WorldWideScience

Sample records for antarctic sea ice

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. 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.)

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

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

    Science.gov (United States)

    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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

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

    Science.gov (United States)

    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. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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...

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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

  18. 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.

  19. 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).

  20. 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

  1. 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...

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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.

  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. 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

  10. 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.

  11. 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

  12. 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.

  13. 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

  14. 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.

  15. 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

  16. 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

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  5. 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.

  6. 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.

  7. 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.

  8. 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...

  9. 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.

  10. 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

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  13. 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.

  14. Relationship between Antarctic sea ice and the climate in summer of China

    Institute of Scientific and Technical Information of China (English)

    Ma Lijuan; Lu Longhua; Bian Lingen

    2006-01-01

    The variations of sea ice are different in different regions in Antarctica,thus have different impacts on local atmospheric circulation and global climatic system. The relationships between the sea ice in Ross Sea and Weddell Sea regions and the synoptic climate in summer of China are investigated in this paper via diagnostic analysis methods by using global sea ice concentration gridded data covering Jan. 1968through Dec. 2002 obtained from Hadley Center, combined with Geopotential Height on 500hPa and 100hPa over North Hemisphere and monthly precipitation and air temperatures data covering the corresponding period over 160 meteorological stations in China obtained from CMA (China Meteorological Administration). Results disclose that both these two regions are of indicative meanings to the climate in summer of China. The Ross Sea Region is the key sea ice region to the precipitation in Northeast China in summer. More sea ice in this region in September will result in less precipitation in Northeast China in the following June. Weddell Sea Region is the key sea ice region to the air temperature in Northeast China in summer. More sea ice in this region in September will contribute to lower air temperature in Northeast China in the following June.

  15. 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°.

  16. 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.

  17. Austral Summer Sea Ice Melt Revealed in Antarctic ERS-1/2 and NSCAT Scatterometer Data

    Science.gov (United States)

    Drinkwater, M.; Liu, X.

    1999-01-01

    The first in-situ field observations of Antarcic austral summer sea-ice melt were made in the Bellingshausen Sea by Arctowski (1908) on Belgica in 1899, and later by Wordie (1921) during the ill-fated drift of Endurance in the Weddell Sea from 1914-1916.

  18. 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.

  19. 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

  20. 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

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Sea Ice

    Science.gov (United States)

    Perovich, D.; Gerland, S.; Hendricks, S.; Meier, Walter N.; Nicolaus, M.; Richter-Menge, J.; Tschudi, M.

    2013-01-01

    During 2013, Arctic sea ice extent remained well below normal, but the September 2013 minimum extent was substantially higher than the record-breaking minimum in 2012. Nonetheless, the minimum was still much lower than normal and the long-term trend Arctic September extent is -13.7 per decade relative to the 1981-2010 average. The less extreme conditions this year compared to 2012 were due to cooler temperatures and wind patterns that favored retention of ice through the summer. Sea ice thickness and volume remained near record-low levels, though indications are of slightly thicker ice compared to the record low of 2012.

  8. 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.

  9. 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.

  10. 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

  11. Arctic Landfast Sea Ice 1953-1998

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The files in this data set contain landfast sea ice data (monthly means) gathered from both Russian Arctic and Antarctic Research Institute (AARI) and Canadian Ice...

  12. Seasonal-to-Interannual Variability in Antarctic Sea-Ice Dynamics, and Its Impact on Surface Fluxes and Water Mass Production

    Science.gov (United States)

    Drinkwater, Mark R.

    1999-01-01

    Strong seasonal and interannual signals in Antarctic bottom-water outflow remain unexplained yet are highly correlated with anomalies in net sea-ice growth in coastal polynyas. The mechanisms responsible for driving salination and replenishment and rejuvenation of the dense shelf "source" waters likely also generate pulses of bottom water outflow. The objective of this research is to investigate time-scales of variability in the dynamics of sea-ice in the Southern Ocean in order to determine the primary sites for production of dense shelf waters. We are using a merged satellite/buoy sea-ice motion data set for the period 1978-present day to compute the dynamics of opening and closing of coastal polynyas over the continental shelf. The Ocean Circulation and Climate Advanced Model (OCCAM) ocean general circulation model with coupled sea-ice dynamics is presently forced using National Center for Environmental Prediction (NCEP) data to simulate fluxes and the salination impact of the ocean shelf regions. This work is relevant in the context of measuring the influence of polar sea-ice dynamics upon polar ocean characteristics, and thereby upon global thermohaline ocean circulation. Interannual variability in simulated net freezing rate in the Southern Weddell Sea is shown for the period 1986-1993. There is a pronounced maximum of ice production in 1988 and minimum in 1991 in response to anomalies in equatorward meridional wind velocity. This follows a similar approximate 8-year interannual cycle in Sea Surface Temperature (SST) and satellite-derived ice-edge anomalies reported elsewhere as the "Antarctic Circumpolar Wave." The amplitude of interannual fluctuations in annual net ice production are about 40% of the mean value, implying significant interannual variance in brine rejection and upper ocean heat loss. Southward anomalies in wind stress induce negative anomalies in open water production, which are observed in passive microwave satellite images. Thus, cycles of

  13. Synergism between elevated pCO2 and temperature on the Antarctic sea ice diatom Nitzschia lecointei

    Directory of Open Access Journals (Sweden)

    A. Torstensson

    2013-10-01

    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 (FA content. Optimal growth rate was observed around 5 °C in a separate experiment. Carbon enrichment only promoted (6% growth rate closer to the optimal growth, but not at the control temperature (−1.8 °C. At −1.8 °C and at ∼960 μatm pCO2, the total FA content was reduced relative to the ∼390 μatm treatment, although no difference between pCO2 treatments was observed at 2.5 °C. A large proportion (97% of the total FAs comprised on average of polyunsaturated fatty acids (PUFA at −1.8 °C. Cellular PUFA content was reduced at ∼960 relative to ∼390 μatm pCO2. Effects of carbon enrichment may be different depending on ocean warming scenario or season, e.g. reduced cellular FA content in response to elevated CO2 at low temperatures only, reflected as reduced food quality for higher trophic levels. Synergy between warming and acidification may be particularly important in polar areas since a narrow thermal window generally limits cold-water organisms.

  14. The importance of sea ice area biases in 21st century multimodel projections of Antarctic temperature and precipitation

    Science.gov (United States)

    Bracegirdle, Thomas J.; Stephenson, David B.; Turner, John; Phillips, Tony

    2015-12-01

    Climate models exhibit large biases in sea ice area (SIA) in their historical simulations. This study explores the impacts of these biases on multimodel uncertainty in Coupled Model Intercomparison Project phase 5 (CMIP5) ensemble projections of 21st century change in Antarctic surface temperature, net precipitation, and SIA. The analysis is based on time slice climatologies in the Representative Concentration Pathway 8.5 future scenario (2070-2099) and historical (1970-1999) simulations across 37 different CMIP5 models. Projected changes in net precipitation, temperature, and SIA are found to be strongly associated with simulated historical mean SIA (e.g., cross-model correlations of r = 0.77, 0.71, and -0.85, respectively). Furthermore, historical SIA bias is found to have a large impact on the simulated ratio between net precipitation response and temperature response. This ratio is smaller in models with smaller-than-observed SIA. These strong emergent relationships on SIA bias could, if found to be physically robust, be exploited to give more precise climate projections for Antarctica.

  15. Cloning, Expression, Purification, and Characterization of Glutaredoxin from Antarctic Sea-Ice Bacterium Pseudoalteromonas sp. AN178

    Directory of Open Access Journals (Sweden)

    Quanfu Wang

    2014-01-01

    Full Text Available Glutaredoxins (Grxs are small ubiquitous redox enzymes that catalyze glutathione-dependent reactions to reduce protein disulfide. In this study, a full-length Grx gene (PsGrx with 270 nucleotides was isolated from Antarctic sea-ice bacterium Pseudoalteromonas sp. AN178. It encoded deduced 89 amino acid residues with the molecular weight 9.8 kDa. Sequence analysis of the amino acid sequence revealed the catalytic motif CPYC. Recombinant PsGrx (rPsGrx stably expressed in E. coli BL21 was purified to apparent homogeneity by Ni-affinity chromatography. rPsGrx exhibited optimal activity at 30°C and pH 8.0 and showed 25.5% of the activity at 0°C. It retained 65.0% of activity after incubation at 40°C for 20 min and still exhibited 37.0% activity in 1.0 M NaCl. These results indicated that rPsGrx was a typical cold active protein with low thermostability.

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

    Directory of Open Access Journals (Sweden)

    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

  17. Early spawning of Antarctic krill in the Scotia Sea is fuelled by “superfluous” feeding on non-ice associated phytoplankton blooms

    Science.gov (United States)

    Schmidt, Katrin; Atkinson, Angus; Venables, Hugh J.; Pond, David W.

    2012-01-01

    The spawning success of Antarctic krill ( Euphausia superba) is generally assumed to depend on substantial winter sea ice extent, as ice biota can serve as a food source during winter/spring and the seasonal ice melt conditions the upper water column for extensive phytoplankton blooms. However, direct observations during spring are rare. Here we studied krill body condition and maturity stage in relation to feeding (i.e. stomach fullness, diet, absorption of individual fatty acids and defecation rate) across the Scotia Sea in November 2006. The phytoplankton concentrations were low at the marginal ice zone (MIZ) in the southern Scotia Sea (Stn. 1, 2, and 3), high in open waters of the Southern Antarctic Circumpolar Current Front (SACCF) in the central Scotia Sea (Stn. 5), and moderate further north (Stn. 6 and 7). Krill had low lipid reserves (˜6.5% of dry mass, DM), low mass:length ratios (˜1.7 mg DM mm -1), and small digestive glands (˜7% of total DM) near the ice edge. The stomachs contained lithogenic particles, diatom debris, and bacterial fatty acids, but low proportions of diatom-indicating fatty acids, which suggest that these krill were feeding on detritus rather than on fresh ice algae. In the SACCF, krill had higher lipid reserves (˜10% of DM), high mass:length ratios (˜2.2 mg DM mm -1), and large digestive glands (˜16% of total DM). Stomach content and tissue composition indicate feeding on diatoms. In the north, moderate food concentrations co-occurred with low lipid reserves in krill, and moderate mass:length ratios and digestive gland sizes. Only in the phytoplankton bloom in the SACCF had the mating season already started and some females were about to spawn. Based on the way krill processed their food at the different stations, we indicate two mechanisms that can lead to fast regeneration of body reserves and oocyte maturation in E. superba. One is "superfluous" feeding at high food concentrations, which maximises the overall nutrient gain

  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. Sea ice pCO2 dynamics and air-ice CO2 fluxes during the Sea Ice Mass Balance in the Antarctic (SIMBA) experiment - Bellingshausen Sea, Antarctica

    DEFF Research Database (Denmark)

    Geilfus, Nicolas-Xavier; Tison, J.-L.; Ackley, S.F.

    2014-01-01

    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 sec- ond site, where the snow cover was up to 38 cm thick and therefore better...... insulated the underlying sea ice. We show that each cooling/warming event was associated with an in- crease/decrease in the brine salinity, total alkalinity (TA), to- tal dissolved inorganic carbon (T CO2), and in situ brine and bulk ice CO2 partial pressures (pCO2). Thicker snow covers reduced...... the amplitude of these changes: snow cover influ- ences the sea ice carbonate system by modulating the temper- ature and therefore the salinity of the sea ice cover. Results indicate that pCO2 was undersaturated with respect to the at- mosphere both in the in situ bulk ice (from 10 to 193 μatm) and brine (from...

  20. Variability and Trends in Sea Ice Extent and Ice Production in the Ross Sea

    Science.gov (United States)

    Comiso, Josefino; Kwok, Ronald; Martin, Seelye; Gordon, Arnold L.

    2011-01-01

    Salt release during sea ice formation in the Ross Sea coastal regions is regarded as a primary forcing for the regional generation of Antarctic Bottom Water. Passive microwave data from November 1978 through 2008 are used to examine the detailed seasonal and interannual characteristics of the sea ice cover of the Ross Sea and the adjacent Bellingshausen and Amundsen seas. For this period the sea ice extent in the Ross Sea shows the greatest increase of all the Antarctic seas. Variability in the ice cover in these regions is linked to changes in the Southern Annular Mode and secondarily to the Antarctic Circumpolar Wave. 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 sq km/yr. For a characteristic ice thickness of 0.6 m, this yields a volume transport of about 20 cu km/yr, which is almost identical, within error bars, to our estimate of the trend in ice production. The increase in brine rejection in the Ross Shelf Polynya associated with the estimated increase with the ice production, however, is not consistent with the reported Ross Sea salinity decrease. The locally generated sea ice enhancement of Ross Sea salinity may be offset by an increase of relatively low salinity of the water advected into the region from the Amundsen Sea, a consequence of increased precipitation and regional glacial ice melt.

  1. 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.

  2. Simulating the mass balance and salinity of Arctic and Antarctic sea ice. 1. Model description and validation

    OpenAIRE

    Vancoppenolle, M.; Fichefet, T.; Goosse, H.; Bouillon, S; Madec, G.; Maqueda, M.A.M.

    2009-01-01

    This paper is the first part of a twofold contribution dedicated to the new version of the Louvain-la-Neuve sea ice model LIM3. In this part, LIM3 is described and its results arc, compared with observations. LIM3 is a C-grid dynamic-thermodynamic model, including the representation of the subgrid-scale distributions of ice thickness, enthalpy, salinity and age. Brine entrapment and drainage as well as brine impact on ice thermodynamics are explicitly included. LIM3 is embedded into the ocean...

  3. 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

  4. Influence of wet conditions on snow temperature diurnal variations: An East Antarctic sea-ice case study

    Science.gov (United States)

    Lecomte, O.; Toyota, T.

    2016-09-01

    A one-dimensional snow-sea-ice model is used to simulate the evolution of temperature profiles in dry and wet snow over a diurnal cycle, at locations where associated observations collected during the Sea Ice Physics and Ecosystem eXperiment (SIPEX-II) are available. The model is used at two sites, corresponding to two of the field campaign's sea-ice stations (2 and 6), and under two configurations: dry and wet snow conditions. In the wet snow model setups, liquid water may refreeze internally into the snow. At station 6, this releases latent heat to the snow and results in temperature changes at the base of the snow pack of a magnitude comparing to the model-observation difference (1 - 2 ° C). As the temperature gradient across the snow is in turn weakened, the associated conductive heat flux through snow decreases. At station 2, internal refreezing also occurs but colder air temperatures and the competing process of strengthened heat conduction in snow concurrent to snow densification maintain a steady temperature profile. However, both situations share a common feature and show that the conductive heat flux through the snow may significantly be affected (by 10-20% in our simulations) as a result of the liquid water refreezing in snow, either through thermal conductivity enhancement or direct temperature gradient alteration. This ultimately gives motivation for further investigating the impacts of these processes on the sea-ice mass balance in the framework of global scale model simulations.

  5. 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,

  6. 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.

  7. RING-TENSILE-STRENGTH AND FLEXURE-STRENGTH CORRELATIONS OF SEA ICE.

    Science.gov (United States)

    SEA ICE, MECHANICAL PROPERTIES), TENSILE PROPERTIES, SALINITY, TEMPERATURE, ICE, FLEXURAL STRENGTH , CORRELATION TECHNIQUES, ACCURACY, SAMPLING, THICKNESS, PREDICTIONS, ANTARCTIC REGIONS, LOADS(FORCES)

  8. Ice Tank Experiments Highlight Changes in Sea Ice Types

    Science.gov (United States)

    Wilkinson, Jeremy P.; DeCarolis, Giacomo; Ehlert, Iris; Notz, Dirk; Evers, Karl-Ulrich; Jochmann, Peter; Gerland, Sebastian; Nicolaus, Marcel; Hughes, Nick; Kern, Stefan; de la Rosa, Sara; Smedsrud, Lars; Sakai, Shigeki; Shen, Hayley; Wadhams, Peter

    2009-03-01

    With the current and likely continuing reduction of summer sea ice extent in the Arctic Ocean, the predominant mechanism of sea ice formation in the Arctic is likely to change in the future. Although substantial new ice formation occurred under preexisting ice in the past, the fraction of sea ice formation in open water likely will increase significantly. In open water, sea ice formation starts with the development of small ice crystals, called frazil ice, which are suspended in the water column [World Meteorological Organization, 1985]. Under quiescent conditions, these crystals accumulate at the surface to form an unbroken ice sheet known in its early stage as nilas. Under turbulent conditions, caused by wind and waves, frazil ice continues to grow and forms into a thick, soupy mixture called grease ice. Eventually the frazil ice will coalesce into small, rounded pieces known as pancake ice, which finally consolidate into an ice sheet with the return of calm conditions. This frazil/pancake/ice sheet cycle is currently frequently observed in the Antarctic [Lange et al., 1989]. The cycle normally occurs in regions that have a significant stretch of open water, because this allows for the formation of larger waves and hence increased turbulence. Given the increase of such open water in the Arctic Ocean caused by retreating summer sea ice, the frazil/pancake/ice sheet cycle may also become the dominant ice formation process during freezeup in the Arctic.

  9. The importance of sea-ice area biases in 21st century multi-model projections of Antarctic net precipitation and temperature and their relative change

    Science.gov (United States)

    Bracegirdle, T.

    2015-12-01

    Climate models exhibit large biases in sea ice area (SIA) in their historical simulations. This study has explored the impacts of these biases on multi-model uncertainty in CMIP5 ensemble projections of 21st century change in Antarctic surface temperature, net precipitation and SIA. The analysis is based on time slice climatologies in the RCP8.5 future scenario (2070-2099) and historical (1970-1999) simulations across 37 different CMIP5 models. Projected changes in net precipitation, temperature and SIA are found to be strongly associated with simulated historical mean SIA (e.g. cross-model correlations of r = 0.77, 0.70 and -0.86, respectively). Furthermore, historical SIA bias is found to have a large impact on the simulated ratio between net precipitation response and temperature response. This ratio is smaller in models with smaller-than-observed historical SIA. These findings are particularly relevant to quantifying and reducing model uncertainty in projections of Antarctic surface mass balance and associated contributions to sea level change.

  10. Impact of sea ice initialization on sea ice and atmosphere prediction skill on seasonal timescales

    Science.gov (United States)

    Guemas, V.; Chevallier, M.; Déqué, M.; Bellprat, O.; Doblas-Reyes, F.

    2016-04-01

    We present a robust assessment of the impact of sea ice initialization from reconstructions of the real state on the sea ice and atmosphere prediction skill. We ran two ensemble seasonal prediction experiments from 1979 to 2012 : one using realistic sea ice initial conditions and another where sea ice is initialized from a climatology, with two forecast systems. During the melting season in the Arctic Ocean, sea ice forecasts become skilful with sea ice initialization until 3-5 months ahead, thanks to the memory held by sea ice thickness. During the freezing season in both the Arctic and Antarctic Oceans, sea ice forecasts are skilful for 7 and 2 months, respectively, with negligible differences between the two experiments, the memory being held by the ocean heat content. A weak impact on the atmosphere prediction skill is obtained.

  11. Sea ice, climate, and multiscale composites

    Science.gov (United States)

    Golden, Kenneth

    2014-03-01

    In September of 2012, the area of the Arctic Ocean covered by sea ice reached its lowest level ever recorded in more than three decades of satellite measurements. In fact, compared to the 1980's and 1990's, this represents a loss of more than half of the summer Arctic sea ice pack. While global climate models generally predict sea ice declines over the 21st century, the precipitous losses observed so far have significantly outpaced most projections. I will discuss how mathematical models of composite materials and statistical physics are being used to study key sea ice processes and advance how sea ice is represented in climate models. This work is helping to improve projections of the fate of Earth's ice packs, and the response of polar ecosystems. A brief video of a recent Antarctic expedition where sea ice properties were measured will be shown. Supported by NSF and ONR.

  12. Long-Term Record of Arctic and Antarctic Sea and Ice Surface Temperatures from Thermal Infrared Satellite Sensors

    Science.gov (United States)

    Luis, Cristina; Dybkjær, Gorm; Eastwood, Steinar; Tonboe, Rasmus; Høyer, Jacob

    2015-04-01

    Surface temperature is among the most important variables in the surface energy balance equation and it significantly affects the atmospheric boundary layer structure, the turbulent heat exchange and, over ice, the ice growth rate. Here we measure the surface temperature using thermal infrared sensors from 10-12 µm wavelength, a method whose primary limitation over sea ice is the detection of clouds. However, in the Arctic and around Antarctica there are very few conventional observations of surface temperature from buoys, and it is sometimes difficult to determine if the temperature is measured at the surface or within the snowpack, the latter of which often results in a warm bias. To reduce this bias, much interest is being paid to alternative remote sensing methods for monitoring high latitude surface temperature. We used Advanced Very High Resolution Radiometer (AVHRR) global area coverage (GAC) data to produce a high latitude sea surface temperature (SST), ice surface temperature (IST) and ice cap skin temperature dataset spanning 27 years (1982-2009). This long-term climate record is the first of its kind for IST. In this project we used brightness temperatures from the infrared channels of AVHRR sensors aboard NOAA and Metop polar-orbiting satellites. Surface temperatures were calculated using separate split window algorithms for day SST, night SST, and IST. The snow surface emissivity across all angles of the swath were simulated specifically for all sensors using an emission model. Additionally, all algorithms were tuned to the Arctic using simulated brightness temperatures from a radiative transfer model with atmospheric profiles and skin temperatures from European Centre for Medium-Range Forecasts (ECMWF) re-analysis data (ERA-Interim). Here we present the results of product quality as compared to in situ measurements from buoys and infrared radiometers, as well as a preliminary analysis of climate trends revealed by the record.

  13. 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.

  14. Better constraints on the sea-ice state using global sea-ice data assimilation

    Directory of Open Access Journals (Sweden)

    P. Mathiot

    2012-06-01

    Full Text Available Short-term and decadal sea-ice prediction systems need a realistic initial state, generally obtained using ice-ocean model simulations with data assimilation. However, only sea-ice concentration and velocity data are currently assimilated. In this work, an Ensemble Kalman Filter system is used to assimilate observed ice concentration and freeboard (i.e. thickness of emerged sea ice data into a global coupled ocean–sea-ice model. The impact and effectiveness of our data assimilation system is assessed in two steps: firstly, through the assimilation of synthetic data (i.e., model-generated data and, secondly, through the assimilation of satellite data. While ice concentrations are available daily, freeboard data used in this study are only available during six one-month periods spread over 2005–2007. Our results show that the simulated Arctic and Antarctic sea-ice extents are improved by the assimilation of synthetic ice concentration data. Assimilation of synthetic ice freeboard data improves the simulated sea-ice thickness field. Using real ice concentration data enhances the model realism in both hemispheres. Assimilation of ice concentration data significantly improves the total hemispheric sea-ice extent all year long, especially in summer. Combining the assimilation of ice freeboard and concentration data leads to better ice thickness, but does not further improve the ice extent. Moreover, the improvements in sea-ice thickness due to the assimilation of ice freeboard remain visible well beyond the assimilation periods.

  15. 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...

  16. 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.

  17. Miocene Antarctic ice dynamics in the Ross Embayment (Western Ross Sea, Antarctica): Insights from provenance analyses of sedimentary clasts in the AND-2A drill core

    Science.gov (United States)

    Cornamusini, Gianluca; Talarico, Franco M.

    2016-11-01

    A detailed study of gravel-size sedimentary clasts in the ANDRILL-2A (AND-2A) drill core reveals distinct changes in provenance and allows reconstructions to be produced of the paleo ice flow in the McMurdo Sound region (Ross Sea) from the Early Miocene to the Holocene. The sedimentary clasts in AND-2A are divided into seven distinct petrofacies. A comparison of these with potential source rocks from the Transantarctic Mountains and the coastal Southern Victoria Land suggests that the majority of the sedimentary clasts were derived from formations within the Devonian-Triassic Beacon Supergroup. The siliciclastic-carbonate petrofacies are similar to the fossiliferous erratics found in the Quaternary Moraine in the southern McMurdo Sound and were probably sourced from Eocene strata that are currently hidden beneath the Ross Ice Shelf. Intraformational clasts were almost certainly reworked from diamictite and mudstone sequences that were originally deposited proximal to the drill site. The distribution of sedimentary gravel clasts in AND-2A suggests that sedimentary sequences in the drill core were deposited under two main glacial scenarios: 1) a highly dynamic ice sheet that did not extend beyond the coastal margin and produced abundant debris-rich icebergs from outlet glaciers in the central Transantarctic Mountains and South Victoria Land; 2) and an ice sheet that extended well beyond the coastal margin and periodically advanced across the Ross Embayment. Glacial scenario 1 dominated the early to mid-Miocene (between ca. 1000 and 225 mbsf in AND-2A) and scenario 2 the early Miocene (between ca. 1138 and 1000 mbsf) and late Neogene to Holocene (above ca. 225 mbsf). This study augments previous research on the clast provenance and highlights the added value that sedimentary clasts offer in terms of reconstructing past glacial conditions from Antarctic drill core records.

  18. IOMASA SEA ICE DEVELOPMENTS

    DEFF Research Database (Denmark)

    Andersen, Søren; Tonboe, Rasmus; Heygster, Georg

    2005-01-01

    Sensitivity studies show that the radiometer ice concentration estimate can be biased by +10% by anomalous atmospheric emissivity and -20% by anomalous ice surface emissivity. The aim of the sea ice activities in EU 5th FP project IOMASA is to improve sea ice concentration estimates at higher...... spatial resolution. The project is in the process of facilitating an ice concentration observing system through validation and a better understanding of the microwave radiative transfer of the sea ice and overlying snow layers. By use of a novel modelling approach, it is possible to better detect...... and determine the circumstances that may lead to anomalous sea ice concentration retrieval as well as to assess and possibly minimize the sensitivities of the retrieval system. Through an active partnership with the SAF on Ocean and Sea Ice, a prototype system will be implemented as an experimental product...

  19. Evidence for the Late Cenozoic Antarctic Ice Sheet evolution and bottom current dynamics in the central-western Ross Sea outer margin, Antarctica

    Science.gov (United States)

    Kim, Sookwan; De Santis, Laura; Kuk Hong, Jong; Cottlerle, Diego; Petronio, Lorenzo; Colizza, Ester; Bergamasco, Andrea; Kim, Young-Gyun; Kang, Seung-Goo; Kim, Hyoungjun; Kim, Suhwan; Wardell, Nigel; Geletti, Riccardo; McKay, Robert; Jin, Young Keun; Kang, Sung-Ho

    2016-04-01

    Sedimentary records in polar continental margins provide clues for understanding paleo-depositional environments, related to ice sheet evolution and bottom-water current dynamics, during times of past climate and global sea level changes. Previous seismostratigraphic studies of the Ross Sea embayment, Antarctica, illustrated its general stratigraphic framework and the distribution of glacial sedimentary features over the continental shelf, since the onset of Antarctic ice-sheets at the Eocene-Oligocene boundary (~34.0 Ma). In contrast, there are a fewer studies for the outer continental margin, where continuous sedimentary deposits generally preserve the record of past climate cycles with minimum hiatus, comparing to the inner- and mid-continental shelf, where grounding ice streams eroded most of the sediments. Here we present a seismostratigraphic analysis of 2-D multichannel seismic reflection profiles, from the Central Basin located in the central-western Ross Sea outer margin. A glacial prograding wedge developed at the mouth of the Joides Basin since early-middle Miocene times (RSU4: ~14.0 Ma). And the Central Basin was filled with stacked debris-flow deposits and turbidites. The sediment depocenter shifted from the Central Basin toward the slope in the Pliocene (after RSU2: ~3.3 Ma). Pliocene foreset beds are steep and pinch out at the base of the continental slope. Bottom current controlled sediment drifts well developed since the middle Miocene, along the western slope of the central Basin and on the basement highs These areas are far from the mouth of the Joides trough, where most of the glacial sediment is deposited, and they are also more elevated than the basinal areas, where gravity flow maximum thickness accumulated. Along the western slope of the central Basin and over the basement highs, the signature in the sediments of the action of bottom current reworking and shaping the sea floor can be then clearly recognized. We present the sediment drifts

  20. 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.

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

    NARCIS (Netherlands)

    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

  2. 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

  3. Simulation of the crystal growth of platelet sea ice with diffusive heat and mass transfer

    NARCIS (Netherlands)

    Wangpan, Pat; Langhorne, Patricia J.; Dempsey, David E.; Hahn-Woernle, L.; Sun, Zhifa

    2015-01-01

    Antarctic coastal sea ice often grows in water that has been supercooled by interaction with an ice shelf. In these situations, ice crystals can form at depth, rise and deposit under the sea-ice cover to form a porous layer that eventually consolidates near the base of the existing sea ice. The leas

  4. The EUMETSAT sea ice concentration climate data record

    Science.gov (United States)

    Tonboe, Rasmus T.; Eastwood, Steinar; Lavergne, Thomas; Sørensen, Atle M.; Rathmann, Nicholas; Dybkjær, Gorm; Toudal Pedersen, Leif; Høyer, Jacob L.; Kern, Stefan

    2016-09-01

    An Arctic and Antarctic sea ice area and extent dataset has been generated by EUMETSAT's Ocean and Sea Ice Satellite Application Facility (OSISAF) using the record of microwave radiometer data from NASA's Nimbus 7 Scanning Multichannel Microwave radiometer (SMMR) and the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave/Imager (SSM/I) and Special Sensor Microwave Imager and Sounder (SSMIS) satellite sensors. The dataset covers the period from October 1978 to April 2015 and updates and further developments are planned for the next phase of the project. The methodology for computing the sea ice concentration uses (1) numerical weather prediction (NWP) data input to a radiative transfer model for reduction of the impact of weather conditions on the measured brightness temperatures; (2) dynamical algorithm tie points to mitigate trends in residual atmospheric, sea ice, and water emission characteristics and inter-sensor differences/biases; and (3) a hybrid sea ice concentration algorithm using the Bristol algorithm over ice and the Bootstrap algorithm in frequency mode over open water. A new sea ice concentration uncertainty algorithm has been developed to estimate the spatial and temporal variability in sea ice concentration retrieval accuracy. A comparison to US National Ice Center sea ice charts from the Arctic and the Antarctic shows that ice concentrations are higher in the ice charts than estimated from the radiometer data at intermediate sea ice concentrations between open water and 100 % ice. The sea ice concentration climate data record is available for download at www.osi-saf.org, including documentation.

  5. Sea Ice Edge Location and Extent in the Russian Arctic, 1933-2006

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Sea Ice Edge Location and Extent in the Russian Arctic, 1933-2006 data are derived from sea ice charts from the Arctic and Antarctic Research Institute (AARI),...

  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. 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 ...

  8. Influence of short-term synoptic events and snow depth on DMS, DMSP, and DMSO dynamics in Antarctic spring sea ice

    Directory of Open Access Journals (Sweden)

    Gauthier Carnat

    2016-10-01

    Full Text Available Abstract Temporal changes in the concentration profiles of dimethylsulfide (DMS, dimethylsulfoniopropionate (DMSP, and dimethylsulfoxide (DMSO were measured in pack ice from the Bellingshausen Sea (Antarctica during the winter-spring transition of 2007. Two sites with contrasting snow and ice thicknesses were sampled, with high concentrations of DMS, DMSP, and DMSO observed at both sites, especially in surface ice. These high concentrations were shown to correspond to the development of a surface ice microalgal community dominated by strong DMSP producers (flagellates and dinoflagellates following flooding of the ice cover. Several short-term synoptic events were observed and shown to influence strongly the dynamics of sea ice DMS, DMSP, and DMSO. In particular, a cold spell event was associated with drastic changes in the environmental conditions for the sea ice microbial communities and to a remarkable increase in the production of dimethylated sulfur compounds at both sites. A good correlation between all dimethylated sulfur compounds, sea ice temperature, and brine salinity suggested that the observed increase was triggered mainly by increased thermal and osmotic stresses on microalgal cells. Atmospheric forcing, by controlling sea ice temperature and hence the connectivity and instability of the brine network, was also shown to constrain the transfer of dimethylated sulfur compounds in the ice towards the ocean via brine drainage. Analysis of the two contrasting sampling sites shed light on the key role played by the snow cover in the sea ice DMS cycle. Thicker snow cover, by insulating the underlying sea ice, reduced the amplitude of environmental changes associated with the cold spell, leading to a weaker physiological response and DMS, DMSP, and DMSO production. Thicker snow also hampered the development of steep gradients in sea ice temperature and brine salinity, thereby decreasing the potential for the release of dimethylated sulfur

  9. 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 ...

  10. Sensitivity of sea ice and ocean simulations to sea ice salinity in a coupled global climate model

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The impacts of the spatiotemporal variations of sea ice salinity on sea ice and ocean characteristics have not been studied in detail, as the existing climate models neglect or misrepresent this process. To address this issue, this paper formulated a parameterization with more realistic sea ice salinity budget, and examined the sensitivity of sea ice and ocean simulations to the ice salinity variations and associated salt flux into the ocean using a coupled global climate model. Results show that the inclusion of such a parameterization leads to an increase and thickening of sea ice in the Eurasian Arctic and within the ice pack in the Antarctic circumpolar region, and a weakening of the North Atlantic Deep Water and a strengthening of the Antarctic Bottom Water. The atmospheric responses associated with the ice changes were also discussed.

  11. 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.

  12. 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

  13. 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...

  14. 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

  15. Iron in sea ice: Review and new insights

    Directory of Open Access Journals (Sweden)

    D. Lannuzel

    2016-10-01

    Full Text Available Abstract The discovery that melting sea ice can fertilize iron (Fe-depleted polar waters has recently fostered trace metal research efforts in sea ice. The aim of this review is to summarize and synthesize the current understanding of Fe biogeochemistry in sea ice. To do so, we compiled available data on particulate, dissolved, and total dissolvable Fe (PFe, DFe and TDFe, respectively from sea-ice studies from both polar regions and from sub-Arctic and northern Hemisphere temperate areas. Data analysis focused on a circum-Antarctic Fe dataset derived from 61 ice cores collected during 10 field expeditions carried out between 1997 and 2012 in the Southern Ocean. Our key findings are that 1 concentrations of all forms of Fe (PFe, DFe, TDFe are at least a magnitude larger in fast ice and pack ice than in typical Antarctic surface waters; 2 DFe, PFe and TDFe behave differently when plotted against sea-ice salinity, suggesting that their distributions in sea ice are driven by distinct, spatially and temporally decoupled processes; 3 DFe is actively extracted from seawater into growing sea ice; 4 fast ice generally has more Fe-bearing particles, a finding supported by the significant negative correlation observed between both PFe and TDFe concentrations in sea ice and water depth; 5 the Fe pool in sea ice is coupled to biota, as indicated by the positive correlations of PFe and TDFe with chlorophyll a and particulate organic carbon; and 6 the vast majority of DFe appears to be adsorbed onto something in sea ice. This review also addresses the role of sea ice as a reservoir of Fe and its role in seeding seasonally ice-covered waters. We discuss the pivotal role of organic ligands in controlling DFe concentrations in sea ice and highlight the uncertainties that remain regarding the mechanisms of Fe incorporation in sea ice.

  16. Storm-induced sea-ice breakup and the implications for ice extent

    Science.gov (United States)

    Kohout, A. L.; Williams, M. J. M.; Dean, S. M.; Meylan, M. H.

    2014-05-01

    The propagation of large, storm-generated waves through sea ice has so far not been measured, limiting our understanding of how ocean waves break sea ice. Without improved knowledge of ice breakup, we are unable to understand recent changes, or predict future changes, in Arctic and Antarctic sea ice. Here we show that storm-generated ocean waves propagating through Antarctic sea ice are able to transport enough energy to break sea ice hundreds of kilometres from the ice edge. Our results, which are based on concurrent observations at multiple locations, establish that large waves break sea ice much farther from the ice edge than would be predicted by the commonly assumed exponential decay. We observed the wave height decay to be almost linear for large waves--those with a significant wave height greater than three metres--and to be exponential only for small waves. This implies a more prominent role for large ocean waves in sea-ice breakup and retreat than previously thought. We examine the wider relevance of this by comparing observed Antarctic sea-ice edge positions with changes in modelled significant wave heights for the Southern Ocean between 1997 and 2009, and find that the retreat and expansion of the sea-ice edge correlate with mean significant wave height increases and decreases, respectively. This includes capturing the spatial variability in sea-ice trends found in the Ross and Amundsen-Bellingshausen seas. Climate models fail to capture recent changes in sea ice in both polar regions. Our results suggest that the incorporation of explicit or parameterized interactions between ocean waves and sea ice may resolve this problem.

  17. On the Predictability of Sea Ice

    Science.gov (United States)

    Blanchard-Wrigglesworth, Edward

    anomalies. We run the GCM in a slab-ocean model configuration and obtain predictability that is lower than expected from the perfect model fully coupled GCM. We next make use of models submitted to the CMIP5 archive to investigate the spatial and temporal characteristics of ice thickness anomalies, together with the CCSM3, CCSM4 and two forced ice-ocean models, PIOMAS and CCSM4 in ice-ocean mode. We find that there is a wide spread in the characteristics of ice thickness anomalies across models, partially explained by biases in mean thickness. Additionally, forced ice-ocean models show reduced ice-thickness variability. These results have significant implications for the initialization of fully-coupled GCMs from forced GCM output. Finally we investigate the initial-value predictability of Antarctic sea ice in the CCSM3. We find that Antarctic sea-ice anomaly persistence is comparable to that of Arctic sea-ice anomalies. High values of initial-value predictability of sea-ice area can last for up to two years, and tend to advect eastward in time. We also find memory re-emergence that is driven by upper ocean heat anomalies from the melt to the growth season. Unlike the Arctic, we do not find evidence for an ice-thickness driven mechanism of memory re-emergence

  18. 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

  19. 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.

  20. 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

  1. 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

  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. On sea level - ice sheet interactions

    Science.gov (United States)

    Gomez, Natalya Alissa

    grounding-line migration. Finally, I confirm the universality of this conclusion in a more realistic setting by coupling a 3-D, Antarctic Ice Sheet (AIS) model to a global sea-level model and simulating the evolution of the AIS over the last 40,000 years.

  4. 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

  5. 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.

  6. 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.

  7. The ASIBIA sea-ice facility: First results from the Atmosphere-Sea-Ice-Biogeochemistry in the Arctic chamber

    Science.gov (United States)

    France, James L.; Thomas, Max

    2016-04-01

    Working in the natural ocean-ice-atmosphere system is very difficult, as conducting fieldwork on sea-ice presents many challenges ice including costs, safety, experimental controls and access. The new ASIBIA (Atmosphere-Sea-Ice-Biogeochemistry in the Arctic) coupled Ocean-Sea-Ice-(Snow)-Atmosphere chamber facility at the University of East Anglia, UK, we are aiming to perform controlled first-year sea-ice investigations in areas such as sea-ice physics, physicochemical and biogeochemical processes in sea-ice and quantification of the bi-directional flux of gases in various states of first-year sea-ice conditions. The facility is a medium sized chamber with programmable temperatures from -55°C to +30°C, allowing a full range of first year sea-ice growing conditions in both the Arctic and Antarctic to be simulated. The water depth can be up to 1 m (including up to 25 cm of sea-ice) and an optional 1 m tall Teflon film atmosphere on top of the sea-ice, thus creating a closed and coupled ocean-sea-ice-atmosphere mesocosm. Ice growth in the tank is well suited for studying first-year sea-ice physical properties, with in-situ ice-profile measurements of temperature, salinity, conductivity, pressure and spectral light transmission. Underwater and above ice cameras are installed to record the physical development of the sea-ice. Here, we present the data from the first suites of experiments in the ASIBIA chamber focussing on sea-ice physics and give a brief description of the capabilities of the facility going forward. The ASIBIA chamber was funded as part of an ERC consolidator grant to the late Prof. Roland von Glasow and we hope this work and further development of the facility will act as a lasting legacy.

  8. How reversible is sea ice loss?

    Directory of Open Access Journals (Sweden)

    J. K. Ridley

    2012-02-01

    Full Text Available It is well accepted that increasing atmospheric CO2 results in global warming, leading to a decline in polar sea ice area. Here, the specific question of whether there is a tipping point in the sea ice cover is investigated. The global climate model HadCM3 is used to map the trajectory of sea ice area under idealised scenarios. The atmospheric CO2 is first ramped up to four times pre-industrial levels (4 × CO2, then ramped down to pre-industrial levels. We also examine the impact of stabilising climate at 4 × CO2 prior to ramping CO2 down to pre-industrial levels. Against global mean temperature, Arctic sea ice area is reversible, while the Antarctic sea ice shows some asymmetric behaviour – its rate of change slower, with falling temperatures, than its rate of change with rising temperatures. However, we show that the asymmetric behaviour is driven by hemispherical differences in temperature change between transient and stabilisation periods. We find no irreversible behaviour in the sea ice cover.

  9. How reversible is sea ice loss?

    Directory of Open Access Journals (Sweden)

    J. K. Ridley

    2011-09-01

    Full Text Available It is well accepted that increasing atmospheric CO2 results in global warming, leading to a decline in polar sea ice area. Here, the specific question of whether there is a tipping point in the sea ice cover is investigated. The global climate model HadCM3, is used to map the trajectory of sea ice area under idealised scenarios. The atmospheric CO2 is first ramped up to four times pre-industrial levels (4 × CO2 then ramped down back to pre-industrial levels. We also examine the impact of stabilising climate at 4 × CO2 prior to ramping CO2 down to pre-industrial levels. Against global mean temperature Arctic sea ice area has little hysteresis while the Antarctic sea ice shows significant hysteresis – its rate of change slower, with falling temperatures, than its rate of change with rising temperatures. However, we show that the driver of the hysteresis is the hemispherical differences in temperature change between transient and stabilisation periods. We find no irreversible behaviour in the sea ice cover.

  10. Seafloor Control on Sea Ice

    Science.gov (United States)

    Nghiem, S. V.; Clemente-Colon, P.; Rigor, I. G.; Hall, D. K.; Neumann, G.

    2011-01-01

    The seafloor has a profound role in Arctic sea ice formation and seasonal evolution. Ocean bathymetry controls the distribution and mixing of warm and cold waters, which may originate from different sources, thereby dictating the pattern of sea ice on the ocean surface. Sea ice dynamics, forced by surface winds, are also guided by seafloor features in preferential directions. Here, satellite mapping of sea ice together with buoy measurements are used to reveal the bathymetric control on sea ice growth and dynamics. Bathymetric effects on sea ice formation are clearly observed in the conformation between sea ice patterns and bathymetric characteristics in the peripheral seas. Beyond local features, bathymetric control appears over extensive ice-prone regions across the Arctic Ocean. The large-scale conformation between bathymetry and patterns of different synoptic sea ice classes, including seasonal and perennial sea ice, is identified. An implication of the bathymetric influence is that the maximum extent of the total sea ice cover is relatively stable, as observed by scatterometer data in the decade of the 2000s, while the minimum ice extent has decreased drastically. Because of the geologic control, the sea ice cover can expand only as far as it reaches the seashore, the continental shelf break, or other pronounced bathymetric features in the peripheral seas. Since the seafloor does not change significantly for decades or centuries, sea ice patterns can be recurrent around certain bathymetric features, which, once identified, may help improve short-term forecast and seasonal outlook of the sea ice cover. Moreover, the seafloor can indirectly influence cloud cover by its control on sea ice distribution, which differentially modulates the latent heat flux through ice covered and open water areas.

  11. 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.

  12. 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.

  13. Applicability of highly branched isoprenoids as a sea ice proxy in the Ross Sea

    Science.gov (United States)

    Kim, Jung-Hyun; Lee, Jae Il; Belt, Simon T.; Gal, Jong-Ku; Smik, Lukas; Shin, Kyung-Hoon

    2016-04-01

    Sea ice is an integral component of the polar climate system, constraining the effect of changing surface albedo, ocean-atmosphere heat exchanges, the formation of deep and intermediate waters that participate in driving the meridional overturning circulation and thus global climate. In recent years, a mono-unsaturated highly branched isoprenoid (HBI) alkene which is biosynthesised by certain sea ice diatoms during the spring bloom and, upon ice melt, deposited into underlying sediments, has been uniquely observed in Arctic sea ice and in Arctic sediments. Hence, the term IP25 (ice proxy with 25 carbon atoms) was proposed to distinguish this compound from other HBI isomers and has become an established proxy for the reconstruction of Arctic sea ice. In contrast, a monounsaturated HBI alkene, i.e. IP25, has not been observed in sea ice or sediments from the Antarctic. Hence, the application of diene and triene HBI concentrations and the resulting diene/triene (D/T) ratio was alternatively introduced as sea ice/open water indicators in the Southern Ocean. However, there is still lack of data covering the wide areas around the Antarctic, especially from the Ross Sea. Hence, we investigated surface sediment samples from the Ross Sea (n=14) collected during the R/V ARAON cruise in 2015 as well as from the Antarctic Peninsula (n=17) collected during several R/V ARAON cruises between 2001 and 2013. We will present our preliminary results and will discuss the applicability of the HBI in the Ross Sea.

  14. 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.

  15. 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.

  16. 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

  17. The multi-millennial Antarctic commitment to future sea-level rise.

    Science.gov (United States)

    Golledge, N R; Kowalewski, D E; Naish, T R; Levy, R H; Fogwill, C J; Gasson, E G W

    2015-10-15

    Atmospheric warming is projected to increase global mean surface temperatures by 0.3 to 4.8 degrees Celsius above pre-industrial values by the end of this century. If anthropogenic emissions continue unchecked, the warming increase may reach 8-10 degrees Celsius by 2300 (ref. 2). The contribution that large ice sheets will make to sea-level rise under such warming scenarios is difficult to quantify because the equilibrium-response timescale of ice sheets is longer than those of the atmosphere or ocean. Here we use a coupled ice-sheet/ice-shelf model to show that if atmospheric warming exceeds 1.5 to 2 degrees Celsius above present, collapse of the major Antarctic ice shelves triggers a centennial- to millennial-scale response of the Antarctic ice sheet in which enhanced viscous flow produces a long-term commitment (an unstoppable contribution) to sea-level rise. Our simulations represent the response of the present-day Antarctic ice-sheet system to the oceanic and climatic changes of four representative concentration pathways (RCPs) from the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. We find that substantial Antarctic ice loss can be prevented only by limiting greenhouse gas emissions to RCP 2.6 levels. Higher-emissions scenarios lead to ice loss from Antarctic that will raise sea level by 0.6-3 metres by the year 2300. Our results imply that greenhouse gas emissions in the next few decades will strongly influence the long-term contribution of the Antarctic ice sheet to global sea level.

  18. Influence of stochastic sea ice parametrization on climate and the role of atmosphere-sea ice-ocean interaction.

    Science.gov (United States)

    Juricke, Stephan; Jung, Thomas

    2014-06-28

    The influence of a stochastic sea ice strength parametrization on the mean climate is investigated in a coupled atmosphere-sea ice-ocean model. The results are compared with an uncoupled simulation with a prescribed atmosphere. It is found that the stochastic sea ice parametrization causes an effective weakening of the sea ice. In the uncoupled model this leads to an Arctic sea ice volume increase of about 10-20% after an accumulation period of approximately 20-30 years. In the coupled model, no such increase is found. Rather, the stochastic perturbations lead to a spatial redistribution of the Arctic sea ice thickness field. A mechanism involving a slightly negative atmospheric feedback is proposed that can explain the different responses in the coupled and uncoupled system. Changes in integrated Antarctic sea ice quantities caused by the stochastic parametrization are generally small, as memory is lost during the melting season because of an almost complete loss of sea ice. However, stochastic sea ice perturbations affect regional sea ice characteristics in the Southern Hemisphere, both in the uncoupled and coupled model. Remote impacts of the stochastic sea ice parametrization on the mean climate of non-polar regions were found to be small.

  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. 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.

  1. Snow on Sea Ice Workshop - An Icy Meeting of the Minds: Modelers and Measurers

    Science.gov (United States)

    2015-09-30

    cover resides atop Arctic and Antarctic sea ice for much of the...year. This snow cover impacts the surface heat budget, the atmosphere– ocean heat exchange, ice growth, ice melt, and light transmission to the ocean . It...period, the group went out on the ice and made measurements of snow and ice cover , and spent time indoors talking about how large scale sea ice

  2. EASE-Grid Sea Ice Age

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set provides weekly estimates of sea ice age for the Arctic Ocean from remotely sensed sea ice motion and sea ice extent. The ice age data are derived from...

  3. 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.

  4. The future of ice sheets and sea ice: between reversible retreat and unstoppable loss.

    Science.gov (United States)

    Notz, Dirk

    2009-12-08

    We discuss the existence of cryospheric "tipping points" in the Earth's climate system. Such critical thresholds have been suggested to exist for the disappearance of Arctic sea ice and the retreat of ice sheets: Once these ice masses have shrunk below an anticipated critical extent, the ice-albedo feedback might lead to the irreversible and unstoppable loss of the remaining ice. We here give an overview of our current understanding of such threshold behavior. By using conceptual arguments, we review the recent findings that such a tipping point probably does not exist for the loss of Arctic summer sea ice. Hence, in a cooler climate, sea ice could recover rapidly from the loss it has experienced in recent years. In addition, we discuss why this recent rapid retreat of Arctic summer sea ice might largely be a consequence of a slow shift in ice-thickness distribution, which will lead to strongly increased year-to-year variability of the Arctic summer sea-ice extent. This variability will render seasonal forecasts of the Arctic summer sea-ice extent increasingly difficult. We also discuss why, in contrast to Arctic summer sea ice, a tipping point is more likely to exist for the loss of the Greenland ice sheet and the West Antarctic ice sheet.

  5. Can natural variability explain the discrepancy between observed and modeled sea ice trends?

    CERN Document Server

    Rosenblum, Erica

    2016-01-01

    Observations indicate that the Arctic sea ice cover is rapidly retreating while the Antarctic sea ice cover is steadily expanding. State-of-the-art climate models, by contrast, tend to predict a moderate decrease in both the Arctic and Antarctic sea ice covers. A number of recent studies have attributed this discrepancy in each hemisphere to natural variability, suggesting that the models are consistent with the observations when simulated natural variability is taken into account. Here we examine sea ice changes during 1979-2013 in simulations from the most recent Coupled Model Intercomparison Project (CMIP5) as well as the Community Earth System Model Large Ensemble (CESM-LE). We find that accurately simulated Arctic sea ice retreat occurs only in simulations with too much global warming, whereas accurately simulated Antarctic sea ice expansion tends to occur in simulations with too little global warming. We show that because of this, simulations from both ensembles do not capture the observed asymmetry bet...

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Ice cores and SeaRISE: What we do (and don't) know

    Science.gov (United States)

    Alley, Richard B.

    1991-01-01

    Ice core analyses are needed in SeaRISE to learn what the West Antarctic ice sheet and other marine ice sheets were like in the past, what climate changes led to their present states, and how they behave. The major results of interest to SeaRISE from previous ice core analyses in West Antarctic are that the end of the last ice age caused temperature and accumulation rate increases in inland regions, leading to ice sheet thickening followed by thinning to the present.

  13. 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.

  14. Antartic sea ice, 1973 - 1976: Satellite passive-microwave observations

    Science.gov (United States)

    Zwally, H. J.; Comiso, J. C.; Parkinson, C. L.; Campbell, W. J.; Carsey, F. D.; Gloersen, P.

    1983-01-01

    Data from the Electrically Scanning Microwave Radiometer (ESMR) on the Nimbus 5 satellite are used to determine the extent and distribution of Antarctic sea ice. The characteristics of the southern ocean, the mathematical formulas used to obtain quantitative sea ice concentrations, the general characteristics of the seasonal sea ice growth/decay cycle and regional differences, and the observed seasonal growth/decay cycle for individual years and interannual variations of the ice cover are discussed. The sea ice data from the ESMR are presented in the form of color-coded maps of the Antarctic and the southern oceans. The maps show brightness temperatures and concentrations of pack ice averaged for each month, 4-year monthly averages, and month-to-month changes. Graphs summarizing the results, such as areas of sea ice as a function of time in the various sectors of the southern ocean are included. The images demonstrate that satellite microwave data provide unique information on large-scale sea ice conditions for determining climatic conditions in polar regions and possible global climatic changes.

  15. 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.

  16. Sea Ice Charts of the Russian Arctic in Gridded Format, 1933-2006

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Arctic and Antarctic Research Institute (AARI) in St. Petersburg, Russia, produces sea ice charts for safety of navigation in the polar regions and for other...

  17. Effects of Mackenzie River Discharge and Bathymetry on Sea Ice in the Beaufort Sea

    Science.gov (United States)

    Nghiem, S. V.; Hall, D. K.; Rigor, I. G; Li, P.; Neumann, G.

    2014-01-01

    Mackenzie River discharge and bathymetry effects on sea ice in the Beaufort Sea are examined in 2012 when Arctic sea ice extent hit a record low. Satellite-derived sea surface temperature revealed warmer waters closer to river mouths. By 5 July 2012, Mackenzie warm waters occupied most of an open water area about 316,000 sq km. Surface temperature in a common open water area increased by 6.5 C between 14 June and 5 July 2012, before and after the river waters broke through a recurrent landfast ice barrier formed over the shallow seafloor offshore the Mackenzie Delta. In 2012, melting by warm river waters was especially effective when the strong Beaufort Gyre fragmented sea ice into unconsolidated floes. The Mackenzie and other large rivers can transport an enormous amount of heat across immense continental watersheds into the Arctic Ocean, constituting a stark contrast to the Antarctic that has no such rivers to affect sea ice.

  18. Arctic Sea Ice Predictability and the Sea Ice Prediction Network

    Science.gov (United States)

    Wiggins, H. V.; Stroeve, J. C.

    2014-12-01

    Drastic reductions in Arctic sea ice cover have increased the demand for Arctic sea ice predictions by a range of stakeholders, including local communities, resource managers, industry and the public. The science of sea-ice prediction has been challenged to keep up with these developments. Efforts such as the SEARCH Sea Ice Outlook (SIO; http://www.arcus.org/sipn/sea-ice-outlook) and the Sea Ice for Walrus Outlook have provided a forum for the international sea-ice prediction and observing community to explore and compare different approaches. The SIO, originally organized by the Study of Environmental Change (SEARCH), is now managed by the new Sea Ice Prediction Network (SIPN), which is building a collaborative network of scientists and stakeholders to improve arctic sea ice prediction. The SIO synthesizes predictions from a variety of methods, including heuristic and from a statistical and/or dynamical model. In a recent study, SIO data from 2008 to 2013 were analyzed. The analysis revealed that in some years the predictions were very successful, in other years they were not. Years that were anomalous compared to the long-term trend have proven more difficult to predict, regardless of which method was employed. This year, in response to feedback from users and contributors to the SIO, several enhancements have been made to the SIO reports. One is to encourage contributors to provide spatial probability maps of sea ice cover in September and the first day each location becomes ice-free; these are an example of subseasonal to seasonal, local-scale predictions. Another enhancement is a separate analysis of the modeling contributions. In the June 2014 SIO report, 10 of 28 outlooks were produced from models that explicitly simulate sea ice from dynamic-thermodynamic sea ice models. Half of the models included fully-coupled (atmosphere, ice, and ocean) models that additionally employ data assimilation. Both of these subsets (models and coupled models with data

  19. 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).

  20. Sunlight, Sea Ice, and the Ice Albedo Feedback in a Changing Arctic Sea Ice Cover

    Science.gov (United States)

    2015-09-30

    the Arctic Ocean and surrounding seas, with particular emphasis on the Chukchi and Beaufort Seas. Some of the largest changes to the sea ice cover are...Changing Arctic Sea Ice Cover Don Perovich ERDC – CRREL 72 Lyme Road Hanover, NH 03755 Phone: 603-646-4255 Email: donald.k.perovich...quantitative understanding of the partitioning of solar radiation by the Arctic sea ice cover and its impact on the heat and mass balance of the ice and upper

  1. 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

  2. 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.

  3. 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.

  4. Global Sea Ice Charting at the National Ice Center

    Science.gov (United States)

    Clemente-Colon, P.

    2006-12-01

    The National Ice Center (NIC) is a U.S. government tri-agency operational center comprised of components from the United States Navy, the National Oceanic and Atmospheric Administration (NOAA), and the U. S. Coast Guard (USCG). The mission of the NIC is to provide the highest quality strategic and tactical ice services tailored to meet operational requirements of U.S. national interests. This includes broad responsibilities to monitor all frozen ocean regions of the world in support of coastal and marine sea ice operations and research. Sea ice conditions are routinely monitored and mapped using satellite imagery along with ancillary model and in-situ data. Active microwave images from Synthetic Aperture Radar (SAR) sensors are the data of choice for NIC analysts because of their high spatial resolution (~100 m). SAR is in fact the primary data source for ice analysis when available. The high spatial resolution of available SAR data and the reliability shown by the RADARSAT- 1 mission in particular have made the use of these data critical for vessels operating in or near the ice. Limited data from the ESA Envisat Advanced SAR (ASAR) are also used in the analyses when available. Preparations for the use of the Phased Array type L-band SAR (PALSAR) aboard the soon to be launched Japanese ALOS satellite are also underway. Scatterometer backscatter imagery from QuikSCAT is also routinely used for basin-scale and circumpolar ice edge mapping. Automated algorithms for ice type and melt ponds detection as well as the synergy between these observations and the QuikSCAT wind vectors off the marginal ice zone (MIZ) are been explored. ESA Envisat Advanced SAR (ASAR) Global Monitoring Mode (GMM) mosaics of the Arctic and Antarctic regions are becoming an important tool for sea ice edge delineation too. Although SAR observations are the choice for NIC analysts to produce high spatial resolution products gear toward tactical support, passive microwave data such as those from the

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Sea ice characteristics between the middle Weddell Sea and the Prydz Bay, Antarctica during the austral summer of 2003

    Institute of Scientific and Technical Information of China (English)

    TANG Shulin; KANG Jiancheng; ZHOU Shangzhe; LI Zhijun

    2005-01-01

    The antarctic sea ice was investigated upon five occasions between January 4 and February 15, 2003. The investigations included: (1)estimation of sea ice distribution by ship-based observations between the middle Weddell Sea and the Prydz Bay; (2) estimation of sea ice distribution by aerial photography in the Prydz Bay; (3) direct measurements of fast ice thickness and snow cover, as well as ice core sampling in Nella Fjord; (4) estimation of melting sea ice distribution near the Zhongshan Station; and (5) observation of sea ice early freeze near the Zhongshan Station. On average, sea ice covered 14.4% of the study area. The highest sea ice concentration (80%)was observed in the Weddell Sea. First-year ice was dominant (99.7%~99.8%). Sea ice distributions in the Prydz Bay were more variable due to complex inshore topography, proximity of the Larsemann Hills, and/or grounded icebergs. The average thickness of landfast ice in Nella Fjord was 169.5 cm. Wind-blown snow redistribution plays an important role in affecting the ice thickness in Nella Fjord. Preliminary freezing of sea ice near the Zhongshan Station follows the first two phases of the pancake cycle.

  10. Sunlight, Sea Ice, and the Ice Albedo Feedback in a Changing Artic Sea Ice Cover

    Science.gov (United States)

    2015-11-30

    Arctic sea ice cover and its impact on the heat and mass balance of the ice and upper ocean ... Arctic Ocean and surrounding seas, with particular emphasis on the Chukchi and Beaufort Seas. Some of the largest changes to the sea ice cover are...other parts of the Arctic ice cover appear to now be accelerating. Figure 6. Maps of the linear trend of annual solar heat input to the ocean

  11. 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.

  12. First Results from the ASIBIA (Arctic Sea-Ice, snow, Biogeochemistry and Impacts on the Atmosphere) Sea-Ice Chamber

    Science.gov (United States)

    Frey, M. M.; France, J.; von Glasow, R.; Thomas, M.

    2015-12-01

    The ocean-ice-atmosphere system is very complex, and there are numerous challenges with conducting fieldwork on sea-ice including costs, safety, experimental controls and access. By creating a new coupled Ocean-Sea-Ice-(Snow)-Atmosphere facility at the University of East Anglia, UK, we are able to perform controlled investigations in areas such as sea-ice physics, physicochemical and biogeochemical processes in sea-ice, and to quantify the bi-directional flux of gases in established, freezing and melting sea-ice. The environmental chamber is capable of controlled programmable temperatures from -55°C to +30°C, allowing a full range of first year sea-ice growing conditions in both the Arctic and Antarctic to be simulated. The sea-ice tank within the chamber measures 2.4 m x 1.4 m x 1 m water depth, with an identically sized Teflon film atmosphere on top of the tank. The tank and atmosphere forms a coupled, isolated mesocosm. Above the atmosphere is a light bank with dimmable solar simulation LEDs, and UVA and UVB broadband fluorescent battens, providing light for a range of experiments such as under ice biogeochemistry and photochemistry. Ice growth in the tank will be ideally suited for studying first-year sea-ice physical properties, with in-situ ice-profile measurements of temperature, salinity, conductivity, pressure and spectral light transmission. Under water and above ice cameras are installed to observe the physical development of the sea-ice. The ASIBIA facility is also well equipped for gas exchange and diffusion studies through sea-ice with a suite of climate relevant gas measuring instruments (CH4, CO2, O3, NOx, NOy permanently installed, further instruments available) able to measure either directly in the atmospheric component, or via a membrane for water side dissolved gases. Here, we present the first results from the ASIBIA sea-ice chamber, focussing on the physical development of first-year sea-ice and show the future plans for the facility over

  13. 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.

  14. 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.

  15. Analysis on long-term variability of sea ice albedo and its relationship with sea ice concentration over Antarctica

    Science.gov (United States)

    Seo, Minji; Kim, Hyun-cheol; Seong, Noh-hun; Kwon, Chaeyoung; Kim, Honghee; Han, Kyung-Soo

    2016-10-01

    Sea ice is an important factor for understanding Antarctic climate change. Especially, annual change of sea ice shows different trend in Antarctica and Arctic. This different variation need to continuously observe the Polar Regions. Sea Ice Albedo (SIA) and Sea Ice Concentration (SIC) are an indicator of variation on sea ice. In addition, albedo is key parameter to understand the energy budget in Antarctica. This being so, it is important to analyze long-term variation of the two factors for observing of change of Antarctic environment. In this study, we analyzed long-term variability of SIC and SIA to understand the changes of sea ice over Antarctic and researched the relationship with two factors. We used the SIA data at The Satellite Application Facility on Climate Monitoring (CM SAF) and the SIC data provided by Ocean and Sea Ice Satellite Application Facility (OSI-SAF) from 1982 to 2009. The study period was selected to Antarctic summer season due to polar nights. We divided study periods into two terms, Nov-Dec(ND) and Jan-Feb(JF) in order to reflect the characteristics of sea ice area, which minimum extend occurred in September and maximum extend occurred in February. We analyzed the correlation between SIA and SIC. As a results, two variables have a strong positive correlation (each correlation coefficients are 0.91 in Nov-Dec and 0.90 in Jan-Feb). We performed time series analysis using linear regression to understand the spatial and temporal tendency of SIA and SIC. As a results, SIA and SIC have a same spatial trend such as Weddle sea and Ross sea sections show the positive trend and Bellingshausen Amundsen sea shows the negative trend of two factors. Moreover, annual SIA change rate is 0.26% 0.04% yr-1 over section where represent positive trend during two study periods. And annual SIA change rate is - 0.14 - 0.25 % yr-1 of in the other part where represent negative trend during two study periods.

  16. 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.

  17. Modelling sea ice for climate studies: recent advances and future challenges (Louis Agassiz Medal Lecture)

    Science.gov (United States)

    Fichefet, Thierry

    2016-04-01

    Since the beginning of satellite measurements in 1979, the summer Arctic sea ice extent has shrunk at a mean rate of ~12% per decade, and there is evidence that the rate of decline has accelerated over the last decade. Current global climate models project further decrease in Arctic sea ice areal coverage through the 21st century if atmospheric greenhouse gas concentrations continue to increase. However, rates of loss vary greatly between models, yielding a large uncertainty as to when a seasonally ice-free Arctic Ocean may be realized. Narrowing this uncertainty is of crucial importance since such changes in the Arctic sea ice cover might have profound ramifications, including the global ocean circulation and heat budget, regional ecosystems and wildlife, the indigenous human population, and commercial exploration and transportation. Regarding the Antarctic sea ice, its extent has been observed to slightly increase during the last 37 years, which appears puzzling in a global warming context. Several hypotheses have been proposed to explain this feature, but the issue is far from being settled. On the other hand, the majority of global climate models simulate a decreasing trend in Antarctic sea ice extent over this period, which questions the validity of their Antarctic sea ice projections for the coming decades. In this lecture, we show through simulations conducted with the state of the art Louvain-la-Neuve Sea Ice Model (LIM) coupled to the Nucleous European Modelling of the Ocean (NEMO) platform that a number of small-scale sea ice processes, which are omitted or crudely represented in global climate models (in particular, the subgrid-scale sea ice thickness distribution, the thermodynamics and dynamics of brine pockets trapped within sea ice, processes related to snow on top of sea ice, including surface melt ponds, the sea ice mechanical deformation, and the subgrid-scale heterogeneity of atmosphere-ice-ocean interactions), play a significant role in

  18. 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

  19. 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

  20. 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

  1. Constraining the Antarctic contribution to global sea-level change: ANDRILL and beyond

    Science.gov (United States)

    Naish, Timothy

    2016-04-01

    Observations, models and paleoclimate reconstructions suggest that Antarctica's marine-based ice sheets behave in an unstable manner with episodes of rapid retreat in response to warming climate. Understanding the processes involved in this "marine ice sheet instability" is key for improving estimates of Antarctic ice sheet contribution to future sea-level rise. Another motivating factor is that far-field sea-level reconstructions and ice sheet models imply global mean sea level (GMSL) was up to 20m and 10m higher, respectively, compared with present day, during the interglacials of the warm Pliocene (~4-3Ma) and Late Pleistocene (at ~400ka and 125ka). This was when atmospheric CO2 was between 280 and 400ppm and global average surface temperatures were 1 to 3°C warmer, suggesting polar ice sheets are highly sensitive to relatively modest increases in climate forcing. Such magnitudes of GMSL rise not only require near complete melt of the Greenland Ice Sheet and the West Antarctic Ice Sheet, but a substantial retreat of marine-based sectors of East Antarctic Ice Sheet. Recent geological drilling initiatives on the continental margin of Antarctica from both ship- (e.g. IODP; International Ocean Discovery Program) and ice-based (e.g. ANDRILL/Antarctic Geological Drilling) platforms have provided evidence supporting retreat of marine-based ice. However, without direct access through the ice sheet to archives preserved within sub-glacial sedimentary basins, the volume and extent of ice sheet retreat during past interglacials cannot be directly constrained. Sediment cores have been successfully recovered from beneath ice shelves by the ANDRILL Program and ice streams by the WISSARD (Whillans Ice Stream Sub-glacial Access Research Drilling) Project. Together with the potential of the new RAID (Rapid Access Ice Drill) initiative, these demonstrate the technological feasibility of accessing the subglacial bed and deeper sedimentary archives. In this talk I will outline the

  2. 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.

  3. 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

  4. Improving Constraints on Paleo Ice Sheets in the Amundsen Sea Embayment

    Science.gov (United States)

    Larter, Robert D.; Gohl, Karsten; Bentley, Michael J.

    2010-01-01

    Amundsen Sea Embayment: Tectonic and Climatic Evolution; Granada, Spain, 9 September 2009; Geoscientists working on the Amundsen Sea Embayment (ASE) of West Antarctica met at a workshop during the First Antarctic Climate Evolution Symposium to discuss recent advances from, and future priorities for, work in this region. The ASE is the most rapidly changing sector of the West Antarctic Ice Sheet (WAIS) and contains enough ice to raise sea level by 1.2 meters. Ice sheet modeling studies suggest that this sector of the WAIS is potentially unstable. Considerable efforts have been made through several national Antarctic programs to acquire new data on the geological structure, subglacial topography, bathymetry, and glacial history of this remote region. These data are important for establishing boundary conditions for ice sheet modeling, for providing constraints on past ice sheet changes that can be used to test models, and for putting recent changes into a longer-term context.

  5. 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

  6. Jet formation at the sea ice edge

    Science.gov (United States)

    Feltham, D. L.; Heorton, H. D.

    2014-12-01

    The sea ice edge presents a region of many feedback processes between the atmosphere, ocean and sea ice, which are inadequately represented in current climate models. Here we focus on on-ice atmospheric and oceanic flows at the sea ice edge. Mesoscale jet formation due to the Coriolis effect is well understood over sharp changes in surface roughness such as coastlines. This sharp change in surface roughness is experienced by the atmosphere flowing over, and ocean flowing under, a compacted sea ice edge. We have studied a dynamic sea ice edge responding to atmospheric and oceanic jet formation. The shape and strength of atmospheric and oceanic jets during on-ice flows is calculated from existing studies of the sea ice edge and prescribed to idealised models of the sea ice edge. An idealised analytical model of sea ice drift is developed and compared to a sea ice climate model (the CICE model) run on an idealised domain. The response of the CICE model to jet formation is tested at various resolutions. We find that the formation of atmospheric jets during on-ice winds at the sea ice edge increases the wind speed parallel to the sea ice edge and results in the formation of a sea ice edge jet. The modelled sea ice edge jet is in agreement with an observed jet although more observations are needed for validation. The increase in ice drift speed is dependent upon the angle between the ice edge and wind and can result in a 40% increase in ice transport along the sea ice edge. The possibility of oceanic jet formation during on-ice currents and the resultant effect upon the sea ice edge is less conclusive. Observations and climate model data of the polar oceans has been analysed to show areas of likely atmospheric jet formation, with the Fram Strait being of particular interest.

  7. Modelling sea ice formation in the Terra Nova Bay polynya

    Science.gov (United States)

    Sansiviero, M.; Morales Maqueda, M. Á.; Fusco, G.; Aulicino, G.; Flocco, D.; Budillon, G.

    2017-02-01

    Antarctic sea ice is constantly exported from the shore by strong near surface winds that open leads and large polynyas in the pack ice. The latter, known as wind-driven polynyas, are responsible for significant water mass modification due to the high salt flux into the ocean associated with enhanced ice growth. In this article, we focus on the wind-driven Terra Nova Bay (TNB) polynya, in the western Ross Sea. Brine rejected during sea ice formation processes that occur in the TNB polynya densifies the water column leading to the formation of the most characteristic water mass of the Ross Sea, the High Salinity Shelf Water (HSSW). This water mass, in turn, takes part in the formation of Antarctic Bottom Water (AABW), the densest water mass of the world ocean, which plays a major role in the global meridional overturning circulation, thus affecting the global climate system. A simple coupled sea ice-ocean model has been developed to simulate the seasonal cycle of sea ice formation and export within a polynya. The sea ice model accounts for both thermal and mechanical ice processes. The oceanic circulation is described by a one-and-a-half layer, reduced gravity model. The domain resolution is 1 km × 1 km, which is sufficient to represent the salient features of the coastline geometry, notably the Drygalski Ice Tongue. The model is forced by a combination of Era Interim reanalysis and in-situ data from automatic weather stations, and also by a climatological oceanic dataset developed from in situ hydrographic observations. The sensitivity of the polynya to the atmospheric forcing is well reproduced by the model when atmospheric in situ measurements are combined with reanalysis data. Merging the two datasets allows us to capture in detail the strength and the spatial distribution of the katabatic winds that often drive the opening of the polynya. The model resolves fairly accurately the sea ice drift and sea ice production rates in the TNB polynya, leading to

  8. 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

  9. 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...

  10. Improved sea-ice radiative processes in a global coupled climate model

    Institute of Scientific and Technical Information of China (English)

    LIU Jiping; ZHANG Zhanhai; WU Huiding

    2005-01-01

    The NASA Goddard Institute for Space Studies (GISS) coupled global climate model was used to investigate the sensitivity of sea ice to improved representations of sea-ice radiative processes: (1) a more sophisticated surface albedo scheme and (2) the penetration of solar radiation in sea ice. The results show that the large-scale sea-ice conditions are very sensitive to the aforementioned parameterizations. Although the more sophisticated surface albedo scheme produces a more realistic seasonal cycle of the surface albedo as compared with the baseline simulation, the resulting higher albedo relative to the baseline simulation generates much more and thicker ice in the arctic. The penetration of solar radiation in sea-ice itself tends to reduce the ice cover and thickness in the entire arctic and the western antarctic, and increase the ice cover and thickness in the eastern antarctic. The combination of (1) and (2) significantly improves the simulations of the average ice thickness and its spatial distribution in the arctic. The atmospheric responses associated with sea-ice changes were also discussed. While improvements are seen, particularly of the ice thickness distribution, there are still some unrealistic aspects that will require further improvements to the sea-ice component.

  11. 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.

  12. Sea Ice Concentration and Extent

    Science.gov (United States)

    Comiso, Josefino C.

    2014-01-01

    Among the most seasonal and most dynamic parameters on the surface of the Earth is sea ice which at any one time covers about 3-6% of the planet. In the Northern Hemisphere, sea ice grows in extent from about 6 x 10(exp 6) sq km to 16 x 10(exp 6) sq km, while in the Southern Hemisphere, it grows from about 3 x 10(exp 6) sq km to about 19 x 10(exp 6) sq km (Comiso, 2010; Gloersen et al., 1992). Sea ice is up to about 2-3 m thick in the Northern Hemisphere and about 1 m thick in the Southern Hemisphere (Wadhams, 2002), and compared to the average ocean depth of about 3 km, it is a relatively thin, fragile sheet that can break due to waves and winds or melt due to upwelling of warm water. Being constantly advected by winds, waves, and currents, sea ice is very dynamic and usually follows the directions of the many gyres in the polar regions. Despite its vast expanse, the sea ice cover was previously left largely unstudied and it was only in recent years that we have understood its true impact and significance as related to the Earths climate, the oceans, and marine life.

  13. 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.

  14. 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

  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. 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.

  17. 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.

  18. Sea ice thickness and recent Arctic warming

    Science.gov (United States)

    Lang, Andreas; Yang, Shuting; Kaas, Eigil

    2017-01-01

    The climatic impact of increased Arctic sea ice loss has received growing attention in the last years. However, little focus has been set on the role of sea ice thickness, although it strongly determines surface heat fluxes. Here ensembles of simulations using the EC-Earth atmospheric model (Integrated Forecast System) are performed and analyzed to quantify the atmospheric impacts of Arctic sea ice thickness change since 1982 as revealed by the sea ice model assimilation Global Ice-Ocean Modeling and Assimilation System. Results show that the recent sea ice thinning has significantly affected the Arctic climate, while remote atmospheric responses are less pronounced owing to a high internal atmospheric variability. Locally, the sea ice thinning results in enhancement of near-surface warming of about 1°C per decade in winter, which is most pronounced over marginal sea ice areas with thin ice. This leads to an increase of the Arctic amplification factor by 37%.

  19. Summer sea ice characteristics of the Chukchi Sea

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    During August 1999, we investigated sea ice characteristics; its distribution, surface feature, thickness, ice floe movement, and the temperature field around inter-borders of air/ice/seawater in the Chukchi Sea. Thirteen ice cores were drilled at 11 floe stations in the area of 72°24′ 77°18′N, 153°34′ 163°28′W and the ice core structure was observed. From field observation, three melting processes of ice were observed; surface layer melting, surface and bottom layers melting, and all of ice melting. The observation of temperature fields around sea ice floes showed that the bottom melting under the ice floes were important process. As ice floes and open water areas were alternately distributed in summer Arctic Ocean; the water under ice was colder than the open water by 0.4 2.8℃. The sun radiation heated seawater in open sea areas so that the warmer water went to the bottom when the ice floes move to those areas. This causes ice melting to start at the bottom of the ice floes. This process can balance effectively the temperature fluctuating in the sea in summer. From the crystalline structure of sea ice observed from the cores, it was concluded that the ice was composed of ice crystals and brine-ice films. During the sea ice melting, the brine-ice films between ice crystals melted firstly; then the ice crystals were encircled by brine films; the sea ice became the mixture of ice and liquid brine. At the end of melting, the ice crystals would be separated each other, the bond between ice crystals weakens and this leads to the collapse of the ice sheet.

  20. 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.

  1. Atmospheric forcing of sea ice anomalies in the Ross Sea Polynya region

    Science.gov (United States)

    Dale, Ethan; McDonald, Adrian; Rack, Wolfgang

    2016-04-01

    Despite warming trends in global temperatures, sea ice extent in the southern hemisphere has shown an increasing trend over recent decades. Wind-driven sea ice export from coastal polynyas is an important source of sea ice production. Areas of major polynyas in the Ross Sea, the region with largest increase in sea ice extent, have been suggested to produce the vast amount of the sea ice in the region. We investigate the impacts of strong wind events on polynyas and the subsequent sea ice production. We utilize Bootstrap sea ice concentration (SIC) measurements derived from satellite based, Special Sensor Microwave Imager (SSM/I) brightness temperature images. These are compared with surface wind measurements made by automatic weather stations of the University of Wisconsin-Madison Antarctic Meteorology Program. Our analysis focusses on the winter period defined as 1st April to 1st November in this study. Wind data was used to classify each day into characteristic regimes based on the change of wind speed. For each regime, a composite of SIC anomaly was formed for the Ross Sea region. We found that persistent weak winds near the edge of the Ross Ice Shelf are generally associated with positive SIC anomalies in the Ross Sea polynya area (RSP). Conversely we found negative SIC anomalies in this area during persistent strong winds. By analyzing sea ice motion vectors derived from SSM/I brightness temperatures, we find significant sea ice motion anomalies throughout the Ross Sea during strong wind events. These anomalies persist for several days after the strong wing event. Strong, negative correlations are found between SIC within the RSP and wind speed indicating that strong winds cause significant advection of sea ice in the RSP. This rapid decrease in SIC is followed by a more gradual recovery in SIC. This increase occurs on a time scale greater than the average persistence of strong wind events and the resulting Sea ice motion anomalies, highlighting the production

  2. EXPERIMENTS OF SEA ICE SIMULATION

    Institute of Scientific and Technical Information of China (English)

    LIU Xi-ying; ZHANG Xue-hong; YU Ru-cong; LIU Hai-long; YU Yong-qiang

    2005-01-01

    As a substitute for the original displaced pole grids, a simple rotated spherical coordinate system was introduced into the Community Sea Ice Model version 4(CSIM4), which is a component of the Community Climate System Model(CCSM) of the American National Center of Atmospheric Research(NCAR), to deal with the "pole problems".In the new coordinates, both the geographical North Pole and South Pole lie in the model equator and grid sizes near the polar region are more uniform.With reanalysis dataset of American National Centers for Environment Prediction(NCEP) and Levitus dataset without considering sub-mixed layer heat flux, the model was integrated for 100 years with thermodynamics process involved only in the former 49 years and both dynamic and thermodynamic processes involved in the left time.Inner consistency of model results was checked with no contradiction found.The results of last 10 years' model output were analyzed and it is shown that the simulated sea ice seasonal variation is rational whereas sea ice extent in the Barents Sea in winter is larger than that of observation.Numerical experiment on influence of sub-mixed layer heat flux was also carried out and it is shown that the sub-mixed layer heat flux can modulate seasonal variation of sea ice greatly.As a model component, the sea ice model with rotated spherical coordinates was coupled with other models (the oceanic general circulation model is the LASG/IAP Climate System Ocean Model(LICOM) with reduced grid, other models are components of NCAR CCSM2) forming a climate system model and its preliminary results were also given briefly.

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

    Directory of Open Access Journals (Sweden)

    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.

  4. Loss of sea ice in the Arctic.

    Science.gov (United States)

    Perovich, Donald K; Richter-Menge, Jacqueline A

    2009-01-01

    The Arctic sea ice cover is in decline. The areal extent of the ice cover has been decreasing for the past few decades at an accelerating rate. Evidence also points to a decrease in sea ice thickness and a reduction in the amount of thicker perennial sea ice. A general global warming trend has made the ice cover more vulnerable to natural fluctuations in atmospheric and oceanic forcing. The observed reduction in Arctic sea ice is a consequence of both thermodynamic and dynamic processes, including such factors as preconditioning of the ice cover, overall warming trends, changes in cloud coverage, shifts in atmospheric circulation patterns, increased export of older ice out of the Arctic, advection of ocean heat from the Pacific and North Atlantic, enhanced solar heating of the ocean, and the ice-albedo feedback. The diminishing Arctic sea ice is creating social, political, economic, and ecological challenges.

  5. The Sea Ice Board Game

    Science.gov (United States)

    Bertram, Kathryn Berry

    2008-01-01

    The National Science Foundation-funded Arctic Climate Modeling Program (ACMP) provides "curriculum resource-based professional development" materials that combine current science information with practical classroom instruction embedded with "best practice" techniques for teaching science to diverse students. The Sea Ice Board…

  6. Radar for Mapping Sea Ice

    Science.gov (United States)

    Barath, F. T.; Jordan, R. L.

    1983-01-01

    X-band system has 100-m2 resolution. Wide swath imaging radar of synthetic aperature type transmits signal to ground station for subsequent processing into imagery. Concept meets functional requirements for continuously mapping sea ice in north and south polar regions.

  7. 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

  8. 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

  9. 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.

  10. Changes in sea-ice cover and temperature in the Western Ross Sea during the Holocene

    Science.gov (United States)

    Fleury, Sophie; Kim, Jung-Hyun; Gal, Jong-Ku; Mezgec, Karin; Belt, Simon; Smik, Lukas; Stenni, Barbara; Melis, Romana; Crosta, Xavier; Shin, Kyung-Hoon

    2016-04-01

    Although changes in sea-ice cover contribute to global climatic variations, they are poorly constrained for periods earlier than the last decades. More records are especially required around Antarctica, where the formation of Antarctic Bottom Waters participates to global thermohaline circulation. However, this region provided only a few marine sediment cores spanning the entire Holocene, especially because of generally low sedimentation rates. This study focuses on marine sediment core ANTA99-CJ5 (73°49'S; 175°39'E), located in the open sea ice zone (OSIZ) of the western Ross Sea. We analyzed several lipid biomarkers: highly branched isoprenoids (HBIs), sterols, diols and GDGTs. The combination of several biomarkers and the comparison of these results with a diatom record previously published on the same core enabled us to trace past changes in temperatures as well as in sea-ice condition over the last 11,600 years.

  11. Satellite information of sea ice for model validation

    Science.gov (United States)

    Saheed, P. P.; Mitra, Ashis K.; Momin, Imranali M.; Mahapatra, Debasis K.; Rajagopal, E. N.

    2016-05-01

    Emergence of extensively large computational facilities have enabled the scientific world to use earth system models for understating the prevailing dynamics of the earth's atmosphere, ocean and cryosphere and their inter relations. The sea ice in the arctic and the Antarctic has been identified as one of the main proxies to study the climate changes. The rapid sea-ice melting in the Arctic and disappearance of multi-year sea ice has become a matter of concern. The earth system models couple the ocean, atmosphere and sea-ice in order to bring out the possible inter connections between these three very important components and their role in the changing climate. The Indian monsoon is seen to be subjected to nonlinear changes in the recent years. The rapid ice melt in the Arctic sea ice is apparently linked to the changes in the weather and climate of the Indian subcontinent. The recent findings reveal the relation between the high events occurs in the Indian subcontinent and the Arctic sea ice melt episodes. The coupled models are being used in order to study the depth of these relations. However, the models have to be validated extensively by using measured parameters. The satellite measurements of sea-ice starts from way back in 1979. There have been many data sets available since then. Here in this study, an evaluation of the existing data sets is conducted. There are some uncertainties in these data sets. It could be associated with the absence of a single sensor for a long period of time and also the absence of accurate in-situ measurements in order to validate the satellite measurements.

  12. Ecological consequences of sea-ice decline.

    Science.gov (United States)

    Post, Eric; Bhatt, Uma S; Bitz, Cecilia M; Brodie, Jedediah F; Fulton, Tara L; Hebblewhite, Mark; Kerby, Jeffrey; Kutz, Susan J; Stirling, Ian; Walker, Donald A

    2013-08-02

    After a decade with nine of the lowest arctic sea-ice minima on record, including the historically low minimum in 2012, we synthesize recent developments in the study of ecological responses to sea-ice decline. Sea-ice loss emerges as an important driver of marine and terrestrial ecological dynamics, influencing productivity, species interactions, population mixing, gene flow, and pathogen and disease transmission. Major challenges in the near future include assigning clearer attribution to sea ice as a primary driver of such dynamics, especially in terrestrial systems, and addressing pressures arising from human use of arctic coastal and near-shore areas as sea ice diminishes.

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

    Science.gov (United States)

    Chown, Steven L

    2012-01-01

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

  14. 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.

  15. Variability and Anomalous Trends in the Global Sea Ice Cover

    Science.gov (United States)

    Comiso, Josefino C.

    2012-01-01

    The advent of satellite data came fortuitously at a time when the global sea ice cover has been changing rapidly and new techniques are needed to accurately assess the true state and characteristics of the global sea ice cover. The extent of the sea ice in the Northern Hemisphere has been declining by about -4% per decade for the period 1979 to 2011 but for the period from 1996 to 2010, the rate of decline became even more negative at -8% per decade, indicating an acceleration in the decline. More intriguing is the drastically declining perennial sea ice area, which is the ice that survives the summer melt and observed to be retreating at the rate of -14% per decade during the 1979 to 2012 period. Although a slight recovery occurred in the last three years from an abrupt decline in 2007, the perennial ice extent was almost as low as in 2007 in 2011. The multiyear ice, which is the thick component of the perennial ice and regarded as the mainstay of the Arctic sea ice cover is declining at an even higher rate of -19% per decade. The more rapid decline of the extent of this thicker ice type means that the volume of the ice is also declining making the survival of the Arctic ice in summer highly questionable. The slight recovery in 2008, 2009 and 2010 for the perennial ice in summer was likely associated with an apparent cycle in the time series with a period of about 8 years. Results of analysis of concurrent MODIS and AMSR-E data in summer also provide some evidence of more extensive summer melt and meltponding in 2007 and 2011 than in other years. Meanwhile, the Antarctic sea ice cover, as observed by the same set of satellite data, is showing an unexpected and counter intuitive increase of about 1 % per decade over the same period. Although a strong decline in ice extent is apparent in the Bellingshausen/ Amundsen Seas region, such decline is more than compensated by increases in the extent of the sea ice cover in the Ross Sea region. The results of analysis of

  16. Sea Ice Processes

    Science.gov (United States)

    1988-01-01

    aq pnoiqs suol)0!pOid AixoolQA 00! 191100 (1I ’uoTow poAlosqo aql jo lqlgti 04) ol a~xe juqp suotioaJip 4)!A% parto s~t S stqi pule ’spoods 001 a)tUJT...to provide information as ating characteristics of PIPS. These factors in- to processes and their scales (as ascertained by elude the vertical grid...warranted horizontal compression being compensated by at this time. Further investigation is needed. vertical motion. In the case of ice, upward The space

  17. Sea-ice algal primary production and nitrogen uptake rates off East Antarctica

    Science.gov (United States)

    Roukaerts, Arnout; Cavagna, Anne-Julie; Fripiat, François; Lannuzel, Delphine; Meiners, Klaus M.; Dehairs, Frank

    2016-09-01

    Antarctic pack ice comprises about 90% of the sea ice in the southern hemisphere and plays an important structuring role in Antarctic marine ecosystems, yet measurements of ice algal primary production and nitrogen uptake rates remain scarce. During the early austral spring of 2012, measurements for primary production rates and uptake of two nitrogen substrates (nitrate and ammonium) were conducted at 5 stations in the East Antarctic pack ice (63-66°S, 115-125°E). Carbon uptake was low (3.52 mg C m-2 d-1) but a trend of increased production was observed towards the end of the voyage suggesting pre-bloom conditions. Significant snow covers reaching, up to 0.8 m, induced strong light limitation. Two different regimes were observed in the ice with primarily nitrate based 'new' production (f-ratio: 0.80-0.95) at the bottom of the ice cover, due to nutrient-replete conditions at the ice-water interface, and common for pre-bloom conditions. In the sea-ice interior, POC:PN ratios (20-70) and higher POC:Chl a ratios suggested the presence of large amounts of detrital material trapped in the ice and here ammonium was the prevailing nitrogen substrate. This suggests that most primary production in the sea-ice interior was regenerated and supported by a microbial food web, recycling detritus.

  18. Past ice-sheet behaviour: retreat scenarios and changing controls in the Ross Sea, Antarctica

    Science.gov (United States)

    Halberstadt, Anna Ruth W.; Simkins, Lauren M.; Greenwood, Sarah L.; Anderson, John B.

    2016-05-01

    Studying the history of ice-sheet behaviour in the Ross Sea, Antarctica's largest drainage basin can improve our understanding of patterns and controls on marine-based ice-sheet dynamics and provide constraints for numerical ice-sheet models. Newly collected high-resolution multibeam bathymetry data, combined with two decades of legacy multibeam and seismic data, are used to map glacial landforms and reconstruct palaeo ice-sheet drainage. During the Last Glacial Maximum, grounded ice reached the continental shelf edge in the eastern but not western Ross Sea. Recessional geomorphic features in the western Ross Sea indicate virtually continuous back-stepping of the ice-sheet grounding line. In the eastern Ross Sea, well-preserved linear features and a lack of small-scale recessional landforms signify rapid lift-off of grounded ice from the bed. Physiography exerted a first-order control on regional ice behaviour, while sea floor geology played an important subsidiary role. Previously published deglacial scenarios for Ross Sea are based on low-spatial-resolution marine data or terrestrial observations; however, this study uses high-resolution basin-wide geomorphology to constrain grounding-line retreat on the continental shelf. Our analysis of retreat patterns suggests that (1) retreat from the western Ross Sea was complex due to strong physiographic controls on ice-sheet drainage; (2) retreat was asynchronous across the Ross Sea and between troughs; (3) the eastern Ross Sea largely deglaciated prior to the western Ross Sea following the formation of a large grounding-line embayment over Whales Deep; and (4) our glacial geomorphic reconstruction converges with recent numerical models that call for significant and complex East Antarctic ice sheet and West Antarctic ice sheet contributions to the ice flow in the Ross Sea.

  19. 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.

  20. 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

  1. Greenland ice sheet initiation and Arctic sea ice coincide with Eocene and Oligocene CO2 changes

    Science.gov (United States)

    Tripati, Aradhna; Darby, Dennis

    2016-04-01

    Earth's modern ocean-climate system is largely defined by the presence of glacial ice on landmasses in both hemispheres. Northern Hemisphere ice was previously thought to have formed no earlier than the Miocene or Oligocene, about 20-30 million years after the widespread onset of Antarctic glaciation at the Eocene-Oligocene boundary. Controversially, the episodic presence of seasonal Arctic sea ice and glacial ice in the Northern Hemisphere beginning in the early Oligocene to Middle Eocene has been inferred from multiple observations. Here we use precise source determinations based on geochemical measurements of ice-rafted debris (IRD) from an ODP core in the Greenland Sea (75° N) to constrain glacial ice and sea ice-rafting in the Northern Hemisphere during the middle Eocene through early Oligocene. The chemical fingerprint of 2,334 detrital Fe oxide grains indicates most of these grains are from Greenland with >98% certainty. Thus the coarse IRD in the Greenland Sea originates from widespread areas of east Greenland as far south as the Denmark Strait area (~68° N), with additional IRD sources from the circum-Arctic Ocean. This is the first definitive evidence that mid-Eocene IRD in the Greenland Sea is from Greenland. Episodic glaciation of different source regions on Greenland is synchronous with times of ice-rafting in the western Arctic and ephemeral perennial Arctic ice cover. Intervals of bipolar glacial ice storage in the middle Eocene through early Oligocene coincide with evidence for periods of reduced CO2, associated with carbon cycle perturbations.

  2. Multiscale Models of Melting Arctic Sea Ice

    Science.gov (United States)

    2014-09-30

    1 Multiscale Models of Melting Arctic Sea Ice Kenneth M. Golden University of Utah, Department of Mathematics phone: (801) 581-6851...feedback has played a major role in the recent declines of the summer Arctic sea ice pack. However, understanding the evolution of melt ponds and sea...Models of Melting Arctic Sea Ice 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER

  3. SIPEX 2012: Extreme sea-ice and atmospheric conditions off East Antarctica

    Science.gov (United States)

    Heil, P.; Stammerjohn, S.; Reid, P.; Massom, R. A.; Hutchings, J. K.

    2016-09-01

    In 2012, Antarctic sea-ice coverage was marked by weak annual-mean climate anomalies that consisted of opposing anomalies early and late in the year (some setting new records) which were interspersed by near-average conditions for most of the austral autumn and winter. Here, we investigate the ocean-ice-atmosphere system off East Antarctica, prior to and during the Sea Ice Physics and Ecosystems eXperiment [SIPEX] 2012, by exploring relationships between atmospheric and oceanic forcing together with the sea-ice and snow characteristics. During August and September 2012, just prior to SIPEX 2012, atmospheric circulation over the Southern Ocean was near-average, setting up the ocean-ice-atmosphere system for near-average conditions. However, below-average surface pressure and temperature as well as strengthened circumpolar winds prevailed during June and July 2012. This led to a new record (19.48×106 km2) in maximum Antarctic sea-ice extent recorded in late September. In contrast to the weak circum-Antarctic conditions, the East Antarctic sector (including the SIPEX 2012 region) experienced positive sea-ice extent and concentration anomalies during most of 2012, coincident with negative atmospheric pressure and sea-surface temperature anomalies. Heavily deformed sea ice appeared to be associated with intensified wind stress due to increased cyclonicity as well as an increased influx of sea ice from the east. This increased westward ice flux is likely linked to the break-up of nearly 80% of the Mertz Glacier Tongue in 2010, which strongly modified the coastal configuration and hence the width of the westward coastal current. Combined with favourable atmospheric conditions the associated changed coastal configuration allowed more sea ice to remain within the coastal current at the expense of a reduced northward flow in the region around 141°-145°E. In addition a westward propagating positive anomaly of sea-ice extent from the western Ross Sea during austral winter

  4. 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.

  5. Albedo evolution of seasonal Arctic sea ice

    Science.gov (United States)

    Perovich, Donald K.; Polashenski, Christopher

    2012-04-01

    There is an ongoing shift in the Arctic sea ice cover from multiyear ice to seasonal ice. Here we examine the impact of this shift on sea ice albedo. Our analysis of observations from four years of field experiments indicates that seasonal ice undergoes an albedo evolution with seven phases; cold snow, melting snow, pond formation, pond drainage, pond evolution, open water, and freezeup. Once surface ice melt begins, seasonal ice albedos are consistently less than albedos for multiyear ice resulting in more solar heat absorbed in the ice and transmitted to the ocean. The shift from a multiyear to seasonal ice cover has significant implications for the heat and mass budget of the ice and for primary productivity in the upper ocean. There will be enhanced melting of the ice cover and an increase in the amount of sunlight available in the upper ocean.

  6. New IceTracker Tool Depicts Forward and Backward Arctic Sea Ice Trajectories

    Science.gov (United States)

    Pfirman, S. L.; Campbell, G.; Tremblay, B.; Newton, R.; Meier, W.

    2013-12-01

    The IceTracker allows researchers, educators and the public to depict the forward drift trajectories of sea ice, as well as back trajectories showing the path the ice took to the specified location. Users enter in the location and date of an ice parcel - or parcels -- of interest, then select a later or earlier date, depending on whether they want to see the forward or the backward trajectory. The database for the IceTracker contains ice motion vectors based upon a pattern recognition algorithm applied to images of sea ice derived from microwave satellite data. Ice motion vector plots are single day motion estimates. The available database starts November 1978 and runs to the present with ca. 1 month delay. IceTracker output includes both an image of the ice motion path as well as a data file that has quasi-daily date, latitude, longitude, estimated sea ice age, ice drift speed, mean air temperature, and water depth. One can overlay different days on the same plot in different colors for comparing different seasons. This presentation highlights research, education, and outreach applications of the tool. Research applications include estimating the origin and melt location of sediment and contaminants sampled on or in sea ice, assessing potential trajectories oil spilled in ice-infested waters, documenting seasonal and interannual variability in ice drift trajectories from specific locations, defining the typical origins of ice that tend to melt in an area of interest, such as a polynya, and assessing the deviation from drift of polar bear foraging. The IceTracker can also be used in the social sciences, for example recreating Nansen's historic 1893-1896 trans-Arctic drift with the Fram under modern conditions and considering the implications of alternative fates. Educational purposes include teaching students about ice dynamics and interannual variability by setting up team competitions to be the first to reach the North Pole or some other location. Applications

  7. Online sea ice data platform: www.seaiceportal.de

    Science.gov (United States)

    Nicolaus, Marcel; Asseng, Jölund; Bartsch, Annekathrin; Bräuer, Benny; Fritzsch, Bernadette; Grosfeld, Klaus; Hendricks, Stefan; Hiller, Wolfgang; Heygster, Georg; Krumpen, Thomas; Melsheimer, Christian; Ricker, Robert; Treffeisen, Renate; Weigelt, Marietta; Nicolaus, Anja; Lemke, Peter

    2016-04-01

    There is an increasing public interest in sea ice information from both Polar Regions, which requires up-to-date background information and data sets at different levels for various target groups. In order to serve this interest and need, seaiceportal.de (originally: meereisportal.de) was developed as a comprehensive German knowledge platform on sea ice and its snow cover in the Arctic and Antarctic. It was launched in April 2013. Since then, the content and selection of data sets increased and the data portal received increasing attention, also from the international science community. Meanwhile, we are providing near-real time and archive data of many key parameters of sea ice and its snow cover. The data sets result from measurements acquired by various platforms as well as numerical simulations. Satellite observations of sea ice concentration, freeboard, thickness and drift are available as gridded data sets. Sea ice and snow temperatures and thickness as well as atmospheric parameters are available from autonomous platforms (buoys). Additional ship observations, ice station measurements, and mooring time series are compiled as data collections over the last decade. In parallel, we are continuously extending our meta-data and uncertainty information for all data sets. In addition to the data portal, seaiceportal.de provides general comprehensive background information on sea ice and snow as well as expert statements on recent observations and developments. This content is mostly in German in order to complement the various existing international sites for the German speaking public. We will present the portal, its content and function, but we are also asking for direct user feedback.

  8. Sea Ice Mapping using Unmanned Aerial Systems

    Science.gov (United States)

    Solbø, S.; Storvold, R.

    2011-12-01

    Mapping of sea ice extent and sea ice features is an important task in climate research. Since the arctic coastal and oceanic areas have a high probability of cloud coverage, aerial platforms are superior to satellite measurements for high-resolution optical measurements. However, routine observations of sea ice conditions present a variety of problems using conventional piloted aircrafts. Specially, the availability of suitable aircrafts for lease does not cover the demand in major parts of the arctic. With the recent advances in unmanned aerial systems (UAS), there is a high possibility of establishing routine, cost effective aerial observations of sea ice conditions in the near future. Unmanned aerial systems can carry a wide variety of sensors useful for characterizing sea-ice features. For instance, the CryoWing UAS, a system initially designed for measurements of the cryosphere, can be equipped with digital cameras, surface thermometers and laser altimeters for measuring freeboard of ice flows. In this work we will present results from recent CryoWing sea ice flights on Svalbard, Norway. The emphasis will be on data processing for stitching together images acquired with the non-stabilized camera payload, to form high-resolution mosaics covering large spatial areas. These data are being employed to map ice conditions; including ice and lead features and melt ponds. These high-resolution mosaics are also well suited for sea-ice mechanics, classification studies and for validation of satellite sea-ice products.

  9. Impacts of sea ice on the marine iron cycle and phytoplankton productivity

    Directory of Open Access Journals (Sweden)

    S. Wang

    2014-02-01

    Full Text Available Iron is a key nutrient for phytoplankton growth in the surface ocean. At high latitudes, the iron cycle is closely related to sea ice. In recent decades, Arctic sea ice cover has been declining rapidly and Antarctic sea ice has exhibited large regional trends. A significant reduction of sea ice in both hemispheres is projected in future climate scenarios. To study impacts of sea ice on the iron cycle, iron sequestration in ice is incorporated to the Biogeochemical Elemental Cycling (BEC model. Sea ice acts as a reservoir of iron during winter and releases iron to the surface ocean in spring and summer. Simulated iron concentrations in sea ice generally agree with observations, in regions where iron concentrations are lower. The maximum iron concentrations simulated in the Arctic sea ice and the Antarctic sea ice are 192 nM and 134 nM, respectively. These values are much lower than observed, which is likely due to missing biological processes in sea ice. The largest iron source to sea ice is suspended sediments, contributing fluxes of iron of 2.2 × 108 mol Fe month−1 to the Arctic and 4.1 × 106 mol Fe month−1 to the Southern Ocean during summer. As a result of the iron flux from ice, iron concentrations increase significantly in the Arctic. Iron released from melting ice increases phytoplankton production in spring and summer and shifts phytoplankton community composition in the Southern Ocean. Simulation results for the period of 1998 to 2007 indicate that a reduction of sea ice in the Southern Ocean will have a negative influence on phytoplankton production. Iron transport by sea ice appears to be an important process bringing iron to the central Arctic. Impacts of iron fluxes from ice to ocean on marine ecosystems are negligible in the current Arctic Ocean, as iron is not typically the growth-limiting nutrient. However, it may become a more important factor in the future, particularly in the central Arctic, as iron concentrations will

  10. Predictability of the Arctic sea ice edge

    Science.gov (United States)

    Goessling, H. F.; Tietsche, S.; Day, J. J.; Hawkins, E.; Jung, T.

    2016-02-01

    Skillful sea ice forecasts from days to years ahead are becoming increasingly important for the operation and planning of human activities in the Arctic. Here we analyze the potential predictability of the Arctic sea ice edge in six climate models. We introduce the integrated ice-edge error (IIEE), a user-relevant verification metric defined as the area where the forecast and the "truth" disagree on the ice concentration being above or below 15%. The IIEE lends itself to decomposition into an absolute extent error, corresponding to the common sea ice extent error, and a misplacement error. We find that the often-neglected misplacement error makes up more than half of the climatological IIEE. In idealized forecast ensembles initialized on 1 July, the IIEE grows faster than the absolute extent error. This means that the Arctic sea ice edge is less predictable than sea ice extent, particularly in September, with implications for the potential skill of end-user relevant forecasts.

  11. 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)

  12. Southern Ocean CO2 sink: the contribution of the sea ice

    DEFF Research Database (Denmark)

    Delille, B.; Vancoppenolle, Martin; Geilfus, Nicolas-Xavier

    2014-01-01

    undersaturation while the underlying oceanic waters remains slightly oversaturated. The decrease from winter to summer of pCO2 in the brines is driven by dilution with melting ice, dissolution of carbonate crystals, and net primary production. As the ice warms, its permeability increases, allowing CO2 transfer......We report first direct measurements of the partial pressure of CO2 (pCO2) within Antarctic pack sea ice brines and related CO2 fluxes across the air-ice interface. From late winter to summer, brines encased in the ice change from a CO2 large oversaturation, relative to the atmosphere, to a marked...... at the air-sea ice interface. The sea ice changes from a transient source to a sink for atmospheric CO2. We upscale these observations to the whole Antarctic sea ice cover using the NEMO-LIM3 large-scale sea ice-ocean and provide first esti- mates of spring and summer CO2 uptake from the atmosphere...

  13. 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.

  14. The Last Arctic Sea Ice Refuge

    Science.gov (United States)

    Pfirman, S. L.; Tremblay, B.; Newton, R.; Fowler, C.

    2010-12-01

    Summer sea ice may persist along the northern flank of Canada and Greenland for decades longer than the rest of the Arctic, raising the possibility of a naturally formed refugium for ice-associated species. Observations and models indicate that some ice in this region forms locally, while some is transported to the area by winds and ocean currents. Depending on future changes in melt patterns and sea ice transport rates, both the central Arctic and Siberian shelf seas may be sources of ice to the region. An international system of monitoring and management of the sea ice refuge, along with the ice source regions, has the potential to maintain viable habitat for ice-associated species, including polar bears, for decades into the future. Issues to consider in developing a strategy include: + the likely duration and extent of summer sea ice in this region based on observations, models and paleoenvironmental information + the extent and characteristics of the “ice shed” contributing sea ice to the refuge, including its dynamics, physical and biological characteristics as well as potential for contamination from local or long-range sources + likely assemblages of ice-associated species and their habitats + potential stressors such as transportation, tourism, resource extraction, contamination + policy, governance, and development issues including management strategies that could maintain the viability of the refuge.

  15. Fracture Networks in Sea Ice

    Directory of Open Access Journals (Sweden)

    Jonas Nesland Vevatne

    2014-04-01

    Full Text Available Fracturing and refreezing of sea ice in the Kara sea are investigated using complex networkanalysis. By going to the dual network, where the fractures are nodes and their intersectionslinks, we gain access to topological features which are easy to measure and hence comparewith modeled networks. Resulting network reveal statistical properties of the fracturing process.The dual networks have a broad degree distribution, with a scale-free tail, high clusteringand efficiency. The degree-degree correlation profile shows disassortative behavior, indicatingpreferential growth. This implies that long, dominating fractures appear earlier than shorterfractures, and that the short fractures which are created later tend to connect to the longfractures.The knowledge of the fracturing process is used to construct growing fracture network (GFNmodel which provides insight into the generation of fracture networks. The GFN model isprimarily based on the observation that fractures in sea ice are likely to end when hitting existingfractures. Based on an investigation of which fractures survive over time, a simple model forrefreezing is also added to the GFN model, and the model is analyzed and compared to the realnetworks.

  16. Recent increase in Antarctic Peninsula ice core uranium concentrations

    Science.gov (United States)

    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.

  17. Modified PIC Method for Sea Ice Dynamics

    Institute of Scientific and Technical Information of China (English)

    WANG Rui-xue; JI Shun-ying; SHEN Hung-tao; YUE Qian-jin

    2005-01-01

    The sea ice cover displays various dynamical characteristics such as breakup, rafting, and ridging under external forces. To model the ice dynamic process accurately, the effective numerical modeling method should be established. In this paper, a modified particle-in-cell (PIC) method for sea ice dynamics is developed coupling the finite difference (FD) method and smoothed particle hydrodynamics (SPH). In this method, the ice cover is first discretized into a series of Lagrangian ice particles which have their own sizes, thicknesses, concentrations and velocities. The ice thickness and concentration at Eulerian grid positions are obtained by interpolation with the Gaussian function from their surrounding ice particles. The momentum of ice cover is solved with FD approach to obtain the Eulerian cell velocity, which is used to estimate the ice particle velocity with the Gaussian function also. The thickness and concentration of ice particles are adjusted with particle mass density and smooth length, which are adjusted with the redistribution of ice particles. With the above modified PIC method, numerical simulations for ice motion in an idealized rectangular basin and the ice dynamics in the Bohai Sea are carried out. These simulations show that this modified PIC method is applicable to sea ice dynamics simulation.

  18. 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

  19. SMOS sea ice product: Operational application and validation in the Barents Sea marginal ice zone

    DEFF Research Database (Denmark)

    Kaleschke, Lars; Tian-Kunze, Xiangshan; Maaß, Nina

    2016-01-01

    Brightness temperatures at 1.4. GHz (L-band) measured by the Soil Moisture and Ocean Salinity (SMOS) Mission have been used to derive the thickness of sea ice. The retrieval method is applicable only for relatively thin ice and not during the melting period. Hitherto, the availability of ground...... truth sea ice thickness measurements for validation of SMOS sea ice products was mainly limited to relatively thick ice. The situation has improved with an extensive field campaign in the Barents Sea during an anomalous ice edge retreat and subsequent freeze-up event in March 2014. A sea ice forecast...... system for ship route optimisation has been developed and was tested during this field campaign with the ice-strengthened research vessel RV Lance. The ship cruise was complemented with coordinated measurements from a helicopter and the research aircraft Polar 5. Sea ice thickness was measured using...

  20. Brief communication: ikaite (CaCO3*6H2O discovered in Arctic sea ice

    Directory of Open Access Journals (Sweden)

    M. A. Granskog

    2010-02-01

    Full Text Available We report for the first time on the discovery of calcium carbonate crystals as ikaite (CaCO3*6H2O in sea ice from the Arctic (Kongsfjorden, Svalbard. This finding demonstrates that the precipitation of calcium carbonate during the freezing of sea ice is not restricted to the Antarctic, where it was observed for the first time in 2008. This finding is an important step in the quest to quantify its impact on the sea ice driven carbon cycle and should in the future enable improvement parametrization sea ice carbon models.

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

    Directory of Open Access Journals (Sweden)

    Steven L Chown

    2012-01-01

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

  2. The consolidation of rafted sea ice

    Science.gov (United States)

    Bailey, E.; Feltham, D.; Sammonds, P.

    2009-04-01

    Rafting is an important process in the deformation of sea ice that occurs when two ice sheets collide. This process is particularly common in the North Caspian Sea, where ice floes override one another multiple times to produce thick sea ice features. To date, rafting has received little attention in the literature perhaps because in most regions pressure ridges produce the greatest loads on offshore structures. In the North Caspian Sea the shallow waters constrain the size to which pressure ridges can grow and the low salinity seems to favor rafting over ridging. Therefore it is likely that multiply-rafted sea ice may be the governing design feature for ice loads in the Caspian Sea. Here we present a one-dimensional, thermal-consolidation model for rafted sea ice. This is of interest because the degree of consolidation will affect the strength of a rafted structure, and therefore may be of value for modeling rafted ice loads. Results show that the thickness of the liquid layers reduces asymptotically with time, such that there always remains a thin liquid layer. We propose that when the liquid layer is equal to the surface roughness the adjacent layers can be considered consolidated. Using parameters specific to the North Caspian Sea, calculations show that it took 1hr, 14mins for the ice sheets to consolidate. To test the accuracy of the model concurrent experiments were carried out in the HSVA ice basin. During an experiment, equally sized portions of level ice were manually piled on top of one another to produce a rafted section. The rate of consolidation or bonding of the layers was then monitored by coring and using thermistors that were frozen into the level ice prior to rafting. Once consolidated, strength tests were carried out on the rafted ice and compared with those of level ice.

  3. 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-.

  4. 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.

  5. Multisensor Analyzed Sea Ice Extent - Northern Hemisphere (MASIE-NH)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Multisensor Analyzed Sea Ice Extent Northern Hemisphere (MASIE-NH) products provide measurements of daily sea ice extent and sea ice edge boundary for the...

  6. Fine-Scale Sea Ice Structure Characterized Using Underwater Acoustic Methods

    Directory of Open Access Journals (Sweden)

    Vanessa Lucieer

    2016-10-01

    Full Text Available Antarctic sea ice is known to provide unique ecosystem habitat at the ice–ocean interface. Mapping sea ice characteristics—such as thickness and roughness—at high resolution from beneath the ice is difficult due to access. A Geoswath Plus phase-measuring bathymetric sonar mounted on an autonomous underwater vehicle (AUV was employed in this study to collect data underneath the sea ice at Cape Evans in Antarctica in November 2014. This study demonstrates how acoustic data can be collected and processed to resolutions of 1 m for acoustic bathymetry and 5 cm for acoustic backscatter in this challenging environment. Different ice textures such as platelet ice, smooth ice, and sea ice morphologies, ranging in size from 1 to 50 m were characterized. The acoustic techniques developed in this work could provide a key to understanding the distribution of sea ice communities, as they are nondisruptive to the fragile ice environments and provide geolocated data over large spatial extents. These results improve our understanding of sea ice properties and the complex, highly variable ecosystem that exists at this boundary.

  7. 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.

  8. Sea salt aerosol from blowing snow on sea ice - modeling vs observation

    Science.gov (United States)

    Yang, Xin; Frey, Markus; Norris, Sarah; Brooks, Ian; Anderson, Philip; Jones, Anna; wolff, Eric; Legrand, Michel

    2016-04-01

    Blowing snow over sea ice, through a subsequent sublimation process of salt-containing blown snow particles, has been hypothesized as a significant sea salt aerosol (SSA) source in high latitudes. This mechanism has been strongly supported by a winter cruise in the Weddell Sea (during June-August 2013). The newly collected data, including both physical and chemical components, provide a unique way to test and validate the parameterisation used for describing the SSA production from blowing snow events. With updates to some key parameters such as snow salinity in a global Chemistry-transport model pTOMCAT, simulated SSA concentrations can be well compared with measured SSA data. In this presentation, I will report modeled SSA number density against collected data on board of Polarstern ship during the Weddell Sea cruise, as well as modeled SSA massive concentrations against those measured at both coastal sites such as Alert in the North and Dumont d'Urville (DDU) in the South and central Antarctic sites such as Concordia and Kohnen stations. Model experiments indicated that open ocean-sourced SSA could not explain the observed winter SSA peaks seen in most polar sites, while with sea ice-sourced SSA in the model, the winter peaks can be well improved indicating the importance of sea ice-sourced SSA as a significant contributor to the salts (Na+, Cl-) recorded in the ice core.

  9. Analogue modelling of the influence of ice shelf collapse on the flow of ice sheets grounded below sea-level

    Science.gov (United States)

    Corti, Giacomo; Zeoli, Antonio

    2016-04-01

    The sudden breakup of ice shelves is expected to result in significant acceleration of inland glaciers, a process related to the removal of the buttressing effect exerted by the ice shelf on the tributary glaciers. This effect has been tested in previous analogue models, which however applied to ice sheets grounded above sea level (e.g., East Antarctic Ice Sheet; Antarctic Peninsula and the Larsen Ice Shelf). In this work we expand these previous results by performing small-scale laboratory models that analyse the influence of ice shelf collapse on the flow of ice streams draining an ice sheet grounded below sea level (e.g., the West Antarctic Ice Sheet). The analogue models, with dimensions (width, length, thickness) of 120x70x1.5cm were performed at the Tectonic Modelling Laboratory of CNR-IGG of Florence, Italy, by using Polydimethilsyloxane (PDMS) as analogue for the flowing ice. This transparent, Newtonian silicone has been shown to well approximate the rheology of natural ice. The silicone was allowed to flow into a water reservoir simulating natural conditions in which ice streams flow into the sea, terminating in extensive ice shelves which act as a buttress for their glaciers and slow their flow. The geometric scaling ratio was 10(-5), such that 1cm in the models simulated 1km in nature; velocity of PDMS (a few mm per hour) simulated natural velocities of 100-1000 m/year. Instability of glacier flow was induced by manually removing a basal silicone platform (floating on water) exerting backstresses to the flowing analogue glacier: the simple set-up adopted in the experiments isolates the effect of the removal of the buttressing effect that the floating platform exerts on the flowing glaciers, thus offering insights into the influence of this parameter on the flow perturbations resulting from a collapse event. The experimental results showed a significant increase in glacier velocity close to its outlet following ice shelf breakup, a process similar to what

  10. 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.

  11. 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

  12. On the measure of sea ice area from sea ice concentration data sets

    Science.gov (United States)

    Boccolari, Mauro; Parmiggiani, Flavio

    2015-10-01

    The measure of sea ice surface variability provides a fundamental information on the climatology of the Arctic region. Sea ice extension is conventionally measured by two parameters, i.e. Sea Ice Extent (SIE) and Sea Ice Area (SIA), both parameters being derived from Sea Ice Concentration (SIC) data sets. In this work a new parameter (CSIA) is introduced, which takes into account only the compact sea-ice, which is defined as the sea-ice having concentration at least equal the 70%. Aim of this study is to compare the performances of the two parameters, SIA and CSIA, in analyzing the trends of three monthly time-series of the whole Arctic region. The SIC data set used in this study was produced by the Institute of Environmental Physics of the University of Bremen and covers the period January 2003 - December 2014, i.e. the period in which the data set is built using the new AMSR passive microwave sensor.

  13. History of sea ice in the Arctic

    DEFF Research Database (Denmark)

    Polyak, Leonid; Alley, Richard B.; Andrews, John T.

    2010-01-01

    Arctic sea-ice extent and volume are declining rapidly. Several studies project that the Arctic Ocean may become seasonally ice-free by the year 2040 or even earlier. Putting this into perspective requires information on the history of Arctic sea-ice conditions through the geologic past....... This information can be provided by proxy records fromthe Arctic Ocean floor and from the surrounding coasts. Although existing records are far from complete, they indicate that sea ice became a feature of the Arctic by 47 Ma, following a pronounced decline in atmospheric pCO2 after the Paleocene–Eocene Thermal...... Optimum, and consistently covered at least part of the Arctic Ocean for no less than the last 13–14 million years. Ice was apparently most widespread during the last 2–3 million years, in accordance with Earth’s overall cooler climate. Nevertheless, episodes of considerably reduced sea ice or even...

  14. Massive phytoplankton blooms under Arctic sea ice.

    Science.gov (United States)

    Arrigo, Kevin R; Perovich, Donald K; Pickart, Robert S; Brown, Zachary W; van Dijken, Gert L; Lowry, Kate E; Mills, Matthew M; Palmer, Molly A; Balch, William M; Bahr, Frank; Bates, Nicholas R; Benitez-Nelson, Claudia; Bowler, Bruce; Brownlee, Emily; Ehn, Jens K; Frey, Karen E; Garley, Rebecca; Laney, Samuel R; Lubelczyk, Laura; Mathis, Jeremy; Matsuoka, Atsushi; Mitchell, B Greg; Moore, G W K; Ortega-Retuerta, Eva; Pal, Sharmila; Polashenski, Chris M; Reynolds, Rick A; Schieber, Brian; Sosik, Heidi M; Stephens, Michael; Swift, James H

    2012-06-15

    Phytoplankton blooms over Arctic Ocean continental shelves are thought to be restricted to waters free of sea ice. Here, we document a massive phytoplankton bloom beneath fully consolidated pack ice far from the ice edge in the Chukchi Sea, where light transmission has increased in recent decades because of thinning ice cover and proliferation of melt ponds. The bloom was characterized by high diatom biomass and rates of growth and primary production. Evidence suggests that under-ice phytoplankton blooms may be more widespread over nutrient-rich Arctic continental shelves and that satellite-based estimates of annual primary production in these waters may be underestimated by up to 10-fold.

  15. 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.

  16. The sea-level fingerprints of ice-sheet collapse during interglacial periods

    Science.gov (United States)

    Hay, Carling; Mitrovica, Jerry X.; Gomez, Natalya; Creveling, Jessica R.; Austermann, Jacqueline; E. Kopp, Robert

    2014-03-01

    Studies of sea level during previous interglacials provide insight into the stability of polar ice sheets in the face of global climate change. Commonly, these studies correct ancient sea-level highstands for the contaminating effect of isostatic adjustment associated with past ice age cycles, and interpret the residuals as being equivalent to the peak eustatic sea level associated with excess melting, relative to present day, of ancient polar ice sheets. However, the collapse of polar ice sheets produces a distinct geometry, or fingerprint, of sea-level change, which must be accounted for to accurately infer peak eustatic sea level from site-specific residual highstands. To explore this issue, we compute fingerprints associated with the collapse of the Greenland Ice Sheet, West Antarctic Ice Sheet, and marine sectors of the East Antarctic Ice Sheet in order to isolate regions that would have been subject to greater-than-eustatic sea-level change for all three cases. These fingerprints are more robust than those associated with modern melting events, when applied to infer eustatic sea level, because: (1) a significant collapse of polar ice sheets reduces the sensitivity of the computed fingerprints to uncertainties in the geometry of the melt regions; and (2) the sea-level signal associated with the collapse will dominate the signal from steric effects. We evaluate these fingerprints at a suite of sites where sea-level records from interglacial marine isotopes stages (MIS) 5e and 11 have been obtained. Using these results, we demonstrate that previously discrepant estimates of peak eustatic sea level during MIS5e based on sea-level markers in Australia and the Seychelles are brought into closer accord.

  17. A toy model of sea ice growth

    Science.gov (United States)

    Thorndike, Alan S.

    1992-01-01

    My purpose here is to present a simplified treatment of the growth of sea ice. By ignoring many details, it is possible to obtain several results that help to clarify the ways in which the sea ice cover will respond to climate change. Three models are discussed. The first deals with the growth of sea ice during the cold season. The second describes the cycle of growth and melting for perennial ice. The third model extends the second to account for the possibility that the ice melts away entirely in the summer. In each case, the objective is to understand what physical processes are most important, what ice properties determine the ice behavior, and to which climate variables the system is most sensitive.

  18. Record Arctic Sea Ice Loss in 2007

    Science.gov (United States)

    2007-01-01

    This image of the Arctic was produced from sea ice observations collected by the Advanced Microwave Scanning Radiometer (AMSR-E) Instrument on NASA's Aqua satellite on September 16, overlaid on the NASA Blue Marble. The image captures ice conditions at the end of the melt season. Sea ice (white, image center) stretches across the Arctic Ocean from Greenland to Russia, but large areas of open water were apparent as well. In addition to record melt, the summer of 2007 brought an ice-free opening though the Northwest Passage that lasted several weeks. The Northeast Passage did not open during the summer of 2007, however, as a substantial tongue of ice remained in place north of the Russian coast. According to the National Snow and Ice Data Center (NSIDC), on September 16, 2007, sea ice extent dropped to 4.13 million square kilometers (1.59 million square miles)--38 percent below average and 24 percent below the 2005 record.

  19. 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.

  20. 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.

  1. 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

  2. Arctic tides from GPS on sea ice

    DEFF Research Database (Denmark)

    Kildegaard Rose, Stine; Skourup, Henriette; Forsberg, René

    The presence of sea-ice in the Arctic Ocean plays a significant role in the Arctic climate. Sea ice dampens the ocean tide amplitude with the result that global tidal models which use only astronomical data perform less accurately in the polar regions. This study presents a kinematic processing...... of Global Positioning System (GPS) buoys placed on sea-ice at five different sites north of Greenland for the study of sea level height and tidal analysis to improve tidal models in the Central Arctic. The GPS measurements are compared with the Arctic tidal model AOTIM-5, which assimilates tide...

  3. Sea Ice Biogeochemistry: A Guide for Modellers

    Science.gov (United States)

    Tedesco, Letizia; Vichi, Marcello

    2014-01-01

    Sea ice is a fundamental component of the climate system and plays a key role in polar trophic food webs. Nonetheless sea ice biogeochemical dynamics at large temporal and spatial scales are still rarely described. Numerical models may potentially contribute integrating among sparse observations, but available models of sea ice biogeochemistry are still scarce, whether their relevance for properly describing the current and future state of the polar oceans has been recently addressed. A general methodology to develop a sea ice biogeochemical model is presented, deriving it from an existing validated model application by extension of generic pelagic biogeochemistry model parameterizations. The described methodology is flexible and considers different levels of ecosystem complexity and vertical representation, while adopting a strategy of coupling that ensures mass conservation. We show how to apply this methodology step by step by building an intermediate complexity model from a published realistic application and applying it to analyze theoretically a typical season of first-year sea ice in the Arctic, the one currently needing the most urgent understanding. The aim is to (1) introduce sea ice biogeochemistry and address its relevance to ocean modelers of polar regions, supporting them in adding a new sea ice component to their modelling framework for a more adequate representation of the sea ice-covered ocean ecosystem as a whole, and (2) extend our knowledge on the relevant controlling factors of sea ice algal production, showing that beyond the light and nutrient availability, the duration of the sea ice season may play a key-role shaping the algal production during the on going and upcoming projected changes. PMID:24586604

  4. Sea ice biogeochemistry: a guide for modellers.

    Science.gov (United States)

    Tedesco, Letizia; Vichi, Marcello

    2014-01-01

    Sea ice is a fundamental component of the climate system and plays a key role in polar trophic food webs. Nonetheless sea ice biogeochemical dynamics at large temporal and spatial scales are still rarely described. Numerical models may potentially contribute integrating among sparse observations, but available models of sea ice biogeochemistry are still scarce, whether their relevance for properly describing the current and future state of the polar oceans has been recently addressed. A general methodology to develop a sea ice biogeochemical model is presented, deriving it from an existing validated model application by extension of generic pelagic biogeochemistry model parameterizations. The described methodology is flexible and considers different levels of ecosystem complexity and vertical representation, while adopting a strategy of coupling that ensures mass conservation. We show how to apply this methodology step by step by building an intermediate complexity model from a published realistic application and applying it to analyze theoretically a typical season of first-year sea ice in the Arctic, the one currently needing the most urgent understanding. The aim is to (1) introduce sea ice biogeochemistry and address its relevance to ocean modelers of polar regions, supporting them in adding a new sea ice component to their modelling framework for a more adequate representation of the sea ice-covered ocean ecosystem as a whole, and (2) extend our knowledge on the relevant controlling factors of sea ice algal production, showing that beyond the light and nutrient availability, the duration of the sea ice season may play a key-role shaping the algal production during the on going and upcoming projected changes.

  5. Sea ice biogeochemistry: a guide for modellers.

    Directory of Open Access Journals (Sweden)

    Letizia Tedesco

    Full Text Available Sea ice is a fundamental component of the climate system and plays a key role in polar trophic food webs. Nonetheless sea ice biogeochemical dynamics at large temporal and spatial scales are still rarely described. Numerical models may potentially contribute integrating among sparse observations, but available models of sea ice biogeochemistry are still scarce, whether their relevance for properly describing the current and future state of the polar oceans has been recently addressed. A general methodology to develop a sea ice biogeochemical model is presented, deriving it from an existing validated model application by extension of generic pelagic biogeochemistry model parameterizations. The described methodology is flexible and considers different levels of ecosystem complexity and vertical representation, while adopting a strategy of coupling that ensures mass conservation. We show how to apply this methodology step by step by building an intermediate complexity model from a published realistic application and applying it to analyze theoretically a typical season of first-year sea ice in the Arctic, the one currently needing the most urgent understanding. The aim is to (1 introduce sea ice biogeochemistry and address its relevance to ocean modelers of polar regions, supporting them in adding a new sea ice component to their modelling framework for a more adequate representation of the sea ice-covered ocean ecosystem as a whole, and (2 extend our knowledge on the relevant controlling factors of sea ice algal production, showing that beyond the light and nutrient availability, the duration of the sea ice season may play a key-role shaping the algal production during the on going and upcoming projected changes.

  6. Assessment of the sea-ice carbon pump: Insights from a three-dimensional ocean-sea-ice-biogeochemical model (MPIOM/HAMOCC

    Directory of Open Access Journals (Sweden)

    R. Grimm

    2016-11-01

    Full Text Available Abstract It has been suggested that geochemical processes related to sea-ice growth and melt might be important for the polar carbon cycle via the so called sea-ice carbon pump (SICP. The SICP affects the air-sea CO2 exchange by influencing the composition of dissolved inorganic carbon (DIC and total alkalinity (TA in the surface ocean. Here we quantify the strength of the SICP-induced air-sea CO2 flux using the global three-dimensional ocean-sea-ice-biogeochemical model MPIOM/HAMOCC. Simulations prescribing the range of observed DIC and TA concentrations in the sea ice were performed under two idealized climate scenarios for the present-day and the future oceanic and sea-ice state, both forced with a fixed atmospheric CO2 concentration. Model results indicate that the SICP-induced air-sea CO2 uptake increases with higher ratios of TA:DIC prescribed in the sea ice relative to the basic oceanic TA:DIC ratios. Independent of the modeled scenario, the simulated strength of the SICP is larger in the Antarctic than in the Arctic, because of more efficient export of brine-associated DIC from the Antarctic mixed layer. On an annual basis, we generally find an enhanced SICP-induced oceanic CO2 uptake in regions with net sea-ice melt, and enhanced SICP-induced oceanic CO2 out-gassing in regions with net sea-ice growth. These general regional patterns are modified further by the blockage of air-sea gas exchange through sea-ice coverage. Integrated over the sea-ice zones of both hemispheres, the SICP-induced oceanic CO2 uptake ranges from 2 to 14 Tg C yr−1, which is up to 7% of the simulated net CO2 uptake in polar regions, but far less than 1% of the current global oceanic CO2 uptake. Hence, while we find that the SICP plays a minor role in the modern global carbon cycle, it is of importance for the regional carbon cycle at high latitudes.

  7. Correlated Energy Exchange in Drifting Sea Ice

    Directory of Open Access Journals (Sweden)

    A. Chmel

    2011-01-01

    Full Text Available The ice floe speed variations were monitored at the research camp North Pole 35 established on the Arctic ice pack in 2008. A three-month time series of measured speed values was used for determining changes in the kinetic energy of the drifting ice floe. The constructed energy distributions were analyzed by methods of nonextensive statistical mechanics based on the Tsallis statistics for open nonequilibrium systems, such as tectonic formations and drifting sea ice. The nonextensivity means the nonadditivity of externally induced energy changes in multicomponent systems due to dynamic interrelation of components having no structural links. The Tsallis formalism gives one an opportunity to assess the correlation between ice floe motions through a specific parameter, the so-called parameter of nonextensivity. This formalistic assessment of the actual state of drifting pack allows one to forecast some important trends in sea ice behavior, because the level of correlated dynamics determines conditions for extended mechanical perturbations in ice pack. In this work, we revealed temporal fluctuations of the parameter of nonextensivity and observed its maximum value before a large-scale sea ice fragmentation (faulting of consolidated sea ice. The correlation was not detected in fragmented sea ice where long-range interactions are weakened.

  8. Arctic sea-ice ridges—Safe heavens for sea-ice fauna during periods of extreme ice melt?

    Science.gov (United States)

    Gradinger, Rolf; Bluhm, Bodil; Iken, Katrin

    2010-01-01

    The abundances and distribution of metazoan within-ice meiofauna (13 stations) and under-ice fauna (12 stations) were investigated in level sea ice and sea-ice ridges in the Chukchi/Beaufort Seas and Canada Basin in June/July 2005 using a combination of ice coring and SCUBA diving. Ice meiofauna abundance was estimated based on live counts in the bottom 30 cm of level sea ice based on triplicate ice core sampling at each location, and in individual ice chunks from ridges at four locations. Under-ice amphipods were counted in situ in replicate ( N=24-65 per station) 0.25 m 2 quadrats using SCUBA to a maximum water depth of 12 m. In level sea ice, the most abundant ice meiofauna groups were Turbellaria (46%), Nematoda (35%), and Harpacticoida (19%), with overall low abundances per station that ranged from 0.0 to 10.9 ind l -1 (median 0.8 ind l -1). In level ice, low ice algal pigment concentrations (3 m where abundances were up to 42-fold higher compared with level ice. We propose that the summer ice melt impacted meiofauna and under-ice amphipod abundance and distribution through (a) flushing, and (b) enhanced salinity stress at thinner level sea ice (less than 3 m thickness). We further suggest that pressure ridges, which extend into deeper, high-salinity water, become accumulation regions for ice meiofauna and under-ice amphipods in summer. Pressure ridges thus might be crucial for faunal survival during periods of enhanced summer ice melt. Previous estimates of Arctic sea ice meiofauna and under-ice amphipods on regional and pan-Arctic scales likely underestimate abundances at least in summer because they typically do not include pressure ridges.

  9. Antarctic contribution to sea level rise observed by GRACE with improved GIA correction

    Science.gov (United States)

    Ivins, Erik R.; James, Thomas S.; Wahr, John; Schrama, Ernst J. O.; Landerer, Felix W.; Simon, Karen M.

    2013-06-01

    Antarctic volume changes during the past 21 thousand years are smaller than previously thought, and here we construct an ice sheet history that drives a forward model prediction of the glacial isostatic adjustment (GIA) gravity signal. The new model, in turn, should give predictions that are constrained with recent uplift data. The impact of the GIA signal on a Gravity Recovery and Climate Experiment (GRACE) Antarctic mass balance estimate depends on the specific GRACE analysis method used. For the method described in this paper, the GIA contribution to the apparent surface mass change is re-evaluated to be +55±13 Gt/yr by considering a revised ice history model and a parameter search for vertical motion predictions that best fit the GPS observations at 18 high-quality stations. Although the GIA model spans a range of possible Earth rheological structure values, the data are not yet sufficient for solving for a preferred value of upper and lower mantle viscosity nor for a preferred lithospheric thickness. GRACE monthly solutions from the Center for Space Research Release 04 (CSR-RL04) release time series from January 2003 to the beginning of January 2012, uncorrected for GIA, yield an ice mass rate of +2.9± 29 Gt/yr. The new GIA correction increases the solved-for ice mass imbalance of Antarctica to -57±34 Gt/yr. The revised GIA correction is smaller than past GRACE estimates by about 50 to 90 Gt/yr. The new upper bound to the sea level rise from the Antarctic ice sheet, averaged over the time span 2003.0-2012.0, is about 0.16±0.09 mm/yr.

  10. Introduction: SIPEX-2: A study of sea-ice physical, biogeochemical and ecosystem processes off East Antarctica during spring 2012

    Science.gov (United States)

    Meiners, Klaus M.; Golden, Ken M.; Heil, Petra; Lieser, Jan L.; Massom, Rob; Meyer, Bettina; Williams, Guy D.

    2016-09-01

    This editorial introduces a suite of articles resulting from the second Sea Ice Physics and Ecosystems eXperiment (SIPEX-2) voyage by presenting some background information on the study area and Antarctic sea-ice conditions, and summarising the key findings from the project. Using the Australian icebreaker RV Aurora Australis, SIPEX-2 was conducted in the area between 115-125°E and 62-66°S off East Antarctica during September to November 2012. This region had been sampled during two previous experiments, i.e. ARISE in 2003 (Massom et al., 2006a) and SIPEX in 2007 (Worby et al., 2011a). The 2012 voyage combined traditional and newly developed sampling methods with satellite and other data to measure sea-ice physical properties and processes on large scales, which provided context for biogeochemical and ecological case studies. The specific goals of the SIPEX-2 project were to: (i) measure the spatial variability in sea-ice and snow-cover properties over small- to regional-length scales; (ii) improve understanding of sea-ice kinematic processes; and (iii) advance knowledge of the links between sea-ice physical characteristics, sea-ice biogeochemical cycling and ice-associated food-web dynamics. Our field-based activities were designed to inform modelling approaches and to improve our capability to assess impacts of predicted changes in Antarctic sea ice on Southern Ocean biogeochemical cycles and ecosystem function.

  11. Comparing sea ice, hydrography and circulation between NEMO3.6 LIM3 and LIM2

    Science.gov (United States)

    Uotila, Petteri; Iovino, Doroteaciro; Vancoppenolle, Martin; Lensu, Mikko; Rousset, Clement

    2017-03-01

    A set of hindcast simulations with the new version 3.6 of the Nucleus for European Modelling of the Ocean (NEMO) ocean-ice model in the ORCA1 configuration and forced by the DRAKKAR Forcing Set version 5.2 (DFS5.2) atmospheric data was performed from 1958 to 2012. Simulations differed in their sea-ice component: the old standard version Louvain-la-Neuve Sea Ice Model (LIM2) and its successor LIM3. Main differences between these sea-ice models are the parameterisations of sub-grid-scale sea-ice thickness distribution, ice deformation, thermodynamic processes, and sea-ice salinity. Our main objective was to analyse the response of the ocean-ice system sensitivity to the change in sea-ice physics. Additional sensitivity simulations were carried out for the attribution of observed differences between the two main simulations.In the Arctic, NEMO-LIM3 compares better with observations by realistically reproducing the sea-ice extent decline during the last few decades due to its multi-category sea-ice thickness. In the Antarctic, NEMO-LIM3 more realistically simulates the seasonal evolution of sea-ice extent than NEMO-LIM2. In terms of oceanic properties, improvements are not as evident, although NEMO-LIM3 reproduces a more realistic hydrography in the Labrador Sea and in the Arctic Ocean, including a reduced cold temperature bias of the Arctic Intermediate Water at 250 m. In the extra-polar regions, the oceanographic conditions of the two NEMO-LIM versions remain relatively similar, although they slowly drift apart over decades. This drift is probably due to a stronger deep water formation around Antarctica in LIM3.

  12. Isolation of novel psychrophilic bacteria from Arctic sea ice

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The phylogenetic diversity of culturable psychrophilic bacteria associated with sea ice from the high latitude regions of Canadian Basin and Chukchi Sea, Arctic, was investigated. A total of 34 psychropilic strains were isolated using three methods of (Ⅰ) dilution plating (at 4 ℃), (Ⅱ) bath culturing (at -1 ℃) and dilution plating, and (Ⅲ) cold shock (-20 ℃ for 24 h), bath culturing and dilution plating under aerobic conditions. Sea-ice samples were exposed to -20 ℃ for 24 h that might reduce the number of common microorganisms and encourage outgrowth of psychrophilic strains. This process might be able to be introduced to isolation psychrophilic bacteria from other environmental samples in future study. 16S rDNA nearly full-length sequence analysis revealed that psychrophilic strains felled in two phylogenetic divisions, γ-proteobacteria (in the genera Colwellia、Marinobacter、Shewanella、Glaciecola、Marinomonas and Pseudoalteromonas) and Cytophaga-Flexibacter-Bacteroides (Flavobacterium and Psychroflexus). Fifteen of bacterial isolates quite likely represented novel species (16S rDNA sequence similarity below 98%). One of strains (BSi20002) from Canadian Basin showed 100% sequence similarity to that of Marinobacter sp. ANT8277 isolated from the Antarctic Weddell sea ice, suggesting bacteria may have a bipolar distribution at the species level.

  13. History of sea ice in the Arctic

    DEFF Research Database (Denmark)

    Polyak, Leonid; Alley, Richard B.; Andrews, John T.

    2010-01-01

    -scale) and lower-magnitude variability. The current reduction in Arctic ice cover started in the late 19th century, consistent with the rapidly warming climate, and became very pronounced over the last three decades. This ice loss appears to be unmatched over at least the last few thousand years and unexplainable......Arctic sea-ice extent and volume are declining rapidly. Several studies project that the Arctic Ocean may become seasonally ice-free by the year 2040 or even earlier. Putting this into perspective requires information on the history of Arctic sea-ice conditions through the geologic past....... This information can be provided by proxy records fromthe Arctic Ocean floor and from the surrounding coasts. Although existing records are far from complete, they indicate that sea ice became a feature of the Arctic by 47 Ma, following a pronounced decline in atmospheric pCO2 after the Paleocene–Eocene Thermal...

  14. Linking scales in sea ice mechanics

    Science.gov (United States)

    Weiss, Jérôme; Dansereau, Véronique

    2017-02-01

    Mechanics plays a key role in the evolution of the sea ice cover through its control on drift, on momentum and thermal energy exchanges between the polar oceans and the atmosphere along cracks and faults, and on ice thickness distribution through opening and ridging processes. At the local scale, a significant variability of the mechanical strength is associated with the microstructural heterogeneity of saline ice, however characterized by a small correlation length, below the ice thickness scale. Conversely, the sea ice mechanical fields (velocity, strain and stress) are characterized by long-ranged (more than 1000 km) and long-lasting (approx. few months) correlations. The associated space and time scaling laws are the signature of the brittle character of sea ice mechanics, with deformation resulting from a multi-scale accumulation of episodic fracturing and faulting events. To translate the short-range-correlated disorder on strength into long-range-correlated mechanical fields, several key ingredients are identified: long-ranged elastic interactions, slow driving conditions, a slow viscous-like relaxation of elastic stresses and a restoring/healing mechanism. These ingredients constrained the development of a new continuum mechanics modelling framework for the sea ice cover, called Maxwell-elasto-brittle. Idealized simulations without advection demonstrate that this rheological framework reproduces the main characteristics of sea ice mechanics, including anisotropy, spatial localization and intermittency, as well as the associated scaling laws. This article is part of the themed issue 'Microdynamics of ice'.

  15. 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.

  16. Constraining projections of summer Arctic sea ice

    Directory of Open Access Journals (Sweden)

    F. Massonnet

    2012-11-01

    Full Text Available We examine the recent (1979–2010 and future (2011–2100 characteristics of the summer Arctic sea ice cover as simulated by 29 Earth system and general circulation models from the Coupled Model Intercomparison Project, phase 5 (CMIP5. As was the case with CMIP3, a large intermodel spread persists in the simulated summer sea ice losses over the 21st century for a given forcing scenario. The 1979–2010 sea ice extent, thickness distribution and volume characteristics of each CMIP5 model are discussed as potential constraints on the September sea ice extent (SSIE projections. Our results suggest first that the future changes in SSIE with respect to the 1979–2010 model SSIE are related in a complicated manner to the initial 1979–2010 sea ice model characteristics, due to the large diversity of the CMIP5 population: at a given time, some models are in an ice-free state while others are still on the track of ice loss. However, in phase plane plots (that do not consider the time as an independent variable, we show that the transition towards ice-free conditions is actually occurring in a very similar manner for all models. We also find that the year at which SSIE drops below a certain threshold is likely to be constrained by the present-day sea ice properties. In a second step, using several adequate 1979–2010 sea ice metrics, we effectively reduce the uncertainty as to when the Arctic could become nearly ice-free in summertime, the interval [2041, 2060] being our best estimate for a high climate forcing scenario.

  17. Enhancing calculation of thin sea ice growth

    Science.gov (United States)

    Appel, Igor

    2016-12-01

    The goal of the present study is to develop, generate, and integrate into operational practice a new model of ice growth. The development of this Sea Ice Growth Model for Arctic (SIGMA), a description of the theoretical foundation, the model advantages and analysis of its results are considered in the paper. The enhanced model includes two principal modifications. Surface temperature of snow on ice is defined as internal model parameter maintaining rigorous consistency between processes of atmosphere-ice thermodynamic interaction and ice growth. The snow depth on ice is naturally defined as a function of a local snowfall rate and linearly depends on time rather than ice thickness. The model was initially outlined in the Visible Infrared Radiometer Suite (VIIRS) Sea Ice Characterization Algorithm Theoretical Basis Document (Appel et al., 2005) that included two different approaches to retrieve sea ice age: reflectance analysis for daytime and derivation of ice thickness using energy balance for nighttime. Only the latter method is considered in this paper. The improved account for the influence of surface temperature and snow depth increases the reliability of ice thickness calculations and is used to develop an analytical Snow Depth/Ice Thickness Look up table suitable to the VIIRS observations as well as to other instruments. The applicability of SIGMA to retrieve ice thickness from the VIIRS satellite observations and the comparison of its results with the One-dimensional Thermodynamic Ice Model (OTIM) are also considered. The comparison of the two models demonstrating the difference between their assessments of heat fluxes and radical distinction between the influences of snow depth uncertainty on errors of ice thickness calculations is of great significance to further improve the retrieval of ice thickness from satellite observations.

  18. 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.

  19. Stratospheric Impacts on Arctic Sea Ice

    Science.gov (United States)

    Reichler, Thomas

    2016-04-01

    Long-term circulation change in the stratosphere can have substantial effects on the oceans and their circulation. In this study we investigate whether and how sea ice at the ocean surface responds to intraseasonal stratospheric variability. Our main question is whether the surface impact of stratospheric sudden warmings (SSWs) is strong and long enough to affect sea ice. A related question is whether the increased frequency of SSWs during the 2000s contributed to the rapid decrease in Arctic sea ice during this time. To this end we analyze observations of sea ice, NCEP/NCAR reanalysis, and a long control integration with a stratospherically-enhanced version of the GFDL CM2.1 climate model. From both observations and the model we find that stratospheric extreme events have a demonstrable impact on the distribution of Arctic sea ice. The areas most affected are near the edge of the climatological ice line over the North Atlantic, North Pacific, and the Arctic Ocean. The absolute changes in sea ice coverage amount to +/-10 %. Areas and magnitudes of increase and decrease are about the same. It is thus unlikely that the increased SSW frequency during the 2000s contributed to the decline of sea ice during that period. The sea ice changes are consistent with the impacts of a negative NAO at the surface and can be understood in terms of (1) dynamical change due to altered surface wind stress and (2) thermodynamical change due to altered temperature advection. Both dynamical and thermodynamical change positively reinforce each other in producing sea change. A simple advection model is used to demonstrate that most of the sea ice change can be explained from the sea ice drift due to the anomalous surface wind stress. Changes in the production or melt of sea ice by thermodynamical effects are less important. Overall, this study adds to an increasing body of evidence that the stratosphere not only impacts weather and climate of the atmosphere but also the surface and

  20. Transport of Antarctic krill ( Euphausia superba) across the Scotia Sea. Part II: Krill growth and survival

    Science.gov (United States)

    Fach, Bettina A.; Hofmann, Eileen E.; Murphy, Eugene J.

    2006-06-01

    A time-dependent, size-structured, physiologically based krill growth model was used in conjunction with a circulation model to test the hypothesis that Antarctic krill ( Euphausia superba) populations at South Georgia are sustained by import of individuals from upstream regions. Surface phytoplankton concentrations along the simulated drifter trajectories were extracted from historical Coastal Zone Color Scanner (CZCS) measurements and sea ice biota concentrations were calculated from sea ice concentration and extent extracted along drifter trajectories from Special Sensor Microwave/Imager measurements. As additional food sources, a time series of heterotrophic food was constructed from historical data, and time series of detritus concentrations were calculated using phytoplankton concentrations extracted from CZCS measurements together with measured particulate organic carbon to chlorophyll a ratios. These food resources along specified drifter trajectories were then input to the krill growth model to determine the size and viability of krill during transport from the source region to South Georgia. The krill growth model simulations showed that no single food source can support continuous growth of krill during the 58-306 days needed for transport to South Georgia. However, under the current assumptions results indicate that combinations of food sources during the transport time enhanced krill survival, with heterotrophic food and detritus being particularly important during periods of low phytoplankton concentrations. The growth model simulations also showed that larval and juvenile krill originating along the western Antarctic Peninsula can grow to 1+ (14-36 mm) and 2+ (26-45 mm) age and size classes observed at South Georgia during the time needed for transport to this region. Krill originating in the Weddell Sea need 20 months for transport, which allows retention in a potentially high food environment, provided by sea ice, for almost 1 year. Krill then

  1. 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.

  2. Global Changes in the Sea Ice Cover and Associated Surface Temperature Changes

    Science.gov (United States)

    Comiso, Josefino C.

    2016-06-01

    The trends in the sea ice cover in the two hemispheres have been observed to be asymmetric with the rate of change in the Arctic being negative at -3.8 % per decade while that of the Antarctic is positive at 1.7 % per decade. These observations are confirmed in this study through analyses of a more robust data set that has been enhanced for better consistency and updated for improved statistics. With reports of anthropogenic global warming such phenomenon appears physically counter intuitive but trend studies of surface temperature over the same time period show the occurrence of a similar asymmetry. Satellite surface temperature data show that while global warming is strong and dominant in the Arctic, it is relatively minor in the Antarctic with the trends in sea ice covered areas and surrounding ice free regions observed to be even negative. A strong correlation of ice extent with surface temperature is observed, especially during the growth season, and the observed trends in the sea ice cover are coherent with the trends in surface temperature. The trend of global averages of the ice cover is negative but modest and is consistent and compatible with the positive but modest trend in global surface temperature. A continuation of the trend would mean the disappearance of summer ice by the end of the century but modelling projections indicate that the summer ice could be salvaged if anthropogenic greenhouse gases in the atmosphere are kept constant at the current level.

  3. 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,

  4. Mirabilite solubility in equilibrium sea ice brines

    Science.gov (United States)

    Butler, Benjamin Miles; Papadimitriou, Stathys; Santoro, Anna; Kennedy, Hilary

    2016-06-01

    The sea ice microstructure is permeated by brine channels and pockets that contain concentrated seawater-derived brine. Cooling the sea ice results in further formation of pure ice within these pockets as thermal equilibrium is attained, resulting in a smaller volume of increasingly concentrated residual brine. The coupled changes in temperature and ionic composition result in supersaturation of the brine with respect to mirabilite (Na2SO4·10H2O) at temperatures below -6.38 °C, which consequently precipitates within the sea ice microstructure. Here, mirabilite solubility in natural and synthetic seawater derived brines, representative of sea ice at thermal equilibrium, has been measured in laboratory experiments between 0.2 and -20.6 °C, and hence we present a detailed examination of mirabilite dynamics within the sea ice system. Below -6.38 °C mirabilite displays particularly large changes in solubility as the temperature decreases, and by -20.6 °C its precipitation results in 12.90% and 91.97% reductions in the total dissolved Na+ and SO42- concentrations respectively, compared to that of conservative seawater concentration. Such large non-conservative changes in brine composition could potentially impact upon the measurement of sea ice brine salinity and pH, whilst the altered osmotic conditions may create additional challenges for the sympagic organisms that inhabit the sea ice system. At temperatures above -6.38 °C, mirabilite again displays large changes in solubility that likely aid in impeding its identification in field samples of sea ice. Our solubility measurements display excellent agreement with that of the FREZCHEM model, which was therefore used to supplement our measurements to colder temperatures. Measured and modelled solubility data were incorporated into a 1D model for the growth of first-year Arctic sea ice. Model results ultimately suggest that mirabilite has a near ubiquitous presence in much of the sea ice on Earth, and illustrate the

  5. Early Student Support to Investigate the Role of Sea Ice Albedo Feedback in Sea Ice Predictions

    Science.gov (United States)

    2015-09-30

    Qu, 2009: September sea- ice cover in the Arctic Ocean expected to vanish by 2100, Nature Geosciences, doi:10.1038/NGEO467. Kay, J.E, M.M. Holland...predictive capability. IMPACT/APPLICATIONS Loss of sea ice in recent decades has opened the Arctic Ocean to increasing access of wide-ranging...vessels and activities. The Navy is concerned about the potential for conflict and need for search and rescue on the Arctic Ocean . Each year the sea ice

  6. 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

  7. Influence of sea ice on Arctic precipitation.

    Science.gov (United States)

    Kopec, Ben G; Feng, Xiahong; Michel, Fred A; Posmentier, Eric S

    2016-01-05

    Global climate is influenced by the Arctic hydrologic cycle, which is, in part, regulated by sea ice through its control on evaporation and precipitation. However, the quantitative link between precipitation and sea ice extent is poorly constrained. Here we present observational evidence for the response of precipitation to sea ice reduction and assess the sensitivity of the response. Changes in the proportion of moisture sourced from the Arctic with sea ice change in the Canadian Arctic and Greenland Sea regions over the past two decades are inferred from annually averaged deuterium excess (d-excess) measurements from six sites. Other influences on the Arctic hydrologic cycle, such as the strength of meridional transport, are assessed using the North Atlantic Oscillation index. We find that the independent, direct effect of sea ice on the increase of the percentage of Arctic sourced moisture (or Arctic moisture proportion, AMP) is 18.2 ± 4.6% and 10.8 ± 3.6%/100,000 km(2) sea ice lost for each region, respectively, corresponding to increases of 10.9 ± 2.8% and 2.7 ± 1.1%/1 °C of warming in the vapor source regions. The moisture source changes likely result in increases of precipitation and changes in energy balance, creating significant uncertainty for climate predictions.

  8. Simulation of Sea Ice in FGOALS-g2: Climatology and Late 20th Century Changes

    Institute of Scientific and Technical Information of China (English)

    XU Shiming; SONG Mirong; LIU Jiping; WANG Bin; LI Lijuan; HUANG Wenyu; LIU Li

    2013-01-01

    Sea ice is an important component in the Earth's climate system.Coupled climate system models are indispensable tools for the study of sea ice,its internal processes,interaction with other components,and projection of future changes.This paper evaluates the simulation of sea ice by the Flexible Global Ocean-Atmosphere-Land System model Grid-point Version 2 (FGOALS-g2),in the fifth phase of the Coupled Model Inter-comparison Project (CMIP5),with a focus on historical experiments and late 20th century simulation.Through analysis,we find that FGOALS-g2 produces reasonable Arctic and Antarctic sea ice climatology and variability.Sea ice spatial distribution and seasonal change characteristics are well captured.The decrease of Arctic sea ice extent in the late 20th century is reproduced in simulations,although the decrease trend is lower compared with observations.Simulated Antarctic sea ice shows a reasonable distribution and seasonal cycle with high accordance to the amplitude of winter summer changes.Large improvement is achieved as compared with FGOALS-g1.0 in CMIP3.Diagnosis of atmospheric and oceanic forcing on sea ice reveals several shortcomings and major aspects to improve upon in the future:(1) ocean model improvements to remove the artificial island at the North Pole;(2) higher resolution of the atmosphere model for better simulation of important features such as,among others,the Icelandic Low and westerly wind over the Southern Ocean; and (3) ocean model improvements to accurately receive freshwater input from land,and higher resolution for resolving major water channels in the Canadian Arctic Archipelago.

  9. 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.

  10. 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.

  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. Halocarbons associated with Arctic sea ice

    OpenAIRE

    Atkinson, Helen M.; Hughes, Claire; Shaw, Marvin J.; Roscoe, Howard K.; Carpenter, Lucy J.; Liss, Peter S.

    2014-01-01

    Short-lived halocarbons were measured in Arctic sea-ice brine, seawater and air above the Greenland and Norwegian seas (∼81°N, 2 to 5°E) in mid-summer, from a melting ice floe at the edge of the ice pack. In the ice floe, concentrations of C2H5I, 2-C3H7I and CH2Br2 showed significant enhancement in the sea ice brine, of average factors of 1.7, 1.4 and 2.5 times respectively, compared to the water underneath and after normalising to brine volume. Concentrations of mono-iodocarbons in air are t...

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. Seasonal and interannual variability of fast ice extent in the southeastern Laptev Sea between 1999 and 2013

    Science.gov (United States)

    Selyuzhenok, V.; Krumpen, T.; Mahoney, A.; Janout, M.; Gerdes, R.

    2015-12-01

    Along with changes in sea ice extent, thickness, and drift speed, Arctic sea ice regime is characterized by a decrease of fast ice season and reduction of fast ice extent. The most extensive fast ice cover in the Arctic develops in the southeastern Laptev Sea. Using weekly operational sea ice charts produced by Arctic and Antarctic Research Institute (AARI, Russia) from 1999 to 2013, we identified five main key events that characterize the annual evolution of fast ice in the southeastern Laptev Sea. Linking the occurrence of the key events with the atmospheric forcing, bathymetry, freezeup, and melt onset, we examined the processes driving annual fast ice cycle. The analysis revealed that fast ice in the region is sensitive to thermodynamic processes throughout a season, while the wind has a strong influence only on the first stages of fast ice development. The maximal fast ice extent is closely linked to the bathymetry and local topography and is primarily defined by the location of shoals, where fast ice is likely grounded. The annual fast ice cycle shows significant changes over the period of investigation, with tendencies toward later fast ice formation and earlier breakup. These tendencies result in an overall decrease of the fast ice season by 2.8 d/yr, which is significantly higher than previously reported trends.

  18. Floating ice-algal aggregates below melting arctic sea ice.

    Science.gov (United States)

    Assmy, Philipp; Ehn, Jens K; Fernández-Méndez, Mar; Hop, Haakon; Katlein, Christian; Sundfjord, Arild; Bluhm, Katrin; Daase, Malin; Engel, Anja; Fransson, Agneta; Granskog, Mats A; Hudson, Stephen R; Kristiansen, Svein; Nicolaus, Marcel; Peeken, Ilka; Renner, Angelika H H; Spreen, Gunnar; Tatarek, Agnieszka; Wiktor, Jozef

    2013-01-01

    During two consecutive cruises to the Eastern Central Arctic in late summer 2012, we observed floating algal aggregates in the melt-water layer below and between melting ice floes of first-year pack ice. The macroscopic (1-15 cm in diameter) aggregates had a mucous consistency and were dominated by typical ice-associated pennate diatoms embedded within the mucous matrix. Aggregates maintained buoyancy and accumulated just above a strong pycnocline that separated meltwater and seawater layers. We were able, for the first time, to obtain quantitative abundance and biomass estimates of these aggregates. Although their biomass and production on a square metre basis was small compared to ice-algal blooms, the floating ice-algal aggregates supported high levels of biological activity on the scale of the individual aggregate. In addition they constituted a food source for the ice-associated fauna as revealed by pigments indicative of zooplankton grazing, high abundance of naked ciliates, and ice amphipods associated with them. During the Arctic melt season, these floating aggregates likely play an important ecological role in an otherwise impoverished near-surface sea ice environment. Our findings provide important observations and measurements of a unique aggregate-based habitat during the 2012 record sea ice minimum year.

  19. Arctic and Southern Ocean Sea Ice Concentrations

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Monthly sea ice concentration for Arctic (1901 to 1995) and Southern oceans (1973 to 1990) were digitized on a standard 1-degree grid (cylindrical projection) to...

  20. 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.

  1. SENTINEL-1 RESULTS: SEA ICE OPERATIONAL MONITORING

    DEFF Research Database (Denmark)

    Toudal Pedersen, Leif; Saldo, Roberto; Fenger-Nielsen, Rasmus

    2015-01-01

    In the present paper we demonstrate the capabilities of the Sentinel-1 SAR data for operational sea-ice and iceberg monitoring. Most of the examples are drawn from the Copernicus Marine Environmental Monitoring Service (CMEMS) production.......In the present paper we demonstrate the capabilities of the Sentinel-1 SAR data for operational sea-ice and iceberg monitoring. Most of the examples are drawn from the Copernicus Marine Environmental Monitoring Service (CMEMS) production....

  2. Observed sea ice extent in the Russian Arctic, 1933-2006

    Science.gov (United States)

    Mahoney, Andrew R.; Barry, Roger G.; Smolyanitsky, Vasily; Fetterer, Florence

    2008-11-01

    We present a time series of sea ice extent in the Russian Arctic based on observational sea ice charts compiled by the Arctic and Antarctic Research Institute (AARI). These charts are perhaps the oldest operational sea ice data in existence and show that sea ice extent in the Russian Arctic has generally decreased since the beginning of the chart series in 1933. This retreat has not been continuous, however. For the Russian Arctic as a whole in summer, there have been two periods of retreat separated by a partial recovery between the mid-1950s and mid-1980s. The AARI charts, combined with air temperature records, suggest that the retreat in recent decades is pan-Arctic and year-round in some regions, whereas the early twentieth century retreat was only observed in summer in the Russian Arctic. The AARI ice charts indicate that a significant transition occurred in the Russian Arctic in the mid-1980s, when its sea ice cover began to retreat along with that of the rest of the Arctic. Summertime sea ice extents derived from the AARI data set agree with those derived from passive microwave, including the Hadley Centre's global sea ice coverage and sea surface temperature (HadISST) data set. The HadISST results do not indicate the 1980s transition or the partial recovery that took place before it. The AARI charts therefore add significantly to our understanding of the variability of Arctic sea ice over the last 8 decades, and we recommend their inclusion in future historical data sets of Arctic sea ice.

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

    Directory of Open Access Journals (Sweden)

    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.

  4. Mapping wave heights in sea ice with Sentinel 1

    Science.gov (United States)

    Stopa, Justin; Ardhuin, Fabrice; Collard, Fabrice; Mouche, Alexis; Guitton, Gilles; Sutherland, Peter

    2016-04-01

    Sea ice plays an important role in the Earth system by regulating air-sea fluxes. These fluxes can be enhanced by the breaking of ice into floes which critically depends on wave heights propagating across the ice. Remote sensing with SAR provides a unique coverage of the polar regions but so far the measurement of wave heights has been performed routinely only for open water. The presence of ice completely changes the mechanisms by which waves make patterns in radar images. Namely, in the open ocean, the constructed images appear blurred due to the fact that the high frequency waves are unresolved by the sensor. Instead, in ice-covered seas, high frequency waves have been dissipated or scattered away, and only the low-frequency swell components are observed. Two new algorithms have been proposed by Ardhuin et al. (2015). Refining these algorithms, we analyze the intricate wave patterns captured over sea ice by Sentinel 1-A, and measure both the wave heights and directional spreading of the wave spectrum. The procedure is a two-step process which uses an estimation of the orbital vertical velocities that produce the observed image intensity. The first step is implemented when wiggly lines are present. Wiggly lines are created by the presence of two swell systems and are removed by estimating the wave orbital velocity that causes the amplitude in the wiggly line. The second step uses Fourier analysis to invert the straightened image into a velocity field. As a result we obtain a full non-linear inversion the mapping from the velocity field to the SAR intensity image. The inverted velocities can be used to obtain the wavenumber-direction spectrum. Our algorithm is applied to S1A images from the Arctic and Antarctic and discussions follow in terms of wave-ice interaction. These data will be validated using in situ measurements from the ONR Sea State DRI (Beaufort sea, 2016), and combined with numerical modeling using the WAVEWATCH III model to adjust parameterization

  5. Last Interglacial climate and sea-level evolution from a coupled ice sheet-climate model

    Science.gov (United States)

    Goelzer, Heiko; Huybrechts, Philippe; Loutre, Marie-France; Fichefet, Thierry

    2016-12-01

    As the most recent warm period in Earth's history with a sea-level stand higher than present, the Last Interglacial (LIG, ˜ 130 to 115 kyr BP) is often considered a prime example to study the impact of a warmer climate on the two polar ice sheets remaining today. Here we simulate the Last Interglacial climate, ice sheet, and sea-level evolution with the Earth system model of intermediate complexity LOVECLIM v.1.3, which includes dynamic and fully coupled components representing the atmosphere, the ocean and sea ice, the terrestrial biosphere, and the Greenland and Antarctic ice sheets. In this setup, sea-level evolution and climate-ice sheet interactions are modelled in a consistent framework.Surface mass balance change governed by changes in surface meltwater runoff is the dominant forcing for the Greenland ice sheet, which shows a peak sea-level contribution of 1.4 m at 123 kyr BP in the reference experiment. Our results indicate that ice sheet-climate feedbacks play an important role to amplify climate and sea-level changes in the Northern Hemisphere. The sensitivity of the Greenland ice sheet to surface temperature changes considerably increases when interactive albedo changes are considered. Southern Hemisphere polar and sub-polar ocean warming is limited throughout the Last Interglacial, and surface and sub-shelf melting exerts only a minor control on the Antarctic sea-level contribution with a peak of 4.4 m at 125 kyr BP. Retreat of the Antarctic ice sheet at the onset of the LIG is mainly forced by rising sea level and to a lesser extent by reduced ice shelf viscosity as the surface temperature increases. Global sea level shows a peak of 5.3 m at 124.5 kyr BP, which includes a minor contribution of 0.35 m from oceanic thermal expansion. Neither the individual contributions nor the total modelled sea-level stand show fast multi-millennial timescale variations as indicated by some reconstructions.

  6. High-resolution ice nucleation spectra of sea-ice bacteria: implications for cloud formation and life in frozen environments

    Directory of Open Access Journals (Sweden)

    K. Junge

    2008-05-01

    Full Text Available Even though studies of Arctic ice forming particles suggest that a bacterial or viral source derived from open leads could be important for ice formation in Arctic clouds (Bigg and Leck, 2001, the ice nucleation potential of most polar marine psychrophiles or viruses has not been examined under conditions more closely resembling those in the atmosphere. In this paper, we examined the ice nucleation activity (INA of several representative Arctic and Antarctic sea-ice bacterial isolates and a polar Colwellia phage virus. High-resolution ice nucleation spectra were obtained for droplets containing bacterial cells or virus particles using a free-fall freezing tube technique. The fraction of frozen droplets at a particular droplet temperature was determined by measuring the depolarized light scattering intensity from solution droplets in free-fall. Our experiments revealed that all sea-ice isolates and the virus nucleated ice at temperatures very close to the homogeneous nucleation temperature for the nucleation medium – which for artificial seawater was –42.2±0.3°C. Our results suggest that immersion freezing of these marine psychro-active bacteria and viruses would not be important for heterogeneous ice nucleation processes in polar clouds or to the formation of sea ice. These results also suggested that avoidance of ice formation in close proximity to cell surfaces might be one of the cold-adaptation and survival strategies for sea-ice bacteria. The fact that INA occurs at such low temperature could constitute one factor that explains the persistence of metabolic activities at temperatures far below the freezing point of seawater.

  7. 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...

  8. 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

  9. Canadian Ice Service Arctic Regional Sea Ice Charts in SIGRID-3 Format

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Canadian Ice Service (CIS) produces digital Arctic regional sea ice charts for marine navigation, climate research, and input to the Global Digital Sea Ice Data...

  10. Grease ice in basin-scale sea-ice ocean models

    OpenAIRE

    Lars H. Smedsrud; Martin, Torge

    2015-01-01

    The first stage of sea-ice formation is often grease ice, a mixture of sea water and frazil ice crystals. Over time, grease ice typically congeals first to pancake ice floes and then to a solid sea-ice cover. Grease ice is commonly not explicitly simulated in basin-scale sea-ice ocean models, though it affects oceanic heat loss and ice growth and is expected to play a greater role in a more seasonally icecovered Arctic Ocean. We present an approach to simulate the grease-ice layer with, as ba...

  11. Arctic sea ice thickness changes in terms of sea ice age

    Institute of Scientific and Technical Information of China (English)

    BI Haibo; FU Min; SUN Ke; LIU Yilin; XU Xiuli; HUANG Haijun

    2016-01-01

    In this study, changes in Arctic sea ice thickness for each ice age category were examined based on satellite observations and modelled results. Interannual changes obtained from Ice, Cloud, and Land Elevation Satellite (ICESat)-based results show a thickness reduction over perennial sea ice (ice that survives at least one melt season with an age of no less than 2 year) up to approximately 0.5–1.0 m and 0.6–0.8 m (depending on ice age) during the investigated winter and autumn ICESat periods, respectively. Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS)-based results provide a view of a continued thickness reduction over the past four decades. Compared to 1980s, there is a clear thickness drop of roughly 0.50 m in 2010s for perennial ice. This overall decrease in sea ice thickness can be in part attributed to the amplified warming climate in north latitudes. Besides, we figure out that strongly anomalous southerly summer surface winds may play an important role in prompting the thickness decline in perennial ice zone through transporting heat deposited in open water (primarily via albedo feedback) in Eurasian sector deep into a broader sea ice regime in central Arctic Ocean. This heat source is responsible for enhanced ice bottom melting, leading to further reduction in ice thickness.

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

    Science.gov (United States)

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

    2016-08-01

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

  13. Response of passive microwave sea ice concentration algorithms to thin ice

    DEFF Research Database (Denmark)

    Heygster, Georg; Huntemann, Marcus; Ivanova, Natalia;

    2014-01-01

    The influence of sea ice thickness brightness temperatures and ice concentrations retrieved from passive microwave observations is quantified, using horizontally homogeneous sea ice thickness retrievals from ESA's SMOS sensor observations at high incidence angles. Brightness temperatures are infl......The influence of sea ice thickness brightness temperatures and ice concentrations retrieved from passive microwave observations is quantified, using horizontally homogeneous sea ice thickness retrievals from ESA's SMOS sensor observations at high incidence angles. Brightness temperatures...

  14. Using Sea Ice Age as a Proxy for Sea Ice Thickness

    Science.gov (United States)

    Stroeve, J. C.; Tschudi, M. A.; Maslanik, J. A.

    2014-12-01

    Since the beginning of the modern satellite record starting in October 1978, the Arctic sea ice cover has been shrinking, with the largest changes observed at the end of the melt season in September. Through 2013, the September ice extent has declined at a rate of -14.0% dec-1, or -895,300 km2 dec-1. The seven lowest September extents in the satellite record have all occurred in the past seven years. This reduction in ice extent is accompanied by large reductions in winter ice thicknesses that are primarily explained by changes in the ocean's coverage of multiyear ice (MYI). Using the University of Colorado ice age product developed by J. Maslanik and C. Fowler, and currently produced by M. Tschudi we present recent changes in the distribution of ice age from the mid 1980s to present. The CU ice age product is based on (1) the use of ice motion to track areas of sea ice and thus estimate how long the ice survives within the Arctic, and (2) satellite imagery of sea ice concentration to determine when the ice disappears. Age is assigned on a yearly basis, with the age incremented by one year if the ice survives summer melt and stays within the Arctic domain. Age is counted from 1 to 10 years, with all ice older than 10 years assigned to the "10+" age category. The position of the ice is calculated on weekly time steps on NSIDC's 12.5-km EASE-grid. In the mid-1980s, MYI accounted for 70% of total winter ice extent, whereas by the end of 2012 it had dropped to less than 20%. This reflects not only a change in ice type, but also a general thinning of the ice pack, as older ice tends to be thicker ice. Thus, with older ice being replaced by thinner first-year ice, the ice pack is more susceptible to melting out than it was in 1980's. It has been suggested that ice age may be a useful proxy for long-term changes in ice thickness. To assess the relationship between ice age and thickness, and how this may be changing over time, we compare the ice age fields to several

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

    Directory of Open Access Journals (Sweden)

    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

  17. Sea-ice dynamics strongly promote Snowball Earth initiation and destabilize tropical sea-ice margins

    Directory of Open Access Journals (Sweden)

    A. Voigt

    2012-12-01

    Full Text Available The Snowball Earth bifurcation, or runaway ice-albedo feedback, is defined for particular boundary conditions by a critical CO2 and a critical sea-ice cover (SI, both of which are essential for evaluating hypotheses related to Neoproterozoic glaciations. Previous work has shown that the Snowball Earth bifurcation, denoted as (CO2, SI*, differs greatly among climate models. Here, we study the effect of bare sea-ice albedo, sea-ice dynamics and ocean heat transport on (CO2, SI* in the atmosphere–ocean general circulation model ECHAM5/MPI-OM with Marinoan (~ 635 Ma continents and solar insolation (94% of modern. In its standard setup, ECHAM5/MPI-OM initiates a~Snowball Earth much more easily than other climate models at (CO2, SI* ≈ (500 ppm, 55%. Replacing the model's standard bare sea-ice albedo of 0.75 by a much lower value of 0.45, we find (CO2, SI* ≈ (204 ppm, 70%. This is consistent with previous work and results from net evaporation and local melting near the sea-ice margin. When we additionally disable sea-ice dynamics, we find that the Snowball Earth bifurcation can be pushed even closer to the equator and occurs at a hundred times lower CO2: (CO2, SI* ≈ (2 ppm, 85%. Therefore, the simulation of sea-ice dynamics in ECHAM5/MPI-OM is a dominant determinant of its high critical CO2 for Snowball initiation relative to other models. Ocean heat transport has no effect on the critical sea-ice cover and only slightly decreases the critical CO2. For disabled sea-ice dynamics, the state with 85% sea-ice cover is stabilized by the Jormungand mechanism and shares characteristics with the Jormungand climate states. However, there is no indication of the Jormungand bifurcation and hysteresis in ECHAM5/MPI-OM. The state with 85% sea-ice cover therefore is a soft Snowball state rather than a true

  18. 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

  19. High-resolution ice nucleation spectra of sea-ice bacteria: implications for cloud formation and life in frozen environments

    Directory of Open Access Journals (Sweden)

    K. Junge

    2007-11-01

    Full Text Available Even though studies of Arctic ice forming particles suggest that a bacterial or viral source derived from open leads could be important for cloud formation in the Arctic (Bigg and Leck, 2001, the ice nucleation potential of most polar marine psychrophiles or viruses has not been examined under conditions more closely resembling those in the atmosphere. In this paper, we examined the ice nucleation activity (INA of several representative Arctic and Antarctic sea-ice bacterial isolates and a polar Colwellia phage virus. High-resolution ice nucleation spectra were obtained for droplets containing bacterial cells or virus particles using a free-fall freezing tube technique. The fraction of frozen droplets at a particular droplet temperature was determined by measuring the depolarized light scattering intensity from solution droplets in free-fall. Our experiments revealed that all sea-ice isolates and the virus nucleated ice at temperatures very close to the homogeneous nucleation temperature for the nucleation medium – which for artificial seawater was −42.2±0.3°C. Our results indicated that these marine psychro-active bacteria and viruses are not important for heterogeneous ice nucleation processes in sea ice or polar clouds. These results also suggested that avoidance of ice formation in close proximity to cell surfaces might be one of the cold-adaptation and survival strategies for sea-ice bacteria. The fact that INA occurs at such low temperature could constitute one factor that explains the persistence of metabolic activities at temperatures far below the freezing point of seawater.

  20. Arctic sea-ice cover and sea-ice cover anomalies over eastern Canadian waters

    Energy Technology Data Exchange (ETDEWEB)

    Agnew, T.

    1990-01-01

    Concerns about global climate warming have increased interest in climate monitoring and analysis of climate trends in Canada. Sea-ice cover is of interest for climate monitoring since it is very sensitive to changes in the climate controls over a region and is an integrator of temperature anomalies over periods of a week and longer. In addition, climate models suggest that polar regions will have the largest climate warming signal. The existence of long-term digital sea-ice databases makes analysis of sea ice as a climate change indicator possible. The northern hemisphere sea-ice concentration database for 1953 to 1988 was qualitatively evaluated for its representativeness over eastern Canadian Arctic waters. Despite inhomogeneity problems, the database identifies the average freezeup and breakup patterns in the Canadian Arctic islands, Baffin Bay/Davis Strait, and the Hudson Bay area, and can be used for sea-ice variability and anomaly studies. However, inhomogeneity problems put into question the use of the database for sea-ice trend analysis. Sea-ice anomalies for the 1982/83 El Nino winter are compared to atmospheric temperature and circulation anomalies over the Baffin Bay/Davis Strait area. Sea-ice anomaly charts for 1953-1988 are calculated and have been made available as an unpublished catalogue within the Canadian Climate Centre. 15 refs., 27 figs.

  1. 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

  2. Intercomparison of passive microwave sea ice concentration retrievals over the high-concentration Arctic sea ice

    DEFF Research Database (Denmark)

    andersen, susanne; Tonboe, R.; Kaleschke, L.

    2007-01-01

    -swath synthetic aperture radar (SAR) scenes. The analysis is confined to the high-concentration Arctic sea ice, where the ice cover is near 100%. During winter the results indicate that the variability of the SSM/I concentration estimates is larger than the true variability of ice concentration. Results from...... a trusted subset of the SAR scenes across the central Arctic allow the separation of the ice concentration uncertainty due to emissivity variations and sensor noise from other error sources during the winter of 2003-2004. Depending on the algorithm, error standard deviations from 2.5 to 5.0% are found......[1] Measurements of sea ice concentration from the Special Sensor Microwave Imager (SSM/I) using seven different algorithms are compared to ship observations, sea ice divergence estimates from the Radarsat Geophysical Processor System, and ice and water surface type classification of 59 wide...

  3. A New Discrete Element Sea-Ice Model for Earth System Modeling

    Energy Technology Data Exchange (ETDEWEB)

    Turner, Adrian Keith [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-03-10

    Sea ice forms a frozen crust of sea water oating in high-latitude oceans. It is a critical component of the Earth system because its formation helps to drive the global thermohaline circulation, and its seasonal waxing and waning in the high north and Southern Ocean signi cantly affects planetary albedo. Usually 4{6% of Earth's marine surface is covered by sea ice at any one time, which limits the exchange of heat, momentum, and mass between the atmosphere and ocean in the polar realms. Snow accumulates on sea ice and inhibits its vertical growth, increases its albedo, and contributes to pooled water in melt ponds that darken the Arctic ice surface in the spring. Ice extent and volume are subject to strong seasonal, inter-annual and hemispheric variations, and climatic trends, which Earth System Models (ESMs) are challenged to simulate accurately (Stroeve et al., 2012; Stocker et al., 2013). This is because there are strong coupled feedbacks across the atmosphere-ice-ocean boundary layers, including the ice-albedo feedback, whereby a reduced ice cover leads to increased upper ocean heating, further enhancing sea-ice melt and reducing incident solar radiation re ected back into the atmosphere (Perovich et al., 2008). A reduction in perennial Arctic sea-ice during the satellite era has been implicated in mid-latitude weather changes, including over North America (Overland et al., 2015). Meanwhile, most ESMs have been unable to simulate observed inter-annual variability and trends in Antarctic sea-ice extent during the same period (Gagne et al., 2014).

  4. On the extraordinary snow on the sea ice off East Antarctica in late winter, 2012

    Science.gov (United States)

    Toyota, Takenobu; Massom, Robert; Lecomte, Olivier; Nomura, Daiki; Heil, Petra; Tamura, Takeshi; Fraser, Alexander D.

    2016-09-01

    In late winter-early spring 2012, the second Sea Ice Physics and Ecosystems Experiment (SIPEX II) was conducted off Wilkes Land, East Antarctica, onboard R/V Aurora Australis. The sea-ice conditions were characterized by significantly thick first-year ice and snow, trapping the ship for about 10 days in the near coastal region. The deep snow cover was particularly remarkable, in that its average value of 0.45 m was almost three times that observed between 1992 and 2007 in the region. To reveal factors responsible, we used in situ observations and ERA-Interim reanalysis (1990-2012) to examine the relative contribution of the different components of the local-regional snow mass balance equation i.e., snow accumulation on sea ice, precipitation minus evaporation (P-E), and loss by (i) snow-ice formation and (ii) entering into leads due to drifting snow. Results show no evidence for significantly high P-E in the winter of 2012. Ice core analysis has shown that although the snow-ice layer was relatively thin, indicating less transformation from snow to snow-ice in 2012 as compared to measurements from 2007, the difference was not enough to explain the extraordinarily deep snow. Based on these results, we deduce that lower loss of snow into leads was probably responsible for the extraordinary snow in 2012. Statistical analysis and satellite images suggest that the reduction in loss of snow into leads is attributed to rough ice surface associated with active deformation processes and larger floe size due to sea-ice expansion. This highlights the importance of snow-sea ice interaction in determining the mean snow depth on Antarctic sea ice.

  5. 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.

  6. Ice sheet systems and sea level change.

    Science.gov (United States)

    Rignot, E. J.

    2015-12-01

    Modern views of ice sheets provided by satellites, airborne surveys, in situ data and paleoclimate records while transformative of glaciology have not fundamentally changed concerns about ice sheet stability and collapse that emerged in the 1970's. Motivated by the desire to learn more about ice sheets using new technologies, we stumbled on an unexplored field of science and witnessed surprising changes before realizing that most were coming too fast, soon and large. Ice sheets are integrant part of the Earth system; they interact vigorously with the atmosphere and the oceans, yet most of this interaction is not part of current global climate models. Since we have never witnessed the collapse of a marine ice sheet, observations and exploration remain critical sentinels. At present, these observations suggest that Antarctica and Greenland have been launched into a path of multi-meter sea level rise caused by rapid climate warming. While the current loss of ice sheet mass to the ocean remains a trickle, every mm of sea level change will take centuries of climate reversal to get back, several major marine-terminating sectors have been pushed out of equilibrium, and ice shelves are irremediably being lost. As glaciers retreat from their salty, warm, oceanic margins, they will melt away and retreat slower, but concerns remain about sea level change from vastly marine-based sectors: 2-m sea level equivalent in Greenland and 23-m in Antarctica. Significant changes affect 2/4 marine-based sectors in Greenland - Jakobshavn Isb. and the northeast stream - with Petermann Gl. not far behind. Major changes have affected the Amundsen Sea sector of West Antarctica since the 1980s. Smaller yet significant changes affect the marine-based Wilkes Land sector of East Antarctica, a reminder that not all marine-based ice is in West Antarctica. Major advances in reducing uncertainties in sea level projections will require massive, interdisciplinary efforts that are not currently in place

  7. Arctic Sea Ice : Trends, Stability and Variability

    Science.gov (United States)

    Moon, W.; Wettlaufer, J. S.

    2014-12-01

    A stochastic Arctic sea-ice model is derived and analysed in detail to interpret the recent decay and associated variability of Arctic sea-ice under changes in radiative forcing. The approach begins from a deterministic model of the heat flux balance through the air/sea/ice system, which uses observed monthly-averaged heat fluxesto drive a time evolution of sea-ice thickness. This model reproduces the observed seasonal cycle of the ice cover and it is to this that stochastic noise--representing high frequency variability--is introduced.The model takes the form of a single periodic non-autonomous stochastic ordinary differential equation. The value of such a model is that it provides a relatively simple framework to examine the role of noise in the basic nonlinear interactions at play as transitions in the state of the ice cover (e.g., from perennial to seasonal) are approached. Moreover, the stability and the noise conspire to underlie the inter annual variability and how that variability changes as one approaches the deterministic bifurcations in the system.

  8. 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

  9. 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

  10. Assessment of C-band compact polarimetry SAR for sea ice classification

    Institute of Scientific and Technical Information of China (English)

    ZHANG Xi; ZHANG Jie; LIU Meijie; MENG Junmin

    2016-01-01

    0HH 0V V 0 HV The C-band synthetic aperture radar (SAR) data from the Bohai Sea of China, the Labrador Sea in the Arctic and the Weddell Sea in the Antarctic are used to analyze and discuss the sea ice full polarimetric information reconstruction ability under compact polarimetric modes. The type of compact polarimetric mode which has the highest reconstructed accuracy is analyzed, along with the performance impact of the reconstructed pseudo quad-pol SAR data on the sea ice detection and sea ice classification. According to the assessment and analysis, it is recommended to adopt the CTLR mode for reconstructing the polarimetric parameters , ,H andα, while for reconstructing the polarimetric parameters ,ρH-V,λ1 andλ2, it is recommended to use the π/4 mode. Moreover, it is recommended to use the π/4 mode in studying the action effects between the electromagnetic waves and sea ice, but it is recommended to use the CTLR mode for studying the sea ice classification.

  11. 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.

  12. 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.

  13. 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.

  14. Drivers of sea-level change - using relative sea level records from the North and South Atlantic to fingerprint sources of mid-Holocene ice melt

    Science.gov (United States)

    Horton, B.; Khan, N.; Ashe, E.; Kopp, R. E.; Long, A. J.; Gehrels, W. R.

    2015-12-01

    Many factors give rise to relative sea-level (RSL) changes that are far from globally uniform. For example, spatially variable sea-level responses arise because of the exchange of mass between ice sheets and oceans. Gravitational, flexural, and rotational processes generate a distinct spatial pattern - or "fingerprint" - of sea-level change associated with each shrinking land ice mass. As a land ice mass shrinks, sea-level rise is greater in areas geographically distal to the ice mass than in areas proximal to it, in large part because the gravitational attraction between the ice mass and the ocean is reduced. Thus, the U.S. mid-Atlantic coastline experiences about 50% of the global average sea-level-rise due to Greenland Ice Sheet melt, but about 120% of the global average due to West Antarctic Ice Sheet melt. Separating the Greenland and Antarctic ice sheet contributions during the past 7,000 years requires analysis of sea-level changes from sites in the northern and southern hemisphere. Accordingly we present sea-level records within a hierarchical statistical modeling to: (1) quantify rates of change; (2) compare rates of change among sites, including full quantification of the uncertainty in their differences; and (3) test hypotheses about the sources of meltwater through their sea-level fingerprints. Preliminary analysis of three sites within our North and South Atlantic sea-level database indicates sea-level gradient in the rate of RSL rise during the mid Holocene between 6000 and 4000 years BP; a greater change in rate is found in Brazil than St Croix than New Jersey, consistent with an increase and then decrease in Greenland Ice Sheet mass.

  15. 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

  16. 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

    regime during the Pliocene-Pleistocene, when most sediment delivered to the margin is trapped in the outer shelf and slope-forming steep prograding wedges. During the warmer but still polar, Holocene, biogenic sediment accumulates quickly in deep inner-shelf basins during the high-stand intervals. These sediments contain an ultrahigh resolution (annual to millennial) record of climate variability. Validation of our inferences about the nature and timing of Wilkes Land glacial sequences can be achieved by deep sampling (i.e., using IODP-type techniques). The most complete record of the long-term history of glaciation in this margin can be obtained by sampling both (1) the shelf, which contains the direct (presence or no presence of ice) but low-resolution record of glaciation, and (2) the rise, which contains the distal (cold vs. warm) but more complete record of glaciation. The Wilkes Land margin is the only known Antarctic margin where the presumed "onset" of glaciation unconformity (WL-U3) can be traced from shelf to the abyssal plain, allowing links between the proximal and the distal records of glaciation to be established. Additionally, the eastern segment of the Wilkes Land margin may be more sensitive to climate change because the East Antarctic Ice Sheet (EAIS) is grounded below sea level. Therefore, the Wilkes Land margin is not only an ideal location to obtain the long-term EAIS history but also to obtain the shorter-term record of ice sheet fluctuations at times that the East Antarctic Ice Sheet is thought to have been more stable (after 15 Ma-recent). ?? 2004 Elsevier B.V. All rights reserved.

  17. Evaluation of the ESA Sea Ice CCI (SICCI) project sea ice concentration data set

    DEFF Research Database (Denmark)

    Kern, Stefan; Bell, Louisa; Ivanova, Natalia;

    around these two SIC values; consequently SIC can be negative or above 100%. In order to fully evaluate SICCI SIC this natural variability needs to be taken into account. In contrast to most other SIC retrieval algorithms the SICCI algorithm does not filter spurious sea ice over open water with a weather......During phase 1 of the European Space Agency’s (ESA) climate change initiative (CCI) sea ice project (SICCI project) a sea ice concentration (SIC) data product was produced by employing a hybrid SIC retrieval algorithm comprising the Bristol and the Comiso-Bootstrap algorithm in frequency mode. SIC...... filter because by doing so often substantial portions of the sea ice cover along the ice edge are discarded....

  18. Impacts of Organic Macromolecules, Chlorophyll and Soot on Arctic Sea Ice

    Science.gov (United States)

    Ogunro, O. O.; Wingenter, O. W.; Elliott, S.; Flanner, M.; Dubey, M. K.

    2014-12-01

    Recent intensification of Arctic amplification can be strongly connected to positive feedback relating black carbon deposition to sea ice surface albedo. In addition to soot deposition on the ice and snow pack, ice algal chlorophyll is likely to compete as an absorber and redistributor of energy. Hence, solar radiation absorption by chlorophyll and some components of organic macromolecules in/under the ice column is currently being examined to determine the level of influence on predicted rate of ice loss. High amounts of organic macromolecules and chlorophyll are produced in global sea ice by the bottom microbial community and also in vertically distributed layers where substantial biological activities take place. Brine channeling in columnar ice can allow for upward flow of nutrients which leads to greater primary production in the presence of moderate light. Modeling of the sea-ice processes in tandem with experiments and field observations promises rapid progress in enhancing Arctic ice predictions. We are designing and conducting global climate model experiments to determine the impact of organic macromolecules and chlorophyll on Arctic sea ice. Influences on brine network permeability and radiation/albedo will be considered in this exercise. Absorption by anthropogenic materials such as soot and black carbon will be compared with that of natural pigments. We will indicate areas of soot and biological absorption dominance in the sense of single scattering, then couple into a full radiation transfer scheme to attribute the various contributions to polar climate change amplification. The work prepares us to study more traditional issues such as chlorophyll warming of the pack periphery and chemical effects of the flow of organics from ice internal communities. The experiments started in the Arctic will broaden to include Antarctic sea ice and shelves. Results from the Arctic simulations will be presented.

  19. 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.

  20. Influence of sea ice on ocean water vapor isotopes and Greenland ice core records

    Science.gov (United States)

    Klein, Eric S.; Welker, Jeffrey M.

    2016-12-01

    A warming climate results in sea ice loss and impacts to the Arctic water cycle. The water isotope parameter deuterium excess, a moisture source proxy, can serve as a tracer to help understand hydrological changes due to sea ice loss. However, unlocking the sea ice change signal of isotopes from ice cores requires understanding how sea ice changes impact deuterium excess, which is unknown. Here we present the first isotope data linking a gradient of sea ice extents to oceanic water vapor deuterium excess values. Initial loss of sea ice extent leads to lower deuterium excess moisture sources, and then values progressively increase with further ice loss. Our new process-based interpretation suggests that past rapid (1-3 years) Greenland ice core changes in deuterium excess during warming might not be the result of abrupt atmospheric circulation shifts, but rather gradual loss of sea ice extent at northern latitude moisture sources.

  1. Arctic Sea Salt Aerosol from Blowing Snow and Sea Ice Surfaces - a Missing Natural Source in Winter

    Science.gov (United States)

    Frey, M. M.; Norris, S. J.; Brooks, I. M.; Nishimura, K.; Jones, A. E.

    2015-12-01

    Atmospheric particles in the polar regions consist mostly of sea salt aerosol (SSA). SSA plays an important role in regional climate change through influencing the surface energy balance either directly or indirectly via cloud formation. SSA irradiated by sunlight also releases very reactive halogen radicals, which control concentrations of ozone, a pollutant and greenhouse gas. However, models under-predict SSA concentrations in the Arctic during winter pointing to a missing source. It has been recently suggested that salty blowing snow above sea ice, which is evaporating, to be that source as it may produce more SSA than equivalent areas of open ocean. Participation in the 'Norwegian Young Sea Ice Cruise (N-ICE 2015)' on board the research vessel `Lance' allowed to test this hypothesis in the Arctic sea ice zone during winter. Measurements were carried out from the ship frozen into the pack ice North of 80º N during February to March 2015. Observations at ground level (0.1-2 m) and from the ship's crows nest (30 m) included number concentrations and size spectra of SSA (diameter range 0.3-10 μm) as well as snow particles (diameter range 50-500 μm). During and after blowing snow events significant SSA production was observed. In the aerosol and snow phase sulfate is fractionated with respect to sea water, which confirms sea ice surfaces and salty snow, and not the open ocean, to be the dominant source of airborne SSA. Aerosol shows depletion in bromide with respect to sea water, especially after sunrise, indicating photochemically driven release of bromine. We discuss the SSA source strength from blowing snow in light of environmental conditions (wind speed, atmospheric turbulence, temperature and snow salinity) and recommend improved model parameterisations to estimate regional aerosol production. N-ICE 2015 results are then compared to a similar study carried out previously in the Weddell Sea during the Antarctic winter.

  2. Influence of the Southern Annular Mode on the sea ice-ocean system: the role of the thermal and mechanical forcing

    Directory of Open Access Journals (Sweden)

    W. Lefebvre

    2005-06-01

    Full Text Available The global sea ice-ocean model ORCA2-LIM is used to investigate the impact of the thermal and mechanical forcing associated to the Southern Annular Mode (SAM on the Antarctic sea ice-ocean system. To do so, the model is driven by idealized forcings based on regressions of the wind stress and the air temperature to SAM. The wind-stress component strongly affects the overall patterns of the ocean circulation with a northward surface drift, a downwelling at about 45° S and an upwelling in the vicinity of the Antarctic continent when SAM is positive. On the other hand, the thermal forcing has a negligible effect on the ocean currents. For sea ice, both the wind-stress (mechanical and the air temperature (thermal components have a significant impact. The mechanical part induces a decrease of the sea ice thickness close to the continent and a sharp decrease of the mean sea ice thickness in the Weddell sector. In general, the sea ice area also diminishes, with a maximum decrease in the Weddell Sea. On the contrary, the thermal part tends to increase the ice concentration in all sectors except in the Weddell Sea, where the ice area shrinks. This thermal effect is the strongest in autumn and in winter due to the larger temperature differences associated with SAM during these seasons. The sum of the thermal and mechaninal effects gives a dipole response of sea ice to the SAM, with a decrease of the ice area in the Weddell Sea and around the Antarctic Peninsula and an increase in the Ross and Amundsen Seas during high SAM years. This is in good agreement with the observed response of the ice cover to SAM.

  3. 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

  4. Arctic Sea Ice Decline - Results from Winter 2015/16

    OpenAIRE

    Nicolaus, Marcel; Hendricks, Stefan; Ricker, Robert

    2016-01-01

    Sea ice physicists from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), are anticipating that the sea ice cover in the Arctic Ocean this summer may shrink to the record low of 2012. The scientists made this projection after evaluating current satellite data about the thickness of the ice cover. The data show that the arctic sea ice was already extraordinarily thin in the summer of 2015. Comparably little new ice formed during the past winter.

  5. 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 area.

  6. Inter-hemispheric asymmetry in the sea-ice response to volcanic forcing simulated by MPI-ESM (COSMOS-Mill

    Directory of Open Access Journals (Sweden)

    D. Zanchettin

    2014-02-01

    Full Text Available The decadal evolution of Arctic and Antarctic sea ice following strong volcanic eruptions is investigated in four climate simulation ensembles performed with the COSMOS-Mill version of the Max Planck Institute-Earth System Model. The ensembles differ in the magnitude of the imposed volcanic perturbations, with sizes representative of historical tropical eruptions (1991 Pinatubo and 1815 Tambora and of tropical and extra-tropical "supervolcano" eruptions. A post-eruption Arctic sea-ice expansion is robustly detected in all ensembles, while Antarctic sea ice responds only to "supervolcano" eruptions, undergoing an initial short-lived expansion and a subsequent prolonged contraction phase. Strong volcanic forcing therefore emerges as a potential source of inter-hemispheric interannual-to-decadal climate variability, although the inter-hemispheric signature is weak in the case of historical-size eruptions. The post-eruption inter-hemispheric decadal asymmetry in sea ice is interpreted as a consequence mainly of different exposure of Arctic and Antarctic regional climates to induced meridional heat transport changes and of dominating local feedbacks that set in within the Antarctic region. "Supervolcano" experiments help clarifying differences in simulated hemispheric internal dynamics related to imposed negative net radiative imbalances, including the relative importance of the thermal and dynamical components of the sea-ice response. "Supervolcano" experiments could therefore serve the assessment of climate models' behavior under strong external forcing conditions and, consequently, favor advancements in our understanding of simulated sea-ice dynamics.

  7. Lower satellite-gravimetry estimates of Antarctic sea-level contribution.

    Science.gov (United States)

    King, Matt A; Bingham, Rory J; Moore, Phil; Whitehouse, Pippa L; Bentley, Michael J; Milne, Glenn A

    2012-11-22

    Recent estimates of Antarctica's present-day rate of ice-mass contribution to changes in sea level range from 31 gigatonnes a year (Gt yr(-1); ref. 1) to 246 Gt yr(-1) (ref. 2), a range that cannot be reconciled within formal errors. Time-varying rates of mass loss contribute to this, but substantial technique-specific systematic errors also exist. In particular, estimates of secular ice-mass change derived from Gravity Recovery and Climate Experiment (GRACE) satellite data are dominated by significant uncertainty in the accuracy of models of mass change due to glacial isostatic adjustment (GIA). Here we adopt a new model of GIA, developed from geological constraints, which produces GIA rates systematically lower than those of previous models, and an improved fit to independent uplift data. After applying the model to 99 months (from August 2002 to December 2010) of GRACE data, we estimate a continent-wide ice-mass change of -69 ± 18 Gt yr(-1) (+0.19 ± 0.05 mm yr(-1) sea-level equivalent). This is about a third to a half of the most recently published GRACE estimates, which cover a similar time period but are based on older GIA models. Plausible GIA model uncertainties, and errors relating to removing longitudinal GRACE artefacts ('destriping'), confine our estimate to the range -126 Gt yr(-1) to -29 Gt yr(-1) (0.08-0.35 mm yr(-1) sea-level equivalent). We resolve 26 independent drainage basins and find that Antarctic mass loss, and its acceleration, is concentrated in basins along the Amundsen Sea coast. Outside this region, we find that West Antarctica is nearly in balance and that East Antarctica is gaining substantial mass.

  8. Predicting Land-Ice Retreat and Sea-Level Rise with the Community Earth System Model

    Energy Technology Data Exchange (ETDEWEB)

    Lipscomb, William [Los Alamos National Laboratory

    2012-06-19

    Coastal stakeholders need defensible predictions of 21st century sea-level rise (SLR). IPCC assessments suggest 21st century SLR of {approx}0.5 m under aggressive emission scenarios. Semi-empirical models project SLR of {approx}1 m or more by 2100. Although some sea-level contributions are fairly well constrained by models, others are highly uncertain. Recent studies suggest a potential large contribution ({approx}0.5 m/century) from the marine-based West Antarctic Ice Sheet, linked to changes in Southern Ocean wind stress. To assess the likelihood of fast retreat of marine ice sheets, we need coupled ice-sheet/ocean models that do not yet exist (but are well under way). CESM is uniquely positioned to provide integrated, physics based sea-level predictions.

  9. Mechanism of seasonal Arctic sea ice evolution and Arctic amplification

    OpenAIRE

    Kim, Kwang-Yul; Hamlington, Benjamin D.; Na, Hanna; Kim, Jinju

    2016-01-01

    Sea ice loss is proposed as a primary reason for the Arctic amplification, although the physical mechanism of the Arctic amplification and its connection with sea ice melting is still in debate. In the present study, monthly ERA-Interim reanalysis data are analyzed via cyclostationary empirical orthogonal function analysis to understand the seasonal mechanism of sea ice loss in the Arctic Ocean and the Arctic amplification. While sea ice loss is widespread over much of the p...

  10. Validation of Airborne FMCW Radar Measurements of Snow Thickness Over Sea Ice in Antarctica

    Science.gov (United States)

    Galin, Natalia; Worby, Anthony; Markus, Thorsten; Leuschen, Carl; Gogineni, Prasad

    2012-01-01

    Antarctic sea ice and its snow cover are integral components of the global climate system, yet many aspects of their vertical dimensions are poorly understood, making their representation in global climate models poor. Remote sensing is the key to monitoring the dynamic nature of sea ice and its snow cover. Reliable and accurate snow thickness data are currently a highly sought after data product. Remotely sensed snow thickness measurements can provide an indication of precipitation levels, predicted to increase with effects of climate change in the polar regions. Airborne techniques provide a means for regional-scale estimation of snow depth and distribution. Accurate regional-scale snow thickness data will also facilitate an increase in the accuracy of sea ice thickness retrieval from satellite altimeter freeboard estimates. The airborne data sets are easier to validate with in situ measurements and are better suited to validating satellite algorithms when compared with in situ techniques. This is primarily due to two factors: better chance of getting coincident in situ and airborne data sets and the tractability of comparison between an in situ data set and the airborne data set averaged over the footprint of the antennas. A 28-GHz frequency modulated continuous wave (FMCW) radar loaned by the Center for Remote Sensing of Ice Sheets to the Australian Antarctic Division is used to measure snow thickness over sea ice in East Antarctica. Provided with the radar design parameters, the expected performance parameters of the radar are summarized. The necessary conditions for unambiguous identification of the airsnow and snowice layers for the radar are presented. Roughnesses of the snow and ice surfaces are found to be dominant determinants in the effectiveness of layer identification for this radar. Finally, this paper presents the first in situ validated snow thickness estimates over sea ice in Antarctica derived from an FMCW radar on a helicopterborne platform.

  11. Polar Sea Ice Monitoring Using HY-2A Scatterometer Measurements

    Directory of Open Access Journals (Sweden)

    Mingming Li

    2016-08-01

    Full Text Available A sea ice detection algorithm based on Fisher’s linear discriminant analysis is developed to segment sea ice and open water for the Ku-band scatterometer onboard the China’s Hai Yang 2A Satellite (HY-2A/SCAT. Residual classification errors are reduced through image erosion/dilation techniques and sea ice growth/retreat constraint methods. The arctic sea-ice-type classification is estimated via a time-dependent threshold derived from the annual backscatter trends based on previous HY-2A/SCAT derived sea ice extent. The extent and edge of the sea ice obtained in this study is compared with the Special Sensor Microwave Imager/Sounder (SSMIS sea ice concentration data and the Sentinel-1 SAR imagery for verification, respectively. Meanwhile, the classified sea ice type is compared with a multi-sensor sea ice type product based on data from the Advanced Scatterometer (ASCAT and SSMIS. Results show that HY-2A/SCAT is powerful in providing sea ice extent and type information, while differences in the sensitivities of active/passive products are found. In addition, HY-2A/SCAT derived sea ice products are also proved to be valuable complements for existing polar sea ice data products.

  12. Quaternary Sea-ice history in the Arctic Ocean based on a new Ostracode sea-ice proxy

    Science.gov (United States)

    Cronin, T. M.; Gemery, L.; Briggs, W.M.; Jakobsson, M.; Polyak, L.; Brouwers, E.M.

    2010-01-01

    Paleo-sea-ice history in the Arctic Ocean was reconstructed using the sea-ice dwelling ostracode Acetabulastoma arcticum from late Quaternary sediments from the Mendeleyev, Lomonosov, and Gakkel Ridges, the Morris Jesup Rise and the Yermak Plateau. Results suggest intermittently high levels of perennial sea ice in the central Arctic Ocean during Marine Isotope Stage (MIS) 3 (25-45 ka), minimal sea ice during the last deglacial (16-11 ka) and early Holocene thermal maximum (11-5 ka) and increasing sea ice during the mid-to-late Holocene (5-0 ka). Sediment core records from the Iceland and Rockall Plateaus show that perennial sea ice existed in these regions only during glacial intervals MIS 2, 4, and 6. These results show that sea ice exhibits complex temporal and spatial variability during different climatic regimes and that the development of modern perennial sea ice may be a relatively recent phenomenon. ?? 2010.

  13. The high tide of the warm Pliocene: Implications of ~20 m Peak Eustatic Sea-Levels for Antarctic Deglaciation

    Science.gov (United States)

    Miller, K. G.; Browning, J. V.; Kulpecz, A. A.; Kominz, M. A.; Naish, T.; Rosenthal, Y.; Peltier, W. R.; Sosdian, S. M.; Wright, J. D.

    2010-12-01

    The eustatic peak of the Pliocene (ca. 3 Ma) allows evaluation of sea-level response to conditions warmer than present and with atmospheric carbon dioxide levels similar to the early 21st century. We provide new eustatic estimates for the Pliocene from backstripping shallow-marine, siliciclastic sections in Virginia, U.S.A., and New Zealand, accounting for the effects of compaction, Airy loading, and thermal subsidence. We compare our backstripped eustatic estimates with previously published estimates from a carbonate atoll (Enewetak), deep sea benthic foraminiferal oxygen isotopes, Mg-Ca, and uplifted marine terraces in the Carolinas and Alaska and conclude that the peak was 19±5 m, significantly lower than previously published estimates of 30-40 m derived from uplifted terraces. The 19-m peak implies not only the loss of the total equivalent of Greenland and West Antarctic ice sheets, but suggests volume loss of the East Antarctic Ice Sheet (EAIS) of ~4 m of sea-level equivalent. Our estimates provide helps resolve the long-standing controversy of the stability of the EAIS during the warmer-than-present Pliocene climatic optimum. The sea-level fall at MIC 100 (ca. 2.7 Ma) associated with the growth of large northern hemisphere ice sheets was remarkably large (~100 m) and may have cause a glacial isotostatic adjustment the resulted in uplift of the otherwise tectonically stable New Jersey coastal plain. Despite uncertainties in pre-ice core CO2 and global temperature measurements, the Pliocene provides a critical sea level-atmospheric CO2 calibration point for climates significantly warmer than the last major interglacial, MIC 5e.

  14. High resolution modelling of the decreasing Arctic sea ice

    DEFF Research Database (Denmark)

    Madsen, K. S.; Rasmussen, T. A. S.; Blüthgen, Jonas

    2012-01-01

    The Arctic sea ice cover has been rapidly decreasing and thinning over the last decade, with minimum ice extent in 2007 and almost as low extent in 2011. This study investigates two aspects of the decreasing ice cover; first the large scale thinning and changing dynamics of the polar sea ice......, and secondly oceanic oil drift in ice affected conditions. Both investigations are made with the coupled ocean - sea ice model HYCOM-CICE at 10 km resolution, which is also used operationally at DMI and allows detailed studies of sea ice build-up, drift and melt. To investigate the sea ice decrease of the last...... and changing dynamics and discuss how they relate to satellite observations. The relation to the upper ocean heat content is also investigated. The decreasing sea ice has opened up for increased ship traffic and oil exploration in the polar oceans. To avoid damage on the pristine Arctic ecosystem...

  15. 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.

  16. Early Student Support to Investigate the Role of Sea Ice-Albedo Feedback in Sea Ice Predictions

    Science.gov (United States)

    2014-09-30

    all its versions employs the Los Alamos National Laboratory ( LANL ) sea ice model, known as CICE. The sea ice in CESM1 has been documented in a...their method so successful and yet a nonlocal relationship exists between sea ice meltponds and the location Report Documentation Page Form ApprovedOMB... LANL , who is the chief developer of CICE. Dr. Hunke is a partner with the sea ice prediction network and has a postdoc working with her to improve CICE

  17. 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.

  18. Forecasting Future Sea Ice Conditions: A Lagrangian Approach

    Science.gov (United States)

    2014-09-30

    that survives the summer melt season in each of the Arctic peripheral seas. The Lagrangian Model is forced with weekly mean satellite-derived sea- ice ...GCM to drive the Lagrangian code and map the regions for the multi-year ice surviving the summer melt in each of the Arctic peripheral seas in todays...1995, Emery et al. 1997, Meier et al. 2000, Tschudi et al. 2010) 3- Assess whether the source region of sea ice melting in peripheral seas in the

  19. Chemical Atmosphere-Snow-Sea Ice Interactions: defining future research in the field, lab and modeling

    Science.gov (United States)

    Frey, Markus

    2015-04-01

    The air-snow-sea ice system plays an important role in the global cycling of nitrogen, halogens, trace metals or carbon, including greenhouse gases (e.g. CO2 air-sea flux), and therefore influences also climate. Its impact on atmospheric composition is illustrated for example by dramatic ozone and mercury depletion events which occur within or close to the sea ice zone (SIZ) mostly during polar spring and are catalysed by halogens released from SIZ ice, snow or aerosol. Recent field campaigns in the high Arctic (e.g. BROMEX, OASIS) and Antarctic (Weddell sea cruises) highlight the importance of snow on sea ice as a chemical reservoir and reactor, even during polar night. However, many processes, participating chemical species and their interactions are still poorly understood and/or lack any representation in current models. Furthermore, recent lab studies provide a lot of detail on the chemical environment and processes but need to be integrated much better to improve our understanding of a rapidly changing natural environment. During a 3-day workshop held in Cambridge/UK in October 2013 more than 60 scientists from 15 countries who work on the physics, chemistry or biology of the atmosphere-snow-sea ice system discussed research status and challenges, which need to be addressed in the near future. In this presentation I will give a summary of the main research questions identified during this workshop as well as ways forward to answer them through a community-based interdisciplinary approach.

  20. The effects of additional black carbon on Arctic sea ice surface albedo: variation with sea ice type and snow cover

    Directory of Open Access Journals (Sweden)

    A. A. Marks

    2013-03-01

    Full Text Available Black carbon in sea ice will decrease sea ice surface albedo through increased absorption of incident solar radiation, exacerbating sea ice melting. Previous literature has reported different albedo responses to additions of black carbon in sea ice and has not considered how a snow cover may mitigate the effect of black carbon in sea ice. Sea ice is predominately snow covered. Visible light absorption and light scattering coefficients are calculated for a typical first year and multi-year sea ice and "dry" and "wet" snow types that suggest black carbon is the dominating absorbing impurity. The albedo response of first year and multi-year sea ice to increasing black carbon, from 1–1024 ng g−1, in a top 5 cm layer of a 155 cm thick sea ice was calculated using the radiative transfer model: TUV-snow. Sea ice albedo is surprisingly unresponsive to black carbon additions up to 100 ng g−1 with a decrease in albedo to 98.7% of the original albedo value due to an addition of 8 ng g−1 of black carbon in first year sea ice compared to an albedo decrease to 99.6% for the same black carbon mass ratio increase in multi-year sea ice. The first year sea ice proved more responsive to black carbon additions than the multi-year ice. Comparison with previous modelling of black carbon in sea ice suggests a more scattering sea ice environment will be less responsive to black carbon additions. Snow layers on sea ice may mitigate the effects of black carbon in sea ice. "Wet" and "dry" snow layers of 0.5, 1, 2, 5 and 10 cm were added onto the sea ice surface and the snow surface albedo calculated with the same increase in black carbon in the underlying sea ice. Just a 0.5 cm layer of snow greatly diminishes the effect of black carbon on surface albedo, and a 2–5 cm layer (less than half the e-folding depth of snow is enough to "mask" any change in surface albedo owing to additional black carbon in sea ice, but not thick enough to ignore the underlying sea ice.

  1. 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.

  2. Recent sea-ice reduction and possible causes

    Science.gov (United States)

    Park, Doo-Sun R.

    2016-04-01

    Arctic sea-ice extent has been rapidly declining since the late 20th century. Given the accelerating rate of the sea-ice decline, an ice-free Arctic Ocean is expected to occur within this century. This rapid sea-ice melting is attributable to various Arctic environmental changes, such as increased downward infrared radiation (IR), sea-ice preconditioning, temperate ocean water inflow, and sea-ice export. However, their relative contributions are uncertain. Assessing the relative contributions is essential for improving our prediction of the future state of the Arctic sea ice. Most of the previous research had focused on summer sea ice, which is however sensitive to previous winter sea ice, suggesting that winter sea-ice processes are also important for understanding sea-ice variability and its trend. Here we show, for the Arctic winter of 1979-2011, that a positive trend of downward IR accounts for nearly half of the sea-ice concentration (SIC) decline. Furthermore, we show that the Arctic downward IR increase is driven by horizontal atmospheric water flux into the Arctic, and not by evaporation from the Arctic Ocean. The rest of the SIC decline likely comes from warm ocean.

  3. The influence of sea ice, wind speed and marine mammals on Southern Ocean ambient sound

    Science.gov (United States)

    Menze, Sebastian; Zitterbart, Daniel P.; van Opzeeland, Ilse; Boebel, Olaf

    2017-01-01

    This paper describes the natural variability of ambient sound in the Southern Ocean, an acoustically pristine marine mammal habitat. Over a 3-year period, two autonomous recorders were moored along the Greenwich meridian to collect underwater passive acoustic data. Ambient sound levels were strongly affected by the annual variation of the sea-ice cover, which decouples local wind speed and sound levels during austral winter. With increasing sea-ice concentration, area and thickness, sound levels decreased while the contribution of distant sources increased. Marine mammal sounds formed a substantial part of the overall acoustic environment, comprising calls produced by Antarctic blue whales (Balaenoptera musculus intermedia), fin whales (Balaenoptera physalus), Antarctic minke whales (Balaenoptera bonaerensis) and leopard seals (Hydrurga leptonyx). The combined sound energy of a group or population vocalizing during extended periods contributed species-specific peaks to the ambient sound spectra. The temporal and spatial variation in the contribution of marine mammals to ambient sound suggests annual patterns in migration and behaviour. The Antarctic blue and fin whale contributions were loudest in austral autumn, whereas the Antarctic minke whale contribution was loudest during austral winter and repeatedly showed a diel pattern that coincided with the diel vertical migration of zooplankton.

  4. Iodine emissions from the sea ice of the Weddell Sea

    Directory of Open Access Journals (Sweden)

    H. M. Atkinson

    2012-11-01

    Full Text Available Iodine compounds were measured above, below and within the sea ice of the Weddell Sea during a cruise in 2009, to make progress in elucidating the mechanism of local enhancement and volatilisation of iodine. I2 mixing ratios of up to 12.4 pptv were measured 10 m above the sea ice, and up to 31 pptv was observed above surface snow on the nearby Brunt Ice Shelf – large amounts. Atmospheric IO of up to 7 pptv was measured from the ship, and the average sum of HOI and ICl was 1.9 pptv. These measurements confirm the Weddell Sea as an iodine hotspot. Average atmospheric concentrations of CH3I, C2H5I, CH2ICl, 2-C3H7I, CH2IBr and 1-C3H7I were each 0.2 pptv or less. On the Brunt Ice Shelf, enhanced concentrations of CH3I and C2H5I (up to 0.5 and 1 pptv respectively were observed in firn air, with a diurnal profile that suggests the snow may be a source. In the sea ice brine, iodocarbons concentrations were over 10 times those of the sea water below. The sum of iodide + iodate was depleted in sea ice samples, suggesting some missing iodine chemistry. Flux calculations suggest I2 dominates the iodine atom flux to the atmosphere, but models cannot reconcile the observations and suggest either a missing iodine source or other deficiencies in our understanding of iodine chemistry. The observation of new particle formation, consistent with the model predictions, strongly suggests an iodine source. This combined study of iodine compounds is the first of its kind in this unique region of sea ice rich in biology and rich in iodine chemistry.

  5. Iodine emissions from the sea ice of the Weddell Sea

    Directory of Open Access Journals (Sweden)

    H. M. Atkinson

    2012-05-01

    Full Text Available Iodine compounds were measured above, below and within the sea ice of the Weddell Sea during a cruise in 2009, to elucidate the mechanism of local enhancement and volatilisation of iodine. I2 mixing ratios of up to 12.4 pptv were measured 10 m above the sea ice, and up to 31 pptv was observed above surface snow on the nearby Brunt Ice Shelf – large amounts. Atmospheric IO of up to 7 pptv was measured from the ship, and the average sum of HOI and ICl was 1.9 pptv. These measurements confirm the Weddell Sea as an iodine hotspot. Average atmospheric concentrations of CH3I, C2H5I, CH2ICl, 2-C3H7I, CH2IBr and 1-C3H7I were each 0.2 pptv or less. On the Brunt Ice Shelf, enhanced concentrations of CH3I and C2H5I (up to 0.5 and 1 pptv, respectively were observed in firn air, with a diurnal profile that suggests the snow may be a source. In the sea ice brine, iodocarbons concentrations were over 10 times those of the sea water below. The sum of iodide + iodate was depleted in sea ice samples, suggesting some missing iodine chemistry. Flux calculations suggest I2 dominates the iodine atom flux to the atmosphere, but models cannot reconcile the observations and suggest either a missing iodine source or other deficiencies in our understanding of iodine chemistry. The observation of new particle formation, consistent with the model predictions, strongly suggests an iodine source. This combined study of iodine compounds is the first of its kind in this unique region of sea ice rich in biology and rich in iodine chemistry.

  6. 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

  7. Simulation of the satellite radar altimeter sea ice thickness retrieval uncertainty

    Science.gov (United States)

    Tonboe, R. T.; Pedersen, L. T.; Haas, C.

    2009-07-01

    Although it is well known that radar waves penetrate into snow and sea ice, the exact mechanisms for radar-altimeter scattering and its link to the depth of the effective scattering surface from sea ice are still unknown. Previously proposed mechanisms linked the snow ice interface, i.e. the dominating scattering horizon, directly with the depth of the effective scattering surface. However, simulations using a multilayer radar scattering model show that the effective scattering surface is affected by snow-cover and ice properties. With the coming Cryosat-2 (planned launch 2009) satellite radar altimeter it is proposed that sea ice thickness can be derived by measuring its freeboard. In this study we evaluate the radar altimeter sea ice thickness retrieval uncertainty in terms of floe buoyancy, radar penetration and ice type distribution using both a scattering model and ''Archimedes' principle''. The effect of the snow cover on the floe buoyancy and the radar penetration and on the ice cover spatial and temporal variability is assessed from field campaign measurements in the Arctic and Antarctic. In addition to these well known uncertainties we use high resolution RADARSAT SAR data to simulate errors due to the variability of the effective scattering surface as a result of the sub-footprint spatial backscatter and elevation distribution sometimes called preferential sampling. In particular in areas where ridges represent a significant part of the ice volume (e.g. the Lincoln Sea) the simulated altimeter thickness estimate is lower than the real average footprint thickness. This means that the errors are large, yet manageable if the relevant quantities are known a priori. A discussion of the radar altimeter ice thickness retrieval uncertainties concludes the paper.

  8. Simulation of the satellite radar altimeter sea ice thickness retrieval uncertainty

    Directory of Open Access Journals (Sweden)

    R. T. Tonboe

    2009-07-01

    Full Text Available Although it is well known that radar waves penetrate into snow and sea ice, the exact mechanisms for radar-altimeter scattering and its link to the depth of the effective scattering surface from sea ice are still unknown. Previously proposed mechanisms linked the snow ice interface, i.e. the dominating scattering horizon, directly with the depth of the effective scattering surface. However, simulations using a multilayer radar scattering model show that the effective scattering surface is affected by snow-cover and ice properties. With the coming Cryosat-2 (planned launch 2009 satellite radar altimeter it is proposed that sea ice thickness can be derived by measuring its freeboard. In this study we evaluate the radar altimeter sea ice thickness retrieval uncertainty in terms of floe buoyancy, radar penetration and ice type distribution using both a scattering model and ''Archimedes' principle''. The effect of the snow cover on the floe buoyancy and the radar penetration and on the ice cover spatial and temporal variability is assessed from field campaign measurements in the Arctic and Antarctic. In addition to these well known uncertainties we use high resolution RADARSAT SAR data to simulate errors due to the variability of the effective scattering surface as a result of the sub-footprint spatial backscatter and elevation distribution sometimes called preferential sampling. In particular in areas where ridges represent a significant part of the ice volume (e.g. the Lincoln Sea the simulated altimeter thickness estimate is lower than the real average footprint thickness. This means that the errors are large, yet manageable if the relevant quantities are known a priori. A discussion of the radar altimeter ice thickness retrieval uncertainties concludes the paper.

  9. Ocean circulation: its effects on seasonal sea-ice simulations.

    Science.gov (United States)

    Hibler, W D; Bryan, K

    1984-05-04

    A diagnostic ice-ocean model of the Arctic, Greenland, and Norwegian seas is constructed and used to examine the role of ocean circulation in seasonal sea-ice simulations. The model includes lateral ice motion and three-dimensional ocean circulation. The ocean portion of the model is weakly forced by observed temperature and salinity data. Simulation results show that including modeled ocean circulation in seasonal sea-ice simulations substantially improves the predicted ice drift and ice margin location. Simulations that do not include lateral ocean movment predict a much less realistic ice edge.

  10. 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

  11. Wave-Ice and Air-Ice-Ocean Interaction During the Chukchi Sea Ice Edge Advance

    Science.gov (United States)

    2015-09-30

    Ocean Heat: In the new Arctic summer ice regime, with extended open water periods in areas previously covered with sea ice, ocean heat, received...additional buoy with an 80m temperature chain for monitoring the upper ocean evolution has been built at WHOI to replace the loss of one of the UpTempo...addition was made to the Sea State field program through separate funding to Luc Rainville of APL, who will provide an underway temperature and salinity

  12. Recent wind driven high sea ice export in the Fram Strait contributes to Arctic sea ice decline

    Directory of Open Access Journals (Sweden)

    L. H. Smedsrud

    2011-05-01

    Full Text Available Arctic sea ice area decrease has been visible for two decades, and continues at a steady rate. Apart from melting, the southward drift through Fram Strait is the main loss. We present high resolution sea ice drift across 79° N from 2004 to 2010. The ice drift is based on radar satellite data and correspond well with variability in local geostrophic wind. The underlying current contributes with a constant southward speed close to 5 cm s−1, and drives about 33 % of the ice export. We use geostrophic winds derived from reanalysis data to calculate the Fram Strait ice area export back to 1957, finding that the sea ice area export recently is about 25 % larger than during the 1960's. The increase in ice export occurred mostly during winter and is directly connected to higher southward ice drift velocities, due to stronger geostrophic winds. The increase in ice drift is large enough to counteract a decrease in ice concentration of the exported sea ice. Using storm tracking we link changes in geostrophic winds to more intense Nordic Sea low pressure systems. Annual sea ice export likely has a significant influence on the summer sea ice variability and we find low values in the 60's, the late 80's and 90's, and particularly high values during 2005–2008. The study highlight the possible role of variability in ice export as an explanatory factor for understanding the dramatic loss of Arctic sea ice the last decades.

  13. 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.

  14. 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.

  15. 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.

  16. Sea ice classification using dual polarization SAR data

    Science.gov (United States)

    Huiying, Liu; Huadong, Guo; Lu, Zhang

    2014-03-01

    Sea ice is an indicator of climate change and also a threat to the navigation security of ships. Polarimetric SAR images are useful in the sea ice detection and classification. In this paper, backscattering coefficients and texture features derived from dual polarization SAR images are used for sea ice classification. Firstly, the HH image is recalculated based on the angular dependences of sea ice types. Then the effective gray level co-occurrence matrix (GLCM) texture features are selected for the support vector machine (SVM) classification. In the end, because sea ice concentration can provide a better separation of pancake ice from old ice, it is used to improve the SVM result. This method provides a good classification result, compared with the sea ice chart from CIS.

  17. Thermal Diffusivity Identification of Distributed Parameter Systems to Sea Ice

    Directory of Open Access Journals (Sweden)

    Liqiong Shi

    2013-01-01

    Full Text Available A method of optimal control is presented as a numerical tool for solving the sea ice heat transfer problem governed by a parabolic partial differential equation. Taken the deviation between the calculated ice temperature and the measurements as the performance criterion, an optimal control model of distributed parameter systems with specific constraints of thermal properties of sea ice was proposed to determine the thermal diffusivity of sea ice. Based on sea ice physical processes, the parameterization of the thermal diffusivity was derived through field data. The simulation results illustrated that the identified parameterization of the thermal diffusivity is reasonably effective in sea ice thermodynamics. The direct relation between the thermal diffusivity of sea ice and ice porosity is physically significant and can considerably reduce the computational errors. The successful application of this method also explained that the optimal control model of distributed parameter systems in conjunction with the engineering background has great potential in dealing with practical problems.

  18. Recent contributions of glaciers and ice caps to sea level rise.

    Science.gov (United States)

    Jacob, Thomas; Wahr, John; Pfeffer, W Tad; Swenson, Sean

    2012-02-08

    Glaciers and ice caps (GICs) are important contributors to present-day global mean sea level rise. Most previous global mass balance estimates for GICs rely on extrapolation of sparse mass balance measurements representing only a small fraction of the GIC area, leaving their overall contribution to sea level rise unclear. Here we show that GICs, excluding the Greenland and Antarctic peripheral GICs, lost mass at a rate of 148 ± 30 Gt yr(-1) from January 2003 to December 2010, contributing 0.41 ± 0.08 mm yr(-1) to sea level rise. Our results are based on a global, simultaneous inversion of monthly GRACE-derived satellite gravity fields, from which we calculate the mass change over all ice-covered regions greater in area than 100 km(2). The GIC rate for 2003-2010 is about 30 per cent smaller than the previous mass balance estimate that most closely matches our study period. The high mountains of Asia, in particular, show a mass loss of only 4 ± 20 Gt yr(-1) for 2003-2010, compared with 47-55 Gt yr(-1) in previously published estimates. For completeness, we also estimate that the Greenland and Antarctic ice sheets, including their peripheral GICs, contributed 1.06 ± 0.19 mm yr(-1) to sea level rise over the same time period. The total contribution to sea level rise from all ice-covered regions is thus 1.48 ± 0.26 mm (-1), which agrees well with independent estimates of sea level rise originating from land ice loss and other terrestrial sources.

  19. A network model for electrical transport in sea ice

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, J., E-mail: zhu@math.utah.ed [University of Utah, Department of Mathematics, 155 S 1400 E RM 233, Salt Lake City, UT 84112-0090 (United States); Golden, K.M., E-mail: golden@math.utah.ed [University of Utah, Department of Mathematics, 155 S 1400 E RM 233, Salt Lake City, UT 84112-0090 (United States); Gully, A., E-mail: gully@math.utah.ed [University of Utah, Department of Mathematics, 155 S 1400 E RM 233, Salt Lake City, UT 84112-0090 (United States); Sampson, C., E-mail: christian.sampson@gmail.co [University of Utah, Department of Mathematics, 155 S 1400 E RM 233, Salt Lake City, UT 84112-0090 (United States)

    2010-07-15

    Monitoring the thickness of sea ice is an important tool in assessing the impact of global warming on Earth's polar regions, and most methods of measuring ice thickness depend on detailed knowledge of its electrical properties. We develop a network model for the electrical conductivity of sea ice, which incorporates statistical measurements of the brine microstructure. The numerical simulations are in close agreement with direct measurements we made in Antarctica on the vertical conductivity of first year sea ice.

  20. Ice and AIS: ship speed data and sea ice forecasts in the Baltic Sea

    Directory of Open Access Journals (Sweden)

    U. Löptien

    2014-12-01

    Full Text Available The Baltic Sea is a seasonally ice-covered marginal sea located in a densely populated area in northern Europe. Severe sea ice conditions have the potential to hinder the intense ship traffic considerably. Thus, sea ice fore- and nowcasts are regularly provided by the national weather services. Typically, the forecast comprises several ice properties that are distributed as prognostic variables, but their actual usefulness is difficult to measure, and the ship captains must determine their relative importance and relevance for optimal ship speed and safety ad hoc. The present study provides a more objective approach by comparing the ship speeds, obtained by the automatic identification system (AIS, with the respective forecasted ice conditions. We find that, despite an unavoidable random component, this information is useful to constrain and rate fore- and nowcasts. More precisely, 62–67% of ship speed variations can be explained by the forecasted ice properties when fitting a mixed-effect model. This statistical fit is based on a test region in the Bothnian Sea during the severe winter 2011 and employs 15 to 25 min averages of ship speed.

  1. Role of sea ice in air-sea exchange and its relation to sea fog

    Institute of Scientific and Technical Information of China (English)

    解思梅; 包澄澜; 姜德中; 邹斌

    2001-01-01

    Synchronous or quasi-synchronous stereoscopic sea-ice-air comprehensive observation was conducted during the First China Arctic Expedition in summer of 1999. Based on these data, the role of sea ice in sea-air exchange was studied. The study shows that the kinds, distribution and thickness of sea ice and their variation significantly influence the air-sea heat exchange. In floating ice area, the heat momentum transferred from ocean to atmosphere is in form of latent heat; latent heat flux is closely related to floating ice concentration; if floating ice is less, the heat flux would be larger. Latent heat flux is about 21 23.6 W*m-2, which is greater than sensible heat flux. On ice field or giant floating ice, heat momentum transferred from atmosphere to sea ice or snow surface is in form of sensible heat. In the floating ice area or polynya, sea-air exchange is the most active, and also the most sensible for climate. Also this area is the most important condition for the creation of Arctic vapor fog. The heat exchange of a large-scale vapor fog process of about 500000 km2 on Aug. 21 22,1999 was calculated; the heat momentum transferred from ocean to air was about 14.8×109 kW. There are various kinds of sea fog, radiation fog, vapor fog and advection fog, forming in the Arctic Ocean in summer. One important cause is the existence of sea ice and its resultant complexity of both underlying surface and sea-air exchange.

  2. 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.

  3. Evidence for middle Eocene Arctic sea ice from diatoms and ice-rafted debris.

    Science.gov (United States)

    Stickley, Catherine E; St John, Kristen; Koç, Nalân; Jordan, Richard W; Passchier, Sandra; Pearce, Richard B; Kearns, Lance E

    2009-07-16

    Oceanic sediments from long cores drilled on the Lomonosov ridge, in the central Arctic, contain ice-rafted debris (IRD) back to the middle Eocene epoch, prompting recent suggestions that ice appeared in the Arctic about 46 million years (Myr) ago. However, because IRD can be transported by icebergs (derived from land-based ice) and also by sea ice, IRD records are restricted to providing a history of general ice-rafting only. It is critical to differentiate sea ice from glacial (land-based) ice as climate feedback mechanisms vary and global impacts differ between these systems: sea ice directly affects ocean-atmosphere exchanges, whereas land-based ice affects sea level and consequently ocean acidity. An earlier report assumed that sea ice was prevalent in the middle Eocene Arctic on the basis of IRD, and although somewhat preliminary supportive evidence exists, these data are neither comprehensive nor quantified. Here we show the presence of middle Eocene Arctic sea ice from an extraordinary abundance of a group of sea-ice-dependent fossil diatoms (Synedropsis spp.). Analysis of quartz grain textural characteristics further supports sea ice as the dominant transporter of IRD at this time. Together with new information on cosmopolitan diatoms and existing IRD records, our data strongly suggest a two-phase establishment of sea ice: initial episodic formation in marginal shelf areas approximately 47.5 Myr ago, followed approximately 0.5 Myr later by the onset of seasonally paced sea-ice formation in offshore areas of the central Arctic. Our data establish a 2-Myr record of sea ice, documenting the transition from a warm, ice-free environment to one dominated by winter sea ice at the start of the middle Eocene climatic cooling phase.

  4. 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.

  5. Mechanical sea-ice strength parameterized as a function of ice temperature

    Science.gov (United States)

    Hata, Yukie; Tremblay, Bruno

    2016-04-01

    Mechanical sea-ice strength is key for a better simulation of the timing of landlock ice onset and break-up in the Canadian Arctic Archipelago (CAA). We estimate the mechanical strength of sea ice in the CAA by analyzing the position record measured by the several buoys deployed in the CAA between 2008 and 2013, and wind data from the Canadian Meteorological Centre's Global Deterministic Prediction System (CMC_GDPS) REforecasts (CGRF). First, we calculate the total force acting on the ice using the wind data. Next, we estimate upper (lower) bounds on the sea-ice strength by identifying cases when the sea ice deforms (does not deform) under the action of a given total force. Results from this analysis show that the ice strength of landlock sea ice in the CAA is approximately 40 kN/m on the landfast ice onset (in ice growth season). Additionally, it becomes approximately 10 kN/m on the landfast ice break-up (in melting season). The ice strength decreases with ice temperature increase, which is in accord with results from Johnston [2006]. We also include this new parametrization of sea-ice strength as a function of ice temperature in a coupled slab ocean sea ice model. The results from the model with and without the new parametrization are compared with the buoy data from the International Arctic Buoy Program (IABP).

  6. 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...

  7. Air-sea carbon fluxes and their controlling factors in the Prydz Bay in the Antarctic

    Institute of Scientific and Technical Information of China (English)

    GAO Zhongyong; CHEN Liqi; GAO Yuan

    2008-01-01

    The Prydz Bay in the Antarctic is an important area in the Southern Ocean due to its unique geographic feature. It plays an important role in the carbon cycle in the Southern Ocean. To investigate the distributions of carbon dioxide in the atmosphere and surface sea-water and its air-sea exchange rates in this region, the Chinese National Antarctic Research Expedition (CHINARE) had set up sev-eral sections in the Prydz Bay. Here we present the results from the CHINARE--XVI cruises were presented onboard R/V Xuelong from November 1999 to April 2000 and the main driving forces were discussed controlling the distributions of partial pressure of car-bon dioxide. According to the partial pressure of carbon dioxide distributions, the Prydz Bay can be divided into the inside and out-side regions. The partial pressure of carbon dioxide was low in the inside region but higher in the outside region during the measure-ment period. This distribution had a good negative correlation with the concentrations of chlorophyll-a in general, suggesting that the partial pressure of carbon dioxide was substantially affected by biological production. The results also indicate that the biological pro-duction is most likely the main driving force in the marginal ice zone in the Southern Ocean in summer. However, in the Antarctic divergence sector of the Prydz Bay (about 64°S), the hydrological processes become the controlling factor as the sea surface partialp ressure of carbon dioxide is much higher than the atmospheric one due to the upwelling of the high DIC CDW, and this made the outside of Prydz Bay a source of carbon dioxide. On the basis of the calculations, the CO2 flux in January (austral summer) was 3.23 mmol/(m2·d) in the inner part of Prydz Bay, I.e.,a sink of atmospheric CO2,and was 0.62 mmol/(m2·d) in the outside part of the bay, a weak source of atmospheric CO2.The average air-sea flux of CO2 in the Prydz Bay was 2.50 mmol/(m2·d).

  8. 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.

  9. Multifractals, random walks and Arctic sea ice

    Science.gov (United States)

    Agarwal, Sahil; Wettlaufer, John

    We examine the long-term correlations and multifractal properties of daily satellite retrievals of Arctic sea ice albedo, extent, and ice velocity for decadal periods. The approach harnesses a recent development called Multifractal Temporally Weighted Detrended Fluctuation Analysis (MF-TWDFA), which exploits the intuition that points closer in time are more likely to be related than distant points. In both data sets we extract multiple crossover times, as characterized by generalized Hurst exponents, ranging from synoptic to decadal. The method goes beyond treatments that assume a single decay scale process, such as a first-order autoregression, which cannot be justifiably fit to these observations. The ice extent data exhibits white noise behavior from seasonal to bi-seasonal time scales, whereas the clear fingerprints of the short (weather) and long (~ 7 and 9 year) time scales remain, the latter associated with the recent decay in the ice cover. Thus, long term persistence is reentrant beyond the seasonal scale and it is not possible to distinguish whether a given ice extent minimum/maximum will be followed by a minimum/maximum that is larger or smaller in magnitude. The ice velocity data show long term persistence in auto covariance. NASA Grant NNH13ZDA001N-CRYO and Swedish Research Council Grant No. 638-2013-9243.

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

    Science.gov (United States)

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

    2016-09-01

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

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

    Science.gov (United States)

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

    2016-09-01

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

  12. Operationally Merged Satellite Visible/IR and Passive Microwave Sea Ice Information for Improved Sea Ice Forecasts and Ship Routing

    Science.gov (United States)

    2015-09-30

    contrast between ice and water becomes small, rendering the extraction of sea ice concentration impossible for IR data; however, IR is usable during...are often at their melting temperatures, causing the temperature contrast between ice and water to become small and rendering the extraction of sea...those data and make them available to NRL/SSC. New satellite algorithms will be developed to integrate passive microwave and Vis/NIR/IR sea ice

  13. Canadian Arctic sea ice reconstructed from bromine in the Greenland NEEM ice core

    Science.gov (United States)

    Spolaor, Andrea; Vallelonga, Paul; Turetta, Clara; Maffezzoli, Niccolò; Cozzi, Giulio; Gabrieli, Jacopo; Barbante, Carlo; Goto-Azuma, Kumiko; Saiz-Lopez, Alfonso; Cuevas, Carlos A.; Dahl-Jensen, Dorthe

    2016-09-01

    Reconstructing the past variability of Arctic sea ice provides an essential context for recent multi-year sea ice decline, although few quantitative reconstructions cover the Holocene period prior to the earliest historical records 1,200 years ago. Photochemical recycling of bromine is observed over first-year, or seasonal, sea ice in so-called “bromine explosions” and we employ a 1-D chemistry transport model to quantify processes of bromine enrichment over first-year sea ice and depositional transport over multi-year sea ice and land ice. We report bromine enrichment in the Northwest Greenland Eemian NEEM ice core since the end of the Eemian interglacial 120,000 years ago, finding the maximum extension of first-year sea ice occurred approximately 9,000 years ago during the Holocene climate optimum, when Greenland temperatures were 2 to 3 °C above present values. First-year sea ice extent was lowest during the glacial stadials suggesting complete coverage of the Arctic Ocean by multi-year sea ice. These findings demonstrate a clear relationship between temperature and first-year sea ice extent in the Arctic and suggest multi-year sea ice will continue to decline as polar amplification drives Arctic temperatures beyond the 2 °C global average warming target of the recent COP21 Paris climate agreement.

  14. Canadian Arctic sea ice reconstructed from bromine in the Greenland NEEM ice core.

    Science.gov (United States)

    Spolaor, Andrea; Vallelonga, Paul; Turetta, Clara; Maffezzoli, Niccolò; Cozzi, Giulio; Gabrieli, Jacopo; Barbante, Carlo; Goto-Azuma, Kumiko; Saiz-Lopez, Alfonso; Cuevas, Carlos A; Dahl-Jensen, Dorthe

    2016-09-21

    Reconstructing the past variability of Arctic sea ice provides an essential context for recent multi-year sea ice decline, although few quantitative reconstructions cover the Holocene period prior to the earliest historical records 1,200 years ago. Photochemical recycling of bromine is observed over first-year, or seasonal, sea ice in so-called "bromine explosions" and we employ a 1-D chemistry transport model to quantify processes of bromine enrichment over first-year sea ice and depositional transport over multi-year sea ice and land ice. We report bromine enrichment in the Northwest Greenland Eemian NEEM ice core since the end of the Eemian interglacial 120,000 years ago, finding the maximum extension of first-year sea ice occurred approximately 9,000 years ago during the Holocene climate optimum, when Greenland temperatures were 2 to 3 °C above present values. First-year sea ice extent was lowest during the glacial stadials suggesting complete coverage of the Arctic Ocean by multi-year sea ice. These findings demonstrate a clear relationship between temperature and first-year sea ice extent in the Arctic and suggest multi-year sea ice will continue to decline as polar amplification drives Arctic temperatures beyond the 2 °C global average warming target of the recent COP21 Paris climate agreement.

  15. Canadian Arctic sea ice reconstructed from bromine in the Greenland NEEM ice core

    Science.gov (United States)

    Spolaor, Andrea; Vallelonga, Paul; Turetta, Clara; Maffezzoli, Niccolò; Cozzi, Giulio; Gabrieli, Jacopo; Barbante, Carlo; Goto-Azuma, Kumiko; Saiz-Lopez, Alfonso; Cuevas, Carlos A.; Dahl-Jensen, Dorthe

    2016-01-01

    Reconstructing the past variability of Arctic sea ice provides an essential context for recent multi-year sea ice decline, although few quantitative reconstructions cover the Holocene period prior to the earliest historical records 1,200 years ago. Photochemical recycling of bromine is observed over first-year, or seasonal, sea ice in so-called “bromine explosions” and we employ a 1-D chemistry transport model to quantify processes of bromine enrichment over first-year sea ice and depositional transport over multi-year sea ice and land ice. We report bromine enrichment in the Northwest Greenland Eemian NEEM ice core since the end of the Eemian interglacial 120,000 years ago, finding the maximum extension of first-year sea ice occurred approximately 9,000 years ago during the Holocene climate optimum, when Greenland temperatures were 2 to 3 °C above present values. First-year sea ice extent was lowest during the glacial stadials suggesting complete coverage of the Arctic Ocean by multi-year sea ice. These findings demonstrate a clear relationship between temperature and first-year sea ice extent in the Arctic and suggest multi-year sea ice will continue to decline as polar amplification drives Arctic temperatures beyond the 2 °C global average warming target of the recent COP21 Paris climate agreement. PMID:27650478

  16. Albedo parametrization and reversibility of sea ice decay

    OpenAIRE

    M. Müller-Stoffels; R. Wackerbauer

    2012-01-01

    The Arctic's sea ice cover has been receding rapidly in recent years, and global climate models typically predict a further decline over the next century. It is an open question whether a possible loss of Arctic sea ice is reversible. We study the stability of Arctic model sea ice in a conceptual, two-dimensional energy-based regular network model of the ice-ocean layer that considers ARM's longwave radiative budget data and SHEBA albedo measurements. Seasonal ice cover, perennial ice and per...

  17. Knowledge-based sea ice classification by polarimetric SAR

    DEFF Research Database (Denmark)

    Skriver, Henning; Dierking, Wolfgang

    2004-01-01

    Polarimetric SAR images acquired at C- and L-band over sea ice in the Greenland Sea, Baltic Sea, and Beaufort Sea have been analysed with respect to their potential for ice type classification. The polarimetric data were gathered by the Danish EMISAR and the US AIRSAR which both are airborne...... systems. A hierarchical classification scheme was chosen for sea ice because our knowledge about magnitudes, variations, and dependences of sea ice signatures can be directly considered. The optimal sequence of classification rules and the rules themselves depend on the ice conditions/regimes. The use...... of the polarimetric phase information improves the classification only in the case of thin ice types but