WorldWideScience

Sample records for hunt ice shelf

  1. Antarctica - Ross Ice Shelf

    Science.gov (United States)

    1990-01-01

    This color picture of Antarctica is one part of a mosaic of pictures covering the entire polar continent taken during the hours following Galileo's historic first encounter with its home planet. The view shows the Ross Ice Shelf to the right and its border with the sea. An occasional mountain can be seen poking through the ice near the McMurdo Station. It is late spring in Antarctica, so the sun never sets on the frigid, icy continent. This picture was taken about 6:20 p.m. PST on December 8, 1990. From top to bottom, the frame looks across about half of Antarctica.

  2. Ross Ice Shelf, Antarctic Ice and Clouds

    Science.gov (United States)

    1991-01-01

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

  3. Amery ice shelf DEM and its marine ice distribution

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The Amery Ice Shelf is the largest ice shelf in East Antarctica. A new DEM was generated for this ice shelf, using kriging to interpolate the data from ICESat altimetry and the AIS-DEM. The ice thickness distribution map is converted from the new DEM, assuming hydrostatic equilibrium. The Amery Ice Shelf marine ice, up to 230 m thick, is concentrated in the northwest of the ice shelf. The volume of the marine ice is 2.38×103 km3 and accounts for about 5.6% of the shelf volume.

  4. Earth - Ross Ice Shelf, Antarctica

    Science.gov (United States)

    1991-01-01

    This color picture of Antarctica is one part of a mosaic of pictures covering the entire Antarctic continent taken during the hours following Galileo's historic first encounter with its home planet. The view shows the Ross Ice Shelf. An occasional mountain can be seen poking through the ice. It is late spring in Antarctica, so the sun never sets on the frigid, icy continent. This picture was taken on December 8, 1990.

  5. Ice-shelf – ocean interactions at Fimbul Ice Shelf, Antarctica from oxygen isotope ratio measurements

    Directory of Open Access Journals (Sweden)

    K. W. Nicholls

    2007-09-01

    Full Text Available Melt water from the floating ice shelves at the margins of the southeastern Weddell Sea makes a significant contribution to the fresh water budget of the region. In February 2005 a multi-institution team conducted an oceanographic campaign at Fimbul Ice Shelf on the Greenwich Meridian as part of the Autosub Under Ice programme. This included a mission of the autonomous submarine Autosub 25 km into the cavity beneath Fimbul Ice Shelf, and a number of ship-based hydrographic sections on the continental shelf and adjacent to the ice shelf front. The measurements reveal two significant sources of glacial melt water at Fimbul Ice Shelf: the main cavity under the ice shelf and an ice tongue that protrudes from the main ice front and out over the continental slope into deep water. Glacial melt water is concentrated in a 200 m thick Ice Shelf Water (ISW layer below the base of the ice shelf at 150–200 m, with a maximum glacial melt concentration of up to 1.16%. Some glacial melt is found throughout the water column, and much of this is from sources other than Fimbul Ice Shelf. However, at least 0.2% of the water in the ISW layer cannot be accounted for by other processes and must have been contributed by the ice shelf. Just downstream of Fimbul Ice Shelf we observe locally created ISW mixing out across the continental slope. The ISW formed here is much less dense than that formed in the southwest Weddell Sea, and will ultimately contribute a freshening (and reduction in δ18O to the upper 100–150 m of the water column in the southeast Weddell Sea.

  6. Ice-shelf – ocean interactions at Fimbul Ice Shelf, Antarctica from oxygen isotope ratio measurements

    Directory of Open Access Journals (Sweden)

    K. W. Nicholls

    2008-03-01

    Full Text Available Melt water from the floating ice shelves at the margins of the southeastern Weddell Sea makes a significant contribution to the fresh water budget of the region. In February 2005 a multi-institution team conducted an oceanographic campaign at Fimbul Ice Shelf on the Greenwich Meridian as part of the Autosub Under Ice programme. This included a mission of the autonomous submarine Autosub 25 km into the cavity beneath Fimbul Ice Shelf, and a number of ship-based hydrographic sections on the continental shelf and adjacent to the ice shelf front. The measurements reveal two significant sources of glacial melt water at Fimbul Ice Shelf: the main cavity under the ice shelf and an ice tongue, Trolltunga, that protrudes from the main ice front and out over the continental slope into deep water. Glacial melt water is concentrated in a 200 m thick Ice Shelf Water (ISW layer below the base of the ice shelf at 150–200 m, with a maximum glacial melt concentration of up to 1.16%. Some glacial melt is found throughout the water column, and much of this is from sources other than Fimbul Ice Shelf. However, at least 0.2% of the water in the ISW layer cannot be accounted for by other processes and must have been contributed by the ice shelf. Just downstream of Fimbul Ice Shelf we observe locally created ISW mixing out across the continental slope. The ISW formed here is much less dense than that formed in the southwest Weddell Sea, and will ultimately contribute a freshening (and reduction in δ18O to the upper 100–150 m of the water column in the southeast Weddell Sea.

  7. Glacier surge after ice shelf collapse.

    Science.gov (United States)

    De Angelis, Hernán; Skvarca, Pedro

    2003-03-07

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

  8. Tidal Modulation of Ice-shelf Flow: a Viscous Model of the Ross Ice Shelf

    Science.gov (United States)

    Brunt, Kelly M.; MacAyeal, Douglas R.

    2014-01-01

    Three stations near the calving front of the Ross Ice Shelf, Antarctica, recorded GPS data through a full spring-neap tidal cycle in November 2005. The data revealed a diurnal horizontal motion that varied both along and transverse to the long-term average velocity direction, similar to tidal signals observed in other ice shelves and ice streams. Based on its periodicity, it was hypothesized that the signal represents a flow response of the Ross Ice Shelf to the diurnal tides of the Ross Sea. To assess the influence of the tide on the ice-shelf motion, two hypotheses were developed. The first addressed the direct response of the ice shelf to tidal forcing, such as forces due to sea-surface slopes or forces due to sub-ice-shelf currents. The second involved the indirect response of ice-shelf flow to the tidal signals observed in the ice streams that source the ice shelf. A finite-element model, based on viscous creep flow, was developed to test these hypotheses, but succeeded only in falsifying both hypotheses, i.e. showing that direct tidal effects produce too small a response, and indirect tidal effects produce a response that is not smooth in time. This nullification suggests that a combination of viscous and elastic deformation is required to explain the observations.

  9. Breakup of the Larsen Ice Shelf, Antarctica

    Science.gov (United States)

    2002-01-01

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

  10. Mass Balance and Structure of the Ross Ice Shelf

    Science.gov (United States)

    Das, I.; Padman, L.; Chu, W.; Fricker, H. A.; Becker, M. K.; Bell, R. E.; Tinto, K. J.; Millstein, J. D.

    2016-12-01

    Changes in ice shelf mass balance is key to the long term stability of the Antarctic ice sheet. Although the most extensive thinning occurs on the Amundsen Sea sector of West Antarctica, recent studies indicate that many other ice shelves are also experiencing widespread thinning. Here, we focus on the Ross Ice Self. An 18-year record (1994-2012) of satellite radar altimetry shows elevation change 1 m/yr across the shelf. Significant variability in ice shelf height on interannual time scales makes it difficult to detect a long-term mass budget trend of this ice shelf. Variability of radar signal penetration into the ice-shelf snow and firn layers further complicates assessment of mass changes. In this work, we investigate the Ross Ice Shelf mass balance using aerogeophyical data from the ROSETTA-ICE IcePod and NASA's Operation IceBridge. ROSSETTA-ICE is an aerogeophysical program planned to survey the ice shelf at a 10 km spacing over the course of two field seasons-2015 and 2016. This NSF/Moore Foundation supported multi-University collaborative project is designed to provide an integrated view of the ice shelf and the underlying bathymetry using the IcePod system including its ice-penetrating radars, laser altimetry, gravity meters and magnetometers. We present preliminary results from our ongoing efforts of quantifying the mass balance of the ice shelf using IcePod ice penetrating radars and laser altimetry along with satellite data. We will use internal layers traced from ice penetrating radars to outline the structure of the ice shelf. Airborne laser altimetry measurements from this IcePod survey and IceBridge will be used to study the elevation change of the ice shelf. Spatial variations of thickness of the internal layers in the first few meters of the ice shelf, particularly near the grounding line, will indicate the impact of wind-blown snow coming from the continent onto the ice shelf. In order to infer conditions of melt and freeze-on at the ice

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

    Science.gov (United States)

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

    2016-05-01

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

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

    Science.gov (United States)

    2002-01-01

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

  13. Massive subsurface ice formed by refreezing of ice-shelf melt ponds

    NARCIS (Netherlands)

    Hubbard, Bryn; Luckman, A.; Ashmore, David; Bevan, S.; Kulessa, Bernd; Kuipers Munneke, P.|info:eu-repo/dai/nl/304831891; phillipe, morgane; Jansen, Daniela; Booth, Adam; Sevestre, Heidi; Tison, Jean-Louis; O'Leary, Martin; Rutt, Ian

    2016-01-01

    Surface melt ponds form intermittently on several Antarctic ice shelves. Although implicated in ice-shelf break up, the consequences of such ponding for ice formation and ice-shelf structure have not been evaluated. Here we report the discovery of a massive subsurface ice layer, at least 16 km acros

  14. Massive subsurface ice formed by refreezing of ice-shelf melt ponds

    NARCIS (Netherlands)

    Hubbard, Bryn; Luckman, A.; Ashmore, David; Bevan, S.; Kulessa, Bernd; Kuipers Munneke, P.; phillipe, morgane; Jansen, Daniela; Booth, Adam; Sevestre, Heidi; Tison, Jean-Louis; O'Leary, Martin; Rutt, Ian

    2016-01-01

    Surface melt ponds form intermittently on several Antarctic ice shelves. Although implicated in ice-shelf break up, the consequences of such ponding for ice formation and ice-shelf structure have not been evaluated. Here we report the discovery of a massive subsurface ice layer, at least 16 km acros

  15. Massive subsurface ice formed by refreezing of ice-shelf melt ponds

    NARCIS (Netherlands)

    Hubbard, Bryn; Luckman, A.; Ashmore, David; Bevan, S.; Kulessa, Bernd; Kuipers Munneke, P.; phillipe, morgane; Jansen, Daniela; Booth, Adam; Sevestre, Heidi; Tison, Jean-Louis; O'Leary, Martin; Rutt, Ian

    2016-01-01

    Surface melt ponds form intermittently on several Antarctic ice shelves. Although implicated in ice-shelf break up, the consequences of such ponding for ice formation and ice-shelf structure have not been evaluated. Here we report the discovery of a massive subsurface ice layer, at least 16 km

  16. Evidence for basal marine ice in the Filchner-Ronne ice shelf

    OpenAIRE

    Oerter, Hans; kipfstuhl, J.; Determann, Jürgen; Miller, Heinrich; Wagenbach, D.; Minikin, A; Graf, W.

    1992-01-01

    The Filchner-Ronne ice shelf, which drains most of the marine-based portions of the West Antarctic ice sheet, is the largest ice shelf on Earth by volume. The origin and properties of the ice that constitutes this shelf are poorly understood, because a strong reflecting interface within the ice and the diffuse nature of the ice-ocean interface make seismic and radio echo sounding data difficult to interpret(1,2). Ice in the upper part of the shelf is of meteoric origin, but it has been propos...

  17. Massive Ice Layer Formed by Refreezing of Ice-shelf Surface Melt Ponds: Larsen C Ice Shelf, Antarctica

    Science.gov (United States)

    Hubbard, Bryn; Luckman, Adrian; Ashmore, David; Bevan, Suzanne; Kulessa, Bernd; Kuipers Munneke, Peter; Jansen, Daniela; O'Leary, Martin

    2016-04-01

    Surface melt ponds now form frequently on ice shelves across the northern sector of the Antarctic Peninsula in response to regional warming and local föhn winds. A potentially important, but hitherto unknown, consequence of this surface melting and ponding is the formation of high-density near-surface ice from the refreezing of that water. We report the discovery and physical character of a massive subsurface ice layer located in an area of intense melting and intermittent ponding on Larsen C Ice Shelf, Antarctica. We combine borehole optical televiewer logging and ground-based radar measurements with remote sensing and firn modelling to investigate the formation and spatial extent of this layer, found to be tens of kilometres across and tens of metres deep. The presence of this ice layer has the effect of raising local ice shelf density by ~190 kg m^-3 and temperature by 5 - 10 degrees C above values found in areas unaffected by ponding and hitherto used in models of ice-shelf fracture and flow.

  18. Ice Shelf Modeling: A Cross-Polar Bayesian Statistical Approach

    Science.gov (United States)

    Kirchner, N.; Furrer, R.; Jakobsson, M.; Zwally, H. J.

    2010-12-01

    Ice streams interlink glacial terrestrial and marine environments: embedded in a grounded inland ice such as the Antarctic Ice Sheet or the paleo ice sheets covering extensive parts of the Eurasian and Amerasian Arctic respectively, ice streams are major drainage agents facilitating the discharge of substantial portions of continental ice into the ocean. At their seaward side, ice streams can either extend onto the ocean as floating ice tongues (such as the Drygalsky Ice Tongue/East Antarctica), or feed large ice shelves (as is the case for e.g. the Siple Coast and the Ross Ice Shelf/West Antarctica). The flow behavior of ice streams has been recognized to be intimately linked with configurational changes in their attached ice shelves; in particular, ice shelf disintegration is associated with rapid ice stream retreat and increased mass discharge from the continental ice mass, contributing eventually to sea level rise. Investigations of ice stream retreat mechanism are however incomplete if based on terrestrial records only: rather, the dynamics of ice shelves (and, eventually, the impact of the ocean on the latter) must be accounted for. However, since floating ice shelves leave hardly any traces behind when melting, uncertainty regarding the spatio-temporal distribution and evolution of ice shelves in times prior to instrumented and recorded observation is high, calling thus for a statistical modeling approach. Complementing ongoing large-scale numerical modeling efforts (Pollard & DeConto, 2009), we model the configuration of ice shelves by using a Bayesian Hiearchial Modeling (BHM) approach. We adopt a cross-polar perspective accounting for the fact that currently, ice shelves exist mainly along the coastline of Antarctica (and are virtually non-existing in the Arctic), while Arctic Ocean ice shelves repeatedly impacted the Arctic ocean basin during former glacial periods. Modeled Arctic ocean ice shelf configurations are compared with geological spatial

  19. Mathematical Modelling of Melt Lake Formation On An Ice Shelf

    Science.gov (United States)

    Buzzard, Sammie; Feltham, Daniel; Flocco, Daniela

    2016-04-01

    The accumulation of surface meltwater on ice shelves can lead to the formation of melt lakes. These structures have been implicated in crevasse propagation and ice-shelf collapse; the Larsen B ice shelf was observed to have a large amount of melt lakes present on its surface just before its collapse in 2002. Through modelling the transport of heat through the surface of the Larsen C ice shelf, where melt lakes have also been observed, this work aims to provide new insights into the ways in which melt lakes are forming and the effect that meltwater filling crevasses on the ice shelf will have. This will enable an assessment of the role of meltwater in triggering ice-shelf collapse. The Antarctic Peninsula, where Larsen C is situated, has warmed several times the global average over the last century and this ice shelf has been suggested as a candidate for becoming fully saturated with meltwater by the end of the current century. Here we present results of a 1-D mathematical model of heat transfer through an idealized ice shelf. When forced with automatic weather station data from Larsen C, surface melting and the subsequent meltwater accumulation, melt lake development and refreezing are demonstrated through the modelled results. Furthermore, the effect of lateral meltwater transport upon melt lakes and the effect of the lakes upon the surface energy balance are examined. Investigating the role of meltwater in ice-shelf stability is key as collapse can affect ocean circulation and temperature, and cause a loss of habitat. Additionally, it can cause a loss of the buttressing effect that ice shelves can have on their tributary glaciers, thus allowing the glaciers to accelerate, contributing to sea-level rise.

  20. Massive subsurface ice formed by refreezing of ice-shelf melt ponds

    Science.gov (United States)

    Hubbard, Bryn; Luckman, Adrian; Ashmore, David W.; Bevan, Suzanne; Kulessa, Bernd; Kuipers Munneke, Peter; Philippe, Morgane; Jansen, Daniela; Booth, Adam; Sevestre, Heidi; Tison, Jean-Louis; O'Leary, Martin; Rutt, Ian

    2016-06-01

    Surface melt ponds form intermittently on several Antarctic ice shelves. Although implicated in ice-shelf break up, the consequences of such ponding for ice formation and ice-shelf structure have not been evaluated. Here we report the discovery of a massive subsurface ice layer, at least 16 km across, several kilometres long and tens of metres deep, located in an area of intense melting and intermittent ponding on Larsen C Ice Shelf, Antarctica. We combine borehole optical televiewer logging and radar measurements with remote sensing and firn modelling to investigate the layer, found to be ~10 °C warmer and ~170 kg m-3 denser than anticipated in the absence of ponding and hitherto used in models of ice-shelf fracture and flow. Surface ponding and ice layers such as the one we report are likely to form on a wider range of Antarctic ice shelves in response to climatic warming in forthcoming decades.

  1. Seabed topography beneath Larsen C Ice Shelf from seismic soundings

    Science.gov (United States)

    Brisbourne, A. M.; Smith, A. M.; King, E. C.; Nicholls, K. W.; Holland, P. R.; Makinson, K.

    2014-01-01

    Seismic reflection soundings of ice thickness and seabed depth were acquired on the Larsen C Ice Shelf in order to test a sub-ice shelf bathymetry model derived from the inversion of IceBridge gravity data. A series of lines was collected, from the Churchill Peninsula in the north to the Joerg Peninsula in the south, and also towards the ice front. Sites were selected using the bathymetry model derived from the inversion of free-air gravity data to indicate key regions where sub-ice shelf oceanic circulation may be affected by ice draft and seabed depth. The seismic velocity profile in the upper 100 m of firn and ice was derived from shallow refraction surveys at a number of locations. Measured temperatures within the ice column and at the ice base were used to define the velocity profile through the remainder of the ice column. Seismic velocities in the water column were derived from previous in situ measurements. Uncertainties in ice and water cavity thickness are in general model, significantly modifying the expected oceanic circulation beneath the ice shelf. Similar features have previously been shown to be highly significant in affecting basal melt rates predicted by ocean models. The discrepancies between the gravity inversion results and the seismic bathymetry are attributed to the assumption of uniform geology inherent in the gravity inversion process and also the sparsity of IceBridge flight lines. Results indicate that care must be taken when using bathymetry models derived by the inversion of free-air gravity anomalies. The bathymetry results presented here will be used to improve existing sub-ice shelf ocean circulation models.

  2. Ocean mixing beneath Pine Island Glacier Ice Shelf

    Science.gov (United States)

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

    2016-04-01

    Ice shelves around Antarctica are vulnerable to increase in ocean-driven melting, with the melt rate depending on ocean temperature and strength of sub-ice-shelf-cavity circulations. We present repeated measurements of velocity, temperature, salinity, turbulent kinetic energy dissipation rate and thermal variance dissipation rate beneath Pine Island Glacier Ice Shelf, collected by CTD, ADCP and turbulence sensors mounted on an Autonomous Underwater Vehicle (AUV). The turbulence quantities measured by the AUV outside the ice shelf are in good agreement with ship-based measurements. The highest rate of turbulent kinetic energy dissipation is found near the grounding line, while its temporal fluctuation over seabed ridge within the cavity corresponds to the tidal fluctuation predicted in the Pine Island Bay to the west. The highest thermal variance dissipation rate is found when the AUV was 0.5 m away from the ice, and the thermal variance dissipation generally increases with decreasing distance between the AUV and ice.

  3. Ice-Shelf Tidal Flexure and Subglacial Pressure Variations

    Science.gov (United States)

    Walker, Ryan T.; Parizek, Byron R.; Alley, Richard B.; Anandakrishnan, Sridhar; Riverman, Kiya L.; Christianson, Knut

    2013-01-01

    We develop a model of an ice shelf-ice stream system as a viscoelastic beam partially supported by an elastic foundation. When bed rock near the grounding line acts as a fulcrum, leverage from the ice shelf dropping at low tide can cause significant (approx 1 cm) uplift in the first few kilometers of grounded ice.This uplift and the corresponding depression at high tide lead to basal pressure variations of sufficient magnitude to influence subglacial hydrology.Tidal flexure may thus affect basal lubrication, sediment flow, and till strength, all of which are significant factors in ice-stream dynamics and grounding-line stability. Under certain circumstances, our results suggest the possibility of seawater being drawn into the subglacial water system. The presence of sea water beneath grounded ice would significantly change the radar reflectivity of the grounding zone and complicate the interpretation of grounded versus floating ice based on ice-penetrating radar observations.

  4. Seabed topography beneath Larsen C Ice Shelf from seismic soundings

    Directory of Open Access Journals (Sweden)

    A. M. Brisbourne

    2013-08-01

    Full Text Available Seismic reflection soundings of ice thickness and seabed depth were acquired on the Larsen C Ice Shelf in order to test a sub-shelf bathymetry model derived from the inversion of IceBridge gravity data. A series of lines were collected, from the Churchill Peninsula in the north to the Joerg Peninsula in the south, and also towards the ice front. Sites were selected using the bathymetry model derived from the inversion of free-air gravity data to indicate key regions where sub-shelf oceanic circulation may be affected by ice draft and sub-shelf cavity thickness. The seismic velocity profile in the upper 100 m of firn and ice was derived from shallow refraction surveys at a number of locations. Measured temperatures within the ice column and at the ice base were used to define the velocity profile through the remainder of the ice column. Seismic velocities in the water column were derived from previous in situ measurements. Uncertainties in ice and water cavity thickness are in general <10 m. Compared with the seismic measurements, the root-mean-square error in the gravimetrically derived bathymetry at the seismic sites is 162 m. The seismic profiles prove the non-existence of several bathymetric features that are indicated in the gravity inversion model, significantly modifying the expected oceanic circulation beneath the ice shelf. Similar features have previously been shown to be highly significant in affecting basal melt rates predicted by ocean models. The discrepancies between the gravity inversion results and the seismic bathymetry are attributed to the assumption of uniform geology inherent in the gravity inversion process and also the sparsity of IceBridge flight lines. Results indicate that care must be taken when using bathymetry models derived by the inversion of free-air gravity anomalies. The bathymetry results presented here will be used to improve existing sub-shelf ocean circulation models.

  5. Spatial distribution of Ice Shelf Water in front of the Amery Ice Shelf, Antarctica in summer

    Institute of Scientific and Technical Information of China (English)

    ZHENG Shaojun; SHI Jiuxin; JIAO Yutian; GE Renfeng

    2011-01-01

    As a unique low-temperature water mass in Antarctic coastal region,the Ice Shelf Water (ISW) is an important component for the formation of the Antarctic Bottom Water (AABW).In this paper,we present a criterion for ISW identification based on freezing point at the sea surface,and we study spatial distribution of ISW in front of the Amery Ice Shelf (AIS) and its flow path in Prydz Bay by analyzing hydrographic data from Australian cruises in 2001 and 2002,as well as Chinese cruises in 2003,2005,2006,and 2008,all being made in the austral summer.The relatively cold and fresh ISW occurred as several discrete water blocks with cold cores in front of the AIS,within the depth range of 100-600 m,under the seasonal thermocline.ISW had obvious temporal and spatial variations and the spatial distribution pattern changed greatly after 2005.Most of ISW was concentrated west of 73°E during 2001 to 2003 and 2006,but it was widespread to east in 2005 and 2008.In all observation years,a small amount of cold ISW always occurs at the west end of the AIS front section,where the coldest ISW in the whole section also occurred in 2001,2003 and 2006.Considering general cyclonic circulation pattern under the AIS,the ISW flowing out from west end of the AIS front might have experienced the longest cooling period under ice shelf,so it would have the lowest temperature.Analysis of data from meridian sections in Prydz Bay in 2003 implied that ISW in the west could spread north to the continental break along the east flank of the Fram Bank near 70.5°E,mix with the upwelling Circumpolar Deep Water and possibly contribute to the formation of AABW.

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

    Science.gov (United States)

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

    2015-12-01

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

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

    Directory of Open Access Journals (Sweden)

    T. O. Holt

    2013-05-01

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

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

    Science.gov (United States)

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

    2017-05-09

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

  9. Antarctic Ice-Shelf Front Dynamics from ICESat

    Science.gov (United States)

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

    2012-01-01

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

  10. Ross Ice Shelf Seismic Survey and Future Drilling Recommendation

    Science.gov (United States)

    van Haastrecht, Laurine; Ohneiser, Christian; Gorman, Andrew; Hulbe, Christina

    2016-04-01

    The Ross Ice Shelf (RIS) is one of three gateways through which change in the ocean can be propagated into the interior of West Antarctica. Both the geologic record and ice sheet models indicate that it has experienced widespread retreat under past warm climates. But inland of the continental shelf, there are limited data available to validate the models. Understanding what controls the rate at which the ice shelf will respond to future climate change is central to making useful climate projections. Determining the retreat rate at the end of the last glacial maximum is one part of this challenge. In November 2015, four lines of multi-channel seismic data, totalling over 45 km, were collected on the Ross Ice Shelf, approximately 300 km south of Ross Island using a thumper seismic source and a 96 channel snow streamer. The seismic survey was undertaken under the New Zealand Antarctic Research Institute (NZARI) funded Aotearoa New Zealand Ross Ice Shelf Programme to resolve bathymetric details and to image sea floor sediments under a proposed drilling site on the ice shelf, at about 80.7 S and 174 E. The thumper, a purpose-built, trailer mounted, weight-drop seismic source was towed behind a Hägglund tracked vehicle to image the bathymetry and sediments underneath the RIS. Seismic data collection on an ice shelf has unique challenges, in particular strong attenuation of the seismic energy by snow and firn, and complex multiple ray paths. The thumper, which consists of a heavy weight (250kg) that is dropped on a large, ski mounted steel plate, produced a consistent, repeatable higher energy signal when compared to sledge hammer source and allowed for a greater geographic coverage and lower environmental impact than an explosive source survey. Our survey revealed that the seafloor is smooth and that there may be up to 100 m of layered sediments beneath the seafloor and possibly deeper, more complex structures. A multiple generated by internally reflected seismic energy

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

    Science.gov (United States)

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

    2016-12-01

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

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

    Science.gov (United States)

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

    2016-04-01

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

  13. A vertically integrated treatment of ice stream and ice shelf thermodynamics

    Science.gov (United States)

    Sergienko, O. V.

    2014-04-01

    The extremely small vertical shear in ice stream and ice shelf flow simplifies the equations, which govern their thermodynamic evolution. Complemented by the widely used shallow shelf approximation used to simplify the ice flow momentum balance, a vertically integrated formulation of heat transfer presented here reduces the dimensionality of the thermodynamic problem from three to two (plan view) dimensions and thus significantly reduces the computational cost of treating ice stream and ice shelf thermodynamics in models. For realistic conditions, errors in ice stiffness parameter, ice thickness, and speed caused by the vertically integrated treatment of heat transfer are less than 5% of magnitudes of these values compared to the standard three-dimensional thermomechanical computations. In addition, for the specific case of ice shelves with strong bottom melting, the governing equation describing evolution of the vertically integrated ice stiffness parameter is derived, which further reduces computational cost. The presented error analysis and formulations of ice stream and ice shelf thermodynamics in terms of the vertically integrated temperature allow the thermodynamic effects on ice deformation to be easily incorporated into studies that traditionally disregard them.

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

    Science.gov (United States)

    Scambos, T. A.; Shuman, C. A.; Truffer, M.; Pettit, E. C.; Huber, B. A.; Haran, T. M.; Ross, R.; Domack, E. W.

    2013-12-01

    Ice shelf / ice tongue disintegrations and break-ups have a major effect on glacier mass balance, and nowhere has this been more evident than in the northern sections of the Larsen Ice Shelf in the Antarctic Peninsula. Ice flux in this region surged 2- to 6-fold after the 1995 and 2002 ice shelf disintegration events, driven by a group of processes based on the presence of extensive surface melt lakes. However, precursor changes in the ice shelves beginning more than a decade before the events have been identified. A new assessment of these provides insight on the earliest causes of ice shelf change. Among the precursor changes are an increase in meltwater lake extent, structural changes in the ice shelf shear margins, grounding line changes, and pre-breakup acceleration of the ice shelves and feeder glaciers. In the aftermath of the 2002 disintegration of the Larsen B, the two large remnant ice shelves at Seal Nunataks (~400 km2) and Scar Inlet (~2400 km2) have also evolved in these ways. These changes have been measured by a combination of in situ automated observation systems (AMIGOS: see Scambos et al., 2013, J. Glaciol.) and remote sensing as part of the Larsen Ice Shelf System, Antarctica (LARISSA) NSF project and NASA Cryosphere Program funding. Ice flow speed on the central Scar Inlet ice shelf has increased 60% between 2002 and 2012 (425 to 675 m/yr), and by 20% (540 to 660 m/yr) just above the grounding line of Flask Glacier, a tributary. Elevation change data from ICESat altimetry and ASTER stereo images show evidence of grounding line movement for Flask between 2003 and 2008, and for Crane Glacier prior to the 2002 break-up. In late 2002, and again in late 2012, major new rifts have formed on the southern portion of the Scar Inlet shelf, and the northwestern shear zone has rapidly evolved. The ice speed increase and the new rifts are inferred to be due to significant structural changes in the ice shelf shear margin on its northern side (concentration of

  15. High Resolution Ice Surface of the Ross Ice Shelf: Accuracy and Links to Basal Processes

    Science.gov (United States)

    Starke, S. E.

    2015-12-01

    We use airborne laser altimetry data from IcePod and IceBridge to map the surface across the Ross Ice Shelf in Antarctica. Laser altimetry and radar data is analyzed from the IcePod 2014 and 2015 field campaigns as well as IceBridge 2013. Icepod is a multi sensor suite that includes ice penetrating radars, a swath scanning laser, visible and IR cameras as well as GPS mounted on a LC-130. Using shallow ice radar data from both IcePod and IceBridge we identify the base of the ice shelf. Across the shelf we observe distinct areas of high reflectivity in the radar data suggesting basal crevassing. In some regions, the basal reflector is not well defined. Laser altimetry profiles correlate surface morphology with features at the base including basal crevasses and marine ice formed by freezing on to the base of the ice shelf. Building Digital Elevation Models (DEMs) from the laser altimetry data, we investigate the relationship between the surface expressions of these ice shelf dynamics including thickness changes, potential sites of marine ice at the base and basal morphology in regions where a well defined basal reflector does not exist in the radar profiles. We present accuracy of the IcePod laser altimetry dataset using ground control points and GPS grids from Greenland and Antarctica as well as Photogrammetric DEMs. Our laser altimetry analysis resolves sub-meter surface features which, combined with coincident radar, provides a link between basal processes and their surface expressions.

  16. Evidence for an ice shelf covering the central Arctic Ocean during the penultimate glaciation.

    Science.gov (United States)

    Jakobsson, Martin; Nilsson, Johan; Anderson, Leif; Backman, Jan; Björk, Göran; Cronin, Thomas M; Kirchner, Nina; Koshurnikov, Andrey; Mayer, Larry; Noormets, Riko; O'Regan, Matthew; Stranne, Christian; Ananiev, Roman; Barrientos Macho, Natalia; Cherniykh, Denis; Coxall, Helen; Eriksson, Björn; Flodén, Tom; Gemery, Laura; Gustafsson, Örjan; Jerram, Kevin; Johansson, Carina; Khortov, Alexey; Mohammad, Rezwan; Semiletov, Igor

    2016-01-18

    The hypothesis of a km-thick ice shelf covering the entire Arctic Ocean during peak glacial conditions was proposed nearly half a century ago. Floating ice shelves preserve few direct traces after their disappearance, making reconstructions difficult. Seafloor imprints of ice shelves should, however, exist where ice grounded along their flow paths. Here we present new evidence of ice-shelf groundings on bathymetric highs in the central Arctic Ocean, resurrecting the concept of an ice shelf extending over the entire central Arctic Ocean during at least one previous ice age. New and previously mapped glacial landforms together reveal flow of a spatially coherent, in some regions >1-km thick, central Arctic Ocean ice shelf dated to marine isotope stage 6 (∼ 140 ka). Bathymetric highs were likely critical in the ice-shelf development by acting as pinning points where stabilizing ice rises formed, thereby providing sufficient back stress to allow ice shelf thickening.

  17. Evidence for an ice shelf covering the central Arctic Ocean during the penultimate glaciation

    Science.gov (United States)

    Jakobsson, Martin; Nilsson, Johan; Anderson, Leif G.; Backman, Jan; Bjork, Goran; Cronin, Thomas M.; Kirchner, Nina; Koshurnikov, Andrey; Mayer, Larry; Noormets, Riko; O'Regan, Matthew; Stranne, Christian; Ananiev, Roman; Macho, Natalia Barrientos; Cherniykh, Dennis; Coxall, Helen; Eriksson, Bjorn; Floden, Tom; Gemery, Laura; Gustafsson, Orjan; Jerram, Kevin; Johansson, Carina; Khortov, Alexey; Mohammad, Rezwan; Semiletov, Igor

    2016-01-01

    The hypothesis of a km-thick ice shelf covering the entire Arctic Ocean during peak glacial conditions was proposed nearly half a century ago. Floating ice shelves preserve few direct traces after their disappearance, making reconstructions difficult. Seafloor imprints of ice shelves should, however, exist where ice grounded along their flow paths. Here we present new evidence of ice-shelf groundings on bathymetric highs in the central Arctic Ocean, resurrecting the concept of an ice shelf extending over the entire central Arctic Ocean during at least one previous ice age. New and previously mapped glacial landforms together reveal flow of a spatially coherent, in some regions >1-km thick, central Arctic Ocean ice shelf dated to marine isotope stage 6 (~140 ka). Bathymetric highs were likely critical in the ice-shelf development by acting as pinning points where stabilizing ice rises formed, thereby providing sufficient back stress to allow ice shelf thickening.

  18. Influence of tides on melting and freezing beneath Filchner-Ronne Ice Shelf, Antarctica

    OpenAIRE

    Makinson, Keith; Holland, Paul R.; Jenkins, Adrian; Nicholls, Keith W.; Holland, David M.

    2011-01-01

    An isopycnic coordinate ocean circulation model is applied to the ocean cavity beneath Filchner-Ronne Ice Shelf, investigating the role of tides on sub-ice shelf circulation and ice shelf basal mass balance. Including tidal forcing causes a significant intensification in the sub-ice shelf circulation, with an increase in melting (3-fold) and refreezing (6-fold); the net melt rate and seawater flux through the cavity approximately doubles. With tidal forcing, the spatial pattern and magnitude ...

  19. Atmospheric and oceanic forcing of Larsen C Ice Shelf thinning

    Directory of Open Access Journals (Sweden)

    P. R. Holland

    2015-01-01

    Full Text Available The catastrophic collapses of Larsen A and B ice shelves on the eastern Antarctic Peninsula have caused their tributary glaciers to accelerate, contributing to sea-level rise and freshening the Antarctic Bottom Water formed nearby. The surface of Larsen C Ice Shelf (LCIS, the largest ice shelf on the peninsula, is lowering. This could be caused by unbalanced ocean melting (ice loss or enhanced firn melting and compaction (englacial air loss. Using a novel method to analyse eight radar surveys, this study derives separate estimates of ice and air thickness changes during a 15 year period. The uncertainties are considerable, but the primary estimate is that the surveyed lowering (0.066 ± 0.017 m yr−1 is caused by both ice loss (0.28 ± 0.18 m yr−1 and firn air loss (0.037 ± 0.026 m yr−1. Though the ice loss is much larger, ice and air loss contribute approximately equally to the lowering. The ice loss could be explained by high basal melting and/or ice divergence, and the air loss by low surface accumulation or high surface melting and/or compaction. The primary estimate therefore requires that at least two forcings caused the surveyed lowering. Mechanisms are discussed by which LCIS stability could be compromised in future, suggesting destabilisation timescales of a few centuries. The most rapid pathways to collapse are offered by a flow perturbation arising from the ungrounding of LCIS from Bawden Ice Rise, or ice-front retreat past a "compressive arch" in strain rates.

  20. Ross Ice Shelf and the Queen Maude Mounains, Antarctica

    Science.gov (United States)

    1991-01-01

    Part of the Ross Ice Shelf and the Queen Maude Mounains of Antarctica (55.5N, 178.0W) are in the background of this scene, oriented toward the south. Low stratocumulus clouds are predominant throughout most of the scene.

  1. Modelling snowdrift sublimation on an Antarctic ice shelf

    NARCIS (Netherlands)

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

    2010-01-01

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

  2. The seasonal appearance of ice shelf water in coastal Antarctica and its effect on sea ice growth

    National Research Council Canada - National Science Library

    Andrew R. Mahoney; Alexander J. Gough; Patricia J. Langhorne; Natalie J. Robinson; Craig L. Stevens; Michael M. J. Williams; Timothy G. Haskell

    2011-01-01

      We present data from first year-round mooring beneath sea ice in McMurdo Sound Presence of ice shelf water below sea ice is related to enhanced growth We identify distinct stages in arrival of ISW...

  3. Ice-shelf melting around Antarctica

    National Research Council Canada - National Science Library

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

    2013-01-01

    We compare the volume flux divergence of Antarctic ice shelves in 2007 and 2008 with 1979 to 2010 surface accumulation and 2003 to 2008 thinning to determine their rates of melting and mass balance...

  4. Massive subsurface ice formed by refreezing of ice-shelf melt ponds.

    Science.gov (United States)

    Hubbard, Bryn; Luckman, Adrian; Ashmore, David W; Bevan, Suzanne; Kulessa, Bernd; Kuipers Munneke, Peter; Philippe, Morgane; Jansen, Daniela; Booth, Adam; Sevestre, Heidi; Tison, Jean-Louis; O'Leary, Martin; Rutt, Ian

    2016-06-10

    Surface melt ponds form intermittently on several Antarctic ice shelves. Although implicated in ice-shelf break up, the consequences of such ponding for ice formation and ice-shelf structure have not been evaluated. Here we report the discovery of a massive subsurface ice layer, at least 16 km across, several kilometres long and tens of metres deep, located in an area of intense melting and intermittent ponding on Larsen C Ice Shelf, Antarctica. We combine borehole optical televiewer logging and radar measurements with remote sensing and firn modelling to investigate the layer, found to be ∼10 °C warmer and ∼170 kg m(-3) denser than anticipated in the absence of ponding and hitherto used in models of ice-shelf fracture and flow. Surface ponding and ice layers such as the one we report are likely to form on a wider range of Antarctic ice shelves in response to climatic warming in forthcoming decades.

  5. Large flux of iron from the Amery Ice Shelf marine ice to Prydz Bay, East Antarctica

    Science.gov (United States)

    Herraiz-Borreguero, L.; Lannuzel, D.; van der Merwe, P.; Treverrow, A.; Pedro, J. B.

    2016-08-01

    The Antarctic continental shelf supports a high level of marine primary productivity and is a globally important carbon dioxide (CO2) sink through the photosynthetic fixation of CO2 via the biological pump. Sustaining such high productivity requires a large supply of the essential micronutrient iron (Fe); however, the pathways for Fe delivery to these zones vary spatially and temporally. Our study is the first to report a previously unquantified source of concentrated bioavailable Fe to Antarctic surface waters. We hypothesize that Fe derived from subglacial processes is delivered to euphotic waters through the accretion (Fe storage) and subsequent melting (Fe release) of a marine-accreted layer of ice at the base of the Amery Ice Shelf (AIS). Using satellite-derived Chlorophyll-a data, we show that the soluble Fe supplied by the melting of the marine ice layer is an order of magnitude larger than the required Fe necessary to sustain the large annual phytoplankton bloom in Prydz Bay. Our finding of high concentrations of Fe in AIS marine ice and recent data on increasing rates of ice shelf basal melt in many of Antarctica's ice shelves should encourage further research into glacial and marine sediment transport beneath ice shelves and their sensitivity to current changes in basal melt. Currently, the distribution, volume, and Fe concentration of Antarctic marine ice is poorly constrained. This uncertainty, combined with variable forecasts of increased rates of ice shelf basal melt, limits our ability to predict future Fe supply to Antarctic coastal waters.

  6. Does Arctic sea ice reduction foster shelf-basin exchange?

    Science.gov (United States)

    Ivanov, Vladimir; Watanabe, Eiji

    2013-12-01

    The recent shift in Arctic ice conditions from prevailing multi-year ice to first-year ice will presumably intensify fall-winter sea ice freezing and the associated salt flux to the underlying water column. Here, we conduct a dual modeling study whose results suggest that the predicted catastrophic consequences for the global thermohaline circulation (THC), as a result of the disappearance of Arctic sea ice, may not necessarily occur. In a warmer climate, the substantial fraction of dense water feeding the Greenland-Scotland overflow may form on Arctic shelves and cascade to the deep basin, thus replenishing dense water, which currently forms through open ocean convection in the sub-Arctic seas. We have used a simplified model for estimating how increased ice production influences shelf-basin exchange associated with dense water cascading. We have carried out case studies in two regions of the Arctic Ocean where cascading was observed in the past. The baseline range of buoyancy-forcing derived from the columnar ice formation was calculated as part of a 30-year experiment of the pan-Arctic coupled ice-ocean general circulation model (GCM). The GCM results indicate that mechanical sea ice divergence associated with lateral advection accounts for a significant part of the interannual variations in sea ice thermal production in the coastal polynya regions. This forcing was then rectified by taking into account sub-grid processes and used in a regional model with analytically prescribed bottom topography and vertical stratification in order to examine specific cascading conditions in the Pacific and Atlantic sectors of the Arctic Ocean. Our results demonstrate that the consequences of enhanced ice formation depend on geographical location and shelf-basin bathymetry. In the Pacific sector, strong density stratification in slope waters impedes noticeable deepening of shelf-origin water, even for the strongest forcing applied. In the Atlantic sector, a 1.5x increase of

  7. Marine ice regulates the future stability of a large Antarctic ice shelf

    Science.gov (United States)

    Kulessa, Bernd; Jansen, Daniela; Luckman, Adrian J.; King, Edward C.; Sammonds, Peter R.

    2014-01-01

    The collapses of the Larsen A and B ice shelves on the Antarctic Peninsula in 1995 and 2002 confirm the impact of southward-propagating climate warming in this region. Recent mass and dynamic changes of Larsen B’s southern neighbour Larsen C, the fourth largest ice shelf in Antarctica, may herald a similar instability. Here, using a validated ice-shelf model run in diagnostic mode, constrained by satellite and in situ geophysical data, we identify the nature of this potential instability. We demonstrate that the present-day spatial distribution and orientation of the principal stresses within Larsen C ice shelf are akin to those within pre-collapse Larsen B. When Larsen B’s stabilizing frontal portion was lost in 1995, the unstable remaining shelf accelerated, crumbled and ultimately collapsed. We hypothesize that Larsen C ice shelf may suffer a similar fate if it were not stabilized by warm and mechanically soft marine ice, entrained within narrow suture zones. PMID:24751641

  8. Ice-Shelf Flexure and Tidal Forcing of Bindschadler Ice Stream, West Antarctica

    Science.gov (United States)

    Walker, Ryan T.; Parizek, Bryron R.; Alley, Richard B.; Brunt, Kelly M.; Anandakrishnan, Sridhar

    2014-01-01

    Viscoelastic models of ice-shelf flexure and ice-stream velocity perturbations are combined into a single efficient flowline model to study tidal forcing of grounded ice. The magnitude and timing of icestream response to tidally driven changes in hydrostatic pressure and/or basal drag are found to depend significantly on bed rheology, with only a perfectly plastic bed allowing instantaneous velocity response at the grounding line. The model can reasonably reproduce GPS observations near the grounding zone of Bindschadler Ice Stream (formerly Ice Stream D) on semidiurnal time scales; however, other forcings such as tidally driven ice-shelf slope transverse to the flowline and flexurally driven till deformation must also be considered if diurnal motion is to be matched

  9. Ambient noise correlation on the Amery Ice Shelf, East Antarctica

    Science.gov (United States)

    Zhan, Zhongwen; Tsai, Victor C.; Jackson, Jennifer M.; Helmberger, Don

    2014-03-01

    The structure of ice shelves is important for modelling the dynamics of ice flux from the continents to the oceans. While other, more traditional techniques provide many constraints, passive imaging with seismic noise is a complementary tool for studying and monitoring ice shelves. As a proof of concept, here we study noise cross-correlations and autocorrelations on the Amery Ice Shelf, East Antarctica. We find that the noise field on the ice shelf is dominated by energy trapped in a low-velocity waveguide caused by the water layer below the ice. Within this interpretation, we explain spectral ratios of the noise cross-correlations as P-wave resonances in the water layer, and obtain an independent estimate of the water-column thickness, consistent with other measurements. For stations with noise dominated by elastic waves, noise autocorrelations also provide similar results. High-frequency noise correlations also require a 50-m firn layer near the surface with P-wave velocity as low as 1 km s-1. Our study may also provide insight for future planetary missions that involve seismic exploration of icy satellites such as Titan and Europa.

  10. Surface melt and ponding on Larsen C Ice shelf and the impact of foehn winds

    OpenAIRE

    Luckman, Adrian; Elvidge, Andrew; Jansen, Daniela; Kulessa, Bernd; Kuipers-Munneke, Peter; King, John; Barrand, Nick

    2014-01-01

    A common precursor to ice shelf disintegration, most notably that of Larsen B Ice Shelf, is unusually intense or prolonged surface melt and the presence of surface standing water. However, there has been little research into detailed patterns of melt on ice shelves or the nature of summer melt ponds. We investigated surface melt on Larsen C Ice Shelf at high resolution using Envisat advanced synthetic aperture radar (ASAR) data and explored melt ponds in a range of satellite image...

  11. Glider observations of the Dotson Ice Shelf outflow

    Science.gov (United States)

    Miles, Travis; Lee, Sang Hoon; Wåhlin, Anna; Ha, Ho Kyung; Kim, Tae Wan; Assmann, Karen M.; Schofield, Oscar

    2016-01-01

    The Amundsen Sea is one of the most productive polynyas in the Antarctic per unit area and is undergoing rapid changes including a reduction in sea ice duration, thinning ice sheets, retreat of glaciers and the potential collapse of the Thwaites Glacier in Pine Island Bay. A growing body of research has indicated that these changes are altering the water mass properties and associated biogeochemistry within the polynya. Unfortunately difficulties in accessing the remote location have greatly limited the amount of in situ data that has been collected. In this study data from a Teledyne-Webb Slocum glider was used to supplement ship-based sampling along the Dotson Ice Shelf (DIS). This autonomous underwater vehicle revealed a detailed view of a meltwater laden outflow from below the western flank of the DIS. Circumpolar Deep Water intruding onto the shelf drives glacial melt and the supply of macronutrients that, along with ample light, supports the large phytoplankton blooms in the Amundsen Sea Polynya. Less well understood is the source of micronutrients, such as iron, necessary to support this bloom to the central polynya where chlorophyll concentrations are highest. This outflow region showed decreasing optical backscatter with proximity to the bed indicating that particulate matter was sourced from the overlying glacier rather than resuspended sediment. This result suggests that particulate iron, and potentially phytoplankton primary productivity, is intrinsically linked to the magnitude and duration of sub-glacial melt from Circumpolar Deep Water intrusions onto the shelf.

  12. Surface melt and ponding of Larsen C Ice Shelf and the impact of foehn winds

    NARCIS (Netherlands)

    Luckman, Adrian; Elvidge, Andrew; Jansen, Daniela; Kulessa, Bernd; Kuipers Munneke, Peter|info:eu-repo/dai/nl/304831891; King, John; Barrand, Nicholas

    2014-01-01

    A common precursor to ice shelf disintegration, most notably that of Larsen B Ice Shelf, is unusually intense or prolonged surface melt and the presence of surface standing water. However, there has been little research into detailed patterns of melt on ice shelves or the nature of summer melt

  13. A Theoretical and Experimental Investigation of Ice-Shelf Flow Dynamics

    Science.gov (United States)

    Wearing, M.; Worster, G.; Hindmarsh, R. C. A.

    2015-12-01

    Ice-shelf buttressing is a major control on the rate of ice discharged from fast-flowing ice streams that drain the Antarctic Ice Sheet. The collapse of an ice shelf can lead to dramatic acceleration and thinning of the ice streams and glaciers that flowed into the former shelf. The magnitude of the buttressing force depends on the shelf geometry and confinement. This geometry is determined by the ice-shelf extent, resulting from retreat due to iceberg calving and shelf advance due to flow. In contrast to large-scale ice-sheet models, which require high resolution datasets, we aim to gain insight using simple idealized models, focusing on the transition from lateral confinement to non-confinement. By considering a confined shelf with lateral shear stresses controlling the flow, steady-state analytical solutions can be calculated. These solutions are then compared to a numerical model for a confined flow, which incorporates both shear and extensional stresses. A boundary layer close to the calving front is identified, where both extensional and shear stresses control the dynamics. We test these idealized models against fluid-mechanical laboratory experiments, designed to simulate the flow of an ice shelf in a narrow channel. From these experiments velocity fields and altimetry for the ice-shelf are collected, allowing for comparison with the theoretical models and geophysical data.

  14. Observation and parameterization of ablation at the base of Ronne Ice Shelf, Antarctica

    OpenAIRE

    Jenkins, Adrian; Nicholls, Keith W.; Corr, Hugh F. J.

    2010-01-01

    Parameterizations of turbulent transfer through the oceanic boundary layer beneath an ice shelf are tested using direct measurements of basal ablation. Observations were made in the southwestern part of Ronne Ice Shelf, about 500 km from open water. The mean basal ablation rate was measured over a month-long and a year-long period using phase-sensitive radar to record the thinning of the ice shelf. Ocean temperatures were observed within about 25 m of the ice shelf base over the period of the...

  15. Surface ice flow velocity and tide retrieval of the amery ice shelf using precise point positioning

    DEFF Research Database (Denmark)

    Zhang, X.H.; Andersen, Ole Baltazar

    2006-01-01

    Five days of continuous GPS observation data were collected in the frontal zone of the Amery ice shelf and subsequently post-processed using precise point position (PPP) technology based on precise orbit and clock products from the International GNSS service. The surface ice flow velocity of the ...... replace double-difference GPS positioning in remote or hostile environments, and be used to retrieve the surface ice flow velocity without any reference station. Furthermore, the solution can be derived epoch-by-epoch with accuracy in the centimeters to decimeter range....

  16. Surface ice flow velocity and tide retrieval of the amery ice shelf using precise point positioning

    DEFF Research Database (Denmark)

    Zhang, X.H.; Andersen, Ole Baltazar

    2006-01-01

    Five days of continuous GPS observation data were collected in the frontal zone of the Amery ice shelf and subsequently post-processed using precise point position (PPP) technology based on precise orbit and clock products from the International GNSS service. The surface ice flow velocity...... replace double-difference GPS positioning in remote or hostile environments, and be used to retrieve the surface ice flow velocity without any reference station. Furthermore, the solution can be derived epoch-by-epoch with accuracy in the centimeters to decimeter range....

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

    Science.gov (United States)

    Goeller, Sebastian; Timmermann, Ralph

    2016-04-01

    The ice flow at the margins of the West Antarctic Ice Sheet is moderated by large ice shelves. Their buttressing effect substantially controls the mass balance of the WAIS and thus its contribution to sea level rise. The stability of these ice shelves results from the balance of mass gain by accumulation and ice flow from the adjacent ice sheet and mass loss by calving and basal melting due to the ocean heat flux. Recent results of ocean circulation models indicate that warm circumpolar water of the Southern Ocean may override the submarine slope front of the Antarctic Continent and boost basal ice shelf melting. In particular, ocean simulations for several of the IPCC's future climate scenarios demonstrate the redirection of a warm coastal current into the Filchner Trough and underneath the Filchner-Ronne Ice Shelf within the next decades. In this study, we couple the finite elements ocean circulation model FESOM and the three-dimensional thermomechanical ice flow model RIMBAY to investigate the complex interactions between ocean and ice dynamics at the Filchner-Ronne Ice Shelf. We focus on the impact of a changing ice shelf cavity on ocean dynamics as well as the feedback of the resulting sub-shelf melting rates on the ice shelf geometry and implications for the dynamics of the adjacent marine-based Westantarctic Ice Sheet. Our simulations reveal the high sensitivity of grounding line migration to ice-ocean interactions within the Filchner-Ronne Ice Shelf and emphasize the importance of coupled model studies for realistic assessments of the Antarctic mass balance in future global warming scenarios.

  18. Ecosystems on ice: the microbial ecology of Markham Ice Shelf in the high Arctic.

    Science.gov (United States)

    Vincent, Warwick F; Mueller, Derek R; Bonilla, Sylvia

    2004-04-01

    Microbial communities occur throughout the cryosphere in a diverse range of ice-dominated habitats including snow, sea ice, glaciers, permafrost, and ice clouds. In each of these environments, organisms must be capable of surviving freeze-thaw cycles, persistent low temperatures for growth, extremes of solar radiation, and prolonged dormancy. These constraints may have been especially important during global cooling events in the past, including the Precambrian glaciations. One analogue of these early Earth conditions is the thick, landfast sea ice that occurs today at certain locations in the Arctic and Antarctic. These ice shelves contain liquid water for a brief period each summer, and support luxuriant microbial mat communities. Our recent studies of these mats on the Markham Ice Shelf (Canadian high Arctic) by high performance liquid chromatography (HPLC) showed that they contain high concentrations of chlorophylls a and b, and several carotenoids notably lutein, echinenone and beta-carotene. The largest peaks in the HPLC chromatograms were two UV-screening compounds known to be produced by cyanobacteria, scytonemin, and its decomposition product scytonemin-red. Microscopic analyses of the mats showed that they were dominated by the chlorophyte genera cf. Chlorosarcinopsis, Pleurastrum, Palmellopsis, and Bracteococcus, and cyanobacteria of the genera Nostoc, Phormidium, Leptolyngbya, and Gloeocapsa. From point transects and localized sampling we estimated a total standing stock on this ice shelf of up to 11,200 tonnes of organic matter. These observations underscore the ability of microbial communities to flourish despite the severe constraints imposed by the cryo-ecosystem environment.

  19. SAR observations of the Nansen Ice Shelf fracture

    Science.gov (United States)

    Moctezuma-Flores, M.; Parmiggiani, F.

    2016-11-01

    This paper presents a study, by means of of Synthetic Aperture Radar (SAR) images, of the fracture of the Nansen Ice Shelf, from its first appearance in SAR images to the final collapse on 7 April 2016. Both Sentinel-1 and Cosmo-SkyMed images have been used. First, the images were remapped onto an equidistant cylindrical projection; from these a subset, or imagette, only covering the fracture was extracted. A segmentation scheme was then applied to the sequence of imagettes in order to produce a sequence of binary imagettes with only the fracture area enhanced; from these, the computation of fracture area became a trivial task.

  20. Ice shelf flexures modeled with a 2-D elastic flow line model

    Directory of Open Access Journals (Sweden)

    Y. V. Konovalov

    2011-10-01

    Full Text Available Ice shelf flexures modeling was performed using a 2-D finite-difference elastic model, which takes into account sub-ice-shelf sea water flow. The sub-ice water flow was described by the wave equation for the sub-ice-shelf pressure perturbations (Holdsworth and Glynn, 1978. In the model ice shelf flexures result from variations in ocean pressure due to changes in prescribed sea levels. The numerical experiments were performed for a flow line down one of the fast flowing ice streams of the Academy of Sciences Ice Cap. The profile includes a part of the adjacent ice shelf. The numerical experiments were carried out for harmonic incoming pressure perturbations P' and the ice shelf flexures were obtained for a wide spectrum of the pressure perturbations frequencies, ranging from tidal periods down to periods of a few seconds (0.004..0.02 Hz. The amplitudes of the ice shelf deflections obtained by the model achieve a maxima at about T ≈ 165 s in concordance with previous investigations of the impact of waves on Antarctic ice shelves (Bromirski et al., 2010. The explanation of the effect is found in the solution of the corresponding eigenvalue problem revealing the existence of a resonance at these high frequencies.

  1. A laboratory scale model of abrupt ice-shelf disintegration

    Science.gov (United States)

    Macayeal, D. R.; Boghosian, A.; Styron, D. D.; Burton, J. C.; Amundson, J. M.; Cathles, L. M.; Abbot, D. S.

    2010-12-01

    An important mode of Earth’s disappearing cryosphere is the abrupt disintegration of ice shelves along the Peninsula of Antarctica. This disintegration process may be triggered by climate change, however the work needed to produce the spectacular, explosive results witnessed with the Larsen B and Wilkins ice-shelf events of the last decade comes from the large potential energy release associated with iceberg capsize and fragmentation. To gain further insight into the underlying exchanges of energy involved in massed iceberg movements, we have constructed a laboratory-scale model designed to explore the physical and hydrodynamic interactions between icebergs in a confined channel of water. The experimental apparatus consists of a 2-meter water tank that is 30 cm wide. Within the tank, we introduce fresh water and approximately 20-100 rectangular plastic ‘icebergs’ having the appropriate density contrast with water to mimic ice. The blocks are initially deployed in a tight pack, with all blocks arranged in a manner to represent the initial state of an integrated ice shelf or ice tongue. The system is allowed to evolve through time under the driving forces associated with iceberg hydrodynamics. Digitized videography is used to quantify how the system of plastic icebergs evolves between states of quiescence to states of mobilization. Initial experiments show that, after a single ‘agitator’ iceberg begins to capsize, an ‘avalanche’ of capsizing icebergs ensues which drives horizontal expansion of the massed icebergs across the water surface, and which stimulates other icebergs to capsize. A surprise initially evident in the experiments is the fact that the kinetic energy of the expanding mass of icebergs is only a small fraction of the net potential energy released by the rearrangement of mass via capsize. Approximately 85 - 90 % of the energy released by the system goes into water motion modes, including a pervasive, easily observed seich mode of the tank

  2. Response to a warming inflow in a coupled model of Filchner-Ronne Ice Shelf cavity

    Science.gov (United States)

    Timmermann, Ralph; Goeller, Sebastian

    2017-04-01

    To study the interaction between the Southern Ocean and the Antarctic ice sheet, a Regional Antarctic and Global Ocean (RAnGO) model has been developed. The coupled model is based on a global implementation of the Finite Element Sea ice—Ocean Model (FESOM) with a mesh refinement in the Southern Ocean, particularly in its marginal seas and in the sub-ice shelf cavities. The cryosphere is represented by a regional setup of the ice flow model RIMBAY, which comprises the Filchner-Ronne Ice Shelf and the grounded ice in its catchment area up to the ice divides. At the base of the RIMBAY ice shelf, melt rates from FESOM's ice shelf component are prescribed. RIMBAY returns ice thickness and the position of the grounding line. Model runs with a 20th-century climate forcing yield realistic basal melt rates and a quasi-stable grounding line position close to the presently observed state. In a centennial-scale warm-water-inflow scenario, the model suggests a substantial thinning of the ice shelf and a gradual retreat of the grounding line. A more dramatic response is prevented by the steep topography upstream from most of current grounding lines in this area. The potentially negative feedback from ice shelf thinning through a rising in-situ freezing temperature is more than outweighed by the increase of deep-drafted ice shelf area. Compared to a control simulation with fixed ice shelf geometry, the coupled model thus yields a slightly stronger increase of ice shelf basal melt rates.

  3. Antarctic Ice Shelf Potentially Stabilized by Export of Meltwater in Surface River

    Science.gov (United States)

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

    2017-01-01

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

  4. Widespread collapse of the Ross Ice Shelf during the late Holocene.

    Science.gov (United States)

    Yokoyama, Yusuke; Anderson, John B; Yamane, Masako; Simkins, Lauren M; Miyairi, Yosuke; Yamazaki, Takahiro; Koizumi, Mamito; Suga, Hisami; Kusahara, Kazuya; Prothro, Lindsay; Hasumi, Hiroyasu; Southon, John R; Ohkouchi, Naohiko

    2016-03-01

    The stability of modern ice shelves is threatened by atmospheric and oceanic warming. The geologic record of formerly glaciated continental shelves provides a window into the past of how ice shelves responded to a warming climate. Fields of deep (-560 m), linear iceberg furrows on the outer, western Ross Sea continental shelf record an early post-Last Glacial Maximum episode of ice-shelf collapse that was followed by continuous retreat of the grounding line for ∼200 km. Runaway grounding line conditions culminated once the ice became pinned on shallow banks in the western Ross Sea. This early episode of ice-shelf collapse is not observed in the eastern Ross Sea, where more episodic grounding line retreat took place. More widespread (∼280,000 km(2)) retreat of the ancestral Ross Ice Shelf occurred during the late Holocene. This event is recorded in sediment cores by a shift from terrigenous glacimarine mud to diatomaceous open-marine sediment as well as an increase in radiogenic beryllium ((10)Be) concentrations. The timing of ice-shelf breakup is constrained by compound specific radiocarbon ages, the first application of this technique systematically applied to Antarctic marine sediments. Breakup initiated around 5 ka, with the ice shelf reaching its current configuration ∼1.5 ka. In the eastern Ross Sea, the ice shelf retreated up to 100 km in about a thousand years. Three-dimensional thermodynamic ice-shelf/ocean modeling results and comparison with ice-core records indicate that ice-shelf breakup resulted from combined atmospheric warming and warm ocean currents impinging onto the continental shelf.

  5. Boundary condition of grounding lines prior to collapse, Larsen-B Ice Shelf, Antarctica.

    Science.gov (United States)

    Rebesco, M; Domack, E; Zgur, F; Lavoie, C; Leventer, A; Brachfeld, S; Willmott, V; Halverson, G; Truffer, M; Scambos, T; Smith, J; Pettit, E

    2014-09-12

    Grounding zones, where ice sheets transition between resting on bedrock to full floatation, help regulate ice flow. Exposure of the sea floor by the 2002 Larsen-B Ice Shelf collapse allowed detailed morphologic mapping and sampling of the embayment sea floor. Marine geophysical data collected in 2006 reveal a large, arcuate, complex grounding zone sediment system at the front of Crane Fjord. Radiocarbon-constrained chronologies from marine sediment cores indicate loss of ice contact with the bed at this site about 12,000 years ago. Previous studies and morphologic mapping of the fjord suggest that the Crane Glacier grounding zone was well within the fjord before 2002 and did not retreat further until after the ice shelf collapse. This implies that the 2002 Larsen-B Ice Shelf collapse likely was a response to surface warming rather than to grounding zone instability, strengthening the idea that surface processes controlled the disintegration of the Larsen Ice Shelf.

  6. Creep deformation and buttressing capacity of damaged ice shelves: theory and application to Larsen C ice shelf

    Directory of Open Access Journals (Sweden)

    C. P. Borstad

    2013-07-01

    Full Text Available Around the perimeter of Antarctica, much of the ice sheet discharges to the ocean through floating ice shelves. The buttressing provided by ice shelves is critical for modulating the flux of ice into the ocean, and the presently observed thinning of ice shelves is believed to be reducing their buttressing capacity and contributing to the acceleration and thinning of the grounded ice sheet. However, relatively little attention has been paid to the role that fractures play in the flow and stability of ice shelves and their capacity to buttress the flow of grounded ice. Here, we develop an analytical framework for describing the role that fractures play in the creep deformation and buttressing capacity of ice shelves. We apply principles of continuum damage mechanics to derive a new analytical relation for the creep of an ice shelf as a function of ice thickness, temperature, material properties, resistive backstress and damage. By combining this analytical theory with an inverse method solution for the spatial rheology of an ice shelf, both backstress and damage can be calculated. We demonstrate the applicability of this new theory using satellite remote sensing and Operation IceBridge data for the Larsen C ice shelf, finding damage associated with known crevasses and rifts. We find that increasing thickness of mélange between rift flanks correlates with decreasing damage, with some rifts deforming coherently with the ice shelf as if completely healed. We quantify the stabilizing backstress caused by ice rises and lateral confinement, finding high backstress associated with two ice rises that likely stabilize the ice front in its current configuration. Though overall the ice shelf appears stable at present, the ice in contact with the Bawden ice rise is weakened by fractures, and additional damage or thinning in this area could portend significant change for the shelf. Using this new approach, field and remote sensing data can be utilized to

  7. The relevance of buttressing for Filchner-Ronne and Ross Ice Shelf

    Science.gov (United States)

    Reese, Ronja; Gudmundsson, Hilmar; Levermann, Anders; Winkelmann, Ricarda

    2016-04-01

    Sub-shelf melting is an important component of Antarctica's mass budget. Although thinning of ice shelves does not directly contribute to sea-level rise, it may have a significant indirect impact through the potential of ice shelves to buttress their adjacent ice sheet. This is clearly seen in recent observations, e.g. in the Amundsen region (Pritchard et al., 2012) or at the Southern Antarctic Peninsula (Wouters et al, 2015) where increased ice loss of the adjacent upstream drainage basins is attributed to enhanced sub-shelf melting. In the extreme case, the complete disintegration of an ice shelf, e.g. during the calving events of Larsen A and B in 1995 and 2002, respectively, the adjacent ice streams subsequently accelerated significantly (Scambos et al., 2014). Here, we investigate the importance of buttressing using the finite-element, shallow-stream approximation numerical model Úa. We derive transfer functions for an idealized setup (Gudmundsson et al. 2012) and the Filchner-Ronne and Ross Ice Shelf. They allow for the computation of instantaneous changes in velocities to thickness perturbation patterns. Based on the transfer functions, we calculate the sensitivity of flux across the grounding line to regional varying melting patterns for the idealized setup and for Filchner-Ronne and Ross Ice Shelf. We find that the immediate response of velocities in the ice shelf-ice sheet system to changes in sub-shelf melting can be understood as the interaction of two effects: On the one hand, the spreading rate is a function of local ice thickness, indicating that a thinning of the ice shelf reduces velocities. On the other hand, ice shelf thinning weakens its ability to buttress, and thus enhances velocities. These two processes compete, leading to a complex pattern of velocity changes within the ice shelf. We find - both in the idealized setup and for Ross and Filchner-Ronne Ice Shelves - that the reduction in buttressing is dominating the velocity changes in the

  8. A constitutive framework for predicting weakening and reduced buttressing of ice shelves based on observations of the progressive deterioration of the remnant Larsen B Ice Shelf

    Science.gov (United States)

    Borstad, Chris; Khazendar, Ala; Scheuchl, Bernd; Morlighem, Mathieu; Larour, Eric; Rignot, Eric

    2016-03-01

    The increasing contribution of the Antarctic Ice Sheet to sea level rise is linked to reductions in ice shelf buttressing, driven in large part by basal melting of ice shelves. These ocean-driven buttressing losses are being compounded as ice shelves weaken and fracture. To date, model projections of ice sheet evolution have not accounted for weakening ice shelves. Here we present the first constitutive framework for ice deformation that explicitly includes mechanical weakening, based on observations of the progressive degradation of the remnant Larsen B Ice Shelf from 2000 to 2015. We implement this framework in an ice sheet model and are able to reproduce most of the observed weakening of the ice shelf. In addition to predicting ice shelf weakening and reduced buttressing, this new framework opens the door for improved understanding and predictions of iceberg calving, meltwater routing and hydrofracture, and ice shelf collapse.

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

    Science.gov (United States)

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

    2015-12-01

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

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

    Science.gov (United States)

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

    2017-04-01

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

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

    Science.gov (United States)

    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.

  12. Structural map of flow variability and propagation behavior in the Ross Ice Shelf

    Science.gov (United States)

    LeDoux, C. M.; Hulbe, C. L.

    2011-12-01

    Fracture geometries in the Ross Ice Shelf, observable using visible band satellite imagery from the MODIS Mosaic of Antarctica (MOA) and the Landsat Image Mosaic of Antarctica (LIMA) provide a unique opportunity to study fracture propagation behavior and discharge variability in the ice streams and outlet glaciers feeding the shelf. Propagation is driven by changes in fracture length, near-field stress conditions, and the material properties of the ice. Changes in ice stream discharge and the development of "sticky spots," in both ice streams and within the shelf, lead to redirection of flow, changes in lateral gradients of ice velocity, and the propagation of fractures in response to changes in near-field stresses. The propagation behaviors most commonly observed in the ice shelf are the growth in the transverse direction of a fracture that formed within a shear zone and mechanical interactions between adjacent fracture tips. We use fracture mechanics theory and remote-sensed imagery to categorize fracture patterns and longitudinal zones of fractured ice in the Ross Ice Shelf. Near current sites of formation, simple fracture geometries and principal stresses are used to illustrate physical processes related to the formation and propagation of fractures. To compute flow lines and principal stresses, we derive a velocity map of the Ross Ice Shelf by merging two velocity datasets using a combination of statistical methods. A structural map of fracture geometries, relict shear margins, and structural boundaries is constructed. Using the ice shelf features, present-day flow lines, and principal stresses, we investigate the manner in which principal stresses affect fracture formation and propagation behavior and the variability of ice stream discharge into the shelf.

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

    Science.gov (United States)

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

    2016-04-01

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

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

    Science.gov (United States)

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

    2011-01-01

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

  15. High basal melting forming a channel at the grounding line of Ross Ice Shelf, Antarctica

    Science.gov (United States)

    Marsh, Oliver J.; Fricker, Helen A.; Siegfried, Matthew R.; Christianson, Knut; Nicholls, Keith W.; Corr, Hugh F. J.; Catania, Ginny

    2016-01-01

    Antarctica's ice shelves are thinning at an increasing rate, affecting their buttressing ability. Channels in the ice shelf base unevenly distribute melting, and their evolution provides insight into changing subglacial and oceanic conditions. Here we used phase-sensitive radar measurements to estimate basal melt rates in a channel beneath the currently stable Ross Ice Shelf. Melt rates of 22.2 ± 0.2 m a-1 (>2500% the overall background rate) were observed 1.7 km seaward of Mercer/Whillans Ice Stream grounding line, close to where subglacial water discharge is expected. Laser altimetry shows a corresponding, steadily deepening surface channel. Two relict channels to the north suggest recent subglacial drainage reorganization beneath Whillans Ice Stream approximately coincident with the shutdown of Kamb Ice Stream. This rapid channel formation implies that shifts in subglacial hydrology may impact ice shelf stability.

  16. Rheology of the Ronne Ice Shelf, Antarctica, Inferred from Satellite Radar Interferometry Data using an Inverse Control Method

    Science.gov (United States)

    Larour, E.; Rignot, E.; Joughin, I.; Aubry, D.

    2005-01-01

    The Antarctic Ice Sheet is surrounded by large floating ice shelves that spread under their own weight into the ocean. Ice shelf rigidity depends on ice temperature and fabrics, and is influenced by ice flow and the delicate balance between bottom and surface accumulation. Here, we use an inverse control method to infer the rigidity of the Ronne Ice Shelf that best matches observations of ice velocity from satellite radar interferometry. Ice rigidity, or flow law parameter B, is shown to vary between 300 and 900 kPa a(sup 1/3). Ice is softer along the side margins due to frictional heating, and harder along the outflow of large glaciers, which advect cold continental ice. Melting at the bottom surface of the ice shelf increases its rigidity, while freezing decreases it. Accurate numerical modelling of ice shelf flow must account for this spatial variability in mechanical characteristics.

  17. Rheology of the Ronne Ice Shelf, Antarctica, Inferred from Satellite Radar Interferometry Data using an Inverse Control Method

    Science.gov (United States)

    Larour, E.; Rignot, E.; Joughin, I.; Aubry, D.

    2005-01-01

    The Antarctic Ice Sheet is surrounded by large floating ice shelves that spread under their own weight into the ocean. Ice shelf rigidity depends on ice temperature and fabrics, and is influenced by ice flow and the delicate balance between bottom and surface accumulation. Here, we use an inverse control method to infer the rigidity of the Ronne Ice Shelf that best matches observations of ice velocity from satellite radar interferometry. Ice rigidity, or flow law parameter B, is shown to vary between 300 and 900 kPa a(sup 1/3). Ice is softer along the side margins due to frictional heating, and harder along the outflow of large glaciers, which advect cold continental ice. Melting at the bottom surface of the ice shelf increases its rigidity, while freezing decreases it. Accurate numerical modelling of ice shelf flow must account for this spatial variability in mechanical characteristics.

  18. Hydrological character and sea-current structure in the front of Amery Ice Shelf

    Institute of Scientific and Technical Information of China (English)

    Chen Hongxia; Pan Zengdi; Jiao Yutian; Xiang Baoqiang

    2005-01-01

    Hydrological character and Sea-current profiles structure are studied and analyzed in sea-area of the front of Amery Ice Shelf, Prydz Bay with LADCP, CTD dana. These LADCP, CTD data were acquired during the 19th Chinese Antarctic Scientific Expedition. Results of this study agree with that, there exist four different kinds of water masses in the area of the front of Amery Ice Shelf in the summer of Antarctica. Current distribution presents a semi-circumfluence which flows in at the east and flows out in the west. Moreover, clockwise andd anti -clockwise vortices were found in upper layer and mid-layer in the Prydz Bay. Western areas of these anticlockwise vortices are positions of inflows from Prydz Bay to Amery Ice Shelf. The source of these inflows is the coastal westward current originated in the east of Prydz Bay. All these characteristics come down to the pattern of circumfluence, ice melt rate under Ice Shelf, scale of Ice Shelf water production and form of water exchanges between area of Ice Shelf and area of Prydz Bay.

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

    Science.gov (United States)

    Mathiot, Pierre; Jenkins, Adrian; Harris, Christopher; Madec, Gurvan

    2017-07-01

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

  20. Larsen C Ice Shelf rheology inferred by combining InSAR observations and numerical modeling

    Science.gov (United States)

    Khazendar, A.; Rignot, E. J.; Larour, E. Y.

    2009-12-01

    Larsen C Ice Shelf presents a valuable setting for investigating the many connected processes involved in the evolution of ice shelves in a warming climate. The stability of this ice shelf has become a topic of keen interest, especially following the disintegration of Larsen B and other Peninsular ice shelves, and the consequent increase in continental ice flow to the ocean. We are addressing this complex question in a multi-disciplinary manner by combining remote sensing and numerical modeling. Thus, we analyzed satellite InSAR observations of Larsen C obtained in the years 2000 and 2007 which revealed that ice shelf flow velocity in some areas have had some changes. We then applied inverse modeling, combining the observed velocity field with numerical flow models, to infer a spatial distribution of the flow parameter for the ice shelf, which is indispensable for accurately modeling ice shelf flow and evolution. The inferred rheology field allowed us to detect zones of weakness, including a large area in the middle of the ice shelf, many of which are associated with fracture features. Our similar previous analysis of Larsen B at the eve of its disintegration in 2002 emphasizes the significant interaction and interdependence among frontal calving, flow acceleration, variable rheology including fracture zones, and the ultimate destabilization of the ice shelf. Therefore, this work, by measuring any recent acceleration in the flow of Larsen C and inferring its rheology provides essential tools to evaluate its stability and long-term prospects. This work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration, Cryospheric Sciences Program.

  1. Boundary condition of grounding lines prior to collapse, Larsen-B Ice Shelf, Antarctica

    OpenAIRE

    Rebesco, M.; Domack, E.; Zgur, F.; Lavoie, C.; Leventer, A.; Brachfeld, S.; Willmott, V.; Halverson, G.; M. Truffer; Scambos, T; Smith, J.; E. Pettit

    2014-01-01

    Grounding zones, where ice sheets transition between resting on bedrock to full floatation, help regulate ice flow. Exposure of the sea floor by the 2002 Larsen-B Ice Shelf collapse allowed detailed morphologic mapping and sampling of the embayment sea floor. Marine geophysical data collected in 2006 reveal a large, arcuate, complex grounding zone sediment system at the front of Crane Fjord. Radiocarbon-constrained chronologies from marine sediment cores indicate loss of ice contact with the ...

  2. Derivation of a numerical solution of the 3D coupled velocity field for an ice sheet – ice shelf system, incorporating both full and approximate stress solutions

    NARCIS (Netherlands)

    Reerink, T.J.; van de Wal, R.S.W.; Borsboom, P.-P.

    2009-01-01

    To overcome the mechanical coupling of an ice sheet with an ice shelf, one single set of velocity equations is presented covering both the sheet and the shelf. This set is obtained by applying shared sheet-shelf approximations. The hydrostatic approximation and a constant density are the only approx

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

    Science.gov (United States)

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

    2013-01-01

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

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

    Science.gov (United States)

    Corti, Giacomo; Zeoli, Antonio

    2016-04-01

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

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

    Directory of Open Access Journals (Sweden)

    P. Mathiot

    2017-07-01

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

  6. Modelling snowdrift sublimation on an Antarctic ice shelf

    Directory of Open Access Journals (Sweden)

    J. T. M. Lenaerts

    2010-05-01

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

  7. Coupling a thermodynamically active ice shelf to a regional simulation of the Weddell Sea

    Directory of Open Access Journals (Sweden)

    V. Meccia

    2013-08-01

    Full Text Available A thermodynamically interactive ice shelf cavity parameterization is coupled to the Regional Ocean Model System (ROMS and is applied to the Southern Ocean domain with enhanced resolution in the Weddell Sea. This implementation is tested in order to assess its degree of improvement to the hydrography (and circulation of the Weddell Sea. Results show that the inclusion of ice shelf cavities in the model is feasible and somewhat realistic (considering the lack of under-ice observations for validation. Ice shelf–ocean interactions are an important process to be considered in order to obtain realistic hydrographic values under the ice shelf. The model framework presented in this work is a promising tool for analyzing the Southern Ocean's response to future climate change scenarios.

  8. Kinematic first-order calving law implies potential for abrupt ice-shelf retreat

    Science.gov (United States)

    Levermann, A.; Albrecht, T.; Winkelmann, R.; Martin, M. A.; Haseloff, M.; Joughin, I. R.

    2012-12-01

    Recently observed large-scale disintegration of Antarctic ice shelves has moved their fronts closer towards grounded ice. In response, ice-sheet discharge into the ocean has accelerated, contributing to global sea-level rise and emphasizing the importance of calving-front dynamics. The position of the ice front strongly influences the stress field within the entire sheet-shelf-system and thereby the mass flow across the grounding line. While theories for an advance of the ice-front are readily available, no general rule exists for its retreat, making it difficult to incorporate the retreat in predictive models. Here we extract the first-order large-scale kinematic contribution to calving which is consistent with large-scale observation. We emphasize that the proposed equation does not constitute a comprehensive calving law but represents the first-order kinematic contribution which can and should be complemented by higher order contributions as well as the influence of potentially heterogeneous material properties of the ice. When applied as a calving law, the equation naturally incorporates the stabilizing effect of pinning points and inhibits ice shelf growth outside of embayments. It depends only on local ice properties which are, however, determined by the full topography of the ice shelf. In numerical simulations the parameterization reproduces multiple stable fronts as observed for the Larsen A and B Ice Shelves including abrupt transitions between them which may be caused by localized ice weaknesses. We also find multiple stable states of the Ross Ice Shelf at the gateway of the West Antarctic Ice Sheet with back stresses onto the sheet reduced by up to 90% compared to the present state. Eigencalving: Universal kinematic contribution to iceberg calving of ice shelves. Calving rate C is proportional to the eigenvalues of the horizontal spreading rate tensor.

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

    Science.gov (United States)

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

    2016-04-01

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

  10. Dynamics and Mass Balance of Riiser-Larsen Ice Shelf, Antarctica, and its Drainage Area

    Science.gov (United States)

    Klauke, S.; Oelke, C.; Kleiner, T.; Lange, M. A.; Baessler, M.; Dietrich, R.

    2006-12-01

    A coupled finite difference ice sheet/ice shelf model is used to investigate the flow regime of Riiser-Larsen ice shelf, Eastern Weddell Sea, Antarctica, and its drainage area. The model takes into account higher order terms that are neglected in the popular shallow ice approximation. The modeled region has a total area of roughly 130 · 103 km2. The model grid consists of 2.5 km × 2.5 km cells horizontally, and of 10 sigma layers vertically. As input data for the simulation, a new DEM is derived mainly from recent ICESat/GLAS laser-altimetry data. In the ice sheet part of the modeled area, ice thickness data are taken from the BEDMAP data set. For the ice shelf, the thickness distribution is computed from the DEM by assuming isostatic equilibrium. For this purpose, vertical density variations inside the ice shelf are derived by comparison of GLAS altimetry data with airborne RES ice thickness measurements from the EPICA mission. The modeled ice flow velocity is compared with interferometrically derived surface flow velocities from ERS-SAR scenes of the ice sheet and with published in-situ measurements of the ice shelf. In order to minimize the difference between modeled and measured velocities, the boundary conditions and free parameters of the flow model are adjusted. The boundary condition at the ice-rock interface turns out to play a crucial role in optimizing the agreement. Thus, the basal sliding velocity of the ice body is calculated from the basal temperature and the basal shear stress following a widely used relation originally proposed by Weertman, and by adjusting its parameters. In the ice shelf, the viscosity of the ice is used as a tuning parameter and is adjusted to maximize the agreement with in-situ measurements. From the result of the simulation with an optimal set of parameters a mass flow over the grounding line of roughly 2 · 1013 kg yr-1 is derived. The comparison with published surface accumulation data suggests a stable mass balance for

  11. Icepod Plus Potential Field: An Integrated Approach For Understanding Ice Shelf Processes

    Science.gov (United States)

    Frearson, N.

    2015-12-01

    Warm water flowing beneath the large floating ice shelves in Antarctica will play an important role in how fast sea level rises. The lack of detailed bathymetry beneath the large ice shelves and lack of understanding of their internal structure inherently limits our knowledge of how ice shelves will thin and collapse. Understanding the bathymetry beneath the remaining ice shelves is critical to understanding how ice shelves will thin in the future and how that will impact the flux of ice into the global ocean. The Ross Ice Shelf, the largest ice shelf remaining on our planet, buttresses the West Antarctic Ice Sheet. The bathymetry beneath the Ross Ice Shelf is the least explored piece of ocean floor on our planet. The IcePod is a compact integrated ice imaging system developed for use on any C-130 aircraft developed with NSF support. The initial development program was targeted towards investigating glacial and ice-sheet processes. In this program, deep and shallow ice radars were developed. Optical instruments, including a scanning laser, Infra-red camera and visible wave camera were integrated into the pod. We have expanded the IcePod instrument suite to include the potential field measurements of magnetic and gravity anomalies with support from the Moore Foundation. During the development, a total field cesium sensor magnetometer and 3-axis fluxgate from previously funded work were also incorporated into the pod. Their behavioral response to being located close to high-frequency electronics, power supplies and metallic objects were studied. We describe in part some of that development process and the positive findings that resulted. The Icepod group is also actively pursuing the development, modification and incorporation of a new gravimeter into the suite of instruments available to the program and is investigating reduction in size of this that may eventually lead to incorporating the gravimeter into the pod itself. As part of this program we are also

  12. Persistent Surface River on Nansen Ice Shelf Drains Meltwater Preventing Collapse for Decades

    Science.gov (United States)

    Bell, R. E.; Chu, W.; Kingslake, J.; Das, I.; Tedesco, M.; Tinto, K. J.; Zappa, C. J.; Frezzotti, M.

    2016-12-01

    Meltwater ponding on the surface of Antarctic ice shelves has been advanced as the trigger for their collapse through loading and hydrofracturing. While ponding was associated with the Larsen B Ice Shelf collapse, draining meltwater off an ice shelf could limit the destructive role of increasing surface melt in the future. In this regard, we present the first evidence of the presence and evolution of a persistent active network of streams, ponds, and rivers on the Nansen Ice Shelf, Antarctica. This active drainage system has delivered meltwater into the Ross Sea since at least 1908, reducing the volume of water seasonally stored on the ice surface and protecting the ice shelf from collapsing. We integrated early 20th century observations with modern airborne and satellite imagery to identify three distinct surface hydrology systems on the Nansen Ice Shelf. Near the calving front, surface meltwater coalesces into surface streams and ponds that grow over days to weeks, eventually connecting to a shear margin river that drains at a large waterfall into the Ross Sea. Between 1989 and 2016, the shear margin river drained into a rift associated with a large calving event in 2016. The second system forms close to the grounding line where surface meltwater drains into regions of rifted mélange, possibly explaining the low salinity of the ice drilled in these regions. This surface meltwater is injected into the ice shelf cavity through the mélange and may foster basal melting beneath the shear margins. The third system develops on the steeper Priestly Glacier flow where surface melt is produced adjacent to exposed bedrock and moraines and then is transported by surface streams that terminate in firn-covered regions. Ice shelf hydrology is spatially complex, sensitive to glaciological and climatic conditions, and evolves seasonally. Surface streams that coalesce melt and rivers that export water off the ice shelf will limit the damage from ponding-induced hydrofracturing

  13. Marine ice sheet model performance depends on basal sliding physics and sub-shelf melting

    Science.gov (United States)

    Gladstone, Rupert Michael; Warner, Roland Charles; Galton-Fenzi, Benjamin Keith; Gagliardini, Olivier; Zwinger, Thomas; Greve, Ralf

    2017-01-01

    Computer models are necessary for understanding and predicting marine ice sheet behaviour. However, there is uncertainty over implementation of physical processes at the ice base, both for grounded and floating glacial ice. Here we implement several sliding relations in a marine ice sheet flow-line model accounting for all stress components and demonstrate that model resolution requirements are strongly dependent on both the choice of basal sliding relation and the spatial distribution of ice shelf basal melting.Sliding relations that reduce the magnitude of the step change in basal drag from grounded ice to floating ice (where basal drag is set to zero) show reduced dependence on resolution compared to a commonly used relation, in which basal drag is purely a power law function of basal ice velocity. Sliding relations in which basal drag goes smoothly to zero as the grounding line is approached from inland (due to a physically motivated incorporation of effective pressure at the bed) provide further reduction in resolution dependence.A similar issue is found with the imposition of basal melt under the floating part of the ice shelf: melt parameterisations that reduce the abruptness of change in basal melting from grounded ice (where basal melt is set to zero) to floating ice provide improved convergence with resolution compared to parameterisations in which high melt occurs adjacent to the grounding line.Thus physical processes, such as sub-glacial outflow (which could cause high melt near the grounding line), impact on capability to simulate marine ice sheets. If there exists an abrupt change across the grounding line in either basal drag or basal melting, then high resolution will be required to solve the problem. However, the plausible combination of a physical dependency of basal drag on effective pressure, and the possibility of low ice shelf basal melt rates next to the grounding line, may mean that some marine ice sheet systems can be reliably simulated at

  14. Bimodal pattern of seismicity detected at the ocean margin of an Antarctic ice shelf

    Science.gov (United States)

    Lombardi, Denis; Benoit, Lionel; Camelbeeck, Thierry; Martin, Olivier; Meynard, Christophe; Thom, Christian

    2016-08-01

    In Antarctica, locally grounded ice, such as ice rises bordering floating ice shelves, plays a major role in the ice mass balance as it stabilizes the ice sheet flow from the hinterland. When in direct contact with the ocean, the ice rise buttressing effect may be altered in response of changing ocean forcing. To investigate this vulnerable zone, four sites near the boundary of an ice shelf with an ice rise promontory in Dronning Maud Land, East-Antarctica were monitored for a month in early 2014 with new instruments that include both seismic and GPS sensors. Our study indicated that this transition zone experiences periodic seismic activity resulting from surface crevassing during oceanic tide-induced flexure of the ice shelf. The most significant finding is the observation of apparent fortnightly tide-modulated low-frequency, long-duration seismic events at the seaward front of the ice rise promontory. A basal origin of these events is postulated with the ocean water surge at each new spring tide triggering basal crevassing or basal slip on a local bedrock asperity. Detection and monitoring of such seismicity may help identifying ice rise zones vulnerable to intensified ocean forcing.

  15. Ocean heat drives rapid basal melt of the Totten Ice Shelf.

    Science.gov (United States)

    Rintoul, Stephen Rich; Silvano, Alessandro; Pena-Molino, Beatriz; van Wijk, Esmee; Rosenberg, Mark; Greenbaum, Jamin Stevens; Blankenship, Donald D

    2016-12-01

    Mass loss from the West Antarctic ice shelves and glaciers has been linked to basal melt by ocean heat flux. The Totten Ice Shelf in East Antarctica, which buttresses a marine-based ice sheet with a volume equivalent to at least 3.5 m of global sea-level rise, also experiences rapid basal melt, but the role of ocean forcing was not known because of a lack of observations near the ice shelf. Observations from the Totten calving front confirm that (0.22 ± 0.07) × 10(6) m(3) s(-1) of warm water enters the cavity through a newly discovered deep channel. The ocean heat transport into the cavity is sufficient to support the large basal melt rates inferred from glaciological observations. Change in ocean heat flux is a plausible physical mechanism to explain past and projected changes in this sector of the East Antarctic Ice Sheet and its contribution to sea level.

  16. New evidence for ice shelf flow across the Alaska and Beaufort margins, Arctic Ocean

    Science.gov (United States)

    Engels, Jennifer L.

    The Arctic Ocean may act as a lynchpin for global climate change due to its unique physiography as a mediterranean sea located in polar latitudes. In our modern warming climate, debate over the bounds of natural versus anthropogenically-induced climate variability necessitates a comprehensive understanding of Arctic ice extent and configuration over the last interglacial cycle. Longstanding controversy exists as to the volume, timing, and flow trajectories of ice in the Arctic Ocean during glacial maxima when continental ice sheets mantled circum-arctic landmasses. As a result of the Science Ice Exercise surveys of the Arctic Ocean in 1999, new evidence for ice grounding at depths down to 980 m on the Lomonosov Ridge and 750 m on the Chukchi Borderland indicates the likelihood that large ice shelves flowed into the ocean from both the Barents/Kara Sea and the Canadian Arctic Archipelago or eastern Alaska. Sidescan imagery of ˜14100 km2 of seafloor along the Alaska and Beaufort margins in water depths from 250--2800 m maps a repetitive association of recognizable sub-glacially generated bedforms, ice carved-bathymerry, and ice-marginal turbidite gullies over a 640 km stretch of the margin between Point Barrow and the MacKenzie River delta. Glaciogenic bedforms occur across the surface of a flattened bathymetric bench or 'second shelf break' that is interpreted to have been formed by an ice shelf eroding the continental slope. The glacial geology of surrounding areas suggests that an ice shelf on the Alaska and Beaufort margins likely flowed from the mouths of overdeepened glacial troughs in the Canadian Arctic Archipelago westward and across the Chukchi Borderland due to an obstruction in the central Canadian basin. Evidence for an ice shelf along the Alaska and Beaufort margins supports an expanded interpretation of ice volume and extent during Pleistocene glacial periods. This has far-reaching implications for Arctic climate studies, ocean circulation, sediment

  17. Ice-shelf height variability in Amundsen Sea linked to ENSO

    Science.gov (United States)

    Paolo, Fernando; Fricker, Helen; Padman, Laurie

    2016-04-01

    Atmospheric and sea-ice conditions around Antarctica, particularly in the Amundsen and Bellingshausen seas, respond to climate dynamics in the tropical Pacific Ocean on interannual time scales including the El Nino-Southern Oscillation (ENSO). It has been hypothesized that the mass balance of the Antarctic Ice Sheet, including its floating ice shelves, also responds to this climate signal; however, this has not yet been unambiguously demonstrated. We apply multivariate singular spectrum analysis (MSSA) to 18-year (1994-2012) time series of ice-shelf height derived from satellite radar altimetry in the Amundsen Sea (AS) region. This advanced spectral method distinguishes between regular deterministic behavior ("cycles") at sub-decadal time scale and irregular behavior ("noise") at shorter time scales. Although the long-term trends in ice-shelf height change are much larger than the range of interannual variability in the AS region, the short-term rate of change dh/dt can vary about the trend by more than 50%. We extract the principal modes of variability (EOFs) based on common spectral properties from a set of 140 height time series. The mode of interannual variability in the AS ice-shelf height is strongly correlated with the low-frequency mode of ENSO (periodicity of ~4.5 years) as represented by the Southern Oscillation Index. This interannual mode in ice-shelf height, represented by the two leading EOFs, is responsible for about 25% of the variance in the de-trended data set. The ice-shelf height in the AS is expected to respond to changes in precipitation and inflows of warm subsurface Circumpolar Deep Water (CDW) into the ocean cavities under the ice shelves, altering basal melt rates. While we find a correlation between modeled precipitation anomalies and ice-shelf height, we are investigating (a) errors in model precipitation, (b) radar backscatter and firn-density issues, and (c) ocean contribution correlated with atmosphere through wind-stress forcing. We

  18. Response to Filchner-Ronne Ice Shelf cavity warming in a coupled ocean-ice sheet model - Part 1: The ocean perspective

    Science.gov (United States)

    Timmermann, Ralph; Goeller, Sebastian

    2017-09-01

    The Regional Antarctic ice and Global Ocean (RAnGO) model has been developed to study the interaction between the world ocean and the Antarctic ice sheet. The coupled model is based on a global implementation of the Finite Element Sea-ice Ocean Model (FESOM) with a mesh refinement in the Southern Ocean, particularly in its marginal seas and in the sub-ice-shelf cavities. The cryosphere is represented by a regional setup of the ice flow model RIMBAY comprising the Filchner-Ronne Ice Shelf and the grounded ice in its catchment area up to the ice divides. At the base of the RIMBAY ice shelf, melt rates from FESOM's ice-shelf component are supplied. RIMBAY returns ice thickness and the position of the grounding line. The ocean model uses a pre-computed mesh to allow for an easy adjustment of the model domain to a varying cavity geometry. RAnGO simulations with a 20th-century climate forcing yield realistic basal melt rates and a quasi-stable grounding line position close to the presently observed state. In a centennial-scale warm-water-inflow scenario, the model suggests a substantial thinning of the ice shelf and a local retreat of the grounding line. The potentially negative feedback from ice-shelf thinning through a rising in situ freezing temperature is more than outweighed by the increasing water column thickness in the deepest parts of the cavity. Compared to a control simulation with fixed ice-shelf geometry, the coupled model thus yields a slightly stronger increase in ice-shelf basal melt rates.

  19. Evolution of basal crevasses links ice shelf stability to ocean forcing

    Science.gov (United States)

    Bassis, J. N.; Ma, Y.

    2015-01-01

    Iceberg calving is one of the primary mechanisms responsible for transferring ice from the Antarctic ice shelves to the ocean, but remains poorly understood. Previous theories of calving have sought to explain the calving process as a brittle phenomenon that occurs rapidly when surface or basal crevasses penetrate the entire ice thickness. Here we show that the strain-rate-weakening nature of ice permits initially narrow basal crevasses to seed an instability that gives rise to locally enhanced ductile deformation and thinning over length scales that are large compared to the ice thickness. This ductile failure process, called necking, amplifies long wavelength features of bottom topography and allows basal crevasses to penetrate an increasing fraction of the ice thickness as they advect downstream. Application of the model to the four largest Antarctic ice shelves shows that necking occurs downstream of pinning points and sharp protrusions in the ice shelf embayment where stress is highly concentrated. However, model predictions are sensitive to assumptions about basal melting and refreezing within crevasses, suggesting that the combination of mechanical instability and ice-ocean interaction on the scale of an individual crevasse may play a leading role in controlling ice shelf stability.

  20. Thermohaline structure inhomogeneity associated with polynia at the northern margin of Emery Ice-shelf

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Based on the hydrographic data in austral summer during the 22nd Antarctic Expedition of China (2005/2006), some features can be found about the northern margin of Emery ice shelf as follows. The heat content in the surface layer(0-50 m) at the eastern end and the western end of the ice-shelf margin is much higher than that at the middle. The upper mixing-layer depth and the seasonal thermocline depth at the middle of the ice-shelf northern margin are much shallower than those at the both ends. However there is much less difference between the middle and the ends in the bottom layer. The remote sensing photos show that the inhomogeneity in the surface-layer water is closely related to the spatial distribution of the floes and polynia in the area.

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

    Science.gov (United States)

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

    2016-11-01

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

  2. Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier.

    Science.gov (United States)

    Smith, J A; Andersen, T J; Shortt, M; Gaffney, A M; Truffer, M; Stanton, T P; Bindschadler, R; Dutrieux, P; Jenkins, A; Hillenbrand, C-D; Ehrmann, W; Corr, H F J; Farley, N; Crowhurst, S; Vaughan, D G

    2017-01-05

    The West Antarctic Ice Sheet is one of the largest potential sources of rising sea levels. Over the past 40 years, glaciers flowing into the Amundsen Sea sector of the ice sheet have thinned at an accelerating rate, and several numerical models suggest that unstable and irreversible retreat of the grounding line-which marks the boundary between grounded ice and floating ice shelf-is underway. Understanding this recent retreat requires a detailed knowledge of grounding-line history, but the locations of the grounding line before the advent of satellite monitoring in the 1990s are poorly dated. In particular, a history of grounding-line retreat is required to understand the relative roles of contemporaneous ocean-forced change and of ongoing glacier response to an earlier perturbation in driving ice-sheet loss. Here we show that the present thinning and retreat of Pine Island Glacier in West Antarctica is part of a climatically forced trend that was triggered in the 1940s. Our conclusions arise from analysis of sediment cores recovered beneath the floating Pine Island Glacier ice shelf, and constrain the date at which the grounding line retreated from a prominent seafloor ridge. We find that incursion of marine water beyond the crest of this ridge, forming an ocean cavity beneath the ice shelf, occurred in 1945 (±12 years); final ungrounding of the ice shelf from the ridge occurred in 1970 (±4 years). The initial opening of this ocean cavity followed a period of strong warming of West Antarctica, associated with El Niño activity. Thus our results suggest that, even when climate forcing weakened, ice-sheet retreat continued.

  3. Ice shelf breaking and increase velocity of glacier: the view from analogue experiment

    Science.gov (United States)

    Corti, Giacomo; Iandelli, Irene

    2013-04-01

    Collapse of the Larsen II platform during the late 90s has generated an increase in velocity if ice sheet discharge, highlighting that these processes may strongly destabilize large ice masses speeding up the plateau discharge toward the sea. Parameters such as ice thickness, valley width and slope, ice pack dimensions may contribute to modulate the effect of increase in ice flow velocity following the removal of ice. We analyze this process through scale analogue models, aimed at reproducing the flow of ice from a plateau into the sea through a narrow valley. The ice is reproduced with a transparent silicone (Polydimethisiloxane), flowing at velocities of a few centimeters per hour and simulating natural velocities in the range of a few meters per year. Having almost the same density of the ice, PDMS floats on water and simulate the ice-shelf formation. Results of preliminary experimental series support that this methodology is able to reasonably reproduce the process and support a significant increase in velocity discharge following the removal of ice pack. Additional tests are designed to verify the influence of the above-mentioned parameters on the increase in ice velocity.

  4. Competing connections between the Ross Ice Shelf with the Southern Ocean.

    Science.gov (United States)

    Jendersie, Stefan

    2016-04-01

    The stability of the Ross Ice Shelf (RIS) is critical to both the East Antarctic Ice Sheet, and the West Antarctic Ice Sheet. Results from a climatological ice shelf-ocean coupled numerical model (ROMS) suggest a new circulation mechanism associated with High Salinity Water (HSSW) production in the Ross Sea Polynya (RSP) that controls oceanic heat access to the RIS cavity. Within the RSP the dense water-saturated water column contracts during winter and causes a seasonal drop in Sea Surface Height (SSH) localised to a convection chimney under the RSP. The SSH gradients of up to 1.5 mm per km are sufficient to generate a barotropic pressure gradient that can counteract the wide scale horizontal baroclinic force and reverse the geostrophic circulation. In water depths between 600 and 800 m north of the western RIS the effect causes the seasonal occurrence of a cyclonic circulation cell with transports greater than 1Sv. Appearing with the beginning of winter sea ice formation in the RSP it significantly changes the dynamics at the ice shelf front. The new mechanism is described as one element in a framework of oceanographic processes that mitigate the exchange between the deep ocean and the ocean cavity under the RIS. Our study links local circulation features that are known from observation and previous model studies, and for the first time establishes a coherent system of responsible physical forcing processes in the Ross Sea.​

  5. Ice-shelf collapse from subsurface warming as a trigger for Heinrich events.

    Science.gov (United States)

    Marcott, Shaun A; Clark, Peter U; Padman, Laurie; Klinkhammer, Gary P; Springer, Scott R; Liu, Zhengyu; Otto-Bliesner, Bette L; Carlson, Anders E; Ungerer, Andy; Padman, June; He, Feng; Cheng, Jun; Schmittner, Andreas

    2011-08-16

    Episodic iceberg-discharge events from the Hudson Strait Ice Stream (HSIS) of the Laurentide Ice Sheet, referred to as Heinrich events, are commonly attributed to internal ice-sheet instabilities, but their systematic occurrence at the culmination of a large reduction in the Atlantic meridional overturning circulation (AMOC) indicates a climate control. We report Mg/Ca data on benthic foraminifera from an intermediate-depth site in the northwest Atlantic and results from a climate-model simulation that reveal basin-wide subsurface warming at the same time as large reductions in the AMOC, with temperature increasing by approximately 2 °C over a 1-2 kyr interval prior to a Heinrich event. In simulations with an ocean model coupled to a thermodynamically active ice shelf, the increase in subsurface temperature increases basal melt rate under an ice shelf fronting the HSIS by a factor of approximately 6. By analogy with recent observations in Antarctica, the resulting ice-shelf loss and attendant HSIS acceleration would produce a Heinrich event.

  6. The seasonal appearance of ice shelf water in coastal Antarctica and its effect on sea ice growth

    Science.gov (United States)

    Mahoney, Andrew R.; Gough, Alexander J.; Langhorne, Patricia J.; Robinson, Natalie J.; Stevens, Craig L.; Williams, Michael M. J.; Haskell, Timothy G.

    2011-11-01

    In this paper we report measurements from the first year-round mooring underneath sea ice in McMurdo Sound, Antarctica, which we combine with full-depth ocean profiles to identify the incremental appearance of potentially supercooled ice shelf water (ISW). We investigate the effects of ISW on sea ice using observations of sea ice growth and crystal structure together with under-ice photography. We show that the appearance of ISW at the surface leads to a disruption in the columnar texture of the sea ice, but that persistent growth enhancement occurs only once the entire water column has cooled to the surface freezing point. In doing so, we demonstrate the possibility of inferring the presence of ISW beneath sea ice through crystallographic analysis of cores. These findings will be useful for both modeling and observing the extent of ISW-enhanced ice growth. In addition, we found that the local growth of first-year landfast sea ice only accounted for half of the observed increase in salinity over the water column, which indicates that polynyas are responsible for approximately half of the salt flux into McMurdo Sound.

  7. Thermohaline circulation below the Ross Ice Shelf - A consequence of tidally induced vertical mixing and basal melting

    Science.gov (United States)

    Macayeal, D. R.

    1984-01-01

    The warmest water below parts of the Ross Ice Shelf resides in the lowest portion of the water column because of its high salinity. Vertical mixing caused by tidal stirring can thus induce ablation by lifting the warm but dense water into contact with the ice shelf. A numerical tidal simulation indicates that vertically well-mixed conditions predominate in the southeastern part of the sub-ice shelf cavity, where the water column thickness is small. Basal melting in this region is expected to be between 0.05 and 0.5 m/yr and will drive a thermohaline circulation having the following characteristics: high salinity shelf water (at - 1.8 C), formed by winter sea ice production in the open Ross Sea, flows along the seabed toward the tidal mixing fronts below the ice shelf; and meltwater (at -2.2 C), produced in the well-mixed region, flows out of the sub-ice shelf cavity along the ice shelf bottom. Sensitivity of this ablation process to climatic change is expected to be small because high salinity shelf water is constrained to have the sea surface freezing temperature.

  8. Observed vulnerability of Filchner-Ronne Ice Shelf to wind-driven inflow of warm deep water

    Science.gov (United States)

    Darelius, E.; Fer, I.; Nicholls, K. W.

    2016-08-01

    The average rate of melting at the base of the large Filchner-Ronne Ice Shelf in the southern Weddell Sea is currently low, but projected to increase dramatically within the next century. In a model study, melt rates increase as changing ice conditions cause a redirection of a coastal current, bringing warm water of open ocean origin through the Filchner Depression and into the Filchner Ice Shelf cavity. Here we present observations from near Filchner Ice Shelf and from the Filchner Depression, which show that pulses of warm water already arrive as far south as the ice front. This southward heat transport follows the eastern flank of the Filchner Depression and is found to be directly linked to the strength of a wind-driven coastal current. Our observations emphasize the potential sensitivity of Filchner-Ronne Ice Shelf melt rates to changes in wind forcing.

  9. Crevasse Extent and Lateral Shearing of the McMurdo Shear Zone, Antarctica: Implications of Ice Shelf Stability

    Science.gov (United States)

    Kaluzienski, L. M.; Hamilton, G. S.; Koons, P. O.; Enderlin, E. M.; Arcone, S. A.; Borstad, C.; Walker, B.

    2016-12-01

    Antarctica's ice shelves modulate the flow of inland ice towards the ocean. Understanding the controls on ice-shelf stability is critical for predicting the future evolution of the ice sheet. For the western sector of the Ross Ice Shelf (RIS), a potentially important region of lateral resistance is the McMurdo Shear Zone (MSZ) just downstream of Minna Bluff. Here the fast-moving Ross Ice Shelf ( 450 m/yr) shears past the slower-moving McMurdo Ice Shelf ( 200 m/yr) creating a zone of intense crevassing. An analysis of several satellite image datasets including a high-resolution digital elevation model (DEM) extracted from stereo Worldview imagery suggests that many of these flow features originate as the RIS flows past Minna Bluff. Here we present a sensitivity analysis of RIS ice flow using the Ice Sheet System Model (ISSM) (Larour et al. 2012) and the Design Analysis Kit for Optimization and Terascale Applications (DAKOTA). In this analysis we assess the sensitivity of model flow of RIS tributary glaciers to boundary condition perturbations within the Minna Bluff/MSZ region. Perturbations include ice shelf thickness variations as well as a scalar damage variable that quantifies the loss of load-bearing surface area due to ice shelf fracture. Field observations of surface flow and strain (GPS) and crevasse distribution and geometry (GPR)in the MSZ help constrain the model simulations. Initial results point to the importance of sub-ice shelf topography and its interaction with features such as Minna Bluff in determining stress distribution on the western RIS. Larour, E.; Seroussi, H.; Morlighem, M.; Rignot, E. 2012. Continental scale, high order, high spatial resolution, ice sheet modeling using the Ice Sheet System Model (ISSM), Journal of Geophysical Research

  10. Dating ice shelf edge marine sediments: A new approach using single-grain quartz luminescence

    DEFF Research Database (Denmark)

    Berger, G.W.; Murray, A.S.; Thomsen, Kristina Jørkov

    2010-01-01

    To develop an alternative dating tool for the Antarctic Peninsula (where the 14C method requires large, spatially variable reservoir corrections), we tested the clock-zeroing assumption of photon-stimulated luminescence (PSL) dating using a variety of PSL procedures. At ice shelf edges around...

  11. Geophysical Survey of McMurdo Ice Shelf to Determine Infrastructure Stability and for Future Planning

    Science.gov (United States)

    2017-01-01

    fieldwork with field assistance provided by Stephen Zellerhoff, Marie McLane, Paul Koubek, Jonathan White, Laura Gerwin, Michael Pfalmer, and Ester...Jansen, B. Kulessa, E. C. King , P. Sammonds, and D.I. Benn. 2012. Basal Crevasses in Larsen C Ice Shelf and Implications for Their Global Abundance

  12. The Effect of Ice Shelf Meltwater on Antarctic Sea Ice and the Southern Ocean in an Earth System Model

    Science.gov (United States)

    Pauling, A.; Bitz, C. M.; Smith, I.; Langhorne, P.

    2015-12-01

    It has been suggested that recent Antarctic sea ice expansion resulted from an increase in fresh water reaching the Southern Ocean. This presentation investigates this conjecture in an Earth System Model. The freshwater flux from ice sheet and ice shelf mass imbalance is largely missing in models that participated in the Fifth Coupled Model Intercomparison Project (CMIP5). However, CMIP5 models do account for the fresh water from precipitation minus evaporation (P-E). On average in CMIP5 models P- E reaching the Southern Ocean has increased to a present value of about 2600 Gt yr-1 greater than pre-industrial times and 3-8 times larger than estimates of the mass imbalance of Antarctic ice sheets and shelves. Two sets of model experiments were conducted from 1980-2013 in CESM1-CAM5 artificially distributing fresh water either at the ocean surface according to an estimate of iceberg melt, or at the ice shelf fronts at depth. An anomalous reduction in vertical advection of heat into the surface mixed layer resulted in sea surface cooling at high southern latitudes, and an associated increase in sea ice area. A freshwater enhancement of 1780 Gt yr-1 (approximately 1.3 times either present day basal melt or iceberg calving freshwater fluxes) raised the sea ice total area by 1×106 km2. Yet, even a freshwater enhancement up to 2670 Gt yr-1 was insufficient to offset the sea ice decline due to anthropogenic forcing for any period of 20 years or longer. Further, the sea ice response was found to be insensitive to the depth of fresh water injection.

  13. Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier

    Science.gov (United States)

    Smith, J. A.; Andersen, T. J.; Shortt, M.; Gaffney, A. M.; Truffer, M.; Stanton, T. P.; Bindschadler, R.; Dutrieux, P.; Jenkins, A.; Hillenbrand, C.-D.; Ehrmann, W.; Corr, H. F. J.; Farley, N.; Crowhurst, S.; Vaughan, D. G.

    2016-11-01

    The West Antarctic Ice Sheet is one of the largest potential sources of rising sea levels. Over the past 40 years, glaciers flowing into the Amundsen Sea sector of the ice sheet have thinned at an accelerating rate, and several numerical models suggest that unstable and irreversible retreat of the grounding line—which marks the boundary between grounded ice and floating ice shelf—is underway. Understanding this recent retreat requires a detailed knowledge of grounding-line history, but the locations of the grounding line before the advent of satellite monitoring in the 1990s are poorly dated. In particular, a history of grounding-line retreat is required to understand the relative roles of contemporaneous ocean-forced change and of ongoing glacier response to an earlier perturbation in driving ice-sheet loss. Here we show that the present thinning and retreat of Pine Island Glacier in West Antarctica is part of a climatically forced trend that was triggered in the 1940s. Our conclusions arise from analysis of sediment cores recovered beneath the floating Pine Island Glacier ice shelf, and constrain the date at which the grounding line retreated from a prominent seafloor ridge. We find that incursion of marine water beyond the crest of this ridge, forming an ocean cavity beneath the ice shelf, occurred in 1945 (±12 years); final ungrounding of the ice shelf from the ridge occurred in 1970 (±4 years). The initial opening of this ocean cavity followed a period of strong warming of West Antarctica, associated with El Niño activity. Thus our results suggest that, even when climate forcing weakened, ice-sheet retreat continued.

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

    Science.gov (United States)

    Timmermann, Ralph

    2010-05-01

    Sub-ice shelf circulation and freezing/melting rates depend critically on an accurate and consistent representation of cavity geometry (i.e. ice-shelf draft and ocean bathymetry). Existing global or pan-Antarctic data sets have turned out to contain various inconsistencies and inaccuracies. The goal of this work is to compile independent regional fields into a global data set. We use the S-2004 global 1-minute bathymetry as the backbone and add an improved version of the BEDMAP topography for an area that roughly coincides with the Antarctic continental shelf. Locations of the merging line have been carefully adjusted in order to get the best out of each data set. High-resolution gridded data for the Amery, Fimbul, Filchner-Ronne, Larsen C and George VI Ice Shelves and for Pine Island Glacier have been carefully merged into the ambient ice and ocean topographies. Multibeam ship survey data for bathymetry in the former Larsen B cavity and the southeastern Bellingshausen Sea have been obtained from the data centers of Alfred Wegener Institute (AWI), British Antarctic Survey (BAS) and Lamont-Doherty Earth Observatory (LDEO), gridded, and again carefully merged into the existing bathymetry map. The resulting global 1-minute data set contains consistent masks for open ocean, grounded ice, floating ice, and bare land surface. The Ice Shelf Cavern Geometry Team: Anne Le Brocq, Tara Deen, Eugene Domack, Pierre Dutrieux, Ben Galton-Fenzi, Dorothea Graffe, Hartmut Hellmer, Angelika Humbert, Daniela Jansen, Adrian Jenkins, Astrid Lambrecht, Keith Makinson, Fred Niederjasper, Frank Nitsche, Ole Anders Nøst, Lars Henrik Smedsrud, and Walter Smith

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

    Science.gov (United States)

    Nelson, C. B.; King, K.

    2015-12-01

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

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

    Science.gov (United States)

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

    2017-03-01

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

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

    Directory of Open Access Journals (Sweden)

    D. P. Grosvenor

    2012-12-01

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

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

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

    Science.gov (United States)

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

    2012-12-01

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

  19. Ice interaction with the Arctic shelf and coast: Constraints on and implication for petroleum development

    Energy Technology Data Exchange (ETDEWEB)

    Barnes, P.W.; Reimnitz, E. (Geological Survey, Menlo Park, CA (USA))

    1990-05-01

    Along the Arctic coast of Alaska sea ice affects structures placed on and under the sea bed and influences the erosion and dispersal patterns of sedimentary particulates and pollutants. Most directly, ice gouges the sea floor to depths of a few meters, with return periods on the inner shelf of tens of years and, in places, annually, primarily during freezeup and breakup. These sea-floor ice-gouge patterns provide information on the motion and characteristics of the local ice canopy. The design and alignment of pipelines and coast structures should consider that ice gouging extends to the coast and onto the beaches; however, ice gouging is less apparent on beaches owing to lower gouge intensities and vigorous wave reworking. In the long term, gouging contributes to high rates of coastal and shelf erosion. Protruding ice keels extending downward from the sea-ice canopy divert and focus currents causing increased sea-floor scour to depths of a few meters below the sea floor. Sea-ice freezing during the commonly turbulent fall storms causes large volumes of sediment and pollutants to be sorted, resuspended, and, ultimately, incorporated into the ice canopy. Most entrained material is re-released to the nearshore the following open-water season however, some material may be transported offshore to become part of the Arctic pack. During freezeup and breakup (4-5 months/yr) when these processes are most active, trafficability in the Arctic nearshore is nil owing to the instability of the ice canopy, and so our comprehension of this processes is limited.

  20. Ice stream reorganization and glacial retreat on the northwest Greenland shelf

    Science.gov (United States)

    Newton, A. M. W.; Knutz, P. C.; Huuse, M.; Gannon, P.; Brocklehurst, S. H.; Clausen, O. R.; Gong, Y.

    2017-08-01

    Understanding conditions at the grounding-line of marine-based ice sheets is essential for understanding ice sheet evolution. Offshore northwest Greenland, knowledge of the Last Glacial Maximum (LGM) ice sheet extent in Melville Bugt was previously based on sparse geological evidence. This study uses multibeam bathymetry, combined with 2-D and 3-D seismic reflection data, to present a detailed landform record from Melville Bugt. Seabed landforms include mega-scale glacial lineations, grounding-zone wedges, iceberg scours, and a lateral shear margin moraine, formed during the last glacial cycle. The geomorphology indicates that the LGM ice sheet reached the shelf edge before undergoing flow reorganization. After retreat of 80 km across the outer shelf, the margin stabilized in a mid-shelf position, possibly during the Younger Dryas (12.9-11.7 ka). The ice sheet then decoupled from the seafloor and retreated to a coast-proximal position. This landform record provides an important constraint on deglaciation history offshore northwest Greenland.

  1. The effect of basal channels on oceanic ice-shelf melting

    Science.gov (United States)

    Millgate, Thomas; Holland, Paul R.; Jenkins, Adrian; Johnson, Helen L.

    2013-12-01

    The presence of ice-shelf basal channels has been noted in a number of Antarctic and Greenland ice shelves, but their impact on basal melting is not fully understood. Here we use the Massachusetts Institute of Technology general circulation model to investigate the effect of ice-shelf basal channels on oceanic melt rate for an idealized ice shelf resembling the floating tongue of Petermann Glacier in Greenland. The introduction of basal channels prevents the formation of a single geostrophically balanced boundary current; instead the flow is diverted up the right-hand (Coriolis-favored) side of each channel, with a return flow in the opposite direction on the left-hand side. As the prescribed number of basal channels is increased the mean basal melt rate decreases, in agreement with previous studies. For a small number of relatively wide channels the subice flow is found to be a largely geostrophic horizontal circulation. The reduction in melt rate is then caused by an increase in the relative contribution of weakly melting channel crests and keels. For a larger number of relatively narrow channels, the subice flow changes to a vertical overturning circulation. This change in circulation results in a weaker sensitivity of melt rates to channel size. The transition between the two regimes is governed by the Rossby radius of deformation. Our results explain why basal channels play an important role in regulating basal melting, increasing the stability of ice shelves.

  2. Anomalously-dense firn in an ice-shelf channel revealed by wide-angle radar

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    R. Drews

    2015-10-01

    Full Text Available The thickness of ice shelves, a basic parameter for mass balance estimates, is typically inferred using hydrostatic equilibrium for which knowledge of the depth-averaged density is essential. The densification from snow to ice depends on a number of local factors (e.g. temperature and surface mass balance causing spatial and temporal variations in density–depth profiles. However, direct measurements of firn density are sparse, requiring substantial logistical effort. Here, we infer density from radio-wave propagation speed using ground-based wide-angle radar datasets (10 MHz collected at five sites on Roi Baudouin Ice Shelf (RBIS, Dronning Maud Land, Antarctica. Using a novel algorithm including traveltime inversion and raytracing with a prescribed shape of the depth–density relationship, we show that the depth to internal reflectors, the local ice thickness and depth-averaged densities can reliably be reconstructed. For the particular case of an ice-shelf channel, where ice thickness and surface slope change substantially over a few kilometers, the radar data suggests that firn inside the channel is about 5 % denser than outside the channel. Although this density difference is at the detection limit of the radar, it is consistent with a similar density anomaly reconstructed from optical televiewing, which reveals 10 % denser firn inside compared to outside the channel. The denser firn in the ice-shelf channel should be accounted for when using the hydrostatic ice thickness for determining basal melt rates. The radar method presented here is robust and can easily be adapted to different radar frequencies and data-acquisition geometries.

  3. Finite element analysis of surface cracks in the Wilkins Ice Shelf using fracture mechanics

    Science.gov (United States)

    Plate, Carolin; Müller, Ralf; Gross, Dietmar; Humbert, Angelika; Braun, Matthias

    2010-05-01

    Ice shelves, located between the warming atmosphere and the ocean, are sensitive elements of the climate system. The Wilkins Ice Shelf is situated in the south-western part of the Antarctic Peninsula, a well known hot spot of global warming. Recent break-up events exemplified the potential of disintegration of the ice shelf. A multi interdisciplinary project consisting of remote sensing, modeling of the ice dynamics and fracture mechanics intends to improve the understanding of the impacts of temperature increase on ice shelf stability. As a part of this project the aim of this presentation is to demonstrate the fracture mechanical approach using finite elements and configurational forces. For fracture mechanical purposes the material behavior of ice is treated as a brittle solid, and linear fracture mechanics is used. Crucial to all methods in linear fracture mechanics is the evaluation of the stress intensity factor K which is a measure for the load concentration at the crack tip and which depends on the geometry of the body and on the applied loading. The computed value of K can be compared to the critical stress intensity factor Kc, a material property obtained from experimental examinations, to judge whether a crack will propagate. One very effective procedure to obtain the stress intensity factor takes advantage of configurational forces, which can be easily obtained in the finite element analysis. An initial investigation is based on a 2-dimensional analysis of a single crack with a mode-I load type using a static plane strain model in the finite element analysis software COMSOL and additional routines to compute and evaluate the configurational forces. Analytical solutions of simple geometry and load cases are called on in comparison. The application to the Wilkins Ice Shelf follows by using material parameters, geometries and loading situations, which are obtained from literature values, remote sensing data analysis and modeling of the ice dynamics

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

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    T. Haug

    2010-01-01

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

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

    Directory of Open Access Journals (Sweden)

    P. Skvarca

    2010-05-01

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

  6. Water mass modification over the continental shelf north of Ronne Ice Shelf, Antarctica

    OpenAIRE

    Nicholls, Keith W.; L. Padman; Schröder, Michael; Woodgate, R. A.; Jenkins, Adrian; Østerhus, Svein

    2003-01-01

    We use new data from the southern Weddell Sea continental shelf to describe water mass conversion processes in a formation region for cold and dense precursors of Antarctic Bottom Water. The cruises took place in early 1995, 1998, and 1999, and the time series obtained from moored instruments were up to 30 months in length, starting in 1995. We obtained new bathymetric data that greatly improve our definition of the Ronne Depression, which is now shown to be limited to the sout...

  7. Divergent trajectories of Antarctic ice shelf surface melt under 21st century climate scenarios

    Science.gov (United States)

    Trusel, L. D.; Frey, K. E.; Das, S. B.; Kuipers Munneke, P.; van Meijgaard, E.

    2014-12-01

    Antarctic ice shelves represent a critical interface between continental ice masses and the surrounding ocean. Breakup events of several ice shelves in recent decades have been linked to an increase in intense surface melting, and have in turn lead to cascading effects including accelerated glacier discharge into the ocean. In this study, we utilized sophisticated regional and global climate models (GCMs) to assess potential future surface melt trajectories across Antarctica under two climate scenarios (RCP4.5 and RCP8.5). RACMO2.1, a polar-adapted regional atmospheric climate model, was forced by the ERA-Interim reanalysis (1980-2010) and by two GCMs, EC-EARTH and HadGEM2-ES (2007-2100). Using RACMO2.1, we observed an exponential growth function well represents the relationship between ice shelf surface meltwater production and mean summer (DJF) 2-meter air temperature (t2m). We employed this melt-t2m relationship to project melt using t2m output from an ensemble of five CMIP5-based GCMs incorporating the NCAR Community Land Model 4 (CLM4), following spatial downscaling and bias correction using t2m from ERA-Interim-forced RACMO2.1. Our resulting GCM-derived melt projections provide an independent and methodologically unique perspective into potential future melt pathways, complementary to those derived from RACMO2.1. Most notably, both RACMO2.1 and the CMIP5 ensemble reveal divergent trajectories of meltwater production beyond 2050 under the two climate scenarios. For many ice shelves in RCP4.5, meltwater production through 2100 remains at levels comparable to present. Conversely, under RCP8.5 all methods indicate non-linear melt intensification, resulting in a four-fold increase in the Antarctic-wide meltwater volume by the end of the 21st century. For some ice shelves, including Larsen C and Wilkins (Antarctic Peninsula), and Shackleton and West (Wilkes Land), spatially averaged end-of-century meltwater production within RCP8.5 approaches or surpasses levels

  8. The crucial influence of different material models on ice shelf calving

    Science.gov (United States)

    Christmann, Julia; Müller, Ralf; Humbert, Angelika

    2015-04-01

    The aim of this study is to investigate the position and rate of small scale calving from Antarctic ice shelves. Thereby small scale calving happens on rather continuous timescales of several days to few years and contribute to the mass balance of an ice shelf. For a better understanding of the calving behavior, the stress and deformation states at the ice front are analyzed. The influence of geometry, material parameters and some model assumptions are discussed. The ice shelf is modeled as a two, respectively three, dimensional body loaded by gravity and water pressure. There are two responses of ice to load: on long time scales ice reacts like a viscous fluid, and on short time scale like an elastic solid. Until now it is not obviously verified, if small scale calving is related to a purely elastic, a viscous or a visco-elastic material behavior. Therefore, the stresses and deformations due to these material models and their applicability on ice shelf calving are demonstrated. The maximum tensile stress respectively strain serve as a calving criterion, namely if one of these values exceed a critical bound at some point, a crack originates and the position of calving is determined. The position of calving for a linear elastic material is unique, due to an instantaneous time-independent answer on the load situation. In this case, the determination of a calving rate is only possible, if a rate dependent geometry, loading or boundary conditions exist. Directly after a calving event the ice front is nearly vertical, however after a certain time interval the exposure, due to melting, waves and water flow, leads to time-dependent geometry variations whose influences on position and calving rate is indicated. Also the analysis of calving with a rate dependent material model leads to a calving rate, incorporating the position of maximum stress, detachment time and flow velocity of the ice shelf. The comparison of these results are established and the advantages and

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

    Science.gov (United States)

    Garabato, Alberto C. Naveira; Forryan, Alexander; Dutrieux, Pierre; Brannigan, Liam; Biddle, Louise C.; Heywood, Karen J.; Jenkins, Adrian; Firing, Yvonne L.; Kimura, Satoshi

    2017-01-01

    The instability and accelerated melting of the Antarctic Ice Sheet are among the foremost elements of contemporary global climate change. The increased freshwater output from Antarctica is important in determining sea level rise, the fate of Antarctic sea ice and its effect on the Earth’s albedo, ongoing changes in global deep-ocean ventilation, and the evolution of Southern Ocean ecosystems and carbon cycling. A key uncertainty in assessing and predicting the impacts of Antarctic Ice Sheet melting concerns the vertical distribution of the exported meltwater. This is usually represented by climate-scale models as a near-surface freshwater input to the ocean, yet measurements around Antarctica reveal the meltwater to be concentrated at deeper levels. Here we use observations of the turbulent properties of the meltwater outflows from beneath a rapidly melting Antarctic ice shelf to identify the mechanism responsible for the depth of the meltwater. We show that the initial ascent of the meltwater outflow from the ice shelf cavity triggers a centrifugal overturning instability that grows by extracting kinetic energy from the lateral shear of the background oceanic flow. The instability promotes vigorous lateral export, rapid dilution by turbulent mixing, and finally settling of meltwater at depth. We use an idealized ocean circulation model to show that this mechanism is relevant to a broad spectrum of Antarctic ice shelves. Our findings demonstrate that the mechanism producing meltwater at depth is a dynamically robust feature of Antarctic melting that should be incorporated into climate-scale models.

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

    Science.gov (United States)

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

    2017-01-01

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

  11. Mixing at the fringes of a rapidly melting Antarctic ice shelf

    Science.gov (United States)

    Naveira Garabato, A.; Forryan, A.; Dutrieux, P.; Brannigan, L.; Biddle, L. C.; Heywood, K. J.; Jenkins, A.; Firing, Y. L.; Kimura, S.

    2016-02-01

    The processes regulating the physical exchanges across the front of the Pine Island Ice Shelf (one of the most rapidly melting Antarctic ice shelves) in the Amundsen Sea are investigated through the analysis of an extensive set of full-depth hydrographic, velocity and microstructure measurements, obtained as part of the ISTAR expedition in February 2014, and an idealised high-resolution numerical circulation model. The outflows of Ice Cavity Water (ICW), which contains elevated concentrations of meltwater from the ice shelf, are shown to be subject to very intense small-scale turbulent mixing within 5 kilometres of the ice front. The rates of turbulent kinetic energy dissipation and diapycnal mixing in the outflows are enhanced by up to four orders of magnitude relative to those in surrounding waters, which are characterised by turbulence levels typical of the open ocean. An investigation of the causes of the intensified turbulence reveals that it is sustained by centrifugal instability of the ICW outflows. The instability drives a secondary ageostrophic circulation that induces rapid lateral mixing between ICW and pycnocline waters offshore, thereby preventing the ICW outflows from reaching the upper-ocean mixed layer and directly influencing surface climate in the region. The significance of this process for the fate of meltwater outflows from other Antarctic ice shelves will be discussed.

  12. Ross ice shelf cavity circulation, residence time, and melting: Results from a model of oceanic chlorofluorocarbons

    Science.gov (United States)

    Reddy, Tasha E.; Holland, David M.; Arrigo, Kevin R.

    2010-04-01

    Despite their harmful effects in the upper atmosphere, anthropogenic chlorofluorocarbons dissolved in seawater are extremely useful for studying ocean circulation and ventilation, particularly in remote locations. Because they behave as a passive tracer in seawater, and their atmospheric concentrations are well-mixed, well-known, and have changed over time, they are ideal for gaining insight into the oceanographic characteristics of the isolated cavities found under Antarctic ice shelves, where direct observations are difficult to obtain. Here we present results from a modeling study of air-sea chlorofluorocarbon exchange and ocean circulation in the Ross Sea, Antarctica. We compare our model estimates of oceanic CFC-12 concentrations along an ice shelf edge transect to field data collected during three cruises spanning 16 yr. Our model produces chlorofluorocarbon concentrations that are quite similar to those measured in the field, both in magnitude and distribution, showing high values near the surface, decreasing with depth, and increasing over time. After validating modeled circulation and air-sea gas exchange through comparison of modeled temperature, salinity, and chlorofluorocarbons with field data, we estimate that the residence time of water in the Ross Ice Shelf cavity is approximately 2.2 yr and that basal melt rates for the ice shelf average 10 cm yr -1. The model predicts a seasonal signature to basal melting, with highest melt rates in the spring and also the fall.

  13. The evolution of the western rift area of the Fimbul Ice Shelf, Antarctica

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    A. Humbert

    2011-10-01

    Full Text Available This paper studies the evolution of a zone in the Fimbul Ice Shelf that is characterised by large crevasses and rifts west of Jutulstraumen, an outlet glacier flowing into Fimbulisen. High-resolution radar imagery and radio echo sounding data were used to study the surface and internal structure of this rift area and to define zones of similar characteristics. The western rift area is dominated by two factors: a small ice rumple that leads to basal crevasses and disturbs the homogeneity of the ice, and a zone with fibre-like blocks. Downstream of the rumple we found down-welling of internal layers and local thinning, which we explain as a result of basal crevasses due to the basal drag at the ice rumple. North of Ahlmannryggen the ice loses its lateral constraint and forms individual blocks, which are deformed like fibres under shear, where the ice stream merges with slower moving ice masses of the western side. There, the ice loses its integrity, which initiates the western rift system. The velocity difference between the slow moving western part and the fast moving extension of Jutulstraumen produces shear stress that causes the rifts to form tails and expand them to the major rifts of up to 30 km length.

  14. Identification of Late Pleistocene Ice-Rafted Debris (IRD) on the New Jersey Shelf

    Science.gov (United States)

    Turner, R. J.; Christensen, B. A.; Wampler, J.; Uptegrove, J.; Goff, J.

    2004-12-01

    The purpose of this study is to evaluate the potential for ice-rafted debris (IRD) on the New Jersey shelf and develop procedures for IRD identification on a shelf environment using a variety of techniques to assess texture and age of the sediments. Pleistocene New Jersey shelf sedimentology is strongly defined by glacially driven sea level changes. IRD and its provenance may be identified on a shelf environment through analysis of grain size distribution, heavy mineral content (higher % suggests non-fluvial processes), mineralogical point counts (anomalous mineralogy indicates distal source), isotopic dating methods (age value determination to narrow down potential source rocks), and surface texture analysis (specific glacial transport features). IRD must be differentiated from sediment derived from the NJ bedrock. Likely sources for IRD include the bedrock of Maine and of the southeastern Canadian Shield. Duncan and Goff (2001) reported iceberg grounding along the NJ shelf. IRD is typically identified in the deep sea through anomalously large grain size within pelagic mud, but different methods are needed for the shelf, where regressive shoreline processes, subaerial exposure, fluvial downcutting, and deposition and reworking during transgression have influenced the sediment composition found today. We analyzed grab samples in or near the features believed to be iceberg scour marks and downcore samples from recent Geoclutter drilling in the same area. The coarse grain size fractions of shelf samples were separated by phi classes before heavy mineral separation methods were employed. Initial analyses show high percentages of heavy minerals in the 2 phi and 3 phi size fractions, consistent with past NJ shelf studies. Hornblende grains were hand-picked from select samples for K-Ar dating, providing age values of about 0.96 ± 0.03 Ga for three sites within iceberg scours. Mineral content of each size fraction is determined by point count. Qualitative assessment of

  15. Amundsen Sea sector ice shelf thickness, melt rates, and inland response from annual high-resolution DEM mosaics

    Science.gov (United States)

    Shean, D. E.; Joughin, I. R.; Smith, B. E.; Alexandrov, O.; Moratto, Z.; Porter, C. C.; Morin, P. J.

    2014-12-01

    Significant grounding line retreat, acceleration, and thinning have occurred along the Amundsen Sea sector of West Antarctica in recent decades. These changes are driven primarily by ice-ocean interaction beneath ice shelves, but existing observations of the spatial distribution, timing, and magnitude of ice shelf melt are limited. Using the NASA Ames Stereo Pipeline, we generated digital elevation models (DEMs) with ~2 m posting from all ~450 available WorldView-1/2 along-track stereopairs for the Amundsen Sea sector. A novel iterative closest point algorithm was used to coregister DEMs to filtered Operation IceBridge ATM/LVIS data and ICESat-1 GLAS data, offering optimal sub-meter horizontal/vertical accuracy. The corrected DEMs were used to produce annual mosaics for the entire ~500x700 km region with focused, sub-annual products for ice shelves and grounding zones. These mosaics provide spatially-continuous measurements of ice shelf topography with unprecedented detail. Using these data, we derive estimates of ice shelf thickness for regions in hydrostatic equilibrium and map networks of sub-shelf melt channels for the Pine Island (PIG), Thwaites, Crosson, and Dotson ice shelves. We also document the break-up of the Thwaites ice shelf and PIG rift evolution leading up to the 2013 calving event. Eulerian difference maps document 2010-2014 thinning over fast-flowing ice streams and adjacent grounded ice. These data reveal the greatest thinning rates over the Smith Glacier ice plain and slopes beyond the margins of the fast-flowing PIG trunk. Difference maps also highlight the filling of at least two subglacial lakes ~30 km upstream of the PIG grounding line in 2011. Lagrangian difference maps reveal the spatial distribution of ice shelf thinning, which can primarily be attributed to basal melt. Preliminary results show focused ice shelf thinning within troughs and large basal channels, especially along the western margin of the Dotson ice shelf. These new data

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

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    H. Rott

    2011-03-01

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

  17. Exploring beneath the PIG Ice Shelf with the Autosub3 AUV

    OpenAIRE

    McPhail, Stephen D.; Furlong, Maaten E; Perrett, James R.; Stevenson, Peter; Webb, Andy; White, Davie

    2009-01-01

    On 31st January 2009, two numbers: “range and bearing” flashing up on a laptop screen, indicated that Autosub3 had returned from its last mission beneath the Pine Island Glacier (PIG) Ice Shelf in the Western Antarctic. The Autosub technical team from NOCS, Southampton, onboard the US ice breaker Nathanial B Palmer breathed a collective sigh of relief. Any significant technical failure would have resulted in total loss of the multi million Euro Autonomous Underwater Vehicle with no hope of re...

  18. Glacier Acceleration and Thinning after Ice Shelf Collapse in the Larsen B Embayment, Antarctica

    Science.gov (United States)

    Scambos, T. A.; Bohlander, J. A.; Shuman, C. A.; Skvarca, P.

    2004-01-01

    Ice velocities derived from five Landsat 7 images acquired between January 2000 and February 2003 show a two- to six-fold increase in centerline speed of four glaciers flowing into the now-collapsed section of the Larsen B Ice Shelf. Satellite laser altimetry from ICEsat indicates the surface of Hektoria Glacier lowered by up to 38 +/- 6 m a six-month period beginning one year after the break-up in March 2002. Smaller elevation losses are observed for Crane and Jorum glaciers over a later 5-month period. Two glaciers south of the collapse area, Flask and Leppard, show little change in speed or elevation. Seasonal variations in speed preceding the large post-collapse velocity increases suggest that both summer melt percolation and changes in the stress field due to shelf removal play a major role in glacier dynamics.

  19. Field Investigation of Surface-Lake Processes on Ice Shelves: Results of the 2015/16 Field Campaign on McMurdo Ice Shelf, Antarctica

    Science.gov (United States)

    MacAyeal, Doug; Banwell, Alison; Willis, Ian; Macdonald, Grant

    2016-04-01

    Ice-shelf instability and breakup of the style exhibited by Larsen B Ice Shelf in 2002 remains the most difficult glaciological process of consequence to observe in detail. It is, however, vital to do so because ice-shelf breakup has the potential to influence the buttressing controls on inland ice discharge, and thus to affect sea level. Several mechanisms enabling Larsen B style breakup have been proposed, including the ability of surface lakes to introduce ice-shelf fractures when they fill and drain, thereby changing the surface loads the ice-shelf must adjust to. Our model suggest that these fractures resulted in a chain-reaction style drainage of >2750 surface lakes on the Larsen B in the days prior to its demise. To validate this and other models, we began a field project on the McMurdo Ice Shelf (MIS) during the 2015/16 austral summer. Advantages of the MIS study site are: there is considerable surface melting during 3-6 weeks of the summer season, the ice is sufficiently thin (logistical support (McMurdo Station). Here we show initial results from the field campaign, including GPS and water-depth observations of a lake that has filled and drained over multiple week timescales in previous austral summers. We also report on the analysis of high-resolution WorldView satellite imagery from several summers that reveals the complexity of surface meltwater movement in channels and subsurface void spaces. Initial reconnaissance of the largest surface-lake features reveal that they have a central circular depression surrounded by an uplifted ring, which supports one of the central tenets of our ice-shelf flexure theory. A second field season is anticipated for the 2016/17 austral summer.

  20. McMurdo Ice Shelf Sounding and Radar Statistical Reconnaissance at 60-MHz: Brine Infiltration Extent and Surface Properties

    Science.gov (United States)

    Grima, C.; Rosales, A.; Blankenship, D. D.; Young, D. A.

    2014-12-01

    McMurdo Ice Shelf, Antarctica, is characterized by two particular geophysical processes. (1) Marine ice accretion supplies most of the ice shelf material rather than meteoric ice from glacier outflow and snow-falls. (2) A brine layer infiltrates the ice shelf laterally up to 20-km inward. The infiltration mainly initiates at the ice-front from sea water percolation when the firn/snow transition is below sea-level. A better characterization of the McMurdo ice shelf could constrain our knowledges of these mechanisms and assess the stability of the region that hosts numerous human activities from the close McMurdo station (USA) and Scott base (New-Zealand). McMurdo ice shelf is also an analog for the Jovian icy moon Europa where brine pockets are supposed to reside in the ice crust and accretion to occur at the 10-30-km deep ice-ocean interface.The University of Texas Institute for Geophysics (UTIG) acquired two radar survey grids over the McMurdo Ice Shelf during southern summers 2011-2012 and 2012-2013 with the High Capability Radar Sounder (HiCARS) on-board a Basler DC-3 aircraft. HiCARS transmits a chirped signal at 60-MHz central frequency and 15-MHz bandwidth. The corresponding vertical resolution in ice is 5-10 m. An important design goal of the radar was to maintain sufficient dynamic range to correctly measure echo intensities.Here we present the brine infiltration extent and bathymetry derived from its dielectric horizon well distinguishable on the HiCARS radargram. We complement the ice-shelf characterization by classifying its surface thanks to the novel Radar Statistical Reconnaissance (RSR) methodology. The RSR observable is the statistical distribution of the surface echo amplitudes from successive areas defined along-track. The distributions are best-fitted with a theoretical stochastic envelop parameterized with the signal reflectance and scattering. Once those two components are deduced from the fit, they are used in a backscattering model to invert

  1. The Turbulent Convective Plume at Ice Shelf Fronts and the Sides of Tabular Icebergs

    Science.gov (United States)

    Kerr, R. C.; McConnochie, C. D.

    2015-12-01

    We present laboratory experiments and theoretical analysis that quantify the turbulent buoyant plume formed by the dissolution of a vertical ice face in homogeneous salt water. In our experiments, we vary the temperature and salinity of the salt water and measure the dissolution rate of the ice, the temperature of the ice-water interface, the maximum vertical velocity of the buoyant plume, and the rate at which the laboratory tank becomes stratified with buoyant fluid. Using this experimental information, we then construct a theoretical model of the turbulent buoyant plume as a function of height. The plume has a top-hat entrainment coefficient of 0.048 ± 0.006, and is found to have substantial drag. The plume model is used to calculate a plume width, velocity, buoyancy and Reynolds number for typical dissolving icebergs and ice shelf fronts. Our laboratory experiments also examine the effect of a linear salinity gradient on the dissolution of a vertical ice face. As the stratification is increased, the dissolution rate, the interface temperature and the maximum vertical plume velocity all decrease, and their dependence on height changes. We also outline a method of scaling the effects of stratification from our laboratory experiments to the much larger vertical scales of ice shelves and icebergs.

  2. Ice shelf-ocean interactions, mechanisms of change in the Amundsen Sea, West Antarctica

    Science.gov (United States)

    Dutrieux, P.

    2015-12-01

    Over the length of the observational record, the Antarctic Ice Sheet has been loosing ice to the ocean, significantly contributing to global sea level rise. This signal is largely due to glacial flow acceleration in West Antarctica, driven by oceanic melting at its margin and the induced thinning of the glacier buttressing ice shelves. Pine Island Glacier is one stellar example where vigorous oceanic melting fundamentally modifies the geometry of the ice-ocean interface and the associated ice dynamics. Since the early 1970's, the glacier terminating ice shelf has thinned, its grounding line has retreated, and its speed has doubled, now reaching close to 11 m/day. During that time, oceanic melting has increased, injecting fresh and nutrient-rich waters between the surface and intermediate depth in the coastal southern ocean. Using autonomous platforms, ship-borne ocean observations, ground-based and airborne radar observations, satellite observations and numerical modelling, this talk will review the mechanisms behind this trajectory of change and open perspectives on its potential impacts in the Southern Ocean.

  3. Ice streaming in western Scotland and the deglaciation of the Hebrides Shelf and Firth of Lorn

    Science.gov (United States)

    Arosio, Riccardo; Howe, John; O'Cofaigh, Colm; Crocket, Kirsty

    2014-05-01

    Previously, numerous studies have been undertaken both onshore and offshore to decipher the morphological and sedimentological record in order to better constrain the limits and duration of the British-Irish Ice Sheet (BIIS) (Ballantyne et al. 2009, Bradwell et al. 2008b, Clark et al. 2011, Dunlop et al. 2010, Howe et al. 2012, O'Cofaigh et al., 2012). Late glacial ice sheet dynamics have been revealed to be far more rapid and responsive to climatic amelioration than had previously been considered. Notable in this debate has been the evidence that has been obtained in the inshore and, to a lesser extent, offshore on the UK continental shelf. Here new geomorphological data, principally multibeam echo sounder (MBES) data has provided imagery of previously unseen features interpreted as being glacial in origin. In the wake of these new discoveries this projects aims to investigate the extent, timing, growth and final disintegration of the BIIS across Western Scotland. This area of particular interest for the development of the glaciated North Atlantic margin has been generally neglected in past studies, especially across the mid-outer shelf, which constitutes a missing part in the jigsaw of the reconstructed BIIS during the last ~20.000yrs. We aim to mainly focus on geomorphological analyses of MBES data collected in the Firth of Lorn and Sea of Hebrides; a study of features as moraines, glacial lineations and drumlins will provide important clues on the dynamics and maximum extension of the sheet. Subsequently we will examine the geometry and composition of the shelf sediment infill, aiming to constrain the influence of ice retreat on depositional environments using multi-element geochemical (Pb-isotopes ratios, 14C and OSL dating) and sedimentological techniques. Such an investigation will also give retrospective information on the sources for these sediments, hence more indications on ice configuration. Ultimately we aim to provide a model of deglaciation for the

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

    Science.gov (United States)

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

    2014-01-01

    Nearly three decades of stable isotope ratios and surface mass balance (SMB) data from eight shallow firn cores retrieved at Fimbul Ice Shelf, East Antarctica, in the Austral summers 2009–2011 have been investigated. An additional longer core drilled in 2000/2001 extends the series back to the early eighteenth century. Isotope ratios and SMB from the stacked record of all cores were also related to instrumental temperature data from Neumayer Station on Ekström Ice Shelf. Since the second half of the twentieth century, the SMB shows a statistically significant negative trend, whereas the δ18O of the cores shows a significant positive trend. No trend is found in air temperature at the nearest suitable weather station, Neumayer (available since 1981). This does not correspond to the statistically significant positive trend in Southern Annular Mode (SAM) index, which is usually associated with a cooling of East Antarctica. SAM index and SMB are negatively correlated, which might be explained by a decrease in meridional exchange of energy and moisture leading to lower precipitation amounts. Future monitoring of climate change on the sensitive Antarctic ice shelves is necessary to assess its consequences for sea level change. Key Points Mass balance and stable oxygen isotope ratios from shallow firn cores Decreasing trend in surface mass balance, no trend in stable isotopes Negative correlation between SAM and SMB PMID:25821663

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

    Science.gov (United States)

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

    2014-06-16

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

  6. Shear, Stability and Mixing within the Ice-Shelf-Ocean Boundary Layer

    Science.gov (United States)

    Jenkins, Adrian

    2016-04-01

    Ocean-forced basal melting has been implicated in the widespread thinning of Antarctic ice shelves that has been causally linked with acceleration in the outflow of grounded ice. What determines the distribution and rates of basal melting and freezing beneath an ice shelf and how these respond to changes in the ocean temperature or circulation are therefore key questions. Recent years have seen major progress in our ability to observe basal melting and the ocean conditions that drive it, but data on the latter remain sparse, limiting our understanding of the key processes of ice-ocean heat transfer. In particular, we have no observations of current profiles through the buoyancy- and frictionally-controlled flows along the ice shelf base that drive mixing through the ice-ocean boundary layer. This presentation represents an attempt to address this gap in our knowledge through application of a very simple model of such boundary flows that considers only the spatial dimension perpendicular to the boundary. Initial results obtained with an unrealistic assumuption of constant eddy viscosity/diffusivity are nevertheless informative. For the buoyancy-driven flow two possible regimes exist: a weakly-stratified, geostrophic cross-slope current with an embedded Ekman layer, somewhat analogous to a conventional density current on a slope; or a strongly-stratified upslope jet with weak cross-slope flow, more analogous to an inverted katabatic wind. The latter is most appropriate when the ice-ocean interface is very steep, while for the gentle slopes typical of ice shelves the buoyant Ekman regime prevails. Introduction of a variable eddy viscosity/diffusivity derived from a local turbulence closure scheme modifies the current structure and stratification. There is a sharp step in properties across the surface layer, where the viscosity/diffusivity is low, weak gradients across the outer part of the boundary layer, where shear-driven mixing is strong, and a relatively strong

  7. Response of Southern Ocean circulation to global warming may enhance basal ice shelf melting around Antarctica

    Energy Technology Data Exchange (ETDEWEB)

    Hattermann, Tore; Levermann, Anders [Potsdam University, Earth System Analysis, Potsdam Institute for Climate Impact Research, Potsdam (Germany)

    2010-10-15

    We investigate the large-scale oceanic features determining the future ice shelf-ocean interaction by analyzing global warming experiments in a coarse resolution climate model with a comprehensive ocean component. Heat and freshwater fluxes from basal ice shelf melting (ISM) are parameterized following Beckmann and Goosse [Ocean Model 5(2):157-170, 2003]. Melting sensitivities to the oceanic temperature outside of the ice shelf cavities are varied from linear to quadratic (Holland et al. in J Clim 21, 2008). In 1% per year CO{sub 2}-increase experiments the total freshwater flux from ISM triples to 0.09 Sv in the linear case and more than quadruples to 0.15 Sv in the quadratic case after 140 years at which 4 x 280 ppm = 1,120 ppm was reached. Due to the long response time of subsurface temperature anomalies, ISM thereafter increases drastically, if CO{sub 2} concentrations are kept constant at 1,120 ppm. Varying strength of the Antarctic circumpolar current (ACC) is crucial for ISM increase, because southward advection of heat dominates the warming along the Antarctic coast. On centennial timescales the ACC accelerates due to deep ocean warming north of the current, caused by mixing of heat along isopycnals in the Southern Ocean (SO) outcropping regions. In contrast to previous studies we find an initial weakening of the ACC during the first 150 years of warming. This purely baroclinic effect is due to a freshening in the SO which is consistent with present observations. Comparison with simulations with diagnosed ISM but without its influence on the ocean circulation reveal a number of ISM-related feedbacks, of which a negative ISM-feedback, due to the ISM-related local oceanic cooling, is the dominant one. (orig.)

  8. An unusual early Holocene diatom event north of the Getz Ice Shelf (Amundsen Sea): Implications for West Antarctic Ice Sheet development

    Science.gov (United States)

    Esper, O.; Gersonde, R.; Hillenbrand, C.; Kuhn, G.; Smith, J.

    2011-12-01

    Modern global change affects not only the polar north but also, and to increasing extent, the southern high latitudes, especially the Antarctic regions covered by the West Antarctic Ice Sheet (WAIS). Consequently, knowledge of the mechanisms controlling past WAIS dynamics and WAIS behaviour at the last deglaciation is critical to predict its development in a future warming world. Geological and palaeobiological information from major drainage areas of the WAIS, like the Amundsen Sea Embayment, shed light on the history of the WAIS glaciers. Sediment records obtained from a deep inner shelf basin north of Getz Ice Shelf document a deglacial warming in three phases. Above a glacial diamicton and a sediment package barren of microfossils that document sediment deposition by grounded ice and below an ice shelf or perennial sea ice cover (possibly fast ice), respectively, a sediment section with diatom assemblages dominated by sea ice taxa indicates ice shelf retreat and seasonal ice-free conditions. This conclusion is supported by diatom-based summer temperature reconstructions. The early retreat was followed by a phase, when exceptional diatom ooze was deposited around 12,500 cal. years B.P. [1]. Microscopical inspection of this ooze revealed excellent preservation of diatom frustules of the species Corethron pennatum together with vegetative Chaetoceros, thus an assemblage usually not preserved in the sedimentary record. Sediments succeeding this section contain diatom assemblages indicating rather constant Holocene cold water conditions with seasonal sea ice. The deposition of the diatom ooze can be related to changes in hydrographic conditions including strong advection of nutrients. However, sediment focussing in the partly steep inner shelf basins cannot be excluded as a factor enhancing the thickness of the ooze deposits. It is not only the presence of the diatom ooze but also the exceptional preservation and the species composition of the diatom assemblage

  9. Late Quaternary glaciation history of northernmost Greenland - Evidence of shelf-based ice

    DEFF Research Database (Denmark)

    Larsen, Nicolaj; Kjær, Kurt H.; Funder, Svend Visby;

    2011-01-01

    to retreat ca 16 ka to 10.3 cal ka BP before the final break-up, which took place ca 10.1 cal ka BP probably as a combined result of increased inflow of warm Atlantic water through the Fram Strait, a shallower halocline and higher summer temperatures, corresponding to orbital maximum solar insolation...... at this time. The existence of extensive shelf-based ice north of Greenland provides an important contribution to the understanding of the LGM glaciation history of the Arctic Ocean....

  10. Autonomous ocean observations beneath Pine Island Glacier Ice Shelf, West Antarctica

    Science.gov (United States)

    Dutrieux, P.; Jenkins, A.; Jacobs, S.; Heywood, K. J.

    2015-12-01

    Warm circumpolar deep water reaching 3.5ºC above the in situ freezing point pervasively fills a network of glacially carved troughs in the Amundsen sea, West Antarctica, and melts and thins neighbouring ice shelves, including Pine Island glacier Ice Shelf (PIIS). Hydrographic, current, and microstructure observations obtained in austral summer 2009 and 2014 by an autonomous underwater vehicle beneath the PIIS are used here to detail the complex ice-ocean interaction and resulting ocean circulation. The theoretical schematic of deeply incoming warm and saline water melting the grounding line and generating a buoyant plume upwelling along the ice draft is generally consistent with observations. The cavity beneath PIIS is clearly divided in two by a seabed ridge, constraining the oceanic circulation and water masses distribution. On the seaward side of the ridge, a thick warm deep water layer circulates cyclonically and is overlaid by a thin meltwater layer. Only intermediate depth waters are allowed to overflow from the ridge top into the inner cavity, where a much thinner warm water layer is now overlaid by a thicker meltwater layer. At the ice/ocean interface, melt induced freshening is forcing an upwelling which in turn injects cyclonic vorticity and participates in creating a vigorous cyclonic recirculation in the inner cavity. The top of the ridge, where warm waters overflow in the inner cavity, is a dynamical boundary characterized by northward along-ridge currents up to 0.2 m/s and enhanced shear, thermal gradient, and mixing. Observations at two points at the ice interface indicate that the ocean remains stratified within 2 meters of the ice.

  11. Northern Hemisphere millennial-scale ice discharges as a response to oceanic forcing simulated with a hybrid ice-sheet/ice-shelf model

    Science.gov (United States)

    Alvarez-Solas, J.; Montoya, M.; Robinson, A. J.; Banderas-Carreño, R.; Ritz, C.; Ganopolski, A.

    2012-04-01

    formation takes place (Nordic and Labrador Seas). We show that subsurface warming is a crucial mechanism to destabilize the Labrador Sea ice shelves favoring the acceleration of the Laurentide ice streams. Iceberg production is then enhanced during stadial periods. However, this pattern is not monotonically present through all DO events: the combination of both a characteristic ice-shelf break-up and re-developing time larger than the DO forcing period and the fact that ice-streams need to flow extremely fast to create major calving rates explains the different magnitude of iceberg discharge during different stadial periods. Finally, when applying a time-evolving basal melt rate of the Labrador ice shelf calibrated (in anti-phase) against the GRIP curve, the ice sheet models produces ice discharges that compare well with ice rafted debris records. These results suggest that oceanic forcing can be considered as a sufficient condition for triggering the observed millennial-scale ice discharges, including Heinrich events.

  12. Resonance vibrations of the Ross Ice Shelf and observations of persistent atmospheric waves

    Science.gov (United States)

    Godin, Oleg A.; Zabotin, Nikolay A.

    2016-10-01

    Recently reported lidar observations have revealed a persistent wave activity in the Antarctic middle and upper atmosphere that has no counterpart in observations at midlatitude and low-latitude locations. The unusual wave activity suggests a geographically specific source of atmospheric waves with periods of 3-10 h. Here we investigate theoretically the hypothesis that the unusual atmospheric wave activity in Antarctica is generated by the fundamental and low-order modes of vibrations of the Ross Ice Shelf (RIS). Simple models are developed to describe basic physical properties of resonant vibrations of large ice shelves and their coupling to the atmosphere. Dispersion relation of the long surface waves, which propagate in the floating ice sheet and are responsible for its low-order resonances, is found to be similar to the dispersion relation of infragravity waves in the ice-free ocean. The phase speed of the surface waves and the resonant frequencies determine the periods and wave vectors of atmospheric waves that are generated by the RIS resonant oscillations. The altitude-dependent vertical wavelengths and the periods of the acoustic-gravity waves in the atmosphere are shown to be sensitive to the physical parameters of the RIS, which can be difficult to measure by other means. Predicted properties of the atmospheric waves prove to be in a remarkable agreement with the key features of the observed persistent wave activity.

  13. Resonance vibrations of the Ross Ice Shelf cause persistent atmospheric waves

    Science.gov (United States)

    Godin, Oleg; Zabotin, Nikolay

    2017-04-01

    Recently reported lidar observations have revealed a persistent wave activity in the Antarctic middle and upper atmosphere that has no counterpart in observations at mid- and low-latitude locations [Chen et al., 2016]. The unusual wave activity suggests a geographically specific source of atmospheric waves with periods of 3-10 hours. Here, we investigate theoretically the hypothesis that the unusual atmospheric wave activity in Antarctica is generated by the fundamental and low-order modes of vibrations of the Ross Ice Shelf (RIS). Simple models are developed to describe basic physical properties of resonant vibrations of large ice shelves and their coupling to the atmosphere. Dispersion relation of the long surface waves, which propagate in the floating ice sheet and are responsible for its low-order resonances, is found to be similar to the dispersion relation of infragravity waves in the ice-free ocean. The phase speed of the surface waves and the resonant frequencies determine the periods and wave vectors of atmospheric waves that are generated by the RIS resonant oscillations. The altitude-dependent vertical wavelengths and the periods of the acoustic-gravity waves in the atmosphere are shown to be sensitive to the physical parameters of the RIS, which can be difficult to measure by other means. Predicted properties of the atmospheric waves prove to be in a remarkable agreement with the key features of the observed persistent wave activity], including frequency band, vertical wavelength range, and weak variation of the vertical wavelength with the height. The present work is a motivation for in-depth studies of coupling between vibrations of ice shelves and waves in the upper and middle atmosphere at high latitudes.

  14. Combining ozone and slurry ice to maximize shelf-life and quality of bighead croaker (Collichthys niveatus).

    Science.gov (United States)

    Chen, Jing; Huang, Ju; Deng, Shanggui; Huang, Yuting

    2016-10-01

    Slurry ice possesses several advantages for seafood preservation, such as faster chilling rate, reduced physical damage, and complete coverage of the fish surface. In this paper, the efficiency of its employment, either applied alone or combined with ozone, was evaluated for bighead croaker and compared with traditional flake ice. Changes of a series of microbial, biochemical and sensory parameters including total viable count (TVC), sensory scores, total volatile basic nitrogen (TVB-N), peroxide value (PV), thiobarbituric acid (TBA), hardness and springiness were investigated up to 21 days. TVC, sensory attributes, hardness and springiness of fish stored in ozonised slurry ice, were significantly different from fish stored flake ice and slurry ice, indicating that a combination of slurry ice and ozone allowed better quality maintenance. Increase in TVB-N, PV and TBA values of the fish treated with ozonised slurry ice and slurry ice were found to be noticeably reduced compared to those of the flake ice ones. Based on the acceptable limits of TVC and other quantifiable attributes, a prolonged shelf life of 18 days was estimated for the bighead croaker stored in ozonised-slurry ice, whereas the counterpart batches treated with flake and slurry ice would exceed these limits after 9 and 15 days, respectively. Additionally, sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis and scanning electron microscope observation also revealed that ozonised-slurry ice could effectively retard the degradation of myofibrillar proteins and reduce the deterioration of microstructure.

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

    Science.gov (United States)

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

    2010-12-01

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

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

    Science.gov (United States)

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

    2005-01-01

    Changes in the area and volume of polar ice sheets are intricately linked to changes in global climate, and the resulting changes in sea level may severely impact the densely populated coastal regions on Earth. Melting of the West Antarctic part alone of the Antarctic ice sheet could cause a sea-level rise of approximately 6 meters (m). The potential sea-level rise after melting of the entire Antarctic ice sheet is estimated to be 65 m (Lythe and others, 2001) to 73 m (Williams and Hall, 1993). In spite of its importance, the mass balance (the net volumetric gain or loss) of the Antarctic ice sheet is poorly known; it is not known for certain whether the ice sheet is growing or shrinking. In a review paper, Rignot and Thomas (2002) concluded that the West Antarctic part of the Antarctic ice sheet is probably becoming thinner overall; although it is thickening in the west, it is thinning in the north. Joughin and Tulaczyk (2002), on the basis of analysis of ice-flow velocities derived from synthetic aperture radar, concluded that most of the Ross ice streams (ice streams on the east side of the Ross Ice Shelf) have a positive mass balance, whereas Rignot and others (in press) infer even larger negative mass balance for glaciers flowing northward into the Amundsen Sea, a trend suggested by Swithinbank and others (2003a,b, 2004). The mass balance of the East Antarctic part of the Antarctic ice sheet is unknown, but thought to be in near equilibrium. Measurement of changes in area and mass balance of the Antarctic ice sheet was given a very high priority in recommendations by the Polar Research Board of the National Research Council (1986), in subsequent recommendations by the Scientific Committee on Antarctic Research (SCAR) (1989, 1993), and by the National Science Foundation's (1990) Division of Polar Pro-grams. On the basis of these recommendations, the U.S. Geo-logical Survey (USGS) decided that the archive of early 1970s Landsat 1, 2, and 3 Multispectral Scanner

  17. Brief communication "Can recent ice discharges following the Larsen-B ice-shelf collapse be used to infer the driving mechanisms of millennial-scale variations of the Laurentide ice sheet?"

    Directory of Open Access Journals (Sweden)

    J. Alvarez-Solas

    2012-06-01

    Full Text Available The effects of an ice-shelf collapse on inland glacier dynamics have recently been widely studied, especially since the breakup of the Antarctic Peninsula's Larsen-B ice shelf in 2002. Several studies have documented acceleration of the ice streams that were flowing into the former ice shelf. The mechanism responsible for such a speed-up lies with the removal of the ice-shelf backforce. Independently, it is also well documented that during the last glacial period, the Northern Hemisphere ice sheets experienced large discharges into the ocean, likely reflecting ice flow acceleration episodes on the millennial time scale. The classic interpretation of the latter is based on the existence of an internal thermo-mechanical feedback with the potential to generate oscillatory behavior in the ice sheets. Here we would like to widen the debate by considering that Larsen-B-like glacial analog episodes could have contributed significantly to the registered millennial-scale variablity.

  18. Regional characteristics of sea ice thickness in Canadian shelf and Arctic Archipelago measured by Ground Penetrating Radar

    Institute of Scientific and Technical Information of China (English)

    LI Tao; ZHAO Jinping; JIAO Yutian; HOU Jiaqiang; MU Longjiang

    2015-01-01

    Ground Penetrating Radar (GPR) measurements of sea ice thickness including undeformed ice and ridged ice were carried out in the central north Canadian Archipelago in spring 2010. Results have shown a significant spatial heterogeneity of sea ice thickness across the shelf. The undeformed multi-year fast ice of (2.05±0.09) m thick was investigated southern inshore zone of Borden island located at middle of the observational section, which was the observed maximum thickness in the field work. The less thick sea ice was sampled across a flaw lead with the thicknesses of (1.05±0.11) m for the pack ice and (1.24±0.13) m for the fast ice. At the northernmost spot of the section, the undeformed multi-year pack ice was (1.54±0.22) m thick with a ridged ice of 2.5 to 3 m, comparing to the multi-year fast ice with the thickness of (1.67±0.16) m at the southernmost station in the Prince Gustaf Adolf Sea.

  19. Mg/Casea surface temperatures during the Marine Isotope Stage 31 collapse of the Ross Ice Shelf

    Science.gov (United States)

    Dunbar, G. B.

    2012-04-01

    The recovery of the AND-1b and CRP-1 drill cores from the Southwest Ross Sea highlighted the potential instability in of the Ross Ice Shelf and the West Antarctic Ice Sheet it buttresses. Both cores recovered a few individuals of the planktonic foraminifera Neogloboquadrina pachyderma from marine isotope stage (MIS) 31. This interval is significant because it marks the youngest occurrence of open ocean diatom sediment at AND-1b, which is now situated under the McMurdo Ice Shelf, indicating a substantial retreat of the Ross Ice Shelf occurred during this interglacial. However, sediment deposited after MIS 31 at both sites is represented only by glacial-dominated sediment, suggesting a critical environmental threshold had been crossed enabling the Ross Ice Shelf to form and persist. Numerical modeling by Pollard and DeConto (Nature, 2009) suggested that sub-ice oceanic melting is a critical element in the stability of ice shelves and that "WAIS will begin to collapse when nearby ocean temperatures warm by roughly 5°C." Laser ablation ICPMS measurement of the Mg/Ca content of N. pachyderma shows that although there is considerable heterogeneity in the distribution of Mg in their tests the mean Mg/Ca of a sample population appears proportional to calcification temperature. By empirically calibrating Mg/Ca in CRP-1 N. pachyderma against values measured in modern populations collected from Ross Sea and Southern Ocean sites with SSTs ranging from 1.2°C to 14°C it is concluded that SST during MIS 31 was warmer than today by 5-9°C, consistent with model projections.

  20. The impact of early Holocene Arctic Shelf flooding on climate in an atmosphere–ocean–sea–ice model

    Directory of Open Access Journals (Sweden)

    M. Blaschek

    2013-07-01

    Full Text Available Glacial terminations are characterized by a strong rise in sea level related to melting ice sheets. This rise in sea level is not uniform all over the world, because regional effects (uplift and subsidence of coastal zones are superimposed on global trends. During the early Holocene the Siberian Shelf became flooded before 7.5 ka BP and the coastline reached modern-day high stands at 5 ka BP. This area is currently known as a sea–ice production area and contributes significantly to the sea–ice exported from the Arctic through the Fram Strait. This leads to the following hypothesis: during times of rising sea levels, shelves become flooded, increasing sea–ice production on these shelves, increasing sea–ice volume and export through Fram Strait and causing the sea–ice extent to advance in the Nordic Seas, yielding cooler and fresher sea surface conditions. We have tested this hypothesis in an ocean–sea–ice–atmosphere coupled model of intermediate complexity (LOVECLIM. Our results of an early Holocene Siberian Shelf flooding show that in our model the Northern Hemisphere sea–ice production is increased (15% and that the Northern Hemisphere sea–ice extent increases (14% contrary to our hypothesis with lower sea–ice export through Fram Strait (−15%. The reason of this unexpected behaviour has its origin in a weakened polar vortex, induced by the land-ocean changes due to the shelf flooding, and a resulting decrease of zonality in the Nordic Seas pressure regime. Hence the winter Greenland high and the Icelandic low strengthen, yielding stronger winds on both sides of the Nordic Seas. Increased winds along the East Greenland Current support local sea–ice production and transport towards the south, resulting in a wider sea–ice cover and a southward shift of convection areas. The overall strength of the Atlantic Meridional Overturning Circulation is reduced by 4% and the heat transport in the Atlantic basin by 7%, resulting

  1. The impact of early Holocene Arctic shelf flooding on climate in an atmosphere-ocean-sea-ice model

    Science.gov (United States)

    Blaschek, M.; Renssen, H.

    2013-11-01

    Glacial terminations are characterized by a strong rise in sea level related to melting ice sheets. This rise in sea level is not uniform all over the world, because regional effects (uplift and subsidence of coastal zones) are superimposed on global trends. During the early Holocene the Siberian Shelf became flooded before 7.5 ka BP and the coastline reached modern-day high stands at 5 ka BP. This area is currently known as a sea-ice production area and contributes significantly to the sea-ice exported from the Arctic through the Fram Strait. This leads to the following hypothesis: during times of rising sea levels, shelves become flooded, increasing sea-ice production on these shelves, increasing sea-ice volume and export through the Fram Strait and causing the sea-ice extent to advance in the Nordic Seas, yielding cooler and fresher sea surface conditions. We have tested this hypothesis in an atmosphere-ocean-sea-ice coupled model of intermediate complexity (LOVECLIM). Our experiment on early Holocene Siberian Shelf flooding shows that in our model sea-ice production in the Northern Hemisphere increases (15%) and that sea-ice extent in the Northern Hemisphere increases (14%) but sea-ice export decreases (-15%) contrary to our hypothesis. The reason of this unexpected behaviour has its origin in a weakened polar vortex, induced by the land-ocean changes due to the shelf flooding, and a resulting decrease of zonality in the Nordic Seas pressure regime. Hence the winter Greenland high and the Icelandic low strengthen, yielding stronger winds on both sides of the Nordic Seas. Increased winds along the East Greenland Current support local sea-ice production and transport towards the South, resulting in a wider sea-ice cover and a southward shift of convection areas. The overall strength of the Atlantic meridional overturning circulation is reduced by 4% and the heat transport in the Atlantic basin by 7%, resulting in an annual cooling pattern over the Nordic Seas by

  2. Surface mass balance and water stable isotopes derived from firn cores on three ice rises, Fimbul Ice Shelf, Antarctica

    Science.gov (United States)

    Vega, Carmen P.; Schlosser, Elisabeth; Divine, Dmitry V.; Kohler, Jack; Martma, Tõnu; Eichler, Anja; Schwikowski, Margit; Isaksson, Elisabeth

    2016-11-01

    Three shallow firn cores were retrieved in the austral summers of 2011/12 and 2013/14 on the ice rises Kupol Ciolkovskogo (KC), Kupol Moskovskij (KM), and Blåskimen Island (BI), all part of Fimbul Ice Shelf (FIS) in western Dronning Maud Land (DML), Antarctica. The cores were dated back to 1958 (KC), 1995 (KM), and 1996 (BI) by annual layer counting using high-resolution oxygen isotope (δ18O) data, and by identifying volcanic horizons using non-sea-salt sulfate (nssSO42-) data. The water stable isotope records show that the atmospheric signature of the annual snow accumulation cycle is well preserved in the firn column, especially at KM and BI. We are able to determine the annual surface mass balance (SMB), as well as the mean SMB values between identified volcanic horizons. Average SMB at the KM and BI sites (0.68 and 0.70 mw. e. yr-1) was higher than at the KC site (0.24 mw. e. yr-1), and there was greater temporal variability as well. Trends in the SMB and δ18O records from the KC core over the period of 1958-2012 agree well with other previously investigated cores in the area, thus the KC site could be considered the most representative of the climate of the region. Cores from KM and BI appear to be more affected by local meteorological conditions and surface topography. Our results suggest that the ice rises are suitable sites for the retrieval of longer firn and ice cores, but that BI has the best preserved seasonal cycles of the three records and is thus the most optimal site for high-resolution studies of temporal variability of the climate signal. Deuterium excess data suggest a possible effect of seasonal moisture transport changes on the annual isotopic signal. In agreement with previous studies, large-scale atmospheric circulation patterns most likely provide the dominant influence on water stable isotope ratios preserved at the core sites.

  3. Late Quaternary Advance and Retreat of an East Antarctic Ice Shelf System: Insights from Sedimentary Beryllium-10 Concentrations

    Science.gov (United States)

    Guitard, M. E.; Shevenell, A.; Domack, E. W.; Rosenheim, B. E.; Yokoyama, Y.

    2014-12-01

    Observed retreat of Antarctica's marine-based glaciers and the presence of warm (~2°C) modified Circumpolar Deep Water on Antarctica's continental shelves imply ocean temperatures may influence Antarctic cryosphere stability. A paucity of information regarding Late Quaternary East Antarctic cryosphere-ocean interactions makes assessing the variability, timing, and style of deglacial retreat difficult. Marine sediments from Prydz Bay, East Antarctica contain hemipelagic siliceous mud and ooze units (SMO) alternating with glacial marine sediments. The record suggests Late Quaternary variability of local outlet glacier systems, including the Lambert Glacier/Amery Ice Shelf system that drains 15% of the East Antarctic Ice Sheet. We present a refined radiocarbon chronology and beryllium-10 (10Be) record of Late Quaternary depositional history in Prydz Channel, seaward of the Amery Ice Shelf system, which provides insight into the timing and variability of this important outlet glacier system. We focus on three piston cores (NBP01-01, JPC 34, 35, 36; 750 m water depth) that contain alternating SMO and granulated units uninterrupted by glacial till; the record preserves a succession of glacial marine deposits that pre-date the Last Glacial Maximum. We utilize the ramped pyrolysis preparatory method to improve the bulk organic carbon 14C-based chronology for Prydz Channel. To determine if the SMO intervals reflect open water conditions or sub-ice shelf advection, we measured sedimentary 10Be concentrations. Because ice cover affects 10Be pathways through the water column, sedimentary concentrations should provide information on past depositional environments in Prydz Channel. In Prydz Channel sediments, 10Be concentrations are generally higher in SMO units and lower in glacial units, suggesting Late Quaternary fluctuations in the Amery Ice Shelf. Improved chronologic constraints indicate that these fluctuations occurred on millennial timescales during the Last Glacial

  4. Processes influencing formation of low-salinity high-biomass lenses near the edge of the Ross Ice Shelf

    Science.gov (United States)

    Li, Yizhen; McGillicuddy, Dennis J.; Dinniman, Michael S.; Klinck, John M.

    2017-02-01

    Both remotely sensed and in situ observations in austral summer of early 2012 in the Ross Sea suggest the presence of cold, low-salinity, and high-biomass eddies along the edge of the Ross Ice Shelf (RIS). Satellite measurements include sea surface temperature and ocean color, and shipboard data sets include hydrographic profiles, towed instrumentation, and underway acoustic Doppler current profilers. Idealized model simulations are utilized to examine the processes responsible for ice shelf eddy formation. 3-D model simulations produce similar cold and fresh eddies, although the simulated vertical lenses are quantitatively thinner than observed. Model sensitivity tests show that both basal melting underneath the ice shelf and irregularity of the ice shelf edge facilitate generation of cold and fresh eddies. 2-D model simulations further suggest that both basal melting and downwelling-favorable winds play crucial roles in forming a thick layer of low-salinity water observed along the edge of the RIS. These properties may have been entrained into the observed eddies, whereas that entrainment process was not captured in the specific eddy formation events studied in our 3-D model-which may explain the discrepancy between the simulated and observed eddies, at least in part. Additional sensitivity experiments imply that uncertainties associated with background stratification and wind stress may also explain why the model underestimates the thickness of the low-salinity lens in the eddy interiors. Our study highlights the importance of incorporating accurate wind forcing, basal melting, and ice shelf irregularity for simulating eddy formation near the RIS edge. The processes responsible for generating the high phytoplankton biomass inside these eddies remain to be elucidated.

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

    NARCIS (Netherlands)

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

    2016-01-01

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

  6. Extremotrophs, extremophiles and broadband pigmentation strategies in a high arctic ice shelf ecosystem.

    Science.gov (United States)

    Mueller, Derek R; Vincent, Warwick F; Bonilla, Sylvia; Laurion, Isabelle

    2005-06-01

    Remnant ice shelves along the northern coast of Ellesmere Island, Nunavut, Canada ( approximately 83 degrees N) provide a habitat for cryo-tolerant microbial mat communities. Bioassays of bacterial and primary production were undertaken to quantify the short-term physiological response of the mats to changes in key variables that characterize this cryo-ecosystem (salinity, irradiance and temperature). The heterotrophic versus autotrophic community responses to these stressors differed markedly. The heterotrophic bacteria were extremophilic and specifically adapted to ambient conditions on the ice shelf, whereas the autotrophic community had broader tolerance ranges and optima outside the ambient range. This latter, extremotrophic response may be partly due to a diverse suite of pigments including oligosaccharide mycosporine-like amino acids, scytonemins, carotenoids, phycobiliproteins and chlorophylls that absorb from the near UV-B to red wavelengths. These pigments provide a comprehensive broadband strategy for coping with the multiple stressors of high irradiance, variable salinity and low temperatures in this extreme cryo-environment.

  7. Downhole measurements in the AND-1B borehole, ANDRILL McMurdo Ice Shelf Project, Antarctica

    Science.gov (United States)

    Morin, R.; Williams, T.; Henrys, S.; Crosby, T.; Hansaraj, D.

    2007-01-01

    A comprehensive set of downhole measurements was collected in the AND-1B drillhole as part of the on-ice scientific programme defined for the McMurdo Ice Shelf (MIS) Project. Geophysical logs were recorded over two operation phases and consisted of calliper, temperature, fluid conductivity, induction resistivity, magnetic susceptibility, natural gamma activity, acoustic televiewer, borehole deviation, and dipmeter. In addition, two standard vertical seismic profiles (VSP) and one walk-away VSP were obtained. Radioactive logs (porosity and density) were not run because of unstable borehole conditions. Although the total depth of the hole is 1285 metres below seafloor (mbsf), the depth range for in situ measurements was limited by the length of the wireline (1018 mbsf) and by the nullification of some geophysical logs due to the presence of steel casing. A depth correction was derived to account for systematic discrepancies in depth between downhole measurements and cores; consequently, log responses can be directly compared to core properties. The resulting data are amenable to studies of cyclicity and climate, heat flux and fluid flow, and stricture and stress. When integrated with physical properties and fractures measured on the core, this information should play a significant role in addressing many of the scientific objectives of the ANDRILL programme.

  8. Radio-frequency Attenuation Length, Basal-Reflectivity, Depth, and Polarization Measurements from Moore's Bay in the Ross Ice-Shelf

    CERN Document Server

    Barwick, S W; Besson, D; Duffin, T; Hanson, J C; Klein, S R; Kleinfelder, S A; Reed, C; Roumi, M; Stezelberger, T; Tatar, J; Walker, J; Zou, L

    2014-01-01

    Radio-glaciological parameters from Moore's Bay, in the Ross Ice Shelf, have been measured. The thickness of the ice shelf in Moore's Bay was measured from reflection times of radio-frequency pulses propagating vertically through the shelf and reflecting from the ocean. The average depth obtained is $576\\pm8$ m. The temperature-averaged attenuation length of the ice column, $\\langle L \\rangle$, is derived from the returned power assuming 100\\% reflection. A linear fit to the data yields $\\langle L(\

  9. Mass budgets of the Lambert, Mellor and Fisher Glaciers and basal fluxes beneath their flowbands on Amery Ice Shelf

    Institute of Scientific and Technical Information of China (English)

    WEN; JiaHong

    2007-01-01

    [1]Bentley C R,Giovinetto M R.Mass balance of Antarctica and sea level change.In:Weller G,Wilson C L,Severin B AB,eds.Collection in International Conference on the Role of the Polar Regions in Global Change:Proceedings of a Conference Held June 11―15,1990 at the University of Alaska Fairbanks.Vol II.Fairbanks:Geophysical Institute/Center for Global Change and Arctic System Research,University of Alaska,1991.481―488[2]Jacobs S S,Helmer H H,Doake C S M,et al.Melting of ice shelves and the mass balance of Antarctica.J Glaciol,1992,38(130):375―387[3]Rignot E,Thomas R H.Mass balance of polar ice sheets.Science,2002,297:1502―1506[4]Davis C H,Li Y,McConnell J R et al.Snowfall-driven growth in East Antarctic Ice Sheet mitigates recent sea-level rise.Science,2005,308:1898―1901[5]Zwally H J,Giovinetto M B,Li J,et al.Mass changes of the Greenland and Antarctic ice sheets and shelves and contributions to sea-level rise:1992―2002.J Glaciol,2005,51(175):509―527[6]Velicogna I,Wahr J.Measurements of time-variable gravity show mass loss in Antarctica.Science,2006,311:1754―1756[7]Whillans I M,Bindschadler R A.Mass balance of Ice Stream B,West Antarctica.Ann Glaciol,1998,11:187―193.[8]Berthier E,Raup B,Scambos E.New velocity map and mass-balance estimate of Mertz Glacier,East Antarctica,derived from Landsat sequential imagery.J Glaciol,2003,49(167):503―511[9]The ISMASS Committee.Recommendations for the collection and synthesis of Antarctic Ice Sheet mass balance data.Glob Planet Change,2004,42:1―15[10]Jacobs S S,Hellmer H H,Jenkins A.Antarctic ice sheet melting in the Southeast Pacific.Geophys Res Lett,1996,23(9):957―960[11]Rignot E,Jacobs S S.Rapid bottom melting widespread near Antarctic Ice Sheet grounding lines.Science,2002,296:2020―2023[12]Jenkins A and Doake C S M.Ice-ocean interaction on Ronne Ice Shelf,Antarctica.J Geophys Res,1991,96(C1):791―813[13]Gray L,Short N,Bindschadler R,et al.RADARSAT interferometry for Antarctic grounding-zone mapping

  10. A three-dimensional full Stokes model of the grounding line dynamics: effect of a pinning point beneath the ice shelf

    Directory of Open Access Journals (Sweden)

    L. Favier

    2012-01-01

    Full Text Available The West Antarctic ice sheet is confined by a large area of ice shelves, fed by inland ice through fast flowing ice streams. The dynamics of the grounding line, which is the line-boundary between grounded ice and the downstream ice shelf, has a major influence on the dynamics of the whole ice sheet. However, most ice sheet models use simplifications of the flow equations, as they do not include all the stress components, and are known to fail in their representation of the grounding line dynamics. Here, we present a 3-D full Stokes model of a marine ice sheet, in which the flow problem is coupled with the evolution of the upper and lower free surfaces, and the position of the grounding line is determined by solving a contact problem between the shelf/sheet lower surface and the bedrock. Simulations are performed using the open-source finite-element code Elmer/Ice within a parallel environment. The model's ability to cope with a curved grounding line and the effect of a pinning point beneath the ice shelf are investigated through prognostic simulations. Starting from a steady state, the sea level is slightly decreased to create a contact point between a seamount and the ice shelf. The model predicts a dramatic decrease of the shelf velocities, leading to an advance of the grounding line until both grounded zones merge together, during which an ice rumple forms above the contact area at the pinning point. Finally, we show that once the contact is created, increasing the sea level to its initial value does not release the pinning point and has no effect on the ice dynamics, indicating a stabilising effect of pinning points.

  11. Unique manifestations of mixed-phase cloud microphysics over Ross Island and the Ross Ice Shelf, Antarctica

    Science.gov (United States)

    Scott, Ryan C.; Lubin, Dan

    2016-03-01

    Spaceborne radar and lidar observations from the CloudSat and CALIPSO satellites are used to compare seasonal variations in the microphysical and radiative properties of clouds over Ross Island, Antarctica, with two contrasting Arctic atmospheric observatories located in Barrow, Alaska, and Summit, Greenland. At Ross Island, downstream from recurrent intrusions of marine air over the West Antarctic Ice Sheet and eastern Ross Ice Shelf, clouds exhibit a tendency toward the greatest geometrical thickness and coldest temperatures in summer, the largest average ice water content, IWC, at low altitude during summer and autumn, the most abundant IWC at cold mixed-phase temperatures (-40°C ice water on the surface energy budget year round, all with likely origins in orographic lifting of marine air over complex ice sheet and mountainous terrain. Clouds over Barrow form and evolve in a contrastingly warm and moist atmosphere and on average contain the largest liquid water content and ice and liquid water effective particle radii, re, year round. In contrast, clouds observed atop the central Greenland Ice Sheet are relatively tenuous, containing the smallest IWC and ice re of all sites.

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

    Science.gov (United States)

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

    2016-04-01

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

  13. Mass budgets of the Lambert, Mellor and Fisher Glaciers and basal fluxes beneath their flowbands on Amery Ice Shelf

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    We used in situ measurements and remote-sensing data sets to evaluate the mass budgets of the Lambert,Mellor and Fisher Glaciers and the basal melting and freezing rates beneath their flowbands on the Amery Ice Shelf.Our findings show the Lambert and Mellor Glaciers upstream of the ANARE Lambert Glacier Basin (LGB) traverse may have positive imbalances of 3.9±2.1 Gt a-1 and 2.1±2.4 Gt a-1,respectively,while the Fisher Glacier is approximately in balance.The upstream region as a whole has a positive imbalance of 5.9±4.9 Gt a-1.The three same glaciers downstream of the ANARE LGB traverse line are in negative imbalance,where the whole downstream region has a negative imbalance of -8.5±5.8 Gt a-1.Overall the mass budgets of the Lambert,Mellor,and Fisher Glaciers are close to balance,and the collective three-glacier system is also nearly in balance with a mass budget of -2.6±6.5 Gt a-1.The significant positive imbalances for the interior basin upstream of the ice-movement stations established in the early 1970s (GL line) reported previously are possibly due to an overestimate of the total accumulation and an underestimate of the ice flux through the GL line.The mean melting rate is -23.0±3.5 m ice a-1 near the southern grounding line,which decreases rapidly downstream,and transitions to refreezing at around 300 km from the southern extremity of the Amery Ice Shelf.Freezing rates along the flowbands are around 0.5±0.1 to 1.5±0.2 m ice a-1.The percentage of ice lost from the interior by basal melting beneath the flowbands is about 80%±5%.The total basal melting and refreezing beneath the three flowbands is 50.3±7.5 Gt ice a-1 and 7.0±1.1 Gt ice a-1,respectively.We find a much larger total basal melting and net melting than the results for the whole Amery Ice Shelf derived from previous modeling and oceanographic measurements.

  14. Sinking Particle Flux in the Sea Ice Zone of the Amundsen Shelf, Antarctica

    Science.gov (United States)

    Kim, M.; Hwang, J.; Kim, H. J.; Kim, D.; Ducklow, H. W.; Lee, S. H.; Yang, E. J.; Lee, S.

    2014-12-01

    We have examined the flux, compositions of biogenic components, and isotopic values of sinking particles collected by a sediment trap deployed in the sea ice zone (SIZ) of the Amundsen Sea from January 2011 for one year. Major portion of the particle flux occurred during the austral summer in January and February when sea ice concentration was reduced to below 60 %. Biogenic components, dominated by opal, accounted for over 75 % during this high flux period. The dominant source of sinking particles shifted from diatoms to soft-tissued organisms, evidenced by high particulate organic carbon (POC) content (> 30 %) during the polar night. CaCO3 content and its contribution to total particle flux were low throughout the study period. Contribution of aged POC likely supplied from sediment resuspension was considerable only from October to December, evidenced by low radiocarbon content and relatively high (30-50 %) content of the non-biogenic component. When compared to POC flux inside the Amundsen Sea polynya obtained by the US Amundsen Sea Polynya International Research Expedition (ASPIRE), the POC flux integrated over the austral summer in the SIZ was virtually identical although maximum POC flux was about half that inside the Amundsen Sea polynya. This comparatively high POC flux in the SIZ may be caused by persistence of phytoplankton bloom for longer period and more efficient export of organic matter owing to the diatom-dominant plankton community. If this observation is a general phenomenon on the Amundsen shelf, the role of the SIZ compared to the polynyas need to be examined more carefully when trying to characterize the POC export in this region.

  15. Snow on the Ross Ice Shelf: comparison of reanalyses and observations from automatic weather stations

    Directory of Open Access Journals (Sweden)

    L. Cohen

    2013-03-01

    Full Text Available An analysis of precipitation from the ECMWF ERA-Interim and NCEP/NCAR Reanalysis-2 datasets is developed using snow accumulation measurements from Automatic Weather Stations (AWS around the Ross Ice Shelf (RIS, Antarctica. The high temporal resolution of the AWS snow accumulation measurements allow for a new, event-based comparison of reanalyses precipitation to in-situ observations. Snow accumulation records from nine AWS provide multiple years of accumulation data between 2008–2012 over a relatively large, homogeneous region of Antarctica and provide the basis for a statistical evaluation of accumulation events. The analysis shows that ERA-Interim reproduces significantly more precipitation events than NCEP-2 and these events correspond to an average 8.2% more precipitation. Correlations between reanalyses and AWS event sizes are seen at several stations (at > 90% significance levels and show that ERA-Interim consistently produces larger precipitation events than NCEP-2. The significant and complex effects of wind on snow accumulation (which can both limit and enhance accumulation make determining biases in the reanalyses data not possible with the AWS data, however the analysis does illustrate significant and important differences between ERA-Interim and NCEP-2 precipitation.

  16. Characteristics of the near-surface atmosphere over the Ross Ice Shelf, Antarctica

    Science.gov (United States)

    Cassano, John J.; Nigro, Melissa A.; Lazzara, Matthew A.

    2016-04-01

    Two years of data from a 30 m instrumented tower are used to characterize the near-surface atmospheric state over the Ross Ice Shelf, Antarctica. Stable stratification dominates the surface layer at this site, occurring 83% of the time. The strongest inversions occur for wind speeds less than 4 m s-1 and the inversion strength decreases rapidly as wind speed increases above 4 m s-1. In summer unstable stratification occurs 50% of the time and unstable conditions are observed in every season. A novel aspect of this work is the use of an artificial neural network pattern identification technique, known as self-organizing maps, to objectively identify characteristic potential temperature profiles that span the range of profiles present in the 2 year study period. The self-organizing map clustering technique allows the more than 100,000 observed potential temperature profiles to be represented by just 30 patterns. The pattern-averaged winds show distinct and physically consistent relationships with the potential temperature profiles. The strongest winds occur for the nearly well mixed but slightly stable patterns and the weakest winds occur for the strongest inversion patterns. The weakest wind shear over the depth of the tower occurs for slightly unstable profiles and the largest wind shear occurs for moderately strong inversions. Pattern-averaged log wind profiles are consistent with theoretical expectations. The log wind profiles exhibit a kinked profile for the strongest inversion cases indicative of decoupling of the winds between the bottom and top of the tower.

  17. Observations and modeling of ocean-induced melt beneath Petermann Glacier Ice Shelf in northwestern Greenland

    Science.gov (United States)

    Cai, Cilan; Rignot, Eric; Menemenlis, Dimitris; Nakayama, Yoshihiro

    2017-08-01

    We update observationally based estimates of subaqueous melt, Qm, beneath Petermann Glacier Ice Shelf (PGIS), Greenland, and model its sensitivity to oceanic thermal forcing, TF, and subglacial runoff, Qsg, using the Massachusetts Institute of Technology general circulation model (MITgcm), in a two-dimensional domain, with 20 m vertical and 40 m horizontal resolution at the grounding line. We adjust the drag coefficient to match the observationally based Qm. With the inclusion of Qsg, the maximum melt rate (Qmmax) is 2 times larger in summer and 1/3 larger annually than in winter. Qmmax increases above linear with TF and below linear with Qsg. We estimate that Qmmax increased by 24% (+8.1 m/yr) beneath PGIS from the 1990s to the 2000s from a 0.21°C warming in ocean temperature and a doubling in Qsg, hence contributing to its thinning. If the PGIS is removed, we estimate that the modeled melt rate near the grounding line will increase 13-16 times.

  18. Seafloor glacial geomorphology in a cross shelf trough: insights into the deglaciation of the Melville Bay Ice Stream

    Science.gov (United States)

    Newton, Andrew; Huuse, Mads

    2016-04-01

    Compared to other glaciated margins such as offshore mid-Norway and Svalbard, the Greenland continental shelf has, until recently, been the subject of only a limited amount of academic and industry research. This has been mainly due to the difficulty and expense of obtaining data in such harsh and operationally complex settings. Climate amelioration and technological advance has, particularly in recent years, allowed both academics and industry to substantially increase data collection across the many glaciated continental shelves in the Northern Hemisphere. Baffin Bay has been one of the primary regions of interest for the hydrocarbon industry which has sought to operate in the frontier basins offshore Greenland. As a result of these industry operations, a large database of geophysical and geological data has been collected. Some of this data has been made available to glacial scientists and provides a unique opportunity to investigate the seafloor geomorphology for regions where the majority of previous work has been hypothetical rather than grounded in geological evidence. In the work presented here we present a landform record offshore NW Greenland in the Melville Bay cross-shelf trough. This is one of the largest troughs on the entire Greenland shelf and measures up to 140 km in width. Shallow-marine cores collected in the coastal part of the trough show bedrock of Miocene age and indicate that a significant cover has likely been removed from the shelf by ice streams operating through the Late Cenozoic. This material has then been deposited at the shelf edge as a trough mouth fan. Using multibeam and seismic reflection data a large number of glacial landforms are observed and mapped in the trough. These include mega-scale glacial lineations, grounding-zone wedges, iceberg scours, and iceberg grounding pits. These landforms are used to reconstruct the ice dynamics of the Melville Bugt Ice Stream at the last glacial maximum and during its deglaciation. The

  19. Ice Velocity Mapping of Ross Ice Shelf, Antarctica by Matching Surface Undulations Measured by Icesat Laser Altimetry

    Science.gov (United States)

    Lee, Choon-Ki; Han, Shin-Chan; Yu, Jaehyung; Scambos, Ted A.; Seo, Ki-Weon

    2012-01-01

    We present a novel method for estimating the surface horizontal velocity on ice shelves using laser altimetrydata from the Ice Cloud and land Elevation Satellite (ICESat; 20032009). The method matches undulations measured at crossover points between successive campaigns.

  20. The sensitivity of Arctic sea ice production to shelf flooding during the early Holocene: a modelling study

    Science.gov (United States)

    Blaschek, M.; Renssen, H.

    2012-04-01

    During the last deglaciation, the global sea-level started rising, changing the coastlines from an early Holocene stand (40 m lower than today at approximately 10 kyr BP, Siddall et al., 2003) to modern day coastlines. Proxy evidence shows that this transgression occurred non-uniformly over the globe. For instance, Bauch et al. (2001) report for the Laptev Sea (Arctic Ocean), that the modern coastline was only established at 5 kyr BP after a fast transgression from the early Holocene, leading to a flooding of the extensive shelf area. This shelf area is presently regarded to be an important production zone of Arctic sea ice, playing an important role in the dynamics of sea ice in the Arctic, as well as its export to the Nordic Seas along the East Greenland Current (EGC). Through this sea ice export, changes in the Laptev Sea shelf area during the Holocene could potentially have had a substantial impact on the sea surface conditions of the EGC, and the Denmark Strait, which is known to be sensitive to sea ice. This is consistent with a rapid increase in sea ice export through the EGC around 5 kyr BP as reported by Jennings et al. (2002). In this study we investigate the impact of this Arctic shelf flooding on sea ice production in the Holocene, and on the climate of the Nordic Seas in the LOVECLIM1.2 global ocean-atmosphere-vegetation model. We present results of several experiments in which we study the sensitivity of Arctic sea ice production to various Arctic shelf areas under early Holocene conditions (9 kyr BP). We approach this by changing the land-sea mask to represent different lower-than-present sea-level coastlines. For example, we perform experiments with the Last Glacial Maximum (LGM) land-sea mask, representing a lowering of the sea-level by 120 m, while keeping other forcings at 9 kyr BP. A further step is to modify selected areas in the Arctic, such as the Laptev Sea area, to examine the importance of different areas. Our results help to explain long

  1. Melt rate sensitivities underneath Pine Island Ice Shelf derived from an adjoint general circulation model

    OpenAIRE

    Losch, Martin; Heimbach, Patrick

    2012-01-01

    Increased melt rates under floating ice shelves around Antarctica have been suggested as a dominant cause for observed acceleration of marine ice sheets that feed these ice shelves. The associated melt rates are difficult to observe directly. We present first steps towards estimating the melt rates underneath floating ice shelves from accessible hydrography data and optimal control methods. We address to which extent ocean hydrographic observations away from the ice-ocean boundary can be...

  2. Sedimentology and chronology of the advance and retreat of the last British-Irish Ice Sheet on the continental shelf west of Ireland

    Science.gov (United States)

    Peters, Jared L.; Benetti, Sara; Dunlop, Paul; Ó Cofaigh, Colm; Moreton, Steven G.; Wheeler, Andrew J.; Clark, Christopher D.

    2016-05-01

    The last British-Irish Ice Sheet (BIIS) had extensive marine-terminating margins and was drained by multiple large ice streams and is thus a useful analogue for marine-based areas of modern ice sheets. However, despite recent advances from investigating the offshore record of the BIIS, the dynamic history of its marine margins, which would have been sensitive to external forcing(s), remain inadequately understood. This study is the first reconstruction of the retreat dynamics and chronology of the western, marine-terminating, margin of the last (Late Midlandian) BIIS. Analyses of shelf geomorphology and core sedimentology and chronology enable a reconstruction of the Late Midlandian history of the BIIS west of Ireland, from initial advance to final retreat onshore. Five AMS radiocarbon dates from marine cores constrain the timing of retreat and associated readvances during deglaciation. The BIIS advanced without streaming or surging, depositing a bed of highly consolidated subglacial traction till, and reached to within ˜20 km of the shelf break by ˜24,000 Cal BP. Ice margin retreat was likely preceded by thinning, grounding zone retreat and ice shelf formation on the outer shelf by ˜22,000 Cal BP. This ice shelf persisted for ≤2500 years, while retreating at a minimum rate of ˜24 m/yr and buttressing a >150-km long, 20-km wide, bathymetrically-controlled grounding zone. A large (˜150 km long), arcuate, flat-topped grounding-zone wedge, termed here the Galway Lobe Grounding-Zone Wedge (GLGZW), was deposited below this ice shelf and records a significant stillstand in BIIS retreat. Geomorphic relationships indicate that the BIIS experienced continued thinning during its retreat across the shelf, which led to increased topographic influence on its flow dynamics following ice shelf break up and grounding zone retreat past the GLGZW. At this stage of retreat the western BIIS was comprised of several discrete, asynchronous lobes that underwent several readvances

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

    Science.gov (United States)

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

    2015-05-01

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

  4. Rapid drawdown of Antarctica's Wordie Ice Shelf glaciers in response to ENSO/Southern Annular Mode-driven warming in the Southern Ocean

    Science.gov (United States)

    Walker, C. C.; Gardner, A. S.

    2017-10-01

    Here we investigate the largest acceleration in ice flow across all of Antarctica between ∼2008 InSAR and 2014 Landsat velocity mappings. This occurred in glaciers that used to feed into the Wordie Ice Shelf on the west Antarctic Peninsula, which rapidly disintegrated in ∼1989. Between 2008 and 2014, these glaciers experienced at least a threefold increase in surface elevation drawdown relative to the 2002-2008 time period. After ∼20 yrs of relative stability, it is unlikely that the ice shelf collapse played a role in the large response. Instead, we find that the rapid acceleration and surface drawdown is linked to enhanced melting at the ice-ocean boundary, attributable to changes in winds driven by global atmospheric circulation patterns, namely the El Niño-Southern Oscillation (ENSO) and Southern Annular Mode (SAM), linking changes in grounded ice to atmospheric-driven ocean warming.

  5. Widespread collapse of the Ross Ice Shelf during the late Holocene reconstracted from compound specific C-14 and meteoric Be-10

    Science.gov (United States)

    Yokoyama, Y.; Anderson, J. B.; Yamane, M.; Simkins, L. M.; Miyairi, Y.; Yamazaki, T.; Koizumi, M.; Kusahara, K.; Suga, H.; Prothro, L. O.; Hasumi, H.; Southon, J. R.; Ohkouchi, N.

    2016-12-01

    Ice shelves are among the most rapidly changing elements of the modern cryosphere, due to their sensitivity to atmospheric warming and to melting from beneath by warm ocean currents. The marine-based West Antarctic Ice Sheet (WAIS) is vulnerable to future climate change, but the degree to which is not well constrained. Obtaining a better understanding requires geological evidence of retreat history, which is complicated by the lack of proximal marine calcareous sediment, largely preventing construction of a precise chronology. Here we reconstruct the history of Ross Ice Shelf retreat based on compound specific (CS) radiocarbon dating and meteoric 10Be measurement . Taken together with land-based grounding line reconstructions, our results provide strong constraints on numerical glacial models (Yokoyama et al., 2016 PNAS). Dynamic retreat of the ice shelf edge, by as much as 400 km occurred between 5,000 and 1,500 years ago, resulting in a maritime climate for inland Antarctica as recorded in ice cores from Siple Dome and Byrd. This coincided with ocean volume increase observed in far field sea level records (Yokoyama et al., 2012 GRL; Yokoyama et al., 2016 QI). Modeling results indicate that retreat of the ice shelf resulted from combined atmospheric warming and warm ocean currents impinging onto the continental shelf.

  6. Preliminary ice shelf-ocean simulation results from idealized standalone-ocean and coupled model intercomparison projects (MIPs)

    Science.gov (United States)

    Asay-Davis, Xylar; Martin, Daniel

    2016-04-01

    The second Ice Shelf-Ocean MIP (ISOMIP+) and the first Marine Ice Sheet-Ocean MIP (MISOMIP1) prescribe a set of idealized experiments for ocean models with ice-shelf cavities and coupled ice sheet-ocean models, respectively. ISOMIP+ and MISOMIP1 were designed together with the third Marine Ice Sheet MIP (MISMIP+) with three main goals, namely that the MIPs should provide: a controlled forum for researchers to compare their model results with those from other models during model development. a path for testing components in the process of developing coupled ice sheet-ocean models. a basic setup from which a large variety of parameter and process studies can usefully be performed. The experimental design for the three MIPs is currently under review in Geoscientific Model Development (Asay-Davis et al. 2015, doi:10.5194/gmdd-8-9859-2015). We present preliminary results from ISOMIP+ and MISOMIP1 experiments using several ocean-only and coupled ice sheet-ocean models. Among ocean models, we show that differences in model behavior are significant enough that similar results can only be achieved by tuning model parameters (e.g. boundary-layer transfer coefficients, drag coefficients, vertical mixing parameterizations) for each models. This tuning is constrained by a desired mean melt rate in quasi-steady state under specified forcing conditions, akin to how models would be tuned based on observations for non-idealized simulations. We also present a number of parameter studies based the MIP experiments. Again, using several models, we show that melt rates respond sub-linearly to both changes in the square root of the drag coefficient and the heat-transfer coefficient, and that melting is relatively insensitive to horizontal-mixing coefficients (perhaps because the resolution is sufficient to permit eddies) but more sensitive to vertical-mixing coefficients. We show that the choice of the equation of state (linear or nonlinear) does not have a significant impact as long as

  7. Long-term record of Barents Sea Ice Sheet advance to the shelf edge from a 140,000 year record

    Science.gov (United States)

    Pope, Ed L.; Talling, Peter J.; Hunt, James E.; Dowdeswell, Julian A.; Allin, Joshua R.; Cartigny, Matthieu J. B.; Long, David; Mozzato, Alessandro; Stanford, Jennifer D.; Tappin, David R.; Watts, Millie

    2016-10-01

    The full-glacial extent and deglacial behaviour of marine-based ice sheets, such as the Barents Sea Ice Sheet, is well documented since the Last Glacial Maximum about 20,000 years ago. However, reworking of older sea-floor sediments and landforms during repeated Quaternary advances across the shelf typically obscures their longer-term behaviour, which hampers our understanding. Here, we provide the first detailed long-term record of Barents Sea Ice Sheet advances, using the timing of debris-flows on the Bear Island Trough-Mouth Fan. Ice advanced to the shelf edge during four distinct periods over the last 140,000 years. By far the largest sediment volumes were delivered during the oldest advance more than 128,000 years ago. Later advances occurred from 68,000 to 60,000, 39,400 to 36,000 and 26,000 to 20,900 years before present. The debris-flows indicate that the dynamics of the Saalian and the Weichselian Barents Sea Ice Sheet were very different. The repeated ice advance and retreat cycles during the Weichselian were shorter lived than those seen in the Saalian. Sediment composition shows the configuration of the ice sheet was also different between the two glacial periods, implying that the ice feeding the Bear Island Ice stream came predominantly from Scandinavia during the Saalian, whilst it drained more ice from east of Svalbard during the Weichselian.

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

    NARCIS (Netherlands)

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

    2014-01-01

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

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

    Science.gov (United States)

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

    2007-01-01

    Changes in the area and volume of polar ice sheets are intricately linked to changes in global climate, and the resulting changes in sea level could severely impact the densely populated coastal regions on Earth. Melting of the West Antarctic part alone of the Antarctic ice sheet would cause a sea-level rise of approximately 6 meters (m). The potential sea-level rise after melting of the entire Antarctic ice sheet is estimated to be 65 m (Lythe and others, 2001) to 73 m (Williams and Hall, 1993). The mass balance (the net volumetric gain or loss) of the Antarctic ice sheet is highly complex, responding differently to different conditions in each region (Vaughan, 2005). In a review paper, Rignot and Thomas (2002) concluded that the West Antarctic ice sheet is probably becoming thinner overall; although it is thickening in the west, it is thinning in the north. Thomas and others (2004), on the basis of aircraft and satellite laser altimetry surveys, believe the thinning may be accelerating. Joughin and Tulaczyk (2002), on the basis of analysis of ice-flow velocities derived from synthetic aperture radar, concluded that most of the Ross ice streams (ice streams on the east side of the Ross Ice Shelf) have a positive mass balance, whereas Rignot and others (2004) infer even larger negative mass balance for glaciers flowing northward into the Amundsen Sea, a trend suggested by Swithinbank and others (2003a,b; 2004). The mass balance of the East Antarctic ice sheet is thought by Davis and others (2005) to be strongly positive on the basis of the change in satellite altimetry measurements made between 1992 and 2003. Measurement of changes in area and mass balance of the Antarctic ice sheet was given a very high priority in recommendations by the Polar Research Board of the National Research Council (1986), in subsequent recommendations by the Scientific Committee on Antarctic Research (SCAR) (1989, 1993), and by the National Science Foundation?s (1990) Division of Polar

  10. Nitrogen and carbon limitation of planktonic primary production and phytoplankton-bacterioplankton coupling in ponds on the McMurdo Ice Shelf, Antarctica

    DEFF Research Database (Denmark)

    Sorrell, B.K.; Hawes, I.; Safi, K.

    2013-01-01

    The nature of nutrient limitation and coupling of planktonic primary and secondary production were investigated in meltwater ponds of the Ross Ice Shelf, Antarctica, using regression tree analysis and multiple regression. Phytoplankton were primaril N-limited but inorganic carbon apparently co...

  11. Glacial landforms on German Bank, Scotian Shelf: evidence for Late Wisconsinan ice-sheet dynamics and implications for the formation of De Geer moraines

    Science.gov (United States)

    Todd, Brian J.; Valentine, Page C.; Longva, Oddvar; Shaw, John

    2007-01-01

    The extent and behaviour of the southeast margin of the Laurentide Ice Sheet in Atlantic Canada is of significance in the study of Late Wisconsinan ice sheet-ocean interactions. Multibeam sonar imagery of subglacial, ice-marginal and glaciomarine landforms on German Bank, Scotian Shelf, provides evidence of the pattern of glacial-dynamic events in the eastern Gulf of Maine. Northwest-southeast trending drumlins and megaflutes dominate northern German Bank. On southern German Bank, megaflutes of thin glacial deposits create a distinct northwest-southeast grain. Lobate regional moraines (>10km long) are concave to the northwest, up-ice direction and strike southwest-northeast, normal to the direction of ice flow. Ubiquitous, overlying De Geer moraines (

  12. Subglacial bathymetry and sediment distribution beneath Pine Island Glacier ice shelf modeled using aerogravity and in situ geophysical data: New results

    Science.gov (United States)

    Muto, Atsuhiro; Peters, Leo E.; Gohl, Karsten; Sasgen, Ingo; Alley, Richard B.; Anandakrishnan, Sridhar; Riverman, Kiya L.

    2016-01-01

    Pine Island Glacier (PIG) in the Amundsen Sea sector of the West Antarctic Ice Sheet (WAIS) is losing mass and contributing to global sea-level rise at an accelerating rate. Although recent observations and modeling have identified the incursion of relatively warm Circumpolar Deep Water (CDW) beneath the PIG ice shelf (PIGIS) as the main driver of this ice-mass loss, the lack of precise bathymetry limits furthering our understanding of the ice-ocean interactions and improving the accuracy of modeling. Here we present updated bathymetry and sediment distribution beneath the PIGIS, modeled by the inversion of aerogravity data with constraints from active-source seismic data, observations from an autonomous underwater vehicle, and the regional gravity-anomaly field derived from satellite gravity observations. Modeled bathymetry shows a submarine ridge beneath the middle of PIGIS that rises ∼350 to 400 m above the surrounding sea floor, with a minimum water-column thickness of ∼200 m above it. This submarine ridge continues across the whole width of the 45-km wide ice shelf, with no deep troughs crossing it, confirming the general features of the previously predicted sub-ice-shelf ocean circulation. However, the relatively low resolution of the aerogravity data and limitations in our inversion method leave a possibility that there is an undetected, few-kilometers-wide or narrower trough that may alter the predicted sub-ice-shelf ocean circulation. Modeled sediment distribution indicates a sedimentary basin of up to ∼800 m thick near the current grounding zone of the main PIG trunk and extending farther inland, and a region seaward of the submarine ridge where sediments are thin or absent with exposed crystalline basement that extends seaward into Pine Island Bay. Therefore, the submarine ridge marks the transition from a thick sedimentary basin providing a smooth interface over which ice could flow easily by sliding or sediment deformation, to a region with no to

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

    Science.gov (United States)

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

    2008-01-01

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

  14. Hunting Plan

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This plan provides guidelines for administration of hunting activity and for development, maintenance, and enforcement of regulations and guidelines on Tamarac...

  15. Rift in Antarctic Glacier: a Unique Chance to Study Ice Shelf Retreat

    Science.gov (United States)

    Howat, Ian M.; Jezek, Ken; Studinger, Michael; Macgregor, Joseph A.; Paden, John; Floricioiu, Dana; Russell, Rob; Linkswiler, Matt; Dominguez, Roseanne T.

    2012-01-01

    It happened again, but this time it was caught in the act. During the last week of September 2011 a large transverse rift developed across thefloating terminus of West Antarcticas PineIsland Glacier, less than 5 years after its lastlarge calving event, in 2007 (Figure 1). PineIsland Glaciers retreat has accelerated substantiallyin the past 2 decades, and it is nowlosing 50 gigatons of ice per year, or roughly 25 of Antarcticas total annual contributionto sea level rise [Rignot et al., 2008]. The glaciers recent accelerated retreat is likely triggered by ocean warming and increased submarine melting. As such, it is of significant interest to glaciologists and of heightened societal relevance.

  16. Current surges and seabed erosion near the shelf break in the Canadian Beaufort Sea: A response to wind and ice motion stress

    Science.gov (United States)

    Forest, Alexandre; Osborne, Philip D.; Curtiss, Gregory; Lowings, Malcolm G.

    2016-08-01

    Estimating the erosion potential of seabed sediments and the magnitude of the resulting suspended load in relation to current dynamics near the shelf break is a key issue for better understanding shelf-slope sediment transport. On the outer Mackenzie Shelf (Canadian Beaufort Sea, Arctic Ocean), a thin and discontinuous veneer of recent surficial clays overlie old glaciomarine sediments that further pinch out at the shelf edge. Gas and fluid venting is known to underlie part of sediment instability in the area, but recent mooring-based measurements also indicate that sediments near the shelf break are recurrently remobilized by strong subsurface currents. Here, we relate storms to the development of current surges that resulted in the abrupt resuspension of sediments at two locations along the shelf break. Near-bottom concentrations of suspended sediments were estimated using the acoustic backscatter of high-frequency acoustic Doppler current profilers deployed from September 2011 to September 2013 as part of the Beaufort Regional Environmental Assessment (BREA) program. Near-bottom currents near the shelf edge (140 to 150 m isobaths) were characterized by recurring episodes of elevated velocities (instantaneous speeds up to ~ 40-50 cm s-1) that were extensions of current surges (~ 60-80 cm s-1) occurring in the core of the shelfbreak jet located at ca. 90-120 m. Sudden peaks in suspended sediments (above 100 g m-3) corresponded closely with current surges in the near-bottom boundary layer (fade, such as during the major ice fracturing events of January to March 2013 that were associated with strong and persistent current speeds.

  17. Study of inter-annual variations in surface melting over Amery Ice Shelf, East Antarctica, using space-borne scatterometer data

    Indian Academy of Sciences (India)

    S R Oza; R K K Singh; N K Vyas; Abhijit Sarkar

    2011-04-01

    The widespread retreat of glaciers can be considered as a response to the climate change. Being the largest retreating glacier–ice shelf system in East Antarctica, the Amery Ice Shelf–Lambert Glacier system plays an important role in contributing to sea level rise as well as the surrounding environment and climate. The present study is focused on the investigation of surface melting over the ice shelf using QuikSCAT Ku-band scatterometer data for more than 100 months covering the period from January 2000 to July 2009. The corresponding weather data of Davis Station was obtained from the website of Australian Antarctic Division. Very prominent dips in the backscatter observed in the month of January form a distinct signature caused by physical process of significant melting of the ice/snow surface. The steep increase again in February is attributed to the initiation of the freezing phenomenon. The derived melting index compared well with the passive microwave-based melting index derived by other researchers. A strong relationship was found between the scatterometer-derived melting index and the cumulative monthly mean air temperature. The highest melting was observed in the summer (January) of 2004, and thereafter gradual cooling appeared to take place in the subsequent years. The snow pack thickness, inferred from the backscatter variations, was found to be higher during winters (June) of 2004 and 2005, compared with other years.

  18. Hunting Jobs

    Institute of Scientific and Technical Information of China (English)

    Sun Jishan

    2006-01-01

    @@ 4.13 million college graduates areexpected to join the job-hunting army,putting additional pressure on China'sclimbing jobless rate. Some peoplemight blame the difficulties graduatesface in finding jobs on the expandedenrolment policy, which was introducedin 1999.

  19. Hunting Stories.

    Science.gov (United States)

    Johnson, Frank

    Eleven stories describe traditional practices and true adventures of the Tlingit hunters of Southeast Alaska. The stories are accompanied by learning activities and discussion questions for students and are arranged under the headings of bear, mountain goat and deer, and seal and sea lion. Topics include hunting weapons and strategies, bravery,…

  20. Circulation and fjord-shelf exchange during the ice-covered period in Young Sound-Tyrolerfjord, Northeast Greenland (74°N)

    Science.gov (United States)

    Boone, W.; Rysgaard, S.; Kirillov, S.; Dmitrenko, I.; Bendtsen, J.; Mortensen, J.; Meire, L.; Petrusevich, V.; Barber, D. G.

    2017-07-01

    Fjords around Greenland connect the Greenland Ice Sheet to the ocean and their hydrography and circulation are determined by the interplay between atmospheric forcing, runoff, topography, fjord-shelf exchange, tides, waves, and seasonal growth and melt of sea ice. Limited knowledge exists on circulation in high-Arctic fjords, particularly those not impacted by tidewater glaciers, and especially during winter, when they are covered with sea-ice and freshwater input is low. Here, we present and analyze seasonal observations of circulation, hydrography and cross-sill exchange of the Young Sound-Tyrolerfjord system (74°N) in Northeast Greenland. Distinct seasonal circulation phases are identified and related to polynya activity, meltwater and inflow of coastal water masses. Renewal of basin water in the fjord is a relatively slow process that modifies the fjord water masses on a seasonal timescale. By the end of winter, there is two-layer circulation, with outflow in the upper 45 m and inflow extending down to approximately 150 m. Tidal analysis showed that tidal currents above the sill were almost barotropic and dominated by the M2 tidal constituent (0.26 m s-1), and that residual currents (∼0.02 m s-1) were relatively small during the ice-covered period. Tidal pumping, a tidally driven fjord-shelf exchange mechanism, drives a salt flux that is estimated to range between 145 kg s-1 and 603 kg s-1. Extrapolation of these values over the ice-covered period indicates that tidal pumping is likely a major source of dense water and driver of fjord circulation during the ice-covered period.

  1. A precise monitoring of snow surface height in the region of Lambert Glacier basin-Amery Ice Shelf, East Antarctica

    Institute of Scientific and Technical Information of China (English)

    XIAO Cunde; QIN Dahe; BIAN Lingen; ZHOU Xiuji; I. Allison; YAN Ming

    2005-01-01

    The net surface snow accumulation on the Antarctic ice sheet is determined by a combination of precipitation, sublimation and wind redistribution. We present a one-year record of hourly snow-height measurements at LGB69 (70°50'S, 77°04(E,1850 m a.s.l.), east side of Lambert Glacier basin (LGB), and 4 year record at G3 (70°53'S, 69°52'E, 84 m a.s.l.), Amery Ice Shelf (AIS). The measurements were made with ultrasonic sensors mounted on automatic weather stations installed at two sites. The snow accumulation at LGB69 is approximately 70 cm. Throughout the winter, between April and September, there was little change in surface snow height (SSH) at the two sites. The negative SSH change is due to densification at LGB69, and is due to both ablation and densification at G3. The strongest accumulation at two sites occurred during the period between Octobers and March (accounting for 101.6% at LGB69), with four episodic increasing events occurring during 2002 for LGB69, and eight events during 1999-2002 for G3 (2 to 3 events per year). At LGB69, these episodic events coincided with obvious humidity "pulses" and decreases of incoming solar radiation as recorded by the AWS. Observations of the total cloud amount at Davis station, 160 km NNE of LGB69, showed good correlation with major accumulation events recorded at LGB69. There was an obvious anti-correlation between the lowest cloud height at Davis and the daily accumulation rate at LGB69. Although there was no correlation over the total year between wind speed and accumulation at LGB69, large individual accumulation events are associated with episodes of strong wind (>7 m/s), we estimate drift snow may contribute to total SSH up to 35%. Strong accumulation events at LGB69 are associated with major storms in the region and inland transport of moist air masses from the coast.

  2. Heat Flow and Hydrologic Characteristics at the AND-1B borehole, ANDRILL McMurdo Ice Shelf Project, Antarctica

    Science.gov (United States)

    Morin, Roger H.; Williams, Trevor; Henry, Stuart; ,; Hansaraj, Dhiresh

    2010-01-01

    The Antarctic Drilling Program (ANDRILL) successfully drilled and cored a borehole, AND-1B, beneath the McMurdo Ice Shelf and into a flexural moat basin that surrounds Ross Island. Total drilling depth reached 1285 m below seafloor (mbsf) with 98 percent core recovery for the detailed study of glacier dynamics. With the goal of obtaining complementary information regarding heat flow and permeability, which is vital to understanding the nature of marine hydrogeologic systems, a succession of three temperature logs was recorded over a five-day span to monitor the gradual thermal recovery toward equilibrium conditions. These data were extrapolated to true, undisturbed temperatures, and they define a linear geothermal gradient of 76.7 K/km from the seafloor to 647 mbsf. Bulk thermal conductivities of the sedimentary rocks were derived from empirical mixing models and density measurements performed on core, and an average value of 1.5 W/mK ± 10 percent was determined. The corresponding estimate of heat flow at this site is 115 mW/m2. This value is relatively high but is consistent with other elevated heat-flow data associated with the Erebus Volcanic Province. Information regarding the origin and frequency of pathways for subsurface fluid flow is gleaned from drillers' records, complementary geophysical logs, and core descriptions. Only two prominent permeable zones are identified and these correspond to two markedly different features within the rift basin; one is a distinct lithostratigraphic subunit consisting of a thin lava flow and the other is a heavily fractured interval within a single thick subunit.

  3. Sedimentary record of postglacial variability in near-bottom currents, sediment supply and ice rafting on the continental shelf off SW Spitsbergen

    Science.gov (United States)

    Sternal, B.; Szczuciński, W.; Forwick, M.; ZajÄ czkowski, M.; Lorenc, S.; Vorren, T. O.

    2012-04-01

    The continental shelf off the west coast of southern Spitsbergen is influenced by the northward-flowing water masses (warmer and more saline Atlantic Water carried by the West Spitsbergen Current and colder, fresher Arctic Water carried by the East Spitsbergen Current), as well as ice rafting. The present study was conducted to identify the influence of these factors on the sedimentary environment and to decipher temporal variations in the intensity of bottom currents, ice rafting off and glacial activity on southwestern Spitsbergen during the past 14,000 years. The study is based on a multiproxy analyses of one gravity core from the outer continental shelf (148 m water depth) in decadal to centennial resolution. Age control was obtained on a basis of ten AMS 14C dates along with 210Pb and 137Cs datings. To infer the style of sedimentation and the sediment supply the core was measured for magnetic susceptibility, X-rayed, analysed for grain-size distribution of bulk sediment and for coarse sand fraction components. The assessment of ice rafting intensity was based on coarse sand fraction counting (IRD), whereas to assume the type of ice rafting, whether by icebergs or sea ice, the analysis of quartz grains roundness was performed. Moreover, relative velocity of bottom currents was estimated by grain-size analysis of sortable silt fraction. We distinguish seven intervals: c. 14,000 - 12,600 cal yr BP - Bølling/Allerød (unit 1); 12,600 - 11,500 cal yr BP - Younger Dryas (unit 2) and 11,500 cal yr BP to present - Holocene (units 3 - 7). The smallest mean sortable silt values, reflecting relatively low bottom current velocity, occurred from the Bølling/Allerød to the early Younger Dryas and after ~0.5 cal ka BP. Increased velocities were inferred for the early Holocene as well as period between 8.8 - 7.8 cal yr BP. The IRD was present throughout the entire record indicating continuous supply of a material delivered from ice rafting, with variable dominance of

  4. TREASURE HUNT

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    A Chinese NGO aims to develop a model for recovering Chinese cultural treasures overseas On May 9, the first group of Chinese collectors taking part in an "Overseas Treasure Hunting Activity" arrived back in Beijing after a one-week trip to Japan. On their visit to Tokyo, Yokohama, Nagoya, Kyoto and Osaka, they found about 20 rare Chinese cultural relics of significant value. Since the Opium War in 1840, large quantities of Chinese treasures have been taken abroad. According to statistics from the China ...

  5. Variability in drift ice export from the Arctic Ocean to the North Icelandic Shelf over the last 8000 years: A multi-proxy evaluation

    Science.gov (United States)

    Cabedo-Sanz, Patricia; Belt, Simon T.; Jennings, Anne E.; Andrews, John T.; Geirsdóttir, Áslaug

    2016-08-01

    North Iceland represents a climatically sensitive region, in part, due to its location at the confluence of southward flowing and drift ice-laden polar waters from the Arctic Ocean delivered by the East Greenland Current, and the relatively warm and saline Irminger Current, a northerly flowing branch of the North Atlantic Current. Despite its pivotal location, there is a paucity of high resolution and long-term sea ice records for the region, with some disparities in certain previous investigations. Here, the identification of the biomarker IP25 as a reliable proxy for drift ice for North Iceland has been confirmed by measuring its abundance in surface sediments from the region and comparison of outcomes with documentary records of sea ice and other proxy data. By analysing IP25 in a well-dated marine sediment core from the North Icelandic Shelf (NIS) (MD99-2269), we also provide a high resolution (ca. 25 yr) record of drift sea ice for the region and complement this with a lower resolution record (ca. 100 yr) obtained from a second core site, located further east (JR51-GC35). Statistical treatment of equi-spaced time series reveals strong linear correlations between IP25 and a further drift ice proxy (quartz) in each core. Thus, linear regression analysis between both proxies gave correlation coefficients (R2) of 0.74 and 0.66 for MD99-2269 (25 yr) and JR51-GC35 (100 yr), respectively. Further, the individual proxies were well correlated between the two cores, with R = 0.91 and 0.77 for IP25 and quartz, respectively. The IP25-based sea ice record for MD99-2269, combined with other new biomarker and foraminifera data, and previously published proxy data for primary productivity and sea surface temperature, suggest that the paleoceanographic evolution for the NIS over the last 8 ka can be classified into three main intervals. The early mid Holocene (ca 8-6.2 cal ka BP) was characterized by relatively low or absent drift ice, low primary productivity and relatively

  6. Seasonal variation in particulate organic matter and its cnstituent fractions under the ice covered sea near the shelf, Antarctica

    Digital Repository Service at National Institute of Oceanography (India)

    Dhargalkar, V.K.

    Particulate organic matter (POM) collected at a single station in the shelf waters of Princess Astrid coast (70 degrees S : 11 degrees E), Antarctica from May to December, 1986 was analyzed for chl @ia@@, POC and other constituent fractions at three...

  7. Deglacial-Holocene short-term variability in sea-ice distribution on the Eurasian shelf (Arctic Ocean) - An IP25 biomarker reconstruction.

    Science.gov (United States)

    Hörner, Tanja; Stein, Ruediger; Fahl, Kirsten

    2016-04-01

    Four well-dated sediment cores from the Eurasian continental shelf, i.e., the Kara Sea (Cores BP99/07 and BP00/07) and Laptev Sea (Cores PS51/154 and PS51/159), were selected for high-resolution reconstruction of past Arctic environmental conditions during the deglacial-Holocene time interval. These marginal seas are strongly affected by the post-glacial sea-level rise of about 120m. The major focus of our study was the reconstruction of the paleo-sea-ice distribution as sea-ice plays a key role within the modern and past climate system. For reconstruction of paleo-sea ice, the sea-ice proxy IP25 in combination with open-water phytoplankton biomarkers was used (for approach see Belt et al., 2007; Müller et al., 2009, 2011). In addition, specific sterols were determined to reconstruct changes in river run-off and biological production. The post-glacial sea-level rise is especially reflected in prominent decrease in terrigenous biomarkers. Deglacial variations in sea-ice cover sustained for thousand of years, mostly following climatic changes like the Bølling/Allerød (14.7-12.9 ka), Younger Dryas (12.9-11.6 ka) and Holocene warm phase (10-8 ka). Superimposed on a (Late) Holocene cooling trend, short-term fluctuations in sea-ice cover (on centennial scale) are distinctly documented in the distal/off-shore Core BP00/07 from the Kara Sea, less pronounced in the proximal/near-shore Core PS99/07 and in the Laptev Sea cores. Interestingly, this short-term variability in sea-ice cover correlates quite well to changes in Siberian river run-off (e.g., Stein et al. 2004), pointing to a direct linkage between precipitation (atmospheric circulation) and sea-ice formation. References Belt, S.T., Massé, G., Rowland, S.J., Poulin, M., Michel, C., LeBlanc, B., 2007. A novel chemical fossil of palaeo sea ice: IP25. Organic Geochemistry 38, 16-27. Müller, J., Masse, G., Stein, R., Belt, S.T., 2009. Variability of sea-ice conditions in the Fram Strait over the past 30,000 years

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

    Science.gov (United States)

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

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

  9. Attitudes towards recreational hunting

    DEFF Research Database (Denmark)

    Gamborg, Christian; Jensen, Frank Søndergaard

    2017-01-01

    What is the attitude of the general public towards hunting? As a recreational activity, hunting stands apart from other forms of outdoor recreation like birdwatching in that it involves the pursuit and killing of wild animals. Today, it is in a tight spot. It has been criticized from animal ethics......, hunting organized as a group hunt, and single day leases of hunting grounds. Respondents with a “mutualist” wildlife value orientation had the most negative attitude towards hunting (39%), “distanced” respondents were the most indifferent (44%), and “utilitarians” were the most positive (61%). Assessing...

  10. Physical and biological controls on DMS,P dynamics in ice shelf-influenced fast ice during a winter-spring and a spring-summer transitions

    NARCIS (Netherlands)

    Carnat, G.; Zhou, J.; Papakyriakou, T.; Delille, B.; Goossens, T.; Haskell, T.; Schoemann, V.; Fripiat, F.; Rintala, J.-M.; Tison, J.-L.

    2014-01-01

    We report the seasonal and vertical variations of dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) in fast ice at Cape Evans, McMurdo Sound (Antarctica) during the spring-summer transition in 2011 and winter-spring transition in 2012. We compare the variations of DMS,P obser

  11. Physical and biological controls on DMS,P dynamics in ice shelf-influenced fast ice during a winter-spring and a spring-summer transitions

    NARCIS (Netherlands)

    Carnat, G.; Zhou, J.; Papakyriakou, T.; Delille, B.; Goossens, T.; Haskell, T.; Schoemann, V.; Fripiat, F.; Rintala, J.-M.; Tison, J.-L.

    2014-01-01

    We report the seasonal and vertical variations of dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) in fast ice at Cape Evans, McMurdo Sound (Antarctica) during the spring-summer transition in 2011 and winter-spring transition in 2012. We compare the variations of DMS,P obser

  12. Observing Muostakh Island disappear: erosion of a ground-ice-rich coast in response to summer warming and sea ice reduction on the East Siberian shelf

    Directory of Open Access Journals (Sweden)

    F. Günther

    2013-08-01

    Full Text Available Observations of coastline retreat using contemporary very high resolution satellite and historical aerial imagery were compared to measurements of open water fractions and summer air temperatures. We analyzed seasonal and interannual variations of thawing-induced cliff top retreat (thermo-denudation and marine abrasion (thermo-abrasion on Muostakh Island in the southern central Laptev Sea. The island is composed of ground-ice-rich permafrost deposits of Ice Complex type that render it particularly susceptible to erosion along the coast, resulting in land loss. Based on topographic reference measurements during field campaigns, we generated digital elevation models using stereophotogrammetry, in order to block adjust and ortho-rectify aerial photographies from 1951 and GeoEye, QuickBird, WorldView-1, and WorldView-2 imagery from 2010 to 2012 for change detection. Coastline retreat for erosive segments ranged from −13 to −585 m and was −109 ± 81 m (–1.8 ± 1.3 m a−1 on average during the historical period. Current seasonal dynamics of cliff top retreat revealed rapid thermo-denudation rates of –10.2 ± 4.5 m a−1 in mid summer and –4.1 ± 2.0 m a−1 on average during the 2010–2012 observation period. Using sea ice concentration data from the Special Sensor Microwave Imager (SSM/I and air temperature time series from Tiksi, we calculated seasonal duration available for thermo-abrasion, expressed as open water days, and for thermo-denudation, based on thawing degree days. Geomorphometric analysis revealed that total ground ice content on Muostakh is made up of equal amounts of intrasedimentary and macro ground ice, while its vertical hourglass distribution provides favorable local preconditions for subsidence and the acceleration of coastal thermo-erosion under intensifying environmental forcings. Our results showed a~close relationship between mean summer air temperature and coastal thermo-erosion rates, in agreement with

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

    Science.gov (United States)

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

    2015-04-01

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

  14. Neogene sea surface temperature reconstructions from the Southern McMurdo Sound and the McMurdo Ice Shelf (ANDRILL Program, Antarctica)

    Science.gov (United States)

    Sangiorgi, Francesca; Willmott, Veronica; Kim, Jung-Hyun; Schouten, Stefan; Brinkhuis, Henk; Sinninghe Damsté, Jaap S.; Florindo, Fabio; Harwood, David; Naish, Tim; Powell, Ross

    2010-05-01

    During the austral summers 2006 and 2007 the ANtarctic DRILLing Program (ANDRILL) drilled two cores, each recovering more than 1000m of sediment from below the McMurdo Ice-Shelf (MIS, AND-1B), and sea-ice in Southern McMurdo Sound (SMS, AND-2A), respectively, revealing new information about Neogene Antarctic cryosphere evolution. Core AND-1B was drilled in a more distal location than core AND-2A. With the aim of obtaining important information for the understanding of the history of Antarctic climate and environment during selected interval of the Neogene, we applied novel organic geochemistry proxies such as TEX86 (Tetra Ether IndeX of lipids with 86 carbon atoms) using a new calibration equation specifically developed for polar areas and based on 116 surface sediment samples collected from polar oceans (Kim et al., subm.), and BIT (Branched and Isoprenoid Tetraether), to derive absolute (sea surface) temperature values and to evaluate the relative contribution of soil organic matter versus marine organic matter, respectively. We will present the state-of-the-art of the methodology applied, discussing its advantages and limitations, and the results so far obtained from the analysis of 60 samples from core AND-2A covering the Miocene Climatic Optimum (and the Mid-late Miocene transition) and of 20 pilot samples from core AND-1B covering the late Pliocene.

  15. Deglacial to Holocene history of ice-sheet retreat and bottom current strength on the western Barents Sea shelf

    Science.gov (United States)

    Lantzsch, Hendrik; Hanebuth, Till J. J.; Horry, Jan; Grave, Marina; Rebesco, Michele; Schwenk, Tilmann

    2017-10-01

    High-resolution sediment echosounder data combined with radiocarbon-dated sediment cores allowed us to reconstruct the Late Quaternary stratigraphic architecture of the Kveithola Trough and surrounding Spitsbergenbanken. The deposits display the successive deglacial retreat of the Svalbard-Barents Sea Ice Sheet. Basal subglacial till indicates that the grounded ice sheet covered both bank and trough during the Late Weichselian. A glaciomarine blanket inside the trough coinciding with laminated plumites on the bank formed during the initial ice-melting phase from at least 16.1 to 13.5 cal ka BP in close proximity to the ice margin. After the establishment of open-marine conditions at around 13.5 cal ka BP, a sediment drift developed in the confined setting of the Kveithola Trough, contemporary with crudely laminated mud, an overlying lag deposit, and modern bioclastic-rich sand on Spitsbergenbanken. The Kveithola Drift shows a remarkable grain-size coarsening from the moat towards the southern flank of the trough. This trend contradicts the concept of a separated drift (which would imply coarser grain sizes in proximity of the moat) and indicates that the southern bank is the main sediment source for the coarse material building up the Kveithola Drift. This depocenter represents, therefore, a yet undescribed combination of off-bank wedge and confined drift. Although the deposits inside Kveithola Trough and on Spitsbergenbanken display different depocenter geometries, time-equivalent grain-size changes imply a region-wide sediment-dynamic connection. We thus relate a phase of coarsest sediment supply (8.8-6.3 cal ka BP) to an increase in bottom current strength, which might be related to a stronger Atlantic Water inflow from the Southeast across the bank leading to winnowing and off-bank export of sandy sediments.

  16. Sediment movement and dispersal patterns on the Grand Banks continental shelf and slope were tied to the dynamics of the Laurentide ice-sheet margin

    Science.gov (United States)

    Rashid, H.; MacKillop, K.; Piper, D.; Vermooten, M.; Higgins, J.; Marche, B.; Langer, K.; Brockway, B.; Spicer, H. E.; Webb, M. D.; Fournier, E.

    2015-12-01

    The expansion and contraction of the late Pleistocene Laurentide ice-sheet (LIS) was the crucial determining factor for the geomorphic features and shelf and slope sediment mobility on the eastern Canadian continental margin, with abundant mass-transport deposits (MTDs) seaward of ice margins on the upper slope. Here, we report for the first time sediment failure and mass-transport deposits from the central Grand Banks slope in the Salar and Carson petroleum basins. High-resolution seismic profiles and multibeam bathymetry show numerous sediment failure scarps in 500-1600 m water depth. There is no evidence for an ice margin on the upper slope younger than MIS 6. Centimeter-scale X-ray fluorescence analysis (XRF), grain size, and oxygen isotope data from piston cores constrain sediment processes over the past 46 ka. Geotechnical measurements including Atterberg limit tests, vane shear measurements and triaxial and multi-stage isotropic consolidation tests allowed us to assess the instability on the continental margin. Cores with continuous undisturbed stratigraphy in contourite silty muds show normal downcore increase in bulk density and undrained peak shear strength. Heinrich (H) layers are identifiable by a marked increase in the bulk density, high Ca (ppm), increase in iceberg-rafted debris and lighter δ18O in the polar planktonic foram Neogloboquadrina pachyderma (sinistral): with a few C-14 dates they provide a robust chronology. There is no evidence for significant supply of sediment from the Grand Banks at the last-glacial maximum. Mass-transport deposits (MTD) are marked by variability in the bulk density, undrained shear strength and little variation in bulk density or Ca (ppm) values. The MTD are older than 46 ka on the central Grand Banks slope, whereas younger MTDs are present in southern Flemish Pass. Factor of safety calculations suggest the slope is statically stable up to gradients of 10°, but more intervals of silty mud may fail during earthquake

  17. Hunting liquid micro-pockets in snow and ice: Phase transition in salt solutions at the bulk and interface with X-ray photoelectron spectroscopy.

    Science.gov (United States)

    Bartels-Rausch, Thorsten; Orlando, Fabrizio; Kong, Xiangrui; Waldner, Astrid; Artiglia, Luca; Ammann, Markus; Huthwelker, Thomas

    2016-04-01

    Sea salt, and in particular chloride, is an important reactant in the atmosphere. Chloride in air-borne sea salt aerosol is - once chemically converted to a molecular halogen (Cl2, BrCl) and released to the atmosphere - well known as important atmospheric reactant, driving large-scale changes to the atmospheric composition and in particular to ozone levels in remote areas, but also in coastal mega cities. Similar chemistry has been proposed for sea salt deposits in polar snow covers. A crucial factor determining the overall reactivity is the local physical environment of the chloride ion. For example, the reactivity of liquid aerosols decreases significantly upon crystallization. Surprisingly, the phases of NaCl-containing systems are still under debate, partially due to the limited availability of in situ measurements directly probing the local environment at the surface of frozen NaCl-water binary systems. Using core electron spectroscopy of the oxygen atoms in water, we previously showed that these systems follow the phase rules at the air-ice interface. This finding contrasts some earlier observations, where the presence of liquid below the eutectic point of bulk solutions was postulated. In the present study, we present new electron yield near-edge X-ray absorption fine structure spectroscopy (NEXAFS) data obtained at near-ambient pressures up to 20 mbar of NaCl frozen solutions. The method is sensitive to small changes in the local environment of the chlorine atom. The measurements were performed at the PHOENIX beamline at SLS. The study indicates frapant differences in the phases of NaCl - water mixtures at temperatures blow the freezing point for the surface of the ice vs. the bulk. This has significant impact on modelling chemical reactions in snow or ice and it's environmental consequences.

  18. Hunting for Ecological Learning

    Science.gov (United States)

    Pontius, Joel B.; Greenwood, David A.; Ryan, Jessica L.; Greenwood, Eli A.

    2013-01-01

    Considering (a) the many potential connections between hunting, culture, and environmental thought, (b) how much hunters have contributed to the conservation movement and to the protection of a viable land base, and (c) renewed interest in hunting as part of the wider movement toward eating local, non-industrialized food, we seek to bring hunting…

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

    NARCIS (Netherlands)

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

    2015-01-01

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

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

    NARCIS (Netherlands)

    Matsuoka, Kenichi; Hindmarsh, Richard C A; Moholdt, Geir; Bentley, Michael J.; Pritchard, Hamish D.; Brown, Joel; Conway, Howard; Drews, Reinhard; Durand, Gaël; Goldberg, Daniel; Hattermann, Tore; Kingslake, Jonathan; Lenaerts, Jan T M|info:eu-repo/dai/nl/314850163; Martín, Carlos; Mulvaney, Robert; Nicholls, Keith W.; Pattyn, Frank; Ross, Neil; Scambos, Ted; Whitehouse, Pippa L.

    2015-01-01

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

  1. HUNT: Scavenger Hunt with Augmented Reality

    Directory of Open Access Journals (Sweden)

    Yan Lu

    2015-04-01

    Full Text Available This project shows a creative approach to the familiar scavenger hunt game. It involved the implementation of an iPhone application, HUNT, with Augmented Reality (AR capability for the users to play the game as well as an administrative website that game organizers can use to create and make available games for users to play. Using the HUNT mobile app, users will first make a selection from a list of games, and they will then be shown a list of objects that they must seek. Once the user finds a correct object and scans it with the built-in camera on the smartphone, the application will attempt to verify if it is the correct object and then display associated multi-media AR content that may include images and videos overlaid on top of real world views. HUNT not only provides entertaining activities within an environment that players can explore, but the AR contents can serve as an educational tool. The project is designed to increase user involvement by using a familiar and enjoyable game as a basis and adding an educational dimension by incorporating AR technology and engaging and interactive multimedia to provide users with facts about the objects that they have located

  2. 捕猎%HUNTING

    Institute of Scientific and Technical Information of China (English)

    杨帆(译)

    2012-01-01

    Do you think it' s right to hunt wild animals? Why? Why not? What are the different reasons modern humans hunt? Have you ever been hunting? If so, what was it like? If not, what do you think it would be like? Do you think it' s more ethical to kill animals for meat yourself rather than buying pre-packaged meat from a shop?%在过去。捕猎是很常见的事。因为这是人类的求生手段。如今。捕猎已成为一种休闲运动项目,对此。有人支持。有人反对。你是怎么看的呢?欢迎来信与我们分享。

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

    Science.gov (United States)

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

    2017-08-01

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

  4. TOLOSA HUNT SYNDROME

    Directory of Open Access Journals (Sweden)

    Padmini

    2013-03-01

    Full Text Available ABSTRACT: Tolosa-Hunt syndrome (THS is a painful ophthalmoplegi a caused by nonspecific inflammation of the cavernous sinus or superior orbi tal fissure. The syndrome consists of periorbital or hemicranial pain, combined with ipsilat eral ocular motor nerve palsies, oculosympathetic paralysis, and sensory loss in the distribution of the ophthalmic and occasionally the maxillary division of the trigemin al nerve. Although they have relapsing and remitting course, they respond promptly to systemic co rticosteroid therapy. The diagnostic eponym Tolosa-Hunt syndrome has been applied to these patients and it is this entity which forms the basis of this review

  5. Detrital carbonate peaks on the Labrador shelf, a 13-7 ka template for freshwater forcing from the Hudson Strait outlet of the Laurentide Ice Sheet into the subpolar gyre

    Science.gov (United States)

    Jennings, Anne; Andrews, John; Pearce, Christof; Wilson, Lindsay; Ólfasdótttir, Sædís

    2015-01-01

    The Laurentide Ice Sheet (LIS) was a large, dynamic ice sheet in the early Holocene. The glacial events through Hudson Strait leading to its eventual demise are recorded in the well-dated Labrador shelf core, MD99-2236 from the Cartwright Saddle. We develop a detailed history of the timing of ice-sheet discharge events from the Hudson Strait outlet of the LIS during the Holocene using high-resolution detrital carbonate, ice rafted detritus (IRD), δ18O, and sediment color data. Eight detrital carbonate peaks (DCPs) associated with IRD peaks and light oxygen isotope events punctuate the MD99-2236 record between 11.5 and 8.0 ka. We use the stratigraphy of the DCPs developed from MD99-2236 to select the appropriate ΔR to calibrate the ages of recorded glacial events in Hudson Bay and Hudson Strait such that they match the DCPs in MD99-2236. We associate the eight DCPs with H0, Gold Cove advance, Noble Inlet advance, initial retreat of the Hudson Strait ice stream (HSIS) from Hudson Strait, opening of the Tyrrell Sea, and drainage of glacial lakes Agassiz and Ojibway. The opening of Foxe Channel and retreat of glacial ice from Foxe Basin are represented by a shoulder in the carbonate data. ΔR of 350 years applied to the radiocarbon ages constraining glacial events H0 through the opening of the Tyrell Sea provided the best match with the MD99-2236 DCPs; ΔR values and ages from the literature are used for the younger events. A very close age match was achieved between the 8.2 ka cold event in the Greenland ice cores, DCP7 (8.15 ka BP), and the drainage of glacial lakes Agassiz and Ojibway. Our stratigraphic comparison between the DCPs in MD99-2236 and the calibrated ages of Hudson Strait/Bay deglacial events shows that the retreat of the HSIS, the opening of the Tyrell Sea, and the catastrophic drainage of glacial lakes Agassiz and Ojibway at 8.2 ka are separate events that have been combined in previous estimates of the timing of the 8.2 ka event from marine records

  6. Dissolved iron in the Arctic shelf seas and surface waters of the central Arctic Ocean : Impact of Arctic river water and ice-melt

    NARCIS (Netherlands)

    Klunder, M. B.; Bauch, D.; Laan, P.; de Baar, H. J. W.; van Heuven, S.; Ober, S.

    2012-01-01

    Concentrations of dissolved (10 nM) in the bottom waters of the Laptev Sea shelf may be attributed to either sediment resuspension, sinking of brine or regeneration of DFe in the lower layers. A significant correlation (R-2 = 0.60) between salinity and DFe is observed. Using delta O-18, salinity, nu

  7. The hunt for axions

    Energy Technology Data Exchange (ETDEWEB)

    Ringwald, Andreas

    2015-06-15

    Many theoretically well-motivated extensions of the Standard Model of particle physics predict the existence of the axion and further ultralight axion-like particles. They may constitute the mysterious dark matter in the universe and solve some puzzles in stellar and high-energy astrophysics. There are new, relatively small experiments around the globe, which started to hunt for these elusive particles and complement the accelerator based search for physics beyond the Standard Model.

  8. Consumer Profile Of Hunting Tourism

    Directory of Open Access Journals (Sweden)

    Diana Marin

    2015-10-01

    Full Text Available Knowing the profileof hunting tourism consumers is particularly useful to the administrators ofhunting funds or natural parks, and of travel agencies that develop huntingtourism products for the hunting of large game for trophy, of small game asrecreational activity and also for the experienced hunting tourists who loveadventure and hunting with traditional weapons. The motivation for huntingconsists in the existing fauna in a certain area, but there are also cultural,historical reasons or spending time in the middle of nature. Consumers ofhunting tourism have a wide range of ages: hunting tourists prefer watching theanimals in their natural habitat and are less adventure-oriented, unlike trophyhunting tourists who are self-contended, travel much and wish to know thehistory, the culture and the behaviour of animals in protected areas. Theyprefer special accommodation and transport conditions and rely on largeincomes: they wish to get the rarest trophies to display back home as a symbolof their hunting skills and courage

  9. WILD PIG HUNTING IN PETUNGKRIONO

    Directory of Open Access Journals (Sweden)

    Pujo Semedi

    2010-02-01

    Full Text Available Anthropologists have been studying hunting from the economic, ecological, and symbolical perspectives. The third perspective has been used to comprehend the hunting activities among the farmers of Petungkriono who have used hunting to show masculinity. Further investigation has revealed that the arena is created as a compensation for the fragile position of the local male inhabitants in the household social economic condition as connected to the matrilinear land inheritance system.

  10. ORR Deer Hunt Monitoring Program

    Energy Technology Data Exchange (ETDEWEB)

    Scofield, P.A.; Teasley, N.A.

    1999-09-01

    The primary purpose for the initiation of deer hunts on the Oak Ridge Reservation (ORR) was deer population control to reduce collisions with vehicles and maintain a healthy herd and habitat. As of 1997, thirteen annual deer hunts have been conducted on the ORR. The deer hunt monitoring program (DHMP) has two components -- a field screening monitoring program and a confirmatory laboratory analysis program of both retained and randomly selected released deer samples.

  11. Rheology of glacier ice

    Science.gov (United States)

    Jezek, K. C.; Alley, R. B.; Thomas, R. H.

    1985-01-01

    A new method for calculating the stress field in bounded ice shelves is used to compare strain rate and deviatoric stress on the Ross Ice Shelf, Antarctica. The analysis shows that strain rate (per second) increases as the third power of deviatoric stress (in newtons/sq meter), with a constant of proportionality equal to 2.3 x 10 to the -25th.

  12. Hunting plan amendment: Choctaw National Wildlife Refuge

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This amendment allows the hunting plan for Choctaw National Wildlife Refuge to add raccoon and opossum hunting to the existing small game hunting program.

  13. The Hunt Is Not On

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    China’s ban on trophy hunting remains despite calls for a relaxation WDulan,a small town in northwest China’s Qinghai Province, would have been an unfamiliar name to most Chinese, if not for the recent high-profile debate regarding the possible relaxation of a six-year ban on hunting in the vicinity of the town.

  14. SINDROM RAMSAY HUNT

    Directory of Open Access Journals (Sweden)

    Ni Luh Indri Astari

    2015-07-01

    Full Text Available Sindrom Ramsay Hunt atau herpes  zoster  otikus merupakan neuropati akut  saraf  fasialis perifermengenai daun telinga, liang telinga dan atau mukosa orofaring. Terjadinya infeksi pada gangliongenikulatum oleh human herpes virus 3 atau varicella-zoster virus. Insiden sindrom Ramsay Huntsekitar 10-15% dari seluruh kasus paralisis  fasialis akut. Dilaporkan satu kasus sindrom RamsayHunt dengan paresis nervus fasialis sinistra lesi setinggi ganglion genikulatum, saat datang kekuatanmotorik 20% dengan House Brackmann IV. Penderita diberi terapi metilprednisolon, mekobalamin,betahistin mesilat, flunarizin. Bagian kulit kelamin memberikan terapi asam mefenamat, kompresNacl  0,9%,  dan  gentamisin  salep. Fisioterapi  oleh  bagian  rehabilitasi medis. Terapi  bagian Mataantara  lain  tarsoterapi  temporer,  gentamisin  salep mata,  dan  cendo  lyters  tetes mata.  Setelahmendapatkan terapi selama hampir 2 bulan, didapatkan perbaikan dengan kekuatan motorik 76%dengan House Brackmann II. [MEDICINA 2014;45:199-203].

  15. HUNTing the Overlap

    Energy Technology Data Exchange (ETDEWEB)

    Iancu, Costin; Parry, Husbands; Hargrove, Paul

    2005-07-08

    Hiding communication latency is an important optimization for parallel programs. Programmers or compilers achieve this by using non-blocking communication primitives and overlapping communication with computation or other communication operations. Using non-blocking communication raises two issues: performance and programmability. In terms of performance, optimizers need to find a good communication schedule and are sometimes constrained by lack of full application knowledge. In terms of programmability, efficiently managing non-blocking communication can prove cumbersome for complex applications. In this paper we present the design principles of HUNT, a runtime system designed to search and exploit some of the available overlap present at execution time in UPC programs. Using virtual memory support, our runtime implements demand-driven synchronization for data involved in communication operations. It also employs message decomposition and scheduling heuristics to transparently improve the non-blocking behavior of applications. We provide a user level implementation of HUNT on a variety of modern high performance computing systems. Results indicate that our approach is successful in finding some of the overlap available at execution time. While system and application characteristics influence performance, perhaps the determining factor is the time taken by the CPU to execute a signal handler. Demand driven synchronization at execution time eliminates the need for the explicit management of non-blocking communication. Besides increasing programmer productivity, this feature also simplifies compiler analysis for communication optimizations.

  16. 伽马辐照对冰藏大黄鱼品质和货架期的影响%Effects of gamma irradiation on quality and shelf life of iced Pseudosciaena crocea

    Institute of Scientific and Technical Information of China (English)

    杨宪时; 姜兴为; 李学英; 郭全友; 蒋慧亮

    2011-01-01

    为探索伽马辐照处理对冰藏鲜鱼的保鲜效果,试验分析了大黄鱼冰藏期间微生物、生化指标和感官指标的变化,探讨了低剂量辐照处理(1 kGy和2 kGy)对大黄鱼品质和货架期的影响.结果表明,辐照处理后人黄鱼的菌落总数、假单胞菌和产硫化氢细菌数量显著减少;在贮藏期间辐照处理的大黄鱼各种菌数量始终比对照组少:辐照处理可显著减缓大黄鱼挥发性盐摹氮和三甲胺的增加;但会促进脂肪的氧化,2 kGy组大黄鱼在贮藏后期能闻到脂肪酸败的味道,而1 kGy组和对照组大黄鱼始终没有闻到这种味道.辐照处理可增加大黄鱼的货架期,对照组货架期为17 d,而辐照剂量为1 kGy和2 kGy的货架期可延长至30 d和26 d.本试验为辐照商业化应用提供了技术依据.%To explore the preservation effect of gamma irradiation on ice-storaged fish, the influence of gamma irradiation (1 kGy and 2 kGy) on quality and shelf life of iced Pseudosciaena crocea was discussed by analyzing the microbiological, biochemical and organoleptic changes occurring in fish samples. The results showed that the numbers of total viable counts, Pseudomonas spp. and H2S-producing bacteria significantly decreased after irradiation; during storage the bacteria numbers of Pseudosciaena crocea treated with irradiation were always less than the control simples;the concentrations of total volatile basic nitrogen and trimethylamine were conspicuously reduced by irradiation,whereas lipid oxidation was accelerated. At the end of storage the smell of lipid rancidity could be smelled for fish treated with 2 kGy dose, but that smell could not be smelled for 1 kGy and control simples. The shelf life could be remarkably prolonged by irradiation, and compared to a shelf life of 17 days for non-irradiated samples, the shelf life of Pseudosciaena crocea treated with 1 kGy and 2 kGy were extended to 30 days and 26 days, respectively. The work can provide

  17. 77 FR 29515 - Migratory Bird Hunting; Supplemental Proposals for Migratory Game Bird Hunting Regulations for...

    Science.gov (United States)

    2012-05-17

    ... Bird Hunting; Supplemental Proposals for Migratory Game Bird Hunting Regulations for the 2012-13... RIN 1018-AX97 Migratory Bird Hunting; Supplemental Proposals for Migratory Game Bird Hunting... in an earlier document to establish annual hunting regulations for certain migratory game birds...

  18. Effect of chitosan-carvacrol edible coatings on the quality and shelf life of tilapia (Oreochromis niloticus fillets stored in ice

    Directory of Open Access Journals (Sweden)

    Saraí CHAPARRO-HERNÁNDEZ

    2015-01-01

    Full Text Available Abstract Fish consumption has increased in recent years. However, fish meat is highly perishable, which demonstrates the need for technologies to preserve its quality. Edible coatings (EC might provide an alternative to extend the shelf life of fish. The goal of this study was to evaluate the effect of EC of chitosan (C in combination with carvacrol (CAR on the physical and microbiological changes of tilapia fillets. Fillets were submerged for two minutes in different treatments (T1: control; T2: C 2%; T3: C 2% + 0.125% CAR; T 4: C 2% + 0.25% CAR. At the end of storage, T1 and T2 showed the lowest values of total volatile bases (TVB. The color parameters L*, a* and b* varied from each treatment. The texture decreased and the different treatments reduced the microbial population in relation to the control; T3 and T4 were the most effective. These results show that the use of C with CAR might be an alternative method to preserve the quality and safety of tilapia fillets.

  19. Game animals & hunting : Law enforcement

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This is a summary of hunting activities, game mammal surveys, and law enforcement on Neal Smith National Wildlife Refuge between 1992 and 2009. For each year, a list...

  20. Hunting Plan: Amendment to conduct Becoming an Outdoors Woman Feral Hog Hunt

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This is the hog hunt plan for the Becoming an Outdoors Woman (BOW) program on St. Vincent NWR. The objective of the BOW hunt is to provide a quality hunting...

  1. Kinematics of the Neogene Terror Rift: Constraints from calcite twinning strain in AND-1B core, McMurdo Ice Shelf

    Science.gov (United States)

    Paulsen, T.; Wilson, T. J.; Demosthenous, C.; Millan, C.; Jarrard, R. D.; Laufer, A.

    2013-12-01

    Strain analyses of mechanically twinned calcite in veins and faults hosted by Neogene (13.6 Ma to 4.3 Ma) sedimentary and volcanic rocks recovered within the ANDRILL AND-1B drill core from the Terror Rift in the southern Ross Sea, Antarctica, yield prolate and oblate ellipsoids with principal shortening and extension strains ranging from 0.1% to 8.5%. The majority of samples show homogeneous coaxial strain predominantly characterized by subvertical shortening, which we attribute to lithostatic loading in an Andersonian normal faulting stress regime during sedimentary and ice sheet burial of the stratigraphic sequence. The overall paucity of a non-coaxial layer-parallel shortening signal in the AND-1B twin populations suggests that horizontal compressive stresses predicted by Neogene transtensional kinematic models for the rift system have been absent or of insufficient magnitude to cause a widespread noncoaxial strain overprint. Limited numbers of oriented samples yield a possible average ESE extension direction for the rift that is subparallel to other indicators of Neogene extension. The lack of horizontal shortening in the twin data suggests the Neogene Terror Rift system either lacks a strong longitudinal strike-slip component, or that spatial partitioning of strain controls the maximum shortening axes seen in rocks of this age.

  2. George's cosmic treasure hunt

    CERN Document Server

    Hawking, Lucy; Parsons, Gary

    2009-01-01

    George and Annie explore the galaxy in this cosmic adventure from Stephen Hawking and Lucy Hawking, complete with essays from Professor Hawking about the latest in space travel. George is heartbroken when he learns that his friend Annie and her father are moving to the US. Eric has a new job working for the space program, looking for signs of life in the Universe. Eric leaves George with a gift—a book called The User’s Guide to the Universe. But Annie and Eric haven’t been gone for very long when Annie believes that she is being contacted by aliens, who have a terrible warning for her. George joins her in the US to help her with her quest—and before he knows it, he, Annie, Cosmos, and Annie’s annoying cousin Emmett have been swept up in a cosmic treasure hunt, spanning the whole galaxy and beyond. Lucy Hawking's own experiences in zero-gravity flight and interviews with astronauts at Cape Kennedy and the Johnson Space Center lend the book a sense of realism and excitement that is sure to fire up ima...

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

    Science.gov (United States)

    Scambos, Ted

    2002-01-01

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

  4. Galaxy 'Hunting' Made Easy

    Science.gov (United States)

    2007-09-01

    Galaxies found under the Glare of Cosmic Flashlights Astronomers using ESO's Very Large Telescope have discovered in a single pass about a dozen otherwise invisible galaxies halfway across the Universe. The discovery, based on a technique that exploits a first-class instrument, represents a major breakthrough in the field of galaxy 'hunting'. ESO PR Photo 40a/07 ESO PR Photo 40a/07 Newly Found Galaxies (SINFONI/VLT) The team of astronomers led by Nicolas Bouché have used quasars to find these galaxies. Quasars are very distant objects of extreme brilliance, which are used as cosmic beacons that reveal galaxies lying between the quasar and us. The galaxy's presence is revealed by a 'dip' in the spectrum of the quasar - caused by the absorption of light at a specific wavelength. The team used huge catalogues of quasars, the so-called SDSS and 2QZ catalogues, to select quasars with dips. The next step was then to observe the patches of the sky around these quasars in search for the foreground galaxies from the time the Universe was about 6 billion years old, almost half of its current age. "The difficulty in actually spotting and seeing these galaxies stems from the fact that the glare of the quasar is too strong compared to the dim light of the galaxy," says Bouché. This is where observations taken with SINFONI on ESO's VLT made the difference. SINFONI is an infrared 'integral field spectrometer' that simultaneously delivers very sharp images and highly resolved colour information (spectra) of an object on the sky. ESO PR Photo 32e/07 ESO PR Photo 40b/07 Chasing 'Hidden' Galaxies (Artist's Impression) With this special technique, which untangles the light of the galaxy from the quasar light, the team detected 14 galaxies out of the 20 pre-selected quasar patches of sky, a hefty 70% success rate. "This high detection rate alone is a very exciting result," says Bouché. "But, these are not just ordinary galaxies: they are most notable ones, actively forming a lot of

  5. Parker River NWR : Revised Hunting Plan

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This document contains revisions to the 1978 Parker River National Wildlife Refuge Hunt Management Plan. Refuge hunters must obtain a permit to use the hunting...

  6. Waterfowl Hunting Plan : Mingo National Wildlife Refuge

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This Waterfowl Hunting Plan for Mingo NWR summarizes how the Waterfowl Hunting Program relates to Refuge objectives, outlines Program policies and control, and lists...

  7. 76 FR 48693 - Migratory Bird Hunting; Proposed Migratory Bird Hunting Regulations on Certain Federal Indian...

    Science.gov (United States)

    2011-08-08

    ... August 8, 2011 Part V Department of the Interior Fish and Wildlife Service 50 CFR Part 20 Migratory Bird Hunting; Proposed Migratory Bird Hunting Regulations on Certain Federal Indian Reservations and Ceded... RIN 1018-AX34 Migratory Bird Hunting; Proposed Migratory Bird Hunting Regulations on Certain...

  8. 76 FR 36508 - Migratory Bird Hunting; Supplemental Proposals for Migratory Game Bird Hunting Regulations for...

    Science.gov (United States)

    2011-06-22

    ... Fish and Wildlife Service 50 CFR Part 20 RIN 1018-AX34 Migratory Bird Hunting; Supplemental Proposals for Migratory Game Bird Hunting Regulations for the 2011-12 Hunting Season; Notice of Meetings AGENCY... regulations for certain migratory game birds for the 2011-12 hunting season. This supplement to the...

  9. 75 FR 53774 - Migratory Bird Hunting; Migratory Bird Hunting Regulations on Certain Federal Indian Reservations...

    Science.gov (United States)

    2010-09-01

    ... Wildlife Service 50 CFR Part 20 Migratory Bird Hunting; Migratory Bird Hunting Regulations on Certain...-1231-9BPP-L2] RIN 1018-AX06 Migratory Bird Hunting; Migratory Bird Hunting Regulations on Certain..., Interior. ACTION: Final rule. SUMMARY: This rule prescribes special early-season migratory bird...

  10. 76 FR 54051 - Migratory Bird Hunting; Final Frameworks for Early-Season Migratory Bird Hunting Regulations

    Science.gov (United States)

    2011-08-30

    ... Bird Hunting; Final Frameworks for Early-Season Migratory Bird Hunting Regulations; Final Rule #0;#0... OF THE INTERIOR Fish and Wildlife Service 50 CFR Part 20 RIN 1018-AX34 Migratory Bird Hunting; Final Frameworks for Early-Season Migratory Bird Hunting Regulations AGENCY: Fish and Wildlife Service,...

  11. 75 FR 47681 - Migratory Bird Hunting; Proposed Migratory Bird Hunting Regulations on Certain Federal Indian...

    Science.gov (United States)

    2010-08-06

    ... Interior Fish and Wildlife Service 50 CFR Part 20 Migratory Bird Hunting; Proposed Migratory Bird Hunting... INTERIOR Fish and Wildlife Service 50 CFR Part 20 RIN 1018-AX06 Migratory Bird Hunting; Proposed Migratory Bird Hunting Regulations on Certain Federal Indian Reservations and Ceded Lands for the 2010-11...

  12. 78 FR 52657 - Migratory Bird Hunting; Final Frameworks for Early-Season Migratory Bird Hunting Regulations

    Science.gov (United States)

    2013-08-23

    ... Bird Hunting; Final Frameworks for Early Season Migratory Bird Hunting Regulations; Final Rule #0;#0... OF THE INTERIOR Fish and Wildlife Service 50 CFR Part 20 RIN 1018-AY87 Migratory Bird Hunting; Final Frameworks for Early-Season Migratory Bird Hunting Regulations AGENCY: Fish and Wildlife Service,...

  13. Banning Trophy Hunting Will Exacerbate Biodiversity Loss.

    Science.gov (United States)

    Di Minin, Enrico; Leader-Williams, Nigel; Bradshaw, Corey J A

    2016-02-01

    International pressure to ban trophy hunting is increasing. However, we argue that trophy hunting can be an important conservation tool, provided it can be done in a controlled manner to benefit biodiversity conservation and local people. Where political and governance structures are adequate, trophy hunting can help address the ongoing loss of species.

  14. Channelized bottom melting and stability of floating ice shelves

    OpenAIRE

    Rignot, E; Steffen, K.

    2008-01-01

    The floating ice shelf in front of Petermann Glacier, in northwest Greenland, experiences massive bottom melting that removes 80% of its ice before calving into the Arctic Ocean. Detailed surveys of the ice shelf reveal the presence of 1-2 km wide, 200-400 in deep, sub-ice shelf channels, aligned with the flow direction and spaced by 5 km. We attribute their formation to the bottom melting of ice from warm ocean waters underneath. Drilling at the center of one of channel, only 8 m above sea l...

  15. The last glaciation and deglaciation of the Northeast Greenland continental shelf revealed by hydro-acoustic data

    Science.gov (United States)

    Arndt, Jan Erik; Jokat, Wilfried; Dorschel, Boris

    2017-03-01

    About 16% of the Greenland Ice Sheet drains in the area of the Northeast Greenland shelf between 76°N and 80.5°N via marine terminating glaciers. Most of it is via the Northeast Greenland Ice Stream, the largest ice stream of Greenland. During ice ages, the ice sheet extended onto the continental shelf and modern-day cross-shelf troughs were filled by ice streams. In this study, high-resolution hydro-acoustic data acquired during three decades of research were jointly investigated to reveal the past glacial conditions. Our data shows that Westwind Trough and Norske Trough were filled by fast flowing ice streams that extended to the shelf edge during the last glacial maximum. In between the cross-shelf troughs, ice domes resided on shallow banks that may have contributed about a decimetre to global sea level. Most probably these ice domes initiated fast ice flow through sinks in the inter-trough area. In Westwind Trough, ice sheet retreat to the inner shelf after the last glacial maximum was intermittent. In contrast, in Norske Trough the ice sheet retreat appears relatively rapid with no evidences for phases of grounding line stabilization. Probably during the Younger Dryas, the ice sheet readvanced to a mid-shelf position in both troughs documented by grounding zone wedges. During this time, a thick ice shelf was present in Norske Trough releasing tabular icebergs. Ice sheet retreat from the mid-shelf to the coastline during Holocene deglaciation was rapid.

  16. Should China Allow Game Hunting?

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Public opinion is having an increasing impact on decision-making in China, as witnessed last month when the State Forestry Administration announced it was postponing plans to auction the first ever hunting licenses in the country's history. This move, brought about by a backlash in the media and online forums, prompted officials to disclose more details to justify

  17. The Great Bug Hunt 2011

    Science.gov (United States)

    Dixon-Watmough, Rebecca

    2011-01-01

    The Association For Science Education's "schoolscience.co.uk Great Bug Hunt 2011," in association with Martin Rapley and Gatekeeper Educational, has been a resounding success--not only because it fits into the science curriculum so neatly, but also because of the passion it evoked in the children who took part. This year's entries were…

  18. Exoplanets: The Hunt Continues!

    Science.gov (United States)

    2001-04-01

    Swiss Telescope at La Silla Very Successful Summary The intensive and exciting hunt for planets around other stars ( "exoplanets" ) is continuing with great success in both hemispheres. Today, an international team of astronomers from the Geneva Observatory and other research institutes [1] is announcing the discovery of no less than eleven new, planetary companions to solar-type stars, HD 8574, HD 28185, HD 50554, HD 74156, HD 80606, HD 82943, HD 106252, HD 141937, HD 178911B, HD 141937, among which two new multi-planet systems . The masses of these new objects range from slightly less than to about 10 times the mass of the planet Jupiter [2]. The new detections are based on measured velocity changes of the stars [3], performed with the CORALIE spectrometer on the Swiss 1.2-m Leonard Euler telescope at the ESO La Silla Observatory , as well as with instruments on telescopes at the Haute-Provence Observatory and on the Keck telescopes on Mauna Kea (Hawaii, USA). Some of the new planets are unusual: * a two-planet system (around the star HD 82943) in which one orbital period is nearly exactly twice as long as the other - cases like this (refered to as "orbital resonance") are well known in our own solar system; * another two-planet system (HD 74156), with a Jupiter-like planet and a more massive planet further out; * a planet with the most elongated orbit detected so far (HD 80606), moving between 5 and 127 million kilometers from the central star; * a giant planet moving in an orbit around its Sun-like central star that is very similar to the one of the Earth and whose potential satellites (in theory, at least) might be "habitable". At this moment, there are 63 know exoplanet candidates with minimum masses below 10 Jupiter masses, and 67 known objects with minimum masses below 17 Jupiter masses. The present team of astronomers has detected about half of these. PR Photo 13a/01 : Radial-velocity measurements of HD 82943, a two-planet system . PR Photo 13b/01 : Radial

  19. Final Environmental Assessment Proposed Opening of Bogue Chitto National Wildlife Refuge to Upland Game Hunting, Migratory Waterfowl Hunting, Big Game Hunting and Sport and Commercial Fishing

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — 1985 Final Environmental Assessment Proposed Opening of Bogue Chitto National Wildlife Refuge to Upland Game Hunting, Migratory Waterfoul Hunting, Big Game Hunting...

  20. [Role of modern hunting in wildlife management].

    Science.gov (United States)

    Cao, Shi; Zhou, Xue-Hong; Zhang, Wei

    2014-01-01

    Although modern hunting is different from traditional hunting, it remains a controversial topic. A large number of scholars in the world have studied the effects of hunting on wild animals from an ecological, ethological, genetic and economic aspect. This paper reviewed the role of controlled hunting in wildlife production from population dynamics, behavior, genetic and a phenotypic level, and by integrating a large number of domestic and foreign literatures. Many studies have shown that regulated hunting is an efficient approach in managing wildlife populations, which could be beneficial to the recovery and possibly even growth of wildlife populations. Meanwhile, over-exploitation or inappropriate hunting could affect the sex, birth and mortality ratios of wildlife populations, change foraging behavior and socio-spatial behavior and generate artificial selection of their genotype and phenotype. To apply modern hunting properly to wildlife management, China could learn from successful hunting programs implemented in many other countries, which are based on ecological and economic principles to formulate scientifically determined hunting quotas and set up an effective system to regulate and manage the hunting of wildlife populations.

  1. Hunting, law enforcement, and African primate conservation.

    Science.gov (United States)

    N'Goran, Paul K; Boesch, Christophe; Mundry, Roger; N'Goran, Eliezer K; Herbinger, Ilka; Yapi, Fabrice A; Kühl, Hjalmar S

    2012-06-01

    Primates are regularly hunted for bushmeat in tropical forests, and systematic ecological monitoring can help determine the effect hunting has on these and other hunted species. Monitoring can also be used to inform law enforcement and managers of where hunting is concentrated. We evaluated the effects of law enforcement informed by monitoring data on density and spatial distribution of 8 monkey species in Taï National Park, Côte d'Ivoire. We conducted intensive surveys of monkeys and looked for signs of human activity throughout the park. We also gathered information on the activities of law-enforcement personnel related to hunting and evaluated the relative effects of hunting, forest cover and proximity to rivers, and conservation effort on primate distribution and density. The effects of hunting on monkeys varied among species. Red colobus monkeys (Procolobus badius) were most affected and Campbell's monkeys (Cercopithecus campbelli) were least affected by hunting. Density of monkeys irrespective of species was up to 100 times higher near a research station and tourism site in the southwestern section of the park, where there is little hunting, than in the southeastern part of the park. The results of our monitoring guided law-enforcement patrols toward zones with the most hunting activity. Such systematic coordination of ecological monitoring and law enforcement may be applicable at other sites. ©2012 Society for Conservation Biology.

  2. On the difficulty of modeling Circumpolar Deep Water intrusions onto the Amundsen Sea continental shelf

    Science.gov (United States)

    Nakayama, Y.; Timmermann, R.; Schröder, M.; Hellmer, H. H.

    2014-12-01

    In the Amundsen Sea, warm Circumpolar Deep Water (CDW) intrudes onto the continental shelf and flows into the ice shelf cavities of the West Antarctic Ice Sheet, resulting in high basal melt rates. However, none of the high resolution global models resolving all the small ice shelves around Antarctica can reproduce a realistic CDW flow onto the Amundsen Sea continental shelf, and previous studies show simulated bottom potential temperature at the Pine Island Ice Shelf front of about -1.8 °C. In this study, using the Finite-Element Sea ice-ice shelf-Ocean Model (FESOM), we reproduce warm CDW intrusions onto the Amundsen Sea continental shelf and realistic melt rates of the ice shelves in West Antarctica. To investigate the importance of horizontal resolution, forcing, horizontal diffusivity, and the effect of grounded icebergs, eight sensitivity experiments are conducted. To simulate the CDW intrusion realistically, a horizontal resolution of about 5 km or smaller is required. The choice of forcing is also important and the cold bias in the NCEP/NCAR reanalysis over the eastern Amundsen Sea prevents warm CDW from intruding onto the continental shelf. On the other hand, the CDW intrusion is not highly sensitive to the strength of horizontal diffusion. The effect of grounded icebergs located off Bear Peninsula is minor, but may act as a buffer to an anomalously cold year.

  3. Ethical aspects of hunting tourism in Serbia

    Directory of Open Access Journals (Sweden)

    Prentović Risto

    2013-01-01

    Full Text Available The aim of this paper is to examine contemporary moral controversies about hunting tourism in Serbia in the context of defined value orientations and norms of ethics of hunting tourism, as a branch of applied ethics. On the one hand, this paper summarizes conceptual definitions and specificities of hunting tourism, as a special form of tourism, and the crucial value postulates derived from the assumptions of the concept of sustainable development and biodiversity conservation, and philosophical, theological and legal settings of man’s attitude towards animals and their welfare, as well as the standard code of hunting ethics and issues of business ethics in hunting tourism, on the other. The paper also cites some examples of ethically problematic phenomena in modern hunting tourism in Serbia and offers possible solutions to overcome them.

  4. Amendment #3 : Hunting and Fishing Plan : Mingo National Wildlife Refuge : Historic Weapons Deer Hunt

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This amendment to the Mingo NWR Hunting and Fishing Plan opens an additional 5,000 acres in the southwest portion of the Refuge to a historic weapons deer hunt.

  5. Rgyas bzang Tibetan Tribe Hunting Lore

    Directory of Open Access Journals (Sweden)

    Bkra shis dpal 'bar

    2011-12-01

    Full Text Available The Yul shul (Yushu Rgyas bzang Tribe historically possessed a rich hunting tradition. Wildlife was hunted for food and other animal products. By 2007, hunting culture had diminished due to improvements in living conditions, wildlife protection laws, greater state control of wildlife product skin market and gun ownership, animal diseases, and the absence of such wildlife as wild yaks in local areas.

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

    NARCIS (Netherlands)

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

    2015-01-01

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

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

    NARCIS (Netherlands)

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

    2015-01-01

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

  8. 77 FR 38317 - Wildlife and Hunting Heritage Conservation Council

    Science.gov (United States)

    2012-06-27

    ... Fish and Wildlife Service Wildlife and Hunting Heritage Conservation Council AGENCY: Fish and Wildlife..., announce a public teleconference of the Wildlife and Hunting Heritage Conservation Council (Council). DATES... that Wildlife and Hunting Heritage Conservation Council will hold a teleconference. Background...

  9. 76 FR 3155 - Wildlife and Hunting Heritage Conservation Council

    Science.gov (United States)

    2011-01-19

    ... Fish and Wildlife Service Wildlife and Hunting Heritage Conservation Council AGENCY: Fish and Wildlife... public meeting of the Wildlife and Hunting Heritage Conservation Council (Council). DATES: Meeting... that Wildlife and Hunting Heritage Conservation Council will hold a meeting. Background Formed...

  10. 78 FR 42104 - Wildlife and Hunting Heritage Conservation Council

    Science.gov (United States)

    2013-07-15

    ... Fish and Wildlife Service Wildlife and Hunting Heritage Conservation Council AGENCY: Fish and Wildlife..., announce a public teleconference of the Wildlife and Hunting Heritage Conservation Council (Council). DATES... Wildlife and Hunting Heritage Conservation Council will hold a teleconference. Background Formed...

  11. 77 FR 74864 - Wildlife and Hunting Heritage Conservation Council

    Science.gov (United States)

    2012-12-18

    ... Fish and Wildlife Service Wildlife and Hunting Heritage Conservation Council AGENCY: Fish and Wildlife... public meeting of the Wildlife and Hunting Heritage Conservation Council (Council). DATES: Meeting.... App., we announce that Wildlife and Hunting Heritage Conservation Council will hold a...

  12. 77 FR 10543 - Wildlife and Hunting Heritage Conservation Council Charter

    Science.gov (United States)

    2012-02-22

    ... Office of the Secretary Wildlife and Hunting Heritage Conservation Council Charter AGENCY: Office of the... Secretary of Agriculture have renewed the Wildlife and Hunting Heritage Conservation Council (Council..., providing recommendations for: (a) Implementing the Recreational Hunting and Wildlife Resource...

  13. 75 FR 57292 - Wildlife and Hunting Heritage Conservation Council

    Science.gov (United States)

    2010-09-20

    ... Fish and Wildlife Service Wildlife and Hunting Heritage Conservation Council AGENCY: Fish and Wildlife... public meeting of the Wildlife and Hunting Heritage Conservation Council (Council). DATES: Meeting... that Wildlife and Hunting Heritage Conservation Council will hold a meeting. Background Formed...

  14. 77 FR 15386 - Wildlife and Hunting Heritage Conservation Council

    Science.gov (United States)

    2012-03-15

    ... Fish and Wildlife Service Wildlife and Hunting Heritage Conservation Council AGENCY: Fish and Wildlife..., announce a public teleconference of the Wildlife and Hunting Heritage Conservation Council (Council). DATES... that Wildlife and Hunting Heritage Conservation Council will hold a teleconference. Background...

  15. Greenland ice sheet retreat history in the northeast Baffin Bay based on high-resolution bathymetry

    Science.gov (United States)

    Slabon, Patricia; Dorschel, Boris; Jokat, Wilfried; Myklebust, Reidun; Hebbeln, Dierk; Gebhardt, Catalina

    2016-12-01

    New swath-bathymetric data acquired in 2010 and 2015 indicate a variety of glacial landforms in cross-shelf troughs of the Melville Bay (northeast Baffin Bay). These landforms reveal that, at their maximum extent, ice streams in the troughs crossed the shelf all the way to the shelf edge. Moraines, grounding-zone wedges (GZWs) and subglacial till lobes on the continental shelf define a pattern of variable ice stream retreat in the individual troughs. On the outer shelf, in the northern cross-shelf trough, ice-stream retreat was slow compared to more episodic retreat in the central (at least one stabilization on the outer shelf) and southern cross-shelf trough (re-advances at the shelf edge and fast retreat thereafter). Large GZWs on the mid-to inner shelf of the troughs indicate periods of grounding-zone stabilization. According to glacial landforms, the final retreat across the inner shelf (before 8.41 ka BP) was episodic to slow. Furthermore, evidence has been found for localized ice domes with minor ice-streams on inter-trough banks. The glacial landforms in Melville Bay, thus, indicate the varying and discontinuous ice sheet retreat history across the Northwest Greenland continental shelf.

  16. Neurosyphilis Mimicking Ramsay Hunt Syndrome.

    Science.gov (United States)

    Maeda, Tadashi; Yoshizawa, Sadako; Hirayama, Takehisa; Saga, Tomoo; Tateda, Kazuhiro; Urita, Yoshihisa

    2015-01-01

    A 36-year-old man presented with facial nerve palsy, hearing loss, vertigo and headache. He was initially diagnosed with Ramsay Hunt syndrome and treated with a systemic steroid and valaciclovir; however, his symptoms deteriorated. Serum rapid plasma reagin (RPR) and treponema pallidum hemagglutination tests were positive. Cerebrospinal fluid analysis revealed an elevated white blood cell count and positive RPR, confirming the diagnosis of neurosyphilis. Penicillin G (PCG) was administered, and his facial nerve function and headache improved. However, left-side hearing loss worsened temporarily, which was assumed to be a Jarisch-Herxheimer reaction. Betamethasone was administered along with PCG, and he recovered completely.

  17. Triggers for the Collapse of Ice Shelves in Antarctica: Investigating Compressive Arch Failure with Numerical Models

    Science.gov (United States)

    Huth, A.; Smith, B. E.

    2015-12-01

    Antarctic ice shelves restrain, or buttress, grounded ice from flowing freely into the ocean by redistributing the force of the ice flow to pinning points (ice rises) at the ice front and shear margins at adjacent bay walls. This buttressing process typically defines a 'compressive arch' in the strain rate-field of the ice shelf, where the smallest principal component transitions from compressive inland of the arch to extensive seaward of the arch. If the compressive arch is breached due to iceberg calving at the ice front or thinning at the shear margins, the ice shelf will retreat irreversibly to a new stable configuration or collapse entirely. This retreat can compromise ice shelf buttressing, resulting in sea-level rise and ocean freshening as grounded ice flows unrestricted into the ocean. Here, we investigate the dynamics of compressive arch failure using Larsen C ice shelf as a test case for a larger study that will include several other ice shelves and projections for sea-level rise. We use satellite observations to develop a steady state model of Larsen C in Elmer/ICE, a finite element ice sheet/ice flow software package. We run calving and thinning simulations to determine the conditions needed to trigger ice shelf retreat via compressive arch failure and discuss the likelihood of these scenarios occurring in relation to extrapolations of current melt profiles and calving trends.

  18. Hunting Motifs in Situla Art

    Directory of Open Access Journals (Sweden)

    Andrej Preložnik

    2013-07-01

    Full Text Available Situla art developed as an echo of the toreutic style which had spread from the Near East through the Phoenicians, Greeks and Etruscans as far as the Veneti, Raeti, Histri, and their eastern neighbours in the region of Dolenjska (Lower Carniola. An Early Iron Age phenomenon (c. 600—300 BC, it rep- resents the major and most arresting form of the contemporary visual arts in an area stretching from the foot of the Apennines in the south to the Drava and Sava rivers in the east. Indeed, individual pieces have found their way across the Alpine passes and all the way north to the Danube. In the world and art of the situlae, a prominent role is accorded to ani- mals. They are displayed in numerous representations of human activities on artefacts crafted in the classic situla style – that is, between the late 6th  and early 5th centuries BC – as passive participants (e.g. in pageants or in harness or as an active element of the situla narrative. The most typical example of the latter is the hunting scene. Today we know at least four objects decorat- ed exclusively with hunting themes, and a number of situlae and other larger vessels where hunting scenes are embedded in composite narratives. All this suggests a popularity unparallelled by any other genre. Clearly recognisable are various hunting techniques and weapons, each associated with a particu- lar type of game (Fig. 1. The chase of a stag with javelin, horse and hound is depicted on the long- familiar and repeatedly published fibula of Zagorje (Fig. 2. It displays a hound mauling the stag’s back and a hunter on horseback pursuing a hind, her neck already pierced by the javelin. To judge by the (so far unnoticed shaft end un- der the stag’s muzzle, the hunter would have been brandishing a second jave- lin as well, like the warrior of the Vače fibula or the rider of the Nesactium situla, presumably himself a hunter. Many parallels to his motif are known from Greece, Etruria, and

  19. Seafloor Control on Sea Ice

    Science.gov (United States)

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

    2011-01-01

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

  20. Phytoplankton and other data from net and bottle casts from the ICE ISLANDS and other platforms as part of Outer Continental Shelf Environmental Assessment Program (OCSEAP) from 19 April 1979 to 23 June 1980 (NODC Accession 8200100)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Phytoplankton and other data were collected from net and bottle casts from the ICE ISLANDS and other platforms from 19 April 1979 to 23 June 1980. Data were...

  1. Pressure gauge and CTD data from ICE ISLANDS and other platforms from the Beaufort and Chukchi Seas in support of the Outer Continental Shelf Environmental Assessment Program (OCSEAP) from 25 July 1982 to 08 March 1984 (NODC Accession 8500129)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Pressure gauge and CTD data were collected from the ICE ISLANDS and other platforms in the Beaufort and Chukchi Seas from 25 July 1982 to 08 March 1984. Data were...

  2. Thermostabilized Shelf Life Study

    Science.gov (United States)

    Perchonok, Michele H.; Catauro, Patricia M.

    2009-01-01

    The objective of this project is to determine the shelf life end-point of various food items by means of actual measurement or mathematical projection. The primary goal of the Advanced Food Technology Project in these long duration exploratory missions is to provide the crew with a palatable, nutritious and safe food system while minimizing volume, mass, and waste. The Mars missions could be as long as 2.5 years with the potential of the food being positioned prior to the crew arrival. Therefore, it is anticipated that foods that are used during the Mars missions will require a 5 year shelf life. Shelf life criteria are safety, nutrition, and acceptability. Any of these criteria can be the limiting factor in determining the food's shelf life. Due to the heat sterilization process used for the thermostabilized food items, safety will be preserved as long as the integrity of the package is maintained. Nutrition and acceptability will change over time. Since the food can be the sole source of nutrition to the crew, a significant loss in nutrition may determine when the shelf life endpoint has occurred. Shelf life can be defined when the food item is no longer acceptable. Acceptability can be defined in terms of appearance, flavor, texture, or aroma. Results from shelf life studies of the thermostabilized food items suggest that the shelf life of the foods range from 0 months to 8 years, depending on formulation.

  3. Thermostable Shelf Life Study

    Science.gov (United States)

    Perchonok, M. H.; Antonini, D. K.

    2008-01-01

    The objective of this project is to determine the shelf life end-point of various food items by means of actual measurement or mathematical projection. The primary goal of the Advanced Food Technology Project in these long duration exploratory missions is to provide the crew with a palatable, nutritious and safe food system while minimizing volume, mass, and waste. The Mars missions could be as long as 2.5 years with the potential of the food being positioned prior to the crew arrival. Therefore, it is anticipated that foods that are used during the Mars missions will require a 5 year shelf life. Shelf life criteria are safety, nutrition, and acceptability. Any of these criteria can be the limiting factor in determining the food's shelf life. Due to the heat sterilization process used for the thermostabilized food items, safety will be preserved as long as the integrity of the package is maintained. Nutrition and acceptability will change over time. Since the food can be the sole source of nutrition to the crew, a significant loss in nutrition may determine when the shelf life endpoint has occurred. Shelf life can be defined when the food item is no longer acceptable. Acceptability can be defined in terms of appearance, flavor, texture, or aroma. Results from shelf life studies of the thermostabilized food items suggest that the shelf life of the foods range from 0 months to 8 years, depending on formulation.

  4. The geomorphology of a glaciated continental shelf, Western Scotland, UK

    Science.gov (United States)

    Howe, John; Dove, Dayton; Bradwell, Tom

    2013-04-01

    We present recently collected swath bathymetry and legacy seismic data from two regions of the north-west UK continental shelf: the Sea of the Hebrides; and the Firth of Lorn, western Scotland. Both regions have experienced extensive Pleistocene ice sheet glaciation and both provide abundant geomorphological evidence of subglacial and postglacial processes. The Sea of the Hebrides bathymetry data cover 2200 km2 and provide new geomorphological evidence for an ice stream flowing from western Scotland and the Inner Hebrides focusing towards a trough-mouth fan (the Barra Fan) at the continental shelf break during the height of the last glaciation. Notably, bedrock structures provide a control on the location and orientation of glacially overdeepened basins and troughs on the inner shelf. Whilst around the Islands of Canna and Rum, convergent seabed glacial lineations and other subglacially streamlined features eroded in bedrock preserve the direction of ice sheet movement - indicating ice streaming in a south-westerly direction across the continental shelf. We propose that this fast-flow zone formed part of a larger convergent ice stream system draining much of western Scotland and the north of Ireland. The Firth of Lorn bathymetry acquisition comprises 553km2 of data, collected as part of the INIS Hydro program (Ireland, Northern Ireland and Scotland Hydrographic Survey). This region of nearshore continental shelf is revealed as predominantly bedrock-dominated seabed, characterised by a series of narrow, strongly fault-controlled troughs, part of the Great Glen Fault Zone complex. Evidence for glaciation is widespread and well preserved in the Firth of Lorn and surrounding seabed with moraines, bedrock lineations (?megagrooves?) and overdeepened basins common across the area. Initial mapping shows that our understanding of the configuration and style of deglaciation in these sectors of the former British-Irish Ice Sheet can be greatly improved by the collection of

  5. ON THE SUBJECT OF ILLEGAL HUNTING

    Directory of Open Access Journals (Sweden)

    M. G. Abdulmutalibov

    2014-01-01

    Full Text Available Aim. The article considers a notion of subject of such crime as illegal hunting. Only a man can be a subject of this crime. The content of such crime is revealed with the help of such properties as guilt, motive and aim. The article considers different properties of a subject of crime: 1 Physical nature Illegal actions can be committed by a man directly or indirectly. If during hunting a dog without its master’s command got a wild animal, the hunter is not liable as here intentional crime is absent. Juridical entities also are not admitted a subject of crime, only their representative if he committed this crime. 2 Criminal capacity. A person is not liable for this crime if he committed it in the state of criminal incapacity (CC Art.21. If illegal hunting is committed by a person in the state of drunkenness he is admitted capable and is liable for the crime(Criminal Code art.23. 3 A definite age. According to Art.23 of RF CC criminal responsibility for illegal hunting comes from the age of 16 . Performance of art.11, 12, 13 of CC concerns citizens of Russia, foreign citizens and persons without citizenship who committed poaching on the territory of Russia. Thus, the subject of poaching is a capable physical person reached the age of 16 by the moment of committing the crime. Methods. questionnaire method was applied for finding out the predominant motive and aim of illegal hunting. Result. 82% of pollee officials of hunting supervision bodies indicated the motive of profit as a predominant in committing illegal hunting.Location. Pskovskaya, Tulskaya, Moskovskaya regions. Conclusions. 1.Illegal hunting is committed only intentionally.2.The aim of poaching is killing wild animals and further use of their meat, skin, down, and active rest3.The more spread motives of poaching are: mercenary motives (35% and hunting passion

  6. Drivers of bushmeat hunting and perceptions of zoonoses in Nigerian hunting communities.

    Directory of Open Access Journals (Sweden)

    Sagan Friant

    2015-05-01

    Full Text Available Bushmeat hunting threatens biodiversity and increases the risk of zoonotic pathogen transmission. Nevertheless, limited information exists on patterns of contact with wildlife in communities that practice bushmeat hunting, especially with respect to social drivers of hunting behavior. We used interview responses from hunters and non-hunters in rural hunting communities in Nigeria to: 1 quantify contact rates with wildlife, 2 identify specific hunting behaviors that increase frequency of contact, 3 identify socioeconomic factors that predispose individuals to hunt, and 4 measure perceptions of risk. Participants engaged in a variety of behaviors that increased contact with wild animals, including: butchering to sell (37%, being injured (14%, using body parts for traditional medicine (19%, collecting carcasses found in forests and/or farms (18%, and keeping as pets (16%. Hunters came into contact with wildlife significantly more than non-hunters, even through non-hunting exposure pathways. Participants reported hunting rodents (95%, ungulates (93%, carnivores (93%, primates (87%, and bats (42%, among other prey. Reported hunting frequencies within taxonomic groups of prey were different for different hunting behaviors. Young age, lower education level, larger household size, having a father who hunts, and cultural group were all associated with becoming a hunter. Fifty-five percent of respondents were aware that they could contract diseases from wild animals, but only 26% of these individuals reported taking protective measures. Overall, hunters in this setting frequently contact a diversity of prey in risky ways, and the decision to become a hunter stems from family tradition, modified by economic necessity. Conservation and public health interventions in such settings may be most efficient when they capitalize on local knowledge and target root socio-economic and cultural drivers that lead to hunting behavior. Importantly, interventions that

  7. Note On The Ross Sea Shelf Water Downflow Processes (antarctica)

    Science.gov (United States)

    Bergamasco, A.; Defendi, V.; Spezie, G.; Budillon, G.; Carniel, S.

    In the framework of the CLIMA Project of the Italian National Program for Research in Antarctica, three different experimental data sets were acquired along the continental shelf break; two of them (in 1997 and 2001) close to Cape Adare, the 1998 one in the middle of the Ross Sea (i.e. 75 S, 177 W). The investigations were chosen in order to explore the downslope flow of the bottom waters produced in the Ross Sea, namely the High Salinity Shelf Water (HSSW, the densest water mass of the southern ocean coming from its formation site in the polynya region in Terra Nova bay), and the Ice Shelf Water (ISW, originated below the Ross Ice Shelf and outflowing northward). Both bottom waters spill over the shelf edge and mix with the Circumpolar Deep Water (CDW) contributing to the formation of the Antarctic Bottom Waters (AABW). Interpreting temperature, salinity and density maps in terms of cascading processes, both HSSW and ISW overflows are evidenced during, respectively, 1997 and 1998. During the 2001 acquisition there is no presence of HSSW along the shelf break, nevertheless distribution captures the evidence of a downslope flow process.

  8. On the freshening of the northwestern Weddell Sea continental shelf

    Directory of Open Access Journals (Sweden)

    H. H. Hellmer

    2011-05-01

    Full Text Available We analyzed hydrographic data from the northwestern Weddell Sea continental shelf of the three austral winters 1989, 1997, and 2006 and two summers following the last winter cruise. During summer a thermal front exists at ~64° S separating cold southern waters from warm northern waters that have similar characteristics as the deep waters of the central basin of the Bransfield Strait. In winter, the whole continental shelf exhibits southern characteristics with high Neon (Ne concentrations, indicating a significant input of glacial melt water. The comparison of the winter data from the shallow shelf off the tip of the Antarctic Peninsula, spanning a period of 17 yr, shows a salinity decrease of 0.09 for the whole water column, which has a residence time of <1 yr. We interpret this freshening as being caused by a combination of reduced salt input due to a southward sea ice retreat and higher precipitation during the late 20th century on the western Weddell Sea continental shelf. However, less salinification might also result from a delicate interplay between enhanced salt input due to sea ice formation in coastal areas formerly occupied by Larsen A and B ice shelves and increased Larsen C ice loss.

  9. On the freshening of the northwestern Weddell Sea continental shelf

    Directory of Open Access Journals (Sweden)

    H. H. Hellmer

    2010-12-01

    Full Text Available We analysed hydrographic data from the northwestern Weddell Sea continental shelf of three austral winters (1989, 1997 and 2006 and two summers following the last winter cruise. During summer a thermal front exists at ~64° S separating cold southern waters from warm northern waters that have similar characteristics as the deep waters of the central basin of the Bransfield Strait. In winter, the whole continental shelf exhibits southern characteristics with high Neon (Ne concentrations, indicating a significant input of glacial melt water. The comparison of the winter data at the tip of the Antarctic Peninsula, spanning a period of 17 years, shows a salinity decrease of 0.09 for the whole water column. We interpret this freshening as a reduction in salt input to the water masses being advected northward on the western Weddell Sea continental shelf. Possible causes for the reduced winter salinification are a southward retreat of the summer sea ice edge together with more precipitation in this sector. However, the latter might have happened in conjunction with an increase in ice shelf mass loss, counteracting an enhanced salt input due to sea ice formation in coastal areas formerly occupied by Larsen A and B ice shelves.

  10. Greenland Ice Shelves and Ice Tongues

    DEFF Research Database (Denmark)

    Reeh, Niels

    2017-01-01

    literature and physical properties are reviewed. There exists a difference between: (1) Floating glaciers in northern Greenland (>77°N) which experience bottom melting as their dominant ablation mechanism and calve relatively thin, but large (km-sized) tabular icebergs (‘ice islands’), and (2) Grounded......This chapter focuses on a review of the glaciers on north and northeast Greenland that terminate in fiords with long glacier tongues and floating, ice-shelf-like margins. There is some debate as to whether these glacier tongues can be classified as a traditional ice shelf, so the relevant...... glaciers further south (melting estimated at up to 10 m year−1 for locations...

  11. Hunting Plan : Mingo National Wildlife Refuge

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This plan provides guidelines for the administration of hunting activity and for the development, maintenance, and enforcement of regulations and guidelines on Mingo...

  12. Cat Island NWR Recreational Hunting Plan

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — A natural resource management plan describing the regulations and decision processes for sport hunting at Cat Island NWR. This plan has been replaced by a more...

  13. Hunting Plan: St. Vincent National Wildlife Refuge

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This plan provides guidelines for the administration of hunting activity and for the development, maintenance, and enforcement of regulations and guidelines on St....

  14. Hunt Plan : Pocosin Lakes National Wildlife Refuge

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This plan provides guidelines for the administration of hunting activity and for the development, maintenance, and enforcement of regulations and guidelines on...

  15. Back Bay National Wildlife Refuge: Hunting Plan

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This plan provides guidelines for the administration of hunting activity and for the development, maintenance, and enforcement of regulations and guidelines on Back...

  16. Hunting Plan Morgan Brake National Wildlife Refuge

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This plan provides guidelines for administration of hunting activity and for development, maintenance, and enforcement of regulations and guidelines on Morgan Brake...

  17. Hunting Plan Mathew's Brake National Wildlife Refuge

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This plan provides guidelines for administration of hunting activity and for development, maintenance, and enforcement of regulations and guidelines on Mathew’s...

  18. Hunting Plan : Seney National Wildlife Refuge

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — Hunting has been and is a traditional use of the Seney Refuge dating back to its establishment in 1935. This recreational activity has strong support from the...

  19. Hunting Plan : Malheur National Wildlife Refuge

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — The purpose of this plan is to provide guidelines for administration of hunting activity and for development, maintenance, and enforcement of regulations and...

  20. Revised Hunting Plan : Sherburne National Wildlife Refuge

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This plan provides guidelines for the administration of hunting activity and for the development, maintenance, and enforcement of regulations and guidelines on...

  1. Hunting Plan : Shiawassee National Wildlife Refuge

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This plan provides guidelines for administration of hunting activity and for development, maintenance, and enforcement of regulations and guidelines on Shiawassee...

  2. Benton Lake National Wildlife Refuge : Hunting Plan

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This plan provides guidelines for the administration of hunting activity and for the development, maintenance, and enforcement of regulations and guidelines on...

  3. Crab Orchard National Wildlife Refuge : Hunting Plan

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This plan provides guidelines for the administration of hunting activity and for the development, maintenance, and enforcement of regulations and guidelines on Crab...

  4. Fact sheet : Hunting and Fishing Plan

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This document provides information about the opening of portions of Eufaula National Wildlife Refuge to the hunting of eastern mourning doves and migratory...

  5. Hunting Plan : Trempealeau National Wildlife Refuge

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This plan provides guidelines for administration of hunting activity and for development, maintenance, and enforcement of regulations and guidelines on Trempealeau...

  6. Sport Hunting Plan Decision Document Package

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — Objectives of plan are to provide high quality hunting opportunities, maintain populations within seasonal carrying capacities, and allow compatible public use.

  7. Hunting Management Plan Erie NWR 1995

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This plan provides guidelines for the administration of hunting activity and for the development, maintenance, and enforcement of regulations and guidelines on Erie...

  8. Locomotion dynamics of hunting in wild cheetahs.

    Science.gov (United States)

    Wilson, A M; Lowe, J C; Roskilly, K; Hudson, P E; Golabek, K A; McNutt, J W

    2013-06-13

    Although the cheetah is recognised as the fastest land animal, little is known about other aspects of its notable athleticism, particularly when hunting in the wild. Here we describe and use a new tracking collar of our own design, containing a combination of Global Positioning System (GPS) and inertial measurement units, to capture the locomotor dynamics and outcome of 367 predominantly hunting runs of five wild cheetahs in Botswana. A remarkable top speed of 25.9 m s(-1) (58 m.p.h. or 93 km h(-1)) was recorded, but most cheetah hunts involved only moderate speeds. We recorded some of the highest measured values for lateral and forward acceleration, deceleration and body-mass-specific power for any terrestrial mammal. To our knowledge, this is the first detailed locomotor information on the hunting dynamics of a large cursorial predator in its natural habitat.

  9. Hunting Plan : Rice Lake National Wildlife Refuge

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — The objectives of this hunting plan for Rice Lake NWR are to: provide a method of removing white-tailed deer from the area population to maintain the general health...

  10. St. Vincent Offers Special Archery & Primitive Hunts

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — St. Vincent National Wildlife Refuge's archery hunt is scheduled for November 28-30, 1984. White-tailed deer, turkeys, and hogs may be taken.

  11. Hunting Plan Squaw Creek National Wildlife Refuge

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This plan provides guidelines for the administration of hunting activity and for the development, maintenance, and enforcement of regulations and guidelines on Squaw...

  12. Ice Draft and Ice Velocity Data in the Beaufort Sea, 1990-2003

    Data.gov (United States)

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

  13. Ramsay hunt syndrome (herpes zoster oticus

    Directory of Open Access Journals (Sweden)

    S Karthiga Kannan

    2012-01-01

    Full Text Available Ramsay Hunt syndrome (RHS is defined as an acute peripheral facial neuropathy caused by the reactivated latent varicella zoster virus (VZV in the geniculate ganglion; characterized with erythematous vesicular rash of the skin of the ear canal, auricle, facial skin, oral mucosa and facial palsy (also known as herpes zoster oticus. This article reports a case of Ramsay Hunt Syndrome (RHS in a 37-year-old male patient depicting the classical signs.

  14. The Myanmar continental shelf

    Digital Repository Service at National Institute of Oceanography (India)

    Ramaswamy, V.; Rao, P.S.

    conditions, and neotectonic activity. The most prominent bathymetric feature on the Ayeyarwady continental shelf is the 120 km-wide Martaban Depression, at the centre of which is located the Martaban Canyon. Most of the suspended sediment discharge...

  15. Laurentide ice sheet dynamics during the last glacial period

    Science.gov (United States)

    Montoya, M.; Alvarez-Solas, J.; Robinson, A.; Banderas, R.

    2016-12-01

    Heinrich events (HEs) are interpreted as the result of massive large-scale ice discharges from the Laurentice ice sheet (LIS) into the North Atlantic that occurred during the Last Glacial Period (LGP). Classically they have been attributed to internal oscillations of the LIS, a mechanism that has been mimicked using three-dimensional ice-sheet models within the Shallow Ice Approximation (SIA) together with a modified basal sliding parameterisation accounting for enhanced ice-flow over a melting ice bed. However, recent studies using hybrid ice sheet-ice shelf models with more comprehensive dynamics combining the SIA and the Shallow Shelf Approximation (SSA) have proposed an alternative explanation involving the effects of oceanic circulation changes on the ice shelves. Up to now the plausibility of internal LIS instabilities in a hybrid ice sheet-ice shelf model combining SSA and SIA has seldom been investigated. Here we address this issue in the framework of the LGP by modifying the dynamics in a hybrid ice sheet-ice shelf model to mimick two different levels of complexity. We firstly suppress the binary mode mixture of sheet and stream ice in order to mimick the SIA, and include a basal sliding parameterisation. Under constant external climate forcing, quasi-periodic LIS instabilities are simulated in response to internal basal temperature oscillations. We then consider a more realistic dynamical formulation by incorporating the treatment of ice flow under the SSA. Internal basal temperature oscillations, and thereby LIS instabilities, are found to vanish under constant external forcing. Our results demonstrate how accounting for the longitudinal stresses of the ice streams, which is not possible within the pure SIA, is critical to stabilize ice flow and prevents the occurrence of the binge-purge oscillations.

  16. 7th Higgs Hunting 2016

    CERN Document Server

    2016-01-01

    A subject of major importance in fundamental physics is the investigation of the origin of Electroweak Symmetry Breaking. The mechanism of mass generation through the spontaneous breaking of a gauge symmetry is called the Brout-Englert-Higgs mechanism and is associated with the appearance of a physical scalar boson. The discovery announced at CERN on 4th July 2012 by the ATLAS and CMS Collaborations of a boson at a mass close to 125 GeV/c2, compatible with this scalar boson of the Standard Model, the so-called Higgs boson, mainly in γγ, ZZ and WW decay modes, with compatible evidence also found at Fermilab in the bb mode, changed the landscape. This important discovery was acknowledged as decisive for the attribution of the 2013 Nobel Prize in Physics awarded jointly to François Englert and Peter Higgs . This 7th workshop of the "Higgs Hunting" series organized in Paris on August 31 - September 2, 2016 will discuss the developments of LHC run 2 analyses, detailed studies of the new boson and possible de...

  17. Hunting for Conservation? The Re-introduction of Sport Hunting in Uganda Examined

    NARCIS (Netherlands)

    Ochieng, A.; Ahebwa, W.M.; Visseren-Hamakers, I.J.

    2015-01-01

    Uganda reintroduced sport hunting in 2001. The policy was piloted around Lake Mburo National Park and later replicated around other protected areas. This chapter analyses the development, implementation and impact of sport hunting policy in Uganda. We do so through literature review, document

  18. 75 FR 32872 - Migratory Bird Hunting; Supplemental Proposals for Migratory Game Bird Hunting Regulations for...

    Science.gov (United States)

    2010-06-10

    ... alternatives for duck hunting seasons remain the same as those used in 2009. Service Response: As we stated in... Council Recommendations: The Atlantic Flyway Council recommended adoption of a derived Northern Pintail... usefulness of sex-specific regulations for pintails as a way to increase hunting opportunity on male...

  19. 77 FR 42919 - Migratory Bird Hunting; Proposed Frameworks for Early-Season Migratory Bird Hunting Regulations...

    Science.gov (United States)

    2012-07-20

    ... July 20, 2012 Part V Department of the Interior Fish and Wildlife Service 50 CFR Part 20 Migratory Bird Hunting; Proposed Frameworks for Early-Season Migratory Bird Hunting Regulations; Notice of Meetings...; ] DEPARTMENT OF THE INTERIOR Fish and Wildlife Service 50 CFR Part 20 RIN 1018-AX97 Migratory Bird...

  20. The Quabbin controlled deer hunt 1991 - 2001: limitations of a controlled hunt

    Science.gov (United States)

    Beth E. Cohen; David K. Loomis

    2003-01-01

    The Quabbin Reservoir, built in the 1930's as a water supply for Boston, is an unfiltered source of water. The agency responsible for managing the reservoir wants it to remain unfiltered. As a result, human activity is kept to a minimum, including (until recently) a prohibition on hunting. The lack of natural predators and the ban on recreational hunting allowed...

  1. Exchange across the shelf break at high southern latitudes

    Directory of Open Access Journals (Sweden)

    J. M. Klinck

    2010-01-01

    Full Text Available Exchange of water across the Antarctic shelf break has considerable scientific and societal importance due to its effects on circulation and biology of the region, conversion of water masses as part of the global overturning circulation and basal melt of glacial ice and the consequent effect on sea level rise. The focus in this paper is the onshore transport of warm, oceanic Circumpolar Deep Water (CDW; export of dense water from these shelves is equally important, but has been the focus of other recent papers and will not be considered here. A variety of physical mechanisms are described which could play a role in this onshore flux. The relative importance of some processes are evaluated by simple calculations. A numerical model for the Ross Sea continental shelf is used as an example of a more comprehensive evaluation of the details of cross-shelf break exchange. In order for an ocean circulation model simulate these processes at high southern latitudes, it needs to have high spatial resolution, realistic geometry and bathymetry. Grid spacing smaller than the first baroclinic radius deformation (a few km is required to adequately represent the circulation. Because of flow-topography interactions, bathymetry needs to be represented at these same small scales. Atmospheric conditions used to force these circulation models also need to be known at a similar small spatial resolution (a few km in order to represent orographically controlled winds (coastal jets and katabatic winds. Significantly, time variability of surface winds strongly influences the structure of the mixed layer. Daily, if not more frequent, surface fluxes must be imposed for a realistic surface mixed layer. Sea ice and ice shelves are important components of the coastal circulation. Ice isolates the ocean from exchange with the atmosphere, especially in the winter. Melting and freezing of both sea ice and glacial ice influence salinity and thereby the character of shelf water

  2. Exchange across the shelf break at high southern latitudes

    Directory of Open Access Journals (Sweden)

    J. M. Klinck

    2010-05-01

    Full Text Available Exchange of water across the Antarctic shelf break has considerable scientific and societal importance due to its effects on circulation and biology of the region, conversion of water masses as part of the global overturning circulation and basal melt of glacial ice and the consequent effect on sea level rise. The focus in this paper is the onshore transport of warm, oceanic Circumpolar Deep Water (CDW; export of dense water from these shelves is equally important, but has been the focus of other recent papers and will not be considered here. A variety of physical mechanisms are described which could play a role in this onshore flux. The relative importance of some processes are evaluated by simple calculations. A numerical model for the Ross Sea continental shelf is used as an example of a more comprehensive evaluation of the details of cross-shelf break exchange. In order for an ocean circulation model to simulate these processes at high southern latitudes, it needs to have high spatial resolution, realistic geometry and bathymetry. Grid spacing smaller than the first baroclinic radius of deformation (a few km is required to adequately represent the circulation. Because of flow-topography interactions, bathymetry needs to be represented at these same small scales. Atmospheric conditions used to force these circulation models also need to be known at a similar small spatial resolution (a few km in order to represent orographically controlled winds (coastal jets and katabatic winds. Significantly, time variability of surface winds strongly influences the structure of the mixed layer. Daily, if not more frequent, surface fluxes must be imposed for a realistic surface mixed layer. Sea ice and ice shelves are important components of the coastal circulation. Ice isolates the ocean from exchange with the atmosphere, especially in the winter. Melting and freezing of both sea ice and glacial ice influence salinity and thereby the character of shelf

  3. The management of hunting of Anatidae

    Science.gov (United States)

    Nichols, J.D.; Johnson, F.A.; Birkan, Marcel

    1996-01-01

    The objectives of harvest management for members of family Anatidae typically involve the size of the harvested population and the size of the harvest. Hunting regulations are the primary tool used to try to achieve the objectives of harvest management. Informed harvest management thus requires a knowledge of the relationship between hunting regulations and both Anatid abundance and harvest. Results of retrospective studies in North America provide evidence that generally restrictive regulations produce lower harvest rates than generally liberal regulations. However, such studies have provided little evidence that specific hunting regulations designed to produce a change in the relative harvest rates of different species, or of the sexes within a species, have been successful in 'directing' harvest toward specific groups of birds and away from other groups. Estimates of the strength of the relationship between harvest mortality rates and annual survival rates of Anatidae have ranged from weak to strong. Thus, the key relationships for harvest management of Anatidae, those between hunting regulations and the size of both the subsequent harvest and the subsequent population, are not 'known' but are characterized by uncertainty. In the United States, this uncertainty led to a risk-aversive conservatism that characterized the setting of hunting regulations during the last decade. Recently, managers have begun to consider using hunting regulations themselves as a means to better understand the system being managed. This approach, referred to as active adaptive management, attempts to balance short-term demands for hunting opportunity with the learning needed to improve long-term management performance. Learning is accomplished by periodically comparing observed system response, as estimated by ongoing survey and data collection programs, with predictions of competing models. These periodic comparisons lead to changes in measures of credibility associated with the

  4. Ice Sheets & Ice Cores

    DEFF Research Database (Denmark)

    Mikkelsen, Troels Bøgeholm

    Since the discovery of the Ice Ages it has been evident that Earth’s climate is liable to undergo dramatic changes. The previous climatic period known as the Last Glacial saw large oscillations in the extent of ice sheets covering the Northern hemisphere. Understanding these oscillations known...... as Dansgaard-Oeschger (DO) events would add to our knowledge of the climatic system and – hopefully – enable better forecasts. Likewise, to forecast possible future sea level rise it is crucial to correctly model the large ice sheets on Greenland and Antarctica. This project is divided into two parts...

  5. A coupled oscillator model of shelf and ocean tides

    Science.gov (United States)

    Arbic, Brian K.; Garrett, Chris

    2010-04-01

    The resonances of tides in the coupled open ocean and shelf are modeled by a mechanical analogue consisting of a damped driven larger mass and spring (the open-ocean) connected to a damped smaller mass and spring (the shelf). When both masses are near resonance, the addition of even a very small mass can significantly affect the oscillations of the larger mass. The influence of the shelf is largest if the shelf is resonant with weak friction. In particular, an increase of friction on a near-resonant shelf can, perhaps surprisingly, lead to an increase in ocean tides. On the other hand, a shelf with large friction has little effect on ocean tides. Comparison of the model predictions with results from numerical models of tides during the ice ages, when lower sea levels led to a much reduced areal extent of shelves, suggests that the predicted larger tidal dissipation then is related to the ocean basins being close to resonance. New numerical simulations with a forward global tide model are used to test expectations from the mechanical analogue. Setting friction to unrealistically large values in Hudson Strait yields larger North Atlantic M2 amplitudes, very similar to those seen in a simulation with the Hudson Strait blocked off. Thus, as anticipated, a shelf with very large friction is nearly equivalent in its effect on the open ocean to the removal of the shelf altogether. Setting friction in shallow waters throughout the globe to unrealistically large values yields even larger open ocean tidal amplitudes, similar to those found in simulations of ice-age tides. It thus appears that larger modeled tides during the ice ages can be a consequence of enhanced friction in shallower water on the shelf in glacial times as well as a reduced shelf area then. Single oscillator and coupled oscillator models for global tides show that the maximum extractable power for human use is a fraction of the present dissipation rate, which is itself a fraction of global human power

  6. A hedonic analysis of the complex hunting experience

    DEFF Research Database (Denmark)

    Lundhede, Thomas; Jacobsen, Jette Bredahl; Thorsen, Bo Jellesmark

    2015-01-01

    In Denmark, the right to hunt is vested with the land owner but can be transferred to others and is traded on a well-established market. The dominant form of hunting leases is time limited contract transferring the hunting rights on a piece of land to one or more persons. We analyze this market...... of a lease is determined by the location and size of the hunting area, the game harvest and hunting activity itself, several landscape qualities affecting the recreational nature experience, several social aspects of hunting and the relation between the landowner, the hunters and their activities...

  7. Sustainable trophy hunting of African lions.

    Science.gov (United States)

    Whitman, Karyl; Starfield, Anthony M; Quadling, Henley S; Packer, Craig

    2004-03-11

    In most species, sport hunting of male trophy animals can only reduce overall population size when the rate of removal of males is so high that females can no longer be impregnated. However, where males provide extensive paternal care, the removal of even a few individuals could harm the population as a whole. In species such as lions, excessive trophy hunting could theoretically cause male replacements (and associated infanticide) to become sufficiently common to prevent cubs reaching adulthood. Here we simulate the population consequences of lion trophy hunting using a spatially explicit, individual-based, stochastic model parameterized with 40 years of demographic data from northern Tanzania. Although our simulations confirm that infanticide increases the risk of population extinction, trophy hunting could be sustained simply by hunting males above a minimum age threshold, and this strategy maximizes both the quantity and the quality of the long-term kill. We present a simple non-invasive technique for estimating lion age in populations lacking long-term records, and suggest that quotas would be unnecessary in any male-only trophy species where age determination could be reliably implemented.

  8. Downslope flow across the Ross Sea shelf break (Antarctica)

    Science.gov (United States)

    Bergamasco, A.; Budillon, G.; Carniel, S.; Defendi, V.; Meloni, R.; Paschini, E.; Sclavo, M.; Spezie, G.

    2003-12-01

    The analysis of some high-resolution hydrological data sets acquired during the 1997, 1998, 2001 and 2003 austral summers across the Ross Sea continental shelf break are here presented. The main focus of these cruises carried out in the framework of the Italian National Antarctic Program was the investigation of the downslope flow of the dense waters originated inside the Ross Sea. Such dense waters, flow near the bottom and, reaching the continental shelf break, ventilate the deep ocean. Two Antarctic continental shelf mechanisms can originate dense and deep waters. The former mechanism involves the formation, along the Victoria Land coasts, of a dense and saline water mass, the High Salinity Shelf Water (HSSW). The HSSW formation is linked to the rejection of salt into the water column as sea ice freezes, especially during winter, in the polynya areas, where the ice is continuously pushed offshore by the strong katabatic winds. The latter one is responsible of the formation of a supercold water mass, the Ice Shelf Water (ISW). The salt supplied by the HSSW recirculated below the Ross Ice Shelf, the latent heat of melting and the heat sink provided by the Ross Ice Shelf give rise to plumes of ISW, characterized by temperatures below the sea-surface freezing point. The dense shelf waters migrate to the continental shelf-break, spill over the shelf edge and descend the continental slope as a shelf-break gravity current, subject to friction and possibly enhanced by topographic channelling. Friction, in particular, breaks the constraint of potential vorticity conservation, counteracting the geostrophic tendency for along slope flow. The density-driven downslope motion or cascading entrains ambient water, namely the lower layer of the CDW, reaches a depth where density is the same and spreads off-slope. In fact, the cascading event is inhibited by friction without entrainment. The downslope processes are important for the ocean and climate system because they play a

  9. 'Impact hunters' catalyse cooperative hunting in two wild chimpanzee communities.

    Science.gov (United States)

    Gilby, Ian C; Machanda, Zarin P; Mjungu, Deus C; Rosen, Jeremiah; Muller, Martin N; Pusey, Anne E; Wrangham, Richard W

    2015-12-05

    Even when hunting in groups is mutually beneficial, it is unclear how communal hunts are initiated. If it is costly to be the only hunter, individuals should be reluctant to hunt unless others already are. We used 70 years of data from three communities to examine how male chimpanzees 'solve' this apparent collective action problem. The 'impact hunter' hypothesis proposes that group hunts are sometimes catalysed by certain individuals that hunt more readily than others. In two communities (Kasekela and Kanyawara), we identified a total of five males that exhibited high hunt participation rates for their age, and whose presence at an encounter with red colobus monkeys increased group hunting probability. Critically, these impact hunters were observed to hunt first more often than expected by chance. We argue that by hunting first, these males dilute prey defences and create opportunities for previously reluctant participants. This by-product mutualism can explain variation in group hunting rates within and between social groups. Hunting rates declined after the death of impact hunter FG in Kasekela and after impact hunter MS stopped hunting frequently in Kanyawara. There were no impact hunters in the third, smaller community (Mitumba), where, unlike the others, hunting probability increased with the number of females present at an encounter with prey.

  10. The hunting season’s over

    CERN Multimedia

    2014-01-01

    Hundreds of Internet users from across the globe have been scouring the Computer Centre for LEGO figurines in recent weeks (see here). The time has come to announce the results…   We’ve received nearly 5,000 screen-shots, the precious trophies gleaned from hours of virtual scavenging through the CERN Computing Centre, and we’re pleased to see our hunt raised so much interest. Unfortunately, rules being rules, we have to choose the two winners by drawing lots, so prizes will be winging their way to… Sarah Charley (CERN) Stefan Hayes We kindly thank everyone who took part in the hunt with so much gusto and hope you all had as much fun as we did! You can discover all the figurines here: http://lego-scavenger-hunt.web.cern.ch/ The CERN Bulletin team

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

    Science.gov (United States)

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

    2011-01-01

    Salt release during sea ice formation in the Ross Sea coastal regions is regarded as a primary forcing for the regional generation of Antarctic Bottom Water. Passive microwave data from November 1978 through 2008 are used to examine the detailed seasonal and interannual characteristics of the sea ice cover of the Ross Sea and the adjacent Bellingshausen and Amundsen seas. For this period the sea ice extent in the Ross Sea shows the greatest increase of all the Antarctic seas. Variability in the ice cover in these regions is linked to changes in the Southern Annular Mode and secondarily to the Antarctic Circumpolar Wave. Over the Ross Sea shelf, analysis of sea ice drift data from 1992 to 2008 yields a positive rate of increase in the net ice export of about 30,000 sq km/yr. For a characteristic ice thickness of 0.6 m, this yields a volume transport of about 20 cu km/yr, which is almost identical, within error bars, to our estimate of the trend in ice production. The increase in brine rejection in the Ross Shelf Polynya associated with the estimated increase with the ice production, however, is not consistent with the reported Ross Sea salinity decrease. The locally generated sea ice enhancement of Ross Sea salinity may be offset by an increase of relatively low salinity of the water advected into the region from the Amundsen Sea, a consequence of increased precipitation and regional glacial ice melt.

  12. Ice sheet topography from retracked ERS-1 altimetry

    Science.gov (United States)

    Zwally, H. Jay; Brenner, Anita C.; Dimarzio, John; Seiss, Timothy

    1994-01-01

    An objective of the ERS-1 radar altimeter is to measure the surface topography of the polar ice sheets to a precision on the order of a meter. ERS-1 Waveform Altimeter Product (WAP) data was corrected for several processing errors. A range correction from the WAP waveforms, using the multiparameter retracking algorithm to account for range tracking limitations inherent to radar altimetry, was derived. From crossover analysis, the resulting precision is shown to be about 2.1 m in ocean mode and 2.2 m in ice mode. A topography map, produced with 23 days of corrected data, shows details of the western part of west Antarctic ice sheet and part of the Ross ice shelf including ice divides, ice stream boundaries, and ice shelf grounding lines.

  13. Cheetah do not abandon hunts because they overheat.

    Science.gov (United States)

    Hetem, Robyn S; Mitchell, Duncan; de Witt, Brenda A; Fick, Linda G; Meyer, Leith C R; Maloney, Shane K; Fuller, Andrea

    2013-10-23

    Hunting cheetah reportedly store metabolic heat during the chase and abandon chases because they overheat. Using biologging to remotely measure the body temperature (every minute) and locomotor activity (every 5 min) of four free-living cheetah, hunting spontaneously, we found that cheetah abandoned hunts, but not because they overheated. Body temperature averaged 38.4°C when the chase was terminated. Storage of metabolic heat did not compromise hunts. The increase in body temperature following a successful hunt was double that of an unsuccessful hunt (1.3°C ± 0.2°C versus 0.5°C ± 0.1°C), even though the level of activity during the hunts was similar. We propose that the increase in body temperature following a successful hunt is a stress hyperthermia, rather than an exercise-induced hyperthermia.

  14. Sport hunting decision document package : North Platte National Wildlife Refuge

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — The U.S. Fish and Wildlife Service proposes limited hunting opportunities at North Platte NWR. Hunting activities will be permitted, but administratively limited to...

  15. Wildlife reserves, populations, and hunting outcome with smart wildlife

    DEFF Research Database (Denmark)

    Jensen, Frank; Jacobsen, Jette Bredahl; Strange, Niels

    2014-01-01

    We consider a hunting area and a wildlife reserve and answer the question: How does clever migration decision affect the social optimal and the private optimal hunting levels and population stocks? We analyze this in a model allowing for two-way migration between hunting and reserve areas, where...... the populations’ migration decisions depend on both hunting pressure and relative population densities. In the social optimum a pure stress effect on the behavior of smart wildlife exists. This implies that the population level in the wildlife reserve tends to increase and the population level in the hunting area...... and hunting levels tend to decrease. On the other hand, the effect on stock tends to reduce the population in the wildlife reserve and increase the population in the hunting area and thereby also increase hunting. In the case of the private optimum, open-access is assumed and we find that the same qualitative...

  16. Hunting Plan Prime Hook National Wildlife Refuge 1987

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This plan sets forth a proposal for public hunting on the refuge as a form of wildlife-oriented recreation. Hunting of deer, waterfowl, other migratory game birds...

  17. 78 FR 48460 - Wildlife and Hunting Heritage Conservation Council

    Science.gov (United States)

    2013-08-08

    ... Fish and Wildlife Service Wildlife and Hunting Heritage Conservation Council AGENCY: Fish and Wildlife... public meeting of the Wildlife and Hunting Heritage Conservation Council (Council). DATES: Meeting... wildlife and habitat conservation endeavors that: 1. Benefit wildlife resources; 2. Encourage...

  18. 76 FR 17442 - Wildlife and Hunting Heritage Conservation Council Teleconference

    Science.gov (United States)

    2011-03-29

    ... Fish and Wildlife Service Wildlife and Hunting Heritage Conservation Council Teleconference AGENCY... February 2010, the Council provides advice about wildlife and habitat conservation endeavors that: (a... public, the sporting conservation community, the shooting and hunting sports industry,...

  19. 78 FR 25463 - Wildlife and Hunting Heritage Conservation Council

    Science.gov (United States)

    2013-05-01

    ... Fish and Wildlife Service Wildlife and Hunting Heritage Conservation Council AGENCY: Fish and Wildlife... public meeting of the Wildlife and Hunting Heritage Conservation Council (Council). DATES: Meeting... advice about wildlife and habitat conservation endeavors that: 1. Benefit wildlife resources;...

  20. 77 FR 16051 - Wildlife and Hunting Heritage Conservation Council

    Science.gov (United States)

    2012-03-19

    ... Office of the Secretary Wildlife and Hunting Heritage Conservation Council AGENCY: Office of the... Hunting Heritage Conservation Council (Council). The Council provides advice about wildlife and habitat conservation endeavors that (a) benefit wildlife resources; (b) encourage partnership among the...

  1. 77 FR 57577 - Wildlife and Hunting Heritage Conservation Council

    Science.gov (United States)

    2012-09-18

    ... Fish and Wildlife Service Wildlife and Hunting Heritage Conservation Council AGENCY: Fish and Wildlife... public meeting of the Wildlife and Hunting Heritage Conservation Council (Council). DATES: Meeting... wildlife and habitat conservation endeavors that: 1. Benefit wildlife resources; 2. Encourage...

  2. 78 FR 73205 - Wildlife and Hunting Heritage Conservation Council

    Science.gov (United States)

    2013-12-05

    ... Fish and Wildlife Service Wildlife and Hunting Heritage Conservation Council AGENCY: Fish and Wildlife... public meeting of the Wildlife and Hunting Heritage Conservation Council (Council). DATES: Meeting... advice about wildlife and habitat conservation endeavors that: 1. Benefit wildlife resources;...

  3. 77 FR 31636 - Wildlife and Hunting Heritage Conservation Council

    Science.gov (United States)

    2012-05-29

    ... Fish and Wildlife Service Wildlife and Hunting Heritage Conservation Council AGENCY: Fish and Wildlife... public meeting of the Wildlife and Hunting Heritage Conservation Council (Council). DATES: Meeting... Council provides advice about wildlife and habitat conservation endeavors that: 1. Benefit...

  4. 76 FR 12130 - Wildlife and Hunting Heritage Conservation Council Teleconference

    Science.gov (United States)

    2011-03-04

    ... Fish and Wildlife Service Wildlife and Hunting Heritage Conservation Council Teleconference AGENCY... February 2010, the Council provides advice about wildlife and habitat conservation endeavors that: (a... public, the sporting conservation community, the shooting and hunting sports industry,...

  5. [Bear River Migratory Bird Refuge Hunt Plan & Related Documents : 1995

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — The 'Bear River Migratory Bird Refuge Hunt Plan', beginning on page 66 and continuing through the end of the document, is focused on public hunting and the...

  6. Walnut Creek National Wildlife Refuge : Interim hunting plan

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This interim hunting plan for Neal Smith National Wildlife Refuge (formerly Walnut Creek National Wildlife Refuge) outlines hunting guidelines for the Refuge....

  7. Pocosin Lakes National Wildlife Refuge : Annual Hunt Evaluation for 2011.

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This report summarizes the activities and results of the annual deer hunt on Pocosin Lakes National Wildlife Refuge for fall 2011. Topics covered include hunt...

  8. Environmental Assessment : Bear River Migratory Bird Refuge Hunt Plan

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This Environmental Assessment (EA) is designed to evaluate possible actions for modifying the Bear River Migratory Bird Refuge (Refuge) public hunt plan. The hunt...

  9. trophy hunting and trophy size in ugalla game reserve, western ...

    African Journals Online (AJOL)

    Mgina

    the Ugalla Game Reserve (UGR) of western Tanzania, in relation to hunting success (animals shot species-1 quota-1) ... take, which through effective management is considered to be ... are several requirements for a successful trophy hunting ...

  10. Compatibility Determination : Hunting of migratory birds and resident game

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This is the Compatibility Determination for the Minnesota Valley NWR and WMD proposed Hunting Plan. Refuge purposes are outlined and proposed hunting activities are...

  11. Pocosin Lakes National Wildlife Refuge : Annual Hunt Evaluation for 2005.

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This report summarizes the activities and results of the annual deer hunt on Pocosin Lakes National Wildlife Refuge for fall 2005. Topics covered include hunt...

  12. Canada goose kill statistics: Swan Lake Public Hunting Area

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This document discusses how the flexible kill formula for Canada goose hunting at Swan Lake Public Hunting Area was reached. Methods used to collect Canada goose...

  13. Pocosin Lakes National Wildlife Refuge : Annual Hunt Evaluation for 2007.

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This report summarizes the activities and results of the annual deer hunt on Pocosin Lakes National Wildlife Refuge for fall 2007. Topics covered include hunt...

  14. Pocosin Lakes National Wildlife Refuge : Annual Hunt Evaluation for 2004.

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This report summarizes the activities and results of the annual deer hunt on Pocosin Lakes National Wildlife Refuge for fall 2004. Topics covered include hunt...

  15. Pocosin Lakes National Wildlife Refuge : Annual Hunt Evaluation for 2010.

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This report summarizes the activities and results of the annual deer hunt on Pocosin Lakes National Wildlife Refuge for fall 2010. Topics covered include hunt...

  16. Modify hunting program on Arapaho NWR [Environmental Assesment

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — The purpose for this Environmental Assessment (EA) is to evaluate the hunting program onArapaho National Wildlife Refuge (NWR). This EA, and hunting plan that will...

  17. Outreach Plan : Sherburne National Wildlife Refuge for Expanded Hunting Opportunities

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This Outreach Plan for Sherburne NWR states that hunting opportunities will be expanded on the Refuge to include wild turkey hunting by disabled and youth hunters.

  18. Pocosin Lakes National Wildlife Refuge : Annual Hunt Evaluation for 2002.

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This report summarizes the activities and results of the annual deer hunt on Pocosin Lakes National Wildlife Refuge for fall 2002. Topics covered include hunt...

  19. Pocosin Lakes National Wildlife Refuge : Annual Hunt Evaluation for 2008.

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This report summarizes the activities and results of the annual deer hunt on Pocosin Lakes National Wildlife Refuge for fall 2008. Topics covered include hunt...

  20. Pocosin Lakes National Wildlife Refuge : Annual Hunt Evaluation for 2009.

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This report summarizes the activities and results of the annual deer hunt on Pocosin Lakes National Wildlife Refuge for fall 2009. Topics covered include hunt...

  1. Pocosin Lakes National Wildlife Refuge : Annual Hunt Evaluation for 2003.

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This report summarizes the activities and results of the annual deer hunt on Pocosin Lakes National Wildlife Refuge for fall 2003. Topics covered include hunt...

  2. Pocosin Lakes National Wildlife Refuge : Annual Hunt Evaluation for 2006.

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This report summarizes the activities and results of the annual deer hunt on Pocosin Lakes National Wildlife Refuge for fall 2006. Topics covered include hunt...

  3. Hunting plan for San Francisco Bay National Wildlife Refuge

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This migratory waterfowl hunting plan for Don Edwards San Francisco Bay National Wildlife Refuge allows waterfowl hunting on certain areas of the Refuge. Aerial...

  4. Walk-In Hunting Access (WIHA) Fall 2009

    Data.gov (United States)

    Kansas Data Access and Support Center — This shapefile represents the private lands leased by the Kansas Department of Wildlife and Parks for fall 2009 public hunting access through the Walk-In Hunting...

  5. Walk-In Hunting Access (WIHA) Fall 2008

    Data.gov (United States)

    Kansas Data Access and Support Center — This shapefile represents the private lands leased by the Kansas Department of Wildlife and Parks for fall 2008 public hunting access through the Walk-In Hunting...

  6. Walk-In Hunting Access (WIHA) Fall 2010

    Data.gov (United States)

    Kansas Data Access and Support Center — This shapefile represents the private lands leased by the Kansas Department of Wildlife and Parks for fall 2010 public hunting access through the Walk-In Hunting...

  7. The Hunt Is Not On China's ban on trophy hunting remains despite calls for a relaxation

    Institute of Scientific and Technical Information of China (English)

    YUAN YUAN

    2011-01-01

    Dulan,a small town in northwest China's Qinghai Province,would have been an unfamiliar name to most Chinese,if not for the recent high-profile debate regarding the possible relaxation of a six-year ban on hunting in the vicinity of the town.Foreign hunters have been familiar with Dulan since 1992 when they were tirst granted permits to hunt in the area.The State Forestry Administration (SFA) banned hunting in the region in 2006 amidst concerns that hunters were killing too many animals and damaging the local ecosystem.

  8. Big game hunting practices, meanings, motivations and constraints: a survey of Oregon big game hunters

    Science.gov (United States)

    Suresh K. Shrestha; Robert C. Burns

    2012-01-01

    We conducted a self-administered mail survey in September 2009 with randomly selected Oregon hunters who had purchased big game hunting licenses/tags for the 2008 hunting season. Survey questions explored hunting practices, the meanings of and motivations for big game hunting, the constraints to big game hunting participation, and the effects of age, years of hunting...

  9. Cat Dilemma: Too Protected To Escape Trophy Hunting?

    OpenAIRE

    2011-01-01

    Trophy hunting is one of the most controversial issues in the field of biodiversity conservation. In particular, proponents and opponents debate fiercely over whether it poses a threat to hunted populations. Here, we show that trophy hunting constitutes a greater menace to threatened species than previously realized. Because humans value rarity, targeted species that are threatened are likely to be disproportionately hunted, thereby becoming even more vulnerable, which could eventually push t...

  10. 77 FR 4575 - Wildlife and Hunting Heritage Conservation Council

    Science.gov (United States)

    2012-01-30

    ... Fish and Wildlife Service Wildlife and Hunting Heritage Conservation Council AGENCY: Fish and Wildlife... public meeting of the Wildlife and Hunting Heritage Conservation Council (Council). DATES: Meeting... Wildlife and Hunting Heritage Conservation Council will hold a meeting. Background Formed in February...

  11. 76 FR 30192 - Wildlife and Hunting Heritage Conservation Council

    Science.gov (United States)

    2011-05-24

    ... Fish and Wildlife Service Wildlife and Hunting Heritage Conservation Council AGENCY: Fish and Wildlife... public meeting of the Wildlife and Hunting Heritage Conservation Council (Council). DATES: Meeting... Advisory Committee Act, 5 U.S.C. App., we announce that Wildlife and Hunting Heritage Conservation...

  12. 76 FR 66955 - Wildlife and Hunting Heritage Conservation Council

    Science.gov (United States)

    2011-10-28

    ... Fish and Wildlife Service Wildlife and Hunting Heritage Conservation Council AGENCY: Fish and Wildlife... public meeting of the Wildlife and Hunting Heritage Conservation Council (Council). DATES: Meeting... Wildlife and Hunting Heritage Conservation Council will hold a meeting. Background Formed in February...

  13. The impact of hunting on tropical mammal and bird populations

    NARCIS (Netherlands)

    Benítez-López, A.; Alkemade, R.; Schipper, A.M.; Ingram, D.J.; Verweij, P.A.; Eikelboom, J.A.J.; Huijbregts, M.A.J.

    2017-01-01

    Hunting is a major driver of biodiversity loss, but a systematic large-scale estimate of hunting-induced defaunation is lacking. We synthesized 176 studies to quantify hunting-induced declines of mammal and bird populations across the tropics. Bird and mammal abundances declined by 58% (25 to

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

    Science.gov (United States)

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

    2014-06-01

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

  15. Bathymetry of the Amundsen Sea Embayment sector of West Antarctica from Operation IceBridge gravity and other data

    Science.gov (United States)

    Millan, Romain; Rignot, Eric; Bernier, Vincent; Morlighem, Mathieu; Dutrieux, Pierre

    2017-02-01

    We employ airborne gravity data from NASA's Operation IceBridge collected in 2009-2014 to infer the bathymetry of sub-ice shelf cavities in front of Pine Island, Thwaites, Smith, and Kohler glaciers, West Antarctica. We use a three-dimensional inversion constrained by multibeam echo sounding data offshore and bed topography from a mass conservation reconstruction on land. The seamless bed elevation data refine details of the Pine Island sub-ice shelf cavity, a slightly thinner cavity beneath Thwaites, and previously unknown deep (>1200 m) channels beneath the Crosson and Dotson ice shelves that shallow (500 m and 750 m, respectively) near the ice shelf fronts. These sub-ice shelf channels define the natural pathways for warm, circumpolar deep water to reach the glacier grounding lines, melt the ice shelves from below, and constrain the pattern of past and future glacial retreat.

  16. 76 FR 44729 - Migratory Bird Hunting; Proposed Frameworks for Early-Season Migratory Bird Hunting Regulations...

    Science.gov (United States)

    2011-07-26

    ... normally migrated through the State, reducing the likelihood that sandhill crane hunters would encounter..., conditional on successful monitoring being conducted as called for in the Flyway hunt plan for this...

  17. Parker River National Wildlife Refuge deer hunt : Gatehouse guidelines during hunt

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This document outlines the gatehouse guidelines for Parker River National Wildlife Refuge during the 1993 deer hunt. Key responsibilities include: checking in each...

  18. Hunting Elusive SPRITEs with Spitzer

    Science.gov (United States)

    Kohler, Susanna

    2017-05-01

    In recent years, astronomers have developed many wide-field imaging surveys in which the same targets are observed again and again. This new form of observing has allowed us to discover optical and radio transients explosive or irregular events with durations ranging from seconds to years. The dynamic infrared sky, however, has remained largely unexplored until now.Infrared ExplorationExample of a transient: SPIRITS 14ajc was visible when imaged by SPIRITS in 2014 (left) but it wasnt there during previous imaging between 2004 and 2008 (right). The bottom frame shows the difference between the two images. [Adapted from Kasliwal et al. 2017]Why hunt for infrared transients? Optical wavelengths dont allow us to observe events that are obscured, such that their own structure or their surroundings hide them from our view. Both supernovae and luminous red novae (associated with stellar mergers) are discoverable as infrared transients, and there may well be new types of transients in infrared that we havent seen before!To explore this uncharted territory, a team of scientists developed SPIRITS, the Spitzer Infrared Intensive Transients Survey. Begun in 2014, SPIRITS is a five-year long survey that uses the Spitzer Space Telescope to conduct a systematic search for mid-infrared transients in nearby galaxies.In a recent publication led by Mansi Kasliwal (Caltech and the Carnegie Institution for Science), the SPIRITS team has now detailed how their survey works and what theyve discovered in its first year.The light curves of SPRITEs (red stars) lie in the mid-infared luminosity gap between novae (orange) and supernovae (blue). [Kasliwal et al. 2017]Mystery TransientsKasliwal and collaborators used Spitzer to monitor 190 nearby galaxies. In SPIRITS first year, they found over 1958 variable stars and 43 infrared transient sources. Of these 43 transients, 21 were known supernovae, 4 were in the luminosity range of novae, and 4 had optical counterparts. The remaining 14 events

  19. 6 mln Graduates,Tough Job Hunting?

    Institute of Scientific and Technical Information of China (English)

    Maggie Zang

    2009-01-01

    @@ It is never easy for graduates to hunt their first jobs, and it becomes even harder for them due to the ongoing financial crisis, which spread over the whole world and made enterprises and various institutes cut their employment numbers. According to the incomplete statistics, over 6 million Chinese students graduate from school, are seeking a suitable position for living in 2009.

  20. American Indians, Witchcraft, and Witch-hunting.

    Science.gov (United States)

    Dennis, Matthew

    2003-01-01

    Explores North American Indian beliefs about witchcraft and witch-hunting. Focuses on the ideas and actions of the Iroquois about witchcraft. Addresses the changes in ideas of North American Indians living in the nineteenth century. Notes the transition from men and women perceived as witches to mostly females. (CMK)

  1. Concerning Hunt's New Ways of Assessing Intelligence.

    Science.gov (United States)

    Belmont, John M.

    1983-01-01

    In an earlier article, Hunt envisions the automation of intelligence testing, but he appears to be overly optimistic. He neglects to mention conceptual and practical difficulties at the interface of measurement and theory that place psychometry not in the dawn of microcomputerization, but rather more nearly in its primordium. (Author)

  2. The Simulation of Prehistoric Hunting Practices.

    Science.gov (United States)

    Rick, John W.

    1986-01-01

    Discusses use of computer simulation as an archeological tool for research and teaching involving the remains of prehistoric game animals to aid in understanding effects of various strategies of prehistoric hunters on populations of game animals. A simulation involving possible vicuna hunting strategies is described. (MBR)

  3. Nature or Nurture? Gender Roles Scavenger Hunt

    Science.gov (United States)

    Whalen, Shannon; Maurer-Starks, Suanne

    2008-01-01

    The examination of gender roles and stereotypes and their subsequent impact on sexual behavior is a concept for discussion in many sex education courses in college and sex education units in high school. This analysis often leads to a discussion of the impact of nature vs. nurture on gender roles. The gender roles scavenger hunt is an interactive…

  4. Nature or Nurture? Gender Roles Scavenger Hunt

    Science.gov (United States)

    Whalen, Shannon; Maurer-Starks, Suanne

    2008-01-01

    The examination of gender roles and stereotypes and their subsequent impact on sexual behavior is a concept for discussion in many sex education courses in college and sex education units in high school. This analysis often leads to a discussion of the impact of nature vs. nurture on gender roles. The gender roles scavenger hunt is an interactive…

  5. Hunting the Shadow, Catching the Light

    DEFF Research Database (Denmark)

    Toft, Anne Elisabeth; Nielsen, Torben

    2009-01-01

    From 28 October to 6 November 2009 twenty-one 3rd year students in interior design from Central Academy of Fine Arts (CAFA), School of Architecture, Beijing participated in the workshop Hunting the Shadow - Catching the Light. The workshop was conceived and led by the Danish architects Torben Nie...

  6. Undesirable evolutionary consequences of trophy hunting.

    Science.gov (United States)

    Coltman, David W; O'Donoghue, Paul; Jorgenson, Jon T; Hogg, John T; Strobeck, Curtis; Festa-Bianchet, Marco

    2003-12-11

    Phenotype-based selective harvests, including trophy hunting, can have important implications for sustainable wildlife management if they target heritable traits. Here we show that in an evolutionary response to sport hunting of bighorn trophy rams (Ovis canadensis) body weight and horn size have declined significantly over time. We used quantitative genetic analyses, based on a partly genetically reconstructed pedigree from a 30-year study of a wild population in which trophy hunting targeted rams with rapidly growing horns, to explore the evolutionary response to hunter selection on ram weight and horn size. Both traits were highly heritable, and trophy-harvested rams were of significantly higher genetic 'breeding value' for weight and horn size than rams that were not harvested. Rams of high breeding value were also shot at an early age, and thus did not achieve high reproductive success. Declines in mean breeding values for weight and horn size therefore occurred in response to unrestricted trophy hunting, resulting in the production of smaller-horned, lighter rams, and fewer trophies.

  7. The Last Arctic Sea Ice Refuge

    Science.gov (United States)

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

    2010-12-01

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

  8. Ice Velocity Estimation Using SAR Data in PANDA Section, East Antarctica

    Science.gov (United States)

    Deng, F.; Zhou, C.; Zhou, Y.

    2015-12-01

    Ice-flow velocity is a significant parameter in dynamic models of the Antarctic ice sheet, indicating how ice is transported from the interior to the ocean and how ice mass evolves. PANDA (Prydz Bay - Amery Ice shelf - Dome A) section is the key area of Chinese expedition in the Antarctic, and many scientific studies have been conducted here. In this research, SAR images including ERS-1/2, Envisat and ALOS were applied to estimate the ice velocity of PANDA Section using DInSAR and offset-tracking methods. Compared to MEaSUREs velocity (ice velocity map of the Antarctic released by National Snow and Ice Data Center) of 450 m resolution, our result with 200 m resolution achieved similar accuracy. Ice mass of PANDA section flows into the ocean mainly through Amery Ice Shelf and Polar Record Glacier. The ice velocity at the front edge of Amery Ice shelf is almost 1500 m/a, and the ice velocity of Polar Record Glacier can reach as high as 800 m/a. At most inner area of PANDA section, ice velocity is below 40 m/a. Due to the blocking of rocks and nunataks, ice flow feature in Grove Mountains area is quite complicated, which can help to demonstrate the meteorite concentration mechanism in this area.

  9. Southeast continental shelf studies

    Energy Technology Data Exchange (ETDEWEB)

    Menzel, D.W.

    1979-02-12

    Research efforts on the southeast continental shelf currently describe the manner in which fluctuations in Gulf Stream motion influence biological and chemical processes. Current meter arrays are maintained in the Georgia Bight and in Onslow Bay to describe general circulation patterns and to identify forcing functions. biological studies describe processes affecting temporal and spatial variations on the shelf and have attempted to track the biological history of intruded Gulf Stream water masses. Chemical studies examine the influence of both physical and biological variables on the distribution and fate of trace elements. The current state of knowledge is reviewed, the hypotheses developed and are described, a rationale for testing these hypotheses is given. 1 figure, 1 table.

  10. Channelization of plumes beneath ice shelves

    KAUST Repository

    Dallaston, M. C.

    2015-11-11

    © 2015 Cambridge University Press. We study a simplified model of ice-ocean interaction beneath a floating ice shelf, and investigate the possibility for channels to form in the ice shelf base due to spatial variations in conditions at the grounding line. The model combines an extensional thin-film description of viscous ice flow in the shelf, with melting at its base driven by a turbulent ocean plume. Small transverse perturbations to the one-dimensional steady state are considered, driven either by ice thickness or subglacial discharge variations across the grounding line. Either forcing leads to the growth of channels downstream, with melting driven by locally enhanced ocean velocities, and thus heat transfer. Narrow channels are smoothed out due to turbulent mixing in the ocean plume, leading to a preferred wavelength for channel growth. In the absence of perturbations at the grounding line, linear stability analysis suggests that the one-dimensional state is stable to initial perturbations, chiefly due to the background ice advection.

  11. Evolution of surface velocities and ice discharge of Larsen B outlet glaciers from 1995 to 2013

    Directory of Open Access Journals (Sweden)

    J. Wuite

    2014-12-01

    Full Text Available We use repeat-pass SAR data to produce detailed maps of surface motion covering the glaciers draining into the former Larsen B ice shelf, Antarctic Peninsula, for different epochs between 1995 and 2013. We combine the velocity maps with estimates of ice thickness to analyze fluctuations of ice discharge. The collapse of the central and northern sections of the ice shelf in 2002 led to a near-immediate acceleration of tributary glaciers as well as of the remnant ice shelf in Scar Inlet. Velocities of the glaciers discharging directly into the ocean remain to date well above the velocities of the pre-collapse period. The response of individual glaciers differs and velocities show significant temporal fluctuations, implying major variations in ice discharge and mass balance as well. Due to reduced velocity and ice thickness the ice discharge of Crane Glacier decreased from 5.02 Gt a−1 in 2007 to 1.72 Gt a−1 in 2013, whereas Hektoria and Green glaciers continue to show large temporal fluctuations in response to successive stages of frontal retreat. The velocity on Scar Inlet ice shelf increased two- to three fold since 1995, with the largest increase in the first years after the break-up of the main section of Larsen B. Flask and Leppard glaciers, the largest tributaries to Scar Inlet ice shelf, accelerated. In 2013 their discharge was 38%, respectively 45%, higher than in 1995.

  12. Evolution of surface velocities and ice discharge of Larsen B outlet glaciers from 1995 to 2013

    Science.gov (United States)

    Wuite, J.; Rott, H.; Hetzenecker, M.; Floricioiu, D.; De Rydt, J.; Gudmundsson, G. H.; Nagler, T.; Kern, M.

    2015-05-01

    We use repeat-pass SAR data to produce detailed maps of surface motion covering the glaciers draining into the former Larsen B Ice Shelf, Antarctic Peninsula, for different epochs between 1995 and 2013. We combine the velocity maps with estimates of ice thickness to analyze fluctuations of ice discharge. The collapse of the central and northern sections of the ice shelf in 2002 led to a near-immediate acceleration of tributary glaciers as well as of the remnant ice shelf in Scar Inlet. Velocities of most of the glaciers discharging directly into the ocean remain to date well above the velocities of the pre-collapse period. The response of individual glaciers differs and velocities show significant temporal fluctuations, implying major variations in ice discharge as well. Due to reduced velocity and ice thickness the ice discharge of Crane Glacier decreased from 5.02 Gt a-1 in 2007 to 1.72 Gt a-1 in 2013, whereas Hektoria and Green glaciers continue to show large temporal fluctuations in response to successive stages of frontal retreat. The velocity on Scar Inlet ice shelf increased 2-3-fold since 1995, with the largest increase in the first years after the break-up of the main section of Larsen B. Flask and Leppard glaciers, the largest tributaries to Scar Inlet ice shelf, accelerated. In 2013 their discharge was 38% and 46% higher than in 1995.

  13. Ice gouge processes in the Alaskan Beaufort Sea

    Science.gov (United States)

    Rearic, Douglas M.; Ticken, Edward J.

    1988-01-01

    A generalized picture of ice gouge characteristics from shallow inshore depths to the outer shelf at about 60 m of water is presented. Data from recent studies show that the size and quantity of gouging increases in an offshore direction to depths of about 45 m where this trend then reverses and the features decrease in size and quantity as the shelf break is approached. Ice gouges are oriented east-west and this suggests that most gouging is caused by ice approaching from the east, possibly driven by the Beaufort Sea gyre. The most intense gouging occurs in the stamukhi zone, between 20 and 40 m of water, and is caused by a high rate of ice keel production owing to shearing forces between mobile and stable sea ice. Inshore of the stamukhi zone, ice gouging still presents a significant hazard but their greatly decreased size and number make it possible to design against this hazard.

  14. Wolves on the hunt: The behavior of wolves hunting wild prey

    Science.gov (United States)

    Mech, L. David; Smith, Douglas W.; MacNulty, Daniel R.

    2015-01-01

    The interactions between apex predators and their prey are some of the most awesome and meaningful in nature—displays of strength, endurance, and a deep coevolutionary history. And there is perhaps no apex predator more impressive and important in its hunting—or more infamous, more misjudged—than the wolf. Because of wolves’ habitat, speed, and general success at evading humans, researchers have faced great obstacles in studying their natural hunting behaviors. The first book to focus explicitly on wolf hunting of wild prey, Wolves on the Hunt seeks to fill these gaps in our knowledge and understanding. Combining behavioral data, thousands of hours of original field observations, research in the literature, a wealth of illustrations, and—in the e-book edition and online—video segments from cinematographer Robert K. Landis, the authors create a compelling and complex picture of these hunters. The wolf is indeed an adept killer, able to take down prey much larger than itself. While adapted to hunt primarily hoofed animals, a wolf—or especially a pack of wolves—can kill individuals of just about any species. But even as wolves help drive the underlying rhythms of the ecosystems they inhabit, their evolutionary prowess comes at a cost: wolves spend one-third of their time hunting—the most time consuming of all wolf activities—and success at the hunt only comes through traveling long distances, persisting in the face of regular failure, detecting and taking advantage of deficiencies in the physical condition of individual prey, and through ceaseless trial and error, all while risking injury or death. By describing and analyzing the behaviors wolves use to hunt and kill various wild prey—including deer, moose, caribou, elk, Dall sheep, mountain goats, bison, musk oxen, arctic hares, beavers, and others—Wolves on the Hunt provides a revelatory portrait of one of nature’s greatest hunters.

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

    Science.gov (United States)

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

    2009-07-16

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

  16. Identity-driven differences in stakeholder concerns about hunting wolves.

    Science.gov (United States)

    Lute, Michelle L; Bump, Adam; Gore, Meredith L

    2014-01-01

    Whereas past wolf management in the United States was restricted to recovery, managers must now contend with publicly contentious post-recovery issues including regulated hunting seasons. Understanding stakeholder concerns associated with hunting can inform stakeholder engagement, communication, and policy development and evaluation. Social identity theory (SIT) has been used to understand how groups interact, why they conflict, and how collaboration may be achieved. Applying SIT to stakeholder conflicts about wolf hunting may help delineate groups according to their concern about, support for or opposition to the policy choice of hunting wolves. Our objective was to assess concerns about hunting as a tool to resolve conflict in Michigan, using SIT as a framework. We used a mixed-modal sampling approach (e.g., paper, Internet) with wolf hunting-related public meeting participants in March 2013. Survey questions focused on 12 concerns previously identified as associated with hunting as a management tool to resolve conflict. Respondents (n  =  666) cared greatly about wolves but were divided over hunting wolves. Wolf conflicts, use of science in policy decisions, and maintaining a wolf population were the highest ranked concerns. Principle components analysis reduced concerns into three factors that explained 50.7% of total variance; concerns crystallized over justifications for hunting. General linear models revealed a lack of geographic influence on care, fear and support for hunting related to wolves. These findings challenge assumptions about regional differences and suggest a strong role for social identity in driving dichotomized public perceptions in wildlife management.

  17. Ice Cores

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Records of past temperature, precipitation, atmospheric trace gases, and other aspects of climate and environment derived from ice cores drilled on glaciers and ice...

  18. Proto-cooperation: group hunting sailfish improve hunting success by alternating attacks on grouping prey.

    Science.gov (United States)

    Herbert-Read, James E; Romanczuk, Pawel; Krause, Stefan; Strömbom, Daniel; Couillaud, Pierre; Domenici, Paolo; Kurvers, Ralf H J M; Marras, Stefano; Steffensen, John F; Wilson, Alexander D M; Krause, Jens

    2016-11-16

    We present evidence of a novel form of group hunting. Individual sailfish (Istiophorus platypterus) alternate attacks with other group members on their schooling prey (Sardinella aurita). While only 24% of attacks result in prey capture, multiple prey are injured in 95% of attacks, resulting in an increase of injured fish in the school with the number of attacks. How quickly prey are captured is positively correlated with the level of injury of the school, suggesting that hunters can benefit from other conspecifics' attacks on the prey. To explore this, we built a mathematical model capturing the dynamics of the hunt. We show that group hunting provides major efficiency gains (prey caught per unit time) for individuals in groups of up to 70 members. We also demonstrate that a free riding strategy, where some individuals wait until the prey are sufficiently injured before attacking, is only beneficial if the cost of attacking is high, and only then when waiting times are short. Our findings provide evidence that cooperative benefits can be realized through the facilitative effects of individuals' hunting actions without spatial coordination of attacks. Such 'proto-cooperation' may be the pre-cursor to more complex group-hunting strategies.

  19. Polar bears and sea ice habitat change

    Science.gov (United States)

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

    2017-01-01

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

  20. Ice cores

    DEFF Research Database (Denmark)

    Svensson, Anders

    2014-01-01

    Ice cores from Antarctica, from Greenland, and from a number of smaller glaciers around the world yield a wealth of information on past climates and environments. Ice cores offer unique records on past temperatures, atmospheric composition (including greenhouse gases), volcanism, solar activity......, dustiness, and biomass burning, among others. In Antarctica, ice cores extend back more than 800,000 years before present (Jouzel et al. 2007), whereas. Greenland ice cores cover the last 130,000 years...

  1. Ice cores

    DEFF Research Database (Denmark)

    Svensson, Anders

    2014-01-01

    Ice cores from Antarctica, from Greenland, and from a number of smaller glaciers around the world yield a wealth of information on past climates and environments. Ice cores offer unique records on past temperatures, atmospheric composition (including greenhouse gases), volcanism, solar activity......, dustiness, and biomass burning, among others. In Antarctica, ice cores extend back more than 800,000 years before present (Jouzel et al. 2007), whereas. Greenland ice cores cover the last 130,000 years...

  2. Ice Cream

    NARCIS (Netherlands)

    Scholten, E.

    2014-01-01

    Ice cream is a popular dessert, which owes its sensorial properties (mouth feel) to its complex microstructure. The microstructure is a result of the combination of the ingredients and the production process. Ice cream is produced by simultaneous freezing and shearing of the ice cream mix, which

  3. Ice Cream

    NARCIS (Netherlands)

    Scholten, E.

    2014-01-01

    Ice cream is a popular dessert, which owes its sensorial properties (mouth feel) to its complex microstructure. The microstructure is a result of the combination of the ingredients and the production process. Ice cream is produced by simultaneous freezing and shearing of the ice cream mix, which res

  4. Adaptation of an unstructured-mesh, finite-element ocean model to the simulation of ocean circulation beneath ice shelves

    Science.gov (United States)

    Kimura, Satoshi; Candy, Adam S.; Holland, Paul R.; Piggott, Matthew D.; Jenkins, Adrian

    2013-07-01

    Several different classes of ocean model are capable of representing floating glacial ice shelves. We describe the incorporation of ice shelves into Fluidity-ICOM, a nonhydrostatic finite-element ocean model with the capacity to utilize meshes that are unstructured and adaptive in three dimensions. This geometric flexibility offers several advantages over previous approaches. The model represents melting and freezing on all ice-shelf surfaces including vertical faces, treats the ice shelf topography as continuous rather than stepped, and does not require any smoothing of the ice topography or any of the additional parameterisations of the ocean mixed layer used in isopycnal or z-coordinate models. The model can also represent a water column that decreases to zero thickness at the 'grounding line', where the floating ice shelf is joined to its tributary ice streams. The model is applied to idealised ice-shelf geometries in order to demonstrate these capabilities. In these simple experiments, arbitrarily coarsening the mesh outside the ice-shelf cavity has little effect on the ice-shelf melt rate, while the mesh resolution within the cavity is found to be highly influential. Smoothing the vertical ice front results in faster flow along the smoothed ice front, allowing greater exchange with the ocean than in simulations with a realistic ice front. A vanishing water-column thickness at the grounding line has little effect in the simulations studied. We also investigate the response of ice shelf basal melting to variations in deep water temperature in the presence of salt stratification.

  5. Ocean-ice interactions with possible implications for Arctic ice shelves

    Science.gov (United States)

    Alley, R. B.

    2015-12-01

    Confined ice shelves restrain flow of non-floating ice, allowing ice sheets to grow larger than they otherwise would. Ice shelves lead a precarious existence, subject to fragmentation if sufficient meltwater fills crevasses, and very sensitive to even slight warming of water beneath. Ice shelves tend to exist in the coldest waters in the world ocean, often overlying warmer, more-saline waters. Changes in water temperature or circulation generally shrink existing ice shelves and raise sea level by unbuttressing the non-floating ice, and this is likely the most important control on marine-ending parts of land ice, exceeding the influence of sea-level or accumulation-rate changes. Advance of an ice-shelf grounding line into warmer, deeper water will increase melting rates, reduce buttressing, and tend to stabilize the grounding line near or above the upper limit of that warmer water. This physical understanding indicates that the oceanographic state, and its interaction with tributary ice streams, must have been central in the extent of Arctic ice shelves once sufficient cooling occurred to allow extensive advance of land ice into the ocean.

  6. A 9,000 Year History of Seal Hunting on Lake Baikal, Siberia: The Zooarchaeology of Sagan-Zaba II.

    Directory of Open Access Journals (Sweden)

    Tatiana Nomokonova

    Full Text Available Sagan-Zaba II, a habitation site on the shore of Siberia's Lake Baikal, contains a record of seal hunting that spans much of the Holocene, making it one of the longest histories of seal use in North Asia. Zooarchaeological analyses of the 16,000 Baikal seal remains from this well-dated site clearly show that sealing began here at least 9000 calendar years ago. The use of these animals at Sagan-Zaba appears to have peaked in the Middle Holocene, when foragers used the site as a spring hunting and processing location for yearling and juvenile seals taken on the lake ice. After 4800 years ago, seal use declined at the site, while the relative importance of ungulate hunting and fishing increased. Pastoralists began occupying Sagan-Zaba at some point during the Late Holocene, and these groups too utilized the lake's seals. Domesticated animals are increasingly common after about 2000 years ago, a pattern seen elsewhere in the region, but spring and some summer hunting of seals was still occurring. This use of seals by prehistoric herders mirrors patterns of seal use among the region's historic and modern groups. Overall, the data presented in the paper demonstrate that Lake Baikal witnessed thousands of years of human use of aquatic resources.

  7. Hydroelastic analysis of ice shelves under long wave excitation

    Science.gov (United States)

    Papathanasiou, Theodosios; Karperaki, Angeliki; Theotokoglou, Efstathios; Belibassakis, Kostas

    2014-05-01

    The transient hydroelastic response of an ice shelf, under long wave forcing, is analysed by means of the Finite Element method. Our main goal is to provide a simple model for tsunami wave - ice shelf interaction, capable of reproducing, in an at least qualitative manner, the stress field induced in the ice shelf, when excited by a tsunami wave. The analysis is aimed to model ice calving caused by wave impact, as was the case after the Honsu 2011 incident [1]. Adopting several simplifying but realistic assumptions, the ice shelf is modeled as a variable thickness, Euler-Bernoulli, cantilever beam, while the 1+1 linear shallow water equations are employed for the hydrodynamic field representation, as described in [2]. The fixed cantilever beam resembles a constrained, continuous ice shelf extending into the ocean. The solution of such a system, for a freely floating plate, has been presented by Sturova [3], where a modal expansion of the hydroelastic response with respect to the dry modes of the beam has been used. Our solution approach is based on the development of a special hydroelastic finite element for the governing equations. Cases of constant and variable bathymetry are considered. Bending moment time profiles yield the maximum tensile stress at the upper and lower surfaces of the ice shelf, which is the critical parameter for crack initiation or propagation. As expected, maximum absolute bending moment values appear at the base of the ice shelf, where no deflection or rotation occurs. The fact that the wave is fully reflected on the vertical impermeable boundary, corresponding to the continental shelf under the base of the floe, leads to extreme focusing and thus extreme bending moment values. Finally, the case of cracked shelves has been considered with use of the elementary defective beam theory of Kienzler and Herrmann [4]. Future enhancement of the present model is proposed on the grounds of a higher order beam/plate theory and a 2-D formulation

  8. The dynamics of climate-induced deglacial ice stream acceleration

    Science.gov (United States)

    Robel, A.; Tziperman, E.

    2015-12-01

    Geological observations indicate that ice streams were a significant contributor to ice flow in the Laurentide Ice Sheet during the Last Glacial Maximum. Conceptual and simple model studies have also argued that the gradual development of ice streams increases the sensitivity of large ice sheets to weak climate forcing. In this study, we use an idealized configuration of the Parallel Ice Sheet Model to explore the role of ice streams in rapid deglaciation. In a growing ice sheet, ice streams develop gradually as the bed warms and the margin expands outward onto the continental shelf. Then, a weak change in equilibrium line altitude commensurate with Milankovitch forcing results in a rapid deglacial response, as ice stream acceleration leads to enhanced calving and surface melting at low elevations. We explain the dynamical mechanism that drives this ice stream acceleration and its broader applicability as a feedback for enhancing ice sheet decay in response to climate forcing. We show how our idealized ice sheet simulations match geomorphological observations of deglacial ice stream variability and previous model-data analyses. We conclude with observations on the potential for interaction between ice streams and other feedback mechanisms within the earth system.

  9. Pediatric Ramsay Hunt syndrome: A rare clinical entity

    Directory of Open Access Journals (Sweden)

    Natashya Hilda Sima

    2016-01-01

    Full Text Available Ramsay Hunt syndrome is a rare cause of facial nerve paralysis in children, caused due to reactivation of latent Varicella–Zoster virus within the geniculate ganglion. In addition to the facial nerve, Ramsay Hunt syndrome may also affect the vestibulocochlear nerve leading to inner ear dysfunction and in severe case may also involve other cranial nerves. We report a case of Ramsay Hunt syndrome in a 15-year-old child.

  10. Damage Mechanics in the Community Ice Sheet Model

    Science.gov (United States)

    Whitcomb, R.; Cathles, L. M. M., IV; Bassis, J. N.; Lipscomb, W. H.; Price, S. F.

    2016-12-01

    Half of the mass that floating ice shelves lose to the ocean comes from iceberg calving, which is a difficult process to simulate accurately. This is especially true in the large-scale ice dynamics models that couple changes in the cryosphere to climate projections. Damage mechanics provide a powerful technique with the potential to overcome this obstacle by describing how fractures in ice evolve over time. Here, we demonstrate the application of a damage model to ice shelves that predicts realistic geometries. We incorporated this solver into the Community Ice Sheet Model, a three dimensional ice sheet model developed at Los Alamos National Laboratory. The damage mechanics formulation that we use comes from a first principles-based evolution law for the depth of basal and surface crevasses and depends on the large scale strain rate, stress state, and basal melt. We show that under idealized conditions it produces ice tongue lengths that match well with observations for a selection of natural ice tongues, including Erebus, Drygalski, and Pine Island in Antarctica, as well as Petermann in Greenland. We also apply the model to more generalized ideal ice shelf geometries and show that it produces realistic calving front positions. Although our results are preliminary, the damage mechanics model that we developed provides a promising first principles method for predicting ice shelf extent and how the calving margins of ice shelves respond to climate change.

  11. Salinity variability along the eastern continental shelf of Canada and the United States, 1973-2013

    Science.gov (United States)

    Bisagni, James J.

    2016-09-01

    Continental shelf waters located off the east coast of Canada and the United States are part of a long shelf current system that is partly comprised of colder, less-saline waters originating from high latitudes, including waters from the North Atlantic sub-polar gyre, along with ice-melt and freshwater input from local rivers. A 41-year analysis (1973-2013) of near-surface salinity (NSS) using three hydrographic datasets (Bedford Institute of Oceanography "Climate", NOAA/ESDIM, and Canadian Marine Environmental Data Service (MEDS)) allowed an examination of NSS variability within 11 continental shelf sub-regions, extending from the southern Newfoundland Shelf of eastern Canada to the DelMarVa/Hatteras Shelf of the United States. Although the periods of record containing sufficient data vary between sub-regions, regional mean NSS values are lowest within the Gulf of St. Lawrence and highest on the DelMarVa/Hatteras shelf, with largest annual variability within the Gulf of St. Lawrence. After removal of outliers, long-term linear trends computed from annual mean NSS were detected along the Newfoundland Shelf (+0.011 y-1), Western Scotian Shelf (-0.007 y-1), Gulf of Maine (-0.014 y-1), Georges Bank (-0.011 y-1), and DelMarVa/Hatteras Shelf (+0.024 y-1). A long-term quadratic fit to annual mean NSS from the Eastern Scotian Shelf displays a salinity increase through 1992 of +0.026 y-1, decreasing thereafter until 2013 by -0.028 y-1. A quadratic fit for the Western Grand Banks displays a NSS increase through 2007 of +0.022 y-1, decreasing thereafter through 2013 by -0.006 y-1. Annual mean NSS from the Eastern Grand Banks, Tail of the Grand Banks, Gulf of St. Lawrence, and Middle Atlantic Bight display no long-term trends. Inter-annual variability (IAV) of NSS residuals shows similar small mean squared error (mse) of 0.02-0.04 for the four northern-most sub-regions (Newfoundland Shelf, Eastern, Tail and Western Grand Banks) and are correlated at 0-year lag. IAV of NSS

  12. Wildlife reserves, populations and hunting outcome with smart wildlife

    DEFF Research Database (Denmark)

    Jensen, Frank; Jacobsen, Jette Bredahl; Thorsen, Bo Jellesmark

    2014-01-01

    There is a very small natural resource economic literature on natural reserves and hunting that consider potential stress effects of hunting on the game population and its migration in and out of hunting and reserve areas. In this literature private optimal solution with and without stress effect...... from the wildlife reserve to the hunting area in the social optimum. The total effect is, therefore, ambiguous. For the private optimum open-access is assumed and exactly the same results arise as in the social optimum when comparing a situation with and without stress effects....

  13. Cosmetics Safety Q&A: Shelf Life

    Science.gov (United States)

    ... Resources for You Consumers Cosmetics Safety Q&A: Shelf Life Share Tweet Linkedin Pin it More sharing ... Email Print FAQs Main Page What is the shelf life of cosmetics? The shelf life for eye- ...

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

    Science.gov (United States)

    Comiso, Josefino C.

    2011-01-01

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

  15. A glimpse beneath Antarctic sea ice: observation of platelet-layer thickness and ice-volume fraction with multifrequency EM

    Science.gov (United States)

    Hoppmann, Mario; Hunkeler, Priska A.; Hendricks, Stefan; Kalscheuer, Thomas; Gerdes, Rüdiger

    2016-04-01

    In Antarctica, ice crystals (platelets) form and grow in supercooled waters below ice shelves. These platelets rise, accumulate beneath nearby sea ice, and subsequently form a several meter thick, porous sub-ice platelet layer. This special ice type is a unique habitat, influences sea-ice mass and energy balance, and its volume can be interpreted as an indicator of the health of an ice shelf. Although progress has been made in determining and understanding its spatio-temporal variability based on point measurements, an investigation of this phenomenon on a larger scale remains a challenge due to logistical constraints and a lack of suitable methodology. In the present study, we applied a lateral constrained Marquardt-Levenberg inversion to a unique multi-frequency electromagnetic (EM) induction sounding dataset obtained on the ice-shelf influenced fast-ice regime of Atka Bay, eastern Weddell Sea. We adapted the inversion algorithm to incorporate a sensor specific signal bias, and confirmed the reliability of the algorithm by performing a sensitivity study using synthetic data. We inverted the field data for sea-ice and platelet-layer thickness and electrical conductivity, and calculated ice-volume fractions within the platelet layer using Archie's Law. The thickness results agreed well with drillhole validation datasets within the uncertainty range, and the ice-volume fraction yielded results comparable to other studies. Both parameters together enable an estimation of the total ice volume within the platelet layer, which was found to be comparable to the volume of landfast sea ice in this region, and corresponded to more than a quarter of the annual basal melt volume of the nearby Ekström Ice Shelf. Our findings show that multi-frequency EM induction sounding is a suitable approach to efficiently map sea-ice and platelet-layer properties, with important implications for research into ocean/ice-shelf/sea-ice interactions. However, a successful application of this

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

    Directory of Open Access Journals (Sweden)

    D. Price

    2014-02-01

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

  17. New Jersey shallow shelf

    DEFF Research Database (Denmark)

    Expedition 313 Scientists; Bjerrum, Christian J.

    2009-01-01

    Integrated Ocean Drilling Program (IODP) Expedition 313 to the New Jersey Shallow Shelf off the east coast of the United States is the third IODP expedition to use a mission-specific platform. It was conducted by the European Consortium for Ocean Research Drilling (ECORD) Science Operator (ESO...... to sea level change. We drilled at three locations in 35 m of water 45–67 km offshore, targeting the topsets, foresets, and toesets of several clinoforms at 180–750 m core depth below seafloor (CSF-A). Seismic correlations to previously drilled holes on the continental slope and extrapolations of depths...... successions to as many as 16 surfaces and/or sequence-bounding unconformities mapped in the regional seismic grid. Eight lithologic units are recognized that contain important physical and biofacies indicators of paleobathymetry. Reliable zonations of multiple fossil groups, Sr isotopic ages measured...

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

    Science.gov (United States)

    Lee, V.; Payne, A. J.; Gregory, J. M.

    2011-01-01

    We develop a two-dimensional two-layer flow model that can calculate melt rates beneath ice shelves from ocean temperature and salinity fields at the shelf front. The cavity motion is split into two layers where the upper plume layer represents buoyant meltwater-rich water rising along the underside of the ice to the shelf front, while the lower layer represents the ambient water connected to the open ocean circulating beneath the plume. Conservation of momentum has been reduced to a frictional geostrophic balance, which when linearized provides algebraic equations for the plume velocity. The turbulent exchange of heat and salt between the two layers is modelled through an entrainment rate which is directed into the faster flowing layer. The numerical model is tested using an idealized geometry based on the dimensions of Pine Island Ice Shelf. We find that the spatial distribution of melt rates is fairly robust. The rates are at least 2.5 times higher than the mean in fast flowing regions corresponding to the steepest section of the underside of the ice shelf close to the grounding line and to the converged geostrophic flow along the rigid lateral boundary. Precise values depend on a combination of entrainment and plume drag coefficients. The flow of the ambient is slow and the spread of ocean scalar properties is dominated by diffusion.

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

    Directory of Open Access Journals (Sweden)

    V. Lee

    2011-01-01

    Full Text Available We develop a two-dimensional two-layer flow model that can calculate melt rates beneath ice shelves from ocean temperature and salinity fields at the shelf front. The cavity motion is split into two layers where the upper plume layer represents buoyant meltwater-rich water rising along the underside of the ice to the shelf front, while the lower layer represents the ambient water connected to the open ocean circulating beneath the plume. Conservation of momentum has been reduced to a frictional geostrophic balance, which when linearized provides algebraic equations for the plume velocity. The turbulent exchange of heat and salt between the two layers is modelled through an entrainment rate which is directed into the faster flowing layer.

    The numerical model is tested using an idealized geometry based on the dimensions of Pine Island Ice Shelf. We find that the spatial distribution of melt rates is fairly robust. The rates are at least 2.5 times higher than the mean in fast flowing regions corresponding to the steepest section of the underside of the ice shelf close to the grounding line and to the converged geostrophic flow along the rigid lateral boundary. Precise values depend on a combination of entrainment and plume drag coefficients. The flow of the ambient is slow and the spread of ocean scalar properties is dominated by diffusion.

  20. Hunting for Knowledge: Using a Scavenger Hunt to Orient Graduate Veterinary Students

    Science.gov (United States)

    Pike, Caitlin; Alpi, Kristine M.

    2015-01-01

    Active participation in orientation is hoped to increase understanding and use of library resources and services beyond the effect of tours or welcome lectures. Timed scavenger hunts have been used to orient undergraduate and medical students to academic libraries. This report describes the planning, execution, and evaluation of an untimed…

  1. 76 FR 59298 - Migratory Bird Hunting; Migratory Bird Hunting Regulations on Certain Federal Indian Reservations...

    Science.gov (United States)

    2011-09-26

    ... Survey; population status reports for blue-winged teal, sandhill cranes, woodcock, mourning doves, white... has reviewed this rule under Executive Order 12866. OMB bases its determination of regulatory... of age or older must carry on his/her person a valid Migratory Bird Hunting and Conservation...

  2. 75 FR 52398 - Migratory Bird Hunting; Proposed Frameworks for Late-Season Migratory Bird Hunting Regulations

    Science.gov (United States)

    2010-08-25

    .... Pintails vi. Scaup vii. Mottled ducks viii. Wood ducks ix. Youth Hunt 2. Sea Ducks 3. Mergansers 4. Canada... year's frameworks. Due to the comprehensive nature of the annual review of the frameworks performed by... options had increased harvest pressure; however, the ability to detect the impact of zone/split...

  3. 77 FR 23093 - Migratory Bird Hunting; Proposed 2012-13 Migratory Game Bird Hunting Regulations (Preliminary...

    Science.gov (United States)

    2012-04-17

    ... viii. Wood Ducks ix. Youth Hunt x. Mallard Management Units xi. Other 2. Sea Ducks 3. Mergansers 4... breeding population size) did not perform adequately, resulting in a consistent over-prediction of mallard... increased harvest pressure; however, the ability to detect the impact of zone/split configurations was poor...

  4. 77 FR 49867 - Migratory Bird Hunting; Proposed Frameworks for Late-Season Migratory Bird Hunting Regulations

    Science.gov (United States)

    2012-08-17

    .... Mottled Ducks viii. Wood Ducks ix. Youth Hunt x. Mallard Management Units xi. Other 2. Sea Ducks 3... year's frameworks. Due to the comprehensive nature of the annual review of the frameworks performed by... harvest pressure, in particular the Tall Grass Prairie (TGP) population. We recognize the continuing...

  5. 78 FR 52337 - Migratory Bird Hunting; Proposed Frameworks for Late-Season Migratory Bird Hunting Regulations

    Science.gov (United States)

    2013-08-22

    .... Mottled ducks viii. Wood ducks ix. Youth Hunt x. Mallard Management Units xi. Other 2. Sea Ducks 3... frameworks. Due to the comprehensive nature of the annual review of the frameworks performed by the Councils... pressure. We recognize the continuing problems posed by increasing numbers of resident Canada geese and...

  6. 75 FR 44855 - Migratory Bird Hunting; Proposed Frameworks for Early-Season Migratory Bird Hunting Regulations...

    Science.gov (United States)

    2010-07-29

    ... harvest of MCP cranes in hunt areas outside of the Central Flyway (Arizona, Pacific Flyway portion of New... North American MCP sport harvest, including crippling losses, was 25,731 birds, which was a 39 percent... options for providing production States an opportunity to harvest teal outside the regular duck...

  7. Hunting for Knowledge: Using a Scavenger Hunt to Orient Graduate Veterinary Students

    Science.gov (United States)

    Pike, Caitlin; Alpi, Kristine M.

    2015-01-01

    Active participation in orientation is hoped to increase understanding and use of library resources and services beyond the effect of tours or welcome lectures. Timed scavenger hunts have been used to orient undergraduate and medical students to academic libraries. This report describes the planning, execution, and evaluation of an untimed…

  8. Traditional Saami hunting in relation to drum motifs of animals and hunting

    Directory of Open Access Journals (Sweden)

    Rolf Kjellström

    1991-01-01

    Full Text Available The focus of this paper is on the traditional Saami hunting in relation to the animal and hunting motifs on their drum, more specifially the southern Saami drums. One may wonder if it is possible for anyone to interpret a picture unconditionally. One has a certain ground of one's own to stand on and the question arises of whether this is the correct position, when -as in the present case — we approach another culture. We naturally include the experiences of our own culture in interpretations of another culture. The animal which is the commonest species on the southern Saami drums, is the reindeer. Other animals that occur are elks, wolves, beavers, foxes, snakes, among others. Considering the Saamis' hunting weapons, the most important of these were the bow and arrow, and the spear or spear shaft. Of these weapons it is the bow which is most often portrayed on drums. Also some trapping implement like a gin may appear on a drum, but in general we have little or no information about hunting or trapping methods at all.

  9. 77 FR 54451 - Migratory Bird Hunting; Migratory Bird Hunting Regulations on Certain Federal Indian Reservations...

    Science.gov (United States)

    2012-09-05

    ... flocks were 5.0 times more likely to fly within gun range ( http://www.fws.gov/migratorybirds... cranes. Crane carcass tags are required prior to hunting. Sora and Virginia Rails: All Areas. Season Dates: Begin September 1 and end November 25, 2012. Daily Bag Limit: 25 sora and Virginia rails,...

  10. 78 FR 53217 - Migratory Bird Hunting; Migratory Bird Hunting Regulations on Certain Federal Indian Reservations...

    Science.gov (United States)

    2013-08-28

    ... goose flocks were 5.0 times more likely to fly within gun range ( http://www.regulations.gov at Docket... carcass tags are required prior to hunting. Sora and Virginia Rails: All Areas Season Dates: Begin September 1 and end November 24, 2013. Daily Bag Limit: 25 sora and Virginia rails, singly or in...

  11. 78 FR 58233 - Migratory Bird Hunting; Migratory Bird Hunting Regulations on Certain Federal Indian Reservations...

    Science.gov (United States)

    2013-09-23

    ... would have an annual effect of $100 million or more on the economy. Executive Order 13563 reaffirms the... effect on the economy of $100 million or more. However, because this rule establishes hunting seasons, we... insufficient time to select season dates and limits; to communicate those selections to us; and to establish...

  12. Hunting for Livelihood in Northeast Gabon: Patterns, Evolution, and Sustainability

    Directory of Open Access Journals (Sweden)

    Robert Nasi

    2008-12-01

    Full Text Available We suggest an ethno-biological approach to analyze the cultural and social drivers of hunting activities and assess sustainability in villages near Makokou, northeast Gabon, based on interviews with hunters, participatory mapping of hunting territories, and daily records of offtakes for 1 yr. Hunting in villages of northeast Gabon is practiced for both local consumption and cash income to cover basic family expenses. There appears to be no clear tendency to abandon subsistence hunting for commercial hunting as in other regions of Africa. Cultural and socioeconomic factors explain the temporal and spatial variation in hunting activities. Hunting increases in the dry season during circumcision ceremonies, when it is practiced mainly at > 10 km from villages, and decreases during the rainy season because most hunters are occupied by other economic activities. Degraded forest such as secondary regrowth supplies 20% of the animals killed and the greatest diversity of species at short distances from villages. Mature forest supplies the species with the greatest commercial value, e.g., red river hog (Potamochoerus porcus, and is the preferred source of meat for traditional ceremonies. In the last 15 yr, hunting patterns have changed rapidly, mainly because of the spread of gun hunting, which had serious implications for the nature of offtakes. Our results suggest that there is potential to allow hunting for resistant species such as blue duiker (Cephalophus monticola and African brush-tailed porcupine (Atherurus africanus. Other species such as red river hog and small diurnal monkeys require more attention. Specific management systems could be discussed in participatory hunting management plans to identify possible solutions to maintain the population levels of the more critical species.

  13. Study of Under-ice Blooms In the Chukchi Ecosystem (SUBICE) (HLY1401, EM122)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The primary objectives of SUBICE were to determine the spatial distribution of large under-ice phytoplankton blooms on the Chukchi Shelf and the physical mechanisms...

  14. Legal Ice?

    DEFF Research Database (Denmark)

    Strandsbjerg, Jeppe

    The idealised land|water dichotomy is most obviously challenged by ice when ‘land practice’ takes place on ice or when ‘maritime practice’ is obstructed by ice. Both instances represent disparity between the legal codification of space and its social practice. Logically, then, both instances call...... for alternative legal thought and practice; in the following I will emphasise the former and reflect upon the relationship between ice, law and politics. Prior to this workshop I had worked more on the relationship between cartography, geography and boundaries than specifically on ice. Listening to all...... the interesting conversations during the workshop, however, made me think that much of the concern with the Polar Regions in general, and the presence of ice in particular, reverberates around the question of how to accommodate various geographical presences and practices within the regulatory framework that we...

  15. A Pediatric Case of Ramsay Hunt Syndrome

    Directory of Open Access Journals (Sweden)

    Serhan Derin

    2014-01-01

    Full Text Available Ramsay Hunt syndrome (RHS is characterized by facial paralysis, inner ear dysfunction, periauricular pain, and herpetiform vesicles. The reported incidence in children is 2.7/100,000. The pathogenesis involves the reactivation of latent varicella zoster virus (VZV in the geniculate ganglion of the facial nerve. The recovery rate is better in children than in adults. This paper discusses a 12-year-old girl with a rare case of peripheral facial paralysis caused by RHS and reviews the literature.

  16. Hunting: Death and the signs of life

    DEFF Research Database (Denmark)

    Østergaard, Jens Sand

    2013-01-01

    In this essay I have reworked the question of death in hunting by defining it as an activity whose nature implies a relation of being by living the death of the animal. Once this relation is understood more fully, it becomes obvious that the animal is not an isolated totality of relations......, but is instead a relative being whose being merits a moral obligation on the part of the hunter to make the manner of its death worthy of the manner of its being....

  17. Síndrome de Tolosa-Hunt

    OpenAIRE

    2016-01-01

    RESUMO A Síndrome de Tolosa Hunt é uma doença rara, cuja etiopatogenia é desconhecida. Apresenta-se como uma oftalmoplegia dolorosa de um ou mais nervos cranianos oculomotores, que regride espontaneamente e responde bem ao tratamento com corticoides. O presente estudo trata-se de um relato de caso de um paciente que apresentou seguidos casos de oftalmoplegias dolorosas, envolvendo o nervo oculomotor e o abducente sendo tratado com corticoesteroides obteve uma resposta dramática. Objetiva-se a...

  18. IcePod: Imaging Ice-Ocean Process from Top to Bottom

    Science.gov (United States)

    Bell, R. E.; Frearson, N.; Zappa, C. J.; Tinto, K. J.; Das, I.; Dhakal, T.; Bertinato, C.; Dong, L.; Brown, S.; Le Bel, D. A.

    2014-12-01

    November 2014, the IcePod system will be operated in Antarctica targeting the formation of polynyas, the Ross Ice Shelf structure and stability and the distribution of subglacial water in East Antarctica.

  19. Sea Ice

    Science.gov (United States)

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

    2013-01-01

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

  20. Polar bear and walrus response to the rapid decline in Arctic sea ice

    Science.gov (United States)

    Oakley, K.; Whalen, M.; Douglas, D.; Udevitz, M.; Atwood, T.; Jay, C.

    2012-01-01

    The Arctic is warming faster than other regions of the world due to positive climate feedbacks associated with loss of snow and ice. One highly visible consequence has been a rapid decline in Arctic sea ice over the past 3 decades - a decline projected to continue and result in ice-free summers likely as soon as 2030. The polar bear (Ursus maritimus) and the Pacific walrus (Odobenus rosmarus divergens) are dependent on sea ice over the continental shelves of the Arctic Ocean's marginal seas. The continental shelves are shallow regions with high biological productivity, supporting abundant marine life within the water column and on the sea floor. Polar bears use sea ice as a platform for hunting ice seals; walruses use sea ice as a resting platform between dives to forage for clams and other bottom-dwelling invertebrates. How have sea ice changes affected polar bears and walruses? How will anticipated changes affect them in the future?

  1. The Evolution of Lateralization in Group Hunting Sailfish

    DEFF Research Database (Denmark)

    Kurvers, Ralf H J M; Krause, Stefan; Viblanc, Paul E

    2017-01-01

    of a lack of population-level lateralization. Our results present a novel benefit of group hunting: by alternating attacks, individual-level attack lateralization can evolve, without the negative consequences of individual-level predictability. More generally, our results suggest that group hunting...... in predators might provide more suitable conditions for the evolution of strategy diversity compared to solitary life....

  2. 78 FR 3446 - Migratory Bird Hunting; Service Regulations Committee Meeting

    Science.gov (United States)

    2013-01-16

    ... Fish and Wildlife Service Migratory Bird Hunting; Service Regulations Committee Meeting AGENCY: Fish... issues concerning the 2013-14 migratory bird hunting regulations. DATES: The meeting will be held..., Division of Migratory Bird Management, U.S. Fish and Wildlife Service, Department of the Interior,...

  3. 78 FR 78377 - Migratory Bird Hunting; Service Regulations Committee Meeting

    Science.gov (United States)

    2013-12-26

    ... Fish and Wildlife Service RIN 1018-AZ80 Migratory Bird Hunting; Service Regulations Committee Meeting... preliminary issues concerning the 2014-15 migratory bird hunting regulations. DATES: The meeting will be held..., Division of Migratory Bird Management, U.S. Fish and Wildlife Service, Department of the Interior,...

  4. 77 FR 1718 - Migratory Bird Hunting; Service Regulations Committee Meeting

    Science.gov (United States)

    2012-01-11

    ... Fish and Wildlife Service Migratory Bird Hunting; Service Regulations Committee Meeting AGENCY: Fish... issues concerning the 2012-13 migratory bird hunting regulations. DATES: The meeting will be held... CONTACT: Chief, Division of Migratory Bird Management, U.S. Fish and Wildlife Service, Department of...

  5. The impact of hunting on tropical mammal and bird populations

    NARCIS (Netherlands)

    Benítez-López, A.; Alkemade, R.; Schipper, A. M.; Ingram, D. J.; Verweij, P. A.; Eikelboom, J. A. J.; Huijbregts, M. A. J.

    2017-01-01

    As the human population grows and increasingly encroaches on remaining wildlife habitat, hunting threatens many species. Benítez-López et al. conducted a large-scale meta-analysis of hunting trends and impacts across the tropics (see the Perspective by Brashares and Gaynor). Bird and mammal

  6. 50 CFR 20.133 - Hunting regulations for crows.

    Science.gov (United States)

    2010-10-01

    ... 50 Wildlife and Fisheries 6 2010-10-01 2010-10-01 false Hunting regulations for crows. 20.133... Hunting regulations for crows. (a) Crows may be taken, possessed, transported, exported, or imported, only.... (b) Except in the State of Hawaii, where no crows shall be taken, States may by statute or regulation...

  7. Demand for resident hunting in the southeastern United States

    Science.gov (United States)

    Neelam Poudyal; Seong Hoon Cho; J. Michael Bowker

    2008-01-01

    We modeled hunting demand among resident hunters in the Southeastern United States. Our model revealed that future hunting demand will likely decline in this region. Population growth in the region will increase demand but structural change in the region's demography (e.g., "browning" and "aging "), along with declining forestland access will...

  8. Cat dilemma: too protected to escape trophy hunting?

    Directory of Open Access Journals (Sweden)

    Lucille Palazy

    Full Text Available Trophy hunting is one of the most controversial issues in the field of biodiversity conservation. In particular, proponents and opponents debate fiercely over whether it poses a threat to hunted populations. Here, we show that trophy hunting constitutes a greater menace to threatened species than previously realized. Because humans value rarity, targeted species that are threatened are likely to be disproportionately hunted, thereby becoming even more vulnerable, which could eventually push them to extinction. With the ten felid species currently hunted for their trophies, we present evidence that (1 the number of killed individuals increases with time, in several cases exponentially, despite population declines, (2 the price of trophies is strongly dependent on species protection status, (3 changes of protection status coincide with counter-intuitive changes of hunting pressures: protection intensification with augmented hunting effort, and protection relaxation with lower effort. This suggests an over-exploitation of trophy-hunted felids and the necessity of a better quota system coupled with reconsidered protection methods.

  9. Cat dilemma: too protected to escape trophy hunting?

    Science.gov (United States)

    Palazy, Lucille; Bonenfant, Christophe; Gaillard, Jean-Michel; Courchamp, Franck

    2011-01-01

    Trophy hunting is one of the most controversial issues in the field of biodiversity conservation. In particular, proponents and opponents debate fiercely over whether it poses a threat to hunted populations. Here, we show that trophy hunting constitutes a greater menace to threatened species than previously realized. Because humans value rarity, targeted species that are threatened are likely to be disproportionately hunted, thereby becoming even more vulnerable, which could eventually push them to extinction. With the ten felid species currently hunted for their trophies, we present evidence that (1) the number of killed individuals increases with time, in several cases exponentially, despite population declines, (2) the price of trophies is strongly dependent on species protection status, (3) changes of protection status coincide with counter-intuitive changes of hunting pressures: protection intensification with augmented hunting effort, and protection relaxation with lower effort. This suggests an over-exploitation of trophy-hunted felids and the necessity of a better quota system coupled with reconsidered protection methods.

  10. UH joins hunt for elusive neutrino

    CERN Multimedia

    Creamer, B

    2003-01-01

    "The University of Hawaii has landed a $35 million, five-year grant from NASA to capture ultra-high frequency neutrinos in the Antarctic ice sheet with the hope of better understanding the origins of the universe" (1 page).

  11. The Greenland ice sheet and the climate – a review

    DEFF Research Database (Denmark)

    Funder, Svend Visby; Kjeldsen, Kristian Kjellerup; Kjær, Kurt H.;

    During LGM the margins of the Greenland ice sheet around the whole perimeter stood on the shelf – but where? The first estimates had to be based on evidence from land such as weathering limits on coastal mountains, major moraine belts, and altitudes of marine limits. Still the estimates ranged fr...... to climate change during and after LGM, and that coverage of the shelf may have been variable from one sector to another. Will the margin respond with similar complexity to global warming?...

  12. Scavenger hunt in the CERN Computing Centre

    CERN Multimedia

    CERN Bulletin

    2013-01-01

    Hidden among the racks of servers and disks in the CERN Computing Centre, you’ll find Hawaiian dancers, space aliens, gorillas… all LEGO® figurines! These characters were placed about the Centre for the arrival of Google’s Street View team for the world to discover.   PLEASE NOTE THAT THE COMPETITION IS OVER. ONLY FOR REFERENCE, HERE IS THE ORIGINAL ARTICLE. We’re pleased to announce our first global scavenger hunt! Spot three LEGO® figurines using Google’s Street View and you’ll be entered to win a gift of your choice from our CERN Gift Guide. A LEGO® figurine in the CERN Computing Centre, as seen on Google Street View. Here are the details: Find at least three LEGO® figurines hidden around the CERN Computing Centre using Google Street View.   Take screencaps of the figurines and e-mail the pictures to TreasureHunt-ComputingCentre@cern.ch. This email is no longer active.   The...

  13. The Elementary Marine Ice Sheet Model (EMISM)

    Science.gov (United States)

    Pattyn, Frank

    2015-04-01

    Ice sheet models become more and more components of global climate system modelling instead of stand-alone features to study cryospheric processes. Full coupling of ice sheet models to atmospheric and ocean models requires a standard for ice sheet models, and more precisely for marine ice sheet models, where complex feedbacks between ice and ocean, such as marine ice sheet instability, and the atmosphere, such as the elevation-mass balance feedback, operate at different time scales. Recent model intercomparisons (e.g., SeaRISE, MISMIP) have shown that basic requirements for marine ice sheet models are still lacking and that the complexity of many ice sheet models is focused on processes that are either not well captured numerically (spatial resolution issue) or are of secondary importance compared to the essential features of marine ice sheet dynamics. Here, we propose a new and fast computing ice sheet model, devoid of most complexity, but capturing the essential feedbacks when coupled to ocean or atmospheric models. Its computational efficiency guarantees to easily tests its advantages as well as limits through ensemble modelling. EMISM (Elementary Marine Ice Sheet Model) is a vertically integrated ice sheet model based on the Shallow-Ice Approximation extended a Weertman sliding law. Although vertically integrated, thermomechanical coupling is ensured through a simplified representation of ice sheet thermodynamics based on an analytical solution of the vertical temperature profile, enhanced with strain heating. The marine boundary is represented by a parameterized flux condition similar to Pollard & Deconto (2012), based on Schoof (2007). A simplified ice shelf is added to account for buttressing of ice shelves in this parameterization. The ice sheet model is solved on a finite difference grid and special care is taken to its numerical efficiency and stability. While such model has a series of (known) deficiencies with respect to short time effects, its overall

  14. Identity-driven differences in stakeholder concerns about hunting wolves.

    Directory of Open Access Journals (Sweden)

    Michelle L Lute

    Full Text Available Whereas past wolf management in the United States was restricted to recovery, managers must now contend with publicly contentious post-recovery issues including regulated hunting seasons. Understanding stakeholder concerns associated with hunting can inform stakeholder engagement, communication, and policy development and evaluation. Social identity theory (SIT has been used to understand how groups interact, why they conflict, and how collaboration may be achieved. Applying SIT to stakeholder conflicts about wolf hunting may help delineate groups according to their concern about, support for or opposition to the policy choice of hunting wolves. Our objective was to assess concerns about hunting as a tool to resolve conflict in Michigan, using SIT as a framework. We used a mixed-modal sampling approach (e.g., paper, Internet with wolf hunting-related public meeting participants in March 2013. Survey questions focused on 12 concerns previously identified as associated with hunting as a management tool to resolve conflict. Respondents (n  =  666 cared greatly about wolves but were divided over hunting wolves. Wolf conflicts, use of science in policy decisions, and maintaining a wolf population were the highest ranked concerns. Principle components analysis reduced concerns into three factors that explained 50.7% of total variance; concerns crystallized over justifications for hunting. General linear models revealed a lack of geographic influence on care, fear and support for hunting related to wolves. These findings challenge assumptions about regional differences and suggest a strong role for social identity in driving dichotomized public perceptions in wildlife management.

  15. Limited grounding-line advance onto the West Antarctic continental shelf in the easternmost Amundsen Sea Embayment during the last glacial period.

    Science.gov (United States)

    Klages, Johann P; Kuhn, Gerhard; Hillenbrand, Claus-Dieter; Smith, James A; Graham, Alastair G C; Nitsche, Frank O; Frederichs, Thomas; Jernas, Patrycja E; Gohl, Karsten; Wacker, Lukas

    2017-01-01

    Precise knowledge about the extent of the West Antarctic Ice Sheet (WAIS) at the Last Glacial Maximum (LGM; c. 26.5-19 cal. ka BP) is important in order to 1) improve paleo-ice sheet reconstructions, 2) provide a robust empirical framework for calibrating paleo-ice sheet models, and 3) locate potential shelf refugia for Antarctic benthos during the last glacial period. However, reliable reconstructions are still lacking for many WAIS sectors, particularly for key areas on the outer continental shelf, where the LGM-ice sheet is assumed to have terminated. In many areas of the outer continental shelf around Antarctica, direct geological data for the presence or absence of grounded ice during the LGM is lacking because of post-LGM iceberg scouring. This also applies to most of the outer continental shelf in the Amundsen Sea. Here we present detailed marine geophysical and new geological data documenting a sequence of glaciomarine sediments up to ~12 m thick within the deep outer portion of Abbot Trough, a palaeo-ice stream trough on the outer shelf of the Amundsen Sea Embayment. The upper 2-3 meters of this sediment drape contain calcareous foraminifera of Holocene and (pre-)LGM age and, in combination with palaeomagnetic age constraints, indicate that continuous glaciomarine deposition persisted here since well before the LGM, possibly even since the last interglacial period. Our data therefore indicate that the LGM grounding line, whose exact location was previously uncertain, did not reach the shelf edge everywhere in the Amundsen Sea. The LGM grounding line position coincides with the crest of a distinct grounding-zone wedge ~100 km inland from the continental shelf edge. Thus, an area of ≥6000 km2 remained free of grounded ice through the last glacial cycle, requiring the LGM grounding line position to be re-located in this sector, and suggesting a new site at which Antarctic shelf benthos may have survived the last glacial period.

  16. Dynamics of the Greenland Ice Sheet over multiple timescales

    DEFF Research Database (Denmark)

    Kjeldsen, Kristian Kjellerup

    behavior of the Greenland Ice Sheet on multiple timescales is investigated. These range from annual/decadal scale variations of ice surface heights and cyclic drainage patterns of ice-dammed lakes to long-term response of the ice sheet margin during the past 300,000 years. The results presented here show...... that the ice margin of the Greenland Ice Sheet responds highly dynamic and variable to climate change and oceanic forcing, with behavior additionally being governed by regional/local settings, e.g. topographical settings such as low-lying/mountainous areas and the presence or absence of deep fjords or shelf....../crossshelf troughs. Warming of ocean temperatures is suggested as being a main driver for periodic dynamic ice loss events in northwest Greenland while cooling of ocean temperatures around southern Greenland, in conjunction with increased snow accumulation, is found to drive a rapid readvance of glaciers in response...

  17. The Greenland ice sheet - a model for its culmination and decay during and after the last glacial maximum

    DEFF Research Database (Denmark)

    Funder, Svend Visby; Hansen, Louise

    1996-01-01

    LGM, only southern Greenland (south of lat. 69°-72°N) saw a major expansion of the ice sheet with thick cover over the present coastline and onto the shelf. In the north, outlet glaciers filled fjord basins, including the Nares Strait between Canada and Greenland, and piedmont glaciers descended from...... coastal mountains onto the coastline, but the glaciers did not cover the shelf. Break up probably began after c. 15 ka, and took place in two discrete steps. First, the shelf and major inlets were cleared of marine based ice. There was little thinning of the ice on land, and in the northern parts...

  18. Interstellar Ices

    CERN Document Server

    Boogert, A C A

    2003-01-01

    Currently ~36 different absorption bands have been detected in the infrared spectra of cold, dense interstellar and circumstellar environments. These are attributed to the vibrational transitions of ~17 different molecules frozen on dust grains. We review identification issues and summarize the techniques required to extract information on the physical and chemical evolution of these ices. Both laboratory simulations and line of sight studies are essential. Examples are given for ice bands observed toward high mass protostars, fields stars and recent work on ices in disks surrounding low mass protostars. A number of clear trends have emerged in recent years. One prominent ice component consists of an intimate mixture between H2O, CH3OH and CO2 molecules. Apparently a stable balance exists between low temperature hydrogenation and oxidation reactions on grain surfaces. In contrast, an equally prominent ice component, consisting almost entirely of CO, must have accreted directly from the gas phase. Thermal proc...

  19. On the distribution of batch shelf lives.

    Science.gov (United States)

    Quinlan, Michelle; Stroup, Walter; Christopher, David; Schwenke, James

    2013-01-01

    Implicit in ICH Q1E (International Conference on Harmonization [ICH], 2003b ) are definitions of batch shelf life (the time the batch mean crosses the acceptance limit) and product shelf life (the minimum batch shelf life). The distribution of batch means over time projects to a distribution of batch shelf lives on the x-axis. Assuming multivariate normality, shelf life is the ratio of correlated Gaussian variables. Using Hinkley ( 1969 ), we describe the relationship between quantiles of the distributions of batch shelf lives and batch means. Exploiting this relationship, a linear mixed model is used to estimate a target quantile of batch shelf lives to address the ICH objective.

  20. Managing hunting under uncertainty: from one-off ecological indicators to resilience approaches in assessing the sustainability of bushmeat hunting

    Directory of Open Access Journals (Sweden)

    Nathalie van Vliet

    2015-09-01

    Full Text Available Despite the fact that sustainability of bushmeat hunting in tropical areas is of major concern for conservation and development practitioners, we still know very little about how to measure sustainability and how to put in place sustainable bushmeat hunting systems. We review the current limits of traditional methods used to investigate sustainability of bushmeat hunting, discuss the need to incorporate the characteristics of complex systems into sustainability assessments, and suggest how resilience theories could assist in understanding bushmeat sustainability and more effective conservation of wildlife in tropical areas. Traditional methods used to assess the sustainability of bushmeat hunting include demographic models of population growth, one-off biological indicators, population trend methods, harvest-based indicators, and comparisons of demographic parameters between sites. These traditional biological sustainability indices have proved inadequate for measuring the impact of bushmeat hunting because sustainability is treated as a static, binary (yes or no question, thus ignoring stochastic processes, the inherent variability of natural systems, and the complexity of hunting systems. We suggest that bushmeat hunting systems in tropical areas should be regarded as social-ecological systems in which the impacts of hunting on prey populations are not the only focus. Instead, the analysis of resilience aims at understanding the complex and dynamic relationships between the hunting ground, its resources, the stakeholders, and the different exogenous drivers of change that affect the components of the system at different scales. The main implication of using the resilience theory in the context of bushmeat hunting is the shift from the need to assess stocks with imprecise measures to the incorporation of the uncertainty and stochasticity inherent to complex systems in participatory and adaptive management processes. As such, the resilience

  1. Tidally induced variations in vertical and horizontal motion on Rutford Ice Stream, West Antarctica, inferred from remotely sensed observations

    Science.gov (United States)

    Minchew, B. M.; Simons, M.; Riel, B.; Milillo, P.

    2017-01-01

    To better understand the influence of stress changes over floating ice shelves on grounded ice streams, we develop a Bayesian method for inferring time-dependent 3-D surface velocity fields from synthetic aperture radar (SAR) and optical remote sensing data. Our specific goal is to observe ocean tide-induced variability in vertical ice shelf position and horizontal ice stream flow. Thus, we consider the special case where observed surface displacement at a given location can be defined by a 3-D secular velocity vector, a family of 3-D sinusoidal functions, and a correction to the digital elevation model used to process the SAR data. Using nearly 9 months of SAR data collected from multiple satellite viewing geometries with the COSMO-SkyMed 4-satellite constellation, we infer the spatiotemporal response of Rutford Ice Stream, West Antarctica, to ocean tidal forcing. Consistent with expected tidal uplift, inferred vertical motion over the ice shelf is dominated by semidiurnal and diurnal tidal constituents. Horizontal ice flow variability, on the other hand, occurs primarily at the fortnightly spring-neap tidal period (Msf). We propose that periodic grounding of the ice shelf is the primary mechanism for translating vertical tidal motion into horizontal flow variability, causing ice flow to accelerate first and most strongly over the ice shelf. Flow variations then propagate through the grounded ice stream at a mean rate of ˜29 km/d and decay quasi-linearly with distance over ˜85 km upstream of the grounding zone.

  2. "Hunt"-ing for post-translational modifications that underlie the histone code

    Science.gov (United States)

    Taverna, Sean D.; David Allis, C.; Hake, Sandra B.

    2007-01-01

    Eukaryotic cells package their DNA with histone proteins to form chromatin that can be regulated to enable transcription, DNA repair and replication in response to cellular needs and external stimuli. A wealth of recent studies of post-translational histone modifications and histone variants have led to an explosion of insights into and more questions about how these processes might be regulated. Work from Donald Hunt and colleagues contributed greatly to our understanding of the "histone code" by developing novel methods to study and identify histone modifications in both generic and specialized variant histone proteins. Without his expertise, the field of chromatin biology would not be where it is today. In recognition, we are pleased to contribute to a special issue of the International Journal of Mass Spectrometry dedicated to the many advances pioneered by the Hunt laboratory, which have enhanced the science of many fields and the careers of many scientists.

  3. Hunting for the optimal hunt - Contributions to a sustainable harvest strategy for pink-footed geese

    DEFF Research Database (Denmark)

    Jensen, Gitte Høj

    in order to reduce conflicts with agriculture and degradation of tundra vegetation in Svalbard. The population target shall be achieved through an adaptive harvest management (AHM) framework and optimization of hunting practices and organisation. The objective of this thesis has been to support...... the development of the AHM plan. This has been done at the flyway level by developing demographic population models and exploring the application of dynamic optimization methods to find an optimal management strategy. At the local and regional levels I explored effects of hunting practises and organisation at one......As part of the recently endorsed African-Eurasian Migratory Waterbird (AEWA) International Species Management Plan for the Svalbard population of the pink-footed goose Anser brachyrhynchus, a stable population target of 60,000 (current population is c. 80,000 during 2011-2013) has been agreed...

  4. Production of organic matter in Antarctic ice shelf

    Digital Repository Service at National Institute of Oceanography (India)

    Dhargalkar, V.K.; Verlecar, X.N.

    stream_size 5 stream_content_type text/plain stream_name Indian_J_Mar_Sci_21_1.pdf.txt stream_source_info Indian_J_Mar_Sci_21_1.pdf.txt Content-Encoding ISO-8859-1 Content-Type text/plain; charset=ISO-8859-1 ...

  5. Air-sea CO2 fluxes on the Bering Sea shelf

    Directory of Open Access Journals (Sweden)

    M. A. Jeffries

    2011-05-01

    Full Text Available There have been few previous studies of surface seawater CO2 partial pressure (pCO2 variability and air-sea CO2 gas exchange rates for the Bering Sea shelf. In 2008, spring and summertime observations were collected in the Bering Sea shelf as part of the Bering Sea Ecological Study (BEST. Our results indicate that the Bering Sea shelf was close to neutral in terms of CO2 sink-source status in springtime due to relatively small air-sea CO2 gradients (i.e., ΔpCO2 and sea-ice cover. However, by summertime, very low seawater pCO2 values were observed and much of the Bering Sea shelf became strongly undersaturated with respect to atmospheric CO2 concentrations. Thus the Bering Sea shelf transitions seasonally from mostly neutral conditions to a strong oceanic sink for atmospheric CO2 particularly in the "green belt" region of the Bering Sea where there are high rates of phytoplankton primary production (PPand net community production (NCP. Ocean biological processes dominate the seasonal drawdown of seawater pCO2 for large areas of the Bering Sea shelf, with the effect partly countered by seasonal warming. In small areas of the Bering Sea shelf south of the Pribilof Islands and in the SE Bering Sea, seasonal warming is the dominant influence on seawater pCO2, shifting localized areas of the shelf from minor/neutral CO2 sink status to neutral/minor CO2 source status, in contrast to much of the Bering Sea shelf. Overall, we compute that the Bering Sea shelf CO2 sink in 2008 was 157 ± 35 Tg C yr−1 (Tg = 1012 g C and thus a strong sink for CO2.

  6. Water exchange between the continental shelf and the cavity beneath Nioghalvfjerdsbræ (79 North Glacier)

    Science.gov (United States)

    Wilson, N. J.; Straneo, F.

    2015-09-01

    The mass loss at Nioghalvfjerdsbræ is primarily due to rapid submarine melting. Ocean data obtained from beneath the Nioghalvfjerdsbræ ice tongue show that melting is driven by the presence of warm (1°C) Atlantic Intermediate Water (AIW). A sill prevents AIW from entering the cavity from Dijmphna Sund, requiring that it flow into the cavity via bathymetric channels to the south at a pinned ice front. Comparison of water properties from the cavity, Dijmphna Sund, and the continental shelf support this conclusion. Overturning circulation rates inferred from observed melt rates and cavity stratification suggest an exchange flow between the cavity and the continental shelf of 38mSv, sufficient to flush cavity waters in under 1 year. These results place upper bounds on the timescales of external variability that can be transmitted to the glacier via the ice tongue cavity.

  7. Climate Modeling: Ocean Cavities below Ice Shelves

    Energy Technology Data Exchange (ETDEWEB)

    Petersen, Mark Roger [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Computer, Computational, and Statistical Sciences Division

    2016-09-12

    The Accelerated Climate Model for Energy (ACME), a new initiative by the U.S. Department of Energy, includes unstructured-mesh ocean, land-ice, and sea-ice components using the Model for Prediction Across Scales (MPAS) framework. The ability to run coupled high-resolution global simulations efficiently on large, high-performance computers is a priority for ACME. Sub-ice shelf ocean cavities are a significant new capability in ACME, and will be used to better understand how changing ocean temperature and currents influence glacial melting and retreat. These simulations take advantage of the horizontal variable-resolution mesh and adaptive vertical coordinate in MPAS-Ocean, in order to place high resolution below ice shelves and near grounding lines.

  8. Ramsay Hunt Syndrome in a Child Case

    Directory of Open Access Journals (Sweden)

    Arzu Karataş

    2013-09-01

    Full Text Available Ramsay-Hunt Syndrome (RHS is a rare disease characterized by peripheral facial paralysis, cochleovestibular symptoms, skin lesions in the auricular canal and/or in the auricula and rarely skin lesions in the hard palate. The disease is also known as Herpes zoster oticus or herpes zoster cephalicus. Early diagnosis and antiviral treatment of peripheral nerve paralysis associated with higher rates of improvement. RHS, which is a rare disease in children should be considered in the differential diagnosis in children presenting with peripheral nerve palsy, erythema, vesicular lesions and/or ear pain. Here we presented a child case in which the first symptom was ear pain and facial palsy, followed by vesicular lesions in the ear pinna, and in the external auditory meatus.The patient recovered without squela of oral steroids and antiviral therapy.

  9. Hunting for the Quantum Cheshire Cat

    CERN Document Server

    Di Lorenzo, Antonio

    2012-01-01

    The proposal of Aharonov, Popescu, and Skrzypczyk [arXiv:1202.0631] of disembodying physical properties from particles is analyzed. It is argued that: (1) in order to state that the cat is at one location and the smile at another, one should look at correlations, not mean values; (2) a weak value of one for the presence of the cat describes the average over a large number of trials, where the detector gives in each trial outputs that are not zero nor one, and that are much larger than unity (they can be large and negative as well); (3) once these issues are addressed, the specific model proposed does not provide evidence for disembodiment of physical properties. Here, the exact probability distribution and its characteristic function are derived for arbitrary coupling strength, preparation and post-selection. This allows to successfully hunt down the quantum Cheshire cat.

  10. Bump-hunting in LHC ttbar events

    CERN Document Server

    Czakon, Michal; Mitov, Alexander

    2016-01-01

    We demonstrate that a purposefully normalised NNLO top pair invariant mass differential spectrum can have very small theoretical uncertainty and, in particular, a small sensitivity to the top quark mass. Such observable can thus be a very effective bump-hunting tool for resonances decaying to top pair events during LHC Run II and beyond. To illustrate how the approach works, we concentrate on one specific example of current interest, namely, the possible 750 GeV di-gamma excess resonance Phi. Considering only theoretical uncertainties, we demonstrate that it is possible to distinguish pp -> Phi -> tt signals studied in the recent literature [Hespel, Maltoni and Vryonidou, arXiv:1606.04149] from the pure SM background with very high significance. Alternatively, in case of non-observation, a strong upper limit on the decay rate Phi -> tt can be placed.

  11. Evaluating the Effects of Climate Change on Indigenous Marine Mammal Hunting in Northern and Western Alaska Using Traditional Knowledge

    Directory of Open Access Journals (Sweden)

    Henry P. Huntington

    2017-09-01

    Full Text Available Iñupiaq, Yup'ik, and Cup'ik hunters in 14 Alaska Native communities described a rapidly changing marine environment in qualitative traditional knowledge interviews conducted over the course of a decade with 110 individuals. Based on their observations, sea ice conditions are the most notable change, with later freeze-up, thinner and less reliable ice, and earlier and more rapid break-up. Marine mammal populations in northern and western Alaska have been affected by changes in the physical environment, with alterations to migratory timing and routes, distribution, abundance, health, and behavior. Despite these changes, marine mammal populations in the region remain generally healthy and abundant. For hunters, access is the biggest challenge posed by changing conditions. Sea ice is less safe for travel, particularly for more southerly communities, making hunting more dangerous or impossible. Rapid break-up has reduced the time available for hunting amid broken ice in spring, formerly a dependable and preferred season. Social change also affects the ways in which hunting patterns change. Increased industrial development, for example, can also alter marine mammal distribution and reduce hunting opportunity. Reduced use of animal skins for clothing and other purposes has reduced demand. More powerful and reliable engines make day trips easier, reducing the time spent camping. An essential component of adjustment and adaptation to changing conditions is the retention of traditional values and the acquisition of new information to supplement traditional knowledge. Our findings are consistent with, and add detail to, what is known from previous traditional knowledge and scientific studies. The ways in which hunters gather new information and incorporate it into their existing understanding of the marine environment deserves further attention, both as a means of monitoring change and as a key aspect of adaptation. While the changes to date have been

  12. Glacial landforms identified in high-resolution bathymetry indicate past Greenland ice sheet dynamics in Melville Bay, northeast Baffin Bay

    Science.gov (United States)

    Slabon, Patricia; Dorschel, Boris; Jokat, Wilfried; Myklebust, Reidun; Hebbeln, Dierk; Gebhardt, Catalina

    2017-04-01

    The maximum glacial extent of the Greenland Ice Sheet (GIS) and its advance and retreat across the continental shelf are crucial to better understand past ice-sheet dynamics and to predict its future development in times of climate change. Analyses of distribution and shape of glacial landforms are, thus, used to interpret information on ice-stream advances and retreats across the shelf. This study focuses on the past dynamics of the northwest GIS across the Greenland continental shelf. The research area is located in the Melville Bay, northeast Baffin Bay. Our interpretations base on analyses of high-resolution swath-bathymetric data acquired in 2010 and 2015 with the research vessels RV Polarstern and RV Maria S. Merian. The bathymetric data provide information along and across the axes of the major cross-shelf troughs of Melville Bay, allowing us to reconstruct the ice-sheet dynamics between the shelf edge and the present-day coast. The results of the analyses show glacial landforms that document former dynamics of the Greenland Ice Sheet (GIS). Moraines at the shelf edge give evidence for the maximum GIS extent. Grounding-zone wedges (GZWs), till lobes and glacial lineations define a pattern of variable ice-stream retreat in the individual cross-shelf troughs. Slow ice-stream retreat occurred in the northern cross-shelf trough compared to more episodic retreats in the central and southern cross-shelf troughs of Melville Bay. Periods of ice sheet grounding-zone stabilizations are indicated by large GZW-complexes on the mid- to inner shelf. Finally, the northwest GIS retreated across the inner continental shelf before 8.41 ka BP as revealed by an age-dated geological sample. Furthermore, on inter-trough banks, evidence has been found for minor ice-stream activity on localized ice domes. The glacial landforms across the northwest Greenland continental shelf, thus, host records of varying and discontinuous ice-sheet retreats since the last glacial maximum.

  13. Incentivizing monitoring and compliance in trophy hunting.

    Science.gov (United States)

    Bunnefeld, Nils; Edwards, Charles T T; Atickem, Anagaw; Hailu, Fetene; Milner-Gulland, E J

    2013-12-01

    Conservation scientists are increasingly focusing on the drivers of human behavior and on the implications of various sources of uncertainty for management decision making. Trophy hunting has been suggested as a conservation tool because it gives economic value to wildlife, but recent examples show that overharvesting is a substantial problem and that data limitations are rife. We use a case study of trophy hunting of an endangered antelope, the mountain nyala (Tragelaphus buxtoni), to explore how uncertainties generated by population monitoring and poaching interact with decision making by 2 key stakeholders: the safari companies and the government. We built a management strategy evaluation model that encompasses the population dynamics of mountain nyala, a monitoring model, and a company decision making model. We investigated scenarios of investment into antipoaching and monitoring by governments and safari companies. Harvest strategy was robust to the uncertainty in the population estimates obtained from monitoring, but poaching had a much stronger effect on quota and sustainability. Hence, reducing poaching is in the interests of companies wishing to increase the profitability of their enterprises, for example by engaging community members as game scouts. There is a threshold level of uncertainty in the population estimates beyond which the year-to-year variation in the trophy quota prevented planning by the safari companies. This suggests a role for government in ensuring that a baseline level of population monitoring is carried out such that this level is not exceeded. Our results illustrate the importance of considering the incentives of multiple stakeholders when designing frameworks for resource use and when designing management frameworks to address the particular sources of uncertainty that affect system sustainability most heavily. Incentivando el Monitoreo y el Cumplimiento en la Caza de Trofeos. © 2013 The Authors. Conservation Biology published by

  14. Bear-baiting may exacerbate wolf-hunting dog conflict.

    Science.gov (United States)

    Bump, Joseph K; Murawski, Chelsea M; Kartano, Linda M; Beyer, Dean E; Roell, Brian J

    2013-01-01

    The influence of policy on the incidence of human-wildlife conflict can be complex and not entirely anticipated. Policies for managing bear hunter success and depredation on hunting dogs by wolves represent an important case because with increasing wolves, depredations are expected to increase. This case is challenging because compensation for wolf depredation on hunting dogs as compared to livestock is less common and more likely to be opposed. Therefore, actions that minimize the likelihood of such conflicts are a conservation need. We used data from two US states with similar wolf populations but markedly different wolf/hunting dog depredation patterns to examine the influence of bear hunting regulations, bear hunter to wolf ratios, hunter method, and hunter effort on wolf depredation trends. Results indicated that the ratio of bear hunting permits sold per wolf, and hunter method are important factors affecting wolf depredation trends in the Upper Great Lakes region, but strong differences exist between Michigan and Wisconsin related in part to the timing and duration of bear-baiting (i.e., free feeding). The probability that a wolf depredated a bear-hunting dog increases with the duration of bear-baiting, resulting in a relative risk of depredation 2.12-7.22× greater in Wisconsin than Michigan. The net effect of compensation for hunting dog depredation in Wisconsin may also contribute to the difference between states. These results identified a potential tradeoff between bear hunting success and wolf/bear-hunting dog conflict. These results indicate that management options to minimize conflict exist, such as adjusting baiting regulations. If reducing depredations is an important goal, this analysis indicates that actions aside from (or in addition to) reducing wolf abundance might achieve that goal. This study also stresses the need to better understand the relationship among baiting practices, the effect of compensation on hunter behavior, and depredation

  15. Bear-baiting may exacerbate wolf-hunting dog conflict.

    Directory of Open Access Journals (Sweden)

    Joseph K Bump

    Full Text Available BACKGROUND: The influence of policy on the incidence of human-wildlife conflict can be complex and not entirely anticipated. Policies for managing bear hunter success and depredation on hunting dogs by wolves represent an important case because with increasing wolves, depredations are expected to increase. This case is challenging because compensation for wolf depredation on hunting dogs as compared to livestock is less common and more likely to be opposed. Therefore, actions that minimize the likelihood of such conflicts are a conservation need. METHODOLOGY/PRINCIPAL FINDINGS: We used data from two US states with similar wolf populations but markedly different wolf/hunting dog depredation patterns to examine the influence of bear hunting regulations, bear hunter to wolf ratios, hunter method, and hunter effort on wolf depredation trends. Results indicated that the ratio of bear hunting permits sold per wolf, and hunter method are important factors affecting wolf depredation trends in the Upper Great Lakes region, but strong differences exist between Michigan and Wisconsin related in part to the timing and duration of bear-baiting (i.e., free feeding. The probability that a wolf depredated a bear-hunting dog increases with the duration of bear-baiting, resulting in a relative risk of depredation 2.12-7.22× greater in Wisconsin than Michigan. The net effect of compensation for hunting dog depredation in Wisconsin may also contribute to the difference between states. CONCLUSIONS/SIGNIFICANCE: These results identified a potential tradeoff between bear hunting success and wolf/bear-hunting dog conflict. These results indicate that management options to minimize conflict exist, such as adjusting baiting regulations. If reducing depredations is an important goal, this analysis indicates that actions aside from (or in addition to reducing wolf abundance might achieve that goal. This study also stresses the need to better understand the relationship

  16. Archimedean Ice

    CERN Document Server

    Eloranta, Kari

    2009-01-01

    The striking boundary dependency (the Arctic Circle phenomenon) exhibited in the ice model on the square lattice extends to other planar set-ups. We present these findings for the triangular and the Kagome lattices. Critical connectivity results guarantee that ice configurations can be generated using the simplest and most efficient local actions. Height functions are utilized throughout the analysis. At the end there is a surprise in store: on the remaining Archimedean lattice for which the ice model can be defined, the 3.4.6.4. lattice, the long range behavior is completely different from the other cases.

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

    Science.gov (United States)

    Haid, Verena; Iovino, Doroteaciro; Masina, Simona

    2017-06-01

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

  18. Is recreational hunting important for landscape multi-functionality?

    DEFF Research Database (Denmark)

    Lund, Jens Friis; Jensen, Frank Søndergaard

    2017-01-01

    , and preservation of valued and/or threatened animal and plant species. Recreational hunting may thus contribute to preserve and enhance landscape multifunctionality. Yet, little is known about the importance of hunting interests in motivating such landscape management. In this article, we seek to shed light...... on these issues on the basis of data from a nationally representative survey of Danish landowners. Our findings show a mixed picture of the role of recreational hunting in supporting multifunctional landscapes. We observe a broad swathe of landscape changes for multifunctionality cross properties with different...

  19. Herpes zoster laryngitis accompanied by Ramsay Hunt syndrome.

    Science.gov (United States)

    Lee, Dong Hoon; Yoon, Tae Mi; Lee, Joon Kyoo; Joo, Young Eun; Lim, Sang Chul

    2013-01-01

    The most common presentation of herpes zoster in the head and neck region is called Ramsay Hunt syndrome (RHS), which rarely accompanies multiple cranial neuropathy. Herpes zoster also involves the mucous membrane of the tongue, palate, pharynx, and larynx. Herpes zoster infection of the larynx accompanied by Ramsay Hunt syndrome with cranial polyneuropathy is extremely rare, with only few reported cases in the literature. At the time of this report, a review of the medical literature disclosed 4 reported cases of herpes zoster laryngitis accompanied by Ramsay Hunt syndrome. Herein, we present 2 additional cases and report the clinical outcome of cranial polyneuropathy with a review of the literature.

  20. Ramsay hunt syndrome: A diagnostic challenge for general dental practitioners

    Directory of Open Access Journals (Sweden)

    Gautham Singh

    2017-01-01

    Full Text Available Ramsay hunt syndrome is not just a syndrome but it's rather an infectious disease caused by reactivation of latent varicella-zoster virus in geniculate ganglion. This was first explained by J. Ramsay Hunt as a triad of complications like otalgia, mucosal and cutaneous rashes with or without trigeminal facial palsy. The facial palsy can occur with characteristic vesicles along the path of nerve. We present a case of Ramsay Hunt syndrome in a 48-year-old male. The unilateral pattern of facial involvement and presence of vesicles assisted us for early diagnosis, distinguishing the syndrome with diseases mimicking other severe neurological illnesses and prompt treatment.

  1. Arctic Summer Sea-Ice Extent: How Free is Free?

    Science.gov (United States)

    Tremblay, B.; Cullather, R. I.; DeRepentigny, P.; Pfirman, S. L.; Newton, R.

    2015-12-01

    As Northern Hemisphere perennial sea ice cover continues a long-term downward trend, attention has begun to focus on the implications of the changing conditions. A summertime ice-free Arctic Ocean is frequently indicated as a signature milestone for these changes, however "ice-free" has a substantially different meaning among scientists and interested stakeholders. To climate scientists it may mean when there is so little sea ice that it plays a minimal role in the climate system. To those interested in development, it may mean a threshold where icebreaker support is not required. To coastal communities it may mean so little ice that hunting is not possible. To species dependent on sea ice, it may mean the point where they cannot find sufficient habitat to survive from spring until fall. In this contribution we document the projected seasonality of the sea ice retreat and address the following questions. For how long will the Arctic Ocean be ice free on average each year? What is the impact of such changes in the seasonality of the sea ice cover on species that are dependent on sea ice? To this end, we analyze the seasonal cycle in the sea-ice extent simulated by the Community Earth System Model 1 - Large Ensemble (CESM1-LE) output for the 21st century. CESM1-LE simulates a realistic late 20th, early 21st century Arctic climate with a seasonal cycle in sea ice extent and rate of decline in good agreement with observations. Results from this model show that even by the end of the 21st century, the length of the ice-free season is relatively short, with ice-free conditions mainly present for 2-3 months between August and October. The result is a much larger amplitude seasonal cycle when compared with the late 20th century climate.

  2. Hunting and hallucinogens: The use psychoactive and other plants to improve the hunting ability of dogs.

    Science.gov (United States)

    Bennett, Bradley C; Alarcón, Rocío

    2015-08-02

    Cultures throughout the world give plants to their dogs in order to improve hunting success. These practices are best developed in lowland Ecuador and Peru. There is no experimental evidence for the efficacy of these practices nor critical reviews that consider possible pharmacological effects on dogs based on the chemistry of the ethnoverterinary plants. This review has three specific aims: (1) determine what plants the Ecuadorian Shuar and Quichua give to dogs to improve their hunting abilities, (2) determine what plants other cultures give to dogs for the same purpose, and (3) assess the possible pharmacological basis for the use of these plants, particularly the psychoactive ones. We gathered Shuar (Province of Morona-Santiago) and Quichua (Napo and Orellano Provinces) data from our previous publications and field notes. All specimens were vouchered and deposited in QCNE with duplicates sent to NY and MO. Data presented from other cultures derived from published studies on ethnoveterinary medicine. Species names were updated, when necessary, and family assignments follow APG III (Angiosperm Phylogeny Group, 2009. An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III. Bot. J. Linn. Soc. 161, 105-121). Chemical data were found using PubMed and SciFinder. The Shuar and Quichua of Ecuador use at least 22 species for ethnoveterinary purposes, including all but one of their principal hallucinogens. Literature surveys identified 43 species used in other cultures to improve hunting ability. No published studies have examined the pharmacological active of these plant species in dogs. We, thus, combined phytochemical data with the ethnobotanical reports of each plant and then classified each species into a likely pharmacological category: depuratives/deodorant, olfactory sensitizer, ophthalmic, or psychoactive. The use of psychoactive substances to improve a dog׳s hunting ability seems counterintuitive, yet

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

    Science.gov (United States)

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

    2010-12-01

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

  4. Winter use of sea ice and ocean water mass habitat by southern elephant seals: The length and breadth of the mystery

    Science.gov (United States)

    Labrousse, Sara; Vacquié-Garcia, Jade; Heerah, Karine; Guinet, Christophe; Sallée, Jean-Baptiste; Authier, Matthieu; Picard, Baptiste; Roquet, Fabien; Bailleul, Frédéric; Hindell, Mark; Charrassin, Jean-Benoit

    2015-09-01

    Understanding the responses of animals to the environment is crucial for identifying critical foraging habitat. Elephant seals (Mirounga leonina) from the Kerguelen Islands (49°20‧S, 70°20‧E) have several different foraging strategies. Why some individuals undertake long trips to the Antarctic continent while others utilize the relatively close frontal zones is poorly understood. Here, we investigate how physical properties within the sea ice zone are linked to foraging activities of southern elephant seals (SES). To do this, we first developed a new approach using indices of foraging derived from high temporal resolution dive and accelerometry data to predict foraging behaviour in an extensive, low resolution dataset from CTD-Satellite Relay Data Loggers (CTD-SRDLs). A sample of 37 post-breeding SES females were used to construct a predictive model applied to demersal and pelagic dive strategies relating prey encounter events (PEE) to dive parameters (dive duration, bottom duration, hunting-time, maximum depth, ascent speed, descent speed, sinuosity, and horizontal speed) for each strategy. We applied these models to a second sample of 35 seals, 20 males and 15 females, during the post-moult foraging trip to the Antarctic continental shelf between 2004 and 2013, which did not have fine-scale behavioural data. The females were widely distributed with important foraging activity south of the Southern Boundary Front, while males predominately travelled to the south-eastern part of the East Antarctica region. Combining our predictions of PEE with environmental features (sea ice concentration, water masses at the bottom phase of dives, bathymetry and slope index) we found higher foraging activity for females over shallower seabed depths and at the boundary between the overlying Antarctic Surface Water (AASW) and the underlying Modified Circumpolar Deep Water (MCDW). Increased biological activity associated with the upper boundary of MCDW, may provide

  5. Obliquity-paced Pliocene West Antarctic ice sheet oscillations

    Science.gov (United States)

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

    2009-01-01

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

  6. Greenland Ice Sheet response to mid-Pliocene summer Arctic sea ice-free conditions

    Science.gov (United States)

    Koenig, S. J.; DeConto, R.; Pollard, D.

    2011-12-01

    A critical uncertainty in future predictions of climate and sea level is the response of the cryosphere. Proxy reconstructions for the mid-Pliocene Arctic Ocean (~ 3 Ma) are indicative of summer Arctic ice-free conditions and higher than modern sea surface temperatures, conditions that are analogous to projections for the end of the 21st century. We implement available mid-Pliocene boundary conditions into a fully-coupled Global Circulation Model with interactive vegetation. We use a 3-D thermo-mechanical ice sheet-shelf model to simulate the equilibrated response of the Greenland Ice Sheet (GIS) to the combined effect of reduced sea ice conditions and increased sea surface temperatures during the mid-Pliocene Warm Period. Reductions in Arctic sea ice are shown to enhance ocean/land-to-atmosphere fluxes, increasing heat and moisture transport in the high latitudes. In particular, changes in the North Atlantic exert a strong influence on the storm track and seasonal temperatures and precipitation over Greenland. Despite increased precipitation, warmer temperatures generally reduce snow mass balance. As a result, an initial present-day ice sheet forced by Pliocene climate undergoes rapid melting, limiting the ice sheet to the only highest elevations in South and East Greenland. Once the ice sheet is lost, local surface characteristics and associated feedbacks dominates Greenland climate, precluding the regrowth of the ice sheet. Depending on the initial state of the ice sheet, the equilibrated ice sheet loss is equivalent to between 5.8 to 6.4 m of sea level. We assess the sensitivity of the GIS to Pliocene forcing and internal feedbacks, adding to the understanding of land-ice sea-ice hysteresis in a world warmer than today.

  7. Improved Bathymetry Resolution in the Ross Sea from Aerogravity and Magnetics: Examples from Operation IceBridge.

    Science.gov (United States)

    Tinto, K. J.; Cochran, J. R.; Bell, R. E.; Charles, K.; Burton, B.

    2014-12-01

    The Ross Ice Shelf, located in the embayment between East and West Antarctica, is one of the largest underexplored patches of ocean on the planet. Sediment cores show that the Ross Ice Shelf can disintegrate during some interglacial periods. The conditions required for sudden collapse are not well constrained. A key to understanding the dynamics and long-term stability of the Ross Ice Shelf system is having high-resolution constraints on its boundary conditions, including sea floor bathymetry. The sea floor under the Ross Ice Shelf has developed in response to both the tectonic development of the West Antarctic Rift and the glacial signature of the waxing and waning Antarctic Ice Sheets. A mixture of fabrics and orientations in its bathymetry reflect this complex development. However, present oceanographic models of water circulation under the ice are based on low-resolution bathymetric maps drawn from stations spaced 55 km apart obtained during the RIGGS project in the 1970s. In contrast, most of the bathymetry of the world's oceans has been mapped to approximately 15 km resolution from satellite altimetry and much higher resolution from acoustic surveys. Improvement of Ross Ice Shelf bathymetry can be achieved from combined analysis and inversion of gravity and magnetic data acquired from airborne surveys over the Ross Ice Shelf. Survey lines flown in 2013 by Operation IceBridge, with the Sander Geophysics Ltd AIRGrav system over the central and northern Ross Embayment provide a tenfold increase, to 5 km, of the along track resolution of bathymetry. Newly resolved bathymetric highs and lows have amplitudes of up to 200 km. Combining the gravity and magnetic surveys also reveals the differing geology across the embayment. Results from these surveys, including comparison with ship-based bathymetry data from the Ross Sea, demonstrate the value of gravity and magnetic surveys for mapping the bathymetry of the Ross Ice Shelf and the need for more comprehensive

  8. Spring hunting of European roe deer in Vojvodina: Age structure and trophy value

    OpenAIRE

    2005-01-01

    Trophies of the European roe deer are the main source of income in Vojvodina hunting grounds managed by hunting associations. The specificity of site conditions (agro-biotope) aggravates the hunting, especially regarding the assessment of the age and trophy value, so the best males are hunted before they reach the culmination of trophy development. The aim of this study is to define reliably the age of males in spring hunting and to analyze their trophy structure. The study results show that,...

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

    Science.gov (United States)

    Nowicki, Sophie; Bindschadler, Robert A.; Abe-Ouchi, Ayako; Aschwanden, Andy; Bueler, Ed; Choi, Hyengu; Fastook, Jim; Granzow, Glen; Greve, Ralf; Gutowski, Gail; Herzfeld, Ute; Jacskon, Charles; Johnson, Jesse; Khroulev, Constantine; Larour, Eric; Levermann, Anders; Lipscomb, William H.; Martin, Maria A.; Morlighem, Mathieu; Parizek, Byron R; Pollard, David; Price, Stephen F.; Seroussi, Helene; Walker, Ryan; Wang, Wei Li

    2013-01-01

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

  10. Impact of melt ponds on Arctic sea ice in past and future climate as simulated by MPI-ESN

    OpenAIRE

    E. Roeckner; T. Mauritsen; Esch, M.; Brokopf, R.

    2012-01-01

    The impact of melt ponds on Arctic sea ice is estimated from model simulations of the historical and future climate. The simulations were performed with and without the effect of melt ponds on sea ice melt, respectively. In the last thirty years of the historical simulations, melt ponds develop predominantly in the continental shelf regions and in the Canadian archipelago. Accordingly, the ice albedo in these regions is systematically smaller than in the no-pond simulations, the sea ice melt ...

  11. Impact of melt ponds on Arctic sea ice in past and future climates as simulated by MPI-ESM

    OpenAIRE

    Erich Roeckner; Thorsten Mauritsen; Renate Brokopf

    2012-01-01

    The impact of melt ponds on Arctic sea ice is estimated from model simulations of the historical and future climate. The simulations were performed with and without the effect of melt ponds on sea ice melt, respectively. In the last thirty years of the historical simulations, melt ponds develop predominantly in the continental shelf regions and in the Canadian archipelago. Accordingly, the ice albedo in these regions is systematically smaller than in the no-pond simulations, the sea ice melt ...

  12. The Bering Sea: Communication with the Western Subarctic Gyre, Mesoscale Activity, Shelf-Basin Exchange, and the Flow Through Bering Strait

    Science.gov (United States)

    2011-03-01

    occurs primarily in the north, ice is advected southward due to wind stress, and ice melt occurs at the thermodynamic limit. Subsequently, as meltwater ...advect further north onto the Bering-Chukchi shelf. Arctic freshwater budgets were also improved, with increased freshwater storage in the Greenland ...Treguier A.M., Scheinert M., Penduff T. (2009) A model-based study of ice and freshwater transport variability along both sides of Greenland . Climate

  13. Sport Hunting Decision Document Package for Parker River NWR

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This hunt plan initiates the effort to reduce the Parker River National Wildlife Refuge’s white-tailed deer herd numbers to a level compatible with the habitat's...

  14. Environmental Assessment : Marais Des Cygnes NWR hunt plan

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — The U.S. Fish and Wildlife Service proposes to allow hunting of resident and migratory game species on three-quarters of the existing acreage of Marais des Cygnes...

  15. Walk-In Hunting Access (WIHA) Fall 2011

    Data.gov (United States)

    Kansas Data Access and Support Center — This shapefile represents the private lands leased by the Kansas Department of Wildlife, Parks and Tourism (KDWPT) for fall 2011 public hunting access through the...

  16. St. Catherine Creek NWR Hunting Season Harvest Totals

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — Data summaries from hunting that occurs on St. Catherine Creek NWR. Reports include summarized harvest and hunter effort data and basic analysis of these data.

  17. Mingo National Wildlife Refuge : Hunting and Fishing Plan

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This plan provides guidelines for the administration of hunting activity and for the development, maintenance, and enforcement of regulations and guidelines on Mingo...

  18. Valentine National Wildlife Refuge : Hunting and fishing regulations

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This brochure is refuge-specific fishing regulations, hunting regulations and a map showing refuge use areas for the Valentine National Wildlife Refuge.

  19. Environmental Assessment : Crescent Lake National Wildlife Refuge Hunting Plan

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This Environmental Assessment (EA) is for the implementation of the Crescent Lake National Wildlife Refuge Hunting Plan that serves as a step down management plan to...

  20. Hunt Plan for Montezuma National Wildlife Refuge 1995

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — The objectives of the white-tailed deer hunting program are: 1. To maintain the deer population at a level compatible with the quality and diversity of habitats not...