be PCR-positive, indicating that placental transmission might have occurred and the newborn could act as a bacterial reservoir. Marked granulomatous testes were observed only in mature animals of the three species of baleen whales in the western North Pacific offshore surveys, especially in common minke whales, and 29% (307/1064) of total mature males had abnormal testes. This study provides an insight into the status of marine Brucella infection at a global level. PMID:27320816

  8. Long-term and large-scale epidemiology of Brucella infection in baleen whales and sperm whales in the western North Pacific and Antarctic Oceans.

    PubMed

    Ohishi, Kazue; Bando, Takeharu; Abe, Erika; Kawai, Yasushi; Fujise, Yoshihiro; Maruyama, Tadashi

    2016-10-01

    In a long-term, large-scale serologic study in the western North Pacific Ocean, anti-Brucella antibodies were detected in common minke whales (Balaenoptera acutorostrata) in the 1994-2010 offshore surveys (21%, 285/1353) and in the 2006-2010 Japanese coastal surveys (20%, 86/436), in Bryde's whales (B. edeni brydei) in the 2000-2010 offshore surveys (9%, 49/542), in sei whales (B. borealis) in the 2002-2010 offshore surveys (5%, 40/788) and in sperm whales (Physeter macrocephalus) in the 2000-2010 offshore surveys (8%, 4/50). Anti-Brucella antibodies were not detected in 739 Antarctic minke whales (B. bonaerensis) in the 2000-2010 Antarctic surveys. This suggests that Brucella was present in the four large whale populations inhabiting the western North Pacific, but not in the Antarctic minke whale population. By PCR targeting for genes of outer membrane protein 2, the Brucella infection was confirmed in tissue DNA samples from Bryde's whales (14%, 2/14), sei whales (11%, 1/9) and sperm whales (50%, 2/4). A placental tissue and an apparently healthy fetus from a sperm whale were found to be PCR-positive, indicating that placental transmission might have occurred and the newborn could act as a bacterial reservoir. Marked granulomatous testes were observed only in mature animals of the three species of baleen whales in the western North Pacific offshore surveys, especially in common minke whales, and 29% (307/1064) of total mature males had abnormal testes. This study provides an insight into the status of marine Brucella infection at a global level.

  9. Changes in oxygenation reveal an asymmetry in the Antarctic Intermediate Water production of the Pacific sector of the Southern Ocean during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Chase, Z.; Durand, A.; Noble, T. L.; Townsend, A.; Bostock, H. C.; Neil, H.; Jaccard, S.

    2016-12-01

    We studied 21 sediment cores located on the Campbell and Challenger Plateaux surrounding New Zealand to investigate changes in oxygenation at intermediate depths of southwest Pacific sector the Southern-Ocean since the Last Glacial Maximum (LGM). The cores span Antarctic Intermediate Water (AAIW) and Upper Circumpolar Deep Water (UCDW). The sedimentary concentrations of redox sensitive elements reveal that intermediate depths of the southwest Pacific sector of the Southern Ocean (800-1500m) were oxygen depleted during the LGM compared to the Holocene and present day. These data, together with variations in benthic foraminiferal δ13C are consistent with a shallower AAIW-UCDW boundary in the southwest Pacific sector of the Southern Ocean during the LGM (800m vs 1200m today). Moreover, δ 13C data indicate that AAIW still bathed the shallower core sites (< 800m depth) during the LGM and Holocene; however redox sensitive elements in these cores also reveal lower oxygen content in glacial AAIW compared to the Holocene. These findings are in opposition to what has been found in the South East Pacific sector of the Southern Ocean, where redox sensitive element variations showed that AAIW was more oxygenated and extended deeper during the LGM. Therefore, during the LGM, AAIW extent and oxygen content were asymmetrical between the eastern and western regions of the Pacific sector of the Southern Ocean. Consequently, the AAIW repartition in the Pacific sector of the Southern Ocean was dramatically different during the LGM compared to present, where AAIW depth range is quasi constant. Differences in the position of the Westerlies between the eastern and western side, as well as differences in sea-ice melt discharges could have potentially driven this glacial asymmetry.

  10. 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.

  11. 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.

  12. 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

  13. The South Georgia and the South Sandwich Islands MPA: protecting a biodiverse oceanic island chain situated in the flow of the antarctic circumpolar current.

    PubMed

    Trathan, Philip N; Collins, Martin A; Grant, Susie M; Belchier, Mark; Barnes, David K A; Brown, Judith; Staniland, Iain J

    2014-01-01

    South Georgia and the South Sandwich Islands (SGSSI) are surrounded by oceans that are species-rich, have high levels of biodiversity, important endemism and which also support large aggregations of charismatic upper trophic level species. Spatial management around these islands is complex, particularly in the context of commercial fisheries that exploit some of these living resources. Furthermore, management is especially complicated as local productivity relies fundamentally upon biological production transported from outside the area. The MPA uses practical management boundaries, allowing access for the current legal fisheries for Patagonian toothfish, mackerel icefish and Antarctic krill. Management measures developed as part of the planning process designated the whole SGSSI Maritime Zone as an IUCN Category VI reserve, within which a number of IUCN Category I reserves were identified. Multiple-use zones and temporal closures were also designated. A key multiple-use principle was to identify whether the ecological impacts of a particular fishery threatened either the pelagic or benthic domain.

  14. Effects of ocean acidification on the physiological performance and carbon production of the Antarctic sea ice diatom Nitzschia sp. ICE-H.

    PubMed

    Qu, Chang-Feng; Liu, Fang-Ming; Zheng, Zhou; Wang, Yi-Bin; Li, Xue-Gang; Yuan, Hua-Mao; Li, Ning; An, Mei-Ling; Wang, Xi-Xi; He, Ying-Ying; Li, Lu-Lu; Miao, Jin-Lai

    2017-07-15

    Ocean acidification (OA) resulting from increasing atmospheric CO2 strongly influences marine ecosystems, particularly in the polar ocean due to greater CO2 solubility. Here, we grew the Antarctic sea ice diatom Nitzschia sp. ICE-H in a semicontinuous culture under low (~400ppm) and high (1000ppm) CO2 levels. Elevated CO2 resulted in a stimulated physiological response including increased growth rates, chlorophyll a contents, and nitrogen and phosphorus uptake rates. Furthermore, high CO2 enhanced cellular particulate organic carbon production rates, indicating a greater shift from inorganic to organic carbon. However, the cultures grown in high CO2 conditions exhibited a decrease in both extracellular and intracellular carbonic anhydrase activity, suggesting that the carbon concentrating mechanisms of Nitzschia sp. ICE-H may be suppressed by elevated CO2. Our results revealed that OA would be beneficial to the survival of this sea ice diatom strain, with broad implications for global carbon cycles in the future ocean. Copyright © 2017. Published by Elsevier Ltd.

  15. Long-term experiment on physiological responses to synergetic effects of ocean acidification and photoperiod in the Antarctic sea ice algae Chlamydomonas sp. ICE-L.

    PubMed

    Xu, Dong; Wang, Yitao; Fan, Xiao; Wang, Dongsheng; Ye, Naihao; Zhang, Xiaowen; Mou, Shanli; Guan, Zheng; Zhuang, Zhimeng

    2014-07-15

    Studies on ocean acidification have mostly been based on short-term experiments of low latitude with few investigations of the long-term influence on sea ice communities. Here, the combined effects of ocean acidification and photoperiod on the physiological response of the Antarctic sea ice microalgae Chlamydomonas sp. ICE-L were examined. There was a general increase in growth, PSII photosynthetic parameters, and N and P uptake in continuous light, compared to those exposed to regular dark and light cycles. Elevated pCO2 showed no consistent effect on growth rate (p=0.8) and N uptake (p=0.38) during exponential phrase, depending on the photoperiod but had a positive effect on PSII photosynthetic capacity and P uptake. Continuous dark reduced growth, photosynthesis, and nutrient uptake. Moreover, intracellular lipid, mainly in the form of PUFA, was consumed at 80% and 63% in low and high pCO2 in darkness. However, long-term culture under high pCO2 gave a more significant inhibition of growth and Fv/Fm to high light stress. In summary, ocean acidification may have significant effects on Chlamydomonas sp. ICE-L survival in polar winter. The current study contributes to an understanding of how a sea ice algae-based community may respond to global climate change at high latitudes.

  16. 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.

  17. Centennial-millennial scale variations in Western Antarctic Ice Sheet discharge and their relationship to climate and ocean changes during the late Holocene

    NASA Astrophysics Data System (ADS)

    Snilstveit Hoem, Frida; Ninnemann, Ulysses S.; Kleiven, Helga (Kikki) F.; Irvali, Nil

    2017-04-01

    The Western Antarctic Ice Sheet (WAIS) may be highly sensitive to future warming and to ocean driven changes in subsurface melting. Understanding this sensitivity is critical as WAIS dynamics are a major source of uncertainty in sea level rise and regional climate projections. Although there is increasing evidence that WAIS discharge has varied on centennial to multi-millennial timescales since the last glacial period much less is known about its most recent (late Holocene) behavior. This period is particularly important as a baseline for delineating natural and anthropogenic influences and understanding potential coupling between climate, ocean circulation, and WAIS discharge. Here we present high-resolution records of WAIS discharge together with co-registered signals of surface and deep ocean physical property changes in a multicore taken from the southern flank of the North Scotia Sea Ridge (53˚ 31.813 S; 44˚ 42.143 W at 2750m water depth) spanning the past 4000 years. The site is situated just south/east of the polar front beyond the reach of seasonal sea ice and its potentially confounding influence on the ice-rafted debris (IRD) signal but still influenced by icebergs mostly originating from the WAIS. Our record of IRD from core GS08-151-02MC provides a centennially resolved record of iceberg supply from which we infer Antarctic ice-sheet dynamics and variability, while we use the oxygen and carbon isotopic composition of benthic (U. peregrina) and planktonic (N. pachyderma (s)) foraminifera to give (regional) information on past polar deep water and surface water temperatures, circulation and nutrients. Our results show higher amount of IRD between 4200-1800 cal yr B.P. This is in agreement with paleoclimate records reconstructing the onset of the neoglacial, sea ice expansion at about 5000 cal yr B.P. in the Atlantic sector of the Southern Ocean, and glaciers advancing in South America. The strongest IRD peak of the past millennium, which is otherwise a

  18. Ocean barriers and glaciation: evidence for explosive radiation of mitochondrial lineages in the Antarctic sea slug Doris kerguelenensis (Mollusca, Nudibranchia).

    PubMed

    Wilson, Nerida G; Schrödl, M; Halanych, Kenneth M

    2009-03-01

    Strong currents and deep passages of water can be barriers for larval dispersal of continental marine animals, but potential effects on direct developers are under-investigated. We examined the genetic structure of Doris kerguelenensis, a directly developing sea slug that occurs across the Drake Passage, the body of water separating Antarctica from South America. We found deep mitochondrial divergences within populations on both sides of the Drake Passage, and South American animals formed multiple sister-group relationships with Antarctic animals. A generalised molecular clock suggested these trans-Drake pairs diverged during the Pliocene–Pleistocene, after the formation of the Drake Passage. Statistical parsimony methods recovered 29 separate haplotype networks (many sympatric) that likely correlate with allopatric events caused by repeated glacial cycles. Data from 16S were congruent but more conserved than COI, and the estimated ancestral 16S haplotype was widespread. The marked difference in the substitution rates between these two mitochondrial genes results in different estimates of connectivity. Demographic analyses on networks revealed some evidence for selection and expanding populations. Contrasting with the Northern Hemisphere, glaciation in Antarctica appears to have increased rather than reduced genetic diversity. This suggests orbitally forced range dynamics based on Northern Hemisphere phylogeography do not hold for Antarctica. The diverse lineages found in D. kerguelenensis point towards a recent, explosive radiation, likely reflecting multiple refuges during glaciation events, combined with limited subsequent dispersal. Whether recognised as cryptic species or not, genetic diversity in Antarctic marine invertebrates appears higher than expected from morphological analyses, and supports the Antarctic biodiversity pump phenomenon.

  19. The International Bathymetric Chart of the Southern Ocean (IBCSO) Version 1.0 - A new bathymetric compilation covering circum-Antarctic waters

    NASA Astrophysics Data System (ADS)

    Arndt, Jan Erik; Schenke, Hans Werner; Jakobsson, Martin; Nitsche, Frank O.; Buys, Gwen; Goleby, Bruce; Rebesco, Michele; Bohoyo, Fernando; Hong, Jongkuk; Black, Jenny; Greku, Rudolf; Udintsev, Gleb; Barrios, Felipe; Reynoso-Peralta, Walter; Taisei, Morishita; Wigley, Rochelle

    2013-06-01

    International Bathymetric Chart of the Southern Ocean (IBCSO) Version 1.0 is a new digital bathymetric model (DBM) portraying the seafloor of the circum-Antarctic waters south of 60°S. IBCSO is a regional mapping project of the General Bathymetric Chart of the Oceans (GEBCO). The IBCSO Version 1.0 DBM has been compiled from all available bathymetric data collectively gathered by more than 30 institutions from 15 countries. These data include multibeam and single-beam echo soundings, digitized depths from nautical charts, regional bathymetric gridded compilations, and predicted bathymetry. Specific gridding techniques were applied to compile the DBM from the bathymetric data of different origin, spatial distribution, resolution, and quality. The IBCSO Version 1.0 DBM has a resolution of 500 × 500 m, based on a polar stereographic projection, and is publicly available together with a digital chart for printing from the project website (www.ibcso.org) and at http://dx.doi.org/10.1594/PANGAEA.805736.

  20. 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.

  1. Holocene glacial activity in Barilari Bay, west Antarctic Peninsula, tracked by magnetic mineral assemblages: Linking ice, ocean, and atmosphere

    NASA Astrophysics Data System (ADS)

    Reilly, Brendan T.; Natter, Carl J.; Brachfeld, Stefanie A.

    2016-11-01

    We investigate the origin and fate of lithogenic sediments using magnetic mineral assemblages in Barilari Bay, west Antarctic Peninsula (AP) from sediment cores recovered during the Larsen Ice Shelf System, Antarctica (LARISSA) NBP10-01 cruise. To quantify and reconstruct Holocene changes in covarying magnetic mineral assemblages, we adopt an unsupervised mathematical unmixing strategy and apply it to measurements of magnetic susceptibility as a function of increasing temperature. Comparisons of the unmixed end-members with magnetic observations of northwestern AP bedrock and the spatial distribution of magnetic mineral assemblages within the fjord, allow us to identify source regions, including signatures for "inner bay," "outer bay," and "northwestern AP" sources. We find strong evidence that supports the establishment of a late Holocene ice shelf in the fjord coeval with the Little Ice Age. Additionally, we present new evidence for late Holocene sensitivity to conditions akin to positive mean Southern Annual Mode states for western AP glaciers at their advanced Neoglacial positions.

  2. Dissolved Iron in the Australian Sector of the Southern Ocean During Spring: Implications for the Seasonal Cycle of Iron in Antarctic Surface Waters

    NASA Astrophysics Data System (ADS)

    Sedwick, P. N.; Bowie, A. R.; Ussher, S. J.; Mackey, D. J.; Trull, T. W.; Worsfold, P. J.

    2002-12-01

    Colorimetric flow injection analysis was used to measure dissolved iron (<0.4 μm, dFe) in upper-ocean (<400 m depth) water samples collected from the CLIVAR SR3 section (~142°E) between Tasmania and Antarctica in November-December 2001. These are the first such data for this region during austral spring, and include results from two stations occupied in melting pack ice, as well as one station near the 61°S SOIREE site, occupied twice. Combining these new results with data from a March 1998 cruise and the February 1999 SOIREE campaign allows us to infer seasonal (spring-fall) changes in dFe concentrations in surface waters of our study region, assuming interannual variability is small. The data suggest a seasonal drawdown of ~0.1-0.2 nM dFe in the Subantarctic Zone waters (~47°S); a seasonal accumulation of ~0.1 nM dFe in near-surface (~25 m) waters and a drawdown of ~0.05 nM dFe in deeper (~50-300 m) waters of the Subantarctic Front (~51°S); and little or no seasonal dFe drawdown (~0.05 nM or less) in surface waters south of the Subantarctic Front, where dFe concentrations were uniformly low (~0.1 nM). Thus, if winter mixing provides a significant vertical resupply of dFe to Antarctic surface waters, our results suggest that most of this winter reserve of dissolved iron is removed from the upper water column very early in the growing season. In addition, our new data provide no evidence of significant iron inputs to surface waters from melting sea ice, which may explain the lack of ice-edge algal blooms in this sector of the Southern Ocean, as inferred from ocean-color satellite images.

  3. Investigating the Sources of Decadal-Scale Property Changes in Antarctic Bottom Water in the Southeast Indian Ocean (80-90°E)

    NASA Astrophysics Data System (ADS)

    Gottschalk, K.; Macdonald, A. M.

    2016-12-01

    A recognizable warming and freshening of Antarctic Bottom Water (AABW) throughout much of the Southern Ocean is one of the major findings of the international long-line hydrographic programs of 1990's and the 2000's. A recent GO-SHIP repeat of the I08S line in the southeast Indian Ocean in 2016 found continued, but weaker, AABW warming and significantly strong freshening in the Antarctic-Australian Basin (A-AB). It has been proposed that the 2010 B9b iceberg calving along the Adélie Land Coast may be linked to the sharp increase in A-AB AABW freshening. The present study seeks to affirm or challenge this hypothesis through a quantitative investigation into the origins of A-AB (i.e. I08S) bottom water. The investigation takes the form of an Extended Optimum MultiParameter mixing analysis (eOMP) to determine a) the contribution of individual formation regions to the bottom water seen at I08S, and b) how these contributions may have changed over the twenty years since the first occupation of the line. The initial investigation that used mean source water properties found Adélie Bottom Water (ADLBW) to be the dominant source of AABW in the A-AB. However, by calculating source water properties from times preceding the occupations of the I08S line (1994, 2007, 2016), it was determined that in both 1994 and 2007, Ross Sea Bottom Water (RSBW) was the dominant source of AABW (approx. 61 & 75 %, respectively) in the A-AB. This dominance shifted in 2016, to ADLBW composing approximately 44% of AABW. This result suggests that it is feasible that the B9b calving that impacted ADLBW in the formation region is, at least, partially responsible for the changes seen at I08S. Nevertheless, given that there are significant contributions from both RSBW and Weddell Sea Bottom Water, it seems unlikely that this single alteration of ADLBW is the sole driver of the observed freshening. Further investigation seeks to determine the sensitivity of the solution to particular source water

  4. 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

  5. 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

  6. Distribution and long-range transport of polyfluoroalkyl substances in the Arctic, Atlantic Ocean and Antarctic coast.

    PubMed

    Zhao, Zhen; Xie, Zhiyong; Möller, Axel; Sturm, Renate; Tang, Jianhui; Zhang, Gan; Ebinghaus, Ralf

    2012-11-01

    The global distribution and long-range transport of polyfluoroalkyl substances (PFASs) were investigated using seawater samples collected from the Greenland Sea, East Atlantic Ocean and the Southern Ocean in 2009-2010. Elevated levels of ΣPFASs were detected in the North Atlantic Ocean with the concentrations ranging from 130 to 650 pg/L. In the Greenland Sea, the ΣPFASs concentrations ranged from 45 to 280 pg/L, and five most frequently detected compounds were perfluorooctanoic acid (PFOA), perfluorohexanesulfonate (PFHxS), perfluorohexanoic acid (PFHxA), perfluorooctane sulfonate (PFOS) and perfluorobutane sulfonate (PFBS). PFOA (15 pg/L) and PFOS (25-45 pg/L) were occasionally found in the Southern Ocean. In the Atlantic Ocean, the ΣPFASs concentration decreased from 2007 to 2010. The elevated PFOA level that resulted from melting snow and ice in Greenland Sea implies that the Arctic may have been driven by climate change and turned to be a source of PFASs for the marine ecosystem. Copyright © 2012 Elsevier Ltd. All rights reserved.

  7. Breakup of Pack Ice, Antarctic Ice Shelf

    NASA Image and Video Library

    1991-09-18

    STS048-152-007 (12-18 Sept 1991) --- The periphery of the Antarctic ice shelf and the Antarctic Peninsula were photographed by the STS 48 crew members. Strong offshore winds, probably associated with katabatic winds from the interior of the continent, are peeling off the edges of the ice shelf into ribbons of sea ice, icebergs, bergy bits and growlers into the cold waters of the circum-Antarctic southern ocean.

  8. Near-shore Antarctic pH variability has implications for the design of ocean acidification experiments

    PubMed Central

    Kapsenberg, Lydia; Kelley, Amanda L.; Shaw, Emily C.; Martz, Todd R.; Hofmann, Gretchen E.

    2015-01-01

    Understanding how declining seawater pH caused by anthropogenic carbon emissions, or ocean acidification, impacts Southern Ocean biota is limited by a paucity of pH time-series. Here, we present the first high-frequency in-situ pH time-series in near-shore Antarctica from spring to winter under annual sea ice. Observations from autonomous pH sensors revealed a seasonal increase of 0.3 pH units. The summer season was marked by an increase in temporal pH variability relative to spring and early winter, matching coastal pH variability observed at lower latitudes. Using our data, simulations of ocean acidification show a future period of deleterious wintertime pH levels potentially expanding to 7–11 months annually by 2100. Given the presence of (sub)seasonal pH variability, Antarctica marine species have an existing physiological tolerance of temporal pH change that may influence adaptation to future acidification. Yet, pH-induced ecosystem changes remain difficult to characterize in the absence of sufficient physiological data on present-day tolerances. It is therefore essential to incorporate natural and projected temporal pH variability in the design of experiments intended to study ocean acidification biology.

  9. Threshold Behavior of a Marine-Based Sector of the East Antarctic Ice Sheet in Response to Early Pliocene Ocean Warming

    NASA Astrophysics Data System (ADS)

    Hansen, Melissa; Passchier, Sandra; Khim, Boo-Keun; Williams, Trevor

    2015-04-01

    We investigate the stability of the East Antarctic Ice Sheet (EAIS) on the Wilkes Land continental margin, Antarctica, utilizing a high-resolution record of ice-rafted debris (IRD) mass accumulation rates (MAR) from Integrated Ocean Drilling Program (IODP) Site U1359. The relationship between orbital variations in the IRD record and climate drivers was evaluated to capture changes in the dynamics of a marine-based ice sheet in response to early Pliocene warming. Three IRD MAR excursions were observed in the early Pliocene and confirmed via Scanning Electron Microscope (SEM) microtextural analysis of sand grains. Time series analysis of the IRD MAR reveals obliquity paced expansions of the ice sheet to the outer shelf prior to ~4.6 Ma. A decline in the obliquity and a transition into a dominant precession response of IRD MAR occurs at ~4.6 Ma along with a decline in the amplitude of IRD MAR maxima to low background levels between ~4.0 and ~3.5 Ma. We speculate that as SST began to peak above 3°C in the early Pliocene warm period, the ice shelves thinned leading to a greater susceptibility to precession forced high-latitude climate variability and the onset of persistent retreat of the marine-based portion of the EAIS.

  10. Threshold behavior of a marine-based sector of the East Antarctic Ice Sheet in response to early Pliocene ocean warming

    NASA Astrophysics Data System (ADS)

    Hansen, Melissa A.; Passchier, Sandra; Khim, Boo-Keun; Song, Buhan; Williams, Trevor

    2015-06-01

    We investigate the stability of the East Antarctic Ice Sheet (EAIS) on the Wilkes Land continental margin, Antarctica, utilizing a high-resolution record of ice-rafted debris (IRD) mass accumulation rates (MAR) from Integrated Ocean Drilling Program Site U1359. The relationship between orbital variations in the IRD record and climate drivers was evaluated to capture changes in the dynamics of a marine-based ice sheet in response to early Pliocene warming. Three IRD MAR excursions were observed and confirmed via scanning electron microscope microtextural analysis of sand grains. Time series analysis of the IRD MAR reveals obliquity-paced expansions of the ice sheet to the outer shelf prior to ~4.6 Ma. A decline in the obliquity and a transition into a dominant precession response of IRD MAR occur at ~4.6 Ma along with a decline in the amplitude of IRD MAR maxima to low background levels between ~4.0 and ~3.5 Ma. We speculate that as sea surface temperatures began to peak above 3°C during the early Pliocene climatic optimum, the ice shelves thinned, leading to a greater susceptibility to precession-forced summer insolation and the onset of persistent retreat of a marine-based portion of the EAIS.

  11. Carbon isotope evidence for changes in Antarctic Intermediate Water circulation and ocean ventilation in the southwest Pacific during the last deglaciation

    NASA Astrophysics Data System (ADS)

    Bostock, Helen C.; Opdyke, Bradley N.; Gagan, Michael K.; Fifield, L. Keith

    2004-12-01

    Deep-sea sediment core FR1/97 GC-12 is located 990 mbsl in the northern Tasman Sea, southwest Pacific, where Antarctic Intermediate Water (AAIW) presently impinges the continental slope of the southern Great Barrier Reef. Analysis of carbon (δ13C) and oxygen (δ18O) isotope ratios on a suite of planktonic and benthic foraminifera reveals rapid changes in surface and intermediate water circulation over the last 30 kyr. During the Last Glacial Maximum, there was a large δ13C offset (1.1‰) between the surface-dwelling planktonic foraminifera and benthic species living within the AAIW. In contrast, during the last deglaciation (Termination 1), the δ13Cplanktonic-benthic offset reduced to 0.4‰ prior to an intermediate offset (0.7‰) during the Holocene. We suggest that variations in the dominance and direction of AAIW circulation in the Tasman Sea, and increased oceanic ventilation, can account for the rapid change in the water column δ13Cplanktonic-benthic offset during the glacial-interglacial transition. Our results support the hypothesis that intermediate water plays an important role in propagating climatic changes from the polar regions to the tropics. In this case, climatic variations in the Southern Hemisphere may have led to the rapid ventilation of deep water and AAIW during Termination 1, which contributed to the postglacial rise in atmospheric CO2.

  12. An assessment of Antarctic Circumpolar Current and Southern Ocean meridional overturning circulation during 1958-2007 in a suite of interannual CORE-II simulations

    NASA Astrophysics Data System (ADS)

    Farneti, Riccardo; Downes, Stephanie M.; Griffies, Stephen M.; Marsland, Simon J.; Behrens, Erik; Bentsen, Mats; Bi, Daohua; Biastoch, Arne; Böning, Claus; Bozec, Alexandra; Canuto, Vittorio M.; Chassignet, Eric; Danabasoglu, Gokhan; Danilov, Sergey; Diansky, Nikolay; Drange, Helge; Fogli, Pier Giuseppe; Gusev, Anatoly; Hallberg, Robert W.; Howard, Armando; Ilicak, Mehmet; Jung, Thomas; Kelley, Maxwell; Large, William G.; Leboissetier, Anthony; Long, Matthew; Lu, Jianhua; Masina, Simona; Mishra, Akhilesh; Navarra, Antonio; George Nurser, A. J.; Patara, Lavinia; Samuels, Bonita L.; Sidorenko, Dmitry; Tsujino, Hiroyuki; Uotila, Petteri; Wang, Qiang; Yeager, Steve G.

    2015-09-01

    In the framework of the second phase of the Coordinated Ocean-ice Reference Experiments (CORE-II), we present an analysis of the representation of the Antarctic Circumpolar Current (ACC) and Southern Ocean meridional overturning circulation (MOC) in a suite of seventeen global ocean-sea ice models. We focus on the mean, variability and trends of both the ACC and MOC over the 1958-2007 period, and discuss their relationship with the surface forcing. We aim to quantify the degree of eddy saturation and eddy compensation in the models participating in CORE-II, and compare our results with available observations, previous fine-resolution numerical studies and theoretical constraints. Most models show weak ACC transport sensitivity to changes in forcing during the past five decades, and they can be considered to be in an eddy saturated regime. Larger contrasts arise when considering MOC trends, with a majority of models exhibiting significant strengthening of the MOC during the late 20th and early 21st century. Only a few models show a relatively small sensitivity to forcing changes, responding with an intensified eddy-induced circulation that provides some degree of eddy compensation, while still showing considerable decadal trends. Both ACC and MOC interannual variabilities are largely controlled by the Southern Annular Mode (SAM). Based on these results, models are clustered into two groups. Models with constant or two-dimensional (horizontal) specification of the eddy-induced advection coefficient κ show larger ocean interior decadal trends, larger ACC transport decadal trends and no eddy compensation in the MOC. Eddy-permitting models or models with a three-dimensional time varying κ show smaller changes in isopycnal slopes and associated ACC trends, and partial eddy compensation. As previously argued, a constant in time or space κ is responsible for a poor representation of mesoscale eddy effects and cannot properly simulate the sensitivity of the ACC and MOC

  13. Modification of the deep salinity-maximum in the Southern Ocean by circulation in the Antarctic Circumpolar Current and the Weddell Gyre

    NASA Astrophysics Data System (ADS)

    Donnelly, Matthew; Leach, Harry; Strass, Volker

    2017-07-01

    The evolution of the deep salinity-maximum associated with the Lower Circumpolar Deep Water (LCDW) is assessed using a set of 37 hydrographic sections collected over a 20-year period in the Southern Ocean as part of the WOCE/CLIVAR programme. A circumpolar decrease in the value of the salinity-maximum is observed eastwards from the North Atlantic Deep Water (NADW) in the Atlantic sector of the Southern Ocean through the Indian and Pacific sectors to Drake Passage. Isopycnal mixing processes are limited by circumpolar fronts, and in the Atlantic sector, this acts to limit the direct poleward propagation of the salinity signal. Limited entrainment occurs into the Weddell Gyre, with LCDW entering primarily through the eddy-dominated eastern limb. A vertical mixing coefficient, κV of (2.86 ± 1.06) × 10-4 m2 s-1 and an isopycnal mixing coefficient, κI of (8.97 ± 1.67) × 102 m2 s-1 are calculated for the eastern Indian and Pacific sectors of the Antarctic Circumpolar Current (ACC). A κV of (2.39 ± 2.83) × 10-5 m2 s-1, an order of magnitude smaller, and a κI of (2.47 ± 0.63) × 102 m2 s-1, three times smaller, are calculated for the southern and eastern Weddell Gyre reflecting a more turbulent regime in the ACC and a less turbulent regime in the Weddell Gyre. In agreement with other studies, we conclude that the ACC acts as a barrier to direct meridional transport and mixing in the Atlantic sector evidenced by the eastward propagation of the deep salinity-maximum signal, insulating the Weddell Gyre from short-term changes in NADW characteristics.

  14. Ocean Color Reveals Multi-scale Responses of Phytoplankton to Changing Sea Ice and Ocean Temperatures along the Western Antarctic Peninsula.

    NASA Astrophysics Data System (ADS)

    Kavanaugh, M.; Schofield, O.; Ducklow, H. W.; Doney, S. C.

    2016-02-01

    The western Antarctic Peninsula (WAP) is experiencing dramatic climate change as maritime conditions expand poleward and interact with regional physics and local topography. In situ observations collected by the Palmer LTER project have provided three decades of insight regarding changes in phytoplankton abundance and community structure seasonally at Palmer station, and spatially during annual cruises across the WAP shelf. Despite the challenges with cloud cover and high latitude retrieval, satellite-based phytoplankton observations have extended inference from in situ observations and have improved our understanding of ecological pattern and process in this region. Multi-sensor satellite analyses were conducted to extend in situ observations and determine the multi-scale response of phytoplankton to changes in sea-ice and temperature. At local scales, enhanced phytoplankton standing stock and diatom dominance were evident at canyons, which act as conduits or reservoirs for warm, nutrient rich Upper Circumpolar Deep Water. However, this positive effect was absent during low ice years. At regional scales, sea-ice declines and warming temperatures were evident over the modern satellite era (since 1997) and were consistent with cross-shelf and latitudinal gradients in phytoplankton responses. Shifts towards smaller size classes were evident across the entire shelf, suggesting a decline in export potential. Phytoplankton abundance in the northern WAP decreased over time, and increased in the southern WAP, although the spatial extent of positive response appears to have retreated in the past decade. Thus, while positive responses to sea-ice loss are evident at both local and regional scales, their capacity to offset climate trends appear to be diminishing.

  15. Antarctic Fishes.

    ERIC Educational Resources Information Center

    Eastman, Joseph T.; DeVries, Arthur L.

    1986-01-01

    Explains the adaptations to Antarctic waters that Notothenioidei, a group of advanced bony fishes, have exhibited. Discusses the fishes' mechanisms of production of antifreeze properties and their capacities for neutral buoyancy in water. (ML)

  16. Antarctic Entomology.

    PubMed

    Chown, Steven L; Convey, Peter

    2016-01-01

    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.

  17. Antarctic Fishes.

    ERIC Educational Resources Information Center

    Eastman, Joseph T.; DeVries, Arthur L.

    1986-01-01

    Explains the adaptations to Antarctic waters that Notothenioidei, a group of advanced bony fishes, have exhibited. Discusses the fishes' mechanisms of production of antifreeze properties and their capacities for neutral buoyancy in water. (ML)

  18. 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

  19. Vulnerability of the calcifying larval stage of the Antarctic sea urchin Sterechinus neumayeri to near-future ocean acidification and warming.

    PubMed

    Byrne, Maria; Ho, Melanie A; Koleits, Lucas; Price, Casandra; King, Catherine K; Virtue, Patti; Tilbrook, Bronte; Lamare, Miles

    2013-07-01

    Stenothermal polar benthic marine invertebrates are highly sensitive to environmental perturbations but little is known about potential synergistic effects of concurrent ocean warming and acidification on development of their embryos and larvae. We examined the effects of these stressors on development to the calcifying larval stage in the Antarctic sea urchin Sterechinus neumayeri in embryos reared in present and future (2100+) ocean conditions from fertilization. Embryos were reared in 2 temperature (ambient: -1.0 °C, + 2 °C : 1.0 °C) and 3 pH (ambient: pH 8.0, -0.2-0.4 pH units: 7.8,7.6) levels. Principle coordinates analysis on five larval metrics showed a significant effect of temperature and pH on the pattern of growth. Within each temperature, larvae were separated by pH treatment, a pattern primarily influenced by larval arm and body length. Growth was accelerated by temperature with a 20-28% increase in postoral (PO) length at +2 °C across all pH levels. Growth was strongly depressed by reduced pH with a 8-19% decrease in PO length at pH 7.6-7.8 at both temperatures. The boost in growth caused by warming resulted in larvae that were larger than would be observed if acidification was examined in the absence of warming. However, there was no significant interaction between these stressors. The increase in left-right asymmetry and altered body allometry indicated that decreased pH disrupted developmental patterning and acted as a teratogen (agent causing developmental malformation). Decreased developmental success with just a 2 °C warming indicates that development in S. neumayeri is particularly sensitive to increased temperature. Increased temperature also altered larval allometry. Altered body shape impairs swimming and feeding in echinoplutei. In the absence of adaptation, it appears that the larval phase may be a bottleneck for survivorship of S. neumayeri in a changing ocean in a location where poleward migration to escape inhospitable

  20. 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.

  1. 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.

  2. 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

  3. 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

  4. Viral-mediated lysis of microbes and carbon release in the sub-Antarctic and Polar Frontal zones of the Australian Southern Ocean.

    PubMed

    Evans, Claire; Pearce, Imojen; Brussaard, Corina P D

    2009-11-01

    Viral production was determined in the sub-Antarctic zone (SAZ) to the southwest and southeast of Tasmania and in the Polar Frontal zone (PFZ) of the Australian sector of the Southern Ocean during Austral summer (January-February 2007). Concentrations of viruses were the lowest (6.6 x 10(9) particles l(-1)) in the PFZ and the highest (2.1 x 10(10) particles l(-1)) in the eastern SAZ where nutrient input from the East Australian Current (EAC) sustained higher concentrations of bacteria and bacterial production relative to the west. Rates of viral production in the PFZ (1.8 x 10(10) viruses l(-1) day(-1)) were lower than those in the western SAZ (2.5 x 10(10) viruses l(-1) day(-1)). Viral production in the eastern SAZ (2.2 x 10(11) viruses l(-1) day(-1)) was the highest recorded and was approximately one order of magnitude higher than at the other sites. In the western SAZ and PFZ, the percentage of available bacterial biomass lysed by viruses was similar (23.5% and 23% respectively) equating to the release of 3.3 and 2.3 microg carbon l(-1) day(-1) respectively (assuming a burst size of 50 viruses host(-1)). In the eastern SAZ the potential bacterial biomass lysed was higher (on average 40%) and corresponded to the release of 26.5 microg carbon l(-1) day(-1). These findings suggest the importance of the viral shunt in carbon cycling within these regions.

  5. Distribution in the abundance and biomass of shelled pteropods in surface waters of the Indian sector of the Antarctic Ocean in mid-summer

    NASA Astrophysics Data System (ADS)

    Akiha, Fumihiro; Hashida, Gen; Makabe, Ryosuke; Hattori, Hiroshi; Sasaki, Hiroshi

    2017-06-01

    We investigated shelled pteropod abundance and biomass with a 100-μm closing net, and their estimated downward fluxes using a sediment trap installed in a drifter buoy in the Indian sector of the Antarctic Ocean during the austral summer. Over 90% pteropod abundance was distributed in the upper 50 m; 70-100% were immature veligers. Limacina retroversa was dominant in the >0.2 mm individuals north of 60°S, L. helicina dominated south of 62°S, while populations around 60-62°S were mixed. Unidentifiable small Limacina spp. (ssL) were highly abundant in the upper 50 m at 60°S, 63°S, and 64°S on 110°E and 63°S on 115°E, although their estimated particulate organic carbon (POC) biomasses were less than that of Limacina adults. Adult females bearing egg clusters were found in the 0-50 m layer; the veligers likely grew within a short period. The mean downward flux of ssL and veligers at 70 m around 60°S, 110°E was 5.1 ± 1.6 × 103 ind. m-2 d-1 (0.6 ± 0.2 mg C m-2 d-1), which was 3.8% of the integrated ssL and veligers in the upper 70 m, suggesting that at least 4% of the veligers were produced daily in the surface layers. The mid-summer spawned ssL and veligers likely contributed to the subsequent increase in large pteropods in the area.

  6. A Prediction of Increase in Subglacial Volcanism Beneath the West Antarctic Ice Sheet (WAIS) as Future Deglaciation Caused by Ocean Circulation Proceeds

    NASA Astrophysics Data System (ADS)

    Behrendt, J. C.; LeMasurier, W. E.

    2015-12-01

    Many decades of aeromagnetic surveying (e.g. Behrendt, 1964; 2013; and others) over the West Antarctic Ice sheet (WAIS) have shown >1000 high amplitude, shallow source magnetic anomalies interpreted as as indicating subglacial volcanic centers of late Cenozoic age to presently active. Similar anomalies exist over exposed volcanic rocks bordering the WAIS in places.Recent papers (e.g. Wouters et al., 2015; Paolo, et al.; 2015 and others) based on satellite altimetry have shown dramatic thinning and retreat of ice shelves, particularly those bordering the Amundsen and Bellingshausen Seas, caused by melting from circulation of warming sea water. Previous workers have shown that when ice shelves collapse, the ice streams previously dammed by them accelerate an order of magnitude higher velocity, and surface elevation decreases. GRACE satellite interpretations (e.g. Velicogna et al., and others) indicate mass loss of WAIS in recent years.The bed elevation beneath the WAIS deepens inland from the Amundsen and Bellingshausen coasts, although high relief volcanic topography is present in a number of areas beneath the ice.Crowley et a. (2015) have shown that glacial cycles may drive production of oceanic crust by lowering pressure in the mantle resulting in increased melting and magma production. Increased volcanism due to deglaciation in Iceland has apparently produced increased in volcanic activity there. Deglaciation of the Norwegian continental shelf has resulted in faulting of the sea floor and similar faulting has been reported of the Ross Sea shelf following deglaciation there.I suggest here that as the WAIS collapses in the future resulting from climate change, an increase in volcanic activity beneath the ice might be expected. This may provide a feedback mechanism for increase in ice melting.

  7. Formation and evolution of a metasomatized lithospheric root at the motionless Antarctic plate: the case of East Island, Crozet Archipelago (Indian Ocean)

    NASA Astrophysics Data System (ADS)

    Meyzen, Christine; Marzoli, Andrea; Bellieni, Giuliano; Levresse, Gilles

    2016-04-01

    Sitting atop the nearly stagnant Antarctic plate (ca. 6.46 mm/yr), the Crozet archipelago midway between Madagascar and Antarctica constitutes a region of unusually shallow (1543-1756 m below sea level) and thickened oceanic crust (10-16.5 km), high geoid height, and deep low-velocity zone, which may reflect the surface expression of a mantle plume. Here, we present new major and trace element data for Quaternary sub-aerial alkali basalts from East Island, the easterly and oldest island (ca. 9 Ma) of the Crozet archipelago. Crystallization at uppermost mantle depth and phenocryst accumulation have strongly affected their parental magma compositions. Their trace element patterns show a large negative K anomaly relative to Ta-La, moderate depletions in Rb and Ba with respect to Th-U, and heavy rare earth element (HREE) depletions relative to light REE. These characteristics allow limits to be placed upon the composition and mineralogy of their mantle source. The average trace element spectrum of East Island basalts can be matched by melting of about 2 % of a garnet-phlogopite-bearing peridotite source. The stability field of phlogopite restricts melting depth to lithospheric levels. The modelled source composition requires a multistage evolution, where the mantle has been depleted by melt extraction before having been metasomatized by alkali-rich plume melts. The depleted mantle component may be sourced by residual mantle plume remnants stagnated at the melting locus due to a weak lateral flow velocity inside the melting regime, whose accumulation progressively edifies a depleted lithospheric root above the plume core. Low-degree alkali-rich melts are likely derived from the plume source. Such a mantle source evolution may be general to both terrestrial and extraterrestrial environments where the lateral component velocity of the mantle flow field is extremely slow.

  8. Productivity cycles of 200-300 years in the Antarctic Peninsula region: Understanding linkages among the sun, atmosphere, oceans, sea ice, and biota

    USGS Publications Warehouse

    Leventer, A.; Domack, E.W.; Ishman, S.E.; Brachfeld, S.; McClennen, C.E.; Manley, P.

    1996-01-01

    Compared to the rest of the world's oceans, high-resolution late Holocene paleoclimatic data from the Southern Ocean are still rare. We present a multiproxy record from a sediment core retrieved from a deep basin on the western side of the Antarctic Peninsula that reveals a dramatic perspective on paleoclimatic changes over the past 3700 yr. Analyses completed include measurement of magnetic susceptibility and granulometry, bed thickness, particle size, percent organic carbon, bulk density, and microscopic evaluation of diatom and benthic foraminiferal assemblages and abundances. Downcore variability of these parameters demonstrates the significance of both short-term cycles, which recur approximately every 200 yr, and longer term events (???2500 yr cycles) that are most likely related to global climatic fluctuations. In the upper 600 cm of the core, lower values of magnetic susceptibility (MS) are correlated with lower bulk density, the presence of thinly laminated units, specific diatom assemblages, and generally higher total organic carbon content. Below 600 cm, magnetic susceptibility is uniformly low, though variability in other parameters continues. The magnetic susceptibility signal is controlled primarily by dilution of ferromagnetic phases with biosiliceous material. This signal may be enhanced further by dissolution of magnetite in the magnetic susceptibility lows (high total organic carbon). The role of variable primary productivity and its relationship to paleoclimate is assessed through the diatom data. In particular, magnetic susceptibility lows are characterized by higher than normal abundances of Chaetoceros resting spores. Corethron criophilum and/or Rhizosolenia spp. also are found, as is a higher ratio of the most common species of Fragilariopsis versus species of Thalassiosira. These assemblages are indicative of periods of high primary productivity driven by the presence of a melt-water stabilized water column. The 200 yr cyclicity noted in

  9. Dynamic constraints on CO2 uptake by an iron-fertilized Antarctic

    NASA Technical Reports Server (NTRS)

    Peng, Tsung-Hung; Broecker, Wallace S.; Oestlund, H. G.

    1992-01-01

    The topics covered include the following: tracer distribution and dynamics in the Antarctic Ocean; a model of Antarctic and Non-Antarctic Oceans; effects on an anthropogenically affected atmosphere; effects of seasonal iron fertilization; and implications of the South Atlantic Ventilation Experiment C-14 results.

  10. Extent of the Antarctic Continent.

    PubMed

    Press, F; Dewart, G

    1959-02-20

    Group velocities of eartquake-generated Love and Rayleigh waves for certain transantarctic paths are abnormally high when compared with data from other continents. For these paths, the data indicate that at most only three-fourths of the antarctic ice sheet is underlain by continent, the remaining area being oceanic in structure.

  11. Atmospheric electric conductivity measurements over the Indian Ocean during the Indian Antarctic Expedition in 1996-1997

    NASA Astrophysics Data System (ADS)

    Deshpande, C. G.; Kamra, A. K.

    2002-11-01

    The atmospheric electric conductivity measurements made over the Indian Ocean with a Gerdien's apparatus mounted aboard MV Polarbird during the XVI Indian Scientific Expedition in 1996-1997 are reported. Simultaneous three-hourly measurements of aerosol concentrations of 13-1000 nm size and some meteorological parameters are also reported. Latitudinal variation of conductivity along the cruise route shows a minimum at ˜28°S. Further, the variations in conductivity in the 10°N-20°S and 60°-70°S latitudinal belts show opposite trends on the outward and return cruises, which fall near to the onset and withdrawal phases of the northeast monsoon season, respectively. The results are explained on the basis of the well-known northward shift of the subsidence leg of the southern Hadley cell and of the position of the Intertropical Convergence Zone during the months of March-April in this region and the observations of the cyclonic systems near the continent of Antarctica during the period of outward cruise.

  12. Seismic tomographic constraints on the Antarctic-Eastern Australian margin of Gondwanaland and the southwest Pacific oceans

    NASA Astrophysics Data System (ADS)

    Liu, H. F.; Wu, J. E.; Suppe, J.; Renqi, L.; Kanda, R. V. S.

    2014-12-01

    We have mapped a distinct swath of flat slabs at depths of 1900 to 2500 km below present-day West Antarctica and the southernmost Pacific. The slab anomalies occupy a minimum area of 8000 x 5000 km and are distinguishable on multiple global tomography datasets including TX2011 (Grand and Simmons, 2011) and MIT-P08 (Li et al., 2008). When reconstructed within a lower mantle reference, the restored slab positions show a compelling fit opposite the pre-breakup (~185 Ma) southern margin of Gondwanaland from published plate reconstructions (Seton et al., 2012). Here we present a new plate reconstruction with the subducted slab constraints. At ~185 Ma the southern mapped slabs began to subduct under a SSE-moving Eastern Gondwanaland margin formed by Antarctica-Eastern Australia. The northern slabs were subducted during the formation of the new oceans at the Ellice Basin, Osbourn Trough and the present-day Tonga-Kermadec slabs. The mapped flat slabs were completely subducted by ~85 Ma, at which time subduction ceased at the Eastern Australian-Antarctica margin. We mapped subducted slabs by manually picking the midpoints of fast seismic tomographic anomalies and constructing meshed mid-slab surfaces. Slabs were restored to their pre-subduction geometries by structurally unfolding to a spherical Earth model surface. Unfolded slabs were used as plate reconstruction constraints using Gplates software.

  13. Antarctic meteorites

    NASA Astrophysics Data System (ADS)

    Cassidy, W. A.; Rancitelli, L. A.

    1982-04-01

    An abundance of meteorites has been discovered on two sites in the Antarctic which may assist in the study of the origins of meteorites and the history of the solar system. Characteristics particular to those meteorites discovered in this region are explained. These specimens, being well preserved due to the climate, have implications in the study of the cosmic ray flux through time, the meteoroid complex in space, and cosmic ray exposure ages. Implications for the study of the Antarctic, particularly the ice flow, are also discussed. Further discoveries of meteorites in this region are anticipated.

  14. 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

  15. Antarctic crabs: invasion or endurance?

    PubMed

    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 "invasion hypothesis".

  16. 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

  17. 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

    2016-09-06

    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).

  18. Biogeography of Antarctic sea anemones (Anthozoa, Actiniaria): What do they tell us about the origin of the Antarctic benthic fauna?

    NASA Astrophysics Data System (ADS)

    Rodríguez, E.; López-González, P. J.; Gili, J. M.

    2007-08-01

    The present study of the biogeography of the Antarctic sea anemone fauna is based on new records and redescriptions of material collected from the Weddell Sea and Peninsula Antarctica, and on an update of the bibliographic data of the Antarctic and sub-Antarctic regions. The faunal compositions at different levels, the geographic and bathymetric distributions of the sea anemone fauna, and the affinities within the continent and with the sub-Antarctic fauna have been studied. Furthermore, the relationships of the sea anemone fauna, of the Southern Ocean, the Mediterranean Sea and Hawaii have been analysed. In this context, the origin of the Antarctic benthic fauna is discussed.

  19. Multidecadal warming of Antarctic waters.

    PubMed

    Schmidtko, Sunke; Heywood, Karen J; Thompson, Andrew F; Aoki, Shigeru

    2014-12-05

    Decadal trends in the properties of seawater adjacent to Antarctica are poorly known, and the mechanisms responsible for such changes are uncertain. Antarctic ice sheet mass loss is largely driven by ice shelf basal melt, which is influenced by ocean-ice interactions and has been correlated with Antarctic Continental Shelf Bottom Water (ASBW) temperature. We document the spatial distribution of long-term large-scale trends in temperature, salinity, and core depth over the Antarctic continental shelf and slope. Warming at the seabed in the Bellingshausen and Amundsen seas is linked to increased heat content and to a shoaling of the mid-depth temperature maximum over the continental slope, allowing warmer, saltier water greater access to the shelf in recent years. Regions of ASBW warming are those exhibiting increased ice shelf melt. Copyright © 2014, American Association for the Advancement of Science.

  20. 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

  1. Evolving Toward the Next Antarctic Ice Shelf Disintegration: Recent Ice Velocity, Climate, and Ocean Observations of the Larsen B Ice Shelf Remnants

    NASA Astrophysics Data System (ADS)

    Scambos, T. A.; Shuman, C. A.; Truffer, M.; Pettit, E. C.; Huber, B. A.; Haran, T. M.; Ross, R.; Domack, E. W.

    2013-12-01

    Ice shelf / ice tongue disintegrations and break-ups have a major effect on glacier mass balance, and nowhere has this been more evident than in the northern sections of the Larsen Ice Shelf in the Antarctic Peninsula. Ice flux in this region surged 2- to 6-fold after the 1995 and 2002 ice shelf disintegration events, driven by a group of processes based on the presence of extensive surface melt lakes. However, precursor changes in the ice shelves beginning more than a decade before the events have been identified. A new assessment of these provides insight on the earliest causes of ice shelf change. Among the precursor changes are an increase in meltwater lake extent, structural changes in the ice shelf shear margins, grounding line changes, and pre-breakup acceleration of the ice shelves and feeder glaciers. In the aftermath of the 2002 disintegration of the Larsen B, the two large remnant ice shelves at Seal Nunataks (~400 km2) and Scar Inlet (~2400 km2) have also evolved in these ways. These changes have been measured by a combination of in situ automated observation systems (AMIGOS: see Scambos et al., 2013, J. Glaciol.) and remote sensing as part of the Larsen Ice Shelf System, Antarctica (LARISSA) NSF project and NASA Cryosphere Program funding. Ice flow speed on the central Scar Inlet ice shelf has increased 60% between 2002 and 2012 (425 to 675 m/yr), and by 20% (540 to 660 m/yr) just above the grounding line of Flask Glacier, a tributary. Elevation change data from ICESat altimetry and ASTER stereo images show evidence of grounding line movement for Flask between 2003 and 2008, and for Crane Glacier prior to the 2002 break-up. In late 2002, and again in late 2012, major new rifts have formed on the southern portion of the Scar Inlet shelf, and the northwestern shear zone has rapidly evolved. The ice speed increase and the new rifts are inferred to be due to significant structural changes in the ice shelf shear margin on its northern side (concentration of

  2. Antarctic Data Management as Part of the IPY Legacy

    NASA Astrophysics Data System (ADS)

    de Bruin, T.

    2006-12-01

    The Antarctic Treaty states that "scientific observations and results from Antarctica shall be exchanged and made freely available". Antarctica includes the Southern Ocean. In support of this, National Antarctic Data Centres (NADC) are being established to catalogue data sets and to provide information on data sets to scientists and others with interest in Antarctic science. The Joint Committee on Antarctic Data Management (JCADM) was established by the Scientific Committee on Antarctic Research (SCAR) and the Council of Managers of National Antarctic Programs (COMNAP). JCADM comprises representatives of the National Antarctic Data Centres. Currently 30 nations around the world are represented in JCADM. JCADM is responsible for the Antarctic Master Directory (AMD), the internationally accessible, web-based, searchable record of Antarctic and Southern Ocean data set descriptions. The AMD is directly integrated into the international Global Change Master Directory (GCMD) to help further merge Antarctic science into global science. The AMD is a resource for scientists to advertise the data they have collected and to search for data they may need. JCADM is the Antarctic component of the IPY Data Infrastructure, which is presently being developed. This presentation will give an overview of the organization of Antarctic and Southern Ocean data management with sections on the organizational structure of JCADM, contents of the Antarctic Master Directory, relationships to the SCAR Scientific Research Programmes (SRP) and IPY, international embedding and connections with discipline-based peer organizations like the International Oceanographic Data and Information Exchange Committee (IODE). It will focus primarily on the role that an existing infrastructure as JCADM, may play in the development of the IPY Data Infrastructure and will provide considerations for IPY data management, based on the experiences in Antarctic and oceanographic data management.

  3. Breakup of Pack Ice, Antarctic Ice Shelf

    NASA Technical Reports Server (NTRS)

    1991-01-01

    Breakup of Pack Ice along the periphery of the Antarctic Ice Shelf (53.5S, 3.0E) produced this mosaic of ice floes off the Antarctic Ice Shelf. Strong offshore winds, probably associated with strong katabatic downdrafts from the interior of the continent, are seen peeling off the edges of the ice shelf into long filamets of sea ice, icebergs, bergy bits and growlers to flow northward into the South Atlantic Ocean. 53.5S, 3.0E

  4. The changing form of Antarctic biodiversity.

    PubMed

    Chown, Steven L; Clarke, Andrew; Fraser, Ceridwen I; Cary, S Craig; Moon, Katherine L; McGeoch, Melodie A

    2015-06-25

    Antarctic biodiversity is much more extensive, ecologically diverse and biogeographically structured than previously thought. Understanding of how this diversity is distributed in marine and terrestrial systems, the mechanisms underlying its spatial variation, and the significance of the microbiota is growing rapidly. Broadly recognizable drivers of diversity variation include energy availability and historical refugia. The impacts of local human activities and global environmental change nonetheless pose challenges to the current and future understanding of Antarctic biodiversity. Life in the Antarctic and the Southern Ocean is surprisingly rich, and as much at risk from environmental change as it is elsewhere.

  5. JCADM, new directions in Antarctic data management

    NASA Astrophysics Data System (ADS)

    Campbell, H.; de Bruin, T. F.

    2008-12-01

    The Joint Committee on Antarctic Data Management (JCADM) was established by the Scientific Committee on Antarctic Research (SCAR) and the Council of Managers of National Antarctic Programs (COMNAP), to assist in the fulfilment of the data management obligations imposed by the Antarctic Treaty (section III.1.c): "Scientific observations and results from Antarctica shall be exchanged and made freely available." JCADM comprises representatives of the National Antarctic Data Centres or national points of contact. Currently 31 nations around the world are represented in JCADM. So far, JCADM has been focussing on the coordination of the Antarctic Master Directory (AMD), the internationally accessible, web-based, searchable record of Antarctic and Southern Ocean data set descriptions. The AMD is directly integrated into the international Global Change Master Directory (GCMD) to help further merge Antarctic science into global science. The AMD is a resource for scientists to advertise the data they have collected and to search for data they may need. Currently, JCADM is in a transition phase, moving forward to provide data access. Existing systems and web services technology will be used as much as possible, to increase efficiency and prevent 're-inventing the wheel' This poster will give an overview of this process, the current status and the expected results.

  6. Climate sensitivity of the Antarctic ventilation

    NASA Astrophysics Data System (ADS)

    Ito, T.; Lynch-Stieglitz, J.

    2014-12-01

    Simple box models of ocean-atmosphere carbon cycle predict that Antarctic ventilation can regulate the steady-state atmospheric CO2 through its control over the biological carbon storage in the deep ocean. A weakened upwelling would lead to a more complete nutrient utilization at the surface and an increased retention of biogenic carbon in the deep ocean. We perform a suite of numerical sensitivity experiments using a coupled seaice and global ocean circulation model to better understand what regulates the Antarctic ventilation and its link to glacial climate. The model is first spun up with a modern climatological surface forcing, which exhibits a multi-decadal oscillation, where the Southern Ocean is heated from below through the influx of warm and salty North Atlantic Deep Water, and the accumulation of heat induces intermittent convective overturning. Through the sensitivity experiments, we explore and illustrate the rich and complex behavior of the Antarctic ventilation and its response to the northern sinking, the surface wind stress, and the global mean temperature. When the northern sinking is weakened by a freshwater perturbation, the intermittent convection events are suppressed as the heat source is reduced. When the atmospheric temperature is lowered uniformly, the Antarctic seaice extent increases and the southern overturning weakens on centennial timescales. However, the convective overturning rebounds on the millennial timescale if the northern sinking is active. We will discuss implications of our results to the deep ventilation of the Southern Ocean and its impact on the ocean carbon storage.

  7. Antarctic Genomics

    PubMed Central

    Clarke, Andrew; Cockell, Charles S.; Convey, Peter; Detrich III, H. William; Fraser, Keiron P. P.; Johnston, Ian A.; Methe, Barbara A.; Murray, Alison E.; Peck, Lloyd S.; Römisch, Karin; Rogers, Alex D.

    2004-01-01

    With the development of genomic science and its battery of technologies, polar biology stands on the threshold of a revolution, one that will enable the investigation of important questions of unprecedented scope and with extraordinary depth and precision. The exotic organisms of polar ecosystems are ideal candidates for genomic analysis. Through such analyses, it will be possible to learn not only the novel features that enable polar organisms to survive, and indeed thrive, in their extreme environments, but also fundamental biological principles that are common to most, if not all, organisms. This article aims to review recent developments in Antarctic genomics and to demonstrate the global context of such studies. PMID:18629155

  8. Antarctic micrometeorites

    NASA Technical Reports Server (NTRS)

    Kurat, G.; Koeberl, C.; Presper, T.; Brandstaetter, F.; Maurette, Michel

    1994-01-01

    Micrometeoroids in the size range 50-500 micron dominate the flux onto the Earth. Contrary to theoretical predictions, many of them survive atmospheric entry almost unchanged. Such micrometeorites can be collected from the Antarctic ice sheet where they account for a surprisingly large proportion of the total dust content of the ice. Early studies of this important class of extraterrestrial material have revealed that some Antarctic micrometeorites are similar to CM chondrites in chemical bulk composition and mineral composition, and a few seem to resemble CI chondrites. However, none of the micrometeorites investigated so far match CM or CI chondrites exactly, nor is there a match between average bulk micrometeorite composition and that of any other chondrite class. Also, the micrometeorite mineral chemistry is different from that of carbonaceous chondrites. Several elements are depleted in micrometeorites as compared to carbonaceous chondrites and some are enriched. The question arises whether these differences are pristine or if some of them are of secondary origin. On the basis of our data we will attempt to answer these questions, some of which have been addressed by us before.

  9. Improving Antarctic infrastructure

    NASA Astrophysics Data System (ADS)

    Showstack, Randy

    2012-07-01

    Noting that U.S. activities in Antarctica “are very well managed but suffer from an aging infrastructure, lack of a capital budget, and the effects of operating in an extremely unforgiving environment,” a 23 July report from the U.S. Antarctic Program Blue Ribbon Panel recommends a number of measures to improve the infrastructure, logistics, and other concerns. The panel's recommendations include continued use of the McMurdo, South Pole, and Palmer stations as the primary U.S. science and logistics hubs in Antarctica—because there are no reasonable alternatives, according to the panel—while upgrading or replacing some facilities, restoring the U.S. polar ocean feet, implementing state of-the-art logistics and transportation support, and establishing a long-term facilities capital plan and budget for the U.S. Antarctic Program. “The essence of our findings is that the lack of capital budgeting has placed operations at McMurdo, and to a somewhat lesser extent at Palmer Station, in unnecessary jeopardy—at least in terms of prolonged inefficiency due to deteriorating or otherwise inadequate physical assets,” the panel wrote in the cover letter accompanying the report entitled, More and Better Science in Antarctica Through Increased Logistical Effectiveness. “The Antarctica Blue Ribbon Panel encourages us to take a hard look at how we support Antarctic science and to make the structural changes, however difficult in the current fiscal environment, that will allow us to do more science in the future,” said U.S. National Science Foundation (NSF) Director Subra Suresh.

  10. The effect of changing wind forcing on Antarctic ice shelf melting in high-resolution, global sea ice-ocean simulations with the Accelerated Climate Model for Energy (ACME)

    NASA Astrophysics Data System (ADS)

    Asay-Davis, Xylar; Price, Stephen; Petersen, Mark; Wolfe, Jonathan

    2017-04-01

    The capability for simulating sub-ice shelf circulation and submarine melting and freezing has recently been added to the U.S. Department of Energy's Accelerated Climate Model for Energy (ACME). With this new capability, we use an eddy permitting ocean model to conduct two sets of simulations in the spirit of Spence et al. (GRL, 41, 2014), who demonstrate increased warm water upwelling along the Antarctic coast in response to poleward shifting and strengthening of Southern Ocean westerly winds. These characteristics, symptomatic of a positive Southern Annular Mode (SAM), are projected to continue into the 21st century under anthropogenic climate change (Fyfe et al., J. Clim., 20, 2007). In our first simulation, we force the climate model using the standard CORE interannual forcing dataset (Large and Yeager; Clim. Dyn., 33, 2009). In our second simulation, we force our climate model using an altered version of CORE interannual forcing, based on the latter half of the full time series, which we take as a proxy for a future climate state biased towards a positive SAM. We compare ocean model states and sub-ice shelf melt rates with observations, exploring sources of model biases as well as the effects of the two forcing scenarios.

  11. The SCAR Standing Committee on Antarctic Data Management - new directions in access to Antarctic research data

    NASA Astrophysics Data System (ADS)

    de Bruin, T.

    2009-04-01

    The SCAR Standing Committee on Antarctic Data Management (SC-ADM) was established by the Scientific Committee on Antarctic Research (SCAR) and the Council of Managers of National Antarctic Programs (COMNAP), to assist in the fulfillment of the data management obligations imposed by the Antarctic Treaty (section III.1.c): "Scientific observations and results from Antarctica shall be exchanged and made freely available." SC-ADM comprises representatives of the National Antarctic Data Centres or national points of contact. Currently 31 nations around the world are represented in SC-ADM. So far, SC-ADM has been focussing on the coordination of the Antarctic Master Directory (AMD), the internationally accessible, web-based, searchable record of Antarctic and Southern Ocean data set descriptions. The AMD is directly integrated into the international Global Change Master Directory (GCMD) to help further merge Antarctic science into global science. The AMD is a resource for scientists to advertise the data they have collected and to search for data they may need. Currently, SC-ADM is in a transition phase, moving forward to provide data access. Existing systems and web services technology will be used as much as possible, to increase efficiency and prevent 're-inventing the wheel' This poster will give an overview of this process, the current status and the expected results.

  12. Adult antarctic krill feeding at abyssal depths.

    PubMed

    Clarke, Andrew; Tyler, Paul A

    2008-02-26

    Antarctic krill (Euphausia superba) is a large euphausiid, widely distributed within the Southern Ocean [1], and a key species in the Antarctic food web [2]. The Discovery Investigations in the early 20(th) century, coupled with subsequent work with both nets and echosounders, indicated that the bulk of the population of postlarval krill is typically confined to the top 150 m of the water column [1, 3, 4]. Here, we report for the first time the existence of significant numbers of Antarctic krill feeding actively at abyssal depths in the Southern Ocean. Biological observations from the deep-water remotely operated vehicle Isis in the austral summer of 2006/07 have revealed the presence of adult krill (Euphausia superba Dana), including gravid females, at unprecedented depths in Marguerite Bay, western Antarctic Peninsula. Adult krill were found close to the seabed at all depths but were absent from fjords close inshore. At all locations where krill were detected they were seen to be actively feeding, and at many locations there were exuviae (cast molts). These observations revise significantly our understanding of the depth distribution and ecology of Antarctic krill, a central organism in the Southern Ocean ecosystem.

  13. Antarctic analogs for Enceladus

    NASA Astrophysics Data System (ADS)

    Murray, A. E.; Andersen, D. T.; McKay, C. P.

    2014-12-01

    Enceladus is a new world for Astrobiology. The Cassini discovery of the icy plume emanating from the South Polar region indicates an active world, where detection of water, organics, sodium, and nano-particle silica in the plume strongly suggests that the source is a subsurface salty ocean reservoir. Recent gravity data from Cassini confirms the presence of a regional sea extending north to 50°S. An ocean habitat under a thick ice cover is perhaps a recurring theme in the Outer Solar System, but what makes Enceladus unique is that the plume jetting out into space is carrying samples of this ocean. Therefore, through the study of Enceladus' plumes we can gain new insights not only of a possible habitable world in the Solar Systems, but also about the formation and evolution of other icy-satellites. Cassini has been able to fly through this plume - effectively sampling the ocean. It is time to plan for future missions that do more detailed analyses, possibly return samples back to Earth and search for evidence of life. To help prepare for such missions, the need for earth-based analog environments is essential for logistical, methodological (life detection) and theoretical development. We have undertaken studies of two terrestrial environments that are close analogs to Enceladus' ocean: Lake Vida and Lake Untersee - two ice-sealed Antarctic lakes that represent physical, chemical and possibly biological analogs for Enceladus. By studying the diverse biology and physical and chemical constraints to life in these two unique lakes we will begin to understand the potential habitability of Enceladus and other icy moons, including possible sources of nutrients and energy, which together with liquid water are the key ingredients for life. Analog research such as this will also enable us to develop and test new strategies to search for evidence of life on Enceladus.

  14. Sea-surface temperature and sea ice distribution of the Southern Ocean at the EPILOG Last Glacial Maximum—a circum-Antarctic view based on siliceous microfossil records

    NASA Astrophysics Data System (ADS)

    Gersonde, Rainer; Crosta, Xavier; Abelmann, Andrea; Armand, Leanne

    2005-04-01

    Based on the quantitative study of diatoms and radiolarians, summer sea-surface temperature (SSST) and sea ice distribution were estimated from 122 sediment core localities in the Atlantic, Indian and Pacific sectors of the Southern Ocean to reconstruct the last glacial environment at the EPILOG (19.5-16.0 ka or 23 000-19 000 cal yr. B.P.) time-slice. The statistical methods applied include the Imbrie and Kipp Method, the Modern Analog Technique and the General Additive Model. Summer SSTs reveal greater surface-water cooling than reconstructed by CLIMAP (Geol. Soc. Am. Map Chart. Ser. MC-36 (1981) 1), reaching a maximum (4-5 °C) in the present Subantarctic Zone of the Atlantic and Indian sector. The reconstruction of maximum winter sea ice (WSI) extent is in accordance with CLIMAP, showing an expansion of the WSI field by around 100% compared to the present. Although only limited information is available, the data clearly show that CLIMAP strongly overestimated the glacial summer sea ice extent. As a result of the northward expansion of Antarctic cold waters by 5-10° in latitude and a relatively small displacement of the Subtropical Front, thermal gradients were steepened during the last glacial in the northern zone of the Southern Ocean. Such reconstruction may, however, be inapposite for the Pacific sector. The few data available indicate reduced cooling in the southern Pacific and give suggestion for a non-uniform cooling of the glacial Southern Ocean. This study is part of MARGO, a multiproxy approach for the reconstruction of the glacial ocean surface.

  15. Year-round records of gas and particulate carboxylic acids (formate and acetate) in the boundary layer at Dumont d'Urville (coastal Antarctica): Production of carboxylic acids from biogenic NMHC emissions from the Antarctic ocean

    NASA Astrophysics Data System (ADS)

    Legrand, M.; Preunkert, S.; Jourdain, B.

    2003-04-01

    Multiple year-round concentrations of acetic and formic acids were measured both in gas and aerosol phases at Dumont d'Urville (DDU, a coastal Antarctic site: 66^o40'S, 140^o01'E) by using mist chamber and aerosol filter sampling. Aerosol levels of the 2 carboxylates range from less than one ng m-3 in winter to 5--10 ng m-3 in summer. Comparison with gas phase concentrations shows that almost 99% of the 2 carboxylic acids are present in the gas phase. Concentrations of formic acid in the gas phase are minima in June--July (70 ng m-3) and increase regularly towards summer months when levels reach ˜400 ng m-3. Concentrations of acetic acid in the gas phase exhibit a more well-marked seasonal cycle with values remaining close to 50 ng m-3 from April to October and strongly increase during summer months (mean value of 800 ng m-3). Such a strong seasonal cycle of carboxylic acids in the high southern latitude marine boundary layer displays with observations made at numerous continental sites where a more weak seasonality is generally observed. It is suggested that carboxylic acids present at DDU mainly originate from biogenic emissions from the Antarctic ocean which are expected to closely follow annual cycle of the sea ice extent and solar radiation, affecting in particular photochemical production of alkenes from dissolved organic carbon released from phytoplancton. Summer levels of carboxylic acids are discussed in terms of air-sea fluxes of NMHCs and photochemical production of carboxylic acids from ozone-alkene reactions and HO_2 reaction with peroxyacetal radical in these poor NOx environments.

  16. Development of the Circum-Antarctic Current

    USGS Publications Warehouse

    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.

    1974-01-01

    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 Soulth Tasman Rise. Australia had commenced drifting northward from Antarctica 20 million years before this.

  17. 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.

  18. Sub-Antarctic glacier extensions in the Kerguelen region (49°S, Indian Ocean) over the past 24,000 years constrained by 36Cl moraine dating

    NASA Astrophysics Data System (ADS)

    Jomelli, Vincent; Mokadem, Fatima; Schimmelpfennig, Irene; Chapron, Emmanuel; Rinterknecht, Vincent; Favier, Vincent; Verfaillie, Deborah; Brunstein, Daniel; Legentil, Claude; Michel, Elisabeth; Swingedouw, Didier; Jaouen, Alain; Aumaitre, Georges; Bourlès, Didier L.; Keddadouche, Karim

    2017-04-01

    Similar to many other regions in the world, glaciers in the southern sub-polar regions are currently retreating. In the Kerguelen Islands (49°S, 69°E), the mass balance of the Cook Ice Cap (CIC), the largest ice cap in this region, experienced dramatic shrinking between 1960 and 2013 with retreat rates among the highest in the world. This observation needs to be evaluated in a long-term context. However, data on the past glacier extents are sparse in the sub-Antarctic regions. To investigate the deglaciation pattern since the Last Glacial Maximum (LGM) period, we present the first 13 cosmogenic 36Cl surface exposure ages from four sites in the Kerguelen Islands. The 36Cl ages from erratic and moraine boulders span from 24.4 ± 2.7 ka to 0.3 ± 0.1 ka. We combined these ages with existing glacio-marine radiocarbon ages and bathymetric data to document the temporal and spatial changes of the island's glacial history. Ice began to retreat on the main island before 24.4 ± 2.7 ka until around the time of the Antarctic Cold Reversal (ACR) period (∼14.5-12.9 ka), during which the Bontemps moraine was formed by the advance of a CIC outlet glacier. Deglaciation continued during the Holocene probably until 3 ka with evidence of minor advances during the last millennium. This chronology is in pace with major changes in δ18O in a recent West Antarctica ice core record, showing that Kerguelen Islands glaciers are particularly sensitive and relevant to document climate change in the southern polar regions.

  19. Controls and variability of solute and sedimentary fluxes in Antarctic and sub-Antarctic Environments

    NASA Astrophysics Data System (ADS)

    Zwolinski, Zbigniew

    2015-04-01

    The currently prepared SEDIBUD Book on "Source-to-Sink Fluxes in Undisturbed Cold Environments" (edited by Achim A. Beylich, John C. Dixon and Zbigniew Zwolinski and published by Cambridge University Press) is summarizing and synthesizing the achievements of the International Association of Geomorphologists` (I.A.G./A.I.G.) Working Group SEDIBUD (Sediment Budgets in Cold Environments), which has been active since 2005 (http://www.geomorph.org/wg/wgsb.html). The book comprises five parts. One of them is part about sub-Antarctic and Antarctic Environments. This part "Sub-Antarctic and Antarctic Environments" describes two different environments, namely oceanic and continental ones. Each part contains results of research on environmental drivers and rates of contemporary solute and sedimentary fluxes in selected sites. Apart from describing the environmental conditions of the whole continent of Antarctica and sub-Antarctic islands (Zb.Zwolinski, M.Kejna, A.N.Lastochkin, A.Zhirov, S.Boltramovich) this part of the book characterizes terrestrial polar oases free from multi-year ice and snow covers (Zb.Zwolinski). The detailed results of geoecological and sedimentological research come from different parts of Antarctica. Antarctic continental shelf (E.Isla) is an example of sub-Antarctic oceanic environment. South Shetlands, especially King George Island (Zb.Zwolinski, M.Kejna, G.Rachlewicz, I.Sobota, J.Szpikowski), is an example of sub-Antarctic terrestrial environment. Antarctic Peninsula (G.Vieira, M.Francelino, J.C.Fernandes) and surroundings of McMurdo Dry Valleys (W.B.Lyons, K.A.Welch, J.Levy, A.Fountain, D.McKnight) are examples of Antarctic continental environments. The key goals of the Antarctic and sub-Antarctic book chapters are following: (i) identify the main environmental drivers and rates of contemporary solute and sedimentary fluxes, and (ii) model possible effects of projected climate change on solute and sedimentary fluxes in cold climate environments

  20. Examining Differences in Arctic and Antarctic Sea Ice Change

    NASA Astrophysics Data System (ADS)

    Nghiem, S. V.; Rigor, I. G.; Clemente-Colon, P.; Neumann, G.; Li, P.

    2015-12-01

    The paradox of the rapid reduction of Arctic sea ice versus the stability (or slight increase) of Antarctic sea ice remains a challenge in the cryospheric science research community. Here we start by reviewing a number of explanations that have been suggested by different researchers and authors. One suggestion is that stratospheric ozone depletion may affect atmospheric circulation and wind patterns such as the Southern Annular Mode, and thereby sustaining the Antarctic sea ice cover. The reduction of salinity and density in the near-surface layer may weaken the convective mixing of cold and warmer waters, and thus maintaining regions of no warming around the Antarctic. A decrease in sea ice growth may reduce salt rejection and upper-ocean density to enhance thermohalocline stratification, and thus supporting Antarctic sea ice production. Melt water from Antarctic ice shelves collects in a cool and fresh surface layer to shield the surface ocean from the warmer deeper waters, and thus leading to an expansion of Antarctic sea ice. Also, wind effects may positively contribute to Antarctic sea ice growth. Moreover, Antarctica lacks of additional heat sources such as warm river discharge to melt sea ice as opposed to the case in the Arctic. Despite of these suggested explanations, factors that can consistently and persistently maintains the stability of sea ice still need to be identified for the Antarctic, which are opposed to factors that help accelerate sea ice loss in the Arctic. In this respect, using decadal observations from multiple satellite datasets, we examine differences in sea ice properties and distributions, together with dynamic and thermodynamic processes and interactions with land, ocean, and atmosphere, causing differences in Arctic and Antarctic sea ice change to contribute to resolving the Arctic-Antarctic sea ice paradox.

  1. Heavy metals in Antarctic organisms

    SciTech Connect

    Moreno, J.E.A. de; Moreno, V.J.; Gerpe, M.S.; Vodopivez, C.

    1997-02-01

    To evaluate levels of essential (zinc and copper) and non-essential (mercury and cadmium) heavy metals, 34 species of organisms from different areas close to the Antarctic Peninsula were analysed. These included algae, filter-feeders, omnivorous invertebrates and vertebrates. Mercury was not detected, while cadmium was found in the majority of organisms analysed (detection limit was 0.05 ppm for both metals). The highest cadmium concentration was observed in the starfish Odontaster validus. Anthozoans, sipunculids and nudibranchs showed maximum levels of zinc, while the highest copper level was found in the gastropod Trophon brevispira. Mercury and cadmium levels in fishes were below the detection limit. Concentrations of essential and non-essential metals in birds were highest in liver followed by muscle and eggs. Cadmium and mercury levels in muscle of southern elephant seals were above the detection limit, whereas in Antarctic fur seals they were below it. The objective of the study was to gather baseline information for metals in Antarctic Ocean biota that may be needed to detect, measure and monitor future environmental changes. 46 refs., 7 figs., 8 tabs.

  2. Arctic and Antarctic Ice Pack Changes during the Past Decade from a High Resolution Global Coupled Sea Ice-Ocean Model

    NASA Astrophysics Data System (ADS)

    Ivanova, D. P.; McClean, J. L.; Thoppil, P.; Hunke, E.; Stark, D.; Maltrud, M. E.; Lipscomb, W.

    2004-12-01

    Changes over the past decade in the global ice pack are analyzed using a coupled ice-ocean model and observational data sets. The model consists of the latest versions of the Los Alamos Parallel Ocean Program (POP) and sea ice model (CICE) and is configured on a moderately high-resolution global grid (0.4° and 40 vertical levels). A model simulation forced with high frequency daily NCEP/NCAR atmospheric fields was integrated for 23 years (1979-2002). Following a decade-long ice spin-up, the model's ability to reproduce observed ice extent, ice thickness and ice drift distributions is evaluated by statistical comparisons using satellite, upward looking sonar and ice drift buoy data. In particular, the realism of the ice mean state and variability on time scales from daily to interannual are examined. To better understand ocean-ice interaction processes, coupled model results are compared to stand alone integrations of the ice and ocean models. Mean ice states are examined during the positive/negative phases of the North Atlantic Oscillation and Arctic Oscillation in the last decade of the coupled simulation. Particularly ice export from the Fram and Bering Straits during these phases will be considered.

  3. Cryosphere: Warming ocean erodes ice sheets

    NASA Astrophysics Data System (ADS)

    Kusahara, Kazuya

    2016-01-01

    Antarctic ice sheets are a key player in sea-level rise in a warming climate. Now an ice-sheet modelling study clearly demonstrates that an Antarctic ice sheet/shelf system in the Atlantic Ocean will be regulated by the warming of the surrounding Southern Ocean, not by marine-ice-sheet instability.

  4. Antarctic culture: 50 years of Antarctic expeditions.

    PubMed

    Sarris, Aspa

    2007-09-01

    Analyses of data collected on returned Australian Antarctic personnel were conducted to examine links between personality traits, perceptions of Antarctic station culture, and perceptions of subjective fit with Antarctic station life and culture. Participants were 103 men who participated in Australian National Antarctic Research Expeditions (ANARE) over a 50-yr period from 1950 to 2000 representing the first 50 yr of ANARE and all positions and occupations included in Australian Antarctic expeditions. Participants completed self-report measures of personality, organizational culture, and subjective fit. Results showed that those who described the culture as satisfaction-oriented (more friendly and participatory) reported better fit, increased satisfaction with their group membership, and less role conflict in terms of their work role. Results also showed a relationship between personality, perceptions of behavioral norms and expectations, and perceived fit. Specifically, openness and perceptions of station culture as satisfaction-oriented were identified as predictors of good fit with station life and culture. The implications of the results for Antarctic personnel selection and recruitment are discussed and the importance of further research in other analogous isolated, confined, and extreme settings is highlighted.

  5. The Antarctic ozone hole

    NASA Astrophysics Data System (ADS)

    Molina, Mario J.

    Observations of Antarctic ozone levels and the discovery of a hole in the Antarctic region are examined. The effects of chlorofluorocarbons (CFCs) on the level of stratospheric ozone are analyzed. Three cycles explaining the cause of ozone depletion in the poles are proposed. A comparison of field data and proposed depletion cycles reveals that the chemical origin of the ozone hole is due to CFCs. The potential global effects of the Antarctic ozone hole are discussed.

  6. Reconsidering connectivity in the sub-Antarctic.

    PubMed

    Moon, Katherine L; Chown, Steven L; Fraser, Ceridwen I

    2017-03-29

    Extreme and remote environments provide useful settings to test ideas about the ecological and evolutionary drivers of biological diversity. In the sub-Antarctic, isolation by geographic, geological and glaciological processes has long been thought to underpin patterns in the region's terrestrial and marine diversity. Molecular studies using increasingly high-resolution data are, however, challenging this perspective, demonstrating that many taxa disperse among distant sub-Antarctic landmasses. Here, we reconsider connectivity in the sub-Antarctic region, identifying which taxa are relatively isolated, which are well connected, and the scales across which this connectivity occurs in both terrestrial and marine systems. Although many organisms show evidence of occasional long-distance, trans-oceanic dispersal, these events are often insufficient to maintain gene flow across the region. Species that do show evidence of connectivity across large distances include both active dispersers and more sedentary species. Overall, connectivity patterns in the sub-Antarctic at intra- and inter-island scales are highly complex, influenced by life-history traits and local dynamics such as relative dispersal capacity and propagule pressure, natal philopatry, feeding associations, the extent of human exploitation, past climate cycles, contemporary climate, and physical barriers to movement. An increasing use of molecular data - particularly genomic data sets that can reveal fine-scale patterns - and more effective international collaboration and communication that facilitates integration of data from across the sub-Antarctic, are providing fresh insights into the processes driving patterns of diversity in the region. These insights offer a platform for assessing the ways in which changing dispersal mechanisms, such as through increasing human activity and changes to wind and ocean circulation, may alter sub-Antarctic biodiversity patterns in the future.

  7. 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.

  8. Instruments and MethodsAutonomous underwater vehicles (AUVs) and investigations of the ice-ocean interface in Antarctic and Arctic waters

    NASA Astrophysics Data System (ADS)

    Dowdeswell, J. A.; Evans, J.; Mugford, R.; Griffiths, G.; McPhail, S.; Millard, N.; Stevenson, P.; Brandon, M. A.; Banks, C.; Heywood, K. J.; Price, M. R.; Dodd, P. A.; Jenkins, A.; Nicholls, K. W.; Hayes, D.; Abrahamsen, E. P.; Tyler, P.; Bett, B.; Jones, D.; Wadhams, P.; Wilkinson, J. P.; Stansfield, K.; Ackley, S.

    are described and examples of observational data collected from each sensor in Arctic or Antarctic waters are given (e.g. of roughness at the underside of floating ice shelves and sea ice).

  9. 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

  10. Cross-disciplinarity in the advance of Antarctic ecosystem research.

    PubMed

    Gutt, J; Isla, E; Bertler, A N; Bodeker, G E; Bracegirdle, T J; Cavanagh, R D; Comiso, J C; Convey, P; Cummings, V; De Conto, R; De Master, D; di Prisco, G; d'Ovidio, F; Griffiths, H J; Khan, A L; López-Martínez, J; Murray, A E; Nielsen, U N; Ott, S; Post, A; Ropert-Coudert, Y; Saucède, T; Scherer, R; Schiaparelli, S; Schloss, I R; Smith, C R; Stefels, J; Stevens, C; Strugnell, J M; Trimborn, S; Verde, C; Verleyen, E; Wall, D H; Wilson, N G; Xavier, J C

    2017-09-29

    The biodiversity, ecosystem services and climate variability of the Antarctic continent and the Southern Ocean are major components of the whole Earth system. Antarctic ecosystems are driven more strongly by the physical environment than many other marine and terrestrial ecosystems. As a consequence, to understand ecological functioning, cross-disciplinary studies are especially important in Antarctic research. The conceptual study presented here is based on a workshop initiated by the Research Programme Antarctic Thresholds - Ecosystem Resilience and Adaptation of the Scientific Committee on Antarctic Research, which focussed on challenges in identifying and applying cross-disciplinary approaches in the Antarctic. Novel ideas and first steps in their implementation were clustered into eight themes. These ranged from scale problems, through risk maps, and organism/ecosystem responses to multiple environmental changes and evolutionary processes. Scaling models and data across different spatial and temporal scales were identified as an overarching challenge. Approaches to bridge gaps in Antarctic research programmes included multi-disciplinary monitoring, linking biomolecular findings and simulated physical environments, as well as integrative ecological modelling. The results of advanced cross-disciplinary approaches can contribute significantly to our knowledge of Antarctic and global ecosystem functioning, the consequences of climate change, and to global assessments that ultimately benefit humankind. Copyright © 2017. Published by Elsevier B.V.

  11. Reaching for the Horizon: Enabling 21st Century Antarctic Science

    NASA Astrophysics Data System (ADS)

    Rogan-Finnemore, M.; Kennicutt, M. C., II; Kim, Y.

    2015-12-01

    The Council of Managers of National Antarctic Programs' (COMNAP) Antarctic Roadmap Challenges(ARC) project translated the 80 highest priority Antarctic and Southern Ocean scientific questionsidentified by the community via the SCAR Antarctic Science Horizon Scan into the highest prioritytechnological, access, infrastructure and logistics needs to enable the necessary research to answer thequestions. A workshop assembled expert and experienced Antarctic scientists and National AntarcticProgram operators from around the globe to discern the highest priority technological needs includingthe current status of development and availability, where the technologies will be utilized in the Antarctic area, at what temporal scales and frequencies the technologies will be employed,and how broadly applicable the technologies are for answering the highest priority scientific questions.Secondly the logistics, access, and infrastructure requirements were defined that are necessary todeliver the science in terms of feasibility including cost and benefit as determined by expected scientific return on investment. Finally, based on consideration of the science objectives and the mix oftechnologies implications for configuring National Antarctic Program logistics capabilities andinfrastructure architecture over the next 20 years were determined. In particular those elements thatwere either of a complexity, requiring long term investments to achieve and/or having an associated cost that realistically can only (or best) be achieved by international coordination, planning and partnerships were identified. Major trends (changes) in logistics, access, and infrastructure requirements were identified that allow for long-term strategic alignment of international capabilities, resources and capacity. The outcomes of this project will be reported.

  12. 75 FR 18110 - Antarctic Marine Living Resources; Use of Centralized-Vessel Monitoring System and Importation of...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-04-09

    ... National Oceanic and Atmospheric Administration 50 CFR Part 300 RIN 0648-AX80 Antarctic Marine Living...: National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration (NOAA), Commerce... facilitate conservation and management of Antarctic Marine Living Resources (AMLR). The regulations: further...

  13. The Antarctic Ozone Hole.

    ERIC Educational Resources Information Center

    Stolarski, Richard S.

    1988-01-01

    Discusses the Airborne Antarctic Ozone Experiment (1987) and the findings of the British Antarctic Survey (1985). Proposes two theories for the appearance of the hole in the ozone layer over Antarctica which appears each spring; air pollution and natural atmospheric shifts. Illustrates the mechanics of both. Supports worldwide chlorofluorocarbon…

  14. The Antarctic Ozone Hole.

    ERIC Educational Resources Information Center

    Stolarski, Richard S.

    1988-01-01

    Discusses the Airborne Antarctic Ozone Experiment (1987) and the findings of the British Antarctic Survey (1985). Proposes two theories for the appearance of the hole in the ozone layer over Antarctica which appears each spring; air pollution and natural atmospheric shifts. Illustrates the mechanics of both. Supports worldwide chlorofluorocarbon…

  15. Antarctic news clips, 1991

    NASA Astrophysics Data System (ADS)

    1991-08-01

    Published stories are presented that sample a year's news coverage of Antarctica. The intent is to provide the U.S. Antarctic Program participants with a digest of current issues as presented by a variety of writers and popular publications. The subject areas covered include the following: earth science; ice studies; stratospheric ozone; astrophysics; life science; operations; education; antarctic treaty issues; and tourism

  16. The Antarctic Ice.

    ERIC Educational Resources Information Center

    Radok, Uwe

    1985-01-01

    The International Antarctic Glaciological Project has collected information on the East Antarctic ice sheet since 1969. Analysis of ice cores revealed climatic history, and radar soundings helped map bedrock of the continent. Computer models of the ice sheet and its changes over time will aid in predicting the future. (DH)

  17. The Antarctic Ice.

    ERIC Educational Resources Information Center

    Radok, Uwe

    1985-01-01

    The International Antarctic Glaciological Project has collected information on the East Antarctic ice sheet since 1969. Analysis of ice cores revealed climatic history, and radar soundings helped map bedrock of the continent. Computer models of the ice sheet and its changes over time will aid in predicting the future. (DH)

  18. Seasonal to decadal pH and fCO2 changes in the subtropical, sub-antarctic and polar waters of the SW Indian ocean

    NASA Astrophysics Data System (ADS)

    Lourantou, A.; Lo Monaco, C.; Brunet, C.; Ridame, C.; Metzl, N.

    2012-04-01

    Human-induced CO2 emissions are constantly increasing and the role of the ocean carbon sink becomes crucial for the global carbon budget (Peters et al., 2011). The Southern Ocean is a key area of carbon sink (Takahashi et al. 2009) and thus more susceptible to pH changes, according to model predictions (Orr et al., 2005; McNeil & Matear, 2008). Little is known from in situ observations. The SW Indian Ocean is being regularly visited in the framework of the OISO (Océan Indien Service d'Observation) program. This extended area is annually a carbon sink (Metzl, 2009; Lourantou and Metzl, 2011). Here we examine three distinct stations located south of the Polar Front (50°S, KERFIX station), in the frontal zone (40°S) and in the Subtropical Zone (30°S). These stations differ by their hydrological properties, their potential in assimilating atmospheric CO2 and their associated nutritional and ecosystem regime, from a HNLC -High Nutrient Low Chlorophyll- area (50°S), to a region of formation of Subantarctic Mode Waters (40°S), and oligotrophic waters in the north (30°S). By using CARINA (Key et al., 2010) and SOCAT (Pfeil et al., in prep.) databases, for the water column and surface waters, respectively, and the addition of recent OISO data, we computed the evolution of pH along depth and time (from 1978- 2010) at these stations. We present: (i) the temporal evolution of the rate of change of computed pH and fCO2 at the 3 stations from surface to deep waters; (ii) a comparison with anthropogenic carbon estimates, Cant (Touratier et al., 2007) and the change in measured Dissolved Inorganic Carbon, DIC; (iii) a comparison with the evolution of chlorophyll a concentrations. Based on these results, we discuss the dominant mechanisms responsible for the changes in pH observed at different depths and latitudes. For KERFIX station we also assess the distinction between seasonality and decadal evolution of biogeochemical parameters. Our first results point towards a

  19. Antarctic Ice Charts, 1987-1988

    DTIC Science & Technology

    1988-01-01

    U.S. Navy has a long and eventful history of polar exploration from Robert E. Peary in the Arctic to Richard E. Byrd in the Antarctic. In recent...environmental information. Since 1976, the National Oceanic and Atmospheric Administration (NOAA) and the Navy have worked together at the Joint Ice Center...to provide the user with reliable weekly hemispheric ice analyses. Both Navy and NOAA personnel with considerable experience in sea ice analysis

  20. Satellites reveal Antarctic mass imbalance

    NASA Astrophysics Data System (ADS)

    Shepherd, A.

    2004-05-01

    Satellite radar observations have revealed a widespread mass imbalance in western Antarctica and rapid thinning of ice shelves at the Antarctic Peninsula. The former shows grounded ice retreat in a region previously considered unstable to such events, and the latter illuminates an ongoing debate as to the mechanism through which ice shelves have disintegrated over the past decade. Both measurements inform us as to the present state of balance of the cryosphere and its interactions with the southern oceans. Since 1992, the Amundsen Sea sector of the West Antarctic Ice Sheet has lost 39 cubic kilometers of its volume each year due to an imbalance between snow accumulation and ice discharge. A flow disturbance is responsible for removing the majority of that ice from the trunks of the Pine Island, Thwaites and Smith glacier drainage systems, raising global sea level by over 1 mm during the past decade alone. The coincidence of rapid ice thinning at the Amundsen Coast and warm circumpolar deep water intrusion in Pine Island Bay, coupled with a ~ 50 cubic kilometre annual freshening of the Ross Sea Gyre downstream, makes ocean melting an attractive proposition for the origin of the regional disturbance. At the same time, the Larsen Ice Shelf surface has lowered by up to 0.27 m per year, in tandem with a period of atmospheric warming and ice shelf collapse. The lowering cannot be explained by increased summer melt-water production alone, and must reflect a loss of basal ice through melting. Ocean temperature measurements close to the ice shelf barrier support this conclusion, making enhanced basal ice melting a likely factor linking the regional climate warming and the successive disintegration of sections of the Larsen Ice Shelf.

  1. Feeding, respiration and egg production rates of copepods during austral spring in the Indian sector of the Antarctic Ocean: role of the zooplankton community in carbon transformation

    NASA Astrophysics Data System (ADS)

    Mayzaud, P.; Razouls, S.; Errhif, A.; Tirelli, V.; Labat, J. P.

    2002-06-01

    During the austral spring period of 1996, the composition, age structure and physiological activity of zooplankton were studied in the Indian sector of the Southern Ocean. Zooplankton biomass ranged from less than 1 g m -2 in the Northern Polar Front Zone (PFZ) to 16 g m -2 near the ice edge in the Seasonal Ice Zone (SIZ). Zooplankton communities were dominated by copepods associated with euphausiid larvae. At all stations, species composition of copepods was dominated in number by small species ( Oithona spp, Ctenocalanus citer). Northern stations were characterized by Calanus simillimus and Metridia lucens. Southern stations showed high abundance of Calanoides acutus, Calanus propinquus and Rhincalanus gigas. Stage distribution was analyzed for the four main contributors to the copepod biomass ( Calanus simillimus, Calanoides acutus, Calanus propinquus and Rhincalanus gigas). Gut pigment content and gut transit time showed a strong day-night periodicity. Gut transit times were usually high with values ranging from 1 h ( Calanus propinquus) to 1 h 30 min ( Rhincalanus gigas). Maximum ingestion rates were recorded for Calanus propinquus and Pleuromamma robusta. Respiration rates were measured for 13 species of copepods and varied from 0.5-0.6 μl O 2 ind -1 day -1 for smaller species to 20-62 μl O 2 ind -1 day -1 for the larger ones. The impact of the copepod population was estimated from the CO 2 produced per m -2 and per day, which showed a release of 4.2-4.5 mmol. It corresponded to a minimum ingestion of 41.4% in the Permanent Open Ocean Zone (POOZ) and 22.6% in the SIZ of the daily primary production. The budget between carbon ingestion and respiratory requirements appears to be nearly balanced, but with the exception of Calanus propinquus, cannot accommodate the addition of the cost of egg production, which only partially relies on food intake. During austral spring, the population studied appeared to rely mostly on phytoplankton as food, though additional

  2. The spatial extent and dynamics of the Antarctic Cold Reversal

    NASA Astrophysics Data System (ADS)

    Pedro, Joel B.; Bostock, Helen C.; Bitz, Cecilia M.; He, Feng; Vandergoes, Marcus J.; Steig, Eric J.; Chase, Brian M.; Krause, Claire E.; Rasmussen, Sune O.; Markle, Bradley R.; Cortese, Giuseppe

    2016-01-01

    Antarctic ice cores show that a millennial-scale cooling event, the Antarctic Cold Reversal (14,700 to 13,000 years ago), interrupted the last deglaciation. The Antarctic Cold Reversal coincides with the Bølling-Allerød warm stage in the North Atlantic, providing an example of the inter-hemispheric coupling of abrupt climate change generally referred to as the bipolar seesaw. However, the ocean-atmosphere dynamics governing this coupling are debated. Here we examine the extent and expression of the Antarctic Cold Reversal in the Southern Hemisphere using a synthesis of 84 palaeoclimate records. We find that the cooling is strongest in the South Atlantic and all regions south of 40° S. At the same time, the terrestrial tropics and subtropics show abrupt hydrologic variations that are significantly correlated with North Atlantic climate changes. Our transient global climate model simulations indicate that the observed extent of Antarctic Cold Reversal cooling can be explained by enhanced northward ocean heat transport from the South to North Atlantic, amplified by the expansion and thickening of sea ice in the Southern Ocean. The hydrologic variations at lower latitudes result from an opposing enhancement of southward heat transport in the atmosphere mediated by the Hadley circulation. Our findings reconcile previous arguments about the relative dominance of ocean and atmospheric heat transports in inter-hemispheric coupling, demonstrating that the spatial pattern of past millennial-scale climate change reflects the superposition of both.

  3. Oceanology of the antarctic continental shelf: Volume 43

    SciTech Connect

    Jacobs, S.S.

    1985-01-01

    This book discusses the seas of the deep continental shelf, which play an important climatic role in sea ice production, deep ocean ventilation and wastage of the Antarctic ice sheet. This volume includes analyses of measurements taken from ships and satellites, and from sea ice and glacial ice. High resolution profiling equipment, long term bottom-moored instruments, continuous remote sensors, geochemical tracers and computer models have provided the basis for new insights into the continental shelf circulation. Color plates and an accompanying GEBCO Circum-Antarctic map effectively portray the continental shelf in relation to the glaciated continent, the sea ice and the surrounding Southern Ocean.

  4. Melting West Antarctic ice-shelves: role of coastal warming versus changes in cavity geometries

    NASA Astrophysics Data System (ADS)

    Jourdain, Nicolas; Mathiot, Pierre; Durand, Gael; Le Sommer, Julien; Spence, Paul

    2015-04-01

    The mass loss of West Antarctic glaciers has accelerated over the last 15 years, most likely in response to ocean warming in Antarctic coastal waters. This oceanic warming in Antarctic coastal waters has recently been suggested to be caused by the positive trend of the Southern Annular Mode. But the mechanisms controlling he changes in melt rates underneath outlet glaciers are still poorly understood. For instance, despite recent developments in glacier modeling, melt rates are usually prescribed in glacier models. This strongly limits the ability of glacier models to predict the future evolution of West Antarctic glaciers. Several ocean models are now able to simulate ocean circulation beneath ice-shelves, therefore allowing a direct study of the mechanisms controlling the changes in melting rates underneath outlet glaciers. Building upon these developments, we here investigate the relative influence of ocean warming in coastal waters and changes in ice-shelves cavern geometries on melting rates underneath West Antarctic glaciers. To this purpose, we use a regional ocean/sea-ice model configuration based on NEMO, centered on the Admundsen sea, that explicitly represents flows in ice-shelves cavities. A series of sensitivity experiments is conducted with different cavern geometries and under different atmospheric forcing scenarios in order to identify the leading mechanism controlling the changes in melt rates underneath West Antarctic glaciers over the 21st century. Our results provide a first assessment on the importance of coupling glacier models to ocean models for predicting the future evolution of outlet glaciers.

  5. Antarctic accumulation seasonality.

    PubMed

    Sime, Louise C; Wolff, Eric W

    2011-11-09

    The resemblance of the orbitally filtered isotope signal from the past 340 kyr in Antarctic ice cores to Northern Hemisphere summer insolation intensity has been used to suggest that the northern hemisphere may drive orbital-scale global climate changes. A recent Letter by Laepple et al. suggests that, contrary to this interpretation, this semblance may instead be explained by weighting the orbitally controlled Antarctic seasonal insolation cycle with a static (present-day) estimate of the seasonal cycle of accumulation. We suggest, however, that both time variability in accumulation seasonality and alternative stable seasonality can markedly alter the weighted insolation signal. This indicates that, if the last 340 kyr of Antarctic accumulation has not always looked like the estimate of precipitation and accumulation seasonality made by Laepple et al., this particular accumulation weighting explanation of the Antarctic orbital-scale isotopic signal might not be robust.

  6. Ice sheets. Volume loss from Antarctic ice shelves is accelerating.

    PubMed

    Paolo, Fernando S; Fricker, Helen A; Padman, Laurie

    2015-04-17

    The floating ice shelves surrounding the Antarctic Ice Sheet restrain the grounded ice-sheet flow. Thinning of an ice shelf reduces this effect, leading to an increase in ice discharge to the ocean. Using 18 years of continuous satellite radar altimeter observations, we have computed decadal-scale changes in ice-shelf thickness around the Antarctic continent. Overall, average ice-shelf volume change accelerated from negligible loss at 25 ± 64 cubic kilometers per year for 1994-2003 to rapid loss of 310 ± 74 cubic kilometers per year for 2003-2012. West Antarctic losses increased by ~70% in the past decade, and earlier volume gain by East Antarctic ice shelves ceased. In the Amundsen and Bellingshausen regions, some ice shelves have lost up to 18% of their thickness in less than two decades.

  7. The Seasonality of Antarctic Sea Ice Trends

    NASA Astrophysics Data System (ADS)

    Holland, P.

    2014-12-01

    Unlike the strong decline in Arctic sea ice, Antarctic sea ice is experiencing a weak overall increase in area that is the residual of opposing regional trends. This study considers the seasonal pattern of these trends. In addition to traditional ice concentration and ice area, temporal rates of change of these quantities are investigated ("intensification" and "expansion," respectively). This is crucial to the attribution of the Antarctic sea ice trends, since changes in wind or thermal forcing directly affect ice areal change, rather than ice area itself. The study shows that diverse regional trends all contribute significantly to the overall Antarctic sea-ice increase. In contrast to the widely-held view of a 'south Pacific dipole', trends in the Weddell and Amundsen-Bellingshausen regions are found to best compensate in magnitude and seasonality. Perhaps most importantly, the largest concentration trends, in autumn, are actually caused by intensification trends during spring. Autumn intensification trends directly oppose autumn concentration trends in most places, seemingly as a result of ice and ocean feedbacks. Further study of changes during the spring melting season is therefore required to unravel the Antarctic sea ice increase.

  8. 2015 Antarctic Maximum Sea Ice Extent Breaks Streak of Record Highs

    NASA Image and Video Library

    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 ...

  9. Was the Antarctic Circumpolar Current initiated by the Cenozoic cooling?

    NASA Astrophysics Data System (ADS)

    Lefebvre, Vincent; Donnadieu, Yannick; Sepulchre, Pierre; Swingedouw, Didier; Zhang, Zongshi

    2013-04-01

    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 modelling 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 used a fully coupled atmosphere-ocean model (FOAM) with a mid-Oligocene geography to depict the response of the ACC to changes in the atmospheric CO2 level. Our results suggest that the opening of southern oceanic gateways does not trigger the onset of the ACC for CO2 typical of the late Eocene (> 840 ppm). We find that 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 favouring the compensation of the Ekman transport, and consequently the ACC. Our results imply that the ACC was initiated after the onset of the Antarctic ice sheet growth, acting as a feedback rather than as a driver of the global cooling.

  10. Microbial mercury methylation in Antarctic sea ice.

    PubMed

    Gionfriddo, Caitlin M; Tate, Michael T; Wick, Ryan R; Schultz, Mark B; Zemla, Adam; Thelen, Michael P; Schofield, Robyn; Krabbenhoft, David P; Holt, Kathryn E; Moreau, John W

    2016-08-01

    Atmospheric deposition of mercury onto sea ice and circumpolar sea water provides mercury for microbial methylation, and contributes to the bioaccumulation of the potent neurotoxin methylmercury in the marine food web. Little is known about the abiotic and biotic controls on microbial mercury methylation in polar marine systems. However, mercury methylation is known to occur alongside photochemical and microbial mercury reduction and subsequent volatilization. Here, we combine mercury speciation measurements of total and methylated mercury with metagenomic analysis of whole-community microbial DNA from Antarctic snow, brine, sea ice and sea water to elucidate potential microbially mediated mercury methylation and volatilization pathways in polar marine environments. Our results identify the marine microaerophilic bacterium Nitrospina as a potential mercury methylator within sea ice. Anaerobic bacteria known to methylate mercury were notably absent from sea-ice metagenomes. We propose that Antarctic sea ice can harbour a microbial source of methylmercury in the Southern Ocean.

  11. Sugars in Antarctic aerosol

    NASA Astrophysics Data System (ADS)

    Barbaro, Elena; Kirchgeorg, Torben; Zangrando, Roberta; Vecchiato, Marco; Piazza, Rossano; Barbante, Carlo; Gambaro, Andrea

    2015-10-01

    The processes and transformations occurring in the Antarctic aerosol during atmospheric transport were described using selected sugars as source tracers. Monosaccharides (arabinose, fructose, galactose, glucose, mannose, ribose, xylose), disaccharides (sucrose, lactose, maltose, lactulose), alcohol-sugars (erythritol, mannitol, ribitol, sorbitol, xylitol, maltitol, galactitol) and anhydrosugars (levoglucosan, mannosan and galactosan) were measured in the Antarctic aerosol collected during four different sampling campaigns. For quantification, a sensitive high-pressure anion exchange chromatography was coupled with a single quadrupole mass spectrometer. The method was validated, showing good accuracy and low method quantification limits. This study describes the first determination of sugars in the Antarctic aerosol. The total mean concentration of sugars in the aerosol collected at the "Mario Zucchelli" coastal station was 140 pg m-3; as for the aerosol collected over the Antarctic plateau during two consecutive sampling campaigns, the concentration amounted to 440 and 438 pg m-3. The study of particle-size distribution allowed us to identify the natural emission from spores or from sea-spray as the main sources of sugars in the coastal area. The enrichment of sugars in the fine fraction of the aerosol collected on the Antarctic plateau is due to the degradation of particles during long-range atmospheric transport. The composition of sugars in the coarse fraction was also investigated in the aerosol collected during the oceanographic cruise.

  12. At-Sea Distribution and Prey Selection of Antarctic Petrels and Commercial Krill Fisheries.

    PubMed

    Descamps, Sébastien; Tarroux, Arnaud; Cherel, Yves; Delord, Karine; Godø, Olaf Rune; Kato, Akiko; Krafft, Bjørn A; Lorentsen, Svein-Håkon; Ropert-Coudert, Yan; Skaret, Georg; Varpe, Øystein

    2016-01-01

    Commercial fisheries may impact marine ecosystems and affect populations of predators like seabirds. In the Southern Ocean, there is an extensive fishery for Antarctic krill Euphausia superba that is projected to increase further. Comparing distribution and prey selection of fishing operations versus predators is needed to predict fishery-related impacts on krill-dependent predators. In this context, it is important to consider not only predators breeding near the fishing grounds but also the ones breeding far away and that disperse during the non-breeding season where they may interact with fisheries. In this study, we first quantified the overlap between the distribution of the Antarctic krill fisheries and the distribution of a krill dependent seabird, the Antarctic petrel Thalassoica antarctica, during both the breeding and non-breeding season. We tracked birds from the world biggest Antarctic petrel colony (Svarthamaren, Dronning Maud Land), located >1000 km from the main fishing areas, during three consecutive seasons. The overall spatial overlap between krill fisheries and Antarctic petrels was limited but varied greatly among and within years, and was high in some periods during the non-breeding season. In a second step, we described the length frequency distribution of Antarctic krill consumed by Antarctic petrels, and compared this with results from fisheries, as well as from diet studies in other krill predators. Krill taken by Antarctic petrels did not differ in size from that taken by trawls or from krill taken by most Antarctic krill predators. Selectivity for specific Antarctic krill stages seems generally low in Antarctic predators. Overall, our results show that competition between Antarctic petrels and krill fisheries is currently likely negligible. However, if krill fisheries are to increase in the future, competition with the Antarctic petrel may occur, even with birds breeding thousands of kilometers away.

  13. At-Sea Distribution and Prey Selection of Antarctic Petrels and Commercial Krill Fisheries

    PubMed Central

    Descamps, Sébastien; Tarroux, Arnaud; Cherel, Yves; Delord, Karine; Godø, Olaf Rune; Kato, Akiko; Krafft, Bjørn A.; Lorentsen, Svein-Håkon; Ropert-Coudert, Yan; Skaret, Georg; Varpe, Øystein

    2016-01-01

    Commercial fisheries may impact marine ecosystems and affect populations of predators like seabirds. In the Southern Ocean, there is an extensive fishery for Antarctic krill Euphausia superba that is projected to increase further. Comparing distribution and prey selection of fishing operations versus predators is needed to predict fishery-related impacts on krill-dependent predators. In this context, it is important to consider not only predators breeding near the fishing grounds but also the ones breeding far away and that disperse during the non-breeding season where they may interact with fisheries. In this study, we first quantified the overlap between the distribution of the Antarctic krill fisheries and the distribution of a krill dependent seabird, the Antarctic petrel Thalassoica antarctica, during both the breeding and non-breeding season. We tracked birds from the world biggest Antarctic petrel colony (Svarthamaren, Dronning Maud Land), located >1000 km from the main fishing areas, during three consecutive seasons. The overall spatial overlap between krill fisheries and Antarctic petrels was limited but varied greatly among and within years, and was high in some periods during the non-breeding season. In a second step, we described the length frequency distribution of Antarctic krill consumed by Antarctic petrels, and compared this with results from fisheries, as well as from diet studies in other krill predators. Krill taken by Antarctic petrels did not differ in size from that taken by trawls or from krill taken by most Antarctic krill predators. Selectivity for specific Antarctic krill stages seems generally low in Antarctic predators. Overall, our results show that competition between Antarctic petrels and krill fisheries is currently likely negligible. However, if krill fisheries are to increase in the future, competition with the Antarctic petrel may occur, even with birds breeding thousands of kilometers away. PMID:27533327

  14. Antarctic Geoscience Initiative

    NASA Astrophysics Data System (ADS)

    Dalziel, Ian W. D.; Zimmerman, Herman B.

    Antarctia has recently been described as a continent surrounded by advice. The advice stems from growing realization of the Antarctic's importance in many aspects of globalscale Earth science. This article outlines a U.S. and international initiative to move solid-Earth scientists from an advisory role to one of acquiring new data bearing on the structure and evolution of the ice-covered Antarctic lithosphere.The initiative has marine, airborne, and terrestrial components; plans for all three are underway. Platforms exist for undertaking the work at sea and in the air, but land geophysical techniques need to be adapted to the Antarctic environment. An international workshop to plan modern over-ice geoscience transects will be convened in Washington, D.C., July 19-22 in conjunction with the 28th International Geological Congress (IGC).

  15. Antarctic Crustal Thickness from Gravity Inversion

    NASA Astrophysics Data System (ADS)

    Vaughan, A. P.; Kusznir, N. J.; Ferraccioli, F.; Jordan, T. A.

    2013-12-01

    Using gravity anomaly inversion, we have produced the first comprehensive regional maps of crustal thickness and oceanic lithosphere distribution for Antarctica and the Southern Ocean. We determine Moho depth, crustal basement thickness, continental lithosphere thinning (1-1/β) and ocean-continent transition location using a 3D spectral domain gravity inversion method, which incorporates a lithosphere thermal gravity anomaly correction. The continental lithosphere thinning distribution, used to define the initial thermal model temperature perturbation is derived from the gravity inversion and uses no a priori isochron information; as a consequence the gravity inversion method provides a prediction of ocean-continent transition location, which is independent of ocean isochron information. The gravity anomaly contribution from ice thickness is included in the gravity inversion, as is the contribution from sediments which assumes a compaction controlled sediment density increase with depth. Data used in the gravity inversion are elevation and bathymetry, free-air gravity anomaly, the most recent Bedmap2 ice thickness and bedrock topography compilation south of 60 degrees south (Fretwell et al., 2013) and relatively sparse constraints on sediment thickness. Our gravity inversion study predicts thick crust (> 45 km) under interior East Antarctica penetrated by narrow continental rifts that feature relatively thinner crust. The East Antarctic Rift System (EARS) is a major Permian to Cretaceous age rift system that appears to extend from the continental margin at the Lambert Rift to the South Pole region, a distance of 2500 km. This is comparable in scale to the well-studied East African rift system. Intermediate crustal thickness with an inferred linear rift fabric is predicted under Coates Land. An extensive region of either thick oceanic crust or highly thinned continental crust is predicted offshore Oates Land and north Victoria Land, and also off West Antarctica

  16. Antarctic marine biodiversity and deep-sea hydrothermal vents.

    PubMed

    Chown, Steven L

    2012-01-01

    The diversity of many marine benthic groups is unlike that of most other taxa. Rather than declining from the tropics to the poles, much of the benthos shows high diversity in the Southern Ocean. Moreover, many species are unique to the Antarctic region. Recent work has shown that this is also true of the communities of Antarctic deep-sea hydrothermal vents. Vent ecosystems have been documented from many sites across the globe, associated with the thermally and chemically variable habitats found around these, typically high temperature, streams that are rich in reduced compounds and polymetallic sulphides. The animal communities of the East Scotia Ridge vent ecosystems are very different to those elsewhere, though the microbiota, which form the basis of vent food webs, show less differentiation. Much of the biological significance of deep-sea hydrothermal vents lies in their biodiversity, the diverse biochemistry of their bacteria, the remarkable symbioses among many of the marine animals and these bacteria, and the prospects that investigations of these systems hold for understanding the conditions that may have led to the first appearance of life. The discovery of diverse and unusual Antarctic hydrothermal vent ecosystems provides opportunities for new understanding in these fields. Moreover, the Antarctic vents south of 60°S benefit from automatic conservation under the Convention on the Conservation of Antarctic Marine Living Resources and the Antarctic Treaty. Other deep-sea hydrothermal vents located in international waters are not protected and may be threatened by growing interests in deep-sea mining.

  17. The ARM West Antarctic Radiation Experiment (AWARE)

    NASA Astrophysics Data System (ADS)

    Lubin, Dan; Bromwich, David; Vogelmann, Andrew; Verlinde, Johannes; Russell, Lynn

    2016-04-01

    West Antarctica is one of the most rapidly warming regions on Earth, and its changing climate in both atmosphere and ocean is linked to loss of Antarctic ice mass and global sea level rise. The specific mechanisms for West Antarctic Ice Sheet (WAIS) warming are not fully understood, but are hypothesized to involve linkage between moisture from Southern Ocean storm tracks and the surface energy balance over the WAIS, and related teleconnections with subtropical and tropical meteorology. This present lack of understanding has motivated a climate science and cloud physics campaign jointly supported by the US National Science Foundation (NSF) and Department of Energy (DOE), called the Atmospheric Radiation Measurement Program (ARM) West Antarctic Radiation Experiment (AWARE). The DOE's second ARM Mobile Facility (AMF2) was deployed to McMurdo Station on Ross Island in November 2015 and will operate through December 2016. The AMF2 includes (1) cloud research radars, both scanning and zenith, operating in the Ka- and X-bands, (2) high spectral resolution and polarized micropulse lidars, and (3) a suite of shortwave and longwave broadband and spectral radiometers. A second suite of instruments is deployed at the WAIS Divide Ice Camp on the West Antarctic plateau during December 2015 and January 2016. The WAIS instrument suite provides (1) measurement of all surface energy balance components, (2) a polarized micropulse lidar and shortwave spectroradiometer, (3) microwave total water column measurement, and (4) four times daily rawinsonde launches which are the first from West Antarctica since 1967. There is a direct linkage between the WAIS instrument suite and the AMF2 at McMurdo, in that air masses originating in Southern Ocean storm tracks that are driven up over the WAIS often subsequently descend over the Ross Ice Shelf and arrive at Ross Island. Preliminary data are already illustrating the prevalence of mixed-phase clouds and their role in the surface energy balance

  18. Relative changes in krill abundance inferred from Antarctic fur seal.

    PubMed

    Huang, Tao; Sun, Liguang; Stark, John; Wang, Yuhong; Cheng, Zhongqi; Yang, Qichao; Sun, Song

    2011-01-01

    Antarctic krill Euphausia superba is a predominant species in the Southern Ocean, it is very sensitive to climate change, and it supports large stocks of fishes, seabirds, seals and whales in Antarctic marine ecosystems. Modern krill stocks have been estimated directly by net hauls and acoustic surveys; the historical krill density especially the long-term one in the Southern Ocean, however, is unknown. Here we inferred the relative krill population changes along the West Antarctic Peninsula (WAP) over the 20th century from the trophic level change of Antarctic fur seal Arctocephalus gazella using stable carbon (δ(13)C) and nitrogen (δ(15)N) isotopes of archival seal hairs. Since Antarctic fur seals feed preferentially on krill, the variation of δ(15)N in seal hair indicates a change in the proportion of krill in the seal's diets and thus the krill availability in local seawater. For the past century, enriching fur seal δ(15)N values indicated decreasing krill availability. This is agreement with direct observation for the past ∼30 years and suggests that the recently documented decline in krill populations began in the early parts of the 20th century. This novel method makes it possible to infer past krill population changes from ancient tissues of krill predators.

  19. Vigorous lateral export of the meltwater outflow from beneath an Antarctic ice shelf.

    PubMed

    Garabato, Alberto C Naveira; Forryan, Alexander; Dutrieux, Pierre; Brannigan, Liam; Biddle, Louise C; Heywood, Karen J; Jenkins, Adrian; Firing, Yvonne L; Kimura, Satoshi

    2017-02-09

    The instability and accelerated melting of the Antarctic Ice Sheet are among the foremost elements of contemporary global climate change. The increased freshwater output from Antarctica is important in determining sea level rise, the fate of Antarctic sea ice and its effect on the Earth's albedo, ongoing changes in global deep-ocean ventilation, and the evolution of Southern Ocean ecosystems and carbon cycling. A key uncertainty in assessing and predicting the impacts of Antarctic Ice Sheet melting concerns the vertical distribution of the exported meltwater. This is usually represented by climate-scale models as a near-surface freshwater input to the ocean, yet measurements around Antarctica reveal the meltwater to be concentrated at deeper levels. Here we use observations of the turbulent properties of the meltwater outflows from beneath a rapidly melting Antarctic ice shelf to identify the mechanism responsible for the depth of the meltwater. We show that the initial ascent of the meltwater outflow from the ice shelf cavity triggers a centrifugal overturning instability that grows by extracting kinetic energy from the lateral shear of the background oceanic flow. The instability promotes vigorous lateral export, rapid dilution by turbulent mixing, and finally settling of meltwater at depth. We use an idealized ocean circulation model to show that this mechanism is relevant to a broad spectrum of Antarctic ice shelves. Our findings demonstrate that the mechanism producing meltwater at depth is a dynamically robust feature of Antarctic melting that should be incorporated into climate-scale models.

  20. Vigorous lateral export of the meltwater outflow from beneath an Antarctic ice shelf

    NASA Astrophysics Data System (ADS)

    Garabato, Alberto C. Naveira; Forryan, Alexander; Dutrieux, Pierre; Brannigan, Liam; Biddle, Louise C.; Heywood, Karen J.; Jenkins, Adrian; Firing, Yvonne L.; Kimura, Satoshi

    2017-01-01

    The instability and accelerated melting of the Antarctic Ice Sheet are among the foremost elements of contemporary global climate change. The increased freshwater output from Antarctica is important in determining sea level rise, the fate of Antarctic sea ice and its effect on the Earth’s albedo, ongoing changes in global deep-ocean ventilation, and the evolution of Southern Ocean ecosystems and carbon cycling. A key uncertainty in assessing and predicting the impacts of Antarctic Ice Sheet melting concerns the vertical distribution of the exported meltwater. This is usually represented by climate-scale models as a near-surface freshwater input to the ocean, yet measurements around Antarctica reveal the meltwater to be concentrated at deeper levels. Here we use observations of the turbulent properties of the meltwater outflows from beneath a rapidly melting Antarctic ice shelf to identify the mechanism responsible for the depth of the meltwater. We show that the initial ascent of the meltwater outflow from the ice shelf cavity triggers a centrifugal overturning instability that grows by extracting kinetic energy from the lateral shear of the background oceanic flow. The instability promotes vigorous lateral export, rapid dilution by turbulent mixing, and finally settling of meltwater at depth. We use an idealized ocean circulation model to show that this mechanism is relevant to a broad spectrum of Antarctic ice shelves. Our findings demonstrate that the mechanism producing meltwater at depth is a dynamically robust feature of Antarctic melting that should be incorporated into climate-scale models.

  1. Antarctic terrestrial ecosystems

    SciTech Connect

    Walton, D.W.H.

    1987-01-01

    The Maritime and Continental Antarctic terrestrial ecosystems are considered in the context of environmental impacts - habitat destruction, alien introductions, and pollution. Four types of pollution are considered: nutrients, radionuclides, inert materials, and noxious chemicals. Their ability to recover from perturbation is discussed in the light of present scientific knowledge, and the methods used to control impacts are reviewed. It is concluded that techniques of waste disposal are still inadequate, adequate training in environmental and conservation principles for Antarctic personnel in many countries is lacking, and scientific investigations may be a much more serious threat than tourism to the integrity of these ecosystems. Some priorities crucial to future management are suggested.

  2. The Southern Ocean silica cycle

    NASA Astrophysics Data System (ADS)

    Tréguer, Paul J.

    2014-11-01

    The Southern Ocean is a major opal sink and plays a key role in the silica cycle of the world ocean. So far however, a complete cycle of silicon in the Southern Ocean has not been published. On one hand, Southern Ocean surface waters receive considerable amounts of silicic acid (dissolved silica, DSi) from the rest of the world ocean through the upwelling of the Circumpolar Deep Water, fed by contributions of deep waters of the Atlantic, Indian, and Pacific Oceans. On the other hand, the Southern Ocean exports a considerable flux of the silicic acid that is not used by diatoms in surface waters through the northward pathways of the Sub-Antarctic Mode Water, of the Antarctic Intermediate Water, and of the Antarctic Bottom Water. Thus the Southern Ocean is a source of DSi for the rest of the world ocean. Here we show that the Southern Ocean is a net importer of DSi: because there is no significant external input of DSi, the flux of DSi imported through the Circumpolar Deep Water pathway compensates the sink flux of biogenic silica in sediments.

  3. Unexpectedly high ultrafine aerosol concentrations above East Antarctic sea ice

    NASA Astrophysics Data System (ADS)

    Humphries, R. S.; Klekociuk, A. R.; Schofield, R.; Keywood, M.; Ward, J.; Wilson, S. R.

    2016-02-01

    Better characterisation of aerosol processes in pristine, natural environments, such as Antarctica, have recently been shown to lead to the largest reduction in uncertainties in our understanding of radiative forcing. Our understanding of aerosols in the Antarctic region is currently based on measurements that are often limited to boundary layer air masses at spatially sparse coastal and continental research stations, with only a handful of studies in the vast sea-ice region. In this paper, the first observational study of sub-micron aerosols in the East Antarctic sea ice region is presented. Measurements were conducted aboard the icebreaker Aurora Australis in spring 2012 and found that boundary layer condensation nuclei (CN3) concentrations exhibited a five-fold increase moving across the polar front, with mean polar cell concentrations of 1130 cm-3 - higher than any observed elsewhere in the Antarctic and Southern Ocean region. The absence of evidence for aerosol growth suggested that nucleation was unlikely to be local. Air parcel trajectories indicated significant influence from the free troposphere above the Antarctic continent, implicating this as the likely nucleation region for surface aerosol, a similar conclusion to previous Antarctic aerosol studies. The highest aerosol concentrations were found to correlate with low-pressure systems, suggesting that the passage of cyclones provided an accelerated pathway, delivering air masses quickly from the free troposphere to the surface. After descent from the Antarctic free troposphere, trajectories suggest that sea-ice boundary layer air masses travelled equatorward into the low-albedo Southern Ocean region, transporting with them emissions and these aerosol nuclei which, after growth, may potentially impact on the region's radiative balance. The high aerosol concentrations and their transport pathways described here, could help reduce the discrepancy currently present between simulations and observations of

  4. Diagnosing Antarctic Fog

    NASA Astrophysics Data System (ADS)

    Lazzara, M. A.

    2010-07-01

    Fog affects aviation and other logistical operations in the Antarctic; nevertheless limited studies have been conducted to understand fog behavior in this part of the world. A study has been conducted in the Ross Island region of Antarctica, the location of McMurdo Station and Scott Base - the main stations of the United States and New Zealand Antarctic programs, respectively. Using tools such as multi-channel satellites observations and supported by in situ radiosonde and ground-based automatic weather station observations, combined with back trajectory and mesoscale numerical models, discover that austral summer fog events are "advective" in temperament. The diagnosis finds a primary source region from the southeast over the Ross Ice Shelf (over 72% of the cases studied) while a minority of cases point toward a secondary fog source region to the north along the Scott Coast of the Ross Sea with influences from the East Antarctic Plateau. Part of this examination confirms existing anecdotes from forecasters and weather observers, while refuting others about fog and its behavior in this environment. This effort marks the beginning of our understanding of Antarctic fog behavior.

  5. Antarctic Atmospheric Infrasound.

    DTIC Science & Technology

    1981-11-30

    A summary is given of the project chronology and the reports describing our research in Antarctic Atmospheric infrasound. Analysis of selected infrasonic signals is discussed and a list is given of all infrasonic waves received on the digital system with correlation coefficient greater than 0.6. (Author)

  6. The ARM West Antarctic Radiation Experiment (AWARE)

    NASA Astrophysics Data System (ADS)

    Scott, R. C.; Lubin, D.; Bromwich, D. H.; Vogelmann, A. M.; Verlinde, J.; Russell, L. M.

    2016-12-01

    West Antarctica is one of the most rapidly warming regions on Earth, and its changing climate in both atmosphere and ocean is linked to loss of Antarctic ice mass and global sea level rise. The specific mechanisms for West Antarctic Ice Sheet (WAIS) warming are not fully understood, but are hypothesized to involve linkage between moisture from Southern Ocean storm tracks and the surface energy balance over the WAIS, and related teleconnections with subtropical and tropical meteorology. This present lack of understanding has motivated a climate science and cloud physics campaign jointly supported by the US National Science Foundation (NSF) and Department of Energy (DOE), called the Atmospheric Radiation Measurement Program (ARM) West Antarctic Radiation Experiment (AWARE). The DOE's second ARM Mobile Facility (AMF2) was deployed to McMurdo Station on Ross Island in November 2015 and will operate through December 2016. The AMF2 includes (1) cloud research radars, both scanning and zenith, operating in the Ka- and X-bands, (2) high spectral resolution and polarized micropulse lidars, and (3) a suite of shortwave and longwave broadband and spectral radiometers. A second suite of instruments is deployed at the WAIS Divide Ice Camp on the West Antarctic plateau during December 2015 and January 2016. The WAIS instrument suite provides (1) measurement of all surface energy balance components, (2) a polarized micropulse lidar and shortwave spectroradiometer, (3) microwave total water column measurement, and (4) four times daily rawinsonde launches which are the first from West Antarctica since 1967. There is a direct linkage between the WAIS instrument suite and the AMF2 at McMurdo, in that air masses originating in Southern Ocean storm tracks that are driven up over the WAIS often subsequently descend over the Ross Ice Shelf and arrive at Ross Island. Preliminary data are already illustrating (1) the prevalence of single- versus mixed-phase clouds and their role in the

  7. 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.

    2014-12-01

    During Marine Isotope Stage 3, the Atlantic Meridional Overturning Circulation (AMOC) weakened significantly on a millennial time-scale leading to Dansgaard-Oeschger (DO) and Heinrich stadials. Ice core records reveal that each Northern Hemisphere stadial is associated with a warming over Antarctica, so-called Antarctic Isotope Maximum (AIM), and that atmospheric CO2 varies in phase with Antarctic temperature. 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 link between changes in the AMOC, changes in high latitude Southern Hemispheric climate and evolution of atmospheric CO2. Given the latest Antarctic ice core chronology, we find that part of the atmospheric CO2 increase occurring during AIM12 (DO12, ~48 ka B.P.) and at the end of AIM8 (DO8, 38 ka B.P.) can be attributed to the AMOC resumption. In contrast, the atmospheric CO2 increase observed at the beginning of AIM8 (~39.6 ka B.P.) occurs during a period of weak AMOC and can instead be explained by enhanced Antarctic Bottom Water production. Enhanced Antarctic Bottom Water formation is shown to effectively ventilate the deep Pacific carbon and thus 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 enhances the southern high latitude warming and leads 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. Finally, our simulations also suggest that the Antarctic cooling should be in phase, or lag by a maximum of ~200 years, the North Atlantic

  8. Expanding Antarctic Sea Ice: Anthropogenic or Natural Variability?

    NASA Astrophysics Data System (ADS)

    Bitz, C. M.

    2016-12-01

    Antarctic sea ice extent has increased over the last 36 years according to the satellite record. Concurrent with Antarctic sea-ice expansion has been broad cooling of the Southern Ocean sea-surface temperature. Not only are Southern Ocean sea ice and SST trends at odds with expectations from greenhouse gas-induced warming, the trend patterns are not reproduced in historical simulations with comprehensive global climate models. While a variety of different factors may have contributed to the observed trends in recent decades, we propose that it is atmospheric circulation changes - and the changes in ocean circulation they induce - that have emerged as the most likely cause of the observed Southern Ocean sea ice and SST trends. I will discuss deficiencies in models that could explain their incorrect response. In addition, I will present results from a series of experiments where the Antarctic sea ice and ocean are forced by atmospheric perturbations imposed within a coupled climate model. Figure caption: Linear trends of annual-mean SST (left) and annual-mean sea-ice concentration (right) over 1980-2014. SST is from NOAA's Optimum Interpolation SST dataset (version 2; Reynolds et al. 2002). Sea-ice concentration is from passive microwave observations using the NASA Team algorithm. Only the annual means are shown here for brevity and because the signal to noise is greater than in the seasonal means. Figure from Armour and Bitz (2015).

  9. Marine pelagic ecosystems: the west Antarctic Peninsula.

    PubMed

    Ducklow, Hugh W; Baker, Karen; Martinson, Douglas G; Quetin, Langdon B; Ross, Robin M; Smith, Raymond C; Stammerjohn, Sharon E; Vernet, Maria; Fraser, William

    2007-01-29

    The marine ecosystem of the West Antarctic Peninsula (WAP) extends from the Bellingshausen Sea to the northern tip of the peninsula and from the mostly glaciated coast across the continental shelf to the shelf break in the west. The glacially sculpted coastline along the peninsula is highly convoluted and characterized by deep embayments that are often interconnected by channels that facilitate transport of heat and nutrients into the shelf domain. The ecosystem is divided into three subregions, the continental slope, shelf and coastal regions, each with unique ocean dynamics, water mass and biological distributions. The WAP shelf lies within the Antarctic Sea Ice Zone (SIZ) and like other SIZs, the WAP system is very productive, supporting large stocks of marine mammals, birds and the Antarctic krill, Euphausia superba. Ecosystem dynamics is dominated by the seasonal and interannual variation in sea ice extent and retreat. The Antarctic Peninsula is one among the most rapidly warming regions on Earth, having experienced a 2 degrees C increase in the annual mean temperature and a 6 degrees C rise in the mean winter temperature since 1950. Delivery of heat from the Antarctic Circumpolar Current has increased significantly in the past decade, sufficient to drive to a 0.6 degrees C warming of the upper 300 m of shelf water. In the past 50 years and continuing in the twenty-first century, the warm, moist maritime climate of the northern WAP has been migrating south, displacing the once dominant cold, dry continental Antarctic climate and causing multi-level responses in the marine ecosystem. Ecosystem responses to the regional warming include increased heat transport, decreased sea ice extent and duration, local declines in icedependent Adélie penguins, increase in ice-tolerant gentoo and chinstrap penguins, alterations in phytoplankton and zooplankton community composition and changes in krill recruitment, abundance and availability to predators. The climate

  10. Marine pelagic ecosystems: the West Antarctic Peninsula

    PubMed Central

    Ducklow, Hugh W; Baker, Karen; Martinson, Douglas G; Quetin, Langdon B; Ross, Robin M; Smith, Raymond C; Stammerjohn, Sharon E; Vernet, Maria; Fraser, William

    2006-01-01

    The marine ecosystem of the West Antarctic Peninsula (WAP) extends from the Bellingshausen Sea to the northern tip of the peninsula and from the mostly glaciated coast across the continental shelf to the shelf break in the west. The glacially sculpted coastline along the peninsula is highly convoluted and characterized by deep embayments that are often interconnected by channels that facilitate transport of heat and nutrients into the shelf domain. The ecosystem is divided into three subregions, the continental slope, shelf and coastal regions, each with unique ocean dynamics, water mass and biological distributions. The WAP shelf lies within the Antarctic Sea Ice Zone (SIZ) and like other SIZs, the WAP system is very productive, supporting large stocks of marine mammals, birds and the Antarctic krill, Euphausia superba. Ecosystem dynamics is dominated by the seasonal and interannual variation in sea ice extent and retreat. The Antarctic Peninsula is one among the most rapidly warming regions on Earth, having experienced a 2°C increase in the annual mean temperature and a 6°C rise in the mean winter temperature since 1950. Delivery of heat from the Antarctic Circumpolar Current has increased significantly in the past decade, sufficient to drive to a 0.6°C warming of the upper 300 m of shelf water. In the past 50 years and continuing in the twenty-first century, the warm, moist maritime climate of the northern WAP has been migrating south, displacing the once dominant cold, dry continental Antarctic climate and causing multi-level responses in the marine ecosystem. Ecosystem responses to the regional warming include increased heat transport, decreased sea ice extent and duration, local declines in ice-dependent Adélie penguins, increase in ice-tolerant gentoo and chinstrap penguins, alterations in phytoplankton and zooplankton community composition and changes in krill recruitment, abundance and availability to predators. The climate/ecological gradients

  11. Active margin processes along the Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Henriet, J. P.; Meissner, R.; Miller, H.; The Grape Team

    1992-01-01

    The Antarctic Peninsula has a remarkable record of active margin processes, which include subduction with progressive ridge-trench collisions, margin segmentation by major fracture zones, rifting in a hybrid back-arc and sheared plate margin context, fore-arc basin development and glacial-marine controlled trench fill processes. Several facets of these active margin processes both of internal (crustal dynamic) and external origin (climate-controlled) have been documented by a geophysical survey during the Antarktis VI/2 cruise of R.V. Polarstem(October-December 1987). Reflection seismic profiles have been shot over the rift basin of Bransfield Strait, over an elongated sediment-filled trough interpreted as a fore-arc basin, over accretional and progradational slopes, over recent and ancient trench environments and over the facing oceanic domain. In this oceanic domain, different fracture zones have highly contrasting morphological and geophysical expressions. The subduction of a fracture zone like Hero F.Z., characterized by a significant relief possibly related to the presence of buoyant (serpentinite) ridges, may have been a factor of subduction termination for the last segment of the Aluk (Drake) plate; it may also have played a role in the separation of a blueschist-bearing fragment (Smith Island) from the base of the accretionary plate margin and in its lift to the surface. The magnetic anomaly pattern of the oceanic slabs facing the northwestern Peninsula margin shows evidence of an intriguing spreading acceleration, which apparently preceded ridge-trench collision. The same anomaly pattern provides a clue to the stratigraphie interpretation of the oceanic sediment cover and of the frontal part of the prograding, now passive margin south of the South Shetland Island Arc. An apparently broken and tilted oceanic plate fragment, squeezed between the South Shetland Trench and Shackleton Fracture Zone, may argue for the role of transpression associated with the

  12. Structural Uncertainty in Antarctic sea ice simulations

    NASA Astrophysics Data System (ADS)

    Schneider, D. P.

    2016-12-01

    The inability of the vast majority of historical climate model simulations to reproduce the observed increase in Antarctic sea ice has motivated many studies about the quality of the observational record, the role of natural variability versus forced changes, and the possibility of missing or inadequate forcings in the models (such as freshwater discharge from thinning ice shelves or an inadequate magnitude of stratospheric ozone depletion). In this presentation I will highlight another source of uncertainty that has received comparatively little attention: Structural uncertainty, that is, the systematic uncertainty in simulated sea ice trends that arises from model physics and mean-state biases. Using two large ensembles of experiments from the Community Earth System Model (CESM), I will show that the model is predisposed towards producing negative Antarctic sea ice trends during 1979-present, and that this outcome is not simply because the model's decadal variability is out-of-synch with that in nature. In the "Tropical Pacific Pacemaker" ensemble, in which observed tropical Pacific SST anomalies are prescribed, the model produces very realistic atmospheric circulation trends over the Southern Ocean, yet the sea ice trend is negative in every ensemble member. However, if the ensemble-mean trend (commonly interpreted as the forced response) is removed, some ensemble members show a sea ice increase that is very similar to the observed. While this results does confirm the important role of natural variability, it also suggests a strong bias in the forced response. I will discuss the reasons for this systematic bias and explore possible remedies. This an important problem to solve because projections of 21st -Century changes in the Antarctic climate system (including ice sheet surface mass balance changes and related changes in the sea level budget) have a strong dependence on the mean state of and changes in the Antarctic sea ice cover. This problem is not unique to

  13. Evolution of the early Antarctic ice ages

    NASA Astrophysics Data System (ADS)

    Liebrand, Diederik; de Bakker, Anouk T. M.; Beddow, Helen M.; Wilson, Paul A.; Bohaty, Steven M.; Ruessink, Gerben; Pälike, Heiko; Batenburg, Sietske J.; Hilgen, Frederik J.; Hodell, David A.; Huck, Claire E.; Kroon, Dick; Raffi, Isabella; Saes, Mischa J. M.; van Dijk, Arnold E.; Lourens, Lucas J.

    2017-04-01

    Understanding the stability of the early Antarctic ice cap in the geological past is of societal interest because present-day atmospheric CO2 concentrations have reached values comparable to those estimated for the Oligocene and the Early Miocene epochs. Here we analyze a new high-resolution deep-sea oxygen isotope (δ18O) record from the South Atlantic Ocean spanning an interval between 30.1 My and 17.1 My ago. The record displays major oscillations in deep-sea temperature and Antarctic ice volume in response to the ˜110-ky eccentricity modulation of precession. Conservative minimum ice volume estimates show that waxing and waning of at least ˜85 to 110% of the volume of the present East Antarctic Ice Sheet is required to explain many of the ˜110-ky cycles. Antarctic ice sheets were typically largest during repeated glacial cycles of the mid-Oligocene (˜28.0 My to ˜26.3 My ago) and across the Oligocene-Miocene Transition (˜23.0 My ago). However, the high-amplitude glacial-interglacial cycles of the mid-Oligocene are highly symmetrical, indicating a more direct response to eccentricity modulation of precession than their Early Miocene counterparts, which are distinctly asymmetrical—indicative of prolonged ice buildup and delayed, but rapid, glacial terminations. We hypothesize that the long-term transition to a warmer climate state with sawtooth-shaped glacial cycles in the Early Miocene was brought about by subsidence and glacial erosion in West Antarctica during the Late Oligocene and/or a change in the variability of atmospheric CO2 levels on astronomical time scales that is not yet captured in existing proxy reconstructions.

  14. Evolution of the early Antarctic ice ages

    PubMed Central

    de Bakker, Anouk T. M.; Beddow, Helen M.; Wilson, Paul A.; Bohaty, Steven M.; Pälike, Heiko; Batenburg, Sietske J.; Hilgen, Frederik J.; Hodell, David A.; Huck, Claire E.; Kroon, Dick; Raffi, Isabella; Saes, Mischa J. M.; van Dijk, Arnold E.; Lourens, Lucas J.

    2017-01-01

    Understanding the stability of the early Antarctic ice cap in the geological past is of societal interest because present-day atmospheric CO2 concentrations have reached values comparable to those estimated for the Oligocene and the Early Miocene epochs. Here we analyze a new high-resolution deep-sea oxygen isotope (δ18O) record from the South Atlantic Ocean spanning an interval between 30.1 My and 17.1 My ago. The record displays major oscillations in deep-sea temperature and Antarctic ice volume in response to the ∼110-ky eccentricity modulation of precession. Conservative minimum ice volume estimates show that waxing and waning of at least ∼85 to 110% of the volume of the present East Antarctic Ice Sheet is required to explain many of the ∼110-ky cycles. Antarctic ice sheets were typically largest during repeated glacial cycles of the mid-Oligocene (∼28.0 My to ∼26.3 My ago) and across the Oligocene−Miocene Transition (∼23.0 My ago). However, the high-amplitude glacial−interglacial cycles of the mid-Oligocene are highly symmetrical, indicating a more direct response to eccentricity modulation of precession than their Early Miocene counterparts, which are distinctly asymmetrical—indicative of prolonged ice buildup and delayed, but rapid, glacial terminations. We hypothesize that the long-term transition to a warmer climate state with sawtooth-shaped glacial cycles in the Early Miocene was brought about by subsidence and glacial erosion in West Antarctica during the Late Oligocene and/or a change in the variability of atmospheric CO2 levels on astronomical time scales that is not yet captured in existing proxy reconstructions. PMID:28348211

  15. Evolution of the early Antarctic ice ages.

    PubMed

    Liebrand, Diederik; de Bakker, Anouk T M; Beddow, Helen M; Wilson, Paul A; Bohaty, Steven M; Ruessink, Gerben; Pälike, Heiko; Batenburg, Sietske J; Hilgen, Frederik J; Hodell, David A; Huck, Claire E; Kroon, Dick; Raffi, Isabella; Saes, Mischa J M; van Dijk, Arnold E; Lourens, Lucas J

    2017-04-11

    Understanding the stability of the early Antarctic ice cap in the geological past is of societal interest because present-day atmospheric CO2 concentrations have reached values comparable to those estimated for the Oligocene and the Early Miocene epochs. Here we analyze a new high-resolution deep-sea oxygen isotope (δ(18)O) record from the South Atlantic Ocean spanning an interval between 30.1 My and 17.1 My ago. The record displays major oscillations in deep-sea temperature and Antarctic ice volume in response to the ∼110-ky eccentricity modulation of precession. Conservative minimum ice volume estimates show that waxing and waning of at least ∼85 to 110% of the volume of the present East Antarctic Ice Sheet is required to explain many of the ∼110-ky cycles. Antarctic ice sheets were typically largest during repeated glacial cycles of the mid-Oligocene (∼28.0 My to ∼26.3 My ago) and across the Oligocene-Miocene Transition (∼23.0 My ago). However, the high-amplitude glacial-interglacial cycles of the mid-Oligocene are highly symmetrical, indicating a more direct response to eccentricity modulation of precession than their Early Miocene counterparts, which are distinctly asymmetrical-indicative of prolonged ice buildup and delayed, but rapid, glacial terminations. We hypothesize that the long-term transition to a warmer climate state with sawtooth-shaped glacial cycles in the Early Miocene was brought about by subsidence and glacial erosion in West Antarctica during the Late Oligocene and/or a change in the variability of atmospheric CO2 levels on astronomical time scales that is not yet captured in existing proxy reconstructions.

  16. Antarctic macrozooplankton of the southwest Atlantic sector and Bellingshausen Sea: Baseline historical distributions ( Discovery Investigations, 1928-1935) related to temperature and food, with projections for subsequent ocean warming

    NASA Astrophysics Data System (ADS)

    Mackey, A. P.; Atkinson, A.; Hill, S. L.; Ward, P.; Cunningham, N. J.; Johnston, N. M.; Murphy, E. J.

    2012-01-01

    Since the Discovery Investigations of the 1920s and 1930s, seawater temperatures have increased in the Atlantic sector by ˜1 °C; greater than the global mean rise. The aims of this paper were first to rescue the Discovery macrozooplankton data, second to provide quantitative "baseline" distribution maps, relating these to indices of temperature and food. Our third aim was to use the relationships we derived between abundance and temperature to project the potential affect of a 1 °C warming on the Discovery era distribution patterns. Based on the 1 m ringnet data retrieved from 615 stations (Nov-March), four taxa comprised >90% of the Antarctic macrozooplankton abundance: Rhincalanus gigas, Thysanoessa spp., Euphausia superba, and Chaetognaths. Most of the taxa, especially the more abundant ones, were warm water species penetrating into Antarctica and thus total macrozooplankton abundance decreased about 100-fold from 50°S to 70°S. While temperature correlated best with distribution at this large scale, food availability (proxied by a present-day satellite-based Chlorophyll a climatology) had a secondary effect, with the major euphausiids Euphausia superba and Thysanoessa spp. concentrated in high chl a areas. A modelled uniform 1 °C temperature rise produced a poleward shift for all taxa, but the Antarctic continent blocked this re-adjustment for the high latitude species, constricting their predicted range. More widespread polar/sub-polar species were predicted to increase their penetration into Antarctica by 4-12° in latitude, whereas the poleward shift in potential range of sub-Antarctic taxa were limited by the steep temperature gradient across the Antarctic Polar Front (APF). However, within the Scotia Sea the relatively warm temperatures of the northern Antarctic Zone, abundant food due to iron fertilisation and intense eddy activity provide a "gateway" for northern species to penetrate south of the APF. Our model predictions, based on measured

  17. Differences between Antarctic and non-Antarctic meteorites: An assessment

    SciTech Connect

    Koeberl, C. ); Cassidy, W.A. )

    1991-01-01

    The discovery of a statistically significant number of meteorites in Antarctica over the past 20 years has posed many questions. One of the most intriguing suggestions that came up during the study of the Antarctic samples was that there might be a difference between the parent populations of Antarctic and non-Antarctic samples was that there might be a difference between the parent populations of Antarctic and non-Antarctic meteorites. This interpretation was put forward after the detection of a significant difference in the abundances of volatile and mobile trace elements in H, L, and C chondrites and achondrites. Other major differences include the occurrence of previously rare or unknown meteorites, different meteorite-type frequencies, petrographic characteristics, oxygen isotopic compositions, and smaller average masses. Not all differences between the Antarctic and non-Antarctic meteorite populations can be explained by weathering, pairing, or different collection procedures. Variable trace element abundances and distinct differences in the thermal history and thermoluminescence characteristics have to be interpreted as being pre-terrestrial in origin. Such differences imply the existence of meteoroid streams, whose existence poses problems in the framework of our current knowledge of celestial mechanics. In this paper we summarize the contributions in this series and provide a review of the current state of the question for the reality and cause of differences between Antarctic and non-Antarctic meteorites.

  18. Evolution of the Antarctic ice sheet: new understanding and challenges.

    PubMed

    Payne, Antony J; Hunt, Julian C R; Wingham, Duncan J

    2006-07-15

    This brief paper has two purposes. First, we gauge developments in the study of the Antarctic ice sheet over the last seven years by comparing the contents of this issue with the volume produced from an American Geophysical Union meeting, held in September 1998, on the West Antarctic ice sheet. We focus on the uptake of satellite-based observation; ice-ocean interactions; ice streams as foci of change within the ice sheet; and the time scales on which the ice sheet is thought to operate. Second, we attempt to anticipate the future challenges that the study of the Antarctic ice sheet will present. We highlight the role of the upcoming International Polar Year in facilitating a better coverage of in situ climatic observations over the continent; the pressing need to understand the causes and consequences of the contemporary changes observed in the Amundsen Sea sector of West Antarctica; and the need for improved physics in predictive models of the ice sheet.

  19. Evidence for an extensive Antarctic Ice Sheet by 37 Ma

    NASA Astrophysics Data System (ADS)

    Carter, Andrew; Riley, Teal; Hillenbrand, Claus-Dieter; Rittner, Martin

    2016-04-01

    We present observational evidence that both the East and West Antarctic ice sheets had expanded to the coast by 37 Ma, predating, by at least 3 Myr, a major drop in atmospheric CO2 at the Eocene-Oligocene boundary widely considered responsible for Antarctic Ice Sheet expansion. Our evidence comes from the provenance (geochronology, thermochronometry, mineralogy) of iceberg-rafted debris identified in Late Eocene marine sediments from (ODP) Leg 113 Site 696 in the NW Weddell Sea. The existence of an significant Antarctic Ice Sheet in a Late Eocene high pCO2 world calls into question the role of atmospheric CO2 concentrations as the dominant mechanism for ice sheet expansion and whether topography and ocean circulation only play a secondary role.

  20. Antarctic Porifera database from the Spanish benthic expeditions.

    PubMed

    Rios, Pilar; Cristobo, Javier

    2014-01-01

    THE INFORMATION ABOUT THE SPONGES IN THIS DATASET IS DERIVED FROM THE SAMPLES COLLECTED DURING FIVE SPANISH ANTARCTIC EXPEDITIONS: Bentart 94, Bentart 95, Gebrap 96, Ciemar 99/00 and Bentart 2003. Samples were collected in the Antarctic Peninsula and Bellingshausen Sea at depths ranging from 4 to 2044 m using various sampling gears. The Antarctic Porifera database from the Spanish benthic expeditions is unique as it provides information for an under-explored region of the Southern Ocean (Bellingshausen Sea). It fills an information gap on Antarctic deep-sea sponges, for which there were previously very few data. This phylum is an important part of the Antarctic biota and plays a key role in the structure of the Antarctic marine benthic community due to its considerable diversity and predominance in different areas. It is often a dominant component of Southern Ocean benthic communities. The quality of the data was controlled very thoroughly with GPS systems onboard the R/V Hesperides and by checking the data against the World Porifera Database (which is part of the World Register of Marine Species, WoRMS). The data are therefore fit for completing checklists, inclusion in biodiversity pattern analysis and niche modelling. The authors can be contacted if any additional information is needed before carrying out detailed biodiversity or biogeographic studies. The dataset currently contains 767 occurrence data items that have been checked for systematic reliability. This database is not yet complete and the collection is growing. Specimens are stored in the author's collection at the Spanish Institute of Oceanography (IEO) in the city of Gijón (Spain). The data are available in GBIF.

  1. Mitochondrial function in Antarctic nototheniids with ND6 translocation.

    PubMed

    Mark, Felix C; Lucassen, Magnus; Strobel, Anneli; Barrera-Oro, Esteban; Koschnick, Nils; Zane, Lorenzo; Patarnello, Tomaso; Pörtner, Hans O; Papetti, Chiara

    2012-01-01

    Fish of the suborder Notothenioidei have successfully radiated into the Southern Ocean and today comprise the dominant fish sub-order in Antarctic waters in terms of biomass and species abundance. During evolution in the cold and stable Antarctic climate, the Antarctic lineage of notothenioids developed several unique physiological adaptations, which make them extremely vulnerable to the rapid warming of Antarctic waters currently observed. Only recently, a further phenomenon exclusive to notothenioid fish was reported: the translocation of the mitochondrial gene encoding the NADH Dehydrogenase subunit 6 (ND6), an indispensable part of complex I in the mitochondrial electron transport system.This study investigated the potential physiological consequences of ND6 translocation for the function and thermal sensitivity of the electron transport system in isolated liver mitochondria of the two nototheniid species Notothenia coriiceps and Notothenia rossii, with special attention to the contributions of complex I (NADH DH) and complex II (Succinate DH) to oxidative phosphorylation. Furthermore, enzymatic activities of NADH:Cytochrome c Oxidoreductase and Cytochrome C Oxidase were measured in membrane-enriched tissue extracts.During acute thermal challenge (0-15°C), capacities of mitochondrial respiration and enzymatic function in the liver could only be increased until 9°C. Mitochondrial complex I (NADH Dehydrogenase) was fully functional but displayed a higher thermal sensitivity than the other complexes of the electron transport system, which may specifically result from its unique amino acid composition, revealing a lower degree of stability in notothenioids in general. We interpret the translocation of ND6 as functionally neutral but the change in amino acid sequence as adaptive and supportive of cold stenothermy in Antarctic nototheniids. From these findings, an enhanced sensitivity to ocean warming can be deduced for Antarctic notothenioid fish.

  2. Mitochondrial Function in Antarctic Nototheniids with ND6 Translocation

    PubMed Central

    Mark, Felix C.; Lucassen, Magnus; Strobel, Anneli; Barrera-Oro, Esteban; Koschnick, Nils; Zane, Lorenzo; Patarnello, Tomaso; Pörtner, Hans O.; Papetti, Chiara

    2012-01-01

    Fish of the suborder Notothenioidei have successfully radiated into the Southern Ocean and today comprise the dominant fish sub-order in Antarctic waters in terms of biomass and species abundance. During evolution in the cold and stable Antarctic climate, the Antarctic lineage of notothenioids developed several unique physiological adaptations, which make them extremely vulnerable to the rapid warming of Antarctic waters currently observed. Only recently, a further phenomenon exclusive to notothenioid fish was reported: the translocation of the mitochondrial gene encoding the NADH Dehydrogenase subunit 6 (ND6), an indispensable part of complex I in the mitochondrial electron transport system. This study investigated the potential physiological consequences of ND6 translocation for the function and thermal sensitivity of the electron transport system in isolated liver mitochondria of the two nototheniid species Notothenia coriiceps and Notothenia rossii, with special attention to the contributions of complex I (NADH DH) and complex II (Succinate DH) to oxidative phosphorylation. Furthermore, enzymatic activities of NADH∶Cytochrome c Oxidoreductase and Cytochrome C Oxidase were measured in membrane-enriched tissue extracts. During acute thermal challenge (0–15°C), capacities of mitochondrial respiration and enzymatic function in the liver could only be increased until 9°C. Mitochondrial complex I (NADH Dehydrogenase) was fully functional but displayed a higher thermal sensitivity than the other complexes of the electron transport system, which may specifically result from its unique amino acid composition, revealing a lower degree of stability in notothenioids in general. We interpret the translocation of ND6 as functionally neutral but the change in amino acid sequence as adaptive and supportive of cold stenothermy in Antarctic nototheniids. From these findings, an enhanced sensitivity to ocean warming can be deduced for Antarctic notothenioid fish. PMID

  3. Antarctic Porifera database from the Spanish benthic expeditions

    PubMed Central

    Rios, Pilar; Cristobo, Javier

    2014-01-01

    Abstract The information about the sponges in this dataset is derived from the samples collected during five Spanish Antarctic expeditions: Bentart 94, Bentart 95, Gebrap 96, Ciemar 99/00 and Bentart 2003. Samples were collected in the Antarctic Peninsula and Bellingshausen Sea at depths ranging from 4 to 2044 m using various sampling gears. The Antarctic Porifera database from the Spanish benthic expeditions is unique as it provides information for an under-explored region of the Southern Ocean (Bellingshausen Sea). It fills an information gap on Antarctic deep-sea sponges, for which there were previously very few data. This phylum is an important part of the Antarctic biota and plays a key role in the structure of the Antarctic marine benthic community due to its considerable diversity and predominance in different areas. It is often a dominant component of Southern Ocean benthic communities. The quality of the data was controlled very thoroughly with GPS systems onboard the R/V Hesperides and by checking the data against the World Porifera Database (which is part of the World Register of Marine Species, WoRMS). The data are therefore fit for completing checklists, inclusion in biodiversity pattern analysis and niche modelling. The authors can be contacted if any additional information is needed before carrying out detailed biodiversity or biogeographic studies. The dataset currently contains 767 occurrence data items that have been checked for systematic reliability. This database is not yet complete and the collection is growing. Specimens are stored in the author’s collection at the Spanish Institute of Oceanography (IEO) in the city of Gijón (Spain). The data are available in GBIF. PMID:24843257

  4. The Antarctic Planet Interferometer

    NASA Technical Reports Server (NTRS)

    Swain, Mark R.; Walker, Christopher K.; Traub, Wesley A.; Storey, John W.; CoudeduForesto, Vincent; Fossat, Eric; Vakili, Farrok; Stark, Anthony A.; Lloyd, James P.; Lawson, Peter R.; hide

    2004-01-01

    The Antarctic Planet Interferometer is an instrument concept designed to detect and characterize extrasolar planets by exploiting the unique potential of the best accessible site on earth for thermal infrared interferometry. High-precision interferometric techniques under development for extrasolar planet detection and characterization (differential phase, nulling and astrometry) all benefit substantially from the slow, low-altitude turbulence, low water vapor content, and low temperature found on the Antarctic plateau. At the best of these locations, such as the Concordia base being developed at Dome C, an interferometer with two-meter diameter class apertures has the potential to deliver unique science for a variety of topics, including extrasolar planets, active galactic nuclei, young stellar objects, and protoplanetary disks.

  5. Antarctic science preserve polluted

    NASA Astrophysics Data System (ADS)

    Simarski, Lynn Teo

    Geophysicists are alarmed at the electromagnetic pollution of a research site in the Antarctic specifically set aside to study the ionosphere and magnetosphere. A private New Zealand communications company called Telecom recently constructed a satellite ground station within the boundaries of this Site of Special Scientific Interest (SSSI), protected since the mid-1970s. The placement of a commercial facility within this site sets an ominous precedent not only for the sanctity of other SSSIs, but also for Specially Protected Areas—preserves not even open to scientific research, such as certain penguin rookeries.The roughly rectangular, one-by-one-half mile site, located at Arrival Heights not far from McMurdo Station, is one of a number of areas protected under the Antarctic treaty for designated scientific activities. Many sites are set aside for geological or biological research, but this is the only one specifically for physical science.

  6. Viruses in Antarctic lakes

    NASA Technical Reports Server (NTRS)

    Kepner, R. L. Jr; Wharton, R. A. Jr; Suttle, C. A.; Wharton RA, J. r. (Principal Investigator)

    1998-01-01

    Water samples collected from four perennially ice-covered Antarctic lakes during the austral summer of 1996-1997 contained high densities of extracellular viruses. Many of these viruses were found to be morphologically similar to double-stranded DNA viruses that are known to infect algae and protozoa. These constitute the first observations of viruses in perennially ice-covered polar lakes. The abundance of planktonic viruses and data suggesting substantial production potential (relative to bacteria] secondary and photosynthetic primary production) indicate that viral lysis may be a major factor in the regulation of microbial populations in these extreme environments. Furthermore, we suggest that Antarctic lakes may be a reservoir of previously undescribed viruses that possess novel biological and biochemical characteristics.

  7. Viruses in Antarctic lakes

    NASA Technical Reports Server (NTRS)

    Kepner, R. L. Jr; Wharton, R. A. Jr; Suttle, C. A.; Wharton RA, J. r. (Principal Investigator)

    1998-01-01

    Water samples collected from four perennially ice-covered Antarctic lakes during the austral summer of 1996-1997 contained high densities of extracellular viruses. Many of these viruses were found to be morphologically similar to double-stranded DNA viruses that are known to infect algae and protozoa. These constitute the first observations of viruses in perennially ice-covered polar lakes. The abundance of planktonic viruses and data suggesting substantial production potential (relative to bacteria] secondary and photosynthetic primary production) indicate that viral lysis may be a major factor in the regulation of microbial populations in these extreme environments. Furthermore, we suggest that Antarctic lakes may be a reservoir of previously undescribed viruses that possess novel biological and biochemical characteristics.

  8. Antarctic shelf warming under climate change: Insights from eddying climate models

    NASA Astrophysics Data System (ADS)

    Goddard, Paul; Dufour, Carolina O.; Yin, Jianjun; Griffies, Stephen M.; Winton, Michael

    2017-04-01

    Ocean warming around the Antarctic Ice Sheet has important implications for ice sheet mass loss and global sea level rise. Understanding the ocean processes responsible for Antarctic shelf warming is thus critical to improve climate projections. Several recent studies have pointed out the role of ocean mesoscale eddies in bringing heat onto the shelf with a focus on specific regions, such as the Western Antarctic Peninsula. However, we still lack a more general picture of ocean warming over the whole Antarctic shelf region and a detailed analysis of the response of heat transport to climate change. In this study, we present an analysis of the response of ocean heat transport at the Antarctic shelf break to climate change, and we address the role of mesoscale eddies in this transport. To do so, we use two eddying climate models of different resolutions in the ocean (0.25° and 0.10°) each run under a preindustrial forcing scenario and a climate change forcing scenario. Analyses of the heat transport across the Antarctic Slope Front (ASF) are carried out with a decomposition of the transport into its time-mean and eddy components. Heat budgets over the shelf region are also performed to investigate the role of other processes (e.g. surface fluxes) in shelf warming. Finally, the Antarctic shelf region is divided into several sub-regions to examine geographical variations in the warming. We find that the shelf regions warm under climate change due to a combination of warmer atmospheric temperatures, a large reduction of sea ice coverage, increased heat transport across the ASF or increased freshening at the surface. We discuss the impact of each of these factors on shelf warming in the different regions, as well as the contribution of mesoscale eddies to this warming.

  9. Antarctic Meteorite Newsletter

    NASA Technical Reports Server (NTRS)

    Lindstrom, Marilyn

    2000-01-01

    This newsletter contains something for everyone! It lists classifications of about 440 meteorites mostly from the 1997 and 1998 ANSMET (Antarctic Search for Meteorites) seasons. It also gives descriptions of about 45 meteorites of special petrologic type. These include 1 iron, 17 chondrites (7 CC, 1 EC, 9 OC) and 27 achondrites (25 HED, UR). Most notable are an acapoloite (GRA98028) and an olivine diogenite (GRA98108).

  10. Extremophiles in an Antarctic Marine Ecosystem

    PubMed Central

    Dickinson, Iain; Goodall-Copestake, William; Thorne, Michael A.S.; Schlitt, Thomas; Ávila-Jiménez, Maria L.; Pearce, David A.

    2016-01-01

    Recent attempts to explore marine microbial diversity and the global marine microbiome have indicated a large proportion of previously unknown diversity. However, sequencing alone does not tell the whole story, as it relies heavily upon information that is already contained within sequence databases. In addition, microorganisms have been shown to present small-to-large scale biogeographical patterns worldwide, potentially making regional combinations of selection pressures unique. Here, we focus on the extremophile community in the boundary region located between the Polar Front and the Southern Antarctic Circumpolar Current in the Southern Ocean, to explore the potential of metagenomic approaches as a tool for bioprospecting in the search for novel functional activity based on targeted sampling efforts. We assessed the microbial composition and diversity from a region north of the current limit for winter sea ice, north of the Southern Antarctic Circumpolar Front (SACCF) but south of the Polar Front. Although, most of the more frequently encountered sequences  were derived from common marine microorganisms, within these dominant groups, we found a proportion of genes related to secondary metabolism of potential interest in bioprospecting. Extremophiles were rare by comparison but belonged to a range of genera. Hence, they represented interesting targets from which to identify rare or novel functions. Ultimately, future shifts in environmental conditions favoring more cosmopolitan groups could have an unpredictable effect on microbial diversity and function in the Southern Ocean, perhaps excluding the rarer extremophiles. PMID:27681902

  11. Extremophiles in an Antarctic Marine Ecosystem.

    PubMed

    Dickinson, Iain; Goodall-Copestake, William; Thorne, Michael A S; Schlitt, Thomas; Ávila-Jiménez, Maria L; Pearce, David A

    2016-01-11

    Recent attempts to explore marine microbial diversity and the global marine microbiome have indicated a large proportion of previously unknown diversity. However, sequencing alone does not tell the whole story, as it relies heavily upon information that is already contained within sequence databases. In addition, microorganisms have been shown to present small-to-large scale biogeographical patterns worldwide, potentially making regional combinations of selection pressures unique. Here, we focus on the extremophile community in the boundary region located between the Polar Front and the Southern Antarctic Circumpolar Current in the Southern Ocean, to explore the potential of metagenomic approaches as a tool for bioprospecting in the search for novel functional activity based on targeted sampling efforts. We assessed the microbial composition and diversity from a region north of the current limit for winter sea ice, north of the Southern Antarctic Circumpolar Front (SACCF) but south of the Polar Front. Although, most of the more frequently encountered sequences  were derived from common marine microorganisms, within these dominant groups, we found a proportion of genes related to secondary metabolism of potential interest in bioprospecting. Extremophiles were rare by comparison but belonged to a range of genera. Hence, they represented interesting targets from which to identify rare or novel functions. Ultimately, future shifts in environmental conditions favoring more cosmopolitan groups could have an unpredictable effect on microbial diversity and function in the Southern Ocean, perhaps excluding the rarer extremophiles.

  12. Thermoluminescence and Antarctic meteorites

    NASA Technical Reports Server (NTRS)

    Sears, D. W. G.; Hasan, F. A.

    1986-01-01

    The level of natural thermoluminescence (TL) in meteorites is the result of competition between build-up, due to exposure to cosmic radiation, and thermal decay. Antarctic meteorites tend to have lower natural TL than non-Antarctic meteorites because of their generally larger terrestrial ages. However, since a few observed falls have low TL due to a recent heating event, such as passage within approximately 0.7 astronomical units of the Sun, this could also be the case for some Antarctic meteorites. Dose rate variations due to shielding, heating during atmospheric passage, and anomalous fading also cause natural TL variations, but the effects are either relatively small, occur infrequently, or can be experimentally circumvented. The TL sensitivity of meteorites reflects the abundance and nature of the feldspar. Thus intense shock, which destroys feldspar, causes the TL sensitivity to decrease by 1 to 2 orders of magnitude, while metamorphism, which generates feldspar through the devitrification of glass, causes TL sensitivity to increase by a factor of approximately 10000. The TL-metamorphism relationship is particularly strong for the lowest levels of metamorphism. The order-disorder transformation in feldspar also affect the TL emission characteristics and thus TL provides a means of paleothermometry.

  13. Antarctic Photochemistry: Uncertainty Analysis

    NASA Technical Reports Server (NTRS)

    Stewart, Richard W.; McConnell, Joseph R.

    1999-01-01

    Understanding the photochemistry of the Antarctic region is important for several reasons. Analysis of ice cores provides historical information on several species such as hydrogen peroxide and sulfur-bearing compounds. The former can potentially provide information on the history of oxidants in the troposphere and the latter may shed light on DMS-climate relationships. Extracting such information requires that we be able to model the photochemistry of the Antarctic troposphere and relate atmospheric concentrations to deposition rates and sequestration in the polar ice. This paper deals with one aspect of the uncertainty inherent in photochemical models of the high latitude troposphere: that arising from imprecision in the kinetic data used in the calculations. Such uncertainties in Antarctic models tend to be larger than those in models of mid to low latitude clean air. One reason is the lower temperatures which result in increased imprecision in kinetic data, assumed to be best characterized at 298K. Another is the inclusion of a DMS oxidation scheme in the present model. Many of the rates in this scheme are less precisely known than are rates in the standard chemistry used in many stratospheric and tropospheric models.

  14. [Helminths of Antarctic fishes].

    PubMed

    Rocka, Anna

    2008-01-01

    Antarctic fishes are represented by sharks, skates (Chondrichthyes) and bony fishes (Teleostei). Teleosts play an important role in the completion of life cycles of many helminth species. They serve as either definitive or intermediate and paratenic hosts. Chondrichthyes are definitive hosts only. Seventy three helminth species occur as the adult stage in fishes: Digenea (45), Cestoda (14), Nematoda (6), Acanthocephala (8), Also, 11 larval stages of Cestoda (7) and Nematoda (4) are known, together with 7 species of Acanthocephala in the cystacanth stage. One digenean species, Otodistomum cestoides, matures in skates. Among cestodes maturing in fishes only one, Parabothriocephalus johnstoni, occurs in a bony fish, Macrourus whitsoni. Antarctic Chondrichthyes are not infected with nematodes and acanthocephalans. Cestode larvae from teleosts belong to Tetraphyllidea (parasites of skates), and Tetrabothriidae and Diphyllobothriidae (parasites of birds and mammals). Larval nematodes represent Anisakidae, parasites of fishes, birds and mammals. Acanthocephalan cystacanths mature in pinnipeds and birds. The majority of parasites maturing in Antarctic fishes are endemics. Only 4 digenean and one nematode species, Hysterothylacium aduncum, are cosmopolitan. All acanthocephalans, almost all digeneans, the majority of cestodes and some nematodes occur mainly or exclusively in benthic fishes. Specificity of the majority of helminths utilizing teleosts as intermediate and/or paratenic hosts is low. Among parasites using fishes as definitive hosts, all Cestoda, most Digenea and Nematoda, and almost all Acanthocephala have a range of hosts restricted to one order or even to 1-2 host species.

  15. Climatic Drivers of Past Antarctic Ice Sheet Evolution Add Nonlinearly

    NASA Astrophysics Data System (ADS)

    Tigchelaar, M.; Timmermann, A.; Pollard, D.; Friedrich, T.; Heinemann, M.

    2015-12-01

    The Antarctic ice sheet has varied substantially in shape and volume in the past, with evidence for strong regional differences in evolution history. Recent observations of change in the Antarctic environment indicate that different regions respond differently to ongoing changes in global climate -- over the West Antarctic Ice Sheet strong increases in sub-shelf melt rates indicate a sensitivity to changes in ocean temperature and circulation, while in East Antarctica the mass balance is increasingly positive due to an increase in accumulation in response to rising temperatures. Modeling the long term evolution of the Antarctic ice sheet can help address questions about its regional sensitivity to external forcing. We have conducted experiments with an established ice sheet model over the last eight glacial cycles using spatially and temporally varying climate forcing from an EMIC. These simulations indicate a glacial-interglacial amplitude of ~11m SLE. Using a series of sensitivity experiments we address the dominant climatic forcing of this evolution. While sea level changes are the main driver of grounding line movement, they alone are not sufficient to explain the full glacial amplitude. Local insolation changes contribute to the initiation of terminations, while accumulation and sub-shelf melt changes feed back positively and negatively respectively onto the ice sheet evolution. This implies that climatic drivers add nonlinearly and the full spectrum of climate forcing needs to be considered when evaluating the sensitivity of the Antarctic ice sheet to past and future climate change.

  16. Diversity and genomics of Antarctic marine micro-organisms.

    PubMed

    Murray, Alison E; Grzymski, Joseph J

    2007-12-29

    Marine bacterioplanktons are thought to play a vital role in Southern Ocean ecology and ecosystem function, as they do in other ocean systems. However, our understanding of phylogenetic diversity, genome-enabled capabilities and specific adaptations to this persistently cold environment is limited. Bacterioplankton community composition shifts significantly over the annual cycle as sea ice melts and phytoplankton bloom. Microbial diversity in sea ice is better known than that of the plankton, where culture collections do not appear to represent organisms detected with molecular surveys. Broad phylogenetic groupings of Antarctic bacterioplankton such as the marine group I Crenarchaeota, alpha-Proteobacteria (Roseobacter-related and SAR-11 clusters), gamma-Proteobacteria (both cultivated and uncultivated groups) and Bacteriodetes-affiliated organisms in Southern Ocean waters are in common with other ocean systems. Antarctic SSU rRNA gene phylotypes are typically affiliated with other polar sequences. Some species such as Polaribacter irgensii and currently uncultivated gamma-Proteobacteria (Ant4D3 and Ant10A4) may flourish in Antarctic waters, though further studies are needed to address diversity on a larger scale. Insights from initial genomics studies on both cultivated organisms and genomes accessed through shotgun cloning of environmental samples suggest that there are many unique features of these organisms that facilitate survival in high-latitude, persistently cold environments.

  17. Onset of Major Antarctic Ice-Sheet Retreat Driven by Extensive Surface Melt

    NASA Astrophysics Data System (ADS)

    Deconto, R. M.; Pollard, D.

    2016-12-01

    New Antarctic ice-sheet modeling that considers previously underappreciated effects of surface meltwater on ice-sheet dynamics has demonstrated the sensitivity of the ice sheet to atmospheric warming in addition to sub-ice oceanic warming. Here, we improve on our paleo-calibrated modeling of future ice-sheet retreat, using a bias-corrected, high-resolution regional atmospheric model that synchronizes time-evolving atmospheric climatologies with the SSTs and subsurface ocean temperatures that drive oceanic sub-ice melt rates. This approach avoids previous assumptions about the lagged response of Southern Ocean SSTs and Antarctic air temperatures relative to future greenhouse-gas forcing and produces future Antarctic climatologies in better agreement with other recent studies. The specification of modern observed climate, used to apply anomaly corrections with our atmospheric model, is also improved by using a monthly climatology provided by the RACMO2 regional climate model. We find that predicted future rates and magnitudes of ice-sheet retreat and sea-level rise are similar to our previous simulations. However, the revised atmospheric forcing delays the timing of the onset of retreat, with potential implications for coastal planning and policy. These results show that the future onset of major Antarctic ice-sheet retreat will be highly dependent on the details of evolving Antarctic climate, which remains uncertain due to complex linkages with lower-latitude atmospheric dynamics, ocean-ice feedbacks, recovery of the ozone hole, and uncertain future greenhouse-gas forcing.

  18. A review of precipitation-related aspects of West Antarctic meteorology

    NASA Technical Reports Server (NTRS)

    Bromwich, David H.; Carleton, Andrew M.; Parish, Thomas R.

    1991-01-01

    An overview is presented of the factors associated with snowfall over the West Antarctic Ice Sheet. The flux of atmospheric moisture across the coast, the synoptic processes over the South Pacific Ocean, the large scale atmospheric controls, and numerical modeling of the West Antarctic environment are all discussed. Suggestions are made for research needed to substantially upgrade the status of knowledge in these closely interrelated topic areas.

  19. Ocean Cooling Pattern at the Last Glacial Maximum

    DOE PAGES

    Zhuang, Kelin; Giardino, John R.

    2012-01-01

    Ocean temperature and ocean heat content change are analyzed based on four PMIP3 model results at the Last Glacial Maximum relative to the prehistorical run. Ocean cooling mostly occurs in the upper 1000 m depth and varies spatially in the tropical and temperate zones. The Atlantic Ocean experiences greater cooling than the rest of the ocean basins. Ocean cooling is closely related to the weakening of meridional overturning circulation and enhanced intrusion of Antarctic Bottom Water into the North Atlantic.

  20. JCADM, new Directions in Antarctic Data Management in Support of IPY

    NASA Astrophysics Data System (ADS)

    de Bruin, T.

    2007-12-01

    The Joint Committee on Antarctic Data Management (JCADM) was established by the Scientific Committee on Antarctic Research (SCAR) and the Council of Managers of National Antarctic Programs (COMNAP), to assist in the fulfilment of the data management obligations imposed by the Antarctic Treaty (section III.1.c): "Scientific observations and results from Antarctica shall be exchanged and made freely available." JCADM comprises representatives of the National Antarctic Data Centres or national points of contact. Currently 31 nations around the world are represented in JCADM. So far, JCADM has been focussing on the coordination of the Antarctic Master Directory (AMD), the internationally accessible, web-based, searchable record of Antarctic and Southern Ocean data set descriptions. The AMD is directly integrated into the international Global Change Master Directory (GCMD) to help further merge Antarctic science into global science. The AMD is a resource for scientists to advertise the data they have collected and to search for data they may need. Currently, JCADM is in a transition phase, moving forward to provide data access. Existing systems and web services technology will be used as much as possible, to increase efficiency and prevent 're-inventing the wheel' This presentation will give an overview of this process, the current status and the expected results.

  1. Stratospheric Ozone-induced Indirect Radiative Effects on Antarctic Sea Ice

    NASA Astrophysics Data System (ADS)

    Hu, Y.; Xia, Y.; LIU, J.; Huang, Y.

    2015-12-01

    Recent studies demonstrated that the Antarctic Ozone Hole has important influences on Antarctic sea ice. While all these have focused on stratospheric ozone-induced dynamic effects on sea ice, here we show results that ozone-induced indirect radiative effects have important influences on Antarctic sea ice. Our simulations demonstrate that the recovery of the Antarctic Ozone Hole causes equatorward shift of clouds over the Southern Ocean. The cloud-band shift leads to reduction of downward infrared radiation, which causes surface cooling. On the other hand, it also causes increasing solar radiation on the surface. However, the increase in solar radiation is offset by surface reflection due to increasing sea ice. As a result solar radiation absorbed by the surface is reduced, which also causes surface cooling. Therefore, the overall ozone-induced cloud radiative effect is to cool the surface and causes expansion of sea ice around the Antarctic. As shown in previous studies, the cloud-band shift is associated with the equatorward shift of the westerly jet stream around the Antarctic. Our simulations also demonstrate increasing snow rate near the sea ice edge, which also contributes to Antarctic sea-ice expansion. The ozone-induced cloud radiative effect would mitigate Antarctic sea-ice melting due to greenhouse warming in the 21st century.

  2. Modelling the Isotopic Response to Antarctic Ice Sheet Change During the Last Interglacial

    NASA Astrophysics Data System (ADS)

    Holloway, Max; Sime, Louise; Singarayer, Joy; Tindall, Julia; Valdes, Paul

    2015-04-01

    Ice sheet changes can exert major control over spatial water isotope variations in Antarctic surface snow. Consequently a significant mass loss or gain of the West Antarctic Ice Sheet (WAIS) would be expected to cause changes in the water isotope record across Antarctic ice core sites. Analysis of sea level indicators for the last interglacial (LIG), around 125 to 128 ka, suggest a global sea level peak 6 to 9 m higher than present. Recent NEEM Greenland ice core results imply that Greenland likely provided a modest ~2m contribution towards this global sea level rise. This implies that a WAIS contribution is necessary to explain the LIG sea level maxima. In addition, Antarctic ice core records suggest that Antarctic air temperatures during the LIG were up to 6°C warmer than present. Climate models have been unable to recreate such warmth when only orbital and greenhouse gas forcing are considered. Thus changes to the Antarctic ice sheet and ocean circulation may be required to reconcile model simulations with ice core data. Here we model the isotopic response to differing WAIS deglaciation scenarios, freshwater hosing, and sea ice configurations using a fully coupled General Circulation Model (GCM) to help interpret Antarctic ice core records over the LIG. This approach can help isolate the contribution of individual processes and feedbacks to final isotopic signals recorded in Antarctic ice cores.

  3. Role of Indian remote sensing imaging satellites for the Antarctic monitoring and mapping: a case study around Indian Antarctic research stations

    NASA Astrophysics Data System (ADS)

    Jayaprasad, P.; Mehra, Raghav; Chawla, Saket; Rajak, D. Ram; Oza, Sandip R.

    2016-05-01

    Antarctic research station's existence largely depend on the supply of fuel, food and other commodities through Antarctic Scientific Expedition using ship voyage. Safer Ship Navigation demands high resolution satellite monitoring of the ice conditions which varies from 30 km to 200 km from the Antarctic coast of Research stations. During the last couple of years Indian Satellites play a major role in safer ship navigation in sea ice regions of the Arctic and the Antarctic. Specifically Indian Scientific Expedition to the Antarctica (ISEA) through National Centre for Antarctic and Oceanic Research (NCAOR) is one of the beneficiaries for safer ship navigation using information derived from Indian Satellite data. Space Applications Centre, Indian Space Research Organisation (SAC-ISRO) is providing Sea Ice Advisories for the safer optimum entry and exit for the expedition ship at two of the Research stations Bharati and Maitri. Two of the Indian Satellites namely Radar Imaging Satellite-1 (RISAT-1) and ResourceSAT-2 (RS-2) are the two major workhorses of ISRO for monitoring and mapping of the Antarctic terrain. The present study demonstrate the utilisation potential of these satellite images for various Polar Science Applications. Mosaic of the Antarctic Terrain was generated from RISAT-1 CRS data. The preliminary results of the mosaic from CRS- circular polarisation data is presented. Demonstration of the study is extended for other applications such as change detection studies, safer ship navigation and extreme events of Antarctica. The use of multi resolution multi sensor data is also shown in the study.

  4. International Workshop on Antarctic Meteorites

    NASA Technical Reports Server (NTRS)

    Annexstad, J. O.; Schultz, L.; Waenke, H.

    1986-01-01

    Topics addressed include: meteorite concentration mechanisms; meteorites and the Antarctic ice sheet; iron meteorites; iodine overabundance in meteorites; entrainment, transport, and concentration of meteorites in polar ice sheets; weathering of stony meteorites; cosmic ray records; radiocarbon dating; element distribution and noble gas isotopic abundances in lunar meteorites; thermoanalytical characterization; trace elements; thermoluminescence; parent sources; and meteorite ablation and fusion spherules in Antarctic ice.

  5. Antarctic Mapping Tools for MATLAB

    NASA Astrophysics Data System (ADS)

    Greene, Chad A.; Gwyther, David E.; Blankenship, Donald D.

    2017-07-01

    We present the Antarctic Mapping Tools package, an open-source MATLAB toolbox for analysis and plotting of Antarctic geospatial datasets. This toolbox is designed to streamline scientific workflow and maximize repeatability through functions which allow fully scripted data analysis and mapping. Data access is facilitated by several dataset-specific plugins which are freely available online. An open architecture has been chosen to encourage users to develop and share plugins for future Antarctic geospatial datasets. This toolbox includes functions for coordinate transformations, flight line or ship track analysis, and data mapping in georeferenced or projected coordinates. Each function is thoroughly documented with clear descriptions of function syntax alongside examples of data analysis or display using Antarctic geospatial data. The Antarctic Mapping Tools package is designed for ease of use and allows users to perform each step of data processing including raw data import, data analysis, and creation of publication-quality maps, wholly within the numerical environment of MATLAB.

  6. Antarctic Peninsula Tidewater Glacier Dynamics

    NASA Astrophysics Data System (ADS)

    Pettit, E. C.; Scambos, T. A.; Haran, T. M.; Wellner, J. S.; Domack, E. W.; Vernet, M.

    2015-12-01

    The northern Antarctic Peninsula (nAP, north of 66°S) is a north-south trending mountain range extending transverse across the prevailing westerly winds of the Southern Ocean resulting in an extreme west-to-east precipitation gradient. Snowfall on the west side of the AP is one to two orders of magnitude higher than the east side. This gradient drives short, steep, fast-flowing glaciers into narrow fjords on the west side, while longer lower-sloping glaciers flow down the east side into broader fjord valleys. This pattern in ice dynamics affects ice-ocean interaction on timescales of decades to centuries, and shapes the subglacial topography and submarine bathymetry on timescales of glacial cycles. In our study, we calculate ice flux for the western and eastern nAP using a drainage model that incorporates the modern ice surface topography, the RACMO-2 precipitation estimate, and recent estimates of ice thinning. Our results, coupled with observed rates of ice velocity from InSAR (I. Joughin, personal communication) and Landsat 8 -derived flow rates (this study), provide an estimate of ice thickness and fjord depth in grounded-ice areas for the largest outlet glaciers. East-side glaciers either still terminate in or have recently terminated in ice shelves. Sedimentary evidence from the inner fjords of the western glaciers indicates they had ice shelves during LIA time, and may still have transient floating ice tongues (tabular berg calvings are observed). Although direct oceanographic evidence is limited, the high accumulation rate and rapid ice flux implies cold basal ice for the western nAP glaciers and therefore weak subglacial discharge relative to eastern nAP glaciers and or other tidewater fjord systems such as in Alaska. Finally, despite lower accumulation rates on the east side, the large elongate drainage basins result in a greater ice flux funneled through fewer deeper glaciers. Due to the relation between ice flux and erosion, these east-side glaciers

  7. Modelling the Antarctic Ice Sheet for the last 420kyr

    NASA Astrophysics Data System (ADS)

    Blasco, Javier; Álvarez-Solas, Jorge; Robinson, Alexander; Montoya, Marisa

    2017-04-01

    Proxy data reveal that in the last glacial-interglacial cycles the Antarctic Ice Sheet (AIS) has experienced changes of its ice volume contributing to past sea-level variations. The AIS is nowadays the largest ice sheet in the world and potentially the largest contributor to a future long term sea-level rise. Because it suffers no significant ablation, it loses mass via basal melting and calving, driven by oceanic forcing. Therefore understanding ice-ocean interactions is crucial to study its past and future. In particular the West Antarctic Ice Sheet (WAIS) is specially sensitive to changes in oceanic temperatures since it rests in its major part below sea level. It also contains the two largest ice shelves of the world, the Ross Ice Shelf and the Filchner-Ronne Ice Shelf whose collapse is believed could accelerate inland ice flow, due to the loss of their buttressing effect, and enhance sea-level rise. The aim of this work is to simulate the AIS for the last 420kyr under varying orbital forcing using a hybrid ice sheet-ice shelf model. In particular, we will analyze the effect of past oceanic temperatures by including a parametrization for the basal melting of the ice shelves and grounding line dependent on observations and oceanic temperature anomalies. These experiments will shed light into the mechanisms involved in the interactions between ocean and cryosphere relevant for the assessment of the AIS stability in the future.

  8. Notes on Antarctic Aviation

    DTIC Science & Technology

    1993-08-01

    being made around the coast of East operated a DH Fox Moth on floats in the Antarctic Antarctica by Mawson’s expedition (DH Gypsy Peninsula. In late...Wright Condors (modified AT-32s desig- Little America station and were located by an RAAF nated R4C-1 by the U.S. Navy) and a Staggerwing DH Gypsy Moth ...British use DH Fox Moth in Peninsula. 1930 Byrd uses Ford 4T, Fokker Universal and Fairchild, all on skis. Ford 4T flies to South Pole. Coastal flights

  9. Arctic and Antarctic sea ice and climate

    NASA Astrophysics Data System (ADS)

    Barreira, S.

    2014-12-01

    Principal Components Analysis in T-Mode Varimax rotated was performed on Antarctic and Arctic monthly sea ice concentration anomalies (SICA) fields for the period 1979-2014, in order to investigate which are the main spatial characteristics of sea ice and its relationship with atmospheric circulation. This analysis provides 5 patterns of sea ice for inter-spring period and 3 patterns for summer-autumn for Antarctica (69,2% of the total variance) and 3 different patterns for summer-autumn and 3 for winter-spring season for the Arctic Ocean (67,8% of the total variance).Each of these patterns has a positive and negative phase. We used the Monthly Polar Gridded Sea Ice Concentrations database derived from satellite information generated by NASA Team algorithm. To understand the links between the SICA and climate trends, we extracted the mean pressure and, temperature field patterns for the months with high loadings (positive or negative) of the sea ice patterns that gave distinct atmospheric structures associated with each one. For Antarctica, the first SICA spatial winter-spring pattern in positive phase shows a negative SICA centre over the Drake Passage and north region of Bellingshausen and Weddell Seas together with another negative SICA centre over the East Indian Ocean. Strong positive centres over the rest of the Atlantic and Indian Oceans basins and the Amundsen Sea are also presented. A strong negative pressure anomaly covers most of the Antarctic Continent centered over the Bellingshausen Sea accompanied by three positive pressure anomalies in middle-latitudes. During recent years, the Arctic showed persistent associations of sea-ice and climate patterns principally during summer. Our strongest summer-autumn pattern in negative phase showed a marked reduction on SICA over western Arctic, primarily linked to an overall increase in Arctic atmospheric temperature most pronounced over the Beaufort, Chukchi and East Siberian Seas, and a positive anomaly of

  10. Stardust in Antarctic Micrometeorites

    SciTech Connect

    Yada, Toru; Floss, Christine; Stadermann, Frank J.; Zinner, E.; Nakamura, T.; Noguchi, T.; Lea, Alan S.

    2008-03-07

    We report the discovery of presolar silicate, oxide (hibonite) and (possibly) SiC grains from four Antarctic micrometeorites. The oxygen isotopic compositions of the eighteen presolar silicate (and one oxide) grains found are consistent with those observed previously in primitive meteorites and interplanetary dust particles, and indicate origins in oxygen-rich red giant or asymptotic giant branch stars. Four grains with anomalous C isotopic compositions were also detected. 12C/13C as well as Si ratios are similar to those of mainstream SiC grains; the N isotopic composition of one grain is also consistent with a mainstream SiC classification. Presolar silicate grains were found in three of the seven AMMs studied, and are heterogeneously distributed within these micrometeorites. Fourteen of the 18 presolar silicate grains and 3 of the 4 C-anomalous grains were found within one AMM, T98G8. The presence of magnesiowüstite, which forms mainly through the decomposition of carbonates, in AMMs without presolar silicates, and its absence in the presolar silicate-bearing micrometeorites, suggests that parent body processes (specifically aqueous alteration) may determine the presence or absence of presolar silicates in Antarctic micrometeorites.

  11. Antarctic Marine Biodiversity and Deep-Sea Hydrothermal Vents

    PubMed Central

    Chown, Steven L.

    2012-01-01

    The diversity of many marine benthic groups is unlike that of most other taxa. Rather than declining from the tropics to the poles, much of the benthos shows high diversity in the Southern Ocean. Moreover, many species are unique to the Antarctic region. Recent work has shown that this is also true of the communities of Antarctic deep-sea hydrothermal vents. Vent ecosystems have been documented from many sites across the globe, associated with the thermally and chemically variable habitats found around these, typically high temperature, streams that are rich in reduced compounds and polymetallic sulphides. The animal communities of the East Scotia Ridge vent ecosystems are very different to those elsewhere, though the microbiota, which form the basis of vent food webs, show less differentiation. Much of the biological significance of deep-sea hydrothermal vents lies in their biodiversity, the diverse biochemistry of their bacteria, the remarkable symbioses among many of the marine animals and these bacteria, and the prospects that investigations of these systems hold for understanding the conditions that may have led to the first appearance of life. The discovery of diverse and unusual Antarctic hydrothermal vent ecosystems provides opportunities for new understanding in these fields. Moreover, the Antarctic vents south of 60°S benefit from automatic conservation under the Convention on the Conservation of Antarctic Marine Living Resources and the Antarctic Treaty. Other deep-sea hydrothermal vents located in international waters are not protected and may be threatened by growing interests in deep-sea mining. PMID:22235192

  12. Numerical model of circumpolar Antarctic ice shelves

    SciTech Connect

    Johnson, R.C.

    1985-01-01

    Extensive floating ice shelves in the Antarctic have been proposed to explain the discrepancies between Pleistocene high sea levels shown by dated coral reefs and coeval low sea levels inferred from glacial ice volumes calculated from oxygen isotope ratios in deep sea cores. A numerical model using the floating shelf creep analysis of Weertman (1957) has provided a plausible basis for the acceptance of such shelves. Shelf outer limits were set at 55/sup 0/S in East Antarctica and 58/sup 0/S in West Antarctica, based in part on diatom-deficient deep sea sediments deposited prior to the Holocene. Precipitation varied from 10 gm cm/sup -2/yr/sup -1/ at 75/sup 0/S to 80 gm cm/sup -2/yr/sup -1/ at 55/sup 0/S. Mean air temperatures varied from -35/sup 0/C at the 75/sup 0/S coast to -17/sup 0/C at the outer limits. Isotope ratios were those of present Antarctic precipitation at corresponding model shelf temperatures. In the calculation, a steady state is assumed. Integration begins at the coast with summation over successive years as creep and continental ice discharge move the integration element to the outer limits. The oceanic oxygen isotope ratio change required by the discrepancies in the record is 0.40 to 0.50 ppmil. Using the flow law constant of 4.2 and a creep activation energy of 134 kjoules mol/sup -1/, the resulting change is 0.44 ppmil. Difference results reflect the uncertainties associated with the critical creep constants used in the modeling. Nevertheless, the results suggest that a quantity of Antarctic shelf ice comparable to ice volumes in major Northern glacial areas existed at times during the Pleistocene.

  13. Improving Our Understanding of Antarctic Sea Ice with NASA's Operation IceBridge and the Upcoming ICESat-2 Mission

    NASA Technical Reports Server (NTRS)

    Petty, Alek A.; Markus, Thorsten; Kurtz, Nathan T.

    2017-01-01

    Antarctic sea ice is a crucial component of the global climate system. Rapid sea ice production regimes around Antarctica feed the lower branch of the Southern Ocean overturning circulation through intense brine rejection and the formation of Antarctic Bottom Water (e.g., Orsi et al. 1999; Jacobs 2004), while the northward transport and subsequent melt of Antarctic sea ice drives the upper branch of the overturning circulation through freshwater input (Abernathy et al. 2016). Wind-driven trends in Antarctic sea ice (Holland Kwok 2012) have likely increased the transport of freshwater away from the Antarctic coastline, significantly altering the salinity distribution of the Southern Ocean (Haumann et al. 2016). Conversely, weaker sea ice production and the lack of shelf water formation over the Amundsen and Bellingshausen shelf seas promote intrusion of warm Circumpolar Deep Water onto the continental shelf and the ocean-driven melting of several ice shelves fringing the West Antarctic Ice Sheet (e.g., Jacobs et al. 2011; Pritchard et al. 2012; Dutrieux et al. 2014). Sea ice conditions around Antarctica are also increasingly considered an important factor impacting local atmospheric conditions and the surface melting of Antarctic ice shelves (e.g., Scambos et al. 2017). Sea ice formation around Antarctica is responsive to the strong regional variability in atmospheric forcing present around Antarctica, driving this bimodal variability in the behavior and properties of the underlying shelf seas (e.g., Petty et al. 2012; Petty et al. 2014).

  14. Impact of Tropical Teleconnections on Antarctic Sea Ice and Climate

    NASA Astrophysics Data System (ADS)

    Twedt, Judy R.

    The role of tropical teleconnections on Antarctic sea ice and climate is investigated. Teleconnections are generated in a fully coupled and a slab ocean simulation. We find that both experiments are able to replicate the observed satellite-era anomalies in atmospheric circulation in west Antarctica. Perturbation heating anomaly experiments show that Atlantic teleconnections may also impact Amundsen sea ice variability. When ocean circulation response is suppressed, sea ice exhibits a stronger response to circulation anomalies generated by the the tropics. Furthermore, we show that a wind-driven cooling of the tropical Pacific does not generate a slow-down in global warming.

  15. Metazoan Parasites of Antarctic Fishes.

    PubMed

    Oğuz, Mehmet Cemal; Tepe, Yahya; Belk, Mark C; Heckmann, Richard A; Aslan, Burçak; Gürgen, Meryem; Bray, Rodney A; Akgül, Ülker

    2015-06-01

    To date, there have been nearly 100 papers published on metazoan parasites of Antarctic fishes, but there has not yet been any compilation of a species list of fish parasites for this large geographic area. Herein, we provide a list of all documented occurrences of monogenean, cestode, digenean, acanthocephalan, nematode, and hirudinean parasites of Antarctic fishes. The list includes nearly 250 parasite species found in 142 species of host fishes. It is likely that there are more species of fish parasites, which are yet to be documented from Antarctic waters.

  16. RADARSAT: The Antarctic Mapping Project

    NASA Technical Reports Server (NTRS)

    Jezek, Kenneth C.; Lindstrom, E. (Technical Monitor)

    2002-01-01

    The first Antarctic Imaging Campaign (AIC) occurred during the period September 9, 1997 through October 20, 1997. The AIC utilized the unique attributes of the Canadian RADARSAT-1 to acquire the first, high-resolution, synthetic aperture imagery covering the entire Antarctic Continent. Although the primary goal of the mission was the acquisition of image data, the nearly flawless execution of the mission enabled additional collections of exact repeat orbit data. These data, covering an extensive portion of the interior Antarctic, potentially are suitable for interferometric analysis of topography and surface velocity. This document summarizes the Project through completion with delivery of products to the NASA DAACs.

  17. Antarctic and non-Antarctic meteorites form different populations

    NASA Technical Reports Server (NTRS)

    Dennison, J. E.; Lingner, D. W.; Lipschutz, M. E.

    1986-01-01

    The trace element differences between Victoria Land H5 chondrites and non-Antarctic H5 chondrites are studied. The focus on common meteorites was stimulated by Antarctic and non-Antarctic differences in meteorite types and in the trace element contents of congeners of rare type. Thirteen elements were analyzed by neutron activation analysis with radiochemical separation, and eight differed significantly. Eliminating test biasing and the possibility of compositional difference due to Antarctic weathering of the 300,000 year-old (on the average) Victoria Land falls, it is concluded that the two sets of chondrites differ due to extraterrestrial causes. The three possibilities discussed, differences in sample population, physical properties, orbital characteristics, and meteoroid flux with time, are all seen as problematic.

  18. Drag coefficients for winter Antarctic pack ice

    NASA Technical Reports Server (NTRS)

    Wamser, Christian; Martinson, Douglas G.

    1993-01-01

    Air-ice and ice-water drag coefficients referenced to 10-m-height winds for winter Antarctic pack ice based on measurements made from R/V Polarstern during the Winter Weddell Sea Project, 1986 (WWSP-86), and from R/V Akademik Fedorov during the Winter Weddell Gyre Study, 1989 (WWGS-89), are presented. The optimal values of the air-ice drag coefficients, made from turbulent flux measurements, are (1.79 +/- 0.06) x 10 exp -3 for WWSP-86 and (1.45 +/- 0.09) x 10 exp -3 for WWGS-89. A single ice-water drag coefficient for both WWSP-86 and WWGS-89, estimated from periods of ice drift throught to represent free-drift conditions, is (1.13 +/- 0.26) x 10 exp -3, and the ice-water turning angle is 18 +/- 18 deg. It is suggested that for a typical Antarctic winter pack ice cover, the ice cover reduces the momentum flux from the atmosphere to the ocean by about 33 percent.

  19. Widespread Antarctic glaciation during the Late Eocene

    NASA Astrophysics Data System (ADS)

    Carter, Andrew; Riley, Teal R.; Hillenbrand, Claus-Dieter; Rittner, Martin

    2017-01-01

    Marine sedimentary rocks drilled on the southeastern margin of the South Orkney microcontinent in Antarctica (Ocean Drilling Program Leg 113 Site 696) were deposited between ∼36.5 Ma to 33.6 Ma, across the Eocene-Oligocene climate transition. The recovered rocks contain abundant grains exhibiting mechanical features diagnostic of iceberg-rafted debris. Sand provenance based on a multi-proxy approach that included petrographic analysis of over 275,000 grains, detrital zircon geochronology and apatite thermochronometry rule out local sources (Antarctic Peninsula or the South Orkney Islands) for the material. Instead the ice-transported grains show a clear provenance from the southern Weddell Sea region, extending from the Ellsworth-Whitmore Mountains of West Antarctica to the coastal region of Dronning Maud Land in East Antarctica. This study provides the first evidence for a continuity of widespread glacier calving along the coastline of the southern Weddell Sea embayment at least 2.5 million yrs before the prominent oxygen isotope event at 34-33.5 Ma that is considered to mark the onset of widespread glaciation of the Antarctic continent.

  20. Mapping Antarctic grounding lines from Cryosat-2

    NASA Astrophysics Data System (ADS)

    Wouters, B.; Bamber, J. L.

    2014-12-01

    The grounding zone (GZ) of the Antarctic ice sheet is a critical boundary for assessing the mass of ice leaving the continent and the stability (or lack thereof) of the inland, grounded ice sheet. It marks the transition between ice that can contribute to sea level and that which already has. Ice shelf basal melt rates are a maximum close the GZ and can have an important influence on inland flow. Changes in the position of the GZ for an ice stream resting on a bed with a retrograde slope (deepening inland) can provide an early warning of an instability in flow or state transition. Several methods exists to monitor the GZ, however, to date, there has been no method for routinely and regularly monitoring the GZ, nor any method that can be applied unambiguously across its entirety around Antarctica. The CryoSat-2 mission provides year-round coverage of the ice sheets, at a high spatial resolution. On the Antarctic ice shelves, the 369 day repeat period of the observations leads to aliasing of tidal motion induced by ocean tides, resulting in distinct patterns in the CryoSat-2 elevation measurements. Here, we focus on the Filchner-Ronne ice shelf to demonstrate the potential of the Cryosat-2 observations to map the GZ, and compare our results with existing GZ estimates.

  1. Drag coefficients for winter Antarctic pack ice

    NASA Technical Reports Server (NTRS)

    Wamser, Christian; Martinson, Douglas G.

    1993-01-01

    Air-ice and ice-water drag coefficients referenced to 10-m-height winds for winter Antarctic pack ice based on measurements made from R/V Polarstern during the Winter Weddell Sea Project, 1986 (WWSP-86), and from R/V Akademik Fedorov during the Winter Weddell Gyre Study, 1989 (WWGS-89), are presented. The optimal values of the air-ice drag coefficients, made from turbulent flux measurements, are (1.79 +/- 0.06) x 10 exp -3 for WWSP-86 and (1.45 +/- 0.09) x 10 exp -3 for WWGS-89. A single ice-water drag coefficient for both WWSP-86 and WWGS-89, estimated from periods of ice drift throught to represent free-drift conditions, is (1.13 +/- 0.26) x 10 exp -3, and the ice-water turning angle is 18 +/- 18 deg. It is suggested that for a typical Antarctic winter pack ice cover, the ice cover reduces the momentum flux from the atmosphere to the ocean by about 33 percent.

  2. Ice core and climate reanalysis analogs to predict Antarctic and Southern Hemisphere climate changes

    NASA Astrophysics Data System (ADS)

    Mayewski, P. A.; Carleton, A. M.; Birkel, S. D.; Dixon, D.; Kurbatov, A. V.; Korotkikh, E.; McConnell, J.; Curran, M.; Cole-Dai, J.; Jiang, S.; Plummer, C.; Vance, T.; Maasch, K. A.; Sneed, S. B.; Handley, M.

    2017-01-01

    A primary goal of the SCAR (Scientific Committee for Antarctic Research) initiated AntClim21 (Antarctic Climate in the 21st Century) Scientific Research Programme is to develop analogs for understanding past, present and future climates for the Antarctic and Southern Hemisphere. In this contribution to AntClim21 we provide a framework for achieving this goal that includes: a description of basic climate parameters; comparison of existing climate reanalyses; and ice core sodium records as proxies for the frequencies of marine air mass intrusion spanning the past ∼2000 years. The resulting analog examples include: natural variability, a continuation of the current trend in Antarctic and Southern Ocean climate characterized by some regions of warming and some cooling at the surface of the Southern Ocean, Antarctic ozone healing, a generally warming climate and separate increases in the meridional and zonal winds. We emphasize changes in atmospheric circulation because the atmosphere rapidly transports heat, moisture, momentum, and pollutants, throughout the middle to high latitudes. In addition, atmospheric circulation interacts with temporal variations (synoptic to monthly scales, inter-annual, decadal, etc.) of sea ice extent and concentration. We also investigate associations between Antarctic atmospheric circulation features, notably the Amundsen Sea Low (ASL), and primary climate teleconnections including the SAM (Southern Annular Mode), ENSO (El Nîno Southern Oscillation), the Pacific Decadal Oscillation (PDO), the AMO (Atlantic Multidecadal Oscillation), and solar irradiance variations.

  3. Origin, signature and palaeoclimatic influence of the Antarctic Circumpolar Current

    NASA Astrophysics Data System (ADS)

    Barker, P. F.; Thomas, E.

    2004-06-01

    The Antarctic Circumpolar Current (ACC) is today the strongest current in the world's ocean, with a significant influence on global climate. Its assumed history and influence on palaeoclimate, while almost certainly equally profound, are here called into question. In this paper, we review 30 years of accumulated data, interpretation and speculation about the ACC, deriving mainly from DSDP and ODP drilling in the Southern Ocean. For most of this time, a conventional view of ACC development, signature and influence has held sway among palaeoceanographers and marine geologists. In this view, the ACC began at about 34 Ma, close to the Eocene-Oligocene boundary, the time of onset of significant Antarctic glaciation and the time of creation of a deep-water gap (Tasmanian Seaway) between Australia and Antarctica as the South Tasman Rise separated from North Victoria Land. This is the "smoking gun" of synchroneity. The Southern Ocean sediment record shows a latest Eocene development and subsequent geographic expansion of a siliceous biofacies, its northern limit taken to indicate the palaeo-position of the ACC axis. In addition, the ACC was considered to have caused Antarctic glaciation by isolating the continent within a cold-water annulus, reducing north-south heat transport. A different (and later) date for Antarctic-South American opening ("Drake Passage") was proposed, but the timing of ACC onset there was disputed, and the simple story survived. Recent developments, however, call it into question. Modern physical oceanography shows that all or most of present-day ACC transport is confined to narrow jets within deep-reaching circumpolar fronts, and numerical modelling has suggested that a steady reduction in greenhouse gas concentration through the Cenozoic could cause Antarctic glaciation, with or without a contribution from ocean circulation change. The rapidity of Antarctic glacial onset at the Eocene-Oligocene boundary and coeval creation of a deep-water gap south

  4. Are Antarctic minke whales unusually abundant because of 20th century whaling?

    PubMed

    Ruegg, Kristen C; Anderson, Eric C; Scott Baker, C; Vant, Murdoch; Jackson, Jennifer A; Palumbi, Stephen R

    2010-01-01

    Severe declines in megafauna worldwide illuminate the role of top predators in ecosystem structure. In the Antarctic, the Krill Surplus Hypothesis posits that the killing of more than 2 million large whales led to competitive release for smaller krill-eating species like the Antarctic minke whale. If true, the current size of the Antarctic minke whale population may be unusually high as an indirect result of whaling. Here, we estimate the long-term population size of the Antarctic minke whale prior to whaling by sequencing 11 nuclear genetic markers from 52 modern samples purchased in Japanese meat markets. We use coalescent simulations to explore the potential influence of population substructure and find that even though our samples are drawn from a limited geographic area, our estimate reflects ocean-wide genetic diversity. Using Bayesian estimates of the mutation rate and coalescent-based analyses of genetic diversity across loci, we calculate the long-term population size of the Antarctic minke whale to be 670,000 individuals (95% confidence interval: 374,000-1,150,000). Our estimate of long-term abundance is similar to, or greater than, contemporary abundance estimates, suggesting that managing Antarctic ecosystems under the assumption that Antarctic minke whales are unusually abundant is not warranted.

  5. The polar amplification asymmetry: role of Antarctic surface height

    NASA Astrophysics Data System (ADS)

    Salzmann, Marc

    2017-05-01

    Previous studies have attributed an overall weaker (or slower) polar amplification in Antarctica compared to the Arctic to a weaker Antarctic surface albedo feedback and also to more efficient ocean heat uptake in the Southern Ocean in combination with Antarctic ozone depletion. Here, the role of the Antarctic surface height for meridional heat transport and local radiative feedbacks, including the surface albedo feedback, was investigated based on CO2-doubling experiments in a low-resolution coupled climate model. When Antarctica was assumed to be flat, the north-south asymmetry of the zonal mean top of the atmosphere radiation budget was notably reduced. Doubling CO2 in a flat Antarctica (flat AA) model setup led to a stronger increase in southern hemispheric poleward atmospheric and oceanic heat transport compared to the base model setup. Based on partial radiative perturbation (PRP) computations, it was shown that local radiative feedbacks and an increase in the CO2 forcing in the deeper atmospheric column also contributed to stronger Antarctic warming in the flat AA model setup, and the roles of the individual radiative feedbacks are discussed in some detail. A considerable fraction (between 24 and 80 % for three consecutive 25-year time slices starting in year 51 and ending in year 126 after CO2 doubling) of the polar amplification asymmetry was explained by the difference in surface height, but the fraction was subject to transient changes and might to some extent also depend on model uncertainties. In order to arrive at a more reliable estimate of the role of land height for the observed polar amplification asymmetry, additional studies based on ensemble runs from higher-resolution models and an improved model setup with a more realistic gradual increase in the CO2 concentration are required.

  6. Antarctic Meteorite Location Map Series

    NASA Technical Reports Server (NTRS)

    Schutt, John (Editor); Fessler, Brian (Editor); Cassidy, William (Editor)

    1989-01-01

    Antarctica has been a prolific source of meteorites since meteorite concentrations were discovered in 1969. The Antarctic Search For Meteorites (ANSMET) project has been active over much of the Trans-Antarctic Mountain Range. The first ANSMET expedition (a joint U.S.-Japanese effort) discovered what turned out to be a significant concentration of meteorites at the Allan Hills in Victoria Land. Later reconnaissance in this region resulted in the discovery of meteorite concentrations on icefields to the west of the Allan Hills, at Reckling Moraine, and Elephant Moraine. Antarctic meteorite location maps (reduced versions) of the Allan Hills main, near western, middle western, and far western icefields and the Elephant Moraine icefield are presented. Other Antarctic meteorite location maps for the specimens found by the ANSMET project are being prepared.

  7. Antarctic stratospheric ice crystals

    NASA Technical Reports Server (NTRS)

    Goodman, J.; Toon, O. B.; Pueschel, R. F.; Snetsinger, K. G.; Verma, S.

    1989-01-01

    Ice crystals were replicated over the Palmer Peninsula at approximately 72 deg S on six occasions during the 1987 Airboirne Antarctic Ozone Experiment. The sampling altitude was between 12.5 and 18.5 km (45-65 thousand ft pressure altitude) with the temperature between 190 and 201 K. The atmosphere was subsaturated with respect to ice in all cases. The collected crystals were predominantly solid and hollow columns. The largest crystals were sampled at lower altitudes where the potential temperature was below 400 K. While the crystals were larger than anticipated, their low concentration results in a total surface area that is less than one tenth of the total aerosol surface area. The large ice crystals may play an important role in the observed stratospheric dehydration processes through sedimentation. Evidence of scavenging of submicron particles further suggests that the ice crystals may be effective in the removal of stratospheric chemicals.

  8. Projected changes of Antarctic krill habitat by the end of the 21st century

    NASA Astrophysics Data System (ADS)

    Piñones, Andrea; Fedorov, Alexey V.

    2016-08-01

    Climate change is rapidly shaping the living environment of the most abundant keystone species of the Antarctic marine food web, Antarctic krill. Projected future changes for the krill habitat include a sustained increase in ocean temperature and changes in sea ice and chlorophyll a. Here we investigate how these factors affect the early life history of krill and identify the regions around Antarctica where the impact will be greatest. Our tool is a temperature-dependent krill growth model forced by data from comprehensive greenhouse warming simulations. We find that by the year 2100 localized regions along the western Weddell Sea, isolated areas of the Indian Antarctic , and the Amundsen/Bellingshausen Sea will support successful spawning habitats for krill. The failure of potentially successful spawning will have a strong impact on the already declining adult populations with consequences for the Antarctic marine food web, having both ecological and commercial ramifications.

  9. Paleoclimate perspectives on Antarctic ice sheet sensitivity

    NASA Astrophysics Data System (ADS)

    Naish, Timothy

    2015-04-01

    Near- and long-term future projections of global mean sea level rise (SLR) are hampered by a lack of understanding of the potential dynamic contribution of the polar ice sheets, and in particular the Antarctic ice sheets. With the completion of the Intergovernmental Panel on Climate Change's Assessment Report a major challenge continues to be placing an upper bound in sea-level projections for 2100 and beyond. The so-called "deterministic" approach which sums observed- and model-projected trends in the known contributions (e.g. ice sheet and glacier surface mass balance, ocean thermal expansion and ground water storage changes) implies a "likely" upper bound of +100cm by 2080-2100. The "semi-empirical" approach which scales past observed sea-level change to mean surface temperature, and uses this relationship to scale future temperature scenarios, predicts a significantly higher upper bound of up to ~2m by 2100. The discrepancy between the two approaches may in part reflect the poorly understood contribution of ice dynamics - that is the rate of flow of ice sheets into the ocean. An ensemble of Antarctic ice sheet models produces highly divergent results for future sea-level projections, primarily because of uncertainties around the mass changes in the East Antarctic Ice Sheet with some models showing increased precipitation driving a positive mass balance overall, even with loss of the marine-based West Antarctic Ice Sheet (WAIS). Current best estimates suggest a 10-20cm dynamic ice sheet contribution by 2100 to global SLR. Of concern is that marine based ice sheets are highly sensitive to increases in ocean temperature at their margins and rapid disintegration may ensue if the ice sheets grounding lines retreat into deep sub-glacial basins. Recent studies show the highest rates of ice sheet thinning and retreat are occurring at locations around the WAIS where the surface ocean has warmed, and that some WAIS loss may now be irreversible. Geological records allow

  10. Antarctic subglacial lake discharges

    NASA Astrophysics Data System (ADS)

    Pattyn, Frank

    Antarctic subglacial lakes were long time supposed to be relatively closed and stable environments with long residence times and slow circulations. This view has recently been challenged with evidence of active subglacial lake discharge underneath the Antarctic ice sheet. Satellite altimetry observations witnessed rapid changes in surface elevation across subglacial lakes over periods ranging from several months to more than a year, which were interpreted as subglacial lake discharge and subsequent lake filling, and which seem to be a common and widespread feature. Such discharges are comparable to jökulhlaups and can be modeled that way using the Nye-Röthlisberger theory. Considering the ice at the base of the ice sheet at pressure melting point, subglacial conduits are sustainable over periods of more than a year and over distances of several hundreds of kilometers. Coupling of an ice sheet model to a subglacial lake system demonstrated that small changes in surface slope are sufficient to start and sustain episodic subglacial drainage events on decadal time scales. Therefore, lake discharge may well be a common feature of the subglacial hydrological system, influencing the behavior of large ice sheets, especially when subglacial lakes are perched at or near the onset of large outlet glaciers and ice streams. While most of the observed discharge events are relatively small (101-102 m3 s-1), evidence for larger subglacial discharges is found in ice free areas bordering Antarctica, and witnessing subglacial floods of more than 106 m3 s-1 that occurred during the middle Miocene.

  11. A glimpse into the deep of the Antarctic Polar Front - Diversity and abundance of abyssal molluscs

    NASA Astrophysics Data System (ADS)

    Jörger, K. M.; Schrödl, M.; Schwabe, E.; Würzberg, L.

    2014-10-01

    Our knowledge of the biodiversity and distribution patterns of benthic deep-sea faunas is still limited, with large parts of the world's abyss unexplored, lacking α-taxonomic data across oceans basins and especially of biogeographic transition zones between oceans. The Antarctic Polar Frontal Zone has been discussed as major biogeographic barrier hindering faunal exchange between Subantarctic and Antarctic provinces and conserving high rates of endemism in the Southern Ocean benthos. In the present study we report first, exploratory α-taxonomy on the malacofauna sampled by means of an epibenthic sledge from four bathyal respectively abyssal stations (2732-4327 m depth) in the vicinity of the Antarctic Polar Front during the SYSTCO II expedition (SYSTem COupling in the Southern Ocean, RV Polarstern cruise ANT XXVIII/3). We identified 58 distinct molluscan taxa based on external morphology ('morphospecies'); of the 33 taxa successfully assigned to described species 94% were previously reported from the Southern Ocean, but 24% exhibit distribution ranges crossing the Polar Front. One North Atlantic scaphopod is reported for the first time in Antarctic waters. Our study supports that the Antarctic Polar Front does not serve as effective barrier preventing gene flow in deep-sea molluscs. The present dataset shows the general characteristics of deep-sea sampling: patchiness in distribution and a high degree of singletons. Overall molluscan abundances were generally low ranging between 3.60 and 24.65 ind./1000 m², but in comparison with equatorial and subtropic abyssal basins, gastropod species richness and abundance were reaching high values similar to high Antarctic stations. Comparison between high productivity and low productivity zones along the Polar Front suggests increased abundances and species richness in high productivity zones. Intensified sampling is needed, however, to outweigh stochastic errors and to evaluate the influence of carbon flux as driving

  12. Recent changes in Antarctic Sea Ice.

    PubMed

    Turner, John; Hosking, J Scott; Bracegirdle, Thomas J; Marshall, Gareth J; Phillips, Tony

    2015-07-13

    In contrast to the Arctic, total sea ice extent (SIE) across the Southern Ocean has increased since the late 1970s, with the annual mean increasing at a rate of 186×10(3) km(2) per decade (1.5% per decade; p<0.01) for 1979-2013. However, this overall increase masks larger regional variations, most notably an increase (decrease) over the Ross (Amundsen-Bellingshausen) Sea. Sea ice variability results from changes in atmospheric and oceanic conditions, although the former is thought to be more significant, since there is a high correlation between anomalies in the ice concentration and the near-surface wind field. The Southern Ocean SIE trend is dominated by the increase in the Ross Sea sector, where the SIE is significantly correlated with the depth of the Amundsen Sea Low (ASL), which has deepened since 1979. The depth of the ASL is influenced by a number of external factors, including tropical sea surface temperatures, but the low also has a large locally driven intrinsic variability, suggesting that SIE in these areas is especially variable. Many of the current generation of coupled climate models have difficulty in simulating sea ice. However, output from the better-performing IPCC CMIP5 models suggests that the recent increase in Antarctic SIE may be within the bounds of intrinsic/internal variability. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

  13. Thermochronologic constraints on the tectonic evolution of the western Antarctic Peninsula in late Mesozoic and Cenozoic times

    USGS Publications Warehouse

    Brix, M.R.; Faundez, V.; Hervé, F.; Solari, M.; Fernandez, J.; Carter, A.; Stöckhert, B.

    2007-01-01

    West of the Antarctic Peninsula, oceanic lithosphere of the Phoenix plate has been subducted below the Antarctic plate. Subduction has ceased successively from south to north over the last 65 Myr. An influence of this evolution on the segmentation of the crust in the Antarctic plate is disputed. Opposing scenarios consider effects of ridge crest – trench interactions with the subduction zone or differences in slip along a basal detachment in the overriding plate. Fission track (FT) analyses on apatites and zircons may detect thermochronologic patterns to test these hypotheses. While existing data concentrate on accretionary processes in Palmer Land, new data extend information to the northern part of the Antarctic Peninsula. Zircons from different geological units over wide areas of the Antarctic Peninsula yield fission track ages between 90 and 80 Ma, indicating a uniform regional cooling episode. Apatite FT ages obtained so far show considerable regional variability

  14. Centennial-scale Holocene climate variations amplified by Antarctic Ice Sheet discharge

    NASA Astrophysics Data System (ADS)

    Bakker, Pepijn; Clark, Peter U.; Golledge, Nicholas R.; Schmittner, Andreas; Weber, Michael E.

    2017-01-01

    Proxy-based indicators of past climate change show that current global climate models systematically underestimate Holocene-epoch climate variability on centennial to multi-millennial timescales, with the mismatch increasing for longer periods. Proposed explanations for the discrepancy include ocean-atmosphere coupling that is too weak in models, insufficient energy cascades from smaller to larger spatial and temporal scales, or that global climate models do not consider slow climate feedbacks related to the carbon cycle or interactions between ice sheets and climate. Such interactions, however, are known to have strongly affected centennial- to orbital-scale climate variability during past glaciations, and are likely to be important in future climate change. Here we show that fluctuations in Antarctic Ice Sheet discharge caused by relatively small changes in subsurface ocean temperature can amplify multi-centennial climate variability regionally and globally, suggesting that a dynamic Antarctic Ice Sheet may have driven climate fluctuations during the Holocene. We analysed high-temporal-resolution records of iceberg-rafted debris derived from the Antarctic Ice Sheet, and performed both high-spatial-resolution ice-sheet modelling of the Antarctic Ice Sheet and multi-millennial global climate model simulations. Ice-sheet responses to decadal-scale ocean forcing appear to be less important, possibly indicating that the future response of the Antarctic Ice Sheet will be governed more by long-term anthropogenic warming combined with multi-centennial natural variability than by annual or decadal climate oscillations.

  15. Centennial-scale Holocene climate variations amplified by Antarctic Ice Sheet discharge.

    PubMed

    Bakker, Pepijn; Clark, Peter U; Golledge, Nicholas R; Schmittner, Andreas; Weber, Michael E

    2017-01-05

    Proxy-based indicators of past climate change show that current global climate models systematically underestimate Holocene-epoch climate variability on centennial to multi-millennial timescales, with the mismatch increasing for longer periods. Proposed explanations for the discrepancy include ocean-atmosphere coupling that is too weak in models, insufficient energy cascades from smaller to larger spatial and temporal scales, or that global climate models do not consider slow climate feedbacks related to the carbon cycle or interactions between ice sheets and climate. Such interactions, however, are known to have strongly affected centennial- to orbital-scale climate variability during past glaciations, and are likely to be important in future climate change. Here we show that fluctuations in Antarctic Ice Sheet discharge caused by relatively small changes in subsurface ocean temperature can amplify multi-centennial climate variability regionally and globally, suggesting that a dynamic Antarctic Ice Sheet may have driven climate fluctuations during the Holocene. We analysed high-temporal-resolution records of iceberg-rafted debris derived from the Antarctic Ice Sheet, and performed both high-spatial-resolution ice-sheet modelling of the Antarctic Ice Sheet and multi-millennial global climate model simulations. Ice-sheet responses to decadal-scale ocean forcing appear to be less important, possibly indicating that the future response of the Antarctic Ice Sheet will be governed more by long-term anthropogenic warming combined with multi-centennial natural variability than by annual or decadal climate oscillations.

  16. Centennial-scale Holocene climate variations amplified by Antarctic Ice Sheet discharge

    NASA Astrophysics Data System (ADS)

    Bakker, Pepijn; Clark, Peter U.; Golledge, Nicholas R.; Schmittner, Andreas; Weber, Michael E.

    2016-12-01

    Proxy-based indicators of past climate change show that current global climate models systematically underestimate Holocene-epoch climate variability on centennial to multi-millennial timescales, with the mismatch increasing for longer periods. Proposed explanations for the discrepancy include ocean-atmosphere coupling that is too weak in models, insufficient energy cascades from smaller to larger spatial and temporal scales, or that global climate models do not consider slow climate feedbacks related to the carbon cycle or interactions between ice sheets and climate. Such interactions, however, are known to have strongly affected centennial- to orbital-scale climate variability during past glaciations, and are likely to be important in future climate change. Here we show that fluctuations in Antarctic Ice Sheet discharge caused by relatively small changes in subsurface ocean temperature can amplify multi-centennial climate variability regionally and globally, suggesting that a dynamic Antarctic Ice Sheet may have driven climate fluctuations during the Holocene. We analysed high-temporal-resolution records of iceberg-rafted debris derived from the Antarctic Ice Sheet, and performed both high-spatial-resolution ice-sheet modelling of the Antarctic Ice Sheet and multi-millennial global climate model simulations. Ice-sheet responses to decadal-scale ocean forcing appear to be less important, possibly indicating that the future response of the Antarctic Ice Sheet will be governed more by long-term anthropogenic warming combined with multi-centennial natural variability than by annual or decadal climate oscillations.

  17. Cephalopods Occupy the Ecological Niche of Epipelagic Fish in the Antarctic Polar Frontal Zone.

    PubMed

    Rodhouse, P G; White, M G

    1995-10-01

    Recent data from research cruises and explorator fishing in the Antarctic Polar Frontal Zone (APFZ) of the Scotia Sea, together with data from dietary studies of Antarctic vertebrate predators, have revealed a large, previously overlooked trophic system in the Southern Ocean (Fig. 1). The upper trophic levels of this open-ocean epipelagic community are exceptional in that they contain no fish species. Fishes are replaced by cephalopods, including the ommastrephid squid, Martialia hyadesi. This squid preys on mesopelagic m.yctophids (lanternfish), which feed largely on copepods. We identify here a geographically distinct, Antarctic, open-ocean food chain which is of importance to air breathing predator species but where Antarctic krill, Euphausia superba, is absent. This system is probably prevalent in areas of higher primary productivity, especially the Scotia Sea and near the peri-Antarctic islands. Squid stocks in the APFZ may have potential for commercial exploitation, but they, and the predators they support, are likely to be sensitive to overfishing. Squid have a short, semelparous lifecycle, so overfishing in a single year can cause a stock to collapse.

  18. The Antarctic Master Directory -- a resource for Antarctic Scientists

    NASA Astrophysics Data System (ADS)

    Scharfen, G.; Bauer, R.

    2002-12-01

    Under the auspices of the Antarctic Treaty, a group of nations conducting Antarctic scientific research have created the Antarctic Master Directory (AMD), a resource for Antarctic scientists. The AMD is a Web-based, searchable directory containing data descriptions (metadata in the form of DIF entries) of Antarctic scientific data, and is a node of the International Directory Network/Global Change Master Directory (IDN/GCMD). The data descriptions in the AMD, essentially a data catalog of Antarctic scientific data, include information about what data were collected, where they were collected, when they were collected, who the scientists are, who the point of contact is, and information about the format of the data and what documentation and bibliographic information exists. As part of the AMD effort, the National Science Foundation Office of Polar Programs (OPP) funds the National Snow and Ice Data Center to operate the U.S. Antarctic Data Coordination Center (USADCC), the US focal point for the AMD. The USADCC assists PIs as they meet the requirements of the OPP "Guidelines and Award Conditions for Scientific Data", which identify the conditions for awards and responsibilities of PIs regarding the archival of data, and submission of metadata, resulting from their NSF OPP grants. The USADCC offers access to free, easy-to-use online tools that PIs can use to create the data descriptions that the NSF policy data requires. We provide advice to PIs on how to meet the data policy requirements, and can answer specific questions on related issues. Scientists can access data set descriptions submitted to the AMD, by thousands of scientists around the world, from the USADCC web pages.

  19. Modeling Drastic Ice Retreat in Antarctic Subglacial Basins

    NASA Astrophysics Data System (ADS)

    Pollard, D.; Deconto, R. M.

    2013-12-01

    Various data indicate that global mean sea level has fluctuated on O(10,000 to 100,000) year time scales during the last ~25 million years, reaching 20 m or more above modern. If correct, this implies substantial variations in the size of the East Antarctic Ice Sheet (EAIS). However, climate and ice-sheet models have not been able to simulate significant EAIS retreat from continental size, given low proxy atmospheric CO2 levels during this time. Here, we use a new mechanism involving a maximum vertical ice cliff size of ~100 m above the ocean at the grounding line beyond which structural failure occurs, triggered by the complete melting of floating shelves that normally prevent this configuration in large embayments. This is tested in a 3-D ice-sheet model by applying oceanic and climatic warming representing past warm periods, which attacks floating ice shelves by basal melting and by increased calving due to surface melt or rain draining into crevasses. In addition to accelerating the expected collapse of West Antarctic ice, the new mechanisms cause drastic retreat into 3 major East Antarctic subglacial basins, causing ~20 m global sea-level rise within a few thousand years that takes more than 10,000 years to recover. This offers a resolution of the past sea level model-data conflict, but suggests that Antarctica may be more vulnerable to future warming than previously realized.

  20. South-western African climate depends on Antarctic sea ice

    NASA Astrophysics Data System (ADS)

    Stuut, J.-B. W.; Crosta, X.; van der Borg, K.; Schneider, R. R.

    2003-04-01

    The typical Fynbos vegetation of the Cape region of South-western Africa is brought about by the local Mediterranean (winter rainfall) climate and its associated sharp seasonal contrasts, especially in precipitation. This biome is bordered by hyper-arid deserts which may rapidly expand in response to future global warming, such as during the last warm period 125.000 years ago. It is therefore essential to understand the mechanisms that drive the winter rainfall in such a restricted area. We relate variations in South-western African humidity to changes in Antarctic sea-ice extent. New records of Antarctic sea-ice extent compared to existing palaeoclimate records of South-western Africa reveal a coherent signal during the last 50 kyr BP, with enhanced continental humidity and trade-wind intensity during periods of increased sea-ice presence. We propose that greater glacial Antarctic sea-ice extent causes a Northward shift of oceanic and atmospheric frontal zones, thereby increasing latitudinal temperature and pressure gradients, leading to enhanced trade-wind intensities. In addition, the equatorward shift and increased intensity of the Southern Westerlies causes an expansion of the winter-rain region and increased precipitation in South-western Africa. This relationship implies enhanced desertification in South-western Africa in response to retreating sea-ice edge in the Atlantic sector of the Southern Ocean if global warming continues.

  1. Tropical and mid-latitude forcing of continental Antarctic temperatures

    NASA Astrophysics Data System (ADS)

    Turney, C. S. M.; Fogwill, C. J.; Klekociuk, A. R.; van Ommen, T. D.; Curran, M. A. J.; Moy, A. D.; Palmer, J. G.

    2015-12-01

    Future changes in atmospheric circulation and associated modes of variability are a major source of uncertainty in climate projections. Nowhere is this issue more acute than across the mid-latitudes to high latitudes of the Southern Hemisphere (SH), which over the last few decades have experienced extreme and regionally variable trends in precipitation, ocean circulation and temperature, with major implications for Antarctic ice melt and surface mass balance. Unfortunately there is a relative dearth of observational data, limiting our understanding of the driving mechanism(s). Here we report a new 130-year annually resolved record of δD - a proxy for temperature - from the geographic South Pole where we find a significant influence from extratropical pressure anomalies which act as "gatekeepers" to the meridional exchange of air masses. Reanalysis of global atmospheric circulation suggests these pressure anomalies play a significant influence on mid- to high-latitude SH climate, modulated by the tropical Pacific Ocean. This work adds to a growing body of literature confirming the important roles of tropical and mid-latitude atmospheric circulation variability on Antarctic temperatures. Our findings suggest that future increasing tropical warmth will strengthen meridional circulation, exaggerating current trends, with potentially significant impacts on Antarctic surface mass balance.

  2. The influence of Antarctic subglacial volcanism on the global iron cycle during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Frisia, Silvia; Weyrich, Laura S.; Hellstrom, John; Borsato, Andrea; Golledge, Nicholas R.; Anesio, Alexandre M.; Bajo, Petra; Drysdale, Russell N.; Augustinus, Paul C.; Rivard, Camille; Cooper, Alan

    2017-06-01

    Marine sediment records suggest that episodes of major atmospheric CO2 drawdown during the last glacial period were linked to iron (Fe) fertilization of subantarctic surface waters. The principal source of this Fe is thought to be dust transported from southern mid-latitude deserts. However, uncertainty exists over contributions to CO2 sequestration from complementary Fe sources, such as the Antarctic ice sheet, due to the difficulty of locating and interrogating suitable archives that have the potential to preserve such information. Here we present petrographic, geochemical and microbial DNA evidence preserved in precisely dated subglacial calcites from close to the East Antarctic Ice-Sheet margin, which together suggest that volcanically-induced drainage of Fe-rich waters during the Last Glacial Maximum could have reached the Southern Ocean. Our results support a significant contribution of Antarctic volcanism to subglacial transport and delivery of nutrients with implications on ocean productivity at peak glacial conditions.

  3. The influence of Antarctic subglacial volcanism on the global iron cycle during the Last Glacial Maximum

    PubMed Central

    Frisia, Silvia; Weyrich, Laura S.; Hellstrom, John; Borsato, Andrea; Golledge, Nicholas R.; Anesio, Alexandre M.; Bajo, Petra; Drysdale, Russell N.; Augustinus, Paul C.; Rivard, Camille; Cooper, Alan

    2017-01-01

    Marine sediment records suggest that episodes of major atmospheric CO2 drawdown during the last glacial period were linked to iron (Fe) fertilization of subantarctic surface waters. The principal source of this Fe is thought to be dust transported from southern mid-latitude deserts. However, uncertainty exists over contributions to CO2 sequestration from complementary Fe sources, such as the Antarctic ice sheet, due to the difficulty of locating and interrogating suitable archives that have the potential to preserve such information. Here we present petrographic, geochemical and microbial DNA evidence preserved in precisely dated subglacial calcites from close to the East Antarctic Ice-Sheet margin, which together suggest that volcanically-induced drainage of Fe-rich waters during the Last Glacial Maximum could have reached the Southern Ocean. Our results support a significant contribution of Antarctic volcanism to subglacial transport and delivery of nutrients with implications on ocean productivity at peak glacial conditions. PMID:28598412

  4. Antarctic Miocene Climate

    NASA Astrophysics Data System (ADS)

    Ashworth, A. C.; Lewis, A. R.

    2013-12-01

    Fossils from Antarctic Miocene terrestrial deposits, coupled with stratigraphic, geochemical and paleontological data from marine boreholes, provide new insights into the climatic history of the continent. During the Miocene, ice caps coalesced to form ice sheets and vegetated surfaces gave way to barren expanses. The cryospheric changes especially have global climatic implications. The fossil data consists of diatoms, pollen and spores, and macroscopic remains of plants, ostracods, insects, molluscs and a fish. Plant fossils include wood and leaves of Nothofagus (southern beech), seeds of several vascular plants, including Ranunculus (buttercup), Hippuris (mare's-tail) and Myriophyllum (watermilfoil), megaspores of Isoetes (quillwort), and moss species. The insect chitin consists of larval head capsules of Chironomidae (midges) and exoskeletal parts of Coleoptera (beetles). The molluscs include freshwater gastropods and bivalves. The majority of these taxa are likely descendants of taxa that had survived on the continent from the Paleogene or earlier. Even though early Miocene glaciations may have been large, the climate was never cold enough to cause the extinction of the biota, which probably survived in coastal refugia. Early Miocene (c. 20 Ma) macrofossils from the McMurdo Dry Valleys (77°S) support palynological interpretations from the Cape Roberts and ANDRILL marine records that the upland vegetation was a shrub tundra. Mean summer temperature (MST) in the uplands was c. 6°C and possibly higher at the coast. The climate was wet, supporting mires and lakes. By the mid-Miocene, even though the climate continued to be wet. MST was c. 4°C which was too cold to support Nothofagus and most vascular plant species. Stratigraphic evidence indicates that the time between the Early and Mid-Miocene was a time of repeated ice advances and retreats of small glaciers originating from ice caps. At c. 14 Ma there appears to have been a modal shift in climate to

  5. Characterization of the neuropeptidome of a Southern Ocean decapod, the Antarctic shrimp Chorismus antarcticus: Focusing on a new decapod ITP-like peptide belonging to the CHH peptide family.

    PubMed

    Toullec, Jean-Yves; Corre, Erwan; Mandon, Perrine; Gonzalez-Aravena, Marcelo; Ollivaux, Céline; Lee, Chi-Ying

    2017-10-01

    As part of the study of the resilience of Antarctic crustaceans to global warming, the shrimp Chorismus antarcticus was subjected to an analysis of global approach using the Next Generation Sequencing Illumina Hi-Seq platform. With this data a detailed study into the principal neuropeptides and neurohormones of this species have been undertaken. Total RNAs from whole animals were enriched with eyestalk extracts to ensure maximum sequencing depth of the different neurohormones and neuropeptides mainly expressed into the X organ-sinus gland complex, which is a major endocrine organ of their synthesis. Apart from the information that can provide the availability of the transcriptome of a polar crustacean, the study of neuropeptides of a caridean shrimp will partially fill the limited data available for this taxon. Illumina sequencing was used to produce a transcriptome of the polar shrimp. Analysis of the Trinity assembled contigs produced 55 pre-pro-peptides, coding for 111 neuropeptides belonging to the following families: adipokinetic-corazonin-like peptide, Allatostatins (A, B et C), Bursicon (α), CCHamide, Crustacean Hyperglycemic Hormones (CHH), Crustacean Cardioactive Peptide (CCAP), Corazonin, Crustacean Female Sex Hormone (CSFH), Diuretic Hormones 31 and 45 (DH), Eclosion Hormone (EH), FLRFamide, GSEFLamide, Intocin, Ion Transport Peptide-like (ITP-like), Leucokinin, Molt-inhibiting Hormone, Myosuppresin, Neuroparsin, Neuropeptide F (NPF), Orcokinin, Orcomyotropin, Pigment Dispersing Hormone (PDH), Pyrokinin, Red Pigment Concentrating Hormone (RPCH), SIFamide, small Neuropeptide F (sNPF), Sulfakinin and finally Tachykinin Related peptides. Among the new peptides highlighted in this study, the focus was placed on the peptides of the CHH family and more particularly on a new ITP-like in order to confirm its belonging to a new group of peptides of the family. A phylogeny made from more than 200 sequences of peptides, included new sequences from new species

  6. Isotopic evidence for nitrification in the Antarctic winter mixed layer

    NASA Astrophysics Data System (ADS)

    Smart, Sandi M.; Fawcett, Sarah E.; Thomalla, Sandy J.; Weigand, Mira A.; Reason, Chris J. C.; Sigman, Daniel M.

    2015-04-01

    We report wintertime nitrogen and oxygen isotope ratios (δ15N and δ18O) of seawater nitrate in the Southern Ocean south of Africa. Depth profile and underway surface samples collected in July 2012 extend from the subtropics to just beyond the Antarctic winter sea ice edge. We focus here on the Antarctic region (south of 50.3°S), where application of the Rayleigh model to depth profile δ15N data yields estimates for the isotope effect (the degree of isotope discrimination) of nitrate assimilation (1.6-3.3‰) that are significantly lower than commonly observed in the summertime Antarctic (5-8‰). The δ18O data from the same depth profiles and lateral δ15N variations within the mixed layer, however, imply O and N isotope effects that are more similar to those suggested by summertime data. These findings point to active nitrification (i.e., regeneration of organic matter to nitrate) within the Antarctic winter mixed layer. Nitrite removal from samples reveals a low δ15N for nitrite in the winter mixed layer (-40‰ to -20‰), consistent with nitrification, but does not remove the observation of an anomalously low δ15N for nitrate. The winter data, and the nitrification they reveal, explain the previous observation of an anomalously low δ15N for nitrate in the temperature minimum layer (remnant winter mixed layer) of summertime depth profiles. At the same time, the wintertime data require a low δ15N for the combined organic N and ammonium in the autumn mixed layer that is available for wintertime nitrification, pointing to intense N recycling as a pervasive condition of the Antarctic in late summer.

  7. Climate Change and Trophic Response of the Antarctic Bottom Fauna

    PubMed Central

    Aronson, Richard B.; Moody, Ryan M.; Ivany, Linda C.; Blake, Daniel B.; Werner, John E.; Glass, Alexander

    2009-01-01

    Background As Earth warms, temperate and subpolar marine species will increasingly shift their geographic ranges poleward. The endemic shelf fauna of Antarctica is especially vulnerable to climate-mediated biological invasions because cold temperatures currently exclude the durophagous (shell-breaking) predators that structure shallow-benthic communities elsewhere. Methodology/Principal Findings We used the Eocene fossil record from Seymour Island, Antarctic Peninsula, to project specifically how global warming will reorganize the nearshore benthos of Antarctica. A long-term cooling trend, which began with a sharp temperature drop ∼41 Ma (million years ago), eliminated durophagous predators—teleosts (modern bony fish), decapod crustaceans (crabs and lobsters) and almost all neoselachian elasmobranchs (modern sharks and rays)—from Antarctic nearshore waters after the Eocene. Even prior to those extinctions, durophagous predators became less active as coastal sea temperatures declined from 41 Ma to the end of the Eocene, ∼33.5 Ma. In response, dense populations of suspension-feeding ophiuroids and crinoids abruptly appeared. Dense aggregations of brachiopods transcended the cooling event with no apparent change in predation pressure, nor were there changes in the frequency of shell-drilling predation on venerid bivalves. Conclusions/Significance Rapid warming in the Southern Ocean is now removing the physiological barriers to shell-breaking predators, and crabs are returning to the Antarctic Peninsula. Over the coming decades to centuries, we predict a rapid reversal of the Eocene trends. Increasing predation will reduce or eliminate extant dense populations of suspension-feeding echinoderms from nearshore habitats along the Peninsula while brachiopods will continue to form large populations, and the intensity of shell-drilling predation on infaunal bivalves will not change appreciably. In time the ecological effects of global warming could spread to other

  8. Oceanography. Vertical mixing in the ocean.

    PubMed

    Webb, D J; Suginohara, N

    2001-01-04

    The thermohaline circulation of the ocean results primarily from downwelling at sites in the Nordic and Labrador Seas and upwelling throughout the rest of the ocean. The latter is often described as being due to breaking internal waves. Here we reconcile the difference between theoretical and observed estimates of vertical mixing in the deep ocean by presenting a revised view of the thermohaline circulation, which allows for additional upwelling in the Southern Ocean and the separation of the North Atlantic Deep Water cell from the Antarctic Bottom Water cell. The changes also mean that much less wind and tidal energy needs to be dissipated in the deep ocean than was originally thought.

  9. Ozone depletion - Ultraviolet radiation and phytoplankton biology in Antarctic waters

    NASA Technical Reports Server (NTRS)

    Smith, R. C.; Prezelin, B. B.; Baker, K. S.; Bidigare, R. R.; Boucher, N. P.; Coley, T.; Karentz, D.; Macintyre, S.; Matlick, H. A.; Menzies, D.

    1992-01-01

    The near-50-percent thinning of the stratospheric ozone layer over the Antarctic, with increased passage of mid-UV radiation to the surface of the Southern Ocean, has prompted concern over possible radiation damage to the near-surface phytoplankton communities that are the bases of Antarctic marine ecosystems. As the ozone layer thinned, a 6-week study of the marginal ice zone of the Bellingshousen Sea in the austral spring of 1990 noted sea-surface and depth-dependent ratios of mid-UV irradiance to total irradiance increased, and mid-UV inhibition of photosynthesis increased. A 6-12 percent reduction in primary production associated with ozone depletion was estimated to have occurred over the course of the present study.

  10. Topographic vorticity waves forced by Antarctic dense shelf water outflows

    NASA Astrophysics Data System (ADS)

    Marques, Gustavo M.; Padman, Laurie; Springer, Scott R.; Howard, Susan L.; Özgökmen, Tamay M.

    2014-02-01

    We use numerical simulations to investigate excitation of topographic vorticity waves (TVWs) along the Antarctic continental slope by outflows of dense shelf water through troughs. Idealized models show that wave frequency depends on the amount of stretching in the ambient fluid over the outflow and on background along-slope mean flow. Frequency is higher for steeper bottom slope, larger outflow density anomaly, and stronger westward mean flow. For weak stratification and weak westward along-slope flows typical of the Antarctic slope, wave energy propagates eastward, in the opposite direction from phase velocity. Our results are consistent with recent observations of TVWs in the southern Weddell Sea. In a realistic simulation of the Ross Sea, TVW properties are modulated on seasonal and shorter time scales as background ocean state varies. We expect these waves to affect mixing, cross-slope exchanges, and sea ice concentration in the vicinity of sources of dense water outflows.

  11. UAV Observations of an Antarctic Polynya During Winter

    NASA Astrophysics Data System (ADS)

    Cassano, J.; Maslanik, J. A.; Knuth, S.

    2009-12-01

    Aerosonde unmanned aerial vehicles (UAVs) will be used during September 2009 to observe the atmosphere and ocean / sea ice surface state in the vicinity of the Terra Nova Bay polynya, Antarctica. The flights will take place at the end of the Antarctic winter, in an environment characterized by strong katabatic winds and strong air-sea fluxes. Flights of up to 20 hours duration are planned. This mission will be the second deployment of UAVs in the Antarctic, and the first deployment funded by the United States National Science Foundation. Results from this UAV deployment and lessons learned during the deployment will be presented. Visible satellite image of Terra Nova Bay polynya (6 Oct 2007).

  12. Physical model of bathymetric effects on the Antarctic circumpolar current

    SciTech Connect

    Boyer, D.L.; Ruirong Chen; Lijun Tao ); Davies, P.A. )

    1993-02-15

    Laboratory experiments were conducted to simulate some of the effects of the bathymetry of the southern ocean on the physical characteristics of the Antarctic Circumpolar Current (ACC). An idealized zonal wind stress, which varied inversely with the distance from the model Antarctic continent, was simulated in the laboratory model by a radially inward sink-source flow in a thin layer along the surface of the circular test cell. The present model, however, has the limitation of not accounting for such factors as the longitudinal variations in the wind shear and the decrease in wind stress on approaching the Antarctic continent from the north. Planetary beta effects were neglected because the topographic beta term can be shown to dominate over large portions of the model area. The neglect of beta effects is also a limitation of the model. In spite of these limitations, however, the simulations of the physical model for both the homogeneous and linearly stratified cases were shown to be in good agreement with observations of the ACC. These include well-defined strong currents along the mid-ocean ridge; strong perturbations in the vicinity of the Macquarie Ridge, Campbell Plateau, and Kerguelen Gaussberg Plateau; strong meridional transport to the east of the Drake Passage; and anomalies to the south (wave troughs) and to the north (wave ridges) of the main circumpolar current over ocean basins and mountain ridges, respectively. It was shown that the Eltanin and Udintsev fracture zones in the vicinity of 135[degrees]W are important factors in directing the ACC eastward across the Southeast Pacific Basin to the Drake Passage. The estimated volume transports through the Drake Passage based on the model results are in fair agreement with oceanic observations. Estimates of the spin-up time of the system for homogeneous and stratified cases have been provided. 28 refs., 21 figs., 1 tab.

  13. Towers for Antarctic Telescopes

    NASA Astrophysics Data System (ADS)

    Hammerschlag, R. H.; Bettonvil, F. C. M.; Jägers, A. P. L.; Nielsen, G.

    To take advantage of the exceptional seeing above the boundary layer on Antarctic sites, a high-resolution telescope must be mounted on a support tower. An open transparent tower of framework minimizes the upward temperature-disturbed airflow. A typical minimum height is 30m. The tower platform has to be extremely stable against wind-induced rotational motions, which have to be less than fractions of an arc second, unusually small from a mechanical engineering viewpoint. In a traditional structure, structural deflections result in angular deflections of the telescope platform, which introduce tip and tilt motions in the telescope. However, a structure that is designed to deflect with parallel motion relative to the horizontal plane will undergo solely translation deflections in the telescope platform and thus will not degrade the image. The use of a parallel motion structure has been effectively demonstrated in the design of the 15-m tower for the Dutch Open Telescope (DOT) on La Palma. Special framework geometries are developed, which make it possible to construct high towers in stories having platforms with extreme stability against wind-induced tilt. These geometric solutions lead to constructions, being no more massive than a normal steel framework carrying the same load. Consequently, these lightweight towers are well suited to difficult sites as on Antarctica. A geometry with 4 stories has been worked out.

  14. Antarctic radiation exposure doubles

    NASA Astrophysics Data System (ADS)

    Blue, Charles

    New data reveal that the Antarctic Peninsula received twice its normal maximum dose of hazardous solar ultraviolet radiation in December 1990. The prolonged persistence of the ozone hole over Antarctica caused an increased exposure of radiation, according to a paper published in the October issue of Geophysical Research Letters.John Frederick and Amy D. Alberts of the University of Chicago calculated the amount of ultraviolet solar spectral radiation from data collected at Palmer Station, Antarctica. During the spring of 1990 the largest observed values for ultraviolet radiation were approximately double the values expected, based on previous years. “The measurements from Palmer Station are consistent with similar data from McMurdo Sound, where a factor of three [ultraviolet radiation] enhancement was recorded, according to work by Knut Stamnes and colleagues at the University of Alaska,” Frederick said. “The radiation levels observed over Palmer Station in December 1990 may be the largest experienced in this region of the world since the development of the Earth's ozone layer,” he added.

  15. Influence of the Antarctic Circumpolar Current on the Atlantic Meriodional Circulation

    DTIC Science & Technology

    2009-03-01

    central ocean. . 14. SUBJECT TERMS meridional overturning circulation , MOC, Antarctic Circumpolar Current, ACC, thermohaline circulation 15...2 Figure 2. Thermohaline Circulation (from Wyrtki, 1961) .................................................. 2 Figure 3. Two-Cell...et al., 2004) Figure 2. Thermohaline Circulation (from Wyrtki, 1961) - Surface flow - Deep flow - Bottom flow o Deep Water Formation 8 Wind

  16. Antarctic Krill 454 Pyrosequencing Reveals Chaperone and Stress Transcriptome

    PubMed Central

    Clark, Melody S.; Thorne, Michael A. S.; Toullec, Jean-Yves; Meng, Yan; Guan, Le Luo; Peck, Lloyd S.; Moore, Stephen

    2011-01-01

    Background The Antarctic krill Euphausia superba is a keystone species in the Antarctic food chain. Not only is it a significant grazer of phytoplankton, but it is also a major food item for charismatic megafauna such as whales and seals and an important Southern Ocean fisheries crop. Ecological data suggest that this species is being affected by climate change and this will have considerable consequences for the balance of the Southern Ocean ecosystem. Hence, understanding how this organism functions is a priority area and will provide fundamental data for life history studies, energy budget calculations and food web models. Methodology/Principal Findings The assembly of the 454 transcriptome of E. superba resulted in 22,177 contigs with an average size of 492bp (ranging between 137 and 8515bp). In depth analysis of the data revealed an extensive catalogue of the cellular chaperone systems and the major antioxidant proteins. Full length sequences were characterised for the chaperones HSP70, HSP90 and the super-oxide dismutase antioxidants, with the discovery of potentially novel duplications of these genes. The sequence data contained 41,470 microsatellites and 17,776 Single Nucleotide Polymorphisms (SNPs/INDELS), providing a resource for population and also gene function studies. Conclusions This paper details the first 454 generated data for a pelagic Antarctic species or any pelagic crustacean globally. The classical “stress proteins