Sample records for ice core antarctica

  1. The tephrostratigraphy of Mt. Berlin volcano, Antarctica: Integrating blue ice tephra and ice core tephra records

    NASA Astrophysics Data System (ADS)

    Iverson, N. A.; Dunbar, N. W.; McIntosh, W. C.; Kurbatov, A.

    2016-12-01

    Reconstructing volcanic activity in Antarctica is difficult because of the limited outcrop exposure. However, ice is an excellent medium for sampling tephra, allowing for a more complete eruptive record than can be found in other depositional environments. Furthermore, because of low ambient temperature, glass shards trapped in ice remain unaltered and unhydrated. Mt. Berlin is an ice covered volcano in Marie Byrd Land, Antarctica, and, because of heavy glaciation, eruptive records on the volcano itself are sparse. Here, we present the integration of two different records of Mt. Berlin volcanism: the blue ice record found at Mt. Moulton (Dunbar et al., 2008) and the ice core record from the WAIS Divide ice core. Tephra from Mt. Berlin are also found in other ice and marine core records, and these have been correlated and integrated into the combined volcanic record. The Mt. Moulton blue ice area is located 30 km from Mt. Berlin and hosts a fabulous tephra record spanning the last 500 ka. A total of 36 tephra from Mt. Berlin were sampled in stratigraphic order and nine were directly dated by 40Ar/39Ar dating method. Twenty five tephra from WAIS Divide have been analyzed and are geochemically similar to Mt. Berlin with ice core ages dating back to 70 ka. The two tephra records were integrated using their respective timescales. In locations where the Mt. Moulton record does not have precise chronology, the δ18O records from Mt. Moulton (Popp, 2008) and WAIS (WAIS, 2015) were used to integrate the stratigraphy. In total 61 tephra from both ice sections provide an excellent record of the magmatic evolution of Mt. Berlin over the past 500 ka. EMP analyses on glass shards show a gradual change in Fe and S over time. Most of the other major elements remain relatively unchanged. The trend in Fe and S could be produced by progressive tapping of a single, stratified magma chamber, but the long duration of volcanism makes this unlikely. We instead favor small batches of

  2. Estimating Past Temperature Change in Antarctica Based on Ice Core Stable Water Isotope Diffusion

    NASA Astrophysics Data System (ADS)

    Kahle, E. C.; Markle, B. R.; Holme, C.; Jones, T. R.; Steig, E. J.

    2017-12-01

    The magnitude of the last glacial-interglacial transition is a key target for constraining climate sensitivity on long timescales. Ice core proxy records and general circulation models (GCMs) both provide insight on the magnitude of climate change through the last glacial-interglacial transition, but appear to provide different answers. In particular, the magnitude of the glacial-interglacial temperature change reconstructed from East Antarctic ice-core water-isotope records is greater ( 9 degrees C) than that from most GCM simulations ( 6 degrees C). A possible source of this difference is error in the linear-scaling of water isotopes to temperature. We employ a novel, nonlinear temperature-reconstruction technique using the physics of water-isotope diffusion to infer past temperature. Based on new, ice-core data from the South Pole, this diffusion technique suggests East Antarctic temperature change was smaller than previously thought. We are able to confirm this result using a simple, water-isotope fractionation model to nonlinearly reconstruct temperature change at ice core locations across Antarctica based on combined oxygen and hydrogen isotope ratios. Both methods produce a temperature change of 6 degrees C for South Pole, agreeing with GCM results for East Antarctica. Furthermore, both produce much larger changes in West Antarctica, also in agreement with GCM results and independent borehole thermometry. These results support the fidelity of GCMs in simulating last glacial maximum climate, and contradict the idea, based on previous work, that the climate sensitivity of current GCMs is too low.

  3. Ice core evidence for a 20th century increase in surface mass balance in coastal Dronning Maud Land, East Antarctica

    NASA Astrophysics Data System (ADS)

    Philippe, Morgane; Tison, Jean-Louis; Fjøsne, Karen; Hubbard, Bryn; Kjær, Helle A.; Lenaerts, Jan T. M.; Drews, Reinhard; Sheldon, Simon G.; De Bondt, Kevin; Claeys, Philippe; Pattyn, Frank

    2016-10-01

    Ice cores provide temporal records of surface mass balance (SMB). Coastal areas of Antarctica have relatively high and variable SMB, but are under-represented in records spanning more than 100 years. Here we present SMB reconstruction from a 120 m-long ice core drilled in 2012 on the Derwael Ice Rise, coastal Dronning Maud Land, East Antarctica. Water stable isotope (δ18O and δD) stratigraphy is supplemented by discontinuous major ion profiles and continuous electrical conductivity measurements. The base of the ice core is dated to AD 1759 ± 16, providing a climate proxy for the past ˜ 250 years. The core's annual layer thickness history is combined with its gravimetric density profile to reconstruct the site's SMB history, corrected for the influence of ice deformation. The mean SMB for the core's entire history is 0.47 ± 0.02 m water equivalent (w.e.) a-1. The time series of reconstructed annual SMB shows high variability, but a general increase beginning in the 20th century. This increase is particularly marked during the last 50 years (1962-2011), which yields mean SMB of 0.61 ± 0.01 m w.e. a-1. This trend is compared with other reported SMB data in Antarctica, generally showing a high spatial variability. Output of the fully coupled Community Earth System Model (CESM) suggests that, although atmospheric circulation is the main factor influencing SMB, variability in sea surface temperatures and sea ice cover in the precipitation source region also explain part of the variability in SMB. Local snow redistribution can also influence interannual variability but is unlikely to influence long-term trends significantly. This is the first record from a coastal ice core in East Antarctica to show an increase in SMB beginning in the early 20th century and particularly marked during the last 50 years.

  4. RICE ice core: Black Carbon reflects climate variability at Roosevelt Island, West Antarctica

    NASA Astrophysics Data System (ADS)

    Ellis, Aja; Edwards, Ross; Bertler, Nancy; Winton, Holly; Goodwin, Ian; Neff, Peter; Tuohy, Andrea; Proemse, Bernadette; Hogan, Chad; Feiteng, Wang

    2015-04-01

    The Roosevelt Island Climate Evolution (RICE) project successfully drilled a deep ice core from Roosevelt Island during the 2011/2012 and 2012/2013 seasons. Located in the Ross Ice Shelf in West Antarctica, the site is an ideal location for investigating climate variability and the past stability of the Ross Ice Shelf. Black carbon (BC) aerosols are emitted by both biomass burning and fossil fuels, and BC particles emitted in the southern hemisphere are transported in the atmosphere and preserved in Antarctic ice. The past record of BC is expected to be sensitive to climate variability, as it is modulated by both emissions and transport. To investigate BC variability over the past 200 years, we developed a BC record from two overlapping ice cores (~1850-2012) and a high-resolution snow pit spanning 2010-2012 (cal. yr). Consistent results are found between the snow pit profiles and ice core records. Distinct decadal trends are found with respect to BC particle size, and the record indicates a steady rise in BC particle size over the last 100 years. Differences in emission sources and conditions may be a possible explanation for changes in BC size. These records also show a significant increase in BC concentration over the past decade with concentrations rising over 1.5 ppb (1.5*10^-9 ng/g), suggesting a fundamental shift in BC deposition to the site.

  5. Variability of sea salts in ice and firn cores from Fimbul Ice Shelf, Dronning Maud Land, Antarctica

    NASA Astrophysics Data System (ADS)

    Paulina Vega, Carmen; Isaksson, Elisabeth; Schlosser, Elisabeth; Divine, Dmitry; Martma, Tõnu; Mulvaney, Robert; Eichler, Anja; Schwikowski-Gigar, Margit

    2018-05-01

    Major ions were analysed in firn and ice cores located at Fimbul Ice Shelf (FIS), Dronning Maud Land - DML, Antarctica. FIS is the largest ice shelf in the Haakon VII Sea, with an extent of approximately 36 500 km2. Three shallow firn cores (about 20 m deep) were retrieved in different ice rises, Kupol Ciolkovskogo (KC), Kupol Moskovskij (KM), and Blåskimen Island (BI), while a 100 m long core (S100) was drilled near the FIS edge. These sites are distributed over the entire FIS area so that they provide a variety of elevation (50-400 m a.s.l.) and distance (3-42 km) to the sea. Sea-salt species (mainly Na+ and Cl-) generally dominate the precipitation chemistry in the study region. We associate a significant sixfold increase in median sea-salt concentrations, observed in the S100 core after the 1950s, to an enhanced exposure of the S100 site to primary sea-salt aerosol due to a shorter distance from the S100 site to the ice front, and to enhanced sea-salt aerosol production from blowing salty snow over sea ice, most likely related to the calving of Trolltunga occurred during the 1960s. This increase in sea-salt concentrations is synchronous with a shift in non-sea-salt sulfate (nssSO42-) toward negative values, suggesting a possible contribution of fractionated aerosol to the sea-salt load in the S100 core most likely originating from salty snow found on sea ice. In contrast, there is no evidence of a significant contribution of fractionated sea salt to the ice-rises sites, where the signal would be most likely masked by the large inputs of biogenic sulfate estimated for these sites. In summary, these results suggest that the S100 core contains a sea-salt record dominated by the proximity of the site to the ocean, and processes of sea ice formation in the neighbouring waters. In contrast, the ice-rises firn cores register a larger-scale signal of atmospheric flow conditions and a less efficient transport of sea-salt aerosols to these sites. These findings are a

  6. In situ-measurement of ice deformation from repeated borehole logging of the EPICA Dronning Maud Land (EDML) ice core, East Antarctica.

    NASA Astrophysics Data System (ADS)

    Jansen, Daniela; Weikusat, Ilka; Kleiner, Thomas; Wilhelms, Frank; Dahl-Jensen, Dorthe; Frenzel, Andreas; Binder, Tobias; Eichler, Jan; Faria, Sergio H.; Sheldon, Simon; Panton, Christian; Kipfstuhl, Sepp; Miller, Heinrich

    2017-04-01

    The European Project for Ice Coring in Antarctica (EPICA) ice core was drilled between 2001 and 2006 at the Kohnen Station, Antarctica. During the drilling process the borehole was logged repeatedly. Repeated logging of the borehole shape is a means of directly measuring the deformation of the ice sheet not only on the surface but also with depth, and to derive shear strain rates for the lower part, which control the volume of ice transported from the inner continent towards the ocean. The logging system continuously recorded the tilt of the borehole with respect to the vertical (inclination) as well as the heading of the borehole with respect to magnetic north (azimuth) by means of a compass. This dataset provides the basis for a 3-D reconstruction of the borehole shape, which is changing over time according to the predominant deformation modes with depth. The information gained from this analysis can then be evaluated in combination with lattice preferred orientation, grain size and grain shape derived by microstructural analysis of samples from the deep ice core. Additionally, the diameter of the borehole, which was originally circular with a diameter of 10 cm, was measured. As the ice flow velocity at the position of the EDML core is relatively slow (about 0.75 m/a), the changes of borehole shape between the logs during the drilling period were very small and thus difficult to interpret. Thus, the site has been revisited in the Antarctic summer season 2016 and logged again using the same measurement system. The change of the borehole inclination during the time period of 10 years clearly reveals the transition from a pure shear dominated deformation in the upper part of the ice sheet to shear deformation at the base. We will present a detailed analysis of the borehole parameters and the deduced shear strain rates in the lower part of the ice sheet. The results are discussed with respect to ice microstructural data derived from the EDML ice core. Microstructural

  7. A new method for geochemical characterization of atmospheric mineral dust from polar ice cores: preliminary results from Talos Dome ice core (East Antarctica, Pacific-Ross Sea sector)

    NASA Astrophysics Data System (ADS)

    Baccolo, Giovanni; Delmonte, Barbara; Clemenza, Massimiliano; Previtali, Ezio; Maggi, Valter

    2015-04-01

    Assessing the elemental composition of atmospheric dust entrapped in polar ice cores is important for the identification of the potential dust sources and thus for the reconstruction of past atmospheric circulation, at local, regional and global scale. Accurate determination of major and trace elements in the insoluble fraction of dust extracted from ice cores is also useful to better understand some geochemical and biogeochemical mechanisms which are linked with the climate system. The extremely reduced concentration of dust in polar ice (typical Antarctic concentrations during interglacials are in the range of 10 ppb), the limited availability of such samples and the high risk of contamination make these analyses a challenge. A new method based on low background Instrumental Neutron Activation Analysis (INAA) was specifically developed for this kind of samples. The method allows the determination of the concentration of up to 35 elements in extremely reduced dust samples (20-30 μg). These elements span from major to trace and ultra-trace elements. Preliminary results from TALDICE (TALos Dome Ice CorE, East Antarctica, Pacific-Ross Sea Sector) ice core are presented along with results from potential source areas in Victoria Land. A set of 5 samples from Talos Dome, corresponding to the last termination, MIS3, MIS4 and MIS6 were prepared and analyzed by INAA.

  8. Abrupt Late Holocene Shift in Atmospheric Circulation Recorded by Mineral Dust in the Siple Dome Ice Core, Antarctica

    NASA Astrophysics Data System (ADS)

    Koffman, B. G.; Goldstein, S. L.; Kaplan, M. R.; Winckler, G.; Bory, A. J. M.; Biscaye, P.

    2015-12-01

    Atmospheric dust directly influences Earth's climate by altering the radiative balance and by depositing micronutrients in the surface ocean, affecting global biogeochemical cycling. In addition, mineral dust particles provide observational evidence constraining past atmospheric circulation patterns. Because dust can originate from both local and distant terrestrial sources, knowledge of dust provenance can substantially inform our understanding of past climate history, atmospheric transport pathways, and differences in aerosol characteristics between glacial and interglacial climate states. Dust provenance information from Antarctic ice cores has until now been limited to sites in East Antarctica. Here we present some of the first provenance data from West Antarctica. We use Sr-Nd isotopes to characterize dust extracted from late Holocene ice (~1000-1800 C.E.) from the Siple Dome ice core. The data form a tight array in Sr-Nd isotope space, with 87Sr/86Sr ranging between ~0.7087 and 0.7102, and ɛNd ranging between ~ -7 and -16. This combination is unique for Antarctica, with low Nd and low Sr isotope ratios compared to high-elevation East Antarctic sites, requiring a dust source from ancient (Archean to early Proterozoic) and unweathered continental crust, which mixes with young volcanic material. Both components are likely sourced from Antarctica. We also observe significant, systematic variability in Sr and Nd isotopic signatures through time, reflecting changes in the mixing ratio of these sources, and hypothesize that these changes are driven by shifts in circulation patterns. A large change occurs over about 10 years at ca. 1125 C.E. (ΔɛNd = +3 and Δ87Sr/86Sr = -0.0014). This shift coincides with changes in climate proxies in Southern Hemisphere paleoclimate records reflecting variability in the Westerlies. We therefore interpret the shift in dust provenance at Siple Dome to be related to larger-scale circulation changes. In general, the observed shifts

  9. Extensive massive basal-ice structures in West Antarctica relate to ice-sheet anisotropy and ice-flow

    NASA Astrophysics Data System (ADS)

    Ross, N.; Bingham, R. G.; Corr, H. F. J.; Siegert, M. J.

    2016-12-01

    Complex structures identified within both the East Antarctic and Greenland ice sheets are thought to be generated by the action of basal water freezing to the ice-sheet base, evolving under ice flow. Here, we use ice-penetrating radar to image an extensive series of similarly complex basal ice facies in West Antarctica, revealing a thick (>500 m) tectonised unit in an area of cold-based and relatively slow-flowing ice. We show that major folding and overturning of the unit perpendicular to ice flow elevates deep, warm ice into the mid ice-sheet column. Fold axes align with present ice flow, and axis amplitudes increase down-ice, suggesting long-term consistency in the direction and convergence of flow. In the absence of basal water, and the draping of the tectonised unit over major subglacial mountain ranges, the formation of the unit must be solely through the deformation of meteoric ice. Internal layer radar reflectivity is consistently greater parallel to flow compared with the perpendicular direction, revealing ice-sheet crystal anisotropy is associated with the folding. By linking layers to the Byrd ice-core site, we show the basal ice dates to at least the last glacial cycle and may be as old as the last interglacial. Deformation of deep-ice in this sector of WAIS, and potentially elsewhere in Antarctica, may be caused by differential shearing at interglacial-glacial boundaries, in a process analogous to that proposed for interior Greenland. The scale and heterogeneity of the englacial structures, and their subsequent impact on ice sheet rheology, means that the nature of ice flow across the bulk of West Antarctica must be far more complex that is currently accounted for by any numerical ice sheet model.

  10. Balloons on Ice: Launch # 2 takes flight in Antarctica

    NASA Image and Video Library

    2017-12-08

    The second of three missions as part of NASA’s Antarctica Long Duration Balloon Flight Campaign was successfully launched at 8:10 a.m. EDT, Dec. 2. The Antarctic Impulsive Transient Antenna (ANITA) from the University of Hawaii at Manoa was launched from Antarctica’s Ross Ice Shelf near McMurdo Station with support from the National Science Foundation’s United States Antarctic Program. Scientists will use ANITA’s instruments to study the reactions in the core of stars and as they explode via the release of neutrinos that travel to Earth and interact with the Antarctica ice. More: go.nasa.gov/2ghR6Le

  11. Holocene Accumulation and Ice Flow near the West Antarctic Ice Sheet Divide Ice Core Site

    NASA Technical Reports Server (NTRS)

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

    2016-01-01

    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 thousand years 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 kilometers 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 percent lower than modern at 9.2 thousand years before present (B.P.), increased by 40 percent from 9.2 to 2.3 thousand years B.P., and decreased by at least 10 percent over the past 2 thousand years 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 kilometers of its modern position. Continent-scale ice-sheet models used for reconstructions of West Antarctic ice volume should incorporate this accumulation history.

  12. Raman spectroscopy on ice cores from Greenland and Antarctica

    NASA Astrophysics Data System (ADS)

    Weikusat, C.; Kipfstuhl, S.

    2012-04-01

    Ice cores are invaluable archives for the reconstruction of the climatic history of the earth. Besides the analysis of various climatic processes from isotopes and chemical signatures they offer the unique possibility of directly extracting the past atmosphere from gaseous inclusions in the ice. Many aspects of the formation and alterations of these inclusions, e.g. the entrapment of air at the firn-ice-transition, the formation of crystalline gas hydrates (clathrates) from the bubbles or the structural relaxation during storage of the cores, need to be better understood to enable reliable interpretations of the obtained data. Modern micro Raman spectroscopy is an excellent tool to obtain high-quality data for all of these aspects. It has been productively used for phase identification of solid inclusions [1], investigation of air clathrates [2] and high-resolution measurements of N2/O2 mixing ratios inside individual air bubbles [3,4]. Detailed examples of the various uses of Raman spectroscopy will be presented along with practical information about the techniques required to obtain high-quality spectra. Retrieval and interpretation of quantitative data from the spectra will be explained. Future possibilities for advanced uses of Raman spectroscopy for ice core research will be discussed. [1] T. Sakurai et al., 2009, Direct observation of salts as micro-inclusions in the Greenland GRIP ice core. Journal of Glaciology, 55, 777-783. [2] F. Pauer et al., 1995, Raman spectroscopic study of nitrogen/oxygen ratio in natural ice clathrates in the GRIP ice core. Geophysical Research Letters, 22, 969-971. [3] T. Ikeda-Fukazawa et al., 2001, Variation in N2/O2 ratio of occluded air in Dome Fuji antarctic ice. Journal of Geophysical Research, 106, 17799-17810. [4] C. Weikusat et al., Raman spectroscopy of gaseous inclusions in EDML ice core: First results - microbubbles. Journal of Glaciology, accepted.

  13. Ice crystal c-axis orientation and mean grain size measurements from the Dome Summit South ice core, Law Dome, East Antarctica

    NASA Astrophysics Data System (ADS)

    Treverrow, Adam; Jun, Li; Jacka, Tim H.

    2016-06-01

    We present measurements of crystal c-axis orientations and mean grain area from the Dome Summit South (DSS) ice core drilled on Law Dome, East Antarctica. All measurements were made on location at the borehole site during drilling operations. The data are from 185 individual thin sections obtained between a depth of 117 m below the surface and the bottom of the DSS core at a depth of 1196 m. The median number of c-axis orientations recorded in each thin section was 100, with values ranging from 5 through to 111 orientations. The data from all 185 thin sections are provided in a single comma-separated value (csv) formatted file which contains the c-axis orientations in polar coordinates, depth information for each core section from which the data were obtained, the mean grain area calculated for each thin section and other data related to the drilling site. The data set is also available as a MATLAB™ structure array. Additionally, the c-axis orientation data from each of the 185 thin sections are summarized graphically in figures containing a Schmidt diagram, histogram of c-axis colatitudes and rose plot of c-axis azimuths. All these data are referenced by doi:10.4225/15/5669050CC1B3B and are available free of charge at antarctica.gov.au" target="_blank">https://data.antarctica.gov.au.<

  14. Chemistry of microparticles trapped in last glacial period ice of EPICA-DML deep ice core

    NASA Astrophysics Data System (ADS)

    Nedelcu, Aneta F.; Faria, Sérgio H.; Kipfstuhl, Sepp; Kuhs, Werner F.

    2010-05-01

    The EDML ice core, drilled within the framework of the European project for Ice Coring in Antarctica, (EPICA), in the interior of Dronning Maud Land, DML, Antarctica (at 75°S, 0°E), is the first deep ice core in the Atlantic sector of the Southern Ocean region that provides higher-resolution atmosphere and climate records for the last glacial period, when compared with other ice cores retrieved from the East Antarctic plateau [1]. The chemical impurities embedded in the ice matrix of an ice sheet are basic proxies for climate reconstruction, and their concentration and composition usually determine the occurrence of distinct (cloudy or clear) strata in the ice sheet structure. The easiest observable impurities in polar ice are air bubbles. But a considerable amount of the impurities trapped inside ice layers are observed as microscopic deposits of solid (soluble or insoluble) particles, not bigger than a few micra in size, called microinclusions. Layers of ice with a high content of (micro)inclusions are in general called cloudy bands and are considered to have been formed from the precipitations deposited during colder periods. Roughly, we expect that the colder the climate during the time the snow accumulated, the cloudier the ice stratum that forms afterwards [2]. Mainly by means of in-situ micro-Raman spectroscopy, it has been shown that in Antarctic glacial ice the soluble microinclusions occur mostly as sulphate and nitrate salts [3], while in Arctic ice more commonly as carbonate salts [4]. These findings could be explained in terms of different aerosol compositions determined by the specific regional environments and climatic conditions [5]. Regarding the insoluble particles that might exist in natural ice, with higher frequency in ice layers formed during glacial type stages, the general findings classify them in the (alumino)silicate mineralogical class [6]. Microinclusions existent in solid samples taken from clear and cloudy ice layers, corresponding

  15. Roosevelt Island Climate Evolution Project (RICE): A 65 Kyr ice core record of black carbon aerosol deposition to the Ross Ice Shelf, West Antarctica.

    NASA Astrophysics Data System (ADS)

    Edwards, Ross; Bertler, Nancy; Tuohy, Andrea; Neff, Peter; Proemse, Bernedette; Feiteng, Wang; Goodwin, Ian; Hogan, Chad

    2015-04-01

    Emitted by fires, black carbon aerosols (rBC) perturb the atmosphere's physical and chemical properties and are climatically active. Sedimentary charcoal and other paleo-fire records suggest that rBC emissions have varied significantly in the past due to human activity and climate variability. However, few paleo rBC records exist to constrain reconstructions of the past rBC atmospheric distribution and its climate interaction. As part of the international Roosevelt Island Climate Evolution (RICE) project, we have developed an Antarctic rBC ice core record spanning the past ~65 Kyr. The RICE deep ice core was drilled from the Roosevelt Island ice dome in West Antarctica from 2011 to 2013. The high depth resolution (~ 1 cm) record was developed using a single particle intracavity laser-induced incandescence soot photometer (SP2) coupled to an ice core melter system. The rBC record displays sub-annual variability consistent with both austral dry-season and summer biomass burning. The record exhibits significant decadal to millennial-scale variability consistent with known changes in climate. Glacial rBC concentrations were much lower than Holocene concentrations with the exception of several periods of abrupt increases in rBC. The transition from glacial to interglacial rBC concentrations occurred over a much longer time relative to other ice core climate proxies such as water isotopes and suggests . The protracted increase in rBC during the transition may reflected Southern hemisphere ecosystem / fire regime changes in response to hydroclimate and human activity.

  16. Cryoconite and Ice-bubble Microbial Ecosystems in Antarctica

    NASA Technical Reports Server (NTRS)

    Hoover, Richard B.; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    During the Antarctica 2000 Expedition samples of rocks and ice bubbles entrained in ice were collected from the blue ice fields near the Moulton Escarpment of the Thiel Mountains (85S, 94W) and the Morris Moraine of the Patriot Hills (80S, 8 1 W) Ellsworth Mountains of Antarctica. Investigation of the microbiota of these cryoconite and ice bubble ecosystems are now being conducted to help refine chemical and morphological biomarkers of potential significance to Astrobiology. The Antarctica 2000 Expedition will be discussed and the preliminary results of the studies of the ice bubble and cryoconite microbial ecosystems discussed. Recent ESEM images of the Antarctic microbiota will be presented a the relevance of ice ecosystems to Astrobiology will be discussed.

  17. Ice core carbonyl sulfide measurements from a new South Pole ice core (SPICECORE)

    NASA Astrophysics Data System (ADS)

    Aydin, M.; Nicewonger, M. R.; Saltzman, E. S.

    2017-12-01

    Carbonyl sulfide (COS) is the most abundant sulfur gas in the troposphere with a present-day mixing ratio of about 500 ppt. Direct and indirect emissions from the oceans are the predominant sources of atmospheric COS. The primary removal mechanism is uptake by terrestrial plants during photosynthesis. Because plants do not respire COS, atmospheric COS levels are linked to terrestrial gross primary productivity (GPP). Ancient air trapped in polar ice cores has been used to reconstruct COS records of the past atmosphere, which can be used to infer past GPP variability and potential changes in oceanic COS emission. We are currently analyzing samples from a newly drilled intermediate depth ice core from South Pole, Antarctica (SPICECORE). This core is advantageous for studying COS because the cold temperatures of South Pole ice lead to very slow rates of in situ loss due to hydrolysis. One hundred and eighty-four bubbly ice core samples have been analyzed to date with gas ages ranging from about 9.2 thousand (733 m depth) to 75 years (126 m depth) before present. After a 2% correction for gravitational enrichment in the firn, the mean COS mixing ratio for the data set is 312±15 ppt (±1s), with the data set median also equal to 312 ppt. The only significant long-term trend in the record is a 5-10% increase in COS during the last 2-3 thousand years of the Holocene. The SPICECORE data agree with previously published ice core COS records from other Antarctic sites during times of overlap, confirming earlier estimates of COS loss rates to in situ hydrolysis in ice cores. Antarctic ice core data place strict constraints on the COS mixing ratio and its range of variability in the southern hemisphere atmosphere during the last several millennia. Implications for the atmospheric COS budget will be discussed.

  18. Isotopic (δ18O, δD and deuterium excess) records from the TALDICE ice core (East Antarctica) (Invited)

    NASA Astrophysics Data System (ADS)

    Stenni, B.; Buiron, D.; Masson-Delmotte, V.; Bonazza, M.; Braida, M.; Chappellaz, J.; Frezzotti, M.; Falourd, S.; Minster, B.; Selmo, E.

    2010-12-01

    Paleotemperature reconstructions from Antarctic ice cores rely mainly on δD and δ18O records and the main key factors controlling the observed distribution of δD and δ18O in Antarctic surface snow are mainly related to the condensation temperature of the precipitation and the origin of moisture. The deuterium excess, d = δD - 8*δ18O, contains information about climate conditions prevailing in the source regions of precipitation and can be used as an integrated tracer of past hydrological cycle changes. In the framework of the TALos Dome Ice CorE (TALDICE) project, a deep ice core (1620 m) has been drilled at Talos Dome, a peripheral dome of East Antarctica facing the Ross Sea, about 550 km north of Taylor Dome and 1100 km East from the EPICA Dome C drilling site. The TALDICE coring site (159°11'E 72°49'S; 2315 m; T -41°C; www.taldice.org) is located near the dome summit and is characterised by an annual snow accumulation rate of 80 mm water equivalent. Backtrajectory analyses suggest that Talos Dome is mainly influenced by air masses arriving both from the Pacific (Ross Sea) and Indian Ocean sectors. A preliminary dating based on an ice flow model and an inverse method suggests for the upper 1580 m an age of about 300,000 years BP. The full TALDICE δ18O record obtained from the bag samples as well as δD and deuterium excess data are presented here. The δ18O and δD measurements were carried out in Italy and France on a continuous basis of 1 m. These new records will be compared to the ones obtained from the EDC ice core as well as with other East Antarctic ice core records. In particular, we will focus on the whole isotopic profiles, in good agreement with other inland deep ice cores, and on the last deglaciation, showing climatic changes at Talos Dome in phase with the Antarctic plateau and suggesting that the bipolar see saw with Greenland temperature is also valid for this new coastal site facing the Ross Sea sector.

  19. Surface studies of water isotopes in Antarctica for quantitative interpretation of deep ice core data

    NASA Astrophysics Data System (ADS)

    Landais, Amaelle; Casado, Mathieu; Prié, Frédéric; Magand, Olivier; Arnaud, Laurent; Ekaykin, Alexey; Petit, Jean-Robert; Picard, Ghislain; Fily, Michel; Minster, Bénédicte; Touzeau, Alexandra; Goursaud, Sentia; Masson-Delmotte, Valérie; Jouzel, Jean; Orsi, Anaïs

    2017-07-01

    Polar ice cores are unique climate archives. Indeed, most of them have a continuous stratigraphy and present high temporal resolution of many climate variables in a single archive. While water isotopic records (δD or δ18O) in ice cores are often taken as references for past atmospheric temperature variations, their relationship to temperature is associated with a large uncertainty. Several reasons are invoked to explain the limitation of such an approach; in particular, post-deposition effects are important in East Antarctica because of the low accumulation rates. The strong influence of post-deposition processes highlights the need for surface polar research programs in addition to deep drilling programs. We present here new results on water isotopes from several recent surface programs, mostly over East Antarctica. Together with previously published data, the new data presented in this study have several implications for the climatic reconstructions based on ice core isotopic data: (1) The spatial relationship between surface mean temperature and mean snow isotopic composition over the first meters in depth can be explained quite straightforwardly using simple isotopic models tuned to d-excess vs. δ18O evolution in transects on the East Antarctic sector. The observed spatial slopes are significantly higher (∼ 0.7-0.8‰·°C-1 for δ18O vs. temperature) than seasonal slopes inferred from precipitation data at Vostok and Dome C (0.35 to 0.46‰·°C-1). We explain these differences by changes in condensation versus surface temperature between summer and winter in the central East Antarctic plateau, where the inversion layer vanishes in summer. (2) Post-deposition effects linked to exchanges between the snow surface and the atmospheric water vapor lead to an evolution of δ18O in the surface snow, even in the absence of any precipitation event. This evolution preserves the positive correlation between the δ18O of snow and surface temperature, but is

  20. Records of climatic changes and volcanic events in an ice core from Central Dronning Maud Land (East Antarctica) during the past century

    NASA Astrophysics Data System (ADS)

    Nijampurkar, V. N.; Rao, D. K.; Clausen, H. B.; Kaul, M. K.; Chaturvedi, A.

    2002-03-01

    The depth profiles of electrical conductance, δ18O,210Pb and cosmogenic radio isotopes10Be and36Cl have been measured in a 30 m ice core from east Antarctica near the Indian station, Dakshin Gangotri. Using210Pb and δ18O, the mean annual accumulation rates have been calculated to be 20 and 21 cm of ice equivalent per year during the past ˜ 150 years. Using these acumulation rates, the volcanic event that occurred in 1815 AD, has been identified based on electrical conductance measurements. Based on δ18O measurements, the mean annual surface air temperatures (MASAT) data observed during the last 150 years indicates that the beginning of the 19th century was cooler by about 2‡ C than the recent past and the middle of 18th century. The fallout of cosmogenic radio isotope10Be compares reasonably well with those obtained on other stations (73‡ S to 90‡ S) from Antarctica and higher latitudes beyond 77‡N. The fallout of36Cl calculated based on the present work agrees well with the mean global production rate estimated earlier by Lal and Peters (1967). The bomb pulse of36Cl observed in Greenland is not observed in the present studies - a result which is puzzling and needs to be studied on neighbouring ice cores from the same region.

  1. Ice core age dating and paleothermometer calibration based on isotope and temperature profiles from deep boreholes at Vostok Station (East Antarctica)

    NASA Astrophysics Data System (ADS)

    Salamatin, Andrey N.; Lipenkov, Vladimir Y.; Barkov, Nartsiss I.; Jouzel, Jean; Petit, Jean Robert; Raynaud, Dominique

    1998-04-01

    An interpretation of the deuterium profile measured along the Vostok (East Antarctica) ice core down to 2755 m has been attempted on the basis of the borehole temperature analysis. An inverse problem is solved to infer a local "geophysical metronome," the orbital signal in the surface temperature oscillations expressed as a sum of harmonics of Milankovich periods. By correlating the smoothed isotopic temperature record to the metronome, a chronostratigraphy of the Vostok ice core is derived with an accuracy of ±3.0-4.5 kyr. The developed timescale predicts an age of 241 kyr at a depth of 2760 m. The ratio δD/δTi between deuterium content and cloud temperature fluctuations (at the top of the inversion layer) is examined by fitting simulated and measured borehole temperature profiles. The conventional estimate of the deuterium-temperature slope corresponding to the present-day spatial ratio (9 per mil/°C) is confirmed in general. However, the mismatch between modeled and measured borehole temperatures decreases noticeably if we allow surface temperature, responsible for the thermal state of the ice sheet, to undergo more intensive precession oscillations than those of the inversion temperature traced by isotope record. With this assumption, we obtain the long-term temporal deuterium-temperature slope to be 5.8-6.5 per mil/°C which implies that the glacial-interglacial temperature increase over central Antarctica was about 15°C in the surface temperature and 10°C in the inversion temperature. Past variations of the accumulation rate and the corresponding changes in the ice-sheet surface elevation are simultaneously simulated.

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

    PubMed

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

    2016-07-05

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

  3. A review of sea ice proxy information from polar ice cores

    NASA Astrophysics Data System (ADS)

    Abram, Nerilie J.; Wolff, Eric W.; Curran, Mark A. J.

    2013-11-01

    Sea ice plays an important role in Earth's climate system. The lack of direct indications of past sea ice coverage, however, means that there is limited knowledge of the sensitivity and rate at which sea ice dynamics are involved in amplifying climate changes. As such, there is a need to develop new proxy records for reconstructing past sea ice conditions. Here we review the advances that have been made in using chemical tracers preserved in ice cores to determine past changes in sea ice cover around Antarctica. Ice core records of sea salt concentration show promise for revealing patterns of sea ice extent particularly over glacial-interglacial time scales. In the coldest climates, however, the sea salt signal appears to lose sensitivity and further work is required to determine how this proxy can be developed into a quantitative sea ice indicator. Methane sulphonic acid (MSA) in near-coastal ice cores has been used to reconstruct quantified changes and interannual variability in sea ice extent over shorter time scales spanning the last ˜160 years, and has potential to be extended to produce records of Antarctic sea ice changes throughout the Holocene. However the MSA ice core proxy also requires careful site assessment and interpretation alongside other palaeoclimate indicators to ensure reconstructions are not biased by non-sea ice factors, and we summarise some recommended strategies for the further development of sea ice histories from ice core MSA. For both proxies the limited information about the production and transfer of chemical markers from the sea ice zone to the Antarctic ice sheets remains an issue that requires further multidisciplinary study. Despite some exploratory and statistical work, the application of either proxy as an indicator of sea ice change in the Arctic also remains largely unknown. As information about these new ice core proxies builds, so too does the potential to develop a more comprehensive understanding of past changes in sea

  4. Ice-shelf melting around Antarctica

    NASA Astrophysics Data System (ADS)

    Rignot, E.; Jacobs, S.

    2008-12-01

    The traditional view on the mass balance of Antarctic ice shelves is that they loose mass principally from iceberg calving with bottom melting a much lower contributing factor. Because ice shelves are now known to play a fundamental role in ice sheet evolution, it is important to re-evaluate their wastage processes from a circumpolar perspective using a combination of remote sensing techniques. We present area average rates deduced from grounding line discharge, snow accumulation, firn depth correction and ice shelf topography. We find that ice shelf melting accounts for roughly half of ice-shelf ablation, with a total melt water production of 1027 Gt/yr. The attrition fraction due to in-situ melting varies from 9 to 90 percent around Antarctica. High melt producers include the Ronne, Ross, Getz, Totten, Amery, George VI, Pine Island, Abbot, Dotson/Crosson, Shackleton, Thwaites and Moscow University Ice Shelves. Low producers include the Larsen C, Princess Astrid and Ragnhild coast, Fimbul, Brunt and Filchner. Correlation between melt water production and grounding line discharge is low (R2 = 0.65). Correlation with thermal ocean forcing from the ocean are highest in the northern parts of West Antarctica where regressions yield R2 of 0.93-0.97. Melt rates in the Amundsen Sea exhibit a quadratic sensitivity to thermal ocean forcing. We conclude that ice shelf melting plays a dominant role in ice shelf mass balance, with a potential to change rapidly in response to altered ocean heat transport onto the Antarctic continental shelf.

  5. Assessment of local and regional climate signals in water stable isotopes and chemistry records from new high resolution shallow ice cores in Adélie Land, Antarctica

    NASA Astrophysics Data System (ADS)

    Goursaud, Sentia; Masson Delmotte, Valerie; Preunkert, Susanne; Legrand, Michel; Werner, Martin

    2017-04-01

    Documenting climatic variations in Antarctica is important to characterize natural climate variability and to provide a long-term context for recent changes. For this purpose, ice cores are unique archives providing a variety of proxy records. While water stable isotopes are commonly used to reconstruct past temperatures, their variability may also reflect changes in moisture origin and evaporation conditions. Further information on the origin of air masses can be obtained from aerosols, through the chemical analyses of ice cores. In high accumulation regions, such as the coastal Adélie Land area, the combination of water stable isotope and chemical records is crucial to date ice cores by annual layer counting and assess the associated uncertainty on annual accumulation rates, but may also help to unveil past changes in regional atmospheric circulation. In order to document accumulation in the area from Dumont d'Urville station to the central Antarctic plateau, towards Dome C, the Agence Nationale de la Recherche ASUMA project (Improving the Accuracy of the Surface Mass Balance of Antarctica, 2014-2018) initiated new field campaigns and was successful in obtaining a network of new shallow ice cores in a previously undocumented region. Here, we will present new results from two shallow ice cores drilled in Adélie Land, the S1C1 ice core (67.71 °S, 139.83 °E ,279 m a.s.l.) drilled in January 2007 and the TA192A ice core (66.78 °S, 139.56 °E, 602 m a.s.l.). We have dated the ice cores by combining multi-parameter annual layer counting using major ions and δ18O, as well as reference horizons. This allowed us to estimate very contrasted accumulation rates (respectively 21.8 ± 6.9 cm w.e. y-1 and 73.38±21.9 cm w.e. y-1), averaged respectively over the period from 1946 to 2006 and from 1998 to 2014 . As a result, we have reconstructed annual accumulation rates, isotopic and ion time series, and investigated their characteristics (mean values, trends and

  6. Chemical compositions of sulfate and chloride salts over the last termination reconstructed from the Dome Fuji ice core, inland Antarctica

    NASA Astrophysics Data System (ADS)

    Oyabu, Ikumi; Iizuka, Yoshinori; Uemura, Ryu; Miyake, Takayuki; Hirabayashi, Motohiro; Motoyama, Hideaki; Sakurai, Toshimitsu; Suzuki, Toshitaka; Hondoh, Takeo

    2014-12-01

    The flux and chemical composition of aerosols impact the climate. Antarctic ice cores preserve the record of past atmospheric aerosols, providing useful information about past atmospheric environments. However, few studies have directly measured the chemical composition of aerosol particles preserved in ice cores. Here we present the chemical compositions of sulfate and chloride salts from aerosol particles in the Dome Fuji ice core. The analysis method involves ice sublimation, and the period covers the last termination, 25.0-11.0 thousand years before present (kyr B.P.), with a 350 year resolution. The major components of the soluble particles are CaSO4, Na2SO4, and NaCl. The dominant sulfate salt changes at 16.8 kyr B.P. from CaSO4, a glacial type, to Na2SO4, an interglacial type. The sulfate salt flux (CaSO4 plus Na2SO4) inversely correlates with δ18O in Dome Fuji over millennial timescales. This correlation is consistent with the idea that sulfate salt aerosols contributed to the last deglacial warming of inland Antarctica by reducing the aerosol indirect effect. Between 16.3 and 11.0 kyr B.P., the presence of NaCl suggests that winter atmospheric aerosols are preserved. A high NaCl/Na2SO4 fraction between 12.3 and 11.0 kyr B.P. indicates that the contribution from the transport of winter atmospheric aerosols increased during this period.

  7. The Ross Sea Dipole - temperature, snow accumulation and sea ice variability in the Ross Sea region, Antarctica, over the past 2700 years

    NASA Astrophysics Data System (ADS)

    Bertler, Nancy A. N.; Conway, Howard; Dahl-Jensen, Dorthe; Emanuelsson, Daniel B.; Winstrup, Mai; Vallelonga, Paul T.; Lee, James E.; Brook, Ed J.; Severinghaus, Jeffrey P.; Fudge, Taylor J.; Keller, Elizabeth D.; Baisden, W. Troy; Hindmarsh, Richard C. A.; Neff, Peter D.; Blunier, Thomas; Edwards, Ross; Mayewski, Paul A.; Kipfstuhl, Sepp; Buizert, Christo; Canessa, Silvia; Dadic, Ruzica; Kjær, Helle A.; Kurbatov, Andrei; Zhang, Dongqi; Waddington, Edwin D.; Baccolo, Giovanni; Beers, Thomas; Brightley, Hannah J.; Carter, Lionel; Clemens-Sewall, David; Ciobanu, Viorela G.; Delmonte, Barbara; Eling, Lukas; Ellis, Aja; Ganesh, Shruthi; Golledge, Nicholas R.; Haines, Skylar; Handley, Michael; Hawley, Robert L.; Hogan, Chad M.; Johnson, Katelyn M.; Korotkikh, Elena; Lowry, Daniel P.; Mandeno, Darcy; McKay, Robert M.; Menking, James A.; Naish, Timothy R.; Noerling, Caroline; Ollive, Agathe; Orsi, Anaïs; Proemse, Bernadette C.; Pyne, Alexander R.; Pyne, Rebecca L.; Renwick, James; Scherer, Reed P.; Semper, Stefanie; Simonsen, Marius; Sneed, Sharon B.; Steig, Eric J.; Tuohy, Andrea; Ulayottil Venugopal, Abhijith; Valero-Delgado, Fernando; Venkatesh, Janani; Wang, Feitang; Wang, Shimeng; Winski, Dominic A.; Winton, V. Holly L.; Whiteford, Arran; Xiao, Cunde; Yang, Jiao; Zhang, Xin

    2018-02-01

    High-resolution, well-dated climate archives provide an opportunity to investigate the dynamic interactions of climate patterns relevant for future projections. Here, we present data from a new, annually dated ice core record from the eastern Ross Sea, named the Roosevelt Island Climate Evolution (RICE) ice core. Comparison of this record with climate reanalysis data for the 1979-2012 interval shows that RICE reliably captures temperature and snow precipitation variability in the region. Trends over the past 2700 years in RICE are shown to be distinct from those in West Antarctica and the western Ross Sea captured by other ice cores. For most of this interval, the eastern Ross Sea was warming (or showing isotopic enrichment for other reasons), with increased snow accumulation and perhaps decreased sea ice concentration. However, West Antarctica cooled and the western Ross Sea showed no significant isotope temperature trend. This pattern here is referred to as the Ross Sea Dipole. Notably, during the Little Ice Age, West Antarctica and the western Ross Sea experienced colder than average temperatures, while the eastern Ross Sea underwent a period of warming or increased isotopic enrichment. From the 17th century onwards, this dipole relationship changed. All three regions show current warming, with snow accumulation declining in West Antarctica and the eastern Ross Sea but increasing in the western Ross Sea. We interpret this pattern as reflecting an increase in sea ice in the eastern Ross Sea with perhaps the establishment of a modern Roosevelt Island polynya as a local moisture source for RICE.

  8. The design and performance of IceCube DeepCore

    NASA Astrophysics Data System (ADS)

    Abbasi, R.; Abdou, Y.; Abu-Zayyad, T.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Allen, M. M.; Altmann, D.; Andeen, K.; Auffenberg, J.; Bai, X.; Baker, M.; Barwick, S. W.; Bay, R.; Bazo Alba, J. L.; Beattie, K.; Beatty, J. J.; Bechet, S.; Becker, J. K.; Becker, K.-H.; Benabderrahmane, M. L.; BenZvi, S.; Berdermann, J.; Berghaus, P.; Berley, D.; Bernardini, E.; Bertrand, D.; Besson, D. Z.; Bindig, D.; Bissok, M.; Blaufuss, E.; Blumenthal, J.; Boersma, D. J.; Bohm, C.; Bose, D.; Böser, S.; Botner, O.; Brown, A. M.; Buitink, S.; Caballero-Mora, K. S.; Carson, M.; Chirkin, D.; Christy, B.; Clevermann, F.; Cohen, S.; Colnard, C.; Cowen, D. F.; Cruz Silva, A. H.; D'Agostino, M. V.; Danninger, M.; Daughhetee, J.; Davis, J. C.; De Clercq, C.; Degner, T.; Demirörs, L.; Descamps, F.; Desiati, P.; de Vries-Uiterweerd, G.; DeYoung, T.; Díaz-Vélez, J. C.; Dierckxsens, M.; Dreyer, J.; Dumm, J. P.; Dunkman, M.; Eisch, J.; Ellsworth, R. W.; Engdegård, O.; Euler, S.; Evenson, P. A.; Fadiran, O.; Fazely, A. R.; Fedynitch, A.; Feintzeig, J.; Feusels, T.; Filimonov, K.; Finley, C.; Fischer-Wasels, T.; Fox, B. D.; Franckowiak, A.; Franke, R.; Gaisser, T. K.; Gallagher, J.; Gerhardt, L.; Gladstone, L.; Glüsenkamp, T.; Goldschmidt, A.; Goodman, J. A.; Góra, D.; Grant, D.; Griesel, T.; Groß, A.; Grullon, S.; Gurtner, M.; Ha, C.; Haj Ismail, A.; Hallgren, A.; Halzen, F.; Han, K.; Hanson, K.; Heinen, D.; Helbing, K.; Hellauer, R.; Hickford, S.; Hill, G. C.; Hoffman, K. D.; Hoffmann, B.; Homeier, A.; Hoshina, K.; Huelsnitz, W.; Hülß, J.-P.; Hulth, P. O.; Hultqvist, K.; Hussain, S.; Ishihara, A.; Jacobi, E.; Jacobsen, J.; Japaridze, G. S.; Johansson, H.; Kampert, K.-H.; Kappes, A.; Karg, T.; Karle, A.; Kenny, P.; Kiryluk, J.; Kislat, F.; Klein, S. R.; Köhne, J.-H.; Kohnen, G.; Kolanoski, H.; Köpke, L.; Koskinen, D. J.; Kowalski, M.; Kowarik, T.; Krasberg, M.; Kroll, G.; Kurahashi, N.; Kuwabara, T.; Labare, M.; Laihem, K.; Landsman, H.; Larson, M. J.; Lauer, R.; Lünemann, J.; Madsen, J.; Marotta, A.; Maruyama, R.; Mase, K.; Matis, H. S.; Meagher, K.; Merck, M.; Mészáros, P.; Meures, T.; Miarecki, S.; Middell, E.; Milke, N.; Miller, J.; Montaruli, T.; Morse, R.; Movit, S. M.; Nahnhauer, R.; Nam, J. W.; Naumann, U.; Nygren, D. R.; Odrowski, S.; Olivas, A.; Olivo, M.; O'Murchadha, A.; Panknin, S.; Paul, L.; Pérez de los Heros, C.; Petrovic, J.; Piegsa, A.; Pieloth, D.; Porrata, R.; Posselt, J.; Price, P. B.; Przybylski, G. T.; Rawlins, K.; Redl, P.; Resconi, E.; Rhode, W.; Ribordy, M.; Richman, M.; Rodrigues, J. P.; Rothmaier, F.; Rott, C.; Ruhe, T.; Rutledge, D.; Ruzybayev, B.; Ryckbosch, D.; Sander, H.-G.; Santander, M.; Sarkar, S.; Schatto, K.; Schmidt, T.; Schönwald, A.; Schukraft, A.; Schultes, A.; Schulz, O.; Schunck, M.; Seckel, D.; Semburg, B.; Seo, S. H.; Sestayo, Y.; Seunarine, S.; Silvestri, A.; Spiczak, G. M.; Spiering, C.; Stamatikos, M.; Stanev, T.; Stezelberger, T.; Stokstad, R. G.; Stößl, A.; Strahler, E. A.; Ström, R.; Stüer, M.; Sullivan, G. W.; Swillens, Q.; Taavola, H.; Taboada, I.; Tamburro, A.; Tepe, A.; Ter-Antonyan, S.; Tilav, S.; Toale, P. A.; Toscano, S.; Tosi, D.; van Eijndhoven, N.; Vandenbroucke, J.; Van Overloop, A.; van Santen, J.; Vehring, M.; Voge, M.; Walck, C.; Waldenmaier, T.; Wallraff, M.; Walter, M.; Weaver, Ch.; Wendt, C.; Westerhoff, S.; Whitehorn, N.; Wiebe, K.; Wiebusch, C. H.; Williams, D. R.; Wischnewski, R.; Wissing, H.; Wolf, M.; Wood, T. R.; Woschnagg, K.; Xu, C.; Xu, D. L.; Xu, X. W.; Yanez, J. P.; Yodh, G.; Yoshida, S.; Zarzhitsky, P.; Zoll, M.

    2012-05-01

    The IceCube neutrino observatory in operation at the South Pole, Antarctica, comprises three distinct components: a large buried array for ultrahigh energy neutrino detection, a surface air shower array, and a new buried component called DeepCore. DeepCore was designed to lower the IceCube neutrino energy threshold by over an order of magnitude, to energies as low as about 10 GeV. DeepCore is situated primarily 2100 m below the surface of the icecap at the South Pole, at the bottom center of the existing IceCube array, and began taking physics data in May 2010. Its location takes advantage of the exceptionally clear ice at those depths and allows it to use the surrounding IceCube detector as a highly efficient active veto against the principal background of downward-going muons produced in cosmic-ray air showers. DeepCore has a module density roughly five times higher than that of the standard IceCube array, and uses photomultiplier tubes with a new photocathode featuring a quantum efficiency about 35% higher than standard IceCube PMTs. Taken together, these features of DeepCore will increase IceCube's sensitivity to neutrinos from WIMP dark matter annihilations, atmospheric neutrino oscillations, galactic supernova neutrinos, and point sources of neutrinos in the northern and southern skies. In this paper we describe the design and initial performance of DeepCore.

  9. The Design and Performance of IceCube DeepCore

    NASA Technical Reports Server (NTRS)

    Stamatikos, M.

    2012-01-01

    The IceCube neutrino observatory in operation at the South Pole, Antarctica, comprises three distinct components: a large buried array for ultrahigh energy neutrino detection, a surface air shower array, and a new buried component called DeepCore. DeepCore was designed to lower the IceCube neutrino energy threshold by over an order of magnitude, to energies as low as about 10 GeV. DeepCore is situated primarily 2100 m below the surface of the icecap at the South Pole, at the bottom center of the existing IceCube array, and began taking pbysics data in May 2010. Its location takes advantage of the exceptionally clear ice at those depths and allows it to use the surrounding IceCube detector as a highly efficient active veto against the principal background of downward-going muons produced in cosmic-ray air showers. DeepCore has a module density roughly five times higher than that of the standard IceCube array, and uses photomultiplier tubes with a new photocathode featuring a quantum efficiency about 35% higher than standard IceCube PMTs. Taken together, these features of DeepCore will increase IceCube's sensitivity to neutrinos from WIMP dark matter annihilations, atmospheric neutrino oscillations, galactic supernova neutrinos, and point sources of neutrinos in the northern and southern skies. In this paper we describe the design and initial performance of DeepCore.

  10. Core drilling through the ross ice shelf (antarctica) confirmed Basal freezing.

    PubMed

    Zotikov, I A; Zagorodnov, V S; Raikovsky, J V

    1980-03-28

    New techniques that have been used to obtain a continuous ice core through the whole 416-meter thickness of the Ross Ice Shelf at Camp J-9 have demonstrated that the bottom 6 meters of the ice shelf consists of sea ice. The rate of basal freezing that is forming this ice is estimated by different methods to be 2 centimeters of ice per year. The sea ice is composed of large vertical crystals, which form the waffle-like lower boundary of the shelf. A distinct alignment of the crystals throughout the sea ice layer suggests the presence of persistent long-term currents beneath the ice shelf.

  11. Measurements of acetylene in air extracted from polar ice cores

    NASA Astrophysics Data System (ADS)

    Nicewonger, M. R.; Aydin, M.; Montzka, S. A.; Saltzman, E. S.

    2016-12-01

    Acetylene (ethyne) is a non-methane hydrocarbon emitted during combustion of fossil fuels, biofuels, and biomass. The major atmospheric loss pathway of acetylene is oxidation by hydroxyl radical with a lifetime estimated at roughly two weeks. The mean annual acetylene levels over Greenland and Antarctica are 250 ppt and 20 ppt, respectively. Firn air measurements suggest atmospheric acetylene is preserved unaltered in polar snow and firn. Atmospheric reconstructions based on firn air measurements indicate acetylene levels rose significantly during the twentieth century, peaked near 1980, then declined to modern day levels. This historical trend is similar to that of other fossil fuel-derived non-methane hydrocarbons. In the preindustrial atmosphere, acetylene levels should primarily reflect emissions from biomass burning. In this study, we present the first measurements of acetylene in preindustrial air extracted from polar ice cores. Air from fluid and dry-drilled ice cores from Summit, Greenland and WAIS-Divide Antarctica is extracted using a wet-extraction technique. The ice core air is analyzed using gas chromatography and high-resolution mass spectrometry. Between 1400 to 1800 C.E., acetylene levels over Greenland and Antarctica varied between roughly 70-120 ppt and 10-30 ppt, respectively. The preindustrial Greenland acetylene levels are significantly lower than modern levels, reflecting the importance of northern hemisphere fossil fuel sources today. The preindustrial Antarctic acetylene levels are comparable to modern day levels, indicating similar emissions in the preindustrial atmosphere, likely from biomass burning. The implications of the preindustrial atmospheric acetylene records from both hemispheres will be discussed.

  12. Ice-Shelf Melting Around Antarctica

    NASA Astrophysics Data System (ADS)

    Rignot, E.; Jacobs, S.; Mouginot, J.; Scheuchl, B.

    2013-07-01

    We compare the volume flux divergence of Antarctic ice shelves in 2007 and 2008 with 1979 to 2010 surface accumulation and 2003 to 2008 thinning to determine their rates of melting and mass balance. Basal melt of 1325 ± 235 gigatons per year (Gt/year) exceeds a calving flux of 1089 ± 139 Gt/year, making ice-shelf melting the largest ablation process in Antarctica. The giant cold-cavity Ross, Filchner, and Ronne ice shelves covering two-thirds of the total ice-shelf area account for only 15% of net melting. Half of the meltwater comes from 10 small, warm-cavity Southeast Pacific ice shelves occupying 8% of the area. A similar high melt/area ratio is found for six East Antarctic ice shelves, implying undocumented strong ocean thermal forcing on their deep grounding lines.

  13. Synoptic controls on precipitation pathways and snow delivery to high-accumulation ice core sites in the Ross Sea region, Antarctica

    NASA Astrophysics Data System (ADS)

    Sinclair, K. E.; Bertler, N. A. N.; Trompetter, W. J.

    2010-11-01

    Dominant storm tracks to two ice core sites on the western margin of the Ross Sea, Antarctica (Skinner Saddle (SKS) and Evans Piedmont Glacier), are investigated to establish key synoptic controls on snow accumulation. This is critical in terms of understanding the seasonality, source regions, and transport pathways of precipitation delivered to these sites. In situ snow depth and meteorological observations are used to identify major accumulation events in 2007-2008, which differ considerably between sites in terms of their magnitude and seasonal distribution. While snowfall at Evans Piedmont Glacier occurs almost exclusively during summer and spring, Skinner Saddle receives precipitation year round with a lull during the months of April and May. Cluster analysis of daily back trajectories reveals that the highest-accumulation days at both sites result from fast-moving air masses, associated with synoptic-scale low-pressure systems. There is evidence that short-duration pulses of snowfall at SKS also originate from mesocyclone development over the Ross Ice Shelf and local moisture sources. Changes in the frequency and seasonal distribution of these mechanisms of precipitation delivery will have a marked impact on annual accumulation over time and will therefore need careful consideration during the interpretation of stable isotope and geochemical records from these ice cores.

  14. Characterization of organic material in ice core samples from North America, Greenland, and Antarctica using ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry

    NASA Astrophysics Data System (ADS)

    Catanzano, V.; Grannas, A. M.; Sleighter, R. L.; Hatcher, P. G.

    2013-12-01

    Historically, it has been an analytical challenge to detect and identify the organic components present in ice cores, due to the low abundance of organic carbon. In order to detect and characterize the small amounts of organic matter in ice cores, ultra high resolution instrumentation is required. Here we report the use of ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry, coupled with electrospray ionization, to identify the molecular formulas and compound classes of organic matter in both modern and ancient ice core and glacial samples from Wyoming, Greenland, and Antarctica. A suite of 21 samples were analyzed and thousands of distinct molecular species were identified in each sample, providing clues to the nature and sources of organic matter in these regions. Major biochemical classes of compounds were detected such as lignins, tannins, carbohydrates, proteins, lipids, unsaturated hydrocarbons, and condensed aromatic compounds. We will compare the nature of the organic matter present in the samples in order to determine the differences in dominant organic compound classes and in heteroatom (nitrogen and sulfur) abundance. By analyzing these differences, it is possible to investigate the historical patterns of organic matter deposition/source, and begin to investigate the influence of climate change, volcanism, and onset of the industrial revolution on the nature of organic matter preserved in ice cores.

  15. Physical analysis of an Antarctic ice core-towards an integration of micro- and macrodynamics of polar ice*

    NASA Astrophysics Data System (ADS)

    Weikusat, Ilka; Jansen, Daniela; Binder, Tobias; Eichler, Jan; Faria, Sérgio H.; Wilhelms, Frank; Kipfstuhl, Sepp; Sheldon, Simon; Miller, Heinrich; Dahl-Jensen, Dorthe; Kleiner, Thomas

    2017-02-01

    Microstructures from deep ice cores reflect the dynamic conditions of the drill location as well as the thermodynamic history of the drill site and catchment area in great detail. Ice core parameters (crystal lattice-preferred orientation (LPO), grain size, grain shape), mesostructures (visual stratigraphy) as well as borehole deformation were measured in a deep ice core drilled at Kohnen Station, Dronning Maud Land (DML), Antarctica. These observations are used to characterize the local dynamic setting and its rheological as well as microstructural effects at the EDML ice core drilling site (European Project for Ice Coring in Antarctica in DML). The results suggest a division of the core into five distinct sections, interpreted as the effects of changing deformation boundary conditions from triaxial deformation with horizontal extension to bedrock-parallel shear. Region 1 (uppermost approx. 450 m depth) with still small macroscopic strain is dominated by compression of bubbles and strong strain and recrystallization localization. Region 2 (approx. 450-1700 m depth) shows a girdle-type LPO with the girdle plane being perpendicular to grain elongations, which indicates triaxial deformation with dominating horizontal extension. In this region (approx. 1000 m depth), the first subtle traces of shear deformation are observed in the shape-preferred orientation (SPO) by inclination of the grain elongation. Region 3 (approx. 1700-2030 m depth) represents a transitional regime between triaxial deformation and dominance of shear, which becomes apparent in the progression of the girdle to a single maximum LPO and increasing obliqueness of grain elongations. The fully developed single maximum LPO in region 4 (approx. 2030-2385 m depth) is an indicator of shear dominance. Region 5 (below approx. 2385 m depth) is marked by signs of strong shear, such as strong SPO values of grain elongation and strong kink folding of visual layers. The details of structural observations are

  16. Measurements of ethane in Antarctic ice cores

    NASA Astrophysics Data System (ADS)

    Verhulst, K. R.; Fosse, E. K.; Aydin, K. M.; Saltzman, E. S.

    2011-12-01

    Ethane is one of the most abundant hydrocarbons in the atmosphere. The major ethane sources are fossil fuel production and use, biofuel combustion, and biomass-burning emissions and the primary loss pathway is via reaction with OH. A paleoatmospheric ethane record would be useful as a tracer of biomass-burning emissions, providing a constraint on past changes in atmospheric methane and methane isotopes. An independent biomass-burning tracer would improve our understanding of the relationship between biomass burning and climate. The mean annual atmospheric ethane level at high southern latitudes is about 230 parts per trillion (ppt), and Antarctic firn air measurements suggest that atmospheric ethane levels in the early 20th century were considerably lower (Aydin et al., 2011). In this study, we present preliminary measurements of ethane (C2H6) in Antarctic ice core samples with gas ages ranging from 0-1900 C.E. Samples were obtained from dry-drilled ice cores from South Pole and Vostok in East Antarctica, and from the West Antarctic Ice Sheet Divide (WAIS-D). Gases were extracted from the ice by melting under vacuum in a glass vessel sealed by indium wire and were analyzed using high resolution GC/MS with isotope dilution. Ethane levels measured in ice core samples were in the range 100-220 ppt, with a mean of 157 ± 45 ppt (n=12). System blanks contribute roughly half the amount of ethane extracted from a 300 g ice core sample. These preliminary data exhibit a temporal trend, with higher ethane levels from 0-900 C.E., followed by a decline, reaching a minimum between 1600-1700 C.E. These trends are consistent with variations in ice core methane isotopes and carbon monoxide isotopes (Ferretti et al., 2005, Wang et al., 2010), which indicate changes in biomass burning emissions over this time period. These preliminary data suggest that Antarctic ice core bubbles contain paleoatmospheric ethane levels. With further improvement of laboratory techniques it appears

  17. Topographic Steering of Enhanced Ice Flow at the Bottleneck Between East and West Antarctica

    NASA Astrophysics Data System (ADS)

    Winter, Kate; Ross, Neil; Ferraccioli, Fausto; Jordan, Tom A.; Corr, Hugh F. J.; Forsberg, René; Matsuoka, Kenichi; Olesen, Arne V.; Casal, Tania G.

    2018-05-01

    Hypothesized drawdown of the East Antarctic Ice Sheet through the "bottleneck" zone between East and West Antarctica would have significant impacts for a large proportion of the Antarctic Ice Sheet. Earth observation satellite orbits and a sparseness of radio echo sounding data have restricted investigations of basal boundary controls on ice flow in this region until now. New airborne radio echo sounding surveys reveal complex topography of high relief beneath the southernmost Weddell/Ross ice divide, with three subglacial troughs connecting interior Antarctica to the Foundation and Patuxent Ice Streams and Siple Coast ice streams. These troughs route enhanced ice flow through the interior of Antarctica but limit potential drawdown of the East Antarctic Ice Sheet through the bottleneck zone. In a thinning or retreating scenario, these topographically controlled corridors of enhanced flow could however drive ice divide migration and increase mass discharge from interior West Antarctica to the Southern Ocean.

  18. Microshear in the deep EDML ice core analyzed using cryogenic EBSD

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

    Ice sheets play an important role in sea level evolution by storing large amounts of fresh water on land. The ice in an ice sheet flows from the interior of the ice sheet to the edges where it either melts or calves into the ocean. This flow of ice results from internal deformation of the ice aggregate. Dislocation creep is assumed to be the dominant deformation mechanism for polar ice and is grain size insensitive. Recently, a different deformation mechanism was identified in the deeper part of the EDML ice core (Antarctica) where, at a depth of 2385 meters, the grain size strongly decreases, the grain aspect ratio increase and, the inclination of the grain elongation changes (Faria et al., 2006; Weikusat et al., 2017). At this depth the borehole displacement increases strongly (Weikusat et al., 2017), which indicates a relatively high strain rate. Part of this EDML ice core section was studied using cryogenic electron backscattered diffraction (cryo-EBSD) (Weikusat et al, 2011). EBSD produces high resolution, full crystallographic (a-axis and c-axis) maps of the ice core samples. EBSD samples were taken from an ice core section at 2392.2 meter depth. This section was chosen for its very small grain size and the strongly aligned grain boundaries. The EBSD maps show a very low orientation gradient of <0.3° per millimetre inside the grains, which is 5-10 times lower than the orientation gradients found in other parts of the ice core. Furthermore, close to some grain boundaries, a relatively strong orientation gradient of 1°-2° per millimetre was found. The subgrain boundaries developed such that they elongate the sliding boundaries in order to accommodate the incompatibilities and maintain the strongly aligned grain boundary network. We identify the dominant deformation mechanism in this part of the ice core as grain boundary sliding accommodated by localized dislocation creep, which is a process similar to microshear (Drury and Humpreys, 1988). The existence of

  19. Antarctica and Its Ice Sheet: Knowledge Gained During the IGY/IGC

    NASA Astrophysics Data System (ADS)

    Bentley, C. R.

    2006-12-01

    At the end of World War II, the interior of Antarctica, with the exception of the mountains south of the Ross Ice Shelf, was still terra incognita. It was described simply as a nearly continuous high plateau. Even less was known about the ice thickness; the eminent glacial geologist, Richard Foster Flint, believed it "unlikely that the ice thickness exceeds 2000 feet except very locally; probably its average thickness is considerably less." Then in the late 1940's and early 1950's, seismic sounding in Greenland by the Expéditions Polaires Françaises and in Queen Maud Land by the Norwegian-British-Swedish Antarctic Expedition, 1949-52, revealed that, inland of the coastal mountains, the beds in both regions lie close to sea level. This led to a reappraisal of the Antarctic ice sheet, such that the prescient glaciologist, Robert P. Sharp, could predict, on the eve of the IGY, that "between 3000 and 4000 meters of ice will be found" in East Antarctica and that "work during IGY will establish an average thickness for Antarctic inland ice in excess of 1600 m." Seismic and gravity soundings on oversnow traverses conducted by eight countries during the IGY and the succeeding IGC showed Sharp to be basically correct, but there were major surprises, such as the vast Gamburtsev Subglacial Mountains, completely hidden by the ice in central East Antarctica, and the equally vast Byrd Subglacial Basin beneath much of the West Antarctic ice sheet, so deep that roughly half the ice in the region lies below sea level. There were major discoveries on and above the surface too, such as the huge size of the Filchner/Ronne Ice Shelf, and the very existence of the Ellsworth and Pensacola Mountains, the former including the highest peak on the continent. Further, the fundamental difference between the crustal structures of East and West Antarctica became clear. A summary paper published in 1960, looking primarily at West Antarctica where the main U.S. activity lay, could conclude that

  20. A 100-year Reconstruction of Regional Sea Ice Extent in the Ross and Amundsen-Bellingshausen Seas as Derived from the RICE Ice Core, Coastal West Antarctica

    NASA Astrophysics Data System (ADS)

    Emanuelsson, D. B.; Bertler, N. A. N.; Baisden, W. T.; Keller, E. D.

    2014-12-01

    Antarctic sea ice increased over the past decades. This increase is the result of an increase in the Ross Sea (RS) and along the coast of East Antarctica, whereas the Amundsen-Bellingshausen Seas (ABS) and the Antarctic Peninsula has seen a general decline. Several mechanisms have been suggested as drivers for the regional, complex sea ice pattern, which include changes in ocean currents, wind pattern, as well as ocean and atmospheric temperature. As part of the Roosevelt Island Climate Evolution (RICE) project, a 763 m deep ice core was retrieved from Roosevelt Island (RI; W161° 21', S79°41', 560 m a.s.l.), West Antarctica. The new record provides a unique opportunity to investigate mechanism driving sea ice variability in the RS and ABS sectors. Here we present the water stable isotope record (δD) from the upper part of the RICE core 0-40 m, spanning the time period from 1894 to 2011 (Fig. 1a). Annual δD are correlated with Sea Ice Concentration (SIC). A significant negative (r= -0.45, p≤ 0.05) correlation was found between annual δD and SIC in the eastern RS sector (boxed region in Fig. 1b) for the following months NDJFMA (austral summer and fall). During NDJFMA, RI receives local moisture input from the RS, while during the rest of the year a large extent of this local moisture source area will be covered with sea ice with the exception of the RS Polynya. Concurrently, we observe positive δD and SIC correlations in the ABS, showing a dipole pattern with the eastern RS. For this reason, we suggest that the RICE δD might be used as a proxy for past SIC for the RS and ABS region. There is no overall trend in δD over 100 years (r= -0.08 ‰ dec-1, p= 0.81, 1894-2011). However, we observe a strong increase from 2000-2011 of 17.7 ‰ dec-1(p≤ 0.1), yet the recent δD values and trend of the last decade are not unprecedented (Fig. 1a). We investigate changes in sea surface temperature, atmospheric temperature, inferred surface ocean currents and

  1. New Crustal Boundary Revealed Beneath the Ross Ice Shelf, Antarctica, through ROSETTA-Ice Integrated Aerogeophysics, Geology, and Ocean Research

    NASA Astrophysics Data System (ADS)

    Tinto, K. J.; Siddoway, C. S.; Bell, R. E.; Lockett, A.; Wilner, J.

    2017-12-01

    Now submerged within marine plateaus and rises bordering Antarctica, Australia and Zealandia, the East Gondwana accretionary margin was a belt of terranes and stitched by magmatic arcs, later stretched into continental ribbons separated by narrow elongate rifts. This crustal architecture is known from marine geophysical exploration and ocean drilling of the mid-latitude coastal plateaus and rises. A concealed sector of the former East Gondwana margin that underlies the Ross Ice Shelf (RIS), Antarctica, is the focus of ROSETTA-ICE, a new airborne data acquisition campaign that explores the crustal makeup, tectonic boundaries and seafloor bathymetry beneath RIS. Gravimeters and a magnetometer are deployed by LC130 aircraft surveying along E-W lines spaced at 10 km, and N-S tie lines at 55 km, connect 1970s points (RIGGS) for controls on ocean depth and gravity. The ROSETTA-ICE survey, 2/3 completed thus far, provides magnetic anomalies, Werner depth-to-basement solutions, a new gravity-based bathymetric model at 20-km resolution, and a new crustal density map tied to the 1970s data. Surprisingly, the data reveal that the major lithospheric boundary separating East and West Antarctica lies 300 km east of the Transantarctic Mountains, beneath the floating RIS. The East and West regions have contrasting geophysical characteristics and bathymetry, with relatively dense lithosphere, low amplitude magnetic anomalies, and deep bathymetry on the East Antarctica side, and high amplitude magnetic anomalies, lower overall density and shallower water depths on the West Antarctic side. The Central High, a basement structure cored at DSDP Site 270 and seismically imaged in the Ross Sea, continues beneath RIS as a faulted but coherent crustal ribbon coincident with the tectonic boundary. The continuity of Gondwana margin crustal architecture discovered beneath the West Antarctic Ice Sheet requires a revision of the existing tectonic framework. The sub-RIS narrow rift basins and

  2. Characteristics of basal ice and subglacial water at Dome Fuji, Antarctica ice sheet

    NASA Astrophysics Data System (ADS)

    Motoyama, H.; Uemura, R.; Hirabayashi, M.; Miyake, T.; Kuramoto, T.; Tanaka, Y.; Dome Fuji Ice Core Project, M.

    2008-12-01

    (Introduction): The second deep ice coring project at Dome Fuji, Antarctica reached a depth of 3035.22 m during the austral summer season in 2006/2007. The recovered ice cores contain records of global environmental changes going back about 720,000 years. (Estimation of basal ice melt): The borehole measurement was carried out on January 2nd in 2007 when the temperature disturbance in the borehole calmed down by the rest of drilling for 2 days. Temperature measurement was performed after 0 C thermometer test was done in the ground. The temperature sensor of pt100 installed in the skate-like anti-torque was used. We did not have the enough time until the temperature of thermometer was matched with the temperature of ice sheet. Some error was included in ice temperature data. The resistance of pt100 sensor was converted to temperature in the borehole measurement machine. But we used only two electrical lines for pt100 sensor. Rate of heat flow in the ice sheet was calculated using the vertical temperature gradient of the ice sheet and rate of heat conductivity of ice. The deepest part of heat flux using temperatures at 3000m and 3030m was about 45mW/m2. We assumed that this value was the heat flux from the bedrock in the ice sheet. Heat flux to the bedrock surface in the ground was assumed 54.6mW/m2 adopted by ice sheet model (P. Huybrechts, 2006). Then the heat flux for basal ice melt was about 10mW/m2. This value was equaled to melting of 1.1mm of ice thickness per year. On the other hand, the annual layer thickness under 2500m was not changed so much and its average was 1.3mm of ice thickness. So the annual layer thickness and melting rate of basal ice was the same in ordering way. Or ice equivalent in annual layer is melting every year. The age of the deepest part of ice core is guessed at 720,000 years old and the ice older than basal ice has melted away. (The state of basal ice): When the ice core drilling depth passed 3031.44m, amount of ice chip more abundant

  3. Physical analysis of an Antarctic ice core-towards an integration of micro- and macrodynamics of polar ice.

    PubMed

    Weikusat, Ilka; Jansen, Daniela; Binder, Tobias; Eichler, Jan; Faria, Sérgio H; Wilhelms, Frank; Kipfstuhl, Sepp; Sheldon, Simon; Miller, Heinrich; Dahl-Jensen, Dorthe; Kleiner, Thomas

    2017-02-13

    Microstructures from deep ice cores reflect the dynamic conditions of the drill location as well as the thermodynamic history of the drill site and catchment area in great detail. Ice core parameters (crystal lattice-preferred orientation (LPO), grain size, grain shape), mesostructures (visual stratigraphy) as well as borehole deformation were measured in a deep ice core drilled at Kohnen Station, Dronning Maud Land (DML), Antarctica. These observations are used to characterize the local dynamic setting and its rheological as well as microstructural effects at the EDML ice core drilling site (European Project for Ice Coring in Antarctica in DML). The results suggest a division of the core into five distinct sections, interpreted as the effects of changing deformation boundary conditions from triaxial deformation with horizontal extension to bedrock-parallel shear. Region 1 (uppermost approx. 450 m depth) with still small macroscopic strain is dominated by compression of bubbles and strong strain and recrystallization localization. Region 2 (approx. 450-1700 m depth) shows a girdle-type LPO with the girdle plane being perpendicular to grain elongations, which indicates triaxial deformation with dominating horizontal extension. In this region (approx. 1000 m depth), the first subtle traces of shear deformation are observed in the shape-preferred orientation (SPO) by inclination of the grain elongation. Region 3 (approx. 1700-2030 m depth) represents a transitional regime between triaxial deformation and dominance of shear, which becomes apparent in the progression of the girdle to a single maximum LPO and increasing obliqueness of grain elongations. The fully developed single maximum LPO in region 4 (approx. 2030-2385 m depth) is an indicator of shear dominance. Region 5 (below approx. 2385 m depth) is marked by signs of strong shear, such as strong SPO values of grain elongation and strong kink folding of visual layers. The details of structural

  4. Historical Isotopic Temperature Record from the Vostok Ice Core (420,000 years BP-present)

    DOE Data Explorer

    Petit, J. R. [Laboratoire de Glaciogie et Geophysique de l'Environnement; Raynaud, D. [Laboratoire de Glaciogie et Geophysique de l'Environnement; Lorius, C. [Laboratoire de Glaciogie et Geophysique de l'Environnement; Jouzel, J. [Laboratoire des Sciences du Climat et de l'Environnement; Delaygue, G. [Laboratoire des Sciences du Climat et de l'Environnement; Barkov, N. I. [Arctic and Antarctic Research Inst. (AARI), St. Petersburg (Russian Federation); Kotlyakov, V. M. [Institute of Geography, Russia

    2000-01-01

    Because isotopic fractions of the heavier oxygen-18 (18O) and deuterium (D) in snowfall are temperature-dependent and a strong spatial correlation exists between the annual mean temperature and the mean isotopic ratio (18O or δD) of precipitation, it is possible to derive ice-core climate records. The record presented by Jouzel et al. (1987) was the first ice core record to span a full glacial-interglacial cycle. That record was based on an ice core drilled at the Russian Vostok station in central east Antarctica. The 2083-m ice core was obtained during a series of drillings in the early 1970s and 1980s and was the result of collaboration between French and former-Soviet scientists. Drilling continued at Vostok and was completed in January 1998, reaching a depth of 3623 m, the deepest ice core ever recovered (Petit et al. 1997, 1999). The resulting core allows the ice core record of climate properties at Vostok to be extended to ~420 kyr BP.

  5. Bipolar volcanic events in ice cores and the Toba eruption at 74 ka BP (Invited)

    NASA Astrophysics Data System (ADS)

    Svensson, A.

    2013-12-01

    Acidity spikes in Greenland and Antarctic ice cores are applied as tracers of past volcanic activity. Besides providing information on the timing and magnitude of past eruptions, the acidity spikes are also widely used for synchronization of ice cores. All of the deep Greenland ice cores are thus synchronized throughout the last glacial cycle based on volcanic markers. Volcanic matching of ice cores from the two Hemispheres is much more challenging but it is feasible in periods of favourable conditions. Over the last two millennia, where ice cores are precisely dated, some 50 bipolar volcanic events have thus been identified. In order for an eruption to express a bipolar fingerprint it generally needs to be a low latitude eruption with stratospheric injection. Sometimes tephra is associated with the ice-core acidity spikes, but most often there is no tephra present in the ice. As yet, an unknown eruption occurring in 1259 AD is the only event reported to have deposited tephra in both Greenland and Antarctica. During the last glacial period bipolar volcanic matching is very challenging and very little work has been done, but recent high-resolution ice core records have the potential to provide bipolar ice core matching for some periods. Recently, Greenland and Antarctic ice cores have been linked by acidity spikes in the time window of the most recent eruption (the YTT eruption) of the Indonesian Toba volcano that is situated close to equator in Sumatra. Ash from this Toba event is widespread over large areas in Asia and has been identified as far west as Africa, but no corresponding tephra has been found in polar ice cores despite several attempts. The age of the YTT eruption is well constrained by recent Ar-Ar dating to have occurred some 74 ka ago close to the Marine Isotope Stage 4/5 boundary and close to the onset of the cold Greenland Stadial 20 and the corresponding mild Antarctic Isotopic Maxima 19 and 20. Surprisingly, no single outstanding acidity spike

  6. An Optical Dye Method for Continuous Determination of Acidity in Ice Cores.

    PubMed

    Kjær, Helle Astrid; Vallelonga, Paul; Svensson, Anders; Elleskov L Kristensen, Magnus; Tibuleac, Catalin; Winstrup, Mai; Kipfstuhl, Sepp

    2016-10-04

    The pH of polar ice is important for the stability and mobility of impurities in ice cores and can be strongly influenced by volcanic eruptions or anthropogenic emissions. We present a simple optical method for continuous determination of acidity in ice cores based on spectroscopically determined color changes of two common pH-indicator dyes, bromophenol blue, and chlorophenol red. The sealed-system method described here is not equilibrated with CO 2 , making it simpler than existing methods for pH determination in ice cores and offering a 10-90% peak response time of 45 s and a combined uncertainty of 9%. The method is applied to Holocene ice core sections from Greenland and Antarctica and compared to standard techniques such as electrical conductivity measurement (ECM) conducted on the solid ice, and electrolytic meltwater conductivity, EMWC. Acidity measured in the Greenland NGRIP ice core shows good agreement with acidity calculated from ion chromatography. Conductivity and dye-based acidity H dye + are found to be highly correlated in the Greenland NEGIS firn core (75.38° N, 35.56° W), with all signals greater than 3σ variability coinciding with either volcanic eruptions or possible wild fire activity. In contrast, the Antarctic Roosevelt Island ice core (79.36° S, 161.71° W) features an anticorrelation between conductivity and H dye + , likely due to strong influence of marine salts.

  7. The far reach of ice-shelf thinning in Antarctica

    NASA Astrophysics Data System (ADS)

    Reese, R.; Gudmundsson, G. H.; Levermann, A.; Winkelmann, R.

    2018-01-01

    Floating ice shelves, which fringe most of Antarctica's coastline, regulate ice flow into the Southern Ocean1-3. Their thinning4-7 or disintegration8,9 can cause upstream acceleration of grounded ice and raise global sea levels. So far the effect has not been quantified in a comprehensive and spatially explicit manner. Here, using a finite-element model, we diagnose the immediate, continent-wide flux response to different spatial patterns of ice-shelf mass loss. We show that highly localized ice-shelf thinning can reach across the entire shelf and accelerate ice flow in regions far from the initial perturbation. As an example, this `tele-buttressing' enhances outflow from Bindschadler Ice Stream in response to thinning near Ross Island more than 900 km away. We further find that the integrated flux response across all grounding lines is highly dependent on the location of imposed changes: the strongest response is caused not only near ice streams and ice rises, but also by thinning, for instance, well-within the Filchner-Ronne and Ross Ice Shelves. The most critical regions in all major ice shelves are often located in regions easily accessible to the intrusion of warm ocean waters10-12, stressing Antarctica's vulnerability to changes in its surrounding ocean.

  8. Polar ice magnetization: Comparison of results from NorthGRIP (Greenland) and Vostok (Antarctica) ice cores

    NASA Astrophysics Data System (ADS)

    Lanci, L.; Kent, D. V.

    2007-12-01

    Low temperature measurements of isothermal remanent magnetization (IRM) in Greenland ice spanning the last glacial and Holocene have shown that ice samples contain a measurable concentration of magnetic minerals which are part of the atmospheric aerosol. Assuming that the source materials do not change much with time, the concentration of magnetic minerals should be proportional to the measured concentration of dust in ice. We have indeed found a consistent linear relationship with the contents of dust. However, the linear relationship between low temperature ice magnetization vs. dust concentration has an offset, which when extrapolated to zero dust concentration would seemingly indicate that a significantly large magnetization corresponds to a null amount of dust in ice. Thermal relaxation experiments have shown that magnetic grains of nanometric size carry virtually all the uncorrelated magnetization. Magnetic measurements in Antarctic ice cores confirm the existence of a similar nanometric-size magnetic fraction, which also appear uncorrelated with measured aerosol concentration. The magnitude of the uncorrelated magnetization from Vostok is similar to that measured in NorthGRIP ice. Measurements of IRM at 250K suggest that the SP magnetic particles are in the size range of about 7-17 nm, which is compatible with the expected size of particles produced by ablation and subsequent condensation of meteorites in the atmosphere. The concentration of extraterrestrial material in NorthGRIP ice was estimated from the magnetic relaxation data based on a crude estimate of chondritic Ms. The resulting concentration of 0.78±0.22 ppb for Greenland is in good agreement with the outcome based on published iridium concentrations; a virtually identical concentration of 0.53±0.18 ppb has been measured in Vostok ice core.

  9. Low latitude ice core evidence for dust deposition on high altitude glaciers

    NASA Astrophysics Data System (ADS)

    Gabrielli, P.; Thompson, L. G.

    2017-12-01

    Polar ice cores from Antarctica and Greenland have provided a wealth of information on dust emission, transport and deposition over glacial to interglacial timescales. These ice cores mainly entrap dust transported long distances from source areas such as Asia for Greenland and South America for Antarctica. Thus, these dust records provide paleo-information about the environmental conditions at the source and the strength/pathways of atmospheric circulation at continental scales. Ice cores have also been extracted from high altitude glaciers in the mid- and low-latitudes and provide dust records generally extending back several centuries and in a few cases back to the last glacial period. For these glaciers the potential sources of dust emission include areas that are close or adjacent to the drilling site which facilitates the potential for a strong imprinting of local dust in the records. In addition, only a few high altitude glaciers allow the reconstruction of past snow accumulation and hence the expression of the dust records in terms of fluxes. Due to their extreme elevation, a few of these high altitude ice cores offer dust histories with the potential to record environmental conditions at remote sources. Dust records (in terms of dust concentration/size, crustal trace elements and terrigenous cations) from Africa, the European Alps, South America and the Himalayas are examined over the last millennium. The interplay of the seasonal atmospheric circulation (e.g. westerlies, monsoons and vertical convection) is shown to play a major role in determining the intensity and origin of dust fallout to the high altitude glaciers around the world.

  10. Eastern Ross Ice Sheet Deglacial History inferred from the Roosevelt Island Ice Core

    NASA Astrophysics Data System (ADS)

    Fudge, T. J.; Buizert, C.; Lee, J.; Waddington, E. D.; Bertler, N. A. N.; Conway, H.; Brook, E.; Severinghaus, J. P.

    2017-12-01

    The Ross Ice Sheet drains large portions of both West and East Antarctica. Understanding the retreat of the Ross Ice Sheet following the Last Glacial Maximum is particularly difficult in the eastern Ross area where there is no exposed rock and the Ross Ice Shelf prevents extensive bathymetric mapping. Coastal domes, by preserving old ice, can be used to infer the establishment of grounded ice and be used to infer past ice thickness. Here we focus on Roosevelt Island, in the eastern Ross Sea, where the Roosevelt Island Climate Evolution project recently completed an ice core to bedrock. Using ice-flow modeling constrained by the depth-age relationship and an independent estimate of accumulation rate from firn-densification measurements and modeling, we infer ice thickness histories for the LGM (20ka) to present. Preliminary results indicate thinning of 300m between 15ka and 12ka is required. This is similar to the amount and timing of thinning inferred at Siple Dome, in the central Ross Sea (Waddington et al., 2005; Price et al., 2007) and supports the presence of active ice streams throughout the Ross Ice Sheet advance during the LGM.

  11. Victoria Land, Ross Sea, and Ross Ice Shelf, Antarctica

    NASA Technical Reports Server (NTRS)

    2002-01-01

    On December 19, 2001, MODIS acquired data that produced this image of Antarctica's Victoria Land, Ross Ice Shelf, and the Ross Sea. The coastline that runs up and down along the left side of the image denotes where Victoria Land (left) meets the Ross Ice Shelf (right). The Ross Ice Shelf is the world's largest floating body of ice, approximately the same size as France. Credit: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC

  12. 10Be evidence for the Matuyama-Brunhes geomagnetic reversal in the EPICA Dome C ice core.

    PubMed

    Raisbeck, G M; Yiou, F; Cattani, O; Jouzel, J

    2006-11-02

    An ice core drilled at Dome C, Antarctica, is the oldest ice core so far retrieved. On the basis of ice flow modelling and a comparison between the deuterium signal in the ice with climate records from marine sediment cores, the ice at a depth of 3,190 m in the Dome C core is believed to have been deposited around 800,000 years ago, offering a rare opportunity to study climatic and environmental conditions over this time period. However, an independent determination of this age is important because the deuterium profile below a depth of 3,190 m depth does not show the expected correlation with the marine record. Here we present evidence for enhanced 10Be deposition in the ice at 3,160-3,170 m, which we interpret as a result of the low dipole field strength during the Matuyama-Brunhes geomagnetic reversal, which occurred about 780,000 years ago. If correct, this provides a crucial tie point between ice cores, marine cores and a radiometric timescale.

  13. Basal melt rates of Filchner Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Humbert, A.; Nicholls, K. W.; Corr, H. F. J.; Steinhage, D.; Stewart, C.; Zeising, O.

    2017-12-01

    Thinning of ice shelves around Antarctica has been found to be partly driven by an increase in basal melt as a result of warmer waters entering the sub-ice shelf cavity. In-situ observations of basal melt rate are, however, sparse. A new robust and efficient phase sensitive radio echo sounder (pRES) allows to measure change in ice thickness and vertical strain at high accuracy, so that the contribution of basal melt to the change in thickness can be estimated. As modeling studies suggest that the cavity beneath Filchner Ice Shelf, Antarctica, might be prone to intrusion of warm water pulses within this century, we wished to derive a baseline dataset and an understanding of its present day spatial variability. Here we present results from pRES measurements over two field seasons, 2015/16-16/17, comprising 86 datasets over the southern Filchner Ice Shelf, covering an area of about 6500km2. The maximum melt rate is only slightly more than 1m/a, but the spatial distribution exhibits a complex pattern. For the purpose of testing variability of basal melt rates on small spatial scales, we performed 26 measurements over distances of about 1km, and show that the melt rates do not vary by more than 0.25m/a.

  14. Calcareous nannofossil evidence for Marine Isotope Stage 31 (1 Ma) in the AND-1B Core, ANDRILL McMurdo Ice Shelf Project (Antarctica).

    NASA Astrophysics Data System (ADS)

    Villa, G.; Persico, D.; Wise, S. W.; Gadaleta, A.

    2009-04-01

    During the austral summer 2006 the ANDRILL Program recovered a 1285 m-long succession of cyclic glacimarine sediments from the McMurdo Ice Shelf (MIS). The aim of the MIS Project was to obtain continuous Neogene (c. 0-10 Ma) glacial, glacimarine, volcanic, and biogenic sediments that have accumulated in the region of the McMurdo Ice Shelf (Ross Sea) nourished by ice flowing from East Antarctic Ice Sheet (EAIS) outlet glaciers in the Transantarctic Mountains (TAM). The MIS AND-1B drill core represents the longest and most complete (98% recovery) geological record from the Antarctic continental margin to date, and will provide a key reference record of climate and ice-sheet variability through the Late Neogene; detailed investigations of this record will contribute for improving our knowledge of Antarctica's influence on global climate. Preliminary on-ice analysis of the smear slides of the Andrill core revealed calcareous microfossils (dinoflagellates, calciosponge spicula and small foraminifera) occurring with variable concentrations. The presence of thoracosphaerid fragments in the smear slides of the first 600 mbsf (Quaternary), probably belong to the species Thoracosphaera saxea (Stradner 1961), and Thoracosphaera heimi (Kamptner, 1941) and other, potentially undescribed species (Villa & Wise 1998), suggests either a peculiar adaptation to this environment, due to their ability to develop cysts or warmer conditions at the time of their deposition, or a combination of both. However, they represent an additional element to use with the other proxies for inferring palaeoenvironmental conditions of the core. Subsequent shore-based analyses of 100 samples from 86-96 mbsf revealed for the first time the presence of Pleistocene coccolithophorids at these high southern latitudes (77° S), including: Coccolithus pelagicus, small Gephyrocapsa, Reticulofenestra asanoi, Pseudoemiliania lacunosa, Dictyoccocites productus, Reticulofenestra sp., Reticulofenestra minutula

  15. 9,400 years of cosmic radiation and solar activity from ice cores and tree rings

    PubMed Central

    Steinhilber, Friedhelm; Beer, Jürg; Brunner, Irene; Christl, Marcus; Fischer, Hubertus; Heikkilä, Ulla; Kubik, Peter W.; Mann, Mathias; McCracken, Ken G.; Miller, Heinrich; Miyahara, Hiroko; Oerter, Hans

    2012-01-01

    Understanding the temporal variation of cosmic radiation and solar activity during the Holocene is essential for studies of the solar-terrestrial relationship. Cosmic-ray produced radionuclides, such as 10Be and 14C which are stored in polar ice cores and tree rings, offer the unique opportunity to reconstruct the history of cosmic radiation and solar activity over many millennia. Although records from different archives basically agree, they also show some deviations during certain periods. So far most reconstructions were based on only one single radionuclide record, which makes detection and correction of these deviations impossible. Here we combine different 10Be ice core records from Greenland and Antarctica with the global 14C tree ring record using principal component analysis. This approach is only possible due to a new high-resolution 10Be record from Dronning Maud Land obtained within the European Project for Ice Coring in Antarctica in Antarctica. The new cosmic radiation record enables us to derive total solar irradiance, which is then used as a proxy of solar activity to identify the solar imprint in an Asian climate record. Though generally the agreement between solar forcing and Asian climate is good, there are also periods without any coherence, pointing to other forcings like volcanoes and greenhouse gases and their corresponding feedbacks. The newly derived records have the potential to improve our understanding of the solar dynamics and to quantify the solar influence on climate. PMID:22474348

  16. 9,400 years of cosmic radiation and solar activity from ice cores and tree rings.

    PubMed

    Steinhilber, Friedhelm; Abreu, Jose A; Beer, Jürg; Brunner, Irene; Christl, Marcus; Fischer, Hubertus; Heikkilä, Ulla; Kubik, Peter W; Mann, Mathias; McCracken, Ken G; Miller, Heinrich; Miyahara, Hiroko; Oerter, Hans; Wilhelms, Frank

    2012-04-17

    Understanding the temporal variation of cosmic radiation and solar activity during the Holocene is essential for studies of the solar-terrestrial relationship. Cosmic-ray produced radionuclides, such as (10)Be and (14)C which are stored in polar ice cores and tree rings, offer the unique opportunity to reconstruct the history of cosmic radiation and solar activity over many millennia. Although records from different archives basically agree, they also show some deviations during certain periods. So far most reconstructions were based on only one single radionuclide record, which makes detection and correction of these deviations impossible. Here we combine different (10)Be ice core records from Greenland and Antarctica with the global (14)C tree ring record using principal component analysis. This approach is only possible due to a new high-resolution (10)Be record from Dronning Maud Land obtained within the European Project for Ice Coring in Antarctica in Antarctica. The new cosmic radiation record enables us to derive total solar irradiance, which is then used as a proxy of solar activity to identify the solar imprint in an Asian climate record. Though generally the agreement between solar forcing and Asian climate is good, there are also periods without any coherence, pointing to other forcings like volcanoes and greenhouse gases and their corresponding feedbacks. The newly derived records have the potential to improve our understanding of the solar dynamics and to quantify the solar influence on climate.

  17. Ocean mixing beneath Pine Island Glacier ice shelf, West Antarctica

    NASA Astrophysics Data System (ADS)

    Kimura, Satoshi; Jenkins, Adrian; Dutrieux, Pierre; Forryan, Alexander; Naveira Garabato, Alberto C.; Firing, Yvonne

    2016-12-01

    Ice shelves around Antarctica are vulnerable to an increase in ocean-driven melting, with the melt rate depending on ocean temperature and the strength of flow inside the ice-shelf cavities. We present measurements of velocity, temperature, salinity, turbulent kinetic energy dissipation rate, and thermal variance dissipation rate beneath Pine Island Glacier ice shelf, West Antarctica. These measurements were obtained by CTD, ADCP, and turbulence sensors mounted on an Autonomous Underwater Vehicle (AUV). The highest turbulent kinetic energy dissipation rate is found near the grounding line. The thermal variance dissipation rate increases closer to the ice-shelf base, with a maximum value found ˜0.5 m away from the ice. The measurements of turbulent kinetic energy dissipation rate near the ice are used to estimate basal melting of the ice shelf. The dissipation-rate-based melt rate estimates is sensitive to the stability correction parameter in the linear approximation of universal function of the Monin-Obukhov similarity theory for stratified boundary layers. We argue that our estimates of basal melting from dissipation rates are within a range of previous estimates of basal melting.

  18. A new 10Be record recovered from an Antarctic ice core: validity and limitations to record the solar activity

    NASA Astrophysics Data System (ADS)

    Baroni, Mélanie; Bard, Edouard; Aster Team

    2015-04-01

    Cosmogenic nuclides provide the only possibility to document solar activity over millennia. Carbon-14 (14C) and beryllium-10 (10Be) records are retrieved from tree rings and ice cores, respectively. Recently, 14C records have also proven to be reliable to detect two large Solar Proton Events (SPE) (Miyake et al., Nature, 2012, Miyake et al., Nat. Commun., 2013) that occurred in 774-775 A.D. and in 993-994 A.D.. The origin of these events is still under debate but it opens new perspectives for the interpretation of 10Be ice core records. We present a new 10Be record from an ice core from Dome C (Antarctica) covering the last millennium. The chronology of this new ice core has been established by matching volcanic events on the WAIS Divide ice core (WDC06A) that is the best dated record in Antarctica over the Holocene (Sigl et al., JGR, 2013, Sigl et al., Nat. Clim. Change, 2014). The five minima of solar activity (Oort, Wolf, Spörer, Maunder and Dalton) are detected and characterized by a 10Be concentration increase of ca. 20% above average in agreement with previous studies of ice cores drilled at South Pole and Dome Fuji in Antarctica (Bard et al., EPSL, 1997; Horiuchi et al., Quat. Geochrono., 2008) and at NGRIP and Dye3 in Greenland (Berggren et al., GRL, 2009). The high resolution, on the order of a year, allows the detection of the 11-year solar cycle. Sulfate concentration, a proxy for volcanic eruptions, has also been measured in the very same samples, allowing a precise comparison of both 10Be and sulfate profiles. We confirm the systematic relationship between stratospheric eruptions and 10Be concentration increases, first evidenced by observations of the stratospheric volcanic eruptions of Agung in 1963 and Pinatubo in 1991 (Baroni et al., GCA, 2011). This relationship is due to an increase in 10Be deposition linked to the role played by the sedimentation of volcanic aerosols. In the light of these new elements, we will discuss the limitations and

  19. Detection and Analysis of Complex Patterns of Ice Dynamics in Antarctica from ICESat Laser Altimetry

    NASA Astrophysics Data System (ADS)

    Babonis, Gregory Scott

    There remains much uncertainty in estimating the amount of Antarctic ice mass change, its dynamic component, and its spatial and temporal patterns. This work remedies the limitations of previous studies by generating the first detailed reconstruction of total and dynamic ice thickness and mass changes across Antarctica, from ICESat satellite altimetry observations in 2003-2009 using the Surface Elevation Reconstruction and Change Detection (SERAC) method. Ice sheet thickness changes are calculated with quantified error estimates for each time when ICESat flew over a ground-track crossover region, at approximately 110,000 locations across the Antarctic Ice Sheet. The time series are partitioned into changes due to surficial processes and ice dynamics. The new results markedly improve the spatial and temporal resolution of surface elevation, volume, and mass change rates for the AIS, and can be sampled at annual temporal resolutions. The results indicate a complex spatiotemporal pattern of dynamic mass loss in Antarctica, especially along individual outlet glaciers, and allow for the quantification of the annual contribution of Antarctic ice loss to sea level rise. Over 5000 individual locations exhibit either strong dynamic ice thickness change patterns, accounting for approximately 500 unique spatial clusters that identify regions likely influenced by subglacial hydrology. The spatial distribution and temporal behavior of these regions reveal the complexity and short-time scale variability in the subglacial hydrological system. From the 500 unique spatial clusters, over 370 represent newly identified, and not previously published, potential subglacial water bodies indicating an active subglacial hydrological system over a much larger region than previously observed. These numerous new observations of dynamic changes provide more than simply a larger set of data. Examination of both regional and local scale dynamic change patterns across Antarctica shows newly

  20. Forced Climate Changes in West Antarctica and the Indo-Pacific by Northern Hemisphere Ice Sheet Topography

    NASA Astrophysics Data System (ADS)

    Jones, T. R.; Roberts, W. H. G.; Steig, E. J.; Cuffey, K. M.; Markle, B. R.; White, J. W. C.

    2017-12-01

    The behavior of the Indo-Pacific climate system across the last deglaciation is widely debated. Resolving these debates requires long term and continuous climate proxy records. Here, we use an ultra-high resolution and continuous water isotope record from an ice core in the Pacific sector of West Antarctica. In conjunction with the HadCM3 coupled ocean-atmosphere GCM, we demonstrate that the climate of both West Antarctica and the Indo-Pacific were substantially altered during the last deglaciation by the same forcing mechanism. Critically, these changes are not dependent on ENSO strength, but rather the location of deep tropical convection, which shifts at 16 ka in response to climate perturbations induced by the Laurentide Ice Sheet. The changed rainfall patterns in the tropics explain the deglacial shift from expanded-grasslands to rainforest-dominated ecosystems in Indonesia. High-frequency climate variability in the Southern Hemisphere is also changed, through a tropical Pacific teleconnection link dependent on the propogration of Rossby Waves.

  1. Life on ice, Antarctica and Mars

    NASA Technical Reports Server (NTRS)

    Anderson, D. T.; Mckay, C. P.; Wharton, Robert A., Jr.; Sagan, C.; Squyres, S. W.; Simmons, G. M.

    1991-01-01

    The study of the origin of life and the prospects for human exploration of Mars are two themes developed in a new 57-minute film, Life on Ice, Antarctica, and Mars, produced by the InnerSpace Foundation and WHRO Television for broadcast by the Public Broadcasting System (PBS). A brief explanation of the film and how it relates to the future human exploration of space is presented.

  2. Ice-shelf Dynamics Near the Front of Filchner-Ronne Ice Shelf, Antarctica, Revealed by SAR Interferometry

    NASA Technical Reports Server (NTRS)

    Rignot, E.; MacAyeal, D. R.

    1998-01-01

    Fifteen synthetic-aperture radar (SAR) images of the Ronne Ice Shelf, Antarctica, obtained by the European Space Agency (ESA)'s Earth Remote Sensing satellites (ERS) 1 & 2 are used to study ice-shelf dynamics near two ends of the iceberg-calving front.

  3. Eight glacial cycles from an Antarctic ice core.

    PubMed

    Augustin, Laurent; Barbante, Carlo; Barnes, Piers R F; Barnola, Jean Marc; Bigler, Matthias; Castellano, Emiliano; Cattani, Olivier; Chappellaz, Jerome; Dahl-Jensen, Dorthe; Delmonte, Barbara; Dreyfus, Gabrielle; Durand, Gael; Falourd, Sonia; Fischer, Hubertus; Flückiger, Jacqueline; Hansson, Margareta E; Huybrechts, Philippe; Jugie, Gérard; Johnsen, Sigfus J; Jouzel, Jean; Kaufmann, Patrik; Kipfstuhl, Josef; Lambert, Fabrice; Lipenkov, Vladimir Y; Littot, Geneviève C; Longinelli, Antonio; Lorrain, Reginald; Maggi, Valter; Masson-Delmotte, Valerie; Miller, Heinz; Mulvaney, Robert; Oerlemans, Johannes; Oerter, Hans; Orombelli, Giuseppe; Parrenin, Frederic; Peel, David A; Petit, Jean-Robert; Raynaud, Dominique; Ritz, Catherine; Ruth, Urs; Schwander, Jakob; Siegenthaler, Urs; Souchez, Roland; Stauffer, Bernhard; Steffensen, Jorgen Peder; Stenni, Barbara; Stocker, Thomas F; Tabacco, Ignazio E; Udisti, Roberto; Van De Wal, Roderik S W; Van Den Broeke, Michiel; Weiss, Jerome; Wilhelms, Frank; Winther, Jan-Gunnar; Wolff, Eric W; Zucchelli, Mario

    2004-06-10

    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 possible to infer the abundance of greenhouse gases in the atmosphere from marine records. Here we report the recovery of a deep ice core from Dome C, Antarctica, that provides a climate record for the past 740,000 years. For the four most recent glacial cycles, the data agree well with the record from Vostok. The earlier period, between 740,000 and 430,000 years ago, was characterized by less pronounced warmth in interglacial periods in Antarctica, but a higher proportion of each cycle was spent in the warm mode. The transition from glacial to interglacial conditions about 430,000 years ago (Termination V) resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases, but there are significant differences in the patterns of change. The interglacial stage following Termination V was exceptionally long--28,000 years compared to, for example, the 12,000 years recorded so far in the present interglacial period. Given the similarities between this earlier warm period and today, our results may imply that without human intervention, a climate similar to the present one would extend well into the future.

  4. Antarctic ice core samples: culturable bacterial diversity.

    PubMed

    Shivaji, Sisinthy; Begum, Zareena; Shiva Nageswara Rao, Singireesu Soma; Vishnu Vardhan Reddy, Puram V; Manasa, Poorna; Sailaja, Buddi; Prathiba, Mambatta S; Thamban, Meloth; Krishnan, Kottekkatu P; Singh, Shiv M; Srinivas, Tanuku N R

    2013-01-01

    Culturable bacterial abundance at 11 different depths of a 50.26 m ice core from the Tallaksenvarden Nunatak, Antarctica, varied from 0.02 to 5.8 × 10(3) CFU ml(-1) of the melt water. A total of 138 bacterial strains were recovered from the 11 different depths of the ice core. Based on 16S rRNA gene sequence analyses, the 138 isolates could be categorized into 25 phylotypes belonging to phyla Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria. All isolates had 16S rRNA sequences similar to previously determined sequences (97.2-100%). No correlation was observed in the distribution of the isolates at the various depths either at the phylum, genus or species level. The 25 phylotypes varied in growth temperature range, tolerance to NaCl, growth pH range and ability to produce eight different extracellular enzymes at either 4 or 18 °C. Iso-, anteiso-, unsaturated and saturated fatty acids together constituted a significant proportion of the total fatty acid composition. Copyright © 2012 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.

  5. Climate Proxies: An Inquiry-Based Approach to Discovering Climate Change on Antarctica

    NASA Astrophysics Data System (ADS)

    Wishart, D. N.

    2016-12-01

    An attractive way to advance climate literacy in higher education is to emphasize its relevance while teaching climate change across the curriculum to science majors and non-science majors. An inquiry-based pedagogical approach was used to engage five groups of students on a "Polar Discovery Project" aimed at interpreting the paleoclimate history of ice cores from Antarctica. Learning objectives and student learning outcomes were clearly defined. Students were assigned several exercises ranging from examination of Antarctic topography to the application of physical and chemical measurements as proxies for climate change. Required materials included base and topographic maps of Antarctica; graph sheets for construction of topographic cross-sectional profiles from profile lines of the Western Antarctica Ice Sheet (WAIS) Divide and East Antarctica; high-resolution photographs of Antarctic ice cores; stratigraphic columns of ice cores; borehole and glaciochemical data (i.e. anions, actions, δ18O, δD etc.); and isotope data on greenhouse gases (CH4, O2, N2) extracted from gas bubbles in ice cores. The methodology was to engage students in (2) construction of topographic profiles; (2) suggest directions for ice flow based on simple physics; (3) formulate decisions on suitable locations for drilling ice cores; (4) visual ice stratigraphy including ice layer counting; (5) observation of any insoluble particles (i.e. meteoritic and volcanic material); (6) analysis of borehole temperature profiles; and (7) the interpretation of several datasets to derive a paleoclimate history of these areas of the continent. The overall goal of the project was to improve the students analytical and quantitative skills; their ability to evaluate relationships between physical and chemical properties in ice cores, and to advance the understanding the impending consequences of climate change while engaging science, technology, engineering and mathematics (STEM). Student learning outcomes

  6. Historical Carbon Dioxide Record from the Siple Station Ice Core (1734-1983)

    DOE Data Explorer

    Neftel, A. [Physics Institute, University of Bern, Bern, Switzerland; Friedli, H. [Physics Institute, University of Bern, Bern, Switzerland; Moor, E. [Physics Institute, University of Bern, Bern, Switzerland; Lotscher, H. [Physics Institute, University of Bern, Bern, Switzerland; Oeschger, H. [Physics Institute, University of Bern, Bern, Switzerland; Siegenthaler, U. [Physics Institute, University of Bern, Bern, Switzerland; Stauffer, B. [Physics Institute, University of Bern, Bern, Switzerland

    1994-09-01

    Determinations of ancient atmospheric CO2 concentrations for Siple Station, located in West Antarctica, were derived from measurements of air occluded in a 200-m core drilled at Siple Station in the Antarctic summer of 1983-84. The core was drilled by the Polar Ice Coring Office in Nebraska and the Physics Institute at the University of Bern. The ice could be dated with an accuracy of approximately ±2 years to a depth of 144 m (which corresponds to the year 1834) by counting seasonal variations in electrical conductivity. Below that depth, the core was dated by extrapolation (Friedli et al. 1986). The gases from ice samples were extracted by a dry-extraction system, in which bubbles were crushed mechanically to release the trapped gases, and then analyzed for CO2 by infrared laser absorption spectroscopy or by gas chromatography (Neftel et al. 1985). After the ice samples were crushed, the gas expanded over a cold trap, condensing the water vapor at -80°C in the absorption cell. The analytical system was calibrated for each ice sample measurement with a standard mixture of CO2 in nitrogen and oxygen. For further details on the experimental and dating procedures, see Neftel et al. (1985), Friedli et al. (1986), and Schwander and Stauffer (1984).

  7. Coupled ice sheet-ocean modelling to investigate ocean driven melting of marine ice sheets in Antarctica

    NASA Astrophysics Data System (ADS)

    Jong, Lenneke; Gladstone, Rupert; Galton-Fenzi, Ben

    2017-04-01

    Ocean induced melting below the ice shelves of marine ice sheets is a major source of uncertainty for predictions of ice mass loss and Antarctica's resultant contribution to future sea level rise. The floating ice shelves provide a buttressing force against the flow of ice across the grounding line into the ocean. Thinning of these ice shelves due to an increase in melting reduces this force and can lead to an increase in the discharge of grounded ice. Fully coupled modelling of ice sheet-ocean interactions is key to improving understanding the influence of the Southern ocean on the evolution of the Antarctic ice sheet, and to predicting its future behaviour under changing climate conditions. Coupling of ocean and ice sheet models is needed to provide more realistic melt rates at the base of ice shelves and hence make better predictions of the behaviour of the grounding line and the shape of the ice-shelf cavity as the ice sheet evolves. The Framework for Ice Sheet - Ocean Coupling (FISOC) has been developed to provide a flexible platform for performing coupled ice sheet - ocean modelling experiments. We present preliminary results using FISOC to couple the Regional Ocean Modelling System (ROMS) with Elmer/Ice in idealised experiments Marine Ice Sheet-Ocean Model Intercomparison Project (MISOMIP). These experiments use an idealised geometry motivated by that of Pine Island glacier and the adjacent Amundsen Sea in West Antarctica, a region which has shown shown signs of thinning ice and grounding line retreat.

  8. Changes in Black Carbon Deposition to Antarctica from Two Ice Core Records, A.D. 1850-2000

    NASA Technical Reports Server (NTRS)

    Bisiaux, Marion M.; Edward, Ross; McConnell, Joseph R.; Curran, Mark A. J.; VanOmmen, Tas D.; Smith, Andrew M.; Neumann, Thomas A.; Pasteris, Daniel R.; Penner, Joyce E.; Taylor, Kendrick

    2012-01-01

    Continuous flow analysis was based on a steady sample flow and in-line detection of BC and other chemical substances as described in McConnell et al. (2007). In the cold room, previously cut one meter ice core sticks of 3x3cm, are melted continuously on a heated melter head specifically designed to eliminate contamination from the atmosphere or by the external parts of the ice. The melted ice from the most inner part of the ice stick is continuously pumped by a peristaltic pump and carried to a clean lab by Teflon lines. The recorded signal is continuous, integrating a sample volume of about 0.05 mL, for which the temporal resolution depends on the speed of melting, ice density and snow accumulation rate at the ice core drilling site. For annual accumulation derived from the WAIS and Law Dome ice cores, we assumed 3.1 cm water equivalent uncertainty in each year's accumulation from short scale spatial variability (glaciological noise) which was determined from several measurements of annual accumulation in multiple parallel ice cores notably from the WAIS Divide ice core site (Banta et al., 2008) and from South Pole site (McConnell et al., 1997; McConnell et al., 2000). Refractory black carbon (rBC) concentrations were determined using the same method as in (Bisiaux et al., 2011) and adapted to continuous flow measurements as described by (McConnell et al., 2007). The technique uses a single particle intracavity laser induced incandescence photometer (SP2, Droplet Measurement Technologies, Boulder, Colorado) coupled to an ultrasonic nebulizer/desolvation (CETAC UT5000) Flow Injection Analysis (FIA). All analyses, sample preparation etc, were performed in a class 100 cleanroom using anti contamination "clean techniques". The samples were not acidified.

  9. Raman spectroscopy, an innovative tool to explore the mineralogy and provenance of dust (1-5 µm): Dome B ice core, East Antarctica

    NASA Astrophysics Data System (ADS)

    Ileana Paleari, Chiara; Andò, Sergio; Delmonte, Barbara; Maggi, Valter; Garzanti, Eduardo

    2017-04-01

    The polar ice sheets are invaluable archives preserving information about past climate changes and atmosphere composition. Deep ice cores from Greenland and Antarctica provide records of several climate-dependent proxies allowing climate reconstructions at different time scales, among which greenhouse gases, atmospheric aerosol and aeolian dust. In this project, the mineralogy of dust preserved in the Dome B (77°05'S, 94°55'E, 3650 m a.s.l.) ice core was investigated using Raman spectroscopy. The thermal drilled ice core, made during the 1987-1988 Austral season by the 33rd Soviet Antarctic Expedition, covers the last 30 kyr. The record thus encompasses the last glacial period, the Last Glacial Maximum (LGM), the deglaciation and the beginning of the Holocene. Four Dome B ice core samples from the LGM were selected, and the mineralogical fingerprint of dust particles was investigated. Dust in central Antarctic ice cores is clay to finest silt, the volume-size distribution of particles showing modal values around 2-2.6 µm at the Dome B site. Detrital minerals of such a fine grain-size range are exceedingly difficult to determine one by one, a task that to the best of our knowledge has never been accomplished so far. In order to meet this challenge, we have developed a new protocol for the preparation and analysis of particles between 1 and 5 µm in diameter, in a clean room at the EuroCold Lab and at the Laboratory for Provenance Studies of Milano-Bicocca University. Three slides were prepared for each sample, and 962 particles were studied overall. In total, 41 different minerals were recognized, including species derived from granitoid, metamorphic or siliciclastic rocks (e.g., quartz, feldspars and phyllosilicates), from volcanic source rocks (e.g., sanidine, anorthite, pyroxenes, zeolites) associated with biogenic marine aragonite and iron oxides probably derived from erosion of soil profiles. Our observations indicate southern South America as the most

  10. Morphological evidence and direct estimates of rapid melting beneath Totten Glacier Ice Shelf, East Antarctica

    NASA Astrophysics Data System (ADS)

    Greenbaum, Jamin; Schroeder, Dustin; Grima, Cyril; Habbal, Feras; Dow, Christine; Roberts, Jason; Gwyther, David; van Ommen, Tas; Siegert, Martin; Blankenship, Donald

    2017-04-01

    Totten Glacier drains at least 3.5 meters of eustatic sea level potential from marine-based ice in the Aurora Subglacial Basin (ASB) in East Antarctica, more than the combined total of all glaciers in West Antarctica. Totten Glacier has been the most rapidly thinning glacier in East Antarctica since satellite altimetry time series began and the nature of the thinning suggests that it is driven by enhanced basal melting due to ocean processes. While grounded ice thinning rates have been steady, recent work has shown that Totten's floating ice shelf may not have the same thinning behavior; as a result, it is critical to observe ice shelf and cavity boundary conditions and basal processes to understand this apparent discrepancy. Warm Modified Circumpolar Deep Water (MCDW), which has been linked to glacier retreat in West Antarctica, has been observed in summer and winter on the nearby Sabrina Coast continental shelf and deep depressions in the seafloor provide access for MCDW to reach the ice shelf cavity. Given its northern latitude, numerical ice sheet modeling indicates that Totten Glacier may be prone to retreat caused by hydrofracture in a warming climate, so it is important to understand how intruding MCDW is affecting thinning of Totten Glacier's ice shelf. Here we use post-processed, focused airborne radar observations of the Totten Glacier Ice Shelf to delineate multi-km wide basal channels and flat basal terraces associated with high basal reflectivity and specularity (flatness) anomalies and correspondingly large ice surface depressions that indicate active basal melting. Using a simple temperature-attenuation model, and basal roughness corrections, we present basal melt rates associated with the radar reflection and specularity anomalies and compare them to those derived from numerical ocean circulation modeling and an ice flow divergence calculation. Sub-ice shelf ocean circulation modeling and under-ice robotic observations of Pine Island Glacier Ice

  11. Towards a new common Greenland Ice Core Chronology for the last 5000 years

    NASA Astrophysics Data System (ADS)

    Winstrup, Mai; Olander Rasmussen, Sune; Møllesøe Vinther, Bo; Cook, Eliza; Svensson, Anders; McConnell, Joe; Steffensen, Jørgen Peder

    2017-04-01

    Since the development of the Greenland Ice Core Chronology 2005 (GICC05), it has been widely used as a reference chronology in paleoclimate research. However, recent research (Sigl et al, 2015) demonstrated that this timescale has small, but significant, issues over historical time. These discrepancies was found by counting annual layers in high-resolution chemistry records from the NEEM S1 shallow core, and confirmed by linking via 10Be marker horizons to the layer-counted WAIS Divide ice core, Antarctica, and accurately-dated tree-ring series. This work showed that a revision of GICC05 is required prior to 1250AD. We here refine and extend this work. Layer-counting in a single core will always involve some uncertainty, and we hence use data from multiple Greenland ice cores, for which high-resolution impurity records recently have been measured. These ice cores have been synchronized using volcanic marker horizons, and the layer-counting is performed automatically using the StratiCounter algorithm (Winstrup et al, 2012), while ensuring that the number of layers between volcanic horizons are the same in all cores. Based on this extended multiple-core data set, we are further able to extend the new Greenland timescale another few thousand years back in time. This will, among others, provide a new ice-core date for the catastrophic volcanic eruption ( 1600 BC) that destroyed the Greek Minoan culture, an important time marker in Greek history.

  12. Ultra-low rare earth element content in accreted ice from sub-glacial Lake Vostok, Antarctica

    NASA Astrophysics Data System (ADS)

    Gabrielli, Paolo; Planchon, Frederic; Barbante, Carlo; Boutron, Claude F.; Petit, Jean Robert; Bulat, Sergey; Hong, Sungmin; Cozzi, Giulio; Cescon, Paolo

    2009-10-01

    This paper reports the first rare earth element (REE) concentrations in accreted ice refrozen from sub-glacial Lake Vostok (East Antarctica). REE were determined in various sections of the Vostok ice core in order to geochemically characterize its impurities. Samples were obtained from accreted ice and, for comparison, from the upper glacier ice of atmospheric origin (undisturbed, disturbed and glacial flour ice). REE concentrations ranged between 0.8-56 pg g -1 for Ce and 0.0035-0.24 pg g -1 for Lu in glacier ice, and between <0.1-24 pg g -1 for Ce and <0.0004-0.02 pg g -1 for Lu in accreted ice. Interestingly, the REE concentrations in the upper accreted ice (AC 1; characterized by visible aggregates containing a mixture of very fine terrigenous particles) and in the deeper accreted ice (AC 2; characterized by transparent ice) are lower than those in fresh water and seawater, respectively. We suggest that such ultra-low concentrations are unlikely to be representative of the real REE content in Lake Vostok, but instead may reflect phase exclusion processes occurring at the ice/water interface during refreezing. In particular, the uneven spatial distribution (on the order of a few cm) and the large range of REE concentrations observed in AC 1 are consistent with the occurrence/absence of the aggregates in adjacent ice, and point to the presence of solid-phase concentration/exclusion processes occurring within separate pockets of frazil ice during AC 1 formation. Interestingly, if the LREE enrichment found in AC 1 was not produced by chemical fractionation occurring in Lake Vostok water, this may reflect a contribution of bedrock material, possibly in combination with aeolian dust released into the lake by melting of the glacier ice. Collectively, this valuable information provides new insight into the accreted ice formation processes, the bedrock geology of East Antarctica as well as the water chemistry and circulation of Lake Vostok.

  13. Ultra-low rare earth element content in accreted ice from sub-glacial Lake Vostok, Antarctica

    NASA Astrophysics Data System (ADS)

    Barbante, C.; Gabrielli, P.; Turetta, C.; Planchon, F.; Boutron, C.; Petit, J. R.; Bulat, S.; Hong, S.; Cozzi, G.; Cescon, P.

    2009-12-01

    We report the first rare earth element (REE) concentrations in accreted ice refrozen from sub-glacial Lake Vostok (East Antarctica). REE were determined in various sections of the Vostok ice core in order to geochemically characterize its impurities. Samples were obtained from accreted ice and, for comparison, from the upper glacier ice of atmospheric origin (undisturbed, disturbed and glacial flour ice). REE concentrations ranged between 0.8-56 pg g-1 for Ce and 0.0035- 0.24 pg g-1 for Lu in glacier ice, and between <0.1-24 pg g-1 for Ce and <0.0004-0.02 pg g-1 for Lu in accreted ice. Interestingly, the REE concentrations in the upper accreted ice (AC1;characterized by visible aggregates containing a mixture of very fine terrigenous particles) and in the deeper accreted ice (AC2; characterized by transparent ice) are lower than those in fresh water and seawater, respectively. We suggest that such ultra-low concentrations are unlikely to be representative of the real REE content in Lake Vostok, but instead may reflect phase exclusion processes occurring at the ice/water interface during refreezing. In particular, the uneven spatial distribution (on the order of a few cm) and the large range of REE concentrations observed in AC1 are consistent with the occurrence/absence of the aggregates in adjacent ice, and point to the presence of solid-phase concentration/exclusion processes occurring within separate pockets of frazil ice during AC1 formation. Interestingly, if the LREE enrichment found in AC1 was not produced by chemical fractionation occurring in Lake Vostok water, this may reflect a contribution of bedrock material, possibly in combination with aeolian dust released into the lake by melting of the glacier ice. Collectively, this valuable information provides new insight into the accreted ice formation processes, the bedrock geology of East Antarctica as well as the water chemistry and circulation of Lake Vostok.

  14. Antarctica: Is It More Than Just Ice?

    ERIC Educational Resources Information Center

    Johnson, Cheryl; Gutierrez, Melida

    2009-01-01

    The authors introduced polar science in a fourth-grade classroom by means of 3 hands-on activities that addressed (1) the melting of glaciers and ice, (2) the differences between the North and the South Pole, and (3) the geography and landforms of Antarctica. An assessment 4 months after the original activity showed that students remembered the…

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

    NASA Technical Reports Server (NTRS)

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

    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.

  17. Volcanic ash layers in blue ice fields (Beardmore Glacier Area, Antarctica): Iridium enrichments

    NASA Technical Reports Server (NTRS)

    Koeberl, Christian

    1988-01-01

    Dust bands on blue ice fields in Antarctica have been studied and have been identified to originate from two main sources: bedrock debris scraped up from the ground by the glacial movement (these bands are found predominantly at fractures and shear zones in the ice near moraines), and volcanic debris deposited on and incorporated in the ice by large-scale eruptions of Antarctic (or sub-Antractic) volcanoes. Ice core studies have revealed that most of the dust layers in the ice cores are volcanic (tephra) deposits which may be related to some specific volcanic eruptions. These eruptions have to be related to some specific volcanic eruptions. These eruptions have to be relatively recent (a few thousand years old) since ice cores usually incorporate younger ice. In contrast, dust bands on bare blue ice fields are much older, up to a few hundred thousand years, which may be inferred from the rather high terrestrial age of meteorites found on the ice and from dating the ice using the uranium series method. Also for the volcanic ash layers found on blue ice fields correlations between some specific volcanoes (late Cenozoic) and the volcanic debris have been inferred, mainly using chemical arguments. During a recent field expedition samples of several dust bands found on blue ice fields at the Lewis Cliff Ice Tongue were taken. These dust band samples were divided for age determination using the uranium series method, and chemical investigations to determine the source and origin of the dust bands. The investigations have shown that most of the dust bands found at the Ice Tongue are of volcanic origin and, for chemical and petrological reasons, may be correlated with Cenozoic volcanoes in the Melbourne volcanic province, Northern Victoria Land, which is at least 1500 km away. Major and trace element data have been obtained and have been used for identification and correlation purposes. Recently, some additional trace elements were determined in some of the dust band

  18. Increased future ice discharge from Antarctica owing to higher snowfall

    NASA Astrophysics Data System (ADS)

    Winkelmann, Ricarda; Levermann, Anders; Martin, Maria A.; Frieler, Katja

    2013-04-01

    Anthropogenic climate change is likely to cause continuing global sea-level rise, but some processes within the Earth system may mitigate the magnitude of the projected effect. Regional and global climate models simulate enhanced snowfall over Antarctica, which would provide a direct offset of the future contribution to global sea level rise from cryospheric mass loss and ocean expansion. Uncertainties exist in modelled snowfall, but even larger uncertainties exist in the potential changes of dynamic ice discharge from Antarctica. Here we show that snowfall and discharge are not independent, but that future ice discharge will increase by up to three times as a result of additional snowfall under global warming. Our results, based on an ice-sheet model forced by climate simulations through to the end of 2500, show that the enhanced discharge effect exceeds the effect of surface warming as well as that of basal ice-shelf melting, and is due to the difference in surface elevation change caused by snowfall on grounded versus floating ice. Although different underlying forcings drive ice loss from basal melting versus increased snowfall, similar ice dynamical processes are nonetheless at work in both; therefore results are relatively independent of the specific representation of the transition zone. In an ensemble of simulations designed to capture ice-physics uncertainty, the additional dynamic ice loss along the coastline compensates between 30 and 65 per cent of the ice gain due to enhanced snowfall over the entire continent. This results in a dynamic ice loss of up to 1.25 metres in the year 2500 for the strongest warming scenario.

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

    NASA Astrophysics Data System (ADS)

    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.

  20. Iceberg B-15, Ross Ice Shelf, Antarctica

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Iceberg B-15 broke from the Ross Ice Shelf in Antarctica in late March. Among the largest ever observed, the new iceberg is approximately 170 miles long x 25 miles wide. Its 4,250 square-mile area is nearly as large as the state of Connecticut. The iceberg was formed from glacial ice moving off the Antarctic continent and calved along pre-existing cracks in the Ross Ice Shelf near Roosevelt Island. The calving of the iceberg essentially moves the northern boundary of the ice shelf about 25 miles to the south, a loss that would normally take the ice shelf as long as 50-100 years to replace. This infrared image was acquired by the DMSP (Defense Meteorological Satellite Program) F-13 satellite on April 13, 2000. For more images see Antarctic Meteorological Research Center Image courtesy of the University of Wisconsin - Madison, Space Science and Engineering Center, Antarctic Meteorological Research Center

  1. Perennially ice-covered Lake Hoare, Antarctica: physical environment, biology and sedimentation

    NASA Technical Reports Server (NTRS)

    Wharton, R. A. Jr; Simmons, G. M. Jr; McKay, C. P.; Wharton RA, J. r. (Principal Investigator)

    1989-01-01

    Lake Hoare (77 degrees 38' S, 162 degrees 53' E) is a perennially ice-covered lake at the eastern end of Taylor Valley in southern Victoria Land, Antarctica. The environment of this lake is controlled by the relatively thick ice cover (3-5 m) which eliminates wind generated currents, restricts gas exchange and sediment deposition, and reduces light penetration. The ice cover is in turn largely controlled by the extreme seasonality of Antarctica and local climate. Lake Hoare and other dry valley lakes may be sensitive indicators of short term (< 100 yr) climatic and/or anthropogenic changes in the dry valleys since the onset of intensive exploration over 30 years ago. The time constants for turnover of the water column and lake ice are 50 and 10 years, respectively. The turnover time for atmospheric gases in the lake is 30-60 years. Therefore, the lake environment responds to changes on a 10-100 year timescale. Because the ice cover has a controlling influence on the lake (e.g. light penetration, gas content of water, and sediment deposition), it is probable that small changes in ice ablation, sediment loading on the ice cover, or glacial meltwater (or groundwater) inflow will affect ice cover dynamics and will have a major impact on the lake environment and biota.

  2. Ice crystal precipitation at Dome C site (East Antarctica)

    NASA Astrophysics Data System (ADS)

    Santachiara, G.; Belosi, F.; Prodi, F.

    2016-01-01

    For the first time, falling ice crystals were collected on glass slides covered with a thin layer of 2% formvar in chloroform at the Dome Concordia site (Dome C), Antarctica. Samplings were performed in the framework of the 27th Italian Antarctica expedition of the Italian National Program for Research in Antarctica in the period 21 February-6 August 2012. Events of clear-sky precipitations and precipitations from clouds were considered and the replicas obtained were examined under Scanning Electron Microscope (SEM). Several shapes of ice crystals were identified, including ;diamond dust; (plates, pyramids, hollow and solid columns), and crystal aggregates varying in complexity. Single events often contained both small (10 μm to 50 μm) and large (hundreds of microns) crystals, suggesting that crystals can form simultaneously near the ground (height of a few hundred metres) and at higher layers (height of thousands of metres). Images of sampled crystal replicas showed that single bullets are not produced separately, but by the disintegration of combinations of bullets. Rimed ice crystals were absent in the Dome C samples, i.e. the only mode of crystal growth was water vapour diffusion. On considering the aerosol in the sampled crystals, we reached the conclusion that inertial impaction, interception and Brownian motion were insufficient to explain the scavenged aerosol. We therefore presume that phoretic forces play a role in scavenging during the crystal growth process.

  3. Onset of deglacial warming in West Antarctica driven by local orbital forcing.

    PubMed

    2013-08-22

    The cause of warming in the Southern Hemisphere during the most recent deglaciation remains a matter of debate. Hypotheses for a Northern Hemisphere trigger, through oceanic redistributions of heat, are based in part on the abrupt onset of warming seen in East Antarctic ice cores and dated to 18,000 years ago, which is several thousand years after high-latitude Northern Hemisphere summer insolation intensity began increasing from its minimum, approximately 24,000 years ago. An alternative explanation is that local solar insolation changes cause the Southern Hemisphere to warm independently. Here we present results from a new, annually resolved ice-core record from West Antarctica that reconciles these two views. The records show that 18,000 years ago snow accumulation in West Antarctica began increasing, coincident with increasing carbon dioxide concentrations, warming in East Antarctica and cooling in the Northern Hemisphere associated with an abrupt decrease in Atlantic meridional overturning circulation. However, significant warming in West Antarctica began at least 2,000 years earlier. Circum-Antarctic sea-ice decline, driven by increasing local insolation, is the likely cause of this warming. The marine-influenced West Antarctic records suggest a more active role for the Southern Ocean in the onset of deglaciation than is inferred from ice cores in the East Antarctic interior, which are largely isolated from sea-ice changes.

  4. Onset of deglacial warming in West Antarctica driven by local orbital forcing

    USGS Publications Warehouse

    WAIS Divide Project Members,; Fudge, T. J.; Steig, Eric J.; Markle, Bradley R.; Schoenemann, Spruce W.; Ding, Qinghua; Taylor, Kendrick C.; McConnell, Joseph R.; Brook, Edward J.; Sowers, Todd; White, James W. C.; Alley, Richard B.; Cheng, Hai; Clow, Gary D.; Cole-Dai, Jihong; Conway, Howard; Cuffey, Kurt M.; Edwards, Jon S.; Edwards, R. Lawrence; Edwards, Ross; Fegyveresi, John M.; Ferris, David; Fitzpatrick, Joan J.; Johnson, Jay; Hargreaves, Geoffrey; Lee, James E.; Maselli, Olivia J.; Mason, William; McGwire, Kenneth C.; Mitchell, Logan E.; Mortensen, Nicolai B.; Neff, Peter; Orsi, Anais J.; Popp, Trevor J.; Schauer, Andrew J.; Severinghaus, Jeffrey P.; Sigl, Michael; Spencer, Matthew K.; Vaughn, Bruce H.; Voigt, Donald E.; Waddington, Edwin D.; Wang, Xianfeng; Wong, Gifford J.

    2013-01-01

    The cause of warming in the Southern Hemisphere during the most recent deglaciation remains a matter of debate. Hypotheses for a Northern Hemisphere trigger, through oceanic redistributions of heat, are based in part on the abrupt onset of warming seen in East Antarctic ice cores and dated to 18,000 years ago, which is several thousand years after high-latitude Northern Hemisphere summer insolation intensity began increasing from its minimum, approximately 24,000 years ago. An alternative explanation is that local solar insolation changes cause the Southern Hemisphere to warm independently. Here we present results from a new, annually resolved ice-core record from West Antarctica that reconciles these two views. The records show that 18,000 years ago snow accumulation in West Antarctica began increasing, coincident with increasing carbon dioxide concentrations, warming in East Antarctica and cooling in the Northern Hemisphere associated with an abrupt decrease in Atlantic meridional overturning circulation. However, significant warming in West Antarctica began at least 2,000 years earlier. Circum-Antarctic sea-ice decline, driven by increasing local insolation, is the likely cause of this warming. The marine-influenced West Antarctic records suggest a more active role for the Southern Ocean in the onset of deglaciation than is inferred from ice cores in the East Antarctic interior, which are largely isolated from sea-ice changes.

  5. Ice recrystallization inhibition proteins (IRIPs) and freeze tolerance in the cryophilic Antarctic hair grass Deschampsia antarctica E. Desv.

    PubMed

    John, Ulrik P; Polotnianka, Renatam M; Sivakumaran, Kailayapillai A; Chew, Orinda; Mackin, Leanne; Kuiper, Micheal J; Talbot, Jonathan P; Nugent, Gregory D; Mautord, Julie; Schrauf, Gustavo E; Spangenberg, German C

    2009-04-01

    Antarctic hair grass (Deschampsia antarctica E. Desv.), the only grass indigenous to Antarctica, has well-developed freezing tolerance, strongly induced by cold acclimation. Here, we show that in response to low temperatures, D. antarctica expresses potent recrystallization inhibition (RI) activity that, inhibits the growth of small ice crystals into potentially damaging large ones, is proteinaceous and localized to the apoplasm. A gene family from D. antarctica encoding putative homologs of an ice recrystallization inhibition protein (IRIP) has been isolated and characterized. IRIPs are apoplastically targeted proteins with two potential ice-binding motifs: 1-9 leucine-rich repeats (LRRs) and c. 16 'IRIP' repeats. IRIP genes appear to be confined to the grass subfamily Pooideae and their products, exhibit sequence similarity to phytosulphokine receptors and are predicted to adopt conformations with two ice-binding surfaces. D. antarctica IRIP (DaIRIP) transcript levels are greatly enhanced in leaf tissue following cold acclimation. Transgenic Arabidopsis thaliana expressing a DaIRIP has novel RI activity, and purified DaIRIP, when added back to extracts of leaves from non-acclimated D. antarctica, can reconstitute the activity found in acclimated plants. We propose that IRIP-mediated RI activity may contribute to the cryotolerance of D. antarctica, and thus to its unique ability to have colonized Antarctica.

  6. Historical CO2 Records from the Law Dome DE08, DE08-2, and DSS Ice Cores (1006 A.D.-1978 A.D)

    DOE Data Explorer

    Etheridge, D. M. [Commonwealth Scientific and Industrial Research Organization (CSIRO), Aspendale, Australia; Barnola, J. M. [Laboratoire de Glaciologie et Géophysique de l'Environnement, Saint Martin d'Hères-Cedex, France; Morgan, V. I. [Antarctic CRC and Australian Antarctic Division, Hobart, Tasmania, Australia; Steele, L. P. [Commonwealth Scientific and Industrial Research Organization (CSIRO), Aspendale, Australia; Langenfelds, R. L. [Commonwealth Scientific and Industrial Research Organization (CSIRO), Aspendale, Australia; Francey, R. J. [Commonwealth Scientific and Industrial Research Organization (CSIRO), Aspendale, Australia; Martinez, Monica [Oak Ridge National Laboratory, Oak Ridge, TN (USA)

    1998-01-01

    The CO2 records presented here are derived from three ice cores obtained at Law Dome, East Antarctica from 1987 to 1993. The Law Dome site satisfies many of the desirable characteristics of an ideal ice core site for atmospheric CO2 reconstructions including negligible melting of the ice sheet surface, low concentrations of impurities, regular stratigraphic layering undisturbed at the surface by wind or at depth by ice flow, and high snow accumulation rate. Further details on the site, drilling, and cores are provided in Etheridge et al. (1996), Etheridge and Wookey (1989), and Morgan et al (1997).

  7. Evaluating the Duration and Continuity of Potential Climate Records From the Allan Hills Blue Ice Area, East Antarctica

    NASA Astrophysics Data System (ADS)

    Kehrl, Laura; Conway, Howard; Holschuh, Nicholas; Campbell, Seth; Kurbatov, Andrei V.; Spaulding, Nicole E.

    2018-05-01

    The current ice core record extends back 800,000 years. Geologic and glaciological evidence suggests that the Allan Hills Blue Ice Area, East Antarctica, may preserve a continuous record that extends further back in time. In this study, we use ice-penetrating radar and existing age constraints to map the internal stratigraphy and age structure of the Allan Hills Main Ice Field. The dated isochrones provide constraints for an ice flow model to estimate the age of ice near the bed. Previous drilling in the region recovered stratigraphically disturbed sections of ice up to 2.7 million years old. Our study identifies a site 5 km upstream, which likely preserves a continuous record through Marine Isotope Stage 11 with the possibility that the record extends back 1 million years. Such records would provide new insight into the past climate and glacial history of the Ross Sea Sector.

  8. Tephra layers in the Siple Dome and Taylor Dome ice cores, Antarctica: Sources and correlations

    NASA Astrophysics Data System (ADS)

    Dunbar, Nelia W.; Zielinski, Gregory A.; Voisins, Daniel T.

    2003-08-01

    Volcanic ash, or tephra layers, are found in the Taylor Dome, Siple Dome A, and Siple Dome B ice cores. Significant shard concentrations are found at a number of depths in all three cores. Electron and ion microprobe analyses indicate that the geochemical composition of most layers is basaltic, basanitic, or trachytic, and the geochemical signatures of the layers suggest derivation from the Pleiades volcanic center, Mt. Melbourne volcano, or small mafic centers, probably in the Royal Society Range area. Presence of tephra layers suggests an episode of previously unrecognized Antarctic volcanic activity between 1776 and 1805 A.D., from at least two volcanic centers. A strong geochemical correlation (D = 3.49 and 3.97 with a value of 4 considered identical) is observed between tephra layers at depth of 79.2 m in the Taylor Dome ice core, and layers between 97.2 and 97.7 m depth in the Siple B core. This correlation, and the highly accurate depth-age scale of the Siple B core suggest that the age of this horizon in the Taylor Dome ice core presented by [1998a, 2000] should be revised downward, to the younger age of 675 ± 25 years before 1995. This revised chronology is consistent with vertical strain measurements presented by [2003].

  9. Climatic Changes on Tibetan Plateau Based on Ice Core Records

    NASA Astrophysics Data System (ADS)

    Yao, T.

    2008-12-01

    Climatic changes have been reconstructed for the Tibetan Plateau based on ice core records. The Guliya ice core on the Tibetan Plateau presents climatic changes in the past 100,000 years, thus is comparative with that from Vostok ice core in Antarctica and GISP2 record in Arctic. These three records share an important common feature, i.e., our climate is not stable. It is also evident that the major patterns of climatic changes are similar on the earth. Why does climatic change over the earth follow a same pattern? It might be attributed to solar radiation. We found that the cold periods correspond to low insolation periods, and warm periods to high insolation periods. We found abrupt climatic change in the ice core climatic records, which presented dramatic temperature variation of as much as 10 °C in 50 or 60 years. Our major challenge in the study of both climate and environment is that greenhouse gases such as CO2, CH4 are possibly amplifying global warming, though at what degree remains unclear. One of the ways to understand the role of greenhouse gases is to reconstruct the past greenhouse gases recorded in ice. In 1997, we drilled an ice core from 7100 m a.s.l. in the Himalayas to reconstruct methane record. Based on the record, we found seasonal cycles in methane variation. In particular, the methane concentration is high in summer, suggestiing active methane emission from wet land in summer. Based on the seasonal cycle, we can reconstruct the methane fluctuation history in the past 500 years. The most prominent feature of the methane record in the Himalayan ice core is the abrupt increase since 1850 A.D.. This is closely related to the industrial revolution worldwide. We can also observe sudden decrease in methane concentration during the World War I and World War II. It implies that the industrial revolution has dominated the atmospheric greenhouse gas emission for about 100 years. Besides, the average methane concentration in the Himalayan ice core is

  10. Sediment features at the grounding zone and beneath Ekström Ice Shelf, East Antarctica, imaged using on-ice vibroseis.

    NASA Astrophysics Data System (ADS)

    Smith, Emma C.; Eisen, Olaf; Hofstede, Coen; Lambrecht, Astrid; Mayer, Christoph

    2017-04-01

    The grounding zone, where an ice sheet becomes a floating ice shelf, is known to be a key threshold region for ice flow and stability. A better understanding of ice dynamics and sediment transport across such zones will improve knowledge about contemporary and palaeo ice flow, as well as past ice extent. Here we present a set of seismic reflection profiles crossing the grounding zone and continuing to the shelf edge of Ekström Ice Shelf, East Antarctica. Using an on-ice vibroseis source combined with a snowstreamer we have imaged a range of sub-glacial and sub-shelf sedimentary and geomorphological features; from layered sediment deposits to elongated flow features. The acoustic properties of the features as well as their morphology allow us to draw conclusions as to their material properties and origin. These results will eventually be integrated with numerical models of ice dynamics to quantify past and present interactions between ice and the solid Earth in East Antarctica; leading to a better understanding of future contributions of this region to sea-level rise.

  11. Meteorites and Microbes: Meteorite Collection and Ice Sampling at Patriot Hills, Thiel Mountains, and South Pole, Antarctica

    NASA Technical Reports Server (NTRS)

    Sipiera, Paul P.; Hoover, Richard B.; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    During the Antarctica 2000 Expedition, sponsored by the Planetary Studies Foundation, meteorites and ice microbiota were collected from the Patriot Hills, and Thiel Mountains of Antarctica and snow samples were at the South Pole. Psychrophilic and psychrotrophic microbiota were obtained from blue ice, cryoconite and ice-bubble systems. Twenty frozen meteorites were collected using aseptic techniques from the blue ice fields near the Moulton Escarpment of the Thiel Mountains (85 S, 94 W) and from the Morris Moraine of the Patriot Hills (80 S, 81 W) Ellsworth Mountains. These ice and meteorite samples are of potential significance to Astrobiology. They may help refine chemical and morphological biomarkers and refine characteristics of microbial life in one of the harshest environments on Earth. We discuss the Antarctica 2000 Expedition and provide preliminary results of the investigation of the meteorites and ice microbiota recovered.

  12. Solving the riddle of interglacial temperatures over the last 1.5 million years with a future IPICS "Oldest Ice" ice core

    NASA Astrophysics Data System (ADS)

    Fischer, Hubertus

    2014-05-01

    The sequence of the last 8 glacial cycles is characterized by irregular 100,000 year cycles in temperature and sea level. In contrast, the time period between 1.5-1.2 million years ago is characterized by more regular cycles with an obliquity periodicity of 41,000 years. Based on a deconvolution of deep ocean temperature and ice volume contributions to benthic δ18O (Elderfield et al., Science, 2012), it is suggested that glacial sea level became progressively lower over the last 1.5 Myr, while glacial deep ocean temperatures were very similar. At the same time many interglacials prior to the Mid Brunhes event showed significantly cooler deep ocean temperatures than the Holocene, while at the same time interglacial ice volume remained essentially the same. In contrast, interglacial sea surface temperatures in the tropics changed little (Herbert et al., Science,2010) and proxy reconstructions of atmospheric CO2 using δ11B in planktic foraminifera (Hönisch et al., Science, 2009) suggest that prior to 900,000 yr before present interglacial CO2 levels did not differ substantially from those over the last 450,000 years. Accordingly, the conundrum arises how interglacials can differ in deep ocean temperature without any obvious change in ice volume or greenhouse gas forcing and what caused the change in cyclicity of glacial interglacial cycles over the Mid Pleistocene Transition. Probably the most important contribution to solve this riddle is the recovery of a 1.5 Myr old ice core from Antarctica, which among others would provide an unambiguous, high-resolution record of the greenhouse gas history over this time period. Accordingly, the international ice core community, as represented by the International Partnership for Ice Core Science (IPICS), has identified such an 'Oldest Ice' ice core as one of the most important scientific targets for the future (http://www.pages.unibe.ch/ipics/white-papers). However, finding stratigraphically undisturbed ice, which covers this

  13. Increased future ice discharge from Antarctica owing to higher snowfall.

    PubMed

    Winkelmann, R; Levermann, A; Martin, M A; Frieler, K

    2012-12-13

    Anthropogenic climate change is likely to cause continuing global sea level rise, but some processes within the Earth system may mitigate the magnitude of the projected effect. Regional and global climate models simulate enhanced snowfall over Antarctica, which would provide a direct offset of the future contribution to global sea level rise from cryospheric mass loss and ocean expansion. Uncertainties exist in modelled snowfall, but even larger uncertainties exist in the potential changes of dynamic ice discharge from Antarctica and thus in the ultimate fate of the precipitation-deposited ice mass. Here we show that snowfall and discharge are not independent, but that future ice discharge will increase by up to three times as a result of additional snowfall under global warming. Our results, based on an ice-sheet model forced by climate simulations through to the end of 2500 (ref. 8), show that the enhanced discharge effect exceeds the effect of surface warming as well as that of basal ice-shelf melting, and is due to the difference in surface elevation change caused by snowfall on grounded versus floating ice. Although different underlying forcings drive ice loss from basal melting versus increased snowfall, similar ice dynamical processes are nonetheless at work in both; therefore results are relatively independent of the specific representation of the transition zone. In an ensemble of simulations designed to capture ice-physics uncertainty, the additional dynamic ice loss along the coastline compensates between 30 and 65 per cent of the ice gain due to enhanced snowfall over the entire continent. This results in a dynamic ice loss of up to 1.25 metres in the year 2500 for the strongest warming scenario. The reported effect thus strongly counters a potential negative contribution to global sea level by the Antarctic Ice Sheet.

  14. Late Summer Frazil Ice-Associated Algal Blooms around Antarctica

    NASA Astrophysics Data System (ADS)

    DeJong, Hans B.; Dunbar, Robert B.; Lyons, Evan A.

    2018-01-01

    Antarctic continental shelf waters are the most biologically productive in the Southern Ocean. Although satellite-derived algorithms report peak productivity during the austral spring/early summer, recent studies provide evidence for substantial late summer productivity that is associated with green colored frazil ice. Here we analyze daily Moderate Resolution Imaging Spectroradiometer satellite images for February and March from 2003 to 2017 to identify green colored frazil ice hot spots. Green frazil ice is concentrated in 11 of the 13 major sea ice production polynyas, with the greenest frazil ice in the Terra Nova Bay and Cape Darnley polynyas. While there is substantial interannual variability, green frazil ice is present over greater than 300,000 km2 during March. Late summer frazil ice-associated algal productivity may be a major phenomenon around Antarctica that is not considered in regional carbon and ecosystem models.

  15. Mezozooplankton Beneath the Summer Sea Ice in McMurdo Sound, Antarctica: Abundance, Species Composition, and DMSP content

    EPA Science Inventory

    The Ross Sea Phaeocystis antarctica bloom contributes to a summer increase in under-ice planton biomass in McMurdo Sound, Antarctica. Due to difficulties of under-ice sampling, information on the mesozooplankton in McMurdo Sound is limited. We measured the abundance of mesooopl...

  16. Influence of West Antarctic Ice Sheet collapse on Antarctic surface climate

    NASA Astrophysics Data System (ADS)

    Steig, Eric J.; Huybers, Kathleen; Singh, Hansi A.; Steiger, Nathan J.; Ding, Qinghua; Frierson, Dargan M. W.; Popp, Trevor; White, James W. C.

    2015-06-01

    Climate model simulations are used to examine the impact of a collapse of the West Antarctic Ice Sheet (WAIS) on the surface climate of Antarctica. The lowered topography following WAIS collapse produces anomalous cyclonic circulation with increased flow of warm, maritime air toward the South Pole and cold-air advection from the East Antarctic plateau toward the Ross Sea and Marie Byrd Land, West Antarctica. Relative to the background climate, areas in East Antarctica that are adjacent to the WAIS warm, while substantial cooling (several °C) occurs over parts of West Antarctica. Anomalously low isotope-paleotemperature values at Mount Moulton, West Antarctica, compared with ice core records in East Antarctica, are consistent with collapse of the WAIS during the last interglacial period, Marine Isotope Stage 5e. More definitive evidence might be recoverable from an ice core record at Hercules Dome, East Antarctica, which would experience significant warming and positive oxygen isotope anomalies if the WAIS collapsed.

  17. Insight into the latitudinal distribution of methane emissions throughout the Holocene from ice core methane records.

    NASA Astrophysics Data System (ADS)

    Sowers, T. A.; Vladimirova, D.; Blunier, T.

    2017-12-01

    During the preAnthropogenic era (prior to 1600AD) the interpolar CH4 gradient (IPG) is effectively dictated by the ratio of tropical to Pan Arctic CH4 emissions. IPG records from ice cores in Greenland and Antarctica provide fundamental information for assessing the latitudinal distribution of CH4 emissions and their relation to global climate change. We recently constructed a high-resolution (100yr) record of IPG changes throughout the Holocene using the ReCAP (E. Greenland) and WAIS (W. Antarctica) ice cores. Contemporaneous samples from both cores were analyzed on the same day to minimize analytical uncertainties associated with IPG reconstructions. CH4results from the WAIS core were indistinguishable from previous results suggesting our analytical scheme was intact (± 3ppb). Our reconstructed IPG showed early Holocene IPG values of 65ppb declining throughout the Holocene to values approximating 45 ppb during the latest portion of the Holocene (preAnthropogenic). We then utilized an eight box atmospheric methane box model (EBAMM) to quantify emission scenarios that agree with ice core CH4 records (concentration, IPG and isotopic composition). Our results are consistent with the idea that early Holocene peatland development in the PanArctic regions followed glacier retreat near the end of the last glacial termination contributing an additional 20Tg of CH4/yr relative to the late Holocene. In addition, we had to invoke elevated biomass burning emissions (40Tg/yr) during the early Holocene to account for the elevated d13CH4 values.

  18. Radiometric 81Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica

    PubMed Central

    Buizert, Christo; Baggenstos, Daniel; Jiang, Wei; Purtschert, Roland; Petrenko, Vasilii V.; Lu, Zheng-Tian; Müller, Peter; Kuhl, Tanner; Lee, James; Severinghaus, Jeffrey P.; Brook, Edward J.

    2014-01-01

    We present successful 81Kr-Kr radiometric dating of ancient polar ice. Krypton was extracted from the air bubbles in four ∼350-kg polar ice samples from Taylor Glacier in the McMurdo Dry Valleys, Antarctica, and dated using Atom Trap Trace Analysis (ATTA). The 81Kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean absolute age offset of 6 ± 2.5 ka. Our experimental methods and sampling strategy are validated by (i) 85Kr and 39Ar analyses that show the samples to be free of modern air contamination and (ii) air content measurements that show the ice did not experience gas loss. We estimate the error in the 81Kr ages due to past geomagnetic variability to be below 3 ka. We show that ice from the previous interglacial period (Marine Isotope Stage 5e, 130–115 ka before present) can be found in abundance near the surface of Taylor Glacier. Our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available, greatly enhancing their scientific value as archives of old ice and meteorites. At present, ATTA 81Kr analysis requires a 40–80-kg ice sample; as sample requirements continue to decrease, 81Kr dating of ice cores is a future possibility. PMID:24753606

  19. Radiometric 81Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica.

    PubMed

    Buizert, Christo; Baggenstos, Daniel; Jiang, Wei; Purtschert, Roland; Petrenko, Vasilii V; Lu, Zheng-Tian; Müller, Peter; Kuhl, Tanner; Lee, James; Severinghaus, Jeffrey P; Brook, Edward J

    2014-05-13

    We present successful (81)Kr-Kr radiometric dating of ancient polar ice. Krypton was extracted from the air bubbles in four ∼350-kg polar ice samples from Taylor Glacier in the McMurdo Dry Valleys, Antarctica, and dated using Atom Trap Trace Analysis (ATTA). The (81)Kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean absolute age offset of 6 ± 2.5 ka. Our experimental methods and sampling strategy are validated by (i) (85)Kr and (39)Ar analyses that show the samples to be free of modern air contamination and (ii) air content measurements that show the ice did not experience gas loss. We estimate the error in the (81)Kr ages due to past geomagnetic variability to be below 3 ka. We show that ice from the previous interglacial period (Marine Isotope Stage 5e, 130-115 ka before present) can be found in abundance near the surface of Taylor Glacier. Our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available, greatly enhancing their scientific value as archives of old ice and meteorites. At present, ATTA (81)Kr analysis requires a 40-80-kg ice sample; as sample requirements continue to decrease, (81)Kr dating of ice cores is a future possibility.

  20. Ice shelf structure and stability: Larsen C Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Hubbard, B. P.; Ashmore, D.; Bevan, S. L.; Booth, A. D.; Holland, P.; Jansen, D.; Kuipers Munneke, P.; Kulessa, B.; Luckman, A. J.; Sevestre, H.; O'Leary, M.

    2017-12-01

    We report on recent empirical investigations of the internal structure and stability (or otherwise) of Larsen C Ice Shelf (LCIS), Antarctica, focusing on research carried out for the MIDAS research project between 2014 and 2017. Borehole- and surface geophysics-based fieldwork carried out in austral springs 2014 and 2015 revealed that ephemeral surface ponds, preferentially located within the major inlets within the northern sector of the ice shelf, result in the formation of several tens of metres of (relatively dense) subsurface ice within what would otherwise have been a progressively densifying snow and firn column. Five boreholes were drilled throughout the sector and logged by optical televiewer, showing this refrozen ice to be extensive and of variable composition depending on its process of formation. Mapping the depth-distribution of the resulting ice types and associating each with a simple flow-line model of ice motion and accumulation indicates that this area of LCIS has experienced substantial melting for some centuries but that surface ponding has only occurred in recent decades, possibly restricted to the past 20 years. We also present near-surface temperature data that reveal surprising temporal patterns in foehn wind activity and intensity. Finally, we report on the geometrical extension and widening of a rift that was responsible for calving a 5,800 km^2 iceberg from the LCIS in July 2017. The nature of rift propagation through `suture' ice bands, widely considered to be composed of marine ice, is contrasted with that of its propagation through meteoric ice.

  1. Solid and gaseous inclusions in the EDML deep ice core: origins and implications for the physical properties of polar ice

    NASA Astrophysics Data System (ADS)

    Faria, S. H.; Kipfstuhl, S.; Garbe, C. S.; Bendel, V.; Weikusat, C.; Weikusat, I.

    2010-12-01

    The great value of polar deep ice cores stems mainly from two essential features of polar ice: its crystalline structure and its impurities. They determine the physical properties of the ice matrix and provide proxies for the investigation of past climates. Experience shows that these two essential features of polar ice manifest themselves in a multiscale diversity of dynamic structures, including dislocations, grain boundaries, solid particles, air bubbles, clathrate hydrates and cloudy bands, among others. The fact that these structures are dynamic implies that they evolve with time through intricate interactions between the crystalline structure, impurities, and the ice flow. Records of these interactions have been carefully investigated in samples of the EPICA deep ice core drilled in Dronning Maud Land, Antarctica (75°S, 0°E, 2882 m elevation, 2774.15 m core length). Here we show how the distributions of sizes and shapes of air bubbles correlate with impurities and the crystalline structure, how the interaction between moving grain boundaries and micro-inclusions changes with ice depth and temperature, as well as the possible causes for the abrupt change in ice rheology observed in the MIS6-MIS5e transition. We also discuss how these observations may affect the flow of the ice sheet and the interpretation of paleoclimate records. Micrograph of an EDML sample from 555m depth. One can identify air bubbles (dark, round objects), microinclusions (tiny defocused spots), and a grain boundary pinned by a bubble. The width of the image is 700 micrometers.

  2. Globally synchronous ice core volcanic tracers and abrupt cooling during the last glacial period

    USGS Publications Warehouse

    Bay, R.C.; Bramall, N.E.; Price, P.B.; Clow, G.D.; Hawley, R.L.; Udisti, R.; Castellano, E.

    2006-01-01

    We perform a Monte Carlo pattern recognition analysis of the coincidence between three regional volcanic histories from ice coring of Greenland and Antarctica over the period 2 to 45 ka, using SO4 anomalies in Greenland and East Antarctica determined by continuous core chemistry, together with West Antarctic volcanic ash layers determined by remote optical borehole logging and core assays. We find that the Antarctic record of volcanism correlates with Glacial abrupt climate change at a 95% to >99.8% (???3??) significance level and that volcanic depositions at the three locations match at levels exceeding 3??, likely indicating that many common horizons represent single eruptive events which dispersed material world wide. These globally coincident volcanics were associated with abrupt cooling, often simultaneous with onsets or sudden intensifications of millennial cold periods. The striking agreement between sites implies that the consistency of current timescales obtained by isotopic and glaciological dating methods is better than estimated. Copyright 2006 by the American Geogphysical Union.

  3. Marine Isotope Stage 11 : The Role of Co2, Insolation and Antarctica Ice Sheet On This Interglacial

    NASA Astrophysics Data System (ADS)

    Raynaud, D.; Loutre, M. F.; Ritz, C.; Barnola, J.-M.; Berger, A.; Chappellaz, J.; Jouzel, J.; Lipenkov, V.; Petit, J.-R.; Vimeux, F.

    The Marine Isotopic Stage 11 (MIS 11), around 400kyr BP ago, has been suggested as an analogue for a future climate under natural forcing because of the similar condi- tions of orbitally driven insolation during this interglacial period and the one covering the Holocene and the near future. There are many open questions about unusual MIS 11 climatic conditions (length of the interglacial, temperature, sea level, marine car- bonate system), as recorded in different marine and continental records. The Antarctic Vostok ice core provides the only atmospheric record extending back to MIS 11 and we use it to discuss the Antarctic temperature, the atmospheric CO2 concentration and the ice sheet stability in the central part of East Antarctica during this interglacial. The unique nature of the Vostok atmospheric record leads us to use the available Vos- tok data to drive climate and ice sheet models for MIS 11. A model of intermediate complexity (LLN-2D model) is used to investigate the sensitivity of the simulated MIS 11 deglaciation to the interplay between insolation and CO2. It is shown that the length of the simulated interglacial depends strongly on the phasing between these two climate forcings. We also investigate the response of the Antarctic Ice Sheet to changing climate through simulations performed with the LGGE 3-D ice sheet model. The results indicate that sea level stands during MIS 11 as high as 20 m. above present level, as suggested by different elevated marine terraces, cannot be explained, except by assuming that MIS 11 was very dry over Antarctica.

  4. 10Be in ice at high resolution: Solar activity and climate signals observed and GCM-modeled in Law Dome ice cores

    NASA Astrophysics Data System (ADS)

    Pedro, Joel; Heikkilä, Ulla; van Ommen, T. D.; Smith, A. M.

    2010-05-01

    Changes in solar activity modulate the galactic cosmic ray flux, and in turn, the production rate of 10Be in the earth's atmosphere. The best archives of past changes in 10Be production rate are the polar ice cores. Key challenges in interpreting these archives as proxies for past solar activity lie in separating the useful solar activity (or production) signal from the interfering meteorological (or climate) signal, and furthermore, in determining the atmospheric source regions of 10Be deposited to the ice core site. In this study we use a new monthly resolution composite 10Be record, which spans the past decade, and a general circulation model (ECHAM5-HAM), to constrain both the production and climate signals in 10Be concentrations at the Law Dome ice core site, East Antarctica. This study differs from most previous work on 10Be in Antarctica due to the very high sample resolution achieved. This high resolution, through a time period where accurate instrumental measurements of solar activity and climate are available, allows us to examine the response of 10Be concentrations in ice to short-term (monthly to annual) variations in solar activity, and to short-term variations in climate, including seasonality. We find a significant correlation (r2 = 0.56, P < 0.005, n = 92) between observed 10Be concentrations and solar activity (represented by the neutron counting rate). The most pervasive climate influence is a seasonal cycle, which shows maximum concentrations in mid-to-late-summer and minimum concentrations in winter. Model results show reasonable agreement with observations; both a solar activity signal and seasonal cycle in 10Be are captured. However, the modeled snow accumulation rate is too high by approximately 60%. According to the model, the main atmospheric source region of 10Be deposited to Law Dome is the 30-90°S stratosphere (~50%), followed by the 30-90°S troposphere (~30%). An enhancement in the fraction of 10Be arriving to Law Dome from the

  5. Dust flux in peripheral East Antarctica: preliminary results from GV7 ice core and extension of the TALDICE dust record to the sub-micron range

    NASA Astrophysics Data System (ADS)

    Delmonte, Barbara; Giovanni, Baccolo; Fausto, Marasci; Iizuka, Yoshinori; Valter, Maggi

    2015-04-01

    Improved understanding of climate variability over the last two millennia - that is a critical time period for investigating natural and anthropogenic climate change - is one of the key priorities of the International Partnership in Ice Core Sciences (IPICS). The Italian contribution to this concerted international effort is represented by the project IPICS-2kyr-Italy supported by PNRA. In this context, a novel intermediate core (about 250 m deep) was drilled during the 2013/14 field season at the peripheral site of GV7 in East Antarctica (70°41'S, 158°52'E; elevation 1950 m), where snow accumulation is very high (about 3 times Talos Dome, 10 times EPICA Dome C). After the ice core processing campaign at EuroCold (UNIMIB) carried out in synergy between Italy and Korea teams, measurements of dust concentration and size distribution are now in progress. A novel Coulter Counter apparatus has been set up in order to extend dust size spectra down to 600 nm. Samples are analyzed immediately after melting and also 24h later under identical conditions, for a quantitative assessment of the contribution of water-soluble microparticles (salts). Seasonal variability and trends of insoluble dust, metastable salts and size distribution of these compounds is under study. The possibility to extended the size range of dust measurements has allowed refining estimates of dust flux at Talos Dome and an adjustment of published data.

  6. Critical Fracture Toughness Measurements of an Antarctic Ice Core

    NASA Astrophysics Data System (ADS)

    Christmann, Julia; Müller, Ralf; Webber, Kyle; Isaia, Daniel; Schader, Florian; Kippstuhl, Sepp; Freitag, Johannes; Humbert, Angelika

    2014-05-01

    Fracture toughness is a material parameter describing the resistance of a pre-existing defect in a body to further crack extension. The fracture toughness of glacial ice as a function of density is important for modeling efforts aspire to predict calving behavior. In the presented experiments this fracture toughness is measured using an ice core from Kohnen Station, Dronning Maud Land, Antarctica. The samples were sawed in an ice lab at the Alfred Wegener Institute in Bremerhaven at -20°C and had the dimensions of standard test samples with thickness 14 mm, width 28 mm and length 126 mm. The samples originate from a depth of 94.6 m to 96 m. The grain size of the samples was also identified. The grain size was found to be rather uniform. The critical fracture toughness is determined in a four-point bending approach using single edge V-notch beam samples. The initial notch length was around 2.5 mm and was prepared using a drilling machine. The experimental setup was designed at the Institute of Materials Science at Darmstadt. In this setup the force increases linearly, until the maximum force is reached, where the specific sample fractures. This procedure was done in an ice lab with a temperature of -15°C. The equations to calculate the fracture toughness for pure bending are derived from an elastic stress analysis and are given as a standard test method to detect the fracture toughness. An X-ray computer tomography (CT scanner) was used to determine the ice core densities. The tests cover densities from 843 kg m-3 to 871 kg m-3. Thereby the influence of the fracture toughness on the density was analyzed and compared to previous investigations of this material parameter. Finally the dependence of the measured toughness on thickness, width, and position in the core cross-section was investigated.

  7. Relative sea-level rise around East Antarctica during Oligocene glaciation

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

    During the middle and late Eocene (~ 48-34Myr ago), the Earth's climate cooled and an ice sheet built up on Antarctica. The stepwise expansion of ice on Antarctica induced crustal deformation and gravitational perturbations around the continent. Close to the ice sheet, sea level rose despite an overall reduction in the mass of the ocean caused by the transfer of water to the ice sheet. Here we identify the crustal response to ice-sheet growth by forcing a glacial-hydro isostatic adjustment model with an Antarctic ice-sheet model. We find that the shelf areas around East Antarctica first shoaled as upper mantle material upwelled and a peripheral forebulge developed. The inner shelf subsequently subsided as lithosphere flexure extended outwards from the ice-sheet margins. Consequently the coasts experienced a progressive relative sea-level rise. Our analysis of sediment cores from the vicinity of the Antarctic ice sheet are in agreement with the spatial patterns of relative sea-level change indicated by our simulations. Our results are consistent with the suggestion that near-field processes such as local sea-level change influence the equilibrium state obtained by an ice-sheet grounding line.

  8. Insights into Spatial Sensitivities of Ice Mass Response to Environmental Change from the SeaRISE Ice Sheet Modeling Project I: Antarctica

    NASA Technical Reports Server (NTRS)

    Nowicki, Sophie; Bindschadler, Robert A.; Abe-Ouchi, Ayako; Aschwanden, Andy; Bueler, Ed; Choi, Hyengu; Fastook, Jim; Granzow, Glen; Greve, Ralf; Gutowski, Gail; hide

    2013-01-01

    Atmospheric, oceanic, and subglacial forcing scenarios from the Sea-level Response to Ice Sheet Evolution (SeaRISE) project are applied to six three-dimensional thermomechanical ice-sheet models to assess Antarctic ice sheet sensitivity over a 500 year timescale and to inform future modeling and field studies. Results indicate (i) growth with warming, except within low-latitude basins (where inland thickening is outpaced by marginal thinning); (ii) mass loss with enhanced sliding (with basins dominated by high driving stresses affected more than basins with low-surface-slope streaming ice); and (iii) mass loss with enhanced ice shelf melting (with changes in West Antarctica dominating the signal due to its marine setting and extensive ice shelves; cf. minimal impact in the Terre Adelie, George V, Oates, and Victoria Land region of East Antarctica). Ice loss due to dynamic changes associated with enhanced sliding and/or sub-shelf melting exceeds the gain due to increased precipitation. Furthermore, differences in results between and within basins as well as the controlling impact of sub-shelf melting on ice dynamics highlight the need for improved understanding of basal conditions, grounding-zone processes, ocean-ice interactions, and the numerical representation of all three.

  9. Nitrate flux on the Ross Ice Shelf, Antarctica and its relation to solar cosmic rays

    NASA Astrophysics Data System (ADS)

    Zeller, Edward J.; Dreschhoff, Gisela A. M.; Laird, Claude M.

    1986-11-01

    Nitrate flux has been determined in the snow sequence deposited at Windless Bight on the Ross Ice Shelf (Antarctica). The data were obtained from on-site analysis of nitrate concentrations from a glaciological pit and a firn core spanning the time interval from midwinter 1971 to January 1986. The high resolution data can be combined with precipitation records collected from adjacent areas to provide a record of nitrate flow. The resulting time series contains a signal which corresponds to the two major solar events of 1972 and 1984. The concentration and flux profiles may be useful in studies of Antarctic ozone depletion.

  10. The Late Holocene Atmospheric Methane Budget Reconstructed from Ice Cores

    NASA Astrophysics Data System (ADS)

    Mitchell, Logan E.

    In this thesis I used a newly developed methane measurement line to make high-resolution, high-precision measurements of methane during the late Holocene (2800 years BP to present). This new measurement line is capable of an analytical precision of < 3 ppb using ˜120 g samples. The reduced sample size requirements as well as automation of a significant portion of the analysis process have enabled me to make >1500 discrete ice core methane measurements and construct the highest resolution records of methane available over the late Holocene. I first used a shallow ice core from WAIS Divide (WDC05A) to produce a 1000 year long methane record with a ˜9 year temporal resolution. This record confirmed the existence of multidecadal scale variations that were first observed in the Law Dome, Antarctica ice core. I then explored a range of paleoclimate archives for possible mechanistic connections with methane concentrations on multidecadal timescales. In addition, I present a detailed description of the analytical methods used to obtain high-precision measurements of methane including the effects of solubility and a new chronology for the WDC05A ice core. I found that, in general, the correlations with paleoclimate proxies for temperature and precipitation were low over a range of geographic regions. Of these, the highest correlations were found from 1400-1600 C.E. during the onset of the Little Ice Age and with a drought index in the headwater region of the major East Asian rivers. Large population losses in Asia and the Americas are also coincident with methane concentration decreases indicating that anthropogenic activities may have been impacting multidecadal scale methane variability. In the second component I extended the WAIS Divide record back to 2800 years B.P. and also measured methane from GISP2D over this time interval. These records allowed me to examine the methane Inter-Polar Difference (IPD) which is created by greater northern hemispheric sources. The IPD

  11. Post-LGM grounding line and calving front translations of the West Antarctic Ice Sheet in the Whales Deep paleo-ice-stream trough, eastern Ross Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    McGlannan, A. J.; Bart, P. J.; Chow, J.

    2016-12-01

    A large-area (2500 km2) multibeam survey of the Whales Deep paleo-ice-stream trough, eastern Ross Sea, Antarctica was acquired during NBP1502B. This sector of the continental shelf is important as it was covered by grounded and floating ice, which drained the central part of an expanded West Antarctic Ice Sheet (WAIS) during the last glacial cycle. The seafloor geomorphology shows a well-defined cluster of four back stepping grounding zone wedges (GZWs) that were deposited in a partly overlapping fashion on the middle continental shelf during WAIS retreat. These observations permit two end-member possibilities for how the WAIS grounding line and calving front vacated the trough. In the first scenario, each GZW represents successive landward shifts of the grounding line and calving front. In the second scenario, each GZW represents a large-scale retreat and re-advance of grounded and floating ice. To determine which of these two end-member scenarios most accurately describes WAIS retreat from this sector of Ross Sea, we evaluated a grid of kasten and piston cores. The core stations were selected on the basis of backstepping GZWs along the trough axis. Our core data analyses included an integration of visual core descriptions, x-ray images, grain size, water content, total organic carbon, shear strengths, and diatom assemblage data. Core data reveal a single transgressive succession from proximal diamict overlain by sub-ice-shelf and/or open-marine sediments. These data strongly support the first scenario, suggesting that an ice shelf remained continuously intact during the time that the grounding line successively moved from the shelf edge to the middle shelf by small-scale landward translations until the end of the fourth grounding event. Sedimentologic and diatom-assemblage data from the inner shelf show that only the last middle shelf grounding event ended with a long-distance retreat of grounded and then floating ice to south of the modern calving front.

  12. Archival processes of the water stable isotope signal in East Antarctic ice cores

    NASA Astrophysics Data System (ADS)

    Casado, Mathieu; Landais, Amaelle; Picard, Ghislain; Münch, Thomas; Laepple, Thomas; Stenni, Barbara; Dreossi, Giuliano; Ekaykin, Alexey; Arnaud, Laurent; Genthon, Christophe; Touzeau, Alexandra; Masson-Delmotte, Valerie; Jouzel, Jean

    2018-05-01

    The oldest ice core records are obtained from the East Antarctic Plateau. Water isotopes are key proxies to reconstructing past climatic conditions over the ice sheet and at the evaporation source. The accuracy of climate reconstructions depends on knowledge of all processes affecting water vapour, precipitation and snow isotopic compositions. Fractionation processes are well understood and can be integrated in trajectory-based Rayleigh distillation and isotope-enabled climate models. However, a quantitative understanding of processes potentially altering snow isotopic composition after deposition is still missing. In low-accumulation sites, such as those found in East Antarctica, these poorly constrained processes are likely to play a significant role and limit the interpretability of an ice core's isotopic composition. By combining observations of isotopic composition in vapour, precipitation, surface snow and buried snow from Dome C, a deep ice core site on the East Antarctic Plateau, we found indications of a seasonal impact of metamorphism on the surface snow isotopic signal when compared to the initial precipitation. Particularly in summer, exchanges of water molecules between vapour and snow are driven by the diurnal sublimation-condensation cycles. Overall, we observe in between precipitation events modification of the surface snow isotopic composition. Using high-resolution water isotopic composition profiles from snow pits at five Antarctic sites with different accumulation rates, we identified common patterns which cannot be attributed to the seasonal variability of precipitation. These differences in the precipitation, surface snow and buried snow isotopic composition provide evidence of post-deposition processes affecting ice core records in low-accumulation areas.

  13. Records of past ice sheet fluctuations in interior East Antarctica

    USGS Publications Warehouse

    Liu, Xiaohan; Huang, Feixin; Kong, Ping; Fang, Aimin; Li, Xiaoli

    2007-01-01

    The results of a land-based multi-disciplinary study of the past ice surface elevation in the Grove Mountains of interior East Antarctica support a dynamic evolution of the East Antarctic Ice Sheet (EAIS). Moraine boulders of sedimentary rocks and spore pollen assemblage imply a significant shrinkage of the EAIS, with its margin retreating south of the Grove Mountains (~450 km south of recent coast line) before the middle Pliocene. The exposure ages indicate that the ice sheet subsequently re-advanced, with the ice surface rising locally at least 450 m higher than today. It then went back down constantly from before 2.3 Ma to 1.6 Ma. The glacial topography and existence of soil show that the ice surface fluctuation continued since the early Quaternary, but with highest levels never exceeding ~100 m higher than today.

  14. Ice Core Investigations

    ERIC Educational Resources Information Center

    Krim, Jessica; Brody, Michael

    2008-01-01

    What can glaciers tell us about volcanoes and atmospheric conditions? How does this information relate to our understanding of climate change? Ice Core Investigations is an original and innovative activity that explores these types of questions. It brings together popular science issues such as research, climate change, ice core drilling, and air…

  15. 740,000-year Deuterium Record in an Ice Core from Dome C, Antarctica

    DOE Data Explorer

    Jouzel, Jean [Laboratoire des Sciences du Climat et de l'Environnement

    2004-01-01

    Because isotopic fractions of the heavier oxygen-18 (18O) and deuterium (2H) in snowfall are temperature-dependent and a strong spatial correlation exists between the annual mean temperature and the mean isotopic fraction of 18O or 2H in precipitation, it is possible to derive temperature records from the records of those isotopes in ice cores.

  16. A method to precisely measure Ar isotopes and Xe/Kr ratios in air trapped in ice cores for simultaneous ice core dating and mean ocean temperature reconstruction

    NASA Astrophysics Data System (ADS)

    Yan, Y.; Ng, J.; Higgins, J. A.; Kurbatov, A.; Clifford, H.; Spaulding, N. E.; Mayewski, P. A.; Brook, E.; Bender, M. L.; Severinghaus, J. P.

    2017-12-01

    Antarctic efforts are underway to find and retrieve ice cores older than 800 thousand years (kyr) by both shallow drilling in "blue ice" areas and classic deep ice coring. Ice stratigraphy at "blue ice" sites is typically disordered, and the high cost of deep drilling mandates rapid reconnaissance drilling (e.g. RAID) with very small sample size. Both approaches therefore require methods of absolute dating on a single piece of ice without stratigraphic context. Here we present a dating method modified from Bender et al. (2008; PNAS) to precisely measure the isotopic composition of argon (36Ar, 38Ar, and 40Ar) in air bubbles trapped in the ice, which changes over time in a known way. Our method has an analytical uncertainty of 110 kyr (1σ) or 10% of the age of the sample, whichever is greater. We measured Ar isotopes from the Allan Hills blue ice areas, East Antarctica, where 1 Ma ice was previously found by Higgins et al. (2015; PNAS). Results show ice as old as 2.7±0.3 million years, but the ice column is stratigraphically disturbed. Hence Allan Hills ice core records should be viewed as a series of "climate snapshots" rather than a continuum. Xenon-to-krypton (Xe/Kr) ratios are also measured in the same aliquot of extracted gas to reconstruct mean ocean temperature (Shackleton et al., 2016; Fall AGU). Preliminary mean ocean temperature in ice older than 1 Ma ranges from -0.3 to -1.2 deg. colder than present with an uncertainty of 0.24 deg., which agrees well with other Pleistocene ocean temperature records (e.g. Rohling et al., 2014; Nature and Elderfield et al., 2012; Science). The observed range is 40% of the glacial-interglacial variability in the 100-kyr climate cycles ( 2 deg.), close to the 50% reduction in the glacial-interglacial δ18O amplitude across the Mid-Pleistocene Transition. Finally, Xe/Kr ratios are found to correlate positively with δD of the ice, implying a coupling between the global ocean temperature and Antarctic temperature throughout

  17. Annually resolved southern hemisphere volcanic history from two Antarctic ice cores

    NASA Astrophysics Data System (ADS)

    Cole-Dai, Jihong; Mosley-Thompson, Ellen; Thompson, Lonnie G.

    1997-07-01

    The continuous sulfate analysis of two Antarctic ice cores, one from the Antarctic Peninsula region and one from West Antarctica, provides an annually resolved proxy history of southern semisphere volcanism since early in the 15th century. The dating is accurate within ±3 years due to the high rate of snow accumulation at both core sites and the small sample sizes used for analysis. The two sulfate records are consistent with each other. A systematic and objective method of separating outstanding sulfate events from the background sulfate flux is proposed and used to identify all volcanic signals. The resulting volcanic chronology covering 1417-1989 A.D. resolves temporal ambiguities about several recently discovered events. A number of previously unknown, moderate eruptions during late 1600s are uncovered in this chronology. The eruption of Tambora (1815) and the recently discovered eruption of Kuwae (1453) in the tropical South Pacific injected the greatest amount of sulfur dioxide into the southern hemisphere stratosphere during the last half millennium. A technique for comparing the magnitude of volcanic events preserved within different ice cores is developed using normalized sulfate flux. For the same eruptions the variability of the volcanic sulfate flux between the cores is within ±20% of the sulfate flux from the Tambora eruption.

  18. ICE-VOLC Project: unravelling the dynamics of Antarctica volcanoes

    NASA Astrophysics Data System (ADS)

    Cannata, Andrea; Del Carlo, Paola; Giudice, Gaetano; Giuffrida, Giovanni; Larocca, Graziano; Liuzzo, Marco

    2017-04-01

    Melbourne and Rittmann volcanoes are located in the Victoria Land. Whilst Rittmann's last eruption dates probably to Pleistocene, Melbourne's most recent eruption between 1862 and 1922, testifying it is still active. At present, both volcanoes display fumarolic activity. Melbourne was discovered in 1841 by James Clark Ross, Rittmann during the 4th Italian Expedition (1988/1989). Our knowledge on both volcanoes is really little. The position of these volcanoes in the Antarctic region (characterised by absence of anthropic noise) and its proximity with the Italian Mario Zucchelli Station makes them ideal sites for studying volcano seismic sources, geothermal emissions, seismo-acoustic signals caused by cryosphere-hydrosphere-atmosphere dynamics, and volcanic gas impact on environment. Hence, the main aim of the ICE-VOLC ("multiparametrIC Experiment at antarctica VOLCanoes: data from volcano and cryosphere-ocean-atmosphere dynamics") project is the study of Melbourne and Rittmann, by acquisition, analysis and integration of multiparametric geophysical, geochemical and thermal data. Complementary objectives include investigation of the relationship between seismo-acoustic activity recorded in Antarctica and cryosphere-hydrosphere-atmosphere dynamics, evaluation of the impact of volcanic gas in atmosphere. This project involves 26 researchers, technologists and technicians from University of Perugia and from Istituto Nazionale di Geofisica e Vulcanologia of Catania, Palermo, Pisa and Rome. In this work, we show the preliminary results obtained after the first expedition in Antarctica, aiming to perform geochemical-thermal surveys in the volcano ice caves, as well as to collect ash samples and to install temporary seismic stations.

  19. The Antarctica component of postglacial rebound model ICE-6G_C (VM5a) based on GPS positioning, exposure age dating of ice thicknesses, and relative sea level histories

    NASA Astrophysics Data System (ADS)

    Argus, Donald F.; Peltier, W. R.; Drummond, R.; Moore, Angelyn W.

    2014-07-01

    viscous response to the early Holocene unloading of ice from the current locations of the ice shelf centers. ICE-6G_C (VM5A) fits the horizontal observations well (wrms residual speed of 0.7 mm yr-1), there being no need to invoke any influence of lateral variation in mantle viscosity. ICE-6G_C (VM5A) differs in several respects from the recently published W12A model of Whitehouse et al. First, the upper-mantle viscosity in VM5a is 5 × 1020 Pa s, half that in W12A. The VM5a profile, which is identical to that inferred on the basis of the Fennoscandian relaxation spectrum, North American relative sea level histories and Earth rotation constraints, when coupled with the revised ICE-6G_C deglaciation history, fits all of the available constraints. Secondly, the net contribution of Antarctica ice loss to global sea level rise is 13.6 m, 2/3 greater than the 8 m in W12A. Thirdly, ice loss occurs quickly from 12 to 5 ka, and the contribution to global sea level rise during Meltwater Pulse 1B (11.5 ka) is large (5 m), consistent with sedimentation constraints from cores from the Antarctica ice shelf. Fourthly, in ICE-6G_C there is no ice gain in the East Antarctica interior, as there is in W12A. Finally, the new model of Antarctic deglaciation reconciles the global constraint upon the global mass loss during deglaciation provided by the Barbados record of relative sea level history when coupled with the Northern Hemisphere counterpart of this new model.

  20. Modeling englacial radar attenuation at Siple Dome, West Antarctica, using ice chemistry and temperature data

    USGS Publications Warehouse

    MacGregor, J.A.; Winebrenner, D.P.; Conway, H.; Matsuoka, K.; Mayewski, P.A.; Clow, G.D.

    2007-01-01

    The radar reflectivity of an ice-sheet bed is a primary measurement for discriminating between thawed and frozen beds. Uncertainty in englacial radar attenuation and its spatial variation introduces corresponding uncertainty in estimates of basal reflectivity. Radar attenuation is proportional to ice conductivity, which depends on the concentrations of acid and sea-salt chloride and the temperature of the ice. We synthesize published conductivity measurements to specify an ice-conductivity model and find that some of the dielectric properties of ice at radar frequencies are not yet well constrained. Using depth profiles of ice-core chemistry and borehole temperature and an average of the experimental values for the dielectric properties, we calculate an attenuation rate profile for Siple Dome, West Antarctica. The depth-averaged modeled attenuation rate at Siple Dome (20.0 ?? 5.7 dB km-1) is somewhat lower than the value derived from radar profiles (25.3 ?? 1.1 dB km-1). Pending more experimental data on the dielectric properties of ice, we can match the modeled and radar-derived attenuation rates by an adjustment to the value for the pure ice conductivity that is within the range of reported values. Alternatively, using the pure ice dielectric properties derived from the most extensive single data set, the modeled depth-averaged attenuation rate is 24.0 ?? 2.2 dB km-1. This work shows how to calculate englacial radar attenuation using ice chemistry and temperature data and establishes a basis for mapping spatial variations in radar attenuation across an ice sheet. Copyright 2007 by the American Geophysical Union.

  1. Constraining ice sheet history in the Weddell Sea, West Antarctica, using ice fabric at Korff Ice Rise

    NASA Astrophysics Data System (ADS)

    Brisbourne, A.; Smith, A.; Kendall, J. M.; Baird, A. F.; Martin, C.; Kingslake, J.

    2017-12-01

    The grounding history of ice rises (grounded area of independent flow regime within a floating ice shelf) can be used to constrain large scale ice sheet history: ice fabric, resulting from the preferred orientation of ice crystals due to the stress regime, can be used to infer this grounding history. With the aim of measuring the present day ice fabric at Korff Ice Rise, West Antarctica, a multi-azimuth wide-angle seismic experiment was undertaken. Three wide-angle common-midpoint gathers were acquired centred on the apex of the ice rise, at azimuths of 60 degrees to one another, to measure variation in seismic properties with offset and azimuth. Both vertical and horizontal receivers were used to record P and S arrivals including converted phases. Measurements of the variation with offset and azimuth of seismic traveltimes, seismic attenuation and shear wave splitting have been used to quantify seismic anisotropy in the ice column. The observations cannot be reproduced using an isotropic ice column model. Anisotropic ray tracing has been used to test likely models of ice fabric by comparison with the data. A model with a weak girdle fabric overlying a strong cluster fabric provides the best fit to the observations. Fabric of this nature is consistent with Korff Ice Rise having been stable for the order of 10,000 years without any ungrounding or significant change in the ice flow configuration across the ice rise for this period. This observation has significant implications for the ice sheet history of the Weddell Sea sector.

  2. Historical Carbon Dioxide Record from the Vostok Ice Core (417,160 - 2,342 years BP)

    DOE Data Explorer

    Barnola, J. M. [CNRS, Saint Martin d'Heres Cedex, France; Raynaud, D. [CNRS, Saint Martin d'Heres Cedex, France; Lorius, C. [CNRS, Saint Martin d'Heres Cedex, France; Barkov, N. I.

    2003-01-01

    In January 1998, the collaborative ice-drilling project between Russia, the United States, and France at the Russian Vostok station in East Antarctica yielded the deepest ice core ever recovered, reaching a depth of 3,623 m (Petit et al. 1997, 1999). Ice cores are unique with their entrapped air inclusions enabling direct records of past changes in atmospheric trace-gas composition. Preliminary data indicate the Vostok ice-core record extends through four climate cycles, with ice slightly older than 400 kyr (Petit et al. 1997, 1999). Because air bubbles do not close at the surface of the ice sheet but only near the firn-ice transition (that is, at ~90 m below the surface at Vostok), the air extracted from the ice is younger than the surrounding ice (Barnola et al. 1991). Using semiempirical models of densification applied to past Vostok climate conditions, Barnola et al. (1991) reported that the age difference between air and ice may be ~6000 years during the coldest periods instead of ~4000 years, as previously assumed. Ice samples were cut with a bandsaw in a cold room (at about -15°C) as close as possible to the center of the core in order to avoid surface contamination (Barnola et al. 1983). Gas extraction and measurements were performed with the "Grenoble analytical setup," which involved crushing the ice sample (~40 g) under vacuum in a stainless steel container without melting it, expanding the gas released during the crushing in a pre-evacuated sampling loop, and analyzing the CO2 concentrations by gas chromatography (Barnola et al. 1983). The analytical system, except for the stainless steel container in which the ice was crushed, was calibrated for each ice sample measurement with a standard mixture of CO2 in nitrogen and oxygen. For further details on the experimental procedures and the dating of the successive ice layers at Vostok, see Barnola et al. (1987, 1991), Lorius et al. (1985), and Petit et al. (1999).

  3. Microbiota within the perennial ice cover of Lake Vida, Antarctica.

    PubMed

    Mosier, Annika C; Murray, Alison E; Fritsen, Christian H

    2007-02-01

    Lake Vida, located in the McMurdo Dry Valleys, Antarctica, is an 'ice-sealed' lake with approximately 19 m of ice covering a highly saline water column (approximately 245 ppt). The lower portions of the ice cover and the lake beneath have been isolated from the atmosphere and land for circa 2800 years. Analysis of microbial assemblages within the perennial ice cover of the lake revealed a diverse array of bacteria and eukarya. Bacterial and eukaryal denaturing gradient gel electrophoresis phylotype profile similarities were low (<59%) between all of the depths compared (five depths spanning 11 m of the ice cover), with the greatest differences occurring between surface and deep ice. The majority of bacterial 16S rRNA gene sequences in the surface ice were related to Actinobacteria (42%) while Gammaproteobacteria (52%) dominated the deep ice community. Comparisons of assemblage composition suggest differences in ice habitability and organismal origin in the upper and lower portions of ice cover. Specifically, the upper ice cover microbiota likely reflect the modern day transport and colonization of biota from the terrestrial landscape, whereas assemblages in the deeper ice are more likely to be persistent remnant biota that originated from the ancient liquid water column of the lake that froze.

  4. Recent rift formation and impact on the structural integrity of the Brunt Ice Shelf, East Antarctica

    NASA Astrophysics Data System (ADS)

    De Rydt, Jan; Hilmar Gudmundsson, G.; Nagler, Thomas; Wuite, Jan; King, Edward C.

    2018-02-01

    We report on the recent reactivation of a large rift in the Brunt Ice Shelf, East Antarctica, in December 2012 and the formation of a 50 km long new rift in October 2016. Observations from a suite of ground-based and remote sensing instruments between January 2000 and July 2017 were used to track progress of both rifts in unprecedented detail. Results reveal a steady accelerating trend in their width, in combination with alternating episodes of fast ( > 600 m day-1) and slow propagation of the rift tip, controlled by the heterogeneous structure of the ice shelf. A numerical ice flow model and a simple propagation algorithm based on the stress distribution in the ice shelf were successfully used to hindcast the observed trajectories and to simulate future rift progression under different assumptions. Results show a high likelihood of ice loss at the McDonald Ice Rumples, the only pinning point of the ice shelf. The nascent iceberg calving and associated reduction in pinning of the Brunt Ice Shelf may provide a uniquely monitored natural experiment of ice shelf variability and provoke a deeper understanding of similar processes elsewhere in Antarctica.

  5. How does ice sheet loading affect ocean flow around Antarctica?

    NASA Astrophysics Data System (ADS)

    Dijkstra, H. A.; Rugenstein, M. A.; Stocchi, P.; von der Heydt, A. S.

    2012-12-01

    Interactions and dynamical feedbacks between ocean circulation, heat and atmospheric moisture transport, ice sheet evolution, and Glacial Isostatic Adjustment (GIA) are overlooked issues in paleoclimatology. Here we will present first results on how ocean flows were possibly affected by the glaciation of Antarctica across the Eocene-Oligocene Transition (~ 34 Ma) through GIA and bathymetry variations. GIA-induced gravitationally self-consistent bathymetry variations are determined by solving the Sea Level Equation (SLE), which describes the time dependent shape of (i) the solid Earth and (ii) the equipotential surface of gravity. Since the ocean circulation equations are defined relative to the equipotential surface of gravity, only bathymetry variations can influence ocean flows, although the sea surface slope will also change through time due to gravitational attraction. We use the Hallberg Isopycnal Model under late Eocene conditions to calculate equilibrium ocean flows in a domain in which the bathymetry evolves under ice loading according to the SLE. The bathymetric effects of the glaciation of Antarctica lead to substantial spatial changes in ocean flows, and close to the coast, the flow even reverses direction. Volume transports through the Drake Passage and Tasman Seaway adjust to the new bathymetry. The results indicate that GIA-induced ocean flow variations alone may have had an impact on sedimentation and erosion patterns, the repositioning of fronts, ocean heat transport and grounding line and ice sheet stability.

  6. The internal structure of the Brunt Ice Shelf, Antarctica from ice-penetrating radar

    NASA Astrophysics Data System (ADS)

    King, Edward; De Rydt, Jan; Gudmundsson, Hilmar

    2016-04-01

    The Brunt Ice Shelf is a small feature on the Coats Land Coast of the Weddell Sea, Antarctica. It is unusual among Antarctic ice shelves because the ice crossing the grounding line from the ice sheet retains no structural integrity, so the ice shelf comprises icebergs of continental ice cemented together by sea ice, with the whole blanketed by in-situ snowfall. The size and distribution of the icebergs is governed by the thickness profile along the grounding line. Where bedrock troughs discharge thick ice to the ice shelf, the icebergs are large and remain close together with little intervening sea ice. Where bedrock ridges mean the ice crossing the grounding line is thin, the icebergs are small and widely-scattered with large areas of sea ice between them. To better understand the internal structure of the Brunt Ice Shelf and how this might affect the flow dynamics we conducted ice-penetrating radar surveys during December 2015 and January 2016. Three different ground-based radar systems were used, operating at centre frequencies of 400, 50 and 10 MHz respectively. The 400 MHz system gave detailed firn structure and accumulation profiles as well as time-lapse profiles of the active propagation of a crevasse. The 50 MHz system provided intermediate-level detail of iceberg distribution and thickness as well as information on the degree of salt water infiltration into the accumulating snow pack. The 10 MHz system used a high-power transmitter in an attempt to measure ice thickness beneath salt-impregnated ice. In this poster we will present example data from each of the three radar systems which will demonstrate the variability of the internal structure of the ice shelf. We will also present preliminary correlations between the internal structure and the surface topography from satellite data.

  7. Historic CH4 Records from Antarctic and Greenland Ice Cores, Antarctic Firn Data, and Archived Air Samples from Cape Grim, Tasmania

    DOE Data Explorer

    Etheridge, D. M. [Division of Atmospheric Research, CSIRO, Aspendale, Victoria, Australia; Steele, L. P. [Division of Atmospheric Research, CSIRO, Aspendale, Victoria, Australia; Francey, R. J. [Division of Atmospheric Research, CSIRO, Aspendale, Victoria, Australia; Langenfelds, R. L. [Division of Atmospheric Research, CSIRO, Aspendale, Victoria, Australia

    2002-01-01

    The Antarctic CH4 records presented here are derived from three ice cores obtained at Law Dome, East Antarctica (66°44'S, 112°50'E, 1390 meters above mean sea level). Law Dome has many qualities of an ideal ice core site for the reconstruction of past concentrations of atmospheric gases; these qualities include: negligible melting of the ice sheet surface, low concentrations of impurities, regular stratigraphic layering undisturbed by wind stress at the surface or differential ice flow at depth, and a high snow accumulation rate. Further details on the site, drilling, and cores are provided by Etheridge et al. (1998), Etheridge et al. (1996), Etheridge and Wookey (1989), and Morgan et al. (1997). The two Greenland ice cores are from the Summit region (72°34' N, 37°37' W, 3200 meters above mean sea level). Lower snow accumulation rate there results in lower air-age resolution, and measurements presented here cover only the pre-industrial period (until 1885). More details about these measurements are presented in Etheridge et al. (1998). Additionally, this site contains firn data from Core DE08-2, and archived air samples from Cape Grim, Tasmania, for comparison.

  8. Dating an 800,000 year Antarctic ice core record using the isotopic composition of trapped air

    NASA Astrophysics Data System (ADS)

    Dreyfus, Gabrielle Boissier

    Here we measure the isotopic composition of air trapped in the European Project for Ice Coring in Antarctica Dome C (EDC) ice core, and use this geochemical information to improve the ice core agescale and our understanding of air enclosure processes. A first result is the detection of a flow anomaly in the bottom 500m of the EDC ice core using the delta18O of atmospheric oxygen (noted delta18Oatm). By tuning the measured delta18Oatm to the orbital precession signal, we correct the EDC agescale over 400-800 ka for flow-induced distortions in the duration of events. Uncertainty in delta 18Oatm phasing with respect to precession limits the accuracy of the tuned agescale to +/-6 ka. We use this improved agescale to date two 10Be peaks detected in the EDC ice core and associated with the Matuyama-Brunhes geomagnetic boundary. While the ice age of the "precursor" event agrees within uncertainty with the age of radioisotopically dated lavas, the volcanic age for the younger reversal is approximately 10 ka older than the mid-point of the 10 Be peak in the ice. Since 80% of the lavas recording the Matuyama-Brunhes reversal are located in the Central Pacific, the observed age difference may indicate that the magnetic field orientation at this location changed prior to the dipole intensity minimum recorded by the ice core 10Be, as suggested by recent geodynamo modeling. A particular challenge for ice core dating is accurately accounting for the age difference between the trapped air and surrounding ice. This gas age - ice age difference (noted Deltaage) depends on the age of the ice at the bottom of the firn. delta15N of N2 is constant in the atmosphere over the timescales considered here, so any deviation from atmospheric composition reflects fractionation processes in the firn. We show that delta15N is positively correlated with the ice deuterium content, a proxy for temperature, over the entire EDC record, and propose an accumulation-permeability-convection mechanism

  9. Evaluation of solar flares and electron precipitation by nitrate distribution in Antarctica

    NASA Astrophysics Data System (ADS)

    Dreschhoff, Gisela A.; Zeller, Edward J.

    1991-10-01

    Most of the time devoted to project research was spent in Antarctica. A firm core was drilled by hand to a depth of 29 meters at Windless Bight on the Ross Ice Shelf. The main result is that all of the major peaks identified as resulting from ionization caused by SPEs that were found in the 1988-89 core could also be identified in the analytical sequence from the 1990-91 core. Following the Antarctic field season, a set of snow samples were obtained that had been collected by the International Trans-Antarctica Expedition. The analysis of these samples showed nitrate flux that correlates closely with known spatial distribution of electron precipitation in the south polar region. A new apparatus has been build for field analysis on a continuous basis of nitrate and conductivity in a melt derived from the vertical melting of ice cores.

  10. Ice Cores Dating With a New Inverse Method Taking Account of the Flow Modeling Errors

    NASA Astrophysics Data System (ADS)

    Lemieux-Dudon, B.; Parrenin, F.; Blayo, E.

    2007-12-01

    Deep ice cores extracted from Antarctica or Greenland recorded a wide range of past climatic events. In order to contribute to the Quaternary climate system understanding, the calculation of an accurate depth-age relationship is a crucial point. Up to now ice chronologies for deep ice cores estimated with inverse approaches are based on quite simplified ice-flow models that fail to reproduce flow irregularities and consequently to respect all available set of age markers. We describe in this paper, a new inverse method that takes into account the model uncertainty in order to circumvent the restrictions linked to the use of simplified flow models. This method uses first guesses on two flow physical entities, the ice thinning function and the accumulation rate and then identifies correction functions on both flow entities. We highlight two major benefits brought by this new method: first of all the ability to respect large set of observations and as a consequence, the feasibility to estimate a synchronized common ice chronology for several cores at the same time. This inverse approach relies on a bayesian framework. To respect the positive constraint on the searched correction functions, we assume lognormal probability distribution on one hand for the background errors, but also for one particular set of the observation errors. We test this new inversion method on three cores simultaneously (the two EPICA cores : DC and DML and the Vostok core) and we assimilate more than 150 observations (e.g.: age markers, stratigraphic links,...). We analyze the sensitivity of the solution with respect to the background information, especially the prior error covariance matrix. The confidence intervals based on the posterior covariance matrix calculation, are estimated on the correction functions and for the first time on the overall output chronologies.

  11. Combined ice core and climate-model evidence for the collapse of the West Antarctic Ice Sheet during Marine Isotope Stage 5e.

    NASA Astrophysics Data System (ADS)

    Steig, Eric J.; Huybers, Kathleen; Singh, Hansi A.; Steiger, Nathan J.; Frierson, Dargan M. W.; Popp, Trevor; White, James W. C.

    2015-04-01

    It has been speculated that collapse of the West Antarctic Ice Sheet explains the very high eustatic sea level rise during the last interglacial period, marine isotope stage (MIS) 5e, but the evidence remains equivocal. Changes in atmospheric circulation resulting from a collapse of the West Antarctic Ice Sheet (WAIS) would have significant regional impacts that should be detectable in ice core records. We conducted simulations using general circulation models (GCMs) at varying levels of complexity: a gray-radiation aquaplanet moist GCM (GRaM), the slab ocean version of GFDL-AM2 (also as an aquaplanet), and the fully-coupled version of NCAR's CESM with realistic topography. In all the experiments, decreased elevation from the removal of the WAIS leads to greater cyclonic circulation over the West Antarctic region. This creates increased advection of relatively warm marine air from the Amundsen-Bellingshausen Seas towards the South Pole, and increased cold-air advection from the East Antarctic plateau towards the Ross Sea and coastal Marie Byrd Land. The result is anomalous warming in some areas of the East Antarctic interior, and significant cooling in Marie Byrd Land. Comparison of ice core records shows good agreement with the model predictions. In particular, isotope-paleotemperature records from ice cores in East Antarctica warmed more between the previous glacial period (MIS 6) and MIS 5e than coastal Marie Byrd Land. These results add substantial support to other evidence for WAIS collapse during the last interglacial period.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  13. Deglacial temperature history of West Antarctica.

    PubMed

    Cuffey, Kurt M; Clow, Gary D; Steig, Eric J; Buizert, Christo; Fudge, T J; Koutnik, Michelle; Waddington, Edwin D; Alley, Richard B; Severinghaus, Jeffrey P

    2016-12-13

    The most recent glacial to interglacial transition constitutes a remarkable natural experiment for learning how Earth's climate responds to various forcings, including a rise in atmospheric CO 2 This transition has left a direct thermal remnant in the polar ice sheets, where the exceptional purity and continual accumulation of ice permit analyses not possible in other settings. For Antarctica, the deglacial warming has previously been constrained only by the water isotopic composition in ice cores, without an absolute thermometric assessment of the isotopes' sensitivity to temperature. To overcome this limitation, we measured temperatures in a deep borehole and analyzed them together with ice-core data to reconstruct the surface temperature history of West Antarctica. The deglacial warming was [Formula: see text]C, approximately two to three times the global average, in agreement with theoretical expectations for Antarctic amplification of planetary temperature changes. Consistent with evidence from glacier retreat in Southern Hemisphere mountain ranges, the Antarctic warming was mostly completed by 15 kyBP, several millennia earlier than in the Northern Hemisphere. These results constrain the role of variable oceanic heat transport between hemispheres during deglaciation and quantitatively bound the direct influence of global climate forcings on Antarctic temperature. Although climate models perform well on average in this context, some recent syntheses of deglacial climate history have underestimated Antarctic warming and the models with lowest sensitivity can be discounted.

  14. The subglacial roughness of Antarctica: Analogs, interpretation and implications for ice thickness uncertainities

    NASA Astrophysics Data System (ADS)

    Young, D. A.; Grima, C.; Greenbaum, J. S.; Beem, L.; Cavitte, M. G.; Quartini, E.; Kempf, S. D.; Roberts, J. L.; Siegert, M. J.; Ritz, C.; Blankenship, D. D.

    2017-12-01

    Over the last twenty five years, extensive ice penetrating radar (IPR) coverage of Antarctica has been obtained, at lines spacings down to 1 km in some cases. However, many glacial processes occur at finer scales, so infering likely landscape parameters is required for a useful interpolation between lines. Profile roughness is also important for understanding the uncertainties inherent in IPR observations. Subglacial roughness has also been used to infer large scale bed rock properties and history. Similar work has been conducted on a regional basis with complilations of data from the 1970's and more recent local studies. Here we present a compilation of IPR-derived profile roughness data covering three great basins of Antarctica: the Byrd Subglacial Basin in West Antarctica, and the Wilkes Subglacial Basin and Aurora Subglacial Basins in East Antarctica; and treat these data using root mean squared deviation (RMSD). Coverage is provied by a range of IPR systems with varying vintages with differing instrument and processing parameters; we present approaches to account for the differences between these systems. We use RMSD, a tool commonly used in planetary investigations, to investigate the self-affine behaviour of the bed at kilometer scales and extract fractal parameters from the data to predict roughness and uncertainties in ice thickness measurement. Lastly, we apply a sensor model to a range of bare-earth terrestrial digital elevation models to futher understand the impact of the sensor model on the inference of subglacial topography and roughness, and to the first order analogies for the lithology of the substrate. This map of roughness, at scales between the pulse limited radar footprint and typical line spacings, provides an understanding of the distribution of Paleogene subglacial sediments, insight in to the distribution of uncertainties and a potential basal properties mask for ice sheet models. A particular goal of this map is to provide insight into

  15. Geostatistical analysis and isoscape of ice core derived water stable isotope records in an Antarctic macro region

    NASA Astrophysics Data System (ADS)

    Hatvani, István Gábor; Leuenberger, Markus; Kohán, Balázs; Kern, Zoltán

    2017-09-01

    Water stable isotopes preserved in ice cores provide essential information about polar precipitation. In the present study, multivariate regression and variogram analyses were conducted on 22 δ2H and 53 δ18O records from 60 ice cores covering the second half of the 20th century. Taking the multicollinearity of the explanatory variables into account, as also the model's adjusted R2 and its mean absolute error, longitude, elevation and distance from the coast were found to be the main independent geographical driving factors governing the spatial δ18O variability of firn/ice in the chosen Antarctic macro region. After diminishing the effects of these factors, using variography, the weights for interpolation with kriging were obtained and the spatial autocorrelation structure of the dataset was revealed. This indicates an average area of influence with a radius of 350 km. This allows the determination of the areas which are as yet not covered by the spatial variability of the existing network of ice cores. Finally, the regional isoscape was obtained for the study area, and this may be considered the first step towards a geostatistically improved isoscape for Antarctica.

  16. Growing Crack in Antarctica Larsen C Ice Shelf Spotted by NASA MISR

    NASA Image and Video Library

    2016-08-31

    Project MIDAS, a United Kingdom-based group that studies the Larsen Ice Shelf in Antarctica, reported Aug. 18, 2016, that a large crack in the Larsen C shelf has grown by another 13 miles (22 kilometers) in the past six months. The crack is now more than 80 miles (130 kilometers) long. Larsen C is the fourth largest ice shelf in Antarctica, with an area of about 19,300 square miles (50,000 square kilometers), greater than the size of Maryland. Computer modeling by Project MIDAS predicts that the crack will continue to grow and eventually cause between nine and twelve percent of the ice shelf to collapse, resulting in the loss of 2,300 square miles (6,000 square kilometers) of ice -- more than the area of Delaware. This follows the collapse of the Larsen B shelf in 2002 and the Larsen A shelf in 1995, which removed about 1,255 square miles (3,250 square kilometers) and 580 square miles (1,500 square kilometers) of ice, respectively. The Multiangle Imaging SpectroRadiometer (MISR) instrument aboard NASA's Terra satellite flew over Larsen C on Aug. 22, 2016. The MISR instrument views Earth with nine cameras pointed at different angles, which provides information about the texture of the surface. On the left is a natural-color image of the shelf from MISR's vertical-viewing camera. Antarctica is slowly emerging from its polar night, and the low light gives the scene a bluish tint. The Larsen C shelf is on the left, while thinner sea ice is present on the right. A variety of cracks are visible in the Larsen C shelf, all appearing roughly the same. The image is about 130 by 135 miles (210 by 220 kilometers) in size. On the right is a composite image made by combining data from MISR's 46-degree backward-pointing camera (plotted as blue), the vertical-pointing camera (plotted as green), and the 46-degree forward-pointing camera (plotted as red). This has the effect of highlighting surface roughness; smooth surfaces appear as blue-purple, while rough surfaces appear as

  17. Reconstructed plutonium fallout in the GV7 firn core from Northern Victoria Land, East Antarctica

    NASA Astrophysics Data System (ADS)

    Hwang, H.; Han, Y.; Kang, J.; Lee, K.; Hong, S.; Hur, S. D.; Narcisi, B.; Frezzotti, M.

    2017-12-01

    Atmospheric nuclear explosions during the period from the 1940s to the 1980s are the major anthropogenic source of plutonium (Pu) in the environment. In this work, we analyzed fg g-1 levels of artificial Pu, released predominantly by atmospheric nuclear weapons tests. We measured 351 samples which collected a 78 m-depth fire core at the site of GV7 (S 70°41'17.1", E 158°51'48.9", 1950 m a.s.l.), Northern Victoria Land, East Antarctica. To determine the Pu concentration in the samples, we used an inductively coupled plasma sector field mass spectrometry coupled with an Apex high-efficiency sample introduction system, which has the advantages of small sample consumption and simple sample preparation. We reconstructed the firn core Pu fallout record for the period after 1954 CE shows a significant fluctuation in agreement with past atmospheric nuclear testing. These data will contribute to ice core research by providing depth-age information.

  18. Improved estimate of accelerated Antarctica ice mass loses from GRACE, Altimetry and surface mass balance from regional climate model output

    NASA Astrophysics Data System (ADS)

    Velicogna, I.; Sutterley, T. C.; A, G.; van den Broeke, M. R.; Ivins, E. R.

    2016-12-01

    We use Gravity Recovery and Climate Experiment (GRACE) monthly gravity fields to determine the regional acceleration in ice mass loss in Antarctica for 2002-2016. We find that the total mass loss is controlled by only a few regions. In Antarctica, the Amundsen Sea (AS) sector and the Antarctic Peninsula account for 65% and 18%, respectively, of the total loss (186 ± 10 Gt/yr) mainly from ice dynamics. The AS sector contributes most of the acceleration in loss (9 ± 1 Gt/yr2 ), and Queen Maud Land, East Antarctica, is the only sector with a significant mass gain due to a local increase in SMB (57 ± 5 Gt/yr). We compare GRACE regional mass balance estimates with independent estimates from ICESat-1 and Operation IceBridge laser altimetry, CryoSat-2 radar altimetry, and surface mass balance outputs from RACMO2.3. In the Amundsen Sea Embayment of West Antarctica, an area experiencing rapid retreat and mass loss to the sea, we find good agreement between GRACE and altimetry estimates. Comparison of GRACE with these independent techniques in East Antarctic shows that GIA estimates from the new regional ice deglaciation models underestimate the GIA correction in the EAIS interior, which implies larger losses of the Antarctica ice sheet by about 70 Gt/yr. Sectors where we are observing the largest losses are closest to warm circumpolar water, and with polar constriction of the westerlies enhanced by climate warming, we expect these sectors to contribute more and more to sea level as the ice shelves that protect these glaciers will melt faster in contact with more heat from the surrounding oc

  19. Oceanic Forcing of Ice-Sheet Retreat: West Antarctica and More

    NASA Astrophysics Data System (ADS)

    Alley, Richard B.; Anandakrishnan, Sridhar; Christianson, Knut; Horgan, Huw J.; Muto, Atsu; Parizek, Byron R.; Pollard, David; Walker, Ryan T.

    2015-05-01

    Ocean-ice interactions have exerted primary control on the Antarctic Ice Sheet and parts of the Greenland Ice Sheet, and will continue to do so in the near future, especially through melting of ice shelves and calving cliffs. Retreat in response to increasing marine melting typically exhibits threshold behavior, with little change for forcing below the threshold but a rapid, possibly delayed shift to a reduced state once the threshold is exceeded. For Thwaites Glacier, West Antarctica, the threshold may already have been exceeded, although rapid change may be delayed by centuries, and the reduced state will likely involve loss of most of the West Antarctic Ice Sheet, causing >3 m of sea-level rise. Because of shortcomings in physical understanding and available data, uncertainty persists about this threshold and the subsequent rate of change. Although sea-level histories and physical understanding allow the possibility that ice-sheet response could be quite fast, no strong constraints are yet available on the worst-case scenario. Recent work also suggests that the Greenland and East Antarctic Ice Sheets share some of the same vulnerabilities to shrinkage from marine influence.

  20. Ocean interactions with the base of Amery Ice Shelf, Antarctica

    NASA Technical Reports Server (NTRS)

    Hellmer, Hartmut H.; Jacobs, Stanley S.

    1992-01-01

    Using a two-dimensional ocean themohaline circulation model, we varied the cavity shape beneath Amery Ice Shelf in an attempt to reproduce the 150-m-thick marine ice layer observed at the 'G1' ice core site. Most simulations caused melting rates which decrease the ice thickness by as much as 400 m between grounding line and G1, but produce only minor accumulation at the ice core site and closer to the ice front. Changes in the sea floor and ice topographies revealed a high sensitivity of the basal mass balance to water column thickness near the grounding line, to submarine sills, and to discontinuities in ice thickness. Model results showed temperature/salinity gradients similar to observations from beneath other ice shelves where ice is melting into seawater. Modeled outflow characteristics at the ice front are in general agreement with oceanographic data from Prydz Bay. We concur with Morgan's inference that the G1 core may have been taken in a basal crevasse filled with marine ice. This ice is formed from water cooled by ocean/ice shelf interactions along the interior ice shelf base.

  1. Geological control of flow in the Institute and Möller Ice Streams, West Antarctica

    NASA Astrophysics Data System (ADS)

    Jordan, T. A.; Ferraccioli, F.; Ross, N.; Corr, H.; Bingham, R. G.; Rippin, D. M.; Le Brocq, A.; Siegert, M. J.

    2012-12-01

    The conditions at the base of an ice sheet influence its flow, and reflect the ongoing interaction between moving ice and the underlying geology. Critical influences on ice flow include subglacial topography, bed lithology, and geothermal heat flux. These factors are influenced either directly by local geology, or by the regional tectonic setting. Geophysical methods have been used in many parts of Antarctica, such as the Siple Coast, to reveal the role subglacial geology plays in influencing ice flow. Until recently, however, the Institute and Möller Ice Streams, which drain ~20% of the West Antarctic Ice Sheet into the Weddell Sea, were only covered by sparse airborne radar (~50 km line spacing), and reconnaissance aeromagnetic data, limiting our understanding of the geological template for this sector of the West Antarctic Ice Sheet. Here we present our geological interpretation of the first integrated aerogeophysical survey over the catchments of the Institute and Möller Ice Streams, which collected ~25,000 km of new aerogeophysical data during the 2010/11 field season. These new airborne radar, magnetic and gravity data reveals both the subglacial topography, and the subglacial geology. Our maps show the fastest flowing coastal part of the Institute Ice Stream crosses a sedimentary basin underlain by thinned continental crust. Further inland two distinct ice flow provinces are recognised: the Pagano Ice Flow Province, which follows the newly identified, ~75 km wide, sinistral strike-slip Pagano Fault Zone at the boundary between East and West Antarctica; and the Ellsworth Ice Flow Province, which is controlled by the Permo-Triassic structural grain of folded Middle Cambrian-Permian meta-sediments, and Jurassic granitic rocks which form significant subglacial highlands. Our new data highlight the importance of understanding subglacial geology when explaining the complex pattern of ice flow observed in the ice sheet interior.

  2. Eemian and penultimate transition reflected in the chemical ice core record from Dome C

    NASA Astrophysics Data System (ADS)

    Bigler, M.; Lambert, F.; Stauffer, B.; Röthlisberger, R.; Wolff, E. W.

    2003-04-01

    Within the scope of the European Project for Ice Coring in Antarctica (EPICA) chemical analyses have been done along the Dome C ice core. Among other substances, Ca2+, dust, Na+, NH_4{}+, NO_3{}- and electrolytical melt water conductivity have been measured at 1 cm resolution with the Bern Continuous Flow Analysis (CFA) system. Here we present new data from the Eemian and the preceding transition covering an age interval from approximately 180 kyr to 110 kyr before present. This sequence is compared with the Holocene and the last transition, mainly with emphasis on terrestrial and marine tracers. Concentration levels for the two periods compare quite well, but the general shape differs considerably. The changes in dust input to Dome C seemed to have been much more abrupt during the penultimate transition than during the last transition (18 to 15 kyr BP). This may reflect different conditions and/or processes in the dust source region.

  3. Coastal-Change and Glaciological Map of the Larsen Ice Shelf Area, Antarctica, 1940-2005

    USGS Publications Warehouse

    Ferrigno, Jane G.; Cook, Alison J.; Mathie, Amy M.; Williams, Richard S.; Swithinbank, Charles; Foley, Kevin M.; Fox, Adrian J.; Thomson, Janet W.; Sievers, Jorn

    2008-01-01

    Changes in the area and volume of polar ice sheets are intricately linked to changes in global climate, and the resulting changes in sea level could severely impact the densely populated coastal regions on Earth. Antarctica is Earth's largest reservoir of glacial ice. Melting of the West Antarctic part alone of the Antarctic ice sheet would cause a sea-level rise of approximately 6 meters (m), and the potential sea-level rise after melting of the entire Antarctic ice sheet is estimated to be 65 m (Lythe and others, 2001) to 73 m (Williams and Hall, 1993). The mass balance (the net volumetric gain or loss) of the Antarctic ice sheet is highly complex, responding differently to different climatic and other conditions in each region (Vaughan, 2005). In a review paper, Rignot and Thomas (2002) concluded that the West Antarctic ice sheet is probably becoming thinner overall; although it is known to be thickening in the west, it is thinning in the north. The mass balance of the East Antarctic ice sheet is thought by Davis and others (2005) to be positive on the basis of the change in satellite-altimetry measurements made between 1992 and 2003. Measurement of changes in area and mass balance of the Antarctic ice sheet was given a very high priority in recommendations by the Polar Research Board of the National Research Council (1986), in subsequent recommendations by the Scientific Committee on Antarctic Research (SCAR) (1989, 1993), and by the National Science Foundation's (1990) Division of Polar Programs. On the basis of these recommendations, the U.S. Geological Survey (USGS) decided that the archive of early 1970s Landsat 1, 2, and 3 Multispectral Scanner (MSS) images of Antarctica and the subsequent repeat coverage made possible with Landsat and other satellite images provided an excellent means of documenting changes in the cryospheric coastline of Antarctica (Ferrigno and Gould, 1987). The availability of this information provided the impetus for carrying out a

  4. Making an Ice Core.

    ERIC Educational Resources Information Center

    Kopaska-Merkel, David C.

    1995-01-01

    Explains an activity in which students construct a simulated ice core. Materials required include only a freezer, food coloring, a bottle, and water. This hands-on exercise demonstrates how a glacier is formed, how ice cores are studied, and the nature of precision and accuracy in measurement. Suitable for grades three through eight. (Author/PVD)

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

    NASA Astrophysics Data System (ADS)

    Svensson, A.; Bigler, M.; Blunier, T.; Clausen, H. B.; Dahl-Jensen, D.; Fischer, H.; Fujita, S.; Goto-Azuma, K.; Johnsen, S. J.; Kawamura, K.; Kipfstuhl, S.; Kohno, M.; Parrenin, F.; Popp, T.; Rasmussen, S. O.; Schwander, J.; Seierstad, I.; Severi, M.; Steffensen, J. P.; Udisti, R.; Uemura, R.; Vallelonga, P.; Vinther, B. M.; Wegner, A.; Wilhelms, F.; Winstrup, M.

    2013-03-01

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

  6. Methane and nitrous oxide in the ice core record.

    PubMed

    Wolff, Eric; Spahni, Renato

    2007-07-15

    Polar ice cores contain, in trapped air bubbles, an archive of the concentrations of stable atmospheric gases. Of the major non-CO2 greenhouse gases, methane is measured quite routinely, while nitrous oxide is more challenging, with some artefacts occurring in the ice and so far limited interpretation. In the recent past, the ice cores provide the only direct measure of the changes that have occurred during the industrial period; they show that the current concentration of methane in the atmosphere is far outside the range experienced in the last 650,000 years; nitrous oxide is also elevated above its natural levels. There is controversy about whether changes in the pre-industrial Holocene are natural or anthropogenic in origin. Changes in wetland emissions are generally cited as the main cause of the large glacial-interglacial change in methane. However, changing sinks must also be considered, and the impact of possible newly described sources evaluated. Recent isotopic data appear to finally rule out any major impact of clathrate releases on methane at these time-scales. Any explanation must take into account that, at the rapid Dansgaard-Oeschger warmings of the last glacial period, methane rose by around half its glacial-interglacial range in only a few decades. The recent EPICA Dome C (Antarctica) record shows that methane tracked climate over the last 650,000 years, with lower methane concentrations in glacials than interglacials, and lower concentrations in cooler interglacials than in warmer ones. Nitrous oxide also shows Dansgaard-Oeschger and glacial-interglacial periodicity, but the pattern is less clear.

  7. Deglacial temperature history of West Antarctica

    USGS Publications Warehouse

    Cuffey, Kurt M.; Clow, Gary D.; Steig, Eric J.; Buizert, Christo; Fudge, T.J.; Koutnik, Michelle; Waddington, Edwin D.; Alley, Richard B.; Severinghaus, Jeffrey P.

    2016-01-01

    The most recent glacial to interglacial transition constitutes a remarkable natural experiment for learning how Earth’s climate responds to various forcings, including a rise in atmospheric CO2. This transition has left a direct thermal remnant in the polar ice sheets, where the exceptional purity and continual accumulation of ice permit analyses not possible in other settings. For Antarctica, the deglacial warming has previously been constrained only by the water isotopic composition in ice cores, without an absolute thermometric assessment of the isotopes’ sensitivity to temperature. To overcome this limitation, we measured temperatures in a deep borehole and analyzed them together with ice-core data to reconstruct the surface temperature history of West Antarctica. The deglacial warming was 11.3±1.8∘">11.3±1.8∘11.3±1.8∘C, approximately two to three times the global average, in agreement with theoretical expectations for Antarctic amplification of planetary temperature changes. Consistent with evidence from glacier retreat in Southern Hemisphere mountain ranges, the Antarctic warming was mostly completed by 15 kyBP, several millennia earlier than in the Northern Hemisphere. These results constrain the role of variable oceanic heat transport between hemispheres during deglaciation and quantitatively bound the direct influence of global climate forcings on Antarctic temperature. Although climate models perform well on average in this context, some recent syntheses of deglacial climate history have underestimated Antarctic warming and the models with lowest sensitivity can be discounted.

  8. Deglacial temperature history of West Antarctica

    PubMed Central

    Clow, Gary D.; Steig, Eric J.; Buizert, Christo; Fudge, T. J.; Koutnik, Michelle; Waddington, Edwin D.; Alley, Richard B.

    2016-01-01

    The most recent glacial to interglacial transition constitutes a remarkable natural experiment for learning how Earth’s climate responds to various forcings, including a rise in atmospheric CO2. This transition has left a direct thermal remnant in the polar ice sheets, where the exceptional purity and continual accumulation of ice permit analyses not possible in other settings. For Antarctica, the deglacial warming has previously been constrained only by the water isotopic composition in ice cores, without an absolute thermometric assessment of the isotopes’ sensitivity to temperature. To overcome this limitation, we measured temperatures in a deep borehole and analyzed them together with ice-core data to reconstruct the surface temperature history of West Antarctica. The deglacial warming was 11.3±1.8∘C, approximately two to three times the global average, in agreement with theoretical expectations for Antarctic amplification of planetary temperature changes. Consistent with evidence from glacier retreat in Southern Hemisphere mountain ranges, the Antarctic warming was mostly completed by 15 kyBP, several millennia earlier than in the Northern Hemisphere. These results constrain the role of variable oceanic heat transport between hemispheres during deglaciation and quantitatively bound the direct influence of global climate forcings on Antarctic temperature. Although climate models perform well on average in this context, some recent syntheses of deglacial climate history have underestimated Antarctic warming and the models with lowest sensitivity can be discounted. PMID:27911783

  9. Reactivation of Kamb Ice Stream tributaries triggers century-scale reorganization of Siple Coast ice flow in West Antarctica

    DOE PAGES

    Bougamont, M.; Christoffersen, P.; Price, S. F.; ...

    2015-10-21

    Ongoing, centennial-scale flow variability within the Ross ice streams of West Antarctica suggests that the present-day positive mass balance in this region may reverse in the future. Here we use a three-dimensional ice sheet model to simulate ice flow in this region over 250 years. The flow responds to changing basal properties, as a subglacial till layer interacts with water transported in an active subglacial hydrological system. We show that a persistent weak bed beneath the tributaries of the dormant Kamb Ice Stream is a source of internal ice flow instability, which reorganizes all ice streams in this region, leadingmore » to a reduced (positive) mass balance within decades and a net loss of ice within two centuries. This hitherto unaccounted for flow variability could raise sea level by 5 mm this century. Furthermore, better constraints on future sea level change from this region will require improved estimates of geothermal heat flux and subglacial water transport.« less

  10. DEM, tide and velocity over sulzberger ice shelf, West Antarctica

    USGS Publications Warehouse

    Baek, S.; Shum, C.K.; Lee, H.; Yi, Y.; Kwoun, Oh-Ig; Lu, Z.; Braun, Andreas

    2005-01-01

    Arctic and Antarctic ice sheets preserve more than 77% of the global fresh water and could raise global sea level by several meters if completely melted. Ocean tides near and under ice shelves shifts the grounding line position significantly and are one of current limitations to study glacier dynamics and mass balance. The Sulzberger ice shelf is an area of ice mass flux change in West Antarctica and has not yet been well studied. In this study, we use repeat-pass synthetic aperture radar (SAR) interferometry data from the ERS-1 and ERS-2 tandem missions for generation of a high-resolution (60-m) Digital Elevation Model (DEM) including tidal deformation detection and ice stream velocity of the Sulzberger Ice Shelf. Other satellite data such as laser altimeter measurements with fine foot-prints (70-m) from NASA's ICESat are used for validation and analyses. The resulting DEM has an accuracy of-0.57??5.88 m and is demonstrated to be useful for grounding line detection and ice mass balance studies. The deformation observed by InSAR is found to be primarily due to ocean tides and atmospheric pressure. The 2-D ice stream velocities computed agree qualitatively with previous methods on part of the Ice Shelf from passive microwave remote-sensing data (i.e., LANDSAT). ?? 2005 IEEE.

  11. Recent Climate and Ice-Sheet Changes in West Antarctica Compared with the Past 2,000 Years

    NASA Technical Reports Server (NTRS)

    Steig, Eric J.; Ding, Qinghua; White, James W.; Kuttel, Marcel; Rupper, Summer B.; Neumann, Thomas Allen; Neff, Peter D.; Gallant, Ailie J. E.; Mayewski, Paul A.; Taylor, Kendrick C.; hide

    2013-01-01

    Changes in atmospheric circulation over the past five decades have enhanced the wind-driven inflow of warm ocean water onto the Antarctic continental shelf, where it melts ice shelves from below1-3. Atmospheric circulation changes have also caused rapid warming4 over the West Antarctic Ice Sheet, and contributed to declining sea-ice cover in the adjacent Amundsen-Bellingshausen seas5. It is unknown whether these changes are part of a longer-term trend. Here, we use waterisotope (Delta O-18) data from an array of ice-core records to place recent West Antarctic climate changes in the context of the past two millennia. We find that the d18O of West Antarctic precipitation has increased significantly in the past 50 years, in parallel with the trend in temperature, and was probably more elevated during the 1990s than at any other time during the past 200 years. However, Delta O-18 anomalies comparable to those of recent decades occur about 1% of the time over the past 2,000 years. General circulation model simulations suggest that recent trends in Delta O-18 and climate in West Antarctica cannot be distinguished from decadal variability that originates in the tropics. We conclude that the uncertain trajectory of tropical climate variability represents a significant source of uncertainty in projections of West Antarctic climate and ice-sheet change.

  12. Recent high-resolution Antarctic ice velocity maps reveal increased mass loss in Wilkes Land, East Antarctica.

    PubMed

    Shen, Qiang; Wang, Hansheng; Shum, C K; Jiang, Liming; Hsu, Hou Tse; Dong, Jinglong

    2018-03-14

    We constructed Antarctic ice velocity maps from Landsat 8 images for the years 2014 and 2015 at a high spatial resolution (100 m). These maps were assembled from 10,690 scenes of displacement vectors inferred from more than 10,000 optical images acquired from December 2013 through March 2016. We estimated the mass discharge of the Antarctic ice sheet in 2008, 2014, and 2015 using the Landsat ice velocity maps, interferometric synthetic aperture radar (InSAR)-derived ice velocity maps (~2008) available from prior studies, and ice thickness data. An increased mass discharge (53 ± 14 Gt yr -1 ) was found in the East Indian Ocean sector since 2008 due to unexpected widespread glacial acceleration in Wilkes Land, East Antarctica, while the other five oceanic sectors did not exhibit significant changes. However, present-day increased mass loss was found by previous studies predominantly in west Antarctica and the Antarctic Peninsula. The newly discovered increased mass loss in Wilkes Land suggests that the ocean heat flux may already be influencing ice dynamics in the marine-based sector of the East Antarctic ice sheet (EAIS). The marine-based sector could be adversely impacted by ongoing warming in the Southern Ocean, and this process may be conducive to destabilization.

  13. Recent and past dust concentrations and fluxes from a developing array of Antarctic ice cores

    NASA Astrophysics Data System (ADS)

    McConnell, J. R.; Anschütz, H.; Baggenstos, D.; Das, S. B.; Isaksson, E. D.; Lawrence, R.; Layman, L.; Maselli, O.; Severinghaus, J. P.; Sigl, M.; Petit, J. R.; Grente, B.

    2012-12-01

    Continental dust is an important component of climate forcing, both because of its interaction with incoming solar and outgoing long wave radiation and because of its impact on albedo when deposited on bright surfaces such as fresh snow. Continental dust may also play an important role in ocean fertilization and carbon sequestration. Because the lifetime of dust aerosol in the atmosphere is only on the order of days to weeks, spatial and temporal variability in concentrations and fluxes is high and understanding of recent and long term changes is limited. Here we present and discuss detailed continuous, high depth resolution measurements of a range of dust proxies in a developing array of Antarctic ice cores. Included are traditional proxies such as non-sea-salt (nss) calcium and insoluble particle number and size distribution as well as less traditional proxies such as aluminum, vanadium, manganese, rare earth elements, and nss uranium which together provide important insights into how dust sources and transport may have changed in the past. The array includes a number of new shallow ice core records from East and West Antarctica spanning recent centuries to millennia, as well as Last Glacial Maximum to early Holocene records from the deep WAIS Divide and Taylor Glacier Horizontal ice cores.

  14. Coastal-change and glaciological map of the Amery Ice Shelf area, Antarctica: 1961–2004

    USGS Publications Warehouse

    Foley, Kevin M.; Ferrigno, Jane G.; Swithinbank, Charles; Williams, Richard S.; Orndorff, Audrey L.

    2013-01-01

    Reduction in the area and volume of Earth’s two polar ice sheets is intricately linked to changes in global climate and to the resulting rise in sea level. Measurement of changes in area and mass balance of the Antarctic ice sheet was given a very high priority in recommendations by the Polar Research Board of the National Research Council. On the basis of these recommendations, the U.S. Geological Survey used its archive of satellite images to document changes in the cryospheric coastline of Antarctica and analyze the glaciological features of the coastal regions. Amery Ice Shelf, lying between 67.5° and 75° East longitude and 68.5° and 73.2° South latitude, is the largest ice shelf in East Antarctica. The latest measurements of the area of the ice shelf range between 62,620 and 71,260 square kilometers. The ice shelf is fed primarily by Lambert, Mellor, and Fisher Glaciers; its thickness ranges from 3,000 meters in the center of the grounding line to less than 300 meters at the ice front. Lambert Glacier is considered to be the largest glacier in the world, and its drainage basin is more than 1 million square kilometers in area. It is possible to see some coastal change on the outlet glaciers along the coast, but most of the noticeable change occurs on the Amery Ice Shelf front.

  15. First Results of Nitrate and its Stable Isotopic Composition in an Ice Core from Dome A, East Antarctica

    NASA Astrophysics Data System (ADS)

    Jiang, S.

    2017-12-01

    During the 21st Chinese Antarctic Research Expedition in 2004/2005 austral summer, a 109.91 m ice core (hereafter DA2005 core) was recovered at the site about 300 m away from the summit of Dome A. The top 100.42 m was analyzed for major chemical impurities and isotopic composition of nitrate. Dating was based on the volcanic stratigraphy and average annual accumulation rate. Results showed that the analyzed 100.42 m part of the core covers the last 2840 years before present, from 840 BC to AD 1998. Nitrate concentration in the DA2005 core varies between 2.86 μg kg-1 and 30.75 μg kg-1 throughout the 2840 years, with the mean concentration of 11.84 µg kg-1. Comparisons with previous Antarctic ice core nitrate records show that the DA2005 core has the lowest mean concentration of nitrate, which is consistent with the lowest accumulation rate at Dome A among these sampling sites. Decreased nitrate concentration during the period of Little Ice Age (AD 1500-1900) is observed in the DA2005 core. The δ15N(NO3-) values vary between 235.4 ‰ and 279.4 ‰, which suggest strong 15N enrichment in the DA2005 core. The sample covering the most recent time period (AD 1695-1838) has the lowest δ15N(NO3-) value. The Δ17O(NO3-) values span from 28.9 ‰ to 31.4 ‰, which is among the range ever observed. An increasing trend is seen during the period of AD 1225-1838, which corresponds to the time period when nitrate concentration remains low. The maximum Δ17O(NO3-) value occurs in the period AD 1695-1838, and the minimum value occurs in the period AD 62-166.

  16. Antarctic-Wide Array of High-Resolution Ice Core Records Reveals Pervasive Lead Pollution Began in 1889 and Persists Today

    NASA Technical Reports Server (NTRS)

    McConnell, J. R.; Maselli, O. J.; Sigl, M.; Vallelonga, P.; Neumann, Thomas Allen; Anschutz, H.; Bales, R. C.; Curran, M. A. J.; Das, S. B.; Edwards, R.; hide

    2014-01-01

    Interior Antarctica is among the most remote places on Earth and was thought to be beyond the reach of human impacts when Amundsen and Scott raced to the South Pole in 1911. Here we show detailed measurements from an extensive array of 16 ice cores quantifying substantial toxic heavy metal lead pollution at South Pole and throughout Antarctica by 1889 - beating polar explorers by more than 22 years. Unlike the Arctic where lead pollution peaked in the 1970s, lead pollution in Antarctica was as high in the early 20th century as at any time since industrialization. The similar timing and magnitude of changes in lead deposition across Antarctica, as well as the characteristic isotopic signature of Broken Hill lead found throughout the continent, suggest that this single emission source in southern Australia was responsible for the introduction of lead pollution into Antarctica at the end of the 19th century and remains a significant source today. An estimated 660 t of industrial lead have been deposited over Antarctica during the past 130 years as a result of mid-latitude industrial emissions, with regional-to-global scale circulation likely modulating aerosol concentrations. Despite abatement efforts, significant lead pollution in Antarctica persists into the 21st century.

  17. Antarctic-wide array of high-resolution ice core records reveals pervasive lead pollution began in 1889 and persists today.

    PubMed

    McConnell, J R; Maselli, O J; Sigl, M; Vallelonga, P; Neumann, T; Anschütz, H; Bales, R C; Curran, M A J; Das, S B; Edwards, R; Kipfstuhl, S; Layman, L; Thomas, E R

    2014-07-28

    Interior Antarctica is among the most remote places on Earth and was thought to be beyond the reach of human impacts when Amundsen and Scott raced to the South Pole in 1911. Here we show detailed measurements from an extensive array of 16 ice cores quantifying substantial toxic heavy metal lead pollution at South Pole and throughout Antarctica by 1889 - beating polar explorers by more than 22 years. Unlike the Arctic where lead pollution peaked in the 1970s, lead pollution in Antarctica was as high in the early 20(th) century as at any time since industrialization. The similar timing and magnitude of changes in lead deposition across Antarctica, as well as the characteristic isotopic signature of Broken Hill lead found throughout the continent, suggest that this single emission source in southern Australia was responsible for the introduction of lead pollution into Antarctica at the end of the 19(th) century and remains a significant source today. An estimated 660 t of industrial lead have been deposited over Antarctica during the past 130 years as a result of mid-latitude industrial emissions, with regional-to-global scale circulation likely modulating aerosol concentrations. Despite abatement efforts, significant lead pollution in Antarctica persists into the 21(st) century.

  18. Antarctic-wide array of high-resolution ice core records reveals pervasive lead pollution began in 1889 and persists today

    PubMed Central

    McConnell, J. R.; Maselli, O. J.; Sigl, M.; Vallelonga, P.; Neumann, T.; Anschütz, H.; Bales, R. C.; Curran, M. A. J.; Das, S. B.; Edwards, R.; Kipfstuhl, S.; Layman, L.; Thomas, E. R.

    2014-01-01

    Interior Antarctica is among the most remote places on Earth and was thought to be beyond the reach of human impacts when Amundsen and Scott raced to the South Pole in 1911. Here we show detailed measurements from an extensive array of 16 ice cores quantifying substantial toxic heavy metal lead pollution at South Pole and throughout Antarctica by 1889 – beating polar explorers by more than 22 years. Unlike the Arctic where lead pollution peaked in the 1970s, lead pollution in Antarctica was as high in the early 20th century as at any time since industrialization. The similar timing and magnitude of changes in lead deposition across Antarctica, as well as the characteristic isotopic signature of Broken Hill lead found throughout the continent, suggest that this single emission source in southern Australia was responsible for the introduction of lead pollution into Antarctica at the end of the 19th century and remains a significant source today. An estimated 660 t of industrial lead have been deposited over Antarctica during the past 130 years as a result of mid-latitude industrial emissions, with regional-to-global scale circulation likely modulating aerosol concentrations. Despite abatement efforts, significant lead pollution in Antarctica persists into the 21st century. PMID:25068819

  19. Ice formation in subglacial Lake Vostok, Central Antarctica

    NASA Astrophysics Data System (ADS)

    Souchez, R.; Petit, J. R.; Tison, J.-L.; Jouzel, J.; Verbeke, V.

    2000-09-01

    The investigation of chemical and isotopic properties in the lake ice from the Vostok ice core gives clues to the mechanisms involved in ice formation within the lake. A small lake water salinity can be reasonably deduced from the chemical data. Possible implications for the water circulation of Lake Vostok are developed. The characteristics of the isotopic composition of the lake ice indicate that ice formation in Lake Vostok occurred by frazil ice crystal generation due to supercooling as a consequence of rising waters and a possible contrast in water salinity. Subsequent consolidation of the developed loose ice crystals results in the accretion of ice to the ceiling of the lake.

  20. Arctic Circle Traverse 2010 (ACT-10): South East Greenland snow accumulation variability from firn coring and ice sounding radar

    NASA Astrophysics Data System (ADS)

    Forster, R. R.; Miege, C.; Box, J. E.; McConnell, J.; Spikes, V. B.; Burgess, E. W.

    2010-12-01

    The Greenland Ice Sheet plays an important role in Earth’s climate system evolution. The snow accumulation rate is the largest single mass budget term. With only 14% of the ice sheet area, Southeast Greenland contains the highest accumulation rates, accounting for one third of the total snow accumulation and annual variability. The high accumulation rates have made the region less desirable for long climate record ice cores and therefore, contain relatively very few in situ measurements to constrain the ice sheet mass budget. We present annual snow accumulation rates from the Arctic Circle Traverse 2010 (ACT-10). During April and May 2010 we acquired three 50 m firn cores connected by surface-based 400 MHz ground penetrating radar (GPR) in Southeast Greenland. The traverse repeated and extended the original Arctic Circle Traverse in 2004 (Spikes et al., 2004). Dating is achieved using geochemical analysis of the cores to identify isochronal layers detected by the GPR yielding annual accumulation estimates along the traverse between the core sites. The 300 km ACT-10 GPR snowmobile traverse extended the ACT-04 path 80 km to the lowest elevation core site at 1776 m. Meanwhile, airborne radars, operating as part of NASA’s Operation IceBridge also acquired data over the full length of the ACT-10 path, simultaneously with a portion of the traverse and within days for the remaining segments. The IceBridge and ACT-10 data are to be combined in a calibration effort such that snow accumulation rates may be mapped elsewhere in Greenland and even in Antarctica.

  1. Aerosol size distribution at Nansen Ice Sheet Antarctica

    NASA Astrophysics Data System (ADS)

    Belosi, F.; Contini, D.; Donateo, A.; Santachiara, G.; Prodi, F.

    2012-04-01

    During austral summer 2006, in the framework of the XXII Italian Antarctic expedition of PNRA (Italian National Program for Research in Antarctica), aerosol particle number size distribution measurements were performed in the 10-500 range nm over the Nansen Ice Sheet glacier (NIS, 74°30' S, 163°27' E; 85 m a.s.l), a permanently iced branch of the Ross Sea. Observed total particle number concentrations varied between 169 and 1385 cm- 3. A monomodal number size distribution, peaking at about 70 nm with no variation during the day, was observed for continental air mass, high wind speed and low relative humidity. Trimodal number size distributions were also observed, in agreement with measurements performed at Aboa station, which is located on the opposite side of the Antarctic continent to the NIS. In this case new particle formation, with subsequent particle growth up to about 30 nm, was observed even if not associated with maritime air masses.

  2. Carbonyl sulfide during the late Holocene from measurements in Antarctic ice cores (Invited)

    NASA Astrophysics Data System (ADS)

    Aydin, M.; Fudge, T. J.; Verhulst, K. R.; Waddington, E. D.; Saltzman, E. S.

    2013-12-01

    Carbonyl sulfide (COS) is the most abundant sulfur gas in the troposphere with a global average mixing ratio of about 500 parts per trillion (ppt) and a lifetime of 3 years. It is produced by a variety of natural and anthropogenic sources. Oceans are the largest source, emitting COS and precursors carbon disulfide and dimethyl sulfide. The most important removal process of COS is uptake by terrestrial plants during photosynthesis. Interest in the atmospheric variability of COS is primarily due to its potential value as a proxy for changes in gross primary productivity of the land biosphere. Ice core COS records may provide the long term observational basis needed to explore climate driven changes in terrestrial productivity and the resulting impacts, for example, on atmospheric CO2 levels. Previous measurements in a South Pole ice core established the preindustrial COS levels at ~30% of the modern atmosphere and revealed that atmospheric COS increased at an average rate of 1.8 ppt per 100 years over the last 2,000 years [Aydin et al., 2008]. We have since measured COS in 5 additional ice cores from 4 different sites in Antarctica. These measurements display a site-dependent downcore decline in COS, apparently driven by in situ hydrolysis. The reaction is strongly temperature dependent, with the hydrolysis lifetimes (e-folding) ranging from thousands to hundreds of thousands of years. We implement a novel technique that uses ice and heat flow models to predict temperature histories for the ice core samples from different sites and correct for the COS lost to in situ hydrolysis assuming first order kinetics. The 'corrected' COS records confirm the trend observed previously in the COS record from the South Pole ice core. The new, longer record suggests the slow increase in atmospheric COS may have started about 5,000 years ago and continued for 4,500 years until levels stabilized about 500 years ago. Atmospheric CO2 was also rising during this time period, suggesting

  3. Ice Chemistry in Starless Molecular Cores

    NASA Astrophysics Data System (ADS)

    Kalvāns, J.

    2015-06-01

    Starless molecular cores are natural laboratories for interstellar molecular chemistry research. The chemistry of ices in such objects was investigated with a three-phase (gas, surface, and mantle) model. We considered the center part of five starless cores, with their physical conditions derived from observations. The ice chemistry of oxygen, nitrogen, sulfur, and complex organic molecules (COMs) was analyzed. We found that an ice-depth dimension, measured, e.g., in monolayers, is essential for modeling of chemistry in interstellar ices. Particularly, the H2O:CO:CO2:N2:NH3 ice abundance ratio regulates the production and destruction of minor species. It is suggested that photodesorption during the core-collapse period is responsible for the high abundance of interstellar H2O2 and O2H and other species synthesized on the surface. The calculated abundances of COMs in ice were compared to observed gas-phase values. Smaller activation barriers for CO and H2CO hydrogenation may help explain the production of a number of COMs. The observed abundance of methyl formate HCOOCH3 could be reproduced with a 1 kyr, 20 K temperature spike. Possible desorption mechanisms, relevant for COMs, are gas turbulence (ice exposure to interstellar photons) or a weak shock within the cloud core (grain collisions). To reproduce the observed COM abundances with the present 0D model, 1%-10% of ice mass needs to be sublimated. We estimate that the lifetime for starless cores likely does not exceed 1 Myr. Taurus cores are likely to be younger than their counterparts in most other clouds.

  4. Annually-resolved temperature reconstructions of the past 2000 years from Dome-Fuji, East Antarctica

    NASA Astrophysics Data System (ADS)

    Motizuki, Yuko; Takahashi, Kazuya; Nakai, Yoichi; Motoyama, Hideaki

    2016-04-01

    We present annually-resolved temperature and SST reconstructions of the past 2000 years based on water (oxygen and deuterium) isotope measurement on a shallow ice core drilled in 2010 at Dome Fuji station, East Antarctica. These time series records will be an essential contribution to the PAGES 2k project from sparse data area in Antarctica. Dome Fuji station is located on a summit of Dronning Maud Land at an altitude of 3810 m a.s.l. (above sea level) (77o19'01'' S, 39o42'12'' E) in East Antarctica. The 10 m depth mean snow temperature at Dome Fuji is -57.3oC1). The inland area around Dome Fuji has been recognized to be especially unique: The snow and ice there contain much stratospheric information. The direct evidence for this comes from tritium contents originated from the nuclear bomb tests in the 1960s; the tritium fallout at the Dome Fuji site is outstandingly high among 16 snow pit samples widely collected over Antarctica2). To date the concerned Dome Fuji ice core, we applied volcanic signature matching to transfer the West Antarctic Ice Sheet (WAIS) Divide ice core chronology constructed by annual layer counting as used in the study by Sigl et al. (2014)3). In our presentation, we confine ourselves to discuss the oscillation periodicity that we observed in the oxygen isotope record in our data: The periods of approximately 10, 20, and 200 years were found. We will present the time series analyses for this in detail, and will discuss the origin of this periodicity. References: 1) Kameda, T., Motoyama, H., Fujita, S., and Takahashi, S.: "Past temporal and spatial variability of surface mass balance at Dome Fuji", East Antarctica, by the stake method from 1995 to 2006, J. Glaciol., 54, 107-116, 2008. 2) Fourre, E., Jean-Baptiste, P., Dapoigny, A., Baumier, D., Petit, J.-R., and Jouzel, J.: "Past and recent tritium levels in Arctic and Antarctic polar caps", Earth Planet. Sc. Lett., 245, 56-64, 2006. 3) Sigl, M., J. McConnell, M. Toohey, M. Curran, S. Das, R

  5. Airborne thickness and freeboard measurements over the McMurdo Ice Shelf, Antarctica, and implications for ice density

    NASA Astrophysics Data System (ADS)

    Rack, Wolfgang; Haas, Christian; Langhorne, Pat J.

    2013-11-01

    We present airborne measurements to investigate the thickness of the western McMurdo Ice Shelf in the western Ross Sea, Antarctica. Because of basal accretion of marine ice and brine intrusions conventional radar systems are limited in detecting the ice thickness in this area. In November 2009, we used a helicopter-borne laser and electromagnetic induction sounder (EM bird) to measure several thickness and freeboard profiles across the ice shelf. The maximum electromagnetically detectable ice thickness was about 55 m. Assuming hydrostatic equilibrium, the simultaneous measurement of ice freeboard and thickness was used to derive bulk ice densities ranging from 800 to 975 kg m-3. Densities higher than those of pure ice can be largely explained by the abundance of sediments accumulated at the surface and present within the ice shelf, and are likely to a smaller extent related to the overestimation of ice thickness by the electromagnetic induction measurement related to the presence of a subice platelet layer. The equivalent thickness of debris at a density of 2800 kg m-3 is found to be up to about 2 m thick. A subice platelet layer below the ice shelf, similar to what is observed in front of the ice shelf below the sea ice, is likely to exist in areas of highest thickness. The thickness and density distribution reflects a picture of areas of basal freezing and supercooled Ice Shelf Water emerging from below the central ice shelf cavity into McMurdo Sound.

  6. Ice Sheet Temperature Records - Satellite and In Situ Data from Antarctica and Greenland

    NASA Astrophysics Data System (ADS)

    Shuman, C. A.; Comiso, J. C.

    2001-12-01

    Recently completed decadal-length surface temperature records from Antarctica and Greenland are providing insights into the challenge of detecting climate change. Ice and snow cover at high latitudes influence the global climate system by reflecting much of the incoming solar energy back to space. An expected consequence of global warming is a decrease in area covered by snow and ice and an increase in Earth's absorption of solar radiation. Models have predicted that the effects of climate warming may be amplified at high latitudes; thinning of the Greenland ice sheet margins and the breakup of Antarctic Peninsula ice shelves suggest this process may have begun. Satellite data provide an excellent means of observing climate parameters across both long temporal and remote spatial domains but calibration and validation of their data remains a challenge. Infrared sensors can provide excellent temperature information but cloud cover and calibration remain as problems. Passive-microwave sensors can obtain data during the long polar night and through clouds but have calibration issues and a much lower spatial resolution. Automatic weather stations are generally spatially- and temporally-restricted and may have long gaps due to equipment failure. Stable isotopes of oxygen and hydrogen from ice sheet locations provide another means of determining temperature variations with time but are challenging to calibrate to observed temperatures and also represent restricted areas. This presentation will discuss these issues and elaborate on the development and limitations of composite satellite, automatic weather station, and proxy temperature data from selected sites in Antarctica and Greenland.

  7. Siple Dome ice reveals two modes of millennial CO2 change during the last ice age

    PubMed Central

    Ahn, Jinho; Brook, Edward J.

    2014-01-01

    Reconstruction of atmospheric CO2 during times of past abrupt climate change may help us better understand climate-carbon cycle feedbacks. Previous ice core studies reveal simultaneous increases in atmospheric CO2 and Antarctic temperature during times when Greenland and the northern hemisphere experienced very long, cold stadial conditions during the last ice age. Whether this relationship extends to all of the numerous stadial events in the Greenland ice core record has not been clear. Here we present a high-resolution record of atmospheric CO2 from the Siple Dome ice core, Antarctica for part of the last ice age. We find that CO2 does not significantly change during the short Greenlandic stadial events, implying that the climate system perturbation that produced the short stadials was not strong enough to substantially alter the carbon cycle. PMID:24781344

  8. Environmental and ice volume changes based on seismic stratigraphy in Sabrina Coast, East Antarctica: Preliminary results from NBP1402

    NASA Astrophysics Data System (ADS)

    Gulick, S. P. S.; Fernandez-Vasquez, R. A.; Frederick, B.; Saustrup, S., Sr.; Domack, E. W.; Lavoie, C.; Shevenell, A.; Blankenship, D. D.; Leventer, A.

    2014-12-01

    . The unconformity is overlain by glacial diamict, representing an incomplete record of cold-based glaciations after the ASB became ice-filled. Correlations with cores collected above and below the unconformity and deltaic unit should allow us to determine the ages of these transitions from fluvial to polythermal to ice sheets in East Antarctica.

  9. Glacial-interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-δ15N measurements

    NASA Astrophysics Data System (ADS)

    Capron, E.; Landais, A.; Buiron, D.; Cauquoin, A.; Chappellaz, J.; Debret, M.; Jouzel, J.; Leuenberger, M.; Martinerie, P.; Masson-Delmotte, V.; Mulvaney, R.; Parrenin, F.; Prié, F.

    2012-12-01

    Correct estimate of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice cores studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: output of a firn densification model and measurements of δ15N of N2 in air trapped in ice core. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI) and semi coastal (TALDICE and EPICA Dronning Maud Land, EDML) Antarctic regions. Combined with available δ15N measurements performed from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rate and temperature conditions. While firn densification simulations are able to correctly represent most of the δ15N trends over the last deglaciation measured in the EDC, BI, TALDICE and EDML ice cores, they systematically fail to capture BI and EDML δ15N glacial levels, a mismatch previously seen for Central East Antarctic ice cores. Using empirical constraints of the EDML gas-ice depth offset during the Laschamp event (~ 41 ka), we can rule out the existence of a large convective zone as the explanation of the glacial firn model-δ15N data mismatch for this site. The good match between modelled and measured δ15N at TALDICE as well as the lack of any clear correlation between insoluble dust concentration in snow and δ15N records in the different ice cores suggest that past changes in loads of impurities are not the only main driver of glacial-interglacial changes in firn lock-in depth. We conclude that firn densification dynamics may instead be driven mostly by accumulation rate changes. The mismatch between modelled and measured δ15N may be due to inaccurate reconstruction of past accumulation rate or underestimated influence of accumulation rate in firnification models.

  10. Life in ice: implications to astrobiology

    NASA Astrophysics Data System (ADS)

    Hoover, Richard B.; Pikuta, Elena V.

    2009-08-01

    During previous research expeditions to Siberia, Alaska and Antarctica, it was observed that glaciers and ice wedges contained bacterial cells that became motile as soon as the ice melted. This phenomenon of live bacteria in ice was first documented for microbes in ancient ice cores from Vostok, Antarctica. The first validly published species of Pleistocene bacteria alive on Earth today was Carnobacterium pleistocenium. This extremophile had remained for 32,000 years, encased in ice recently exposed in the Fox Tunnel of Alaska. These frozen bacteria began to swim as soon as the ice was thawed. Dark field microscopy studies revealed that large numbers of bacteria exhibited motility as soon as glacial ice was melted during our recent Expeditions to Alaska and Antarctica led to the conclusion that microbial life in ice was not a rare phenomenon. The ability of bacteria to remain alive while frozen in ice for long periods of time is of great significance to Astrobiology. In this paper, we describe the recent observations and advance the hypothesis that life in ice provides valuable clues to how we can more easily search for evidence of life on the Polar Caps of Mars, comets and other icy bodies of our Solar System. It is suggested that cryopanspermia may have played a far more important role in Origin of Life on Earth and the distribution of Life throughout the Cosmos and than previously thought possible.

  11. Breakup of the Larsen Ice Shelf, Antarctica

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Recent Moderate-resolution Imaging Spectroradiometer (MODIS) satellite imagery analyzed at the University of Colorado's National Snow and Ice Data Center revealed that the northern section of the Larsen B ice shelf, a large floating ice mass on the eastern side of the Antarctic Peninsula, has shattered and separated from the continent. This particular image was taken on March 5, 2002. The shattered ice formed a plume of thousands of icebergs adrift in the Weddell Sea. A total of about 3,250 square kilometers of shelf area disintegrated in a 35-day period beginning on January 31, 2002. Over the last five years, the shelf has lost a total of 5,700 square kilometers and is now about 40 percent the size of its previous minimum stable extent. Ice shelves are thick plates of ice, fed by glaciers, that float on the ocean around much of Antarctica. The Larsen B shelf was about 220 meters thick. Based on studies of ice flow and sediment thickness beneath the ice shelf, scientists believe that it existed for at least 400 years prior to this event and likely existed since the end of the last major glaciation 12,000 years ago. For reference, the area lost in this most recent event dwarfs Rhode Island (2,717 square kilometers) in size. In terms of volume, the amount of ice released in this short time is 720 billion tons--enough ice for about 12 trillion 10-kilogram bags. This is the largest single event in a series of retreats by ice shelves along the peninsula over the last 30 years. The retreats are attributed to a strong climate warming in the region. The rate of warming is approximately 0.5 degrees Celsius per decade, and the trend has been present since at least the late 1940s. Overall in the peninsula, the extent of seven ice shelves has declined by a total of about 13,500 square kilometers since 1974. This value excludes areas that would be expected to calve under stable conditions. Ted Scambos, a researcher with the National Snow and Ice Data Center (NSIDC) at

  12. Ross Ice Shelf, Antarctica: Bathymetry, Structural Geology and Ocean Circulation from New IcePod Airborne Geophysical Data

    NASA Astrophysics Data System (ADS)

    Siddoway, C. S.; Tinto, K. J.; Bell, R. E.; Padman, L.; Fricker, H. A.; Springer, S. R.

    2016-12-01

    Rock exposures in the Ford Ranges, Marie Byrd Land (MBL), on the eastern margin of the Ross Embayment, contain direct evidence of the geological processes that led to formation of West Antarctica's continental lithosphere. Processes include wide regional extension, volcanism, and thermal reequilibration, with creation of crustal structures that are prone to reactivation today. Marie Byrd Land is tectonically active, as is evident from Late Pleistocene to Holocene eruptive centers, englacial volcanic tephra as young as 2200 years, a site of magma propagation inferred from POLEnet seismic records, and the occurrence of a 2012 earthquake cluster of magnitude M4.4 to M5.5 north of Edward VII Peninsula. However, the lithosphere underlying the Ross Ice Shelf (RIS) is poorly known due to the thick cover of shelf ice floating on the ocean, difficult to penetrate by satellite remote sensing or other methods. Airborne geophysical data for the Ford Ranges and the Ross Ice Shelf (RIS) suggest that the rock formations and structures that underlie MBL continue beneath the RIS. Notable features known in outcrop and detected/inferred from potential fields data are Pleistocene or younger mafic volcanic centers and Cretaceous core complexes, both likely associated with wrench faults. The Ford Ranges legacy dataset that now provides a fundamental basis for sub-RIS geological interpretation is a product of research in coastal MBL led by B.P. Luyendyk from 1989 - 2006. To improve our knowledge of lithospheric evolution, identify active faults and prospective zones of volcanism/heat flow, and to determine the sub-RIS bathymetry, the RIS sector is being explored via new Icepod aerogeophysics acquisition during the ROSETTA-Ice project (Ross Ocean and ice Shelf Environment, and Tectonic setting Through Aerogeophysical surveys and modeling), now underway over this vast under-explored sector of the Ross Embayment. ROSETTA-Ice collects and employs new gravity data with magnetics to delineate

  13. Seasonal Outflow of Ice Shelf Water Across the Front of the Filchner Ice Shelf, Weddell Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    Darelius, E.; Sallée, J. B.

    2018-04-01

    The ice shelf water (ISW) found in the Filchner Trough, located in the southern Weddell Sea, Antarctica, is climatically important; it descends into the deep Weddell Sea contributing to bottom water formation, and it blocks warm off-shelf waters from accessing the Filchner ice shelf cavity. Yet the circulation of ISW within the Filchner Trough and the processes determining its exchange across the ice shelf front are to a large degree unknown. Here mooring records from the ice shelf front are presented, the longest of which is 4 years long. They show that the coldest (Θ =- 2.3∘C) ISW, which originates from the Ronne Trough in the west, exits the cavity across the western part of the ice shelf front during late austral summer and early autumn. The supercooled ISW escaping the cavity flows northward with a velocity of about 0.03 m/s. During the rest of the year, there is no outflow at the western site: the current is directed eastward, parallel to the ice shelf front, and the temperatures at the mooring site are slightly higher (Θ =- 2.0∘C). The eastern records show a more persistent outflow of ISW.

  14. Seasonal climate information preserved within West Antarctic ice cores and its relation to large-scale atmospheric circulation and regional sea ice variations

    NASA Astrophysics Data System (ADS)

    Küttel, M.; Steig, E. J.; Ding, Q.; Battisti, D. S.

    2010-12-01

    Recent evidence suggests that West Antarctica has been warming since at least the 1950s. With the instrumental record being limited to the mid-20th century, indirect information from stable isotopes (δ18O and δD, hereafter collectively δ) preserved within ice cores have commonly been used to place this warming into a long term context. Here, using a large number of δ records obtained during the International Trans-Antarctic Scientific Expedition (ITASE), past variations in West Antarctic δ are not only investigated over time but also in space. This study therefore provides an important complement to longer records from single locations as e.g. the currently being processed West Antarctic ice sheet (WAIS) Divide ice core. Although snow accumulation rates at the ITASE sites in West Antarctica are variable, they are generally high enough to allow studies on sub-annual scale over the last 50-100 years. Here, we show that variations in δ in this region are strongly related to the state of the large-scale atmospheric circulation as well as sea ice variations in the adjacent Southern Ocean, with important seasonal changes. While a strong relationship to sea ice changes in the Ross and Amundsen Sea as well as to the atmospheric circulation offshore is found during austral fall (MAM) and winter (JJA), only modest correlations are found during spring (SON) and summer (DJF). Interestingly, the correlations with the atmospheric circulation in the latter two seasons have the strongest signal over the Antarctic continent, but not offshore - an important difference to MAM and JJA. These seasonal changes are in good agreement with the seasonally varying predominant circulation: meridional with more frequent storms in the Amundsen Sea during MAM and JJA and more zonal and stable during SON and DJF. The relationship to regional temperature is similarly seasonally variable with highest correlations found during MAM and JJA. Notably, the circulation pattern found to be strongest

  15. Iron-oxide Magnetic, Morphologic, and Compositional Tracers of Sediment Provenance and Ice Sheet Extent in the ANDRILL AND-1B Drill Core, Ross Sea, Antarctica (Invited)

    NASA Astrophysics Data System (ADS)

    Brachfeld, S. A.; Pinzon, J.; Darley, J. S.; Sagnotti, L.; Kuhn, G.; Florindo, F.; Wilson, G. S.; Ohneiser, C.; Monien, D.; Joseph, L. H.

    2013-12-01

    The first drilling season of the Antarctic Drilling Program (ANDRILL) recovered a 13.57 million year Miocene through Pleistocene record of paleoclimate change (core AND-1B) within the Ross Sea. The magnetic mineral assemblage records the varying contributions of biological productivity, changing sediment sources, the emergence of volcanic centers, and post-depositional diagenesis. Characterization of bedrock samples from the McMurdo Volcanic Group (MVG) and Transantarctic Mountain (TAM) lithologic units allows us to construct fingerprints for the major source rocks bordering the Ross Sea, and identify their signatures within the AND-1B sediment. Key parameters that can be traced from source rock to sediment for the MVG-derived sediment include a 100-200 C order-disorder transition, titanomaghemite grains with homogenous textures but with substantial Al and Mg content, Fe-spinels with substantial Al, Cr, Mg, and Ti content, and titanomagnetite host grains with 1-3 swarms of ilmenite lamellae (both with variable amounts of oxidation). Distinctive signatures in TAM lithologies include low S-ratios in Koettlitz Group gneisses and Fe-sulfides with magnetite intergrowths in Byrd Glacier basement samples. The Cambrian Granite Harbor Intrusive Complex is characterized by coarse, homogeneous Mn-bearing ilmenite and nearly pure magnetite. The Jurassic dolerites and basalts of the Ferrar Group contain pseudo single domain to stable single domain-sized Fe-oxides with low-Ti content and homogeneous textures. Cu-Fe sulfides are also present in the Ferrar Group. Diamictites in the Pliocene-Pleistocene section of the AND-1B drill core contains Fe-oxide assemblages with MVG-type rock magnetic and textural characteristics, while the Miocene diamictites contain TAM-type signatures. These observations can be explained by increased ice flow from the west during the Miocene and/or the absence of MVG volcanic centers, which had not yet reached a significant size. During the Pliocene and

  16. Glacial-interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-?15N measurements

    NASA Astrophysics Data System (ADS)

    Capron, E.; Landais, A.; Buiron, D.; Cauquoin, A.; Chappellaz, J. A.; Debret, M.; Jouzel, J.; Leuenberger, M.; Martinerie, P.; Masson-Delmotte, V.; Mulvaney, R.; Parrenin, F.; Prié, F.

    2013-12-01

    Correct estimation of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice core studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: outputs of a firn densification model, and measurements of δ15N of N2 in air trapped in ice core, assuming that δ15N is only affected by gravitational fractionation in the firn column. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI) and semi-coastal (TALDICE and EPICA Dronning Maud Land, EDML) Antarctic regions. Combined with available ice core air- δ15N measurements from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rates and temperature conditions. Our δ15N profiles reveal a heterogeneous response of the firn structure to glacial-interglacial climatic changes. While firn densification simulations correctly predict TALDICE δ15N variations, they systematically fail to capture the large millennial-scale δ15N variations measured at BI and the δ15N glacial levels measured at JRI and EDML - a mismatch previously reported for central East Antarctic ice cores. New constraints of the EDML gas-ice depth offset during the Laschamp event (41 ka) and the last deglaciation do not favour the hypothesis of a large convective zone within the firn as the explanation of the glacial firn model- δ15N data mismatch for this site. While we could not conduct an in-depth study of the influence of impurities in snow for firnification from the existing datasets, our detailed comparison between the δ15N profiles and firn model simulations under different temperature and accumulation rate scenarios suggests that the role of accumulation rate may have been underestimated in the current description of firnification models.

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

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

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

  18. Analysis and Characterization of Dissolved Organic Matter in Ice Cores as Indicators of Past Environmental Conditions Using High Resolution FTICR-MS

    NASA Astrophysics Data System (ADS)

    Boschi, V.; Grannas, A. M.; Willoughby, A. S.; Catanzano, V.; Hatcher, P.

    2015-12-01

    With rapid changes in global temperatures, research aimed at better understanding past climatic events in order to predict future trends is an area of growing importance. Carbonaceous gases stored in ice cores are known to correlate with temperature change and provide evidence of such events. However, more complex forms of carbon preserved in ice cores such as dissolved organic matter (DOM) can provide additional information relating to changes in environmental conditions over time. The examination of ice core samples presents unique challenges including detection of ultra-low concentrations of organic material and extremely limited sample amounts. In this study, solid phase extraction techniques combined with ultra-high resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FTICR-MS) were utilized to successfully extract, concentrate and analyze the low concentrations of DOM in only 100 mL of ice core samples originating from various regions of Antarctica and Greenland. We characterize the DOM composition in each sample by evaluating elemental ratios, molecular formula distribution (CHO, CHON, CHOS and CHNOS) and compound class composition (lignin, tannin, lipid, condensed aromatic, protein and unsaturated hydrocarbon content). Upon characterization, we identified molecular trends in ice core DOM chemistry that correlated with past climatic events in addition to observing possible photochemical and microbial influences affecting DOM chemistry. Considering these samples range in age from 350-1175 years old, thus being formed during the Medieval Warm Period and Little Ice Age, we observed that DOM properties reflected anticipated changes in composition as influenced by warming and cooling events occurring during that time period.

  19. Ice shelf structure from dispersion curve analysis of passive-source seismic data, Ross Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Diez, A.; Bromirski, P. D.; Gerstoft, P.; Stephen, R. A.; Anthony, R. E.; Aster, R. C.; Cai, C.; Nyblade, A.; Wiens, D.

    2015-12-01

    An L-shaped array of three-component short period seismic stations was deployed at the Ross Ice Shelf, Antarctica approximately 100 km south of the ice edge, near 180° longitude, from November 18 through 28, 2014. Polarization analysis of data from these stations clearly shows propagating waves from below the ice shelf for frequencies below 2 Hz. Energy above 2 Hz is dominated by Rayleigh and Love waves propagating from the north. Frequency-slowness plots were calculated using beamforming. Resulting Love and Rayleigh wave dispersion curves were inverted for the shear wave velocity profile, from which we derive a density profile. The derived shear wave velocity profiles differ within the firn for the inversions using Rayleigh and Love wave dispersion curves. This difference is attributed to an effective anisotropy due to fine layering. The layered structure of firn, ice, water, and ocean floor results in a characteristic dispersion curve pattern below 7 Hz. We investigate the observed structures in more detail by forward modeling of Rayleigh wave dispersion curves for representative firn, ice, water, sediment structures. Rayleigh waves are observed when wavelengths are long enough to span the distance from the ice shelf surface to the seafloor. Our results show that the analysis of high frequency Rayleigh waves on an ice shelf has the ability to resolve ice shelf thickness, water column thickness, and the physical properties of the underlying ocean floor using passive-source seismic data.

  20. Geoologic controls on the architecture of the Antarctic Ice Sheet's basal interface: New results from West and East Antarctica from long range geophysics (Invited)

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    The ice-rock interface underlying the Antarctic Ice Sheet was shaped by interactions between underlying gondwanan geology and the overlying ice sheet. The ice sheet now preserves from sedimentary infill an incredibly rugged terrain which now plays a critical role in shaping subglacial hydrology, and thus shape ice sheet behavior. This terrain can by imaged through aerogeophysical means, in particular through ice penetrating radar, while airborne potential fields measurements provide insight into the geological framework that controlled erosion. Over the post IPY era, the density of airborne coverage is only now reaching the point where small scale structure can be identified and placed in context. Of particular importance is understanding the formation of focused erosional valleys, 30-50 km wide, representing now buried subglacial fjords. After initial data from the GIMBLE project in West Antarctica, and five years of sustained long range ICECAP surveys over East Antarctica , we now have a better view of the diversity of these features. The local erosion of these valleys, often cutting through significant topographic barriers, irregularly samples the underlying geology, provided a complex story in the sediment to the Antarctic margin. These valleys now provide the subglacial conduits for significant ice sheet catchments, in particular for subglacial water, including the inland catchments of DeVicq, Thwaites, and Pine Island Glaciers in West Antarctica, and Denman Glacier, Totten Glacier, Byrd Glacier and Cook Ice Shelf in East Antarctica. We find that these features, now sometimes hundreds of kilometers inland of the modern grounding line, often nucleate on or are aligned with structure inherited from the assembly of the Antarctic continent. While many of these features currently host active outlet glaciers or their tributaries, some do not, implying avenues for ice sheet change. In West Antarctica, we find a new deep connection between the coast and interior basin

  1. Deglacial temperature history of West Antarctica

    NASA Astrophysics Data System (ADS)

    Cuffey, Kurt M.; Clow, Gary D.; Steig, Eric J.; Buizert, Christo; Fudge, T. J.; Koutnik, Michelle; Waddington, Edwin D.; Alley, Richard B.; Severinghaus, Jeffrey P.

    2016-12-01

    The most recent glacial to interglacial transition constitutes a remarkable natural experiment for learning how Earth’s climate responds to various forcings, including a rise in atmospheric CO2. This transition has left a direct thermal remnant in the polar ice sheets, where the exceptional purity and continual accumulation of ice permit analyses not possible in other settings. For Antarctica, the deglacial warming has previously been constrained only by the water isotopic composition in ice cores, without an absolute thermometric assessment of the isotopes’ sensitivity to temperature. To overcome this limitation, we measured temperatures in a deep borehole and analyzed them together with ice-core data to reconstruct the surface temperature history of West Antarctica. The deglacial warming was 11.3±1.811.3±1.8∘C, approximately two to three times the global average, in agreement with theoretical expectations for Antarctic amplification of planetary temperature changes. Consistent with evidence from glacier retreat in Southern Hemisphere mountain ranges, the Antarctic warming was mostly completed by 15 kyBP, several millennia earlier than in the Northern Hemisphere. These results constrain the role of variable oceanic heat transport between hemispheres during deglaciation and quantitatively bound the direct influence of global climate forcings on Antarctic temperature. Although climate models perform well on average in this context, some recent syntheses of deglacial climate history have underestimated Antarctic warming and the models with lowest sensitivity can be discounted.

  2. Fabric and texture at Siple Dome, Antarctica

    USGS Publications Warehouse

    Diprinzio, C.L.; Wilen, Lawrence A.; Alley, R.B.; Fitzpatrick, J.J.; Spencer, M.K.; Gow, A.J.

    2005-01-01

    Preferred c-axis orientations are present in the firn at Siple Dome, West Antarctica, and recrystallization begins as shallow as 200 m depth in ice below -20??C, based on digital analysis of c-axis fabrics, grain-sizes and other characteristics of 52 vertical thin sections prepared in the field from the kilometer-long Siple Dome ice core. The shallowest section analyzed, from 22 m, shows clustering of c axes toward the vertical. By 200 m depth, girdle fabric and other features of recrystallized ice are evident in layers (or regions), separated by layers (regions) of typically finer-grained ice lacking evidence of recrystallization. Ice from about 700-780 m depth, which was deposited during the last ice age, is especially fine-grained, with strongly vertical c axes, but deeper ice shows much larger crystals and strong evidence of recrystallization. Azimuthal asymmetry of some c-axis fabrics, trends in grain-size, and other indicators reveal additional information on processes and history of ice flow at Siple Dome.

  3. Subglacial conditions at a sticky spot along Kamb Ice Stream, West Antarctica

    USGS Publications Warehouse

    Peters, L.E.; Anandakrishnan, S.

    2007-01-01

    We present the results of a seismic reflection experiment performed transverse to flow a few tens of kilometers above the main trunk of Kamb Ice Stream, West Antarctica, where we image a basal high surrounded by variable subglacial conditions. This high rises as much as 200 m above the surrounding bed, acting as a major sticking point that resists fast flow. Application of the amplitude variation with offset (AVO) seismic technique has highlighted regions of frozen sediments along our profile, suggesting that the ice stream is experiencing basal freeze-on in the region. The bedrock high appears to be at least partially draped in sediment cover, with a concentrated area of weak, dilatant till flanking one edge. This dilatant till is further dispersed along our profile, though it does not possess enough continuity to maintain streaming ice conditions. These results support the hypothesis that the ongoing shutdown of Kamb Ice Stream is due to a loss in continuous basal lubrication.

  4. Rapid changes in ice core gas records - Part 1: On the accuracy of methane synchronisation of ice cores

    NASA Astrophysics Data System (ADS)

    Köhler, P.

    2010-08-01

    Methane synchronisation is a concept to align ice core records during rapid climate changes of the Dansgaard/Oeschger (D/O) events onto a common age scale. However, atmospheric gases are recorded in ice cores with a log-normal-shaped age distribution probability density function, whose exact shape depends mainly on the accumulation rate on the drilling site. This age distribution effectively shifts the mid-transition points of rapid changes in CH4 measured in situ in ice by about 58% of the width of the age distribution with respect to the atmospheric signal. A minimum dating uncertainty, or artefact, in the CH4 synchronisation is therefore embedded in the concept itself, which was not accounted for in previous error estimates. This synchronisation artefact between Greenland and Antarctic ice cores is for GRIP and Byrd less than 40 years, well within the dating uncertainty of CH4, and therefore does not calls the overall concept of the bipolar seesaw into question. However, if the EPICA Dome C ice core is aligned via CH4 to NGRIP this synchronisation artefact is in the most recent unified ice core age scale (Lemieux-Dudon et al., 2010) for LGM climate conditions of the order of three centuries and might need consideration in future gas chronologies.

  5. Could a new ice core offer an insight into the stability of the West Antarctic Ice Sheet during the last interglacial?

    NASA Astrophysics Data System (ADS)

    Mulvaney, R.; Hindmarsh, R. C.

    2013-12-01

    Vaughan et al., in their 2011 paper 'Potential Seaways across West Antarctica' (Geochem. Geophys. Geosyst., 12, Q10004, doi:10.1029/2011GC003688), offer the intriguing prospect that substantial ice loss from the West Antarctic Ice Sheet during the previous interglacial period might have resulted in the opening of a seaway between the Weddell Sea and the Amundsen Sea. One of their potential seaways passes between the south western corner of the present Ronne Ice Shelf and the Pine Island Bay, through what is currently the course of the Rutford Ice Stream, between the Ellsworth Mountains and the Fletcher Promontory. To investigate whether this seaway could have existed (and to recover a paleoclimate and ice sheet history from the Weddell Sea), a team from the British Antarctic Survey and the Laboratoire de Glaciologie et Géophysique de l'Environnement drilled an ice core from a close to a topographic dome in the ice surface on the Fletcher Promontory in January 2012, reaching the bedrock at 654.3m depth from the surface. The site was selected to penetrate directly through the centre of a Raymond cupola observed in internal radar reflections from the ice sheet, with the intention that this would ensure we obtained the oldest ice available from the Fletcher Promontory. The basal ice sheet temperature measured was -18°C, implying the oldest ice would not have melted away from the base, while the configuration of the Raymond cupola in the radar horizons suggested stability in the ice dome topography during the majority of the Holocene. Our hypothesis is that chemical analysis of the ice core will reveal whether the site was ever relatively close to open sea water or ice shelf in the Rutford channel 20 km distant, rather than the current 700 km distance to sea ice/open water in either the Weddell Sea or the Amundsen Sea. While we do not yet have the chemistry data to test this hypothesis, in this poster we will discuss whether there is in reality any potential local

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

    NASA Astrophysics Data System (ADS)

    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.

  7. Improvements in the chronology, geochemistry and correlation techniques of tephra in Antarctic ice

    NASA Astrophysics Data System (ADS)

    Iverson, N. A.; Dunbar, N. W.; McIntosh, W. C.; Pearce, N. J.; Kyle, P. R.

    2013-12-01

    Visible and crypto tephra layers found in West Antarctic ice provide an excellent record of Antarctic volcanism over the past 100ka. Tephra layers are deposited almost instantaneously across wide areas creating horizons that, if found in several locations, provide 'pinning points' to adjust ice time scales that may otherwise be lacking detailed chronology. Individual tephra layers can have distinct chemical fingerprints allowing them to correlate over great distances. Advances in sample preparation, geochemical analyses (major and trace elements) of fine grained tephra and higher precision 40Ar/39Ar dating of young (<100ka) proximal volcanic deposits are improving an already established tephra record in West Antarctica. Forty three of the potential hundreds of silicate layers found in a recently drilled deep West Antarctic Ice Sheet Divide core (WDC06A) have been analyzed for major elements and a subset for trace elements. Of these layers, at least 16 are homogenous tephra that could be correlated to other ice cores (e.g. Siple Dome, SDMA) and/or to source volcanoes found throughout Antarctica and even extra-continental eruptions (e.g. Sub-Antarctic islands and South America). Combining ice core tephra with those exposed in blue ice areas provide more locations to correlate widespread eruptions. For example, a period of heightened eruptive activity at Mt. Berlin, West Antarctica between 24 and 28ka produced a set of tephra layers that are found in WDC06A and SDMA ice cores, as well as at a nearby blue ice area at Mt. Moulton (BIT-151 and BIT-152). Possible correlative tephra layers are found at ice ages of 26.4, 26.9 and 28.8ka in WDC06A and 26.5, 27.0, and 28.7ka in SDMA cores. The geochemical similarities of major elements in these layers mean that ongoing trace element analyses will be vital to decipher the sequence of events during this phase of activity at Mt. Berlin. Sample WDC06A-2767.117 (ice age of 28.6×1.0ka) appears to correlate to blue ice tephra BIT

  8. Toward unified ice core chronologies with the DatIce tool

    NASA Astrophysics Data System (ADS)

    Toye Mahamadou Kele, H.; Lemieux-Dudon, B.; Blayo, E.

    2012-04-01

    Antarctic and Greenland ice cores provide a means to study the phase relationships of climate changes in both hemispheres. They also enable to study the timing between climate, and greenhouse gases or orbital forcings. One key step for such studies is to improve the absolute and relative precisions of ice core age scales (for ice and trapped gas), and beyond that, to try to reach the best consistency between chronologies of paleo records of any kind. The DatIce tool is designed to increase the consistency between pre-existing (also called background) core chronologies. It formulates a variational inverse problem which aims at correcting three key quantities that uniquely define the core age scales: the accumulation rate, the total thinning function, and the close-off depth. For that purpose, it integrates paleo data constraints of many types among which age markers (with for instance documented volcanoes eruptions), and stratigraphic links (with for instance abrupt changes in methane concentration). A cost function is built that enables to calculate new chronologies by making a trade-off between all the constraints (background chronologies and paleo data). The method presented in Lemieux-Dudon et al (2010) has already been applied simultaneously to EPICA EDML and EDC, Vostok and NGRIP. Currently, on going works are conducted at LSCE Saclay and LGGE Grenoble laboratories to construct unified Antarctic chronologies by applying the DatIce tool with new ice cores and new sets of paleo measurements. We here present the DatIce tool, the underlying methodology, and its potential applications. We further show some improvements that have been made recently. We especially adress the issue related to the calibration of the error of pre-existing core chronologies. They are inputs that may have a strong impact on the results. However these uncertainties are uneasy to analyze, since prior chronologies are most of the time assessed on the basis of glaciological models (firn

  9. Ice Core Records of Recent Northwest Greenland Climate

    NASA Astrophysics Data System (ADS)

    Osterberg, E. C.; Wong, G. J.; Ferris, D.; Lutz, E.; Howley, J. A.; Kelly, M. A.; Axford, Y.; Hawley, R. L.

    2014-12-01

    Meteorological station data from NW Greenland indicate a 3oC temperature rise since 1990, with most of the warming occurring in fall and winter. According to remote sensing data, the NW Greenland ice sheet (GIS) and coastal ice caps are responding with ice mass loss and margin retreat, but the cryosphere's response to previous climate variability is poorly constrained in this region. We are developing multi-proxy records (lake sediment cores, ice cores, glacial geologic data, glaciological models) of Holocene climate change and cryospheric response in NW Greenland to improve projections of future ice loss and sea level rise in a warming climate. As part of our efforts to develop a millennial-length ice core paleoclimate record from the Thule region, we collected and analyzed snow pit samples and short firn cores (up to 21 m) from the coastal region of the GIS (2Barrel site; 76.9317o N, 63.1467o W, 1685 m el.) and the summit of North Ice Cap (76.938o N, 67.671o W, 1273 m el.) in 2011, 2012 and 2014. The 2Barrel ice core record has statistically significant relationships with regional spring and fall Baffin Bay sea ice extent, summertime temperature, and annual precipitation. Here we evaluate relationships between the 2014 North Ice Cap firn core glaciochemical record and climate variability from regional instrumental stations and reanalysis datasets. We compare the coastal North Ice Cap record to more inland records from 2Barrel, Camp Century and NEEM to evaluate spatial and elevational gradients in recent NW Greenland climate change.

  10. Glacial-interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-δ15N measurements

    NASA Astrophysics Data System (ADS)

    Capron, E.; Landais, A.; Buiron, D.; Cauquoin, A.; Chappellaz, J.; Debret, M.; Jouzel, J.; Leuenberger, M.; Martinerie, P.; Masson-Delmotte, V.; Mulvaney, R.; Parrenin, F.; Prié, F.

    2013-05-01

    Correct estimation of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice core studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: outputs of a firn densification model, and measurements of δ15N of N2 in air trapped in ice core, assuming that δ15N is only affected by gravitational fractionation in the firn column. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI) and semi-coastal (TALDICE and EPICA Dronning Maud Land, EDML) Antarctic regions. Combined with available ice core air-δ15N measurements from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rates and temperature conditions. Our δ15N profiles reveal a heterogeneous response of the firn structure to glacial-interglacial climatic changes. While firn densification simulations correctly predict TALDICE δ15N variations, they systematically fail to capture the large millennial-scale δ15N variations measured at BI and the δ15N glacial levels measured at JRI and EDML - a mismatch previously reported for central East Antarctic ice cores. New constraints of the EDML gas-ice depth offset during the Laschamp event (~41 ka) and the last deglaciation do not favour the hypothesis of a large convective zone within the firn as the explanation of the glacial firn model-δ15N data mismatch for this site. While we could not conduct an in-depth study of the influence of impurities in snow for firnification from the existing datasets, our detailed comparison between the δ15N profiles and firn model simulations under different temperature and accumulation rate scenarios suggests that the role of accumulation rate may have been underestimated in the current description of firnification models.

  11. Modeling ground thermal regime of an ancient buried ice body in Beacon Valley, Antarctica using a 1-D heat equation with latent heat effect

    NASA Astrophysics Data System (ADS)

    Liu, L.; Sletten, R. S.; Hallet, B.; Waddington, E. D.; Wood, S. E.

    2013-12-01

    An ancient massive ice body buried under several decimeters of debris in Beacon Valley, Antarctica is believed to be over one million years old, making it older than any known glacier or ice cap. It is fundamentally important as a reservoir of water, proxy for climatic information, and an expression of the periglacial landscape. It is also one of Earth's closest analog for widespread, near-surface ice found in Martian soils and ice-cored landforms. We are interested in understanding controls on how long this ice may persist since our physical model of sublimation suggests it should not be stable. In these models, the soil temperatures and the gradient are important because it determines the direction and magnitude of the vapor flux, and thus sublimation rates. To better understand the heat transfer processes and constrain the rates of processes governing ground ice stability, a model of the thermal behavior of the permafrost is applied to Beacon Valley, Antarctica. It calculates soil temperatures based on a 1-D thermal diffusion equation using a fully implicit finite volume method (FVM). This model is constrained by soil physical properties and boundary conditions of in-situ ground surface temperature measurements (with an average of -23.6oC, a maximum of 20.5oC and a minimum of -54.3oC) and ice-core temperature record at ~30 m. Model results are compared to in-situ temperature measurements at depths of 0.10 m, 0.20 m, 0.30 m, and 0.45 m to assess the model's ability to reproduce the temperature profile for given thermal properties of the debris cover and ice. The model's sensitivity to the thermal diffusivity of the permafrost and the overlaying debris is also examined. Furthermore, we incorporate the role of ice condensation/sublimation which is calculated using our vapor diffusion model in the 1-D thermal diffusion model to assess potential latent heat effects that in turn affect ground ice sublimation rates. In general, the model simulates the ground thermal

  12. Miocene-Pliocene ice-volcano interactions at monogenetic volcanoes near Hobbs Coast, Marie Byrd Land, Antarctica

    USGS Publications Warehouse

    Wilch, T.I.; McIntosh, W.C.

    2007-01-01

    Ar geochronology of seven eroded monogenetic volcanoes near the Hobbs Coast, Marie Byrd Land, West Antarctica provide proxy records of WAIS paleo-ice-levels in Miocene-Pliocene times. Interpretations, based on lithofacies analysis, indicate whether the volcanoes erupted below, near, or above the level of the ice sheet. Our interpretations differ significantly from previous interpretations as they highlight the abundant evidence for ice-volcano interactions at emergent paleoenvironments but limited evidence of higher-than-present syn-eruptive ice-levels. Evidence for subglacial volcanic paleoenvironments is limited to Kennel Peak, a ~8 Ma volcano where a pillow lava sequence extending 25 m above current ice level overlies an inferred glacial till and unconformity. A major complication in the Hobbs Coast region is that the volcanism occurred on interfluves between regions of fast-flowing ice. Such a setting precludes establishing precise regional paleo-ice-levels although the presence or absence of ice at times of eruptions can be inferred.

  13. Palaeoglaciology of the Alexander Island ice cap, western Antarctic Peninsula, reconstructed from marine geophysical and core data

    NASA Astrophysics Data System (ADS)

    Graham, Alastair G. C.; Smith, James A.

    2012-03-01

    The glacial history of the continental shelf northwest of Alexander Island is not well known, due mainly to a lack of targeted marine data on Antarctica's palaeo-ice sheets in their inter-ice-stream areas. Recently it has been argued that the region was ice-free at the Last Glacial Maximum (LGM) and thus a potential site for glacial refugia. In this paper, multibeam swath bathymetry, sub-bottom profiles and sediment cores are used to map the Alexander Island sector of the Antarctic Peninsula margin, in order to reconstruct the shelf's palaeoglaciology. Sea-floor bedforms provide evidence that an independent ice cap persisted on Alexander Island through the LGM and deglaciation. We show that this ice cap drained via two major, previously-undescribed tidewater outlets (Rothschild and Charcot Glaciers) sourced from an ice dome centred over the west of the island and near-shore areas. The glaciers grounded along deep, fjord-like cross-shelf troughs to within at least ˜10-20 km of the shelf edge, and probably reached the shelf break. Only one small outer-shelf zone appears to have remained free of ice throughout an otherwise extensive LGM. During retreat, grounding-line geomorphology indicates periodic stabilisation of Charcot Glacier on the mid-shelf after 13,500 cal yrs BP, while Rothschild Glacier retreated across its mid-shelf by 14,450 cal yrs BP. The timing of these events is in phase with retreat in nearby Marguerite Trough, and we take this as evidence of a common history and forcing with the Antarctic Peninsula Ice Sheet. The fine details of ice flow documented by our new reconstruction highlight the importance of capturing complex ice flow patterns in models (e.g. in inter-stream areas), for understanding how region-specific parts of Antarctica may change in the future. Moreover, the reconstruction shows that glacial refugia, if present, cannot have been extensive on the Alexander Island shelf at the LGM as indicated by previous biological studies; instead

  14. A novel fast ion chromatographic method for the analysis of fluoride in Antarctic snow and ice.

    PubMed

    Severi, Mirko; Becagli, Silvia; Frosini, Daniele; Marconi, Miriam; Traversi, Rita; Udisti, Roberto

    2014-01-01

    Ice cores are widely used to reconstruct past changes of the climate system. For instance, the ice core record of numerous water-soluble and insoluble chemical species that are trapped in snow and ice offer the possibility to investigate past changes of various key compounds present in the atmosphere (i.e., aerosol, reactive gases). We developed a new method for the quantitative determination of fluoride in ice cores at sub-μg L(-1) levels by coupling a flow injection analysis technique with a fast ion chromatography separation based on the "heart cut" column switching technology. Sensitivity, linear range (up to 60 μg L(-1)), reproducibility, and detection limit (0.02 μg L(-1)) were evaluated for the new method. This method was successfully applied to the analysis of fluoride at trace levels in more than 450 recent snow samples collected during the 1998-1999 International Trans-Antarctica Scientific Expedition traverse in East Antarctica at sites located between 170 and 850 km from the coastline.

  15. Variability of Basal Melt Beneath the Pine Island Glacier Ice Shelf, West Antarctica

    NASA Technical Reports Server (NTRS)

    Bindschadler, Robert; Vaughan, David G.; Vornberger, Patricia

    2011-01-01

    Observations from satellite and airborne platforms are combined with model calculations to infer the nature and efficiency of basal melting of the Pine Island Glacier ice shelf, West Antarctica, by ocean waters. Satellite imagery shows surface features that suggest ice-shelf-wide changes to the ocean s influence on the ice shelf as the grounding line retreated. Longitudinal profiles of ice surface and bottom elevations are analyzed to reveal a spatially dependent pattern of basal melt with an annual melt flux of 40.5 Gt/a. One profile captures a persistent set of surface waves that correlates with quasi-annual variations of atmospheric forcing of Amundsen Sea circulation patterns, establishing a direct connection between atmospheric variability and sub-ice-shelf melting. Ice surface troughs are hydrostatically compensated by ice-bottom voids up to 150m deep. Voids form dynamically at the grounding line, triggered by enhanced melting when warmer-than-average water arrives. Subsequent enlargement of the voids is thermally inefficient (4% or less) compared with an overall melting efficiency beneath the ice shelf of 22%. Residual warm water is believed to cause three persistent polynyas at the ice-shelf front seen in Landsat imagery. Landsat thermal imagery confirms the occurrence of warm water at the same locations.

  16. State dependence of climatic instability over the past 720,000 years from Antarctic ice cores and climate modeling.

    PubMed

    Kawamura, Kenji; Abe-Ouchi, Ayako; Motoyama, Hideaki; Ageta, Yutaka; Aoki, Shuji; Azuma, Nobuhiko; Fujii, Yoshiyuki; Fujita, Koji; Fujita, Shuji; Fukui, Kotaro; Furukawa, Teruo; Furusaki, Atsushi; Goto-Azuma, Kumiko; Greve, Ralf; Hirabayashi, Motohiro; Hondoh, Takeo; Hori, Akira; Horikawa, Shinichiro; Horiuchi, Kazuho; Igarashi, Makoto; Iizuka, Yoshinori; Kameda, Takao; Kanda, Hiroshi; Kohno, Mika; Kuramoto, Takayuki; Matsushi, Yuki; Miyahara, Morihiro; Miyake, Takayuki; Miyamoto, Atsushi; Nagashima, Yasuo; Nakayama, Yoshiki; Nakazawa, Takakiyo; Nakazawa, Fumio; Nishio, Fumihiko; Obinata, Ichio; Ohgaito, Rumi; Oka, Akira; Okuno, Jun'ichi; Okuyama, Junichi; Oyabu, Ikumi; Parrenin, Frédéric; Pattyn, Frank; Saito, Fuyuki; Saito, Takashi; Saito, Takeshi; Sakurai, Toshimitsu; Sasa, Kimikazu; Seddik, Hakime; Shibata, Yasuyuki; Shinbori, Kunio; Suzuki, Keisuke; Suzuki, Toshitaka; Takahashi, Akiyoshi; Takahashi, Kunio; Takahashi, Shuhei; Takata, Morimasa; Tanaka, Yoichi; Uemura, Ryu; Watanabe, Genta; Watanabe, Okitsugu; Yamasaki, Tetsuhide; Yokoyama, Kotaro; Yoshimori, Masakazu; Yoshimoto, Takayasu

    2017-02-01

    Climatic variabilities on millennial and longer time scales with a bipolar seesaw pattern have been documented in paleoclimatic records, but their frequencies, relationships with mean climatic state, and mechanisms remain unclear. Understanding the processes and sensitivities that underlie these changes will underpin better understanding of the climate system and projections of its future change. We investigate the long-term characteristics of climatic variability using a new ice-core record from Dome Fuji, East Antarctica, combined with an existing long record from the Dome C ice core. Antarctic warming events over the past 720,000 years are most frequent when the Antarctic temperature is slightly below average on orbital time scales, equivalent to an intermediate climate during glacial periods, whereas interglacial and fully glaciated climates are unfavourable for a millennial-scale bipolar seesaw. Numerical experiments using a fully coupled atmosphere-ocean general circulation model with freshwater hosing in the northern North Atlantic showed that climate becomes most unstable in intermediate glacial conditions associated with large changes in sea ice and the Atlantic Meridional Overturning Circulation. Model sensitivity experiments suggest that the prerequisite for the most frequent climate instability with bipolar seesaw pattern during the late Pleistocene era is associated with reduced atmospheric CO 2 concentration via global cooling and sea ice formation in the North Atlantic, in addition to extended Northern Hemisphere ice sheets.

  17. State dependence of climatic instability over the past 720,000 years from Antarctic ice cores and climate modeling

    PubMed Central

    Kawamura, Kenji; Abe-Ouchi, Ayako; Motoyama, Hideaki; Ageta, Yutaka; Aoki, Shuji; Azuma, Nobuhiko; Fujii, Yoshiyuki; Fujita, Koji; Fujita, Shuji; Fukui, Kotaro; Furukawa, Teruo; Furusaki, Atsushi; Goto-Azuma, Kumiko; Greve, Ralf; Hirabayashi, Motohiro; Hondoh, Takeo; Hori, Akira; Horikawa, Shinichiro; Horiuchi, Kazuho; Igarashi, Makoto; Iizuka, Yoshinori; Kameda, Takao; Kanda, Hiroshi; Kohno, Mika; Kuramoto, Takayuki; Matsushi, Yuki; Miyahara, Morihiro; Miyake, Takayuki; Miyamoto, Atsushi; Nagashima, Yasuo; Nakayama, Yoshiki; Nakazawa, Takakiyo; Nakazawa, Fumio; Nishio, Fumihiko; Obinata, Ichio; Ohgaito, Rumi; Oka, Akira; Okuno, Jun’ichi; Okuyama, Junichi; Oyabu, Ikumi; Parrenin, Frédéric; Pattyn, Frank; Saito, Fuyuki; Saito, Takashi; Saito, Takeshi; Sakurai, Toshimitsu; Sasa, Kimikazu; Seddik, Hakime; Shibata, Yasuyuki; Shinbori, Kunio; Suzuki, Keisuke; Suzuki, Toshitaka; Takahashi, Akiyoshi; Takahashi, Kunio; Takahashi, Shuhei; Takata, Morimasa; Tanaka, Yoichi; Uemura, Ryu; Watanabe, Genta; Watanabe, Okitsugu; Yamasaki, Tetsuhide; Yokoyama, Kotaro; Yoshimori, Masakazu; Yoshimoto, Takayasu

    2017-01-01

    Climatic variabilities on millennial and longer time scales with a bipolar seesaw pattern have been documented in paleoclimatic records, but their frequencies, relationships with mean climatic state, and mechanisms remain unclear. Understanding the processes and sensitivities that underlie these changes will underpin better understanding of the climate system and projections of its future change. We investigate the long-term characteristics of climatic variability using a new ice-core record from Dome Fuji, East Antarctica, combined with an existing long record from the Dome C ice core. Antarctic warming events over the past 720,000 years are most frequent when the Antarctic temperature is slightly below average on orbital time scales, equivalent to an intermediate climate during glacial periods, whereas interglacial and fully glaciated climates are unfavourable for a millennial-scale bipolar seesaw. Numerical experiments using a fully coupled atmosphere-ocean general circulation model with freshwater hosing in the northern North Atlantic showed that climate becomes most unstable in intermediate glacial conditions associated with large changes in sea ice and the Atlantic Meridional Overturning Circulation. Model sensitivity experiments suggest that the prerequisite for the most frequent climate instability with bipolar seesaw pattern during the late Pleistocene era is associated with reduced atmospheric CO2 concentration via global cooling and sea ice formation in the North Atlantic, in addition to extended Northern Hemisphere ice sheets. PMID:28246631

  18. Radar Interferometry Detection of Hinge Line Migration on Rutford Ice Stream and Carlson Inlet, Antarctica

    NASA Technical Reports Server (NTRS)

    Rignot, Eric

    1997-01-01

    Satellite synthetic-aperture radar (SAR) Interferometry is employed to map the hinge line, or limit of tidal flexing, of Rutford Ice Stream and Carlson Inlet, Antarctica, and detect its migration between 1992 and 1996. The hinge line is mapped using a model fit from an elastic beam theory.

  19. Effects on skylight at South Pole Station, Antarctica, by ice crystal precipitation in the atmosphere

    NASA Technical Reports Server (NTRS)

    Fitch, B. W.; Coulson, K. L.

    1983-01-01

    Measurements of the radiance and polarization of the skylight at South Pole Station, Antarctica, were made for clear cloud-free skies and cloudless skies with ice crystal precipitation. The measurements were made at six narrowband wavelengths from 321 to 872 nm in the principal plane. The data show that scattering by ice crystals increases the radiance in the backscatter plane, decreases it in the solar plane, and shifts the radiance minimum to a point closer to the sun. The crystals decrease the maximum value of linear polarization and shift the position of the maximum away from the sun. The influence of ice crystal scattering is greatest at the longer wavelengths.

  20. Effects on skylight at South Pole Station, Antarctica, by ice crystal precipitation in the atmosphere.

    PubMed

    Fitch, B W; Coulson, K L

    1983-01-01

    Measurements of the radiance and polarization of the skylight at South Pole Station, Antarctica, were made for clear cloud-free skies and cloudless skies with ice crystal precipitation. The measurements were made at six narrowband wavelengths from 321 to 872 nm in the principal plane. The data show that scattering by ice crystals increases the radiance in the backscatter plane, decreases it in the solar plane, and shifts the radiance minimum to a point closer to the sun. The crystals decrease the maximum value of linear polarization and shift the position of the maximum away from the sun. The influence of ice crystal scattering is greatest at the longer wavelengths.

  1. Coastal-change and glaciological map of the Ronne Ice Shelf area, Antarctica, 1974-2002

    USGS Publications Warehouse

    Ferrigno, Jane G.; Foley, K.M.; Swithinbank, C.; Williams, R.S.; Dalide, L.M.

    2005-01-01

    (MSS) images of Ant-arctica and the subsequent repeat coverage made possible with Landsat and other satellite images provided an excellent means of documenting changes in the coastline of Antarctica (Ferrigno and Gould, 1987). The availability of this information provided the impetus for carrying out a comprehensive analysis of the glaciological features of the coastal regions and changes in ice fronts of Antarctica (Swithinbank, 1988; Williams and Ferrigno, 1988). The project was later modified to include Landsat 4 and 5 MSS and Thematic Mapper (TM) (and in some areas Landsat 7 Enhanced Thematic Mapper Plus (ETM+)), RADARSAT images, and other data where available, to compare changes during a 20- to 25- or 30-year time interval (or longer where data were available, as in the Antarctic Peninsula). The results of the analysis are being used to produce a digital database and a series of USGS Geologic Investigations Series Maps (I-2600) consisting of 23 maps at 1:1,000,000 scale and 1 map at 1:5,000,000 scale, in both paper and digital format (Williams and others, 1995; Williams and Ferrigno, 1998; Ferrigno and others, 2002) (available online at http://www.glaciers.er.usgs.gov).

  2. Sea Ice Freeboard and Thickness from the 2013 IceBridge ATM and DMS Data in Ross Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    Xie, H.; Tian, L.; Tang, J.; Ackley, S. F.

    2016-12-01

    In November (20, 21, 27, and 28) 2013, NASA's IceBridge mission flew over the Ross Sea, Antarctica and collected important sea ice data with the ATM and DMS for the first time. We will present our methods to derive the local sea level and total freeboard for ice thickness retrieval from these two datasets. The methods include (1) leads classification from DMS data using an automated lead detection method, (2) potential leads from the reflectance of less than 0.25 from the ATM laser shots of L1B data, (3) local sea level retrieval based on these qualified ATM laser shots (L1B) within the DMS-derived leads (after outliers removal from the mean ± 2 standard deviation of these ATM elevations), (4) establishment of an empirical equation of local sea level as a function of distance from the starting point of each IceBridge flight, (5) total freeboard retrieval from the ATM L2 elevations by subtracting the local sea level derived from the empirical equation, and (6) ice thickness retrieval. The ice thickness derived from this method will be analyzed and compared with ICESat data (2003-2009) and other available data for the same region at the similar time period. Possible change and potential reasons will be identified and discussed.

  3. Antarctica

    Atmospheric Science Data Center

    2013-04-16

    article title:  Twilight in Antarctica     View larger JPEG ... SpectroRadiometer (MISR) instrument on board Terra. The Ross Ice Shelf and Transantarctic Mountains are illuminated by low Sun. MISR was ...

  4. A common and optimized age scale for Antarctic ice cores

    NASA Astrophysics Data System (ADS)

    Parrenin, F.; Veres, D.; Landais, A.; Bazin, L.; Lemieux-Dudon, B.; Toye Mahamadou Kele, H.; Wolff, E.; Martinerie, P.

    2012-04-01

    Dating ice cores is a complex problem because 1) there is a age shift between the gas bubbles and the surrounding ice 2) there are many different ice cores which can be synchronized with various proxies and 3) there are many methods to date the ice and the gas bubbles, each with advantages and drawbacks. These methods fall into the following categories: 1) Ice flow (for the ice) and firn densification modelling (for the gas bubbles); 2) Comparison of ice core proxies with insolation variations (so-called orbital tuning methods); 3) Comparison of ice core proxies with other well dated archives; 4) Identification of well-dated horizons, such as tephra layers or geomagnetic anomalies. Recently, an new dating tool has been developped (DATICE, Lemieux-Dudon et al., 2010), to take into account all the different dating information into account and produce a common and optimal chronology for ice cores with estimated confidence intervals. In this talk we will review the different dating information for Antarctic ice cores and show how the DATICE tool can be applied.

  5. Ice shelf structure derived from dispersion curve analysis of ambient seismic noise, Ross Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Diez, A.; Bromirski, P. D.; Gerstoft, P.; Stephen, R. A.; Anthony, R. E.; Aster, R. C.; Cai, C.; Nyblade, A.; Wiens, D. A.

    2016-05-01

    An L-configured, three-component short period seismic array was deployed on the Ross Ice Shelf, Antarctica during November 2014. Polarization analysis of ambient noise data from these stations shows linearly polarized waves for frequency bands between 0.2 and 2 Hz. A spectral peak at about 1.6 Hz is interpreted as the resonance frequency of the water column and is used to estimate the water layer thickness below the ice shelf. The frequency band from 4 to 18 Hz is dominated by Rayleigh and Love waves propagating from the north that, based on daily temporal variations, we conclude were generated by field camp activity. Frequency-slowness plots were calculated using beamforming. Resulting Love and Rayleigh wave dispersion curves were inverted for the shear wave velocity profile within the firn and ice to ˜150 m depth. The derived density profile allows estimation of the pore close-off depth and the firn-air content thickness. Separate inversions of Rayleigh and Love wave dispersion curves give different shear wave velocity profiles within the firn. We attribute this difference to an effective anisotropy due to fine layering. The layered structure of firn, ice, water and the seafloor results in a characteristic dispersion curve below 7 Hz. Forward modelling the observed Rayleigh wave dispersion curves using representative firn, ice, water and sediment structures indicates that Rayleigh waves are observed when wavelengths are long enough to span the distance from the ice shelf surface to the seafloor. The forward modelling shows that analysis of seismic data from an ice shelf provides the possibility of resolving ice shelf thickness, water column thickness and the physical properties of the ice shelf and underlying seafloor using passive-source seismic data.

  6. eVolv2k: A new ice core-based volcanic forcing reconstruction for the past 2000 years

    NASA Astrophysics Data System (ADS)

    Toohey, Matthew; Sigl, Michael

    2016-04-01

    Radiative forcing resulting from stratospheric aerosols produced by major volcanic eruptions is a dominant driver of climate variability in the Earth's past. The ability of climate model simulations to accurately recreate past climate is tied directly to the accuracy of the volcanic forcing timeseries used in the simulations. We present here a new volcanic forcing reconstruction, based on newly updated ice core composites from Antarctica and Greenland. Ice core records are translated into stratospheric aerosol properties for use in climate models through the Easy Volcanic Aerosol (EVA) module, which provides an analytic representation of volcanic stratospheric aerosol forcing based on available observations and aerosol model results, prescribing the aerosol's radiative properties and primary modes of spatial and temporal variability. The evolv2k volcanic forcing dataset covers the past 2000 years, and has been provided for use in the Paleo-Modeling Intercomparison Project (PMIP), and VolMIP experiments within CMIP6. Here, we describe the construction of the eVolv2k data set, compare with prior forcing sets, and show initial simulation results.

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

    PubMed Central

    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

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

    PubMed

    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.

  9. Large subglacial lakes in East Antarctica at the onset of fast-flowing ice streams.

    PubMed

    Bell, Robin E; Studinger, Michael; Shuman, Christopher A; Fahnestock, Mark A; Joughin, Ian

    2007-02-22

    Water plays a crucial role in ice-sheet stability and the onset of ice streams. Subglacial lake water moves between lakes and rapidly drains, causing catastrophic floods. The exact mechanisms by which subglacial lakes influence ice-sheet dynamics are unknown, however, and large subglacial lakes have not been closely associated with rapidly flowing ice streams. Here we use satellite imagery and ice-surface elevations to identify a region of subglacial lakes, similar in total area to Lake Vostok, at the onset region of the Recovery Glacier ice stream in East Antarctica and predicted by ice-sheet models. We define four lakes through extensive, flat, featureless regions of ice surface bounded by upstream troughs and downstream ridges. Using ice velocities determined using interferometric synthetic aperture radar (InSAR), we find the onset of rapid flow (moving at 20 to 30 m yr(-1)) of the tributaries to the Recovery Glacier ice stream in a 280-km-wide segment at the downslope margins of these four subglacial lakes. We conclude that the subglacial lakes initiate and maintain rapid ice flow through either active modification of the basal thermal regime of the ice sheet by lake accretion or through scouring bedrock channels in periodic drainage events. We suggest that the role of subglacial lakes needs to be considered in ice-sheet mass balance assessments.

  10. Surface winds over West Antarctica

    NASA Astrophysics Data System (ADS)

    Bromwich, David

    1993-07-01

    Five winter months (April-August 1988) of thermal infrared satellite images were examined to investigate the occurrence of dark (warm) signatures across the Ross Ice Shelf in the Antarctic continent. These features are inferred to be generated by katabatic winds that descend from southern Marie Byrd Land and then blow horizontally across the ice shelf. Significant mass is added to this airstream by katabatic winds blowing from the major glaciers that flow through the Transantarctic Mountains from East Antarctica. These negatively buoyant katabatic winds can reach the northwestern edge of the shelf - a horizontal propagation distance of up to 1,000 km - 14 percent of the time. Where the airstream crosses from the ice shelf to the ice-covered Ross Sea, a prominent coastal polynya is formed. Because the downslope buoyancy force is near zero over the Ross Ice Shelf, the northwestward propagation of the katabatic air mass requires pressure gradient support. The study shows that the extended horizontal propagation of this atmospheric density current occurred in conjunction with the passage of synoptic cyclones over the southern Amundsen Sea. These cyclones can strengthen the pressure gradient in the interior of West Antarctica and make the pressure field favorable for northwestward movement of the katabatic winds from West Antarctica across the ice shelf in a geostrophic direction. The glacier winds from East Antarctica are further accelerated by the synoptic pressure gradient, usually undergo abrupt adjustment beyond the exit to the glacier valley, and merge into the mountain-parallel katabatic air mass.

  11. The influence of sea ice on Antarctic ice core sulfur chemistry and on the future evolution of Arctic snow depth: Investigations using global models

    NASA Astrophysics Data System (ADS)

    Hezel, Paul J.

    Observational studies have examined the relationship between methanesulfonic acid (MSA) measured in Antarctic ice cores and sea ice extent measured by satellites with the aim of producing a proxy for past sea ice extent. MSA is an oxidation product of dimethylsulfide (DMS) and is potentially linked to sea ice based on observations of very high surface seawater DMS in the sea ice zone. Using a global chemical transport model, we present the first modeling study that specifically examines this relationship on interannual and on glacial-interglacial time scales. On interannual time scales, the model shows no robust relationship between MSA deposited in Antarctica and sea ice extent. We show that lifetimes of MSA and DMS are longer in the high latitudes than in the global mean, interannual variability of sea ice is small (<25%) as a fraction of sea ice area, and sea ice determines only a fraction of the variability (<30%) of DMS emissions from the ocean surface. A potentially larger fraction of the variability in DMS emissions is determined by surface wind speed (up to 46%) via the parameterization for ocean-to-atmosphere gas exchange. Furthermore, we find that a significant fraction (up to 74%) of MSA deposited in Antarctica originates from north of 60°S, north of the seasonal sea ice zone. We then examine the deposition of MSA and non-sea-salt sulfate (nss SO2-4 ) on glacial-interglacial time scales. Ice core observations on the East Antarctic Plateau suggest that MSA increases much more than nss SO2-4 during the last glacial maximum (LGM) compared to the modern period. It has been suggested that high MSA during the LGM is indicative of higher primary productivity and DMS emissions in the LGM compared to the modern day. Studies have also shown that MSA is subject to post-depositional volatilization, especially during the modern period. Using the same chemical transport model driven by meteorology from a global climate model, we examine the sensitivity of MSA and nss

  12. Dibble Ice Shelf

    NASA Image and Video Library

    2013-06-13

    This photo, aken onboard a National Science Foundation/NASA chartered Twin Otter aircraft, shows the ice front of Dibble Ice Shelf, East Antarctica, a significant melt water producer from the Wilkes Land region, East Antarctica.

  13. Detecting high spatial variability of ice shelf basal mass balance, Roi Baudouin Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Berger, Sophie; Drews, Reinhard; Helm, Veit; Sun, Sainan; Pattyn, Frank

    2017-11-01

    Ice shelves control the dynamic mass loss of ice sheets through buttressing and their integrity depends on the spatial variability of their basal mass balance (BMB), i.e. the difference between refreezing and melting. Here, we present an improved technique - based on satellite observations - to capture the small-scale variability in the BMB of ice shelves. As a case study, we apply the methodology to the Roi Baudouin Ice Shelf, Dronning Maud Land, East Antarctica, and derive its yearly averaged BMB at 10 m horizontal gridding. We use mass conservation in a Lagrangian framework based on high-resolution surface velocities, atmospheric-model surface mass balance and hydrostatic ice-thickness fields (derived from TanDEM-X surface elevation). Spatial derivatives are implemented using the total-variation differentiation, which preserves abrupt changes in flow velocities and their spatial gradients. Such changes may reflect a dynamic response to localized basal melting and should be included in the mass budget. Our BMB field exhibits much spatial detail and ranges from -14.7 to 8.6 m a-1 ice equivalent. Highest melt rates are found close to the grounding line where the pressure melting point is high, and the ice shelf slope is steep. The BMB field agrees well with on-site measurements from phase-sensitive radar, although independent radar profiling indicates unresolved spatial variations in firn density. We show that an elliptical surface depression (10 m deep and with an extent of 0.7 km × 1.3 km) lowers by 0.5 to 1.4 m a-1, which we tentatively attribute to a transient adaptation to hydrostatic equilibrium. We find evidence for elevated melting beneath ice shelf channels (with melting being concentrated on the channel's flanks). However, farther downstream from the grounding line, the majority of ice shelf channels advect passively (i.e. no melting nor refreezing) toward the ice shelf front. Although the absolute, satellite-based BMB values remain uncertain, we have

  14. Modeling of cryoseismicity observed at the Fimbulisen Ice Shelf, East Antarctica

    NASA Astrophysics Data System (ADS)

    Hainzl, S.; Pirli, M.; Dahm, T.; Schweitzer, J.; Köhler, A.

    2017-12-01

    A source region of repetitive cryoseismic activity has been identified at the Fimbulisen ice shelf, in Dronning Maud Land, East Antarctica. The specific area is located at the outlet of the Jutulstraumen glacier, near the Kupol Moskovskij ice rise. A unique event catalog extending over 13 years, from 2003 to 2016 has been built based on waveform cross-correlation detectors and Hidden Markov Model classifiers. Phases of low seismicity rates are alternating with intense activity intervals that exhibit a strong tidal modulation. We performed a detailed analysis and modeling of the more than 2000 events recorded between July and October 2013. The observations are characterized by a number of very clear signals: (i) the event rate follows both the neap-spring and the semi-diurnal ocean-tide cycle; (ii) recurrences have a characteristic time of approximately 8 minutes; (iii) magnitudes vary systematically both on short and long time scales; and (iv) the events migrate within short-time clusters. We use these observations to constrain the dynamic processes at work at this particular region of the Fimbulisen ice shelf. Our model assumes a local grounding of the ice shelf, where stick-slip motion occurs. We show that the observations can be reproduced considering the modulation of the Coulomb-Failure stress by ocean tides.

  15. Phreatomagmatic eruptions under the West Antarctic Ice Sheet: potential hazard for ice sheet stability

    NASA Astrophysics Data System (ADS)

    Iverson, N. A.; Dunbar, N. W.; Lieb-Lappen, R.; Kim, E. J.; Golden, E. J.; Obbard, R. W.

    2014-12-01

    Volcanic tephra layers have been seen in most ice cores in Antarctica. These tephra layers are deposited almost instantaneously across wide areas of ice sheets, creating horizons that can provide "pinning points" to adjust ice time scales that may otherwise be lacking detailed chronology. A combination of traditional particle morphology characterization by SEM with new non-destructive X-ray micro-computed tomography (Micro-CT) has been used to analyze selected coarse grained tephra in the West Antarctica Ice Sheet (WAIS) Divide WDC06A ice core. Micro-CT has the ability to image particles as small as 50µm in length (15µm resolution), quantifying both particle shape and size. The WDC06A contains hundreds of dusty layers of which 36 have so far been identified as primary tephra layers. Two of these tephra layers have been characterized as phreatomagmatic eruptions based on SEM imagery and are blocky and platy in nature, with rare magmatic particles. These layers are strikingly different in composition from the typical phonolitic and trachytic tephra produced from West Antarctic volcanoes. These two layers are coarser in grain size, with many particles (including feldspar crystals) exceeding 100µm in length. One tephra layer found at 3149.138m deep in the ice core is a coarse ~1mm thick basanitic tephra layer with a WDC06-7 ice core age of 45,381±2000yrs. The second layer is a ~1.3 cm thick zoned trachyandesite to trachydacite tephra found at 2569.205m deep with an ice core age 22,470±835yrs. Micro-CT analysis shows that WDC06A-3149.138 has normal grading with the largest particles at the bottom of the sample (~160μm). WDC06A-2569.205 has a bimodal distribution of particles with large particles at the top and bottom of the layer. These large particles are more spherical in shape at the base and become more irregular and finer grained higher in the layer, likely showing changes in eruption dynamics. The distinct chemistry as well as the blocky and large grain size

  16. Abbot Ice Shelf, structure of the Amundsen Sea continental margin and the southern boundary of the Bellingshausen Plate seaward of West Antarctica.

    PubMed

    Cochran, James R; Tinto, Kirsty J; Bell, Robin E

    2015-05-01

    Inversion of NASA Operation IceBridge airborne gravity over the Abbot Ice Shelf in West Antarctica for subice bathymetry defines an extensional terrain made up of east-west trending rift basins formed during the early stages of Antarctica/Zealandia rifting. Extension is minor, as rifting jumped north of Thurston Island early in the rifting process. The Amundsen Sea Embayment continental shelf west of the rifted terrain is underlain by a deeper, more extensive sedimentary basin also formed during rifting between Antarctica and Zealandia. A well-defined boundary zone separates the mildly extended Abbot extensional terrain from the deeper Amundsen Embayment shelf basin. The shelf basin has an extension factor, β , of 1.5-1.7 with 80-100 km of extension occurring across an area now 250 km wide. Following this extension, rifting centered north of the present shelf edge and proceeded to continental rupture. Since then, the Amundsen Embayment continental shelf appears to have been tectonically quiescent and shaped by subsidence, sedimentation, and the advance and retreat of the West Antarctic Ice Sheet. The Bellingshausen Plate was located seaward of the Amundsen Sea margin prior to incorporation into the Antarctic Plate at about 62 Ma. During the latter part of its independent existence, Bellingshausen plate motion had a clockwise rotational component relative to Antarctica producing convergence across the north-south trending Bellingshausen Gravity Anomaly structure at 94°W and compressive deformation on the continental slope between 94°W and 102°W. Farther west, the relative motion was extensional along an east-west trending zone occupied by the Marie Byrd Seamounts. Abbot Ice Shelf is underlain by E-W rift basins created at ∼90 Ma Amundsen shelf shaped by subsidence, sedimentation, and passage of the ice sheet Bellingshausen plate boundary is located near the base of continental slope and rise.

  17. Abbot Ice Shelf, structure of the Amundsen Sea continental margin and the southern boundary of the Bellingshausen Plate seaward of West Antarctica

    PubMed Central

    Cochran, James R; Tinto, Kirsty J; Bell, Robin E

    2015-01-01

    Inversion of NASA Operation IceBridge airborne gravity over the Abbot Ice Shelf in West Antarctica for subice bathymetry defines an extensional terrain made up of east-west trending rift basins formed during the early stages of Antarctica/Zealandia rifting. Extension is minor, as rifting jumped north of Thurston Island early in the rifting process. The Amundsen Sea Embayment continental shelf west of the rifted terrain is underlain by a deeper, more extensive sedimentary basin also formed during rifting between Antarctica and Zealandia. A well-defined boundary zone separates the mildly extended Abbot extensional terrain from the deeper Amundsen Embayment shelf basin. The shelf basin has an extension factor, β, of 1.5–1.7 with 80–100 km of extension occurring across an area now 250 km wide. Following this extension, rifting centered north of the present shelf edge and proceeded to continental rupture. Since then, the Amundsen Embayment continental shelf appears to have been tectonically quiescent and shaped by subsidence, sedimentation, and the advance and retreat of the West Antarctic Ice Sheet. The Bellingshausen Plate was located seaward of the Amundsen Sea margin prior to incorporation into the Antarctic Plate at about 62 Ma. During the latter part of its independent existence, Bellingshausen plate motion had a clockwise rotational component relative to Antarctica producing convergence across the north-south trending Bellingshausen Gravity Anomaly structure at 94°W and compressive deformation on the continental slope between 94°W and 102°W. Farther west, the relative motion was extensional along an east-west trending zone occupied by the Marie Byrd Seamounts. Key Points: Abbot Ice Shelf is underlain by E-W rift basins created at ∼90 Ma Amundsen shelf shaped by subsidence, sedimentation, and passage of the ice sheet Bellingshausen plate boundary is located near the base of continental slope and rise PMID:26709352

  18. Regional ice-mass changes and glacial-isostatic adjustment in Antarctica from GRACE

    NASA Astrophysics Data System (ADS)

    Sasgen, Ingo; Martinec, Zdeněk; Fleming, Kevin

    2007-12-01

    We infer regional mass changes in Antarctica using ca. 4 years of Gravity Recovery and Climate Experiment (GRACE) level 2 data. We decompose the time series of the Stokes coefficients into their linear as well as annual and semi-annual components by a least-squares adjustment and apply a statistical reliability test to the Stokes potential-coefficients' linear temporal trends. Mass changes in three regions of Antarctica that display prominent geoid-height change are determined by adjusting predictions of glacier melting at the tip of the Antarctic Peninsula and in the Amundsen Sea Sector, and of the glacial-isostatic adjustment (GIA) over the Ronne Ice Shelf. We use the GFZ RL04, CNES RL01C, JPL RL04 and CSR RL04 potential-coefficient releases, and show that, although all data sets consistently reflect the prominent mass changes, differences in the mass-change estimates are considerably larger than the uncertainties estimated by the propagation of the GRACE errors. We then use the bootstrapping method based on the four releases and six time intervals, each with 3.5 years of data, to quantify the variability of the mean mass-change estimates. We find 95% of our estimates to lie within 0.08 and 0.09 mm/a equivalent sea-level (ESL) change for the Antarctic Peninsula and within 0.18 and 0.20 mm/a ESL for the Amundsen Sea Sector. Forward modelling of the GIA over the Ronne Ice Shelf region suggests that the Antarctic continent was covered by 8.4 to 9.4 m ESL of additional ice during the Last-Glacial Maximum (ca. 22 to 15 ka BP). With regards to the mantle-viscosity values and the glacial history used, this value is considered as a minimum estimate. The mass-change estimates derived from all GRACE releases and time intervals lie within ca. 20% (Amundsen Sea Sector), 30% (Antarctic Peninsula) and 50% (Ronne Ice Shelf region) of the bootstrap-estimated mean, demonstrating the reliability of results obtained using GRACE observations.

  19. The geomorphic signature of present ice-sheet flow in the radar-sounded subglacial record: Pine Island Glacier, West Antarctica

    NASA Astrophysics Data System (ADS)

    Bingham, R. G.; Davies, D.; King, E. C.; Vaughan, D. G.; Cornford, S. L.; Brisbourne, A.; Smith, A.; De Rydt, J.; Graham, A. G. C.; Spagnolo, M.

    2016-12-01

    Deglaciated landscapes and landforms are much used in the quest to reconstruct past ice-sheet behaviour, on the principle that aspects of landform shapes, sizes and relative associations "fossilise" palaeo-ice-sheet processes. Such techniques have been widely used around the margin of the marine West Antarctic Ice Sheet, taking advantage of bathymetric surveying techniques which have exposed a rich suite of landform assemblages across West Antarctica's continental shelf. Though these geomorphological interpretations are solidly grounded in glacial geological theory, there has, until now, been little ability to compare these deglaciated, and potentially postglacially-modified, landforms offshore with landforms currently situated (and potentially still evolving) beneath the contemporary ice sheet. This paper presents a widespread view of glacial landforms presently situated beneath 1-2 km of ice in multi-square-km "windows to the bed" distributed throughout the catchment of Pine Island Glacier, West Antarctica. Imaged over three field seasons between 2007 and 2013 by dedicated radar surveys designed specifically to capture landforms analogous to those surveyed offshore by bathymetric surveying, the results provide significant insights for the interpretation of palaeo-ice-stream landforms, and their use in modelling ice-ocean interactions around the fringes of marine ice sheets. We show that landform sizes, shapes and associations vary significantly around Pine Island Glacier's catchment. The key controls appear to be substrate composition, pre-existing tectonic structure, and longstanding spatial stability of the ice-stream's flow distribution. The findings offer crucial information for modelling ice coupling to the bed, which should feed through to wider efforts to reconstruct the past behaviour of this significant marine ice sheet using its palaeoglacial landforms.

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

    PubMed

    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.

  1. Ice cover, landscape setting, and geological framework of Lake Vostok, East Antarctica

    USGS Publications Warehouse

    Studinger, M.; Bell, R.E.; Karner, G.D.; Tikku, A.A.; Holt, J.W.; Morse, D.L.; David, L.; Richter, T.G.; Kempf, S.D.; Peters, M.E.; Blankenship, D.D.; Sweeney, R.E.; Rystrom, V.L.

    2003-01-01

    Lake Vostok, located beneath more than 4 km of ice in the middle of East Antarctica, is a unique subglacial habitat and may contain microorganisms with distinct adaptations to such an extreme environment. Melting and freezing at the base of the ice sheet, which slowly flows across the lake, controls the flux of water, biota and sediment particles through the lake. The influx of thermal energy, however, is limited to contributions from below. Thus the geological origin of Lake Vostok is a critical boundary condition for the subglacial ecosystem. We present the first comprehensive maps of ice surface, ice thickness and subglacial topography around Lake Vostok. The ice flow across the lake and the landscape setting are closely linked to the geological origin of Lake Vostok. Our data show that Lake Vostok is located along a major geological boundary. Magnetic and gravity data are distinct east and west of the lake, as is the roughness of the subglacial topography. The physiographic setting of the lake has important consequences for the ice flow and thus the melting and freezing pattern and the lake's circulation. Lake Vostok is a tectonically controlled subglacial lake. The tectonic processes provided the space for a unique habitat and recent minor tectonic activity could have the potential to introduce small, but significant amounts of thermal energy into the lake. ?? 2002 Elsevier Science B.V. All rights reserved.

  2. The structure and effect of suture zones in the Larsen C Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    McGrath, Daniel; Steffen, Konrad; Holland, Paul R.; Scambos, Ted; Rajaram, Harihar; Abdalati, Waleed; Rignot, Eric

    2014-03-01

    Ice shelf fractures frequently terminate where they encounter suture zones, regions of material heterogeneity that form between meteoric inflows in ice shelves. This heterogeneity can consist of marine ice, meteoric ice with modified rheological properties, or the presence of fractures. Here, we use radar observations on the Larsen C Ice Shelf, Antarctica, to investigate (i) the termination of a 25 km long rift in the Churchill Peninsula suture zone, which was found to contain 60 m of accreted marine ice, and (ii) the along-flow evolution of a suture zone originating at Cole Peninsula. We determine a steady state field of basal melting/freezing rates and apply it to a flowline model to delineate the along-flow evolution of layers within the ice shelf. The thickening surface wedge of locally accumulated meteoric ice, which likely has limited lateral variation in its mechanical properties, accounts for 60% of the total ice thickness near the calving front. Thus, we infer that the lower 40% of the ice column and the material heterogeneities present there are responsible for resisting fracture propagation and thereby delaying tabular calving events, as demonstrated in the >40 year time series leading up to the 2004/2005 calving event for Larsen C. This likely represents a highly sensitive aspect of ice shelf stability, as changes in the oceanic forcing may lead to the loss of this heterogeneity.

  3. Remote Characterization of Ice Shelf Surface and Basal Processes: Examples from East Antarctica

    NASA Astrophysics Data System (ADS)

    Greenbaum, J. S.; Blankenship, D. D.; Grima, C.; Schroeder, D. M.; Soderlund, K. M.; Young, D. A.; Kempf, S. D.; Siegert, M. J.; Roberts, J. L.; Warner, R. C.; van Ommen, T. D.

    2017-12-01

    The ability to remotely characterize surface and basal processes of ice shelves has important implications for conducting systematic, repeatable, and safe evaluations of their stability in the context of atmospheric and oceanic forcing. Additionally, techniques developed for terrestrial ice shelves can be adapted to orbital radar sounding datasets planned for forthcoming investigations of icy moons. This has been made possible through recent advances in radar signal processing that enable these data to be used to test hypotheses derived from conceptual and numerical models of ice shelf- and ice shell-ocean interactions. Here, we present several examples of radar sounding-derived characterizations of surface and basal processes underway on ice shelves in East Antarctica. These include percolation of near-surface meltwater in warm austral summers, brine infiltration along ice shelf calving fronts, basal melt rate and distribution, and basal freeze distribution. On Europa, near-surface brines and their migration may impact local geological variability, while basal processes likely control the distribution of melt and freeze. Terrestrially, we emphasize radar-sounding records of the Totten Glacier Ice Shelf which hosts each of these processes as well as the highest known density of basal melt channels of any terrestrial ice shelf. Further, with a maximum floating ice thickness of over 2.5 km, the pressure at Totten's basal interface may be similar to that at Europa's ice-ocean interface; therefore, evaluating surface and basal processes of Totten Glacier and other ice shelves could serve as analogs for understanding melting processes of Europa's ice shell.

  4. Modeling the Thickness of Perennial Ice Covers on Stratified Lakes of the Taylor Valley, Antarctica

    NASA Technical Reports Server (NTRS)

    Obryk, M. K.; Doran, P. T.; Hicks, J. A.; McKay, C. P.; Priscu, J. C.

    2016-01-01

    A one-dimensional ice cover model was developed to predict and constrain drivers of long term ice thickness trends in chemically stratified lakes of Taylor Valley, Antarctica. The model is driven by surface radiative heat fluxes and heat fluxes from the underlying water column. The model successfully reproduced 16 years (between 1996 and 2012) of ice thickness changes for west lobe of Lake Bonney (average ice thickness = 3.53 m; RMSE = 0.09 m, n = 118) and Lake Fryxell (average ice thickness = 4.22 m; RMSE = 0.21 m, n = 128). Long-term ice thickness trends require coupling with the thermal structure of the water column. The heat stored within the temperature maximum of lakes exceeding a liquid water column depth of 20 m can either impede or facilitate ice thickness change depending on the predominant climatic trend (temperature cooling or warming). As such, shallow (< 20 m deep water columns) perennially ice-covered lakes without deep temperature maxima are more sensitive indicators of climate change. The long-term ice thickness trends are a result of surface energy flux and heat flux from the deep temperature maximum in the water column, the latter of which results from absorbed solar radiation.

  5. Glaciers of Antarctica

    USGS Publications Warehouse

    Williams, Richard S.; Ferrigno, Jane G.

    1988-01-01

    Of all the world?s continents Antarctica is the coldest, the highest, and the least known. It is one and a half times the size of the United States, and on it lies 91 percent (30,109,800 km3) of the estimated volume of all the ice on Earth. Because so little is known about Antarctic glaciers compared with what is known about glaciers in populated countries, satellite imagery represents a great leap forward in the provision of basic data. From the coast of Antarctica to about 81?south latitude, there are 2,514 Landsat nominal scene centers (the fixed geographic position of the intersection of orbital paths and latitudinal rows). If there were cloud-free images for all these geographic centers, only about 520 Landsat images would be needed to provide complete coverage. Because of cloud cover, however, only about 70 percent of the Landsat imaging area, or 55 percent of the continent, is covered by good quality Landsat images. To date, only about 20 percent of Antarctica has been mapped at scales of 1:250,000 or larger, but these maps do include about half of the coastline. The area of Antarctica that could be planimetrically mapped at a scale of 1:250,000 would be tripled if the available Landsat images were used in image map production. This chapter contains brief descriptions and interpretations of features seen in 62 carefully selected Landsat images or image mosaics. Images were chosen on the basis of quality and interest; for this reason they are far from evenly spaced around the continent. Space limitations allow less than 15 percent of the Landsat imaging area of Antarctica to be shown in the illustrations reproduced in this chapter. Unfortunately, a wealth of glaciological and other features of compelling interest is present in the many hundreds of images that could not be included. To help show some important features beyond the limit of Landsat coverage, and as an aid to the interpretation of certain features seen in the images, 38 oblique aerial photographs

  6. Basal Settings Control Fast Ice Flow in the Recovery/Slessor/Bailey Region, East Antarctica

    NASA Astrophysics Data System (ADS)

    Diez, Anja; Matsuoka, Kenichi; Ferraccioli, Fausto; Jordan, Tom A.; Corr, Hugh F.; Kohler, Jack; Olesen, Arne V.; Forsberg, René

    2018-03-01

    The region of Recovery Glacier, Slessor Glacier, and Bailey Ice Stream, East Antarctica, has remained poorly explored, despite representing the largest potential contributor to future global sea level rise on a centennial to millennial time scale. Here we use new airborne radar data to improve knowledge about the bed topography and investigate controls of fast ice flow. Recovery Glacier is underlain by an 800 km long trough. Its fast flow is controlled by subglacial water in its upstream and topography in its downstream region. Fast flow of Slessor Glacier is controlled by the presence of subglacial water on a rough crystalline bed. Past ice flow of adjacent Recovery and Slessor Glaciers was likely connected via the newly discovered Recovery-Slessor Gate. Changes in direction and speed of past fast flow likely occurred for upstream parts of Recovery Glacier and between Slessor Glacier and Bailey Ice Stream. Similar changes could also reoccur here in the future.

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

    NASA Astrophysics Data System (ADS)

    Nelson, C. B.; King, K.

    2015-12-01

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

  8. Physical analysis of an Antarctic ice core—towards an integration of micro- and macrodynamics of polar ice*

    PubMed Central

    Jansen, Daniela; Binder, Tobias; Eichler, Jan; Faria, Sérgio H.; Wilhelms, Frank; Kipfstuhl, Sepp; Sheldon, Simon; Miller, Heinrich; Dahl-Jensen, Dorthe; Kleiner, Thomas

    2017-01-01

    Microstructures from deep ice cores reflect the dynamic conditions of the drill location as well as the thermodynamic history of the drill site and catchment area in great detail. Ice core parameters (crystal lattice-preferred orientation (LPO), grain size, grain shape), mesostructures (visual stratigraphy) as well as borehole deformation were measured in a deep ice core drilled at Kohnen Station, Dronning Maud Land (DML), Antarctica. These observations are used to characterize the local dynamic setting and its rheological as well as microstructural effects at the EDML ice core drilling site (European Project for Ice Coring in Antarctica in DML). The results suggest a division of the core into five distinct sections, interpreted as the effects of changing deformation boundary conditions from triaxial deformation with horizontal extension to bedrock-parallel shear. Region 1 (uppermost approx. 450 m depth) with still small macroscopic strain is dominated by compression of bubbles and strong strain and recrystallization localization. Region 2 (approx. 450–1700 m depth) shows a girdle-type LPO with the girdle plane being perpendicular to grain elongations, which indicates triaxial deformation with dominating horizontal extension. In this region (approx. 1000 m depth), the first subtle traces of shear deformation are observed in the shape-preferred orientation (SPO) by inclination of the grain elongation. Region 3 (approx. 1700–2030 m depth) represents a transitional regime between triaxial deformation and dominance of shear, which becomes apparent in the progression of the girdle to a single maximum LPO and increasing obliqueness of grain elongations. The fully developed single maximum LPO in region 4 (approx. 2030–2385 m depth) is an indicator of shear dominance. Region 5 (below approx. 2385 m depth) is marked by signs of strong shear, such as strong SPO values of grain elongation and strong kink folding of visual layers. The details of structural

  9. Greenhouse Gas Concentration Records Extended Back to 800,000 Years From the EPICA Dome C Ice Core

    NASA Astrophysics Data System (ADS)

    Chappellaz, J.; Luethi, D.; Loulergue, L.; Barnola, J.; Bereiter, B.; Blunier, T.; Jouzel, J.; Lefloch, M.; Lemieux, B.; Masson-Delmotte, V.; Raynaud, D.; Schilt, A.; Siegenthaler, U.; Spahni, R.; Stocker, T.

    2007-12-01

    The deep ice core recovered from Dome Concordia in the framework of EPICA, the European Project for Ice Coring in Antarctica, has extended the record of Antarctic climate history back to 800,000 years [Jouzel et al., 2007]. We present the current status of measurements of CO2, CH4 and N2O on air trapped in the bubbles of the Dome C ice core. CO2 is measured in two laboratories using different techniques (laser absorption spectroscopy or gas chromatography on samples of 8 and 40 g of ice which are mechanically crushed or milled, respectively). CH4 and N2O are extracted using a melt-refreeze technique and then measured by gas chromatography (in two laboratories for CH4). The greenhouse gas concentrations have now been measured on the lowest 200 m of the Dome C core, going back to Marine Isotope Stage 20 (MIS 20) as verified by a consistent gas age/ice age difference determined at termination IX [Jouzel et al., 2007]. The atmospheric CO2 concentration mostly lagged the Antarctic temperature with a rather strong correlation throughout the eight and a half glacial cycles, but with significantly lower CO2 values between 650 and 750 kyr BP. Its lowest level ever measured in ice cores (172 ppmv) is observed during MIS 16 (minimum centered at 667 kyr BP according to the EDC3 chronology) redetermining the natural span of CO2 to 172-300 ppmv. With 2245 individual measurements, the CH4 concentration is now reconstructed over 800,000 years from a single core, with an average time resolution of 380 years. Spectral analyses of the CH4 signal show an increasing contribution of precession during the last four climatic cycles compared with the four older ones, suggesting an increasing impact of low latitudes sources/sinks. Millennial scale features in this very detailed signal allows us to compare their occurrence with ice volume reconstructions and the isotopic composition of precipitation over the East Antarctic plateau. N2O is still affected by glaciological artefacts involving

  10. All-year-round aerosol chemical composition at Dome C, Antarctica

    NASA Astrophysics Data System (ADS)

    Udisti, Roberto; Becagli, Silvia; Frosini, Daniele; Galli, Gaia; Ghedini, Costanza; Rugi, Francesco; Severi, Mirko; Traversi, Rita

    2010-05-01

    Since 2005, continuous, all-year-round aerosol sampling was carried out at Dome C (Central East Antarctica, 3233 m a.s.l., about 1100 km far from the coastline), in the framework of "Station Concordia" project, an Italian PNRA - French IPEV joint program. Size-segregated aerosol samples were collected in summer and winter periods by using different low- and medium-volume systems, including pre-selected cut-off samplers (with PM10, PM2.5 and PM1 cut-off heads) and multi-stage (Andersen 8-stage and Dekati 4-stage) impactors. Sampling resolution and volumes ranged from 1 day to 1 month and from 2.3 to 12 m3/h, respectively. Aerosol study at Dome C is expected improving our knowledge on present-day source intensity, transport efficiency and pathways (including stratosphere-troposphere interchanges) of particles reaching internal sites of Antarctica. Besides, more detailed information on atmosphere-snow interactions, including depositional and post-depositional processes, as well as the effect of sublimation/condensation processes on snow surface, will be used for improving the reconstruction of past atmosphere composition from ice core chemical stratigraphies (EPICA Dome C ice core). Here we report major results from the chemical composition of the Antarctic background aerosol reaching Dome C, pointing out the seasonal pattern and the temporal trend of some ionic components used as tracers of sea spray, marine biogenic and crustal emissions. Oxidised sulfur compounds are assumed to affect the climate system by influencing the Earth's radiative budget, both directly (solar light scattering) and indirectly (acting as cloud condensation nuclei). Among these compounds, methanesulphonic acid (MSA) and H2SO4 (arising from the atmospheric oxidation of phytoplanktonic dimethylsulphide - DMS), are considered the best tracers of marine productivity. Their use as reliable markers of oceanic biogenic emissions is hindered by poorly known mechanisms (temperature and photochemistry

  11. Ice-flow reorganization in West Antarctica 2.5 kyr ago dated using radar-derived englacial flow velocities

    NASA Astrophysics Data System (ADS)

    Kingslake, Jonathan; Martín, Carlos; Arthern, Robert J.; Corr, Hugh F. J.; King, Edward C.

    2016-09-01

    We date a recent ice-flow reorganization of an ice divide in the Weddell Sea Sector, West Antarctica, using a novel combination of inverse methods and ice-penetrating radars. We invert for two-dimensional ice flow within an ice divide from data collected with a phase-sensitive ice-penetrating radar while accounting for the effect of firn on radar propagation and ice flow. By comparing isochronal layers simulated using radar-derived flow velocities with internal layers observed with an impulse radar, we show that the divide's internal structure is not in a steady state but underwent a disturbance, potentially implying a regional ice-flow reorganization, 2.5 (1.8-2.9) kyr B.P. Our data are consistent with slow ice flow in this location before the reorganization and the ice divide subsequently remaining stationary. These findings increase our knowledge of the glacial history of a region that lacks dated constraints on late-Holocene ice-sheet retreat and provides a key target for models that reconstruct and predict ice-sheet behavior.

  12. Diatoms in sediments of perennially ice-covered Lake Hoare, and implications for interpreting lake history in the McMurdo Dry Valleys of Antarctica

    USGS Publications Warehouse

    Spaulding, S.A.; McKnight, Diane M.; Stoermer, E.F.; Doran, P.T.

    1997-01-01

    Diatom assemblages in surficial sediments, sediment cores, sediment traps, and inflowing streams of perennially ice-covered Lake Hore, South Victorialand, Antarctica were examined to determine the distribution of diatom taxa, and to ascertain if diatom species composition has changed over time. Lake Hoare is a closed-basin lake with an area of 1.8 km2, maximum depth of 34 m, and mean depth of 14 m, although lake level has been rising at a rate of 0.09 m yr-1 in recent decades. The lake has an unusual regime of sediment deposition: coarse grained sediments accumulate on the ice surface and are deposited episodically on the lake bottom. Benthic microbial mats are covered in situ by the coarse episodic deposits, and the new surfaces are recolonized. Ice cover prevents wind-induced mixing, creating the unique depositional environment in which sediment cores record the history of a particular site, rather than a lake=wide integration. Shallow-water (<1 m) diatom assemblages (Stauroneis anceps, Navicula molesta, Diadesmis contenta var. parallela, Navicula peraustralis) were distinct from mid-depth (4-16 m) assemblages (Diadesmis contenta, Luticola muticopsis fo. reducta, Stauroneis anceps, Diadesmis contenta var. parallela, Luticola murrayi) and deep-water (2-31 m) assemblages (Luticola murrayi, Luticola muticopsis fo. reducta, Navicula molesta. Analysis of a sediment core (30 cm long, from 11 m water depth) from Lake Hoare revealed two abrupt changes in diatom assemblages. The upper section of the sediment core contained the greatest biomass of benthic microbial mat, as well as the greatest total abundance and diversity of diatoms. Relative abundances of diatoms in this section are similar to the surficial samples from mid-depths. An intermediate zone contained less organic material and lower densities of diatoms. The bottom section of core contained the least amount of microbial mat and organic material, and the lowest density of diatoms. The dominant process

  13. Measurements of 14C in ancient ice from Taylor Glacier, Antarctica constrain in situ cosmogenic 14CH4 and 14CO production rates

    NASA Astrophysics Data System (ADS)

    Petrenko, Vasilii V.; Severinghaus, Jeffrey P.; Schaefer, Hinrich; Smith, Andrew M.; Kuhl, Tanner; Baggenstos, Daniel; Hua, Quan; Brook, Edward J.; Rose, Paul; Kulin, Robb; Bauska, Thomas; Harth, Christina; Buizert, Christo; Orsi, Anais; Emanuele, Guy; Lee, James E.; Brailsford, Gordon; Keeling, Ralph; Weiss, Ray F.

    2016-03-01

    Carbon-14 (14C) is incorporated into glacial ice by trapping of atmospheric gases as well as direct near-surface in situ cosmogenic production. 14C of trapped methane (14CH4) is a powerful tracer for past CH4 emissions from ;old; carbon sources such as permafrost and marine CH4 clathrates. 14C in trapped carbon dioxide (14CO2) can be used for absolute dating of ice cores. In situ produced cosmogenic 14C in carbon monoxide (14CO) can potentially be used to reconstruct the past cosmic ray flux and past solar activity. Unfortunately, the trapped atmospheric and in situ cosmogenic components of 14C in glacial ice are difficult to disentangle and a thorough understanding of the in situ cosmogenic component is needed in order to extract useful information from ice core 14C. We analyzed very large (≈1000 kg) ice samples in the 2.26-19.53 m depth range from the ablation zone of Taylor Glacier, Antarctica, to study in situ cosmogenic production of 14CH4 and 14CO. All sampled ice is >50 ka in age, allowing for the assumption that most of the measured 14C originates from recent in situ cosmogenic production as ancient ice is brought to the surface via ablation. Our results place the first constraints on cosmogenic 14CH4 production rates and improve on prior estimates of 14CO production rates in ice. We find a constant 14CH4/14CO production ratio (0.0076 ± 0.0003) for samples deeper than 3 m, which allows the use of 14CO for correcting the 14CH4 signals for the in situ cosmogenic component. Our results also provide the first unambiguous confirmation of 14C production by fast muons in a natural setting (ice or rock) and suggest that the 14C production rates in ice commonly used in the literature may be too high.

  14. Coastal-Change and Glaciological Map of the Northern Ross Ice Shelf Area, Antarctica: 1962-2004

    USGS Publications Warehouse

    Ferrigno, Jane G.; Foley, Kevin M.; Swithinbank, Charles; Williams, Richard S.

    2007-01-01

    Programs. On the basis of these recommendations, the U.S. Geological Survey (USGS) decided that the archive of early 1970s Landsat 1, 2, and 3 Multispectral Scanner (MSS) images of Antarctica and the subsequent repeat coverage made possible with Landsat and other satellite images provided an excellent means of documenting changes in the coastline of Antarctica (Ferrigno and Gould, 1987). The availability of this information provided the impetus for carrying out a comprehensive analysis of the glaciological features of the coastal regions and changes in ice fronts of Antarctica (Swithinbank, 1988; Williams and Ferrigno, 1988). The project was later modified to include Landsat 4 and 5 MSS and Thematic Mapper (TM) images (and in some areas Landsat 7 Enhanced Thematic Mapper Plus [ETM+] images), RADARSAT images, and other data where available, in order to compare changes that occurred during a 20- to 25- or 30-year time interval (or longer where data were available, as in the Antarctic Peninsula). The results of the analysis are being used to produce a digital database and a series of USGS Geologic Investigations Series Maps (I?2600) (Williams and others, 1995; Williams and Ferrigno, 1998; Ferrigno and others, 2002) (available online at http://www.glaciers.er.usgs.gov).

  15. Crustal heat production and estimate of terrestrial heat flow in central East Antarctica, with implications for thermal input to the East Antarctic ice sheet

    NASA Astrophysics Data System (ADS)

    Goodge, John W.

    2018-02-01

    Terrestrial heat flow is a critical first-order factor governing the thermal condition and, therefore, mechanical stability of Antarctic ice sheets, yet heat flow across Antarctica is poorly known. Previous estimates of terrestrial heat flow in East Antarctica come from inversion of seismic and magnetic geophysical data, by modeling temperature profiles in ice boreholes, and by calculation from heat production values reported for exposed bedrock. Although accurate estimates of surface heat flow are important as an input parameter for ice-sheet growth and stability models, there are no direct measurements of terrestrial heat flow in East Antarctica coupled to either subglacial sediment or bedrock. As has been done with bedrock exposed along coastal margins and in rare inland outcrops, valuable estimates of heat flow in central East Antarctica can be extrapolated from heat production determined by the geochemical composition of glacial rock clasts eroded from the continental interior. In this study, U, Th, and K concentrations in a suite of Proterozoic (1.2-2.0 Ga) granitoids sourced within the Byrd and Nimrod glacial drainages of central East Antarctica indicate average upper crustal heat production (Ho) of about 2.6 ± 1.9 µW m-3. Assuming typical mantle and lower crustal heat flux for stable continental shields, and a length scale for the distribution of heat production in the upper crust, the heat production values determined for individual samples yield estimates of surface heat flow (qo) ranging from 33 to 84 mW m-2 and an average of 48.0 ± 13.6 mW m-2. Estimates of heat production obtained for this suite of glacially sourced granitoids therefore indicate that the interior of the East Antarctic ice sheet is underlain in part by Proterozoic continental lithosphere with an average surface heat flow, providing constraints on both geodynamic history and ice-sheet stability. The ages and geothermal characteristics of the granites indicate that crust in central

  16. Devon island ice cap: core stratigraphy and paleoclimate.

    PubMed

    Koerner, R M

    1977-04-01

    Valuable paleoclimatic information can be gained by studying the distribution of melt layers in deep ice cores. A profile representing the percentage of ice in melt layers in a core drilled from the Devon Island ice cap plotted against both time and depth shows that the ice cap has experienced a period of very warm summers since 1925, following a period of colder summers between about 1600 and 1925. The earlier period was coldest between 1680 and 1730. There is a high correlation between the melt-layer ice percentage and the mass balance of the ice cap. The relation between them suggests that the ice cap mass balance was zero (accumulation equaled ablation) during the colder period but is negative in the present warmer one. There is no firm evidence of a present cooling trend in the summer conditions on the ice cap. A comparison with the melt-layer ice percentage in cores from the other major Canadian Arctic ice caps shows that the variation of summer conditions found for the Devon Island ice cap is representative for all the large ice caps for about 90 percent of the time. There is also a good correlation between melt-layer percentage and summer sea-ice conditions in the archipelago. This suggests that the search for the northwest passage was influenced by changing climate, with the 19th-century peak of the often tragic exploration coinciding with a period of very cold summers.

  17. Dust Records in Ice Cores from the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Wang, N.; Yao, T.; Thompson, L. G.

    2014-12-01

    Dust plays an important role in the Earth system, and it usually displays largely spatial and temporal variations. It is necessary for us to reconstruct the past variations of dust in different regions to better understand the interactions between dust and environments. Ice core records can reveal the history of dust variations. In this paper, we used the Guliya, Dunde, Malan and Dasuopu ice cores from the Tibetan Plateau to study the spatial distribution, the seasonal variations and the secular trends of dust. It was found that the mean dust concentration was higher by one or two order of magnitudes in the Guliya and Dunde ice cores from the northern Tibetan Plateau than in the Dasuopu ice core from the southern Tibetan Plateau. During the year, the highest dust concentration occurs in the springtime in the northern Tibetan Plateau while in the non-monsoon season in the southern Tibetan Plateau. Over the last millennium, the Dasuopu ice core record shows that the 1270s~1380s and 1870s~1990s were the two epochs with high dust concentration. However, the Malan ice core from the northern Tibetan Plateau indicates that high dust concentration occurred in the 1130s~1550s and 1770s~1940s. Interestingly, climatic and environmental records of the ice cores from the Tibetan Plateau reflected that the correlation between dust concentration and air temperature was strongly positive in the southern Plateau while negative in the northern Plateau over the last millennium. This implies that climatic and environmental changes existed considerable differences in the different parts of the Plateau. Moreover, four Asian megadroughts occurred in 1638~1641, 1756~1758, 1790~1796 and 1876~1878, which caused more than tens millions people died, were revealed clearly by dust record in the Dasuopu ice core.

  18. Geoethical approach to mineral activities in Antarctica

    NASA Astrophysics Data System (ADS)

    Talalay, Pavel

    2013-04-01

    Antarctica is the outermost from civilization space continent. From 14.0 million km2 of surface area about 98% of Antarctica is covered by ice that averages at least 1.6 km in thickness. Geologically, the continent is the least explored in the world, and it is almost absolutely unknown what mineral resources Antarctica has as they are buried in rock that is covered by a thick ice sheet. It is thought to have large and valuable mineral deposits under the ice. This is because of what has been found in samples taken from the small areas of rock that are exposed, and also from what has been found in South Africa and South America. Up until 180 million years ago, Antarctica was a part of the Gondwanaland super continent, attached to South America, the Southern part of Africa, India and Australia, these continents then drifted apart until they reached their current positions. This leads to a possibility that Antarctica may also share some of the mineral wealth of these continents. Right now on the ice-free areas of Antarctica iron ore, chromium, copper, gold, nickel, platinum, coal and hydrocarbons have been found. The Protocol on Environmental Protection to the Antarctic Treaty, also known as the Madrid Protocol, was signed in 1991 by the signatories to the Antarctic Treaty and became law in January 1998. The Protocol provides for comprehensive protection of the Antarctic environment and associated ecosystems and includes a ban on all commercial mining for at least fifty years (this is up for review in 2041). Current climate change and melting ice in Polar Regions is opening up new opportunities to exploit mineral and oil resources. Even Antarctica's weather, ice and distance from any industrialized areas mean that mineral extraction would be extremely expensive and also extremely dangerous, the depletion of mineral recourses on the Earth can reverse banning of mining in Antarctica in future. There is no question that any resource exploitation in Antarctica will cause

  19. IceChrono1: a probabilistic model to compute a common and optimal chronology for several ice cores

    NASA Astrophysics Data System (ADS)

    Parrenin, F.; Bazin, L.; Capron, E.; Landais, A.; Lemieux-Dudon, B.; Masson-Delmotte, V.

    2015-05-01

    Polar ice cores provide exceptional archives of past environmental conditions. The dating of ice cores and the estimation of the age-scale uncertainty are essential to interpret the climate and environmental records that they contain. It is, however, a complex problem which involves different methods. Here, we present IceChrono1, a new probabilistic model integrating various sources of chronological information to produce a common and optimized chronology for several ice cores, as well as its uncertainty. IceChrono1 is based on the inversion of three quantities: the surface accumulation rate, the lock-in depth (LID) of air bubbles and the thinning function. The chronological information integrated into the model are models of the sedimentation process (accumulation of snow, densification of snow into ice and air trapping, ice flow), ice- and air-dated horizons, ice and air depth intervals with known durations, depth observations (depth shift between synchronous events recorded in the ice and in the air) and finally air and ice stratigraphic links in between ice cores. The optimization is formulated as a least squares problem, implying that all densities of probabilities are assumed to be Gaussian. It is numerically solved using the Levenberg-Marquardt algorithm and a numerical evaluation of the model's Jacobian. IceChrono follows an approach similar to that of the Datice model which was recently used to produce the AICC2012 (Antarctic ice core chronology) for four Antarctic ice cores and one Greenland ice core. IceChrono1 provides improvements and simplifications with respect to Datice from the mathematical, numerical and programming point of views. The capabilities of IceChrono1 are demonstrated on a case study similar to the AICC2012 dating experiment. We find results similar to those of Datice, within a few centuries, which is a confirmation of both IceChrono1 and Datice codes. We also test new functionalities with respect to the original version of Datice

  20. Pre-cometary ice composition from hot core chemistry.

    PubMed

    Tornow, Carmen; Kührt, Ekkehard; Motschmann, Uwe

    2005-10-01

    Pre-cometary ice located around star-forming regions contains molecules that are pre-biotic compounds or pre-biotic precursors. Molecular line surveys of hot cores provide information on the composition of the ice since it sublimates near these sites. We have combined a hydrostatic hot core model with a complex network of chemical reactions to calculate the time-dependent abundances of molecules, ions, and radicals. The model considers the interaction between the ice and gas phase. It is applied to the Orion hot core where high-mass star formation occurs, and to the solar-mass binary protostar system IRAS 16293-2422. Our calculations show that at the end of the hot core phase both star-forming sites produce the same prebiotic CN-bearing molecules. However, in the Orion hot core these molecules are formed in larger abundances. A comparison of the calculated values with the abundances derived from the observed line data requires a chemically unprocessed molecular cloud as the initial state of hot core evolution. Thus, it appears that these objects are formed at a much younger cloud stage than previously thought. This implies that the ice phase of the young clouds does not contain CN-bearing molecules in large abundances before the hot core has been formed. The pre-biotic molecules synthesized in hot cores cause a chemical enrichment in the gas phase and in the pre-cometary ice. This enrichment is thought to be an important extraterrestrial aspect of the formation of life on Earth and elsewhere.

  1. Non-climatic signal in ice core records: Lessons from Antarctic mega-dunes

    NASA Astrophysics Data System (ADS)

    Ekaykin, Alexey; Eberlein, Lutz; Lipenkov, Vladimir; Popov, Sergey; Schroder, Ludwig

    2015-04-01

    We present the results of glaciological investigations in the mega-dune area located 30 km to the east from Vostok Station (central East Antarctica) implemented during the 58th and 59th Russian Antarctic Expedition (January 2013 and January 2014). Snow accumulation rate and isotope content (δD and δ18O) were measured along the 2-km profile across the mega-dune ridge accompanied by precise GPS altitude measurements and GPR survey. It is shown that the spatial variability of snow accumulation and isotope content covaries with the surface slope. The accumulation rate regularly changes by 1 order of magnitude within the distance < 1 km, with the reduced accumulation at the leeward slope of the dune and increased accumulation in the hollow between the dunes. At the same time, the accumulation rate averaged over the length of a dune wave (25 mm w.e.) corresponds well with the value obtained at Vostok Station, which suggests no additional wind-driven snow sublimation in the mega-dunes comparing to the surrounding plateau. The snow isotope content is in negative correlation with the snow accumulation, which could be explained by post-depositional snow modification and/or by enhanced redistribution by wind of winter precipitation comparing to summer precipitation. Using the GPR data, we estimated the dune drift velocity (5.5 ± 1.3 m yr-1). The full cycle of the dune drift is thus about 340 years. Since the spatial anomalies of snow accumulation and isotope content are supposed to drift with the dune, an ice core drilled in the mega-dune area would exhibit the non-climatic 340-yr cycle of these two parameters. We made an attempt to simulate a vertical profile of isotope content with such a non-climatic variability in a virtual ice core, using the data on the dune size and velocity. The obtained results are discussed in terms of real ice core data interpretation.

  2. Towards multi-decadal to multi-millennial ice core records from coastal west Greenland ice caps

    NASA Astrophysics Data System (ADS)

    Das, Sarah B.; Osman, Matthew B.; Trusel, Luke D.; McConnell, Joseph R.; Smith, Ben E.; Evans, Matthew J.; Frey, Karen E.; Arienzo, Monica; Chellman, Nathan

    2017-04-01

    The Arctic region, and Greenland in particular, is undergoing dramatic change as characterized by atmospheric warming, decreasing sea ice, shifting ocean circulation patterns, and rapid ice sheet mass loss, but longer records are needed to put these changes into context. Ice core records from the Greenland ice sheet have yielded invaluable insight into past climate change both regionally and globally, and provided important constraints on past surface mass balance more directly, but these ice cores are most often from the interior ice sheet accumulation zone, at high altitude and hundreds of kilometers from the coast. Coastal ice caps, situated around the margins of Greenland, have the potential to provide novel high-resolution records of local and regional maritime climate and sea surface conditions, as well as contemporaneous glaciological changes (such as accumulation and surface melt history). But obtaining these records is extremely challenging. Most of these ice caps are unexplored, and thus their thickness, age, stratigraphy, and utility as sites of new and unique paleoclimate records is largely unknown. Access is severely limited due to their high altitude, steep relief, small surface area, and inclement weather. Furthermore, their relatively low elevation and marine moderated climate can contribute to significant surface melting and degradation of the ice stratigraphy. We recently targeted areas near the Disko Bay region of central west Greenland where maritime ice caps are prevalent but unsampled, as potential sites for new multi-decadal to multi-millennial ice core records. In 2014 & 2015 we identified two promising ice caps, one on Disko Island (1250 m. asl) and one on Nuussuaq Peninsula (1980 m. asl) based on airborne and ground-based geophysical observations and physical and glaciochemical stratigraphy from shallow firn cores. In spring 2015 we collected ice cores at both sites using the Badger-Eclipse electromechanical drill, transported by a medley

  3. Characteristics and processing of seismic data collected on thick, floating ice: Results from the Ross Ice Shelf, Antarctica

    USGS Publications Warehouse

    Beaudoin, Bruce C.; ten Brink, Uri S.; Stern, Tim A.

    1992-01-01

    Coincident reflection and refraction data, collected in the austral summer of 1988/89 by Stanford University and the Geophysical Division of the Department of Scientific and Industrial Research, New Zealand, imaged the crust beneath the Ross Ice Shelf, Antarctica. The Ross Ice Shelf is a unique acquisition environment for seismic reflection profiling because of its thick, floating ice cover. The ice shelf velocity structure is multilayered with a high velocity‐gradient firn layer constituting the upper 50 to 100 m. This near surface firn layer influences the data character by amplifying and frequency modulating the incoming wavefield. In addition, the ice‐water column introduces pervasive, high energy seafloor, intra‐ice, and intra‐water multiples that have moveout velocities similar to the expected subseafloor primary velocities. Successful removal of these high energy multiples relies on predictive deconvolution, inverse velocity stack filtering, and frequency filtering. Removal of the multiples reveals a faulted, sedimentary wedge which is truncated at or near the seafloor. Beneath this wedge the reflection character is diffractive to a two‐way traveltime of ∼7.2 s. At this time, a prominent reflection is evident on the southeast end of the reflection profile. This reflection is interpreted as Moho indicating that the crust is ∼21-km thick beneath the profile. These results provide seismic evidence that the extensional features observed in the Ross Sea region of the Ross Embayment extend beneath the Ross Ice Shelf.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  5. Modelling of mineral dust for interglacial and glacial climate conditions with a focus on Antarctica

    DOE PAGES

    Sudarchikova, Natalia; Mikolajewicz, Uwe; Timmreck, C.; ...

    2015-05-19

    The mineral dust cycle responds to climate variations and plays an important role in the climate system by affecting the radiative balance of the atmosphere and modifying biogeochemistry. Polar ice cores provide unique information about deposition of aeolian dust particles transported over long distances. These cores are a palaeoclimate proxy archive of climate variability thousands of years ago. The current study is a first attempt to simulate past interglacial dust cycles with a global aerosol–climate model ECHAM5-HAM. The results are used to explain the dust deposition changes in Antarctica in terms of quantitative contribution of different processes, such as emission,more » atmospheric transport and precipitation, which will help to interpret palaeodata from Antarctic ice cores. The investigated periods include four interglacial time slices: the pre-industrial control (CTRL), mid-Holocene (6000 yr BP; hereafter referred to as \\"6 kyr\\"), last glacial inception (115 000 yr BP; hereafter \\"115 kyr\\") and Eemian (126 000 yr BP; hereafter \\"126 kyr\\"). One glacial time interval, the Last Glacial Maximum (LGM) (21 000 yr BP; hereafter \\"21 kyr\\"), was simulated as well to be a reference test for the model. Results suggest an increase in mineral dust deposition globally, and in Antarctica, in the past interglacial periods relative to the pre-industrial CTRL simulation. Approximately two-thirds of the increase in the mid-Holocene and Eemian is attributed to enhanced Southern Hemisphere dust emissions. Slightly strengthened transport efficiency causes the remaining one-third of the increase in dust deposition. The moderate change in dust deposition in Antarctica in the last glacial inception period is caused by the slightly stronger poleward atmospheric transport efficiency compared to the pre-industrial. Maximum dust deposition in Antarctica was simulated for the glacial period. LGM dust deposition in Antarctica is substantially increased due to 2.6 times

  6. Abbot Ice Shelf, the Amundsen Sea Continental Margin and the Southern Boundary of the Bellingshausen Plate Seaward of West Antarctica

    NASA Astrophysics Data System (ADS)

    Cochran, J. R.; Tinto, K. J.; Bell, R. E.

    2014-12-01

    The Abbot Ice Shelf extends 450 km along the coast of West Antarctica between 103°W and 89°W and straddles the boundary between the Bellingshausen Sea continental margin, which overlies a former subduction zone, and Amundsen Sea rifted continental margin. Inversion of NASA Operation IceBridge airborne gravity data for sub-ice bathymetry shows that the western part of the ice shelf, as well as Cosgrove Ice Shelf to the south, are underlain by a series of east-west trending rift basins. The eastern boundary of the rifted terrain coincides with the eastern boundary of rifting between Antarctica and Zealandia and the rifts formed during the early stages of this rifting. Extension in these rifts is minor as rifting quickly jumped north of Thurston Island. The southern boundary of the Cosgrove Rift is aligned with the southern boundary of a sedimentary basin under the Amundsen Embayment continental shelf to the west, also formed by Antarctica-Zealandia rifting. The shelf basin has an extension factor, β, of 1.5 - 1.7 with 80 -100 km of extension occurring in an area now ~250 km wide. Following this extension early in the rifting process, rifting centered to the north of the present shelf edge and proceeded to continental rupture. Since then, the Amundsen Embayment continental shelf has been tectonically quiescent and has primarily been shaped though subsidence, sedimentation and the passage of the West Antarctic Ice Sheet back and forth across it. The former Bellingshausen Plate was located seaward of the Amundsen Sea margin prior to its incorporation into the Antarctic Plate at ~62 Ma. During the latter part of its existence, Bellingshausen plate motion had a clockwise rotational component relative to Antarctica producing convergence between the Bellingshausen and Antarctic plates east of 102°W. Seismic reflection and gravity data show that this convergence is expressed by an area of intensely deformed sediments beneath the continental slope from 102°W to 95°W and

  7. The isotopic composition of methane in polar ice cores

    NASA Technical Reports Server (NTRS)

    Craig, H.; Chou, C. C.; Welhan, J. A.; Stevens, C. M.; Engelkemeir, A.

    1988-01-01

    Air bubbles in polar ice cores indicate that about 300 years ago the atmospheric mixing ratio of methane began to increase rapidly. Today the mixing ratio is about 1.7 parts per million by volume, and, having doubled once in the past several hundred years, it will double again in the next 60 years if current rates continue. Carbon isotope ratios in methane up to 350 years in age have been measured with as little as 25 kilograms of polar ice recovered in 4-meter-long ice-core segments. The data show that: (1) in situ microbiology or chemistry has not altered the ice-core methane concentrations, and (2) that the carbon-13 to carbon-12 ratio of atmospheric CH4 in ice from 100 years and 300 years ago was about 2 per mil lower than at present. Atmospheric methane has a rich spectrum of isotopic sources: the ice-core data indicate that anthropogenic burning of the earth's biomass is the principal cause of the recent C-13H4 enrichment, although other factors may also contribute.

  8. Depositional environment of near-surface sediments, King George Basin, Bransfield Strait, Antarctica

    NASA Astrophysics Data System (ADS)

    Yoon, H. I.; Park, B. K.; Chang, S. K.; Han, M. W.; Oh, J. K.

    1994-03-01

    Four sediment cores were collected to determine the depositional environments of the King George Basin northeast of Bransfield Strait, Antarctica. The cored section revealed three distinct lithofacies: laminated siliceous ooze derived from an increased paleoproductivity near the receding sea-ice edges, massive muds that resulted from hemipelagic sedimentation in open water, and graded sediments that originated from nearby local seamounts by turbidity currents. Clay mineral data of the cores indicate a decreasing importance of volcanic activity through time. Active volcanism and hydrothermal activity appear to be responsible for the enrichment of smectite near the Penguin and Bridgeman Islands.

  9. Phase-sensitive radar on thick Antarctic ice - how well does it work?

    NASA Astrophysics Data System (ADS)

    Binder, Tobias; Eisen, Olaf; Helm, Veit; Humbert, Angelika; Steinhage, Daniel

    2016-04-01

    Phase-sensitive radar (pRES) has become one of the mostly used tools to determine basal melt rates as well as vertical strain in ice sheets. Whereas most applications are performed on ice shelves, only few experiments were conducted on thick ice in Greenland or Antarctica. The technical constrains on an ice shelf to deduce basal melt rates are less demanding than on inland ice of more than 2 km thickness. First, the ice itself is usually only several 100s of meters thick; and, second, the reflection coefficient at the basal interface between sea water and ice is the second strongest one possible. Although the presence of marine ice with higher conductivities might increase attenuation in the lower parts, most experiments on shelves were successful. To transfer this technology to inland regions, either for the investigation of basal melt rates of subglacial hydrological networks or for determining vertical strain rates in basal regions, a reliable estimate of the current system performance is necessary. To this end we conducted an experiment at and in the vicinity of the EPICA deep ice core drill site EDML in Dronning Maud Land, Antarctica. That site has been explored in extraordinary detail with different geophysical methods and provides an already well-studied ice core and borehole, in particular with respect to physical properties like crystal orientation fabric, dielectric properties and matching of internal radar horizons with conductivity signals. We present data from a commercially available pRES system initially recorded in January 2015 and repeated measurements in January 2016. The pRES data are matched to existing and already depth-calibrated airborne radar data. Apart from identifying prominent internal layers, e.g. the one originating from the deposits of the Toba eruption at around 75 ka, we put special focus on the identification of the basal reflection at multiple polarizations. We discuss the potential uncertainty estimates and requirements to

  10. Low-latitude ice cores and freshwater availability

    NASA Astrophysics Data System (ADS)

    Kehrwald, Natalie Marie

    2009-12-01

    Recent retreat of Tibetan Plateau glaciers affects at least half a billion people. Himalayan glaciers seasonally release meltwater into tributaries of the Indus, Ganges, and Brahmaputra Rivers and supply freshwater necessary to support agricultural and economic practices. Tibetan Plateau glaciers are retreating more rapidly than mountain glaciers elsewhere in the world, and this retreat is accelerating. The Naimona'nyi (30°27'N; 81°91'E, 6050 m a.s.l), Guliya (35°17'N; 81°29'E, 6710 m a.s.l.) and Dasuopu (28°23'N; 85°43'E, 7200 m a.s.l.) ice cores place this recent retreat into a longer time perspective through quantifying climate parameters such as past temperature, aridity, and atmospheric chemistry. Naimona'nyi has not accumulated mass since at least 1950, as evidenced by the virtual lack of radiogenic isotopes (36Cl, 3 H, and beta radioactivity) present in the ice core. These isotopes were produced by U.S. and Soviet atmospheric thermonuclear bomb tests conducted in the 1950s and 1960s and provide independent dating horizons for the ice cores. Lead-210 dates imply that the uppermost preserved glacial ice on Naimona'nyi formed during the 1940s. While this is the highest documented glacial thinning in the world other glaciers at elevations similar to that of Naimona'nyi, such as Kilimanjaro (3°4'S; 37°21'E, 5893 m a.s.l.), are also losing mass at their summits. The global scope of high-elevation glacial thinning suggests that ablation on the Earth's highest ice fields may be more prevalent as global mean temperatures continue to increase. Glacial thinning has not been taken into account in future projections of regional freshwater availability, and the net mass loss indicates that Himalayan glaciers currently store less freshwater than assumed in models. The acceleration of Tibetan Plateau glacial retreat has been hypothesized to be due in part to deposition of black carbon (BC) from biomass burning on to ice fields, thereby lowering the reflectivity of

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

    PubMed

    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.

  12. Ice Front at Venable Ice Shelf

    NASA Image and Video Library

    2013-06-13

    This photo, taken onboard the Chilean Navy P3 aircraft, shows the ice front of Venable Ice Shelf, West Antarctica, in October 2008. It is an example of a small-size ice shelf that is a large melt water producer.

  13. Ice Bridge Antarctic Sea Ice

    NASA Image and Video Library

    2009-10-21

    Sea ice is seen out the window of NASA's DC-8 research aircraft as it flies 2,000 feet above the Bellingshausen Sea in West Antarctica on Wednesday, Oct., 21, 2009. This was the fourth science flight of NASA’s Operation Ice Bridge airborne Earth science mission to study Antarctic ice sheets, sea ice, and ice shelves. Photo Credit: (NASA/Jane Peterson)

  14. IceChrono1: a probabilistic model to compute a common and optimal chronology for several ice cores

    NASA Astrophysics Data System (ADS)

    Parrenin, Frédéric; Bazin, Lucie; Capron, Emilie; Landais, Amaëlle; Lemieux-Dudon, Bénédicte; Masson-Delmotte, Valérie

    2016-04-01

    Polar ice cores provide exceptional archives of past environmental conditions. The dating of ice cores and the estimation of the age scale uncertainty are essential to interpret the climate and environmental records that they contain. It is however a complex problem which involves different methods. Here, we present IceChrono1, a new probabilistic model integrating various sources of chronological information to produce a common and optimized chronology for several ice cores, as well as its uncertainty. IceChrono1 is based on the inversion of three quantities: the surface accumulation rate, the Lock-In Depth (LID) of air bubbles and the thinning function. The chronological information integrated into the model are: models of the sedimentation process (accumulation of snow, densification of snow into ice and air trapping, ice flow), ice and air dated horizons, ice and air depth intervals with known durations, Δdepth observations (depth shift between synchronous events recorded in the ice and in the air) and finally air and ice stratigraphic links in between ice cores. The optimization is formulated as a least squares problem, implying that all densities of probabilities are assumed to be Gaussian. It is numerically solved using the Levenberg-Marquardt algorithm and a numerical evaluation of the model's Jacobian. IceChrono follows an approach similar to that of the Datice model which was recently used to produce the AICC2012 chronology for 4 Antarctic ice cores and 1 Greenland ice core. IceChrono1 provides improvements and simplifications with respect to Datice from the mathematical, numerical and programming point of views. The capabilities of IceChrono is demonstrated on a case study similar to the AICC2012 dating experiment. We find results similar to those of Datice, within a few centuries, which is a confirmation of both IceChrono and Datice codes. We also test new functionalities with respect to the original version of Datice: observations as ice intervals

  15. Top predators in relation to bathymetry, ice and krill during austral winter in Marguerite Bay, Antarctica

    USGS Publications Warehouse

    Ribic, C.A.; Chapman, E.; Fraser, William R.; Lawson, G.L.; Wiebe, P.H.

    2008-01-01

    A key hypothesis guiding the US Southern Ocean Global Ocean Ecosystems Dynamics (US SO GLOBEC) program is that deep across-shelf troughs facilitate the transport of warm and nutrient-rich waters onto the continental shelf of the Western Antarctic Peninsula, resulting in enhanced winter production and prey availability to top predators. We tested aspects of this hypothesis during austral winter by assessing the distribution of the resident pack-ice top predators in relation to these deep across-shelf troughs and by investigating associations between top predators and their prey. Surveys were conducted July-August 2001 and August-September 2002 in Marguerite Bay, Antarctica, with a focus on the main across-shelf trough in the bay, Marguerite Trough. The common pack-ice seabird species were snow petrel (Pagodroma nivea, 1.2 individuals km-2), Antarctic petrel (Thalassoica antarctica, 0.3 individuals km-2), and Ade??lie penguin (Pygoscelis adeliae, 0.5 individuals km-2). The most common pack-ice pinniped was crabeater seal (Lobodon carcinophagus). During both winters, snow and Antarctic petrels were associated with low sea-ice concentrations independent of Marguerite Trough, while Ade??lie penguins occurred in association with this trough. Krill concentrations, both shallow and deep, also were associated with Ade??lie penguin and snow petrel distributions. During both winters, crabeater seal occurrence was associated with deep krill concentrations and with regions of lower chlorophyll concentration. The area of lower chlorophyll concentrations occurred in an area with complex bathymetry close to land and heavy ice concentrations. Complex or unusual bathymetry via its influence on physical and biological processes appears to be one of the keys to understanding how top predators survive during the winter in this Antarctic region. ?? 2007 Elsevier Ltd. All rights reserved.

  16. Estimating Last Glacial Maximum Ice Thickness Using Porosity and Depth Relationships: Examples from AND-1B and AND-2A Cores, McMurdo Sound, Antarctica

    NASA Astrophysics Data System (ADS)

    Hayden, T. G.; Kominz, M. A.; Magens, D.; Niessen, F.

    2009-12-01

    We have estimated ice thicknesses at the AND-1B core during the Last Glacial Maximum by adapting an existing technique to calculate overburden. As ice thickness at Last Glacial Maximum is unknown in existing ice sheet reconstructions, this analysis provides constraint on model predictions. We analyze the porosity as a function of depth and lithology from measurements taken on the AND-1B core, and compare these results to a global dataset of marine, normally compacted sediments compiled from various legs of ODP and IODP. Using this dataset we are able to estimate the amount of overburden required to compact the sediments to the porosity observed in AND-1B. This analysis is a function of lithology, depth and porosity, and generates estimates ranging from zero to 1,000 meters. These overburden estimates are based on individual lithologies, and are translated into ice thickness estimates by accounting for both sediment and ice densities. To do this we use a simple relationship of Xover * (ρsed/ρice) = Xice; where Xover is the overburden thickness, ρsed is sediment density (calculated from lithology and porosity), ρice is the density of glacial ice (taken as 0.85g/cm3), and Xice is the equalivant ice thickness. The final estimates vary considerably, however the “Best Estimate” behavior of the 2 lithologies most likely to compact consistently is remarkably similar. These lithologies are the clay and silt units (Facies 2a/2b) and the diatomite units (Facies 1a) of AND-1B. These lithologies both produce best estimates of approximately 1,000 meters of ice during Last Glacial Maximum. Additionally, while there is a large range of possible values, no combination of reasonable lithology, compaction, sediment density, or ice density values result in an estimate exceeding 1,900 meters of ice. This analysis only applies to ice thicknesses during Last Glacial Maximum, due to the overprinting effect of Last Glacial Maximum on previous ice advances. Analysis of the AND-2A

  17. Gradual slowdown and thickening of Fimbulisen ice shelf, East Antarctica, over the past decade

    NASA Astrophysics Data System (ADS)

    van Oostveen, Jelte; Moholdt, Geir; Kääb, Andreas; Matsuoka, Kenichi

    2017-04-01

    Fimbulisen is a fast-flowing (up to 780±10 ma-1) ice shelf in the Dronning Maud Land region of East Antarctica. Fed by one of the few major outlet glaciers along that coast, Jutulstraumen, the ice shelf has the potential to affect the stability of a considerable part of the inland ice sheet. Here we present evidence of a slowdown and thickening of Fimbulisen over the last decade. We derive ice shelf velocities using synthetic aperture radar (SAR) data from Envisat in 2008 and Radarsat-2 in 2015. We find that the speeds of Fimbulisen have decreased by 10±2 ma-1 over the last 7 years, which is confirmed with repeated GPS stake readings from 2010-2011. The slow-down of Fimbulisen coincides with a gradual ice shelf thickening that we infer from ICESat (2003-2009) and CryoSat-2 (2010-2016) altimetry. Available surface mass balance data from Fimbulisen show no clear trends over the past decades, suggesting that ice dynamics is the main explanation for the observed thickening. Considering that Fimbulisen is in a long-term phase of advance after its main tongue calved off in 1967, it is plausible that the slowdown is cyclic and related to the longitudinal expansion of the ice shelf. In support of this theory we have found several uncharted ice rumples and stationary icebergs near the eastern front of the ice shelf, indicating the presence of shallow bathymetry that might affect the ice shelf dynamics considerably in the event of ice shelf grounding or ungrounding.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  19. Galileo spacecraft solid-state imaging system view of Antarctica

    NASA Technical Reports Server (NTRS)

    1990-01-01

    Galileo spacecraft solid-state imaging system view of Antarctica was taken during its first encounter with the Earth. This color picture of Antarctica is part of a mosaic of pictures covering the entire polar continent showing the Ross Ice Shelf and its border with the sea and mountains poking through the ice near the McMurdo Station. From top to bottom, the frame looks across about half of Antarctica. View provided by the Jet Propulsion Laboratory (JPL) with alternate number P-37297.

  20. Gas discharges in fumarolic ice caves of Erebus volcano, Antarctica

    NASA Astrophysics Data System (ADS)

    Fischer, T. P.; Curtis, A. G.; Kyle, P. R.; Sano, Y.

    2013-12-01

    reactions. We are confident that the atmospheric component is not the result of sampling procedure but intrinsic to the ice cave system. In addition to carbon dioxide, magmatic gases emitted from Erebus lava lake contain significant amounts of SO2, HCl, HF, CO and H2 [1,2]. The acid magmatic gases (SO2, HCl, HF) and a significant amount of the CO2 are likely absorbed by the subsurface ice/water system. The atmospheric components (Ar, nitrogen, oxygen) likely enter the system at shallow levels. The relative abundances of these components reflect degassing fractionation of these volatiles from liquid water at low temperatures, suggesting the presence of liquid water in the subsurface. [1] Oppenheimer, C., Kyle, P.R., 2008. Probing the magma plumbing of Erebus volcano, Antarctica, by open-path FTIR spectroscopy of gas emissions. J. Vol. Geoth. Res. 177, 743-754. [2] Moussallam, Y., Oppenheimer, C., et al., 2012. Hydrogen emission from Erebus volcano, Antarctica. Bull. Volcan 74, 2109-2120.

  1. Reassessment of the Upper Fremont Glacier Ice-Core Chronologies by Synchronizing of Ice-Core-Water Isotopes to a Nearby Tree-Ring Chronology.

    PubMed

    Chellman, Nathan; McConnell, Joseph R; Arienzo, Monica; Pederson, Gregory T; Aarons, Sarah M; Csank, Adam

    2017-04-18

    The Upper Fremont Glacier (UFG), Wyoming, is one of the few continental glaciers in the contiguous United States known to preserve environmental and climate records spanning recent centuries. A pair of ice cores taken from UFG have been studied extensively to document changes in climate and industrial pollution (most notably, mid-19th century increases in mercury pollution). Fundamental to these studies is the chronology used to map ice-core depth to age. Here, we present a revised chronology for the UFG ice cores based on new measurements and using a novel dating approach of synchronizing continuous water isotope measurements to a nearby tree-ring chronology. While consistent with the few unambiguous age controls underpinning the previous UFG chronologies, the new interpretation suggests a very different time scale for the UFG cores with changes of up to 80 years. Mercury increases previously associated with the mid-19th century Gold Rush now coincide with early-20th century industrial emissions, aligning the UFG record with other North American mercury records from ice and lake sediment cores. Additionally, new UFG records of industrial pollutants parallel changes documented in ice cores from southern Greenland, further validating the new UFG chronologies while documenting the extent of late 19th and early 20th century pollution in remote North America.

  2. Reassessment of the Upper Fremont Glacier ice-core chronologies by synchronizing of ice-core-water isotopes to a nearby tree-ring chronology

    USGS Publications Warehouse

    Chellman, Nathan J.; McConnell, Joseph R.; Arienzo, Monica; Pederson, Gregory T.; Aarons, Sarah; Csank, Adam

    2017-01-01

    The Upper Fremont Glacier (UFG), Wyoming, is one of the few continental glaciers in the contiguous United States known to preserve environmental and climate records spanning recent centuries. A pair of ice cores taken from UFG have been studied extensively to document changes in climate and industrial pollution (most notably, mid-19th century increases in mercury pollution). Fundamental to these studies is the chronology used to map ice-core depth to age. Here, we present a revised chronology for the UFG ice cores based on new measurements and using a novel dating approach of synchronizing continuous water isotope measurements to a nearby tree-ring chronology. While consistent with the few unambiguous age controls underpinning the previous UFG chronologies, the new interpretation suggests a very different time scale for the UFG cores with changes of up to 80 years. Mercury increases previously associated with the mid-19th century Gold Rush now coincide with early-20th century industrial emissions, aligning the UFG record with other North American mercury records from ice and lake sediment cores. Additionally, new UFG records of industrial pollutants parallel changes documented in ice cores from southern Greenland, further validating the new UFG chronologies while documenting the extent of late 19th and early 20th century pollution in remote North America.

  3. Widespread surface meltwater drainage in Antarctica

    NASA Astrophysics Data System (ADS)

    Kingslake, J.; Ely, J.; Das, I.; Bell, R. E.

    2016-12-01

    Surface meltwater is thought to cause ice-shelf disintegration, which accelerates the contribution of ice sheets to sea-level rise. Antarctic surface melting is predicted to increase and trigger further ice-shelf disintegration during this century. These climate-change impacts could be modulated by an active hydrological network analogous to the one in operation in Greenland. Despite some observations of Antarctic surface and sub-surface hydrological systems, large-scale active surface drainage in Antarctica has rarely been studied. We use satellite imagery and aerial photography to reveal widespread active hydrology on the surface of the Antarctic Ice Sheet as far south as 85o and as high as 1800 m a.s.l., often near mountain peaks that protrude through the ice (nunataks) and relatively low-albedo `blue-ice areas'. Despite predominantly sub-zero regional air temperatures, as simulated by a regional climate model, Antarctic active drainage has persisted for decades, transporting water through surface streams and feeding vast melt ponds up to 80 km long. Drainage networks (the largest are over 100 km in length) form on flat ice shelves, steep outlet glaciers and ice-sheet flanks across the West and East Antarctica Ice Sheets. Motivated by the proximity of many drainage systems to low-albedo rock and blue-ice areas, we hypothesize a positive feedback between exposed-rock extent, BIA formation, melting and ice-sheet thinning. This feedback relies on drainage moving water long distances from areas near exposed rock, across the grounding line onto and across ice shelves - a process we observe, but had previously thought to be unlikely in Antarctica. This work highlights previously-overlooked processes, not captured by current regional-scale models, which may accelerate the retreat of the Antarctic Ice Sheet.

  4. Experimental Analysis of Sublimation Dynamics for Buried Glacier Ice in Beacon Valley, Antarctica

    NASA Astrophysics Data System (ADS)

    Ehrenfeucht, S.; Dennis, D. P.; Marchant, D. R.

    2017-12-01

    The age of the oldest known buried ice in Beacon Valley, McMurdo Dry Valleys (MDV) Antarctica is a topic of active debate due to its implications for the stability of the East Antarctic Ice Sheet. Published age estimates range from as young as 300 ka to as old as 8.1 Ma. In the upland MDV, ablation occurs predominantly via sublimation. The relict ice in question (ancient ice from Taylor Glacier) lies buried beneath a thin ( 30-70 cm) layer of sublimation till, which forms as a lag deposit as underlying debris-rich ice sublimes. As the ice sublimates, the debris held within the ice accumulates slowly on the surface, creating a porous boundary between the buried-ice surface and the atmosphere, which in turn influences gas exchange between the ice and the atmosphere. Additionally, englacial debris adds several salt species that are ultimately concentrated on the ice surface. It is well documented the rate of ice sublimation varies as a function of overlying till thickness. However, the rate-limiting dynamics under varying environmental conditions, including the threshold thicknesses at which sublimation is strongly retarded, are not yet defined. To better understand the relationships between sublimation rate, till thickness, and long-term surface evolution, we build on previous studies by Lamp and Marchant (2017) and evaluate the role of till thickness as a control on ice loss in an environmental chamber capable of replicating the extreme cold desert conditions observed in the MDV. Previous work has shown that this relationship exhibits exponential decay behavior, with sublimation rate significantly dampened under less than 10 cm of till. In our experiments we pay particular attention to the effect of the first several cm of till in order to quantify the dynamics that govern the transition from bare ice to debris-covered ice. We also examine this transition for various forms of glacier ice, including ice with various salt species.

  5. Methodological synergies for glaciological constraints to find Oldest Ice

    NASA Astrophysics Data System (ADS)

    Eisen, Olaf

    2017-04-01

    The Beyond EPICA - Oldest Ice (BE-OI) consortium and its international partners unite a globally unique concentration of scientific expertise and infrastructure for ice-core investigations. It delivers the technical, scientific and financial basis for a comprehensive plan to retrieve an ice core up to 1.5 million years old. The consortium takes care of the pre-site surveys for site selection around Dome C and Dome Fuji, both potentially appropriate regions in East Antarctica. Other science consortia will investigate other regions under the umbrella of the International Partnerships in Ice Core Sciences (IPICS). Of major importance to obtain reliable estimates of the age of the ice in the basal layers of the ice sheet are the physical boundary conditions and ice-flow dynamics: geothermal heat flux, advection and layer integrity to avoid layer overturning and the formation of folds. The project completed the first field season at both regions of interest. This contribution will give an overview how the combined application of various geophysical, geodetical and glaciological methods applied in the field in combination with ice-flow modelling can constrain the glaciological boundary conditions and thus age at depth.

  6. The Landsat Image Mosaic of Antarctica (LIMA): A Cutting-Edge Way for Students and Teachers to Learn about Antarctica

    ERIC Educational Resources Information Center

    Campbell, Brian; Bindschadler, Robert

    2009-01-01

    By studying Antarctica via satellite and through ground-truthing research, we can learn where the ice is melting and why. The Landsat Image Mosaic of Antarctica (LIMA), a new and cutting-edge way for scientists, researchers, educators, students, and the public to look at Antarctica, supports this research and allows for unprecedented views of our…

  7. Subglacial Volcanism in West-Antarctica - A Geologic and Ice Dynamical Perspective

    NASA Astrophysics Data System (ADS)

    Vogel, S. W.; Tulaczyk, S.; Carter, S.; Renne, P.; Turrin, B. D.; Joughin, I.

    2004-12-01

    means to resolve any further questions on the existence of subglacial volcanism in West-Antarctica and its potential impact on the dynamic of the ice sheet, requires drilling into potential volcanic centers and the recovery of volcanic rocks for dating and geochemical analysis.

  8. Ocean as the main driver of Antarctic ice sheet retreat during the Holocene

    NASA Astrophysics Data System (ADS)

    Crosta, Xavier; Crespin, Julien; Swingedouw, Didier; Marti, Olivier; Masson-Delmotte, Valérie; Etourneau, Johan; Goosse, Hugues; Braconnot, Pascale; Yam, Ruth; Brailovski, Irena; Shemesh, Aldo

    2018-07-01

    Ocean-driven basal melting has been shown to be the main ablation process responsible for the recession of many Antarctic ice shelves and marine-terminating glaciers over the last decades. However, much less is known about the drivers of ice shelf melt prior to the short instrumental era. Based on diatom oxygen isotope (δ18Odiatom; a proxy for glacial ice discharge in solid or liquid form) records from western Antarctic Peninsula (West Antarctica) and Adélie Land (East Antarctica), higher ocean temperatures were suggested to have been the main driver of enhanced ice melt during the Early-to-Mid Holocene while atmosphere temperatures were proposed to have been the main driver during the Late Holocene. Here, we present a new Holocene δ18Odiatom record from Prydz Bay, East Antarctica, also suggesting an increase in glacial ice discharge since 4500 years before present ( 4.5 kyr BP) as previously observed in Antarctic Peninsula and Adélie Land. Similar results from three different regions around Antarctica thus suggest common driving mechanisms. Combining marine and ice core records along with new transient accelerated simulations from the IPSL-CM5A-LR climate model, we rule out changes in air temperatures during the last 4.5 kyr as the main driver of enhanced glacial ice discharge. Conversely, our simulations evidence the potential for significant warmer subsurface waters in the Southern Ocean during the last 6 kyr in response to enhanced summer insolation south of 60°S and enhanced upwelling of Circumpolar Deep Water towards the Antarctic shelf. We conclude that ice front and basal melting may have played a dominant role in glacial discharge during the Late Holocene.

  9. First investigations of an ice core from Eisriesenwelt cave (Austria)

    NASA Astrophysics Data System (ADS)

    May, B.; Spötl, C.; Wagenbach, D.; Dublyansky, Y.; Liebl, J.

    2010-09-01

    Investigations into the genesis and dynamical properties of cave ice are essential for assessing the climate significance of these underground glaciers. We drilled an ice core through a 7.1 m thick ice body filling a large cavern of the dynamic ice cave Eisenriesenwelt (Austria). In addition to visual core inspections, quasi-continuous measurements at 2 cm resolution comprised particulate matter, stable water isotope (δ18O, δD) and electrolytic conductivity profiles supplemented by specifically selected samples analysed for tritium and radiocarbon. We found that recent ablation led to an almost complete loss of bomb derived tritium removing any ice accumulated, since at least, the early fifties leaving the actual ice surface even below the natural tritium level. The small particulate organic masses made radiocarbon dating inconclusive, though a crude estimate gave a maximum ice age in the order of several thousand years. The visual stratigraphy and all investigated parameters showed a clear dichotomy between the upper 4 m and the bottom 3 m of the core, which points to a substantial change in the ice formation process. Main features of the core comprise the changing appearance and composition of distinct cyro-calcite layers, a extremely low total ion content and a surprisingly high variability of the isotope signature. Co-isotope evaluation (δD versus δ18O) of the core in comparison with data from precipitation and karst spring water clearly indicate that ice formation is governed by (slow) freezing of dripping water.

  10. First investigations of an ice core from Eisriesenwelt cave (Austria)

    NASA Astrophysics Data System (ADS)

    May, B.; Spötl, C.; Wagenbach, D.; Dublyansky, Y.; Liebl, J.

    2011-02-01

    Investigations into the genesis and dynamical properties of cave ice are essential for assessing the climate significance of these underground glaciers. We drilled an ice core through a 7.1 m-thick ice body filling a large cavern of the dynamic ice cave Eisenriesenwelt (Austria). In addition to visual core inspections, quasi-continuous measurements at 2 cm resolution comprised particulate matter, stable water isotope (δ18O, δD) and electrolytic conductivity profiles supplemented by specifically selected samples analyzed for tritium and radiocarbon. We found that recent ablation led to an almost complete loss of bomb-derived tritium removing any ice accumulated since, at least, the early fifties leaving the actual ice surface even below the natural tritium level. The small particulate organic masses rendered radiocarbon dating inconclusive, though a crude estimate gave a basal ice age in the order of several thousand years. The visual stratigraphy and all investigated parameters showed a clear dichotomy between the upper 2 m and the bottom 3 m of the core, which points to a substantial change in the ice formation process. Main features of the core comprise the changing appearance and composition of distinct cryocalcite layers, extremely low total ion content and a surprisingly high variability of the isotope signature. Co-isotope evaluation (δD versus δ18O) of the core in comparison with data from precipitation and karst spring water clearly indicate that ice formation is governed by (slow) freezing of dripping water.

  11. Bearing Capacity of Floating Ice Sheets under Short-Term Loads: Over-Sea-Ice Traverse from McMurdo Station to Marble Point

    DTIC Science & Technology

    2015-01-01

    crafts on floating ice sheets near McMurdo, Antarctica (Katona and Vaudrey 1973; Katona 1974; Vaudrey 1977). To comply with the first criterion, one...Nomographs for operating wheeled aircraft on sea- ice runways: McMurdo Station, Antarctica . In Proceedings of the Offshore Mechanics and Arctic Engineering... Ice Thickness Requirements for Vehicles and Heavy Equipment at McMurdo Station, Antarctica . CRREL Project Report 04- 09, “Safe Sea Ice for Vehicle

  12. Assimilating the ICE-6G_C Reconstruction of the Latest Quaternary Ice Age Cycle Into Numerical Simulations of the Laurentide and Fennoscandian Ice Sheets

    NASA Astrophysics Data System (ADS)

    Stuhne, G. R.; Peltier, W. R.

    2017-12-01

    We analyze the effects of nudging 100 kyr numerical simulations of the Laurentide and Fennoscandian ice sheets toward the glacial isostatic adjustment-based (GIA-based) ICE-6G_C reconstruction of the most recent ice age cycle. Starting with the ice physics approximations of the PISM ice sheet model and the SeaRISE simulation protocols, we incorporate nudging at characteristic time scales, τf, through anomalous mass balance terms in the ice mass conservation equation. As should be expected, these mass balances exhibit physically unrealistic details arising from pure GIA-based reconstruction geometry when nudging is very strong (τf=20 years for North America), while weakly nudged (τf=1,000 years) solutions deviate from ICE-6G_C sufficiently to degrade its observational fit quality. For reasonable intermediate time scales (τf=100 years and 200 years), we perturbatively analyze nudged ice dynamics as a superposition of "leading-order smoothing" that diffuses ICE-6G_C in a physically and observationally consistent manner and "higher-order" deviations arising, for instance, from biases in the time dependence of surface climate boundary conditions. Based upon the relative deviations between respective nudged simulations in which these biases follow surface temperature from ice cores and eustatic sea level from marine sediment cores, we compute "ice core climate adjustments" that suggest how local paleoclimate observations may be applied to the systematic refinement of ICE-6G_C. Our results are consistent with a growing body of evidence suggesting that the geographical origins of Meltwater Pulse 1B (MWP1b) may lie primarily in North America as opposed to Antarctica (as reconstructed in ICE-6G_C).

  13. An Ice Core Melter System for Continuous Major and Trace Chemical Analyses of a New Mt. Logan Summit Ice Core

    NASA Astrophysics Data System (ADS)

    Osterberg, E. C.; Handley, M. J.; Sneed, S. D.; Mayewski, P. A.; Kreutz, K. J.; Fisher, D. A.

    2004-12-01

    The ice core melter system at the University of Maine Climate Change Institute has been recently modified and updated to allow high-resolution (<1-2 cm ice/sample), continuous and coregistered sampling of ice cores, most notably the 2001 Mt. Logan summit ice core (187 m to bedrock), for analyses of 34 trace elements (Sr, Cd, Sb, Cs, Ba, Pb, Bi, U, As, Al, S, Ca, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, REE suite) by inductively coupled plasma mass spectrometry (ICP-MS), 8 major ions (Na+, Ca2+, Mg2+, K+, Cl-, SO42-, NO3-, MSA) by ion chromatography (IC), stable water isotopes (δ 18O, δ D, d) and volcanic tephra. The UMaine continuous melter (UMCoM) system is housed in a dedicated clean room with HEPA filtered air. Standard clean room procedures are employed during melting. A Wagenbach-style continuous melter system has been modified to include a pure Nickel melthead that can be easily dismantled for thorough cleaning. The system allows melting of both ice and firn without wicking of the meltwater into unmelted core. Contrary to ice core melter systems in which the meltwater is directly channeled to online instruments for continuous flow analyses, the UMCoM system collects discrete samples for each chemical analysis under ultraclean conditions. Meltwater from the pristine innermost section of the ice core is split between one fraction collector that accumulates ICP-MS samples in acid pre-cleaned polypropylene vials under a class-100 HEPA clean bench, and a second fraction collector that accumulates IC samples. A third fraction collector accumulates isotope and tephra samples from the potentially contaminated outer portion of the core. This method is advantageous because an archive of each sample remains for subsequent analyses (including trace element isotope ratios), and ICP-MS analytes are scanned for longer intervals and in replicate. Method detection limits, calculated from de-ionized water blanks passed through the entire UMCoM system, are below 10% of average Mt

  14. Ice Elevation Changes in the Ellsworth Mountains, Antarctica Using Multiple Cosmogenic Nuclides

    NASA Astrophysics Data System (ADS)

    Marrero, S.; Hein, A.; Sugden, D.; Woodward, J.; Dunning, S.; Reid, K.

    2014-12-01

    Well-dated geologic data points provide important indicators that can be used for the reconstruction of ice sheet dynamics and as constraints in ice sheet models predicting future change. Cosmogenic nuclides, which accumulate in rocks exposed at the earth's surface, can be used to directly date the exposure age of the rock surfaces that have been created through glacial erosion or deposition. The technique requires a detailed understanding of the local geomorphology as well as awareness of the post-depositional processes that may affect the interpretation of exposure ages. Initial surface exposure ages (10Be, 26Al, 21Ne, and 36Cl ) from local limestone bedrock and other glacially deposited exotic lithologies provide a history spanning from 0 to 1.1 Ma in the Patriot, Independence, and Marble Hills in the southern Ellsworth Mountains, Antarctica. Using the new surface exposure ages combined with geomorphological mapping, we will discuss the implications for the glacial history of the southern Ellsworth Mountains.

  15. Preliminary CFA measurements of Al and Fe "available" fraction in EPICA-Dome C ice core (East Antarctica)

    NASA Astrophysics Data System (ADS)

    Udisti, R.; Barbante, C.; Cozzi, G.; Fattori, I.; Largiuni, O.; Magaldi, L.; Traversi, R.

    2003-04-01

    Aerosol load of Al and Fe allows estimating the crustal contribution to the primary aerosol sources. While continental dust is the only significant source for Al, Fe takes part also to metabolic processes of living species as an essential oligo-element. For this reason, it has been assumed that atmospheric deposition of desert dust on the oceanic surface can constitute a phytoplanktonic growth factor. Besides, Fe content in aerosol during glacial/interglacial transitions is believed to play a relevant role in controlling oceanic phytoplanktonic uptake of atmospheric CO2. A detailed stratigraphy of Al and Fe in ice cores is basic in understanding the correlation between environmental and climatic changes. Here we report preliminary results of CFA methods able to determine, in field, the "available" (free form and labile complexes) fraction of Al and Fe in ice cores with high sensitivity (D.L. of 10 ppt for Al and 300 ppt for Fe) and reproducibility (around 2 % at ppb level). The two methods were applied to 32 selected sections coming from the EPICA-Dome C ice core (EDC96): 10 sections belonging to Holocene, 10 to the transition and 12 to the LGM. Though Al and Fe determined by CFA is representative of the only soluble fraction (or "available" in the measurement conditions after filtration on 5.0 um), a comparison with the Al and Fe "total" content, as measured by ICP-MS, was made. "Available" fractions represent a minor contribution to the ICP-MS Fe and Al content in the LGM, but this contribution increases during the transition. In the Holocene, the two different analytical methods give similar values. Anyway, also CFA Fe and Al profiles show a sharp concentration decrease in the glacial/interglacial transition, reflecting the lowering dust aerosol load. Fe, especially, shows a very high sensitivity for the ACR climatic change. Whereas CFA-Fe in the LGM is more than 10 times lower than ICP-MS-Fe, ACR values are similar. This evidence could be explained considering

  16. Expression and Characterization of an Ice Binding Protein from a Bacterium Isolated at a Depth of 3,519 Meters in the Vostok Ice Core, Antarctica

    NASA Astrophysics Data System (ADS)

    Christner, B. C.; Achberger, A.; Brox, T. I.; Skidmore, M. L.

    2011-12-01

    The cryopreservation of microorganisms in ancient glacial ice is possible if lethal levels of macromolecular damage are not incurred and cellular integrity is not compromised via intracellular ice formation or recrystallization. There are numerous examples of cold-adapted species that prevent or limit ice crystal growth by producing ice-binding proteins (IBP). Previously, a bacterium (isolate 3519-10; Flavobacteriaceae family) recovered from a depth of 3,519 meters below the surface in the Vostok ice core was shown to produce and secrete an IBP that inhibits the recrystallization of ice. To explore the phenotypic advantage that IBPs confer to ice-entrapped cells, experiments were designed to examine the expression of 3519-10's IBP gene and protein at different temperatures, assess the effect of the IBP on bacterial viability in ice, and determine how the IBP influences the physical structure of the ice. Total RNA isolated from aerobic cultures grown at temperatures between 4C to 25C and analyzed by reverse transcription-PCR indicated constitutive expression of the IBP gene. Additionally, SDS-PAGE analysis of 3519-10's extracellular proteins revealed a polypeptide corresponding to the predicted size of the 54 kDa IBP at all temperatures tested. The total extracellular protein fraction was subsequently used in assays with Escherichia coli to examine the effect of the IBP on bacterial survival in warm ice (-5C) and after freeze-thaw cycling. In the presence of 100 μg mL-1 of extracellular protein from 3519-10, the survival of E. coli was increased by greater than 100-fold; however, the survival of E. coli suspensions containing the same concentration of bovine serum albumin was not significantly different than controls (p<0.05). Microscopic analysis of ice formed in the presence of the IBP indicated that in a mm^2 field of view, there were 5 times as many crystals as in ice formed in the presence of washed 3519-10 cells and non-IBP producing bacteria, and 10 times as

  17. Fives decades of strong temporal variability in the flow of the Brunt Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    De Rydt, Jan; Gudmundsson, Hilmar; Nagler, Thomas

    2017-04-01

    The Brunt Ice Shelf, East Antarctica, is a complex conglomerate of meteoric and marine ice, weakly connected to the much larger and faster-flowing Stancomb Wills Glacier Tongue to the east, and pinned down to the seabed in a small area around the McDonalds Ice Rumples in the north. The ice shelf is home to the UK research station Halley, from which changes to the ice shelf have been monitored closely since the 1960s. A unique 50-year record of the flow speed and an intense surveying programme over the past 10 years, have revealed a strong temporal variability in the flow. In particular, the speed of the ice shelf has increased by 10% each year over the past few years. In order to understand these rapid changes, we use a state-of-the-art flow model in combination with a range of satellite, ground-based and airborne radar data, to accurately simulate the historical flow and recent changes. In particular, we model the effects of a recently formed rift that is propagating at a speed of up to 600m/day and threatens to dislodge the ice shelf from its pinning point at the McDonalds Ice Rumples. We also report on the recent reactivation of a large chasm which has prompted the relocation of the station during the 2016/17 austral summer.

  18. Nature and History of Cenozoic Polar Ice Covers: The Case of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Spielhagen, R.; Thiede, J.

    2009-04-01

    The nature of the modern climate System is characterized by steep temperature gradients between the tropical and polar climatic zones and finds its most spectacular expression in the formation of ice caps in high Northern and Southern latitudes. While polar regions of Planet Earth have been glaciated repeatedly in the long course of their geological history, the Cenozoic transition from a „greenhouse" to an „icehouse" has in fact produced a unique climatic scenario with bipolar glacation, different from all previous glacial events. The Greenland ice sheet is a remainder of the Northern Hemisphere last glacial maximum ice sheets and represents hence a spectacular anomaly. Geological records from Tertiary and Quaternary terrestrial and oceanic sections have documented the presence of ice caps and sea ice covers both on the Southern as well on the Northern hemisphere since Eocene times, aqpprox. 45 Mio. years ago. While this was well known in the case of Antarctica already for some time, previous ideas about the origin of Northern hemisphere glaciation during Pliocene times (approx. 2-3 Mio. years ago) have been superceded by the dramatic findings of coarse, terrigenous ice rafted detritus in Eocene sediments from Lomonosov Ridge (close to the North Pole) apparently slightly older than the oldest Antarctic records of ice rafting.The histories of the onset of Cenozoic glaciation in high Northern and Southern latitudes remain enigmatic and are presently subjects of international geological drilling projects, with prospects to reveal some of their secrets over the coming decades. By virtue of the physical porperties of ice and the processes controlling the dynamics of the turn-over of the ice-sheets only young records of glacial ice caps on Antarctica and on Greemnland have been preserved, on Greenland with ice probably not older than a few hundred thousand years, on Antarctica potentially as old as 1.5-2 Mio. years. Deep-sea cores with their records od ice

  19. Potential methane reservoirs beneath Antarctica.

    PubMed

    Wadham, J L; Arndt, S; Tulaczyk, S; Stibal, M; Tranter, M; Telling, J; Lis, G P; Lawson, E; Ridgwell, A; Dubnick, A; Sharp, M J; Anesio, A M; Butler, C E H

    2012-08-30

    Once thought to be devoid of life, the ice-covered parts of Antarctica are now known to be a reservoir of metabolically active microbial cells and organic carbon. The potential for methanogenic archaea to support the degradation of organic carbon to methane beneath the ice, however, has not yet been evaluated. Large sedimentary basins containing marine sequences up to 14 kilometres thick and an estimated 21,000 petagrams (1 Pg equals 10(15) g) of organic carbon are buried beneath the Antarctic Ice Sheet. No data exist for rates of methanogenesis in sub-Antarctic marine sediments. Here we present experimental data from other subglacial environments that demonstrate the potential for overridden organic matter beneath glacial systems to produce methane. We also numerically simulate the accumulation of methane in Antarctic sedimentary basins using an established one-dimensional hydrate model and show that pressure/temperature conditions favour methane hydrate formation down to sediment depths of about 300 metres in West Antarctica and 700 metres in East Antarctica. Our results demonstrate the potential for methane hydrate accumulation in Antarctic sedimentary basins, where the total inventory depends on rates of organic carbon degradation and conditions at the ice-sheet bed. We calculate that the sub-Antarctic hydrate inventory could be of the same order of magnitude as that of recent estimates made for Arctic permafrost. Our findings suggest that the Antarctic Ice Sheet may be a neglected but important component of the global methane budget, with the potential to act as a positive feedback on climate warming during ice-sheet wastage.

  20. Determination of lead, cadmium, indium, thallium and silver in ancient ices from Antarctica by isotope dilution-thermal ionization mass spectrometry

    USGS Publications Warehouse

    Matsumoto, A.; Hinkley, T.K.

    1997-01-01

    The concentrations of five chalcophile elements (Pb, Cd, In, Tl and Ag) and the lead isotope rarios in ancient ices from the Taylor Dome near coastal Antarctica, have been determined by the isotope dilutionthermal ionization mass spectrometry (ID-TIMS), with ultra-clean laboratory techniques. The samples were selected from segments of cores, one of which included a visible ash layer. Electric conductivity measurement (ECM) or dielectric properties (DEP) gave distinctive sharp peaks for some of the samples c hosen. Exterior portions of the sample segments were trimmed away by methods described here. Samples w ere evaporated to dryness and later separated into fractions for the five elements using an HBr-HNO3 a nion exchange column method. The concentrations are in the range 2.62-36.7 pg Pb/g of ice, 0.413-2.83 pg Cd/g, 0.081-0.34 pg In/g, 0.096-2.8 pg Tl/g and 0.15-0.84 pg Ag/g. respectively. The dispersions in duplicate analyses are about ??1% for lead and cadmium, ??2% for indium. ??4% for thallium and ??6% for silver, respectively. The concentrations of lead obtained are commonly higher than those in the present-day Antarctic surface snows, but the isotope ratios are distinctively higher than those of the present-day snows and close to those of the other ancient ice collected from a different Antarctic area.

  1. Slow-slip events on the Whillans Ice Plain, Antarctica, described using rate-and-state friction as an ice stream sliding law

    NASA Astrophysics Data System (ADS)

    Lipovsky, Bradley Paul; Dunham, Eric M.

    2017-04-01

    The Whillans Ice Plain (WIP), Antarctica, experiences twice daily tidally modulated stick-slip cycles. Slip events last about 30 min, have sliding velocities as high as ˜0.5 mm/s (15 km/yr), and have total slip ˜0.5 m. Slip events tend to occur during falling ocean tide: just after high tide and just before low tide. To reproduce these characteristics, we use rate-and-state friction, which is commonly used to simulate tectonic faulting, as an ice stream sliding law. This framework describes the evolving strength of the ice-bed interface throughout stick-slip cycles. We present simulations that resolve the cross-stream dimension using a depth-integrated treatment of an elastic ice layer loaded by tides and steady ice inflow. Steady sliding with rate-weakening friction is conditionally stable with steady sliding occurring for sufficiently narrow ice streams relative to a nucleation length. Stick-slip cycles occur when the ice stream is wider than the nucleation length or, equivalently, when effective pressures exceed a critical value. Ice streams barely wider than the nucleation length experience slow-slip events, and our simulations suggest that the WIP is in this slow-slip regime. Slip events on the WIP show a sense of propagation, and we reproduce this behavior by introducing a rate-strengthening region in the center of the otherwise rate-weakening ice stream. If pore pressures are raised above a critical value, our simulations predict that the WIP would exhibit quasi-steady tidally modulated sliding as observed on other ice streams. This study validates rate-and-state friction as a sliding law to describe ice stream sliding styles.

  2. Mass balance reassessment of glaciers draining into the Abbot and Getz Ice Shelves of West Antarctica

    NASA Astrophysics Data System (ADS)

    Chuter, S. J.; Martín-Español, A.; Wouters, B.; Bamber, J. L.

    2017-07-01

    We present a reassessment of input-output method ice mass budget estimates for the Abbot and Getz regions of West Antarctica using CryoSat-2-derived ice thickness estimates. The mass budget is 8 ± 6 Gt yr-1 and 5 ± 17 Gt yr-1 for the Abbot and Getz sectors, respectively, for the period 2006-2008. Over the Abbot region, our results resolve a previous discrepancy with elevation rates from altimetry, due to a previous 30% overestimation of ice thickness. For the Getz sector, our results are at the more positive bound of estimates from other techniques. Grounding line velocity increases up to 20% between 2007 and 2014 alongside mean elevation rates of -0.67 ± 0.13 m yr-1 between 2010 and 2013 indicate the onset of a dynamic thinning signal. Mean snowfall trends of -0.33 m yr-1 water equivalent since 2006 indicate recent mass trends are driven by both ice dynamics and surface processes.

  3. Establishing a Reliable Depth-Age Relationship for the Denali Ice Core

    NASA Astrophysics Data System (ADS)

    Wake, C. P.; Osterberg, E. C.; Winski, D.; Ferris, D.; Kreutz, K. J.; Introne, D.; Dalton, M.

    2015-12-01

    Reliable climate reconstruction from ice core records requires the development of a reliable depth-age relationship. We have established a sub-annual resolution depth-age relationship for the upper 198 meters of a 208 m ice core recovered in 2013 from Mt. Hunter (3,900 m asl), Denali National Park, central Alaska. The dating of the ice core was accomplished via annual layer counting of glaciochemical time-series combined with identification of reference horizons from volcanic eruptions and atmospheric nuclear weapons testing. Using the continuous ice core melter system at Dartmouth College, sub-seasonal samples have been collected and analyzed for major ions, liquid conductivity, particle size and concentration, and stable isotope ratios. Annual signals are apparent in several of the chemical species measured in the ice core samples. Calcium and magnesium peak in the spring, ammonium peaks in the summer, methanesulfonic acid (MSA) peaks in the autumn, and stable isotopes display a strong seasonal cycle with the most depleted values occurring during the winter. Thin ice layers representing infrequent summertime melt were also used to identify summer layers in the core. Analysis of approximately one meter sections of the core via nondestructive gamma spectrometry over depths from 84 to 124 m identified a strong radioactive cesium-137 peak at 89 m which corresponds to the 1963 layer deposited during extensive atmospheric nuclear weapons testing. Peaks in the sulfate and chloride record have been used for the preliminary identification of volcanic signals preserved in the ice core, including ten events since 1883. We are confident that the combination of robust annual layers combined with reference horizons provides a timescale for the 20th century that has an error of less than 0.5 years, making calibrations between ice core records and the instrumental climate data particularly robust. Initial annual layer counting through the entire 198 m suggests the Denali Ice

  4. Toward an integrated ice core chronology using relative and orbital tie-points

    NASA Astrophysics Data System (ADS)

    Bazin, L.; Landais, A.; Lemieux-Dudon, B.; Toyé Mahamadou Kele, H.; Blunier, T.; Capron, E.; Chappellaz, J.; Fischer, H.; Leuenberger, M.; Lipenkov, V.; Loutre, M.-F.; Martinerie, P.; Parrenin, F.; Prié, F.; Raynaud, D.; Veres, D.; Wolff, E.

    2012-04-01

    Precise ice cores chronologies are essential to better understand the mechanisms linking climate change to orbital and greenhouse gases concentration forcing. A tool for ice core dating (DATICE [developed by Lemieux-Dudon et al., 2010] permits to generate a common time-scale integrating relative and absolute dating constraints on different ice cores, using an inverse method. Nevertheless, this method has only been applied for a 4-ice cores scenario and for the 0-50 kyr time period. Here, we present the bases for an extension of this work back to 800 ka using (1) a compilation of published and new relative and orbital tie-points obtained from measurements of air trapped in ice cores and (2) an adaptation of the DATICE inputs to 5 ice cores for the last 800 ka. We first present new measurements of δ18Oatm and δO2/N2 on the Talos Dome and EPICA Dome C (EDC) ice cores with a particular focus on Marine Isotopic Stages (MIS) 5, and 11. Then, we show two tie-points compilations. The first one is based on new and published CH4 and δ18Oatm measurements on 5 ice cores (NorthGRIP, EPICA Dronning Maud Land, EDC, Talos Dome and Vostok) in order to produce a table of relative gas tie-points over the last 400 ka. The second one is based on new and published records of δO2/N2, δ18Oatm and air content to provide a table of orbital tie-points over the last 800 ka. Finally, we integrate the different dating constraints presented above in the DATICE tool adapted to 5 ice cores to cover the last 800 ka and show how these constraints compare with the established gas chronologies of each ice core.

  5. Observed platelet ice distributions in Antarctic sea ice: An index for ocean-ice shelf heat flux

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    Antarctic sea ice that has been affected by supercooled Ice Shelf Water (ISW) has a unique crystallographic structure and is called platelet ice. In this paper we synthesize platelet ice observations to construct a continent-wide map of the winter presence of ISW at the ocean surface. The observations demonstrate that, in some regions of coastal Antarctica, supercooled ISW drives a negative oceanic heat flux of -30 Wm-2 that persists for several months during winter, significantly affecting sea ice thickness. In other regions, particularly where the thinning of ice shelves is believed to be greatest, platelet ice is not observed. Our new data set includes the longest ice-ocean record for Antarctica, which dates back to 1902 near the McMurdo Ice Shelf. These historical data indicate that, over the past 100 years, any change in the volume of very cold surface outflow from this ice shelf is less than the uncertainties in the measurements.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  7. Initial Continuous Chemistry Results From The Roosevelt Island Ice Core (RICE)

    NASA Astrophysics Data System (ADS)

    Kjær, H. A.; Vallelonga, P. T.; Simonsen, M. F.; Neff, P. D.; Bertler, N. A. N.; Svensson, A.; Dahl-Jensen, D.

    2014-12-01

    The Roosevelt Island ice core (79.36° S, -161.71° W) was drilled in 2011-13 at the top of the Roosevelt Island ice dome, a location surrounded by the Ross ice shelf. The RICE ice core provides a unique opportunity to look into the past evolution of the West Antarctic Ice sheet. Further the site has high accumulation; 0.26 m of ice equivalent is deposited annually allowing annual layer determination for many chemical parameters. The RICE core was drilled to bedrock and has a total length of 763 metres. Preliminary results derived from water isotopes suggest that the oldest ice reaches back to the Eemian, with the last glacial being compressed in the bottom 60 metres. We present preliminary results from the RICE ice core including continuous measurements of acidity using an optical dye method, insoluble dust particles, conductivity and calcium. The core was analyzed at the New Zealand National Ice Core Research Facility at GNS Science in Wellington. The analytical set up used to determine climate proxies in the ice core was a modified version of the Copenhagen CFA system (Bigler et al., 2011). Key volcanic layers have been matched to those from the WAIS record (Sigl et al., 2013). A significant anti-correlation between acidity and calcium was seen in the Holocene part of the record. Due to the proximity to the ocean a large fraction of the calcium originates from sea salt and is in phase with total conductivity and sodium. In combination with the insoluble dust record, calcium has been apportioned into ocean-related and dust-related sources. Variability over the Holocene is presented and attributed to changing inputs of marine and dust aerosols.

  8. Dansgaard-Oeschger cycles observed in the Greenland ReCAP ice core project

    NASA Astrophysics Data System (ADS)

    Kjær, Helle Astrid; Vallelonga, Paul; Vinther, Bo; Simonsen, Marius; Maffezzoli, Niccoló; Gkinis, Vasileios; Svensson, Anders; Jensen, Camilla Marie; Dallmayr, Remi; Spolaor, Andrea; Edwards, Ross

    2017-04-01

    The new REnland ice CAP (RECAP) ice core was drilled in summer 2015 in Greenland and measured by means of Continuous flow analysis (CFA) during the last 3 months of 2015. The Renland ice core was obtained as part of the ReCAP project, extending 584.11 meters to the bottom of the Renland ice cap located in east Greenland. The unique position on a mountain saddle above 2000 meters altitude, but close to the coast, ensures that the Renland ice core offers high accumulation, but also reaches far back in time. Results show that despite the short length the RECAP ice core holds ice all the way back to the past warm interglacial period, the Eemian. The glacial section is strongly thinned and covers on 20 meters of the ReCAP core, but nonetheless due to the high resolution of the measurements all 25 expected DO events could be identified. The record was analyzed for multiple elements including the water isotopes, forest fire tracers NH4+ and black carbon, insoluble dust particles by means of Abakus laser particle counter and the dust ion Ca2+, sea salt Na+, and sea ice proxies as well as acidity useful for finding volcanic layers to date the core. Below the glacial section another 20 meters of warm Eemian ice have been analysed. Here we present the chemistry results as obtained by continuous flow analysis (CFA) and compare the glacial section with the chemistry profile from other Greenland ice cores.

  9. Ice Bridge Antarctic Sea Ice

    NASA Image and Video Library

    2009-10-21

    An iceberg is seen out the window of NASA's DC-8 research aircraft as it flies 2,000 feet above the Amundsen Sea in West Antarctica on Wednesday, Oct., 21, 2009. This was the fourth science flight of NASA’s Operation Ice Bridge airborne Earth science mission to study Antarctic ice sheets, sea ice, and ice shelves. Photo Credit: (NASA/Jane Peterson)

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

    NASA Astrophysics Data System (ADS)

    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.

  11. Crevasse detection with GPR across the Ross Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Delaney, A.; Arcone, S.

    2005-12-01

    We have used 400-MHz ground penetrating radar (GPR) to detect crevasses within a shear zone on the Ross Ice Shelf, Antarctica, to support traverse operations. The transducer was attached to a 6.5-m boom and pushed ahead of an enclosed tracked vehicle. Profile speeds of 4.8-11.3 km / hr allowed real-time crevasse image display and a quick, safe stop when required. Thirty-two crevasses were located with radar along the 4.8 km crossing. Generally, crevasse radar images were characterized by dipping reflections above the voids, high-amplitude reflections originating from ice layers at the base of the snow-bridges, and slanting, diffracting reflections from near-vertical crevasse walls. New cracks and narrow crevasses (<50 cm width) show no distinct snow bridge structure, few diffractions, and a distinct band where pulse reflections are absent. Wide (0.5-5.0 m), vertical wall crevasses show distinct dipping snow bridge layering and intense diffractions from ice layers near the base of the snow bridge. Pulse reflections are absent from voids beneath the snow bridges. Old, wide (3.0-8.0 m) and complexly shaped crevasses show well-developed, broad, dipping snow-bridge layers and a high-amplitude, complex, diffraction pattern. The crevasse mitigation process, which included hot-water drilling, destroying the bridges with dynamite, and back-filling with bulldozed snow, afforded an opportunity to ground-truth GPR interpretations by comparing void size and snow-bridge geometry with the radar images. While second and third season radar profiles collected along the identical flagged route confirmed stability of the filled crevasses, those profiles also identified several new cracks opened by ice extension. Our experiments demonstrate capability of high-frequency GPR in a cold-snow environment for both defining snow layers and locating voids.

  12. Fire beneath the ice

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Monastersky, R.

    1993-02-13

    A volcano discovered six years ago by researchers Blankenship and Bell under Antarctica poses questions about a potential climatic catastrophe. The researchers claim that the volcano is still active, erupting occasionally and growing. A circular depression on the surface of the ice sheet has ice flowing into it and is used to provide a portrait of the heat source. The volcano is on a critical transition zone within West Antarctica with fast flowing ice streams directly downhill. Work by Blankenship shows that a soft layer of water-logged sediments called till provide the lubricating layer on the underside of the icemore » streams. Volcanos may provide the source of this till. The ice streams buffer the thick interior ice from the ocean and no one know what will happen if the ice streams continue to shorten. These researchers believe their results indicate that the stability of West Antarctica ultimately depends less on the current climate than on the location of heat and sediments under the ice and the legacy of past climatic changes.« less

  13. Effects of summer ice coverage on phytoplankton assemblages in the Ross Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    Mangoni, O.; Modigh, M.; Conversano, F.; Carrada, G. C.; Saggiomo, V.

    2004-11-01

    An oceanographic cruise was conducted in the Ross Sea (Antarctica) during summer 2001 as part of the Italian National Program for Antarctic Research (PNRA). Extensive areas of pack ice occurred over the Ross Sea, atypical for summer when offshore waters are normally free of ice. The present study focuses on the effects of increased ice coverage on phytoplankton assemblages. Water samples collected at various depths at 72 hydrographical stations in offshore and coastal waters were used to determine size-fractionated phytoplankton biomass as chlorophyll a (chla) concentrations, and HPLC photosynthetic pigments. For the offshore waters, the average chla concentration was 57.8 mg m-2, approximately three times the values recorded under ice-free conditions during summer 1996. In coastal waters, the average chla concentrations were 102 and 206 mg m-2 during January and February, respectively, i.e., up to 2.5 times those of 1996. Micro- and nano-phytoplankton size fractions made up about 90% of the phytoplankton biomass over the entire study area and were composed primarily of diatoms with a pico-phytoplankton fraction dominated by prymnesiophyceans. The broken pack and melting ice was strongly coloured by an extensive algal biomass suggesting that the phytoplankton was a result of seeding from ice algal communities. The Ross Sea considered to be one of the most productive areas of the Southern Ocean, had primary production values about four-fold those of other areas. The lengthening of the ice season observed in the Western Ross Sea, associated with a considerable increase in phytoplankton biomass as observed in summer 2001, would have a major impact on the trophic structure of the entire ecosystem, and presumably, also on carbon export.

  14. Two-dimensional ice mapping of molecular cores

    NASA Astrophysics Data System (ADS)

    Noble, J. A.; Fraser, H. J.; Pontoppidan, K. M.; Craigon, A. M.

    2017-06-01

    We present maps of the column densities of H2O, CO2 and CO ices towards the molecular cores B 35A, DC 274.2-00.4, BHR 59 and DC 300.7-01.0. These ice maps, probing spatial distances in molecular cores as low as 2200 au, challenge the traditional hypothesis that the denser the region observed, the more ice is present, providing evidence that the relationships between solid molecular species are more varied than the generic picture we often adopt to model gas-grain chemical processes and explain feedback between solid phase processes and gas phase abundances. We present the first combined solid-gas maps of a single molecular species, based upon observations of both CO ice and gas phase C18O towards B 35A, a star-forming dense core in Orion. We conclude that molecular species in the solid phase are powerful tracers of 'small-scale' chemical diversity, prior to the onset of star formation. With a component analysis approach, we can probe the solid phase chemistry of a region at a level of detail greater than that provided by statistical analyses or generic conclusions drawn from single pointing line-of-sight observations alone.

  15. Pedogenesis on ice (Invited)

    NASA Astrophysics Data System (ADS)

    Hodson, A. J.

    2010-12-01

    It is well known from ice cores that organic and mineral debris accumulates within glacier ice following atmospheric deposition. However, the concentrations of such debris are usually greatest upon the ice surface, especially at the margins of continental glaciers and ice sheets, where it forms mm-scale aggregate particles called “cryoconite”. According to the literature, cryoconite covers about 2 % of the ablation areas of glaciers outside Greenland and Antarctica, equivalent to a mass loading of ca. 25 g/m2. Of the great ice sheets not included in this figure, Greenland is the easiest to estimate, and new observations from the NE and SW sectors indicate mass loadings in the range 17 - 440 g/m2. Studies of cryoconite often report the presence of a significant biomass (usually 10^4 - 10^7 cells/g) that is capable of a wide range of biogeochemical functions. The first part of this presentation will therefore explore the contention that the formation of cryoconite represents the first stages of pedogenesis, resulting in the production of soil-type aggregates that inoculate glacial forefields following glacier retreat. Emphasis will be given to the relevant processes that result in aggregate formation, including rapid cell-mineral attachment within melting snowpacks and the slower, biological processes of cementation within thermodynamically stable habitats such as cryoconite holes. The second part of the presentation will use examples from Svalbard, Greenland and Antarctica to consider the carbon balance of the cryoconite during the longest phase of its life cycle: upon the ice. It will be demonstrated how the efficacy of photosynthesis is strongly influenced by thermodynamic conditions at or near this surface. Data from the Greenland and Antarctic ice sheets will show how thermal equilibration decouples variations in photosynthesis from variations in incident radiation over timescales > 1 d, resulting in an equitable, low-carbon economy for aggregates within

  16. IceChrono v1: a probabilistic model to compute a common and optimal chronology for several ice cores

    NASA Astrophysics Data System (ADS)

    Parrenin, Frédéric

    2015-04-01

    Polar ice cores provide exceptional archives of past environmental conditions. The dating of ice cores is essential to interpret the paleo records that they contain, but it is a complicated problem since it involves different dating methods. Here I present IceChrono v1, a new probabilistic model to combine different kinds of chronological information to obtain a common and optimized chronology for several ice cores, as well as its uncertainty. It is based on the inversion of three quantities: the surface accumulation rate, the Lock-In Depth (LID) of air bubbles and the vertical thinning function. The chronological information used are: models of the sedimentation process (accumulation of snow, densification of snow into ice and air trapping, ice flow), ice and gas dated horizons, ice and gas dated depth intervals, Δdepth observations (depth shift between synchronous events recorded in the ice and in the air), stratigraphic links in between ice cores (ice-ice, air-air or mix ice-air and air-ice links). The optimization problem is formulated as a least squares problems, that is, all densities of probabilities are assumed gaussian. It is numerically solved using the Levenberg-Marquardt algorithm and a numerical evaluation of the model's Jacobian. IceChrono is similar in scope to the Datice model, but has differences from the mathematical, numerical and programming point of views. I apply IceChrono on an AICC2012-like experiment and I find similar results than Datice within a few centuries, which is a confirmation of both IceChrono and Datice codes. IceChrono v1 is freely available under the GPL v3 open source license.

  17. Eemian interglacial reconstructed from a Greenland folded ice core.

    PubMed

    2013-01-24

    Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling ('NEEM') ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 ± 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 ± 250 metres, reaching surface elevations 122,000 years ago of 130 ± 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future.

  18. On the use of δ18Oatm for ice core dating

    NASA Astrophysics Data System (ADS)

    Extier, Thomas; Landais, Amaelle; Bréant, Camille; Prié, Frédéric; Bazin, Lucie; Dreyfus, Gabrielle; Roche, Didier M.; Leuenberger, Markus

    2018-04-01

    Deep ice core chronologies have been improved over the past years through the addition of new age constraints. However, dating methods are still associated with large uncertainties for ice cores from the East Antarctic plateau where layer counting is not possible. Indeed, an uncertainty up to 6 ka is associated with AICC2012 chronology of EPICA Dome C (EDC) ice core, which mostly arises from uncertainty on the delay between changes recorded in δ18Oatm and in June 21st insolation variations at 65°N used for ice core orbital dating. Consequently, we need to enhance the knowledge of this delay to improve ice core chronologies. We present new high-resolution EDC δ18Oatm record (153-374 ka) and δO2/N2 measurements (163-332 ka) performed on well-stored ice to provide continuous records of δ18Oatm and δO2/N2 between 100 and 800 ka. The comparison of δ18Oatm with the δ18Ocalcite from East Asian speleothems shows that both signals present similar orbital and millennial variabilities, which may represent shifts in the InterTropical Convergence Zone position, themselves associated with Heinrich events. We thus propose to use the δ18Ocalcite as target for δ18Oatm orbital dating. Such a tuning method improves the ice core chronology of the last glacial inception compared to AICC2012 by reconciling NGRIP and mid-latitude climatic records. It is especially marked during Dansgaard-Oeschger 25 where the proposed chronology is 2.2 ka older than AICC2012. This δ18Oatm - δ18Ocalcite alignment method applied between 100 and 640 ka improves the EDC ice core chronology, especially over MIS 11, and leads to lower ice age uncertainties compared to AICC2012.

  19. Earth - Ross Ice Shelf, Antarctica

    NASA Image and Video Library

    1996-02-09

    This color picture of Antarctica is one part of a mosaic of pictures covering the entire Antarctic continent taken during the hours following NASA's Galileo historic first encounter with its home planet. http://photojournal.jpl.nasa.gov/catalog/PIA00117

  20. Greenland ice cores tell tales on past sea level changes

    NASA Astrophysics Data System (ADS)

    Dahl-Jensen, D.

    2017-12-01

    All the deep ice cores drilled to the base of the Greenland ice sheet contain ice from the previous warm climate period, the Eemian 130-115 thousand years before present. This demonstrates the resilience of the Greenland ice sheet to a warming of 5 oC. Studies of basal material further reveal the presence of boreal forest over Greenland before ice covered Greenland. Conditions for Boreal forest implies temperatures at this time has been more than 10 oC warmer than the present. To compare the paleo-behavior of the Greenland ice sheet to the present in relation to sea level rise knowledge gabs include the reaction of ice streams to climate changes. To address this the international EGRIP-project is drilling an ice core in the center of the North East Greenland Ice Stream (NEGIS). The first results will be presented.

  1. Balloons on Ice: NASA Launches Antarctica Scientific Balloon Campaign

    NASA Image and Video Library

    2017-12-08

    Cosmic rays and the chemicals and atoms that make up the interstellar space between stars are the focus of this year’s NASA Antarctica Long Duration Balloon Flight Campaign, which kicked into high gear with the launch of the Boron And Carbon Cosmic rays in the Upper Stratosphere (BACCUS) payload Nov. 28. The University of Maryland’s BACCUS mission is the first of three payloads taking flight from a balloon launch site on Antarctica’s Ross Ice Shelf near McMurdo Station with support from the National Science Foundation’s United States Antarctic Program. Read more: go.nasa.gov/2gCMtyP NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  2. Cosmogenic 10Be Depth Profile in top 560 m of West Antarctic Ice Sheet Divide Ice Core

    NASA Astrophysics Data System (ADS)

    Welten, K. C.; Woodruff, T. E.; Caffee, M. W.; Edwards, R.; McConnell, J. R.; Bisiaux, M. M.; Nishiizumi, K.

    2009-12-01

    Concentrations of cosmogenic 10Be in polar ice samples are a function of variations in solar activity, geomagnetic field strength, atmospheric mixing and annual snow accumulation rates. The 10Be depth profile in ice cores also provides independent chronological markers to tie Antarctic to Greenland ice cores and to tie Holocene ice cores to the 14C dendrochronology record. We measured 10Be concentrations in 187 samples from depths of 0-560 m of the main WAIS Divide core, WDC06A. The ice samples are typically 1-2 kg and represent 2-4 m of ice, equivalent to an average temporal resolution of ~12 years, based on the preliminary age-depth scale proposed for the WDC core, (McConnell et al., in prep). Be, Al and Cl were separated using ion exchange chromatography techniques and the 10Be concentrations were measured by accelerator mass spectrometry (AMS) at PRIME lab. The 10Be concentrations range from 8.1 to 19.1 x 10^3 at/g, yielding an average of (13.1±2.1) x 10^3 at/g. Adopting an average snow accumulation rate of 20.9 cm weq/yr, as derived from the age-depth scale, this value corresponds to an average 10Be flux of (2.7±0.5) x 10^5 atoms/yr/cm2. This flux is similar to that of the Holocene part of the Siple Dome (Nishiizumi and Finkel, 2007) and Dome Fuji (Horiuchi et al. 2008) ice cores, but ~30% lower than the value of 4.0 x 10^5 atoms/yr/cm2 for GISP2 (Finkel and Nishiizumi, 1997). The periods of low solar activity, known as Oort, Wolf, Spörer, Maunder and Dalton minima, show ~20% higher 10Be concentrations/fluxes than the periods of average solar activity in the last millennium. The maximum 10Be fluxes during some of these periods of low solar activity are up to ~50% higher than average 10Be fluxes, as seen in other polar ice cores, which makes these peaks suitable as chronologic markers. We will compare the 10Be record in the WAIS Divide ice core with that in other Antarctic as well as Greenland ice cores and with the 14C treering record. Acknowledgment. This

  3. Recent Increases in Snow Accumulation and Decreases in Sea-Ice Concentration Recorded in a Coastal NW Greenland Ice Core

    NASA Astrophysics Data System (ADS)

    Osterberg, E. C.; Thompson, J. T.; Wong, G. J.; Hawley, R. L.; Kelly, M. A.; Lutz, E.; Howley, J.; Ferris, D. G.

    2013-12-01

    A significant rise in summer temperatures over the past several decades has led to widespread retreat of the Greenland Ice Sheet (GIS) margin and surrounding sea ice. Recent observations from geodetic stations and GRACE show that ice mass loss progressed from South Greenland up to Northwest Greenland by 2005 (Khan et al., 2010). Observations from meteorological stations at the U.S. Thule Air Force Base, remote sensing platforms, and climate reanalyses indicate a 3.5C mean annual warming in the Thule region and a 44% decrease in summer (JJAS) sea-ice concentrations in Baffin Bay from 1980-2010. Mean annual precipitation near Thule increased by 12% over this interval, with the majority of the increase occurring in fall (SON). To improve projections of future ice loss and sea-level rise in a warming climate, we are currently developing multi-proxy records (lake sediment cores, ice cores, glacial geologic data, glaciological models) of Holocene climate variability and cryospheric response in NW Greenland, with a focus on past warm periods. As part of our efforts to develop a millennial-length ice core paleoclimate record from the Thule region, we collected and analyzed snow pit samples and short firn cores (up to 20 m) from the coastal region of the GIS (2Barrel site; 76.9317 N, 63.1467 W) and the summit of North Ice Cap (76.938 N, 67.671 W) in 2011 and 2012, respectively. The 2Barrel ice core was sampled using a continuous ice core melting system at Dartmouth, and subsequently analyzed for major anion and trace element concentrations and stable water isotope ratios. Here we show that the 2Barrel ice core spanning 1990-2010 records a 25% increase in mean annual snow accumulation, and is positively correlated (r = 0.52, p<0.01) with ERA-Interim precipitation. The 2Barrel annual sea-salt Na concentration is strongly correlated (r = 0.5-0.8, p<0.05) with summer and fall sea-ice concentrations in northern Baffin Bay near Thule (Figure 1). We hypothesize that the positive

  4. Luminescence dating of paleolake deltas and glacial deposits in Garwood Valley, Antarctica: Implications for climate, Ross ice sheet dynamics, and paleolake duration

    USGS Publications Warehouse

    Levy, Joseph S.; Rittenour, Tammy M.; Fountain, Andrew G.; O'Connor, Jim E.

    2017-01-01

    The formation of perched deltas and other lacustrine deposits in the McMurdo Dry Valleys of Antarctica is widely considered to be evidence of valley-filling lakes dammed by the grounded Ross Sea ice sheet during the local Last Glacial Maximum, with lake drainage interpreted as a record of grounding line retreat. We used luminescence dating to determine the age of paleolake deltas and glacial tills in Garwood Valley, a coastal dry valley that opens to the Ross Sea. Luminescence ages are stratigraphically consistent with radiocarbon results from algal mats within the same delta deposits but suggest radiocarbon dates from lacustrine carbonates may overestimate deposit ages by thousands of years. Results suggest that late Holocene delta deposition into paleolake Howard in Garwood Valley persisted until ca. 3.5 ka. This is significantly younger than the date when grounded ice is thought to have retreated from the Ross Sea. Our evidence suggests that the local, stranded ice-cored till topography in Garwood Valley, rather than regional ice-sheet dynamics, may have controlled lake levels for some McMurdo Dry Valleys paleolakes. Age control from the supraglacial Ross Sea drift suggests grounding and up-valley advance of the Ross Sea ice sheet into Garwood valley during marine oxygen isotope stage (MIS) 4 (71–78 ka) and the local Last Glacial Maximum (9–10 ka). This work demonstrates the power of combining luminescence dating with existing radiocarbon data sets to improve understanding of the relationships among paleolake formation, glacial position, and stream discharge in response to climate change.

  5. Abbot Ice Shelf, structure of the Amundsen Sea continental margin and the southern boundary of the Bellingshausen Plate seaward of West Antarctica

    NASA Astrophysics Data System (ADS)

    Cochran, James R.; Tinto, Kirsty J.; Bell, Robin E.

    2015-05-01

    Inversion of NASA Operation IceBridge airborne gravity over the Abbot Ice Shelf in West Antarctica for subice bathymetry defines an extensional terrain made up of east-west trending rift basins formed during the early stages of Antarctica/Zealandia rifting. Extension is minor, as rifting jumped north of Thurston Island early in the rifting process. The Amundsen Sea Embayment continental shelf west of the rifted terrain is underlain by a deeper, more extensive sedimentary basin also formed during rifting between Antarctica and Zealandia. A well-defined boundary zone separates the mildly extended Abbot extensional terrain from the deeper Amundsen Embayment shelf basin. The shelf basin has an extension factor, β, of 1.5-1.7 with 80-100 km of extension occurring across an area now 250 km wide. Following this extension, rifting centered north of the present shelf edge and proceeded to continental rupture. Since then, the Amundsen Embayment continental shelf appears to have been tectonically quiescent and shaped by subsidence, sedimentation, and the advance and retreat of the West Antarctic Ice Sheet. The Bellingshausen Plate was located seaward of the Amundsen Sea margin prior to incorporation into the Antarctic Plate at about 62 Ma. During the latter part of its independent existence, Bellingshausen plate motion had a clockwise rotational component relative to Antarctica producing convergence across the north-south trending Bellingshausen Gravity Anomaly structure at 94°W and compressive deformation on the continental slope between 94°W and 102°W. Farther west, the relative motion was extensional along an east-west trending zone occupied by the Marie Byrd Seamounts. The copyright line for this article was changed on 5 JUN 2015 after original online publication.

  6. POLLiCE (POLLen in the iCE): climate history from Adamello ice cores

    NASA Astrophysics Data System (ADS)

    Cristofori, Antonella; Festi, Daniela; Maggi, Valter; Casarotto, Christian; Bertoni, Elena; Vernesi, Cristiano

    2017-04-01

    Glaciers can be viewed as the most complete and effective past climate and environment archives severely threatened by climate change. These threats are particularly dramatic across European Alps. The Adamello glacier is the largest, 16.4 km2, and deepest, 270 m, Italian glacier. We aim at estimating biodiversity changes over the last centuries in relation to climate and human activities in the Adamello catchment area. We, therefore, recently launched the POLLiCE project (pollice.fmach.it) for specifically targeting the biological component (e.g. pollen, leaves, plant remains) trapped in ice cores. Classical morphological pollen analysis will be accompanied by DNA metabarcoding. This approach has the potential to provide a detailed taxonomical identification - at least genus level- thus circumventing the limitations of microscopic analysis such as time-consuming procedures and shared features of pollen grains among different taxa. Moreover, ice cores are subjected to chemical and physical analyses - stable isotopes, ions, hyperspectral imaging, etc.- for stratigraphic and climatic determination of seasonality. A pilot drilling was conducted on March 2015 and the resulting 5 m core has been analysed in terms of pollen spectrum, stable isotopes and ions in order to demonstrate the feasibility of the study. The first encouraging results showed that even in this superficial core a stratigraphy is evident with indication of seasonality as highlighted by both by pollen taxa and stable isotopes. Finally, DNA has been successfully extracted and amplified with specific DNA barcodes. A medium drilling was performed on April 2016 with the extraction of a 45 m ice core. The analysis of this core constitutes the subject of a specific research project, CALICE*, just funded by Euregio Science Fund (IPN57). The entire depth, 270 m, of the Adamello glacier is scheduled to be drilled in 2018 winter to secure the unique memory archived by the ice. * See EGU2017 poster by Festi et al

  7. In Situ Observational Constraints on GIA in Antarctica

    NASA Astrophysics Data System (ADS)

    Wilson, T. J.; Bevis, M. G.; Kendrick, E. C.; Konfal, S.; Dalziel, I. W.; Smalley, R.; Willis, M. J.; Wiens, D. A.; Heeszel, D. S.

    2012-12-01

    Geodetic and seismologic data sets have been acquired across a significant portion of Antarctica through deployment of autonomous, remote instrumentation by the Antarctic Network (ANET) project of the Polar Earth Observing Network (POLENET). Continuous GPS measurements of bedrock crustal motions are yielding a synoptic picture of vertical and horizontal crustal motion patterns from the Transantarctic Mountains to the Ellsworth-Whitmore Mountains and Marie Byrd Land regions. Vertical motion patterns are broadly compatible with predictions from current GIA models, but the magnitudes of the vertical motions are substantially lower than predicted. Slower rates of uplift due to GIA can be attributed to factors including errors in ice history, a superposed solid earth response to modern ice mass change, and/or the influence of laterally varying earth properties on the GIA response. Patterns of horizontal motions measured by ANET show that the role of laterally varying earth rheology is extremely important in Antarctica. Crustal motion vectors are closely aligned and document motion from East toward West Antarctica, in contradiction to ice sheet reconstructions placing maximum LGM ice mass loss in West Antarctica and GIA models that predict motions in the opposite direction. When compared to earth structure mapped by seismology, the horizontal crustal motions are consistently near-perpendicular to the very strong gradient in crust and mantle properties, perhaps the first confirmation of predictions from modeling studies that horizontal motions can be deflected or even reversed where such a lateral earth property exists. Accurate GIA models for Antarctica clearly require a laterally-varying earth model and tuning based on these new GPS and seismological constraints.

  8. Estimating Antarctica land topography from GRACE gravity and ICESat altimetry data

    NASA Astrophysics Data System (ADS)

    Wu, I.; Chao, B. F.; Chen, Y.

    2009-12-01

    We propose a new method combining GRACE (Gravity Recovery and Climate Experiment) gravity and ICESat (Ice, Cloud, and land Elevation Satellite) altimetry data to estimate the land topography for Antarctica. Antarctica is the fifth-largest continent in the world and about 98% of Antarctica is covered by ice, where in-situ measurements are difficult. Some experimental airborne radar and ground-based radar data have revealed very limited land topography beneath heavy ice sheet. To estimate the land topography for the full coverage of Antarctica, we combine GRACE data that indicate the mass distribution, with data of ICESat laser altimetry that provide high-resolution mapping of ice topography. Our approach is actually based on some geological constraints: assuming uniform densities of the land and ice considering the Airy-type isostasy. In the beginning we construct an initial model for the ice thickness and land topography based on the BEDMAP ice thickness and ICESat data. Thereafter we forward compute the model’s gravity field and compare with the GRACE observed data. Our initial model undergoes the adjustments to improve the fit between modeled results and the observed data. Final examination is done by comparing our results with previous but sparse observations of ice thickness to reconfirm the reliability of our results. As the gravitational inversion problem is non-unique, our estimating result is just one of all possibilities constrained by available data in optimal way.

  9. Formation processes of sea ice floe size distribution in the interior pack and its relationship to the marginal ice zone off East Antarctica

    NASA Astrophysics Data System (ADS)

    Toyota, Takenobu; Kohout, Alison; Fraser, Alexander D.

    2016-09-01

    To understand the behavior of the Seasonal Ice Zone (SIZ), which is composed of sea-ice floes of various sizes, knowledge of the floe size distribution (FSD) is important. In particular, FSD in the Marginal Ice Zone (MIZ), controlled by wave-ice interaction, plays an important role in determining the retreating rates of sea-ice extent on a global scale because the cumulative perimeter of floes enhances melting. To improve the understanding of wave-ice interaction and subsequent effects on FSD in the MIZ, FSD measurements were conducted off East Antarctica during the second Sea Ice Physics and Ecosystems eXperiment (SIPEX-2) in late winter 2012. Since logistical reasons limited helicopter operations to two interior ice regions, FSD in the interior ice region was determined using a combination of heli-photos and MODIS satellite visible images. The possible effect of wave-ice interaction in the MIZ was examined by comparison with past results obtained in the same MIZ, with our analysis showing: (1) FSD in the interior ice region is basically scale invariant for both small- (<100 m) and large- (>1 km) scale regimes; (2) although fractal dimensions are quite different between these two regimes, they are both rather close to that in the MIZ; and (3) for floes <100 m in diameter, a regime shift which appeared at 20-40 m in the MIZ is absent. These results indicate that one role of wave-ice interaction is to modulate the FSD that already exists in the interior ice region, rather than directly determine it. The possibilities of floe-floe collisions and storm-induced lead formation are considered as possible formation processes of FSD in the interior pack.

  10. The Antarctic Ice Sheet during the last Interglaciation: Insights from my Thesis

    NASA Astrophysics Data System (ADS)

    Whipple, Matthew; Lunt, Dan; Singarayer, Joy; Bradley, Sarah; Milne, Glenn; Wolff, Eric; Siddall, Mark

    2015-04-01

    The last interglaciation represents a period of warmer climates and higher sea levels, and a useful analogue to future climate. While many studies have focussed on the response of the Greenland Ice sheet, far less is known about the response of the Antarctic ice sheet. Here, I present the summarised results of my PhD thesis "Constraints on the minimum extent of the Antarctic ice sheet during the last interglaciation". Firstly, I cover the timings of interglaciation in Antarctica, and their differences with respect to the Northern Hemisphere timings, based on paleo sea level indicators, and oceanic temperature records. I move on to cover climate forcings, and how they influence the ice sheet, relative to present, and early Holocene. Secondly, I present thesis results, from looking at ice core stable water isotopes. These are compared with Isostatic and Climatic modelling results, for various different Ice sheet scenarios, as to the resulting Climate, from changes in Elevation, Temperature, Precipitation, and Sublimation, all contributing to the recorded stable water isotope record. Thirdly, I move on to looking at the mid-field relative sea level records, from Australia and Argentina. Using isostatic modelling, these are used to assess the relative contribution of the Eastern and Western Antarctic Ice sheets. Although data uncertainties result in us being to identify the contribution from West Antarctica. Overall, using model-data comparison, we find a lack of evidence for a substantial retreat of the Wilkes Subglacial basin. No data location is close enough to determine the existence of the marine based West Antarctic Ice sheet. Model uncertainty is unable to constrain evidence of variations in ice thickness in East Antarctica.

  11. Diversity and physiology of culturable bacteria associated with a coastal Antarctic ice core.

    PubMed

    Antony, Runa; Krishnan, K P; Laluraj, C M; Thamban, Meloth; Dhakephalkar, P K; Engineer, Anupama S; Shivaji, S

    2012-06-20

    Microbiological studies of polar ice at different depths may provide important comparisons, as they preserve records of microbial cells and past climate. In this study, we examined bacterial abundance, diversity and glaciochemical composition from three depths of an ice core from coastal Dronning Maud Land, East Antarctica. Higher bacterial abundance corresponded with high in situ sea-salt Na(+) and dust concentration, suggesting that bacteria might have been transported and deposited into ice along with dust particles and marine aerosols. Fourteen bacterial isolates belonging to the genera Methylobacterium, Brevundimonas, Paenibacillus, Bacillus and Micrococcus were retrieved. Frequent isolation of similar bacterial genera from different cold environments suggests that they possess features that enable survival and metabolism for extended periods of time at sub-zero temperatures. The highest number and diversity of recoverable bacteria was obtained from 49 m depth corresponding to 1926 AD and consisted of bacteria from 4 different genera whereas at 11 m (1989 AD) and 33 m (1953 AD) samples only species belonging to the genera Bacillus was recovered. Among the Bacillus species, Bacillus aryabhattai which has been reported only from the upper stratosphere, was isolated and is the first record from the Earth's surface. Methylobacterium was the most dominant genera at 49 m depth and its prevalence is attributable to a combination of high in situ methanesulfonate concentration, specialized metabolism and environmental hardiness of Methylobacterium. Some of the isolated bacteria were found to respire and grow using methanesulfonate, suggesting that they may utilize this substrate to sustain growth in ice. In addition, NO(3)(-) (2.93-3.69 μM), NH(4)(+) (1.45-3.90 μM) and PO(4)(3-) (0.01-0.75 μM) present in the ice could be potential sources fueling bacterial metabolism in this environment. It could be deduced from the study that variation in bacterial abundance and

  12. Constraining the sources of CH4 emissions during past abrupt climate change using CH4 triple isotopes mass balance from the ice core records

    NASA Astrophysics Data System (ADS)

    Dyonisius, M.; Petrenko, V. V.; Smith, A. W.; Hmiel, B.; Beck, J.; Seth, B.; Bock, M.; Hua, Q.; Yang, B.; Harth, C. M.; Beaudette, R.; Lee, J.; Erhardt, T.; Schmitt, J.; Brook, E.; Weiss, R. F.; Fischer, H.; Severinghaus, J. P.

    2017-12-01

    Methane (CH4) is the third most important greenhouse gas in the atmosphere after water vapor and CO2. Understanding how the natural CH4 budget has changed in response to changing climate in the past can provide insights on the sensitivity of the natural CH4 emissions to the current anthropogenic warming. CH4 isotopes (Δ14CH4, δ13C-CH4, and δD-CH4) from ice cores can be used to fingerprint the sources of CH4 increases in the past. We have successfully extracted 6 large volume (>1000kg) ice core samples from Taylor Glacier, Antarctica spanning the Oldest Dryas-Bølling transition ( 14.7ka) - the first abrupt warming and CH4 rise since the Last Glacial Maximum. Among the CH4 isotopes, our Δ 14CH4 data are unique in their ability to unambiguously distinguish between "old" CH4 sources (e.g. marine clathrate, geologic sources, old permafrost) and "modern" CH4 sources (e.g. tropical and boreal wetlands). Our Δ14CH4 data unambiguously rule out marine clathrate and old permafrost as the sources of the abrupt CH4 rise. Preliminary CH4 stable isotopes box modeling combined with interpolar CH4 concentration gradient from existing ice core records suggest that tropical wetlands were the dominant driver for the Oldest Dryas-Bølling CH4 rise.

  13. Detailed history of atmospheric trace elements from the Quelccaya ice core (Southern Peru) during the last 1200 years

    NASA Astrophysics Data System (ADS)

    Uglietti, C.; Gabrielli, P.; Thompson, L. G.

    2013-12-01

    indicates that there have been additional anthropogenic sources that have impacted the South American atmosphere during the past ~550 years. Furthermore, As, Bi and Pb record shows, the two most significant increases have occurred in the 20th century, one beginning in ~1905 AD and peaking in the 1920s and the second beginning in ~1955 AD and peaking in the 1970s. Comparison with other trace element records from Greenland and Antarctica reveals concomitant peaks of different amplitude in Pb concentration and crustal enrichment factor, possibly pointing to an unexpected larger than regional scale significance for the Quelccaya ice core record during the last century. In conclusion, the Quelccaya ice core indicates that societal and industrial development influenced the atmospheric composition in South America, from different large scale sources, during the last ~550 years. This is the first time that a low latitude ice core record has been used to reconstruct pre-industrial anthropogenic forcing on the atmosphere.

  14. Development and applications of a radar-attenuation model for polar ice sheets

    NASA Astrophysics Data System (ADS)

    MacGregor, Joseph A.

    Modern ice sheets are currently responding to significant climatic forcings and undergoing ice-dynamics changes that are not yet well understood. Ice-penetrating radar surveys are often used to infer their basal condition (e.g., is the bed wet or dry?) and internal properties. However, such inferences typically require a model of the electromagnetic attenuation through the ice sheet. Here I first develop and test a radar-attenuation model that is based on a synthesis of existing laboratory measurements of the dielectric properties of ice. This synthesis shows that radar attenuation in polar ice has a strong non-linear temperature dependence and a weaker linear dependence on the concentrations of acid and sea-salt chloride. This model was tested at Siple Dome, West Antarctica, using ice-core-chemistry and borehole-temperature data, and the model agreed well with an existing radar-attenuation measurement. I then use this model to investigate the nature of radar detection of accreted ice over Lake Vostok, East Antarctica. My analysis of ice-core and radar data found that the observed reflection is likely due to a fabric contrast near the boundary between the dirty and clean accreted ices. This reflection mechanism is also consistent with the spatial pattern of detection of the reflection. In anticipation of the requirements of a thermomechanical ice-sheet model to predict the spatial variation of attenuation over Lake Vostok, I develop an accumulation-rate map for the Lake Vostok region using radar data, a steady-state flow-band model, and inverse methods. I found that accumulation rates there are not inversely correlated with surface elevation, that there is a broad maximum above the lake's northwestern corner, and a minimum above most of its eastern shoreline. Finally, I investigate the spatial variability of attenuation in an ice sheet, using the flowline that crosses through the Vostok ice core as an example. I use radar layers and ice-velocity and temperature

  15. Life in Ice: Implications to Astrobiology

    NASA Technical Reports Server (NTRS)

    Hoover, Richard B.

    2009-01-01

    During the 2008 Tawani International Expedition Schirmacher Oasis/Lake Untersee Antarctica Expedition, living and instantly motile bacteria were found in freshly thawed meltwater from ice of the Schirmacher Oasis Lakes, the Anuchin Glacier ice and samples of the that perennial ice sheet above Lake Untersee. This phenomenon of living bacteria encased in ice had previously been observed in the 32,000 year old ice of the Fox Tunnel. The bacteria found in this ice included the strain FTR1T which was isolated and published as valid new species (Carnobacterium pleistocenium) the first validly published living Pleistocene organism still alive today. Living bacteria were also extracted from ancient ice cores from Vostok, Antarctica. The discovery that many strains of bacteria are able to survive and remain alive while frozen in ice sheets for long periods of time may have direct relevance to Astrobiology. The abundance of viable bacteria in the ice sheets of Antarctica suggests that the presence of live bacteria in ice is common, rather than an isolated phenomenon. This paper will discuss the results of recent studies at NSSTC of bacteria cryopreserved in ice. This paper advances the hypothesis that cryopreserved cells, and perhaps even viable bacterial cells, may exist today--frozen in the water-ice of lunar craters, the Polar Caps or craters of Mars; or in the permafrost of Mars; ice and rocks of comets or water bearing asteroids; or in the frozen crusts of the icy moons of Jupiter and Saturn. The existence of bacterial life in ice suggests that it may not be necessary to drill through a thick ice crust to reach liquid water seas deep beneath the icy crusts of Europa, Ganymede and Enceladus. The presence of viable bacteria in the ice of the Earth s Polar Caps suggests that the possibility that cryo-panspermia (i.e., the trans-planetary transfer of microbial life by impact ejection/spallation of bacteria-rich polar ice masses) deserves serious consideration and study as a

  16. Byrd Glacier, Antarctica

    NASA Image and Video Library

    2008-11-17

    Byrd Glacier is a major glacier in Antarctica; it drains an extensive area of the polar plateau and flows eastward between the Britannia Range and the Churchill Mountains to discharge into the Ross Ice Shelf. This image is from NASA Terra satellite.

  17. Ice sheets and nitrogen.

    PubMed

    Wolff, Eric W

    2013-07-05

    Snow and ice play their most important role in the nitrogen cycle as a barrier to land-atmosphere and ocean-atmosphere exchanges that would otherwise occur. The inventory of nitrogen compounds in the polar ice sheets is approximately 260 Tg N, dominated by nitrate in the much larger Antarctic ice sheet. Ice cores help to inform us about the natural variability of the nitrogen cycle at global and regional scale, and about the extent of disturbance in recent decades. Nitrous oxide concentrations have risen about 20 per cent in the last 200 years and are now almost certainly higher than at any time in the last 800 000 years. Nitrate concentrations recorded in Greenland ice rose by a factor of 2-3, particularly between the 1950s and 1980s, reflecting a major change in NOx emissions reaching the background atmosphere. Increases in ice cores drilled at lower latitudes can be used to validate or constrain regional emission inventories. Background ammonium concentrations in Greenland ice show no significant recent trend, although the record is very noisy, being dominated by spikes of input from biomass burning events. Neither nitrate nor ammonium shows significant recent trends in Antarctica, although their natural variations are of biogeochemical and atmospheric chemical interest. Finally, it has been found that photolysis of nitrate in the snowpack leads to significant re-emissions of NOx that can strongly impact the regional atmosphere in snow-covered areas.

  18. Ice sheets and nitrogen

    PubMed Central

    Wolff, Eric W.

    2013-01-01

    Snow and ice play their most important role in the nitrogen cycle as a barrier to land–atmosphere and ocean–atmosphere exchanges that would otherwise occur. The inventory of nitrogen compounds in the polar ice sheets is approximately 260 Tg N, dominated by nitrate in the much larger Antarctic ice sheet. Ice cores help to inform us about the natural variability of the nitrogen cycle at global and regional scale, and about the extent of disturbance in recent decades. Nitrous oxide concentrations have risen about 20 per cent in the last 200 years and are now almost certainly higher than at any time in the last 800 000 years. Nitrate concentrations recorded in Greenland ice rose by a factor of 2–3, particularly between the 1950s and 1980s, reflecting a major change in NOx emissions reaching the background atmosphere. Increases in ice cores drilled at lower latitudes can be used to validate or constrain regional emission inventories. Background ammonium concentrations in Greenland ice show no significant recent trend, although the record is very noisy, being dominated by spikes of input from biomass burning events. Neither nitrate nor ammonium shows significant recent trends in Antarctica, although their natural variations are of biogeochemical and atmospheric chemical interest. Finally, it has been found that photolysis of nitrate in the snowpack leads to significant re-emissions of NOx that can strongly impact the regional atmosphere in snow-covered areas. PMID:23713125

  19. Late Holocene sedimentation in coastal areas of the northwestern Ross Sea (Antarctica)

    NASA Astrophysics Data System (ADS)

    Colizza, Ester; Finocchiaro, Furio; Kuhn, Gerhard; Langone, Leonardo; Melis, Romana; Mezgec, Karin; Severi, Mirko; Traversi, Rita; Udisti, Roberto; Stenni, Barbara; Braida, Martina

    2013-04-01

    Sediment cores and box cores collected in two coastal areas of the northwestern Ross Sea (Antarctica) highlight the possibility of studying the Late Holocene period in detail. In this work we propose a study on two box cores and two gravity cores collected in the Cape Hallett and Wood Bay areas during the 2005 PNRA oceanographic cruise. The two sites are feed by Eastern Antarctic Ice Shelf (EAIS) and previous studies have highlighted a complex postglacial sedimentary sequence, also influenced by local morphology. This study is performed within the framework of the PNRA-ESF PolarCLIMATE HOLOCLIP (Holocene climate variability at high-southern latitudes: an integrated perspective) Project. The data set includes: magnetic susceptibility, X-ray analyses, 210Pb, 14C dating, diatoms and foraminifera assemblages, organic carbon, and grain-size analyses. Furthermore XRF core scanner analyses, colour analysis from digital images, and major, minor and trace element concentration analyses (ICP-AES) are performed. Data show that the box core and upper core sediments represent a very recent sedimentation in which it is possible to observe the parameter variability probably linked to climate variability/changes: these variation will be compared with isotopic record form ice cores collected form the same Antarctic sector.

  20. Cleaning the IceMole: collection of englacial samples from Blood Falls, Antarctica

    NASA Astrophysics Data System (ADS)

    Mikucki, J.; Digel, I.; Chua, M.; Davis, J.; Ghosh, D.; Lyons, W. B.; Welch, K. A.; Purcell, A.; Francke, G.; Feldmann, M.; Espe, C.; Heinen, D.; Dachwald, B.; Kowalski, J.; Tulaczyk, S. M.

    2016-12-01

    The Minimally Invasive Direct Glacial Access project (MIDGE) used a maneuverable thermoelectric melting probe called the IceMole to collect the first englacial samples of brine from Blood Falls, Antarctica. In order to maintain the scientific integrity of samples collected and minimize impact to this specially protected ecosystem, microbial and chemical contamination of the IceMole needed to be minimized. Guidelines have been established for research in Antarctic subglacial systems by the scientific and regulatory community and have been detailed by the "Code of Conduct for the Exploration and Research of Subglacial Aquatic Environments" put forth by the Scientific Committee on Antarctic Research (SCAR) Action Group, and was submitted to the Antarctic Treaty System. This Code of Conduct (CoC) recognizes the ecological importance and pristine nature of subglacial habitats and recommends a path forward towards clean exploration. Similarly, the US and European space agencies (NASA and ESA) have detailed instrument preparation protocols for the exploration of icy worlds in our solar system for planetary protection. Given the synergistic aims of these two groups we have adopted protocols from both subglacial and space exploration approaches. Here we present our approach to cleaning the IceMole in the field and report on ability to reduce the bioload inherent on the melter. Specifically our protocol reduced the exterior bio-load by an order of magnitude, to levels common in most clean rooms, and 1-3 orders of magnitude below that of Taylor Glacier ice surrounding Blood Falls. Our results indicate that the collection of englacial samples for microbiological analysis is feasible with melting probes.

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

    NASA Technical Reports Server (NTRS)

    Alley, Richard B.

    1991-01-01

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

  2. Influence of Persistent Wind Scour on the Surface Mass Balance of Antarctica

    NASA Technical Reports Server (NTRS)

    Das, Indrani; Bell, Robin E.; Scambos, Ted A.; Wolovick, Michael; Creyts, Timothy T.; Studinger, Michael; Fearson, Nicholas; Nicolas, Julien P.; Lenaerts, Jan T. M.; vandenBroeke, Michiel R.

    2013-01-01

    Accurate quantification of surface snow accumulation over Antarctica is a key constraint for estimates of the Antarctic mass balance, as well as climatic interpretations of ice-core records. Over Antarctica, near-surface winds accelerate down relatively steep surface slopes, eroding and sublimating the snow. This wind scour results in numerous localized regions (< or = 200 sq km) with reduced surface accumulation. Estimates of Antarctic surface mass balance rely on sparse point measurements or coarse atmospheric models that do not capture these local processes, and overestimate the net mass input in wind-scour zones. Here we combine airborne radar observations of unconformable stratigraphic layers with lidar-derived surface roughness measurements to identify extensive wind-scour zones over Dome A, in the interior of East Antarctica. The scour zones are persistent because they are controlled by bedrock topography. On the basis of our Dome A observations, we develop an empirical model to predict wind-scour zones across the Antarctic continent and find that these zones are predominantly located in East Antarctica. We estimate that approx. 2.7-6.6% of the surface area of Antarctica has persistent negative net accumulation due to wind scour, which suggests that, across the continent, the snow mass input is overestimated by 11-36.5 Gt /yr in present surface-mass-balance calculations.

  3. An automated approach for annual layer counting in ice cores

    NASA Astrophysics Data System (ADS)

    Winstrup, M.; Svensson, A.; Rasmussen, S. O.; Winther, O.; Steig, E.; Axelrod, A.

    2012-04-01

    The temporal resolution of some ice cores is sufficient to preserve seasonal information in the ice core record. In such cases, annual layer counting represents one of the most accurate methods to produce a chronology for the core. Yet, manual layer counting is a tedious and sometimes ambiguous job. As reliable layer recognition becomes more difficult, a manual approach increasingly relies on human interpretation of the available data. Thus, much may be gained by an automated and therefore objective approach for annual layer identification in ice cores. We have developed a novel method for automated annual layer counting in ice cores, which relies on Bayesian statistics. It uses algorithms from the statistical framework of Hidden Markov Models (HMM), originally developed for use in machine speech recognition. The strength of this layer detection algorithm lies in the way it is able to imitate the manual procedures for annual layer counting, while being based on purely objective criteria for annual layer identification. With this methodology, it is possible to determine the most likely position of multiple layer boundaries in an entire section of ice core data at once. It provides a probabilistic uncertainty estimate of the resulting layer count, hence ensuring a proper treatment of ambiguous layer boundaries in the data. Furthermore multiple data series can be incorporated to be used at once, hence allowing for a full multi-parameter annual layer counting method similar to a manual approach. In this study, the automated layer counting algorithm has been applied to data from the NGRIP ice core, Greenland. The NGRIP ice core has very high temporal resolution with depth, and hence the potential to be dated by annual layer counting far back in time. In previous studies [Andersen et al., 2006; Svensson et al., 2008], manual layer counting has been carried out back to 60 kyr BP. A comparison between the counted annual layers based on the two approaches will be presented

  4. Accurate determination of surface reference data in digital photographs in ice-free surfaces of Maritime Antarctica.

    PubMed

    Pina, Pedro; Vieira, Gonçalo; Bandeira, Lourenço; Mora, Carla

    2016-12-15

    The ice-free areas of Maritime Antarctica show complex mosaics of surface covers, with wide patches of diverse bare soils and rock, together with various vegetation communities dominated by lichens and mosses. The microscale variability is difficult to characterize and quantify, but is essential for ground-truthing and for defining classifiers for large areas using, for example high resolution satellite imagery, or even ultra-high resolution unmanned aerial vehicle (UAV) imagery. The main objective of this paper is to verify the ability and robustness of an automated approach to discriminate the variety of surface types in digital photographs acquired at ground level in ice-free regions of Maritime Antarctica. The proposed method is based on an object-based classification procedure built in two main steps: first, on the automated delineation of homogeneous regions (the objects) of the images through the watershed transform with adequate filtering to avoid an over-segmentation, and second, on labelling each identified object with a supervised decision classifier trained with samples of representative objects of ice-free surface types (bare rock, bare soil, moss and lichen formations). The method is evaluated with images acquired in summer campaigns in Fildes and Barton peninsulas (King George Island, South Shetlands). The best performances for the datasets of the two peninsulas are achieved with a SVM classifier with overall accuracies of about 92% and kappa values around 0.89. The excellent performances allow validating the adequacy of the approach for obtaining accurate surface reference data at the complete pixel scale (sub-metric) of current very high resolution (VHR) satellite images, instead of a common single point sampling. Copyright © 2016 Elsevier B.V. All rights reserved.

  5. The roughness of grounded ice sheet beds: Case studies from high resolution radio echo sounding studies in Antarctica

    NASA Astrophysics Data System (ADS)

    Young, Duncan; Blankeship, Donald; Beem, Lucas; Cavitte, Marie; Quartini, Enrica; Lindzey, Laura; Jackson, Charles; Roberts, Jason; Ritz, Catherine; Siegert, Martin; Greenbaum, Jamin; Frederick, Bruce

    2017-04-01

    The roughness of subglacial interfaces (as measured by airborne radar echo sounding) at length scales between profile line spacing and the footprint of the instrument is a key, but complex, signature of glacial and geomorphic processes, material lithology and integrated history at the bed of ice sheets. Subglacial roughness is also intertwined with assessments of ice thickness uncertainty using radar echo sounding, the utility of interpolation methodologies, and a key aspect of subglacial assess strategies. Here we present an assessment of subglacial roughness estimation in both West and East Antarctica, and compare this to exposed subglacial terrains. We will use recent high resolution aerogeophysical surveys to examine what variations in roughness are a fingerprint for, assess the limits of ice thickness uncertainty quantification and compare strategies for roughness assessment and utilization.

  6. Syntectonic fluid flux during rift faulting: Record from the MIS core, Victoria Land Basin, Antarctica

    NASA Astrophysics Data System (ADS)

    Millan, C.; Wilson, T. J.; Paulsen, T. S.

    2009-12-01

    The McMurdo Ice Shelf project successfully recovered 1285 m of Neogene sedimentary core from the Victoria Land Basin, a large rift basin within the West Antarctic Rift System (WARS) of Antarctica. The core contains 1475 natural fractures that were logged as faults, veins and clastic dikes, associated with the southern extension of the Neogene-active? Terror Rift fault zone. Veins constitute about 625 of this population. Most veins are filled with calcite, although zeolites and minor chlorite are common towards the bottom of the core. In the lower ~300 m of the core, veins contain opening-mode fiber fills and are wavy to tightly folded due to vertical shortening. Folded, opening-mode folded veins are filled by calcite fibers that grew normal to vein walls, indicating the host sediment was cohesive enough to fracture but was not fully lithified and accommodated vein buckling during compaction. Fold hinges are fractured and wedging of vein segments is marked by overlapping tips separated by zones with strong chlorite and clay fabrics, suggesting shearing during further vertical contraction of the host rock. Calcite veins are commonly strongly twinned. Cathodoluminescence microscopy shows minor changes in color and intensity and minimal concentric or sectoral zoning, suggesting relatively rapid crystallization of fluids of similar chemistry. However, stable isotope analyses reveal large variations in values, with carbon values ranging from -21.91 to -7.15 (VPBD) and oxygen values ranging from -5.35 to -11.97 (VPBD). Further detailed investigation of the fracture fills using cathodoluminescence and electron microscopy combined with isotopic analysis of carbon and oxygen will document the generations of the filling material in more detail and will constrain the sources and evolution of the fluids. There has clearly been significant structural control on fluid pathways during lithification, compaction and diagenesis of strata deforming within the Terror Rift zone.

  7. Operation IceBridge Turns Five

    NASA Image and Video Library

    2017-12-08

    In May 2014, two new studies concluded that a section of the land-based West Antarctic ice sheet had reached a point of inevitable collapse. Meanwhile, fresh observations from September 2014 showed sea ice around Antarctica had reached its greatest extent since the late 1970s. To better understand such dynamic and dramatic differences in the region's land and sea ice, researchers are travelling south to Antarctica this month for the sixth campaign of NASA’s Operation IceBridge. The airborne campaign, which also flies each year over Greenland, makes annual surveys of the ice with instrumented research aircraft. Instruments range from lasers that map the elevation of the ice surface, radars that "see" below it, and downward looking cameras to provide a natural-color perspective. The Digital Mapping System (DMS) camera acquired the above photo during the mission’s first science flight on October 16, 2009. At the time of the image, the DC-8 aircraft was flying at an altitude of 515 meters (1,700 feet) over heavily compacted first-year sea ice along the edge of the Amundsen Sea. Since that first flight, much has been gleaned from IceBridge data. For example, images from an IceBridge flight in October 2011 revealed a massive crack running about 29 kilometers (18 miles) across the floating tongue of Antarctica's Pine Island Glacier. The crack ultimately led to a 725-square-kilometer (280-square-mile) iceberg. In 2012, IceBridge data was a key part of a new map of Antarctica called Bedmap2. By combining surface elevation, ice thickness, and bedrock topography, Bedmap2 gives a clearer picture of Antarctica from the ice surface down to the land surface. Discoveries have been made in Greenland, too, including the identification of a 740-kilometer-long (460-mile-long) mega canyon below the ice sheet. Repeated measurements of land and sea ice from aircraft extend the record of observations once made by NASA’s Ice, Cloud, and Land Elevation Satellite, or ICESat, which

  8. Distributions of larval and juvenile/adult stages of the Antarctic myctophid fish, Electrona antarctica, off Wilkes Land in East Antarctica

    NASA Astrophysics Data System (ADS)

    Moteki, Masato; Fujii, Kentaro; Amakasu, Kazuo; Shimada, Keishi; Tanimura, Atsushi; Odate, Tsuneo

    2017-06-01

    Myctophid fish are an important component of the Southern Ocean food web because of their very high biomass. This study investigated the spatial distributions of larval and juvenile/adult stages of the Antarctic myctophid Electrona antarctica. Fish were sampled in January 2011 and 2012 on a transect along 140°E and in January 2013 along 110°E using two different opening/closing net systems. In total, 1075 specimens of E. antarctica were collected: 948 larvae, 127 juveniles/adults, and 2 in the transformation stage. Most larvae were collected at 5-200 m depth, with diel vertical migration (DVM) not apparent. Larvae were mainly distributed in the Modified Circumpolar Deep Water (-1.5 °C-2.0 °C). By contrast, an analysis of the echogram at 38 kHz and discrete depth samples implied that juveniles/adults undertook DVM except in the continental slope area (65.5°S). As the distribution of krill is limited to the cold water mass (<-1.5 °C) along the continental slope, E. antarctica and krill populations are spatially separated off Wilkes Land during summer. According to the previously estimated larval period of 30-47 days, E. antarctica may spawn in late November to December in the marginal ice zone or near the sea ice edge. This study suggests that the environment related to sea ice provides a nursery ground for early stage larvae of E. antarctica.

  9. Dry Valleys, Antarctica

    NASA Image and Video Library

    2009-11-02

    The McMurdo Dry Valleys are a row of valleys west of McMurdo Sound, Antarctica. They are so named because of their extremely low humidity and lack of snow and ice cover. This image was acquired December 8, 2002 by NASA Terra spacecraft.

  10. Multi-Decadal Averages of Basal Melt for Ross Ice Shelf, Antarctica Using Airborne Observations

    NASA Astrophysics Data System (ADS)

    Das, I.; Bell, R. E.; Tinto, K. J.; Frearson, N.; Kingslake, J.; Padman, L.; Siddoway, C. S.; Fricker, H. A.

    2017-12-01

    Changes in ice shelf mass balance are key to the long term stability of the Antarctic Ice Sheet. Although the most extensive ice shelf mass loss currently is occurring in the Amundsen Sea sector of West Antarctica, many other ice shelves experience changes in thickness on time scales from annual to ice age cycles. Here, we focus on the Ross Ice Shelf. An 18-year record (1994-2012) of satellite radar altimetry shows substantial variability in Ross Ice Shelf height on interannual time scales, complicating detection of potential long-term climate-change signals in the mass budget of this ice shelf. Variability of radar signal penetration into the ice-shelf surface snow and firn layers further complicates assessment of mass changes. We investigate Ross Ice Shelf mass balance using aerogeophysical data from the ROSETTA-Ice surveys using IcePod. We use two ice-penetrating radars; a 2 GHz unit that images fine-structure in the upper 400 m of the ice surface and a 360 MHz radar to identify the ice shelf base. We have identified internal layers that are continuous along flow from the grounding line to the ice shelf front. Based on layer continuity, we conclude that these layers must be the horizons between the continental ice of the outlet glaciers and snow accumulation once the ice is afloat. We use the Lagrangian change in thickness of these layers, after correcting for strain rates derived using modern day InSAR velocities, to estimate multidecadal averaged basal melt rates. This method provides a novel way to quantify basal melt, avoiding the confounding impacts of spatial and short-timescale variability in surface accumulation and firn densification processes. Our estimates show elevated basal melt rates (> -1m/yr) around Byrd and Mullock glaciers within 100 km from the ice shelf front. We also compare modern InSAR velocity derived strain rates with estimates from the comprehensive ground-based RIGGS observations during 1973-1978 to estimate the potential magnitude of

  11. Accumulation in coastal West Antarctic ice core records and the role of cyclone activity

    NASA Astrophysics Data System (ADS)

    Hosking, J. Scott; Fogt, Ryan; Thomas, Elizabeth R.; Moosavi, Vahid; Phillips, Tony; Coggins, Jack; Reusch, David

    2017-09-01

    Cyclones are an important component of Antarctic climate variability, yet quantifying their impact on the polar environment is challenging. We assess how cyclones which pass through the Bellingshausen Sea affect accumulation over Ellsworth Land, West Antarctica, where we have two ice core records. We use self-organizing maps (SOMs), an unsupervised machine learning technique, to group cyclones into nine SOM nodes differing by their trajectories (1980-2015). The annual frequency of cyclones associated with the first SOM node (SOM1, which generally originate from lower latitudes over the South Pacific Ocean) is significantly (p < 0.001) correlated with annual accumulation, with the highest seasonal correlations (p < 0.001) found during autumn. While significant (p < 0.01) increases in vertically integrated water vapor over the South Pacific Ocean coincide with this same group of cyclones, we find no indication that this has led to an increase in moisture advection into, nor accumulation over, Ellsworth Land over this short time period.

  12. Uneven onset and pace of ice-dynamical imbalance in the Amundsen Sea Embayment, West Antarctica

    NASA Astrophysics Data System (ADS)

    Konrad, Hannes; Gilbert, Lin; Cornford, Stephen L.; Payne, Antony; Hogg, Anna; Muir, Alan; Shepherd, Andrew

    2017-01-01

    We combine measurements acquired by five satellite altimeter missions to obtain an uninterrupted record of ice sheet elevation change over the Amundsen Sea Embayment, West Antarctica, since 1992. Using these data, we examine the onset of surface lowering arising through ice-dynamical imbalance, and the pace at which it has propagated inland, by tracking elevation changes along glacier flow lines. Surface lowering has spread slowest (<6 km/yr) along the Pope, Smith, and Kohler (PSK) Glaciers, due to their small extent. Pine Island Glacier (PIG) is characterized by a continuous inland spreading of surface lowering, notably fast at rates of 13 to 15 km/yr along tributaries draining the southeastern lobe, possibly due to basal conditions or tributary geometry. Surface lowering on Thwaites Glacier (THG) has been episodic and has spread inland fastest (10 to 12 km/yr) along its central flow lines. The current episodes of surface lowering started approximately 10 years before the first measurements on PSK, around 1990 on PIG, and around 2000 on THG. Ice-dynamical imbalance across the sector has therefore been uneven during the satellite record.

  13. Earth's Climate History from Glaciers and Ice Cores

    NASA Astrophysics Data System (ADS)

    Thompson, Lonnie

    2013-03-01

    Glaciers serve both as recorders and early indicators of climate change. Over the past 35 years our research team has recovered climatic and environmental histories from ice cores drilled in both Polar Regions and from low to mid-latitude, high-elevation ice fields. Those ice core -derived proxy records extending back 25,000 years have made it possible to compare glacial stage conditions in the Tropics with those in the Polar Regions. High-resolution records of δ18O (in part a temperature proxy) demonstrate that the current warming at high elevations in the mid- to lower latitudes is unprecedented for the last two millennia, although at many sites the early Holocene was warmer than today. Remarkable similarities between changes in the highland and coastal cultures of Peru and regional climate variability, especially precipitation, imply a strong connection between prehistoric human activities and regional climate. Ice cores retrieved from shrinking glaciers around the world confirm their continuous existence for periods ranging from hundreds to thousands of years, suggesting that current climatological conditions in those regions today are different from those under which these ice fields originated and have been sustained. The ongoing widespread melting of high-elevation glaciers and ice caps, particularly in low to middle latitudes, provides strong evidence that a large-scale, pervasive and, in some cases, rapid change in Earth's climate system is underway. Observations of glacier shrinkage during the 20th and 21st century girdle the globe from the South American Andes, the Himalayas, Kilimanjaro (Tanzania, Africa) and glaciers near Puncak Jaya, Indonesia (New Guinea). The history and fate of these ice caps, told through the adventure, beauty and the scientific evidence from some of world's most remote mountain tops, provide a global perspective for contemporary climate. NSF Paleoclimate Program

  14. Low-frequency radar sounder over Glaciers in Alaska, Greenland and Antarctica

    NASA Astrophysics Data System (ADS)

    Mouginot, J.; Rignot, E. J.; Gim, Y.; Kirchner, D. L.; Merritt, S.; Robison, W. T.

    2009-12-01

    Ice-thickness and basal layer topography measurements are needed to calculate fluxes through fast-flowing outlet glaciers in Greenland, Alaska, Patagonia and Antarctica. However, relatively high attenuation of radio waves by dielectric absorption and volume scattering from englacial water restrains detection of the bed through warm deep ice. Using a low-frequency (1-5 MHz) airborne radar, we have sounded outlet fast glaciers over Greenland (Store, Upernavik, Hellheim, …), East Antarctica (David, Mertz, Dibble, Byrd, …) and Alaska (Bering, Maslapina, Bagley, …). We will show that we detected the bed through temperate ice up to 1000m thick over Bering and Maslapina Glaciers and also point out difficulty in detecting bed of other Alaska glaciers due to off-nadir returns. We will also make direct comparison of this radar and previous airborne measurements in Greenland and Antarctica in order to discuss a potential improvement of bedrock detectability in temperate ice.

  15. Evaluation of Ice sheet evolution and coastline changes from 1960s in Amery Ice Shelf using multi-source remote sensing images

    NASA Astrophysics Data System (ADS)

    Qiao, G.; Ye, W.; Scaioni, M.; Liu, S.; Feng, T.; Liu, Y.; Tong, X.; Li, R.

    2013-12-01

    Global change is one of the major challenges that all the nations are commonly facing, and the Antarctica ice sheet changes have been playing a critical role in the global change research field during the past years. Long time-series of ice sheet observations in Antarctica would contribute to the quantitative evaluation and precise prediction of the effects on global change induced by the ice sheet, of which the remote sensing technology would make critical contributions. As the biggest ice shelf and one of the dominant drainage systems in East Antarctic, the Amery Ice Shelf has been making significant contributions to the mass balance of the Antarctic. Study of Amery Ice shelf changes would advance the understanding of Antarctic ice shelf evolution as well as the overall mass balance. At the same time, as one of the important indicators of Antarctica ice sheet characteristics, coastlines that can be detected from remote sensing imagery can help reveal the nature of the changes of ice sheet evolution. Most of the scientific research on Antarctica with satellite remote sensing dated from 1970s after LANDSAT satellite was brought into operation. It was the declassification of the cold war satellite reconnaissance photographs in 1995, known as Declassified Intelligence Satellite Photograph (DISP) that provided a direct overall view of the Antarctica ice-sheet's configuration in 1960s, greatly extending the time span of Antarctica surface observations. This paper will present the evaluation of ice-sheet evolution and coastline changes in Amery Ice Shelf from 1960s, by using multi-source remote sensing images including the DISP images and the modern optical satellite images. The DISP images scanned from negatives were first interior-oriented with the associated parameters, and then bundle block adjustment technology was employed based on the tie points and control points, to derive the mosaic image of the research region. Experimental results of coastlines generated

  16. High Resolution Continuous Flow Analysis System for Polar Ice Cores

    NASA Astrophysics Data System (ADS)

    Dallmayr, Remi; Azuma, Kumiko; Yamada, Hironobu; Kjær, Helle Astrid; Vallelonga, Paul; Azuma, Nobuhiko; Takata, Morimasa

    2014-05-01

    In the last decades, Continuous Flow Analysis (CFA) technology for ice core analyses has been developed to reconstruct the past changes of the climate system 1), 2). Compared with traditional analyses of discrete samples, a CFA system offers much faster and higher depth resolution analyses. It also generates a decontaminated sample stream without time-consuming sample processing procedure by using the inner area of an ice-core sample.. The CFA system that we have been developing is currently able to continuously measure stable water isotopes 3) and electrolytic conductivity, as well as to collect discrete samples for the both inner and outer areas with variable depth resolutions. Chemistry analyses4) and methane-gas analysis 5) are planned to be added using the continuous water stream system 5). In order to optimize the resolution of the current system with minimal sample volumes necessary for different analyses, our CFA system typically melts an ice core at 1.6 cm/min. Instead of using a wire position encoder with typical 1mm positioning resolution 6), we decided to use a high-accuracy CCD Laser displacement sensor (LKG-G505, Keyence). At the 1.6 cm/min melt rate, the positioning resolution was increased to 0.27mm. Also, the mixing volume that occurs in our open split debubbler is regulated using its weight. The overflow pumping rate is smoothly PID controlled to maintain the weight as low as possible, while keeping a safety buffer of water to avoid air bubbles downstream. To evaluate the system's depth-resolution, we will present the preliminary data of electrolytic conductivity obtained by melting 12 bags of the North Greenland Eemian Ice Drilling (NEEM) ice core. The samples correspond to different climate intervals (Greenland Stadial 21, 22, Greenland Stadial 5, Greenland Interstadial 5, Greenland Interstadial 7, Greenland Stadial 8). We will present results for the Greenland Stadial -8, whose depths and ages are between 1723.7 and 1724.8 meters, and 35.520 to

  17. Landscape evolution of Antarctica

    USGS Publications Warehouse

    Jamieson, S.S.R.; Sugden, D.E.

    2007-01-01

    shelf before retreating to its present dimensions at ~13.5 Ma. Subsequent changes in ice extent have been forced mainly by sea-level change. Weathering rates of exposed bedrock have been remarkably slow at high elevations around the margin of East Antarctica under the hyperarid polar climate of the last ~13.5 Ma, offering potential for a long quantitative record of ice-sheet evolution with techniques such as cosmogenic isotope analysis

  18. Larsen Ice Shelf, Antarctica

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Warmer surface temperatures over just a few months in the Antarctic can splinter an ice shelf and prime it for a major collapse, NASA and university scientists report in the latest issue of the Journal of Glaciology. Using satellite images of tell-tale melt water on the ice surface and a sophisticated computer simulation of the motions and forces within an ice shelf, the scientists demonstrated that added pressure from surface water filling crevasses can crack the ice entirely through. The process can be expected to become more widespread if Antarctic summer temperatures increase. This true-color image from Landsat 7, acquired on February 21, 2000, shows pools of melt water on the surface of the Larsen Ice Shelf, and drifting icebergs that have split from the shelf. The upper image is an overview of the shelf's edge, while the lower image is displayed at full resolution of 30 meters (98 feet) per pixel. The labeled pond in the lower image measures roughly 1.6 by 1.6 km (1.0 x 1.0 miles). Full text of Press Release More Images and Animations Image courtesy Landsat 7 Science Team and NASA GSFC

  19. The 1500m South Pole Ice Core: Recovering a 40 Ka Environmental Record

    NASA Technical Reports Server (NTRS)

    Casey, Kimberly Ann; Neumann, Thomas Allen; Fudge, T. J.; Neumann, T. A.; Steig, E. J.; Cavitte, M. G. P.; Blankenship, D. D.

    2014-01-01

    Supported by the US National Science Foundation, a new 1500 m, approximately 40 ka old ice core will be recovered from South Pole during the 2014/15 and 2015/16 austral summer seasons using the new US Intermediate Depth Drill. The combination of low temperatures, relatively high accumulation rates and low impurity concentrations at South Pole will yield detailed records of ice chemistry and trace atmospheric gases. The South Pole ice core will provide a climate history record of a unique area of the East Antarctic plateau that is partly influenced by weather systems that cross the West Antarctic ice sheet. The ice at South Pole flows at approximately 10m a(exp-1) and the South Pole ice-core site is a significant distance from an ice divide. Therefore, ice recovered at depth originated progressively farther upstream of the coring site. New ground-penetrating radar collected over the drill site location shows no anthropogenic influence over the past approximately 50 years or upper 15 m. Depth-age scale modeling results show consistent and plausible annual-layer thicknesses and accumulation rate histories, indicating that no significant stratigraphic disturbances exist in the upper 1500m near the ice-core drill site.

  20. Facility for testing ice drills

    NASA Astrophysics Data System (ADS)

    Nielson, Dennis L.; Delahunty, Chris; Goodge, John W.; Severinghaus, Jeffery P.

    2017-05-01

    The Rapid Access Ice Drill (RAID) is designed for subsurface scientific investigations in Antarctica. Its objectives are to drill rapidly through ice, to core samples of the transition zone and bedrock, and to leave behind a borehole observatory. These objectives required the engineering and fabrication of an entirely new drilling system that included a modified mining-style coring rig, a unique fluid circulation system, a rod skid, a power unit, and a workshop with areas for the storage of supplies and consumables. An important milestone in fabrication of the RAID was the construction of a North American Test (NAT) facility where we were able to test drilling and fluid processing functions in an environment that is as close as possible to that expected in Antarctica. Our criteria for site selection was that the area should be cold during the winter months, be located in an area of low heat flow, and be at relatively high elevation. We selected a site for the facility near Bear Lake, Utah, USA. The general design of the NAT well (NAT-1) started with a 27.3 cm (10.75 in.) outer casing cemented in a 152 m deep hole. Within that casing, we hung a 14 cm (5.5 in.) casing string, and, within that casing, a column of ice was formed. The annulus between the 14 and 27.3 cm casings provided the path for circulation of a refrigerant. After in-depth study, we chose to use liquid CO2 to cool the hole. In order to minimize the likelihood of the casing splitting due to the volume increase associated with freezing water, the hole was first cooled and then ice was formed in increments from the bottom upward. First, ice cubes were placed in the inner liner and then water was added. Using this method, a column of ice was incrementally prepared for drilling tests. The drilling tests successfully demonstrated the functioning of the RAID system. Reproducing such a facility for testing of other ice drilling systems could be advantageous to other research programs in the future.

  1. How Will Sea Ice Loss Affect the Greenland Ice Sheet? On the Puzzling Features of Greenland Ice-Core Isotopic Composition

    NASA Technical Reports Server (NTRS)

    Pausata, Francesco S. R.; Legrande, Allegra N.; Roberts, William H. G.

    2016-01-01

    The modern cryosphere, Earth's frozen water regime, is in fast transition. Greenland ice cores show how fast theses changes can be, presenting evidence of up to 15 C warming events over timescales of less than a decade. These events, called Dansgaard/Oeschger (D/O) events, are believed to be associated with rapid changes in Arctic sea ice, although the underlying mechanisms are still unclear. The modern demise of Arctic sea ice may, in turn, instigate abrupt changes on the Greenland Ice Sheet. The Arctic Sea Ice and Greenland Ice Sheet Sensitivity (Ice2Ice Chttps://ice2ice.b.uib.noD) initiative, sponsored by the European Research Council, seeks to quantify these past rapid changes to improve our understanding of what the future may hold for the Arctic. Twenty scientists gathered in Copenhagen as part of this initiative to discuss the most recent observational, technological, and model developments toward quantifying the mechanisms behind past climate changes in Greenland. Much of the discussion focused on the causes behind the changes in stable water isotopes recorded in ice cores. The participants discussed sources of variability for stable water isotopes and framed ways that new studies could improve understanding of modern climate. The participants also discussed how climate models could provide insights into the relative roles of local and nonlocal processes in affecting stable water isotopes within the Greenland Ice Sheet. Presentations of modeling results showed how a change in the source or seasonality of precipitation could occur not only between glacial and modern climates but also between abrupt events. Recent fieldwork campaigns illustrate an important role of stable isotopes in atmospheric vapor and diffusion in the final stable isotope signal in ice. Further, indications from recent fieldwork campaigns illustrate an important role of stable isotopes in atmospheric vapor and diffusion in the final stable isotope signal in ice. This feature complicates

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

    NASA Technical Reports Server (NTRS)

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

    2017-01-01

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

  3. Variation of Accumulation Rates Over the Last Eight Centuries on the East Antarctic Plateau Derived from Volcanic Signals in Ice Cores

    NASA Technical Reports Server (NTRS)

    Anschuetz, H.; Sinisalo, A.; Isaksson, E.; McConnell, J. R.; Hamran, S.-E.; Bisiaux, M. M.; Pasteris, D.; Neumann, T. A.; Winther, J.-G.

    2011-01-01

    Volcanic signatures in ice-core records provide an excellent means to date the cores and obtain information about accumulation rates. From several ice cores it is thus possible to extract a spatio-temporal accumulation pattern. We show records of electrical conductivity and sulfur from firn cores from the Norwegian-USA scientific traverse during the International Polar Year 2007-2009 (IPY) through East Antarctica. Major volcanic eruptions are identified and used to assess century-scale accumulation changes. The largest changes seem to occur in the most recent decades with accumulation over the period 1963- 2007/08 being up to 25 % different from the long-term record. There is no clear overall trend, some sites show an increase in accumulation over the period 1963 to present while others show a decrease. Almost all of the sites above 3200 m above sea level (asl) suggest a decrease. These sites also show a significantly lower accumulation value than large-scale assessments both for the period 1963 to present and for the long-term mean at the respective drill sites. The spatial accumulation distribution is influenced mainly by elevation and distance to the ocean (continentality), as expected. Ground-penetrating radar data around the drill sites show a spatial variability within 10-20 % over several tens of kilometers, indicating that our drill sites are well representative for the area around them. Our results are important for large-scale assessments of Antarctic mass balance and model validation.

  4. Satellite imagery of the onset of streaming flow of ice streams C and D, West Antarctica

    USGS Publications Warehouse

    Hodge, S.M.; Doppelhammer, S.K.

    1996-01-01

    Five overlapping Landsat multispectral scanner satellite images of the interior of the West Antarctic ice sheet were enhanced with principal component analysis, high-pass filtering, and linear contrast stretching and merged into a mosaic by aligning surface features in the overlap areas. The mosaic was registered to geodetic coordinates, to an accuracy of about 1 km, using the five scene centers as control points. The onset of streaming flow of two tributaries of ice stream C and one tributary of ice stream D is visible in the mosaic. The onset appears to occur within a relatively short distance, less than the width of the ice stream, typically at a subglacial topographic feature such as a step or ridge. The ice streams extend farther up into the interior than previously mapped. Ice stream D starts about 150 km from the ice divide, at an altitude of about 1500 m, approximately halfway up the convex-upward dome shape of the interior ice sheet. Ice stream D is relatively much longer than ice stream C, possibly because ice stream D is currently active whereas ice stream C is currently inactive. The grounded portion of the West Antarctic ice sheet is perhaps best conceptualized as an ice sheet in which ice streams are embedded over most of its area, with slow moving ice converging into fast moving ice streams in a widely distributed pattern, much like that of streams and rivers in a hydrologic basin. A relic margin appears to parallel most of the south margin of the tributary of ice stream D, separated from the active shear margin by about 10 km or less for a distance of over 200 km. This means there is now evidence for recent changes having occurred in three of the five major ice streams which drain most of West Antarctica (B, C, and D), two of which (B and D) are currently active.

  5. Using Multiple Cosmogenic Nuclides to Investigate Ice Elevation Changes in the Ellsworth Mountains, Antarctica

    NASA Astrophysics Data System (ADS)

    Marrero, Shasta; Hein, Andy; Sugden, David; Woodward, John; Dunning, Stuart; Freeman, Stewart; Shanks, Richard

    2015-04-01

    Well-dated geologic data points provide important indicators that can be used for the reconstruction of ice sheet dynamics and as constraints in ice sheet models predicting future change. Cosmogenic nuclides, which accumulate in rocks exposed at the earth's surface, can be used to directly date the exposure age of the rock surfaces that have been created through glacial erosion or deposition. The technique requires a detailed understanding of the local geomorphology as well as awareness of the post-depositional processes that may affect the interpretation of exposure ages. Surface exposure ages (10Be, 26Al, 21Ne, and 36Cl) from local limestone bedrock and other glacially deposited exotic lithologies provide a history spanning from 0 to more than 1 million years in the Patriot, Independence, and Marble Hills in the southern Ellsworth Mountains, Antarctica. Using the new surface exposure ages combined with geomorphological mapping, we will discuss the implications for the glacial history of the southern Ellsworth Mountains.

  6. Clouds and Ice of the Lambert-Amery System, East Antarctica

    NASA Technical Reports Server (NTRS)

    2002-01-01

    These views from the Multi-angle Imaging SpectroRadiometer (MISR) illustrate ice surface textures and cloud-top heights over the Amery Ice Shelf/Lambert Glacier system in East Antarctica on October 25, 2002.

    The left-hand panel is a natural-color view from MISR's downward-looking (nadir) camera. The center panel is a multi-angular composite from three MISR cameras, in which color acts as a proxy for angular reflectance variations related to texture. Here, data from the red-band of MISR's 60o forward-viewing, nadir and 60o backward-viewing cameras are displayed as red, green and blue, respectively. With this display technique, surfaces which predominantly exhibit backward-scattering (generally rough surfaces) appear red/orange, while surfaces which predominantly exhibit forward-scattering (generally smooth surfaces) appear blue. Textural variation for both the grounded and sea ice are apparent. The red/orange pixels in the lower portion of the image correspond with a rough and crevassed region near the grounding zone, that is, the area where the Lambert and four other smaller glaciers merge and the ice starts to float as it forms the Amery Ice Shelf. In the natural-color view, this rough ice is spectrally blue in color.

    Clouds exhibit both forward and backward-scattering properties in the middle panel and thus appear purple, in distinct contrast with the underlying ice and snow. An additional multi-angular technique for differentiating clouds from ice is shown in the right-hand panel, which is a stereoscopically derived height field retrieved using automated pattern recognition involving data from multiple MISR cameras. Areas exhibiting insufficient spatial contrast for stereoscopic retrieval are shown in dark gray. Clouds are apparent as a result of their heights above the surface terrain. Polar clouds are an important factor in weather and climate. Inadequate characterization of cloud properties is currently responsible for large uncertainties in climate

  7. A Sled-Mounted Vibroseis Seismic Source for Geological Studies in Antarctica

    NASA Astrophysics Data System (ADS)

    Speece, M. A.; Luyendyk, B. P.; Harwood, D. M.; Powell, R. D.; Wilson, D. S.; Pekar, S. F.; Tulaczyk, S. M.; Rack, F. R.

    2013-12-01

    Given the success of recent vibrator seismic source (vibroseis) tests in Antarctica, we propose the purchase of a large vibroseis for dedicated use by United States Antarctic Program (USAP) projects in Antarctica. Long seismic reflection profiles across Antarctica can be accomplished efficiently by pulling a sled-mounted vibrator that in turn pulls a snow streamer of gimbaled geophones. A baseplate or pad in the center of the sled will be lowered to the ground and support most of the weight of the vibrator assembly while an actuator vibrates the ground at each source location. The vibroseis will be moved to remote locations using over-ice/snow traverses given the increased reliance on traversing for supplying remote sites in Antarctica. Total vibrator hold-down weight when fully assembled will be ~66,000 lbs. Other design features include a 475 HP Caterpillar C15 diesel engine for the hydraulic power unit. The new vibrator will use an INOVA P-wave vibrator system: new Model PLS-362 actuator with up to 60,000 lbs of peak force and frequency limit of 5 Hz to 250Hz. Antarctic research objectives that could be impacted by the use of a vibrator include: (1) mapping of sub-ice stratigraphic sequences for drilling for paleoclimate information, e.g. the deep sedimentary basins of West Antarctica (Ross and Ronne-Filchner Ice Shelves and related divides); (2) correlating offshore and onshore seismic data and complementing airborne geophysical surveys to help determine Antarctica's geologic history; (3) identifying ice-bedrock interface properties and exploring grounding-line processes for ice dynamics; (4) exploring subglacial lakes and water-routing systems; and, (5) investigating the physical properties of ice sheets. An Antarctic Vibroseis Advisory Committee (AVAC) will promote the use of the vibroseis capability among Antarctic geophysical, geological, glaciological and related scientists and groups by encouraging and facilitating the development and submission of

  8. A tuff cone erupted under frozen-bed ice (northern Victoria Land, Antarctica): linking glaciovolcanic and cosmogenic nuclide data for ice sheet reconstructions

    NASA Astrophysics Data System (ADS)

    Smellie, J. L.; Rocchi, S.; Johnson, J. S.; Di Vincenzo, G.; Schaefer, J. M.

    2018-01-01

    The remains of a small volcanic centre are preserved on a thin bedrock ridge at Harrow Peaks, northern Victoria Land, Antarctica. The outcrop is interpreted as a monogenetic tuff cone relict formed by a hydrovolcanic (phreatomagmatic) eruption of mafic magma at 642 ± 20 ka (by 40Ar-39Ar), corresponding to the peak of the Marine Isotope Stage 16 (MIS16) glacial. Although extensively dissected and strewn with glacial erratics, the outcrop shows no evidence for erosion by ice. From interpretation of the lithofacies and eruptive mechanisms, the weight of the evidence suggests that eruptions took place under a cold-based (frozen-bed) ice sheet. This is the first time that a tuff cone erupted under cold ice has been described. The most distinctive feature of the lithofacies is the dominance of massive lapilli tuff rich in fine ash matrix and abraded lapilli. The lack of stratification is probably due to repeated eruption through a conduit blasted through the ice covering the vent. The ice thickness is uncertain but it might have been as little as 100 m and the preserved tephra accumulated mainly as a crater (or ice conduit) infill. The remainder of the tuff cone edifice was probably deposited supraglacially and underwent destruction by ice advection and, particularly, collapse during a younger interglacial. Dating using 10Be cosmogenic exposure of granitoid basement erratics indicates that the erratics are unrelated to the eruptive period. The 10Be ages suggest that the volcanic outcrop was most recently exposed by ice decay at c. 20.8 ± 0.8 ka (MIS2) and the associated ice was thicker than at 642 ka and probably polythermal rather than cold-based, which is normally assumed for the period.

  9. Geothermal Heat Flux: Linking Deep Earth's Interior and the Dynamics of Large-Scale Ice Sheets

    NASA Astrophysics Data System (ADS)

    Rogozhina, Irina; Vaughan, Alan

    2014-05-01

    Regions covered by continental-scale ice sheets have the highest degree of uncertainty in composition and structure of the crust and lithospheric mantle, compounded by the poorest coverage on Earth of direct heat flow measurements. In addition to challenging conditions that make direct measurements and geological survey difficult Greenland and Antarctica are known to be geologically complex. Antarctica in particular is marked by two lithospherically distinct zones. In contrast to young and thin lithosphere of West Antarctica, East Antarctica is a collage of thick Precambrian fragments of Gondwana and earlier supercontinents. However, recent observations and modeling studies have detected large systems of subglacial lakes extending beneath much of the East Antarctic ice sheet base that have been linked to anomalously elevated heat flow. Outcrop samples from the rift margin with Australia (Prydz Bay) have revealed highly radiogenic Cambrian granite intrusives that are implicated in regional increase of crustal heat flux by a factor of two to three compared to the estimated continental background. Taken together, these indicate high variability of heat flow and properties of rocks across Antarctica. Similar conclusions have been made based on direct measurements and observations of the Greenland ice sheet. Airborne ice-penetrating radar and deep ice core projects show very high rates of basal melt for parts of the ice sheet in northern and central Greenland that have been explained by abnormally high heat flux. Archaean in age, the Greenland lithosphere was significantly reworked during the Early Proterozoic. In this region, the interpretation of independent geophysical data is complicated by Proterozoic and Phanerozoic collision zones, compounded by strong thermochemical effects of rifting along the western and eastern continental margins between 80 and 25 million years ago. In addition, high variability of heat flow and thermal lithosphere structure in central

  10. Ross Ice Shelf, Antarctic Ice and Clouds

    NASA Technical Reports Server (NTRS)

    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.

  11. Allan Hills Pleistocene Ice Project (PIP)

    NASA Astrophysics Data System (ADS)

    Kurbatov, A.; Brook, E.; Campbell, S. W.; Conway, H.; Dunbar, N. W.; Higgins, J. A.; Iverson, N. A.; Kehrl, L. M.; McIntosh, W. C.; Spaulding, N. E.; Yan, Y.; Mayewski, P. A.

    2016-12-01

    A major international effort to identify at least 1.5 Ma old ice for paleoclimate reconstructions has successfully resulted in the selection of several potential drill sites in East Antarctica. At this point it is indisputable that the Antarctic ice sheet captures a continuous envinronmental record of the Earth that spans the Mid Pleistocene Transition (MPT). In addition to traditional ice coring approaches, the oldest ice can also be recovered in Antarctic Blue Ice Areas (BIA). We have already successfully demonstrated that the Allan Hills (AH) BIA captures a regional climate signal and robust record of 1Ma atmosphere that can be studied with a relatively uncomplicated logistical imprint and essentially unlimited sampling volume. The attractiveness of unlimited sampling of known age ice is the basis for the "ice park" concept proposed earlier by our research team. The idea is that, once the age of ice exposed along the flow line at the surface of BIA is mapped, it could be sampled for numerous research projects as needed. Here we propose an intermediate ( 1,150 m deep) ice core drill site, located only 240 km away from McMurdo base that will help to develop a, continuous, high quality regional paleoclimate record that is at least 1Ma old. We will introduce and discuss the glaciological settings, paleoclimate signals and possible limitations and advantages of the 1 Ma AH BIA regional paleoclimate record. The research was funded by NSF Division of Polar Programs.

  12. Recent Antarctic Peninsula warming relative to Holocene climate and ice-shelf history.

    PubMed

    Mulvaney, Robert; Abram, Nerilie J; Hindmarsh, Richard C A; Arrowsmith, Carol; Fleet, Louise; Triest, Jack; Sime, Louise C; Alemany, Olivier; Foord, Susan

    2012-09-06

    Rapid warming over the past 50 years on the Antarctic Peninsula is associated with the collapse of a number of ice shelves and accelerating glacier mass loss. In contrast, warming has been comparatively modest over West Antarctica and significant changes have not been observed over most of East Antarctica, suggesting that the ice-core palaeoclimate records available from these areas may not be representative of the climate history of the Antarctic Peninsula. Here we show that the Antarctic Peninsula experienced an early-Holocene warm period followed by stable temperatures, from about 9,200 to 2,500 years ago, that were similar to modern-day levels. Our temperature estimates are based on an ice-core record of deuterium variations from James Ross Island, off the northeastern tip of the Antarctic Peninsula. We find that the late-Holocene development of ice shelves near James Ross Island was coincident with pronounced cooling from 2,500 to 600 years ago. This cooling was part of a millennial-scale climate excursion with opposing anomalies on the eastern and western sides of the Antarctic Peninsula. Although warming of the northeastern Antarctic Peninsula began around 600 years ago, the high rate of warming over the past century is unusual (but not unprecedented) in the context of natural climate variability over the past two millennia. The connection shown here between past temperature and ice-shelf stability suggests that warming for several centuries rendered ice shelves on the northeastern Antarctic Peninsula vulnerable to collapse. Continued warming to temperatures that now exceed the stable conditions of most of the Holocene epoch is likely to cause ice-shelf instability to encroach farther southward along the Antarctic Peninsula.

  13. Late Oligocene glacimarine sedimentation of the central Ross Sea and implications for the evolution of the West Antarctic Ice Sheet

    NASA Astrophysics Data System (ADS)

    Kraus, C.; Mckay, R. M.; Naish, T.; Levy, R. H.; Kulhanek, D. K.

    2015-12-01

    Today the West Antarctic Ice Sheet (WAIS) is grounded mostly below sea level, making it sensitive to oceanic temperature and circulation changes. However, recent reconstructions of the Cenozoic bedrock topographic evolution of West Antarctica have suggested that the West Antarctic Ice Sheet (WAIS) may have first formed as a terrestrial ice sheet at the Eocene-Oligocene boundary (33 Ma), when there was up to 20% more land area in West Antarctica. At some point during the Oligocene or Miocene (23 - 5 Ma) vast areas of West Antarctica became an over-deepened marine-based continental shelf, as is observed today. The evolution of the WAIS through this transition is largely unconstrained, but as atmospheric CO2 fluctuated between 600 and 200 ppm over the past 34 Ma, determining the development of a marine-based WAIS is critical in the context of understanding the sensitivity of ice sheet systems to environmental change. Our research re-examines the sediment cores recovered from the central Ross Sea, a principal drainage area of the WAIS, at Deep Sea Drilling Project Site 270 (77°26.48'S, 178°30.19'W). These cores contain a glacimarine sequence of late Oligocene age (28 - 23.1 Ma). Sedimentological (visual core description, facies, grain size analysis), geochemical (x-ray fluorescence), geophysical (seismic) techniques, and physical properties (magnetic susceptibility) are used to construct a sedimentation model of this sequence, in order to track the late Oligocene evolution of the WAIS. The late Oligocene warming (25 - 23 Ma) is examined in detail because proximal Antarctic geological records of ice sheet extent, proxy environmental data, and atmospheric CO2 appear to be at odds with the composite δ18O record of global temperature and ice volume at this time. Moreover, our research provides insights into the sensitivity of marine-based ice sheets, and supports the hypothesis that they are unstable above a CO2 threshold of 400 ppm. Our preliminary results also

  14. Visual-Stratigraphic Dating of the GISP2 Ice Core: Basis, Reproducibility, and Application

    NASA Technical Reports Server (NTRS)

    Alley, R. B.; Shuman, C. A.; Meese, D. A.; Gow, A. J.; Taylor, K. C.; Cuffey, K. M.; Fitzpatrick, J. J.; Grootes, P. M.; Zielinski, G. A.; Ram, M.; hide

    1997-01-01

    Annual layers are visible in the Greenland Ice Sheet Project 2 ice core from central Greenland, allowing rapid dating of the core. Changes in bubble and grain structure caused by near-surface, primarily summertime formation of hoar complexes provide the main visible annual marker in the Holocene, and changes in "cloudiness" of the ice correlated with dustiness mark Wisconsinan annual cycles; both markers are evident and have been intercalibrated in early Holocene ice. Layer counts are reproducible between different workers and for one worker at different times, with 1% error over century-length times in the Holocene. Reproducibility is typically 5% in Wisconsinan ice-age ice and decreases with increasing age and depth. Cumulative ages from visible stratigraphy are not significantly different from independent ages of prominent events for ice older than the historical record and younger than approximately 50,000 years. Visible observations are not greatly degraded by "brittle ice" or many other core-quality problems, allowing construction of long, consistently sampled time series. High accuracy requires careful study of the core by dedicated observers.

  15. Visual-stratigraphic dating of the GISP2 ice core: Basis, reproducibility, and application

    NASA Astrophysics Data System (ADS)

    Alley, R. B.; Shuman, C. A.; Meese, D. A.; Gow, A. J.; Taylor, K. C.; Cuffey, K. M.; Fitzpatrick, J. J.; Grootes, P. M.; Zielinski, G. A.; Ram, M.; Spinelli, G.; Elder, B.

    1997-11-01

    Annual layers are visible in the Greenland Ice Sheet Project 2 ice core from central Greenland, allowing rapid dating of the core. Changes in bubble and grain structure caused by near-surface, primarily summertime formation of hoar complexes provide the main visible annual marker in the Holocene, and changes in "cloudiness" of the ice correlated with dustiness mark Wisconsinan annual cycles; both markers are evident and have been intercalibrated in early Holocene ice. Layer counts are reproducible between different workers and for one worker at different times, with 1% error over century-length times in the Holocene. Reproducibility is typically 5% in Wisconsinan ice-age ice and decreases with increasing age and depth. Cumulative ages from visible stratigraphy are not significantly different from independent ages of prominent events for ice older than the historical record and younger than approximately 50,000 years. Visible observations are not greatly degraded by "brittle ice" or many other core-quality problems, allowing construction of long, consistently sampled time series. High accuracy requires careful study of the core by dedicated observers.

  16. Glacio-isostasy and Glacial Ice Load at Law Dome, Wilkes Land, East Antarctica

    NASA Astrophysics Data System (ADS)

    Goodwin, Ian D.; Zweck, Christopher

    2000-05-01

    The Holocene sea-level high stand or "marine limit" in Wilkes Land, East Antarctica, reached ˜30 m above present sea level at a few dispersed sites. The most detailed marine limit data have been recorded for the Windmill Islands and Budd Coast at the margin of the Law Dome ice cap, a dome of the East Antarctic Ice Sheet (EAIS). Relative sea-level lowering of 30 m and the associated emergence of the Windmill Islands have occurred since 6900 14C (corr.) yr B.P. Numerical modeling of the Earth's rheology is used to determine the glacio-isostatic component of the observed relative sea-level lowering. Glaciological evidence suggests that most of EAIS thickening occurred around its margin, with expansion onto the continental shelf. Consequently, a regional ice history for the last glacial maximum (LGM) was applied in the glacio-isostatic modeling to test whether the observed relative sea-level lowering was primarily produced by regional ice-sheet changes. The results of the modeling indicate that the postglacial (13,000 to 8000 14C yr B.P) removal of an ice load of between 770 and 1000 m from around the margin of the Law Dome and adjacent EAIS have produced the observed relative sea-level lowering. Such an additional ice load would have been associated with a 40- to 65-km expansion of the Law Dome to near the continental shelf break, together with a few hundred meters of ice thickening on the adjoining coastal slope of the EAIS up to 2000 m elevation. Whereas the observed changes in relative sea level are shown to be strongly influenced by regional ice sheet changes, the glacio-isostatic response at the Windmill Islands results from a combination of regional and, to a lesser extent, Antarctic-wide effects. The correspondence between the Holocene relative sea-level lowering interpreted at the margin of the Law Dome and the lowering interpreted along the remainder of the Wilkes Land and Oates Land coasts (105°-160° E) suggests that a similar ice load of up to 1000 m

  17. Wave-Ice interaction in the Marginal Ice Zone: Toward a Wave-Ocean-Ice Coupled Modeling System

    DTIC Science & Technology

    2015-09-30

    MIZ using WW3 (3 frequency bins, ice retreat in August and ice advance in October); Blue (solid): Based on observations near Antarctica by Meylan...1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Wave- Ice interaction in the Marginal Ice Zone: Toward a...Wave-Ocean- Ice Coupled Modeling System W. E. Rogers Naval Research Laboratory, Code 7322 Stennis Space Center, MS 39529 phone: (228) 688-4727

  18. High-resolution mineral dust and sea ice proxy records from the Talos Dome ice core

    NASA Astrophysics Data System (ADS)

    Schüpbach, S.; Federer, U.; Kaufmann, P. R.; Albani, S.; Barbante, C.; Stocker, T. F.; Fischer, H.

    2013-12-01

    In this study we report on new non-sea salt calcium (nssCa2+, mineral dust proxy) and sea salt sodium (ssNa+, sea ice proxy) records along the East Antarctic Talos Dome deep ice core in centennial resolution reaching back 150 thousand years (ka) before present. During glacial conditions nssCa2+ fluxes in Talos Dome are strongly related to temperature as has been observed before in other deep Antarctic ice core records, and has been associated with synchronous changes in the main source region (southern South America) during climate variations in the last glacial. However, during warmer climate conditions Talos Dome mineral dust input is clearly elevated compared to other records mainly due to the contribution of additional local dust sources in the Ross Sea area. Based on a simple transport model, we compare nssCa2+ fluxes of different East Antarctic ice cores. From this multi-site comparison we conclude that changes in transport efficiency or atmospheric lifetime of dust particles do have a minor effect compared to source strength changes on the large-scale concentration changes observed in Antarctic ice cores during climate variations of the past 150 ka. Our transport model applied on ice core data is further validated by climate model data. The availability of multiple East Antarctic nssCa2+ records also allows for a revision of a former estimate on the atmospheric CO2 sensitivity to reduced dust induced iron fertilisation in the Southern Ocean during the transition from the Last Glacial Maximum to the Holocene (T1). While a former estimate based on the EPICA Dome C (EDC) record only suggested 20 ppm, we find that reduced dust induced iron fertilisation in the Southern Ocean may be responsible for up to 40 ppm of the total atmospheric CO2 increase during T1. During the last interglacial, ssNa+ levels of EDC and EPICA Dronning Maud Land (EDML) are only half of the Holocene levels, in line with higher temperatures during that period, indicating much reduced sea

  19. Ice Mass Change in Greenland and Antarctica Between 1993 and 2013 from Satellite Gravity Measurements

    NASA Technical Reports Server (NTRS)

    Talpe, Matthieu J.; Nerem, R. Steven; Forootan, Ehsan; Schmidt, Michael; Lemoine, Frank G.; Enderlin, Ellyn M.; Landerer, Felix W.

    2017-01-01

    We construct long-term time series of Greenland and Antarctic ice sheet mass change from satellite gravity measurements. A statistical reconstruction approach is developed based on a principal component analysis (PCA) to combine high-resolution spatial modes from the Gravity Recovery and Climate Experiment (GRACE) mission with the gravity information from conventional satellite tracking data. Uncertainties of this reconstruction are rigorously assessed; they include temporal limitations for short GRACE measurements, spatial limitations for the low-resolution conventional tracking data measurements, and limitations of the estimated statistical relationships between low- and high-degree potential coefficients reflected in the PCA modes. Trends of mass variations in Greenland and Antarctica are assessed against a number of previous studies. The resulting time series for Greenland show a higher rate of mass loss than other methods before 2000, while the Antarctic ice sheet appears heavily influenced by interannual variations.

  20. Climatic change and evaporative processes in the development of Common Era hypersaline lakes, East Antarctica: A study of Lake Suribati

    NASA Astrophysics Data System (ADS)

    Nakashima, H.; Seto, K.; Katsuki, K.; Kaneko, H.; yamada, K.; Imura, S.; Dettman, D. L.

    2011-12-01

    The Antarctic continent was uplifted by glacioisostatic rebound due to the regression of ice sheets after the last glacial period. Today's saline lakes were formed in shallow basins originally below sea level. Antarctic hypersaline lakes are formed by concentration of isolated seawater bodies as affected by recent climate change. Many saline lakes are found in the ice-free area of the Soya coast, East Antarctica. Lake Suribati is located in Sukarvsnes on the Soya coast. It is a hypersaline lake with maximum salinity ~200 psu, and an observable stable halocline at 7~12m depth. This study uses Lake Suribati sediment core Sr4C-01, collected by the 46th Japanese Antarctica Research Expedition, to examine the relationship of climatic change to evaporative processes and solute concentration in Lake Suribati in the Common Era. Sr4C-01 core was collected at 9.53m water depth in Lake Suribati in 2005 (core length is 63cm). This core primarily consists of black mud and laminated black organic mud. In the interval from 10 to 24cm below the sediment surface evaporite crystals occur. The age of the Sr4C-01 core bottom is estimated to be ~3,500 cal yrs BP, based on AMS carbon-14 dating at 6 core horizons. The evaporite crystals were indentified as aragonite based on XRD. Total inorganic carbon (TIC) content is low, around 0.5%, throughout the Sr4C-01 core, with higher values, approximately 1~4%, in two intervals, 57~52cm and 29~10cm core depth. Variation in CaO content tracks TIC content. We suggest that synchronous change in CaO and TIC contents indicate the vertical change in the amount of aragonite. Two intervals of evaporite precipition imply two intervals of evaporation and concentration of lake water. Hypersaline lake conditions did not occur soon after the isolation from the sea, rather these occurred under repeated concentration and dilution of lake water. Dilution of saline lake water could occur through the inflow of melt water from local snow or ice, indicating a warm

  1. Heating the Ice-Covered Lakes of the McMurdo Dry Valleys, Antarctica - Decadal Trends in Heat Content, Ice Thickness, and Heat Exchange

    NASA Astrophysics Data System (ADS)

    Gooseff, M. N.; Priscu, J. C.; Doran, P. T.; Chiuchiolo, A.; Obryk, M.

    2014-12-01

    Lakes integrate landscape processes and climate conditions. Most of the permanently ice-covered lakes in the McMurdo Dry Valleys, Antarctica are closed basin, receiving glacial melt water from streams for 10-12 weeks per year. Lake levels rise during the austral summer are balanced by sublimation of ice covers (year-round) and evaporation of open water moats (summer only). Vertical profiles of water temperature have been measured in three lakes in Taylor Valley since 1988. Up to 2002, lake levels were dropping, ice covers were thickening, and total heat contents were decreasing. These lakes have been gaining heat since the mid-2000s, at rates as high as 19.5x1014 cal/decade). Since 2002, lake levels have risen substantially (as much as 2.5 m), and ice covers have thinned (1.5 m on average). Analyses of lake ice thickness, meteorological conditions, and stream water heat loads indicate that the main source of heat to these lakes is from latent heat released when ice-covers form during the winter. An aditional source of heat to the lakes is water inflows from streams and direct glacieal melt. Mean lake temperatures in the past few years have stabilized or cooled, despite increases in lake level and total heat content, suggesting increased direct inflow of meltwater from glaciers. These results indicate that McMurdo Dry Valley lakes are sensitive indicators of climate processes in this polar desert landscape and demonstrate the importance of long-term data sets when addressing the effects of climate on ecosystem processes.

  2. Role of Atmospheric CO2 in the Ice Ages (Invited)

    NASA Astrophysics Data System (ADS)

    Toggweiler, J. R.

    2010-12-01

    Ice cores from Antarctica provide our most highly resolved records of glacial-interglacial climate change. They feature big transitions every 100,000 years or so in which Antarctica warms by up to 10 deg. C while the level of atmospheric CO2 rises by up to 100 ppm. We have no other records like these from any other location, so the assumption is often made that the Earth's mean temperature varies like the temperatures in Antarctica. The striking co-variation between the two records is taken to mean 1) that there is a causal relationship between the global temperature and atmospheric CO2 and 2) that atmospheric CO2 is a powerful agent of climate change during the ice ages. The problem is that the mechanism most often invoked to explain the CO2 variations operates right next to Antarctica and, as such, provides a fairly direct way to explain the temperature variations in Antarctica as well. If so, Antarctic temperatures go up and down for the same reason that atmospheric CO2 goes up and down, in which case no causation can be inferred. Climate models suggest that the 100-ppm CO2 increases during the big transitions did not increase surface temperatures by more than 2 deg. C. This is not nearly enough to explain the observed variability. A better reason for thinking that atmospheric CO2 is important is that its temporal variations are concentrated in the 100,000-yr band. In my presentation I will argue that atmospheric CO2 is important because it has the longest time scale in the system. We observe empirically that atmospheric CO2 remains low for 50,000 years during the second half of each 100,000-yr cycle. The northern ice sheets become especially large toward the ends of these intervals, and it is large ice sheets that make the Earth especially cold. This leads me to conclude that atmospheric CO2 is important because of its slow and persistent influence on the northern ice sheets over the second half of each 100,000-yr cycle.

  3. Ice-Borehole Probe

    NASA Technical Reports Server (NTRS)

    Behar, Alberto; Carsey, Frank; Lane, Arthur; Engelhardt, Herman

    2006-01-01

    An instrumentation system has been developed for studying interactions between a glacier or ice sheet and the underlying rock and/or soil. Prior borehole imaging systems have been used in well-drilling and mineral-exploration applications and for studying relatively thin valley glaciers, but have not been used for studying thick ice sheets like those of Antarctica. The system includes a cylindrical imaging probe that is lowered into a hole that has been bored through the ice to the ice/bedrock interface by use of an established hot-water-jet technique. The images acquired by the cameras yield information on the movement of the ice relative to the bedrock and on visible features of the lower structure of the ice sheet, including ice layers formed at different times, bubbles, and mineralogical inclusions. At the time of reporting the information for this article, the system was just deployed in two boreholes on the Amery ice shelf in East Antarctica and after successful 2000 2001 deployments in 4 boreholes at Ice Stream C, West Antarctica, and in 2002 at Black Rapids Glacier, Alaska. The probe is designed to operate at temperatures from 40 to +40 C and to withstand the cold, wet, high-pressure [130-atm (13.20-MPa)] environment at the bottom of a water-filled borehole in ice as deep as 1.6 km. A current version is being outfitted to service 2.4-km-deep boreholes at the Rutford Ice Stream in West Antarctica. The probe (see figure) contains a sidelooking charge-coupled-device (CCD) camera that generates both a real-time analog video signal and a sequence of still-image data, and contains a digital videotape recorder. The probe also contains a downward-looking CCD analog video camera, plus halogen lamps to illuminate the fields of view of both cameras. The analog video outputs of the cameras are converted to optical signals that are transmitted to a surface station via optical fibers in a cable. Electric power is supplied to the probe through wires in the cable at a

  4. Carbonaceous aerosol tracers in ice-cores record multi-decadal climate oscillations

    PubMed Central

    Seki, Osamu; Kawamura, Kimitaka; Bendle, James A. P.; Izawa, Yusuke; Suzuki, Ikuko; Shiraiwa, Takayuki; Fujii, Yoshiyuki

    2015-01-01

    Carbonaceous aerosols influence the climate via direct and indirect effects on radiative balance. However, the factors controlling the emissions, transport and role of carbonaceous aerosols in the climate system are highly uncertain. Here we investigate organic tracers in ice cores from Greenland and Kamchatka and find that, throughout the period covered by the records (1550 to 2000 CE), the concentrations and composition of biomass burning-, soil bacterial- and plant wax- tracers correspond to Arctic and regional temperatures as well as the warm season Arctic Oscillation (AO) over multi-decadal time-scales. Specifically, order of magnitude decreases (increases) in abundances of ice-core organic tracers, likely representing significant decreases (increases) in the atmospheric loading of carbonaceous aerosols, occur during colder (warmer) phases in the high latitudinal Northern Hemisphere. This raises questions about causality and possible carbonaceous aerosol feedback mechanisms. Our work opens new avenues for ice core research. Translating concentrations of organic tracers (μg/kg-ice or TOC) from ice-cores, into estimates of the atmospheric loading of carbonaceous aerosols (μg/m3) combined with new model constraints on the strength and sign of climate forcing by carbonaceous aerosols should be a priority for future research. PMID:26411576

  5. Wind-driven Sea-Ice Changes Intensify Subsurface Warm Water Intrusion into the West Antarctic Land Ice Front

    NASA Astrophysics Data System (ADS)

    Li, X.; Gille, S. T.; shang-Ping, X.; Xie, S. P.; Holland, D. M.; Holland, M. M.

    2016-12-01

    The climate change observed around Antarctica in recent decades is characterized by distinct zonally asymmetric patterns, with the strongest changes over West Antarctica. These changes are marked by strong land ice melting and sea ice redistribution around West Antarctica. This is associated with temperature and circulation anomalies in the ocean and atmosphere around the same area. In this study, we comprehensively examine the coherency between these changes using a combination of observations and numerical simulations. Results show that the atmospheric circulation changes distinctly drive the changes in ocean circulation and sea ice distribution. In addition, the atmospheric circulation induced sea ice changes play an important role in lifting the subsurface ocean temperature and salinity around the West Antarctica. During recent decades, the Amundsen Sea Low (ASL) has deepened, especially in austral autumn and winter. This deepened ASL has intensified the offshore wind near the coastal regions of the Ross Sea. Driven by these atmospheric changes, more sea ice has formed near West Antarctica in winter. In contrast, more sea ice melts during the summer. This strengthened sea ice seasonality has been observed and successfully reproduced in the model simulation. The wind-driven sea ice changes causes a surface freshening over the Ross and Amundsen Seas, with a subsurface salinity increase over the Ross Sea. The additional fresh/salt water fluxes thus further change the vertical distribution of salinity and strengthen the stratification in the Ross and Amundsen Seas. As a result of the above ice-ocean process, the mixed-layer depth around the Ross and Amundsen Seas shallows. By weakening the vertical heat transport near the surface layer, and inducing an upward movement of the circumpolar deep water (CDW), this process freshened and cooled the surface layer, while the salinity and temperature in the sub-surface ocean are increased, extending from 150 meters to >700

  6. Neogene ice sheet, paleoclimatic and geological history of the McMurdo Sound region, Victoria Land Basin, Antarctica: overview of ANDRILL's first two drilling projects

    NASA Astrophysics Data System (ADS)

    Powell, R.; Naish, T.; Harwood, D.; Florindo, F.; Levy, R.; Teams, M. S.

    2008-12-01

    The ANtarctic geological DRILLing Program (ANDRILL), an international collaboration within IPY, has recovered 2 cores: from under the Ross Ice Shelf (McMurdo Ice Shelf Project (MIS) - AND-1B), and from the land-fast sea-ice of McMurdo Sound (Southern McMurdo Sound Project (SMS) - AND-2A). Drill cores reached respective total depths of 1285mbsf in c. 850m of water (MIS) and 1138.54mbsf in c. 380m of water (SMS). Repetitive facies successions in AND-1B core imply at least 60 fluctuations, of probable Milankovitch- duration, between subglacial, ice proximal and ice distal open marine environments. These are grouped into 3 types of facies cycles corresponding to glacial-interglacial variability during climatically distinct periods of Late Neogene: (1) cold-polar climate and ice (late Miocene and Pleistocene); (2) relatively warmer climate, polythermal ice and interglacials dominated by pelagic diatomite (Pliocene); (3) warmer climate, polythermal ice with interglacials dominated by hemipelagites (early late Miocene). A c. 80m-thick interval of diatomite of mid to late Pliocene age shows no apparent glacial cyclicity and represents an extended period of ice-free conditions indicating reduced or absent WAIS. Late Pliocene glacial-interglacial cycles characterized by abrupt alternations between subglacial/ice-proximal facies and open marine diatomite units imply significant WAIS dynamism, and contribution to global ice volume changes coeval with the initiation of Northern Hemisphere glaciations. A c. 4m-thick interval of diatomaceous mudstone in the mid-Pleistocene also represents warm-interglacial ice-free conditions. Intriguingly, glacial deposits interrupted by periodic, small- scale grounding-line retreats dominate the last 1m.y. Inter-hemispheric ice sheet coupling was probably controlled by Northern Hemispheric insolation and consequent glacial eustasy to account for much of the orbital-scale WAIS variability since 2.5Ma. A further expansion of WAIS occurred across

  7. Rapid drawdown of Antarctica's Wordie Ice Shelf glaciers in response to ENSO/Southern Annular Mode-driven warming in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Walker, C. C.; Gardner, A. S.

    2017-10-01

    Here we investigate the largest acceleration in ice flow across all of Antarctica between ∼2008 InSAR and 2014 Landsat velocity mappings. This occurred in glaciers that used to feed into the Wordie Ice Shelf on the west Antarctic Peninsula, which rapidly disintegrated in ∼1989. Between 2008 and 2014, these glaciers experienced at least a threefold increase in surface elevation drawdown relative to the 2002-2008 time period. After ∼20 yrs of relative stability, it is unlikely that the ice shelf collapse played a role in the large response. Instead, we find that the rapid acceleration and surface drawdown is linked to enhanced melting at the ice-ocean boundary, attributable to changes in winds driven by global atmospheric circulation patterns, namely the El Niño-Southern Oscillation (ENSO) and Southern Annular Mode (SAM), linking changes in grounded ice to atmospheric-driven ocean warming.

  8. Modelling the influence of tides on ice-shelf melt rates in the Amundsen Sea, Antarctica.

    NASA Astrophysics Data System (ADS)

    Jourdain, Nicolas C.; Molines, Jean-Marc; Le Sommer, Julien; Mathiot, Pierre; Chanut, Jérome; Madec, Gurvan

    2017-04-01

    Variations in melt beneath ice- shelves may trigger ice-sheet instabilities, in particular in West Antarctica. Therefore, improving the understanding and modelling of ice-shelf basal melt rates has been a major focus over the last decades. In this presentation, we provide further insight into the role of tides on basal melt rates, and we assess several methods to account for tides in models that do not include an explicit representation of tides. First, we use an explicit representation of tides in a regional configuration of the NEMO-3.6 model deployed over the Amundsen Sea. We show that most of the tidal influence on ice-shelf melt is explained by four tidal constituents. Tides enhance melt by more than 30% in some cavities like Abbot, Cosgrove and Dotson, but by less than 10% in others like Thwaites and Pine Island. Over the entire Amundsen Sea sector, tides enhance melt by 92 Gt/yr, which is mostly induced by tidal velocities along ice drafts (+148 Gt/yr), partly compensated by tide-induced change in thermal forcing (-31 Gt/yr) and co-variations between tidal velocities and thermal forcing (-26 Gt/yr). In the second part of this presentation, we show that using uniform tidal velocities to account for tides effects in ocean models with no explicit tides produces large biases in melt rates. By contrast, prescribing non-uniform tidal velocities allows an accurate representation of the dynamical effects of tides on melt rates.

  9. Physical properties of the WAIS Divide ice core

    USGS Publications Warehouse

    Fitzpatrick, Joan J.; Voigt, Donald E.; Fegyveresi, John M.; Stevens, Nathan T.; Spencer, Matthew K.; Cole-Dai, Jihong; Alley, Richard B.; Jardine, Gabriella E.; Cravens, Eric; Wilen, Lawrence A.; Fudge, T. J.; McConnell, Joseph R.

    2014-01-01

    The WAIS (West Antarctic Ice Sheet) Divide deep ice core was recently completed to a total depth of 3405 m, ending ∼50 m above the bed. Investigation of the visual stratigraphy and grain characteristics indicates that the ice column at the drilling location is undisturbed by any large-scale overturning or discontinuity. The climate record developed from this core is therefore likely to be continuous and robust. Measured grain-growth rates, recrystallization characteristics, and grain-size response at climate transitions fit within current understanding. Significant impurity control on grain size is indicated from correlation analysis between impurity loading and grain size. Bubble-number densities and bubble sizes and shapes are presented through the full extent of the bubbly ice. Where bubble elongation is observed, the direction of elongation is preferentially parallel to the trace of the basal (0001) plane. Preferred crystallographic orientation of grains is present in the shallowest samples measured, and increases with depth, progressing to a vertical-girdle pattern that tightens to a vertical single-maximum fabric. This single-maximum fabric switches into multiple maxima as the grain size increases rapidly in the deepest, warmest ice. A strong dependence of the fabric on the impurity-mediated grain size is apparent in the deepest samples.

  10. Volcanic synchronization of Dome Fuji and Dome C Antarctic deep ice cores over the past 216 kyr

    NASA Astrophysics Data System (ADS)

    Fujita, S.; Parrenin, F.; Severi, M.; Motoyama, H.; Wolff, E. W.

    2015-10-01

    Two deep ice cores, Dome Fuji (DF) and EPICA Dome C (EDC), drilled at remote dome summits in Antarctica, were volcanically synchronized to improve our understanding of their chronologies. Within the past 216 kyr, 1401 volcanic tie points have been identified. DFO2006 is the chronology for the DF core that strictly follows O2 / N2 age constraints with interpolation using an ice flow model. AICC2012 is the chronology for five cores, including the EDC core, and is characterized by glaciological approaches combining ice flow modelling with various age markers. A precise comparison between the two chronologies was performed. The age differences between them are within 2 kyr, except at Marine Isotope Stage (MIS) 5. DFO2006 gives ages older than AICC2012, with peak values of 4.5 and 3.1 kyr at MIS 5d and MIS 5b, respectively. Accordingly, the ratios of duration (AICC2012 / DFO2006) range between 1.4 at MIS 5e and 0.7 at MIS 5a. When making a comparison with accurately dated speleothem records, the age of DFO2006 agrees well at MIS 5d, while the age of AICC2012 agrees well at MIS 5b, supporting their accuracy at these stages. In addition, we found that glaciological approaches tend to give chronologies with younger ages and with longer durations than age markers suggest at MIS 5d-6. Therefore, we hypothesize that the causes of the DFO2006-AICC2012 age differences at MIS 5 are (i) overestimation in surface mass balance at around MIS 5d-6 in the glaciological approach and (ii) an error in one of the O2 / N2 age constraints by ~ 3 kyr at MIS 5b. Overall, we improved our knowledge of the timing and duration of climatic stages at MIS 5. This new understanding will be incorporated into the production of the next common age scale. Additionally, we found that the deuterium signals of ice, δDice, at DF tends to lead the one at EDC, with the DF lead being more pronounced during cold periods. The lead of DF is by +710 years (maximum) at MIS 5d, -230 years (minimum) at MIS 7a and +60

  11. Cryostratigraphy and the Sublimation Unconformity in Permafrost from an Ultraxerous Environment, University Valley, McMurdo Dry Valleys of Antarctica

    NASA Technical Reports Server (NTRS)

    Lapalme, Caitlin M.; Fortier, Daniel; Pollard, Wayne; Lacelle, Denis; Davila, Alfonso; McKay, Christopher P.

    2017-01-01

    The cryostratigraphy of permafrost in ultraxerous environments is poorly known. In this study, icy permafrost cores from University Valley (McMurdo Dry Valleys, Antarctica) were analyzed for sediment properties, ground-ice content, types and distribution of cryostructures, and presence of unconformities. No active layer exists in the valley, but the ice table, a sublimation unconformity, ranges from 0 to 60 cm depth. The sediments are characterized as a medium sand, which classifies them as low to non-frost susceptible. Computed tomography (CT) scan images of the icy permafrost cores revealed composite cryostructures that included the structureless, porous visible, suspended and crustal types. These cryostructures were observed irrespective of ground-ice origin (vapour deposited and freezing of snow meltwater), suggesting that the type and distribution of cryostructures could not be used as a proxy to infer the mode of emplacement of ground ice. Volumetric ice content derived from the CT scan images underestimated measured volumetric ice content, but approached measured excess ice content. A palaeo-sublimation unconformity could not be detected from a change in cryostructures, but could be inferred from an increase in ice content at the maximum predicted ice table depth. This study highlights some of the unique ground-ice processes and cryostructures in ultraxerous environments.

  12. Heat flux variations over sea-ice observed at the coastal area of the Sejong Station, Antarctica

    NASA Astrophysics Data System (ADS)

    Park, S.; Choi, T.; Kim, S.

    2012-12-01

    This study presents variations of sensible heat flux and latent heat flux over sea-ice observed in 2011 from the 10-m flux tower located at the coast of the Sejong Station on King George Island, Antarctica. A period from June to November was divided into three parts: "Freezing", "Frozen", and "Melting" periods based on daily monitoring of sea state and hourly photos looking at the Marian Cove in front of the Sejong Station. The division of periods enabled us to look into the heat flux variations depending on the sea-ice conditions. Over freezing sea surface during the freezing period of late June, daily mean sensible heat flux was -11.9 Wm-2 and daily mean latent heat flux was +16.3 Wm-2. Over the frozen sea-ice, daily mean sensible heat flux was -10.4 Wm-2 while daily mean latent heat flux was +2.4 Wm-2. During the melting period of mid-October to early November, magnitudes of sensible heat flux increased to -14.2 Wm-2 and latent heat flux also increased to +13.5 Wm-2. In short, latent heat flux was usually upward over sea-ice most of the time while sensible heat flux was downward from atmosphere to sea-ice. Magnitudes of the fluxes were small but increased when freezing or melting of sea-ice was occurring. Especially, latent heat flux increased five to six times compared to that of "frozen" period implying that early melting of sea-ice may cause five to six times larger supply of moisture to the atmosphere.

  13. Ice-sheet response to oceanic forcing.

    PubMed

    Joughin, Ian; Alley, Richard B; Holland, David M

    2012-11-30

    The ice sheets of Greenland and Antarctica are losing ice at accelerating rates, much of which is a response to oceanic forcing, especially of the floating ice shelves. Recent observations establish a clear correspondence between the increased delivery of oceanic heat to the ice-sheet margin and increased ice loss. In Antarctica, most of these processes are reasonably well understood but have not been rigorously quantified. In Greenland, an understanding of the processes by which warmer ocean temperatures drive the observed retreat remains elusive. Experiments designed to identify the relevant processes are confounded by the logistical difficulties of instrumenting ice-choked fjords with actively calving glaciers. For both ice sheets, multiple challenges remain before the fully coupled ice-ocean-atmosphere models needed for rigorous sea-level projection are available.

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

    NASA Astrophysics Data System (ADS)

    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

  15. Seismic wave propagation in anisotropic ice - Part 2: Effects of crystal anisotropy in geophysical data

    NASA Astrophysics Data System (ADS)

    Diez, A.; Eisen, O.; Hofstede, C.; Lambrecht, A.; Mayer, C.; Miller, H.; Steinhage, D.; Binder, T.; Weikusat, I.

    2015-02-01

    We investigate the propagation of seismic waves in anisotropic ice. Two effects are important: (i) sudden changes in crystal orientation fabric (COF) lead to englacial reflections; (ii) the anisotropic fabric induces an angle dependency on the seismic velocities and, thus, recorded travel times. Velocities calculated from the polycrystal elasticity tensor derived for the anisotropic fabric from measured COF eigenvalues of the EDML ice core, Antarctica, show good agreement with the velocity trend determined from vertical seismic profiling. The agreement of the absolute velocity values, however, depends on the choice of the monocrystal elasticity tensor used for the calculation of the polycrystal properties. We make use of abrupt changes in COF as a common reflection mechanism for seismic and radar data below the firn-ice transition to determine COF-induced reflections in either data set by joint comparison with ice-core data. Our results highlight the possibility to complement regional radar surveys with local, surface-based seismic experiments to separate isochrones in radar data from other mechanisms. This is important for the reconnaissance of future ice-core drill sites, where accurate isochrone (i.e. non-COF) layer integrity allows for synchronization with other cores, as well as studies of ice dynamics considering non-homogeneous ice viscosity from preferred crystal orientations.

  16. Ice-sheet mass balance and climate change.

    PubMed

    Hanna, Edward; Navarro, Francisco J; Pattyn, Frank; Domingues, Catia M; Fettweis, Xavier; Ivins, Erik R; Nicholls, Robert J; Ritz, Catherine; Smith, Ben; Tulaczyk, Slawek; Whitehouse, Pippa L; Zwally, H Jay

    2013-06-06

    Since the 2007 Intergovernmental Panel on Climate Change Fourth Assessment Report, new observations of ice-sheet mass balance and improved computer simulations of ice-sheet response to continuing climate change have been published. Whereas Greenland is losing ice mass at an increasing pace, current Antarctic ice loss is likely to be less than some recently published estimates. It remains unclear whether East Antarctica has been gaining or losing ice mass over the past 20 years, and uncertainties in ice-mass change for West Antarctica and the Antarctic Peninsula remain large. We discuss the past six years of progress and examine the key problems that remain.

  17. High-resolution Sulfur Isotopes in Ice Cores Identify Large Stratospheric Eruptions

    NASA Astrophysics Data System (ADS)

    Burke, A.; Sigl, M.; Moore, K.; Nita, D. C.; Adkins, J. F.; Paris, G.; McConnell, J.

    2016-12-01

    The record of the volcanic forcing of climate over the past 2500 years is reconstructed primarily from sulfate concentrations in ice cores. Of particular interest are stratospheric eruptions, as these afford sulfate aerosols the longest residence time and largest dispersion in the atmosphere, and thus the greatest impact on radiative forcing. Identification of stratospheric eruptions currently relies on the successful matching of the same volcanic sulfate peak in ice cores from both the Northern and Southern hemispheres (a "bipolar event"). These are interpreted to reflect the global distribution of sulfur aerosols by the stratospheric winds. Despite its recent success, this method relies on precise and accurate dating of ice cores, in order to distinguish between a true `bipolar event' and two separate eruptions that occurred in close temporal succession. Sulfur isotopes can been used to distinguish between these two scenarios since stratospheric sulfur aerosols are exposed to UV radiation which imparts a mass independent fractionation (Baroni et al., 2007). Mass independent fractionation of sulfate in ice cores thus offers a novel method of fingerprinting stratospheric eruptions, and thus refining the historic record of explosive volcanism and its forcing of climate. Here we present new high-resolution (sub-annual) sulfur isotope data from the Tunu Ice core in Greenland over seven eruptions. Sulfur isotopes were measured by MC-ICP-MS, which substantially reduces sample size requirements and allows high temporal resolution from a single ice core. We demonstrate the efficacy of the method on recent, well-known eruptions (including Pinatubo and Katmai/Novarupta), and then apply it to unidentified sulfate peaks, allowing us to identify new stratospheric eruptions. Baroni, M., Thiemens, M. H., Delmas, R. J., & Savarino, J. (2007). Mass-independent sulfur isotopic compositions in stratospheric volcanic eruptions. Science, 315(5808), 84-87. http://doi.org/10

  18. Holocene glacier and deep water dynamics, Adélie Land region, East Antarctica

    NASA Astrophysics Data System (ADS)

    Denis, Delphine; Crosta, Xavier; Schmidt, Sabine; Carson, Damien S.; Ganeshram, Raja S.; Renssen, Hans; Bout-Roumazeilles, Viviane; Zaragosi, Sebastien; Martin, Bernard; Cremer, Michel; Giraudeau, Jacques

    2009-06-01

    This study presents a high-resolution multi-proxy investigation of sediment core MD03-2601 and documents major glacier oscillations and deep water activity during the Holocene in the Adélie Land region, East Antarctica. A comparison with surface ocean conditions reveals synchronous changes of glaciers, sea ice and deep water formation at Milankovitch and sub-Milankovitch time scales. We report (1) a deglaciation of the Adélie Land continental shelf from 11 to 8.5 cal ka BP, which occurred in two phases of effective glacier grounding-line retreat at 10.6 and 9 cal ka BP, associated with active deep water formation; (2) a rapid glacier and sea ice readvance centred around 7.7 cal ka BP; and (3) five rapid expansions of the glacier-sea ice systems, during the Mid to Late Holocene, associated to a long-term increase of deep water formation. At Milankovich time scales, we show that the precessionnal component of insolation at high and low latitudes explains the major trend of the glacier-sea ice-ocean system throughout the Holocene, in the Adélie Land region. In addition, the orbitally-forced seasonality seems to control the coastal deep water formation via the sea ice-ocean coupling, which could lead to opposite patterns between north and south high latitudes during the Mid to Late Holocene. At sub-Milankovitch time scales, there are eight events of glacier-sea ice retreat and expansion that occurred during atmospheric cooling events over East Antarctica. Comparisons of our results with other peri-Antarctic records and model simulations from high southern latitudes may suggest that our interpretation on glacier-sea ice-ocean interactions and their Holocene evolutions reflect a more global Antarctic Holocene pattern.

  19. Evolution of Meltwater on the McMurdo Ice Shelf, Antarctica During Two Summer Melt Seasons

    NASA Astrophysics Data System (ADS)

    Macdonald, G. J.; Banwell, A. F.; Willis, I.; Mayer, D. P.; Hansen, E. K.; MacAyeal, D. R.

    2017-12-01

    Ice shelves surround > 50% of Antarctica's coast and their response to climate change is key to the ice sheet's future and global sea-level rise. Observations of the development and drainage of 2750 lakes prior to the collapse of the Larsen B Ice Shelf, combined with our understanding of ice-shelf flexure/fracture, suggest that surface meltwater plays a key role in ice-shelf stability, although the present state of knowledge remains limited. Here, we report results of an investigation into the seasonal evolution of meltwater on the McMurdo Ice Shelf (MIS) during the 2015/16 and 2016/17 austral summers using satellite remote sensing, complemented by ground survey. Although the MIS is relatively far south (78° S), it experiences relatively high ablation rates in the west due to adiabatically warmed winds, making it a useful example of how meltwater could evolve on more southerly ice shelves in a warming climate. We calculate the areas and depths of ponded surface meltwater on the ice shelf at different stages of the two melt seasons using a modified NDWI approach and water-depth algorithm applied to both Landsat 8 and Worldview imagery. Data from two automatic weather stations on the ice shelf are used to drive a positive degree-day model to compare our observations of surface water volumes with modelled meltwater production. Results suggest that the spatial and temporal variations in surface meltwater coverage on the ice shelf vary not only with climatic conditions but also in response to other important processes. First, a rift that widens and propagates between the two melt seasons intercepts meltwater streams, redirecting flow and facilitating ponding elsewhere. Second, some lakes from previous years remain frozen over and become pedestalled, causing streams to divert around their perimeter. Third, surface debris conditions also cause large-scale spatial variation in melt rates and the flow and storage of water.

  20. Motion of Major Ice Shelf Fronts in Antarctica from Slant Range Analysis of Radar Altimeter Data, 1978 - 1998

    NASA Technical Reports Server (NTRS)

    Zwally, H. J.; Beckley, M. A.; Brenner, A. C.; Giovinetto, M. B.; Koblinsky, Chester J. (Technical Monitor)

    2001-01-01

    Slant range analysis of radar altimeter data from the Seasat, Geosat, ERS-1 and ERS-2 databases are used to determine barrier location at particular times, and estimate barrier motion (km/yr) for major Antarctic ice shelves. The barrier locations, which are the seaward edges or fronts of floating ice shelves, advance with time as the ice flows from the grounded ice sheets and retreat whenever icebergs calve from the fronts. The analysis covers various multiyear intervals from 1978 to 1998, supplemented by barrier location maps produced elsewhere for 1977 and 1986. Barrier motion is estimated as the ratio between mean annual ice shelf area change for a particular interval, and the length of the discharge periphery. This value is positive if the barrier location progresses seaward, or negative if the barrier location regresses (break-back). Either positive or negative values are lower limit estimates because the method does not detect relatively small area changes due to calving or surge events. The findings are discussed in the context of the three ice shelves that lie in large embayments (the Filchner-Ronne, Amery, and Ross), and marginal ice shelves characterized by relatively short distances between main segments of grounding line and barrier (those in the Queen Maud Land sector between 10.1 deg. W and 32.5 deg. E, and the West and Shackleton ice shelves). All the ice shelves included in the study account for approximately three-fourths of the total ice shelf area of Antarctica, and discharge approximately two-thirds of the total grounded ice area.

  1. Abrupt climate warming in East Antarctica during the early Holocene

    NASA Astrophysics Data System (ADS)

    Cremer, Holger; Heiri, Oliver; Wagner, Bernd; Wagner-Cremer, Friederike

    2007-08-01

    We report a centennial-scale warming event between 8600 and 8400 cal BP from Amery Oasis, East Antarctica, that is documented by the geochemical record in a lacustrine sediment sequence. The organic carbon content, the C/S ratio, and the sedimentation rate in this core have distinctly elevated values around 8500 y ago reflecting relatively warm and ice-free conditions that led to well-ventilated conditions in the lake and considerable sedimentation of both autochthonous and allochthonous organic matter on the lake bottom. This abrupt warming event occurred concurrently with reported warm climatic conditions in the Southern Ocean while the climate in central East Antarctic remained cold. The comparison of the spatial and temporal variability of warm climatic periods documented in various terrestrial, marine, and glacial archives from East Antarctica elucidates the uniqueness of the centennial-scale warming event in the Amery Oasis. We also discuss a possible correlation of the Amery warming event with the abrupt climatic deterioration around 8200 cal BP on the Northern Hemisphere.

  2. Trace and Ultra-trace Elements in the Deepest Part of the Vostok Ice Core, Antarctica: Geochemical Characterization of the Sub-glacial Lake Environment

    NASA Astrophysics Data System (ADS)

    Turetta, C.; Planchon, F.; Gabrielli, P.; Cozzi, G.; Cairns, W.; Barbaro, E.; Petit, J. R.; Bulat, S.; Boutron, C.; Barbante, C.

    2016-12-01

    We present in this study comprehensive data on the occurrence of 25 trace and ultra-trace elements in the deepest part of the Vostok ice core. The determination of Li, Na, Mg, Al, K, Ca, V, Cr, Mn, Fe, Co, Cu, Zn, As, Se, Rb, Sr, Mo, Ag, Cd, Sb, Ba, Pb, Bi and U has been performed in the different types of ice encountered from 3271 m to 3609 m of depth, corresponding to atmospheric ice, glacial flour and to accreted ice originating from the freezing of Lake Vostok waters. From atmospheric ice and glacial flour, the relative contributions of primary aerosols were evaluated for each element using a chemical mass balance approach in order to provide a first order evaluation of their partition between soluble (sea-salt) and insoluble (wind-blown dust) fractions in the ice. Sea-salt spray aerosols are the main source of impurities to the ice for certain elements (Na, Mg and K levels, and in a lesser extent to Ca, Sr, Rb, Li and U) while for other elements (Al, V, Cr, Mn, Fe, Co, Cu, Zn, Mo, Sb, Ba and Pb as well as the non sea salt fractions of Mg, K, Ca, Sr, Rb, Li and U) dust inputs appear to primarily control their depositional variability. For the glacial flour, the comparable levels of elements with the overlying atmospheric ice suggest that incorporation of abrasion debris at the glacier is quite limited in the sections considered. For the accreted ice originating from the subglacial waters of Lake Vostok, we observed a major chemical shift in the composition of the ice showing two distinct trends that we assumed to be derived from the chemical speciation of elements. The study of the glacier ice and the glacial flour has allowed us to perform a detailed characterisation of elemental abundances related to the aerosol sources variability and also to illustrate the interaction between the ice-sheet and the bedrock.

  3. Microbiological and Biogeochemical Investigations of the Accreted Ice Above Subglacial Lake Vostok, Antarctica

    NASA Astrophysics Data System (ADS)

    Christner, B. C.; Foreman, C. F.; Arnold, B. R.; Welch, K. A.; Lyons, W. B.; Priscu, J. C.

    2004-12-01

    Subglacial Lake Vostok is located ~4 km beneath the surface of the East Antarctic ice sheet and has been isolated from the atmosphere for at least 15 million years. The lake has a surface area near 14,000 km2 and a depth exceeding 1000 m. While the nature of the environment within Subglacial Lake Vostok remains uncertain, if a sustained microbial ecosystem is present, life in this subsurface environment operates under arguably the most extreme conditions in the biosphere (i.e., high pressure, constant cold, high oxygen concentrations, and no light). The lake represents an analogue for ecosystems that may exist in Europa's ice-covered ocean and also provides an Earthly-based model for the evaluation of technology to search for life in icy extraterrestrial subsurface environments. Concerns for environmental protection have prevented direct sampling of the lake water thus far, as a prudent sampling plan that will not contaminate this pristine environment has yet to be developed and tested. However, an ice core has been retrieved at Vostok Station in which the bottom ~85 meters consists of lake water that has accreted to the bottom of the ice sheet, providing frozen samples of water from the lakes' surface. The ice from 3539 to 3609 mbs (accretion ice I) contains visible inclusions due to accretion in the shallow embayment or western grounding line, whereas ice from 3610-3623 mbs (accretion ice II) is very clean, forming above the deep eastern basin of the main lake. Using a multifaceted protocol to monitor cellular and molecular decontamination of ice cores, we show that the microbiology and geochemistry (i.e., dissolve organic carbon, nutrients, and ions) of accretion ice is very different from the overlying glacial ice. The numbers of cells are 2- to 7-fold higher in accretion ice I than in the overlying glacial ice, and decrease with increasing depth in accretion ice II. Cell viability in accretion ice samples has been confirmed by the measurable respiration of 14C

  4. Detection of Organic Matter in Greenland Ice Cores by Deep-UV Fluorescence

    NASA Astrophysics Data System (ADS)

    Willis, M.; Malaska, M.; Wanger, G.; Bhartia, R.; Eshelman, E.; Abbey, W.; Priscu, J. C.

    2017-12-01

    The Greenland Ice Sheet is an Earthly analog for icy ocean worlds in the outer Solar System. Future missions to such worlds including Europa, Enceladus, and Titan may potentially include spectroscopic instrumentation to examine the surface/subsurface. The primary goal of our research is to test deep UV/Raman systems for in the situ detection and localization of organics in ice. As part of this effort we used a deep-UV fluorescence instrument able to detect naturally fluorescent biological materials such as aromatic molecules found in proteins and whole cells. We correlated these data with more traditional downstream analyses of organic material in natural ices. Supraglacial ice cores (2-4 m) were collected from several sites on the southwest outlet of the Greenland Ice Sheet using a 14-cm fluid-free mechanical coring system. Repeat spectral mapping data were initially collected longitudinally on uncut core sections. Cores were then cut into 2 cm thick sections along the longitudinal axis, slowly melted and analyzed for total organic carbon (TOC), total dissolved nitrogen (TDN), and bacterial density. These data reveal a spatial correlation between organic matter concentration, cell density, and the deep UV fluorescence maps. Our results provide a profile of the organics embedded within the ice from the top surface into the glacial subsurface, and the TOC:TDN data from the clean interior of the cores are indicative of a biological origin. This work provides a background dataset for future work to characterize organic carbon in the Greenland Ice Sheet and validation of novel instrumentation for in situ data collection on icy bodies.

  5. Late-Holocene climate evolution at the WAIS Divide site, West Antarctica: Bubble number-density estimates

    USGS Publications Warehouse

    Fegyveresi, John M.; Alley, R.B.; Spencer, M.K.; Fitzpatrick, J.J.; Steig, E.J.; White, J.W.C.; McConnell, J.R.; Taylor, K.C.

    2011-01-01

    A surface cooling of ???1.7??C occurred over the ???two millennia prior to ???1700 CE at the West Antarctic ice sheet (WAIS) Divide site, based on trends in observed bubble number-density of samples from the WDC06A ice core, and on an independently constructed accumulation-rate history using annual-layer dating corrected for density variations and thinning from ice flow. Density increase and grain growth in polar firn are both controlled by temperature and accumulation rate, and the integrated effects are recorded in the number-density of bubbles as the firn changes to ice. Numberdensity is conserved in bubbly ice following pore close-off, allowing reconstruction of either paleotemperature or paleo-accumulation rate if the other is known. A quantitative late-Holocene paleoclimate reconstruction is presented for West Antarctica using data obtained from the WAIS Divide WDC06A ice core and a steady-state bubble number-density model. The resultant temperature history agrees closely with independent reconstructions based on stable-isotopic ratios of ice. The ???1.7??C cooling trend observed is consistent with a decrease in Antarctic summer duration from changing orbital obliquity, although it remains possible that elevation change at the site contributed part of the signal. Accumulation rate and temperature dropped together, broadly consistent with control by saturation vapor pressure.

  6. The East Antarctic Ice Sheet and the Gamburtsev Subglacial Mountains (Invited)

    NASA Astrophysics Data System (ADS)

    Bell, R. E.; Studinger, M.; Ferraccioli, F.; Damaske, D.; Finn, C.; Braaten, D. A.; Fahnestock, M. A.; Jordan, T. A.; Corr, H.; Elieff, S.; Frearson, N.; Block, A. E.; Rose, K.

    2009-12-01

    Models of the onset of glaciation in Antarctica routinely document the early growth of the ice sheet on the summit of the Gamburtsev Subglacial Mountains in the center of the East Antarctic Craton. While ice sheet models replicate the formation of the East Antarctic ice sheet 35 million years ago, the age, evolution and structure of the Gamburtsev Mountains remain completely unresolved. During the International Polar Year scientists from seven nations have launched a major collaborative program (AGAP) to explore the Gamburtsev Subglacial Mountains buried by the East Antarctic ice sheet and bounded by numerous subglacial lakes. The AGAP umbrella is a multi-national, multi-disciplinary effort and includes aerogeophysics, passive seismology, traverse programs and will be complimented by future ice core and bedrock drilling. A major new airborne data set including gravity; magnetics; ice thickness; SAR images of the ice-bed interface; near-surface and deep internal layers; and ice surface elevation is providing insights into a more dynamic East Antarctica. More than 120,000 km of aerogeophysical data have been acquired from two remote field camps during the 2008/09 field season. AGAP effort was designed to address several fundamental questions including: 1) What role does topography play in the nucleation of continental ice sheets? 2) How do tectonic processes control the formation, distribution, and stability of subglacial lakes? The preliminary analysis of this major new data set indicated these 3000m high mountains are deeply dissected by a dendritic system. The northern margin of the mountain range terminates against the inland extent of the Lambert Graben. Evidence of the onset of glaciation is preserved as cirques and U shaped valleys along the axis of the uplifted massifs. The geomorphology reflects the interaction between the ice sheet and the Gamburtsev Mountains. Bright reflectors in the radar data in the deep valleys indicate the presence of water that has

  7. Tidally induced variations in vertical and horizontal motion on Rutford Ice Stream, West Antarctica, inferred from remotely sensed observations

    NASA Astrophysics Data System (ADS)

    Minchew, B. M.; Simons, M.; Riel, B.; Milillo, P.

    2017-01-01

    To better understand the influence of stress changes over floating ice shelves on grounded ice streams, we develop a Bayesian method for inferring time-dependent 3-D surface velocity fields from synthetic aperture radar (SAR) and optical remote sensing data. Our specific goal is to observe ocean tide-induced variability in vertical ice shelf position and horizontal ice stream flow. Thus, we consider the special case where observed surface displacement at a given location can be defined by a 3-D secular velocity vector, a family of 3-D sinusoidal functions, and a correction to the digital elevation model used to process the SAR data. Using nearly 9 months of SAR data collected from multiple satellite viewing geometries with the COSMO-SkyMed 4-satellite constellation, we infer the spatiotemporal response of Rutford Ice Stream, West Antarctica, to ocean tidal forcing. Consistent with expected tidal uplift, inferred vertical motion over the ice shelf is dominated by semidiurnal and diurnal tidal constituents. Horizontal ice flow variability, on the other hand, occurs primarily at the fortnightly spring-neap tidal period (Msf). We propose that periodic grounding of the ice shelf is the primary mechanism for translating vertical tidal motion into horizontal flow variability, causing ice flow to accelerate first and most strongly over the ice shelf. Flow variations then propagate through the grounded ice stream at a mean rate of ˜29 km/d and decay quasi-linearly with distance over ˜85 km upstream of the grounding zone.

  8. Two decades of ice melt reconstruction in Greenland and Antarctica from time-variable gravity

    NASA Astrophysics Data System (ADS)

    Talpe, M.; Nerem, R. S.; Lemoine, F. G.

    2014-12-01

    In this study, we present a record of ice-sheet melt derived from space-borne gravity that spans over two decades—beyond the time-frame of the GRACE mission. GRACE fields are merged with conventional tracking data (SLR/DORIS) spanning 1992 to the present. They are provided as weekly global fields of degree and order five without C50 and S50 but with C61 and S61. Their multi-decade timespan complements the monthly fields of GRACE of degree and order 60 that start in 2003 and will end when the GRACE mission terminates. The two datasets are combined via an empirical orthogonal function analysis, whereby the conventional tracking data temporal modes are obtained by fitting the SLR/DORIS coefficients to the GRACE spatial modes via linear least squares. Combining those temporal modes with GRACE spatial modes yields the reconstructed global gravity fields. The error budget of the reconstructions is composed of three components: the SLR/DORIS covariances, the errors estimated from the assumption that GRACE spatial modes can be mapped over the SLR/DORIS timeframe, and the covariances from the least squares fit applied to obtain the SLR/DORIS temporal modes. The reconstructed surface mass changes in Greenland and Antarctica, predominantly captured in the first mode, show a rate of mass loss that is increasing since 1992. The trend of mass changes in Greenland over various epochs match with an overarching study assembling altimetry, gravimetry, and interferometry estimates of ice-sheet balance over a 1992-2011 time-frame [Shepherd et al., 2012]. Antarctica shows a trend that is different because of updated GIA models [A et al., 2013] compared to the other studies. We will also show regional mass changes over various other basins, as well as the influence of each SLR/DORIS coefficient on the reconstructions. The consistency of these results underscores the possibility of using low-resolution SLR/DORIS time-variable gravity solutions as a way to continuously monitor the

  9. Methanesulfonic acid (MSA) migration in polar ice: data synthesis and theory

    NASA Astrophysics Data System (ADS)

    Osman, Matthew; Das, Sarah B.; Marchal, Olivier; Evans, Matthew J.

    2017-11-01

    Methanesulfonic acid (MSA; CH3SO3H) in polar ice is a unique proxy of marine primary productivity, synoptic atmospheric transport, and regional sea-ice behavior. However, MSA can be mobile within the firn and ice matrix, a post-depositional process that is well known but poorly understood and documented, leading to uncertainties in the integrity of the MSA paleoclimatic signal. Here, we use a compilation of 22 ice core MSA records from Greenland and Antarctica and a model of soluble impurity transport in order to comprehensively investigate the vertical migration of MSA from summer layers, where MSA is originally deposited, to adjacent winter layers in polar ice. We find that the shallowest depth of MSA migration in our compilation varies over a wide range (˜ 2 to 400 m) and is positively correlated with snow accumulation rate and negatively correlated with ice concentration of Na+ (typically the most abundant marine cation). Although the considered soluble impurity transport model provides a useful mechanistic framework for studying MSA migration, it remains limited by inadequate constraints on key physico-chemical parameters - most notably, the diffusion coefficient of MSA in cold ice (DMS). We derive a simplified version of the model, which includes DMS as the sole parameter, in order to illuminate aspects of the migration process. Using this model, we show that the progressive phase alignment of MSA and Na+ concentration peaks observed along a high-resolution West Antarctic core is most consistent with 10-12 m2 s-1 < DMS < 10-11 m2 s-1, which is 1 order of magnitude greater than the DMS values previously estimated from laboratory studies. More generally, our data synthesis and model results suggest that (i) MSA migration may be fairly ubiquitous, particularly at coastal and (or) high-accumulation regions across Greenland and Antarctica; and (ii) can significantly change annual and multiyear MSA concentration averages. Thus, in most cases, caution should be

  10. Boundary condition of grounding lines prior to collapse, Larsen-B Ice Shelf, Antarctica.

    PubMed

    Rebesco, M; Domack, E; Zgur, F; Lavoie, C; Leventer, A; Brachfeld, S; Willmott, V; Halverson, G; Truffer, M; Scambos, T; Smith, J; Pettit, E

    2014-09-12

    Grounding zones, where ice sheets transition between resting on bedrock to full floatation, help regulate ice flow. Exposure of the sea floor by the 2002 Larsen-B Ice Shelf collapse allowed detailed morphologic mapping and sampling of the embayment sea floor. Marine geophysical data collected in 2006 reveal a large, arcuate, complex grounding zone sediment system at the front of Crane Fjord. Radiocarbon-constrained chronologies from marine sediment cores indicate loss of ice contact with the bed at this site about 12,000 years ago. Previous studies and morphologic mapping of the fjord suggest that the Crane Glacier grounding zone was well within the fjord before 2002 and did not retreat further until after the ice shelf collapse. This implies that the 2002 Larsen-B Ice Shelf collapse likely was a response to surface warming rather than to grounding zone instability, strengthening the idea that surface processes controlled the disintegration of the Larsen Ice Shelf. Copyright © 2014, American Association for the Advancement of Science.

  11. Neutrino oscillation studies with IceCube-DeepCore

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Aartsen, M. G.; Abraham, K.; Ackermann, M.

    IceCube, a gigaton-scale neutrino detector located at the South Pole, was primarily designed to search for astrophysical neutrinos with energies of PeV and higher. This goal has been achieved with the detection of the highest energy neutrinos to date. At the other end of the energy spectrum, the DeepCore extension lowers the energy threshold of the detector to approximately 10 GeV and opens the door for oscillation studies using atmospheric neutrinos. An analysis of the disappearance of these neutrinos has been completed, with the results produced being complementary with dedicated oscillation experiments. Following a review of the detector principle andmore » performance, the method used to make these calculations, as well as the results, is detailed. Finally, the future prospects of IceCube-DeepCore and the next generation of neutrino experiments at the South Pole (IceCube-Gen2, specifically the PINGU sub-detector) are briefly discussed.« less

  12. Neutrino oscillation studies with IceCube-DeepCore

    DOE PAGES

    Aartsen, M. G.; Abraham, K.; Ackermann, M.; ...

    2016-03-30

    IceCube, a gigaton-scale neutrino detector located at the South Pole, was primarily designed to search for astrophysical neutrinos with energies of PeV and higher. This goal has been achieved with the detection of the highest energy neutrinos to date. At the other end of the energy spectrum, the DeepCore extension lowers the energy threshold of the detector to approximately 10 GeV and opens the door for oscillation studies using atmospheric neutrinos. An analysis of the disappearance of these neutrinos has been completed, with the results produced being complementary with dedicated oscillation experiments. Following a review of the detector principle andmore » performance, the method used to make these calculations, as well as the results, is detailed. Finally, the future prospects of IceCube-DeepCore and the next generation of neutrino experiments at the South Pole (IceCube-Gen2, specifically the PINGU sub-detector) are briefly discussed.« less

  13. Tree ring and ice core time scales around the Santorini eruption

    NASA Astrophysics Data System (ADS)

    Löfroth, Elin; Muscheler, Raimund; Aldahan, Ala; Possnert, Göran; Berggren, Ann-Marie

    2010-05-01

    When studying cosmogenic radionuclides in ice core and tree ring archives around the Santorini eruption a ~20 year discrepancy was found between the records (Muscheler 2009). In this study a new 10Be dataset from the NGRIP ice core is presented. It has a resolution of 7 years and spans the period 3752-3244 BP (1803-1295 BC). The NGRIP 10Be record and the previously published 10Be GRIP record were compared to the IntCal datasets to further investigate the discrepancy between the ice core and tree ring chronologies. By modelling the 14C production rate based on atmospheric 14C records a comparison could be made to the 10Be flux which is assumed to represent the 10Be production rate. This showed a time shift of ~23 years between the records. The sensitivity of the results to changes in important model parameters was evaluated. Uncertainties in the carbon cycle model cannot explain a substantial part of the timing differences. Potential influences of climate and atmospheric processes on the 10Be deposition were studied using δ18O from the respective cores and GISP2 ice core ion data. The comparison to δ18O revealed a small but significant correlation between 10Be flux and δ18O when the 14C-derived production signal was removed from the 10Be curves. The ion data, as proxies for atmospheric circulation changes, did not show any correlations to the 10Be record or the 10Be/14C difference. When including possible data uncertainties there is still a minimum discrepancy of ~10 years between the 10Be ice core and the 14C tree ring record. Due to lack of alternative explanations it is concluded that the ice core and/or the tree ring chronologies contains unaccounted errors in this range. This also reconciles the radiocarbon 1627-1600 BC (Friedrich et al., 2006) and ice core 1642±5 BC (Vinther et al., 2006) datings of the Santorini eruption. Friedrich, W.L., Kromer, B., Friedrich, M., Heinemeier, J., Pfeiffer, T., & Talamo, S., 2006: Santorini eruption radiocarbon dated to

  14. 14CO in Antarctic Glacial Ice as a Tracer of Changes in Atmospheric OH Abundance from 1880 AD to Present

    NASA Astrophysics Data System (ADS)

    Neff, P. D.; Petrenko, V. V.; Hmiel, B.; Smith, A. W.; Buizert, C.; Etheridge, D. M.; Murray, L. T.; Dyonisius, M.

    2017-12-01

    OH is the main tropospheric oxidant and determines the lifetime of methane and most other trace gases in the atmosphere, thereby controlling the amount of greenhouse warming that these gases can produce. Changes in [OH] in response to large changes in reactive trace gas emissions (which may occur in the future) are uncertain. Measurements of 14C-containing carbon monoxide (14CO) and other tracers such as methyl chloroform over the last ≈25 years have been successfully used to monitor changes in average OH concentration ([OH]), but there are no observational constraints on [OH] further back in time. Reconstructions of 14CO from ice cores could in principle provide such constraints but are complicated by in-situ production of 14CO by cosmic rays directly in the ice. Recent work in Antarctica and Greenland shows that this in-situ component would be relatively small and can be accurately corrected for at sites with very high snow accumulation rates. We propose to sample firn-air and shallow ice to ≈230 m depth at Law Dome, Antarctica (site DE-08, 1.2 m a-1 ice-equivalent snow accumulation), extracting trapped air from the ice cores on-site using a new large-volume ice melting system. 14CO will be analyzed in firn and ice core air samples, and accurate corrections made for the in-situ cosmogenic 14CO component in the ice—allowing for the atmospheric 14CO history to be reconstructed. This 14CO history will be interpreted with the aid of a chemistry-transport model to place the first observational constraints on the variability of Southern Hemisphere [OH] since ≈1880 AD.

  15. Clay mineralogy of the ocean sediments from the Wilkes Land margin, east Antarctica: implications on the paleoclimate, provenance and sediment dispersal pattern

    NASA Astrophysics Data System (ADS)

    Verma, Kamlesh; Bhattacharya, Sanjeeb; Biswas, P.; Shrivastava, Prakash K.; Pandey, Mayuri; Pant, N. C.

    2014-11-01

    Core U1359 collected from the continental rise off Wilkes Land, east Antarctica, is analyzed for the clay mineralogy and carbon content. The temporal variation of the clay mineralogical data shows a dominance of illite with chlorite, smectite and kaolinite in decreasing concentration. Clay mineral illite is negatively correlated with smectite which shows enrichment during 6.2-6.8, 5.5-5.8, 4.5 and 2.5 Ma. The mineralogical analyses on the silt size fraction (2-53 μm) of some selected samples were also carried out. The combined result of both the size fractions shows the presence of chlorite and illite in both size fractions, smectite and kaolinite only in clay size fraction (<2 μm) and similarity in the crystallinity and chemistry of illite in both fractions. Similar nature of illite in both fractions suggests negligible role of sorting probably due to the deposition from the waxing ice sheet. During times of ice growth, nearby cratonic east Antarctica shield provided biotite-rich sediments to the depositional site. On the other hand, the presence of smectite, only in the clay size fraction, suggests the effective role of sorting probably due to the deposition from distal source in ice retreat condition. During times of ice retreat, smectite-rich sediment derived from Ross Orogen is transported to the core site through surface or bottom water currents. Poor crystallinity of illite due to degradation further corroborates the ice retreat condition. The ice sheet proximal sediments of U1359 show that in the eastern part of Wilkes Land, the `warming' was initiated during late Miocene.

  16. Deposition velocity of ultrafine particles measured with the Eddy-Correlation Method over the Nansen Ice Sheet (Antarctica)

    NASA Astrophysics Data System (ADS)

    Contini, D.; Donateo, A.; Belosi, F.; Grasso, F. M.; Santachiara, G.; Prodi, F.

    2010-08-01

    This work reports an analysis of the concentration, size distribution, and deposition velocity of atmospheric particles over snow and iced surfaces on the Nansen Ice Sheet (Antarctica). Measurements were performed using the eddy-correlation method at a remote site during the XXII Italian expedition of the National Research Program in Antarctica (PNRA) in 2006. The measurement system was based on a condensation particle counter (CPC) able to measure particles down to 9 nm in diameter with a 50% efficiency and a Differential Mobility Particle Sizer for evaluating particle size distributions from 11 to 521 nm diameter in 39 channels. A method based on postprocessing with digital filters was developed to take into account the effect of the slow time response of the CPC. The average number concentration was 1338 cm-3 (median, 978 cm-3; interquartile range, 435-1854 cm-3). Higher concentrations were observed at low wind velocities. Results gave an average deposition velocity of 0.47 mm/s (median, 0.19 mm/s; interquartile range, -0.21 -0.88 mm/s). Deposition increased with the friction velocity and was on average 0.86 mm/s during katabatic wind characterized by velocities higher than 4 m/s. Observed size distributions generally presented two distinct modes, the first at approximately 15-20 nm and the second (representing on average 70% of the total particles) at 60-70 nm. Under strong-wind conditions, the second mode dominated the average size distribution.

  17. Spatial and temporal distributions of surface mass balance between Concordia and Vostok stations, Antarctica, from combined radar and ice core data: first results and detailed error analysis

    NASA Astrophysics Data System (ADS)

    Le Meur, Emmanuel; Magand, Olivier; Arnaud, Laurent; Fily, Michel; Frezzotti, Massimo; Cavitte, Marie; Mulvaney, Robert; Urbini, Stefano

    2018-05-01

    Results from ground-penetrating radar (GPR) measurements and shallow ice cores carried out during a scientific traverse between Dome Concordia (DC) and Vostok stations are presented in order to infer both spatial and temporal characteristics of snow accumulation over the East Antarctic Plateau. Spatially continuous accumulation rates along the traverse are computed from the identification of three equally spaced radar reflections spanning about the last 600 years. Accurate dating of these internal reflection horizons (IRHs) is obtained from a depth-age relationship derived from volcanic horizons and bomb testing fallouts on a DC ice core and shows a very good consistency when tested against extra ice cores drilled along the radar profile. Accumulation rates are then inferred by accounting for density profiles down to each IRH. For the latter purpose, a careful error analysis showed that using a single and more accurate density profile along a DC core provided more reliable results than trying to include the potential spatial variability in density from extra (but less accurate) ice cores distributed along the profile. The most striking feature is an accumulation pattern that remains constant through time with persistent gradients such as a marked decrease from 26 mm w.e. yr-1 at DC to 20 mm w.e. yr-1 at the south-west end of the profile over the last 234 years on average (with a similar decrease from 25 to 19 mm w.e. yr-1 over the last 592 years). As for the time dependency, despite an overall consistency with similar measurements carried out along the main East Antarctic divides, interpreting possible trends remains difficult. Indeed, error bars in our measurements are still too large to unambiguously infer an apparent time increase in accumulation rate. For the proposed absolute values, maximum margins of error are in the range 4 mm w.e. yr-1 (last 234 years) to 2 mm w.e. yr-1 (last 592 years), a decrease with depth mainly resulting from the time-averaging when

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

    PubMed

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

    2016-09-21

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

  19. Glacial-Geomorphological Evidence for Past Ice Cover in the Western Amundsen Sea Embayment of Antarctica

    NASA Astrophysics Data System (ADS)

    Roberts, S. J.; Johnson, J.; Ireland, L.; Rood, D. H.; Schaefer, J. M.; Whitehouse, P. L.; Pollard, D.

    2016-12-01

    Reliable model predictions of the future evolution of the West Antarctic Ice Sheet in the Amundsen Sea Embayment of Antarctica are currently hindered by a lack of data on the regional thinning history, particularly to the west of Thwaites Glacier. Our project will fill this critical gap by acquiring glacial-geological data, in particular, a high density of cosmogenic exposure ages that record ice sheet changes in the western Amundsen Sea Embayment over the past 20,000 years. In 2015/6, during the first of two field seasons in the region, we collected glacial-geomorphological evidence and cosmogenic surface exposure dating samples to constrain past ice cover of nunataks around Mt Murphy, which are adjacent to the Pope Glacier. The presence of abundant rounded granite and gneiss cobbles perched on bedrock ridges and terraces up to 885 m asl, as well as extensive striated bedrock above this height, indicate that ice was much thicker in the past. We also present preliminary results from a novel study on Turtle Rock, a key site for understanding past fluctuations of Pope Glacier. We used an unmanned aerial vehicle (UAV) to map the geomorphology of selected areas in greater detail than is currently possible from high-resolution satellite imagery, and ground-truthed the data by measuring the size, orientation and lithological composition of erratic cobbles and boulders. Combined with surface exposure dating, we will use these datasets to determine whether there were multiple phases of ice overriding, and the timing of thinning of Pope Glacier since the Last Glacial Maximum.

  20. Tectonomagmatic activity and ice dynamics in the Bransfield Strait back-arc basin, Antarctica

    NASA Astrophysics Data System (ADS)

    Dziak, Robert P.; Park, Minkyu; Lee, Won Sang; Matsumoto, Haru; Bohnenstiehl, Delwayne R.; Haxel, Joseph H.

    2010-01-01

    An array of moored hydrophones was used to monitor the spatiotemporal distribution of small- to moderate-sized earthquakes and ice-generated sounds within the Bransfield Strait, Antarctica. During a 2 year period, a total of 3900 earthquakes, 5925 icequakes and numerous ice tremor events were located throughout the region. The seismic activity included eight space-time earthquake clusters, positioned along the central neovolcanic rift zone of the young Bransfield back-arc basin. These sequences of small magnitude earthquakes, or swarms, suggest ongoing magmatic activity that becomes localized along isolated volcanic features and fissure-like ridges in the southwest portion of the basin. A total of 122 earthquakes were located along the South Shetland trench, indicating continued deformation and possibly ongoing subduction along this margin. The large number of icequakes observed show a temporal pattern related to seasonal freeze-thaw cycles and a spatial distribution consistent with channeling of sea ice along submarine canyons from glacier fronts. Several harmonic tremor episodes were sourced from a large (˜30 km2) iceberg that entered northeast portion of the basin. The spectral character of these signals suggests they were produced by either resonance of a small chamber of fluid within the iceberg, or more likely, due to periodicity of discrete stick-slip events caused by contact of the moving iceberg with the seafloor. These pressure waves appear to have been excited by abrasion of the iceberg along the seafloor as it passed Clarence and Elephant Islands.

  1. Improved methodologies for continuous-flow analysis of stable water isotopes in ice cores

    NASA Astrophysics Data System (ADS)

    Jones, Tyler R.; White, James W. C.; Steig, Eric J.; Vaughn, Bruce H.; Morris, Valerie; Gkinis, Vasileios; Markle, Bradley R.; Schoenemann, Spruce W.

    2017-02-01

    Water isotopes in ice cores are used as a climate proxy for local temperature and regional atmospheric circulation as well as evaporative conditions in moisture source regions. Traditional measurements of water isotopes have been achieved using magnetic sector isotope ratio mass spectrometry (IRMS). However, a number of recent studies have shown that laser absorption spectrometry (LAS) performs as well or better than IRMS. The new LAS technology has been combined with continuous-flow analysis (CFA) to improve data density and sample throughput in numerous prior ice coring projects. Here, we present a comparable semi-automated LAS-CFA system for measuring high-resolution water isotopes of ice cores. We outline new methods for partitioning both system precision and mixing length into liquid and vapor components - useful measures for defining and improving the overall performance of the system. Critically, these methods take into account the uncertainty of depth registration that is not present in IRMS nor fully accounted for in other CFA studies. These analyses are achieved using samples from a South Pole firn core, a Greenland ice core, and the West Antarctic Ice Sheet (WAIS) Divide ice core. The measurement system utilizes a 16-position carousel contained in a freezer to consecutively deliver ˜ 1 m × 1.3 cm2 ice sticks to a temperature-controlled melt head, where the ice is converted to a continuous liquid stream and eventually vaporized using a concentric nebulizer for isotopic analysis. An integrated delivery system for water isotope standards is used for calibration to the Vienna Standard Mean Ocean Water (VSMOW) scale, and depth registration is achieved using a precise overhead laser distance device with an uncertainty of ±0.2 mm. As an added check on the system, we perform inter-lab LAS comparisons using WAIS Divide ice samples, a corroboratory step not taken in prior CFA studies. The overall results are important for substantiating data obtained from LAS

  2. Human and climate impacts on Holocene fire activity recorded in polar and mountain ice cores

    NASA Astrophysics Data System (ADS)

    Kehrwald, Natalie; Zennaro, Piero; Kirchgeorg, Torben; Li, Quanlian; Wang, Ninglian; Power, Mitchell; Zangrando, Roberta; Gabrielli, Paolo; Thompson, Lonnie; Gambaro, Andrea; Barbante, Carlo

    2014-05-01

    Fire is one of the major influences of biogeochemical change on local to hemispheric scales through emitting greenhouse gases, altering atmospheric chemistry, and changing primary productivity. Levoglucosan (1,6-anhydro-β-D-glucopyranose) is a specific molecular that can only be produced by cellulose burning at temperatures > 300°C, comprises a major component of smoke plumes, and can be transported across > 1000 km distances. Levoglucosan is deposited on and archived in glaciers over glacial interglacial cycles resulting in pyrochemical evidence for exploring interactions between fire, climate and human activity. Ice core records provide records of past biomass burning from regions of the world with limited paleofire data including polar and low-latitude, high-altitude regions. Here, we present Holocene fire activity records from the NEEM, Greenland (77° 27'N; 51° 3'W; 2454 masl), EPICA Dome C, Antarctica (75° 06'S; 123° 21'E; 3233 masl), Kilimanjaro, Tanzania (3° 05'S, 21.2° E, 5893 masl) and the Muztagh, China (87.17° E; 36.35° N; 5780 masl ice cores. The NEEM ice core reflects boreal fire activity from both North American and Eurasian sources. Temperature is the dominant control of NEEM levoglucosan flux over decadal to millennial time scales, while droughts influence fire activity over sub-decadal timescales. Our results demonstrate the prominence of Siberian fire sources during intense multiannual droughts. Unlike the NEEM core, which incorporates the largest land masses in the world as potential fire sources, EPICA Dome C is located far from any possible fire source. However, EPICA Dome C levoglucosan concentrations are consistently above detection limits and demonstrate a substantial 1000-fold increase in fire activity beginning approximately 800 years ago. This significant and sustained increase coincides with Maori arrival and dispersal in New Zealand augmented by later European arrival in Australia. The EPICA Dome C levoglucosan profile is

  3. Laser Induced Fluorescence Imaging: Searching for Organics from the Dry Valleys of Queen Maud Land Antarctica to the Regolith and Ices of Mars

    NASA Astrophysics Data System (ADS)

    Storrie-Lombardi, M. C.; Sattler, B.; Muller, J.-P.; Fisk, M.; Cousins, C.; Dartnell, L.

    2009-04-01

    . Rev. Sci. Ins., 72(12): 4452-4459. 2. Nealson, K.H., Tsapin, A., and Storrie-Lombardi, M. 2002. Searching for life in the universe: unconventional methods for an unconventional problem. International Microbio., 5: 223-230. 3. Storrie-Lombardi, M.C., Muller, J.-P., Fisk, M.R., Griffiths, A.D., and Coates, A.J. 2008a. Potential for non-destructive astrochemistry using the ExoMars PanCam. Geophys. Res. Lett., 35: L12201, doi 10.1029/2008GL034296. 4. Storrie-Lombardi, M.C., Muller, J.-P., Fisk, M.R., Griffiths, A.D., and Coates, A.J. 2008b. Epifluorescence surveys of extreme environments using PanCam imaging systems: Antarctica and the Mars regolith. Instruments, Methods, and Missions for Astrobiology XI (R.B. Hoover, G.V. Levin, & A.Y. Rozanov, Eds.) Proc. SPIE, 7097 (25): 1-10. 5. Storrie-Lombardi, M.C. 2005. Post-Bayesian strategies to optimize astrobiology instrument suites: lessons from Antarctica and the Pilbara. Astrobiology and Planetary Missions (R. B. Hoover, G. V. Levin and A. Y. Rozanov, Eds.), Proc. SPIE, 5906: 288-301. 6. Psenner, R. and Sattler, B. 1998. Life at the freezing point. Science, 280: 2073-2074. 7. Sattler, B., Puxbaum, H., and Psenner, R. 2001. Bacterial growth in supercooled cloud droplets. Geophys. Res. Ltrs., 28(2): 239-242. 8. Sattler, B., Waldhuber, S., Fischer, H., Semmler, H., Sipiera, P., and Psenner, R. 2004. Microbial activity and phylogeny in ice cores retrieved from Lake Paula, a newly detected freshwater lake in Antarctica. Instruments, Methods, and Missions for Astrobiology VIII (R. B. Hoover, G. V. Levin and A. Y. Rozanov, Eds.) Proc. SPIE, 5555: 170-179. 9. Muller, J.-P., Storrie-Lombardi, M.C., Fisk, M.R., Coates, A., Griffiths, A., Rees, K., Walton, D., Theobald, C., Brockley-Blatt, C., and Rousseau, A. 2009. WALI - Wide Angle Laser Imaging enhancement to ExoMars PanCam: a system for organics and life detection in European Geosciences Union General Assembly 2009. Vienna, Austria.

  4. Greenhouse to Icehouse Antarctic Paleoclimate and Ice History from George V Land and Adélie Land Shelf Sediments

    NASA Astrophysics Data System (ADS)

    Williams, T.; Escutia, C.; De Santis, L.; O'Brien, P.; Pekar, S. F.; Brinkhuis, H.; Domack, E. W.

    2013-12-01

    Along the George V and Adélie Land continental shelf of East Antarctica, shallowly-buried strata contain a record of Antarctica's climate and ice history from the lush forests of the Eocene greenhouse to the dynamic ice sheet margins of the Neogene. Short piston cores and dredges have recovered Early Cretaceous and Eocene organic-rich sediment at the seabed, and in 2010, IODP Expedition 318 recovered earliest Oligocene and early Pliocene subglacial and proglacial diamictites. However, challenging ice and drilling conditions from the JOIDES Resolution on the shelf resulted in poor core recovery and sites had to be abandoned before the stratigraphic targets could be reached. Therefore, in a new IODP drilling proposal submitted earlier this year, we propose to use the MeBo sea bed drill for improved core recovery and easier access to the shelf, and drill a stratigraphic transect of shallow (~80m) holes. To investigate the evolution of the Antarctic ice sheet in this sector, we target strata above and below regional erosional and downlap surfaces to date and characterize major episodes of ice sheet advance and retreat. These direct records of ice extent on the shelf can be set in the context of Southern Ocean records of temperature, ice-rafted debris (IRD) and latitudinal fluctuations of the opal belt, and hence we can relate ice sheet evolution to paleoclimate conditions. Targets include possible late Eocene precursor glaciations, the Eocene/Oligocene boundary erosion surface, Oligocene and Miocene ice extents, and ice margin fluctuations in the Pliocene. At the Cretaceous and Eocene proposed sites, marine and terrestrial temperature proxies and palynological records will provide information on high-latitude paleoenvironments and pole-equator temperature gradients. Here we present existing data from the area and the proposed new drill sites. The ice and climate history of the George V and Adélie Land margin can provide warm-world scenarios to help understand ice

  5. Ice Velocity Mapping in Antarctica - Towards a Virtual Satellite Constellation

    NASA Astrophysics Data System (ADS)

    Scheuchl, B.; Mouginot, J.; Rignot, E. J.; Crevier, Y.

    2013-12-01

    Ice sheets are acknowledged by the World Meteorological Organization (WMO) and the United Nations Framework Convention on Climate Change (UNFCCC) as an Essential Climate Variable (ECV) needed to make significant progress in the generation of global climate products and derived information. Ice velocity is a crucial geophysical parameter that can be measured using spaceborne Synthetic Aperture Radar (SAR) data. Here, we report on an update to available Earth System Data Records (ESDR) of ice velocity in Antarctica based on data from a suite of spaceborne (SAR) sensors and provide an overview on international coordination in an effort to best utilize the available SAR satellites. Building on the first complete mapping of the flow of ice surface over the Antarctic continent using data predominantly acquired during IPY, we are working on a series of regional studies analyzing data from several different epochs. The analysis of velocity changes between discrete measurements requires even more careful data processing in order to be able to accurately measure subtle changes. Examples for Larsen-C and the Amundsen Sea Embayment will be presented. Data continuity is a crucial aspect to this work, particularly in light of the fact that 4 SAR missions have ceased operations since IPY and all available missions have a primary mandate that is not scientific data collection. Following the successful internationally coordinated SAR data acquisitions over ice sheets during the International Polar Year 2007/2008, efforts are undertaken to continue data acquisitions in the spirit of collaboration. The Polar Space Task Group (PSTG) is succeeding the IPY coordinating body of international space agencies, Space Task Group (STG). The PSTG SAR Coordination Working Group was created to address the issue of SAR data acquisitions in the cryosphere. A review of ice sheet requirements was undertaken by the science community, presented to PSTG, and followed up with a set of sensor specific

  6. Formation and character of an ancient 19-m ice cover and underlying trapped brine in an "ice-sealed" east Antarctic lake.

    PubMed

    Doran, Peter T; Fritsen, Christian H; McKay, Christopher P; Priscu, John C; Adams, Edward E

    2003-01-07

    Lake Vida, one of the largest lakes in the McMurdo Dry Valleys of Antarctica, was previously believed to be shallow (<10 m) and frozen to its bed year-round. New ice-core analysis and temperature data show that beneath 19 m of ice is a water column composed of a NaCl brine with a salinity seven times that of seawater that remains liquid below -10 degrees C. The ice cover thickens at both its base and surface, sealing concentrated brine beneath. The ice cover is stabilized by a negative feedback between ice growth and the freezing-point depression of the brine. The ice cover contains frozen microbial mats throughout that are viable after thawing and has a history that extends to at least 2,800 (14)C years B.P., suggesting that the brine has been isolated from the atmosphere for as long. To our knowledge, Lake Vida has the thickest subaerial lake ice cover recorded and may represent a previously undiscovered end-member lacustrine ecosystem on Earth.

  7. The Larsen Ice Shelf in Antarctica viewed from NASA's DC-8 aircraft during the AirSAR 2004 campaign

    NASA Image and Video Library

    2004-03-16

    The Larsen Ice Shelf in Antarctica viewed from NASA's DC-8 aircraft during the AirSAR 2004 campaign. AirSAR 2004 is a three-week expedition in Central and South America by an international team of scientists that is using an all-weather imaging tool, called the Airborne Synthetic Aperture Radar (AirSAR), located onboard NASA's DC-8 airborne laboratory. Scientists from many parts of the world are combining ground research with NASA's AirSAR technology to improve and expand on the quality of research they are able to conduct. These photos are from the DC-8 aircraft while flying an AirSAR mission over Antarctica. The Antarctic Peninsula is more similar to Alaska and Patagonia than to the rest of the Antarctic continent. It is drained by fast glaciers, receives abundant precipitation, and melts significantly in the summer months. In recent decades, the Peninsula has experienced significant atmospheric warming (about 2 degrees C since 1950), which has triggered a vast and spectacular retreat of its floating ice shelves, glacier reduction, a decrease in permanent snow cover and a lengthening of the melt season. As a result, the contribution to sea level from this region could be rapid and substantial. With an area of 120,000 km, or ten times the Patagonia ice fields, the Peninsula could contribute as much as 0.4mm/yr sea level rise, which would be the largest single contribution to sea level from anywhere in the world. This region is being studied by NASA using a DC-8 equipped with the Airborne Synthetic Aperture Radar developed by scientists from NASA’s Jet Propulsion Laboratory. AirSAR will provide a baseline model and unprecedented mapping of the region. This data will make it possible to determine whether the warming trend is slowing, continuing or accelerating. AirSAR will also provide reliable information on ice shelf thickness to measure the contribution of the glaciers to sea level.

  8. The Larsen Ice Shelf in Antarctica viewed from NASA's DC-8 aircraft during the AirSAR 2004 campaign

    NASA Image and Video Library

    2004-03-13

    The Larsen Ice Shelf in Antarctica viewed from NASA's DC-8 aircraft during the AirSAR 2004 campaign. AirSAR 2004 is a three-week expedition in Central and South America by an international team of scientists that is using an all-weather imaging tool, called the Airborne Synthetic Aperture Radar (AirSAR), located onboard NASA's DC-8 airborne laboratory. Scientists from many parts of the world are combining ground research with NASA's AirSAR technology to improve and expand on the quality of research they are able to conduct. These photos are from the DC-8 aircraft while flying an AirSAR mission over Antarctica. The Antarctic Peninsula is more similar to Alaska and Patagonia than to the rest of the Antarctic continent. It is drained by fast glaciers, receives abundant precipitation, and melts significantly in the summer months. In recent decades, the Peninsula has experienced significant atmospheric warming (about 2 degrees C since 1950), which has triggered a vast and spectacular retreat of its floating ice shelves, glacier reduction, a decrease in permanent snow cover and a lengthening of the melt season. As a result, the contribution to sea level from this region could be rapid and substantial. With an area of 120,000 km, or ten times the Patagonia ice fields, the Peninsula could contribute as much as 0.4mm/yr sea level rise, which would be the largest single contribution to sea level from anywhere in the world. This region is being studied by NASA using a DC-8 equipped with the Airborne Synthetic Aperture Radar developed by scientists from NASA’s Jet Propulsion Laboratory. AirSAR will provide a baseline model and unprecedented mapping of the region. This data will make it possible to determine whether the warming trend is slowing, continuing or accelerating. AirSAR will also provide reliable information on ice shelf thickness to measure the contribution of the glaciers to sea level.

  9. The Larsen Ice Shelf in Antarctica viewed from NASA's DC-8 aircraft during the AirSAR 2004 campaign

    NASA Image and Video Library

    2004-03-16

    The Larsen Ice Shelf in Antarctica viewed from NASA's DC-8 aircraft during the AirSAR 2004 campaign. AirSAR 2004 is a three-week expedition in Central and South America by an international team of scientists that is using an all-weather imaging tool, called the Airborne Synthetic Aperture Radar (AirSAR), located onboard NASA's DC-8 airborne laboratory. Scientists from many parts of the world are combining ground research with NASA's AirSAR technology to improve and expand on the quality of research they are able to conduct. These photos are from the DC-8 aircraft while flying an AirSAR mission over Antarctica. The Antarctic Peninsula is more similar to Alaska and Patagonia than to the rest of the Antarctic continent. It is drained by fast glaciers, receives abundant precipitation, and melts significantly in the summer months. In recent decades, the Peninsula has experienced significant atmospheric warming (about 2 degrees C since 1950), which has triggered a vast and spectacular retreat of its floating ice shelves, glacier reduction, a decrease in permanent snow cover and a lengthening of the melt season. As a result, the contribution to sea level from this region could be rapid and substantial. With an area of 120,000 km, or ten times the Patagonia ice fields, the Peninsula could contribute as much as 0.4mm/yr sea level rise, which would be the largest single contribution to sea level from anywhere in the world. This region is being studied by NASA using a DC-8 equipped with an Airborne Synthetic Aperture Radar (AirSAR) developed by scientists from NASA’s Jet Propulsion Laboratory. AirSAR will provide a baseline model and unprecedented mapping of the region. This data will make it possible to determine whether the warming trend is slowing, continuing or accelerating. AirSAR will also provide reliable information on ice shelf thickness to measure the contribution of the glaciers to sea level.

  10. Bacterial abundance and composition in marine sediments beneath the Ross Ice Shelf, Antarctica.

    PubMed

    Carr, S A; Vogel, S W; Dunbar, R B; Brandes, J; Spear, J R; Levy, R; Naish, T R; Powell, R D; Wakeham, S G; Mandernack, K W

    2013-07-01

    Marine sediments of the Ross Sea, Antarctica, harbor microbial communities that play a significant role in the decomposition, mineralization, and recycling of organic carbon (OC). In this study, the cell densities within a 153-cm sediment core from the Ross Sea were estimated based on microbial phospholipid fatty acid (PLFA) concentrations and acridine orange direct cell counts. The resulting densities were as high as 1.7 × 10⁷ cells mL⁻¹ in the top ten centimeters of sediments. These densities are lower than those calculated for most near-shore sites but consistent with deep-sea locations with comparable sedimentation rates. The δ¹³C measurements of PLFAs and sedimentary and dissolved carbon sources, in combination with ribosomal RNA (SSU rRNA) gene pyrosequencing, were used to infer microbial metabolic pathways. The δ¹³C values of dissolved inorganic carbon (DIC) in porewaters ranged downcore from -2.5‰ to -3.7‰, while δ¹³C values for the corresponding sedimentary particulate OC (POC) varied from -26.2‰ to -23.1‰. The δ¹³C values of PLFAs ranged between -29‰ and -35‰ throughout the sediment core, consistent with a microbial community dominated by heterotrophs. The SSU rRNA gene pyrosequencing revealed that members of this microbial community were dominated by β-, δ-, and γ-Proteobacteria, Actinobacteria, Chloroflexi and Bacteroidetes. Among the sequenced organisms, many appear to be related to known heterotrophs that utilize OC sources such as amino acids, oligosaccharides, and lactose, consistent with our interpretation from δ¹³CPLFA analysis. Integrating phospholipids analyses with porewater chemistry, δ¹³CDIC and δ¹³CPOC values and SSU rRNA gene sequences provides a more comprehensive understanding of microbial communities and carbon cycling in marine sediments, including those of this unique ice shelf environment. © 2013 John Wiley & Sons Ltd.

  11. Deriving micro- to macro-scale seismic velocities from ice-core c axis orientations

    NASA Astrophysics Data System (ADS)

    Kerch, Johanna; Diez, Anja; Weikusat, Ilka; Eisen, Olaf

    2018-05-01

    One of the great challenges in glaciology is the ability to estimate the bulk ice anisotropy in ice sheets and glaciers, which is needed to improve our understanding of ice-sheet dynamics. We investigate the effect of crystal anisotropy on seismic velocities in glacier ice and revisit the framework which is based on fabric eigenvalues to derive approximate seismic velocities by exploiting the assumed symmetry. In contrast to previous studies, we calculate the seismic velocities using the exact c axis angles describing the orientations of the crystal ensemble in an ice-core sample. We apply this approach to fabric data sets from an alpine and a polar ice core. Our results provide a quantitative evaluation of the earlier approximative eigenvalue framework. For near-vertical incidence our results differ by up to 135 m s-1 for P-wave and 200 m s-1 for S-wave velocity compared to the earlier framework (estimated 1 % difference in average P-wave velocity at the bedrock for the short alpine ice core). We quantify the influence of shear-wave splitting at the bedrock as 45 m s-1 for the alpine ice core and 59 m s-1 for the polar ice core. At non-vertical incidence we obtain differences of up to 185 m s-1 for P-wave and 280 m s-1 for S-wave velocities. Additionally, our findings highlight the variation in seismic velocity at non-vertical incidence as a function of the horizontal azimuth of the seismic plane, which can be significant for non-symmetric orientation distributions and results in a strong azimuth-dependent shear-wave splitting of max. 281 m s-1 at some depths. For a given incidence angle and depth we estimated changes in phase velocity of almost 200 m s-1 for P wave and more than 200 m s-1 for S wave and shear-wave splitting under a rotating seismic plane. We assess for the first time the change in seismic anisotropy that can be expected on a short spatial (vertical) scale in a glacier due to strong variability in crystal-orientation fabric (±50 m s-1 per 10 cm

  12. Science goals for a Mars Polar Cap subsurface mission : optical approaches for investiagations of inclusions in ice

    NASA Technical Reports Server (NTRS)

    Mogensen, Claus T.; Carsey, Frank D.; Behar, Alberto; Engelhardt, Hermann; Lane, Arthur L.

    2002-01-01

    The Mars Polar Caps are highly interesting features of Mars and have received much recent attention with new and exciting data on morphology, basal units, and layered outcroppings. We have examined the climatological, glaciological, and geological issues associated with a subsurface exploration of the Mars North Polar Cap and have determined that a finescale optical examination of ice in a borehole, to examine the stratigraphy, geochemistry and geochronology of the ice, is feasible. This information will enable reconstruction of the development of the cap as well as predication of the properties of its ice. We present visible imagery taken of dust inclusions in archived Greenland ice cores as well as in-situ images of accreted lithologic inclusions in West Antarctica, and we argue for use of this kind of data in Mars climate reconstruction as has been successful with Greenland and Antarctic ice core anlaysis.

  13. Science goals for a Mars Polar Cap subsurface mission : optical approaches for investigations of inclusions in ice

    NASA Technical Reports Server (NTRS)

    Carsey, Frank; Mogensen, Claus T.; Behar, Alberto; Engelhardt, Hermann; Lane, Arthur L.

    2002-01-01

    The Mars Polar Caps are highly interesting features of Mars and have received much recent attention with new and exciting data on morphology, basal units, and layered outcroppings. We have examined the climatological, glaciological, and geological issues associated with a subsurface exploration of the Mars North Polar Cap and have determined that a finescale optical examination of ice in a borehole, to examine the stratigraphy, geochemistry and geochronology of the ice, is feasible. This information will enable reconstruction of the development of the cap as well as prediction of the properties of its ice. We present visible imagery taken of dust inclusions in archived Greenland ice cores as well as in-situ images of accreted lithologic inclusions in West Antarctica, and we argue for use of this kind of data in Mars climate reconstruction as has been successful with Greenland and Antarctic ice core analysis. .

  14. New constraints on the structure and dynamics of the East Antarctic Ice Sheet from the joint IPY/Ice Bridge ICECAP aerogeophysical project

    NASA Astrophysics Data System (ADS)

    Blankenship, D. D.; Young, D. A.; Siegert, M. J.; van Ommen, T. D.; Roberts, J. L.; Wright, A.; Warner, R. C.; Holt, J. W.; Young, N. W.; Le Meur, E.; Legresy, B.; Cavitte, M.; Icecap Team

    2010-12-01

    Ice within marine basins of East Antarctica, and their outlets, represent the ultimate limit on sea level change. The region of East Antarctica between the Ross Sea and Wilkes Land hosts a number of major basin, but has been poorly understood. Long range aerogeophysics from US, Australian and French stations, with significant British and IceBridge support, has, under the banner of the ICECAP project, greatly improved our knowledge of ice thickness, surface elevation, and crustal structure of the Wilkes and Aurora Subglacial Basins, as well as the Totten Glacier, Cook Ice Shelf, and Byrd Glacier. We will discuss the evolution of the Wilkes and Aurora Subglacial Basins, new constraints on the geometry of the major outlet glaciers, as well as our results from surface elevation change measurements over dynamic regions of the ice sheet. We will discuss the implications of our data for the presence of mid Pleistocene ice in central East Antarctica. Future directions for ICECAP will be discussed.

  15. Heat flux variations over sea ice observed at the coastal area of the Sejong Station, Antarctica

    NASA Astrophysics Data System (ADS)

    Park, Sang-Jong; Choi, Tae-Jin; Kim, Seong-Joong

    2013-08-01

    This study presents variations of sensible heat flux and latent heat flux over sea ice observed in 2011 from the 10-m flux tower located at the coast of the Sejong Station on King George Island, Antarctica. A period from July to September was selected as a sea ice period based on daily record of sea state and hourly photos looking at the Marian Cove in front of the Sejong Station. For the sea ice period, mean sensible heat flux is about -11 Wm-2, latent heat flux is about +2 W m-2, net radiation is -12 W m-2, and residual energy is -3 W m-2 with clear diurnal variations. Estimated mean values of surface exchange coefficients for momentum, heat and moisture are 5.15 × 10-3, 1.19 × 10-3, and 1.87 × 10-3, respectively. The observed exchange coefficients of heat shows clear diurnal variations while those of momentum and moisture do not show diurnal variation. The parameterized exchange coefficients of heat and moisture produces heat fluxes which compare well with the observed diurnal variations of heat fluxes.

  16. Ice sheet systems and sea level change.

    NASA Astrophysics Data System (ADS)

    Rignot, E. J.

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

    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. Identifying the AD 1257 Salamas volcanic event from micron-size tephra composition in two East Antarctic ice cores

    NASA Astrophysics Data System (ADS)

    Petit, Jean Robert; Narcisi, Biancamaria; Batanova, Valentina G.; Joël, Savarino; Komorowski, Jean Christophe; Michel, Agnes; Metrich, Nicole; Besson, Pascale; Vidal, Celine; Sobolev, Alexander V.

    2016-04-01

    A wealth of valuable data about the history of explosive volcanic history can be extracted from polar ice successions. Both the volatile by-products and the solid silicate (tephra) components of volcanic plumes can be incorporated into snow layers, providing tools for chronostratigraphic correlations and for interpretation of climate-volcanism interactions. Volcanic events from low-latitude regions are of particular interest as the related sulphate aerosol travelling through the stratosphere can reach the polar sheets forming inter-hemispheric (Greenland and Antarctica) signals preserved in the ice. Within the glaciological record of globally significant volcanic markers, the AD1259 signal represents one of most prominent events over the last thousands years. Its source has been long debated. On the basis of recent field investigations (Lavigne et al., 2013; Vidal et al., 2015), it has been proposed that Mount Samalas on Lombok Island (Indonesia) represents the source responsible for the polar event. With the goal of bringing distal tephrochronological evidence to source identification, we have attempted to identify volcanic ash associated to the AD 1259 sulphate pulse. To this purpose we used firn and ice-core samples from two East Antarctic Plateau sites: Concordia-Dome C (75°06' S, 123°20' E, 3233 m) and Talos Dome (72°49'S, 159°11'E, 2315 m). Our high-resolution studies included sample processing in a Class 100 clean room using established ultra-clean procedures for insoluble microparticle analyses, Coulter counter grain size measurements, scanning electron microscope observations and the geochemical (major elements) composition from the recently set ISTERRE Jeol JXA 8230 Superprobe and calibrated for small particles analysis. Despite the difficulty of studying such minute fragments, within both cores we located and characterised multiple tiny (micron-size) glass shards concomitant with the volcanic peak. We present preliminary results alongside comparison

  19. High-resolution sulfur isotopes in ice cores identify large stratospheric volcanic eruptions

    NASA Astrophysics Data System (ADS)

    Burke, Andrea; Sigl, Michael; Adkins, Jess; Paris, Guillaume; McConnell, Joe

    2016-04-01

    The record of the volcanic forcing of climate over the past 2500 years is reconstructed primarily from sulfate concentrations in ice cores. Of particular interest are stratospheric eruptions, as these afford sulfate aerosols the longest residence time and largest dispersion in the atmosphere, and thus the greatest impact on radiative forcing. Identification of stratospheric eruptions currently relies on the successful matching of the same volcanic sulphate peak in ice cores from both the Northern and Southern hemispheres (a "bipolar event"). These are interpreted to reflect the global distribution of sulfur aerosols by the stratospheric winds. Despite its recent success, this method relies on precise and accurate dating of ice cores, in order to distinguish between a true 'bipolar event' and two separate eruptions that occurred in close temporal succession. Sulfur isotopes can been used to distinguish between these two scenarios since stratospheric sulfur aerosols are exposed to UV radiation which imparts a mass independent fractionation (Baroni et al., 2007). Mass independent fractionation of sulfate in ice cores thus offers a novel method of fingerprinting stratospheric eruptions, and thus refining the historic record of explosive volcanism and its forcing of climate. Here we present new high-resolution (sub-annual) sulfur isotope data from the Tunu Ice core in Greenland over seven eruptions. Sulfur isotopes were measured by MC-ICP-MS, which substantially reduces sample size requirements and allows high temporal resolution from a single ice core. We demonstrate the efficacy of the method on recent, well-known eruptions (including Pinatubo and Katmai/Novarupta), and then apply it to unidentified sulfate peaks, allowing us to identify new stratospheric eruptions. Baroni, M., Thiemens, M. H., Delmas, R. J., & Savarino, J. (2007). Mass-independent sulfur isotopic compositions in stratospheric volcanic eruptions. Science, 315(5808), 84-87. http://doi.org/10

  20. Spatial Variability of Perchlorate along a Traverse Route from Zhongshan Station to Dome A, East Antarctica

    NASA Astrophysics Data System (ADS)

    Jiang, S.; Cole-Dai, J.; Li, Y.; An, C.

    2016-12-01

    Snow deposition and accumulation on the Antarctic ice sheet preserve records of climatic change, as well as those of chemical characteristics of the environment. Chemical composition of snow and ice cores can be used to track the sources of important substances including pollutants and to investigate relationships between atmospheric chemistry and climatic conditions. Recent development in analytical methodology has enabled the determination of ultra-trace levels of perchlorate in polar snow. We have measured perchlorate concentrations in surface snow samples collected along a traverse route from Zhongshan Station to Dome A in East Antarctica to determine the level of atmospheric perchlorate in East Antarctica and to assess the spatial variability of perchlorate along the traverse route. Results show that the perchlorate concentrations vary between 32 and 200 ng kg-1, with an average of 104.3 ng kg-1. And perchlorate concentration profile presents regional variation patterns along the traverse route. In the coastal region, perchlorate concentration displays an apparent decreasing relationship with increasing distance inland; it exhibits no apparent trend in the intermediate region from 200 to 1000 km. The inland region from 1000 to 1244 km presents a generally increasing trend of perchlorate concentration approaching the dome. Different rates of atmospheric production, dilution by snow accumulation and re-deposition of snow-emitted perchlorate (post-depositional change) are the three possible factors influencing the spatial variability of perchlorate over Antarctica.

  1. Summer Drivers of Atmospheric Variability Affecting Ice Shelf Thinning in the Amundsen Sea Embayment, West Antarctica

    NASA Astrophysics Data System (ADS)

    Deb, Pranab; Orr, Andrew; Bromwich, David H.; Nicolas, Julien P.; Turner, John; Hosking, J. Scott

    2018-05-01

    Satellite data and a 35-year hindcast of the Amundsen Sea Embayment summer climate using the Weather Research and Forecasting model are used to understand how regional and large-scale atmospheric variability affects thinning of ice shelves in this sector of West Antarctica by melting from above and below (linked to intrusions of warm water caused by anomalous westerlies over the continental shelf edge). El Niño episodes are associated with an increase in surface melt but do not have a statistically significant impact on westerly winds over the continental shelf edge. The location of the Amundsen Sea Low and the polarity of the Southern Annular Mode (SAM) have negligible impact on surface melting, although a positive SAM and eastward shift of the Amundsen Sea Low cause anomalous westerlies over the continental shelf edge. The projected future increase in El Niño episodes and positive SAM could therefore increase the risk of disintegration of West Antarctic ice shelves.

  2. Sedimentology and geochemistry of a perennially ice-covered epishelf lake in Bunger Hills Oasis, East Antarctica.

    PubMed

    Doran, P T; Wharton, R A; Lyons, W B; Des Marais, D J; Andersen, D T

    2000-01-01

    A process-oriented study was carried out in White Smoke lake, Bunger Hills, East Antarctica, a perennially ice-covered (1.8 to 2.8 m thick) epishelf (tidally-forced) lake. The lake water has a low conductivity and is relatively well mixed. Sediments are transferred from the adjacent glacier to the lake when glacier ice surrounding the sediment is sublimated at the surface and replaced by accumulating ice from below. The lake bottom at the west end of the lake is mostly rocky with a scant sediment cover. The east end contains a thick sediment profile. Grain size and delta 13C increase with sediment depth, indicating a more proximal glacier in the past. Sedimentary 210Pb and 137Cs signals are exceptionally strong, probably a result of the focusing effect of the large glacial catchment area. The post-bomb and pre-bomb radiocarbon reservoirs are c. 725 14C yr and c. 1950 14C yr, respectively. Radiocarbon dating indicates that the east end of the lake is >3 ka BP, while photographic evidence and the absence of sediment cover indicate that the west end has formed only over the last century. Our results indicate that the southern ice edge of Bunger Hills has been relatively stable with only minor fluctuations (on the scale of hundreds of metres) over the last 3000 years.

  3. Formation and character of an ancient 19-m ice cover and underlying trapped brine in an “ice-sealed” east Antarctic lake

    PubMed Central

    Doran, Peter T.; Fritsen, Christian H.; McKay, Christopher P.; Priscu, John C.; Adams, Edward E.

    2003-01-01

    Lake Vida, one of the largest lakes in the McMurdo Dry Valleys of Antarctica, was previously believed to be shallow (<10 m) and frozen to its bed year-round. New ice-core analysis and temperature data show that beneath 19 m of ice is a water column composed of a NaCl brine with a salinity seven times that of seawater that remains liquid below −10°C. The ice cover thickens at both its base and surface, sealing concentrated brine beneath. The ice cover is stabilized by a negative feedback between ice growth and the freezing-point depression of the brine. The ice cover contains frozen microbial mats throughout that are viable after thawing and has a history that extends to at least 2,800 14C years B.P., suggesting that the brine has been isolated from the atmosphere for as long. To our knowledge, Lake Vida has the thickest subaerial lake ice cover recorded and may represent a previously undiscovered end-member lacustrine ecosystem on Earth. PMID:12518052

  4. A TEM analysis of nanoparticulates in a Polar ice core

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Esquivel, E.V.; Murr, L.E

    2004-03-15

    This paper explores the prospect for analyzing nanoparticulates in age-dated ice cores representing times in antiquity to establish a historical reference for atmospheric particulate regimes. Analytical transmission electron microscope (TEM) techniques were utilized to observe representative ice-melt water drops dried down on carbon/formvar or similar coated grids. A 10,000-year-old Greenland ice core was melted, and representative water drops were transferred to coated grids in a clean room environment. Essentially, all particulates observed were aggregates and either crystalline or complex mixtures of nanocrystals. Especially notable was the observation of carbon nanotubes and related fullerene-like nanocrystal forms. These observations are similar withmore » some aspects of contemporary airborne particulates including carbon nanotubes and complex nanocrystal aggregates.« less

  5. Ice core records of climate variability on the Third Pole with emphasis on the Guliya ice cap, western Kunlun Mountains

    NASA Astrophysics Data System (ADS)

    Thompson, Lonnie G.; Yao, Tandong; Davis, Mary E.; Mosley-Thompson, Ellen; Wu, Guangjian; Porter, Stacy E.; Xu, Baiqing; Lin, Ping-Nan; Wang, Ninglian; Beaudon, Emilie; Duan, Keqin; Sierra-Hernández, M. Roxana; Kenny, Donald V.

    2018-05-01

    Records of recent climate from ice cores drilled in 2015 on the Guliya ice cap in the western Kunlun Mountains of the Tibetan Plateau, which with the Himalaya comprises the Third Pole (TP), demonstrate that this region has become warmer and moister since at least the middle of the 19th century. Decadal-scale linkages are suggested between ice core temperature and snowfall proxies, North Atlantic oceanic and atmospheric processes, Arctic temperatures, and Indian summer monsoon intensity. Correlations between annual-scale oxygen isotopic ratios (δ18O) and tropical western Pacific and Indian Ocean sea surface temperatures are also demonstrated. Comparisons of climate records during the last millennium from ice cores acquired throughout the TP illustrate centennial-scale differences between monsoon and westerlies dominated regions. Among these records, Guliya shows the highest rate of warming since the end of the Little Ice Age, but δ18O data over the last millennium from TP ice cores support findings that elevation-dependent warming is most pronounced in the Himalaya. This, along with the decreasing precipitation rates in the Himalaya region, is having detrimental effects on the cryosphere. Although satellite monitoring of glaciers on the TP indicates changes in surface area, only a few have been directly monitored for mass balance and ablation from the surface. This type of ground-based study is essential to obtain a better understanding of the rate of ice shrinkage on the TP.

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

    NASA Astrophysics Data System (ADS)

    Cornamusini, Gianluca; Talarico, Franco M.

    2016-11-01

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

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

    PubMed

    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.

  8. Ancient Biomolecules from Deep Ice Cores Reveal a Forested Southern Greenland

    PubMed Central

    Willerslev, Eske; Cappellini, Enrico; Boomsma, Wouter; Nielsen, Rasmus; Hebsgaard, Martin B.; Brand, Tina B.; Hofreiter, Michael; Bunce, Michael; Poinar, Hendrik N.; Dahl-Jensen, Dorthe; Johnsen, Sigfus; Steffensen, Jørgen Peder; Bennike, Ole; Schwenninger, Jean-Luc; Nathan, Roger; Armitage, Simon; de Hoog, Cees-Jan; Alfimov, Vasily; Christl, Marcus; Beer, Juerg; Muscheler, Raimund; Barker, Joel; Sharp, Martin; Penkman, Kirsty E.H.; Haile, James; Taberlet, Pierre; Gilbert, M. Thomas P.; Casoli, Antonella; Campani, Elisa; Collins, Matthew J.

    2009-01-01

    One of the major difficulties in paleontology is the acquisition of fossil data from the 10% of Earth’s terrestrial surface that is covered by thick glaciers and ice sheets. Here we reveal that DNA and amino acids from buried organisms can be recovered from the basal sections of deep ice cores and allow reconstructions of past flora and fauna. We show that high altitude southern Greenland, currently lying below more than two kilometers of ice, was once inhabited by a diverse array of conifer trees and insects that may date back more than 450 thousand years. The results provide the first direct evidence in support of a forested southern Greenland and suggest that many deep ice cores may contain genetic records of paleoenvironments in their basal sections. PMID:17615355

  9. Antarctica: intellectual Armistice Since 1961

    DTIC Science & Technology

    2015-05-21

    exploration and exploitation.101 Antarctic sea ice has increased on average 1.5% per decade between 1979 and 2012 and yet, due to the size of Antarctica...climates, soaring global populations, and expiring international agreements. In particular, regional demands for water in Africa are likely to exceed

  10. Identifying deformation mechanisms in the NEEM ice core using EBSD measurements

    NASA Astrophysics Data System (ADS)

    Kuiper, Ernst-Jan; Weikusat, Ilka; Drury, Martyn R.; Pennock, Gill M.; de Winter, Matthijs D. A.

    2015-04-01

    Deformation of ice in continental sized ice sheets determines the flow behavior of ice towards the sea. Basal dislocation glide is assumed to be the dominant deformation mechanism in the creep deformation of natural ice, but non-basal glide is active as well. Knowledge of what types of deformation mechanisms are active in polar ice is critical in predicting the response of ice sheets in future warmer climates and its contribution to sea level rise, because the activity of deformation mechanisms depends critically on deformation conditions (such as temperature) as well as on the material properties (such as grain size). One of the methods to study the deformation mechanisms in natural materials is Electron Backscattered Diffraction (EBSD). We obtained ca. 50 EBSD maps of five different depths from a Greenlandic ice core (NEEM). The step size varied between 8 and 25 micron depending on the size of the deformation features. The size of the maps varied from 2000 to 10000 grid point. Indexing rates were up to 95%, partially by saving and reanalyzing the EBSP patterns. With this method we can characterize subgrain boundaries and determine the lattice rotation configurations of each individual subgrain. Combining these observations with arrangement/geometry of subgrain boundaries the dislocation types can be determined, which form these boundaries. Three main types of subgrain boundaries have been recognized in Antarctic (EDML) ice core¹². Here, we present the first results obtained from EBSD measurements performed on the NEEM ice core samples from the last glacial period, focusing on the relevance of dislocation activity of the possible slip systems. Preliminary results show that all three subgrain types, recognized in the EDML core, occur in the NEEM samples. In addition to the classical boundaries made up of basal dislocations, subgrain boundaries made of non-basal dislocations are also common. ¹Weikusat, I.; de Winter, D. A. M.; Pennock, G. M.; Hayles, M

  11. Initial results from geophysical surveys and shallow coring of the Northeast Greenland Ice Stream (NEGIS)

    NASA Astrophysics Data System (ADS)

    Vallelonga, P.; Christianson, K.; Alley, R. B.; Anandakrishnan, S.; Christian, J. E. M.; Dahl-Jensen, D.; Gkinis, V.; Holme, C.; Jacobel, R. W.; Karlsson, N. B.; Keisling, B. A.; Kipfstuhl, S.; Kjær, H. A.; Kristensen, M. E. L.; Muto, A.; Peters, L. E.; Popp, T.; Riverman, K. L.; Svensson, A. M.; Tibuleac, C.; Vinther, B. M.; Weng, Y.; Winstrup, M.

    2014-07-01

    The Northeast Greenland Ice Stream (NEGIS) is the sole interior Greenlandic ice stream. Fast flow initiates near the summit dome, and the ice stream terminates approximately 1000 km downstream in three large outlet glaciers that calve into the Greenland Sea. To better understand this important system, in the summer of 2012 we drilled a 67 m firn core and conducted ground-based radio-echo sounding (RES) and active-source seismic surveys at a site approximately 150 km downstream from the onset of streaming flow (NEGIS firn core, 75°37.61' N, 35°56.49' W). The site is representative of the upper part of the ice stream, while also being in a crevasse-free area for safe surface operations. Annual cycles were observed for insoluble dust, sodium and ammonium concentrations and for electrolytic conductivity, allowing a seasonally resolved chronology covering the past 400 yr. Annual layer thicknesses averaged 0.11 m ice equivalent (i.e.) for the period 1607-2011, although accumulation varied between 0.08 and 0.14 m i.e., likely due to flow-related changes in surface topography. Tracing of RES layers from the NGRIP (North Greenland Ice Core Project) ice core site shows that the ice at NEGIS preserves a climatic record of at least the past 51 kyr. We demonstrate that deep ice core drilling in this location can provide a reliable Holocene and late-glacial climate record, as well as helping to constrain the past dynamics and ice-lithosphere interactions of the Greenland Ice Sheet.

  12. Modelling stable water isotopes during "high-precipitation" events at Dome C, Antarctica

    NASA Astrophysics Data System (ADS)

    Schlosser, Elisabeth; Masson-Delmotte, Valérie; Risi, Camille; Stenni, Barbara; Valt, Mauro; Powers, Jordan G.; Manning, Kevin W.; Duda, Michael G.; Cagnati, Anselmo

    2014-05-01

    For a correct paleoclimatologic interpretation of stable water isotopes from ice cores both pre- and post-depositional processes and their role for isotope fractionation have to be better understood. Our study focusses on "pre-depositional processes", namely the atmospheric processes that determine moisture transport and precipitation formation. At the deep ice core drilling site "Dome C", East Antarctica, fresh snow samples have been taken since 2006. These samples have been analysed crystallographically, which enables us to clearly distinguish between blowing snow, diamond dust, and "synoptic precipitation". Also the stable oxygen/hydrogen isotope ratios of the snow samples were measured, including measurements of 17-O. This is the first and only multi-year fresh-snow data series from an Antarctic deep drilling site. The Antarctic Mesoscale Prediction System (AMPS) employs Polar WRF for aviation weather forecasts in Antarctica. The data are archived and can be used for scientific purposes. The mesoscale atmospheric model was adapted especially for polar regions. The horizontal resolution for the domain that covers the Antarctic continent is 10 km. It was shown that precipitation at Dome C is temporally dominated by diamond dust. However, comparatively large amounts of precipitation are observed during several "high-precipitation" events per year, caused by synoptic activity in the circumpolar trough and related advection of relatively warm and moist air from lower latitudes to the interior of Antarctica. AMPS archive data are used to investigate the synoptic situations that lead to "high-precipitation" events at Dome C; in particular, possible moisture sources are determined using back-trajectories. With this meteorological information, the isotope ratios are calculated using two different isotope models, the Mixed Cloud Isotope Model, a simple Rayleigh-type model, and the LMDZ-iso (Laboratoire de Météorologie Dynamic Zoom), a General Circulation Model (GCM

  13. 33 CFR 151.79 - Operating requirements: Discharge of sewage within Antarctica.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... of sewage within Antarctica. 151.79 Section 151.79 Navigation and Navigable Waters COAST GUARD... Pollution and Sewage § 151.79 Operating requirements: Discharge of sewage within Antarctica. (a) A vessel... miles of Antarctic land or ice shelves; beyond such distance, sewage stored in a holding tank must not...

  14. 33 CFR 151.79 - Operating requirements: Discharge of sewage within Antarctica.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... of sewage within Antarctica. 151.79 Section 151.79 Navigation and Navigable Waters COAST GUARD... Pollution and Sewage § 151.79 Operating requirements: Discharge of sewage within Antarctica. (a) A vessel... miles of Antarctic land or ice shelves; beyond such distance, sewage stored in a holding tank must not...

  15. 33 CFR 151.79 - Operating requirements: Discharge of sewage within Antarctica.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... of sewage within Antarctica. 151.79 Section 151.79 Navigation and Navigable Waters COAST GUARD... Pollution and Sewage § 151.79 Operating requirements: Discharge of sewage within Antarctica. (a) A vessel... miles of Antarctic land or ice shelves; beyond such distance, sewage stored in a holding tank must not...

  16. 33 CFR 151.79 - Operating requirements: Discharge of sewage within Antarctica.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... of sewage within Antarctica. 151.79 Section 151.79 Navigation and Navigable Waters COAST GUARD... Pollution and Sewage § 151.79 Operating requirements: Discharge of sewage within Antarctica. (a) A vessel... miles of Antarctic land or ice shelves; beyond such distance, sewage stored in a holding tank must not...

  17. 33 CFR 151.79 - Operating requirements: Discharge of sewage within Antarctica.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... of sewage within Antarctica. 151.79 Section 151.79 Navigation and Navigable Waters COAST GUARD... Pollution and Sewage § 151.79 Operating requirements: Discharge of sewage within Antarctica. (a) A vessel... miles of Antarctic land or ice shelves; beyond such distance, sewage stored in a holding tank must not...

  18. Ice core evidence for extensive melting of the greenland ice sheet in the last interglacial.

    PubMed

    Koerner, R M

    1989-05-26

    Evidence from ice at the bottom of ice cores from the Canadian Arctic Islands and Camp Century and Dye-3 in Greenland suggests that the Greenland ice sheet melted extensively or completely during the last interglacial period more than 100 ka (thousand years ago), in contrast to earlier interpretations. The presence of dirt particles in the basal ice has previously been thought to indicate that the base of the ice sheets had melted and that the evidence for the time of original growth of these ice masses had been destroyed. However, the particles most likely blew onto the ice when the dimensions of the ice caps and ice sheets were much smaller. Ice texture, gas content, and other evidence also suggest that the basal ice at each drill site is superimposed ice, a type of ice typical of the early growth stages of an ice cap or ice sheet. If the present-day ice masses began their growth during the last interglacial, the ice sheet from the earlier (Illinoian) glacial period must have competely or largely melted during the early part of the same interglacial period. If such melting did occur, the 6-meter higher-than-present sea level during the Sangamon cannot be attributed to disintegration of the West Antarctic ice sheet, as has been suggested.

  19. Combined Gravimetric-Seismic Crustal Model for Antarctica

    NASA Astrophysics Data System (ADS)

    Baranov, Alexey; Tenzer, Robert; Bagherbandi, Mohammad

    2018-01-01

    The latest seismic data and improved information about the subglacial bedrock relief are used in this study to estimate the sediment and crustal thickness under the Antarctic continent. Since large parts of Antarctica are not yet covered by seismic surveys, the gravity and crustal structure models are used to interpolate the Moho information where seismic data are missing. The gravity information is also extended offshore to detect the Moho under continental margins and neighboring oceanic crust. The processing strategy involves the solution to the Vening Meinesz-Moritz's inverse problem of isostasy constrained on seismic data. A comparison of our new results with existing studies indicates a substantial improvement in the sediment and crustal models. The seismic data analysis shows significant sediment accumulations in Antarctica, with broad sedimentary basins. According to our result, the maximum sediment thickness in Antarctica is about 15 km under Filchner-Ronne Ice Shelf. The Moho relief closely resembles major geological and tectonic features. A rather thick continental crust of East Antarctic Craton is separated from a complex geological/tectonic structure of West Antarctica by the Transantarctic Mountains. The average Moho depth of 34.1 km under the Antarctic continent slightly differs from previous estimates. A maximum Moho deepening of 58.2 km under the Gamburtsev Subglacial Mountains in East Antarctica confirmed the presence of deep and compact orogenic roots. Another large Moho depth in East Antarctica is detected under Dronning Maud Land with two orogenic roots under Wohlthat Massif (48-50 km) and the Kottas Mountains (48-50 km) that are separated by a relatively thin crust along Jutulstraumen Rift. The Moho depth under central parts of the Transantarctic Mountains reaches 46 km. The maximum Moho deepening (34-38 km) in West Antarctica is under the Antarctic Peninsula. The Moho depth minima in East Antarctica are found under the Lambert Trench (24

  20. Moat Development and Evolution on a Perennialy Ice-Covered Lake in East Antarctica

    NASA Astrophysics Data System (ADS)

    Wayt, M. E.; Myers, K. F.; Doran, P.

    2017-12-01

    Lake Fryxell is a closed basin lake located in the lower end of Taylor Valley in McMurdo Dry Valleys of east Antarctica. The lake has an 4 m thick perennial ice-cover, however during the austral summers an ice-free moat forms around the lake margin due to increased temperatures and stream run off. Satellite imagery paired with ground-based camera data from Lake Fryxell were used to determine onset of moat formation, moat duration, and total area of open water at peak formation from 2009 through 2015. Temperature data from a meteorological station on the shore of Lake Fryxell were used to correlate degree days above freezing (DDAF) with moat formation and extent. The results showed that overall, the moat was smallest in 2009-10, accounting for roughly .61% percent of the surface area of Lake Fryxell. In 2010-11 and 2011-12 moat extent increase by roughly 1% and then decreased by 4% in 2012-13. In 2013-14 the moat was at its largest, accounting for about 11% with a decrease in area of 6% the following summer. Preliminary analysis of temperature data suggest a correlation between DDAF and moat extent. Moats make up on average 9% of lake area and are likely sites of elevated primary productivity in the summer. Moats are ice free which allows for unobstructed photosynthetically active radiation to penetrate the shallow water column. We hypothesize projected increases in air temperatures will lead to continued rise in lake level and larger moat areas, making it critical to understand these delicate and rapidly changing ecosystems.

  1. Integrating terrestrial and marine records of the LGM in McMurdo Sound, Antarctica: implications for grounded ice expansion, ice flow, and deglaciation of the Ross Sea Embayment

    NASA Astrophysics Data System (ADS)

    Christ, A. J.; Marchant, D. R.

    2017-12-01

    During the LGM, grounded glacier ice filled the Ross Embayment and deposited glacial drift on volcanic islands and peninsulas in McMurdo Sound, as well as along coastal regions of the Transantarctic Mountains (TAM), including the McMurdo Dry Valleys and Royal Society Range. The flow geometry and retreat history of this ice remains debated, with contrasting views yielding divergent implications for both the fundamental cause of Antarctic ice expansion as well as the interaction and behavior of ice derived from East and West Antarctica during late Quaternary time. We present terrestrial geomorphologic evidence that enables the reconstruction of former ice elevations, ice-flow paths, and ice-marginal environments in McMurdo Sound. Radiocarbon dates of fossil algae interbedded with ice-marginal sediments provide a coherent timeline for local ice retreat. These data are integrated with marine-sediment records and multi-beam data to reconstruct late glacial dynamics of grounded ice in McMurdo Sound and the western Ross Sea. The combined dataset suggest a dominance of ice flow toward the TAM in McMurdo Sound during all phases of glaciation, with thick, grounded ice at or near its maximum extent between 19.6 and 12.3 calibrated thousands of years before present (cal. ka). Our data show no significant advance of locally derived ice from the TAM into McMurdo Sound, consistent with the assertion that Late Pleistocene expansion of grounded ice in McMurdo Sound, and throughout the wider Ross Embayment, occurs in response to lower eustatic sea level and the resulting advance of marine-based outlet glaciers and ice streams (and perhaps also reduced oceanic heat flux), rather than local increases in precipitation and ice accumulation. Finally, when combined with allied data across the wider Ross Embayment, which show that widespread deglaciation outside McMurdo Sound did not commence until 13.1 ka, the implication is that retreat of grounded glacier ice in the Ross Embayment did

  2. Continuous analysis of phosphate in a Greenland shallow ice core

    NASA Astrophysics Data System (ADS)

    Kjær, Helle Astrid; Svensson, Anders; Bigler, Matthias; Vallelonga, Paul; Kettner, Ernesto; Dahl-Jensen, Dorthe

    2010-05-01

    Phosphate is an important and sometimes limiting nutrient for primary production in the oceans. Because of deforestation and the use of phosphate as a fertilizer changes in the phosphate cycle have occurred over the last centuries. On longer time scales, sea level changes are thought to have also caused changes in the phosphate cycle. Analyzing phosphate concentrations in ice cores may help to gain important knowledge about those processes. In the present study, we attach a phosphate detection line to an existing continuous flow analysis (CFA) setup for ice core analysis at the University of Copenhagen. The CFA system is optimized for high-resolution measurements of insoluble dust particles, electrolytic melt water conductivity, and the concentrations of ammonium and sodium. For the phosphate analysis we apply a continuous and highly sensitive absorption method that has been successfully applied to determine phosphate concentrations of sea water (Zhang and Chi, 2002). A line of melt water from the CFA melt head (1.01 ml per minute) is combined with a molybdate blue reagent and an ascorbic acid buffer. An uncompleted reaction takes place in five meters of heated mixing coils before the absorption measurement at a wavelength of 710 nanometer takes place in a 2 m long liquid waveguide cell (LWCC) with an inner volume of 0.5 ml. The method has a detection limit of around 0.1 ppb and we are currently investigating a possible interference from molybdate reacting with silicates that are present in low amounts in the ice. Preliminary analysis of early Holocene samples from the NGRIP ice core show phosphate concentration values of a few ppb. In this study, we will attempt to determine past levels of phosphate in a shallow Northern Greenland firn core with an annual layer thickness of about 20 cm ice equivalent. With a melt speed of 2.5 cm ice per minute our method should allow the resolution of any seasonal variability in phosphate concentrations.

  3. Data report for the Siple Coast (Antarctica) project

    NASA Technical Reports Server (NTRS)

    Bindschadler, R. A.; Stephenson, S. N.; Roberts, E. P.; Macayeal, D. R.; Lindstrom, D. R.

    1988-01-01

    This report presents data collected during three field seasons of glaciological studies in the Antarctica and describes the methods employed. The region investigated covers the mouths of Ice Streams B and C (the Siple Coast) and Crary Ice Rise on the Ross Ice Shelf. Measurements included in the report are as follows: surface velocity and deformation from repeated satellite geoceiver positions; surface topography from optical levelling; radar sounding of ice thickness; accumulation rates; near-surface densities and temperature profiles; and mapping from aerial photography.

  4. Airborne geophysical study in the pensacola mountains of antarctica

    USGS Publications Warehouse

    Behrendt, John C.; Meister, L.; Henderson, J.R.

    1966-01-01

    A seismic reflection, gravity, and aeromagnetic reconnaissance was made in the Pensacola Mountains, Antarctica, during the 1965-66 austral summer. Prominent ice streams located between the Neptune and Patuxent Ranges and east of the Forrestal Range overlie channels in the rock surface 2000 meters below sea level which are probably of glacial origin. Seismic reflections show that the Filchner Ice Shelf is 1270 meters thick near its southern margin. Along the boundary between West and East Antarctica, Bouguer anomalies decrease from +60 milligals in West Antarctica to -80 milligals in East Antarctica. An abrupt change in crustal structure across this boundary is required to explain the 2 milligals per kilometer gradient. This may indicate a fault extending through the crust into the mantle. Aeromagnetic profiles delineate anomalies up to 1800 ?? associated with the basic stratiform intrusion which comprises the Dufek and Forrestal ranges. A probable minimum area of 9500 square kilometers is calculated for the intrusive body on the basis of the magnetic anomalies, making it one of the largest bodies of its type. The extension of this magnetic anomaly across a fault forming the north border of the Pensacola Mountains probably precludes transcurrent movement.

  5. Airborne geophysical study in the pensacola mountains of antarctica.

    PubMed

    Behrendt, J C; Meister, L; Henderson, J R

    1966-09-16

    A seismic reflection, gravity, and aeromagnetic reconnaissance was made in the Pensacola Mountains, Antarctica, during the 1965-66 austral summer. Prominent ice streams located between the Neptune and Patuxent Ranges and east of the Forrestal Range overlie channels in the rock surface 2000 meters below sea level which are probably of glacial origin. Seismic reflections show that the Filchner Ice Shelf is 1270 meters thick near its southern margin. Along the boundary between West and East Antarctica, Bouguer anomalies decrease from +60 milligals in West Antarctica to -80 milligals in East Antarctica. An abrupt change in crustal structure across this boundary is required to explainl the 2 milligals per kilometer gradient. This may indicate a fault extending through the crust into the mantle. Aeromagnetic profiles delineate anomalies up to 1800 gamma associated with the basic stratiform intrusion which comprises the Dufek and Forrestal ranges. A probable minimum area of 9500 square kilometers is calculated for the intrusive body on the basis of the magnetic anomalies, making it one of the largest bodies of its type. The extension of this magnetic anominaly across a fault forming the north border of the Pensacola Mountains probably precludes transcurrent movement.

  6. Chronicling ice shelf history in the sediments left behind

    NASA Astrophysics Data System (ADS)

    Rosenheim, B. E.; Subt, C.; Shevenell, A.; Guitard, M.; Vadman, K. J.; DeCesare, M.; Wellner, J. S.; Bart, P. J.; Lee, J. I.; Domack, E. W.; Yoo, K. C.; Hayes, J. M.

    2017-12-01

    Collapsing and retreating ice shelves leave unmistakable sediment sequences on the Antarctic margin. These sequences tell unequivocal stories of collapse or retreat through a typical progression of sub-ice shelf diamicton (marking the past positions of grounding lines), sequentially overlain by a granulated facies from beneath the ice shelf, ice rafted debris from the calving line, and finally open marine sediment. The timelines to these stories, however, are troublesome. Difficulties in chronicling these stories recorded in sediment have betrayed their importance to our understanding of a warming world in many cases. The difficulties involve the concerted lack of preservation/production of calcium carbonate tests from the water column above and admixture of relict organic material from older sources of carbon. Here, we summarize our advances in the last decade of overcoming difficulties associated with the paucity of carbonate and creating chronologies of ice shelf retreat into the deglacial history of Antarctica by exploiting the range of thermochemical stability in organic matter (Ramped PyrOx) from these sediment sequences. We describe our success in comparing Ramped PyrOx 14C dates with foraminiferal dates, the relationship between sediment facies and radiocarbon age spectrum, and our ability to push limits of dating sediments deposited underneath ice shelves. With attention to the caveats of recent dating developments, we summarize expectations that geologist should have when coring the Antarctic margins to discern deglacial history. Perhaps most important among these expectations is the ability to design coring expeditions without regard to our ability to date calcium carbonate microfossils within the cores, in essence removing suspense of knowing whether cores taken from crucial paleo ice channels and other bathymetric features will ultimately yield a robust chronology for its sedimentary sequence.

  7. Dynamic influence of pinning points on marine ice-sheet stability: a numerical study in Dronning Maud Land, East Antarctica

    DOE PAGES

    Favier, Lionel; Pattyn, Frank; Berger, Sophie; ...

    2016-11-09

    The East Antarctic ice sheet is likely more stable than its West Antarctic counterpart because its bed is largely lying above sea level. However, the ice sheet in Dronning Maud Land, East Antarctica, contains marine sectors that are in contact with the ocean through overdeepened marine basins interspersed by grounded ice promontories and ice rises, pinning and stabilising the ice shelves. In this paper, we use the ice-sheet model BISICLES to investigate the effect of sub-ice-shelf melting, using a series of scenarios compliant with current values, on the ice-dynamic stability of the outlet glaciers between the Lazarev and Roi Baudouinmore » ice shelves over the next millennium. Overall, the sub-ice-shelf melting substantially impacts the sea-level contribution. Locally, we predict a short-term rapid grounding-line retreat of the overdeepened outlet glacier Hansenbreen, which further induces the transition of the bordering ice promontories into ice rises. Furthermore, our analysis demonstrated that the onset of the marine ice-sheet retreat and subsequent promontory transition into ice rise is controlled by small pinning points, mostly uncharted in pan-Antarctic datasets. Pinning points have a twofold impact on marine ice sheets. They decrease the ice discharge by buttressing effect, and they play a crucial role in initialising marine ice sheets through data assimilation, leading to errors in ice-shelf rheology when omitted. Our results show that unpinning increases the sea-level rise by 10%, while omitting the same pinning point in data assimilation decreases it by 10%, but the more striking effect is in the promontory transition time, advanced by two centuries for unpinning and delayed by almost half a millennium when the pinning point is missing in data assimilation. As a result, pinning points exert a subtle influence on ice dynamics at the kilometre scale, which calls for a better knowledge of the Antarctic margins.« less

  8. Dynamic influence of pinning points on marine ice-sheet stability: a numerical study in Dronning Maud Land, East Antarctica

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Favier, Lionel; Pattyn, Frank; Berger, Sophie

    The East Antarctic ice sheet is likely more stable than its West Antarctic counterpart because its bed is largely lying above sea level. However, the ice sheet in Dronning Maud Land, East Antarctica, contains marine sectors that are in contact with the ocean through overdeepened marine basins interspersed by grounded ice promontories and ice rises, pinning and stabilising the ice shelves. In this paper, we use the ice-sheet model BISICLES to investigate the effect of sub-ice-shelf melting, using a series of scenarios compliant with current values, on the ice-dynamic stability of the outlet glaciers between the Lazarev and Roi Baudouinmore » ice shelves over the next millennium. Overall, the sub-ice-shelf melting substantially impacts the sea-level contribution. Locally, we predict a short-term rapid grounding-line retreat of the overdeepened outlet glacier Hansenbreen, which further induces the transition of the bordering ice promontories into ice rises. Furthermore, our analysis demonstrated that the onset of the marine ice-sheet retreat and subsequent promontory transition into ice rise is controlled by small pinning points, mostly uncharted in pan-Antarctic datasets. Pinning points have a twofold impact on marine ice sheets. They decrease the ice discharge by buttressing effect, and they play a crucial role in initialising marine ice sheets through data assimilation, leading to errors in ice-shelf rheology when omitted. Our results show that unpinning increases the sea-level rise by 10%, while omitting the same pinning point in data assimilation decreases it by 10%, but the more striking effect is in the promontory transition time, advanced by two centuries for unpinning and delayed by almost half a millennium when the pinning point is missing in data assimilation. As a result, pinning points exert a subtle influence on ice dynamics at the kilometre scale, which calls for a better knowledge of the Antarctic margins.« less

  9. Antarctica and global change research

    NASA Astrophysics Data System (ADS)

    Weller, Gunter; Lange, Manfred

    1992-03-01

    The Antarctic, including the continent and Southern Ocean with the subantarctic islands, is a critical area in the global change studies under the International Geosphere-Biosphere Program (IGBP) and the World Climate Research Program (WCRP). Major scientific problems include the impacts of climate warming, the ozone hole, and sea level changes. Large-scale interactions between the atmosphere, ice, ocean, and biota in the Antarctic affect the entire global system through feedbacks, biogeochemical cycles, deep-ocean circulation, atmospheric transport of heat, moisture, and pollutants, and changes in ice mass balances. Antarctica is also a rich repository of paleoenvironmental information in its ice sheet and its ocean and land sediments.

  10. ICESat Observations of Seasonal and Interannual Variations of Sea-Ice Freeboard and Estimated Thickness in the Weddell Sea, Antarctica (2003-2009)

    NASA Technical Reports Server (NTRS)

    Yi, Donghui; Robbins, John W.

    2010-01-01

    Sea-ice freeboard heights for 17 ICESat campaign periods from 2003 to 2009 are derived from ICESat data. Freeboard is combined with snow depth from Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) data and nominal densities of snow, water and sea ice, to estimate sea-ice thickness. Sea-ice freeboard and thickness distributions show clear seasonal variations that reflect the yearly cycle of growth and decay of the Weddell Sea (Antarctica) pack ice. During October-November, sea ice grows to its seasonal maximum both in area and thickness; the mean freeboards are 0.33-0.41 m and the mean thicknesses are 2.10-2.59 m. During February-March, thinner sea ice melts away and the sea-ice pack is mainly distributed in the west Weddell Sea; the mean freeboards are 0.35-0.46 m and the mean thicknesses are 1.48-1.94 m. During May-June, the mean freeboards and thicknesses are 0.26-0.29 m and 1.32-1.37 m, respectively. The 6 year trends in sea-ice extent and volume are (0.023+/-0.051) x 10(exp 6)sq km/a (0.45%/a) and (0.007+/-1.0.092) x 10(exp 3)cu km/a (0.08%/a); however, the large standard deviations indicate that these positive trends are not statistically significant.

  11. SPME-GCMS study of the natural attenuation of aviation diesel spilled on the perennial ice cover of Lake Fryxell, Antarctica.

    PubMed

    Jaraula, Caroline M B; Kenig, Fabien; Doran, Peter T; Priscu, John C; Welch, Kathleen A

    2008-12-15

    In January 2003, a helicopter crashed on the 5 m thick perennial ice cover of Lake Fryxell (McMurdo Dry Valleys, East Antarctica), spilling approximately 730 l of aviation diesel fuel (JP5-AN8 mixture). The molecular composition of the initial fuel was analyzed by solid phase microextraction (SPME) gas chromatography-mass spectrometry (GC-MS), then compared to the composition of the contaminated ice, water, and sediments collected a year after the spill. Evaporation is the major agent of diesel weathering in meltpool waters and in the ice. This process is facilitated by the light non-aqueous phase liquid properties of the aviation diesel and by the net upward movement of the ice as a result of ablation. In contrast, in sediment-bearing ice, biodegradation by both alkane- and aromatic-degraders was the prominent attenuation mechanism. The composition of the diesel contaminant in the ice was also affected by the differential solubility of its constituents, some ice containing water-washed diesel and some ice containing exclusively relatively soluble low molecular weight aromatic hydrocarbons such as alkylbenzene and naphthalene homologues. The extent of evaporation, water washing and biodegradation between sites and at different depths in the ice are evaluated on the basis of molecular ratios and the results of JP5-AN8 diesel evaporation experiment at 4 degrees C. Immediate spread of the aviation diesel was enhanced where the presence of aeolian sediments induced formations of meltpools. However, in absence of melt pools, slow spreading of the diesel is possible through the porous ice and the ice cover aquifer.

  12. Historic First Landing of NASA's P-3B in Antarctica

    NASA Image and Video Library

    2014-01-03

    NASA's first ever historic P-3B landing in McMurdo Station, Antarctica on the sea ice runway, which occurred on Nov. 16, 2013. It took the craft 5 days to reach Antarctica from the NASA Wallops Flight Facility in Wallops Island, Virginia. You can see the IceBridge Team waiting to greet the flight crew as they taxied for the very first time right up to the IceBridge team tents. Credit: NASA/Justin Miller/Indiana University NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  13. Dating of 30m ice cores drilled by Japanese Antarctic Research Expedition and environmental change study

    NASA Astrophysics Data System (ADS)

    Motoyama, H.; Suzuki, T.; Fukui, K.; Ohno, H.; Hoshina, Y.; Hirabayashi, M.; Fujita, S.

    2017-12-01

    1. Introduction It is possible to reveal the past climate and environmental change from the ice core drilled in polar ice sheet and glaciers. The 54th Japanese Antarctic Research Expedition conducted several shallow core drillings up to 30 m depth in the inland and coastal areas of the East Antarctic ice sheet. Ice core sample was cut out at a thickness of about 5 cm in the cold room of the National Institute of Polar Research, and analyzed ion, water isotope, dust and so one. We also conducted dielectric profile measurement (DEP measurement). The age as a key layer of large-scale volcanic explosion was based on Sigl et al. (Nature Climate Change, 2014). 2. Inland ice core Ice cores were collected at the NDF site (77°47'14"S, 39°03'34"E, 3754 m.a.s.l.) and S80 site (80°00'00"S, 40°30'04"E, 3622 m.a.s.l.). Dating of ice core was done as follows. Calculate water equivalent from core density. Accumulate water equivalent from the surface. Approximate the relation of depth - cumulative water equivalent by a quartic equation. We determined the key layer with nssSO42 - peak corresponding to several large volcanic explosions. The accumulation rate was kept constant between the key layers. As a result, NDF was estimated to be around 1360 AD and S80 was estimated to be around 1400 AD in the deepest ice core. 3. Coastal ice core An ice core was collected at coastal H15 sites (69°04'10"S, 40°44'51"E, 1030 m.a.s.l.). Dating of ice core was done as follows. Calculate water equivalent from ice core density. Accumulate water equivalent from the surface. Approximate the relation of depth - cumulative water equivalent by a quartic equation. Basically we decided to summer (December) and winter (June) due to the seasonal change of the water isotope (δD or δ18O). In addition to the seasonal change of isotope, confirm the following. Maximum of SO42- / Na +, which is earlier in time than the maximum of water isotope. Maximum of MSA at about the same time as the maximum of the

  14. Multiple sources supply eolian mineral dust to the Atlantic sector of coastal Antarctica: Evidence from recent snow layers at the top of Berkner Island ice sheet

    NASA Astrophysics Data System (ADS)

    Bory, Aloys; Wolff, Eric; Mulvaney, Robert; Jagoutz, Emil; Wegner, Anna; Ruth, Urs; Elderfield, Harry

    2010-03-01

    The Sr and Nd isotopic composition of dust extracted from recent snow layers at the top of Berkner Island ice sheet (located within the Filchner-Ronne Ice Shelf at the southern end of the Weddell Sea) enables us, for the first time, to document dust provenance in Antarctica outside the East Antarctic Plateau (EAP) where all previous studies based on isotopic fingerprinting were carried out. Berkner dust displays an overall crust-like isotopic signature, characterized by more radiogenic 87Sr/ 86Sr and much less radiogenic 143Nd/ 144Nd compared to dust deposited on the EAP during glacial periods. Differences with EAP interglacial dust are not as marked but still significant, indicating that present-day Berkner dust provenance is distinct, at least to some extent, from that of the dust reaching the EAP. The fourteen snow-pit sub-seasonal samples that were obtained span a two-year period (2002-2003) and their dust Sr and Nd isotopic composition reveals that multiple sources are at play over a yearly time period. Southern South America, Patagonia in particular, likely accounts for part of the observed spring/summer dust deposition maxima, when isotopic composition is shifted towards "younger" isotopic signatures. In the spring, possible additional inputs from Australian sources would also be supported by the data. Most of the year, however, the measured isotopic signatures would be best explained by a sustained background supply from putative local sources in East Antarctica, which carry old-crust-like isotopic fingerprints. Whether the restricted East Antarctic ice-free areas produce sufficient eolian material has yet to be substantiated however. The fact that large (> 5 μm) particles represent a significant fraction of the samples throughout the entire time-series supports scenarios that involve contributions from proximal sources, either in Patagonia and/or Antarctica (possibly including snow-free areas in the Antarctic Peninsula and other areas as well). This also

  15. Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier [Sub-ice shelf sediments record 20 th century retreat history of Pine Island Glacier

    DOE PAGES

    Smith, J. A.; Andersen, T. J.; Shortt, M.; ...

    2016-11-23

    The West Antarctic Ice Sheet is one of the largest potential sources of rising sea levels. Over the past 40 years, glaciers flowing into the Amundsen Sea sector of the ice sheet have thinned at an accelerating rate, and several numerical models suggest that unstable and irreversible retreat of the grounding line—which marks the boundary between grounded ice and floating ice shelf—is underway. Understanding this recent retreat requires a detailed knowledge of grounding-line history, but the locations of the grounding line before the advent of satellite monitoring in the 1990s are poorly dated. In particular, a history of grounding-line retreatmore » is required to understand the relative roles of contemporaneous ocean-forced change and of ongoing glacier response to an earlier perturbation in driving ice-sheet loss. Here we show that the present thinning and retreat of Pine Island Glacier in West Antarctica is part of a climatically forced trend that was triggered in the 1940s. Our conclusions arise from analysis of sediment cores recovered beneath the floating Pine Island Glacier ice shelf, and constrain the date at which the grounding line retreated from a prominent seafloor ridge. We find that incursion of marine water beyond the crest of this ridge, forming an ocean cavity beneath the ice shelf, occurred in 1945 (±12 years); final ungrounding of the ice shelf from the ridge occurred in 1970 (±4 years). The initial opening of this ocean cavity followed a period of strong warming of West Antarctica, associated with El Niño activity. Furthermore our results suggest that, even when climate forcing weakened, ice-sheet retreat continued.« less

  16. Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier [Sub-ice shelf sediments record 20 th century retreat history of Pine Island Glacier

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Smith, J. A.; Andersen, T. J.; Shortt, M.

    The West Antarctic Ice Sheet is one of the largest potential sources of rising sea levels. Over the past 40 years, glaciers flowing into the Amundsen Sea sector of the ice sheet have thinned at an accelerating rate, and several numerical models suggest that unstable and irreversible retreat of the grounding line—which marks the boundary between grounded ice and floating ice shelf—is underway. Understanding this recent retreat requires a detailed knowledge of grounding-line history, but the locations of the grounding line before the advent of satellite monitoring in the 1990s are poorly dated. In particular, a history of grounding-line retreatmore » is required to understand the relative roles of contemporaneous ocean-forced change and of ongoing glacier response to an earlier perturbation in driving ice-sheet loss. Here we show that the present thinning and retreat of Pine Island Glacier in West Antarctica is part of a climatically forced trend that was triggered in the 1940s. Our conclusions arise from analysis of sediment cores recovered beneath the floating Pine Island Glacier ice shelf, and constrain the date at which the grounding line retreated from a prominent seafloor ridge. We find that incursion of marine water beyond the crest of this ridge, forming an ocean cavity beneath the ice shelf, occurred in 1945 (±12 years); final ungrounding of the ice shelf from the ridge occurred in 1970 (±4 years). The initial opening of this ocean cavity followed a period of strong warming of West Antarctica, associated with El Niño activity. Furthermore our results suggest that, even when climate forcing weakened, ice-sheet retreat continued.« less

  17. Balance of the West Antarctic Ice Sheet

    NASA Technical Reports Server (NTRS)

    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

  18. Oceanographic Influences on Ice Shelves and Drainage in the Amundsen Sea

    NASA Astrophysics Data System (ADS)

    Minzoni, R. T.; Anderson, J. B.; Majewski, W.; Yokoyama, Y.; Fernandez, R.; Jakobsson, M.

    2016-12-01

    Marine sediment cores collected during the IB OdenSouthern Ocean 2009-2010 cruise are used to reconstruct the Holocene history of the Cosgrove Ice Shelf, which today occupies Ferrero Bay, a large embayment of eastern Pine Island Bay. Detailed sedimentology, geochemistry, and micropaleontology of cores, in conjunction with subbottom profiles, reveal an unexpected history of recession. Presence of planktic foraminifera at the base of Kasten Core-15 suggests an episode of enhanced circulation beneath a large ice shelf that covered the Amundsen Sea during the Early Holocene, and relatively warm water incursion has been interpreted as a potential culprit for major recession and ice mass loss by 10.7 cal kyr BP from radiocarbon dating. Fine sediment deposition and low productivity throughout the Mid Holocene indicate long-lived stability of the Cosgrove Ice Shelf in Ferrero Bay, despite regional warming evident from ice core data and ice shelf loss in the Antarctic Peninsula. High productivity and diatom abundance signify opening of Ferrero Bay and recession of the Cosgrove Ice Shelf to its present day configuration by 2.0 cal kyr BP. This coincides with deglaciation of an island near Canisteo Peninsula according to published cosmogenic exposure ages. Presence of benthic foraminifera imply that warm deep water influx beneath the extended Cosgrove Ice Shelf was a mechanism for under-melting the ice shelf and destabilizing the grounding line. Major ice shelf recession may also entail continental ice mass loss from the eastern sector of the Amundsen Sea during the Late Holocene. Oceanographic forcing remains a key concern for the current stability of the Antarctic Ice Sheet, especially along the tidewater margins of West Antarctica. Ongoing work on diatom and foraminiferal assemblages of the Late Holocene in Ferrero Bay and other fjord settings will improve our understanding of recent oceanographic changes and their potential influence on ice shelves and outlet glaciers

  19. Chronology of Pu isotopes and 236U in an Arctic ice core.

    PubMed

    Wendel, C C; Oughton, D H; Lind, O C; Skipperud, L; Fifield, L K; Isaksson, E; Tims, S G; Salbu, B

    2013-09-01

    In the present work, state of the art isotopic fingerprinting techniques are applied to an Arctic ice core in order to quantify deposition of U and Pu, and to identify possible tropospheric transport of debris from former Soviet Union test sites Semipalatinsk (Central Asia) and Novaya Zemlya (Arctic Ocean). An ice core chronology of (236)U, (239)Pu, and (240)Pu concentrations, and atom ratios, measured by accelerator mass spectrometry in a 28.6m deep ice core from the Austfonna glacier at Nordaustlandet, Svalbard is presented. The ice core chronology corresponds to the period 1949 to 1999. The main sources of Pu and (236)U contamination in the Arctic were the atmospheric nuclear detonations in the period 1945 to 1980, as global fallout, and tropospheric fallout from the former Soviet Union test sites Novaya Zemlya and Semipalatinsk. Activity concentrations of (239+240)Pu ranged from 0.008 to 0.254 mBq cm(-2) and (236)U from 0.0039 to 0.053 μBq cm(-2). Concentrations varied in concordance with (137)Cs concentrations in the same ice core. In contrast to previous published results, the concentrations of Pu and (236)U were found to be higher at depths corresponding to the pre-moratorium period (1949 to 1959) than to the post-moratorium period (1961 and 1962). The (240)Pu/(239)Pu ratio ranged from 0.15 to 0.19, and (236)U/(239)Pu ranged from 0.18 to 1.4. The Pu atom ratios ranged within the limits of global fallout in the most intensive period of nuclear atmospheric testing (1952 to 1962). To the best knowledge of the authors the present work is the first publication on biogeochemical cycles with respect to (236)U concentrations and (236)U/(239)Pu atom ratios in the Arctic and in ice cores. Copyright © 2013 Elsevier B.V. All rights reserved.

  20. Ice cores and calcite precipitates from alpine ice caves as useful proxies in paleoclimate reconstructions

    NASA Astrophysics Data System (ADS)

    Colucci, Renato R.; Barbante, Carlo; Bertò, Michele; Dreossi, Giuliano; Festi, Daniela; Forte, Emanuele; Gabrieli, Jacopo; Guglielmin, Mauro; Lenaz, Davide; Luetscher, Marc; Maggi, Valter; Princivalle, Francesco; Schwikowski, Margit; Stenni, Barbara; Žebre, Manja

    2017-04-01

    In the last years a growing set of research campaigns have been undertaken in the European southeastern Alps. The aim of such interest is mainly due to the peculiar climatic conditions of this area, allowing the existence of periglacial and glacial evidence at the lowest altitude in the Alps. The reason for such "anomaly" is likely ascribable to very high mean annual precipitation and local topoclimatic amplifications. In the frame of this research, in the fall 2013 a 7.8 m long ice-core has been extracted from a permanent cave ice deposit located in the area of Mt. Canin (2,587 masl) in the Julian Alps. The ice-core has been cut and analysed in terms of: a) oxygen and hydrogen isotope composition; b); black carbon and dust concentrations; c) water conductivity; d) mineralogical analyses via X-ray powder diffraction. In the fall 2016, in the same area, a set of 1.0 m long horizontal ice cores have been extracted in another ice cave deposit, intercepting a preserved layer of coarse cryogenic cave carbonates (CCCcoarse). Such original finding represents the first alpine evidence of in situ CCCcoarse and the first occurrence from the southern side of the Alps. A unique opportunity to better understand the processes associated with the formation of CCCcoarse and the well-preserved status of samples allow planning, besides U/Th datings, several different analyses which may be associated with the precipitation of CCC. Subglacial calcite crusts, widespread in the area, represents a further proxy able to help understanding the evolution of climate during the holocene in this alpine sector. In the light of accelerated climate change we discuss here the potential of this still untapped and fragile cryospheric archives for paleoclimatic reconstructions in high elevated areas of the Alps.

  1. Bellingshausen Sea Ice Extent Recorded in an Antarctic Peninsula Ice Core

    NASA Technical Reports Server (NTRS)

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

    2016-01-01

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

  2. Eurasian methoxy aromatic acid ice core record of biomass burning

    NASA Astrophysics Data System (ADS)

    Grieman, M. M.; Aydin, M.; Fritzsche, D.; McConnell, J. R.; Opel, T.; Sigl, M.; Saltzman, E. S.

    2017-12-01

    On a global basis, wildfires affect the carbon cycle, atmospheric chemistry, climate, and ecosystem dynamics. Well-dated regional proxy records can provide insight into the relationship between biomass burning and climate on millennial and centennial timescales. There is little historical information about long-term regional biomass burning variability in Siberia, the largest forested area in the Northern Hemisphere. In this study, vanillic acid and para-hydroxybenzoic acid were analyzed in the Eurasian Arctic Akademii Nauk ice core in samples covering the past 2600 years. These aromatic acids are generated during burning from the pyrolysis of lignin and transported as atmospheric aerosol. This is the first millennial-scale ice core record of these aromatic acids. Ice core meltwater samples were analyzed for vanillic acid and para-hydroxybenzoic acid using ion chromatography and electrospray tandem mass spectrometric detection. The levels of vanillic acid and para-hydroxybenzoic acid ranged from <0.05 to about 1 ppb. Three periods of strongly elevated levels were found during the preindustrial late Holocene: 650-300 BCE, 340-660 CE, and 1460-1660 CE. The most recent of these periods coincides with increased pulsing of ice-rafted debris in the North Atlantic (or Bond event) and a weakened Asian monsoon suggesting a link between Siberian burning and global patterns of climate change on centennial timescales.

  3. An Ice Core Perspective on Aleutian Low Variability over the Common Era

    NASA Astrophysics Data System (ADS)

    Osterberg, E. C.; Winski, D.; Kreutz, K. J.; Wake, C. P.; Ferris, D. G.; Campbell, S.; Introne, D.

    2016-12-01

    The Aleutian Low (ALow) is the dominant feature of atmospheric circulation in the North Pacific, strongly influencing wintertime temperature, precipitation and wind patterns in Alaska and the Yukon Territory, as well as further downstream in North America via atmospheric teleconnections. Changes in ALow strength are known to impact marine ecosystems by contributing to the multi-decadal sea-surface temperature mode in the North Pacific known as the Pacific Decadal Oscillation (PDO). Meteorological records show that in addition to distinct PDO-like variability, the ALow has intensified over the 20th century. However, ALow variability prior to the instrumental period remains unclear due to generally poor correlations among published ALow and PDO reconstructions, including the Mt. Logan ice core ALow record. An improved understanding of past ALow variability is critical for evaluating natural ALow forcing mechanisms, placing the 20th century intensification in context, and improving ALow projections under increased anthropogenic forcing. Here we combine ALow-sensitive time series from the new Denali ice core and the Mt. Logan ice core to develop a high-resolution (1-3 year) multi-ice-core record of ALow variability over the past 1500 years. The Denali ice core was collected from the summit plateau (3900 m) of Mt. Hunter in 2013, and was sampled using the Dartmouth continuous melter system with discrete sampling for major ion (IC), trace element (ICP-MS), and stable isotope ratios (Picarro), as well as continuous flow analyses for dust size and concentration (Klotz Abakus). We focus here on the sea-salt sodium time series, and calibrate our record over the 20th century with reanalysis wind speed and pressure data. The Denali sodium record of ALow strength strongly resembles the Mt. Logan ALow record, with both showing a recent intensification of the ALow that started in the late 1600s and continues into the 20th century. Both records reveal that the ALow was stronger

  4. Ice flow in the Weddell Sea sector of West Antarctica as elucidated by radar-imaged internal layering

    NASA Astrophysics Data System (ADS)

    Bingham, R. G.; Rippin, D. M.; Karlsson, N. B.; Corr, H.; Ferraccioli, F.; Jordan, T. A.; Le Brocq, A.; Ross, N.; Wright, A.; Siegert, M. J.

    2012-12-01

    Radio-echo sounding (RES) across polar ice sheets reveals extensive, isochronous internal layers, whose stratigraphy, and especially their degree of continuity over multi-km distances, can inform us about both present ice flow and past ice-flow histories. Here, we bring together for the first time two recent advances in this field of cryospheric remote sensing to analyse ice flow into the Weddell Sea sector of West Antarctica. Firstly, we have developed a new quantitative routine for analysing the continuity of internal layers obtained over large areas of ice by airborne RES surveys - we term this routine the "Internal-Layering Continuity-Index (ILCI)". Secondly, in the austral season 2010-11 we acquired, by airborne RES survey, the first comprehensive dataset of deep internal layering across Institute and Möller Ice Streams, two of the more significant feeders of ice into the Filchner-Ronne Ice Shelf. Applying the ILCI to SAR-processed (migrated) RES profiles across Institute Ice Stream's catchment reveals two contrasting regions of internal-layering continuity behaviour. In the western portion of the catchment, where ice-stream tributaries incise deeply through the Ellsworth Subglacial Highlands, the continuity of internal layers is most disrupted across the present ice streams. We therefore interpret the ice-flow configuration in this western region as predominantly spatially stable over the lifetime of the ice. Further east, towards Möller Ice Stream, and towards the interior of the ice sheet, the ILCI does not closely match the present ice flow configuration, while across most of present-day Möller Ice Stream itself, the continuity of internal layers is generally low. We propose that the variation in continuity of internal layering across eastern Institute Ice Stream and the neighbouring Möller results primarily from two factors. Firstly, the noncorrespondence of some inland tributaries with internal-layering continuity acts as evidence for past spatial

  5. A reconciled estimate of ice-sheet mass balance.

    PubMed

    Shepherd, Andrew; Ivins, Erik R; A, Geruo; Barletta, Valentina R; Bentley, Mike J; Bettadpur, Srinivas; Briggs, Kate H; Bromwich, David H; Forsberg, René; Galin, Natalia; Horwath, Martin; Jacobs, Stan; Joughin, Ian; King, Matt A; Lenaerts, Jan T M; Li, Jilu; Ligtenberg, Stefan R M; Luckman, Adrian; Luthcke, Scott B; McMillan, Malcolm; Meister, Rakia; Milne, Glenn; Mouginot, Jeremie; Muir, Alan; Nicolas, Julien P; Paden, John; Payne, Antony J; Pritchard, Hamish; Rignot, Eric; Rott, Helmut; Sørensen, Louise Sandberg; Scambos, Ted A; Scheuchl, Bernd; Schrama, Ernst J O; Smith, Ben; Sundal, Aud V; van Angelen, Jan H; van de Berg, Willem J; van den Broeke, Michiel R; Vaughan, David G; Velicogna, Isabella; Wahr, John; Whitehouse, Pippa L; Wingham, Duncan J; Yi, Donghui; Young, Duncan; Zwally, H Jay

    2012-11-30

    We combined an ensemble of satellite altimetry, interferometry, and gravimetry data sets using common geographical regions, time intervals, and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of Earth's polar ice sheets. We find that there is good agreement between different satellite methods--especially in Greenland and West Antarctica--and that combining satellite data sets leads to greater certainty. Between 1992 and 2011, the ice sheets of Greenland, East Antarctica, West Antarctica, and the Antarctic Peninsula changed in mass by -142 ± 49, +14 ± 43, -65 ± 26, and -20 ± 14 gigatonnes year(-1), respectively. Since 1992, the polar ice sheets have contributed, on average, 0.59 ± 0.20 millimeter year(-1) to the rate of global sea-level rise.

  6. Accuracy Assessment of Recent Global Ocean Tide Models around Antarctica

    NASA Astrophysics Data System (ADS)

    Lei, J.; Li, F.; Zhang, S.; Ke, H.; Zhang, Q.; Li, W.

    2017-09-01

    Due to the coverage limitation of T/P-series altimeters, the lack of bathymetric data under large ice shelves, and the inaccurate definitions of coastlines and grounding lines, the accuracy of ocean tide models around Antarctica is poorer than those in deep oceans. Using tidal measurements from tide gauges, gravimetric data and GPS records, the accuracy of seven state-of-the-art global ocean tide models (DTU10, EOT11a, GOT4.8, FES2012, FES2014, HAMTIDE12, TPXO8) is assessed, as well as the most widely-used conventional model FES2004. Four regions (Antarctic Peninsula region, Amery ice shelf region, Filchner-Ronne ice shelf region and Ross ice shelf region) are separately reported. The standard deviations of eight main constituents between the selected models are large in polar regions, especially under the big ice shelves, suggesting that the uncertainty in these regions remain large. Comparisons with in situ tidal measurements show that the most accurate model is TPXO8, and all models show worst performance in Weddell sea and Filchner-Ronne ice shelf regions. The accuracy of tidal predictions around Antarctica is gradually improving.

  7. Ice core δD(CH4) record precludes marine hydrate CH4 emissions at the onset of Dansgaard-Oeschger events

    NASA Astrophysics Data System (ADS)

    Bock, M.; Schmitt, J.; Möller, L.; Spahni, R.; Blunier, T.; Fischer, H.

    2010-12-01

    Air enclosures in polar ice cores represent the only direct paleoatmospheric archive (besides firn air) and show that atmospheric CH4 concentrations changed in concert with northern hemisphere temperature during both glacial/interglacial transitions as well as rapid climate changes (Dansgaard-Oeschger events). For stadials and interstadials during Marine Isotope Stage 3 concentration jumps of 100 - 200 ppbv within a few decades are observed. A concentration gradient with higher values in the northern versus the southern hemisphere during warm stages was reconstructed from ice core methane data from Greenland and Antarctica. This gradient indicates additional methane emissions during warm periods located in the northern hemisphere. However, the underlying processes for these changes are still not well understood. With tropical and boreal wetlands, biomass burning, thermokarst lakes, ruminants, termites, UV-induced emissions from organic matter and marine gas hydrates all contributing to the natural atmospheric CH4 level, an unambiguous source attribution remains difficult. Also changes in the methane sinks can modify the tropospheric CH4 budget, as trace gases like volatile organic compounds are competing for the major reactant - the OH radical. Additionally, the changing global atmospheric methane concentration itself feeds back on its lifetime. Together with the CH4 interhemispheric gradient, stable hydrogen and carbon isotopic studies on methane (δD(CH4) and δ13CH4) in ice cores allow to constrain individual CH4 source/sink changes. Here we present clear evidence from the North Greenland Ice Core Project ice core based on the hydrogen isotopic composition of methane δD(CH4) that clathrates did not cause atmospheric methane concentration to rise at the onset of Dansgaard-Oeschger (DO) events 7 and 8 (34 - 41 kilo years before present), however, we can not exclude that they played a minor role during and at the end of an interstadial. Box modeling supports

  8. Dating a tropical ice core by time-frequency analysis of ion concentration depth profiles

    NASA Astrophysics Data System (ADS)

    Gay, M.; De Angelis, M.; Lacoume, J.-L.

    2014-09-01

    Ice core dating is a key parameter for the interpretation of the ice archives. However, the relationship between ice depth and ice age generally cannot be easily established and requires the combination of numerous investigations and/or modelling efforts. This paper presents a new approach to ice core dating based on time-frequency analysis of chemical profiles at a site where seasonal patterns may be significantly distorted by sporadic events of regional importance, specifically at the summit area of Nevado Illimani (6350 m a.s.l.), located in the eastern Bolivian Andes (16°37' S, 67°46' W). We used ion concentration depth profiles collected along a 100 m deep ice core. The results of Fourier time-frequency and wavelet transforms were first compared. Both methods were applied to a nitrate concentration depth profile. The resulting chronologies were checked by comparison with the multi-proxy year-by-year dating published by de Angelis et al. (2003) and with volcanic tie points. With this first experiment, we demonstrated the efficiency of Fourier time-frequency analysis when tracking the nitrate natural variability. In addition, we were able to show spectrum aliasing due to under-sampling below 70 m. In this article, we propose a method of de-aliasing which significantly improves the core dating in comparison with annual layer manual counting. Fourier time-frequency analysis was applied to concentration depth profiles of seven other ions, providing information on the suitability of each of them for the dating of tropical Andean ice cores.

  9. Cosmogenic 10Be ages from the Meirs and Garwood Valleys, Denton Hills, West Antarctica, suggest an absence in LGM Ice Sheet expansion.

    NASA Astrophysics Data System (ADS)

    Fink, David; Joy, Kurt; Storey, Bryan

    2014-05-01

    It has been hypothesised that during interglacials, thinning of the Ross Ice Shelf allowed a more open water environment with increased local precipitation. This resulted in outlet glaciers, which drain the Transantarctic Mountains and fed by the East Antarctic Ice Sheet, advancing during moist warmer periods, apparently out of phase with colder arid dry periods. Significantly the ice core record during these warm periods also shows increased accumulation continent wide The geomorphology of the Denton Hills in the Royal Society Range, West Antarctica, is a result of Miocene fluvial incision reworked by subsequent glacial advances throughout the Quaternary. The Garwood and Miers glacial valleys drain ice across the Denton Hills into the Shelf, and should thus show maximum extent during interstadials. To understand the chronology of late Quaternary glaciations, 15 granitic boulders from terminal moraines were sampled for 10Be and 26Al cosmogenic dating. Obtaining reliable exposure ages of erratics within moraines that represent timing of deposition (i.e. glacial advances) is problematic in polar regions, where glacial activity is principally controlled by ice sheet dynamics. Recycling of previously exposed debris, uncertainty in provenance of glacially transported boulders and a lack of a post-depositional hydrologic process to remove previously exposed material from a valley system, leads to ambiguities in multiple exposure ages from a single coeval glacial landform. More importantly, cold-based ice advance can leave a landform unmodified resulting in young erratics deposited on bedrock that shows weathering and/or inconsistent age-altitude relationships. Primarily, inheritance becomes a difficulty in qualifying exposure ages from polar regions. Preliminary results from the Garwood and Miers Valleys indicate that glaciers in the Denton Hills had begun to retreat from their last maximum positions no later than 23-37 ka, and thus the local last glacial maximum

  10. Coastal-change and glaciological map of the Bakutis Coast, Antarctica

    USGS Publications Warehouse

    Swithinbank, Charles; Williams, Richard S.; Ferrigno, Jane G.; Seekins, B.A.; Lucchita, B.K.; Rosanova, Christine E.

    1997-01-01

    Changes in the area and volume of the polar ice sheets are intricately linked to changes in global climate, and the resulting changes in sea level may severely impact the densely populated coastal regions on Earth. Loss of the West Antarctic part of the Antarctic ice sheet alone could cause a sea-level rise of approximately 6 m. The potential sea-level rise after melting of the entire Antarctic ice sheet is estimated to be 65 m to 73 m. In spite of its importance, the mass balance (the net volumetric gain or loss) of the Antarctic ice sheet is poorly known; it is not known whether the ice sheet is growing or shrinking. As a result, measurement of changes in the Antarctic ice sheet was given a very high priority in recommendations by the Polar Research Board of the National Research Council (1986), by the Scientific Committee on Antarctic Research (SCAR) (1989), and by the National Science Foundation's (1990) Division of Polar Programs. An archive of early 1970's Landsat 1, 2, and 3 Multispectral Scanner (MSS) images of Antarctica and the fact that the repeat coverage with satellite images provided an excellent means of documenting changes in the coastline of Antarctica provided the impetus for carrying out a comprehensive analysis of the glaciological features of the coastal regions and changes in ice fronts of Antarctica. The project was later modified to include Landsat 4 and 5 MSS and Thematic Mapper (TM) and RADARSAT images to compare changes over a 20- to 25- year time interval and to prepare a series of 24 1:1,000,000-scale and 1 1:5,000,000-scale U.S. Geological Survey Geologic Investigations Series Maps ('I-Maps') (Williams and others, 1995; Williams and Ferrigno, 1998; and Ferrigno and others, 2002) in both paper and digital format.

  11. Calving of Talyor Glacier, Dry Valleys, Antarctica

    NASA Astrophysics Data System (ADS)

    Carmichael, J. D.; Pettit, E. C.; Creager, K. C.; Hallet, B.

    2007-12-01

    Calving of tide-water glaciers has received considerable attention, with seismic arrays in Alaska, Greenland, and Antarctica devoted to their observation. In these environments, ice cliffs are directly coupled to oceanic temperatures. The land-based polar glaciers of the McMurdo Dry Valleys in Antarctica represent a simpler environment unaffected directly by water contact where other factors can be isolated. In particular, summer calving events of Taylor Glacier are observed to consist of precursory activity including crack growth, cliff overhang, and active seismicity at least 1 hour before collapse. We propose that collapse occurs only after a stress threshold has been crossed, evident from 'pre-calving' of ice from the cliff base 1-3 days prior to the major event. We provide photographic, seismic, and temperature data to illustrate the thermal and stress landscape for land-based calving of polar glaciers.

  12. Ocean Disposal of Man-Made Ice Piers

    EPA Pesticide Factsheets

    The National Science Foundation is permitted to ocean dump man-made ice piers from its base at McMurdo Sound in Antarctica under a MPRSA general permit. Information is provided about ice piers and impacts of ice pier disposal.

  13. Antarctic Ice Mass Balance from GRACE

    NASA Astrophysics Data System (ADS)

    Boening, C.; Firing, Y. L.; Wiese, D. N.; Watkins, M. M.; Schlegel, N.; Larour, E. Y.

    2014-12-01

    The Antarctic ice mass balance and rates of change of ice mass over the past decade are analyzed based on observations from the Gravity Recovery and Climate Experiment (GRACE) satellites, in the form of JPL RL05M mascon solutions. Surface mass balance (SMB) fluxes from ERA-Interim and other atmospheric reanalyses successfully account for the seasonal GRACE-measured mass variability, and explain 70-80% of the continent-wide mass variance at interannual time scales. Trends in the residual (GRACE mass - SMB accumulation) mass time series in different Antarctic drainage basins are consistent with time-mean ice discharge rates based on radar-derived ice velocities and thicknesses. GRACE also resolves accelerations in regional ice mass change rates, including increasing rates of mass gain in East Antarctica and accelerating ice mass loss in West Antarctica. The observed East Antarctic mass gain is only partially explained by anomalously large SMB events in the second half of the record, potentially implying that ice discharge rates are also decreasing in this region. Most of the increasing mass loss rate in West Antarctica, meanwhile, is explained by decreasing SMB (principally precipitation) over this time period, part of the characteristic decadal variability in regional SMB. The residual acceleration of 2+/-1 Gt/yr, which is concentrated in the Amundsen Sea Embayment (ASE) basins, represents the contribution from increasing ice discharge rates. An Ice Sheet System Model (ISSM) run with constant ocean forcing and stationary grounding lines both underpredicts the largest trends in the ASE and produces negligible acceleration or interannual variability in discharge, highlighting the potential importance of ocean forcing for setting ice discharge rates at interannual to decadal time scales.

  14. A cryptic Gondwana-forming orogen located in Antarctica.

    PubMed

    Daczko, Nathan R; Halpin, Jacqueline A; Fitzsimons, Ian C W; Whittaker, Joanne M

    2018-05-30

    The most poorly exposed and least understood Gondwana-forming orogen lies largely hidden beneath ice in East Antarctica. Called the Kuunga orogen, its interpolation between scattered outcrops is speculative with differing and often contradictory trends proposed, and no consensus on the location of any sutures. While some discount a suture altogether, paleomagnetic data from Indo-Antarctica and Australo-Antarctica do require 3000-5000 km relative displacement during Ediacaran-Cambrian Gondwana amalgamation, suggesting that the Kuunga orogen sutured provinces of broadly Indian versus Australian affinity. Here we use compiled data from detrital zircons offshore of East Antarctica that fingerprint two coastal subglacial basement provinces between 60 and 130°E, one of Indian affinity with dominant ca. 980-900 Ma ages (Indo-Antarctica) and one of Australian affinity with dominant ca. 1190-1140 and ca. 1560 Ma ages (Australo-Antarctica). We combine this offshore compilation with existing and new onshore U-Pb geochronology and previous geophysical interpretations to delimit the Indo-Australo-Antarctic boundary at a prominent geophysical lineament which intersects the coast east of Mirny at ~94°E.

  15. No nitrate spikes detectable in several polar ice cores following the largest known solar events

    NASA Astrophysics Data System (ADS)

    Mekhaldi, Florian; McConnell, Joseph R.; Adolphi, Florian; Arienzo, Monica; Chellman, Nathan J.; Maselli, Olivia; Sigl, Michael; Muscheler, Raimund

    2017-04-01

    Solar energetic particle (SEP) events are a genuine and recognized threat to our modern society which is increasingly relying on satellites and technological infrastructures. However, knowledge on the frequency and on the upper limit of the intensity of major solar storms is largely limited by the relatively short direct observation period. In an effort to extend the observation period and because atmospheric ionization induced by solar particles can lead to the production of odd nitrogen, spikes in the nitrate content of ice cores have been tentatively used to reconstruct both the occurrence and intensity of past SEP events. Yet the reliability of its use as such a proxy has been long debated. This is partly due to differing chemistry-climate model outputs, equivocal detection of nitrate spikes in single ice cores for single events, and possible alternative sources to explain nitrate spikes in ice cores. Here we present nitrate measurements from several Antarctic and Greenland ice cores for time periods covering the largest known solar events. More specifically, we use new highly-resolved nitrate and biomass burning proxy species data (e.g. black carbon) from continuous flow analysis following the largest known solar events from the paleo record - the SEP events of 775 and 994 AD. We also consider the historical Carrington event of 1859 as well as contemporary events from the past 60 years which were observed by satellites. Doing so we show that i) there are no reproducible nitrate spikes in Greenland and Antarctic ice cores following any of these major events and that ii) most nitrate spikes found in ice cores are related to biomass burning plumes. Our analysis thus suggests that ice-core nitrate data is not a reliable proxy for atmospheric ionization by SEP events. In light of our results, we advocate that nitrate spikes so far identified from single ice cores should not be used to assess the intensity and occurrence rate of extreme solar events.

  16. Space Radar Image of Weddell Sea, Antarctica

    NASA Image and Video Library

    1999-05-01

    This Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar color composite shows a portion of the Weddell Sea, which is adjacent to the continent of Antarctica. The image shows extensive coverage of first-year sea ice mixtures and patches of open water inside the ice margin. The image covers a 100 kilometer by 30 kilometer (62 mile by 18.5 mile) region of the southern ocean, centered at approximately 57 degrees south latitude and 3 degrees east longitude, which was acquired on October 3, 1994. Data used to create this image were obtained using the L-band (horizontally transmitted and vertically received) in red; the L-band (horizontally transmitted and received) in green; and the C-band (horizontally transmitted and received) in blue. The sea ice, which appears rust-brown in the image, is composed of loosely packed floes from approximately 1 meter to 2 meters (3 feet to 6.5 feet) thick and ranging from 1 meter to 20 meters (3 feet to 65.5 feet) in diameter. Large patches of open water, shown as turquoise blue, are scattered throughout the area, which is typical for ice margins experiencing off-ice winds. The thin, well-organized lines clearly visible in the ice pack are caused by radar energy reflected by floes riding the crest of ocean swells. The wispy, black features seen throughout the image represent areas where new ice is forming. Sea ice, because it acts as an insulator, reduces the loss of heat between the relatively warm ocean and cold atmosphere. This interaction is an important component of the global climate system. Because of the unique combination of winds, currents and temperatures found in this region, ice can extend many hundreds of kilometers north of Antarctica each winter, which classifies the Weddell Sea as one of nature's greatest ice-making engines. During the formation of sea ice, great quantities of salt are expelled from the frozen water. The salt increases the density of the upper layer of sea water, which then sinks to great depths

  17. Glacial isostatic crustal uplift in southern Victoria Land, Antarctica, from geologic and geodetic records

    NASA Astrophysics Data System (ADS)

    Konfal, S.; Wilson, T.; Bevis, M. G.; Kendrick, E. C.; Hall, B. L.

    2011-12-01

    Geologic records and geodetic measurements of glacial isostatic crustal motions are presented from the southern Victoria Land region of Antarctica. In much of the world, key records used for mapping and modeling glacial isostatic crustal motions come from raised paleoshorelines and beaches of ice-marginal lakes and seas. While such records are scarce in Antarctica, preserved paleoshorelines are present in the southern Victoria Land region of Antarctica. Light detection and ranging (LiDAR) data coverages of these features were acquired during the 2001-2002 austral summer field season by NASA's Airborne Topographic Mapper (ATM) system, resulting in 2 meter horizontal resolution digital elevation models (DEMs). This study utilizes these DEM data to derive crustal tilt values from observed changes in elevation along the length of the shorelines. Radiocarbon age data are correlated with the associated degree of shoreline tilt to derive a rate of crustal deformation since deglaciation. Modern rates of glacial isostatic crustal motion are derived from GPS stations in the same region. Campaign station occupation began in 1996-1997 under the TAMDEF (Transantarctic Mountain DEFormation Network) project, and continuous GPS data collected began in 1999 and continues under the ANET/POLENET (Antarctica Polar Earth Observing Network) project, enabling analysis of decadal scale time series. Integrated gradient curves from paleoshoreline records and GPS crustal velocities show exponential form and indicate tilting down to the east. Eastward tilt may be the result of substantial loss of East Antarctic ice, a collapsing forebulge linked to ice centers in the Ross Sea region or in interior West Antarctica, or differences in earth response due to laterally varying earth structure. Modeling of these new data, along with comparison of tilt directions to centers of ice mass loss, provide tests of these scenarios and yield new insights into earth models and ice history.

  18. Collapse of the West Antarctic Ice Sheet after local destabilization of the Amundsen Basin

    PubMed Central

    Feldmann, Johannes; Levermann, Anders

    2015-01-01

    The future evolution of the Antarctic Ice Sheet represents the largest uncertainty in sea-level projections of this and upcoming centuries. Recently, satellite observations and high-resolution simulations have suggested the initiation of an ice-sheet instability in the Amundsen Sea sector of West Antarctica, caused by the last decades’ enhanced basal ice-shelf melting. Whether this localized destabilization will yield a full discharge of marine ice from West Antarctica, associated with a global sea-level rise of more than 3 m, or whether the ice loss is limited by ice dynamics and topographic features, is unclear. Here we show that in the Parallel Ice Sheet Model, a local destabilization causes a complete disintegration of the marine ice in West Antarctica. In our simulations, at 5-km horizontal resolution, the region disequilibrates after 60 y of currently observed melt rates. Thereafter, the marine ice-sheet instability fully unfolds and is not halted by topographic features. In fact, the ice loss in Amundsen Sea sector shifts the catchment's ice divide toward the Filchner–Ronne and Ross ice shelves, which initiates grounding-line retreat there. Our simulations suggest that if a destabilization of Amundsen Sea sector has indeed been initiated, Antarctica will irrevocably contribute at least 3 m to global sea-level rise during the coming centuries to millennia. PMID:26578762

  19. Glaciological constraints on current ice mass changes from modelling the ice sheets over the glacial cycles

    NASA Astrophysics Data System (ADS)

    Huybrechts, P.

    2003-04-01

    The evolution of continental ice sheets introduces a long time scale in the climate system. Large ice sheets have a memory of millenia, hence the present-day ice sheets of Greenland and Antarctica are still adjusting to climatic variations extending back to the last glacial period. This trend is separate from the direct response to mass-balance changes on decadal time scales and needs to be correctly accounted for when assessing current and future contributions to sea level. One way to obtain estimates of current ice mass changes is to model the past history of the ice sheets and their underlying beds over the glacial cycles. Such calculations assist to distinguish between the longer-term ice-dynamic evolution and short-term mass-balance changes when interpreting altimetry data, and are helpful to isolate the effects of postglacial rebound from gravity and altimetry trends. The presentation will discuss results obtained from 3-D thermomechanical ice-sheet/lithosphere/bedrock models applied to the Antarctic and Greenland ice sheets. The simulations are forced by time-dependent boundary conditions derived from sediment and ice core records and are constrained by geomorphological and glacial-geological data of past ice sheet and sea-level stands. Current simulations suggest that the Greenland ice sheet is close to balance, while the Antarctic ice sheet is still losing mass, mainly due to incomplete grounding-line retreat of the West Antarctic ice sheet since the LGM. The results indicate that altimetry trends are likely dominated by ice thickness changes but that the gravitational signal mainly reflects postglacial rebound.

  20. Long-term observing system for the oceanic regime of Filchner-Ronne Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Østerhus, Svein; Schröder, Michael; Hellmer, Hartmunt; Darelius, Elin; Nicholls, Keith; Makinson, Keith

    2014-05-01

    Long term observations of the flow of dense waters from their area of formation to the abyss of the World Ocean, and the return flow of warm waters, are central to climate research. For the Weddell Sea an important component of such a system entails monitoring the formation of High Salinity Shelf Water (HSSW) on the continental shelf north of Ronne Ice Front, the transformation to Ice Shelf Water (ISW) beneath the floating Filchner-Ronne ice shelf, and the flux of ISW overflowing the shelf break to the deep Weddell Sea. Equally important is the return flow of warm water toward the Filchner-Ronne Ice Shelf system. AWI, BAS and UNI/UIB operate a number of monitoring stations in the southern Weddell Sea. The systems build upon techniques and methods developed over several decades and have a proven record of high data return. Here we present plans for extending, integrating and operating the existing long term observatories to increase our knowledge of the natural variability of the ocean-ice shelf system, and to allow early identification of possible changes of regional or global importance. The S2 observatory at the Filchner sill was established in 1977 and continues to deliver the longest existing marine time series from Antarctica. As a key site for monitoring the ISW overflow S2 is a part of the global net of monitoring sites under CLIVAR Southern Ocean Observing System (SOOS) and OceanSITES. The existing S2 observatory consists of a sub-surface mooring carrying sensors for current velocity, temperature, salinity and dissolved oxygen measurements. Observations at the Filchner sill also show a seasonal inflow of relatively warm water that is able to reach Filchner Ice Front. New model results indicate that this flow of water might increase in the future and we have deployed a number of instrumented moorings in the Filchner Depression to estimate the heat flux towards the ice shelf. In 1999 we established Site 5 on Ronne Ice Shelf using a hot-water drill to access

  1. Hemispheric atmospheric variations and oceanographic impacts associated with katabatic surges across the Ross Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Bromwich, David H.; Carrasco, Jorge F.; Liu, Zhong; Tzeng, Ren-Yow

    1993-07-01

    Numerical simulations and surface-based observations show that katabatic winds persistently converge toward and blow across the Siple Coast part of West Antarctica onto the Ross Ice Shelf. About 14% of the time during winter (April to August 1988), thermal infrared satellite images reveal the horizontal propagation of this negatively buoyant katabatic airstream for about 1000 km across the ice shelf to its northwestern edge, a trajectory that nearly parallels the Transantarctic Mountains. This takes place when the pressure field supports such airflow, and is caused by synoptic scale cyclones that decay near and/or over Marie Byrd Land. The northwestward propagation of the katabatic winds is accompanied by other changes in the hemispheric long wave pattern. An upper level ridge develops over Wilkes Land, resulting in an enhancement of the split jet in the Pacific Ocean. Then, more frequent and/or intensified synoptic scale cyclones are steered toward Marie Byrd Land where they become nearly stationary to the northeast of the climatological location. The resulting isobaric configuration accelerates the katabatic winds crossing Siple Coast and supports their horizontal propagation across the Ross Ice Shelf. An immediate impact of this katabatic airflow, that crosses from the ice shelf to the Ross Sea, is expansion of the persistent polynya that is present just to the east of Ross Island. This polynya is a conspicuous feature on passive microwave images of Antarctic sea ice and plays a central role in the salt budget of water masses over the Ross Sea continental shelf. The impact of this katabatic airflow upon mesoscale cyclogenesis over the South Pacific Ocean is also discussed.

  2. NASA-ISRO synthetic aperture radar (NISAR) for temporal tracking of iceberg calving events in the Antarctica

    NASA Astrophysics Data System (ADS)

    Jawak, S. D.; Luis, A. J.

    2017-12-01

    Estimating mass loss of the Antarctic ice sheet caused by iceberg calving is a challenging job. Antarctica is surrounded by a variety of large, medium and small sized ice shelves, glacier tongues and coastal areas without offshore floating ice masses. It is possible to monitor surface structures on the continental ice and the ice shelves as well as calved icebergs using NASA-ISRO synthetic aperture radar (NISAR) satellite images in future. The NISAR, which is planned to be launched in 2020, can be used as an all-weather and all-season system to classify the coastline of Antarctica to map patterns of surface structures close to the calving front. Additionally, classifying patterns and density of surface structures distributed over the ice shelves and ice tongues can be a challenging research where NISAR can be of a great advantage. So this work explores use of NISAR to map surface structures visible on ice shelves which can provide advisories to field teams. The ice shelf fronts has been categorized into various classes based on surface structures relative to the calving front within a 30 km-wide seaward strip. The resulting map of the classified calving fronts around Antarctica and their description would provide a detailed representation of crevasse formation and dominant iceberg in the southern ocean which pose a threat to navigation of Antarctic bound ships.

  3. Aeromagnetic and radio echo ice-sounding measurements show much greater area of the Dufek intrusion, Antarctica

    USGS Publications Warehouse

    Behrendt, John C.; Drewry, D.J.; Jankowski, E.; Grim, M.S.

    1980-01-01

    A combined aeromagnetic and radio echo ice-sounding survey made in 1978 in Antarctica over the Dufek layered mafic intrusion suggests a minimum area of the intrusion of about 50,000 square kilometers, making it comparable in size with the Bushveld Complex of Africa. Comparisons of the magnetic and subglacial topographic profiles illustrate the usefulness of this combination of methods in studying bedrock geology beneath ice-covered areas. Magnetic anomalies range in peak-to-trough amplitude from about 50 nanoteslas over the lowermost exposed portion of the section in the Dufek Massif to about 3600 nanoteslas over the uppermost part of the section in the Forrestal Range. Theoretical magnetic anomalies, computed from a model based on the subice topography fitted to the highest amplitude observed magnetic anomalies, required normal and reversed magnetizations ranging from 10-3 to 10-2 electromagnetic units per cubic centimeter. This result is interpreted as indicating that the Dufek intrusion cooled through the Curie isotherm during one or more reversals of the earth's magnetic field. Copyright ?? 1980 AAAS.

  4. Shape-from-shading using Landsat 8 and airborne laser altimetry over ice sheets: toward new regional DEMs of Greenland and Antarctica

    NASA Astrophysics Data System (ADS)

    Moussavi, M. S.; Scambos, T.; Haran, T. M.; Klinger, M. J.; Abdalati, W.

    2015-12-01

    We investigate the capability of Landsat 8's Operational Land Imager (OLI) instrument to quantify subtle ice sheet topography of Greenland and Antarctica. We use photoclinometry, or 'shape-from-shading', a method of deriving surface topography from local variations in image brightness due to varying surface slope. Photoclinomeetry is applicable over ice sheet areas with highly uniform albedo such as regions covered by recent snowfall. OLI imagery is available from both ascending and descending passes near the summer solstice period for both ice sheets. This provides two views of the surface features from two distinct solar azimuth illumination directions. Airborne laser altimetry data from the Airborne Topographic Mapper (ATM) instrument (flying on the Operation Ice Bridge program) are used to quantitatively convert the image brightness variations of surface undulations to surface slope. To validate the new DEM products, we use additional laser altimetry profiles collected over independent sites from Ice Bridge and ICESat, and high-resolution WorldView-2 DEMs. The photoclinometry-derived DEM products will be useful for studying surface elevation changes, enhancing bedrock elevation maps through inversion of surface topography, and inferring local variations in snow accumulation rates.

  5. The significance of volcanic ash in Greenland ice cores during the Common Era

    NASA Astrophysics Data System (ADS)

    Plunkett, G.; Pilcher, J. R.; McConnell, J. R.; Sigl, M.; Chellman, N.

    2017-12-01

    Volcanic forcing is now widely regarded as a leading natural factor in short-term climate variability. Polar ice cores provide an unrivalled and continuous record of past volcanism through their chemical and particulate content. With an almost annual precision for the Common Era, the ice core volcanic record can be combined with historical data to investigate the climate and social impacts of the eruptions. The sulfate signature in ice cores is critical for determining the possible climate effectiveness of an eruption, but the presence and characterization of volcanic ash (tephra) in the ice is requisite for establishing the source eruption so that location and eruptive style can be better factored in to climate models. Here, we review the Greenland tephra record for the Common Era, and present the results of targeted sampling for tephra of volcanic events that are of interest either because of their suspected climate and societal impacts or because of their potential as isochrons in paleoenvironmental (including ice core) archives. The majority of identifiable tephras derive from Northern Hemisphere mid- to high latitude eruptions, demonstrating the significance of northern extra-tropical volcanic regions as a source of sulfates in Greenland. A number of targets are represented by sparse or no tephra, or shards that cannot be firmly correlated with a source. We consider the challenges faced in isolating and characterizing tephra from low latitude eruptions, and the implications for accurately modelling climate response to large, tropical events. Finally, we compare the ice core tephra record with terrestrial tephrostratigraphies in the circum-North Atlantic area to evaluate the potential for intercontinental tephra linkages and the refinement of volcanic histories.

  6. Quantification of ikaite in Antarctic sea ice

    NASA Astrophysics Data System (ADS)

    Fischer, M.; Thomas, D. N.; Krell, A.; Nehrke, G.; Göttlicher, J.; Norman, L.; Riaux-Gobin, C.; Dieckmann, G. S.

    2012-02-01

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

  7. Draft genome sequence of Paenisporosarcina sp. strain TG-14, a psychrophilic bacterium isolated from sediment-laden stratified basal ice from Taylor Glacier, McMurdo Dry Valleys, Antarctica.

    PubMed

    Koh, Hye Yeon; Lee, Sung Gu; Lee, Jun Hyuck; Doyle, Shawn; Christner, Brent C; Kim, Hak Jun

    2012-12-01

    The psychrophilic bacterium Paenisporosarcina sp. TG-14 was isolated from sediment-laden stratified basal ice from Taylor Glacier, McMurdo Dry Valleys, Antarctica. Here we report the draft genome sequence of this strain, which may provide useful information on the cold adaptation mechanism in extremely variable environments.

  8. The Landsat Image Mosaic of Antarctica

    USGS Publications Warehouse

    Bindschadler, Robert; Vornberger, P.; Fleming, A.; Fox, A.; Mullins, J.; Binnie, D.; Paulsen, S.J.; Granneman, Brian J.; Gorodetzky, D.

    2008-01-01

    The Landsat Image Mosaic of Antarctica (LIMA) is the first true-color, high-spatial-resolution image of the seventh continent. It is constructed from nearly 1100 individually selected Landsat-7 ETM+ scenes. Each image was orthorectified and adjusted for geometric, sensor and illumination variations to a standardized, almost seamless surface reflectance product. Mosaicing to avoid clouds produced a high quality, nearly cloud-free benchmark data set of Antarctica for the International Polar Year from images collected primarily during 1999-2003. Multiple color composites and enhancements were generated to illustrate additional characteristics of the multispectral data including: the true appearance of the surface; discrimination between snow and bare ice; reflectance variations within bright snow; recovered reflectance values in regions of sensor saturation; and subtle topographic variations associated with ice flow. LIMA is viewable and individual scenes or user defined portions of the mosaic are downloadable at http://lima.usgs.gov. Educational materials associated with LIMA are available at http://lima.nasa.gov.

  9. Tidal influences on a future evolution of the Filchner-Ronne Ice Shelf cavity in the Weddell Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    Mueller, Rachael D.; Hattermann, Tore; Howard, Susan L.; Padman, Laurie

    2018-02-01

    Recent modeling studies of ocean circulation in the southern Weddell Sea, Antarctica, project an increase over this century of ocean heat into the cavity beneath Filchner-Ronne Ice Shelf (FRIS). This increase in ocean heat would lead to more basal melting and a modification of the FRIS ice draft. The corresponding change in cavity shape will affect advective pathways and the spatial distribution of tidal currents, which play important roles in basal melting under FRIS. These feedbacks between heat flux, basal melting, and tides will affect the evolution of FRIS under the influence of a changing climate. We explore these feedbacks with a three-dimensional ocean model of the southern Weddell Sea that is forced by thermodynamic exchange beneath the ice shelf and tides along the open boundaries. Our results show regionally dependent feedbacks that, in some areas, substantially modify the melt rates near the grounding lines of buttressed ice streams that flow into FRIS. These feedbacks are introduced by variations in meltwater production as well as the circulation of this meltwater within the FRIS cavity; they are influenced locally by sensitivity of tidal currents to water column thickness (wct) and non-locally by changes in circulation pathways that transport an integrated history of mixing and meltwater entrainment along flow paths. Our results highlight the importance of including explicit tidal forcing in models of future mass loss from FRIS and from the adjacent grounded ice sheet as individual ice-stream grounding zones experience different responses to warming of the ocean inflow.

  10. Compiling Techniques for East Antarctic Ice Velocity Mapping Based on Historical Optical Imagery

    NASA Astrophysics Data System (ADS)

    Li, X.; Li, R.; Qiao, G.; Cheng, Y.; Ye, W.; Gao, T.; Huang, Y.; Tian, Y.; Tong, X.

    2018-05-01

    Ice flow velocity over long time series in East Antarctica plays a vital role in estimating and predicting the mass balance of Antarctic Ice Sheet and its contribution to global sea level rise. However, there is no Antarctic ice velocity product with large space scale available showing the East Antarctic ice flow velocity pattern before the 1990s. We proposed three methods including parallax decomposition, grid-based NCC image matching, feature and gird-based image matching with constraints for estimation of surface velocity in East Antarctica based on ARGON KH-5 and LANDSAT imagery, showing the feasibility of using historical optical imagery to obtain Antarctic ice motion. Based on these previous studies, we presented a set of systematic method for developing ice surface velocity product for the entire East Antarctica from the 1960s to the 1980s in this paper.

  11. 1500 Years of Annual Climate and Environmental Variability as Recorded in Bona-Churchill (Alaska) Ice Cores

    NASA Astrophysics Data System (ADS)

    Thompson, L. G.; Mosley-Thompson, E. S.; Zagorodnov, V.; Davis, M. E.; Mashiotta, T. A.; Lin, P.

    2004-12-01

    In 2003, six ice cores measuring 10.5, 11.5, 11.8, 12.4, 114 and 460 meters were recovered from the col between Mount Bona and Mount Churchill (61° 24'N; 141° 42'W; 4420 m asl). These cores have been analyzed for stable isotopic ratios, insoluble dust content and concentrations of major chemical species. Total Beta radioactivity was measured in the upper sections. The 460-meter core, extending to bedrock, captured the entire depositional record at this site where ice temperatures ranged from -24° C at 10 meters to -19.8° C at the ice/bedrock contact. The shallow cores allow assessment of surface processes under modern meteorological conditions while the deep core offers a ˜1500-year climate and environmental perspective. The average annual net balance is ˜~1000 mm of water equivalent and distinct annual signals in dust and calcium concentrations along with δ 18O allow annual resolution over most of the core. The excess sulfate record reflects many known large volcanic eruptions such as Katmai, Krakatau, Tambora, and Laki which allow validation of the time scale in the upper part of the core. The lower part of the core yields a history of earlier volcanic events. The 460-m Bona-Churchill ice core provides a detailed history of the `Little Ice Age' and medieval warm periods for southeastern Alaska. The source of the White River Ash will be discussed in light of the evidence from this core. The 460-m core also provides a long-term history of the dust fall that originates in north-central China. The annual ice core-derived climate records from southeastern Alaska will facilitate an investigation of the likelihood that the high resolution 1500-year record from the tropical Quelccaya Ice Cap (Peru) preserves a history of the variability of both the PDO and the Aleutian Low.

  12. EBSD in Antarctic and Greenland Ice

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

    Ice, particularly the extensive amounts found in the polar ice sheets, impacts directly on the global climate by changing the albedo and indirectly by supplying an enormous water reservoir that affects sea level change. The discharge of material into the oceans is partly controlled by the melt excess over snow accumulation, partly by the dynamic flow of ice. In addition to sliding over bedrock, an ice body deforms gravitationally under its own weight. In order to improve our description of this flow, ice microstructure studies are needed that elucidate the dominant deformation and recrystallization mechanisms involved. Deformation of hexagonal ice is highly anisotropic: ice is easily sheared in the basal plane and is about two orders of magnitude harder parallel to the c-axis. As dislocation creep is the dominant deformation mechanism in polar ice this strong anisotropy needs to be understood in terms of dislocation activity. The high anisotropy of the ice crystal is usually ascribed to a particular behaviour of dislocations in ice, namely the extension of dislocations into partials on the basal plane. Analysis of EBSD data can help our understanding of dislocation activity by characterizing subgrain boundary types thus providing a tool for comprehensive dislocation characterization in polar ice. Cryo-EBSD microstructure in combination with light microscopy measurements from ice core material from Antarctica (EPICA-DML deep ice core) and Greenland (NEEM deep ice core) are presented and interpreted regarding substructure identification and characterization. We examined one depth for each ice core (EDML: 656 m, NEEM: 719 m) to obtain the first comparison of slip system activity from the two ice sheets. The subgrain boundary to grain boundary threshold misorientation was taken to be 3-5° (Weikusat et al. 2011). EBSD analyses suggest that a large portion of edge dislocations with slip systems basal gliding on the basal plane were indeed involved in forming

  13. Modeling of water isotopes in polar regions and application to ice core studies

    NASA Astrophysics Data System (ADS)

    Jouzel, J.

    2012-04-01

    Willi Dansgaard spear-headed the use of the stable isotopes of water in climatology and palaeoclimatology especially as applied to deep ice cores for which measurements of the oxygen and hydrogen isotope ratios remain the key tools for reconstructing continuous palaeotemperature records. In the line of his pioneering work on "Stable isotopes in precipitation" published in Tellus in 1964, I will review how isotopic models, either Rayleigh type or based on the implementation of water isotopes in General Circulation Models, have developed and been used for applications in polar ice core studies. This will include a discussion of the conventional approach for interpreting water isotopes in ice cores and of additional information provided by measurements of the deuterium excess and more recently of the 17O-excess.

  14. Antarctic Ice Shelf Loss Comes From Underneath

    NASA Image and Video Library

    2017-12-08

    Calving front of an ice shelf in West Antarctica. The traditional view on ice shelves, the floating extensions of seaward glaciers, has been that they mostly lose ice by shedding icebergs. A new study by NASA and university researchers has found that warm ocean waters melting the ice sheets from underneath account for 55 percent of all ice shelf mass loss in Antarctica. This image was taken during the 2012 Antarctic campaign of NASA's Operation IceBridge, a mission that provided data for the new ice shelf study. Read more: www.nasa.gov/topics/earth/features/earth20130613.html Credit: NASA/GSFC/Jefferson Beck NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  15. Enhancing Europa surface characterization with ice penetrating radar: A Comparative study in Antarctica

    NASA Astrophysics Data System (ADS)

    Curra, C.; Arnold, E.; Karwoski, B.; Grima, C.; Schroeder, D. M.; Young, D. A.; Blankenship, D. D.

    2013-12-01

    The shape and composition of the surface of Europa result from multiple processes, most of them involving direct and indirect interactions between the liquid and solid phases of its outer water layer. The surface ice composition is likely to reflect the material exchanged with the sub-glacial ocean and potentially holds signatures of organic compounds that could demonstrate the ability of the icy moon to sustain life. Therefore, the most likely targets for in-situ landing missions are primarily located in complex terrains disrupted by exchange mechanisms with the ocean/lenses of sub-glacial liquid water. Any landing site selection process to ensure a safe delivery of a future lander, will then have to confidently characterize its surface roughness. We evaluate the capability of an ice-penetrating radar to characterize the roughness using a statistical method applied to the surface echoes. Our approach is to compare radar-derived data with nadir-imagery and laser altimetry simultaneously acquired on an airborne platform over Marie Byrd Land, West Antarctica, during the 2012-13 GIMBLE survey. The radar is the High-Capability Radar Sounder 2 (HiCARS 2, 60 MHz) system operated by the University of Texas Institute for Geophysics (UTIG), with specifications similar to the Ice Penetrating Radar (IPR) of the Europa Clipper project. Surface textures as seen by simultaneously collected nadir imagery are manually classified, allowing individual contrast stretching for better identification. We identified crevasse fields, blue ice patches, and families of wind-blown patterns. Homogeneity/heterogeneity of the textures has also been an important classification criterion. The various textures are geolocated and compared to the evolution and amplitude of laser-derived and radar-derived roughness. Similarities and discrepancies between these three datasets are illustrated and analyzed to qualitatively constrain radar sensitivity to the surface textures. The result allows for a

  16. Automated Laser-Light Scattering measurements of Impurities, Bubbles, and Imperfections in Ice Cores

    NASA Astrophysics Data System (ADS)

    Stolz, M. R.; Ram, M.

    2004-12-01

    Laser- light scattering (LLS) on polar ice, or on polar ice meltwater, is an accepted method for measuring the concentration of water insoluble aerosol deposits (dust) in the ice. LLS on polar ice can also be used to measure water soluble aerosols, as well as imperfections (air bubbles and cavities) in the ice. LLS was originally proposed by Hammer (1977a, b) as a method for measuring the dust concentration in polar ice meltwater. Ram et al. (1995) later advanced the method and applied it to solid ice, measuring the dust concentration profile along the deep, bubble-free sections of the Greenland Ice Sheet Projetct 2 (GISP2) ice core (Ram et al., 1995, 2000) from central Greenland. In this paper, we will put previous empirical findings (Ram et al., 1995, 2000) on a theoretical footing, and extend the usability of LLS on ice into the realm of the non-transparent, bubbly polar ice. For LLS on clear, bubble-free polar ice, we studied numerically the scattering of light by soluble and insoluble (dust) aerosol particles embedded in the ice to complement previous experimental studies (Ram et al., 2000). For air bubbles in polar ice, we calculated the effects of multiple light scattering using Mie theory and Monte Carlo simulations, and found a method for determining the bubble number size and concentration using LLS on bubbly ice. We also demonstrated that LLS can be used on bubbly ice to measure annual layers rapidly in an objective manner. Hammer, C. U. (1977a), Dating of Greenland ice cores by microparticle concentration analyses., in International Symposium on Isotopes and Impurities in Snow and Ice, pp. 297-301, IAHS publ. no. 118. Hammer, C. U. (1977b), Dust studies on Greenland ice cores, in International Symposium on Isotopes and Impurities in Snow and Ice, pp. 365-370, IAHS publ. no. 118. Ram, M., M. Illing, P. Weber, G. Koenig, and M. Kaplan (1995), Polar ice stratigraphy from laser-light scattering: Scattering from ice, Geophys. Res. Lett., 22(24), 3525

  17. Variations in West Antarctic Ice Front and Passive Microwave Brightness Temperature for 8 Years Duration in 2000s

    NASA Astrophysics Data System (ADS)

    Kim, J.; Yu, J.; Wang, L.; Liu, H.

    2017-12-01

    Changes in Antarctic ice sheet are caused by various reasons such as changes in Holocene climate, precipitation, and ocean temperature. Such issues of changes in ice sheet has been mainly focused on the Antarctic peninsula, and it is known that ice retreat of the area is caused by changes in atmospheric and ocean temperatures. For the case of West Antarctica, ice front change research is relatively rarely conducted except the Pine island glacier area. This study has monitored ice front changes of West Antarctica and compared the patterns with the changes in brightness temperature based on remote sensing techniques. We used 2000 Radarsat-1 and 2008 Rasarsat-2 SAR data to delineate coastlines of whole West Antarctica based on the locally thresholding adaptive algorithm. The delineated coast lines are analyzed to figure out ice front change patterns between the duration. The variations in brightness temperature for the same duration are calculated based on Defense Meteorological Satellite Program (DMSP)'s Special Sensor Microwave/Images-Special Sensor Microwave Imager/Sounder (SSM/I-SSMIS) passive microwave data. The results show ice front of West Antarctica shows advancing trend except the pine island glacier area. The brightness temperature had decreasing trend during the study period. It infers that changes in ice front and brightness temperature of West Antarctica have considerable relationships. It is expected that a long term monitoring of the relationship would contribute understanding ice dynamics of West Antarctica significantly.

  18. Initial results from geophysical surveys and shallow coring of the Northeast Greenland Ice Stream (NEGIS)

    NASA Astrophysics Data System (ADS)

    Vallelonga, P.; Christianson, K.; Alley, R. B.; Anandakrishnan, S.; Christian, J. E. M.; Dahl-Jensen, D.; Gkinis, V.; Holme, C.; Jacobel, R. W.; Karlsson, N.; Keisling, B. A.; Kipfstuhl, S.; Kjær, H. A.; Kristensen, M. E. L.; Muto, A.; Peters, L. E.; Popp, T.; Riverman, K. L.; Svensson, A. M.; Tibuleac, C.; Vinther, B. M.; Weng, Y.; Winstrup, M.

    2014-01-01

    The Northeast Greenland Ice Stream (NEGIS) is the sole interior Greenlandic ice stream. Fast flow initiates near the summit dome, and the ice stream terminates approximately 1000 km downstream in three large outlet glaciers that calve into the Greenland Sea. To better understand this important system, in the summer of 2012 we drilled a 67 m firn core and conducted ground-based radio-echo sounding (RES) and active-source seismic surveys at a site approximately 150 km downstream from the onset of streaming flow (NEGIS firn core, 75° 37.61' N, 35°56.49' W). The site is representative of the upper part of the ice stream, while also being in a crevasse-free area for safe surface operations. Annual cycles were observed for insoluble dust, sodium and ammonium concentrations and for electrolytic conductivity, allowing a seasonally resolved chronology covering the past 400 yr. Annual layer thicknesses averaged 0.11 m ice equivalent (i.e.) for the period 1607-2011, although accumulation varied between 0.08 and 0.14 m i.e., likely due to flow-related changes in surface topography. Tracing of RES layers from the NGRIP ice core site shows that the ice at NEGIS preserves a climatic record of at least the past 51 kyr. We demonstrate that a deep ice core drilling in this location can provide a reliable Holocene and late-glacial climate record, as well as helping to constrain the past dynamics and ice-lithosphere interactions of the Greenland Ice Sheet.

  19. A Reconciled Estimate of Ice-Sheet Mass Balance

    NASA Technical Reports Server (NTRS)

    Shepherd, Andrew; Ivins, Erik R.; Geruo, A.; Barletta, Valentia R.; Bentley, Mike J.; Bettadpur, Srinivas; Briggs, Kate H.; Bromwich, David H.; Forsberg, Rene; Galin, Natalia; hide

    2012-01-01

    We combined an ensemble of satellite altimetry, interferometry, and gravimetry data sets using common geographical regions, time intervals, and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of Earth's polar ice sheets. We find that there is good agreement between different satellite methods-especially in Greenland and West Antarctica-and that combining satellite data sets leads to greater certainty. Between 1992 and 2011, the ice sheets of Greenland, East Antarctica, West Antarctica, and the Antarctic Peninsula changed in mass by -142 plus or minus 49, +14 plus or minus 43, -65 plus or minus 26, and -20 plus or minus 14 gigatonnes year(sup -1), respectively. Since 1992, the polar ice sheets have contributed, on average, 0.59 plus or minus 0.20 millimeter year(sup -1) to the rate of global sea-level rise.

  20. Potassium alum and aluminum sulfate micro-inclusions in polar ice from Dome Fuji, East Antarctica

    NASA Astrophysics Data System (ADS)

    Ohno, Hiroshi; Iizuka, Yoshinori; Horikawa, Shinichiro; Sakurai, Toshimitsu; Hondoh, Takeo; Motoyama, Hideaki

    2014-03-01

    Water-soluble trace constituents affect the physicochemical properties of polar ice. Their structural distribution provides important insights into the formation history of ice and inclusions. We report the first finding of KAl(SO4)2·12H2O (potassium alum) and Al2(SO4)3·nH2O (aluminum sulfate) micro-inclusions in the Dome Fuji ice core, East Antartica, using a micro-Raman technique. Eutectic temperatures of these water-soluble species determined using thermal analysis were -0.4 °C for potassium alum and -8.0 °C for aluminum sulfate. Although the formation process of the aluminum-bearing sulfates remains unclear, the occurrence of these salts largely depends on ice depth.