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Sample records for antarctic peninsula ice

  1. Speedup and fracturing of George VI Ice Shelf, Antarctic Peninsula

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    T. O. Holt

    2013-05-01

    Full Text Available George VI Ice Shelf (GVIIS is located on the Antarctic Peninsula, a region where several ice shelves have undergone rapid breakup in response to atmospheric and oceanic warming. We use a combination of optical (Landsat, radar (ERS 1/2 SAR and laser altimetry (GLAS datasets to examine the response of GVIIS to environmental change and to offer an assessment on its future stability. The spatial and structural changes of GVIIS (ca. 1973 to ca. 2010 are mapped and surface velocities are calculated at different time periods (InSAR and optical feature tracking from 1989 to 2009 to document changes in the ice shelf's flow regime. Surface elevation changes are recorded between 2003 and 2008 using repeat track ICESat acquisitions. We note an increase in fracture extent and distribution at the south ice front, ice-shelf acceleration towards both the north and south ice fronts and spatially varied negative surface elevation change throughout, with greater variations observed towards the central and southern regions of the ice shelf. We propose that whilst GVIIS is in no imminent danger of collapse, it is vulnerable to ongoing atmospheric and oceanic warming and is more susceptible to breakup along its southern margin in ice preconditioned for further retreat.

  2. Recent increase in Antarctic Peninsula ice core uranium concentrations

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    Potocki, Mariusz; Mayewski, Paul A.; Kurbatov, Andrei V.; Simões, Jefferson C.; Dixon, Daniel A.; Goodwin, Ian; Carleton, Andrew M.; Handley, Michael J.; Jaña, Ricardo; Korotkikh, Elena V.

    2016-09-01

    Understanding the distribution of airborne uranium is important because it can result in both chemical and radiological toxicity. Ice cores offer the most robust reconstruction of past atmospheric levels of toxic substances. Here we present the first sub-annually dated, continuously sampled ice core documenting change in U levels in the Southern Hemisphere. The ice core was recovered from the Detroit Plateau, northern Antarctic Peninsula, in 2007 by a joint Brazilian-Chilean-US team. It displays a significant increase in U concentration that coincides with reported mining activities in the Southern Hemisphere, notably Australia. Raw U concentrations in the Detroit Plateau ice core increased by as much as 102 between the 1980s and 2000s accompanied by increased variability in recent years. Decadal mean U concentrations increased by a factor of ∼3 from 1980 to 2007, reaching a mean of 205 pg/L from 2000 to 2007. The fact that other terrestrial source dust elements such as Ce, La, Pr, and Ti do not show a similar increase and that the increased U concentrations are enriched above natural crustal levels, supports an anthropogenic source for the U as opposed to a change in atmospheric circulation.

  3. Computing the volume response of the Antarctic Peninsula ice sheet to warming scenarios to 2200

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    Barrand, N.E.; Hindmarsh, R.C.A.; Arthern, R.J.; Williams, C.R.; Mouginot, J.; Scheuchl, B.; Rignot, Eric; Ligtenberg, S.R.M.; van den Broeke, M.R.; Edwards, T.L.; Cook, A.J.; Simonsen, S.B.

    2013-01-01

    The contribution to sea level to 2200 from the grounded, mainland Antarctic Peninsula ice sheet (APIS) was calculated using an ice-sheet model initialized with a new technique computing ice fluxes based on observed surface velocities, altimetry and surface mass balance, and computing volume response

  4. Rapid bedrock uplift in the Antarctic Peninsula explained by viscoelastic response to recent ice unloading

    DEFF Research Database (Denmark)

    Nield, Grace A.; Barletta, Valentina Roberta; Bordoni, Andrea;

    2014-01-01

    Since 1995 several ice shelves in the Northern Antarctic Peninsula have collapsed and triggered ice-mass unloading, invoking a solid Earth response that has been recorded at continuous GPS (cGPS) stations. A previous attempt to model the observation of rapid uplift following the 2002 breakup of L...

  5. Bellingshausen Sea ice extent recorded in an Antarctic Peninsula ice core

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    Porter, Stacy E.; Parkinson, Claire L.; Mosley-Thompson, Ellen

    2016-12-01

    Annual net accumulation (An) from the Bruce Plateau (BP) ice core retrieved from the Antarctic Peninsula exhibits a notable relationship with sea ice extent (SIE) in the Bellingshausen Sea. Over the satellite era, both BP An and Bellingshausen SIE are influenced by large-scale climatic factors such as the Amundsen Sea Low, Southern Annular Mode, and Southern Oscillation. In addition to the direct response of BP An to Bellingshausen SIE (e.g., more open water as a moisture source), these large-scale climate phenomena also link the BP and the Bellingshausen Sea indirectly such that they exhibit similar responses (e.g., northerly wind anomalies advect warm, moist air to the Antarctic Peninsula and neighboring Bellingshausen Sea, which reduces SIE and increases An). Comparison with a time series of fast ice at South Orkney Islands reveals a relationship between BP An and sea ice in the northern Weddell Sea that is relatively consistent over the twentieth century, except when it is modulated by atmospheric wave patterns described by the Trans-Polar Index. The trend of increasing accumulation on the Bruce Plateau since 1970 agrees with other climate records and reconstructions in the region and suggests that the current rate of sea ice loss in the Bellingshausen Sea is unrivaled in the twentieth century.

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

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    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.

  7. Detailed ice loss pattern in the northern Antarctic Peninsula: widespread decline driven by ice front retreats

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    T. A. Scambos

    2014-06-01

    Full Text Available The northern Antarctic Peninsula (nAP, 3 a−1 and 24.9 ± 7.8 Gt a−1. This mass loss is compatible with recent gravimetric assessments, but it implies that almost all the gravimetry-inferred loss lies in the nAP sector. Mass loss is highest for eastern glaciers affected by major ice shelf collapses in 1995 and 2002, where twelve glaciers account for 60% of the total imbalance. However, losses at smaller rates occur throughout the nAP, and at high and low elevation, despite increased snow accumulation along the western coast and at high elevations. We interpret the widespread mass loss to be driven by decades of ice front retreats on both sides of the nAP, and by the propagation of kinematic waves triggered at the fronts into the interior.

  8. Mass Balance of the Northern Antarctic Peninsula and its Ongoing Response to Ice Shelf Loss

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    Scambos, T. A.; Berthier, E.; Haran, T. M.; Shuman, C. A.; Cook, A. J.; Bohlander, J. A.

    2012-12-01

    An assessment of the most rapidly changing areas of the Antarctic Peninsula (north of 66°S) shows that ice mass loss for the region is dominated by areas affected by eastern-Peninsula ice shelf losses in the past 20 years. Little if any of the mass loss is compensated by increased snowfall in the northwestern or far northern areas. We combined satellite stereo-image DEM differencing and ICESat-derived along-track elevation changes to measure ice mass loss for the Antarctic Peninsula north of 66°S between 2001-2010, focusing on the ICESat-1 period of operation (2003-2009). This mapping includes all ice drainages affected by recent ice shelf loss in the northeastern Peninsula (Prince Gustav, Larsen Inlet, Larsen A, and Larsen B) as well as James Ross Island, Vega Island, Anvers Island, Brabant Island and the adjacent west-flowing glaciers. Polaris Glacier (feeding the Larsen Inlet, which collapsed in 1986) is an exception, and may have stabilized. Our method uses ASTER and SPOT-5 stereo-image DEMs to determine dh/dt for elevations below 800 m; at higher elevations ICESat along-track elevation differencing is used. To adjust along-track path offsets between its 2003-2009 campaigns, we use a recent DEM of the Peninsula to establish and correct for cross-track slope (Cook et al., 2012, doi:10.5194/essdd-5-365-2012; http://nsidc.org/data/nsidc-0516.html) . We reduce the effect of possible seasonal variations in elevation by using only integer-year repeats of the ICESat tracks for comparison. Mass losses are dominated by the major glaciers that had flowed into the Prince Gustav (Boydell, Sjorgren, Röhss), Larsen A (Edgeworth, Bombardier, Dinsmoor, Drygalski), and Larsen B (Hektoria, Jorum, and Crane) embayments. The pattern of mass loss emphasizes the significant and multi-decadal response to ice shelf loss. Areas with shelf losses occurring 30 to 100s of years ago seem to be relatively stable or losing mass only slowly (western glaciers, northernmost areas). The

  9. Firn structure of Larsen C Ice Shelf, Antarctic Peninsula, from in-situ geophysical surveys

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    Kulessa, B.; Brisbourne, A.; Kuipers Munneke, P.; Bevan, S. L.; Luckman, A. J.; Hubbard, B. P.; Ashmore, D.; Holland, P.; Jansen, D.; King, E. C.; O'Leary, M.; McGrath, D.

    2015-12-01

    Rising surface temperatures have been causing firn layers on Antarctic Peninsula ice shelves to compact, a process that is strongly implicated in ice shelf disintegration. Firn compaction is expected to warm the ice column and given sufficiently wet and compacted firn layers, to allow meltwater to penetrate into surface crevasses and thus enhance the potential for hydrofracture. On Larsen C Ice Shelf a compacting firn layer has previously been inferred from airborne radar and satellite data, with strongly reduced air contents in Larsen C's north and north-west. The hydrological processes governing firn compaction, and the detailed firn structures they produce, have so far remained uncertain however. Using integrated seismic refraction, MASW (Multi-Channel Analysis of Surface Waves), seismoelectric and ground-penetrating radar (GPR) data, we reveal vertical and horizontal changes in firn structure across Larsen C Ice Shelf. Particular attention is paid to the spatial prevalence of refrozen meltwaters within firn, such as the massive subsurface ice layer discovered recently by the NERC-funded MIDAS project in Cabinet Inlet in Larsen C's extreme northwest. Such ice layers or lenses are particularly dramatic manifestations of increased ice shelf densities and temperatures, and contrast sharply with the relatively uncompacted firn layers present in the ice shelf's southeast. We consider our observations in the context of a one-dimensional firn model for Larsen C Ice Shelf that includes melt percolation and refreezing, and discuss temporal changes in firn layer structures due to surface melt and ponding.

  10. In-situ aircraft observations of ice concentrations within clouds over the Antarctic Peninsula and Larsen Ice Shelf

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    D. P. Grosvenor

    2012-12-01

    Full Text Available In-situ aircraft observations of ice crystal concentrations in Antarctic clouds are presented for the first time. Orographic, layer and wave clouds around the Antarctic Peninsula and Larsen Ice shelf regions were penetrated by the British Antarctic Survey's Twin Otter aircraft, which was equipped with modern cloud physics probes. The clouds studied were mostly in the free troposphere and hence ice crystals blown from the surface are unlikely to have been a major source for the ice phase. The temperature range covered by the experiments was 0 to −21 °C. The clouds were found to contain supercooled liquid water in most regions and at heterogeneous ice formation temperatures ice crystal concentrations (60 s averages were often less than 0.07 l−1, although values up to 0.22 l−1 were observed. Estimates of observed aerosol concentrations were used as input into the DeMott et al. (2010 ice nuclei (IN parameterisation. The observed ice crystal number concentrations were generally in broad agreement with the IN predictions, although on the whole the predicted values were higher. Possible reasons for this are discussed and include the lack of IN observations in this region with which to characterise the parameterisation, and/or problems in relating ice concentration measurements to IN concentrations. Other IN parameterisations significantly overestimated the number of ice particles. Generally ice particle concentrations were much lower than found in clouds in middle latitudes for a given temperature.

    Higher ice crystal concentrations were sometimes observed at temperatures warmer than −9 °C, with values of several per litre reached. These were attributable to secondary ice particle production by the Hallett Mossop process. Even in this temperature range it was observed that there were regions with little or no ice that were dominated by supercooled liquid water. It is likely that in some cases this was due to a

  11. Multi-temporal satellite analysis of Wilkins Ice Shelf, Antarctic Peninsula, and consequences for its stability

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    Rankl, Melanie; Fürst, Johannes; Helm, Veit; Humbert, Angelika; Braun, Matthias

    2016-04-01

    Antarctic Peninsula (AP) ice shelves have been affected by ice front retreat and surface lowering over the past decades. 12 major ice shelves have disintegrated or significantly retreated and have been affected by volume loss. Longterm ice shelf thinning is twice as high at western AP ice shelves than at eastern AP ice shelves. Wilkins Ice Shelf (WIS), located at the western AP, has undergone considerable ice front retreat since the 1990s. It lost ~ 5000 km² of its size since then. Surface lowering at WIS was found to be the largest at AP ice shelves between 1978 and 2008. Here, we analyze time-series of satellite data in order to assess dynamic changes of WIS following the ice front retreat between 1994 and 2010. We present multi-temporal changes in surface velocities and deduced products, such as strain rate and stress regimes. Surface flow was derived from SAR intensity offset tracking applied to ALOS PALSAR image pairs. In addition, we show variations in ice thickness between 2003 and 2012 derived from TanDEM-X satellite acquisitions and altimetry datasets (CryoSAT-2, ICESat). The bistatic TanDEM-X acquisitions are very suitable for interferometric processing due to highly coherent image pairs. The results showed surface velocity speed up during break-up of an ice bridge between two confining islands in 2006-2008, when an area of ~ 1800 km² broke off. A sharp transition between compressive and extensive in-flow strain rates evolved at the narrowest part of the ice bridge, which contributed to the formation of a crack and hence, failure of the ice bridge in April 2009. First principal stresses were estimated to amount to ~ 250 kPa in the vicinity of the crack formation. The imaging TanDEM-X radar geometry allowed for a comprehensive ice thickness mapping of the ice shelf in 2012 and resolved many details due to the high spatial resolution. The ice thickness at WIS was found to be very heterogeneous. Thickness changes between 2003 and 2012 revealed increased

  12. Paleo-ice flow directions of the Northern Antarctic Peninsula ice sheet based upon a new synthesis of seabed imagery

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    C. Lavoie

    2014-10-01

    Full Text Available We present a new seafloor map for the northern Antarctic Peninsula (AP, including swath multibeam data sets from five national programs. Our map allows for the examination and interpretation of Last Glacial Maximum (LGM paleo-ice sheet/stream flow directions developed upon the seafloor from the preservation of: mega-scale glacial lineations, drumlinized features, and selective linear erosion. We combine this with terrestrial observations of flow direction to place constraints on ice divides and accumulation centers (ice domes on the AP continental shelf. The results show a flow bifurcation as ice exits the Larsen-B embayment. Flow emanating off the Seal Nunataks (including Robertson Island is directed toward the southeast, then eastward as the flow transits toward the Robertson Trough. A second, stronger "streaming flow" is directed toward the southeast then southward, as ice overflowed the tip of the Jason Peninsula to reach the southern perimeter of the embayment. Our reconstruction also refines the extent of at least five other distinct paleo-ice stream systems which, in turn, serve to delineate seven broad regions where contemporaneous ice domes must have been centered on the continental shelf during the LGM time interval. Our reconstruction is more detailed than other recent compilations because we followed specific flow indicators and have kept tributary flow paths parallel.

  13. Glacial geomorphology of the northwestern Weddell Sea, eastern Antarctic Peninsula continental shelf: Shifting ice flow patterns during deglaciation

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    Campo, Jennifer M.; Wellner, Julia S.; Domack, Eugene; Lavoie, Caroline; Yoo, Kyu-Cheul

    2017-03-01

    During the Last Glacial Maximum, grounded ice from the expanded Antarctic Peninsula Ice Sheet extended across the continental shelf. Grounded and flowing ice created a distinctive array of glacial geomorphic features on the sea floor, which were then exposed as the ice sheet retreated. The recent disintegration of the northern parts of the Larsen Ice Shelf (Larsen A and B) have permitted acquisition of marine geophysical data in previously inaccessible and unmapped areas. We present a reconstruction of the evolving ice-flow path and ice sheet geometry of the eastern Antarctic Peninsula, with particular focus paid to newly surveyed areas that shed light on the dynamics of a marine-terminating glacial geomorphic environment, where ice shelves play a major role in grounding line stability. Shifting flow directions were mapped in several areas, including across the Seal Nunataks, which divide Larsen A and B, and offshore of Larsen C, indicating flow reorientation that reflects the changing ice sheet geometry as retreat neared the modern coastline. The measured flow indicators in this area reveal comparatively high elongation ratios (> 20), indicating rapid ice flow. Evidence of possible previous ice-shelf collapses are noted near the shelf break, further illustrating the critical, protective effect that ice shelves impart to marine-terminating glacial environments. Modern ice retreat is governed in part by reorganization of flow patterns accompanying grounding line movement; such reorganizations happened in the past and can aid understanding of modern processes.

  14. Thirty years of elevation change on Antarctic Peninsula ice shelves from multimission satellite radar altimetry

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    Fricker, Helen Amanda; Padman, Laurie

    2012-02-01

    We use data acquired between 1978 and 2008 by four satellite radar altimeter missions (Seasat, ERS-1, ERS-2 and Envisat) to determine multidecadal elevation change rates (dhi/dt) for six major Antarctic Peninsula (AP) ice shelves. In areas covered by the Seasat orbit (to 72.16°S), regional-averaged 30-year trends were negative (surface lowering), with rates between -0.03 and -0.16 m a-1. Surface lowering preceded the start of near-continuous radar altimeter operations that began with ERS-1 in 1992. The average rate of lowering for the first 14 years of the period was typically smaller than the 30-year average; the exception was the southern Wilkins Ice Shelf, which experienced negligible lowering between 2000 and 2008, when a series of large calving events began. Analyses of the continuous ERS/Envisat time series (to 81.5°) for 1992-2008 reveal a period of strong negative dhi/dt on most ice shelves between 1992 and 1995. Based on prior studies of regional atmospheric and oceanic conditions, we hypothesize that the observed elevation changes on Larsen C Ice Shelf are driven primarily by firn compaction while the western AP ice shelves are responding to changes in both surface mass balance and basal melt rates. Our time series also show that large changes in dhi/dt can occur on interannual time scales, reinforcing the importance of long time series altimetry to separate long-term trends associated with climate change from interannual to interdecadal natural variability.

  15. Dynamic response of Sjögren Inlet glaciers, Antarctic Peninsula, to ice shelf breakup derived from multi-mission remote sensing time series.

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    Seehaus, T.C.; Marinsek, S.; Skvarca, P.; van Wessem, J.M.; Reijmer, C.H.; Seco, J.L.; Braun, M.

    2016-01-01

    The substantial retreat or disintegration of numerous ice shelves has been observed on the Antarctic Peninsula. The ice shelf in the Prince Gustav Channel has retreated gradually since the late 1980s and broke up in 1995. Tributary glaciers reacted with speed-up, surface lowering and increased ice d

  16. Future sea-level rise from tidewater and ice-shelf tributary glaciers of the Antarctic Peninsula

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    Schannwell, Clemens; Barrand, Nicholas E.; Radić, Valentina

    2016-11-01

    Iceberg calving and increased ice discharge from ice-shelf tributary glaciers contribute significant amounts to global sea-level rise (SLR) from the Antarctic Peninsula (AP). Owing to ongoing ice dynamical changes (collapse of buttressing ice shelves), these contributions have accelerated in recent years. As the AP is one of the fastest warming regions on Earth, further ice dynamical adjustment (increased ice discharge) is expected over the next two centuries. In this paper, the first regional SLR projection of the AP from both iceberg calving and increased ice discharge from ice-shelf tributary glaciers in response to ice-shelf collapse is presented. An ice-sheet model forced by temperature output from 13 global climate models (GCMs), in response to the high greenhouse gas emission scenario (RCP8.5), projects AP contribution to SLR of 28 ± 16 to 32 ± 16 mm by 2300, partitioned approximately equally between contributions from tidewater glaciers and ice-shelf tributary glaciers. In the RCP4.5 scenario, sea-level rise projections to 2300 are dominated by tidewater glaciers (∼8-18 mm). In this cooler scenario, 2.4 ± 1 mm is added to global sea levels from ice-shelf tributary drainage basins as fewer ice-shelves are projected to collapse. Sea-level projections from ice-shelf tributary glaciers are dominated by drainage basins feeding George VI Ice Shelf, accounting for ∼70% of simulated SLR. Combined total ice dynamical SLR projections to 2300 from the AP vary between 11 ± 2 and 32 ± 16 mm sea-level equivalent (SLE), depending on the emission scenario used. These simulations suggest that omission of tidewater glaciers could lead to a substantial underestimation of the ice-sheet's contribution to regional SLR.

  17. Ice-Core Study of the Link between Sea-Salt Aerosol, Sea-Ice Cover and Climate in the Antarctic Peninsula Area

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    Aristarain, A.J. [Laboratorio de Estratigrafia Glaciar y Geoquimica del Agua y de la Nieve LEGAN, Instituto Antartico Argentino, Mendoza (Argentina); Delmas, R.J. [Laboratoire de Glaciologie et Geophysique de l' Environnement LGGE, Centre National de la Recherche Scientifique, BP 96, 38402 St. Martin d' Heres Cedex (France); Stievenard, M. [Laboratoire des Sciences du Climat et de l' Environnement LSCE, Centre d' Etudes de Saclay, 91191 Gif-sur-Yvette, Cedex (France)

    2004-11-01

    Three ice cores and a set of snow pit samples collected on James Ross Island, Antarctic Peninsula, in 1979, 1981 and 1991 have been analyzed for water stable isotope content D or 18O (isotopic temperature) and major chemical species. A reliable and detailed chronological scale has been established first for the upper 24.5 m of water equivalent (1990-1943) where various data sets can be compared, then extended down to 59.5 m of water equivalent (1847) with the aid of seasonal variations and the sulphate peak reflecting the 1883 Krakatoa volcanic eruption. At James Ross Island, sea-salt aerosol is generally produced by ice-free marine surfaces during the summer months, although some winter sea-salt events have been observed. For the upper part of the core (1990-1943), correlations (positive or negative) were calculated between isotopic temperature, chloride content (a sea-salt indicator), sea-ice extent, regional atmospheric temperature changes and atmospheric circulation. The D and chloride content correlation was then extended back to 1847, making it possible to estimate decadal sea-ice cover fluctuations over the study period. Our findings suggest that ice-core records from James Ross Island reflect the recent warming and sea-ice decrease trends observed in the Antarctic Peninsula area from the mid-1940s.

  18. Firn air-content of Larsen C Ice Shelf, Antarctic Peninsula, from seismic velocities, borehole surveys and firn modelling

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    Kulessa, Bernd; Brisbourne, Alex; Booth, Adam; Kuipers Munneke, Peter; Bevan, Suzanne; Luckman, Adrian; Hubbard, Bryn; Gourmelen, Noel; Palmer, Steve; Holland, Paul; Ashmore, David; Shepherd, Andrew

    2016-04-01

    The rising surface temperature of Antarctic Peninsula ice shelves is strongly implicated in ice shelf disintegration, by exacerbating the compaction of firn layers. Firn compaction is expected to warm the ice column and, given sufficiently wet and compacted layers, to allow meltwater to penetrate into surface crevasses and thus enhance hydrofracture potential. Integrating seismic refraction surveys with borehole neutron and firn core density logging, we reveal vertical and horizontal changes in firn properties across Larsen C Ice Shelf. Patterns of firn air-content derived from seismic surveys are broadly similar to those estimated previously from airborne radar and satellite data. Specifically, these estimates show greater firn compaction in the north and landward inlets compared to the south, although spatial gradients in seismic-derived air-contents are less pronounced than those previously inferred. Firn thickness is less than 10 m in the extreme northwest of Larsen C, in Cabinet Inlet, yet exceeds 40 m in the southeast, suggesting that the inlet is a focus of firn compaction; indeed, buried layers of massive refrozen ice were observed in 200 MHz GPR data in Cabinet and Whirlwind Inlets during a field campaign in the 2014-15 austral summer. Depth profiles of firn density provide a reasonable fit with those derived from closely-located firn cores and neutron probe data. Our model of firn structure is driven by RACMO and includes a 'bucket'-type hydrological implementation, and simulates the depth-density profiles in the inlets well. Discrepancies between measured and modelled depth-density profiles become progressively greater towards the ice-shelf front. RACMO incorrectly simulates the particular leeward (sea-ice-influenced) microclimate of the shallow boundary layer, leading to excess melt and/or lack of snowfall. The spatial sampling density of our seismic observations will be augmented following a further field campaign in the 2016-17 austral summer

  19. The imbalance of glaciers after disintegration of Larsen-B ice shelf, Antarctic Peninsula

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    H. Rott

    2011-03-01

    Full Text Available The outlet glaciers to the embayment of the Larsen-B Ice Shelf started to accelerate soon after the ice shelf disintegrated in March 2002. We analyse high resolution radar images of the TerraSAR-X satellite, launched in June 2007, to map the motion of outlet glaciers in detail. The frontal velocities are used to estimate the calving fluxes for 2008/2009. As reference for pre-collapse conditions, when the glaciers were in balanced state, the ice fluxes through the same gates are computed using ice motion maps derived from interferometric data of the ERS-1/ERS-2 satellites in 1995 and 1999. Profiles of satellite laser altimetry from ICESat, crossing the terminus of several glaciers, indicate considerable glacier thinning between 2003 and 2007/2008. This is taken into account for defining the calving cross sections. The difference between the pre- and post-collapse fluxes provides an estimate on the mass imbalance. For the Larsen-B embayment the 2008 mass deficit is estimated at 4.34 ± 1.64 Gt a−1, significantly lower than previously published values. The ice flow acceleration follows a similar pattern on the various glaciers, gradually decreasing in magnitude with distance upstream from the calving front. This suggests stress perturbation at the glacier front being the main factor for acceleration. So far there are no signs of slow-down indicating that dynamic thinning and frontal retreat will go on.

  20. Surface energy budget on Larsen and Wilkins ice shelves in the Antarctic Peninsula: results based on reanalyses in 1989–2010

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    I. Välisuo

    2013-03-01

    Full Text Available Ice shelves in the Antarctic Peninsula have significantly disintegrated during the recent decades. To better understand the atmospheric contribution in the process, we have analysed the inter-annual variations in radiative and turbulent surface fluxes and weather conditions over Larsen C Ice Shelf (LCIS and Wilkins Ice Shelf (WIS in the Antarctic Peninsula in 1989–2010. Three atmospheric reanalyses were applied: ERA-Interim by ECMWF, Climate Forecast System Reanalysis (CFSR by NCEP, and JRA-25/JCDAS by the Japan Meteorological Agency. In addition, in situ observations from an automatic weather station (AWS on LCIS were applied, mainly for validation of the reanalyses. The AWS observations on LCIS did not show any significant temperature trend, and the reanalyses showed warming trends only over WIS: ERA-Interim in winter (0.23 °C yr−1 and JRA in autumn (0.13 °C yr−1. In LCIS from December through August and in WIS from March through August, the variations of surface net flux were partly explained by the combined effects of atmospheric pressure, wind, and cloud fraction. The explained variance was much higher in LCIS (up to 80% than in WIS (26–27%. Summer melting on LCIS varied between 0 and 45 cm water equivalent (w.e., which is comparable to previous results. The mean amount of melt days per summer on LCIS was only 17. The high values of melting in summer 2001–2002 presented in previous studies on the basis of simple calculations were not supported by our study. Instead, our calculations based on ERA-Interim yielded strongest melting in summer 1992–1993 on both ice shelves. On WIS the summer melting ranged between 2 and 40 cm w.e., and the peak values coincided with the largest disintegrations of the ice shelf.

  1. Holocene climate variations in the western Antarctic Peninsula: evidence for sea ice extent predominantly controlled by insolation and ENSO variability changes

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    J. Etourneau

    2013-01-01

    Full Text Available The West Antarctic ice sheet is particularly sensitive to global warming and its evolution and impact on global climate over the next few decades remains difficult to predict. In this context, investigating past sea ice conditions around Antarctica is of primary importance. Here, we document changes in sea ice presence, upper water column temperatures (0–200 m and primary productivity over the last 9000 yr BP (before present in the western Antarctic Peninsula (WAP margin from a sedimentary core collected in the Palmer Deep basin. Employing a multi-proxy approach, we derived new Holocene records of sea ice conditions and upper water column temperatures, based on the combination of two biomarkers proxies (highly branched isoprenoid (HBI alkenes for sea ice and TEXL86 for temperature and micropaleontological data (diatom assemblages. The early Holocene (9000–7000 yr BP was characterized by a cooling phase with a short sea ice season. During the mid-Holocene (~ 7000–3000 yr BP, local climate evolved towards slightly colder conditions and a prominent extension of the sea ice season occurred, promoting a favorable environment for intensive diatom growth. The late Holocene (the last ~ 3000 yr was characterized by more variable temperatures and increased sea ice presence, accompanied by reduced local primary productivity likely in response to a shorter growing season compared to the early or mid-Holocene. The stepwise increase in annual sea ice duration over the last 7000 yr might have been influenced by decreasing mean annual and spring insolation despite an increasing summer insolation. We postulate that in addition to precessional changes in insolation, seasonal variability, via changes in the strength of the circumpolar Westerlies and upwelling activity, was further amplified by the increasing frequency/amplitude of El Niño-Southern Oscillation (ENSO. However, between 4000 and 2100 yr BP, the lack of correlation between

  2. Surface energy budget on Larsen and Wilkins ice shelves in the Antarctic Peninsula: results based on reanalyses in 1989-2010

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    Välisuo, I.; Vihma, T.; King, J. C.

    2014-08-01

    Ice shelves in the Antarctic Peninsula have significantly disintegrated during recent decades. To better understand the atmospheric contribution in the process, we have analysed the inter-annual variations in radiative and turbulent surface fluxes and weather conditions over Larsen C Ice Shelf (LCIS) and Wilkins Ice Shelf (WIS) in the Antarctic Peninsula in 1989-2010. Three atmospheric reanalyses were applied: ERA-Interim by ECMWF, Climate Forecast System Reanalysis (CFSR) by NCEP, and JRA-25/JCDAS by the Japan Meteorological Agency. In addition, in situ observations from an automatic weather station (AWS) on LCIS were applied, mainly for validation of the reanalyses. The AWS observations on LCIS did not show any significant temperature trend, and the reanalyses showed warming trends only over WIS: ERA-Interim in winter (0.23 °C yr-1) and JRA-25/JCDAS in autumn (0.13 °C yr-1). In LCIS from December through August and in WIS from March through August, the variations of surface net flux were partly explained by the combined effects of atmospheric pressure, wind and cloud fraction. The explained variance was much higher in LCIS (up to 80%) than in WIS (26-27%). Summer melting on LCIS varied between 11 and 58 cm water equivalent (w.e.), which is comparable to previous results. The mean amount of melt days per summer on LCIS was 69. The high values of melting in summer 2001-2002 presented in previous studies on the basis of simple calculations were not supported by our study. Instead, our calculations based on ERA-Interim yielded strongest melting in summer 1992-1993 on both ice shelves. On WIS the summer melting ranged between 10 and 23 cm w.e., and the peak values coincided with the largest disintegrations of the ice shelf. The amount of melt on WIS may, however, be underestimated by ERA-Interim, as previously published satellite observations suggest that it suffers from a significant bias over WIS.

  3. Modelling the Antarctic Ice Sheet

    DEFF Research Database (Denmark)

    Pedersen, Jens Olaf Pepke; Holm, A.

    2015-01-01

    The Antarctic ice sheet is a major player in the Earth’s climate system and is by far the largest depository of fresh water on the planet. Ice stored in the Antarctic ice sheet (AIS) contains enough water to raise sea level by about 58 m, and ice loss from Antarctica contributed significantly...... Science) Antarctic Ice Sheet (DAIS) model (Shaffer 2014) is forced by reconstructed time series of Antarctic temperature, global sea level and ocean subsurface temperature over the last two glacial cycles. In this talk a modelling work of the Antarctic ice sheet over most of the Cenozoic era using...... the DAIS model will be presented. G. Shaffer (2014) Formulation, calibration and validation of the DAIS model (version 1), a simple Antarctic ice sheet model sensitive to variations of sea level and ocean subsurface temperature, Geosci. Model Dev., 7, 1803‐1818...

  4. Monitoring ice shelf velocities from repeat MODIS and Landsat data – a method study on the Larsen C ice shelf, Antarctic Peninsula, and 10 other ice shelves around Antarctica

    Directory of Open Access Journals (Sweden)

    T. Haug

    2010-01-01

    Full Text Available We investigate the velocity field of the Larsen C ice shelf, Antarctic Peninsula, over the periods 2002–2006 and 2006–2009 based on repeat optical satellite data. The velocity field of the entire ice shelf is measured using repeat low resolution MODIS data (250 m spatial resolution. The measurements are validated for two ice shelf sections against repeat medium resolution Landsat 7 ETM+ pan data (15 m spatial resolution. Horizontal surface velocities are obtained through image matching in both frequency and spatial domain, and the two methods compared. The uncertainty in the displacement measurements turns out to be less than 70 m for the MODIS derived data, and less than 15 m for the Landsat derived ones. The difference between MODIS and Landsat based speeds is −15.4 m a−1 and 13.0 m a−1, respectively, for the first period for the two different validation sections on the ice shelf, and −26.7 m a−1 and 27.9 m a−1 for the second period for the same sections. This leads us to conclude that repeat MODIS images are well suited to measure ice shelf velocity fields and monitor their changes over time. The frequency domain image correlation method seems better suited for this purpose because it is faster, produces fewer mismatches, and is able to match images with regular noise and data voids. The latter makes it possible to match Landsat 7 ETM+ images even after the 2003 failure of the Scan Line Corrector (SLC off that leaves significant image sections with no data. Image matching based on the original 12-bit radiometric resolution MODIS data produced slightly better results than using the 8-bit version of the same images. Streamline interpolation from the obtained surface velocity field on Larsen C indicates ice travel times of up to 450 to 550 a between the inland boundary and the ice shelf edge. In a second step of the study we test our method successfully on 10 other ice shelves around

  5. Monitoring ice shelf velocities from repeat MODIS and Landsat data – a method study on the Larsen C ice shelf, Antarctic Peninsula, and 10 other ice shelves around Antarctica

    Directory of Open Access Journals (Sweden)

    P. Skvarca

    2010-05-01

    Full Text Available We investigate the velocity field of the Larsen C ice shelf, Antarctic Peninsula, over the periods 2002–2006 and 2006–2009 based on repeat optical satellite data. The velocity field of the entire ice shelf is measured using repeat low resolution MODIS data (250 m spatial resolution. The measurements are validated for two ice shelf sections against repeat medium resolution Landsat 7 ETM + pan data (15 m spatial resolution. Horizontal surface velocities are obtained through image matching using both orientation correlation operated in the frequency domain and normalized crosscorrelation operated in the spatial domain, and the two methods compared. The uncertainty in the displacement measurements turns out to be about one fourth of the pixel size for the MODIS derived data, and about one pixel for the Landsat derived data. The difference between MODIS and Landsat based speeds is −15.4 m a−1 and 13.0 m a−1, respectively, for the first period for the two different validation sections on the ice shelf, and −26.7 m a−1 and 27.9 m a−1 for the second period for the same sections. This leads us to conclude that repeat MODIS images are well suited to measure ice shelf velocity fields and monitor their changes over time. Orientation correlation seems better suited for this purpose because it produces fewer mismatches, is able to match images with regular noise and data voids, and is faster. Since it can match images with regular data voids it is possible to match Landsat 7 ETM+ images even after the 2003 failure of the Scan Line Corrector (SLC off that leaves significant image stripes with no data. Image matching based on the original 12-bit radiometric resolution MODIS data produced slightly better results than using the 8-bit version of the same images. Streamline interpolation from the obtained surface velocity field on Larsen~C indicates ice travel times of up to 450 to 550 years between the inland boundary and the ice shelf edge. In a

  6. Soil thermal regime on ice-free areas in Livingston Island and James Ross Island, Antarctic Peninsula region

    Science.gov (United States)

    Hrbáček, Filip; Oliva, Marc; Láska, Kamil; Ruiz-Fernández, Jesús; Ángel de Pablo, Miguel; Vieira, Gonçalo; Ramos, Miguel; Nývlt, Daniel

    2016-04-01

    Permafrost and active layer are considered prominent components of the Cryosphere, which react very sensitively to small climate variations. The Antarctic Peninsula (AP) region is considered as one of the fastest warming regions on Earth, where mean annual air temperature locally increased more than 2.5°C over the last 60 years. Significant climate differences are found between the eastern and western sides of the AP. While mean annual air temperatures (MAAT) oscillate around -1 to -2 °C and precipitation reach 800 mm w.e. year-1 in the western AP, the MAAT in the eastern AP are below -6 °C and precipitation does not exceed 500 mm. These differences determine different permafrost thickness and spatial distribution in these two regions, as well as diverse patterns of active layer dynamics. With the purpose to better understand the factors controlling the soil thermal regime in maritime permafrost environments, we examine data from 2014 acquired from several sites in Livingston Island (western AP) and James Ross Island (eastern AP). The study sites show similar characteristics in terms of topography (slope Ross Island ranged from -7.0 to -7.9 °C. Mean soil temperature at 5 cm depth was slightly higher than air temperature in both areas: -0.7 to -1.3 °C in Livingston Island and -6.2 to -6.3 °C in James Ross Island; the same occurred for soil temperature at 75 cm: -0.4 to -0.7 °C in Livingston Island and -6.0 to -6.6 °C James Ross Island. Significantly lower values of mean daily amplitude of soil temperature at 5 cm depth and the freezing n-factor values observed during the freezing season on Livingston Island suggest a pronounced insulating effect of snow cover in this area in comparison to James Ross Island. The mean daily amplitude of soil temperature at 5 cm ranged from 0.9 to 1.7 °C in Livingston Island, while it reached 3.0 to 4.0 °C in James Ross Island. The freezing n-factor reached 0.33 and 0.63 on Livingston Island, while 0.88 and 0.98 were

  7. Spatiotemporal variations in the surface velocities of Antarctic Peninsula glaciers

    Directory of Open Access Journals (Sweden)

    J. Chen

    2014-11-01

    Full Text Available Velocity is an important parameter for the estimation of glacier mass balance, which directly signals the response of glaciers to climate change. Antarctic ice sheet movement and the associated spatiotemporal velocity variations are of great significance to global sea level rise. In this study, we estimate Antarctic Peninsula glacier velocities using the co-registration of optically sensed images and correlation (hereafter referred to as COSI-Corr based on moderate-resolution imaging spectroradiometer Level 1B data (hereafter referred to as MODIS L1B. The results show that the glaciers of Graham Land and the Larsen Ice Shelf have substantially different velocity features. The Graham Land glaciers primarily flow from the peninsula ridge towards the Weddell Sea and Bellingshausen Sea on the east and west sides, respectively. There are very large velocity variations among the different ice streams, with a minimum of −1 and a maximum of 1500 m a−1 (with an average of 100–150 m a−1. Over the period 2000–2012, the glaciers of Graham Land accelerated in the south but slowed down in the north. In contrast, the Larsen Ice Shelf flows in a relatively uniform direction, mainly towards the northeast into the Weddell Sea. Its average velocity is 750–800 m a−1 and the maximum is > 1500 m a−1. During the period 2000–2012, the Larsen Ice Shelf experienced significant acceleration. The use of COSI-Corr based on MODIS L1B data is suitable for glacier velocity monitoring on the Antarctic Peninsula over long time series and large spatial scales. This method is clearly advantageous for analysing macro-scale spatiotemporal variations in glacier movement.

  8. A paleomagnetic study of the Antarctic Peninsula

    Science.gov (United States)

    Poblete, F.; Arriagada, C.; Roperch, P.

    2009-05-01

    In the Paleozoic, South America, South Africa and Antarctica were part of Gondwana. The Weddell Sea began to form at about 146 Ma, after rifting between the Antarctic Peninsula and southernmost South America. Much uncertainty still exists about the geometrical fit and subsequent drift history between Patagonia and Antarctica. Geophysical and geological data which describe the tectonic history are sparsely distributed and often of poor quality. During the last two years we have collected more than 1000 paleomagnetic samples from 70 sites at several localities (King George Island, Robert Island, Yankee Bay, Half Moon Island, Byers Peninsula and Snow Island) from the South Shetland Islands and Anderson Island in the northern tip of Antarctic Peninsula. Our main objective was to provide first-order constraints on latitudinal displacements and the amount of tectonic rotations as an essential test of published tectonic models. Paleomagnetic results were obtained from 50 sites. All samples from sites in volcanic and intrusive rocks have well-defined univectorial magnetizations. Unfortunately, all sites in late Paleozoic sediments have been remagnetized and the magnetizations are often unstable upon thermal demagnetization. Cretaceous and Cenozoic units display very little apparent polar wander. Results from intrusive rocks of expected Jurassic age do not confirm the expected relative rotation betwen the Antarctic Peninsula and East Antarctica. Further radiometric dating are needed to confirm the age of these units.

  9. Ross Ice Shelf, Antarctic Ice and Clouds

    Science.gov (United States)

    1991-01-01

    In this view of Antarctic ice and clouds, (56.5S, 152.0W), the Ross Ice Shelf of Antarctica is almost totally clear, showing stress cracks in the ice surface caused by wind and tidal drift. Clouds on the eastern edge of the picture are associated with an Antarctic cyclone. Winds stirred up these storms have been known to reach hurricane force.

  10. Holocene glacier dynamics on James Ross Island, NE Antarctic Peninsula

    Science.gov (United States)

    Davies, B. J.; Glasser, N. F.; Hambrey, M.

    2013-12-01

    The northern Antarctic Peninsula is currently warming very rapidly, which has resulted in ice sheet thinning, ice-shelf collapse, and rapid and widespread glacier recession. These small mountain glaciers are predicted to make a large sea level contribution over the coming century. Reconstructing past rates, volumes and magnitudes of change, particularly with respect to the former configuration of former ice sheets and ice shelves, is vital to contextualise contemporary change and to improve predictions of future ice-sheet behaviour. The aim of this research is therefore to investigate the relationship of deglacial ice sheet thinning and Holocene glacier fluctuations around James Ross Island, northeast Antarctic Peninsula, with temperature changes recorded in the Mount Haddington Ice Core. We use a combination of geomorphological mapping, from field campaigns and remotely sensed images, cosmogenic nuclide ages on glacially transported boulders, and numerical modelling with a simple 1D flowline model. Prior to 18 ka, James Ross Island was inundated by a thick and mainly cold-based ice sheet, which scattered granite erratics across the island. Ice sheet thickness and the rate of thinning is constrained by granite erratics on Terrapin Hill (610 m a.s.l.), and from flat-topped mesas at 370 m a.s.l. on Ulu Peninsula. During deglaciation and a period of rapid warming and eustatic sea level rise, the area was drained by Prince Gustav Ice Stream. The ice sheet reached its current configuration by around 6 ka, with glacier readvances around 4-5 ka. At Boulder Valley, near Terrapin Hill on James Ross Island, a large glacial readvance reached the current shoreline. It pre-dated the Mid-Holocene sea level high-stand, and has shorelines imprinted upon its seaward face. After 5.3 cal. ka BP and post-dating the mid-Holocene sea level high-stand, there was a readvance of at least 7 km by glacier 'IJR-45' on Ulu Peninsula. Rapid glacier recession occurred during a period of

  11. Spatial-temporal characters of Antarctic sea ice variation

    Institute of Scientific and Technical Information of China (English)

    Ma Lijuan; Lu Longhua; Bian Lingen

    2004-01-01

    Using sea ice concentration dataset covering the period of 1968-2002 obtained from the Hadley Center of UK, this paper investigates characters of Antarctic sea ice variations .The finding demonstrates that the change of mean sea-ice extent is almost consistent with that of sea-ice area, so sea-ice extent can be chosen to go on this research. The maximum and the minimum of Antarctic sea ice appear in September and February respectively. The maximum and the maximal variation of sea ice appear in Weddell Sea and Ross Sea, while the minimum and the minimal variation of sea-ice appear in Antarctic Peninsula. In recent 35 years, as a whole, Antarctic sea ice decreased distinctly. Moreover, there are 5 subdivision characteristic regions considering their different variations. Hereinto, the sea-ice extent of Weddell Sea and Ross Sea regions extends and area increases, while the sea-ice extent of the other three regions contracts and area decreases. They are all of obvious 2-4 years and 5-7 years significant oscillation periods. It is of significance for further understanding the sea-ice-air interaction in Antarctica region and discussing the relationship between sea-ice variation and atmospheric circulation.

  12. Is the Wilkins Ice Shelf a Firn Aquifer? Spaceborne Observation of Subsurface Winter Season Liquid Meltwater Storage on the Antarctic Peninsula using Multi-Frequency Active and Passive Microwave Remote Sensing

    Science.gov (United States)

    Miller, J.; Scambos, T.; Forster, R. R.; Long, D. G.; Ligtenberg, S.; van den Broeke, M.; Vaughan, D. G.

    2015-12-01

    Near-surface liquid meltwater on ice shelves has been inferred to influence ice shelf stability if it induces hydrofracture and is linked to disintegration events on the Larsen B and the Wilkins ice shelves on the Antarctic Peninsula during the summer months. While the initial Wilkins disintegration event occurred in March of 2009, two smaller disintegration events followed in May and in July of that year. It has long been assumed meltwater refreezes soon after surface melt processes cease. Given this assumption, an earlier hypothesis for the two winter season disintegration events was hydrofracture via a brine infiltration layer. Two lines of evidence supported this hypothesis 1) early airborne radar surveys did not record a reflection from the bottom of the ice shelf, and 2) a shallow core drilled in 1972 on the Wilkins encountered liquid water at a depth of ~7 m. The salinity of the water and the temperature at the base of the core, however, were not described. The recent discovery of winter season liquid meltwater storage on the Greenland ice sheet has changed perceptions on meltwater longevity at depth in firn. Evidence of Greenland's firn aquifer includes liquid meltwater encountered in shallow firn cores at 5 m depth and a lack of reflections from the base of the ice sheet in airborne surveys. Thus, previous lines of evidence suggesting brine infiltration may alternatively suggest the presence of a perennial firn aquifer. We recently demonstrated the capability for observation of Greenland's firn aquifer from space using multi-frequency active and passive microwave remote sensing. This research exploits the retrieval technique developed for Greenland to provide the first spaceborne mappings of winter season liquid meltwater storage on the Wilkins. We combine L-band brightness temperature and backscatter data from the MIRAS instrument (1.4 GHz) aboard ESA's Soil Moisture and Ocean Salinity mission and the radar (1.3 GHZ) and radiometer(1.4 GHz) aboard NASA

  13. Snow on Antarctic sea ice

    Science.gov (United States)

    Massom, Robert A.; Eicken, Hajo; Hass, Christian; Jeffries, Martin O.; Drinkwater, Mark R.; Sturm, Matthew; Worby, Anthony P.; Wu, Xingren; Lytle, Victoria I.; Ushio, Shuki; Morris, Kim; Reid, Phillip A.; Warren, Stephen G.; Allison, Ian

    2001-08-01

    Snow on Antarctic sea ice plays a complex and highly variable role in air-sea-ice interaction processes and the Earth's climate system. Using data collected mostly during the past 10 years, this paper reviews the following topics: snow thickness and snow type and their geographical and seasonal variations; snow grain size, density, and salinity; frequency of occurrence of slush; thermal conductivity, snow surface temperature, and temperature gradients within snow; and the effect of snow thickness on albedo. Major findings include large regional and seasonal differences in snow properties and thicknesses; the consequences of thicker snow and thinner ice in the Antarctic relative to the Arctic (e.g., the importance of flooding and snow-ice formation); the potential impact of increasing snowfall resulting from global climate change; lower observed values of snow thermal conductivity than those typically used in models; periodic large-scale melt in winter; and the contrast in summer melt processes between the Arctic and the Antarctic. Both climate modeling and remote sensing would benefit by taking account of the differences between the two polar regions.

  14. Geomorphic and shallow-acoustic investigation of an Antarctic Peninsula fjord system using high-resolution ROV and shipboard geophysical observations: Ice dynamics and behaviour since the Last Glacial Maximum

    Science.gov (United States)

    García, Marga; Dowdeswell, J. A.; Noormets, R.; Hogan, K. A.; Evans, J.; Ó Cofaigh, C.; Larter, R. D.

    2016-12-01

    Detailed bathymetric and sub-bottom acoustic observations in Bourgeois Fjord (Marguerite Bay, Antarctic Peninsula) provide evidence on sedimentary processes and glacier dynamics during the last glacial cycle. Submarine landforms observed in the 50 km-long fjord, from the margins of modern tidewater glaciers to the now ice-distal Marguerite Bay, are described and interpreted. The landforms are grouped into four morpho-sedimentary systems: (i) glacial advance and full-glacial; (ii) subglacial and ice-marginal meltwater; (iii) glacial retreat and neoglaciation; and (iv) Holocene mass-wasting. These morpho-sedimentary systems have been integrated with morphological studies of the Marguerite Bay continental shelf and analysed in terms of the specific sedimentary processes and/or stages of the glacial cycle. They demonstrate the action of an ice-sheet outlet glacier that produced drumlins and crag-and-tail features in the main and outer fjord. Meltwater processes eroded bedrock channels and ponds infilled by fine-grained sediments. Following the last deglaciation of the fjord at about 9000 yr BP, subsequent Holocene neoglacial activity involved minor readvances of a tidewater glacier terminus in Blind Bay. Recent stillstands and/or minor readvances are inferred from the presence of a major transverse moraine that indicates grounded ice stabilization, probably during the Little Ice Age, and a series of smaller landforms that reveal intermittent minor readvances. Mass-wasting processes also affected the walls of the fjord and produced scars and fan-shaped deposits during the Holocene. Glacier-terminus changes during the last six decades, derived from satellite images and aerial photographs, reveal variable behaviour of adjacent tidewater glaciers. The smaller glaciers show the most marked recent retreat, influenced by regional physiography and catchment-area size.

  15. Pteropods and climate off the Antarctic Peninsula

    Science.gov (United States)

    Loeb, Valerie J.; Santora, Jarrod A.

    2013-09-01

    Shelled (thecosome) and naked (gymnosome) pteropods are regular, at times abundant, members of Southern Ocean zooplankton assemblages. Regionally, shelled species can play a major role in food webs and carbon cycling. Because of their aragonite shells thecosome pteropods may be vulnerable to the impacts of ocean acidification; without shells they cannot survive and their demise would have major implications for food webs and carbon cycling in the Southern Ocean. Additionally, pteropod species in the southwest Atlantic sector of the Southern Ocean inhabit a region of rapid warming and climate change, the impacts of which are predicted to be observed as poleward distribution shifts. Here we provide baseline information on intraseasonal, interannual and longer scale variability of pteropod populations off the Antarctic Peninsula between 1994 and 2009. Concentrations of the 4 dominant taxa, Limacina helicina antarctica f. antarctica, Clio pyramidata f. sulcata, Spongiobranchaea australis and Clione limacina antarctica, are similar to those monitored during the 1928-1935 Discovery Investigations and reflect generally low values but with episodic interannual abundance peaks that, except for C. pyr. sulcata, are related to basin-scale climate forcing associated with the El Niño-Southern Oscillation (ENSO) climate mode. Significant abundance increases of L. helicina and S. australis after 1998 were associated with a climate regime shift that initiated a period dominated by cool La Niña conditions and increased nearshore influence of the Antarctic Circumpolar Current (ACC). This background information is essential to assess potential future changes in pteropod species distribution and abundance associated with ocean warming and acidification. construct maps of pteropod spatial frequency and mean abundance to assess their oceanographic associations; quantify pteropod abundance anomalies for comparing intraseasonal and interannual variability relative to m-3 environmental

  16. Stable isotopes and Antarctic moss banks: Plants and soil microbes respond to recent warming on the Antarctic Peninsula

    Science.gov (United States)

    Royles, Jessica; Amesbury, Matthew; Ogée, Jérôme; Wingate, Lisa; Convey, Peter; Hodgson, Dominic; Griffiths, Howard; Leng, Melanie; Charman, Dan

    2014-05-01

    The Antarctic Peninsula is one of the most rapidly warming regions on Earth, with air temperature increases of as much as 3°C recorded since the 1950s. However, the longer-term context of this change is limited and existing records, largely relying on ice core data, are not suitably located to be able to trace the spatial signature of change over time. We are working on a project exploiting stable isotope records preserved in moss peat banks spanning 10 degrees of latitude along the Antarctic Peninsula as an archive of late Holocene climate variability. Here we present a unique time series of past moss growth and soil microbial activity that has been produced from a 150 year old moss bank at Lazarev Bay, Alexander Island (69°S), a site at the southern limit of significant plant growth in the Antarctic Peninsula region. These moss banks are ideal archives for palaeoclimate research as they are well-preserved by freezing, generally monospecific, easily dated by radiocarbon techniques, and have sufficiently high accumulation rates to permit decadal resolution. We use accumulation rates, cellulose δ13C and fossil testate amoebae to show that growth rates, assimilation and microbial productivity rose rapidly in the 1960s, consistent with temperature change, although recently may have stalled, concurrent with other evidence. The increase in biological activity is unprecedented in the last 150 years. Along with work completed on Signy Island (60°S), in the South Orkney Islands, in which we used carbon isotope evidence to show recent climate-related enhancement of CO2 assimilation and peat accumulation rates in Antarctica, the observed relationships between moss growth, microbial activity and climate suggests that moss bank records have the potential to test the regional expression of temperature variability shown by instrumental data on the Antarctic Peninsula over centennial to millennial timescales, by providing long-term records of summer growth conditions

  17. Global dynamics of the Antarctic ice sheet

    NARCIS (Netherlands)

    Oerlemans, J.

    2002-01-01

    The total mass budget of the Antarctic ice sheet is studied with a simple axi-symmetrical model. The ice-sheet has a parabolic profile resting on a bed that slopes linearly downwards from the centre of the ice sheet into the ocean. The mean ice velocity at the grounding line is assumed to be proport

  18. Mass Gains of the Antarctic Ice Sheet Exceed Losses

    Science.gov (United States)

    Zwally, H. Jay; Li, Jun; Robbins, John; Saba, Jack L.; Yi, Donghui; Brenner, Anita; Bromwich, David

    2012-01-01

    During 2003 to 2008, the mass gain of the Antarctic ice sheet from snow accumulation exceeded the mass loss from ice discharge by 49 Gt/yr (2.5% of input), as derived from ICESat laser measurements of elevation change. The net gain (86 Gt/yr) over the West Antarctic (WA) and East Antarctic ice sheets (WA and EA) is essentially unchanged from revised results for 1992 to 2001 from ERS radar altimetry. Imbalances in individual drainage systems (DS) are large (-68% to +103% of input), as are temporal changes (-39% to +44%). The recent 90 Gt/yr loss from three DS (Pine Island, Thwaites-Smith, and Marie-Bryd Coast) of WA exceeds the earlier 61 Gt/yr loss, consistent with reports of accelerating ice flow and dynamic thinning. Similarly, the recent 24 Gt/yr loss from three DS in the Antarctic Peninsula (AP) is consistent with glacier accelerations following breakup of the Larsen B and other ice shelves. In contrast, net increases in the five other DS of WA and AP and three of the 16 DS in East Antarctica (EA) exceed the increased losses. Alternate interpretations of the mass changes driven by accumulation variations are given using results from atmospheric-model re-analysis and a parameterization based on 5% change in accumulation per degree of observed surface temperature change. A slow increase in snowfall with climate waRMing, consistent with model predictions, may be offsetting increased dynamic losses.

  19. Concentration and environmental significance of lead in surface snow of Antarctic ice sheet (III)

    Institute of Scientific and Technical Information of China (English)

    秦大河; 任贾文; 孙俊英; 陈瓞延; 文克玲; 李良权

    1995-01-01

    Lead as an ultra-trace heavy metal becomes one of popular topics in glaciochemistry of the Antarctic ice sheet, because of its very low concertration (pg·g-1) and background and its sensitivity to the quality of the environment. The lead concentration of surface snow of the Antarctic ice sheet (corresponding to modern precipitation) applying LEAF technique by Chinese scholars has systematically been studied for the first time in the world. The distribution principle of lead concentration of surface snow of the Antarctic ice sheet is "low in the west and high in the east" along the route of 1990 International Trans-Antarctic Expedition (ITAE). The concentration of lead in East Antarctica is 2 - 3 fold higher than that in Larsen ice shelf and Antarctic Peninsula, which majorly results from the activity of pre-Soviet Antarctic Expedition The concentration of lead in Larsen ice shelf and Antarctic Peninsula can be regarded as the background value of modern precipitation of the Antarctic ice sheet in the en

  20. Firn air depletion as a precursor of Antarctic ice-shelf collapse

    NARCIS (Netherlands)

    Kuipers Munneke, P.; Ligtenberg, S.R.M.; van den Broeke, M.R.; Vaughan, D.G.

    2014-01-01

    Since the 1970s, the sudden, rapid collapse of 20% of ice shelves on the Antarctic Peninsula has led to large-scale thinning and acceleration of its tributary glaciers. The leading hypothesis for the collapse of most of these ice shelves is the process of hydrofracturing, whereby a water-filled crev

  1. Geodetic implications on block formation and geodynamic domains in the South Shetland Islands, Antarctic Peninsula

    Science.gov (United States)

    Berrocoso, M.; Fernández-Ros, A.; Prates, G.; García, A.; Kraus, S.

    2016-01-01

    The South Shetland Islands archipelago is dynamically complex due to its tectonic surroundings. Most islands are part of a formerly active volcanic arc, although Deception, Penguin and Bridgeman Islands, as well as several submarine volcanoes, are characterized by active back-arc volcanism. Geodetic benchmarks were deployed and the movement of the lithosphere to which they were fixed measured to provide geodynamic insight for the South Shetland Islands, Bransfield Basin and Antarctic Peninsula area based on surface deformation. These benchmarks' data add spatial and temporal coverage to previous results. The results reveal two different geodynamic patterns, each confined to a distinct part of the South Shetland Islands archipelago. The inferred absolute horizontal velocity vectors for the benchmarks in the northeastern part of the archipelago are consistent with the opening of the Bransfield Basin, while benchmark vectors in the southwestern part of the archipelago are similar to those of the benchmarks on the Antarctic Peninsula. In between, Snow, Deception and Livingston Islands represent a transition zone. In this area, the horizontal velocity vectors relative to the Antarctic plate shift northeastwards from N to NW. Furthermore, the South Shetland Islands benchmarks, except for that at Gibbs (Elephant) Islands, indicate subsidence, which might be a consequence of the slab roll-back at the South Shetland Trench. In contrast, the uplift revealed by the Antarctic Peninsula benchmarks suggests glacial isostatic adjustment after the Larson B ice-shelf breakup.

  2. Meltwater produced by wind-albedo interaction stored in an East Antarctic ice shelf

    Science.gov (United States)

    Lenaerts, J. T. M.; Lhermitte, S.; Drews, R.; Ligtenberg, S. R. M.; Berger, S.; Helm, V.; Smeets, C. J. P. P.; Broeke, M. R. Van Den; van de Berg, W. J.; van Meijgaard, E.; Eijkelboom, M.; Eisen, O.; Pattyn, F.

    2017-01-01

    Surface melt and subsequent firn air depletion can ultimately lead to disintegration of Antarctic ice shelves causing grounded glaciers to accelerate and sea level to rise. In the Antarctic Peninsula, foehn winds enhance melting near the grounding line, which in the recent past has led to the disintegration of the most northerly ice shelves. Here, we provide observational and model evidence that this process also occurs over an East Antarctic ice shelf, where meltwater-induced firn air depletion is found in the grounding zone. Unlike the Antarctic Peninsula, where foehn events originate from episodic interaction of the circumpolar westerlies with the topography, in coastal East Antarctica high temperatures are caused by persistent katabatic winds originating from the ice sheet’s interior. Katabatic winds warm and mix the air as it flows downward and cause widespread snow erosion, explaining >3 K higher near-surface temperatures in summer and surface melt doubling in the grounding zone compared with its surroundings. Additionally, these winds expose blue ice and firn with lower surface albedo, further enhancing melt. The in situ observation of supraglacial flow and englacial storage of meltwater suggests that ice-shelf grounding zones in East Antarctica, like their Antarctic Peninsula counterparts, are vulnerable to hydrofracturing.

  3. Impact of the El Nino on the Variability of the Antarctic Sea Ice Extent

    Institute of Scientific and Technical Information of China (English)

    陈锦年; 褚健婷; 徐兰英

    2004-01-01

    In this paper, the spreading way in the southern hemisphere that anomalous warm water piled in tropical eastern Pacific is analysed and then impact of El Nino on the variability of the Antarctic sea ice extent is investigated by using a dataset from 1970 to 2002. The analysis result show that in El Nino event the anomalous warm water piled in tropical eastern Pacific is poleward propagation yet the westward propagation along southern equator current hasn 't been discovered . The poleward propagation time of the anomalous warm water is about 1 year or so. El Nino event has a close relationship with the sea ice extent in the Amundsen sea , Bellingshausen sea and Antarctic peninsula. After El Nino appears , there is a lag of two years that the sea ice in the Amundsen sea , Bellingshausea sea, especially in the Antarctic peninsula decreases obviously. The processes that El Nino has influence with Antarctic sea ice extent is the warm water piled in tropical eastern Pacific poleward propagation along off the coast of southern America and cause the anomalous temperature raise in near pole and then lead the sea ice in Amundsen sea , Bellingshausen sea and Antarctic peninsula to decrease where the obvious decrease of the sea ice since 80 'decade has close relation to the frequently appearance of El Nino.

  4. Blue and fin whale acoustics and ecology off Antarctic Peninsula

    OpenAIRE

    2006-01-01

    Blue (Balaenoptera musculus) and fin whales (B. physalus) in the Southern Ocean were subjects of extensive whaling industry during the twentieth century. Their current population numbers remain low, making population monitoring using traditional visual surveys difficult. Both blue and fin whales produce low frequency, regularly repeated calls and are suitable for acoustic monitoring. Eight, continuously recording acoustic recorders were deployed off the Western Antarctic Peninsula (WAP) betwe...

  5. A simulated Antarctic fast ice ecosystem

    Science.gov (United States)

    Arrigo, Kevin R.; Kremer, James N.; Sullivan, Cornelius W.

    1993-01-01

    A 2D numerical ecosystem model of Antarctic land fast ice is developed to elucidate the primary production with the Antarctic sea ice zone. The physical component employs atmospheric data to simulate congelation ice growth, initial brine entrapment, desalination, and nutrient flux. The biological component is based on the concept of a maximum temperature-dependent algal growth rate which is reduced by limitations imposed from insufficient light or nutrients, as well as suboptimal salinity. Preliminary simulations indicate that, during a bloom, microalgae are able to maintain their vertical position relative to the lower congelation ice margin and are not incorporated into the crystal matrix as the ice sheet thickens. It is inferred that land fast sea ice contains numerous microhabitats that are functionally distinct based upon the unique set of processes that control microalgal growth and accumulation within each.

  6. Distributions of surface sediments surrounding the Antarctic Peninsula and its environmental significance

    Institute of Scientific and Technical Information of China (English)

    WANG Chunjuan; CHEN Zhihua; LI Chunshun; DU Dewen; YAN Shijuan; ZHU Zhiwei

    2014-01-01

    We analyzed grain size composition to provide information on the types and distributions as well as depositional varieties of marine surface sediments from the area surrounding the Antarctic Peninsula. The samples retrieved from the study area contain gravel, sand, silt and clay. As suggested by bathymetry and morphology, the study area is characterized by neritic, hemipelagic and pelagic deposits. The glacial-marine sediments can be divided into two types, residual paratill and compound paratill, which are primarily transported by glaciers and as ice-rafted debris. Ocean current effects on deposition are more obvious, and the deposit types are distributed consistently with terrain variations.

  7. Absence of 21st century warming on Antarctic Peninsula consistent with natural variability.

    Science.gov (United States)

    Turner, John; Lu, Hua; White, Ian; King, John C; Phillips, Tony; Hosking, J Scott; Bracegirdle, Thomas J; Marshall, Gareth J; Mulvaney, Robert; Deb, Pranab

    2016-07-21

    Since the 1950s, research stations on the Antarctic Peninsula have recorded some of the largest increases in near-surface air temperature in the Southern Hemisphere. This warming has contributed to the regional retreat of glaciers, disintegration of floating ice shelves and a 'greening' through the expansion in range of various flora. Several interlinked processes have been suggested as contributing to the warming, including stratospheric ozone depletion, local sea-ice loss, an increase in westerly winds, and changes in the strength and location of low-high-latitude atmospheric teleconnections. Here we use a stacked temperature record to show an absence of regional warming since the late 1990s. The annual mean temperature has decreased at a statistically significant rate, with the most rapid cooling during the Austral summer. Temperatures have decreased as a consequence of a greater frequency of cold, east-to-southeasterly winds, resulting from more cyclonic conditions in the northern Weddell Sea associated with a strengthening mid-latitude jet. These circulation changes have also increased the advection of sea ice towards the east coast of the peninsula, amplifying their effects. Our findings cover only 1% of the Antarctic continent and emphasize that decadal temperature changes in this region are not primarily associated with the drivers of global temperature change but, rather, reflect the extreme natural internal variability of the regional atmospheric circulation.

  8. Environmental responses of the Northeast Antarctic Peninsula to the Holocene climate variability

    Science.gov (United States)

    Barbara, Loïc.; Crosta, Xavier; Leventer, Amy; Schmidt, Sabine; Etourneau, Johan; Domack, Eugene; Massé, Guillaume

    2016-01-01

    In this study, we present a unique high-resolution Holocene record of oceanographic and climatic change based on analyses of diatom assemblages combined with biomarker data from a sediment core collected from the Vega Drift, eastern Antarctic Peninsula (EAP). These data add to the climate framework already established by high-resolution marine sedimentary records from the Palmer Deep, western Antarctic Peninsula (WAP). Heavy sea ice conditions and reduced primary productivity were observed prior to 7.4 ka B.P. in relation with the proximity of the glacial ice melt and calving. Subsequent Holocene oceanographic conditions were controlled by the interactions between the Westerlies-Antarctic Circumpolar Current (ACC)-Weddell Gyre dynamics. A warm period characterized by short seasonal sea ice duration associated with a southern shift of both ACC and Westerlies field persisted until 5 ka B.P. This warm episode was then followed by climate deterioration during the middle-to-late Holocene (5 to 1.9 ka B.P.) with a gradual increase in annual sea ice duration triggered by the expansion of the Weddell Gyre and a strong oceanic connection from the EAP to the WAP. Increase of benthic diatom species during this period was indicative of more summer/autumn storms, which was consistent with changes in synoptic atmospheric circulation and the establishment of low- to high-latitude teleconnections. Finally, the multicentennial scale variability of the Weddell Gyre intensity and storm frequency during the late Holocene appeared to be associated with the increased El Niño-Southern Oscillation frequency.

  9. Ice Shelves and Landfast Ice on the Antarctic Perimeter: Revised Scope of Work

    Science.gov (United States)

    Scambos, Ted

    2002-01-01

    Ice shelves respond quickly and profoundly to a warming climate. Within a decade after mean summertime temperature reaches approx. O C and persistent melt pending is observed, a rapid retreat and disintegration occurs. This link was documented for ice shelves in the Antarctic Peninsula region (the Larsen 'A', 'B' and Wilkins Ice shelves) by the results of a previous grant under ADRO-1. Modeling of ice flow and the effects of meltwater indicated that melt pending accelerates shelf breakup by increasing fracture penetration. SAR data supplemented an AVHRR- and SSM/I-based image analysis of extent and surface characteristic changes. This funded grant is a revised, scaled-down version of an earlier proposal under the ADRO-2 NRA. The overall objective remains the same: we propose to build on the previous study by examining other ice shelves of the Antarctic and incorporate an examination of the climate-related characteristics of landfast ice. The study now considers just a few shelf and fast ice areas for study, and is funded for two years. The study regions are the northeastern Ross Ice Shelf, the Larsen 'B' and 'C' shelves, fast ice and floating shelf ice in the Pine Island Glacier area, and fast ice along the Wilkes Land coast. Further, rather than investigating a host of shelf and fast ice processes, we will home in on developing a series of characteristics associated with climate change over shelf and fast ice areas. Melt pending and break-up are the end stages of a response to a warming climate that may begin with increased melt event frequency (which changes both albedo and emissivity temporarily), changing firn backscatter (due to percolation features), and possibly increased rifting of the shelf surface. Fast ice may show some of these same processes on a seasonal timescale, providing insight into shelf evolution.

  10. Quantification of ikaite in Antarctic sea ice

    Directory of Open Access Journals (Sweden)

    M. Fischer

    2012-02-01

    Full Text Available Calcium carbonate precipitation in sea ice can increase pCO2 during precipitation in winter and decrease pCO2 during dissolution in spring. CaCO3 precipitation in sea ice is thought to potentially drive significant CO2 uptake by the ocean. However, little is known about the quantitative spatial and temporal distribution of CaCO3 within sea ice. This is the first quantitative study of hydrous calcium carbonate, as ikaite, in sea ice and discusses its potential significance for the carbon cycle in polar oceans. Ice cores and brine samples were collected from pack and land fast sea ice between September and December 2007 during an expedition in the East Antarctic and another off Terre Adélie, Antarctica. Samples were analysed for CaCO3, Salinity, DOC, DON, Phosphate, and total alkalinity. A relationship between the measured parameters and CaCO3 precipitation could not be observed. We found calcium carbonate, as ikaite, mostly in the top layer of sea ice with values up to 126 mg ikaite per liter melted sea ice. This potentially represents a contribution between 0.12 and 9 Tg C to the annual carbon flux in polar oceans. The horizontal distribution of ikaite in sea ice was heterogenous. We also found the precipitate in the snow on top of the sea ice.

  11. Land Ice: Greenland & Antarctic ice mass anomaly

    Data.gov (United States)

    National Aeronautics and Space Administration — Data from NASA's Grace satellites show that the land ice sheets in both Antarctica and Greenland are losing mass. The continent of Antarctica (left chart) has been...

  12. 'Unlocking the archive': Using photogrammetry of historic aerial photographs to extend the record of glacier change on the Antarctic Peninsula

    Science.gov (United States)

    Clarke, Lucy; Fox, Adrian

    2014-05-01

    Changes to glacier fronts and ice shelves and glacier acceleration are well documented, but there is almost no data on mass changes for the more than 400 glaciers on the Antarctic Peninsula. Current research demonstrates that the Antarctic Peninsula is contributing to sea-level change at a similar rate to that of other fast-changing near-polar or large mountain-glacier environments such as Iceland, Patagonia and Alaska (Hock, 2009). Forecasting the future impacts of the Antarctic Peninsula ice sheet on sea level will require a much improved understanding of 20th Century and contemporary glacier mass changes. Satellite data has been used to calculate these changes over the last three decades, but methods to quantify this over a longer time scale have eluded researchers. However, there is an archive of aerial photography of the Antarctic Peninsula dating back to the 1940s, this has been largely ignored due to the range of technical problems associated with deriving quantitative data from historic aerial photographs. This presentation demonstrates how advances in photogrammetric processing and capture of modern aerial photography have allowed this archive to be 'unlocked'. Accurate photogrammetric reconstruction from aerial photographs traditionally requires known ground control points acquired in the field; in remote and inaccessible areas, such as the Antarctic Peninsula, this is often impossible and so has restricted the use of photogrammetric analysis of the available aerial photography. A method for providing control for historic photos without fieldwork on the ground, by linking them to a newly acquired, highly accurate photogrammetric model adjusted through direct kinematic GPS positioning of the camera was developed by Fox and Cziferszky (2008), and this is now being applied to a number of glaciers across the Antarctic Peninsular using Intergraph Photogrammetry Suite (Erdas LPS 2013) software. This presentation will outline the photogrammetric workflow and

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

    Science.gov (United States)

    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.

  14. Antarctic Ice-Sheet Mass Balance from Satellite Altimetry 1992 to 2001

    Science.gov (United States)

    Zwally, H. Jay; Brenner, Anita C.; Cornejo, Helen; Giovinetto, Mario; Saba, Jack L.; Yi, Donghui

    2003-01-01

    A major uncertainty in understanding the causes of the current rate of sea level rise is the potential contributions from mass imbalances of the Greenland and Antarctic ice sheets. Estimates of the current mass balance of the Antarctic ice sheet are derived from surface- elevation changes obtained from 9 years of ERS - 1 & 2 radar altimeter data. Elevation time-series are created from altimeter crossovers among 90-day data periods on a 50 km grid to 81.5 S. The time series are fit with a multivariate linear/sinusoidal function to give the average rate of elevation change (dH/dt). On the major Rome-Filchner, Ross, and Amery ice shelves, the W d t are small or near zero. In contrast, the ice shelves of the Antarctic Peninsula and along the West Antarctic coast appear to be thinning significantly, with a 23 +/- 3 cm per year surface elevation decrease on the Larsen ice shelf and a 65 +/- 4 cm per year decrease on the Dotson ice shelf. On the grounded ice, significant elevation decreases are obtained over most of the drainage basins of the Pine Island and Thwaites glaciers in West Antarctica and inland of Law Dome in East Antarctica. Significant elevation increases are observed within about 200 km of the coast around much of the rest of the ice sheet. Farther inland, the changes are a mixed pattern of increases and decreases with increases of a few centimeters per year at the highest elevations of the East Antarctic plateau. The derived elevation changes are combined with estimates of the bedrock uplift from several models to provide maps of ice thickness change. The ice thickness changes enable estimates of the ice mass balances for the major drainage basins, the overall mass balance, and the current contribution of the ice sheet to global sea level change.

  15. Multichannel Seismic Reflection Data - SCAR - Antarctic Peninsula - 1985, SDLS CD-ROM vol 16

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — These data are stacked multichannel marine seismic reflection data recorded during 1985 field season along the north side of the Antarctic-Peninsula by the British...

  16. Multichannel Seismic Reflection Data - SCAR - Antarctic Peninsula - 1988-1989, SDLS CD-ROM vol 25

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — These data are stacked multichannel marine seismic reflection data recorded during 1988-89 in the Antarctic Peninsula, Antarctica, by the Japan National Oil...

  17. Multichannel Seismic Reflection Data - SCAR - Antarctic Peninsula 1987-88, SDLS CD-ROM vol 24

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — These data are stacked multichannel marine seismic reflection data recorded during 1987-88 in the Antarctic Peninsula, Antarctica, by the Japan National Oil...

  18. Snow chemistry measurements on James Ross Island (Antarctic Peninsula) showing sea-salt aerosol modifications

    Energy Technology Data Exchange (ETDEWEB)

    Aristarain, A.J. [Instituto Antartico Argentino (Argentina). Lab. de Estratigrafia Glaciar y Geoquimica de la Nieve; Consejo Nacional de Investigaciones Cientificas y Tecnicas, Mendoza (Argentina); Delmas, R.J. [Laboratoire de Glaciologie et Geophysique de l' Environnement du CNRS, St Martin d' Heres (France)

    2002-07-01

    The fractionation of atmospheric sea-salt has been investigated by glaciochemical analysis of the sea-salt deposited on the snow covering the small ice cap of James Ross Island, Antarctic Peninsula, at an elevation of 1640m. The data show that, generally, but not always, the sea-salt deposited at this location most likely originates directly from seawater, as is the case at lower latitudes. It is found that the original chemical composition of the sea-salt aerosol is significantly modified, in particular by the reaction of sea-salt particles in the atmosphere with acid species. A ternary diagram (sodium, chloride, sulfate) is used to enlighten the involved modification processes. The study points out the frequent formation of HCl in the regional atmosphere. (Author)

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

    Science.gov (United States)

    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

  20. The pressure-temperature-time evolution of the Antarctic Peninsula - magmatic arc and/or terrane tectonics?

    Science.gov (United States)

    Wendt, A. S.; Vidal, O.; Vaughan, A.

    2003-04-01

    The tectonic mobility in orogenic systems requires that the geologic history of each rock unit must be evaluated on the merits of the information gleaned more from individual outcrops than from regional generalisation. Continental margins affected by tectonic processes commonly have a region where the stratigraphic elements should be considered suspect in regard to palaeogeographic linkages both among the elements and between each element and the adjoining continent. Such occurrences might be considered as a natural consequence of the mobility and transient state of oceanic crust so that exotic far-travelled crustal fragments can be expected. The collision of those fragments and their distribution patterns reflect in general a combination of several tectonic phases such as overthrusting, stitching of plutons along the contact and welding metamorphism. The Antarctic Peninsula is an example "par excellence" for testing those tectonic processes occurring along continental margins. Prior to Mid-Jurassic times, the peninsula in its entity is thought to have formed a part of the palaeo-Pacific margin. East-directed subduction along the margin occurred during Mesozoic-Tertiary times producing a magmatic arc complex, in which volcanic and plutonic rocks are distributed widely along the length of the peninsula. However, recent discoveries suggest also that the Antarctic Peninsula is composed of at least two terranes in transpressional contact with para-autochthonous continental Gondwana margin. The reconstruction of the geological history becomes a challenging task in the hostile environment of the Antarctic where individual outcrops are scattered over large geographical distances, and structural relationships are obscured by thick layers of ice. In this work, we are attempting to correlate for the first time the pressure-temperature-time evolution of metamorphic rocks parallel to the spine of the peninsula and their structural relationship to the volcanic and plutonic

  1. Arctic and Antarctic sea ice and climate

    Science.gov (United States)

    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

  2. Simultaneous solution for mass trends on the West Antarctic Ice Sheet

    Directory of Open Access Journals (Sweden)

    N. Schön

    2014-06-01

    Full Text Available The Antarctic Ice Sheet is the largest potential source of future sea-level rise. Mass loss has been increasing over the last two decades in the West Antarctic Ice Sheet (WAIS, but with significant discrepancies between estimates, especially for the Antarctic Peninsula. Most of these estimates utilise geophysical models to explicitly correct the observations for (unobserved processes. Systematic errors in these models introduce biases in the results which are difficult to quantify. In this study, we provide a statistically rigorous, error-bounded trend estimate of ice mass loss over the WAIS from 2003–2009 which is almost entirely data-driven. Using altimetry, gravimetry, and GPS data in a hierarchical Bayesian framework, we derive spatial fields for ice mass change, surface mass balance, and glacial isostatic adjustment (GIA without relying explicitly on forward models. The approach we use separates mass and height change contributions from different processes, reproducing spatial features found in, for example, regional climate and GIA forward models, and provides an independent estimate, which can be used to validate and test the models. In addition, full spatial error estimates are derived for each field. The mass loss estimates we obtain are smaller than some recent results, with a time-averaged mean rate of −76 ± 15 GT yr−1 for the WAIS and Antarctic Peninsula (AP, including the major Antarctic Islands. The GIA estimate compares very well with results obtained from recent forward models (IJ05-R2 and inversion methods (AGE-1. Due to its computational efficiency, the method is sufficiently scalable to include the whole of Antarctica, can be adapted for other ice sheets and can easily be adapted to assimilate data from other sources such as ice cores, accumulation radar data and other measurements that contain information about any of the processes that are solved for.

  3. Simultaneous solution for mass trends on the West Antarctic Ice Sheet

    Science.gov (United States)

    Schoen, N.; Zammit-Mangion, A.; Rougier, J. C.; Flament, T.; Rémy, F.; Luthcke, S.; Bamber, J. L.

    2015-04-01

    The Antarctic Ice Sheet is the largest potential source of future sea-level rise. Mass loss has been increasing over the last 2 decades for the West Antarctic Ice Sheet (WAIS) but with significant discrepancies between estimates, especially for the Antarctic Peninsula. Most of these estimates utilise geophysical models to explicitly correct the observations for (unobserved) processes. Systematic errors in these models introduce biases in the results which are difficult to quantify. In this study, we provide a statistically rigorous error-bounded trend estimate of ice mass loss over the WAIS from 2003 to 2009 which is almost entirely data driven. Using altimetry, gravimetry, and GPS data in a hierarchical Bayesian framework, we derive spatial fields for ice mass change, surface mass balance, and glacial isostatic adjustment (GIA) without relying explicitly on forward models. The approach we use separates mass and height change contributions from different processes, reproducing spatial features found in, for example, regional climate and GIA forward models, and provides an independent estimate which can be used to validate and test the models. In addition, spatial error estimates are derived for each field. The mass loss estimates we obtain are smaller than some recent results, with a time-averaged mean rate of -76 ± 15 Gt yr-1 for the WAIS and Antarctic Peninsula, including the major Antarctic islands. The GIA estimate compares well with results obtained from recent forward models (IJ05-R2) and inverse methods (AGE-1). The Bayesian framework is sufficiently flexible that it can, eventually, be used for the whole of Antarctica, be adapted for other ice sheets and utilise data from other sources such as ice cores, accumulation radar data, and other measurements that contain information about any of the processes that are solved for.

  4. The role of glacial and tectonic genesis in forming of the Antarctic Peninsula's shelf topography

    Science.gov (United States)

    Greku, Rudolf; Greku, Tatyana

    2015-04-01

    The influence of endogenous and exogenous factors on the topography of the West Antarctic shelf is shown. 1. The gravity tomography models [Atlas…] show that the non-geotectonic depressions about 300 m of depth extends to the south from the Bransfield Rift along the western and eastern shelves of the Antarctic Peninsula (AP) up to 69 °S. This is due to the glacial tectonic, which was caused by lithostatic pressure of ice mass and the corresponding deviatoric stress (as а horizontal stretching) in a period of an intense glaciation. Ice mass increases towards the south, therefore the deviatoric stretch and the width of the shelves increases also. 2. Besides such external factors, deep tomography data were taken into account. Results of tomographic modelling show the structure of the AP along its crest and along several cross sections. The AP body, as a single structure, is submerged into the lithospheres of the Pacific Ocean and the Weddell Sea to the depth of 150 km. Some layers of its deepened part are displaced concerning the AP's crest axis. The largest of these shifts are observed up to 50 km from the axis to the east at the latitude of 63°S at the depths of 6-7 km, then a shift up to 100 km to the west at 66°S at the depth of 9 km and at 67°S to the east up to 150 km at the depth of 13 km. 3. After breakup of the ice shelf to the west of the AP, the outflow of ice weight from the main ice board on the Peninsula increased. The consumption of the ice is evaluated now by the discharge of glaciers. Informative data for that are the satellite radar altimetry and interferometry. Several pairs of the ERS1/2 images of 1995-2008 were processed for the area of the Vernadsky Ukrainian Antarctic Station. These 100km x 100km images show 4 glaciers (Deloncle, Girard, Waddington and Collins) along transverse faults. The Collins glacier is the most active one. It starts at the crest of the Bruce Plateau АР at the height of 1450 m. Three smaller glaciers provide an

  5. Metatranscriptomes reveal functional variation in diatom communities from the Antarctic Peninsula

    KAUST Repository

    Pearson, Gareth A

    2015-04-14

    Functional genomics of diatom-dominated communities fromthe Antarctic Peninsula was studied using comparative metatranscriptomics. Samples obtained from diatom-rich communities in the Bransfield Strait, the western Weddell Sea and sea ice in the Bellingshausen Sea/Wilkins Ice Shelf yielded more than 500K pyrosequencing reads that were combined to produce a global metatranscriptome assembly. Multi-gene phylogenies recovered three distinct communities, and diatom-assigned contigs further indicated little read-sharing between communities, validating an assembly-based annotation and analysis approach. Although functional analysis recovered a core of abundant shared annotations that were expressed across the three diatom communities, over 40% of annotations (but accounting for <10% of sequences) were community-specific. The two pelagic communities differed in their expression of N-metabolism and acquisition genes, which was almost absent in post-bloom conditions in the Weddell Sea community, while enrichment of transporters for ammonia and urea in Bransfield Strait diatoms suggests a physiological stance towards acquisition of reduced N-sources. The depletion of carbohydrate and energy metabolism pathways in sea ice relative to pelagic communities, together with increased light energy dissipation (via LHCSR proteins), photorespiration, and NO3 - uptake and utilization all pointed to irradiance stress and/or inorganic carbon limitation within sea ice. Ice-binding proteins and cold-shock transcription factors were also enriched in sea ice diatoms. Surprisingly, the abundance of gene transcripts for the translational machinery tracked decreasing environmental temperature across only a 4 °C range, possibly reflecting constraints on translational efficiency and protein production in cold environments. © 2015 International Society for Microbial Ecology All rights reserved.

  6. Evolution of the Antarctic Peninsula lithosphere: Evidence from Mesozoic mafic rocks

    Science.gov (United States)

    Riley, T. R.; Curtis, M. L.; Flowerdew, M. J.; Whitehouse, M. J.

    2016-02-01

    New geochronology from a thick (> 800 m) basaltic succession along the eastern margin of the Antarctic Peninsula confirm a Middle Jurassic age (178 ± 1 Ma). This marginally postdates the adjacent Ferrar large igneous province of the Transantarctic Mountains and predates the extensive silicic volcanism of the Mapple Formation (~ 170 Ma) of the Antarctic Peninsula. The geochemistry of other rare, but broadly contemporaneous, basaltic successions of the Antarctic Peninsula, along with Cretaceous-age mafic dykes, are used to interpret the influences of lithospheric and asthenospheric mantle sources during the Mesozoic. Two significant high magmatic addition rate events occurred along the Antarctic Peninsula continental margin at 170 and 110 Ma and can be correlated to events along the South American Cordillera. These 'flare-up' events are characterised by extensive silicic (mostly ignimbrite) volcanism of the Chon Aike Province (V2 event: 170 Ma) and significant granitoid batholith emplacement of the Lassiter Coast intrusive suite (110 Ma). The 170 Ma event is exposed across large parts of the northern Antarctic Peninsula, whilst the 110 Ma event is more widespread across the southern Antarctic Peninsula. The basaltic volcanism described here precedes the 'flare-up' event at 170 Ma and has geochemical characteristics that indicate a thickened lithosphere prevailed. A major dyke swarm that followed the 170 Ma event indicates that extensive lithospheric thinning had occurred, which allowed the ascent of depleted mafic melts. The thinning was the direct result of widespread lower crustal/upper lithospheric melting associated with the silicic volcanism. In the southern Antarctic Peninsula, the lithosphere remained over thickened until the emplacement of the major batholiths of the Lassiter Coast intrusive suite at 110 Ma and was then immediately followed by the emplacement of more asthenosphere-like melts indicating extensive lithospheric thinning.

  7. Penguin eggshell membranes reflect homogeneity of mercury in the marine food web surrounding the Antarctic Peninsula

    Energy Technology Data Exchange (ETDEWEB)

    Brasso, Rebecka L., E-mail: rlb1196@uncw.edu [University of North Carolina Wilmington, Department of Biology and Marine Biology, 601 South College Road, Wilmington, NC 28403 (United States); Polito, Michael J. [University of North Carolina Wilmington, Department of Biology and Marine Biology, 601 South College Road, Wilmington, NC 28403 (United States); Lynch, Heather J. [Ecology and Evolution Department, 640 Life Sciences Bldg., Stony Brook University, Stony Brook, NY 11794 (United States); Naveen, R. [Oceanites Inc., PO Box 15259, Chevy Chase, MD 20825 (United States); Emslie, Steven D. [University of North Carolina Wilmington, Department of Biology and Marine Biology, 601 South College Road, Wilmington, NC 28403 (United States)

    2012-11-15

    Remote regions such as the Antarctic have become increasingly important for investigations into far-reaching anthropogenic impacts on the environment, most recently in regard to the global mercury cycle. Spatial patterns of mercury availability in four regions of the Antarctic Peninsula were investigated using three species of sympatrically breeding Pygoscelis penguins as biomonitors. Eggshells with intact membranes from Adelie, Gentoo, and Chinstrap penguins were collected at 24 breeding colonies in the South Orkney Islands, South Shetland Islands, eastern Antarctic Peninsula, and western Antarctic Peninsula during the 2006/2007 austral summer. In addition, we compared eggshell membrane mercury concentrations with eggshell stable isotope values ({delta}{sup 15}N and {delta}{sup 13}C) to determine if species-specific trophic or foraging habitat preferences influenced female mercury exposure prior to breeding. With few exceptions, mercury concentrations were found to be fairly homogeneous throughout the Antarctic Peninsula suggesting little spatial variation in the risk of exposure to dietary mercury in this food web. Mercury concentrations in Gentoo and Adelie penguins were similar while Chinstrap penguins tended to have higher eggshell membrane mercury concentrations than their congeners. However, inter and intra-specific differences in eggshell membrane mercury concentration were not related to eggshell {delta}{sup 15}N or {delta}{sup 13}C values, a likely result of all three species foraging at similar trophic positions. The lack of regional-scale differences in mercury availability in this marine ecosystem may be a reflection of generally uniform atmospheric deposition and upwelling of regionally homogeneous deep water rather than from geographically distinct point sources. -- Highlights: Black-Right-Pointing-Pointer We examined regional patterns of mercury availability in the Antarctic Peninsula. Black-Right-Pointing-Pointer Three species of Pygoscelis

  8. Modelling mass loss and spatial uncertainty of the West Antarctic Ice Sheet: a data assimilation approach

    Science.gov (United States)

    Bamber, Jonathan L.; Schoen, Nana; Zammit-Mangion, Andrew; Rougier, Jonty; Luthcke, Scott; King, Matt

    2013-04-01

    Quantifying ice mass loss from the Antarctic Ice Sheet remains an important, yet still challenging problem. Although some agreement has been reached as to the order of magnitude of ice loss over the last two decades, in general methods lack statistical rigour in deriving uncertainties and for East Antarctica and the Peninsula significant inconsistencies remain. Here, we present rigorously-derived, error-bounded mass balance trends for part of the Antarctic ice sheet from a combination of satellite, in situ and regional climate model data sets for 2003-2009. Estimates for glacial isostatic adjustment (GIA), surface mass balance (SMB) anomaly, and ice mass change are derived from satellite gravimetry (the Gravity Recovery and Climate Experiment, GRACE), laser altimetry (ICESat, the Ice, Cloud and land Elevation Satellite) and GPS bedrock elevation rates. We use a deterministic Bayes approach to simultaneously solve for the unknown parameters and the covariance matrix which provides the uncertainties. The data were distributed onto a finite element grid the resolution of which reflects the gradients in the underlying process: here ice dynamics and surface mass balance. In this proof of concept study we solve for the time averaged, spatial distribution of mass trends over the 7 year time interval. The results illustrate the potential of the approach, especially for the Antarctic Peninsula (AP), where, due to its narrow width and steep orography, data coverage is sparse and error-prone for satellite altimetry. Results for the ice mass balance estimates are consistent with previous estimates and demonstrate the strength of the approach. Well-known patterns of ice mass change over the WAIS, like the stalled Kamb Ice Stream and the rapid thinning in the Amundsen Sea Embayment, are reproduced in terms of mass trend. Also, without relying on information on ice dynamics, the method correctly places ice loss maxima at the outlets of major glaciers on the AP. Combined ice mass

  9. Antarctic ice volume for the last 740 ka calculated with a simple ice sheet model

    NARCIS (Netherlands)

    Oerlemans, J.

    2005-01-01

    Fluctuations in the volume of the Antarctic ice sheet for the last 740 ka are calculated by forcing a simple ice sheet model with a sea-level history (from a composite deep sea δ18O record) and a temperature history (from the Dome C deuterium record). Antarctic ice volume reaches maximum values of a

  10. Super-aggregations of krill and humpback whales in Wilhelmina Bay, Antarctic Peninsula.

    Directory of Open Access Journals (Sweden)

    Douglas P Nowacek

    Full Text Available Ecological relationships of krill and whales have not been explored in the Western Antarctic Peninsula (WAP, and have only rarely been studied elsewhere in the Southern Ocean. In the austral autumn we observed an extremely high density (5.1 whales per km(2 of humpback whales (Megaptera novaeangliae feeding on a super-aggregation of Antarctic krill (Euphausia superba in Wilhelmina Bay. The krill biomass was approximately 2 million tons, distributed over an area of 100 km(2 at densities of up to 2000 individuals m(-3; reports of such 'super-aggregations' of krill have been absent in the scientific literature for >20 years. Retentive circulation patterns in the Bay entrained phytoplankton and meso-zooplankton that were grazed by the krill. Tagged whales rested during daylight hours and fed intensively throughout the night as krill migrated toward the surface. We infer that the previously unstudied WAP embayments are important foraging areas for whales during autumn and, furthermore, that meso-scale variation in the distribution of whales and their prey are important features of this system. Recent decreases in the abundance of Antarctic krill around the WAP have been linked to reductions in sea ice, mediated by rapid climate change in this area. At the same time, baleen whale populations in the Southern Ocean, which feed primarily on krill, are recovering from past exploitation. Consideration of these features and the effects of climate change on krill dynamics are critical to managing both krill harvests and the recovery of baleen whales in the Southern Ocean.

  11. Super-aggregations of krill and humpback whales in Wilhelmina Bay, Antarctic Peninsula.

    Science.gov (United States)

    Nowacek, Douglas P; Friedlaender, Ari S; Halpin, Patrick N; Hazen, Elliott L; Johnston, David W; Read, Andrew J; Espinasse, Boris; Zhou, Meng; Zhu, Yiwu

    2011-04-27

    Ecological relationships of krill and whales have not been explored in the Western Antarctic Peninsula (WAP), and have only rarely been studied elsewhere in the Southern Ocean. In the austral autumn we observed an extremely high density (5.1 whales per km(2)) of humpback whales (Megaptera novaeangliae) feeding on a super-aggregation of Antarctic krill (Euphausia superba) in Wilhelmina Bay. The krill biomass was approximately 2 million tons, distributed over an area of 100 km(2) at densities of up to 2000 individuals m(-3); reports of such 'super-aggregations' of krill have been absent in the scientific literature for >20 years. Retentive circulation patterns in the Bay entrained phytoplankton and meso-zooplankton that were grazed by the krill. Tagged whales rested during daylight hours and fed intensively throughout the night as krill migrated toward the surface. We infer that the previously unstudied WAP embayments are important foraging areas for whales during autumn and, furthermore, that meso-scale variation in the distribution of whales and their prey are important features of this system. Recent decreases in the abundance of Antarctic krill around the WAP have been linked to reductions in sea ice, mediated by rapid climate change in this area. At the same time, baleen whale populations in the Southern Ocean, which feed primarily on krill, are recovering from past exploitation. Consideration of these features and the effects of climate change on krill dynamics are critical to managing both krill harvests and the recovery of baleen whales in the Southern Ocean.

  12. Monitoring of land-based glaciers on James Ross Island, Antarctic Peninsula

    Science.gov (United States)

    Laska, Kamil; Nyvlt, Daniel; Engel, Zbynek; Stachon, Zdenek

    2015-04-01

    Antarctic Peninsula has been considered one of the most rapidly warming parts of our planet during the second half of the 20th century. Therefore, James Ross Island located near the northern tip of the Antarctic Peninsula, represents a unique place to study the sensitivity of glacier systems to regional atmospheric warming. Since 2006, an integrated multidisciplinary study of glaciers and terrestrial ecosystems has been carried out in the northern part of Ulu Peninsula, James Ross Island. In this contribution, glacier monitoring network consisting of four dominant land-based glaciers at the Ulu Peninsula is presented. Davies Dome (DD) is an ice dome, which originates on the surface of a flat volcanic mesa at >400 m a.s.l. and terminates as a single 700 m wide outlet in Whisky Bay. In 2006, Davies Dome had an area of 6.5 km2 and lay in the altitude range 0-514 m a.s.l. Whisky Glacier (WG) is a cold-based land-terminating valley glacier, which is surrounded by an extensive area of debris-covered ice. WG covered an area of 2.4 km2 and ranged from 215 to 520 m a.s.l. Triangular Glacier (TG) is a southwest-facing land-terminating glacier with an area of 0.6 km2 ranging from 302 to 107 m a.s.l. with well-developed ice-cored terminal moraine. San Jose Glacier (SJG) is a south-facing land-terminating piedmont glacier rejuvenated from the above lying Lachman Crags Dome (~640 m a.s.l.). SJG covers an area of 0.6 km2 and extends between 138 and 310 m a.s.l. Moreover, monitoring network consists of five automatic weather stations (AWS) placed in the central and marginal parts of the selected glaciers. Each AWS was equipped with the EMS33 air temperature and humidity probes placed inside the radiation shields. Apart from that, additional instruments, e.g. albedometer, propeller anemometer, snow depth sensors were installed on the central part of DD and WG. Since 2009, annual mass balance measurements have been realized on the DD, WG and TG glaciers. In 2010, ice thickness and

  13. Stable water isotopes of precipitation and firn cores from the northern Antarctic Peninsula region as a proxy for climate reconstruction

    Directory of Open Access Journals (Sweden)

    F. Fernandoy

    2012-03-01

    Full Text Available In order to investigate the climate variability in the northern Antarctic Peninsula region, this paper focuses on the relationship between stable isotope content of precipitation and firn, and main meteorological variables (air temperature, relative humidity, sea surface temperature, and sea ice extent. Between 2008 and 2010, we collected precipitation samples and retrieved firn cores from several key sites in this region. We conclude that the deuterium excess oscillation represents a robust indicator of the meteorological variability on a seasonal to sub-seasonal scale. Low absolute deuterium excess values and the synchronous variation of both deuterium excess and air temperature imply that the evaporation of moisture occurs in the adjacent Southern Ocean. The δ18O-air temperature relationship is complicated and significant only at a (multiseasonal scale. Backward trajectory calculations show that air-parcels arriving at the region during precipitation events predominantly originate at the South Pacific Ocean and Bellingshausen Sea. These investigations will be used as a calibration for ongoing and future research in the area, suggesting that appropriate locations for future ice core research are located above 600 m a.s.l. We selected the Plateau Laclavere, Antarctic Peninsula as the most promising site for a deeper drilling campaign.

  14. Antarctic ice rises and rumples : Their properties and significance for ice-sheet dynamics and evolution

    NARCIS (Netherlands)

    Matsuoka, Kenichi; Hindmarsh, Richard C A; Moholdt, Geir; Bentley, Michael J.; Pritchard, Hamish D.; Brown, Joel; Conway, Howard; Drews, Reinhard; Durand, Gaël; Goldberg, Daniel; Hattermann, Tore; Kingslake, Jonathan; Lenaerts, Jan T M; Martín, Carlos; Mulvaney, Robert; Nicholls, Keith W.; Pattyn, Frank; Ross, Neil; Scambos, Ted; Whitehouse, Pippa L.

    2015-01-01

    Locally grounded features in ice shelves, called ice rises and rumples, play a key role buttressing discharge from the Antarctic Ice Sheet and regulating its contribution to sea level. Ice rises typically rise several hundreds of meters above the surrounding ice shelf; shelf flow is diverted around

  15. Ice core reconstruction of Antarctic climate change and implications

    OpenAIRE

    Mayewski,Paul Andrew

    2012-01-01

    Antarctica is the Earth’s largest environmental library for ice cores. Examples of the scientific fin-dings of the 21-nation consortium called the International Trans Antarctic Scientific Expedition (ITASE) under the auspices of the Scientific Committee for Antarctic Research (SCAR) are presented with special emphasis on the value of these records in reconstructing atmospheric circulation over Antarctica and the Southern Ocean.

  16. A new 100-m Digital Elevation Model of the Antarctic Peninsula derived from ASTER Global DEM: methods and accuracy assessment

    Directory of Open Access Journals (Sweden)

    A. J. Cook

    2012-10-01

    Full Text Available A high resolution surface topography Digital Elevation Model (DEM is required to underpin studies of the complex glacier system on the Antarctic Peninsula. A complete DEM with better than 200 m pixel size and high positional and vertical accuracy would enable mapping of all significant glacial basins and provide a dataset for glacier morphology analyses. No currently available DEM meets these specifications. We present a new 100-m DEM of the Antarctic Peninsula (63–70° S, based on ASTER Global Digital Elevation Model (GDEM data. The raw GDEM products are of high-quality on the rugged terrain and coastal-regions of the Antarctic Peninsula and have good geospatial accuracy, but they also contain large errors on ice-covered terrain and we seek to minimise these artefacts. Conventional data correction techniques do not work so we have developed a method that significantly improves the dataset, smoothing the erroneous regions and hence creating a DEM with a pixel size of 100 m that will be suitable for many glaciological applications. We evaluate the new DEM using ICESat-derived elevations, and perform horizontal and vertical accuracy assessments based on GPS positions, SPOT-5 DEMs and the Landsat Image Mosaic of Antarctica (LIMA imagery. The new DEM has a mean elevation difference of −4 m (± 25 m RMSE from ICESat (compared to −13 m mean and ±97 m RMSE for the original ASTER GDEM, and a horizontal error of less than 2 pixels, although elevation accuracies are lower on mountain peaks and steep-sided slopes. The correction method significantly reduces errors on low relief slopes and therefore the DEM can be regarded as suitable for topographical studies such as measuring the geometry and ice flow properties of glaciers on the Antarctic Peninsula. The DEM is available for download from the NSIDC website: http://nsidc.org/data/nsidc-0516.html (A Comparative Study of Antarctic Arctic and Himalayan Ice

    Directory of Open Access Journals (Sweden)

    R. C. Pathak

    1989-07-01

    Full Text Available Arctic, Antarctic and inaccessible lofty regions of Himalayas,which are geographically diverse areas and have been a constant source of inspiration, envisages a challenging field of study 'by early adventurers and scientists of the world. Characteristics of ice obtained at Arctic and Antarctic do not possess similar properties. Even thesalient properties of snow and ice of western and central Himalayas vary due to its differing free water content. A study has been carriedout based on recent Antarctic Expedition by Indian scientists and the data gathered along litha-tectonic regions of Himalayas and their characteristics have been compared, wkich brings out stratigraphic and metamorphic characteristics of the ice and snow. In the present paper,an analysis of the ice and snow properties of Arctic, Antarctic and Himalayan regions has been presented.

  17. Spatial distribution and characteristics of permafrost in Hurd Peninsula, Livingston Island, Maritime Antarctic

    Science.gov (United States)

    Vieira, G.; Ramos, M.; Trindade, A.; Gruber, S.; Hauck, C.; Mora, C.; Batista, V.; Neves, M.; Pimpirev, C.; Kenderova, R.

    2009-04-01

    The Antarctic Peninsula is one of Earth's regions experiencing a faster increase on temperatures, with Mean Annual Air Temperatures (MAAT) rising ca. 2.5 °C in the last 50 years. The northerly location of the Antarctic Peninsula in respect to the Antarctic and its oceanic setting originate a milder and moister climate than in the Antarctic continent. The Northern Antarctic Peninsula is roughly located between the isotherms of MAAT of -1 °C to -8 °C at sea-level and therefore the northern tip and especially the South Shetlands are close to the limits of permafrost occurrence. If the observed warming trend is to continue in the near future, the region might suffer widespread permafrost degradation. Research on the permafrost environment of Hurd Peninsula has been taking place with systematical measurements by our group since January 2000 and currently we are able to provide a good overview of the spatial distribution and characteristics of permafrost terrain in Hurd Peninsula. Our research is based on shallow boreholes (Collado Ramos (115m). In 2006 Electrical Tomography Resistivity and refraction seismic profiles have been performed, providing us with a good overview of the general conditions of the permafrost terrain in the area. Air temperatures are measured at different sites accounting for altitude since a few years and during 3 summer campaigns the radiation balance was monitored continuously at two sites. Detailed geomorphological mapping of periglacial features has been conducted at a scale 1:5,000 providing important information about the geomorphological dynamics. Using the data gathered since 2000 it is now possible to present the general characteristics of the permafrost distribution in Hurd Peninsula as a first step towards a more comprehensive approach that is now starting that involves empirico-statistical modeling, remote sensing, as well as downscaling of mesoscale climate data.

  18. 'Unlocking the archive': Using digital photogrammetry of modern and historic aerial photography to reconstruct 60 years of volumetric change on the Moider Glacier, Antarctic Peninsula

    Science.gov (United States)

    Clarke, Lucy; Miller, Pauline; Ireland, Louise; Fox, Adrian; Mills, Jon; Fieber, Karolina

    2016-04-01

    The Antarctic Peninsula is a mountain glacier system comprised of over 400 glaciers, and is an important contributor to historical and future sea level rise. Assessment and monitoring of AP glaciers is crucial for understanding sensitivity to climate change. Changes to glacier fronts and ice shelves and glacier acceleration are well documented, but there are almost no data on mass changes on the Antarctic Peninsula. Satellite data have been used to calculate change over the last 3 decades, but methods to quantify this over longer timescales have eluded researchers. However there is an archive of aerial photography dating back to the 1940s, this has been largely ignored due to the range of technical problems associated with deriving quantitative data from historic imagery and the lack of ground control data. This presentation demonstrates how advances in photogrammetric processing and capture of modern aerial photography has allowed this archive to be 'unlocked'. Accurate photogrammetric reconstruction from aerial photographs traditionally requires known ground control points acquired in the field; in remote and inaccessible areas, such as the Antarctic Peninsula, this is often impossible. A method for providing control for historic photos without fieldwork, by linking them to a newly acquired, highly accurate photogrammetric model adjusted through direct kinematic GPS positioning of the camera has been applied to a number of glaciers across the Antarctic Peninsula. This presentation will outline the photogrammetric workflow with focus on the Moider Glacier in the Marguerite Bay region of the western Antarctic Peninsula to investigate the quality of data that can be obtained. Volumetric changes on the glaciers from the 1950s to present day (2015) have been reconstructed and can be used to explore the spatial and temporal changes that have occurred on this glacier. In particular, there is near-annual data over the last 5 years recording a period when there has been

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

    Directory of Open Access Journals (Sweden)

    Robert P Dziak

    Full Text Available 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.

  1. Ecological controls on biogeochemical lfuxes in the western Antarctic Peninsula studied with an inverse foodweb model

    Institute of Scientific and Technical Information of China (English)

    Hugh W Ducklow; S C Doney; S F Sailley

    2015-01-01

    Sea ice in the western Antarctic Peninsula (WAP) region is both highly variable and rapidly changing. In the Palmer Station region, the ice season duration has decreased by 92 d since 1978. The sea-ice changes affect ocean stratification and freshwater balance and in turn impact every component of the polar marine ecosystem. Long-term observations from the WAP nearshore and offshore regions show a pattern of chlorophyll (Chl) variability with three to ifve years of negative Chl anomalies interrupted by one or two years of positive anomalies (high and low Chl regimes). Both ifeld observations and results from an inverse food-web model show that these high and low Chl regimes differed significantly from each other, with high primary productivity and net community production (NCP) and other rates associated with the high Chl years and low rates with low Chl years. Gross primary production rates (GPP) averaged 30 mmolC.m-2.d-1 in the low Chl years and 100 mmolC.m-2.d-1 in the high Chl years. Both large and small phytoplankton were more abundant and more productive in high Chl years than in low Chl years. Similarly, krill were more important as grazers in high Chl years, but did not differ from microzooplankton in high or low Chl years. Microzooplankton did not differ between high and low Chl years. Net community production differed signiifcantly between high and low Chl years, but mobilized a similar proportion of GPP in both high and low Chl years. The composition of the NCP was uniform in high and low Chl years. These results emphasize the importance of microbial components in the WAP plankton system and suggest that food webs dominated by small phytoplankton can have pathways that funnel production into NCP, and likely, export.

  2. High-resolution climate modelling of Antarctica and the Antarctic Peninsula

    NARCIS (Netherlands)

    van Wessem, J.M.

    2016-01-01

    In this thesis we have used a high-resolution regional atmospheric climate model (RACMO2.3) to simulate the present-day climate (1979-2014) of Antarctica and the Antarctic Peninsula. We have evaluated the model results with several observations, such as in situ surface energy balance (SEB) observati

  3. The Antarctic Ice Sheet, Sea Ice, and the Ozone Hole: Satellite Observations of how they are Changing

    Science.gov (United States)

    Parkinson, Claire L.

    2012-01-01

    Antarctica is the Earth's coldest and highest continent and has major impacts on the climate and life of the south polar vicinity. It is covered almost entirely by the Earth's largest ice sheet by far, with a volume of ice so great that if all the Antarctic ice were to go into the ocean (as ice or liquid water), this would produce a global sea level rise of about 60 meters (197 feet). The continent is surrounded by sea ice that in the wintertime is even more expansive than the continent itself and in the summertime reduces to only about a sixth of its wintertime extent. Like the continent, the expansive sea ice cover has major impacts, reflecting the sun's radiation back to space, blocking exchanges between the ocean and the atmosphere, and providing a platform for some animal species while impeding other species. Far above the continent, the Antarctic ozone hole is a major atmospheric phenomenon recognized as human-caused and potentially quite serious to many different life forms. Satellites are providing us with remarkable information about the ice sheet, the sea ice, and the ozone hole. Satellite visible and radar imagery are providing views of the large scale structure of the ice sheet never seen before; satellite laser altimetry has produced detailed maps of the topography of the ice sheet; and an innovative gravity-measuring two-part satellite has allowed mapping of regions of mass loss and mass gain on the ice sheet. The surrounding sea ice cover has a satellite record that goes back to the 1970s, allowing trend studies that show a decreasing sea ice presence in the region of the Bellingshausen and Amundsen seas, to the west of the prominent Antarctic Peninsula, but increasing sea ice presence around much of the rest of the continent. Overall, sea ice extent around Antarctica has increased at an average rate of about 17,000 square kilometers per year since the late 1970s, as determined from satellite microwave data that can be collected under both light and

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

    Science.gov (United States)

    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

  5. Mixing and phytoplankton dynamics in a submarine canyon in the West Antarctic Peninsula

    Science.gov (United States)

    Carvalho, Filipa; Kohut, Josh; Oliver, Matthew J.; Sherrell, Robert M.; Schofield, Oscar

    2016-07-01

    Bathymetric depressions (canyons) exist along the West Antarctic Peninsula shelf and have been linked with increased phytoplankton biomass and sustained penguin colonies. However, the physical mechanisms driving this enhanced biomass are not well understood. Using a Slocum glider data set with over 25,000 water column profiles, we evaluate the relationship between mixed layer depth (MLD, estimated using the depth of maximum buoyancy frequency) and phytoplankton vertical distribution. We use the glider deployments in the Palmer Deep region to examine seasonal and across canyon variability. Throughout the season, the ML becomes warmer and saltier, as a result of vertical mixing and advection. Shallow ML and increased stratification due to sea ice melt are linked to higher chlorophyll concentrations. Deeper mixed layers, resulting from increased wind forcing, show decreased chlorophyll, suggesting the importance of light in regulating phytoplankton productivity. Spatial variations were found in the canyon head region where local physical water column properties were associated with different biological responses, reinforcing the importance of local canyon circulation in regulating phytoplankton distribution in the region. While the mechanism initially hypothesized to produce the observed increases in phytoplankton over the canyons was the intrusion of warm, nutrient enriched modified Upper Circumpolar Deep Water (mUCDW), our analysis suggests that ML dynamics are key to increased primary production over submarine canyons in the WAP.

  6. Mercury accumulation in sediments and seabird feathers from the Antarctic Peninsula.

    Science.gov (United States)

    Calle, Paola; Alvarado, Omar; Monserrate, Lorena; Cevallos, Juan Manuel; Calle, Nastenka; Alava, Juan José

    2015-02-28

    In an effort to assess the impact of mercury in the Antarctic Peninsula, we conducted ecotoxicological research in this region during the summer of 2012 and 2013. The objectives were to assess: (a) mercury levels in sediment samples; (b) mercury accumulation in Antarctic seabird feathers: Catharacta lonnbergi (brown skua), Pygoscelis papua (gentoo penguin) and Pygoscelis antarctica (chinstrap penguin); and (c) biomagnification (BMF predator/prey) and biota sediment accumulation (BSAF skuas/sediment) factors. Mercury concentrations in sediment were relatively low. Mercury concentrations were significantly higher in brown skuas and gentoo penguins than in chinstrap penguins (2012), and significantly higher in brown skuas than in both penguins (2013). BMF indicated 2-7.5 times greater mercury levels in brown skuas than in penguins. BSAF values suggested an apparent temporal decrease of 18.2% of this ratio from 2012 to 2013. Long-range environmental transport is the likely route of entry of mercury into the Antarctic Peninsula.

  7. Obliquity-paced Pliocene West Antarctic ice sheet oscillations

    Science.gov (United States)

    Naish, T.; Powell, R.; Levy, R.; Wilson, G.; Scherer, R.; Talarico, F.; Krissek, L.; Niessen, F.; Pompilio, M.; Wilson, T.; Carter, L.; DeConto, R.; Huybers, P.; McKay, R.; Pollard, D.; Ross, J.; Winter, D.; Barrett, P.; Browne, G.; Cody, R.; Cowan, E.; Crampton, J.; Dunbar, G.; Dunbar, N.; Florindo, F.; Gebhardt, C.; Graham, I.; Hannah, M.; Hansaraj, D.; Harwood, D.; Helling, D.; Henrys, S.; Hinnov, L.; Kuhn, G.; Kyle, P.; Laufer, A.; Maffioli, P.; Magens, D.; Mandernack, K.; McIntosh, W.; Millan, C.; Morin, R.; Ohneiser, C.; Paulsen, T.; Persico, D.; Raine, I.; Reed, J.; Riesselman, C.; Sagnotti, L.; Schmitt, D.; Sjunneskog, C.; Strong, P.; Taviani, M.; Vogel, S.; Wilch, T.; Williams, T.

    2009-01-01

    Thirty years after oxygen isotope records from microfossils deposited in ocean sediments confirmed the hypothesis that variations in the Earth's orbital geometry control the ice ages, fundamental questions remain over the response of the Antarctic ice sheets to orbital cycles. Furthermore, an understanding of the behaviour of the marine-based West Antarctic ice sheet (WAIS) during the 'warmer-than-present' early-Pliocene epoch (???5-3 Myr ago) is needed to better constrain the possible range of ice-sheet behaviour in the context of future global warming. Here we present a marine glacial record from the upper 600 m of the AND-1B sediment core recovered from beneath the northwest part of the Ross ice shelf by the ANDRILL programme and demonstrate well-dated, ???40-kyr cyclic variations in ice-sheet extent linked to cycles in insolation influenced by changes in the Earth's axial tilt (obliquity) during the Pliocene. Our data provide direct evidence for orbitally induced oscillations in the WAIS, which periodically collapsed, resulting in a switch from grounded ice, or ice shelves, to open waters in the Ross embayment when planetary temperatures were up to ???3??C warmer than today and atmospheric CO 2 concentration was as high as ???400 p.p.m.v. (refs 5, 6). The evidence is consistent with a new ice-sheet/ice-shelf model that simulates fluctuations in Antarctic ice volume of up to +7 m in equivalent sea level associated with the loss of the WAIS and up to +3 m in equivalent sea level from the East Antarctic ice sheet, in response to ocean-induced melting paced by obliquity. During interglacial times, diatomaceous sediments indicate high surface-water productivity, minimal summer sea ice and air temperatures above freezing, suggesting an additional influence of surface melt under conditions of elevated CO2. ??2009 Macmillan Publishers Limited. All rights reserved.

  8. Definition of Arctic and Antarctic Sea Ice Variation Index

    Institute of Scientific and Technical Information of China (English)

    Chen Hongxia; Liu Na; Pan Zengdi; Zhang Qinghua

    2004-01-01

    It is well known that varying of the sea ice not only in the Antarctic but also in the Arctic has an active influence on the globe atmosphere and ocean. In order to understand the sea ice variation in detail, for the first time, an objective index of the Arctic and Antarctic sea ice variation is defined by projecting the monthly sea ice concentration anomalies poleward of 20°N or 20°S onto the EOF (empirical orthogonal function)-1 spatial pattern. Comparing with some work in former studies of polar sea ice, the index has the potential for clarifying the variability of sea ice in northern and southern high latitudes.

  9. The modelled surface mass balance of the Antarctic Peninsula at 5.5 km horizontal resolution

    Science.gov (United States)

    van Wessem, J. M.; Ligtenberg, S. R. M.; Reijmer, C. H.; van de Berg, W. J.; van den Broeke, M. R.; Barrand, N. E.; Thomas, E. R.; Turner, J.; Wuite, J.; Scambos, T. A.; van Meijgaard, E.

    2016-02-01

    This study presents a high-resolution (˜ 5.5 km) estimate of surface mass balance (SMB) over the period 1979-2014 for the Antarctic Peninsula (AP), generated by the regional atmospheric climate model RACMO2.3 and a firn densification model (FDM). RACMO2.3 is used to force the FDM, which calculates processes in the snowpack, such as meltwater percolation, refreezing and runoff. We evaluate model output with 132 in situ SMB observations and discharge rates from six glacier drainage basins, and find that the model realistically simulates the strong spatial variability in precipitation, but that significant biases remain as a result of the highly complex topography of the AP. It is also clear that the observations significantly underrepresent the high-accumulation regimes, complicating a full model evaluation. The SMB map reveals large accumulation gradients, with precipitation values above 3000 mm we yr-1 in the western AP (WAP) and below 500 mm we yr-1 in the eastern AP (EAP), not resolved by coarser data sets such as ERA-Interim. The average AP ice-sheet-integrated SMB, including ice shelves (an area of 4.1 × 105 km2), is estimated at 351 Gt yr-1 with an interannual variability of 58 Gt yr-1, which is dominated by precipitation (PR) (365 ± 57 Gt yr-1). The WAP (2.4 × 105 km2) SMB (276 ± 47 Gt yr-1), where PR is large (276 ± 47 Gt yr-1), dominates over the EAP (1.7 × 105 km2) SMB (75 ± 11 Gt yr-1) and PR (84 ± 11 Gt yr-1). Total sublimation is 11 ± 2 Gt yr-1 and meltwater runoff into the ocean is 4 ± 4 Gt yr-1. There are no significant trends in any of the modelled AP SMB components, except for snowmelt that shows a significant decrease over the last 36 years (-0.36 Gt yr-2).

  10. Characterization of winter foraging locations of Adélie penguins along the Western Antarctic Peninsula, 2001-2002

    Science.gov (United States)

    Erdmann, Eric S.; Ribic, Christine A.; Patterson-Fraser, Donna L.; Fraser, William R.

    2011-07-01

    In accord with the hypotheses driving the Southern Ocean Global Ocean Ecosystems Dynamics (SO GLOBEC) program, we tested the hypothesis that the winter foraging ecology of a major top predator in waters off the Western Antarctic Peninsula (WAP), the Adélie penguin ( Pygoscelis adeliae), is constrained by oceanographic features related to the physiography of the region. This hypothesis grew from the supposition that breeding colonies in the WAP during summer are located adjacent to areas of complex bathymetry where circulation and upwelling processes appear to ensure predictable food resources. Therefore, we tested the additional hypothesis that these areas continue to contribute to the foraging strategy of this species throughout the non-breeding winter season. We used satellite telemetry data collected as part of the SO GLOBEC program during the austral winters of 2001 and 2002 to characterize individual penguin foraging locations in relation to bathymetry, sea ice variability within the pack ice, and wind velocity and divergence (as a proxy for potential areas with cracks and leads). We also explored differences between males and females in core foraging area overlap. Ocean depth was the most influential variable in the determination of foraging location, with most birds focusing their effort on shallow (penguin's foraging, the analysis of sea ice data of a higher resolution than was available for this study may help elucidate the role of sea ice in affecting Adélie penguin winter foraging behavior within the pack ice.

  11. Characterization of winter foraging locations of Adélie penguins along the Western Antarctic Peninsula, 2001–2002

    Science.gov (United States)

    Erdmann, Eric S.; Ribic, Christine; Patterson-Fraser, Donna L.; Fraser, William R.

    2011-01-01

    In accord with the hypotheses driving the Southern Ocean Global Ocean Ecosystems Dynamics (SO GLOBEC) program, we tested the hypothesis that the winter foraging ecology of a major top predator in waters off the Western Antarctic Peninsula (WAP), the Adélie penguin (Pygoscelis adeliae), is constrained by oceanographic features related to the physiography of the region. This hypothesis grew from the supposition that breeding colonies in the WAP during summer are located adjacent to areas of complex bathymetry where circulation and upwelling processes appear to ensure predictable food resources. Therefore, we tested the additional hypothesis that these areas continue to contribute to the foraging strategy of this species throughout the non-breeding winter season. We used satellite telemetry data collected as part of the SO GLOBEC program during the austral winters of 2001 and 2002 to characterize individual penguin foraging locations in relation to bathymetry, sea ice variability within the pack ice, and wind velocity and divergence (as a proxy for potential areas with cracks and leads). We also explored differences between males and females in core foraging area overlap. Ocean depth was the most influential variable in the determination of foraging location, with most birds focusing their effort on shallow (penguin's foraging, the analysis of sea ice data of a higher resolution than was available for this study may help elucidate the role of sea ice in affecting Adélie penguin winter foraging behavior within the pack ice.

  12. Arctic and Antarctic Sea Ice Changes and Impacts (Invited)

    Science.gov (United States)

    Nghiem, S. V.

    2013-12-01

    The extent of springtime Arctic perennial sea ice, important to preconditioning summer melt and to polar sunrise photochemistry, continues its precipitous reduction in the last decade marked by a record low in 2012, as the Bromine, Ozone, and Mercury Experiment (BROMEX) was conducted around Barrow, Alaska, to investigate impacts of sea ice reduction on photochemical processes, transport, and distribution in the polar environment. In spring 2013, there was further loss of perennial sea ice, as it was not observed in the ocean region adjacent to the Alaskan north coast, where there was a stretch of perennial sea ice in 2012 in the Beaufort Sea and Chukchi Sea. In contrast to the rapid and extensive loss of sea ice in the Arctic, Antarctic sea ice has a trend of a slight increase in the past three decades. Given the significant variability in time and in space together with uncertainties in satellite observations, the increasing trend of Antarctic sea ice may arguably be considered as having a low confidence level; however, there was no overall reduction of Antarctic sea ice extent anywhere close to the decreasing rate of Arctic sea ice. There exist publications presenting various factors driving changes in Arctic and Antarctic sea ice. After a short review of these published factors, new observations and atmospheric, oceanic, hydrological, and geological mechanisms contributed to different behaviors of sea ice changes in the Arctic and Antarctic are presented. The contribution from of hydrologic factors may provide a linkage to and enhance thermal impacts from lower latitudes. While geological factors may affect the sensitivity of sea ice response to climate change, these factors can serve as the long-term memory in the system that should be exploited to improve future projections or predictions of sea ice changes. Furthermore, similarities and differences in chemical impacts of Arctic and Antarctic sea ice changes are discussed. Understanding sea ice changes and

  13. In situ primary production in young Antarctic sea ice

    OpenAIRE

    Mock, Thomas

    2002-01-01

    An in situ incubation technique used successfully to measure the photosynthetic carbon assimilation of internal algal assemblages within thick multiyear Arctic sea ice was developed and improved to measure the photosynthetic carbon assimilation within young sea ice only 50 cm thick (Eastern Weddell Sea, Antarctica). The new device enabled some of the first precise measurements of in situ photosynthetic carbon assimilation in newly formed Antarctic sea ice.

  14. Evidence for warmer interglacials in East Antarctic ice cores.

    Science.gov (United States)

    Sime, L C; Wolff, E W; Oliver, K I C; Tindall, J C

    2009-11-19

    Stable isotope ratios of oxygen and hydrogen in the Antarctic ice core record have revolutionized our understanding of Pleistocene climate variations and have allowed reconstructions of Antarctic temperature over the past 800,000 years (800 kyr; refs 1, 2). The relationship between the D/H ratio of mean annual precipitation and mean annual surface air temperature is said to be uniform +/-10% over East Antarctica and constant with time +/-20% (refs 3-5). In the absence of strong independent temperature proxy evidence allowing us to calibrate individual ice cores, prior general circulation model (GCM) studies have supported the assumption of constant uniform conversion for climates cooler than that of the present day. Here we analyse the three available 340 kyr East Antarctic ice core records alongside input from GCM modelling. We show that for warmer interglacial periods the relationship between temperature and the isotopic signature varies among ice core sites, and that therefore the conversions must be nonlinear for at least some sites. Model results indicate that the isotopic composition of East Antarctic ice is less sensitive to temperature changes during warmer climates. We conclude that previous temperature estimates from interglacial climates are likely to be too low. The available evidence is consistent with a peak Antarctic interglacial temperature that was at least 6 K higher than that of the present day -approximately double the widely quoted 3 +/- 1.5 K (refs 5, 6).

  15. Investigations of fungal diversity in wooden structures and soils at historic sites on the Antarctic Peninsula.

    Science.gov (United States)

    Arenz, Brett E; Blanchette, Robert A

    2009-01-01

    Investigations of microbial diversity in Antarctic are important to begin to understand ecosystem functioning and decomposition processes. This study documents fungi at 9 historic sites on the Antarctic Peninsula collected from wooden structures, other organic materials, and soils during a joint National Science Foundation and British Antarctic Survey expedition in 2007. Many of these sites had wooden structures built by the British during the World War II Operation Tabarin, but others visited included the American "East Base" on Stonington Island and the Swedish hut on Snow Hill Island. Fungi were cultured on several different media and pure cultures were obtained and identified by DNA sequencing of the internal transcribed spacer region. Cadophora species previously found to attack historic wooden structures on Ross Island, Antarctica, were found at all but 1 location sampled in the Peninsula region. Fungi causing decay in the historic wooden structures and artifacts and those causing mold problems inside the structures are of great concern, and conservation efforts are urgently needed to help preserve these important polar heritage structures. The results presented also expand our knowledge on the identity of fungi present throughout the Antarctic Peninsula region and provide insights into the organisms responsible for decomposition and nutrient recycling.

  16. The modelled surface mass balance of the Antarctic Peninsula at 5.5 km horizontal resolution

    Directory of Open Access Journals (Sweden)

    J. M. van Wessem

    2015-09-01

    Full Text Available This study presents a high-resolution (~ 5.5 km estimate of Surface Mass Balance (SMB over the period 1979–2014 for the Antarctic Peninsula (AP, generated by the regional atmospheric climate model RACMO2.3 and a Firn Densification Model (FDM. RACMO2.3 is used to force the FDM, which calculates processes in the snowpack, such as meltwater percolation, refreezing and runoff. We evaluate model output with 132 in-situ SMB observations and discharge rates from 6 glacier drainage basins, and find that the model realistically simulates the strong spatial variability in precipitation, but that significant biases remain as a result of the highly complex topography of the AP. It is also clear that the observations significantly underrepresent the high-accumulation regimes. The SMB map reveals large accumulation gradients, with precipitation values above 3000 mm we yr−1 over the western AP (WAP and below 500 mm we yr−1 on the eastern AP (EAP, not resolved by coarser data-sets such as ERA-Interim. The other SMB components are one order of magnitude smaller, with drifting snow sublimation the largest ablation term removing up to 100 mm we yr−1 of mass. Snowmelt is widespread over the AP, reaching 500 mm we yr−1 towards the northern ice shelves, but the meltwater mostly refreezes. As a result runoff fluxes are low, but still considerable (200 mm we yr−1 over the Larsen (B/C, Wilkins and George VI ice shelves. The average AP ice sheet integrated SMB, including ice shelves (an area of 4.1 × 105 km2, is estimated at 351 Gt yr−1 with an interannual variability of 58 Gt yr−1, which is dominated by precipitation (PR (365 ± 57 Gt yr−1. The WAP (2.4 × 105 km2 SMB (276 ± 47 Gt yr−1, where PR is large (276 ± 47 Gt yr−1, dominates over the EAP (1.7 × 105 km2 SMB (75 ± 11 Gt yr−1 and PR (84 ± 11 Gt yr−1. Total sublimation is 11 ± 2 Gt yr−1 and meltwater runoff into the ocean is 4 ± 4 Gt yr−1. There are no significant trends in any

  17. A multivariate analysis of Antarctic sea ice since 1979

    Energy Technology Data Exchange (ETDEWEB)

    Magalhaes Neto, Newton de; Evangelista, Heitor [Universidade do Estado do Rio de Janeiro (Uerj), LARAMG - Laboratorio de Radioecologia e Mudancas Globais, Maracana, Rio de Janeiro, RJ (Brazil); Tanizaki-Fonseca, Kenny [Universidade do Estado do Rio de Janeiro (Uerj), LARAMG - Laboratorio de Radioecologia e Mudancas Globais, Maracana, Rio de Janeiro, RJ (Brazil); Universidade Federal Fluminense (UFF), Dept. Analise Geoambiental, Inst. de Geociencias, Niteroi, RJ (Brazil); Penello Meirelles, Margareth Simoes [Universidade do Estado do Rio de Janeiro (UERJ)/Geomatica, Maracana, Rio de Janeiro, RJ (Brazil); Garcia, Carlos Eiras [Universidade Federal do Rio Grande (FURG), Laboratorio de Oceanografia Fisica, Rio Grande, RS (Brazil)

    2012-03-15

    Recent satellite observations have shown an increase in the total extent of Antarctic sea ice, during periods when the atmosphere and oceans tend to be warmer surrounding a significant part of the continent. Despite an increase in total sea ice, regional analyses depict negative trends in the Bellingshausen-Amundsen Sea and positive trends in the Ross Sea. Although several climate parameters are believed to drive the formation of Antarctic sea ice and the local atmosphere, a descriptive mechanism that could trigger such differences in trends are still unknown. In this study we employed a multivariate analysis in order to identify the response of the Antarctic sea ice with respect to commonly utilized climate forcings/parameters, as follows: (1) The global air surface temperature, (2) The global sea surface temperature, (3) The atmospheric CO{sub 2} concentration, (4) The South Annular Mode, (5) The Nino 3, (6) The Nino (3 + 4, 7) The Nino 4, (8) The Southern Oscillation Index, (9) The Multivariate ENSO Index, (10) the Total Solar Irradiance, (11) The maximum O{sub 3} depletion area, and (12) The minimum O{sub 3} concentration over Antarctica. Our results indicate that western Antarctic sea ice is simultaneously impacted by several parameters; and that the minimum, mean, and maximum sea ice extent may respond to a separate set of climatic/geochemical parameters. (orig.)

  18. Mapping and Assessing Variability in the Antarctic Marginal Ice Zone, the Pack Ice and Coastal Polynyas

    Science.gov (United States)

    Stroeve, Julienne; Jenouvrier, Stephanie

    2016-04-01

    Sea ice variability within the marginal ice zone (MIZ) and polynyas plays an important role for phytoplankton productivity and krill abundance. Therefore mapping their spatial extent, seasonal and interannual variability is essential for understanding how current and future changes in these biological active regions may impact the Antarctic marine ecosystem. Knowledge of the distribution of different ice types to the total Antarctic sea ice cover may also help to shed light on the factors contributing towards recent expansion of the Antarctic ice cover in some regions and contraction in others. The long-term passive microwave satellite data record provides the longest and most consistent data record for assessing different ice types. However, estimates of the amount of MIZ, consolidated pack ice and polynyas depends strongly on what sea ice algorithm is used. This study uses two popular passive microwave sea ice algorithms, the NASA Team and Bootstrap to evaluate the distribution and variability in the MIZ, the consolidated pack ice and coastal polynyas. Results reveal the NASA Team algorithm has on average twice the MIZ and half the consolidated pack ice area as the Bootstrap algorithm. Polynya area is also larger in the NASA Team algorithm, and the timing of maximum polynya area may differ by as much as 5 months between algorithms. These differences lead to different relationships between sea ice characteristics and biological processes, as illustrated here with the breeding success of an Antarctic seabird.

  19. Investigation of the 3D temperature distribution patterns above the Antarctic Peninsula using remote sensing data - A contribution for polar climate monitoring

    Science.gov (United States)

    Wachter, Paul; Höppner, Kathrin; Jacobeit, Jucundus; Diedrich, Erhard

    2015-04-01

    West Antarctica and the Antarctic Peninsula are in the focus of current studies on a changing environment and climate of the polar regions. A recently founded Junior Researchers Group at the German Aerospace Center (DLR) is studying changing processes in cryosphere and atmosphere above the Antarctic Peninsula. It is the aim of the group to make use of long-term remote sensing data sets of the land and ice surfaces and the atmosphere in order to characterize environmental changes in this highly sensitive region. One of the PhD projects focuses on the investigation of the 3D temperature distribution patterns above the Antarctic Peninsula. Temperature data sets ranging from MODIS land surface temperatures up to middle atmosphere data of AURA/MLS will be evaluated over the last approx. 12 years. This 3-dimensional view allows comprehensive investigations of the thermal structure and spatio-temporal characteristics of the southern polar atmosphere. Tropospheric data sets will be analyzed by multivariate statistical methods and will allow the identification of dominant atmospheric circulation patterns as well as their temporal variability. An overview of the data sets and first results will be presented.

  20. Validation of the Antarctic Snow Accumulation and Ice Discharge Basal Stress Boundary in the South Eastern Region of the Ross Ice Shelf, Antarctica

    Science.gov (United States)

    Nelson, C. B.; King, K.

    2015-12-01

    The largest ice shelf in Antarctic, Ross Ice Shelf, was investigated over the years of (1970-2015). Near the basal stress boundary between the ice shelf and the West Antarctic ice sheet, ice velocity ranges from a few meters per year to several hundred meters per year in ice streams. Most of the drainage from West Antarctica into the Ross Ice Shelf flows down two major ice streams, each of which discharges more than 20 km3 of ice each year. Along with velocity changes, the warmest water below parts of the Ross Ice Shelf resides in the lowest portion of the water column because of its high salinity. Vertical mixing caused by tidal stirring can thus induce ablation by lifting the warm water into contact with the ice shelf. This process can cause melting over a period of time and eventually cause breakup of ice shelf. With changes occurring over many years a validation is needed for the Antarctic Snow Accumulation and Ice Discharge (ASAID) basal stress boundary created in 2003. After the 2002 Larsen B Ice Shelf disintegration, nearby glaciers in the Antarctic Peninsula accelerated up to eight times their original speed over the next 18 months. Similar losses of ice tongues in Greenland have caused speed-ups of two to three times the flow rates in just one year. Rapid changes occurring in regions surrounding Antarctica are causing concern in the polar science community to research changes occurring in coastal zones over time. During the research, the team completed study on the Ross Ice Shelf located on the south western coast of the Antarctic. The study included a validation of the ABSB vs. the natural basal stress boundary (NBSB) along the Ross Ice Shelf. The ASAID BSB was created in 2003 by a team of researchers headed by National Aeronautics and Space Administration Goddard Space Flight Center (NASA GSFC), with an aim of studying coastal deviations as it pertains to the mass balance of the entire continent. The point data file was aimed at creating a replica of the

  1. Regional Changes in the Sea Ice Cover and Ice Production in the Antarctic

    Science.gov (United States)

    Comiso, Josefino C.

    2011-01-01

    Coastal polynyas around the Antarctic continent have been regarded as sea ice factories because of high ice production rates in these regions. The observation of a positive trend in the extent of Antarctic sea ice during the satellite era has been intriguing in light of the observed rapid decline of the ice extent in the Arctic. The results of analysis of the time series of passive microwave data indicate large regional variability with the trends being strongly positive in the Ross Sea, strongly negative in the Bellingshausen/Amundsen Seas and close to zero in the other regions. The atmospheric circulation in the Antarctic is controlled mainly by the Southern Annular Mode (SAM) and the marginal ice zone around the continent shows an alternating pattern of advance and retreat suggesting the presence of a propagating wave (called Antarctic Circumpolar Wave) around the circumpolar region. The results of analysis of the passive microwave data suggest that the positive trend in the Antarctic sea ice cover could be caused primarily by enhanced ice production in the Ross Sea that may be associated with more persistent and larger coastal polynyas in the region. Over the Ross Sea shelf, analysis of sea ice drift data from 1992 to 2008 yields a positive rate-of-increase in the net ice export of about 30,000 km2 per year. For a characteristic ice thickness of 0.6 m, this yields a volume transport of about 20 km3/year, which is almost identical, within error bars, to our estimate of the trend in ice production. In addition to the possibility of changes in SAM, modeling studies have also indicated that the ozone hole may have a role in that it causes the deepening of the lows in the western Antarctic region thereby causing strong winds to occur offthe Ross-ice shelf.

  2. Seasonal variability in whale encounters in the Western Antarctic Peninsula

    Science.gov (United States)

    Thiele, Deborah; Chester, Edwin T.; Moore, Sue E.; Širovic, Ana; Hildebrand, John A.; Friedlaender, Ari S.

    2004-08-01

    Cetacean sighting surveys were conducted as part of nine multidisciplinary research cruises over late summer, autumn and winter of 2 years (2001-2003) during the Southern Ocean Global Ocean Ecosystems (SO GLOBEC) program. Sea-ice cover differed markedly between years, with apparent effects on cetacean distribution. No ice was present until late June in 2001, while the previous winter sea ice never fully retreated (>30% cover) during the 2002 or 2003 summer, thus increasing the proportion of thicker and more complex ice, including multi-year floes. Humpback (237 sightings; 537 individuals) and minke (103 sightings: 267 individuals) whales were the most commonly detected species. Data from seven comparable cruises were used to identify habitat for minke and humpback whales over five geographically distinct spatial divisions in the study area. In all years, both species were predominantly found in near coastal habitat, particularly in the fjords where complex habitat likely concentrated prey. In 2002 and 2003 the presence of sea ice provided additional feeding habitat, and the numbers of minkes (in winter) and humpbacks (late summer and autumn) in the area doubled compared with 2001. Humpbacks in particular were concentrated at the ice boundaries during late summer and autumn, while minke numbers increased in the winter that followed and occupied ice-covered areas along the entire shelf edge. Important resource sites for these species are mainly located in near-coastal areas and are used in all years, but when ice margins exist and intersect with resource sites they attract much larger numbers of animals due to the dynamics between sea ice and prey.

  3. Particle flux on the continental shelf in the Amundsen Sea Polynya and Western Antarctic Peninsula

    Directory of Open Access Journals (Sweden)

    Hugh W. Ducklow

    2015-04-01

    Full Text Available Abstract We report results from a yearlong, moored sediment trap in the Amundsen Sea Polynya (ASP, the first such time series in this remote and productive ecosystem. Results are compared to a long-term (1992–2013 time series from the western Antarctic Peninsula (WAP. The ASP trap was deployed from December 2010 to December 2011 at 350 m depth. We observed two brief, but high flux events, peaking at 8 and 5 mmol C m−2 d−1 in January and December 2011, respectively, with a total annual capture of 315 mmol C m−2. Both peak fluxes and annual capture exceeded the comparable WAP observations. Like the overlying phytoplankton bloom observed during the cruise in the ASP (December 2010 to January 2011, particle flux was dominated by Phaeocystis antarctica, which produced phytodetrital aggregates. Particles at the start of the bloom were highly depleted in 13C, indicating their origin in the cold, CO2-rich winter waters exposed by retreating sea ice. As the bloom progressed, microscope visualization and stable isotopic composition provided evidence for an increasing contribution by zooplankton fecal material. Incubation experiments and zooplankton observations suggested that fecal pellet production likely contributed 10–40% of the total flux during the first flux event, and could be very high during episodic krill swarms. Independent estimates of export from the surface (100 m were about 5–10 times that captured in the trap at 350 m. Estimated bacterial respiration was sufficient to account for much of the decline in the flux between 50 and 350 m, whereas zooplankton respiration was much lower. The ASP system appears to export only a small fraction of its production deeper than 350 m within the polynya region. The export efficiency was comparable to other polar regions where phytoplankton blooms were not dominated by diatoms.

  4. Thermal regime of active layer at two lithologically contrasting sites on James Ross Island, Antarctic Peninsula.

    Science.gov (United States)

    Hrbáček, Filip; Nývlt, Daniel; Láska, Kamil

    2016-04-01

    Antarctic Peninsula region (AP) represents one of the most rapidly warming parts of our planet in the last 50 years. Despite increasing research activities along both western and eastern sides of AP in last decades, there is still a lot of gaps in our knowledge relating to permafrost, active layer and its thermal and physical properties. This study brings new results of active layer monitoring on James Ross Island, which is the largest island in northern AP. Its northern part, Ulu Peninsula, is the largest ice-free area (more than 200 km2) in the region. Due its large area, we focused this study on sites located in different lithologies, which would affect local thermal regime of active layer. Study site (1) at Abernethy Flats area (41 m a.s.l.) lies ~7 km from northern coast. Lithologically is formed by disintegrated Cretaceous calcareous sandstones and siltstones of the Santa Marta Formation. Study site (2) is located at the northern slopes of Berry Hill (56 m a.s.l.), about 0.4 km from northern coastline. Lithology is composed of muddy to intermediate diamictites, tuffaceous siltstones to fine grained sandstones of the Mendel Formation. Data of air temperature at 2 meters above ground and the active layer temperatures at 75 cm deep profiles were obtained from both sites in period 1 January 2012 to 31 December 2014. Small differences were found when comparing mean air temperatures and active temperatures at 5 and 75 cm depth in the period 2012-2014. While the mean air temperatures varied between -7.7 °C and -7.0 °C, the mean ground temperatures fluctuated between -6.6 °C and -6.1 °C at 5 cm and -6.9 °C and -6.0 °C at 75 cm at Abernethy Flats and Berry Hill slopes respectively. Even though ground temperature differences along the profiles weren't pronounced during thawing seasons, the maximum active layer thickness was significantly larger at Berry Hill slopes (80 to 82 cm) than at Abernethy Flats (52 to 64 cm). We assume this differences are affected by

  5. Abundance and breeding distribution of seabirds in the northern part of the Danco Coast, Antarctic Peninsula

    Directory of Open Access Journals (Sweden)

    Mariana A. Juáres

    2013-02-01

    Full Text Available Seabird abundances and breeding distribution have the potential to serve as ecological indicators. The western Antarctic Peninsula is one of the three sites in the world with the greatest increases in local temperature during the last 50 years. The aim of this study was to monitor the distribution and abundance of breeding populations of seabirds in the northern sector of the Danco Coast, north-west of the Antarctic Peninsula, during the breeding season 2010/11. The birds were the Wilson′s storm petrel (Oceanites oceanicus, South Polar skua (Stercorarius maccormicki, kelp gull (Larus dominicanus, Antarctic tern (Sterna vittata, snowy sheathbill (Chionis alba, chinstrap penguin (Pygoscelis antarctica, southern giant petrel (Macronectes giganteus, gentoo penguin (Pygoscelis papua, Cape petrel (Daption capense and Antarctic shag (Phalacrocorax bransfieldensis. Annual breeding population growth increased in pygoscelids, southern giant petrel and sheathbill, and for the remaining species, breeding population trends were stable. Given that seabird populations can provide valuable information on the conditions of their feeding and nesting environments, this study highlights the need to maintain basics monitoring studies.

  6. Divergent trajectories of Antarctic surface melt under two 21st century climate scenarios

    NARCIS (Netherlands)

    Trusel, L.D.; Frey, Karen; Das, Sarah; Karnauskas, Kristopher; Kuipers Munneke, P.; van Meijgaard, E.; van den Broeke, M.R.

    2015-01-01

    Ice shelves modulate Antarctic contributions to sea-level rise and thereby represent a critical, climate-sensitive interface between the Antarctic ice sheet and the global ocean. Following rapid atmospheric warming over the past decades, Antarctic Peninsula ice shelves have progressively retreated,

  7. Spectral distribution of gravity wave momentum fluxes over the Antarctic Peninsula from Concordiasi superpressure balloon data

    Science.gov (United States)

    Walterscheid, R. L.; Gelinas, L. J.; Mechoso, C. R.; Schubert, G.

    2016-07-01

    Gravity waves generated by flow over the steep topography of the Antarctic Peninsula transport significant amounts of zonal and meridional momentum into the stratosphere. Quantitative determination of this transport has been carried out for wave periods of 1 h or greater using data from a previous Antarctic superpressure balloon campaign in austral spring 2005 (VORCORE). The present study uses data from the later Concordiasi campaign (2010) to extend the momentum flux determination to shorter periods. Maps of the vertical fluxes of meridional and zonal momentum are presented for periods down to 12 min. We find that the momentum fluxes for periods below 1 h are comparable to those at longer periods, despite larger variances at longer periods. The momentum fluxes in the vicinity of the peninsula provide a significant zonal acceleration of the lower stratosphere, confirming a conclusion from the VORCORE data. The geographical distribution of fluxes around the peninsula has peaks both leeward and windward of the main terrain features. Numerical simulations suggest that the separate peaks may be related to wave transience caused by unsteady winds over the peninsula. Momentum fluxes comprise a main distribution maximizing at moderate flux values and a secondary distribution maximizing at high values exhibiting a high degree of intermittency. The high flux events account for the largest part of the average flux and suggest that drag parameterizations should take them into account. It is found that waves generated by the jet stream are also a significant source of momentum flux.

  8. Kelp gulls, Larus dominicanus (Aves: Laridae, breeding in Keller Peninsula, King George Island, Antarctic Peninsula

    Directory of Open Access Journals (Sweden)

    Joaquim O. Branco

    2009-09-01

    Full Text Available We examined the distribution, abundance and density of the Kelp Gull, Larus dominicanus (Lichtenstein, 1823, at Keller Peninsula on two occasions during the breeding season of 2007-2008 (once for incubation and once for chick stages and compared our results with previously published data. We present information on the number of eggs, incubation success, and initial development of L. dominicanus chicks in the studied sites. The abundance and density of the species has remained statistically similar in Keller Peninsula over the last 30 years (since 1978-1979. Although the abundance and density were almost unchanged, we recorded alterations in the occupation of the breeding areas by L. dominicanus, mainly the abandonment of breeding sites in the eastern portion of Keller Peninsula. The results of the present study compared with similar previous investigations on the abundance of L. dominicanus indicate that the populations have been in equilibrium over the years.

  9. Emplacement of Antarctic ice sheet mass affects circumpolar ocean flow

    NARCIS (Netherlands)

    Rugenstein, M.; Stocchi, P.; van der Heydt, A.; Brinkhuis, H.

    2014-01-01

    During the Cenozoic the Antarctic continent experienced large fluctuations in ice-sheet volume. We investigate the effects of Glacial Isostatic Adjustment (GIA) on Southern Ocean circulation for the first continental scale glaciation of Antarctica (~ 34 Myr) by combining solid Earth and ocean dynami

  10. Iron biogeochemistry in Antarctic pack ice during SIPEX-2

    Science.gov (United States)

    Lannuzel, Delphine; Chever, Fanny; van der Merwe, Pier C.; Janssens, Julie; Roukaerts, Arnout; Cavagna, Anne-Julie; Townsend, Ashley T.; Bowie, Andrew R.; Meiners, Klaus M.

    2016-09-01

    Our study quantified the spatial and temporal distribution of Fe and ancillary biogeochemical parameters at six stations visited during an interdisciplinary Australian Antarctic marine science voyage (SIPEX-2) within the East Antarctic first-year pack ice zone during September-October 2012. Unlike previous studies in the area, the sea ice Chlorophyll a, Particulate Organic Carbon and Nitrogen (POC and PON) maxima did not occur at the ice/water interface because of the snow loading and dynamic processes under which the sea ice formed. Iron in sea ice ranged from 0.9 to 17.4 nM for the dissolved (0.2 μm) fraction. Our results highlight that the concentration of particulate Fe in sea ice was highest when approaching the continent. The high POC concentration and high particulate iron to aluminium ratio in sea ice samples demonstrate that 71% of the particulate Fe was biogenic in composition. Our estimated Fe flux from melting pack ice to East Antarctic surface waters over a 30 day melting period was 0.2 μmol/m2/d of DFe, 2.7 μmol/m2/d of biogenic PFe and 1.3 μmol/m2/d of lithogenic PFe. These estimates suggest that the fertilization potential of the particulate fraction of Fe may have been previously underestimated due to the assumption that it is primarily lithogenic in composition. Our new measurements and calculated fluxes indicate that a large fraction of the total Fe pool within sea ice may be bioavailable and therefore, effective in promoting primary productivity in the marginal ice zone.

  11. Antarctic last interglacial isotope peak in response to sea ice retreat not ice-sheet collapse.

    Science.gov (United States)

    Holloway, Max D; Sime, Louise C; Singarayer, Joy S; Tindall, Julia C; Bunch, Pete; Valdes, Paul J

    2016-08-16

    Several studies have suggested that sea-level rise during the last interglacial implies retreat of the West Antarctic Ice Sheet (WAIS). The prevalent hypothesis is that the retreat coincided with the peak Antarctic temperature and stable water isotope values from 128,000 years ago (128 ka); very early in the last interglacial. Here, by analysing climate model simulations of last interglacial WAIS loss featuring water isotopes, we show instead that the isotopic response to WAIS loss is in opposition to the isotopic evidence at 128 ka. Instead, a reduction in winter sea ice area of 65±7% fully explains the 128 ka ice core evidence. Our finding of a marked retreat of the sea ice at 128 ka demonstrates the sensitivity of Antarctic sea ice extent to climate warming.

  12. Towards Resolving the Paradox of Antarctic Sea Ice: A New Integrated Framework for Observing the Antarctic Marginal Ice Zone

    Science.gov (United States)

    Williams, G. D.

    2014-12-01

    Antarctic sea ice distribution, a canary in the coal mine for climate change in the Southern Hemisphere, is controlled by the marginal ice zone (MIZ). The MIZ is the dynamic outer part of the sea-ice zone, where it interacts with the high-energy open ocean and is strongly affected by waves and storms. As an interface between ocean and atmosphere with extreme vertical and horizontal temperature gradients and large variations in mechanical properties, the MIZ is a complex system that evolves with, and impacts upon, the advancing/receding ice edge. More than a zone, it is a migratory transition in 'phase space' that biannually passes across the entire Antarctic SIZ. During the advance phase of sea-ice seasonality, and under freezing conditions, wave-induced pancake-ice formation can lead to rapid ice-edge advance. During the retreat phase, the dynamic break-up and modification of sea ice by passing storms, winds and waves greatly modifies the floe-size distribution within the MIZ, to create smaller floes that melt more rapidly and accelerate sea-ice retreat as spring progresses. Inspired by the current Arctic MIZ efforts, new fieldwork is proposed to resolve the key characteristics of the Antarctic MIZ and the processes controlling its extent. Combining new autonomous observation technology with ship-based techniques, integrated experiments are being designed to advance our understanding of the MIZ and its role in driving seasonal sea ice advance and retreat around Antarctica. The proposed project provides a unique opportunity to develop an observational, analytical, and science-policy framework for coordinated monitoring of sea ice in both the northern and southern hemispheres, with implications for forecasting, monitoring, and prediction that are essential with increasingly dynamic and variable polar climate systems.

  13. A model of the Antarctic Ice Sheet

    NARCIS (Netherlands)

    Oerlemans, J.

    1982-01-01

    Numerical modelling of ice sheets and glaciers has become a useful tool in glaciological research. A model described here deals with the vertical mean ice velocity, is time dependent, computes bedrock adjustment and uses an empirical diagnostic relationship to derive the distribution of ice thicknes

  14. Neogene kinematic history of Nazca-Antarctic-Phoenix slab windows beneath Patagonia and the Antarctic Peninsula

    Science.gov (United States)

    Breitsprecher, Katrin; Thorkelson, Derek J.

    2009-01-01

    The Patagonian slab window is a subsurface tectonic feature resulting from subduction of the Nazca-Antarctic spreading-ridge system (Chile Rise) beneath southern South America. The geometry of the slab window had not been rigorously defined, in part because of the complex nature of the history of ridge subduction in the southeast Pacific region, which includes four interrelated spreading-ridge systems since 20 Ma: first, the Nazca-Phoenix ridge beneath South America, then simultaneous subduction of the Nazca-Antarctic and the northern Phoenix-Antarctic spreading-ridge systems beneath South America, and the southern Phoenix-Antarctic spreading-ridge system beneath Antarctica. Spreading-ridge paleo-geographies and rotation poles for all relevant plate pairs (Nazca, Phoenix, Antarctic, South America) are available from 20 Ma onward, and form the mathematical basis of our kinematic reconstruction of the geometry of the Patagonia and Antarctic slab windows through Neogene time. At approximately 18 Ma, the Nazca-Phoenix-Antarctic oceanic (ridge-ridge-ridge) triple junction enters the South American trench; we recognize this condition as an unstable quadruple junction. Heat flow at this junction and for some distance beneath the forearc would be considerably higher than is generally recognized in cases of ridge subduction. From 16 Ma onward, the geometry of the Patagonia slab window developed from the subduction of the trailing arms of the former oceanic triple junction. The majority of the slab window's areal extent and geometry is controlled by the highly oblique (near-parallel) subduction angle of the Nazca-Antarctic ridge system, and by the high contrast in relative convergence rates between these two plates relative to South America. The very slow convergence rate of the Antarctic slab is manifested by the shallow levels achieved by the slab edge (< 45 km); thus no point on the Antarctic slab is sufficiently deep to generate "normal" mantle-derived arc-type magmas

  15. High Prevalence of Gammaproteobacteria in the Sediments of Admiralty Bay and North Bransfield Basin, Northwestern Antarctic Peninsula

    Science.gov (United States)

    Franco, Diego C.; Signori, Camila N.; Duarte, Rubens T. D.; Nakayama, Cristina R.; Campos, Lúcia S.; Pellizari, Vivian H.

    2017-01-01

    Microorganisms dominate most Antarctic marine ecosystems, in terms of biomass and taxonomic diversity, and play crucial role in ecosystem functioning due to their high metabolic plasticity. Admiralty Bay is the largest bay on King George Island (South Shetland Islands, Antarctic Peninsula) and a combination of hydro-oceanographic characteristics (bathymetry, sea ice and glacier melting, seasonal entrance of water masses, turbidity, vertical fluxes) create conditions favoring organic carbon deposition on the seafloor and microbial activities. We sampled surface sediments from 15 sites across Admiralty Bay (100–502 m total depth) and the adjacent North Bransfield Basin (693–1147 m), and used the amplicon 454-sequencing of 16S rRNA gene tags to compare the bacterial composition, diversity, and microbial community structure across environmental parameters (sediment grain size, pigments and organic nutrients) between the two areas. Marine sediments had a high abundance of heterotrophic Gammaproteobacteria (92.4% and 83.8% inside and outside the bay, respectively), followed by Alphaproteobacteria (2.5 and 5.5%), Firmicutes (1.5 and 1.6%), Bacteroidetes (1.1 and 1.7%), Deltaproteobacteria (0.8 and 2.5%) and Actinobacteria (0.7 and 1.3%). Differences in alpha-diversity and bacterial community structure were found between the two areas, reflecting the physical and chemical differences in the sediments, and the organic matter input. PMID:28210255

  16. Antarctic ice-sheet loss driven by basal melting of ice shelves

    NARCIS (Netherlands)

    Pritchard, H.D.; Ligtenberg, S.R.M.; Fricker, H.A.; Vaughan, D.G.; van den Broeke, M.R.; Padman, L.

    2012-01-01

    Accurate prediction of global sea-level rise requires that we understand the cause of recent, widespread and intensifying1,2 glacier acceleration along Antarctic ice-sheet coastal margins3. Atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves,

  17. Pliocene retreat of Greenland and Antarctic Ice Sheet margins (Invited)

    Science.gov (United States)

    Deconto, R. M.; Pollard, D.

    2013-12-01

    The middle Pliocene epoch (~3 million years ago) is often considered an analogue for future global climatic conditions, because global mean temperatures were comparable to projections of future climate at the end of this century. Importantly, some estimates of mid-Pliocene sea level are >20 m higher than today, implying the potential for significant retreat of the East Antarctic Ice Sheet (EAIS), in addition to the loss of the Greenland and West Antarctic Ice Sheets (WAIS). Here, we use a hybrid ice sheet-shelf model with freely migrating grounding lines coupled to a high-resolution regional climate model to test the potential for both West and East Antarctic Ice Sheet retreat during the warm Pliocene and in long-term future scenarios with elevated CO2. In these simulations we apply new treatments of i) ice shelf calving (accounting for the effects of divergent ice flow and surface melt water on crevassing), ii) ice-cliff mechanics at the grounding line, iii) improved sub-glacial bathymetry using BEDMAP2, and iv) a range of plausible ocean warming scenarios based on offline ocean modeling. In warm Pliocene simulations, the combination of improved bathymetric detail and more physically based model treatments of floating and grounded calving fronts substantially increases the rates and magnitudes of ice sheet retreat into over-deepened subglacial basins in both in West and East Antarctica. These new results imply the EAIS margin did indeed contribute to elevated (and orbitally paced) Pliocene sea levels, with Antarctica contributing up to ~20m equivalent sea level during the warmest intervals. In long-term (10^3-4-yr) future simulations using the same model physics, we find these new mechanisms produce a much more sensitive and vulnerable ice sheet than previously considered, with the potential for substantial future retreat of both WAIS and parts of the East Antarctic margin in response to the combined effects of increased surface melt on ice shelf surfaces and

  18. A reversal of fortunes: climate change 'winners' and 'losers' in Antarctic Peninsula penguins.

    Science.gov (United States)

    Clucas, Gemma V; Dunn, Michael J; Dyke, Gareth; Emslie, Steven D; Naveen, Ron; Polito, Michael J; Pybus, Oliver G; Rogers, Alex D; Hart, Tom

    2014-06-12

    Climate change is a major threat to global biodiversity. Antarctic ecosystems are no exception. Investigating past species responses to climatic events can distinguish natural from anthropogenic impacts. Climate change produces 'winners', species that benefit from these events and 'losers', species that decline or become extinct. Using molecular techniques, we assess the demographic history and population structure of Pygoscelis penguins in the Scotia Arc related to climate warming after the Last Glacial Maximum (LGM). All three pygoscelid penguins responded positively to post-LGM warming by expanding from glacial refugia, with those breeding at higher latitudes expanding most. Northern (Pygoscelis papua papua) and Southern (Pygoscelis papua ellsworthii) gentoo sub-species likely diverged during the LGM. Comparing historical responses with the literature on current trends, we see Southern gentoo penguins are responding to current warming as they did during post-LGM warming, expanding their range southwards. Conversely, Adélie and chinstrap penguins are experiencing a 'reversal of fortunes' as they are now declining in the Antarctic Peninsula, the opposite of their response to post-LGM warming. This suggests current climate warming has decoupled historic population responses in the Antarctic Peninsula, favoring generalist gentoo penguins as climate change 'winners', while Adélie and chinstrap penguins have become climate change 'losers'.

  19. Ocean-atmosphere exchange of organic carbon and CO2 surrounding the Antarctic Peninsula

    Science.gov (United States)

    Ruiz-Halpern, S.; Calleja, M. Ll.; Dachs, J.; Del Vento, S.; Pastor, M.; Palmer, M.; Agustí, S.; Duarte, C. M.

    2014-05-01

    Exchangeable organic carbon (OC) dynamics and CO2 fluxes in the Antarctic Peninsula during austral summer were highly variable, but the region appeared to be a net sink for OC and nearly in balance for CO2. Surface exchangeable dissolved organic carbon (EDOC) measurements had a 43 ± 3 (standard error, hereafter SE) μmol C L-1 overall mean and represented around 66% of surface non-purgeable dissolved organic carbon (DOC) in Antarctic waters, while the mean concentration of the gaseous fraction of organic carbon (GOC H-1) was 46 ± 3 SE μmol C L-1. There was a tendency towards low fugacity of dissolved CO2 (fCO2-w) in waters with high chlorophyll a (Chl a) content and high fCO2-w in areas with high krill densities. However, such relationships were not found for EDOC. The depth profiles of EDOC were also quite variable and occasionally followed Chl a profiles. The diel cycles of EDOC showed two distinct peaks, in the middle of the day and the middle of the short austral dark period, concurrent with solar radiation maxima and krill night migration patterns. However, no evident diel pattern for GOC H-1 or CO2 was observed. The pool of exchangeable OC is an important and active compartment of the carbon budget surrounding the Antarctic Peninsula and adds to previous studies highlighting its importance in the redistribution of carbon in marine environments.

  20. Remotely-Sensed Glacier Change Estimation: a Case Study at Lindblad Cove, Antarctic Peninsula

    Science.gov (United States)

    Fieber, K. D.; Mills, J. P.; Miller, P. E.; Fox, A. J.

    2016-06-01

    This study builds on existing literature of glacier change estimation in polar regions and is a continuation of efforts aimed at unlocking the information encapsulated in archival aerial photography of Antarctic Peninsula glaciers. Historical aerial imagery acquired in 1957 over three marine-terminating glaciers at Lindblad Cove on the West Coast of Trinity Peninsula is processed to extract digital elevation models (DEMs) which are subsequently compared to DEMs generated from present day (2014) WorldView-2 satellite stereo-imagery. The new WorldView-2 images offer unprecedented sub-metre resolution of the Antarctic Peninsula and are explored here to facilitate improved registration and higher accuracy analysis of glacier changes. Unlike many studies, which focus on glacier fronts or only restricted regions of glaciers, this paper presents a complete coverage of elevation changes across the glacier surfaces for two of the studied glaciers. The study utilises a robust least squares matching technique to ensure precise registration of the archival and modern DEMs, which is applied due to lack of existing ground control in this remote region. This case study reveals that, while many glaciers in polar regions are reported as experiencing significant mass loss, some glaciers are stable or even demonstrate mass gain. All three glaciers reported here demonstrated overall mean increases in surface elevation, indicative of positive mass balance ranging from 0.6 to 5.8 metre water equivalent between 1957 and 2014.

  1. REMOTELY-SENSED GLACIER CHANGE ESTIMATION: A CASE STUDY AT LINDBLAD COVE, ANTARCTIC PENINSULA

    Directory of Open Access Journals (Sweden)

    K. D. Fieber

    2016-06-01

    Full Text Available This study builds on existing literature of glacier change estimation in polar regions and is a continuation of efforts aimed at unlocking the information encapsulated in archival aerial photography of Antarctic Peninsula glaciers. Historical aerial imagery acquired in 1957 over three marine-terminating glaciers at Lindblad Cove on the West Coast of Trinity Peninsula is processed to extract digital elevation models (DEMs which are subsequently compared to DEMs generated from present day (2014 WorldView-2 satellite stereo-imagery. The new WorldView-2 images offer unprecedented sub-metre resolution of the Antarctic Peninsula and are explored here to facilitate improved registration and higher accuracy analysis of glacier changes. Unlike many studies, which focus on glacier fronts or only restricted regions of glaciers, this paper presents a complete coverage of elevation changes across the glacier surfaces for two of the studied glaciers. The study utilises a robust least squares matching technique to ensure precise registration of the archival and modern DEMs, which is applied due to lack of existing ground control in this remote region. This case study reveals that, while many glaciers in polar regions are reported as experiencing significant mass loss, some glaciers are stable or even demonstrate mass gain. All three glaciers reported here demonstrated overall mean increases in surface elevation, indicative of positive mass balance ranging from 0.6 to 5.8 metre water equivalent between 1957 and 2014.

  2. Antarctic Sea Ice Variability and Trends, 1979-2010

    Science.gov (United States)

    Parkinson, C. L.; Cavalieri, D. J.

    2012-01-01

    In sharp contrast to the decreasing sea ice coverage of the Arctic, in the Antarctic the sea ice cover has, on average, expanded since the late 1970s. More specifically, satellite passive-microwave data for the period November 1978 - December 2010 reveal an overall positive trend in ice extents of 17,100 +/- 2,300 square km/yr. Much of the increase, at 13,700 +/- 1,500 square km/yr, has occurred in the region of the Ross Sea, with lesser contributions from the Weddell Sea and Indian Ocean. One region, that of the Bellingshausen/Amundsen Seas, has, like the Arctic, instead experienced significant sea ice decreases, with an overall ice extent trend of -8,200 +/- 1,200 square km/yr. When examined through the annual cycle over the 32-year period 1979-2010, the Southern Hemisphere sea ice cover as a whole experienced positive ice extent trends in every month, ranging in magnitude from a low of 9,100 +/- 6,300 square km/yr in February to a high of 24,700 +/- 10,000 square km/yr in May. The Ross Sea and Indian Ocean also had positive trends in each month, while the Bellingshausen/Amundsen Seas had negative trends in each month, and the Weddell Sea and Western Pacific Ocean had a mixture of positive and negative trends. Comparing ice-area results to ice-extent results, in each case the ice-area trend has the same sign as the ice-extent trend, but differences in the magnitudes of the two trends identify regions with overall increasing ice concentrations and others with overall decreasing ice concentrations. The strong pattern of decreasing ice coverage in the Bellingshausen/Amundsen Seas region and increasing ice coverage in the Ross Sea region is suggestive of changes in atmospheric circulation. This is a key topic for future research.

  3. Antarctic sea ice variability and trends, 1979–2010

    Directory of Open Access Journals (Sweden)

    D. J. Cavalieri

    2012-03-01

    Full Text Available In sharp contrast to the decreasing sea ice coverage of the Arctic, in the Antarctic the sea ice cover has, on average, expanded since the late 1970s. More specifically, satellite passive-microwave data for the period November 1978–December 2010 reveal an overall positive trend in ice extents of 17 100 ± 2300 km2 yr−1. Much of the increase, at 13 700 ± 1500 km2 yr−1, has occurred in the region of the Ross Sea, with lesser contributions from the Weddell Sea and Indian Ocean. One region, that of the Bellingshausen/Amundsen Seas, has, like the Arctic, instead experienced significant sea ice decreases, with an overall ice extent trend of −8200 ± 1200 km2 yr−1. When examined through the annual cycle over the 32-yr period 1979–2010, the Southern Hemisphere sea ice cover as a whole experienced positive ice extent trends in every month, ranging in magnitude from a low of 9100 ± 6300 km2 yr−1 in February to a high of 24 700 ± 10 000 km2 yr−1 in May. The Ross Sea and Indian Ocean also had positive trends in each month, while the Bellingshausen/Amundsen Seas had negative trends in each month, and the Weddell Sea and Western Pacific Ocean had a mixture of positive and negative trends. Comparing ice-area results to ice-extent results, in each case the ice-area trend has the same sign as the ice-extent trend, but differences in the magnitudes of the two trends identify regions with overall increasing ice concentrations and others with overall decreasing ice concentrations. The strong pattern of decreasing ice coverage in the Bellingshausen/Amundsen Seas region and increasing ice coverage in the Ross Sea region is suggestive of changes in atmospheric circulation. This is a key topic for future research.

  4. Antarctic sea ice variability and trends, 1979–2010

    Directory of Open Access Journals (Sweden)

    D. J. Cavalieri

    2012-08-01

    Full Text Available In sharp contrast to the decreasing sea ice coverage of the Arctic, in the Antarctic the sea ice cover has, on average, expanded since the late 1970s. More specifically, satellite passive-microwave data for the period November 1978–December 2010 reveal an overall positive trend in ice extents of 17 100 ± 2300 km2 yr−1. Much of the increase, at 13 700 ± 1500 km2 yr−1, has occurred in the region of the Ross Sea, with lesser contributions from the Weddell Sea and Indian Ocean. One region, that of the Bellingshausen/Amundsen Seas, has (like the Arctic instead experienced significant sea ice decreases, with an overall ice extent trend of −8200 ± 1200 km2 yr−1. When examined through the annual cycle over the 32-yr period 1979–2010, the Southern Hemisphere sea ice cover as a whole experienced positive ice extent trends in every month, ranging in magnitude from a low of 9100 ± 6300 km2 yr−1 in February to a high of 24 700 ± 10 000 km2 yr−1 in May. The Ross Sea and Indian Ocean also had positive trends in each month, while the Bellingshausen/Amundsen Seas had negative trends in each month, and the Weddell Sea and western Pacific Ocean had a mixture of positive and negative trends. Comparing ice-area results to ice-extent results, in each case the ice-area trend has the same sign as the ice-extent trend, but the magnitudes of the two trends differ, and in some cases these differences allow inferences about the corresponding changes in sea ice concentrations. The strong pattern of decreasing ice coverage in the Bellingshausen/Amundsen Seas region and increasing ice coverage in the Ross Sea region is suggestive of changes in atmospheric circulation. This is a key topic for future research.

  5. The Last Interglacial History of the Antarctic Ice sheet

    Science.gov (United States)

    Bradley, Sarah; Siddall, Mark; Milne, Glenn A.; Masson-Delmotte, Valerie; Wolff, Eric; Hindmarsh, Richard C. A.

    2014-05-01

    In this paper we present a summary of the work which was conducted as part of the 'PAST4FUTURE -WP4.1: Sea Level and Ice sheets' project. The overall aim of this study was to understand the response of the Antarctic Ice sheet (AIS) to climate forcing during the Last interglacial (LIG) and its contribution to the observed higher than present sea level during this period. The study involved the application and development of a novel technique which combined East Antarctic stable isotope ice core data with the output from a Glacial Isostatic Adjustment (GIA) model [Bradley et al., 2012]. We investigated if the stable isotope ice core data are sensitive to detecting isostatically driven changes in the surface elevation driven by changes in the ice-loading history of the AIS and if so, could we address some key questions relating to the LIG history of the AIS. Although it is believed that the West Antarctic Ice sheet (WAIS) reduced in size during the LIG compared to the Holocene, major uncertainties and unknowns remain unresolved: Did the WAIS collapse? What would the contribution of such a collapse be the higher than present LIG eustatic sea level (ESL)? We will show that a simulated collapse of the WAIS does not generate a significant elevation driven signal at the EAIS LIG ice core sites, and as such, these ice core records cannot be used to assess WAIS stability over this period. However, we will present 'treasure maps' [Bradley et al., 2012] to identify regions of the AIS where results from geological studies and/or new paleoclimate data may be sensitive to detecting a WAIS collapse. These maps can act as a useful tool for the wider science community/field scientists as a guide to highlight sites suitable to constrain the evolution of the WAIS during the LIG. Studies have proposed that the surface temperature across the East Antarctic Ice Sheet (EAIS) was significantly warmer, 2-5°C during the LIG compared to present [Lang and Wolff, 2011]. These higher

  6. Phylogenetic analysis and in vitro culture of mosses from the Antarctic Fildes Peninsula

    Institute of Scientific and Technical Information of China (English)

    LIU Shenghao; ZHANG Zhaohui; WANG Nengfei; CONG Bailin; ZHANG Pengying; LIN Xuezheng; HUANG Xiaohang

    2014-01-01

    Molecular genetic techniques have proven very useful for initial analysis of the extent of genetic variation and dispersal in several Antarctic moss species. In the present study, the small subunit ribosomal RNA (SSU rDNA) and internal transcribed spacers of the nuclear ribosomal DNA (ITS rDNA) were sequenced in nine individuals of different mosses from the Fildes Peninsula of Antarctica. Sequence alignment showed that the extreme environment tended to increase the genetic diversity of Antarctic mosses. In addition, in our phylogenetic analysis, one previously unidentiifed Antarctic moss species was characterized by comparison with SSU and ITS rDNA sequences of known moss species. Moreover, the optimal culture medium and conditions for surface explant sterilization and protonemata induction in tissue culture of Pohlia nutans were investigated. The successful establishment of a tissue culture protocol together with the phylogenetic analysis of Antarctic mosses will provide technological support to establish an effective resource regeneration method for discovering new functional genes and gaining novel insights into the mechanisms of stress acclimation.

  7. Ecological niche modeling of sympatric krill predators around Marguerite Bay, Western Antarctic Peninsula

    Science.gov (United States)

    Friedlaender, Ari S.; Johnston, David W.; Fraser, William R.; Burns, Jennifer; Halpin, Patrick N.; Costa, Daniel P.

    2011-07-01

    Adélie penguins ( Pygoscelis adeliae), carabeater seals ( Lobodon carcinophagus), humpback ( Megaptera novaeangliae), and minke whales ( Balaenoptera bonaernsis) are found in the waters surrounding the Western Antarctic Peninsula. Each species relies primarily on Antarctic krill ( Euphausia superba) and has physiological constraints and foraging behaviors that dictate their ecological niches. Understanding the degree of ecological overlap between sympatric krill predators is critical to understanding and predicting the impacts on climate-driven changes to the Antarctic marine ecosystem. To explore ecological relationships amongst sympatric krill predators, we developed ecological niche models using a maximum entropy modeling approach (Maxent) that allows the integration of data collected by a variety of means (e.g. satellite-based locations and visual observations). We created spatially explicit probability distributions for the four krill predators in fall 2001 and 2002 in conjunction with a suite of environmental variables. We find areas within Marguerite Bay with high krill predator occurrence rates or biological hot spots. We find the modeled ecological niches for Adélie penguins and crabeater seals may be affected by their physiological needs to haul-out on substrate. Thus, their distributions may be less dictated by proximity to prey and more so by physical features that over time provide adequate access to prey. Humpback and minke whales, being fully marine and having greater energetic demands, occupy ecological niches more directly proximate to prey. We also find evidence to suggest that the amount of overlap between modeled niches is relatively low, even for species with similar energetic requirements. In a rapidly changing and variable environment, our modeling work shows little indication that krill predators maintain similar ecological niches across years around Marguerite Bay. Given the amount of variability in the marine environment around the

  8. Windblown Pliocene diatoms and East Antarctic Ice Sheet retreat.

    Science.gov (United States)

    Scherer, Reed P; DeConto, Robert M; Pollard, David; Alley, Richard B

    2016-09-20

    Marine diatoms in tillites along the Transantarctic Mountains (TAMs) have been used to suggest a diminished East Antarctic Ice Sheet (EAIS) during Pliocene warm periods. Updated ice-sheet modelling shows significant Pliocene EAIS retreat, creating marine embayments into the Wilkes and Aurora basins that were conducive to high diatom productivity and rapid accumulation of diatomaceous sediments. Here we show that subsequent isostatic uplift exposed accumulated unconsolidated marine deposits to wind erosion. We report new atmospheric modelling utilizing Pliocene climate and derived Antarctic landscapes indicating that prevailing mid-altitude winds transported diatoms towards the TAMs, dominantly from extensive emerged coastal deposits of the Aurora Basin. This result unifies leading ideas from competing sides of a contentious debate about the origin of the diatoms in the TAMs and their link to EAIS history, supporting the view that parts of the EAIS are vulnerable to relatively modest warming, with possible implications for future sea-level rise.

  9. Windblown Pliocene diatoms and East Antarctic Ice Sheet retreat

    Science.gov (United States)

    Scherer, Reed P.; DeConto, Robert M.; Pollard, David; Alley, Richard B.

    2016-01-01

    Marine diatoms in tillites along the Transantarctic Mountains (TAMs) have been used to suggest a diminished East Antarctic Ice Sheet (EAIS) during Pliocene warm periods. Updated ice-sheet modelling shows significant Pliocene EAIS retreat, creating marine embayments into the Wilkes and Aurora basins that were conducive to high diatom productivity and rapid accumulation of diatomaceous sediments. Here we show that subsequent isostatic uplift exposed accumulated unconsolidated marine deposits to wind erosion. We report new atmospheric modelling utilizing Pliocene climate and derived Antarctic landscapes indicating that prevailing mid-altitude winds transported diatoms towards the TAMs, dominantly from extensive emerged coastal deposits of the Aurora Basin. This result unifies leading ideas from competing sides of a contentious debate about the origin of the diatoms in the TAMs and their link to EAIS history, supporting the view that parts of the EAIS are vulnerable to relatively modest warming, with possible implications for future sea-level rise. PMID:27649516

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

    Science.gov (United States)

    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.

  11. Response of the Antarctic ice sheet to future greenhouse warming

    OpenAIRE

    Oerlemans, J.; Huybrechts, P.

    1990-01-01

    Possible future changes in land ice volume are mentioned frequently as an important aspect of the greenhouse problem. This paper deals with the response ofthe Antarctic ice sheet and presents a tentative projection of changes in global sea level for the next few hundred years, due to changes in its surface massbalance. We imposed a temperature scenario, in which surface air temperature rises to 4.2¡C in the year 2100 AD and is kept constant afterwards. As GCMstudies seem to indicate a higher ...

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

    Science.gov (United States)

    Le Roux, J. P.

    2012-03-01

    uninterruptedly into the Pleistocene. The Antarctic Peninsula saw its first mountain glaciation between 45 and 41 Ma, with major ice sheet expansion commencing at about 34 Ma. Isolated stands of Nothofagus forests were still present in low-lying areas, suggesting that the glaciers were initially wet-based, but dry-based glaciers were established at around 8 Ma. Although temperatures rose briefly during the Messinian-Pliocene transition, causing sub-Antarctic flora to retreat to higher elevations of the Transantarctic Mountains, the present cold polar conditions were finally established by about 3 Ma.

  13. Mass Balance Changes and Ice Dynamics of Greenland and Antarctic Ice Sheets from Laser Altimetry

    Science.gov (United States)

    Babonis, G. S.; Csatho, B.; Schenk, T.

    2016-06-01

    During the past few decades the Greenland and Antarctic ice sheets have lost ice at accelerating rates, caused by increasing surface temperature. The melting of the two big ice sheets has a big impact on global sea level rise. If the ice sheets would melt down entirely, the sea level would rise more than 60 m. Even a much smaller rise would cause dramatic damage along coastal regions. In this paper we report about a major upgrade of surface elevation changes derived from laser altimetry data, acquired by NASA's Ice, Cloud and land Elevation Satellite mission (ICESat) and airborne laser campaigns, such as Airborne Topographic Mapper (ATM) and Land, Vegetation and Ice Sensor (LVIS). For detecting changes in ice sheet elevations we have developed the Surface Elevation Reconstruction And Change detection (SERAC) method. It computes elevation changes of small surface patches by keeping the surface shape constant and considering the absolute values as surface elevations. We report about important upgrades of earlier results, for example the inclusion of local ice caps and the temporal extension from 1993 to 2014 for the Greenland Ice Sheet and for a comprehensive reconstruction of ice thickness and mass changes for the Antarctic Ice Sheets.

  14. Borehole temperatures reveal details of 20th century warming at Bruce Plateau, Antarctic Peninsula

    Directory of Open Access Journals (Sweden)

    V. Zagorodnov

    2011-11-01

    Full Text Available Two ice core boreholes of 143.74 m and 447.65 m (bedrock were drilled during the 2009–2010 austral summer on the Bruce Plateau at a location named LARISSA Site Beta (66°02' S, 64°04' W, 1975.5 m a.s.l.. Both boreholes were logged with thermistors shortly after drilling. The shallow borehole was instrumented for 4 months with a series of resistance thermometers with satellite uplink. Surface temperature proxy data derived from an inversion of the borehole temperature profiles are compared to available multi-decadal records from weather stations and ice cores located along a latitudinal transect of the Antarctic Peninsula to West Antarctica. The LARISSA Site Beta profiles show temperatures decreasing from the surface downward through the upper third of the ice, and warming thereafter to the bed. The average temperature for the most recent year is −14.78 °C (measured at 15 m depth, abbreviated T15. A minimum temperature of −15.8 °C is measured at 173 m depth and basal temperature is estimated to be −10.2 °C. Current mean annual temperature and the gradient in the lower part of the measured temperature profile have a best fit with an accumulation rate of 1.9 × 103 kg m−2 a−1 and basal heat flux (q of 88 mW m−2, if steady-state conditions are assumed. However, the mid-level temperature variations show that recent temperature has varied significantly. Reconstructed surface temperatures (Ts=T15 over the last 200 yr are derived by an inversion technique. From this, we find that cold temperatures (minimum Ts=−16.2 °C prevailed from ~1920 to ~1940, followed by a gradual rise of temperature to −14.2 °C around 1995, then cooling over the following decade and warming in the last few years. The coldest period was preceded by a relatively warm 19th century at T15 ≥ −15 °C. To facilitate

  15. Borehole temperatures reveal details of 20th century warming at Bruce Plateau, Antarctic Peninsula

    Directory of Open Access Journals (Sweden)

    V. Zagorodnov

    2012-06-01

    Full Text Available Two ice core boreholes of 143.18 m and 447.73 m (bedrock were drilled during the 2009–2010 austral summer on the Bruce Plateau at a location named LARISSA Site Beta (66°02' S, 64°04' W, 1975.5 m a.s.l.. Both boreholes were logged with thermistors shortly after drilling. The shallow borehole was instrumented for 4 months with a series of resistance thermometers with satellite uplink. Surface temperature proxy data derived from an inversion of the borehole temperature profiles are compared to available multi-decadal records from weather stations and ice cores located along a latitudinal transect of the Antarctic Peninsula to West Antarctica. The LARISSA Site Beta profiles show temperatures decreasing from the surface downward through the upper third of the ice, and warming thereafter to the bed. The average temperature for the most recent year is −14.78°C (measured at 15 m depth, abbreviated T15. A minimum temperature of −15.8°C is measured at 173 m depth, and basal temperature is estimated to be −10.2°C. Current mean annual temperature and the gradient in the lower part of the measured temperature profile have a best fit with an accumulation rate of 1.9×103 kg m−2 a−1 and basal heat flux (q of 88 mW m−2, if steady-state conditions are assumed. However, the mid-level temperature variations show that recent temperature has varied significantly. Reconstructed surface temperatures (Ts=T15 over the last 200 yr are derived by an inversion technique (Tikhonov and Samarskii, 1990. From this, we find that cold temperatures (minimum Ts=−16.2°C prevailed from ~1920 to ~1940, followed by a gradual rise of temperature to −14.2°C around 1995, then cooling over the following decade and warming in the last few years. The coldest period was preceded by a relatively warm 19th century at T15≥−15

  16. Where might we find evidence of a Last Interglacial West Antarctic Ice Sheet collapse in Antarctic ice core records?

    Science.gov (United States)

    Bradley, S. L.; Siddall, M.; Milne, G. A.; Masson-Delmotte, V.; Wolff, E.

    2012-05-01

    Abundant indirect evidence suggests that the West Antarctic Ice Sheet (WAIS) reduced in size during the Last Interglacial (LIG) compared to the Holocene. This study explores this possibility by comparing, for the first time, ice core stable isotope records for the LIG with output from a glacio-isostatic adjustment (GIA) model. The results show that ice core records from East Antarctica are remarkably insensitive to vertical movement of the solid land motion driven by a simulated hypothetical collapse of the WAIS. However, new and so far unexplored sites are identified which are sensitive to the isostatic signal associated with WAIS collapse and so ice core proxy data from these sites would be effective in testing this hypothesis further.

  17. MASS BALANCE CHANGES AND ICE DYNAMICS OF GREENLAND AND ANTARCTIC ICE SHEETS FROM LASER ALTIMETRY

    OpenAIRE

    Babonis, G. S.; Csatho, B; Schenk, T.

    2016-01-01

    During the past few decades the Greenland and Antarctic ice sheets have lost ice at accelerating rates, caused by increasing surface temperature. The melting of the two big ice sheets has a big impact on global sea level rise. If the ice sheets would melt down entirely, the sea level would rise more than 60 m. Even a much smaller rise would cause dramatic damage along coastal regions. In this paper we report about a major upgrade of surface elevation changes derived from laser...

  18. A Modified NASA Team Sea Ice Algorithm for the Antarctic

    Science.gov (United States)

    Cavalieri, Donald J.; Markus, Thorsten

    1998-01-01

    A recent comparative study of the NASA Team and Bootstrap passive microwave sea ice algorithms revealed significantly different sea ice concentration retrievals in some parts of the Antarctic. The study identified potential reasons for the discrepancies including the influence of sea ice temperature variability on the Bootstrap retrievals and the influence of ice surface reflectivity on the horizontally polarized emissivity in the NASA Team retrievals. In this study, we present a modified version of the NASA Team algorithm which reduces the error associated with the use of horizontally polarized radiance data, while retaining the relative insensitivity to ice temperature variations provided by radiance ratios. By retaining the 19 GHz polarization as an independent variable, we also maintain a relatively large dynamic range in sea ice concentration. The modified algorithm utilizes the 19 GHz polarization (PR19) and both gradient ratios, GRV and GRH defined by (37V-19V)/(37V+19V) and (37H-19H)/(37H+19H), respectively, rather than just GRV used in the current NASA Team algorithm. A plot of GRV versus GRH shows that the preponderance of points lie along a quadratic curve, whereas those points affected by surface reflectivity anomalies deviate from this curve. This serves as a method of identifying the problems points. The 19H brightness temperature of these problem points is increased so they too fall along quadratic curve. Sea ice concentrations derived from AVHRR imagery illustrate the extent to which this method reduces the error associated with surface layering.

  19. Response of Peat-forming Ecosystems of the Western Antarctic Peninsula to Recent Climate Change

    Science.gov (United States)

    Tardona, M.; Beilman, D.; Yu, Z.; Loisel, J.

    2014-12-01

    Amplified warming and related environmental changes in the high latitudes have a complex geographic pattern, with the Western Antarctic Peninsula experiencing one of the fastest rates of recent warming globally. To better understand the response of terrestrial Antarctic ecosystems to polar change, we applied a paleoscience approach to organic soil profiles from 13 aerobic peatbank ecosystems on 7 islands along the peninsula from 67.6 to 64.2°S. Peatbank ecosystem ages were obtained by Radiocarbon measurements of organic matter from the base of these profiles and cluster in three groups: older than 1000 years old (as old as 2750 years old), 400-500 years old, and younger than 65 years with fixed bomb-spike carbon. Three of these peatbank profiles were studied in detail, and show growth rates over the last 65 years of ~2.5 mm yr-1. This rate is faster than those observed during previous periods but is similar to other recent nearby studies that report recent growth rates of ~2.6 mm yr-1. Organic carbon storage ranged from 6.1 to 21.3 kgC m-2. Values of moss bank organic matter δ13C show progressively more depleted δ13C values; in which depletion increases 3.0‰ over recent decades. Overall increase in source-independent discrimination is 1.7‰, consistent with published records from other locations and an increase in photosynthetic activity at the regional scale. Source-independent discrimination displays substantial variations corresponding negatively to variation of organic matter C:N values. Our results imply several recent changes in Antarctic peat forming ecosystem processes including formation of new moss banks, increased accumulation rates, and high variability in source-independent discrimination. These changes are complex but affected by contemporary climate changes of the region including increasing temperatures over the past century.

  20. Distribution of metals and trace elements in adult and juvenile penguins from the Antarctic Peninsula area.

    Science.gov (United States)

    Jerez, Silvia; Motas, Miguel; Benzal, Jesús; Diaz, Julia; Vidal, Virginia; D'Amico, Verónica; Barbosa, Andrés

    2013-05-01

    The presence of metals in the Antarctic environment is principally a natural phenomenon caused by geochemical characteristics of the region, although some anthropogenic activities can increase these natural levels. Antarctic penguins present several of the characteristics of useful sentinels of pollution in Antarctica such as they are long-lived species situated at the top of food web. The concentrations of Al, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Cd, and Pb were determined by inductively coupled plasma-mass spectrometry in samples of liver, kidney, muscle, bone, feather, and stomach contents of gentoo, chinstrap, and Adélie penguin (12 adults, five juveniles) from carcasses of naturally dead individuals collected opportunistically in the Antarctic Peninsula area. The obtained results showed that accumulation and magnification of several elements can be occurring, so that Cd and Se reached levels potentially toxic in some specimens. The presence of human activities seems to be increasing the presence of toxic metals such as Mn, Cr, Ni, or Pb in penguins.

  1. Measurements of sea ice proxies from Antarctic coastal shallow cores

    Science.gov (United States)

    Maffezzoli, Niccolò; Vallelonga, Paul; Spolaor, Andrea; Barbante, Carlo; Frezzotti, Massimo

    2015-04-01

    Despite its close relationship with climate, the climatic impact of sea ice remains only partially understood: an indication of this is the Arctic sea ice which is declining at a faster rate than models predict. Thus, the need for reliable sea ice proxies is of crucial importance. Among the sea ice proxies that can be extracted from ice cores, interest has recently been shown in the halogens Iodine (I) and Bromine (Br) (Spolaor, A., et al., 2013a, 2013b). The production of sea ice is a source of Sodium and Bromine aerosols through frost flower crystal formation and sublimation of salty blowing snow, while Iodine is emitted by the algae living underneath sea ice. We present here the results of Na, Br and I measurements in Antarctic shallow cores, drilled during a traverse made in late 2013 - early 2014 from Talos Dome (72° 00'S, 159°12'E) to GV7 (70° 41'S, 158° 51'E) seeking for sea ice signature. The samples were kept frozen until the analyses, that were carried out by Sector Field Mass Spectroscopy Inductive Coupled Plasma (SFMS-ICP): special precautions and experimental steps were adopted for the detection of such elements. The coastal location of the cores allows a clear signal from the nearby sea ice masses. The multiple cores are located about 50 km from each other and can help us to infer the provenance of the sea ice that contributed to the proxy signature. Moreover, by simultaneously determining other chemical elements and compounds in the snow, it is possible to determine the relative timing of their deposition, thus helping us to understand their processes of emission and deposition.

  2. STUDY OF SNOWMELT DETECTION ON THE ANTARCTIC PENINSULA ICE SHEET DERIVED FROM RADARSAT-2 DUAL-POL DATA%基于 Radarsat-2双极化数据的南极半岛冰盖冻融探测研究

    Institute of Scientific and Technical Information of China (English)

    王蒙; 李新武; 梁雷; 陆万雨

    2016-01-01

    南极冰盖的融化对全球海平面上升和气候环境变化具有重要影响,合成孔径雷达( SAR)用于划分南极冰盖冰川带及冻融探测具有不可替代的作用。本文以南极半岛地区为例,基于C波段星载SAR影像进行南极冰盖冻融探测方法研究。通过对于南极冰盖干雪带、渗浸带和湿雪带的后向散射特征的分析,采用基于后向散射因子阈值的决策树分类划分冰盖冰川带。统计分析表明,冰川带后向散射因子分布并不集中,尤其是融化强烈时的湿雪带受融化程度影响很大,与干雪带相近而不能仅从后向散射因子数值区分。为将冰盖的冰川带分类,引入干雪带分布和海拔高度作为辅助信息,分别发展了两种决策树分类方法并比较分析,同时利用微波辐射计冰盖冻融探测结果和自动气象站数据做验证。结果表明利用双极化SAR数据的后向散射因子基于两种决策树分类都能够有效地划分冰川带并区分冻融状态,实现高分辨率的冰盖冻融探测。%Snowmelt in Antarctica has considerable impact on sea level rise and climate change .We investigated the de-tection of snowmelt on the Antarctic Peninsula ice sheet using C-band spaceborne synthetic aperture radar imagery . Based on an analysis of the backscatter characteristics of dry , percolation , and wet snow , we used a decision tree classification to divide the ice sheet into zones .The statistical analysis demonstrated that the backscatter coefficients of snow zones , especially the wet snow zone , depend mainly upon melt level and do not have a centralized distribu-tion.The wet snow zone in drastic melt is too similar to the dry snow zone to be distinguished using the backscatter coefficient alone .Therefore , we introduced the dry snow distribution and elevation into the classification , and com-pared the two decision tree methods .We verified the detection results using microwave

  3. Thermodynamics of slush and snow-ice formation in the Antarctic sea-ice zone

    Science.gov (United States)

    Jutras, Mathilde; Vancoppenolle, Martin; Lourenço, Antonio; Vivier, Frédéric; Carnat, Gauthier; Madec, Gurvan; Rousset, Clément; Tison, Jean-Louis

    2016-09-01

    Snow over Antarctic sea ice is often flooded by brine or seawater, particularly in spring, forming slush and snow ice. Here, we evaluate the representation of the thermodynamics of slush and snow-ice formation in large-scale sea-ice models, using laboratory experiments (NaCl solutions poured into grated ice in an isolated container). Scaling analysis highlights latent heat as the main term of the energy budget. The temperature of the new sea ice immediately after flooding is found very close to the saltwater freezing point, whereas its bulk salinity is typically > 20 g / kg. Large-scale sea-ice models faithfully represent such physics, yet the uncertainty on the origin of flooding saltwater impacts the calculated new ice temperature, because of the different salinities of seawater and brine. The laboratory experiments also suggest a potential limitation to the existing physical representations of flooding: for brine fractions > 60 %, ice crystals start floating upon saltwater. Natural sea-ice observations suggest that the isolated system assumption holds for a few hours at most, after which rapid heat and salt exchanges mostly destroy the initial flooding signature on temperature and salinity. A small footprint on ice salinity remains however, natural snow ice is found 3-5 g/kg more saline than other forms of sea ice.

  4. Evaluation of soil bioremediation techniques in an aged diesel spill at the Antarctic Peninsula.

    Science.gov (United States)

    de Jesus, Hugo E; Peixoto, Raquel S; Cury, Juliano C; van Elsas, Jan D; Rosado, Alexandre S

    2015-12-01

    Many areas on the Antarctic continent already suffer from the direct and indirect influences of human activities. The main cause of contamination is petroleum hydrocarbons because this compound is used as a source of energy at the many research stations around the continent. Thus, the current study aims to evaluate treatments for bioremediation (biostimulation, bioaugmentation, and bioaugmentation + biostimulation) using soils from around the Brazilian Antarctic Station "Comandante Ferraz" (EACF), King George Island, Antarctic Peninsula. The experiment lasted for 45 days, and at the end of this period, chemical and molecular analyses were performed. Those analyses included the quantification of carbon and nitrogen, denaturing gradient gel electrophoresis (DGGE) analysis (with gradient denaturation), real-time PCR, and quantification of total hydrocarbons and polyaromatics. Molecular tests evaluated changes in the profile and quantity of the rrs genes of archaea and bacteria and also the alkB gene. The influence of the treatments tested was directly related to the type of soil used. The work confirmed that despite the extreme conditions found in Antarctic soils, the bacterial strains degraded hydrocarbons and bioremediation treatments directly influenced the microbial communities present in these soils even in short periods. Although the majority of the previous studies demonstrate that the addition of fertilizer seems to be most effective at promoting bioremediation, our results show that for some conditions, autochthonous bioaugmentation (ABA) treatment is indicated. This work highlights the importance of understanding the processes of recovery of contaminated environments in polar regions because time is crucial to the soil recovery and to choosing the appropriate treatment.

  5. Calving fluxes and basal melt rates of Antarctic ice shelves.

    Science.gov (United States)

    Depoorter, M A; Bamber, J L; Griggs, J A; Lenaerts, J T M; Ligtenberg, S R M; van den Broeke, M R; Moholdt, G

    2013-10-03

    Iceberg calving has been assumed to be the dominant cause of mass loss for the Antarctic ice sheet, with previous estimates of the calving flux exceeding 2,000 gigatonnes per year. More recently, the importance of melting by the ocean has been demonstrated close to the grounding line and near the calving front. So far, however, no study has reliably quantified the calving flux and the basal mass balance (the balance between accretion and ablation at the ice-shelf base) for the whole of Antarctica. The distribution of fresh water in the Southern Ocean and its partitioning between the liquid and solid phases is therefore poorly constrained. Here we estimate the mass balance components for all ice shelves in Antarctica, using satellite measurements of calving flux and grounding-line flux, modelled ice-shelf snow accumulation rates and a regional scaling that accounts for unsurveyed areas. We obtain a total calving flux of 1,321 ± 144 gigatonnes per year and a total basal mass balance of -1,454 ± 174 gigatonnes per year. This means that about half of the ice-sheet surface mass gain is lost through oceanic erosion before reaching the ice front, and the calving flux is about 34 per cent less than previous estimates derived from iceberg tracking. In addition, the fraction of mass loss due to basal processes varies from about 10 to 90 per cent between ice shelves. We find a significant positive correlation between basal mass loss and surface elevation change for ice shelves experiencing surface lowering and enhanced discharge. We suggest that basal mass loss is a valuable metric for predicting future ice-shelf vulnerability to oceanic forcing.

  6. Exposure age and ice-sheet model constraints on Pliocene East Antarctic ice sheet dynamics.

    Science.gov (United States)

    Yamane, Masako; Yokoyama, Yusuke; Abe-Ouchi, Ayako; Obrochta, Stephen; Saito, Fuyuki; Moriwaki, Kiichi; Matsuzaki, Hiroyuki

    2015-04-24

    The Late Pliocene epoch is a potential analogue for future climate in a warming world. Here we reconstruct Plio-Pleistocene East Antarctic Ice Sheet (EAIS) variability using cosmogenic nuclide exposure ages and model simulations to better understand ice sheet behaviour under such warm conditions. New and previously published exposure ages indicate interior-thickening during the Pliocene. An ice sheet model with mid-Pliocene boundary conditions also results in interior thickening and suggests that both the Wilkes Subglacial and Aurora Basins largely melted, offsetting increased ice volume. Considering contributions from West Antarctica and Greenland, this is consistent with the most recent IPCC AR5 estimate, which indicates that the Pliocene sea level likely did not exceed +20 m on Milankovitch timescales. The inception of colder climate since ∼3 Myr has increased the sea ice cover and inhibited active moisture transport to Antarctica, resulting in reduced ice sheet thickness, at least in coastal areas.

  7. Overview of the chemical ecology of benthic marine invertebrates along the western Antarctic peninsula.

    Science.gov (United States)

    McClintock, James B; Amsler, Charles D; Baker, Bill J

    2010-12-01

    Thirteen years ago in a review that appeared in the American Zoologist, we presented the first survey of the chemical and ecological bioactivity of Antarctic shallow-water marine invertebrates. In essence, we reported that despite theoretical predictions to the contrary the incidence of chemical defenses among sessile and sluggish Antarctic marine invertebrates was widespread. Since that time we and others have significantly expanded upon the base of knowledge of Antarctic marine invertebrates' chemical ecology, both from the perspective of examining marine invertebrates in new, distinct geographic provinces, as well as broadening the evaluation of the ecological significance of secondary metabolites. Importantly, many of these studies have been framed within established theoretical constructs, particularly the Optimal Defense Theory. In the present article, we review the current knowledge of chemical ecology of benthic marine invertebrates comprising communities along the Western Antarctic Peninsula (WAP), a region of Antarctica that is both physically and biologically distinct from the rest of the continent. Our overview indicates that, similar to other regions of Antarctica, anti-predator chemical defenses are widespread among species occurring along the WAP. In some groups, such as the sponges, the incidence of chemical defenses against predation is comparable to, or even slightly higher than, that found in tropical marine systems. While there is substantial knowledge of the chemical defenses of benthic marine invertebrates against predators, much less is known about chemical anti-foulants. The sole survey conducted to date suggests that secondary metabolites in benthic sponges are likely to be important in the prevention of fouling by benthic diatoms, yet generally lack activity against marine bacteria. Our understanding of the sensory ecology of Antarctic benthic marine invertebrates, despite its great potential, remains in its infancy. For example, along the

  8. Impact of the variability of the seasonal snow cover on the ground surface regimes in Hurd Peninsula (Livingston Island, Antarctic)

    Science.gov (United States)

    Nieuwendam, Alexandre; Ramos, Miguel; Vieira, Gonçalo

    2014-05-01

    Seasonally snow cover has a great impact on the thermal regime of the active layer and permafrost. Ground temperatures over a year are strongly affected by the timing, duration, thickness, structure and physical and thermal properties of snow cover. The purpose of this communication is to characterize the shallow ground thermal regimes, with special reference to the understanding of the influence snow cover in permafrost spatial distribution, in the ice-free areas of the north western part of Hurd Peninsula in the vicinity of the Spanish Antarctic Station "Juan Carlos I" and Bulgarian Antarctic Station "St. Kliment Ohridski". We have analyzed and ground temperatures as well as snow thickness data in four sites distributed along an altitudinal transect in Hurd Peninsula from 2007 to 2013: Nuevo Incinerador (25 m asl), Collado Ramos (110 m), Ohridski (140 m) and Reina Sofia Peak (275 m). At each study site, data loggers were installed for the monitoring of air temperatures (at 1.5 m high), ground temperatures (5, 20 and 40 cm depth) and for snow depth (2, 5, 10, 20, 40, 80 and 160 cm) at 4-hour intervals. The winter data suggests the existence of three types of seasonal stages regarding the ground surface thermal regime and the thickness of snow cover: (a) shallow snow cover with intense ground temperatures oscillations; (b) thick snow cover and low variations of soil temperatures; and (c) stability of ground temperatures. Ground thermal conditions are also conditioned by a strong variability. Winter data indicates that Nuevo Incinerador site experiences more often thicker snow cover with higher ground temperatures and absence of ground temperatures oscillations. Collado Ramos and Ohridski show frequent variations of snow cover thickness, alternating between shallow snow cover with high ground temperature fluctuation and thick snow cover and low ground temperature fluctuation. Reina Sofia in all the years has thick snow cover with little variations in soil

  9. 30-Year Satellite Record Reveals Accelerated Arctic Sea Ice Loss, Antarctic Sea Ice Trend Reversal

    Science.gov (United States)

    Cavalieri, Donald J.; Parkinson, C. L.; Vinnikov, K. Y.

    2003-01-01

    Arctic sea ice extent decreased by 0.30 plus or minus 0.03 x 10(exp 6) square kilometers per decade from 1972 through 2002, but decreased by 0.36 plus or minus 0.05 x 10(exp 6) square kilometers per decade from 1979 through 2002, indicating an acceleration of 20% in the rate of decrease. In contrast to the Arctic, the Antarctic sea ice extent decreased dramatically over the period 1973-1977, then gradually increased, with an overall 30-year trend of -0.15 plus or minus 0.08 x 10(exp 6) square kilometers per 10yr. The trend reversal is attributed to a large positive anomaly in Antarctic sea ice extent observed in the early 1970's.

  10. The circum-Antarctic sedimentary record; a dowsing rod for Antarctic ice in the Eocene

    Science.gov (United States)

    Scher, H.

    2012-12-01

    Arguments for short-lived Antarctic glacial events during the Eocene (55-34 Ma) are compelling, however the paleoceanographic proxy records upon which these arguments are based (e.g., benthic δ18O, eustatic sea level, deep sea carbonate deposition) are global signals in which the role of Antarctic ice volume variability is ambiguous. That is to say, the proxy response to ice volume may be masked other processes. As a result broad correlations between proxies for ice volume are lacking during suspected Eocene glacial events. I will present a more direct approach for detecting Antarctic ice sheets in the Eocene; utilizing provenance information derived from the radiogenic isotopic composition of the terrigenous component of marine sediments near Antarctica. The method relies on knowledge that marine sediments represent a mixture derived from different basement terrains with different isotopic fingerprints. A key issue when using sedimentary deposits to characterize continental sediment sources is to deconvolve different sources from the mixed signal of the bulk sample. The pioneering work of Roy et al. (2007) and van de Flierdt et al. (2007) represents a major advance in Antarctic provenance studies. It is now known that the isotopic composition of neodymium (Nd) and hafnium (Hf) in modern circum-Antarctic sediments are distributed in a pattern that mimics the basement age of sediment sources around Antarctica. For this study I selected two Ocean Drilling Program (ODP) sites on southern Kerguelen Plateau (ODP Sites 738 and 748) because of their proximity to Prydz Bay, where Precambrian sediment sources contribute to extremely nonradiogenic isotopic signatures in modern sediments in the Prydz Bay region. New detrital Nd isotope records from these sediment cores reveal an Nd isotope excursion at the Bartonian/Priabonian boundary (ca. 37 Ma) that coincides with a 0.5 ‰ increase in benthic foram δ18O values. Detrital sediment ɛNd values are around -12 in intervals

  11. Industrial heritage sites in Spitsbergen (Svalbard), South Georgia and the Antarctic Peninsula: Sources of historical information

    Science.gov (United States)

    Hacquebord, Louwrens; Avango, Dag

    2016-09-01

    Industrial heritage sites in Polar Regions are very important as sources of historical information. Together with archival documents this information gives us the possibility to complete the picture of the exploitation of natural resources in those regions. Thirty years of historical-archaeological field research at whaling and mining sites in Spitsbergen (Svalbard), South Georgia and the Antarctic Peninsula has shown that these sites can provide unique evidence about the driving forces behind industrial development, the design of industrial technology, the structure of the settlements, strategies to control natural resources and achieve political influence, and the impact of resource extraction on the local environment. In this article we will give examples of the results of our research at these sites.

  12. Two decades of inorganic carbon dynamics along the Western Antarctic Peninsula

    Science.gov (United States)

    Hauri, C.; Doney, S. C.; Takahashi, T.; Erickson, M.; Jiang, G.; Ducklow, H. W.

    2015-05-01

    We present 20 years of seawater inorganic carbon measurements collected along the western shelf and slope of the Antarctic Peninsula. Water column observations from summertime cruises and seasonal surface underway pCO2 measurements provide unique insights into the spatial, seasonal and interannual variability of the dynamic system. The discrete measurements from depths > 2000 m align well with World Ocean Circulation Experiment observations across the time-series and underline the consistency of the data set. Analysis shows large spatial gradients in surface alkalinity and dissolved inorganic carbon content, with a concomitant wide range of Ωarag from values statistically significant increasing trend of up to 23 μatm per decade in fall and spring and a concomitant decreasing pH, pointing towards first signs of ocean acidification in the region. The combination of ongoing ocean acidification and freshwater input may soon provoke more unfavorable conditions than what the ecosystem experiences today.

  13. Two decades of inorganic carbon dynamics along the West Antarctic Peninsula

    Science.gov (United States)

    Hauri, C.; Doney, S. C.; Takahashi, T.; Erickson, M.; Jiang, G.; Ducklow, H. W.

    2015-11-01

    We present 20 years of seawater inorganic carbon measurements collected along the western shelf and slope of the Antarctic Peninsula. Water column observations from summertime cruises and seasonal surface underway pCO2 measurements provide unique insights into the spatial, seasonal, and interannual variability in this dynamic system. Discrete measurements from depths > 2000 m align well with World Ocean Circulation Experiment observations across the time series and underline the consistency of the data set. Surface total alkalinity and dissolved inorganic carbon data showed large spatial gradients, with a concomitant wide range of Ωarag (statistically significant long-term trends, the combination of on-going ocean acidification and freshwater input may soon induce more unfavorable conditions than the ecosystem experiences today.

  14. Microwave emissivity of fresh water ice--Lake ice and Antarctic ice pack--Radiative transfer simulations versus satellite radiances

    CERN Document Server

    Mills, Peter

    2012-01-01

    Microwave emissivity models of sea ice are poorly validated empirically. Typical validation studies involve using averaged or stereotyped profiles of ice parameters against averaged radiance measurements. Measurement sites are rarely matched and even less often point-by-point. Because of saline content, complex permittivity of sea ice is highly variable and difficult to predict. Therefore, to check the validity of a typical, plane-parallel, radiative-transfer-based ice emissivity model, we apply it to fresh water ice instead of salt-water ice. Radiance simulations for lake ice are compared with measurements over Lake Superior from the Advanced Microwave Scanning Radiometer on EOS (AMSR-E). AMSR-E measurements are also collected over Antarctic icepack. For each pixel, a thermodynamic model is driven by four years of European Center for Medium Range Weather Forecasts (ECMWF) reanalysis data and the resulting temperature profiles used to drive the emissivity model. The results suggest that the relatively simple ...

  15. The 2014 high record of Antarctic sea ice extent

    Science.gov (United States)

    Massonnet, Francois; Guemas, Virginie; Fuckar, Neven; Doblas-Reyes, Francisco

    2016-04-01

    In September 2014, Antarctic sea ice extent exceeded the symbolic level of 20 million km²for the first time since 1978, when reliable satellite measurements became available. After the successive records of 2012 and 2013, sea ice extent in 2014 once again reinforced the positive trend observed since the late 1970s. We conduct here a dedicated study to elucidate the origins of a major, and perhaps the most intriguing, event that happened at our Poles recently. Observations, reanalyses and model results all point towards the important role of winds in modifying near-surface heat advection patterns around Antarctica. The role of pre-conditioning (summer conditions) is found to be of lesser importance. Finally, we find no evidence that anomalous freshwater forcing (from atmospheric or continental origin) could have explained the record extent of 2014.

  16. Assessment of trace metals in droppings of Adélie penguins (Pygoscelis adeliae) from different locations of the Antarctic Peninsula area

    Institute of Scientific and Technical Information of China (English)

    Jos E Celis; Winfred Espejo; Ricardo Barra; Daniel Gonzalez-Acua; Francisca Gonzalez; Solange Jara

    2015-01-01

    In recent decades, polar regions of the planet have witnessed an increase in human presence. Antarctica is considered one of the most pristine regions of the world, but it could be affected by pollution owing to anthropogenic activities, particularly in the Antarctic Peninsula. Human presence can increase the levels of some trace metals in Antarctic environments, an issue that needs to be evaluated. To acquire data of trace metal contamination in the Antarctic Peninsula region, concentrations (dry weight) of Cd, Pb, As, Cu, Hg and Zn in fresh excrement of Adélie penguins were determined by atomic absorption spectrophotometry. During the 2012/2013 austral summer, samples were collected from four important nesting sites on the Antarctic Peninsula:Arctowski Base, Kopaitic Island (both sites in the northern Antarctic Peninsula), Yalour Island and Avian Island (both sites in the southern Antarctic Peninsula). Data showed that Adélie penguin excreta had significantly higher levels (mg·kg-1) of As, Cd, Hg, Pb and Cu at Arctowski Base and Kopaitic Island, both sites that have major anthropogenic activities that probably contributed to increased metal levels. The levels of trace metals in Adélie penguins were similar to those reported in excreta of Antarctic species in previous studies, and lower than those in excreta of other Antarctic animals. Data suggest that metals ingested by these penguin species that feed in the sea, end up in terrestrial ecosystems.

  17. Role of Lichens in Weathering and Soil—Forming Processes in Fildes Peninsula,Antarctic

    Institute of Scientific and Technical Information of China (English)

    CHENJIE; GONGZi-TONG

    1995-01-01

    Lichens play an unparalleledly vital role in weathering and soil-forming processes in Antarctic region,In this study some related chemical components and micromorphological analyses have been carried out on the samples of the weathered rocks and the lichens grown on them from Files Peninsula,Antarctic,The results indicatied that the major chemical components in the bioweathering surface layer of the sampled rocks have been obviously altered and the weathering potential in this layer has greatly decreased by and average range around 4.66 percent in 4 samples,In the weathering surface layer ferruginiztion of some minerals in varying degress was seen by means of microscopic examination through the thin section of the weathered rocks,and its products proved to be dominated by hematitie,limonite,goethite and free iron oxides Meanwhile,the study suggested that the dissolution and absorption of lichens by their secretion accelerated the process of calcitization of minerals in the bio-weathering suface layer,Eventually,the results also show that different species of lichens play different roles in weathering and soil-forming proesses.

  18. Acute gastrointestinal haemorrhage on board a cruise ship in the Antarctic Peninsula.

    Science.gov (United States)

    Carron, Mathieu; Globokar, Peter; Sicard, Bruno A

    2016-01-01

    Antarctic tourism on board cruise ships has expanded since the 1990s, essentially in the Antarctic Peninsula. Due to remoteness, medical cases may evolve into life threatening conditions as emergency medical evacuations are challenging. We discuss the case of a young crew member who suddenly fainted with an epigastric pain and abundant rectal bleeding while on board a cruise ship heading to the Deception Island (62°57.6 South, 60°29.5 West), 44 h away from Ushuaia by sea. A medical evacuation was necessary to save the patient whose haemoglobin level rapidly decreased from 11 g/dL to 8.7 g/dL over an 8 h period due to uncontrolled gastrointestinal bleeding. Following discussions between the French, Chilean and Argentinean Medical Top Side Support and Maritime Rescue Authorities and despite poor weather conditions, an emergency medical evacuation by air to Chile was made possible. The evacuation, which was 2 days shorter compared to an evacuation by sea, allowed the patient to reach a hospital facility in time to save his life whereas he decompensated in haemorrhagic shock. As passengers on cruise ships are typically elderly and often following anticoagulant therapies, the risk of bleeding is most important. Facing a gastric haemorrhage, a transfusion is often required. In remote areas, transfusion of fresh whole blood to stabilize a critical patient until he reaches a hospital must be considered.

  19. Signals of Antarctic Circum-polar Wave over the Southern Indian Ocean as recorded in an Antarctica ice core

    Institute of Scientific and Technical Information of China (English)

    XIAO Cunde; CHENG Yanjie; REN Jiawen; LU Longhua; LI Zhongqin; QIN Dahe; ZHOU Xiuji

    2005-01-01

    Oxygen stable isotopic and ionic records, covering a period of 1745-1996, are recovered in DT001 ice core drilled in Princess Elizabeth Land, East Antarctica. Using empirical orthogonal function (EOF) analysis of the annually resolved glaciochemical time series, we find the first EOF (EOF1) represents sea-salt aerosols and is the proxy of sea level pressure (SLP) over a quasi-stationary low in the Southern Indian Ocean (SIO).δ18O represents the sea surface temperature (SST) of the same ocean area. In the past two decades, four climatic waves as represented by SLP and SST proxies are found in the DT001 ice core, which in coincident with four Antarctic Circum-polar Waves (ACW) as revealed by NCEP/NCAR reanalysis. The phase difference between SST and SLP in the ice core is also coincident with that in ACW. Both ice-core record and reanalysis suggest that there were no signals of ACW during 1958-1980, none during the overall recording period between 1745-1996, as there is no regular phase difference between SST and SLP. The ACW signal after early 1980s is probably attributable to the climate shift occurring over Antarctic Peninsula-Drake Passage region.

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

    Science.gov (United States)

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

    2014-12-01

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

  1. Sub-Kilometer Scale Basal Roughness of the Siple Coast Ice Streams, West Antarctic Ice Sheet

    Science.gov (United States)

    Young, D. A.; Blankenship, D. D.; Peters, M. E.

    2006-12-01

    The anastomosing series of dynamic, basally lubricated ice streams found on the Siple Coast of West Antarctica play an important role in regulating the mass balance of the West Antarctic Ice Sheet (WAIS). Geological controls on lubrication, elucidated by gravity, magnetics and seismic data, have proven important in understanding the evolution of these features. An additional indicator of basal properties, the basal roughness of ice sheets, may be an indicator of crustal geology and glacial modification, as well as a controlling parameter on ice dynamics and subglacial hydrology. For the Siple Coast ice streams, Fourier analysis of > 5 kilometer morphology (Siegert et al. 2004) revealed a correlation between ice streams and low bed roughness. Coherent high resolution data allows analysis of along track roughness at tens of meters resolution (Peters et al. 2005), however these data are limited in coverage. We extend roughness estimates into to the hundreds-of-meters length scale, using both frequency domain and autocorrelation methods, using incoherent 60 MHz radio echo sounding data collected between 1991 and 1996 on a five kilometer grid. The data cover the Bentley Subglacial Trench, Bindschadler Ice Stream, Siple Dome and the onset region of Kamb Ice Stream. SAR-processed coherent sounding data collected in 2001 are used to confirm these methods. We test for confinement of ice stream rapid basal motion to distinct morphological provinces; assess the hypothesis that marine sediments blanket much of interior of the basal WAIS; and look for correlation between ice flow and textural anisotropy.

  2. [Two comments on “Historic cartographic evidence for Holocene changes in the Antarctic ice cover”] Antarctic ice cover

    Science.gov (United States)

    Milton, Daniel J.; Lliboutry, Louis

    1984-04-01

    Readers of John G. Weihaupt's “Historic Cartographic Evidence for Holocene Changes in the Antarctic Ice Cover” (Eos, August 28, 1984, p. 493) may wish to consult Charles H. Hapgood, Maps of the Ancient Sea Kings, Evidence of Advanced Civilization in the Ice Ages (Chilton, Radnor, Penn., 1966). The major part of this book is a presentation of the thesis that Weihaupt has independently developed: that early sixteenth century maps portray Antarctica, and in particular an ice-free Ross Sea, and that such knowledge must have been obtained and transmitted from a remote, perhaps prehistoric, epoch. Hapgood is perhaps better known to the geophysical community for his earlier book, Earth's Shifting Crust (Pantheon, New York, 1958), which proposed that the growth of ice caps unbalances the crust so that it can, and during the Pleistocene frequently did, slide over the interior, displacing the poles several thousand kilometers.The more conservative literature on Terra Australis of the sixteenth century cartographers is extensive; Acta Cartographica, a collection of reprinted papers on historical cartography, has over two dozen references in its indexes. A plausible hypothesis by J. Enterline (Imago Mundi, 26, pp. 48-58, 1972) is that it reflects Portugese acquisition of Indonesian knowledge of Australia, the prominent embayment (Hapgood's and Weihaupt's ice-free Ross Sea) being the Gulf of Carpentaria. Underestimation of the size of the globe forced Australia to extend over the pole, just as it forced newly discovered America to lie close to Japan.

  3. Presence of endocrine disruptors in freshwater in the northern Antarctic Peninsula region.

    Science.gov (United States)

    Esteban, S; Moreno-Merino, L; Matellanes, R; Catalá, M; Gorga, M; Petrovic, M; López de Alda, M; Barceló, D; Silva, A; Durán, J J; López-Martínez, J; Valcárcel, Y

    2016-05-01

    The increasing human presence in Antarctica and the waste it generates is causing an impact on the environment at local and border scale. The main sources of anthropic pollution have a mainly local effect, and include the burning of fossil fuels, waste incineration, accidental spillage and wastewater effluents, even when treated. The aim of this work is to determine the presence and origin of 30 substances of anthropogenic origin considered to be, or suspected of being, endocrine disruptors in the continental waters of the Antarctic Peninsula region. We also studied a group of toxic metals, metalloids and other elements with possible endocrine activity. Ten water samples were analyzed from a wide range of sources, including streams, ponds, glacier drain, and an urban wastewater discharge into the sea. Surprisingly, the concentrations detected are generally similar to those found in other studies on continental waters in other parts of the world. The highest concentrations of micropollutants found correspond to the group of organophosphate flame retardants (19.60-9209ngL(-1)) and alkylphenols (1.14-7225ngL(-1)); and among toxic elements the presence of aluminum (a possible hormonal modifier) (1.7-127µgL(-1)) is significant. The concentrations detected are very low and insufficient to cause acute or subacute toxicity in aquatic organisms. However, little is known as yet of the potential sublethal and chronic effects of this type of pollutants and their capacity for bioaccumulation. These results point to the need for an ongoing system of environmental monitoring of these substances in Antarctic continental waters, and the advisability of regulating at least the most environmentally hazardous of these in the Antarctic legislation.

  4. Interhemispheric coupling, the West Antarctic Ice Sheet and warm Antarctic interglacials

    Directory of Open Access Journals (Sweden)

    P. B. Holden

    2010-07-01

    Full Text Available Ice core evidence indicates that even though atmospheric CO2 concentrations did not exceed ~300 ppm at any point during the last 800 000 years, East Antarctica was at least ~3–4 °C warmer than preindustrial (CO2~280 ppm in each of the last four interglacials. During the previous three interglacials, this anomalous warming was short lived (~3000 years and apparently occurred before the completion of Northern Hemisphere deglaciation. Hereafter, we refer to these periods as "Warmer than Present Transients" (WPTs. We present a series of experiments to investigate the impact of deglacial meltwater on the Atlantic Meridional Overturning Circulation (AMOC and Antarctic temperature. It is well known that a slowed AMOC would increase southern sea surface temperature (SST through the bipolar seesaw and observational data suggests that the AMOC remained weak throughout the terminations preceding WPTs, strengthening rapidly at a time which coincides closely with peak Antarctic temperature. We present two 800 kyr transient simulations using the Intermediate Complexity model GENIE-1 which demonstrate that meltwater forcing generates transient southern warming that is consistent with the timing of WPTs, but is not sufficient (in this single parameterisation to reproduce the magnitude of observed warmth. In order to investigate model and boundary condition uncertainty, we present three ensembles of transient GENIE-1 simulations across Termination II (135 000 to 124 000 BP and three snapshot HadCM3 simulations at 130 000 BP. Only with consideration of the possible feedback of West Antarctic Ice Sheet (WAIS retreat does it become possible to simulate the magnitude of observed warming.

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

    Science.gov (United States)

    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

  6. Thick and deformed Antarctic sea ice mapped with autonomous underwater vehicles

    Science.gov (United States)

    Williams, G.; Maksym, T.; Wilkinson, J.; Kunz, C.; Murphy, C.; Kimball, P.; Singh, H.

    2015-01-01

    Satellites have documented trends in Antarctic sea-ice extent and its variability for decades, but estimating sea-ice thickness in the Antarctic from remote sensing data remains challenging. In situ observations needed for validation of remote sensing data and sea-ice models are limited; most have been restricted to a few point measurements on selected ice floes, or to visual shipboard estimates. Here we present three-dimensional (3D) floe-scale maps of sea-ice draft for ten floes, compiled from two springtime expeditions by an autonomous underwater vehicle to the near-coastal regions of the Weddell, Bellingshausen, and Wilkes Land sectors of Antarctica. Mean drafts range from 1.4 to 5.5 m, with maxima up to 16 m. We also find that, on average, 76% of the ice volume is deformed ice. Our surveys indicate that the floes are much thicker and more deformed than reported by most drilling and ship-based measurements of Antarctic sea ice. We suggest that thick ice in the near-coastal and interior pack may be under-represented in existing in situ assessments of Antarctic sea ice and hence, on average, Antarctic sea ice may be thicker than previously thought.

  7. Giant solar flares in Antarctic ice. [nitrate ions in ice core samples

    Science.gov (United States)

    Stothers, R.

    1980-01-01

    A new hypothesis proposes an explanation for the presence of four prominent spikes in a long time record of the NO3(-) concentration inside the Antarctic ice. This solar flare hypothesis suggests that the ionizing radiation necessary in the spike formation could have come from extremely powerful solar flares. It is proposed that these flares would have occurred during the times of the largest maxima in the solar cycle. The solar flare hypothesis is compared with the supernova hypothesis.

  8. East Antarctic ice sheet stability recorded in a high-elevation ice-cored moraine

    Science.gov (United States)

    Bader, Nicole A.; Licht, Kathy J.; Kaplan, Michael R.; Kassab, Christine; Winckler, Gisela

    2017-03-01

    Till in an extensive blue ice moraine in the central Transantarctic Mountains at Mt. Achernar shows relatively continuous deposition by East Antarctic derived ice throughout the last glacial cycle. The most recently exposed material along the active margin of the Law Glacier (Zone 1) has hummocky topography that transitions into to a relatively flat region (Zone 2), followed by a series of ∼2 m high continuous, parallel/sub-parallel ridges and troughs (Zones 3-5). The entire moraine is ice-cored. Past surface changes of data, the U-Pb zircon data from till across all zones show little variability and are consistent with a Beacon Supergroup source, as samples show significant populations from the Proterozoic, ∼550-600 Ma and ∼950-1270 Ma, as well as the late Archean ∼2700-2770 Ma. The Mackellar, Fairchild, and lower Buckley Formations are interpreted as dominant sources of the detrital zircons. The zircon data lack the spatio-temporal variability indicated by the pebble fraction because the local Ferrar dolerite is not zircon bearing, highlighting the broader importance of using multiple techniques when interpreting provenance changes over time. Rather than reflecting major changes in ice flow path over time, the provenance changes are interpreted to indicate relative stability of the East Antarctic ice sheet, as the Law Glacier tapped into and eroded successively lower stratigraphic units of the Beacon Supergroup. This has important implications for interpreting offshore provenance records.

  9. Combustion of available fossil fuel resources sufficient to eliminate the Antarctic Ice Sheet.

    Science.gov (United States)

    Winkelmann, Ricarda; Levermann, Anders; Ridgwell, Andy; Caldeira, Ken

    2015-09-01

    The Antarctic Ice Sheet stores water equivalent to 58 m in global sea-level rise. We show in simulations using the Parallel Ice Sheet Model that burning the currently attainable fossil fuel resources is sufficient to eliminate the ice sheet. With cumulative fossil fuel emissions of 10,000 gigatonnes of carbon (GtC), Antarctica is projected to become almost ice-free with an average contribution to sea-level rise exceeding 3 m per century during the first millennium. Consistent with recent observations and simulations, the West Antarctic Ice Sheet becomes unstable with 600 to 800 GtC of additional carbon emissions. Beyond this additional carbon release, the destabilization of ice basins in both West and East Antarctica results in a threshold increase in global sea level. Unabated carbon emissions thus threaten the Antarctic Ice Sheet in its entirety with associated sea-level rise that far exceeds that of all other possible sources.

  10. A complete glacier inventory of the Antarctic Peninsula based on Landsat 7 images from 2000 to 2002 and other preexisting data sets

    Science.gov (United States)

    Huber, Jacqueline; Cook, Alison J.; Paul, Frank; Zemp, Michael

    2017-02-01

    The glaciers on the Antarctic Peninsula (AP) potentially make a large contribution to sea level rise. However, this contribution has been difficult to estimate since no complete glacier inventory (outlines, attributes, separation from the ice sheet) is available. This work fills the gap and presents a new glacier inventory of the AP north of 70° S, based on digitally combining preexisting data sets with geographic information system (GIS) techniques. Rock outcrops have been removed from the glacier basin outlines of Cook et al. (2014) by intersection with the latest layer of the Antarctic Digital Database (Burton-Johnson et al., 2016). Glacier-specific topographic parameters (e.g., mean elevation, slope and aspect) as well as hypsometry have been calculated from the DEM of Cook et al. (2012). We also assigned connectivity levels to all glaciers following the concept by Rastner et al. (2012). Moreover, the bedrock data set of Huss and Farinotti (2014) enabled us to add ice thickness and volume for each glacier. The new inventory is available from the Global Land Ice Measurements from Space (GLIMS) database (doi:10.7265/N5V98602) and consists of 1589 glaciers covering an area of 95 273 km2, slightly more than the 89 720 km2 covered by glaciers surrounding the Greenland Ice Sheet. Hence, compared to the preexisting data set of Cook et al. (2014), this data set covers a smaller area and one glacier less due to the intersection with the rock outcrop data set. The total estimated ice volume is 34 590 km3, of which one-third is below sea level. The hypsometric curve has a bimodal shape due to the unique topography of the AP, which consists mainly of ice caps with outlet glaciers. Most of the glacierized area is located at 200-500 m a.s.l., with a secondary maximum at 1500-1900 m. Approximately 63 % of the area is drained by marine-terminating glaciers, and ice-shelf tributary glaciers cover 35 % of the area. This combination indicates a high sensitivity of the glaciers

  11. Rapid Access Ice Drill: A New Tool for Exploration of the Deep Antarctic Ice Sheets and Subglacial Geology

    Science.gov (United States)

    Goodge, J. W.; Severinghaus, J. P.

    2014-12-01

    The Rapid Access Ice Drill (RAID) will penetrate the Antarctic ice sheets in order to core through deep ice, the glacial bed, and into bedrock below. This new technology will provide a critical first look at the interface between major ice caps and their subglacial geology. Currently in construction, RAID is a mobile drilling system capable of making several long boreholes in a single field season in Antarctica. RAID is interdisciplinary and will allow access to polar paleoclimate records in ice >1 Ma, direct observation at the base of the ice sheets, and recovery of rock cores from the ice-covered East Antarctic craton. RAID uses a diamond rock-coring system as in mineral exploration. Threaded drill-pipe with hardened metal bits will cut through ice using reverse circulation of Estisol for pressure-compensation, maintenance of temperature, and removal of ice cuttings. Near the bottom of the ice sheet, a wireline bottom-hole assembly will enable diamond coring of ice, the glacial bed, and bedrock below. Once complete, boreholes will be kept open with fluid, capped, and made available for future down-hole measurement of thermal gradient, heat flow, ice chronology, and ice deformation. RAID will also sample for extremophile microorganisms. RAID is designed to penetrate up to 3,300 meters of ice and take sample cores in less than 200 hours. This rapid performance will allow completion of a borehole in about 10 days before moving to the next drilling site. RAID is unique because it can provide fast borehole access through thick ice; take short ice cores for paleoclimate study; sample the glacial bed to determine ice-flow conditions; take cores of subglacial bedrock for age dating and crustal history; and create boreholes for use as an observatory in the ice sheets. Together, the rapid drilling capability and mobility of the drilling system, along with ice-penetrating imaging methods, will provide a unique 3D picture of the interior Antarctic ice sheets.

  12. A Palaeohydrological Shift during Neogene East Antarctic Ice Sheet Retreat

    Science.gov (United States)

    Rees-Owen, R. L.; Newton, R.; Ivanovic, R. F.; Francis, J.; Tindall, J. C.; Riding, J. B.

    2015-12-01

    The East Antarctic Ice Sheet is an important driver of global climate, playing a particular role in governing albedo and atmospheric circulation (eg. Singh et al., 2013). Recent evidence from marine sediment and terrestrial glaciovolcanic sequences suggests that the EAIS underwent periodic retreat and collapse in response to warmer climates during the late Neogene (14 to 3 million years ago). Mummified prostrate trees recovered from palaeosols at Oliver Bluffs in the Beardmore Glacier region, Transantarctic Mountains (85° S), represent a rare insight into the terrestrial palaeoclimate during one of these periods of retreat. Prostrate trees are an understudied but useful tool for interrogating endmember (e.g. periglacial) environments at high altitudes and latitudes. We present exciting new palaeoclimate data from the sequence at Oliver Bluffs. δ18O analysis of tree ring cellulose suggests that Antarctic summer palaeoprecipitation was enriched relative to today (-25 to -5‰ for ancient, -35 to -20‰ for modern); consistent with our isotope-enabled general circulation model simulations. The MBT/CBT palaeothermometer gives a summer temperature of 3-6ºC, consistent with other palaeobotanical climate indices. These geological and model data have wide-ranging implications for our understanding of the hydrological cycle during this time period. We present data suggesting that changes in moisture recycling and source region indicate a markedly different hydrological cycle.

  13. Response of the Antarctic Ice Sheet to a climatic warming: a model study

    NARCIS (Netherlands)

    Oerlemans, J.

    1982-01-01

    It is generally believed that the increasing C02 content of the atmosphere will lead to a substantial climatic warming in the polar regions. In this study the effect of consequent changes in the ice accumulation rate over the Antarctic Ice Sheet is investigated by means of a numerical ice flow model

  14. Impact of model resolution for on-shelf heat transport along the West Antarctic Peninsula

    Science.gov (United States)

    Graham, Jennifer A.; Dinniman, Michael S.; Klinck, John M.

    2016-10-01

    The flux of warm deep water onto Antarctic continental shelves plays a vital role in determining water mass properties adjacent to the continent. A regional model, with two different grid resolutions, has been used to simulate ocean processes along the West Antarctic Peninsula. At both 4 km and 1.5 km resolution, the model reproduces the locations of warm intrusions, as shown through comparison with observations from instrumented seals. However, the 1.5 km simulation shows greater on-shelf heat transport, leading to improved representation of heat content on the shelf. This increased heat transport is associated with increased eddy activity, both at the shelf-break and in the deep ocean off-shore. Cross-shelf troughs are key locations of on-shelf heat transport. Comparison of two troughs, Belgica and Marguerite, shows differing responses to increased resolution. At higher resolution, there is an increased on-shelf volume transport at Belgica Trough, but not at Marguerite Trough. This is likely related to the differing structure of the shelf-break jet between these two locations. The increased heat flux at Marguerite Trough is attributed to increased heat content in the on-shelf transport. Increased eddy activity off-shelf may lead to greater cross-front heat transport, and therefore increased heat available above the continental slope. While these simulations differ in their magnitude of heat transport, both show similar patterns of variability. Variations in wind stress lead to variations in speed of the shelf-break jet, and therefore on-shelf heat transport. These results demonstrate the importance of model resolution for understanding cross-shelf transport around Antarctica.

  15. Rock weathering Tendency at Different Stages of Soil—Forming Processes in Fildes Peninsula,Antarctic

    Institute of Scientific and Technical Information of China (English)

    CHENJIE; GONGZITONG

    1996-01-01

    From the view of energy state of material,this paper introduces a concept a concept of weathering potential in carrying out quantitative calculation of the relevant products at different stages of rock-weathering and primary soil-forming processes,elaborates respectively on weathering degree in the bio-weathering layer of rocks and during the formation of soil material and clay,and evaluats the further tendency of weathering in the above-mentioned stages.The authors have discovered that the scales of weathering potential of the materials increase successively in the three stages,which indicates that the products in the above-mentioned three stages must have undergone stronger and stronger weathering in the primitive forming process of soil in Fildes Peninsula,Antarctic.But,Because of relatively weak chemical weathering,it is reasonable that there are much more skeleton grains and little clay in priamry soils in this region.Meanwhile the authors have also verified that the weathering potential of crde rock determines to some extent decrease in the products' weathering potential in the different stages in primary soil-forming,thereby plays an important role in the genesis and development of the primary soil in the studied area.

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

    Science.gov (United States)

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

    Science.gov (United States)

    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.

  18. The signature analysis of summer Antarctic sea-ice distribution by ship-based sea-ice observation

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Based on the Chinese 19th National Antarctic Research Expedition,we carried out ship-based Antarctic sea-ice observa-tion on icebreaker Xue Long using Antarctic sea-ice process and climate (ASPeCt) criteria during austral summer.Sea-ice distribution data were obtained along nearly 6,500 km of the ship’s track.The measurement parameters included sea-ice thickness,sea-ice concentration,snow thickness,and floe size.Analysis showed the presence of the large spatial varia-tions of the observed sea-ice characteristics.Sea-ice concentration varied between 0 and 80 percent and reached its peak value in Weddell Sea because of the specific dynamical process affecting in summer sea-ice melting.There are large areas of open water along the study section.Sea ice and the upper snow thickness of the section varied between 10 cm and 210 cm and 2 cm and 80 cm,respectively,and each reaches its peak values near Amery ice shelf.The floe size varied from less than 10 cm and the maximum of more than 2,000 km along the section.

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

    Science.gov (United States)

    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.

  20. The LARsen Ice Shelf System, Antarctica, LARISSA a Model for Antarctic Integrated System Science (AISS) Investigations using Marine Platforms

    Science.gov (United States)

    Domack, E. W.; Huber, B. A.; Vernet, M.; Leventer, A.; Scambos, T. A.; Mosley-Thompson, E. S.; Smith, C. R.; de Batist, M. A.; Yoon, H.; Larissa

    2010-12-01

    The LARISSA program is the first interdisciplinary project funded in the AISS program of the NSF Office of Polar Programs and was officially launched in the closing days of the IPY. This program brings together investigators, students, and media to address the rapid and fundamental changes taking place in the region of the Larsen Ice Shelf and surrounding areas. Scientific foci include: glaciologic and oceanographic interactions, the response of pelagic and benthic ecosystems to ice shelf decay, sedimentary record of ice shelf break disintegration, the geologic evolution of ice shelf systems over the last 100,000 years, paleoclimate/environmental records from marine sediment and ice cores, and the crustal response to ice mass loss at decade to millennial time scales. The first major field season took place this past austral summer aboard the NB Palmer (cruise NBP10-01) which deployed with a multi-layered logistical infrastructure that included: two Bell 220 aircraft, a multifunctional deep water ROV, video guided sediment corer, jumbo piston core, and an array of oceanographic and biological sensors and instruments. In tandem with this ship based operation Twin Otter aircraft supported an ice core team upon the crest of the Bruce Plateau with logistic support provided by the BAS at Rothera Station. Although unusually heavy sea ice prevented much of the original work from being completed in the Larsen Embayment the interdisciplinary approach proved useful. Further the logistical model of ship based aircraft to support interdisciplinary work proved viable, again despite an unusually severe summer meterologic pattern across the northern Antarctic Peninsula. As the program moves forward other vessels will come into play and the model can be applied to interdisciplinary objectives in other regions of Antarctica which are remote and lack land based infrastructure to support coastal field programs in glaciology, geology, or meteorology. This work could then be completed

  1. Sublimation: A Mechanism for the Enrichment of Organics in Antarctic Ice

    Science.gov (United States)

    Becker, Luann; McDonald, Gene D.; Glavin, Daniel P.; Bada, Jeffrey L.; Bunch, Theodore E.; Chang, Sherwood (Technical Monitor)

    1997-01-01

    Recent analyses of the carbonate globules present in the Martian meteorite ALH84001 have detected polycyclic aromatic hydrocarbons (PAHs) at the ppm level. The distribution of PAHs observed in ALH84001 was interpreted as being inconsistent with a terrestrial origin and were claimed to be indigenous to the meteorite, perhaps derived from an ancient Martian biota. However, Becker et al., have examined PAHs in the Martian meteorite EETA79001, in several Antarctic carbonaceous chondrites and Antarctic Allan Hills Ice and detected many of the same PAHs found in ALH84001. The reported presence of L-amino acids of apparent terrestrial origin in the EETA79001 druse material, suggests that this meteorite is contaminated with terrestrial/extraterrestrial organics probably derived from Antarctic ice meltwater that had percolated through the meteorite. The detection of PAHs and L-amino acids in these Martian meteorites suggests that despite storage in the Antarctic ice, selective changes of certain chemical and mineralogical phases has occurred.

  2. Holocene records of geomagnetic field behavior from a north-south transect along the western Antarctic Peninsula

    Science.gov (United States)

    Brachfeld, S. A.; Shah, D. P.; St-Onge, M.; St-Onge, G.

    2013-12-01

    Geochronology is inherently difficult when working with Antarctic margin sediments. Radiocarbon dating and oxygen isotope stratigraphy are challenging or impossible in sites with poor preservation of biogenic calcite. Radiocarbon dating of the acid insoluble organic matter (AIOM) is further complicated by organically lean sediment and the presence of reworked organic carbon or detrital carbon from sedimentary rocks. These complications limit the ability to interpret a paleoclimate record. Geomagnetic paleointensity dating is a proven 'tuning' technique that has been successfully applied in several studies around the Antarctic margin. However, the reference curves to which these sites were tuned were constructed primarily from Northern Hemisphere data. Here we present paleomagnetic secular variation (PSV) and relative paleointensity (RPI) data from three Antarctic Peninsula sites that possess independent chronologies and which have moderate to ultra-high sedimentation rates (40 - 700 cm/ka). Maxwell Bay, located in the volcanic South Shetland Islands, is an ultra-high-resolution site with strongly magnetic sediments from which the Shallow Drilling (SHALDRIL) program recovered a 108-m record spanning the last 14 ka. Outer Barilari Bay and Hugo Island Trough, which lie to the South along the western Antarctic Peninsula, are moderate resolution sites with a high proportion of biogenic silica. Maxwell Bay and Bariliari Bay are unique in that they possess homogenous sediment and uniform magnetic mineral assemblages, while also preserving biogenic calcite, a rare combination on the Antarctic margin. All three sites preserve strong, stable remanent magnetizations with an easily isolated characteristic component and MAD values generally < 2°, with the exception of turbidites, intervals with abundant dropstones, and biosiliceous ooze intervals. Inclination values fluctuate between the present-day value at the cores sites (-58°) and the geomagnetic axial dipole inclination

  3. INTERPRETATIONS OF COMPLICATED FOLDED STRUCTURES AT THE LOWER PARTS OF ANTARCTIC AND GREENLAND ICE SHEETS

    Directory of Open Access Journals (Sweden)

    Alexey N. Markov

    2015-01-01

    Full Text Available Complicated folded structures were recently recorded by radar survey in the lower portions of the Antarctic and Greenland ice sheets. From a geological point of view the Antarctic and Greenland ice sheets are considered as geological features, while the ice is classified as sedimentary or metamorphic rock. In this regard the genesis of the ice sheets is analyzed from the perspective of geodynamics and metamorphism, and complicated folded structures on radar profiles are interpreted as tectonic and metamorphic structures. This study considers the processes of three kinds of tectonic structures: glacial diapirs, glacial diapir folds and glacial intrusions. Radar profiles not only capture ice flow structure but can also detect the thermobaric field in ice sheet, and in this case the complicated folded structures are interpreted as representative of recorded metastable boundaries of ice recrystallization.

  4. Variability in sea ice cover and climate elicit sex specific responses in an Antarctic predator

    Science.gov (United States)

    Labrousse, Sara; Sallée, Jean-Baptiste; Fraser, Alexander D.; Massom, Rob A.; Reid, Phillip; Hobbs, William; Guinet, Christophe; Harcourt, Robert; McMahon, Clive; Authier, Matthieu; Bailleul, Frédéric; Hindell, Mark A.; Charrassin, Jean-Benoit

    2017-01-01

    Contrasting regional changes in Southern Ocean sea ice have occurred over the last 30 years with distinct regional effects on ecosystem structure and function. Quantifying how Antarctic predators respond to such changes provides the context for predicting how climate variability/change will affect these assemblages into the future. Over an 11-year time-series, we examine how inter-annual variability in sea ice concentration and advance affect the foraging behaviour of a top Antarctic predator, the southern elephant seal. Females foraged longer in pack ice in years with greatest sea ice concentration and earliest sea ice advance, while males foraged longer in polynyas in years of lowest sea ice concentration. There was a positive relationship between near-surface meridional wind anomalies and female foraging effort, but not for males. This study reveals the complexities of foraging responses to climate forcing by a poleward migratory predator through varying sea ice property and dynamic anomalies. PMID:28233791

  5. Future Antarctic Bed Topography and Its Implications for Ice Sheet Dynamics

    Science.gov (United States)

    Adhikari, Surendra; Ivins, Erik R.; Larour, Eric Y.; Seroussi, Helene L.; Morlighem, Mathieu; Nowicki, S.

    2014-01-01

    The Antarctic bedrock is evolving as the solid Earth responds to the past and ongoing evolution of the ice sheet. A recently improved ice loading history suggests that the Antarctic Ice Sheet (AIS) has generally been losing its mass since the Last Glacial Maximum. In a sustained warming climate, the AIS is predicted to retreat at a greater pace, primarily via melting beneath the ice shelves.We employ the glacial isostatic adjustment (GIA) capability of the Ice Sheet System Model (ISSM) to combine these past and future ice loadings and provide the new solid Earth computations for the AIS.We find that past loading is relatively less important than future loading for the evolution of the future bed topography. Our computations predict that the West Antarctic Ice Sheet (WAIS) may uplift by a few meters and a few tens of meters at years AD 2100 and 2500, respectively, and that the East Antarctic Ice Sheet is likely to remain unchanged or subside minimally except around the Amery Ice Shelf. The Amundsen Sea Sector in particular is predicted to rise at the greatest rate; one hundred years of ice evolution in this region, for example, predicts that the coastline of Pine Island Bay will approach roughly 45mmyr-1 in viscoelastic vertical motion. Of particular importance, we systematically demonstrate that the effect of a pervasive and large GIA uplift in the WAIS is generally associated with the flattening of reverse bed slope, reduction of local sea depth, and thus the extension of grounding line (GL) towards the continental shelf. Using the 3-D higher-order ice flow capability of ISSM, such a migration of GL is shown to inhibit the ice flow. This negative feedback between the ice sheet and the solid Earth may promote stability in marine portions of the ice sheet in the future.

  6. Changes in Arctic and Antarctic Sea Ice as a Microcosm of Global Climate Change

    Science.gov (United States)

    Parkinson, Claire L.

    2014-01-01

    Polar sea ice is a key element of the climate system and has now been monitored through satellite observations for over three and a half decades. The satellite observations reveal considerable information about polar ice and its changes since the late 1970s, including a prominent downward trend in Arctic sea ice coverage and a much lesser upward trend in Antarctic sea ice coverage, illustrative of the important fact that climate change entails spatial contrasts. The decreasing ice coverage in the Arctic corresponds well with contemporaneous Arctic warming and exhibits particularly large decreases in the summers of 2007 and 2012, influenced by both preconditioning and atmospheric conditions. The increasing ice coverage in the Antarctic is not as readily explained, but spatial differences in the Antarctic trends suggest a possible connection with atmospheric circulation changes that have perhaps been influenced by the Antarctic ozone hole. The changes in the polar ice covers and the issues surrounding those changes have many commonalities with broader climate changes and their surrounding issues, allowing the sea ice changes to be viewed in some important ways as a microcosm of global climate change.

  7. Recent regional climate cooling on the Antarctic Peninsula and associated impacts on the cryosphere.

    Science.gov (United States)

    Oliva, M; Navarro, F; Hrbáček, F; Hernández, A; Nývlt, D; Pereira, P; Ruiz-Fernández, J; Trigo, R

    2017-02-15

    The Antarctic Peninsula (AP) is often described as a region with one of the largest warming trends on Earth since the 1950s, based on the temperature trend of 0.54°C/decade during 1951-2011 recorded at Faraday/Vernadsky station. Accordingly, most works describing the evolution of the natural systems in the AP region cite this extreme trend as the underlying cause of their observed changes. However, a recent analysis (Turner et al., 2016) has shown that the regionally stacked temperature record for the last three decades has shifted from a warming trend of 0.32°C/decade during 1979-1997 to a cooling trend of -0.47°C/decade during 1999-2014. While that study focuses on the period 1979-2014, averaging the data over the entire AP region, we here update and re-assess the spatially-distributed temperature trends and inter-decadal variability from 1950 to 2015, using data from ten stations distributed across the AP region. We show that Faraday/Vernadsky warming trend is an extreme case, circa twice those of the long-term records from other parts of the northern AP. Our results also indicate that the cooling initiated in 1998/1999 has been most significant in the N and NE of the AP and the South Shetland Islands (>0.5°C between the two last decades), modest in the Orkney Islands, and absent in the SW of the AP. This recent cooling has already impacted the cryosphere in the northern AP, including slow-down of glacier recession, a shift to surface mass gains of the peripheral glacier and a thinning of the active layer of permafrost in northern AP islands.

  8. The potential macroalgae habitat shifts in an Antarctic Peninsula fjord due to climate change

    Science.gov (United States)

    Jerosch, Kerstin; Scharf, Frauke; Deregibus, Dolores; Campana, Gabriela; Zacher, Katharina; Hass, Christian; Quartino, Liliana; Abele, Doris

    2016-04-01

    The Western Antarctic Peninsula (WAP) region is one of the most rapidly warming on earth since the last 50 yr. The WAP glaciers currently contribute one third of the melt water to global sea level rise. Climate warming is supposed to induce important changes in polar ecosystems, from microbial communities to apex predators' levels. Macroalgae are the main biomass producers in Potter Cove located at King George Island, the biggest island of the South Shetland Arc. They are sensitive to climate change factors such as suspended particulate matter (SPM). Macroalgae presence and absence data were used to test SDMs suitability and, simultaneously, to assess the environmental response of macroalgae as well as to model four scenarios of distribution shifts by varying SPM conditions due to climate change. Species distribution models (SDM) predict species occurrence based on statistical relationships with environmental conditions. The R-package 'biomod2' which includes 10 different SDM techniques and 10 different evaluation methods was used in this study. According to the averaged evaluation scores of Relative Operating Characteristics (ROC) and True scale statistics (TSS) by models, those methods based on a multitude of decision trees such as Random Forest and Classification Tree Analysis, reached the highest predictive power followed by generalized boosted models (GBM) and maximum-entropy approaches (Maxent). The final ensemble model (EM) used 135 of 200 calculated models (TSS > 0.7) and identified hard substrate and SPM as the most influencing parameters followed by distance to glacier, total organic carbon (TOC), bathymetry and slope. The modeled current status of macroalgae distribution results in only 18.25% of earlier estimated areas populated by macroalgae in Potter Cove. The climate change scenarios show an invasive reaction of the macroalgae in case of less SPM and a retreat of the macroalgae in case of higher assumed SPM values.

  9. Magnetostratigraphic Dating of Paleogene Sediments in the Seymour Island (Antarctic Peninsula): A Preliminary Chronostratigraphy

    Science.gov (United States)

    Beamud, E.; Montes, M. J.; Santillana, S.; Nozal, F.; Marenssi, S.

    2015-12-01

    Seymour Island is located at 64 º S, close to the northeastern tip of the Antarctic Peninsula. This glacier-free island contains the southernmost exposures of the K/Pg boundary and it has the most complete record of the Paleogene in Antarctica. The base of the Paleogene is represented by the Early Paleocene shallow marine shelf deposits of the Marambio Group; which are unconformably overlain by the Late Paleocene to Late Eocene Seymour Island Group. The Marambio Group is divided into the quartz-rich silty sandstones and mudstones of the López de Bertodano Fm and the mudstones to quartz-rich sandstones of the Sobral Fm. The overlaying Seymour Island Group records the erosion and filling of incised valleys. This group is made up by the Cross Valley-Wiman, La Meseta and the uppermost new Submeseta Formations. Main regressive periods are evidenced by the erosional unconformities and their related time gaps at the base of these three Formations. The La Meseta and Submeseta Formations are composed by poorly consolidated marine sandstones and siltstones deposited in a shallow coastal (possibly estuarine) environment. Several biostratigraphic and isotopic studies have been conducted in the Seymour Island due to its extremely rich fossil record, and the age of the López de Bertodano Fm has been recently refined by magnetostratigraphy. However, the overlying Paleogene formations lack a reliable absolute continuous dating. To solve this problem, a composite magnetostratigraphic section spanning more than 1300 m from the K/Pg boundary up to the top of the Submeseta Fm was conducted, with an average sampling resolution of 3 m per site. Although many samples yielded weak results, a local magnetostratigraphy was obtained which has been correlated to the GPTS. The new derived ages range from Danian (~ 66 Ma) up to Priabonian (~ 34 Ma). These results have been integrated with previous litho-, bio- and isotopic data to build a new Paleogene chronostratigraphy for the Seymour

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

    Science.gov (United States)

    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

  11. The association of Antarctic krill Euphausia superba with the under-ice habitat.

    Directory of Open Access Journals (Sweden)

    Hauke Flores

    Full Text Available The association of Antarctic krill Euphausia superba with the under-ice habitat was investigated in the Lazarev Sea (Southern Ocean during austral summer, autumn and winter. Data were obtained using novel Surface and Under Ice Trawls (SUIT, which sampled the 0-2 m surface layer both under sea ice and in open water. Average surface layer densities ranged between 0.8 individuals m(-2 in summer and autumn, and 2.7 individuals m(-2 in winter. In summer, under-ice densities of Antarctic krill were significantly higher than in open waters. In autumn, the opposite pattern was observed. Under winter sea ice, densities were often low, but repeatedly far exceeded summer and autumn maxima. Statistical models showed that during summer high densities of Antarctic krill in the 0-2 m layer were associated with high ice coverage and shallow mixed layer depths, among other factors. In autumn and winter, density was related to hydrographical parameters. Average under-ice densities from the 0-2 m layer were higher than corresponding values from the 0-200 m layer collected with Rectangular Midwater Trawls (RMT in summer. In winter, under-ice densities far surpassed maximum 0-200 m densities on several occasions. This indicates that the importance of the ice-water interface layer may be under-estimated by the pelagic nets and sonars commonly used to estimate the population size of Antarctic krill for management purposes, due to their limited ability to sample this habitat. Our results provide evidence for an almost year-round association of Antarctic krill with the under-ice habitat, hundreds of kilometres into the ice-covered area of the Lazarev Sea. Local concentrations of postlarval Antarctic krill under winter sea ice suggest that sea ice biota are important for their winter survival. These findings emphasise the susceptibility of an ecological key species to changing sea ice habitats, suggesting potential ramifications on Antarctic ecosystems induced by climate

  12. Dynamic Antarctic ice sheet during the early to mid-Miocene.

    Science.gov (United States)

    Gasson, Edward; DeConto, Robert M; Pollard, David; Levy, Richard H

    2016-03-29

    Geological data indicate that there were major variations in Antarctic ice sheet volume and extent during the early to mid-Miocene. Simulating such large-scale changes is problematic because of a strong hysteresis effect, which results in stability once the ice sheets have reached continental size. A relatively narrow range of atmospheric CO2 concentrations indicated by proxy records exacerbates this problem. Here, we are able to simulate large-scale variability of the early to mid-Miocene Antarctic ice sheet because of three developments in our modeling approach. (i) We use a climate-ice sheet coupling method utilizing a high-resolution atmospheric component to account for ice sheet-climate feedbacks. (ii) The ice sheet model includes recently proposed mechanisms for retreat into deep subglacial basins caused by ice-cliff failure and ice-shelf hydrofracture. (iii) We account for changes in the oxygen isotopic composition of the ice sheet by using isotope-enabled climate and ice sheet models. We compare our modeling results with ice-proximal records emerging from a sedimentological drill core from the Ross Sea (Andrill-2A) that is presented in a companion article. The variability in Antarctic ice volume that we simulate is equivalent to a seawater oxygen isotope signal of 0.52-0.66‰, or a sea level equivalent change of 30-36 m, for a range of atmospheric CO2 between 280 and 500 ppm and a changing astronomical configuration. This result represents a substantial advance in resolving the long-standing model data conflict of Miocene Antarctic ice sheet and sea level variability.

  13. Climate Model Dependency and Understanding the Antarctic Ice Sheet during the Warm Late Pliocene

    Science.gov (United States)

    Dolan, Aisling; de Boer, Bas; Bernales, Jorge; Hunter, Stephen; Haywood, Alan

    2016-04-01

    In the context of future climate change, understanding the nature and behaviour of ice sheets during warm intervals of Earth history is fundamentally important. A warm period in the Late Pliocene (3.264 to 3.025 million years before present) can serve as a potential analogue for projected future climates. Although Pliocene ice locations and extents are still poorly constrained, a significant contribution to sea-level rise should be expected from both the Greenland ice sheet and the West and East Antarctic ice sheets based on palaeo sea-level reconstructions and geological evidence. Following a five year international project PLISMIP (Pliocene Ice Sheet Modeling Intercomparison Project) we present the final set of results which quantify uncertainty in climate model-based predictions of the Antarctic ice sheet. In this study we use an ensemble of climate model forcings within a multi-ice sheet model framework to assess the climate (model) dependency of large scale features of the Antarctic ice sheet. Seven coupled atmosphere-ocean climate models are used to derive surface temperature, precipitation and oceanic forcing that drive three ice sheet models (over the grounded and floating domain). Similar to results presented over Greenland, we show that the reconstruction of the Antarctic ice sheet is sensitive to which climate model is used to provide the forcing field. Key areas of uncertainty include West Antarctica, the large subglacial basins of East Antarctica and the overall thickness of the continental interior of East Antarctica. We relate the results back to geological proxy data, such as those relating to exposure rates which provide information on potential ice sheet thickness. Finally we discuss as to whether the choice of modelling framework (i.e. climate model and ice sheet model used) or the choice of boundary conditions causes the greatest uncertainty in ice sheet reconstructions of the warm Pliocene.

  14. The Importance of History for Predicting the Future of the West Antarctic Ice Sheet

    Science.gov (United States)

    Bindschadler, R.

    2008-12-01

    The West Antarctic Ice Sheet (WAIS) initiative began in 1990, following on earlier studies of the 'Siple Coast' ice streams and the Ross Ice Shelf. The past nearly two decades of field and satellite research of the West Antarctic ice sheet have produced an astounding number of discoveries, not the least of which is the variability of the West Antarctic ice sheet on time scales from seconds (yes, seconds!) to many millennia. The shorter-time-scale variations, such as the recent acceleration and thinning of glaciers draining into the Amundsen Sea, have illustrated serious weaknesses in what were once regarded as excellent models of ice sheet dynamics. Repairing this modeling capability requires understanding and incorporating external and internal processes previously regarded as less important. Ice-sheet history remains the best means to test, tune and validate numerical models of ice sheets. Cenozoic-age behavior may seem too ancient to matter to a centennial-time-scale focus on the future, but it is precisely through a long history, that the variety of more extreme ice sheet configurations can be extracted. Such upper or lower bound estimates have served the WAIS community well over the years to help justify research needed to assess the probability of dramatic behavior. Now, with the necessity of model revisions central to the WAIS effort, time histories of ice sheet behavior over both short and long time scales will return to a position of extreme importance.

  15. Measurement of the fracture toughness of polycrystalline bubbly ice from an Antarctic ice core

    Directory of Open Access Journals (Sweden)

    J. Christmann

    2015-05-01

    Full Text Available The critical fracture toughness is a material parameter describing the resistance of a cracked body to further crack extension. It is an important parameter for simulating and predicting the breakup behavior of ice shelves from the calving of single icebergs to the disintegration of entire ice shelves over a wide range of length scales. The fracture toughness values are calculated with equations that are derived from an elastic stress analysis. Additionally, an X-ray computer tomography (CT scanner was used to identify the density as a function of depth. The critical fracture toughness of 91 Antarctic bubbly ice samples with densities between 840 and 870 kg m−3 has been determined by applying a four-point bending technique on single-edge v-notched beam samples. The examined ice core was drilled 70 m north of Kohnen Station, Dronnning Maud Land (75°00' S, 00°04' E; 2882 m. Supplementary data are available at doi:10.1594/PANGAEA.835321.

  16. Oxygen Isotope Mass-Balance Constraints on Pliocene Sea Level and East Antarctic Ice Sheet Stability

    Science.gov (United States)

    Winnick, M. J.; Caves, J. K.

    2015-12-01

    The mid-Pliocene Warm Period (MPWP, 3.3-2.9 Ma), with reconstructed atmospheric pCO2 of 350-450 ppm, represents a potential analogue for climate change in the near future. Current highly cited estimates place MPWP maximum global mean sea level (GMSL) at 21 ± 10 m above modern, requiring total loss of the Greenland (GIS) and marine West Antarctic Ice Sheets (WAIS) and a substantial loss of the East Antarctic Ice Sheet (EAIS), with only a concurrent 2-3 ºC rise in global temperature. Many estimates of Pliocene GMSL are based on the partitioning of oxygen isotope records from benthic foraminifera (δ18Ob) into changes in deep-sea temperatures and terrestrial ice sheets. These isotopic budgets are underpinned by the assumption that the δ18O of Antarctic ice (δ18Oi) was the same in the Pliocene as it is today, and while the sensitivity of δ18Ob to changing meltwater δ18O has been previously considered, these analyses neglect conservation of 18O/16O in the ocean-ice system. Using well-calibrated δ18O-temperature relationships for Antarctic precipitation along with estimates of Pliocene Antarctic surface temperatures, we argue that the δ18Oi of the Pliocene Antarctic ice sheet was at minimum 1‰-4‰ higher than present. Assuming conservation of 18O/16O in the ocean-ice system, this requires lower Pliocene seawater δ18O (δ18Osw) without a corresponding change in ice sheet mass. This effect alone accounts for 5%-20% of the δ18Ob difference between the MPWP interglacials and the modern. With this amended isotope budget, we suggest that Pliocene GMSL was likely 9-13.5 m and very likely 5-17 m above modern, which suggests the EAIS is less sensitive to radiative forcing than previously inferred from the geologic record.

  17. Fluxes of microbes, organic aerosols, dust, and methanesulfonate onto Greenland and Antarctic ice

    Directory of Open Access Journals (Sweden)

    P. B. Price

    2008-12-01

    Full Text Available Using a spectrofluorimeter with 224-nm laser excitation to measure fluorescence intensity at 300-μm depth intervals, we report results of the first comparative study of concentrations of microbial cells (using the spectrum of protein-bound tryptophan (Trp as a proxy and of aerosols with an autofluorescence spectrum different from Trp as a function of depth in ice cores from west Antarctica (WAIS Divide and Siple Dome and Greenland (GISP 2. The ratio of fluxes of microbial cells onto Antarctic Greenland ice is 0.23±0.11 and of non-Trp aerosols is 0.17±0.08, both of which are comparable to the ratio of fluxes of mineral dust at Antarctic and Greenland sites (0.09±0.06. In contrast, the ratio of fluxes of methanesulfonate (MSA onto Antarctic relative to Greenland sites is 1.86±0.4, a factor 20 higher. The lower fluxes of microbes, non-Trp aerosols, and dust onto Antarctic ice may be due to the smaller areas of their source regions, together with less favorable wind patterns for Antarctic ice than Greenland ice. We attribute the higher fluxes of MSA in Antarctic ice to the concentration of haptophytes, a phylum of marine algae, in the far more extensive sea ice margin around Antarctica than around Greenland. The similarity of flux ratios of microbes and non-Trp aerosols to dust flux ratios suggests that their source regions overlap with dust sources rather than with MSA sources. A new version of the spectrofluorimeter with additional channels for mapping chlorophyll and volcanic tephra will be used to map WAIS Divide ice at 1 mm intervals to bedrock.

  18. Fluxes of microbes, organic aerosols, dust, and methanesulfonate onto Greenland and Antarctic ice

    Science.gov (United States)

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

    2008-12-01

    Using a spectrofluorimeter with 224-nm laser excitation to measure fluorescence intensity at 300-μm depth intervals, we report results of the first comparative study of concentrations of microbial cells (using the spectrum of protein-bound tryptophan (Trp) as a proxy) and of aerosols with an autofluorescence spectrum different from Trp as a function of depth in ice cores from west Antarctica (WAIS Divide and Siple Dome) and Greenland (GISP 2). The ratio of fluxes of microbial cells onto Antarctic Greenland ice is 0.23±0.11 and of non-Trp aerosols is 0.17±0.08, both of which are comparable to the ratio of fluxes of mineral dust at Antarctic and Greenland sites (0.09±0.06). In contrast, the ratio of fluxes of methanesulfonate (MSA) onto Antarctic relative to Greenland sites is 1.86±0.4, a factor 20 higher. The lower fluxes of microbes, non-Trp aerosols, and dust onto Antarctic ice may be due to the smaller areas of their source regions, together with less favorable wind patterns for Antarctic ice than Greenland ice. We attribute the higher fluxes of MSA in Antarctic ice to the concentration of haptophytes, a phylum of marine algae, in the far more extensive sea ice margin around Antarctica than around Greenland. The similarity of flux ratios of microbes and non-Trp aerosols to dust flux ratios suggests that their source regions overlap with dust sources rather than with MSA sources. A new version of the spectrofluorimeter with additional channels for mapping chlorophyll and volcanic tephra will be used to map WAIS Divide ice at 1 mm intervals to bedrock.

  19. Incorporation of iron and organic matter into young Antarctic sea ice during its initial growth stages

    Directory of Open Access Journals (Sweden)

    Julie Janssens

    2016-08-01

    Full Text Available Abstract This study reports concentrations of iron (Fe and organic matter in young Antarctic pack ice and during its initial growth stages in situ. Although the importance of sea ice as an Fe reservoir for oceanic waters of the Southern Ocean has been clearly established, the processes leading to the enrichment of Fe in sea ice have yet to be investigated and quantified. We conducted two in situ sea-ice growth experiments during a winter cruise in the Weddell Sea. Our aim was to improve the understanding of the processes responsible for the accumulation of dissolved Fe (DFe and particulate Fe (PFe in sea ice, and of particulate organic carbon and nitrogen, dissolved organic carbon, extracellular polymeric substances, inorganic macro-nutrients (silicic acid, nitrate and nitrite, phosphate and ammonium, chlorophyll a and bacteria. Enrichment indices, calculated for natural young ice and ice newly formed in situ, indicate that during Antarctic winter all of the measured forms of particulate matter were enriched in sea ice compared to underlying seawater, and that enrichment started from the initial stages of sea-ice formation. Some dissolved material (DFe and ammonium was also enriched in the ice but at lower enrichment indices than the particulate phase, suggesting that size is a key factor for the incorporation of impurities in sea ice. Low chlorophyll a concentrations and the fit of the macro-nutrients (with the exception of ammonium with their theoretical dilution lines indicated low biological activity in the ice. From these and additional results we conclude that physical processes are the dominant mechanisms leading to the enrichment of DFe, PFe, organic matter and bacteria in young sea ice, and that PFe and DFe are decoupled during sea-ice formation. Our study thus provides unique quantitative insight into the initial incorporation of impurities, in particular DFe and PFe, into Antarctic sea ice.

  20. DMSP and DMS cycling within Antarctic sea ice during the winter-spring transition

    Science.gov (United States)

    Damm, E.; Nomura, D.; Martin, A.; Dieckmann, G. S.; Meiners, K. M.

    2016-09-01

    This study describes within-ice concentrations of dimethylsulfoniopropionate (DMSP), its degradation product dimethylsulphide (DMS), as well as nutrients and chlorophyll a, that were sampled during the Sea Ice Physics and Ecosystems eXperiment-2 (SIPEX-2) in 2012. DMSP is a methylated substrate produced in large amounts annually by ice-associated microalgae, while DMS plays a significant role in carbon and sulphur cycling in the Southern Ocean. In the East Antarctic study area between 115-125°E and 64-66°S, ice and slush cores, brine, under-ice seawater and zooplankton (Antarctic krill) samples were collected at 6 ice stations. The pack-ice was characterised by high snow loading which initiated flooding events and triggered nutrient supply to the sea-ice surface, while variation in ice conditions influenced sea-ice permeability. This ranged from impermeable surface and middle sections of the sea ice, to completely permeable ice cores at some stations. Chlorophyll a maxima shifted from the sea-ice surface horizon at the first station to the sea ice bottom layer at the last station. Highest DMSP concentrations were detected in brine samples at the sea-ice surface, reflecting a mismatch with respect to the distribution of chlorophyll a. Our data suggest enhanced DMSP production by sea-ice surface algal communities and its release into brine during freezing and melting, which in turn is coupled to flooding events early in the season. A time-cycle of DMS production by DMSP degradation and DMS efflux is evident at the sea ice-snow interface when slush is formed during melt. Seawater under the ice contained only low concentrations of DMSP and DMS, even when brine drainage was evident and the sea ice became permeable. We postulate that in situ grazing by zooplankton may act as sink for the DMSP produced early in the season.

  1. Were West Antarctic Ice Sheet grounding events in the Ross Sea a consequence of East Antarctic Ice Sheet expansion during the middle Miocene?

    Science.gov (United States)

    Bart, Philip J.

    2003-11-01

    Seismic correlation of glacial unconformities from the Ross Sea outer continental shelf to chronostratigraphic control at DSDP sites 272 and 273 indicates that at least two West Antarctic Ice Sheet (WAIS) expansions occurred during the early part of the middle Miocene (i.e. well before completion of continental-scale expansion of the East Antarctic Ice Sheet (EAIS) inferred from δ 18O and eustatic shifts). Therefore, if the volume of the EAIS was indeed relatively low, and if the Ross Sea age model is valid, then these WAIS expansions/contractions were not a direct consequence of EAIS expansion over the Transantarctic Mountains onto West Antarctica. An in-situ development of the WAIS during the middle Miocene suggests that either West Antarctic land elevations were above sea level and/or that air and water temperatures were sufficiently cold to support a marine-based ice sheet. Additional chronostratigraphic and lithologic data are needed from Antarctic margins to test these speculations.

  2. Effect of Cd on GSH and GSH-related enzymes of Chlamydomonas sp. ICE-L existing in Antarctic ice

    Institute of Scientific and Technical Information of China (English)

    DING Yu; MIAO Jin-lai; LI Guang-you; WANG Quan-fu; KAN Guang-feng; WANG Guo-dong

    2005-01-01

    Glutathione(GSH) and GSH-related enzymes play a great role in protecting organisms from oxidative damage. The GSH level and GSH-related enzymes activities were investigated as well as the growth yield and malonyldialdehyde(MDA) content in the Antarctic ice microalga Chlamydomonas sp. ICE-L exposure to the different cadmium concentration in this paper. The results showed that the higher concentration Cd inhibited the growth of ICE-L significantly and Cd would induce formation of MDA. At the same time, it is clear that GSH level, glutathione peroxidases(GPx) activity and glutathione S-transferases(GST), activity were higher in ICE-L exposed to Cd than the control. But GR activity dropped notably when ICE-L were cultured in the medium containing Cd. Increase of GSH level, GPx and GST activities acclimate to oxidative stress induced by Cd and protect Antarctic ice microalga Chlamydomonas sp. ICE-L from toxicity caused by Cd exposure. These parameters may be used to assess the biological impact of Cd in the Antarctic pole region environment.

  3. Extensive dynamic thinning on the margins of the Greenland and Antarctic ice sheets.

    Science.gov (United States)

    Pritchard, Hamish D; Arthern, Robert J; Vaughan, David G; Edwards, Laura A

    2009-10-15

    Many glaciers along the margins of the Greenland and Antarctic ice sheets are accelerating and, for this reason, contribute increasingly to global sea-level rise. Globally, ice losses contribute approximately 1.8 mm yr(-1) (ref. 8), but this could increase if the retreat of ice shelves and tidewater glaciers further enhances the loss of grounded ice or initiates the large-scale collapse of vulnerable parts of the ice sheets. Ice loss as a result of accelerated flow, known as dynamic thinning, is so poorly understood that its potential contribution to sea level over the twenty-first century remains unpredictable. Thinning on the ice-sheet scale has been monitored by using repeat satellite altimetry observations to track small changes in surface elevation, but previous sensors could not resolve most fast-flowing coastal glaciers. Here we report the use of high-resolution ICESat (Ice, Cloud and land Elevation Satellite) laser altimetry to map change along the entire grounded margins of the Greenland and Antarctic ice sheets. To isolate the dynamic signal, we compare rates of elevation change from both fast-flowing and slow-flowing ice with those expected from surface mass-balance fluctuations. We find that dynamic thinning of glaciers now reaches all latitudes in Greenland, has intensified on key Antarctic grounding lines, has endured for decades after ice-shelf collapse, penetrates far into the interior of each ice sheet and is spreading as ice shelves thin by ocean-driven melt. In Greenland, glaciers flowing faster than 100 m yr(-1) thinned at an average rate of 0.84 m yr(-1), and in the Amundsen Sea embayment of Antarctica, thinning exceeded 9.0 m yr(-1) for some glaciers. Our results show that the most profound changes in the ice sheets currently result from glacier dynamics at ocean margins.

  4. Hibernation in an antarctic fish: on ice for winter.

    Directory of Open Access Journals (Sweden)

    Hamish A Campbell

    Full Text Available Active metabolic suppression in anticipation of winter conditions has been demonstrated in species of mammals, birds, reptiles and amphibians, but not fish. This is because the reduction in metabolic rate in fish is directly proportional to the decrease in water temperature and they appear to be incapable of further suppressing their metabolic rate independently of temperature. However, the Antarctic fish (Notothenia coriiceps is unusual because it undergoes winter metabolic suppression irrespective of water temperature. We assessed the seasonal ecological strategy by monitoring swimming activity, growth, feeding and heart rate (f(H in N. coriiceps as they free-ranged within sub-zero waters. The metabolic rate of wild fish was extrapolated from f(H recordings, from oxygen consumption calibrations established in the laboratory prior to fish release. Throughout the summer months N. coriiceps spent a considerable proportion of its time foraging, resulting in a growth rate (G(w of 0.18 +/- 0.2% day(-1. In contrast, during winter much of the time was spent sedentary within a refuge and fish showed a net loss in G(w (-0.05 +/- 0.05% day(-1. Whilst inactive during winter, N. coriiceps displayed a very low f(H, reduced sensory and motor capabilities, and standard metabolic rate was one third lower than in summer. In a similar manner to other hibernating species, dormancy was interrupted with periodic arousals. These arousals, which lasted a few hours, occurred every 4-12 days. During arousal activity, f(H and metabolism increased to summer levels. This endogenous suppression and activation of metabolic processes, independent of body temperature, demonstrates that N. coriiceps were effectively 'putting themselves on ice' during winter months until food resources improved. This study demonstrates that at least some fish species can enter a dormant state similar to hibernation that is not temperature driven and presumably provides seasonal energetic

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

    Science.gov (United States)

    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.

  6. The suppression of Antarctic bottom water formation by melting ice shelves in Prydz Bay

    Science.gov (United States)

    Williams, G. D.; Herraiz-Borreguero, L.; Roquet, F.; Tamura, T.; Ohshima, K. I.; Fukamachi, Y.; Fraser, A. D.; Gao, L.; Chen, H.; McMahon, C. R.; Harcourt, R.; Hindell, M.

    2016-08-01

    A fourth production region for the globally important Antarctic bottom water has been attributed to dense shelf water formation in the Cape Darnley Polynya, adjoining Prydz Bay in East Antarctica. Here we show new observations from CTD-instrumented elephant seals in 2011-2013 that provide the first complete assessment of dense shelf water formation in Prydz Bay. After a complex evolution involving opposing contributions from three polynyas (positive) and two ice shelves (negative), dense shelf water (salinity 34.65-34.7) is exported through Prydz Channel. This provides a distinct, relatively fresh contribution to Cape Darnley bottom water. Elsewhere, dense water formation is hindered by the freshwater input from the Amery and West Ice Shelves into the Prydz Bay Gyre. This study highlights the susceptibility of Antarctic bottom water to increased freshwater input from the enhanced melting of ice shelves, and ultimately the potential collapse of Antarctic bottom water formation in a warming climate.

  7. The suppression of Antarctic bottom water formation by melting ice shelves in Prydz Bay.

    Science.gov (United States)

    Williams, G D; Herraiz-Borreguero, L; Roquet, F; Tamura, T; Ohshima, K I; Fukamachi, Y; Fraser, A D; Gao, L; Chen, H; McMahon, C R; Harcourt, R; Hindell, M

    2016-01-01

    A fourth production region for the globally important Antarctic bottom water has been attributed to dense shelf water formation in the Cape Darnley Polynya, adjoining Prydz Bay in East Antarctica. Here we show new observations from CTD-instrumented elephant seals in 2011-2013 that provide the first complete assessment of dense shelf water formation in Prydz Bay. After a complex evolution involving opposing contributions from three polynyas (positive) and two ice shelves (negative), dense shelf water (salinity 34.65-34.7) is exported through Prydz Channel. This provides a distinct, relatively fresh contribution to Cape Darnley bottom water. Elsewhere, dense water formation is hindered by the freshwater input from the Amery and West Ice Shelves into the Prydz Bay Gyre. This study highlights the susceptibility of Antarctic bottom water to increased freshwater input from the enhanced melting of ice shelves, and ultimately the potential collapse of Antarctic bottom water formation in a warming climate.

  8. The Brazilian research contribution to knowledge of the plant communities from Antarctic ice free areas

    Directory of Open Access Journals (Sweden)

    ANTONIO B. PEREIRA

    2013-09-01

    Full Text Available This work aims to summarize the results of research carried out by Brazilian researchers on the plant communities of Antarctic ice free areas during the last twenty five years. Since 1988 field work has been carried out in Elephant Island, King George Island, Nelson Island and Deception Island. During this period six papers were published on the chemistry of lichens, seven papers on plant taxonomy, five papers on plant biology, two studies on UVB photoprotection, three studies about the relationships between plant communities and bird colonies and eleven papers on plant communities from ice free areas. At the present, Brazilian botanists are researching the plant communities of Antarctic ice free areas in order to understand their relationships to soil microbial communities, the biodiversity, the distribution of the plants populations and their relationship with birds colonies. In addition to these activities, a group of Brazilian researchers are undertaking studies related to Antarctic plant genetic diversity, plant chemistry and their biotechnological applications.

  9. Diagnostic modeling of dimethylsulfide production in coastal water west of the Antarctic Peninsula

    Science.gov (United States)

    Hermann, Maria; Najjar, Raymond G.; Neeley, Aimee R.; Vila-Costa, Maria; Dacey, John W. H.; DiTullio, Giacomo, R.; Kieber, David J.; Kiene, Ronald P.; Matrai, Patricia A.; Simo, Rafel; Vernet, Maria

    2012-01-01

    The rate of gross biological dimethylsulfide (DMS) production at two coastal sites west of the Antarctic Peninsula, off Anvers Island, near Palmer Station, was estimated using a diagnostic approach that combined field measurements from 1 January 2006 through 1 March 2006 and a one-dimensional physical model of ocean mixing. The average DMS production rate in the upper water column (0-60 m) was estimated to be 3.1 +/- 0.6 nM/d at station B (closer to shore) and 2.7 +/- 0.6 nM/d1 at station E (further from shore). The estimated DMS replacement time was on the order of 1 d at both stations. DMS production was greater in the mixed layer than it was below the mixed layer. The average DMS production normalized to chlorophyll was 0.5 +/- nM/d)/(mg cubic m) at station B and 0.7 +/- 0.2 (nM/d)/(mg/cubic m3) at station E. When the diagnosed production rates were normalized to the observed concentrations of total dimethylsulfoniopropionate (DMSPt, the biogenic precursor of DMS), we found a remarkable similarity between our estimates at stations B and E (0.06 +/- 0.02 and 0.04 +/- 0.01 (nM DMS / d1)/(nM DMSP), respectively) and the results obtained in a previous study from a contrasting biogeochemical environment in the North Atlantic subtropical gyre (0.047 =/- 0.006 and 0.087 +/- 0.014 (nM DMS d1)/(nM DMSP) in a cyclonic and anticyclonic eddy, respectively).We propose that gross biological DMS production normalized to DMSPt might be relatively independent of the biogeochemical environment, and place our average estimate at 0.06 +/- 0.01 (nM DMS / d)/(nM DMSPt). The significance of this finding is that it can provide a means to use DMSPt measurements to extrapolate gross biological DMS production, which is extremely difficult to measure experimentally under realistic in situ conditions.

  10. Developmental History of an Intriguing Peat-Forming Community Along the West Antarctic Peninsula

    Science.gov (United States)

    Loisel, J.; Yu, Z.; Beilman, D.; Kaiser, K.

    2014-12-01

    Permafrost peatbanks along the West Antarctic Peninsula (WAP) have become valuable high-resolution archives for late-Holocene climatic conditions recently. We recently observed and studied a few water-saturated peatlands that had formed in rocky depressions near Vernadsky Station and in mainland Antarctica (~ 65°S, 64°W). Remarkably, we seem to be the very first ones to analyze these systems for environmental reconstructions. The similarity between these peatlands and fens from the lower latitudes is striking, and the rarity of these systems along the WAP is intriguing. We present a high-resolution, multi-proxy record of ecosystem development and paleoenvironmental conditions for Rasmussen peatland. The ecosystem is ~100 m2 in size and is characterized by a shallow water table depth at 7 cm below the surface. Surface vegetation is dominated by Calliergon spp., a wet-adapted moss found along the WAP. The studied moss deposit is 50 cm thick and has a high organic matter content (> 90% dry weight). Plant macrofossil analysis reveals that the peatland was initially a wet Sanionia spp. carpet and that a sharp transition to Calliergon spp. occurred about half way through the deposit. A distinct layer of highly decomposed organic matter was observed from 32 to 40 cm and could indicate a period of slowed peat formation, potentially due to dry conditions (enhanced peat decay) or perennial snow cover (limited plant growth). Biochemical decomposition indicators such as carbohydrate yields, acid:aldehyde ratios of lignin phenols, and hydroxyproline yields are being determined to better understand the extent of peat decay that has occurred at this site throughout its development, particularly to further address the nature of the observed stratigraphic changes. Preliminary results indicate that carbohydrate yields of the bottom half of the core are about 1/3 smaller than those of the top half, indicating substantial carbon loss due to decomposition. Overall, these peatlands

  11. Assessment of Arctic and Antarctic sea ice predictability in CMIP5 decadal hindcasts

    Science.gov (United States)

    Yang, Chao-Yuan; Liu, Jiping; Hu, Yongyun; Horton, Radley M.; Chen, Liqi; Cheng, Xiao

    2016-10-01

    This paper examines the ability of coupled global climate models to predict decadal variability of Arctic and Antarctic sea ice. We analyze decadal hindcasts/predictions of 11 Coupled Model Intercomparison Project Phase 5 (CMIP5) models. Decadal hindcasts exhibit a large multi-model spread in the simulated sea ice extent, with some models deviating significantly from the observations as the predicted ice extent quickly drifts away from the initial constraint. The anomaly correlation analysis between the decadal hindcast and observed sea ice suggests that in the Arctic, for most models, the areas showing significant predictive skill become broader associated with increasing lead times. This area expansion is largely because nearly all the models are capable of predicting the observed decreasing Arctic sea ice cover. Sea ice extent in the North Pacific has better predictive skill than that in the North Atlantic (particularly at a lead time of 3-7 years), but there is a re-emerging predictive skill in the North Atlantic at a lead time of 6-8 years. In contrast to the Arctic, Antarctic sea ice decadal hindcasts do not show broad predictive skill at any timescales, and there is no obvious improvement linking the areal extent of significant predictive skill to lead time increase. This might be because nearly all the models predict a retreating Antarctic sea ice cover, opposite to the observations. For the Arctic, the predictive skill of the multi-model ensemble mean outperforms most models and the persistence prediction at longer timescales, which is not the case for the Antarctic. Overall, for the Arctic, initialized decadal hindcasts show improved predictive skill compared to uninitialized simulations, although this improvement is not present in the Antarctic.

  12. High Abundance of the Epibenthic Trachymedusa Ptychogastria polaris Allman, 1878 (Hydrozoa, Trachylina) in Subpolar Fjords along the West Antarctic Peninsula

    Science.gov (United States)

    Smith, Craig R.; Lindsay, Dhugal J.; Bentlage, Bastian; Youngbluth, Marsh J.

    2017-01-01

    Medusae can be conspicuous and abundant members of seafloor communities in deep-sea benthic boundary layers. The epibenthic trachymedusa, Ptychogastria polaris Allman, 1878 (Hydrozoa: Trachylina: Ptychogastriidae) occurs in the cold, high latitude systems of both the northern and southern hemispheres, with a circumpolar distribution in Arctic and sub-Arctic areas, and disjunct reports of a few individuals from Antarctica. In January-February 2010, during benthic megafaunal photosurveys in three subpolar fjords along the West Antarctic Peninsula (Andvord, Flandres and Barilari Bays), P. polaris was recorded in Antarctic Peninsula waters. The trachymedusa, identified from megacore-collected specimens, was a common component of the epifauna in the sediment floored basins at 436–725 m depths in Andvord and Flandres Bays, reaching densities up to 13 m-2, with mean densities in individual basins ranging from 0.06 to 4.19 m-2. These densities are 2 to 400-fold higher than previously reported for P. polaris in either the Arctic or Antarctic. This trachymedusa had an aggregated distribution, occurring frequently in Andvord Bay, but was often solitary in Flandres Bay, with a distribution not significantly different from random. Epibenthic individuals were similar in size, typically measuring 15–25 mm in bell diameter. A morphologically similar trachymedusa, presumably the same species, was also observed in the water column near the bottom in all three fjords. This benthopelagic form attained abundances of up to 7 m-2 of seafloor; however, most P. polaris (~ 80%), were observed on soft sediments. Our findings indicate that fjords provide a prime habitat for the development of dense populations of P. polaris, potentially resulting from high and varied food inputs to the fjord floors. Because P. polaris resides in the water column and at the seafloor, large P. polaris populations may contribute significantly to pelagic-benthic coupling in the WAP fjord ecosystems. PMID

  13. Levels, sources and chemical fate of persistent organic pollutants in the atmosphere and snow along the western Antarctic Peninsula.

    Science.gov (United States)

    Khairy, Mohammed A; Luek, Jenna L; Dickhut, Rebecca; Lohmann, Rainer

    2016-09-01

    The Antarctic continent is among the most pristine regions; yet various organic contaminants have been measured there routinely. Air and snow samples were collected during the austral spring (October-November, 2010) along the western Antarctic Peninsula and analyzed for organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) to assess the relative importance of long-range transport versus local primary or secondary emissions. Highest concentrations of PCBs, PBDEs and DDTs were observed in the glacier's snow sample, highlighting the importance of melting glaciers as a possible secondary source of legacy pollutants to the Antarctic. In the atmosphere, contaminants were mainly found in the vapor phase (>65%). Hexachlorobenzene (33.6 pg/m(3)), PCBs (11.6 pg/m(3)), heptachlor (5.64 pg/m(3)), PBDEs (4.22 pg/m(3)) and cis-chlordane (2.43 pg/m(3)) were the most abundant contaminants. In contrast to other compounds, PBDEs seem to have originated from local sources, possibly the research station itself. Gas-particle partitioning for analytes were better predicted using the adsorption partitioning model than an octanol-based absorption approach. Diffusive flux calculations indicated that net deposition is the dominant pathway for PBDEs and chlordanes, whereas re-volatilization from snow (during melting or metamorphosis) was observed for PCBs and some OCPs.

  14. Sponge richness on algae-dominated rocky reefs in the western Antarctic Peninsula and the Magellan Strait

    Directory of Open Access Journals (Sweden)

    César A. Cárdenas

    2016-11-01

    Full Text Available Sponges are important components of high-latitude benthic communities, but their diversity and abundance in algal-dominated rocky reefs has been underestimated because of the difficulty of in situ identification. Further, the influence of canopy-forming algae on sponge richness has been poorly studied in southern high-latitude rocky reefs compared to other latitudes. Here, we quantified taxon richness of sponges in algae-dominated rocky reefs at three sites in the western Antarctic Peninsula (62–64° S and two sites in the Magellan region (53° S. We found higher sponge richness at sites in Antarctica (15 than in Magallanes (8, with Antarctic sponge richness higher than that reported for Arctic algal beds and similar to that reported for temperate regions. Estimated sponge richness at our Antarctic sites highlights diverse sponge assemblages (16–26 taxa between 5 and 20 m that are typically dominated by macroalgae. Our results suggest that sponge assemblages associated with canopy-forming macroalgae on southern high-latitude reefs are more diverse than previously thought.

  15. Plankton assembly in an ultra-oligotrophic Antarctic lake over the summer transition from the ice-cover to ice-free period: A size spectra approach

    Science.gov (United States)

    Rochera, Carlos; Quesada, Antonio; Toro, Manuel; Rico, Eugenio; Camacho, Antonio

    2017-03-01

    Lakes from the Antarctic maritime region experience climate change as a main stressor capable of modifying their plankton community structure and function, essentially because summer temperatures are commonly over the freezing point and the lake's ice cap thaws. This study was conducted in such seasonally ice-covered lake (Lake Limnopolar, Byers Peninsula, Livingston Is., Antarctica), which exhibits a microbial dominated pelagic food web. An important feature is also the occurrence of benthic mosses (Drepanocladus longifolius) covering the lake bottom. Plankton dynamics were investigated during the ice-thawing transition to the summer maximum. Both bacterioplankton and viral-like particles were higher near the lake's bottom, suggesting a benthic support. When the lake was under dim conditions because of the snow-and-ice cover, autotrophic picoplankters dominated at deep layers. The taxa-specific photopigments indicated dominance of picocyanobacteria among them when the light availability was lower. By contrast, larger and less edible phytoplankton dominated at the onset of the ice melting. The plankton size spectra were fitted to the continuous model of Pareto distribution. Spectra evolved similarly at two sampled depths, in surface and near the bottom, with slopes increasing until mid-January. However, slopes were less steep (i.e., size classes more uniformly distributed) at the bottom, thus denoting a more efficient utilization of resources. These findings suggest that microbial loop pathways in the lake are efficiently channelized during some periods to the metazoan production (mainly the copepod Boeckella poppei). Our results point to that trophic interactions may still occur in these lakes despite environmental harshness. This results of interest in a framework of increasing temperatures that may reduce the climatic restrictions and therefore stimulate biotic interactions.

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

    Science.gov (United States)

    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.

  17. Physicochemical control of bacterial and protist community composition and diversity in Antarctic sea ice.

    Science.gov (United States)

    Torstensson, Anders; Dinasquet, Julie; Chierici, Melissa; Fransson, Agneta; Riemann, Lasse; Wulff, Angela

    2015-10-01

    Due to climate change, sea ice experiences changes in terms of extent and physical properties. In order to understand how sea ice microbial communities are affected by changes in physicochemical properties of the ice, we used 454-sequencing of 16S and 18S rRNA genes to examine environmental control of microbial diversity and composition in Antarctic sea ice. We observed a high diversity and richness of bacteria, which were strongly negatively correlated with temperature and positively with brine salinity. We suggest that bacterial diversity in sea ice is mainly controlled by physicochemical properties of the ice, such as temperature and salinity, and that sea ice bacterial communities are sensitive to seasonal and environmental changes. For the first time in Antarctic interior sea ice, we observed a strong eukaryotic dominance of the dinoflagellate phylotype SL163A10, comprising 63% of the total sequences. This phylotype is known to be kleptoplastic and could be a significant primary producer in sea ice. We conclude that mixotrophic flagellates may play a greater role in the sea ice microbial ecosystem than previously believed, and not only during the polar night but also during summer when potential food sources are abundant.

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

    Science.gov (United States)

    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.

  19. In situ expression of eukaryotic ice-binding proteins in microbial communities of Arctic and Antarctic sea ice

    Science.gov (United States)

    Uhlig, Christiane; Kilpert, Fabian; Frickenhaus, Stephan; Kegel, Jessica U; Krell, Andreas; Mock, Thomas; Valentin, Klaus; Beszteri, Bánk

    2015-01-01

    Ice-binding proteins (IBPs) have been isolated from various sea-ice organisms. Their characterisation points to a crucial role in protecting the organisms in sub-zero environments. However, their in situ abundance and diversity in natural sea-ice microbial communities is largely unknown. In this study, we analysed the expression and phylogenetic diversity of eukaryotic IBP transcripts from microbial communities of Arctic and Antarctic sea ice. IBP transcripts were found in abundances similar to those of proteins involved in core cellular processes such as photosynthesis. Eighty-nine percent of the IBP transcripts grouped with known IBP sequences from diatoms, haptophytes and crustaceans, but the majority represented novel sequences not previously characterized in cultured organisms. The observed high eukaryotic IBP expression in natural eukaryotic sea ice communities underlines the essential role of IBPs for survival of many microorganisms in communities living under the extreme conditions of polar sea ice. PMID:25885562

  20. The sub-ice platelet layer and its influence on freeboard to thickness conversion of Antarctic sea ice

    Science.gov (United States)

    Price, D.; Rack, W.; Langhorne, P. J.; Haas, C.; Leonard, G.; Barnsdale, K.

    2014-06-01

    This is an investigation to quantify the influence of the sub-ice platelet layer on satellite measurements of total freeboard and their conversion to thickness of Antarctic sea ice. The sub-ice platelet layer forms as a result of the seaward advection of supercooled ice shelf water from beneath ice shelves. This ice shelf water provides an oceanic heat sink promoting the formation of platelet crystals which accumulate at the sea ice-ocean interface. The build-up of this porous layer increases sea ice freeboard, and if not accounted for, leads to overestimates of sea ice thickness from surface elevation measurements. In order to quantify this buoyant effect, the solid fraction of the sub-ice platelet layer must be estimated. An extensive in situ data set measured in 2011 in McMurdo Sound in the southwestern Ross Sea is used to achieve this. We use drill-hole measurements and the hydrostatic equilibrium assumption to estimate a mean value for the solid fraction of this sub-ice platelet layer of 0.16. This is highly dependent upon the uncertainty in sea ice density. We test this value with independent Global Navigation Satellite System (GNSS) surface elevation data to estimate sea ice thickness. We find that sea ice thickness can be overestimated by up to 19%, with a mean deviation of 12% as a result of the influence of the sub-ice platelet layer. It is concluded that within 100 km of an ice shelf this influence might need to be considered when undertaking sea ice thickness investigations using remote sensing surface elevation measurements.

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

    Science.gov (United States)

    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.

  2. Estimating small-scale snow depth and ice thickness from total freeboard for East Antarctic sea ice

    Science.gov (United States)

    Steer, Adam; Heil, Petra; Watson, Christopher; Massom, Robert A.; Lieser, Jan L.; Ozsoy-Cicek, Burcu

    2016-09-01

    Deriving the snow depth on Antarctic sea ice is a key factor in estimating sea-ice thickness distributions from space or airborne altimeters. Using a linear regression to model snow depth from observed 'total freeboard', or the snow/ice surface elevation relative to sea level is an efficient and promising method for the estimation of snow depth for instruments which only detect the uppermost surface of the sea-ice conglomerate (e.g. laser altimetry). However the Antarctic pack-ice zone is subject to substantial variability due to synoptic-scale weather forcing. Ice formation, motion and melt undergo large spatio-temporal variability throughout the year. In this paper we estimate snow depth from total freeboard for the ARISE (2003), SIPEX (2007) and SIPEX-II (2012) research voyages to the East Antarctic pack-ice zone. Using in situ data we investigate variability in snow depth and show that for East Antarctica, relationships between snow depth and total freeboard vary between each voyage. At a resolution of metres to tens of metres, we show how regression-based snow-depth models track total freeboard and generally over-estimate snow depth, especially on highly deformed sea ice and at sites where ice freeboard makes a substantial contribution to total freeboard. For a set of 3192 records we obtain an in situ mean snow depth of 0.21 m (σ = 0.19 m). Using a regression model derived from all in situ points we obtain the same mean, with a slightly lower variability (σ = 0.16 m). Using voyage-specific subsets of the data to derive regression models and estimate snow depth, mean snow depths ranged from 0.19 m (model derived from SIPEX observations) to 0.25 m (model derived from SIPEX-II observations). While small, these discrepancies impact ice thickness estimation using the assumption of hydrostatic equilibrium. Mean in situ ice thickness for all samples is 1.44 m (σ = 1.19 m). Using empirical models for snow depth, ice thickness varies from 1.0 to 1.8 m with the best

  3. Direct linking of Greenland and Antarctic ice cores at the Toba eruption (74 kyr BP

    Directory of Open Access Journals (Sweden)

    A. Svensson

    2012-11-01

    Full Text Available The Toba eruption that occurred some 74 kyr ago in Sumatra, Indonesia, is among the largest volcanic events on Earth over the last 2 million years. Tephra from this eruption has been spread over vast areas in Asia where it constitutes a major time marker close to the Marine Isotope Stage 4/5 boundary. As yet, no tephra associated with Toba has been identified in Greenland or Antarctic ice cores. Based on new accurate dating of Toba tephra from Malaysia and on accurately dated European stalagmites the Toba event is known to occur between the onsets of Greenland Interstadials (GI 19 and 20. Furthermore, the existing linking of Greenland and Antarctic ice cores by gas records and by the bipolar seesaw hypothesis suggests that the Antarctic counterpart is situated between Antarctic Isotope Maxima (AIM 19 and 20.

    In this work we suggest a direct synchronization of Greenland (NGRIP and Antarctic (EDML ice cores at the Toba eruption based on matching of a pattern of bipolar volcanic spikes. Annual layer counting between volcanic spikes in both cores allows for a unique match. We first demonstrate this bipolar matching technique at the already synchronized Laschamp geomagnetic excursion (41 kyr BP before we apply it to the suggested Toba interval. The Toba synchronization pattern covers some 2000 yr in GI-20 and AIM 19/20 and includes nine acidity peaks that are recognized in both ice cores.

    The suggested bipolar Toba synchronization has decadal precision. It thus allows a determination of the exact phasing of inter-hemispheric climate in a time interval of poorly constrained ice core records, and it allows for a discussion of the climatic impact of the Toba eruption in a global perspective. Furthermore, our bipolar match provides a way to place paleo-environmental records other than ice cores into a precise climatic context.

  4. Mapping and assessing variability in the Antarctic marginal ice zone, pack ice and coastal polynyas in two sea ice algorithms with implications on breeding success of snow petrels

    Science.gov (United States)

    Stroeve, Julienne C.; Jenouvrier, Stephanie; Campbell, G. Garrett; Barbraud, Christophe; Delord, Karine

    2016-08-01

    Sea ice variability within the marginal ice zone (MIZ) and polynyas plays an important role for phytoplankton productivity and krill abundance. Therefore, mapping their spatial extent as well as seasonal and interannual variability is essential for understanding how current and future changes in these biologically active regions may impact the Antarctic marine ecosystem. Knowledge of the distribution of MIZ, consolidated pack ice and coastal polynyas in the total Antarctic sea ice cover may also help to shed light on the factors contributing towards recent expansion of the Antarctic ice cover in some regions and contraction in others. The long-term passive microwave satellite data record provides the longest and most consistent record for assessing the proportion of the sea ice cover that is covered by each of these ice categories. However, estimates of the amount of MIZ, consolidated pack ice and polynyas depend strongly on which sea ice algorithm is used. This study uses two popular passive microwave sea ice algorithms, the NASA Team and Bootstrap, and applies the same thresholds to the sea ice concentrations to evaluate the distribution and variability in the MIZ, the consolidated pack ice and coastal polynyas. Results reveal that the seasonal cycle in the MIZ and pack ice is generally similar between both algorithms, yet the NASA Team algorithm has on average twice the MIZ and half the consolidated pack ice area as the Bootstrap algorithm. Trends also differ, with the Bootstrap algorithm suggesting statistically significant trends towards increased pack ice area and no statistically significant trends in the MIZ. The NASA Team algorithm on the other hand indicates statistically significant positive trends in the MIZ during spring. Potential coastal polynya area and amount of broken ice within the consolidated ice pack are also larger in the NASA Team algorithm. The timing of maximum polynya area may differ by as much as 5 months between algorithms. These

  5. Acclimation of Antarctic Chlamydomonas to the sea-ice environment: a transcriptomic analysis.

    Science.gov (United States)

    Liu, Chenlin; Wang, Xiuliang; Wang, Xingna; Sun, Chengjun

    2016-07-01

    The Antarctic green alga Chlamydomonas sp. ICE-L was isolated from sea ice. As a psychrophilic microalga, it can tolerate the environmental stress in the sea-ice brine, such as freezing temperature and high salinity. We performed a transcriptome analysis to identify freezing stress responding genes and explore the extreme environmental acclimation-related strategies. Here, we show that many genes in ICE-L transcriptome that encoding PUFA synthesis enzymes, molecular chaperon proteins, and cell membrane transport proteins have high similarity to the gens from Antarctic bacteria. These ICE-L genes are supposed to be acquired through horizontal gene transfer from its symbiotic microbes in the sea-ice brine. The presence of these genes in both sea-ice microalgae and bacteria indicated the biological processes they involved in are possibly contributing to ICE-L success in sea ice. In addition, the biological pathways were compared between ICE-L and its closely related sister species, Chlamydomonas reinhardtii and Volvox carteri. In ICE-L transcripome, many sequences homologous to the plant or bacteria proteins in the post-transcriptional, post-translational modification, and signal-transduction KEGG pathways, are absent in the nonpsychrophilic green algae. These complex structural components might imply enhanced stress adaptation capacity. At last, differential gene expression analysis at the transcriptome level of ICE-L indicated that genes that associated with post-translational modification, lipid metabolism, and nitrogen metabolism are responding to the freezing treatment. In conclusion, the transcriptome of Chlamydomonas sp. ICE-L is very useful for exploring the mutualistic interaction between microalgae and bacteria in sea ice; and discovering the specific genes and metabolism pathways responding to the freezing acclimation in psychrophilic microalgae.

  6. The sub-ice platelet layer and its influence on freeboard to thickness conversion of Antarctic sea ice

    Directory of Open Access Journals (Sweden)

    D. Price

    2014-02-01

    Full Text Available This is an investigation to quantify the influence of the sub-ice platelet layer on satellite measurements of total freeboard and their conversion to thickness of Antarctic sea ice. The sub-ice platelet layer forms as a result of the seaward advection of supercooled ice shelf water from beneath ice shelves. This ice shelf water provides an oceanic heat sink promoting the formation of platelet crystals which accumulate at the sea ice–ocean interface. The build-up of this porous layer increases sea ice freeboard, and if not accounted for, leads to overestimates of sea ice thickness from surface elevation measurements. In order to quantify this buoyant effect, the solid fraction of the sub-ice platelet layer must be estimated. An extensive in situ data set measured in 2011 in McMurdo Sound in the south-western Ross Sea is used to achieve this. We use drill-hole measurements and the hydrostatic equilibrium assumption to estimate a mean value for the solid fraction of this sub-ice platelet layer of 0.16. This is highly dependent upon the uncertainty in sea ice density. We test this value with independent Global Navigation Satellite System (GNSS surface elevation data to estimate sea ice thickness. We find that sea ice thickness can be overestimated by up to 19%, with a mean deviation of 12% as a result of the influence of the sub-ice platelet layer. It is concluded that in close proximity to ice shelves this influence should be considered universally when undertaking sea ice thickness investigations using remote sensing surface elevation measurements.

  7. Viruses and Protists Induced-mortality of Prokaryotes around the Antarctic Peninsula during the Austral Summer

    KAUST Repository

    Vaque, Dolors

    2017-03-27

    During the Austral summer 2009 we studied three areas surrounding the Antarctic Peninsula: the Bellingshausen Sea, the Bransfield Strait and the Weddell Sea. We aimed to investigate, whether viruses or protists were the main agents inducing prokaryotic mortality rates, and the sensitivity to temperature of prokaryotic heterotrophic production and mortality based on the activation energy (Ea) for each process. Seawater samples were taken at seven depths (0.1-100 m) to quantify viruses, prokaryotes and protists abundances, and heterotrophic prokaryotic production (PHP). Viral lytic production, lysogeny, and mortality rates of prokaryotes due to viruses and protists were estimated at surface (0.1-1 m) and at the Deep Fluorescence Maximum (DFM, 12-55 m) at eight representative stations of the three areas. The average viral lytic production ranged from 1.0 +/- 0.3 x 10(7) viruses ml(-1) d(-1) in the Bellingshausen Sea to1.3 +/- 0.7 x 10(7) viruses ml(-1) d(-1) in the Bransfield Strait, while lysogeny, when detectable, recorded the lowest value in the Bellingshausen Sea (0.05 +/- 0.05 x 10(7) viruses ml(-1) d(-1)) and the highest in the Weddell Sea (4.3 +/- 3.5 x 10(7) viruses ml(-1) d(-1)). Average mortality rates due to viruses ranged from 9.7 +/- 6.1 x 10(4) cells ml(-1) d(-1) in the Weddell Sea to 14.3 +/- 4.0 x 10(4) cells ml(-1) d(-1) in the Bellingshausen Sea, and were higher than averaged grazing rates in the Weddell Sea (5.9 +/- 1.1 x 10(4) cells ml(-1) d(-1)) and in the Bellingshausen Sea (6.8 +/- 0.9 x 10(4) cells ml-1 d(-1)). The highest impact on prokaryotes by viruses and main differences between viral and protists activities were observed in surface samples: 17.8 +/- 6.8 x 10(4) cells ml(-1) d(-1) and 6.5 +/- 3.9 x 10(4) cells ml(-1) d(-1) in the Weddell Sea; 22.1 +/- 9.6 x 10(4) cells ml(-1) d(-1) and 11.6 +/- 1.4 x 10(4) cells ml(-1) d(-1) in the Bransfield Strait; and 16.1 +/- 5.7 x 10(4) cells ml(-1) d(-1) and 7.9 +/- 2.6 x 10(4) cells ml(-1) d(-1) in

  8. Development and Applications of Dome A-DEM in Antarctic Ice Sheet

    Institute of Scientific and Technical Information of China (English)

    LIU Jiying; WEN Jiahong; WANG Yafeng; WANG Weili; Beata M CATHSO; Kenneth C JEZEK

    2007-01-01

    Dome A, the highest dome of East Antarctic Ice Sheet, is being an area focused by international Antarctic community after Chinese Antarctic Expedition finally reached there in 2005, and with the ongoing International Polar Year (IPY) during August 2007. In this paper two data processing methods are used together to generate two 100-m cell size digital elevation models (DEMs) of the Dome A region (Dome A-DEM) by using Cokriging method to interpolate the ICESat GLAS data, with Ihde-DEM as a constraint. It provides fundamental data to glaciological and geophysical investigation in this area. The Dome A-DEM was applied to determining the ice-sheet surface elevations and coordinates of the south and north summits, defining boundaries of basins and ice flowlines, deducing subglacial topography, and mapping surface slope and aspect in Dome A region. The DEM shows there are two (north and south) summits in Dome A region. The coordinate and the surface elevation of the highest point (the north summit) are 80°21'29.86"S, 77°21'50.29"E and 4092.71±1.43m, respectively. The ice thickness and sub-ice bedrock elevation at north summit are 2420m and 1672m, respectively. Dome A region contains four drainage basins that meet together near the south summit. Ice flowlines, slope and aspect in detail are also derived using the DEM.

  9. Impacts of warm water on Antarctic ice shelf stability through basal channel formation

    Science.gov (United States)

    Alley, Karen E.; Scambos, Ted A.; Siegfried, Matthew R.; Fricker, Helen Amanda

    2016-04-01

    Antarctica's ice shelves provide resistance to the flow of grounded ice towards the ocean. If this resistance is decreased as a result of ice shelf thinning or disintegration, acceleration of grounded ice can occur, increasing rates of sea-level rise. Loss of ice shelf mass is accelerating, especially in West Antarctica, where warm seawater is reaching ocean cavities beneath ice shelves. Here we use satellite imagery, airborne ice-penetrating radar and satellite laser altimetry spanning the period from 2002 to 2014 to map extensive basal channels in the ice shelves surrounding Antarctica. The highest density of basal channels is found in West Antarctic ice shelves. Within the channels, warm water flows northwards, eroding the ice shelf base and driving channel evolution on annual to decadal timescales. Our observations show that basal channels are associated with the development of new zones of crevassing, suggesting that these channels may cause ice fracture. We conclude that basal channels can form and grow quickly as a result of warm ocean water intrusion, and that they can structurally weaken ice shelves, potentially leading to rapid ice shelf loss in some areas.

  10. Towards quantifying the contribution of the Antarctic ice sheet to global sea level change

    NARCIS (Netherlands)

    van den Broeke, M.R.

    2006-01-01

    At present, the mass balance of the Antarctic Ice Sheet (AIS) and its contribution to global sea level change are poorly known. Current methods to determine AIS mass balance as well as the inherent uncertainties are discussed. Special emphasis is placed on the increasingly important role of regional

  11. Sympagic occurrence of Eusirid and Lysianassoid amphipods under Antarctic pack ice

    NARCIS (Netherlands)

    Krapp, R.H.; Berge, J.; Florentino De Souza Silva, A.P.; Gulliksen, B.; Werner, I.

    2008-01-01

    During three Antarctic expeditions (2004, ANT XXI-4 and XXII-2; 2006, ANT XXIII-6) with the German research icebreaker R/V Polarstern, six different amphipod species were recorded under the pack ice of the Weddell Sea and the Lazarev Sea. These cruises covered Austral autumn (April), summer (Decembe

  12. Ice Streams as the Critical Link Between the Interior Ice Reservoir of the Antarctic Ice Sheet and the Global Climate System - a WISSARD Perspective (Invited)

    Science.gov (United States)

    Tulaczyk, S. M.; Beem, L.; Walter, J. I.; Hossainzadeh, S.; Mankoff, K. D.

    2010-12-01

    Fast flowing ice streams represent crucial features of the Antarctic ice sheet because they provide discharge ‘valves’ for the interior ice reservoir and because their grounding lines are exposed to ocean thermal forcing. Even with no/little topographic control ice flow near the perimeter of a polar ice sheet self-organizes into discrete, fast-flowing ice streams. Within these features basal melting (i.e. lubrication for ice sliding) is sustained through elevated basal shear heating in a region of thin ice that would otherwise be characterized by basal freezing and slow ice motion. Because faster basal ice motion is typically associated with faster subglacial erosion, ice streams tend to localize themselves over time by carving troughs into underlying rocks and sediments. Debris generated by this erosional activity is carried to the continental shelf and/or continental slope where it may be deposited at very high rates, rivaling these associated with deposition by some of the largest rivers on Earth. In terms of their hydrologic and geological functions, Antarctic ice streams play pretty much the same role as rivers do on non-glaciated continents. However, understanding of their dynamics is still quite rudimentary, largely because of the relative inaccessibility of the key basal and marine boundaries of ice streams where pertinent measurements need to be made. The present elevated interest in predicting future contribution of Antarctica to global sea level changes is driving ambitious research programs aimed at scientific exploration of these poorly investigated environments that will play a key role in defining the response of the ice sheet to near future climate changes. We will review one of these programs, the Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) with particular focus on its planned contributions to understanding of ice stream dynamics.

  13. Ice core melt features in relation to Antarctic coastal climate

    NARCIS (Netherlands)

    Kaczmarska, M.; Isaksson, E.; Karlöf, L.; Brandt, O.; Winther, J.G.; van de Wal, R.S.W.; van den Broeke, M.R.; Johnsen, S.J.

    2006-01-01

    Measurement of light intensity transmission was carried out on an ice core S100 from coastal Dronning Maud Land (DML). Ice lenses were observed in digital pictures of the core and recorded as peaks in the light transmittance record. The frequency of ice layer occurrence was compared with climate pro

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

    Science.gov (United States)

    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

  15. Impact of surface wind biases on the Antarctic sea ice concentration budget in climate models

    Science.gov (United States)

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

    2016-09-01

    We derive the terms in the Antarctic sea ice concentration budget from the output of three models, and compare them to observations of the same terms. Those models include two climate models from the 5th Coupled Model Intercomparison Project (CMIP5) and one ocean-sea ice coupled model with prescribed atmospheric forcing. Sea ice drift and wind fields from those models, in average over April-October 1992-2005, all exhibit large differences with the available observational or reanalysis datasets. However, the discrepancies between the two distinct ice drift products or the two wind reanalyses used here are sometimes even greater than those differences. Two major findings stand out from the analysis. Firstly, large biases in sea ice drift speed and direction in exterior sectors of the sea ice covered region tend to be systematic and consistent with those in winds. This suggests that sea ice errors in these areas are most likely wind-driven, so as errors in the simulated ice motion vectors. The systematic nature of these biases is less prominent in interior sectors, nearer the coast, where sea ice is mechanically constrained and its motion in response to the wind forcing more depending on the model rheology. Second, the intimate relationship between winds, sea ice drift and the sea ice concentration budget gives insight on ways to categorize models with regard to errors in their ice dynamics. In exterior regions, models with seemingly too weak winds and slow ice drift consistently yield a lack of ice velocity divergence and hence a wrong wintertime sea ice growth rate. In interior sectors, too slow ice drift, presumably originating from issues in the physical representation of sea ice dynamics as much as from errors in surface winds, leads to wrong timing of the late winter ice retreat. Those results illustrate that the applied methodology provides a valuable tool for prioritizing model improvements based on the ice concentration budget-ice drift biases-wind biases

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

    Science.gov (United States)

    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.

  17. Polycyclic aromatic hydrocarbons (PAHs) in Antarctic Martian meteorites, carbonaceous chondrites, and polar ice

    Energy Technology Data Exchange (ETDEWEB)

    Becker, L. [Univ. of California, San Diego, La Jolla, CA (United States)]|[National Aeronautics and Space Administration, Moffett Field, CA (United States); Glavin, D.P.; Bada, J.L. [Univ. of California, San Diego, La Jolla, CA (United States)

    1997-01-01

    Recent analyses of the carbonate globules present in the Martian meteorite ALH84001 have detected polycyclic aromatic hydrocarbons (PAHs) at the ppm level. The distribution of PAHs observed in ALH84001 was interpreted as being inconsistent with a terrestrial origin and were claimed to be indigenous to the meteorite, perhaps derived from an ancient martian biota. We have examined PAHs in the Antarctic shergottite EETA79001, which is also considered to be from Mars, as well as several Antarctic carbonaceous chondrites. We have found that many of the same PAHs detected in the ALH84001 carbonate globules are present in Antarctic carbonaceous chondrites and in both the matrix and carbonate (druse) component of EETA79001. We also investigated PAHs in polar ice and found that carbonate is an effective scavenger of PAHs in ice meltwater. Moreover, the distribution of PAHs in the carbonate extract of Antarctic Allan Hills ice is remarkably similar to that found in both EETA79001 and ALH84001. The reported presence of L-amino acids of apparent terrestrial origin in the EETA79001 druse material suggests that this meteorite is contaminated with terrestrial organics probably derived from Antarctic ice meltwater that had percolated through the meteorite. Our data suggests that the PAHs observed in both ALH84001 and EETA79001 are derived from either the exogenous delivery of organics to Mars or extraterrestrial and terrestrial PAHs present in the ice meltwater or, more likely, from a mixture of these sources. It would appear that PAHs are not useful biomarkers in the search for extinct or extant life on Mars. 33 refs., 3 figs., 1 tab.

  18. A GIS-BASED GLACIER INVENTORY FOR THE ANTARCTIC PENINSULA AND THE SOUTH SHETLAND ISLANDS ——A FIRST CASE STUDY ON KING GEORGE ISLAND

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The aim of the international project “Global Land Ice Measurements from Space (GLIMS)" headed by the US Geological Survey is to establish a world wide glacier inventory based on satellite imagery.This data set will form a first digital baseline study for future glacier monitoring.The presented GIS_based glacier inventory for King George Island is a case study for the area of the Antarctic Peninsula.In the database of the glacier inventory topographic information,specific glaciological parameters as well as metadata will be included.The topographic data consists of drainage basin limits,basin areas,altitudinal ranges,perimeters and mean lengths.Glaciological data sets should comprise information on glacier retreat in different periods,glacier velocities,ice thickness and bedrock topography as well as derived parameters.Modelled and measured mass balance parameters could be included as additional data layers.In particular,these metadata records must comprise background information on data accuracy and data sources and should be compatible with a future data model for the King George Island GIS (KGIS).Three examples illustrate that the GLIMS database will not only contain information valuable for glaciological applications,but also other environmental studies on the island will benefit from this standardised remote sensing data sets.Therefore,a very close link between the data models of KGIS and GLIMS has to be established to enable these synergisms.Finally,better access to historic aerial photography would enable a continuous record of glacier retreat from the beginning of the 1950's onward.

  19. Evidence for link between modelled trends in Antarctic sea ice and underestimated westerly wind changes

    Science.gov (United States)

    Purich, Ariaan; Cai, Wenju; England, Matthew H.; Cowan, Tim

    2016-02-01

    Despite global warming, total Antarctic sea ice coverage increased over 1979-2013. However, the majority of Coupled Model Intercomparison Project phase 5 models simulate a decline. Mechanisms causing this discrepancy have so far remained elusive. Here we show that weaker trends in the intensification of the Southern Hemisphere westerly wind jet simulated by the models may contribute to this disparity. During austral summer, a strengthened jet leads to increased upwelling of cooler subsurface water and strengthened equatorward transport, conducive to increased sea ice. As the majority of models underestimate summer jet trends, this cooling process is underestimated compared with observations and is insufficient to offset warming in the models. Through the sea ice-albedo feedback, models produce a high-latitude surface ocean warming and sea ice decline, contrasting the observed net cooling and sea ice increase. A realistic simulation of observed wind changes may be crucial for reproducing the recent observed sea ice increase.

  20. Direct linking of Greenland and Antarctic ice cores at the Toba eruption (74 ka BP)

    Science.gov (United States)

    Svensson, A.; Bigler, M.; Fischer, H.; Johnsen, S. J.; Kipfstuhl, S.; Parrenin, F.; Rasmussen, S. O.; Steffensen, J. P.; Vinther, B. M.; Wegner, A.

    2012-04-01

    The Toba eruption that occurred some 74 ka ago in Sumatra, Indonesia, is among the largest volcanic events on Earth over the last 2 million years. Tephra from this eruption has been spread over vast areas in Asia where it constitutes a major reference horizon close to the Marine Isotope Stage 3/4 (MIS 3/4) boundary. Up to now, no tephra has been associated with Toba neither in Greenland nor in Antarctic ice cores, but based on Toba tephra identified in marine records from the Arabian Sea it is very likely that Greenland ice core acidity spikes related to Toba occur towards the end of Greenland Interstadial 20 (GI-20). Furthermore, the linking of Greenland and Antarctic ice cores by gas records suggests that the Antarctica counterpart should be situated between Antarctic Isotope Maxima (AIM) 19 and 20. In this work we suggest a direct synchronization of Greenland (NGRIP) and Antarctic (EDML) ice cores based on matching of a pattern of bi-polar volcanic spikes and annual layer counting in both cores around 74 ka BP. The synchronization pattern covers some 2000 years in GI-20 and AIM 19/20 and includes 5 major and several minor acidity peaks that are recognized in both ice cores. The most prominent acidity spikes in this time interval that occur towards the end of GI-20, are those thought to originate from Toba, but the proposed linking is independent of the source of the volcanic spikes. Although the linking of Greenland and Antarctic ice cores around Toba is already quite well constrained by matching of gas records, the relative phasing between ice cores from the two hemispheres still has some uncertainty related to the offset in the age of ice and air bubbles in the ice cores (delta-gas age). The identification of a direct Toba synchronization may help to determine the exact phasing of inter-hemispheric climate during this period and to constrain delta-gas ages. It also provides a way to place paleo-environmental records other than ice cores into a precise climatic

  1. Proteomic Alterations of Antarctic Ice Microalga Chlamydomonas sp. Under Low-Temperature Stress

    Institute of Scientific and Technical Information of China (English)

    Guang-Feng Kan; Jin-Lai Miao; Cui-Juan Shi; Guang-You Li

    2006-01-01

    Antarctic ice microalga can survive and thrive in cold channels or pores in the Antarctic ice layer. In order to understand the adaptive mechanisms to low temperature, in the present study we compared two-dimensional polyacrylamide gel electrophoresis (2-DE) profiles of normal and low temperature-stressed Antarctic ice microalga Chlamydomonas sp. cells. In addition, new protein spots induced by low temperature were identified with peptide mass fingerprinting based on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and database searching. Well-resolved and reproducible 2-DE patterns of both normal and low temperature-stressed cells were acquired. A total of 626 spots was detected in control cells and 652 spots were detected in the corresponding low temperature-stressed cells. A total of 598 spots was matched between normal and stressed cells. Two newly synthesized proteins (a and b) in low temperature-stressed cells were characterized. Protein spot A (53 kDa, pI 6.0) was similar to isopropylmalate/homocitrate/citramalate synthases, which act in the transport and metabolism of amino acids. Protein spot b (25 kDa, pI 8.0) was related to glutathione S-transferase, which functions as a scavenger of active oxygen, free radicals, and noxious metabolites. The present study is valuable for the application of ice microalgae, establishing an ice microalga Chlamydomonas sp. proteome database, and screening molecular biomarkers for further studies.

  2. Ice cores record significant 1940s Antarctic warmth related to tropical climate variability.

    Science.gov (United States)

    Schneider, David P; Steig, Eric J

    2008-08-26

    Although the 20th Century warming of global climate is well known, climate change in the high-latitude Southern Hemisphere (SH), especially in the first half of the century, remains poorly documented. We present a composite of water stable isotope data from high-resolution ice cores from the West Antarctic Ice Sheet. This record, representative of West Antarctic surface temperature, shows extreme positive anomalies in the 1936-45 decade that are significant in the context of the background 20th Century warming trend. We interpret these anomalies--previously undocumented in the high-latitude SH--as indicative of strong teleconnections in part driven by the major 1939-42 El Niño. These anomalies are coherent with tropical sea-surface temperature, mean SH air temperature, and North Pacific sea-level pressure, underscoring the sensitivity of West Antarctica's climate, and potentially its ice sheet, to large-scale changes in the global climate.

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

    Energy Technology Data Exchange (ETDEWEB)

    Asay-Davis, Xylar Storm [Potsdam Institute for Climate Impact Research, Potdam (Germany)

    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.

  4. Source-specific diatom lipid biomarkers as proxies for Arctic and Antarctic sea ice

    Science.gov (United States)

    Belt, Simon

    2016-04-01

    Sea ice plays a key role in controlling global climate due its influence over heat and gas exchange between the oceans and the atmosphere. In addition, sea ice exerts a strong influence over the absorption of incoming radiation at the ocean surface as a result of its high reflectivity or albedo. Driven, in part, by the recent dramatic changes to sea ice cover in both the Arctic and the Antarctic, the development of proxies for sea ice has received growing attention over the last 10 years or so. Amongst these, some so-called highly branched isoprenoid (HBI) lipid biomarkers have attracted considerable interest, not least, because they are derived from certain diatoms that reside and bloom within the sea ice matrix itself, thus providing a more direct indication of sea ice presence compared with some other proxies. The signature HBI sea proxies are a mono-unsaturated HBI (IP25) for the Arctic and a di-unsaturated HBI (C25:2) for the Antarctic, with different source organisms for each. Although the variability in sedimentary abundances of IP25 and C25:2 in Arctic and Antarctic sediments generally reflect the corresponding changes in sea ice conditions, a more complete picture of reconstructing sea ice conditions likely requires a multi-proxy approach involving, for example, other lipid biomarkers that serve as proxy measures of nearby open water conditions or sea surface temperature. By adoption of such an approach, a research strategy aimed at improving estimates of sea ice concentrations or better definitions of sea ice conditions (e.g. marginal ice zone, polynyas, permanent ice cover) represents the next stage in lipid-based sea ice proxy development. This presentation will focus on recent developments and future plans that involve a multi-proxy approach to improving sea ice reconstruction. An understanding of sources, ecology and environmental fate of various HBIs and other diatom lipids will likely be key in shaping the future direction of lipid-based sea ice

  5. Thermal Regime at the Base of the West-Antarctic Ice Stream Tributaries - is the Holocene Decay of the West Antarctic Ice Sheet Coming to an End?

    Science.gov (United States)

    Vogel, S. W.; Tulaczyk, S.; Joughin, I.

    2001-12-01

    The possible instability of the West-Antarctic Ice Sheet (WAIS) and its effects on global sea level was in the focus of Antarctic research for more then three decades, since Mercer (1968) proposed that the ice sheet collapsed during previous interglacials. Subsequent collection of field and remotely-sensed data has revealed, among other things, a complex structure in the WAIS drainage system and enabled us to better elucidate the basal processes that permit fast ice-stream motion under low driving stresses (e.g. Kamb, 2001). With high basal water pressures and a layer of weak, highly porous water saturated sediments playing a key role in facilitating the fast motion of ice in West-Antarctica, the spatial and temporal availability of basal water has to be incorporated into models simulating the present and future WAIS behavior. Borehole observations in the interior of the WAIS (Robin, 1983) and in the Siple Coast ice streams (Engelhardt and Kamb, 1987) revealed a wet ice sheet bed and the ice at the base of the ice sheet being at its pressure melting. However the recent discovery of an up to 25 m thick basal ice layer at Ice Stream C indicates that basal melting either does not persist along the entire ice stream tributaries or did not persisted in the past. Lacking direct observations from the ice stream tributaries we are currently using finite-difference and analytical models to assess their basal energy balance; heat conduction away from the bed, geothermal flux and shear heating. Taking into account the uncertainty in the estimation of the geothermal flux (50 to 80 mW*m\\^-2 ), the results of our calculations can be summarized as followed 1) the basal ice layer formed in the central part of the northern Ice Stream C tributary; 2) post Last Glacial Maximum conditions favor basal freezing in spite of higher surface temperatures; 3) the presence of a 12-25-m-thick basal ice layer request that either 3a) flow in the ice stream tributaries had stopped in the past

  6. Cook Inlet and Kenai Peninsula, Alaska ESI: ICE (Ice Extent Lines)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This data set contains locations of ice extent in Cook Inlet, Alaska. Vector lines in the data set represent 50 percent ice coverage. Location-specific type and...

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

    Science.gov (United States)

    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.

  8. Bacteria Biomass and Chlorophyll-a depth profiles from bottle casts off the western Antarctic Peninsula from the R/V LAURENCE M. GOULD from 23 April 2001 to 01 September 2001 (NODC Accession 0000820)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Bacteria and Chlorophyll data were collected from bottle cast of the western Antarctic peninsula from the R/V Laurence M. Gould. Data were collected by the...

  9. A smaller Antarctic Ice Sheet in the Pliocene and in the Future

    Science.gov (United States)

    DeConto, Robert; Pollard, David

    2013-04-01

    The middle Pliocene epoch (around 3.3 to 3) million years ago is often considered an analogue for future global climatic conditions, because mixing ratios of atmospheric CO2 were similar to today and global mean temperature was about 3°C warmer, comparable to projections of future climate at the end of this century (IPCC 2007). Importantly, some estimates of mid-Pliocene sea level are >20 m higher than today, implying the potential for significant retreat of the East Antarctic Ice Sheet (EAIS), in addition to complete loss of the Greenland and West Antarctic Ice Sheets (WAIS). Until now, most climate-ice sheet modeling studies have failed to simulate substantial Pliocene retreat of the East Antarctic ice margin, because at 400 ppmv CO2, atmospheric conditions on the steep flanks of the ice sheet remain relatively cold, even during the warmest austral summer orbits. Here, we use a hybrid ice sheet-shelf model coupled to a high-resolution regional climate model, to test the potential for both West and East Antarctic Ice Sheet retreat during the warm Pliocene and in the long-term future. In these simulations we apply new treatments of ice shelf calving and basal sliding (assuming a relationship between basal sliding coefficients and the rate of liquid water supply at the bed), and improved sub-glacial bathymetry using BEDMAP2. A range of plausible ocean warming scenarios (based on offline ocean modeling) are combined with the high-resolution regional climate model simulations to simulate the ice sheet's response to both Pliocene and long term future scenarios with elevated CO2. Unlike our previous studies, the combination of improved bathymetric detail and more physically based model treatments of calving and basal sliding result in substantial grounding line retreat into the Wilkes sub-glacial basin of East Antarctica during the Pliocene, adding several meters of equivalent sea level in addition to the contribution from a retreated WAIS. In long-term (10^3-yr

  10. Unexpectedly high ultrafine aerosol concentrations above East Antarctic sea-ice

    Directory of Open Access Journals (Sweden)

    R. S. Humphries

    2015-10-01

    Full Text Available The effect of aerosols on clouds and their radiative properties is one of the largest uncertainties in our understanding of radiative forcing. A recent study has concluded that better characterisation of pristine, natural aerosol processes leads to the largest reduction in these uncertainties. Antarctica, being far from anthropogenic activities, is an ideal location for the study of natural aerosol processes. Aerosol measurements in Antarctica are often limited to boundary layer air-masses at spatially sparse coastal and continental research stations, with only a handful of studies in the 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 ice-breaker 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 equator-ward into the low albedo Southern Ocean region, transporting with them emissions and these aerosol nuclei where, after growth, may potentially impact on the region's radiative balance. The high aerosol

  11. Dynamic ancient ice caps in the sub-Antarctic suggested by new mapping of submarine ice-formed landscapes

    Science.gov (United States)

    Graham, Alastair; Hodgson, Dominic; Cofaigh, Colm Ó.; Hillenbrand, Claus-Dieter; Kuhn, Gerhard

    2014-05-01

    Recent bathymetric investigations have provided hints of significant past glaciations on several Southern Ocean sub-polar islands. The extent and behaviour of ice cover in these regions is important because it provides critical limits on the evolution of refugia and marine benthic organisms, as well as unique far-field constraints for improving polar ice-sheet model sensitivity. However, despite improvements in regional mapping, sea-floor acoustic data from key shelf areas have still not been of sufficient quality, or broad enough in their coverage, to resolve the number, form or flow of past glacial episodes. Hence the history and style of sub-Antarctic glaciation remains poorly known. Here we use a compilation of multibeam bathymetry and fisheries echo-sounding data to provide evidence for dynamic, widespread ice caps on sub-Antarctic South Georgia during past glacial periods. We present a hitherto unmapped record of sea-bed glacigenic structures, including end moraines and subglacial landforms, from which the flow and form of at least three major, entirely marine-terminating configurations is resolved. The largest glaciation covered the majority of the continental shelf, and included fast-flowing outlets, possible switching of internal flow, meltwater activity, warm-based ice erosion, and substantial marginal deposition during retreat: all features of dynamic ice-cap behaviour. Existing biological evidence suggests the largest glaciation likely pre-dated the Last Glacial Maximum, which may have been restricted in extent reaching to the island's fjord mouths, while a third mid-shelf limit appears partially recorded. Work on dating the relict landscape of ancient ice cap advance and retreat is ongoing, but our preliminary age model suggests that South Georgia's history is unique from the Antarctic polar glacial record, and may be more similar to that of past ice caps on Patagonia. The glacial configurations revealed by these data will provide the basis of new

  12. Evaluation of soil bioremediation techniques in an aged diesel spill at the Antarctic Peninsula

    NARCIS (Netherlands)

    de Jesus, Hugo E.; Peixoto, Raquel S.; Cury, Juliano C.; van Elsas, Jan D.; Rosado, Alexandre S.

    2015-01-01

    Many areas on the Antarctic continent already suffer from the direct and indirect influences of human activities. The main cause of contamination is petroleum hydrocarbons because this compound is used as a source of energy at the many research stations around the continent. Thus, the current study

  13. The study on an Antarctic sea ice identification algorithm of the HY-2A microwave scatterometer data

    Institute of Scientific and Technical Information of China (English)

    ZOU Juhong; ZENG Tao; GUO Maohua; CUI Songxue

    2016-01-01

    An Antarctic sea ice identification algorithm on the HY-2A scatterometer (HSCAT) employs backscattering coefficient (σ0) and active polarization ratio (APR) for a preliminary sea ice identification. Then standard deviation (STD) filtering and space filtering are carried out. Finally, it is used to identify sea ice. A process uses aσ0, STD threshold and an APR as sea ice indicators. The sea ice identification results are verified using the sea ice distribution data of the ASMR2 released by the National Snow and Ice Data Center as a reference. The results show very good consistence of sea ice development trends, seasonal changes, area distribution, and sea ice edge distribution of the sea ice identification results obtained by this algorithm relative to the ASMR2 sea ice results. The accuracy of a sea ice coverage is 90.8% versus the ASMR2 sea ice results. This indicates that this algorithm is reliable.

  14. Comparing ice discharge through West Antarctic Gateways: Weddell vs. Amundsen Sea warming

    Directory of Open Access Journals (Sweden)

    M. A. Martin

    2015-03-01

    Full Text Available Future changes in Antarctic ice discharge will be largely controlled by the fate of the floating ice shelves, which exert a back-stress onto Antarctica's marine outlet glaciers. Ice loss in response to warming of the Amundsen Sea has been observed and investigated as a potential trigger for the marine ice-sheet instability. Recent observations and simulations suggest that the Amundsen Sea Sector might already be unstable which would have strong implications for global sea-level rise. At the same time, regional ocean projections show much stronger warm-water intrusion into ice-shelf cavities in the Weddell Sea compared to the observed Amundsen warming. Here we present results of numerical ice sheet modelling with the Parallel Ice Sheet Model (PISM which show that idealized, step-function type ocean warming in the Weddell Sea leads to more immediate ice discharge with a higher sensitivity to small warming levels than the same warming in the Amundsen Sea. This is consistent with the specific combination of bedrock and ice topography in the Weddell Sea Sector which results in an ice sheet close to floatation. In response to even slight ocean warming, ice loss increases rapidly, peaks and declines within one century. While the cumulative ice loss in the Amundsen Sea Sector is of similar magnitude after five centuries of continued warming, ice loss increases at a slower pace and only for significantly higher warming levels. Although there is more marine ice stored above sea level in close vicinity of the grounding line compared to the Weddell Sea Sector, the ice sheet is farther from floatation and the grounding line initially retreats more slowly.

  15. Deep Radiostratigraphy of the East Antarctic Plateau: Connecting the Dome C and Vostok Ice Core Sites

    Science.gov (United States)

    Cavitte, Marie G. P.; Blankenship, Donald D.; Young, Duncan A.; Schroeder, Dustin M.; Parrenin, Frederic; Lemeur, Emmanuel; Macgregor, Joseph A.; Siegert, Martin J.

    2016-01-01

    Several airborne radar-sounding surveys are used to trace internal reflections around the European Project for Ice Coring in Antarctica Dome C and Vostok ice core sites. Thirteen reflections, spanning the last two glacial cycles, are traced within 200 km of Dome C, a promising region for million-year-old ice, using the University of Texas Institute for Geophysics High-Capacity Radar Sounder. This provides a dated stratigraphy to 2318 m depth at Dome C. Reflection age uncertainties are calculated from the radar range precision and signal-to-noise ratio of the internal reflections. The radar stratigraphy matches well with the Multichannel Coherent Radar Depth Sounder (MCoRDS) radar stratigraphy obtained independently. We show that radar sounding enables the extension of ice core ages through the ice sheet with an additional radar-related age uncertainty of approximately 1/3-1/2 that of the ice cores. Reflections are extended along the Byrd-Totten Glacier divide, using University of Texas/Technical University of Denmark and MCoRDS surveys. However, core-to-core connection is impeded by pervasive aeolian terranes, and Lake Vostok's influence on reflection geometry. Poor radar connection of the two ice cores is attributed to these effects and suboptimal survey design in affected areas. We demonstrate that, while ice sheet internal radar reflections are generally isochronal and can be mapped over large distances, careful survey planning is necessary to extend ice core chronologies to distant regions of the East Antarctic ice sheet.

  16. A consistent data set of Antarctic ice sheet topography, cavity geometry, and global bathymetry

    Directory of Open Access Journals (Sweden)

    R. Timmermann

    2010-12-01

    Full Text Available Sub-ice shelf circulation and freezing/melting rates in ocean general circulation models depend critically on an accurate and consistent representation of cavity geometry. Existing global or pan-Antarctic topography data sets have turned out to contain various inconsistencies and inaccuracies. The goal of this work is to compile independent regional surveys and maps into a global data set. We use the S-2004 global 1-min bathymetry as the backbone and add an improved version of the BEDMAP topography (ALBMAP bedrock topography for an area that roughly coincides with the Antarctic continental shelf. The position of the merging line is individually chosen in different sectors in order to capture the best of both data sets. High-resolution gridded data for ice shelf topography and cavity geometry of the Amery, Fimbul, Filchner-Ronne, Larsen C and George VI Ice Shelves, and for Pine Island Glacier are carefully merged into the ambient ice and ocean topographies. Multibeam 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 blended into the existing bathymetry map. The resulting global 1-min Refined Topography data set (RTopo-1 contains self-consistent maps for upper and lower ice surface heights, bedrock topography, and surface type (open ocean, grounded ice, floating ice, bare land surface. The data set is available in NetCDF format from the PANGAEA database at doi:10.1594/pangaea.741917.

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

    Science.gov (United States)

    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

  18. Origin of spherule samples recovered from antarctic ice sheet-Terrestrial or extraterrestrial?

    Energy Technology Data Exchange (ETDEWEB)

    Sekimoto, Shun; Takamiya, Koichi; Shibata, Seiichi [Research Reactor Institute, Kyoto University, Osaka (Japan); Kobayashi, Takayuki [College of Humanities and Sciences, Nihon University, Tokyo (Japan); Ebihara, Mitsuru [Dept. of Chemistry, Tokyo Metropolitan University, Tokyo (Japan)

    2016-04-15

    Thirty-eight spherules from the Antarctic ice sheet were analyzed using neutron activation analysis under two different conditions to investigate their origin. In almost all of these spherules, the contents of iron, cobalt, and manganese were determined to be 31% to 88%, 17 mg/kg to 810 mg/kg, and 0.017% to 7%, respectively. A detectable iridium content of 0.84 mg/kg was found in only one spherule, which was judged to be extraterrestrial in origin. A comparison of elemental compositions of the Antarctic spherules analyzed in this study with those of deep-sea sediment spherules and those of terrestrial materials revealed that most of the Antarctic spherules except for the sample in which iridium was detected could not be identified as extraterrestrial in origin.

  19. Subsurface imaging reveals a confined aquifer beneath an ice-sealed Antarctic lake

    DEFF Research Database (Denmark)

    Dugan, H. A.; Doran, P. T.; Tulaczyk, S.;

    2015-01-01

    Liquid water oases are rare under extreme cold desert conditions found in the Antarctic McMurdo Dry Valleys. Here we report geophysical results that indicate that Lake Vida, one of the largest lakes in the region, is nearly frozen and underlain by widespread cryoconcentrated brine. A ground...... Geophysical survey finds low resistivities beneath a lake in Antarctic Dry Valleys Liquid brine abundant beneath Antarctic lake Aquifer provides microbial refugium in cold desert environment...... penetrating radar survey profiled 20 m into lake ice and facilitated bathymetric mapping of the upper lake basin. An airborne transient electromagnetic survey revealed a low-resistivity zone 30-100 m beneath the lake surface. Based on previous knowledge of brine chemistry and local geology, we interpret...

  20. Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene.

    Science.gov (United States)

    Levy, Richard; Harwood, David; Florindo, Fabio; Sangiorgi, Francesca; Tripati, Robert; von Eynatten, Hilmar; Gasson, Edward; Kuhn, Gerhard; Tripati, Aradhna; DeConto, Robert; Fielding, Christopher; Field, Brad; Golledge, Nicholas; McKay, Robert; Naish, Timothy; Olney, Matthew; Pollard, David; Schouten, Stefan; Talarico, Franco; Warny, Sophie; Willmott, Veronica; Acton, Gary; Panter, Kurt; Paulsen, Timothy; Taviani, Marco

    2016-03-29

    Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23-14 Mya) is a compelling interval to study as global temperatures and atmospheric CO2 concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3-4 °C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core identifies four distinct environmental motifs based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO2 concentrations were at or below preindustrial levels (∼280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (∼500 ppm) atmospheric CO2 These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO2 during the early to mid-Miocene.

  1. Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene

    Science.gov (United States)

    Levy, Richard; Harwood, David; Florindo, Fabio; Sangiorgi, Francesca; Tripati, Robert; von Eynatten, Hilmar; Gasson, Edward; Kuhn, Gerhard; Tripati, Aradhna; DeConto, Robert; Fielding, Christopher; Field, Brad; Golledge, Nicholas; McKay, Robert; Naish, Timothy; Olney, Matthew; Pollard, David; Schouten, Stefan; Talarico, Franco; Warny, Sophie; Willmott, Veronica; Acton, Gary; Panter, Kurt; Paulsen, Timothy; Taviani, Marco; SMS Science Team; Acton, Gary; Askin, Rosemary; Atkins, Clifford; Bassett, Kari; Beu, Alan; Blackstone, Brian; Browne, Gregory; Ceregato, Alessandro; Cody, Rosemary; Cornamusini, Gianluca; Corrado, Sveva; DeConto, Robert; Del Carlo, Paola; Di Vincenzo, Gianfranco; Dunbar, Gavin; Falk, Candice; Field, Brad; Fielding, Christopher; Florindo, Fabio; Frank, Tracy; Giorgetti, Giovanna; Grelle, Thomas; Gui, Zi; Handwerger, David; Hannah, Michael; Harwood, David M.; Hauptvogel, Dan; Hayden, Travis; Henrys, Stuart; Hoffmann, Stefan; Iacoviello, Francesco; Ishman, Scott; Jarrard, Richard; Johnson, Katherine; Jovane, Luigi; Judge, Shelley; Kominz, Michelle; Konfirst, Matthew; Krissek, Lawrence; Kuhn, Gerhard; Lacy, Laura; Levy, Richard; Maffioli, Paola; Magens, Diana; Marcano, Maria C.; Millan, Cristina; Mohr, Barbara; Montone, Paola; Mukasa, Samuel; Naish, Timothy; Niessen, Frank; Ohneiser, Christian; Olney, Mathew; Panter, Kurt; Passchier, Sandra; Patterson, Molly; Paulsen, Timothy; Pekar, Stephen; Pierdominici, Simona; Pollard, David; Raine, Ian; Reed, Joshua; Reichelt, Lucia; Riesselman, Christina; Rocchi, Sergio; Sagnotti, Leonardo; Sandroni, Sonia; Sangiorgi, Francesca; Schmitt, Douglas; Speece, Marvin; Storey, Bryan; Strada, Eleonora; Talarico, Franco; Taviani, Marco; Tuzzi, Eva; Verosub, Kenneth; von Eynatten, Hilmar; Warny, Sophie; Wilson, Gary; Wilson, Terry; Wonik, Thomas; Zattin, Massimiliano

    2016-03-01

    Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23-14 Mya) is a compelling interval to study as global temperatures and atmospheric CO2 concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3-4 °C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core identifies four distinct environmental motifs based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO2 concentrations were at or below preindustrial levels (˜280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (˜500 ppm) atmospheric CO2. These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO2 during the early to mid-Miocene.

  2. Source identification and distribution reveals the potential of the geochemical Antarctic sea ice proxy IPSO25

    Science.gov (United States)

    Belt, S. T.; Smik, L.; Brown, T. A.; Kim, J.-H.; Rowland, S. J.; Allen, C. S.; Gal, J.-K.; Shin, K.-H.; Lee, J. I.; Taylor, K. W. R.

    2016-01-01

    The presence of a di-unsaturated highly branched isoprenoid (HBI) lipid biomarker (diene II) in Southern Ocean sediments has previously been proposed as a proxy measure of palaeo Antarctic sea ice. Here we show that a source of diene II is the sympagic diatom Berkeleya adeliensis Medlin. Furthermore, the propensity for B. adeliensis to flourish in platelet ice is reflected by an offshore downward gradient in diene II concentration in >100 surface sediments from Antarctic coastal and near-coastal environments. Since platelet ice formation is strongly associated with super-cooled freshwater inflow, we further hypothesize that sedimentary diene II provides a potentially sensitive proxy indicator of landfast sea ice influenced by meltwater discharge from nearby glaciers and ice shelves, and re-examination of some previous diene II downcore records supports this hypothesis. The term IPSO25—Ice Proxy for the Southern Ocean with 25 carbon atoms—is proposed as a proxy name for diene II. PMID:27573030

  3. Modeling brine and nutrient dynamics in Antarctic sea ice: the case of dissolved silica

    Science.gov (United States)

    Vancoppenolle, M.; Goosse, H.; de Montety, A.; Fichefet, T.; Tremblay, B.; Tison, J.

    2009-12-01

    Sea ice ecosystems are characterized by micro-algae living in brine inclusions. The growth rate of ice algae depends on light and nutrient supply. Here, the interactions between nutrients and brine dynamics under the influence of algae are investigated using a one-dimensional model. The model includes snow and ice thermodynamics with brine physics and an idealized sea ice biological component, characterized by one nutrient, namely dissolved silica (DSi). In the model, DSi follows brine motion and is consumed by ice algae. Depending on physical ice characteristics, the brine flow is either advective, diffusive or turbulent. The vertical profiles of ice salinity and DSi concentration are solutions of advection-diffusion equations. The model is configured to simulate the typical thermodynamic regimes of first-year Antarctic pack ice. The simulated vertical profiles of salinity and DSi qualitatively reproduce observations. Analysis of results highlights the role of convection in the lowermost 5-10 cm of ice. Convection mixes saline, nutrient-poor brine with comparatively fresh, nutrient-rich seawater. This implies a rejection of salt to the ocean and a flux of DSi to the ice. In presence of growing algae, the simulated ocean-to-ice DSi flux increases by 0-115% compared to an abiotic situation. In turn, primary production and brine convection act in synergy to form a nutrient pump. The other important processes are the flooding of the surface by seawater and the percolation of meltwater. The former refills nutrients near the ice surface in spring. The latter, if present, tends to expell nutrients from the ice in summer. Sketch of salt (left) and nutrient (right) exchanges at the ice-ocean interface proposed in this paper.

  4. Satellite Remote Sensing of Snow Depth on Antarctic Sea Ice: An Inter-Comparison of Two Empirical Approaches

    OpenAIRE

    Stefan Kern; Burcu Ozsoy-Çiçek

    2016-01-01

    Snow on Antarctic sea ice plays a key role for sea ice physical processes and complicates retrieval of sea ice thickness using altimetry. Current methods of snow depth retrieval are based on satellite microwave radiometry, which perform best for dry, homogeneous snow packs on level sea ice. We introduce an alternative approach based on in-situ measurements of total (sea ice plus snow) freeboard and snow depth, which we use to compute snow depth on sea ice from Ice, Cloud, and land Elevation S...

  5. Antarctic Ice-Shelf Front Dynamics from ICESat

    Science.gov (United States)

    Robbins, John W.; Zwally, H. Jay; Saba, Jack L.; Yi, Donghui

    2012-01-01

    Time variable elevation profiles from ICESat Laser Altimetry over the period 2003-2009 provide a means to quantitatively detect and track topographic features on polar ice surfaces. The results of this study provide a measure of the horizontal motion of ice-shelf fronts. We examine the time histories of elevation profiles crossing the ice fronts of the Ross, Ronne, Filchner, Riiser-Larson and Fimbul shelves. This provides a basis for estimating dynamics in two dimensions, i.e. in elevation and horizontally in the along-track direction. Ice front velocities, corrected for ground-track intersection angle, range from nearly static to 1.1 km/yr. In many examples, a decrease in elevation up to 1 m/yr near the shelf frontis also detectable. Examples of tabular calving along shelf fronts are seen in some elevation profiles and are confirmed by corresponding MODIS imagery.

  6. Late Miocene-Pliocene Asian monsoon intensification linked to Antarctic ice-sheet growth

    Science.gov (United States)

    Ao, Hong; Roberts, Andrew P.; Dekkers, Mark J.; Liu, Xiaodong; Rohling, Eelco J.; Shi, Zhengguo; An, Zhisheng; Zhao, Xiang

    2016-06-01

    Environmental conditions in one of Earth's most densely populated regions, East Asia, are dominated by the monsoon. While Quaternary monsoon variability is reasonably well understood, pre-Quaternary monsoon variability and dynamics remain enigmatic. In particular, little is known about potential relationships between northern hemispheric monsoon response and major Cenozoic changes in Antarctic ice cover. Here we document long-term East Asian summer monsoon (EASM) intensification through the Late Miocene-Pliocene (∼8.2 to 2.6 Ma), and attribute this to progressive Antarctic glaciation. Our new high-resolution magnetic records of long-term EASM intensification come from the Late Miocene-Pliocene Red Clay sequence on the Chinese Loess Plateau; we identify underlying mechanisms using a numerical climate-model simulation of EASM response to an idealized stepwise increase in Antarctic ice volume. We infer that progressive Antarctic glaciation caused intensification of the cross-equatorial pressure gradient between an atmospheric high-pressure cell over Australia and a low-pressure cell over mid-latitude East Asia, as well as intensification of the cross-equatorial sea-surface temperature (SST) gradient. These combined atmospheric and oceanic adjustments led to EASM intensification. Our findings offer a new and more global perspective on the controls behind long-term Asian monsoon evolution.

  7. Aerosols in King George Island (Antarctic peninsula) using PIXE and alpha spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Dias da Cunha, K.; Medeiros, G., E-mail: kenya@ird.gov.b, E-mail: kenya@vdg.fis.puc-rio.b [Instituto de Radioprotecao e Dosimetria (IRD/CNEN-RJ), Rio de Janeiro, RJ (Brazil); Leal, M.A.; Lima, C. [Instituto Militar de Engenharia (IME), Rio de Janeiro, RJ (Brazil); Dalia, K.C. [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil). Centro de Ciencias da Saude; Barros Leite, C.V. [Pontificia Universidade Catolica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, RJ (Brazil)

    2009-07-01

    The aim of this study was to characterize the airborne particles and particles deposited in the recent snow samples collected at King George Island (Admiralty Bay) in order to evaluate the possible local sources of airborne particles and the aerosol transport from South America to Antarctic at sea level. Airborne particles samples were collected using a cascade impactor and cyclones at several sampling points at Admiralty Bay. Airborne particles were also collected during the ship travel from Rio de Janeiro to Antarctica. The recent snow samples and aerosols collected at several sampling points at Admiralty Bay were analyzed by PIXE for the determination of the elemental mass concentration. Snow samples were analyzed by alpha spectrometry to determine the 232Th, 228Th, 238U and 234U concentrations in snow. The Mass Median Aerodynamic Diameter of airborne particles was determined. The results suggest that there is a correlation between the aerosol samples and the particles deposited in the snow, but the elemental mass distributions are not equal. The snow elemental concentration can be used as an indicator of the elements present in the aerosols. The local aerosol sources (natural and anthropogenic) have been considered to characterize the aerosol transport to Antarctic, mainly King George Island. The main aerosol sources are the marine spray, weathering of local rocks and anthropogenic sources, as the diesel burning in the island. Besides the local aerosol sources the transport of airborne particles from south Atlantic to Antarctic is an important source of airborne particles at King George Island. (author)

  8. The Roles of Sea-Ice, Light and Sedimentation in Structuring Shallow Antarctic Benthic Communities.

    Science.gov (United States)

    Clark, Graeme F; Stark, Jonathan S; Palmer, Anne S; Riddle, Martin J; Johnston, Emma L

    2017-01-01

    On polar coasts, seasonal sea-ice duration strongly influences shallow marine environments by affecting environmental conditions, such as light, sedimentation, and physical disturbance. Sea-ice dynamics are changing in response to climate, but there is limited understanding of how this might affect shallow marine environments and benthos. Here we present a unique set of physical and biological data from a single region of Antarctic coast, and use it to gain insights into factors shaping polar benthic communities. At sites encompassing a gradient of sea-ice duration, we measured temporal and spatial variation in light and sedimentation and hard-substrate communities at different depths and substrate orientations. Biological trends were highly correlated with sea-ice duration, and appear to be driven by opposing gradients in light and sedimentation. As sea-ice duration decreased, there was increased light and reduced sedimentation, and concurrent shifts in community structure from invertebrate to algal dominance. Trends were strongest on shallower, horizontal surfaces, which are most exposed to light and sedimentation. Depth and substrate orientation appear to mediate exposure of benthos to these factors, thereby tempering effects of sea-ice and increasing biological heterogeneity. However, while light and sedimentation both varied spatially with sea-ice, their dynamics differed temporally. Light was sensitive to the site-specific date of sea-ice breakout, whereas sedimentation fluctuated at a regional scale coincident with the summer phytoplankton bloom. Sea-ice duration is clearly the overarching force structuring these shallow Antarctic benthic communities, but direct effects are imposed via light and sedimentation, and mediated by habitat characteristics.

  9. Proxies and measurement techinques for mineral dust in antarctic ice cores

    DEFF Research Database (Denmark)

    Ruth..[], Urs; Bigler, Matthias

    2008-01-01

    To improve quantitative interpretation of ice core aeolian dust records, a systematic methodological comparison was made. This involved methods for water-insoluble particle counting (Coulter counter and laser-sensing particle detector), soluble ion analysis (ion chromatography and continuous flow...... analysis), elemental analysis (inductively coupled plasma mass spectroscopy at pH 1 and after full acid digestion), and water-insoluble elemental analysis (proton induced X-ray emission). Antarctic ice core samples covering the last deglaciation from the EPICA Dome C (EDC) and the EPICA Dronning Maud Land...

  10. Direct linking of Greenland and Antarctic ice cores at the Toba eruption (74 ka BP

    Directory of Open Access Journals (Sweden)

    A. Svensson

    2013-03-01

    Full Text Available The Toba eruption that occurred some 74 ka ago in Sumatra, Indonesia, is among the largest volcanic events on Earth over the last 2 million years. Tephra from this eruption has been spread over vast areas in Asia, where it constitutes a major time marker close to the Marine Isotope Stage 4/5 boundary. As yet, no tephra associated with Toba has been identified in Greenland or Antarctic ice cores. Based on new accurate dating of Toba tephra and on accurately dated European stalagmites, the Toba event is known to occur between the onsets of Greenland interstadials (GI 19 and 20. Furthermore, the existing linking of Greenland and Antarctic ice cores by gas records and by the bipolar seesaw hypothesis suggests that the Antarctic counterpart is situated between Antarctic Isotope Maxima (AIM 19 and 20. In this work we suggest a direct synchronization of Greenland (NGRIP and Antarctic (EDML ice cores at the Toba eruption based on matching of a pattern of bipolar volcanic spikes. Annual layer counting between volcanic spikes in both cores allows for a unique match. We first demonstrate this bipolar matching technique at the already synchronized Laschamp geomagnetic excursion (41 ka BP before we apply it to the suggested Toba interval. The Toba synchronization pattern covers some 2000 yr in GI-20 and AIM-19/20 and includes nine acidity peaks that are recognized in both ice cores. The suggested bipolar Toba synchronization has decadal precision. It thus allows a determination of the exact phasing of inter-hemispheric climate in a time interval of poorly constrained ice core records, and it allows for a discussion of the climatic impact of the Toba eruption in a global perspective. The bipolar linking gives no support for a long-term global cooling caused by the Toba eruption as Antarctica experiences a major warming shortly after the event. Furthermore, our bipolar match provides a way to place palaeo-environmental records other than ice cores into a

  11. A seismological examination of the structure and tectonics of southernmost South America and the Antarctic Peninsula region

    Science.gov (United States)

    Maurice, Stacey Diane Robertson

    Three different seismological investigations of southernmost South America and the Antarctic Peninsula region are presented in this thesis. Using new data obtained from the Seismic Experiment in Patagonia and Antarctica, I invert regional waveforms, locate earthquake hypocenters, calculate focal mechanisms, and investigate Rayleigh wave phase velocities. These techniques all provide insight into the structure and tectonics of these unique regions. The crustal and upper mantle structure of southern South America is determined using a regional waveform inversion method that incorporates a niching genetic algorithm. This technique performs a broad search of the model space and enables examination of alternative local error minima. The vertical and transverse waveforms are used, and anisotropy is identified by solving for separate SV and SH structures in the upper mantle. Results indicate crustal thickness varies from 26 to 36 km, with thicker values towards the northeast, suggesting little crustal thickening beneath the Austral Andes. The average upper mantle velocities are similar to PREM, except in the southernmost region where velocities are 5% slower than PREM. The upper mantle has up to 5% polarization anisotropy. The anisotropic signature is limited to lithospheric depths and may imply the absence of a strong mantle flow pattern in the asthenosphere. In the Antarctic Peninsula region 150 local earthquake hypocenters are determined (mb 2--5), with locations and depths indicative of ongoing subduction. A local focal mechanism indicates shallow angle thrusting. The South Shetland trench thus represents an extreme end member of hot subduction resulting from slow convergence of young lithosphere, and the absence of intermediate depth earthquakes is consistent with thermal assimilation of the slab at shallow depths. Earthquake locations in the backarc are consistent with the propagation of spreading from northeast to southwest. Rayleigh wave phase velocity dispersion

  12. The role of organic ligands in iron cycling and primary productivity in the Antarctic Peninsula: A modeling study

    Science.gov (United States)

    Jiang, Mingshun; Barbeau, Katherine A.; Selph, Karen E.; Measures, Christopher I.; Buck, Kristen N.; Azam, Farooq; Greg Mitchell, B.; Zhou, Meng

    2013-06-01

    Iron (Fe) is the limiting nutrient for primary productivity in the Southern Ocean, with much of the dissolved iron (dFe) bound to organic ligands or colloids. A Fe model for the Southern Ocean (SOFe) is developed to understand the role of bacteria and organic ligands in controlling Fe cycling and productivity. The model resolves the classical food web and microbial loop, including three types of nutrients (N, Si, Fe) and two types of Fe ligands. Simulations of the zero-dimensional (0-D) model are calibrated with detailed results of shipboard grow-out incubation experiments conducted with Antarctic Peninsula phytoplankton communities during winter 2006 to provide the best estimate of key biological parameters. Then a one-dimensional (1-D) model is developed by coupling the biological model with the Regional Oceanic Modeling System (ROMS) for a site on the Antarctic Peninsula shelf, and the model parameters are further calibrated with data collected from two surveys (summer 2004 and winter 2006) in the area. The results of the numerical simulations agree reasonably well with observations. An analysis of the 1-D model results suggests that bacteria and organic ligands may play an important role in Fe cycling, which can be categorized into a relatively fast mode within the euphotic zone dominated by photo-reactions (summer d Fe residence time about 600 days) and complexation and a slow mode below with most of the dFe biologically complexed (summer dFe residence time >10 years). The dFe removal from the euphotic zone is dominated by colloidal formation and further aggregations with additional contribution from biological uptake, and an increase of organic ligands would reduce Fe export. The decrease of Fe removal rate over depth is due to the continuous dissolution and remineralization of particulate Fe. A number of sensitivity experiments are carried out for both 0-D and 1-D models to understand the importance of photo-reactive processes in primary productivity

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

    Science.gov (United States)

    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.

  14. MAGIC-DML: Mapping/Measuring/Modeling Antarctic Geomorphology & Ice Change in Dronning Maud Land

    Science.gov (United States)

    Rogozhina, Irina; Bernales, Jorge; Newall, Jennifer; Stroeven, Arjen; Harbor, Jonathan; Glasser, Neil; Fredin, Ola; Fabel, Derek; Hättestrand, Class; Lifton, Nat

    2016-04-01

    Reconstructing and predicting the response of the Antarctic Ice Sheet to climate change is one of the major challenges facing the Earth Science community. There are critical gaps in our knowledge of past changes in ice elevation and extent in many regions of East Antarctica, including a large area of Dronning Maud Land. An international Swedish-UK-US-Norwegian-German project MAGIC-DML aims to reconstruct the timing and pattern of ice surface elevation (thus ice sheet volume) fluctuations since the mid-Pliocene warm period on the Dronning Maud Land margin of the East Antarctic Ice Sheet. A combination of remotely sensed geomorphological mapping, field investigations, surface exposure dating and numerical modelling are being used in an iterative manner to produce a comprehensive reconstruction of the glacial history of Dronning Maud Land. Here we present the results from the first phase of this project, which involves high-resolution numerical simulations of the past glacial geometries and mapping of the field area using historic and recent aerial imagery together with a range of satellite acquired data.

  15. IMPACTS OF MESOGRAZERS ON EPIPHYTE AND ENDOPHYTE GROWTH ASSOCIATED WITH CHEMICALLY DEFENDED MACROALGE FROM THE WESTERN ANTARCTIC PENINSULA: A MESOCOSM EXPERIMENT(1).

    Science.gov (United States)

    Aumack, Craig F; Amsler, Charles D; McClintock, James B; Baker, Bill J

    2011-02-01

    It has been hypothesized that the extensive mesograzer community along the western Antarctic Peninsula regulates epiphytic algae as well as emergent filaments from endophytic species. Should grazing limit growth of fouling or potentially pathogenic microphytes, then Antarctic macrophytes may actually benefit from the remarkably high densities of mesograzer amphipods that occur in these waters. Although initially counterintuitive, the negative impacts of epi/endophyte fouling may outweigh stresses caused by limited amphipod grazing on chemically defended macrophytes by reducing stress from endo/epiphyte biomass. If so, then alleviating mesograzing stress should result in significant increases in endo/epiphytic biomass. To test this hypothesis, a mesocosm experiment was conducted. Individuals representing four common species of Antarctic macroalgae were placed in flow-through seawater mesocosms. Amphipods were added to five mesocosms at simulated natural densities, while the other five remained herbivore free. At the end of 7 weeks, endo/epiphytic growth on individual macrophytes was quantified. Most species of macroalgae demonstrated noticeably higher instances of endophyte coverage, epiphytic diversity, and diatom colonization in consumer-free mesocosms than in the presence of amphipods. These data suggest that macroalgae along the western Antarctic Peninsula rely on grazers to control populations of potentially harmful epiphytes. We hypothesize that the chemically defended macroalgal flora lives in mutualism with high densities of mesograzers, providing amphipods with shelter from predation while continually being cleaned of potentially harmful endo/epiphytes.

  16. History of views on the relative positions of Antarctica and South America: A 100-year tango between Patagonia and the Antarctic Peninsula

    Science.gov (United States)

    Miller, H.

    2007-01-01

    Discussion of continental drift around Antarctica began nearly 100 years ago. While the Gondwana connections of Antarctica to Africa and Australia have been well defined for decades, the relative pre-drift positions of the Antarctic Peninsula and Patagonia continue to be subjects of controversy. Certainly older figures, which showed a paleo-position of the Peninsula crossing over continental crust of the Falkland Plateau or even South Africa or Patagonia, are out of consideration now. But contradictory opinions remain over the relative paleo-position of the Peninsula as a more or less straight prolongation of the Patagonian Andes, versus a position parallel to Patagonia along the Pacific coast. Geological reasons are found for both opinions, but geophysical observations on the adjacent ocean floors, particularly the evolution of the Weddell Sea crust, speak for the last-mentioned reconstruction.

  17. Magnitude and timing of orbitally paced Antarctic ice sheet variations through the Pliocene and Pleistocene

    Science.gov (United States)

    Deconto, R.; Pollard, D.; Kowalewski, D. E.; Scherer, R. P.; Naish, T.; Seth, A.

    2009-12-01

    A new 3-D ice sheet-shelf model, Global Climate Model (GCM) and nested Regional Climate Model (RCM) are applied to the Antarctic region, with simulations designed to span the full range of Pliocene to modern climatic forcing. The ice sheet model simulates a dynamic West Antarctic Ice Sheet (WAIS), with repeated, sudden retreats and readvances throughout the Pliocene and Pleistocene. Simulated WAIS variability in the Pliocene is dominated by 40-kyr cyclicity. Major WAIS collapses are less frequent in the Pleistocene, but do occur during a number of apparent “super-interglacials”, including MIS 31. WAIS is shown to be most sensitive to changes in sub-ice oceanic melt, however changes in East Antarctic Ice Sheet (EAIS) volume driven by this mechanism are shown to be limited. Maximum equivalent sea level rise simulated by the model is ~7 m, most of which is contributed by WAIS retreat. This is significantly less than the amount required to match estimates of sea level during the Pliocene (~25-40 m) and some Pleistocene interglacials (e.g., MIS 11; 20+ m), even with an additional contribution from Greenland (~7 m). We use a nested, high resolution GCM-RCM to test the potential for an additional contribution to sea level rise via surface melt on the EAIS, but find that the combined forcing from elevated Pliocene CO2 (400 ppmv), increased oceanic heat flux and reduced sea ice, warm austral summer orbits, and the loss of WAIS do not provide enough additive warming to produce significant summer ablation on the flanks or interior of the EAIS. This important model-data discrepancy implies either that the ice sheet model is lacking some critical underlying physical processes, the climate model is undersensitive to greenhouse gas forcing, or the sea level estimates during these periods are unrealistically high. We conclude by exploring the potential for more EAIS variability in the ice model by considering alternative treatments of both the conditions at the bed of the ice

  18. Miocene to recent ice elevation variations from the interior of the West Antarctic ice sheet: Constraints from geologic observations, cosmogenic nuclides and ice sheet modeling

    Science.gov (United States)

    Mukhopadhyay, Sujoy; Ackert, Robert P.; Pope, Allen E.; Pollard, David; DeConto, Robert M.

    2012-07-01

    Observations of long-term West Antarctic Ice Sheet (WAIS) behavior can be used to test and constrain dynamic ice sheet models. Long-term observational constraints are however, rare. Here we present the first constraints on long-term (Miocene-Holocene) WAIS elevation from the interior of the ice sheet near the WAIS divide. We use geologic observations and measurements of cosmogenic 21Ne and 10Be in bedrock surfaces to constrain WAIS elevation variations to WAIS elevations to have been similar to, or lower than present, since the beginning of the Pliocene warm period. We use a continental ice sheet model to simulate the history of ice cover at our sampling sites and thereby compute the expected concentration of the cosmogenic nuclides. The ice sheet model indicates that during the past 5 Ma interior WAIS elevations of >65 m above present-day ice levels at the Ohio Range occur only rarely during brief ice sheet highstands, consistent with the observed cosmogenic nuclide data. Furthermore, the model's prediction that highstand elevations have increased on average since the Pliocene is in good agreement with the cosmogenic nuclide data that indicate the highest ice elevation over the past 5 Ma was reached during the highstand at 11 ka. Since the simulated cosmogenic nuclide concentrations derived from the model's ice elevation history are in good agreement with our measurements, we suggest that the model's prediction of more frequent collapsed-WAIS states and smaller WAIS volumes during the Pliocene are also correct.

  19. Characteristics and primary productivity of East Antarctic pack ice during the winter-spring transition

    Science.gov (United States)

    Ugalde, Sarah C.; Westwood, Karen J.; van den Enden, Rick; McMinn, Andrew; Meiners, Klaus M.

    2016-09-01

    Microbial communities have evolved mechanisms to allow them to survive within the challenging and changing pack ice environment. One such mechanism may be the exudation of photosynthetically-derived organic carbon into various extracellular pools. During the 2nd Sea Ice Physics and Ecosystems eXperiment (SIPEX-2), East Antarctic pack ice productivity and subsequent carbon allocation were quantified, together with physico-biogeochemical characteristics (29 September-28 October, 2012). Mean ice thickness ranged between 0.80 and 2.16 m, and typically exhibited a warm ice interior with weak temperature gradients. All stations, with one exception, were layered with granular (mean: 78%), columnar (mean: 15%), and mixed granular/columnar (mean: 4%) ice. Highest ice brine-volume fractions were at the ice-water interface, but all ice had high brine-volume fractions conducive for brine percolation (mean: 15%). Dissolved inorganic nutrient concentrations in the brine were scattered around theoretical dilution lines (TDLs), with some values of nitrate and nitrite, ammonium and silicic acid falling below TDLs, indicating nutrient depletion. Bulk ice dissolved organic carbon was low (mean: 64 μmol kg-1), but most samples showed enrichment in relation to TDLs. Microbial biomass (bacterial and algal) was low, and generally showed maxima in the sea-ice interior. Bottom ice algal communities were dominated by pennate diatom species (mean: 86% of total cell abundance). 14C-total primary productivity (14C-TPP) ranged from mean: 61%), with the remaining proportion allocated to 14C-colloidal organic carbon. Production of 14C-extracellular polymeric substances was not detected at any station.

  20. Penguin response to the Eocene climate and ecosystem change in the northern Antarctic Peninsula region

    Science.gov (United States)

    Jadwiszczak, Piotr

    2010-08-01

    Eocene Antarctic penguins are known solely from the La Meseta Formation (Seymour Island, James Ross Basin). They are most numerous and taxonomically diverse (at least ten species present) within strata formed at the end of this epoch, which is concomitant with a significant cooling trend and biotic turnover prior to the onset of glaciation. Moreover, all newly appeared taxa were small-bodied, and most probably evolved in situ. Interestingly, some chemical proxies suggest enhanced nutrient upwelling events that coincided with obvious changes in the record of La Meseta penguins.

  1. Modelling snowdrift sublimation on an Antarctic ice shelf

    NARCIS (Netherlands)

    Lenaerts, J.T.M.; van den Broeke, M.R.; Déry, S. J.; König-Langlo, G.; Ettema, J.; Kuipers Munneke, P.

    2010-01-01

    In this paper, we estimate the contribution of snowdrift sublimation (SUds) to the surface mass balance at Neumayer, located on the Ekström ice shelf in Eastern Antarctica. A single column version of the RACMO2-ANT model is used as a physical interpolation tool of high-quality radiosonde and surface

  2. An Antarctic ice core recording both supernovae and solar cycles

    CERN Document Server

    Motizuki, Yuko; Makishima, Kazuo; Bamba, Aya; Nakai, Yoichi; Yano, Yasushige; Igarashi, Makoto; Motoyama, Hideaki; Kamiyama, Kokichi; Suzuki, Keisuke; Imamura, Takashi

    2009-01-01

    Ice cores are known to be rich in information regarding past climates, and the possibility that they record astronomical phenomena has also been discussed. Rood et al. were the first to suggest, in 1979, that nitrate ion (NO3-) concentration spikes observed in the depth profile of a South Pole ice core might correlate with the known historical supernovae (SNe), Tycho (AD 1572), Kepler (AD 1604), and SN 1181 (AD 1181). Their findings, however, were not supported by subsequent examinations by different groups using different ice cores, and the results have remained controversial and confusing. Here we present a precision analysis of an ice core drilled in 2001 at Dome Fuji station in Antarctica. It revealed highly significant three NO3- spikes dating from the 10th to the 11th century. Two of them are coincident with SN 1006 (AD 1006) and the Crab Nebula SN (AD 1054), within the uncertainty of our absolute dating based on known volcanic signals. Moreover, by applying time-series analyses to the measured NO3- con...

  3. Drifting snow climate of the Antarctic and Greenland ice sheets

    NARCIS (Netherlands)

    Lenaerts, J.T.M.

    2013-01-01

    This study presents the drifting snow climate of the Earth's ice sheets, Antarctica and Greenland. For that purpose we use a regional atmospheric climate model, RACMO2. We included a routine that is able to calculate the drifting snow fluxes and accounts for the interaction between drifting snow on

  4. Dynamic response of Antarctic ice shelves to bedrock uncertainty

    Directory of Open Access Journals (Sweden)

    S. Sun

    2014-01-01

    Full Text Available Bedrock geometry is an essential boundary condition in ice sheet modelling. The shape of the bedrock on fine scales can influences ice sheet evolution, for example through the formation of pinning points that alter grounding line dynamics. Here we test the sensitivity of the BISICLES adaptive mesh ice sheet model to small amplitude height fluctuations on different spatial scales in the bed rock topography provided by bedmap2 in the catchments of Pine Island Glacier, the Amery Ice Shelf, and a region of East Antarctica including the Denman and Totten Glaciers. We generate an ensemble of bedrock topographies by adding random noise to the bedmap2 data with amplitude determined by the accompanying estimates of bedrock uncertainty. Lower frequency coherent noise, which generates broad spatial scale (over 10s of km errors in topography with relatively gently slopes, while higher frequency noise has steeper slopes over smaller spatial scales. We find that the small amplitude fluctuations result in only minor changes in the way these glaciers evolve. However, lower frequency noise is more important than higher frequency noise even when the features have the same height amplitudes and the total noise power is maintained. This provides optimism for credible sea level rise estimates with presently achievable densities of thickness measurements. Pine Island Glacier appears to be the most sensitive to errors in bed topography, while Lambert–Amery is stable under the present day observational data uncertainty. Totten–Denman region may undergo a retreat around Totten ice shelf, where the bedrock is lower than the sea level, especially if basal melt rates increase.

  5. New Visualizations Highlight New Information on the Contrasting Arctic and Antarctic Sea-Ice Trends Since the Late 1970s

    Science.gov (United States)

    Parkinson, Claire L.; DiGirolamo, Nicolo E.

    2016-01-01

    Month-by-month ranking of 37 years (1979-2015) of satellite-derived sea-ice extents in the Arctic and Antarctic reveals interesting new details in the overall trends toward decreasing sea-ice coverage in the Arctic and increasing sea-ice coverage in the Antarctic. The Arctic decreases are so definitive that there has not been a monthly record high in Arctic sea-ice extents in any month since 1986, a time period during which there have been 75 monthly record lows. The Antarctic, with the opposite but weaker trend toward increased ice extents, experienced monthly record lows in 5 months of 1986, then 6 later monthly record lows scattered through the dataset, with the last two occurring in 2006, versus 45 record highs since 1986. However, in the last three years of the 1979-2015 dataset, the downward trends in Arctic sea-ice extents eased up, with no new record lows in any month of 2013 or 2014 and only one record low in 2015,while the upward trends in Antarctic ice extents notably strengthened, with new record high ice extents in 4 months (August-November) of 2013, in 6 months (April- September) of 2014, and in 3 months (January, April, and May) of 2015. Globally, there have been only 3 monthly record highs since 1986 (only one since 1988), whereas there have been 43 record lows, although the last record lows (in the 1979-2015 dataset) occurred in 2012.

  6. Present-day and future Antarctic ice sheet climate and surface mass balance in the Community Earth System Model

    Science.gov (United States)

    Lenaerts, Jan T. M.; Vizcaino, Miren; Fyke, Jeremy; van Kampenhout, Leo; van den Broeke, Michiel R.

    2016-09-01

    We present climate and surface mass balance (SMB) of the Antarctic ice sheet (AIS) as simulated by the global, coupled ocean-atmosphere-land Community Earth System Model (CESM) with a horizontal resolution of {˜ }1° in the past, present and future (1850-2100). CESM correctly simulates present-day Antarctic sea ice extent, large-scale atmospheric circulation and near-surface climate, but fails to simulate the recent expansion of Antarctic sea ice. The present-day Antarctic ice sheet SMB equals 2280 ± 131 {Gt year^{-1}}, which concurs with existing independent estimates of AIS SMB. When forced by two CMIP5 climate change scenarios (high mitigation scenario RCP2.6 and high-emission scenario RCP8.5), CESM projects an increase of Antarctic ice sheet SMB of about 70 {Gt year^{-1}} per degree warming. This increase is driven by enhanced snowfall, which is partially counteracted by more surface melt and runoff along the ice sheet's edges. This intensifying hydrological cycle is predominantly driven by atmospheric warming, which increases (1) the moisture-carrying capacity of the atmosphere, (2) oceanic source region evaporation, and (3) summer AIS cloud liquid water content.

  7. Boundary layer new particle formation over East Antarctic sea ice – possible Hg-driven nucleation?

    Directory of Open Access Journals (Sweden)

    R. S. Humphries

    2015-12-01

    Full Text Available Aerosol observations above the Southern Ocean and Antarctic sea ice are scarce. Measurements of aerosols and atmospheric composition were made in East Antarctic pack ice on board the Australian icebreaker Aurora Australis during the spring of 2012. One particle formation event was observed during the 32 days of observations. This event occurred on the only day to exhibit extended periods of global irradiance in excess of 600 W m−2. Within the single air mass influencing the measurements, number concentrations of particles larger than 3 nm (CN3 reached almost 7700 cm−3 within a few hours of clouds clearing, and grew at rates of 5.6 nm h−1. Formation rates of 3 nm particles were in the range of those measured at other Antarctic locations at 0.2–1.1 ± 0.1 cm−3 s−1. Our investigations into the nucleation chemistry found that there were insufficient precursor concentrations for known halogen or organic chemistry to explain the nucleation event. Modelling studies utilising known sulfuric acid nucleation schemes could not simultaneously reproduce both particle formation or growth rates. Surprising correlations with total gaseous mercury (TGM were found that, together with other data, suggest a mercury-driven photochemical nucleation mechanism may be responsible for aerosol nucleation. Given the very low vapour pressures of the mercury species involved, this nucleation chemistry is likely only possible where pre-existing aerosol concentrations are low and both TGM concentrations and solar radiation levels are relatively high (∼ 1.5 ng m−3 and ≥ 600 W m−2, respectively, such as those observed in the Antarctic sea ice boundary layer in this study or in the global free troposphere, particularly in the Northern Hemisphere.

  8. Where is the evidence of past collapse of the West Antarctic Ice Sheet?

    Science.gov (United States)

    Gutowski, G.

    2015-12-01

    Sea level rise estimates from the Last Interglacial period suggest collapse of part of the Antarctic ice sheet. However, there is no direct evidence of this from the ice sheet itself. Englacial layers in ice sheets, sampled directly by ice core drilling and indirectly by ice-penetrating radar, reveal a significant amount about glacial change over time and may contain a signature of the last ice sheet collapse. We hypothesize there is evidence of ice sheet instability where the observed englacial record deviates from that expected for a steady state WAIS simulated using ice sheet models. However, discrepancies between modeled steady state and observed englacial layer geometry are confounded by uncertainties in model boundary conditions, observed layer ages, and model parameters. To know where the signal of collapse may be best preserved, we must account for the affect of these uncertainties on layer geometry. We present several tests quantifying the sensitivity of simulated layer geometry to changes in model boundary conditions. We look to areas where englacial geometry has low sensitivity to uncertain boundary conditions to provide the largest signal of ice sheet instability. Where simulated layer geometry is responding strongly to uncertain boundary conditions, we are unlikely to be able to discern a signal of past deglaciation. In the latter case, uncertainty in layer geometry may overwhelm the signal of past ice sheet collapse. We perform the simulations using the Variational Glacier Simulator (VarGlaS), an ice sheet model with the capacity to model the age of englacial isochrones (Figure 1). We use the latest boundary conditions for geothermal flux, basal topography, and surface mass balance to simulate the steady state behavior of englacial layers in the Thwaites Glacier catchment and the Marie Byrd Land dome. Ensembles of model runs sample the uncertainty in each of the boundary conditions, creating a distribution of simulated englacial layers which accounts

  9. Antifreeze protein-induced superheating of ice inside Antarctic notothenioid fishes inhibits melting during summer warming.

    Science.gov (United States)

    Cziko, Paul A; DeVries, Arthur L; Evans, Clive W; Cheng, Chi-Hing Christina

    2014-10-07

    Antifreeze proteins (AFPs) of polar marine teleost fishes are widely recognized as an evolutionary innovation of vast adaptive value in that, by adsorbing to and inhibiting the growth of internalized environmental ice crystals, they prevent death by inoculative freezing. Paradoxically, systemic accumulation of AFP-stabilized ice could also be lethal. Whether or how fishes eliminate internal ice is unknown. To investigate if ice inside high-latitude Antarctic notothenioid fishes could melt seasonally, we measured its melting point and obtained a decadal temperature record from a shallow benthic fish habitat in McMurdo Sound, Antarctica. We found that AFP-stabilized ice resists melting at temperatures above the expected equilibrium freezing/melting point (eqFMP), both in vitro and in vivo. Superheated ice was directly observed in notothenioid serum samples and in solutions of purified AFPs, and ice was found to persist inside live fishes at temperatures more than 1 °C above their eqFMP for at least 24 h, and at a lower temperature for at least several days. Field experiments confirmed that superheated ice occurs naturally inside wild fishes. Over the long-term record (1999-2012), seawater temperature surpassed the fish eqFMP in most summers, but never exceeded the highest temperature at which ice persisted inside experimental fishes. Thus, because of the effects of AFP-induced melting inhibition, summer warming may not reliably eliminate internal ice. Our results expose a potentially antagonistic pleiotropic effect of AFPs: beneficial freezing avoidance is accompanied by melting inhibition that may contribute to lifelong accumulation of detrimental internal ice crystals.

  10. Effect of elevated CO2 concentration on microalgal communities in Antarctic pack ice

    Science.gov (United States)

    Coad, Thomas; McMinn, Andrew; Nomura, Daiki; Martin, Andrew

    2016-09-01

    Increased anthropogenic CO2 emissions are causing changes to oceanic pH and CO2 concentrations that will impact many marine organisms, including microalgae. Phytoplankton taxa have shown mixed responses to these changes with some doing well while others have been adversely affected. Here, the photosynthetic response of sea-ice algal communities from Antarctic pack ice (brine and infiltration microbial communities) to a range of CO2 concentrations (400 ppm to 11,000 ppm in brine algae experiments, 400 ppm to 20,000 ppm in the infiltration ice algae experiment) was investigated. Incubations were conducted as part of the Sea-Ice Physics and Ecosystem Experiment II (SIPEX-2) voyage, in the austral spring (September-November), 2012. In the brine incubations, maximum quantum yield (Fv/Fm) and relative electron transfer rate (rETRmax) were highest at ambient and 0.049% (experiment 1) and 0.19% (experiment 2) CO2 concentrations, although, Fv/Fm was consistently between 0.53±0.10-0.68±0.01 across all treatments in both experiments. Highest rETRmax was exhibited by brine cultures exposed to ambient CO2 concentrations (60.15). In a third experiment infiltration ice algal communities were allowed to melt into seawater modified to simulate the changed pH and CO2 concentrations of future springtime ice-edge conditions. Ambient and 0.1% CO2 treatments had the highest growth rates and Fv/Fm values but only the highest CO2 concentration produced a significantly lower rETRmax. These experiments, conducted on natural Antarctic sea-ice algal communities, indicate a strong level of tolerance to elevated CO2 concentrations and suggest that these communities might not be adversely affected by predicted changes in CO2 concentration over the next century.

  11. Postglacial relative sea level change at Fildes Peninsula, King George Island (West Antarctic

    Directory of Open Access Journals (Sweden)

    K. V. Polishchuk

    2016-01-01

    Full Text Available Analysis and integration of data obtained in our field and laboratory investigations of 2008–2012 together with results of previous paleogeographic studies were conducted to reveal parameters and factors of the post-glacial changes in the relative sea-level on the Fildes Peninsula and the King George Island. Results of dating of organic material taken from cross-sections of Quaternary deposits, data on morphology of marine landforms as well as on bottom sediments in lakes were used to construct a curve of changes in the relative sea-level.Our research has shown that the rapid rise of relative sea level in the area (since the beginning of the Holocene decelerated about 8000 years BP, achieving its maximum about 7000 years BP. This was followed by the fall of relative sea-level (the land elevation by 18–20  m in total, and it was characterized by relatively high rate of fall during periods of 6000– 5000 years BP, 4000–2500 years BP, and during the last 1500 years; the rate decreased in 5000–4000 years BP and 2500– 1600 years BP. The changes in relative sea level in this region were determined by the following factors: the eustatic component of the global changes in sea-level and, possibly, oscillations in the global sea level of another nature; local parameters of the Last glacial maximum; a course of the Peninsula deglaciation; regional physical characteristics of the Earth's crust and the mantle substances; local tectonic processes, including the isostatic rebound. Since the beginning of the Holocene up to about 7000 years BP, the main contribution to changes of the relative sea-level in this area was made by the global eustatic factor. The subsequent fall of the relative sea-level (elevation of the Peninsula surface proceeded under condition of reduced role of the eustatic factor and predominance of other factors.

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

    Science.gov (United States)

    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. Measurement of 26Al in Antarctic ice with the MALT-AMS system at the University of Tokyo

    Science.gov (United States)

    Horiuchi, Kazuho; Matsuzaki, Hiroyuki; Ohta, Aoi; Shibata, Yasuyuki; Motoyama, Hideaki

    2007-06-01

    We have attempted to determine the 26Al concentration of Antarctic ice sampled from the vicinity of the Dome Fuji Research Station using accelerator mass spectrometry (AMS) at MALT (MicroAnalysis Laboratory, Tandem accelerator) of the University of Tokyo. Because the expected concentration of 26Al in ice is very low, our standard procedure for the AMS measurement was re-examined and refined. The observed 26Al concentration ranged between 160 and 210 atoms g-1. The averaged value of the 26Al/10Be ratio from two samples was 1.75 ± 0.19 × 10-3, which agrees well with recently reported values for the meteoric 26Al/10Be ratio from Antarctic ice and air filter residues. This result implies the possibility of future 26Al/10Be dating of old Antarctic ice.

  14. Antarctic ice sheet mass loss, glacio-isostatic adjustment and surface processes from a Bayesian combination of gravimetry, altimetry and GPS data

    Science.gov (United States)

    Bamber, J. L.; Martin, A.; Zammit-Mangion, A.; Clarke, P. J.; Flament, T.; Helm, V.; King, M. A.; Luthcke, S. B.; Petrie, L.; Remy, F.; Wouters, B.

    2015-12-01

    Constraining past ice mass changes, identifying their cause(s) and determining rigorous error estimates, is important for closing the sea level budget and as an input for and test of numerical models. Despite the progress that has been made over the last decade, significant differences remain for estimates of the mass evolution of the Antarctic ice sheet. These estimates often yield conflicting results with non-overlapping error bars, while the commonly adopted use of different forward models to isolate and remove the effects of glacio-isostatic adjustment (GIA) and surface mass balance (SMB) processes introduces another source of uncertainty which is hard to quantify. To address both these issues, we present a statistical modeling approach that utilises a spatio-temporal Bayesian hierarchical model, alongside novel dimensional reduction methods to allow the solution to remain tractable in the presence of the large number (> 10^7) of observations. We solve simultaneously for GIA, surface processes, elastic rebound, firn compaction and ice dynamics. Over 2003-2013, Antarctica has been losing mass at a rate of -82+-23 Gt/yr. West Antarctica is the largest contributor with -114+-10 Gt/yr, mainly triggered by high thinning rates of glaciers draining into the Amundsen Sea Embayment. The Antarctic Peninsula has experienced a dramatic increase in mass loss in the last decade, with a mean rate of -25+-6 Gt/yr, and significantly higher values for the most recent years following the destabilization of the Southern Antarctic Peninsula around 2010. The total mass loss is partly compensated by a significant mass gain of 57+-20 Gt/yr in East Antarctica due to positive SMB anomalies and an interesting small dynamic component. We compare our time series of SMB anomalies with those from RACMO-2.3, obtaining good agreement for the large-scale patterns, although differences arise at a basin scale. Also, a data-driven GIA solution is obtained which could be used to constrain and

  15. The Surface Mass Balance of the Antarctic Peninsula at 5.5 km horizontal resolution, as simulated by a regional atmospheric climate model

    Science.gov (United States)

    van Wessem, M.; Reijmer, C.; van den Broeke, M. R.; Ligtenberg, S.; Scambos, T. A.; Barrand, N. E.; Van De Berg, W. J.; Thomas, E. R.; Wuite, J.; van Meijgaard, E.; Turner, J.

    2015-12-01

    The Antarctic Peninsula (AP) is one of the most rapidly changing regions on earth, but limited detailed information is available about AP climate due to a lack of observational data. Here, we present a high-resolution (5.5 km) estimate of the surface mass balance (SMB) for the AP, from 1979 to 2014, calculated by the regional atmospheric climate model RACMO2.3, that is specifically adapted for use over the polar regions. Next to this, a firn densification model is used to calculate the processes in the snowpack, such as firn compaction and meltwater percolation, refreezing, and runoff. A comparison with the few available in-situ observations shows that the AP SMB is well modeled, but that discrepancies remain that are mainly related to the highly variable AP topography compared to the model resolution. Integrated over an ice sheet area of 4.1 105 km2, the climatological (1979-2014) SMB of the AP amounts to 351 Gt y-1 (with interannual variability = 58 Gt y-1), which mostly consists of snowfall (363 ± 56 Gt y-1). The other SMB components, sublimation, drifting snow erosion and meltwater runoff, are small (11, 0.5 and 4 Gt y-1, respectively). The AP mountains act as an important climate barrier, leading to distinct differences between the climate of the western AP (WAP) and the eastern AP (EAP). For instance, 77% of all AP snowfall falls over the WAP, where strong orographic forcing leads to snowfall rates >4 m w.e. y-1 on the northwestern slopes, while snowfall rates are <400 mm w.e. y-1 over the EAP ice shelves. These results, and further investigations of this sharp west-to-east climate distinction, clearly highlight the different forcing mechanisms of the SMB over the WAP and the EAP: over the WAP most snowfall is orographically induced, while over the EAP it is generated by depressions over the Weddell Sea. Furthermore, no significant trends are found in any of the SMB components, except for a slight decrease in snowmelt.

  16. The neglect of cliff instability can underestimate warming period melting in Antarctic ice sheet models

    CERN Document Server

    Ruckert, Kelsey L; Pollard, Dave; Guan, Yawen; Wong, Tony E; Forest, Chris E; Keller, Klaus

    2016-01-01

    The response of the Antarctic ice sheet (AIS) to changing climate forcings is an important driver of sea-level changes. Anthropogenic climate changes may drive a sizeable AIS tipping point response with subsequent increases in coastal flooding risks. Many studies analyzing flood risks use simple models to project the future responses of AIS and its sea-level contributions. These analyses have provided important new insights, but they are often silent on the effects of potentially important processes such as Marine Ice Sheet Instability (MISI) or Marine Ice Cliff Instability (MICI). These approximations can be well justified and result in more parsimonious and transparent model structures. This raises the question how this approximation impacts hindcasts and projections. Here, we calibrate a previously published AIS model, which neglects the effects of MICI, using a combination of observational constraints and a Bayesian inversion method. Specifically, we approximate the effects of missing MICI by comparing ou...

  17. Dynamics of Antarctic and Greenland ice sheets using the borehole, radio sounding and space observations

    Directory of Open Access Journals (Sweden)

    A. N. Markov

    2016-01-01

    Full Text Available Based on data of measurements in deep ice boreholes, as well as of radar and space geodetic observations in Antarctica and Greenland, a number of new features of the ice mass transport had been revealed. Note that these features do not correspond to the traditional but still hypothetical notions (ideas of the monotonous and uniform spatial changes in the ice sheet dynamics. Using results of the long-term monitoring of the borehole coordinate axes at the Vostok station (down to 1920 m, east profile Vostok – Vostok 1 – Pionerskaya – Mirny (1409 km, down to the depth of 450 m, and analysis of radar sections, Russian specialists revealed the following: a the Antarctic ice sheet has stratified changes in speed and a fan-like change in the flow direction along the depth; b plastic firn layer has individual parameters of dynamics and actually flows down from more monolithic body of the ice sheet (the flow directions differ by 30–80°; c in some places inside the sheet, the underlying ice masses flow faster than the upper ones. Researchers from the United States and Denmark registered on the radar sections of the lowest third of the ice domes in the central regions of the Antarctica (AGAP and Greenland (NEEM some folded structures, which were not typical of ice sheets (vertical amplitude of the folds is about 400 m, inclination of the wings is about 45 degrees or more. The tectonic analysis we have performed allows making a conclusion that a genesis of these ice structures is identical to the diapir folds and to diapirs which are formed at a displacement of lower plastic ice masses by the upper monolithic ones, or to echelon folds of crumpling of lower ice layers at their faster flow along original bed as compared with the overlying ice mass. This makes possible to suggest that a turbulent ice flow can occur in the spacious near-bottom and the most plastic area, and a model of the ice sheet dynamics is considered as extruding of

  18. Marine and terrestrial factors affecting Adélie penguin Pygoscelis adeliae chick growth and recruitment off the western Antarctic Peninsula

    Science.gov (United States)

    Chapman, Erik W.; Hofmann, Eileen E.; Patterson, Donna L.; Ribic, Christine A.; Fraser, William R.

    2011-01-01

    An individual-based bioenergetics model that simulates the growth of an Adélie penguin Pygoscelis adeliaechick from hatching to fledging was used to assess marine and terrestrial factors that affect chick growth and fledging mass off the western Antarctic Peninsula. Simulations considered the effects on Adélie penguin fledging mass of (1) modification of chick diet through the addition of Antarctic silverfish Pleuragramma antarcticum to an all-Antarctic krillEuphausia superba diet, (2) reduction of provisioning rate which may occur as a result of an environmental stress such as reduced prey availability, and (3) increased thermoregulatory costs due to wetting of chicks which may result from increased precipitation or snow-melt in colonies. Addition of 17% Antarctic silverfish of Age-Class 3 yr (AC3) to a penguin chick diet composed of Antarctic krill increased chick fledging mass by 5%. Environmental stress that results in >4% reduction in provisioning rate or wetting of just 10% of the chick’s surface area decreased fledging mass enough to reduce the chick’s probability of successful recruitment. The negative effects of reduced provisioning and wetting on chick growth can be compensated for by inclusion of Antarctic silverfish of AC3 and older in the chick diet. Results provide insight into climate-driven processes that influence chick growth and highlight a need for field research designed to investigate factors that determine the availability of AC3 and older Antarctic silverfish to foraging Adélie penguins and the influence of snowfall on chick wetting, thermoregulation and adult provisioning rate.

  19. The Development of a Sea Ice Edge Validation Proxy in the Antarctic with the Use of Nic Charts

    Science.gov (United States)

    Wagner, P. M.; Helfrich, S.; Geiger, C. A.

    2011-12-01

    Sea ice edge location data is an integral component of both climate models and forecast projections, as well as ice charting analysis for safe navigation. The National Ice Center (NIC) generates various products pertaining to sea ice conditions that aid in navigation, which includes records for ice edge location, sea ice concentration, thickness, and extent (http://www.natice.noaa.gov/products/). The NIC Antarctic archive dating from 1972 is relevant because it is the only continuous dataset available by any ice charting operational facility and could be used to provide a large-scale in situ dataset for remote-sensing validations of sea ice. However, some fundamental science questions develop as to what are the climatological value of these products. The NIC daily and weekly sea ice charts differ in how each represents the Antarctic sea ice edge. The daily charts are created to depict the warning zones along the sea ice edge, whereas the weekly charts consist of more detail and include information on sea ice concentration and sea ice types. Though the daily charts have a higher temporal resolution, the weekly charts contain a higher spatial resolution. To quantify this difference both charts were compared with the use of statistical analysis of area measurements and position data to identify their consistency to detect the Antarctic sea ice edge. Years 2004 - present were used to confirm which chart should be used as in situ data for large-scale monitoring in Antarctica and climatology purposes. Overall ice extent in the weekly charts differed approximately 1 x 106 km2 than that of the daily charts. The largest variation occurred during the melt season at approximately 2 x 106 km2, whereas there was less change at approximately between 0.5 x 106 km2 - 1 x 106 km2 throughout the rest of the year. A running standard deviation was performed to show the consistency of the Daily and Weekly products.

  20. Detecting extra-galactic supernova neutrinos in the Antarctic ice

    CERN Document Server

    Böser, Sebastian; Schulte, Lukas; Strotjohann, Nora Linn; Voge, Markus

    2013-01-01

    Building on the technological success of the IceCube neutrino telescope, we outline a prospective low-energy extension that utilizes the clear ice of the South Pole. Aiming at a 10 Mton effective volume and a 10 MeV threshold, the detector would provide sufficient sensitivity to detect neutrino bursts from core-collapse supernovae (SNe) in nearby galaxies. The detector geometry and required density of instrumentation are discussed along with the requirements to control the various sources of background. We find that the resulting detector will be able to detect SNe from beyond 10 Mpc, delivering between 11 and 46 regular core-collapse SN detections per decade. It would further allow to study more speculative phenomena, such as optically dark (failed) SNe, where the collapse proceeds directly to a black hole, at a detection rate similar to the regular SNe. We find that the biggest technological challenge lies in the required large number of large area photo-sensors, with simultaneous strict limits on the allow...

  1. Individual particle morphology, coatings, and impurities of black carbon aerosols in Antarctic ice and tropical rainfall

    Science.gov (United States)

    Ellis, Aja; Edwards, Ross; Saunders, Martin; Chakrabarty, Rajan K.; Subramanian, R.; Timms, Nicholas E.; Riessen, Arie; Smith, Andrew M.; Lambrinidis, Dionisia; Nunes, Laurie J.; Vallelonga, Paul; Goodwin, Ian D.; Moy, Andrew D.; Curran, Mark A. J.; Ommen, Tas D.

    2016-11-01

    Black carbon (BC) aerosols are a large source of climate warming, impact atmospheric chemistry, and are implicated in large-scale changes in atmospheric circulation. Inventories of BC emissions suggest significant changes in the global BC aerosol distribution due to human activity. However, little is known regarding BC's atmospheric distribution or aged particle characteristics before the twentieth century. Here we investigate the prevalence and structural properties of BC particles in Antarctic ice cores from 1759, 1838, and 1930 Common Era (C.E.) using transmission electron microscopy and energy-dispersive X-ray spectroscopy. The study revealed an unexpected diversity in particle morphology, insoluble coatings, and association with metals. In addition to conventionally occurring BC aggregates, we observed single BC monomers, complex aggregates with internally, and externally mixed metal and mineral impurities, tar balls, and organonitrogen coatings. The results of the study show BC particles in the remote Antarctic atmosphere exhibit complexity that is unaccounted for in atmospheric models of BC.

  2. A Method for Continuous (239)Pu Determinations in Arctic and Antarctic Ice Cores.

    Science.gov (United States)

    Arienzo, M M; McConnell, J R; Chellman, N; Criscitiello, A S; Curran, M; Fritzsche, D; Kipfstuhl, S; Mulvaney, R; Nolan, M; Opel, T; Sigl, M; Steffensen, J P

    2016-07-05

    Atmospheric nuclear weapons testing (NWT) resulted in the injection of plutonium (Pu) into the atmosphere and subsequent global deposition. We present a new method for continuous semiquantitative measurement of (239)Pu in ice cores, which was used to develop annual records of fallout from NWT in ten ice cores from Greenland and Antarctica. The (239)Pu was measured directly using an inductively coupled plasma-sector field mass spectrometer, thereby reducing analysis time and increasing depth-resolution with respect to previous methods. To validate this method, we compared our one year averaged results to published (239)Pu records and other records of NWT. The (239)Pu profiles from the Arctic ice cores reflected global trends in NWT and were in agreement with discrete Pu profiles from lower latitude ice cores. The (239)Pu measurements in the Antarctic ice cores tracked low latitude NWT, consistent with previously published discrete records from Antarctica. Advantages of the continuous (239)Pu measurement method are (1) reduced sample preparation and analysis time; (2) no requirement for additional ice samples for NWT fallout determinations; (3) measurements are exactly coregistered with all other chemical, elemental, isotopic, and gas measurements from the continuous analytical system; and (4) the long half-life means the (239)Pu record is stable through time.

  3. Sea-level feedback lowers projections of future Antarctic Ice-Sheet mass loss.

    Science.gov (United States)

    Gomez, Natalya; Pollard, David; Holland, David

    2015-11-10

    The stability of marine sectors of the Antarctic Ice Sheet (AIS) in a warming climate has been identified as the largest source of uncertainty in projections of future sea-level rise. Sea-level fall near the grounding line of a retreating marine ice sheet has a stabilizing influence on the ice sheets, and previous studies have established the importance of this feedback on ice age AIS evolution. Here we use a coupled ice sheet-sea-level model to investigate the impact of the feedback mechanism on future AIS retreat over centennial and millennial timescales for a range of emission scenarios. We show that the combination of bedrock uplift and sea-surface drop associated with ice-sheet retreat significantly reduces AIS mass loss relative to a simulation without these effects included. Sensitivity analyses show that the stabilization tends to be greatest for lower emission scenarios and Earth models characterized by a thin elastic lithosphere and low-viscosity upper mantle, as is the case for West Antarctica.

  4. Multi-frequency observations of seawater carbonate chemistry on the central coast of the western Antarctic Peninsula

    Directory of Open Access Journals (Sweden)

    Julie B. Schram

    2015-07-01

    Full Text Available Assessments of benthic coastal seawater carbonate chemistry in Antarctica are sparse. The studies have generally been short in duration, during the austral spring/summer, under sea ice, or offshore in ice-free water. Herein we present multi-frequency measurements for seawater collected from the shallow coastal benthos on a weekly schedule over one year (May 2012–May 2013, daily schedule over three months (March–May 2013 and semidiurnal schedule over five weeks (March–April 2013. A notable pH increase (max pH = 8.62 occurred in the late austral spring/summer (November–December 2012, coinciding with sea-ice break-out and subsequent increase in primary productivity. We detected semidiurnal variation in seawater pH with a maximum variation of 0.13 pH units during the day and 0.11 pH units during the night. Daily variation in pH is likely related to biological activity, consistent with previous research. We calculated the variation in dissolved inorganic carbon (DIC over each seawater measurement frequency, focusing on the primary DIC drivers in the Palmer Station region. From this, we estimated net biological activity and found it accounts for the greatest variations in DIC. Our seasonal data suggest that this coastal region tends to act as a carbon dioxide source during austral winter months and as a strong sink during the summer. These data characterize present-day seawater carbonate chemistry and the extent to which these measures vary over multiple time scales. This information will inform future experiments designed to evaluate the vulnerability of coastal benthic Antarctic marine organisms to ocean acidification.

  5. Retrieving the antarctic sea-ice concentration based on AMSR-E 89 GHz data

    Institute of Scientific and Technical Information of China (English)

    YU Qinglong; WANG Hui; WAN Liying; BI Haibo

    2013-01-01

    Sea-ice concentration is a key item in global climate change research. Recent progress in remotely sensed sea-ice concentration product has been stimulated by the use of a new sensor, advanced microwave scan-ning radiometer for EOS (AMSR-E), which offers a spatial resolution of 6 km×4 km at 89GHz. A new inver-sion algorithm named LASI (linear ASI) using AMSR-E 89GHz data was proposed and applied in the antarc-tic sea areas. And then comparisons between the LASI ice concentration products and those retrieved by the other two standard algorithms, ASI (arctic radiation and turbulence interaction study sea-ice algorithm) and bootstrap, were made. Both the spatial and temporal variability patterns of ice concentration differ-ences, LASI minus ASI and LASI minus bootstrap, were investigated. Comparative data suggest a high result consistency, especially between LASI and ASI. On the other hand, in order to estimate the LASI ice concen-tration errors introduced by the tie-points uncertainties, a sensitivity analysis was carried out. Additionally an LASI algorithm error estimation based on the field measurements was also completed. The errors suggest that the moderate to high ice concentration areas (>70%) are less affected (never exceeding 10%) than those in the low ice concentration. LASI and ASI consume 75 and 112 s respectively when processing the same AMSR-E time series thourghout the year 2010. To conclude, by using the LASI algorithm, not only the sea-ice concentration can be retrieved with at least an equal quality as that of the two extensively demonstrated operational algorithms, ASI and bootstrap, but also in a more efficient way than ASI.

  6. Antarctic sea-ice expansion between 2000 and 2014 driven by tropical Pacific decadal climate variability

    Science.gov (United States)

    Meehl, Gerald A.; Arblaster, Julie M.; Bitz, Cecilia M.; Chung, Christine T. Y.; Teng, Haiyan

    2016-08-01

    Antarctic sea-ice extent has been slowly increasing in the satellite record that began in 1979. Since the late 1990s, the increase has accelerated, but the average of all climate models shows a decline. Meanwhile, the Interdecadal Pacific Oscillation, an internally generated mode of climate variability, transitioned from positive to negative, with an average cooling of tropical Pacific sea surface temperatures, a slowdown of the global warming trend and a deepening of the Amundsen Sea Low near Antarctica that has contributed to regional circulation changes in the Ross Sea region and expansion of sea ice. Here we show that the negative phase of the Interdecadal Pacific Oscillation in global coupled climate models is characterized by anomalies similar to the observed sea-level pressure and near-surface 850 hPa wind changes near Antarctica since 2000 that are conducive to expanding Antarctic sea-ice extent, particularly in the Ross Sea region in all seasons, involving a deepening of the Amundsen Sea Low. These atmospheric circulation changes are shown to be mainly driven by precipitation and convective heating anomalies related to the Interdecadal Pacific Oscillation in the equatorial eastern Pacific, with additional contributions from convective heating anomalies in the South Pacific convergence zone and tropical Atlantic regions.

  7. Antarctic ice-mass balance 2002 to 2011: regional re-analysis of GRACE satellite gravimetry measurements with improved estimate of glacial-isostatic adjustment

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    I. Sasgen

    2012-09-01

    Full Text Available We present regional-scale mass balances for 25 drainage basins of the Antarctic Ice Sheet (AIS from satellite observations of the Gravity and Climate Experiment (GRACE for the years 2002–2011. Satellite gravimetry estimates of the AIS mass balance are strongly influenced by mass movement in the Earth interior caused by ice advance and retreat during the last glacial cycle. Here, we develop an improved glacial-isostatic adjustment (GIA estimate for Antarctica using newly available GPS uplift rates, allowing us to more accurately separate GIA-induced trends in the GRACE gravity fields from those caused by current imbalances of the AIS. Our revised GIA estimate is considerably lower than previous predictions, yielding an (upper estimate of apparent mass change of 48 ± 18 Gt yr−1. Therefore, our AIS mass balance of −103 ± 23 Gt yr−1 is considerably less negative than previous GRACE estimates. The Northern Antarctic Peninsula and the Amundsen Sea Sector exhibit the largest mass loss (−25 ± 6 Gt yr−1 and −126 ± 11 Gt yr−1, respectively. In contrast, East Antarctica exhibits a slightly positive mass balance (19 ± 16 Gt yr−1, which is, however, mostly the consequence of compensating mass anomalies in Dronning Maud and Enderby Land (positive and Wilkes and George V Land (negative due to interannual accumulation variations. In total, 7% of the area constitute more than half of the AIS imbalance (53%, contributing −151 ± 9 Gt yr−1 to global mean sea-level change. Most of this imbalance is caused by long-term ice-dynamic speed up expected to prevail in the future.

  8. Geochemical characteristics and zones of surface snow on east Antarctic Ice Sheet

    Institute of Scientific and Technical Information of China (English)

    KANG Jiancheng; LIU Leibao; QIN Dahe; WANG Dali; WEN Jiahong; TAN Dejun; LI Zhongqin; LI Jun; ZHANG Xiaowei

    2004-01-01

    The surface-snow geochemical characteristics are discussed on the East Antarctic Ice Sheet, depending on the stable isotopes ratios of oxygen and hydrogen, concentration of impurities (soluble-ions and insoluble micro-particle) in surface snow collected on the ice sheet. The purpose is to study geochemical zones on the East Antarctic Ice Sheet and to research sources and transportation route of the water vapor and the impurities in surface snow. It has been found that the ratio coefficients, as S1, d1 in the equation δD = S1δ18O + d1, are changed near the elevation 2000 m on the ice sheet. The weight ratio of Cl(-)/Na+ at the area below the elevation of 2000 m is close to the ratio in the sea salt; but it is about 2 times that of the sea salt, at the inland area up to the elevation of 2000 m. The concentrations of non-sea-salt Ca2+ ion (nssCa2+) and fine-particle increase at the interior up to the elevation 2000 m. At the region below the elevation of 2000 m, the impurity concentration is decreasing with the elevation increasing. Near coastal region, the surface snow has a high concentration of impurity, where the elevation is below 800 m. Combining the translating processes of water-vapor and impurities, it suggests that the region up to the elevation 2000 m is affected by large-scale circulation with longitude-direction, and that water-vapor and impurities in surface snow come from long sources. The region below the elevation 2000 m is affected by some strong cyclones acting at peripheral region of the ice sheet, and the sources of water and impurities could be at high latitude sea and coast. The area below elevation 800 m is affected by local coastal cyclones.

  9. West Antarctic Ice Sheet dynamics recorded in Plio-Pleistocene strata of the Ross Sea, Antarctica

    Science.gov (United States)

    Loth, A. S.; Bartek, L. R.; Luyendyk, B. P.; Wilson, D. S.

    2008-12-01

    Within the 100,000 square kilometer Eastern Basin of the Ross Sea, a 290 km section, oriented parallel to depostional dip along with 10 intersecting seismic sections that are oriented parallel to depositional strike were analyzed. Using Single-Channel Seismic (SCS) data from three different seismic surveys (NBP 0306, PD9022, and NBP 9308) 36 Plio-Pleistocene sequences were correlated across the basin from the modern ice shelf edge to the contemporary shelf break. Few of the sequences are continuous across the shelf, the majority of the sequences are of limited lateral extent. The facies within the sequences were analyzed to determine ice sheet behavior at the time of deposition. Three distinct depositional environments were interpreted based upon variations in the reflection attributes within the seismic data. Subglacial facies have a spectrum of reflection attributes from reflection-free to parallel, low-amplitude, discontinuous facies. The Grounding Line Zone facies are characterized by high amplitude, mildly discontinuous reflections. Proglacial environments are distinguished by parallel, high amplitude, continuous reflection packages. The facies distribution within many of the sequences consists of Subglacial facies in updip locales, Grounding Line Zone facies widely distributed across the shelf, and Proglacial facies present at downdip sites. The facies distribution within the sequences provides a record of the variation of the extent of the West Antarctic Ice Sheet (WAIS) throughout the Plio-Pleistocene. Not all sequences have a consecutive facies relationship, which may have resulted from several causes: 1) changes in the flow of the WAIS, 2) interplay between the East Antarctic Ice Sheet (EAIS) with the WAIS, or 3) additional grounding of the WAIS on paleobasin highs. Understanding the short-lived glacial events, whether they are a function of non-deposition or cannibalization of previous deposits, provides insight into the dynamics of marine based ice

  10. Late Cretaceous-early Eocene counterclockwise rotation of the Fueguian Andes and evolution of the Patagonia-Antarctic Peninsula system

    Science.gov (United States)

    Poblete, F.; Roperch, P.; Arriagada, C.; Ruffet, G.; Ramírez de Arellano, C.; Hervé, F.; Poujol, M.

    2016-02-01

    The southernmost Andes of Patagonia and Tierra del Fuego present a prominent arc-shaped structure: the Patagonian Bend. Whether the bending is a primary curvature or an orocline is still matter of controversy. New paleomagnetic data have been obtained south of the Beagle Channel in 39 out of 61 sites. They have been drilled in Late Jurassic and Early Cretaceous sediments and interbedded volcanics and in mid-Cretaceous to Eocene intrusives of the Fuegian Batholith. The anisotropy of magnetic susceptibility was measured at each site and the influence of magnetic fabric on the characteristic remanent magnetizations (ChRM) in plutonic rocks was corrected using inverse tensors of anisotropy of remanent magnetizations. Normal polarity secondary magnetizations with west-directed declination were obtained in the sediments and they did not pass the fold test. These characteristic directions are similar to those recorded by mid Cretaceous intrusives suggesting a remagnetization event during the normal Cretaceous superchron and describe a large (> 90°) counterclockwise rotation. Late Cretaceous to Eocene rocks of the Fueguian Batholith, record decreasing counterclockwise rotations of 45° to 30°. These paleomagnetic results are interpreted as evidence of a large counterclockwise rotation of the Fueguian Andes related to the closure of the Rocas Verdes Basin and the formation of the Darwin Cordillera during the Late Cretaceous and Paleocene. The tectonic evolution of the Patagonian Bend can thus be described as the formation of a progressive arc from an oroclinal stage during the closure of the Rocas Verdes basin to a mainly primary arc during the final stages of deformation of the Magallanes fold and thrust belt. Plate reconstructions show that the Antarctic Peninsula would have formed a continuous margin with Patagonia between the Early Cretaceous and the Eocene, and acted as a non-rotational rigid block facilitating the development of the Patagonian Bend.

  11. A Novel Remote Sensing Approach for Determining 20th Century Multi-Decadal Glacial Change Across the Antarctic Peninsula

    Science.gov (United States)

    Miller, P. E.; Mills, J. P.; Fox, A. J.; Clarke, L. E.; King, M. A.

    2014-12-01

    The Antarctic Peninsula (AP) is a mountain glacier system comprised of over 400 glaciers, and is an important contributor to historical and future sea level rise. Assessment and monitoring of AP glaciers is crucial for understanding sensitivity to climate change. However, whilst retreat of glacier fronts and the behaviour of individual glaciers has been extensively documented, wide-area assessment of AP glacier mass change is lacking. This research addresses this by unlocking a unique historical archive of aerial imagery through a remote sensing approach. This is enabling quantitative, wide-area assessment of glacier change across the AP. Understanding AP change over the 20th Century is vital for modelling future changes. However, satellite measurements span only a few decades, and to-date there has been no means of quantifying change over longer periods. However, this research presents a novel methodology to extract 3D measurements from an archive of > 30,000 aerial images dating back to the 1940s. This overcomes the requirement for ground control by employing an automated registration technique. Control is derived from digital elevations models (DEMs) generated from present-day ASTER satellite imagery. Through least squares surface matching, DEMs extracted from archival imagery are registered to scale-stable ASTER DEMs to determine relative change. This minimises offsets between the two DEMs, allowing robust determination of elevation changes. The spatial pattern of 20thC change is being assessed at 50 benchmark glaciers distributed across the AP, for periods of up to 65 years. In complement, a temporally refined assessment is being undertaken at 10 glaciers with multiple epochs of aerial imagery. Results to-date indicate a general trend of surface lowering, most notably over frontal regions. Spatial and temporal patterns of change will be used to investigate the drivers of AP change and establish a suite of benchmark glaciers for future monitoring.

  12. Modelling snowdrift sublimation on an Antarctic ice shelf

    Directory of Open Access Journals (Sweden)

    J. T. M. Lenaerts

    2010-05-01

    Full Text Available In this paper, we estimate the contribution of snowdrift sublimation (SUds to the surface mass balance at Neumayer, located on the Ekström ice shelf in Eastern Antarctica. A single column version of the RACMO2-ANT model is used as a physical interpolation tool of high-quality radiosonde and surface measurements for a 15-yr period (1993–2007, and combined with a routine to calculate snowdrift sublimation and horizontal snow transport. The site is characterised by a relatively mild, wet and windy climate, so snowdrift is a common phenomenon. The modelled timing and frequency of snowdrift events compares well with observations. This is further illustrated by an additional simulation for Kohnen base, where the timing of snowdrift is realistic, although the modelled horizontal transport is overestimated. Snowdrift sublimation is mainly dependent on wind speed, but also on relative humidity and temperature. During high wind speeds, SUds saturates and cools the air, limiting its own strength. We estimate that SUds removes around 16%±8% of the accumulated snow from the surface. The total sublimation more than triples when snowdrift is considered, although snowdrift sublimation limits sublimation at the surface. SUds shows a strong seasonal cycle, as well as large inter-annual variability. This variability can be related to the variability of the atmospheric conditions in the surface layer.

  13. Modelling acoustic propagation beneath Antarctic sea ice using measured environmental parameters

    Science.gov (United States)

    Alexander, Polly; Duncan, Alec; Bose, Neil; Williams, Guy

    2016-09-01

    Autonomous underwater vehicles are improving and expanding in situ observations of sea ice for the validation of satellite remote sensing and climate models. Missions under sea ice, particularly over large distances (up to 100 km) away from the immediate vicinity of a ship or base, require accurate acoustic communication for monitoring, emergency response and some navigation systems. We investigate the propagation of acoustic signals in the Antarctic seasonal ice zone using the BELLHOP model, examining the influence of ocean and sea ice properties. We processed available observations from around Antarctica to generate input variables such as sound speed, surface reflection coefficient (R) and roughness parameters. The results show that changes in the sound speed profile make the most significant difference to the propagation of the direct path signal. The inclusion of the surface reflected signals from a flat ice surface was found to greatly decrease the transmission loss with range. When ice roughness was added, the transmission loss increased with roughness, in a manner similar to the direct path transmission loss results. The conclusions of this work are that: (1) the accuracy of acoustic modelling in this environment is greatly increased by using realistic sound speed data; (2) a risk averse ranging model would use only the direct path signal transmission; and (3) in a flat ice scenario, much greater ranges can be achieved if the surface reflected transmission paths are included. As autonomous missions under sea ice increase in scale and complexity, it will be increasingly important for operational procedures to include effective modelling of acoustic propagation with representative environmental data.

  14. High geothermal heat flux measured below the West Antarctic Ice Sheet.

    Science.gov (United States)

    Fisher, Andrew T; Mankoff, Kenneth D; Tulaczyk, Slawek M; Tyler, Scott W; Foley, Neil

    2015-07-01

    The geothermal heat flux is a critical thermal boundary condition that influences the melting, flow, and mass balance of ice sheets, but measurements of this parameter are difficult to make in ice-covered regions. We report the first direct measurement of geothermal heat flux into the base of the West Antarctic Ice Sheet (WAIS), below Subglacial Lake Whillans, determined from the thermal gradient and the thermal conductivity of sediment under the lake. The heat flux at this site is 285 ± 80 mW/m(2), significantly higher than the continental and regional averages estimated for this site using regional geophysical and glaciological models. Independent temperature measurements in the ice indicate an upward heat flux through the WAIS of 105 ± 13 mW/m(2). The difference between these heat flux values could contribute to basal melting and/or be advected from Subglacial Lake Whillans by flowing water. The high geothermal heat flux may help to explain why ice streams and subglacial lakes are so abundant and dynamic in this region.

  15. Glacier surge after ice shelf collapse.

    Science.gov (United States)

    De Angelis, Hernán; Skvarca, Pedro

    2003-03-07

    The possibility that the West Antarctic Ice Sheet will collapse as a consequence of ice shelf disintegration has been debated for many years. This matter is of concern because such an event would imply a sudden increase in sea level. Evidence is presented here showing drastic dynamic perturbations on former tributary glaciers that fed sections of the Larsen Ice Shelf on the Antarctic Peninsula before its collapse in 1995. Satellite images and airborne surveys allowed unambiguous identification of active surging phases of Boydell, Sjögren, Edgeworth, Bombardier, and Drygalski glaciers. This discovery calls for a reconsideration of former hypotheses about the stabilizing role of ice shelves.

  16. Increase of the Antarctic Sea Ice Extent is highly significant only in the Ross Sea

    Science.gov (United States)

    Yuan, Naiming; Ding, Minghu; Ludescher, Josef; Bunde, Armin

    2017-01-01

    In the context of global warming, the question of why Antarctic sea ice extent (SIE) has increased is one of the most fundamental unsolved mysteries. Although many mechanisms have been proposed, it is still unclear whether the increasing trend is anthropogenically originated or only caused by internal natural variability. In this study, we employ a new method where the underlying natural persistence in the Antarctic SIE can be correctly accounted for. We find that the Antarctic SIE is not simply short-term persistent as assumed in the standard significance analysis, but actually characterized by a combination of both short- and long-term persistence. By generating surrogate data with the same persistence properties, the SIE trends over Antarctica (as well as five sub-regions) are evaluated using Monte-Carlo simulations. It is found that the SIE trends over most sub-regions of Antarctica are not statistically significant. Only the SIE over Ross Sea has experienced a highly significant increasing trend (p = 0.008) which cannot be explained by natural variability. Influenced by the positive SIE trend over Ross Sea, the SIE over the entire Antarctica also increased over the past decades, but the trend is only at the edge of being significant (p = 0.034).

  17. Lipophilic pigments from the benthos of a perennially ice-covered Antarctic lake

    Science.gov (United States)

    Palmisano, A. C.; Wharton, R. A. Jr; Cronin, S. E.; Des Marais, D. J.; Wharton RA, J. r. (Principal Investigator)

    1989-01-01

    The benthos of a perennially ice-covered Antarctic lake, Lake Hoare, contained three distinct 'signatures' of lipophilic pigments. Cyanobacterial mats found in the moat at the periphery of the lake were dominated by the carotenoid myxoxanthophyll; carotenoids: chlorophyll a ratios in this high light environment ranged from 3 to 6.8. Chlorophyll c and fucoxanthin, pigments typical of golden-brown algae, were found at 10 to 20 m depths where the benthos is aerobic. Anaerobic benthic sediments at 20 to 30 m depths were characterized by a third pigment signature dominated by a carotenoid, tentatively identified as alloxanthin from planktonic cryptomonads, and by phaeophytin b from senescent green algae. Pigments were not found associated with alternating organic and sediment layers. As microzooplankton grazers are absent from this closed system and transformation rates are reduced at low temperatures, the benthos beneath the lake ice appears to contain a record of past phytoplankton blooms undergoing decay.

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

    Science.gov (United States)

    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.

  19. New Cysteine-Rich Ice-Binding Protein Secreted from Antarctic Microalga, Chloromonas sp.

    Science.gov (United States)

    Jung, Woongsic; Campbell, Robert L; Gwak, Yunho; Kim, Jong Im; Davies, Peter L; Jin, EonSeon

    2016-01-01

    Many microorganisms in Antarctica survive in the cold environment there by producing ice-binding proteins (IBPs) to control the growth of ice around them. An IBP from the Antarctic freshwater microalga, Chloromonas sp., was identified and characterized. The length of the Chloromonas sp. IBP (ChloroIBP) gene was 3.2 kb with 12 exons, and the molecular weight of the protein deduced from the ChloroIBP cDNA was 34.0 kDa. Expression of the ChloroIBP gene was up- and down-regulated by freezing and warming conditions, respectively. Western blot analysis revealed that native ChloroIBP was secreted into the culture medium. This protein has fifteen cysteines and is extensively disulfide bonded as shown by in-gel mobility shifts between oxidizing and reducing conditions. The open-reading frame of ChloroIBP was cloned and over-expressed in Escherichia coli to investigate the IBP's biochemical characteristics. Recombinant ChloroIBP produced as a fusion protein with thioredoxin was purified by affinity chromatography and formed single ice crystals of a dendritic shape with a thermal hysteresis activity of 0.4±0.02°C at a concentration of 5 mg/ml. In silico structural modeling indicated that the three-dimensional structure of ChloroIBP was that of a right-handed β-helix. Site-directed mutagenesis of ChloroIBP showed that a conserved region of six parallel T-X-T motifs on the β-2 face was the ice-binding region, as predicted from the model. In addition to disulfide bonding, hydrophobic interactions between inward-pointing residues on the β-1 and β-2 faces, in the region of ice-binding motifs, were crucial to maintaining the structural conformation of ice-binding site and the ice-binding activity of ChloroIBP.

  20. Antarctic Mirabilite Mounds as Mars Analogs: The Lewis Cliffs Ice Tongue Revisited

    Science.gov (United States)

    Socki, Richard A.; Sun, Tao; Niles, Paul B.; Harvey, Ralph P.; Bish, David L.; Tonui, Eric

    2012-01-01

    It has been proposed, based on geomorphic and geochemical arguments, that subsurface water has played an important role in the history of water on the planet Mars [1]. Subsurface water, if present, could provide a protected and long lived environment for potential life. Discovery of gullies [2] and recurring slopes [3] on Mars suggest the potential for subsurface liquid water or brines. Recent attention has also focused on small (Tongue (LCIT) [6] in the Transantarctic Mountains, Antarctica, and are potential terrestrial analogs for mounds observed on the martian surface. The following characteristics distinguish LCIT evaporite mounds from other evaporite mounds found in Antarctic coastal environments and/or the McMurdo Dry Valleys: (1) much greater distance from the open ocean (approx.500 km); (2) higher elevation (approx.2200 meters); and (3) colder average annual temperature (average annual temperature = -30 C for LCIT [7] vs. 20 C at sea level in the McMurdo region [8]. Furthermore, the recent detection of subsurface water ice (inferred as debris-covered glacial ice) by the Mars Reconnaissance Orbiter [9] supports the use of an Antarctic glacial environment, particularly with respect to the mirabilite deposits described in this work, as an ideal terrestrial analog for understanding the geochemistry associated with near-surface martian processes. S and O isotopic compositions.

  1. El Grupo Trinity Peninsula en la península Tabarin, extremo norte de la península Antártica The Trinity Peninsula Group in the Tabarin Peninsula, northern end of the Antarctic Peninsula

    Directory of Open Access Journals (Sweden)

    R.A. del Valle

    2007-12-01

    Full Text Available La península Tabarin, Antártida Occidental, exhibe rocas deformadas durante los ciclos orogénicos gondwánico y ándico. La Formación Hope Bay y Formación Düse Bay (Carbonífero tardío-Triásico están incluidas dentro del Grupo Trinity Peninsula, registrando el ciclo orogénico gondwánico. Las estructuras sedimentarias, asociaciones de facies y rasgos deposicionales de la Formación Hope Bay, sugieren sedimentación en ambientes marinos someros. La presencia de capas calcáreas con morfología build-up y matas calcáreas, y rocas piroclásticas, incluyendo ignimbritas, peperitas y depósitos ricos es escoria volcánica, también indican escasa profundidad del mar para la sedimentación de la Formación Düse Bay. El área de aporte del Grupo Trinity Peninsula estaba compuesta por rocas volcánicas y plutónicas con cantidades menores de rocas sedimentarias y metamórficas, probablemente ubicadas hacia el este para la parte inferior Formación Hope Bay de la secuencia, y hacia el oeste para la parte superior de la Formación Düse Bay, con mayor participación volcánica en el último caso. El ambiente de sedimentación más probable para la Formación Hope Bay fue una plataforma silícicoclástica somera y de baja energía, y una cuenca de retroarco de antepaís, relacionada con la orogenia gondwánica, en el caso de la Formación Düse Bay.The Tabarin Peninsula, West Antarctica, showsrocks deformed by both the Gondwanic and Andean orogenic cycles. The Hope Bay Formation and Düse Bay Formation (Late Carboniferous-Triassic are included within the Trinity Peninsula Group, recording the Gondwanic orogenic cycle. Sedimentary structures, facies associations and depositional features of Hope Bay Formation, suggest shallow marine deposition. The presence in the Düse Bay Formation of calcareous beds with build-up morphology and algal mats, and primary pyroclastic rocks including: ignimbrites, peperites and scoria-rich fall deposits, also

  2. Inclusion of mountain wave-induced cooling for the formation of PSCs over the Antarctic Peninsula in a chemistry–climate model

    Directory of Open Access Journals (Sweden)

    A. Orr

    2014-07-01

    Full Text Available An important source of polar stratospheric clouds (PSCs, which play a crucial role in controlling polar stratospheric ozone depletion, is from the temperature fluctuations induced by mountain waves. However, this formation mechanism is usually missing in chemistry–climate models because these temperature fluctuations are neither resolved nor parameterised. Here, we investigate the representation of stratospheric mountain wave-induced temperature fluctuations by the UK Met Office Unified Model (UM at high and low spatial resolution against Atmospheric Infrared Sounder satellite observations for three case studies over the Antarctic Peninsula. At a high horizontal resolution (4 km the mesoscale configuration of the UM correctly simulates the magnitude, timing, and location of the measured temperature fluctuations. By comparison, at a low horizontal resolution (2.5° × 3.75° the climate configuration fails to resolve such disturbances. However, it is demonstrated that the temperature fluctuations computed by a mountain wave parameterisation scheme inserted into the climate configuration (which computes the temperature fluctuations due to unresolved mountain waves are in excellent agreement with the mesoscale configuration responses. The parameterisation was subsequently used to compute the local mountain wave-induced cooling phases in the chemistry–climate configuration of the UM. This increased stratospheric cooling was passed to the PSC scheme of the chemistry–climate model, and caused a 30–50% increase in PSC surface area density over the Antarctic Peninsula compared to a 30 year control simulation.

  3. Changes in snow distribution and surface topography following a snowstorm on Antarctic sea ice

    Science.gov (United States)

    Trujillo, Ernesto; Leonard, Katherine; Maksym, Ted; Lehning, Michael

    2016-11-01

    Snow distribution over sea ice is an important control on sea ice physical and biological processes. We combine measurements of the atmospheric boundary layer and blowing snow on an Antarctic sea ice floe with terrestrial laser scanning to characterize a typical storm and its influence on the spatial patterns of snow distribution at resolutions of 1-10 cm over an area of 100 m × 100 m. The pre-storm surface exhibits multidirectional elongated snow dunes formed behind aerodynamic obstacles. Newly deposited dunes are elongated parallel to the predominant wind direction during the storm. Snow erosion and deposition occur over 62% and 38% of the area, respectively. Snow deposition volume is more than twice that of erosion (351 m3 versus 158 m3), resulting in a modest increase of 2 ± 1 cm in mean snow depth, indicating a small net mass gain despite large mass relocation. Despite significant local snow depth changes due to deposition and erosion, the statistical distributions of elevation and the two-dimensional correlation functions remain similar to those of the pre-storm surface. Pre-storm and post-storm surfaces also exhibit spectral power law relationships with little change in spectral exponents. These observations suggest that for sea ice floes with mature snow cover features under conditions similar to those observed in this study, spatial statistics and scaling properties of snow surface morphology may be relatively invariant. Such an observation, if confirmed for other ice types and conditions, may be a useful tool for model parameterizations of the subgrid variability of sea ice surfaces.

  4. Phase relationships between orbital forcing and the composition of air trapped in Antarctic ice cores

    Directory of Open Access Journals (Sweden)

    L. Bazin

    2015-04-01

    Full Text Available Orbital tuning is central for ice core chronologies beyond annual layer counting, available back to 60 ka (i.e. thousand of years before 1950 for Greenland ice cores. While several complementary orbital tuning tools have recently been developed using δ18Oatm, δO2/N2 and air content with different orbital targets, quantifying their uncertainties remains a challenge. Indeed, the exact processes linking variations of these parameters, measured in the air trapped in ice, to their orbital targets are not yet fully understood. Here, we provide new series of δO2/N2 and δ18Oatm data encompassing Marine Isotopic Stage (MIS 5 (between 100–160 ka and the oldest part (380–800 ka of the East Antarctic EPICA Dome C (EDC ice core. For the first time, the measurements over MIS 5 allow an inter-comparison of δO2/N2 and δ18Oatm records from three East Antarctic ice core sites (EDC, Vostok and Dome F. This comparison highlights a site-specific relationship between δO2/N2 and its local summer solstice insolation. Such a relationship increases the uncertainty associated with the use of δO2/N2 as a tool for orbital tuning. Combining records of δ18Oatm and δO2/N2 from Vostok and EDC, we evidence a loss of orbital signature for these two parameters during periods of minimum eccentricity (∼400, ∼720–800 ka. Our dataset reveals a time-varying lag between δO2/N2 and δ18Oatm over the last 800 ka that we interpret as variations of the lag between δ18Oatm and precession. Large lags of ∼5 ka are identified during Terminations I and II, associated with strong Heinrich events. On the opposite, minimal lags (∼1–2 ka are identified during four periods characterized by high eccentricity, intermediate ice volume and no Heinrich events (MIS 6–7, the end of MIS 9, MIS 15 and MIS 17. We therefore suggest that the occurrence of Heinrich events influences the response of δ18Oatm to precession.

  5. Empirical estimation of present-day Antarctic glacial isostatic adjustment and ice mass change

    Directory of Open Access Journals (Sweden)

    B. C. Gunter

    2013-07-01

    Full Text Available This study explores an approach that simultaneously estimates Antarctic mass balance and glacial isostatic adjustment (GIA through the combination of satellite gravity and altimetry data sets. The results improve upon previous efforts by incorporating reprocessed data sets over a longer period of time, and now include a firn densification model to account for firn compaction and surface processes. A range of different GRACE gravity models were evaluated, as well as a new ICESat surface height trend map computed using an overlapping footprint approach. When the GIA models created from the combination approach were compared to in-situ GPS ground station displacements, the vertical rates estimated showed consistently better agreement than existing GIA models. In addition, the new empirically derived GIA rates suggest the presence of strong uplift in the Amundsen Sea and Philippi/Denman sectors, as well as subsidence in large parts of East Antarctica. The total GIA mass change estimates for the entire Antarctic ice sheet ranged from 53 to 100 Gt yr−1, depending on the GRACE solution used, and with an estimated uncertainty of ±40 Gt yr−1. Over the time frame February 2003–October 2009, the corresponding ice mass change showed an average value of −100 ± 44 Gt yr−1 (EA: 5 ± 38, WA: −105 ± 22, consistent with other recent estimates in the literature, with the mass loss mostly concentrated in West Antarctica. The refined approach presented in this study shows the contribution that such data combinations can make towards improving estimates of present day GIA and ice mass change, particularly with respect to determining more reliable uncertainties.

  6. Using fluorescence to characterize dissolved organic matter in Antarctic sea ice brines

    Science.gov (United States)

    Stedmon, Colin A.; Thomas, David N.; Papadimitriou, Stathys; Granskog, Mats A.; Dieckmann, Gerhard S.

    2011-09-01

    Sea ice plays a dynamic role in the air-sea exchange of CO2. In addition to abiotic inorganic carbon fluxes, an active microbial community produces and remineralizes organic carbon, which can accumulate in sea ice brines as dissolved organic matter (DOM). In this study, the characteristics of DOM fluorescence in Antarctic sea ice brines from the western Weddell Sea were investigated. Two humic-like components were identified, which were identical to those previously found to accumulate in the deep ocean and represent refractory material. Three amino-acid-like signals were found, one of which was unique to the brines and another that was spectrally very similar to tryptophan and found both in seawater and in brine samples. The tryptophan-like fluorescence in the brines exhibited intensities higher than could be explained by conservative behavior during the freezing of seawater. Its fluorescence was correlated with the accumulation of nitrogen-rich DOM to concentrations up to 900 μmol L-1 as dissolved organic carbon (DOC) and, thus, potentially represented proteins released by ice organisms. A second, nitrogen-poor DOM fraction also accumulated in the brines to concentrations up to 200 μmol L-1 but was not correlated with any of the fluorescence signals identified. Because of the high C:N ratio and lack of fluorescence, this material is thought to represent extracellular polymeric substances, which consist primarily of polysaccharides. The clear grouping of the DOM pool into either proteinaceous or carbohydrate-dominated material indicates that the production and accumulation of these two subpools of DOM in sea ice brines is, to some extent, decoupled.

  7. Recent climate tendencies on an East Antarctic ice shelf inferred from a shallow firn core network.

    Science.gov (United States)

    Schlosser, E; Anschütz, H; Divine, D; Martma, T; Sinisalo, A; Altnau, S; Isaksson, E

    2014-06-16

    Nearly three decades of stable isotope ratios and surface mass balance (SMB) data from eight shallow firn cores retrieved at Fimbul Ice Shelf, East Antarctica, in the Austral summers 2009-2011 have been investigated. An additional longer core drilled in 2000/2001 extends the series back to the early eighteenth century. Isotope ratios and SMB from the stacked record of all cores were also related to instrumental temperature data from Neumayer Station on Ekström Ice Shelf. Since the second half of the twentieth century, the SMB shows a statistically significant negative trend, whereas the δ(18)O of the cores shows a significant positive trend. No trend is found in air temperature at the nearest suitable weather station, Neumayer (available since 1981). This does not correspond to the statistically significant positive trend in Southern Annular Mode (SAM) index, which is usually associated with a cooling of East Antarctica. SAM index and SMB are negatively correlated, which might be explained by a decrease in meridional exchange of energy and moisture leading to lower precipitation amounts. Future monitoring of climate change on the sensitive Antarctic ice shelves is necessary to assess its consequences for sea level change.

  8. Cascading water underneath Wilkes Land, East Antarctic Ice Sheet, observed using altimetry and digital elevation models

    Directory of Open Access Journals (Sweden)

    T. Flament

    2013-03-01

    Full Text Available We describe a major subglacial lake drainage close to the ice divide in Wilkes Land, East Antarctica, and the subsequent cascading of water underneath the ice sheet toward the coast. To analyze the event, we combined altimetry data from several sources and bedrock data. We estimated the total volume of water that drained from Lake CookE2 by differencing digital elevation models (DEM derived from ASTER and SPOT5 stereo-imagery. With 5.2 ± 0.5 km3, this is the largest single subglacial drainage event reported so far in Antarctica. Elevation differences between ICESat laser altimetry and the SPOT5 DEM indicate that the discharge lasted approximately 2 yr. A 13-m uplift of the surface, corresponding to a refilling of about 0.64 ± 0.32 km3, was observed between the end of the discharge in October 2008 and February 2012. Using Envisat radar altimetry, with its high 35-day temporal resolution, we monitored the subsequent filling and drainage of connected subglacial lakes located downstream. In particular, a transient temporal signal can be detected within the theoretical 500-km long flow paths computed with the BEDMAP2 data set. The volume of water traveling in this wave is in agreement with the volume that drained from Lake CookE2. These observations contribute to a better understanding of the water transport beneath the East Antarctic ice sheet.

  9. Quasi-parabolic reflecting bottom surfaces of the Drygalski Antarctic floating ice tongue

    Directory of Open Access Journals (Sweden)

    E. Zuccheretti

    2001-06-01

    Full Text Available Very high frequency deep radio sounding systems for ice thickness measurements are practically the only useful apparatuses for large scale radar flight surveys in polar regions. The morphology of the bottom surface of an Antarctic floating ice tongue, in the Ross Sea area, East Antarctica, was studied using the arrival times of signal echoes of the radio sounding system. The amplitude variations of radar signals from the reflecting surface were analyzed to determine the gain or the loss of the reflectors. Such surfaces show quasi-parabolic geometrical shapes at the ice/water interface with both concave and convex faces towards the sounding system. Electromagnetic analysis performed on radar echoes indicates that amplitude variations detected by the antenna are focusing or defocusing effects only due to the reflector's shape. A factor in the radar equation that represents the surface shape when coherent reflectors are involved is introduced. This factor allows us to determine more precisely the morphology and electromagnetic characteristics of the interface between the media investigated by means of radio echo sounding.

  10. Forecasting Antarctic Sea Ice Concentrations Using Results of Temporal Mixture Analysis

    Science.gov (United States)

    Chi, Junhwa; Kim, Hyun-Cheol

    2016-06-01

    Sea ice concentration (SIC) data acquired by passive microwave sensors at daily temporal frequencies over extended areas provide seasonal characteristics of sea ice dynamics and play a key role as an indicator of global climate trends; however, it is typically challenging to study long-term time series. Of the various advanced remote sensing techniques that address this issue, temporal mixture analysis (TMA) methods are often used to investigate the temporal characteristics of environmental factors, including SICs in the case of the present study. This study aims to forecast daily SICs for one year using a combination of TMA and time series modeling in two stages. First, we identify temporally meaningful sea ice signatures, referred to as temporal endmembers, using machine learning algorithms, and then we decompose each pixel into a linear combination of temporal endmembers. Using these corresponding fractional abundances of endmembers, we apply a autoregressive model that generally fits all Antarctic SIC data for 1979 to 2013 to forecast SIC values for 2014. We compare our results using the proposed approach based on daily SIC data reconstructed from real fractional abundances derived from a pixel unmixing method and temporal endmember signatures. The proposed method successfully forecasts new fractional abundance values, and the resulting images are qualitatively and quantitatively similar to the reference data.

  11. Quasi-parabolic reflecting bottom surfaces of the Drygalski Antarctic floating ice tongue

    Energy Technology Data Exchange (ETDEWEB)

    Bianchi, C.; Chiappini, M.; Zirizzotti, A.; Zuccheretti, E. [Istituto Nazionale di Geofisica e Vulcanologia, Rome (Italy); Tabacco, I. E. [Milan Univ., Milan (Italy). Sez. Geofisica

    2001-06-01

    Very high frequency deep radio sounding systems for ice thickness measurements are practically the only useful apparatuses for large scale radar flight surveys in polar regions. The morphology of the bottom surface of a n Antarctic floating ice tongue, in the Ross Sea area, East Antarctica, was studied using the arrival times of signal echoes of the radio sounding system. The amplitude variations of radar signals from the reflecting surface were analyzed to determine the gain or the loss of the reflectors. Such surfaces show quasi-parabolic geometrical shapes at the ice/water interface with both concave and convex faces towards the sounding system. Electromagnetic analysis performed on radar echoes indicates that amplitude variations detected by the antenna are focusing or defocusing effects only due to the reflector's shape. A factor in the radar equation that represents the surface shape when coherent reflectors are involved is introduced. This factor allows everyone to determine more precisely the morphology and electromagnetic characteristics of the interface between the media investigated by means of radio echo sounding.

  12. Cenozoic ice sheet history from East Antarctic Wilkes Land continental margin sediments

    Science.gov (United States)

    Escutia, C.; De Santis, L.; Donda, F.; Dunbar, R.B.; Cooper, A. K.; Brancolini, Giuliano; Eittreim, S.L.

    2005-01-01

    The long-term history of glaciation along the East Antarctic Wilkes Land margin, from the time of the first arrival of the ice sheet to the margin, through the significant periods of Cenozoic climate change is inferred using an integrated geophysical and geological approach. We postulate that the first arrival of the ice sheet to the Wilkes Land margin resulted in the development of a large unconformity (WL-U3) between 33.42 and 30 Ma during the early Oligocene cooling climate trend. Above WL-U3, substantial margin progradation takes place with early glacial strata (e.g., outwash deposits) deposited as low-angle prograding foresets by temperate glaciers. The change in geometry of the prograding wedge across unconformity WL-U8 is interpreted to represent the transition, at the end of the middle Miocene "climatic optimum" (14-10 Ma), from a subpolar regime with dynamic ice sheets (i.e., ice sheets come and go) to a regime with persistent but oscillatory ice sheets. The steep foresets above WL-U8 likely consist of ice proximal sediments (i.e., water-lain till and debris flows) deposited when grounded ice-sheets extended into the shelf. On the continental rise, shelf progradation above WL-U3 results in an up-section increase in the energy of the depositional environment (i.e., seismic facies indicative of more proximal turbidite and of bottom contour current deposition from the deposition of the lower WL-S5 sequence to WL-S7). Maximum rates of sediment delivery to the rise occur during the development of sequences WL-S6 and WL-S7, which we infer to be of middle Miocene age. During deposition of the two uppermost sequences, WL-S8 and WL-S9, there is a marked decrease in the sediment supply to the lower continental rise and a shift in the depocenters to more proximal areas of the margin. We believe WL-S8 records sedimentation during the final transition from a dynamic to a persistent but oscillatory ice sheet in this margin (14-10 Ma). Sequence WL-S9 forms under a polar

  13. A two-layer flow model to represent ice-ocean interactions beneath Antarctic ice shelves

    Directory of Open Access Journals (Sweden)

    V. Lee

    2011-01-01

    Full Text Available We develop a two-dimensional two-layer flow model that can calculate melt rates beneath ice shelves from ocean temperature and salinity fields at the shelf front. The cavity motion is split into two layers where the upper plume layer represents buoyant meltwater-rich water rising along the underside of the ice to the shelf front, while the lower layer represents the ambient water connected to the open ocean circulating beneath the plume. Conservation of momentum has been reduced to a frictional geostrophic balance, which when linearized provides algebraic equations for the plume velocity. The turbulent exchange of heat and salt between the two layers is modelled through an entrainment rate which is directed into the faster flowing layer.

    The numerical model is tested using an idealized geometry based on the dimensions of Pine Island Ice Shelf. We find that the spatial distribution of melt rates is fairly robust. The rates are at least 2.5 times higher than the mean in fast flowing regions corresponding to the steepest section of the underside of the ice shelf close to the grounding line and to the converged geostrophic flow along the rigid lateral boundary. Precise values depend on a combination of entrainment and plume drag coefficients. The flow of the ambient is slow and the spread of ocean scalar properties is dominated by diffusion.

  14. Refinement of the ice absorption spectrum in the visible using radiance profile measurements in Antarctic snow

    Science.gov (United States)

    Picard, Ghislain; Libois, Quentin; Arnaud, Laurent

    2016-11-01

    Ice is a highly transparent material in the visible. According to the most widely used database (IA2008; Warren and Brandt, 2008), the ice absorption coefficient reaches values lower than 10-3 m-1 around 400 nm. These values were obtained from a vertical profile of spectral radiance measured in a single snow layer at Dome C in Antarctica. We reproduced this experiment using an optical fiber inserted in the snow to record 56 profiles from which 70 homogeneous layers were identified. Applying the same estimation method on every layer yields 70 ice absorption spectra. They present a significant variability but absorption coefficients are overall larger than IA2008 by 1 order of magnitude at 400-450 nm. We devised another estimation method based on Bayesian inference that treats all the profiles simultaneously. It reduces the statistical variability and confirms the higher absorption, around 2 × 10-2 m-1 near the minimum at 440 nm. We explore potential instrumental artifacts by developing a 3-D radiative transfer model able to explicitly account for the presence of the fiber in the snow. The simulation shows that the radiance profile is indeed perturbed by the fiber intrusion, but the error on the ice absorption estimate is not larger than a factor of 2. This is insufficient to explain the difference between our new estimate and IA2008. The same conclusion applies regarding the plausible contamination by black carbon or dust, concentrations reported in the literature are insufficient. Considering the large number of profiles acquired for this study and other estimates from the Antarctic Muon and Neutrino Detector Array (AMANDA), we nevertheless estimate that ice absorption values around 10-2 m-1 at the minimum are more likely than under 10-3 m-1. A new estimate in the range 400-600 nm is provided for future modeling of snow, cloud, and sea-ice optical properties. Most importantly, we recommend that modeling studies take into account the large uncertainty of the ice

  15. Could a new ice core offer an insight into the stability of the West Antarctic Ice Sheet during the last interglacial?

    Science.gov (United States)

    Mulvaney, R.; Hindmarsh, R. C.

    2013-12-01

    Vaughan et al., in their 2011 paper 'Potential Seaways across West Antarctica' (Geochem. Geophys. Geosyst., 12, Q10004, doi:10.1029/2011GC003688), offer the intriguing prospect that substantial ice loss from the West Antarctic Ice Sheet during the previous interglacial period might have resulted in the opening of a seaway between the Weddell Sea and the Amundsen Sea. One of their potential seaways passes between the south western corner of the present Ronne Ice Shelf and the Pine Island Bay, through what is currently the course of the Rutford Ice Stream, between the Ellsworth Mountains and the Fletcher Promontory. To investigate whether this seaway could have existed (and to recover a paleoclimate and ice sheet history from the Weddell Sea), a team from the British Antarctic Survey and the Laboratoire de Glaciologie et Géophysique de l'Environnement drilled an ice core from a close to a topographic dome in the ice surface on the Fletcher Promontory in January 2012, reaching the bedrock at 654.3m depth from the surface. The site was selected to penetrate directly through the centre of a Raymond cupola observed in internal radar reflections from the ice sheet, with the intention that this would ensure we obtained the oldest ice available from the Fletcher Promontory. The basal ice sheet temperature measured was -18°C, implying the oldest ice would not have melted away from the base, while the configuration of the Raymond cupola in the radar horizons suggested stability in the ice dome topography during the majority of the Holocene. Our hypothesis is that chemical analysis of the ice core will reveal whether the site was ever relatively close to open sea water or ice shelf in the Rutford channel 20 km distant, rather than the current 700 km distance to sea ice/open water in either the Weddell Sea or the Amundsen Sea. While we do not yet have the chemistry data to test this hypothesis, in this poster we will discuss whether there is in reality any potential local

  16. Origin and sources of dissolved organic matter in snow on the East Antarctic ice sheet.

    Science.gov (United States)

    Antony, Runa; Grannas, Amanda M; Willoughby, Amanda S; Sleighter, Rachel L; Thamban, Meloth; Hatcher, Patrick G

    2014-06-03

    Polar ice sheets hold a significant pool of the world's carbon reserve and are an integral component of the global carbon cycle. Yet, organic carbon composition and cycling in these systems is least understood. Here, we use ultrahigh resolution mass spectrometry to elucidate, at an unprecedented level, molecular details of dissolved organic matter (DOM) in Antarctic snow. Tens of thousands of distinct molecular species are identified, providing clues to the nature and sources of organic carbon in Antarctica. We show that many of the identified supraglacial organic matter formulas are consistent with material from microbial sources, and terrestrial inputs of vascular plant-derived materials are likely more important sources of organic carbon to Antarctica than previously thought. Black carbon-like material apparently originating from biomass burning in South America is also present, while a smaller fraction originated from soil humics and appears to be photochemically or microbially modified. In addition to remote continental sources, we document signals of oceanic emissions of primary aerosols and secondary organic aerosol precursors. The new insights on the diversity of organic species in Antarctic snowpack reinforce the importance of studying organic carbon associated with the Earth's polar regions in the face of changing climate.

  17. Antarctic sea ice increase consistent with intrinsic variability of the Amundsen Sea Low

    Science.gov (United States)

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

    2016-04-01

    We investigate the relationship between atmospheric circulation variability and the recent trends in Antarctic sea ice extent (SIE) using Coupled Model Intercomparison Project Phase 5 (CMIP5) atmospheric data, ECMWF Interim reanalysis fields and passive microwave satellite data processed with the Bootstrap version 2 algorithm. Over 1979-2013 the annual mean total Antarctic SIE increased at a rate of 195 × 103 km2 dec-1 (1.6 % dec-1), p 4.0 % dec-1) has been in the Ross Sea sector. Off West Antarctica there is a high correlation between trends in SIE and trends in the near-surface winds. The Ross Sea SIE seasonal trends are positive throughout the year, but largest in spring. The stronger meridional flow over the Ross Sea has been driven by a deepening of the Amundsen Sea Low (ASL). Pre-industrial control and historical simulations from CMIP5 indicate that the observed deepening of the ASL and stronger southerly flow over the Ross Sea are within the bounds of modeled intrinsic variability. The spring trend would need to continue for another 11 years for it to fall outside the 2 standard deviation range seen in 90 % of the simulations.

  18. Titanium carbide and titania phases on Antarctic ice particles of probable extraterrrestrial origin

    Science.gov (United States)

    Zolensky, M. E.; Pun, A.; Thomas, K. L.

    1989-01-01

    Two unique titania-rich particles, found within ancient Antarctic ice have been discovered and characterized, and are believed to be of extraterrestrial origin. Both particles contain abundant submicron-sized crystals of Magneli phases (Ti(n)O(2n-1). In addition, one particle contains a core of TiC. Whereas the Magneli phases would have been stable in the early solar nebula, and so probably formed there, the TiC is more likely to have condensed in the cool, dusty, carbon-rich outer shell of a red giant star. It is suggested that both particles are interplanetary dust particles whose Magneli phases carry a record of the PO2-T conditions of the early solar nebula. It is further suggested that the TiC grain in particle 705 is remnant interstellar dust.

  19. Study on changes of plasmalemma permeability and some primary inorganic ions of Antarctic ice microalgae (Chlamydomonas sp. ICE-L) in the low-temperature stress

    Institute of Scientific and Technical Information of China (English)

    Zheng Zhou; Miao Jinlai; Chen Hao; Zhang Botao; Li Guangyou

    2006-01-01

    The changes of plasrnalemma permeability and some primary inorganic ions of Antarctic ice microalgae (Chlamydomonas sp. ICE-L) in the low-temperature stress were examined. The plasmalemma of ICE-L could maintain the stability at the freezing condition of -6℃. That signifies that it could maintain the proper function of plasmalemma and stability of the intracellular environment during sea ice formation. The function of inorganic ions on low-temperature adaptation of ICE-L was investigated by using the X-ray microanalysis method. Low temperature (0~-6℃) induces Ca2 + concentration increment of cytoplasm, but after 24 h the content decrease quickly to normal value. As a matter of fact, Ca2 + plays an important role as the second messenger in the low temperature adaptation of ICE-L. In addition, low temperature also influences on the other primary inorganic ions transfer and the cell maintains activity by keeping ratio balance among different ions. Above all, it is necessary for Antarctic ice microalgae to survive and breed by maintaining the stability of K + content and the balance of Na +/Cl-.

  20. Coring to the West Antarctic ice sheet bed with a new Deep Ice Sheet Coring (DISC) drill

    Science.gov (United States)

    Bentley, C. R.; Taylor, K. C.; Shturmakov, A. J.; Mason, W. P.; Emmel, G. R.; Lebar, D. A.

    2005-05-01

    As a contribution to IPY 2007-2008, the U.S. ice core research community, supported by the National Science Foundation, plans to core through the West Antarctic ice sheet (WAIS) at the ice-flow divide between the Ross Sea and Amundsen Sea drainage systems. The aim is to develop a unique series of interrelated climatic, ice-dynamic, and biologic records focused on understanding interactions among global earth systems. There will be approximately 15 separate but synergistic projects to analyze the ice and interpret the records. The most significant expected outcome of the WAIS Divide program will be climate records for the last ~40,000 years with an annually resolved chronology (through layer counting), comparable to the records from central Greenland. The data will also extend, at lower temporal resolution, to approximately 100,000 BP. These records will permit comparison of environmental conditions between the northern and southern hemispheres, and study of greenhouse gas concentrations in the paleoatmosphere, with unprecedented detail. To accomplish the coring, an innovative new Deep Ice Sheet Coring (DISC) drill is being built at the University of Wisconsin. The modular design of the bore-hole assembly (sonde) provides high flexibility for producing a 122 mm diameter ice core to depths of 4,000 m with maximum core lengths of 4 m. The DISC drill has a rotating outer barrel that can be used with or without an inner barrel designed to improve core recovery in brittle ice. Separate and independent motors for the drill and pump allow cutter speeds from 0 to 150 rpm and pump rates from 0 to 140 gpm. The high pumping rate should alleviate problems drilling in warm ice near the bed; it also helps make tripping speeds several times faster than with the old US drill. Other innovations include vibration and acoustic sensors for monitoring the drilling process, a segmented core barrel to avoid the formerly persistent problem of bent core barrels, and a high-speed data

  1. Uplift of the Transantarctic Mountains and the bedrock beneath the East Antarctic ice sheet

    Science.gov (United States)

    ten Brink, U.S.; Hackney, R.I.; Bannister, S.; Stern, T.A.; Makovsky, Y.

    1997-01-01

    In recent years the Transantarctic Mountains (TAM), the largest noncontractional mountain belt in the world, have become the focus of modelers who explained their uplift by a variety of isostatic and thermal mechanisms. A problem with these models is a lack of available data to compare with model predictions. We report here the results of a 312-km-long geophysical traverse conducted in 1993/1994 in the hinterland of the TAM. Using detailed subglacial topography and gravity measurements, we confirm the origin of the TAM as a flexural uplift of the edge of East Antarctica. Using an elastic model with a free edge, we can jointly fit the topography and the gravity with a plate having an elastic thickness of 85 ?? 15 km and a preuplift elevation of 700 ?? 50 m for East Antarctica. Using a variety of evidence, we argue that the uplift is coincident with a relatively minor tectonic event of transtensional motion between East and West Antarctica during the Eocene rather than the Late Cretaceous rifting event that created the Ross Embayment. We suggest that this transtensional motion caused the continuous plate to break, which created an escarpment that significantly increased the rates of erosion and exhumation. Results from the geophysical traverse also extend our knowledge of the bedrock geology from the exposures within the TAM to the ice covered interior. Our interpretation suggests that the Ferrar flood basalts extend at least 100 km westward under the ice. The Beacon Supergroup of Paleozoic and Mesozoic sediments thins gradually under the ice and its reconstructed thickness is reminiscent of profiles of foreland basins. Finally, there is no indication in the gravity field for an incomplete rebound due to significant melting of the East Antarctic ice sheet since the last glacial period.

  2. Some Recent Progress of Antarctic Ice Sheet Research%南极冰盖研究最新进展

    Institute of Scientific and Technical Information of China (English)

    唐学远; 孙波; 李院生; 崔祥斌; 李鑫

    2009-01-01

    南极冰盖是地球系统的重要组成部分,在全球气候系统中扮演着重要角色.通过对南极冰盖的研究将有助于了解其在全球气候系统中的作用,并为探讨全球气候过去、现在以及未来的演化提供支撑.总结分析了近年来南极冰盖研究的一些重要进展,并在此基础上对南极冰盖研究领域的一些主要结果、观测事实以及未来变化展开讨论,重点介绍南极物质平衡、冰芯研究、冰下水系统、冰盖数值模拟方面最近的进展,评述未来可能的研究方向和应该关注的问题.%Antarctic ice sheet , as an important part of the Earth system, plays a critical role in the global climate change. The understanding of the Antarctic ice sheet will help in making sense of the global climate system, and support exploring the evolution of the global climate in the past, present and the future. By analysing the significant progress of Antarctic ice sheet research in recent years, on the basis of these major findings, observations, as well as the fact that future changes in the discussions, some recent progress is focused, including mass balance, ice cores, subglacial lakes and water system, numerical model of Antarctic ice sheet. Review of the possible future research directions should also be of concern.

  3. Proxies and measurement techniques for mineral dust in Antarctic ice cores.

    Science.gov (United States)

    Ruth, Urs; Barbante, Carlo; Bigler, Matthias; Delmonte, Barbara; Fischer, Hubertus; Gabrielli, Paolo; Gaspari, Vania; Kaufmann, Patrik; Lambert, Fabrice; Maggi, Valter; Marino, Federica; Petit, Jean-Robert; Udisti, Roberto; Wagenbach, Dietmar; Wegner, Anna; Wolff, Eric W

    2008-08-01

    To improve quantitative interpretation of ice core aeolian dust records, a systematic methodological comparison was made. This involved methods for water-insoluble particle counting (Coulter counter and laser-sensing particle detector), soluble ion analysis (ion chromatography and continuous flow analysis), elemental analysis (inductively coupled plasma mass spectroscopy at pH 1 and after full acid digestion), and water-insoluble elemental analysis (proton induced X-ray emission). Antarctic ice core samples covering the last deglaciation from the EPICA Dome C (EDC) and the EPICA Dronning Maud Land (EDML) cores were used. All methods correlate very well among each other, but the ratios of glacial age to Holocene concentrations, which are typically a factor approximately 100, differ between the methods by up to a factor of 2 with insoluble particles showing the largest variability. The recovery of ICP-MS measurements depends on the digestion method and is differentfor different elements and during different climatic periods. EDC and EDML samples have similar dust composition, which suggests a common dust source or a common mixture of sources for the two sites. The analyzed samples further reveal a change of dust composition during the last deglaciation.

  4. Non-climatic signal in ice core records: lessons from Antarctic mega-dunes

    Directory of Open Access Journals (Sweden)

    A. Ekaykin

    2015-12-01

    Full Text Available We present the results of glaciological investigations in the mega-dune area located 30 km to the east from Vostok Station (central East Antarctica implemented during the 58th, 59th and 60th Russian Antarctic Expedition (January 2013–January 2015. Snow accumulation rate and isotope content (δD, δ18O and δ17O were measured along the 2 km profile across the mega-dune ridge accompanied by precise GPS altitude measurements and GPR survey. It is shown that the spatial variability of snow accumulation and isotope content covaries with the surface slope. The accumulation rate regularly changes by one order of magnitude within the distance −1. The full cycle of the dune drift is thus about 410 years. Since the spatial anomalies of snow accumulation and isotopic composition are supposed to drift with the dune, an ice core drilled in the mega-dune area would exhibit the non-climatic 410 year cycle of these two parameters. We simulated a vertical profile of snow isotopic composition with such a non-climatic variability, using the data on the dune size and velocity. This artificial profile is then compared with the real vertical profile of snow isotopic composition obtained from a core drilled in the mega-dune area. We note that the two profiles are very similar. The obtained results are discussed in terms of interpretation of data obtained from ice cores drilled beyond the mega-dune areas.

  5. Potential of the solid-Earth response for limiting long-term West Antarctic Ice Sheet retreat

    Science.gov (United States)

    Konrad, Hannes; Sasgen, Ingo; Pollard, David; Klemann, Volker

    2016-04-01

    The West Antarctic Ice Sheet (WAIS) is assumed to be inherently unstable because it is grounded below sea level in a large part, where the bedrock deepens from today's grounding line towards the interior of the ice sheet. Idealized simulations have shown that bedrock uplift due to isostatic adjustment of the solid Earth and the associated sea-level fall may stop the retreat of such a marine-based ice sheet (Gomez et al., 2012). Here, we employ a coupled model for ice-sheet dynamics and solid-Earth dynamics, including a gravitationally consistent description of sea level, to investigate the influence of the viscoelastic Earth structure on the WAIS' future stability (Konrad et al. 2015). For this, we start from a steady-state condition for the Antarctic Ice Sheet close to present-day observations and apply atmospheric and oceanic forcing of different strength to initiate the retreat of the WAIS and investigate the effect of the viscoelastic deformation on the ice evolution for a range of solid-Earth rheologies. We find that the climate forcing is the primary control on the occurrence of the WAIS collapse. However, for moderate climate forcing and a weak solid-Earth rheology associated with the West Antarctic rift system (asthenosphere viscosities of 3x10^19 Pa s or less), we find that the combined effect of bedrock uplift and gravitational sea-level fall limits the retreat to the Amundsen Sea embayment on millennial time scales. In contrast, a stiffer Earth rheology yields a collapse under these conditions. Under a stronger climate forcing, weak Earth structures do not prevent the WAIS collapse; however, they produce a delay of up to 5000 years in comparison to a stiffer solid-Earth rheology. In an additional experiment, we test the impact of sea-level rise from an assumed fast deglaciation of the Greenland Ice Sheet. In cases when the climatic forcing is too weak to force WAIS collapse by itself, the additional rise in sea-level leads to disintegration of the WAIS

  6. Assessing the Impact of Retreat Mechanisms in a Simple Antarctic Ice Sheet Model Using Bayesian Calibration

    Science.gov (United States)

    Shaffer, Gary; Pollard, David; Guan, Yawen; Wong, Tony E.; Forest, Chris E.; Keller, Klaus

    2017-01-01

    The response of the Antarctic ice sheet (AIS) to changing climate forcings is an important driver of sea-level changes. Anthropogenic climate change may drive a sizeable AIS tipping point response with subsequent increases in coastal flooding risks. Many studies analyzing flood risks use simple models to project the future responses of AIS and its sea-level contributions. These analyses have provided important new insights, but they are often silent on the effects of potentially important processes such as Marine Ice Sheet Instability (MISI) or Marine Ice Cliff Instability (MICI). These approximations can be well justified and result in more parsimonious and transparent model structures. This raises the question of how this approximation impacts hindcasts and projections. Here, we calibrate a previously published and relatively simple AIS model, which neglects the effects of MICI and regional characteristics, using a combination of observational constraints and a Bayesian inversion method. Specifically, we approximate the effects of missing MICI by comparing our results to those from expert assessments with more realistic models and quantify the bias during the last interglacial when MICI may have been triggered. Our results suggest that the model can approximate the process of MISI and reproduce the projected median melt from some previous expert assessments in the year 2100. Yet, our mean hindcast is roughly 3/4 of the observed data during the last interglacial period and our mean projection is roughly 1/6 and 1/10 of the mean from a model accounting for MICI in the year 2100. These results suggest that missing MICI and/or regional characteristics can lead to a low-bias during warming period AIS melting and hence a potential low-bias in projected sea levels and flood risks. PMID:28081273

  7. Assessing the Impact of Retreat Mechanisms in a Simple Antarctic Ice Sheet Model Using Bayesian Calibration.

    Science.gov (United States)

    Ruckert, Kelsey L; Shaffer, Gary; Pollard, David; Guan, Yawen; Wong, Tony E; Forest, Chris E; Keller, Klaus

    2017-01-01

    The response of the Antarctic ice sheet (AIS) to changing climate forcings is an important driver of sea-level changes. Anthropogenic climate change may drive a sizeable AIS tipping point response with subsequent increases in coastal flooding risks. Many studies analyzing flood risks use simple models to project the future responses of AIS and its sea-level contributions. These analyses have provided important new insights, but they are often silent on the effects of potentially important processes such as Marine Ice Sheet Instability (MISI) or Marine Ice Cliff Instability (MICI). These approximations can be well justified and result in more parsimonious and transparent model structures. This raises the question of how this approximation impacts hindcasts and projections. Here, we calibrate a previously published and relatively simple AIS model, which neglects the effects of MICI and regional characteristics, using a combination of observational constraints and a Bayesian inversion method. Specifically, we approximate the effects of missing MICI by comparing our results to those from expert assessments with more realistic models and quantify the bias during the last interglacial when MICI may have been triggered. Our results suggest that the model can approximate the process of MISI and reproduce the projected median melt from some previous expert assessments in the year 2100. Yet, our mean hindcast is roughly 3/4 of the observed data during the last interglacial period and our mean projection is roughly 1/6 and 1/10 of the mean from a model accounting for MICI in the year 2100. These results suggest that missing MICI and/or regional characteristics can lead to a low-bias during warming period AIS melting and hence a potential low-bias in projected sea levels and flood risks.

  8. An unusual early Holocene diatom event north of the Getz Ice Shelf (Amundsen Sea): Implications for West Antarctic Ice Sheet development

    Science.gov (United States)

    Esper, O.; Gersonde, R.; Hillenbrand, C.; Kuhn, G.; Smith, J.

    2011-12-01

    Modern global change affects not only the polar north but also, and to increasing extent, the southern high latitudes, especially the Antarctic regions covered by the West Antarctic Ice Sheet (WAIS). Consequently, knowledge of the mechanisms controlling past WAIS dynamics and WAIS behaviour at the last deglaciation is critical to predict its development in a future warming world. Geological and palaeobiological information from major drainage areas of the WAIS, like the Amundsen Sea Embayment, shed light on the history of the WAIS glaciers. Sediment records obtained from a deep inner shelf basin north of Getz Ice Shelf document a deglacial warming in three phases. Above a glacial diamicton and a sediment package barren of microfossils that document sediment deposition by grounded ice and below an ice shelf or perennial sea ice cover (possibly fast ice), respectively, a sediment section with diatom assemblages dominated by sea ice taxa indicates ice shelf retreat and seasonal ice-free conditions. This conclusion is supported by diatom-based summer temperature reconstructions. The early retreat was followed by a phase, when exceptional diatom ooze was deposited around 12,500 cal. years B.P. [1]. Microscopical inspection of this ooze revealed excellent preservation of diatom frustules of the species Corethron pennatum together with vegetative Chaetoceros, thus an assemblage usually not preserved in the sedimentary record. Sediments succeeding this section contain diatom assemblages indicating rather constant Holocene cold water conditions with seasonal sea ice. The deposition of the diatom ooze can be related to changes in hydrographic conditions including strong advection of nutrients. However, sediment focussing in the partly steep inner shelf basins cannot be excluded as a factor enhancing the thickness of the ooze deposits. It is not only the presence of the diatom ooze but also the exceptional preservation and the species composition of the diatom assemblage

  9. Comparison of hybrid schemes for the combination of shallow approximations in numerical simulations of the Antarctic Ice Sheet

    Science.gov (United States)

    Bernales, Jorge; Rogozhina, Irina; Greve, Ralf; Thomas, Maik

    2017-01-01

    The shallow ice approximation (SIA) is commonly used in ice-sheet models to simplify the force balance equations within the ice. However, the SIA cannot adequately reproduce the dynamics of the fast flowing ice streams usually found at the margins of ice sheets. To overcome this limitation, recent studies have introduced heuristic hybrid combinations of the SIA and the shelfy stream approximation. Here, we implement four different hybrid schemes into a model of the Antarctic Ice Sheet in order to compare their performance under present-day conditions. For each scheme, the model is calibrated using an iterative technique to infer the spatial variability in basal sliding parameters. Model results are validated against topographic and velocity data. Our analysis shows that the iterative technique compensates for the differences between the schemes, producing similar ice-sheet configurations through quantitatively different results of the sliding coefficient calibration. Despite this we observe a robust agreement in the reconstructed patterns of basal sliding parameters. We exchange the calibrated sliding parameter distributions between the schemes to demonstrate that the results of the model calibration cannot be straightforwardly transferred to models based on different approximations of ice dynamics. However, easily adaptable calibration techniques for the potential distribution of basal sliding coefficients can be implemented into ice models to overcome such incompatibility, as shown in this study.

  10. Influence of temperature on glutathione level and glutathione-related enzyme activities of Antarctic ice microalgae Chlamydomonas sp.ICE-L

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    GSH system plays a role in the control of the redox balance state, anti-oxidation and protecting life from injury of ROS (reactive oxygen species).In present paper, the possible GSH system of Chlamydomonas sp.ICE-L has been investigated by evaluating GSH and GSH-related enzymatic responses at different temperatures using speetrophotometer methods.The results showed that the GSH system is correlated positively to low temperature, and other factors but GR are correlated negatively to high temperature.So GSH and GSH-related enzymes play an important role in the adaptation of Antarctic ice microulgae to low temperature.

  11. Emperors in hiding: when ice-breakers and satellites complement each other in Antarctic exploration.

    Directory of Open Access Journals (Sweden)

    André Ancel

    Full Text Available Evaluating the demographic trends of marine top predators is critical to understanding the processes involved in the ongoing rapid changes in Antarctic ecosystems. However, the remoteness and logistical complexity of operating in Antarctica, especially during winter, make such an assessment difficult. Satellite imaging is increasingly recognised as a valuable method for remote animal population monitoring, yet its accuracy and reliability are still to be fully evaluated. We report here the first ground visit of an emperor penguin colony first discovered by satellite, but also the discovery of a second one not indicated by satellite survey at that time. Several successive remote surveys in this coastal region of East Antarctica, both before and after sudden local changes, had indeed only identified one colony. These two colonies (with a total of ca. 7,400 breeding pairs are located near the Mertz Glacier in an area that underwent tremendous habitat change after the glacier tongue broke off in February 2010. Our findings therefore suggest that a satellite survey, although offering a major advance since it allows a global imaging of emperor penguin colonies, may miss certain colony locations when challenged by certain features of polar ecosystems, such as snow cover, evolving ice topology, and rapidly changing habitat. Moreover our survey shows that this large seabird has considerable potential for rapid adaptation to sudden habitat loss, as the colony detected in 2009 may have moved and settled on new breeding grounds. Overall, the ability of emperor penguin colonies to relocate following habitat modification underlines the continued need for a mix of remote sensing and field surveys (aerial photography and ground counts, especially in the less-frequented parts of Antarctica, to gain reliable knowledge about the population demography and dynamics of this flagship species of the Antarctic ecosystem.

  12. Emperors in hiding: when ice-breakers and satellites complement each other in Antarctic exploration.

    Science.gov (United States)

    Ancel, André; Cristofari, Robin; Fretwell, Peter T; Trathan, Phil N; Wienecke, Barbara; Boureau, Matthieu; Morinay, Jennifer; Blanc, Stéphane; Le Maho, Yvon; Le Bohec, Céline

    2014-01-01

    Evaluating the demographic trends of marine top predators is critical to understanding the processes involved in the ongoing rapid changes in Antarctic ecosystems. However, the remoteness and logistical complexity of operating in Antarctica, especially during winter, make such an assessment difficult. Satellite imaging is increasingly recognised as a valuable method for remote animal population monitoring, yet its accuracy and reliability are still to be fully evaluated. We report here the first ground visit of an emperor penguin colony first discovered by satellite, but also the discovery of a second one not indicated by satellite survey at that time. Several successive remote surveys in this coastal region of East Antarctica, both before and after sudden local changes, had indeed only identified one colony. These two colonies (with a total of ca. 7,400 breeding pairs) are located near the Mertz Glacier in an area that underwent tremendous habitat change after the glacier tongue broke off in February 2010. Our findings therefore suggest that a satellite survey, although offering a major advance since it allows a global imaging of emperor penguin colonies, may miss certain colony locations when challenged by certain features of polar ecosystems, such as snow cover, evolving ice topology, and rapidly changing habitat. Moreover our survey shows that this large seabird has considerable potential for rapid adaptation to sudden habitat loss, as the colony detected in 2009 may have moved and settled on new breeding grounds. Overall, the ability of emperor penguin colonies to relocate following habitat modification underlines the continued need for a mix of remote sensing and field surveys (aerial photography and ground counts), especially in the less-frequented parts of Antarctica, to gain reliable knowledge about the population demography and dynamics of this flagship species of the Antarctic ecosystem.

  13. Determination of Antarctic Ice Sheet stability over the last ˜500 ka through a study of iceberg-rafted debris

    Science.gov (United States)

    Teitler, Lora; Warnke, Detlef A.; Venz, Kathryn A.; Hodell, David A.; Becquey, Sabine; Gersonde, Rainer; Teitler, Winston

    2010-01-01

    We have analyzed ice-rafted debris (IRD) from the South Atlantic Ocean (˜43°S, 9°E) in order to investigate Antarctic Ice Sheet history during the late Pleistocene; the cores examined for this study include piston core TN057-6-PC4 and Ocean Drilling Program Leg 177 drill core Site 1090 (177-1090). Over the last 500 ka at this distal location, IRD arrived during both glacials and interglacials. IRD is present even during warmer intervals, is greatest during colder intervals, and is absent only during terminations and a few other brief intervals. Four different methods are used to normalize the IRD counts, which are then compared to support our interpretation. Several other high-quality climate proxies from this location also aid our interpretations. We conclude that sea surface temperatures are the primary control on the delivery of IRD to this site. During cold times more icebergs survived to reach this distal location. During warm times only a few of the largest icebergs could travel this far. Garnets found in these sediments suggest a likely East Antarctic origin for the IRD; the presence of garnets even during warm intervals further strongly supports that the iceberg source must be the East Antarctic Ice Sheet (EAIS). Therefore, the EAIS must have continued to reach the ocean at least in some part of its margin throughout the last 500 ka. On the other hand, we cannot specifically trace any IRD to the West Antarctic Ice Sheet (WAIS), so WAIS persistence cannot be tested. A particular radiolarian, identified as Dictyocoryne profunda (Ehrenberg) (sensu Boltovskoy (1998)), shows up in the examined size fraction generally only during warm phases. We suggest that D. profunda is a sensitive indicator of warm water temperatures and that it deserves further study.

  14. Changes of proteins in the Antarctic ice microalga Chlamydomonas sp. cultured under UV-B radiation stress

    Institute of Scientific and Technical Information of China (English)

    KAN Guangfeng; MIAO Jinlai; SHI Cuijuan; LI Guangyou

    2006-01-01

    Antarctic ice microalga Chlamydomonas sp. can thrive undisturbed under high UV radiation in the Antarctic ice layer. However, it is unknown that the initial adaptation mechanisms in protein level occurring in response to high UV radiation. Global-expression profiling of proteins in response to stress was analyzed by two-dimensional electrophoresis (2-DE) and image analysis. In the 2-DE analysis,protein preparation is the key step. Three different protein extract methods were compared, and the results showed that the trichloroacetic acid (TCA)-acetone fractional precipitation method was the fittest one. At the same time, the proteins in Chlamydomonas sp. were compared in 2-DE way, and the synthesis of seven protein spots was found disappeared and 18 decreased after exposed to UV-B radiation. In addition, 14 protein spots were enhanced or induced, among which two new peptides (20 and 21 kDa) appeared whose isoelectric point (pI) was 7.05 and 4.60 respectively. These changed proteins might act as key role in the acclimation of Antarctic ice microalga to UV-B radiation

  15. Preliminary research on the transmission path of nssSO2-4- and NO-3 in Antarctic ice sheet

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The main sources of nssSO24- and NO-3 were summarized in this paper. By analyzing the spatial distribution features of major ions in Antarctic ice sheet and studying on the different time of the same volcanic event recorded by different ice cores from different regions in Antarctica, this paper intends to study the transmission path of nssSO24- and NO-3. Results show that nssSO24- and NO-3 are transmitted to the ice sheet through long distance and high altitude. The procedure of the transmission is that nssSO24- and NO-2 are transmitted to the level between the top of troposphere and the bottom of stratosphere, then subsided to the ice sheet surface and spread to other regions.

  16. State dependence of climatic instability over the past 720,000 years from Antarctic ice cores and climate modeling

    Science.gov (United States)

    Kawamura, Kenji; Abe-Ouchi, Ayako; Motoyama, Hideaki; Ageta, Yutaka; Aoki, Shuji; Azuma, Nobuhiko; Fujii, Yoshiyuki; Fujita, Koji; Fujita, Shuji; Fukui, Kotaro; Furukawa, Teruo; Furusaki, Atsushi; Goto-Azuma, Kumiko; Greve, Ralf; Hirabayashi, Motohiro; Hondoh, Takeo; Hori, Akira; Horikawa, Shinichiro; Horiuchi, Kazuho; Igarashi, Makoto; Iizuka, Yoshinori; Kameda, Takao; Kanda, Hiroshi; Kohno, Mika; Kuramoto, Takayuki; Matsushi, Yuki; Miyahara, Morihiro; Miyake, Takayuki; Miyamoto, Atsushi; Nagashima, Yasuo; Nakayama, Yoshiki; Nakazawa, Takakiyo; Nakazawa, Fumio; Nishio, Fumihiko; Obinata, Ichio; Ohgaito, Rumi; Oka, Akira; Okuno, Jun’ichi; Okuyama, Junichi; Oyabu, Ikumi; Parrenin, Frédéric; Pattyn, Frank; Saito, Fuyuki; Saito, Takashi; Saito, Takeshi; Sakurai, Toshimitsu; Sasa, Kimikazu; Seddik, Hakime; Shibata, Yasuyuki; Shinbori, Kunio; Suzuki, Keisuke; Suzuki, Toshitaka; Takahashi, Akiyoshi; Takahashi, Kunio; Takahashi, Shuhei; Takata, Morimasa; Tanaka, Yoichi; Uemura, Ryu; Watanabe, Genta; Watanabe, Okitsugu; Yamasaki, Tetsuhide; Yokoyama, Kotaro; Yoshimori, Masakazu; Yoshimoto, Takayasu

    2017-01-01

    Climatic variabilities on millennial and longer time scales with a bipolar seesaw pattern have been documented in paleoclimatic records, but their frequencies, relationships with mean climatic state, and mechanisms remain unclear. Understanding the processes and sensitivities that underlie these changes will underpin better understanding of the climate system and projections of its future change. We investigate the long-term characteristics of climatic variability using a new ice-core record from Dome Fuji, East Antarctica, combined with an existing long record from the Dome C ice core. Antarctic warming events over the past 720,000 years are most frequent when the Antarctic temperature is slightly below average on orbital time scales, equivalent to an intermediate climate during glacial periods, whereas interglacial and fully glaciated climates are unfavourable for a millennial-scale bipolar seesaw. Numerical experiments using a fully coupled atmosphere-ocean general circulation model with freshwater hosing in the northern North Atlantic showed that climate becomes most unstable in intermediate glacial conditions associated with large changes in sea ice and the Atlantic Meridional Overturning Circulation. Model sensitivity experiments suggest that the prerequisite for the most frequent climate instability with bipolar seesaw pattern during the late Pleistocene era is associated with reduced atmospheric CO2 concentration via global cooling and sea ice formation in the North Atlantic, in addition to extended Northern Hemisphere ice sheets. PMID:28246631

  17. A one-dimensional heat transfer model of the Antarctic Ice Sheet and modeling of snow temperatures at Dome A, the summit of Antarctic Plateau

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    A vertical one-dimensional numerical model for heat transferring within the near-surface snow layer of the Antarctic Ice Sheet was developed based on simplified parameterizations of associated physical processes for the atmosphere, radiation, and snow/ice systems. Using the meteorological data of an automatic weather station (AWS) at Dome A (80°22′S, 70°22′E), we applied the model to simulate the seasonal temperature variation within a depth of 20 m. Comparison of modeled results with observed snow temperatures at 4 measurement depths (0.1, 1, 3, 10 m) shows good agreement and consistent seasonal variations. The model results reveal the vertical temperature structure within the near-surface snow layer and its seasonal variance with more details than those by limited measurements. Analyses on the model outputs of the surface energy fluxes show that: 1) the surface energy balance at Dome A is characterized by the compensation between negative net radiation and the positive sensible fluxes, and 2) the sensible heat is on average transported from the atmosphere to the snow, and has an evident increase in spring. The results are considered well representative for the highest interior Antarctic Plateau.

  18. Antarctic ice sheet mass loss, glacio-isostatic adjustment and surface processes from ENVISAT, ICESat, CryoSat-2, GRACE and GPS

    Science.gov (United States)

    Bamber, Jonathan L.; Martin-Espanol, Alba; Schoen, Nana; Zammit-Mangion, Andrew; Luthcke, Scott; Petrie, Liz; Remy, Frederique; Wouters, Bert; King, Matt; Rougier, Jonty

    2015-04-01

    Constraining past ice mass changes, identifying their cause(s) and determining rigorous error estimates, is important for closing the sea level budget and as an input for and test of numerical models. For the Antarctic ice sheet, considerable uncertainty remains between different methods and groups. Estimates obtained from altimetry, gravimetry, and mass-budget methods can yield conflicting results with error estimates that do not always overlap, while the, commonly adopted, use of different forward models to isolate and remove the effects of glacio-isostatic adjustment (GIA) and surface mass balance (SMB) processes introduces another source of uncertainty which is hard to quantify. To address both these issues, we present a statistical modelling approach to the problem. We combine the observational data, including satellite altimetry, GRACE, GPS and InSAR, and use the different degrees of spatial and temporal smoothness to constrain the underlying geophysical processes. This is achieved via a spatio-temporal Bayesian hierarchical model, employing dimensionality reduction methods to allow the solution to remain tractable in the presence of the large number (> 10^7) of observations involved. The resulting trend estimates are only dependent on length and smoothness properties obtained from numerical models, but are otherwise entirely data-driven. As a consequence, the solutions provide a valuable independent test of the forward models. Here, we present the annually-resolved spatial fields for i) dynamic ice loss, ii) SMB anomaly, iii) firn compaction and iv) (the time invariant) GIA, using a combination of GRACE, ICESat, ENVISat, CryoSat 2 and GPS vertical uplift rates, for 2003-2013. The elastic flexure of the crust is also determined simultaneously. We focus here primarily on the mass trends rather than solid earth effects. We obtain a mean rate of -97+-16 Gt/yr for the 11 year period with a statstically significant positive trend for East Antarctica and negative

  19. Mass change detection in Antarctic ice sheet using ICESat block analysis techniques from 2003~2008%基于ICESat块域分析法探测2003~2008年南极冰盖质量变化

    Institute of Scientific and Technical Information of China (English)

    史红岭; 陆洋; 杜宗亮; 贾路路; 张子占; 周春霞

    2011-01-01

    In this paper, the ICESat laser altimetry data is used to obtain an estimate of the mass balance of Antarctic ice sheet from February 2003 to March 2008. The time series of elevation change in Antarctic ice sheet are derived by the block crossover analysis using the ICESat nadir ground track, and the calculation of the campaign basis is discussed. A least square regression of crossover difference is applied to calculate the average elevation change trend and the seasonal cycle, and then the mass changes of Antarctic ice sheet are estimated by combining the elevation change rate with the surface firn density model. The result shows that seasonal cycle signals are obvious in Antarctic ice sheet height changes, and the average annual amplitude is about 2.21 cm. On the coast of the Antarctica continent, there are significant thinning and thickening, especially near the Amundsen Sea embayment of west Antarctic and Antarctic Peninsula. Considering the influence of GIA (three public GIA models), our best estimate of the mass change in Antarctic ice sheet is about -82~-73Gt/yr. For the ICESat, the ice sheet surface firn density model and the GIA model are the main factors in the mass change estimates.%利用2003~2008年间的ICESat卫星激光测高数据,通过块域交叉点分析提取南极大陆冰盖表面高程变化信息,同时探讨了卫星激光测高不同任务间的系统偏差,结合冰盖地表粒雪密度模型探测南极大陆冰盖质量变化,并对其原因做了初步分析.结果显示南极大陆冰盖高度变化具有明显的年周期信号,平均周年振幅为2.21 cm.在南极大陆的边缘,存在着明显的消融和增长,尤其是在西南极阿蒙森海湾附近的冰川和南极半岛.利用目前常用的三种不同的冰后回弹模型,计算得到南极大陆冰盖整体平均质量变化趋势约为-82~-73 Gt/yr.在由ICESat高度变化到质量变化过程中,冰盖地表粒雪密度和冰后回弹模型的不确定性是

  20. Dynamics of the late Plio-Pleistocene West Antarctic Ice Sheet documented in subglacial diamictites, AND-1B drill core

    Science.gov (United States)

    Cowan, Ellen A.; Christoffersen, Poul; Powell, Ross D.; Talarico, Franco M.

    2014-08-01

    Geologic studies of sediment deposited by glaciers can provide crucial insights into the subglacial environment. We studied muddy diamictites in the ANtarctic geological DRILLing (ANDRILL) AND-1B drill core, acquired from beneath the Ross Ice Shelf in McMurdo Sound, with the aim of identifying paleo-ice stream activity in the Plio-Pleistocene. Glacial advances were identified from glacial surfaces of erosion (GSEs) and subglacial diamictites within three complete sequences were investigated using lithofacies associations, micromorphology, and quartz sand grain microtextures. Whereas conditions in the Late Pliocene resemble the modern Greenland Ice Sheet where fast flowing glaciers lubricated by surface meltwater terminate directly in the sea (interval 201-212 mbsl) conditions in the Late Pleistocene are similar to modern West Antarctic Ice Sheet (WAIS) ice streams (38-49 mbsl). We identify the latter from ductile deformation and high pore-water pressure, which resulted in pervasive rotation and formation of till pellets and low relief, rounded sand grains dominated by abrasion. In the transitional period during the Mid-Pleistocene (55-68 mbsf), a slow moving inland ice sheet deposited tills with brittle deformation, producing lineations and bi-masepic and unistrial plasma fabric, along with high relief, conchoidally fractured quartz grains. Changes in the provenance of gravel to cobble-size clasts support a distant source area of Byrd Glacier for fast-flowing paleo-ice streams and a proximal area between Darwin and Skelton Glaciers for the slow-moving inland ice sheet. This difference in till provenance documents a shift in direction of glacial flow at the core site, which indirectly reflects changes in the size and thickness of the WAIS. Hence, we found that fast ice streaming motion is a consequence of a thicker WAIS pushing flow lines to the west and introducing clasts from the Byrd Glacier source area to the drill site. The detailed analysis of diamictites in

  1. Late Quaternary Advance and Retreat of an East Antarctic Ice Shelf System: Insights from Sedimentary Beryllium-10 Concentrations

    Science.gov (United States)

    Guitard, M. E.; Shevenell, A.; Domack, E. W.; Rosenheim, B. E.; Yokoyama, Y.

    2014-12-01

    Observed retreat of Antarctica's marine-based glaciers and the presence of warm (~2°C) modified Circumpolar Deep Water on Antarctica's continental shelves imply ocean temperatures may influence Antarctic cryosphere stability. A paucity of information regarding Late Quaternary East Antarctic cryosphere-ocean interactions makes assessing the variability, timing, and style of deglacial retreat difficult. Marine sediments from Prydz Bay, East Antarctica contain hemipelagic siliceous mud and ooze units (SMO) alternating with glacial marine sediments. The record suggests Late Quaternary variability of local outlet glacier systems, including the Lambert Glacier/Amery Ice Shelf system that drains 15% of the East Antarctic Ice Sheet. We present a refined radiocarbon chronology and beryllium-10 (10Be) record of Late Quaternary depositional history in Prydz Channel, seaward of the Amery Ice Shelf system, which provides insight into the timing and variability of this important outlet glacier system. We focus on three piston cores (NBP01-01, JPC 34, 35, 36; 750 m water depth) that contain alternating SMO and granulated units uninterrupted by glacial till; the record preserves a succession of glacial marine deposits that pre-date the Last Glacial Maximum. We utilize the ramped pyrolysis preparatory method to improve the bulk organic carbon 14C-based chronology for Prydz Channel. To determine if the SMO intervals reflect open water conditions or sub-ice shelf advection, we measured sedimentary 10Be concentrations. Because ice cover affects 10Be pathways through the water column, sedimentary concentrations should provide information on past depositional environments in Prydz Channel. In Prydz Channel sediments, 10Be concentrations are generally higher in SMO units and lower in glacial units, suggesting Late Quaternary fluctuations in the Amery Ice Shelf. Improved chronologic constraints indicate that these fluctuations occurred on millennial timescales during the Last Glacial

  2. LGM-extent of the West Antarctic Ice Sheet offshore from the Hobbs Coast, based on paleo-ice stream bed observations

    Science.gov (United States)

    Klages, J.; Kuhn, G.; Hillenbrand, C.; Graham, A. G.; Smith, J.; Larter, R. D.; Gohl, K.

    2012-12-01

    Paleo-ice stream beds that are exposed today on the West Antarctic continental shelf provide unique archives of conditions at the base of the past ice sheet, that are difficult to assess beneath its modern, extant counterpart. During the last decade, several of these paleo-ice stream beds have been studied in detail to reconstruct the extent of the West Antarctic Ice Sheet (WAIS) at the Last Glacial Maximum (LGM), the patterns of ice drainage, and the timing of grounding-line retreat during the last deglaciation. However, despite significant advances, such information still remains poorly constrained in numerous drainage sectors of the WAIS. In particular, the maximum extent of ice at the LGM remains ambiguous for key drainage basins of the ice sheet. Whether the WAIS extended to the shelf break around the continent, or advanced only partially across its sea bed, is a crucial piece of information required for reconstructing and modeling patterns of ice-sheet change from past to present. Here we present marine geological and geophysical data that we collected on R/V "Polarstern" expedition ANT-XXVI/3 in early 2010 to investigate the extent, flow, and retreat of the WAIS, from an especially poorly studied part of the West Antarctic shelf, offshore from the Hobbs Coast in the western Amundsen Sea. Here, a landward deepening paleo-ice stream trough is incised into the shelf. The seafloor within the western-central part of the trough is characterized by a large trough-wide grounding zone wedge, ~70 m thick and ~17 km long, which overlies a high of seaward dipping sedimentary strata. The back-slope of the GZW is characterized by highly elongate streamlined bedforms suggesting fast paleo-ice flow towards NW. The crest of the wedge has been cross-cutted by iceberg keels. In contrast, the outer shelf seafloor offshore the GZW is predominantly smooth and featureless, although there is some evidence locally for iceberg scouring. A radiocarbon age from calcareous microfossils

  3. CEDEX research activities in Antarctica. Aquatic ecosystems in Byers Peninsula (Livingston Island, maritime Antarctica); Actividad investigadora del CEDEX en la Antartida. Ecosistemas acuaticos de la Peninsula Byers (Isla Livingston, Antartida)

    Energy Technology Data Exchange (ETDEWEB)

    Toro, M.; Quesada, A.; Camacho, A.; Oliva, M.; Alcami, A.; Antoniades, D.; Banon, M.; Fassnacht, S.; Fernandez-Valiente, E.; Galan, L.; Giralt, S.; Granados, I.; Justel, A.; Liu, E. J.; Lopez-Bravo, A.; Martinez-Cortizas, A.; Pla-Rabes, S.; Rastrojo, A.; Rico, E.; Rochera, C.; Van de Vijver, B.; Velazquez, D.; Villaescusa, J. A.; Vicent, W. F.

    2015-07-01

    Since 2001 CEDEX has taken part in many Antarctic joint research projects with different institutions from Spain and other countries, developing scientific activities in the International Camp of Byers Peninsular (Livingston Island, South Shetland Islands, Antarctica). This place was designed as an Antarctic Specially Protected Area (No.126) because the importance and value of its terrestrial and aquatic habitats. It is one of the largest ice-free areas of maritime Antarctica, with the highest diversity of environments and geological, hydrological and biological processes in the whole region, all of them in a pristine state. Byers Peninsula is considered the most significant limnological area in the Antarctic Peninsula region because it hosts a high number of lakes, ponds and streams, with an exceptional fauna and flora diversity, including the most singular, representative or endemic Antarctic species. Furthermore, the lakes sedimentary record is one of the widest and complete archives in Antarctic Peninsula region for the palaeocological and climatic study of the Holocene. Because Byers Peninsula is an Antarctic biodiversity hotspot, and it is located in one of the areas in the Earth where global warming is being more significant, it must be considered as a suitable international reference site for limnetic, terrestrial and coastal studies, and long term monitoring programmes. (Author)

  4. Boundary conditions of an active West Antarctic subglacial lake: implications for storage of water beneath the ice sheet

    Directory of Open Access Journals (Sweden)

    M. J. Siegert

    2013-06-01

    Full Text Available Repeat-pass IceSat altimetry has revealed 124 discrete surface height changes across the Antarctic Ice Sheet, interpreted to be caused by subglacial lake discharges (surface lowering and inputs (surface uplift. Few of these active lakes have been confirmed by radio-echo sounding (RES despite several attempts (notable exceptions are Lake Whillans and three in the Adventure Subglacial Trench. Here we present targeted RES and radar altimeter data from an "active lake" location within the upstream Institute Ice Stream, into which 0.12 km3 of water is calculated to have flowed between October 2003 and February 2008. We use a series of transects to establish an accurate appreciation of the influences of bed topography and ice-surface elevation on water storage potential. The location of surface height change is over the downslope flank of a distinct topographic hollow, where RES reveals no obvious evidence for deep (> 10 m water. The regional hydropotential reveals a sink coincident with the surface change, however. Governed by the location of the hydrological sink, basal water will likely "drape" over existing topography in a manner dissimilar to subglacial lakes where flat strong specular RES reflections are measured. The inability of RES to detect the active lake means that more of the Antarctic ice sheet bed may contain stored water than is currently appreciated. Variation in ice surface elevation datasets leads to significant alteration in calculations of the local flow of basal water indicating the value of, and need for, high resolution RES datasets in both space and time to establish and characterise subglacial hydrological processes.

  5. An Improved Method for Modeling Spatial Distribution of δD in Surface Snow over Antarctic Ice Sheet

    Institute of Scientific and Technical Information of China (English)

    WANG Yetang; HOU Shugui; Bjorn GRIGHOLM; SONG Linlin

    2009-01-01

    Using the recent compilation of the isotopic composition data of surface snow of Antarctic ice sheet, we proposed an improved interpolation method of δD, which utilizes geographical factors (i.e., latitude and altitude) as the primary predictors and incorporates inverse distance weighting (IDW) technique. The method was applied to a high-resolution digital elevation model (DEM) to produce a grid map of multi-year mean δD values with 1km spatial resolution for Antarctic& The mean absolute deviation between observed and estimated data in the map is about 5.4‰, and the standard deviation is 9‰. The resulting δD pattern resembles well known characteristics such as the depletion of the heavy isotopes with increasing latitude and distance from coast line, but also reveals the complex topographic effects.

  6. Seasonal Forcing of Summer Dissolved Inorganic Carbon and Chlorophyll a on the Western Shelf of the Antarctic Peninsula

    Science.gov (United States)

    2010-03-30

    region that plays an important role in the regional and global modulation of atmospheric CO2. Based on satellite‐derived sea ice data, wind and... warming (>0.5°C per decade) on Earth [Vaughan et al., 2003]. These air temperature trends have been accompanied by an abbreviated sea ice season...potential variations in seawater carbonate system are expected since phyto- plankton is a major biological factor modulating the amount of inorganic carbon

  7. The Role of the Tropics in Last Glacial Abrupt Climate Change from a West Antarctic Ice Core

    Science.gov (United States)

    Jones, T. R.; White, J. W. C.; Steig, E. J.; Cuffey, K. M.; Vaughn, B. H.; Morris, V. A.; Vasileios, G.; Markle, B. R.; Schoenemann, S. W.

    2014-12-01

    Debate exists as to whether last glacial abrupt climate changes in Greenland, and associated changes in Antarctica, had a high-latitude or tropical trigger. An ultra high-resolution water isotope record from the West Antarctic Ice Sheet Divide (WAIS Divide) Ice Core Project has been developed with three key water isotope parameters that offer insight into this debate: δD, δ18O, and deuterium excess (dxs). δD and δ18O are a proxy for local temperature and regional atmospheric circulation, while dxs is primarily a proxy for sea surface temperature at the ice core's moisture source(s) (relative humidity and wind speed also play a role). We build on past studies that show West Antarctic climate is modulated by El Niño Southern Oscillation (ENSO) teleconnection mechanisms, which originate in the equatorial Pacific Ocean, to infer how past ENSO changes may have influenced abrupt climate change. Using frequency analysis of the water isotope data, we can reconstruct the amplitude of ENSO-scale climate oscillations in the 2-15 year range within temporal windows as low as 100 years. Our analysis uses a back diffusion model that estimates initial amplitudes before decay in the firn column. We combine δD, δ18O, and dxs frequency analysis to evaluate how climate variability at WAIS Divide is influenced by tropical climate forcing. Our results should ultimately offer insight into the role of the tropics in abrupt climate change.

  8. Non-climatic signal in ice core records: lessons from Antarctic megadunes

    Science.gov (United States)

    Ekaykin, Alexey; Eberlein, Lutz; Lipenkov, Vladimir; Popov, Sergey; Scheinert, Mirko; Schröder, Ludwig; Turkeev, Alexey

    2016-06-01

    We present the results of glaciological investigations in the megadune area located 30 km to the east of Vostok Station (central East Antarctica) implemented during the 58th, 59th and 60th Russian Antarctic Expedition (January 2013-2015). Snow accumulation rate and isotope content (δD, δ18O and δ17O) were measured along the 2 km profile across the megadune ridge accompanied by precise GPS altitude measurements and ground penetrating radar (GPR) survey. It is shown that the spatial variability of snow accumulation and isotope content covaries with the surface slope. The accumulation rate regularly changes by 1 order of magnitude within the distance negative correlation with the snow accumulation. Analysing dxs / δD and 17O-excess / δD slopes (where dxs = δD - 8 ṡ δ18O and 17O-excess = ln(δ17O / 1000 + 1) -0.528 ṡ ln (δ18O / 1000 + 1)), we conclude that the spatial variability of the snow isotopic composition in the megadune area could be explained by post-depositional snow modifications. Using the GPR data, we estimated the apparent dune drift velocity (4.6 ± 1.1 m yr-1). The full cycle of the dune drift is thus about 410 years. Since the spatial anomalies of snow accumulation and isotopic composition are supposed to drift with the dune, a core drilled in the megadune area would exhibit the non-climatic 410-year cycle of these two parameters. We simulated a vertical profile of snow isotopic composition with such a non-climatic variability, using the data on the dune size and velocity. This artificial profile is then compared with the real vertical profile of snow isotopic composition obtained from a core drilled in the megadune area. We note that the two profiles are very similar. The obtained results are discussed in terms of interpretation of data obtained from ice cores drilled beyond the megadune areas.

  9. Influence of the West Antarctic Ice Sheet and its collapse on the wind and precipitation regimes of the Ross Embayment

    Science.gov (United States)

    Seles, D.; Kowalewski, D. E.

    2015-12-01

    Marine Isotope Stage 31 (MIS 31) is a key analogue for current warming trends yet the extent of the East Antarctic Ice Sheet (EAIS) and the West Antarctic Ice Sheet (WAIS) during this interglacial remains unresolved. Inconsistencies persist between offshore records (suggesting the instability of WAIS) and McMurdo Dry Valley (MDV) terrestrial datasets (indicating long-term ice sheet stability). Here we use a high-resolution regional scale climate model (RegCM3_Polar) to reconstruct paleoclimate during MIS 31 (warm orbit, 400 ppm CO2) and assess changes in precipitation and winds (including katabatic) with WAIS present versus WAIS absent. The MIS 31 scenario with WAIS present resulted in minimal changes in wind magnitude compared with current climate conditions. With WAIS absent, the model predicts a decrease in coastal and highland monthly mean average wind velocities. The greatest rates of snowfall remain along the coast but shift towards higher latitudes with the interior continent remaining dry when WAIS is removed. Focusing on the Ross Embayment, this decreased monthly mean wind velocity and shift of winds to the east indicate a greater influence of offshore winds from the Ross Sea, enabling the increase of precipitation southward along the Transantarctic Mountains (TAM) (i.e. MDV). The apparent decrease of katabatic winds with no WAIS implies that offshore winds may be responsible for bringing the warmer, wetter air into the TAM. The change in wind and precipitation in the Ross Embayment and specifically the MDV highlights the impact of WAIS on Antarctic climate and its subsequent influence on the mass balance of peripheral EAIS domes (i.e. Taylor Dome). Modeling suggests that if WAIS was absent during MIS 31, we would expect (1) greater accumulation at such domes and (2) MDV terrestrial records that reflect a wetter climate, and (3) weaker winds suggesting possibly lower ablation/erosion rates compared to if WAIS was present.

  10. Assessment of the MAR regional climate model over the Antarctic Peninsula (1999 - 2009) through spaceborne enhanced spatial resolution melting maps and near-surface observations

    Science.gov (United States)

    Datta, R.; Tedesco, M.; Alexander, P. M.; Fettweis, X.; Steiner, N.; Gallee, H.

    2012-12-01

    We report results assessing the outputs of the regional climate model Modèle Atmosphérique Régionale (MAR) over the Antarctic peninsula for the period 1999 - 2009. Specifically, we compare maps of melt extent and duration generated by MAR with those obtained from the enhanced spatial resolution product (~ 5 km) distributed by the NASA Scatterometer Climate Record Pathfinder (SCP), at Brigham Young University (Utah, USA). Snowmelt is estimated from remote sensing observations using both a canonical threshold-based approach and a novel method based on wavelet methodology. MAR outputs are also evaluated against available surface observations (e.g., near-surface temperature, wind speed and direction, etc.). The additional effects of blowing snow upon the surface and energy balance can be uniquely explored by simulations in Antarctica (as compared to Greenland, for example). Because of this, as of the time of abstract submission, MAR is set up to run for a scenario with blowing snow as well as a scenario without blowing snow. Our final assessment will present the results of both, providing insight into the sensitivity of MAR outputs to the blowing snow model.

  11. Moss stable isotopes (carbon-13, oxygen-18) and testate amoebae reflect environmental inputs and microclimate along a latitudinal gradient on the Antarctic Peninsula.

    Science.gov (United States)

    Royles, Jessica; Amesbury, Matthew J; Roland, Thomas P; Jones, Glyn D; Convey, Peter; Griffiths, Howard; Hodgson, Dominic A; Charman, Dan J

    2016-07-01

    The stable isotope compositions of moss tissue water (δ(2)H and δ(18)O) and cellulose (δ(13)C and δ(18)O), and testate amoebae populations were sampled from 61 contemporary surface samples along a 600-km latitudinal gradient of the Antarctic Peninsula (AP) to provide a spatial record of environmental change. The isotopic composition of moss tissue water represented an annually integrated precipitation signal with the expected isotopic depletion with increasing latitude. There was a weak, but significant, relationship between cellulose δ(18)O and latitude, with predicted source water inputs isotopically enriched compared to measured precipitation. Cellulose δ(13)C values were dependent on moss species and water content, and may reflect site exposure to strong winds. Testate amoebae assemblages were characterised by low concentrations and taxonomic diversity, with Corythion dubium and Microcorycia radiata types the most cosmopolitan taxa. The similarity between the intra- and inter-site ranges measured in all proxies suggests that microclimate and micro-topographical conditions around the moss surface were important determinants of proxy values. Isotope and testate amoebae analyses have proven value as palaeoclimatic, temporal proxies of climate change, whereas this study demonstrates that variations in isotopic and amoeboid proxies between microsites can be beyond the bounds of the current spatial variability in AP climate.

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

    Science.gov (United States)

    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.

  13. Distribution and characteristics of overdeepenings beneath the Greenland and Antarctic ice sheets: Implications for overdeepening origin and evolution

    Science.gov (United States)

    Patton, H.; Swift, D. A.; Clark, C. D.; Livingstone, S. J.; Cook, S. J.

    2016-09-01

    Glacier bed overdeepenings are ubiquitous in glacier systems and likely exert significant influence on ice dynamics, subglacial hydrology, and ice stability. Understanding of overdeepening formation and evolution has been hampered by an absence of quantitative empirical studies of their distribution and morphology, with process insights having been drawn largely from theoretical or numerical studies. To address this shortcoming, we first map the distribution of potential overdeepenings beneath the Antarctic and Greenland ice sheets using a GIS-based algorithm that identifies closed-contours in the bed topography and then describe and analyse the characteristics and metrics of a subset of overdeepenings that pass further quality control criteria. Overdeepenings are found to be widespread, but are particularly associated with areas of topographically laterally constrained ice flow, notably near the ice sheet margins where outlet systems follow deeply incised troughs. Overdeepenings also occur in regions of topographically unconstrained ice flow (for example, beneath the Siple Coast ice streams and on the Greenland continental shelf). Metrics indicate that overdeepening growth is generally allometric and that topographic confinement of ice flow in general enhances overdeepening depth. However, overdeepening depth is skewed towards shallow values - typically 200-300 m - indicating that the rate of deepening slows with overdeepening age. This is reflected in a decline in adverse slope steepness with increasing overdeepening planform size. Finally, overdeepening long-profiles are found to support headward quarrying as the primary factor in overdeepening development. These observations support proposed negative feedbacks related to hydrology and sediment transport that stabilise overdeepening growth through sedimentation on the adverse slope but permit continued overdeepening planform enlargement by processes of headward erosion.

  14. An optimized multi-proxy, multi-site Antarctic ice and gas orbital chronology (AICC2012: 120–800 ka

    Directory of Open Access Journals (Sweden)

    H. Fischer

    2012-11-01

    Full Text Available An accurate and coherent chronological framework is essential for the interpretation of climatic and environmental records obtained from deep polar ice cores. Until now, one common ice core age scale has been developed based on an inverse dating method (Datice combining glaciological modelling with absolute and stratigraphic markers between 4 ice cores covering the last 50 ka (thousand of years before present (Lemieux-Dudon et al., 2010. In this paper, together with the companion paper of Veres et al. (2012, we present an extension of this work back to 800 ka for the NGRIP, TALDICE, EDML, Vostok and EDC ice cores using an improved version of the Datice tool. The AICC2012 (Antarctic Ice Core Chronology 2012 chronology includes numerous new gas and ice stratigraphic links as well as improved evaluation of background and associated variance scenarios. This paper concentrates on the long timescales between 120–800 ka. In this frame, new measurements of δ18Oatm over Marine Isotope Stage (MIS 11–12 on EDC and a complete δ18Oatm record of the TALDICE ice cores permit us to derive new orbital gas age constraints. The coherency of the different orbitally deduced ages (from δ18Oatm, δO2/N2 and air content has been verified before implementation in AICC2012. The new chronology shows only small differences, well within the original uncertainty range, when compared with the previous ice core reference age scale EDC3. For instance, the duration of the last four interglacial periods is not affected by more than 5%. The largest deviation between AICC2012 and EDC3 (4.4 ka is obtained around MIS 12. Despite significant modifications of the chronological constraints around MIS 5, now independent of speleothem records in AICC2012, the date of Termination II is very close to the EDC3 one.

  15. NOAA/NMC/CAC Arctic and Antarctic Monthly Sea Ice Extent, 1973-1990

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Sea ice extent from January 1973 through August 1990 was digitized from weekly operational sea ice charts produced by the Navy/NOAA Joint Ice Center. Charts were...

  16. Longitudinal surface structures (flowstripes on Antarctic glaciers

    Directory of Open Access Journals (Sweden)

    N. F. Glasser

    2011-11-01

    Full Text Available Longitudinal surface structures (''flowstripes'' are common on many glaciers but their origin and significance are poorly understood. In this paper we present observations of the development of these longitudinal structures from four different Antarctic glacier systems (the Lambert Glacier/Amery Ice Shelf area, outlet glaciers in the Ross Sea sector, ice-shelf tributary glaciers on the Antarctic Peninsula, and the onset zone of a tributary to the Recovery Glacier Ice Stream in the Filchner Ice Shelf area. Mapping from optical satellite images demonstrates that longitudinal surface structures develop in two main situations: (1 as relatively wide flow stripes within glacier flow units and (2 as relatively narrow flow stripes where there is convergent flow around nunataks or at glacier confluence zones. Our observations indicate that the confluence features are narrower, sharper, and more clearly defined features. They are characterised by linear troughs or depressions on the ice surface and are much more common than the former type. Longitudinal surface structures within glacier flow units have previously been explained as the surface expression of localised bed perturbations but a universal explanation for those forming at glacier confluences is lacking. Here we propose that these features are formed at zones of ice acceleration and extensional flow at glacier confluences. We provide a schematic model for the development of longitudinal surface structures based on extensional flow that can explain their ridge and trough morphology as well as their down-ice persistence.

  17. When a habitat freezes solid: microorganisms over-winter within the ice column of a coastal Antarctic lake.

    Science.gov (United States)

    Foreman, Christine M; Dieser, Markus; Greenwood, Mark; Cory, Rose M; Laybourn-Parry, Johanna; Lisle, John T; Jaros, Christopher; Miller, Penney L; Chin, Yu-Ping; McKnight, Diane M

    2011-06-01

    A major impediment to understanding the biology of microorganisms inhabiting Antarctic environments is the logistical constraint of conducting field work primarily during the summer season. However, organisms that persist throughout the year encounter severe environmental changes between seasons. In an attempt to bridge this gap, we collected ice core samples from Pony Lake in early November 2004 when the lake was frozen solid to its base, providing an archive for the biological and chemical processes that occurred during winter freezeup. The ice contained bacteria and virus-like particles, while flagellated algae and ciliates over-wintered in the form of inactive cysts and spores. Both bacteria and algae were metabolically active in the ice core melt water. Bacterial production ranged from 1.8 to 37.9 μg CL(-1) day(-1). Upon encountering favorable growth conditions in the melt water, primary production ranged from 51 to 931 μg CL(-1) day(-1). Because of the strong H(2) S odor and the presence of closely related anaerobic organisms assigned to Pony Lake bacterial 16S rRNA gene clones, we hypothesize that the microbial assemblage was strongly affected by oxygen gradients, which ultimately restricted the majority of phylotypes to distinct strata within the ice column. This study provides evidence that the microbial community over-winters in the ice column of Pony Lake and returns to a highly active metabolic state when spring melt is initiated.

  18. Did the continent and sea have different temperatures in the northern Antarctic Peninsula during the Middle Eocene?

    Directory of Open Access Journals (Sweden)

    A.L. Cione

    2007-12-01

    Full Text Available The Seymour Island beds include a remarkable representation of the continental flora and fauna and marine fauna of Eocene in southern high latitudes. We suggest that, at least during the deposition of the best sampled unit, the Cucullaea I Allomember of the La Meseta Alloformation in the Seymour Island area, a cold temperate terrestrial environment co-existed with relatively warmer temperatures in the adjacent shallow shelf sea. This is suggested by the fish and invertebrate fauna and could have been due to the presence of warmer waters of a current reaching the region from the north. The temperature drop proposed for the time of deposition of the uppermost part of the La Meseta Formation (Submeseta Allomember appears to correspond to the global drop of the end of the Eocene and beginning of Oligocene and not to the establishment of the Antarctic Circumpolar Current.

  19. Glacial-interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-δ15N measurements

    Directory of Open Access Journals (Sweden)

    R. Mulvaney

    2012-12-01

    Full Text Available Correct estimate of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice cores studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: output of a firn densification model and measurements of δ15N of N2 in air trapped in ice core. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI and semi coastal (TALDICE and EPICA Dronning Maud Land, EDML Antarctic regions. Combined with available δ15N measurements performed from the EPICA Dome C (EDC site, the studied regions encompass a large range of surface accumulation rate and temperature conditions. While firn densification simulations are able to correctly represent most of the δ15N trends over the last deglaciation measured in the EDC, BI, TALDICE and EDML ice cores, they systematically fail to capture BI and EDML δ15N glacial levels, a mismatch previously seen for Central East Antarctic ice cores. Using empirical constraints of the EDML gas-ice depth offset during the Laschamp event (~ 41 ka, we can rule out the existence of a large convective zone as the explanation of the glacial firn model-δ15N data mismatch for this site. The good match between modelled and measured δ15N at TALDICE as well as the lack of any clear correlation between insoluble dust concentration in snow and δ15N records in the different ice cores suggest that past changes in loads of impurities are not the only main driver of glacial-interglacial changes in firn lock-in depth. We conclude that firn densification dynamics may instead be driven mostly by accumulation rate changes. The mismatch between modelled and measured δ15N may be due to inaccurate reconstruction of past accumulation rate or underestimated influence of accumulation rate in firnification models.

  20. Ice core reconstruction of sea ice change in the Amundsen-Ross Seas since 1702 A.D.

    Science.gov (United States)

    Thomas, Elizabeth R.; Abram, Nerilie J.

    2016-05-01

    Antarctic sea ice has been increasing in recent decades, but with strong regional differences in the expression of sea ice change. Declining sea ice in the Bellingshausen Sea since 1979 (the satellite era) has been linked to the observed warming on the Antarctic Peninsula, while the Ross Sea sector has seen a marked increase in sea ice during this period. Here we present a 308 year record of methansulphonic acid from coastal West Antarctica, representing sea ice conditions in the Amundsen-Ross Sea. We demonstrate that the recent increase in sea ice in this region is part of a longer trend, with an estimated ~1° northward expansion in winter sea ice extent (SIE) during the twentieth century and a total expansion of ~1.3° since 1702. The greatest reconstructed SIE occurred during the mid-1990s, with five of the past 30 years considered exceptional in the context of the past three centuries.

  1. Large-Ensemble modeling of past and future variations of the Antarctic Ice Sheet with a coupled ice-Earth-sea level model

    Science.gov (United States)

    Pollard, David; DeConto, Robert; Gomez, Natalya

    2016-04-01

    To date, most modeling of the Antarctic Ice Sheet's response to future warming has been calibrated using recent and modern observations. As an alternate approach, we apply a hybrid 3-D ice sheet-shelf model to the last deglacial retreat of Antarctica, making use of geologic data of the last ~20,000 years to test the model against the large-scale variations during this period. The ice model is coupled to a global Earth-sea level model to improve modeling of the bedrock response and to capture ocean-ice gravitational interactions. Following several recent ice-sheet studies, we use Large Ensemble (LE) statistical methods, performing sets of 625 runs from 30,000 years to present with systematically varying model parameters. Objective scores for each run are calculated using modern data and past reconstructed grounding lines, relative sea level records, cosmogenic elevation-age data and uplift rates. The LE results are analyzed to calibrate 4 particularly uncertain model parameters that concern marginal ice processes and interaction with the ocean. LE's are extended into the future with climates following RCP scenarios. An additional scoring criterion tests the model's ability to reproduce estimated sea-level high stands in the warm mid-Pliocene, for which drastic retreat mechanisms of hydrofracturing and ice-cliff failure are needed in the model. The LE analysis provides future sea-level-rise envelopes with well-defined parametric uncertainty bounds. Sensitivities of future LE results to Pliocene sea-level estimates, coupling to the Earth-sea level model, and vertical profiles of Earth properties, will be presented.

  2. About the consistency between Envisat and CryoSat-2 radar freeboard retrieval over Antarctic sea ice

    Directory of Open Access Journals (Sweden)

    S. Schwegmann

    2015-09-01

    Full Text Available Knowledge about Antarctic sea-ice volume and its changes over the past decades has been sparse due to the lack of systematic sea-ice thickness measurements in this remote area. Recently, first attempts have been made to develop a sea-ice thickness product over the Southern Ocean from space-borne radar altimetry and results look promising. Today, more than 20 years of radar altimeter data are potentially available for such products. However, data come from different sources, and the characteristics of individual sensors differ. Hence, it is important to study the consistency between single sensors in order to develop long and consistent time series over the potentially available measurement period. Here, the consistency between freeboard measurements of the Radar Altimeter 2 on-board Envisat and freeboard measurements from the Synthetic-Aperture Interferometric Radar Altimeter on-board CryoSat-2 is tested for their overlap period in 2011. Results indicate that mean and modal values are comparable over the sea-ice growth season (May–October and partly also beyond. In general, Envisat data shows higher freeboards in the seasonal ice zone while CryoSat-2 freeboards are higher in the perennial ice zone and near the coasts. This has consequences for the agreement in individual sectors of the Southern Ocean, where one or the other ice class may dominate. Nevertheless, over the growth season, mean freeboard for the entire (regional separated Southern Ocean differs generally by not more than 2 cm (5 cm, except for the Amundsen/Bellingshausen Sea between Envisat and CryoSat-2, and the differences between modal freeboard lie generally within ±10 cm and often even below.

  3. Metabolism of Antarctic micronektonic crustacea across a summer ice-edge bloom: respiration, composition, and enzymatic activity

    Science.gov (United States)

    Donnelly, Joseph; Kawall, Helena; Geiger, Stephen P.; Torres, Joseph J.

    2004-08-01

    The Antarctic marginal ice zone is an important oceanic front separating the pack-ice and open-water environments. During summer, the retreating pack ice creates a meltwater lens in the euphotic zone, allowing primary producers and microheterotrophs to flourish in a discrete bloom just seaward of the retreating ice edge that lasts about 60 days. The purpose of the present study was to see if the ice-edge bloom had a discernible effect on the metabolism and physiological condition of Antarctic micronekton similar to that observed in zooplankton species. We also wished to assess the importance of the summer season to species' life cycles. Two major data sets were collected on 25 species in the following taxonomic groups: amphipods, cephalopods, decapods, euphausiids, isopods, mysids, ostracods, and polychaetes. The first data set described the metabolic rates of individuals in areas of the marginal ice zone with widely different levels of chlorophyll biomass to investigate the effect of the ice-edge bloom on metabolism. Additionally, summer metabolic rates were compared with data from other seasons. The second data set detailed the levels of protein, water, ash, RNA and DNA, and the activities of metabolic enzymes (citrate synthase and malate dehydrogenase) to examine the efficacy of biochemical indices as predictive tools for metabolism. Results suggested that the mobility of the micronektonic species eliminated most direct effects of the bloom on metabolism. Individuals captured in very different productivity regimes showed few significant differences in the metabolic indicators listed above. Isolated cases of changes in body composition and enzyme activity, however, implied that longer-term effects of the bloom may be exhibited. Seasonal increases in metabolism from winter to summer were observed in the euphausiids Euphausia superba, E. triacantha, and Thysanoessa macrura and the amphipod Vibilia stebbingi. It was concluded that the seasonal shifts were indicative

  4. Glacial–interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-δ15N measurements

    Directory of Open Access Journals (Sweden)

    E. Capron

    2013-05-01

    Full Text Available Correct estimation of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice core studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: outputs of a firn densification model, and measurements of δ15N of N2 in air trapped in ice core, assuming that δ15N is only affected by gravitational fractionation in the firn column. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI and semi-coastal (TALDICE and EPICA Dronning Maud Land, EDML Antarctic regions. Combined with available ice core air-δ15N measurements from the EPICA Dome C (EDC site, the studied regions encompass a large range of surface accumulation rates and temperature conditions. Our δ15N profiles reveal a heterogeneous response of the firn structure to glacial–interglacial climatic changes. While firn densification simulations correctly predict TALDICE δ15N variations, they systematically fail to capture the large millennial-scale δ15N variations measured at BI and the δ15N glacial levels measured at JRI and EDML – a mismatch previously reported for central East Antarctic ice cores. New constraints of the EDML gas–ice depth offset during the Laschamp event (~41 ka and the last deglaciation do not favour the hypothesis of a large convective zone within the firn as the explanation of the glacial firn model–δ15N data mismatch for this site. While we could not conduct an in-depth study of the influence of impurities in snow for firnification from the existing datasets, our detailed comparison between the δ15N profiles and firn model simulations under different temperature and accumulation rate scenarios suggests that the role of accumulation rate may have been underestimated in the current description of firnification

  5. A glimpse beneath Antarctic sea ice: observation of platelet-layer thickness and ice-volume fraction with multifrequency EM

    Science.gov (United States)

    Hoppmann, Mario; Hunkeler, Priska A.; Hendricks, Stefan; Kalscheuer, Thomas; Gerdes, Rüdiger

    2016-04-01

    In Antarctica, ice crystals (platelets) form and grow in supercooled waters below ice shelves. These platelets rise, accumulate beneath nearby sea ice, and subsequently form a several meter thick, porous sub-ice platelet layer. This special ice type is a unique habitat, influences sea-ice mass and energy balance, and its volume can be interpreted as an indicator of the health of an ice shelf. Although progress has been made in determining and understanding its spatio-temporal variability based on point measurements, an investigation of this phenomenon on a larger scale remains a challenge due to logistical constraints and a lack of suitable methodology. In the present study, we applied a lateral constrained Marquardt-Levenberg inversion to a unique multi-frequency electromagnetic (EM) induction sounding dataset obtained on the ice-shelf influenced fast-ice regime of Atka Bay, eastern Weddell Sea. We adapted the inversion algorithm to incorporate a sensor specific signal bias, and confirmed the reliability of the algorithm by performing a sensitivity study using synthetic data. We inverted the field data for sea-ice and platelet-layer thickness and electrical conductivity, and calculated ice-volume fractions within the platelet layer using Archie's Law. The thickness results agreed well with drillhole validation datasets within the uncertainty range, and the ice-volume fraction yielded results comparable to other studies. Both parameters together enable an estimation of the total ice volume within the platelet layer, which was found to be comparable to the volume of landfast sea ice in this region, and corresponded to more than a quarter of the annual basal melt volume of the nearby Ekström Ice Shelf. Our findings show that multi-frequency EM induction sounding is a suitable approach to efficiently map sea-ice and platelet-layer properties, with important implications for research into ocean/ice-shelf/sea-ice interactions. However, a successful application of this

  6. Ice recrystallization inhibition proteins (IRIPs) and freeze tolerance in the cryophilic Antarctic hair grass Deschampsia antarctica E. Desv.

    Science.gov (United States)

    John, Ulrik P; Polotnianka, Renatam M; Sivakumaran, Kailayapillai A; Chew, Orinda; Mackin, Leanne; Kuiper, Micheal J; Talbot, Jonathan P; Nugent, Gregory D; Mautord, Julie; Schrauf, Gustavo E; Spangenberg, German C

    2009-04-01

    Antarctic hair grass (Deschampsia antarctica E. Desv.), the only grass indigenous to Antarctica, has well-developed freezing tolerance, strongly induced by cold acclimation. Here, we show that in response to low temperatures, D. antarctica expresses potent recrystallization inhibition (RI) activity that, inhibits the growth of small ice crystals into potentially damaging large ones, is proteinaceous and localized to the apoplasm. A gene family from D. antarctica encoding putative homologs of an ice recrystallization inhibition protein (IRIP) has been isolated and characterized. IRIPs are apoplastically targeted proteins with two potential ice-binding motifs: 1-9 leucine-rich repeats (LRRs) and c. 16 'IRIP' repeats. IRIP genes appear to be confined to the grass subfamily Pooideae and their products, exhibit sequence similarity to phytosulphokine receptors and are predicted to adopt conformations with two ice-binding surfaces. D. antarctica IRIP (DaIRIP) transcript levels are greatly enhanced in leaf tissue following cold acclimation. Transgenic Arabidopsis thaliana expressing a DaIRIP has novel RI activity, and purified DaIRIP, when added back to extracts of leaves from non-acclimated D. antarctica, can reconstitute the activity found in acclimated plants. We propose that IRIP-mediated RI activity may contribute to the cryotolerance of D. antarctica, and thus to its unique ability to have colonized Antarctica.

  7. Invited Article: SUBGLACIOR: An optical analyzer embedded in an Antarctic ice probe for exploring the past climate

    Energy Technology Data Exchange (ETDEWEB)

    Grilli, R.; Marrocco, N.; Desbois, T. [CNRS, LIPhy, F-38000 Grenoble (France); Guillerm, C. [DT INSU CNRS, Bât. IPEV BP 74, Technopole Brest Iroise, 29280 Plouzané (France); Triest, J. [CNRS, LGGE, F-38000 Grenoble (France); Kerstel, E.; Romanini, D. [CNRS, LIPhy, F-38000 Grenoble (France); Univ. Grenoble Alpes, LIPhy, F-38000 Grenoble (France)

    2014-11-15

    This article describes the advances made in the development of a specific optical spectrometer based on the Optical Feedback-Cavity Enhanced Absorption Spectroscopy technique for exploring past climate by probing the original composition of the atmosphere stored in the ice sheet of a glacier. Based on significant technological progresses and unconventional approaches, SUBGLACIOR will be a revolutionary tool for ice-core research: the optical spectrometer, directly embedded in the drilling probe, will provide in situ real-time measurements of deuterium isotopic variations (δ{sup 2}H ) and CH{sub 4} concentrations down to 3500 m of ice depth within a single Antarctic season. The instrument will provide simultaneous and real-time vertical profiles of these two key climate signatures in order to evaluate if a target site can offer ice cores as old as 1.5 million years by providing direct insight into past temperatures and climate cycles. The spectrometer has a noise equivalent absorption coefficient of 2.8 × 10{sup −10} cm{sup −1} Hz{sup −1/2}, corresponding to a detection limit of 0.2 ppbv for CH{sub 4} and a precision of 0.2‰ on the δ{sup 2}H of H{sub 2}O within 1 min acquisition time.

  8. Anomalously high arsenic concentration in a West Antarctic ice core and its relationship to copper mining in Chile

    Science.gov (United States)

    Schwanck, Franciele; Simões, Jefferson C.; Handley, Michael; Mayewski, Paul A.; Bernardo, Ronaldo T.; Aquino, Francisco E.

    2016-01-01

    Arsenic variability records are preserved in snow and ice cores and can be utilized to reconstruct air pollution history. The Mount Johns ice core (79°55‧S; 94°23‧W and 91.2 m depth) was collected from the West Antarctic Ice Sheet in the 2008/09 austral summer. Here, we report the As concentration variability as determined by 2137 samples from the upper 45 m of this core using ICP-SFMS (CCI, University of Maine, USA). The record covers approximately 125 years (1883-2008) showing a mean concentration of 4.32 pg g-1. The arsenic concentration in the core follows global copper mining evolution, particularly in Chile (the largest producer of Cu). From 1940 to 1990, copper-mining production increased along with arsenic concentrations in the MJ core, from 1.92 pg g-1 (before 1900) to 7.94 pg g-1 (1950). In the last two decades, environmental regulations for As emissions have been implemented, forcing smelters to treat their gases to conform to national and international environmental standards. In Chile, decontamination plants required by the government started operating from 1993 to 2000. Thereafter, Chilean copper production more than doubled while As emission levels declined, and the same reduction was observed in the Mount Johns ice core. After 1999, arsenic concentrations in our samples decreased to levels comparable to the period before 1900.

  9. Post-coring entrapment of modern air in some shallow ice cores collected near the firn-ice transition: evidence from CFC-12 measurements in Antarctic firn air and ice cores

    Directory of Open Access Journals (Sweden)

    M. Aydin

    2010-06-01

    Full Text Available In this study, we report measurements of CFC-12 (CCl2F2 in firn air and in air extracted from shallow ice cores from three Antarctic sites. The firn air data are consistent with the known atmospheric history of CFC-12. In contrast, some of the ice core samples collected near the firn-ice transition exhibit anomalously high CFC-12 levels. Together, the ice core and firn air data provide evidence for the presence of modern air entrapped in the shallow ice core samples that likely contained open pores at the time of collection. We propose that this is due to closure of the open pores after drilling, entrapping modern air and resulting in elevated CFC-12 mixing ratios. Our results reveal that open porosity can exist below the maximum depth at which firn air samples can be collected, particularly at sites with lower accumulation rates. CFC-12 measurements demonstrate that post-drilling closure of open pores can lead to a change in the composition of bubble air in shallow ice cores through purely physical processes. The results have implications for investigations involving trace gas composition of bubbles in shallow ice cores collected near the firn-ice transition.

  10. A record of Antarctic sea ice extent in the Southern Indian Ocean for the past 300 yr and its relationship with global mean temperature

    Directory of Open Access Journals (Sweden)

    C. Xiao

    2013-07-01

    Full Text Available The differing response of ice extent in the Arctic and Antarctic to global average temperature change, over approximately the last three decades, highlights the importance of reconstructing long-term sea ice history. Here, using high-resolution ice core records of methanesulfonate (MS− from the East Antarctic Ice Sheet in Princess Elizabeth Land, we reconstruct southern Indian Ocean sea ice extent (SIE for the sector 70° E–100° E for the period 1708–2000 A.D. Annual MS− concentration positively correlates in this sector with satellite-derived SIE for the period 1973–2000 (P − record of proxy SIE shows multi-decadal variations, with large decreases occurring in two warm intervals during the Little Ice Age, and during the 1940s. However, after the 1980s there is a change in phase between Antarctic SIE and global temperature change, with both increasing. This paradox is probably attributable to the strong anomaly in the Southern Annular Mode (SAM in the recent three decades.

  11. Antarctic ice-mass balance 2003 to 2012: regional reanalysis of GRACE satellite gravimetry measurements with improved estimate of glacial-isostatic adjustment based on GPS uplift rates

    NARCIS (Netherlands)

    Sasgen, I.; Konrad, H.; Ivins, E.R.; van den Broeke, M.R.; Bamber, J.L.; Martinec, Z.; Klemann, V.

    2013-01-01

    We present regional-scale mass balances for 25 drainage basins of the Antarctic Ice Sheet (AIS) from satellite observations of the Gravity and Climate Experiment (GRACE) for time period January 2003 to September 2012. Satellite gravimetry estimates of the AIS mass balance are strongly influenced by

  12. Application of remotely piloted aircraft systems in observing the atmospheric boundary layer over Antarctic sea ice in winter

    Directory of Open Access Journals (Sweden)

    Marius O. Jonassen

    2015-10-01

    Full Text Available The main aim of this paper is to explore the potential of combining measurements from fixed- and rotary-wing remotely piloted aircraft systems (RPAS to complement data sets from radio soundings as well as ship and sea-ice-based instrumentation for atmospheric boundary layer (ABL profiling. This study represents a proof-of-concept of RPAS observations in the Antarctic sea-ice zone. We present first results from the RV Polarstern Antarctic winter expedition in the Weddell Sea in June–August 2013, during which three RPAS were operated to measure temperature, humidity and wind; a fixed-wing small unmanned meteorological observer (SUMO, a fixed-wing meteorological mini-aerial vehicle, and an advanced mission and operation research quadcopter. A total of 86 RPAS flights showed a strongly varying ABL structure ranging from slightly unstable temperature stratification near the surface to conditions with strong surface-based temperature inversions. The RPAS observations supplement the regular upper air soundings and standard meteorological measurements made during the campaign. The SUMO and quadcopter temperature profiles agree very well and, excluding cases with strong temperature inversions, 70% of the variance in the difference between the SUMO and quadcopter temperature profiles can be explained by natural, temporal, temperature fluctuations. Strong temperature inversions cause the largest differences, which are induced by SUMO's high climb rates and slow sensor response. Under such conditions, the quadcopter, with its slower climb rate and faster sensor, is very useful in obtaining accurate temperature profiles in the lowest 100 m above the sea ice.

  13. Dating ice shelf edge marine sediments: A new approach using single-grain quartz luminescence

    DEFF Research Database (Denmark)

    Berger, G.W.; Murray, A.S.; Thomsen, Kristina Jørkov

    2010-01-01

    To develop an alternative dating tool for the Antarctic Peninsula (where the 14C method requires large, spatially variable reservoir corrections), we tested the clock-zeroing assumption of photon-stimulated luminescence (PSL) dating using a variety of PSL procedures. At ice shelf edges around...

  14. Fluxes of microbes, organic aerosols, dust, sea-salt Na ions, non-sea-salt Ca ions, and methanesulfonate onto Greenland and Antarctic ice

    Directory of Open Access Journals (Sweden)

    P. B. Price

    2009-03-01

    Full Text Available Using a spectrofluorimeter with 224-nm laser excitation and six emission bands from 300 to 420 nm to measure fluorescence intensities at 0.3-mm depth intervals in ice cores, we report results of the first comparative study of concentrations of microbial cells (using the spectrum of protein-bound tryptophan (Trp as a proxy and of aerosols with autofluorescence spectra different from Trp (denoted "non-Trp" as a function of depth in ice cores from West Antarctica (WAIS Divide and Siple Dome and Greenland (GISP2. The ratio of fluxes of microbial cells onto West Antarctic (WAIS Divide versus Greenland sites is 0.13±0.06; the ratio of non-Trp aerosols onto WAIS Divide versus Greenland sites is 0.16±0.08; and the ratio of non-sea-salt Ca2+ ions (a proxy for dust grains onto WAIS Divide versus Greenland sites is 0.06±0.03. All of these are roughly comparable to the ratio of fluxes of dust onto Antarctic versus Greenland sites (0.08±0.05. By contrast to those values, which are considerably lower than unity, the ratio of fluxes of methanesulfonate (MSA onto Antarctic versus Greenland sites is 1.9±0.4 and the ratio of sea-salt Na2+ ions onto WAIS Divide versus Greenland sites is 3.0±2. These ratios are more than an order of magnitude higher than those in the first grouping. We infer that the correlation of microbes and non-Trp aerosols with non-sea-salt Ca and dust suggests a largely terrestrial rather than marine origin. The lower fluxes of microbes, non-Trp aerosols, non-sea-salt Ca and dust onto WAIS Divide ice than onto Greenland ice may be due to the smaller areas of their source regions and less favorable wind patterns for transport onto Antarctic ice than onto Greenland ice. The correlated higher relative fluxes of MSA and marine Na onto Antarctic versus Greenland ice is consistent with the view that both originate largely on or around sea ice, with the Antarctic sea ice being far more extensive than that around Greenland.

  15. Negative magnetic anomaly over Mt. Resnik, a subaerially erupted volcanic peak beneath the West Antarctic Ice Sheet

    Science.gov (United States)

    Behrendt, John C.; Finn, C.; Morse, D.L.; Blankenship, D.D.

    2006-01-01

    Mt. Resnik is one of the previously reported 18 subaerially erupted volcanoes (in the West Antarctic rift system), which have high elevation and high bed relief beneath the WAIS in the Central West Antarctica (CWA) aerogeophysical survey. Mt. Resnik lies 300 m below the surface of the West Antarctic Ice Sheet (WAIS); it has 1.6 km topographic relief, and a conical form defined by radar ice-sounding of bed topography. It has an associated complex negative magnetic anomaly revealed by the CWA survey. We calculated and interpreted magnetic models fit to the Mt. Resnik anomaly as a volcanic source comprising both reversely and normally magnetized (in the present field direction) volcanic flows, 0.5-2.5-km thick, erupted subaerially during a time of magnetic field reversal. The Mt. Resnik 305-nT anomaly is part of an approximately 50- by 40-km positive anomaly complex extending about 30 km to the west of the Mt. Resnik peak, associated with an underlying source complex of about the same area, whose top is at the bed of the WAIS. The bed relief of this shallow source complex has a maximum of only about 400 m, whereas the modeled source is >3 km thick. From the spatial relationship we interpret that this source and Mt Resnik are approximately contemporaneous. Any subglacially (older?) erupted edifices comprising hyaloclastite or other volcanic debris, which formerly overlaid the source to the west, were removed by the moving WAIS into which they were injected as is the general case for the ???1000 volcanic centers at the base of the WAIS. The presence of the magnetic field reversal modeled for Mt. Resnik may represent the Bruhnes-Matayama reversal at 780 ka (or an earlier reversal). There are ???100 short-wavelength, steep-gradient, negative magnetic anomalies observed over the West Antarctic Ice Sheet (WAIS), or about 10% of the approximately 1000 short-wavelength, shallow-source, high-amplitude (50- >1000 nT) "volcanic" magnetic anomalies in the CWA survey. These

  16. GLAS/ICESat L2 Global Antarctic and Greenland Ice Sheet Altimetry Data V033

    Data.gov (United States)

    National Aeronautics and Space Administration — GLA12 contains the ice sheet elevation and elevation distribution corrected for geodetic and atmospheric affects calculated from algorithms fine-tuned for ice sheet...

  17. High variability of climate and surface mass balance induced by Antarctic ice rises

    NARCIS (Netherlands)

    Lenaerts, Jan; Brown, Joel; van den Broeke, Michiel; Matsuoka, Kenichi; Drews, Reinhard; Callens, Denis; Philippe, Morgane; Gorodetskaya, I.V.; van Meijgaard, E.; Tijm - Reijmer, Catharina; Pattyn, F.; van Lipzig, N.P.M.

    2014-01-01

    Ice rises play key roles in buttressing the neighbouring ice shelves and potentially provide palaeoclimate proxies from ice cores drilled near their divides. Little is known, however, about their influence on local climate and surface mass balance (SMB). Here we combine 12 years (2001–12) of regiona

  18. Post-coring entrapment of modern air in polar ice cores collected near the firn-ice transition: evidence from CFC-12 measurements in Antarctic firn air and shallow ice cores

    Directory of Open Access Journals (Sweden)

    M. Aydin

    2010-01-01

    Full Text Available In this study, we report the first measurements of CFC-12 (CCl2F2 in air extracted from shallow ice cores along with firn air CFC-12 measurements from three Antarctic sites. The firn air data are consistent with the known atmospheric history of CFC-12. In contrast, the ice core samples collected near the firn-ice transition exhibit anomalously high CFC-12 levels. Together, the ice core and firn air data provide evidence for presence of modern air entrapped in shallow ice core samples. We propose that this is due to closure of open pores after drilling, entrapping modern air and resulting in elevated CFC-12 mixing ratios. Our measurements reveal the presence of open porosity below the depth at which firn air samples can be collected and demonstrate how the composition of bubble air in shallow ice cores can be altered during the post-drilling period through purely physical processes. These results have implications for investigations involving trace gas composition of bubbles in shallow ice cores.

  19. Interdecadal oscillations of temperatures in 1903 - 2002 over the Antarctic Peninula

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    In the paper, by use of the monthly mean temperature data of 12 stations in the vicinity of Antarctic Peninsula, the temperature series during 1903-2000 is founded and the interdecadal oscillation of the temperature are discussed.The results indicate that 1) There are three jumps during 1919 - 1923, 1947-1953 and 1976 - 1982 in recent hundred years and the stable climate step between two jump points lasted about 30 years. 2) Annual mean temperature is increased by 0. 730℃ in an echelon during 1903 -2000, the warming extent is dissimilarity in each season, the maximum of warming is in the winter and the minimum of warming is in summer. 3) The ice decline trend is presented in the index of Ice concentration in the vicinity sea of Antarctic Peninsula, which shows a - 0.2053/10a drop, and the decrease trend of the ice concentration index in summer half year (Dee-May) is found much more obviously than that in winter half year (Jun-Nov). 4) There is better negative relationship between the temperature and the Ice concentration index in Antarctic Peninsula and its vicinity sea, which correlation coefficient of is exceed the significance level of 5% in summer, autumn and annual.

  20. 南半球降水对南极海冰涛动异常的响应%RESPONSE OF SOUTHERN HEMISPHERE PRECIPITATION TO ANTARCTIC SEA ICE OSCILLATION ANOMALIES

    Institute of Scientific and Technical Information of China (English)

    窦挺峰; 效存德

    2013-01-01

    We analyzed the impact of Antarctic sea ice oscillation anomalies on Southern Hemisphere precipitation patterns using the global atmospheric general circulation model, NCAR/CAM3, and a climatic diagnosis method. We also conducted a preliminary investigation into the possible mechanism of action. Results showed that there was a significant response of precipitation to Antarctic sea ice oscillation anomalies, with a positive center over the Atlantic Ocean to the east of South America and a negative center over the Pacific Ocean to the west of South America. The spatial pattern was similar to the Antarctic sea ice oscillation. The results of numerical experiments indicated that sea ice oscillation anomalies can affect the middle troposphere by changing the surface heat flux which could drive the ascending branch of the Ferrel cell, strengthen or weaken the intensity of the Ferrel cell, and then influence the distribution of Southern Hemisphere precipitation. In the peripheral waters of the Amundsen-Bellingshausen Sea where sea ice concentration is lower than normal, upward heat flux could increase, making the ascending branch of the Ferrel cell abnormally strong. As a result, meridional transport would be enhanced and the descending branch strengthened, which would restrain the formation of precipitation in middle- and lower-latitude areas. In the peripheral waters of the Weddell Sea, where sea ice concentration is higher than normal, the responses of meridional transport and precipitation are almost the opposite. However, the response is much weaker at this longitude because of the land surface effect from the West Antarctic Peninsula and South America.%运用NCAR/CAM3全球大气环流模式,结合气候学诊断方法,分析了南极海冰涛动异常对南半球降水的影响,并对可能的作用机理进行了初步探讨.结果表明,南半球中纬度降水对海冰涛动异常的响应较为显著,且异常响应的空间分布与海冰涛动类似,分别

  1. Seasonal evolution of supraglacial lakes on an East Antarctic outlet glacier

    Science.gov (United States)

    Langley, Emily S.; Leeson, Amber A.; Stokes, Chris R.; Jamieson, Stewart S. R.

    2016-08-01

    Supraglacial lakes are known to influence ice melt and ice flow on the Greenland ice sheet and potentially cause ice shelf disintegration on the Antarctic Peninsula. In East Antarctica, however, our understanding of their behavior and impact is more limited. Using >150 optical satellite images and meteorological records from 2000 to 2013, we provide the first multiyear analysis of lake evolution on Langhovde Glacier, Dronning Maud Land (69°11'S, 39°32'E). We mapped 7990 lakes and 855 surface channels up to 18.1 km inland (~670 m above sea level) from the grounding line and document three pathways of lake demise: (i) refreezing, (ii) drainage to the englacial/subglacial environment (on the floating ice), and (iii) overflow into surface channels (on both the floating and grounded ice). The parallels between these mechanisms, and those observed on Greenland and the Antarctic Peninsula, suggest that lakes may similarly affect rates and patterns of ice melt, ice flow, and ice shelf disintegration in East Antarctica.

  2. Broad-scale predictability of carbohydrates and exopolymers in Antarctic and Arctic sea ice.

    Science.gov (United States)

    Underwood, Graham J C; Aslam, Shazia N; Michel, Christine; Niemi, Andrea; Norman, Louiza; Meiners, Klaus M; Laybourn-Parry, Johanna; Paterson, Harriet; Thomas, David N

    2013-09-24

    Sea ice can contain high concentrations of dissolved organic carbon (DOC), much of which is carbohydrate-rich extracellular polymeric substances (EPS) produced by microalgae and bacteria inhabiting the ice. Here we report the concentrations of dissolved carbohydrates (dCHO) and dissolved EPS (dEPS) in relation to algal standing stock [estimated by chlorophyll (Chl) a concentrations] in sea ice from six locations in the Southern and Arctic Oceans. Concentrations varied substantially within and between sampling sites, reflecting local ice conditions and biological content. However, combining all data revealed robust statistical relationships between dCHO concentrations and the concentrations of different dEPS fractions, Chl a, and DOC. These relationships were true for whole ice cores, bottom ice (biomass rich) sections, and colder surface ice. The distribution of dEPS was strongly correlated to algal biomass, with the highest concentrations of both dEPS and non-EPS carbohydrates in the bottom horizons of the ice. Complex EPS was more prevalent in colder surface sea ice horizons. Predictive models (validated against independent data) were derived to enable the estimation of dCHO concentrations from data on ice thickness, salinity, and vertical position in core. When Chl a data were included a higher level of prediction was obtained. The consistent patterns reflected in these relationships provide a strong basis for including estimates of regional and seasonal carbohydrate and dEPS carbon budgets in coupled physical-biogeochemical models, across different types of sea ice from both polar regions.

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

    Science.gov (United States)

    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.

  4. In situ cosmogenic radiocarbon production and 2-D ice flow line modeling for an Antarctic blue ice area

    Science.gov (United States)

    Buizert, Christo; Petrenko, Vasilii V.; Kavanaugh, Jeffrey L.; Cuffey, Kurt M.; Lifton, Nathaniel A.; Brook, Edward J.; Severinghaus, Jeffrey P.

    2012-06-01

    Radiocarbon measurements at ice margin sites and blue ice areas can potentially be used for ice dating, ablation rate estimates and paleoclimatic reconstructions. Part of the measured signal comes from in situ cosmogenic 14C production in ice, and this component must be well understood before useful information can be extracted from 14C data. We combine cosmic ray scaling and production estimates with a two-dimensional ice flow line model to study cosmogenic 14C production at Taylor Glacier, Antarctica. We find (1) that 14C production through thermal neutron capture by nitrogen in air bubbles is negligible; (2) that including ice flow patterns caused by basal topography can lead to a surface 14C activity that differs by up to 25% from the activity calculated using an ablation-only approximation, which is used in all prior work; and (3) that at high ablation margin sites, solar modulation of the cosmic ray flux may change the strength of the dominant spallogenic production by up to 10%. As part of this effort we model two-dimensional ice flow along the central flow line of Taylor Glacier. We present two methods for parameterizing vertical strain rates, and assess which method is more reliable for Taylor Glacier. Finally, we present a sensitivity study from which we conclude that uncertainties in published cosmogenic production rates are the largest source of potential error. The results presented here can inform ongoing and future 14C and ice flow studies at ice margin sites, including important paleoclimatic applications such as the reconstruction of paleoatmospheric 14C content of methane.

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

    Science.gov (United States)

    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

  6. On the influence of model physics on simulations of Arctic and Antarctic sea ice

    Directory of Open Access Journals (Sweden)

    F. Massonnet

    2011-09-01

    Full Text Available Two hindcast (1983–2007 simulations are performed with the global, ocean-sea ice models NEMO-LIM2 and NEMO-LIM3 driven by atmospheric reanalyses and climatologies. The two simulations differ only in their sea ice component, while all other elements of experimental design (resolution, initial conditions, atmospheric forcing are kept identical. The main differences in the sea ice models lie in the formulation of the subgrid-scale ice thickness distribution, of the thermodynamic processes, of the sea ice salinity and of the sea ice rheology. To assess the differences in model skill over the period of investigation, we develop a set of metrics for both hemispheres, comparing the main sea ice variables (concentration, thickness and drift to available observations and focusing on both mean state and seasonal to interannual variability. Based upon these metrics, we discuss the physical processes potentially responsible for the differences in model skill. In particular, we suggest that (i a detailed representation of the ice thickness distribution increases the seasonal to interannual variability of ice extent, with spectacular improvement for the simulation of the recent observed summer Arctic sea ice retreats, (ii the elastic-viscous-plastic rheology enhances the response of ice to wind stress, compared to the classical viscous-plastic approach, (iii the grid formulation and the air-sea ice drag coefficient affect the simulated ice export through Fram Strait and the ice accumulation along the Canadian Archipelago, and (iv both models show less skill in the Southern Ocean, probably due to the low quality of the reanalyses in this region and to the absence of important small-scale oceanic processes at the models' resolution (~1°.

  7. West Antarctic Ice Sheet retreat from Pine Island Bay during the Holocene: New insights into forcing mechanisms

    Science.gov (United States)

    Hillenbrand, Claus-Dieter; Smith, James; Kuhn, Gerhard; Poole, Chris; Hodell, David; Elderfield, Harry; Kender, Sev; Williams, Mark; Peck, Victoria; Larter, Robert; Klages, Johann; Graham, Alastair; Forwick, Matthias; Gohl, Karsten

    2013-04-01

    The Amundsen Sea sector of the largely marine-based and therefore conditionally unstable West Antarctic Ice Sheet (WAIS) contains enough ice to raise global sea level by ca. 1.5 metres. At present, ice streams draining this sector into the Southern Ocean, especially glaciers flowing into Pine Island Bay in the eastern Amundsen Sea embayment, are undergoing considerable mass loss characterised by major thinning, flow acceleration and rapid grounding-line retreat. Sub-ice shelf melting by relatively warm Circumpolar Deep Water (CDW) upwelling onto the continental shelf is held responsible for these dynamical changes but atmospheric warming in West Antarctica may also have contributed to them. In contrast to the modern situation, the long-term history of the Amundsen Sea sector and the mechanisms forcing its deglaciation during the Holocene are only poorly constrained. We will present new palaeoenvironmenal data obtained from marine sediment cores collected in Pine Island Bay. The cores targeted shallow sites on the inner continental shelf and successfully recovered sedimentary sequences bearing calcareous microfossils. Radiocarbon ages on these microfossils demonstrate that the grounding line of the WAIS retreated to within ~100 km of its modern position before ca. 10 kyr BP (thousand years before present), which is consistent with an early WAIS retreat from near-coastal locations in the western Amundsen Sea embayment. Currently, there is no evidence that the grounding line had retreated landward of its modern position during the Holocene. Therefore, the chronological constraints may imply that during the last 10 kyr any episodes of fast grounding-line retreat similar to those observed today were short-lived and rare. Preliminary geochemical data from benthic and planktonic foraminifera tests in the cores from Pine Island Bay reveals that intense CDW upwelling coincided with and may have forced the deglaciation of the inner continental shelf. Furthermore, we observe

  8. Empirical estimation of present-day Antarctic glacial isostatic adjustment and ice mass change

    NARCIS (Netherlands)

    Gunter, B.C.; Didova, O.; Riva, R.; Ligtenberg, S.R.M.; Lenaerts, J.T.M.; King, M.A.; Van den Broeke, M.R.; Urban, T.

    2014-01-01

    This study explores an approach that simultaneously estimates Antarctic mass balance and glacial isostatic adjustment (GIA) through the combination of satellite gravity and altimetry data sets. The results improve upon previous efforts by incorporating a firn densification model to account for firn

  9. Impact of snow cover on CO2 dynamics in Antarctic pack ice

    Directory of Open Access Journals (Sweden)

    N.-X. Geilfus

    2014-06-01

    Full Text Available Temporal evolution of pCO2 profiles in sea ice in the Bellingshausen Sea, Antarctica, in October 2007 shows that the CO2 system in the ice was primarily controlled by physical and thermodynamic processes. During the survey, a succession of warming and cold events strongly influenced the physical, chemical and thermodynamic properties of the ice cover. Two sampling sites with contrasting characteristics of ice and snow thickness were sampled: one had little snow accumulation (from 8 to 25 cm and larger temperature and salinity variations than the second site, where the snow cover was up to 38 cm thick and therefore better insulated the underlying sea ice. We confirm that each cooling/warming event was associated with an increase/decrease in the brine salinity, total alkalinity (TA, total dissolved inorganic carbon (TCO2, and in situ brine and bulk ice CO2 partial pressures (pCO2. Thicker snow covers muted these changes, suggesting that snow influences changes in the sea ice carbonate system through its impact on the temperature and salinity of the sea ice cover. During this survey, pCO2 was undersaturated with respect to the atmosphere both in situ, in the bulk ice (from 10 to 193 μatm, and in the brine (from 65 to 293 μatm, and the ice acted as a sink for atmospheric CO2 (up to 2.9 mmol m−2 d−1, despite the underlying supersaturated seawater (up to 462 μatm.

  10. The zooplankton food web under East Antarctic pack ice - A stable isotope study

    Science.gov (United States)

    Jia, Zhongnan; Swadling, Kerrie M.; Meiners, Klaus M.; Kawaguchi, So; Virtue, Patti

    2016-09-01

    Understanding how sea ice serves zooplankton species during the food-limited season is crucial information to evaluate the potential responses of pelagic food webs to changes in sea-ice conditions in the Southern Ocean. Stable isotope analyses (13C/12C and 15N/14N) were used to compare the dietary preferences and trophic relationships of major zooplankton species under pack ice during two winter-spring transitions (2007 and 2012). During sampling, furcilia of Euphausia superba demonstrated dietary plasticity between years, herbivory when feeding on sea-ice biota, and with a more heterotrophic diet when feeding from both the sea ice and the water column. Carbon isotope signatures suggested that the pteropod Limacina helicina, small copepods Oithona spp., ostracods and amphipods relied heavily on sea-ice biota. Post larval E. superba and omnivorous krill Thysanoessa macrura consumed both water column and ice biota, but further investigations are needed to estimate the contribution from each source. Large copepods and chaetognaths overwintered on a water column-based diet. Our study suggests that warm and permeable sea ice is more likely to provide food for zooplankton species under the ice than the colder ice.

  11. Testing models of ice cap extent, South Georgia, sub-Antarctic

    OpenAIRE

    Barlow, NLM; Bentley, MJ; G. Spada; Evans, DJA; Hansom, JD; Brader, MD; White, DA; Zander, A; Berg, S.

    2016-01-01

    The extent of Last Glacial Maximum ice in South Georgia is contested, with two alternative hypotheses: an extensive (maximum) model of ice reaching the edge of the continental shelf, or a restricted (minimum) model with ice constrained within the inner fjords. We present a new relative sea-level dataset for South Georgia, summarising published and new geomorphological evidence for the marine limit and elevations of former sea levels on the island. Using a glacial isostatic adjustment model (A...

  12. Physical analysis of an Antarctic ice core-towards an integration of micro- and macrodynamics of polar ice.

    Science.gov (United States)

    Weikusat, Ilka; Jansen, Daniela; Binder, Tobias; Eichler, Jan; Faria, Sérgio H; Wilhelms, Frank; Kipfstuhl, Sepp; Sheldon, Simon; Miller, Heinrich; Dahl-Jensen, Dorthe; Kleiner, Thomas

    2017-02-13

    Microstructures from deep ice cores reflect the dynamic conditions of the drill location as well as the thermodynamic history of the drill site and catchment area in great detail. Ice core parameters (crystal lattice-preferred orientation (LPO), grain size, grain shape), mesostructures (visual stratigraphy) as well as borehole deformation were measured in a deep ice core drilled at Kohnen Station, Dronning Maud Land (DML), Antarctica. These observations are used to characterize the local dynamic setting and its rheological as well as microstructural effects at the EDML ice core drilling site (European Project for Ice Coring in Antarctica in DML). The results suggest a division of the core into five distinct sections, interpreted as the effects of changing deformation boundary conditions from triaxial deformation with horizontal extension to bedrock-parallel shear. Region 1 (uppermost approx. 450 m depth) with still small macroscopic strain is dominated by compression of bubbles and strong strain and recrystallization localization. Region 2 (approx. 450-1700 m depth) shows a girdle-type LPO with the girdle plane being perpendicular to grain elongations, which indicates triaxial deformation with dominating horizontal extension. In this region (approx. 1000 m depth), the first subtle traces of shear deformation are observed in the shape-preferred orientation (SPO) by inclination of the grain elongation. Region 3 (approx. 1700-2030 m depth) represents a transitional regime between triaxial deformation and dominance of shear, which becomes apparent in the progression of the girdle to a single maximum LPO and increasing obliqueness of grain elongations. The fully developed single maximum LPO in region 4 (approx. 2030-2385 m depth) is an indicator of shear dominance. Region 5 (below approx. 2385 m depth) is marked by signs of strong shear, such as strong SPO values of grain elongation and strong kink folding of visual layers. The details of structural

  13. Physical analysis of an Antarctic ice core-towards an integration of micro- and macrodynamics of polar ice*

    Science.gov (United States)

    Weikusat, Ilka; Jansen, Daniela; Binder, Tobias; Eichler, Jan; Faria, Sérgio H.; Wilhelms, Frank; Kipfstuhl, Sepp; Sheldon, Simon; Miller, Heinrich; Dahl-Jensen, Dorthe; Kleiner, Thomas

    2017-02-01

    Microstructures from deep ice cores reflect the dynamic conditions of the drill location as well as the thermodynamic history of the drill site and catchment area in great detail. Ice core parameters (crystal lattice-preferred orientation (LPO), grain size, grain shape), mesostructures (visual stratigraphy) as well as borehole deformation were measured in a deep ice core drilled at Kohnen Station, Dronning Maud Land (DML), Antarctica. These observations are used to characterize the local dynamic setting and its rheological as well as microstructural effects at the EDML ice core drilling site (European Project for Ice Coring in Antarctica in DML). The results suggest a division of the core into five distinct sections, interpreted as the effects of changing deformation boundary conditions from triaxial deformation with horizontal extension to bedrock-parallel shear. Region 1 (uppermost approx. 450 m depth) with still small macroscopic strain is dominated by compression of bubbles and strong strain and recrystallization localization. Region 2 (approx. 450-1700 m depth) shows a girdle-type LPO with the girdle plane being perpendicular to grain elongations, which indicates triaxial deformation with dominating horizontal extension. In this region (approx. 1000 m depth), the first subtle traces of shear deformation are observed in the shape-preferred orientation (SPO) by inclination of the grain elongation. Region 3 (approx. 1700-2030 m depth) represents a transitional regime between triaxial deformation and dominance of shear, which becomes apparent in the progression of the girdle to a single maximum LPO and increasing obliqueness of grain elongations. The fully developed single maximum LPO in region 4 (approx. 2030-2385 m depth) is an indicator of shear dominance. Region 5 (below approx. 2385 m depth) is marked by signs of strong shear, such as strong SPO values of grain elongation and strong kink folding of visual layers. The details of structural observations are

  14. Phase-sensitive radar on thick Antarctic ice - how well does it work?

    Science.gov (United States)

    Binder, Tobias; Eisen, Olaf; Helm, Veit; Humbert, Angelika; Steinhage, Daniel

    2016-04-01

    Phase-sensitive radar (pRES) has become one of the mostly used tools to determine basal melt rates as well as vertical strain in ice sheets. Whereas most applications are performed on ice shelves, only few experiments were conducted on thick ice in Greenland or Antarctica. The technical constrains on an ice shelf to deduce basal melt rates are less demanding than on inland ice of more than 2 km thickness. First, the ice itself is usually only several 100s of meters thick; and, second, the reflection coefficient at the basal interface between sea water and ice is the second strongest one possible. Although the presence of marine ice with higher conductivities might increase attenuation in the lower parts, most experiments on shelves were successful. To transfer this technology to inland regions, either for the investigation of basal melt rates of subglacial hydrological networks or for determining vertical strain rates in basal regions, a reliable estimate of the current system performance is necessary. To this end we conducted an experiment at and in the vicinity of the EPICA deep ice core drill site EDML in Dronning Maud Land, Antarctica. That site has been explored in extraordinary detail with different geophysical methods and provides an already well-studied ice core and borehole, in particular with respect to physical properties like crystal orientation fabric, dielectric properties and matching of internal radar horizons with conductivity signals. We present data from a commercially available pRES system initially recorded in January 2015 and repeated measurements in January 2016. The pRES data are matched to existing and already depth-calibrated airborne radar data. Apart from identifying prominent internal layers, e.g. the one originating from the deposits of the Toba eruption at around 75 ka, we put special focus on the identification of the basal reflection at multiple polarizations. We discuss the potential uncertainty estimates and requirements to

  15. Antarctic Ice Sheet Surface Mass Balance Estimates from 2003 TO 2015 Using Icesat and CRYOSAT-2 Data

    Science.gov (United States)

    Xie, Huan; Hai, Gang; Chen, Lei; Liu, Shijie; Liu, Jun; Tong, Xiaohua; Li, Rongxing

    2016-06-01

    An assessment of Antarctic ice sheet surface mass balance from 2003 to 2015 has been carried out using a combination of ICESat data from 2003 to 2009 and CryoSat-2 data from 2010 to 2015. Both data sets are of L2 and are currently processed separately using different models. First, a repeat-track processing method that includes terms accounting for the trend and the first order fit of topography is applied to repeat-track measurements of all ICESat Campaigns. It uses the Least Squares fitting of the model to all observations in a box of 500 m x 500 m. The estimated trends in these boxes are then averaged inside a 30 km x 30 km cell. Similarly, the cells are used to estimate basin and ice sheet level surface elevation change trends. Mass balance calculating is performed at the cell level by multiplying the ice density by the volume change and then extended to the basin and the ice sheet level. Second, in CryoSat-2 data processing we applied a model within a cell of 5 km x 5 km considering that CryoSat-2 does not maintain repeated tracks. In this model the elevation trend, and a higher order topography are solved in an iterative way using the least squares technique. The mass change is computed at the cell level in the same way as the ICESat data. GIA correction is applied for both ICESat and CryoSat-2 estimates. Detailed information about the data processing, elevation and mass balance changes, and comparison with other studies will be introduced.

  16. Synergism between elevated pCO2 and temperature on the Antarctic sea ice diatom Nitzschia lecointei

    Directory of Open Access Journals (Sweden)

    A. Torstensson

    2013-04-01

    Full Text Available Polar oceans are particularly susceptible to ocean acidification and warming. Diatoms play a significant role in sea ice biogeochemistry and provide an important food source to grazers in ice-covered oceans, especially during early spring. However, the ecophysiology of ice living organisms has received little attention in terms of ocean acidification. In this study, the synergism between temperature and partial pressure of CO2 (pCO2 was investigated in relationship to the optimal growth temperature of the Antarctic sea ice diatom Nitzschia lecointei. Diatoms were kept in cultures at controlled levels of pCO2 (∼390 and ∼960 μatm} and temperature (−1.8 and 2.5 °C for 14 days. Synergism between temperature and pCO2 was detected in growth rate and acyl lipid fatty acid content. Carbon enrichment only promoted (3% growth rate closer to the optimal growth, but not at the control temperature (−1.8 °C. Optimal growth rate was observed around 5 °C in a separate experiment. Polyunsaturated fatty acids (PUFA comprised up to 98% of the total acyl lipid fatty acid pool at −1.8 °C. However, the total content of fatty acids was reduced by 39% at elevated pCO2, but only at the control temperature. PUFAs were reduced by 30% at high pCO2. Effects of carbon enrichment may be different depending on ocean warming scenario or season, e.g. reduced food quality for higher trophic levels during spring. Synergy between temperature and pCO2 may be particularly important in polar areas since a narrow thermal window generally limits cold-water organisms.

  17. Geographic names of the Antarctic

    Science.gov (United States)

    ,; ,; ,; ,; Alberts, Fred G.

    1995-01-01

    This gazetteer contains 12,710 names approved by the United States Board on Geographic Names and the Secretary of the Interior for features in Antarctica and the area extending northward to the Antarctic Convergence. Included in this geographic area, the Antarctic region, are the off-lying South Shetland Islands, the South Orkney Islands, the South Sandwich Islands, South Georgia, Bouvetøya, Heard Island, and the Balleny Islands. These names have been approved for use by U.S. Government agencies. Their use by the Antarctic specialist and the public is highly recommended for the sake of accuracy and uniformity. This publication, which supersedes previous Board gazetteers or lists for the area, contains names approved as recently as December 1994. The basic name coverage of this gazetteer corresponds to that of maps at the scale of 1:250,000 or larger for coastal Antarctica, the off-lying islands, and isolated mountains and ranges of the continent. Much of the interior of Antarctica is a featureless ice plateau. That area has been mapped at a smaller scale and is nearly devoid of toponyms. All of the names are for natural features, such as mountains, glaciers, peninsulas, capes, bays, islands, and subglacial entities. The names of scientific stations have not been listed alphabetically, but they may appear in the texts of some decisions. For the names of submarine features, reference should be made to the Gazetteer of Undersea Features, 4th edition, U.S. Board on Geographic Names, 1990.

  18. GLIMMER Antarctic Ice Sheet Model,an experimental research of moving boundary condition

    Institute of Scientific and Technical Information of China (English)

    Tang Xueyuan; Sun Bo; Zhang Zhanhai; Li Yuansheng; Yang Qinghua

    2008-01-01

    A 3 D coupled ice sheet model,GLIMMER model is introduced,and an idealized ice sheet experiment under the EISMINT 1 criterion of moving boundary condition is presented.The results of the experiment reveal that for a steady state ice sheet profile the characteristic curves describe the process of evolution which are accordant with theoretical estimates.By solving the coupled thermodynamics equations of ice sheet,one may find the characteristic curves which derived from the conservation of the mass,energy and momentum to the ice flow profile.At the same time,an agreement,approximate to the GLIMMER case and the confirmed theoretical results,is found.Present study is explorihg work to introduceand discuss the handicaps of EISMINT criterion and GLIMMER,and prospect a few directions of the GLIMMER model.

  19. Physical analysis of an Antarctic ice core—towards an integration of micro- and macrodynamics of polar ice*

    Science.gov (United States)

    Jansen, Daniela; Binder, Tobias; Eichler, Jan; Faria, Sérgio H.; Wilhelms, Frank; Kipfstuhl, Sepp; Sheldon, Simon; Miller, Heinrich; Dahl-Jensen, Dorthe; Kleiner, Thomas

    2017-01-01

    Microstructures from deep ice cores reflect the dynamic conditions of the drill location as well as the thermodynamic history of the drill site and catchment area in great detail. Ice core parameters (crystal lattice-preferred orientation (LPO), grain size, grain shape), mesostructures (visual stratigraphy) as well as borehole deformation were measured in a deep ice core drilled at Kohnen Station, Dronning Maud Land (DML), Antarctica. These observations are used to characterize the local dynamic setting and its rheological as well as microstructural effects at the EDML ice core drilling site (European Project for Ice Coring in Antarctica in DML). The results suggest a division of the core into five distinct sections, interpreted as the effects of changing deformation boundary conditions from triaxial deformation with horizontal extension to bedrock-parallel shear. Region 1 (uppermost approx. 450 m depth) with still small macroscopic strain is dominated by compression of bubbles and strong strain and recrystallization localization. Region 2 (approx. 450–1700 m depth) shows a girdle-type LPO with the girdle plane being perpendicular to grain elongations, which indicates triaxial deformation with dominating horizontal extension. In this region (approx. 1000 m depth), the first subtle traces of shear deformation are observed in the shape-preferred orientation (SPO) by inclination of the grain elongation. Region 3 (approx. 1700–2030 m depth) represents a transitional regime between triaxial deformation and dominance of shear, which becomes apparent in the progression of the girdle to a single maximum LPO and increasing obliqueness of grain elongations. The fully developed single maximum LPO in region 4 (approx. 2030–2385 m depth) is an indicator of shear dominance. Region 5 (below approx. 2385 m depth) is marked by signs of strong shear, such as strong SPO values of grain elongation and strong kink folding of visual layers. The details of structural

  20. Characteristics of change of the SST in the tropical western Pacific and the tropical Indian Ocean and its response to the change of the Antarctic ice area

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    In this paper, by using ocean surface temperature data (COADS), the study is made of the characteristics of the monthly and annual changes of the SST in the tropical western Pacific and Indian Oceans, which have important influences on the climate change of the whole globe and the relation between ENSO(E1 Nino-Southern Oscillation) and the Antarctic ice area is also discussed. The result indicates that in the tropical western Pacific and the Indian Oceans the change of Sea Surface Temperture (SST) is conspicuous both monthly and armaully, and shows different change tendency between them. This result may be due to different relation in the vibration period of SST between the two Oceans. The better corresponding relationship is obvious in the annual change of SST in the tropical Indian Ocean with the occurrence El Nino and LaNlra. The change of the SST in the tropical western Pacific and the tropical Indian Oceans has a close relation to the Antarctic ice area, especially to the ice areas in the eastern-south Pole and Ross Sea, and its notable correlative relationship appears in 16 months when the SST of the tropical western Pacific and the Indian Oceans lag back the Antarctic ice