Science.gov

Sample records for agassiz ice cap

  1. Trapped Air in Glacial Ice from the base of Penny, Agassiz, and Devon Ice Caps, Canada

    NASA Astrophysics Data System (ADS)

    Yau, A. M.; Fisher, D.

    2013-12-01

    Basal ice from the Canadian Arctic ice caps, Penny, Agassiz, and Devon, has long been suggested to date back into the last interglacial, or Stage 5e. Cores from all three ice caps contain long Holocene sections with heavy δ18Oice values, overlaying condensed glacial sections with light δ18Oice values, which are underlain by ~1-7 m of ice with δ18Oice values similar to that of the Holocene, suggesting accumulation during the last interglacial. However, the origin of the ice, whether the ice is regelation/segregated or pristine glacial ice has been debated, with important implications as to whether or not ice caps in the Canadian arctic persisted through the last interglacial. Here we present analyses of the trapped air from the bottom portions of Penny, Agassiz, and Devon ice caps to provide context about the nature of the basal ice. Geochemical analyses of N2/Ar, O2/Ar, O2/N2, δ15N2, δ18OATM, and total air content (TAC) indicate a spectrum of ice conditions in basal ice. Low N2/Ar ratios and low TAC indicate partial melting in some of the samples from all three ice caps. High δ15N2, high TAC, and N2/Ar ratios close to air indicate that clean glacial ice is also present in the basal section of each ice cap. Low O2/Ar and high δ18OATM indicates microbial respiration in most samples. The lowest δ18OATM values, near 0‰, indicate trapped air ages >80 ka for the Devon and Agassiz ice caps.

  2. A 100 year record of ion chemistry from Agassiz Ice Cap Northern Ellesmere Island NWT, Canada

    NASA Astrophysics Data System (ADS)

    Koerner, Roy M.; Fisher, David A.; Goto-Azuma, Kumiko

    Two ice cores from the top of Agassiz Ice Cap, one from a snow scoured and the other from an unscoured zone, cover 80 and 100 yr of snow deposition respectively. The time scale for the cores is based on seasonal ion signals, a known stratigraphic horizon (1962), and a marked volcanic signature of high SO 2-4, representing Katmai (1912). A marked increase in the SO 2-4 and NO -3 ion which began in the middle of the 19th century is compared with the earlier increase in Greenland and attributed to a different combination of aerosol sources. A case is made for dry deposition of ions in winter, based on the continued presence of winter ion peaks at a site that δ18O indicates has almost no winter snow accumulation. This case is supported by the snowfall record at a nearby Automatic Weather Station, which shows there is very little winter snowfall at these sites, and by the fact that different accumulation rates and ion concentrations at each site effect almost the same ion fluxes. There is no evidence in either of the cores for a change in the levels of pollutant NO -3 and SO 2-4 ion concentrations, due to improvement in emission technologies in the western nations, over the last two decades. The lack of change may indicate that Russia is the dominant source for aerosols at this site.

  3. The historical residue trend of chlorinated hydrocarbons in the Agassiz Ice Cap, Ellesmere I., Canada

    SciTech Connect

    Gregor, D.J.; Peters, A.J.; Backus, S.; Fisher, D.; Zheng, J.

    1995-12-31

    Current detailed measurements of contaminant deposition can not provide a historical perspective except through long term monitoring programs. In the Arctic, ice caps provide an alternative to lake sediments in that the annual snow layers reflect the atmospheric deposition. As a result of the remoteness of the Agassiz Ice Cap (80{degree}49`50``N, 72{degree}56`30``W) and the limited summer melt, annual layers undergo little chemical change, especially after the first summer season, and therefore provide a well defined historical record. PCBs were first measured above detection limit in the core in the late 1950`s. Mean concentration of {Sigma}PCB over the thirty year period is 3.5 ({+-}1.3) ng. L{sup {minus}1}. {Sigma}PCB is dominated by the lower chlorinated congeners with only infrequent detections of congeners with eight or more chlorines. Deposition peaked at 930 ng.m{sup {minus}2}.a{sup {minus}1} in 1967/68 and decreased to 90 ng.m{sup {minus}2}.a{sup {minus}1} in 1980/81. Since 1980/81, deposition has again increased to a local maximum of 850 ng.m{sup {minus}2}.a{sup {minus}1} in 1989/90. PAHs are detectable throughout the sampling period. Only 7 individual PAHs were above the quantification limits including naphthalene (accounting for an overall mean of 88% of the {Sigma}PAH) acenaphthene, fluorene, phenanthrene, fluoranthene, pyrene and chrysene. No PAHs with five or more aromatic rings were observed to be present above the detection limits. The flux of PAHs to the Ice Cap remained relatively constant from 1790 to 1940 at approximately 3 {micro}g.m{sup {minus}2}.a{sup {minus}1}. The period 1940 to 1980 is dominated by a large increase in deposition peaking at 70 {micro}g.m{sup {minus}2}.a{sup {minus}1} in the early 1970`s. The final period, 1980 to 1993 shows a steady increase by a factor of about 2 from a minimum of 10--20 {micro}g.m{sup {minus}2}.a{sup {minus}1}.

  4. Ice - not just H2O (Louis Agassiz Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Wolff, E. W.

    2009-04-01

    Many of the important properties and uses of ice that fascinate cryospheric scientists actually depend on impurities that are present: isotopic variants of water molecules, small amounts of soluble and insoluble material derived from the aerosol and gas phase, and the trace constituents of the air bubbles that make up around 10% of the volume of ice at atmospheric pressure. In this lecture, I will first discuss how these impurities, and their location within the ice structure, affect local properties of the ice such as the electrical conductivity and mechanical strength, which scale up to give ice sheets their geophysical properties. I will then consider how the concentrations of different impurities are used to give unique records of palaeoclimate and palaeoenvironmental properties, extending so far 800,000 years back in time. This will be illustrated particularly with data from the EPICA Dome C ice core. Bringing the presentation full circle (and towards Agassiz!), I will discuss how the data from ice cores and other palaeoclimatic archives are starting to lead us towards understanding of the causes of the most prominent feature of late Quaternary climate: the huge glacial/interglacial swings in temperature, that are accompanied by the waxing and waning, roughly every 100,000 years, of great northern hemisphere ice sheets.

  5. Mars ice caps.

    PubMed

    Leovy, C

    1966-12-01

    Minimum atmospheric temperatures required to prevent CO(2) condensatio in the Mars polar caps are higher than those obtained in a computer experiment to simulate the general circulation of the Mars atmosphere. This observation supports the view that the polar caps are predominantly solid CO(2). However, thin clouds of H(2)0 ice could substantially reduce the surface condensation rate.

  6. Ice caps on venus?

    PubMed

    Libby, W F

    1968-03-01

    The data on Venus obtained by Mariner V and Venera 4 are interpreted as evidence of giant polar ice caps holding the water that must have come out of the volcanoes with the observed carbon dioxide, on the assumption that Earth and Venus are of similar composition and volcanic history. The measurements by Venera 4 of the equatorial surface temperature indicate that the microwave readings were high, so that the polar ice caps may be allowed to exist in the face of the 10-centimeter readings of polar temperature. Life seems to be distinctly possible at the edges of the ice sheets.

  7. North Polar Ice Cap

    NASA Technical Reports Server (NTRS)

    1997-01-01

    North polar ice cap of Mars, as seen during mid summer in the northern hemisphere. The reddish areas consist of eolian dust, bright white areas consist of a mixture of water ice and dust, and the dark blue areas consist of sand dunes forming a huge 'collar' around the polar ice cap. (The colors have been enhanced with a decorrelation stretch to better show the color variability.) Shown here is an oblique view of the polar region, as seen with the Viking 1 spacecraft orbiting Mars over latitude 39 degrees north. The spiral bands consist of valleys which form by a combination of the Coriolis forces, wind erosion, and differential sublimation and condensation. In high-resolution images the polar caps are seen to consist of thick sequences of layered deposits, suggesting that cyclical climate changes have occurred on Mars. Cyclical climate changes are readily explained by quasi-periodic changes in the amount and distribution of solar heating resulting from perturbations in orbital and axial elements. Variations in the Earth's orbit have also been linked to the terrestrial climate changes during the ice ages.

  8. South Polar Ice Cap

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-337, 21 April 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows the 'swiss cheese' pattern of frozen carbon dioxide on the south polar residual cap. Observation of these materials over two Mars years has revealed that the scarps that bound the mesas and small buttes are retreating-the carbon dioxide ice is subliming away-at a rate of about 3 meters (3 yards) per Mars year in some places. The picture covers an area about 900 m (about 900 yards) wide near 87.1oS, 93.7oW. Sunlight illuminates the scene from the upper left.

  9. South Polar Residual Ice Cap

    NASA Technical Reports Server (NTRS)

    1990-01-01

    This mosaic is composed of 18 Viking Orbiter images (6 each in red, green, and violet filters), acquired on September 28, 1977, during revolution 407 of Viking Orbiter 2. The south pole is located just off the lower left edge of the polar cap, and the 0 degree longitude meridian extends toward the top of the mosaic. The large crater near the right edge (named 'South') is about 100 km in diameter. These images were acquired during southern summer on Mars (Ls = 341 degrees); the sub-solar declination was 8 degrees S., and the south polar cap was nearing its final stage of retreat just prior to vernal equinox. The south residual cap is approximately 400 km across, and the exposed surface is thought to consist dominantly of carbon-dioxide frost. This is in contrast to the water-ice surface of the north polar residual cap. It is likely that water ice is present in layers that underlie the south polar cap and that comprise the surrounding layered terrains. Near the top of this image, irregular pits with sharp-rimmed cliffs appear 'etched', presumably by wind. A series of rugged mountains (extending toward the upper right corner of the image) are of unknown origin.

  10. Mountain Glaciers and Ice Caps

    USGS Publications Warehouse

    Ananichheva, Maria; Arendt, Anthony; Hagen, Jon-Ove; Hock, Regine; Josberger, Edward G.; Moore, R. Dan; Pfeffer, William Tad; Wolken, Gabriel J.

    2011-01-01

    Projections of future rates of mass loss from mountain glaciers and ice caps in the Arctic focus primarily on projections of changes in the surface mass balance. Current models are not yet capable of making realistic forecasts of changes in losses by calving. Surface mass balance models are forced with downscaled output from climate models driven by forcing scenarios that make assumptions about the future rate of growth of atmospheric greenhouse gas concentrations. Thus, mass loss projections vary considerably, depending on the forcing scenario used and the climate model from which climate projections are derived. A new study in which a surface mass balance model is driven by output from ten general circulation models (GCMs) forced by the IPCC (Intergovernmental Panel on Climate Change) A1B emissions scenario yields estimates of total mass loss of between 51 and 136 mm sea-level equivalent (SLE) (or 13% to 36% of current glacier volume) by 2100. This implies that there will still be substantial glacier mass in the Arctic in 2100 and that Arctic mountain glaciers and ice caps will continue to influence global sea-level change well into the 22nd century.

  11. Preliminary Cosmogenic Surface Exposure Ages on Laurentide Ice-sheet Retreat and Opening of the Eastern Lake Agassiz Outlets

    NASA Astrophysics Data System (ADS)

    Leydet, D.; Carlson, A. E.; Sinclair, G.; Teller, J. T.; Breckenridge, A. J.; Caffee, M. W.; Barth, A. M.

    2015-12-01

    The chronology for the eastern outlets of glacial Lake Agassiz holds important consequences for the cause of Younger Dryas cold event during the last deglaciation. Eastward routing of Lake Agassiz runoff was originally hypothesized to have triggered the Younger Dryas. However, currently the chronology of the eastern outlets is only constrained by minimum-limiting radiocarbon ages that could suggest the eastern outlets were still ice covered at the start of the Younger Dryas at ~12.9 ka BP, requiring a different forcing of this abrupt climate event. Nevertheless, the oldest radiocarbon ages are still consistent with an ice-free eastern outlet at the start of the Younger Dryas. Here we will present preliminary 10-Be cosmogenic surface exposure ages from the North Lake, Flat Rock Lake, glacial Lake Kaministiquia, and Lake Nipigon outlets located near Thunder Bay, Ontario. These ages will date the timing of the deglaciation of the Laurentide ice sheet in the eastern outlet region of glacial Lake Agassiz. This will provide an important constraint for the hypothesized freshwater forcing of the cause of Younger Dryas cold event.

  12. Airborne geophysical survey of ice caps in the Queen Elizabeth Islands, Arctic Canada

    NASA Astrophysics Data System (ADS)

    Palmer, S. J.; Dowdeswell, J. A.; Christoffersen, P.; Benham, T. J.; Young, D. A.; Blankenship, D. D.; Richter, T.; Ng, G.; Grima, C.; Habbal, F.; Sharp, M. J.; Rutishauser, A.

    2014-12-01

    Previous studies have shown that between 2003 and 2009, 60 ± 6 Gt of ice was lost each year from the Canadian Arctic (Gardner et al., 2013), making the region the largest cryospheric contributor to global sea level rise outside of the great ice sheets. Glacier ice in the Queen Elizabeth Islands (QEI) currently covers more than 100,000 km2, representing 20% of Earth's ice-covered land area outside of Greenland and Antarctica. The vast majority of this ice is stored within six ice caps located on Ellesmere, Devon and Axel Heiberg islands. Recent satellite observations of the outlet glaciers draining these ice caps have revealed significant velocity variability on inter-annual and multi-year timescales (Van Wychen et al., 2014), though the drivers of these dynamics are not yet understood. Here we present results obtained in May 2014 during an airborne geophysical survey of the ice caps of Axel Heiberg, Ellesmere and Devon islands, including Agassiz Ice Cap (17,300 km2), Prince of Wales Icefield (19,300 km2) and Devon Ice Cap (14,000 km2). We used a Basler BT-67 aircraft equipped with a suite of geophysical instruments, including a phase-coherent VHF ice-penetrating radar, to measure ice thickness and investigate ice basal conditions along outlet glacier flow lines and in the interior of the ice caps. We reveal that the glaciers draining the ice caps of the QEI exhibit diverse characteristics over short spatial scales, and that fast-flowing tidewater glaciers are located adjacent to previously fast-flowing areas that have subsequently stagnated. Our results show that many ice cap outlet glaciers on Ellesmere and Devon islands are between 700 and 1000 m thick and flow through deep bedrock troughs whose beds lie below sea-level. Some of the outlet glaciers also have floating tongues of ice which extend into the adjacent fjord waters. We intend to use our results to characterize the substrate beneath the ice, and to reveal any variations in conditions at the ice

  13. Textures in south polar ice cap #1

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Textures of the south polar permanent residual ice cap and polar layered terrains. This 30 x 29 km area image (frame 7709) is centered near 87 degrees south, 77 degrees west.

    Figure caption from Science Magazine

  14. Textures in south polar ice cap #2

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Textures of the south polar permanent residual ice cap and polar layered terrains. This 15 x 14 km area image (frame 7306) is centered near 87 degrees south, 341 degrees west.

    Figure caption from Science Magazine

  15. Shrinking ice caps in the spotlight.

    PubMed

    Gross, Michael

    2014-10-01

    From the disappearing sea ice of the Arctic to the thriving microbial communities in subglacial lakes of Antarctica, the Earth's ice caps have often made the news in recent months and years, and polar science has emerged as being crucial to our understanding of our planet's biology and climate. Michael Gross reports.

  16. What Lies Below a Martian Ice Cap

    NASA Technical Reports Server (NTRS)

    2008-01-01

    [figure removed for brevity, see original site] Click on image for larger annotated version

    This image (top) taken by the Shallow Radar instrument on NASA's Mars Reconnaissance Orbiter reveals the layers of ice, sand and dust that make up the north polar ice cap on Mars. It is the most detailed look to date at the insides of this ice cap. The colored map below the radar picture shows the topography of the corresponding Martian terrain (red and white represent higher ground, and green and yellow lower).

    The radar image reveals four never-before-seen thick layers of ice and dust separated by layers of nearly pure ice. According to scientists, these thick ice-free layers represent approximately one-million-year-long cycles of climate change on Mars caused by variations in the planet's tilted axis and its eccentric orbit around the sun. Adding up the entire stack of ice gives an estimated age for the north polar ice cap of about 4 million years a finding that agrees with previous theoretical estimates. The ice cap is about 2 kilometers (1.2 miles) thick.

    The radar picture also shows that the boundary between the ice layers and the surface of Mars underneath is relatively flat (bottom white line on the right). This implies that the surface of Mars is not sagging, or bending, under the weight of the ice cap and this, in turn, suggests that the planet's lithosphere, a combination of the crust and the strong parts of the upper mantle, is thicker than previously thought.

    A thicker lithosphere on Mars means that temperatures increase more gradually with depth toward the interior. Temperatures warm enough for water to be liquid are therefore deeper than previously thought. Likewise, if liquid water does exist in aquifers below the surface of Mars, and if there are any organisms living in that water, they would have to be located deeper in the planet.

    The topography data are from Mars Orbiter Laser Altimeter, which was flown on NASA's Mars Global

  17. Modelling the influence of Lake Agassiz on Glacial Isostatic Adjustment and deglaciation of the Laurentide ice sheet

    NASA Astrophysics Data System (ADS)

    Berends, Tijn; van de Wal, Roderik; de Boer, Bas; Bradley, Sarah

    2016-04-01

    ANICE is a 3-D ice-sheet-shelf model, which simulates ice dynamics on the continental scale. It uses a combination of the SIA and SSA approximations and here it is forced with benthic δ18O records using an inverse routine. It is coupled to SELEN, a model, which solves the gravitationally self-consistent sea-level equation and the solid earth deformation of a spherically symmetrical rotating Maxwell visco-elastic earth, accounting for all major GIA effects. The coupled ANICE-SELEN model thus captures ice-sea-level feedbacks and can be used to accurately simulate variations in local relative sea-level over geological time scales. In this study it is used to investigate the mass loss of the Laurentide ice-sheet during the last deglaciation, accounting in particular for the presence of the proglacial Lake Agassiz by way of its GIA effects and its effect on the ice sheet itself. We show that the mass of the water can have a significant effect on local relative sea-level through the same mechanisms as the ice-sheet - by perturbing the geoid and by deforming the solid earth. In addition we show that calving of the ice-shelf onto the lake could have had a strong influence on the behaviour of the deglaciation. In particular, when allowing lake calving, the ice-sheet retreats rapidly over the deepening bed of Hudson Bay during the deglaciation, resulting in a narrow ice dam over Hudson Strait. This dam collapses around 8.2 Kyr causing a global sea level rise of approximately 1 meter - an observation that agrees well with field data (for example, LaJeunesse and St. Onge, 2008). Without lake calving the model predicts a drainage towards the Arctic ocean in the North.

  18. Seasat and polar ice. [instrument package for ice cap research

    NASA Technical Reports Server (NTRS)

    Campbell, W. J.

    1974-01-01

    The instrument package for SEASAT-A possesses three tools that could give data greatly needed in ice cap research: the Compressed Pulse Radar Altimeter (CPRA), the Coherent Imaging Radar (CIR), and the Scanning Multifrequency Microwave Radiometer (SMMR). Certain problems that can be studied with each sensor are discussed.

  19. Acoustic Monitoring of the Arctic Ice Cap

    NASA Astrophysics Data System (ADS)

    Porter, D. L.; Goemmer, S. A.; Chayes, D. N.

    2012-12-01

    Introduction The monitoring of the Arctic Ice Cap is important economically, tactically, and strategically. In the scenario of ice cap retreat, new paths of commerce open, e.g. waterways from Northern Europe to the Far East. Where ship-going commerce is conducted, the U.S. Navy and U.S. Coast Guard have always stood guard and been prepared to assist from acts of nature and of man. It is imperative that in addition to measuring the ice from satellites, e.g. Icesat, that we have an ability to measure the ice extent, its thickness, and roughness. These parameters play an important part in the modeling of the ice and the processes that control its growth or shrinking and its thickness. The proposed system consists of three subsystems. The first subsystem is an acoustic source, the second is an array of geophones and the third is a system to supply energy and transmit the results back to the analysis laboratory. The subsystems are described below. We conclude with a plan on how to tackle this project and the payoff to the ice cap modeler and hence the users, i.e. commerce and defense. System Two historically tested methods to generate a large amplitude multi-frequency sound source include explosives and air guns. A new method developed and tested by the University of Texas, ARL is a combustive Sound Source [Wilson, et al., 1995]. The combustive sound source is a submerged combustion chamber that is filled with the byproducts of the electrolysis of sea water, i.e. Hydrogen and Oxygen, an explosive mixture which is ignited via a spark. Thus, no additional compressors, gases, or explosives need to be transported to the Arctic to generate an acoustic pulse capable of the sediment and the ice. The second subsystem would be geophones capable of listening in the O(10 Hz) range and transmitting that data back to the laboratory. Thus two single arrays of geophones arranged orthogonal to each other with a range of 1000's of kilometers and a combustive sound source where the two

  20. 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. PMID:17733504

  1. 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.

  2. Morphology of Mars North Polar Ice Cap

    NASA Technical Reports Server (NTRS)

    Zwally, H. J.; Fountain, A.; Kargel, J.; Kouvaris, L.; Lewis, K.; MacAyeal, D.; Pfeffer, T.; Saba, J. L.

    2000-01-01

    The northern ice cap of Mars consists of a parabolic dome centered within 13 km of the pole, plus an arm-like ridge extending from the dome between about 135 and 225 east. Chasma Boreale lies between the dome and the extended ridge. The base of the dome is approximately elliptical with a major axis of 1100 km along the 90 east to 270 east direction and minor axis of 700 km along zero east to 180 deg. The heights of the dome and the extended ridge are respectively 2900 inches and 1700 inches above the surrounding basin. Least-squares fitting of a parabola through height profiles of the dome along longitudes 90 deg to 270 deg and zero deg to 180 deg gives an elliptic-paraboloid equation for the dome: Z(m) = 2800 - [(X-x)(exp 2)/113.6] - [(Y-y)(exp 2)/50.3], where X is the 90 deg to 270 deg axis, x = 9.90 km, y = 13.32 km, and the slightly-different fitted heights for the two axes are averaged. The center of the dome is shifted 13.32 km from the pole along zero deg longitude and 9.90 km along 90 deg longitude. Typical mean surface slopes on the ice cap are the order of 1/100 (0.6 deg), A small central portion of the cap, about 100 km by 200 km, extends in elevation about 200 inches above the parabolic shape of the cap. Additional information is contained in the original extended abstract.

  3. Total mercury in snow and ice samples from Canadian High Arctic ice caps and glaciers: a practical procedure and method for total Hg quantification at low pg g(-1) level.

    PubMed

    Zheng, Jiancheng; Pelchat, Pierre; Vaive, Judy; Bass, David; Ke, Fu

    2014-01-15

    A newly developed procedure and method for studying total Hg (THg) in the High Arctic glaciers and ice caps, including container type selection, on-site sampling, sample protection and storage, and sample decontamination is reported in this study. Two analytical systems for THg quantification were also compared to confirm the accuracy and reproducibility. This study found that container types, storage time, sample protection from exposure to light and environment are all important for precise quantification of THg in snow and ice samples from the Canadian High Arctic glaciers and ice caps. With this newly developed procedure and method, we retrieved 28-year and 73-year archives for atmospheric THg deposition from Mt. Oxford and Agassiz Ice Cap respectively. Our results show that snow and ice samples contain THg concentrations varying from sub pg g(-1) to low pg g(-1). Comparison of THg concentration trends and fluxes from the two sites demonstrates that quantification of THg from the two locations with similar altitudes and latitudes can be reproducible, which suggests that historical THg information from atmospheric deposition can be preserved in snow and ice in the glaciers and ice caps. The high reproducibility of results achieved by this procedure and method, in return, confirmed its suitability for studies of THg in snow and ice samples from ice caps and glaciers.

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

    NASA Astrophysics Data System (ADS)

    Fichefet, Thierry

    2016-04-01

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

  5. Glaciers and ice caps outside Greenland

    USGS Publications Warehouse

    Sharp, Marin; Wolken, G.; Burgess, D.; Cogley, J.G.; Copland, L.; Thomson, L.; Arendt, A.; Wouters, B.; Kohler, J.; Andreassen, L.M.; O'Neel, Shad; Pelto, M.

    2015-01-01

    Mountain glaciers and ice caps cover an area of over 400 000 km2 in the Arctic, and are a major influence on global sea level (Gardner et al. 2011, 2013; Jacob et al. 2012). They gain mass by snow accumulation and lose mass by meltwater runoff. Where they terminate in water (ocean or lake), they also lose mass by iceberg calving. The climatic mass balance (Bclim, the difference between annual snow accumulation and annual meltwater runoff) is a widely used index of how glaciers respond to climate variability and change. The total mass balance (ΔM) is defined as the difference between annual snow accumulation and annual mass losses (by iceberg calving plus runoff).

  6. Greenland ice cores tell tales on past climate changes (Louis Agassiz Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Dahl-Jensen, Dorthe

    2014-05-01

    Greenland ice cores contain very highly resolved climate records reaching 128.000 years back in time. When dated and matched they tell tales on very abrupt climate changes especially during the glacial period demonstrating that internal energy exchange in the climate system can cause dramatic and fast changes with no external forcing. When the water stable isotope records from the six deep ice cores are compared they inform on both temperature changes and elevation changes of the Greenland ice sheet during glacial and interglacial periods. The temperature and elevation changes during the last 128.000 years are presented and the knowledge gained is used to discuss how this knowledge can be used to predict the future volume change of the Greenland ice sheet. This knowledge can improve estimates of future sea level rise predictions and is a demonstration of how knowledge from the past can be used to predict the future.

  7. Ice Sheets from Space: The Big Picture View (Louis Agassiz Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Joughin, I. R.

    2012-04-01

    Instead of heroic efforts to acquire a few dozen field-based measurements of ice-flow velocity at some of the Earth's most remote locations, computer servers now crunch satellite data to spew out millions of measurements, providing a whole new perspective on how ice sheets function. Prior to such observations, outlet glaciers and ice streams were perceived to respond slowly to climate change, with little change at timescales of months to decades. While some glaciers flow at steady rates, a remarkable number have responded to recent warming with large variations in speed over periods as short as seconds. A wide variety of behavior is observed with some glaciers steadily gaining speed, others accelerating and then leveling off, and a handful varying substantially with no clear trend. While in the minority, a few glaciers have steadily decelerated over the last decade. As examples ofrecent change, two of the most rapidly changing glaciers are examined: Jakobshavn Isbrae in Greenland and Pine Island Glacier in West Antarctica. In addition to documenting the dramatic changes on these glaciers, satellite observations provide important new spatio-temporal data sets with which to understand such change, particularly when used in conjunction with ice sheet models. Although models constrained by these data reveal that ice-shelf buttressing is an important control on ice-sheet flow, the actual speedups are a complex response to the loss of buttressing, involving several other feedbacks that contribute to the acceleration.Although satellite observations have produced tremendous progress in understanding ice sheets, so far these data have raised more questions than they have answered. The contribution that ice dynamics will make to future sea level remains poorly understood and remains a grand challenge for glaciology. The ongoing record of spaceborne measurements is and will remain a key component in addressing this challenge.

  8. Fast-flowing outlet glaciers on Svalbard ice caps

    SciTech Connect

    Dowdeswell, J.A. ); Collin, R.L. )

    1990-08-01

    Four well-defined outlet glaciers are present on the 2510 km{sup 2} cap of Vestfonna in Nordaustlandet, Svalbard. Airborne radio echo sounding and aerial-photograph and satellite-image analysis methods are used to analyze the morphology and dynamics of the ice cap and its component outlet glaciers. The heavily crevassed outlets form linear depressions in the ice-cap surface and flow an order of magnitude faster than the ridges of uncrevassed ice between them. Ice flow on the ridges is accounted for by internal deformation alone, whereas rates of outlet glacier flow require basal motion. One outlet has recently switched into and out of a faster mode of flow. Rapid terminal advance, a change from longitudinal compression to tension, and thinning in the upper basin indicate surge behavior. Observed outlet glacier discharge is significantly greater than current inputs of mass of the ice cap, indicating that present rates of flow cannot be sustained under the contemporary climate.

  9. Holocene fluctuations of Bregne ice cap, Scoresby Sund, eastern Greenland

    NASA Astrophysics Data System (ADS)

    Levy, L.; Kelly, M. A.; Lowell, T. V.; Hall, B. L.

    2011-12-01

    The Arctic cryosphere is responding rapidly to modern global warming. Documenting past changes in the Arctic cryosphere, particularly during times of warmer than present conditions such as the Holocene Thermal Maximum (HTM; 9,000-5,000 yr BP) provides an important background against which the present response and potential for future changes can be compared. Small ice caps located adjacent to the Greenland Ice Sheet respond sensitively to climate change and their past extents provide a proxy for the climatic conditions that have influenced the ice sheet margin. In order to document cryosphere and climatic changes during warmer conditions, we are constructing records of Holocene fluctuations of small ice caps in the Scoresby Sund region of eastern Greenland (71° N, 25.6° W). We use geomorphic mapping, lake sediment records, radiocarbon, and surface exposure (10Be) dating to reconstruct past ice extents. Lake sediment records are from both glacially fed (i.e., threshold) lakes and lakes with no glacial input during the time of interest (i.e., control). Here we present a record of the Holocene extents of Bregne ice cap, Milne Land, western Scoresby Sund, ~50 km southeast of Renland ice cap. Sediments from Two Move Lake (TML), a threshold lake, register the entire Holocene in a thickness of ~70 cm. Radiocarbon dates of lake sediments indicate that the onset of organic accumulation in the lake following the Last Glacial Maximum occurred 8,890±120 cal yr BP. The mid-Holocene is characterized by organic rich mud that is finely laminated in some sections. The onset of Neoglaciation (cooling after HTM) occurs at 2,810±50 cal yr BP and finely laminated sediments during Neoglaciation may register annual deposition. The sediment record from Last Chance Lake, a control lake located 0.5 km from TML, indicates that there has been no glacial input since deglaciation from the Last Glacial Maximum. Unweathered moraines occur <0.5 km from the modern ice cap margin, inboard from

  10. Elevation Changes of Ice Caps in the Canadian Arctic Archipelago

    NASA Technical Reports Server (NTRS)

    Abdalati, W.; Krabill, W.; Frederick, E.; Manizade, S.; Martin, C.; Sonntag, J.; Swift, R.; Thomas, R.; Yungel, J.; Koerner, R.

    2004-01-01

    Precise repeat airborne laser surveys were conducted over the major ice caps in the Canadian Arctic Archipelago in the spring of 1995 and 2000 in order to measure elevation changes in the region. Our measurements reveal thinning at lower elevations (below 1600 m) on most of the ice caps and glaciers, but either very little change or thickening at higher elevations in the ice cap accumulation zones. Recent increases in precipitation in the area can account for the slight thickening where it was observed, but not for the thinning at lower elevations. For the northern ice caps on the Queen Elizabeth Islands, thinning was generally less than 0.5 m/yr , which is consistent with what would be expected from the warm temperature anomalies in the region for the 5-year period between surveys and appears to be a continuation of a trend that began in the mid 1980s. Further south, however, on the Barnes and Penny ice caps on Baffin Island, this thinning was much more pronounced at over 1 m/yr in the lower elevations. Here temperature anomalies were very small, and the thinning at low elevations far exceeds any associated enhanced ablation. The observations on Barnes, and perhaps Penny are consistent with the idea that the observed thinning is part of a much longer term deglaciation, as has been previously suggested for Barnes Ice Cap. Based on the regional relationships between elevation and elevation-change in our data, the 1995-2000 mass balance for the region is estimated to be 25 cu km/yr of ice, which corresponds to a sea level increase of 0.064 mm/ yr . This places it among the more significant sources of eustatic sea level rise, though not as substantial as Greenland ice sheet, Alaskan glaciers, or the Patagonian ice fields.

  11. Surface mass balance of Greenland mountain glaciers and ice caps

    NASA Astrophysics Data System (ADS)

    Benson, R. J.; Box, J. E.; Bromwich, D. H.; Wahr, J. M.

    2009-12-01

    Mountain glaciers and ice caps contribute roughly half of eustatic sea-level rise. Greenland has thousands of small mountain glaciers and several ice caps > 1000 sq. km that have not been included in previous mass balance calculations. To include small glaciers and ice caps in our study, we use Polar WRF, a next-generation regional climate data assimilation model is run at grid resolution less than 10 km. WRF provides surface mass balance data at sufficiently high resolution to resolve not only the narrow ice sheet ablation zone, but provides information useful in downscaling melt and accumulation rates on mountain glaciers and ice caps. In this study, we refine Polar WRF to simulate a realistic surface energy budget. Surface melting is calculated in-line from surface energy budget closure. Blowing snow sublimation is computed in-line. Melt water re-freeze is calculated using a revised scheme. Our results are compared with NASA's Gravity Recovery and Climate Experiment (GRACE) and associated error is calculated on a regional and local scale with validation from automated weather stations (AWS), snow pits and ice core data from various regions along the Greenland ice sheet.

  12. Driving Stresses in Mars Polar Ice Caps and Conditions for Ice Flow

    NASA Technical Reports Server (NTRS)

    Zwally, H. Jay; Saba, Jack L.

    1999-01-01

    Measurements of the topography of the North polar ice cap by the Mars Orbiter Laser Altimeter (MOLA) show that the ice cap is 2950 +/- 200 meters thick. The volume of the cap is about 1.2 x 10(exp 6) cu km covering an area of 1.04 x 10(exp 6) sq km, which is about 40 percent of the Greenland ice sheet in volume and 62 percent in area. The composition of the Northern cap was previously concluded to be predominately H2O, rather than CO2 ice, based on thermodynamic considerations of the insustainablity of CO2 during summer. Principal questions about the cap are: does the ice move and at what rate, is the cap currently growing or depleting in volume, and how and when was the cap formed? Recent research on terrestrial ice sheets indicates that rates of ice deformation at the low stress values characteristic of ice sheets are significantly higher than the rates given by the classic viscous-plastic flow laws commonly used.

  13. The small ice cap instability in diffusive climate models

    NASA Technical Reports Server (NTRS)

    North, G. R.

    1984-01-01

    Simple climate models which invoke diffusive heat transport and ice cap albedo feedback have equilibrium solutions with no stable ice cap smaller than a radius of about 20 deg on a great circle. Attention is presently given to a solution of this phenomenon which is physically appealing. The ice-free solution has a thermal minimum, and if the minimum temperature is just above the critical value for ice formation, then the artificial addition of a patch of ice leads to a widespread depression of the temperature below the critical freezing temperature. A second stable solution will then exist whose spatial extent is determined by the range of the influence function of a point sink of heat, due to the albedo shift in the patch.

  14. The Medieval Warm/Little Ice Age Transition as Recorded by Ice Caps in East Greenland

    NASA Astrophysics Data System (ADS)

    Lowell, T. V.; Kelly, M. A.; Hall, B. L.; Bennike, O.; Honsaker, W. M.; Levy, L.; Lusas, A.

    2011-12-01

    The spatial-temporal distribution of late Holocene temperature changes over the last 2000 yr is still being defined. The high Arctic is often represented by the borehole tem-perature records from GISP and Dye 3. These both show a distinct, but different magni-tude, Medieval warm interval from ~500 to ~1200 AD, with two cold intervals after 1500 AD. However small glaciers in the high Arctic appear reflect a more complex late Holo-cene pattern. On the eastern coast of Greenland two ice caps record a warm interval from 400 AD to 600 AD but cooling after that. These ice caps, Istorvet ,on the coast beside the cold East Greenland Current, and Bregne ice cap, ~ 100 km inland, have yielded organic remains from > 50 sites. A preliminary interpretation is that the organic remains record the last time these ice caps were as small or smaller than the present configuration. Exposure ages show these ice caps reached their post glacial maximum extent within the last 1000 yr. The Istorvet ice cap is thought to show initial cooling at ~AD 884 and an advance to within 500 m of the Little Ice Age extent at AD 1022 and its fullest extent at 1125 AD. Core sediments suggest that extent was maintained until 1750 AD. Results from the inland site indicate a retracted ice cap from AD 1054 to 1393, followed by expansion. Although some of these events appear to have correlative events recorded in SST or sea ice near Iceland. Taken together they appear to have a different signature than lo-cations further south. This may indicate that temperature patterns at high latitudes are only partly coupled with those at lower latitudes.

  15. Contribution of Iceland's Ice Caps to Sea Level Change

    NASA Astrophysics Data System (ADS)

    Bjornsson, H.; Gudmundsson, S.; Pálsson, F.; Magnusson, E.; Sigurdsson, O.; Johannesson, T.; Thorsteinsson, T.; Berthier, E.

    2011-12-01

    We report on the volume change of Icelandic ice caps during several time intervals from the 1980s until present. Changes in ice volume have been monitored by both annual mass balance measurements on the glaciers and by comparison of multi-temporal digital surface elevation models derived from various satellite and airborne remote observations. The glaciers' mass budgets have declined significantly, from being close to zero in the 1980s and early 1990s, to becoming on average negative by -0.7 to -1.8 m w.e. per year since the mid 1990s. This reduction in mass balance is related to rapid climate warming in Iceland, approx. 1.5 °C since the early 1980s. High mass balance sensitivities of -1 to -2 m w. e. per °C are identified. The current contribution of Icelandic ice caps to sea level change is estimated to be ~0.03 mm SLE per year. Icelandic ice caps contain in total approx. 3,600 cubic km of ice, which if melted would raise sea level by approx. 1 cm.

  16. Extending Icelandic volcanological network operations into the ice caps

    NASA Astrophysics Data System (ADS)

    Vogfjord, Kristin; Bean, Chris; Roberts, Matthew; Ofeigsson, Benedikt; Guralp Systems Ltd.

    2013-04-01

    Many of Iceland's most active volcanoes are located under glaciers, with limited access for monitoring equipment. In the warming climate however, a few rock outcrops (nunataks) have emerged from the ice permitting some access improvement, but to properly monitor seismic signals from volcanoes deep inside the ice caps, instruments placed in the ice itself are needed. Continuous, real-time operation of monitoring equipment in harsh climate, heavy snow accumulation and icing conditions on a glacier is a considerable challenge. The FP7 project FUTUREVOLC, which focusses on Icelandic volcanoes, aims for the development of a multiparametric volcano monitoring and early warning system. One of the new developments in the project involves strengthening the existing real-time seismic monitoring and analysis systems by extending the permanent network into the Vatnajökull ice cap. The goal is to improve detection and location of seismic signals, such as microseismicity, LP events, ice-quakes and continuous tremor due to volcanic eruptions at the volcanoes under the ice cap. Real-time processing and discrimination of these signals could give early warnings of an imminent eruption. At subglacial volcanoes however, other processes, such as subglacial floods (jökulhlaup) and subglacial hydrothermal systems - boiling due to sudden drainage -also generate continuous tremor and can therefore lead to false eruption alarms. To minimise the number of false alarms, the network and processing will need to discriminate between the different tremor sources by determining their characteristics and track the temporal evolution and location of the source. For this purpose broad-band instruments will be placed on nunataks as well as in the ice and two short-period arrays will be located at the margin of Vatnajökull, close to subglacial flood paths from the Skaftár ice cauldrons. To record ice movements associated with the jökulhlaups, GPS receivers will be placed on outlet glaciers during

  17. The Search for Subsurface Ice Caps on Mercury

    NASA Astrophysics Data System (ADS)

    Allen, R. A.; Barlow, N. G.; Vilas, F.

    1996-03-01

    Recent ground-based radar observations of Mercury have detected strong, highly depolarized echoes from the north and south polar regions which have been interpreted as possible polar ice deposits. These radar echoes have been correlated with a number of impact craters. Theoretical studies indicate that such surface ice can be stable within permanently shadowed areas, such as the floors of high latitude impact craters. One proposed hypothesis suggests that stable subsurface ice caps exist at the poles of Mercury, and that several of the impact events that created the high latitude craters exposed this subsurface ice. Thus, our study focused on the possibility of ice caps extending below the mercurian surface, down to some unknown latitude in the polar regions. We used the experiences from Mars, where the depth/diameter ratio (d/D) is smaller for ice rich areas, to investigate whether a comparable latitudinal change in d/D is detectable on Mercury. We found no significant latitudinal differences within the two polar regions of our study or between the north polar and equatorial quadrangles, but craters in the south polar region tend to have slightly lower d/D than those in the north polar region.

  18. Water Ice Albedo Variations on the Martian Northern Polar Cap

    NASA Technical Reports Server (NTRS)

    Hale, A. S.; Bass, D. S.; Tamppari, L. K.

    2003-01-01

    The Viking Orbiters determined that the surface of Mars northern residual cap is water ice. Many researchers have related observed atmospheric water vapor abundances to seasonal exchange between reservoirs such as the polar caps, but the extent to which the exchange between the surface and the atmosphere remains uncertain. Early studies of the ice coverage and albedo of the northern residual Martian polar cap using Mariner 9 and Viking images reported that there were substantial internannual differences in ice deposition on the polar cap, a result which suggested a highly variable Martian climate. However, some of the data used in these studies were obtained at differing values of heliocentric solar longitude (L(sub s)). Reevaluation of this dataset indicated that the residual cap undergoes seasonal brightening throughout the summer, and indicated that this process repeats from year to year. In this study we continue to compare Mariner 9 and Viking Orbiter imaging observations and thermal data of the north residual polar cap to data acquired with Mars Global Surveyor s Mars Orbiter Camera (MOC) instrument. In the current study, our goal is to examine all released data from MGS MOC in the northern summer season, along with applicable TES data in order to better understand the albedo variations in the northern summer and their implications on water transport. To date, work has focused primarily on the MOC dataset. In 1999, data acquisition of the northern polar regions began at L(sub s) = 107, although there was little north polar data acquired from L(sub s)= 107 to L(sub s) = 109. We examined a total of 409 images from L(sub s) = 107 to L(sub s)=148. We have also examined data from 2000 from L(sub s)= 93 to L(sub s)= 110; additional progress is ongoing. Here we present a progress report of our observations, and continue to determine their implications for the Martian water cycle.

  19. Effects of ice-cap unloading on shallow magmatic reservoirs

    NASA Astrophysics Data System (ADS)

    Bakker, Richard; Frehner, Marcel; Lupi, Matteo

    2015-04-01

    One of the effects of global warming is the increase of volcanic activity. Glacial melting has been shown to cause visco-elastic relaxation of the upper mantle, which in turn promotes upwelling of magmas through the crust. To date, the effects of ice-cap melting on shallow (i.e., less than 10 km depth) plumbing systems of volcanoes are still not clear. We investigate the pressure changes due to glacial unloading around a magmatic reservoir by combining laboratory and numerical methods. As a case study we focus on Snæfellsjökull, a volcano in Western Iceland whose ice cap is currently melting 1.25 meters (thickness) per year. Our approach is as follows: we obtain representative rock samples from the field, preform tri-axial deformation tests at relevant pressure and temperature (PT) conditions and feed the results into a numerical model in which the stress fields before and after ice cap removal are compared. A suite of deformation experiments were conducted using a Paterson-type tri-axial deformation apparatus. All experiments were performed at a constant strain rate of 10-5 s-1, while varying the PT conditions. We applied confining pressures between 50 and 150 MPa and temperatures between 200 and 1000 ° C. Between 200 and 800 ° C we observe a localized deformation and a slight decrease of the Young's modulus from 41 to 38 GPa. Experiments at 900 and 1000 ° C exhibit macroscopically ductile behavior and a marked reduction of the Young's modulus down to 4 GPa at 1000 ° C. These results are used to construct a numerical finite-element model in which we approximate the volcanic edifice and basement by a 2D axisymmetric half-space. We first calculate the steady-state temperature field in the volcanic system and assign the laboratory-derived temperature-dependent Young's modulus to every element of the model. Then the pressure in the edifice is calculated for two scenarios: with and without ice cap. The comparison between the two scenarios allows us estimate the

  20. Field-calibrated model of melt, refreezing, and runoff for polar ice caps: Application to Devon Ice Cap

    NASA Astrophysics Data System (ADS)

    Morris, Richard M.; Mair, Douglas W. F.; Nienow, Peter W.; Bell, Christina; Burgess, David O.; Wright, Andrew P.

    2014-09-01

    Understanding the controls on the amount of surface meltwater that refreezes, rather than becoming runoff, over polar ice masses is necessary for modeling their surface mass balance and ultimately for predicting their future contributions to global sea level change. We present a modified version of a physically based model that includes an energy balance routine and explicit calculation of near-surface meltwater refreezing capacity, to simulate the evolution of near-surface density and temperature profiles across Devon Ice Cap in Arctic Canada. Uniquely, our model is initiated and calibrated using high spatial resolution measurements of snow and firn densities across almost the entire elevation range of the ice cap for the summer of 2004 and subsequently validated with the same type of measurements obtained during the very different meteorological conditions of summer 2006. The model captures the spatial variability across the transect in bulk snowpack properties although it slightly underestimates the flow of meltwater into the firn of previous years. The percentage of meltwater that becomes runoff is similar in both years; however, the spatial pattern of this melt-runoff relationship is different in the 2 years. The model is found to be insensitive to variation in the depth of impermeable layers within the firn but is very sensitive to variation in air temperature, since the refreezing capacity of firn decreases with increasing temperature. We highlight that the sensitivity of the ice cap's surface mass balance to air temperature is itself dependent on air temperature.

  1. Mars Secular Obliquity Change Due to Water Ice Caps

    NASA Technical Reports Server (NTRS)

    Rubincam, David P.

    1998-01-01

    Mars may have substantially changed its average axial tilt over geologic time due to the waxing and waning of water ice caps. Depending upon Mars' climate and internal structure, the average obliquity could have increased or decreased through climate friction by tens of degrees. A decrease could account for the apparent youthfulness of the polar layered terrain. Alternatively, Mars' average obliquity may have changed until it became "stuck" at its present value of 24.4 deg.

  2. Allerod Collapse of the Newfoundland Ice Cap, northwestern Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Gosse, J. C.; Bell, T.; Yang, G.; Fastook, J.

    2007-12-01

    Control on the timing of deglaciation of the island of Newfoundland was mostly restricted to offshore records although a few lakes have yielded latest Pleistocene paleovegetation proxies of paleoclimate. Twenty-three cosmogenic 10Be ages on boulders throughout Newfoundland have a range of 11.6 to 14.1 ka and mean of 13.1 +/- 0.1 ka (standard error). The samples indicate near-synchronous deglaciation (collapse) in all the regions sampled over a >100,000 km2 area: St. John's Highlands (on the Great Northern Peninsula once believed to be a nunatak); head of White Bay (northcentral NF); Gaff Topsails Region central NF; Anniopsquotch Mountains and Burgeo region (southwestern NF); Granite Lake (southcentral NF); head of Baie d'Espoir (southern NF); and northern Burin Peninsula (southeastern NF). The large (>2 m) boulders with flat horizontal surfaces are unlikely to have been influenced by snow cover, exhumation through till, boulder erosion, or inheritance. Lake bottom (most bulk sediment) conventional and AMS radiocarbon dates support this exposure chronology, and UMISM simulations of ice sheet decay (driven by a scaled GISP temperature record) is consistent with a rapid melting of the ice cap after retreating from (modern) continental shelf regions. Coincidence of the collapse of the Newfoundland Ice Sheet with the timing of Allerod warming provides an example of the sensitivity of large peripheral ice caps to rapid regional climate change.

  3. Seasonal Changes in Mars' North Polar Ice Cap

    NASA Technical Reports Server (NTRS)

    1997-01-01

    These images, which seem to have been taken while NASA's Hubble Space Telescope (HST) was looking directly down on the Martian North Pole, were actually created by assembling mosaics of three sets of images taken by HST in October, 1996 and in January and March, 1997 and projecting them to appear as they would if seen from above the pole. This first mosaic is a view which could not actually be seen in nature because at this season a portion of the pole would have actually been in shadow; the last view, taken near the summer solstice, would correspond to the Midnight Sun on Earth with the pole fully illuminated all day. The resulting polar maps begin at 50 degrees N latitude and are oriented with 0 degrees longitude at the 12 o'clock position. This series of pictures captures the seasonal retreat of Mars' north polar cap.

    October 1996 (early spring in the Northern hemisphere): In this map, assembled from images obtained between Oct. 8 and 15, the cap extends down to 60 degrees N latitude, nearly it's maximum winter extent. (The notches are areas where Hubble data were not available). A thin, comma-shaped cloud of dust can be seen as a salmon-colored crescent at the 7 o'clock position. The cap is actually fairly circular about the geographic pole at this season; the bluish 'knobs' where the cap seems to extend further are actually clouds that occurred near the edges of the three separate sets of images used to make the mosaic.

    January 1997 (mid-spring): Increased warming as spring progresses in the northern hemisphere has sublimated the carbon dioxide ice and frost below 70 degrees north latitude. The faint darker circle inside the cap boundary marks the location of circumpolar sand dunes (see March '97 map); these dark dunes are warmed more by solar heating than are the brighter surroundings, so the surface frost sublimates from the dunes earlier than from the neighboring areas. Particularly evident is the marked hexagonal shape of the polar cap at this season

  4. Surface exposure dating of Little Ice Age ice cap advances on Disko Island, West Greenland

    NASA Astrophysics Data System (ADS)

    Lane, Timothy; Jomelli, Vincent; Rinterknecht, Vincent; Brunstein, Daniel; Schimmelpfennig, Irene; Swingedouw, Didier; Favier, Vincent; Masson-Delmotte, Valerie

    2015-04-01

    Little Ice Age (LIA: 1200-1920 AD) glacier advances in Greenland often form the most extensive positions of Greenland Ice Sheet (GrIS) ice cap and margins since the Early Holocene. Across Greenland these advances are commonly represented by un-vegetated moraines, usually within 1-5 km of the present ice margin. However, chronological constraints on glacier advances during this period are sparse, meaning that GrIS and ice cap behavior and advance/retreat chronology remains poorly understood during this period. At present the majority of ages are based on historical accounts, ice core data, and radiocarbon ages from proglacial threshold lakes. However, developments in the accuracy and precision of surface exposure methods allow dating of LIA moraine boulders, permitting an opportunity to better understand of ice dynamics during this period. Geomorphological mapping and surface exposure dating (36Cl) were used to interpret moraine deposits from the Lyngmarksbræen on Disko Island, West Greenland. A Positive Degree Day (PDD) model was used to estimate Equilibrium Line Altitude (ELA) and mass balance changes for two distinct paleo-glacial extents. Three moraines (M1, M2, and M3) were mapped in the field, and sampled for 36Cl surface exposure dating. The outermost moraine (M1) was of clearly different morphology to the inner moraines, and present only in small fragments. M2 and M3 were distinct arcuate termino-lateral moraines within 50 m of one another, 1.5 km from the present ice margin. The weighted average of four 36Cl ages from M1 returned an early Holocene age of 8.4 ± 0.6 ka. M2 (four samples) returned an age of 0.57 ± 0.04 ka (1441 AD) and M3 (four samples) returned an age of 0.28 ± 0.02 ka (1732 AD). These surface exposure ages represent the first robustly dated Greenlandic ice cap moraine sequence from the LIA. The two periods of ice cap advance and marginal stabilisation are similar to recorded periods of LIA GrIS advance in west Greenland, constrained

  5. The little ice age as recorded in the stratigraphy of the tropical quelccaya ice cap.

    PubMed

    Thompson, L G; Mosley-Thompson, E; Dansgaard, W; Grootes, P M

    1986-10-17

    The analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent. Annual variations in visible dust layers, oxygen isotopes, microparticle concentrations, conductivity, and identification of the historical (A.D. 1600) Huaynaputina ash permit accurate dating and time-scale verification. The fact that the Little Ice Age (about A.D. 1500 to 1900) stands out as a significant climatic event in the oxygen isotope and electrical conductivity records confirms the worldwide character of this event.

  6. Microbial diversity on Icelandic glaciers and ice caps

    PubMed Central

    Lutz, Stefanie; Anesio, Alexandre M.; Edwards, Arwyn; Benning, Liane G.

    2015-01-01

    Algae are important primary colonizers of snow and glacial ice, but hitherto little is known about their ecology on Iceland's glaciers and ice caps. Due do the close proximity of active volcanoes delivering large amounts of ash and dust, they are special ecosystems. This study provides the first investigation of the presence and diversity of microbial communities on all major Icelandic glaciers and ice caps over a 3 year period. Using high-throughput sequencing of the small subunit ribosomal RNA genes (16S and 18S), we assessed the snow community structure and complemented these analyses with a comprehensive suite of physical-, geo-, and biochemical characterizations of the aqueous and solid components contained in snow and ice samples. Our data reveal that a limited number of snow algal taxa (Chloromonas polyptera, Raphidonema sempervirens and two uncultured Chlamydomonadaceae) support a rich community comprising of other micro-eukaryotes, bacteria and archaea. Proteobacteria and Bacteroidetes were the dominant bacterial phyla. Archaea were also detected in sites where snow algae dominated and they mainly belong to the Nitrososphaerales, which are known as important ammonia oxidizers. Multivariate analyses indicated no relationships between nutrient data and microbial community structure. However, the aqueous geochemical simulations suggest that the microbial communities were not nutrient limited because of the equilibrium of snow with the nutrient-rich and fast dissolving volcanic ash. Increasing algal secondary carotenoid contents in the last stages of the melt seasons have previously been associated with a decrease in surface albedo, which in turn could potentially have an impact on the melt rates of Icelandic glaciers. PMID:25941518

  7. Microbial diversity on Icelandic glaciers and ice caps.

    PubMed

    Lutz, Stefanie; Anesio, Alexandre M; Edwards, Arwyn; Benning, Liane G

    2015-01-01

    Algae are important primary colonizers of snow and glacial ice, but hitherto little is known about their ecology on Iceland's glaciers and ice caps. Due do the close proximity of active volcanoes delivering large amounts of ash and dust, they are special ecosystems. This study provides the first investigation of the presence and diversity of microbial communities on all major Icelandic glaciers and ice caps over a 3 year period. Using high-throughput sequencing of the small subunit ribosomal RNA genes (16S and 18S), we assessed the snow community structure and complemented these analyses with a comprehensive suite of physical-, geo-, and biochemical characterizations of the aqueous and solid components contained in snow and ice samples. Our data reveal that a limited number of snow algal taxa (Chloromonas polyptera, Raphidonema sempervirens and two uncultured Chlamydomonadaceae) support a rich community comprising of other micro-eukaryotes, bacteria and archaea. Proteobacteria and Bacteroidetes were the dominant bacterial phyla. Archaea were also detected in sites where snow algae dominated and they mainly belong to the Nitrososphaerales, which are known as important ammonia oxidizers. Multivariate analyses indicated no relationships between nutrient data and microbial community structure. However, the aqueous geochemical simulations suggest that the microbial communities were not nutrient limited because of the equilibrium of snow with the nutrient-rich and fast dissolving volcanic ash. Increasing algal secondary carotenoid contents in the last stages of the melt seasons have previously been associated with a decrease in surface albedo, which in turn could potentially have an impact on the melt rates of Icelandic glaciers. PMID:25941518

  8. Microbial diversity on Icelandic glaciers and ice caps.

    PubMed

    Lutz, Stefanie; Anesio, Alexandre M; Edwards, Arwyn; Benning, Liane G

    2015-01-01

    Algae are important primary colonizers of snow and glacial ice, but hitherto little is known about their ecology on Iceland's glaciers and ice caps. Due do the close proximity of active volcanoes delivering large amounts of ash and dust, they are special ecosystems. This study provides the first investigation of the presence and diversity of microbial communities on all major Icelandic glaciers and ice caps over a 3 year period. Using high-throughput sequencing of the small subunit ribosomal RNA genes (16S and 18S), we assessed the snow community structure and complemented these analyses with a comprehensive suite of physical-, geo-, and biochemical characterizations of the aqueous and solid components contained in snow and ice samples. Our data reveal that a limited number of snow algal taxa (Chloromonas polyptera, Raphidonema sempervirens and two uncultured Chlamydomonadaceae) support a rich community comprising of other micro-eukaryotes, bacteria and archaea. Proteobacteria and Bacteroidetes were the dominant bacterial phyla. Archaea were also detected in sites where snow algae dominated and they mainly belong to the Nitrososphaerales, which are known as important ammonia oxidizers. Multivariate analyses indicated no relationships between nutrient data and microbial community structure. However, the aqueous geochemical simulations suggest that the microbial communities were not nutrient limited because of the equilibrium of snow with the nutrient-rich and fast dissolving volcanic ash. Increasing algal secondary carotenoid contents in the last stages of the melt seasons have previously been associated with a decrease in surface albedo, which in turn could potentially have an impact on the melt rates of Icelandic glaciers.

  9. Extending permanent volcano monitoring networks into Iceland's ice caps

    NASA Astrophysics Data System (ADS)

    Vogfjörd, Kristín S.; Bergsson, Bergur H.; Kjartansson, Vilhjálmur; Jónsson, Thorsteinn; Ófeigsson, Benedikt G.; Roberts, Matthew J.; Jóhannesson, Tómas; Pálsson, Finnur; Magnússon, Eyjólfur; Erlendsson, Pálmi; Ingvarsson, Thorgils; Pálssson, Sighvatur K.

    2015-04-01

    The goals of the FUTUREVOLC project are the establishment of a volcano Supersite in Iceland to enable access to volcanological data from the country's many volcanoes and the development of a multiparametric volcano monitoring and early warning system. However, the location of some of Iceland's most active volcanoes inside the country's largest ice cap, Vatnajökull, makes these goals difficult to achieve as it hinders access and proper monitoring of seismic and deformation signals from the volcanoes. To overcome these obstacles, one of the developments in the project involves experimenting with extending the permanent real-time networks into the ice cap, including installation of stations in the glacier ice. At the onset of the project, only one permanent seismic and GPS site existed within Vatnajökull, on the caldera rim of the Grímsvötn volcano. Two years into the project both seismic and GPS stations have been successfully installed and operated inside the glacier; on rock outcrops as well as on the glacier surface. The specific problems to overcome are (i) harsh weather conditions requiring sturdy and resilient equipment and site installations, (ii) darkness during winter months shutting down power generation for several weeks, (iii) high snow accumulation burying the instruments, solar panels and communication and GPS antennae, and in some locations (iv) extreme icing conditions blocking transmission signals and connection to GPS satellites, as well as excluding the possibility of power generation by wind generators. In 2013, two permanent seismic stations and one GPS station were installed on rock outcrops within the ice cap in locations with 3G connections and powered by solar panels and enough battery storage to sustain operation during the darkest winter months. These sites have successfully operated for over a year with mostly regular maintenance requirements, transmitting data in real-time to IMO for analysis. Preparations for two permanent seismic

  10. Holocene Fluctuations of North Ice Cap, a Proxy for Climate Conditions along the Northwestern Margin of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Kelly, M. A.; Osterberg, E. C.; Lasher, G. E.; Farnsworth, L. B.; Howley, J. A.; Axford, Y.; Zimmerman, S. R. H.

    2015-12-01

    North Ice Cap (~76.9°N, 68°W, summit elevation 1322 m asl), a small, independent ice cap in northwestern Greenland, is located within ~25 km of the Greenland Ice Sheet margin and Harald Molkte Bræ outlet glacier. We present geochronological, geomorphic and sedimentological data constraining the Holocene extents of North Ice Cap and suggest that its past fluctuations can be used as a proxy for climate conditions along the northwestern margin of the Greenland Ice Sheet. Prior work by Goldthwait (1960) used glacial geomorphology and radiocarbon ages of subfossil plants emerging along shear planes in the ice cap margin to suggest that that North Ice Cap was not present during the early Holocene and nucleated in the middle to late Holocene time, with the onset of colder conditions. Subfossil plants emerging at shear planes in the North Ice Cap margin yield radiocarbon ages of ~4.8-5.9 cal kyr BP (Goldthwait, 1960) and ~AD 1000-1350 (950-600 cal yr BP), indicating times when the ice cap was smaller than at present. In situ subfossil plants exposed by recent ice cap retreat date to ~AD 1500-1840 (450-110 cal yr BP) and indicate small fluctuations of the ice cap margin. 10Be ages of an unweathered, lichen-free drift <100 m from the present North Ice Cap margin range from ~500 to 8000 yrs ago. We suggest that the drift was deposited during the last ~500 yrs and that the older 10Be ages are influenced by 10Be inherited from a prior period of exposure. We also infer ice cap fluctuations using geochemical data from a Holocene-long sediment core from Deltasø, a downstream lake that currently receives meltwater from North Ice Cap. The recent recession of the North Ice Cap margin influenced a catastrophic drainage of a large proglacial lake, Søndre Snesø, that our field team documented in August 2012. To our knowledge, this is the first significant lowering of Søndre Snesø in historical time.

  11. Nonequilibrium air clathrate hydrates in Antarctic ice: a paleopiezomdter for polar ice caps.

    PubMed

    Craig, H; Shoji, H; Langway, C C

    1993-12-01

    "Craigite," the mixed-air clathrate hydrate found in polar ice caps below the depth of air-bubble stability, is a clathrate mixed crystal of approximate composition (N2O2).6H2O. Recent observations on the Byrd Station Antarctic core show that the air hydrate is present at a depth of 727 m, well above the predicted depth for the onset of hydrate stability. We propose that the air hydrate occurs some 100 m above the equilibrium phase boundary at Byrd Station because of "piezometry"--i.e., that the anomalous depth of hydrate occurrence is a relic of a previous greater equilibrium depth along the flow trajectory, followed by vertical advection of ice through the local phase-boundary depth. Flowline trajectories in the ice based on numerical models show that the required vertical displacement does indeed occur just upstream of Byrd Station. Air-hydrate piezometry can thus be used as a general parameter to study the details of ice flow in polar ice caps and the metastable persistence of the clathrate phase in regions of upwelling blue ice.

  12. Rapidly Melting Ice Caps of Northern Baffin Island: Insights From Cosmogenic and Conventional Radiocarbon Dating

    NASA Astrophysics Data System (ADS)

    Anderson, R. K.; Miller, G. H.; Briner, J. P.; Lifton, N.; Devogel, S. B.

    2006-12-01

    The interior plateau of northern Baffin Island in the eastern Canadian Arctic is home to several small (< 50 km2) ice caps whose melt has been well recorded since 1949. Modern equilibrium line altitude (ELA) is well above all existing ice and a continuation of current climatic conditions will lead to the disappearance of all ice on the plateau in the future. Between 2000 and 2005, approximately 1 km2 of ice was lost per year, equivalent to ~1.3% of the total ice cover on the plateau. To put this current melt into a larger picture of ice-cap history on the plateau since deglaciation 6 ka, several techniques have been used in concert. The recent extent of the ice caps during the Little Ice Age can be estimated from the preservation of lichen trimlines across much of the plateau. These trimlines represent previous multi-year snow or ice cover and their aerial extent can be measured via satellite imagery. Based on these measurements, modern ice caps represent only ~3% of ice-cap extent during the Little Ice Age. Radiocarbon dating of moss, preserved beneath the ice caps due to their cold-based nature, suggests a sudden expansion of ice cover around 520 calendar years before present (cal BP), indicated by a mode of 7 dates of approximately this age. This coincides with a pulse of global volcanic activity; predicted cooling from increased aerosol loading may have triggered rapid ice-cap growth. However, dead moss emerging at three sites is more than 1000 years old, with a maximum age of 1326±15 cal BP, indicating that portions of the remaining ice caps have remained intact from more than 1000 years Further constraints on ice cap size are provided by 14C cosmogenic exposure dating. 14C concentrations in rocks at the modern ice margin are too low to be the result of continuous exposure since deglaciation followed by shielding for 500-1000 years by ice cover. Exposure history modeling indicates at least one additional prior period of ice cover of approximately 1000 years

  13. Recent Changes in Arctic Glaciers, Ice Caps, and the Greenland Ice Sheet: Cold Facts About Warm Ice

    NASA Astrophysics Data System (ADS)

    Abdalati, W.

    2005-12-01

    One of the major manifestations of Arctic change can be observed in the state of balance of Arctic glaciers and ice caps and the Greenland ice sheet. These ice masses are estimated to contain nearly 3 million cubic kilometers of ice, which is more than six times greater than all the water stored in the Earth's lakes, rivers, and snow combined and is the equivalent of over 7 meters of sea level. Most of these ice masses have been shrinking in recent in years, but their mass balance is highly variable on a wide range of spatial and temporal scales. On the Greenland ice sheet most of the coastal regions have thinned substantially as melt has increased and some of its outlet glaciers have accelerated. Near the equilibrium line in West Greenland, we have seen evidence of summer acceleration that is linked to surface meltwater production, suggesting a relatively rapid response mechanism of the ice sheet change to a warming climate. At the same time, however, the vast interior regions of the Greenland ice sheet have shown little change or slight growth, as accumulation in these areas may have increased. Throughout much of the rest of the Arctic, many glaciers and ice caps have been shrinking in the past few decades, and in Canada and Alaska, the rate of ice loss seems to have accelerated during the late 1990s. These recent observations offer only a snapshot in time of the long-term behavior, but they are providing crucial information about the current state of ice mass balance and the mechanisms that control it in one of the most climatically sensitive regions on Earth. As we continue to learn more through a combination of remote sensing observations, in situ measurements and improved modeling capabilities, it is important that we coordinate and integrate these approaches effectively in order to predict future changes and their impact on sea level, freshwater discharge, and ocean circulation.

  14. Interannual observations and quantification of summertime H2O ice deposition on the Martian CO2 ice south polar cap

    USGS Publications Warehouse

    Brown, Adrian J.; Piqueux, Sylvain; Titus, Timothy N.

    2014-01-01

    The spectral signature of water ice was observed on Martian south polar cap in 2004 by the Observatoire pour l'Mineralogie, l'Eau les Glaces et l'Activite (OMEGA) ( Bibring et al., 2004). Three years later, the OMEGA instrument was used to discover water ice deposited during southern summer on the polar cap ( Langevin et al., 2007). However, temporal and spatial variations of these water ice signatures have remained unexplored, and the origins of these water deposits remains an important scientific question. To investigate this question, we have used observations from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter (MRO) spacecraft of the southern cap during austral summer over four Martian years to search for variations in the amount of water ice. We report below that for each year we have observed the cap, the magnitude of the H2O ice signature on the southern cap has risen steadily throughout summer, particularly on the west end of the cap. The spatial extent of deposition is in disagreement with the current best simulations of deposition of water ice on the south polar cap (Montmessin et al., 2007). This increase in water ice signatures is most likely caused by deposition of atmospheric H2O ice and a set of unusual conditions makes the quantification of this transport flux using CRISM close to ideal. We calculate a ‘minimum apparent‘ amount of deposition corresponding to a thin H2O ice layer of 0.2 mm (with 70% porosity). This amount of H2O ice deposition is 0.6–6% of the total Martian atmospheric water budget. We compare our ‘minimum apparent’ quantification with previous estimates. This deposition process may also have implications for the formation and stability of the southern CO2 ice cap, and therefore play a significant role in the climate budget of modern day Mars.

  15. Diurnal Albedo Variations of the Martian North Polar Water Ice Cap

    NASA Technical Reports Server (NTRS)

    Troy, R. F.; Bass, D.

    2002-01-01

    Presentation of findings regarding diurnal variations in the north polar water ice cap of Mars as part of a larger study of the interannual and seasonal variations of the Martian north polar water ice cap. Additional information is contained in the original extended abstract.

  16. Dissolved Chemical Ions in an Ice Core of Grigoriev Ice Cap, Kyrgyz Tien Shan

    NASA Astrophysics Data System (ADS)

    SHUN, A.; Takeuchi, N.; Sera, S.; Fujita, K.; Okamoto, S.; Naoki, K.; Aizen, V. B.

    2012-12-01

    Snow and ice of glaciers contain various chemical ions supplied through the atmosphere and preserve them for a long period of time. Thus, analysis of soluble ions in glaciers is important to reveal material circulation and climate change in the cryosphere. Many glaciers are distributed over the mountains of the Central Asia. Chemical analysis of ice cores recovered from there play an important role to understand the atmosphere and material circulation peculiar to the Eurasian Continent. In this study, we analyzed the concentration of major ions in the ice core drilled on Grigoriev Ice Cap, Kyrgys Tien Shan, located in the northwestern part of Central Asia. We aim to understand material circulation in this area based on the chemical records. Then, we have attempted to reconstruct the environmental change of Central Asia, combining the chronology, hydrogen and oxygen stable isotope ratio, and density of dust in the ice core analyzed by prior researches. In this study, we used 2,176 samples of a snow pit and ice core from the surface to bed (86.87 m total length) on the top of Grigoriev Ice Cap (4,660 m high), Kyrgys Tien Shan in September, 2007. Samples were cut every 1-5 cm and scraped thinly, and transported frozen to Chiba University, Japan. After that, we dispensed those for various experiments, and analyzed the concentration of major ions using ion chromatography. By the way, it is estimated that the date of the bottom of this ice core is approximately 12,000 years ago by prior researches. The concentration of major ions dissolved in the ice core of Grigoriev Ice Cap revealed that Ca is the most dominant species in the measured ions and it accounted for more than 50 % (Eq ratio) of the mean of the entire core. This suggests that CaCO3 included in mineral dust derived from deserts around Tien Shan strongly influence the chemical composition of the Ice Cap. In addition, this composition is similar to those of Urumqi No.1 Glacier (Tien Shan), Mustagh Ata Glacier

  17. Tracking and responding to a changing Arctic sea-ice cover: How ice users can help the scientific community design better observing systems (Louis Agassiz Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Eicken, Hajo

    2010-05-01

    The Arctic sea-ice cover is undergoing a major transformation, with substantial reductions in summer ice extent reflecting changes in ice thickness, age, and circulation. These changes are impacting Arctic ecosystems and a range of human activities. Anticipating and responding to such impacts, exacerbated by increasing economic activity in parts of the Arctic, requires a foundation of environmental observations and model predictions. Recent increases in industrial activities such as shipping and resource development in parts of the Arctic have further highlighted the need for an integrated observing system. In the case of a changing sea-ice cover, how would one best design and optimize such a system? One of the challenges is to meet the information needs of the scientific community in furthering fundamental understanding of the Arctic system, as well as those of key stakeholders and society, helping them to prepare for and respond to Arctic change. This presentation focuses on how the concept of sea-ice system services, i.e., the uses and benefits (or harm) derived from sea ice, may help guide the implementation of an effective observing system. Principal service categories are (1) sea ice as climate regulator, marine hazard, and coastal buffer; (2) transportation and use of ice as a platform; (3) cultural services obtained from the "icescape"; and (4) support of food webs and biological diversity by sea ice. An analysis of the different ice services provided to different user groups can help prioritize different types of observations and determine optimal measurement strategies. Moreover, the focus on different uses of the ice cover may also help synthesize fundamental and applied research to help Arctic communities adapt in a changing environment. Alaska has experienced some of the most substantial changes in sea-ice conditions throughout the Arctic over the past three decades and is used to illustrate the concepts discussed above. Specifically, we have examined

  18. Perennial water ice identified in the south polar cap of Mars.

    PubMed

    Bibring, Jean-Pierre; Langevin, Yves; Poulet, François; Gendrin, Aline; Gondet, Brigitte; Berthé, Michel; Soufflot, Alain; Drossart, Pierre; Combes, Michel; Bellucci, Giancarlo; Moroz, Vassili; Mangold, Nicolas; Schmitt, Bernard

    2004-04-01

    The inventory of water and carbon dioxide reservoirs on Mars are important clues for understanding the geological, climatic and potentially exobiological evolution of the planet. From the early mapping observation of the permanent ice caps on the martian poles, the northern cap was believed to be mainly composed of water ice, whereas the southern cap was thought to be constituted of carbon dioxide ice. However, recent missions (NASA missions Mars Global Surveyor and Odyssey) have revealed surface structures, altimetry profiles, underlying buried hydrogen, and temperatures of the south polar regions that are thermodynamically consistent with a mixture of surface water ice and carbon dioxide. Here we present the first direct identification and mapping of both carbon dioxide and water ice in the martian high southern latitudes, at a resolution of 2 km, during the local summer, when the extent of the polar ice is at its minimum. We observe that this south polar cap contains perennial water ice in extended areas: as a small admixture to carbon dioxide in the bright regions; associated with dust, without carbon dioxide, at the edges of this bright cap; and, unexpectedly, in large areas tens of kilometres away from the bright cap.

  19. Recent volcano ice interaction and outburst flooding in a Mars polar cap re-entrant

    NASA Astrophysics Data System (ADS)

    Hovius, Niels; Lea-Cox, Andrew; Turowski, Jens M.

    2008-09-01

    Formation of chasms in the polar ice caps of Mars has been attributed to meltwater outburst floods, but the cause of melting has remained uncertain. In a cap re-entrant enveloping Abalos Colles, west of Casma Boreale in the north polar cap, we have found possible evidence of recent volcano-ice interaction and outburst flooding. In this paper we demonstrate that these two mechanisms can have acted together to form or expand the Abalos re-entrant. Flat-topped ridges and circular rims protruding above the ice cap surface in the re-entrant apex may be lava ridges and volcano craters, and can have caused melting of 3.3 to 7.7×10 km of ice. The surrounding cap surface appears to have subsided and the likely volume of missing ice matches the melt estimate. Outburst flooding from this area may have reached peak discharges of 0.3 to 1.5×10 ms according to scour patterns in one of the re-entrant channels. This required ponding of melt water during lava eruption and catastrophic release through a sub- or englacial melt water tunnel, the collapse of which has left a chasm in the ice cap margin. The flood features are geologically recent, and volcano-ice interaction may have occurred within the last 20,000 years.

  20. Expanded Late Wisconsinan ice cap and ice sheet margins in the western Queen Elizabeth Islands, Arctic Canada

    NASA Astrophysics Data System (ADS)

    Nixon, F. Chantel; England, John H.

    2014-05-01

    Recent mapping of surficial geology and geomorphology in the western Canadian High Arctic (Melville and Eglinton islands), together with new radiocarbon dates acquired from ice-contact raised marine sediments, document expanded late Wisconsinan ice limits for the northwest Laurentide Ice Sheet and the western Innuitian Ice Sheet. An extension of the northwestern margin of the Laurentide Ice Sheet onto Eglinton Island is proposed based on evidence from till containing erratics derived from the Canadian Shield and a pattern of meltwater channels indicating ice retreat offshore into M'Clure Strait. Expansion of the western Melville Island Ice Cap (part of the western, lowland sector of the Innuitian Ice Sheet) to its offshore late Wisconsinan limit was facilitated by coalescence with the Laurentide Ice Sheet, whose buttressing allowed thickening to occur. Estimates of ice extent and thickness (>500 m) of the western Melville Island Ice Cap are in agreement with high marine limits (≤70 m asl). Lateral and proglacial meltwater channels, moraines and glaciomarine, glaciolacustrine and glaciofluvial deposits indicate radial retreat of the western Melville Island Ice Cap onto central highlands after ˜13.0 cal ka BP. Older marine limit shorelines on southern Eglinton Island (˜13.6 cal ka BP) are broadly synchronous with the early and rapid deglaciation of other areas formerly glaciated by the northwestern Laurentide Ice Sheet to the southeast and southwest (˜14.2-13.6 cal ka BP). The collapse of the northwest Laurentide Ice Sheet in M'Clure Strait beginning at ˜14.2 cal ka BP, in addition to prior inferred thinning, opens the possibility that it made a significant contribution to meltwater pulse 1A.

  1. Penny ice cap cores, baffin island, canada, and the wisconsinan foxe dome connection: two states of hudson bay ice cover

    PubMed

    Fisher; Koerner; Bourgeois; Zielinski; Wake; Hammer; Clausen; Gundestrup; Johnsen; Goto-Azuma; Hondoh; Blake; Gerasimoff

    1998-01-30

    Ice cores from Penny Ice Cap, Baffin Island, Canada, provide continuous Holocene records of oxygen isotopic composition (delta18O, proxy for temperature) and atmospheric impurities. A time scale was established with the use of altered seasonal variations, some volcanic horizons, and the age for the end of the Wisconsin ice age determined from the GRIP and GISP2 ice cores. There is pre-Holocene ice near the bed. The change in delta18O since the last glacial maximum (LGM) is at least 12.5 per mil, compared with an expected value of 7 per mil, suggesting that LGM ice originated at the much higher elevations of the then existing Foxe Dome and Foxe Ridge of the Laurentide Ice Sheet. The LGM delta18O values suggest thick ice frozen to the bed of Hudson Bay.

  2. Penny ice cap cores, baffin island, canada, and the wisconsinan foxe dome connection: two states of hudson bay ice cover

    PubMed

    Fisher; Koerner; Bourgeois; Zielinski; Wake; Hammer; Clausen; Gundestrup; Johnsen; Goto-Azuma; Hondoh; Blake; Gerasimoff

    1998-01-30

    Ice cores from Penny Ice Cap, Baffin Island, Canada, provide continuous Holocene records of oxygen isotopic composition (delta18O, proxy for temperature) and atmospheric impurities. A time scale was established with the use of altered seasonal variations, some volcanic horizons, and the age for the end of the Wisconsin ice age determined from the GRIP and GISP2 ice cores. There is pre-Holocene ice near the bed. The change in delta18O since the last glacial maximum (LGM) is at least 12.5 per mil, compared with an expected value of 7 per mil, suggesting that LGM ice originated at the much higher elevations of the then existing Foxe Dome and Foxe Ridge of the Laurentide Ice Sheet. The LGM delta18O values suggest thick ice frozen to the bed of Hudson Bay. PMID:9445472

  3. Glacio-isostatic crustal movements caused by historical volume change of the Vatnajokull ice cap, Iceland

    NASA Technical Reports Server (NTRS)

    Sigmundsson, Freysteinn; Einarsson, Pall

    1992-01-01

    Measurements of the lake level of Lake Langisjor at the SW edge of the Vatnajokull ice cap indicate a tilt of 0.26 +/- 0.06 microrad/yr away from the ice cap in the years of 1959-1991. The tilt is too large to be explained as an elastic Earth response to ice retreat this century, or to be caused by change in the gravitational pull of the ice cap, but it can be explained by sub-lithospheric viscous adjustment. Regional subsidence in historical times in SE Iceland can similarly be attributed to viscous adjustment resulting from the increased load of Vatnajokull during the Little Ice Age. The inferred sublithospheric viscosity is 1 x 10 exp 18 - 5 x 10 exp 19 Pa s.

  4. The Drangajökull ice cap, northwest Iceland, persisted into the early-mid Holocene

    NASA Astrophysics Data System (ADS)

    Schomacker, Anders; Brynjólfsson, Skafti; Andreassen, Julie M.; Gudmundsdóttir, Esther Ruth; Olsen, Jesper; Odgaard, Bent V.; Håkansson, Lena; Ingólfsson, Ólafur; Larsen, Nicolaj K.

    2016-09-01

    Most glaciers and ice caps in Iceland experienced rapid deglaciation in the early Holocene, reaching a minimum extent during the Holocene Thermal Maximum. Here we present evidence of the Holocene glacial history from lake sediment cores retrieved from seven threshold lakes around the Drangajökull ice cap in the Vestfirðir peninsula, NW Iceland. The sediment cores show on/off signals of glacial meltwater activity, as minerogenic material deposited from glacial meltwater alternates with organic-rich material (gyttja) deposited without glacial meltwater. We base the chronology of the sediment cores on 14C ages and geochemical identification of key tephra layers with known ages. A 25-cm thick layer of the Saksunarvatn tephra in Lake Skorarvatn indicates that the northern part of the ice cap had reached a similar size as today or was smaller already by 10.2 cal kyr BP. However, 14C ages of lake sediment cores from the highlands southeast of Drangajökull suggest that this part of the ice cap was larger than today until 7.8-7.2 cal kyr BP. Even today, the Drangajökull ice cap has a different behavior than the main ice caps in Iceland, characterized by a very low glaciation limit. Because palaeoclimatic proxies show an early-mid Holocene temperature optimum in this part of Iceland, we suggest that the persistence of Drangajökull into the early Holocene and, possibly, also the entire Holocene was due to high winter precipitation.

  5. Integrated firn elevation change model for glaciers and ice caps

    NASA Astrophysics Data System (ADS)

    Saß, Björn; Sauter, Tobias; Braun, Matthias

    2016-04-01

    We present the development of a firn compaction model in order to improve the volume to mass conversion of geodetic glacier mass balance measurements. The model is applied on the Arctic ice cap Vestfonna. Vestfonna is located on the island Nordaustlandet in the north east of Svalbard. Vestfonna covers about 2400 km² and has a dome like shape with well-defined outlet glaciers. Elevation and volume changes measured by e.g. satellite techniques are becoming more and more popular. They are carried out over observation periods of variable length and often covering different meteorological and snow hydrological regimes. The elevation change measurements compose of various components including dynamic adjustments, firn compaction and mass loss by downwasting. Currently, geodetic glacier mass balances are frequently converted from elevation change measurements using a constant conversion factor of 850 kg m-³ or the density of ice (917 kg m-³) for entire glacier basins. However, the natural conditions are rarely that static. Other studies used constant densities for the ablation (900 kg m-³) and accumulation (600 kg m-³) areas, whereby density variations with varying meteorological and climate conditions are not considered. Hence, each approach bears additional uncertainties from the volume to mass conversion that are strongly affected by the type and timing of the repeat measurements. We link and adapt existing models of surface energy balance, accumulation and snow and firn processes in order to improve the volume to mass conversion by considering the firn compaction component. Energy exchange at the surface is computed by a surface energy balance approach and driven by meteorological variables like incoming short-wave radiation, air temperature, relative humidity, air pressure, wind speed, all-phase precipitation, and cloud cover fraction. Snow and firn processes are addressed by a coupled subsurface model, implemented with a non-equidistant layer discretisation. On

  6. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap

    USGS Publications Warehouse

    Kieffer, H.H.; Christensen, P.R.; Titus, T.N.

    2006-01-01

    The martian polar caps are among the most dynamic regions on Mars, growing substantially in winter as a significant fraction of the atmosphere freezes out in the form of CO2 ice. Unusual dark spots, fans and blotches form as the south-polar seasonal CO2 ice cap retreats during spring and summer. Small radial channel networks are often associated with the location of spots once the ice disappears. The spots have been proposed to be simply bare, defrosted ground; the formation of the channels has remained uncertain. Here we report infrared and visible observations that show that the spots and fans remain at CO2 ice temperatures well into summer, and must be granular materials that have been brought up to the surface of the ice, requiring a complex suite of processes to get them there. We propose that the seasonal ice cap forms an impermeable, translucent slab of CO2 ice that sublimates from the base, building up high-pressure gas beneath the slab. This gas levitates the ice, which eventually ruptures, producing high-velocity CO 2 vents that erupt sand-sized grains in jets to form the spots and erode the channels. These processes are unlike any observed on Earth. ?? 2006 Nature Publishing Group.

  7. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap.

    PubMed

    Kieffer, Hugh H; Christensen, Philip R; Titus, Timothy N

    2006-08-17

    The martian polar caps are among the most dynamic regions on Mars, growing substantially in winter as a significant fraction of the atmosphere freezes out in the form of CO2 ice. Unusual dark spots, fans and blotches form as the south-polar seasonal CO2 ice cap retreats during spring and summer. Small radial channel networks are often associated with the location of spots once the ice disappears. The spots have been proposed to be simply bare, defrosted ground; the formation of the channels has remained uncertain. Here we report infrared and visible observations that show that the spots and fans remain at CO2 ice temperatures well into summer, and must be granular materials that have been brought up to the surface of the ice, requiring a complex suite of processes to get them there. We propose that the seasonal ice cap forms an impermeable, translucent slab of CO2 ice that sublimates from the base, building up high-pressure gas beneath the slab. This gas levitates the ice, which eventually ruptures, producing high-velocity CO2 vents that erupt sand-sized grains in jets to form the spots and erode the channels. These processes are unlike any observed on Earth.

  8. Recent Changes in High-Latitude Glaciers, Ice Caps, and Ice Sheets

    NASA Technical Reports Server (NTRS)

    Abdalati, Waleed

    2006-01-01

    ). While the expansion of the warming oceans is estimated to be about a third of recent sea level rise, (Miller and Douglas 2004) the greatest potential for significantly increasing sea level lies in the Greenland and Antarctic ice sheets. For different reasons, each exhibits characteristics that suggest they are potentially unstable. In Antarctica, large portions of the ice cover rest on a soft bed that lies below sea level, making it vulnerable to runaway retreat. The Greenland ice sheet experiences considerable melt, which has the potential to rapidly accelerate the flow of ice toward the sea. While smaller ice masses, such as the Alaskan Glaciers and the Canadian ice caps, do not have anywhere near the same potential to impact sea level as the vast ice sheets do, many are melting rapidly, posing a significant near-term threat.

  9. Late Holocene expansion of Istorvet ice cap, Liverpool Land, east Greenland

    NASA Astrophysics Data System (ADS)

    Lowell, Thomas V.; Hall, Brenda L.; Kelly, Meredith A.; Bennike, Ole; Lusas, Amanda R.; Honsaker, William; Smith, Colby A.; Levy, Laura B.; Travis, Scott; Denton, George H.

    2013-03-01

    The Greenland Ice Sheet is undergoing dynamic changes that will have global implications if they continue into the future. In this regard, an understanding of how the ice sheet responded to past climate changes affords a baseline for anticipating future behavior. Small, independent ice caps adjacent to the Greenland Ice Sheet (hereinafter called "local ice caps") are sensitive indicators of the response of Greenland ice-marginal zones to climate change. Therefore, we reconstructed late Holocene ice-marginal fluctuations of the local Istorvet ice cap in east Greenland, using radiocarbon dates of subfossil plants, 10Be dates of surface boulders, and analyses of sediment cores from both threshold and control lakes. During the last termination, the Istorvet ice cap had retreated close to its maximum Holocene position by ˜11,730 cal yr BP. Radiocarbon dates of subfossil plants exposed by recent recession of the ice margin indicate that the Istorvet cap was smaller than at present from AD 200 to AD 1025. Sediments from a threshold lake show no glacial input until the ice cap advanced to within 365 m of its Holocene maximum position by ˜AD 1150. Thereafter the ice cap remained at or close to this position until at least AD 1660. The timing of this, the most extensive of the Holocene, expansion is similar to that recorded at some glaciers in the Alps and in southern Alaska. However, in contrast to these other regions, the expansion in east Greenland at AD 1150 appears to have been very close to, if not at, a maximum Holocene value. Comparison of the Istorvet ice-cap fluctuations with Holocene glacier extents in Southern Hemisphere middle-to-high latitude locations on the Antarctic Peninsula and in the Andes and the Southern Alps suggests an out-of-phase relationship. If correct, this pattern supports the hypothesis that a bipolar see-saw of oceanic and/or atmospheric circulation during the Holocene produced asynchronous glacier response at some localities in the two

  10. Neoglacial ice expansion and late Holocene cold-based ice cap dynamics on Cumberland Peninsula, Baffin Island, Arctic Canada

    NASA Astrophysics Data System (ADS)

    Margreth, Annina; Dyke, Arthur S.; Gosse, John C.; Telka, Alice M.

    2014-05-01

    Radiocarbon dating of fossil flora and fauna collected along receding cold-based ice caps and cold-based sections of polythermal glaciers on Cumberland Peninsula reveal insights into Neoglacial ice expansion and late Holocene ice dynamics. The taphonomic advantages of subfossilized moss were exploited to precisely document regional expansions of ice caps through the late Holocene. When compared with climate proxies and records of volcanic eruptions, the moss radiocarbon age distributions indicate i) onset of Neoglaciation shortly after 5 ka, concomitant with increased sea ice cover, ii) intensification of ice expansion between 1.9 and 1.1 ka, followed by halt of ice growth, or ice recession during the Medieval Warm Period, and iii) renewed ice expansion after 0.8 ka, in response to cooling related to a combination of large volcanic eruptions and low solar activity. Overall, the observations support a model of near-instantaneous glacial response to regional climate controls and that these responses were synchronous throughout eastern Canadian Arctic and possibly eastern Greenland.

  11. Preservation of glaciochemical time-series in snow and ice from the Penny Ice Cap, Baffin Island

    NASA Astrophysics Data System (ADS)

    Grumet, Nancy S.; Wake, Cameron P.; Zielinski, Greg A.; Fisher, David; Koerner, Roy; Jacobs, John D.

    A detailed investigation of major ion concentrations of snow and ice in the summit region of Penny Ice Cap (PIC) was performed to determine the effects of summer melt on the glaciochemical time-series. While ion migration due to meltwater percolation makes it difficult to confidently count annual layers in the glaciochemical profiles, time-series of these parameters do show good structure and a strong one year spectral component, suggesting that annual to biannual signals are preserved in PIC glaciochemical records.

  12. Snow algae in an ice core drilled on Grigoriev Ice cap in the Kyrgyz Tien Shen Mountains

    NASA Astrophysics Data System (ADS)

    Honda, M.; Takeuchi, N.; Sera, S.; Fujita, K.; Okamoto, S.; Naoki, K.; Aizen, V. B.

    2012-12-01

    Snow algae are photosynthetic microorganisms and are living on the surfase of glaciers. They grow on melting surface from spring to summer and their biomass and community structure are changed with physical and chemical conditions on glaciers. Ice cores drilled from glaciers also contain snow algae that grew in the past. Studying biomass and community structure of snow algae in ice cores could reveal the temporal variation in snow algae in the past, and also environmental conditions relating propagation of snow algae. In this study, we anlalyzed snow algae preserved in an ice core of Grigoriev Ice cap located in eastern Kyrgyzstan of the central Asia, and to describe their temporal variations for the last 200 years. The ice core drilling was carried out on September in 2007 on the Grigoriev Ice cap in the Kyrgyz Tien Shen Mountains. A 87 m long ice core from the surface to the bedrock was recovered at the top of the ice cap. The core was horizontally cut every 5 cm (total 1212 samples). The samples were melted and preserved as a 3% formalin solution. After the sample water was filtered through a hydrophilized PTFE membrane filter, observed by microscope. Snow algae in the sample water were counting. The algal biomass was represented by the cell number per unit water volume. Here, we showed the results between the surface to the 64 m in depth. We also analyzed the snow algal communities on the surface of the ice cap collected from five different sites from the top down to the terminus. Microscopy revealed that the ice core contained three taxa of filamentous cyanobacteria, an unicellular cyanobacterium, and two green algae. They were also found on the ice or snow surface of the i Ice cap. The quantitative analyses of the algae in the part of upper 64 m deep of the ice core samples revealed that the algal biomass varied significantly and showed many peaks. Furthermore, the biomass profile differed among the taxa. The filamentous cyanobacterium varied from 0.0 to 4

  13. Characteristics and potential climatic significance of ''miniature ice caps'' (crest- and cornice-type low-altitude ice archives)

    NASA Astrophysics Data System (ADS)

    Haeberli, Wilfried; Frauenfelder, Regula; Kääb, Andreas; Wagner, Stephan

    Long-term ice-core records of Alpine glaciers are usually taken from cold-firn areas at high altitudes, as on Mont Blanc and Monte Rosa. Perennial ice bodies at lower altitudes, however, also bear information about the past. Recent findings from the remains of such ice (the Oetztal iceman found in Austria; wooden bows at Lötschen Pass, Switzerland) clearly indicate the hitherto little-recognized fact that small, more-or-less static perennial ice bodies which are cold and frozen to the underlying bedrock may contain very old ice and, hence, important palaeoclimatic information about warm periods with minimum ice extent in the Alps. Since autumn 1998, investigations have been initiated on a crest-type location or ''miniature ice cap'' at Piz Murtél, Engadine, Swiss Alps. First results from shallow drilling, temperature data-logging, geodetic surveying, visual observation, finite-element modelling of simplified basic two-dimensional configurations and comparison to earlier measurements at similar sites provide promising perspectives concerning a little-studied phenomenon with considerable scientific-environmental research potential. Specific characteristics of the investigated site, and probably of many other comparable mountain sites, are: cold ice (about -4°C at 10 m depth), no basal sliding, small mass turnover, striking lack of a firn zone, accumulation mainly by superimposed ice, and direct access to old layers (centuries, millennia?) at the ice/bedrock interface.

  14. Martian Polar Caps: Folding, Faulting, Flowing Glaciers of Multiple Interbedded Ices

    NASA Astrophysics Data System (ADS)

    Kargel, J. S.

    2001-12-01

    The Martian south polar cap (permanent CO2 cap and polar layered deposits), exhibit abundant, varied, and widespread deformational phenomena. Folding and boudinage are very common. Strike-slip or normal faults are rarer. Common in the vicinity of major troughs and scarps are signs of convergent flow tectonics manifested as wrinkle-ridge-like surface folds, thrust faults, and viscous forebulges with thin-skinned extensional crevasses and wrinkle-ridge folds. Such flow convergence is predicted by theory. Boudinage and folding at the 300-m wavelength scale, indicating rheologically contrasting materials, is widely exposed at deep levels along erosional scarps. Independent morphologic evidence indicates south polar materials of contrasting volatility. Hence, the south polar cap appears to be a multiphase structure of interbedded ices. The north polar cap locally also exhibits flow indicators, though they are neither as common nor as varied as in the south. The large-scale quasi-spiral structure of the polar caps could be a manifestation of large-scale boudinage. According to this scenario, deep-level boudinage continuously originates under the glacial divide (the polar cap summit). Rod-like boudin structures are oriented transverse to flow and migrate outward with the large-scale flow field. Troughs develop over areas between major boudins. A dynamic competition, and possibly a rough balance, develops between the local flow field in the vicinity of a trough (which tends to close the trough by lateral closure and upwelling flow) and sublimation erosion (which tends to widen and deepen them). Over time, the troughs flow to the margins of the polar cap where they, along with other polar structures, are destroyed by sublimation. Major ice types contributing to rheological and volatility layering may include, in order of highest to lowest mechanical strength, CO2 clathrate hydrate, water ice containing inert/insoluble dust, pure water ice, water ice containing traces of

  15. Gravitational separation of gases and isotopes in polar ice caps.

    PubMed

    Craig, H; Horibe, Y; Sowers, T

    1988-12-23

    Atmospheric gases trapped in polar ice at the firn to ice transition layer are enriched in heavy isotopes (nitrogen-15 and oxygen-18) and in heavy gases (O(2)/N(2) and Ar/N(2) ratios) relative to the free atmosphere. The maximum enrichments observed follow patterns predicted for gravitational equilibrium at the base of the firn layer, as calculated from the depth to the transition layer and the temperature in the firn. Gas ratios exhibit both positive and negative enrichments relative to air: the negative enrichments of heavy gases are consistent with observed artifacts of vacuum stripping of gases from fractured ice and with the relative values of molecular diameters that govern capillary transport. These two models for isotopic and elemental fractionation provide a basis for understanding the initial enrichments of carbon-13 and oxygen-18 in trapped CO(2), CH(4), and O(2) in ice cores, which must be known in order to decipher ancient atmospheric isotopic ratios.

  16. A Case for Microorganisms on Comets, Europa and the Polar Ice Caps of Mars

    NASA Technical Reports Server (NTRS)

    Hoover, Richard B.; Pikuta, Elena V.

    2003-01-01

    Microbial extremophiles live on Earth wherever there is liquid water and a source of energy. Observations by ground-based observatories, space missions, and satellites have provided strong evidence that water ice exists today on comets, Europa, Callisto, and Ganymede and in the snow, permafrost, glaciers and polar ice caps of Mars. Studies of the cryoconite pools and ice bubble systems of Antarctica suggest that solar heating of dark rocks entrained in ice can cause localized melting of ice providing ideal conditions for the growth of microbial communities with the creation of micro-environments where trapped metabolic gasses produce entrained isolated atmospheres as in the Antarctic ice-bubble systems. It is suggested that these considerations indicate that several groups of microorganisms should be capable of episodic growth within liquid water envelopes surrounding dark rocks in cometary ices and the permafrost and polar caps of Mars. We discuss some of the types of microorganisms we have encountered within the permafrost and snow of Siberia, the cryoconite pools of Alaska, and frozen deep within the Antarctic ice sheet above Lake Vostok.

  17. Drawing to Learn Science: Legacies of Agassiz

    ERIC Educational Resources Information Center

    Lerner, Neal

    2007-01-01

    The use of visual representation to learn science can be traced to Louis Agassiz, Harvard Professor of Zoology, in the mid-19th century. In Agassiz's approach, students were to study nature through carefully observing, drawing and then thinking about what the observations might add up to. However, implementation of Agassiz's student-centered…

  18. Taxon interactions control the distributions of cryoconite bacteria colonizing a High Arctic ice cap.

    PubMed

    Gokul, Jarishma K; Hodson, Andrew J; Saetnan, Eli R; Irvine-Fynn, Tristram D L; Westall, Philippa J; Detheridge, Andrew P; Takeuchi, Nozomu; Bussell, Jennifer; Mur, Luis A J; Edwards, Arwyn

    2016-08-01

    Microbial colonization of glacial ice surfaces incurs feedbacks which affect the melting rate of the ice surface. Ecosystems formed as microbe-mineral aggregates termed cryoconite locally reduce ice surface albedo and represent foci of biodiversity and biogeochemical cycling. Consequently, greater understanding the ecological processes in the formation of functional cryoconite ecosystems upon glacier surfaces is sought. Here, we present the first bacterial biogeography of an ice cap, evaluating the respective roles of dispersal, environmental and biotic filtration occurring at local scales in the assembly of cryoconite microbiota. 16S rRNA gene amplicon semiconductor sequencing of cryoconite colonizing a Svalbard ice cap coupled with digital elevation modelling of physical parameters reveals the bacterial community is dominated by a ubiquitous core of generalist taxa, with evidence for a moderate pairwise distance-decay relationship. While geographic position and melt season duration are prominent among environmental predictors of community structure, the core population of taxa appears highly influential in structuring the bacterial community. Taxon co-occurrence network analysis reveals a highly modular community structured by positive interactions with bottleneck taxa, predominantly Actinobacteria affiliated to isolates from soil humus. In contrast, the filamentous cyanobacterial taxon (assigned to Leptolyngbya/Phormidesmis pristleyi) which dominates the community and binds together granular cryoconite are poorly connected to other taxa. While our study targeted one ice cap, the prominent role of generalist core taxa with close environmental relatives across the global cryosphere indicate discrete roles for cosmopolitan Actinobacteria and Cyanobacteria as respective keystone taxa and ecosystem engineers of cryoconite ecosystems colonizing ice caps. PMID:27261672

  19. Mapping the Variability of Winter Accumulation on the Hofsjökull Ice Cap, Central Iceland

    NASA Astrophysics Data System (ADS)

    Thorsteinsson, Th.; Jóhannesson, T.; Einarsson, B.; Gunnarsson, A.; Kjartansson, V.; Sigurðsson, O.

    2016-09-01

    The poster presents results from the mapping of winter accumulation on the Hofsjökull ice cap, Central Iceland, using a ground penetrating radar. The data are used to correct biases in older mass-balance data with more limited spatial coverage.

  20. Radar scattering from venus at large angles of incidence and the question of polar ice caps.

    PubMed

    Jurgens, R F

    1968-12-20

    Spectrum analysis of radar waves backscattered from an anulus near the limb of Venus shows that a uniform scattering model applies over regions extending from the equator to within approximately 15 degrees of the poles. These observations indicate that large polar ice caps extending to latitudes as low as 60 degrees are very unlikely.

  1. Short-term sea ice forecasting: An assessment of ice concentration and ice drift forecasts using the U.S. Navy's Arctic Cap Nowcast/Forecast System

    NASA Astrophysics Data System (ADS)

    Hebert, David A.; Allard, Richard A.; Metzger, E. Joseph; Posey, Pamela G.; Preller, Ruth H.; Wallcraft, Alan J.; Phelps, Michael W.; Smedstad, Ole Martin

    2015-12-01

    In this study the forecast skill of the U.S. Navy operational Arctic sea ice forecast system, the Arctic Cap Nowcast/Forecast System (ACNFS), is presented for the period February 2014 to June 2015. ACNFS is designed to provide short term, 1-7 day forecasts of Arctic sea ice and ocean conditions. Many quantities are forecast by ACNFS; the most commonly used include ice concentration, ice thickness, ice velocity, sea surface temperature, sea surface salinity, and sea surface velocities. Ice concentration forecast skill is compared to a persistent ice state and historical sea ice climatology. Skill scores are focused on areas where ice concentration changes by ±5% or more, and are therefore limited to primarily the marginal ice zone. We demonstrate that ACNFS forecasts are skilful compared to assuming a persistent ice state, especially beyond 24 h. ACNFS is also shown to be particularly skilful compared to a climatologic state for forecasts up to 102 h. Modeled ice drift velocity is compared to observed buoy data from the International Arctic Buoy Programme. A seasonal bias is shown where ACNFS is slower than IABP velocity in the summer months and faster in the winter months. In February 2015, ACNFS began to assimilate a blended ice concentration derived from Advanced Microwave Scanning Radiometer 2 (AMSR2) and the Interactive Multisensor Snow and Ice Mapping System (IMS). Preliminary results show that assimilating AMSR2 blended with IMS improves the short-term forecast skill and ice edge location compared to the independently derived National Ice Center Ice Edge product.

  2. Reconciling different observations of the CO2 ice mass loading of the Martian north polar cap

    USGS Publications Warehouse

    Haberle, R.M.; Mattingly, B.; Titus, T.N.

    2004-01-01

    The GRS measurements of the peak mass loading of the north polar CO2 ice cap on Mars are about 60% lower than those calculated from MGS TES radiation data and those inferred from the MOLA cap thicknesses. However, the GRS data provide the most accurate measurement of the mass loading. We show that the TES and MOLA data can be reconciled with the GRS data if (1) subsurface heat conduction and atmospheric heat transport are included in the TES mass budget calculations, and (2) the density of the polar deposits is ???600 kg m-3. The latter is much less than that expected for slab ice (???1600 kg m-3) and suggests that processes unique to the north polar region are responsible for the low cap density. Copyright 2004 by the American Geophysical Union.

  3. Tracking Retreat of the North Seasonal Ice Cap on Mars: Results from the THEMIS Investigation

    NASA Technical Reports Server (NTRS)

    Ivanov, A. B.; Wagstaff, K. L.; Ttus, T. N.

    2005-01-01

    The CO2 ice caps on Mars advance and retreat with the seasons. This phenomenon was first observed by Cassini and then confirmed by numerous ground based observations in 19th and 20th centuries. With the advent of the space age observations of the seasonal ice cap were done by all orbiting spacecraft starting with Mariner 7. Viking Orbiters and more recently the Mars Global Surveyor (particularly Mars Orbiter Camera (MOC) and Thermal Emission Spectrometer (TES) instruments) have accumulated significant data on the retreat of the CO2 seasonal cap. During Mars year 2 of THEMIS operations at Mars, we planned an observational campaign in which the THEMIS instrument (onboard the Mars Odyssey spacecraft) repeatedly observed the north seasonal polar cap from midwinter to late spring. THEMIS allows simultaneous observations in both Thermal IR (12.57 m) and Visible wavelengths (0.65 m). One of the goals for this work is to initiate an interannual program for observations of the seasonal ice caps using the THEMIS instrument. The most efficient way to detect the edge between frost and bare ground is directly onboard of the spacecraft. Prior to onboard software design effort, we have developed two groundbased algorithms for automatically finding the edge of the seasonal polar cap in THEMIS IR data. The first algorithm relies on fully calibrated data and can be used for highly reliable groundbased analyses. The second method was specifically developed for processing raw, uncalibrated data in a highly efficient way. It has the potential to enable automatic, onboard detections of the seasonal cap retreat. We have experimentally confirmed that both methods produce similar results, and we have validated both methods against a model constructed from the MGS TES data from the same season.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  5. Tracking the Martian CO2 Polar Ice Caps in Infrared Images

    NASA Technical Reports Server (NTRS)

    Wagstaff, Kiri L.; Castano, Rebecca; Chien, Steve

    2006-01-01

    Researchers at NASA s Jet Propulsion Laboratory have developed a method for automatically tracking the polar caps on Mars as they advance and recede each year (see figure). The seasonal Mars polar caps are composed mainly of CO2 ice and are therefore cold enough to stand out clearly in infrared data collected by the Thermal Emission Imaging System (THEMIS) onboard the Mars Odyssey spacecraft. The Bimodal Image Temperature (BIT) histogram analysis algorithm analyzes raw, uncalibrated data to identify images that contain both "cold" ("polar cap") and "warm" ("not polar cap") pixels. The algorithm dynamically identifies the temperature that separates these two regions. This flexibility is critical, because in the absence of any calibration, the threshold temperature can vary significantly from image to image. Using the identified threshold, the algorithm classifies each pixel in the image as "polar cap" or "not polar cap," then identifies the image row that contains the spatial transition from "polar cap" to "not polar cap." While this method is useful for analyzing data that has already been returned by THEMIS, it has even more significance with respect to data that has not yet been collected. Instead of seeking the polar cap only in specific, targeted images, the simplicity and efficiency of this method makes it feasible for direct, onboard use. That is, THEMIS could continuously monitor its observations for any detections of the polar-cap edge, producing detections over a wide range of spatial and temporal conditions. This effort can greatly contribute to our understanding of long-term climatic change on Mars.

  6. Sensitivity of Barnes Ice Cap, Baffin Island, Canada, to climate state and internal dynamics

    NASA Astrophysics Data System (ADS)

    Gilbert, A.; Flowers, G. E.; Miller, G. H.; Rabus, B. T.; Van Wychen, W.; Gardner, A. S.; Copland, L.

    2016-08-01

    Barnes Ice Cap is a remnant of the Laurentide Ice Sheet, which covered much of northern North America during the Last Glacial Maximum. Barnes reached a quasi-equilibrium state ~2000 years ago and has remained similar in size since then, with a small increase during the Little Ice Age. In this study, we combine historical observations (1960-1980) with more recent satellite and airborne data (1995-2010) to drive a mass balance model coupled to a transient thermomechanical model with an adaptive mesh geometry. The model is used to characterize the current state of the ice cap and to investigate its stability as a function of climate and its own internal dynamics. On millennial time scales we show that ice flow is influenced by adjustment of an unsteady shape, by gently sloping bedrock, and by contrasting viscosities between the Pleistocene and Holocene ice. On shorter time scales, Barnes is affected by surge activity. Sensitivity tests reveal that Barnes experienced climate conditions which enabled its stability 2000 to 3000 years ago but will disappear under current climate conditions in the next millennium.

  7. Geochronology and paleoclimatic implications of the last deglaciation of the Mauna Kea Ice Cap, Hawaii

    USGS Publications Warehouse

    Anslow, Faron S.; Clark, P.U.; Kurz, M.D.; Hostetler, S.W.

    2010-01-01

    We present new 3He surface exposure ages on moraines and bedrock near the summit of Mauna Kea, Hawaii, which refine the age of the Mauna Kea Ice Cap during the Local Last Glacial Maximum (LLGM) and identify a subsequent fluctuation of the ice margin. The 3He ages, when combined with those reported previously, indicate that the local ice-cap margin began to retreat from its LLGM extent at 20.5??2.5ka, in agreement with the age of deglaciation determined from LLGM moraines elsewhere in the tropics. The ice-cap margin receded to a position at least 3km upslope for ~4.5-5.0kyr before readvancing nearly to its LLGM extent. The timing of this readvance at ~15.4ka corresponds to a large reduction of the Atlantic meridional overturning circulation (AMOC) following Heinrich Event 1. Subsequent ice-margin retreat began at 14.6??1.9ka, corresponding to a rapid resumption of the AMOC and onset of the B??lling warm interval, with the ice cap melting rapidly to complete deglaciation. Additional 3He ages obtained from a flood deposit date the catastrophic outburst of a moraine-dammed lake roughly coeval with the Younger Dryas cold interval, suggesting a more active hydrological cycle on Mauna Kea at this time. A coupled mass balance and ice dynamics model is used to constrain the climate required to generate ice caps of LLGM and readvance sizes. The depression of the LLGM equilibrium line altitude requires atmospheric cooling of 4.5??1??C, whereas the mass balance modeling indicates an accompanying increase in precipitation of as much as three times that of present. We hypothesize (1) that the LLGM temperature depression was associated with global cooling, (2) that the temperature depression that contributed to the readvance occurred in response to an atmospheric teleconnection to the North Atlantic, and (3) that the precipitation enhancement associated with both events occurred in response to a southward shift in the position of the inter-tropical convergence zone (ITCZ). Such a

  8. Crustal movements due to Iceland's shrinking ice caps mimic magma inflow signal at Katla volcano.

    PubMed

    Spaans, Karsten; Hreinsdóttir, Sigrún; Hooper, Andrew; Ófeigsson, Benedikt Gunnar

    2015-01-01

    Many volcanic systems around the world are located beneath, or in close proximity to, ice caps. Mass change of these ice caps causes surface movements, which are typically neglected when interpreting surface deformation measurements around these volcanoes. These movements can however be significant, and may closely resemble movements due to magma accumulation. Here we show such an example, from Katla volcano, Iceland. Horizontal movements observed by GPS on the flank of Katla have led to the inference of significant inflow of magma into a chamber beneath the caldera, starting in 2000, and continuing over several years. We use satellite radar interferometry and GPS data to show that between 2001 and 2010, the horizontal movements seen on the flank can be explained by the response to the long term shrinking of ice caps, and that erratic movements seen at stations within the caldera are also not likely to signify magma inflow. It is important that interpretations of geodetic measurements at volcanoes in glaciated areas consider the effect of ice mass change, and previous studies should be carefully reevaluated.

  9. Crustal movements due to Iceland's shrinking ice caps mimic magma inflow signal at Katla volcano.

    PubMed

    Spaans, Karsten; Hreinsdóttir, Sigrún; Hooper, Andrew; Ófeigsson, Benedikt Gunnar

    2015-01-01

    Many volcanic systems around the world are located beneath, or in close proximity to, ice caps. Mass change of these ice caps causes surface movements, which are typically neglected when interpreting surface deformation measurements around these volcanoes. These movements can however be significant, and may closely resemble movements due to magma accumulation. Here we show such an example, from Katla volcano, Iceland. Horizontal movements observed by GPS on the flank of Katla have led to the inference of significant inflow of magma into a chamber beneath the caldera, starting in 2000, and continuing over several years. We use satellite radar interferometry and GPS data to show that between 2001 and 2010, the horizontal movements seen on the flank can be explained by the response to the long term shrinking of ice caps, and that erratic movements seen at stations within the caldera are also not likely to signify magma inflow. It is important that interpretations of geodetic measurements at volcanoes in glaciated areas consider the effect of ice mass change, and previous studies should be carefully reevaluated. PMID:25992847

  10. Improved parameterization of marine ice dynamics and flow instabilities for simulation of the Austfonna ice cap using a large-scale ice sheet model

    NASA Astrophysics Data System (ADS)

    Dunse, T.; Greve, R.; Schuler, T.; Hagen, J. M.; Navarro, F.; Vasilenko, E.; Reijmer, C.

    2009-12-01

    The Austfonna ice cap covers an area of 8120 km2 and is by far the largest glacier on Svalbard. Almost 30% of the entire area is grounded below sea-level, while the figure is as large as 57% for the known surge-type basins in particular. Marine ice dynamics, as well as flow instabilities presumably control flow regime, form and evolution of Austfonna. These issues are our focus in numerical simulations of the ice cap. We employ the thermodynamic, large-scale ice sheet model SICOPOLIS (http://sicopolis.greveweb.net/) which is based on the shallow-ice approximation. We present improved parameterizations of (a) the marine extent and calving and (b) processes that may initiate flow instabilities such as switches from cold to temperate basal conditions, surface steepening and hence, increases in driving stress, enhanced sliding or deformation of unconsolidated marine sediments and diminishing ice thicknesses towards flotation thickness. Space-borne interferometric snapshots of Austfonna revealed a velocity structure of a slow moving polar ice cap (< 10m/a) interrupted by distinct fast flow units with velocities in excess of 100m/a. However, observations of flow variability are scarce. In spring 2008, we established a series of stakes along the centrelines of two fast-flowing units. Repeated DGPS and continuous GPS measurements of the stake positions give insight in the temporal flow variability of these units and provide constrains to the modeled surface velocity field. Austfonna’s thermal structure is described as polythermal. However, direct measurements of the temperature distribution is available only from one single borehole at the summit area. The vertical temperature profile shows that the bulk of the 567m thick ice column is cold, only underlain by a thin temperate basal layer of approximately 20m. To acquire a spatially extended picture of the thermal structure (and bed topography), we used low-frequency (20 MHz) GPR profiling across the ice cap and the

  11. Organic Remains from the Istorvet Ice Cap, Liverpool Land, East Greenland: A Record of Late Holocene Climate Change

    NASA Astrophysics Data System (ADS)

    Lowell, T. V.; Kelly, M. A.; Hall, B.; Smith, C. A.; Garhart, K.; Travis, S.; Denton, G. H.

    2007-12-01

    Radiocarbon dates of emergent organic remains along the western margin of Istorvet ice cap (70.8°N, 22.2°W) indicate a time when the ice cap was smaller than at present. This ice cap, similar to others in east Greenland, exhibits "historic" moraines ~1-2 km in front of the presently retreating ice margins. At Istorvet, ice margin retreat has exposed a thin (~8 cm) organic horizon and in situ plant remains in bedrock cracks lie less than 10 m away from the present ice margin (453 m asl in 2006). Clusters of multi-species vegetation also were found on two nuntaks (to 719 m asl) located ~3 km from the historic drift limit. All organic remains were located in protected bedrock lees. On the west side of the ice-cap, vegetation is sparse but present at elevations near the ice margin. Both the ice cap geometry and the presence of overrun organic remains indicate past temperatures at least as warm as those at present. At Istorvet plant remains yielded 12 number of radiocarbon dates. These ages, when converted to calendar years, range from A.D. 400 to 1014, with the largest concentration from A.D. 800 to 1014. This work hones the conclusion of Funder (1978) who reported general climate deterioration since 800 BC. Moreover, it indicates warm conditons at this latitude at the time of Norse colonization of Greenland.

  12. 110 years of local glacier and ice cap changes in Central- and North East Greenland

    NASA Astrophysics Data System (ADS)

    Bjork, A. A.; Aagaard, S.; Kjaer, K. H.; Khan, S. A.; Box, J.

    2014-12-01

    The local glaciers and ice caps of Greenland are becoming more apparent players in global sea-level rise, and their contribution to future changes is significant. Very little information on their historical fluctuations exists as much of the focus has been on the Greenland Ice Sheet. Now, we can for the first time present historic data that spans 110 years for more than 200 of the local glaciers and ice caps covering this large and important region of the Arctic. The central- and north eastern part of Greenland is of particular interest as these areas are predicted to exhibit a more active behavior with higher mass loss in the future - simultaneously with an increase in precipitation. Our results show that the glaciers and ice caps in the region are responding very rapidly to changes in temperature and precipitation. The present retreat is the fastest observed within the last eight decades, only surpassed by the rapid post LIA retreat. The 1930s was the golden era for scientific exploration in Central- and North East Greenland as several large expeditions visited the area and photographed from land, sea and air. We use historic recordings from Danish and Norwegian aerial missions and terrestrial recordings from the renowned American Explorer Louise Boyd. These unique pictures from the early 1930s form the backbone of the study and are supplemented the more recent aerial photographs the 1940s and onwards and satellite imagery from the mid-1960s and up until present. From high resolution aerial photographs we are able to map the maximum extent of the glaciers during the LIA (Little Ice Age), from which retreat in this area is estimated to commence in 1900. Using a new SMB (Surface Mass Balance) model and its components covering the entire observational period along with high resolution DEMs and historic sea-ice records we are now able to extract valuable information on the past and present triggers of glacial change.

  13. Mass balance of Icelandic ice caps from CryoSat swath mode altimetry

    NASA Astrophysics Data System (ADS)

    Foresta, L.; Gourmelen, N.; Pálsson, F.; Willis, I. C.; Nienow, P. W.; Shepherd, A.

    2015-12-01

    Satellite altimetry has been traditionally used in the past to infer elevation of land ice, quantify changes in ice topography and infer mass balance over large and remote areas such as the Greenland and Antarctic ice sheets. Radar Altimetry (RA) is particularly well suited to this task due to its all-weather year-round capability for observing the ice surface. However, monitoring of ice caps has proven more challenging. The large footprint of a conventional radar altimeter and relatively coarse ground track coverage are less suited to monitoring comparatively small regions with complex topography, so that mass balance estimates from RA rely on extrapolation methods to regionalize elevation change.Since 2010, the Synthetic Interferometric Radar Altimeter (SIRAL) on board the ESA radar altimetry CryoSat mission has collected ice elevation measurements over ice caps. Ground track interspacing (~4km at 60°) is one order of magnitude smaller than ERS/ENVISAT missions and half of ICESAT's, providing dense spatial coverage. Additionally the Synthetic Aperture Radar Interferometric (SARIn) mode of CryoSat provides a reduced footprint and the ability to locate accurately the position of the surface reflection. Conventional altimetry provides the elevation of the Point Of Closest Approach (POCA) within each waveform, every 250 m along the flight path. Time evolution of POCA elevation is then used to investigate ice elevation change.Here, we present an assessment of the geodetic mass balance of Icelandic ice caps using a novel processing approach, swath altimetry, applied to CryoSat SARIn mode data. In swath mode altimetry, elevation beyond the POCA is extracted from the waveform when coherent echoes are present providing between one and two orders of magnitude more elevations when compared to POCA. We generate maps of ice elevation change that are then used to compute geodetic mass balance for the period 2010 to 2015. We compare our results to estimates generated using

  14. Black carbon aerosols and the third polar ice cap

    NASA Astrophysics Data System (ADS)

    Menon, S.; Koch, D.; Beig, G.; Sahu, S.; Fasullo, J.; Orlikowski, D.

    2009-12-01

    Recent thinning of glaciers over the Himalayas (sometimes referred to as the third polar region) have raised concern on future water supplies since these glaciers supply water to large river systems that support millions of people inhabiting the surrounding areas. Black carbon (BC) aerosols, released from incomplete combustion, have been increasingly implicated as causing large changes in the hydrology and radiative forcing over Asia and its deposition on snow is thought to increase snow melt. In India BC from biofuel combustion is highly prevalent and compared to other regions, BC aerosol amounts are high. Here, we quantify the impact of BC aerosols on snow cover and precipitation from 1990 to 2010 over the Indian subcontinental region using two different BC emission inventories. New estimates indicate that Indian BC from coal and biofuel are large and transport is expected to expand rapidly in coming years. We show that over the Himalayas, from 1990 to 2000, simulated snow/ice cover decreases by ~0.9% due to aerosols. The contribution of the enhanced Indian BC to this decline is ~30%, similar to that simulated for 2000 to 2010. Spatial patterns of modeled changes in snow cover and precipitation are similar to observations (from 1990 to 2000), and are mainly obtained with the newer BC estimates.

  15. Black carbon aerosols and the third polar ice cap

    NASA Astrophysics Data System (ADS)

    Menon, S.; Koch, D.; Beig, G.; Sahu, S.; Fasullo, J.; Orlikowski, D.

    2010-05-01

    Recent thinning of glaciers over the Himalayas (sometimes referred to as the third polar region) have raised concern on future water supplies since these glaciers supply water to large river systems that support millions of people inhabiting the surrounding areas. Black carbon (BC) aerosols, released from incomplete combustion, have been increasingly implicated as causing large changes in the hydrology and radiative forcing over Asia and its deposition on snow is thought to increase snow melt. In India BC emissions from biofuel combustion is highly prevalent and compared to other regions, BC aerosol amounts are high. Here, we quantify the impact of BC aerosols on snow cover and precipitation from 1990 to 2010 over the Indian subcontinental region using two different BC emission inventories. New estimates indicate that Indian BC emissions from coal and biofuel are large and transport is expected to expand rapidly in coming years. We show that over the Himalayas, from 1990 to 2000, simulated snow/ice cover decreases by ~0.9% due to aerosols. The contribution of the enhanced Indian BC to this decline is ~36%, similar to that simulated for 2000 to 2010. Spatial patterns of modeled changes in snow cover and precipitation are similar to observations (from 1990 to 2000), and are mainly obtained with the newer BC estimates.

  16. Black carbon aerosols and the third polar ice cap

    SciTech Connect

    Menon, Surabi; Koch, Dorothy; Beig, Gufran; Sahu, Saroj; Fasullo, John; Orlikowski, Daniel

    2010-04-15

    Recent thinning of glaciers over the Himalayas (sometimes referred to as the third polar region) have raised concern on future water supplies since these glaciers supply water to large river systems that support millions of people inhabiting the surrounding areas. Black carbon (BC) aerosols, released from incomplete combustion, have been increasingly implicated as causing large changes in the hydrology and radiative forcing over Asia and its deposition on snow is thought to increase snow melt. In India BC emissions from biofuel combustion is highly prevalent and compared to other regions, BC aerosol amounts are high. Here, we quantify the impact of BC aerosols on snow cover and precipitation from 1990 to 2010 over the Indian subcontinental region using two different BC emission inventories. New estimates indicate that Indian BC emissions from coal and biofuel are large and transport is expected to expand rapidly in coming years. We show that over the Himalayas, from 1990 to 2000, simulated snow/ice cover decreases by {approx}0.9% due to aerosols. The contribution of the enhanced Indian BC to this decline is {approx}36%, similar to that simulated for 2000 to 2010. Spatial patterns of modeled changes in snow cover and precipitation are similar to observations (from 1990 to 2000), and are mainly obtained with the newer BC estimates.

  17. The Effect of CO2 Ice Cap Sublimation on Mars Atmosphere

    NASA Technical Reports Server (NTRS)

    Batterson, Courtney

    2016-01-01

    Sublimation of the polar CO2 ice caps on Mars is an ongoing phenomenon that may be contributing to secular climate change on Mars. The transfer of CO2 between the surface and atmosphere via sublimation and deposition may alter atmospheric mass such that net atmospheric mass is increasing despite seasonal variations in CO2 transfer. My study builds on previous studies by Kahre and Haberle that analyze and compare data from the Phoenix and Viking Landers 1 and 2 to determine whether secular climate change is happening on Mars. In this project, I use two years worth of temperature, pressure, and elevation data from the MSL Curiosity rover to create a program that allows for successful comparison of Curiosity pressure data to Viking Lander pressure data so a conclusion can be drawn regarding whether CO2 ice cap sublimation is causing a net increase in atmospheric mass and is thus contributing to secular climate change on Mars.

  18. The reconstruction and climatic implication of an independent palaeo ice cap within the Andean rain shadow east of the former Patagonian ice sheet, Santa Cruz Province, Argentina

    NASA Astrophysics Data System (ADS)

    Wolff, Ingo W.; Glasser, Neil F.; Hubbard, Alun

    2013-03-01

    This paper describes the reconstruction of the previously undocumented Meseta Cuadrada palaeo ice cap on south-west Meseta del Lago Buenos Aires, Santa Cruz Province, Patagonia. Based on theoretical surface profiles the reconstruction of the Meseta Cuadrada Palaeo Ice Cap indicates an ice mass covering at least 78 km2 with a total ice volume around 9.2 km3. The inferred equilibrium line altitude (ELA) of the palaeo ice cap (2031 m asl) represents a drop of 286 m compared to the ELA of the current Meseta Cuadrada glacier (~ 2317 m asl). We explain this small change in ELA with reference to the flat hypsometry of the palaeo ice cap and an enhanced aridity to the west of the Patagonian Andes caused by the existence of the Last Glacial Maximum (LGM) Patagonian ice sheet. Calculated annual accumulation values of ca. 402 to 957 mm/a at the ELA of the Meseta Cuadrada palaeo ice cap derived by a degree day model (DDM) during the last local glacial maximum extent are low compared with estimations of the current accumulation at the ELA of the remaining glacierized area of around 3789 mm/a. This strongly supports the existence of increased aridity and seasonality east of the Patagonian Andes during the Last Glacial Maximum, provided both maximum extents were synchronous.

  19. Tropical Glaciers in the Common Era: Papua, Indonesia, Quelccaya Ice Cap, Peru and Kilimanjaro, Tanzania

    NASA Astrophysics Data System (ADS)

    Thompson, L. G.; Mosley-Thompson, E. S.; Davis, M. E.

    2011-12-01

    High-resolution ice core stratigraphic records of δ18O (temperature proxy) demonstrate that the current warming at high elevations in mid- to lower latitudes is unprecedented for at least the last two millennia, although at many sites the Early Holocene was much warmer than at present. Here we discuss the interaction of El Niño-Southern Oscillation (ENSO) variability and warming trends as recorded in ice core records from high-altitude tropical glaciers and the implications of the warming trends for the future of these glaciers. ENSO has strong impacts on meteorological phenomena that either directly or indirectly affect most regions on the planet and their populations, particularly throughout the Tropics. Here we examine similarities and differences among ice core records from Papua (Indonesia), Quelccaya Ice Cap (Peru) and Kilimanjaro (Tanzania). Quelccaya, Earth's largest tropical ice cap, has provided continuous, annually-resolved proxy records of climatic and environmental variability preserved in many measurable parameters, especially oxygen and hydrogen isotopic ratios (δ18O, δD) and the net mass balance (accumulation) spanning the last 1800 years. The remarkable similarity between changes in the highland and coastal cultures of Peru and climate variability in the Andes, especially with regard to precipitation, implies a strong connection between prehistoric human activities and climate in this region. The well-documented ice loss on Quelccaya, Kilimanjaro in eastern Africa and the ice fields near Puncak Jaya in Papua, Indonesia presents a possible analog for glacier response in the tropics during the Holocene. The ongoing melting of these ice fields is consistent with model predictions of a vertical amplification of temperature in the Tropics. A sequence of over 50 recently exposed, rooted, soft-bodied plant deposits collected between 2002 and 2011 from the retreating margins of the Quelccaya ice cap provide a longer term perspective for the recent

  20. CGPS as a Tool to Measure Short-Term Mass Balance Variations of Icelandic Ice Caps

    NASA Astrophysics Data System (ADS)

    Compton, K. C.; Bennett, R. A.; Hreinsdottir, S.; van Dam, T. M.; Spada, G.

    2015-12-01

    As the global climate changes, understanding the variations in water storage is increasingly important. In Iceland, glaciers cover approximately 11% of the land surface and comprise the country's largest reservoir of freshwater. Seasonal variations in winter snowfall and summer melting can impact river discharge and water availability for utilities such as hydropower. A dense network of continuously operating GPS sites record rapid crustal uplift exceeding 30 mm/year and accelerations up to 1-2 mm/yr2 reflecting the recent accelerating ice mass loss from the major Icelandic ice caps. Additionally, CGPS records seasonal motion: the elastic response to annual snow and melt seasons. Amplitudes of vertical seasonal motion approach 10 mm for those sites in the Central Highlands region in close proximity to the Vatnajökull ice cap. We demonstrate the utility of CGPS-measured displacements for estimating seasonal ice mass changes using a simple least squares inversion. We utilize all 3 components of motion, taking advantage of the seasonal motion recorded in the horizontal. We remove secular velocities and accelerations as well as seasonal motions due to atmospheric, hydrologic, and non-tidal ocean loading. We model GPS noise as a flicker process and set the standard deviation for that noise to be 1 mm for the horizontal components and 3 mm for the vertical. We calculate unit responses to each of the 5 largest ice caps in central Iceland at each of the 62 CGPS locations using both the RELAX and REAR codes and investigate the impact that Earth's structure has on our modeling results, noting here that the standard PREM Earth model results in calculated displacements smaller than the observations by a factor of two. Our preliminary inversion results match available summer and winter mass balance measurements well. We are often able to reproduce the year-to-year variations in loading and melting within our calculated 95% confidence bounds.

  1. Mars Water Ice and Carbon Dioxide Seasonal Polar Caps: GCM Modeling and Comparison with Mars Express Omega Observations

    NASA Technical Reports Server (NTRS)

    Forget, F.; Levrard, B.; Montmessin, F.; Schmitt, B.; Doute, S.; Langevin, Y.; Bibring, J. P.

    2005-01-01

    To better understand the behavior of the Mars CO2 ice seasonal polar caps, and in particular interpret the the Mars Express Omega observations of the recession of the northern seasonal cap, we present some simulations of the Martian Climate/CO2 cycle/ water cycle as modeled by the Laboratoire de Meteorologie Dynamique (LMD) global climate model.

  2. 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. .

  3. 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.

  4. Ice core from Akademii Nauk ice cap, Severnaya Zemlya (Russian Arctic), dated with a Nye model modified for a growing glacier

    NASA Astrophysics Data System (ADS)

    Fritzsche, Diedrich; Opel, Thomas; Meyer, Hanno

    2010-05-01

    From 1999 to 2001 a 724 m deep ice core has been drilled from surface to bedrock close to summit of the Akademii Nauk ice cap, Severnaya Zemlya (Russian Arctic), within a joint German-Russian project. The analysis of stable water isotopes and major ion concentration in high resolution were used for reconstruction of past climate and environmental changes. The upper 304 m of the core were dated by counting annual stable isotope cycles considering radioactive (1986, 1963) and volcanic events (1956, 1912, 1783, 1259) as reference horizons. The resulting depth-age relationship and the corresponding annual-layer thickness imply that the ice cap was not in dynamic steady state but had been growing until recent times. That does not comply with requirements of a standard Nye or Dansgaard-Johnson flow model approach. To take into account the peculiarities of Akademii Nauk ice cap a Nye model was modified by adding a growing term according to the found relationship between annual layer thickness and depth. Using the volcanoes identified an average increase of altitude of about 0.08 m w.e. per year was calculated since AD 1259. The model enables us to reconstruct the altitude changes of the ice cap with time and to consider an altitude effect to correct the stable isotope values and to explain decreasing sea-salt ion data. Using the suggested model annual layer thickness can be decompressed to accumulation rates at the altitude where the precipitation was originally deposited. The model can also be used for dating deeper parts of ice core where volcanoes are not identified up to now. Applying this model, the ice core has an age of about 2 500 years, much less than claimed for an older core from Akademii Nauk ice cap. Consequently, the ice cap is much younger and only of Late Holocene age, as also assumed for most Arctic ice caps and glaciers outside Greenland. However, the lowest part of Akademii Nauk ice cap is probably a remnant of an older ice cap stage.

  5. Contribution of Icelandic ice caps to sea level rise: Trends and variability since the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Björnsson, Helgi; Pálsson, Finnur; Gudmundsson, Sverrir; Magnússon, Eyjólfur; Adalgeirsdóttir, Gudfinna; Jóhannesson, Tómas; Berthier, Etienne; Sigurdsson, Oddur; Thorsteinsson, Thorsteinn

    2013-04-01

    In total, Icelandic ice caps contain ˜3600 km3 of ice, which if melted would raise sea level by ˜1 cm. Here, we present an overview of mass changes of Icelandic ice masses since the end of the 19th century. They have both gained and lost mass during this period. Changes in ice volume have been estimated both through surface mass balance measurements (performed annually since ˜1990) and differencing of digital elevation models derived from various satellite and airborne observations. While the glaciers showed little mass loss as the 20th century began, losses increased rapidly after 1925, peaked in the 1930s and 1940s, and remained significant until the 1960s. After being near-zero or even positive during the 1980s and early 1990s, glacier mass budgets declined considerably, and have since the mid-1990s shown an average annual loss of 9.5±1.5 Gt a-1, contributing ˜0.03 mm a-1 to sea level rise. Since 1995 interannual variability in mass loss is high, ranging from 2.7 to 25.3±1.5 Gt a-1, corresponding to surface mass balances of -0.2 to -2.2 ± 0.15 m we a-1. This variability is driven by climate fluctuations and also by transient reduction of albedo due to volcanic eruptions.

  6. Ice-Ripples on Martian Polar Caps: Exploration of Their Size and Dynamics by a Linear Instability Analysis

    NASA Astrophysics Data System (ADS)

    Carpy, S.; Bordiec, M.; Blanchard, C.; Perret, L.; Herny, C.; Massé, M.; Bourgeois, O.; Mathis, H.

    2016-09-01

    We have conducted a linear stability analysis of a coupled ice-airflow interface under turbulent boundary layer in order to evaluate whether ice-ripples similar to those observed in Antarctica can develop at the surface of the martian polar caps.

  7. Variability of Mars' North Polar Water Ice Cap: I. Analysis of Mariner 9 and Viking Orbiter Imaging Data

    USGS Publications Warehouse

    Bass, D.S.; Herkenhoff, K. E.; Paige, D.A.

    2000-01-01

    Previous studies interpreted differences in ice coverage between Mariner 9 and Viking Orbiter observations of Mars' north residual polar cap as evidence of interannual variability of ice deposition on the cap. However, these investigators did not consider the possibility that there could be significant changes in the ice coverage within the northern residual cap over the course of the summer season. Our more comprehensive analysis of Mariner 9 and Viking Orbiter imaging data shows that the appearance of the residual cap does not show large-scale variance on an interannual basis. Rather we find evidence that regions that were dark at the beginning of summer look bright by the end of summer and that this seasonal variation of the cap repeats from year to year. Our results suggest that this brightening was due to the deposition of newly formed water ice on the surface. We find that newly formed ice deposits in the summer season have the same red-to-violet band image ratios as permanently bright deposits within the residual cap. We believe the newly formed ice accumulates in a continuous layer. To constrain the minimum amount of deposited ice, we used observed albedo data in conjunction with calculations using Mie theory for single scattering and a delta-Eddington approximation of radiative transfer for multiple scattering. The brightening could have been produced by a minimum of (1) a ???35-??m-thick layer of 50-??m-sized ice particles with 10% dust or (2) a ???14-??m-thick layer of 10-??m-sized ice particles with 50% dust. ?? 2000 Academic Press.

  8. Analysis of Daily, Seasonal, and Interannual Changes in Hofsjokull Ice Cap, Iceland, using Satellite Data

    NASA Technical Reports Server (NTRS)

    Hall, D. K.; Garvin, J. B.; Williams, R. S., Jr.; Barton, J. S.; Sigurosson, O.; Smith, L. C.

    1998-01-01

    Analysis of a time series of European Remote Sensing Satellite (ERS)-1 and -2, RADARSAT ScanSAR synthetic aperture radar (SAR) and Landsat images from 1973 to 1998, shows daily to interannual changes in Hofsjokull, a 923 sq km ice cap in central Iceland. A digital elevation model of Hofsjokull was constructed using interferometry, and then SAR backscatter coefficient (d) was plotted with elevation, and air temperature along a transect across the ice cap. Most of the a' changes measured along the transect are caused by a change in the state (frozen or thawed) of the surficial snow or ice when air temperature rises above or below about -5 to O C. Seasonal (sigma)deg patterns are identified in a 4-year time series of 57 ERS-1 and -2 images. In addition, June 1997 ScanSAR images display rapid changes in brightness that are tied closely to daily meteorological events. SAR and Landsat data were also used to measure changes in the areal extent of Hofsjokull, from 1973 to 1997, and to locate (sigma)deg and reflectance boundaries that relate to the glacier facies. Late-summer 1997 (sigma)deg and reflectance boundaries agree and are coincident with the approximate location of the fim line, and the January 1998 position of the equilibrium line as determined from ERS-2 data.

  9. Holocene fluctuations of Quelccaya Ice Cap, Peru based on lacustrine and surficial geologic archives

    NASA Astrophysics Data System (ADS)

    Stroup, J. S.; Kelly, M. A.; Lowell, T. V.; Beal, S. A.; Smith, C. A.

    2013-12-01

    Peru's Quelccaya Ice Cap (QIC; 13.9°S, 70.8°W, ~5200-5670 m asl) is an important site for understanding tropical paleoclimate, mainly because of annually layered ice cores that provide an ~1800 year long record of tropical paleoclimatic conditions (e.g., Thompson et al., 2013). Here, we present a detailed record of QIC fluctuations using surficial deposits and lake sediments that extend back to late glacial time. We compare the late Holocene records of QIC 10Be-dated moraines and ice core data with lake sediments from a nearby glacially fed lake to establish the framework we use to interpret a Holocene long sediment record from a glacially fed lake. We also examine sediments from a nearby non-glacial lake to constrain non-glacial clastic input. We collected two ~5 m-long sediment cores, one from Laguna Challpacocha, which is currently fed by QIC meltwater, and one from the Laguna Yanacocha, which has not received QIC meltwater since ~12.3 ka. Changes in magnetic susceptibility, loss on ignition, bulk density and X-ray fluorescence chemistry combined with 14C and 210Pb chronologies provide information about sediment transported to the lakes. Retreat from the late Holocene extent defined by the 10Be-dated moraine record (~0.52 ka) is contemporaneous with a sharp transition from organic to clastic sedimentation in the Challpacocha core at ~ 0.52 ka. This implies that glacially-sourced clastic sedimentation, as tracked by loss on ignition, Ti counts and bulk density, increased during ice cap recession. Based on these same proxy data, we suggest the following Holocene history of QIC: QIC receded from the Challpacocha basin by ~10.6 ka. Increased clastic sedimentation at 8.2 - 4.1, 3.6 - 2.7 ka and from 0.55 ka - present are interpreted as times of ice cap recession. The increased clastic sedimentation at ~8.2 - 4.1 ka is consistent with surficial deposits near the present-day ice margin that indicate that at ~7.0 - 4.6 ka QIC was smaller than at present (Buffen et al

  10. Destabilisation of an Arctic ice cap triggered by a hydro-thermodynamic feedback to summer-melt

    NASA Astrophysics Data System (ADS)

    Dunse, T.; Schellenberger, T.; Kääb, A.; Hagen, J. O.; Schuler, T. V.; Reijmer, C. H.

    2014-05-01

    Mass loss from glaciers and ice sheets currently accounts for two-thirds of the observed global sea-level rise and has accelerated since the 1990s, coincident with strong atmospheric warming in the Polar Regions. Here we present continuous GPS measurements and satellite synthetic aperture radar based velocity maps from the Austfonna ice cap, Svalbard, that demonstrate strong links between surface-melt and multiannual ice-flow acceleration. We identify a hydro-thermodynamic feedback that successively mobilizes stagnant ice regions, initially frozen to their bed, thereby facilitating fast basal motion over an expanding area. By autumn 2012, successive destabilization of the marine terminus escalated in a surge of the ice cap's largest drainage basin, Basin-3. The resulting iceberg discharge of 4.2 ± 1.6 Gt a-1 over the period April 2012 to May 2013 triples the calving loss from the entire ice cap. After accounting for the terminus advance, the related sea-level rise contribution of 7.2 ± 2.6 Gt a-1 matches the recent annual ice-mass loss from the entire Svalbard archipelago. Our study highlights the importance of dynamic glacier wastage and illuminates mechanisms that may trigger a sustained increase in dynamic glacier wastage or the disintegration of ice-sheets in response to climate warming, which is acknowledged but not quantified in global projections of sea-level rise.

  11. Energy balance in ice layers - the solid-state greenhouse effect at the Mars polar caps

    NASA Astrophysics Data System (ADS)

    Kaufmann, E.; Kömle, N. I.; Kargl, G.

    Icy surfaces like the polar caps of Mars or the surfaces of the outer Galilean satellites behave different than rock and soil surfaces when they are irradiated by solar light The latter ones absorb and reflect incoming solar radiation immediately at the surface In contrast ices are partially transparent in the visible spectral range and opaque in the infrared Due to this property it is possible for the solar radiation to reach a certain depth and raise the temperature of the ice layer below the surface This internal temperature rise is called solid-state greenhouse effect It may play an important role in the energy balance of icy surfaces in the solar system as already suggested in previous theoretical investigations One possible consequence of the solid-state greenhouse effect are the Martian spiders observed at the cryptic region on Mars by Mars Global Surveyor In the frame of a project performed at the Space Research Institute in Graz the solid-state greenhouse effect was investigated experimentally and theoretically A couple of experiments were performed including diverse samples with the main focus on layered samples with a covering coat consisting of pure H 2 O-ice Different samples were irradiated under cryo-vacuum conditions by a solar simulator The temperature distributions inside the samples were measured and compared with the results of theoretical modelling In addition models describing the influence of the solid-state greenhouse effect on Mars where the surface is partially covered by CO 2 -ice were developed

  12. Numerical modeling of Drangajökull Ice Cap, NW Iceland

    NASA Astrophysics Data System (ADS)

    Anderson, Leif S.; Jarosch, Alexander H.; Flowers, Gwenn E.; Aðalgeirsdóttir, Guðfinna; Magnússon, Eyjólfur; Pálsson, Finnur; Muñoz-Cobo Belart, Joaquín; Þorsteinsson, Þorsteinn; Jóhannesson, Tómas; Sigurðsson, Oddur; Harning, David; Miller, Gifford H.; Geirsdóttir, Áslaug

    2016-04-01

    Over the past century the Arctic has warmed twice as fast as the global average. This discrepancy is likely due to feedbacks inherent to the Arctic climate system. These Arctic climate feedbacks are currently poorly quantified, but are essential to future climate predictions based on global circulation modeling. Constraining the magnitude and timing of past Arctic climate changes allows us to test climate feedback parameterizations at different times with different boundary conditions. Because Holocene Arctic summer temperature changes have been largest in the North Atlantic (Kaufman et al., 2004) we focus on constraining the paleoclimate of Iceland. Glaciers are highly sensitive to changes in temperature and precipitation amount. This sensitivity allows for the estimation of paleoclimate using glacier models, modern glacier mass balance data, and past glacier extents. We apply our model to the Drangajökull ice cap (~150 sq. km) in NW Iceland. Our numerical model is resolved in two-dimensions, conserves mass, and applies the shallow-ice-approximation. The bed DEM used in the model runs was constructed from radio echo data surveyed in spring 2014. We constrain the modern surface mass balance of Drangajökull using: 1) ablation and accumulation stakes; 2) ice surface digital elevation models (DEMs) from satellite, airborne LiDAR, and aerial photographs; and 3) full-stokes model-derived vertical ice velocities. The modeled vertical ice velocities and ice surface DEMs are combined to estimate past surface mass balance. We constrain Holocene glacier geometries using moraines and trimlines (e.g., Brynjolfsson, etal, 2014), proglacial-lake cores, and radiocarbon-dated dead vegetation emerging from under the modern glacier. We present a sensitivity analysis of the model to changes in parameters and show the effect of step changes of temperature and precipitation on glacier extent. Our results are placed in context with local lacustrine and marine climate proxies as well

  13. Evidence for smaller extents of the northwestern Greenland Ice Sheet and North Ice Cap during the Holocene

    NASA Astrophysics Data System (ADS)

    Kelly, M. A.; Osterberg, E. C.; Axford, Y.; Bigl, M.; Birkel, S. D.; Corbett, L. B.; Roy, E. P.; Thompson, J. T.; Whitecloud, S.

    2013-12-01

    The Greenland Ice Sheet (GrIS) and local glaciers on Greenland are responding dynamically to warming temperatures with widespread retreat. GRACE satellite data (e.g., Kahn et al., 2010) and the Petermann Glacier calving events document the recent expansion of ice loss into northwestern Greenland. To improve the ability to estimate future ice loss in a warming climate, we are developing records of the response of the northwestern Greenlandic cryosphere to Holocene climatic conditions, with a focus on past warm periods. Our ongoing research includes analyses of glacial geology, sub-fossil vegetation, lake sediment cores, chironomid assemblages and ice cores combined with glaciological modeling. To constrain past ice extents that were as small as, or smaller than, at present, we recovered sub-fossil vegetation exposed at the receding margins of the GrIS and North Ice Cap (NIC) in the Nunatarssuaq region (~76.7°N, 67.4°W) and of the GrIS near Thule (~76.5°N, 68.7°W). We present vegetation types and radiocarbon ages of 30 plant samples collected in August 2012. In the Nunatarssuaq region, five ages of in situ (rooted) vegetation including Polytrichum moss, Saxifraga nathorstii and grasses located <5 m outboard of the GrIS margin are ~120-200 cal yr BP (range of medians of the 2-sigma calibrated age ranges). Nine ages of in situ Polytrichum, Saxifraga oppositafolia and grasses from ~1-5 m inboard of the NIC margin (excavated from beneath ice) range from ~50 to 310 cal yr BP. The growth of these plants occurred when the GrIS and NIC were at least as small as at present and their ages suggest that ice advances occurred in the last 50-120 yrs. In addition to the in situ samples, we collected plants from well-preserved ground material exposed along shear planes in the GrIS margins. In Nunatarssuaq, two Polytrichum mosses rooted in ground material and exposed along a shear plane in the GrIS margin date to 4680 and 4730 cal yr BP. Near Thule, three ages of Salix arctica

  14. Rapid onset of Little Ice Age summer cold in the northern North Atlantic derived from precisely dated ice cap records (Invited)

    NASA Astrophysics Data System (ADS)

    Miller, G. H.; Larsen, D.; Geirsdottir, A.; Refsnider, K. A.; Anderson, C.

    2009-12-01

    Precise radiocarbon dates on dead vegetation emerging beneath retreating non-erosive ice caps in NE Arctic Canada define the onset of ice cap growth, and provide a Holocene context for 20th Century warming. Although most plateau ice caps melted during the Medieval Warm Period, a few that are now disappearing remained intact since at least 350 AD. Little Ice Age ice cap inception occurred in two pulses, centered on 1250-1300 AD and around 1450 AD, with ice caps remaining in an expanded state until the warming of the past few decades. Ice cap inception occurred simultaneously (±10 years) over a 200 m elevational range, suggesting an abrupt onset of Little Ice Age cold, rather than a slow cooling over many decades. Similarly, a 3000 year annually resolved lacustrine record of glacier power and a complementary independent proxy for landscape instability in the highlands of central Iceland show an initial jump in both glacier power and landscape instability between 1250 and 1300 AD, with a second step-increase around 1450 AD, and dramatic increases in both proxies around 1800 AD, retracting in the 20th Century. A sub-decadal record of hillslope stability and within-lake primary productivity in sediments from a low-elevation lake in northern Iceland shows parallel changes at similar times. Sea ice proxies and historical records document the first appearance of sea ice around Iceland following Medieval time about 1250 AD. The similarity in the onset and intensification of Little Ice Age cold-weather proxies across a wide region of the northern North Atlantic suggests at least a regional driver of abrupt climate change. The time intervals for which these abrupt changes occur coincide with the three most intense episodes of multiple explosive volcanic eruptions that introduced large volumes of sulfate aerosols into the stratosphere during the past millennium. Although the direct impacts of volcanic aerosols have a duration of only a few years, the memory stored by the

  15. Validating Cryosat-2 elevation estimates with airborne laser scanner data for the Greenland ice sheet, Austfonna and Devon ice caps

    NASA Astrophysics Data System (ADS)

    Simonsen, Sebastian B.; Sandberg Sørensen, Louise; Nilsson, Johan; Helm, Veit; Langley, Kirsty A.; Forsberg, Rene; Hvidegaard, Sine M.; Skourup, Henriette

    2015-04-01

    The ESA CryoSat-2 satellite, launched in late 2010, carries a new type of radar altimeter especially designed for monitoring changes of sea and land ice. The radar signal might penetrate into the snow pack and the depth of the radar reflecting surface depends on the ratio between the surface and the volume backscatter, which is a function of several different properties such as snow density, crystal structure and surface roughness. In case of large volume scatter, the radar waveforms become broad and the determination of the range (surface elevation) becomes more difficult. Different algorithms (retrackers) are used for the range determination, and estimated surface penetration is highly dependent on the applied retracker. As part of the ESA-CryoVEx/CryoVal-Land Ice projects, DTU Space has gathered accurate airborne laser scanner elevation measurements. Sites on the Greenland ice sheet, Austfonna and Devon ice caps, has been surveyed repeatedly, aligned with Cryosat-2 ground tracks and surface experiments. Here, we utilize elevation estimates from available Cryosat-2 retrackers (ESA level-2 retracker, DTU retracker, etc.) and validate the elevation measurements against ESA-CryoVEx campaigns. A difference between laser and radar elevations is expected due to radar penetration issues, however an inter-comparison between retrackers will shed light on individual performances and biases. Additionally, the geo-location of the radar return will also be a determining factor for the precision. Ultimately, the use of multiple retrackers can provide information about subsurface conditions and utilize more of the waveform information than presently used in radar altimetry.

  16. No signature of clear CO2 ice from the 'cryptic' regions in Mars' south seasonal polar cap.

    PubMed

    Langevin, Yves; Douté, Sylvain; Vincendon, Mathieu; Poulet, François; Bibring, Jean-Pierre; Gondet, Brigitte; Schmitt, Bernard; Forget, F

    2006-08-17

    The seasonal polar ice caps of Mars are composed mainly of CO2 ice. A region of low (< 30%) albedo has been observed within the south seasonal cap during early to mid-spring. The low temperature of this 'cryptic region' has been attributed to a clear slab of nearly pure CO2 ice, with the low albedo resulting from absorption by the underlying surface. Here we report near-infrared imaging spectroscopy of the south seasonal cap. The deep and broad CO2 absorption bands that are expected in the near-infrared with a thick transparent slab of CO2 ice are not observed. Models of the observed spectra indicate that the low albedo results from extensive dust contamination close to the surface of a CO2 ice layer, which could be linked to atmospheric circulation patterns. The strength of the CO2 absorption increases after mid-spring, so part of the dust is either carried away or buried more deeply in the ice layer during the CO2 ice sublimation process.

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

    PubMed

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

    2012-02-08

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

  18. Mass Loss of Glaciers and Ice Caps From GRACE During 2002-2015

    NASA Astrophysics Data System (ADS)

    Ciraci, E.; Velicogna, I.; Wahr, J. M.; Swenson, S. C.

    2015-12-01

    We use time series of time-variable gravity from the NASA/DLR GRACE mission using a mascon approach to estimate the ice mass balance of the Earth's Mountain Glaciers and Ice Caps (GICs), excluding the Antarctic and the Greenland peripheral glaciers, between January 2003 and October 2014. We estimate a total ice mass loss equal to -217 ± 33 Gt/yr, equivalent to a sea level rise of 0.6±0.09 mm/yr. The global signal is driven by a few regions, contributing to almost of 75% of the total ice mass loss. Among these areas, the main contributor is the Canadian Arctic Archipelago with a total mass loss of -75 ± 9 Gt/yr, followed by Alaska (-51 ± 10 Gt/yr), Patagonia (-26 ± 10 Gt/yr) and the High Mountains of Asia (-25 ± 13 Gt/yr). The mass loss for most of the arctic regions is not constant, but accelerates with time. The Canadian Archipelago, in particular, undergoes a strong acceleration in mass waste (-7±1 Gt/yr2). The signal acceleration is mainly driven by the northern located Queen Elisabeth Islands (-4.5 ± 0.6 Gt/yr2). A similar behavior is observed for Svalbard and the Russian Arctic. In this second case, however, we observe an enhanced mass loss starting from the second decade of the 21st century after a period of nearly stable mass balance. The observed acceleration helps reconcile regional ice mass estimates obtained for different time periods.

  19. Stratigraphic features of firn as proxy climate signals at the summit ice cap of Ushkovsky volcano, Kamchatka, Russia

    SciTech Connect

    Shiraiwa, Takayuki; Yamaguchi, Satoru; Muravyev, Y.D.

    1997-11-01

    Field observations were conducted at the summit ice cap of the Ushkovsky volcano, central Kamchatka, in the summer of 1996, in order to evaluate the potential of the ice cap for reconstruction of the past climate over Kamchatka. A 27-m-long firn-core contains an approximate 27-yr record of net balance with an average accumulation rate of 0.57 m a{sup -1} water equivalent. The temperature of the firn is -16.5{degrees}C at 10-m depth. Average annual accumulation rates are calculated by reference to dated ash layers and amount to between 0.38 and 0.88 m a{sup -1} during six fixed periods. Depth and age of pore close-off are calculated as 58 m and 66 yr at this site by empirical formulas. Comparisons of the accumulation rates with winter precipitation at lowland stations indicate that there is a positive relationship with winter precipitation on the eastern and western coasts of the peninsula. We cannot find a clear relation between the rates and annual average sea-ice extent in the Sea of Okhotsk, which implies the vapor source to the ice cap could have been the North Pacific. Melt feature percentage in the firn core displays a clear positive relationship with summer air temperature at 700 hPa over Kamchatka. The result obtained suggests that the ice cap has potential for the reconstruction of paleoclimate over the Kamchatka Peninsula. 15 refs., 9 figs.

  20. Recent changes at the northwest margin of the Barnes Ice Cap, Baffin Island, N. W. T. , Canada

    SciTech Connect

    Jacobs, J.D. ); Heron, R. ); Luther, J.E. )

    1993-11-01

    A climate change monitoring site has been established at the northwest margin of the Barnes Ice Cap, in the vicinity of the Lewis Glacier. Three years of climatic data (1989 to 1992) and field observations, supplemented by satellite imagery, provide the basis for updating previous studies of local change at the ice cap margin, including climatology and substrate colonization by lichens. Climatic data from the ice cap summit permit extrapolation of seasonal temperatures from the ice marginal station as a basis for equilibrium line altitude estimates. Results are discussed against the background of studies from the 1960s. Retreat of the Lewis Glacier continues at about 25 m yr[sup [minus]1], whereas other areas of the northwest margin are retreating by 10 to 30 m yr[sup [minus]1]. Lower regional summer temperatures over the past three decades have not significantly slowed the recession that has been underway in this sector of the ice cap for the past three centuries. 41 refs., 7 figs., 2 tabs.

  1. The glaciation of Dartmoor: the southernmost independent Pleistocene ice cap in the British Isles

    NASA Astrophysics Data System (ADS)

    Evans, David J. A.; Harrison, Stephan; Vieli, Andreas; Anderson, Ed

    2012-06-01

    The granite uplands of Dartmoor have traditionally been considered to be relict permafrost and periglacial landscapes that lay beyond the limits of Quaternary glaciations but a variety of landform evidence indicates that a plateau icefield existed on the northern part of the moor, constituting the southernmost independent ice cap in the British Isles. Overdeepened or weakly U-shaped valley segments fringing north Dartmoor document an early, extensive phase of glaciation but the most convincing landform evidence relates to more recent, valley-based glacier occupancy. A moraine ridge on the Slipper Stones represents the most unequivocal palaeo-glacier on north Dartmoor with a palaeo-ELA of c.460 m above sea level (asl), although this relates to the youngest and most restricted phase of glaciation. A longer term ELA is likely to be represented by the Corn Ridge proto-cirque at 370-410 m asl. More extensive valley glaciers are recorded in each of the major drainage basins of north Dartmoor by arcuate and linear bouldery ridges and hummocky valley floor drift, which are interpreted as latero-frontal moraines deposited by outlet lobes of a plateau icefield. Recession of these lobes is marked by inset sequences of such ridges and occasional meltwater channels. Plateau ice was predominantly thin and protective, and snowblow and preferential accumulation in valley heads facilitated the modest glacial erosion and debris transport recorded in the landforms and sediments. It is proposed that the highest plateaux have been occupied by ice for the longest cumulative period of time throughout the Quaternary ("average glacial conditions"), explaining the distribution of different tor types on northern Dartmoor. This also explains the lack of tors on the most expansive of the highest plateau terrain (ice dispersal centres) as the product of: a) average glacial conditions preferentially removing tors or dampening their production rates; b) the survival of high relief (Type 1) tors

  2. Coeval fluctuations of the Greenland Ice Sheet and a local ice cap during the Younger Dryas: implications for late-glacial climate

    NASA Astrophysics Data System (ADS)

    Levy, Laura; Kelly, Meredith; Lowell, Tom; Hall, Brenda; Howley, Jennifer; Smith, Colby

    2016-04-01

    Although the Younger Dryas (YD) has been recorded in ice cores atop the Greenland Ice Sheet, past glacier extents on Greenland dating to the YD are rare. In part, this is due to much of the Greenland Ice Sheet being located offshore until early Holocene time. The Scoresby Sund region (~71°N, 26°W) of central East Greenland, however, is one of only a few locations where the margins of the Greenland Ice Sheet and glaciers independent of the ice sheet were located at least partially on land by late-glacial time. In this region, two distinct sets of moraines, known as the inner and outer Milne Land Stade moraines, have been defined and mark a significant readvance or stillstand during deglaciation from the last glacial maximum. Previous work has dated these moraines to late-glacial and early Holocene time. We present a new 10Be chronology on fluctuations of both the Greenland Ice Sheet and the adjacent Milne Land ice cap from the type locality of the Milne Land Stade moraines in Milne Land. 10Be ages of boulders on bedrock distal to the inner Milne Land Stade moraines range from 12.3 to 11.5 ka and indicate that both ice masses retreated during the YD, likely in response to rising summer temperatures. Since Greenland ice-cores register cold mean annual temperatures throughout the YD, these ice-marginal data support climate conditions characterized by strong seasonality. The mean ages (± 1σ uncertainty) of the inner Milne Land Stade moraines date to 11.4 ± 0.8 ka (Greenland Ice Sheet) and 11.4 ± 0.6 ka (ice cap) indicating that they were formed during Preboreal time or at the end of the YD. Based on these coeval moraine ages, we suggest that both ice masses responded to climate conditions acting on the ice margins, specifically ablation. Moreover, our data show that the ice sheet responded sensitively (i.e., on the same time scale as a small ice cap) to late-glacial and early Holocene climate conditions.

  3. Mass loss of Greenland's glaciers and ice caps 2003-2008 from ICESat data

    NASA Astrophysics Data System (ADS)

    Bolch, Tobias; Sandberg Sørensen, Louise; Simonsen, Sebastian B.; Mölg, Nico; Machguth, Horst; Rastner, Philipp; Paul, Frank

    2013-04-01

    The melt water of the glaciers and ice caps (GIC) on Greenland could make a substantial contribution to global sea-level rise during this century. The recently finalized Greenland glacier inventory classified all GIC according to its connectivity to the ice sheet (CL0: no connection, CL1: weak connection, CL2: strong connection). This dataset allowed us for the first time to determine their mass changes separately from the ice sheet using space-borne laser altimetry data from the ICESat GLAS sensor. The accuracy of the altimetry measurements of about ±0.5 m even over rough surfaces along with their small footprint (about 70 m) is making them very suitable to assess elevation changes over GIC. A major challenge with ICESat data is the sparse density of the tracks (horizontal separation is about 30 km in southern and ~10 km in northern Greenland), and the fact that the repeat tracks can be several hundred metres apart. A further challenge is the volume to mass conversion. We extrapolated the elevation changes based on the glacier hypsometry and applied corrections for firn compaction and ice density based on climatic conditions. The Greenland GIC which are clearly separable from the ice-sheet (CL0, CL1) lost 30.1 ± 9.4 Gt a-1 or 0.08 ± 0.026 mm a-1 sea-level equivalent (SLE) between 2003 and 2008. When considering all hydrologically separable GIC (CL0-2, including the Geikie Plateau) the loss is 46.8 ± 13.4 Gt a-1 (0.12 ± 0.038 mm a-1 SLE). This is a significant fraction (about 20%) of the reported overall mass loss of Greenland (including the ice sheet) and up to 10% of the estimated contribution from the world's GIC to global sea-level rise. The mass loss of the GIC is per unit area about 2.5 times higher than for the ice sheet, and marine-terminating glaciers account for about half of the mass loss. The loss was highest in the south-eastern sector and lowest in the northern sector of Greenland.

  4. Rapid thinning of the Welsh Ice Cap at 20-19 ka based on 10Be ages

    NASA Astrophysics Data System (ADS)

    Hughes, Philip D.; Glasser, Neil F.; Fink, David

    2016-01-01

    New 10Be ages from the summits of three mountain areas of North Wales reveal a very similar exposure timing as the Welsh Ice Cap thinned after the global Last Glacial Maximum. Eight bedrock and one boulder sample gave a combined arithmetic mean exposure age of 19.08 ± 0.80 ka (4.2%, 1σ). Similar exposure ages over a 320 m vertical range (824 to 581 m altitude) show that ice cap thinning was very rapid and spatially uniform. Using the same production rate and scaling scheme, we recalculated six published 10Be exposure ages from the nearby Arans, which also covered a similar elevation range from 608 to 901 m and obtained an arithmetic mean of 19.41 ± 1.45 ka (7.5%, 1σ). The average exposure age of all 15 accepted deglaciation ages is 19.21 ± 1.07 (5.6%, 1σ). The complete dataset from North Wales provides very strong evidence indicating that these summits became exposed as nunataks at 20-19 ka. This result provides important insight to the magnitude of ice surface lowering and behavior of the Welsh Ice Cap during the last deglaciation that can be compared to other ice masses that made up the British-Irish Ice Sheet.

  5. Louis Agassiz and the Spirit of Place

    ERIC Educational Resources Information Center

    Schwarz, Jack W.

    1976-01-01

    Agassiz, one of the first great naturalists, who made significant contributions in geology, natural history, and medicine as well, is discussed with regard to his imaginative and creative teaching methods. (LBH)

  6. Ice cap melting and low viscosity crustal root explain narrow geodetic uplift of the Western Alps

    NASA Astrophysics Data System (ADS)

    Chery, Jean; Genti, Manon; Vernant, Philippe

    2016-04-01

    More than 10 years of geodetic measurements demonstrate an uplift rate of 1-3 mm/yr of the high topography region of the Western Alps. By contrast, no significant horizontal motion has been detected. Three uplift mechanisms have been proposed so far: (1) the isostatic response to denudation. However this process is responsible for only a fraction of the observed uplift and (2) the rebound induced by the Wurmian ice cap melting. This process leads to a broader uplifting region than the one evidenced by geodetic observations. (3) a deep source motion associated with slab motion or some deep isostatic unbalance. Using a numerical model accounting for crustal and mantle rheology of the Alps and its foreland, we model the response to Wurmian ice cap melting. We show that a crustal viscosity contrast between the foreland and the central part of the Alps, the later being weaker with a viscosity of 1021 Pa.s, is needed to produce a narrow uplift. The vertical rates are enhanced if the strong uppermost mantle beneath the Moho is interrupted across the Alps, therefore allowing a weak vertical rheological anomaly thanks to the continuity between the low viscosity parts of the crust and mantle. References: Champagnac, J.-D., F. Schlunegger, K. Norton, F. von Blanckenburg, L. M. Abbühl, and M. Schwab (2009), Erosion-driven uplift of the modern Central Alps, Tectonophysics, 474(1-2), 236-249. Vernant, P., F. Hivert, J. Chéry, P. Steer, R. Cattin, and A. Rigo (2013), Erosion-induced isostatic rebound triggers extension in low convergent mountain ranges, geology, 41(4), 467-470.

  7. Projections of 21st Century Sea Level Rise From the Melt of Mountain Glaciers and Ice Caps

    NASA Astrophysics Data System (ADS)

    Radic, V.; Hock, R.

    2008-12-01

    An ensemble of 21st century volume projections for all mountain glaciers and ice caps from the World Glacier Inventory is derived by modeling the surface mass balance coupled with volume--area--length scaling and forced with temperature and precipitation scenarios with A1B emission scenario from ensemble of GCMs. By upscaling the volume projections through a regionally differentiated approach to all mountain glaciers and ice caps outside Greenland and Antarctica (514,380~km2) we estimated total volume change to range from -0.039~m to -0.150~m of sea level equivalent for the time period 2001--2100. A major source of uncertainty in the methodology is the temperature forcing in the mass balance model which depends on bias correction of ERA-40 temperatures in order to simulate the local temperatures on a mountain glacier or ice cap. Other major sources of uncertainties are the volume-area scaling in deriving initial glacier volume and upscaling the volume changes with assumptions on glacier-size distributions in each glacierized region. Our projected 21st century volume loss is probably a lower bound since no calving is modeled and no mountain glaciers and ice caps surrounding Antarctica and Greenland are included due to a lack of glacier inventory data. Nevertheless, the large range of our projections depends on the choice of GCM emphasizing the importance of ensemble projections.

  8. Modeling of Svartisen Ice Cap, Northern Norway, Using In-situ Observations and Remote Sensing of Ice Velocity and Volume Changes

    NASA Astrophysics Data System (ADS)

    Leclercq, P. W.; Nuth, C.; Altena, B.; Reerink, T.; Kaeaeb, A.

    2015-12-01

    We model the evolution of Vestre Svartisen. Vestre Svartisen is located in northern Norway and is the second largest ice cap in Norway with an area of 218 km2. There is an abundance of in-situ observations for this ice cap as a result of the monitoring programs in relation to hydro-power generation. Based on these in-situ observations, we can use the case of Vestre Svartisen to test the performance of glacier evolution modeling based on remote sensing, that provides data on glacier volume and surface velocity changes, instead of in-situ observations that only are available for a limited number of glaciers world-wide. The in-situ observations at Vestre Svartisen include mass balance observations since 1970 on Engabreen catchment and 10 mass balance years on Storglombreen, a glacier length record of Engabreen back to 1600, outlines of the ice cap in 1968, 1988 and 1999, ice thickness observations, and surface velocity measurements. In addition to these in-situ observations, we derive glacier volume and surface velocity changes from ASTER and Landsat imagery, respectively. We model the surface mass balance (SMB) and the ice dynamics using a simplified energy balance model coupled to a vertically integrated shallow ice approximation 2D glacier flow model. The mass balance model is forced with temperature and precipitation measurements from a nearby weather station at Glomfjord. The SMB model is calibrated on individual stake measurements of winter and summer mass balance over the period 1990--2010 in the Engabreen catchment. The bed topography is reconstructed from iteratively matching modeled and observed surface elevation, and the reconstruction reproduces the observed large ice thickness east of the highest point of the ice cap of about 650 m well. We use the calibrated model to reconstruct the 20th century evolution of the Svartisen ice cap and its fate under the projected climate change in the 21st century. In addition, we explore the possibilities of calibrating

  9. Effects of deliquescent salts in soils of polar Mars on the flow of the Northern Ice Cap

    NASA Astrophysics Data System (ADS)

    Fisher, D. A.; Hecht, M. H.; Kounaves, S.; Catling, D.

    2008-12-01

    The discovery of substantial amounts of magnesium and perchlorate by Phoenix' "Wet Chemistry Lab" (WCL) in the soil of Polar Mars suggests that magnesium perchlorate could be the dominant salt in the polar region's soils. This prospect opens some unexpected doors for moving liquid water around at temperatures as low as -68C. In its fully hydrated form ,this salt water mixture has a high density (~ 1700 kgm /cubic meter) (Besley and Bottomley,1969) and a freezing point of -68C (Pestova et al., 2005).This perchlorate is very deliquescent and gives off heat as it melts ice. About 1.8 gram of ice can be 'melted' by 1 gm of pure magnesium perchlorate . If the reported 1 percent perchlorate is typical of polar soils and if 5 percent of the Northern Permanent Ice Cap is soil then the perchorate , makes up about 0.0005 the of the ice cap. Given the average thickness of the ice cap is about 2000 meters,this suggests there enough perchorate in the ice cap to generate about 2m of salty water at the bed. Because of its density the perclorate salty water would pool over impervious layers and make the bed into a perchorate sludge that could be mobilized and deformed by the overburden of ice. The deformation of mobile beds is a well known phenomenon on some terrestrial glaciers presently and was thought to have played a major role during the Wisconsinan ice age (Fisher et al., 1985) . The perchorate sludge would be deformed and moved outwards possibly resulting its re-introduction to the polar environment. Having a deliquescent salt sludge at the bed whose melting point is -68C would mean that the ice cap could slide on its deformable bed while the ice itself was still very cold and stiff . This possibility has been modeled with a 2D time varying model . Adding the deformable bed material allows ice cap motion even at ice temperatures cold enough to generate and preserve the scarp/trough features. When the perchlorate formation mechanisms and rates are known the ultimate

  10. Evaluation of remote-sensing techniques to measure decadal-scale changes of Hofsjokull ice cap, Iceland

    USGS Publications Warehouse

    Hall, D.K.; Williams, R.S.; Barton, J.S.; Sigurdsson, O.; Smith, L.C.; Garvin, J.B.

    2000-01-01

    Dynamic surficial changes and changes in the position of the firn line and the areal extent of Hofsjökull ice cap, Iceland, were studied through analysis of a time series (1973–98) of synthetic-aperture radar (SAR) and Landsat data. A digital elevation model of Hofsjökull, which was constructed using SAR interferometry, was used to plot the SAR backscatter coefficient (σ°) vs elevation and air temperature along transects across the ice cap. Seasonal and daily σ° patterns are caused by freezing or thawing of the ice-cap surface, and abrupt changes in σ° are noted when the air temperature ranges from ∼−5° to 0°C. Late-summer 1997 σ° (SAR) and reflectance (Landsat) boundaries agree and appear to be coincident with the firn line and a SAR σ° boundary that can be seen in the January 1998 SAR image. In January 1994 through 1998, the elevation of this σ° boundary on the ice capwas quite stable, ranging from 1000 to 1300 m, while the equilibrium-line altitude, as measured on the ground, varied considerably. Thus the equilibrium line may be obscured by firn from previous years. Techniques are established to measure long-term changes in the elevation of the firn line and changes in the position of the ice margin.

  11. The extent of middle Pleistocene ice cap in the coastal Dinaric Mountains of Croatia

    NASA Astrophysics Data System (ADS)

    Marjanac, Tihomir; Marjanac, Ljerka

    2016-05-01

    Solitary limestone blocks and groups of blocks occur on Risnjak and Velebit Mountains and on the northern Adriatic islands of Krk and Rab. Previous researchers have interpreted some of these as a) erratic blocks, b) corrosional remnants, or c) rockfalls. We have studied their mode of occurrence and composition, and revised previous interpretations of their origin in the light of transport mechanism and depositional processes. After analyzing the context of the block positions and the physical processes responsible for their emplacement, and taking into account their sedimentological context (their association with glaciogenic sediments), we herein propose a glacial origin for most of these blocks. However, some blocks are indeed shaped by sub-soil corrosion, as evidenced by their structure. The interpreted erratic blocks on the inner northern Adriatic Sea islands document the presence of middle Pleistocene glaciation of Dinaric Mountains though not its maximal extent, which is still unclear as the ice terminus was in the area that is inundated by postglacial rise of Adriatic Sea. The reconstructed ice cap area, which extended along the coastal mountains from Risnjak Mt. to south Velebit Mt. and across the range from Lika Polje to Rab Island, is conservatively estimated to be 5400 km2.

  12. The extent of middle Pleistocene ice cap in the coastal Dinaric Mountains of Croatia

    NASA Astrophysics Data System (ADS)

    Marjanac, Tihomir; Marjanac, Ljerka

    2016-05-01

    Solitary limestone blocks and groups of blocks occur on Risnjak and Velebit Mountains and on the northern Adriatic islands of Krk and Rab. Previous researchers have interpreted some of these as a) erratic blocks, b) corrosional remnants, or c) rockfalls. We have studied their mode of occurrence and composition, and revised previous interpretations of their origin in the light of transport mechanism and depositional processes. After analyzing the context of the block positions and the physical processes responsible for their emplacement, and taking into account their sedimentological context (their association with glaciogenic sediments), we herein propose a glacial origin for most of these blocks. However, some blocks are indeed shaped by sub-soil corrosion, as evidenced by their structure. The interpreted erratic blocks on the inner northern Adriatic Sea islands document the presence of middle Pleistocene glaciation of Dinaric Mountains though not its maximal extent, which is still unclear as the ice terminus was in the area that is inundated by postglacial rise of Adriatic Sea. The reconstructed ice cap area, which extended along the coastal mountains from Risnjak Mt. to south Velebit Mt. and across the range from Lika Polje to Rab Island, is conservatively estimated to be 5400 km2.

  13. Atmospheric Controls of Snow Accumulation on Glaciers and Ice Caps in High Asia

    NASA Astrophysics Data System (ADS)

    Scherer, D.; Curio, J.

    2015-12-01

    Snowfall is the major contributor to snow accumulation on glaciers and ice caps. Unfortunately, its quantification is rather difficult, both by observations and by numerical modelling. Field measurements of snowfall are generally problematic, and particularly inaccurate in mountainous regions. This holds true also for data from remote sensing systems like the TRMM. Numerical modelling of precipitation in general, and of snowfall in particular, is depending on parameterization of sub-grid processes occurring at a wide range of spatial scales. The scarcity of reliable observational data on snowfall required to test and validate the relevant parameterization schemes is one of the major obstacles for deepening our understanding of atmospheric controls of snow accumulation on glaciers and ice caps. In addition, the often made assumption that easy-to-measure snow accumulation equals snowfall is not valid in areas where other processes like snowdrift or avalanches cause snow deposition or erosion. Besides a general discussion of the above-mentioned problems, the presentation will focus on results obtained from a gridded atmospheric data set, i.e., the so-called High Asia Refined analysis (HAR), covering the study region by two nested domains of 30 km and 10 km grid spacing. Starting from autumn 2000, three-hourly (30 km) and hourly (10 km) data are available for a comprehensive set of atmospheric variables (see www.klima.tu-berlin.de/HAR). HAR data was used to analyse annual and seasonal patterns of precipitation and atmospheric water transport, as well as to drive numerical models for surface mass balance of glaciers and ice sheets. A new study, which is the main subject of this presentation, reveals specific regimes of dynamic controls of precipitation in different regions of High Asia. One of the striking results is that the analysis identified a specific regime that is able to explain some of the atmospheric controls behind the so-called Karakoram anomaly (glaciers in

  14. Changes in the southeast Vatnajökull ice cap, Iceland, between ~ 1890 and 2010

    NASA Astrophysics Data System (ADS)

    Hannesdóttir, H.; Björnsson, H.; Pálsson, F.; Aðalgeirsdóttir, G.; Guðmundsson, Sv.

    2015-03-01

    Area and volume changes and the average geodetic mass balance of the non-surging outlet glaciers of the southeast Vatnajökull ice cap, Iceland, during different time periods between ~ 1890 and 2010, are derived from a multi-temporal glacier inventory. A series of digital elevation models (DEMs) (~ 1890, 1904, 1936, 1945, 1989, 2002, 2010) are compiled from glacial geomorphological features, historical photographs, maps, aerial images, DGPS measurements and a lidar survey. Given the mapped basal topography, we estimate volume changes since the end of the Little Ice Age (LIA) ~ 1890. The variable volume loss of the outlets to similar climate forcing is related to their different hypsometry, basal topography, and the presence of proglacial lakes. In the post-LIA period, the glacierized area decreased by 164 km2 (or from 1014 to 851 km2) and the glaciers had lost 10-30 % of their ~ 1890 area by 2010 (anywhere from 3 to 36 km2). The glacier surface lowered by 150-270 m near the terminus and the outlet glaciers collectively lost 60 ± 8 km3 of ice, which is equivalent to 0.15 ± 0.02 mm of sea-level rise. The volume loss of individual glaciers was in the range of 15-50%, corresponding to a geodetic mass balance between -0.70 and -0.32 m w.e. a-1. The annual rate of mass change during the post-LIA period was most negative in 2002-2010, on average -1.34 ± 0.12 m w.e. a-1, which is among the most negative mass balance values recorded worldwide in the early 21st century.

  15. Microbial communities in the subglacial waters of the Vatnajökull ice cap, Iceland

    PubMed Central

    Thór Marteinsson, Viggó; Rúnarsson, Árni; Stefánsson, Andri; Thorsteinsson, Thorsteinn; Jóhannesson, Tómas; Magnússon, Sveinn H; Reynisson, Eyjólfur; Einarsson, Bergur; Wade, Nicole; Morrison, Hilary G; Gaidos, Eric

    2013-01-01

    Subglacial lakes beneath the Vatnajökull ice cap in Iceland host endemic communities of microorganisms adapted to cold, dark and nutrient-poor waters, but the mechanisms by which these microbes disseminate under the ice and colonize these lakes are unknown. We present new data on this subglacial microbiome generated from samples of two subglacial lakes, a subglacial flood and a lake that was formerly subglacial but now partly exposed to the atmosphere. These data include parallel 16S rRNA gene amplicon libraries constructed using novel primers that span the v3–v5 and v4–v6 hypervariable regions. Archaea were not detected in either subglacial lake, and the communities are dominated by only five bacterial taxa. Our paired libraries are highly concordant for the most abundant taxa, but estimates of diversity (abundance-based coverage estimator) in the v4–v6 libraries are 3–8 times higher than in corresponding v3–v5 libraries. The dominant taxa are closely related to cultivated anaerobes and microaerobes, and may occupy unique metabolic niches in a chemoautolithotrophic ecosystem. The populations of the major taxa in the subglacial lakes are indistinguishable (>99% sequence identity), despite separation by 6 km and an ice divide; one taxon is ubiquitous in our Vatnajökull samples. We propose that the glacial bed is connected through an aquifer in the underlying permeable basalt, and these subglacial lakes are colonized from a deeper, subterranean microbiome. PMID:22975882

  16. The first complete inventory of the local glaciers and ice caps on Greenland

    NASA Astrophysics Data System (ADS)

    Rastner, P.; Bolch, T.; Mölg, N.; Machguth, H.; Le Bris, R.; Paul, F.

    2012-12-01

    Glacier inventories provide essential baseline information for the determination of water resources, glacier-specific changes in area and volume, climate change impacts as well as past, potential and future contribution of glaciers to sea-level rise. Although Greenland is heavily glacierised and thus highly relevant for all of the above points, a complete inventory of its glaciers was not available so far. Here we present the results and details of a new and complete inventory that has been compiled from more than 70 Landsat scenes (mostly acquired between 1999 and 2002) using semi-automated glacier mapping techniques. A digital elevation model (DEM) was used to derive drainage divides from watershed analysis and topographic attributes for each glacier entity. To serve the needs of different user communities, we assigned to each glacier one of three connectivity levels with the ice sheet (CL0, CL1, CL2; i.e. no, weak, and strong connection) to clearly, but still flexibly, distinguish the local glaciers and ice caps (GIC) from the ice sheet and its outlet glaciers. In total, we mapped ~ 20 300 glaciers larger than 0.05 km2 (of which ~ 900 are marine terminating), covering an area of 130 076 ± 4032 km2, or 89 720 ± 2781 km2 without the CL2 GIC. The latter value is about 50% higher than the mean value of more recent previous estimates. Glaciers smaller than 0.5 km2 contribute only 1.5% to the total area but more than 50% (11 000) to the total number. In contrast, the 25 largest GIC (> 500 km2) contribute 28% to the total area, but only 0.1% to the total number. The mean elevation of the GIC is 1700 m in the eastern sector and around 1000 m otherwise. The median elevation increases with distance from the coast, but has only a weak dependence on mean glacier aspect.

  17. Crustal movements due to Iceland’s shrinking ice caps mimic magma inflow signal at Katla volcano

    PubMed Central

    Spaans, Karsten; Hreinsdóttir, Sigrún; Hooper, Andrew; Ófeigsson, Benedikt Gunnar

    2015-01-01

    Many volcanic systems around the world are located beneath, or in close proximity to, ice caps. Mass change of these ice caps causes surface movements, which are typically neglected when interpreting surface deformation measurements around these volcanoes. These movements can however be significant, and may closely resemble movements due to magma accumulation. Here we show such an example, from Katla volcano, Iceland. Horizontal movements observed by GPS on the flank of Katla have led to the inference of significant inflow of magma into a chamber beneath the caldera, starting in 2000, and continuing over several years. We use satellite radar interferometry and GPS data to show that between 2001 and 2010, the horizontal movements seen on the flank can be explained by the response to the long term shrinking of ice caps, and that erratic movements seen at stations within the caldera are also not likely to signify magma inflow. It is important that interpretations of geodetic measurements at volcanoes in glaciated areas consider the effect of ice mass change, and previous studies should be carefully reevaluated. PMID:25992847

  18. A late Holocene record of trace metal deposition in lake sediments near Quelccaya Ice Cap, Peru

    NASA Astrophysics Data System (ADS)

    Beal, S. A.; Kelly, M. A.; Jackson, B. P.; Osterberg, E. C.; Stroup, J. S.; Baker, R. A.

    2010-12-01

    Records of atmospheric metal deposition have been used extensively in the Northern Hemisphere to examine historical events ranging from the evolution of ancient metallurgy to climatic change. Establishing such a record in tropical South America is pertinent due to ongoing questions about the metallurgical history of pre-colonial Andean civilizations, recent atmospheric pollution levels, and late Holocene climate variability. Here we present a late Holocene record of the Ag, As, Cd, Co, Cu, Hg, Ni, Pb, Sr, Zn, and Pb isotopic compositions of atmospheric deposition from three 1.5 m-long lake cores and one 5 m-long bog core recovered near Quelccaya Ice Cap (13.9 °S), in the southeastern Peruvian Andes. The bog core, representing deposition from the present to at least 2415 yr BP, records relatively stable concentrations of As, Co, Cu, Hg, Ni, Pb, Sr, and Zn between 2415 (±78) and 916 (±29) yr BP. However, Ag and Cd exhibit brief gradual enrichments over background levels by factors of 6 and 11, respectively, shortly after 2415 (±78) yr BP as a possible result of ancient metallurgy. Sometime following the 916 (±29) yr BP date, Ag, As, Cd, Cu, Hg, Ni, Pb, and Sr abruptly become enriched by factors of 10, 37, 11, 11, 47, 6, 16, and 24, respectively, possibly from anthropogenic sources and/or the 1600 AD eruption of Huaynaputina in southern Peru. These enrichments are concurrent with a shift in 206Pb/207Pb to 1.182 from background levels of 1.213 (±0.002, n=20). A subsequent quiescent period in metal concentrations is marked by a brief return to background 206Pb/207Pb values, followed by erratic 206Pb/207Pb values yet decreased metal concentrations in the most recent sediments. Only Hg is enriched over background levels, by a factor of 3, in the most recent sediment. Forthcoming higher-resolution data from the three lake cores will utilize pre-industrial lead isotope ratios and Ti, Zr, and REE fluxes to examine past variability of the El Niño-Southern Oscillation

  19. Ice-Cap: a method for growing Arabidopsis and tomato plants in 96-well plates for high-throughput genotyping.

    PubMed

    Su, Shih-Heng; Clark, Katie A; Gibbs, Nicole M; Bush, Susan M; Krysan, Patrick J

    2011-11-09

    It is becoming common for plant scientists to develop projects that require the genotyping of large numbers of plants. The first step in any genotyping project is to collect a tissue sample from each individual plant. The traditional approach to this task is to sample plants one-at-a-time. If one wishes to genotype hundreds or thousands of individuals, however, using this strategy results in a significant bottleneck in the genotyping pipeline. The Ice-Cap method that we describe here provides a high-throughput solution to this challenge by allowing one scientist to collect tissue from several thousand seedlings in a single day (1,2). This level of throughput is made possible by the fact that tissue is harvested from plants 96-at-a-time, rather than one-at-a-time. The Ice-Cap method provides an integrated platform for performing seedling growth, tissue harvest, and DNA extraction. The basis for Ice-Cap is the growth of seedlings in a stacked pair of 96-well plates. The wells of the upper plate contain plugs of agar growth media on which individual seedlings germinate. The roots grow down through the agar media, exit the upper plate through a hole, and pass into a lower plate containing water. To harvest tissue for DNA extraction, the water in the lower plate containing root tissue is rapidly frozen while the seedlings in the upper plate remain at room temperature. The upper plate is then peeled away from the lower plate, yielding one plate with 96 root tissue samples frozen in ice and one plate with 96 viable seedlings. The technique is named "Ice-Cap" because it uses ice to capture the root tissue. The 96-well plate containing the seedlings can then wrapped in foil and transferred to low temperature. This process suspends further growth of the seedlings, but does not affect their viability. Once genotype analysis has been completed, seedlings with the desired genotype can be transferred from the 96-well plate to soil for further propagation. We have demonstrated

  20. Constraints on southern hemisphere tropical climate change during the Little Ice Age and Younger Dryas based on glacier modeling of the Quelccaya Ice Cap, Peru

    NASA Astrophysics Data System (ADS)

    Malone, Andrew G. O.; Pierrehumbert, Raymond T.; Lowell, Thomas V.; Kelly, Meredith A.; Stroup, Justin S.

    2015-10-01

    Improving the late Quaternary paleoclimate record through climate interpretations of low-latitude glacier length changes advances our understanding of past climate change events and the mechanisms for past, present, and future climate change. Paleotemperature reconstructions at low-latitude glaciers are uniquely fruitful because they can provide both site-specific information and enhanced understanding of regional-scale variations due to the structure of the tropical atmosphere. We produce Little Ice Age (LIA) and Younger Dryas (YD) paleoclimate reconstructions for the Huancané outlet glacier of the Quelccaya Ice Cap (QIC) and low-latitude southern hemisphere regional sea surface temperatures (SSTs) using a coupled ice-flow and energy balance model. We also model the effects of long-term changes in the summit temperature and precipitiation rate and the effects of interannual climate variability on the Huancané glacier length. We find temperature to be the dominant climate driver of glacier length change. Also, we find that interannual climate variability cannot adequately explain glacier advances inferred from the geomorphic record, necessitating that these features were formed during past colder climates. To constrain our LIA reconstruction, we incorporate the QIC ice core record, finding a LIA air temperature cooling at the ice cap of between ˜0.7 °C and ˜1.1 °C and ˜0.4 °C and regional SSTs cooling of ˜0.6 °C. For the YD paleoclimate reconstructions, we propose two limits on the precipitation rate, since the ice core record does not extend into the Pleistocene: 1) the precipitation rate scales with the Clausius-Clapeyron relationship (upper limit on cooling) and 2) the precipitation rate increases by 40% (lower limit on cooling), which is an increase about twice as great as the regional increases realized in GCM simulations for the period. The first limit requires ˜1.6 °C cooling in ice cap air temperatures and ˜0.9 °C cooling in SSTs, and the

  1. Peruvian Tropical Glacier May Survive Longer Than Previously Thought: Landsat Image Analysis of Nevado Coropuna Ice Cap, Peru

    NASA Astrophysics Data System (ADS)

    Kochtitzky, W. H.; Edwards, B. R.; Marino, J.; Manrique, N.

    2015-12-01

    Nevado Coropuna is a large volcanic complex in southern Peru (15.56°S, 72.62°N; 6,425 m). The complex is approximately 12 km east-west and 8 km north-south with elevation from ~4,500 m at the base to over 6,000 m at the highest points. This ice cap is the largest hosted by a volcano in the tropics, and one of the ten biggest ice masses in the tropics. Previous workers have predicted that the Coropuna ice cap will completely melt by 2050. We present a new analysis of historic satellite imagery to test this hypothesis. In this study, ice and snow are classified based on unique spectral signatures including spectral band thresholds, Normalized Difference Snow Index, and Band 4/5 ratio. Landsat scenes (L2, 4, 5, 7, and 8) from 1975 to present in addition to one SPOT scene (2013) are used. Previous workers used images from June and July, which are peak snow periods in southern Peru, leading to overestimates of ice area. This study uses November and December images when snow is at an annual minimum. Annual equilibrium line altitudes are calculated for each end of year image (November/December). The glaciers of Nevado Coropuna were found to be shrinking at ~0.5 km2/yr, which is ~1/3 the rate previously published. In this study, SPOT (1.5 m resolution) and Landsat 7 ETM scenes from November 23 and 26, 2013 respectively were used to calibrate the spectral band threshold classification. While this study suggests that the ice cap of Coropuna will persist until 2100 given current rates, water quantity and security remains a concern for Peruvian agriculture. Coropuna is an active volcano, so it poses great risk to surrounding inhabitants from lahars, flooding, and debris avalanches. Our new data suggest that these will continue to be risks late into this century.

  2. The role of sublimation and condensation on the development of ice sedimentation waves on the North Polar Cap of Mars

    NASA Astrophysics Data System (ADS)

    Herny, C.; Carpy, S.; Bourgeois, O.; Masse, M.; Spiga, A.; Le Mouélic, S.; Perret, L.; Smith, I. B.; Rodriguez, S.

    2015-10-01

    Mass and energy balance of ice sheets are driven by complex interactions between the atmosphere and the cryosphere. For instance, it has been demonstrated that feedbacks between katabatic winds and the cryosphere lead to the formation of sedimentation waves at the surface of Martian and terrestrial ice sheets [1, 2, 3 and 4]. Here we explore the role of sublimation and condensation of water vapor in the development of these sedimentation waves. We conduct this study by complementary observational and numerical investigations on the North Polar Cap of Mars.

  3. Albedo of Carbon Dioxide Ice in Mars' Residual South Polar Cap

    NASA Astrophysics Data System (ADS)

    James, P. B.; Wolff, M. J.; Bonev, B.

    2015-12-01

    The albedo of surface CO2 deposits in the Residual South Polar Cap (RSPC) of Mars controls their net condensation / sublimation over a martian year and is therefore a crucial parameter in determining RSPC stability. The albedo used in previous analyses is obtained by dividing I/F, determined from radiometrically calibrated imaging data, by the cosine of the incidence angle. Because of atmospheric aerosols, the albedo calculated from I/F above the atmosphere is not the surface albedo that enters into stability considerations. In order to determine the surface albedo, we interpolate optical depths determined from CRISM EPF measurements to provide estimates of the dust and ice opacities over the RSPC (Wolff et al., 2009) and use these to determine the actual surface albedos from MARCI images using the radiative transport program DISORT (Stamnes et al., 1988). Assuming that dust is the only contributor to atmospheric opacity, the retrieved surface albedos for the longer wavelength MARCI filters in MY 28 and 29 are found to be consistent despite very different dust opacities in the two years (James et al., 2014). However, this model fails to reproduce the short wavelength behavior in early summer and suggests either an additional opacity source or modification of the CRISM dust opacity or the dust phase function. The consequences of these changes will be discussed.

  4. Late Quaternary fluvial terraces near the Daocheng Ice Cap, eastern Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Xu, Liubing; Zhou, Shangzhe

    2014-05-01

    The timing of terrace formation relative to the glacial-interglacial cycle and what factors control that timing, such as changes in climate and/or uplift, are controversial. Here we present a study of the terraces along the Yazheku River using electron spin resonance (ESR) dating and analysis of the sedimentary characteristics in order to establish the timing of terrace formation and to assess the forcing mechanisms that have been proposed. The Yazheku River flows in glacial trough leading from the Haizi Shan, on the eastern Tibetan Plateau. The range was uplifted during the Quaternary and repeatedly glaciated by ice caps. The four highest major terraces (T5, T4, T3, and T2) are the result of both climatic and tectonic influences. Strath terraces T5-T2 were created during Haizi Shan glacial expansions during MIS 16, 12, 6 and 3-4, respectively. The major aggradation phases of the four terraces occurred during the deglaciations at the ends of MIS 16, 12, 6, and 2. Down-cutting, which led to the generation of the four terraces, immediately followed the deposition of the T5-T2 gravel units. These incisions occurred during the transitions between MIS 16-15, MIS 12-11, MIS 6-5, and MIS 2-1.

  5. The melting sea ice of Arctic polar cap in the summer solstice month and the role of ocean

    NASA Astrophysics Data System (ADS)

    Lee, S.; Yi, Y.

    2014-12-01

    The Arctic sea ice is becoming smaller and thinner than climatological standard normal and more fragmented in the early summer. We investigated the widely changing Arctic sea ice using the daily sea ice concentration data. Sea ice data is generated from brightness temperature data derived from the sensors: Defense Meteorological Satellite Program (DMSP)-F13 Special Sensor Microwave/Imagers (SSM/Is), the DMSP-F17 Special Sensor Microwave Imager/Sounder (SSMIS) and the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E) instrument on the NASA Earth Observing System (EOS) Aqua satellite. We tried to figure out appearance of arctic sea ice melting region of polar cap from the data of passive microwave sensors. It is hard to explain polar sea ice melting only by atmosphere effects like surface air temperature or wind. Thus, our hypothesis explaining this phenomenon is that the heat from deep undersea in Arctic Ocean ridges and the hydrothermal vents might be contributing to the melting of Arctic sea ice.

  6. Geomorphology and the Little Ice Age extent of the Drangajökull ice cap, NW Iceland, with focus on its three surge-type outlets

    NASA Astrophysics Data System (ADS)

    Brynjólfsson, Skafti; Schomacker, Anders; Ingólfsson, Ólafur

    2014-05-01

    Detailed geomorphological maps from the forefields of three surging outlets of the Drangajökull ice cap, northwest Iceland, are presented. The maps are based on field studies in 2011-2013, high resolution orthorectified aerial photographs recorded in 2005-2006, and airborne LiDAR data from 2011. The maps cover an area of about 40-60 km2 each. Furthermore, we present an overview map that covers the area surrounding the Drangajökull ice cap. Landforms and sediments were manually registered in a geographic information system (ESRI ArcGIS 10). We mapped glacial landforms such as flutes, ice-sculpted bedrock, hummocky moraine, kame terraces, and moraines. Fluvial landforms include outwash plains/sandur, pitted sandur, and eskers. In addition raised beaches were mapped. The Little Ice Age (LIA) maximum extent of Drangajökull and its outlet glaciers are fingerprinted by surficial till deposits and freshly glacially scoured bedrock. Sediments distal to the LIA deposits were recorded and consist mainly of late Weichselian and early Holocene sediments and locally weathered bedrock. Periglacial activity is demonstrated by patterned ground, mainly occurring on the 500-700 m high plateaux, and three rock glaciers. At least 3-4 surge events are described from each of the outlet glaciers, occurring over the last three centuries. In contrast to most other surge-type outlets from Icelandic ice caps, the Drangajökull outlets are confined within valleys, which affect the forefield geomorphology. Glaciofluvial landforms, moraines, and a thin sheet of till with numerous boulders are characteristic for the forefields of the Drangajökull outlets.

  7. Climatic versus topographic forcing on the extend of major Alpine ice-caps

    NASA Astrophysics Data System (ADS)

    Salcher, Bernhard; Sternai, Pietro

    2015-04-01

    Climate exerts the primary control on glaciers' mass balance, in turn affecting the topographic evolution of mountain ranges worldwide by driving glacial erosion. The hypsometry (i.e. the distribution of elevations) of a mountain range, however, is also known to influence the evolution of glaciers and ice-caps, thereby affecting the patterns and magnitudes of glacial erosion (Pedersen and Egholm, 2013). The importance of these interacting factors, climate and landscape hypsometry, on the glacial history and associated erosion is commonly derived from the geomorphic and the stratigraphic records. However, first-order questions are still unanswered and a better understanding of this double forcing is clearly needed. In this presentation, we explore climate vs. hypsometric forcing on glacial dynamics through numerical landscape evolution modeling. We focus on the European Alps, a mountain range that was repeatedly affected by major glaciations throughout the Quaternary. The European Alps show clear east-west topographic variations in spite of relatively uniform climate forcing. While the width across the Western and Central Alps does not exceed 150 km and the highest peaks rise up to more than 4500 m, the Eastern Alps are up to 260 km wide and the highest peaks are clearly lower than 4000 m. This topographic gradient may be critical during major Quaternary climatic transitions (i.e. at 2.5 Ma, 1.4 Ma or at the mid-Pleistocene transition): Did the related ELA (equilibrium line altitude) variations really lead to strong variations in ice extend in the western and eastern Alps? What is the role of the hypsometry, including effects of landscapes very differently preconditioned by glaciers? In fact, stratigraphic records in the foreland of the western Alps suggest the arrival of glaciers at the mountain front probably long before 1 Ma (Akçar et al. 2014), while there is no evidence of such an early extent on the eastern side (e.g. Preusser, 2004). Later ice advances (i

  8. An Intercomparison of Predicted Sea Ice Concentration from Global Ocean Forecast System & Arctic Cap Nowcast/Forecast System

    NASA Astrophysics Data System (ADS)

    Rosemond, K.

    2015-12-01

    The objective of this research is to provide an evaluation of improvements in marginal ice zone (MIZ) and pack ice estimations from the Global Ocean Forecast System (GOFS) model compared to the current operational model, the Arctic Cap Nowcast/Forecast System (ACNFS). This will be determined by an intercomparison between the subjectively estimated operational ice concentration data from the National Ice Center (NIC) MIZ analysis and the ice concentration estimates from GOFS and ACNFS. This will help ascertain which nowcast from the models compares best to the NIC operational data stream needed for vessel support. It will also provide a quantitative assessment of GOFS and ACNFS performance and be used in the Operational Evaluation (OPEVAL) report from the NIC to NRL. The intercomparison results are based on statistical evaluations through a series of map overlays from both models ACNFS, GOFS with the NIC's MIZ data. All data was transformed to a common grid and difference maps were generated to determine which model had the greatest difference compared to the MIZ ice concentrations. This was provided daily for both the freeze-up and meltout seasons. Results indicated the GOFS model surpassed the ACNFS model, however both models were comparable. These results will help US Navy and NWS Anchorage ice forecasters understand model biases and know which model guidance is likely to provide the best estimate of future ice conditions.The objective of this research is to provide an evaluation of improvements in marginal ice zone (MIZ) and pack ice estimations from the Global Ocean Forecast System (GOFS) model compared to the current operational model, the Arctic Cap Nowcast/Forecast System (ACNFS). This will be determined by an intercomparison between the subjectively estimated operational ice concentration data from the National Ice Center (NIC) MIZ analysis and the ice concentration estimates from GOFS and ACNFS. This will help ascertain which nowcast from the models

  9. Analysis of vanillic acid in polar ice cores as a biomass burning proxy - preliminary results from the Akademii Nauk Ice Cap in Siberia

    NASA Astrophysics Data System (ADS)

    Grieman, M. M.; Jimenez, R.; McConnell, J. R.; Fritzsche, D.; Saltzman, E. S.

    2013-12-01

    Biomass burning influences global climate change and the composition of the atmosphere. The drivers, effects, and climate feedbacks related to fire are poorly understood. Many different proxies have been used to reconstruct past fire frequency from lake sediments and polar ice cores. Reconstruction of historical trends in biomass burning is challenging because of regional variability and the qualitative nature of various proxies. Vanillic acid (4-hydroxy-3-methoxybenzoic acid) is a product of the combustion of conifer lignin that is known to occur in biomass burning aerosols. Biomass burning is likely the only significant source of vanillic acid in polar ice. In this study we describe an analytical method for quantifying vanillic acid in polar ice using HPLC with electrospray ionization and tandem mass spectrometric detection. The method has a detection limit of 100 pM and a precision of × 10% at the 100 pM level for analysis of 100 μl of ice melt water. The method was used to analyze more than 1000 discrete samples from the Akademii Nauk ice cap on Severnaya Zemlya in the high Russia Arctic (79°30'N, 97°45'E) (Fritzsche et al., 2002; Fritzsche et al., 2005; Weiler et al., 2005). The samples range in age over the past 2,000 years. The results show a mean vanillic acid concentration of 440 × 710 pM (1σ), with elevated levels during the periods from 300-600 and 1450-1550 C.E.

  10. Quantification of a Process of Multi-Year, Pole-Wide, Summertime H2O Ice Deposition on the CO2 Ice Cap of the South Pole of Mars

    NASA Astrophysics Data System (ADS)

    Brown, A. J.; Piqueux, S.; Titus, T. N.

    2014-07-01

    We report below that an as-yet-undetermined process causes the magnitude of H2O ice signatures on the southern cap to rise steadily throughout summer, particularly on the west end of the cap. We attempt first quantization of said process.

  11. Mars residual north polar cap - Earth-based spectroscopic confirmation of water ice as a major constituent and evidence for hydrated minerals

    NASA Technical Reports Server (NTRS)

    Clark, R. N.; Mccord, T. B.

    1982-01-01

    A description is presented of new earth-based reflectance spectra of the Martian north residual polar cap. The spectra indicate that the composition is at least mostly water ice plus another component with a 'gray' reflectance. The other minerals in the ice cap appear to be hydrated. The data were obtained with a cooled circular variable filter spectrometer on February 20, 1978, using the 2.2-m telescope on Mauna Kea, Hawaii. It is pointed out that the identification of water ice in the north polar cap alone does not indicate that water makes up all or even most of the bulk of the cap. Kieffer (1970) has shown that a small amount of water will mask the spectral features of CO2.

  12. Temporal constraints on future accumulation-area loss of a major Arctic ice cap due to climate change (Vestfonna, Svalbard).

    PubMed

    Möller, Marco; Schneider, Christoph

    2015-01-01

    Arctic glaciers and ice caps are major contributors to past, present and future sea-level fluctuations. Continued global warming may eventually lead to the equilibrium line altitudes of these ice masses rising above their highest points, triggering unstoppable downwasting. This may feed future sea-level rise considerably. We here present projections for the timing of equilibrium-line loss at the major Arctic ice cap Vestfonna, Svalbard. The projections are based on spatially distributed climatic mass balance modelling driven by the outputs of multiple climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) forced by the Representative Concentration Pathways (RCPs) 2.6, 4.5, 6.0 and 8.5. Results indicate strongly decreasing climatic mass balances over the 21(st) century for all RCPs considered. Glacier-wide mass-balance rates will drop down to -4 m a(-1) w.e. (water equivalent) at a maximum. The date at which the equilibrium line rises above the summit of Vestfonna (630 m above sea level) is calculated to range between 2040 and 2150, depending on scenario. PMID:25628045

  13. Temporal constraints on future accumulation-area loss of a major Arctic ice cap due to climate change (Vestfonna, Svalbard).

    PubMed

    Möller, Marco; Schneider, Christoph

    2015-01-28

    Arctic glaciers and ice caps are major contributors to past, present and future sea-level fluctuations. Continued global warming may eventually lead to the equilibrium line altitudes of these ice masses rising above their highest points, triggering unstoppable downwasting. This may feed future sea-level rise considerably. We here present projections for the timing of equilibrium-line loss at the major Arctic ice cap Vestfonna, Svalbard. The projections are based on spatially distributed climatic mass balance modelling driven by the outputs of multiple climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) forced by the Representative Concentration Pathways (RCPs) 2.6, 4.5, 6.0 and 8.5. Results indicate strongly decreasing climatic mass balances over the 21(st) century for all RCPs considered. Glacier-wide mass-balance rates will drop down to -4 m a(-1) w.e. (water equivalent) at a maximum. The date at which the equilibrium line rises above the summit of Vestfonna (630 m above sea level) is calculated to range between 2040 and 2150, depending on scenario.

  14. Temporal constraints on future accumulation-area loss of a major Arctic ice cap due to climate change (Vestfonna, Svalbard)

    PubMed Central

    Möller, Marco; Schneider, Christoph

    2015-01-01

    Arctic glaciers and ice caps are major contributors to past, present and future sea-level fluctuations. Continued global warming may eventually lead to the equilibrium line altitudes of these ice masses rising above their highest points, triggering unstoppable downwasting. This may feed future sea-level rise considerably. We here present projections for the timing of equilibrium-line loss at the major Arctic ice cap Vestfonna, Svalbard. The projections are based on spatially distributed climatic mass balance modelling driven by the outputs of multiple climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) forced by the Representative Concentration Pathways (RCPs) 2.6, 4.5, 6.0 and 8.5. Results indicate strongly decreasing climatic mass balances over the 21st century for all RCPs considered. Glacier-wide mass-balance rates will drop down to −4 m a−1 w.e. (water equivalent) at a maximum. The date at which the equilibrium line rises above the summit of Vestfonna (630 m above sea level) is calculated to range between 2040 and 2150, depending on scenario. PMID:25628045

  15. A 300 Year Surge History of the Drangajökull Ice Cap, Northwest Iceland: Surge Frequency and Little Ice Age Maximum

    NASA Astrophysics Data System (ADS)

    Brynjolfsson, S.; Schomacker, A.; Ingolfsson, O.; Gudmundsdottir, E. R.

    2014-12-01

    Over the last 300 years, each of the three surge-type outlet glaciers of the Drangajökull ice cap in north-west Iceland has surged 2-4 times. There is valuable historical information available on the surge frequencies since the Little Ice Age (LIA) maximum because of the proximity of the surging outlets, Reykjarfjarðarjökull, Leirufjarðarjökull and Kaldalónsjökull to farms and pastures. We have reconstructed the surge history of the Drangajökull ice cap, based on geomorphological mapping, sedimentary studies and review of historical records. Geomorphological mapping of the glacier forefields revealed twice as many end-moraines than previously recognized. This indicates a higher surge frequency than previously perceived. A clear relationship between the surge frequency and climate cannot be established, however, surges were more frequent during the 19th century and the earliest 20th century compared to the cool 18th century and the warmer late part of the 20th century. We have estimated the magnitude of the LIA maximum surge events by reconstruction of Digital Elevation Models (DEMs) that can be compared with modern DEMs. As reference points for the digital elevation modelling we used the recently mapped lateral moraines and historical information on the exposure timing of nunataks. During the LIA maximum surge events the outlet glaciers extended 3-3.5 km further down-valley than at present. Their ice volumes were at least 2-2.5 km3 greater than after their most recent surges in the beginning of the 21st century.

  16. Recent ice cap snowmelt in Russian High Arctic and anti-correlation with late summer sea ice extent

    NASA Astrophysics Data System (ADS)

    Zhao, Meng; Ramage, Joan; Semmens, Kathryn; Obleitner, Friedrich

    2014-04-01

    Glacier surface melt dynamics throughout Novaya Zemlya (NovZ) and Severnaya Zemlya (SevZ) serve as a good indicator of ice mass ablation and regional climate change in the Russian High Arctic. Here we report trends of surface melt onset date (MOD) and total melt days (TMD) by combining multiple resolution-enhanced active and passive microwave satellite datasets and analyze the TMD correlations with local temperature and regional sea ice extent. The glacier surface snowpack on SevZ melted significantly earlier (-7.3 days/decade) from 1992 to 2012 and significantly longer (7.7 days/decade) from 1995 to 2011. NovZ experienced large interannual variability in MOD, but its annual mean TMD increased. The snowpack melt on NovZ is more sensitive to temperature fluctuations than SevZ in recent decades. After ruling out the regional temperature influence using partial correlation analysis, the TMD on both archipelagoes is statistically anti-correlated with regional late summer sea ice extent, linking land ice snowmelt dynamics to regional sea ice extent variations.

  17. Isotopic composition of old ground water from Lake Agassiz: Implications for late Pleistocene climate

    SciTech Connect

    Remenda, V.H.; Cherry, J.A.; Edwards, T.W.D. )

    1994-12-23

    A uniform oxygen isotope value of -25 per mil was obtained from old ground water at depths of 20 to 30 meters in a thick deposit of clay in the southern part of the glacial Lake Agassiz basin. The lake occupied parts of North Dakota and southern Manitoba at the end of the last glacial maximum and received water from the ice margin and the interior plains region of Canada. Ground water from thick late Pleistocene-age clay deposits elsewhere, a till in southern Saskatchewan, and a glaciolacustrine deposit in northern Ontario show the same value at similar depths. These sites are at about 50[degrees]N latitude, span a distance of 2000 kilometers, and like the Lake Agassiz sites, have a ground-water velocity of less than a few millimeters per year. The value of -25 per mil is characteristic of meltwater impounded in the southern basin of Lake Agassiz. This value corresponds to an estimated air temperature of -16[degrees]C, compared with the modern temperature of 0[degrees]C for this area. 15 refs., 5 figs.

  18. Assimilating high horizontal resolution sea ice concentration data into the US Navy's ice forecast systems: Arctic Cap Nowcast/Forecast System (ACNFS) and the Global Ocean Forecast System (GOFS 3.1)

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  19. Historical variations of mercury stable isotope ratios in Arctic glacier firn and ice cores

    NASA Astrophysics Data System (ADS)

    Zdanowicz, C. M.; Krümmel, E. M.; Poulain, A. J.; Yumvihoze, E.; Chen, J.; Å trok, M.; Scheer, M.; Hintelmann, H.

    2016-09-01

    The concentration and isotopic composition of mercury (Hg) were determined in glacier core samples from Canadian Arctic ice caps dating from preindustrial to recent time (early 21st century). Mean Hg levels increased from ≤ 0.2 ng L-1 in preindustrial time to ~0.8-1.2 ng L-1 in the modern industrial era (last ~200 years). Hg accumulated on Arctic ice caps has Δ199Hg and Δ201Hg that are higher (~ -1 to 2.9‰) than previously reported for Arctic snow impacted by atmospheric Hg depletion events (mostly < -1‰), suggesting that these events contribute little to Hg accumulation on ice caps. The range of δ202Hg, Δ199Hg, and Δ201Hg in glacier cores overlaps with that of Arctic Hg0(g) and of seawater in Baffin Bay and also with that of midlatitude precipitation and industrial Hg sources, including coal and Hg ores. A core from Agassiz ice cap (80.7°N) shows a ~ +1‰ shift in δ202Hg over the nineteenth to twentieth centuries that could reflect changes in the isotopic composition of the atmospheric Hg pool in the High Arctic in response to growing industrial emissions at lower latitudes. This study is the first ever to report on historical variations of Hg stable isotope ratios in Arctic ice cores. Results could help constrain future modeling efforts of the global Hg biogeochemical cycle and the atmosphere's response to changing Hg emissions, past and future.

  20. Assessing post-depositional alteration and the integrity of ice core nitrate-N and -O isotopic records at the Quelccaya Ice Cap, Peru

    NASA Astrophysics Data System (ADS)

    Buffen, A. M.; Hastings, M. G.; Thompson, L. G.; Mosley-Thompson, E. S.

    2011-12-01

    Nitrate (NO3-) is a common chemical species found in snow and ice. Both nitrate and its atmospheric precursor NOx (NO and NO2) are of importance to climate, biogeochemistry and the composition of the atmosphere. For instance, nitrate is a critical biological nutrient, while NOx regulates concentrations of ozone (O3) and hydroxyl (OH) and thus influences the chemical and radiative properties of Earth's atmosphere. NOx sources include fossil fuel combustion, biomass burning, soil microbial processes and lightning. Past changes in NOx emissions, tropospheric distributions and consequent effects on the atmosphere, however, are unknown. Interpreting stable nitrogen (δ15N) and oxygen (δ18O and Δ17O) isotope ratios in nitrate preserved in ice cores can address these issues as they contain diagnostic signatures of NOx sources and oxidation processes, respectively. The potential caveat to this is that nitrate can be lost from snow and firn via photolysis (as NOx) and/or volatilization (as nitric acid). Because these processes are isotopically fractionating, it is necessary to determine if, or to what degree, such post-depositional alteration takes place at a given site before an isotopic record from ice core nitrate can be utilized as a paleoenvironmental proxy. This work addresses post-depositional alteration at the Quelccaya Ice Cap (5670 masl) in southeastern Peru in order to assess the integrity of the nitrate record in an 1800-year ice core from the site. This work represents the first of its kind outside the polar regions and is significant in that natural NOx sources and OH production are dominantly located in the Tropics. Additionally, because nitrate and NOx are not uniformly distributed in the troposphere, low-latitude records are needed to bridge ongoing polar work in order to establish a global perspective.

  1. Can the Solid State Greenhouse Effect Produce ~100 Year Cycles in the Mars South Polar Residual CO2 Ice Cap?

    NASA Astrophysics Data System (ADS)

    Line, M. R.; Ingersoll, A. P.

    2010-12-01

    Malin et al. (2001) reported that the south perennial cap consists of quasi-circular pits ~8 meters deep, with a flat surface in between. The walls of the pits are retreating at a rate of 1 to 3 meters per year. Byrne and Ingersoll (2003a, 2003b) showed evidence that the floors of the pits are water ice and the upper layer is CO2. This layer will be gone in a few Martian centuries, if the observations are taken at face value. This raises some difficult questions: How likely is it that mankind would be witnessing the final few hundred years of the residual CO2 frost on Mars? Can one imagine extreme weather events that could recharge the residual CO2 frost once it is gone? Both seem unlikely, and we propose a different mechanism. Kieffer et al. (2000) showed that sunlight can penetrate several meters through the seasonal CO2 frost, where it warms the surface below. We have observational evidence that the same is happening in the perennial CO2 frost. Further, we have a model that shows how this "solid-state greenhouse" can lead to cyclic behavior, in which layers of CO2 build up on a water ice substrate, are heated internally by sunlight and lose mass from within. Eventually the layer becomes too weak to support itself, and it collapses to form pits. Then a new CO2 layer accumulates and the process repeats. Our study addresses fundamental questions of long-term stability of the Martian polar caps and how the caps control the atmospheric pressure. Instead of invoking extreme climate events to explain the data, we propose that processes within the frost itself can lead to cyclic growth and collapse of the pits. Our model implies that there is no long-term change in the ~8 meter layer of CO2 and no extreme weather events to make it change.

  2. Volcanic unrest primed by ice cap melting: A case study of Snæfellsjökull volcano, Western Iceland

    NASA Astrophysics Data System (ADS)

    Bakker, Richard; Lupi, Matteo; Frehner, Marcel; Berger, Julien; Fuchs, Florian

    2014-05-01

    The most dramatic effect of global warming is the water level rise due to rapid melting of ice sheets. In addition, recent studies suggest that accelerated glacial retreat and associated lithospheric relaxation may enhance upwelling of magmatic fluids through the crust. Here, we investigate whether, also at short geological timescales, shallow magmatic systems may be affected by rapid melting of ice caps. As a case study, we chose the Snæfellsjökull volcanic system in western Iceland, whose ice cap is rapidly melting with 1.25 m(w.e.)/year. To investigate the role of deglaciation in promoting volcanic unrest we use a cross-disciplinary approach integrating geophysical field data, laboratory rheological rock tests, and numerical finite-element analysis. Initial results from seismic data acquisition and interpretation in 2011 show seismic activity (occasionally in swarm sequences) at around a depth range of 8-13 km, indicating the presence of a magmatic reservoir in the crust. In addition, a temporary seismic network of 21 broad-band stations has been deployed in spring 2013 and continuously collected data for several months, which will help better constrain the subsurface geometry. During summer 2013 we collected samples of Tertiary basaltic bedrock from the flanks of Snæfellsjökull, which we assume to be representative for the subsurface volcanic system. Cores drilled from these samples were tri-axially deformed in a Paterson-type apparatus at a constant strain rate of 10-5 s-1, a confining pressure of 50 MPa (i.e. ~2 km depth), and a temperature ranging from 200 °C to 1000 °C (i.e. various proximities to magma chamber). From the obtained stress-strain curves the static Young's modulus is calculated to be around 35 (±2) GPa, which is not significantly influenced by increasing temperatures up to 800 °C. Beyond the elastic domain, cataclastic shear bands develop, accommodating up to 7% strain before brittle failure. The subsurface geometrical constraints from

  3. Monitoring and modeling ice-rock avalanches from ice-capped volcanoes: A case study of frequent large avalanches on Iliamna Volcano, Alaska

    USGS Publications Warehouse

    Huggel, C.; Caplan-Auerbach, J.; Waythomas, C.F.; Wessels, R.L.

    2007-01-01

    Iliamna is an andesitic stratovolcano of the Aleutian arc with regular gas and steam emissions and mantled by several large glaciers. Iliamna Volcano exhibits an unusual combination of frequent and large ice-rock avalanches in the order of 1 ?? 106??m3 to 3 ?? 107??m3 with recent return periods of 2-4??years. We have reconstructed an avalanche event record for the past 45??years that indicates Iliamna avalanches occur at higher frequency at a given magnitude than other mass failures in volcanic and alpine environments. Iliamna Volcano is thus an ideal site to study such mass failures and its relation to volcanic activity. In this study, we present different methods that fit into a concept of (1) long-term monitoring, (2) early warning, and (3) event documentation and analysis of ice-rock avalanches on ice-capped active volcanoes. Long-term monitoring methods include seismic signal analysis, and space-and airborne observations. Landsat and ASTER satellite data was used to study the extent of hydrothermally altered rocks and surface thermal anomalies at the summit region of Iliamna. Subpixel heat source calculation for the summit regions where avalanches initiate yielded temperatures of 307 to 613??K assuming heat source areas of 1000 to 25??m2, respectively, indicating strong convective heat flux processes. Such heat flow causes ice melting conditions and is thus likely to reduce the strength at the base of the glacier. We furthermore demonstrate typical seismic records of Iliamna avalanches with rarely observed precursory signals up to two hours prior to failure, and show how such signals could be used for a multi-stage avalanche warning system in the future. For event analysis and documentation, space- and airborne observations and seismic records in combination with SRTM and ASTER derived terrain data allowed us to reconstruct avalanche dynamics and to identify remarkably similar failure and propagation mechanisms of Iliamna avalanches for the past 45??years

  4. Investigating a newly discovered firn aquifer on Disko Ice Cap, west Greenland: Insights from ground observations, remote sensing, and modeling

    NASA Astrophysics Data System (ADS)

    Trusel, L. D.; Das, S. B.; Smith, B.; Kuipers Munneke, P.; Evans, M. J.; Frey, K. E.; Osman, M.; York, A.

    2015-12-01

    Expanding and intensifying surface melt have accelerated contributions from Greenland to global sea level rise in recent decades. Yet, important questions remain regarding the evolution and eventual fate of this meltwater over time and space, a fact underscored by recent observations of expansive aquifers within the Greenland Ice Sheet firn. In April 2015 we observed liquid water retained at depth in an ice cap on Disko Island, central west Greenland. Two adjacent ~20 m firn/ice cores were collected before intercepting a layer saturated with liquid water as evident by water drainage from our cores. Borehole temperature profiling confirms increasing temperature with depth, revealing 0°C isothermal firn below ~10 m depth. Detailed physical stratigraphic analyses conducted on these cores allow us to assess firn properties and their small scale (< 1m) spatial heterogeneity. Notably, multiple, thick (>1 m) and likely impermeable refrozen melt horizons exist above the inferred aquifer surface, raising questions about processes of aquifer formation. To discern the spatial character of the observed firn liquid water and melt stratigraphy, we utilize ground penetrating radar collected in 2014, as well as airborne radar data collected through NASA Operation IceBridge in 2012 and 12 days prior to our field observations in 2015. Glaciochemical analyses on our ice cores reveal preservation of an annual signal allowing derivation of net snow accumulation rates. Combined with surface mass balance modeled by RACMO2.3 and melt assessed via microwave remote sensing, we investigate the recently prevailing climatic and glaciological conditions on Disko. This work will provide new insights into mechanisms of firn aquifer formation and sustenance more broadly, as well as the representation of aquifers in existing radar observations and firn models.

  5. Analog experiments on the formation of spiral troughs on the North Polar Ice cap of Mars : Layered deposits emplaced by cyclic steps on ice

    NASA Astrophysics Data System (ADS)

    Yokokawa, M.; Izumi, N.; Naito, K.; Shimizu, H.; Yamada, T.; Greve, R.

    2012-12-01

    The spiral troughs observed on the Mars' North Polar Layered Deposits (NPLD) show intriguing features that contain a detailed stratigraphic record of surface processes in Mars' recent polar history. SHARAD radar data showed that the troughs have migrated as much as 65 km towards the north during the accumulation of the uppermost ~ 600 m of NPLD (Smith and Holt, 2010). Though they are suspected to have some relation with katabatic wind blowing on the ice cap, it has not been known how the spiral troughs are formed in detail. From their features, the spiral troughs may possibly be cyclic steps formed by a density current created by cooling of the atmosphere due to ice (Smith and Holt, 2010). Cyclic steps are spatially periodic bedforms where each wavelength is delineated by an upstream and downstream hydraulic jump. They migrate upstream keeping the same wavelength. Recently cyclic steps have been reported from various environments on the Earth, such as fluvial and deep-sea settings, and in various bed materials, such as bedrock, non-cohesive sediments, and cohesive sediments (e.g., Kostic et al., 2010). Smith et al (2011) have demonstrated that numerical simulation with a cyclic step model can show reasonable consistency with an observed migration rate. In this study, we have performed a series of physical experiments analogous to the formation of cyclic steps on ice by density currents. The experiments were conducted using the cold laboratory of the Institute of Low Temperature Science, Hokkaido University. In the case of Mars, sublimation by katabatic winds results in erosion in some places and in the other places, water included in the atmosphere blowing on ice is sublimated to become ice and deposited on the bed covered with ice. In order to model this process, we used a hydrophobic liquid that include water but do not freeze even below the ice point, i.e., mixture of silicon oil (20cS) and water (0.5 - 30 volume % of water) whose freezing point is -0.7 degrees

  6. Time Evolution and Inter-Annual Variability of Seasonal Ice on the Mars Northern Polar Cap

    NASA Astrophysics Data System (ADS)

    Mount, C.; Titus, T. N.

    2012-03-01

    We explore the temporal density variations of Mars' NPSC and use ice depth and density estimates to constrain the CROCUS date for a specific location and compare it to the CROCUS dates from three previous Mars years.

  7. Revised estimates of Greenland ice sheet thinning histories based on ice-core records

    NASA Astrophysics Data System (ADS)

    Lecavalier, Benoit S.; Milne, Glenn A.; Vinther, Bo M.; Fisher, David A.; Dyke, Arthur S.; Simpson, Matthew J. R.

    2013-03-01

    Ice core records were recently used to infer elevation changes of the Greenland ice sheet throughout the Holocene. The inferred elevation changes show a significantly greater elevation reduction than those output from numerical models, bringing into question the accuracy of the model-based reconstructions and, to some extent, the estimated elevation histories. A key component of the ice core analysis involved removing the influence of vertical surface motion on the δ18O signal measured from the Agassiz and Renland ice caps. We re-visit the original analysis with the intent to determine if the use of more accurate land uplift curves can account for some of the above noted discrepancy. To improve on the original analysis, we apply a geophysical model of glacial isostatic adjustment calibrated to sea-level records from the Queen Elizabeth Islands and Greenland to calculate the influence of land height changes on the δ18O signal from the two ice cores. This procedure is complicated by the fact that δ18O contained in Agassiz ice is influenced by land height changes distant from the ice cap and so selecting a single location at which to compute the land height signal is not possible. Uncertainty in this selection is further complicated by the possible influence of Innuitian ice during the early Holocene (12-8 ka BP). Our results indicate that a more accurate treatment of the uplift correction leads to elevation histories that are, in general, shifted down relative to the original curves at GRIP, NGRIP, DYE-3 and Camp Century. In addition, compared to the original analysis, the 1-σ uncertainty is considerably larger at GRIP and NGRIP. These changes reduce the data-model discrepancy reported by Vinther et al. (2009) at GRIP, NGRIP, DYE-3 and Camp Century. A more accurate treatment of isostasy and surface loading also acts to improve the data-model fits such that the residuals at all four sites for the period 8 ka BP to present are significantly reduced compared to the

  8. Records of Local Glacier Variability in Western Greenland During the Holocene From Lake Sediments, Ice-cap-killed Vegetation, and 10Be Dating

    NASA Astrophysics Data System (ADS)

    Schweinsberg, A.; Briner, J. P.; Miller, G. H.; Bennike, O.

    2015-12-01

    Local mountain glaciers and ice caps are common and widespread along the periphery of Greenland and provide valuable paleoclimatic records because they respond sensitively to climate change. In contrast to extensive research on Greenland Ice Sheet (GIS) margin changes, the relative timing of mountain glaciation during the Holocene is poorly documented. Here, we use a multi-proxy approach to document the timing of local glacier advance and retreat throughout the past ~10 ka in western Greenland by combining: (1) proglacial lake sediment analysis, (2) 14C-dating of ice-cap-killed in situ plants, and (3) cosmogenic 10Be dating. Radiocarbon-dated sediment cores from Sikuiui and Pauiaivik lakes, eastern Nuussuaq, provide minimum-limiting ages for local deglaciation of 9.4 ± 0.06 and 8.8 ± 0.16 ka, respectively, and are in agreement with 10Be ages of regional deglaciation that average 10.9 ± 0.7 ka (n=8). Radiocarbon ages (n=54) of in situ plants along retreating cold-based ice cap margins reveal net snowline lowering beginning ~5 ka and are concurrent with the onset of Neoglaciation recorded in both lake systems. Modes of vegetation kill dates highlight distinct ice cap expansion phases at ~3.7, ~3.0, ~1.5 ka, and during the Little Ice Age. The most pronounced snowline lowering event ~4-3 ka is expressed in both lake records by deposition of mineral-rich sediments between ~4.5 and 2.5 ka. Ice cap expansion phases are broadly correlative with elevated minerogenic input in both lakes with some modes in the vegetation ages occurring just prior to increases in mineral-rich sediment input. Published studies of the western GIS margin suggest a major cooling event between ~4.3-3.2 ka, which overlaps with periods of enhanced local glacier activity and ice cap expansion in our dataset. Lastly, the dominant ice cap expansion episode ~3.7 ka in western Greenland is synchronous with a significant snowline lowering event on Baffin Island, suggesting a common climate forcing

  9. Additions and corrections to the absorption coefficients of CO2 ice - Applications to the Martian south polar cap

    NASA Technical Reports Server (NTRS)

    Calvin, Wendy M.

    1990-01-01

    Reflectance spectra of carbon dioxide frosts were calculated using the optical constants provided by Warren (1986) for the wavelength region 2-6 microns. In comparing these calculated spectra to spectra of frosts observed in the laboratory and on the surface of Mars, problems in the optical constants presented by Warren (1986) became apparent. Absorption coefficients for CO2 ice have been derived using laboratory reflectance measurements and the Hapke (1981) model for calculating diffuse reflectance. This provides approximate values in regions where no data were previously available and indicates where corrections to the compilation by Warren (1986) are required. Using these coefficients to calculate the reflectance of CO2 ice at varying grain sizes indicates that a typical Mariner polar cap spectrum is dominated by absorptions due to CO2 frost or ice at grain sizes that are quite large, probably of the order of millimeters to centimeters. There are indications of contamination of water frost or dust, but confirmation will require more precise absorption coefficients for solid CO2 than can be obtained from the method used here.

  10. Pleistocene reduction of polar ice caps: Evidence from Cariaco Basin marine sediments

    NASA Astrophysics Data System (ADS)

    Poore, R. Z.; Dowsett, H. J.

    2001-01-01

    Sea level is projected to rise between 13 and 94 cm over the next 100 yr due to continued climate warming. The sea-level projections assume that polar ice sheets will remain stable or even increase on time scales of centuries, but controversial geologic evidence suggests that current polar ice sheets have been eliminated or greatly reduced during previous Pleistocene interglacials indicating that modern polar ice sheets have become unstable within the natural range of interglacial climates. Sea level may have been more than 20 m higher than today during a presumably very warm interglacial about 400 ka during marine isotope stage 11. Because of the implications for future sea level rise, additional study of the conflicting evidence for warmer conditions and higher sea level during marine isotope stage 11 is needed. Here we present microfossil and isotopic data from marine sediments of the Cariaco Basin supporting the interpretation that global sea level was 10 20 m higher than today during marine isotope stage 11. The increased sea level requires reduction in modern polar ice sheets and is consistent with the interpretation that the West Antarctic ice sheet and the Greenland ice sheet were absent or greatly reduced during marine isotope stage 11. Our results show a warm marine isotope stage 11 interglacial climate with sea level as high as or above modern sea level that lasted for 25 to 30 k.y. Variations in Earth's orbit around the sun (Milankovitch cycles) are considered to be a primary external force driving glacial-interglacial cycles. Current and marine isotope stage 11 Milankovitch forcing are very similar, suggesting that the present interglacial (Holocene) that began ca. 10 ka will continue for another 15 to 20 k.y. Therefore any anthropogenic climate warming will accelerate the natural process toward reduction in polar ice sheets. The potential for increased rates of sea level rise related to polar ice sheet decay should be considered as a potential natural

  11. Pleistocene reduction of polar ice caps: Evidence from Cariaco Basin marine sediments

    USGS Publications Warehouse

    Poore, R.Z.; Dowsett, H.J.

    2001-01-01

    Sea level is projected to rise between 13 and 94 cm over the next 100 yr due to continued climate warming. The sea-level projections assume that polar ice sheets will remain stable or even increase on time scales of centuries, but controversial geologic evidence suggests that current polar ice sheets have been eliminated or greatly reduced during previous Pleistocene interglacials indicating that modern polar ice sheets have become unstable within the natural range of interglacial climates. Sea level may have been more than 20 m higher than today during a presumably very warm interglacial about 400 ka during marine isotope stage 11. Because of the implications for future sea level rise, additional study of the conflicting evidence for warmer conditions and higher sea level during marine isotope stage 11 is needed. Here we present microfossil and isotopic data from marine sediments of the Cariaco Basin supporting the interpretation that global sea level was 10-20 m higher than today during marine isotope stage 11. The increased sea level requires reduction in modern polar ice sheets and is consistent with the interpretation that the West Antarctic ice sheet and the Greenland ice sheet were absent or greatly reduced during marine isotope stage 11. Our results show a warm marine isotope stage 11 interglacial climate with sea level as high as or above modern sea level that lasted for 25 to 30 k.y. Variations in Earth's orbit around the sun (Milankovitch cycles) are considered to be a primary external force driving glacial-interglacial cycles. Current and marine isotope stage 11 Milankovitch forcing are very similar, suggesting that the present interglacial (Holocene) that began ca. 10 ka will continue for another 15 to 20 k.y. Therefore any anthropogenic climate warming will accelerate the natural process toward reduction in polar ice sheets. The potential for increased rates of sea level rise related to polar ice sheet decay should be considered as a potential natural

  12. Lake Sediment Records as an Indicator of Holocene Fluctuations of Quelccaya Ice Cap, Peru and Regional Climate

    NASA Astrophysics Data System (ADS)

    Stroup, J. S.; Kelly, M. A.; Lowell, T. V.; Beal, S. A.; Smith, C. A.; Baranes, H. E.

    2012-12-01

    The past fluctuations of Quelccaya Ice Cap, (QIC; 13°S, 70°W, 5200 m asl) located in the southeastern Peruvian Andes, provide a record of tropical climate since the last glacial-interglacial transition. A detailed surficial geomorphic record of past glacial extents developed over the last several decades (e.g. Mercer and Palacios 1977; Buffen et al. 2009; Kelly et al. 2012 accepted) demonstrates that QIC is a dynamic glacial system. These records show that the ice cap was larger than present and retreating by ~11,500 yr BP, and smaller than present between ~7,000 and ~4,600 yr BP. The most recent advance occurred during the late Holocene (Little Ice Age;LIA), dated with 10Be surface exposure ages (510±90 yrs (n = 8)) (Stroup et al. in prep.). This overrode earlier deposits obscuring a complete Holocene record; we aim to address the gaps in glacial chronology using the sedimentary record archived in lakes. We retrieved two sets cores (8 and 5 m-long) from Laguna Challpacocha (13.91°S, 70.86°W, 5040 m asl), a lake that currently receives meltwater from QIC. Four radiocarbon ages from the cores suggest a continuous record dating to at least ~10,500 cal. yr BP. Variations in magnetic susceptibility, percent organic and inorganic carbon, bulk density, grayscale and X-ray fluorescence chemistry indicate changes in the amount of clastic sediment deposition. We interpret clastic sediments to have been deposited from ice cap meltwater, thus indicating more extensive ice. Clastic sediments compose the top of the core from 4 to 30 cm depth, below there is a sharp transition to organic sediments radiocarbon dated to (500±30 and 550±20 cal. yr BP). The radiocarbon ages are similar to the 10Be dated (LIA) glacial position. At least three other clastic units exist in the core; dating to ~2600-4300, ~4800-7300 and older then ~10,500 cal. yr BP based on a linear age model with four radiocarbon dates. We obtained two, ~4 m long, cores from Laguna Yanacocha (13.95°S,70.87

  13. Mass budget of Queen Elizabeth Islands glaciers and ice caps, Canada, from 1992 to present

    NASA Astrophysics Data System (ADS)

    Millan, R.; Rignot, E. J.; Mouginot, J.

    2015-12-01

    Recent studies indicate to say that the Canadian Artic Archipelago's mass loss has increased in recent years. However the role of ice dynamics changes in this area is not well known. In this study, we present a comprehensive velocity mapping of the CAA using ALOS/PALSAR, RADARSAT-1, ERS1 and Landsat data between 1992 and 2015. Glaciers speed are calculated using a speckle and feature tracking algorithm.The results reveals that three large marine-terminating glaciers have accelerated significantly after 2010, while most others have slowed down or retreated to a sill to become similar to land-terminating glaciers. By combining the velocities of these glaciers with ice thickness measurements from NASA's Operation IceBridge, we calculate their ice discharge. The fluxes of these glaciers increased significantly since 2000 with a marked increase after 2011. The comparison of ice discharge with the surface mass balance from RACMO-2, shows that these glaciers came out of balance after 2011, which is also a time period where their discharge almost doubled. The analysis of RACMO-2 reveals an increase in runoff between 1970's and today and a precipitation with no significant trend. We digitalize the calving front positions of the glaciers and show an increasing rate retreat since 1976. We conclude that global pattern of velocity changes shows that the mass losses due to surface mass balance will likely going to raise in the coming years and that ice discharge will have a smaller part in the contribution of the CAA to sea level rise.

  14. Early 21st-Century Mass loss of the North-Atlantic Glaciers and Ice Caps (Arne Richter Award for Outstanding Young Scientists Lecture)

    NASA Astrophysics Data System (ADS)

    Wouters, Bert; Ligtenberg, Stefan; Moholdt, Geir; Gardner, Alex S.; Noel, Brice; Kuipers Munneke, Peter; van den Broeke, Michiel; Bamber, Jonathan L.

    2016-04-01

    Historically, ice loss from mountain glaciers and ice caps has been one of the largest contributors to sea level rise over the last century. Of particular interest are the glaciers and ice caps in the North-Atlantic region of the Arctic. Despite the cold climate in this area, considerable melting and runoff occurs in summer. A small increase in temperature will have an immediate effect on these processes, so that a large change in the Arctic ice volume can be expected in response to the anticipated climate change in the coming century. Unfortunately, direct observations of glaciers are sparse and are biased toward glaciers systems in accessible, mostly maritime, climate conditions. Remote sensing is therefore essential to monitor the state of the the North-Atlantic glaciers and ice caps. In this presentation, we will discuss the progress that has been made in estimating the ice mass balance of these regions, with a particular focus on measurements made by ESA's Cryosat-2 radar altimeter mission (2010-present). Compared to earlier altimeter mission, Cryosat-2 provides unprecedented coverage of the cryosphere, with a resolution down to 1 km or better and sampling at monthly intervals. Combining the Cryosat-2 measurements with the laser altimetry data from ICESat (2003-2009) gives us a 12 yr time series of glacial mass loss in the North Atlantic. We find excellent agreement between the altimetry measurements and independent observations by the GRACE mission, which directly 'weighs' the ice caps, albeit at a much lower resolution. Mass loss in the region has increased from 120 Gigatonnes per year in 2003-2009 to roughly 140 Gt/yr in 2010-2014, with an important contribution from Greenland's peripheral glaciers and ice caps. Importantly, the mass loss is not stationary, but shows large regional interannual variability, with mass loss shifting between eastern and western regions from year to year. Comparison with regional climate models shows that these shifts can be

  15. The Dispersal of the 8.2 ka Lake Agassiz Drainage Waters Into the NW Atlantic: Working Hypothesis

    NASA Astrophysics Data System (ADS)

    Hillaire-Marcel, C.; de Vernal, A.; Weaver, A.; Fisher, D. A.; Solignac, S.

    2004-12-01

    inconclusive. However, off Hudson Strait, near the outlet of the final drainage of Lake Agassiz, a few marine records show a very high time resolution (up to 15 cm/year), and minimum benthic mixing. In these records, some evidence for a very short "sedimentological event" has been found, but none show any indication for a significant concomitant change in sea-surface salinity or temperature, based on micropaleontological or isotopic data. The question thus arises of the fate of the near 160 * 103 km3 of drainage waters released into the Labrador Sea, possibly in a couple of years, based on glaciological models. We hypothesize here that this water merged into the Labrador Sea, after a long subglacial tunnel trajectory, as a dense turbiditic flow, with possibly two spreading routes: one surface branch, nearshore, on the Labrador Shelf, and a deep underflow branch flowing practically along the NAMOC route. In both cases, the influence on open ocean sea surface conditions would have been negligible. In this scenario, the opening of Hudson Bay and the final collapse of the Laurentide ice sheet into two small residual ice caps would have resulted in a major atmospheric reorganization that could explain both long distance correlative climate responses and the influence of more proximal moisture sources indicated by the GRIP records.

  16. Ice cap melting and low-viscosity crustal root explain the narrow geodetic uplift of the Western Alps

    NASA Astrophysics Data System (ADS)

    Chéry, J.; Genti, M.; Vernant, P.

    2016-04-01

    More than 10 years of geodetic measurements demonstrate an uplift rate of 1-3 mm/yr of the high topography region of the Western Alps. By contrast, no significant horizontal motion has been detected. Two uplift mechanisms have been proposed: (1) the isostatic response to denudation responsible for only a fraction of the observed uplift and (2) the rebound induced by the Wurmian ice cap melting which predicts a broader uplifting region than the one evidenced by geodetic observations. Using a numerical model to fit the geodetic data, we show that a crustal viscosity contrast between the foreland and the central part of the Alps, the latter being weaker with a viscosity of 1021 Pa s, is needed. The vertical rates are enhanced if the strong uppermost mantle beneath the Moho is interrupted across the Alps, therefore allowing a weak vertical rheological anomaly over the entire lithosphere.

  17. Simulated influences of Lake Agassiz on the climate of central North America 11,000 years ago

    USGS Publications Warehouse

    Hostetler, S.W.; Bartlein, P.J.; Clark, P.U.; Small, E.E.; Solomon, A.M.

    2000-01-01

    Eleven thousand years ago, large lakes existed in central and eastern North America along the margin of the Laurentide Ice Sheet. The large-scale North American climate at this time has been simulated with atmospheric general circulation models, but these relatively coarse global models do not resolve potentially important features of the mesoscale circulation that arise from interactions among the atmosphere, ice sheet, and proglacial lakes. Here we present simulations of the climate of central and eastern North America 11,000 years ago with a high-resolution, regional climate model nested within a general circulation model. The simulated climate is in general agreement with that inferred from palaeoecological evidence. Our experiments indicate that through mesoscale atmospheric feedbacks, the annual delivery of moisture to the Laurentide Ice Sheet was diminished at times of a large, cold Lake Agassiz relative to periods of lower lake stands. The resulting changes in the mass balance of the ice sheet may have contributed to fluctuations of the ice margin, thus affecting the routing of fresh water to the North Atlantic Ocean. A retreating ice margin during periods of high lake level may have opened an outlet for discharge of Lake Agassiz into the North Atlantic. A subsequent advance of the ice margin due to greater moisture delivery associated with a low lake level could have dammed the outlet, thereby reducing discharge to the North Atlantic. These variations may have been decisive in causing the Younger Dryas cold even.

  18. The Role of Sublimation and Condensation in the Dynamics of Aeolian Ice Sedimentation Waves on the North Polar Cap of Mars

    NASA Astrophysics Data System (ADS)

    Herny, C.; Carpy, S.; Bourgeois, O.; Spiga, A.; Rodriguez, S.; Massé, M.; Le Mouélic, S.

    2016-09-01

    We explore the role of sublimation and condensation of water vapor in the development of ice sedimentation waves on the North Polar Cap of Mars. Our observations and simulations are in accordance with the hypothesis that sedimentation waves can migrate upwind or downwind.

  19. Identification of Younger Dryas outburst flood path from Lake Agassiz to the Arctic Ocean.

    PubMed

    Murton, Julian B; Bateman, Mark D; Dallimore, Scott R; Teller, James T; Yang, Zhirong

    2010-04-01

    The melting Laurentide Ice Sheet discharged thousands of cubic kilometres of fresh water each year into surrounding oceans, at times suppressing the Atlantic meridional overturning circulation and triggering abrupt climate change. Understanding the physical mechanisms leading to events such as the Younger Dryas cold interval requires identification of the paths and timing of the freshwater discharges. Although Broecker et al. hypothesized in 1989 that an outburst from glacial Lake Agassiz triggered the Younger Dryas, specific evidence has so far proved elusive, leading Broecker to conclude in 2006 that "our inability to identify the path taken by the flood is disconcerting". Here we identify the missing flood path-evident from gravels and a regional erosion surface-running through the Mackenzie River system in the Canadian Arctic Coastal Plain. Our modelling of the isostatically adjusted surface in the upstream Fort McMurray region, and a slight revision of the ice margin at this time, allows Lake Agassiz to spill into the Mackenzie drainage basin. From optically stimulated luminescence dating we have determined the approximate age of this Mackenzie River flood into the Arctic Ocean to be shortly after 13,000 years ago, near the start of the Younger Dryas. We attribute to this flood a boulder terrace near Fort McMurray with calibrated radiocarbon dates of over 11,500 years ago. A large flood into the Arctic Ocean at the start of the Younger Dryas leads us to reject the widespread view that Agassiz overflow at this time was solely eastward into the North Atlantic Ocean.

  20. A subtropical fate awaited freshwater discharged from glacial Lake Agassiz

    SciTech Connect

    Condron, Alan; Winsor, Peter

    2011-02-10

    The 8.2 kyr event is the largest abrupt climatic change recorded in the last 10,000 years, and is widely hypothesized to have been triggered by the release of thousands of kilometers cubed of freshwater into the North Atlantic Ocean. Using a high-resolution (1/6°) global, ocean-ice circulation model we present an alternative view that freshwater discharged from glacial Lake Agassiz would have remained on the continental shelf as a narrow, buoyant, coastal current, and would have been transported south into the subtropical North Atlantic. The pathway we describe is in contrast to the conceptual idea that freshwater from this lake outburst spread over most of the sub-polar North Atlantic, and covered the deep, open-ocean, convection regions. This coastally confined freshwater pathway is consistent with the present-day routing of freshwater from Hudson Bay, as well as paleoceanographic evidence of this event. In this study, using a coarse-resolution (2.6°) version of the same model, we demonstrate that the previously reported spreading of freshwater across the sub-polar North Atlantic results from the inability of numerical models of this resolution to accurately resolve narrow coastal flows, producing instead a diffuse circulation that advects freshwater away from the boundaries. To understand the climatic impact of freshwater released in the past or future (e.g. Greenland and Antarctica), the ocean needs to be modeled at a resolution sufficient to resolve the dynamics of narrow, coastal buoyant flows.

  1. Area, volume and mass changes of southeast Vatnajökull ice cap, Iceland, from the Little Ice Age maximum in the late 19th century to 2010

    NASA Astrophysics Data System (ADS)

    Hannesdóttir, H.; Björnsson, H.; Pálsson, F.; Aðalgeirsdóttir, G.; Guðmundsson, S.

    2014-09-01

    Area and volume changes and the average geodetic mass balance of the non-surging outlet glaciers of southeast Vatnajökull ice cap, Iceland, during different time periods between ~1890 and 2010, are derived from a multi-temporal glacier inventory. A series of digital elevation models (DEMs) (∼1890, 1904, 1936, 1945, 1989, 2002, 2010) have been compiled from glacial geomorphological features, historical photographs, maps, aerial images, DGPS measurements and a LiDAR survey. Given the mapped bedrock topography we estimate relative volume changes since the end of the Little Ice Age (LIA) ~1890. The variable dynamic response of the outlets, assumed to have experienced similar climate forcing, is related to their different hypsometry, bedrock topography, and the presence of proglacial lakes. In the post-LIA period the glacierized area decreased by 164 km2 and the glaciers had lost 10-30% of their ~1890 area by 2010. The glacier surface lowered by 150-270 m near the terminus and the outlet glaciers collectively lost 60 ± 8 km3 of ice, which is equivalent to 0.154 ± 0.02 mm of sea level rise. The relative volume loss of individual glaciers was in the range of 15-50%, corresponding to a geodetic mass balance between -0.70 and -0.32 m w.e. a-1. The rate of mass loss was most negative in the period 2002-2010, on average -1.34 ± 0.12 m w.e. a-1, which lists among the most negative mass balance values recorded worldwide in the early 21st century. From the data set of volume and area of the outlets, spanning the 120 years post-LIA period, we evaluate the parameters of a volume-area power law scaling relationship.

  2. Area, Volume and Mass Changes of Southeast Vatnajökull Ice Cap, Iceland, from the Little Ice Age Maximum in the Late 19th Century to 2010

    NASA Astrophysics Data System (ADS)

    Hannesdóttir, H.; Bjornsson, H.; Pálsson, F.; Adalgeirsdottir, G.; Gudmundsson, S.

    2014-12-01

    Areal and volume changes and the average geodetic mass balance of the non-surging outlet glaciers of southeast Vatnajökull ice cap, Iceland, during different time periods between 1890 and 2010, are derived from a multi-temporal glacier inventory. A series of digital elevation models (DEMs) (1890, 1904, 1936, 1945, 1989, 2002, 2010) have been compiled from geomorphological features, historical photographs, maps, aerial images, DGPS measurements and a LiDAR survey. Given the mapped bedrock topography, relative volume changes since the end of the Little Ice Age (LIA) 1890 have been estimated. The variable dynamic response of the outlet glaciers to assumed similar climate forcing, is related to their different hypsometry, bedrock topography, and the presence of proglacial lakes. In the post-LIA period the glacierized area decreased by 164 km2 and the glaciers had lost 10-30% of their 1890 area by 2010. The glacier surface lowered by 150-270 m near the terminus and the outlet glaciers collectively lost 60±8 km3 of ice, which is equivalent to 0.154 mm of sea level rise. The relative volume loss of individual glaciers was in the range of 15-50%, corresponding to a geodetic mass balance between -0.70 and -0.32 m w.e. a-1. The rate of mass loss was most negative in 2002-2010, on average -1.34 m w.e. a-1, which lists among the most negative mass balance values recorded worldwide in the early 21st century. From the data set of volume and area of the outlet glaciers, spanning the whole 120 year post-LIA period, we estimate the parameters of a volume area power-law scaling relationship.

  3. Current use and legacy pesticide deposition to ice caps on Svalbard, Norway

    NASA Astrophysics Data System (ADS)

    Ruggirello, Rachel M.; Hermanson, Mark H.; Isaksson, Elisabeth; Teixeira, Camilla; ForsströM, Sanja; Muir, Derek C. G.; Pohjola, Veijo; van de Wal, Roderik; Meijer, Harro A. J.

    2010-09-01

    Transport and deposition of current use (CUP) and legacy pesticides (LP) and residual products to the Arctic have been documented in abiotic matrices. These observations show that some "low-persistence" pesticides with high OH· reaction rates are stable enough to accumulate in a polar environment. In 2005, we drilled an ice core on Holtedahlfonna, one of the major ice fields on Svalbard, Norway to measure the input of 47 CUPs and 17 LPs to a high-elevation abiotic environment with no local pesticide sources. Of these, 9 CUPs and 12 LPs were observed in at least one of 6 core segments dating to 1953: 15 of these were found in enough core segments to reveal time-related trends. CUPs often observed included chlorpyrifos, dacthal, α- and β- endosulfan, endosulfan sulfate, trifluralin, and γ-HCH. LPs most often observed included methoxychlor, α- and γ-chlordane, cis- and trans- nonachlor, endrin, dieldrin, and p,p'-DDE. In our comparison of core burdens at Holtedahlfonna and Austfonna (220 km ENE from Holtedahlfonna), we found twice as many CUPs at Austfonna along with greater amounts of dieldrin, methoxychlor, α-endosulfan and chlorpyrifos suggesting different accumulation processes or sources. Air mass back trajectories over a 10-year period of comparison between sites (1986-1995) show air mass flow from Eurasia 74% of the time to Austfonna and 45% to Holtedahfonna which may account for some of the differences.

  4. First steps toward development of a stable isotope forward model for tropical ice cores: cold air incursions and snow days at Quelccaya Ice Cap, Peru

    NASA Astrophysics Data System (ADS)

    Hurley, J. V.; Vuille, M. F.; Hardy, D. R.; Burns, S. J.

    2014-12-01

    We are working towards a forward-model reconstruction of the South American Summer Monsoon (SASM) for the last millennium from the Quelccaya Ice Cap (QIC) d18O record. QIC receives precipitation almost exclusively during the SASM season. Initial efforts focus on dynamics that yield precipitation at this receding tropical ice cap, and how they relate to the hydrogen and oxygen stable isotopes. We present over a decade of daily snow-height change observations from the summit of QIC. Accumulation of snow (~2 m yr-1) at the summit occurs October through April, peaking in December. Net monthly snow-height change is negative May through September, though positive snow height change days do occur throughout the year. Snow height change time-series are used to develop d18O age-models for annual snow collected in vertical profiles near the summit of QIC since 2003. Snow d18O decreases during austral summer from about -17 to -24 per mil VSMOW. Post-depositional alteration of late summer snow during austral winter elevates d18O from about -24 to about -15 per mil VSMOW. Timing of 90thpercentile positive snow-height change events at QIC corresponds with regional precipitation and outgoing longwave radiation (OLR) anomalies that are dynamically triggered by cold air incursions propagating from the midlatitudes east of the Andes into the Amazon Basin. Precipitation and OLR anomalies migrate northwest in about 2-3 days from near Rio de la Plata to central Peru. The convective anomalies are the result of southerly horizontal wind anomalies in the lower troposphere that advect cold extratropical air equatorward. Composite analysis of satellite measurements shows that cold air incursions are associated with negative water vapor dD (~ -40 per mil) anomalies at QIC. We expect that snow stable isotope values from QIC are thus not only records of the deep overturning component of the monsoon circulation but also of synoptic scale monsoon disturbances. Cold air incursions into the South

  5. Dynamics of three outlet glaciers on the Vatnajökull ice cap reconstructed through landsystem analysis

    NASA Astrophysics Data System (ADS)

    Maclachlan, John; Lee, Rebecca; Eyles, Carolyn

    2016-04-01

    Landsystem analysis uses genetically related landform-sediment assemblages, known as landsystem tracts, as evidence in the reconstruction of the geomorphic evolution of a landscape and subsequently provides further insight into the morphogenetic record. When used in conjunction with sedimentological data, results from this methodology are used to inform models of the subglacial conditions through the movement characteristics of the overriding glacier. Ultimately landsystem analysis allows modern systems to be used as analogues for ancient systems, which in turn facilitates more accurate paleoenvironmental reconstruction of ancient glacial sediments. The proglacial till plains, consisting of subglacial, proglacial and supraglacial sediments and landforms of three outlet glaciers of the Vatnajökull Ice Cap in southeast Iceland were explored using a combination of remote sensing techniques, geospatial analysis and field investigations. The three glaciers selected for study (Svínafellsjökull, Skaftafellsjökull and Morsárjökull) are separated by small mountain ridges but lie within close spatial proximity, limiting climatic variability on their behavior but allowing for variability in local influences such as variability in valley morphology. Although the three glaciers are sourced by the same ice cap and are within close proximity there are wide variations in the type, distribution and scale of landforms in the proglacial region including the presence of streamlined features, the relative relief of the landforms, and sediment types. Initial mapping of the proglacial region of each glacier was performed using geospatial software to explore and analyze LiDAR data and aerial imagery obtained from the Icelandic Meteorological Office. A high-resolution digital elevation model (DEM) of the proglacial region of each glacier was created from these remotely sensed data to illustrate the spatial distribution and scale of landforms. These features were ground-checked using

  6. Surges of outlet glaciers from the Drangajökull ice cap, northwest Iceland

    NASA Astrophysics Data System (ADS)

    Brynjólfsson, Skafti; Schomacker, Anders; Korsgaard, Niels J.; Ingólfsson, Ólafur

    2016-09-01

    Surface elevation and volume changes of the Drangajökull surge-type glaciers, Reykjarfjarðarjökull and Leirufjarðarjökull, were studied by comparing digital elevation models that pre-date and post-date their most recent surges. Annual glacier-frontal measurements were used to estimate average ice velocities during the last surge of the glaciers. The observations show a distinct ice discharge, most of which was from the upper reservoir areas, down to the receiving areas during the surges. The surface draw-down in the reservoir areas was usually 10-30 m during the surges, while the thickening of the receiving areas was significantly more variable, on the order of 10-120 m. Despite a negative geodetic net mass balance derived from the digital elevation models, the reservoir areas have been gaining mass since the surge terminations. This surface thickening along with considerable ablation of the receiving areas will most likely return the glacier surface profiles to the pre-surge stage. Our results indicate that (a) greatest surface thinning in the upper reservoir areas of Drangajökull rather than proximal to the equilibrium line during Vatnajökull surges and (b) development of Drangajökull surges that resembles Svalbard surge-type glaciers rather than Vatnajökull surge-type glaciers. The contrasting surge characteristics could be explained by differences in glacier geometry, topography and substratum of the Drangajökull and Vatnajökull surge-type glaciers.

  7. Quelccaya Ice Cap extents during the last glacial-interglacial transition: evidence for rapid climate changes in the southern tropics during Younger Dryas time

    NASA Astrophysics Data System (ADS)

    Kelly, M. A.; Lowell, T. V.; Applegate, P. J.; Smith, C.; Phillips, F. M.; Hudson, A. M.

    2011-12-01

    Paleoglacial data from the Peruvian Andes shed light on the mechanisms which influenced rapid climate changes during late glacial time. Here, we present a radiocarbon-based chronology of Quelccaya Ice Cap (QIC) fluctuations during the last glacial-interglacial transition that registers paleoclimatic conditions at high altitude (~5000 m asl) in the southern tropics (~14°S, 70°W). Subsequent to the last glacial maximum, major recession of QIC was underway by ~17.2 ka. The timing of this recession is prior to the warming registered by Greenland ice cores, but similar to the timing of mountain glacier recession in both Northern and Southern hemispheres, likely influenced by rising atmospheric CO2 concentrations. At ~12.6 ka, QIC underwent the most significant readvance during the last glacial-interglacial transition, reaching a position ~4-5 km from the modern ice cap margin and depositing a prominent set of moraines that is nearly continuous on the western side of the ice cap. Recession from this rapid readvance was underway by ~12.3 ka, and QIC was within its Little Ice Age extent (~1-2 km from the modern ice margin) by ~11.2 ka. The readvance of QIC occurred early in the Younger Dryas cold interval (12.9-11.7 ka) and ice cap recession was underway while Greenland ice cores registered continuously cold conditions. Whereas QIC receded by at least 3-4 km between 12.3 and 11.2 ka, paleo-lake levels and other indicators of moisture on the Bolivian Altiplano, document wet conditions in the southern tropics until the end of the Younger Dryas. Thus, we suggest that QIC recession at ~12.3 ka was associated with warming in the tropics that occurred during middle Younger Dryas time. Warming at this time is also registered by climate proxy records from the Cariaco Basion, in the northern tropical Atlantic region, and in the eastern tropical Pacific Ocean. Recent modeling studies suggest that a southerly position of the Intertropical Convergence Zone (ITCZ) associated with

  8. The use of airborne radar reflectometry to characterize near-surface snow/firn stratigraphy on Devon Ice Cap, Canadian Arctic: A path to identifying refrozen melt layers

    NASA Astrophysics Data System (ADS)

    Rutishauser, A.; Grima, C.; Sharp, M. J.; Blankenship, D. D.; Young, D. A.; Dowdeswell, J. A.

    2015-12-01

    Under present warming conditions, summer surface melt has been observed to intensify and shift towards higher elevations in the accumulation zones of Canadian Arctic ice caps. Consequently, more meltwater percolates into the near surface snow and firn, and refreezes as ice layers. This process can lead to a significant increase in firn densification rates. Knowledge of spatiotemporal variations of the near-surface firn density, especially the distribution of ice layer formation is of great importance when assessing mass change estimates from repeat altimetry measurements. Here, we present an approach for characterizing the near-surface firn stratigraphy and determining the spatial distribution of refrozen melt layers on Devon Ice Cap, using the surface echo from airborne radio-echo sounding (RES) measurements. The RES surface echo is affected by the upper few meters of snow/firn/ice and thus contains information about the near-surface properties. More specifically, the radar surface return is a combination of a coherent (Pc) and a scattering signal component (Pn). Pc is related to the dielectric constant of the probed surface, whereas Pn is related to the near surface roughness. Hence, different near-surface snow/firn properties can be investigated by analyzing the signal components Pc and Pn and their spatial variability. The Radar Statistical Reconnaissance (RSR) methodology [1] allows the extraction of Pc and Pn from the surface radar return, which then can be used to compute near-surface roughness and firn density estimates. We apply the RSR method to RES data collected on Devon Ice Cap and determine Pc and Pn values. We then compare the results to ground based RES measurements and shallow firn cores (~11 m deep) collected along the airborne RES flight lines. This comparison shows that variations in the scattering coefficient Pn correlate to changes in the pattern of near-surface firn stratigraphy revealed by the ground based RES data and firn cores. Based on

  9. A renewed argument for crystal size control of ice sheet strain rates

    NASA Astrophysics Data System (ADS)

    Cuffey, K. M.; Thorsteinsson, T.; Waddington, E. D.

    2000-12-01

    At present, it is generally believed that crystal size has no direct influence on strain rate in the ice sheets and that the fraction of strain rate enhancement there which is not ascribable to c axis fabric is due to impurity content. Here we challenge this view because it is not consistent with recent results from analyses of deformation at Meserve Glacier and instead ascribe residual enhancement in the ice sheets to variations in crystal size. We resurrect the idea that variations of crystal size can be an important part of the total shear enhancement in the ice sheets, though agree with Paterson that this effect is generally dominated by variations of crystal fabric. We propose that the enhanced shear strain rate of ice age ice in southern Greenland, as inferred from tilt of the Dye 3 borehole, can be explained as a result of combined fabric variations and crystal size variations, with these two ice properties accounting for roughly 70% and 30% of the average enhancement, respectively. Permitting a grain size dependence of ice viscosity also resolves the quandary concerning closure and tilt of the Agassiz Ice Cap borehole.

  10. Geo-Spatial Browse and Distribution of NSF-OPP's Antarctic Ice and Climate Data via the Web: Antarctic Cryosphere Access Portal (A-CAP)

    NASA Astrophysics Data System (ADS)

    Bauer, R.; Scambos, T.; Haran, T.; Maurer, J.; Bohlander, J.

    2008-12-01

    A prototype of the Antarctic Cryosphere Access Portal (A-CAP) has been released for public use. Developed at the National Snow and Ice Data Center (NSIDC) Antarctic Glaciological Data Center (AGDC), A-CAP aims to be a geo-visualization and data download tool for AGDC data and other Antarctic-wide parameters, including glaciology, ice core data, snow accumulation, satellite imagery, digital elevation models (DEMs), sea ice concentration, and many other cryosphere-related scientific measurements. The user can zoom in to a specific region as well as overlay coastlines, placenames, latitude/longitude, and other geographic information. In addition to providing an interactive Web interface, customizable A-CAP map images and source data are also accessible via specific Uniform Resource Locator strings (URLs) to a standard suite of Open Geospatial Consortium (OGC) services: Web Map Service (WMS), Web Feature Service (WFS), and Web Coverage Service (WCS). The international specifications of these services provide an interoperable framework for sharing maps and geospatial data over the Internet, allowing A-CAP products to be easily exchanged with other data centers worldwide and enabling remote access for users through OGC-compliant software applications such as ArcGIS, Google Earth, ENVI, and many others. A-CAP is built on MapServer, an Open Source development environment for building spatially-enabled Internet applications. MapServer uses data sets that have been formatted as GeoTIFF or Shapefile to allow rapid sub-setting and over-the-Web presentation of large geospatial data files, and has no requirement for a user-installed client software package (besides a Web browser).

  11. Early to middle Pleistocene Arctic coastal ice caps in the Northern Interior Plains of Canada, a comparison with northeastern Siberian coastal uplands

    NASA Astrophysics Data System (ADS)

    Duk-Rodkin, A.; Barendregt, R. W.; Velichko, A. A.; Galloway, J. M.; McNeil, D.

    2012-12-01

    A stratigraphic record of four to five ice-cap developments during the last 2.6 myr was discovered along the Northern Interior Plains (NIP) of the Canadian Continental Arctic Coast below 500 m elevation. Paleomagnetism, macrofossils, foraminifera, till fabrics and pebble lithologies were obtained from outcrops. This glacial stratigraphic record is less extensive than that found west of the continental divide in the Northern Canadian Cordillera, where at least 11 glaciations occurred in the last 2.7 Ma and where uplift along the south side of NW North America during the Pliocene set the stage for large scale glaciations. These coastal mountains and the continental divide created a double rain shadow effect that limited Pacific moisture reaching the NIP. East of the continental divide, moisture supply was only sufficient to form valley glaciers in five of the glacial periods that affected the Cordillera. The NIP was also affected by five glaciations. Ice-caps developed periodically and in the late Pleistocene, the Laurentide Ice Sheet covered all of the NIP. During interglacial times, the NIP experienced dry steppe conditions, similar to modern northern climates found in regions of extreme continentality. The geographic setting along the eastern Siberian coast is comparable to conditions of the NIP, but no record of glaciations exists from upland areas near the Arctic Ocean. Moisture supply and temperature were likely insufficient to form local ice caps at low coastal elevations (<600 m) during the Pleistocene; only in the mountains to the south did glaciers form. Climatic conditions leading to the formation of ice-caps in the NIP may be related to local influences, such as an open or partially open Arctic Ocean. Ice caps may have formed during interglacial times when warm waters periodically entered the Arctic Ocean. There is sufficient data linking marine life from the Bering Sea to western Canadian Arctic to support the idea that warm waters from the NE Pacific

  12. Evaporites on Ice: Experimental Assessment of Evaporites Formation on Antarctica (and on Martian North Polar Residual Cap)

    NASA Astrophysics Data System (ADS)

    Losiak, Anna; Derkowski, Arkadiusz; Skala, Aleksander; Trzcinski, Jerzy

    2016-04-01

    Evaporites are highly water soluble minerals, formed as a result of the evaporation or freezing of bodies of water. They are common weathering minerals found on rocks (including meteorites) on Antarctic ice sheet [1,2,3,4]. The water necessary for the reaction is produced by melting of ice below the dark-colored meteorites which can heat up to a few degrees above 0 °C due to insolation heating during wind-free summer days [5,6]. The Martian North Polar Residual Cap is surrounded by a young [7] dune field that is rich in evaporitic mineral: gypsum [8]. Its existence implies that relatively recently in the Martian history (in late Amazonian, when surface conditions were comparable to the current ones) there was a significant amount of liquid water present on the Mars surface. One of the proposed solutions to this problem is that gypsum is formed by weathering on/in ice [9,10,11,12,13], similarly to the process occurring on the Antarctic ice sheet. Recently, Losiak et al. 2015 showed that that during the warmest days of the Martian summer, solar irradiation may be sufficient to melt pure water ice located below a layer of dark dust particles lying on the steepest sections of the equator-facing slopes of the spiral troughs within Martian NPRC. Under the current irradiation conditions, melting is possible in very restricted areas of the NPRC and it lasts for up to couple of hours, but during the times of high irradiance at the north pole [15] this process could have been much more pronounced. Liquid water can be metastable at the NPRC because the pressure during the summer season is ~760-650 Pa [16] which is above the triple point of water. The rate of free-surface "clean" liquid water evaporation under average Martian conditions determined experimentally by [17] is comparable to the rate of melting determined by [21] (if there is no wind at the surface). In the current study we attempt to determine experimentally how many melting-freezing cycles are required to form

  13. A subtropical fate awaited freshwater discharged from glacial Lake Agassiz

    DOE PAGES

    Condron, Alan; Winsor, Peter

    2011-02-10

    The 8.2 kyr event is the largest abrupt climatic change recorded in the last 10,000 years, and is widely hypothesized to have been triggered by the release of thousands of kilometers cubed of freshwater into the North Atlantic Ocean. Using a high-resolution (1/6°) global, ocean-ice circulation model we present an alternative view that freshwater discharged from glacial Lake Agassiz would have remained on the continental shelf as a narrow, buoyant, coastal current, and would have been transported south into the subtropical North Atlantic. The pathway we describe is in contrast to the conceptual idea that freshwater from this lake outburstmore » spread over most of the sub-polar North Atlantic, and covered the deep, open-ocean, convection regions. This coastally confined freshwater pathway is consistent with the present-day routing of freshwater from Hudson Bay, as well as paleoceanographic evidence of this event. In this study, using a coarse-resolution (2.6°) version of the same model, we demonstrate that the previously reported spreading of freshwater across the sub-polar North Atlantic results from the inability of numerical models of this resolution to accurately resolve narrow coastal flows, producing instead a diffuse circulation that advects freshwater away from the boundaries. To understand the climatic impact of freshwater released in the past or future (e.g. Greenland and Antarctica), the ocean needs to be modeled at a resolution sufficient to resolve the dynamics of narrow, coastal buoyant flows.« less

  14. Gravitational enrichment of {sup 84}Kr/{sup 36}Ar ratios in polar ice caps: A measure of firm thickness and accumulation temperature

    SciTech Connect

    Craig, H.; Wiens, R.C.

    1996-03-22

    Measurements of {sup 84}Kr/{sup 36}Ar ratios in Greenland ice show that gravitational separation in the firn layer is responsible for the enrichments relative to atmospheric ratios. The {sup 84}Kr/{sup 36}Ar ratio is enriched by 12.8 per mil and is 24 times the {sup 18}O/{sup 16}O enrichment in trapped O{sub 2}, as predicted for gravitational fractionation. Because gravitational enrichment depends on firn thickness, which in turn depends on annual mean temperature, noble gas ratios provide a method for determining paleotemperatures and ancient firn thicknesses in polar ice caps. The gravitational effects are modulated by about 10 to 15 percent by atmospheric concentration changes caused by temperature effects on oceanic gas solubilities. The availability of five noble gases should make it possible to deconvolute the solubility and gravitational enrichments for calibration of {sup 18}O paleo-temperature throughout the polar ice sheets. 11 refs., 2 figs., 2 tabs.

  15. Perchlorate Found by Phoenix Could Provide a Mobile Brine Sludge at the Bed of Mars Northern Ice Cap that Would Allow Flow with Very Low Basal Temperatures: Possible Mechanism for Water Table Re-Charge

    NASA Astrophysics Data System (ADS)

    Fisher, D. A.; Hecht, M.; Kounaves, S.; Catling, D.

    2009-03-01

    The north cap of Mars has basal temperature that precludes the flow of ice. Phoenix discovered polar soils contain perchlorate salts. These salts depress the melting point so it could form a sludge that provides a mobile bed that moves the ice outwards.

  16. Measurements of the north polar cap of Mars and the earth's Northern Hemisphere ice and snow cover

    NASA Technical Reports Server (NTRS)

    Foster, J.; Owe, M.; Capen, C.

    1986-01-01

    The boundaries of the polar caps of Mars have been measured on more than 3000 photographs since 1905 from the plate collection at the Lowell Observatory. For the earth, the polar caps have been accurately mapped only since the mid 1960s when satellites were first available to synoptically view the polar regions. The polar caps of both planets wax and wane in response to changes in the seasons, and interannual differences in polar cap behavior on Mars as well as earth are intimately linked to global energy balance. Data on the year to year variations in the extent of the north polar caps of Mars and earth have been assembled and compared, although only 6 years of concurrent data were available for comparison.

  17. Thermal cracking of CO2 slab ice as the main driving force for albedo increase of the martian seasonal polar caps

    NASA Astrophysics Data System (ADS)

    Philippe, S.; Schmitt, B.; Beck, P.; Brissaud, O.

    2015-10-01

    Understanding the microphysical processes occuring on the Martian seasonal cap is critical since their radiative properties can affect the martian climate. A well documented phenomenom is the albedo increase of the Martian seasonal caps during spring, Fig.1. There are a lot of hypotheses that have been proposed as an explanation for this observation : the decrease of the CO2 grain size [2], a cleaning process of the CO2 slab that would imply either the sinking or the ejection of the dust contained in its volume ([1], [2], [5]), a water-layer accumulation on the top of the slab [5], the role played by aerosols [2] etc ... So far, no experimental simulations have been realized to discriminate between these processes. We designed an experiment to investigate the hypothesis of CO2 ice grain size decrease through thermal cracking as well as that of dust segregation as the possible reasons for albedo increase.

  18. Eruptive history of Chimborazo volcano (Ecuador): A large, ice-capped and hazardous compound volcano in the Northern Andes

    NASA Astrophysics Data System (ADS)

    Samaniego, Pablo; Barba, Diego; Robin, Claude; Fornari, Michel; Bernard, Benjamin

    2012-04-01

    century, and the average time interval between the events is about 1000 yr, Chimborazo must be considered as a potentially active volcano. The presence of a thick ice cap covering the summit, its steep flanks and its position above the populated lowland area of Riobamba and Ambato, are factors that result in a high potential risk.

  19. A late Holocene metal record of Andean climate and anthropogenic activity in lake sediments near Quelccaya Ice Cap, Peru

    NASA Astrophysics Data System (ADS)

    Beal, S. A.; Kelly, M. A.; Jackson, B. P.; Stroup, J. S.; Osterberg, E. C.

    2011-12-01

    The tropical hypothesis maintains that major changes in global climate are motivated by phenomena based at tropical latitudes. Evidence for this hypothesis lies in: modern-day observations of El Niño Southern Oscillation (ENSO); East African lake sediment records of Intertropical Convergence Zone (ITCZ) position that precede high-latitude changes; and the potential for ITCZ shifts to cause major CO2 degassing from the Southern Ocean. In order to improve the understanding of these phenomena we present an ~1800 year record of atmospheric metal deposition in a lake sediment core near Quelccaya Ice Cap, Peru (13.9 °S). In June, 2010 we collected a 1.45 meter-long core from Yanacocha - a small, closed-basin tarn that has been isolated from glacial input since ~11,200 BP. The chronology for the core is based on 4 of 6 AMS 14C dates on aquatic macrofossils and one sharp Zr/Ti anomaly at 36 cm, likely derived from the 350 BP eruption of Huaynaputina. We completely digested organic-rich core samples at 1 cm resolution using HNO3, HCl, and HF in a closed-vessel microwave system, and then analyzed the digestates for 67 metals by inductively coupled plasma mass spectrometry. Here we show fluxes of lithogenic metals (Fe, Nb, Ti, and Zr) that reflect changes in wind strength and aridity, fluxes of lithogenic metal isotopes (REEs and Pb) that reflect wind direction, and enrichment factors (EFs) of metals (Ag, As, Cd, Cu, Hg, and Pb) that reflect anthropogenic activity. Five episodic peaks in lithogenic metal fluxes, centered around 1800, 1300, 900, 600, and 100 yrs BP, are thought to result from either drier or windier conditions, potentially caused by a northern ITCZ position or a more persistent El Niño state. The provenance of atmospheric deposition, evidenced by REE ratios (light REEs / heavy REEs), suggest that high lithogenic fluxes are associated with a change in wind direction, possibly caused by a change in the ENSO state, which will be explored with forthcoming Pb

  20. Creating Original Opera at Lake Agassiz Elementary School.

    ERIC Educational Resources Information Center

    Sherwood, Connie; And Others

    1994-01-01

    In 1993 Lake Agassiz School in North Dakota received a Knight Foundation grant so teachers and students could participate in a program to learn how to create an opera. The program instructed teachers on how students could maximize their understanding about producing an opera. The school formed a partnership with the Metropolitan Opera Guild of New…

  1. Closing the balance (Louis Agassiz Medal Lecture)

    NASA Astrophysics Data System (ADS)

    van den Broeke, Michiel

    2015-04-01

    The 4000 Gt of ice that has been lost since 2003 by the ice sheets of Greenland and West Antarctica accounts for about 1/3 of recent global mean sea level rise. Especially the Greenland ice sheet is far out of balance: each year, 30% more mass leaves the ice sheet than is gained by snowfall at its surface; in Antarctica, this imbalance is currently less than 10%. To make matters worse, the mass loss is accelerating: each year it increases by about 10%, making it likely that the ice sheets will soon become the main source of global mean sea level rise. Given their huge volumes, they could remain so for centuries to come. Thirty years ago, the concept of rapid melting of the large ice sheets was purely theoretical. But since that time, the evolution of remote sensing techniques (altimetry, gravimetry and interferometry), in situ observations (automatic weather stations, mass balance and ice velocity measurements) and climate models has revealed a surprising diversity of mass loss mechanisms. This ranges from the relatively steady acceleration of large West-Antarctic ice streams to the highly variable (in space and time) flow speed of outlet glaciers in Greenland. Moreover, both ice sheets experience large interannual fluctuations in snowfall and melt, temporarily masking or accentuating the mass loss. In spite of all the technological developments, there is still room for exciting discoveries. In April 2011, a reservoir of liquid water twice the size of the Netherlands was discovered in the firn in southeast Greenland. In July 2012, an extreme melt event affected the entire Greenland ice sheet, with meltwater runoff destroying infrastructure in west Greenland that had been in place since the 1950's. And in 2014, two separate studies concluded that the mass loss in West Antarctica appears to be irreversible. When will it be possible to model and robustly predict the fully coupled system of atmosphere, ocean, sea ice and ice sheets? To start answering that question, we

  2. Glacial areas, lake areas, and snowlines from 1975 to 2012: status of the Cordillera Vilcanota, including the Quelccaya Ice Cap, northern central Andes, Peru

    NASA Astrophysics Data System (ADS)

    Hanshaw, M. N.; Bookhagen, B.

    2013-02-01

    Glaciers in the tropical Andes of southern Peru have received limited attention compared to glaciers in other regions (both near and far), yet remain of vital importance to agriculture, fresh water, and hydropower supplies of downstream communities. Little is known about recent glacial-area changes and how the glaciers in this region respond to climate changes, and, ultimately, how these changes will affect lake and water supplies. To remedy this, we have used 144 multi-spectral satellite images spanning almost four decades, from 1975-2012, to obtain glacial and lake-area outlines for the understudied Cordillera Vilcanota region, including the Quelccaya Ice Cap. In a second step, we have estimated the snowline altitude of the Quelccaya Ice Cap using spectral unmixing methods. We have made the following four key observations: first, since 1988 glacial areas throughout the Cordillera Vilcanota have been declining at a rate of 5.46 ± 1.70 km2 yr-1 (22-yr average, 1988-2010, with 95% confidence interval). The Quelccaya Ica Cap, specifically, has been declining at a rate of 0.67 ± 0.18 km2 yr-1 since 1980 (31-yr average, 1980-2011, also with 95% confidence interval); Second, decline rates for individual glacierized regions have been accelerating during the past decade (2000-2011) as compared to the preceding decade (1990-2000); Third, the snowline of the Quelccaya Ice Cap is retreating to higher elevations as glacial areas decrease, by a total of almost 300 m between its lowest recorded elevation in 1989 and its highest in 1998; and fourth, as glacial regions have decreased, 61% of lakes connected to glacial watersheds have shown a roughly synchronous increase in lake area, while 84% of lakes not connected to glacial watersheds have remained stable or have declined in area. Our new and detailed data on glacial and lake areas over 37 yr provide an important spatiotemporal assessment of climate variability in this area. These data can be integrated into further studies

  3. Glacial areas, lakes areas, and snowlines from 1975-2012: Status of the Cordillera Vilcanota, including the Quelccaya Ice Cap, northern central Andes, Peru

    NASA Astrophysics Data System (ADS)

    Hanshaw, Maiana Natania

    Glaciers in the tropical Andes of southern Peru have received limited attention compared to glaciers in other regions (both near and far), yet remain of vital importance to agriculture, fresh water, and hydropower supplies of downstream communities. Little is known about recent glacial-area changes and how the glaciers in this region respond to climate changes, and, ultimately, how these changes will affect lake and water supplies. To remedy this, we have used 144 multi-spectral satellite images spanning almost four decades, from 1975-2012, to obtain glacial and lake-area outlines for the understudied Cordillera Vilcanota region, including the Quelccaya Ice Cap. In a second step, we have estimated the snowline altitude of the Quelccaya Ice Cap using spectral unmixing methods. We have made the following four key observations: First, since 1988 glacial areas throughout the Cordillera Vilcanota have been declining at a rate of 5.46 +/- 1.70 km2/yr (22-year average, 1988-2010, with 95 % confidence interval). The Quelccaya Ica Cap, specifically, has been declining at a rate of 0.67 +/- 0.18 km2/yr since 1980 (31-year average, 1980-2011, also with 95 % confidence interval); Second, decline rates for individual glacierized regions have been accelerating during the past decade (2000-2011) as compared to the preceding decade (1990-2000); Third, the snowline of the Quelccaya Ice Cap is retreating to higher elevations as glacial areas decrease, by a total of almost 300 m between its lowest recorded elevation in 1989 and its highest in 1998; and fourth, as glacial regions have decreased, 61 % of lakes connected to glacial watersheds have shown a roughly synchronous increase in lake area, while 84 % of lakes not connected to glacial watersheds have remained stable or have declined in area. Our new and detailed data on glacial and lake areas over 37 years provide an important spatiotemporal assessment of climate variability in this area. These data can be integrated into further

  4. A New Hot Water Drill for Glaciological, Geochemical and Biological Studies of the Subglacial Lakes Beneath the Vatnajokull Ice Cap, Iceland

    NASA Astrophysics Data System (ADS)

    Thorsteinsson, T.; Elefsen, S.; Johannesson, T.; Thorsteinsson, T.

    2005-12-01

    is then heated to 95 °C in a high-pressure pump and passed through filters and a UV-sterilization unit prior to entering the hose and drill stem. The new system has been tested with success on the Langjokull ice cap in June 2005, where the snow melting efficiency was found to be 500 liters/hr and the water consumption during maximum load was 480 liters/hr. The average drilling speed was 45 m/hr in the depth interval 0-100 m, in ice that did not contain any layers of volcanic tephra. The sterilization efficiency of the system is currently being investigated and it is hoped that the new system will be capable of drilling into subglacial lakes with a minimal risk of borehole contamination. Among the targets for future drillings are two hitherto unsampled water bodies, the Skaftarkatlar (Skaftar cauldrons), located beneath 550 m thick ice cover 10-15 km NW of Grimsvotn. The cauldrons empty out in jokulhlaups every 2 years on average, and existing data on the jokulhlaup hydrographs and floodwater geochemistry make these subglacial water bodies prime candidates for future glaciological, geochemical and biological investigations. References: [1] H. Bjornsson (2002), Glob. Planet. Change 35, 255-271. [2] J.C. Priscu et al. (1999), Science, 286, 2141-2144. [3] E.J. Gaidos et al., Astrobiology, 4, 327-344. [4] Thorsteinsson et al. (2003), 3rd Mars Polar Conference, Alberta, Canada (Abstract # 8134).

  5. Late Pleistocene Palaeoenvironments of the Southern Lake Agassiz Basin, USA

    NASA Astrophysics Data System (ADS)

    Yansa, Catherine H.; Ashworth, Allan C.

    2005-03-01

    Macroscopic plant remains, pollen, insect and mollusc fossils recovered from a cut bank on the Red River in North Dakota, USA, provide evidence that an extensive wetland occupied the southern basin of Lake Agassiz from 10 230 to 9900 14C yr BP. Marsh-dwelling plants and invertebrates had colonised the surface of a prograding delta during the low-water Moorhead Phase of Lake Agassiz. A species of Salix (willow) was abundant along distributary channels, and stands of Populus tremuloides (aspen), Ulmus sp. (elm), Betula sp. (birch), and Picea sp. (spruce) grew on the better-drained sand bars and beach ridges. Most of the species of plants, insects, and molluscs represented as fossils are within their existing geographic ranges. Based on a few species with more northerly distributions, mean summer temperature may have been about 1-2°C lower than the present day. No change in species composition occurred in the transition from the Younger Dryas to Preboreal. At the time that the wetland existed, Lake Agassiz was draining either eastward to the North Atlantic Ocean or northwestward to the Arctic Ocean. The wetland was drowned during the Emerson Phase transgression that resulted in meltwater draining southward to the Gulf of Mexico after 9900 14C yr BP.

  6. Glacial areas, lake areas, and snow lines from 1975 to 2012: status of the Cordillera Vilcanota, including the Quelccaya Ice Cap, northern central Andes, Peru

    NASA Astrophysics Data System (ADS)

    Hanshaw, M. N.; Bookhagen, B.

    2014-03-01

    Glaciers in the tropical Andes of southern Peru have received limited attention compared to glaciers in other regions (both near and far), yet remain of vital importance to agriculture, fresh water, and hydropower supplies of downstream communities. Little is known about recent glacial-area changes and how the glaciers in this region respond to climate changes, and, ultimately, how these changes will affect lake and water supplies. To remedy this, we have used 158 multi-spectral satellite images spanning almost 4 decades, from 1975 to 2012, to obtain glacial- and lake-area outlines for the understudied Cordillera Vilcanota region, including the Quelccaya Ice Cap. Additionally, we have estimated the snow-line altitude of the Quelccaya Ice Cap using spectral unmixing methods. We have made the following four key observations: first, since 1988 glacial areas throughout the Cordillera Vilcanota (1988 glacial area: 361 km2) have been declining at a rate of 3.99 ± 1.15 km2 yr-1 (22 year average, 1988-2010, with 95% confidence interval (CI), n = 8 images). Since 1980, the Quelccaya Ice Cap (1980 glacial area: 63.1 km2) has been declining at a rate of 0.57 ± 0.10 km2 yr-1 (30 year average, 1980-2010, with 95% CI, n = 14). Second, decline rates for individual glacierized regions have been accelerating during the past decade (2000-2010) as compared to the preceding decade (1988-1999) with an average increase from 37.5 to 42.3 × 10-3 km2 yr-1 km-2 (13%). Third, glaciers with lower median elevations are declining at higher rates than those with higher median elevations. Specifically, glaciers with median elevations around 5200 m a.s.l. are retreating to higher elevations at a rate of ~1 m yr-1 faster than glaciers with median elevations around 5400 m a.s.l. Fourth, as glacial regions have decreased, 77% of lakes connected to glacial watersheds have either remained stable or shown a roughly synchronous increase in lake area, while 42% of lakes not connected to glacial

  7. The impact of volcanic aerosols on the energy- and mass balance of Langjökull ice cap, SW-Iceland

    NASA Astrophysics Data System (ADS)

    Gudmundsson, S.; Pálsson, F.; Björnsson, H.; Magnússon, E.; Thorsteinsson, T.; Haraldsson, H. H.

    2012-12-01

    The mass balance of the Langjökull ice cap in SW-Iceland has been monitored since 1997. Since the summer 2001 two automatic weather stations (AWSs) have been used to estimate the full energy balance of the glacier surface; one near to the terminus the other close to ELA. Following the subglacial eruptions in the Eyjafjallajökull volcano 14 April to 22 May 2010, and Grímsvötn volcano 21 - 28 May 2011, airborne tephra was deposited on the surface of all the major ice caps in Iceland. The mass balance and AWS records for Langjökull provide valuable data to study the impact of aerosol deposition on albedo and radiative forcing. Here we compare the mass- and energy balance of the Langjökull ice cap during the exceptional circumstances of 2010 and 2011 to the more climatically controlled mass- and energy balance of 1997-2009. Dark tephra from the 2010 Eyjafjallajökull eruption, deposited on Langjökull 18-19 May (3-4 days before the eruption stopped), produced a thin layer of fine grained dark trachyandesite tephra particles on the surface (fraction of a mm). This highly reduced the surface albedo and greatly enhanced melting, especially within the accumulation area, where up to three years of accumulation melted. The resulting negative net balance in 2010 was threefold the average during the preceding warm decade. In 2011, basalt tephra dust from the Grímsvötn eruption was deposited on Langjökull (on 11 June, 2 weeks after the end of the eruption, deposited by wind). The quantity of dust was less than in 2010, and the color of the basaltic tephra particles not as dark, hence smaller reduction in albedo. The weather during the summer 2011 was not favorable to ablation on Langjökull; exceptionally cold period from early May to mid June with occasional snowfall, delayed the start of the ablation season by 3 weeks compared to typical years. Thus, despite the lower albedo, causing fast melt rates after 11 June, the total summer ablation was close to the average

  8. Could massive Arctic sea ice export to the North Atlantic be the real cause of abrupt climate change during the last deglaciation?

    NASA Astrophysics Data System (ADS)

    Coletti, A. J.; Condron, A.

    2015-12-01

    Using a coupled ocean-sea ice model (MITgcm), we investigate whether the break-up and mobilization of thick, multiyear, Arctic sea ice might have supplied enough freshwater to the Nordic Seas to reduce North Atlantic Deep Water (NADW) formation and weaken the Atlantic Meridional Overturning Circulation (AMOC). Numerical simulations of a Last Glacial Maximum (LGM) environment show the potential for sea ice to grow to ~30m thick, storing ~1.41x105 km3 of freshwater as sea ice in the Arctic (this is ~10 times the volume of freshwater stored in the modern-day Arctic). Releasing this volume of sea ice from the Arctic in 1-yr is equivalent to a high-latitude freshwater forcing of ~4.5 Sv, which is comparable (or larger) in magnitude to most meltwater floods emanating from land-based glacial lakes (e.g. Agassiz) during the last deglaciation. Opening of the Bering Strait and Barents Sea are two plausible mechanisms that may have initiated sea ice mobilization. Opening Bering Strait increases sea ice transport through the Fram Strait by 7% and results in a 22% weakening of AMOC for 2000 years and a >3°C warming in the Arctic basin at 800 m depth. Opening Barents Sea to simulate a collapse of the Fennoscandian ice sheet has little impact on Arctic sea ice and freshwater export to the North Atlantic, but weakens AMOC ~8%. In a simulation with both straits open there is a transition to near-modern sea ice circulation pattern and a 24% reduction in AMOC. Experiments with the Bering Strait open and sea ice artificially capped to 10 m show barely any difference to those when sea ice can grow to ~30m, suggesting that changes in topography have a much greater impact on AMOC than the freshwater forcing from sea ice melting in the Nordic Seas.

  9. Volatile-rich Crater Interior Deposits in the Polar Regions of Mars: Evidence for Ice Cap Advance and Retreat

    NASA Technical Reports Server (NTRS)

    Russell, Patrick S.; Head, James W.; Hecht, Michael H.

    2003-01-01

    Many craters on Mars are partially filled by distinctive material emplaced by post-impact processes. This crater fill material is an interior mound which is generally separated from the walls of the crater by a trough that may be continuous along the crater circumference (i.e. a ring-shaped trough), or which may only partially contact the crater walls (i.e. a crescent-shaped trough). The fill deposit is frequently offset from the crater center and may be asymmetric in plan view. Populations of such craters include those in the circum-south polar cap region, in Arabia Terra, associated with the Medusae Fossae Formation, and in the northern lowlands proximal to the north polar cap. We focus on those craters in circumpolar regions and assess their relationship to polar cap advance and retreat, especially the possibility that fill material represents remnants of a formerly larger contiguous cap. Volatile-rich deposits have the property of being modifiable by the local stability of the solid volatile, which is governed by local energy balance. Here we test the hypothesis that asymmetries in volatile fill shape, profile, and center-location within a crater result from asymmetries in local energy balance within the crater, due mainly to variation of solar insolation and radiative effects of the crater walls over the crater interior. Model profiles of crater fill are compared with MOLA topographic profiles to assess this hypothesis. If asymmetry in morphology and location of crater fill are consistent with radiative-dominated asymmetries in energy budget within the crater, then 1) the volatile-rich composition of the fill is supported (this process should not be effective at shaping volcanic or sedimentary deposits), and 2) the dominant factor determining the observed shape of volatile-rich crater fill is the local radiative energy budget (and erosive processes such as eolian deflation are secondary or unnecessary). We also use a geographic and energy model approach to

  10. Two episodes of meltwater influx from glacial Lake Agassiz into the Lake Michigan basin and their climatic contrasts

    USGS Publications Warehouse

    Colman, Steven M.; Keigwin, L.D.; Forester, R.M.

    1994-01-01

    Two episodes of meltwater influx from glacial Lake Agassiz are recorded as prominent sedimentologic, isotopic, magnetic, and faunal signatures in southern Lake Michigan profundal sediments. As a tributary to the main path of eastward Lake Agassiz flow, southern Lake Michigan recorded only the largest, catastrophic discharges. The distinctive Wilmette Bed, a massive gray mud that interrrupts laminated red glaciolacustrine clays, marks the first episode, which occurred near the beginning of the Younger Dryas cooling events. The associated discharge may have played a role in the inception or severity of the Younger Dryas event. An oxygen isotope excursion in biogenic carbonate and changes in ostracode assemblages mark the second episode, which appears to have had at least two pulses, dated by accelerator mass spectrometer 14C ages on biogenic carbonate at about 8.9 and 8.6 ka. The second episode occurred during the early Holocene peak in global meltwater discharge and apparently had little widespread climatic or oceanographic effect. The contrast between the effects associated with these two episodes of meltwater discharge emphasizes the complexity of the ice sheet-ocean-climate system. -Authors

  11. Geodetic mass balance record with rigorous uncertainty estimates deduced from aerial photographs and lidar data - Case study from Drangajökull ice cap, NW Iceland

    NASA Astrophysics Data System (ADS)

    Magnússon, E.; Muñoz-Cobo Belart, J.; Pálsson, F.; Ágústsson, H.; Crochet, P.

    2016-01-01

    In this paper we describe how recent high-resolution digital elevation models (DEMs) can be used to extract glacier surface DEMs from old aerial photographs and to evaluate the uncertainty of the mass balance record derived from the DEMs. We present a case study for Drangajökull ice cap, NW Iceland. This ice cap covered an area of 144 km2 when it was surveyed with airborne lidar in 2011. Aerial photographs spanning all or most of the ice cap are available from survey flights in 1946, 1960, 1975, 1985, 1994 and 2005. All ground control points used to constrain the orientation of the aerial photographs were obtained from the high-resolution lidar DEM. The lidar DEM was also used to estimate errors of the extracted photogrammetric DEMs in ice- and snow-free areas, at nunataks and outside the glacier margin. The derived errors of each DEM were used to constrain a spherical semivariogram model, which along with the derived errors in ice- and snow-free areas were used as inputs into 1000 sequential Gaussian simulations (SGSims). The simulations were used to estimate the possible bias in the entire glaciated part of the DEM and the 95 % confidence level of this bias. This results in bias correction varying in magnitude between 0.03 m (in 1975) and 1.66 m (in 1946) and uncertainty values between ±0.21 m (in 2005) and ±1.58 m (in 1946). Error estimation methods based on more simple proxies would typically yield 2-4 times larger error estimates. The aerial photographs used were acquired between late June and early October. An additional seasonal bias correction was therefore estimated using a degree-day model to obtain the volume change between the start of 2 glaciological years (1 October). This correction was largest for the 1960 DEM, corresponding to an average elevation change of -3.5 m or approx. three-quarters of the volume change between the 1960 and the 1975 DEMs. The total uncertainty of the derived mass balance record is dominated by uncertainty in the volume

  12. High-amplitude, centennial-scale climate oscillations during the last glacial in the western Third Pole as recorded in the Guliya ice cap

    NASA Astrophysics Data System (ADS)

    Thompson, L. G.; Yao, T.; Mosley-Thompson, E.; Wu, G.; Davis, M. E.; Tian, L.; Lin, P. N.

    2015-12-01

    The Guliya ice cap, located in the Kunlun Mountains in the western Third Pole (TP) region near the northern limit of the southwest monsoon influence, may be the only non-polar ice field that provides detailed histories of climate and environment over the last glacial cycle. A continuous climate record from an ice core drilled in 1992 contains Eemian ice, and basal temperatures measured that year confirmed that the record was not being removed from the bottom. The δ18O record throughout Marine Isotope Stage 2 (MIS2) displays the occurrence of high-amplitude (~20‰) episodes of ~200-year periodicity, and the aerosol records suggest snow cover, regional vegetation and fire frequency that vary in synchrony. These oscillations might reflect the movement of the northernmost penetration of the monsoon precipitation through the Late Glacial Stage, which is restricted by the topographic barrier posed by the Kunlun range, and might also reflect solar-driven nonlinearities in the climate system such as sudden shifts in the jet stream. Recent model simulations suggest that glacial cooling over China was significantly amplified by stationary waves, and the Guliya MIS2 oscillations could reflect cyclical variability in these waves. These results are supported by clumped isotope thermometry of carbonates from the Chinese Loess Plateau, which indicate a 6 to 7oC decrease in Last Glacial Maximum summer temperatures. These studies will lead to a better understanding of the mechanisms driving such high-frequency, high-amplitude oscillations. A review of the 2015 Sino-American cooperative ice core drilling program on Guliya is presented. This program will serve as a flagship for the TP Environment Program, an international, multidisciplinary collaboration among professionals and students in 14 countries designed to investigate environmental changes across the TP. The rapidly warming TP contains ~46,000 glaciers that collectively hold one of Earth's largest stores of fresh water that

  13. Application of new GPS aircraft control/display system to topographic mapping of the Greenland ice cap

    SciTech Connect

    Wright, C.W.; Swift, R.N.

    1996-10-01

    NASA has completed an accurate baseline map of the elevation of the Greenland ice sheet using a scanning airborne lidar in combination with differential kinematic Global Positioning System (GPS) techniques. The present plan is to reoccupy these survey lines which are spread over the major regions of the ice sheet beginning in 1997. The results are expected to provide a quantitative answer on how the ice sheet is responding to regional climatic changes. Navigation to within +-100 m of the desired track over lengths of up to 1,000 km are a requirement for the success of the program. To meet this navigational requirement, NASA developed the GPS Flight Management System (GFMS). GFMS is a PC based system that uses the real-time position update from a single GPS receiver located on the aircraft to calculate a cross-track error and generates aircraft steering commands which are converted into analog Instrument Landing System (OM) signals using an RF generator. TU GFMS also updates a cockpit display. 4 refs., 6 figs.

  14. Mapping of the water ice content within the Martian surficial soil on the periphery of the retreating seasonal northern polar cap based on the TES and the OMEGA data

    NASA Astrophysics Data System (ADS)

    Kuzmin, R. O.; Zabalueva, E. V.; Evdokimova, N. A.; Christensen, P. R.

    2012-11-01

    Analysis of seasonal data from the Mars Global Surveyor Thermal Emission Spectrometer (TES) shows a significant increase in thermal inertia during autumn, winter and spring in the middle and high latitudes of Mars. At each stage of the northern seasonal polar cap's recession in spring a distinct high thermal inertia (HTI) annulus arises around the cap's edge. Within this annulus, we estimated and mapped the springtime water ice content in the daily thermal skin depth layer using spring and summer values of the thermal inertia in TES surface footprints. The results show that the average water content in the surface soil within the HTI annulus varies from ˜5 vol % at the early stages of the seasonal polar cap retreating (Ls = 340°-360°) to ˜1 vol % at later stages (Ls = 60°-70°). Maximum values of water ice content within the HTI annulus occur at Ls = 0°-20° (2-6 vol %) and Ls = 20°-40° (4-10 vol %). We analyzed the temporal and spatial relationship between the HTI annuli and the water ice (WI) annuli at the edge of the northern seasonal polar cap. The water ice within the WI annuli was mapped using a water ice spectral index (the absorption band depth at the 1.5 μm wavelength) derived from the OMEGA (Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité) imaging spectrometer aboard the Mars Express spacecraft. Recent OMEGA observations show that the WI annuli formation arises only around the retreating northern seasonal polar cap, never around the retreating southern seasonal cap. For this reason our study is confined only to the northern hemisphere. The observed relationship between the HTI and WI annuli in the northern hemisphere of Mars indicates a close physical interdependence between these two phenomena. Our results confirm that the seasonal permafrost exposed by the retreating northern polar cap (within the HTI annuli) is actively involved today in the condensation and sublimation processes in the modern water cycle on Mars. The water

  15. The Arctic Gakkel Vents (AGAVE) Expedition: Technology Development and the Search for Deep-Sea Hydrothermal Vent Fields Under the Arctic Ice Cap

    NASA Astrophysics Data System (ADS)

    Reves-Sohn, R. A.; Singh, H.; Humphris, S.; Shank, T.; Jakuba, M.; Kunz, C.; Murphy, C.; Willis, C.

    2007-12-01

    Deep-sea hydrothermal fields on the Gakkel Ridge beneath the Arctic ice cap provide perhaps the best terrestrial analogue for volcanically-hosted chemosynthetic biological communities that may exist beneath the ice-covered ocean of Europa. In both cases the key enabling technologies are robotic (untethered) vehicles that can swim freely under the ice and the supporting hardware and software. The development of robotic technology for deep- sea research beneath ice-covered oceans thus has relevance to both polar oceanography and future astrobiological missions to Europa. These considerations motivated a technology development effort under the auspices of NASA's ASTEP program and NSF's Office of Polar Programs that culminated in the AGAVE expedition aboard the icebreaker Oden from July 1 - August 10, 2007. The scientific objective was to study hydrothermal processes on the Gakkel Ridge, which is a key target for global studies of deep-sea vent fields. We developed two new autonomous underwater vehicles (AUVs) for the project, and deployed them to search for vent fields beneath the ice. We conducted eight AUV missions (four to completion) during the 40-day long expedition, which also included ship-based bathymetric surveys, CTD/rosette water column surveys, and wireline photographic and sampling surveys of remote sections of the Gakkel Ridge. The AUV missions, which lasted 16 hours on average and achieved operational depths of 4200 meters, returned sensor data that showed clear evidence of hydrothermal venting, but for a combination of technical reasons and time constraints, the AUVs did not ultimately return images of deep-sea vent fields. Nevertheless we used our wireline system to obtain images and samples of extensive microbial mats that covered fresh volcanic surfaces on a newly discovered set of volcanoes. The microbes appear to be living in regions where reducing and slightly warm fluids are seeping through cracks in the fresh volcanic terrain. These discoveries

  16. Multi-scale, multi-year investigations of H2O ice deposits observed in late summer, at the time of minimum extent of the Southern polar cap of Mars

    NASA Astrophysics Data System (ADS)

    Langevin, Y.; Seelos, K.; Russell, P.; Bibring, J.-P.; Vincendon, M.; Gondet, B.

    2012-09-01

    Extended regions exhibiting water ice signatures have been observed by OMEGA on Mars Express at the boundary of the CO2 perennial cap during the first months of operation of the mission [1]. This period in late summer (Ls 335°-340°) corresponds to the minimum extent of the ice coverage around the South pole. The retreat of the South seasonal cap, spectrally dominated by CO2 frost [2, 3] ends at Ls 310° - 315° for years which do not present a global dust storm [4], and the first signs of H2O frost recondensation are observed before the fall equinox (Ls 0°). A large outlier had been identified by OMEGA observations at longitudes from 290°E to 10°E. It was shown to extend over an area representing ~ 25% of the surface of the perennial cap by Themis observations [5]. The H2O covered regions at the boundary of the cap and within the outlier have an intermediate albedo (30-35%) between that of the perennial cap (> 60%) and that of surrounding terrains (~ 20%). These southern surface H2O ice deposits constitute a major source of atmospheric H2O at the end of the Southern summer. They are much smaller in extent than the northern perennial cap and they are exposed to sunlight for 2 months in late summer instead of 6 months in the North over the whole summer. This is in line with the highly asymmetric seasonal cycle of atmospheric water [6, 7]. In late 2009, OMEGA observations of the South cap at the time of minimum extent (Ls 340°) showed a much larger extent of H2O ice signatures compared to what had been observed in early 2004 [1]. H2O ice covered regions appeared homogeneous at the km scales corresponding to OMEGA observations. A series of CRISM observations were planned for the next southern fall season (mid-2011), in order to further investigate the time variability of the southern H2O ice deposits within the outlier at the 20 m scale (CRISM high resolution mode). Combining OMEGA and CRISM observations demonstrates that variegation of surface H2O ice is mainly

  17. Historical and Future Black Carbon Deposition on the Three Ice Caps: Ice Core Measurements and Model Simulations from 1850 to 2100

    NASA Technical Reports Server (NTRS)

    Bauer, Susanne E.; Bausch, Alexandra; Nazarenko, Larissa; Tsigaridis, Kostas; Xu, Baiqing; Edwards. Ross; Bisiaux, Marion; McConnell, Joe

    2013-01-01

    Ice core measurements in conjunction with climate model simulations are of tremendous value when examining anthropogenic and natural aerosol loads and their role in past and future climates. Refractory black carbon (BC) records from the Arctic, the Antarctic, and the Himalayas are analyzed using three transient climate simulations performed with the Goddard Institute for Space Studies ModelE. Simulations differ in aerosol schemes (bulk aerosols vs. aerosol microphysics) and ocean couplings (fully coupled vs. prescribed ocean). Regional analyses for past (1850-2005) and future (2005-2100) carbonaceous aerosol simulations focus on the Antarctic, Greenland, and the Himalayas. Measurements from locations in the Antarctic show clean conditions with no detectable trend over the past 150 years. Historical atmospheric deposition of BC and sulfur in Greenland shows strong trends and is primarily influenced by emissions from early twentieth century agricultural and domestic practices. Models fail to reproduce observations of a sharp eightfold BC increase in Greenland at the beginning of the twentieth century that could be due to the only threefold increase in the North American emission inventory. BC deposition in Greenland is about 10 times greater than in Antarctica and 10 times less than in Tibet. The Himalayas show the most complicated transport patterns, due to the complex terrain and dynamical regimes of this region. Projections of future climate based on the four CMIP5 Representative Concentration Pathways indicate further dramatic advances of pollution to the Tibetan Plateau along with decreasing BC deposition fluxes in Greenland and the Antarctic.

  18. Acceptance of the Theory of Evolution in America: Louis Agassiz vs. Asa Gray

    ERIC Educational Resources Information Center

    Wolfe, Elaine Claire Daughetee

    1975-01-01

    Provides some background information on the contributions of Louis Agassiz and Asa Gray to the history of American science as these two men disagreed concerning the ideas in Darwin's "The Orgin of Species." (PB)

  19. Selenium and metal concentrations in waterbird eggs and chicks at Agassiz National Wildlife Refuge, Minnesota

    USGS Publications Warehouse

    Custer, T.W.; Custer, Christine M.; Eichhorst, B.A.; Warburton, D.

    2007-01-01

    Exceptionally high cadmium (Cd) and chromium (Cr) concentrations were reported in eggs, feathers, or livers of selected waterbird species nesting at Agassiz National Wildlife Refuge (Agassiz) in 1994. Ten- to 15-day-old Franklin's gull (Larus pipixcan), black-crowned night-heron (Nycticorax nycticorax), and eared grebe (Podiceps nigricollis) chicks were collected in 1998, 1999, and 2001 at Agassiz and analyzed for selenium (Se) and metals including Cd and Cr. Freshly laid eggs were collected in 2001 from Franklin's gull, black-crowned night-heron, eared grebe, and pied-billed grebe (Podilymbus podiceps) nests at Agassiz. Based on a multivariate analysis, the pattern of Se and metal concentrations differed among species for eggs, chick feathers, and chick livers. Low Cd and Cr concentrations were measured in eggs, chick livers, and chick feathers of all four species. Mercury concentrations in black-crowned night-heron and eared grebe eggs collected from Agassiz in 2001 were lower than concentrations reported in 1994. Se and metal concentrations, including Cd and Cr, in waterbird eggs and chicks collected at Agassiz in 1998, 1999, and 2001 were not at toxic levels. ?? 2007 Springer Science+Business Media, LLC.

  20. North Polar Cap

    NASA Technical Reports Server (NTRS)

    2004-01-01

    7 September 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a 1.4 m/pixel (5 ft/pixel) view of a typical martian north polar ice cap texture. The surface is pitted and rough at the scale of several meters. The north polar residual cap of Mars consists mainly of water ice, while the south polar residual cap is mostly carbon dioxide. This picture is located near 85.2oN, 283.2oW. The image covers an area approximately 1 km wide by 1.4 km high (0.62 by 0.87 miles). Sunlight illuminates this scene from the lower left.

  1. Ice core studies of anthropogenic sulfate and nitrate trends in the Arctic

    NASA Astrophysics Data System (ADS)

    Goto-Azuma, Kumiko; Koerner, Roy M.

    2001-03-01

    Ice core studies have shown that sulfate and nitrate concentrations in Arctic snow have increased significantly since the end of the 19th century due to the influx of anthropogenic pollutants transported from industrialized regions. Trends of increasing sulfate and nitrate concentrations in snow are evident in all the ice core data from Greenland, the Canadian Arctic, and Svalbard. Temporal patterns, however, show spatial variation. In the area around Dye 3, south Greenland, significant increases in sulfate are found beginning in the 1890s. Increases in nitrate began ˜50 years later. A similar pattern is seen at Penny Ice Cap, Baffin Island, in the Canadian low Arctic. In contrast, both sulfate and nitrate concentrations started to increase significantly in the 1940s on Agassiz Ice Cap, Ellesmere Island, in the Canadian high Arctic; and Snøfjellafonna, Svalbard. At Summit, central Greenland, and sites in north Greenland, sharp sulfate increases occurred at about the turn of the 20th century and again about 1940 or 1950, where the latter increase is the greater of the two. At these central and north Greenland sites, significant increases in nitrate began about 1940 or 1950. The difference between the magnitude and timing of increasing trends of the sulfate ions at these sites can be attributed to their having different source regions and pathways for these pollutant ions. The pollutant sources appear to be North America for south Greenland and Baffin Island, Eurasia, for Ellesmere Island and Svalbard, and both North America and Eurasia for central and north Greenland.

  2. Hydrogeologic setting of the Glacial Lake Agassiz Peatlands, northern Minnesota

    USGS Publications Warehouse

    Siegel, Donald I.

    1981-01-01

    Seven test holes drilled in the Glacial Lake Agassiz Peatlands indicate that the thickness of surficial materials along a north-south traverse parallel to Minnesota Highway 72 ranges from 163 feet near Blackduck, Minnesota to 57 feet about 3 miles south of Upper Red Lake. Lenses of sand and gravel occur immediately above bedrock on the Itasca moraine and are interbedded with lake clay and till under the peatlands. Vertical head gradients measured in a piezometer nest near Blackduck on the moraine are downward, indicative of recharge to the regional ground-water-flow system. Vertical head gradients are upward in a piezometer nest on a sand beach ridge in the peatlands 12 miles north of Upper Red Lake. Numerical sectional models indicate that this discharge probably comes from local flow systems recharged from ground-water mounds located under large raised bogs.

  3. Evaluating the Surface Conditions of Temperate Ice Cap Hofsjḋ {{o}}kull, Central Iceland, using H/A/barh {α } Decomposition of Fully-Polarimetric UAVSAR Data

    NASA Astrophysics Data System (ADS)

    Minchew, B. M.; Buckley, S. M.; Hensley, S.

    2010-12-01

    Fully-polarimetric SAR offers a means to study the dynamic changes in the near-surface of glaciers. Various decomposition methods can be used to relate the polarimetric signals to some general physical properties of the scattering mechanisms. Further research is needed to define the relationship between these polarimetric radar scattering properties, the radar penetration depth, and the near-surface properties (such as smoothness, contiguity, and moisture content). As a first step in establishing this relationship, we evaluate the scattering mechanisms of the temperate ice cap Hofsjḋokull, located in central Iceland, and compare them to the expected properties of the glacier. We decomposed fully-polarimetric L-band SAR data acquired from JPL's UAVSAR platform over Hofsjḋokull in the early mornings of June 10-12, 2009 using the Cloude-Pottier H/A/barh {α } eigenvector-based decomposition method. The three parameters of this method--entropy (H), anisotropy (A), and the scattering parameter (barh {α })--indicate if a dominant scattering mechanism exists and identify the mechanism of the most dominant scatterer(s)--surface, volumetric, or dihedral. We evaluate the three decomposed parameters as a function of elevation. These results show that the lowest elevation regions have mostly random scatterers in areas with steep topography and pseudo-random scatterers in areas with more moderate topographic slopes. Both terrain types show combinations of surface and volumetric scatterers but the dominant scatterer is indistinguishable. This behavior is consistent with the rough, wet surface of the ablation zone which should have little overlying snow cover in early summer. As the elevation increases towards the accumulation zone, surface scattering dominates. This dominance of surface scattering occurs at 1300-1500 m MSL: an area which has frequent freeze/thaw cycles and orographically-estimated air temperatures between -2 and 0 o C (based on data acquired at the nearby

  4. Polar Cap Formation on Ganymede

    NASA Technical Reports Server (NTRS)

    Pilcher, C. B.; Shaya, E. J.

    1985-01-01

    Since thermal migration is not an effective mechanism for water transport in the polar regions at the Galilean satellites, some other process must be responsible for the formation of Ganymede's polar caps. It is proposed that Ganymede's polar caps are the optical manifestation of a process that began with the distribution of an ice sheet over the surface of Ganymede. The combined processes of impact gardening and thermal migration led, in regions at latitudes less than 40 to 45 deg., to the burial of some fraction of this ice, the migration of some to the polar caps margins, and a depletion of free ice in the optical surface. At higher latitudes, no process was effective in removing ice from the optical surface, so the remanants of the sheet are visible today.

  5. Cervical Cap

    MedlinePlus

    ... and remove the cap. How Much Does It Cost? A cervical cap costs about $70 and should be replaced every year. In addition, there is also the cost of the doctor's visit. Many health insurance plans ...

  6. South Polar Cap

    NASA Technical Reports Server (NTRS)

    2005-01-01

    8 December 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows landforms created by sublimation processes on the south polar residual cap of Mars. The bulk of the ice in the south polar residual cap is frozen carbon dioxide.

    Location near: 86.6oS, 342.2oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Summer

  7. A Warmer Atmosphere on Mars near the Noachian-Hesperian Boundary: Evidence from Basal Melting of the South Polar Ice Cap (Dorsa Argentea Formation)

    NASA Astrophysics Data System (ADS)

    Fastook, J. L.; Head, J. W.; Marchant, D. R.; Forget, F.; Madeleine, J.-B.

    2012-05-01

    Eskers in the Dorsa Argentea Formation imply the presence of an ice sheet with a wet bed. With an ice sheet model, we examine a range of geothermal heat fluxes and warmer climates to determine what conditions could produce such an ice sheet.

  8. Summer South Polar Cap

    NASA Technical Reports Server (NTRS)

    2004-01-01

    13 April 2004 The martian south polar residual ice cap is composed mainly of frozen carbon dioxide. Each summer, a little bit of this carbon dioxide sublimes away. Pits grow larger, and mesas get smaller, as this process continues from year to year. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a view of a small portion of the south polar cap as it appeared in mid-summer in January 2004. The dark areas may be places where the frozen carbon dioxide contains impurities, such as dust, or places where sublimation of ice has roughened the surface so that it appears darker because of small shadows cast by irregularities in the roughened surface. The image is located near 86.9oS, 7.6oW. The image covers an area about 3 km (1.9 mi) across. Sunlight illuminates the scene from the upper left.

  9. Paleochemistry of Lakes Agassiz and Manitoba based on ostracodes

    USGS Publications Warehouse

    Curry, B. Brandon

    1997-01-01

    The ionic composition and salinity of Lake Manitoba and its late-glacial precursor, Lake Agassiz, changed significantly over the past 11 000 years. The paleochemical record reported here is based on modern analog environments of ostracodes identified in a new 14.5 m core from southern Lake Manitoba. The ionic composition of Lake Manitoba today is dominated by Na+, Cl-, and HCO3-, with much less Ca2+, Mg2+, and K+. Evaporative concentration of modern Lake Manitoba water would lead to greater salinity and the near depletion of Ca2+ due to continued precipitation of calcite. During periods of highest salinity in the Holocene, however, Lake Manitoba supported Limnocythere staplini. Today this species inhabits waters in which [Ca2+] > [HCO3-], including springs associated with groundwater in Paleozoic bedrock discharging into Lake Winnipegosis (and eventually, after much dilution, into Lake Manitoba). Further complicating the Holocene record are intervals containing Limnocythere friabilis that suggest periodic influxes of dilute water, probably from the Assiniboine River, which bypasses Lake Manitoba today. The variations in Holocene paleochemistry indicated by the ostracode record imply changes in the proportion of overland flow plus precipitation relative to groundwater inputs to Lake Manitoba, independent of changes in evaporation relative to precipitation.

  10. Is CO2 ice permanent?

    NASA Technical Reports Server (NTRS)

    Lindner, Bernhard Lee

    1992-01-01

    Carbon dioxide ice has been inferred to exist at the south pole in summertime, but Earth based measurements in 1969 of water vapor in the Martian atmosphere suggest that all CO2 ice sublined from the southern polar cap and exposed underlying water ice. This implies that the observed summertime CO2 ice is of recent origin. It appears possible to construct an energy balance model that maintains seasonal CO2 ice at the south pole year round and still reasonably simulates the polar cap regression and atmospheric pressure data. This implies that the CO2 ice observed in the summertime south polar cap could be seasonal in origin, and that minor changes in climate could cause CO2 ice to completely vanish, as would appear to have happened in 1969. However, further research remains before it is certain whether the CO2 ice observed in the summertime south polar cap is seasonal or is part of a permanent reservoir.

  11. Museum of Comparative Zoology Library--The Agassiz Library: Harvard University.

    ERIC Educational Resources Information Center

    Jonas, Eva S.; Regen, Shari S.

    1986-01-01

    Argues that the Museum of Comparative Zoology Library reflects the union between the nineteenth century natural history values of Louis Agassiz and the twentieth century library and information science methodology. Special collections, records, cataloging and classification, serials and their classification, policies, services, and procedures are…

  12. Morton, Agassiz, and the Origins of Scientific Racism in the United States.

    ERIC Educational Resources Information Center

    Menand, Louis

    2002-01-01

    Describes how the racist academic consensus was established at Harvard University, focusing on two professors, Samuel George Morton and Louis Agassiz, who worked to convince U.S. scholars of the inherent inferiority and subhuman status of the black race. Morton published data on the inferiority of the black race based on analysis of his collection…

  13. A chronology for glacial Lake Agassiz shorelines along Upham's namesake transect

    NASA Astrophysics Data System (ADS)

    Lepper, Kenneth; Buell, Alex W.; Fisher, Timothy G.; Lowell, Thomas V.

    2013-07-01

    Four traditionally recognized strandline complexes in the southern basin of glacial Lake Agassiz are the Herman, Norcross, Tintah and Campbell, whose names correspond to towns in west-central Minnesota that lie on a linear transect defined by the Great Northern railroad grade; the active corridor for commerce at the time when Warren Upham was mapping and naming the shorelines of Lake Agassiz (ca.1880-1895). Because shorelines represent static water planes, their extension around the lake margin establishes time-synchronous lake levels. Transitions between shoreline positions represent significant water-level fluctuations. However, geologic ages have never been obtained from sites near the namesake towns in the vicinity of the southern outlet. Here we report the first geologic ages for Lake Agassiz shorelines obtained at field sites along the namesake transect, and evaluate the emerging chronology in light of other paleoclimate records. Our current work from 11 sampling sites has yielded 16 independent ages. These results combined with a growing OSL age data set for Lake Agassiz's southern basin provide robust age constraints for the Herman, Norcross and Campbell strandlines with averages and standard deviations of 14.1 ± 0.3 ka, 13.6 ± 0.2 ka, and 10.5 ± 0.3 ka, respectively.

  14. Frank Parsons's Enablers: Pauline Agassiz Shaw, Meyer Bloomfield, and Ralph Albertson

    ERIC Educational Resources Information Center

    Hershenson, David B.

    2006-01-01

    Frank Parsons was not the 1st American to recognize or address the need for vocational guidance. Why he, rather than his predecessors, is credited with initiating the field can be attributed to the largely overlooked contributions of 3 other persons: Pauline Agassiz Shaw, Meyer Bloomfield, and Ralph Albertson. The author calls attention to the…

  15. Cradle cap

    MedlinePlus

    ... be prescribed. These may include medicated creams or shampoos. Most cases of cradle cap can be managed ... improve scalp circulation. Give your child daily, gentle shampoos with a mild shampoo as long as there ...

  16. Seismic tremor signals from Bárðarbunga, Grímsvötn and other glacier covered volcanoes in Iceland's Vatnajökull ice cap

    NASA Astrophysics Data System (ADS)

    Vogfjörd, Kristin S.; Eibl, Eva; Bean, Chris; Roberts, Matthew; Ófeigsson, Benedikt; Jóhannesson, Tómas

    2016-04-01

    Many of Iceland's most active volcanoes, like Grímsvötn and Bárðarbunga are located under glaciers giving rise to a range of volcanic hazards having both local and cross-border effects on humans, infrastructures and aviation. Volcanic eruptions under ice can lead to explosive hydromagmatic volcanism and generate small to catastrophic subglacial floods that may take hours to days to emerge from the glacier edge. Unrest in subglacial hydrothermal systems and the draining of subglacial meltwater can also lead to flood hazards. These processes and magma-ice interactions in general, generate seismic tremor signals that are commonly observed on seismic systems during volcanic unrest and/or eruptions. The tremor signals exhibit certain characteristics in frequency content, amplitude and behavior with time, but their characteristics overlap. Ability to discriminate between the different processes in real-time or near-real time can support early eruption and flood warnings and help mitigate their detrimental effects. One of the goals set forth in the FUTUREVOLC volcano supersite project was in fact to understand and discriminate between the different types of seismic tremor recorded at subglacial volcanoes. In that pursuit, the seismic network was expanded into the Vatnajökull glacier with four permanent stations on rock and in the ice, in addition to three seismic arrays installed at the ice margin, to enable location and possible tracking of the tremor sources. To track subglacial floods with better resolution three GPS receivers were also installed on the ice, one in an ice cauldron above the Skaftárkatlar geothermal melting area and two down glacier, above the track of the expected subglacial flood. During FUTUREVOLC this infrastructure has recorded all the types of process expected: Magmatic dyke intrusion and propagation from Bárðarbunga, subaerial fissure eruption of that magma at Holuhraun, two subglacial floods, one small and one large, draining from the

  17. Geodetic mass balance record with rigorous uncertainty estimates deduced from aerial photographs and LiDAR data - case study from Drangajökull ice cap, NW-Iceland

    NASA Astrophysics Data System (ADS)

    Magnússon, E.; Belart, J. M. C.; Pálsson, F.; Ágústsson, H.; Crochet, P.

    2015-09-01

    In this paper we describe how recent high resolution Digital Elevation Models (DEMs) can be used as constraints for extracting glacier surface DEMs from old aerial photographs and to evaluate the uncertainty of the mass balance record derived from the DEMs. We present a case study for Drangajökull ice cap, NW-Iceland. This ice cap covered an area of 144 km2 when it was surveyed with airborne LiDAR in 2011. Aerial photographs spanning all or most of the ice cap are available from survey flights in 1946, 1960, 1975, 1985, 1994 and 2005. All ground control points used to constrain the orientation of the aerial photographs were obtained from the high resolution LiDAR DEM (2 m × 2 m cell size and vertical accuracy < 0.5 m). The LiDAR DEM was also used to estimate errors of the extracted photogrammetric DEMs in ice and snow free areas, at nunataks and outside the glacier margin. The derived errors of each DEM were used to constrain a spherical variogram model, which along with the derived errors in ice and snow free areas were used as inputs into 1000 Sequential Gaussian Simulations (SGSim). The simulations were used to estimate the possible bias in the entire glaciated part of the DEM. The derived bias correction, varying in magnitude between DEMs from 0.03 to 1.66 m (1946 DEM) was then applied. The simulation results were also used to calculate the 95 % confidence level of this bias, resulting in values between ±0.21 m (in 2005) and ±1.58 m (in 1946). Error estimation methods based on more simple proxies would typically yield 2-4 times larger error estimates. The aerial photographs used were acquired between late June and early October. An additional bias correction was therefore estimated using a degree day model to obtain the volume change between the start of two hydrological years (1 October). This correction corresponds to an average elevation change of ~ -3 m in the worst case for 1960, or about ~ 2/3 of volume change between the 1960 and the 1975 DEMs. The

  18. A Warmer Atmosphere on Mars Near the Noachian-Hesperian Boundary: Evidence from Basal Melting of the South Polar Ice Cap (Dorsa Argentea Formation)

    NASA Astrophysics Data System (ADS)

    Fastook, J. L.; Head, J. W.; Marchant, D. R.; Forget, F.; Madeleine, J.-B.

    2011-03-01

    Dorsa Argentea Formation (Noachian-Hesperian) eskers are evidence for basal melting. Ice-flow models show that the mean annual south polar temperature must be raised to -50° to -75°C, providing an independent estimate of elevated lower latitude surface temperature.

  19. The feeder system for the 2014 fissure eruption at Holuhraun, Bárðarbunga volcanic system, Iceland: Geodetic and seismic constraints on subsurface activity in the area north of the Vatnajökull ice cap

    NASA Astrophysics Data System (ADS)

    Dumont, Stéphanie; Parks, Michelle; Sigmundsson, Freysteinn; Hooper, Andy; Hreinsdóttir, Sigrun; Ófeigsson, Benedikt; Spaans, Karsten; Vogfjörd, Kristin; Jónsdóttir, Kristín; Hensch, Martin; Gudmundsson, Gunnar; Rafn Heimisson, Elias; Drouin, Vincent; Árnadóttir, Thóra; Pedersen, Rikke; Rut Hjartardóttir, Ásta; Magnússon, Eyjólfur

    2015-04-01

    An intense earthquake swarm began on 16 August 2014 at Bárðarbunga volcano under the Vatnajökull ice cap in Central Iceland. It marked the beginning of an intrusive activity, with a dyke propagating over 45 km northward. Such major magmatic activity has not been observed for the last three decades in Iceland, since the Krafla rifting episode 1975-1984. The dyke propagation stopped 15 days after the onset of the seismic activity, with the dyke distal end in the Holuhraun plain north of the Vatnajökull ice cap. A small 4 hour eruption marked the beginning of extrusive activity. A new fissure eruption opened up on 31 August at the northern dyke tip, with lava fountaining and feeding extensive lava flows. In January 2014 the surface covered by the lava had exceeded 80 km2, and the eruption activity does not show significant decline. We have carried out interferometric analysis of SAR data (InSAR) since the onset of the unrest. X-band satellite images from COSMO-SkyMed and TerraSAR-X satellites were acquired and analyzed to map ground surface deformation associated with the dyke emplacement. Despite most of the dyke propagation occurring under several hundreds meters of ice, the last 10 km were outside the ice cap, allowing better characterisation of the dyke-induced deformation. Here we focus on the deformation in the Holuhraun plain, in order to better understand the link between the surface deformation detected in the vicinity of the dyke by InSAR as well as GPS measurements, and the eruptive activity. The regular SAR acquisitions made over the Holuhraun area since the beginning of the unrest offer a unique opportunity to better understand the evolution of the intrusion feeding the fissure eruption. For that purpose, we focus on the faults and fissures forming the graben borders on the glacier as well as in the Holuhraun plain, initially mapped using high-resolution radar images, acquired by airborne radar. We extract movement along and perpendicular to these

  20. Polar cap formation on Ganymede

    NASA Technical Reports Server (NTRS)

    Shaya, E. J.; Pilcher, C. B.

    1984-01-01

    It is argued that Ganymede's polar caps are the remnants of a more extensive covering of water ice that formed during a period in which the satellite was geologically active. It is inferred that the initial thickness of this covering was a significant fraction of the gardening depth since the covering formed. This suggests an initial thickness of at least a few meters over heavily cratered regions such as the south polar grooved terrain. The absence of similar polar caps on Callisto apparently reflects the absence of comparable geologic activity in the history of this satellite.

  1. Insect-Based Holocene (and Last Interglacial?) Paleothermometry from the E and NW Greenland Ice Sheet Margins: A Fly's-Eye View of Warmth on Greenland

    NASA Astrophysics Data System (ADS)

    Axford, Y.; Bigl, M.; Carrio, C.; Corbett, L. B.; Francis, D. R.; Hall, B. L.; Kelly, M. A.; Levy, L.; Lowell, T. V.; Osterberg, E. C.; Richter, N.; Roy, E.; Schellinger, G. C.

    2011-12-01

    Here we present new paleotemperature reconstructions based upon insect (Chironomidae) assemblages and other proxies from lake sediment cores recovered in east Greenland at ~71° N near Scoresby Sund and in northwest Greenland at ~77° N near Thule/Qaanaaq. In east Greenland, Last Chance Lake (informal name) is a small, non-glacial lake situated ~90 km east of the Greenland Ice Sheet margin. The lake preserves a sedimentary record of the entire Holocene (Levy et al. 2013). Chironomids from Last Chance Lake record cold summer temperatures (and establishment of a cold-climate fauna including abundant Oliveridia and Pseudodiamesa) during the late Holocene, preceded by summer temperatures estimated to have been 3 to 6°C warmer during the first half of the Holocene (when summer insolation forcing was greater than today). In northwest Greenland, Delta Sø and Wax Lips Lake (informal name) both preserve Holocene sediments. Here we discuss the late Holocene chironomid record from Delta Sø, whereas from Wax Lips Lake (a small, non-glacial lake situated ~2 km west of the ice sheet margin) we present a longer sedimentary and biostratigraphic record. The deeper portions of cores from Wax Lips Lake yield pre-Holocene and nonfinite radiocarbon ages, suggesting that this lake preserves sediments predating the Last Glacial Maximum. Abundant chironomids in the pre-glacial sediments appear to record interglacial conditions, and we infer that these sediments may date to the Last Interglacial (Eemian). The preservation of in situ Last Interglacial lacustrine sediments so close to the modern ice sheet margin suggests a minimally erosive glacierization style throughout the last glacial period, like that inferred for other Arctic locales such as on Baffin Island (Briner et al. 2007), ~750 km southwest of our study site. Our study sites are situated nearby key ice core sites (including NEEM, Camp Century, Agassiz and Renland) and very close to the ice sheet margin. These chironomid

  2. Insect-Based Holocene (and Last Interglacial?) Paleothermometry from the E and NW Greenland Ice Sheet Margins: A Fly's-Eye View of Warmth on Greenland

    NASA Astrophysics Data System (ADS)

    Axford, Y.; Bigl, M.; Carrio, C.; Corbett, L. B.; Francis, D. R.; Hall, B. L.; Kelly, M. A.; Levy, L.; Lowell, T. V.; Osterberg, E. C.; Richter, N.; Roy, E.; Schellinger, G. C.

    2013-12-01

    Here we present new paleotemperature reconstructions based upon insect (Chironomidae) assemblages and other proxies from lake sediment cores recovered in east Greenland at ~71° N near Scoresby Sund and in northwest Greenland at ~77° N near Thule/Qaanaaq. In east Greenland, Last Chance Lake (informal name) is a small, non-glacial lake situated ~90 km east of the Greenland Ice Sheet margin. The lake preserves a sedimentary record of the entire Holocene (Levy et al. 2013). Chironomids from Last Chance Lake record cold summer temperatures (and establishment of a cold-climate fauna including abundant Oliveridia and Pseudodiamesa) during the late Holocene, preceded by summer temperatures estimated to have been 3 to 6°C warmer during the first half of the Holocene (when summer insolation forcing was greater than today). In northwest Greenland, Delta Sø and Wax Lips Lake (informal name) both preserve Holocene sediments. Here we discuss the late Holocene chironomid record from Delta Sø, whereas from Wax Lips Lake (a small, non-glacial lake situated ~2 km west of the ice sheet margin) we present a longer sedimentary and biostratigraphic record. The deeper portions of cores from Wax Lips Lake yield pre-Holocene and nonfinite radiocarbon ages, suggesting that this lake preserves sediments predating the Last Glacial Maximum. Abundant chironomids in the pre-glacial sediments appear to record interglacial conditions, and we infer that these sediments may date to the Last Interglacial (Eemian). The preservation of in situ Last Interglacial lacustrine sediments so close to the modern ice sheet margin suggests a minimally erosive glacierization style throughout the last glacial period, like that inferred for other Arctic locales such as on Baffin Island (Briner et al. 2007), ~750 km southwest of our study site. Our study sites are situated nearby key ice core sites (including NEEM, Camp Century, Agassiz and Renland) and very close to the ice sheet margin. These chironomid

  3. Assessment of nutrients and suspended sediment conditions in and near the Agassiz National Wildlife Refuge, Northwest Minnesota, 2008–2010

    USGS Publications Warehouse

    Nustad, Rochelle A.; Galloway, Joel M.

    2012-01-01

    In response to concerns about water-quality impairments that may affect habitat degradation in Agassiz National Wildlife Refuge in northwest Minnesota, the U.S. Geological Survey, in cooperation with the U.S. Fish and Wildlife Service collected streamflow data, discrete nutrient and suspended- sediment samples, and continuous water-quality data from 2008 to 2010. Constituent loads were estimated for nutrients and suspended sediment using sample data and streamflow data. In addition, a potential water-quality and streamflow monitoring program design was developed for Agassiz National Wildlife Refuge. Results from this study can be used by resource managers to address identified impairments and protect wildlife habitat and public water supply, and may contribute toward developing more effective water-management plans for Agassiz National Wildlife Refuge.

  4. Heavy metal and selenium levels in birds at Agassiz National Wildlife Refuge, Minnesota: Food chain differences.

    PubMed

    Burger, J; Gochfeld, M

    1996-12-01

    The levels of heavy metals and selenium in the eggs and in breast feathers of adult doublecrested cormorant (Phalacrocorax auritus), black-crowned night heron (Nycticorax nycticorax), and franklin's gull (Larus pipixcan) nesting at Agassiz National Wildlife Refuge in Marshall County, northwestern Minnesota were examined. Also examined were metal levels in the feathers of fledgling night herons and gulls, in the feathers of adult and fledgling American bittern (Botaurus lentiginosus), in eggs of American coot (Fulica americana) and eared grebe (Podiceps caspicus), and in feathers of adult Canada geese (Branta canadensis). These species represent different levels on the food chain from primarily vegetation-eating species (geese, coot) to species that eat primarily fish (cormorant). A clear, positive relationship between level on the food chain and levels of heavy metals occurred only for mercury in feathers and eggs. Otherwise, eared grebes had the highest levels of all other metals in their eggs compared to the other species. No clear food chain pattern existed for feathers for the other metals. For eggs at Agassiz: 1) lead, selenium, and manganese levels were similar to those reported in the literature, 2) mercury levels were slightly higher for cormorants and night herons, 3) all species had higher chromium and cadmium levels than generally reported, and 4) eared grebes had significantly higher levels of cadmium than reported for any species from elsewhere. For adult feathers: 1) gulls had higher levels of lead than the other species, 2) cadmium levels were elevated in gulls and adult herons and cormorants, 3) mercury levels showed an increase with position on the food chain, 4) selenium and chromium levels of all birds at Agassiz were generally low and 5) manganese levels in adults were generally higher than in the literature for other species. Adults had significantly higher mercury levels than fledgling gulls, night herons, and bitterns.

  5. Ice sheet sources of sea level rise and freshwater discharge during the last deglaciation

    NASA Astrophysics Data System (ADS)

    Carlson, Anders E.; Clark, Peter U.

    2012-12-01

    We review and synthesize the geologic record that constrains the sources of sea level rise and freshwater discharge to the global oceans associated with retreat of ice sheets during the last deglaciation. The Last Glacial Maximum (˜26-19 ka) was terminated by a rapid 5-10 m sea level rise at 19.0-19.5 ka, sourced largely from Northern Hemisphere ice sheet retreat in response to high northern latitude insolation forcing. Sea level rise of 8-20 m from ˜19 to 14.5 ka can be attributed to continued retreat of the Laurentide and Eurasian Ice Sheets, with an additional freshwater forcing of uncertain amount delivered by Heinrich event 1. The source of the abrupt acceleration in sea level rise at ˜14.6 ka (meltwater pulse 1A, ˜14-15 m) includes contributions of 6.5-10 m from Northern Hemisphere ice sheets, of which 2-7 m represents an excess contribution above that derived from ongoing ice sheet retreat. Widespread retreat of Antarctic ice sheets began at 14.0-15.0 ka, which, together with geophysical modeling of far-field sea level records, suggests an Antarctic contribution to this meltwater pulse as well. The cause of the subsequent Younger Dryas cold event can be attributed to eastward freshwater runoff from the Lake Agassiz basin to the St. Lawrence estuary that agrees with existing Lake Agassiz outlet radiocarbon dates. Much of the early Holocene sea level rise can be explained by Laurentide and Scandinavian Ice Sheet retreat, with collapse of Laurentide ice over Hudson Bay and drainage of Lake Agassiz basin runoff at ˜8.4-8.2 ka to the Labrador Sea causing the 8.2 ka event.

  6. The hemispherical asymmetry in the Martian polar caps

    NASA Astrophysics Data System (ADS)

    Lindner, B. L.

    1993-02-01

    An energy balance model is used to study the behavior of CO2 ice on Mars. The effect of the solar zenith angle dependence of albedo is to lengthen CO2 ice lifetimes at the poles. Hemispherical asymmetries in cloud and dust abundance could result in the survival of seasonal CO2 ice through summer in the south and not in the north, in agreement with observations. CO2 ice observed in the summertime polar cap in the south could be of recent origin, although a permanent CO2 polar cap cannot be ruled out.

  7. The name of the father: conflict between Louis and Alexander Agassiz and the Embiotoca surfperch radiation.

    PubMed

    Bernardi, G

    2009-04-01

    The surfperch genus Embiotoca currently comprises two species, Embiotoca jacksoni, the black surfperch, and Embiotoca lateralis, the striped surfperch. Originally, however, Louis Agassiz described a third species in the genus Embiotoca, the rainbow surfperch, Embiotoca caryi. This latter name was changed by Louis' son, Alexander, to Hypsurus caryi, a name that remains valid. In this study, new molecular data (3545 bp of DNA from four mitochondrial and two nuclear DNA regions) indicated that the rainbow surfperch should be retained within the genus Embiotoca, a result consistent with recent morphological data. Adaptive radiation combined with sexual selection resulting in rapid morphological changes in the rainbow surfperch may have contributed to the conflicting position of this species.

  8. Nest guarding by female Agassiz's desert tortoise (Gopherus agassizii) at a wind-energy facility near Palm Springs, California

    USGS Publications Warehouse

    Agha, Mickey; Lovich, Jeffrey E.; Ennen, Joshua R.; Wilcox, Ethan

    2013-01-01

    We observed behavior consistent with nest-guarding in Agassiz's desert tortoise (Gopherus agassizii) at two nests in a large wind-energy-generation facility near Palm Springs, California, locally known as the Mesa Wind Farm. As researchers approached the nests, female desert tortoises moved to the entrance of their burrows and positioned themselves sideways, directly over their nests. One female stretched her limbs outward and wedged herself into the burrow (her plastron directly above the nest). Guarding of nests is rarely observed in Agassiz's desert tortoise but can occur as a result of attempted predation on eggs by Gila monsters (Heloderma suspectum) or in direct response to the perceived threat posed by researchers. This is the first report of nest-guarding for G. agassizii in the Sonoran Desert ecosystem of California.

  9. Summer Arctic Sea Ice Retreat: May - August 2013

    NASA Video Gallery

    The melting of sea ice in the Arctic is well on its way toward its annual "minimum," that time when the floating ice cap covers less of the Arctic Ocean than at any other period during the year. 20...

  10. Martian north polar cap summer water cycle

    NASA Astrophysics Data System (ADS)

    Brown, Adrian J.; Calvin, Wendy M.; Becerra, Patricio; Byrne, Shane

    2016-10-01

    A key outstanding question in Martian science is "are the polar caps gaining or losing mass and what are the implications for past, current and future climate?" To address this question, we use observations from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) of the north polar cap during late summer for multiple Martian years, to monitor the summertime water cycle in order to place quantitative limits on the amount of water ice deposited and sublimed in late summer. We establish here for the first time the summer cycle of water ice absorption band signatures on the north polar cap. We show that in a key region in the interior of the north polar cap, the absorption band depths grow until Ls = 120, when they begin to shrink, until they are obscured at the end of summer by the north polar hood. This behavior is transferable over the entire north polar cap, where in late summer regions 'flip' from being net sublimating into net condensation mode. This transition or 'mode flip' happens earlier for regions closer to the pole, and later for regions close to the periphery of the cap. The observations and calculations presented herein estimate that on average a water ice layer ∼70 microns thick is deposited during the Ls = 135-164 period. This is far larger than the results of deposition on the south pole during summer, where an average layer 0.6-6 microns deep has been estimated by Brown et al. (2014) Earth Planet. Sci. Lett., 406, 102-109.

  11. North Polar Ice

    NASA Technical Reports Server (NTRS)

    2004-01-01

    25 December 2004 For 25 December, the MOC team thought that a visit to a north polar site would be timely. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows, at about 1.5 meters per pixel (5 feet per pixel) resolution, a view of the north polar ice cap of Mars. That the material includes water ice has been known since the mid-1970s, when Viking orbiter observations confirmed that the cap gives off water vapor in the summertime, as the ice is subliming away. The surface shown here, observed by MOC during northern summer in November 2004, is pitted and somewhat grooved. Dark material on pit floors might be trapped, windblown dust. The picture covers an area about 1 km (0.62 mi) across, and is located near 86.8oN, 293.1oW. Sunlight illuminates the scene from the lower left.

  12. Ice-core evidence of abrupt climate changes

    PubMed Central

    Alley, Richard B.

    2000-01-01

    Ice-core records show that climate changes in the past have been large, rapid, and synchronous over broad areas extending into low latitudes, with less variability over historical times. These ice-core records come from high mountain glaciers and the polar regions, including small ice caps and the large ice sheets of Greenland and Antarctica. PMID:10677460

  13. Ice-core evidence of abrupt climate changes.

    PubMed

    Alley, R B

    2000-02-15

    Ice-core records show that climate changes in the past have been large, rapid, and synchronous over broad areas extending into low latitudes, with less variability over historical times. These ice-core records come from high mountain glaciers and the polar regions, including small ice caps and the large ice sheets of Greenland and Antarctica.

  14. South Polar Cap

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    Released 8 March 2004

    The Odyssey spacecraft has completed a full Mars year of observations of the red planet. For the next several weeks the Image of the Day will look back over this first mars year. It will focus on four themes: 1) the poles - with the seasonal changes seen in the retreat and expansion of the caps; 2) craters - with a variety of morphologies relating to impact materials and later alteration, both infilling and exhumation; 3) channels - the clues to liquid surface flow; and 4) volcanic flow features. While some images have helped answer questions about the history of Mars, many have raised new questions that are still being investigated as Odyssey continues collecting data as it orbits Mars.

    This image was collected March 5, 2002 during the southern summer season. Layering in the South polar cap interior is readily visible and may indicate yearly ice/dust deposition.

    Image information: VIS instrument. Latitude -86.6, Longitude 156.8 East (203.2 West). 19 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the

  15. Translocation as a conservation tool for Agassiz's desert tortoises: survivorship, reproduction, and movements

    USGS Publications Warehouse

    Nussear, K.E.; Tracy, C.R.; Medica, P.A.; Wilson, D.S.; Marlow, R.W.; Corn, P.S.

    2012-01-01

    We translocated 120 Agassiz's desert tortoises to 5 sites in Nevada and Utah to evaluate the effects of translocation on tortoise survivorship, reproduction, and habitat use. Translocation sites included several elevations, and extended to sites with vegetation assemblages not typically associated with desert tortoises in order to explore the possibility of moving animals to upper elevation areas. We measured survivorship, reproduction, and movements of translocated and resident animals at each site. Survivorship was not significantly different between translocated and resident animals within and among sites, and survivorship was greater overall during non-drought years. The number of eggs produced by tortoises was similar for translocated and resident females, but differed among sites. Animals translocated to atypical habitat generally moved until they reached vegetation communities more typical of desert tortoise habitat. Even within typical tortoise habitat, tortoises tended to move greater distances in the first year after translocation than did residents, but their movements in the second or third year after translocation were indistinguishable from those of resident tortoises. Our data show that tortoises translocated into typical Mojave desert scrub habitats perform well; however, the large first-year movements of translocated tortoises have important management implications. Projects that employ translocations must consider how much area will be needed to contain translocated tortoises and whether roads need fencing to prevent the loss of animals.

  16. Heat transport in the Red Lake Bog, Glacial Lake Agassiz Peatlands

    USGS Publications Warehouse

    McKenzie, J.M.; Siegel, D.I.; Rosenberry, D.O.; Glaser, P.H.; Voss, C.I.

    2007-01-01

    We report the results of an investigation on the processes controlling heat transport in peat under a large bog in the Glacial Lake Agassiz Peatlands. For 2 years, starting in July 1998, we recorded temperature at 12 depth intervals from 0 to 400 cm within a vertical peat profile at the crest of the bog at sub-daily intervals. We also recorded air temperature 1 m above the peat surface. We calculate a peat thermal conductivity of 0.5 W m-1 ??C-1 and model vertical heat transport through the peat using the SUTRA model. The model was calibrated to the first year of data, and then evaluated against the second year of collected heat data. The model results suggest that advective pore-water flow is not necessary to transport heat within the peat profile and most of the heat is transferred by thermal conduction alone in these waterlogged soils. In the spring season, a zero-curtain effect controls the transport of heat through shallow depths of the peat. Changes in local climate and the resulting changes in thermal transport still may cause non-linear feedbacks in methane emissions related to the generation of methane deeper within the peat profile as regional temperatures increase. Copyright ?? 2006 John Wiley & Sons, Ltd.

  17. Serologic and molecular evidence for Testudinid herpesvirus 2 infection in wild Agassiz's desert tortoises, Gopherus agassizii.

    PubMed

    Jacobson, Elliott R; Berry, Kristin H; Wellehan, James F X; Origgi, Francesco; Childress, April L; Braun, Josephine; Schrenzel, Mark; Yee, Julie; Rideout, Bruce

    2012-07-01

    Following field observations of wild Agassiz's desert tortoises (Gopherus agassizii) with oral lesions similar to those seen in captive tortoises with herpesvirus infection, we measured the prevalence of antibodies to Testudinid herpesvirus (TeHV) 3 in wild populations of desert tortoises in California. The survey revealed 30.9% antibody prevalence. In 2009 and 2010, two wild adult male desert tortoises, with gross lesions consistent with trauma and puncture wounds, respectively, were necropsied. Tortoise 1 was from the central Mojave Desert and tortoise 2 was from the northeastern Mojave Desert. We extracted DNA from the tongue of tortoise 1 and from the tongue and nasal mucosa of tortoise 2. Sequencing of polymerase chain reaction products of the herpesviral DNA-dependent DNA polymerase gene and the UL39 gene respectively showed 100% nucleotide identity with TeHV2, which was previously detected in an ill captive desert tortoise in California. Although several cases of herpesvirus infection have been described in captive desert tortoises, our findings represent the first conclusive molecular evidence of TeHV2 infection in wild desert tortoises. The serologic findings support cross-reactivity between TeHV2 and TeHV3. Further studies to determine the ecology, prevalence, and clinical significance of this virus in tortoise populations are needed.

  18. Vinyl capped addition polyimides

    NASA Technical Reports Server (NTRS)

    Vannucci, Raymond D. (Inventor); Malarik, Diane C. (Inventor); Delvigs, Peter (Inventor)

    1991-01-01

    Polyimide resins (PMR) are generally useful where high strength and temperature capabilities are required (at temperatures up to about 700 F). Polyimide resins are particularly useful in applications such as jet engine compressor components, for example, blades, vanes, air seals, air splitters, and engine casing parts. Aromatic vinyl capped addition polyimides are obtained by reacting a diamine, an ester of tetracarboxylic acid, and an aromatic vinyl compound. Low void materials with improved oxidative stability when exposed to 700 F air may be fabricated as fiber reinforced high molecular weight capped polyimide composites. The aromatic vinyl capped polyimides are provided with a more aromatic nature and are more thermally stable than highly aliphatic, norbornenyl-type end-capped polyimides employed in PMR resins. The substitution of aromatic vinyl end-caps for norbornenyl end-caps in addition polyimides results in polymers with improved oxidative stability.

  19. Decision analysis of mitigation and remediation of sedimentation within large wetland systems: a case study using Agassiz National Wildlife Refuge

    USGS Publications Warehouse

    Post van der Burg, Max; Jenni, Karen E.; Nieman, Timothy L.; Eash, Josh D.; Knutsen, Gregory A.

    2014-01-01

    Sedimentation has been identified as an important stressor across a range of wetland systems. The U.S. Fish and Wildlife Service has the responsibility of maintaining wetlands within its National Wildlife Refuge System for use by migratory waterbirds and other wildlife. Many of these wetlands could be negatively affected by accelerated rates of sedimentation, especially those located in agricultural parts of the landscape. In this report we document the results of a decision analysis project designed to help U.S. Fish and Wildlife Service staff at the Agassiz National Wildlife Refuge (herein referred to as the Refuge) determine a strategy for managing and mitigating the negative effects of sediment loading within Refuge wetlands. The Refuge’s largest wetland, Agassiz Pool, has accumulated so much sediment that it has become dominated by hybrid cattail (Typha × glauca), and the ability of the staff to control water levels in the Agassiz Pool has been substantially reduced. This project consisted of a workshop with Refuge staff, local and regional stakeholders, and several technical and scientific experts. At the workshop we established Refuge management and stakeholder objectives, a range of possible management strategies, and assessed the consequences of those strategies. After deliberating a range of actions, the staff chose to consider the following three strategies: (1) an inexpensive strategy, which largely focused on using outreach to reduce external sediment inputs to the Refuge; (2) the most expensive option, which built on the first option and relied on additional infrastructure changes to the Refuge to increase management capacity; and (3) a strategy that was less expensive than strategy 2 and relied mostly on existing infrastructure to improve management capacity. Despite the fact that our assessments were qualitative, Refuge staff decided they had enough information to select the third strategy. Following our qualitative assessment, we discussed

  20. North Polar Ice

    NASA Technical Reports Server (NTRS)

    2005-01-01

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image illustrates very well the detailed, pitted nature of the north polar residual ice cap. As water ice sublimes away a little bit each summer, dark-floored pits have formed, trapping dust and other debris.

    Location near: 85.1oN, 284.6oW 200 m scale bar = 219 yards Illumination from: lower left Season: Northern Summer

  1. Multiple factors affect a population of Agassiz's desert tortoise (Gopherus agassizii) in the Northwestern Mojave Desert

    USGS Publications Warehouse

    Berry, Kristin H.; Yee, Julie L.; Coble, Ashley A.; Perry, William M.; Shields, Timothy A.

    2013-01-01

    Numerous factors have contributed to declines in populations of the federally threatened Agassiz's Desert Tortoise (Gopherus agassizii) and continue to limit recovery. In 2010, we surveyed a low-density population on a military test facility in the northwestern Mojave Desert of California, USA, to evaluate population status and identify potential factors contributing to distribution and low densities. Estimated densities of live tortoises ranged spatially from 1.2/km2 to 15.1/km2. Although only one death of a breeding-age tortoise was recorded for the 4-yr period prior to the survey, remains of 16 juvenile and immature tortoises were found, and most showed signs of predation by Common Ravens (Corvus corax) and mammals. Predation may have limited recruitment of young tortoises into the adult size classes. To evaluate the relative importance of different types of impacts to tortoises, we developed predictive models for spatially explicit densities of tortoise sign and live tortoises using topography (i.e., slope), predators (Common Raven, signs of mammalian predators), and anthropogenic impacts (distances from paved road and denuded areas, density of ordnance fragments) as covariates. Models suggest that densities of tortoise sign increased with slope and signs of mammalian predators and decreased with Common Ravens, while also varying based on interaction effects involving these predictors as well as distances from paved roads, denuded areas, and ordnance. Similarly, densities of live tortoises varied by interaction effects among distances to denuded areas and paved roads, density of ordnance fragments, and slope. Thus multiple factors predict the densities and distribution of this population.

  2. The hemispherical asymmetry of the residual polar caps on Mars

    NASA Technical Reports Server (NTRS)

    Lindner, Bernhard Lee

    1991-01-01

    A model of the polar caps of Mars was created which allows: (1) for light penetration into the cap; (2) ice albedo to vary with age, latitude, hemisphere, dust content, and solar zenith angle; and (3) for diurnal variability. The model includes the radiative effects of clouds and dust, and heat transport as represented by a thermal wind. The model reproduces polar cap regression data very well, including the survival of CO2 frost at the south pole and reproduces the general trend in the Viking Lander pressure data.

  3. CCiCap: Boeing

    NASA Video Gallery

    NASA announced today its plans to partner with The Boeing Company for the next phase of the agency's Commercial Crew Program (CCP). Called Commercial Crew integrated Capability (CCiCap), the initia...

  4. Icing tunnel tests of a glycol-exuding porous leading edge ice protection system on a general aviation airfoil

    NASA Technical Reports Server (NTRS)

    Kohlman, D. L.; Schweikhard, W. G.; Albright, A. E.; Evanich, P.

    1981-01-01

    A glycol-exuding porous leading edge ice protection system was tested. Results show that the system is very effective in preventing ice accretion (anti-ice mode) or removing ice from an airfoil. Minimum glycol flow rates required for anti-icing are a function of velocity, liquid water content in the air, ambient temperature, and droplet size. Large ice caps were removed in only a few minutes using anti-ice flow rates. It was found that the shed time is a function of the type of ice, size of the ice cap, angle of attack, and glycol flow rate. Wake survey measurements show that there is no significant drag penalty for the installation or operation of the system tested.

  5. Connecting the Final Drainage of Lake Agassiz to the 8.2 ka Event by Means of a High- Resolution Sea-Level Record From the Mississippi Delta

    NASA Astrophysics Data System (ADS)

    Li, Y.; Tornqvist, T. E.; Nevitt, J. M.; Shen, Z.; Yu, S.

    2008-12-01

    The catastrophic drainage of proglacial lakes Agassiz and Ojibway (LAO) in the early Holocene is widely believed to have triggered the 8.2 ka cold event. The timing of the LAO drainage, however, remains poorly constrained, which impedes our understanding of the abruptness of this climate change in response to a rapid freshwater forcing. Dating of the LAO drainage in the Hudson Bay area (Barber et al., 1999) yielded an age of 8.47 ± 0.30 ka, thus leaving large uncertainties about its connection with the 8.2 ka event. Here we refine the chronology of the final LAO drainage by constructing a high-resolution sea-level record from the Mississippi Delta with the basal peat approach. Two separate basal peat beds are interpreted to bracket an abrupt sea-level rise around 8.2 ka. The stratigraphically deeper level (Level A) contains a 2 cm basal peat layer that is abruptly overlain by Rangia cuneata- bearing lagoonal muds, representing the onset of an abrupt sea-level rise. The stratigraphically shallower level (Level B) contains a 6 cm basal peat layer that is covered by organic-rich muds, representing the end of the abrupt sea-level rise. Radiocarbon dating of different fractions of macrofossils from each peat layer yields consistent ages. The peat layer from Level A and the base of the peat layer from Level B yield ages of 8257 Cal. yr BP (median age with 2 sigma range of 8198-8270) and 8258 Cal. yr BP (median age with 2 sigma range of 8198-8270), respectively. The indistinguishable ages from these two peat layers, together with the diagnostic stratigraphic features, confirms that sea-level rise was likely instantaneous. This new chronology of the final LAO drainage is similar to the timings of the onset of the 8.2 ka event determined from high-resolution studies of Greenland ice cores and an Omani stalagmite, suggesting an instantaneous ocean-atmospheric system response to freshwater forcing, consistent with model predictions.

  6. CENTRIFUGE END CAP

    DOEpatents

    Beams, J.W.; Snoddy, L.B.

    1960-08-01

    An end cap for ultra-gas centrifuges is designed to impart or remove angular momentum to or from the gas and to bring the entering gas to the temperature of the gas inside the centrifuge. The end cap is provided with slots or fins for adjusting the temperature and the angular momentum of the entering gas to the temperature and momentum of the gas in the centrifuge and is constructed to introduce both the inner and the peripheral stream into the centrifuge.

  7. ROTOR END CAP

    DOEpatents

    Rushing, F.C.

    1959-02-01

    An improved end cap is described for the cylindrical rotor or bowl of a high-speed centrifugal separator adapted to permit free and efficient continuous counter current flow of gas therethrough for isotope separation. The end cap design provides for securely mounting the same to the hollow central shaft and external wall of the centrifuge. Passageways are incorporated and so arranged as to provide for continuous counter current flow of the light and heavy portions of the gas fed to the centrifuge.

  8. Climate change history stored in Greenland ice

    SciTech Connect

    Stauffer, B.

    1996-12-31

    Core samples drilled deep inside polar ice caps may reveal important clues about the future in an era of global warming. Ice caps are {open_quotes}excellent archives that allow us to document gradual shifts in climate that have occurred over the past millennia,{close_quotes} says Bernhard Stauffer, a researcher at the University of Bern`s Physics Institute in Switzerland. Samples taken deep beneath the surface of the ice cap {open_quotes}allow scientists to reconstruct changes not only in global climate, including temperature and precipitation, but also in atmospheric composition,{close_quotes} Stauffer says. Abrupt, not gradual, temperatures increases were found to correspond to an increase in greenhouse gases. What do these findings bode for the future? {open_quotes}Our exploration of the ice cores has suggested...that global climatic variation can occur in a fraction of a human lifetime,{close_quotes} Stauffer concludes.

  9. Cyclic steps on ice

    NASA Astrophysics Data System (ADS)

    Yokokawa, M.; Izumi, N.; Naito, K.; Parker, G.; Yamada, T.; Greve, R.

    2016-05-01

    Boundary waves often form at the interface between ice and fluid flowing adjacent to it, such as ripples under river ice covers, and steps on the bed of supraglacial meltwater channels. They may also be formed by wind, such as the megadunes on the Antarctic ice sheet. Spiral troughs on the polar ice caps of Mars have been interpreted to be cyclic steps formed by katabatic wind blowing over ice. Cyclic steps are relatives of upstream-migrating antidunes. Cyclic step formation on ice is not only a mechanical but also a thermodynamic process. There have been very few studies on the formation of either cyclic steps or upstream-migrating antidunes on ice. In this study, we performed flume experiments to reproduce cyclic steps on ice by flowing water, and found that trains of steps form when the Froude number is larger than unity. The features of those steps allow them to be identified as ice-bed analogs of cyclic steps in alluvial and bedrock rivers. We performed a linear stability analysis and obtained a physical explanation of the formation of upstream-migrating antidunes, i.e., precursors of cyclic steps. We compared the results of experiments with the predictions of the analysis and found the observed steps fall in the range where the analysis predicts interfacial instability. We also found that short antidune-like undulations formed as a precursor to the appearance of well-defined steps. This fact suggests that such antidune-like undulations correspond to the instability predicted by the analysis and are precursors of cyclic steps.

  10. Seasonal aldedo variations on the Martian north polar cap as seen by MGS

    NASA Technical Reports Server (NTRS)

    Hale, Amy S.; Bass, Deborah S; Tamppari, Leslie K.

    2003-01-01

    The Viking Orbiters determined that the surface of Mars' northern redisual cap is water ice. Many researchers have related observed atmospheric water vapor abundances to seasonal exchange between reservoirs such as the polar caps, but the extent to which the exchange between the surface and the atmosphere remains uncertain.

  11. Stability of the Early Mars Atmosphere to Collapse into Permanent Polar Caps

    NASA Astrophysics Data System (ADS)

    Haberle, R. M.; Kahre, M. A.; Wordsworth, R.; Forget, F.

    2016-09-01

    Snowfall from CO2 ice clouds on early Mars can affect the formation of permanent polar caps. We use a GCM to study the influence of CO2 cloud microphysics on the stability of thick CO2 atmospheres against collapse into permanent polar caps.

  12. Northwest outlet channels of Lake Agassiz, isostatic tilting and a migrating continental drainage divide, Saskatchewan, Canada

    NASA Astrophysics Data System (ADS)

    Fisher, Timothy G.; Souch, Catherine

    1998-10-01

    Lake cores obtained from the northwest outlet of glacial Lake Agassiz in northwest Saskatchewan, Canada, provide a minimum date for the cessation of the flood from the northwest outlet, and a chronology for abandonment of mid-Holocene channels that presently straddle the Mackenzie and Churchill drainage divide. The stratigraphy of a vibracore taken from Long Lake consists of a lower pebble gravel fining to massive sand, silty-clay and then fibrous peat. Wood fragments from the base of the clay yielded an accelerator mass spectrometry (AMS) date of 9120 BP. Because the lake is scour in origin and is in the head of the spillway, the date is considered to be a minimum estimate for cessation of the flood from the northwest outlet at the beginning of the Emerson Phase. A vibracore taken at Haas Lake in an abandoned channel surrounded by muskeg with no influent streams, consists of 0.8 m of stratified, pebble gravel containing abundant shell and wood fragments, overlain by 1.62 m of gyttja with a sharp, conformable lower contact. AMS dates range from 5590 BP from the topmost gravel to 3080 BP within the gyttja. The gravel is interpreted as fluvial, recording a river draining Wasekamio Lake north into the Clearwater River across the present-day drainage divide. Today, a drop of 2 m occurs from Wasekamio Lake southeast to Lac Ile-a-la-Crosse, along 150 km of lake basins parallel to the Cree Lake Moraine. The dates from Haas Lake suggest that before 5200 BP, the drainage divide was about 100 km further southeast, implying that during the Emerson Phase, lake level was controlled by a sill near Flatstone Lake at about 430 m instead of between Wasekamio Lake and the Clearwater River, as was previously proposed. Holocene differential isostatic uplift caused the flow reversal in the upper Churchill basin. Anastomosed channels at the mouth of rivers flowing north into lakes indicate that uplift is still active in the area today.

  13. Effects of Atmospheric Dust on Residual South Polar Cap Stability

    NASA Technical Reports Server (NTRS)

    Bonrv, B. P.; Bjorkman, J. E.; Hansen, G. B.; James, P. B.; Wolff, M. J.

    2005-01-01

    The Martian polar caps have been studied from the time of Herschel. Neither polar cap normally disappears in summer. The Residual North Polar Cap (portion that remains through summer) is composed of a mixture of water ice and dust, and its interannual stability is due to its low sublimation rate at the summer temperatures in the North Polar Region. The Residual South Polar Cap (RSPC) is more enigmatic, surviving the relatively hot perihelic summer season despite being composed of much more volatile CO2. It is able to do so because of its unusually high albedo, which is larger than that of other bright regions in the seasonal cap (e.g. Mountains of Mitchel). The proximity of the albedo of the RSPC to the critical albedo for stability raises the question of whether the RSPC exists in every Martian year. The ground based record is somewhat ambivalent. Douglass and Lowell reported that RSPC suddenly vanished at Ls=297deg in 1894 and did not reappear until Ls=0deg [1], and Kuiper reported that it disappeared in 1956 [2]; but both observations were questioned by contemporaries, who tended to attribute them to obscuring dust. Barker [3] reported a large amount of water vapor over the south polar cap in 1969 that could be attributed to exposure of near surface water ice during partial removal of the CO2 in the RSPC in 1969.

  14. Constraints on the composition of the martian south polar cap from gravity and topography

    NASA Astrophysics Data System (ADS)

    Wieczorek, Mark A.

    2008-08-01

    The polar caps of Mars have long been acknowledged to be composed of unknown proportions of water ice, solid CO 2 (dry ice), and dust. Gravity and topography data are here analyzed over the southern cap to place constraints on its density, and hence composition. Using a localized spectral analysis combined with a lithospheric flexure model of ice cap loading, the best fit density of the volatile-rich south polar layered deposits is found to be 1271 kg m -3 with 1- σ limits of 1166 and 1391 kg m -3. The best fit elastic thickness of this geologically young deposit is 140 km, though any value greater than 102 km can fit the observations. The best fit density implies that about 55% dry ice by volume could be sequestered in these deposits if they were completely dust free. Alternatively, if these deposits were completely free of solid CO 2, the dust content would be constrained to lie between about 14 and 28% by volume. The bulk thermal conductivity of the polar cap is not significantly affected by these maximum allowable concentrations of dust. However, even if a moderate quantity of solid CO 2 were present as horizontal layers, the bulk thermal conductivity of the polar cap would be significantly reduced. Reasonable estimates of the present day heat flow of Mars predict that dry ice beneath the thicker portions of the south polar cap would have melted. Depending on the quantity of solid CO 2 in these deposits today, it is even possible that water ice could melt where the cap is thickest. If independent estimates for either the dust or CO 2 content of the south polar cap could be obtained, and if radar sounding data could determine whether this polar cap is presently experiencing basal melting or not, it would be possible to use these observations to place tight constraints on the present day heat flow of Mars.

  15. Brief communication "The aerophotogrammetric map of Greenland ice masses"

    NASA Astrophysics Data System (ADS)

    Citterio, M.; Ahlstrøm, A. P.

    2013-03-01

    The PROMICE (Programme for Monitoring of the Greenland Ice Sheet) aerophotogrammetric map of Greenland ice masses is the first high resolution dataset documenting the mid-1980s areal extent of the Greenland Ice Sheet and all the local glaciers and ice caps. The total glacierized area excluding nunataks was 1 804 638 km2 ± 2178 km2, of which 88 083 ± 1240 km2 belonged to local glaciers and ice caps (GIC) substantially independent from the Greenland Ice Sheet. This new result of GIC glacierized area is higher than most previous estimates, 81% greater than Weng's (1995) measurements, but is in line with contemporary findings based on independent data sources. A comparison between our map and the recently released Rastner et al. (2012) inventory and GIMP (Greenland Ice Mapping Project) Ice-Cover Mask (Howat and Negrete, 2013) shows potential for change-assessment studies.

  16. Nelson's big horn sheep (Ovis canadensis nelsoni) trample Agassiz's desert tortoise (Gopherus agassizii) burrow at a California wind energy facility

    USGS Publications Warehouse

    Agha, Mickey; Delaney, David F.; Lovich, Jeffrey E.; Briggs, Jessica; Austin, Meaghan; Price, Steven J.

    2015-01-01

    Research on interactions between Agassiz's desert tortoises (Gopherus agassizii) and ungulates has focused exclusively on the effects of livestock grazing on tortoises and their habitat (Oldemeyer, 1994). For example, during a 1980 study in San Bernardino County, California, 164 desert tortoise burrows were assessed for vulnerability to trampling by domestic sheep (Ovis aries). Herds of grazing sheep damaged 10% and destroyed 4% of the burrows (Nicholson and Humphreys 1981). In addition, a juvenile desert tortoise was trapped and an adult male was blocked from entering a burrow due to trampling by domestic sheep. Another study found that domestic cattle (Bos taurus) trampled active desert tortoise burrows and vegetation surrounding burrows (Avery and Neibergs 1997). Trampling also has negative impacts on diversity of vegetation and intershrub soil crusts in the desert southwest (Webb and Stielstra 1979). Trampling of important food plants and overgrazing has the potential to create competition between desert tortoises and domestic livestock (Berry 1978; Coombs 1979; Webb and Stielstra 1979).

  17. Do Porins Pass CAPs?

    NASA Astrophysics Data System (ADS)

    Hanna, C. B.; Pink, D. A.; Gill, T. A.; Beveridge, T. J.; Quinn, B. E.; Durrant, J. J.; Jericho, M. H.

    2008-03-01

    The cationic antimicrobial peptide (CAP) protamine is known to inhibit bacterial survival (Pink et al., Langmuir 19, 8852 (2003), and references therein), but the mechanism of attack is as yet undetermined. For Gram-negative bacteria, two pathways have been proposed: (a) self-promoted uptake, and (b) passage through porins. Here, we study the latter possibility, and model part of the outer membrane of a Gram-negative bacterium in an aqueous solution containing multivalent ions and CAPs. The intent is to determine whether CAPs could pass through porins and, if so, what aspects of external (e.g., ionic concentration) and internal (e.g., porin and O-sidechain characteristics) parameters affect their passage. This study is accomplished via Monte Carlo computer simulations of a ``minimal model'' of the outer membrane of a Gram-negative bacterium with an embedded porin.

  18. Magnetospheric polar cap

    NASA Astrophysics Data System (ADS)

    Akasofu, S. I.; Kan, J. R.

    Mount Denali (McKinley), the Alaska Range, and countless glaciers welcomed all 86 participants of the Chapman Conference on the Magnetospheric Polar Cap, which was held on the University of Alaska, Fairbanks campus (UAF), on August 6-9, 1984. The magnetospheric polar cap is the highest latitude region of the earth which is surrounded by the ring of auroras (the auroral oval). This particular region of the earth has become a focus of magnetospheric physicists during the last several years. This is because a number of upper atmospheric phenomena in the polar cap are found to be crucial in understanding the solar wind—magnetosphere interaction. The conference was opened by J. G. Roederer, who was followed by the UAF Chancellor, P. J. O'Rourke, who officially welcomed the participants.

  19. Reply to Miller et al. (2013) Substantial agreement on the timing and magnitude of Late Holocene ice cap expansion between east Greenland and the eastern Canadian Arctic: a commentary on Lowell et al. (2013)

    NASA Astrophysics Data System (ADS)

    Lowell, Thomas V.; Hall, Brenda L.; Kelly, Meredith A.; Bennike, Ole; Smith, Colby A.; Denton, George H.

    2013-10-01

    Glaciers are sensitive indicators of climate change. Thus recent warming has led to general recession, producing glacier forefields that yield valuable information on the Little Ice Age and the Medieval Warm Period, as well as on older Holocene climate changes. Such forefields in the Swiss Alps and the Canadian Rockies reveal remains of trees killed during past intervals of glacier expansion. From "kill dates" of overridden trees, former glacier advances can be reconstructed in detail. For example, kill dates of larch trees allowed an advance of Gorner Glacier in the Swiss Alps to be tracked for a distance of 1000 m between 1327 AD and a maximum achieved in 1385 AD just short of the Little Ice Age Hochstand of 1859 AD (Holzhauser, 1995; Holzhauser et al., 2005). The same approach was used at Robson Glacier in the Canadian Rockies to show expansion between 1150 and 1350 AD (Luckman, 1995, 2000); an earlier Holocene advance of Peyto Glacier was tracked by kill dates of overridden trees (Luckman et al., 1993).

  20. Characterization of Mars' seasonal caps using neutron spectroscopy

    USGS Publications Warehouse

    Prettyman, T.H.; Feldman, W.C.; Titus, T.N.

    2009-01-01

    Mars' seasonal caps are characterized during Mars years 26 and 27 (April 2002 to January 2006) using data acquired by the 2001 Mars Odyssey Neutron Spectrometer. Time-dependent maps of the column abundance of seasonal CO 2 surface ice poleward of 60?? latitude in both hemispheres are determined from spatially deconvolved, epithermal neutron counting data. Sources of systematic error are analyzed, including spatial blurring by the spectrometer's broad footprint and the seasonal variations in the abundance of noncondensable gas at high southern latitudes, which are found to be consistent with results reported by Sprague et al. (2004, 2007). Corrections for spatial blurring are found to be important during the recession, when the column abundance of seasonal CO2 ice has the largest latitude gradient. The measured distribution and inventory of seasonal CO2 ice is compared to simulations by a general circulation model (GCM) calibrated using Viking lander pressure data, cap edge functions determined by thermal emission spectroscopy, and other nuclear spectroscopy data sets. On the basis of the amount of CO2 cycled through the caps during years 26 and 27, the gross polar energy balance has not changed significantly since Viking. The distribution of seasonal CO2 ice is longitudinally asymmetric: in the north, deposition rates of CO2 ice are elevated in Acidalia, which is exposed to katabatic winds from Chasma Borealis; in the south, CO2 deposition is highest near the residual cap. During southern recession, CO 2 ice is present longer than calculated by the GCM, which has implications for the local polar energy balance. Copyright 2009 by the American Geophysical Union.

  1. Commercialization Assistance Program (CAP)

    SciTech Connect

    Jenny C. Servo, Ph.D.

    2004-07-12

    In order to fulfill the objective of Small Business Innovation Research Program (SBIR), the Department of Energy funds an initiative referred to as the Commercialization Assistance Program (CAP). The over-arching purpose of the CAP is to facilitate transition of the SBIR-funded technology to Phase III defined as private sector investment or receipt of non-sbir dollars to further the commercialization of the technology. Phase III also includes increased sales. This report summarizes the stages involved in the implementation of the Commercialization Assistance Program, a program which has been most successful in fulfilling its objectives.

  2. [Capping strategies in RNA viruses].

    PubMed

    Bouvet, Mickaël; Ferron, François; Imbert, Isabelle; Gluais, Laure; Selisko, Barbara; Coutard, Bruno; Canard, Bruno; Decroly, Etienne

    2012-04-01

    Most viruses use the mRNA-cap dependent cellular translation machinery to translate their mRNAs into proteins. The addition of a cap structure at the 5' end of mRNA is therefore an essential step for the replication of many virus families. Additionally, the cap protects the viral RNA from degradation by cellular nucleases and prevents viral RNA recognition by innate immunity mechanisms. Viral RNAs acquire their cap structure either by using cellular capping enzymes, by stealing the cap of cellular mRNA in a process named "cap snatching", or using virus-encoded capping enzymes. Many viral enzymes involved in this process have recently been structurally and functionally characterized. These studies have revealed original cap synthesis mechanisms and pave the way towards the development of specific inhibitors bearing antiviral drug potential. PMID:22549871

  3. An East Siberian ice shelf during the Late Pleistocene glaciations: Numerical reconstructions

    NASA Astrophysics Data System (ADS)

    Colleoni, Florence; Kirchner, Nina; Niessen, Frank; Quiquet, Aurélien; Liakka, Johan

    2016-09-01

    A recent data campaign in the East Siberian Sea has revealed evidence of grounded and floating ice dynamics in regions of up to 1000 m water depth, and which are attributed to glaciations older than the Last Glacial Maximum (21 kyrs BP). The main hypothesis based on this evidence is that a small ice cap developed over Beringia and expanded over the East Siberian continental margin during some of the Late Pleistocene glaciations. Other similar evidence of ice dynamics that have been previously collected on the shallow continental shelves of the Arctic Ocean have been attributed to the penultimate glaciation, i.e. Marine Isotopes Stage 6 (≈140 kyrs BP). We use an ice sheet model, forced by two previously simulated MIS 6 glacial maximum climates, to carry out a series of sensitivity experiments testing the impact of dynamics and mass-balance related parameters on the geometry of the East Siberian ice cap and ice shelf. Results show that the ice cap developing over Beringia connects to the Eurasian ice sheet in all simulations and that its volume ranges between 6 and 14 m SLE, depending on the climate forcing. This ice cap generates an ice shelf of dimensions comparable with or larger than the present-day Ross ice shelf in West Antarctica. Although the ice shelf extent strongly depends on the ice flux through the grounding line, it is particularly sensitive to the choice of the calving and basal melting parameters. Finally, inhibiting a merging of the Beringia ice cap with the Eurasian ice sheet affects the expansion of the ice shelf only in the simulations where the ice cap fluxes are not large enough to compensate for the fluxes coming from the Eurasian ice sheet.

  4. The Mars water cycle at other epochs - Recent history of the polar caps and layered terrain

    NASA Technical Reports Server (NTRS)

    Jakosky, Bruce M.; Henderson, Bradley G.; Mellon, Michael T.

    1993-01-01

    A numerical model is presented of the integrated role of seasonal water cycle on the evolution of polar deposits on Mars over the last 10 million years. From the model, it is concluded that the only major difference between the polar caps which affects their long-term behavior is ultimately the difference in their elevations. Because of that difference, there is a preference for CO2 frost to stay longer on the northern polar cap. The average difference in sublimation at the caps results in a net south-to-north transport of water ice over long time scales. Superimposed on any long-term behavior is a transfer of water ice between the caps on the 10 exp 5 - 10 exp 6 yr time scales. The amount of water exchanged is small compared to the total ice content of the polar deposits.

  5. Exposed water ice discovered near the south pole of Mars.

    PubMed

    Titus, Timothy N; Kieffer, Hugh H; Christensen, Phillip R

    2003-02-14

    The Mars Odyssey Thermal Emission Imaging System (THEMIS) has discovered water ice exposed near the edge of Mars' southern perennial polar cap. The surface H2O ice was first observed by THEMIS as a region that was cooler than expected for dry soil at that latitude during the summer season. Diurnal and seasonal temperature trends derived from Mars Global Surveyor Thermal Emission Spectrometer observations indicate that there is H2O ice at the surface. Viking observations, and the few other relevant THEMIS observations, indicate that surface H2O ice may be widespread around and under the perennial CO2 cap.

  6. Exposed water ice discovered near the south pole of Mars

    USGS Publications Warehouse

    Titus, T.N.; Kieffer, H.H.; Christensen, P.R.

    2003-01-01

    The Mars Odyssey Thermal Emission Imaging System (THEMIS) has discovered water ice exposed near the edge of Mars' southern perennial polar cap. The surface H2O ice was first observed by THEMIS as a region that was cooler than expected for dry soil at that latitude during the summer season. Diurnal and seasonal temperature trends derived from Mars Global Surveyor Thermal Emission Spectrometer observations indicate that there is H2O ice at the surface. Viking observations, and the few other relevant THEMIS observations, indicate that surface H2O ice may be widespread around and under the perennial CO2 cap.

  7. 3. CAP; CONICAL CAP HAS BOWED RAFTERS MORTISED INTO A ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. CAP; CONICAL CAP HAS BOWED RAFTERS MORTISED INTO A BOSS; ALSO SEEN ARE THE BRAKE WHEEL, WINDSHAFT AND TOP BEARING OF THE UPRIGHT SHAFT - Hayground Windmill, Windmill Lane, East Hampton, Suffolk County, NY

  8. Advising. CAP Job Function.

    ERIC Educational Resources Information Center

    Ohio State Univ., Columbus. National Center for Research in Vocational Education.

    This Job Function Book (Advising) is one of the 14 components (see note) of the Career Alert Planning (CAP) program, a set of individualized materials designed to help participants find out about themselves and about the kind of work for which they are suited. In this program, participants become acquainted with occupations that are representative…

  9. Guard For Fuse Caps

    NASA Technical Reports Server (NTRS)

    Atwell, D. C.

    1985-01-01

    L-shaped guard attached to fuse holder. Guard prevents casual tampering with fuses in electrical junction box or fuse block. Protects fuses from being damaged by handling or by rope or string used to secure them. With fuse-cap guard, only responsible people have access to fuses.

  10. Arranging. CAP Job Function.

    ERIC Educational Resources Information Center

    Ohio State Univ., Columbus. National Center for Research in Vocational Education.

    This Job Function Booklet (Arranging) is one of the 14 components (see note) of the Career Alert Planning (CAP) program, a set of individualized materials designed to help participants find out about themselves and about the kind of work for which they are suited. In this program, participants become acquainted with occupations that are…

  11. Sunlight penetration through the Martian polar caps: Effects on the thermal and frost budgets

    NASA Technical Reports Server (NTRS)

    Lindner, Bernhard Lee

    1992-01-01

    An energy balance model of the seasonal polar caps on Mars is modified to include penetration of solar radiation into and through the ice. Penetration of solar radiation has no effect on subsurface temperature or total frost sublimation if seasonal ice overlies a dust surface. An effect is noted for seasonal ice which overlies the residual polar caps. For the case of an exposed water-ice residual polar cap, the temperature at depth is calculated to be up to several degrees warmer and the calculated lifetime of seasonal CO2 frost is slightly lower when penetration of sunlight is properly treated in the model. For the case of a residual polar cap which is perennially covered by CO2 frost, the calculated lifetime of seasonal CO2 frost is very slightly increased as a result of sunlight penetration through the ice. Hence, penetration of sunlight into the ice helps to stabilize the observed dichotomy in the residual polar caps on Mars, although it is a small effect.

  12. Sunlight penetration through the Martian polar caps - Effects on the thermal and frost budgets

    NASA Technical Reports Server (NTRS)

    Lindner, Bernhard L.

    1992-01-01

    An energy balance model of the seasonal polar caps on Mars is modified to include penetration of solar radiation into and through the ice. Penetration of solar radiation has no effect on subsurface temperature or total frost sublimation if seasonal ice overlies a dust surface. An effect is noted for seasonal ice which overlies the residual polar caps. For the case of an exposed water-ice residual polar cap, the temperature at depth is calculated to be up to several degrees warmer, and the calculated lifetime of seasonal CO2 frost is slightly lower when penetration of sunlight is properly treated in the model. For the case of a residual polar cap which is perennially covered by CO2 frost, the calculated lifetime of seasonal CO2 frost is very slightly increased as a result of sunlight penetration through the ice. Hence, penetration of sunlight into the ice helps to stabilize the observed dichotomy in the residual polar caps on Mars, although it is a small effect.

  13. Model for Formation of Martian Residual Cap Depressions (Swiss Cheese)

    NASA Astrophysics Data System (ADS)

    Byrne, S.; Ingersoll, A. P.

    2001-12-01

    In an effort for explain the formation of the `Swiss-cheese' terrain visible on the southern residual cap of Mars (Thomas et al., Nature, 404,2000); we have developed a radiative model to follow the growth/decay of an initial depression due to sublimation/condensation of carbon dioxide. The pits making up this terrain have many distinctive features; they are shallow (~10m deep), with steep walls and flat floors and contain an interior moat that runs along the bottom of the walls. Their diameters range from a few 10's of meters to a kilometer. The model accounts for incident sunlight, emitted thermal radiation, and scattered short and long wave radiation. We have included the effects of a layer of water ice placed under the carbon dioxide at adjustable depth. The water ice layer is free to store heat during the summer (when the carbon dioxide has been removed) through subsurface diffusion of heat. Release of this heat at the end of the summer can inhibit frost formation. We have investigated many cases involving pure dry ice with constant albedo, albedo as a function of insolation, and differing albedo for fresh and residual frost (the latter has lower albedo). In most cases the initial depressions heal themselves and disappear into the surrounding terrain. Cases involving the layer of water ice provide a much closer approximation to the shape of the observed features (especially the flat bottoms). A problem arises of how much exposed water ice we can have during the summer season and still have temperatures averaged over the footprint of the Thermal Emission Spectrometer be close to the carbon dioxide sublimation temperatures. The depth to the water ice layer is a strong controlling factor of the evolution of depression shape and depth in our model. Matching this shape with observations yields important information regarding the depth to any putative water ice layer within the residual cap itself. It is known from laboratory measurements that carbon dioxide is too

  14. Cap protects aircraft nose cone

    NASA Technical Reports Server (NTRS)

    Bryan, C. F., Jr.; Bryan, D. C.

    1981-01-01

    Inexpensive, easily fabricated cap protects aircraft nose cone from erosion. Made of molded polycarbonate, cap has been flight tested at both subsonic and supesonic speeds. Its strength and erosion characteristics are superior to those of fiberglass cones.

  15. Designing Smart Charter School Caps

    ERIC Educational Resources Information Center

    Dillon, Erin

    2010-01-01

    In 2007, Andrew J. Rotherham proposed a new approach to the contentious issue of charter school caps, the statutory limits on charter school growth in place in several states. Rotherham's proposal, termed "smart charter school caps," called for quality sensitive caps that allow the expansion of high-performing charter schools while also…

  16. Performance of blasting caps

    NASA Technical Reports Server (NTRS)

    Bement, Laurence J. (Inventor); Schimmel, Morry L. (Inventor); Perry, Ronnie B. (Inventor)

    1993-01-01

    Common blasting caps are made from an aluminum shell in the form of a tube which is closed at both ends. One end, which is called the output end, terminates in a principal side or face, and contains a detonating agent which communicates with a means for igniting the detonating agent. The improvement of the present invention is a flat, steel foil bonded to the face in a position which is aligned perpendicularly to the longitudinal axis of the tube.

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  18. Enhanced sea-ice export from the Arctic during the Younger Dryas.

    PubMed

    Not, Christelle; Hillaire-Marcel, Claude

    2012-01-31

    The Younger Dryas cold spell of the last deglaciation and related slowing of the Atlantic meridional overturning circulation have been linked to a large array of processes, notably an influx of fresh water into the North Atlantic related to partial drainage of glacial Lake Agassiz. Here we observe a major drainage event, in marine sediment cores raised from the Lomonosov Ridge, in the central Arctic Ocean marked by a pulse in detrital dolomitic-limestones. This points to an Arctic-Canadian sediment source area with about fivefold higher Younger Dryas ice-rafting deposition rate, in comparison with the Holocene. Our findings thus support the hypothesis of a glacial drainage event in the Canadian Arctic area, at the onset of the Younger Dryas, enhancing sea-ice production and drifting through the Arctic, then export through Fram Strait, towards Atlantic meridional overturning circulation sites of the northern North Atlantic.

  19. 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.

  20. Update on the Dynamics of the Late Wisconsinan Northwestern Laurentide Ice-Sheet

    NASA Astrophysics Data System (ADS)

    Hillaire-Marcel, C.; Tarasov, L.

    2014-12-01

    Ice streams draining ice from major ice divides over Keewatin, New-Quebec and Foxe Basin-Baffin Island areas constitute a key feature of the Last Glacial Maximum (LGM) Laurentide Ice Sheet (LIS). They put constraints on the topographic evolution, volume and stable isotope contents of LIS, thus on LGM ocean volume and isotopic composition. Here, we re-visit field-based information about Laurentide Ice Sheet (LIS) dynamics in the Hudson Bay and Strait area, from the LGM to its final decay, and confront this information with deep-sea core records from Baffin Bay and the Labrador Sea. Core HU08-029-004 raised off Hudson Strait points to continuous in Hudson Strait throughout the whole interval, with acceleration during Heinrich (H) events 2 and 1, possibly triggered (at least for H1) by a delayed LGM-glacio-isostatic response. Streaming sediment supplies from Hudson Strait are recorded by fine detrital carbonates, without evidence of Foxe Basin sediment sources, thus suggesting streaming from the Ungava Peninsula and southern Baffin Island. Later on, in southern Hudson Bay, the Cochrane surges (~8.7 ka BP) illustrate fast ice streaming southwards, mostly from the Keewatin ice-divide, into Lake Agassiz-Ojibway. Ice-thinning in the Bay and the Foxe Basin areas led to the lake final drainage through Hudson Strait, and its replacement by the Tyrrell Sea (~8.3 ka BP). In Baffin Bay, out of phase surgings, mostly from the Inuitian and Greenland ice sheets, are similarly recorded. These new data and re-interpretation of earlier information corroborate the concept of a dynamic (ice-stream prevalent) North American Ice complex during the Late Wisconsin as evident in recent glaciological reconstructions. This along with recent data-calibrated glaciological reconstructions for the other major ice sheets result in a global shortfall of at least 10m compared to far field relative sea-level records.

  1. Sea Ice

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.; Cavalieri, Donald J.

    2005-01-01

    Sea ice covers vast areas of the polar oceans, with ice extent in the Northern Hemisphere ranging from approximately 7 x 10(exp 6) sq km in September to approximately 15 x 10(exp 6) sq km in March and ice extent in the Southern Hemisphere ranging from approximately 3 x 10(exp 6) sq km in February to approximately 18 x 10(exp 6) sq km in September. These ice covers have major impacts on the atmosphere, oceans, and ecosystems of the polar regions, and so as changes occur in them there are potential widespread consequences. Satellite data reveal considerable interannual variability in both polar sea ice covers, and many studies suggest possible connections between the ice and various oscillations within the climate system, such as the Arctic Oscillation, North Atlantic Oscillation, and Antarctic Oscillation, or Southern Annular Mode. Nonetheless, statistically significant long-term trends are also apparent, including overall trends of decreased ice coverage in the Arctic and increased ice coverage in the Antarctic from late 1978 through the end of 2003, with the Antarctic ice increases following marked decreases in the Antarctic ice during the 1970s. For a detailed picture of the seasonally varying ice cover at the start of the 21st century, this chapter includes ice concentration maps for each month of 2001 for both the Arctic and the Antarctic, as well as an overview of what the satellite record has revealed about the two polar ice covers from the 1970s through 2003.

  2. Mars South Polar Cap 'Fingerprint' Terrain

    NASA Technical Reports Server (NTRS)

    2000-01-01

    This picture is illuminated by sunlight from the upper left.

    Some portions of the martian south polar residual cap have long, somewhat curved troughs instead of circular pits. These appear to form in a layer of material that may be different than that in which 'swiss cheese' circles and pits form, and none of these features has any analog in the north polar cap or elsewhere on Mars. This picture shows the 'fingerprint' terrain as a series of long, narrow depressions considered to have formed by collapse and widening by sublimation of ice. Unlike the north polar cap, the south polar region stays cold enough in summer to retain frozen carbon dioxide. Viking Orbiter observations during the late 1970s showed that very little water vapor comes off the south polar cap during summer, indicating that any frozen water that might be there remains solid throughout the year.

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image was obtained in early southern spring on August 4, 1999. It shows an area 3 x 5 kilometers (1.9 x 3.1 miles) at a resolution of about 7.3 meters (24 ft) per pixel. Located near 86.0oS, 53.9oW.

    Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

  3. Ice-atmosphere interactions in the Canadian High Arctic: Implications for the thermo-mechanical evolution of terrestrial ice masses

    NASA Astrophysics Data System (ADS)

    Wohlleben, Trudy M. H.

    Canadian High Arctic terrestrial ice masses and the polar atmosphere evolve codependently, and interactions between the two systems can lead to feedbacks, positive and negative. The two primary positive cryosphere-atmosphere feedbacks are: (1) The snow/ice-albedo feedback (where area changes in snow and/or ice cause changes in surface albedo and surface air temperatures, leading to further area changes in snow/ice); and (2) The elevation - mass balance feedback (where thickness changes in terrestrial ice masses cause changes to atmospheric circulation and precipitation patterns, leading to further ice thickness changes). In this thesis, numerical experiments are performed to: (1) quantify the magnitudes of the two feedbacks for chosen Canadian High Arctic terrestrial ice masses; and (2) to examine the direct and indirect consequences of surface air temperature changes upon englacial temperatures with implications for ice flow, mass flux divergence, and topographic evolution. Model results show that: (a) for John Evans Glacier, Ellesmere Island, the magnitude of the terrestrial snow/ice-albedo feedback can locally exceed that of sea ice on less than decadal timescales, with implications for glacier response times to climate perturbations; (b) although historical air temperature changes might be the direct cause of measured englacial temperature anomalies in various glacier and ice cap accumulation zones, they can also be the indirect cause of their enhanced diffusive loss; (c) while the direct result of past air temperature changes has been to cool the interior of John Evans Glacier, and its bed, the indirect result has been to create and maintain warm (pressure melting point) basal temperatures in the ablation zone; and (d) for Devon Ice Cap, observed mass gains in the northwest sector of the ice cap would be smaller without orographic precipitation and the mass balance---elevation feedback, supporting the hypothesis that this feedback is playing a role in the

  4. Climatic variations on Mars. II - Evolution of carbon dioxide atmosphere and polar caps

    NASA Technical Reports Server (NTRS)

    Ward, W. R.; Murray, B. C.; Malin, M. C.

    1974-01-01

    The long-term variations in the atmospheric pressure and the polar cap temperature of Mars resulting from the obliquity oscillations are discussed. In performing these calculations, the assumption is made that the atmosphere is in equilibrium with perennial CO2 ice deposits at the north pole, as is proposed by Leighton and Murray (1966). If heat transport by the atmosphere is neglected, the temperature of CO2 ice at the poles ranges from about 130 K to about 160 K, the corresponding atmospheric pressure rising from a few tenths of a millibar to about 30 mbar, respectively. The neglect of atmospheric heat transport probably underestimates the peak pressure. Because the altitude of the south cap is about 2 km higher than that of the north cap, CO2 ice is unstable there and will migrate to the north cap at a rate of about 10 g/sq cm yr, the implication being that the south residual cap is water ice. A simplified model of the annual polar caps and pressure fluctuations is also presented.

  5. Saltstone Clean Cap Formulation

    SciTech Connect

    Langton, C

    2005-04-22

    The current operation strategy for using Saltstone Vault 4 to receive 0.2 Ci/gallon salt solution waste involves pouring a clean grout layer over the radioactive grout prior to initiating pour into another cell. This will minimize the radiating surface area and reduce the dose rate at the vault and surrounding area. The Clean Cap will be used to shield about four feet of Saltstone poured into a Z-Area vault cell prior to moving to another cell. The minimum thickness of the Clean Cap layer will be determined by the cesium concentration and resulting dose levels and it is expected to be about one foot thick based on current calculations for 0.1 Ci Saltstone that is produced in the Saltstone process by stabilization of 0.2 Ci salt solution. This report documents experiments performed to identify a formulation for the Clean Cap. Thermal transient calculations, adiabatic temperature rise measurements, pour height, time between pour calculations and shielding calculations were beyond the scope and time limitations of this study. However, data required for shielding calculations (composition and specific gravity) are provided for shielding calculations. The approach used to design a Clean Cap formulation was to produce a slurry from the reference premix (10/45/45 weight percent cement/slag/fly ash) and domestic water that resembled as closely as possible the properties of the Saltstone slurry. In addition, options were investigated that may offer advantages such as less bleed water and less heat generation. The options with less bleed water required addition of dispersants. The options with lower heat contained more fly ash and less slag. A mix containing 10/45/45 weight percent cement/slag/fly ash with a water to premix ratio of 0.60 is recommended for the Clean Cap. Although this mix may generate more than 3 volume percent standing water (bleed water), it has rheological, mixing and flow properties that are similar to previously processed Saltstone. The recommended

  6. Over Ice

    NASA Video Gallery

    All about NASA's IceBridge P-3B plane and its IceBridge retrofit. Upgraded with 21st century "special modifications", the aircraft is less a cold war relic and more like the Space Agency's Millenni...

  7. What can bromine in ice cores tell us about Arctic sea ice in the past?

    NASA Astrophysics Data System (ADS)

    Vallelonga, Paul; Spolaor, Andrea; Maffazzoli, Niccolo; Kjær, Helle; Barbante, Carlo; Saiz-Lopez, Alfonso

    2016-04-01

    Bromine is of interest as a potential sea ice proxy due to its role in polar atmospheric chemistry, particularly the photochemical "bromine explosion" events which occur over the seasonal sea ice surface. A growing body of literature has demonstrated that bromine is reliably deposited and preserved in polar ice caps and can be used to investigate variability over timescales varying from seasonal to multimillenial. For sea ice reconstructions, bromine and sodium are usually evaluated with respect to their relative abundances in seawater. Competing processes of bromine enrichment due to the bromine explosion, and bromine depletion due to scavenging and deposition, must be taken into account when comparing results from coastal and inland sampling sites. We will review existing bromine-based sea ice reconstructions and present new data for locations from Svalbard, Severnaya Zemlya, Northwest Greenland (NEEM ice core) and central East Greenland (Renland ice core).

  8. 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

  9. Vinyl capped addition polyimides

    NASA Technical Reports Server (NTRS)

    Vannucci, Raymond D. (Inventor); Malarik, Diane C. (Inventor); Delvigs, Peter (Inventor)

    1990-01-01

    Polyimide resins having improved thermo-oxidative stability are provided having aromatic vinyl end-caps. The polyimides are prepared by the reaction of a mixture of monomers comprising (1) a diamine, (2) an ester of tetracarboxylic acid and (3) an aromatic vinyl compound in a molar ratio of 1:2:3 of n: (n + 1):2 when the aromatic vinyl compound contains nitrogen and in a ratio of (n + 1):n:2 when the aromatic vinyl compound does not contain nitrogen, wherein n ranges from about 5 to about 20.

  10. Influence of Chemically Enhanced Diffusion on Cap Dolostones?

    NASA Astrophysics Data System (ADS)

    Bristow, T.

    2014-12-01

    Cap dolostones, a globally distributed layer of carbonate rock that sits directly on terminal glacial deposits of the severe Cryogenian ice-age, contain important records of the conditions during the early stage of climatic recovery. Negative carbon isotope signals preserved in the cap are central to discussions of the mechanisms, drivers and time-scale of this interval of extreme climate change. These signals have been attributed to the rapid rise in temperature and acidic ocean conditions predicted to result from huge amounts of CO2 in the atmosphere, which bumped the Earth out of the Snowball state. Questions remain however, because detailed investigations of cap dolostone isotopic variability within individual sedimentary basins show systematic variations that are difficult to explain by temperature effects alone. Furthermore, other influences on cap isotopes have been hypothesized including, the release of massive amounts of methane trapped by the ice and upwelling of deep ocean water with negative signals. This contribution will explore the potential impact of chemically enhanced diffusion (CED) on the carbon isotopic compositions of cap dolostones using a box model. CED is a process by which CO2 gas is transferred to solution via reaction with hydroxide anions. In the modern ocean, rates of CED are thought to be insignificant and CO2 gas transfer is accomplished primarily by diffusion and dissolution, with minimal isotopic fraction. However, in various highly productive lakes, the strong negative isotope fraction of -27 ‰ associated CED impacts the isotopic composition of dissolved inorganic carbon. Post-glacial oceans may have been chemically similar to highly productive lakes and initial modeling results indicate that CED could have influenced the carbon isotopic composition of seawater and thus the cap dolostone. Implications for post-glacial oceanic conditions will be discussed.

  11. Exposure of Water Ice in the Northern Mid-lattitudes of Mars

    NASA Technical Reports Server (NTRS)

    Allen, Carlton C.; Kanner, Lisa C.

    2007-01-01

    Water ice is exposed in the martian north polar cap, and is occasionally exposed beyond the cap boundary. Orbital gamma ray spectrometry data strongly imply the presence of water ice within meters of the surface at latitudes north of approximately 60 deg. We have examined midlatitude areas of the northern plains displaying evidence of residual ice-rich layers, and report possible present-day exposures of ice. These exposures, if confirmed, could constrain the latitudinal and temporal stability of surface ice on Mars.

  12. Present-day Exposures of Water Ice in the Northern Mid-latitudes of Mars

    NASA Technical Reports Server (NTRS)

    Allen, Carlton C.; Kanner, Lisa C.

    2007-01-01

    Water ice is exposed in the martian north polar cap, but is rarely exposed beyond the cap boundary. Orbital gamma ray spectrometry data strongly imply the presence of water ice within meters of the surface at latitudes north of approximately 60deg. We have examined mid-latitude areas of the northern plains displaying residual ice-rich layers, and report evidence of present-day surface exposures of water ice. These exposures, if confirmed, could con-strain the latitudinal and temporal stability of surface ice on Mars.

  13. Evolving Technologies for In-Situ Studies of Mars Ice

    NASA Technical Reports Server (NTRS)

    Carsey, F. D.; Hecht, M. H.

    2003-01-01

    Icy sites on Mars continue to be of high scientific importance. These sites include the polar caps, the southern mid-latitude subsurface permafrost, and the seasonal frost. These sites have interest due to their roles in climate processes, past climates, surface and near-surface water, astrobiology, geomorphology, and other topics. As is the case for many planetary features, remote sensing, while of great value, cannot answer all questions; in-situ examination is essential, and the motivation for in-situ observations generally leads to the subsurface, which, fortunately, is accessible on Mars. It is clear in fact that a Mars polar cap subsurface mission is both scientifically compelling and practical. Recent data from orbiting platforms has provided a remarkable level of information about the Mars ice caps; we know, for example, the size, shape and annual cycle of the cap topography as well as we know that of Earth, and we have more information on stratification that we have of, for example, the ice of East Antarctica. To understand the roles that the Mars polar caps play, it is necessary to gather information on the ice cap surface, strata, composition and bed. In this talk the status of in-situ operations and observations will be summarized, and, since we have conveniently at hand another planet with polar caps, permafrost and ice, the role of testing and validation of experimental procedures on Earth will be addressed.

  14. Possible contemporary evaporites formation at the Martian Northern Polar Cap

    NASA Astrophysics Data System (ADS)

    Losiak, Anna; Czechowski, Leszek

    Evaporitic minerals are abundant on the surface of Mars (e.g., Wentworth et al. 2005, Velbel 2012, Clark and Van Hart 1981, Wang et al. 2006, Kuzmin et al. 2009), especially within the Circumpolar Dune Field and on the Northern Ice Cap itself (e.g., Langevin et al., 2005, Roach et al. 2007, Horgan et al. 2009, Masse et al. 2010, 2012). Most of their proposed formation mechanisms require significant amounts of liquid water and are thus not possible under current Martian conditions (Arvidson et al. 2006, Andrews-Hanna et al. 2007, Fishbaugh et al. 2007, Szynkiewicz et al. 2010). Some authors have considered the potential role of ice and ice- or snowmelt-related alteration in the weathering of Martian materials (e.g., Catling et al. 2006, Zolotov and Mironenko 2007, Niles and Michalski 2009, Masse et al. 2010). However, none of those studies discussed details of the process leading to the formation of the evaporites or the timing of the processes. The aim of this paper is to model numerically if the current radiant heating is sufficient to melt a thin layer of ice surrounding a single dust grain exposed within the south facing side of the Martian North Polar Cap trench. The results of our initial study suggest that for dust grains with basaltic properties and ice with low values of coefficient of heat conduction, and solar constant = 492 W/m2 liquid water may exist below a dust grain for up to 4 hours a sol. This suggest that contemporary evaporites formation on Martian Polar Cap is possible.

  15. Colonization of maritime glacier ice by bdelloid Rotifera.

    PubMed

    Shain, Daniel H; Halldórsdóttir, Katrín; Pálsson, Finnur; Aðalgeirsdóttir, Guðfinna; Gunnarsson, Andri; Jónsson, Þorsteinn; Lang, Shirley A; Pálsson, Hlynur Skagfjörð; Steinþórssson, Sveinbjörn; Arnason, Einar

    2016-05-01

    Very few animal taxa are known to reside permanently in glacier ice/snow. Here we report the widespread colonization of Icelandic glaciers and ice fields by species of bdelloid Rotifera. Specimens were collected within the accumulation zones of Langjökull and Vatnajökull ice caps, among the largest European ice masses. Rotifers reached densities up to ∼100 individuals per liter-equivalent of glacier ice/snow, and were freeze-tolerant. Phylogenetic analyses indicate that glacier rotifers are polyphyletic, with independent ancestries occurring within the Pleistocene. Collectively, these data identify a previously undescribed environmental niche for bdelloid rotifers and suggest their presence in comparable habitats worldwide.

  16. Constraints on Lake Agassiz discharge through the late-glacial Champlain Sea (St. Lawrence Lowlands, Canada) using salinity proxies and an estuarine circulation model

    USGS Publications Warehouse

    Katz, B.; Najjar, R.G.; Cronin, T.; Rayburn, J.; Mann, M.E.

    2011-01-01

    During the last deglaciation, abrupt freshwater discharge events from proglacial lakes in North America, such as glacial Lake Agassiz, are believed to have drained into the North Atlantic Ocean, causing large shifts in climate by weakening the formation of North Atlantic Deep Water and decreasing ocean heat transport to high northern latitudes. These discharges were caused by changes in lake drainage outlets, but the duration, magnitude and routing of discharge events, factors which govern the climatic response to freshwater forcing, are poorly known. Abrupt discharges, called floods, are typically assumed to last months to a year, whereas more gradual discharges, called routing events, occur over centuries. Here we use estuarine modeling to evaluate freshwater discharge from Lake Agassiz and other North American proglacial lakes into the North Atlantic Ocean through the St. Lawrence estuary around 11.5 ka BP, the onset of the Preboreal oscillation (PBO). Faunal and isotopic proxy data from the Champlain Sea, a semi-isolated, marine-brackish water body that occupied the St. Lawrence and Champlain Valleys from 13 to 9 ka, indicate salinity fell about 7-8 (range of 4-11) around 11.5 ka. Model results suggest that minimum (1600 km3) and maximum (9500 km3) estimates of plausible flood volumes determined from Lake Agassiz paleoshorelines would produce the proxy-reconstructed salinity decrease if the floods lasted <1 day to 5 months and 1 month to 2 years, respectively. In addition, Champlain Sea salinity responds very quickly to the initiation (within days) and cessation (within weeks) of flooding events. These results support the hypothesis that a glacial lake flood, rather than a sustained routing event, discharged through the St. Lawrence Estuary during the PBO. ?? 2011 Elsevier Ltd.

  17. Polar Cap Pits

    NASA Technical Reports Server (NTRS)

    2005-01-01

    17 August 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows kidney bean-shaped pits, and other pits, formed by erosion in a landscape of frozen carbon dioxide. This images shows one of about a dozen different patterns that are common in various locations across the martian south polar residual cap, an area that has been receiving intense scrutiny by the MGS MOC this year, because it is visible on every orbit and in daylight for most of 2005.

    Location near: 86.9oS, 6.9oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Spring

  18. Staggering through the ice ages

    SciTech Connect

    Monastersky, R.

    1994-07-30

    Because the steady orbital cycles of earth, thought to control the ice ages, cannot easily account for the evidence of repeated rapid climatic shifts during the last ice age. Without knowing what made the iceage climate so in temperate, scientists cannot tell whether today's interglacial period is immune to the sudden swings. Information about climate instability has emerged from two drilling projects in the middle of Greenland where crews bored through the 3-kilometer think glacial cap. This paper describes the discoveries and the evidence for rapid climatic shifts, including conflicting results from different sites. The concerns about global warming are making questions about these shifts of increased interest. The possibility exists that modern climate harbors an inherently unstable element that could trigger wild wings in response to the atmospheric buildup of greenhouse gases. On the other hand sudden climatic shifts might have been unique to the ice-age Earth.

  19. 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.

  20. Polar ice melting

    NASA Astrophysics Data System (ADS)

    Calvert, Jack G.

    Shrinking polar ice caps may be causing the earth's sea level to rise and its days to lengthen. ‘Rising mean sea level is a significant indication of global climate change,’ R. Etkins and E. Epstein report, pointing out that global sea levels have risen slightly more than one-tenth of an inch each year, on the average, since 1940, for a total of nearly 5 inches (Science, 215, 287-289, 1982). This is triple the rate of rise measured during the preceding half century, from 1890 to 1940.Etkins and Epstein estimate that more than 10,000 cubic miles of polar ice, most of it presumably from Antarctic ice sheets, must have melted in the past 40 years. They calculate that transfer of this great mass to the equivalent of a thin layer of water spread over the world's oceans also would tend to reduce the speed of the earth's rotation. This would lengthen each day by about one-thousandth of a second, they say, accounting for about three-fourths of the actual increase in the length of the day observed by scientists over the past 40 years.

  1. Sea Ice

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

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

  2. 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.

  3. An update on land-ice modeling in the CESM

    SciTech Connect

    Lipscomb, William H

    2011-01-18

    Mass loss from land ice, including the Greenland and Antarctic ice sheets as well as smaller glacier and ice caps, is making a large and growing contribution to global sea-level rise. Land ice is only beginning to be incorporated in climate models. The goal of the Land Ice Working Group (LIWG) is to develop improved land-ice models and incorporate them in CESM, in order to provide useful, physically-based sea-level predictions. LJWG efforts to date have led to the inclusion of a dynamic ice-sheet model (the Glimmer Community Ice Sheet Model, or Glimmer-CISM) in the Community Earth System Model (CESM), which was released in June 2010. CESM also includes a new surface-mass-balance scheme for ice sheets in the Community Land Model. Initial modeling efforts are focused on the Greenland ice sheet. Preliminary results are promising. In particular, the simulated surface mass balance for Greenland is in good agreement with observations and regional model results. The current model, however, has significant limitations: The land-ice coupling is one-way; we are using a serial version of Glimmer-CISM with the shallow-ice approximation; and there is no ice-ocean coupling. During the next year we plan to implement two-way coupling (including ice-ocean coupling with a dynamic Antarctic ice sheet) with a parallel , higher-order version of Glimmer-CISM. We will also add parameterizations of small glaciers and ice caps. With these model improvements, CESM will be able to simulate all the major contributors to 21st century global sea-level rise. Results of the first round of simulations should be available in time to be included in the Fifth Assessment Report (ARS) of the Intergovernmental Panel on Climate Change.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  5. How Thick is the North Polar Ice Cap on Mars?

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This map shows the thickness of the north polar layered deposits on Mars as measured by the Shallow Radar instrument on NASA's Mars Reconnaissance Orbiter.

    The Shallow Radar instrument was provided by the Italian Space Agency. Its operations are led by the University of Rome and its data are analyzed by a joint U.S.-Italian science team. JPL, a division of the California Institute of Technology, Pasadena, manages the Mars Reconnaissance Orbiter for the NASA Science Mission Directorate, Washington

  6. Sensitivity of glaciers and small ice caps to greenhouse warming

    SciTech Connect

    Oerlemans, J.; Fortuin, J.P.F. )

    1992-10-02

    Recent field programs on glaciers have supplied information that makes simulation of glacier mass balance with meteorological models meaningful. An estimate of world-wide glacier sensitivity based on a modeling study of 12 selected glaciers situated in widely differing climatic regimes shows that for a uniform 1 K warming the area-weighted glacier mass balance will decrease by 0.40 meter per year. This corresponds to a sea-level rise of 0.58 millimeter per year, a value significantly less than earlier estimates.

  7. The South Residual CO 2 Cap on Mars: Investigations with a Mars Global Climate Model

    NASA Astrophysics Data System (ADS)

    Kahre, Melinda A.; Dequaire, Julie; Hollingsworth, Jeffery L.; Haberle, Robert

    2016-10-01

    The CO2 cycle is one of the three controlling climate cycles on Mars. One aspect of the CO2 cycle that is not yet fully understood is the existence of a residual CO2 ice cap that is offset from the south pole. Previous investigations suggest that the atmosphere could control the placement of the south residual cap (e.g., Colaprete et al., 2005). These investigations show that topographically forced stationary eddies in the south during southern hemisphere winter produce colder atmospheric temperatures and increased CO2 snowfall over the hemisphere where the residual cap resides. Since precipitated CO2 ice produces higher surface albedos than directly deposited CO2 ice, it is plausible that CO2 snowfall resulting from the zonally asymmetric atmospheric circulation produces surface ice albedos high enough to maintain a residual cap only in one hemisphere. Our current work builds on these initial investigations with a version of the NASA Ames Mars Global Climate Model (GCM) that includes a sophisticated CO2 cloud microphysical scheme. Processes of cloud nucleation, growth, sedimentation, and radiative effects are accounted for. Simulated results thus far agree well with the Colaprete et al. study—the zonally asymmetric nature of the atmospheric circulation produces enhanced snowfall over the residual cap hemisphere throughout much of the winter season. However, the predicted snowfall patterns vary significantly with season throughout the cap growth and recession phases. We will present a detailed analysis of the seasonal evolution of the predicted atmospheric circulation and snowfall patterns to more fully evaluate the hypothesis that the atmosphere controls the placement of the south residual cap.

  8. Observations of the northern seasonal polar cap on Mars: I. Spring sublimation activity and processes

    USGS Publications Warehouse

    Hansen, C.J.; Byrne, S.; Portyankina, G.; Bourke, M.; Dundas, C.; McEwen, A.; Mellon, M.; Pommerol, A.; Thomas, N.

    2013-01-01

    Spring sublimation of the seasonal CO2 northern polar cap is a dynamic process in the current Mars climate. Phenomena include dark fans of dune material propelled out onto the seasonal ice layer, polygonal cracks in the seasonal ice, sand flow down slipfaces, and outbreaks of gas and sand around the dune margins. These phenomena are concentrated on the north polar erg that encircles the northern residual polar cap. The Mars Reconnaissance Orbiter has been in orbit for three Mars years, allowing us to observe three northern spring seasons. Activity is consistent with and well described by the Kieffer model of basal sublimation of the seasonal layer of ice applied originally in the southern hemisphere. Three typical weak spots have been identified on the dunes for escape of gas sublimed from the bottom of the seasonal ice layer: the crest of the dune, the interface of the dune with the interdune substrate, and through polygonal cracks in the ice. Pressurized gas flows through these vents and carries out material entrained from the dune. Furrows in the dunes channel gas to outbreak points and may be the northern equivalent of southern radially-organized channels (“araneiform” terrain), albeit not permanent. Properties of the seasonal CO2 ice layer are derived from timing of seasonal events such as when final sublimation occurs. Modification of dune morphology shows that landscape evolution is occurring on Mars today, driven by seasonal activity associated with sublimation of the seasonal CO2 polar cap.

  9. Can snow save us from global warming? (Louis Agassiz Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Dominé, Florent; Picard, Ghislain; Morin, Samuel; Krinner, Gerhard; Gouttevin, Isabelle; Menegoz, Martin; Gallet, Jean-Charles; Arnaud, Laurent; Dumont, Marie; Lafaysse, Matthieu; Brun, Eric

    2013-04-01

    How snow will interact with climate in the current warming context is an open issue. There is of course the well known snow-albedo feedback, whereby the replacement of snow by darker surfaces positively feedbacks on climate. But many other snow-climate feedbacks have been proposed recently, both positive and negative, so that predictions of future polar climate are rather uncertain. Warming will change precipitation and metamorphic conditions in the snowpack, affecting snow physical properties such as grain size, albedo and thermal conductivity. Their consequences are difficult to predict, with threshold effects between different regimes in snow metamorphism. A significant negative feedback between precipitation, snow albedo and climate has been detected in Antarctica, where increased precipitation increase albedo by bringing small grains to the surface, and this is not compensated by the warmer temperatures that accelerate grain growth. On the contrary, similar processes acting in the Arctic have led to a positive feedback. Changes in snow thermal conductivity can have important effects on the growth of sea ice, with spatially variable effects. In the Arctic, the warming-induced growth of higher vegetation such as shrubs can produce additional effects. Shrubs trap snow, increase snow depth and shield snow from wind erosion. Snow physical properties will change, with the likely partial replacement of wind slabs by layers of depth hoar of lower thermal conductivity. This may limit winter ground cooling, with effects on permafrost stability and on the release of greenhouse gases from thawing carbon stocks. Several examples will be detailed to illustrate the complexity of snow-climate interactions and to stress the need for a detailed description of snow physical properties in climate models, before we can conclude as to whether snow will slow down polar warming or on the contrary accelerate it, with possible catastrophic consequences.

  10. Fourier spectra from exoplanets with polar caps and ocean glint

    NASA Astrophysics Data System (ADS)

    Visser, P. M.; van de Bult, F. J.

    2015-07-01

    Context. The weak orbital-phase dependent reflection signal of an exoplanet contains information on the planet surface, such as the distribution of continents and oceans on terrestrial planets. This light curve is usually studied in the time domain, but because the signal from a stationary surface is (quasi)periodic, analysis of the Fourier series may provide an alternative, complementary approach. Aims: We study Fourier spectra from reflected light curves for geometrically simple configurations. Depending on its atmospheric properties, a rotating planet in the habitable zone could have circular polar ice caps. Tidally locked planets, on the other hand, may have symmetric circular oceans facing the star. These cases are interesting because the high-albedo contrast at the sharp edges of the ice-sheets and the glint from the host star in the ocean may produce recognizable light curves with orbital periodicity, which could also be interpreted in the Fourier domain. Methods: We derive a simple general expression for the Fourier coefficients of a quasiperiodic light curve in terms of the albedo map of a Lambertian planet surface. Analytic expressions for light curves and their spectra are calculated for idealized situations, and dependence of the spectral peaks on the key parameters inclination, obliquity, and cap size is studied. Results: The ice-scattering and ocean glint contributions can be separated out, because the coefficients for glint are all positive, whereas ice sheets lead to even-numbered, higher harmonics. An in-view polar cap on a planet without axial tilt only produces a single peak. The special situation of edge-on observation, which is important for planets in transit, leads to the most pronounced spectral behavior. Then the respective spectra from planets with a circumventing ocean, a circular ocean (eyeball world), polar caps, and rings, have characteristic power-law tails n-2, n-7/2, n-4, and (-1)n + 1n-2. Conclusions: Promising recently discovered

  11. Life in the Ice

    NASA Technical Reports Server (NTRS)

    Allen, C. C.; Wainwright, N. R.; Grasby, S. E.; Harvey, R. P.

    2003-01-01

    The current Martian surface environment is extremely hostile to any known form of life. The combination of subfreezing temperature, low atmospheric pressure and high ultraviolet flux, combined with desiccated and possibly oxidizing soil, could destroy even the hardiest microorganisms. The Viking biology experiments are generally interpreted to indicate that the surface of Mars is currently devoid of life and organic molecules at the part-per-billion level. Speculation on the possibility of extant or preserved microbial life on Mars thus centers on refuges in some manner protected from the current surface environment, either in space or time. Terrestrial analogs include hydrothermal systems, lakes, caves and subsurface aquifers as well as more clement conditions in the distant past. We are examining the evidence for microbiology in Earth's glaciated polar regions as analogs to the polar caps of Mars. This research concerns the detection of microorganisms or their preserved remains at the surface and within polar glacial ice.

  12. Genetics Home Reference: cap myopathy

    MedlinePlus

    ... Groote C, de Jonghe P, Marttila M, Laing NG, Pelin K, Wallgren-Pettersson C. Cap disease caused ... E, Wallefeld W, Memo M, Donner K, Laing NG, Marston S, Grönholm M, Wallgren-Pettersson C. Abnormal actin ...

  13. Stuck fuel rod capping sleeve

    DOEpatents

    Gorscak, Donald A.; Maringo, John J.; Nilsen, Roy J.

    1988-01-01

    A stuck fuel rod capping sleeve to be used during derodding of spent fuel assemblies if a fuel rod becomes stuck in a partially withdrawn position and, thus, has to be severed. The capping sleeve has an inner sleeve made of a lower work hardening highly ductile material (e.g., Inconel 600) and an outer sleeve made of a moderately ductile material (e.g., 304 stainless steel). The inner sleeve may be made of an epoxy filler. The capping sleeve is placed on a fuel rod which is then severed by using a bolt cutter device. Upon cutting, the capping sleeve deforms in such a manner as to prevent the gross release of radioactive fuel material

  14. Ice Accretion Formations on a NACA 0012 Swept Wing Tip in Natural Icing Conditions

    NASA Technical Reports Server (NTRS)

    Vargas, Mario; Giriunas, Julius A.; Ratvasky, Thomas P.

    2002-01-01

    An experiment was conducted in the DeHavilland DHC-6 Twin Otter Icing Research Aircraft at NASA Glenn Research Center to study the formation of ice accretions on swept wings in natural icing conditions. The experiment was designed to obtain ice accretion data to help determine if the mechanisms of ice accretion formation observed in the Icing Research Tunnel are present in natural icing conditions. The experiment in the Twin Otter was conducted using a NACA 0012 swept wing tip. The model enabled data acquisition at 0 deg, 15 deg, 25 deg, 30 deg, and 45 deg sweep angles. Casting data, ice shape tracings, and close-up photographic data were obtained. The results showed that the mechanisms of ice accretion formation observed in-flight agree well with the ones observed in the Icing Research Tunnel. Observations on the end cap of the airfoil showed the same strong effect of the local sweep angle on the formation of scallops as observed in the tunnel.

  15. Albedo Variations on the Martian Northern Polar Cap as Seen by MGS

    NASA Technical Reports Server (NTRS)

    Hale, A. S.; Bass, D. S.; Tamppan, L. K.

    2003-01-01

    The Viking Orbiters determined that the surface of Mars northern residual cap is water ice. Many researchers have related observed atmospheric water vapor abundances to seasonal exchange between reservoirs such as the polar caps, but the extent to which the exchange between the surface and the atmosphere remains uncertain. Early studies of the ice coverage and albedo of the northern residual Martian polar cap using Mariner 9 and Viking images reported that there were substantial internannual differences in ice deposition on the polar cap, a result that suggested a highly variable Martian climate. However, some of the data used in these studies were obtained at differing values of heliocentric solar longitude (Ls). Reevaluation of this dataset in indicated that the residual cap undergoes seasonal brightening throughout the summer, and indicated that this process repeats from year to year. In this study we continue this work with data acquired with Mars Global Surveyor s Mars Orbiter Camera (MOC) and Thermal Emission Spectrometer (TES) instruments. We use MOC Wide Angel (WA) red filter images

  16. H2O grain size and the amount of dust in Mars' residual North polar cap

    USGS Publications Warehouse

    Kieffer, H.H.

    1990-01-01

    In Mars' north polar cap the probable composition of material residual from the annual condensation cycle is a mixture of fine dust and H2O grains of comparable size and abundance. However, metamorphism of such material will gradually lower its albedo by increasing the size of the H2O grains only. If the cap is undergoing net annual sublimation (as inferred from water vapor observations), late summer observations should be of old ice with H2O grain sizes of 100 ??m or more. Ice of this granularity containing 30% fine dust has a reflectivity similar to that of dust alone; the observed albedo and computed ice grain size imply dust concentrations of 1 part per 1000 or less. The brightness of the icy areas conflicts with what would be expected for a residual cap deposited by an annual cycle similar to that observed by Viking and aged for thousands of years. The residual cap surface cannot be "old dirty' ice. It could be old, coarse, and clean; or it could be young, fine, and dirty. This brings into question both the source of the late summer water vapor and the formation rate of laminated terrain. -Author

  17. Investigating Mars South Residual CO2 Cap with a Global Climate Model

    NASA Technical Reports Server (NTRS)

    Kahre, M. A.; Dequaire, J.; Hollingsworth, J. L.; Haberle, R. M.

    2016-01-01

    The CO2 cycle is one of the three controlling climate cycles on Mars. One aspect of the CO2 cycle that is not yet fully understood is the existence of a residual CO2 ice cap that is offset from the south pole. Previous investigations suggest that the atmosphere may control the placement of the south residual cap (e.g., Colaprete et al., 2005). These investigations show that topographically forced stationary eddies in the south during southern hemisphere winter produce colder atmospheric temperatures and increased CO2 snowfall over the hemisphere where the residual cap resides. Since precipitated CO2 ice produces higher surface albedos than directly deposited CO2 ice, it is plausible that CO2 snowfall resulting from the zonally asymmetric atmospheric circulation produces surface ice albedos high enough to maintain a residual cap only in one hemisphere. The goal of the current work is to further evaluate Colaprete et al.'s hypothesis by investigating model-predicted seasonally varying snowfall patterns in the southern polar region and the atmospheric circulation components that control them.

  18. Infrared Observations of Mars South Polar Residual Cap: When Eating Swiss Cheese - Use a Fork

    NASA Astrophysics Data System (ADS)

    Titus, T. N.; Brown, A. J.; Seelos, F. P.; Murchie, S. L.; Piqueux, S.; Christensen, P. R.; CRISM Team

    2008-03-01

    On the edge of the Mars southern residual cap is a region known as the fork region. This region contains scarps, CO2 Swiss cheese mesas, and a strip of exposed H2O ice 10 km wide. We examine this region using both THEMIS and CRISM observations.

  19. Putting Radioactive Wastes on Ice: A Proposal for an International Radionuclide Depository in Antarctica

    ERIC Educational Resources Information Center

    Zeller, E. J.; And Others

    1973-01-01

    Describes need for creating permanent disposal of high-level radioactive wastes accumulating in different countries. Possibilities of establishing facilities for this purpose in Antarctic ice cap are examined. (PS)

  20. The Mars water cycle at other epochs: Recent history of the polar caps and layered terrain

    NASA Technical Reports Server (NTRS)

    Jakosky, Bruce M.; Henderson, Bradley G.; Mellon, Michael T.

    1992-01-01

    The Martian polar caps and layered terrain presumably evolves by the deposition and removal of small amounts of water and dust each year, the current cap attributes therefore represent the incremental transport during a single year as integrated over long periods of time. The role was studied of condensation and sublimation of water ice in this process by examining the seasonal water cycle during the last 10(exp 7) yr. In the model, axial obliquity, eccentricity, and L sub s of perihelion vary according to dynamical models. At each epoch, the seasonal variations in temperature are calculated at the two poles, keeping track of the seasonal CO2 cap and the summertime sublimation of water vapor into the atmosphere; net exchange of water between the two caps is calculated based on the difference in the summertime sublimation between the two caps (or on the sublimation from one cap if the other is covered with CO2 frost all year). Results from the model can help to explain (1) the apparent inconsistency between the timescales inferred for layer formation and the much older crater retention age of the cap and (2) the difference in sizes of the two residual caps, with the south being smaller than the north.

  1. Polar Cap Colors

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    Released 12 May 2004 This daytime visible color image was collected on June 6, 2003 during the Southern Spring season near the South Polar Cap Edge.

    The THEMIS VIS camera is capable of capturing color images of the martian surface using its five different color filters. In this mode of operation, the spatial resolution and coverage of the image must be reduced to accommodate the additional data volume produced from the use of multiple filters. To make a color image, three of the five filter images (each in grayscale) are selected. Each is contrast enhanced and then converted to a red, green, or blue intensity image. These three images are then combined to produce a full color, single image. Because the THEMIS color filters don't span the full range of colors seen by the human eye, a color THEMIS image does not represent true color. Also, because each single-filter image is contrast enhanced before inclusion in the three-color image, the apparent color variation of the scene is exaggerated. Nevertheless, the color variation that does appear is representative of some change in color, however subtle, in the actual scene. Note that the long edges of THEMIS color images typically contain color artifacts that do not represent surface variation.

    Image information: VIS instrument. Latitude -77.8, Longitude 195 East (165 West). 38 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA

  2. Recent Improvements in the U.S. Navy's Ice Modeling Using Merged CryoSat-2/SMOS Ice Thickness

    NASA Astrophysics Data System (ADS)

    Allard, Richard; Hebert, David; Posey, Pamela; Wallcraft, Alan; Li, Li; Johnston, William; Phelps, Michael; Ridout, Andy; Shepherd, Andrew; Tilling, Rachel

    2016-04-01

    The U.S. Navy's Arctic Cap Nowcast/Forecast System (ACNFS) is composed of the Community Ice CodE (CICE) coupled to the HYbrid Community Ocean Model (HYCOM). The system assimilates ocean and ice observations including ice concentration from the Advanced Microwave Scanning Radiometer 2 (AMSR2), Special Sensor Microwave Imager Sounder (SSMIS) and ice edge data from the National Ice Center's Interactive Multisensor Snow and Ice Mapping System (IMS). In this study, we perform a series of experiments in which the ACNFS is initialized with a blended ice thickness field from CryoSat-2 and the Soil Moisture and Ocean Salinity (SMOS) Missions. CryoSat-2 produces a sea ice thickness product which is more accurate for thicknesses greater than 0.46 m while SMOS ice thickness is best for thicknesses less than 0.46 m. The experiments begin in March 2012 and continue through April 2015. ACNFS ice thickness is compared against NASA IceBridge, WHOI Upward Looking Sonar, and Cold Regions Research and Engineering Laboratory (CRREL) ice mass balance buoy data. Preliminary results show reduced ice thickness errors using this blended technique.

  3. Flow-pattern evolution of the last British Ice Sheet

    NASA Astrophysics Data System (ADS)

    Hughes, Anna L. C.; Clark, Chris D.; Jordan, Colm J.

    2014-04-01

    We present a 10-stage reconstruction of the evolution in ice-flow patterns of the last British Ice Sheet from build-up to demise derived from geomorphological evidence. 100 flowsets identified in the subglacial bedform record (drumlins, mega-scale glacial lineations, and ribbed moraine) are combined with ancillary evidence (erratic-transport paths, absolute dates and a semi-independently reconstructed retreat pattern) to define flow patterns, ice divides and ice-sheet margins during build-up, maximum glaciation and retreat. Overprinting and cross-cutting of landform assemblages are used to define the relative chronology of flow patterns and a tentative absolute chronology is presented based on a collation of available dates for ice advance and retreat. The ice-flow configuration of the last British Ice Sheet was not static. Some ice divides were remarkably stable, persisting through multiple stages of the ice-sheet evolution, whereas others were transient features existing for a short time and/or shifting in position 10s km. The 10 reconstructed stages of ice-sheet geometry capture two main modes of operation; first as an integrated ice sheet with a broadly N-S orientated ice divide, and second as a multi-domed ice sheet orientated parallel with the shelf edge. A thick integrated ice sheet developed as ice expanded out of source areas in Scotland to envelop southerly ice caps in northern England and Wales, and connect with the Irish Ice Sheet to the west and the Scandinavian Ice Sheet across the North Sea. Following break-up of ice over the North Sea, ice streaming probably drove mass loss and ice-sheet thinning to create a more complex divide structure, where ice-flow patterns were largely controlled by the form of the underlying topography. Ice surface lowering occurred before separation of, and retreat to, multiple ice centres centred over high ground. We consider this 10-stage reconstruction of the evolution in ice-sheet configuration to be the simplest palaeo

  4. Research Spotlight: No tipping point for Arctic Ocean ice

    NASA Astrophysics Data System (ADS)

    Schultz, Colin

    2011-03-01

    Declines in the summer sea ice extent have led to concerns within the scientific community that the Arctic Ocean may be nearing a tipping point, beyond which the sea ice cap could not recover. In such a scenario, greenhouse gases in the atmosphere trap outgoing radiation, and as the Sun beats down 24 hours a day during the Arctic summer, temperatures rise and melt what remains of the polar sea ice cap. The Arctic Ocean, now less reflective, would absorb more of the Sun’s warmth, a feedback loop that would keep the ocean ice free. However, new research by Tietsche et al. suggests that even if the Arctic Ocean sees an ice-free summer, it would not lead to catastrophic runaway ice melt. The researchers, using a general circulation model of the global ocean and the atmosphere, found that Arctic sea ice recovers within 2 years of an imposed ice-free summer to the conditions dictated by general climate conditions during that time. Furthermore, they found that this quick recovery occurs whether the ice-free summer is triggered in 2000 or in 2060, when global temperatures are predicted to be 2°C warmer. (Geophysical Research Letters, doi:10.1029/2010GL045698, 2011)

  5. Mathematical modeling of cold cap

    SciTech Connect

    Pokorny, Richard; Hrma, Pavel R.

    2012-10-13

    The ultimate goal of studies of cold cap behavior in glass melters is to increase the rate of glass processing in an energy-efficient manner. Regrettably, mathematical models, which are ideal tools for assessing the responses of melters to process parameters, have not paid adequate attention to the cold cap. In this study, we consider a cold cap resting on a pool of molten glass from which it receives a steady heat flux while temperature, velocity, and extent of conversion are functions of the position along the vertical coordinate. A one-dimensional (1D) mathematical model simulates this process by solving the differential equations for mass and energy balances with appropriate boundary conditions and constitutive relationships for material properties. The sensitivity analyses on the effects of incoming heat fluxes to the cold cap through its lower and upper boundaries show that the cold cap thickness increases as the heat flux from above increases, and decreases as the total heat flux increases. We also discuss the effects of foam, originating from batch reactions and from redox reactions in molten glass and argue that models must represent the foam layer to achieve a reliable prediction of the melting rate as a function of feed properties and melter conditions.

  6. Polar Cap Plasma and Convection

    NASA Technical Reports Server (NTRS)

    Elliott, Heather A.; Craven, Paul D.; Comfort, Richard H.; Chandler, Michael O.; Moore, Thomas E.; Ruohoniemi, J. M.

    1998-01-01

    This presentation will describe the character of the polar cap plasma in 10% AGU Spring 1998 particular the convection velocities at the perigee (about 1.8 Re) and apogee( about 8.9 Re) of Polar in relationship to Interplanetary Magnetic Field (IMF) and solar wind parameters. This plasma is thought to be due to several sources; the polar wind, cleft ion fountain, and auroral outflow. The plasma in the polar cap tends to be mostly field-aligned. At any given point in the polar cap, this plasma could be from a different regions since convection of magnetic field lines can transport this material. it is quite difficult to study such a phenomena with single point measurements. Current knowledge of the polar cap plasma obtained by in situ measurements will be presented along with recent results from the Polar mission. This study also examines the direct electrical coupling between the magnetosphere and ionosphere by comparing convection velocities measured by the Thermal Ion Dynamics Experiment (TIDE) and Magnetic Field Experiment (MFE) instruments in magnetosphere and measurements of the ionosphere by ground-based radars. At times such a comparison is difficult because the Polar satellite at apogee spends a large amount of time in the polar cap which is a region that is not coverage well by the current SuperDam coherent radars. This is impart due to the lack of irregularities that returns the radar signal.

  7. Martian North Polar Cap on September 12, 1998 (color)

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Mars Global Surveyor's Mars Orbiter Camera obtained its last SPO-2 images of Mars on September 12, 1998. SPO-2, or 'Science Phasing Orbit-2', took place between early June and mid-September 1998. Shown above are MOC wide angle (red and blue band) images of the martian north polar region obtained around 3:15 a.m. PDT on September 12, 1998. This color composite was made using red and blue wide angle MOC images 55001 and 55002--these were the last pictures taken of the planet until the camera resumes its work in late-March 1999.

    The north polar layered deposits, a terrain believed composed of ice and dust deposited over millions of years, dominates this view. The swirled pattern in the images above are channels eroded into this deposit. The pattern is accentuated by the illumination and seasonal frost differences that arise on sun-facing slopes during the summer. The permanent portion of the north polar cap covers most of the region with a layer of ice of unknown thickness.

    At the time this picture was obtained, the martian northern hemisphere was in the midst of the early Spring season. The margin of the seasonal carbon dioxide frost cap was at about 67o N, so the ground throughout this image is covered by frost. The frost appears pink rather than white; this may result from textural changes in the frost as it sublimes or because the frost is contaminated by a small amount of reddish martian dust. Please note that these pictures have not been 'calibrated' and so the colors are not necessarily accurately portrayed.

    In addition to the north polar cap, the pictures also show some clouds (bluish-white wisps). Some of the clouds on the right side of the images are long, linear features that cast similar long, dark shadows on the ground beneath them.

    When the MOC resumes imaging of Mars in March 1999, summer will have arrived in the north polar regions and the area surrounding the permanent polar cap will appear much darker than it does here. The dark features

  8. Summer evolution of the north polar cap of Mars as observed by OMEGA/Mars Express.

    PubMed

    Langevin, Y; Poulet, F; Bibring, J-P; Schmitt, B; Douté, S; Gondet, B

    2005-03-11

    The Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) visible-infrared imaging spectrometer extensively observed regions of Mars with latitudes above 70 degrees N in late 2004 (heliocentric longitude from Ls 93 degrees to Ls 127 degrees ). The extent of water ice at the surface and the size of ice grains were monitored as a function of time. Bright, small-grained frost, which initially covered a large fraction of the polar cap, waned in favor of large-grained ice. In outlying regions, dominated by large-grained ice, the albedo increased over the period. Evaluating the dust content was model dependent. However, contamination of ice by dust was low.

  9. Stratigraphy and evolution of the buried CO2 deposit in the Martian south polar cap

    NASA Astrophysics Data System (ADS)

    Bierson, C. J.; Phillips, R. J.; Smith, I. B.; Wood, S. E.; Putzig, N. E.; Nunes, D.; Byrne, S.

    2016-05-01

    Observations by the Shallow Radar instrument on Mars Reconnaissance Orbiter reveal several deposits of buried CO2 ice within the south polar layered deposits. Here we present mapping that demonstrates this unit is 18% larger than previously estimated, containing enough mass to double the atmospheric pressure on Mars if sublimated. We find three distinct subunits of CO2 ice, each capped by a thin (10-60 m) bounding layer (BL). Multiple lines of evidence suggest that each BL is dominated by water ice. We model the history of CO2 accumulation at the poles based on obliquity and insolation variability during the last 1 Myr assuming a total mass budget consisting of the current atmosphere and the sequestered ice. Our model predicts that CO2 ice has accumulated over large areas several times during that period, in agreement with the radar findings of multiple periods of accumulation.

  10. The RECAP ice core - recovering a full Glacial record from Eastern Greenland

    NASA Astrophysics Data System (ADS)

    Vinther, Bo

    2016-04-01

    During May-June 2015 the 584m an international team drilled the RECAP (REnland ice CAp Project) ice core to bedrock on the Renland ice cap in Eastern Greenland. The exact drill site selection was determined from a detailed radio echo sounding (RES) grid, that had been measured from the ice cap surface right before drilling operations began. The RES data suggested that the ice cap internal layers are horizontal almost right down to the bed at the selected site, and that ice from the Glacial period was present some 30-50m above bedrock. The RES results have now been confirmed by measurements on the RECAP core that shows the entire Glacial being nicely preserved in the 20m section indicated by the RES measurements. The RECAP core thus yields the first undisturbed ice core record from Eastern Greenland covering the last Glacial, a marked improvement compared to the landmark 1988 Renland ice core that was disturbed by ice flow features both during the mid-Holocene and especially during Marine Isotope Stages 4 and 5.

  11. Ice rheology in the planetary context

    NASA Astrophysics Data System (ADS)

    Durham, W. B.; McDaniel, S.; Stern, L. A.; Kirby, S. H.

    2003-04-01

    The rheological properties of water are a basis for modeling dynamic processes on and within low-density planetary satellites and on the surfaces of Earth and Mars. The model changes quickly, however, if one includes natural complexities that affect the texture and composition of the ice. The study of the effects of these complexities on the rheology of ice and icy compounds is not far advanced, but there already have been a number of interesting findings. Among these are (1) the presence of NH3 in water ice significantly weakens the ice and increases the possibility of a melt phase being present; (2) dispersed hard particulates strengthen ice slightly in most cases, but significant strengthening requires very high particulate concentrations; and (3) in multi-phase mixtures, minor concentrations of a weak phase can have a disproportionate softening effect on the aggregate. In this talk we focus on two additional behaviors with important planetary applications: the very high strength of gas hydrates and sulfate hydrates, and the role of grain size in the creep of ice I. Hydrated sulfate salts and gas hydrates, candidate planetary building materials, are orders of magnitude more viscous than water ice. Methane hydrate is sufficiently strong and potentially present in sufficient volume to radically alter icy models of certain moons (Titan). CO2 hydrate, weaker than methane hydrate but still much stronger than water ice, may be stable in the interior of the Mars south polar cap. Hydrated sulfate salts in turn are much stronger than even methane hydrate, and where they exist in the Europan crust, must be considered essentially undeformable. Laboratory experiments have clearly shown that at finer grain sizes the rheology of ice is strongly dependent on grain size (referred to as grain-size-sensitive (GSS ) creep) and that at larger grain sizes, the deformation mechanism is predominantly grain size insensitive dislocation creep. The two regimes have contrasting flow laws

  12. Geology of the southern hemisphere of Triton: No polar cap

    NASA Technical Reports Server (NTRS)

    Schenk, P.; Moore, J. M.

    1993-01-01

    The bright southern hemisphere, comprising Uhlanga Regio, is perhaps the most poorly understood geologic province on Triton. The entire bright southern hemisphere has been described as a bright polar 'cap', implying a seasonal origin, or as a permanent geologic terrain distinct from the equatorial terrains. Also, thermal models have predicted seasonal migration of frosts and ices from the presently sun-lit south latitudes to the dark northern latitudes. The distribution of frosts and geologic history of this region must be determined observationally. We reexamine the geology of this terrain with the goal of answering these questions.

  13. Grain metamorphism in polar nitrogen ice on Triton

    NASA Technical Reports Server (NTRS)

    Zent, Aaron P.; Mckay, Christopher P.; Pollack, James B.; Cruikshank, Dale P.

    1989-01-01

    The rate of nitrogen grain growth on putative N2-rich polar caps on Triton is calculated. For most plausible assumptions of independent variables, mean grain sizes in polar N2 are meter-scale. Triton's polar caps should constitute the definitive solar-system test bed for the process of ice grain metamorphism. Interpretation of data already in hand may require long path length through condensed N2, possibly due to grain growth. Upcoming Voyager data may clarify the situation, although possible complications in detecting a glaze of N2 ice exist.

  14. Grain metamorphism in polar nitrogen ice on triton

    SciTech Connect

    Zent, A.P.; McKay, C.P.; Pollack, J.B.; Cruikshank, D.P. )

    1989-08-01

    The authors calculate the rate of nitrogen grain growth on putative N{sub 2}-rich polar caps on Triton. For most plausible assumptions of independent variables, mean grain sizes in polar N{sub 2} are meter-scale. Triton's polar caps should constitute the definitive solar-system test bed for the process of ice grain metamorphism. Interpretation of data already in hand many require long path length through condensed N{sub 2}, possibly due to grain growth. Upcoming Voyager data may clarify the situation, although possible complications in detecting a glaze of N{sub 2} ice exist.

  15. CryoScout: A Descent Through the Mars Polar Cap

    NASA Technical Reports Server (NTRS)

    Hecht, M. H.; Saunders, R. S.

    2003-01-01

    CryoScout was proposed as a subsurface investigation of the stratigraphic climate record embedded in Mars North Polar cap. After landing on a gentle landscape in the midst of the mild summer season, CryoScout was to use the continuous polar sunlight to power the descent of a cryobot, a thermal probe, into the ice at a rate of about 1 m per day. CryoScout would probe deep enough into this time capsule to see the effects of planetary obliquity variations and discrete events such as dust storms or volcanic eruptions. By penetrating tens of meters of ice, the mission would explore at least one of the dominant "MOC layers" observed in exposed layered terrain.

  16. An onboard data analysis method to track the seasonal polar caps on Mars

    USGS Publications Warehouse

    Wagstaff, K.L.; Castano, R.; Chien, S.; Ivanov, A.B.; Pounders, E.; Titus, T.N.; ,

    2005-01-01

    The Martian seasonal CO2 ice caps advance and retreat each year. They are currently studied using instruments such as the THermal EMission Imaging System (THEMIS), a visible and infra-red camera on the Mars Odyssey spacecraft [1]. However, each image must be downlinked to Earth prior to analysis. In contrast, we have developed the Bimodal Image Temperature (BIT) histogram analysis method for onboard detection of the cap edge, before transmission. In downlink-limited scenarios when the entire image cannot be transmitted, the location of the cap edge can still be identified and sent to Earth. In this paper, we evaluate our method on uncalibrated THEMIS data and find 1) agreement with manual cap edge identifications to within 28.2 km, and 2) high accuracy even with a smaller analysis window, yielding large reductions in memory requirements. This algorithm is currently being considered as a capability enhancement for the Odyssey second extended mission, beginning in fall 2006.

  17. Volcano-ice interactions on Mars

    NASA Technical Reports Server (NTRS)

    Allen, C. C.

    1979-01-01

    Central volcanic eruptions beneath terrestrial glaciers have built steep-sided, flat-topped mountains composed of pillow lava, glassy tuff, capping flows, and cones of basalt. Subglacial fissure eruptions produced ridges of similar composition. In some places the products from a number of subglacial vents have combined to form widespread deposits. The morphologies of these subglacial volcanoes are distinctive enough to allow their recognition at the resolutions characteristic of Viking orbiter imagery. Analogs to terrestrial subglacial volcanoes have been identified on the northern plains and near the south polar cap of Mars. The polar feature provides probable evidence of volcanic eruptions beneath polar ice. A mixed unit of rock and ice is postulated to have overlain portions of the northern plains, with eruptions into this ground ice having produced mountains and ridges analogous to those in Iceland. Subsequent breakdown of this unit due to ice melting revealed the volcanic features. Estimated heights of these landforms indicate that the ice-rich unit once ranged from approximately 100 to 1200 m thick.

  18. Operation IceBridge: Sea Ice Interlude

    NASA Video Gallery

    Sea ice comes in an array of shapes and sizes and has its own ephemeral beauty. Operation IceBridge studies sea ice at both poles, and also runs across interesting formations en route to other targ...

  19. A GCM Recent History of Northern Martian Polar Layered Deposits: Contribution from Past Equatorial Ice Reservoirs

    NASA Technical Reports Server (NTRS)

    Levrard, B.; Laskar, J.; Montmessin, F.; Forget, F.

    2005-01-01

    Polar layered deposits are exposed in the walls of the troughs cutting the north polar cap of Mars. They consist of alternating ice and dust layers or layers of an ice-dust mixture with varying proportions and are found throughout the cap. Layers thickness ranges from meters to several tens of meters with an approximately 30 meter dominant wavelength. Although their formation processes is not known, they are presumed to reflect changes in ice and dust stability over orbital and axial variations. Intensive 3-D LMD GCM simulations of the martian water cycle have been thus performed to determine the annual rates of exchange of surface ice between the northern cap and tropical areas for a wide range of obliquity and orbital parameters values.These rates have been employed to reconstruct an history of the northern cap and test simple models of dust-ice layers formation over the last 10 Ma orbital variations. We use the 3-D water cycle model simulated by the 3-D LMD GCM with an intermediate grid resolution (7.5 longitude x 5.625 latitude) and 25 vertical levels. The dust opacity is constant and set to 0,15. No exchange of ice with regolith is allowed. The evolution of the northern cap over obliquity and orbital changes (eccentricity, Longitude of perihelion) has been recently described with this model. High summer insolation favors transfer of ice from the northern pole to the Tharsis and Olympus Montes, while at low obliquity, unstable equatorial ice is redeposited in high-latitude and polar areas of both hemisphere. The disappearance of the equatorial ice reservoir leads to a poleward recession of icy high latitude reservoirs, providing an additional source for the cap accumulation during each obliquity or orbital cycle. Furthering the efforts, a quantitative evolution of ice reservoirs is here investigated for various astronomical conditions.

  20. The Enigmatic Martian Polar Caps

    SciTech Connect

    James, Philip

    2005-08-17

    The Martian polar caps have puzzled astronomers for over a century. Extensive study by many instruments on various spacecraft has resolved many questions but has at the same time created a new generation of puzzles. The polar caps are intimately coupled to the current Martian climate and volatile cycles. They also hold clues to climate variations on a variety of longer time scales. The results of recent missions will be reviewed, and the potential outlook for resolution of the outstanding questions will be examined.

  1. Sublimation Model for Formation of Martian Residual Cap Depressions

    NASA Astrophysics Data System (ADS)

    Byrne, S.; Ingersoll, A. P.

    2000-10-01

    In an effort for explain the formation of the 'Swiss-cheese' terrain visible on the southern residual cap of Mars, we have developed a radiative model to follow the growth/decay of an initial depression due to sublimation/condensation of carbon dioxide. The pits making up this terrain have many distinctive features, they are shallow ( 10m deep), with steep walls and flat floors and contain an interior moat which runs along the bottom of the walls. They have lateral sizes ranging from a few 10's of meters to a kilometer and are quasi-circular. The model accounts for incident sunlight, emitted thermal radiation, and scattered short and long wave radiation. We have investigated many cases involving pure dry-ice with constant albedo, albedo as a function of insolation, and differing albedo for fresh and residual frost (the latter has lower albedo). The last case mentioned shows the most promising results to date. With these conditions it is possible for the depressions to grow and develop flat central portions although they still lack the observed steep walls of the pits. In the other cases mentioned the initial depressions heal themselves and disappear into the surrounding terrain. Other processes or materials could be responsible for the remainder of the observed features. Water ice stored a few meters under a carbon dioxide covering would have dramatic effects on the growth of any depression which encounters it, both due to its low sublimation rate and its ability to store heat. We will extend the current model to include a water ice layer and account for the subsequent heat storage which could possibly follow. For water ice models, a challenge is to reproduce the low brightness temperatures that persist throughout the summer at the residual south polar cap.

  2. Breakup of Pack Ice, Antarctic Ice Shelf

    NASA Technical Reports Server (NTRS)

    1991-01-01

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

  3. North-south geological differences between the residual polar caps on Mars.

    PubMed

    Thomas, P C; Malin, M C; Edgett, K S; Carr, M H; Hartmann, W K; Ingersoll, A P; James, P B; Soderblom, L A; Veverka, J; Sullivan, R

    2000-03-01

    Polar processes can be sensitive indicators of global climate, and the geological features associated with polar ice caps can therefore indicate evolution of climate with time. The polar regions on Mars have distinctive morphologic and climatologic features: thick layered deposits, seasonal CO2 frost caps extending to mid latitudes, and near-polar residual frost deposits that survive the summer. The relationship of the seasonal and residual frost caps to the layered deposits has been poorly constrained, mainly by the limited spatial resolution of the available data. In particular, it has not been known if the residual caps represent simple thin frost cover or substantial geologic features. Here we show that the residual cap on the south pole is a distinct geologic unit with striking collapse and erosional topography; this is very different from the residual cap on the north pole, which grades into the underlying layered materials. These findings indicate that the differences between the caps are substantial (rather than reflecting short-lived differences in frost cover), and so support the idea of long-term asymmetry in the polar climates of Mars.

  4. North-south geological differences between the residual polar caps on Mars

    USGS Publications Warehouse

    Thomas, P.C.; Malin, M.C.; Edgett, K.S.; Carr, M.H.; Hartmann, W.K.; Ingersoll, A.P.; James, P.B.; Soderblom, L.A.; Veverka, J.; Sullivan, R.

    2000-01-01

    Polar processes can be sensitive indicators of global climate, and the geological features associated with polar ice caps can therefore indicate evolution of climate with time. The polar regions on Mars have distinctive morphologic and climatologic features: thick layered deposits, seasonal CO2 frost caps extending to mid latitudes, and near-polar residual frost deposits that survive the summer. The relationship of the seasonal and residual frost caps to the layered deposits has been poorly constrained, mainly by the limited spatial resolution of the available data. In particular, it has not been known if the residual caps represent simple thin frost cover or substantial geologic features. Here we show that the residual cap on the south pole is a distinct geologic unit with striking collapse and erosional topography; this is very different from the residual cap on the north pole, which grades into the underlying layered materials. These findings indicate that the differences between the caps are substantial (rather than reflecting short-lived differences in frost cover), and so support the idea of long-term asymmetry in the polar climates of Mars.

  5. The Greenland Ice Mapping Project

    NASA Astrophysics Data System (ADS)

    Joughin, I.; Smith, B.; Howat, I. M.; Moon, T. A.; Scambos, T. A.

    2015-12-01

    Numerous glaciers in Greenland have sped up rapidly and unpredictably during the first part of the 21st Century. We started the Greenland Ice Mapping Project (GIMP) to produce time series of ice velocity for Greenland's major outlet glaciers. We are also producing image time series to document the advance and retreat of glacier calving fronts and other changes in ice-sheet geometry (e.g., shrinking ice caps and ice shelves). When the project began, there was no digital elevation model (DEM) with sufficient accuracy and resolution to terrain-correct the SAR-derived products. Thus, we also produced the 30-m GIMP DEM, which, aside from improving our processing, is an important product in its own right. Although GIMP focuses on time series, complete spatial coverage for initializing ice sheet models also is important. There are insufficient data, however, to map the full ice sheet in any year. There is good RADARSAT coverage for many years in the north, but the C-band data decorrelate too quickly to measure velocity in the high accumulation regions of the southeast. For such regions, ALOS data usually correlate well, but speckle-tracking estimates at L-band are subject to large ionospheric artifacts. Interferometric phase data are far less sensitive to the effect of the ionosphere, but velocity estimates require results from crossing orbits. Thus, to produce a nearly complete mosaic we used data from multiple sensors, beginning with ERS-1/2 data from the mid 1990s. By using a primarily phase-only solution for much of the interior, we have reduced the velocity errors to ~1-3 m/yr. For the faster moving ice-sheet margin where phase data cannot be unwrapped, we used speckle-tracking data. In particular, we have relied on TerraSAR-X for many fast-moving glaciers because the ionosphere far less affects X-band data. This pan-Greenland velocity map as well as many of the time series would not have been possible without an extensive archive of data collected using six

  6. Indirect pulp capping: a survey.

    PubMed

    Kaplowitz, G J

    1992-01-01

    This study addresses the acceptance of the clinical practice of indirect pulp capping. State and regional dental boards and postgraduate dental education programs throughout the United States were surveyed. Results indicate that no clear consensus exists for the acceptance of this clinical procedure.

  7. From Blogs to Bottle Caps

    ERIC Educational Resources Information Center

    Edinger, Ted

    2012-01-01

    There is a wonderful community of art educators connecting a once-isolated profession through blogging. Art educators around the world are sharing ideas and communicating with their peers through this amazing resource. In this article, the author describes the bottle cap mural at Tulip Grove Elementary School which was inspired by this exchange of…

  8. Abrupt onset and intensification of the Little Ice Age in Arctic Canada linked to explosive volcanism and sea-ice/ocean feedbacks

    NASA Astrophysics Data System (ADS)

    Miller, G. H.; Refsnider, K. A.; Zhong, Y.; Otto-Bliesner, B. L.; Lehman, S. J.; Southon, J. R.

    2011-12-01

    At high northern latitudes the most reliable monitors of summer temperature are glaciers and ice caps. Small ice caps are multi-decadal integrators of climate. Precise 14C dates on rooted vegetation exposed by recent recession of more than 70 different ice caps that have remained perpetually frozen to their beds since their inception date ice-cap inception at that site. Unlike valley glacier moraines that are not formed until long after the initial climate shift, entombed plants date the moment of a persistent summer cooling. The composite probability density function of the 138 calibrated 14C ages indicates that ice caps expanded in four discrete intervals within the past 2 ka, with the most abrupt ice-cap growth ~1250 AD following three centuries of relative warmth, and intensified ice expansion ~1450 AD, with maximum ice cover ~1850 AD. These intervals of sudden and sustained ice expansion coincide with the three most volcanically perturbed half centuries of the past millennium. Separating the impacts of solar and volcanic forcings in the late Holocene has been vexing because decades of low solar irradiance largely coincide with decades of frequent explosive volcanism. Transient simulations with a fully coupled climate model show that the main features of our proxy data can be matched by decadally paced explosive volcanism alone, perpetuated by feedbacks related to consequent sea-ice expansion and export into the northern North Atlantic. Exported sea ice cools and freshens surface waters there, leading to a reduction in the AMOC and consequently perpetuation of an expanded sea ice state. The coincidence of low decadal solar irradiance with decades of explosive volcanism suggests that volcanic impacts may have been amplified by solar variability, but scaling the proxies of past solar irradiance remains uncertain. The persistence in the Eastern Canadian Arctic of some ice caps that formed 5000 years ago and remained intact until melting in the past decade

  9. A comparison of Holocene fluctuations of the eastern and western margins of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Levy, L.; Kelly, M. A.; Lowell, T. V.; Hall, B. L.; Applegate, P. J.; Howley, J.; Axford, Y.

    2013-12-01

    Determining how the Greenland Ice Sheet (GrIS) responded to past temperature fluctuations is important for assessing its future stability in a changing climate. We present a record of the Holocene extents of the western GrIS margin near Kangerlussuaq (67.0°N, 50.7°W) and compare this with the past fluctuations of Bregne ice cap (71°N, 25.6° W), a small ice cap in the Scoresby Sund region 90 km from the eastern GrIS margin, to examine the mechanisms that influenced past ice margin fluctuations. The past extents of the Bregne ice cap are a proxy for the climatic conditions that influenced the nearby GrIS margin. We used glacial geomorphic mapping, 10Be dating of boulders and bedrock, and sediment cores from proglacial and non-glacial lakes. In western Greenland, 10Be ages on the Keglen moraines, 13 km west of the current GrIS margin and the Ørkendalen moraines, ≤2 km west of the current ice margin date to 7.3 × 0.1 ka (n=6) and 6.8 × 0.3 ka (n=9), respectively. Fresh moraines, ≤50 m from the current ice margin date to AD 1830-1950 and are likely associated with advances during the Little Ice Age (LIA). In some areas, the LIA moraines lie stratigraphically above the Ørkendalen moraines, indicating the GrIS was inboard of the Ørkendalen limit from 6.8 ka to the 20th century. In eastern Greenland, 10Be ages show that Bregne ice cap retreated within its late Holocene limit by 10.7 ka. A lack of clastic sediment in a proglacial lake suggests the ice cap was smaller or completely absent from ~10-2.6 ka. A snowline analysis indicates that temperatures ~0.5°C warmer than present would render the entire ice cap into an ablation zone. Glacial silts in the proglacial lake at ~2.6 and ~1.9 cal kyr BP to present indicate advances of Bregne ice cap. Fresh moraines ≤200 m of Bregne ice cap were deposited ≤2.6 cal kyr BP and mark the largest advance of the Holocene. Both the western GrIS margin and Bregne ice cap were influenced by Northern Hemisphere summer

  10. Reconstructing the last Irish Ice Sheet 2: a geomorphologically-driven model of ice sheet growth, retreat and dynamics

    NASA Astrophysics Data System (ADS)

    Greenwood, Sarah L.; Clark, Chris D.

    2009-12-01

    The ice sheet that once covered Ireland has a long history of investigation. Much prior work focussed on localised evidence-based reconstructions and ice-marginal dynamics and chronologies, with less attention paid to an ice sheet wide view of the first order properties of the ice sheet: centres of mass, ice divide structure, ice flow geometry and behaviour and changes thereof. In this paper we focus on the latter aspect and use our new, countrywide glacial geomorphological mapping of the Irish landscape (>39 000 landforms), and our analysis of the palaeo-glaciological significance of observed landform assemblages (article Part 1), to build an ice sheet reconstruction yielding these fundamental ice sheet properties. We present a seven stage model of ice sheet evolution, from initiation to demise, in the form of palaeo-geographic maps. An early incursion of ice from Scotland likely coalesced with local ice caps and spread in a south-westerly direction 200 km across Ireland. A semi-independent Irish Ice Sheet was then established during ice sheet growth, with a branching ice divide structure whose main axis migrated up to 140 km from the west coast towards the east. Ice stream systems converging on Donegal Bay in the west and funnelling through the North Channel and Irish Sea Basin in the east emerge as major flow components of the maximum stages of glaciation. Ice cover is reconstructed as extending to the continental shelf break. The Irish Ice Sheet became autonomous (i.e. separate from the British Ice Sheet) during deglaciation and fragmented into multiple ice masses, each decaying towards the west. Final sites of demise were likely over the mountains of Donegal, Leitrim and Connemara. Patterns of growth and decay of the ice sheet are shown to be radically different: asynchronous and asymmetric in both spatial and temporal domains. We implicate collapse of the ice stream system in the North Channel - Irish Sea Basin in driving such asymmetry, since rapid

  11. The hemispherical asymmetry of the residual polar caps on Mars. Semiannual progress report, 1 Sep. 1989 - 1 Mar. 1991

    SciTech Connect

    Lindner, B. L.

    1991-03-01

    A model of the polar caps of Mars was created which allows: (1) for light penetration into the cap; (2) ice albedo to vary with age, latitude, hemisphere, dust content, and solar zenith angle; and (3) for diurnal variability. The model includes the radiative effects of clouds and dust, and heat transport as represented by a thermal wind. The model reproduces polar cap regression data very well, including the survival of CO{sub 2} frost at the south pole and reproduces the general trend in the Viking Lander pressure data.

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

    NASA Astrophysics Data System (ADS)

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

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

  13. Uncovering the footprint of former ice streams off Antarctica

    NASA Astrophysics Data System (ADS)

    COHIMAR/SEDANO Scientific Party

    Antarctic ice sheets and ice caps have been expanding and contracting following global climatic cycles. The last time the Antarctic ice cover peaked, at least in Western Antarctica, was ca. 21 ky ago during the Last Glacial Maximum (LGM). The strong warming (nearly 2.8°C) over the past 50 years, and the yearly recent collapse of limited portions (hundreds to a few thousands of square miles per event) of ice shelves around the Antarctic Peninsula have brought to the headlines the debate about the potential collapse of the West Antarctic Ice Sheet (WAIS) in the near future under the influence of global warming.Such a catastrophe would substantially contribute to global sea level rise (a resulting 5 m increase is expected); alter water mass conditions, circulation, and productivity around Antarctica and in the world ocean; and modify the Earth's climate.The economic,social, and ecological impacts of these changes would depend greatly on the rate at which they might take place [Bindschadler, 1998” . A detailed knowledge of the past extent of ice sheets and the timing of their advances and retreats thus becomes essential to quantify the rates of change and to properly assess the future stability of the WAIS and nearby ice caps. The stability of ice sheets is largely dependent on ice drainage, which mostly occurs via ice streaming along glacial troughs. Ice streams are thus a key element to solve the puzzle linking ice sheet stability, sea level rise, and climate change at a global scale.

  14. Ice crystallization in ultrafine water-salt aerosols: nucleation, ice-solution equilibrium, and internal structure.

    PubMed

    Hudait, Arpa; Molinero, Valeria

    2014-06-01

    Atmospheric aerosols have a strong influence on Earth's climate. Elucidating the physical state and internal structure of atmospheric aqueous aerosols is essential to predict their gas and water uptake, and the locus and rate of atmospherically important heterogeneous reactions. Ultrafine aerosols with sizes between 3 and 15 nm have been detected in large numbers in the troposphere and tropopause. Nanoscopic aerosols arising from bubble bursting of natural and artificial seawater have been identified in laboratory and field experiments. The internal structure and phase state of these aerosols, however, cannot yet be determined in experiments. Here we use molecular simulations to investigate the phase behavior and internal structure of liquid, vitrified, and crystallized water-salt ultrafine aerosols with radii from 2.5 to 9.5 nm and with up to 10% moles of ions. We find that both ice crystallization and vitrification of the nanodroplets lead to demixing of pure water from the solutions. Vitrification of aqueous nanodroplets yields nanodomains of pure low-density amorphous ice in coexistence with vitrified solute rich aqueous glass. The melting temperature of ice in the aerosols decreases monotonically with an increase of solute fraction and decrease of radius. The simulations reveal that nucleation of ice occurs homogeneously at the subsurface of the water-salt nanoparticles. Subsequent ice growth yields phase-segregated, internally mixed, aerosols with two phases in equilibrium: a concentrated water-salt amorphous mixture and a spherical cap-like ice nanophase. The surface of the crystallized aerosols is heterogeneous, with ice and solution exposed to the vapor. Free energy calculations indicate that as the concentration of salt in the particles, the advance of the crystallization, or the size of the particles increase, the stability of the spherical cap structure increases with respect to the alternative structure in which a core of ice is fully surrounded by

  15. Ice crystallization in ultrafine water-salt aerosols: nucleation, ice-solution equilibrium, and internal structure.

    PubMed

    Hudait, Arpa; Molinero, Valeria

    2014-06-01

    Atmospheric aerosols have a strong influence on Earth's climate. Elucidating the physical state and internal structure of atmospheric aqueous aerosols is essential to predict their gas and water uptake, and the locus and rate of atmospherically important heterogeneous reactions. Ultrafine aerosols with sizes between 3 and 15 nm have been detected in large numbers in the troposphere and tropopause. Nanoscopic aerosols arising from bubble bursting of natural and artificial seawater have been identified in laboratory and field experiments. The internal structure and phase state of these aerosols, however, cannot yet be determined in experiments. Here we use molecular simulations to investigate the phase behavior and internal structure of liquid, vitrified, and crystallized water-salt ultrafine aerosols with radii from 2.5 to 9.5 nm and with up to 10% moles of ions. We find that both ice crystallization and vitrification of the nanodroplets lead to demixing of pure water from the solutions. Vitrification of aqueous nanodroplets yields nanodomains of pure low-density amorphous ice in coexistence with vitrified solute rich aqueous glass. The melting temperature of ice in the aerosols decreases monotonically with an increase of solute fraction and decrease of radius. The simulations reveal that nucleation of ice occurs homogeneously at the subsurface of the water-salt nanoparticles. Subsequent ice growth yields phase-segregated, internally mixed, aerosols with two phases in equilibrium: a concentrated water-salt amorphous mixture and a spherical cap-like ice nanophase. The surface of the crystallized aerosols is heterogeneous, with ice and solution exposed to the vapor. Free energy calculations indicate that as the concentration of salt in the particles, the advance of the crystallization, or the size of the particles increase, the stability of the spherical cap structure increases with respect to the alternative structure in which a core of ice is fully surrounded by

  16. Tip cap for a rotor blade

    NASA Technical Reports Server (NTRS)

    Kofel, W. K.; Tuley, E. N.; Gay, C. H., Jr.; Troeger, R. E.; Sterman, A. P. (Inventor)

    1983-01-01

    A replaceable tip cap for attachment to the end of a rotor blade is described. The tip cap includes a plurality of walls defining a compartment which, if desired, can be divided into a plurality of subcompartments. The tip cap can include inlet and outlet holes in walls thereof to permit fluid communication of a cooling fluid there through. Abrasive material can be attached with the radially outer wall of the tip cap.

  17. Rapid marine deglaciation: asynchronous retreat dynamics between the Irish Sea Ice Stream and terrestrial outlet glaciers

    NASA Astrophysics Data System (ADS)

    Patton, H.; Hubbard, A.; Bradwell, T.; Glasser, N. F.; Hambrey, M. J.; Clark, C. D.

    2013-12-01

    Understanding the retreat behaviour of past marine-based ice sheets provides vital context for accurate assessments of the present stability and long-term response of contemporary polar ice sheets to climate and oceanic warming. Here new multibeam swath bathymetry data and sedimentological analysis are combined with high resolution ice-sheet modelling to reveal complex landform assemblages and process dynamics associated with deglaciation of the Celtic ice sheet within the Irish Sea Basin. Our reconstruction indicates a non-linear relationship between the rapidly receding Irish Sea Ice Stream and the retreat of outlet glaciers draining the adjacent, terrestrially based ice cap centred over Wales. Retreat of Welsh ice was episodic; superimposed over low-order oscillations of its margin are asynchronous outlet readvances driven by catchment-wide mass balance variations that are amplified through migration of the ice cap's main ice divide. Formation of large, linear ridges which extend at least 12.5 km offshore (locally known as sarns) and which dominate the regional bathymetry are attributed to repeated frontal and medial morainic deposition associated with the readvancing phases of these outlet glaciers. Our study provides new insight into ice-sheet extent, dynamics and non-linear retreat across a major palaeo-ice stream confluence zone, and has ramifications for the interpretation of recent fluctuations observed by satellites over short timescales across marine sectors of the Greenland and Antarctic ice sheets.

  18. 47 CFR 54.507 - Cap.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Universal Service Support for Schools and Libraries § 54.507 Cap. (a) Amount of the annual cap. The annual funding cap on federal universal service support for schools and libraries shall be $2.25 billion per... into subsequent funding years for use in the schools and libraries support mechanism in accordance...

  19. Dynamic Modeling of an Evapotranspiration Cap

    SciTech Connect

    Jacob J. Jacobson; Steven Piet; Rafael Soto; Gerald Sehlke; Harold Heydt; John Visser

    2005-10-01

    The U.S. Department of Energy is scheduled to design and install hundreds of landfill caps/barriers over the next several decades and these caps will have a design life expectancy of up to 1,000 years. Other landfill caps with 30 year design lifetimes are reaching the end of their original design life; the changes to these caps need to be understood to provide a basis for lifetime extension. Defining the attributes that make a successful cap (one that isolates the waste from the environment) is crucial to these efforts. Because cap systems such as landfill caps are dynamic in nature, it is impossible to understand, monitor, and update lifetime predictions without understanding the dynamics of cap degradation, which is most often due to multiple interdependent factors rather than isolated independent events. In an attempt to understand the dynamics of cap degradation, a computer model using system dynamics is being developed to capture the complex behavior of an evapotranspiration cap. The specific objectives of this project are to capture the dynamic, nonlinear feedback loop structures underlying an evapotranspiration cap and, through computer simulation, gain a better understanding of long-term behavior, influencing factors, and, ultimately, long-term cap performance.

  20. Indoleacetic acid movement in the root cap.

    PubMed

    Pernet, J J; Pilet, P E

    1976-01-01

    When applied on the root cap of Zea mays L., indol-3yl-acetic acid (IAA) may enter the root tip and move basipetally inside the cap. From the cap to the apex (quiescent centre and meristem) the IAA transport is very slow. Polarity of IAA movement, in relation to growth, is discussed.

  1. 21 CFR 888.3000 - Bone cap.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Bone cap. 888.3000 Section 888.3000 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3000 Bone cap. (a) Identification. A bone cap is a...

  2. 21 CFR 888.3000 - Bone cap.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Bone cap. 888.3000 Section 888.3000 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3000 Bone cap. (a) Identification. A bone cap is a...

  3. 21 CFR 888.3000 - Bone cap.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Bone cap. 888.3000 Section 888.3000 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3000 Bone cap. (a) Identification. A bone cap is a...

  4. 47 CFR 54.507 - Cap.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... schools and libraries support mechanism in accordance with the public interest and notwithstanding the... schools and libraries mechanism in accordance with the public interest and notwithstanding the annual cap... Universal Service Support for Schools and Libraries § 54.507 Cap. (a) Amount of the annual cap. In...

  5. 47 CFR 54.507 - Cap.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... schools and libraries support mechanism in accordance with the public interest and notwithstanding the... schools and libraries mechanism in accordance with the public interest and notwithstanding the annual cap... Universal Service Support for Schools and Libraries § 54.507 Cap. (a) Amount of the annual cap. In...

  6. 21 CFR 888.3000 - Bone cap.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Bone cap. 888.3000 Section 888.3000 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3000 Bone cap. (a) Identification. A bone cap is a...

  7. 21 CFR 884.5250 - Cervical cap.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Cervical cap. 884.5250 Section 884.5250 Food and... OBSTETRICAL AND GYNECOLOGICAL DEVICES Obstetrical and Gynecological Therapeutic Devices § 884.5250 Cervical cap. (a) Identification. A cervical cap is a flexible cuplike receptacle that fits over the cervix...

  8. 21 CFR 884.5250 - Cervical cap.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Cervical cap. 884.5250 Section 884.5250 Food and... OBSTETRICAL AND GYNECOLOGICAL DEVICES Obstetrical and Gynecological Therapeutic Devices § 884.5250 Cervical cap. (a) Identification. A cervical cap is a flexible cuplike receptacle that fits over the cervix...

  9. 21 CFR 884.5250 - Cervical cap.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Cervical cap. 884.5250 Section 884.5250 Food and... OBSTETRICAL AND GYNECOLOGICAL DEVICES Obstetrical and Gynecological Therapeutic Devices § 884.5250 Cervical cap. (a) Identification. A cervical cap is a flexible cuplike receptacle that fits over the cervix...

  10. 21 CFR 884.5250 - Cervical cap.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Cervical cap. 884.5250 Section 884.5250 Food and... OBSTETRICAL AND GYNECOLOGICAL DEVICES Obstetrical and Gynecological Therapeutic Devices § 884.5250 Cervical cap. (a) Identification. A cervical cap is a flexible cuplike receptacle that fits over the cervix...

  11. Variability of the martian seasonal CO2 cap extent over eight Mars Years

    NASA Astrophysics Data System (ADS)

    Piqueux, Sylvain; Kleinböhl, Armin; Hayne, Paul O.; Kass, David M.; Schofield, John T.; McCleese, Daniel J.

    2015-05-01

    We present eight Mars Years of nearly continuous tracking of the CO2 seasonal cap edges from Mars Year (MY) 24 to 31 using Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) and Mars Reconnaissance Orbiter (MRO) Mars Climate Sounder (MCS) thermal infrared data. Spatial and temporal resolutions are 1 pixel per degree and 10°Ls (aerocentric longitude of the Sun). The seasonal caps are defined as the regions where the diurnal radiometric temperature variations at ∼32 μm wavelength do not exceed 5 K. With this definition, terrains with small areal fraction of defrosted regolith able to experience measurable diurnal temperature cycles are not mapped as part of the cap. This technique is adequate to distinguish CO2 from H2O ices, and effective during the polar night or under low illumination conditions. The present analysis answers outstanding questions stemming from fragmented observations at visible wavelengths: (1) the previously sparsely documented growth of the North seasonal caps (160° < Ls < 270°) is shown to be repeatable within 1-2° equivalent latitude, and monotonic over the MY 24-31 time period; high repeatability is observed during the retreat of the caps in non-dusty years (∼1° or less equivalent latitude); (2) the MY 25 storm does not seem to have impacted the growth rate, maximal extents, or recession rate of the North seasonal caps, whereas the MY 28 dust storm clearly sped up the recession of the cap (∼2° smaller on average after the storm, during the recession, compared to other years); (3) during non-dusty years, the growth of the South seasonal cap (350° < Ls < 100°) presents noticeable variability (up to ∼4° equivalent latitude near Ls = 20°) with a maximum extent reached near Ls = 90°; (4) the retreat of the Southern seasonal cap (100° < Ls < 310°) exhibits large inter-annual variability, especially near 190° < Ls < 220°; (5) the recession of the MY 25 South seasonal cap is significantly accelerated during the

  12. Constraints on the Within Season and Between Year Variability of the North Residual Cap from MGS-TES

    NASA Technical Reports Server (NTRS)

    Calvin, W. M.; Titus, T. N.; Mahoney, S. A.

    2003-01-01

    There is a long history of telescopic and spacecraft observations of the polar regions of Mars. The finely laminated ice deposits and surrounding layered terrains are commonly thought to contain a record of past climate conditions and change. Understanding the basic nature of the deposits and their mineral and ice constituents is a continued focus of current and future orbited missions. Unresolved issues in Martian polar science include a) the unusual nature of the CO2 ice deposits ("Swiss Cheese", "slab ice" etc.) b) the relationship of the ice deposits to underlying layered units (which differs from the north to the south), c) understanding the seasonal variations and their connections to the finely laminated units observed in high-resolution images and d) the relationship of dark materials in the wind-swept lanes and reentrant valleys to the surrounding dark dune and surface materials. Our work focuses on understanding these issues in relationship to the north residual ice cap. Recent work using Mars Global Surveyor (MGS) data sets have described evolution of the seasonal CO2 frost deposits. In addition, the north polar residual ice cap exhibits albedo variations between Mars years and within the summer season. The Thermal Emission Spectrometer (TES) data set can augment these observations providing additional constraints such as temperature evolution and spectral properties associated with ice and rocky materials. Exploration of these properties is the subject of our current study.

  13. Helix Capping in RNA Structure

    PubMed Central

    Lee, Jung C.; Gutell, Robin R.

    2014-01-01

    Helices are an essential element in defining the three-dimensional architecture of structured RNAs. While internal basepairs in a canonical helix stack on both sides, the ends of the helix stack on only one side and are exposed to the loop side, thus susceptible to fraying unless they are protected. While coaxial stacking has long been known to stabilize helix ends by directly stacking two canonical helices coaxially, based on analysis of helix-loop junctions in RNA crystal structures, herein we describe helix capping, topological stacking of a helix end with a basepair or an unpaired nucleotide from the loop side, which in turn protects helix ends. Beyond the topological protection of helix ends against fraying, helix capping should confer greater stability onto the resulting composite helices. Our analysis also reveals that this general motif is associated with the formation of tertiary structure interactions. Greater knowledge about the dynamics at the helix-junctions in the secondary structure should enhance the prediction of RNA secondary structure with a richer set of energetic rules and help better understand the folding of a secondary structure into its three-dimensional structure. These together suggest that helix capping likely play a fundamental role in driving RNA folding. PMID:24691270

  14. Phytoremediation -- a practical capping alternative

    SciTech Connect

    Beath, J.M.; Peak, M.J.

    1997-12-31

    Much literature has been devoted recently to the use of various plant species for the uptake of heavy metals and organic contaminants. Other uses for plants as part of the remediation process are growing in perceived effectiveness. Consequently, this paper deals with two other equally important potential uses of plants to address environmental problems that are just now evolving to the field trial stage: the use of plants to remediate organic pollutants; and the use of plants to control the rainfall-driven leaching of contaminants and the subsequent delivery to underlying groundwater. The traditional Resource Conservation and Recovery Act (RCRA) approach to capping landfills will be contrasted with the potential benefits of using plants that can balance incoming rainfall with evapotranspiration, as well as plants which can act on organic constituents in soil or sludge by either uptake or by promoting microbial activity in soil. This paper compares traditional RCRA capping costs to those for a phytoremediation capping alternative, whose benefits include significantly lower implementation cost and continued remediation. This paper discusses important elements of a successful approach to phytoremediation including: species selection, implementation techniques, cost-efficient monitoring, regulatory aspects, project timing, and realistic expectations.

  15. Martian North Polar Water-Ice Clouds During the Viking Era

    NASA Technical Reports Server (NTRS)

    Tamppari, L. K.; Bass, D. S.

    2000-01-01

    The Viking Orbiters determined that the surface of Mars' northern residual cap consists of water ice. Observed atmospheric water vapor abundances in the equatorial regions have been related to seasonal exchange between reservoirs such as the polar caps, the regolith and between different phases in the atmosphere. Kahn modeled the physical characteristics of ice hazes seen in Viking Orbiter imaging limb data, hypothesizing that ice hazes provide a method for scavenging water vapor from the atmosphere and accumulating it into ice particles. Given that Jakosky found that these particles had sizes such that fallout times were of order one Martian sol, these water-ice hazes provided a method for returning more water to the regolith than that provided by adsorption alone. These hazes could also explain the rapid hemispheric decrease in atmospheric water in late northern summer as well as the increase during the following early spring. A similar comparison of water vapor abundance versus polar cap brightness has been done for the north polar region. They have shown that water vapor decreases steadily between L(sub s) = 100-150 deg while polar cap albedo increases during the same time frame. As a result, they suggested that late summer water-ice deposition onto the ice cap may be the cause of the cap brightening. This deposition could be due to adsorption directly onto the cap surface or to snowfall. Thus, an examination of north polar waterice clouds could lend insight into the fate of the water vapor during this time period. Additional information is contained in the original extended abstract.

  16. Ice And The Origin Of Life

    NASA Astrophysics Data System (ADS)

    Trinks, Hauke; Schröder, Wolfgang; Biebricher, Christof K.

    2005-10-01

    Sea ice occurs abundantly at the polar caps of the Earth and, probably, of many other planets. Its static and dynamic properties that may be important for prebiotic and early biotic reactions are described. It concentrates substrates and has many features that are important for catalytical actions. We propose that it provided optimal conditions for the early replication of nucleic acids and the RNA world. We repeated a famous prebiotic experiment, the poly-uridylic acid-instructed synthesis of polyadenylic acid from adenylic acid imidazolides in artificial sea ice, simulating the dynamic variability of real sea ice by cyclic temperature variation. Poly(A) was obtained in high yield and reached nucleotide chain lengths up to 400 containing predominantly 3‧→ 5‧ linkages.

  17. Ice and the origin of life.

    PubMed

    Trinks, Hauke; Schröder, Wolfgang; Biebricher, Christof K

    2005-10-01

    Sea ice occurs abundantly at the polar caps of the Earth and, probably, of many other planets. Its static and dynamic properties that may be important for prebiotic and early biotic reactions are described. It concentrates substrates and has many features that are important for catalytical actions. We propose that it provided optimal conditions for the early replication of nucleic acids and the RNA world. We repeated a famous prebiotic experiment, the poly-uridylic acid-instructed synthesis of polyadenylic acid from adenylic acid imidazolides in artificial sea ice, simulating the dynamic variability of real sea ice by cyclic temperature variation. Poly(A) was obtained in high yield and reached nucleotide chain lengths up to 400 containing predominantly 3'--> 5' linkages.

  18. Glaciers and ice sheets as a biome.

    PubMed

    Anesio, Alexandre M; Laybourn-Parry, Johanna

    2012-04-01

    The tundra is the coldest biome described in typical geography and biology textbooks. Within the cryosphere, there are large expanses of ice in the Antarctic, Arctic and alpine regions that are not regarded as being part of any biome. During the summer, there is significant melt on the surface of glaciers, ice caps and ice shelves, at which point microbial communities become active and play an important role in the cycling of carbon and other elements within the cryosphere. In this review, we suggest that it is time to recognise the cryosphere as one of the biomes of Earth. The cryospheric biome encompasses extreme environments and is typified by truncated food webs dominated by viruses, bacteria, protozoa and algae with distinct biogeographical structures.

  19. Where the Ice Ends

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Context image for PIA03636 Where the Ice Ends

    This image shows the margin of the south polar cap. The polar layers are prominently shown against the rocky surroundings.

    Image information: VIS instrument. Latitude 71.7S, Longitude 142.3E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  20. Seasonal CO2 Ice at Mid-Latitudes on Mars: Implications for Subsurface Water Ice

    NASA Astrophysics Data System (ADS)

    Vincendon, M.; Mustard, J. F.; Forget, F.; Kreslavsky, M. A.; Spiga, A.; Murchie, S. L.; Bibring, J.

    2009-12-01

    The seasonal CO2 ice cap of Mars extends down to about 45° of latitude in the southern hemisphere. At more equatorward latitudes, patches of CO2 ice on pole facing slopes have been reported. We have studied the spatial and temporal distribution of these deposits using the near-IR orbital experiments OMEGA and CRISM. CO2 ice is observed down to 34° of latitude in the austral winter. We have compared these observations with the predictions of a one dimensional energy balance code derived from the LMD GCM. On mid-latitudes pole facing slopes, the model requires an additional source of heat to fit the observations. Changing the parameters of the model related to the ice deposits or to the incoming radiations within the range of known properties cannot account for this mismatch. The most plausible source of heat is a high thermal inertia layer buried below a dry regolith cover, with a latitude dependent depth. This is consistent with the presence of subsurface water ice at mid latitudes on pole facing slopes. The equatorward limit of shallow (< 1 m) subsurface ice as constrained from these observations is 25°S. This value is significantly lower than the current limit determined from low-resolution observations (up to 40° locally), which corresponded to shallow subsurface ice below flat surfaces. Some of the candidates landing sites of the Mars Science Laboratory rover, such as Holden crater, are compatible with our new limit.

  1. Seasonal Evolution and Energy Budget of the South Residual Polar Cap of Mars from CRISM and HiRISE Observations

    NASA Astrophysics Data System (ADS)

    Pilorget, C.; Douté, S.; Vincendon, M.

    2016-09-01

    Here we use both HiRISE and CRISM data from the south residual cap to investigate its seasonal behavior (e.g. albedo increase) and determine its energy budget through the retrieval of the directional-hemispheric surface ice albedo.

  2. Icing Simulation

    NASA Technical Reports Server (NTRS)

    Bidwell, Colin

    2009-01-01

    A grid block transformation scheme which allows the input of grids in arbitrary reference frames, the use of mirror planes, and grids with relative velocities has been developed. A simple ice crystal and sand particle bouncing scheme has been included.. Added an SLD splashing model based on that developed by William Wright for the LEWICE 3.2.2 software. A new area based collection efficiency algorithm will be incorporated which calculates trajectories from inflow block boundaries to outflow block boundaries. This method will be used for calculating and passing collection efficiency data between blade rows for turbo-machinery calculations.

  3. Ice Observatory

    NASA Astrophysics Data System (ADS)

    blugerman, n.

    2015-10-01

    My project is to make ice observatories to perceive astral movements as well as light phenomena in the shape of cosmic rays and heat, for example.I find the idea of creating an observation point in space, that in time will change shape and eventually disappear, in consonance with the way we humans have been approaching the exploration of the universe since we started doing it. The transformation in the elements we use to understand big and small transformations, within the universe elements.

  4. Colonization of maritime glacier ice by bdelloid Rotifera.

    PubMed

    Shain, Daniel H; Halldórsdóttir, Katrín; Pálsson, Finnur; Aðalgeirsdóttir, Guðfinna; Gunnarsson, Andri; Jónsson, Þorsteinn; Lang, Shirley A; Pálsson, Hlynur Skagfjörð; Steinþórssson, Sveinbjörn; Arnason, Einar

    2016-05-01

    Very few animal taxa are known to reside permanently in glacier ice/snow. Here we report the widespread colonization of Icelandic glaciers and ice fields by species of bdelloid Rotifera. Specimens were collected within the accumulation zones of Langjökull and Vatnajökull ice caps, among the largest European ice masses. Rotifers reached densities up to ∼100 individuals per liter-equivalent of glacier ice/snow, and were freeze-tolerant. Phylogenetic analyses indicate that glacier rotifers are polyphyletic, with independent ancestries occurring within the Pleistocene. Collectively, these data identify a previously undescribed environmental niche for bdelloid rotifers and suggest their presence in comparable habitats worldwide. PMID:26932187

  5. Initial Insights into the Quaternary Evolution of the Laurentide Ice Sheet on Southeastern Baffin Island

    NASA Astrophysics Data System (ADS)

    Pendleton, S.; Anderson, R. S.; Miller, G. H.; Refsnider, K. A.

    2015-12-01

    Increasing Arctic summer temperatures in recent decades and shrinking cold-based ice caps on Cumberland Peninsula, Baffin Island, are exposing ancient landscapes complete with uneroded bedrock surfaces. Previous work has indicated that these upland surfaces covered with cold-based ice experience negligible erosion compared with the valleys and fjords systems that contain fast-flowing ice. Given the appearance of highly weathered bedrock, it is argued that these landscapes have remained largely unchanged since at least the last interglaciation (~120 ka), and have likely experienced multiple cycles of ice expansion and retraction with little erosion throughout the Quaternary. To explore this hypothesis, we use multiple cosmogenic radionuclides (26Al and 10Be) to investigate and provide insight into longer-term cryosphere activity and landscape evolution. 26Al/10Be in surfaces recently exposed exhibit a wide range of exposure-burial histories. Total exposure-burial times range from ~0.3 - 1.5 My and estimated erosion rates from 0.5 - 6.2 m Ma-1. The upland surfaces of the Penny Ice cap generally experienced higher erosion rates (~0.45 cm ka-1) than those covered by smaller ice caps (~0.2 cm ka-1). The cumulative burial/exposure histories in high, fjord-edge locations indicate that significant erosion north of the Penny Ice Cap ceased between ~600 and 800 ka, suggesting that Laurentide Ice Sheet (LIS) organization and fjord inception was underway by at least this time. Additionally, 26Al/10Be ratios near production values despite high inventories from a coastal summit 50 km east of the Penny Ice Cape suggest that that area has not experienced appreciable burial by ice, suggesting that it was never inundated by the LIS. Moreover, these initial data suggest a variable and dynamic cryosphere in the region and provide insight into how large ice sheets evolved and organized themselves during the Quaternary.

  6. Multiple climate and sea ice states on a coupled Aquaplanet

    NASA Astrophysics Data System (ADS)

    Rose, B.; Ferreira, D.; Marshall, J.

    2010-12-01

    A fully coupled atmosphere-ocean-sea ice GCM is used to explore the climates of Earth-like planets with no continents and idealized ocean basin geometries. We find three qualitatively different stable equilibria under identical external forcing: an equable ice-free climate, a cold climate with ice caps extending into mid-latitudes, and a completely ice-covered "Snowball" state. These multiple states persist for millennia with no drift despite a full seasonal cycle and vigorous internal variability of the system on all time scales. The behavior of the coupled system is rationalized through an extension of the Budyko-Sellers model to include explicit ocean heat transport (OHT), and the insulation of the ice-covered sea surface. Sensitivity tests are also conducted with a slab ocean GCM with prescribed OHT. From these we conclude that albedo feedback and ocean circulation both play essential roles in the maintenance of the multiple states. OHT in the coupled system is dominated by a wind-driven subtropical cell carrying between 2 and 3 PW of thermal energy out of the deep tropics, most of which converges in the subtropics to lower mid-latitudes. This convergence pattern (similar to modern Earth) is robust to changes in the ocean basin geometry, and is directly responsible for the stabilization of the large ice cap. OHT also plays an essential but indirect role in the maintenance of the ice-free pole in the warm states, by driving an enhanced poleward atmospheric latent heat flux. The hysteresis loop for transitions between the warm and large ice cap states spans a much smaller range of parameter space (e.g. ±1.8% variations in solar constant) than the transitions in and out of the Snowball. Three qualitatively different climate states for the same external forcing in a coupled GCM: ice-free, large ice cap, and Snowball. SST and sea ice thickness are plotted. Similar results are found in a pure Aquaplanet (lower) and a "RidgeWorld" with a global-scale ocean basin

  7. North-Polar Martian Cap as Habitat for Elementary Life

    NASA Astrophysics Data System (ADS)

    Wallis, M. K.; Wickramasinghe, J. T.; Wickramasinghe, N. C.

    2008-09-01

    North-polar cap over millenia Atmospheric water in Mars tends currently as for the past millenia to distil onto the polar caps and be buried under dust deposits. Diffusive release from ground-ice (and its excavation in meteorite impacts [1]) replenishes atmospheric water, allowing the gradual build up of polar ice-dust deposits. When sunlit, this warmed and sublimating ice-dust mix has interest as a potential habitat for micro-organisms. Modelling shows precipitable vapour at 10-50μm/yr, varying sensitively with small changes in orbitable obliquity around the present 25° [2]. The modelling applies to a globe with regionally uniform albedo, unlike the steep topography and dark layering of the north polar cap whose upper 300m have accumulated over the last 500 kyr [3]. The cliffs and ravines of the north-polar cap are thought to form through south-facing slopes sublimating and gaining a dirt-encrusted surface, while horizontal surfaces brighten through frost deposits. The two-phase surface derives from the dust and frost feedback on surface albedo [4] and the resulting terrain develops over diurnal cycles of frosting and sublimation, and over annual seasonal cycles. The steep south-facing sides of observed ravines when unshadowed would see for a few hours the full intensity of sunlight at near normal incidence, without the atmospheric dimming at similar inclinations on Earth. As exposed ice sublimates at T > 200K (partial pressure exceeds typical martian 0.1 Pa), a crust of dirt develops to maintain quasi-stability. The dirt crust's main function is to buffer the ice against diurnal temperature fluctuations, but it also slows down vapour diffusion - analogous to south polar ice sublimation [5] and the growth of ground-ice [6]. We envisage 1-10 mm/yr as the net sublimation rate, compatible with the 100 kyr life and scales of the north polar ravines. Modelling of icy-dirt crusts in the polar cap Plane-parallel layers have been used to model the changing temperature

  8. The Contribution of Water Ice Clouds to the Water Cycle in the North Polar Region of Mars: Preliminary Analysis

    NASA Technical Reports Server (NTRS)

    Bass, D. S.; Tamppari, L. K.

    2000-01-01

    While it has long been known that Mars' north residual polar cap and the Martian regolith are significant sources of atmospheric water vapor, the amount of water vapor observed in the northern spring season by the Viking Mars Atmospheric Water Detector instrument (MAWD) cannot be attributed to cap and regolith sources alone. Kahn suggested that ice hazes may be the mechanism by which additional water is supplied to the Martian atmosphere. Additionally, a significant decrease in atmospheric water vapor was observed in the late northern summer that could not be correlated with the return of the cold seasonal C02 ice. While the detection of water ice clouds on Mars indicate that water exists in Mars' atmosphere in several different phases, the extent to which water ice clouds play a role in moving water through the Martian atmosphere remains uncertain. Work by Bass et. al. suggested that the time dependence of water ice cap seasonal variability and the increase in atmospheric water vapor depended on the polar cap center reaching 200K, the night time saturation temperature. Additionally, they demonstrated that a decrease in atmospheric water vapor may be attributed to deposition of water ice onto the surface of the polar cap; temperatures were still too warm at this time in the summer for the deposition of carbon dioxide. However, whether water ice clouds contribute significantly to this variability is unknown. Additional information is contained in original extended abstract.

  9. Constraining the margins of Neoproterozoic ice masses: depositional signature, palaeoflow and glaciodynamics

    NASA Astrophysics Data System (ADS)

    Busfield, Marie; Le Heron, Daniel

    2016-04-01

    The scale and distribution of Neoproterozoic ice masses remains poorly understood. The classic Snowball Earth hypothesis argues for globally extensive ice sheets, separated by small ocean refugia, yet the positions of palaeo-ice sheet margins and the extent of these open water regions are unknown. Abundant evidence worldwide for multiple cycles of ice advance and recession is suggestive of much more dynamic mass balance changes than previously predicted. Sedimentological analysis enables an understanding of the changing ice margin position to be gained through time, in some cases allowing it to be mapped. Where the maximum extent of ice advance varies within a given study area, predictions can also be made on the morphology of the ice margin, and the underlying controls on this morphology e.g. basin configuration. This can be illustrated using examples from the Neoproterozoic Kingston Peak Formation in the Death Valley region of western USA. Throughout the Sperry Wash, northern Kingston Range and southern Kingston Range study sites the successions show evidence of multiple cycles of ice advance and retreat, but the extent of maximum ice advance is extremely variable, reaching ice-contact conditions at Sperry Wash but only ice-proximal settings in the most distal southern Kingston Range. The overall advance is also much more pronounced at Sperry Wash, from ice-distal to ice-contact settings, as compared to ice-distal to ice-proximal settings in the southern Kingston Range. Therefore, the position of the ice margin can be located at the Sperry Wash study site, where the more pronounced progradation is used to argue for topographically constrained ice, feeding the unconstrained shelf through the northern into the southern Kingston Range. This raises the question as to whether Neoproterozoic ice masses could be defined as topographically constrained ice caps, or larger ice sheets feeding topographically constrained outlet glaciers.

  10. Self-sustaining Mars colonies utilizing the North Polar Cap and the Martian atmosphere.

    PubMed

    Powell, J; Maise, G; Paniagua, J

    2001-01-01

    A revolutionary new concept for the early establishment of robust, self-sustaining Martian colonies is described. The colonies would be located on the North Polar Cap of Mars and utilize readily available water ice and the CO2 Martian atmosphere as raw materials to produce all of the propellants, fuel, air, water, plastics, food, and other supplies needed by the colony. The colonists would live in thermally insulated large, comfortable habitats under the ice surface, fully shielded from cosmic rays. The habitats and supplies would be produced by a compact, lightweight (~4 metric tons) nuclear powered robotic unit termed ALPH (Atomic Liberation of Propellant and Habitat), which would land 2 years before the colonists arrived. Using a compact, lightweight 5 MW (th) nuclear reactor/steam turbine (1 MW(e)) power source and small process units (e.g., H2O electrolyzer, H2 and O2 liquefiers, methanator, plastic polymerizer, food producer, etc.) ALPH would stockpile many hundreds of tons of supplies in melt cavities under the ice, plus insulated habitats, to be in place and ready for use when the colonists landed. With the stockpiled supplies, the colonists would construct and operate rovers and flyers to explore the surface of Mars. ALPH greatly reduces the amount of Earth supplied material needed and enables large permanent colonies on Mars. It also greatly reduces human and mission risks and vastly increases the capability not only for exploration of the surrounding Martian surface, but also the ice cap itself. The North Polar Cap is at the center of the vast ancient ocean that covered much of the Martian Northern Hemisphere. Small, nuclear heated robotic probes would travel deep (1 km or more) inside the ice cap, collecting data on its internal structure, the composition and properties of the ancient Martian atmosphere, and possible evidence of ancient life forms (microfossils, traces of DNA, etc.) that were deposited either by wind or as remnants of the ancient ocean

  11. Self-sustaining Mars colonies utilizing the North Polar Cap and the Martian atmosphere.

    PubMed

    Powell, J; Maise, G; Paniagua, J

    2001-01-01

    A revolutionary new concept for the early establishment of robust, self-sustaining Martian colonies is described. The colonies would be located on the North Polar Cap of Mars and utilize readily available water ice and the CO2 Martian atmosphere as raw materials to produce all of the propellants, fuel, air, water, plastics, food, and other supplies needed by the colony. The colonists would live in thermally insulated large, comfortable habitats under the ice surface, fully shielded from cosmic rays. The habitats and supplies would be produced by a compact, lightweight (~4 metric tons) nuclear powered robotic unit termed ALPH (Atomic Liberation of Propellant and Habitat), which would land 2 years before the colonists arrived. Using a compact, lightweight 5 MW (th) nuclear reactor/steam turbine (1 MW(e)) power source and small process units (e.g., H2O electrolyzer, H2 and O2 liquefiers, methanator, plastic polymerizer, food producer, etc.) ALPH would stockpile many hundreds of tons of supplies in melt cavities under the ice, plus insulated habitats, to be in place and ready for use when the colonists landed. With the stockpiled supplies, the colonists would construct and operate rovers and flyers to explore the surface of Mars. ALPH greatly reduces the amount of Earth supplied material needed and enables large permanent colonies on Mars. It also greatly reduces human and mission risks and vastly increases the capability not only for exploration of the surrounding Martian surface, but also the ice cap itself. The North Polar Cap is at the center of the vast ancient ocean that covered much of the Martian Northern Hemisphere. Small, nuclear heated robotic probes would travel deep (1 km or more) inside the ice cap, collecting data on its internal structure, the composition and properties of the ancient Martian atmosphere, and possible evidence of ancient life forms (microfossils, traces of DNA, etc.) that were deposited either by wind or as remnants of the ancient ocean

  12. A microphysically-based approach to modeling emissivity and albedo of the martian seasonal caps

    USGS Publications Warehouse

    Eluszkiewicz, J.; Moncet, J.-L.; Titus, T.N.; Hansen, G.B.

    2005-01-01

    A new model of albedo and emissivity of the martian seasonal caps represented as porous CO2 slabs containing spherical voids and dust particles is described. In the model, a radiative transfer model is coupled with a microphysical model in order to link changes in albedo and emissivity to changes in porosity caused by ice metamorphism. The coupled model is capable of reproducing temporal changes in the spectra of the caps taken by the Thermal Emission Spectrometer onboard the Mars Global Surveyor and it can be used as the forward model in the retrievals of the caps' physical properties (porosity, dust abundance, void and dust grain size) from the spectra. Preliminary results from such inversion studies are presented. ?? 2004 Elsevier Inc. All rights reserved.

  13. Relationship between cap structure and energy gap in capped carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Ono, Shota; Tanikawa, Kousei; Kuwahara, Riichi; Ohno, Kaoru

    2016-07-01

    Revealing a universal relation between geometrical structures and electronic properties of capped carbon nanotubes (CNTs) is one of the current objectives in nanocarbon community. Here, we investigate the local curvature of capped CNTs and define the cap region by a crossover behavior of the curvature energy versus the number of carbon atoms integrated from the tip to the tube region. Clear correlations among the energy gap of the cap localized states, the curvature energy, the number of carbon atoms in the cap region, and the number of specific carbon clusters are observed. The present analysis opens the way to understand the cap states.

  14. Relationship between cap structure and energy gap in capped carbon nanotubes.

    PubMed

    Ono, Shota; Tanikawa, Kousei; Kuwahara, Riichi; Ohno, Kaoru

    2016-07-14

    Revealing a universal relation between geometrical structures and electronic properties of capped carbon nanotubes (CNTs) is one of the current objectives in nanocarbon community. Here, we investigate the local curvature of capped CNTs and define the cap region by a crossover behavior of the curvature energy versus the number of carbon atoms integrated from the tip to the tube region. Clear correlations among the energy gap of the cap localized states, the curvature energy, the number of carbon atoms in the cap region, and the number of specific carbon clusters are observed. The present analysis opens the way to understand the cap states. PMID:27421422

  15. Friction of ice on ice

    NASA Astrophysics Data System (ADS)

    Schulson, Erland M.; Fortt, Andrew L.

    2012-12-01

    New measurements have been made of the friction coefficient of freshwater polycrystalline ice sliding slowly (5 × 10-8 to 1 × 10-3 m s-1) upon itself at temperatures from 98 to 263 K under low normal stresses (≤98 kPa). Sliding obeys Coulomb's law: the shear stress is directly proportional to the normal stress across the interface, while cohesion offers little contribution to frictional resistance. The coefficient of kinetic friction of smooth surfaces varies from μk = 0.15 to 0.76 and, at elevated temperatures (≥223 K), exhibits both velocity strengthening at lower velocities (<10-5 to 10-4 m s-1) and velocity weakening at higher velocities. Strengthening and weakening are attributed to creep deformation of asperities and localized melting, respectively. At intermediate temperatures of 173 and 133 K, the kinetic coefficient appears to not exhibit significant dependence upon velocity. However, at the low temperature of 98 K the coefficient of kinetic friction exhibits moderate velocity strengthening at both the lowest and the highest velocities but velocity independence over the range of intermediate velocities. No effect was detected of either grain size or texture. Over the range of roughness 0.4 × 10-6 m ≤ Ra ≤ 12 × 10-6 m, a moderate effect was detected, where μk ∝ Ra0.08. Slide-hold-slide experiments revealed that the coefficient of static friction increases by an amount that scales logarithmically with holding time. Implications of the results are discussed in relation to shearing across "tiger stripe" faults within the icy crust of Saturn's Enceladus, sliding of the arctic sea ice cover and brittle compressive failure of cold ice.

  16. Observations of the north polar water ice annulus on Mars using THEMIS and TES

    USGS Publications Warehouse

    Wagstaff, K.L.; Titus, T.N.; Ivanov, A.B.; Castano, R.; Bandfield, J.L.

    2008-01-01

    The Martian seasonal CO2 ice caps advance and retreat each year. In the spring, as the CO2 cap gradually retreats, it leaves behind an extensive defrosting zone from the solid CO2 cap to the location where all CO2 frost has sublimated. We have been studying this phenomenon in the north polar region using data from the THermal EMission Imaging System (THEMIS), a visible and infra-red (IR) camera on the Mars Odyssey spacecraft, and the Thermal Emission Spectrometer (TES) on Mars Global Surveyor. Recently, we discovered that some THEMIS images of the CO2 defrosting zone contain evidence for a distinct defrosting phenomenon: some areas just south of the CO2 cap edge are too bright in visible wavelengths to be defrosted terrain, but too warm in the IR to be CO2 ice. We hypothesize that we are seeing evidence for a seasonal annulus of water ice (frost) that recedes with the seasonal CO2 cap, as predicted by previous workers. In this paper, we describe our observations with THEMIS and compare them to simultaneous observations by TES and OMEGA. All three instruments find that this phenomenon is distinct from the CO2 cap and most likely composed of water ice. We also find strong evidence that the annulus widens as it recedes. Finally, we show that this annulus can be detected in the raw THEMIS data as it is collected, enabling future long-term onboard monitoring. ?? 2007.

  17. Observations from the Programme for Monitoring of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Andersen, S. B.; Ahlstrom, A. P.; Andersen, M. L.; Box, J. E.; Citterio, M.; Colgan, W. T.; Fausto, R. S.; van As, D.; Forsberg, R.; Skourup, H.; Sandberg Sørensen, L.; Kristensen, S. S.; Dall, J.; Kusk, A.; Petersen, D.

    2014-12-01

    The Programme for Monitoring of the Greenland Ice Sheet (PROMICE) is as an on-going effort initiated in 2007 to monitor changes in the mass budget of the Greenland Ice Sheet. The aim of the programme is to quantify the mass loss of the Greenland ice sheet and track changes in the extent of the glaciers, ice caps and ice sheet margin. Specifically, PROMICE aims to estimate the mass loss derived from three fundamentally different sources: Surface melt water runoff from the ice sheet margin Iceberg production Mass loss of individual glaciers and ice caps surrounding the ice sheet The first is observed by a network of automatic weather stations (AWS) on the ice sheet margin measuring ice ablation as well as meteorological parameters. The second is determined by establishing a so-called 'flux gate' along the entire ice sheet margin and keeping track of the ice passing through this gate. The flux gate is obtained from airborne surveys of ice sheet surface elevation and thickness. The volume of the ice passing through the gate is derived from maps of the surface velocity of the ice sheet, produced from satellite radar. The third is investigated through regular mapping of area and elevation of the approximately 20.000 individual glaciers and ice caps in Greenland. Mapping is carried out using recent satellite imagery as well as aerial ortho-photos. Within PROMICE data sets from these activities are collected. They include observations from the network of currently about 20 AWS on the margin of the Greenland ice sheet. Airborne surveys, yielding surface elevation and ice depth along the entire margin of the Greenland ice sheet carried out in 2007 and 2011. A map of all Greenland ice masses, based on the highest detail aero-photogrammetric maps produced from mid-80's aerial photographs. Real-time data from the PROMICE AWS network is shown at the web site www.promice.org and the data is freely available for download. Data from the airborne surveys and mapping activities are

  18. Glaciological reconstruction of Holocene ice margins in northwestern Greenland

    NASA Astrophysics Data System (ADS)

    Birkel, S. D.; Osterberg, E. C.; Kelly, M. A.; Axford, Y.

    2014-12-01

    The past few decades of climate warming have brought overall margin retreat to the Greenland Ice Sheet. In order to place recent and projected changes in context, we are undertaking a collaborative field-modeling study that aims to reconstruct the Holocene history of ice-margin fluctuation near Thule (~76.5°N, 68.7°W), and also along the North Ice Cap (NIC) in the Nunatarssuaq region (~76.7°N, 67.4°W). Fieldwork reported by Kelly et al. (2013) reveals that ice in the study areas was less extensive than at present ca. 4700 (GIS) and ca. 880 (NIC) cal. years BP, presumably in response to a warmer climate. We are now exploring Holocene ice-climate coupling using the University of Maine Ice Sheet Model (UMISM). Our approach is to first test what imposed climate anomalies can afford steady state ice margins in accord with field data. A second test encompasses transient simulation of the Holocene, with climate boundary conditions supplied by existing paleo runs of the Community Climate System Model version 4 (CCSM4), and a climate forcing signal derived from Greenland ice cores. In both cases, the full ice sheet is simulated at 10 km resolution with nested domains at 0.5 km for the study areas. UMISM experiments are underway, and results will be reported at the meeting.

  19. Scrambled Ice

    NASA Technical Reports Server (NTRS)

    1998-01-01

    This complex area on the side of Europa which faces away from Jupiter shows several types of features which are formed by disruptions of Europa's icy crust. North is to the top of the image, taken by NASA's Galileo spacecraft, and the Sun illuminates the surface from the left. The prominent wide, dark bands are up to 20 kilometers (12 miles) wide and over 50 kilometers (30 miles) long. They are believed to have formed when Europa's icy crust fractured, separated and filled in with darker, 'dirtier' ice or slush from below. A relatively rare type of feature on Europa is the 15-kilometer-diameter (9.3-mile) impact crater in the lower left corner. The small number of impact craters on Europa's surface is an indication of its relatively young age. A region of chaotic terrain south of this impact crater contains crustal plates which have broken apart and rafted into new positions. Some of these 'ice rafts' are nearly 1 kilometer (about half a mile) across. Other regions of chaotic terrain are visible and indicate heating and disruption of Europa's icy crust from below. The youngest features in this scene are the long, narrow cracks in the ice which cut across all other features. One of these cracks is about 30 kilometers (18 miles) to the right of the impact crater and extends for hundreds of miles from the top to the bottom of the image.

    The image, centered near 23 degrees south latitude and 179 degrees longitude, covers an area about 240 by 215 kilometers (150 by 130 miles) across. The finest details that can be discerned in this picture are about 460 meters (500 yards) across. The image was taken as Galileo flew by Europa on March 29, 1998. The image was taken by the onboard solid state imaging system camera from an altitude of 23,000 kilometers (14,000 miles).

    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech

  20. Climate investigations using ice sheet and mass balance models with emphasis on North American glaciation

    NASA Astrophysics Data System (ADS)

    Birkel, Sean David

    This dissertation describes the application of the University of Maine Ice Sheet Model (UM-ISM) and Environmental Change Model (UM-ECM) to understanding mechanisms of ice-sheet/climate integration during ice ages. The UM-ECM, written by the author for this research, calculates equilibrium biome and snow/ice mass balance solutions for the globe based on modern input climatology and user-defined parameter values. The program was produced in conjunction with a National Science Foundation ITEST grant meant to seed inquiry-based classroom study of Earth systems using computer models. To that end, the UM-ECM serves as both a research and teaching tool. The model has a web-based interface, which has been tested with a group of middle school science teachers with a focus on local to global-scale climate learning. Initially, the UM-ISM and UM-ECM are used to reconstruct the former ice cap of the Wind River Mountains, Wyoming, in a companion study to a UMaine field research effort to document worldwide glacier recession during the last termination. It is found that the ice cap likely formed in response to a 5--6 °C cooling in conjunction with a precipitation doubling relative to modern conditions. Moreover, the maximum ice cap could have disappeared within 90 years if subjected to modem climate conditions. These results support hypotheses that the western U.S. became wetter during glacial stadials due to a southward-shifted North American storm track in response to Laurentide Ice Sheet orography, and that ice caps of the western U.S. are exceptionally sensitivity to climatic perturbation. The UMaine ice sheet and climate models are then used to assess the coupling between the Laurentide Ice Sheet and climate during ice-age cycles. It is shown that the classic "sawtooth" pattern of global sea-level change can be reproduced in the model by linking size of the polar atmospheric cell over eastern Canada to size of the Laurentide Ice Sheet and the magnitude of insolation forcing

  1. Rapid sea level rise and ice sheet response to 8,200-year climate event

    USGS Publications Warehouse

    Cronin, T. M.; Vogt, P.R.; Willard, D.A.; Thunell, R.; Halka, J.; Berke, M.; Pohlman, J.

    2007-01-01

    The largest abrupt climatic reversal of the Holocene interglacial, the cooling event 8.6–8.2 thousand years ago (ka), was probably caused by catastrophic release of glacial Lake Agassiz-Ojibway, which slowed Atlantic meridional overturning circulation (AMOC) and cooled global climate. Geophysical surveys and sediment cores from Chesapeake Bay reveal the pattern of sea level rise during this event. Sea level rose ∼14 m between 9.5 to 7.5 ka, a pattern consistent with coral records and the ICE-5G glacio-isostatic adjustment model. There were two distinct periods at ∼8.9–8.8 and ∼8.2–7.6 ka when Chesapeake marshes were drown as sea level rose rapidly at least ∼12 mm yr−1. The latter event occurred after the 8.6–8.2 ka cooling event, coincided with extreme warming and vigorous AMOC centered on 7.9 ka, and may have been due to Antarctic Ice Sheet decay.

  2. Synsedimentary deformation and the paleoseismic record in Marinoan cap carbonate of the southern Amazon Craton, Brazil

    NASA Astrophysics Data System (ADS)

    Soares, Joelson Lima; Nogueira, Afonso César Rodrigues; Domingos, Fábio; Riccomini, Claudio

    2013-12-01

    Event Layers in Neoproterozoic cap carbonates of Brazil's southwestern Amazon Craton record post-Marinoan synsedimentary seismicity. The 35 m-thick cap carbonates overlie glaciogenic sediments related to the Marinoan glaciation (635 Ma) and are comprised of two units: the lower cap consists of dolomite (˜15 m thick) and the upper cap is limestone (˜25 m thick). The cap dolomite includes pinkish crystalline dolostone with even parallel lamination, stratiform stromatolites, eventual tube structures and megaripple bedded peloidal dolostone interpreted as shallow (euphotic) platform deposits. The cap limestone onlaps the cap dolomite and consists of red marl, gray to black bituminous lime mudstone, bituminous shale with abundant calcite crystal fans (pseudomorphs after aragonite) and even parallel lamination interpreted as moderately deep to deep platform deposits. Five successive events of synsedimentary deformation were recognized in the cap carbonates exposed at Mirassol d'Oeste and Tangará da Serra, in Central Brazil: Event 1 - large to small-scale load cast structures in the contact between dolostones and glaciogenic sediments; Event 2 - stromatolitic lamination truncated by tube structures; Event 3 - vertical to subvertical fractures and faults, and large-scale synclines and anticlines with chevron folds; Event 4 - conglomerate and breccia filling neptunian dykes limited by undeformed beds; and Event 5 - slump and sliding deposits found only in the upper part of the cap limestone. Event 1 was produced by hydroplastic dynamics likely induced by isostatic rebound during ice cap melting in the final stages of the Marinoan glaciation. Events 2 and 5 are autocyclic in nature, and related to depositional processes. Event 2 is linked to fluid and methane escape from organic degradation of microbial mats and domes that formed tubestones; Event 5 is associated to collapse and sliding/slumping in the platform and slope. The reliable orientations of synsedimentary faults

  3. Icing: Accretion, Detection, Protection

    NASA Technical Reports Server (NTRS)

    Reinmann, John J.

    1994-01-01

    The global aircraft industry and its regulatory agencies are currently involved in three major icing efforts: ground icing; advanced technologies for in-flight icing; and tailplane icing. These three major icing topics correspondingly support the three major segments of any aircraft flight profile: takeoff; cruise and hold; and approach and land. This lecture addressess these three topics in the same sequence as they appear in flight, starting with ground deicing, followed by advanced technologies for in-flight ice protection, and ending with tailplane icing.

  4. Palmer Quest: A Feasible Nuclear Fission "Vision Mission" to the Mars Polar Caps

    NASA Technical Reports Server (NTRS)

    Carsey, F. D.; Beegle, L. W.; Nakagawa, R.; Elliott, J. O.; Matthews, J. B.; Coleman, M. L.; Hecht, M. H.; Ivaniov, A. B.; Head, J. W.; Milkovich, S.

    2005-01-01

    We are engaged in a NASA Vision Mission study, called Palmer Quest after the American Antarctic explorer Nathaniel Palmer, to assess the presence of life and evaluate the habitability of the basal domain of the Mars polar caps. We address this goal through four objectives: 1. Determine the presence of amino acids, nutrients, and geochemical heterogeneity in the ice sheet. 2. Quantify and characterize the provenance of the amino acids in Mars ice. 3. Assess the stratification of outcropped units for indications of habitable zones. 4. Determine the accumulation of ice, mineralogic material, and amino acids in Mars ice caps over the present epoch. Because of the defined scientific goal for the vision mission, the Palmer Quest focus is astrobiological; however, the results of the study make us optimistic that aggressive multi-platform in-situ missions that address a wide range of objectives, such as climate change, can be supported by variations of the approach used on this mission. Mission Overview: The Palmer Quest baseline

  5. Possible significance of cubic water-ice, H2O-Ic, in the atmospheric water cycle of Mars

    NASA Technical Reports Server (NTRS)

    Gooding, James L.

    1988-01-01

    The possible formation and potential significance of the cubic ice polymorph on Mars is discussed. When water-ice crystallizes on Earth, the ambient conditions of temperature and pressure result in the formation of the hexagonal ice polymorph; however, on Mars, the much lower termperature and pressures may permit the crystallization of the cubic polymorph. Cubic ice has two properties of possible importance on Mars: it is an excellant nucleator of other volatiles (such as CO2), and it undergoes an exothermic transition to hexagonal ice at temperatures above 170 K. These properties may have significant implications for both martian cloud formation and the development of the seasonal polar caps.

  6. High LMD GCM Resolution Modeling of the Seasonal Evolution of the Martian Northern Permanent Cap: Comparison with Mars Express OMEGA Observations

    NASA Technical Reports Server (NTRS)

    Levrard, B.; Forget, F.; Montmessin, F.; Schmitt, B.; Doute, S.; Langevin, Y.; Poulet, F.; Bibring, J. P.; Gondet, B.

    2005-01-01

    Analyses of imaging data from Mariner, Viking and MGS have shown that surface properties (albedo, temperature) of the northern cap present significant differences within the summer season and between Mars years. These observations include differential brightening and/or darkening between polar areas from the end of the spring to midsummer. These differences are attributed to changes in grain size or dust content of surface ice. To better understand the summer behavior of the permanent northern polar cap, we perfomed a high resolution modeling (approximately 1 deg x 1 deg.) of northern cap in the Martian Climate/water cycle as simulated by the Laboratoire de Meteorologie Dynamique (LMD) global climate model. We compare the predicted properties of the surface ice (ice thickness, temperature) with the Mars Express Omega summer observations of the northern cap. albedo and thermal inertia svariations model. In particular, albedo variations could be constrained by OMEGA data. Meteorological predictions of the LMD GCM wil be presented at the conference to interpret the unprecedently resolved OMEGA observations. The specific evolution of regions of interest (cap center, Chasma Boreal...) and the possibility of late summer global cap brightening will be discussed.

  7. The Residual Polar Caps of Mars: Geological Differences and Possible Consequences

    NASA Technical Reports Server (NTRS)

    Thomas, P. C.; Sullivan, R.; Ingersoll, A. P.; Murray, B. C.; Danielson, G. E.; Herkenhoff, K. E.; Soderblom, L.; Malin, M. C.; Edgett, K. S.; James, P. B.

    2000-01-01

    The Martian polar regions have been known to have thick layered sequences (presumed to consist of silicates and ice), CO2 seasonal frost, and residual frosts that remain through the summer: H2O in the north, largely CO2 in the south. The relationship of the residual frosts to the underlying layered deposits could not be determined from Viking images. The Mars Orbiter Camera on Mars Global Surveyor has provided a 50-fold increase in resolution that shows more differences between the two poles. The north residual cap surface has rough topography of pits, cracks, and knobs, suggestive of ablational forms. This topography is less than a few meters in height, and grades in to surfaces exposing the layers underneath. In contrast, the south residual cap has distinctive collapse and possibly ablational topography emplaced in four or more layers, each approx. two meters thick. The top surface has polygonal depressions suggestive of thermal contraction cracks. The collapse and erosional forms include circular and cycloidal depressions, long sinuous troughs, and nearly parallel sets of troughs. The distinctive topography occurs throughout the residual cap area, but not outside it. Unconformities exposed in polar layers, or other layered materials, do not approximate the topography seen on the south residual cap. The coincidence of a distinct geologic feature, several layers modified by collapse, ablation, and mass movement with the residual cap indicates a distinct composition and/or climate compared to both the remainder of the south polar layered units and those in the north.

  8. Ir Spectral Mapping of the Martian South Polar Residual CAP Using Crism

    NASA Astrophysics Data System (ADS)

    Campbell, Jacqueline; Sidiropoulos, Panagiotis; Muller, Jan-Peter

    2016-06-01

    Polycyclic aromatic hydrocarbons (PAHs) are considered to be important in theories of abiogenesis (Allamandola, 2011) . There is evidence that PAHs have been detected on two icy Saturnian satellites using the Visual and Infrared Mapping Spectrometer (VIMS) on the Cassini spacecraft (Cruikshank et al., 2007). The hypothesised presence of PAHs in Mars south polar cap has not been systematically examined even though the Mars south polar cap may allow the preservation of organic molecules that are typically destroyed at the Martian surface by UV radiation (Dartnell et al. 2012). This hypothesis is supported by recent analyses of South Polar Residual Cap (SPRC) structural evolution (Thomas et al., 2009) that suggest the possibility that seasonal and long term sublimation may excavate dust particles from within the polar ice. Periodic sublimation is believed to be responsible for the formation of so-called "Swiss Cheese Terrain", a unique surface feature found only in the Martian south polar residual cap consisting of flat floored, circular depressions (Byrne, 2009). We show the first examples of work towards the detection of PAHs in Swiss Cheese Terrain, using data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), on board NASA's Mars Reconnaissance Orbiter (MRO). CRISM is designed to search for mineralogical indications of past and present water, thus providing extensive coverage of the south polar cap. In this work, we discuss whether CRISM infrared spectra can be used to detect PAHs in Swiss Cheese Terrain and demonstrate a number of maps showing shifts in spectral profiles over the SPRC.

  9. An explanation of the 100 kyr ice age cycle using a simple box model

    NASA Astrophysics Data System (ADS)

    Fowler, A. C.; Rickaby, R. E. M.; Wolff, E. W.

    2012-04-01

    We have developed a conceptually simple box model, similar in philosophy to those of Saltzman, with a view to explaining the 100 kyr period of the most recent ice age signals. Here we explain in detail how and why the various components of the model have been constructed, and we show how the model can be analysed in order to explain its behaviour. We find that the model can explain the 100 kyr cycles as a self-sustaining oscillation, and in addition we can explain the 40 kyr -100 kyr transition, and indeed the post-Eocene cooling, through the variation of weathering rate over geologic time. The central component of the model is an ocean carbon balance, which receives input from the weathering of silicates and carbonates, and loses CaCO3 by the burial of calcareous biomass. It is therefore necessary to also balance calcium and biomass, and thence phosphorus, which we take to be rate limiting. Charge balance is effected through estimates of the conservative ions Na+, Cl-, etc. To this ocean chemistry model we add a simple ice sheet model of the Weertman/Oerlemans/Ghil type, and we allow for rapid deglaciation through an enhanced wastage rate associated with the growth of proglacial lakes like Agassiz. The oscillations which result are due to the interaction of the hysteretic ice sheet growth (allowing for the elevation-accumulation feedback), and a similar hysteresis in the proglacial lake volume. The effect of this on the atmospheric carbon is controlled by the lowering of the carbonate ion which results when the ice sheet meltwater flows into the ocean.

  10. CAPS Capsule. Volume 5, Number 1.

    ERIC Educational Resources Information Center

    Walz, Garry, Ed.; And Others

    Published 3 times yearly by the ERIC Clearinghouse on Counseling and Personnel Services, CAPS Capsule acquaints the reader with recent projects, meetings, publications and materials which are of interest to those in the helping professions. This issue introduces several new publications offered by CAPS under the name, "The Counselor's S x-Pack."…

  11. 31 CFR 50.15 - Cap disclosure.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 31 Money and Finance: Treasury 1 2013-07-01 2013-07-01 false Cap disclosure. 50.15 Section 50.15 Money and Finance: Treasury Office of the Secretary of the Treasury TERRORISM RISK INSURANCE PROGRAM Disclosures as Conditions for Federal Payment § 50.15 Cap disclosure. (a) General. Under section 103(e)(2)...

  12. 31 CFR 50.15 - Cap disclosure.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 31 Money and Finance: Treasury 1 2011-07-01 2011-07-01 false Cap disclosure. 50.15 Section 50.15 Money and Finance: Treasury Office of the Secretary of the Treasury TERRORISM RISK INSURANCE PROGRAM Disclosures as Conditions for Federal Payment § 50.15 Cap disclosure. (a) General. Under section 103(e)(2)...

  13. 31 CFR 50.15 - Cap disclosure.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 31 Money and Finance: Treasury 1 2014-07-01 2014-07-01 false Cap disclosure. 50.15 Section 50.15 Money and Finance: Treasury Office of the Secretary of the Treasury TERRORISM RISK INSURANCE PROGRAM Disclosures as Conditions for Federal Payment § 50.15 Cap disclosure. (a) General. Under section 103(e)(2)...

  14. 31 CFR 50.15 - Cap disclosure.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 31 Money and Finance: Treasury 1 2012-07-01 2012-07-01 false Cap disclosure. 50.15 Section 50.15 Money and Finance: Treasury Office of the Secretary of the Treasury TERRORISM RISK INSURANCE PROGRAM Disclosures as Conditions for Federal Payment § 50.15 Cap disclosure. (a) General. Under section 103(e)(2)...

  15. 31 CFR 50.15 - Cap disclosure.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 31 Money and Finance: Treasury 1 2010-07-01 2010-07-01 false Cap disclosure. 50.15 Section 50.15 Money and Finance: Treasury Office of the Secretary of the Treasury TERRORISM RISK INSURANCE PROGRAM Disclosures as Conditions for Federal Payment § 50.15 Cap disclosure. (a) General. Under section 103(e)(2)...

  16. Variations in Surface Texture of the North Polar Residual Cap of Mars

    NASA Technical Reports Server (NTRS)

    Milkovich, S. M.; Byrne, S.; Russell, P. S.

    2011-01-01

    The northern polar residual cap (NPRC) of Mars is a water ice deposit with a rough surface made up of pits, knobs, and linear depressions on scales of tens of meters. This roughness manifests as a series of bright mounds and dark hollows in visible images; these bright and dark patches have a characteristic wavelength and orientation. Spectral data indicate that the surface of the NPRC is composed of large-grained (and therefore old) water ice. Due to the presence of this old ice, it is thought that the NPRC is in a current state of net loss of material a result potentially at odds with impact crater statistics, which suggest ongoing deposition over the past 10-20 Kyr.

  17. Ground Ice on Earth and Mars

    NASA Astrophysics Data System (ADS)

    Martineau, N.; Pollard, W.

    2003-12-01

    On Mars, just like on Earth, water exists in various phases and participates in a broad range of key processes. Even though present surface conditions on Mars, as defined by climate and atmospheric pressure, prevents the occurrence of liquid water on the surface, there is strong evidence suggesting that water was an important land-forming agent in the past (Carr 1996). This naturally raises the question, "where has the water gone?" Surficial water reservoirs that are directly observable on Mars include seasonal water ice deposits and permanent water ice deposits at the polar caps (Kieffer and Zent 1992, Clifford et al. 2000). Due to the existence of permafrost landform systems, such as polygonal ground, rootless cones, and frost mounts, it also has been speculated that much more water may be preserved as ground ice (Lucchitta 1981, Squyres and Carr 1986, Lanagan et al. 2001). Nevertheless, comparison of the likely patterns of ground ice on Mars with terrestrial equivalents has been limited. Fortunately, NASA's 2001 Odyssey data lends support to this hypothesis by identifying significant shallow ice-rich sediments by means of flux characteristics of neutrons, and gamma radiation, and spatial correlations to regions where it has been predicted that subsurface ice is stable (Bell 2002). The ice contents and stratigraphic distribution of the subsurface sediments on Mars, derived by the Odyssey Science Team, is not unlike the upper layers of terrestrial permafrost. Terrestrial polar environments, in particular the more stable permafrost and ground ice features like ice wedges and massive ground ice, may thus provide valuable clues in the search for water and ice on Mars. Of importance is the fact that these features of the earth's surface do not owe their origin to the seasonal freezing and thawing of the active layer. Under the cold, dry polar climates of the Arctic and Antarctic, periglacial and permafrost landforms have evolved, giving rise to distinctive landscapes

  18. Arctic ice islands

    SciTech Connect

    Sackinger, W.M.; Jeffries, M.O.; Lu, M.C.; Li, F.C.

    1988-01-01

    The development of offshore oil and gas resources in the Arctic waters of Alaska requires offshore structures which successfully resist the lateral forces due to moving, drifting ice. Ice islands are floating, a tabular icebergs, up to 60 meters thick, of solid ice throughout their thickness. The ice islands are thus regarded as the strongest ice features in the Arctic; fixed offshore structures which can directly withstand the impact of ice islands are possible but in some locations may be so expensive as to make oilfield development uneconomic. The resolution of the ice island problem requires two research steps: (1) calculation of the probability of interaction between an ice island and an offshore structure in a given region; and (2) if the probability if sufficiently large, then the study of possible interactions between ice island and structure, to discover mitigative measures to deal with the moving ice island. The ice island research conducted during the 1983-1988 interval, which is summarized in this report, was concerned with the first step. Monte Carlo simulations of ice island generation and movement suggest that ice island lifetimes range from 0 to 70 years, and that 85% of the lifetimes are less then 35 years. The simulation shows a mean value of 18 ice islands present at any time in the Arctic Ocean, with a 90% probability of less than 30 ice islands. At this time, approximately 34 ice islands are known, from observations, to exist in the Arctic Ocean, not including the 10-meter thick class of ice islands. Return interval plots from the simulation show that coastal zones of the Beaufort and Chukchi Seas, already leased for oil development, have ice island recurrences of 10 to 100 years. This implies that the ice island hazard must be considered thoroughly, and appropriate safety measures adopted, when offshore oil production plans are formulated for the Alaskan Arctic offshore. 132 refs., 161 figs., 17 tabs.

  19. First continuous flow analysis results from the Greenland ReCAP project

    NASA Astrophysics Data System (ADS)

    Kjær, Helle Astrid

    2016-04-01

    The new Renland ice core was drilled in summer 2015 in Greenland and measured by means of Continuous flow analysis 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. Preliminary results show that the record holds ice from the past warm interglacial period, the Eemian. The record was analyzed for multiple elements including the 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 acidity useful for finding volcanic layers to date the core. Further H2O2, and the nutrients Fe and dissolved reactive phosphorus was analyzed as well as the temperature indicator δ18O all by means of continuous flow analysis (CFA). The core was melted at a rate of 3 cm/min providing a temporal resolution for most components determined sufficient to resolve annual layers through the Holocene. The glacial section is strongly thinned, but nonetheless due to the high resolution of the measurements all DO events could be identified. Below the glacial section another ˜20 meters of warm Eemian ice have been analysed. Here we present the first chemistry results as obtained by continuous flow analysis (CFA).

  20. Sea Ice Ecosystems

    NASA Astrophysics Data System (ADS)

    Arrigo, Kevin R.

    2014-01-01

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

  1. Stochastic ice stream dynamics

    NASA Astrophysics Data System (ADS)

    Mantelli, Elisa; Bertagni, Matteo Bernard; Ridolfi, Luca

    2016-08-01

    Ice streams are narrow corridors of fast-flowing ice that constitute the arterial drainage network of ice sheets. Therefore, changes in ice stream flow are key to understanding paleoclimate, sea level changes, and rapid disintegration of ice sheets during deglaciation. The dynamics of ice flow are tightly coupled to the climate system through atmospheric temperature and snow recharge, which are known exhibit stochastic variability. Here we focus on the interplay between stochastic climate forcing and ice stream temporal dynamics. Our work demonstrates that realistic climate fluctuations are able to (i) induce the coexistence of dynamic behaviors that would be incompatible in a purely deterministic system and (ii) drive ice stream flow away from the regime expected in a steady climate. We conclude that environmental noise appears to be crucial to interpreting the past behavior of ice sheets, as well as to predicting their future evolution.

  2. Sea ice ecosystems.

    PubMed

    Arrigo, Kevin R

    2014-01-01

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

  3. Stochastic ice stream dynamics.

    PubMed

    Mantelli, Elisa; Bertagni, Matteo Bernard; Ridolfi, Luca

    2016-08-01

    Ice streams are narrow corridors of fast-flowing ice that constitute the arterial drainage network of ice sheets. Therefore, changes in ice stream flow are key to understanding paleoclimate, sea level changes, and rapid disintegration of ice sheets during deglaciation. The dynamics of ice flow are tightly coupled to the climate system through atmospheric temperature and snow recharge, which are known exhibit stochastic variability. Here we focus on the interplay between stochastic climate forcing and ice stream temporal dynamics. Our work demonstrates that realistic climate fluctuations are able to (i) induce the coexistence of dynamic behaviors that would be incompatible in a purely deterministic system and (ii) drive ice stream flow away from the regime expected in a steady climate. We conclude that environmental noise appears to be crucial to interpreting the past behavior of ice sheets, as well as to predicting their future evolution. PMID:27457960

  4. Top Sounder Ice Penetration

    NASA Astrophysics Data System (ADS)

    Porter, D. L.; Goemmer, S. A.; Sweeney, J. H.

    2014-12-01

    Ice draft measurements are made as part of normal operations for all US Navy submarines operating in the Arctic Ocean. The submarine ice draft data are unique in providing high resolution measurements over long transects of the ice covered ocean. The data has been used to document a multidecadal drop in ice thickness, and for validating and improving numerical sea-ice models. A submarine upward-looking sonar draft measurement is made by a sonar transducer mounted in the sail or deck of the submarine. An acoustic beam is transmitted upward through the water column, reflecting off the bottom of the sea ice and returning to the transducer. Ice thickness is estimated as the difference between the ship's depth (measured by pressure) and the acoustic range to the bottom of the ice estimated from the travel time of the sonar pulse. Digital recording systems can provide the return off the water-ice interface as well as returns that have penetrated the ice. Typically, only the first return from the ice hull is analyzed. Information regarding ice flow interstitial layers provides ice age information and may possibly be derived with the entire return signal. The approach being investigated is similar to that used in measuring bottom sediment layers and will involve measuring the echo level from the first interface, solving the reflection loss from that transmission, and employing reflection loss versus impedance mismatch to ascertain ice structure information.

  5. Amazonian mid- to high-latitude glaciation on Mars: Supply-limited ice sources, ice accumulation patterns, and concentric crater fill glacial flow and ice sequestration

    NASA Astrophysics Data System (ADS)

    Fastook, James L.; Head, James W.

    2014-02-01

    Concentric crater fill (CCF) occurs in the interior of impact craters in mid- to high latitudes on Mars and is interpreted to have formed by glacial ice flow and debris covering. We use the characteristics and orientation of deposits comprising CCF, the thickness of pedestal deposits in mid- to high-latitude pedestal craters (Pd), the volumes of the current polar caps, and information about regional slopes and ice rheology to address questions about (1) the maximum thickness of regional ice deposits during the Late Amazonian, (2) the likelihood that these deposits flowed regionally, (3) the geological regions and features most likely to induce ice-flow, and (4) the locations and environments in which ice is likely to have been sequestered up to the present. We find that regional ice flow under Late Amazonian climate conditions requires ice thicknesses exceeding many hundreds of meters for slopes typical of the vast majority of the surface of Mars, a thickness for the mid-latitudes that is well in excess of the total volume available from polar ice reservoirs. This indicates that although conditions for mid- to high-latitude glaciation may have persisted for tens to hundreds of millions of years, the process is “supply limited”, with a steady state reached when the polar ice cap water ice supply becomes exhausted. Impact craters are by far the most abundant landform with associated slopes (interior wall and exterior rim) sufficiently high to induce glacial ice flow under Late Amazonian climate conditions, and topographic slope data show that Amazonian impact craters have been clearly modified, undergoing crater interior slope reduction and floor shallowing. We show that these trends are the predictable response of ice deposition and preferential accumulation and retention in mid- to high-latitude crater interiors during episodes of enhanced spin-axis obliquity. We demonstrate that flow from a single episode of an inter-crater terrain layer comparable to Pedestal

  6. Microbial Community Structure and Activity Linked to Contrasting Biogeochemical Gradients in Bog and Fen Environments of the Glacial Lake Agassiz Peatland

    PubMed Central

    Lin, X.; Green, S.; Tfaily, M. M.; Prakash, O.; Konstantinidis, K. T.; Corbett, J. E.; Chanton, J. P.; Cooper, W. T.

    2012-01-01

    The abundances, compositions, and activities of microbial communities were investigated at bog and fen sites in the Glacial Lake Agassiz Peatland of northwestern Minnesota. These sites contrast in the reactivity of dissolved organic matter (DOM) and the presence or absence of groundwater inputs. Microbial community composition was characterized using pyrosequencing and clone library construction of phylogenetic marker genes. Microbial distribution patterns were linked to pH, concentrations of dissolved organic carbon and nitrogen, C/N ratios, optical properties of DOM, and activities of laccase and peroxidase enzymes. Both bacterial and archaeal richness and rRNA gene abundance were >2 times higher on average in the fen than in the bog, in agreement with a higher pH, labile DOM content, and enhanced enzyme activities in the fen. Fungi were equivalent to an average of 1.4% of total prokaryotes in gene abundance assayed by quantitative PCR. Results revealed statistically distinct spatial patterns between bacterial and fungal communities. Fungal distribution did not covary with pH and DOM optical properties and was vertically stratified, with a prevalence of Ascomycota and Basidiomycota near the surface and much higher representation of Zygomycota in the subsurface. In contrast, bacterial community composition largely varied between environments, with the bog dominated by Acidobacteria (61% of total sequences), while the Firmicutes (52%) dominated in the fen. Acetoclastic Methanosarcinales showed a much higher relative abundance in the bog, in contrast to the dominance of diverse hydrogenotrophic methanogens in the fen. This is the first quantitative and compositional analysis of three microbial domains in peatlands and demonstrates that the microbial abundance, diversity, and activity parallel with the pronounced differences in environmental variables between bog and fen sites. PMID:22843538

  7. Influence of the flood pulse on the reproduction of Tocantinsia piresi (Miranda Ribeiro) and Auchenipterus nuchalis (Spix & Agassiz) (Auchenipteridae) of the middle Xingu River, Brazil.

    PubMed

    Freitas, T M S; Prudente, B S; Oliveira, V A; Oliveira, M N C; Prata, E G; Leão, H; Montag, L F A

    2015-08-01

    This study investigates the influence of the flood pulse on the reproductive biology of the auchenipterids Tocantisia piresi (Miranda Ribeiro, 1920) and Auchenipterus nuchalis (Spix & Agassiz, 1829) from the middle Xingu River in the Brazilian state of Pará. The specimens were collected every three months between April, 2012, and January, 2014, covering four distinct periods (flood, ebb, dry, and filling). The sex ratio, size at first maturity, gonadosomatic index, and condition factor were analysed in the two species, and evaluated in the context of the different hydrological periods. A total of 897 specimens of T. piresi were collected, of which 467 were female, and 430 males, and 383 A. nuchalis (286 females and 97 males). In T. piresi, the sex ratio was biased only in the filling and ebb periods, whereas in A. nuchalis, it departed significantly from the expected ratio of 1:1 in all periods, with a predominance of females. The female T. piresi mature at a smaller size than the males, with the opposite of the pattern being recorded in A. nuchalis. In T. piresi, the breeding peak was observed during the low water periods, whereas in A. nuchalis, the peak was recorded in the flood periods. Male and female T. piresi presented similar positively allometric growth rates, whereas in A. nuchalis, growth was negatively allometric, but rates were different between genders. A higher condition factor was recorded in the females of both species during the ebb period. Overall, the results of this study reveals distinct flood pulse effects on the reproductive parameters of the two auchenipterid species studied; for A. nuchalis the spawning seems to happen at the flood period and for T. piresi at the dry season of the middle Xingu River.

  8. Time-series analysis for the episodic production and transport of methane from the Glacial Lake Agassiz peatlands, northern Minnesota. Final report

    SciTech Connect

    Siegel, D.I.

    1998-01-01

    The large peat basins of North America are an important reservoir in the global carbon cycle and a significant source of atmospheric methane. The authors investigated carbon cycling in the Glacial Lake Agassiz peatlands (GLAP) of Minnesota. Initially in 1990, they identified a dramatic change in the concentration of methane in the pore-waters of the raised bogs in the GLAP during an extreme drought. This methane dissipated when the drought broke in 1991 and the occurrence of deep methane is related to changes in the direction of groundwater flow in the peat column. The production of methane and its diffusive loss to the atmosphere was modeled and was about 10 times less than that measured directly in chambers at the land surface. It is clear from the reversals in hydraulic heat, changes in pore-water chemical composition over time, and paleostratigraphic markers, that regional ground water flow systems that are controlled by climate change are unexpectedly a major control over methanogenesis and carbon cycling in GLAP. Seismic profiles made showed that buried bedrock ridges particularly deflect regional groundwater flow upwards towards the land surface and towards raised bog landforms. In addition, high-resolution GPS measurements from data stations funded by this DOE project have shown this year that the peakland land surface elevation changes daily on a scale of cms, and seasonally on a scale of 10s of cm. This most recent observation is exciting because it may reflect episodic degassing of free phase methane from the peat column to the atmosphere, a source for methane previously unaccounted for by methane researchers.

  9. Influence of the flood pulse on the reproduction of Tocantinsia piresi (Miranda Ribeiro) and Auchenipterus nuchalis (Spix & Agassiz) (Auchenipteridae) of the middle Xingu River, Brazil.

    PubMed

    Freitas, T M S; Prudente, B S; Oliveira, V A; Oliveira, M N C; Prata, E G; Leão, H; Montag, L F A

    2015-08-01

    This study investigates the influence of the flood pulse on the reproductive biology of the auchenipterids Tocantisia piresi (Miranda Ribeiro, 1920) and Auchenipterus nuchalis (Spix & Agassiz, 1829) from the middle Xingu River in the Brazilian state of Pará. The specimens were collected every three months between April, 2012, and January, 2014, covering four distinct periods (flood, ebb, dry, and filling). The sex ratio, size at first maturity, gonadosomatic index, and condition factor were analysed in the two species, and evaluated in the context of the different hydrological periods. A total of 897 specimens of T. piresi were collected, of which 467 were female, and 430 males, and 383 A. nuchalis (286 females and 97 males). In T. piresi, the sex ratio was biased only in the filling and ebb periods, whereas in A. nuchalis, it departed significantly from the expected ratio of 1:1 in all periods, with a predominance of females. The female T. piresi mature at a smaller size than the males, with the opposite of the pattern being recorded in A. nuchalis. In T. piresi, the breeding peak was observed during the low water periods, whereas in A. nuchalis, the peak was recorded in the flood periods. Male and female T. piresi presented similar positively allometric growth rates, whereas in A. nuchalis, growth was negatively allometric, but rates were different between genders. A higher condition factor was recorded in the females of both species during the ebb period. Overall, the results of this study reveals distinct flood pulse effects on the reproductive parameters of the two auchenipterid species studied; for A. nuchalis the spawning seems to happen at the flood period and for T. piresi at the dry season of the middle Xingu River. PMID:26691087

  10. Antarctic Peninsula Ice Sheet evolution during the Cenozoic Era

    NASA Astrophysics Data System (ADS)

    Davies, Bethan J.; Hambrey, Michael J.; Smellie, John L.; Carrivick, Jonathan L.; Glasser, Neil F.

    2012-01-01

    The Antarctic Peninsula region is currently undergoing rapid environmental change, resulting in the thinning, acceleration and recession of glaciers and the sequential collapse of ice shelves. It is important to view these changes in the context of long-term palaeoenvironmental complexity and to understand the key processes controlling ice sheet growth and recession. In addition, numerical ice sheet models require detailed geological data for tuning and testing. Therefore, this paper systematically and holistically reviews published geological evidence for Antarctic Peninsula Ice Sheet variability for each key locality throughout the Cenozoic, and brings together the prevailing consensus of the extent, character and behaviour of the glaciations of the Antarctic Peninsula region. Major contributions include a downloadable database of 186 terrestrial and marine calibrated dates; an original reconstruction of the LGM ice sheet; and a new series of isochrones detailing ice sheet retreat following the LGM. Glaciation of Antarctica was initiated around the Eocene/Oligocene transition in East Antarctica. Palaeogene records of Antarctic Peninsula glaciation are primarily restricted to King George Island, where glacigenic sediments provide a record of early East Antarctic glaciations, but with modification of far-travelled erratics by local South Shetland Island ice caps. Evidence for Neogene glaciation is derived primarily from King George Island and James Ross Island, where glaciovolcanic strata indicate that ice thicknesses reached 500-850 m during glacials. This suggests that the Antarctic Peninsula Ice Sheet draped, rather than drowned, the topography. Marine geophysical investigations indicate multiple ice sheet advances during this time. Seismic profiling of continental shelf-slope deposits indicates up to ten large advances of the Antarctic Peninsula Ice Sheet during the Early Pleistocene, when the ice sheet was dominated by 40 kyr cycles. Glacials became more

  11. 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.

  12. Assimilation of blended Cryosat-2/SMOS sea ice thickness observations into the U.S. Navy ACNFS.

    NASA Astrophysics Data System (ADS)

    Hebert, D. A.; Wallcraft, A. J.; Posey, P. G.; Li, L.; Allard, R.; Johnston, W.; Kurtz, N. T.

    2015-12-01

    Cryosat-2 and SMOS sea ice thickness observations have been available to the community in recent years. Cryosat-2 gives best ice thicknesses greater than 0.5 meters, while SMOS is best for thicknesses less than 0.5 meters. In this talk we present a method to blend Cryosat-2 and SMOS ice thicknesses to provide one observation dataset that spans the full range of observed ice thickness. The Cryosat-2/SMOS blended sea ice concentration for March, 2014 is assimilated into the U.S. Navy Arctic Cap Nowcast/Forecast System (ACNFS) and run forward for one year. Modeled sea ice thicknesses from this run are compared to those from an ACNFS run without the thickness assimilation and sea ice thicknesses obtained from 2015 NASA operation Ice Bridge.

  13. Thermal stability of ice on Ceres with rough topography

    NASA Astrophysics Data System (ADS)

    Hayne, P. O.; Aharonson, O.

    2015-09-01

    The dwarf planet Ceres may have an ice-rich crust, and subsurface ice exposed by impacts or endogenic activity would be subject to sublimation. We model surface and subsurface temperatures on Ceres to assess lifetimes of water ice and other volatiles. Topographic shadowing allows a small but nonnegligible fraction (˜0.4%) of Ceres' surface to be perennially below the ˜110 K criterion for 1 Gyr of stability. These areas are found above 60° latitude. Other molecules (CH3OH, NH3, SO2, and CO2) may be cold trapped in smaller abundances. A model for the transport, gravitational escape, and photoionization of H2O molecules suggests net accumulation in the cold traps. Buried ice is stable within a meter for > 1 Gyr at latitudes higher than ˜50°. An illuminated polar cap of water ice would be stable within a few degrees of the poles only if it maintained a high albedo (>0.5) at present obliquity. If the obliquity exceeded 5° in the geologically recent past, then a putative polar cap would have been erased. At latitudes 0°-30°, ice is stable under solar illumination only briefly (˜10-100 years), unless it has high albedo and thermal inertia, in which case lifetimes of > 104 years are possible. Finally, a small hemispheric asymmetry exists due to the timing of Ceres' perihelion passage, which would lead to a detectable enhancement of ice in the northern hemisphere if the orbital elements vary slowly relative to the ice accumulation rate. Our model results are potentially testable during the Dawn science mission.

  14. Observational data from the Programme for Monitoring of the Greenland Ice Sheet (PROMICE)

    NASA Astrophysics Data System (ADS)

    Andersen, S. B.; Ahlstrom, A. P.; Andersen, M. L.; Box, J. E.; Citterio, M.; Fausto, R. S.; van As, D.; Forsberg, R.; Skourup, H.; Sandberg, L.; Kristensen, S. S.; Petersen, D.

    2013-12-01

    Climate change in the Arctic has resulted in accelerated mass loss from the Greenland Ice Sheet. The shortage of observations on the Greenland ice sheet infers large uncertainties in estimates of the ice mass loss and in predicting the contribution to sea level rise. For this reason the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) was established in 2007. The aim of the programme is to quantify the mass loss of the Greenland ice sheet and track changes in the extent of the glaciers, ice caps and ice sheet margin. Within PROMICE data sets from several activities are collected. These include: A network of currently 19 automatic weather stations on the margin of the Greenland ice sheet measuring ice ablation and snow fall as well as meteorological parameters. Airborne surveys, yielding surface elevation and ice depth along the entire margin of the Greenland ice sheet. Mapping of all Greenland ice masses, based on the highest detail aero-photogrammetric maps produced from mid-80's aerial photographs. Real-time data from the PROMICE automatic weather station network is shown in at the PROMICE web site www.promice.org and the data is freely available for download. Data from the airborne surveys and mapping activities will also become freely available. Data from PROMICE also contribute to the website www.polarportal.org which is a new Danish web site for providing updated information on the arctic cryosphere to the public.

  15. Rapid marine deglaciation: asynchronous retreat dynamics between the Irish Sea Ice Stream and terrestrial outlet glaciers

    NASA Astrophysics Data System (ADS)

    Patton, H.; Hubbard, A.; Bradwell, T.; Glasser, N. F.; Hambrey, M. J.; Clark, C. D.

    2013-08-01

    Understanding the retreat behaviour of past marine-ice sheets provides vital context to accurate assessment of the present stability and long-term response of contemporary polar-ice sheets to climate and oceanic warming. Here new multibeam swath-bathymetry data and sedimentological analysis are combined with high resolution ice-sheet modelling to reveal complex landform assemblages and process-dynamics associated with deglaciation of the British-Celtic Ice Sheet (BCIS) within the Irish Sea Basin. Our reconstruction indicates a non-linear relationship between the rapidly receding Irish Sea Ice Stream, the largest draining the BCIS, and the retreat of outlet glaciers draining the adjacent, terrestrially based ice sheet centred over Wales. Retreat of Welsh ice was episodic; superimposed over low-order oscillations of its margin are asynchronous outlet re-advances driven by catchment-wide mass balance variations that are amplified through migration of the ice cap's main ice-divide. Formation of large, linear ridges which extend at least 12.5 km offshore (locally known as sarns) and dominate the regional bathymetry are attributed to repeated frontal and medial morainic deposition associated with the re-advancing phases of these outlet glaciers. Our study provides new insight into ice-sheet extent, dynamics and non-linear retreat across a major palaeo-ice stream confluence zone, and has ramifications for the interpretation of recent fluctuations observed by satellites over short-time scales across marine-sectors of the Greenland and Antarctic ice sheets.

  16. CAPS and INMS Major Accomplishments

    NASA Astrophysics Data System (ADS)

    Waite, J. Hunter

    2014-05-01

    The Cassini-Huygens Ion Neutral Mass Spectrometer (Cassini INMS) and the Cassini Plasma Spectrometer (CAPS) have provided "discovery" science at Titan, Enceladus, Rhea/Dione, and throughout the magnetosphere of Saturn during the course of the mission. In this talk we will review some of the major scientific achievements: 1) the discovery of an extremely complex ion neutral organic chemistry in Titan's upper atmosphere that forms the building blocks for aerosol processes below, 2) the discovery of gases and grains emanating from Enceladus' cryo-geysers that tell us about chemical processes in an interior sea, 3) the first direct compositional measurements of sputtered icy moon surfaces, 4) the clearest example to date of the complex plasma interchange processes that occur in rapidly rotating magnetospheres of gas giants, initiating global dynamic processes that enable Saturn to shed the plasma from Enceladus' plume, and complete with a myriad of longitudinal and solar local-time variations, and 5) the dominance of Enceladus water outgassing as a source of magnetospheric plasma that stretches out to Titan and provides oxygen that can convert Titan's rich nitrile populations into amino acids.

  17. Edge of polar cap patches

    NASA Astrophysics Data System (ADS)

    Hosokawa, K.; Taguchi, S.; Ogawa, Y.

    2016-04-01

    On the night of 4 December 2013, a sequence of polar cap patches was captured by an all-sky airglow imager (ASI) in Longyearbyen, Norway (78.1°N, 15.5°E). The 630.0 nm airglow images from the ASI of 4 second exposure time, oversampled the emission of natural lifetime (with quenching) of at least ˜30 sec, introduce no observational blurring effects. By using such high-quality ASI images, we succeeded in visualizing an asymmetry in the gradients between the leading/trailing edges of the patches in a 2-D fashion. The gradient in the leading edge was found to be 2-3 times steeper than that in the trailing edge. We also identified fingerlike structures, appearing only along the trailing edge of the patches, whose horizontal scale size ranged from 55 to 210 km. These fingers are considered to be manifestations of plasma structuring through the gradient-drift instability (GDI), which is known to occur only along the trailing edge of patches. That is, the current 2-D observations visualized, for the first time, how GDI stirs the patch plasma and such a mixing process makes the trailing edge more gradual. This result strongly implies a close connection between the GDI-driven plasma stirring and the asymmetry in the large-scale shape of patches and then suggests that the fingerlike structures can be used as markers to estimate the fine-scale structure in the plasma flow within patches.

  18. Boundary Waves on the Ice Surface Created by Currents

    NASA Astrophysics Data System (ADS)

    Naito, K.; Izumi, N.; Yokokawa, M.; Yamada, T.; de Lima, A. C.

    2013-12-01

    The formation of periodic boundary waves, e.g. antidunes and cyclic steps (Parker & Izumi 2000) has been known to be caused by instabilities between flow and bed (e.g. Engelund 1970), and are observed not only on river beds or ocean floors but also on ice surfaces, such as the surface of glaciers and underside of river ice (Carey 1966). In addition, owing to recent advancements of remote sensing technology, it has been found that the surfaces of the polar ice caps on Mars as well as on the Earth have step-like formations (Smith & Holt 2010) which are assumed to be boundary waves, because they are generated perpendicularly to the direction of the currents. These currents acting on the polar ice caps are density airflow, i.e. katabatic wind (Howard et al 2000). The comprehension of the formation process of the Martian polar ice caps may reveal climate changes which have occurred on Mars. Although the formation of boundary waves on river beds or ocean floors has been studied by a number of researchers, there are few works on their formation on ice surfaces. Yokokawa et al (2013) suggested that the temperature distribution of the ambient air, fluid and ice is a factor which determines the direction of migration of boundary waves formed on ice surfaces through their experiments. In this study, we propose a mathematical model in order to describe the formation process of the boundary waves and the direction of their migration. We consider that a liquid is flowing through a flume filled with a flat ice layer on the bottom. The flow is assumed to be turbulent and its temperature is assumed to merge with the ambient temperature at the flow surface and with the melting point of ice at the bottom (ice surface). The ice surface evolution is dependent on the unbalance between the interfacial heat flux of the liquid and ice, and we employ the Reynolds-averaged Navier-Stokes equation, the continuity equation, heat transfer equations for the liquid and ice, and a heat balance

  19. Meltwater and precipitation runoff to the North Atlantic, Arctic, and Gulf of Mexico from the Laurentide Ice Sheet and adjacent regions during the Younger Dryas

    NASA Astrophysics Data System (ADS)

    Teller, James T.

    1990-12-01

    Runoff from North America may have played a significant role in ocean circulation and climate change during the last deglaciation. Because the driving force behind such changes may have been related to salinity of the north flowing Atlantic Ocean conveyor circulation, it is critical to know the volume, timing, and location of fresh water entering the North Atlantic from the melting Laurentide Ice Sheet. During the Younger Dryas cold episode, 11,000-10,000 years B.P., there was a two-fold increase in the volume of meltwater plus precipitation runoff, to more than 1700 km³ yr-1, flowing through the St. Lawrence valley to the North Atlantic, mainly because retreating ice allowed the glacial Lake Agassiz basin to drain eastward into the Great Lakes at this time. There was a corresponding decline in discharge from Lake Agassiz through the Mississippi River to the Gulf of Mexico. Runoff to the Arctic Ocean also increased at about the beginning of the Younger Dryas, from 740 to 900 km³ yr-1, because of the capture of what is now the headwater region of the Mackenzie River watershed. This, in combination with rising sea level and warming climate, may have increased the amount of pack ice reaching the North Atlantic through the Norwegian Sea from the Arctic Ocean. At 10,000 years B.P., eastward overflow from the western interior of North America was blocked by advancing ice, again forcing overflow to the Gulf of Mexico and, possibly, to the northwest into the Arctic Ocean. Although total runoff to the oceans from all regions draining from the Laurentide Ice Sheet did not vary substantially between 12,000 and 9000 years B.P., if discharge to the Gulf of Mexico is excluded, fresh water reaching the North Atlantic averaged 4000 km³ yr-1 during the Younger Dryas, in contrast to 2870 km³ yr-1 just before this cold episode and 3440 km³ yr-1 just after it.

  20. The pharmaceutical vial capping process: Container closure systems, capping equipment, regulatory framework, and seal quality tests.

    PubMed

    Mathaes, Roman; Mahler, Hanns-Christian; Buettiker, Jean-Pierre; Roehl, Holger; Lam, Philippe; Brown, Helen; Luemkemann, Joerg; Adler, Michael; Huwyler, Joerg; Streubel, Alexander; Mohl, Silke

    2016-02-01

    Parenteral drug products are protected by appropriate primary packaging to protect against environmental factors, including potential microbial contamination during shelf life duration. The most commonly used CCS configuration for parenteral drug products is the glass vial, sealed with a rubber stopper and an aluminum crimp cap. In combination with an adequately designed and controlled aseptic fill/finish processes, a well-designed and characterized capping process is indispensable to ensure product quality and integrity and to minimize rejections during the manufacturing process. In this review, the health authority requirements and expectations related to container closure system quality and container closure integrity are summarized. The pharmaceutical vial, the rubber stopper, and the crimp cap are described. Different capping techniques are critically compared: The most common capping equipment with a rotating capping plate produces the lowest amount of particle. The strength and challenges of methods to control the capping process are discussed. The residual seal force method can characterize the capping process independent of the used capping equipment or CCS. We analyze the root causes of several cosmetic defects associated with the vial capping process.

  1. Martian Ice Caves

    NASA Astrophysics Data System (ADS)

    Frederick, R. D.; Billings, T. L.; McGown, R. D.; Walden, B. E.

    2000-07-01

    Ice in Martian lava tube caves would have scientific and developmental value. These natural channels in rock may hold keys to Mars' past as well as potential resources for humanity's futures. Terrestrial lava tube caves are natural receptacles for accumulations of water. Often, due to lower temperatures coupled with the superior insulation properties of the surrounding rock, these accumulations are in the form of ice. Historically, ice was mined from some lava tube caves. Many of the lava tubes in the Central Oregon area sport such names as "Arnolds Ice Cave," "Surveyors Ice Cave," "South Ice Cave," etc. These caves are not caves in ice, but rather common lava tubes with seasonal, and sometimes perennial ice deposits. Locating and cataloging similar features on Mars, could be of value for the colonization of Mars and the search for life. Such features may also prove useful in helping to determine past climatic conditions on the Red Planet.

  2. Greenland Ice Flow

    NASA Video Gallery

    Greenland looks like a big pile of snow seen from space using a regular camera. But satellite radar interferometry helps us detect the motion of ice beneath the snow. Ice starts flowing from the fl...

  3. Ice electrode electrolytic cell

    SciTech Connect

    Glenn, D.F.; Suciu, D.F.; Harris, T.L.; Ingram, J.C.

    1992-12-31

    This invention relates to a method and apparatus for removing heavy metals from waste water, soils, or process streams by electrolytic cell means. The method includes cooling a cell cathode to form an ice layer over the cathode and then applying an electric current to deposit a layer of the heavy metal over the ice. The metal is then easily removed after melting the ice. In a second embodiment, the same ice-covered electrode can be employed to form powdered metals.

  4. Ice electrode electrolytic cell

    DOEpatents

    Glenn, David F.; Suciu, Dan F.; Harris, Taryl L.; Ingram, Jani C.

    1993-01-01

    This invention relates to a method and apparatus for removing heavy metals from waste water, soils, or process streams by electrolytic cell means. The method includes cooling a cell cathode to form an ice layer over the cathode and then applying an electric current to deposit a layer of the heavy metal over the ice. The metal is then easily removed after melting the ice. In a second embodiment, the same ice-covered electrode can be employed to form powdered metals.

  5. Ice electrode electrolytic cell

    DOEpatents

    Glenn, D.F.; Suciu, D.F.; Harris, T.L.; Ingram, J.C.

    1993-04-06

    This invention relates to a method and apparatus for removing heavy metals from waste water, soils, or process streams by electrolytic cell means. The method includes cooling a cell cathode to form an ice layer over the cathode and then applying an electric current to deposit a layer of the heavy metal over the ice. The metal is then easily removed after melting the ice. In a second embodiment, the same ice-covered electrode can be employed to form powdered metals.

  6. A comprehensive interpretation of the NEEM basal ice build-up using a multi-parametric approach

    NASA Astrophysics Data System (ADS)

    Goossens, Thomas; Sapart, Célia J.; Dahl-Jensen, Dorthe; Popp, Trevor; El Amri, Saïda; Tison, Jean-Louis

    2016-03-01

    Basal ice is a common expression to describe bottom ice layers of glaciers, ice caps and ice sheets in which the ice is primarily conditioned by processes operating at the bed. It is chemically and/or physically distinct from the ice above and can be characterized by a component of basally derived sediments. The study of basal ice properties provides a rare opportunity to improve our understanding of subglacial environments and processes and to refine ice sheet behaviour modelling. Here, we present and discuss the results of water stable isotopes (δ18O and δD), ice fabrics, debris weight/size distribution and gas content of the basal part of the NEEM (North Greenland Eemian Ice Drilling Project) ice core. Below a depth of 2533.85 m, almost 10 m of basal debris-rich material was retrieved from the borehole, and regular occurrence of frozen sediments with only interstitial ice lenses in the bottom 5 m suggest that the ice-bedrock interface was reached. The sequence is composed of an alternation of three visually contrasting types of ice: clear ice with specks (very small amounts) of particulate inclusions, stratified debris-rich layers and ice containing dispersed debris. The use of water stable isotope signatures (δ18O and δD), together with other parameters, allows discrimination between the different types of ice and to unravel the processes involved in their formation and transformation. The basal debris-rich material presents δ18O values [-39.9 ‰; -34.4 ‰] within the range of the above last 300 m of unaltered meteoric ice [-44.9 ‰; -30.6 ‰] spanning a glacial-interglacial range of values. This rules out the hypothesis of a basal ice layer originating from pre-ice sheet ice overridden by the growing ice sheet, as previously suggested e.g. in the case of GRIP (Greenland Ice Core Project). We show that clear basal ice with specks corresponds to altered meteoric glacial ice where some of the climatic signal could have been preserved. However, the

  7. Dust-Driven Halos on the Martian South Polar Residual CAP

    NASA Astrophysics Data System (ADS)

    Becerra, P.; Byrne, S.; Brown, A. J.

    2013-12-01

    The CO2 ice South Polar Residual Cap (SPRC) on Mars may be a sensitive indicator of inter-annual planetary climate variability. Imaging by HiRISE [1], and CTX [2] found that many scarps and pits in the 'Swiss cheese terrain' [3] of the SPRC exhibited a bright 'halo' around their edges. These halos appeared during Martian southern summer in Mars Year 28 (MY28, [4]), and have been observed in only one of eight mars years for which observations at high enough resolution exist. We hypothesize that the formation of these features is linked to the late-summer global dust storm of MY28 and report on observations and formation models. We surveyed HiRISE, CTX, and CRISM [5] data to constrain the optical properties and composition of the halos, as well as their time of appearance and location within the SPRC. The halos appeared throughout most of the surface area of the SPRC between Ls 280° and 330° in MY28. The widest portions of the halos occurred adjacent to north-facing walls, and the brightest parts adjacent to sun-facing walls, which points to a connection between insolation and halo appearance. CRISM spectral products rule out the presence of water ice as a factor in the halos' appearance. These data also imply larger CO2 ice grain sizes where the bright halos were seen, which are normally associated with lower, rather than higher, albedos [6]. Thus, we also ruled out CO2 ice grain size differences as the main cause for the halos. The remaining possibility is that the halos appeared due to differences in dust content between the terrain adjacent to the pit walls and the surrounding ice. To investigate this we made a Hapke [7] surface reflectance model in which the CO2 ice grain size, dust volumetric content and dust particle size were free parameters. We used the HiRISE and CRISM bandpass coefficients to simulate HiRISE I/F values and CRISM spectra, and attempted to match the HiRISE RED I/F, HiRISE BG/RED color ratio, and the CRISM 1.43 μm band depths. A self

  8. Tip cap for a turbine rotor blade

    DOEpatents

    Kimmel, Keith D

    2014-03-25

    A turbine rotor blade with a spar and shell construction, and a tip cap that includes a row of lugs extending from a bottom side that form dovetail grooves that engage with similar shaped lugs and grooves on a tip end of the spar to secure the tip cap to the spar against radial displacement. The lug on the trailing edge end of the tip cap is aligned perpendicular to a chordwise line of the blade in the trailing edge region in order to minimize stress due to the lugs wanting to bend under high centrifugal loads. A two piece tip cap with lugs at different angles will reduce the bending stress even more.

  9. The ATLAS TRT end-cap detectors

    NASA Astrophysics Data System (ADS)

    ATLAS TRT Collaboration; Abat, E.; Addy, T. N.; Åkesson, T. P. A.; Alison, J.; Anghinolfi, F.; Arik, E.; Arik, M.; Atoian, G.; Auerbach, B.; Baker, O. K.; Banas, E.; Baron, S.; Bault, C.; Becerici, N.; Beddall, A.; Beddall, A. J.; Bendotti, J.; Benjamin, D. P.; Bertelsen, H.; Bingul, A.; Blampey, H.; Bocci, A.; Bochenek, M.; Bondarenko, V. G.; Bychkov, V.; Callahan, J.; Capeáns Garrido, M.; Cardiel Sas, L.; Catinaccio, A.; Cetin, S. A.; Chandler, T.; Chritin, R.; Cwetanski, P.; Dam, M.; Danielsson, H.; Danilevich, E.; David, E.; Degenhardt, J.; Di Girolamo, B.; Dittus, F.; Dixon, N.; Dobos, D.; Dogan, O. B.; Dolgoshein, B. A.; Dressnandt, N.; Driouchi, C.; Ebenstein, W. L.; Eerola, P.; Egede, U.; Egorov, K.; Evans, H.; Farthouat, P.; Fedin, O. L.; Fowler, A. J.; Fratina, S.; Froidevaux, D.; Fry, A.; Gagnon, P.; Gavrilenko, I. L.; Gay, C.; Ghodbane, N.; Godlewski, J.; Goulette, M.; Gousakov, I.; Grigalashvili, N.; Grishkevich, Y.; Grognuz, J.; Hajduk, Z.; Hance, M.; Hansen, F.; Hansen, J. B.; Hansen, J. D.; Hansen, P. H.; Hare, G. A.; Harvey, A., Jr.; Hauviller, C.; High, A.; Hulsbergen, W.; Huta, W.; Issakov, V.; Istin, S.; Jain, V.; Jarlskog, G.; Jeanty, L.; Kantserov, V. A.; Kaplan, B.; Kapliy, A. S.; Katounine, S.; Kayumov, F.; Keener, P. T.; Kekelidze, G. D.; Khabarova, E.; Khristachev, A.; Kisielewski, B.; Kittelmann, T. H.; Kline, C.; Klinkby, E. B.; Klopov, N. V.; Ko, B. R.; Koffas, T.; Kondratieva, N. V.; Konovalov, S. P.; Koperny, S.; Korsmo, H.; Kovalenko, S.; Kowalski, T. Z.; Krüger, K.; Kramarenko, V.; Kudin, L. G.; LeBihan, A.-C.; LeGeyt, B. C.; Levterov, K.; Lichard, P.; Lindahl, A.; Lisan, V.; Lobastov, S.; Loginov, A.; Loh, C. W.; Lokwitz, S.; Long, M. C.; Lucas, S.; Lucotte, A.; Luehring, F.; Lundberg, B.; Mackeprang, R.; Maleev, V. P.; Manara, A.; Mandl, M.; Martin, A. J.; Martin, F. F.; Mashinistov, R.; Mayers, G. M.; McFarlane, K. W.; Mialkovski, V.; Mills, B. M.; Mindur, B.; Mitsou, V. A.; Mjörnmark, J. U.; Morozov, S. V.; Morris, E.; Mouraviev, S. V.; Muir, A. M.; Munar, A.; Nadtochi, A. V.; Nesterov, S. Y.; Newcomer, F. M.; Nikitin, N.; Novgorodova, O.; Novodvorski, E. G.; Ogren, H.; Oh, S. H.; Oleshko, S. B.; Olivito, D.; Olszowska, J.; Ostrowicz, W.; Passmore, M. S.; Patrichev, S.; Penwell, J.; Perez-Gomez, F.; Peshekhonov, V. D.; Petersen, T. C.; Petti, R.; Placci, A.; Poblaguev, A.; Pons, X.; Price, M. J.; hne, O. Rø; Reece, R. D.; Reilly, M. B.; Rembser, C.; Romaniouk, A.; Rousseau, D.; Rust, D.; Ryabov, Y. F.; Ryjov, V.; Söderberg, M.; Savenkov, A.; Saxon, J.; Scandurra, M.; Schegelsky, V. A.; Scherzer, M. I.; Schmidt, M. P.; Schmitt, C.; Sedykh, E.; Seliverstov, D. M.; Shin, T.; Shmeleva, A.; Sivoklokov, S.; Smirnov, S. Yu; Smirnova, L.; Smirnova, O.; Smith, P.; Sosnovtsev, V. V.; Sprachmann, G.; Subramania, S.; Suchkov, S. I.; Sulin, V. V.; Szczygiel, R. R.; Tartarelli, G.; Thomson, E.; Tikhomirov, V. O.; Tipton, P.; Valls Ferrer, J. A.; Van Berg, R.; Vassilakopoulos, V. I.; Vassilieva, L.; Wagner, P.; Wall, R.; Wang, C.; Whittington, D.; Williams, H. H.; Zhelezko, A.; Zhukov, K.

    2008-10-01

    The ATLAS TRT end-cap is a tracking drift chamber using 245,760 individual tubular drift tubes. It is a part of the TRT tracker which consist of the barrel and two end-caps. The TRT end-caps cover the forward and backward pseudo-rapidity region 1.0 < |η| < 2.0, while the TRT barrel central η region |η| < 1.0. The TRT system provides a combination of continuous tracking with many measurements in individual drift tubes (or straws) and of electron identification based on transition radiation from fibers or foils interleaved between the straws themselves. Along with other two sub-system, namely the Pixel detector and Semi Conductor Tracker (SCT), the TRT constitutes the ATLAS Inner Detector. This paper describes the recently completed and installed TRT end-cap detectors, their design, assembly, integration and the acceptance tests applied during the construction.

  10. Commercial Crew Program CCiCap Partners

    NASA Video Gallery

    NASA's Commercial Crew Program and its newest Commercial Crew Integrated Capability (CCiCap) partners are embracing the American spirit as they advance their integrated rocket and spacecraft design...

  11. DESIGN CONSIDERATION INVOLVING ACTIVE SEDIMENT CAPS

    EPA Science Inventory

    When contaminated sediments pose unacceptable risks to human health and the environment, management activities such as removal, treatment, or isolation of contaminated sediments may be required. Various capping designs are being considered for isolating contaminated sediment are...

  12. DESIGN CONSIDERATION INVOLVING ACTIVE SEDIMENT CAPS (PRESENTATION)

    EPA Science Inventory

    When contaminated sediments pose unacceptable risks to human health and the environment, management activities such as removal, treatment, or isolation of contaminated sediments may be required. Various capping designs are being considered for isolating contaminated sediment are...

  13. CCiCap: Sierra Nevada Corporation

    NASA Video Gallery

    NASA announced today its plans to partner with Sierra Nevada Corp. (SNC) for the next phase of the agency's Commercial Crew Program (CCP). Called Commercial Crew integrated Capability (CCiCap), the...

  14. Perfluorocarbon vapor tagging of blasting cap detonators

    DOEpatents

    Dietz, R.N.; Senum, G.I.

    A plug for a blasting cap is made of an elastomer in which is dissolved a perfluorocarbon. The perfluorocarbon is released as a vapor into the ambient over a long period of time to serve as a detectable taggant.

  15. 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

  16. Waves on Ice

    Atmospheric Science Data Center

    2013-04-16

    article title:  Waves on White: Ice or Clouds?     ... detecting clouds over snow and ice, but also works well over ocean and land. The rippled area on the surface which could have been mistaken ... date:  Dec 16, 2004 Images:  Waves on Ice location:  Antarctica thumbnail:  ...

  17. Ice Formation on Wings

    NASA Technical Reports Server (NTRS)

    Ritz, L

    1939-01-01

    This report makes use of the results obtained in the Gottingen ice tunnel in which the atmospheric conditions are simulated and the process of ice formation photographed. The effect of ice formation is threefold: 1) added weight to the airplane; 2) a change in the lift and drag forces; 3) a change in the stability characteristics.

  18. Technology for Ice Rinks

    NASA Technical Reports Server (NTRS)

    1983-01-01

    Ron Urban's International Ice Shows set up portable ice rinks for touring troupes performing on temporary rinks at amusement parks, sports arenas, dinner theaters, shopping malls and civic centers. Key to enhanced rink portability, fast freezing and maintaining ice consistency is a mat of flexible tubing called ICEMAT, an offshoot of a solar heating system developed by Calmac, Mfg. under contract with Marshall.

  19. Experiments in Ice Physics.

    ERIC Educational Resources Information Center

    Martin, P. F.; And Others

    1978-01-01

    Describes experiments in ice physics that demonstrate the behavior and properties of ice. Show that ice behaves as an ionic conductor in which charge is transferred by the movement of protons, its electrical conductivity is highly temperature-dependent, and its dielectric properties show dramatic variation in the kilohertz range. (Author/GA)

  20. The Antarctic Ice.

    ERIC Educational Resources Information Center

    Radok, Uwe

    1985-01-01

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

  1. Ice Versus Rock

    ERIC Educational Resources Information Center

    Rule, Audrey C.; Olson, Eric A.; Dehm, Janet

    2005-01-01

    During a snow bank exploration, students noticed "ice caves," or pockets, in some of the larger snow banks, usually below darker layers. Most of these caves had many icicles hanging inside. Students offered reasonable explanations of ice cave formation--squirrels, kids, snow blowers--and a few students came close to the true ice cave-formation…

  2. Secondary capping beams for offshore drilling platforms

    SciTech Connect

    Albaugh, E. K.

    1985-08-13

    A pair of I-shaped elongated girders secured to, and extending outwardly from, the capping beams of a four pile platform, to form cantilever secondary capping beams which support modified self-contained drilling rigs of a size and weight normally installed on eight pile platforms. Rig modifications comprise separation of pump and engine packages, a pipe rack extension, and a novel skidding system.

  3. Truncated Dual-Cap Nucleation Site Development

    NASA Technical Reports Server (NTRS)

    Matson, Douglas M.; Sander, Paul J.

    2012-01-01

    During heterogeneous nucleation within a metastable mushy-zone, several geometries for nucleation site development must be considered. Traditional spherical dual cap and crevice models are compared to a truncated dual cap to determine the activation energy and critical cluster growth kinetics in ternary Fe-Cr-Ni steel alloys. Results of activation energy results indicate that nucleation is more probable at grain boundaries within the solid than at the solid-liquid interface.

  4. Ice loss and sea level rise contribution from Alaskan glaciers

    NASA Astrophysics Data System (ADS)

    Berthier, E.; Schiefer, E.; Clarke, G. K.; Menounos, B.; Rémy, F.; Cazenave, A. A.

    2009-12-01

    Over the last 50 years, retreating glaciers and ice caps (GIC) contributed 0.5 mm/yr to SLR, and one third is believed to originate from ice masses bordering the Gulf of Alaska. However, these estimates of ice wastage in Alaska are based on methods that directly measure mass changes from a limited number of glaciers and extrapolate the results to estimate ice loss for the many thousands of others. Here, using a new glacier inventory with elevation changes derived from sequential digital elevation models (DEMs), we found that, between 1962 and 2006, Alaskan glaciers lost 41.9 ± 8.6 km**3/yr water equivalent (w.e.) and contributed 0.12 ± 0.02 mm/yr to SLR. Our ice loss is 34% lower than previous estimates. Reasons for our lower values include the higher spatial resolution of the glacier inventory used in our study and the complex pattern of ice elevation changes at the scale of individual glaciers and mountain ranges which was not resolved in earlier work. Our ice elevation changes reveal that glacier dynamics (surges, phase of the tidewater cycle, etc...) have a profound effect on the wastage of Alaska glaciers. 3D satellite view of Columbia glacier, Chugach Mountains, Alaska. (Copyright CNES 2007, Distribution Spot Image, processing E. Berthier CNRS)

  5. South Polar Residual Cap Geomorphology and Inferred Environmental Changes

    NASA Astrophysics Data System (ADS)

    Byrne, S.; Ingersoll, A.; Pathare, A.

    2003-12-01

    The CO2 southern residual cap (SRC) both controls circulation patterns regionally and buffers the atmospheric pressure globally. In turn this CO2 deposit is affected by changes in environmental conditions wrought by external forces such as dust storm activity. Mars Global Surveyor data of this area have revealed a rich variety of geomorphic features (1) of which there are several distinct classes. These different classes may be end members of the same basic process of insolation driven ablation. We are currently investigating two types of SRC features. Swiss-cheese features (SCF) are depressions characterized by flat floors and steep walls, which retreat 1-3 meters each Martian year (2). In some regions they have a definite symmetry axis along the north-south direction (3). After the seasonal frost disappears the residual ice exposed in the walls has a lower albedo (4). Previously (5) we modeled the evolution and growth of these depressions as a hole in a layer of CO2 ice underlain by water ice, which best explains their morphologic and thermal properties. The observed thickness of the CO2 slab can be as high as 8 meters but in general is much lower. Larger SCF?s commonly possess a raised central island of CO2 surrounded by a moat that penetrates to the underlying water ice (3). The fast rate of wall retreat observed (2) combined with the small sizes of the SCF?s indicate that all SCF?s visible today were created geologically recently. Within a particular region the size distribution is quite narrow (3): no larger (older) or smaller (younger) features were seen indicating that some relatively abrupt change in environmental conditions initiated the growth of this particular population of features. Fingerprint terrain (1) are areas with evenly spaced parallel ridges, which are steeper on one side. These ridges may have small areas of water ice exposed in the intervening troughs. Their wavelength is on the order of 70-90m with the steep edges facing northeast although

  6. The effect of polar caps on obliquity

    NASA Technical Reports Server (NTRS)

    Lindner, B. L.

    1993-01-01

    Rubincam has shown that the Martian obliquity is dependent on the seasonal polar caps. In particular, Rubincam analytically derived this dependence and showed that the change in obliquity is directly proportional to the seasonal polar cap mass. Rubincam concludes that seasonal friction does not appear to have changed Mars' climate significantly. Using a computer model for the evolution of the Martian atmosphere, Haberle et al. have made a convincing case for the possibility of huge polar caps, about 10 times the mass of the current polar caps, that exist for a significant fraction of the planet's history. Since Rubincam showed that the effect of seasonal friction on obliquity is directly proportional to polar cap mass, a scenario with a ten-fold increase in polar cap mass over a significant fraction of the planet's history would result in a secular increase in Mars' obliquity of perhaps 10 degrees. Hence, the Rubincam conclusion of an insignificant contribution to Mars' climate by seasonal friction may be incorrect. Furthermore, if seasonal friction is an important consideration in the obliquity of Mars, this would significantly alter the predictions of past obliquity.

  7. Spatial, temporal, and inter-annual variability of the Martian northern seasonal polar cap

    NASA Astrophysics Data System (ADS)

    Mount, Christopher P.

    Earth and Mars have nearly the same axial tilt, so seasons on these two bodies progress in a similar manner. During fall and winter on Mars, the primarily CO2 atmosphere (~95% by volume) condenses out onto the poles as ice. Approximately 25% of the entire Martian atmosphere condenses, and then sublimes in the spring, making this cycle a dominant driver in the global climate. Because the water and dust cycles are coupled to this CO2 cycle, we must examine seasonal CO2 processes to understand the global (seasonal) distribution of H2O on Mars. The density of the ice may indicate whether it condensed in the atmosphere and precipitated as "snow" or condensed directly onto the surface as "slab". Variations in density may be controlled by geographic location and surface morphology. The distribution and variations in densities of seasonal deposits on the Martian poles gives us insight to the planet's volatile inventories. Here we analyze density variations over time on Mars' Northern Polar Seasonal Cap (NPSC) using observational data and energy balance techniques. We calculate the bulk density of surface CO2 ice by dividing the column mass abundance (the mass of CO2 per unit area) by the depth of the ice cap at a given location. We use seasonal rock shadow measurements from High Resolution Imaging Science Experiment (HiRISE) images to estimate ice depth. The length of a rock's shadow is related to its height through the solar incidence angle and the slope of the ground. From differences in the height of a rock measured in icy vs. ice-free images, we estimate the depth of surface ice at the time of the icy observation. Averaging over many rocks in a region yields the ice depth for that region. This technique yields minimums for ice depth and therefore maximums for density. Thermal properties of rocks may play an important role in observed ice depths. Crowns of ice may form on the tops of rocks with insufficient heat capacity to inhibit ice condensation, and may cause an

  8. The role of water ice clouds in the Martian hydrologic cycle

    NASA Technical Reports Server (NTRS)

    James, Philip B.

    1990-01-01

    A one-dimensional model for the seasonal cycle of water on Mars has been used to investigate the direction of the net annual transport of water on the planet and to study the possible role of water ice clouds, which are included as an independent phase in addition to ground ice and water vapor, in the cycle. The calculated seasonal and spatial patterns of occurrence of water ice clouds are qualitatively similar to the observed polar hoods, suggesting that these polar clouds are, in fact, an important component of water cycle. A residual dry ice in the south acts as a cold trap which, in the absence of sources other than the caps, will ultimately attract the water ice from the north cap; however, in the presence of a source of water in northern midlatitudes during spring, it is possible that the observed distribution of vapor and ice can be in a steady state even if a residual CO2 cap is a permanent feature of the system.

  9. Structures and fabrics in glacial ice: A review

    NASA Astrophysics Data System (ADS)

    Hudleston, Peter J.

    2015-12-01

    Glaciers, ice sheets and ice caps represent tectonic systems driven by gravity. Their movement can be studied in real time and the rheological properties and strength of ice determined from laboratory experiments and field measurements. All glacial ice has primary stratification, exhibited by variations in grain size, bubble content and debris content. As it deforms, with deformation dominated by plastic flow and recrystallization, accompanied locally by fracture under tension, a suite of structures develops that reflects the primary fabric of the ice and the anisotropy that develops as a result of cumulative deformation. Initial variations in solid impurity content and strain dependent anisotropy as a result of a crystallographic fabric give rise to effective viscosity increases or decreases compared to isotropic polycrystalline ice of about a factor of ten. Foliation develops from inherited (mostly stratification) or introduced (mostly ice veins or fracture traces) fabric elements and from dynamic recrystallization. It is largely dependent on the accumulated strain, which is highest at the base and near the margins of glaciers, ice sheets and ice streams. Folds develop largely passively due to initial amplification of irregularities in the primary stratification, to variations in flow with time or to inhomogeneous flow associated with shear zones and ductile accommodation around open fractures. Buckle folds and boudinage, mostly on a small scale, occur where viscosity contrast is large, mostly in basal ice. Thrusting and wrench faulting are documented in surging glaciers but theoretically most unlikely and rare or absent elsewhere. Many structures interpreted as faults are not due to shear failure but rather result from shear displacements during opening and closing of tensile fractures.

  10. Antarctic lakes (above and beneath the ice sheet): Analogues for Mars

    NASA Technical Reports Server (NTRS)

    Rice, J. W., Jr.

    1992-01-01

    The perennial ice covered lakes of the Antarctic are considered to be excellent analogues to lakes that once existed on Mars. Field studies of ice covered lakes, paleolakes, and polar beaches were conducted in the Bunger Hills Oasis, Eastern Antarctica. These studies are extended to the Dry Valleys, Western Antarctica, and the Arctic. Important distinctions were made between ice covered and non-ice covered bodies of water in terms of the geomorphic signatures produced. The most notable landforms produced by ice covered lakes are ice shoved ridges. These features form discrete segmented ramparts of bou