WorldWideScience

Sample records for antarctic sea ice

  1. Structural Uncertainty in Antarctic sea ice simulations

    Science.gov (United States)

    Schneider, D. P.

    2016-12-01

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

  2. The Influence of Platelet Ice and Snow on Antarctic Land-fast Sea Ice

    OpenAIRE

    Hoppmann, Mario; Nicolaus, Marcel

    2011-01-01

    Sea ice fastened to coasts, icebergs and ice shelves is of crucial importance for climate- and ecosystems. Near Antarctic ice shelves, this land-fast sea ice exhibits two unique characteristics that distinguish it from most other sea ice: 1) Ice platelets form and grow in super-cooled water, which originates from ice shelf cavities. The crystals accumulate beneath the solid sea-ice cover and are incorporated into the sea-ice fabric, contributing between 10 and 60% to the mas...

  3. 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.)

  4. Sudden increase in Antarctic sea ice: Fact or artifact?

    Science.gov (United States)

    Screen, J. A.

    2011-07-01

    Three sea ice data sets commonly used for climate research display a large and abrupt increase in Antarctic sea ice area (SIA) in recent years. This unprecedented change of SIA is diagnosed to be primarily caused by an apparent sudden increase in sea ice concentrations within the ice pack, especially in the area of the most-concentrated ice (greater than 95% concentration). A series of alternative satellite-derived records do not display any abnormal sudden SIA changes, but do reveal substantial discrepancies between different satellite sensors and sea ice algorithms. Sea ice concentrations in the central ice pack and SIA values derived from the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSRE) are consistently greater than those derived from the Special Sensor Microwave Imager (SSMI). A switch in source data from the SSMI to AMSRE in mid-2009 explains most of the SIA increase in all three affected data sets. If uncorrected for, the discontinuity artificially exaggerates the winter Antarctic SIA increase (1979-2010) by more than a factor of 2 and the spring trend by almost a factor of 4. The discontinuity has a weaker influence on the summer and autumn SIA trends, on calculations of Antarctic sea ice extent, and in the Arctic.

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

    Science.gov (United States)

    Bitz, C. M.

    2016-12-01

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

  6. Proteorhodopsin-bearing bacteria in Antarctic sea ice.

    Science.gov (United States)

    Koh, Eileen Y; Atamna-Ismaeel, Nof; Martin, Andrew; Cowie, Rebecca O M; Beja, Oded; Davy, Simon K; Maas, Elizabeth W; Ryan, Ken G

    2010-09-01

    Proteorhodopsins (PRs) are widespread bacterial integral membrane proteins that function as light-driven proton pumps. Antarctic sea ice supports a complex community of autotrophic algae, heterotrophic bacteria, viruses, and protists that are an important food source for higher trophic levels in ice-covered regions of the Southern Ocean. Here, we present the first report of PR-bearing bacteria, both dormant and active, in Antarctic sea ice from a series of sites in the Ross Sea using gene-specific primers. Positive PR sequences were generated from genomic DNA at all depths in sea ice, and these sequences aligned with the classes Alphaproteobacteria, Gammaproteobacteria, and Flavobacteria. The sequences showed some similarity to previously reported PR sequences, although most of the sequences were generally distinct. Positive PR sequences were also observed from cDNA reverse transcribed from RNA isolated from sea ice samples. This finding indicates that these sequences were generated from metabolically active cells and suggests that the PR gene is functional within sea ice. Both blue-absorbing and green-absorbing forms of PRs were detected, and only a limited number of blue-absorbing forms were found and were in the midsection of the sea ice profile in this study. Questions still remain regarding the protein's ecological functions, and ultimately, field experiments will be needed to establish the ecological and functional role of PRs in the sea ice ecosystem.

  7. 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.

  8. Distribution of dissolved and particulate metals in Antarctic sea ice

    NARCIS (Netherlands)

    Lannuzel, D.; Bowie, A.R.; van der Merwe, P.C.; Townsend, A.T.; Schoemann, V.

    2011-01-01

    Samples were collected in East Antarctic sea ice in late winter/early austral spring 2007 to assess the distributions of Al, Cr, Mn, Cu, Zn, Mo. Cd and Ba. Total dissolved (<02 mu m) and particulate (>0.2 mu m) concentrations were measured by Inductively Coupled Plasma-Sector Field Mass Spectrometry

  9. The role of feedbacks in Antarctic sea ice change

    Science.gov (United States)

    Feltham, D. L.; Frew, R. C.; Holland, P.

    2017-12-01

    The changes in Antarctic sea ice over the last thirty years have a strong seasonal dependence, and the way these changes grow in spring and decay in autumn suggests that feedbacks are strongly involved. The changes may ultimately be caused by atmospheric warming, the winds, snowfall changes, etc., but we cannot understand these forcings without first untangling the feedbacks. A highly simplified coupled sea ice -mixed layer model has been developed to investigate the importance of feedbacks on the evolution of sea ice in two contrasting regions in the Southern Ocean; the Amundsen Sea where sea ice extent has been decreasing, and the Weddell Sea where it has been expanding. The change in mixed layer depth in response to changes in the atmosphere to ocean energy flux is implicit in a strong negative feedback on ice cover changes in the Amundsen Sea, with atmospheric cooling leading to a deeper mixed layer resulting in greater entrainment of warm Circumpolar Deep Water, causing increased basal melting of sea ice. This strong negative feedback produces counter intuitive responses to changes in forcings in the Amundsen Sea. This feedback is absent in the Weddell due to the complete destratification and strong water column cooling that occurs each winter in simulations. The impact of other feedbacks, including the albedo feedback, changes in insulation due to ice thickness and changes in the freezing temperature of the mixed layer, were found to be of secondary importance compared to changes in the mixed layer depth.

  10. Antarctic sea ice losses drive gains in benthic carbon drawdown.

    Science.gov (United States)

    Barnes, D K A

    2015-09-21

    Climate forcing of sea-ice losses from the Arctic and West Antarctic are blueing the poles. These losses are accelerating, reducing Earth's albedo and increasing heat absorption. Subarctic forest (area expansion and increased growth) and ice-shelf losses (resulting in new phytoplankton blooms which are eaten by benthos) are the only significant described negative feedbacks acting to counteract the effects of increasing CO2 on a warming planet, together accounting for uptake of ∼10(7) tonnes of carbon per year. Most sea-ice loss to date has occurred over polar continental shelves, which are richly, but patchily, colonised by benthic animals. Most polar benthos feeds on microscopic algae (phytoplankton), which has shown increased blooms coincident with sea-ice losses. Here, growth responses of Antarctic shelf benthos to sea-ice losses and phytoplankton increases were investigated. Analysis of two decades of benthic collections showed strong increases in annual production of shelf seabed carbon in West Antarctic bryozoans. These were calculated to have nearly doubled to >2x10(5) tonnes of carbon per year since the 1980s. Annual production of bryozoans is median within wider Antarctic benthos, so upscaling to include other benthos (combined study species typically constitute ∼3% benthic biomass) suggests an increased drawdown of ∼2.9x10(6) tonnes of carbon per year. This drawdown could become sequestration because polar continental shelves are typically deeper than most modern iceberg scouring, bacterial breakdown rates are slow, and benthos is easily buried. To date, most sea-ice losses have been Arctic, so, if hyperboreal benthos shows a similar increase in drawdown, polar continental shelves would represent Earth's largest negative feedback to climate change. Copyright © 2015 Elsevier Ltd. All rights reserved.

  11. Do pelagic grazers benefit from sea ice? Insights from the Antarctic sea ice proxy IPSO25

    Science.gov (United States)

    Schmidt, Katrin; Brown, Thomas A.; Belt, Simon T.; Ireland, Louise C.; Taylor, Kyle W. R.; Thorpe, Sally E.; Ward, Peter; Atkinson, Angus

    2018-04-01

    Sea ice affects primary production in polar regions in multiple ways. It can dampen water column productivity by reducing light or nutrient supply, provide a habitat for ice algae and condition the marginal ice zone (MIZ) for phytoplankton blooms on its seasonal retreat. The relative importance of three different carbon sources (sea ice derived, sea ice conditioned, non-sea-ice associated) for the polar food web is not well understood, partly due to the lack of methods that enable their unambiguous distinction. Here we analysed two highly branched isoprenoid (HBI) biomarkers to trace sea-ice-derived and sea-ice-conditioned carbon in Antarctic krill (Euphausia superba) and relate their concentrations to the grazers' body reserves, growth and recruitment. During our sampling in January-February 2003, the proxy for sea ice diatoms (a di-unsaturated HBI termed IPSO25, δ13C = -12.5 ± 3.3 ‰) occurred in open waters of the western Scotia Sea, where seasonal ice retreat was slow. In suspended matter from surface waters, IPSO25 was present at a few stations close to the ice edge, but in krill the marker was widespread. Even at stations that had been ice-free for several weeks, IPSO25 was found in krill stomachs, suggesting that they gathered the ice-derived algae from below the upper mixed layer. Peak abundances of the proxy for MIZ diatoms (a tri-unsaturated HBI termed HBI III, δ13C = -42.2 ± 2.4 ‰) occurred in regions of fast sea ice retreat and persistent salinity-driven stratification in the eastern Scotia Sea. Krill sampled in the area defined by the ice edge bloom likewise contained high amounts of HBI III. As indicators for the grazer's performance we used the mass-length ratio, size of digestive gland and growth rate for krill, and recruitment for the biomass-dominant calanoid copepods Calanoides acutus and Calanus propinquus. These indices consistently point to blooms in the MIZ as an important feeding ground for pelagic grazers. Even though ice

  12. Atmospheric influences on the anomalous 2016 Antarctic sea ice decay

    Science.gov (United States)

    Schlosser, Elisabeth; Haumann, F. Alexander; Raphael, Marilyn N.

    2018-03-01

    In contrast to the Arctic, where total sea ice extent (SIE) has been decreasing for the last three decades, Antarctic SIE has shown a small, but significant, increase during the same time period. However, in 2016, an unusually early onset of the melt season was observed; the maximum Antarctic SIE was already reached as early as August rather than the end of September, and was followed by a rapid decrease. The decay was particularly strong in November, when Antarctic SIE exhibited a negative anomaly (compared to the 1979-2015 average) of approximately 2 million km2. ECMWF Interim reanalysis data showed that the early onset of the melt and the rapid decrease in sea ice area (SIA) and SIE were associated with atmospheric flow patterns related to a positive zonal wave number three (ZW3) index, i.e., synoptic situations leading to strong meridional flow and anomalously strong southward heat advection in the regions of strongest sea ice decline. A persistently positive ZW3 index from May to August suggests that SIE decrease was preconditioned by SIA decrease. In particular, in the first third of November northerly flow conditions in the Weddell Sea and the Western Pacific triggered accelerated sea ice decay, which was continued in the following weeks due to positive feedback effects, leading to the unusually low November SIE. In 2016, the monthly mean Southern Annular Mode (SAM) index reached its second lowest November value since the beginning of the satellite observations. A better spatial and temporal coverage of reliable ice thickness data is needed to assess the change in ice mass rather than ice area.

  13. 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.

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

    Directory of Open Access Journals (Sweden)

    R. S. Humphries

    2016-02-01

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

  15. Atmospheric Influences on the Anomalous 2016 Antarctic Sea Ice Decay

    Science.gov (United States)

    Raphael, M. N.; Schlosser, E.; Haumann, A.

    2017-12-01

    Over the past three decades, a small but significant increase in sea ice extent (SIE) has been observed in the Antarctic. However, in 2016 there was a surprisingly early onset of the melt season. The maximum Antarctic SIE was reached in August rather than end of September, and was followed by a rapid decrease. The decline of the sea ice area (SIA) started even earlier, in July. The retreat of the ice was particularly large in November where Antarctic SIE exhibited a negative anomaly (compared to the 1981-2010 average) of almost 2 Mio. km2, which, combined with reduced Arctic SIE, led to a distinct minimum in global SIE. And, satellite observations show that from November 2016 to February 2017, the daily Antarctic SIE has been at record low levels. We use sea level pressure and geopotential height data from the ECMWF- Interim reanalysis, in conjunction with sea ice data obtained from the National Snow and Ice Data Centre (NSIDC), to investigate possible atmospheric influences on the observed phenomena. Indications are that both the onset of the melt in July and the rapid decrease in SIA and SIE in November were triggered by atmospheric flow patterns related to a positive Zonal Wave 3 index, i.e. synoptic situations leading to strong meridional flow. Additionally the Southern Annular Mode (SAM) index reached its second lowest November value since the beginning of the satellite observations. It is likely that the SIE decrease was preconditioned by SIA decrease. Positive feedback effects led to accelerated melt and consequently to the extraordinary low November SIE.

  16. Antarctic sea ice variability using NASA team algorithm data

    Science.gov (United States)

    Barreira, S.; Compagnucci, R.

    Sea ice is an important, highly variable feature of the Earth's surface, both reflecting and influencing climatic conditions. Sea ice covers approximately 7 percent of the world oceans, significantly reduces the amount of solar radiation absorbed at the Earth's surface, greatly restricts the transfer of heat from the ocean to the atmosphere in winter, and influences global atmospheric and oceanic circulation. In this paper, monthly through interannual variability of the sea ice between 0 and 120W is analysed for the 22-year period 1979 through 2000. The monthly Polar Gridded Sea Ice Concentrations data set derived from the Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) and the Defense Meteorological Satellite Program's (DMSP) DMSP-F8, F11 and F13, Special Sensor Microwave/Imager (SSM/I) generated by NASA team algorithm were used. This data were acquired from the National Snow and Ice Data Center (NSIDC) and are gridded on the SSM/I polar stereographic grid (25 x 25 km) provided in two-byte integer format. Principal Components Analysis in T-Mode was performed on pre-processed sea ice data (anomalies from which have been removed continent and perennial open water), in order to investigate which are the main space patterns, when do they present and how they are coupled to different atmospheric variables. This analysis provide 12 patterns (6 in direct mode and 6 in inverse mode) that represent the most important spatial features that dominate sea ice variability in the Weddell, Amudsen and Bellinghausen Seas. These 12 patterns, or their combinations, describe completely the behavior of the 264 month means sea ice concentration anomalies of the record we used of the selected Antarctic region.

  17. Do pelagic grazers benefit from sea ice? Insights from the Antarctic sea ice proxy IPSO25

    Directory of Open Access Journals (Sweden)

    K. Schmidt

    2018-04-01

    Full Text Available Sea ice affects primary production in polar regions in multiple ways. It can dampen water column productivity by reducing light or nutrient supply, provide a habitat for ice algae and condition the marginal ice zone (MIZ for phytoplankton blooms on its seasonal retreat. The relative importance of three different carbon sources (sea ice derived, sea ice conditioned, non-sea-ice associated for the polar food web is not well understood, partly due to the lack of methods that enable their unambiguous distinction. Here we analysed two highly branched isoprenoid (HBI biomarkers to trace sea-ice-derived and sea-ice-conditioned carbon in Antarctic krill (Euphausia superba and relate their concentrations to the grazers' body reserves, growth and recruitment. During our sampling in January–February 2003, the proxy for sea ice diatoms (a di-unsaturated HBI termed IPSO25, δ13C  =  −12.5 ± 3.3 ‰ occurred in open waters of the western Scotia Sea, where seasonal ice retreat was slow. In suspended matter from surface waters, IPSO25 was present at a few stations close to the ice edge, but in krill the marker was widespread. Even at stations that had been ice-free for several weeks, IPSO25 was found in krill stomachs, suggesting that they gathered the ice-derived algae from below the upper mixed layer. Peak abundances of the proxy for MIZ diatoms (a tri-unsaturated HBI termed HBI III, δ13C  =  −42.2 ± 2.4 ‰ occurred in regions of fast sea ice retreat and persistent salinity-driven stratification in the eastern Scotia Sea. Krill sampled in the area defined by the ice edge bloom likewise contained high amounts of HBI III. As indicators for the grazer's performance we used the mass–length ratio, size of digestive gland and growth rate for krill, and recruitment for the biomass-dominant calanoid copepods Calanoides acutus and Calanus propinquus. These indices consistently point to blooms in the MIZ as an important feeding

  18. Analysis on variability and trend in Antarctic sea ice albedo between 1983 and 2009

    Science.gov (United States)

    Seo, Minji; Kim, Hyun-cheol; Choi, Sungwon; Lee, Kyeong-sang; Han, Kyung-soo

    2017-04-01

    Sea ice is key parameter in order to understand the cryosphere climate change. Several studies indicate the different trend of sea ice between Antarctica and Arctic. Albedo is important factor for understanding the energy budget and factors for observing of environment changes of Cryosphere such as South Pole, due to it mainly covered by ice and snow with high albedo value. In this study, we analyzed variability and trend of long-term sea ice albedo data to understand the changes of sea ice over Antarctica. In addiction, sea ice albedo researched the relationship with Antarctic oscillation in order to determine the atmospheric influence. We used the sea ice albedo data at The Satellite Application Facility on Climate Monitoring and Antarctic Oscillation data at NOAA Climate Prediction Center (CPC). We analyzed the annual trend in albedo using linear regression to understand the spatial and temporal tendency. Antarctic sea ice albedo has two spatial trend. Weddle sea / Ross sea sections represent a positive trend (0.26% ˜ 0.04% yr-1) and Bellingshausen Amundsen sea represents a negative trend (- 0.14 ˜ -0.25%yr-1). Moreover, we performed the correlation analysis between albedo and Antarctic oscillation. As a results, negative area indicate correlation coefficient of - 0.3639 and positive area indicates correlation coefficient of - 0.0741. Theses results sea ice albedo has regional trend according to ocean. Decreasing sea ice trend has negative relationship with Antarctic oscillation, its represent a possibility that sea ice influence atmospheric factor.

  19. Contrasting Arctic and Antarctic atmospheric responses to future sea-ice loss

    Science.gov (United States)

    England, M.; Polvani, L. M.; Sun, L.

    2017-12-01

    By the end of this century, the annual mean Antarctic sea ice area is projected to decline by over a third, an amount similar to that in the Arctic, but the effect of Antarctic sea ice loss on the atmosphere remains largely unexplored. Using the Community Earth Systems Model (CESM) Whole Atmosphere Coupled Climate Model (WACCM), we investigate the effect of future Antarctic sea ice loss, and contrast it with its Arctic counterpart. This is accomplished by analyzing integrations of the model with historic and future sea ice levels, using the RCP8.5 scenario. This allows us to disentangle the effect of future sea ice loss on the atmosphere from other aspects of the coupled system. We find that both Antarctic and Arctic sea ice loss act to shift the tropospheric jet equatorwards, counteracting the poleward shift due to increases in greenhouse gases. Although the total forcing to the atmosphere is similar in both hemispheres, the response to Arctic sea ice loss is larger in amplitude and but more seasonally varying, while the response in the Antarctic persists throughout the year but with a smaller amplitude. Furthermore, the atmospheric temperature response over the Antarctic is trapped closer to the surface than in the Arctic, and perhaps surprisingly, we find that the surface temperature response to Antarctic sea ice loss is unable to penetrate the Antarctic continent.

  20. Diatom-induced silicon isotopic fractionation in Antarctic sea ice

    Science.gov (United States)

    Francois, F.; Damien, C.; Jean-Louis, T.; Anthony, W.; Luc, A.

    2006-12-01

    We measured silicon-isotopic composition of dissolved silicon and biogenic silica collected by sequential melting from spring 2003 Antarctic pack ice (Australian sector). Sea ice is a key ecosystem in the Southern Ocean and its melting in spring has been often thought to have a seeding effect for the surface waters, triggering blooms in the mixed layer. This work is the first investigation of the silicon isotopes' proxy in sea ice and allows to estimate the activity of sea-ice diatoms in the different brine structures and the influence of sea- ice diatoms on the spring ice edge blooms. The relative use of the dissolved silicon pool by sea-ice diatoms is usually assessed by calculating nutrient:salinity ratios in the brines. However such an approach is biased by difficulties in evaluating the initial nutrient concentrations in the different brines structures, and by the impossibility to account for late sporadic nutrient replenishments. The silicon-isotopic composition of biogenic silica is a convenient alternative since it integrates an average Si utilization on all generations of diatoms. Measurements were performed on a MC-ICP-MS, in dry plasma mode using external Mg doping. Results are expressed as delta29Si relative to the NBS28 standard. From three sea ice cores with contrasted physico-chemical characteristics, we report significant isotopic fractionations linked to the diatoms activity, with distinct silicon biogeochemical dynamics between different brine structure. The diatoms in snow ice and in brine pockets of frazil or congelation ice have the most positive silicon-isotopic composition (+0.53 to +0.86 p.mil), indicating that they grow in a closed system and use a significant part of the small dissolved silicon pool. In the brine channels and skeletal layer, diatoms display a relatively less positive Si-isotopic composition (+0.41 to +0.70 p.mil), although it is still heavier compared to equilibrium fractionation (+0.38 p.mil). This suggests that they have

  1. Ice matters. Arctic and Antarctic under-ice communities linking sea ice with the pelagic food web

    OpenAIRE

    Flores, Hauke; van Franeker, Jan Andries; Lange, Benjamin; Siegel, Volker; Kruse, Svenja; Hunt, Brian; Pakhomov, E. A.

    2013-01-01

    In both Polar Regions, sea ice environments are undergoing rapid environmental change. Because sea ice constitutes an important habitat for numerous species, as well as an important carbon source during critical periods of the year, these changes impact significantly on ecosystem functioning, biodiversity, species distribution and population sizes, including commercially exploited fish stocks. Species dwelling at the ice-water interface (e.g. Antarctic krill and Arctic cod) play a key role in...

  2. Forecast of Antarctic Sea Ice and Meteorological Fields

    Science.gov (United States)

    Barreira, S.; Orquera, F.

    2017-12-01

    Since 2001, we have been forecasting the climatic fields of the Antarctic sea ice (SI) and surface air temperature, surface pressure and precipitation anomalies for the Southern Hemisphere at the Meteorological Department of the Argentine Naval Hydrographic Service with different techniques that have evolved with the years. Forecast is based on the results of Principal Components Analysis applied to SI series (S-Mode) that gives patterns of temporal series with validity areas (these series are important to determine which areas in Antarctica will have positive or negative SI anomalies based on what happen in the atmosphere) and, on the other hand, to SI fields (T-Mode) that give us the form of the SI fields anomalies based on a classification of 16 patterns. Each T-Mode pattern has unique atmospheric fields associated to them. Therefore, it is possible to forecast whichever atmosphere variable we decide for the Southern Hemisphere. When the forecast is obtained, each pattern has a probability of occurrence and sometimes it is necessary to compose more than one of them to obtain the final result. S-Mode and T-Mode are monthly updated with new data, for that reason the forecasts improved with the increase of cases since 2001. We used the Monthly Polar Gridded Sea Ice Concentrations database derived from satellite information generated by NASA Team algorithm provided monthly by the National Snow and Ice Data Center of USA that begins in November 1978. Recently, we have been experimenting with multilayer Perceptron (neuronal network) with supervised learning and a back-propagation algorithm to improve the forecast. The Perceptron is the most common Artificial Neural Network topology dedicated to image pattern recognition. It was implemented through the use of temperature and pressure anomalies field images that were associated with a the different sea ice anomaly patterns. The variables analyzed included only composites of surface air temperature and pressure anomalies

  3. Roles of wind stress and thermodynamic forcing in recent trends in Antarctic sea ice and Southern Ocean SST: An ocean-sea ice model study

    Science.gov (United States)

    Kusahara, Kazuya; Williams, Guy D.; Massom, Robert; Reid, Phillip; Hasumi, Hiroyasu

    2017-11-01

    In contrast to a strong decrease in Arctic sea ice extent, overall Antarctic sea ice extent has modestly increased since 1979. Several hypotheses have been proposed for the net Antarctic sea ice expansion, including atmosphere/ocean circulation and temperature changes, sea ice-atmospheric-ocean feedback, increased precipitation, and enhanced basal meltwater from ice shelves. Concomitant with this positive trend in Antarctic sea ice, sea surface temperatures (SSTs) over the Southern Ocean south of approximately 45°S have cooled over this period. However, the mechanisms responsible for the Antarctic sea ice expansion and the SST cooling trend remain poorly defined. Here, we conduct comprehensive sensitivity experiments using a coupled ocean-sea ice model with a steady-state ice shelf component in order to investigate the main drivers of recent trends in Antarctic sea ice and SST over the Southern Ocean. The results suggest that Antarctic sea ice expansion is mostly explained by trends in the thermodynamic surface forcing, notably cooling and drying and a reduction in longwave radiation. Similarly, thermodynamic forcing is found to be the main driver of the zonal SST cooling trend. While apparently less influential on sea ice extent and SST, wind stress plays a key role in sea ice motion, thickening coastal sea ice, and thinning and decreasing the concentration of ice in mid-pack regions of the Amundsen-eastern Ross seas and 65-95°E in winter-spring. Furthermore, the model suggests that ocean-ice shelf interaction does not significantly influence the observed trends in Antarctic sea ice coverage and Southern Ocean SST in recent decades.

  4. 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.

  5. Antarctic Circumpolar Current Fronts, Winter Sea Ice and Variability: Topographic Influences

    Science.gov (United States)

    Talley, L. D.

    2017-12-01

    The Antarctic winter sea ice edge is closely associated with the southernmost Antarctic Circumpolar Current (ACC) fronts, which are guided northeastward, with their cold waters, by mid-ocean ridges in the Pacific and Atlantic, and Kerguelen Plateau in the Indian. In the Amundsen/Bellingshausen Seas and along Adelie Land, the southern ACC fronts are free from topographic control, and swing southwards towards Antarctica, carrying warmer waters. This suggests poleward Sverdrup transport due to wind-driven upwelling, distorted by the major topographic ridges. Hydrographic observations show stronger penetration of full-depth ACC water into the Amundsen/ Bellingshausen Seas in 2011 compared with 1992, consistent with decreasing sea ice and increasing ice-shelf melt. Winter sea ice increased where the southern ACC is topographically locked into northeastward pathways. The standing eddy pattern of ACC poleward heat flux, strengthening winds, and decadal winter sea ice changes are consistent with strengthening circulation along the southern side of the ACC.

  6. Observational Evidence of a Hemispheric-wide Ice-ocean Albedo Feedback Effect on Antarctic Sea-ice Decay

    Science.gov (United States)

    Nihashi, Sohey; Cavalieri, Donald J.

    2007-01-01

    The effect of ice-ocean albedo feedback (a kind of ice-albedo feedback) on sea-ice decay is demonstrated over the Antarctic sea-ice zone from an analysis of satellite-derived hemispheric sea ice concentration and European Centre for Medium-Range Weather Forecasts (ERA-40) atmospheric data for the period 1979-2001. Sea ice concentration in December (time of most active melt) correlates better with the meridional component of the wind-forced ice drift (MID) in November (beginning of the melt season) than the MID in December. This 1 month lagged correlation is observed in most of the Antarctic sea-ice covered ocean. Daily time series of ice , concentration show that the ice concentration anomaly increases toward the time of maximum sea-ice melt. These findings can be explained by the following positive feedback effect: once ice concentration decreases (increases) at the beginning of the melt season, solar heating of the upper ocean through the increased (decreased) open water fraction is enhanced (reduced), leading to (suppressing) a further decrease in ice concentration by the oceanic heat. Results obtained fi-om a simple ice-ocean coupled model also support our interpretation of the observational results. This positive feedback mechanism explains in part the large interannual variability of the sea-ice cover in summer.

  7. Improved simulation of Antarctic sea ice due to the radiative effects of falling snow

    Science.gov (United States)

    Li, J.-L. F.; Richardson, Mark; Hong, Yulan; Lee, Wei-Liang; Wang, Yi-Hui; Yu, Jia-Yuh; Fetzer, Eric; Stephens, Graeme; Liu, Yinghui

    2017-08-01

    Southern Ocean sea-ice cover exerts critical control on local albedo and Antarctic precipitation, but simulated Antarctic sea-ice concentration commonly disagrees with observations. Here we show that the radiative effects of precipitating ice (falling snow) contribute substantially to this discrepancy. Many models exclude these radiative effects, so they underestimate both shortwave albedo and downward longwave radiation. Using two simulations with the climate model CESM1, we show that including falling-snow radiative effects improves the simulations relative to cloud properties from CloudSat-CALIPSO, radiation from CERES-EBAF and sea-ice concentration from passive microwave sensors. From 50-70°S, the simulated sea-ice-area bias is reduced by 2.12 × 106 km2 (55%) in winter and by 1.17 × 106 km2 (39%) in summer, mainly because increased wintertime longwave heating restricts sea-ice growth and so reduces summer albedo. Improved Antarctic sea-ice simulations will increase confidence in projected Antarctic sea level contributions and changes in global warming driven by long-term changes in Southern Ocean feedbacks.

  8. Halogen species record Antarctic sea ice extent over glacial–interglacial periods

    Directory of Open Access Journals (Sweden)

    A. Spolaor

    2013-07-01

    Full Text Available Sea ice is an integral part of the earth's climate system because it affects planetary albedo, sea-surface salinity, and the atmosphere–ocean exchange of reactive gases and aerosols. Bromine and iodine chemistry is active at polar sea ice margins with the occurrence of bromine explosions and the biological production of organoiodine from sea ice algae. Satellite measurements demonstrate that concentrations of bromine oxide (BrO and iodine oxide (IO decrease over sea ice toward the Antarctic interior. Here we present speciation measurements of bromine and iodine in the TALDICE (TALos Dome Ice CorE ice core (159°11' E, 72°49' S; 2315 m a.s.l. spanning the last 215 ky. The Talos Dome ice core is located 250 km inland and is sensitive to marine air masses intruding onto the Antarctic Plateau. Talos Dome bromide (Br− is positively correlated with temperature and negatively correlated with sodium (Na. Based on the Br−/Na seawater ratio, bromide is depleted in the ice during glacial periods and enriched during interglacial periods. Total iodine, consisting of iodide (I− and iodate (IO3−, peaks during glacials with lower values during interglacial periods. Although IO3− is considered the most stable iodine species in the atmosphere it was only observed in the TALDICE record during glacial maxima. Sea ice dynamics are arguably the primary driver of halogen fluxes over glacial–interglacial timescales, by altering the distance between the sea ice edge and the Antarctic plateau and by altering the surface area of sea ice available to algal colonization. Based on our results we propose the use of both halogens for examining Antarctic variability of past sea ice extent.

  9. Response of Antarctic sea surface temperature and sea ice to ozone depletion

    Science.gov (United States)

    Ferreira, D.; Gnanadesikan, A.; Kostov, Y.; Marshall, J.; Seviour, W.; Waugh, D.

    2017-12-01

    The influence of the Antarctic ozone hole extends all the way from the stratosphere through the troposphere down to the surface, with clear signatures on surface winds, and SST during summer. In this talk we discuss the impact of these changes on the ocean circulation and sea ice state. We are notably motivated by the observed cooling of the surface Southern Ocean and associated increase in Antarctic sea ice extent since the 1970s. These trends are not reproduced by CMIP5 climate models, and the underlying mechanism at work in nature and the models remain unexplained. Did the ozone hole contribute to the observed trends?Here, we review recent advances toward answering these issues using "abrupt ozone depletion" experiments. The ocean and sea ice response is rather complex, comprising two timescales: a fast ( 1-2y) cooling of the surface ocean and sea ice cover increase, followed by a slower warming trend, which, depending on models, flip the sign of the SST and sea ice responses on decadal timescale. Although the basic mechanism seems robust, comparison across climate models reveal large uncertainties in the timescales and amplitude of the response to the extent that even the sign of the ocean and sea ice response to ozone hole and recovery remains unconstrained. After briefly describing the dynamics and thermodynamics behind the two-timescale response, we will discuss the main sources of uncertainties in the modeled response, namely cloud effects and air-sea heat exchanges, surface wind stress response and ocean eddy transports. Finally, we will consider the implications of our results on the ability of coupled climate models to reproduce observed Southern Ocean changes.

  10. Interaction between Antarctic sea ice and synoptic activity in the circumpolar trough

    Science.gov (United States)

    Schlosser, Elisabeth

    2010-05-01

    Different from conditions in the Arctic, total Antarctic sea ice extent does not show large interannual variability and almost no long-term trend is found. On a regional/monthly scale, however, large differences are observed, depending on winds and oceanic currents, thus on the prevailing synoptic weather situation. At the same time, the sea ice influences atmospheric conditions: presence of sea ice considerably changes the energy exchange between ocean and atmosphere, thus the meridional air temperature gradient, which is usually strongest at the sea ice edge. This leads to high baroclinicity in this area and thus favours cyclogenesis. The position and movement of low pressure systems, in turn, together with the local heat balance, determines sea ice extent and concentration. Divergence and convergence of sea ice also depends on the position of the circumpolar trough relative to the sea ice edge, since its position determines whether the atmospheric flow is predominantly easterly or westerly, which leads to sea ice transport to the southwest or the northeast, respectively. The circumpolar trough is usually situated closer to the coast in spring and autumn and moves north in summer and winter. In this study, meteorological data from the ECMWF ERA-interim reanalysis as well as sea ice extent and concentration derived from passive microwave data (SSMI/SMMR) are used to investigate the interactions between Antarctic sea ice and synoptic activity in the polar ocean. Special consideration is given to the frequency of regional sea ice minima and warm air advection from lower latitudes. A stable synoptic situation with amplified Rossby waves can lead to regional extrema in sea ice extent. An extreme case was observed in the austral summer of 2001/2002 in the Weddell Sea, when continuous northwesterly winds removed the ice from the northwestern part of the Weddell Sea and drove it to the coast of Coats Land, where usually coastal polynyas are observed in summer.

  11. 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.

  12. 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

    2016-02-04

    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.

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

    Directory of Open Access Journals (Sweden)

    C.-Y. Yang

    2016-10-01

    Full Text Available 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.

  14. Organic iodine in Antarctic sea ice: A comparison between winter in the Weddell Sea and summer in the Amundsen Sea

    Science.gov (United States)

    Granfors, Anna; Ahnoff, Martin; Mills, Matthew M.; Abrahamsson, Katarina

    2014-12-01

    Recent studies have recognized sea ice as a source of reactive iodine to the Antarctic boundary layer. Volatile iodinated compounds (iodocarbons) are released from sea ice, and they have been suggested to contribute to the formation of iodine oxide (IO), which takes part in tropospheric ozone destruction in the polar spring. We measured iodocarbons (CH3I, CH2ClI, CH2BrI, and CH2I2) in sea ice, snow, brine, and air during two expeditions to Antarctica, OSO 10/11 to the Amundsen Sea during austral summer and ANT XXIX/6 to the Weddell Sea in austral winter. These are the first reported measurements of iodocarbons from the Antarctic winter. Iodocarbons were enriched in sea ice in relation to seawater in both summer and winter. During summer, the positive relationship to chlorophyll a biomass indicated a biological origin. We suggest that CH3I is formed biotically in sea ice during both summer and winter. For CH2ClI, CH2BrI, and CH2I2, an additional abiotic source at the snow/ice interface in winter is suggested. Elevated air concentrations of CH3I and CH2ClI during winter indicate that they are enriched in lower troposphere and may take part in the formation of IO at polar sunrise.

  15. Possible connections of the opposite trends in Arctic and Antarctic sea-ice cover

    Science.gov (United States)

    Yu, Lejiang; Zhong, Shiyuan; Winkler, Julie A.; Zhou, Mingyu; Lenschow, Donald H.; Li, Bingrui; Wang, Xianqiao; Yang, Qinghua

    2017-04-01

    Sea ice is an important component of the global climate system and a key indicator of climate change. A decreasing trend in Arctic sea-ice concentration is evident in recent years, whereas Antarctic sea-ice concentration exhibits a generally increasing trend. Various studies have investigated the underlying causes of the observed trends for each region, but possible linkages between the regional trends have not been studied. Here, we hypothesize that the opposite trends in Arctic and Antarctic sea-ice concentration may be linked, at least partially, through interdecadal variability of the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO). Although evaluation of this hypothesis is constrained by the limitations of the sea-ice cover record, preliminary statistical analyses of one short-term and two long-term time series of observed and reanalysis sea-ice concentrations data suggest the possibility of the hypothesized linkages. For all three data sets, the leading mode of variability of global sea-ice concentration is positively correlated with the AMO and negatively correlated with the PDO. Two wave trains related to the PDO and the AMO appear to produce anomalous surface-air temperature and low-level wind fields in the two polar regions that contribute to the opposite changes in sea-ice concentration.

  16. Possible connections of the opposite trends in Arctic and Antarctic sea-ice cover.

    Science.gov (United States)

    Yu, Lejiang; Zhong, Shiyuan; Winkler, Julie A; Zhou, Mingyu; Lenschow, Donald H; Li, Bingrui; Wang, Xianqiao; Yang, Qinghua

    2017-04-05

    Sea ice is an important component of the global climate system and a key indicator of climate change. A decreasing trend in Arctic sea-ice concentration is evident in recent years, whereas Antarctic sea-ice concentration exhibits a generally increasing trend. Various studies have investigated the underlying causes of the observed trends for each region, but possible linkages between the regional trends have not been studied. Here, we hypothesize that the opposite trends in Arctic and Antarctic sea-ice concentration may be linked, at least partially, through interdecadal variability of the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO). Although evaluation of this hypothesis is constrained by the limitations of the sea-ice cover record, preliminary statistical analyses of one short-term and two long-term time series of observed and reanalysis sea-ice concentrations data suggest the possibility of the hypothesized linkages. For all three data sets, the leading mode of variability of global sea-ice concentration is positively correlated with the AMO and negatively correlated with the PDO. Two wave trains related to the PDO and the AMO appear to produce anomalous surface-air temperature and low-level wind fields in the two polar regions that contribute to the opposite changes in sea-ice concentration.

  17. 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

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

    Science.gov (United States)

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

    2015-01-01

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

  20. Small scale variability of snow density on Antarctic sea ice

    Science.gov (United States)

    Wever, N.; Leonard, K. C.; Paul, S.; Jacobi, H. W.; Proksch, M.; Lehning, M.

    2016-12-01

    Snow on sea ice plays an important role in air-ice-sea interactions. For example, snow may smooth the ice surface when snow drift is occurring, while at the same time it may also generate roughness elements by interactions with the wind. Snow density is a key property in many processes, for example by influencing the thermal conductivity of the snow layer, radiative transfer inside the snow as well as the effects of aerodynamic forcing on the snowpack. We present data from an in-situ measurement campaign in the Weddell Sea during two subsequent cruises of RV Polarstern. By comparing snow density from snow pits and snow micro penetrometer (SMP) measurements, augmented by terrestrial laser scanning (TLS) on an area of 50x50 m2, highly resolved density profiles and surface topology were acquired at a horizontal resolution of approximately 30 cm. Average snow densities are about 280 kg/m3, but the analysis also reveals a high spatial variability in snow density on sea ice in both horizontal and vertical direction, ranging from roughly 170 to 360 kg/m3. This variability is expressed by coherent snow structures over several meters, which disappear over larger distances. A comparison with TLS data indicates that the spatial variability is related to deviations in surface topology. This suggests a strong influence from surface processes, for example wind, on the temporal development of density profiles. The fundamental relationship between density variations, surface roughness and changes therein as investigated in this study are interpreted with respect to larger-scale ice-movement and the ice mass balance.

  1. Influence of Sea Ice Crack Formation on the Spatial Distribution of Nutrients and Microalgae in Flooded Antarctic Multiyear Ice

    Science.gov (United States)

    Nomura, Daiki; Aoki, Shigeru; Simizu, Daisuke; Iida, Takahiro

    2018-02-01

    Cracks are common and natural features of sea ice formed in the polar oceans. In this study, a sea ice crack in flooded, multiyear, land-fast Antarctic sea ice was examined to assess its influence on biological productivity and the transport of nutrients and microalgae into the upper layers of neighboring sea ice. The water inside the crack and the surrounding host ice were characterized by a strong discoloration (brown color), an indicator of a massive algal bloom. Salinity and oxygen isotopic ratio measurements indicated that 64-84% of the crack water consisted of snow meltwater supplied during the melt season. Measurements of nutrient and chlorophyll a concentrations within the slush layer pool (the flooded layer at the snow-ice interface) revealed the intrusion of water from the crack, likely forced by mixing with underlying seawater during the tidal cycle. Our results suggest that sea ice crack formation provides conditions favorable for algal blooms by directly exposing the crack water to sunlight and supplying nutrients from the under-ice water. Subsequently, constituents of the crack water modified by biological activity were transported into the upper layer of the flooded sea ice. They were then preserved in the multiyear ice column formed by upward growth of sea ice caused by snow ice formation in areas of significant snow accumulation.

  2. Neoglacial Antarctic sea-ice expansion driven by mid-Holocene retreat of the Ross Ice Shelf.

    Science.gov (United States)

    Bendle, J. A.; Newton, K.; Mckay, R. M.; Crosta, X.; Etourneau, J.; Anya, A. B.; Seki, O.; Golledge, N. R.; Bertler, N. A. N.; Willmott, V.; Schouten, S.; Riesselman, C. R.; Masse, G.; Dunbar, R. B.

    2017-12-01

    Recent decades have seen expanding Antarctic sea-ice coverage, coeval with thinning West Antarctic Ice Sheet (WAIS) ice shelves and the rapid freshening of surface and bottom waters along the Antarctic margin. The mid-Holocene Neoglacial transition represents the last comparable baseline shift in sea-ice behaviour. The drivers and feedbacks involved in both the recent and Holocene events are poorly understood and characterised by large proxy-model mismatches. We present new records of compound specific fatty acid isotope analyses (δ2H-FA), highly-branched isoprenoid alkenes (HBIs) TEX86L temperatures, grain-size, mass accumulations rates (MARs) and image analyses from a 171m Holocene sediment sequence from Site U1357 (IODP leg 318). In combination with published records we reconstruct Holocene changes in glacial meltwater, sedimentary inputs and sea-ice. The early Holocene (11 to 10 ka) is characterised by large fluctuations in inputs of deglacial meltwater and sediments and seismic evidence of downlapping material from the south, suggesting a dominating influence from glacial retreat of the local outlet glaciers. From 10 to 8 ka there is decreasing meltwater inputs, an onlapping drift and advection of material from the east. After ca. 8 ka positively correlated δ2H-FA and MARs infer that pulses of glacial melt correlate to stronger easterly currents, driving erosion of material from upstream banks and that the Ross Ice Shelf (RIS) becomes a major influence. A large mid-Holocene meltwater pulse (preceded by warming TEX86L temperatures) is evident between ca. 6 to 4.5 ka, culminating in a rapid and permanent increase in sea-ice from 4.5 ka. This is coeval with cosmogenic nuclide evidence for a rapid thinning of the Antarctic ice sheet during the mid-Holocene (Hein et al., 2016). We suggest this represents a final major pulse of deglaciation from the Ross Ice Shelf, which initiates the Neoglacial, driving cool surface waters along the coast and greater sea-ice

  3. Modelling the Antarctic Ice Sheet

    DEFF Research Database (Denmark)

    Pedersen, Jens Olaf Pepke; Holm, A.

    2015-01-01

    Science) Antarctic Ice Sheet (DAIS) model (Shaffer 2014) is forced by reconstructed time series of Antarctic temperature, global sea level and ocean subsurface temperature over the last two glacial cycles. In this talk a modelling work of the Antarctic ice sheet over most of the Cenozoic era using...... the DAIS model will be presented. G. Shaffer (2014) Formulation, calibration and validation of the DAIS model (version 1), a simple Antarctic ice sheet model sensitive to variations of sea level and ocean subsurface temperature, Geosci. Model Dev., 7, 1803‐1818...

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

    Directory of Open Access Journals (Sweden)

    V. Haid

    2017-06-01

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

  5. Small scale variability of snow properties on Antarctic sea ice

    Science.gov (United States)

    Wever, Nander; Leonard, Katherine; Paul, Stephan; Jacobi, Hans-Werner; Proksch, Martin; Lehning, Michael

    2016-04-01

    Snow on sea ice plays an important role in air-ice-sea interactions, as snow accumulation may for example increase the albedo. Snow is also able to smooth the ice surface, thereby reducing the surface roughness, while at the same time it may generate new roughness elements by interactions with the wind. Snow density is a key property in many processes, for example by influencing the thermal conductivity of the snow layer, radiative transfer inside the snow as well as the effects of aerodynamic forcing on the snowpack. By comparing snow density and grain size from snow pits and snow micro penetrometer (SMP) measurements, highly resolved density and grain size profiles were acquired during two subsequent cruises of the RV Polarstern in the Weddell Sea, Antarctica, between June and October 2013. During the first cruise, SMP measurements were done along two approximately 40 m transects with a horizontal resolution of approximately 30 cm. During the second cruise, one transect was made with approximately 7.5 m resolution over a distance of 500 m. Average snow densities are about 300 kg/m3, but the analysis also reveals a high spatial variability in snow density on sea ice in both horizontal and vertical direction, ranging from roughly 180 to 360 kg/m3. This variability is expressed by coherent snow structures over several meters. On the first cruise, the measurements were accompanied by terrestrial laser scanning (TLS) on an area of 50x50 m2. The comparison with the TLS data indicates that the spatial variability is exhibiting similar spatial patterns as deviations in surface topology. This suggests a strong influence from surface processes, for example wind, on the temporal development of density or grain size profiles. The fundamental relationship between variations in snow properties, surface roughness and changes therein as investigated in this study is interpreted with respect to large-scale ice movement and the mass balance.

  6. Historical whaling records reveal major regional retreat of Antarctic sea ice

    Science.gov (United States)

    Cotté, Cédric; Guinet, Christophe

    2007-02-01

    Several studies have provided evidence of a reduction of the Antarctic sea ice extent. However, these studies were conducted either at a global scale or at a regional scale, and possible inter-regional differences were not analysed. Using the long-term whaling database we investigated circum-Antarctic changes in summer sea ice extent from 1931 to 1987. Accounting for bias inherent in the whaling method, this analysis provides new insight into the historical ice edge reconstruction and inter-regional differences. We highlight a reduction of the sea ice extent occurring in the 1960s, mainly in the Weddell sector where the change ranged from 3° to 7.9° latitude through summer. Although the whaling method may not be appropriate for detecting fine-scale change, these results provide evidence for a heterogeneous circumpolar change of the sea ice extent. The shift is temporally and spatially consistent with other environmental changes detected in the Weddell sector and also with a shift in the Southern Hemisphere annular mode. The large reduction of the sea ice extent has probably influenced the ecosystem of the Weddell Sea, particularly the krill biomass.

  7. 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

  8. Consistent biases in Antarctic sea ice concentration simulated by climate models

    Science.gov (United States)

    Roach, Lettie A.; Dean, Samuel M.; Renwick, James A.

    2018-01-01

    The simulation of Antarctic sea ice in global climate models often does not agree with observations. In this study, we examine the compactness of sea ice, as well as the regional distribution of sea ice concentration, in climate models from the latest Coupled Model Intercomparison Project (CMIP5) and in satellite observations. We find substantial differences in concentration values between different sets of satellite observations, particularly at high concentrations, requiring careful treatment when comparing to models. As a fraction of total sea ice extent, models simulate too much loose, low-concentration sea ice cover throughout the year, and too little compact, high-concentration cover in the summer. In spite of the differences in physics between models, these tendencies are broadly consistent across the population of 40 CMIP5 simulations, a result not previously highlighted. Separating models with and without an explicit lateral melt term, we find that inclusion of lateral melt may account for overestimation of low-concentration cover. Targeted model experiments with a coupled ocean-sea ice model show that choice of constant floe diameter in the lateral melt scheme can also impact representation of loose ice. This suggests that current sea ice thermodynamics contribute to the inadequate simulation of the low-concentration regime in many models.

  9. Antarctic Circumpolar Current Dynamics and Their Relation to Antarctic Ice Sheet and Perennial Sea-Ice Variability in the Central Drake Passage During the Last Climate Cycle

    Science.gov (United States)

    Kuhn, G.; Wu, S.; Hass, H. C.; Klages, J. P.; Zheng, X.; Arz, H. W.; Esper, O.; Hillenbrand, C. D.; Lange, C.; Lamy, F.; Lohmann, G.; Müller, J.; McCave, I. N. N.; Nürnberg, D.; Roberts, J.; Tiedemann, R.; Timmermann, A.; Titschack, J.; Zhang, X.

    2017-12-01

    The evolution of the Antarctic Ice Sheet during the last climate cycle and the interrelation to global atmospheric and ocean circulation remains controversial and plays an important role for our understanding of ice sheet response to modern global warming. The timing and sequence of deglacial warming is relevant for understanding the variability and sensitivity of the Antarctic Ice Sheet to climatic changes, and the continuing rise of atmospheric greenhouse gas concentrations. The Antarctic Ice Sheet is a pivotal component of the global water budget. Freshwater fluxes from the ice sheet may affect the Antarctic Circumpolar Current (ACC), which is strongly impacted by the westerly wind belt in the Southern Hemisphere (SHWW) and constricted to its narrowest extent in the Drake Passage. The flow of ACC water masses through Drake Passage is, therefore, crucial for advancing our understanding of the Southern Ocean's role in global meridional overturning circulation and global climate change. In order to address orbital and millennial-scale variability of the Antarctic ice sheet and the ACC, we applied a multi-proxy approach on a sediment core from the central Drake Passage including grain size, iceberg-rafted debris, mineral dust, bulk chemical and mineralogical composition, and physical properties. In combination with already published and new sediment records from the Drake Passage and Scotia Sea, as well as high-resolution data from Antarctic ice cores (WDC, EDML), we now have evidence that during glacial times a more northerly extent of the perennial sea-ice zone decreased ACC current velocities in the central Drake Passage. During deglaciation the SHWW shifted southwards due to a decreasing temperature gradient between subtropical and polar latitudes caused by sea ice and ice sheet decline. This in turn caused Southern Hemisphere warming, a more vigorous ACC, stronger Southern Ocean ventilation, and warm Circumpolar Deep Water (CDW) upwelling on Antarctic shelves

  10. Model intercomparison of sea-level response to sudden Antarctic ice-shelf collapse

    Science.gov (United States)

    Pattyn, Frank; Sun, Sainan; Golledge, Nicholas

    2017-04-01

    The magnitude of the Antarctic ice sheet's contribution to global sea level is dominated by the potential of its marine sectors to become unstable and collapse to ocean (and atmospheric) forcing. Ice shelf buttressing is a key element in the stability of the Antarctic ice sheet. Therefore, a useful model experiment to test this stability is the sudden removal of all floating ice shelves. It serves several purposes: (i) investigating an upper bound of Antarctic mass loss, and (ii) testing numerical ice sheet models on their sensitivity to grounding line migration and marine ice sheet instability (MISI). Two types of de-buttressing are investigated, i.e., (i) sudden removal followed by ice-shelf regrowth due to increased ice discharge across the grounding line, and (ii) without ice shelf regrowth after de-buttressing (so-called float-kill). Experiments are carried out with two state-of-the-art marine ice sheet models (f.ETISh and PISM) and different settings of grounding-line treatment. For the f.ETISh model these settings pertain to grounding-line flux conditions according to power-law basal sliding and Coulomb friction; for PISM this includes different settings on transition zone width and grounding-line interpolation. Results of the experiments show that regrowth of ice shelves after sudden de-buttressing stabilizes grounding lines and reduces the effect of MISI. Float-kill conditions lead to significant mass loss, which is further exacerbated by the type of grounding-line treatment, i.e., Coulomb friction renders grounding lines more sensitive (Tsai et al., 2015). However, compared to recent model studies where effects of hydro-fracturing and cliff-failure are considered (DeConto and Pollard, 2016), similar amounts of ice loss are only obtained when the highest grounding-line sensitivity is considered.

  11. Seasonal Study of Mercury Species in the Antarctic Sea Ice Environment.

    Science.gov (United States)

    Nerentorp Mastromonaco, Michelle G; Gårdfeldt, Katarina; Langer, Sarka; Dommergue, Aurélien

    2016-12-06

    Limited studies have been conducted on mercury concentrations in the polar cryosphere and the factors affecting the distribution of mercury within sea ice and snow are poorly understood. Here we present the first comprehensive seasonal study of elemental and total mercury concentrations in the Antarctic sea ice environment covering data from measurements in air, sea ice, seawater, snow, frost flowers, and brine. The average concentration of total mercury in sea ice decreased from winter (9.7 ng L -1 ) to spring (4.7 ng L -1 ) while the average elemental mercury concentration increased from winter (0.07 ng L -1 ) to summer (0.105 ng L -1 ). The opposite trends suggest potential photo- or dark oxidation/reduction processes within the ice and an eventual loss of mercury via brine drainage or gas evasion of elemental mercury. Our results indicate a seasonal variation of mercury species in the polar sea ice environment probably due to varying factors such as solar radiation, temperature, brine volume, and atmospheric deposition. This study shows that the sea ice environment is a significant interphase between the polar ocean and the atmosphere and should be accounted for when studying how climate change may affect the mercury cycle in polar regions.

  12. Past and present stability of the Weddell Sea sector of the Antarctic Ice Sheet

    Science.gov (United States)

    Whitehouse, P. L.; Vieli, A.; Jamieson, S.; Bentley, M.; Hein, A.; Sugden, D.

    2016-12-01

    The contribution of the Weddell Sea sector of the Antarctic Ice Sheet to sea-level rise since the Last Glacial Maximum (LGM), along with the processes controlling the past and ongoing dynamics of this sector, are poorly known. Of particular concern is the fact that significant portions of the present-day grounding line are unstably located on bathymetry that deepens towards the interior of the continent. We present new modelling results, constrained by field evidence relating to past ice extent and thickness along the Foundation Ice Stream and Thiel Trough, which suggest that the post-LGM sea-level contribution from this sector was modest, and that the grounding line is unlikely to have been located at the continental shelf break for a prolonged period during the last glacial cycle. Poorly-constrained ice shelf and ocean processes are found to play a crucial role in controlling the past configuration and stability of this sector of the ice sheet. In particular, we find that we cannot rule out a scenario in which the grounding line of the Foundation Ice Stream retreated behind present during deglaciation, and has since re-advanced. This work complements a number of recent studies, based on independent data sets, that explore the possibility that grounding line re-advance occurred within the Weddell Sea sector during the mid-to-late Holocene. If this hypothesis is correct, then current glacial isostatic adjustment models, and hence contemporary estimates of ice mass balance derived from GRACE data, will be significantly biased. Piecing together, and understanding, the reason for recent changes in ice dynamics is crucial for determining the contemporary stability of the Weddell Sea sector of the Antarctic Ice Sheet.

  13. Signals from the south; humpback whales carry messages of Antarctic sea-ice ecosystem variability.

    Science.gov (United States)

    Bengtson Nash, Susan M; Castrillon, Juliana; Eisenmann, Pascale; Fry, Brian; Shuker, Jon D; Cropp, Roger A; Dawson, Amanda; Bignert, Anders; Bohlin-Nizzetto, Pernilla; Waugh, Courtney A; Polkinghorne, Bradley J; Dalle Luche, Greta; McLagan, David

    2018-04-01

    Southern hemisphere humpback whales (Megaptera novaeangliae) rely on summer prey abundance of Antarctic krill (Euphausia superba) to fuel one of the longest-known mammalian migrations on the planet. It is hypothesized that this species, already adapted to endure metabolic extremes, will be one of the first Antarctic consumers to show measurable physiological change in response to fluctuating prey availability in a changing climate; and as such, a powerful sentinel candidate for the Antarctic sea-ice ecosystem. Here, we targeted the sentinel parameters of humpback whale adiposity and diet, using novel, as well as established, chemical and biochemical markers, and assembled a time trend spanning 8 years. We show the synchronous, inter-annual oscillation of two measures of humpback whale adiposity with Southern Ocean environmental variables and climate indices. Furthermore, bulk stable isotope signatures provide clear indication of dietary compensation strategies, or a lower trophic level isotopic change, following years indicated as leaner years for the whales. The observed synchronicity of humpback whale adiposity and dietary markers, with climate patterns in the Southern Ocean, lends strength to the role of humpback whales as powerful Antarctic sea-ice ecosystem sentinels. The work carries significant potential to reform current ecosystem surveillance in the Antarctic region. © 2017 John Wiley & Sons Ltd.

  14. Edwardsiella andrillae, a New Species of Sea Anemone from Antarctic Ice

    Science.gov (United States)

    Daly, Marymegan; Rack, Frank; Zook, Robert

    2013-01-01

    Exploration of the lower surface of the Ross Ice Shelf in Antarctica by the Submersible Capable of under-Ice Navigation and Imaging (SCINI) remotely operated vehicle discovered a new species of sea anemone living in this previously undocumented ecosystem. This discovery was a significant outcome of the Coulman High Project’s geophysical and environmental fieldwork in 2010-2011 as part of the ANDRILL (ANtarctic geologic DRILLing) program. Edwardsiella andrillae n. sp., lives with most of its column in the ice shelf, with only the tentacle crown extending into the seawater below. In addition to being the only Antarctic representative of the genus, Edwardsiella andrillae is distinguished from all other species of the genus in the number of tentacles and in the size and distribution of cnidae. The anatomy and histology of Edwardsiella andrillae present no features that explain how this animal withstands the challenges of life in such an unusual habitat. PMID:24349517

  15. Edwardsiella andrillae, a new species of sea anemone from Antarctic ice.

    Directory of Open Access Journals (Sweden)

    Marymegan Daly

    Full Text Available Exploration of the lower surface of the Ross Ice Shelf in Antarctica by the Submersible Capable of under-Ice Navigation and Imaging (SCINI remotely operated vehicle discovered a new species of sea anemone living in this previously undocumented ecosystem. This discovery was a significant outcome of the Coulman High Project's geophysical and environmental fieldwork in 2010-2011 as part of the ANDRILL (ANtarctic geologic DRILLing program. Edwardsiella andrillae n. sp., lives with most of its column in the ice shelf, with only the tentacle crown extending into the seawater below. In addition to being the only Antarctic representative of the genus, Edwardsiella andrillae is distinguished from all other species of the genus in the number of tentacles and in the size and distribution of cnidae. The anatomy and histology of Edwardsiella andrillae present no features that explain how this animal withstands the challenges of life in such an unusual habitat.

  16. Glacial-interglacial sea ice proxies from the Antarctic Peninsula using the James Ross Island ice core.

    Science.gov (United States)

    Benton, A. K.; Mulvaney, R.; Triest, J.; Abram, N.

    2014-12-01

    Ice core records from Antarctica have shown promise as highly-resolved indicators of regional sea ice change, but to date semi-quantified reconstructions do not extend back more than ~150 years. In this study the chemical composition of the James Ross Island ice core is presented as a potential sea ice proxy record spanning the full Holocene and into the last glacial interval. A CFA-TE method was used to analyse the chemical composition of the entire 363.9m core including final 5m which contains evidence of glacial age ice. MSA- and major anions were measured at 4cm effective resolution, along with trace elements Na, Ca, K, Mg, Mn, H2O2, NO3, total conductivity and dust at <0.5cm effective resolution. Seasonal signals from H2O2 in the upper 50m of the core support the use of non sea salt-SO42- for determining seasonality in deeper sections. This multi-proxy analysis of the oldest ice core to date from the Antarctic Peninsula region allows the concurrent interpretation of sea ice changes and their environmental drivers. The potential dual influence of previous winter sea ice extent and air pathway source region on MSA concentrations in the core are interpreted with use of Na as a winter maximum indicator and Ca and dust signal strength showing changes in dust flux indicating potential source region variation.

  17. 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

  18. A high-end sea level rise probabilistic projection including rapid Antarctic ice sheet mass loss

    NARCIS (Netherlands)

    Le Bars, D.M.; Drijfhout, S.S.; de Vries, Hylke

    2017-01-01

    The potential for break-up of Antarctic ice shelves by hydrofracturing and following ice cliff instability might be important for future ice dynamics. One recent study suggests that the Antarctic ice sheet could lose a lot more mass during the 21st century than previously thought. This increased

  19. 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.

  20. Sea Ice Index, Version 3

    Data.gov (United States)

    National Aeronautics and Space Administration — The Sea Ice Index provides a quick look at Arctic- and Antarctic-wide changes in sea ice. It is a source for consistent, up-to-date sea ice extent and concentration...

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

    Science.gov (United States)

    Su, Zhan

    2017-06-01

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

  2. Potential sea-level rise from Antarctic ice-sheet instability constrained by observations.

    Science.gov (United States)

    Ritz, Catherine; Edwards, Tamsin L; Durand, Gaël; Payne, Antony J; Peyaud, Vincent; Hindmarsh, Richard C A

    2015-12-03

    Large parts of the Antarctic ice sheet lying on bedrock below sea level may be vulnerable to marine-ice-sheet instability (MISI), a self-sustaining retreat of the grounding line triggered by oceanic or atmospheric changes. There is growing evidence that MISI may be underway throughout the Amundsen Sea embayment (ASE), which contains ice equivalent to more than a metre of global sea-level rise. If triggered in other regions, the centennial to millennial contribution could be several metres. Physically plausible projections are challenging: numerical models with sufficient spatial resolution to simulate grounding-line processes have been too computationally expensive to generate large ensembles for uncertainty assessment, and lower-resolution model projections rely on parameterizations that are only loosely constrained by present day changes. Here we project that the Antarctic ice sheet will contribute up to 30 cm sea-level equivalent by 2100 and 72 cm by 2200 (95% quantiles) where the ASE dominates. Our process-based, statistical approach gives skewed and complex probability distributions (single mode, 10 cm, at 2100; two modes, 49 cm and 6 cm, at 2200). The dependence of sliding on basal friction is a key unknown: nonlinear relationships favour higher contributions. Results are conditional on assessments of MISI risk on the basis of projected triggers under the climate scenario A1B (ref. 9), although sensitivity to these is limited by theoretical and topographical constraints on the rate and extent of ice loss. We find that contributions are restricted by a combination of these constraints, calibration with success in simulating observed ASE losses, and low assessed risk in some basins. Our assessment suggests that upper-bound estimates from low-resolution models and physical arguments (up to a metre by 2100 and around one and a half by 2200) are implausible under current understanding of physical mechanisms and potential triggers.

  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. 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.

  5. 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.

  6. Design and implementation of a Cube satellite mission for Antarctic glacier and sea ice observation

    Science.gov (United States)

    Wu, Shufan; Zhao, Tiancheng; Gao, Yuan; Cheng, Xiao

    2017-10-01

    The research for global climate changes calls for high quality satellite data and imageries regarding the Polar Regions. In recent years, the emerging Earth-Observation micro/nano satellite technology provides new data sources for polar region observations. The STU-2A, also named TW-1A, is such a nano satellite designed for polar region observation activities. It is a 3U CubeSat of 2.9 kg with a size of 30 × 10 × 10 cm carrying an Earth observation camera, launched into a Sun Synchronous Orbit (SSO) at 481 km with an inclination of 97.3°, on September 25, 2015. During the Antarctic summer of 2015/16, it has acquired visible-light true color images with a resolution of 94 m, covering different sea and coastal regions including Amundsen Sea, Ross Sea and Vincennes Bay. These images were used to analyze the change of glacier and sea ice, compared and calibrated with reference to the publically available MODIS images with a resolution of 250 m. As the camera was specially designed for the Polar regions which have an environment of low solar elevation angle and high surface reflectance, it eliminates the oversaturation problem of the MODIS sensors and can provide high quality images. Based on data analysis and assessment, it is confirmed that this satellite data can meet the demand of glacier and sea ice observation. This paper presents the Cubesat system design and configuration, the payload camera design, and its application in Antarctic glacier and sea ice observation.

  7. Antarctic Ice Velocity Data

    Data.gov (United States)

    National Aeronautics and Space Administration — This compilation of recent ice velocity data of the Antarctic ice sheet is intended for use by the polar scientific community. The data are presented in tabular form...

  8. 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.

  9. A model study of the effect of climate and sea-level change on the evolution of the Antarctic Ice Sheet from the Last Glacial Maximum to 2100

    NARCIS (Netherlands)

    Maris, M. N. A.; Van Wessem, J. M.; Van De Berg, W. J.; De Boer, B.; Oerlemans, J.

    2014-01-01

    Due to a scarcity of observations and its long memory of uncertain past climate, the Antarctic Ice Sheet remains a largely unknown factor in the prediction of global sea level change. As the history of the ice sheet plays a key role in its future evolution, in this study we model the Antarctic Ice

  10. Role of the Tropical Pacific in recent Antarctic Sea-Ice Trends

    Science.gov (United States)

    Codron, F.; Bardet, D.; Allouache, C.; Gastineau, G.; Friedman, A. R.; Douville, H.; Voldoire, A.

    2017-12-01

    The recent (up to 2016) trends in Antarctic sea-ice cover - a global increase masking a dipole between the Ross and Bellingshausen-Weddel seas - are still not well understood, and not reproduced by CMIP5 coupled climate models. We here explore the potential role of atmospheric circulation changes around the Amundsen Sea, themselves possibly forced by tropical SSTs, an explanation that has been recently advanced. As a first check on this hypothesis, we compare the atmospheric circulation trends simulated by atmospheric GCMs coupled with an ocean or with imposed SSTs (AMIP experiment from CMIP5); the latter being in theory able to reproduce changes caused by natural SST variability. While coupled models simulate in aggregate trends that project on the SAM structure, strongest in summer, the AMIP simulations add in the winter season a pronounced Amundsen Sea Low signature (and a PNA signature in the northern hemisphere) both consistent with a Niña-like trend in the tropical Pacific. We then use a specific coupled GCM setup, in which surface wind anomalies over the tropical Pacific are strongly nudged towards the observed ones, including their interannual variability, but the model is free to evolve elsewhere. The two GCMs used then simulate a deepening trend in the Amundsen-Sea Low in winter, and are able to reproduce a dipole in sea-ice cover. Further analysis shows that the sea-ice dipole is partially forced by surface heat flux anomalies in early winter - the extent varying with the region and GCM used. The turbulent heat fluxes then act to damp the anomalies in late winter, which may however be maintained by ice-albedo feedbacks.

  11. The paradox of a long grounding during West Antarctic Ice Sheet retreat in Ross Sea.

    Science.gov (United States)

    Bart, Philip J; Krogmeier, Benjamin J; Bart, Manon P; Tulaczyk, Slawek

    2017-04-28

    Marine geological data show that the West Antarctic Ice Sheet (WAIS) advanced to the eastern Ross Sea shelf edge during the Last Glacial Maximum (LGM) and eventually retreated ~1000 km to the current grounding-line position on the inner shelf. During the early deglacial, the WAIS deposited a voluminous stack of overlapping grounding zone wedges (GZWs) on the outer shelf of the Whales Deep Basin. The large sediment volume of the GZW cluster suggests that the grounding-line position of the paleo-Bindschadler Ice Stream was relatively stationary for a significant time interval. We used an upper bound estimate of paleo-sediment flux to investigate the lower bound duration over which the ice stream would have deposited sediment to account for the GZW volume. Our calculations show that the cluster represents more than three millennia of ice-stream sedimentation. This long duration grounding was probably facilitated by rapid GZW growth. The subsequent punctuated large-distance (~200 km) grounding-line retreat may have been a highly non-linear ice sheet response to relatively continuous external forcing such as gradual climate warming or sea-level rise. These findings indicate that reliable predictions of future WAIS retreat may require incorporation of realistic calculations of sediment erosion, transport and deposition.

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

    OpenAIRE

    Su, Zhan

    2017-01-01

    This study uses an observationally constrained and dynamically consistent ocean and sea ice state estimate. The author presents a remarkable agreement between the location of the edge of Antarctic maximum sea ice extent, reached in September, and the narrow transition band for the upper ocean (0–100 m depths) stratification, as early as April to June. To the south of this edge, the upper ocean has high stratification, which forbids convective fluxes to cross through; consequently, the ocean h...

  13. Spatial variability and trends of seasonal snowmelt processes over Antarctic sea ice observed by satellite scatterometers

    Science.gov (United States)

    Arndt, S.; Haas, C.

    2017-12-01

    Snow is one of the key drivers determining the seasonal energy and mass budgets of sea ice in the Southern Ocean. Here, we analyze radar backscatter time series from the European Remote Sensing Satellites (ERS)-1 and-2 scatterometers, from the Quick Scatterometer (QSCAT), and from the Advanced Scatterometer (ASCAT) in order to observe the regional and inter-annual variability of Antarctic snowmelt processes from 1992 to 2014. On perennial ice, seasonal backscatter changes show two different snowmelt stages: A weak backscatter rise indicating the initial warming and metamorphosis of the snowpack (pre-melt), followed by a rapid rise indicating the onset of internal snowmelt and thaw-freeze cycles (snowmelt). In contrast, similar seasonal backscatter cycles are absent on seasonal ice, preventing the periodic retrieval of spring/summer transitions. This may be due to the dominance of ice bottom melt over snowmelt, leading to flooding and ice disintegration before strong snowmelt sets in. Resulting snowmelt onset dates on perennial sea ice show the expected latitudinal gradient from early melt onsets (mid-November) in the northern Weddell Sea towards late (end-December) or even absent snowmelt conditions further south. This result is likely related to seasonal variations in solar shortwave radiation (absorption). In addition, observations with different microwave frequencies allow to detect changing snow properties at different depths. We show that short wavelengths of passive microwave observations indicate earlier pre-melt and snowmelt onset dates than longer wavelength scatterometer observations, in response to earlier warming of upper snow layers compared to lower snow layers. Similarly, pre-melt and snowmelt onset dates retrieved from Ku-Band radars were earlier by an average of 11 and 23 days, respectively, than those retrieved from C-Band. This time difference was used to correct melt onset dates retrieved from Ku-Band to compile a consistent time series from

  14. Distribution, density and abundance of Antarctic ice seals off Queen Maud Land and the eastern Weddell Sea

    OpenAIRE

    Gurarie, Eliezer; Bengtson, John L.; Bester, Marthán N.; Blix, Arnoldus Schytte; Cameron, Michael; Bornemann, Horst; Nordøy, Erling S.; Plötz, Joachim; Steinhage, Daniel; Boveng, Peter

    2017-01-01

    The Antarctic Pack Ice Seal (APIS) Program was initiated in 1994 to estimate the abundance of four species of Antarctic phocids: the crabeater seal Lobodon carcinophaga , Weddell seal Leptonychotes weddellii , Ross seal Ommatophoca rossii and leopard seal Hydrurga leptonyx and to identify ecological relationships and habitat use patterns. The Atlantic sector of the Southern Ocean (the eastern sector of the Weddell Sea) was surveyed by research teams from Germany, Norway and South Africa usi...

  15. Air-sea interaction regimes in the sub-Antarctic Southern Ocean and Antarctic marginal ice zone revealed by icebreaker measurements

    Science.gov (United States)

    Yu, Lisan; Jin, Xiangze; Schulz, Eric W.; Josey, Simon A.

    2017-08-01

    This study analyzed shipboard air-sea measurements acquired by the icebreaker Aurora Australis during its off-winter operation in December 2010 to May 2012. Mean conditions over 7 months (October-April) were compiled from a total of 22 ship tracks. The icebreaker traversed the water between Hobart, Tasmania, and the Antarctic continent, providing valuable in situ insight into two dynamically important, yet poorly sampled, regimes: the sub-Antarctic Southern Ocean and the Antarctic marginal ice zone (MIZ) in the Indian Ocean sector. The transition from the open water to the ice-covered surface creates sharp changes in albedo, surface roughness, and air temperature, leading to consequential effects on air-sea variables and fluxes. Major effort was made to estimate the air-sea fluxes in the MIZ using the bulk flux algorithms that are tuned specifically for the sea-ice effects, while computing the fluxes over the sub-Antarctic section using the COARE3.0 algorithm. The study evidenced strong sea-ice modulations on winds, with the southerly airflow showing deceleration (convergence) in the MIZ and acceleration (divergence) when moving away from the MIZ. Marked seasonal variations in heat exchanges between the atmosphere and the ice margin were noted. The monotonic increase in turbulent latent and sensible heat fluxes after summer turned the MIZ quickly into a heat loss regime, while at the same time the sub-Antarctic surface water continued to receive heat from the atmosphere. The drastic increase in turbulent heat loss in the MIZ contrasted sharply to the nonsignificant and seasonally invariant turbulent heat loss over the sub-Antarctic open water.Plain Language SummaryThe icebreaker Aurora Australis is a research and supply vessel that is regularly chartered by the Australian Antarctic Division during the southern summer to operate in waters between Hobart, Tasmania, and Antarctica. The vessel serves as the main lifeline to three permanent research stations on the

  16. Evolving Understanding of Antarctic Ice-Sheet Physics and Ambiguity in Probabilistic Sea-Level Projections

    Science.gov (United States)

    Kopp, Robert E.; DeConto, Robert M.; Bader, Daniel A.; Hay, Carling C.; Horton, Radley M.; Kulp, Scott; Oppenheimer, Michael; Pollard, David; Strauss, Benjamin H.

    2017-12-01

    Mechanisms such as ice-shelf hydrofracturing and ice-cliff collapse may rapidly increase discharge from marine-based ice sheets. Here, we link a probabilistic framework for sea-level projections to a small ensemble of Antarctic ice-sheet (AIS) simulations incorporating these physical processes to explore their influence on global-mean sea-level (GMSL) and relative sea-level (RSL). We compare the new projections to past results using expert assessment and structured expert elicitation about AIS changes. Under high greenhouse gas emissions (Representative Concentration Pathway [RCP] 8.5), median projected 21st century GMSL rise increases from 79 to 146 cm. Without protective measures, revised median RSL projections would by 2100 submerge land currently home to 153 million people, an increase of 44 million. The use of a physical model, rather than simple parameterizations assuming constant acceleration of ice loss, increases forcing sensitivity: overlap between the central 90% of simulations for 2100 for RCP 8.5 (93-243 cm) and RCP 2.6 (26-98 cm) is minimal. By 2300, the gap between median GMSL estimates for RCP 8.5 and RCP 2.6 reaches >10 m, with median RSL projections for RCP 8.5 jeopardizing land now occupied by 950 million people (versus 167 million for RCP 2.6). The minimal correlation between the contribution of AIS to GMSL by 2050 and that in 2100 and beyond implies current sea-level observations cannot exclude future extreme outcomes. The sensitivity of post-2050 projections to deeply uncertain physics highlights the need for robust decision and adaptive management frameworks.

  17. Evolving Understanding of Antarctic Ice-Sheet Physics and Ambiguity in Probabilistic Sea-Level Projections

    Science.gov (United States)

    Kopp, Robert E.; DeConto, Robert M.; Bader, Daniel A.; Hay, Carling C.; Horton, Radley M.; Kulp, Scott; Oppenheimer, Michael; Pollard, David; Strauss, Benjamin

    2017-01-01

    Mechanisms such as ice-shelf hydrofracturing and ice-cliff collapse may rapidly increase discharge from marine-based ice sheets. Here, we link a probabilistic framework for sea-level projections to a small ensemble of Antarctic ice-sheet (AIS) simulations incorporating these physical processes to explore their influence on global-mean sea-level (GMSL) and relative sea-level (RSL). We compare the new projections to past results using expert assessment and structured expert elicitation about AIS changes. Under high greenhouse gas emissions (Representative Concentration Pathway [RCP] 8.5), median projected 21st century GMSL rise increases from 79 to 146 cm. Without protective measures, revised median RSL projections would by 2100 submerge land currently home to 153 million people, an increase of 44 million. The use of a physical model, rather than simple parameterizations assuming constant acceleration of ice loss, increases forcing sensitivity: overlap between the central 90% of simulations for 2100 for RCP 8.5 (93-243 cm) and RCP 2.6 (26-98 cm) is minimal. By 2300, the gap between median GMSL estimates for RCP 8.5 and RCP 2.6 reaches >10 m, with median RSL projections for RCP 8.5 jeopardizing land now occupied by 950 million people (versus 167 million for RCP 2.6). The minimal correlation between the contribution of AIS to GMSL by 2050 and that in 2100 and beyond implies current sea-level observations cannot exclude future extreme outcomes. The sensitivity of post-2050 projections to deeply uncertain physics highlights the need for robust decision and adaptive management frameworks.

  18. 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...

  19. 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.

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

    Science.gov (United States)

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

    2014-06-17

    In the modern climate, the ocean below 2 km is mainly filled by waters sinking into the abyss around Antarctica and in the North Atlantic. Paleoproxies indicate that waters of North Atlantic origin were instead absent below 2 km at the Last Glacial Maximum, resulting in an expansion of the volume occupied by Antarctic origin waters. In this study we show that this rearrangement of deep water masses is dynamically linked to the expansion of summer sea ice around Antarctica. A simple theory further suggests that these deep waters only came to the surface under sea ice, which insulated them from atmospheric forcing, and were weakly mixed with overlying waters, thus being able to store carbon for long times. This unappreciated link between the expansion of sea ice and the appearance of a voluminous and insulated water mass may help quantify the ocean's role in regulating atmospheric carbon dioxide on glacial-interglacial timescales. Previous studies pointed to many independent changes in ocean physics to account for the observed swings in atmospheric carbon dioxide. Here it is shown that many of these changes are dynamically linked and therefore must co-occur.

  1. Pliocene Antarctic sea-ice reconstruction based on the diatom record the ANDRILL 1B core

    Science.gov (United States)

    Scherer, R. P.; Sjunneskog, C. M.; Winter, D.; Riesselman, C.

    2010-12-01

    The ANtarctic DRILLing Program’s AND-1B core, comprising 13 interglacial diatomaceous sections spanning the early Pliocene to the early Pleistocene, provides a largely complete record of Pliocene climate and sea-ice conditions in the Ross Sea. As primary producers, diatoms are directly influenced by surface water conditions, thus fossil assemblages provide a high quality proxy for past surface waters. The modern diatom flora of the Southern Ocean reflects the strong zonal system characterized by a seasonal sea-ice zone (SSIZ), a permanent open ocean zone (POOZ), and a subantarctic zone (SAZ), each with a distinct water column and sedimentary diatom assemblage. The stratigraphic distribution of these assemblages in the AND-1B core provides a history of changing sea surface temperature (SST) and sea-ice conditions through the Pliocene and early Pleistocene. In the early to mid-Pliocene section (4.6-3.3 Ma) the SSIZ is only represented by a few percent, including during glacial stages. This contrasts with the >80% present in the modern western Ross Sea. The SAZ is well represented during this interval in the core, along with the POOZ assemblage, despite the high latitude and proximity to the coastline. This assemblage indicates minimal sea-ice during the summer photoperiod at this latitude. The SSIZ assemblage is present but remains minor during the latter part of the mid-Pliocene (3.3-3.0 Ma). The diatom assemblage suggests surface water stratification, possibly indicating persistent polynya conditions. This period is followed by an interval characterized by both a slight increase in sea-ice and in subantarctic species, which we interpret as reflecting stronger seasonal SST variability compared to prior periods. The sea-ice assemblage and specific sea-ice indicator species increase slightly through the late Pliocene (2.0 Ma) and early Pleistocene (1.07 Ma) but never approach the abundance observed in the modern Ross Sea. These results show that the seasonal sea-ice

  2. High turnover rates indicated by changes in the fixed N forms and their stable isotopes in Antarctic landfast sea ice

    Science.gov (United States)

    Fripiat, François; Sigman, Daniel M.; Massé, Guillaume; Tison, Jean-Louis

    2015-04-01

    We report concentration and nitrogen and oxygen isotopic measurements of nitrate, total dissolved nitrogen, and particulate nitrogen from Antarctic landfast sea ice, covering almost the complete seasonal cycle of sea ice growth and decay (from April to November). When sea ice forms in autumn, ice algae growth depletes nitrate and accumulates organic N within the ice. Subsequent low biological activity in winter imposes minor variations in the partitioning of fixed N. In early spring, the coupling between nitrate assimilation and brine convection at the sea ice bottom traps a large amount of fixed N within sea ice, up to 20 times higher than in the underlying seawater. At this time, remineralization and nitrification also accelerate, yielding nitrate concentrations up to 5 times higher than in seawater. Nitrate δ15N and δ18O are both elevated, indicating a near-balance between nitrification and nitrate assimilation. These findings require high microbially mediated turnover rates for the large fixed N pools, including nitrate. When sea ice warms in the spring, ice algae grow through the full thickness of the ice. The warming stratifies the brine network, which limits the exchange with seawater, causing the once-elevated nitrate pool to be nearly completely depleted. The nitrate isotope data point to light limitation at the base of landfast ice as a central characteristic of the environment, affecting its N cycling (e.g., allowing for nitrification) and impacting algal physiology (e.g., as reflected in the N and O isotope effects of nitrate assimilation).

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

    Science.gov (United States)

    Purich, Ariaan; England, Matthew

    2017-04-01

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

  4. Effects of Increased UV and Sea Ice Retreat on Antarctic Marine Larvae

    Science.gov (United States)

    Isely, N. M.; Lamare, M.; Marshall, C.

    2008-12-01

    Increased UV radiation caused by a decrease in the levels of stratospheric ozone has the potential to harm marine organisms. The sharpest decrease in ozone can be found over the Antarctic continent during the austral spring. Invertebrates may be particularly susceptible to the effects of increased UV-R because most have a planktonic stage in which their embryos and larvae live in surface waters. Marine invertebrates in the Antarctic are likely to be affected to a greater extent than those in tropical and temperate biomes as there is not only a greater amount of UV-R coming through the atmosphere in these latitudes, but the larval stages are in the water column for a greater period, have slower metabolism, and a stenothermal physiology. These factors have the potential to affect recruitment of new individuals into marine populations. One of the major forms of damage is the creation of cyclobutane pyrimidine dimers (CPD) in DNA. Previous work has shown that photolyase, a protein that repairs UV-R induced CPDs on DNA, is present in echinoderm larvae, and increases the repair rates of UV-R damaged DNA. During the austral spring of 2007 laboratory and field experiments were carried out on Sterechinus. neumayeri at Cape Evans on Ross Island, Antarctica, and at the ice edge north of Cape Royds. The effects of depth, and consequently dose of UV-R on expression of photolyase was determined. We established that photolyase can be induced by increased UV-R in S. neumayeri, and consequently is dependent on depth of the water column. There also appears to be an upper limit, where increases in UV-R do not induce further photolyase expression. With predictions that the annual ozone hole will be present for at least another 50 years and the possible retreat of sea ice, ambient levels of UV-R in the marine environment of Antarctica will increase. The results of this research suggest that S. neumayeri can compensate for increased DNA damage to UV-R at relatively low levels. But if

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

    Science.gov (United States)

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

    2014-12-01

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

  6. The response of a simple Antarctic ice-flow model to temperature and sea-level fluctuations over the Cenozoic era

    NARCIS (Netherlands)

    van Tuyll, C.I.|info:eu-repo/dai/nl/304831875; van de Wal, R.S.W.|info:eu-repo/dai/nl/101899556; Oerlemans, J.|info:eu-repo/dai/nl/06833656X

    2007-01-01

    An ice-flow model is used to simulate the Antarctic ice-sheet volume and deep-sea temperature record during Cenozoic times. We used a vertically integrated axisymmetric ice-sheet model, including bedrock adjustment. In order to overcome strong numerical hysteresis effects during climate change, the

  7. 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.

  8. 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°.

  9. 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.

  10. The effect of sea-ice dynamics on Net Community Production (NCP) at the western Antarctic Peninsula (WAP) region

    Science.gov (United States)

    Li, Z.; Cassar, N.; Huang, K.; Ducklow, H. W.; Schofield, O.

    2016-02-01

    The WAP in the Southern Ocean has experienced a decrease in sea-ice extent ( 40%) over the last three decades, which has been associated with changes in the ecosystems. In this study, we examined the effect of sea-ice dynamics on the interannual variability of satellite-derived Annually-integrated NCP (ANCP). We derived a time series of NCP (1997-2014) using satellite observations of chlorophyll a concentration ([Chl]) and a regression between in situ [Chl] and O2/Ar-derived NCP measurements. Overall, our results are consistent with sea-ice dynamics influencing interannual ecosystem variability in the WAP region. ANCP displays an onshore to offshore gradient. Coastal/shelf regions and more specifically submarine canyons are up to eight times more productive than offshore regions. NCP peaks around January (November) when sea ice retreats and is consistently high (low) for the rest of the growing season in the shelf (southern and middle Southern Antarctic Circumpolar Current Front (SACCF)) region. We examined potential drivers of interannual variability in the ANCP through Empirical Orthogonal Function (EOF) analysis. The EOF's first mode explains 50% of the variance, with High Temporal Variability (HTV) observed in the southern and middle SACCF regions. The first principal component of ANCP is significantly correlated with the day of sea-ice retreat (R=-0.58, p<0.05) in the HTV region, and climate indices of Southern Annular Mode (SAM) (R=0.63, p<0.01, in austral spring) and El Niño Southern Oscillation (ENSO) (R=-0.52, p<0.05, in austral spring). Although the most obvious pathway by which day of sea-ice retreat influences NCP is through alleviation of light limitation, we found that the effect persists throughout the growing season, suggesting additional controls such as the influence of sea ice on stratification or iron availability.

  11. 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

  12. The response of a simple Antarctic ice-flow model to temperature and sea-level fluctuations over the Cenozoic era

    Science.gov (United States)

    van Tuyll, C. I.; van de Wal, R. S. W.; Oerlemans, J.

    2007-10-01

    An ice-flow model is used to simulate the Antarctic ice-sheet volume and deep-sea temperature record during Cenozoic times. We used a vertically integrated axisymmetric ice-sheet model, including bedrock adjustment. In order to overcome strong numerical hysteresis effects during climate change, the model is solved on a stretching grid. The Cenozoic reconstruction of the Antarctic ice sheet is accomplished by splitting the global oxygen isotope record derived from benthic foraminifera into an ice-volume and a deep-sea temperature component. The model is tuned to reconstruct the initiation of a large ice sheet of continental size at 34 Ma. The resulting ice volume curve shows that small ice caps (Paleocene and Eocene times. Fluctuations during the Miocene are large, indicating a retreat back from the coast and a vanishing ice flux across the grounding line, but with ice volumes still up to 60% of the present-day volume. The resulting deep-sea temperature curve shows similarities with the paleotemperature curve derived from Mg/Ca in benthic calcite from 25 Ma till the present, which supports the idea that the ice volume is well reproduced for this period. Before 34 Ma, the reproduced deep-sea temperature is slightly higher than is generally assumed. Global sea-level change turns out to be of minor importance when considering the Cenozoic evolution of the ice sheet until 5 Ma.

  13. Observation of hydro-acoustic signal from the Balleny Islands, Ross Sea, Antarctic: Seasonal ice activities and earthquakes from Pacific-Antarctic ridge

    Science.gov (United States)

    Hong, J. K.; Kang, S. G.; Dziak, R. P.; Park, Y.; Lau, T. K. A.; Haxel, J.; Matsumoto, H.

    2017-12-01

    From January 2015 to March 2016, five hydrophone moorings were deployed near the Balleny Islands to obtain the long-term hydroacoustic record as a collaborative effort between the NOAA/Pacific Marine Environmental Laboratory and the Korea Polar Research Institute. The goal of this hydro-acoustic project is to understand seasonal sea-ice activities and identify potential underwater volcanic sources within the Balleny seamounts. All five of the hydrophone moorings were recovered in March 2016, however only three of them recorded 14 months of continuous, broadband (1 kHz sample rate) hydro-acoustic data successfully. In spite of coordinating problem by partial recovery, recorded data contain valuable information for seasonal sea-ice activities and earthquakes from Pacific-Antarctic Ridge. We analyzed events from ice-quakes and earthquakes statistically. The number of ice-quakes is maximum in the austral summer while minimum in the austral winter which shows a clear seasonal pattern consistent with freeze-thaw cycles. Comparing with global earthquakes catalogue, number of earthquake events are correlated well with the catalogue. Because the austral winter is more calm by ice-quakes, however, we can detect more earthquakes in this season.

  14. 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.

    2013-01-01

    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. PMID:24019487

  15. Balance of the West Antarctic Ice Sheet

    Science.gov (United States)

    2002-01-01

    For several decades, measurements of the West Antarctic Ice Sheet showed it to be retreating rapidly. But new data derived from satellite-borne radar sensors show the ice sheet to be growing. Changing Antarctic ice sheets remains an area of high scientific interest, particularly in light of recent global warming concerns. These new findings are significant because scientists estimate that sea level would rise 5-6 meters (16-20 feet) if the ice sheet collapsed into the sea. Do these new measurements signal the end of the ice sheet's 10,000-year retreat? Or, are these new satellite data simply much more accurate than the sparse ice core and surface measurements that produced the previous estimates? Another possibility is that the ice accumulation may simply indicate that the ice sheet naturally expands and retreats in regular cycles. Cryologists will grapple with these questions, and many others, as they examine the new data. The image above depicts the region of West Antarctica where scientists measured ice speed. The fast-moving central ice streams are shown in red. Slower tributaries feeding the ice streams are shown in blue. Green areas depict slow-moving, stable areas. Thick black lines depict the areas that collect snowfall to feed their respective ice streams. Reference: Ian Joughin and Slawek Tulaczyk Science Jan 18 2002: 476-480. Image courtesy RADARSAT Antarctic Mapping Project

  16. Variations of the Antarctic Ice Sheet in a Coupled Ice Sheet-Earth-Sea Level Model: Sensitivity to Viscoelastic Earth Properties

    Science.gov (United States)

    Pollard, David; Gomez, Natalya; Deconto, Robert M.

    2017-11-01

    A coupled ice sheet-solid Earth-sea level model is applied to long-term variations of the Antarctic ice sheet. A set of radially varying viscoelastic profiles in the global Earth model is used to explore feedbacks on ice sheet variability, including one with a very weak upper mantle zone and thin lithosphere representative of West Antarctic regions. Simulations are performed for (1) the deglacial retreat over the last 20,000 years, (2) the future 5,000 years with greenhouse-gas scenario Representative Concentration Pathway 8.5 (RCP8.5), and (3) the warm Pliocene 3 Ma. For the deglacial period a large ensemble of 625 simulations is analyzed, with a score computed for each run based on comparisons to geologic and modern data. For each of the five Earth profiles, the top-scoring combinations of the other model parameters in the ensemble are used to perform future and Pliocene simulations. For the last deglacial retreat, the viscoelastic Earth profiles produce relatively small differences in overall ice volume and equivalent sea level. In contrast, profiles with weak upper mantle and thin lithosphere produce strong negative feedback and less ice retreat in the future and Pliocene runs. This is due to the faster pace of ice sheet retreat in these runs, leading to greater lags in the viscous bedrock rebound behind the unloading, which allows for greater influence of the viscosity profiles. However, the differences in grounding-line retreat are located primarily in East Antarctic basins, where a weak upper mantle and thin lithosphere may not be realistic, emphasizing the need for lateral heterogeneity in the Earth model.

  17. 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.

  18. Arctic and Antarctic Sea Ice Concentrations from Multichannel Passive-Microwave Satellite Data Sets: October 1978-September 1995 User's Guide

    Science.gov (United States)

    Cavalieri, Donald J.; Parkinson, Claire L.; Gloersen, Per; Zwally, H. Jay

    1997-01-01

    Satellite multichannel passive-microwave sensors have provided global radiance measurements with which to map, monitor, and study the Arctic and Antarctic polar sea ice covers. The data span over 18 years (as of April 1997), starting with the launch of the Scanning Multichannel Microwave Radiometer (SMMR) on NASA's SeaSat A and Nimbus 7 in 1978 and continuing with the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave/Imager (SSMI) series beginning in 1987. It is anticipated that the DMSP SSMI series will continue into the 21st century. The SSMI series will be augmented by new, improved sensors to be flown on Japanese and U.S. space platforms. This User's Guide provides a description of a new sea ice concentration data set generated from observations made by three of these multichannel sensors. The data set includes gridded daily ice concentrations (every-other-day for the SMMR data) for both the north and south polar regions from October 26, 1978 through September 30, 1995, with the one exception of a 6-week data gap from December 3, 1987 through January 12, 1988. The data have been placed on two CD-ROMs that include a ReadMeCD file giving the technical details on the file format, file headers, north and south polar grids, ancillary data sets, and directory structure of the CD-ROM. The CD-ROMS will be distributed by the National Snow and Ice Data Center in Boulder, CO.

  19. Climate links and recent extremes in antarctic sea ice, high-latitude cyclones, Southern Annular Mode and ENSO

    Science.gov (United States)

    Pezza, Alexandre Bernardes; Rashid, Harun A.; Simmonds, Ian

    2012-01-01

    In this article, we study the climate link between the Southern Annular Mode (SAM) and the southern sea-ice extent (SIE), and discuss the possible role of stationary waves and synoptic eddies in establishing this link. In doing so, we have used a combination of techniques involving spatial correlations of SIE, eddy streamfunction and wind anomalies, and statistics of high-latitude cyclone strength. It is suggested that stationary waves may be amplified by eddy anomalies associated with high latitude cyclones, resulting in more sea ice when the SAM is in its positive phase for most, but not all, longitudes. A similar association is observed during ENSO (La Niña years). Although this synergy in the SAM/ENSO response may partially reflect preferential areas for wave amplification around Antarctica, the short extent of the climate records does not allow for a definite causality connection to be established with SIE. Stronger polar cyclones are observed over the areas where the stationary waves are amplified. These deeper cyclones will break up and export ice equatorward more efficiently, but the near-coastal regions are cold enough to allow for a rapid re-freeze of the resulting ice break-up. We speculate that if global warming continues this same effect could help reverse the current (positive) Antarctic SIE trends once the ice gets thinner, similarly to what has been observed in the Northern Hemisphere.

  20. 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.

  1. 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.

  2. Short-term under-ice variability of prokaryotic plankton communities in coastal Antarctic waters (Cape Hallett, Ross Sea)

    Science.gov (United States)

    Celussi, Mauro; Paoli, Alessandro; Crevatin, Erica; Bergamasco, Andrea; Margiotta, Francesca; Saggiomo, Vincenzo; Umani, Serena Fonda; Del Negro, Paola

    2009-03-01

    During the 2006 Italian Antarctic expedition a diel sampling was performed close to Cape Hallett (Ross Sea) during the Austral summer. Under-ice seawater samples (˜4 m) were collected every 2 h for 28 h in order to estimate prokaryotic processes' variability and community structure dynamics. Prokaryotic and viral abundances, exoenzymatic activities (β-glucosidase, chitinase, lipase, alkaline phosphatase and leucine aminopeptidase), prokaryotic carbon production ( 3H-leucine incorporation) and community structure (Denaturing Gradient Gel Electrophoresis - DGGE fingerprints) were analysed. Results showed that the diel variability of the prokaryotic activity followed a variation in salinity, probably as a consequence of the periodical thawing of sea ice (driven by solar radiation and air temperature cycles), while negligible variation in viral and prokaryotic abundances occurred. The Bacterial and Archaeal community structures underwent an Operational Taxonomic Units (OTUs) temporal shift from the beginning to the end of the sampling, while Flavobacteria-specific primers highlighted high variations in this group possibly related to sea ice melting and substrate release.

  3. 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.

  4. Interannual variability in phytoplankton biomass and species composition in northern Marguerite Bay (West Antarctic Peninsula) is governed by both winter sea ice cover and summer stratification

    NARCIS (Netherlands)

    Rozema, P.D.; Venables, H.J.; van de Poll, W.H.; Clarke, A.; Meredith, M.P.; Buma, A.G.J.

    2017-01-01

    The rapid warming of the West Antarctic Peninsula region has led to reduced sea ice cover and enhanced glacial melt water input. This has potential implications for marine ecosystems, notably phytoplankton growth, biomass, and composition. Fifteen years (1997–2012) of year-round size fractionated

  5. Images of Antarctic Ice Shelves

    Data.gov (United States)

    National Aeronautics and Space Administration — Recent changes in the extent and stability of ice shelves in the Antarctic Peninsula prompted NSIDC to begin a monitoring program using data from the AVHRR Polar 1...

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

    Science.gov (United States)

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

    2017-07-15

    Ocean acidification (OA) resulting from increasing atmospheric CO 2 strongly influences marine ecosystems, particularly in the polar ocean due to greater CO 2 solubility. Here, we grew the Antarctic sea ice diatom Nitzschia sp. ICE-H in a semicontinuous culture under low (~400ppm) and high (1000ppm) CO 2 levels. Elevated CO 2 resulted in a stimulated physiological response including increased growth rates, chlorophyll a contents, and nitrogen and phosphorus uptake rates. Furthermore, high CO 2 enhanced cellular particulate organic carbon production rates, indicating a greater shift from inorganic to organic carbon. However, the cultures grown in high CO 2 conditions exhibited a decrease in both extracellular and intracellular carbonic anhydrase activity, suggesting that the carbon concentrating mechanisms of Nitzschia sp. ICE-H may be suppressed by elevated CO 2 . Our results revealed that OA would be beneficial to the survival of this sea ice diatom strain, with broad implications for global carbon cycles in the future ocean. Copyright © 2017. Published by Elsevier Ltd.

  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. 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...

  9. Purification and biochemical characterization of a cold-active lipase from Antarctic sea ice bacteria Pseudoalteromonas sp. NJ 70.

    Science.gov (United States)

    Wang, Quanfu; Hou, Yanhua; Ding, Yu; Yan, Peisheng

    2012-09-01

    An extracellular cold-active lipase from Antarctic sea ice bacteria Pseudoalteromonas sp. NJ 70 was purified and characterized. The overall purification based on lipase activity was 27.5-fold with a yield of 25.4 %. The purified lipase showed as a single band on SDS-PAGE with an apparent molecular weight of 37 kDa. The optimum temperature and pH were 35 °C and 7.0, respectively. The lipase activity was enhanced by Ca(2+) and Mg(2+), while was partially inhibited by other metals such as Cu(2+), Zn(2+), Ba(2+), Pb(2+), Fe(2+) and Mn(2+). The lipase had high tolerance to a wide range of NaCl concentrations (0-2 M NaCl). It exhibited high levels of activity in the presence of DTT, Thiourea, H(2)O(2) as well as in the presence of various detergents such as Span 60, Tween-80, Triton X-100. In addition, the lipase showed a preference for long-chain p-nitrophenyl esters (C(12)-C(18)). These results indicated that this lipase could be a novel cold-active lipase.

  10. 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.

  11. Mass balance of the Antarctic ice sheet.

    Science.gov (United States)

    Wingham, D J; Shepherd, A; Muir, A; Marshall, G J

    2006-07-15

    The Antarctic contribution to sea-level rise has long been uncertain. While regional variability in ice dynamics has been revealed, a picture of mass changes throughout the continental ice sheet is lacking. Here, we use satellite radar altimetry to measure the elevation change of 72% of the grounded ice sheet during the period 1992-2003. Depending on the density of the snow giving rise to the observed elevation fluctuations, the ice sheet mass trend falls in the range -5-+85Gtyr-1. We find that data from climate model reanalyses are not able to characterise the contemporary snowfall fluctuation with useful accuracy and our best estimate of the overall mass trend-growth of 27+/-29Gtyr-1-is based on an assessment of the expected snowfall variability. Mass gains from accumulating snow, particularly on the Antarctic Peninsula and within East Antarctica, exceed the ice dynamic mass loss from West Antarctica. The result exacerbates the difficulty of explaining twentieth century sea-level rise.

  12. Phytoplankton-bacterial interactions mediate micronutrient colimitation at the coastal Antarctic sea ice edge.

    Science.gov (United States)

    Bertrand, Erin M; McCrow, John P; Moustafa, Ahmed; Zheng, Hong; McQuaid, Jeffrey B; Delmont, Tom O; Post, Anton F; Sipler, Rachel E; Spackeen, Jenna L; Xu, Kai; Bronk, Deborah A; Hutchins, David A; Allen, Andrew E

    2015-08-11

    Southern Ocean primary productivity plays a key role in global ocean biogeochemistry and climate. At the Southern Ocean sea ice edge in coastal McMurdo Sound, we observed simultaneous cobalamin and iron limitation of surface water phytoplankton communities in late Austral summer. Cobalamin is produced only by bacteria and archaea, suggesting phytoplankton-bacterial interactions must play a role in this limitation. To characterize these interactions and investigate the molecular basis of multiple nutrient limitation, we examined transitions in global gene expression over short time scales, induced by shifts in micronutrient availability. Diatoms, the dominant primary producers, exhibited transcriptional patterns indicative of co-occurring iron and cobalamin deprivation. The major contributor to cobalamin biosynthesis gene expression was a gammaproteobacterial population, Oceanospirillaceae ASP10-02a. This group also contributed significantly to metagenomic cobalamin biosynthesis gene abundance throughout Southern Ocean surface waters. Oceanospirillaceae ASP10-02a displayed elevated expression of organic matter acquisition and cell surface attachment-related genes, consistent with a mutualistic relationship in which they are dependent on phytoplankton growth to fuel cobalamin production. Separate bacterial groups, including Methylophaga, appeared to rely on phytoplankton for carbon and energy sources, but displayed gene expression patterns consistent with iron and cobalamin deprivation. This suggests they also compete with phytoplankton and are important cobalamin consumers. Expression patterns of siderophore- related genes offer evidence for bacterial influences on iron availability as well. The nature and degree of this episodic colimitation appear to be mediated by a series of phytoplankton-bacterial interactions in both positive and negative feedback loops.

  13. 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

  14. The late Cainozoic East Antarctic ice sheet

    International Nuclear Information System (INIS)

    Colhoun, E.A.

    1999-01-01

    A review, mainly of East Antarctic late Cainozoic (post 40 Ma) geological and geomorphological evidence, supports the hypothesis of the continuous presence of an ice sheet, of about the present size, since the late Miocene. Evidence is presented and the view advanced that, during the late Wisconsin maximum of isotope stage 2, ice was not nearly as thick or extensive over the continental shelf as required by the model of 'maximum' Antarctic glaciation. Some of the factors influencing the contribution of Antarctica to post-glacial sea-level rise are discussed. It is considered that Antarctica's contribution was probably considerably less than previously estimated. The dating of marine and freshwater sequences in the Vestfold and Bunger Hills is consistent with deglaciation around the Pleistocene Holocene boundary, after the Late Wisconsin maximum. A date of ∼25 ka BP from permafrost in the Larsemann Hills means that either the Larsemann Hills were not glaciated during the Late Wisconsin or the ice failed to erode much of the permafrost surface. The degree of weathering of rock and glacial drifts in the Vestfold, Larsemann and Bunger Hills suggests a long time for formation, perhaps considerably longer than indicated by the dated marine and freshwater sediment sequences. Cosmogenic isotope dating in the Vestfold Hills has provided equivocal ages for deglaciation. While the results could indicate deglaciation before 80 ka BP, they do not confirm such early deglaciation. If the ice cover was thin and failed to remove the previous rock exposure profile, then the assays could predate the last ice advance. Weathered iron crust fragments in the till suggest little erosion. The raised beaches of the oases are Holocene. Assuming they have been produced by post Late Wisconsin isostatic uplift and by the Holocene transgression, calculations show that the Antarctic continental ice sheet could not have been more than ∼500 m thicker in the inner shelf-coastal zone. The

  15. EBSD in Antarctic and Greenland Ice

    Science.gov (United States)

    Weikusat, Ilka; Kuiper, Ernst-Jan; Pennock, Gill; Sepp, Kipfstuhl; Drury, Martyn

    2017-04-01

    boundaries. However, an almost equal number of tilt subgrain boundaries were measured, involving dislocations gliding on non-basal planes (prism or prism slip). A few subgrain boundaries involving prism edge dislocation glide, as well as boundaries involving basal twist dislocation slip, were also identified. The finding that subgrain boundaries built up by dislocations gliding on non-basal planes are as frequent as those originating from basal plane slip is surprising and has impact on the discussion on rate-controlling processes for the ice flow descriptions of large ice masses with respect to sea-level evolution. Weikusat, I.; Miyamoto, A.; Faria, S. H.; Kipfstuhl, S.; Azuma, N. & Hondoh, T.: Subgrain boundaries in Antarctic ice quantified by X-ray Laue diffraction J. Glaciol., 2011, 57, 85-94

  16. 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

    Temporal evolution of pCO2 profiles in sea ice in the Bellingshausen Sea, Antarctica, in October 2007 shows physical and thermodynamic processes controls the CO2 sys- tem in the ice. During the survey, cyclical warming and cool- ing strongly influenced the physical, chemical, and thermo- dynamic...... 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...

  17. Interannual Variability in Weddell Sea Ice Formation and Bottom Water Outflow in Response to the Antarctic Circumpolar Wave

    Science.gov (United States)

    Drinkwater, M.; Kreyscher, M.

    1997-01-01

    The seasonal sea-ice cover surrounding the continent of Antarctica, together with the circumpolar current belt, form a contiguous pathway for propagation and transfer of climatological anomalies around the Sourthern hemisphere.

  18. Sea-level response to melting of Antarctic ice shelves on multi-centennial timescales with the fast Elementary Thermomechanical Ice Sheet model (f.ETISh v1.0)

    Science.gov (United States)

    Pattyn, Frank

    2017-08-01

    The magnitude of the Antarctic ice sheet's contribution to global sea-level rise is dominated by the potential of its marine sectors to become unstable and collapse as a response to ocean (and atmospheric) forcing. This paper presents Antarctic sea-level response to sudden atmospheric and oceanic forcings on multi-centennial timescales with the newly developed fast Elementary Thermomechanical Ice Sheet (f.ETISh) model. The f.ETISh model is a vertically integrated hybrid ice sheet-ice shelf model with vertically integrated thermomechanical coupling, making the model two-dimensional. Its marine boundary is represented by two different flux conditions, coherent with power-law basal sliding and Coulomb basal friction. The model has been compared to existing benchmarks. Modelled Antarctic ice sheet response to forcing is dominated by sub-ice shelf melt and the sensitivity is highly dependent on basal conditions at the grounding line. Coulomb friction in the grounding-line transition zone leads to significantly higher mass loss in both West and East Antarctica on centennial timescales, leading to 1.5 m sea-level rise after 500 years for a limited melt scenario of 10 m a-1 under freely floating ice shelves, up to 6 m for a 50 m a-1 scenario. The higher sensitivity is attributed to higher ice fluxes at the grounding line due to vanishing effective pressure. Removing the ice shelves altogether results in a disintegration of the West Antarctic ice sheet and (partially) marine basins in East Antarctica. After 500 years, this leads to a 5 m and a 16 m sea-level rise for the power-law basal sliding and Coulomb friction conditions at the grounding line, respectively. The latter value agrees with simulations by DeConto and Pollard (2016) over a similar period (but with different forcing and including processes of hydrofracturing and cliff failure). The chosen parametrizations make model results largely independent of spatial resolution so that f.ETISh can potentially be

  19. Increased West Antarctic and unchanged East Antarctic ice discharge over the last 7 years

    Science.gov (United States)

    Gardner, Alex S.; Moholdt, Geir; Scambos, Ted; Fahnstock, Mark; Ligtenberg, Stefan; van den Broeke, Michiel; Nilsson, Johan

    2018-02-01

    Ice discharge from large ice sheets plays a direct role in determining rates of sea-level rise. We map present-day Antarctic-wide surface velocities using Landsat 7 and 8 imagery spanning 2013-2015 and compare to earlier estimates derived from synthetic aperture radar, revealing heterogeneous changes in ice flow since ˜ 2008. The new mapping provides complete coastal and inland coverage of ice velocity north of 82.4° S with a mean error of the daylight period. Using an optimized flux gate, ice discharge from Antarctica is 1929 ± 40 Gigatons per year (Gt yr-1) in 2015, an increase of 36 ± 15 Gt yr-1 from the time of the radar mapping. Flow accelerations across the grounding lines of West Antarctica's Amundsen Sea Embayment, Getz Ice Shelf and Marguerite Bay on the western Antarctic Peninsula, account for 88 % of this increase. In contrast, glaciers draining the East Antarctic Ice Sheet have been remarkably constant over the period of observation. Including modeled rates of snow accumulation and basal melt, the Antarctic ice sheet lost ice at an average rate of 183 ± 94 Gt yr-1 between 2008 and 2015. The modest increase in ice discharge over the past 7 years is contrasted by high rates of ice sheet mass loss and distinct spatial patters of elevation lowering. The West Antarctic Ice Sheet is experiencing high rates of mass loss and displays distinct patterns of elevation lowering that point to a dynamic imbalance. We find modest increase in ice discharge over the past 7 years, which suggests that the recent pattern of mass loss in Antarctica is part of a longer-term phase of enhanced glacier flow initiated in the decades leading up to the first continent-wide radar mapping of ice flow.

  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. Natural and anthropogenic hydrocarbons in the Antarctic pack ice

    International Nuclear Information System (INIS)

    Nemirovskaya, I.A.; Novigatsky, A.N.

    2004-01-01

    A field experiment was conducted near the Russian Antarctic stations in May, 2001 in the Pridz Bay and coastal part of the Davies Sea to examine the content of dissolved and suspended forms of aliphatic hydrocarbons in melted snow samples, pack ice and ice cores. The site included clean control areas and polluted test areas. A spill was performed by covering the bare ice surface with marine diesel fuel. The different physical characteristics of clean and polluted ice were measured. This included radiation balance, reflected solar radiation, integral albedo radiation, surface temperature, seawater temperature, salinity at depth, and ice salinity. The study showed that accumulation of natural and anthropogenic hydrocarbon took place in the ice-water barrier zone, mostly in suspended form. It was concluded that for oil spills in pack Antarctic ice, the mechanism of filtration due to convection-diffusion plays an important role in the transformation of diesel fuel. 14 refs., 2 tabs., 2 figs

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

    NARCIS (Netherlands)

    Pritchard, H.D.; Ligtenberg, S.R.M.|info:eu-repo/dai/nl/32821177X; Fricker, H.A.; Vaughan, D.G.; van den Broeke, M.R.|info:eu-repo/dai/nl/073765643; 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,

  3. Uncertainties in the Antarctic Ice Sheet Contribution to Sea Level Rise: Exploration of Model Response to Errors in Climate Forcing, Boundary Conditions, and Internal Parameters

    Science.gov (United States)

    Schlegel, N.; Seroussi, H. L.; Boening, C.; Larour, E. Y.; Limonadi, D.; Schodlok, M.; Watkins, M. M.

    2017-12-01

    The Jet Propulsion Laboratory-University of California at Irvine Ice Sheet System Model (ISSM) is a thermo-mechanical 2D/3D parallelized finite element software used to physically model the continental-scale flow of ice at high resolutions. Embedded into ISSM are uncertainty quantification (UQ) tools, based on the Design Analysis Kit for Optimization and Terascale Applications (DAKOTA) software. ISSM-DAKOTA offers various UQ methods for the investigation of how errors in model input impact uncertainty in simulation results. We utilize these tools to regionally sample model input and key parameters, based on specified bounds of uncertainty, and run a suite of continental-scale 100-year ISSM forward simulations of the Antarctic Ice Sheet. Resulting diagnostics (e.g., spread in local mass flux and regional mass balance) inform our conclusion about which parameters and/or forcing has the greatest impact on century-scale model simulations of ice sheet evolution. The results allow us to prioritize the key datasets and measurements that are critical for the minimization of ice sheet model uncertainty. Overall, we find that Antartica's total sea level contribution is strongly affected by grounding line retreat, which is driven by the magnitude of ice shelf basal melt rates and by errors in bedrock topography. In addition, results suggest that after 100 years of simulation, Thwaites glacier is the most significant source of model uncertainty, and its drainage basin has the largest potential for future sea level contribution. This work is performed at and supported by the California Institute of Technology's Jet Propulsion Laboratory. Supercomputing time is also supported through a contract with the National Aeronautics and Space Administration's Cryosphere program.

  4. Deglaciation-Induced Spatially Variable Sea Level Change: A Simple-Model Case Study for the Greenland and Antarctic Ice Sheets

    Directory of Open Access Journals (Sweden)

    M. Kuhn

    2010-06-01

    Full Text Available Some studies on deglaciation-induced sea level change provide only a global average change, thus neglecting the fact that sea level change is spatially variable. This is due mainly to the gravitational and visco-elastic feedback effects of the changing surface mass loads. In order to address this apparent misconception and raise further awareness, we provide a conceptual example based on a simulated total melt of the Greenland and Antarctic ice sheets. This would give a global average sea level change of about 64 m. However, due to the changed distribution of gravitating masses, the sea-level change depends on location, with a range of about −27 m to +79 m (i.e., sea-level will even fall in some places. This spatial dependency has several implications, such as >10% biases in global average sea-level change estimates based only on tide-gauge records, flooding of almost 10% of current land areas, an increase of the length of day by almost a half a second and a northward move of the centre of mass (geocentre by about 20 m.

  5. Enhanced tropospheric BrO over Antarctic sea ice in mid winter observed by MAX-DOAS on board the research vessel Polarstern

    Directory of Open Access Journals (Sweden)

    T. Wagner

    2007-06-01

    Full Text Available We present Multi AXis-Differential Optical Absorption Spectroscopy (MAX-DOAS observations of tropospheric BrO carried out on board the German research vessel Polarstern during the Antarctic winter 2006. Polarstern entered the area of first year sea ice around Antarctica on 24 June 2006 and stayed within this area until 15 August 2006. For the period when the ship cruised inside the first year sea ice belt, enhanced BrO concentrations were almost continuously observed. Outside the first year sea ice belt, typically low BrO concentrations were found. Based on back trajectory calculations we find a positive correlation between the observed BrO differential slant column densities (ΔSCDs and the duration for which the air masses had been in contact with the sea ice surface prior to the measurement. While we can not completely rule out that in several cases the highest BrO concentrations might be located close to the ground, our observations indicate that the maximum BrO concentrations might typically exist in a (possibly extended layer around the upper edge of the boundary layer. Besides the effect of a decreasing pH of sea salt aerosol with altitude and therefore an increase of BrO with height, this finding might be also related to vertical mixing of air from the free troposphere with the boundary layer, probably caused by convection over the warm ocean surface at polynyas and cracks in the ice. Strong vertical gradients of BrO and O3 could also explain why we found enhanced BrO levels almost continuously for the observations within the sea ice. Based on our estimated BrO profiles we derive BrO mixing ratios of several ten ppt, which is slightly higher than many existing observations. Our observations indicate that enhanced BrO concentrations around Antarctica exist about one month earlier than observed by satellite instruments. From detailed radiative transfer simulations we find that MAX-DOAS observations are up to about one order of

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

    Science.gov (United States)

    2006-09-01

    well constrained ( Peters et al., 1988), and any Ri-based estimate of K, will have large errors associated with it. Nevertheless, it is instructive to see...A.J., Muench, R.D., Pinkel, R., 1992. Diurnal tides near the Yermak Plateau. Journal of Geophysical Research 97, 12,639-12,652. Peters , H., Gregg, M.C...S. Stammerjohn, R. Smith, H.R. Krouse, A.J. Gow and S.F. Ackley, 2004: Winter sea ice properties in Marguerite Bay, Antarctica. Deep-Sea Res. 11, 51

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

    Science.gov (United States)

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

    2016-02-01

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

  8. Arctic Landfast Sea Ice 1953-1998, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — 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...

  9. The health of Antarctic ice shelves

    Science.gov (United States)

    Gagliardini, Olivier

    2018-01-01

    The thinning of floating ice shelves around Antarctica enhances upstream ice flow, contributing to sea-level rise. Ice-shelf thinning is now shown to influence glacial movement over much larger distances than previously thought.

  10. Volcanic deposits in Antarctic snow and ice

    Science.gov (United States)

    Delmas, Robert J.; Legrand, Michel; Aristarain, Alberto J.; Zanolini, FrançOise

    1985-12-01

    Major volcanic eruptions are able to spread large amounts of sulfuric acid all over the world. Acid layers of volcanic origin were detected for the first time a few years ago by Hammer in Greenland ice. The present paper deals with volcanic deposits in the Antarctic. The different methods that can be used to find volcanic acid deposits in snow and ice cores are compared: electrical conductivity, sulfate, and acidity measurements. Numerous snow and ice samples collected at several Antarctic locations were analyzed. The results reveal that the two major volcanic events recorded by H2SO4, fallout in Antarctic ice over the last century are the eruptions of Krakatoa (1883) and Agung (1963), both located at equatorial latitudes in the southern hemisphere. The volcanic signals are found to be particularly well defined at central Antarctic locations apparently in relation to the low snow accumulation rates in these areas. It is demonstrated that volcanic sulfuric acid in snow is not even partially neutralized by ammonia. The possible influence of Antarctic volcanic activity on snow chemistry is also discussed, using the three recent eruptions of the Deception Island volcano as examples. Only one of them seems to have had a significant effect on the chemistry of snow at a location 200 km from this volcano. It is concluded that Antarctic volcanic ice records are less complicated than Greenland records because of the limited number of volcanos in the southern hemisphere and the apparently higher signal to background ratio for acidity in Antarctica than in Greenland.

  11. NASA SCP Arctic and Antarctic Ice Extent from QuikSCAT, 1999-2009, Version 2

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set provides sea ice extent for the Arctic (60-90 degrees North) and Antarctic (52-90 degrees South) in Scatterometer Image Reconstruction (SIR) binary...

  12. NASA SCP Arctic and Antarctic Ice Extent from QuikSCAT, 1999-2004

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set provides sea ice extent for the Arctic (60-90 degrees North) and Antarctic (52-90 degrees South) in Scatterometer Image Reconstruction (SIR) binary...

  13. 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 ages1, fundamental questions remain over the response of the Antarctic ice sheets to orbital cycles2. 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 warming3. 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 today4 and atmospheric CO2 concentration was as high as 400 p.p.m.v. (refs 5, 6). The evidence is consistent with a new ice-sheet/ice-shelf model7 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 melt8 under conditions of elevated CO2.

  14. Changes in ice dynamics and mass balance of the Antarctic ice sheet.

    Science.gov (United States)

    Rignot, Eric

    2006-07-15

    The concept that the Antarctic ice sheet changes with eternal slowness has been challenged by recent observations from satellites. Pronounced regional warming in the Antarctic Peninsula triggered ice shelf collapse, which led to a 10-fold increase in glacier flow and rapid ice sheet retreat. This chain of events illustrated the vulnerability of ice shelves to climate warming and their buffering role on the mass balance of Antarctica. In West Antarctica, the Pine Island Bay sector is draining far more ice into the ocean than is stored upstream from snow accumulation. This sector could raise sea level by 1m and trigger widespread retreat of ice in West Antarctica. Pine Island Glacier accelerated 38% since 1975, and most of the speed up took place over the last decade. Its neighbour Thwaites Glacier is widening up and may double its width when its weakened eastern ice shelf breaks up. Widespread acceleration in this sector may be caused by glacier ungrounding from ice shelf melting by an ocean that has recently warmed by 0.3 degrees C. In contrast, glaciers buffered from oceanic change by large ice shelves have only small contributions to sea level. In East Antarctica, many glaciers are close to a state of mass balance, but sectors grounded well below sea level, such as Cook Ice Shelf, Ninnis/Mertz, Frost and Totten glaciers, are thinning and losing mass. Hence, East Antarctica is not immune to changes.

  15. Sea Ice Ecosystems

    Science.gov (United States)

    Arrigo, Kevin R.

    2014-01-01

    Polar sea ice is one of the largest ecosystems on Earth. The liquid brine fraction of the ice matrix is home to a diverse array of organisms, ranging from tiny archaea to larger fish and invertebrates. These organisms can tolerate high brine salinity and low temperature but do best when conditions are milder. Thriving ice algal communities, generally dominated by diatoms, live at the ice/water interface and in recently flooded surface and interior layers, especially during spring, when temperatures begin to rise. Although protists dominate the sea ice biomass, heterotrophic bacteria are also abundant. The sea ice ecosystem provides food for a host of animals, with crustaceans being the most conspicuous. Uneaten organic matter from the ice sinks through the water column and feeds benthic ecosystems. As sea ice extent declines, ice algae likely contribute a shrinking fraction of the total amount of organic matter produced in polar waters.

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

    Directory of Open Access Journals (Sweden)

    G. S. Babonis

    2016-06-01

    Full Text Available 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.

  17. Influence of snow depth and surface flooding on light transmission through Antarctic pack ice

    Science.gov (United States)

    Arndt, Stefanie; Meiners, Klaus M.; Ricker, Robert; Krumpen, Thomas; Katlein, Christian; Nicolaus, Marcel

    2017-03-01

    Snow on sea ice alters the properties of the underlying ice cover as well as associated physical and biological processes at the interfaces between atmosphere, sea ice, and ocean. The Antarctic snow cover persists during most of the year and contributes significantly to the sea-ice mass due to the widespread surface flooding and related snow-ice formation. Snow also enhances the sea-ice surface reflectivity of incoming shortwave radiation and determines therefore the amount of light being reflected, absorbed, and transmitted to the upper ocean. Here, we present results of a case study of spectral solar radiation measurements under Antarctic pack ice with an instrumented Remotely Operated Vehicle in the Weddell Sea in 2013. In order to identify the key variables controlling the spatial distribution of the under-ice light regime, we exploit under-ice optical measurements in combination with simultaneous characterization of surface properties, such as sea-ice thickness and snow depth. Our results reveal that the distribution of flooded and nonflooded sea-ice areas dominates the spatial scales of under-ice light variability for areas smaller than 100 m-by-100 m. However, the heterogeneous and highly metamorphous snow on Antarctic pack ice obscures a direct correlation between the under-ice light field and snow depth. Compared to the Arctic, light levels under Antarctic pack ice are extremely low during spring (<0.1%). This is mostly a result of the distinctly different dominant sea ice and snow properties with seasonal snow cover (including strong surface melt and summer melt ponds) in the Arctic and a year-round snow cover and widespread surface flooding in the Southern Ocean.

  18. Meltwater produced by wind–albedo interaction stored in an East Antarctic ice shelf

    NARCIS (Netherlands)

    Lenaerts, JTM; Lhermitte, S.L.M.; Drews, R.; Ligtenberg, SRM; Berger, S.; Helm, V.; Smeets, C.J.P.P.; van den Broeke, MR; 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 shelves1, 2 causing grounded glaciers to accelerate3 and sea level to rise. In the Antarctic Peninsula, foehn winds enhance melting near the grounding line4, which in the recent past has led to the

  19. Evolution of the early Antarctic ice ages

    NARCIS (Netherlands)

    Liebrand, Diederik; de Bakker, Anouk T M|info:eu-repo/dai/nl/371573734; Beddow, Helen M; Wilson, Paul A; Bohaty, Steven M; Ruessink, Gerben|info:eu-repo/dai/nl/169093360; Pälike, Heiko; Batenburg, Sietske J; Hilgen, Frederik J|info:eu-repo/dai/nl/102639876; Hodell, David A; Huck, Claire E; Kroon, Dick; Raffi, Isabella; Saes, Mischa J M; van Dijk, Arnold E|info:eu-repo/dai/nl/341412082; Lourens, Lucas J|info:eu-repo/dai/nl/125023103

    2017-01-01

    Understanding the stability of the early Antarctic ice cap in the geological past is of societal interest because present-day atmospheric CO2 concentrations have reached values comparable to those estimated for the Oligocene and the Early Miocene epochs. Here we analyze a new high-resolution

  20. Dating Antarctic ice sheet collapse: Proposing a molecular genetic approach

    Science.gov (United States)

    Strugnell, Jan M.; Pedro, Joel B.; Wilson, Nerida G.

    2018-01-01

    Sea levels at the end of this century are projected to be 0.26-0.98 m higher than today. The upper end of this range, and even higher estimates, cannot be ruled out because of major uncertainties in the dynamic response of polar ice sheets to a warming climate. Here, we propose an ecological genetics approach that can provide insight into the past stability and configuration of the West Antarctic Ice Sheet (WAIS). We propose independent testing of the hypothesis that a trans-Antarctic seaway occurred at the last interglacial. Examination of the genomic signatures of bottom-dwelling marine species using the latest methods can provide an independent window into the integrity of the WAIS more than 100,000 years ago. Periods of connectivity facilitated by trans-Antarctic seaways could be revealed by dating coalescent events recorded in DNA. These methods allow alternative scenarios to be tested against a fit to genomic data. Ideal candidate taxa for this work would need to possess a circumpolar distribution, a benthic habitat, and some level of genetic structure indicated by phylogeographical investigation. The purpose of this perspective piece is to set out an ecological genetics method to help resolve when the West Antarctic Ice Shelf last collapsed.

  1. 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.

  2. Relative sea level in the Western Mediterranean basin: A regional test of the ICE-7G_NA (VM7) model and a constraint on late Holocene Antarctic deglaciation

    Science.gov (United States)

    Roy, Keven; Peltier, W. R.

    2018-03-01

    The Mediterranean Basin is a region of special interest in the study of past and present relative sea level evolution, given its location south of the ice sheets that covered large fractions of Northern Europe during the last glaciation, the large number of biological, geological and archaeological sea level indicators that have been retrieved from its coastal regions, as well as its high density of modern coastal infrastructure. Models of the Glacial Isostatic Adjustment (GIA) process provide reconstructions of past relative sea level evolution, and can be tested for validity against past sea level indicators from the region. It is demonstrated herein that the latest ICE-7G_NA (VM7) model of the GIA process, the North American component of which was refined using a full suite of geophysical observables, is able to reconcile the vast majority of uniformly analyzed relative sea level constraints available for the Western part of the Mediterranean basin, a region to which it was not tuned. We also revisit herein the previously published interpretations of relative sea level information obtained from Roman-era coastal Mediterranean "fish tanks", analyze the far-field influence of the rate of late Holocene Antarctic ice sheet melting history on the exceptionally detailed relative sea level history available from southern Tunisia, and extend the analysis to complementary constraints on the history of Antarctic ice-sheet melting available from islands in the equatorial Pacific Ocean. The analyses reported herein provide strong support for the global "exportability" of the ICE-7G_NA (VM7) model, a result that speaks directly to the ability of spherically symmetric models of the internal viscoelastic structure to explain globally distributed observations, while also identifying isolated regions of remaining misfit which will benefit from further study.

  3. Albedo of the ice covered Weddell and Bellingshausen Seas

    OpenAIRE

    Weiss, A. I.; King, J. C.; Lachlan-Cope, T. A.; Ladkin, R. S.

    2012-01-01

    This study investigates the surface albedo of the sea ice areas adjacent to the Antarctic Peninsula during the austral summer. Aircraft measurements of the surface albedo, which were conducted in the sea ice areas of the Weddell and Bellingshausen Seas show significant differences between these two regions. The averaged surface albedo varied between 0.13 and 0.81. The ice cover of the Bellingshausen Sea consisted mainly of first year ice and the sea surface showed an averaged sea ice albedo o...

  4. 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),...

  5. Sea Ice Edge Location and Extent in the Russian Arctic, 1933-2006, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — 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. Meltpond2000 Polarimetric Scanning Radiometer Sea Ice Brightness Temperatures

    Data.gov (United States)

    National Aeronautics and Space Administration — The Meltpond2000 project was the first in a series of Arctic and Antarctic aircraft campaigns to validate sea ice algorithms developed for the Advanced Microwave...

  7. 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...

  8. 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

  9. Observations on the relationship between the Antarctic coastal diatoms Thalassiosira antarctica Comber and Porosira glacialis (Grunow) Jørgensen and sea ice concentrations during the Late Quaternary

    NARCIS (Netherlands)

    Pike, J.; Crosta, X.; Maddison, E.J.; Stickley, C.E.; Denis, D.; Barbara, L.; Renssen, H.

    2009-01-01

    The available ecological and palaeoecological information for two sea ice-related marine diatoms (Bacillariophyceae), Thalassiosira antarctica Comber and Porosira glacialis (Grunow) Jørgensen, suggests that these two species have similar sea surface temperature (SST), sea surface salinity (SSS) and

  10. STS-48 ESC Earth observation of ice pack, Antarctic Ice Shelf

    Science.gov (United States)

    1991-01-01

    STS-48 Earth observation taken aboard Discovery, Orbiter Vehicle (OV) 103, is of the breakup of pack ice along the periphery of the Antarctic Ice Shelf. Strong offshore winds, probably associated with katabatic downdrafts from the interior of the continent, are seen peeling off the edges of the ice shelf into long filaments of sea ice, icebergs, bergy bits, and growlers to flow northward into the South Atlantic Ocean. These photos are used to study ocean wind, tide and current patterns. Similar views photographed during previous missions, when analyzed with these recent views may yield information about regional ice drift and breakup of ice packs. The image was captured using an electronic still camera (ESC), was stored on a removable hard disk or small optical disk, and was converted to a format suitable for downlink transmission. The ESC documentation was part of Development Test Objective (DTO) 648, Electronic Still Photography.

  11. Biodiversity change after climate-induced ice-shelf collapse in the Antarctic

    NARCIS (Netherlands)

    Gutt, J.; Barratt, I.; Domack, E.; Scheidat, M.

    2011-01-01

    The marine ecosystem on the eastern shelf of the Antarctic Peninsula was surveyed 5 and 12 years after the climate-induced collapse of the Larsen A and B ice shelves. An impoverished benthic fauna was discovered, that included deep-sea species presumed to be remnants from ice-covered conditions. The

  12. Millennial-scale instability of the Antarctic Ice Sheet during the last glaciation.

    NARCIS (Netherlands)

    Kanfoush, S.L.; Hodell, D.A.; Charles, C.D.; Guilderson, T.P.; Mortyn, P.G.

    2000-01-01

    Records of ice-rafted detritus (IRD) concentration in deep-sea cores from the southeast Atlantic Ocean reveal millennial-scale pulses of IRD delivery between 20,000 and 74,000 years ago. Prominent IRD layers correlate across the Polar Frontal Zone, suggesting episodes of Antarctic Ice Sheet

  13. Pathways of basal meltwater from Antarctic ice shelves: A model study

    Science.gov (United States)

    Kusahara, Kazuya; Hasumi, Hiroyasu

    2014-09-01

    We investigate spreading pathways of basal meltwater released from all Antarctic ice shelves using a circumpolar coupled ice shelf-sea ice-ocean model that reproduces major features of the Southern Ocean circulation, including the Antarctic Circumpolar Current (ACC). Several independent virtual tracers are used to identify detailed pathways of basal meltwaters. The spreading pathways of the meltwater tracers depend on formation sites, because the meltwaters are transported by local ambient ocean circulation. Meltwaters from ice shelves in the Weddell and Amundsen-Bellingshausen Seas in surface/subsurface layers are effectively advected to lower latitudes with the ACC. Although a large portion of the basal meltwaters is present in surface and subsurface layers, a part of the basal meltwaters penetrates into the bottom layer through active dense water formation along the Antarctic coastal margins. The signals at the seafloor extend along the topography, showing a horizontal distribution similar to the observed spreading of Antarctic Bottom Water. Meltwaters originating from ice shelves in the Weddell and Ross Seas and in the Indian sector significantly contribute to the bottom signals. A series of numerical experiments in which thermodynamic interaction between the ice shelf and ocean is neglected regionally demonstrates that the basal meltwater of each ice shelf impacts sea ice and/or ocean thermohaline circulation in the Southern Ocean. This article was corrected on 10 OCT 2014. See the end of the full text for details.

  14. Airfields on Antarctic Glacier Ice

    Science.gov (United States)

    1989-12-01

    meteorites behind on the surface. excellent friction for tires, to the extent that rubber can be burned off the tire if the wheel locks at high Blue-ice areas...scattered stones are not likely to affect aircraft just a thin layer (about cobblestone thickness) ly- operations, or to cause problems for ice-planing ing...Challenger, tinations. Some sites, e.g. Pegasus site and Casey which has a novel rubber -belt track system, is S-1, are final destinations, intended to

  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. 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

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

    NARCIS (Netherlands)

    Krapp, Rupert H.; Berge, Jorgen; Flores, Hauke; Gulliksen, Bjorn; Werner, Iris

    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

  18. Under Sea Ice phytoplankton bloom detection and contamination in Antarctica

    Science.gov (United States)

    Zeng, C.; Zeng, T.; Xu, H.

    2017-12-01

    Previous researches reported compelling sea ice phytoplankton bloom in Arctic, while seldom reports studied about Antarctic. Here, lab experiment showed sea ice increased the visible light albedo of the water leaving radiance. Even a new formed sea ice of 10cm thickness increased water leaving radiance up to 4 times of its original bare water. Given that phytoplankton preferred growing and accumulating under the sea ice with thickness of 10cm-1m, our results showed that the changing rate of OC4 estimated [Chl-a] varied from 0.01-0.5mg/m3 to 0.2-0.3mg/m3, if the water covered by 10cm sea ice. Going further, varying thickness of sea ice modulated the changing rate of estimating [Chl-a] non-linearly, thus current routine OC4 model cannot estimate under sea ice [Chl-a] appropriately. Besides, marginal sea ice zone has a large amount of mixture regions containing sea ice, water and snow, where is favorable for phytoplankton. We applied 6S model to estimate the sea ice/snow contamination on sub-pixel water leaving radiance of 4.25km spatial resolution ocean color products. Results showed that sea ice/snow scale effectiveness overestimated [Chl-a] concentration based on routine band ratio OC4 model, which contamination increased with the rising fraction of sea ice/snow within one pixel. Finally, we analyzed the under sea ice bloom in Antarctica based on the [Chl-a] concentration trends during 21 days after sea ice retreating. Regardless of those overestimation caused by sea ice/snow sub scale contamination, we still did not see significant under sea ice blooms in Antarctica in 2012-2017 compared with Arctic. This research found that Southern Ocean is not favorable for under sea ice blooms and the phytoplankton bloom preferred to occur in at least 3 weeks after sea ice retreating.

  19. Bayesian Inversion for Large Scale Antarctic Ice Sheet Flow

    KAUST Repository

    Ghattas, Omar

    2015-01-07

    The flow of ice from the interior of polar ice sheets is the primary contributor to projected sea level rise. One of the main difficulties faced in modeling ice sheet flow is the uncertain spatially-varying Robin boundary condition that describes the resistance to sliding at the base of the ice. Satellite observations of the surface ice flow velocity, along with a model of ice as a creeping incompressible shear-thinning fluid, can be used to infer this uncertain basal boundary condition. We cast this ill-posed inverse problem in the framework of Bayesian inference, which allows us to infer not only the basal sliding parameters, but also the associated uncertainty. To overcome the prohibitive nature of Bayesian methods for large-scale inverse problems, we exploit the fact that, despite the large size of observational data, they typically provide only sparse information on model parameters. We show results for Bayesian inversion of the basal sliding parameter field for the full Antarctic continent, and demonstrate that the work required to solve the inverse problem, measured in number of forward (and adjoint) ice sheet model solves, is independent of the parameter and data dimensions

  20. Tracing the sediment provenance in the Bellingshausen Sea for the changes of the West Antarctic Ice Sheet

    Science.gov (United States)

    Park, Y. K.; Jung, J.; Lee, M. K.; Kim, S. H.; Yoo, K. C.; Kim, J. W.

    2017-12-01

    Previously, clay mineral assemblages are frequently used to understand the sediment provenances. However, clay mineralogy may not be sufficient to prove the source of sediments, because even same clay mineral, for example smectite has various chemical composition that may have multi sediment sources. Such that elemental composition of smectite at a nano scale is necessary to confirm clearly the source of sediment. Clay mineralogy, elemental composition and crystal size distributions (CSDs) of smectite from the Bellingshausen Sea was investigated to puzzle out the sediment provenance that was not compatible with clay assemblages. We will test sediments for the sampling site (BS17-GC04, BS17-GC15) that may be affected by various sediment sources from the Ronne Entrance and Beethoven Peninsula, Bellingshausen Sea. Clay size fraction less than 2 mm was used to measure the mineralogy and semi-quantification analysis with depth by X-ray diffractometer (XRD). Smectite, illite, chlorite and kaolinite are dominant phase in sediments. The proportional variation of clay minerals with depth corresponds to the glacier movement. Crystal size distributions and elemental composition of clay mineral using TEM verify the origin of sediments during glacial and interglacial period. New approach to define the source of sediments will be discussed.

  1. Sea ice - Multiyear cycles and white ice

    Science.gov (United States)

    Ledley, T. S.

    1985-01-01

    The multiyear thickness cycles represent one of the interesting features of the sea ice studies performed by Semtner (1976) and Washington et al. (1976) with simple thermodynamic models of sea ice. In the present article, a description is given of results which show that the insulating effect of snow on the surface of the sea ice is important in producing these multiyear cycles given the physics included in the model. However, when the formation of white ice is included, the cycles almost disappear. White ice is the ice which forms at the snow-ice interface when the snow layer becomes thick enough to depress the ice below the water level. Water infiltrates the snow by coming through the ice at leads and generally freezes there, forming white ice.

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

    Science.gov (United States)

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

    2016-03-01

    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.

  3. 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.

  4. The last ice-sheet advance and retreat across the Antarctic continental shelf: Synchrony or diachrony?

    Science.gov (United States)

    Hillenbrand, C.; Livingstone, S. J.; O'Cofaigh, C.; Stokes, C. R.; Vieli, A.; Jamieson, S.; Smith, J.; Kuhn, G.; Melles, M.; Graham, A. G.; Larter, R. D.

    2012-12-01

    Over the last few decades, numerous studies from various sectors of the Antarctic continental shelf have reconstructed the spatial extent of grounded ice-sheet advance during the last glacial period and the timing of its retreat. Most reconstructions were based on the bathymetric mapping of subglacial bedforms on the seabed and the palaeoenvironmental interpretation and dating of sub-seafloor sediments in cores. In addition, surface exposure age dating on rocks from the hinterland using cosmogenic isotopes and ice-sheet models were used to constrain the last ice-sheet advance and retreat. Different regional reconstructions provided consistent results for several study areas. In contrast, recent circum-Antarctic reviews that compiled the spatial and temporal information about maximum ice-sheet advance and retreat from these regional studies came to conflicting conclusions regarding i) the maximum extent of grounded ice, and ii) the synchronous/diachronous behaviour of the northern and southern hemispheric ice sheets and the individual drainage sectors within the Antarctic Ice Sheet, respectively. Resolving these conflicts is essential for identifying the main drivers of Antarctic ice-sheet retreat, evaluating the contribution of Antarctic ice-sheet melting to global sea-level rise over the last ~20 ka, understanding the dynamics of individual drainage sectors within the Antarctic Ice Sheet, and locating possible glacial refuges for benthic organisms on the Antarctic shelf. Here we will present examples of circum-Antarctic reconstructions and discuss possible reasons for conflicting conclusions. In some cases, apparent discrepancies can simply be explained by the ambiguity of terms such as "Last Glacial Maximum", which can refer either to a particular time slice (e.g. 23-19 ka BP) or to the time when grounded ice reached its last maximum extent in a particular sector of the Antarctic continental shelf, and "deglaciation", which can refer either to the time of

  5. Meteorological Drivers of West Antarctic Ice Sheet and Ice Shelf Surface Melt

    Science.gov (United States)

    Scott, R. C.; Nicolas, J. P.; Bromwich, D. H.; Norris, J. R.; Lubin, D.

    2017-12-01

    We identify synoptic patterns and surface energy balance components driving warming and surface melting on the West Antarctic Ice Sheet (WAIS) and ice shelves using reanalysis and satellite remote sensing data from 1973-present. We have developed a synoptic climatology of atmospheric circulation patterns during the summer melt season using k-means cluster and composite analysis of daily 700-mb geopotential height and near-surface air temperature and wind fields from the ECMWF ERA-Interim reanalysis. Surface melt occurrence is detected in satellite passive microwave brightness temperature observations (K-band, horizontal polarization) beginning with the NASA Nimbus-5 Electrically Scanning Microwave Radiometer (ESMR) and continuing with its more familiar descendants SMMR, SSM/I and SSMIS. To diagnose synoptic precursors and physical processes driving surface melt we combine the circulation climatology and multi-decadal records of cloud cover with surface radiative fluxes from the Extended AVHRR Polar Pathfinder (APP-x) project. We identify three distinct modes of regional summer West Antarctic warming since 1979 involving anomalous ridging over West Antarctica (WA) and the Amundsen Sea (AS). During the 1970s, ESMR data reveal four extensive melt events on the Ross Sea sector of the WAIS also linked to AS blocking. We therefore define an Amundsen Sea Blocking Index (ASBI). The ASBI and synoptic circulation pattern occurrence frequencies are correlated with the tropical Pacific (ENSO) and high latitude Southern Annular Mode (SAM) indices and the West Antarctic melt index. Surface melt in WA is favored by enhanced downwelling infrared and turbulent sensible heat fluxes associated with intrusions of warm, moist marine air. Consistent with recent findings from the Atmospheric Radiation Measurement (ARM) West Antarctic Radiation Experiment (AWARE), marine advection to the Ross sector is favored by El Niño conditions in the tropical Pacific and a negative SAM. We also find

  6. Future Antarctic bed topography and its implications for ice sheet dynamics

    Science.gov (United States)

    Adhikari, S.; Ivins, E. R.; Larour, E.; Seroussi, H.; Morlighem, M.; Nowicki, S.

    2014-06-01

    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 45 mm yr-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.

  7. 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.

  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. Variational Ridging in Sea Ice Models

    Science.gov (United States)

    Roberts, A.; Hunke, E. C.; Lipscomb, W. H.; Maslowski, W.; Kamal, S.

    2017-12-01

    This work presents the results of a new development to make basin-scale sea ice models aware of the shape, porosity and extent of individual ridges within the pack. We have derived an analytic solution for the Euler-Lagrange equation of individual ridges that accounts for non-conservative forces, and therefore the compressive strength of individual ridges. Because a region of the pack is simply a collection of paths of individual ridges, we are able to solve the Euler-Lagrange equation for a large-scale sea ice field also, and therefore the compressive strength of a region of the pack that explicitly accounts for the macro-porosity of ridged debris. We make a number of assumptions that have simplified the problem, such as treating sea ice as a granular material in ridges, and assuming that bending moments associated with ridging are perturbations around an isostatic state. Regardless of these simplifications, the ridge model is remarkably predictive of macro-porosity and ridge shape, and, because our equations are analytic, they do not require costly computations to solve the Euler-Lagrange equation of ridges on the large scale. The new ridge model is therefore applicable to large-scale sea ice models. We present results from this theoretical development, as well as plans to apply it to the Regional Arctic System Model and a community sea ice code. Most importantly, the new ridging model is particularly useful for pinpointing gaps in our observational record of sea ice ridges, and points to the need for improved measurements of the evolution of porosity of deformed ice in the Arctic and Antarctic. Such knowledge is not only useful for improving models, but also for improving estimates of sea ice volume derived from altimetric measurements of sea ice freeboard.

  10. 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

    2017-01-05

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

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

    Science.gov (United States)

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

    2012-10-02

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

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

    Science.gov (United States)

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

    2012-01-01

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

  13. IOMASA SEA ICE DEVELOPMENTS

    DEFF Research Database (Denmark)

    Andersen, Søren; Tonboe, Rasmus; Heygster, Georg

    2005-01-01

    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...... chain in order to shorten the loop from development to operational processing. The presentation will present the developments and examples of the new retrievals and finally give an outlook to the future perspectives of the system....

  14. 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.

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

    Science.gov (United States)

    Golledge, Nicholas R.; Kowalewski, Douglas E.; Naish, Timothy R.; Levy, Richard H.; Fogwill, Christopher J.; Gasson, Edward G. W.

    2016-04-01

    Atmospheric warming is projected to increase global mean surface temperatures by 0.3 to 4.8 degrees Celsius above present values by the end of this century (Collins et al., 2013). If anthropogenic emissions continue unchecked, the warming increase may reach 8-10 degrees Celsius by 2300 (Rogelj et al., 2012). 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 (Collins et al., 2013). 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.

  16. Snow thickness profiling on Antarctic sea ice with GPR—Rapid and accurate measurements with the potential to upscale needles to a haystack

    Science.gov (United States)

    Pfaffhuber, Andreas A.; Lieser, Jan L.; Haas, Christian

    2017-08-01

    Snow thickness on sea ice is a largely undersampled parameter yet of importance for the sea ice mass balance and for satellite-based sea ice thickness estimates and thus our general understanding of global ice volume change. Traditional direct thickness measurements with meter sticks can provide accurate but only spot information, referred to as "needles" due to their pinpoint focus and information, while airborne and satellite remote sensing snow products, referred to as "the haystack," have large uncertainties due to their scale. We demonstrate the remarkable accuracy and applicability of ground-penetrating radar (GPR) snow thickness measurements by comparing them with in situ meter stick data from two field campaigns to Antarctica in late winter/early spring. The efficiency and millimeter-to-centimeter accuracy of GPR enables practitioners to acquire extensive, semiregional data with the potential to upscale needles to the haystack and to potentially calibrate satellite remote sensing products that we confirm to derive roughly 30% of the in situ thickness. We find the radar wave propagation velocity in snow to be rather constant (± 6%), encouraging regional snow thickness surveys. Snow thinner than 10 cm is under the detection limit with the off-the-shelf GPR setup utilized in our study.

  17. A comparison of the present and last interglacial periods in six Antarctic ice cores

    Directory of Open Access Journals (Sweden)

    V. Masson-Delmotte

    2011-04-01

    Full Text Available We compare the present and last interglacial periods as recorded in Antarctic water stable isotope records now available at various temporal resolutions from six East Antarctic ice cores: Vostok, Taylor Dome, EPICA Dome C (EDC, EPICA Dronning Maud Land (EDML, Dome Fuji and the recent TALDICE ice core from Talos Dome. We first review the different modern site characteristics in terms of ice flow, meteorological conditions, precipitation intermittency and moisture origin, as depicted by meteorological data, atmospheric reanalyses and Lagrangian moisture source diagnostics. These different factors can indeed alter the relationships between temperature and water stable isotopes. Using five records with sufficient resolution on the EDC3 age scale, common features are quantified through principal component analyses. Consistent with instrumental records and atmospheric model results, the ice core data depict rather coherent and homogenous patterns in East Antarctica during the last two interglacials. Across the East Antarctic plateau, regional differences, with respect to the common East Antarctic signal, appear to have similar patterns during the current and last interglacials. We identify two abrupt shifts in isotopic records during the glacial inception at TALDICE and EDML, likely caused by regional sea ice expansion. These regional differences are discussed in terms of moisture origin and in terms of past changes in local elevation histories, which are compared to ice sheet model results. Our results suggest that elevation changes may contribute significantly to inter-site differences. These elevation changes may be underestimated by current ice sheet models.

  18. 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...

  19. 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.

  20. Multiple Isotope Analysis of Sulfate in the West Antarctic Ice Sheet Divide Ice Core, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set contains measurements of multiple sulfur and oxygen isotopes from sulfates, from an ice core drilled at the West Antarctic Ice Sheet (WAIS) Divide site...

  1. Sensitivity of open-water ice growth and ice concentration evolution in a coupled atmosphere-ocean-sea ice model

    Science.gov (United States)

    Shi, Xiaoxu; Lohmann, Gerrit

    2017-09-01

    A coupled atmosphere-ocean-sea ice model is applied to investigate to what degree the area-thickness distribution of new ice formed in open water affects the ice and ocean properties. Two sensitivity experiments are performed which modify the horizontal-to-vertical aspect ratio of open-water ice growth. The resulting changes in the Arctic sea-ice concentration strongly affect the surface albedo, the ocean heat release to the atmosphere, and the sea-ice production. The changes are further amplified through a positive feedback mechanism among the Arctic sea ice, the Atlantic Meridional Overturning Circulation (AMOC), and the surface air temperature in the Arctic, as the Fram Strait sea ice import influences the freshwater budget in the North Atlantic Ocean. Anomalies in sea-ice transport lead to changes in sea surface properties of the North Atlantic and the strength of AMOC. For the Southern Ocean, the most pronounced change is a warming along the Antarctic Circumpolar Current (ACC), owing to the interhemispheric bipolar seasaw linked to AMOC weakening. Another insight of this study lies on the improvement of our climate model. The ocean component FESOM is a newly developed ocean-sea ice model with an unstructured mesh and multi-resolution. We find that the subpolar sea-ice boundary in the Northern Hemisphere can be improved by tuning the process of open-water ice growth, which strongly influences the sea ice concentration in the marginal ice zone, the North Atlantic circulation, salinity and Arctic sea ice volume. Since the distribution of new ice on open water relies on many uncertain parameters and the knowledge of the detailed processes is currently too crude, it is a challenge to implement the processes realistically into models. Based on our sensitivity experiments, we conclude a pronounced uncertainty related to open-water sea ice growth which could significantly affect the climate system sensitivity.

  2. A mechanism for biologically induced iodine emissions from sea ice

    Science.gov (United States)

    Saiz-Lopez, A.; Blaszczak-Boxe, C. S.; Carpenter, L. J.

    2015-09-01

    Ground- and satellite-based measurements have reported high concentrations of iodine monoxide (IO) in coastal Antarctica. The sources of such a large iodine burden in the coastal Antarctic atmosphere remain unknown. We propose a mechanism for iodine release from sea ice based on the premise that micro-algae are the primary source of iodine emissions in this environment. The emissions are triggered by the biological production of iodide (I-) and hypoiodous acid (HOI) from micro-algae (contained within and underneath sea ice) and their diffusion through sea-ice brine channels, ultimately accumulating in a thin brine layer (BL) on the surface of sea ice. Prior to reaching the BL, the diffusion timescale of iodine within sea ice is depth-dependent. The BL is also a vital component of the proposed mechanism as it enhances the chemical kinetics of iodine-related reactions, which allows for the efficient release of iodine to the polar boundary layer. We suggest that iodine is released to the atmosphere via three possible pathways: (1) emitted from the BL and then transported throughout snow atop sea ice, from where it is released to the atmosphere; (2) released directly from the BL to the atmosphere in regions of sea ice that are not covered with snowpack; or (3) emitted to the atmosphere directly through fractures in the sea-ice pack. To investigate the proposed biology-ice-atmosphere coupling at coastal Antarctica we use a multiphase model that incorporates the transport of iodine species, via diffusion, at variable depths, within brine channels of sea ice. Model simulations were conducted to interpret observations of elevated springtime IO in the coastal Antarctic, around the Weddell Sea. While a lack of experimental and observational data adds uncertainty to the model predictions, the results nevertheless show that the levels of inorganic iodine (i.e. I2, IBr, ICl) released from sea ice through this mechanism could account for the observed IO concentrations during

  3. Monitoring Antarctic ice sheet surface melting with TIMESAT algorithm

    Science.gov (United States)

    Ye, Y.; Cheng, X.; Li, X.; Liang, L.

    2011-12-01

    Antarctic ice sheet contributes significantly to the global heat budget by controlling the exchange of heat, moisture, and momentum at the surface-atmosphere interface, which directly influence the global atmospheric circulation and climate change. Ice sheet melting will cause snow humidity increase, which will accelerate the disintegration and movement of ice sheet. As a result, detecting Antarctic ice sheet melting is essential for global climate change research. In the past decades, various methods have been proposed for extracting snowmelt information from multi-channel satellite passive microwave data. Some methods are based on brightness temperature values or a composite index of them, and others are based on edge detection. TIMESAT (Time-series of Satellite sensor data) is an algorithm for extracting seasonality information from time-series of satellite sensor data. With TIMESAT long-time series brightness temperature (SSM/I 19H) is simulated by Double Logistic function. Snow is classified to wet and dry snow with generalized Gaussian model. The results were compared with those from a wavelet algorithm. On this basis, Antarctic automatic weather station data were used for ground verification. It shows that this algorithm is effective in ice sheet melting detection. The spatial distribution of melting areas(Fig.1) shows that, the majority of melting areas are located on the edge of Antarctic ice shelf region. It is affected by land cover type, surface elevation and geographic location (latitude). In addition, the Antarctic ice sheet melting varies with seasons. It is particularly acute in summer, peaking at December and January, staying low in March. In summary, from 1988 to 2008, Ross Ice Shelf and Ronnie Ice Shelf have the greatest interannual variability in amount of melting, which largely determines the overall interannual variability in Antarctica. Other regions, especially Larsen Ice Shelf and Wilkins Ice Shelf, which is in the Antarctic Peninsula

  4. Quaternary and Tertiary microfossils from beneath Ice Stream B: Evidence for a dynamic West Antarctic Ice Sheet history

    Science.gov (United States)

    Scherer, Reed P.

    1991-10-01

    Some glaciologists have suggested that the West Antarctic Ice Sheet, which is grounded well below sea level, may be susceptible to rapid grounding-line retreat and disintegration. However, until now, geologic evidence of previous ice sheet "collapses" has been lacking. Sediments that have recently been collected from beneath the West Antarctic Ice Sheet at Ice Stream B contain direct evidence of ice-free conditions in the West Antarctic interior during certain Cenozoic intervals, both prior to and subsequent to the development of grounded ice sheets in West Antarctica. The sediments contain rare but diverse microfossils that represent a wide variety of biostratigraphic ages and depositional environments. Microfossils present include relatively common marine and non-marine diatoms and sponge spicules, plus rare foraminifera, nannofossils, radiolarians, silicoflagellates, chrysophyte cysts and palynomorphs. Clasts of Neogene freshwater diatomite demonstrate the former presence of large lake systems in West Antarctica, possibly as part the Cenozoic West Antarctica rift system. Age-diagnostic marine fossils in the sediment include Late Paleogene calcareous nannofossils and planktonic foraminifera, Miocene marine planktonic diatoms and, significantly, late Pleistocene marine diatoms. Relatively common late Miocene diatoms probably reflect marine deposition prior to initiation of a dominantly glacial phase in West Antarctica. It is likely that Pliocene and early Pleistocene diatoms were deposited in the West Antarctic interior during certain warm interglacials, but these have been eroded and transported toward the continental shelf edge during repeated ice sheet expansions. The late Pleistocene diatoms from Upstream B were deposited in the West Antarctic interior basins during a marine phase, subsequent to an ice sheet collapse, during at least one late Pleistocene interglacial. This discovery provides an indication of the complex history of the West Antarctic Ice Sheet

  5. Surface melt on Antarctic ice shelves driven by wind-albedo interactions

    Science.gov (United States)

    Lhermitte, Stef; Lenaerts, Jan

    2017-04-01

    Surface melt and subsequent firn air depletion is considered an important precursor for disintegration of Antarctic ice shelves, causing grounded glaciers to accelerate and sea level to rise. Recent studies have highlighted the impact of surface winds on Antarctic ice shelf melt, both on the Antarctic Peninsula and in East Antarctica. 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. On the East Antarctic ice shelves, on the other hand, meltwater-induced firn air depletion is found in the grounding zone as result of persistent katabatic winds, regionally warming the atmosphere and inducing a melt-albedo feedback. Here, we use a combination multi-source satellite imagery, snow modelling, climate model output and in-situ observations to highlight the importance of this wind-induced melt and to show its widespread occurrence across Antarctica. The satellite imagery gives insight in the meltwater drainage systems, showing spatio-temporal changes in both supraglacial and englacial water throughout the melt season and during the subsequent winter. Although the wind-induced melt is a regional phenomenon with strong inter-annual variability, it is strongly correlated to larger scale climate parameters, such as summer surface temperature. Based on these correlations and snow model output driven by future climate scenarios, we can constrain the future changes to this local melt near the grounding line.

  6. Ice Algae-Produced Carbon Is Critical for Overwintering of Antarctic Krill Euphausia superba

    Directory of Open Access Journals (Sweden)

    Doreen Kohlbach

    2017-09-01

    Full Text Available Antarctic krill Euphausia superba (“krill” constitute a fundamental food source for Antarctic seabirds and mammals, and a globally important fisheries resource. The future resilience of krill to climate change depends critically on the winter survival of young krill. To survive periods of extremely low production by pelagic algae during winter, krill are assumed to rely partly on carbon produced by ice algae. The true dependency on ice algae-produced carbon, however, is so far unquantified. This confounds predictions on the future resilience of krill stocks to sea ice decline. Fatty acid (FA analysis, bulk stable isotope analysis (BSIA, and compound-specific stable isotope analysis (CSIA of diatom- and dinoflagellate-associated marker FAs were applied to quantify the dependency of overwintering larval, juvenile, and adult krill on ice algae-produced carbon (αIce during winter 2013 in the Weddell-Scotia Confluence Zone. Our results demonstrate that the majority of the carbon uptake of the overwintering larval and juvenile krill originated from ice algae (up to 88% of the carbon budget, and that the dependency on ice algal carbon decreased with ontogeny, reaching <56% of the carbon budget in adults. Spatio-temporal variability in the utilization of ice algal carbon was more pronounced in larvae and juvenile krill than in adults. Differences between αIce estimates derived from short- vs. long-term FA-specific isotopic compositions suggested that ice algae-produced carbon gained importance as the winter progressed, and might become critical at the late winter-spring transition, before the phytoplankton bloom commences. Where the sea ice season shortens, reduced availability of ice algae might possibly not be compensated by surplus phytoplankton production during wintertime. Hence, sea ice decline could seriously endanger the winter survival of recruits, and subsequently overall biomass of krill.

  7. Organic compounds and suspended matter in the marine ice of the Eastern Antarctic

    International Nuclear Information System (INIS)

    Nemirovskaya, I.A.; Novigatsky, A.N.

    2005-01-01

    Data on the composition of organic compounds in Antarctic sea ice are virtually non-existent, as most works concentrate on the structure, physical composition and biological properties of the ice. Data is needed for the study of the global carbon cycle and the estimation of background values and anthropogenic compounds. Specific features of the hydrometeorological regime near Antarctica affect the structure of the ice cover and its properties. The transportation of large volumes of snow to the ocean results in the formation of a snow sludge layer which gradually accumulates on the sea surface and freezes into young slush ice. The irregular distribution of snow at the ice surface and seawater infiltration results in the formation of ice with a specific crystalline structure and physiochemical properties. This paper discussed the dissolved and suspended lipids and hydrocarbons, as well as suspended matter (SM) concentrations in snow, sea ice and sub-ice water in coastal zones of the East Antarctic. The data was obtained during the Russian Antarctic Expedition in 2003. Variations in the concentration and distribution of the various substances suggest that they are related to ice forming conditions and to the processes that occur when ice forms, as well as in the interaction of the substances with ice, snow and sub-ice water. The SM and organic compounds are accumulated in layers characterized by intense autochthonous processes. It was noted that the zones stay biogeochemically active even under low temperature conditions. The highest concentrations of organic compounds, along with the biggest variations in their proportions have been discovered in the areas surrounded by penguin colonies near Buromsky Island and Haswell Island's Lake. The presence of significant quantities of PAHs in both pack and seasonal ice of high latitudes indicates that their formation is relatively rapid even at low temperatures. Many biochemical processes are intense under the influence of ice

  8. Winter sea ice export from the Laptev Sea preconditions the local summer sea ice cover

    Science.gov (United States)

    Krumpen, T.; Haas, C.; Itkin, P.

    2016-12-01

    Interannual variability and trends in sea ice export out of the Laptev Sea were investigated using a combination of observations and satellite data. The Laptev Sea shows a statistically positive trend in ice area export that is likely associated to an increase in ice drift velocity being the consequence of a thinning ice cover further north. Moreover, we could show that there is a high statistical connection of the late winter (Jan-May) sea ice export and ice formation in Laptev Sea polynyas to the summer sea ice concentration. By means of a sensitivity study using a coupled sea ice-ocean model (MITgcm), we could highlight the importance of winter sea ice processes for summer sea ice conditions in the Laptev Sea and likewise in the adjacent Siberian Seas. Years of high ice export have a thinning effect on the ice cover, which in turn preconditions early fast ice break up, pack ice melt and the occurrence of negative sea ice extent anomalies in summer. Our model simulation also indicate that observed increase in the sea ice export from the Laptev Sea is accompanied by an increase in the volume export, which is important for the Arctic sea ice budget.

  9. Holocene accumulation and ice flow near the West Antarctic Ice Sheet Divide ice core site

    Science.gov (United States)

    Koutnik, Michelle R.; Fudge, T. J.; Conway, Howard; Waddington, Edwin D.; Neumann, Thomas A.; Cuffey, Kurt M.; Buizert, Christo; Taylor, Kendrick C.

    2016-05-01

    The West Antarctic Ice Sheet Divide Core (WDC) provided a high-resolution climate record from near the Ross-Amundsen Divide in Central West Antarctica. In addition, radar-detected internal layers in the vicinity of the WDC site have been dated directly from the ice core to provide spatial variations in the age structure of the region. Using these two data sets together, we first infer a high-resolution Holocene accumulation-rate history from 9.2 kyr of the ice-core timescale and then confirm that this climate history is consistent with internal layers upstream of the core site. Even though the WDC was drilled only 24 km from the modern ice divide, advection of ice from upstream must be taken into account. We evaluate histories of accumulation rate by using a flowband model to generate internal layers that we compare to observed layers. Results show that the centennially averaged accumulation rate was over 20% lower than modern at 9.2 kyr before present (B.P.), increased by 40% from 9.2 to 2.3 kyr B.P., and decreased by at least 10% over the past 2 kyr B.P. to the modern values; these Holocene accumulation-rate changes in Central West Antarctica are larger than changes inferred from East Antarctic ice-core records. Despite significant changes in accumulation rate, throughout the Holocene the regional accumulation pattern has likely remained similar to today, and the ice-divide position has likely remained on average within 5 km of its modern position. Continent-scale ice-sheet models used for reconstructions of West Antarctic ice volume should incorporate this accumulation history.

  10. A new research project on the interaction of the solid Earth and the Antarctic Ice Sheet

    Science.gov (United States)

    Fukuda, Y.; Nishijima, J.; Kazama, T.; Nakamura, K.; Doi, K.; Suganuma, Y.; Okuno, J.; Araya, A.; Kaneda, H.; Aoyama, Y.

    2017-12-01

    A new research project of "Grant-in-Aid for Scientific Research on Innovative Areas" funded by JSPS (Japan Society for the Promotion of Science) has recently been launched. The title of the project is "Giant reservoirs of heat/water/material: Global environmental changes driven by Southern Ocean and Antarctic Ice Sheet", and as a five years project, is aiming to establish a new research area for Antarctic environmental system science. The project consists of 7 research topics, including Antarctic ice sheet and Southern ocean sciences, new observation methodology, modeling and other interdisciplinary topics, and we are involved in the topic A02-2, "Interaction of the solid Earth and the Antarctic Ice Sheet". The Antarctic ice sheet, which relates to the global climate changes through the sea level rise and ocean circulation, is an essential element of the Earth system for predicting the future environment changes. Thus many studies of the ice sheet changes have been conducted by means of geomorphological, geological, geodetic surveys, as well as satellite gravimetry and satellite altimetry. For these studies, one of the largest uncertainties is the effects of GIA. Therefore, GIA as a key to investigate the interaction between the solid Earth and the ice sheet changes, we plan to conduct geomorphological, geological and geodetic surveys in the inland mountain areas and the coastal areas including the surrounding areas of a Japanese station Syowa in East Antarctica, where the in-situ data for constraining GIA models are very few. Combining these new observations with other in-site data, various satellite data and numerical modeling, we aim to estimating a precise GIA model, constructing a reliable ice melting history after the last glacial maximum and obtaining the viscoelastic structure of the Earth's interior. In the presentation, we also show the five years research plans as well. This study was partially supported by JSPS KAKENHI Grant No. 17H06321.

  11. Analysis of sea ice dynamics

    Science.gov (United States)

    Zwally, J.

    1988-01-01

    The ongoing work has established the basis for using multiyear sea ice concentrations from SMMR passive microwave for studies of largescale advection and convergence/divergence of the Arctic sea ice pack. Comparisons were made with numerical model simulations and buoy data showing qualitative agreement on daily to interannual time scales. Analysis of the 7-year SMMR data set shows significant interannual variations in the total area of multiyear ice. The scientific objective is to investigate the dynamics, mass balance, and interannual variability of the Arctic sea ice pack. The research emphasizes the direct application of sea ice parameters derived from passive microwave data (SMMR and SSMI) and collaborative studies using a sea ice dynamics model. The possible causes of observed interannual variations in the multiyear ice area are being examined. The relative effects of variations in the large scale advection and convergence/divergence within the ice pack on a regional and seasonal basis are investigated. The effects of anomolous atmospheric forcings are being examined, including the long-lived effects of synoptic events and monthly variations in the mean geostrophic winds. Estimates to be made will include the amount of new ice production within the ice pack during winter and the amount of ice exported from the pack.

  12. 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...

  13. Antarctic ice shelf potentially stabilized by export of meltwater in surface river

    Science.gov (United States)

    Bell, Robin E.; Chu, Winnie; Kingslake, Jonathan; Das, Indrani; Tedesco, Marco; Tinto, Kirsty J.; Zappa, Christopher J.; Frezzotti, Massimo; Boghosian, Alexandra; Lee, Won Sang

    2017-04-01

    Meltwater stored in ponds and crevasses can weaken and fracture ice shelves, triggering their rapid disintegration. This ice-shelf collapse results in an increased flux of ice from adjacent glaciers and ice streams, thereby raising sea level globally. However, surface rivers forming on ice shelves could potentially export stored meltwater and prevent its destructive effects. Here we present evidence for persistent active drainage networks—interconnected streams, ponds and rivers—on the Nansen Ice Shelf in Antarctica that export a large fraction of the ice shelf’s meltwater into the ocean. We find that active drainage has exported water off the ice surface through waterfalls and dolines for more than a century. The surface river terminates in a 130-metre-wide waterfall that can export the entire annual surface melt over the course of seven days. During warmer melt seasons, these drainage networks adapt to changing environmental conditions by remaining active for longer and exporting more water. Similar networks are present on the ice shelf in front of Petermann Glacier, Greenland, but other systems, such as on the Larsen C and Amery Ice Shelves, retain surface water at present. The underlying reasons for export versus retention remain unclear. Nonetheless our results suggest that, in a future warming climate, surface rivers could export melt off the large ice shelves surrounding Antarctica—contrary to present Antarctic ice-sheet models, which assume that meltwater is stored on the ice surface where it triggers ice-shelf disintegration.

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

    Science.gov (United States)

    2015-11-30

    1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. SUNLIGHT, SEA ICE , AND THE ICE ALBEDO FEEDBACK IN A...iv) onset dates of melt and freeze up. 4. Assess the magnitude of the contribution from ice - albedo feedback to the observed decrease of sea ice in... sea ice prediction and modeling community to improve the treatment of solar radiation and the ice - albedo feedback. This transfer will take the form of

  15. 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.

  16. Asynchronous behavior of the Antarctic Ice Sheet and local glaciers during and since Termination 1, Salmon Valley, Antarctica

    Science.gov (United States)

    Jackson, Margaret S.; Hall, Brenda L.; Denton, George H.

    2018-01-01

    The stability of the Antarctic Ice Sheet under future warming remains an open question with broad implications for sea-level prediction and adaptation. In particular, knowledge of whether the ice sheet has the capacity for rapid drawdown or collapse, or whether it can remain stable during periods of warming, is essential for predicting its future behavior. Here we use 55 radiocarbon dates, coupled with geomorphologic mapping, to reconstruct the timing of changes in ice extent and elevation during the last ice-age termination in Salmon Valley, adjacent to McMurdo Sound in the western Ross Sea Embayment. Results indicate that a grounded ice sheet in the Ross Sea Embayment achieved its maximum elevation and extent along the headlands of Salmon Valley at ∼18,000 yr BP, during a period of increasing temperatures and accumulation over the Antarctic continent. This ice remained at or near its maximum on the headlands near the valley mouth until after ∼14,000 yr BP. Removal of grounded Ross Sea ice from Salmon Valley was complete shortly after ∼7900 yr BP, indicating that the grounding line had retreated through southern McMurdo Sound by that time. We suggest the primary driver of Ross Sea ice removal from McMurdo Sound was marine-based, either through basal melting or calving due to sea-level rise. When combined with regional data, the Salmon Valley record suggests that this sector of the Antarctic Ice Sheet did not contribute in a significant way to deglacial meltwater pulses, such as meltwater pulse 1a. In contrast to the Ross Sea ice, our work also shows that local, independent alpine glaciers in Salmon Valley have advanced through the Holocene. Land-terminating glaciers such as these elsewhere in the region show a similar pattern, and may reflect the continued influence of increased accumulation following the termination of the last ice age.

  17. Spatio-temporal variability in the winter diet of larval and juvenile Antarctic krill, Euphausia superba, in ice-covered waters

    NARCIS (Netherlands)

    Schaafsma, F.L.; Kohlbach, D.; David, C.; Lange, B.A.; Graeve, M.; Flores, H.; Franeker, van J.A.

    2017-01-01

    Antarctic krill Euphausia superba is an ecological key species in the Southern Ocean and a major fisheries resource. The winter survival of age class 0 (AC0) krill is susceptible to changes in the sea-ice environment due to their association with sea ice and their need to feed during their first

  18. The Sinking and Spreading of The Antarctic Deep Ice Shelf Water In The Ross Sea Studied By In Situ Observaions and Numerical Modeling

    Science.gov (United States)

    Rubino, A.; Budillon, G.; Pierini, S.; Spezie, G.

    The sinking and spreading of the Deep Ice Shelf Water (DISW) in the Ross Sea are analyzed using in situ observations and the results of a nonlinear, reduced-gravity, frontal layered numerical "plume" model which is able to simulate the motion of a bottom-arrested current over realistic topography. The model is forced by prescribing the thickness of the DISW vein as well as its density structure at the southern model boundary. The ambient temperature and salinity are imposed using hydrographic data acquired by the Italian PNRA-CLIMA project. In the model water of the quiescent ambient ocean is allowed to entrain in the active deep layer due to a simple param- eterization of turbulent mixing. The importance of forcing the model with a realistic ambient density is demonstrated by carrying out a numerical simulation in which the bottom active layer is forced using an idealized ambient density. In a more realis- tic simulation the path and the density structure of the DISW vein flowing over the Challenger Basin are obtained and are found to be in good agreement with data. The evolution of the deep current beyond the continental shelf is also simulated. It provides useful information on the water flow and mixing in a region of the Ross Sea where the paucity of experimental data does not allow for a detailed description of the deep ocean dynamics.

  19. Sea Ice Trends in Climate Models Only Accurate in Runs with Biased Global Warming

    Science.gov (United States)

    Rosenblum, Erica; Eisenman, Ian

    2017-08-01

    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, typically simulate a moderate decrease in both the Arctic and Antarctic sea ice covers. However, in each hemisphere there is a small subset of model simulations that have sea ice trends similar to the observations. Based on this, a number of recent studies have suggested that the models are consistent with the observations in each hemisphere when simulated internal climate 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), drawing on previous work that found a close relationship in climate models between global-mean surface temperature and sea ice extent. We find that all of the simulations with 1979-2013 Arctic sea ice retreat as fast as observed have considerably more global warming than observations during this time period. Using two separate methods to estimate the sea ice retreat that would occur under the observed level of global warming in each simulation in both ensembles, we find that simulated Arctic sea ice retreat as fast as observed would occur less than 1% of the time. This implies that the models are not consistent with the observations. In the Antarctic, we find that simulated sea ice expansion as fast as observed typically corresponds with too little global warming, although these results are more equivocal. We show that because of this, the simulations do not capture the observed asymmetry between Arctic and Antarctic sea ice trends. This suggests that the models may be getting the right sea ice trends for the wrong reasons in both polar regions.

  20. Macro-nutrient concentrations in Antarctic pack ice: Overall patterns and overlooked processes

    Directory of Open Access Journals (Sweden)

    François Fripiat

    2017-03-01

    Full Text Available Antarctic pack ice is inhabited by a diverse and active microbial community reliant on nutrients for growth. Seeking patterns and overlooked processes, we performed a large-scale compilation of macro-nutrient data (hereafter termed nutrients in Antarctic pack ice (306 ice-cores collected from 19 research cruises. Dissolved inorganic nitrogen and silicic acid concentrations change with time, as expected from a seasonally productive ecosystem. In winter, salinity-normalized nitrate and silicic acid concentrations (C* in sea ice are close to seawater concentrations (Cw, indicating little or no biological activity. In spring, nitrate and silicic acid concentrations become partially depleted with respect to seawater (C* Cw. The phosphate excess could be explained by a greater allocation to phosphorus-rich biomolecules during ice algal blooms coupled with convective loss of excess dissolved nitrogen, preferential remineralization of phosphorus, and/or phosphate adsorption onto metal-organic complexes. Ammonium also appears to be efficiently adsorbed onto organic matter, with likely consequences to nitrogen mobility and availability. This dataset supports the view that the sea ice microbial community is highly efficient at processing nutrients but with a dynamic quite different from that in oceanic surface waters calling for focused future investigations.

  1. Tracking the El Nino events from Antarctic ice core records

    International Nuclear Information System (INIS)

    Keskin, S.S.; Oelmez, I.

    2004-01-01

    Sodium and chlorine measurements were made by instrumental neutron activation analysis (INAA) on stratigraphically dated ice core samples from Byrd Station, Antarctica, for the last three centuries. The time period between 1969 and 1989 showed an enhanced impact on the Antarctic ice sheets from oceans in the form of marine aerosols. A disturbed ocean-atmosphere interface due to El Ni Southern Oscillation (ENSO) events seems to be a candidate for this observation in Antarctica. (author)

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

    Science.gov (United States)

    2015-09-30

    Figure 1). When the ice is snow covered there is little difference in albedo and partitioning between first year and multiyear ice. Once the snow melts...1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Sunlight, Sea Ice, and the Ice Albedo Feedback in a...and iv) onset dates of melt and freeze up. 4. Assess the magnitude of the contribution from ice- albedo feedback to the observed decrease of sea ice

  3. Photophysiology and cellular composition of sea ice algae

    International Nuclear Information System (INIS)

    Lizotte, M.P.

    1989-01-01

    The productivity of sea ice algae depends on their physiological capabilities and the environmental conditions within various microhabitats. Pack ice is the dominant form of sea ice, but the photosynthetic activity of associated algae has rarely been studied. Biomass and photosynthetic rates of ice algae of the Weddell-Scotia Sea were investigated during autumn and winter, the period when ice cover grows from its minimum to maximum. Biomass-specific photosynthetic rates typically ranged from 0.3 to 3.0 μg C · μg chl -1 · h -1 higher than land-fast ice algae but similar to Antarctic phytoplankton. Primary production in the pack ice during winter may be minor compared to annual phytoplankton production, but could represent a vital seasonal contribution to the Antarctic ecosystem. Nutrient supply may limit the productivity of ice algae. In McMurdo Sound, congelation ice algae appeared to be more nutrient deficient than underlying platelet ice algae based on: lower nitrogen:carbon, chlorophyll:carbon, and protein:carbohydrate; and 14 C-photosynthate distribution to proteins and phospholipids was lower, while distribution to polysaccharides and neutral lipids was higher. Depletion of nitrate led to decreased nitrogen:carbon, chlorophyll:carbon, protein:carbohydrate, and 14 C-photosynthate to proteins. Studied were conducted during the spring bloom; therefore, nutrient limitation may only apply to dense ice algal communities. Growth limiting conditions may be alleviated when algae are released into seawater during the seasonal recession of the ice cover. To continue growth, algae must adapt to the variable light field encountered in a mixed water column. Photoadaptation was studied in surface ice communities and in bottom ice communities

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

    NARCIS (Netherlands)

    Rugenstein, Maria; Stocchi, Paolo; von der Heydt, Anna; Dijkstra, Hendrik; Brinkhuis, Henk

    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 dynamic

  5. 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

  6. Sector of West Antarctic Ice Sheet in "Irreversible Retreat"

    Science.gov (United States)

    Showstack, Randy

    2014-05-01

    A large sector of the West Antarctic Ice Sheet "has gone into a state of irreversible retreat," according to glaciologist Eric Rignot, lead author of the paper "Widespread rapid grounding line retreat of Pine Island, Thwaites, Smith, and Kohler Glaciers in West Antarctica from 1992 to 2011," which has been accepted for publication in Geophysical Research Letters (GRL).

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

    NARCIS (Netherlands)

    Depoorter, M.A.; Bamber, J.L.; Griggs, J.A.; Lenaerts, J.T.M.|info:eu-repo/dai/nl/314850163; Ligtenberg, S.R.M.|info:eu-repo/dai/nl/32821177X; van den Broeke, M.R.|info:eu-repo/dai/nl/073765643; Moholdt, G.

    2013-01-01

    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 year1, 2. More recently, the importance of melting by the ocean has been demonstrated close to the grounding line and near

  8. Eight glacial cycles from an Antarctic ice core

    NARCIS (Netherlands)

    Oerlemans, J.

    2004-01-01

    The Antarctic Vostok ice core provided compelling evidence of the nature of climate, and of climate feedbacks, over the past 420,000 years. Marine records suggest that the amplitude of climate variability was smaller before that time, but such records are often poorly resolved. Moreover, it is not

  9. Arctic Sea Ice Freeboard and Thickness

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set provides measurements of sea ice freeboard and sea ice thickness for the Arctic region. The data were derived from measurements made by from the Ice,...

  10. Deformation-induced melting in the Antarctic Ice Sheet

    Science.gov (United States)

    Minchew, B. M.; Meyer, C. R.

    2017-12-01

    Shear stresses in the lateral margins are important components of the force balance in the glaciers and ice streams of the Antarctic Ice Sheet (AIS). The magnitudes of these stresses are a function of the rheology of ice within the margins, and ice rheology is a function of ice temperature. Here, we focus on deformation-induced heating in AIS, with the goal of understanding the spatial distribution of zones of temperate ice within the ice sheet. We derive a new analytical thermodynamic model that includes advection, diffusion, and deformation heating. Taking downward advection of cold ice to be a function of surface accumulation, we find an expression for 1) the minimum shear strain rate necessary to produce a temperate-ice zone of finite thickness and 2) the thickness of the temperate-ice zone. Applying recently derived surface velocity fields (Gardner et al., 2017), estimates of ice thickness (Bedmap2; Fretwell et al., 2013), and surface mass balance and temperature (RACMO2.3; van Wessem et al., 2014), we predict the prevalence of temperate ice within AIS. Temperate ice zones are spatially extensive and extend from the bed to at least half of the local ice thickness in six distinct regions: Pine Island, Thwaites, and Kohler Glaciers (West Antarctica); Recovery and Slessor Glaciers (eastern Filchner Ice Shelf); Mellor and Lambert Glaciers (Amery Ice Shelf); Denman Glacier (East Antarctica); Byrd Glacier (western Ross Ice Shelf); and Bindschadler Ice Stream (eastern Ross Ice Shelf). In most of these regions, the formation of temperate ice is facilitated by small rates of downward advection of cold ice. The most striking exception is Pine Island Glacier, where extreme shear strain rates in the margins overcome relatively high rates of cold-ice advection to create zones of temperate ice that could exceed 75% of the local ice thickness. Through our model development, we show that the presence of temperate ice is largely governed by the ratio of the rate of deformation

  11. Challenges for understanding Antarctic surface hydrology and ice-shelf stability

    Science.gov (United States)

    Kingslake, J.; Bell, R. E.; Banwell, A. F.; Boghosian, A.; Spergel, J.; Trusel, L. D.

    2017-12-01

    It is widely hypothesized that surface meltwater can contribute to ice mass loss in Antarctica through its impact on ice-shelf stability. Meltwater potentially expedites ice-shelf calving by flowing into and enlarging existing crevasses, and could even trigger ice-shelf disintegration via stresses generated by melt ponds. When ice shelves collapse, the adjacent grounded ice accelerates and thins, which contributes to sea-level rise. How these mechanisms mediate the interactions between the atmosphere, the ocean and the ice sheet is the subject of long-standing research efforts. The drainage of water across the surface of the Antarctic Ice Sheet and its ice shelves is beginning to be recognized as another important aspect of the system. Recent studies have revealed that surface meltwater drainage is more widespread than previously thought and that surface hydrological systems in Antarctica may expand and proliferate this century. Contrasting hypotheses regarding the impact of the proliferation of drainage systems on ice-shelf stability have emerged. Surface drainage could deliver meltwater to vulnerable area or export meltwater from ice shelves entirely. Which behavior dominates may have a large impact on the future response of the Antarctic Ice Sheet to atmospheric warming. We will discuss these recent discoveries and hypotheses, as well as new detailed studies of specific areas where hydrological systems are well developed, such as Amery and Nimrod Ice Shelves. We will highlight analogies that can be drawn with Greenlandic (near-)surface hydrology and, crucially, where hydrological systems on the two ice sheets are very different, leading to potentially important gaps in our understanding. Finally, we will look ahead to the key questions that we argue will need to be if we are to determine the role Antarctic surface hydrology could play in the future of the ice sheet. These include: Where does meltwater pond today and how will this change this century? What

  12. Inverse Relationship of Marine Aerosol and Dust in Antarctic Ice with Fine-Grained Sediment in the South Atlantic Ocean: Implications for Sea-Ice Coverage and Wind Strength

    Directory of Open Access Journals (Sweden)

    Sharon L. Kanfoush

    2012-03-01

    Full Text Available This research seeks to test the hypothesis that natural gamma radiation (NGR from Ocean Drilling Program Site 1094, which displays variability over the last glacial-interglacial cycle similar to dust in the Vostok ice core, reflects fine-grained terrigenous sediment delivered by eolian processes. Grain size was measured on 400 samples spanning 0–20 m in a composite core. Accumulation of the <63μ size fraction at Site 1094 and dust in Vostok exhibit a negative correlation, suggesting the fine sediments are not dominantly eolian. However the technique used for grain size measurements cannot distinguish between terrigenous and biogenous materials; therefore it is possible much fine-grained material is diatoms. An inverse correlation between fine sediments and NGR supports this interpretation, and implies terrigenous materials were at times diluted by microfossils from high biological productivity. Fine marine sediments correlate positively with temperature and negatively with marine aerosol Na+ in Vostok. One plausible explanation is extensive sea-ice of cold intervals steepened ocean-continent temperature gradients, intensified winds, and led to increased transport of dust and marine aerosol to Antarctica yet also reduced biological productivity at Site 1094. Such a reduction despite increases in NGR, potentially representing Fe-rich dust influx, would require light limitation or stratification associated with sea-ice.

  13. Modeling the Thermal Interactions of Meteorites Below the Antarctic Ice

    Science.gov (United States)

    Oldroyd, William Jared; Radebaugh, Jani; Stephens, Denise C.; Lorenz, Ralph; Harvey, Ralph; Karner, James

    2017-10-01

    Meteorites with high specific gravities, such as irons, appear to be underrepresented in Antarctic collections over the last 40 years. This underrepresentation is in comparison with observed meteorite falls, which are believed to represent the actual population of meteorites striking Earth. Meteorites on the Antarctic ice sheet absorb solar flux, possibly leading to downward tunneling into the ice, though observations of this in action are very limited. This descent is counteracted by ice sheet flow supporting the meteorites coupled with ablation near mountain margins, which helps to force meteorites towards the surface. Meteorites that both absorb adequate thermal energy and are sufficiently dense may instead reach a shallow equilibrium depth as downward melting overcomes upward forces during the Antarctic summer. Using a pyronometer, we have measured the incoming solar flux at multiple depths in two deep field sites in Antarctica, the Miller Range and Elephant Moraine. We compare these data with laboratory analogues and model the thermal and physical interactions between a variety of meteorites and their surroundings. Our Matlab code model will account for a wide range of parameters used to characterize meteorites in an Antarctic environment. We will present the results of our model along with depth estimates for several types of meteorites. The recovery of an additional population of heavy meteorites would increase our knowledge of the formation and composition of the solar system.

  14. Biodiversity change after climate-induced ice-shelf collapse in the Antarctic

    Science.gov (United States)

    Gutt, Julian; Barratt, Iain; Domack, Eugene; d'Udekem d'Acoz, Cédric; Dimmler, Werner; Grémare, Antoine; Heilmayer, Olaf; Isla, Enrique; Janussen, Dorte; Jorgensen, Elaina; Kock, Karl-Hermann; Sophia Lehnert, Linn; López-Gonzáles, Pablo; Langner, Stephanie; Linse, Katrin; Eugenia Manjón-Cabeza, Maria; Meißner, Meike; Montiel, Americo; Raes, Maarten; Robert, Henri; Rose, Armin; Sañé Schepisi, Elisabet; Saucède, Thomas; Scheidat, Meike; Schenke, Hans-Werner; Seiler, Jan; Smith, Craig

    2011-03-01

    The marine ecosystem on the eastern shelf of the Antarctic Peninsula was surveyed 5 and 12 years after the climate-induced collapse of the Larsen A and B ice shelves. An impoverished benthic fauna was discovered, that included deep-sea species presumed to be remnants from ice-covered conditions. The current structure of various ecosystem components appears to result from extremely different response rates to the change from an oligotrophic sub-ice-shelf ecosystem to a productive shelf ecosystem. Meiobenthic communities remained impoverished only inside the embayments. On local scales, macro- and mega-epibenthic diversity was generally low, with pioneer species and typical Antarctic megabenthic shelf species interspersed. Antarctic Minke whales and seals utilised the Larsen A/B area to feed on presumably newly established krill and pelagic fish biomass. Ecosystem impacts also extended well beyond the zone of ice-shelf collapse, with areas of high benthic disturbance resulting from scour by icebergs discharged from the Larsen embayments.

  15. Assessment of the sea-ice carbon pump

    DEFF Research Database (Denmark)

    Grimm, R.; Notz, D.; Glud, Ronnie N.

    2016-01-01

    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...

  16. 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

  17. 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.

  18. Climate change drives expansion of Antarctic ice-free habitat.

    Science.gov (United States)

    Lee, Jasmine R; Raymond, Ben; Bracegirdle, Thomas J; Chadès, Iadine; Fuller, Richard A; Shaw, Justine D; Terauds, Aleks

    2017-07-06

    Antarctic terrestrial biodiversity occurs almost exclusively in ice-free areas that cover less than 1% of the continent. Climate change will alter the extent and configuration of ice-free areas, yet the distribution and severity of these effects remain unclear. Here we quantify the impact of twenty-first century climate change on ice-free areas under two Intergovernmental Panel on Climate Change (IPCC) climate forcing scenarios using temperature-index melt modelling. Under the strongest forcing scenario, ice-free areas could expand by over 17,000 km 2 by the end of the century, close to a 25% increase. Most of this expansion will occur in the Antarctic Peninsula, where a threefold increase in ice-free area could drastically change the availability and connectivity of biodiversity habitat. Isolated ice-free areas will coalesce, and while the effects on biodiversity are uncertain, we hypothesize that they could eventually lead to increasing regional-scale biotic homogenization, the extinction of less-competitive species and the spread of invasive species.

  19. Climate change drives expansion of Antarctic ice-free habitat

    Science.gov (United States)

    Lee, Jasmine R.; Raymond, Ben; Bracegirdle, Thomas J.; Chadès, Iadine; Fuller, Richard A.; Shaw, Justine D.; Terauds, Aleks

    2017-07-01

    Antarctic terrestrial biodiversity occurs almost exclusively in ice-free areas that cover less than 1% of the continent. Climate change will alter the extent and configuration of ice-free areas, yet the distribution and severity of these effects remain unclear. Here we quantify the impact of twenty-first century climate change on ice-free areas under two Intergovernmental Panel on Climate Change (IPCC) climate forcing scenarios using temperature-index melt modelling. Under the strongest forcing scenario, ice-free areas could expand by over 17,000 km2 by the end of the century, close to a 25% increase. Most of this expansion will occur in the Antarctic Peninsula, where a threefold increase in ice-free area could drastically change the availability and connectivity of biodiversity habitat. Isolated ice-free areas will coalesce, and while the effects on biodiversity are uncertain, we hypothesize that they could eventually lead to increasing regional-scale biotic homogenization, the extinction of less-competitive species and the spread of invasive species.

  20. 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.

  1. Initiation and long-term instability of the East Antarctic Ice Sheet

    Science.gov (United States)

    Gulick, Sean P. S.; Shevenell, Amelia E.; Montelli, Aleksandr; Fernandez, Rodrigo; Smith, Catherine; Warny, Sophie; Bohaty, Steven M.; Sjunneskog, Charlotte; Leventer, Amy; Frederick, Bruce; Blankenship, Donald D.

    2017-12-01

    Antarctica’s continental-scale ice sheets have evolved over the past 50 million years. However, the dearth of ice-proximal geological records limits our understanding of past East Antarctic Ice Sheet (EAIS) behaviour and thus our ability to evaluate its response to ongoing environmental change. The EAIS is marine-terminating and grounded below sea level within the Aurora subglacial basin, indicating that this catchment, which drains ice to the Sabrina Coast, may be sensitive to climate perturbations. Here we show, using marine geological and geophysical data from the continental shelf seaward of the Aurora subglacial basin, that marine-terminating glaciers existed at the Sabrina Coast by the early to middle Eocene epoch. This finding implies the existence of substantial ice volume in the Aurora subglacial basin before continental-scale ice sheets were established about 34 million years ago. Subsequently, ice advanced across and retreated from the Sabrina Coast continental shelf at least 11 times during the Oligocene and Miocene epochs. Tunnel valleys associated with half of these glaciations indicate that a surface-meltwater-rich sub-polar glacial system existed under climate conditions similar to those anticipated with continued anthropogenic warming. Cooling since the late Miocene resulted in an expanded polar EAIS and a limited glacial response to Pliocene warmth in the Aurora subglacial basin catchment. Geological records from the Sabrina Coast shelf indicate that, in addition to ocean temperature, atmospheric temperature and surface-derived meltwater influenced East Antarctic ice mass balance under warmer-than-present climate conditions. Our results imply a dynamic EAIS response with continued anthropogenic warming and suggest that the EAIS contribution to future global sea-level projections may be under-estimated.

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

    Science.gov (United States)

    Ao, H.; Roberts, A. P.; Dekkers, M. J.; Liu, X.; Rohling, E. J.; Shi, Z.; An, Z.; Zhao, X.

    2016-12-01

    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.

  3. 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.

  4. Multiphase Reactive Transport and Platelet Ice Accretion in the Sea Ice of McMurdo Sound, Antarctica

    Science.gov (United States)

    Buffo, J. J.; Schmidt, B. E.; Huber, C.

    2018-01-01

    Sea ice seasonally to interannually forms a thermal, chemical, and physical boundary between the atmosphere and hydrosphere over tens of millions of square kilometers of ocean. Its presence affects both local and global climate and ocean dynamics, ice shelf processes, and biological communities. Accurate incorporation of sea ice growth and decay, and its associated thermal and physiochemical processes, is underrepresented in large-scale models due to the complex physics that dictate oceanic ice formation and evolution. Two phenomena complicate sea ice simulation, particularly in the Antarctic: the multiphase physics of reactive transport brought about by the inhomogeneous solidification of seawater, and the buoyancy driven accretion of platelet ice formed by supercooled ice shelf water onto the basal surface of the overlying ice. Here a one-dimensional finite difference model capable of simulating both processes is developed and tested against ice core data. Temperature, salinity, liquid fraction, fluid velocity, total salt content, and ice structure are computed during model runs. The model results agree well with empirical observations and simulations highlight the effect platelet ice accretion has on overall ice thickness and characteristics. Results from sensitivity studies emphasize the need to further constrain sea ice microstructure and the associated physics, particularly permeability-porosity relationships, if a complete model of sea ice evolution is to be obtained. Additionally, implications for terrestrial ice shelves and icy moons in the solar system are discussed.

  5. Gaussian Process Model for Antarctic Surface Mass Balance and Ice Core Site Selection

    Science.gov (United States)

    White, P. A.; Reese, S.; Christensen, W. F.; Rupper, S.

    2017-12-01

    Surface mass balance (SMB) is an important factor in the estimation of sea level change, and data are collected to estimate models for prediction of SMB on the Antarctic ice sheet. Using Favier et al.'s (2013) quality-controlled aggregate data set of SMB field measurements, a fully Bayesian spatial model is posed to estimate Antarctic SMB and propose new field measurement locations. Utilizing Nearest-Neighbor Gaussian process (NNGP) models, SMB is estimated over the Antarctic ice sheet. An Antarctic SMB map is rendered using this model and is compared with previous estimates. A prediction uncertainty map is created to identify regions of high SMB uncertainty. The model estimates net SMB to be 2173 Gton yr-1 with 95% credible interval (2021,2331) Gton yr-1. On average, these results suggest lower Antarctic SMB and higher uncertainty than previously purported [Vaughan et al. (1999); Van de Berg et al. (2006); Arthern, Winebrenner and Vaughan (2006); Bromwich et al. (2004); Lenaerts et al. (2012)], even though this model utilizes significantly more observations than previous models. Using the Gaussian process' uncertainty and model parameters, we propose 15 new measurement locations for field study utilizing a maximin space-filling, error-minimizing design; these potential measurements are identied to minimize future estimation uncertainty. Using currently accepted Antarctic mass balance estimates and our SMB estimate, we estimate net mass loss [Shepherd et al. (2012); Jacob et al. (2012)]. Furthermore, we discuss modeling details for both space-time data and combining field measurement data with output from mathematical models using the NNGP framework.

  6. Characteristics of ice-active substances released by sea ice diatoms

    Science.gov (United States)

    Raymond, James A.

    1997-07-01

    Several species of antarctic sea ice diatoms have been found to release ice-active substances (IAS). At natural concentrations, they produce dense pitting on ice crystal surfaces at temperatures slightly below the freezing point, without significantly affecting the freezing point. This phenomenon appears to be associated with cold-adapted species as it has not been found in temperature fresh water and marine diatoms. IASs have been found in several species of sea ice diatoms, including both attached and unattached species. The ice-active substances have been found both in ice platelet water as well as in the solid congelation ice in McMurdo Sound in early summer, and in newly formed ice in winter in the Weddell and Bellinghausen seas. An IAS- producing species (Amphiprora) was cultured in the laboratory and produced noticeable increases in IAS activity. The IAS is retained by dialysis tubing and appears to be proteinaceous, as it is inactivated by proteases and heat. Further attempts to purify and characterize the IAS are in progress. The role of the IAS is unknown. Possible roles involving attachment of diatoms to ice and modification of the optical properties of ice are being considered.

  7. Glacial isostatic stress shadowing by the Antarctic ice sheet

    Science.gov (United States)

    Ivins, E. R.; James, T. S.; Klemann, V.

    2005-01-01

    Numerous examples of fault slip that offset late Quaternary glacial deposits and bedrock polish support the idea that the glacial loading cycle causes earthquakes in the upper crust. A semianalytical scheme is presented for quantifying glacial and postglacial lithospheric fault reactivation using contemporary rock fracture prediction methods. It extends previous studies by considering differential Mogi-von Mises stresses, in addition to those resulting from a Coulomb analysis. The approach utilizes gravitational viscoelastodynamic theory and explores the relationships between ice mass history and regional seismicity and faulting in a segment of East Antarctica containing the great Antarctic Plate (Balleny Island) earthquake of 25 March 1998 (Mw 8.1). Predictions of the failure stress fields within the seismogenic crust are generated for differing assumptions about background stress orientation, mantle viscosity, lithospheric thickness, and possible late Holocene deglaciation for the D91 Antarctic ice sheet history. Similar stress fracture fields are predicted by Mogi-von Mises and Coulomb theory, thus validating previous rebound Coulomb analysis. A thick lithosphere, of the order of 150-240 km, augments stress shadowing by a late melting (middle-late Holocene) coastal East Antarctic ice complex and could cause present-day earthquakes many hundreds of kilometers seaward of the former Last Glacial Maximum grounding line.

  8. Extreme ecological response of a seabird community to unprecedented sea ice cover.

    Science.gov (United States)

    Barbraud, Christophe; Delord, Karine; Weimerskirch, Henri

    2015-05-01

    Climate change has been predicted to reduce Antarctic sea ice but, instead, sea ice surrounding Antarctica has expanded over the past 30 years, albeit with contrasted regional changes. Here we report a recent extreme event in sea ice conditions in East Antarctica and investigate its consequences on a seabird community. In early 2014, the Dumont d'Urville Sea experienced the highest magnitude sea ice cover (76.8%) event on record (1982-2013: range 11.3-65.3%; mean±95% confidence interval: 27.7% (23.1-32.2%)). Catastrophic effects were detected in the breeding output of all sympatric seabird species, with a total failure for two species. These results provide a new view crucial to predictive models of species abundance and distribution as to how extreme sea ice events might impact an entire community of top predators in polar marine ecosystems in a context of expanding sea ice in eastern Antarctica.

  9. Evidence for a dynamic East Antarctic ice sheet during the mid-Miocene climate transition

    Science.gov (United States)

    Pierce, Elizabeth L.; van de Flierdt, Tina; Williams, Trevor; Hemming, Sidney R.; Cook, Carys P.; Passchier, Sandra

    2017-11-01

    The East Antarctic ice sheet underwent a major expansion during the Mid-Miocene Climate Transition, around 14 Ma, lowering sea level by ∼60 m. However, direct or indirect evidence of where changes in the ice sheet occurred is limited. Here we present new insights on timing and locations of ice sheet change from two drill sites offshore East Antarctica. IODP Site U1356, Wilkes Land, and ODP Site 1165, Prydz Bay are located adjacent to two major ice drainage areas, the Wilkes Subglacial Basin and the Lambert Graben. Ice-rafted detritus (IRD), including dropstones, was deposited in concentrations far exceeding those known in the rest of the Miocene succession at both sites between 14.1 and 13.8 Ma, indicating that large amounts of IRD-bearing icebergs were calved from independent drainage basins during this relatively short interval. At Site U1356, the IRD was delivered in distinct pulses, suggesting that the overall ice advance was punctuated by short periods of ice retreat in the Wilkes Subglacial Basin. Provenance analysis of the mid-Miocene IRD and fine-grained sediments provides additional insights on the movement of the ice margin and subglacial geology. At Site U1356, the dominant 40Ar/39Ar thermochronological age of the ice-rafted hornblende grains is 1400-1550 Ma, differing from the majority of recent IRD in the area, from which we infer an inland source area of this thermochronological age extending along the eastern part of the Adélie Craton, which forms the western side of the Wilkes Subglacial Basin. Neodymium isotopic compositions from the terrigenous fine fraction at Site U1356 imply that the ice margin periodically expanded from high ground well into the Wilkes Subglacial Basin during periods of MMCT ice growth. At Site 1165, MMCT pebble-sized IRD are sourced from both the local Lambert Graben and the distant Aurora Subglacial Basin drainage area. Together, the occurrence and provenance of the IRD and glacially-eroded sediment at these two marine

  10. Submesoscale Sea Ice-Ocean Interactions in Marginal Ice Zones

    Science.gov (United States)

    Manucharyan, Georgy E.; Thompson, Andrew F.

    2017-12-01

    Signatures of ocean eddies, fronts, and filaments are commonly observed within marginal ice zones (MIZs) from satellite images of sea ice concentration, and in situ observations via ice-tethered profilers or underice gliders. However, localized and intermittent sea ice heating and advection by ocean eddies are currently not accounted for in climate models and may contribute to their biases and errors in sea ice forecasts. Here, we explore mechanical sea ice interactions with underlying submesoscale ocean turbulence. We demonstrate that the release of potential energy stored in meltwater fronts can lead to energetic submesoscale motions along MIZs with spatial scales O(10 km) and Rossby numbers O(1). In low-wind conditions, cyclonic eddies and filaments efficiently trap the sea ice and advect it over warmer surface ocean waters where it can effectively melt. The horizontal eddy diffusivity of sea ice mass and heat across the MIZ can reach O(200 m2 s-1). Submesoscale ocean variability also induces large vertical velocities (order 10 m d-1) that can bring relatively warm subsurface waters into the mixed layer. The ocean-sea ice heat fluxes are localized over cyclonic eddies and filaments reaching about 100 W m-2. We speculate that these submesoscale-driven intermittent fluxes of heat and sea ice can contribute to the seasonal evolution of MIZs. With the continuing global warming and sea ice thickness reduction in the Arctic Ocean, submesoscale sea ice-ocean processes are expected to become increasingly prominent.

  11. Multiscale Models of Melting Arctic Sea Ice

    Science.gov (United States)

    2014-09-30

    Sea ice reflectance or albedo , a key parameter in climate modeling, is primarily determined by melt pond and ice floe configurations. Ice - albedo ...determine their albedo - a key parameter in climate modeling. Here we explore the possibility of a conceptual sea ice climate model passing through a...bifurcation points. Ising model for melt ponds on Arctic sea ice Y. Ma, I. Sudakov, and K. M. Golden Abstract: The albedo of melting

  12. IceBridge ATM L1B Elevation and Return Strength V002

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set contains spot elevation measurements of Arctic and Antarctic sea ice, and Greenland, Antarctic Peninsula, and West Antarctic region ice surface...

  13. Sea Ice and Ice Temperature Variability as Observed by Microwave and Infrared Satellite Data

    Science.gov (United States)

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

    2001-01-01

    Recent reports of a retreating and thinning sea ice cover in the Arctic have pointed to a strong suggestion of significant warming in the polar regions. It is especially important to understand what these reports mean in light of the observed global warning and because the polar regions are expected to be most sensitive to changes in climate. To gain insight into this phenomenon, co-registered ice concentrations and surface temperatures derived from two decades of satellite microwave and infrared data have been processed and analyzed. While observations from meteorological stations indicate consistent surface warming in both regions during the last fifty years, the last 20 years of the same data set show warming in the Arctic but a slight cooling in the Antarctic. These results are consistent with the retreat in the Arctic ice cover and the advance in the Antarctic ice cover as revealed by historical satellite passive microwave data. Surface temperatures derived from satellite infrared data are shown to be consistent within 3 K with surface temperature data from the limited number of stations. While not as accurate, the former provides spatially detailed changes over the twenty year period. In the Arctic, for example, much of the warming occurred in the Beaufort Sea and the North American region in 1998 while slight cooling actually happened in parts of the Laptev Sea and Northern Siberia during the same time period. Big warming anomalies are also observed during the last five years but a periodic cycle of about ten years is apparent suggesting a possible influence of the North Atlantic Oscillation. In the Antarctic, large interannual and seasonal changes are also observed in the circumpolar ice cover with regional changes showing good coherence with surface temperature anomalies. However, a mode 3 is observed to be more dominant than the mode 2 wave reported in the literature. Some of these spatial and temporal changes appear to be influenced by the Antarctic

  14. Integration of airborne altimetry and in situ radar measurements to estimate marine ice thickness beneath the Larsen C ice shelf, Antarctic Peninsula

    Science.gov (United States)

    McGrath, D.; Steffen, K.; Rodriguez Lagos, J.

    2010-12-01

    Observed atmospheric and oceanic warming is driving significant retreat and / or collapse of ice shelves along the Antarctic Peninsula totaling over 25,000 km2 in the past five decades. Basal melting of meteoric ice can occur near the grounding line of deep glacier inflows if the ocean water is above the pressure melting point. Buoyant meltwater will develop thermohaline circulation, rising beneath the ice shelf, where it may become supercooled and subsequently refreeze in ice draft minima. Marine ice, due to its warm and thus relatively viscous nature, is hypothesized to suture parallel flow bands, increasing ice shelf stability by arresting fracture propagation and controlling iceberg calving dimensions. Thus efforts to model ice shelf stability require accurate estimates of marine ice location and thickness. Ice thickness of a floating ice shelf can be determined in two manners: (1) from measurements of ice elevation above sea level and the calculation of ice thickness from assumptions of hydrostatic equilibrium, and (2) from radar echo measurements of the ice-water interface. Marine ice can confound the latter because its high dielectric constant and strong absorptive properties attenuate the radar energy, often preventing a return signal from the bottom of the ice shelf. These two methods are complementary for determining the marine ice component though because positive anomalies in (1) relative to (2) suggest regions of marine ice accretion. Nearly 350 km of ice penetrating radar (25 MHz) surveys were collected on the Larsen C ice shelf, in conjunction with kinematic GPS measurements and collocated with surface elevation data from the NASA Airborne Topographic Mapper (ATM) as part of the ICE Bridge mission in 2009. Basal ice topography and total ice thickness is accurately mapped along the survey lines and compared with calculated ice thickness from both the kinematic GPS and ATM elevation data. Positive anomalies are discussed in light of visible imagery and

  15. 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

  16. Impact of Greenland and Antarctic ice sheet interactions on climate sensitivity

    Energy Technology Data Exchange (ETDEWEB)

    Goelzer, H.; Huybrechts, P. [Vrije Universiteit Brussel, Earth System Sciences and Departement Geografie, Brussels (Belgium); Loutre, M.F.; Goosse, H.; Fichefet, T. [Universite Catholique de Louvain, Georges Lemaitre Centre for Earth and Climate Research (TECLIM), Earth and Life Institute, Louvain-la-Neuve (Belgium); Mouchet, A. [Universite de Liege, Laboratoire de Physique Atmospherique et Planetaire, Liege (Belgium)

    2011-09-15

    We use the Earth system model of intermediate complexity LOVECLIM to show the effect of coupling interactive ice sheets on the climate sensitivity of the model on a millennial time scale. We compare the response to a 2 x CO{sub 2} warming scenario between fully coupled model versions including interactive Greenland and Antarctic ice sheet models and model versions with fixed ice sheets. For this purpose an ensemble of different parameter sets have been defined for LOVECLIM, covering a wide range of the model's sensitivity to greenhouse warming, while still simulating the present-day climate and the climate evolution over the last millennium within observational uncertainties. Additional freshwater fluxes from the melting ice sheets have a mitigating effect on the model's temperature response, leading to generally lower climate sensitivities of the fully coupled model versions. The mitigation is effectuated by changes in heat exchange within the ocean and at the sea-air interface, driven by freshening of the surface ocean and amplified by sea-ice-related feedbacks. The strength of the effect depends on the response of the ice sheets to the warming and on the model's climate sensitivity itself. The effect is relatively strong in model versions with higher climate sensitivity due to the relatively large polar amplification of LOVECLIM. With the ensemble approach in this study we cover a wide range of possible model responses. (orig.)

  17. Antarctic Ice Sheet variability across the Eocene-Oligocene boundary climate transition.

    Science.gov (United States)

    Galeotti, Simone; DeConto, Robert; Naish, Timothy; Stocchi, Paolo; Florindo, Fabio; Pagani, Mark; Barrett, Peter; Bohaty, Steven M; Lanci, Luca; Pollard, David; Sandroni, Sonia; Talarico, Franco M; Zachos, James C

    2016-04-01

    About 34 million years ago, Earth's climate cooled and an ice sheet formed on Antarctica as atmospheric carbon dioxide (CO2) fell below ~750 parts per million (ppm). Sedimentary cycles from a drill core in the western Ross Sea provide direct evidence of orbitally controlled glacial cycles between 34 million and 31 million years ago. Initially, under atmospheric CO2 levels of ≥600 ppm, a smaller Antarctic Ice Sheet (AIS), restricted to the terrestrial continent, was highly responsive to local insolation forcing. A more stable, continental-scale ice sheet calving at the coastline did not form until ~32.8 million years ago, coincident with the earliest time that atmospheric CO2 levels fell below ~600 ppm. Our results provide insight into the potential of the AIS for threshold behavior and have implications for its sensitivity to atmospheric CO2 concentrations above present-day levels. Copyright © 2016, American Association for the Advancement of Science.

  18. 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

  19. 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.

  20. ICESat-Derived Grounding Zone for Antarctic Ice Shelves, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set includes estimates of the location of the grounding zone of Antarctic ice shelves based on laser altimeter data acquired during the Ice, Cloud, and...

  1. 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.

  2. 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

  3. Do Climate Models Simulate the Right Sea Ice Trends for the Wrong Reasons?

    Science.gov (United States)

    Rosenblum, E. J.; Eisenman, I.

    2016-02-01

    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, predict a moderate decrease in both the Arctic and Antarctic sea ice cover. A number of recent studies have attributed this discrepancy in each hemisphere to natural variability. Here we examine sea ice changes during 1979-2013 in simulations from the most recent Coupled Model Intercomparison Project as well as the Community Earth System Model Large Ensemble. We find that after accounting for biases in the level of global warming in each simulation, the possibility that natural variability alone could explain the difference between models and observations becomes exceedingly small. This suggests instead that there is a systematic bias in the climate models or possibly the observations.

  4. The Influence of Ice Properties on Borehole Deformation at the West Antarctic Ice Sheet Divide

    Science.gov (United States)

    Sinkler, E.; Pettit, E. C.; Obbard, R. W.

    2017-12-01

    It is widely known that ice flow is affected by many properties, including crystal fabric and impurities, though these relationships are not fully understood. This study uses data from the West Antarctic Ice Sheet (WAIS) Divide borehole to better determine the influence of such properties on ice flow. The WAIS Divide borehole, the byproduct of the 2006-2012 coring project, offers a unique opportunity to study deep Antarctic Ice. Thanks to the work of many researchers, extensive data on ice properties are available from both coring and borehole logging at this site. The borehole, kept open with a density-approximating fluid, closes and tilts due to ice flow. We have tracked this deformation over two years using a set of repeat measurements with an Acoustic Televiewer. This tool acts as an acoustic caliper allowing us to view cross-sections of the borehole shape and size with up to 1.25 degree azimuthal resolution and a depth resolution as high as 1.4 mm. In addition, the tool collects tilt and azimuth data. These measurements are compared to a 1D Glen's Flow Law model for borehole closure that uses density differences between the ice and borehole fluid as its driving force and incorporates temperature effects. This is then compared to ice properties like crystal fabric and impurities in order to determine the influence of these properties on ice deformation at this site. Crystal fabric has appeared as an important factor in this study.This work builds on that of others who have studied in-situ deep ice through borehole deformation (e.g. Paterson, 1977 and Dahl-Jensen and Gundestrup, 1987). Our results have implications for ice flow modeling and therefore interpretation of depth-age relationships in deep ice cores.

  5. Synoptic and mesoscale climate forcing on Antarctic ice shelf surface melt dynamics

    Science.gov (United States)

    Karmosky, Christopher

    Given that the polar regions, especially the Antarctic Peninsula, have experienced one of the largest temperature increases on Earth over the last few decades, an understanding of Antarctic climate has become more urgent. Ice shelves themselves are located at the intersection of the atmosphere, hydrosphere and the cryosphere---the air-ice-ocean boundary, and are sensitive to changes in any of these media. In addition to being particularly sensitive to changes in climate, ice shelves play an important role in controlling the flow of glaciers into the ocean, which has important implications for sea level changes. In a warming world, an increased understanding of how climate change is affecting Antarctic ice shelves is valuable for assessing vulnerable regions of the Antarctic that may be prone to further instability. This work focuses on determining the underlying climatic processes controlling energy and mass balance responsible for driving melting over ice shelves. A novel melt-magnitude retrieval method is presented that uses Moderate Resolution Imaging Spectroradiometer (MODIS)-derived near-IR reflectance coupled with ice surface temperature as a proxy for surface melt magnitude. This method has a higher spatial resolution than passive microwave melt detection, has the added benefit of retrieving melt magnitude rather than a binary melt occurrence or non-occurrence, but has a lower temporal resolution than either passive-microwave or microwave-scatterometry melt detection. This limitation is a result of the opacity of cloud cover to both visible and IR radiation, requiring more satellite overpasses to obtain spatially contiguous imagery. This work also examines several weather variables associated with a large-extent, long-duration surface melt event on the Ross Ice Shelf. It is shown that cloudy conditions coupled with increased sensible and latent heat flux to the surface were present during the event, and these conditions are consistent with those that induce

  6. [Bacterial diversity within different sections of summer sea-ice samples from the Prydz Bay, Antarctica].

    Science.gov (United States)

    Ma, Jifei; Du, Zongjun; Luo, Wei; Yu, Yong; Zeng, Yixin; Chen, Bo; Li, Huirong

    2013-02-04

    In order to assess bacterial abundance and diversity within three different sections of summer sea-ice samples collected from the Prydz Bay, Antarctica. Fluorescence in situ hybridization was applied to determine the proportions of Bacteria in sea-ice. Bacterial community composition within sea ice was analyzed by 16S rRNA gene clone library construction. Correlation analysis was performed between the physicochemical parameters and the bacterial diversity and abundance within sea ice. The result of fluorescence in situ hybridization shows that bacteria were abundant in the bottom section, and the concentration of total organic carbon, total organic nitrogen and phosphate may be the main factors for bacterial abundance. In bacterial 16S rRNA gene libraries of sea-ice, nearly complete 16S rRNA gene sequences were grouped into three distinct lineages of Bacteria (gamma-Proteobacteria, alpha-Proteobacteria and Bacteroidetes). Most clone sequences were related to cultured bacterial isolates from the marine environment, arctic and Antarctic sea-ice with high similarity. The member of Bacteroidetes was not detected in the bottom section of sea-ice. The bacterial communities within sea-ice were little heterogeneous at the genus-level between different sections, and the concentration of NH4+ may cause this distribution. The number of bacteria was abundant in the bottom section of sea-ice. Gamma-proteobacteria was the dominant bacterial lineage in sea-ice.

  7. Modelling present-day basal melt rates for Antarctic ice shelves using a parametrization of buoyant meltwater plumes

    Science.gov (United States)

    Lazeroms, Werner M. J.; Jenkins, Adrian; Hilmar Gudmundsson, G.; van de Wal, Roderik S. W.

    2018-01-01

    Basal melting below ice shelves is a major factor in mass loss from the Antarctic Ice Sheet, which can contribute significantly to possible future sea-level rise. Therefore, it is important to have an adequate description of the basal melt rates for use in ice-dynamical models. Most current ice models use rather simple parametrizations based on the local balance of heat between ice and ocean. In this work, however, we use a recently derived parametrization of the melt rates based on a buoyant meltwater plume travelling upward beneath an ice shelf. This plume parametrization combines a non-linear ocean temperature sensitivity with an inherent geometry dependence, which is mainly described by the grounding-line depth and the local slope of the ice-shelf base. For the first time, this type of parametrization is evaluated on a two-dimensional grid covering the entire Antarctic continent. In order to apply the essentially one-dimensional parametrization to realistic ice-shelf geometries, we present an algorithm that determines effective values for the grounding-line depth and basal slope in any point beneath an ice shelf. Furthermore, since detailed knowledge of temperatures and circulation patterns in the ice-shelf cavities is sparse or absent, we construct an effective ocean temperature field from observational data with the purpose of matching (area-averaged) melt rates from the model with observed present-day melt rates. Our results qualitatively replicate large-scale observed features in basal melt rates around Antarctica, not only in terms of average values, but also in terms of the spatial pattern, with high melt rates typically occurring near the grounding line. The plume parametrization and the effective temperature field presented here are therefore promising tools for future simulations of the Antarctic Ice Sheet requiring a more realistic oceanic forcing.

  8. A mechanism for biologically-induced iodine emissions from sea-ice

    Science.gov (United States)

    Boxe, C.

    2015-12-01

    Ground- and satellite-based measurements reported high concentrations of iodine monoxide (IO) in coastal Antarctica. The sources of such a large iodine burden in the coastal Antarctic atmosphere remain unknown. We propose a mechanism for iodine release from sea-ice based on the premise that micro-algae are the primary source of iodine emissions in this environment. The emissions are triggered by the biological production of iodide (I-) and hypoiodous acid (HOI) from micro-algae (contained within and underneath sea-ice) and their diffusion through sea-ice brine channels, to accumulate in a thin brine layer (BL) on the surface of sea-ice. Prior to reaching the BL, the diffusion timescale of iodine within sea-ice is depth-dependent. The BL is also a vital component of the proposed mechanism as it enhances the chemical kinetics of iodine-related reactions, which allows for the efficient release of iodine to the polar boundary layer. We suggest iodine is released to the atmosphere via 3 possible pathways: (1) emitted from the BL and then transported throughout snow atop sea-ice, to be released to the atmosphere; (2) released directly from the BL to the atmosphere in regions of sea-ice that are not covered with snowpack; or (3) emitted to the atmosphere directly through fractures in the sea-ice pack. To investigate the proposed biology-ice-atmosphere coupling at coastal Antarctica we use a multiphase model that incorporates the transport of iodine species, via diffusion, at variable depths, within brine channels of sea-ice. Model simulations were conducted to interpret observations of elevated springtime IO in the coastal Antarctic, around the Weddell Sea. While a lack of experimental and observational data adds uncertainty to the model predictions, nevertheless the results show that the levels of inorganic iodine (i.e., I2, IBr, ICl) released from sea-ice through this mechanism could account for the observed IO concentrations during this timeframe. The model results

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

    Science.gov (United States)

    2015-09-30

    Roberts. Measurers: Don Perovich, Rob Massom, Melinda Webster, Oliver Dammann, Charlie Parr III, Alexandra Arnsten. Topics discussed included...with models. RESULTS A spatially heterogeneous and temporally changing snow cover resides atop Arctic and Antarctic sea ice for much of the...must be accurately represented to properly treat the polar sea ice covers and related feedbacks in climate models, but that is a difficult

  10. Ice matters. Under-ice fauna surveys in the Arctic and Antarctic Oceans

    OpenAIRE

    Flores, Hauke; David, Carmen; Lange, Benjamin; van Franeker, J.-A.; Siegel, Volker; Pakhomov, E. A.; Hunt, B. P. V.; Van de Putte, A. P.; Tonkes, Henrieke; Nicolaus, Marcel; Fernandez Mendez, Mar; Niehoff, Barbara; Peeken, Ilka

    2013-01-01

    In the Polar Regions, sea ice habitats are undergoing rapid environmental change. Because sea ice constitutes an important substrate for numerous species, as well as an important carbon source during critical periods of the year, these changes have a significant impact on ecosystem functioning, biodiversity, species distribution, and population sizes of both commercially exploited species, and species valuable from a conservation perspective. Species dwelling at the ice-water interface (e.g. ...

  11. A geoelectrical survey above an Antarctic ice shelf

    Directory of Open Access Journals (Sweden)

    M. Pavan

    1998-06-01

    Full Text Available A geoelectrical survey was performed on the Hells Gate ice shelf (Victoria Land-Antarctic within the framework of an integrated geophysical and glaciological research program. The resistivity profiles show a similar trend, with resistivity values ranging from about 25000 W · m to 500000 W · m. These results have been interpreted as the effect of a sharp transition from "marine ice" to "continental" ice an interpretation that is consistent with the results of surface mapping. Interpreting the Vertical Electrical Soundings (VES is a complex process. In fact, the alternating layers of ice with different compositions and salt content generate great uncertainty relative to the corresponding electric stratigraphies. To solve these problems of equivalency, all the available constraints were used including the drilling thickness, seismic reflection profiles as well as radar profiles. The results were used to provide what is mainly a qualitative overview that is coherent with the glaciological hypotheses relative to the evolution and structure proposed by some researchers for this ice shelf.

  12. Regionally Optimized GRACE Processing and Inter-comparison on the Antarctic Ice Sheet

    Science.gov (United States)

    Mohajerani, Y.; Velicogna, I.; Sutterley, T. C.; Rignot, E. J.

    2017-12-01

    The Antarctic ice sheet is losing mass at an accelerating rate, with a sea level contribution that changed from 0.08mm/yr from 1992 to 2001 to 0.4mm/yr from 2002 to 2011. While most of this contribution comes from West Antarctica, Totten Glacier has the largest discharge of ice in East Antarctica, with a sea level rise potential of 3.9 m. Furthermore, the drainage basin of Totten Glacier, along the neighboring Moscow University Glacier are below sea level, extending hundreds of kilometers inland. Therefore, obtaining regional estimates of both western and eastern Antarctic basins are of critical importance. The GRACE (Gravity Recovery and Climate Experiment) satellite has been providing mass balance time-series from geoid changes since 2002. Several mascon and harmonic GRACE solutions are available from different processing centers. Here, we evaluate the various solutions across the ice sheet and a new set of regionally optimized mascons to study the mass balance of Totten and Moscow University glaciers. We obtain a trend of -16.5±4.1Gt/yr with an acceleration of -2.0±1.8Gt/yr2 for the two glaciers for the period April 2002 to December 2016 using the Ivins et al (2013) GIA model (errors include leakage, GIA, and regression errors). We compare the results with the Mass Budget Method that combines ice discharge (D) and surface mass balance (SMB) from two models: 1) RACMO2.3, and 2) MAR3.6.4. MBM/RACMO2.3 shows the best agreement with the GRACE estimates. Within the common period from April 2002 to December 2015, the MBM/RACMO2.3 and MAR3.6.4 results are -15.6±1.8Gt/yr and -6.7±1.5Gt/yr respectively, while the GRACE time-series has a trend of -14.8±2.7 Gt/yr. We extend the study to the Getz Ice Shelf, the third largest ice shelf in West Antarctica after Ronne and Ross West ice shelves. We compare our gravity-derived mass estimates, the mass budget estimates, and the volume changes from altimetry data to compare the estimates and obtain a multi-sensor assessment

  13. Anatomy of a meltwater drainage system beneath the ancestral East Antarctic ice sheet

    Science.gov (United States)

    Simkins, Lauren M.; Anderson, John B.; Greenwood, Sarah L.; Gonnermann, Helge M.; Prothro, Lindsay O.; Halberstadt, Anna Ruth W.; Stearns, Leigh A.; Pollard, David; Deconto, Robert M.

    2017-09-01

    Subglacial hydrology is critical to understand the behaviour of ice sheets, yet active meltwater drainage beneath contemporary ice sheets is rarely accessible to direct observation. Using geophysical and sedimentological data from the deglaciated western Ross Sea, we identify a palaeo-subglacial hydrological system active beneath an area formerly covered by the East Antarctic ice sheet. A long channel network repeatedly delivered meltwater to an ice stream grounding line and was a persistent pathway for episodic meltwater drainage events. Embayments within grounding-line landforms coincide with the location of subglacial channels, marking reduced sedimentation and restricted landform growth. Consequently, channelized drainage at the grounding line influenced the degree to which these landforms could provide stability feedbacks to the ice stream. The channel network was connected to upstream subglacial lakes in an area of geologically recent rifting and volcanism, where elevated heat flux would have produced sufficient basal melting to fill the lakes over decades to several centuries; this timescale is consistent with our estimates of the frequency of drainage events at the retreating grounding line. Based on these data, we hypothesize that ice stream dynamics in this region were sensitive to the underlying hydrological system.

  14. Peeking Below the Snow Surface to Explore Amundsen Sea Climate Variability and Locate Optimal Ice-Core Sites

    Science.gov (United States)

    Neff, P. D.; Fudge, T. J.; Medley, B.

    2016-12-01

    Observations over recent decades reveal rapid changes in ice shelves and fast-flowing grounded ice along the Amundsen Sea coast of the West Antarctic Ice Sheet (WAIS). Long-term perspectives on this ongoing ice loss are needed to address a central question of Antarctic research: how much and how fast will Antarctic ice-loss raise sea level? Ice cores can provide insight into past variability of the atmospheric (wind) forcing of regional ocean dynamics affecting ice loss. Interannual variability of snow accumulation on coastal ice domes grounded near or within ice shelves reflects local to regional atmospheric circulation near the ice-ocean interface. Records of snow accumulation inferred from shallow ice cores strongly correlate with reanalysis precipitation and pressure fields, but ice cores have not yet been retrieved along the Amundsen Sea coast. High-frequency airborne radar data (NASA Operation IceBridge), however, have been collected over this region and we demonstrate that these data accurately reflect annual stratigraphy in shallow snow and firn (1 to 2 decades of accumulation). This further validates the agreement between radar snow accumulation records and climate reanalysis products. We then explore regional climate controls on local snow accumulation through comparison with gridded reanalysis products, providing a preview of what information longer coastal ice core records may provide with respect to past atmospheric forcing of ocean circulation and WAIS ice loss.

  15. Investigating Arctic Sea Ice Survivability in the Beaufort Sea

    Directory of Open Access Journals (Sweden)

    Matthew Tooth

    2018-02-01

    Full Text Available Arctic sea ice extent has continued to decline in recent years, and the fractional coverage of multi-year sea ice has decreased significantly during this period. The Beaufort Sea region has been the site of much of the loss of multi-year sea ice, and it continues to play a large role in the extinction of ice during the melt season. We present an analysis of the influence of satellite-derived ice surface temperature, ice thickness, albedo, and downwelling longwave/shortwave radiation as well as latitude and airborne snow depth estimates on the change in sea ice concentration in the Beaufort Sea from 2009 to 2016 using a Lagrangian tracking database. Results from this analysis indicate that parcels that melt during summer in the Beaufort Sea reside at lower latitudes and have lower ice thickness at the beginning of the melt season in most cases. The influence of sea ice thickness and snow depth observed by IceBridge offers less conclusive results, with some years exhibiting higher thicknesses/depths for melted parcels. Parcels that melted along IceBridge tracks do exhibit lower latitudes and ice thicknesses, however, which indicates that earlier melt and breakup of ice may contribute to a greater likelihood of extinction of parcels in the summer.

  16. Recent aerogeophysical exploration under the East Antarctic Ice Sheet in Wilkes Land

    Science.gov (United States)

    Bozzo, E.; Ferraccioli, F.; Armadillo, E.; Jordan, T. A.; Corr, H.; Hill, D. J.

    2009-12-01

    An extensive aerogeophysical survey was flown in Wilkes Land (East Antarctica) during the 2005/06 Antarctic field-campaign as part of a joint Italian-UK exploration project, WISE (Wilkes WIlkes Basin/Transantarctic Mountains System Exploration)/ ISODYN (Icehouse Earth: Stability Or DYNamism?). The Italian Antarctic programme provided major logistic support at Mario Zucchelli Station, at two remote field camps, Talos Dome and Sitry, and at Mid-Point. 68 survey flights led to the collection of over 60,000 line-km of new aerogeophysical data over a frontier region that had not been explored since the 70’s. Airborne radar, aeromagnetic and airborne gravity data were simultaneously collected on a British Antarctic Survey Twin Otter with the overarching aim of providing new basal boundary conditions for the dynamics and stability of the East Antarctic Ice Sheet, and characterizing geological structures in the Wilkes Subglacial Basin (WSB) and adjacent Transantarctic Mountains (TAM). During the International Polar Year our efforts focused on data analysis and subsequent development of new interpretations. Here we review some of the results. Our new bedrock topography map derived from airborne radar reveals major subglacial basins with depths up to 2.1 km below sea-level within the WSB region. These sub-basins are in places up to 1.5 km deeper than imaged by BEDMAP, have different orientations, and are flanked by major bedrock plateaus that differ from alpine-type landscapes exposed over the adjacent TAM in northern Victoria Land. The new subglacial topography for the region is a critical boundary condition to develop next generation coupled ice sheet and climate models over East Antarctica. These models are targeting the contentious stability of this marine-based part of the East Antarctic Ice Sheet during warm periods in the geological past and may provide a tool for assessing its longer term future behaviour in a warmer climate. The airborne radar dataset

  17. Improved Upper Ocean/Sea Ice Modeling in the GISS GCM for Investigating Climate Change

    Science.gov (United States)

    1997-01-01

    This project built on our previous results in which we highlighted the importance of sea ice in overall climate sensitivity by determining that for both warming and cooling climates, when sea ice was not allowed to change, climate sensitivity was reduced by 35-40%. We also modified the Goddard Institute for Space Studies (GISS) 8 deg x lO deg atmospheric General Circulation Model (GCM) to include an upper-ocean/sea-ice model involving the Semtner three-layer ice/snow thermodynamic model, the Price et al. (1986) ocean mixed layer model and a general upper ocean vertical advection/diffusion scheme for maintaining and fluxing properties across the pycnocline. This effort, in addition to improving the sea ice representation in the AGCM, revealed a number of sensitive components of the sea ice/ocean system. For example, the ability to flux heat through the ice/snow properly is critical in order to resolve the surface temperature properly, since small errors in this lead to unrestrained climate drift. The present project, summarized in this report, had as its objectives: (1) introducing a series of sea ice and ocean improvements aimed at overcoming remaining weaknesses in the GCM sea ice/ocean representation, and (2) performing a series of sensitivity experiments designed to evaluate the climate sensitivity of the revised model to both Antarctic and Arctic sea ice, determine the sensitivity of the climate response to initial ice distribution, and investigate the transient response to doubling CO2.

  18. The Formation each Winter of the Circumpolar Wave in the Sea Ice around Antarctica

    Science.gov (United States)

    Gloersen, Per; White, Warren B.

    1999-01-01

    Seeking to improve upon the visualization of the Antarctic Circumpolar Wave (ACW) , we compare a 16-year sequence of 6-month winter averages of Antarctic sea ice extents and concentrations with those of adjacent sea surface temperatures (SSTs). Here we follow SSTs around the globe along the maximum sea ice edge rather than in a zonal band equatorward of it. The results are similar to the earlier ones, but the ACWs do not propagate with equal amplitude or speed. Additionally in a sequence of 4 polar stereographic plots of these SSTs and sea ice concentrations, we find a remarkable correlation between SST minima and sea ice concentration maxima, even to the extent of matching contours across the ice-sea boundary, in the sector between 900E and the Palmer Peninsula. Based on these observations, we suggest that the memory of the ACW in the sea ice is carried from one Austral winter to the next by the neighboring SSTS, since the sea ice is nearly absent in the Austral summer.

  19. 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.

  20. A FUNDAMENTAL EXPERIMENT ON DETECTION OF SEA ICE THICKNESS BY UHF WAVES

    OpenAIRE

    タカシマ, ハヤオ; ヤマコシ, ヒサオ; Hayao, TAKASHIMA; Hisao, YAMAKOSHI

    1994-01-01

    The authors are endeavoring to study radar for detecting sea ice thickness which will help icebreakers transit ice-covered waters, and which makes use of ice thickness observations near the coasts of Arctic and Antarctic regions. It has been reported by K. IIZUKA and A.P. FREUNDOLFER (J. Appl. Phys., 56,2572,1984) that the most useful type of radar to detect sea ice thickness is a step frequency one that sweeps over a wide bandwidth of UHF waves. We constructed a step frequency radar for dete...

  1. Response of Pacific-sector Antarctic ice shelves to the El Niño/Southern Oscillation

    Science.gov (United States)

    Paolo, F. S.; Padman, L.; Fricker, H. A.; Adusumilli, S.; Howard, S.; Siegfried, M. R.

    2018-02-01

    Satellite observations over the past two decades have revealed increasing loss of grounded ice in West Antarctica, associated with floating ice shelves that have been thinning. Thinning reduces an ice shelf's ability to restrain grounded-ice discharge, yet our understanding of the climate processes that drive mass changes is limited. Here, we use ice-shelf height data from four satellite altimeter missions (1994-2017) to show a direct link between ice-shelf height variability in the Antarctic Pacific sector and changes in regional atmospheric circulation driven by the El Niño/Southern Oscillation. This link is strongest from the Dotson to Ross ice shelves and weaker elsewhere. During intense El Niño years, height increase by accumulation exceeds the height decrease by basal melting, but net ice-shelf mass declines as basal ice loss exceeds ice gain by lower-density snow. Our results demonstrate a substantial response of Amundsen Sea ice shelves to global and regional climate variability, with rates of change in height and mass on interannual timescales that can be comparable to the longer-term trend, and with mass changes from surface accumulation offsetting a significant fraction of the changes in basal melting. This implies that ice-shelf height and mass variability will increase as interannual atmospheric variability increases in a warming climate.

  2. Temporal variability of the Antarctic Ice sheet observed from space-based geodesy

    Science.gov (United States)

    Memin, A.; King, M. A.; Boy, J. P.; Remy, F.

    2017-12-01

    Quantifying the Antarctic Ice Sheet (AIS) mass balance still remains challenging as several processes compete to differing degrees at the basin scale with regional variations, leading to multiple mass redistribution patterns. For instance, analysis of linear trends in surface-height variations from 1992-2003 and 2002-2006 shows that the AIS is subject to decimetric scale variability over periods of a few years. Every year, snowfalls in Antarctica represent the equivalent of 6 mm of the mean sea level. Therefore, any fluctuation in precipitation can lead to changes in sea level. Besides, over the last decade, several major glaciers have been thinning at an accelerating rate. Understanding the processes that interact on the ice sheet is therefore important to precisely determine the response of the ice sheet to a rapid changing climate and estimate its contribution to sea level changes. We estimate seasonal and interannual changes of the AIS between January 2003 and October 2010 and to the end of 2016 from a combined analysis of surface-elevation and surface-mass changes derived from Envisat data and GRACE solutions, and from GRACE solutions only, respectively. While we obtain a good correlation for the interannual signal between the two techniques, important differences (in amplitude, phase, and spatial pattern) are obtained for the seasonal signal. We investigate these discrepancies by comparing the crustal motion observed by GPS and those predicted using monthly surface mass balance derived from the regional atmospheric climate model RACMO.

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

    DEFF Research Database (Denmark)

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

    2014-01-01

    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......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...... 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...

  4. 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.

  5. Solar radiation interactions with seasonal sea ice

    Science.gov (United States)

    Ehn, Jens Kristian

    Presently, the Arctic Ocean is undergoing an escalating reduction in sea ice and a transition towards a seasonal sea ice environment. This warrants detailed investigations into improving our understanding of the seasonal evolution of sea ice and snow covers, and their representation in climate models. The interaction of solar radiation with sea ice is an important process influencing the energy balance and biological activity in polar seas, and consequently plays a key role in the earth's climate system. This thesis focuses on characterization of the optical properties---and the underlying physical properties that determine them---of seasonal sea ice during the fall freeze-up and the spring melt periods. Both periods display high spatial heterogeneity and rapid temporal changes in sea ice properties, and are therefore poorly understood. Field data were collected in Amundsen Gulf/Franklin Bay (FB), southern-eastern Beaufort Sea, in Oct.-Nov. 2003 and Apr. 2004 and in Button Bay (BB), western Hudson Bay, in Mar.-May 2005 to address (1) the temporal and spatial evolution of surface albedo and transmittance, (2) how radiative transfer in sea ice is controlled by its physical nature, and (3) the characteristics of the bottom ice algae community and its effect on the optical properties. The fall study showed the importance of surface features such as dry or slushy bare ice, frost flowers and snow cover in determining the surface albedo. Ice thickness was also important, however, mostly because surface features were associated with thickness. For example, nilas (brine skim layer on the surface, while surface conditions on thicker ice types were cold and dry enough to support a snow cover. In general, the surface albedo increased exponentially with an ice thickness increase, however, variability within ice thickness types were very large. It is apparent that a more complete treatment of brine movement towards the surface ice of the ice cover and the formation of surface

  6. Impact of sea ice on the marine iron cycle and phytoplankton productivity

    Science.gov (United States)

    Wang, S.; Bailey, D.; Lindsay, K.; Moore, J. K.; Holland, M.

    2014-09-01

    Iron is a key nutrient for phytoplankton growth in the surface ocean. At high latitudes, the iron cycle is closely related to the dynamics of 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. In order to adequately study the effect of sea ice on the polar iron cycle, sea ice bearing iron was incorporated in the Community Earth System Model (CESM). Sea ice acts as a reservoir for iron during winter and releases the trace metal to the surface ocean in spring and summer. Simulated iron concentrations in sea ice generally agree with observations in regions where iron concentrations are relatively low. The maximum iron concentrations simulated in Arctic and Antarctic sea ice are much lower than observed, which is likely due to underestimation of iron inputs to sea ice or missing mechanisms. The largest iron source to sea ice is suspended sediments, contributing fluxes of iron of 2.2 × 108 mol Fe month-1 in the Arctic and 4.1 × 106 mol Fe month-1 in 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. 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. The impact of ice to ocean iron fluxes on marine ecosystems is 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 decrease with declining sea

  7. [Reflectance of sea ice in Liaodong Bay].

    Science.gov (United States)

    Xu, Zhan-tang; Yang, Yue-zhong; Wang, Gui-fen; Cao, Wen-xi; Kong, Xiang-peng

    2010-07-01

    In the present study, the relationships between sea ice albedo and the bidirectional reflectance distribution in Liaodong Bay were investigated. The results indicate that: (1) sea ice albedo alpha(lambda) is closely related to the components of sea ice, the higher the particulate concentration in sea ice surface is, the lower the sea ice albedo alpha(lambda) is. On the contrary, the higher the bubble concentration in sea ice is, the higher sea ice albedo alpha(lambda) is. (2) Sea ice albedo alpha(lambda) is similar to the bidirectional reflectance factor R(f) when the probe locates at nadir. The R(f) would increase with the increase in detector zenith theta, and the correlation between R(f) and the detector azimuth would gradually increase. When the theta is located at solar zenith 63 degrees, the R(f) would reach the maximum, and the strongest correlation is also shown between the R(f) and the detector azimuth. (3) Different types of sea ice would have the different anisotropic reflectance factors.

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

    Science.gov (United States)

    2014-09-30

    Ice - Albedo Feedback in Sea Ice Predictions Cecilia M. Bitz Atmospheric Sciences MS351640 University of Washington Seattle, WA 98196-1640 phone...TERM GOALS The overarching goals of this project are to understand the role of sea ice - albedo feedback on sea ice predictability, to improve how...sea- ice albedo is modeled and how sea ice predictions are initialized, and then to evaluate how these improvements influence inherent sea ice

  9. Low post-glacial rebound rates in the Weddell Sea due to Late Holocene ice-sheet readvance.

    OpenAIRE

    Bradley, S.L.; Hindmarsh, R.C.A.; Whitehouse, P.L.; Bentley, M.J.; King, M.A.

    2015-01-01

    Many ice-sheet reconstructions assume monotonic Holocene retreat for the West Antarctic Ice Sheet, but an increasing number of glaciological observations infer that some portions of the ice sheet may be readvancing, following retreat behind the present-day margin. A readvance in the Weddell Sea region can reconcile two outstanding problems: (i) the present-day widespread occurrence of seemingly stable ice streams grounded on beds that deepen inland; and (ii) the inability of models of glacial...

  10. 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...

  11. Recent State of Arctic Sea Ice

    Science.gov (United States)

    Nghiem, S. V.; Rigor, I. G.; Clemente-Colón, P.; Perovich, D. K.; Richter-Menge, J. A.; Chao, Y.; Neumann, G.; Ortmeyer, M.

    2008-12-01

    We present the recent state of Arctic sea ice including observations from 2008 in a context of a multi-decadal perspective. A new record has been set in the reduction of Arctic perennial sea ice extent this winter. As of 1 March 2008, the extent of perennial sea ice was reduced by one million km2 compared to that at the same time last year as observed by the NASA SeaWinds scatterometer on the QuikSCAT satellite (QSCAT). This decrease of perennial ice continues the precipitous declining trend observed in this decade. Furthermore, the perennial sea ice pattern change was deduced by buoy-based estimates with 50 years of data from drifting buoys and measurement camps to track sea ice movement around the Arctic Ocean. The combination of the satellite and surface data records confirms that the reduction of winter perennial ice extent broke the record in 2008 compared to data over the last half century. In the winter, the loss of perennial ice extent was driven by winds that compressed the ice and transported it out of the Fram Strait and Nares Strait to warmer ocean waters at lower latitudes, where the ice melted very effectively. Another historical fact is that the boundary of perennial sea ice already crossed the North Pole (NP) in February 2008, leaving the area around the NP occupied by seasonal sea ice. This is the first time, not only from the satellite data record but also in the history of sea ice charting at the National Ice Center since the 1970's, that observations indicate the seasonal ice migration into the NP area so early in winter. In the Bering Sea by 12 March 2008, the sea ice edge reached to an extent that coincided with the continental shelf break, indicating bathymetric effects on the distribution of water masses along the Aleutian North Slope, Bering Slope, Anadyr, and Kamchatka Currents that governed the pattern of sea ice formation in this region. Moreover, QSCAT observations showed that, in the 2008 winter, seasonal ice occupied the Northern Sea

  12. Controls on Last Glacial Maximum ice extent in the Weddell Sea embayment, Antarctica

    Science.gov (United States)

    Whitehouse, Pippa L.; Bentley, Michael J.; Vieli, Andreas; Jamieson, Stewart S. R.; Hein, Andrew S.; Sugden, David E.

    2017-01-01

    The Weddell Sea sector of the Antarctic Ice Sheet is hypothesized to have made a significant contribution to sea-level rise since the Last Glacial Maximum. Using a numerical flowline model we investigate the controls on grounding line motion across the eastern Weddell Sea and compare our results with field data relating to past ice extent. Specifically, we investigate the influence of changes in ice temperature, accumulation, sea level, ice shelf basal melt, and ice shelf buttressing on the dynamics of the Foundation Ice Stream. We find that ice shelf basal melt plays an important role in controlling grounding line advance, while a reduction in ice shelf buttressing is found to be necessary for grounding line retreat. There are two stable positions for the grounding line under glacial conditions: at the northern margin of Berkner Island and at the continental shelf break. Global mean sea-level contributions associated with these two scenarios are 50 mm and 130 mm, respectively. Comparing model results with field evidence from the Pensacola Mountains and the Shackleton Range, we find it unlikely that ice was grounded at the continental shelf break for a prolonged period during the last glacial cycle. However, we cannot rule out a brief advance to this position or a scenario in which the grounding line retreated behind present during deglaciation and has since re-advanced. Better constraints on past ice sheet and ice shelf geometry, ocean temperature, and ocean circulation are needed to reconstruct more robustly past behavior of the Foundation Ice Stream.

  13. A Radial Pattern of Six Paleo Ice Streams Emanating from the Bruce Plateau Ice Dome, Antarctic Peninsula Ice Sheet: Constraints from Multibeam Bathymetry and GPS Rebound

    Science.gov (United States)

    Fried, M.; Domack, E.; Canals, M.; Casamor, J.; King, M.

    2008-12-01

    We reconstructed ice thicknesses along six paleo ice streams emanating out of the Bruce Plateau in the Northern Antarctic Peninsula. This was done in order to generate models of potential isostatic rebound along the flow paths since the LGM and thereby provide a theoretical test for empirical observations of vertical displacement (rebound) as measured by seven coastal GPS stations (to be deployed during the current IPY- LARISSA project). This study is pertinent to realizing the effect of moderate ice sheet size during collapse and resulting sea level rise. The Palmer, Vernadsky, Hugo Island and Gerlache and Boyd Strait ice stream paths (flow lines) were highlighted on the Western side of the Peninsula. The Drygalski, Crane and Hektoria ice streams were studied on the Eastern side. Using detailed and near complete swath bathymetry data available for the Western Peninsula coastal region and partial swath mapping data generated at the site of the former Larsen B ice shelf (and Roberston Trough), we constructed hypothetical longitudinal profiles of all six ice streams along precisely located flow paths. These profiles extended from the accumulation zones in the upper elevations of the Bruce Plateau to the terminus along the continental shelf edge. The profiles included detailed elevations of the bedrock and hypothetical ice thickness values along the ice streams as they would have been during the Last Glacial Maximum (~ 16 ka). Ice thickness values were based on the elevations of bedrock, trim lines, surrounding topography, influence of surrounding glaciers and previous estimates of LGM ice thickness values around the Antarctic Peninsula. Using the components of the hypothetical longitudinal profiles, total isostatic rebound since the LGM can be calculated for the region (assuming reasonable mantle viscosities). In all the profiles reconstructed ice thicknesses are characterized by an order of magnitude increase across inner shelf troughs (such as the Palmer Deep and

  14. Trend analysis of Arctic sea ice extent

    Science.gov (United States)

    Silva, M. E.; Barbosa, S. M.; Antunes, Luís; Rocha, Conceição

    2009-04-01

    The extent of Arctic sea ice is a fundamental parameter of Arctic climate variability. In the context of climate change, the area covered by ice in the Arctic is a particularly useful indicator of recent changes in the Arctic environment. Climate models are in near universal agreement that Arctic sea ice extent will decline through the 21st century as a consequence of global warming and many studies predict a ice free Arctic as soon as 2012. Time series of satellite passive microwave observations allow to assess the temporal changes in the extent of Arctic sea ice. Much of the analysis of the ice extent time series, as in most climate studies from observational data, have been focussed on the computation of deterministic linear trends by ordinary least squares. However, many different processes, including deterministic, unit root and long-range dependent processes can engender trend like features in a time series. Several parametric tests have been developed, mainly in econometrics, to discriminate between stationarity (no trend), deterministic trend and stochastic trends. Here, these tests are applied in the trend analysis of the sea ice extent time series available at National Snow and Ice Data Center. The parametric stationary tests, Augmented Dickey-Fuller (ADF), Phillips-Perron (PP) and the KPSS, do not support an overall deterministic trend in the time series of Arctic sea ice extent. Therefore, alternative parametrizations such as long-range dependence should be considered for characterising long-term Arctic sea ice variability.

  15. Multi-decadal Arctic sea ice roughness.

    Science.gov (United States)

    Tsamados, M.; Stroeve, J.; Kharbouche, S.; Muller, J. P., , Prof; Nolin, A. W.; Petty, A.; Haas, C.; Girard-Ardhuin, F.; Landy, J.

    2017-12-01

    The transformation of Arctic sea ice from mainly perennial, multi-year ice to a seasonal, first-year ice is believed to have been accompanied by a reduction of the roughness of the ice cover surface. This smoothening effect has been shown to (i) modify the momentum and heat transfer between the atmosphere and ocean, (ii) to alter the ice thickness distribution which in turn controls the snow and melt pond repartition over the ice cover, and (iii) to bias airborne and satellite remote sensing measurements that depend on the scattering and reflective characteristics over the sea ice surface topography. We will review existing and novel remote sensing methodologies proposed to estimate sea ice roughness, ranging from airborne LIDAR measurement (ie Operation IceBridge), to backscatter coefficients from scatterometers (ASCAT, QUICKSCAT), to multi angle maging spectroradiometer (MISR), and to laser (Icesat) and radar altimeters (Envisat, Cryosat, Altika, Sentinel-3). We will show that by comparing and cross-calibrating these different products we can offer a consistent multi-mission, multi-decadal view of the declining sea ice roughness. Implications for sea ice physics, climate and remote sensing will also be discussed.

  16. Thin ice and storms: Sea ice deformation from buoy arrays deployed during N-ICE2015

    OpenAIRE

    Itkin, Polona; Spreen, Gunnar; Cheng, Bin; Doble, Martin; Girard-Ardhuin, Fanny; Haapala, Jari; Hughes, Nick; Kaleschke, Lars; Nicolaus, Marcel; Wilkinson, Jeremy

    2017-01-01

    Arctic sea ice has displayed significant thinning as well as an increase in drift speed in recent years. Taken together this suggests an associated rise in sea ice deformation rate. A winter and spring expedition to the sea ice covered region north of Svalbard – the Norwegian young sea ICE 2015 expedition (N-ICE2015) - gave an opportunity to deploy extensive buoy arrays and to monitor the deformation of the first- and second-year ice now common in the majority of the Arctic Basin. During the ...

  17. Channelized melting drives thinning under Dotson ice shelf, Western Antarctic Ice Sheet

    Science.gov (United States)

    Gourmelen, N.; Goldberg, D.; Snow, K.; Henley, S. F.; Bingham, R. G.; Kimura, S.; Hogg, A.; Shepherd, A.; Mouginot, J.; Lenaerts, J.; Ligtenberg, S.; Van De Berg, W. J.

    2017-12-01

    The majority of meteoric ice that forms in West Antarctica leaves the ice sheet through floating ice shelves, many of which have been thinning substantially over the last 25 years. A significant proportion of ice-shelf thinning has been driven by submarine melting facilitated by increased access of relatively warm (>0.6oC) modified Circumpolar Deep Water to sub-shelf cavities. Ice shelves play a significant role in stabilising the ice sheet from runaway retreat and regulating its contribution to sea level change. Ice-shelf melting has also been implicated in sustaining high primary productivity in Antarctica's coastal seas. However, these processes vary regionally and are not fully understood. Under some ice shelves, concentrated melting leads to the formation of inverted channels. These channels guide buoyant melt-laden outflow, which can lead to localised melting of the sea ice cover. The channels may also potentially lead to heightened crevassing, which in turn affects ice-shelf stability. Meanwhile, numerical studies suggest that buttressing loss is sensitive to the location of ice removal within an ice-shelf. Thus it is important that we observe spatial patterns, as well as magnitudes, of ice-shelf thinning, in order to improve understanding of the ocean drivers of thinning and of their impacts on ice-shelf stability. Here we show from high-resolution altimetry measurements acquired between 2010 to 2016 that Dotson Ice Shelf, West Antarctica, thins in response to basal melting focussed along a single 5 km-wide and 60 km-long channel extending from the ice shelf's grounding zone to its calving front. The coupled effect of geostrophic circulation and ice-shelf topography leads to the observed concentration of basal melting. Analysis of previous datasets suggests that this process has been ongoing for at least the last 25 years. If focused thinning continues at present rates, the channel would melt through within 40-50 years, almost two centuries before it is

  18. Temporal and spatial variabilities of Antarctic ice mass changes inferred by GRACE in a Bayesian framework

    Science.gov (United States)

    Wang, L.; Davis, J. L.; Tamisiea, M. E.

    2017-12-01

    The Antarctic ice sheet (AIS) holds about 60% of all fresh water on the Earth, an amount equivalent to about 58 m of sea-level rise. Observation of AIS mass change is thus essential in determining and predicting its contribution to sea level. While the ice mass loss estimates for West Antarctica (WA) and the Antarctic Peninsula (AP) are in good agreement, what the mass balance over East Antarctica (EA) is, and whether or not it compensates for the mass loss is under debate. Besides the different error sources and sensitivities of different measurement types, complex spatial and temporal variabilities would be another factor complicating the accurate estimation of the AIS mass balance. Therefore, a model that allows for variabilities in both melting rate and seasonal signals would seem appropriate in the estimation of present-day AIS melting. We present a stochastic filter technique, which enables the Bayesian separation of the systematic stripe noise and mass signal in decade-length GRACE monthly gravity series, and allows the estimation of time-variable seasonal and inter-annual components in the signals. One of the primary advantages of this Bayesian method is that it yields statistically rigorous uncertainty estimates reflecting the inherent spatial resolution of the data. By applying the stochastic filter to the decade-long GRACE observations, we present the temporal variabilities of the AIS mass balance at basin scale, particularly over East Antarctica, and decipher the EA mass variations in the past decade, and their role in affecting overall AIS mass balance and sea level.

  19. CICE, The Los Alamos Sea Ice Model

    Energy Technology Data Exchange (ETDEWEB)

    2017-05-12

    The Los Alamos sea ice model (CICE) is the result of an effort to develop a computationally efficient sea ice component for a fully coupled atmosphere–land–ocean–ice global climate model. It was originally designed to be compatible with the Parallel Ocean Program (POP), an ocean circulation model developed at Los Alamos National Laboratory for use on massively parallel computers. CICE has several interacting components: a vertical thermodynamic model that computes local growth rates of snow and ice due to vertical conductive, radiative and turbulent fluxes, along with snowfall; an elastic-viscous-plastic model of ice dynamics, which predicts the velocity field of the ice pack based on a model of the material strength of the ice; an incremental remapping transport model that describes horizontal advection of the areal concentration, ice and snow volume and other state variables; and a ridging parameterization that transfers ice among thickness categories based on energetic balances and rates of strain. It also includes a biogeochemical model that describes evolution of the ice ecosystem. The CICE sea ice model is used for climate research as one component of complex global earth system models that include atmosphere, land, ocean and biogeochemistry components. It is also used for operational sea ice forecasting in the polar regions and in numerical weather prediction models.

  20. Antarctic and Greenland ice sheet mass balance products from satellite gravimetry

    Science.gov (United States)

    Horwath, Martin; Groh, Andreas; Horvath, Alexander; Forsberg, René; Meister, Rakia; Barletta, Valentina R.; Shepherd, Andrew

    2017-04-01

    Because of their important role in the Earth's climate system, ESA's Climate Change Initiative (CCI) has identified both the Antarctic Ice Sheet (AIS) and the Greenland Ice Sheet (GIS) as Essential Climate Variables (ECV). Since respondents of a user survey indicated that the ice sheet mass balance is one of the most important ECV data products needed to better understand climate change, the AIS_cci and the GIS_cci project provide Gravimetric Mass Balance (GMB) products based on satellite gravimetry data. The GMB products are derived from GRACE (Gravity Recovery and Climate Experiment) monthly solutions of release ITSG-Grace2016 produced at TU Graz. GMB basin products (i.e. time series of monthly mass changes for the entire ice sheets and selected drainage basins) and GMB gridded products (e.g. mass balance estimates with a formal resolution of about 50km, covering the entire ice sheets) are generated for the period from 2002 until present. The first GMB product was released in mid 2016. Here we present an extended and updated version of the ESA CCI GMB products, which are freely available through data portals hosted by the projects (https://data1.geo.tu-dresden.de/ais_gmb, http://products.esa-icesheets-cci.org/products/downloadlist/GMB). Since the initial product release, the applied processing strategies have been improved in order to further reduce GRACE errors and to enhance the separation of signals super-imposed to the ice mass changes. While a regional integration approach is used by the AIS_cci project, the GMB products of the GIS_cci project are derived using a point mass inversion. The differences between both approaches are investigated through the example of the GIS, where an alternative GMB product was generated using the regional integration approach implemented by the AIS_cci. Finally, we present the latest mass balance estimates for both ice sheets as well as their corresponding contributions to global sea level rise.

  1. MODIS Snow and Sea Ice Products

    Science.gov (United States)

    Hall, Dorothy K.; Riggs, George A.; Salomonson, Vincent V.

    2004-01-01

    In this chapter, we describe the suite of Earth Observing System (EOS) Moderate-Resolution Imaging Spectroradiometer (MODIS) Terra and Aqua snow and sea ice products. Global, daily products, developed at Goddard Space Flight Center, are archived and distributed through the National Snow and Ice Data Center at various resolutions and on different grids useful for different communities Snow products include binary snow cover, snow albedo, and in the near future, fraction of snow in a 5OO-m pixel. Sea ice products include ice extent determined with two different algorithms, and sea ice surface temperature. The algorithms used to develop these products are described. Both the snow and sea ice products, available since February 24,2000, are useful for modelers. Validation of the products is also discussed.

  2. A one stop website for sharing sea ice, ocean and ice sheet data over the polar regions

    Science.gov (United States)

    Chen, Z.; Cheng, X.; Liu, J.; Hui, F.; Ding, Y.

    2017-12-01

    The polar regions, including the Arctic and Antarctic, are changing rapidly. Our capabilities to remotely monitor the state of the polar regions are increasing greatly. Satellite and airborne technologies have been deployed and further improvements are underway. Meanwhile, various algorithms have been developed to retrieve important parameters to maximize the effectiveness of available remote sensing data. These technologies and algorithms promise to greatly increase our understanding of variations in sea ice, ocean and ice sheet. However, so much information is scattered out there. It is challenging to find exactly what you are looking for by just searching it through the network. Therefore, we try to establish a common platform to sharing some key parameters for the polar regions. A group of scientists from Beijing Normal University and University at Albany developed a website as a "one-stop shop" for the current state of the polar regions. The website provides real-time (or near real-time) key parameters derived from a variety of operational satellites in an understandable, accessible and credible way. Three types of parameter, which are sea ice, ocean and ice sheet respectively, are shown and available to be downloaded in the website. Several individual parameters are contained in a specific type of parameter. The parameters of sea ice include sea ice concentration, sea ice thickness, melt pond, sea ice leads and sea ice drift. The ocean parameters contain sea surface temperature and sea surface wind. Ice sheet balance, ice velocity and some other parameters are classified into the type of ice sheet parameter. Some parameters are well-calibrated and available to be obtained from other websites, such as sea ice concentration, sea ice thickness sea surface temperature. Since these parameters are retrieved from different sensors, such as SSMI, AMSR2 etc., data format, spatial resolution of the parameters are not unified. We collected and reprocessed these

  3. Explicit representation and parametrised impacts of under ice shelf seas in the z∗ coordinate ocean model NEMO 3.6

    Directory of Open Access Journals (Sweden)

    P. Mathiot

    2017-07-01

    Full Text Available Ice-shelf–ocean interactions are a major source of freshwater on the Antarctic continental shelf and have a strong impact on ocean properties, ocean circulation and sea ice. However, climate models based on the ocean–sea ice model NEMO (Nucleus for European Modelling of the Ocean currently do not include these interactions in any detail. The capability of explicitly simulating the circulation beneath ice shelves is introduced in the non-linear free surface model NEMO. Its implementation into the NEMO framework and its assessment in an idealised and realistic circum-Antarctic configuration is described in this study. Compared with the current prescription of ice shelf melting (i.e. at the surface, inclusion of open sub-ice-shelf cavities leads to a decrease in sea ice thickness along the coast, a weakening of the ocean stratification on the shelf, a decrease in salinity of high-salinity shelf water on the Ross and Weddell sea shelves and an increase in the strength of the gyres that circulate within the over-deepened basins on the West Antarctic continental shelf. Mimicking the overturning circulation under the ice shelves by introducing a prescribed meltwater flux over the depth range of the ice shelf base, rather than at the surface, is also assessed. It yields similar improvements in the simulated ocean properties and circulation over the Antarctic continental shelf to those from the explicit ice shelf cavity representation. With the ice shelf cavities opened, the widely used three equation ice shelf melting formulation, which enables an interactive computation of melting, is tested. Comparison with observational estimates of ice shelf melting indicates realistic results for most ice shelves. However, melting rates for the Amery, Getz and George VI ice shelves are considerably overestimated.

  4. Temperature Profile of the West Antarctic Ice Sheet Divide Deep Borehole, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set reports depth versus temperatures in the fluid-filled portion of the West Antarctic Ice Sheet Divide (WAIS–D) deep borehole (70 to 3328 meters depth)....

  5. MEaSUREs Annual Antarctic Ice Velocity Maps 2005-2017 V001

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set, part of the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) program, provides 12 annual maps of Antarctic ice...

  6. MEaSUREs Annual Antarctic Ice Velocity Maps 2005-2017, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set, part of the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) program, provides 12 annual maps of Antarctic ice...

  7. MEaSUREs Annual Antarctic Ice Velocity Maps 2005-2016, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set, part of the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) program, provides 11 annual maps of Antarctic ice...

  8. Atmospheric Mixing Ratios of Hydroperoxides above the West Antarctic Ice Sheet, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set contains atmospheric mixing ratios of hydrogen peroxide and methylhydroperoxide at 21 sites on the West Antarctic Ice Sheet (WAIS) were obtained from...

  9. Arctic tides from GPS on sea ice

    OpenAIRE

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

    2012-01-01

    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....

  10. 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...

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

    OpenAIRE

    A. A. Marks; M. D. King

    2013-01-01

    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-y...

  12. 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.

  13. Under the sea ice: Exploring the relationship between sea ice and the foraging behaviour of southern elephant seals in East Antarctica

    Science.gov (United States)

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

    2017-08-01

    Investigating ecological relationships between predators and their environment is essential to understand the response of marine ecosystems to climate variability and change. This is particularly true in polar regions, where sea ice (a sensitive climate variable) plays a crucial yet highly dynamic and variable role in how it influences the whole marine ecosystem, from phytoplankton to top predators. For mesopredators such as seals, sea ice both supports a rich (under-ice) food resource, access to which depends on local to regional coverage and conditions. Here, we investigate sex-specific relationships between the foraging strategies of southern elephant seals (Mirounga leonina) in winter and spatio-temporal variability in sea ice concentration (SIC) and coverage in East Antarctica. We satellite-tracked 46 individuals undertaking post-moult trips in winter from Kerguelen Islands to the peri-Antarctic shelf between 2004 and 2014. These data indicate distinct general patterns of sea ice usage: while females tended to follow the sea ice edge as it extended northward, the males remained on the continental shelf despite increasing sea ice. Seal hunting time, a proxy of foraging activity inferred from the diving behaviour, was longer for females in late autumn in the outer part of the pack ice, ∼150-370 km south of the ice edge. Within persistent regions of compact sea ice, females had a longer foraging activity (i) in the highest sea ice concentration at their position, but (ii) their foraging activity was longer when there were more patches of low concentration sea ice around their position (either in time or in space; 30 days & 50 km). The high spatio-temporal variability of sea ice around female positions is probably a key factor allowing them to exploit these concentrated patches. Despite lack of information on prey availability, females may exploit mesopelagic finfishes and squids that concentrate near the ice-water interface or within the water column (from

  14. Antarctic Ice Sheet Slope and Aspect Based on Icesat's Repeat Orbit Measurement

    Science.gov (United States)

    Yuan, L.; Li, F.; Zhang, S.; Xie, S.; Xiao, F.; Zhu, T.; Zhang, Y.

    2017-09-01

    Accurate information of ice sheet surface slope is essential for estimating elevation change by satellite altimetry measurement. A study is carried out to recover surface slope of Antarctic ice sheet from Ice, Cloud and land Elevation Satellite (ICESat) elevation measurements based on repeat orbits. ICESat provides repeat ground tracks within 200 meters in cross-track direction and 170 meters in along-track direction for most areas of Antarctic ice sheet. Both cross-track and along-track surface slopes could be obtained by adjacent repeat ground tracks. Combining those measurements yields a surface slope model with resolution of approximately 200 meters. An algorithm considering elevation change is developed to estimate the surface slope of Antarctic ice sheet. Three Antarctic Digital Elevation Models (DEMs) were used to calculate surface slopes. The surface slopes from DEMs are compared with estimates by using in situ GPS data in Dome A, the summit of Antarctic ice sheet. Our results reveal an average surface slope difference of 0.02 degree in Dome A. High resolution remote sensing images are also used in comparing the results derived from other DEMs and this paper. The comparison implies that our results have a slightly better coherence with GPS observation than results from DEMs, but our results provide more details and perform higher accuracy in coastal areas because of the higher resolution for ICESat measurements. Ice divides are estimated based on the aspect, and are weakly consistent with ice divides from other method in coastal regions.

  15. ANTARCTIC ICE SHEET SLOPE AND ASPECT BASED ON ICESAT’S REPEAT ORBIT MEASUREMENT

    Directory of Open Access Journals (Sweden)

    L. Yuan

    2017-09-01

    Full Text Available Accurate information of ice sheet surface slope is essential for estimating elevation change by satellite altimetry measurement. A study is carried out to recover surface slope of Antarctic ice sheet from Ice, Cloud and land Elevation Satellite (ICESat elevation measurements based on repeat orbits. ICESat provides repeat ground tracks within 200 meters in cross-track direction and 170 meters in along-track direction for most areas of Antarctic ice sheet. Both cross-track and along-track surface slopes could be obtained by adjacent repeat ground tracks. Combining those measurements yields a surface slope model with resolution of approximately 200 meters. An algorithm considering elevation change is developed to estimate the surface slope of Antarctic ice sheet. Three Antarctic Digital Elevation Models (DEMs were used to calculate surface slopes. The surface slopes from DEMs are compared with estimates by using in situ GPS data in Dome A, the summit of Antarctic ice sheet. Our results reveal an average surface slope difference of 0.02 degree in Dome A. High resolution remote sensing images are also used in comparing the results derived from other DEMs and this paper. The comparison implies that our results have a slightly better coherence with GPS observation than results from DEMs, but our results provide more details and perform higher accuracy in coastal areas because of the higher resolution for ICESat measurements. Ice divides are estimated based on the aspect, and are weakly consistent with ice divides from other method in coastal regions.

  16. Quantification of sea ice production in Weddell Sea polynyas

    Science.gov (United States)

    Zentek, Rolf; Heinemann, Günther; Paul, Stephan; Stulic, Lukrecia; Timmermann, Ralph

    2017-04-01

    The regional climate model COSMO-CLM was used to perform simulations the Weddell Sea region in Antarctica for the time period 2002-2015 with the focus on atmosphere-ocean-sea ice interactions. The original model was adapted to polar regions by the use of a thermodynamic sea ice module with snow cover and an temperature-dependent albedo scheme for sea ice. The recently published topography RTopo2 was used. The model was run with nesting in ERA-Interim data in a forecast mode. Sea ice concentrations were taken from satellite measurements (AMSR-E, SSMI/S, AMSR2) and were updated daily to allow for a close-to-reality hindcast. Simulations were done with 15 km resolution for the whole period 2002-2015 with the goal to force the sea-ice ocean model FESOM. In a second step a 5 km simulation was one-way nested for the winter period (April - September) 2002-2015 to allow for a better quantification of sea ice production in the Weddell Sea. Estimates of sea ice production and comparisons of the results to remote sensing data will be presented.

  17. Recent Measurements of Ice Flux From Outlet Glaciers of the South Shetlands and Antarctic Peninsula

    Science.gov (United States)

    Koppes, M.; Hallet, B.; Rignot, E.; Jaffrey, M.

    2007-12-01

    Islands (62°10' S) to Beascochea Bay, Graham Coast (65°31' S). For the sub-polar glaciers (2 of 16), where the ELA was significantly above sea level, the cross-sectional area at the ELA was measured using ice-penetrating radar. Velocity stakes were also measured at the ELA of these glaciers to ground-truth the satellite measurements of surface velocity. For the remaining polar glaciers, whose ELAs are at sea-level, multi-beam swath bathymetry was used from aboard the RV/IB Nathaniel B. Palmer together with estimates of ice cliff heights to determine the cross-sectional area of the calving front. The variability in ice flux across the sub-polar and polar climatic regimes of the western Antarctic Peninsula reported here will be compared to bathymetric data and sediment accumulation rates derived from 210-Pb and 14-C chronology in the adjacent fjords, as they become available, to examine the influence of both climate and ice flux on the rate of glacial erosion and sedimentation, and to infer potential changes in sediment delivery to the shelf as the region warms.

  18. 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'.

  19. There goes the sea ice: following Arctic sea ice parcels and their properties.

    Science.gov (United States)

    Tschudi, M. A.; Tooth, M.; Meier, W.; Stewart, S.

    2017-12-01

    Arctic sea ice distribution has changed considerably over the last couple of decades. Sea ice extent record minimums have been observed in recent years, the distribution of ice age now heavily favors younger ice, and sea ice is likely thinning. This new state of the Arctic sea ice cover has several impacts, including effects on marine life, feedback on the warming of the ocean and atmosphere, and on the future evolution of the ice pack. The shift in the state of the ice cover, from a pack dominated by older ice, to the current state of a pack with mostly young ice, impacts specific properties of the ice pack, and consequently the pack's response to the changing Arctic climate. For example, younger ice typically contains more numerous melt ponds during the melt season, resulting in a lower albedo. First-year ice is typically thinner and more fragile than multi-year ice, making it more susceptible to dynamic and thermodynamic forcing. To investigate the response of the ice pack to climate forcing during summertime melt, we have developed a database that tracks individual Arctic sea ice parcels along with associated properties as these parcels advect during the summer. Our database tracks parcels in the Beaufort Sea, from 1985 - present, along with variables such as ice surface temperature, albedo, ice concentration, and convergence. We are using this database to deduce how these thousands of tracked parcels fare during summer melt, i.e. what fraction of the parcels advect through the Beaufort, and what fraction melts out? The tracked variables describe the thermodynamic and dynamic forcing on these parcels during their journey. This database will also be made available to all interested investigators, after it is published in the near future. The attached image shows the ice surface temperature of all parcels (right) that advected through the Beaufort Sea region (left) in 2014.

  20. Biogeochemical Impact of Snow Cover and Cyclonic Intrusions on the Winter Weddell Sea Ice Pack

    Science.gov (United States)

    Tison, J.-L.; Schwegmann, S.; Dieckmann, G.; Rintala, J.-M.; Meyer, H.; Moreau, S.; Vancoppenolle, M.; Nomura, D.; Engberg, S.; Blomster, L. J.; Hendrickx, S.; Uhlig, C.; Luhtanen, A.-M.; de Jong, J.; Janssens, J.; Carnat, G.; Zhou, J.; Delille, B.

    2017-12-01

    Sea ice is a dynamic biogeochemical reactor and a double interface actively interacting with both the atmosphere and the ocean. However, proper understanding of its annual impact on exchanges, and therefore potentially on the climate, notably suffer from the paucity of autumnal and winter data sets. Here we present the results of physical and biogeochemical investigations on winter Antarctic pack ice in the Weddell Sea (R. V. Polarstern AWECS cruise, June-August 2013) which are compared with those from two similar studies conducted in the area in 1986 and 1992. The winter 2013 was characterized by a warm sea ice cover due to the combined effects of deep snow and frequent warm cyclones events penetrating southward from the open Southern Ocean. These conditions were favorable to high ice permeability and cyclic events of brine movements within the sea ice cover (brine tubes), favoring relatively high chlorophyll-a (Chl-a) concentrations. We discuss the timing of this algal activity showing that arguments can be presented in favor of continued activity during the winter due to the specific physical conditions. Large-scale sea ice model simulations also suggest a context of increasingly deep snow, warm ice, and large brine fractions across the three observational years, despite the fact that the model is forced with a snowfall climatology. This lends support to the claim that more severe Antarctic sea ice conditions, characterized by a longer ice season, thicker, and more concentrated ice are sufficient to increase the snow depth and, somehow counterintuitively, to warm the ice.

  1. Feeding rates and under-ice foraging strategies of the smallest lunge filter feeder, the Antarctic minke whale (Balaenoptera bonaerensis).

    Science.gov (United States)

    Friedlaender, A S; Goldbogen, J A; Nowacek, D P; Read, A J; Johnston, D; Gales, N

    2014-08-15

    Body size and feeding mode are two fundamental characteristics that determine foraging performance and ecological niche. As the smallest obligate lunge filter feeders, minke whales represent an ideal system for studying the physical and energetic limits of filter feeding in endotherms. We used multi-sensor suction cup tags to quantify the feeding performance of Antarctic minke whales. Foraging dives around and beneath sea ice contained up to 24 lunges per dive, the highest feeding rates for any lunge-feeding whale. Their small size allows minke whales access to krill in sea-ice environments not easily accessible to larger baleen whales. Furthermore, their ability to filter feed provides an advantage over other smaller sympatric krill predators such as penguins and seals that feed on individual prey. The unique combination of body size, feeding mechanism and sea-ice habitat of Antarctic minke whales defines a previously undocumented energetic niche that is unique among aquatic vertebrates. © 2014. Published by The Company of Biologists Ltd.

  2. 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 (the mid to high latitudes on the surface of Mars which may be caused by eruptions of subsurface fluids [4, 5]. We have identified massive but highly localized Na-sulfate deposits (mirabilite mounds, Na2SO4 .10H2O) that may be derived from subsurface fluids and may provide insight into the processes associated with subsurface fluids on Mars. The mounds are found on the end moraine of the Lewis Cliffs Ice 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.

  3. Ice age aerosol content from east Antarctic ice core samples and past wind strength

    International Nuclear Information System (INIS)

    Petit, J.R.; Briat, M.; Royer, A.

    1981-01-01

    The possible link between the aerosol content from the 905 deep Dome C ice core (East Antartica) which spans some 32,000 yr (Lorius et al. Nature; 280:644 (1979)) and climate, is considered. No evidence of major global or local volcanic activity was found though large marine and continental inputs (respectively 5 and 20 times higher than present) were observed at the end of the last Glacial stage. It is considered that they reflect glacial age climate with stronger atmospheric circulation, enhanced aridity and faster aerosol transport towards the Antarctic continent. (U.K.)

  4. Evidence for radionuclide transport by sea ice

    International Nuclear Information System (INIS)

    Meese, D.A.; Tucker, W.B.; Gow, A.J.; Reimnitz, E.; Bischof, J.; Darby, D.

    1997-01-01

    Ice and ice-borne sediments were collected across the Arctic Basin during the Arctic Ocean Section, 1994 (AOS-94), a recent US/Canada trans-Arctic expedition. Sediments were analysed for 137 Cs, clay mineralogy and carbon. Concentrations of 137 Cs ranged from 5 to 73 Bq kg -1 in the ice-borne sediments. Concentrations of ice samples without sediment were all less than 1 Bq m -3 . The sediment sample with the highest 137 Cs concentration (73 Bq kg -1 ) was collected in the Beaufort Sea. This concentration was significantly higher than in bottom sediments collected in the same area, indicating an ice transport mechanism from an area with correspondingly higher concentrations. Recent results from the application of ice transport models and sediment analyses indicate that it is very likely that sediments are transported by ice, from the Siberian shelf areas to the Beaufort Sea

  5. Progress on Antarctic Glacial Isostatic Adjustment and GRACE constraints on ice loss (Invited)

    Science.gov (United States)

    Ivins, E. R.; James, T. S.; Wahr, J. M.; Schrama, E. J.; Simon, K. M.; Landerer, F. W.; Watkins, M. M.; Wiese, D. N.

    2013-12-01

    Preparations for the Intergovermental Panel on Climate Change: Assessment Report 5 (IPCC AR5) has placed pressure on various research groups to accelerate the pace of their work in order to meet the Report deadlines. While this stimulates both positive and negative bi-products, it helped to focus attention to irreconcilable mass balance determinations for the Antarctic Ice Sheet (AIS) using space and airborne data. A glaring ';sore-thumb' for determining AIS trends from Gravity Recovery and Climate Experiment (GRACE) satellite data is the large signal of glacial isostatic adjustment (GIA) that is poorly constrained and possibly of the same magnitude as the present-day mass change. The report published in Science (vol. 338, pp. 1183-89) by S13 [Shepherd et al. 2013] met this challenge head-on by investing heavily in improving the GIA models with new GPS data, and new chronological constraints on ice sheet evolution across the Antarctic continent. This new data has emerged only within the last five years, and it came at a fortuitous time for advancing the IPCC AR5 goals. In this presentation we speak to the improvements developed in a recent JGR Solid Earth publication (14 June 2013). We extend the analysis using all of the official 05 releases of the analysis centers, including the JPL-mascon fields. The total error budgets of GIA correction are poorly determined, in spite of the great model improvements witnessed in the past 5 years. S12 reported the uncertainty for space-based sea level sourcing during 1992-2011 to Antarctica at roughly 0.23 mm/yr. Although GRACE 2002-2013 estimates vary, the uncertainly is about half this value. Here we examine how much of that uncertainty is still caused by GIA models and discuss how new classes of GIA models, and the collection of yet new GPS and ice constraint data for Antarctica, will enhance the value of a GRACE Follow-On mission. However, there will be a limit to constraining GIA, and a limit, therefore, to GIA error due to

  6. A 25-year Record of Antarctic Ice Sheet Elevation and Mass Change

    Science.gov (United States)

    Shepherd, A.; Muir, A. S.; Sundal, A.; McMillan, M.; Briggs, K.; Hogg, A.; Engdahl, M.; Gilbert, L.

    2017-12-01

    Since 1992, the European Remote-Sensing (ERS-1 and ERS-2), ENVISAT, and CryoSat-2 satellite radar altimeters have measured the Antarctic ice sheet surface elevation, repeatedly, at approximately monthly intervals. These data constitute the longest continuous record of ice sheet wide change. In this paper, we use these observations to determine changes in the elevation, volume and mass of the East Antarctic and West Antarctic ice sheets, and of parts of the Antarctic Peninsula ice sheet, over a 25-year period. The root mean square difference between elevation rates computed from our survey and 257,296 estimates determined from airborne laser measurements is 54 cm/yr. The longevity of the satellite altimeter data record allows to identify and chart the evolution of changes associated with meteorology and ice flow, and we estimate that 3.6 % of the continental ice sheet, and 21.7 % of West Antarctica, is in a state of dynamical imbalance. Based on this partitioning, we estimate the mass balance of the East and West Antarctic ice sheet drainage basins and the root mean square difference between these and independent estimates derived from satellite gravimetry is less than 5 Gt yr-1.

  7. Modelling snow ice and superimposed ice on landfast sea ice in Kongsfjorden, Svalbard

    Directory of Open Access Journals (Sweden)

    Caixin Wang

    2015-08-01

    Full Text Available Snow ice and superimposed ice formation on landfast sea ice in a Svalbard fjord, Kongsfjorden, was investigated with a high-resolution thermodynamic snow and sea-ice model, applying meteorological weather station data as external forcing. The model shows that sea-ice formation occurs both at the ice bottom and at the snow/ice interface. Modelling results indicated that the total snow ice and superimposed ice, which formed at the snow/ice interface, was about 14 cm during the simulation period, accounting for about 15% of the total ice mass and 35% of the total ice growth. Introducing a time-dependent snow density improved the modelled results, and a time-dependent oceanic heat flux parameterization yielded reasonable ice growth at the ice bottom. Model results suggest that weather conditions, in particular air temperature and precipitation, as well as snow thermal properties and surface albedo are the most critical factors for the development of snow ice and superimposed ice in Kongsfjorden. While both warming air and higher precipitation led to increased snow ice and superimposed ice forming in Kongsfjorden in the model runs, the processes were more sensitive to precipitation than to air temperature.

  8. Ocean sea-ice modelling in the Southern Ocean around Indian ...

    Indian Academy of Sciences (India)

    An eddy-resolving coupled ocean sea-ice modelling is carried out in the Southern Ocean region (9∘–78∘E; 51∘–71∘S) using the MITgcm. The model domain incorporates the Indian Antarctic stations, Maitri (11.7∘E; 70.7∘S) and Bharati (76.1∘E; 69.4∘S). The realistic simulation of the surface variables, namely, sea ...

  9. MODIS Sea Ice Thickness and Open Water–Sea Ice Charts over the Barents and Kara Seas for Development and Validation of Sea Ice Products from Microwave Sensor Data

    Directory of Open Access Journals (Sweden)

    Marko Mäkynen

    2017-12-01

    Full Text Available We have developed algorithms and procedures for calculating daily sea ice thickness (SIT and open water–sea ice (OWSI charts, based on the Moderate Resolution Imaging Spectroradiometer (MODIS, ice surface temperature (IST (night-time only, and reflectance ( R swath data, respectively. The resolution of the SIT chart is 1 km and that of the OWSI chart is 250 m. The charts are targeted to be used in development and validation of sea ice products from microwave sensor data. We improve the original MODIS cloud masks for the IST and R data, with a focus on identifying larger cloud-free areas in the data. The SIT estimation from the MODIS IST swath data follows previous studies. The daily SIT chart is composed from available swath charts by assigning daily median SIT to a pixel. The OWSI classification is simply conducted by a fixed threshold for the MODIS band 1 R . This was based on manually selected R data for various ice types in late winter, early melt, and advanced melt conditions. The composition procedures for the daily SIT and OWSI charts somewhat compensates for errors due to the undetected clouds. The SIT and OWSI charts were compared against manual ice charts by Arctic and Antarctic Research Institute in Russia and by Norwegian Meteorological Institute, respectively, and on average, a good relationship between the charts was found. Pixel-wise comparison of the SIT and OWSI charts showed very good agreement in open water vs. sea ice classification, which gives further confidence on the reliability of our algorithms. We also demonstrate usage of the MODIS OWSI and SIT charts for validation of sea ice concentration charts based on the SENTINEL-1 SAR and AMSR2 radiometer data and two different algorithms.

  10. The Sea Ice Index: A Resource for Cryospheric Knowledge Mobilization

    Science.gov (United States)

    Windnagel, A. K.; Fetterer, F. M.

    2017-12-01

    The Sea Ice Index is a popular source of information about Arctic and Antarctic sea ice data and trends created at the National Snow and Ice Data Center (NSIDC) in 2002. It has been used by cryospheric scientists, cross-discipline scientists, the press, policy makers, and the public for the past 15 years. The Index started as a prototype sea ice extent product in 2001 and was envisioned as a website that would meet a need for readily accessible, easy-to-use information on sea ice trends and anomalies, with products that would assist in monitoring and diagnosing the ice extent minima that were gaining increasing attention in the research community in the late 1990s. The goal was to easily share these valuable data with everyone that needed them, which is the essence of knowledge mobilization. As time has progressed, we have found new ways of disseminating the information carried by the data by providing simple pictures on a website, animating those images, creating Google Earth animations that show the data on a globe, providing simple text files of data values that do not require special software to read, writing a monthly blog about the data that has over 1.7 million readers annually, providing the data to NOAA's Science on Sphere to be seen in museums and classrooms across 23 countries, and creating geo-registered images for use in geospatial software. The Index helps to bridge the gap between sea ice science and the public. Through NSIDC's User Services Office, we receive feedback on the Index and have endeavored to meet the changing needs of our stakeholder communities to best mobilize this knowledge in their direction. We have learned through trial-by-fire the best practices for delivering these data and data services. This tells the tale of managing an unassuming data set as it has journeyed from a simple product consisting of images of sea ice to one that is robust enough to be used in the IPCC Climate Change Report but easy enough to be understood by K-12

  11. GLOBAL CHANGES IN THE SEA ICE COVER AND ASSOCIATED SURFACE TEMPERATURE CHANGES

    Directory of Open Access Journals (Sweden)

    J. C. Comiso

    2016-06-01

    Full Text Available 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.

  12. Actively evolving subglacial conduits and eskers initiate ice shelf channels at an Antarctic grounding line

    Science.gov (United States)

    Drews, R.; Pattyn, F.; Hewitt, I. J.; Ng, F. S. L.; Berger, S.; Matsuoka, K.; Helm, V.; Bergeot, N.; Favier, L.; Neckel, N.

    2017-05-01

    Ice-shelf channels are long curvilinear tracts of thin ice found on Antarctic ice shelves. Many of them originate near the grounding line, but their formation mechanisms remain poorly understood. Here we use ice-penetrating radar data from Roi Baudouin Ice Shelf, East Antarctica, to infer that the morphology of several ice-shelf channels is seeded upstream of the grounding line by large basal obstacles indenting the ice from below. We interpret each obstacle as an esker ridge formed from sediments deposited by subglacial water conduits, and calculate that the eskers' size grows towards the grounding line where deposition rates are maximum. Relict features on the shelf indicate that these linked systems of subglacial conduits and ice-shelf channels have been changing over the past few centuries. Because ice-shelf channels are loci where intense melting occurs to thin an ice shelf, these findings expose a novel link between subglacial drainage, sedimentation and ice-shelf stability.

  13. Actively evolving subglacial conduits and eskers initiate ice shelf channels at an Antarctic grounding line.

    Science.gov (United States)

    Drews, R; Pattyn, F; Hewitt, I J; Ng, F S L; Berger, S; Matsuoka, K; Helm, V; Bergeot, N; Favier, L; Neckel, N

    2017-05-09

    Ice-shelf channels are long curvilinear tracts of thin ice found on Antarctic ice shelves. Many of them originate near the grounding line, but their formation mechanisms remain poorly understood. Here we use ice-penetrating radar data from Roi Baudouin Ice Shelf, East Antarctica, to infer that the morphology of several ice-shelf channels is seeded upstream of the grounding line by large basal obstacles indenting the ice from below. We interpret each obstacle as an esker ridge formed from sediments deposited by subglacial water conduits, and calculate that the eskers' size grows towards the grounding line where deposition rates are maximum. Relict features on the shelf indicate that these linked systems of subglacial conduits and ice-shelf channels have been changing over the past few centuries. Because ice-shelf channels are loci where intense melting occurs to thin an ice shelf, these findings expose a novel link between subglacial drainage, sedimentation and ice-shelf stability.

  14. Polar bears and sea ice habitat change

    Science.gov (United States)

    Durner, George M.; Atwood, Todd C.; Butterworth, Andy

    2017-01-01

    The polar bear (Ursus maritimus) is an obligate apex predator of Arctic sea ice and as such can be affected by climate warming-induced changes in the extent and composition of pack ice and its impacts on their seal prey. Sea ice declines have negatively impacted some polar bear subpopulations through reduced energy input because of loss of hunting habitats, higher energy costs due to greater ice drift, ice fracturing and open water, and ultimately greater challenges to recruit young. Projections made from the output of global climate models suggest that polar bears in peripheral Arctic and sub-Arctic seas will be reduced in numbers or become extirpated by the end of the twenty-first century if the rate of climate warming continues on its present trajectory. The same projections also suggest that polar bears may persist in the high-latitude Arctic where heavy multiyear sea ice that has been typical in that region is being replaced by thinner annual ice. Underlying physical and biological oceanography provides clues as to why polar bear in some regions are negatively impacted, while bears in other regions have shown no apparent changes. However, continued declines in sea ice will eventually challenge the survival of polar bears and efforts to conserve them in all regions of the Arctic.

  15. Sea-level and solid-Earth deformation feedbacks in ice sheet modelling

    Science.gov (United States)

    Konrad, Hannes; Sasgen, Ingo; Klemann, Volker; Thoma, Malte; Grosfeld, Klaus; Martinec, Zdeněk

    2014-05-01

    The interactions of ice sheets with the sea level and the solid Earth are important factors for the stability of the ice shelves and the tributary inland ice (e.g. Thomas and Bentley, 1978; Gomez et al, 2012). First, changes in ice extent and ice thickness induce viscoelastic deformation of the Earth surface and Earth's gravity field. In turn, global and local changes in sea level and bathymetry affect the grounding line and, subsequently, alter the ice dynamic behaviour. Here, we investigate these feedbacks for a synthetic ice sheet configuration as well as for the Antarctic ice sheet using a three-dimensional thermomechanical ice sheet and shelf model, coupled to a viscoelastic solid-Earth and gravitationally self-consistent sea-level model. The respective ice sheet undergoes a forcing from rising sea level, warming ocean, and/or changing surface mass balance. The coupling is realized by exchanging ice thickness, Earth surface deformation and sea level periodically. We apply several sets of viscoelastic Earth parameters to our coupled model, e.g. simulating a low-viscous upper mantle present at the Antarctic Peninsula (Ivins et al., 2011). Special focus of our study lies on the evolution of Earth surface deformation and local sea level changes, as well as on the accompanying grounding line evolution. N. Gomez, D. Pollard, J. X. Mitrovica, P. Huybers, and P. U. Clark 2012. Evolution of a coupled marine ice sheet-sea level model, J. Geophys. Res., 117, F01013, doi:10.1029/2011JF002128. E. R. Ivins, M. M. Watkins, D.-N. Yuan, R. Dietrich, G. Casassa, and A. Rülke 2011. On-land ice loss and glacial isostatic adjustment at the Drake Passage: 2003-2009, J. Geophys. Res. 116, B02403, doi: 10.1029/2010JB007607 R. H. Thomas and C. R. Bentley 1978. A model for Holocene retreat of the West Antarctic Ice Sheet, Quaternary Research, 10 (2), pages 150-170, doi: 10.1016/0033-5894(78)90098-4.

  16. Body and blubber relationships in antarctic pack ice seals: implications for blubber depth patterns.

    Science.gov (United States)

    Castellini, M A; Trumble, S J; Mau, T L; Yochem, P K; Stewart, B S; Koski, M A

    2009-01-01

    Morphometrics and blubber depths from all four high Antarctic seals (Weddell, Ross, crabeater, and leopard) were obtained during a midsummer research cruise in the Ross Sea as the physiological ecology component of the U.S. Antarctic Pack Ice Seals project. These data are the only in vivo measurements of all four species from the same location and time of year and focused on variances in morphometrics and blubber depth related to species, sex, and age. By controlling for location and season, this cross-species design provided the means to differentiate how blubber mass might be influenced in these groups. We measured both absolute blubber depth and ratio of blubber depth to body core diameter. We found that adult and younger animals showed differences in blubber depth, but male versus female seals did not show differences within any given species. However, when compared across species, the ratio of blubber ring depth to body core diameter suggests that adult Weddell seals differ in their use of blubber compared with the other three species. We propose that this difference in blubber pattern is most likely related to Weddell nutritional requirements during the breeding season having a greater influence on blubber depth than thermal requirements when compared with the other three species.

  17. Autonomous Ice Mass Balance Buoys for Seasonal Sea Ice

    Science.gov (United States)

    Whitlock, J. D.; Planck, C.; Perovich, D. K.; Parno, J. T.; Elder, B. C.; Richter-Menge, J.; Polashenski, C. M.

    2017-12-01

    The ice mass-balance represents the integration of all surface and ocean heat fluxes and attributing the impact of these forcing fluxes on the ice cover can be accomplished by increasing temporal and spatial measurements. Mass balance information can be used to understand the ongoing changes in the Arctic sea ice cover and to improve predictions of future ice conditions. Thinner seasonal ice in the Arctic necessitates the deployment of Autonomous Ice Mass Balance buoys (IMB's) capable of long-term, in situ data collection in both ice and open ocean. Seasonal IMB's (SIMB's) are free floating IMB's that allow data collection in thick ice, thin ice, during times of transition, and even open water. The newest generation of SIMB aims to increase the number of reliable IMB's in the Arctic by leveraging inexpensive commercial-grade instrumentation when combined with specially developed monitoring hardware. Monitoring tasks are handled by a custom, expandable data logger that provides low-cost flexibility for integrating a large range of instrumentation. The SIMB features ultrasonic sensors for direct measurement of both snow depth and ice thickness and a digital temperature chain (DTC) for temperature measurements every 2cm through both snow and ice. Air temperature and pressure, along with GPS data complete the Arctic picture. Additionally, the new SIMB is more compact to maximize deployment opportunities from multiple types of platforms.

  18. 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 (Turbellaria, Nematoda and Harpacticoida also were observed in pressure ridges (0-200 ind l -1, median 40 ind l -1), although values were highly variable and only medians of Turbellaria were significantly higher in ridge ice than in level ice. Median abundances of under-ice amphipods at all ice types (level ice, various ice ridge structures) ranged from 8 to 114 ind m -2 per station and mainly consisted of Apherusa glacialis (87%), Onisimus spp. (7%) and Gammarus wilkitzkii (6%). Highest amphipod abundances were observed in pressure ridges at depths >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

  19. Mass Balance of the West Antarctic Ice-Sheet from ICESat Measurements

    Science.gov (United States)

    Zwally, H. Jay; Li, Jun; Robins, John; Saba, Jack L.; Yi, Donghui

    2011-01-01

    Mass balance estimates for 2003-2008 are derived from ICESat laser altimetry and compared with estimates for 1992-2002 derived from ERS radar altimetry. The net mass balance of 3 drainage systems (Pine Island, Thwaites/Smith, and the coast of Marie Bryd) for 2003-2008 is a loss of 100 Gt/yr, which increased from a loss of 70 Gt/yr for the earlier period. The DS including the Bindschadler and MacAyeal ice streams draining into the Ross Ice Shelf has a mass gain of 11 Gt/yr for 2003-2008, compared to an earlier loss of 70 Gt/yr. The DS including the Whillans and Kamb ice streams has a mass gain of 12 Gt/yr, including a significant thickening on the upper part of the Kamb DS, compared to a earlier gain of 6 Gt/yr (includes interpolation for a large portion of the DS). The other two DS discharging into the Ronne Ice Shelf and the northern Ellsworth Coast have a mass gain of 39 Gt/yr, compared to a gain of 4 Gt/yr for the earlier period. Overall, the increased losses of 30 Gt/yr in the Pine Island, Thwaites/Smith, and the coast of Marie Bryd DSs are exceeded by increased gains of 59 Gt/yr in the other 4 DS. Overall, the mass loss from the West Antarctic ice sheet has decreased to 38 Gt/yr from the earlier loss of 67 Gt/yr, reducing the contribution to sea level rise to 0.11 mm/yr from 0.19 mm/yr

  20. Ages, ablation and accumulation rates from 14C measurements on Antarctic ice

    NARCIS (Netherlands)

    Roijen, J.J. van; Borg, K. van der; Jong, A.F.M. de; Oerlemans, J.

    1995-01-01

    Shallow ice cores from an Antarctic blue-ice area at Scharllenbergbotncn were 14C-analyzed using a dry-extraction technique and accelerator mass spectrometry. The in situ production was determined from the 14CO component and used to deduce the natural 14CO2 component. The ages were measured

  1. Recent Changes in Ices Mass Balance of the Amundsen Sea Sector

    Science.gov (United States)

    Sutterley, T. C.; Velicogna, I.; Rignot, E. J.; Mouginot, J.; Flament, T.; van den Broeke, M. R.; van Wessem, M.; Reijmer, C.

    2014-12-01

    The glaciers flowing into the Amundsen Sea Embayment (ASE) sector of West Antarctica were confirmed in the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) to be the dominant contributors to the current Antarctic ice mass loss, and recently recognized to be undergoing marine ice sheet instability. Here, we investigate their regional ice mass balance using a time series of satellite and airborne data combined with model output products from the Regional Atmospheric and Climate Model (RACMO). Our dataset includes laser altimetry from NASA's ICESat-1 satellite mission and from Operation IceBridge (OIB) airborne surveys, satellite radar altimetry data from ESA's Envisat mission, time-variable gravity data from NASA/DLR's GRACE mission, surface mass balance products from RACMO, ice velocity from a combination of international synthetic aperture radar satellites and ice thickness data from OIB. We find a record of ice mass balance for the ASE where all the analyzed techniques agree remarkably in magnitude and temporal variability. The mass loss of the region has been increasing continuously since 1992, with no indication of a slow down. The mass loss during the common period averaged 91 Gt/yr and accelerated 20 Gt/yr2. In 1992-2013, the ASE contributed 4.5 mm global sea level rise. Overall, our results demonstrate the synergy of multiple analysis techniques for examining Antarctic Ice Sheet mass balance at the regional scale. This work was performed at UCI and JPL under a contract with NASA.

  2. ISLSCP II Global Sea Ice Concentration

    Data.gov (United States)

    National Aeronautics and Space Administration — This International Satellite Land Surface Climatology Project (ISLSCP) Initiative II data set, ISLSCP II Global Sea Ice Concentration, is based on the Goddard Space...

  3. 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...

  4. ISLSCP II Global Sea Ice Concentration

    Data.gov (United States)

    National Aeronautics and Space Administration — ABSTRACT: This International Satellite Land Surface Climatology Project (ISLSCP) Initiative II data set is based on the Goddard Space Flight Center (GSFC) Sea Ice...

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

    Science.gov (United States)

    2015-09-30

    Chukchi Sea in the late summer have potentially changed the impact of fall storms by creating wave fields in the vicinity of the advancing ice edge. A...related to variability in storm and wave activity and changes in ice type and set the historical context for the Sea State field observations. Work...Doble Wave Climate and Wave Mixing in the Marginal Ice Zones of Arctic Seas: Observations and Modeling Babanin Storm Flux: Heat and Momentum

  6. 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....

  7. Forecasting Future Sea Ice Conditions: A Lagrangian Approach

    Science.gov (United States)

    2014-09-30

    the sea-ice extent minimum) is complete. These include, multi-year ice advective flux away from coastlines in winter, Bering Strait heat inflow and...anomalous sea ice extent and position of the MIZ as thermodynamic effect. Results also show a strong correlation (r = 0.8) between the Bering Strait ...melting via radiative/turbulent losses. We define dynamic loss as summer sea ice extent loss via sea ice export through Fram Strait (mainly) or sea

  8. Air-Sea-Ice Interactions at the Dalton Polynya, East Antarctica

    Science.gov (United States)

    Webb, C.; Orsi, A. H.; Zielinski, N. J.

    2015-12-01

    Intensified winter sea-ice formation at some Antarctic coastal polynyas is key to local production of dense Shelf Water. Near the shelf break immediately offshore of these polynyas, outflow of newly formed types of Antarctic Bottom Water results from rapid mixing of local Shelf Water and Circumpolar Deep Water entrained down the continental slope. Located off the Sabrina (120°E) and Adélie (145°E) Coasts, similar characteristics are found at the Dalton and Mertz Polynyas: relatively high rates of sea-ice production, large areal extent and lengthened duration. Until the recent partial breakage of the Mertz Ice Tongue, both Polynyas were limited to the east by grounded northward-protruding ice tongues that provide favorable conditions to form sea-ice. Nevertheless, Shelf Water production and export of Antarctic Bottom Water with origin in the Mertz Depression has been consistently observed during the past two decades, although with progressively fresher characteristics. The first oceanographic expeditions to the shelf depression located off the Sabrina Coast were made in the past two austral summers, by the U.S. in 2014 and Australia in 2015. These new measurements reveal contrasting characteristics to those found at Mertz. They indicate a more prominent role played by local freshwater inputs, which overshadow the effect from winter salt rejection within the Dalton Polynya. Results from a combined study of in-situ, remote sensing, and historical reanalysis datasets for 2014-2015 are used to describe the regional interaction of winds, ocean currents and sea-ice off Sabrina Coast. The inferred interactions at the Dalton and Mertz Polynyas are contrasted for the 2005-2015 period, to distinguish regional influences on the climatic freshening of Antarctic waters.

  9. 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.

  10. Sea-ice production in the northern Japan Sea

    Science.gov (United States)

    Nihashi, Sohey; Ohshima, Kay I.; Saitoh, Sei-Ichi

    2017-09-01

    Sinking of the dense water plays a significant role in the global climate system by driving thermohaline (overturning) circulation and biogeochemical cycles. Deep water convection occurs also in the Japan Sea, and the convection has been considered to be mainly caused by intense cooling of the sea surface. Another possible cause of the convection is brine rejection associated with high sea-ice production in a coastal polynya (thin sea-ice) area in the northern Japan Sea. We have developed an algorithm which detects the thin ice area and estimates the thickness using passive microwave satellite data. Based on a heat flux calculation with the satellite-derived ice thickness, the total sea-ice production in winter (December-March) averaged over 2002/03-2010/11 is estimated to be 4.27 × 1010 m3. This indicates that the ice production was underestimated by about half in a previous study in which the polynya was unrealistically treated as a low ice concentration area. The main determinant factor for the total ice production is the surface air temperature in early winter (December-January), which shows a rapid warming trend of 0.7 °C/decade for this 40-years. Based on a linear regression approach, the total ice production is estimated to have decreased by 5%/decade due to air temperature warming. If brine rejection due to the ice production contributes to the deep water formation in the Japan Sea, this is consistent with the fact that the deep water formation has been decreasing for the last 50-100 years.

  11. 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

  12. Complex bounds and microstructural recovery from measurements of sea ice permittivity

    International Nuclear Information System (INIS)

    Gully, A.; Backstrom, L.G.E.; Eicken, H.; Golden, K.M.

    2007-01-01

    Sea ice is a porous composite of pure ice with brine, air, and salt inclusions. The polar sea ice packs play a key role in the earth's ocean-climate system, and they host robust algal and bacterial communities that support the Arctic and Antarctic ecosystems. Monitoring the sea ice packs on global or regional scales is an increasingly important problem, typically involving the interaction of an electromagnetic wave with sea ice. In the quasistatic regime where the wavelength is much longer than the composite microstructural scale, the electromagnetic behavior is characterized by the effective complex permittivity tensor ε*. In assessing the impact of climate change on the polar sea ice covers, current satellites and algorithms can predict ice extent, but the thickness distribution remains an elusive, yet most important feature. In recent years, electromagnetic induction devices using low frequency waves have been deployed on ships, helicopters and planes to obtain thickness data. Here we compare two sets of theoretical bounds to extensive outdoor tank and in situ field data on ε* at 50MHz taken in the Arctic and Antarctic. The sea ice is assumed to be a two phase composite of ice and brine with known constituent permittivities. The first set of bounds assumes only knowledge of the brine volume fraction or porosity, and the second set further assumes statistical isotropy of the microstructure. We obtain excellent agreement between theory and experiment, and are able to observe the apparent violation of the isotropic bounds as the vertically oriented microstructure becomes increasingly connected for higher porosities. Moreover, these bounds are inverted to obtain estimates of the porosity from the measurements of ε*. We find that the temporal variations of the reconstructed porosity, which is directly related to temperature, closely follow the actual behavior

  13. 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...

  14. Canadian Ice Service Arctic Regional Sea Ice Charts in SIGRID-3 Format, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — 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...

  15. Influence of sea ice on Arctic coasts

    Science.gov (United States)

    Barnhart, K. R.; Kay, J. E.; Overeem, I.; Anderson, R. S.

    2017-12-01

    Coasts form the dynamic interface between the terrestrial and oceanic systems. In the Arctic, and in much of the world, the coast is a focal point for population, infrastructure, biodiversity, and ecosystem services. A key difference between Arctic and temperate coasts is the presence of sea ice. Changes in sea ice cover can influence the coast because (1) the length of the sea ice-free season controls the time over which nearshore water can interact with the land, and (2) the location of the sea ice edge controls the fetch over which storm winds can interact with open ocean water, which in turn governs nearshore water level and wave field. We first focus on the interaction of sea ice and ice-rich coasts. We combine satellite records of sea ice with a model for wind-driven storm surge and waves to estimate how changes in the sea ice-free season have impacted the nearshore hydrodynamic environment along Alaska's Beaufort Sea Coast for the period 1979-2012. This region has experienced some of the greatest changes in both sea ice cover and coastal erosion rates in the Arctic: the median length of the open-water season has expanded by 90 percent, while coastal erosion rates have more than doubled from 8.7 to 19 m yr-1. At Drew Point, NW winds increase shoreline water levels that control the incision of a submarine notch, the rate-limiting step of coastal retreat. The maximum water-level setup at Drew Point has increased consistently with increasing fetch. We extend our analysis to the entire Arctic using both satellite-based observations and global coupled climate model output from the Community Earth System Model Large Ensemble (CESM-LE) project. This 30-member ensemble employs a 1-degree version of the CESM-CAM5 historical forcing for the period 1920-2005, and RCP 8.5 forcing from 2005-2100. A control model run with constant pre-industrial (1850) forcing characterizes internal variability in a constant climate. Finally, we compare observations and model results to

  16. An Ensemble Analysis of Antarctic Glacial Isostatic Adjustment and Sea Level

    Science.gov (United States)

    Lecavalier, B.; Tarasov, L.

    2016-12-01

    Inferences of past ice sheet evolution that lack any uncertainty assessment (implicit or explicit), have little value. A developing technique for explicit uncertainty quantification of glacial systems is Bayesian calibration of models against large observational data-sets (Tarasov et al., 2012). The foundation for a Bayesian calibration of a 3D glacial systems model (GSM) for Antarctica has recently been completed (Briggs et al., 2013; 2014; Briggs and Tarasov, 2013). Bayesian calibration thoroughly samples model uncertainties against fits to observational data to generate a probability distribution for the Antarctic Ice Sheet deglaciation with explicit and well-defined confidence intervals. To have validity as a complete inference of past ice sheet evolution, Bayesian calibration requires a model that "brackets reality".Past work has shown the GSM to have likely inadequate range of grounding line migration in certain sectors as well as persistent ice thickness biases in topographically complex regions (Briggs et al., 2014). To advance towards full calibration, these deficiencies are being addressed through a number of model developments. The grounding line scheme has been revised (Pollard and DeConto, 2012), the horizontal resolution is increased to 20 km, and boundary conditions are updated. The basal drag representation now includes the sub-grid treatment of the thermo-mechanical impacts of high basal roughness. Parametric uncertainties in basal drag for regions that are presently marine have been re-evaluated. The impact of past changes in ocean temperature on sub ice shelf melt is explicitly incorporated in the current ocean forcing parametric scheme. Uncertainties in earth rheology are also probed to robustly quantify uncertainties affiliated with glacial isostatic adjustment. The ensemble analysis of the Antarctic glacial system provides dynamical bounds on past and present Antarctica glacial isostatic adjustment and sea level contributions. This research

  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. Resolving the Antarctic contribution to sea-level rise: a hierarchical modelling framework.

    Science.gov (United States)

    Zammit-Mangion, Andrew; Rougier, Jonathan; Bamber, Jonathan; Schön, Nana

    2014-06-01

    Determining the Antarctic contribution to sea-level rise from observational data is a complex problem. The number of physical processes involved (such as ice dynamics and surface climate) exceeds the number of observables, some of which have very poor spatial definition. This has led, in general, to solutions that utilise strong prior assumptions or physically based deterministic models to simplify the problem. Here, we present a new approach for estimating the Antarctic contribution, which only incorporates descriptive aspects of the physically based models in the analysis and in a statistical manner. By combining physical insights with modern spatial statistical modelling techniques, we are able to provide probability distributions on all processes deemed to play a role in both the observed data and the contribution to sea-level rise. Specifically, we use stochastic partial differential equations and their relation to geostatistical fields to capture our physical understanding and employ a Gaussian Markov random field approach for efficient computation. The method, an instantiation of Bayesian hierarchical modelling, naturally incorporates uncertainty in order to reveal credible intervals on all estimated quantities. The estimated sea-level rise contribution using this approach corroborates those found using a statistically independent method. © 2013 The Authors. Environmetrics Published by John Wiley & Sons, Ltd.

  19. Analysis of the projected regional sea-ice changes in the Southern Ocean during the twenty-first century

    Energy Technology Data Exchange (ETDEWEB)

    Lefebvre, W.; Goosse, H. [Universite Catholique de Louvain, Institut d' Astronomie et de Geophysique Georges Lemaitre, Louvain-la-Neuve (Belgium)

    2008-01-15

    Using the set of simulations performed with atmosphere-ocean general circulation models (AOGCMs) for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4), the projected regional distribution of sea ice for the twenty-first century has been investigated. Averaged over all those model simulations, the current climate is reasonably well reproduced. However, this averaging procedure hides the errors from individual models. Over the twentieth century, the multimodel average simulates a larger sea-ice concentration decrease around the Antarctic Peninsula compared to other regions, which is in qualitative agreement with observations. This is likely related to the positive trend in the Southern Annular Mode (SAM) index over the twentieth century, in both observations and in the multimodel average. Despite the simulated positive future trend in SAM, such a regional feature around the Antarctic Peninsula is absent in the projected sea-ice change for the end of the twenty-first century. The maximum decrease is indeed located over the central Weddell Sea and the Amundsen-Bellingshausen Seas. In most models, changes in the oceanic currents could play a role in the regional distribution of the sea ice, especially in the Ross Sea, where stronger southward currents could be responsible for a smaller sea-ice decrease during the twenty-first century. Finally, changes in the mixed layer depth can be found in some models, inducing locally strong changes in the sea-ice concentration. (orig.)

  20. Ice Draft and Ice Velocity Data in the Beaufort Sea, 1990-2003, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set provides measurement of sea ice draft (m) and the movement of sea ice (cm/s) over the continental shelf of the Eastern Beaufort Sea. The data set spans...

  1. 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

  2. The Sea-Ice Floe Size Distribution

    Science.gov (United States)

    Stern, H. L., III; Schweiger, A. J. B.; Zhang, J.; Steele, M.

    2017-12-01

    The size distribution of ice floes in the polar seas affects the dynamics and thermodynamics of the ice cover and its interaction with the ocean and atmosphere. Ice-ocean models are now beginning to include the floe size distribution (FSD) in their simulations. In order to characterize seasonal changes of the FSD and provide validation data for our ice-ocean model, we calculated the FSD in the Beaufort and Chukchi seas over two spring-summer-fall seasons (2013 and 2014) using more than 250 cloud-free visible-band scenes from the MODIS sensors on NASA's Terra and Aqua satellites, identifying nearly 250,000 ice floes between 2 and 30 km in diameter. We found that the FSD follows a power-law distribution at all locations, with a seasonally varying exponent that reflects floe break-up in spring, loss of smaller floes in summer, and the return of larger floes after fall freeze-up. We extended the results to floe sizes from 10 m to 2 km at selected time/space locations using more than 50 high-resolution radar and visible-band satellite images. Our analysis used more data and applied greater statistical rigor than any previous study of the FSD. The incorporation of the FSD into our ice-ocean model resulted in reduced sea-ice thickness, mainly in the marginal ice zone, which improved the simulation of sea-ice extent and yielded an earlier ice retreat. We also examined results from 17 previous studies of the FSD, most of which report power-law FSDs but with widely varying exponents. It is difficult to reconcile the range of results due to different study areas, seasons, and methods of analysis. We review the power-law representation of the FSD in these studies and discuss some mathematical details that are important to consider in any future analysis.

  3. Predicting subglacial lakes and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets

    Science.gov (United States)

    Livingstone, S. J.; Clark, C. D.; Woodward, J.

    2013-03-01

    In this paper we use the Shreve hydraulic potential equation to predict subglacial lakes and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets. For the Antarctic Ice Sheet we are able to predict known subglacial lakes with a >70% success rate, which demonstrates the validity of this method. Despite the success in predicting known subglacial lakes the calculations produce two-orders of magnitude more lakes than are presently identified, covering 4% of the ice-sheet bed. The difference is thought to result from our poor knowledge of the bed (which has resulted in artefacts associated with the interpolation method), intrinsic errors associated with the simplified modelling approach and because thousands of subglacial lakes, particularly smaller ones, remain to be found. Applying the same modelling approach to the Greenland Ice Sheet predicts only 90 lakes under the present-day ice-sheet configuration, covering 0.2% of the bed. The paucity of subglacial lakes in Greenland is thought to be a function of steeper overall ice-surface gradients. As no lakes have currently been located under Greenland, model predictions will make suitable targets for radar surveys of Greenland to identify subglacial lakes. During deglaciation from the Last Glacial Maximum both ice sheets had more subglacial lakes at their beds, though many of these lakes have persisted to present conditions. These lakes, inherited from past ice-sheet configurations would not form under current surface conditions, suggesting a retreating ice-sheet will have many more subglacial lakes than an advancing ice sheet. This hysteresis effect has implications for ice-stream formation and flow, bed lubrication and meltwater drainage. The lake model also allows modelling of the drainage pathways of the present-day and former Greenland and Antarctic ice sheets. Significantly, key sectors of the ice sheets, such as the Siple Coast (Antarctica) and NE Greenland Ice Stream system, are shown to have

  4. Sea ice dynamics across the Mid-Pleistocene transition in the Bering Sea.

    Science.gov (United States)

    Detlef, H; Belt, S T; Sosdian, S M; Smik, L; Lear, C H; Hall, I R; Cabedo-Sanz, P; Husum, K; Kender, S

    2018-03-05

    Sea ice and associated feedback mechanisms play an important role for both long- and short-term climate change. Our ability to predict future sea ice extent, however, hinges on a greater understanding of past sea ice dynamics. Here we investigate sea ice changes in the eastern Bering Sea prior to, across, and after the Mid-Pleistocene transition (MPT). The sea ice record, based on the Arctic sea ice biomarker IP 25 and related open water proxies from the International Ocean Discovery Program Site U1343, shows a substantial increase in sea ice extent across the MPT. The occurrence of late-glacial/deglacial sea ice maxima are consistent with sea ice/land ice hysteresis and land-glacier retreat via the temperature-precipitation feedback. We also identify interactions of sea ice with phytoplankton growth and ocean circulation patterns, which have important implications for glacial North Pacific Intermediate Water formation and potentially North Pacific abyssal carbon storage.

  5. 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

    [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......-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...

  6. Benthic colonization in newly ice-free soft-bottom areas in an Antarctic fjord.

    Directory of Open Access Journals (Sweden)

    Cristian Lagger

    Full Text Available Extended glacier retreat is among the main consequences of the rapid warming of the West Antarctic Peninsula. Particularly, in the inner part of Potter Cove (South Shetland Islands, Antarctica large areas are now exposed to open sea conditions owing to the retreat of Fourcade glacier. During the 2010 austral summer, underwater photographic surveys were undertaken by SCUBA diving up to 30 m in these new ice-free areas 80 m from the glacier front. Our main aim was to investigate colonization and early succession of the benthic assemblages on soft-bottom areas. Here, we reported a total of 1,146 animals belonging to 13 taxa. Filter-feeders comprised the largest trophic group and sessile fauna showed much higher coverages and densities than mobile fauna at all depths. The most abundant groups were ascidians and bryozoans, which together comprised ~90% of all taxa documented. In a region where most of marine-terminating glaciers are in retreat, these results are an important contribution to improve our knowledge on colonization in the newly ice-free areas.

  7. A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum

    Science.gov (United States)

    Bentley, Michael J.; Ó Cofaigh, Colm; Anderson, John B.; Conway, Howard; Davies, Bethan; Graham, Alastair G. C.; Hillenbrand, Claus-Dieter; Hodgson, Dominic A.; Jamieson, Stewart S. R.; Larter, Robert D.; Mackintosh, Andrew; Smith, James A.; Verleyen, Elie; Ackert, Robert P.; Bart, Philip J.; Berg, Sonja; Brunstein, Daniel; Canals, Miquel; Colhoun, Eric A.; Crosta, Xavier; Dickens, William A.; Domack, Eugene; Dowdeswell, Julian A.; Dunbar, Robert; Ehrmann, Werner; Evans, Jeffrey; Favier, Vincent; Fink, David; Fogwill, Christopher J.; Glasser, Neil F.; Gohl, Karsten; Golledge, Nicholas R.; Goodwin, Ian; Gore, Damian B.; Greenwood, Sarah L.; Hall, Brenda L.; Hall, Kevin; Hedding, David W.; Hein, Andrew S.; Hocking, Emma P.; Jakobsson, Martin; Johnson, Joanne S.; Jomelli, Vincent; Jones, R. Selwyn; Klages, Johann P.; Kristoffersen, Yngve; Kuhn, Gerhard; Leventer, Amy; Licht, Kathy; Lilly, Katherine; Lindow, Julia; Livingstone, Stephen J.; Massé, Guillaume; McGlone, Matt S.; McKay, Robert M.; Melles, Martin; Miura, Hideki; Mulvaney, Robert; Nel, Werner; Nitsche, Frank O.; O'Brien, Philip E.; Post, Alexandra L.; Roberts, Stephen J.; Saunders, Krystyna M.; Selkirk, Patricia M.; Simms, Alexander R.; Spiegel, Cornelia; Stolldorf, Travis D.; Sugden, David E.; van der Putten, Nathalie; van Ommen, Tas; Verfaillie, Deborah; Vyverman, Wim; Wagner, Bernd; White, Duanne A.; Witus, Alexandra E.; Zwartz, Dan

    2014-09-01

    A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20 ka, 15 ka, 10 ka and 5 ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse 1a. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorities for future work. The synthesis is intended to be a resource for the modelling and glacial geological community.

  8. Observations of brine plumes below melting Arctic sea ice

    OpenAIRE

    Peterson, Algot K.

    2018-01-01

    In sea ice, interconnected pockets and channels of brine are surrounded by fresh ice. Over time, brine is lost by gravity drainage and flushing. The timing of salt release and its interaction with the underlying water can impact subsequent sea ice melt. Turbulence measurements 1 m below melting sea ice north of Svalbard reveal anticorrelated heat and salt fluxes. From the observations, 131 salty plumes descending from the warm sea ice are identified, confirming previous obse...

  9. Observations of brine plumes below Arctic sea ice

    OpenAIRE

    Peterson, Algot Kristoffer

    2017-01-01

    In sea ice, interconnected pockets and channels of brine are surrounded by fresh ice. Over time, brine is lost by gravity drainage and flushing. The timing of salt release and its interaction with the underlying water can impact subsequent sea ice melt. Turbulence measurements 1 m below melting sea ice north of Svalbard reveal anti-correlated heat and salt fluxes. From the observations, 131 salty plumes descending from the warm sea ice are identified, confirming previous observations...

  10. 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).

  11. Ocean circulation and sea-ice thinning induced by melting ice shelves in the Amundsen Sea

    Science.gov (United States)

    Jourdain, Nicolas C.; Mathiot, Pierre; Merino, Nacho; Durand, Gaël.; Le Sommer, Julien; Spence, Paul; Dutrieux, Pierre; Madec, Gurvan

    2017-03-01

    A 1/12° ocean model configuration of the Amundsen Sea sector is developed to better understand the circulation induced by ice-shelf melt and the impacts on the surrounding ocean and sea ice. Eighteen sensitivity experiments to drag and heat exchange coefficients at the ice shelf/ocean interface are performed. The total melt rate simulated in each cavity is function of the thermal Stanton number, and for a given thermal Stanton number, melt is slightly higher for lower values of the drag coefficient. Sub-ice-shelf melt induces a thermohaline circulation that pumps warm circumpolar deep water into the cavity. The related volume flux into a cavity is 100-500 times stronger than the melt volume flux itself. Ice-shelf melt also induces a coastal barotropic current that contributes 45 ± 12% of the total simulated coastal transport. Due to the presence of warm circumpolar deep waters, the melt-induced inflow typically brings 4-20 times more heat into the cavities than the latent heat required for melt. For currently observed melt rates, approximately 6-31% of the heat that enters a cavity with melting potential is actually used to melt ice shelves. For increasing sub-ice-shelf melt rates, the transport in the cavity becomes stronger, and more heat is pumped from the deep layers to the upper part of the cavity then advected toward the ocean surface in front of the ice shelf. Therefore, more ice-shelf melt induces less sea-ice volume near the ice sheet margins.Plain Language SummaryThe ice-shelf cavities of the Amundsen Sea, Antarctica, act as very powerful pumps that create strong inflows of warm water under the ice-shelves, as well as significant circulation changes in the entire region. Such warm inflows bring more heat than required to melt ice, so that a large part of that heat exits ice-shelf cavities without being used. Due to mixing between warm deep waters and melt freshwater, melt-induced flows are warm and buoyant when they leave cavities. Therefore, they reach

  12. Carbon Sinks in a Changing Climate: Relative Buoyancy and Sinking Potentials of Various Antarctic Phytoplankton and Ice Algae

    Science.gov (United States)

    Nirmel, S.; Selz, V.

    2016-12-01

    Polar phytoplankton play instrumental roles in global biogeochemical cycles, sometimes serving as massive carbon sinks via the biological pump. In addition to phytoplankton, sea ice supports a significant amount of ice algae, the essential primary producers for the ecosystem in winter and early spring. While sea ice habitat declines on regional scales, the fate of sea ice algae post-ice melt remains relatively unknown, despite its importance in understanding how the biological pump might be affected by sea ice loss. Through a series of settling column experiments on the icebreaker Nathaniel B. Palmer, we aimed to address the question: What controls the fate of the carbon-rich ice algae across the Western Antarctic Peninsula (WAP) during ice melt? We focused on whether species composition affects the sinking potential of ice algal communities. Using FlowCAM imagery, we classified samples collected from the buoyant, neutral, and negatively buoyant portions of the settling columns into genus-level taxonomic classes. We used image parameters and geometric shape equations to calculate the biovolume of each taxonomic group. We further explored relationships between taxa-specific sinking potentials, environmental parameters (temperature and nutrients), and physiological properties of associated algal communities (as described by Fast Rate Repetition fluorometry). Results indicate that colonial Phaeocystis antarctica tends to dominate lower regions of the settling column. Moreover, we observe strong correlations between geographic location and both nutrients and phytoplankton physiology. We found that these three factors are indeed related to taxa-specific buoyancy and sinking indices. An understanding of these relationships sheds more light on the role P. antarctica (a carbon-rich bloom-forming genus) plays in the biological pump; higher sinking rates suggest greater carbon export to depth, while lower sinking rates increase the likelihood of carbon being respired back

  13. Pan-ice-sheet glacier terminus change in East Antarctica reveals sensitivity of Wilkes Land to sea-ice changes.

    Science.gov (United States)

    Miles, Bertie W J; Stokes, Chris R; Jamieson, Stewart S R

    2016-05-01

    The dynamics of ocean-terminating outlet glaciers are an important component of ice-sheet mass balance. Using satellite imagery for the past 40 years, we compile an approximately decadal record of outlet-glacier terminus position change around the entire East Antarctic Ice Sheet (EAIS) marine margin. We find that most outlet glaciers retreated during the period 1974-1990, before switching to advance in every drainage basin during the two most recent periods, 1990-2000 and 2000-2012. The only exception to this trend was in Wilkes Land, where the majority of glaciers (74%) retreated between 2000 and 2012. We hypothesize that this anomalous retreat is linked to a reduction in sea ice and associated impacts on ocean stratification, which increases the incursion of warm deep water toward glacier termini. Because Wilkes Land overlies a large marine basin, it raises the possibility of a future sea level contribution from this sector of East Antarctica.

  14. Pan–ice-sheet glacier terminus change in East Antarctica reveals sensitivity of Wilkes Land to sea-ice changes

    Science.gov (United States)

    Miles, Bertie W. J.; Stokes, Chris R.; Jamieson, Stewart S. R.

    2016-01-01

    The dynamics of ocean-terminating outlet glaciers are an important component of ice-sheet mass balance. Using satellite imagery for the past 40 years, we compile an approximately decadal record of outlet-glacier terminus position change around the entire East Antarctic Ice Sheet (EAIS) marine margin. We find that most outlet glaciers retreated during the period 1974–1990, before switching to advance in every drainage basin during the two most recent periods, 1990–2000 and 2000–2012. The only exception to this trend was in Wilkes Land, where the majority of glaciers (74%) retreated between 2000 and 2012. We hypothesize that this anomalous retreat is linked to a reduction in sea ice and associated impacts on ocean stratification, which increases the incursion of warm deep water toward glacier termini. Because Wilkes Land overlies a large marine basin, it raises the possibility of a future sea level contribution from this sector of East Antarctica. PMID:27386519

  15. Towards Improving Sea Ice Predictabiity: Evaluating Climate Models Against Satellite Sea Ice Observations

    Science.gov (United States)

    Stroeve, J. C.

    2014-12-01

    The last four decades have seen a remarkable decline in the spatial extent of the Arctic sea ice cover, presenting both challenges and opportunities to Arctic residents, government agencies and industry. After the record low extent in September 2007 effort has increased to improve seasonal, decadal-scale and longer-term predictions of the sea ice cover. Coupled global climate models (GCMs) consistently project that if greenhouse gas concentrations continue to rise, the eventual outcome will be a complete loss of the multiyear ice cover. However, confidence in these projections depends o HoHoweon the models ability to reproduce features of the present-day climate. Comparison between models participating in the World Climate Research Programme Coupled Model Intercomparison Project Phase 5 (CMIP5) and observations of sea ice extent and thickness show that (1) historical trends from 85% of the model ensemble members remain smaller than observed, and (2) spatial patterns of sea ice thickness are poorly represented in most models. Part of the explanation lies with a failure of models to represent details of the mean atmospheric circulation pattern that governs the transport and spatial distribution of sea ice. These results raise concerns regarding the ability of CMIP5 models to realistically represent the processes driving the decline of Arctic sea ice and to project the timing of when a seasonally ice-free Arctic may be realized. On shorter time-scales, seasonal sea ice prediction has been challenged to predict the sea ice extent from Arctic conditions a few months to a year in advance. Efforts such as the Sea Ice Outlook (SIO) project, originally organized through the Study of Environmental Change (SEARCH) and now managed by the Sea Ice Prediction Network project (SIPN) synthesize predictions of the September sea ice extent based on a variety of approaches, including heuristic, statistical and dynamical modeling. Analysis of SIO contributions reveals that when the

  16. Potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets

    Science.gov (United States)

    Livingstone, S. J.; Clark, C. D.; Woodward, J.; Kingslake, J.

    2013-11-01

    We use the Shreve hydraulic potential equation as a simplified approach to investigate potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets. We validate the method by demonstrating its ability to recall the locations of >60% of the known subglacial lakes beneath the Antarctic Ice Sheet. This is despite uncertainty in the ice-sheet bed elevation and our simplified modelling approach. However, we predict many more lakes than are observed. Hence we suggest that thousands of subglacial lakes remain to be found. Applying our technique to the Greenland Ice Sheet, where very few subglacial lakes have so far been observed, recalls 1607 potential lake locations, covering 1.2% of the bed. Our results will therefore provide suitable targets for geophysical surveys aimed at identifying lakes beneath Greenland. We also apply the technique to modelled past ice-sheet configurations and find that during deglaciation both ice sheets likely had more subglacial lakes at their beds. These lakes, inherited from past ice-sheet configurations, would not form under current surface conditions, but are able to persist, suggesting a retreating ice-sheet will have many more subglacial lakes than advancing ones. We also investigate subglacial drainage pathways of the present-day and former Greenland and Antarctic ice sheets. Key sectors of the ice sheets, such as the Siple Coast (Antarctica) and NE Greenland Ice Stream system, are suggested to have been susceptible to subglacial drainage switching. We discuss how our results impact our understanding of meltwater drainage, basal lubrication and ice-stream formation.

  17. A sea ice model for the marginal ice zone with an application to the Greenland Sea

    DEFF Research Database (Denmark)

    Pedersen, Leif Toudal; Coon, Max D.

    2004-01-01

    A model is presented that describes the formation, transport, and desalinization of frazil and pancake ice as it is formed in marginal seas. This model uses as input the total ice concentration evaluated from Special Sensor Microwave Imager and wind speed and direction. The model calculates...... the areal concentration, thickness, volume concentration, and salinity of frazil ice as well as the areal concentration, thickness, and salinity of pancakes. A simple parameterization for the Odden region of the Greenland Sea is presented. The model is run for the winter of 1996-1997. There are direct...... observations of the thickness and salinity of pancakes and the volume concentration of frazil ice to compare with the model. The model results compare very well with the measured data. This new ice model can be tuned to work in marginal seas elsewhere to calculate ice thickness, motion, and brine rejection...

  18. On producing sea ice deformation data sets from SAR-derived sea ice motion

    Directory of Open Access Journals (Sweden)

    S. Bouillon

    2015-04-01

    Full Text Available We propose a method to reduce the error generated when computing sea ice deformation fields from synthetic aperture radar (SAR-derived sea ice motion. The method is based on two steps. The first step consists of using a triangulation of the positions taken from the sea ice trajectories to define a mesh on which a first estimate of sea ice deformation is computed. The second step consists of applying a specific smoother to the deformation field to reduce the artificial noise that arises along discontinuities in the sea ice motion field. This method is here applied to RADARSAT Geophysical Processor System (RGPS sea ice trajectories having a temporal and spatial resolution of about 3 days and 10 km, respectively. From the comparison between unfiltered and filtered fields, we estimate that the artificial noise causes an overestimation of about 60% of opening and closing. The artificial noise also has a strong impact on the statistical distribution of the deformation and on the scaling exponents estimated with multifractal analysis. We also show that a similar noise is present in the deformation fields provided in the widely used four-point deformation RGPS data set. These findings may have serious implications for previous studies as the constant overestimation of the opening and closing could lead to a large overestimation of freezing in leads, salt rejection and sea ice ridging.

  19. Assessment of Antarctic Ice-Sheet Mass Balance Estimates: 1992 - 2009

    Science.gov (United States)

    Zwally, H. Jay; Giovinetto, Mario B.

    2011-01-01

    Published mass balance estimates for the Antarctic Ice Sheet (AIS) lie between approximately +50 to -250 Gt/year for 1992 to 2009, which span a range equivalent to 15% of the annual mass input and 0.8 mm/year Sea Level Equivalent (SLE). Two estimates from radar-altimeter measurements of elevation change by European Remote-sensing Satellites (ERS) (+28 and -31 Gt/year) lie in the upper part, whereas estimates from the Input-minus-Output Method (IOM) and the Gravity Recovery and Climate Experiment (GRACE) lie in the lower part (-40 to -246 Gt/year). We compare the various estimates, discuss the methodology used, and critically assess the results. Although recent reports of large and accelerating rates of mass loss from GRACE=based studies cite agreement with IOM results, our evaluation does not support that conclusion. We find that the extrapolation used in the published IOM estimates for the 15 % of the periphery for which discharge velocities are not observed gives twice the rate of discharge per unit of associated ice-sheet area than the 85% faster-moving parts. Our calculations show that the published extrapolation overestimates the ice discharge by 282 Gt/yr compared to our assumption that the slower moving areas have 70% as much discharge per area as the faster moving parts. Also, published data on the time-series of discharge velocities and accumulation/precipitation do not support mass output increases or input decreases with time, respectively. Our modified IOM estimate, using the 70% discharge assumption and substituting input from a field-data compilation for input from an atmospheric model over 6% of area, gives a loss of only 13 Gt/year (versus 136 Gt/year) for the period around 2000. Two ERS-based estimates, our modified IOM, and a GRACE-based estimate for observations within 1992 to 2005 lie in a narrowed range of +27 to - 40 Gt/year, which is about 3% of the annual mass input and only 0.2 mm/year SLE. Our preferred estimate for 1992-2001 is - 47 Gt

  20. Assessing the Global Climate Response to Freshwater Forcing from the Antarctic Ice Sheet Under Future Climate Scenarios

    Science.gov (United States)

    Rogstad, S.; Condron, A.; DeConto, R.; Pollard, D.

    2017-12-01

    Observational evidence indicates that the West Antarctic Ice Sheet (WAIS) is losing mass at an accelerating rate. Impacts to global climate resulting from changing ocean circulation patterns due to increased freshwater runoff from Antarctica in the future could have significant implications for global heat transport, but to-date this topic has not been investigated using complex numerical models with realistic freshwater forcing. Here, we present results from a high resolution fully coupled ocean-atmosphere model (CESM 1.2) forced with runoff from Antarctica prescribed from a high resolution regional ice sheet-ice shelf model. Results from the regional simulations indicate a potential freshwater contribution from Antarctica of up to 1 m equivalent sea level rise by the end of the century under RCP 8.5 indicating that a substantial input of freshwater into the Southern Ocean is possible. Our high resolution global simulations were performed under IPCC future climate scenarios RCP 4.5 and 8.5. We will present results showing the impact of WAIS collapse on global ocean circulation, sea ice, air temperature, and salinity in order to assess the potential for abrupt climate change triggered by WAIS collapse.

  1. Overview and Assessment of Antarctic Ice-Sheet Mass Balance Estimates: 1992-2009

    Science.gov (United States)

    Zwally, H. Jay; Giovinetto, Mario B.

    2011-01-01

    Mass balance estimates for the Antarctic Ice Sheet (AIS) in the 2007 report by the Intergovernmental Panel on Climate Change and in more recent reports lie between approximately ?50 to -250 Gt/year for 1992 to 2009. The 300 Gt/year range is approximately 15% of the annual mass input and 0.8 mm/year Sea Level Equivalent (SLE). Two estimates from radar altimeter measurements of elevation change by European Remote-sensing Satellites (ERS) (?28 and -31 Gt/year) lie in the upper part, whereas estimates from the Input-minus-Output Method (IOM) and the Gravity Recovery and Climate Experiment (GRACE) lie in the lower part (-40 to -246 Gt/year). We compare the various estimates, discuss the methodology used, and critically assess the results. We also modify the IOM estimate using (1) an alternate extrapolation to estimate the discharge from the non-observed 15% of the periphery, and (2) substitution of input from a field data compilation for input from an atmospheric model in 6% of area. The modified IOM estimate reduces the loss from 136 Gt/year to 13 Gt/year. Two ERS-based estimates, the modified IOM, and a GRACE-based estimate for observations within 1992 2005 lie in a narrowed range of ?27 to -40 Gt/year, which is about 3% of the annual mass input and only 0.2 mm/year SLE. Our preferred estimate for 1992 2001 is -47 Gt/year for West Antarctica, ?16 Gt/year for East Antarctica, and -31 Gt/year overall (?0.1 mm/year SLE), not including part of the Antarctic Peninsula (1.07% of the AIS area). Although recent reports of large and increasing rates of mass loss with time from GRACE-based studies cite agreement with IOM results, our evaluation does not support that conclusion

  2. Arctic Ice Algae Distribution as Function of Large Scale Sea Ice Variables

    Science.gov (United States)

    Flores, H.; Castellani, G.; Lange, B. A.; David, C.; Katlein, C.; Peeken, I.; Nicolaus, M.; Losch, M. J.; van Franeker, J. A.

    2016-02-01

    One of the most pronounced impacts of climate change is the declining sea ice cover in the Arctic Ocean, which has implications for sea-ice associated ecosystems that are strongly dependent on carbon produced by ice algae. In order to understand these ecosystems there is a need to understand the interaction between the physical and biological components of sea ice. Our current understanding of Arctic sea ice algae is based on observations with limited spatial coverage. Therefore, we aim to model the spatial distribution of ice-algae on a basin scale. Current sea-ice-ocean models do allow the representation of sea-ice variability on a scale of few km. Large scale characteristics of sea ice such as age, deformation, and snow cover, do affect the small scale ice properties, such as salinity, porosity, light transmission. The latter directly affect the sea ice algae content, but to what extent is not yet well understood. In this work we present a new parameterization for the sea-ice algae content developed with the aim to model the algae content and variability based on large scale sea-ice characteristics. This parameterization is tuned with data collected during a ship-based campaign to the Eastern Central Arctic in summer 2012. Sea-ice thickness and under-ice spectral surveys over different sea ice regimes were conducted with a Surface and Under Ice Trawl (SUIT) and a Remote Operated Vehicle (ROV). In addition, ice cores were extracted at several sites for chl a analysis. We use a coupled sea-ice-ocean model with a spatial scale of 10 km and we show here the results for the temporal evolution of algae content in sea ice.

  3. A Microbial Community in Sediments Beneath the Western Antarctic Ice Sheet, Ice Stream C (Kamb)

    Science.gov (United States)

    Skidmore, M.; Han, S.; Foo, W.; Bui, D.; Lanoil, B.

    2004-12-01

    In 2000, an ice-drilling project focusing on the "sticky spot" of Ice Stream C recovered cores of sub-glacial sediments from beneath the Western Antarctic Ice Sheet. We have characterized several chemical and microbiological parameters of the sole intact sediment core. Pore waters extracted from these sediments were brackish and some were supersaturated with respect to calcite. Ion chromatography demonstrated the presence of several organic acids at low, but detectable, levels in the pore water. DAPI direct cell counts were approximately 107 cells g-1. Aerobic viable plate counts were much lower than direct cell counts; however, they were two orders of magnitude higher on plates incubated at low temperature (4 ° C; 3.63 x 105 CFU ml-1) than at higher temperatures (ca. 22° C; 1.5 x 103 CFU ml-1); no colonies were detected on plates incubated anaerobically at either temperature. 16S rDNA clone library analysis indicates extremely limited bacterial diversity in these samples: six phylogenetic clades were detected. The three dominant bacterial phylogenetic clades in the clone libraries (252 clones total) were most closely related to Thiobacillus thioparus (180 clones), Polaromonas vacuolata (34 clones), and Gallionella ferruginea (35 clones) and their relatives; one clone each represented the other three phylogenetic clades (most closely related to Ralstonia pickettii, Lysobacter antibioticus, and Xylella fastidiosa, respectively). These sequences match closely with sequences previously obtained from other subglacial environments in Alaska, Ellesmere Island, Canada and New Zealand. Implications of this microbial community to subglacial chemistry and microbial biogeography will be discussed.

  4. Improving Arctic Sea Ice Observations and Data Access to Support Advances in Sea Ice Forecasting

    Science.gov (United States)

    Farrell, S. L.

    2017-12-01

    The economic and strategic importance of the Arctic region is becoming apparent. One of the most striking and widely publicized changes underway is the declining sea ice cover. Since sea ice is a key component of the climate system, its ongoing loss has serious, and wide-ranging, socio-economic implications. Increasing year-to-year variability in the geographic location, concentration, and thickness of the Arctic ice cover will pose both challenges and opportunities. The sea ice research community must be engaged in sustained Arctic Observing Network (AON) initiatives so as to deliver fit-for-purpose remote sensing data products to a variety of stakeholders including Arctic communities, the weather forecasting and climate modeling communities, industry, local, regional and national governments, and policy makers. An example of engagement is the work currently underway to improve research collaborations between scientists engaged in obtaining and assessing sea ice observational data and those conducting numerical modeling studies and forecasting ice conditions. As part of the US AON, in collaboration with the Interagency Arctic Research Policy Committee (IARPC), we are developing a strategic framework within which observers and modelers can work towards the common goal of improved sea ice forecasting. Here, we focus on sea ice thickness, a key varaible of the Arctic ice cover. We describe multi-sensor, and blended, sea ice thickness data products under development that can be leveraged to improve model initialization and validation, as well as support data assimilation exercises. We will also present the new PolarWatch initiative (polarwatch.noaa.gov) and discuss efforts to advance access to remote sensing satellite observations and improve communication with Arctic stakeholders, so as to deliver data products that best address societal needs.

  5. 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.

  6. Antarctic ice sheet thickness estimation based on P-receiver function and waveform inversion

    Science.gov (United States)

    Yan, P.; Li, F.; LI, Z.; Li, J.; Yang, Y.; Hao, W.

    2016-12-01

    Antarctic ice sheet thickness is key parameter and boundary condition for ice sheet model construction, which has great significance for glacial isostatic adjustment, ice sheet mass balance and global change study. Ice thickness acquired utilizing seismological receiver function method can complement and verify with results obtained by radar echo sounding method. In this paper, P-receiver functions(PRFs) are extracted for stations deployed on Antarctic ice sheet, then Vp/Vs ratio and ice thickness are obtained using H-Kappa stacking. Comparisons are made between Bedmap2 dataset and the ice thickness from PRFs, most of the absolute value of the differences are less than 200 meters, only a few reach 600 meters. Taking into account of the intensity of Bedmap2 dataset survey lines and the uncertainty of radio echo sounding, as well as the inherit complexity of the internal ice structure beneath some stations, the ice thickness obtained from receiver function method is reliable. However limitation exists when using H-Kappa stacking method for stations where sediment squeezed between the ice and the bed rock layer. For better verifying the PRF result, a global optimizing method-Neighbourhood algotithm(NA) and spline interpolation are used to modeling PRFs assuming an isotropic layered ice sheet with depth varied densities and velocities beneath the stations. Then the velocity structure and ice sheet thickness are obtained through nonlinear searching by optimally fitting the real and the theoretical PRFs. The obtained ice sheet thickness beneath the stations agree well with the former H-Kappa method, but further detailed study are needed to constrain the inner ice velocity structure.

  7. IceBridge KT19 IR Surface Temperature V001

    Data.gov (United States)

    National Aeronautics and Space Administration — The NASA IceBridge KT19 IR Surface Temperature data set contains surface temperature measurements of Arctic and Antarctic sea ice and land ice acquired using the...

  8. Sea Ice Mass Balance Buoys (IMBs): First Results from a Data Processing Intercomparison Study

    Science.gov (United States)

    Hoppmann, Mario; Tiemann, Louisa; Itkin, Polona

    2017-04-01

    IMBs are autonomous instruments able to continuously monitor the growth and melt of sea ice and its snow cover at a single point on an ice floe. Complementing field expeditions, remote sensing observations and modelling studies, these in-situ data are crucial to assess the mass balance and seasonal evolution of sea ice and snow in the polar oceans. Established subtypes of IMBs combine coarse-resolution temperature profiles through air, snow, ice and ocean with ultrasonic pingers to detect snow accumulation and ice thermodynamic growth. Recent technological advancements enable the use of high-resolution temperature chains, which are also able to identify the surrounding medium through a „heating cycle". The temperature change during this heating cycle provides additional information on the internal properties and processes of the ice. However, a unified data processing technique to reliably and accurately determine sea ice thickness and snow depth from this kind of data is still missing, and an unambiguous interpretation remains a challenge. Following the need to improve techniques for remotely measuring sea ice mass balance, an international IMB working group has recently been established. The main goals are 1) to coordinate IMB deployments, 2) to enhance current IMB data processing and -interpretation techniques, and 3) to provide standardized IMB data products to a broader community. Here we present first results from two different data processing algorithms, applied to selected IMB datasets from the Arctic and Antarctic. Their performance with regard to sea ice thickness and snow depth retrieval is evaluated, and an uncertainty is determined. Although several challenges and caveats in IMB data processing and -interpretation are found, such datasets bear great potential and yield plenty of useful information about sea ice properties and processes. It is planned to include many more algorithms from contributors within the working group, and we explicitly invite

  9. Determination of lead isotopes in Arctic and Antarctic snow and ice

    International Nuclear Information System (INIS)

    Rosman, K.J.R.; Chisholm, W.

    1994-01-01

    The development of high sensitivity mass spectrometry to measure Pb isotopes in Arctic and Antarctic snow and ice has provided a powerful tool for identifying sources of global Pb pollution. The combination of isotope abundance information with concentration measurements adds another dimension to analytical chemistry. (authors). 11 refs., 4 figs

  10. Spurious sea ice formation caused by oscillatory ocean tracer advection schemes

    Science.gov (United States)

    Naughten, Kaitlin A.; Galton-Fenzi, Benjamin K.; Meissner, Katrin J.; England, Matthew H.; Brassington, Gary B.; Colberg, Frank; Hattermann, Tore; Debernard, Jens B.

    2017-08-01

    Tracer advection schemes used by ocean models are susceptible to artificial oscillations: a form of numerical error whereby the advected field alternates between overshooting and undershooting the exact solution, producing false extrema. Here we show that these oscillations have undesirable interactions with a coupled sea ice model. When oscillations cause the near-surface ocean temperature to fall below the freezing point, sea ice forms for no reason other than numerical error. This spurious sea ice formation has significant and wide-ranging impacts on Southern Ocean simulations, including the disappearance of coastal polynyas, stratification of the water column, erosion of Winter Water, and upwelling of warm Circumpolar Deep Water. This significantly limits the model's suitability for coupled ocean-ice and climate studies. Using the terrain-following-coordinate ocean model ROMS (Regional Ocean Modelling System) coupled to the sea ice model CICE (Community Ice CodE) on a circumpolar Antarctic domain, we compare the performance of three different tracer advection schemes, as well as two levels of parameterised diffusion and the addition of flux limiters to prevent numerical oscillations. The upwind third-order advection scheme performs better than the centered fourth-order and Akima fourth-order advection schemes, with far fewer incidents of spurious sea ice formation. The latter two schemes are less problematic with higher parameterised diffusion, although some supercooling artifacts persist. Spurious supercooling was eliminated by adding flux limiters to the upwind third-order scheme. We present this comparison as evidence of the problematic nature of oscillatory advection schemes in sea ice formation regions, and urge other ocean/sea-ice modellers to exercise caution when using such schemes.

  11. 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...

  12. Quantification of the Greenland ice sheet contribution to Last Interglacial sea level rise

    Directory of Open Access Journals (Sweden)

    E. J. Stone

    2013-03-01

    Full Text Available During the Last Interglacial period (~ 130–115 thousand years ago the Arctic climate was warmer than today, and global mean sea level was probably more than 6.6 m higher. However, there are large discrepancies in the estimated contributions to this sea level change from various sources (the Greenland and Antarctic ice sheets and smaller ice caps. Here, we determine probabilistically the likely contribution of Greenland ice sheet melt to Last Interglacial sea level rise, taking into account ice sheet model parametric uncertainty. We perform an ensemble of 500 Glimmer ice sheet model simulations forced with climatologies from the climate model HadCM3, and constrain the results with palaeodata from Greenland ice cores. Our results suggest a 90% probability that Greenland ice melt contributed at least 0.6 m, but less than 10% probability that it exceeded 3.5 m, a value which is lower than several recent estimates. Many of these previous estimates, however, did not include a full general circulation climate model that can capture atmospheric circulation and precipitation changes in response to changes in insolation forcing and orographic height. Our combined modelling and palaeodata approach suggests that the Greenland ice sheet is less sensitive to orbital forcing than previously thought, and it implicates Antarctic melt as providing a substantial contribution to Last Interglacial sea level rise. Future work should assess additional uncertainty due to inclusion of basal sliding and the direct effect of insolation on surface melt. In addition, the effect of uncertainty arising from climate model structural design should be taken into account by performing a multi-climate-model comparison.

  13. Two new ways of mapping sea ice thickness using ocean waves

    Science.gov (United States)

    Wadhams, P.

    2010-12-01

    TWO NEW METHODS OF MAPPING SEA ICE THICKNESS USING OCEAN WAVES. P. Wadhams (1,2), Martin Doble (1,2) and F. Parmiggiani (3) (1) Dept. of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 0WA, UK. (2) Laboratoire d’Océanographie de Villefranche, Université Pierre et Marie Curie, 06234 Villefranche-sur-Mer, France (2) ISAC-CNR, Bologna, Italy Two new methods of mapping ice thickness have been recently developed and tested, both making use of the dispersion relation of ocean waves in ice of radically different types. In frazil-pancake ice, a young ice type in which cakes less than 5 m across float in a suspension of individual ice crystals, the propagation of waves has been successfully modelled by treating the ice layer as a highly viscous fluid. The model predicts a shortening of wavelengths within the ice. Two-dimensional Fourier analysis of successive SAR subscenes to track the directional spectrum of a wave field as it enters an ice edge shows that waves do indeed shorten within the ice, and the change has been successfully used to predict the thickness of the frazil-pancake layer. Concurrent shipborne sampling in the Antarctic has shown that the method is accurate, and we now propose its use throughout the important frazil-pancake regimes in the world ocean (Antarctic circumpolar ice edge zone, Greenland Sea, Bering Sea and others). A radically different type of dispersion occurs when ocean waves enter the continuous icefields of the central Arctic, when they couple with the elastic ice cover to propagate as a flexural-gravity wave. A two-axis tiltmeter array has been used to measure the resulting change in the dispersion relation for long ocean swell (15-30 s) originating from storms in the Greenland Sea. The dispersion relation is slightly different from swell in the open ocean, so if two such arrays are placed a substantial distance (100s of km) apart and used to observe the changing wave period of arrivals from a given

  14. Antarctic deglacial pattern in a 30 kyr record of sea surface temperature offshore South Australia

    Science.gov (United States)

    Calvo, Eva; Pelejero, Carles; De Deckker, Patrick; Logan, Graham A.

    2007-07-01

    Comparison of ice cores from Greenland and Antarctica shows an asynchronous two-step warming at these high latitudes during the Last Termination. However, the question whether this asynchrony extends to lower latitudes is unclear mainly due to the scarcity of paleorecords from the Southern Hemisphere. New data from a marine core collected off South Australia (~36°S) allows a detailed reconstruction of sea-surface temperatures over the Last Termination. This confirms the existence of an Antarctic-type deglacial pattern and shows no indication of cooling associated with the Northern Hemisphere YD event. The SST record also provides a new comparison with the more extensive paleoclimatic data available from continental Australia. This shows a strong climatic link between onshore and offshore records for Australia and to Southern Hemisphere paleorecords. We also show a progressive SST drop over the last ~6.5 kyr not seen before for the Australian region.

  15. 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.

  16. 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.

  17. An Innovative Network to Improve Sea Ice Prediction in a Changing Arctic

    Science.gov (United States)

    2015-09-30

    Sea Ice - Albedo Feedback in Sea Ice Predictions is also about understanding sea ice predictability. REFERENCES Wang, W., M. Chen, and A...1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. An Innovative Network to Improve Sea Ice Prediction in a...this project is to understand sea ice predictability and improve sea ice predictions system by defining key observations, improve technical

  18. Identifying metabolic pathways for production of extracellular polymeric substances by the diatom Fragilariopsis cylindrus inhabiting sea ice.

    Science.gov (United States)

    Aslam, Shazia N; Strauss, Jan; Thomas, David N; Mock, Thomas; Underwood, Graham J C

    2018-05-01

    Diatoms are significant primary producers in sea ice, an ephemeral habitat with steep vertical gradients of temperature and salinity characterizing the ice matrix environment. To cope with the variable and challenging conditions, sea ice diatoms produce polysaccharide-rich extracellular polymeric substances (EPS) that play important roles in adhesion, cell protection, ligand binding and as organic carbon sources. Significant differences in EPS concentrations and chemical composition corresponding to temperature and salinity gradients were present in sea ice from the Weddell Sea and Eastern Antarctic regions of the Southern Ocean. To reconstruct the first metabolic pathway for EPS production in diatoms, we exposed Fragilariopsis cylindrus, a key bi-polar diatom species, to simulated sea ice formation. Transcriptome profiling under varying conditions of EPS production identified a significant number of genes and divergent alleles. Their complex differential expression patterns under simulated sea ice formation was aligned with physiological and biochemical properties of the cells, and with field measurements of sea ice EPS characteristics. Thus, the molecular complexity of the EPS pathway suggests metabolic plasticity in F. cylindrus is required to cope with the challenging conditions of the highly variable and extreme sea ice habitat.

  19. 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

  20. Late Holocene sea ice conditions in Herald Canyon, Chukchi Sea

    Science.gov (United States)

    Pearce, C.; O'Regan, M.; Rattray, J. E.; Hutchinson, D. K.; Cronin, T. M.; Gemery, L.; Barrientos, N.; Coxall, H.; Smittenberg, R.; Semiletov, I. P.; Jakobsson, M.

    2017-12-01

    Sea ice in the Arctic Ocean has been in steady decline in recent decades and, based on satellite data, the retreat is most pronounced in the Chukchi and Beaufort seas. Historical observations suggest that the recent changes were unprecedented during the last 150 years, but for a longer time perspective, we rely on the geological record. For this study, we analyzed sediment samples from two piston cores from Herald Canyon in the Chukchi Sea, collected during the 2014 SWERUS-C3 Arctic Ocean Expedition. The Herald Canyon is a local depression across the Chukchi Shelf, and acts as one of the main pathways for Pacific Water to the Arctic Ocean after entering through the narrow and shallow Bering Strait. The study site lies at the modern-day seasonal sea ice minimum edge, and is thus an ideal location for the reconstruction of past sea ice variability. Both sediment cores contain late Holocene deposits characterized by high sediment accumulation rates (100-300 cm/kyr). Core 2-PC1 from the shallow canyon flank (57 m water depth) is 8 meter long and extends back to 4200 cal yrs BP, while the upper 3 meters of Core 4-PC1 from the central canyon (120 mwd) cover the last 3000 years. The chronologies of the cores are based on radiocarbon dates and the 3.6 ka Aniakchak CFE II tephra, which is used as an absolute age marker to calculate the marine radiocarbon reservoir age. Analysis of biomarkers for sea ice and surface water productivity indicate stable sea ice conditions throughout the entire late Holocene, ending with an abrupt increase of phytoplankton sterols in the very top of both sediment sequences. The shift is accompanied by a sudden increase in coarse sediments (> 125 µm) and a minor change in δ13Corg. We interpret this transition in the top sediments as a community turnover in primary producers from sea ice to open water biota. Most importantly, our results indicate that the ongoing rapid ice retreat in the Chukchi Sea of recent decades was unprecedented during the

  1. Dynamics of sea-ice biogeochemistry in the coastal Antarctica during transition from summer to winter

    Directory of Open Access Journals (Sweden)

    Suhas Shetye

    2017-05-01

    Full Text Available The seasonality of carbon dioxide partial pressure (pCO2, air-sea CO2 fluxes and associated environmental parameters were investigated in the Antarctic coastal waters. The in-situ survey was carried out from the austral summer till the onset of winter (January 2012, February 2010 and March 2009 in the Enderby Basin. Rapid decrease in pCO2 was evident under the sea-ice cover in January, when both water column and sea-ice algal activity resulted in the removal of nutrients and dissolved inorganic carbon (DIC and increase in pH. The major highlight of this study is the shift in the dominant biogeochemical factors from summer to early winter. Nutrient limitation (low Si/N, sea-ice cover, low photosynthetically active radiation (PAR, deep mixed layer and high upwelling velocity contributed towards higher pCO2 during March (early winter. CO2 fluxes suggest that the Enderby Basin acts as a strong CO2 sink during January (−81 mmol m−2 d−1, however it acts as a weak sink of CO2 with −2.4 and −1.7 mmol m−2 d−1 during February and March, respectively. The present work, concludes that sea ice plays a dual role towards climate change, by decreasing sea surface pCO2 in summer and enhancing in early winter. Our observations emphasize the need to address seasonal sea-ice driven CO2 flux dynamics in assessing Antarctic contributions to the global oceanic CO2 budget.

  2. 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.

  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. 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...

  5. What's Cooler Than Being Cool? Icefin: Robotic Exploration Beneath Antarctic Ice Shelves

    Science.gov (United States)

    Lawrence, J.; Schmidt, B. E.; Meister, M. R.; Glass, J. B.; Bowman, J. S.; Stockton, A. M.; Dichek, D.; Hurwitz, B.; Ramey, C.; Spears, A.; Walker, C. C.

    2017-12-01

    The 2017-18 Antarctic field season marks the first of three under the RISEUP project (Ross Ice Shelf & Europa Underwater Probe, NASA PSTAR program grant NNX16AL07G, PI B. E. Schmidt). RISEUP expands our efforts to understand the physical processes governing ice-ocean interactions from beneath the McMurdo Ice Shelf (MIS) to the Ross Ice Shelf (RIS), utilizing the modular autonomous or remotely operable submersible vehicle (AUV/ROV) Icefin. The remote, aphotic regions below Antarctic shelves present a unique opportunity- they are both poorly understood terrestrial environments and analogs for similar systems hypothesized to be present on other bodies in our solar system, such as Europa and Enceladus. By developing new robotic technologies to access and explore ice shelf cavities we are advancing our understanding of how temperature, pressure, and salinity influence the ice-ocean interface, the limits of habitable environments on Earth, and what biological processes and adaptations enable the life discovered by the RISP and WISSARD programs during initial exploration beneath the RIS. These investigations further our understanding of ocean world habitability and support planned and proposed planetary missions (e.g. Europa Clipper, Europa Lander) via improved constraint of marine ice accretion processes, organic entrainment, and interface habitability. Custom built at Georgia Tech and first deployed during the 2014/15 Antarctic season, Icefin is 3.5 m, 125 kg modular vehicle that now carries a full suite of oceanographic sensors (including conductivity, temperature, depth, dissolved O2, dissolved organic matter, turbidity, pH, eH, and sonar) that can be deployed through boreholes as small as 25 cm in diameter. Here we present continued analysis of basal ice and oceanographic observations in the McMurdo Sound region from 2012-2015 with, pending anticipated field work, comparisons to preliminary data from the 2017/18 field season beneath both the McMurdo and Ross Ice

  6. Formation of brine channels in sea ice.

    Science.gov (United States)

    Morawetz, Klaus; Thoms, Silke; Kutschan, Bernd

    2017-03-01

    Liquid salty micro-channels (brine) between growing ice platelets in sea ice are an important habitat for CO 2 -binding microalgaea with great impact on polar ecosystems. The structure formation of ice platelets is microscopically described and a phase field model is developed. The pattern formation during solidification of the two-dimensional interstitial liquid is considered by two coupled order parameters, the tetrahedricity as structure of ice and the salinity. The coupling and time evolution of these order parameters are described by a consistent set of three model parameters. They determine the velocity of the freezing process and the structure formation, the phase diagram, the super-cooling and super-heating region, and the specific heat. The model is used to calculate the short-time frozen micro-structures. The obtained morphological structure is compared with the vertical brine pore space obtained from X-ray computed tomography.

  7. Ikaite crystals in melting sea ice - implications for pCO(2) and pH levels in Arctic surface waters

    DEFF Research Database (Denmark)

    Rysgaard, Søren; Glud, Ronnie N.; Lennert, Kunuk

    2012-01-01

    A major issue of Arctic marine science is to understand whether the Arctic Ocean is, or will be, a source or sink for air-sea CO2 exchange. This has been complicated by the recent discoveries of ikaite (a polymorph of CaCO3 center dot 6H(2)O) in Arctic and Antarctic sea ice, which indicate that m...

  8. Climate implications of changing Arctic sea ice

    Science.gov (United States)

    Miller, Gifford H.; Geirsdottir, Áslaug; Koerner, Roy M.

    Straddling the mid-Atlantic ridge, Iceland may be best known to the world for its fiery volcanic history, violent earthquakes, and massive jökulhlaups—episodic outbursts of sub-glacial lakes melted by underlying magma. But this poem, written by Matthias Jochumsson in 1888 and titled simply “The Sea Ice” [Jochumsson, 1915] illustrates why the most insidious disruption to the Icelandic people is the havoc wrought by the quiet approach of sea ice. No other natural disaster has brought such cruelty famine, and death. From Jochumsson: “Where is the ocean, where is the bright, free, silvery ocean?… When you [sea ice] appear, the nation and its history are extinguished; then is death, and deep, dark night…”

  9. Surface and Subsurface Meltwater Ponding and Refreezing on the Bach Ice Shelf, Antarctic Peninsula

    Science.gov (United States)

    Willis, I.; Haggard, E.; Benedek, C. L.; MacAyeal, D. R.; Banwell, A. F.

    2017-12-01

    There is growing concern about the stability and fate of Antarctic ice shelves, as four major ice shelves on the Antarctic Peninsula have completely disintegrated since the 1950s. Their collapse has been linked to the southward movement of the -9 oC mean annual temperature isotherm. The proximal causes of ice shelf instability are not fully known, but an increase in surface melting leading to water ponding and ice flexure, fracture and calving has been implicated. Close to the recently collapsed Wilkins Ice Shelf, the Bach Ice Shelf (72°S 72°W) may be at risk from break up in the near future. Here, we document the changing surface hydrology of the Bach Ice Shelf between 2001 and 2017 using Landsat 7 & 8 imagery. Extensive surface water is identified across the Bach Ice Shelf and its tributary glaciers. Two types of drainage system are observed, drainage into firn via simple stream networks and drainage into the ocean via more complex networks. There are differences between the surface hydrology on the ice shelf and the tributary glaciers, as well as variations within and between summer seasons linked to surface air temperature fluctuations. We also document the changing subsurface hydrology of the ice shelf between 2014 and 2017 using Sentinel 1 A/B SAR imagery. Forty-five subsurface features are identified and analysed for their patterns and temporal evolution. Fourteen of the features show similar characteristics to previously-identified buried lakes and some occur in areas associated with surface lakes in previous years. The buried lakes show seasonal variability in area and surface backscatter, which varies with surface air temperature, and are consistent with the presence, enlargement and contraction of liquid water bodies. Buried lakes are an overlooked source of water loading on ice shelves, which may contribute to ice shelf flexure and potential fracture.

  10. Intercomparison of the Arctic sea ice cover in global ocean-sea ice reanalyses from the ORA-IP project

    Science.gov (United States)

    Chevallier, Matthieu; Smith, Gregory C.; Dupont, Frédéric; Lemieux, Jean-François; Forget, Gael; Fujii, Yosuke; Hernandez, Fabrice; Msadek, Rym; Peterson, K. Andrew; Storto, Andrea; Toyoda, Takahiro; Valdivieso, Maria; Vernieres, Guillaume; Zuo, Hao; Balmaseda, Magdalena; Chang, You-Soon; Ferry, Nicolas; Garric, Gilles; Haines, Keith; Keeley, Sarah; Kovach, Robin M.; Kuragano, Tsurane; Masina, Simona; Tang, Yongming; Tsujino, Hiroyuki; Wang, Xiaochun

    2017-08-01

    Ocean-sea ice reanalyses are crucial for assessing the variability and recent trends in the Arctic sea ice cover. This is especially true for sea ice volume, as long-term and large scale sea ice thickness observations are inexistent. Results from the Ocean ReAnalyses Intercomparison Project (ORA-IP) are presented, with a focus on Arctic sea ice fields reconstructed by state-of-the-art global ocean reanalyses. Differences between the various reanalyses are explored in terms of the effects of data assimilation, model physics and atmospheric forcing on properties of the sea ice cover, including concentration, thickness, velocity and snow. Amongst the 14 reanalyses studied here, 9 assimilate sea ice concentration, and none assimilate sea ice thickness data. The comparison reveals an overall agreement in the reconstructed concentration fields, mainly because of the constraints in surface temperature imposed by direct assimilation of ocean observations, prescribed or assimilated atmospheric forcing and assimilation of sea ice concentration. However, some spread still exists amongst the reanalyses, due to a variety of factors. In particular, a large spread in sea ice thickness is found within the ensemble of reanalyses, partially caused by the biases inherited from their sea ice model components. Biases are also affected by the assimilation of sea ice concentration and the treatment of sea ice thickness in the data assimilation process. An important outcome of this study is that the spatial distribution of ice volume varies widely between products, with no reanalysis standing out as clearly superior as compared to altimetry estimates. The ice thickness from systems without assimilation of sea ice concentration is not worse than that from systems constrained with sea ice observations. An evaluation of the sea ice velocity fields reveals that ice drifts too fast in most systems. As an ensemble, the ORA-IP reanalyses capture trends in Arctic sea ice area and extent

  11. 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.

  12. Dynamic preconditioning of the September sea-ice extent minimum

    Science.gov (United States)

    Williams, James; Tremblay, Bruno; Newton, Robert; Allard, Richard

    2016-04-01

    There has been an increased interest in seasonal forecasting of the sea-ice extent in recent years, in particular the minimum sea-ice extent. We propose a dynamical mechanism, based on winter preconditioning through first year ice formation, that explains a significant fraction of the variance in the anomaly of the September sea-ice extent from the long-term linear trend. To this end, we use a Lagrangian trajectory model to backtrack the September sea-ice edge to any time during the previous winter and quantify the amount of sea-ice divergence along the Eurasian and Alaskan coastlines as well as the Fram Strait sea-ice export. We find that coastal divergence that occurs later in the winter (March, April and May) is highly correlated with the following September sea-ice extent minimum (r = -0.73). This is because the newly formed first year ice will melt earlier allowing for other feedbacks (e.g. ice albedo feedback) to start amplifying the signal early in the melt season when the solar input is large. We find that the winter mean Fram Strait sea-ice export anomaly is also correlated with the minimum sea-ice extent the following summer. Next we backtrack a synthetic ice edge initialized at the beginning of the melt season (June 1st) in order to develop hindcast models of the September sea-ice extent that do not rely on a-priori knowledge of the minimum sea-ice extent. We find that using a multi-variate regression model of the September sea-ice extent anomaly based on coastal divergence and Fram Strait ice export as predictors reduces the error by 41%. A hindcast model based on the mean DJFMA Arctic Oscillation index alone reduces the error by 24%.

  13. Central West Antarctic Glaciochemistry from Ice Cores, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — Glaciochemical and accumulation rate records developed from four ice cores in central West Antarctica are used to reconstruct former atmospheric circulation patterns...

  14. 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.

  15. 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.

  16. 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.

  17. Sea-ice-related halogen enrichment at Law Dome, coastal East Antarctica

    Science.gov (United States)

    Vallelonga, Paul; Maffezzoli, Niccolo; Moy, Andrew D.; Curran, Mark A. J.; Vance, Tessa R.; Edwards, Ross; Hughes, Gwyn; Barker, Emily; Spreen, Gunnar; Saiz-Lopez, Alfonso; Corella, J. Pablo; Cuevas, Carlos A.; Spolaor, Andrea

    2017-02-01

    The Law Dome site is ideal for the evaluation of sea ice proxies due to its location near to the Antarctic coast, regular and high accumulation throughout the year, an absence of surface melting or remobilization, and minimal multiyear sea ice. We present records of bromine and iodine concentrations and their enrichment beyond seawater compositions and compare these to satellite observations of first-year sea ice area in the 90-130° E sector of the Wilkes coast. Our findings support the results of previous studies of sea ice variability from Law Dome, indicating that Wilkes coast sea ice area is currently at its lowest level since the start of the 20th century. From the Law Dome DSS1213 firn core, 26 years of monthly deposition data indicate that the period of peak bromine enrichment is during austral spring-summer, from November to February. Results from a traverse along the lee (western) side of Law Dome show low levels of sodium and bromine deposition, with the greatest fluxes in the vicinity of the Law Dome summit. Finally, multidecadal variability in iodine enrichment appears well correlated to bromine enrichment, suggesting a common source of variability that may be related to the Interdecadal Pacific Oscillation (IPO).

  18. Acceleration of the contribution of the Greenland and Antarctic ice

    NARCIS (Netherlands)

    Rignot, Eric; Velicogna, I.; van den Broeke, M.R.|info:eu-repo/dai/nl/073765643; Monaghan, A.; Lenaerts, J.T.M.|info:eu-repo/dai/nl/314850163

    2011-01-01

    Here, we present a 20‐year record of monthly ice sheet mass balance for Greenland and Antarctica. We examine and reconcile two independent methods for estimating temporal variations in ice sheet mass balance, the mass budget method (MB) and the gravity method, during the last 8 years. The MBM

  19. Evaluation of the sea ice proxy IP25 against observational and diatom proxy data in the SW Labrador Sea

    DEFF Research Database (Denmark)

    Weckstrom, Kaarina; Masse, Guillaume; Collins, Lewis G.

    2013-01-01

    The recent rapid decline in Arctic sea ice cover has increased the need to improve the accuracy of the sea ice component in climate models and to provide detailed long-term sea ice concentration records, which are only available via proxy data. Recently, the highly branched isoprenoid IP25......, identified in marine sediments underlying seasonal sea ice, has emerged as a potential sea ice specific proxy for past sea ice cover. We tested the reliability of this biomarker as a sea ice proxy against observational sea ice data (sea ice concentrations from the global HadISST1 database) and against a more....... When assessed against observational sea ice data, IP25 appears to be a more sensitive indicator of sea ice variability in this setting compared to sea ice diatoms and proved to be a robust and reliable proxy for reconstructing low-frequency variability in past sea ice concentrations. The PIP25 index...

  20. Arctic sea ice decline and ice export in the CMIP5 historical simulations

    Science.gov (United States)

    Langehaug, H. R.; Geyer, F.; Smedsrud, L. H.; Gao, Y.

    2013-11-01

    Arctic sea ice properties and Fram Strait ice export from six CMIP5 Global Climate and Earth System Models are evaluated and investigated for the period 1957-2005. Over the last decades most ensemble members simulate a decreasing September sea ice area and a slow, general thinning of the sea ice cover. While the different ensemble members both under- and overestimate the decline in observed September sea ice area, none of the members reproduce the observed thinning. This study is a first attempt to evaluate the Fram Strait ice area export in the CMIP5 models, and the role it has played for Arctic sea ice area and thickness. Five of the six models evaluated reproduce the seasonal cycle and the inter-annual variance of the ice area export in the Fram Strait reasonably well. The simulated southward export of sea ice in the Fram Strait constitutes a major fraction of the Arctic sea ice in these five models; 10-18% of the sea ice covered Arctic Basin is annually exported. For the same models the year-to-year variability in Fram Strait ice volume export carries 35% of the year-to-year variability in the Arctic Basin sea ice volume. We have found low but significant correlations on inter-annual timescales between the Fram Strait ice export, both in terms of area and volume, and the Arctic Basin sea ice thickness. All six models show that an increase in ice area export leads a decrease in the sea ice thickness. This inverse relationship also holds when considering the long-term trends; the larger the increase in Fram Strait ice area export, the larger the thinning of the Arctic Basin sea ice cover and the larger the loss in the September sea ice area. The different ensemble members show both negative and positive ice export trends. Focusing on the model with the largest number of ensemble members (10), we have been able to quantify the effect of the ice area export on the Arctic Basin sea ice for this particular model. For this model an increase of the ice area export

  1. Online Sea Ice Knowledge and Data Platform: www.seaiceportal.de

    Science.gov (United States)

    Treffeisen, R. E.; Nicolaus, M.; Bartsch, A.; Fritzsch, B.; Grosfeld, K.; Haas, C.; Hendricks, S.; Heygster, G.; Hiller, W.; Krumpen, T.; Melsheimer, C.; Nicolaus, A.; Ricker, R.; Weigelt, M.

    2016-12-01

    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 archived 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 (e.g., AMSR2, CryoSat-2 and SMOS) 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 ice-tethered 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 and are open for potential new partners.

  2. Arctic Sea Ice Decline: Observations, Projections, Mechanisms, and Implications

    Science.gov (United States)

    DeWeaver, Eric T.; Bitz, Cecilia M.; Tremblay, L.-Bruno

    This volume addresses the rapid decline of Arctic sea ice, placing recent sea ice decline in the context of past observations, climate model simulations and projections, and simple models of the climate sensitivity of sea ice. Highlights of the work presented here include • An appraisal of the role played by wind forcing in driving the decline; • A reconstruction of Arctic sea ice conditions prior to human observations, based on proxy data from sediments; • A modeling approach for assessing the impact of sea ice decline on polar bears, used as input to the U.S. Fish and Wildlife Service's decision to list the polar bear as a threatened species under the Endangered Species Act; • Contrasting studies on the existence of a "tipping point," beyond which Arctic sea ice decline will become (or has already become) irreversible, including an examination of the role of the small ice cap instability in global warming simulations; • A significant summertime atmospheric response to sea ice reduction in an atmospheric general circulation model, suggesting a positive feedback and the potential for short-term climate prediction. The book will be of interest to researchers attempting to understand the recent behavior of Arctic sea ice, model projections of future sea ice loss, and the consequences of sea ice loss for the natural and human systems of the Arctic.

  3. Using sea-ice deformation fields to constrain the mechanical strength parameters of geophysical sea ice

    Science.gov (United States)

    Bouchat, Amélie; Tremblay, Bruno

    2017-07-01

    We investigate the ability of viscous-plastic (VP) sea-ice models with an elliptical yield curve and normal flow rule to reproduce the shear and divergence distributions derived from the RADARSAT Geophysical Processor System (RGPS). In particular, we reformulate the VP elliptical rheology to allow independent changes in the ice compressive, shear and isotropic tensile strength parameters (P∗, S∗, and T∗, respectively) in order to study the sensitivity of the deformation distributions to changes in the ice mechanical strength parameters. Our 10 km VP simulation with standard ice mechanical strength parameters P∗ = 27.5 kN m-2, S∗ = 6.9 kN m-2, and T∗ = 0 kN m-2 (ellipse aspect ratio of e = 2) does not reproduce the large shear and divergence deformations observed in the RGPS deformation fields, and specifically lacks well-defined, active linear kinematic features (LKFs). Probability density functions (PDFs) for the shear and divergence of are nonetheless not Gaussian. Reducing the ice compressive strength (with constant S∗ and T∗) or increasing the ice shear strength (with constant P∗ and T∗) both results in shear and divergence PDFs in better agreement with RGPS distributions. The isotropic tensile strength of sea ice does not significantly affect the shear and divergence distributions. When considering additional metrics such as the ice drift error, mean ice thickness fields, and spatial scaling of the total deformations, our results suggest that reducing the ice compressive strength P∗ (while keeping S∗ constant, i.e. reducing the ellipse aspect ratio) is a better solution than increasing the shear strength to improve simulations of the Arctic sea-ice cover with the VP elliptical rheology.

  4. Increased CO2 uptake due to sea ice growth and decay in the Nordic Seas

    DEFF Research Database (Denmark)

    Rysgaard, S.; Bendtsen, J.; Pedersen, L. T.

    2009-01-01

    uptake in the Nordic Seas is currently unknown. We present evidence from 50 localities in the Arctic Ocean that dissolved inorganic carbon is rejected together with brine from growing sea ice and that sea ice melting during summer is rich in carbonates. Model calculations show that melting of sea ice......The uptake rates of atmospheric CO2 in the Nordic Seas are among the highest in the world's oceans. This has been ascribed mainly to a strong biological drawdown, but chemical processes within the sea ice itself have also been suggested to play a role. The importance of sea ice for the carbon...

  5. Precipitation regime influence on oxygen triple-isotope distributions in Antarctic precipitation and ice cores

    Science.gov (United States)

    Miller, Martin F.

    2018-01-01

    The relative abundance of 17O in meteoric precipitation is usually reported in terms of the 17O-excess parameter. Variations of 17O-excess in Antarctic precipitation and ice cores have hitherto been attributed to normalised relative humidity changes at the moisture source region, or to the influence of a temperature-dependent supersaturation-controlled kinetic isotope effect during in-cloud ice formation below -20 °C. Neither mechanism, however, satisfactorily explains the large range of 17O-excess values reported from measurements. A different approach, based on the regression characteristics of 103 ln (1 +δ17 O) versus 103 ln (1 +δ18 O), is applied here to previously published isotopic data sets. The analysis indicates that clear-sky precipitation ('diamond dust'), which occurs widely in inland Antarctica, is characterised by an unusual relative abundance of 17O, distinct from that associated with cloud-derived, synoptic snowfall. Furthermore, this distinction appears to be largely preserved in the ice core record. The respective mass contributions to snowfall accumulation - on both temporal and spatial scales - provides the basis of a simple, first-order explanation for the observed oxygen triple-isotope ratio variations in Antarctic precipitation, surface snow and ice cores. Using this approach, it is shown that precipitation during the last major deglaciation, both in western Antarctica at the West Antarctic Ice Sheet (WAIS) Divide and at Vostok on the eastern Antarctic plateau, consisted essentially of diamond dust only, despite a large temperature differential (and thus different water vapour supersaturation conditions) at the two locations. In contrast, synoptic snowfall events dominate the accumulation record throughout the Holocene at both sites.

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

    Science.gov (United States)

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

    2016-01-01

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

  7. Arctic Sea Ice Changes, Interactions, and Feedbacks on the Arctic Climate during the Satellite Era

    Science.gov (United States)

    Wang, X.; Key, J. R.; Liu, Y.

    2011-12-01

    Of all the components of the Earth climate system, the cryosphere is arguably the least understood even though it is a very important indicator and an effective modulator of regional and global climate change. Changes in sea ice will significantly affect exchanges of momentum, heat, and mass between the ocean and the atmosphere, and have profound socio-economic impacts on transportation, fisheries, hunting, polar animal habitat and more. In the last three decades, the Arctic underwent significant changes in sea ice as part of the accelerated global climate change. With the recently developed One-dimensional Thermodynamic Ice Model (OTIM), sea and lake ice thickness and trends can be reasonably estimated. The OTIM has been extensively validated against submarine and moored upward-looking sonar measurements, meteorological station measurements, and comprehensive numerical model simulations. The Extended AVHRR Polar Pathfinder (APP-x) dataset has 25 climate parameters covering surface, cloud, and sea ice properties as well as surface and top-of-atmosphere radiative fluxes for the period 1982 - 2004 over the Arctic and Antarctic at 25 km resolution. The OTIM has been used with APP-x dataset for Arctic sea ice thickness and volume estimation. Statistical analysis of spatial and temporal distributions and trends in sea ice extent, thickness, and volume over the satellite period has been performed, along with the temporal analysis of first year and multiple year sea ice extent changes. Preliminary results show clear evidence that Arctic sea ice has been experiencing significant changes over the last two decades of the 20th century. The Arctic sea ice has been shrinking unexpectedly fast with the declines in sea ice extent, thickness, and volume, most apparent in the fall season. Moreover, satellites provide an unprecedented opportunity to observe Arctic sea ice and its changes with high spatial and temporal coverage that is making it an ideal data source for mitigating

  8. 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.

  9. Ice formation and growth shape bacterial community structure in Baltic Sea drift ice.

    Science.gov (United States)

    Eronen-Rasimus, Eeva; Lyra, Christina; Rintala, Janne-Markus; Jürgens, Klaus; Ikonen, Vilma; Kaartokallio, Hermanni

    2015-02-01

    Drift ice, open water and under-ice water bacterial communities covering several developmental stages from open water to thick ice were studied in the northern Baltic Sea. The bacterial communities were assessed with 16S rRNA gene terminal-restriction fragment length polymorphism and cloning, together with bacterial abundance and production measurements. In the early stages, open water and pancake ice were dominated by Alphaproteobacteria and Actinobacteria, which are common bacterial groups in Baltic Sea wintertime surface waters. The pancake ice bacterial communities were similar to the open-water communities, suggesting that the parent water determines the sea-ice bacterial community in the early stages of sea-ice formation. In consolidated young and thick ice, the bacterial communities were significantly different from water bacterial communities as well as from each other, indicating community development in Baltic Sea drift ice along with ice-type changes. The thick ice was dominated by typical sea-ice genera from classes Flavobacteria and Gammaproteobacteria, similar to those in polar sea-ice bacterial communities. Since the thick ice bacterial community was remarkably different from that of the parent seawater, results indicate that thick ice bacterial communities were recruited from the rarer members of the seawater bacterial community. © FEMS 2014. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  10. 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 is not necessary for thicker ice (above about 30 cm thickness)...

  11. Arctic sea ice decline: Projected changes in timing and extent of sea ice in the Bering and Chukchi Seas

    Science.gov (United States)

    Douglas, D.C.

    2010-01-01

    The Arctic region is warming faster than most regions of the world due in part to increasing greenhouse gases and positive feedbacks associated with the loss of snow and ice cover. One consequence has been a rapid decline in Arctic sea ice over the past 3 decades?a decline that is projected to continue by state-of-the-art models. Many stakeholders are therefore interested in how global warming may change the timing and extent of sea ice Arctic-wide, and for specific regions. To inform the public and decision makers of anticipated environmental changes, scientists are striving to better understand how sea ice influences ecosystem structure, local weather, and global climate. Here, projected changes in the Bering and Chukchi Seas are examined because sea ice influences the presence of, or accessibility to, a variety of local resources of commercial and cultural value. In this study, 21st century sea ice conditions in the Bering and Chukchi Seas are based on projections by 18 general circulation models (GCMs) prepared for the fourth reporting period by the Intergovernmental Panel on Climate Change (IPCC) in 2007. Sea ice projections are analyzed for each of two IPCC greenhouse gas forcing scenarios: the A1B `business as usual? scenario and the A2 scenario that is somewhat more aggressive in its CO2 emissions during the second half of the century. A large spread of uncertainty among projections by all 18 models was constrained by creating model subsets that excluded GCMs that poorly simulated the 1979-2008 satellite record of ice extent and seasonality. At the end of the 21st century (2090-2099), median sea ice projections among all combinations of model ensemble and forcing scenario were qualitatively similar. June is projected to experience the least amount of sea ice loss among all months. For the Chukchi Sea, projections show extensive ice melt during July and ice-free conditions during August, September, and October by the end of the century, with high agreement

  12. Improving Arctic sea ice edge forecasts by assimilating high horizontal resolution sea ice concentration data into the US Navy's ice forecast systems

    Science.gov (United States)

    Posey, P. G.; Metzger, E. J.; Wallcraft, A. J.; Hebert, D. A.; Allard, R. A.; Smedstad, O. M.; Phelps, M. W.; Fetterer, F.; Stewart, J. S.; Meier, W. N.; Helfrich, S. R.

    2015-08-01

    This study presents the improvement in ice edge error within the US Navy's operational sea ice forecast systems gained by assimilating high horizontal resolution satellite-derived ice concentration products. Since the late 1980's, the ice forecast systems have assimilated near real-time sea ice concentration derived from the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave/Imager (SSMI and then SSMIS). The resolution of the satellite-derived product was approximately the same as the previous operational ice forecast system (25 km). As the sea ice forecast model resolution increased over time, the need for higher horizontal resolution observational data grew. In 2013, a new Navy sea ice forecast system (Arctic Cap Nowcast/Forecast System - ACNFS) went into operations with a horizontal resolution of ~ 3.5 km at the North Pole. A method of blending ice concentration observations from the Advanced Microwave Scanning Radiometer (AMSR2) along with a sea ice mask produced by the National Ice Center (NIC) has been developed, resulting in an ice concentration product with very high spatial resolution. In this study, ACNFS was initialized with this newly developed high resolution blended ice concentration product. The daily ice edge locations from model hindcast simulations were compared against independent observed ice edge locations. ACNFS initialized using the high resolution blended ice concentration data product decreased predicted ice edge location error compared to the operational system that only assimilated SSMIS data. A second evaluation assimilating the new blended sea ice concentration product into the pre-operational Navy Global Ocean Forecast System 3.1 also showed a substantial improvement in ice edge location over a system using the SSMIS sea ice concentration product alone. This paper describes the technique used to create the blended sea ice concentration product and the significant improvements in ice edge forecasting in both of the

  13. Polarimetric Signatures of Sea Ice. Part 1; Theoretical Model

    Science.gov (United States)

    Nghiem, S. V.; Kwok, R.; Yueh, S. H.; Drinkwater, M. R.

    1995-01-01

    Physical, structural, and electromagnetic properties and interrelating processes in sea ice are used to develop a composite model for polarimetric backscattering signatures of sea ice. Physical properties of sea ice constituents such as ice, brine, air, and salt are presented in terms of their effects on electromagnetic wave interactions. Sea ice structure and geometry of scatterers are related to wave propagation, attenuation, and scattering. Temperature and salinity, which are determining factors for the thermodynamic phase distribution in sea ice, are consistently used to derive both effective permittivities and polarimetric scattering coefficients. Polarimetric signatures of sea ice depend on crystal sizes and brine volumes, which are affected by ice growth rates. Desalination by brine expulsion, drainage, or other mechanisms modifies wave penetration and scattering. Sea ice signatures are further complicated by surface conditions such as rough interfaces, hummocks, snow cover, brine skim, or slush layer. Based on the same set of geophysical parameters characterizing sea ice, a composite model is developed to calculate effective permittivities and backscattering covariance matrices at microwave frequencies for interpretation of sea ice polarimetric signatures.

  14. Polarimetric signatures of sea ice. 1: Theoretical model

    Science.gov (United States)

    Nghiem, S. V.; Kwok, R.; Yueh, S. H.; Drinkwater, M. R.

    1995-01-01

    Physical, structral, and electromagnetic properties and interrelating processes in sea ice are used to develop a composite model for polarimetric backscattering signatures of sea ice. Physical properties of sea ice constituents such as ice, brine, air, and salt are presented in terms of their effects on electromagnetic wave interactions. Sea ice structure and geometry of scatterers are related to wave propagation, attenuation, and scattering. Temperature and salinity, which are determining factors for the thermodynamic phase distribution in sea ice, are consistently used to derive both effective permittivities and polarimetric scattering coefficients. Polarmetric signatures of sea ice depend on crystal sizes and brine volumes, which are affected by ice growth rates. Desalination by brine expulsion, drainage, or other mechanisms modifies wave penetration and scattering. Sea ice signatures are further complicated by surface conditions such as rough interfaces, hummocks, snow cover, brine skim, or slush layer. Based on the same set of geophysical parameters characterizing sea ice, a composite model is developed to calculate effective permittivities and backscattering covariance matrices at microwave frequencies to interpretation of sea ice polarimetric signatures.

  15. Genetic signature of Last Glacial Maximum regional refugia in a circum-Antarctic sea spider

    Science.gov (United States)

    Soler-Membrives, Anna; Linse, Katrin; Miller, Karen J.; Arango, Claudia P.

    2017-10-01

    The evolutionary history of Antarctic organisms is becoming increasingly important to understand and manage population trajectories under rapid environmental change. The Antarctic sea spider Nymphon australe, with an apparently large population size compared with other sea spider species, is an ideal target to look for molecular signatures of past climatic events. We analysed mitochondrial DNA of specimens collected from the Antarctic continent and two Antarctic islands (AI) to infer past population processes and understand current genetic structure. Demographic history analyses suggest populations survived in refugia during the Last Glacial Maximum. The high genetic diversity found in the Antarctic Peninsula and East Antarctic (EA) seems related to multiple demographic contraction-expansion events associated with deep-sea refugia, while the low genetic diversity in the Weddell Sea points to a more recent expansion from a shelf refugium. We suggest the genetic structure of N. australe from AI reflects recent colonization from the continent. At a local level, EA populations reveal generally low genetic differentiation, geographically and bathymetrically, suggesting limited restrictions to dispersal. Results highlight regional differences in demographic histories and how these relate to the variation in intensity of glaciation-deglaciation events around Antarctica, critical for the study of local evolutionary processes. These are valuable data for understanding the remarkable success of Antarctic pycnogonids, and how environmental changes have shaped the evolution and diversification of Southern Ocean benthic biodiversity.

  16. Seasonal sea ice cover during the warm Pliocene: Evidence from the Iceland Sea (ODP Site 907)

    Science.gov (United States)

    Clotten, Caroline; Stein, Ruediger; Fahl, Kirsten; De Schepper, Stijn

    2018-01-01

    Sea ice is a critical component in the Arctic and global climate system, yet little is known about its extent and variability during past warm intervals, such as the Pliocene (5.33-2.58 Ma). Here, we present the first multi-proxy (IP25, sterols, alkenones, palynology) sea ice reconstructions for the Late Pliocene Iceland Sea (ODP Site 907). Our interpretation of a seasonal sea ice cover with occasional ice-free intervals between 3.50-3.00 Ma is supported by reconstructed alkenone-based summer sea surface temperatures. As evidenced from brassicasterol and dinosterol, primary productivity was low between 3.50 and 3.00 Ma and the site experienced generally oligotrophic conditions. The East Greenland Current (and East Icelandic Current) may have transported sea ice into the Iceland Sea and/or brought cooler and fresher waters favoring local sea ice formation. Between 3.00 and 2.40 Ma, the Iceland Sea is mainly sea ice-free, but seasonal sea ice occurred between 2.81 and 2.74 Ma. Sea ice extending into the Iceland Sea at this time may have acted as a positive feedback for the build-up of the Greenland Ice Sheet (GIS), which underwent a major expansion ∼2.75 Ma. Thereafter, most likely a stable sea ice edge developed close to Greenland, possibly changing together with the expansion and retreat of the GIS and affecting the productivity in the Iceland Sea.

  17. Validation and evaluation of a workstation for monitoring sea ice

    Science.gov (United States)

    McIntyre, Neil; Boardman, Diane; Darwin, David; Sullivan, Ken

    1994-12-01

    Demand for reliable sea ice information comes from many quarters including ship routing and resource exploitation companies, weather forecasting agencies and glaciological research institution. For operational purposes, this information is typically required for local regions on short timescales. To explore this market a prototype sea ice workstation has been developed. The workstation uses data from several current earth observation sensors, combining the advantages of regional survey, all-weather capability and high-resolution imagery. The output from the workstation is an integrated sea ice chart which can be used to display combinations of ice edge, ice type, ice concentrations, ice motion vectors and sea surface temperatures. During the course of its development significant new progress in automated ice classification has been achieved together with the enhancement of existing ice motion algorithms. The quality of the sea ice information from each geophysical algorithm was assessed through validation campaigns which collected independent datasets. The results of this analysis show the ice type classification to be most accurate in identifying multi-year ice; this is probably the most critical ice category for navigational purposes. A program of end-user evaluation has also been started in which sea ice charts are supplied to operational organizations and value-added services. This will continue during 1994 and provide feedback on the use of the workstation in a semi-operational environment.

  18. 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 influenced by thickness below 18 cm (89GHz) and 50 cm (1.4 GHz). Ice concentration retrievals reduced by ice thickness below 0.17 m and 0.33 m, with higher frequency algorithms being less influenced....

  19. Sea ice trends and cyclone activity in the Southern Ocean

    Science.gov (United States)

    Coggins, Jack; McDonald, Adrian; Rack, Wolfgang; Dale, Ethan

    2015-04-01

    Significant trends in the extent of Southern Hemisphere sea ice have been noted over the course of the satellite record, with highly variable trends between different seasons and regions. In this presentation, we describe efforts to assess the impact of cyclones on these trends. Employing a maximum cross-correlation method, we derive Southern Ocean ice-motion vectors from daily gridded SSMI 85.5 GHz brightness temperatures. We then derive a sea ice budget from the NASA-Team 25 km square daily sea ice concentrations. The budget quantifies the total daily change in sea ice area, and includes terms representing the effects of ice advection and divergence. A residual term represents the processes of rafting, ridging, freezing and thawing. We employ a cyclone tracking algorithm developed at the University of Canterbury to determine the timing, location, size and strength of Southern Hemisphere cyclones from mean sea-level pressure fields of the ERA-Interim reanalysis. We then form composites of the of sea ice budget below the location of cyclones. Unsurprisingly, we find that clockwise atmospheric flow around Southern Hemisphere cyclones exerts a strong influence on the movement of sea ice, an effect which is visible in the advection and divergence terms. Further, we assess the climatological importance of cyclones by comparing seasons of sea ice advance for periods with varying numbers of cyclones. This analysis is performed independently for each sea ice concentration pixel, thus affording us insight into the geographical importance of storm systems. We find that Southern Hemisphere sea ice extent is highly sensitive to the presence of cyclones in the periphery of the pack in the advance season. Notably, the sensitivity is particularly high in the northern Ross Sea, an area with a marked positive trend in sea ice extent. We discuss whether trends in cyclone activity in the Southern Ocean may have contributed to sea ice extent trends in this region.

  20. Arctic Sea Ice and Its Changes during the Satellite Period

    Science.gov (United States)

    Wang, X.; Liu, Y.; Key, J. R.

    2009-12-01

    Sea ice is a very important indicator and an effective modulator of regional and global climate change. Changes in sea ice will significantly affect the complex exchanges of momentum, heat, and mass between sea and the atmosphere, along with profound socio-economic influences due to its role in transportation, fisheries, hunting, polar animal habitat. Over the last two decades of the 20th century, the Arctic underwent significant changes in sea ice as part of the accelerated global warming of that period. More accurate, consistent, and detailed ice thickness, extent, and volume data are critical for a wide range of applications including climate change detection, climate modeling, and operational applications such as shipping and hazard mitigation. Satellite data provide an unprecedented opportunity to estimate and monitor Arctic sea ice routinely with relatively high spatial and temporal resolutions. In this study, a One-dimensional Thermodynamic Ice Model (OTIM) has been developed to estimate sea ice thickness based on the surface energy balance at a thermo-equilibrium state, containing all components of the surface energy balance. The OTIM has been extensively validated against submarine Upward-Looking Sonar (ULS) measurements, meteorological station measurements, and comprehensive numerical model simulations. Overall, OTIM-estimated sea ice thickness is accurate to within about 20% error when compared to submarine ULS ice thickness measurements and Canadian meteorological station measurements for ice less than 3 m. Along with sea ice extent information from the SSM/I, the Arctic sea ice volume can be estimated for the satellite period from 1984 to 2004. The OTIM has been used with satellite data from the extended Advanced Very High Resolution Radiometer (AVHRR) Polar Pathfinder (APP-x) products for the Arctic sea ice thickness, and sequentially sea ice volume estimations, and following statistical analysis of spatial and temporal distribution and trends in sea

  1. Sea ice and pollution-modulated changes in Greenland ice core methanesulfonate and bromine

    Science.gov (United States)

    Maselli, Olivia J.; Chellman, Nathan J.; Grieman, Mackenzie; Layman, Lawrence; McConnell, Joseph R.; Pasteris, Daniel; Rhodes, Rachael H.; Saltzman, Eric; Sigl, Michael

    2017-01-01

    Reconstruction of past changes in Arctic sea ice extent may be critical for understanding its future evolution. Methanesulfonate (MSA) and bromine concentrations preserved in ice cores have both been proposed as indicators of past sea ice conditions. In this study, two ice cores from central and north-eastern Greenland were analysed at sub-annual resolution for MSA (CH3SO3H) and bromine, covering the time period 1750-2010. We examine correlations between ice core MSA and the HadISST1 ICE sea ice dataset and consult back trajectories to infer the likely source regions. A strong correlation between the low-frequency MSA and bromine records during pre-industrial times indicates that both chemical species are likely linked to processes occurring on or near sea ice in the same source regions. The positive correlation between ice core MSA and bromine persists until the mid-20th century, when the acidity of Greenland ice begins to increase markedly due to increased fossil fuel emissions. After that time, MSA levels decrease as a result of declining sea ice extent but bromine levels increase. We consider several possible explanations and ultimately suggest that increased acidity, specifically nitric acid, of snow on sea ice stimulates the release of reactive Br from sea ice, resulting in increased transport and deposition on the Greenland ice sheet.

  2. Limited grounding-line advance onto the West Antarctic continental shelf in the easternmost Amundsen Sea Embayment during the last glacial period.

    Science.gov (United States)

    Klages, Johann P; Kuhn, Gerhard; Hillenbrand, Claus-Dieter; Smith, James A; Graham, Alastair G C; Nitsche, Frank O; Frederichs, Thomas; Jernas, Patrycja E; Gohl, Karsten; Wacker, Lukas

    2017-01-01

    Precise knowledge about the extent of the West Antarctic Ice Sheet (WAIS) at the Last Glacial Maximum (LGM; c. 26.5-19 cal. ka BP) is important in order to 1) improve paleo-ice sheet reconstructions, 2) provide a robust empirical framework for calibrating paleo-ice sheet models, and 3) locate potential shelf refugia for Antarctic benthos during the last glacial period. However, reliable reconstructions are still lacking for many WAIS sectors, particularly for key areas on the outer continental shelf, where the LGM-ice sheet is assumed to have terminated. In many areas of the outer continental shelf around Antarctica, direct geological data for the presence or absence of grounded ice during the LGM is lacking because of post-LGM iceberg scouring. This also applies to most of the outer continental shelf in the Amundsen Sea. Here we present detailed marine geophysical and new geological data documenting a sequence of glaciomarine sediments up to ~12 m thick within the deep outer portion of Abbot Trough, a palaeo-ice stream trough on the outer shelf of the Amundsen Sea Embayment. The upper 2-3 meters of this sediment drape contain calcareous foraminifera of Holocene and (pre-)LGM age and, in combination with palaeomagnetic age constraints, indicate that continuous glaciomarine deposition persisted here since well before the LGM, possibly even since the last interglacial period. Our data therefore indicate that the LGM grounding line, whose exact location was previously uncertain, did not reach the shelf edge everywhere in the Amundsen Sea. The LGM grounding line position coincides with the crest of a distinct grounding-zone wedge ~100 km inland from the continental shelf edge. Thus, an area of ≥6000 km2 remained free of grounded ice through the last glacial cycle, requiring the LGM grounding line position to be re-located in this sector, and suggesting a new site at which Antarctic shelf benthos may have survived the last glacial period.

  3. Sea ice roughness: the key for predicting Arctic summer ice albedo

    Science.gov (United States)

    Landy, J.; Ehn, J. K.; Tsamados, M.; Stroeve, J.; Barber, D. G.

    2017-12-01

    Although melt ponds on Arctic sea ice evolve in stages, ice with smoother surface topography typically allows the pond water to spread over a wider area, reducing the ice-albedo and accelerating further melt. Building on this theory, we simulated the distribution of meltwater on a range of statistically-derived topographies to develop a quantitative relationship between premelt sea ice surface roughness and summer ice albedo. Our method, previously applied to ICESat observations of the end-of-winter sea ice roughness, could account for 85% of the variance in AVHRR observations of the summer ice-albedo [Landy et al., 2015]. Consequently, an Arctic-wide reduction in sea ice roughness over the ICESat operational period (from 2003 to 2008) explained a drop in ice-albedo that resulted in a 16% increase in solar heat input to the sea ice cover. Here we will review this work and present new research linking pre-melt sea ice surface roughness observations from Cryosat-2 to summer sea ice albedo over the past six years, examining the potential of winter roughness as a significant new source of sea ice predictability. We will further evaluate the possibility for high-resolution (kilometre-scale) forecasts of summer sea ice albedo from waveform-level Cryosat-2 roughness data in the landfast sea ice zone of the Canadian Arctic. Landy, J. C., J. K. Ehn, and D. G. Barber (2015), Albedo feedback enhanced by smoother Arctic sea ice, Geophys. Res. Lett., 42, 10,714-10,720, doi:10.1002/2015GL066712.

  4. Calibration of sea ice dynamic parameters in an ocean-sea ice model using an ensemble Kalman filter

    Science.gov (United States)

    Massonnet, F.; Goosse, H.; Fichefet, T.; Counillon, F.

    2014-07-01

    The choice of parameter values is crucial in the course of sea ice model development, since parameters largely affect the modeled mean sea ice state. Manual tuning of parameters will soon become impractical, as sea ice models will likely include more parameters to calibrate, leading to an exponential increase of the number of possible combinations to test. Objective and automatic methods for parameter calibration are thus progressively called on to replace the traditional heuristic, "trial-and-error" recipes. Here a method for calibration of parameters based on the ensemble Kalman filter is implemented, tested and validated in the ocean-sea ice model NEMO-LIM3. Three dynamic parameters are calibrated: the ice strength parameter P*, the ocean-sea ice drag parameter Cw, and the atmosphere-sea ice drag parameter Ca. In twin, perfect-model experiments, the default parameter values are retrieved within 1 year of simulation. Using 2007-2012 real sea ice drift data, the calibration of the ice strength parameter P* and the oceanic drag parameter Cw improves clearly the Arctic sea ice drift properties. It is found that the estimation of the atmospheric drag Ca is not necessary if P* and Cw are already estimated. The large reduction in the sea ice speed bias with calibrated parameters comes with a slight overestimation of the winter sea ice areal export through Fram Strait and a slight improvement in the sea ice thickness distribution. Overall, the estimation of parameters with the ensemble Kalman filter represents an encouraging alternative to manual tuning for ocean-sea ice models.

  5. An analysis of Arctic sea ice-atmosphere interaction

    Science.gov (United States)

    Liptak, Jessica M.

    Arctic sea ice is a key component of the climate system, acting as a reflective barrier between the ocean and the atmosphere. The decrease in sea ice over the observational record is associated with several feedback processes, such as the ice-albedo feedback. Here, general sea ice-atmosphere feedback (SAF) is defined in which a sea ice anomaly causes surface and atmospheric responses that either enhance the initial anomaly (positive feedback) or oppose the initial anomaly (negative feedback). Chapters 2 and 3 examine the local SAF over the Barents Sea in an uncoupled modeling framework. Results indicate that the SAF is positive and dominated by the thermodynamic component of the feedback, where anomalously high sea ice cover over the Barents sea favors additional ice growth because it decreases upward surface turbulent heat fluxes, leading to atmospheric cooling and reduced downwelling longwave radiation flux at the surface, while the opposite scenario occurs for anomalously low sea ice cover. Chapter 4 studies the effect of suppressing the SAF in a coupled model by exposing the atmosphere over the Barents Sea to surface turbulent heat fluxes, longwave heat fluxes, and surface temperatures weighted by climatological sea ice cover. Variability in sea ice, atmospheric temperature, and sea surface temperature decrease in response to SAF suppression, indicating that the coupled feedback over the Barents Sea is positive. While thermodynamic processes play a large role in regional sea ice-atmosphere interactions, wind-driven sea ice transport controls the overall Arctic ice mass on annual-and-shorter time scales. Most sea ice is exported from the Arctic through the Fram Strait, and changes in sea ice export are linked to hemispheric-scale atmospheric variability. In Chapter 5, the leading propagating patterns of variability associated with Fram Strait sea ice flux ( F) are determined by applying Hilbert empirical orthogonal function analysis to reanalysis data. The

  6. Impact of climate change on Antarctic krill

    NARCIS (Netherlands)

    Florentino De Souza Silva, A.P.; Atkinson, A.; Kawaguchi, S.; Bravo Rebolledo, E.; Franeker, van J.A.

    2012-01-01

    Antarctic krill Euphausia superba (hereafter ‘krill’) occur in regions undergoing rapid environmental change, particularly loss of winter sea ice. During recent years, harvesting of krill has increased, possibly enhancing stress on krill and Antarctic ecosystems. Here we review the overall impact of

  7. A network model for characterizing brine channels in sea ice

    Directory of Open Access Journals (Sweden)

    R. M. Lieblappen

    2018-03-01

    Full Text Available The brine pore space in sea ice can form complex connected structures whose geometry is critical in the governance of important physical transport processes between the ocean, sea ice, and surface. Recent advances in three-dimensional imaging using X-ray micro-computed tomography have enabled the visualization and quantification of the brine network morphology and variability. Using imaging of first-year sea ice samples at in situ temperatures, we create a new mathematical network model to characterize the topology and connectivity of the brine channels. This model provides a statistical framework where we can characterize the pore networks via two parameters, depth and temperature, for use in dynamical sea ice models. Our approach advances the quantification of brine connectivity in sea ice, which can help investigations of bulk physical properties, such as fluid permeability, that are key in both global and regional sea ice models.

  8. The Arctic-Subarctic Sea Ice System is Entering a Seasonal Regime: Implications for Future Arctic Amplication

    Science.gov (United States)

    Haine, T. W. N.; Martin, T.

    2017-12-01

    The loss of Arctic sea ice is a conspicuous example of climate change. Climate models project ice-free conditions during summer this century under realistic emission scenarios, reflecting the increase in seasonality in ice cover. To quantify the increased seasonality in the Arctic-Subarctic sea ice system, we define a non-dimensional seasonality number for sea ice extent, area, and volume from satellite data and realistic coupled climate models. We show that the Arctic-Subarctic, i.e. the northern hemisphere, sea ice now exhibits similar levels of seasonality to the Antarctic, which is in a seasonal regime without significant change since satellite observations began in 1979. Realistic climate models suggest that this transition to the seasonal regime is being accompanied by a maximum in Arctic amplification, which is the faster warming of Arctic latitudes compared to the global mean, in the 2010s. The strong link points to a peak in sea-ice-related feedbacks that occurs long before the Arctic becomes ice-free in summer.

  9. Collaborations for Arctic Sea Ice Information and Tools

    Science.gov (United States)

    Sheffield Guy, L.; Wiggins, H. V.; Turner-Bogren, E. J.; Rich, R. H.

    2017-12-01

    The dramatic and rapid changes in Arctic sea ice require collaboration across boundaries, including between disciplines, sectors, institutions, and between scientists and decision-makers. This poster will highlight several projects that provide knowledge to advance the development and use of sea ice knowledge. Sea Ice for Walrus Outlook (SIWO: https://www.arcus.org/search-program/siwo) - SIWO is a resource for Alaskan Native subsistence hunters and other interested stakeholders. SIWO provides weekly reports, during April-June, of sea ice conditions relevant to walrus in the northern Bering and southern Chukchi seas. Collaboration among scientists, Alaskan Native sea-ice experts, and the Eskimo Walrus Commission is fundamental to this project's success. Sea Ice Prediction Network (SIPN: https://www.arcus.org/sipn) - A collaborative, multi-agency-funded project focused on seasonal Arctic sea ice predictions. The goals of SIPN include: coordinate and evaluate Arctic sea ice predictions; integrate, assess, and guide observations; synthesize predictions and observations; and disseminate predictions and engage key stakeholders. The Sea Ice Outlook—a key activity of SIPN—is an open process to share and synthesize predictions of the September minimum Arctic sea ice extent and other variables. Other SIPN activities include workshops, webinars, and communications across the network. Directory of Sea Ice Experts (https://www.arcus.org/researchers) - ARCUS has undertaken a pilot project to develop a web-based directory of sea ice experts across institutions, countries, and sectors. The goal of the project is to catalyze networking between individual investigators, institutions, funding agencies, and other stakeholders interested in Arctic sea ice. Study of Environmental Arctic Change (SEARCH: https://www.arcus.org/search-program) - SEARCH is a collaborative program that advances research, synthesizes research findings, and broadly communicates the results to support

  10. Rapid bottom melting widespread near Antarctic ice sheet grounding lines

    Science.gov (United States)

    Rignot, E.; Jacobs, S.

    2002-01-01

    As continental ice from Antartica reaches the grounding line and begins to float, its underside melts into the ocean. Results obtained with satellite radar interferometry reveal that bottom melt rates experienced by large outlet glaciers near their grounding lines are far higher than generally assumed.

  11. Modeling ocean wave propagation under sea ice covers

    Science.gov (United States)

    Zhao, Xin; Shen, Hayley H.; Cheng, Sukun

    2015-02-01

    Operational ocean wave models need to work globally, yet current ocean wave models can only treat ice-covered regions crudely. The purpose of this paper is to provide a brief overview of ice effects on wave propagation and different research methodology used in studying these effects. Based on its proximity to land or sea, sea ice