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Sample records for ross ice shelf

  1. 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

  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. 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.

  4. Ross Ice Shelf airstream driven by polar vortex cyclone

    Science.gov (United States)

    Schultz, Colin

    2012-07-01

    The powerful air and ocean currents that flow in and above the Southern Ocean, circling in the Southern Hemisphere's high latitudes, form a barrier to mixing between Antarctica and the rest of the planet. Particularly during the austral winter, strong westerly winds isolate the Antarctic continent from heat, energy, and mass exchange, bolstering the scale of the annual polar ozone depletion and driving the continent's record-breaking low temperatures. Pushing through this wall of high winds, the Ross Ice Shelf airstream (RAS) is responsible for a sizable amount of mass and energy exchange from the Antarctic inland areas to lower latitudes. Sitting due south of New Zealand, the roughly 470,000-square-kilometer Ross Ice Shelf is the continent's largest ice shelf and a hub of activity for Antarctic research. A highly variable lower atmospheric air current, RAS draws air from the inland Antarctic Plateau over the Ross Ice Shelf and past the Ross Sea. Drawing on modeled wind patterns for 2001-2005, Seefeldt and Cassano identify the primary drivers of RAS.

  5. 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.

  6. Understanding Ice Shelf Basal Melting Using Convergent ICEPOD Data Sets: ROSETTA-Ice Study of Ross Ice Shelf

    Science.gov (United States)

    Bell, R. E.; Frearson, N.; Tinto, K. J.; Das, I.; Fricker, H. A.; Siddoway, C. S.; Padman, L.

    2017-12-01

    The future stability of the ice shelves surrounding Antarctica will be susceptible to increases in both surface and basal melt as the atmosphere and ocean warm. The ROSETTA-Ice program is targeted at using the ICEPOD airborne technology to produce new constraints on Ross Ice Shelf, the underlying ocean, bathymetry, and geologic setting, using radar sounding, gravimetry and laser altimetry. This convergent approach to studying the ice-shelf and basal processes enables us to develop an understanding of the fundamental controls on ice-shelf evolution. This work leverages the stratigraphy of the ice shelf, which is detected as individual reflectors by the shallow-ice radar and is often associated with surface scour, form close to the grounding line or pinning points on the ice shelf. Surface accumulation on the ice shelf buries these reflectors as the ice flows towards the calving front. This distinctive stratigraphy can be traced across the ice shelf for the major East Antarctic outlet glaciers and West Antarctic ice streams. Changes in the ice thickness below these reflectors are a result of strain and basal melting and freezing. Correcting the estimated thickness changes for strain using RIGGS strain measurements, we can develop decadal-resolution flowline distributions of basal melt. Close to East Antarctica elevated melt-rates (>1 m/yr) are found 60-100 km from the calving front. On the West Antarctic side high melt rates primarily develop within 10 km of the calving front. The East Antarctic side of Ross Ice Shelf is dominated by melt driven by saline water masses that develop in Ross Sea polynyas, while the melting on the West Antarctic side next to Hayes Bank is associated with modified Continental Deep Water transported along the continental shelf. The two sides of Ross Ice Shelf experience differing basal melt in part due to the duality in the underlying geologic structure: the East Antarctic side consists of relatively dense crust, with low amplitude

  7. Changes on the ice plain of Ice Stream B and Ross Ice Shelf

    Science.gov (United States)

    Shabtaie, Sion

    1993-01-01

    During the 1970's and 1980's, nearly 200 stations from which accurate, three dimensional position fixes have been obtained from TRANSIT satellites were occupied throughout the Ross Ice Shelf. We have transformed the elevations obtained by satellite altimetry to the same geodetic datum, and then applied a second transformation to reduce the geodetic heights to elevations above mean sea level using the GEM-10C geoidal height. On the IGY Ross Ice Shelf traverse between Oct. 1957 and Feb. 1958, an accurate method of barometric altimetry was used on a loop around the ice shelf that was directly tied to the sea at both ends of the travel route, thus providing absolute elevations. Comparisons of the two sets of data at 32 station pairs on floating ice show a mean difference of 0 +/- 1 m. The elevation data were also compared with theoretical values of elevations for a hydrostatically floating ice shelf. The mean difference between theoretical and measured values of elevations is -2 +/- 1 m.

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

    Science.gov (United States)

    Delaney, A.; Arcone, S.

    2005-12-01

    We have used 400-MHz ground penetrating radar (GPR) to detect crevasses within a shear zone on the Ross Ice Shelf, Antarctica, to support traverse operations. The transducer was attached to a 6.5-m boom and pushed ahead of an enclosed tracked vehicle. Profile speeds of 4.8-11.3 km / hr allowed real-time crevasse image display and a quick, safe stop when required. Thirty-two crevasses were located with radar along the 4.8 km crossing. Generally, crevasse radar images were characterized by dipping reflections above the voids, high-amplitude reflections originating from ice layers at the base of the snow-bridges, and slanting, diffracting reflections from near-vertical crevasse walls. New cracks and narrow crevasses (back-filling with bulldozed snow, afforded an opportunity to ground-truth GPR interpretations by comparing void size and snow-bridge geometry with the radar images. While second and third season radar profiles collected along the identical flagged route confirmed stability of the filled crevasses, those profiles also identified several new cracks opened by ice extension. Our experiments demonstrate capability of high-frequency GPR in a cold-snow environment for both defining snow layers and locating voids.

  9. The surface climatology of the Ross Ice Shelf Antarctica.

    Science.gov (United States)

    Costanza, Carol A; Lazzara, Matthew A; Keller, Linda M; Cassano, John J

    2016-12-01

    The University of Wisconsin-Madison Antarctic Automatic Weather Station (AWS) project has been making meteorological surface observations on the Ross Ice Shelf (RIS) for approximately 30 years. This network offers the most continuous set of routine measurements of surface meteorological variables in this region. The Ross Island area is excluded from this study. The surface climate of the RIS is described using the AWS measurements. Temperature, pressure, and wind data are analysed on daily, monthly, seasonal, and annual time periods for 13 AWS across the RIS. The AWS are separated into three representative regions - central, coastal, and the area along the Transantarctic Mountains - in order to describe specific characteristics of sections of the RIS. The climatology describes general characteristics of the region and significant changes over time. The central AWS experiences the coldest mean temperature, and the lowest resultant wind speed. These AWSs also experience the coldest potential temperatures with a minimum of 209.3 K at Gill AWS. The AWS along the Transantarctic Mountains experiences the warmest mean temperature, the highest mean sea-level pressure, and the highest mean resultant wind speed. Finally, the coastal AWS experiences the lowest mean pressure. Climate indices (MEI, SAM, and SAO) are compared to temperature and pressure data of four of the AWS with the longest observation periods, and significant correlation is found for most AWS in sea-level pressure and temperature. This climatology study highlights characteristics that influence the climate of the RIS, and the challenges of maintaining a long-term Antarctic AWS network. Results from this effort are essential for the broader Antarctic meteorology community for future research.

  10. Duality of Ross Ice Shelf systems: crustal boundary, ice sheet processes and ocean circulation from ROSETTA-Ice surveys

    Science.gov (United States)

    Tinto, K. J.; Siddoway, C. S.; Padman, L.; Fricker, H. A.; Das, I.; Porter, D. F.; Springer, S. R.; Siegfried, M. R.; Caratori Tontini, F.; Bell, R. E.

    2017-12-01

    Bathymetry beneath Antarctic ice shelves controls sub-ice-shelf ocean circulation and has a major influence on the stability and dynamics of the ice sheets. Beneath the Ross Ice Shelf, the sea-floor bathymetry is a product of both tectonics and glacial processes, and is influenced by the processes it controls. New aerogeophysical surveys have revealed a fundamental crustal boundary bisecting the Ross Ice Shelf and imparting a duality to the Ross Ice Shelf systems, encompassing bathymetry, ocean circulation and ice flow history. The ROSETTA-Ice surveys were designed to increase the resolution of Ross Ice Shelf mapping from the 55 km RIGGS survey of the 1970s to a 10 km survey grid, flown over three years from New York Air National Guard LC130s. Radar, LiDAR, gravity and magnetic instruments provide a top to bottom profile of the ice shelf and the underlying seafloor, with 20 km resolution achieved in the first two survey seasons (2015 and 2016). ALAMO ocean-profiling floats deployed in the 2016 season are measuring the temperature and salinity of water entering and exiting the sub-ice water cavity. A significant east-west contrast in the character of the magnetic and gravity fields reveals that the lithospheric boundary between East and West Antarctica exists not at the base of the Transantarctic Mountains (TAM), as previously thought, but 300 km further east. The newly-identified boundary spatially coincides with the southward extension of the Central High, a rib of shallow basement identified in the Ross Sea. The East Antarctic side is characterized by lower amplitude magnetic anomalies and denser TAM-type lithosphere compared to the West Antarctic side. The crustal structure imparts a fundamental duality on the overlying ice and ocean, with deeper bathymetry and thinner ice on the East Antarctic side creating a larger sub-ice cavity for ocean circulation. The West Antarctic side has a shallower seabed, more restricted ocean access and a more complex history of

  11. Multi-Decadal Averages of Basal Melt for Ross Ice Shelf, Antarctica Using Airborne Observations

    Science.gov (United States)

    Das, I.; Bell, R. E.; Tinto, K. J.; Frearson, N.; Kingslake, J.; Padman, L.; Siddoway, C. S.; Fricker, H. A.

    2017-12-01

    Changes in ice shelf mass balance are key to the long term stability of the Antarctic Ice Sheet. Although the most extensive ice shelf mass loss currently is occurring in the Amundsen Sea sector of West Antarctica, many other ice shelves experience changes in thickness on time scales from annual to ice age cycles. Here, we focus on the Ross Ice Shelf. An 18-year record (1994-2012) of satellite radar altimetry shows substantial variability in Ross Ice Shelf height on interannual time scales, complicating detection of potential long-term climate-change signals in the mass budget of this ice shelf. Variability of radar signal penetration into the ice-shelf surface snow and firn layers further complicates assessment of mass changes. We investigate Ross Ice Shelf mass balance using aerogeophysical data from the ROSETTA-Ice surveys using IcePod. We use two ice-penetrating radars; a 2 GHz unit that images fine-structure in the upper 400 m of the ice surface and a 360 MHz radar to identify the ice shelf base. We have identified internal layers that are continuous along flow from the grounding line to the ice shelf front. Based on layer continuity, we conclude that these layers must be the horizons between the continental ice of the outlet glaciers and snow accumulation once the ice is afloat. We use the Lagrangian change in thickness of these layers, after correcting for strain rates derived using modern day InSAR velocities, to estimate multidecadal averaged basal melt rates. This method provides a novel way to quantify basal melt, avoiding the confounding impacts of spatial and short-timescale variability in surface accumulation and firn densification processes. Our estimates show elevated basal melt rates (> -1m/yr) around Byrd and Mullock glaciers within 100 km from the ice shelf front. We also compare modern InSAR velocity derived strain rates with estimates from the comprehensive ground-based RIGGS observations during 1973-1978 to estimate the potential magnitude of

  12. Geometric controls of the flexural gravity waves on the Ross Ice Shelf

    Science.gov (United States)

    Sergienko, O. V.

    2017-12-01

    Long-period ocean waves, formed locally or at distant sources, can reach sub-ice-shelf cavities and excite coupled motion in the cavity and the ice shelf - flexural gravity waves. Three-dimensional numerical simulations of the flexural gravity waves on the Ross Ice Shelf show that propagation of these waves is strongly controlled by the geometry of the system - the cavity shape, its water-column thickness and the ice-shelf thickness. The results of numerical simulations demonstrate that propagation of the waves is spatially organized in beams, whose orientation is determined by the direction of the of the open ocean waves incident on the ice-shelf front. As a result, depending on the beams orientation, parts of the Ross Ice Shelf experience significantly larger flexural stresses compared to other parts where the flexural gravity beams do not propagate. Very long-period waves can propagate farther away from the ice-shelf front exciting flexural stresses in the vicinity of the grounding line.

  13. Breaking Ice 2: A rift system on the Ross Ice Shelf as an analog for tidal tectonics on icy moons

    Science.gov (United States)

    Brunt, K. M.; Hurford, T., Jr.; Schmerr, N. C.; Sauber, J. M.; MacAyeal, D. R.

    2016-12-01

    Ice shelves are the floating regions of the polar ice sheets. Outside of the influence of the narrow region of their grounding zone, they are fully hydrostatic and strongly influenced by the ocean tides. Recent observational and modeling studies have assessed the effect of tides on ice shelves, including: the tidal influence on the ice-shelf surface height, which changes by as much as 6 to 7 m on the southern extreme of the Ronne-Filchner Ice Shelf; the tidal modulation of the ice-shelf horizontal flow velocities, which changes the mean ice-flow rate by as much as two fold on the Ross Ice Shelf; and the tidal contribution to fracture and rift propagation, which eventually leads to iceberg calving. Here, we present the analysis of 16 days of continuous GPS data from a rift system near the front of the Ross Ice Shelf. While the GPS sites were installed for a different scientific investigation, and not optimized to assess tidal rifting mechanics, they provide a first-order sense of the tidal evolution of the rift system. These analyses can be used as a terrestrial analog for tidal activity on icy satellites, such as Europa and Enceladus, moons of Jupiter and Saturn, respectively. Using remote sensing and modeling of the Ross Ice Shelf rift system, we can investigate the geological processes observed on icy satellites and advance modeling efforts of their tidal-tectonic evolution.

  14. Mapping Ross Ice Shelf with ROSETTA-Ice airborne laser altimetry

    Science.gov (United States)

    Becker, M. K.; Fricker, H. A.; Padman, L.; Bell, R. E.; Siegfried, M. R.; Dieck, C. C. M.

    2017-12-01

    The Ross Ocean and ice Shelf Environment and Tectonic setting Through Aerogeophysical surveys and modeling (ROSETTA-Ice) project combines airborne glaciological, geological, and oceanographic observations to enhance our understanding of the history and dynamics of the large ( 500,000 square km) Ross Ice Shelf (RIS). Here, we focus on the Light Detection And Ranging (LiDAR) data collected in 2015 and 2016. This data set represents a significant advance in resolution: Whereas the last attempt to systematically map RIS (the surface-based RIGGS program in the 1970s) was at 55 km grid spacing, the ROSETTA-Ice grid has 10-20 km line spacing and much higher along-track resolution. We discuss two different strategies for processing the raw LiDAR data: one that requires proprietary software (Riegl's RiPROCESS package), and one that employs open-source programs and libraries. With the processed elevation data, we are able to resolve fine-scale ice-shelf features such as the "rampart-moat" ice-front morphology, which has previously been observed on and modeled for icebergs. This feature is also visible in the ROSETTA-Ice shallow-ice radar data; comparing the laser data with radargrams provides insight into the processes leading to their formation. Near-surface firn state and total firn air content can also be investigated through combined analysis of laser altimetry and radar data. By performing similar analyses with data from the radar altimeter aboard CryoSat-2, we demonstrate the utility of the ROSETTA-Ice LiDAR data set in satellite validation efforts. The incorporation of the LiDAR data from the third and final field season (December 2017) will allow us to construct a DEM and an ice thickness map of RIS for the austral summers of 2015-2017. These products will be used to validate and extend observations of height changes from satellite radar and laser altimetry, as well as to update regional models of ocean circulation and ice dynamics.

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

    Science.gov (United States)

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

    1992-01-01

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

  16. Depositional history of artificial radionuclides in the Ross Ice Shelf, Antarctica

    International Nuclear Information System (INIS)

    Koide, M.; Michel, R.; Goldberg, E.D.; Herron, M.M.; Langway, C.C. Jr.

    1979-01-01

    The annual fluxes of artificial radionuclides ( 238 Pu, sup(239 + 240)Pu, 241 Am, 137 Cs, 90 Sr and 3 H) from the atmosphere to the Ross Ice Shelf in Antarctica were determined from measurements in strata dated by 201 Pb. Recognizable sources include the U.S tests (Mike-Ivy and Castle Hill) in the early 1950s, the U.S.S.R. tests of the early 1960s, the SNAP-9A burnup of 1964 and the French and Chinese tests in the late 1960s and 1970s. There are several problems still awaiting resolution: the differences in atmospheric chemistries of fission products and of transuranics produced in weapons tests and the anomalous fluxes of 238 Pu to the ice shelf which do not appear to reflect a one-year stratospheric residence. There is no evidence for a smearing of the fallout record as a consequence of diffusion of these radionuclides in the glacial column. (Auth.)

  17. Ice Stream Slowdown Will Drive Long-Term Thinning of the Ross Ice Shelf, With or Without Ocean Warming

    Science.gov (United States)

    Campbell, Adam J.; Hulbe, Christina L.; Lee, Choon-Ki

    2018-01-01

    As time series observations of Antarctic change proliferate, it is imperative that mathematical frameworks through which they are understood keep pace. Here we present a new method of interpreting remotely sensed change using spatial statistics and apply it to the specific case of thickness change on the Ross Ice Shelf. First, a numerical model of ice shelf flow is used together with empirical orthogonal function analysis to generate characteristic patterns of response to specific forcings. Because they are continuous and scalable in space and time, the patterns allow short duration observations to be placed in a longer time series context. Second, focusing only on changes that are statistically significant, the synthetic response surfaces are used to extract magnitude and timing of past events from the observational data. Slowdown of Kamb and Whillans Ice Streams is clearly detectable in remotely sensed thickness change. Moreover, those past events will continue to drive thinning into the future.

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

    Science.gov (United States)

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

    2017-12-01

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

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

    Science.gov (United States)

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

    2017-12-01

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

  20. Ocean stratification reduces melt rates at the grounding zone of the Ross Ice Shelf

    Science.gov (United States)

    Begeman, C. B.; Tulaczyk, S. M.; Marsh, O.; Mikucki, J.; Stanton, T. P.; Hodson, T. O.; Siegfried, M. R.; Powell, R. D.; Christianson, K. A.; King, M. A.

    2017-12-01

    Ocean-driven melting of ice shelves is often invoked as the primary mechanism for triggering ice loss from Antarctica. However, due to the difficulty in accessing the sub-ice-shelf ocean cavity, the relationship between ice-shelf melt rates and ocean conditions is poorly understood, particularly near the transition from grounded to floating ice, known as the grounding zone. Here we present the first borehole oceanographic observations from the grounding zone of Antarctica's largest ice shelf. Contrary to predictions that tidal currents near grounding zones should mix the water column, driving high ice-shelf melt rates, we find a stratified sub-ice-shelf water column. The vertical salinity gradient dominates stratification over a weakly unstable vertical temperature gradient; thus, stratification takes the form of a double-diffusive staircase. These conditions limit vertical heat fluxes and lead to low melt rates in the ice-shelf grounding zone. While modern grounding zone melt rates may presently be overestimated in models that assume efficient tidal mixing, the high sensitivity of double-diffusive staircases to ocean freshening and warming suggests future melt rates may be underestimated, biasing projections of global sea-level rise.

  1. 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

  2. Microseismicity along major Ross Ice Shelf rift resulting from thermal contraction of the near-surface firn layer

    Science.gov (United States)

    Olinger, S.; Wiens, D.; Aster, R. C.; Bromirski, P. D.; Gerstoft, P.; Nyblade, A.; Stephen, R. A.

    2017-12-01

    Seismicity within ice shelves arises from a variety of sources, including calving, rifting, and movement along internal discontinuities. In this study, we identify and locate cryoseisms in the Ross Ice Shelf (RIS) to better understand ice shelf internal stress and deformation. We use data from a two-year 34-station deployment of broadband seismographs operational from December 2014 - November 2016. Two lines of seismographs intersect near 79Sº, 180º close to a large rift, and cryoseisms were recorded by up to 10 seismographs within 40 km of the rift tip. We identified 3600 events from 2015 and grouped them by quality based on the number of stations recording and signal-to-noise ratio. The events show a long-period character compared to similar magnitude tectonic earthquakes, with peak amplitudes at 1-4 Hz and P, S, longitudinal, and surface wave arrivals. Cross correlation analysis shows that the events cannot be divided into a small number of repeating event clusters with identical waveforms. 262 A-quality events were located with a least-squares algorithm using P and S arrivals, and the resulting locations show strong spatial correlation with the rift, with events distributed along the rift rather than concentrated at the tip or any other specific feature. The events do not show teleseismic triggering, and did not occur with increased frequency following the Illapel earthquake (8.3 Mw) or subsequent tsunami. Instead, we note a concentration of activity during the winter months, with several days exhibiting particularly high seismicity rates. We compare the full catalog of events with temperature data from the Antarctic Weather Stations (Lazzara et al, 2012) and find that the largest swarms occur during the most rapid periods of seasonal temperature decline. Internal stress in ice floes and shelves is known to vary with air temperature; as temperature drops, the upper layer of ice thermally contracts, causing near-surface extensional stress to accumulate. We

  3. Near-surface elastic changes in the Ross Ice Shelf arising from transient storm and melt forcing observed with high-frequency ambient seismic noise

    Science.gov (United States)

    Chaput, J.; Aster, R. C.; Baker, M. G.; Gerstoft, P.; Bromirski, P. D.; Nyblade, A.; Stephen, R. A.; Wiens, D.

    2017-12-01

    Ice shelf collapse can herald subsequent grounded ice instability. However, robust understanding of external mechanisms capable of triggering rapid changes remains elusive. Improved understanding therefore requires improved remote and in-situ measurements of ice shelf properties. Using nearly three years of continuous data from a recently deployed 34-station broadband seismic array on the Ross Ice Shelf, we analyze persistent temporally varying, anisotropic near-surface resonant wave modes at frequencies above 1 Hz that are highly sensitive to small changes in elastic shelf properties to depths of tens of m. We further find that these modes exhibit both progressive (on the scale of months) and rapid (on the scale of hours) changes in frequency content. The largest and most rapid excursions are associated with forcing from local storms, and with a large regional ice shelf melt event in January 2016. We hypothesize that temporally variable behavior of the resonance features arises from wind slab formation during storms and/or to porosity changes, and to the formation of percolation-related refrozen layers and thinning in the case of surface melting. These resonance variations can be reproduced and inverted for structural changes using numerical wave propagation models, and thus present an opportunity for 4-D structural monitoring of shallow ice shelf elasticity and structure using long-duration seismic recordings.

  4. 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.

  5. 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.

  6. 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.

  7. Climatology and decadal variability of the Ross Sea shelf waters

    Directory of Open Access Journals (Sweden)

    A. Russo

    2011-06-01

    Full Text Available The World Ocean Database 2001 data located in the Ross Sea (named WOD01 and containing data in this region since 1928 are merged with recent data collected by the Italian expeditions (CLIMA dataset in the period November 1994-February 2004 in the same area. From this extended dataset, austral summer climatologies of the main Ross Sea subsurface, intermediate and bottom water masses: High Salinity Shelf Water (HSSW, Low Salinity Shelf Water (LSSW, Ice Shelf Water (ISW and Modified Circumpolar Deep Water (MCDW have been drawn. The comparison between the WOD01_1994 climatologies (a subset of the WOD01 dataset until April 1994 and the CLIMA ones for the period 1994/95-2003/04 showed significant changes occurred during the decade. The freshening of the Ross Sea shelf waters which occurred during the period 1960-2000, was confirmed by our analysis in all the main water masses, even though with a spatially varying intensity. Relevant variations were found for the MCDW masses, which appeared to reduce their presence and to deepen; this can be ascribed to the very limited freshening of the MCDW core, which allowed an increased density with respect to the surrounding waters. Variations in the MCDW properties and extension could have relevant consequences, e.g. a decreased Ross Ice Shelf basal melting or a reduced supply of nutrients, and may also be indicative of a reduced thermohaline circulation within the Ross Sea. Shelf Waters (SW having neutral density γn > 28.7 Kg m-3, which contribute to form the densest Antarctic Bottom Waters (AABW, showed a large volumetric decrease in the 1994/95-2003/04 decade, most likely as a consequence of the SW freshening.

  8. Constraints on ice volume changes of the WAIS and Ross Ice Shelf since the LGM based on cosmogenic exposure ages in the Darwin-Hatherton glacial system of the Transantarctic Mountains

    Science.gov (United States)

    Fink, David; Storey, Bryan; Hood, David; Joy, Kurt; Shulmeister, James

    2010-05-01

    Quantitative assessment of the spatial and temporal scale of ice volume change of the West Antarctic ice sheet (WAIS) and Ross Ice Shelf since the last glacial maximum (LGM) ~20 ka is essential to accurately predict ice sheet response to current and future climate change. Although global sea level rose by approximately 120 metres since the LGM, the contribution of polar ice sheets is uncertain and the timing of any such contribution is controversial. Mackintosh et al (2007) suggest that sectors of the EAIS, similar to those studied at Framnes Mountains where the ice sheet slowly calves at coastal margins, have made marginal contributions to global sea-level rise between 13 and 7 ka. In contrast, Stone et al (2003) document continuing WAIS decay during the mid-late Holocene, raising the question of what was the response of the WAIS since LGM and into the Holocene. Terrestrial evidence is restricted to sparse coastal oasis and ice free mountains which archive limits of former ice advances. Mountain ranges flanking the Darwin-Hatherton glaciers exhibit well-defined moraines, weathering signatures, boulder rich plateaus and glacial tills, which preserve the evidence of advance and retreat of the ice sheet during previous glacial cycles. Previous studies suggest a WAIS at the LGM in this location to be at least 1,000 meters thicker than today. As part of the New Zealand Latitudinal Gradient Project along the Transantarctic, we collected samples for cosmogenic exposure dating at a) Lake Wellman area bordering the Hatherton Glacier, (b) Roadend Nunatak at the confluence of the Darwin and Hatherton glaciers and (c) Diamond Hill which is positioned at the intersection of the Ross Ice Shelf and Darwin Glacier outlet. While the technique of exposure dating is very successful in mid-latitude alpine glacier systems, it is more challenging in polar ice-sheet regions due to the prevalence of cold-based ice over-riding events and absence of outwash processes which removes

  9. 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.

  10. 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

  11. 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.

  12. Ross Ice Drainage System (RIDS) Glaciochemical Analysis, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — The Ross Ice Drainage System (RIDS) project provides a high-resolution record of atmospheric chemical deposition taken from several ice cores and snow pits located...

  13. On the dense water spreading off the Ross Sea shelf (Southern Ocean)

    Science.gov (United States)

    Budillon, G.; Gremes Cordero, S.; Salusti, E.

    2002-07-01

    In this study, current meter and hydrological data obtained during the X Italian Expedition in the Ross Sea (CLIMA Project) are analyzed. Our data show a nice agreement with previous data referring to the water masses present in this area and their dynamics. Here, they are used to further analyze the mixing and deepening processes of Deep Ice Shelf Water (DISW) over the northern shelf break of the Ross Sea. In more detail, our work is focused on the elementary mechanisms that are the most efficient in removing dense water from the shelf: either classical mixing effects or density currents that interact with some topographic irregularity in order to drop to deeper levels, or also the variability of the Antarctic Circumpolar Current (ACC) which, in its meandering, can push the dense water off the shelf, thus interrupting its geostrophic flow. We also discuss in detail the (partial) evidence of dramatic interactions of the dense water with bottom particulate, of geological or biological origin, thus generating impulsive or quasi-steady density-turbidity currents. This complex interaction allows one to consider bottom particular and dense water as a unique self-interacting system. In synthesis, this is a first tentative analysis of the effect of bottom particulate on the dense water dynamics in the Ross Sea.

  14. Early Winter Sea Ice Dynamics in the Ross Sea from In Situ and Satellite Observations

    Science.gov (United States)

    Maksym, T.; Ackley, S. F.; Stammerjohn, S. E.; Tison, J. L.; Hoeppner, K.

    2017-12-01

    The Ross Sea sea ice cover is one of the few regions of the cryosphere that have been expanding in recent decades. However, 2017 saw a significantly delayed autumn ice advance and record low early winter sea ice extent. Understanding the causes and impacts of this variability has been hampered by a lack of in situ observations. A winter cruise into the Ross Sea in April-June 2017 provided some of the only in situ winter observations of sea ice processes in this region in almost 20 years. We present a first look at data from arrays of drifting buoys deployed in the ice pack and outflow from these polynyas, supplemented by a suite of high-resolution synthetic aperture radar (SAR) data. Additional observations included high-resolution sonar imagery of ice deformation features from an autonomous underwater vehicle, shipboard visual observations of sea ice properties, and in situ measurements of snow and thickness and structural properties. These data show that the delay in ice advance led to a thin, highly dynamic sea ice pack, with substantial ice production and export from the Ross Ice Shelf and Terra Nova Bay polynyas. Despite these high rates of ice production, the pack ice remained thin due to rapid export and northward drift. Compared to the only prior winter observations made in 1995 and 1998, the ice was thinner, with less ridging and snow cover, reflecting a younger ice cover. Granular ice was less prevalent than in these prior cruises, particularly in the outer pack, likely due to less snow ice formation and less pancake ice formation at the advancing ice edge. Despite rapid basal ice growth, the buoy data suggest that deformation may be the dominant mechanism for sea ice thickening in the pack once an initial ice cover forms.

  15. Endmembers of Ice Shelf Melt

    Science.gov (United States)

    Boghosian, A.; Child, S. F.; Kingslake, J.; Tedesco, M.; Bell, R. E.; Alexandrov, O.; McMichael, S.

    2017-12-01

    Studies of surface melt on ice shelves have defined a spectrum of meltwater behavior. On one end the storage of meltwater in persistent surface ponds can trigger ice shelf collapse as in the 2002 event leading to the disintegration of the Larsen B Ice Shelf. On the other, meltwater export by rivers can stabilize an ice shelf as was recently shown on the Nansen Ice Shelf. We explore this dichotomy by quantifying the partitioning between stored and transported water on two glaciers adjacent to floating ice shelves, Nimrod (Antarctica) and Peterman (Greenland). We analyze optical satellite imagery (LANDSAT, WorldView), airborne imagery (Operation IceBridge, Trimetrogon Aerial Phototography), satellite radar (Sentinel-1), and digital elevation models (DEMs) to categorize surface meltwater fate and map the evolution of ice shelf hydrology and topographic features through time. On the floating Peterman Glacier tongue a sizable river exports water to the ocean. The surface hydrology of Nimrod Glacier, geometrically similar to Peterman but with ten times shallower surface slope, is dominated by storage in surface lakes. In contrast, the Nansen has the same surface slope as Nimrod but transports water through surface rivers. Slope alone is not the sole control on ice shelf hydrology. It is essential to track the storage and transport volumes for each of these systems. To estimate water storage and transport we analyze high resolution (40 cm - 2 m) modern and historical DEMs. We produce historical (1957 onwards) DEMs with structure-from-motion photogrammetry. The DEMs are used to constrain water storage potential estimates of observed basins and water routing/transport potential. We quantify the total volume of water stored seasonally and interannually. We use the normalize difference water index to map meltwater extent, and estimate lake water depth from optical data. We also consider the role of stored water in subsurface aquifers in recharging surface water after

  16. Ross sea ice motion, area flux, and deformation

    Science.gov (United States)

    kwok, Ron

    2005-01-01

    The sea ice motion, area export, and deformation of the Ross Sea ice cover are examined with satellite passive microwave and RADARSAT observations. The record of high-resolution synthetic aperture radar (SAR) data, from 1998 and 2000, allows the estimation of the variability of ice deformation at the small scale (10 km) and to assess the quality of the longer record of passive microwave ice motion. Daily and subdaily deformation fields and RADARSAT imagery highlight the variability of motion and deformation in the Ross Sea. With the passive microwave ice motion, the area export at a flux gate positioned between Cape Adare and Land Bay is estimated. Between 1992 and 2003, a positive trend can be seen in the winter (March-November) ice area flux that has a mean of 990 x 103 km2 and ranges from a low of 600 x 103 km2 in 1992 to a peak of 1600 x 103 km2 in 2001. In the mean, the southern Ross Sea produces almost twice its own area of sea ice during the winter. Cross-gate sea level pressure (SLP) gradients explain 60% of the variance in the ice area flux. A positive trend in this gradient, from reanalysis products, suggests a 'spinup' of the Ross Sea Gyre over the past 12 yr. In both the NCEP-NCAR and ERA-40 surface pressure fields, longer-term trends in this gradient and mean SLP between 1979 and 2002 are explored along with positive anomalies in the monthly cross-gate SLP gradient associated with the positive phase of the Southern Hemisphere annular mode and the extrapolar Southern Oscillation.

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

    Science.gov (United States)

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

    2017-04-28

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

  18. How ice shelf morphology controls basal melting

    Science.gov (United States)

    Little, Christopher M.; Gnanadesikan, Anand; Oppenheimer, Michael

    2009-12-01

    The response of ice shelf basal melting to climate is a function of ocean temperature, circulation, and mixing in the open ocean and the coupling of this external forcing to the sub-ice shelf circulation. Because slope strongly influences the properties of buoyancy-driven flow near the ice shelf base, ice shelf morphology plays a critical role in linking external, subsurface heat sources to the ice. In this paper, the slope-driven dynamic control of local and area-integrated melting rates is examined under a wide range of ocean temperatures and ice shelf shapes, with an emphasis on smaller, steeper ice shelves. A 3-D numerical ocean model is used to simulate the circulation underneath five idealized ice shelves, forced with subsurface ocean temperatures ranging from -2.0°C to 1.5°C. In the sub-ice shelf mixed layer, three spatially distinct dynamic regimes are present. Entrainment of heat occurs predominately under deeper sections of the ice shelf; local and area-integrated melting rates are most sensitive to changes in slope in this "initiation" region. Some entrained heat is advected upslope and used to melt ice in the "maintenance" region; however, flow convergence in the "outflow" region limits heat loss in flatter portions of the ice shelf. Heat flux to the ice exhibits (1) a spatially nonuniform, superlinear dependence on slope and (2) a shape- and temperature-dependent, internally controlled efficiency. Because the efficiency of heat flux through the mixed layer decreases with increasing ocean temperature, numerical simulations diverge from a simple quadratic scaling law.

  19. Polynyas and Ice Production Evolution in the Ross Sea (PIPERS)

    Science.gov (United States)

    Ackley, S. F.

    2017-12-01

    One focus of the PIPERS cruise into the Ross Sea ice cover during April-June 2017 was the Terra Nova Bay (TNB) polynya where joint measurements of air-ice-ocean wave interaction were conducted over twelve days. In Terra Nova Bay, measurements were made in three katabatic wind events each with sustained winds over 35 ms-1 and air temperatures below -15C. Near shore, intense wave fields with wave amplitudes of over 2m and 7-9 sec periods built and large amounts of frazil ice crystals grew. The frazil ice gathered initially into short and narrow plumes that eventually were added laterally to create longer and wider streaks or bands. Breaking waves within these wider streaks were dampened which appeared to enhance the development of pancake ice. Eventually, the open water areas between the streaks sealed off, developing a complete ice cover of 100 percent concentration (80-90 percent pancakes, 20-10 percent frazil) over a wide front (30km). The pancakes continued to grow in diameter and thickness as waves alternately contracted and expanded the ice cover, with the thicker larger floes further diminishing the wave field and lateral motion between pancakes until the initial pancake ice growth ceased. The equilibrium thickness of the ice was 20-30cm in the pancake ice. While the waves had died off however, katabatic wind velocities were sustained and resulted in a wide area of concentrated, rafted, pancake ice that was rapidly advected downstream until the end of the katabatic event. High resolution TerraSar-X radar satellite imagery showed the length of the ice area produced in one single event extended over 300km or ten times the length of the open water area during one polynya event. The TNB polynya is therefore an "ice factory" where frazil ice is manufactured into pancake ice floes that are then pushed out of the assembly area and advected, rafted (and occasionally piled up into "dragon skin" ice), until the katabatic wind dies off at the coastal source.

  20. Ice shelf fracture parameterization in an ice sheet model

    Directory of Open Access Journals (Sweden)

    S. Sun

    2017-11-01

    Full Text Available Floating ice shelves exert a stabilizing force onto the inland ice sheet. However, this buttressing effect is diminished by the fracture process, which on large scales effectively softens the ice, accelerating its flow, increasing calving, and potentially leading to ice shelf breakup. We add a continuum damage model (CDM to the BISICLES ice sheet model, which is intended to model the localized opening of crevasses under stress, the transport of those crevasses through the ice sheet, and the coupling between crevasse depth and the ice flow field and to carry out idealized numerical experiments examining the broad impact on large-scale ice sheet and shelf dynamics. In each case we see a complex pattern of damage evolve over time, with an eventual loss of buttressing approximately equivalent to halving the thickness of the ice shelf. We find that it is possible to achieve a similar ice flow pattern using a simple rule of thumb: introducing an enhancement factor ∼ 10 everywhere in the model domain. However, spatially varying damage (or equivalently, enhancement factor fields set at the start of prognostic calculations to match velocity observations, as is widely done in ice sheet simulations, ought to evolve in time, or grounding line retreat can be slowed by an order of magnitude.

  1. Ice shelf fracture parameterization in an ice sheet model

    Science.gov (United States)

    Sun, Sainan; Cornford, Stephen L.; Moore, John C.; Gladstone, Rupert; Zhao, Liyun

    2017-11-01

    Floating ice shelves exert a stabilizing force onto the inland ice sheet. However, this buttressing effect is diminished by the fracture process, which on large scales effectively softens the ice, accelerating its flow, increasing calving, and potentially leading to ice shelf breakup. We add a continuum damage model (CDM) to the BISICLES ice sheet model, which is intended to model the localized opening of crevasses under stress, the transport of those crevasses through the ice sheet, and the coupling between crevasse depth and the ice flow field and to carry out idealized numerical experiments examining the broad impact on large-scale ice sheet and shelf dynamics. In each case we see a complex pattern of damage evolve over time, with an eventual loss of buttressing approximately equivalent to halving the thickness of the ice shelf. We find that it is possible to achieve a similar ice flow pattern using a simple rule of thumb: introducing an enhancement factor ˜ 10 everywhere in the model domain. However, spatially varying damage (or equivalently, enhancement factor) fields set at the start of prognostic calculations to match velocity observations, as is widely done in ice sheet simulations, ought to evolve in time, or grounding line retreat can be slowed by an order of magnitude.

  2. 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.

  3. Ross Sea Polynyas: Response of Ice Concentration Retrievals to Large Areas of Thin Ice

    Science.gov (United States)

    Kwok, R.; Comiso, J. C.; Martin, S.; Drucker, R.

    2007-01-01

    For a 3-month period between May and July of 2005, we examine the response of the Advanced Microwave Scanning Radiometer (AMSR-E) Enhanced NASA Team 2 (NT2) and AMSR-E Bootstrap (ABA) ice concentration algorithms to large areas of thin ice of the Ross Sea polynyas. Coincident Envisat Synthetic Aperture Radar (SAR) coverage of the region during this period offers a detailed look at the development of the polynyas within several hundred kilometers of the ice front. The high-resolution imagery and derived ice motion fields show bands of polynya ice, covering up to approximately 105 km(sup 2) of the Ross Sea, that are associated with wind-forced advection. In this study, ice thickness from AMSR-E 36 GHz polarization information serves as the basis for examination of the response. The quality of the thickness of newly formed sea ice (<10 cm) from AMSR-E is first assessed with thickness estimates derived from ice surface temperatures from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument. The effect of large areas of thin ice in lowering the ice concentration estimates from both NT2/ABA approaches is clearly demonstrated. Results show relatively robust relationships between retrieved ice concentrations and thin ice thickness estimates that differ between the two algorithms. These relationships define the approximate spatial coincidence of ice concentration and thickness isopleths. Using the 83% (ABA) and 91% (NT2) isopleths as polynya boundaries, we show that the computed coverage compares well with that using the estimated 10-cm thickness contour. The thin ice response characterized here suggests that in regions with polynyas, the retrieval results could be used to provide useful geophysical information, namely thickness and coverage.

  4. Polynya dynamics and associated atmospheric forcing at the Ronne Ice Shelf

    Science.gov (United States)

    Ebner, Lars; Heinemann, Günther

    2014-05-01

    The Ronne Ice Shelf is known as one of the most active regions of polynya developments around the Antarctic continent. Low temperatures are prevailing throughout the whole year, particularly in winter. It is generally recognized that polynya formations are primarily forced by offshore winds and secondarily by ocean currents. Many authors have addressed this issue previously at the Ross Ice Shelf and Adélie Coast and connected polynya dynamics to strong katabatic surge events. Such investigations of atmospheric dynamics and simultaneous polynya occurrence are still severely underrepresented for the southwestern part of the Weddell Sea and especially for the Ronne Ice Shelf. Due to the very flat terrain gradients of the ice shelf katabatic winds are of minor importance in that area. Other atmospheric processes must therefore play a crucial role for polynya developments at the Ronne Ice Shelf. High-resolution simulations have been carried out for the Weddell Sea region using the non-hydrostatic NWP model COSMO from the German Meteorological Service (DWD). For the austral autumn and winter (March to August) 2008 daily forecast simulations were conducted with the consideration of daily sea-ice coverage deduced from the passive microwave system AMSR-E. These simulations are used to analyze the synoptic and mesoscale atmospheric dynamics of the Weddell Sea region and find linkages to polynya occurrence at the Ronne Ice Shelf. For that reason, the relation between the surface wind speed, the synoptic pressure gradient in the free atmosphere and polynya area is investigated. Seven significant polynya events are identified for the simulation period, three in the autumn and four in the winter season. It can be shown that in almost all cases synoptic cyclones are the primary polynya forcing systems. In most cases the timely interaction of several passing cyclones in the northern and central Weddell Sea leads to maintenance of a strong synoptic pressure gradient above the

  5. Rossing

    International Nuclear Information System (INIS)

    Anon.

    1979-01-01

    Rossing is a uranium mine in the heart of the Namib desert in South West Africa (Namibia). Interms of the material recovered from the huge open pit, it is the largest uranium mine in the world. This article gives a short history of the development of this mine

  6. Influence of sea ice cover and icebergs on circulation and water mass formation in a numerical circulation model of the Ross Sea, Antarctica

    Science.gov (United States)

    Dinniman, Michael S.; Klinck, John M.; Smith, Walker O.

    2007-11-01

    Satellite imagery shows that there was substantial variability in the sea ice extent in the Ross Sea during 2001-2003. Much of this variability is thought to be due to several large icebergs that moved through the area during that period. The effects of these changes in sea ice on circulation and water mass distributions are investigated with a numerical general circulation model. It would be difficult to simulate the highly variable sea ice from 2001 to 2003 with a dynamic sea ice model since much of the variability was due to the floating icebergs. Here, sea ice concentration is specified from satellite observations. To examine the effects of changes in sea ice due to iceberg C-19, simulations were performed using either climatological ice concentrations or the observed ice for that period. The heat balance around the Ross Sea Polynya (RSP) shows that the dominant term in the surface heat budget is the net exchange with the atmosphere, but advection of oceanic warm water is also important. The area average annual basal melt rate beneath the Ross Ice Shelf is reduced by 12% in the observed sea ice simulation. The observed sea ice simulation also creates more High-Salinity Shelf Water. Another simulation was performed with observed sea ice and a fixed iceberg representing B-15A. There is reduced advection of warm surface water during summer from the RSP into McMurdo Sound due to B-15A, but a much stronger reduction is due to the late opening of the RSP in early 2003 because of C-19.

  7. Temporal variability of the Circumpolar Deep Water inflow onto the Ross Sea continental shelf

    Science.gov (United States)

    Castagno, Pasquale; Falco, Pierpaolo; Dinniman, Michael S.; Spezie, Giancarlo; Budillon, Giorgio

    2017-02-01

    The intrusion of Circumpolar Deep Water (CDW) is the primary source of heat, salt and nutrients onto Antarctica's continental shelves and plays a major role in the shelf physical and biological processes. Different studies have analyzed the processes responsible for the transport of CDW across the Ross Sea shelf break, but until now, there are no continuous observations that investigate the timing of the intrusions. Also, few works have focused on the effect of the tides that control these intrusions. In the Ross Sea, the CDW intrudes onto the shelf in several locations, but mostly along the troughs. We use hydrographic observations and a mooring placed on the outer shelf in the middle of the Drygalski Trough in order to characterize the spatial and temporal variability of CDW inflow onto the shelf. Our data span from 2004 to the beginning of 2014. In the Drygalski Trough, the CDW enters as a 150 m thick layer between 250 and 400 m, and moves upward towards the south. At the mooring location, about 50 km from the shelf break, two main CDW cores can be observed: one on the east side of the trough spreading along the west slope of Mawson Bank from about 200 m to the bottom and the other one in the central-west side from 200 m to about 350 m depth. A signature of this lighter and relatively warm water is detected by the instruments on the mooring at bottom of the Drygalski Trough. High frequency periodic CDW intrusion at the bottom of the trough is related to the diurnal and spring/neap tidal cycles. At lower frequency, a seasonal variability of the CDW intrusion is noticed. A strong inflow of CDW is observed every year at the end of December, while the CDW inflow is at its seasonal minimum during the beginning of the austral fall. In addition an interannual variability is also evident. A change of the CDW intrusion before and after 2010 is observed.

  8. Modern shelf ice, equatorial Aeolis Quadrangle, Mars

    Science.gov (United States)

    Brakenridge, G. R.

    1993-01-01

    As part of a detailed study of the geological and geomorphological evolution of Aeolis Quadrangle, I have encountered evidence suggesting that near surface ice exists at low latitudes and was formed by partial or complete freezing of an inland sea. The area of interest is centered at approximately -2 deg, 196 deg. As seen in a suite of Viking Orbiter frames obtained at a range of approximately 600 km, the plains surface at this location is very lightly cratered or uncratered, and it is thus of late Amazonian age. Extant topographic data indicate that the Amazonian plains at this location occupy a trough whose surface lies at least 1000 m below the Mars datum. A reasonable hypothesis is that quite recent surface water releases, perhaps associated with final evolution of large 'outflow chasms' to the south, but possibly from other source areas, filled this trough, that ice floes formed almost immediately, and that either grounded ice or an ice-covered sea still persists. A reasonable hypothesis is that quite recent surface water releases, perhaps associated with final evolution of large 'outflow chasms' to the south, but possibly from other source areas, filled this trough, that ice floes formed almost immediately, and that either grounded ice or an ice-covered sea still persists. In either case, the thin (a few meters at most) high albedo, low thermal inertia cover of aeolian materials was instrumental in allowing ice preservation, and at least the lower portions of this dust cover may be cemented by water ice. Detailed mapping using Viking stereopairs and quantitative comparisons to terrestrial shelf ice geometries are underway.

  9. Lithology and chronology of ice-sheet fluctuations (magnetic susceptibility of cores from the western Ross Sea)

    Science.gov (United States)

    Jennings, Anne E.

    1993-01-01

    The goals of the marine geology part of WAIS include reconstructing the chronology and areal extent of ice-sheet fluctuations and understanding the climatic and oceanographic influences on ice-sheet history. As an initial step toward attaining these goals, down-core volume magnetic susceptibility (MS) logs of piston cores from three N-S transects in the western Ross Sea are compared. The core transects are within separate petrographic provinces based on analyses of till composition. The provinces are thought to reflect the previous locations of ice streams on the shelf during the last glaciation. Magnetic susceptibility is a function of magnetic mineral composition, sediment texture, and sediment density. It is applied in the western Ross Sea for two purposes: (1) to determine whether MS data differentiates the three transects (i.e., flow lines), and thus can be used to make paleodrainage reconstructions of the late Wisconsinan ice sheet; and (2) to determine whether the MS data can aid in distinguishing basal till diamictons from diamictons of glacial-marine origin and thus, aid paleoenvironmental interpretations. A comparison of the combined data of cores in each transect is presented.

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

    Science.gov (United States)

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

    2018-02-01

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

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

    Directory of Open Access Journals (Sweden)

    N. A. N. Bertler

    2018-02-01

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

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

    Directory of Open Access Journals (Sweden)

    S. Berger

    2017-11-01

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

  13. The Satellite Passive-Microwave Record of Sea Ice in the Ross Sea Since Late 1978

    Science.gov (United States)

    Parkinson, Claire L.

    2009-01-01

    Satellites have provided us with a remarkable ability to monitor many aspects of the globe day-in and day-out and sea ice is one of numerous variables that by now have quite substantial satellite records. Passive-microwave data have been particularly valuable in sea ice monitoring, with a record that extends back to August 1987 on daily basis (for most of the period), to November 1970 on a less complete basis (again for most of the period), and to December 1972 on a less complete basis. For the period since November 1970, Ross Sea sea ice imagery is available at spatial resolution of approximately 25 km. This allows good depictions of the seasonal advance and retreat of the ice cover each year, along with its marked interannual variability. The Ross Sea ice extent typically reaches a minimum of approximately 0.7 x 10(exp 6) square kilometers in February, rising to a maximum of approximately 4.0 x 10(exp 6) square kilometers in September, with much variability among years for both those numbers. The Ross Sea images show clearly the day-by-day activity greatly from year to year. Animations of the data help to highlight the dynamic nature of the Ross Sea ice cover. The satellite data also allow calculation of trends in the ice cover over the period of the satellite record. Using linear least-squares fits, the Ross Sea ice extent increased at an average rate of 12,600 plus or minus 1,800 square kilometers per year between November 1978 and December 2007, with every month exhibiting increased ice extent and the rates of increase ranging from a low of 7,500 plus or minus 5,000 square kilometers per year for the February ice extents to a high of 20,300 plus or minus 6,100 kilometers per year for the October ice extents. On a yearly average basis, for 1979-2007 the Ross Sea ice extent increased at a rate of 4.8 plus or minus 1.6 % per decade. Placing the Ross Sea in the context of the Southern Ocean as a whole, over the November 1978-December 2007 period the Ross Sea had

  14. Environmental controls on micro fracture processes in shelf ice

    Science.gov (United States)

    Sammonds, Peter

    2013-04-01

    The recent retreat and collapse of the ice shelves on the Antarctic Peninsula has been associated with regional atmospheric warming, oceanic warming, increased summer melt and shelf flexure. Although the cause of collapse is a matter of active discussion, the process is that of fracture of a creep-brittle material, close to its melting point. The environmental controls on how fracturing initiates, at a micro-scale, strongly determine the macroscopic disintegration of ice shelves. In particular the shelf temperature profile controls the plasticity of the ice shelf; the densification of shelf ice due to melting and re-freezing affects the crack tip stress intensity; the accretion of marine ice at the bottom of the shelf imposes a thermal/mechanical discontinuity; saline environments control crack tip stress corrosion; cyclic loading promotes sub-critical crack propagation. These strong environmental controls on shelf ice fracture means that assessing shelf stability is a non-deterministic problem. How these factors may be parameterized in ice shelf models, through the use of fracture mechanisms maps, is discussed. The findings are discussed in relation to the stability of Larsen C.

  15. 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...

  16. The nepheloid bottom layer and water masses at the shelf break of the western Ross Sea

    Science.gov (United States)

    Capello, Marco; Budillon, Giorgio; Cutroneo, Laura; Tucci, Sergio

    2009-06-01

    In the austral summers of 2000/2001 and 2002/2003 the Italian CLIMA Project carried out two oceanographic cruises along the northwestern margin of the Ross Sea, where the Antarctic Bottom Water forms. Here there is an interaction between the water masses on the sea floor of the outer shelf and slope with a consequent evolution of benthic nepheloid layers and an increase in total particulate matter. We observed three different situations: (a) the presence of triads (bottom structures characterized by a concomitant jump in turbidity, temperature, and salinity data) and high re-suspension phenomena related to the presence of the Circumpolar Deep Water and its mixing with cold, salty shelf waters associated with gravity currents; (b) the absence of triads with high re-suspension, implying that when the gravity currents are no longer active the benthic nepheloid layer may persist until the suspended particles settle to the sea floor, suggesting that the turbidity data can be used to study recent gravity current events; and (c) the absence of turbidity and sediment re-suspension phenomena supports the theory that a steady situation had been re-established and the current interaction no longer occurred or had finished sometime before.

  17. 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.

  18. The South Pole and the Ross Sea

    Science.gov (United States)

    2002-01-01

    This image shows a rare clear view of the South Pole (lower right) and the Ross Sea, Antarctica. The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) acquired the scene on December 26, 2001. The geographic South Pole is located in the center of Antarctica, at an altitude of 2,900 meters (9,300 feet). It rests on a continent-wide ice sheet that is 2,870 m thick, with the underlying bedrock only 30 m (98 feet) above sea level. The ice underlying the South Pole is as much as 140,000 years old, and is currently accumulating at about 82 cm (32 inches) per year. Roughly 2,500 km (1,550 miles) away is the green water of the Ross Sea, which indicates the presence of large numbers of phytoplankton. This is a highly productive part of the world's oceans. Also note the ice gathered around McMurdo Sound, seen toward the lefthand shoreline of the Ross Sea, at the edge of the Ross Ice Shelf. According to National Science Foundation researchers, this ice is making it difficult for penguins to reach their food supply. Separating the continental Antarctic ice sheet from the Ross Sea are the Queen Maud Mountains and the Ross Ice Shelf. Image courtesy the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

  19. 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.

  20. Deformation and failure of the ice bridge on the Wilkins Ice Shelf, Antarctica

    NARCIS (Netherlands)

    Humbert, A.; Gross, D.; Müller, R.; Braun, M.; van de Wal, R.S.W.; van den Broeke, M.R.; Vaughan, D.G.; van de Berg, W.J.

    2010-01-01

    A narrow bridge of floating ice that connected the Wilkins Ice Shelf, Antarctica, to two confining islands eventually collapsed in early April 2009. In the month preceding the collapse, we observed deformation of the ice bridge by means of satellite imagery and from an in situ GPS station.

  1. Spatial patterning and persistence of meltwater on ice shelves and the implications for ice shelf collapse

    Science.gov (United States)

    Robel, A.; MacAyeal, D. R.; Tsai, V. C.; Shean, D. E.

    2017-12-01

    Observations indicate that for at least the last few decades, there has been extensive surface melting over ice shelves in Antarctica. Meltwater either collects in ponds or flows over the surface in streams that discharge to the ocean. The spatial organization and persistence of this meltwater can have a significant influence on the thermomechanical ice shelf state through albedo, turbulent heat exchange, refreezing and hydrofracture. However, as more meltwater forms on Antarctic ice shelves, there is no general theory that predicts the spatial pattern of meltwater ponded on the ice shelf surface and the volume of meltwater runoff to the ocean. Here, we show how dynamical systems tools, such as cellular automata, can be used to calculate the expected distribution of meltwater on ice shelf surfaces. These tools can also be used to explore how ice shelf surface morphology is modified by meltwater albedo and turbulent heating feedbacks. We apply these numerical approaches to new high-resolution digital elevation models for ice shelves in West Antarctica. Additionally, we survey the prospects of developing general rules of meltwater patterning by applying scaling approaches from percolation theory. We conclude by discussing the types of ice shelves that are more likely to cause ice shelf collapse through surface melt-induced hydrofracture or thermomechanical weakening.

  2. Ice gouging effects on the eastern Arctic shelf of Russia

    Directory of Open Access Journals (Sweden)

    Libina N. V.

    2018-03-01

    Full Text Available Results of the latest geological and geophysical marine cruises indicate activating of natural risks (or hazards processes connected with ice gouging, permafrost melting, landslides, coastal thermoerosion and seismic activity. These processes represent great risks for all human marine activities including exploitation of the Northern Sea Route (NSR. One of the most dangerous natural processes is ice gouging, which results in the ploughing of the seabed by an underwater part of ice bodies. Ice gouging processes can create some emergency situation in the construction and operation of any underwater engineering structures. Natural seismoacoustic data obtained within the eastern Arctic shelf of Russia have recorded numerous ice gouging trails both in the coastal shallow and deep parts of the shelf as well. Modern high-resolution seismic devices have allowed receive detailed morphology parameters of underwater ice traces. The actual depth and occurrence of traces of the effect of ice formations on the bottom significantly exceed the calculated probability of occurrence according to ice conditions. Seismic data have allowed classify all these traces and subdivide them on modern coastal and ancient (or relict deep ones. During Late Quaternary sea level down lifting the absence of cover glaciation did not exclude the presence of powerful drifting ice that produced ice gouging processes in the present deep part of the sea. Afterwards during sea level up lifting ice gouging follows to the sea level changes. In this case there could be destructed some dense clay dewatered sediment layer formed during the regression period. Further, during the repeated transgressive-regressive sea level fluctuations the generated ice traces could be frozen and thus preserved until our days. Modern coastal ice traces into marine shallow are the result of nowadays interaction of drifting ice and seabed that in conditions of global climate warming are activated and represent

  3. Ice shelf thickness change from 2010 to 2017

    Science.gov (United States)

    Hogg, A.; Shepherd, A.; Gilbert, L.; Muir, A. S.

    2017-12-01

    Floating ice shelves fringe 74 % of Antarctica's coastline, providing a direct link between the ice sheet and the surrounding oceans. Over the last 25 years, ice shelves have retreated, thinned, and collapsed catastrophically. While change in the mass of floating ice shelves has only a modest steric impact on the rate of sea-level rise, their loss can affect the mass balance of the grounded ice-sheet by influencing the rate of ice flow inland, due to the buttressing effect. Here we use CryoSat-2 altimetry data to map the detailed pattern of ice shelf thickness change in Antarctica. We exploit the dense spatial sampling and repeat coverage provided by the CryoSat-2 synthetic aperture radar interferometric mode (SARIn) to investigate data acquired between 2010 to the present day. We find that ice shelf thinning rates can exhibit large fluctuations over short time periods, and that the improved spatial resolution of CryoSat-2 enables us to resolve the spatial pattern of thinning with ever greater detail in Antarctica. In the Amundsen Sea, ice shelves at the terminus of the Pine Island and Thwaites glaciers have thinned at rates in excess of 5 meters per year for more than two decades. We observe the highest rates of basal melting near to the ice sheet grounding line, reinforcing the importance of high resolution datasets. On the Antarctic Peninsula, in contrast to the 3.8 m per decade of thinning observed since 1992, we measure an increase in the surface elevation of the Larsen-C Ice-Shelf during the CryoSat-2 period.

  4. 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

  5. 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 ...

  6. 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

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

    Science.gov (United States)

    1991-01-01

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

  8. Active and Passive Microwave Determination of the Circulation and Characteristics of Weddell and Ross Sea Ice

    Science.gov (United States)

    Drinkwater, Mark R.; Liu, Xiang

    2000-01-01

    A combination of satellite microwave data sets are used in conjunction with ECMWF (Medium Range Weather Forecasts) and NCEP (National Center for Environment Prediction) meteorological analysis fields to investigate seasonal variability in the circulation and sea-ice dynamics of the Weddell and Ross Seas. Results of sea-ice tracking using SSM/I (Special Sensor Microwave Imager), Scatterometer and SAR images are combined with in-situ data derived from Argos buoys and GPS drifters to validate observed drift patterns. Seasonal 3-month climatologies of ice motion and drift speed variance illustrate the response of the sea-ice system to seasonal forcing. A melt-detection algorithm is used to track the onset of seasonal melt, and to determine the extent and duration of atmospherically-led surface melting during austral summer. Results show that wind-driven drift regulates the seasonal distribution and characteristics of sea-ice and the intensity of the cyclonic Gyre circulation in these two regions.

  9. Chronicling ice shelf history in the sediments left behind

    Science.gov (United States)

    Rosenheim, B. E.; Subt, C.; Shevenell, A.; Guitard, M.; Vadman, K. J.; DeCesare, M.; Wellner, J. S.; Bart, P. J.; Lee, J. I.; Domack, E. W.; Yoo, K. C.; Hayes, J. M.

    2017-12-01

    Collapsing and retreating ice shelves leave unmistakable sediment sequences on the Antarctic margin. These sequences tell unequivocal stories of collapse or retreat through a typical progression of sub-ice shelf diamicton (marking the past positions of grounding lines), sequentially overlain by a granulated facies from beneath the ice shelf, ice rafted debris from the calving line, and finally open marine sediment. The timelines to these stories, however, are troublesome. Difficulties in chronicling these stories recorded in sediment have betrayed their importance to our understanding of a warming world in many cases. The difficulties involve the concerted lack of preservation/production of calcium carbonate tests from the water column above and admixture of relict organic material from older sources of carbon. Here, we summarize our advances in the last decade of overcoming difficulties associated with the paucity of carbonate and creating chronologies of ice shelf retreat into the deglacial history of Antarctica by exploiting the range of thermochemical stability in organic matter (Ramped PyrOx) from these sediment sequences. We describe our success in comparing Ramped PyrOx 14C dates with foraminiferal dates, the relationship between sediment facies and radiocarbon age spectrum, and our ability to push limits of dating sediments deposited underneath ice shelves. With attention to the caveats of recent dating developments, we summarize expectations that geologist should have when coring the Antarctic margins to discern deglacial history. Perhaps most important among these expectations is the ability to design coring expeditions without regard to our ability to date calcium carbonate microfossils within the cores, in essence removing suspense of knowing whether cores taken from crucial paleo ice channels and other bathymetric features will ultimately yield a robust chronology for its sedimentary sequence.

  10. Integrating terrestrial and marine records of the LGM in McMurdo Sound, Antarctica: implications for grounded ice expansion, ice flow, and deglaciation of the Ross Sea Embayment

    Science.gov (United States)

    Christ, A. J.; Marchant, D. R.

    2017-12-01

    During the LGM, grounded glacier ice filled the Ross Embayment and deposited glacial drift on volcanic islands and peninsulas in McMurdo Sound, as well as along coastal regions of the Transantarctic Mountains (TAM), including the McMurdo Dry Valleys and Royal Society Range. The flow geometry and retreat history of this ice remains debated, with contrasting views yielding divergent implications for both the fundamental cause of Antarctic ice expansion as well as the interaction and behavior of ice derived from East and West Antarctica during late Quaternary time. We present terrestrial geomorphologic evidence that enables the reconstruction of former ice elevations, ice-flow paths, and ice-marginal environments in McMurdo Sound. Radiocarbon dates of fossil algae interbedded with ice-marginal sediments provide a coherent timeline for local ice retreat. These data are integrated with marine-sediment records and multi-beam data to reconstruct late glacial dynamics of grounded ice in McMurdo Sound and the western Ross Sea. The combined dataset suggest a dominance of ice flow toward the TAM in McMurdo Sound during all phases of glaciation, with thick, grounded ice at or near its maximum extent between 19.6 and 12.3 calibrated thousands of years before present (cal. ka). Our data show no significant advance of locally derived ice from the TAM into McMurdo Sound, consistent with the assertion that Late Pleistocene expansion of grounded ice in McMurdo Sound, and throughout the wider Ross Embayment, occurs in response to lower eustatic sea level and the resulting advance of marine-based outlet glaciers and ice streams (and perhaps also reduced oceanic heat flux), rather than local increases in precipitation and ice accumulation. Finally, when combined with allied data across the wider Ross Embayment, which show that widespread deglaciation outside McMurdo Sound did not commence until 13.1 ka, the implication is that retreat of grounded glacier ice in the Ross Embayment did

  11. A geoelectrical survey above an Antarctic ice shelf

    Directory of Open Access Journals (Sweden)

    M. Pavan

    1998-06-01

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

  12. Export of Ice-Cavity Water from Pine Island Ice Shelf, West Antarctica

    Science.gov (United States)

    Thurnherr, Andreas; Jacobs, Stanley; Dutrieux, Pierre

    2013-04-01

    Stability of the West Antarctic Ice Sheet is sensitive to changes in melting at the bottom of floating ice shelves that form the seaward extensions of Antarctic glaciers flowing into the ocean. Not least because observations in the cavities beneath ice shelves are difficult, heat fluxes and melt rates have been inferred from oceanographic measurements obtained near the ice edge (calving fronts). Here, we report on a set of hydrographic and velocity data collected in early 2009 near the calving front of the Amundsen Sea's fast-moving and (until recently) accelerating Pine Island Glacier and its associated ice shelf. CTD profiles collected along the southern half of the meridionally-trending ice front show clear evidence for export of ice-cavity water. That water was carried in the upper ocean along the ice front by a southward current that is possibly related to a striking clockwise gyre that dominated the (summertime) upper-ocean circulation in Pine Island Bay. Signatures of ice-cavity water appear unrelated to current direction along most of the ice front, suggesting that cross-frontal exchange is dominated by temporal variability. However, repeated hydrographic and velocity measurements in a small "ice cove" at the southern end of the calving front show a persistent strong (mean velocity peaking near 0.5 ms-1) outflow of ice-cavity water in the upper 500 m. While surface features (boils) suggested upwelling from deep below the ice shelf, vertical velocity measurements reveal 1) that the mean upwelling within the confines of the cove was too weak to feed the observed outflow, and 2) that large high-frequency internal waves dominated the vertical motion of water inside the cove. These observations indicate that water exchange between the Pine Island Ice Shelf cavity and the Amundsen sea is strongly asymmetric with weak broad inflow at depth and concentrated surface-intensified outflow of melt-laden deep water at the southern edge of the calving front. The lack of

  13. 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

  14. Increase in penguin populations during the Little Ice Age in the Ross Sea, Antarctica.

    Science.gov (United States)

    Hu, Qi-Hou; Sun, Li-Guang; Xie, Zhou-Qing; Emslie, Steven D; Liu, Xiao-Dong

    2013-01-01

    Penguins are an important seabird species in Antarctica and are sensitive to climate and environmental changes. Previous studies indicated that penguin populations increased when the climate became warmer and decreased when it became colder in the maritime Antarctic. Here we determined organic markers in a sediment profile collected at Cape Bird, Ross Island, high Antarctic, and reconstructed the history of Adélie penguin colonies at this location over the past 700 years. The region transformed from a seal to a penguin habitat when the Little Ice Age (LIA; 1500-1800 AD) began. Penguins then became the dominant species. Penguin populations were the highest during ca. 1490 to 1670 AD, a cold period, which is contrary to previous results in other regions much farther north. Different responses to climate change may occur at low latitudes and high latitudes in the Antarctic, even if for same species.

  15. Frazil-ice growth rate and dynamics in mixed layers and sub-ice-shelf plumes

    Science.gov (United States)

    Rees Jones, David W.; Wells, Andrew J.

    2018-01-01

    The growth of frazil or granular ice is an important mode of ice formation in the cryosphere. Recent advances have improved our understanding of the microphysical processes that control the rate of ice-crystal growth when water is cooled beneath its freezing temperature. These advances suggest that crystals grow much faster than previously thought. In this paper, we consider models of a population of ice crystals with different sizes to provide insight into the treatment of frazil ice in large-scale models. We consider the role of crystal growth alongside the other physical processes that determine the dynamics of frazil ice. We apply our model to a simple mixed layer (such as at the surface of the ocean) and to a buoyant plume under a floating ice shelf. We provide numerical calculations and scaling arguments to predict the occurrence of frazil-ice explosions, which we show are controlled by crystal growth, nucleation, and gravitational removal. Faster crystal growth, higher secondary nucleation, and slower gravitational removal make frazil-ice explosions more likely. We identify steady-state crystal size distributions, which are largely insensitive to crystal growth rate but are affected by the relative importance of secondary nucleation to gravitational removal. Finally, we show that the fate of plumes underneath ice shelves is dramatically affected by frazil-ice dynamics. Differences in the parameterization of crystal growth and nucleation give rise to radically different predictions of basal accretion and plume dynamics, and can even impact whether a plume reaches the end of the ice shelf or intrudes at depth.

  16. The response of grounded ice to ocean temperature forcing in a coupled ice sheet-ice shelf-ocean cavity model

    Science.gov (United States)

    Goldberg, D. N.; Little, C. M.; Sergienko, O. V.; Gnanadesikan, A.

    2010-12-01

    Ice shelves provide a pathway for the heat content of the ocean to influence continental ice sheets. Changes in the rate or location of basal melting can alter their geometry and effect changes in stress conditions at the grounding line, leading to a grounded ice response. Recent observations of ice streams and ice shelves in the Amundsen Sea sector of West Antarctica have been consistent with this story. On the other hand, ice dynamics in the grounding zone control flux into the shelf and thus ice shelf geometry, which has a strong influence on the circulation in the cavity beneath the shelf. Thus the coupling between the two systems, ocean and ice sheet-ice shelf, can be quite strong. We examine the response of the ice sheet-ice shelf-ocean cavity system to changes in ocean temperature using a recently developed coupled model. The coupled model consists a 3-D ocean model (GFDL's Generalized Ocean Layered Dynamics model, or GOLD) to a two-dimensional ice sheet-ice shelf model (Goldberg et al, 2009), and allows for changing cavity geometry and a migrating grounding line. Steady states of the coupled system are found even under considerable forcing. The ice shelf morphology and basal melt rate patterns of the steady states exhibit detailed structure, and furthermore seem to be unique and robust. The relationship between temperature forcing and area-averaged melt rate is influenced by the response of ice shelf morphology to thermal forcing, and is found to be sublinear in the range of forcing considered. However, results suggest that area-averaged melt rate is not the best predictor of overall system response, as grounding line stability depends on local aspects of the basal melt field. Goldberg, D N, D M Holland and C G Schoof, 2009. Grounding line movement and ice shelf buttressing in marine ice sheets, Journal of Geophysical Research-Earth Surfaces, 114, F04026.

  17. 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

  18. The evolution of a coupled ice shelf-ocean system under different climate states

    Science.gov (United States)

    Grosfeld, Klaus; Sandhäger, Henner

    2004-07-01

    Based on a new approach for coupled applications of an ice shelf model and an ocean general circulation model, we investigate the evolution of an ice shelf-ocean system and its sensitivity to changed climatic boundary conditions. Combining established 3D models into a coupled model system enabled us to study the reaction and feedbacks of each component to changes at their interface, the ice shelf base. After calculating the dynamics for prescribed initial ice shelf and bathymetric geometries, the basal mass balance determines the system evolution. In order to explore possible developments for given boundary conditions, an idealized geometry has been chosen, reflecting basic features of the Filchner-Ronne Ice Shelf, Antarctica. The model system is found to be especially sensitive in regions where high ablation or accretion rates occur. Ice Shelf Water formation as well as the build up of a marine ice body, resulting from accretion of marine ice, is simulated, indicating strong interaction processes. To improve consistency between modeled and observed ice shelf behavior, we incorporate the typical cycle of steady ice front advance and sudden retreat due to tabular iceberg calving in our time-dependent simulations. Our basic hypothesis is that iceberg break off is associated with abrupt crack propagation along elongated anomalies of the inherent stress field of the ice body. This new concept yields glaciologically plausible results and represents an auspicious basis for the development of a thorough calving criterion. Experiments under different climatic conditions (ocean warming of 0.2 and 0.5 °C and doubled surface accumulation rates) show the coupled model system to be sensitive especially to ocean warming. Increased basal melt rates of 100% for the 0.5 °C ocean warming scenario and an asymmetric development of ice shelf thicknesses suggest a high vulnerability of ice shelf regions, which represent pivotal areas between the Antarctic Ice Sheet and the Southern

  19. 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.

  20. Chemotrophic Ecosystem Beneath the Larsen Ice Shelf, Antarctica

    Science.gov (United States)

    Leventer, A.; Domack, E.; Ishman, S.; Sylva, S.; Willmott, V.; Huber, B.; Padman, L.

    2005-12-01

    The first living chemotrophic ecosystem in the Southern Ocean was discovered in a region of the seafloor previously occupied by the Larsen-B Ice Shelf. A towed video survey documents an ecosystem characterized by a bottom-draping white mat that appears similar to mats of Begiattoa, hydrogen sulfide oxidizing bacteria, and bivalves, 20-30 cm large, similar to vesicomyid clams commonly found at cold seeps. The carbon source is unknown; three potential sources are hypothesized. First, thermogenically-produced methane may occur as the marine shales of this region are similar to hydrocarbon-bearing rocks to the north in Patagonia. The site occurs in an 850 m deep glacially eroded trough located along the contact between Mesozoic-Tertiary crystalline basement and Cretaceous-Tertiary marine rocks; decreased overburden could have induced upward fluid flow. Also possible is the dissociation of methane hydrates, a process that might have occurred as a result of warming oceanic bottom waters. This possibility will be discussed in light of the distribution of early diagenetic ikaite in the region. Third, the possibility of a biogenic methane source will be discussed. A microstratigraphic model for the features observed at the vent sites will be presented; the system is comprised of mud mounds with central vents and surrounding mud flow channels. A series of still image mosaics record the dynamic behavior of the system, which appears to demonstrate episodic venting. These images show the spatial relationship between more and less active sites, as reflected in the superposition of several episodes of mud flow activity and the formation of mud channels. In addition, detailed microscale features of the bathymetry of the site will be presented, placing the community within the context of glacial geomorphologic features. The Larsen-B Ice Shelf persisted through the entire Holocene, limiting carbon influx from a photosynthetic source. Tidal modeling of both pre and post breakup

  1. Seismometers on Europa: Insights from Modeling and Antarctic Ice Shelf Analogs (Invited)

    Science.gov (United States)

    Schmerr, N. C.; Brunt, K. M.; Cammarano, F.; Hurford, T. A.; Lekic, V.; Panning, M. P.; Rhoden, A.; Sauber, J. M.

    2013-12-01

    the depth of an ocean layer. Likewise, evaluation of arrival times of reflected wave multiples observed at a single seismic station would record properties of the mantle and core of Europa. Cluster analysis of waveforms from various seismic source mechanisms could be used to classify different types of seismicity originating from the ice and rocky parts of the moon. We examine examples of single station results for analogous seismic experiments on Earth, e.g., where broadband, 3-component seismometers have been placed upon the Ross Ice Shelf of Antarctica. Ultimately this work reveals that seismometer deployments will be essential for understanding the internal dynamics, habitability, and surface evolution of Europa, and that seismic instruments need to be a key component of future missions to surface of Europa and outer satellites.

  2. 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

    2013-12-01

    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 ability of ice shelves to sustain and transmit buttressing stresses. Here, we present a new framework for quantifying 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 that accounts for the softening influence of fractures on longitudinal deformation using a state damage variable. We use this new analytical relation, combined with a temperature calculation for the ice, to partition an inverse method solution for ice shelf rigidity into independent solutions for softening damage and stabilizing backstress. Using this new approach, field and remote sensing data can be utilized to monitor the structural integrity of ice shelves, their ability to buttress the flow of ice at the grounding line, and thus their indirect contribution to ice sheet mass balance and global sea level. We apply this technique to the Larsen C ice shelf using remote sensing and Operation IceBridge data, finding damage in areas with known crevasses and rifts. Backstress is highest near the grounding line and upstream of ice rises, in agreement with patterns observed on other ice shelves. The ice in contact with the Bawden ice rise is weakened by fractures, and additional damage or thinning in this area could diminish the backstress transmitted upstream. We model the consequences for the ice shelf if it loses contact with this small ice rise

  3. Flexural-response of the McMurdo Ice Shelf to surface lake filling and drainage

    Science.gov (United States)

    Banwell, A. F.; MacAyeal, D. R.; Willis, I.; Macdonald, G. J.; Goodsell, B.

    2017-12-01

    Antarctic ice-shelf instability and break-up, as exhibited by the Larsen B ice shelf in 2002, remains one of the most difficult glaciological processes to observe directly. 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 previously been proposed, including the ability of surface lakes to introduce ice-shelf fractures when they fill and drain. During the austral summer of 2016/2017, we monitored the filling and draining of four surface lakes on the McMurdo Ice Shelf, Antarctica, and the effect of these processes on ice-shelf flexure. Water-depth data from pressure sensors reveal that two lakes filled to >2 m in depth and subsequently drained over multiple week timescales, which had a simultaneous effect on vertical ice deflection in the area. Differential GPS data from 12 receivers over three months show that vertical deflection varies as a function of distance from the maximum load change (i.e. at the lake centre). Using remote sensing techniques applied to both Landsat 8 and Worldview imagery, we also quantify the meltwater volume in these two lakes through the melt season, which, together with the vertical deflection data, are used to constrain key flexural parameter values in numerical models of ice-shelf flexure.

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

    DEFF Research Database (Denmark)

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

    2010-01-01

    We present the mapping of glacial landforms and sediments from northernmost Greenland bordering 100 km of the Arctic Ocean coast. One of the most important discoveries is that glacial landforms, sediments, including till fabric measurements, striae and stoss-lee boulders suggest eastward ice......-flow along the coastal plain. Volcanic erratic boulders document ice-transport from 80 to 100 km west of the study area. We argue that these findings are best explained by local outlet glaciers from the Greenland Ice Sheet and local ice caps that merged to form a shelf-based ice in the Arctic Ocean...... and possibly confirming an extensive ice shelf in the Lincoln Sea between Greenland and Ellesmere Island. It is speculated that the shelf-based ice was largely affected by the presence of thick multiyear sea ice in the Arctic Ocean that prevented it from breaking up and forced the outlet glaciers to flow...

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

    Science.gov (United States)

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

    2017-12-01

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

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

    OpenAIRE

    Grosvenor, D. P.; Choularton, T. W.; Lachlan-Cope, T.; Gallagher, M. W.; Crosier, J.; Bower, K. N.; Ladkin, R. S.; Dorsey, J. R.

    2012-01-01

    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 phas...

  7. 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.

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

    Directory of Open Access Journals (Sweden)

    J. De Rydt

    2018-02-01

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

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

    Science.gov (United States)

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

    2018-02-01

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

  10. Simulation of the Greenland Ice Sheet over two glacial–interglacial cycles: investigating a sub-ice-shelf melt parameterization and relative sea level forcing in an ice-sheet–ice-shelf model

    Directory of Open Access Journals (Sweden)

    S. L. Bradley

    2018-05-01

    Full Text Available Observational evidence, including offshore moraines and sediment cores, confirm that at the Last Glacial Maximum (LGM the Greenland ice sheet (GrIS expanded to a significantly larger spatial extent than seen at present, grounding into Baffin Bay and out onto the continental shelf break. Given this larger spatial extent and its close proximity to the neighbouring Laurentide Ice Sheet (LIS and Innuitian Ice Sheet (IIS, it is likely these ice sheets will have had a strong non-local influence on the spatial and temporal behaviour of the GrIS. Most previous paleo ice-sheet modelling simulations recreated an ice sheet that either did not extend out onto the continental shelf or utilized a simplified marine ice parameterization which did not fully include the effect of ice shelves or neglected the sensitivity of the GrIS to this non-local bedrock signal from the surrounding ice sheets. In this paper, we investigated the evolution of the GrIS over the two most recent glacial–interglacial cycles (240 ka BP to the present day using the ice-sheet–ice-shelf model IMAU-ICE. We investigated the solid earth influence of the LIS and IIS via an offline relative sea level (RSL forcing generated by a glacial isostatic adjustment (GIA model. The RSL forcing governed the spatial and temporal pattern of sub-ice-shelf melting via changes in the water depth below the ice shelves. In the ensemble of simulations, at the glacial maximums, the GrIS coalesced with the IIS to the north and expanded to the continental shelf break to the southwest but remained too restricted to the northeast. In terms of the global mean sea level contribution, at the Last Interglacial (LIG and LGM the ice sheet added 1.46 and −2.59 m, respectively. This LGM contribution by the GrIS is considerably higher (∼  1.26 m than most previous studies whereas the contribution to the LIG highstand is lower (∼  0.7 m. The spatial and temporal behaviour of the northern margin was

  11. Ice Penetrating Radar Reveals Spatially Variable Features in Basal Channel under the Nansen Ice Shelf, Terra Nova Bay, Antarctica

    Science.gov (United States)

    Wray, P. L.; Dow, C. F.; Mueller, D.; Lee, W. S.; Lindzey, L.; Greenbaum, J. S.; Blankenship, D. D.

    2017-12-01

    The stability of Antarctic ice shelves is of great concern as their current thinning and future collapse will contribute to sea-level rise via the acceleration of grounded tributary glaciers into the ocean. The study of the sub-ice-shelf environment is essential for understanding ice-ocean interaction, where warming ocean temperatures have already begun to threaten the long-term viability of Antarctic ice shelves. Obtaining direct measurements of the sub-ice-shelf cavity remains challenging. Here, we demonstrate that ground-based geophysical methods can deliver high resolution monitoring and mapping of the spatial and temporal changes in features, melt rates, and ice mass transport of this environment. In November 2016, 84 km of ground-based, low frequency, Ice Penetrating Radar (IPR) surveys were completed on three sites over the Nansen Ice Shelf in Terra Nova Bay, Antarctica. The surveys examined an ocean-sourced basal channel incised into the bottom of the shelf, originally detected from a large surface depression. Results reveal high resolution features of a several kilometre-wide, 100 m high channel, with 40 m high sub-channels, zones of significant marine ice accumulation, and basal crevasses penetrating large fractions of the ice shelf thickness. Data from multiple airborne geophysical surveys were compared to the November 2016 IPR data to calculate mass change both spatially and temporally. Many of the smaller scale features we detected are not represented through hydrostatic equilibrium as calculated from ice thicknesses, due to bridging stresses, and as such can not be detected with satellite based remote sensing methods. Our in-field geophysical methods produced high-resolution information of these features, which underscores the need for similar surveys over vulnerable ice shelves to better understand ice-ocean processes.

  12. Fun at Antarctic grounding lines: Ice-shelf channels and sediment transport

    Science.gov (United States)

    Drews, Reinhard; Mayer, Christoph; Eisen, Olaf; Helm, Veit; Ehlers, Todd A.; Pattyn, Frank; Berger, Sophie; Favier, Lionel; Hewitt, Ian H.; Ng, Felix; Fürst, Johannes J.; Gillet-Chaulet, Fabien; Bergeot, Nicolas; Matsuoka, Kenichi

    2017-04-01

    Meltwater beneath the polar ice sheets drains, in part, through subglacial conduits. Landforms created by such drainages are abundant in areas formerly covered by ice sheets during the last glacial maximum. However, observations of subglacial conduit dynamics under a contemporary ice sheet are lacking. We present results from ice-penetrating radar to infer the existence of subglacial conduits upstream of the grounding line of Roi Baudouin Ice Shelf, Antarctica. The conduits are aligned with ice-shelf channels, and underlain by esker ridges formed from sediment deposition due to reduced water outflow speed near the grounding line. In turn, the eskers modify local ice flow to initiate the bottom topography of the ice-shelf channels, and create small surface ridges extending onto the shelf. Relict features on the shelf are interpreted to indicate a history of these interactions and variability of past subglacial drainages. 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. To investigate the role of sediment transport beneath ice sheets further, we model the sheet-shelf system of the Ekstömisen catchment, Antarctica. A 3D finite element model (Elmer/ICE) is used to solve the transients full Stokes equation for isotropic, isothermal ice with a dynamic grounding line. We initialize the model with surface topography from the TanDEM-X satellites and by inverting simultaneously for ice viscosity and basal drag using present-day surface velocities. Results produce a flow field which is consitent with sattelite and on-site observations. Solving the age-depth relationship allows comparison with radar isochrones from airborne data, and gives information about the atmospheric/dynamic history of this sector. The flow field will eventually be used to identify potential sediment sources and sinks which we compare with more than 400 km of

  13. Oceanographic mechanisms and penguin population increases during the Little Ice Age in the southern Ross Sea, Antarctica

    Science.gov (United States)

    Yang, Lianjiao; Sun, Liguang; Emslie, Steven D.; Xie, Zhouqing; Huang, Tao; Gao, Yuesong; Yang, Wenqing; Chu, Zhuding; Wang, Yuhong

    2018-01-01

    The Adélie penguin is a well-known indicator for climate and environmental changes. Exploring how large-scale climate variability affects penguin ecology in the past is essential for understanding the responses of Southern Ocean ecosystems to future global change. Using ornithogenic sediments at Cape Bird, Ross Island, Antarctica, we inferred relative population changes of Adélie penguins in the southern Ross Sea over the past 500 yr, and observed an increase in penguin populations during the Little Ice Age (LIA; 1500-1850 AD). We used cadmium content in ancient penguin guano as a proxy of ocean upwelling and identified a close linkage between penguin dynamics and atmospheric circulation and oceanic conditions. During the cold period of ∼1600-1825 AD, a deepened Amundsen Sea Low (ASL) led to stronger winds, intensified ocean upwelling, enlarged Ross Sea and McMurdo Sound polynyas, and thus higher food abundance and penguin populations. We propose a mechanism linking Antarctic marine ecology and atmospheric/oceanic dynamics which can help explain and predict responses of Antarctic high latitudes ecosystems to climate change.

  14. The evolving instability of the remnant Larsen B Ice Shelf and its tributary glaciers

    Science.gov (United States)

    Khazendar, Ala; Borstad, Christopher P.; Scheuchl, Bernd; Rignot, Eric; Seroussi, Helene

    2015-06-01

    Following the 2002 disintegration of the northern and central parts of the Larsen B Ice Shelf, the tributary glaciers of the southern surviving part initially appeared relatively unchanged and hence assumed to be buttressed sufficiently by the remnant ice shelf. Here, we modify this perception with observations from IceBridge altimetry and InSAR-inferred ice flow speeds. Our analyses show that the surfaces of Leppard and Flask glaciers directly upstream from their grounding lines lowered by 15 to 20 m in the period 2002-2011. The thinning appears to be dynamic as the flow of both glaciers and the remnant ice shelf accelerated in the same period. Flask Glacier started accelerating even before the 2002 disintegration, increasing its flow speed by ∼55% between 1997 and 2012. Starbuck Glacier meanwhile did not change much. We hypothesize that the different evolutions of the three glaciers are related to their dissimilar bed topographies and degrees of grounding. We apply numerical modeling and data assimilation that show these changes to be accompanied by a reduction in the buttressing afforded by the remnant ice shelf, a weakening of the shear zones between its flow units and an increase in its fracture. The fast flowing northwestern part of the remnant ice shelf exhibits increasing fragmentation, while the stagnant southeastern part seems to be prone to the formation of large rifts, some of which we show have delimited successive calving events. A large rift only 12 km downstream from the grounding line is currently traversing the stagnant part of the ice shelf, defining the likely front of the next large calving event. We propose that the flow acceleration, ice front retreat and enhanced fracture of the remnant Larsen B Ice Shelf presage its approaching demise.

  15. Evolution of Meltwater on the McMurdo Ice Shelf, Antarctica During Two Summer Melt Seasons

    Science.gov (United States)

    Macdonald, G. J.; Banwell, A. F.; Willis, I.; Mayer, D. P.; Hansen, E. K.; MacAyeal, D. R.

    2017-12-01

    Ice shelves surround > 50% of Antarctica's coast and their response to climate change is key to the ice sheet's future and global sea-level rise. Observations of the development and drainage of 2750 lakes prior to the collapse of the Larsen B Ice Shelf, combined with our understanding of ice-shelf flexure/fracture, suggest that surface meltwater plays a key role in ice-shelf stability, although the present state of knowledge remains limited. Here, we report results of an investigation into the seasonal evolution of meltwater on the McMurdo Ice Shelf (MIS) during the 2015/16 and 2016/17 austral summers using satellite remote sensing, complemented by ground survey. Although the MIS is relatively far south (78° S), it experiences relatively high ablation rates in the west due to adiabatically warmed winds, making it a useful example of how meltwater could evolve on more southerly ice shelves in a warming climate. We calculate the areas and depths of ponded surface meltwater on the ice shelf at different stages of the two melt seasons using a modified NDWI approach and water-depth algorithm applied to both Landsat 8 and Worldview imagery. Data from two automatic weather stations on the ice shelf are used to drive a positive degree-day model to compare our observations of surface water volumes with modelled meltwater production. Results suggest that the spatial and temporal variations in surface meltwater coverage on the ice shelf vary not only with climatic conditions but also in response to other important processes. First, a rift that widens and propagates between the two melt seasons intercepts meltwater streams, redirecting flow and facilitating ponding elsewhere. Second, some lakes from previous years remain frozen over and become pedestalled, causing streams to divert around their perimeter. Third, surface debris conditions also cause large-scale spatial variation in melt rates and the flow and storage of water.

  16. Arctic continental shelf morphology related to sea-ice zonation, Beaufort Sea, Alaska

    Science.gov (United States)

    Reimnitz, E.; Toimil, L.; Barnes, P.

    1978-01-01

    Landsat-1 and NOAA satellite imagery for the winter 1972-1973, and a variety of ice and sea-floor data were used to study sea-ice zonation and dynamics and their relation to bottom morphology and geology on the Beaufort Sea continental shelf of arctic Alaska. In early winter the location of the boundary between undeformed fast ice and westward-drifting pack ice of the Pacific Gyre is controlled by major coastal promontories. Pronounced linear pressure- and shear-ridges, as well as hummock fields, form along this boundary and are stabilized by grounding, generally between the 10- and 20-m isobaths. Slippage along this boundary occurs intermittently at or seaward of the grounded ridges, forming new grounded ridges in a widening zone, the stamukhi zone, which by late winter extends out to the 40-m isobath. Between intermittent events along the stamukhi zone, pack-ice drift and slippage is continuous along the shelf edge, at average rates of 3-10 km/day. Whether slippage occurs along the stamukhi zone or along the shelf edge, it is restricted to a zone several hundred meters wide, and ice seaward of the slip face moves at uniform rates without discernible drag effects. A causal relationship is seen between the spatial distribution of major ice-ridge systems and offshore shoals downdrift of major coastal promontories. The shoals appear to have migrated shoreward under the influence of ice up to 400 m in the last 25 years. The sea floor seaward of these shoals within the stamukhi zone shows high ice-gouge density, large incision depths, and a high degree of disruption of internal sedimentary structures. The concentration of large ice ridges and our sea floor data in the stamukhi zone indicate that much of the available marine energy is expended here, while the inner shelf and coast, where the relatively undeformed fast ice grows, are sheltered. There is evidence that anomalies in the overall arctic shelf profile are related to sea-ice zonation, ice dynamics, and bottom

  17. 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.

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

    Science.gov (United States)

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

    2017-04-01

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

  19. 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.|info:eu-repo/dai/nl/304831905; van de Wal, R.S.W.|info:eu-repo/dai/nl/101899556; 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

  20. 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.

  1. Amundsen Sea simulation with optimized ocean, sea ice, and thermodynamic ice shelf model parameters

    Science.gov (United States)

    Nakayama, Y.; Menemenlis, D.; Schodlok, M.; Heimbach, P.; Nguyen, A. T.; Rignot, E. J.

    2016-12-01

    Ice shelves and glaciers of the West Antarctic Ice Sheet are thinning and melting rapidly in the Amundsen Sea (AS). This is thought to be caused by warm Circumpolar Deep Water (CDW) that intrudes via submarine glacial troughs located at the continental shelf break. Recent studies, however, point out that the depth of thermocline, or thickness of Winter Water (WW, potential temperature below -1 °C located above CDW) is critical in determining the melt rate, especially for the Pine Island Glacier (PIG). For example, the basal melt rate of PIG, which decreased by 50% during summer 2012, has been attributed to thickening of WW. Despite the possible importance of WW thickness on ice shelf melting, previous modeling studies in this region have focused primarily on CDW intrusion and have evaluated numerical simulations based on bottom or deep CDW properties. As a result, none of these models have shown a good representation of WW for the AS. In this study, we adjust a small number of model parameters in a regional Amundsen and Bellingshausen Seas configuration of the Massachusetts Institute of Technology general circulation model (MITgcm) to better fit the available observations during the 2007-2010 period. We choose this time period because summer observations during these years show small interannual variability in the eastern AS. As a result of adjustments, our model shows significantly better match with observations than previous modeling studies, especially for WW. Since density of sea water depends largely on salinity at low temperature, this is crucial for assessing the impact of WW on PIG melt rate. In addition, we conduct several sensitivity studies, showing the impact of surface heat loss on the thickness and properties of WW. We also discuss some preliminary results pertaining to further optimization using the adjoint method. Our work is a first step toward improved representation of ice-shelf ocean interactions in the ECCO (Estimating the Circulation and

  2. Quantitative Biostratigraphic Age Control of Glacimarine Sediments, ANDRILL 1B Drillcore, McMurdo Ice Shelf

    Science.gov (United States)

    Cody, R.; Levy, R.; Crampton, J.; Wilson, G.; Naish, T.; Harwood, D.; Winter, D.; Scherer, R.

    2008-12-01

    Interpretation of glacimarine sedimentary records from Antarctic shelf drillholes has been greatly hampered by the ambiguous age of strata where erosional unconformities and coarse diamictite deposits truncate or omit the mangetostratigraphic and biostratigraphic units used for correlation. However, new quantitative biostratigraphic techniques enable the correlation of sparse, incomplete, and reworking-prone Plio- Pleistocene records of Ross Sea fossil diatom flora with the more extensively documented but potentially diachronous offshore history of species' first and last appearances (FAs and LAs). The approach uses a comprehensive regional database of fossil records and computer-automated search algorithms to (a) find the multidimensional line of correlation (LOC) that best fits local observations, and (b) map out confidence intervals based on the full range of equally parsimonious composite FA/LA sequences and local range-end adjustments. An integrated, quantitative chronostratigraphic model for the AND-1B drillcore was constructed iteratively: the initial LOC was based solely on preliminary on-ice observations of fossil diatom highest and lowest occurrences (HOs and LOs) and their correlation with a database of other local event records from 24 DVDP, CIROS, and IODP drillcore sections. The model was subsequently updated as off-ice work yielded additional biostratigraphic marker events and revised event horizons, Ar/Ar ages for volcanic material, better- constrained magnetostratigraphic interpretations, and refinements to computational/analytical methodology. The current quantitative biostratigraphic age model for the AND-1B hole integrates the local ranges of 29 diatom taxa, 5 dated ashes, and independently constrained ages of 5 paleomagnetic reversals. Results corroborate almost all of the on-ice geomagnetic polarity reversal age interpretations, but identify a previously unrecognized major disconformity (~800kyr hiatus) near 440mbsf. It is significant to note

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

    Science.gov (United States)

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

    2010-12-01

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

  4. Radiocarbon and seismic evidence of ice-sheet extent and the last deglaciation on the mid-Norwegian continental shelf

    International Nuclear Information System (INIS)

    Rokoengen, Kaare; Frengstad, Bjoern

    1999-01-01

    Reconstruction of the ice extent and glacier chronology on the continental shelf off mid-Norway has been severely hampered by the lack of dates from the glacial deposits. Seismic interpretation and new accelerator mass spectrometer radiocarbon dates show that the ice sheet extended to the edge of the continental shelf at the last glacial maximum. The two youngest till units near the shelf edge were deposited about 15000 and 13500 BP. The results indicate that the ice sheet partly reached the shelf break as late as 11000 BP followed by a deglaciation of most of the continental shelf in less than 1000 years

  5. Simulating Ice Shelf Response to Potential Triggers of Collapse Using the Material Point Method

    Science.gov (United States)

    Huth, A.; Smith, B. E.

    2017-12-01

    Weakening or collapse of an ice shelf can reduce the buttressing effect of the shelf on its upstream tributaries, resulting in sea level rise as the flux of grounded ice into the ocean increases. Here we aim to improve sea level rise projections by developing a prognostic 2D plan-view model that simulates the response of an ice sheet/ice shelf system to potential triggers of ice shelf weakening or collapse, such as calving events, thinning, and meltwater ponding. We present initial results for Larsen C. Changes in local ice shelf stresses can affect flow throughout the entire domain, so we place emphasis on calibrating our model to high-resolution data and precisely evolving fracture-weakening and ice geometry throughout the simulations. We primarily derive our initial ice geometry from CryoSat-2 data, and initialize the model by conducting a dual inversion for the ice viscosity parameter and basal friction coefficient that minimizes mismatch between modeled velocities and velocities derived from Landsat data. During simulations, we implement damage mechanics to represent fracture-weakening, and track ice thickness evolution, grounding line position, and ice front position. Since these processes are poorly represented by the Finite Element Method (FEM) due to mesh resolution issues and numerical diffusion, we instead implement the Material Point Method (MPM) for our simulations. In MPM, the ice domain is discretized into a finite set of Lagrangian material points that carry all variables and are tracked throughout the simulation. Each time step, information from the material points is projected to a Eulerian grid where the momentum balance equation (shallow shelf approximation) is solved similarly to FEM, but essentially treating the material points as integration points. The grid solution is then used to determine the new positions of the material points and update variables such as thickness and damage in a diffusion-free Lagrangian frame. The grid does not store

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

    Science.gov (United States)

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

    2017-01-01

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

  7. The effects of sub-ice-shelf melting on dense shelf water formation and export in idealized simulations of Antarctic margins

    Science.gov (United States)

    Marques, Gustavo; Stern, Alon; Harrison, Matthew; Sergienko, Olga; Hallberg, Robert

    2017-04-01

    Dense shelf water (DSW) is formed in coastal polynyas around Antarctica as a result of intense cooling and brine rejection. A fraction of this water reaches ice shelves cavities and is modified due to interactions with sub-ice-shelf melt water. This modified water mass contributes to the formation of Antarctic Bottom Water, and consequently, influences the large-scale ocean circulation. Here, we investigate the role of sub-ice-shelf melting in the formation and export of DSW using idealized simulations with an isopycnal ocean model (MOM6) coupled with a sea ice model (SIS2) and a thermodynamic active ice shelf. A set of experiments is conducted with variable horizontal grid resolutions (0.5, 1.0 and 2.0 km), ice shelf geometries and atmospheric forcing. In all simulations DSW is spontaneously formed in coastal polynyas due to the combined effect of the imposed atmospheric forcing and the ocean state. Our results show that sub-ice-shelf melting can significantly change the rate of dense shelf water outflows, highlighting the importance of this process to correctly represent bottom water formation.

  8. Outlet Glacier-Ice Shelf-Ocean Interactions: Is the Tail Wagging the Dog?

    Science.gov (United States)

    Parizek, B. R.; Walker, R. T.; Rinehart, S. K.

    2009-12-01

    While the massive interior regions of the Antarctic and Greenland Ice Sheets are presently ``resting quietly", the lower elevations of many outlet glaciers are experiencing dramatic adjustments due to changes in ice dynamics and/or surface mass balance. Oceanic and/or atmospheric forcing in these marginal regions often leads to mass deficits for entire outlet basins. Therefore, coupling the wagging tail of ice-ocean interactions with the vast ice-sheet reservoirs is imperative for accurate assessments of future sea-level rise. To study ice-ocean dynamic processes, we couple an ocean-plume model that simulates ice-shelf basal melting rates based on temperature and salinity profiles combined with plume dynamics associated with the geometry of the ice-shelf cavity (following Jenkins, 1991 and Holland and Jenkins, 1999) with a two-dimensional, isothermal model of outlet glacier-ice shelf flow (as used in Alley et al., 2007; Walker et al., 2008; Parizek et al., in review). Depending on the assigned temperature and salinity profiles, the ocean model can simulate both water-mass end-members: either cold High Salinity Shelf Water (HSSW) or relatively warm Circumpolar Deep Water (CDW), as well as between-member conditions. Notably, the coupled system exhibits sensitivity to the initial conditions. In particular, melting concentrated near the grounding line has the greatest effect in forcing grounding-line retreat. Retreat is further enhanced by a positive feedback between the ocean and ice, as the focused melt near the grounding line leads to an increase in the local slope of the basal ice, thereby enhancing buoyancy-driven plume flow and subsequent melt rates.

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

    OpenAIRE

    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.

    2016-01-01

    The article of record as published may be found at http://dx.doi.org/10.1038/nature20136 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. Under...

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

    Science.gov (United States)

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

    2017-12-01

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

  11. Ice-dammed lateral lake and epishelf lake insights into Holocene dynamics of Marguerite Trough Ice Stream and George VI Ice Shelf, Alexander Island, Antarctic Peninsula

    Science.gov (United States)

    Davies, Bethan J.; Hambrey, Michael J.; Glasser, Neil F.; Holt, Tom; Rodés, Angél; Smellie, John L.; Carrivick, Jonathan L.; Blockley, Simon P. E.

    2017-12-01

    We present new data regarding the past dynamics of Marguerite Trough Ice Stream, George VI Ice Shelf and valley glaciers from Ablation Point Massif on Alexander Island, Antarctic Peninsula. This ice-free oasis preserves a geological record of ice stream lateral moraines, ice-dammed lakes, ice-shelf moraines and valley glacier moraines, which we dated using cosmogenic nuclide ages. We provide one of the first detailed sediment-landform assemblage descriptions of epishelf lake shorelines. Marguerite Trough Ice Stream imprinted lateral moraines against eastern Alexander Island at 120 m at Ablation Point Massif. During deglaciation, lateral lakes formed in the Ablation and Moutonnée valleys, dammed against the ice stream in George VI Sound. Exposure ages from boulders on these shorelines yielded ages of 13.9 to 9.7 ka. Following recession of the ice stream, George VI Ice Shelf formed in George VI Sound. An epishelf lake formed at 15-20 m asl in Ablation and Moutonnée valleys, dated from 9.4 to 4.6 ka, suggesting that the lake was stable and persistent for some 5000 years. Lake-level lowering occurred after this, with the lake level at 12 m at 3.1 ± 0.4 ka and at 5 m asl today. A readvance of the valley glaciers on Alexander Island at 4.4 ± 0.7 ka is recorded by valley glacier moraines overlying epishelf lake sediments. We speculate that the glacier readvance, which occurred during a period of warmth, may have been caused by a dynamic response of the glaciers to a lowering in surface elevation of George VI Ice Shelf.

  12. 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.

  13. Unravelling InSAR observed Antarctic ice-shelf flexure using 2-D elastic and viscoelastic modelling

    Science.gov (United States)

    Wild, Christian T.; Marsh, Oliver J.; Rack, Wolfgang

    2018-04-01

    Ice-shelf grounding zones link the Antarctic ice-sheets to the ocean. Differential interferometric synthetic aperture radar (DInSAR) is commonly used to monitor grounding-line locations, but also contains information on grounding-zone ice thickness, ice properties and tidal conditions beneath the ice shelf. Here, we combine in-situ data with numerical modelling of ice-shelf flexure to investigate 2-D controls on the tidal bending pattern on the Southern McMurdo Ice Shelf. We validate our results with 9 double-differential TerraSAR-X interferograms. It is necessary to make adjustments to the tidal forcing to directly compare observations with model output and we find that when these adjustments are small (tide models are required to allow for the full exploitation of DInSAR in grounding-zone glaciology.

  14. Intercomparison of Antarctic ice-shelf, ocean, and sea-ice interactions simulated by MetROMS-iceshelf and FESOM 1.4

    Science.gov (United States)

    Naughten, Kaitlin A.; Meissner, Katrin J.; Galton-Fenzi, Benjamin K.; England, Matthew H.; Timmermann, Ralph; Hellmer, Hartmut H.; Hattermann, Tore; Debernard, Jens B.

    2018-04-01

    An increasing number of Southern Ocean models now include Antarctic ice-shelf cavities, and simulate thermodynamics at the ice-shelf/ocean interface. This adds another level of complexity to Southern Ocean simulations, as ice shelves interact directly with the ocean and indirectly with sea ice. Here, we present the first model intercomparison and evaluation of present-day ocean/sea-ice/ice-shelf interactions, as simulated by two models: a circumpolar Antarctic configuration of MetROMS (ROMS: Regional Ocean Modelling System coupled to CICE: Community Ice CodE) and the global model FESOM (Finite Element Sea-ice Ocean Model), where the latter is run at two different levels of horizontal resolution. From a circumpolar Antarctic perspective, we compare and evaluate simulated ice-shelf basal melting and sub-ice-shelf circulation, as well as sea-ice properties and Southern Ocean water mass characteristics as they influence the sub-ice-shelf processes. Despite their differing numerical methods, the two models produce broadly similar results and share similar biases in many cases. Both models reproduce many key features of observations but struggle to reproduce others, such as the high melt rates observed in the small warm-cavity ice shelves of the Amundsen and Bellingshausen seas. Several differences in model design show a particular influence on the simulations. For example, FESOM's greater topographic smoothing can alter the geometry of some ice-shelf cavities enough to affect their melt rates; this improves at higher resolution, since less smoothing is required. In the interior Southern Ocean, the vertical coordinate system affects the degree of water mass erosion due to spurious diapycnal mixing, with MetROMS' terrain-following coordinate leading to more erosion than FESOM's z coordinate. Finally, increased horizontal resolution in FESOM leads to higher basal melt rates for small ice shelves, through a combination of stronger circulation and small-scale intrusions of

  15. Modelling and parameterizing the influence of tides on ice-shelf melt rates

    Science.gov (United States)

    Jourdain, N.; Molines, J. M.; Le Sommer, J.; Mathiot, P.; de Lavergne, C.; Gurvan, M.; Durand, G.

    2017-12-01

    Significant Antarctic ice sheet thinning is observed in several sectors of Antarctica, in particular in the Amundsen Sea sector, where warm circumpolar deep waters affect basal melting. The later has the potential to trigger marine ice sheet instabilities, with an associated potential for rapid sea level rise. It is therefore crucial to simulate and understand the processes associated with ice-shelf melt rates. In particular, the absence of tides representation in ocean models remains a caveat of numerous ocean hindcasts and climate projections. In the Amundsen Sea, tides are relatively weak and the melt-induced circulation is stronger than the tidal circulation. Using a regional 1/12° ocean model of the Amundsen Sea, we nonetheless find that tides can increase melt rates by up to 36% in some ice-shelf cavities. Among the processes that can possibly affect melt rates, the most important is an increased exchange at the ice/ocean interface resulting from the presence of strong tidal currents along the ice drafts. Approximately a third of this effect is compensated by a decrease in thermal forcing along the ice draft, which is related to an enhanced vertical mixing in the ocean interior in presence of tides. Parameterizing the effect of tides is an alternative to the representation of explicit tides in an ocean model, and has the advantage not to require any filtering of ocean model outputs. We therefore explore different ways to parameterize the effects of tides on ice shelf melt. First, we compare several methods to impose tidal velocities along the ice draft. We show that getting a realistic spatial distribution of tidal velocities in important, and can be deduced from the barotropic velocities of a tide model. Then, we explore several aspects of parameterized tidal mixing to reproduce the tide-induced decrease in thermal forcing along the ice drafts.

  16. Western Ross Sea and McMurdo Sound Ice Forecasting Guide.

    Science.gov (United States)

    1975-06-01

    areal ice distribution and follow the sane historical proqression of pack disintergration . This technique assumes that environmental conditions...30-day) are based on historical ice data which cxnbine averaae disintergration rates as well as averace wind and current drift. Iong-range wind...original 2 to 3 okta area and its new cnfiguration remains the same, the products of ocnoentrations and widths at the verifying time must equal the

  17. Western Ross Sea continental slope gravity currents

    Science.gov (United States)

    Gordon, Arnold L.; Orsi, Alejandro H.; Muench, Robin; Huber, Bruce A.; Zambianchi, Enrico; Visbeck, Martin

    2009-06-01

    Antarctic Bottom Water of the world ocean is derived from dense Shelf Water that is carried downslope by gravity currents at specific sites along the Antarctic margins. Data gathered by the AnSlope and CLIMA programs reveal the presence of energetic gravity currents that are formed over the western continental slope of the Ross Sea when High Salinity Shelf Water exits the shelf through Drygalski Trough. Joides Trough, immediately to the east, offers an additional escape route for less saline Shelf Water, while the Glomar Challenger Trough still farther east is a major pathway for export of the once supercooled low-salinity Ice Shelf Water that forms under the Ross Ice Shelf. The Drygalski Trough gravity currents increase in thickness from ˜100 to ˜400 m on proceeding downslope from ˜600 m (the shelf break) to 1200 m (upper slope) sea floor depth, while turning sharply to the west in response to the Coriolis force during their descent. The mean current pathway trends ˜35° downslope from isobaths. Benthic-layer current and thickness are correlated with the bottom water salinity, which exerts the primary control over the benthic-layer density. A 1-year time series of bottom-water current and hydrographic properties obtained on the slope near the 1000 m isobath indicates episodic pulses of Shelf Water export through Drygalski Trough. These cold (34.75) pulses correlate with strong downslope bottom flow. Extreme examples occurred during austral summer/fall 2003, comprising concentrated High Salinity Shelf Water (-1.9 °C; 34.79) and approaching 1.5 m s -1 at descent angles as large as ˜60° relative to the isobaths. Such events were most common during November-May, consistent with a northward shift in position of the dense Shelf Water during austral summer. The coldest, saltiest bottom water was measured from mid-April to mid-May 2003. The summer/fall export of High Salinity Shelf Water observed in 2004 was less than that seen in 2003. This difference, if real

  18. 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.

    2016-01-01

    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. PMID:27481659

  19. 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

  20. Summer Drivers of Atmospheric Variability Affecting Ice Shelf Thinning in the Amundsen Sea Embayment, West Antarctica

    Science.gov (United States)

    Deb, Pranab; Orr, Andrew; Bromwich, David H.; Nicolas, Julien P.; Turner, John; Hosking, J. Scott

    2018-05-01

    Satellite data and a 35-year hindcast of the Amundsen Sea Embayment summer climate using the Weather Research and Forecasting model are used to understand how regional and large-scale atmospheric variability affects thinning of ice shelves in this sector of West Antarctica by melting from above and below (linked to intrusions of warm water caused by anomalous westerlies over the continental shelf edge). El Niño episodes are associated with an increase in surface melt but do not have a statistically significant impact on westerly winds over the continental shelf edge. The location of the Amundsen Sea Low and the polarity of the Southern Annular Mode (SAM) have negligible impact on surface melting, although a positive SAM and eastward shift of the Amundsen Sea Low cause anomalous westerlies over the continental shelf edge. The projected future increase in El Niño episodes and positive SAM could therefore increase the risk of disintegration of West Antarctic ice shelves.

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

    Science.gov (United States)

    Drews, R.; Brown, J.; Matsuoka, K.; Witrant, E.; Philippe, M.; Hubbard, B.; Pattyn, F.

    2015-10-01

    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.

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

    Science.gov (United States)

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

    2018-05-01

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

  3. 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

    2017-02-09

    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.

  4. Coastal-change and glaciological map of the Ross Island area, Antarctica

    Science.gov (United States)

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

    2010-01-01

    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. The Ross Island area map is bounded by long 141? E. and 175? E. and by lat 76? S. and 81? S. The map covers the part of southern Victoria Land that includes the northwestern Ross Ice Shelf, the McMurdo Ice Shelf, part of the polar plateau and Transantarctic Mountains, the McMurdo Dry Valleys, northernmost Shackleton Coast, Hillary Coast, the southern part of Scott Coast, and Ross Island. Little noticeable change has occurred in the ice fronts on the map, so the focus is on glaciological features. In the western part of the map area, the polar plateau of East Antarctica, once thought to be a featureless region, has subtle wavelike surface forms (megadunes) and flow traces of glaciers that originate far inland and extend to the coast or into the Ross Ice Shelf. There are numerous outlet glaciers. Glaciers drain into the McMurdo Dry Valleys, through the Transantarctic Mountains into the Ross Sea, or into the Ross Ice Shelf. Byrd Glacier is the largest. West of the Transantarctic Mountains are areas of blue ice, readily identifiable on Landsat images, that have been determined to be prime areas for finding meteorites. Three subglacial lakes have been identified in the map area. Because McMurdo Station, the main U.S. scientific research station in Antarctica, is located on Ross Island in the map area, many of these and other features in the area have been studied extensively. The paper version of this map is

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

    Directory of Open Access Journals (Sweden)

    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.

  6. Late Quaternary climatic changes in the Ross Sea area, Antarctica

    International Nuclear Information System (INIS)

    Brambati, A.; Melis, R.; Quaia, T.; Salvi, G.

    2002-01-01

    Ten cores from the Ross Sea continental margin were investigated to detect Late Quaternary climatic changes. Two main climatic cycles over the last 300,000 yr (isotope stages 1-8) were recognised in cores from the continental slope, whereas minor fluctuations over the last 30,000 yr were found in cores from the continental shelf. The occurrence of calcareous taxa within the Last Glacial interval and their subsequent disappearance reveal a general raising of the CCD during the last climatic cycle. In addition, periodical trends of c. 400, c. 700, and c. 1400 yr determined on calcareous foraminifers from sediments of the Joides Basin, indicate fluctuations of the Ross Ice Shelf between 15 and 30 ka BP. (author). 24 refs., 5 figs

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

    Directory of Open Access Journals (Sweden)

    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.

  8. Predicting responses of the Adélie penguin population of Edmonson Point to future sea ice changes in the Ross Sea

    Directory of Open Access Journals (Sweden)

    Tosca eBallerini

    2015-02-01

    Full Text Available Atmosphere-Ocean General Circulation Models (AOGCMs predict changes in the sea ice environment and in atmospheric precipitations over larger areas of Antarctica. These changes are expected to affect the population dynamics of seabirds and marine mammals, but the extent of this influence is not clear. We investigated the future population trajectories of the colony of Adélie penguins at Edmonson Point, in the Ross Sea, from 2010 to 2100. To do so, we incorporated the relationship between sea ice and demographic parameters of the studied colony into a matrix population model. Specifically, we used sea ice projections from AOGCMs and a proxy for snowfall precipitation. Simulations of population persistence under future climate change scenarios showed that a reduction in sea ice extent and an increase in precipitation events during the breeding season will drive the population to extinction. However, the population growth rate estimated by the model was lower than the population growth rate observed during the last decades, suggesting that recruits from other colonies maintain the observed population dynamics at Edmonson Point. This local ‘rescue’ effect is consistent with a metapopulation dynamic for Adélie penguins in the Ross Sea, in which neighboring colonies might exhibit contrasting population trends and different density-dependent effects. In the hypothesis that connectivity with larger source colonies or that local recruitment would decrease, the sink colony at Edmonson Point is predicted to disappear.

  9. High-Resolution Body Wave Tomography of the Ross Sea Embayment, Antarctica

    Science.gov (United States)

    White-Gaynor, A.; Nyblade, A.; Wiens, D. A.; Aster, R. C.; Gerstoft, P.; Bromirski, P. D.; Stephen, R. A.

    2017-12-01

    The West Antarctic Rift System (WARS) is one of the least understood continental rift system on the planet. The 1000 km wide WARS includes the Ross Sea Embayment between Marie Byrd Land and the Transantarctic Mountains (TAMS). Active volcanism on Ross Island continues to challenge our understanding of the generally quiescent rift system. Previous regional-scale body wave tomographic investigations have identified areas of low seismic wave speeds to 200 km depth beneath Ross Island. However, the spatial extent of the low velocity structure across the entirety of the WARS remains poorly constrained due to the insufficient resolution of upper mantle structure under the Ross Sea Embayment away from Ross Island. We utilize teleseismic P wave observations recorded on the RIS/DRIS network, which consists of 34 seismometers deployed across the Ross Ice Shelf, along with data from nearby POLENET and TAMSEIS stations to better resolve this region. Relative P wave travel time residuals from 1300 teleseismic events, obtained using a multichannel cross-correlation method, have been inverted for a seismic velocity model of the upper mantle throughout the Ross Sea Embayment. Our results suggest that the low wave speed structure under Ross Island extends roughly halfway across the Embayment and south along the Transantarctic Mountains. This observation is consistent with a two-phase rifting history for the WARS in which broad, late Cretaceous rifting between Marie Byrd Land and the TAMS transitioned to more focused rifting along the TAMS margin in the Cenozoic.

  10. Minimum distribution of subsea ice-bearing permafrost on the US Beaufort Sea continental shelf

    Science.gov (United States)

    Brothers, Laura L.; Hart, Patrick E.; Ruppel, Carolyn D.

    2012-01-01

    Starting in Late Pleistocene time (~19 ka), sea level rise inundated coastal zones worldwide. On some parts of the present-day circum-Arctic continental shelf, this led to flooding and thawing of formerly subaerial permafrost and probable dissociation of associated gas hydrates. Relict permafrost has never been systematically mapped along the 700-km-long U.S. Beaufort Sea continental shelf and is often assumed to extend to ~120 m water depth, the approximate amount of sea level rise since the Late Pleistocene. Here, 5,000 km of multichannel seismic (MCS) data acquired between 1977 and 1992 were examined for high-velocity (>2.3 km s−1) refractions consistent with ice-bearing, coarse-grained sediments. Permafrost refractions were identified along sea ice-bearing permafrost, which does not extend seaward of 30 km offshore or beyond the 20 m isobath.

  11. Observing Physical and Biological Drivers of pH and O2 in a Seasonal Ice Zone in the Ross Sea Using Profiling Float Data

    Science.gov (United States)

    Briggs, E.; Martz, T. R.; Talley, L. D.; Mazloff, M. R.

    2015-12-01

    Ice cover has strong influence over gas exchange, vertical stability, and biological production which are critical to understanding the Southern Ocean's central role in oceanic biogeochemical cycling and heat and carbon uptake under a changing climate. However the relative influence of physical versus biological processes in this hard-to-study region is poorly understood due to limited observations. Here we present new findings from a profiling float equipped with biogeochemical sensors in the seasonal ice zone of the Ross Sea capturing, for the first time, under-ice pH profile data over a two year timespan from 2014 to the present. The relative influence of physical (e.g. vertical mixing and air-sea gas exchange) and biological (e.g. production and respiration) drivers of pH and O2 within the mixed layer are explored during the phases of ice formation, ice cover, and ice melt over the two seasonal cycles. During the austral fall just prior to and during ice formation, O2 increases as expected due to surface-layer undersaturation and enhanced gas exchange. A small increase in pH is also observed during this phase, but without a biological signal in accompanying profiling float chlorophyll data, which goes against common reasoning from both a biological and physical standpoint. During the phase of ice cover, gas exchange is inhibited and a clear respiration signal is observed in pH and O2 data from which respiration rates are calculated. In the austral spring, ice melt gives rise to substantial ice edge phytoplankton blooms indicated by O2 supersaturation and corresponding increase in pH and large chlorophyll signal. The influence of the duration of ice cover and mixed layer depth on the magnitude of the ice edge blooms is explored between the two seasonal cycles.

  12. 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.

  13. 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.

  14. Ice-Shelf Melt Response to Changing Winds and Glacier Dynamics in the Amundsen Sea Sector, Antarctica

    Science.gov (United States)

    Donat-Magnin, Marion; Jourdain, Nicolas C.; Spence, Paul; Le Sommer, Julien; Gallée, Hubert; Durand, Gaël.

    2017-12-01

    It has been suggested that the coastal Southern Ocean subsurface may warm over the 21st century in response to strengthening and poleward shifting winds, with potential adverse effects on West Antarctic glaciers. However, using a 1/12° ocean regional model that includes ice-shelf cavities, we find a more complex response to changing winds in the Amundsen Sea. Simulated offshore subsurface waters get colder under strengthened and poleward shifted winds representative of the SAM projected trend. The buoyancy-driven circulation induced by ice-shelf melt transports this cold offshore anomaly onto the continental shelf, leading to cooling and decreased melt below 450 m. In the vicinity of ice-shelf fronts, Ekman pumping contributes to raise the isotherms in response to changing winds. This effect overwhelms the horizontal transport of colder offshore waters at intermediate depths (between 200 and 450 m), and therefore increases melt rates in the upper part of the ice-shelf cavities, which reinforces the buoyancy-driven circulation and further contributes to raise the isotherms. Then, prescribing an extreme grounding line retreat projected for 2100, the total melt rates simulated underneath Thwaites and Pine Island are multiplied by 2.5. Such increase is explained by a larger ocean/ice interface exposed to CDW, which is then amplified by a stronger melt-induced circulation along the ice draft. Our main conclusions are that (1) outputs from ocean models that do not represent ice shelf cavities (e.g., CMIP5 models) should not be directly used to predict the thermal forcing of future ice shelf cavities; (2) coupled ocean/ice sheet models with a velocity-dependent melt formulation are needed for future projections of glaciers experiencing a significant grounding line retreat.

  15. Eddy-resolving simulations of the Fimbul Ice Shelf cavity circulation: Basal melting and exchange with open ocean

    Science.gov (United States)

    Hattermann, T.; Smedsrud, L. H.; Nøst, O. A.; Lilly, J. M.; Galton-Fenzi, B. K.

    2014-10-01

    Melting at the base of floating ice shelves is a dominant term in the overall Antarctic mass budget. This study applies a high-resolution regional ice shelf/ocean model, constrained by observations, to (i) quantify present basal mass loss at the Fimbul Ice Shelf (FIS); and (ii) investigate the oceanic mechanisms that govern the heat supply to ice shelves in the Eastern Weddell Sea. The simulations confirm the low melt rates suggested by observations and show that melting is primarily determined by the depth of the coastal thermocline, regulating deep ocean heat fluxes towards the ice. Furthermore, the uneven distribution of ice shelf area at different depths modulates the melting response to oceanic forcing, causing the existence of two distinct states of melting at the FIS. In the simulated present-day state, only small amounts of Modified Warm Deep Water enter the continental shelf, and ocean temperatures beneath the ice are close to the surface freezing point. The basal mass loss in this so-called state of "shallow melting" is mainly controlled by the seasonal inflow of solar-heated surface water affecting large areas of shallow ice in the upper part of the cavity. This is in contrast to a state of "deep melting", in which the thermocline rises above the shelf break depth, establishing a continuous inflow of Warm Deep Water towards the deep ice. The transition between the two states is found to be determined by a complex response of the Antarctic Slope Front overturning circulation to varying climate forcings. A proper representation of these frontal dynamics in climate models will therefore be crucial when assessing the evolution of ice shelf basal melting along this sector of Antarctica.

  16. A modeling experiment on the grounding of an ice shelf in the central Arctic Ocean during MIS 6

    Science.gov (United States)

    Jakobsson, M.; Siegert, M.; Paton, M.

    2003-12-01

    High-resolution chirp sonar subbottom profiles from the Lomonosov Ridge in the central Arctic Ocean, acquired from the Swedish icebreaker Oden in 1996, revealed large-scale erosion of the ridge crest down to depths of 1000 m below present sea level [Jakobsson, 1999]. Subsequent acoustic mapping during the SCICEX nuclear submarine expedition in 1999 showed glacial fluting at the deepest eroded areas and subparallel ice scours from 950 m water depth to the shallowest parts of the ridge crest [Polyak et al., 2001]. The directions of the mapped glaciogenic bed-forms and the redeposition of eroded material on the Amerasian side of the ridge indicate ice flow from the Barents-Kara Sea area. Core studies revealed that sediment drape the eroded areas from Marine Isotope Stage (MIS) 5.5 and, thus, it was proposed that the major erosional event took place during Marine Isotope Stage (MIS) 6 [Jakobsson et al., 2001]. Glacial geological evidence suggests strongly that the Late Saalian (MIS 6) ice sheet margin reached the shelf break of the Barents-Kara Sea [Svendsen et al. in press] and this gives us two possible ways to explain the ice erosional features on the Lomonosov Ridge. One is the grounding of a floating ice shelf and the other is the scouring from large deep tabular iceberg. Here we apply numerical ice sheet modeling to test the hypothesis that an ice shelf emanating from the Barents/Kara seas grounded across part of the Lomonsov Ridge and caused the extensive erosion down to a depth of around 1000 m below present sea level. A series of model experiments was undertaken in which the ice shelf mass balance (surface accumulation and basal melting) and ice shelf strain rates were adjusted. Grounding of the Lomonosov Ridge was not achieved when the ice shelf strain rate was 0.005 yr-1 (i.e. a free flowing ice shelf). However this model produced two interesting findings. First, with basal melt rates of up to 50 cm yr-1 an ice shelf grew from the St. Anna Trough ice stream

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

    Science.gov (United States)

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

    2009-04-01

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

  18. Strontium isotopic study of sediment from the Ross Sea

    International Nuclear Information System (INIS)

    Kovach, J.; Faure, G.

    1977-01-01

    A preliminary report summarizing the results of a study of the strontium-87/strontium-86 ratios and of the rubidium and strontium concentrations of the fine-grained (less than 150 microns) noncarbonate fractions of sediment samples from core E32-25 raised from a depth of 327 fathoms in the Ross Sea at 78 0 31.0'S 164 0 24.7'W was presented. The strontium-87/strontium-86 ratios of the samples analyzed range from 0.7119 to 0.7220. Rubidium and strontium concentrations range, respectively, from 126 to 164 parts per million and from 113 to 174 parts per million. The observed strontium-87/strontium-86 ratios and strontium concentrations in sediment samples from core E32-25 fit a hyperbolic curve. These ratios can be used to estimate the concentrations of volcanogenic detritus in the sediment samples. The results of this study provide additional baseline data for anticipated future studies of sediment cores to be recovered from beneath the Ross Ice Shelf by the Ross Ice Shelf Project. 1 figure

  19. Recent dynamic changes on Fleming Glacier after the disintegration of Wordie Ice Shelf, Antarctic Peninsula

    Science.gov (United States)

    Friedl, Peter; Seehaus, Thorsten C.; Wendt, Anja; Braun, Matthias H.; Höppner, Kathrin

    2018-04-01

    The Antarctic Peninsula is one of the world's regions most affected by climate change. Several ice shelves have retreated, thinned or completely disintegrated during recent decades, leading to acceleration and increased calving of their tributary glaciers. Wordie Ice Shelf, located in Marguerite Bay at the south-western side of the Antarctic Peninsula, completely disintegrated in a series of events between the 1960s and the late 1990s. We investigate the long-term dynamics (1994-2016) of Fleming Glacier after the disintegration of Wordie Ice Shelf by analysing various multi-sensor remote sensing data sets. We present a dense time series of synthetic aperture radar (SAR) surface velocities that reveals a rapid acceleration of Fleming Glacier in 2008 and a phase of further gradual acceleration and upstream propagation of high velocities in 2010-2011.The timing in acceleration correlates with strong upwelling events of warm circumpolar deep water (CDW) into Wordie Bay, most likely leading to increased submarine melt. This, together with continuous dynamic thinning and a deep subglacial trough with a retrograde bed slope close to the terminus probably, has induced unpinning of the glacier tongue in 2008 and gradual grounding line retreat between 2010 and 2011. Our data suggest that the glacier's grounding line had retreated by ˜ 6-9 km between 1996 and 2011, which caused ˜ 56 km2 of the glacier tongue to go afloat. The resulting reduction in buttressing explains a median speedup of ˜ 1.3 m d-1 ( ˜ 27 %) between 2008 and 2011, which we observed along a centre line extending between the grounding line in 1996 and ˜ 16 km upstream. Current median ice thinning rates (2011-2014) along profiles in areas below 1000 m altitude range between ˜ 2.6 to 3.2 m a-1 and are ˜ 70 % higher than between 2004 and 2008. Our study shows that Fleming Glacier is far away from approaching a new equilibrium and that the glacier dynamics are not primarily controlled by the loss of the

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

    Science.gov (United States)

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

    2013-12-01

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

  1. Evaluation of Ice sheet evolution and coastline changes from 1960s in Amery Ice Shelf using multi-source remote sensing images

    Science.gov (United States)

    Qiao, G.; Ye, W.; Scaioni, M.; Liu, S.; Feng, T.; Liu, Y.; Tong, X.; Li, R.

    2013-12-01

    Global change is one of the major challenges that all the nations are commonly facing, and the Antarctica ice sheet changes have been playing a critical role in the global change research field during the past years. Long time-series of ice sheet observations in Antarctica would contribute to the quantitative evaluation and precise prediction of the effects on global change induced by the ice sheet, of which the remote sensing technology would make critical contributions. As the biggest ice shelf and one of the dominant drainage systems in East Antarctic, the Amery Ice Shelf has been making significant contributions to the mass balance of the Antarctic. Study of Amery Ice shelf changes would advance the understanding of Antarctic ice shelf evolution as well as the overall mass balance. At the same time, as one of the important indicators of Antarctica ice sheet characteristics, coastlines that can be detected from remote sensing imagery can help reveal the nature of the changes of ice sheet evolution. Most of the scientific research on Antarctica with satellite remote sensing dated from 1970s after LANDSAT satellite was brought into operation. It was the declassification of the cold war satellite reconnaissance photographs in 1995, known as Declassified Intelligence Satellite Photograph (DISP) that provided a direct overall view of the Antarctica ice-sheet's configuration in 1960s, greatly extending the time span of Antarctica surface observations. This paper will present the evaluation of ice-sheet evolution and coastline changes in Amery Ice Shelf from 1960s, by using multi-source remote sensing images including the DISP images and the modern optical satellite images. The DISP images scanned from negatives were first interior-oriented with the associated parameters, and then bundle block adjustment technology was employed based on the tie points and control points, to derive the mosaic image of the research region. Experimental results of coastlines generated

  2. 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.)

  3. 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

  4. Observing the seasonal cycle of the upper ocean in the Ross Sea, Antarctica, with autonomous profiling floats

    Science.gov (United States)

    Porter, D. F.; Springer, S. R.; Padman, L.; Fricker, H. A.; Bell, R. E.

    2017-12-01

    The upper layers of the Southern Ocean where it meets the Antarctic ice sheet undergoes a large seasonal cycle controlled by surface radiation and by freshwater fluxes, both of which are strongly influenced by sea ice. In regions where seasonal sea ice and icebergs limit use of ice-tethered profilers and conventional moorings, autonomous profiling floats can sample the upper ocean. The deployment of seven Apex floats (by sea) and six ALAMO floats (by air) provides unique upper ocean hydrographic data in the Ross Sea close to the Ross Ice Shelf front. A novel choice of mission parameters - setting parking depth deeper than the seabed - limits their drift, allowing us to deploy the floats close to the ice shelf front, while sea ice avoidance algorithms allow the floats to to sample through winter under sea ice. Hydrographic profiles show the detailed development of the seasonal mixed layer close to the Ross front, and interannual variability of the seasonal mixed layer and deeper water masses on the central Ross Sea continental shelf. After the sea ice breakup in spring, a warm and fresh surface mixed layer develops, further warming and deepening throughout the summer. The mixed layer deepens, with maximum temperatures exceeding 0ºC in mid-February. By March, the surface energy budget becomes negative and sea ice begins to form, creating a cold, saline and dense surface layer. Once these processes overcome the stable summer stratification, convection erodes the surface mixed layer, mixing some heat downwards to deeper layers. There is considerable interannual variability in the evolution and strength of the surface mixed layer: summers with shorter ice-free periods result in a cooler and shallower surface mixed layer, which accumulates less heat than the summers with longer ice-free periods. Early ice breakup occurred in all floats in 2016/17 summer, enhancing the absorbed solar flux leading to a warmer surface mixed layer. Together, these unique measurements from

  5. The role of cooperative iceberg capsize during ice-shelf disintegration

    Science.gov (United States)

    Wilder, W. G.; Burton, J. C.; Amundson, J. M.; Cathles, L. M.; Zhang, W. W.

    2011-12-01

    The physical processes responsible for the sudden, rapid collapse of Antarctic ice-shelves (Larsen B, in 2002; Wilkins, in 2008) are poorly understood. Observations are limited to a handful of satellite images. Thus we have undertaken a series of laboratory-scale experiments using a water-filled tank and "ice" made from buoyant plastic blocks to investigate these processes. Previous experiments have quantified how gravitational potential energy of single-iceberg capsize is converted to other forms of energy [described in Burton et al., submitted], including hydrodynamic forms that may feed back on the ice shelf to cause additional calving. The new experiments reported here examine the energetics of hydrodynamically coupled icebergs that exhibit collective behaviors qualitatively similar to features observed in satellite imagery. Our results suggest that there is a critical proximity at which icebergs will capsize in the same direction an overwhelming majority of the time (cooperative capsize), and a significant part of the gravitational potential energy is converted into translational kinetic energy. We speculate that the residual translational energy observed in our experiments may explain the significant expansion rate (~1 meter/second) of collapsing Antarctic ice-shelves. Burton, J. C., J. M. Amundson, D. S. Abbot, A. Boghosian, L. M. Cathles, S. Correa-Legisos, K. N. Darnell, N. Guttenberg, D. M. Holland, and D. R. MacAyeal. submitted. Laboratory investigations of iceberg-capsize dynamics, energy dissipation and tsunamigenesis. J. Geophys. Res.

  6. Using aerogravity and seismic data to model the bathymetry and upper crustal structure beneath the Pine Island Glacier ice shelf, West Antarctica

    Science.gov (United States)

    Muto, A.; Peters, L. E.; Anandakrishnan, S.; Alley, R. B.; Riverman, K. L.

    2013-12-01

    Recent estimates indicate that ice shelves along the Amundsen Sea coast in West Antarctica are losing substantial mass through sub-ice-shelf melting and contributing to the accelerating mass loss of the grounded ice buttressed by them. For Pine Island Glacier (PIG), relatively warm Circumpolar Deep Water has been identified as the key driver of the sub-ice-shelf melting although poor constraints on PIG sub-ice shelf have restricted thorough understanding of these ice-ocean interactions. Aerogravity data from NASA's Operation IceBridge (OIB) have been useful in identifying large-scale (on the order of ten kilometers) features but the results have relatively large uncertainties due to the inherent non-uniqueness of the gravity inversion. Seismic methods offer the most direct means of providing water thickness and upper crustal geological constraints, but availability of such data sets over the PIG ice shelf has been limited due to logistical constraints. Here we present a comparative analysis of the bathymetry and upper crustal structure beneath the ice shelf of PIG through joint inversion of OIB aerogravity data and in situ active-source seismic measurements collected in the 2012-13 austral summer. Preliminary results indicate improved resolution of the ocean cavity, particularly in the interior and sides of the PIG ice shelf, and sedimentary drape across the region. Seismically derived variations in ice and ocean water densities are also applied to the gravity inversion to produce a more robust model of PIG sub-ice shelf structure, as opposed to commonly used single ice and water densities across the entire study region. Misfits between the seismically-constrained gravity inversion and that estimated previously from aerogravity alone provide insights on the sensitivity of gravity measurements to model perturbations and highlight the limitations of employing gravity data to model ice shelf environments when no other sub-ice constraints are available.

  7. Glacial changes in warm pool climate dominated by shelf exposure and ice sheet albedo

    Science.gov (United States)

    Di Nezio, P. N.; Tierney, J. E.; Otto-Bliesner, B. L.; Timmermann, A.; Bhattacharya, T.; Brady, E. C.; Rosenbloom, N. A.

    2017-12-01

    The mechanisms driving glacial-interglacial changes in the climate of the Indo-Pacific warm pool (IPWP) are unclear. We addressed this issue combining model simulations and paleoclimate reconstructions of the Last Glacial Maximum (LGM). Two drivers - the exposure of tropical shelves due to lower sea level and a monsoonal response to ice sheet albedo - explain the proxy-inferred patterns of hydroclimate change. Shelf exposure influences IPWP climate by weakening the ascending branch of the Walker circulation. This response is amplified by coupled interactions akin to the Bjerknes feedback involving a stronger sea-surface temperature (SST) gradient along the equatorial Indian Ocean (IO). Ice sheet albedo enhances the import of cold, dry air into the tropics, weakening the Afro-Asian monsoon system. This "ventilation" mechanism alters temperature contrasts between the Arabian Sea and surrounding land leading to further monsoon weakening. Additional simulations show that the altered SST patterns associated with these responses are essential for explaining the proxy-inferred changes. Together our results show that ice sheets are a first order driver of tropical climate on glacial-interglacial timescales. While glacial climates are not a straightforward analogue for the future, our finding of an active Bjerknes feedback deserves further attention in the context of future climate projections.

  8. Rossing uranium

    International Nuclear Information System (INIS)

    Anon.

    1979-01-01

    In this article the geology of the deposits of the Rossing uranium mine in Namibia is discussed. The planning of the open-pit mining, the blasting, drilling, handling and the equipment used for these processes are described

  9. Alf Ross

    DEFF Research Database (Denmark)

    Ryberg, Jesper

    En (overvejende) ny generation af akademikere møder og prøver Ross' tanker om emner som retfærdighed, demokrati, statsforfatningsret, ytringsfrihed, straf, erkendelsesteori, etik, logik, fri vilje og sygdom.......En (overvejende) ny generation af akademikere møder og prøver Ross' tanker om emner som retfærdighed, demokrati, statsforfatningsret, ytringsfrihed, straf, erkendelsesteori, etik, logik, fri vilje og sygdom....

  10. Observationally constrained surface mass balance of Larsen C ice shelf, Antarctica

    Directory of Open Access Journals (Sweden)

    P. Kuipers Munneke

    2017-11-01

    Full Text Available The surface mass balance (SMB of the Larsen C ice shelf (LCIS, Antarctica, is poorly constrained due to a dearth of in situ observations. Combining several geophysical techniques, we reconstruct spatial and temporal patterns of SMB over the LCIS. Continuous time series of snow height (2.5–6 years at five locations allow for multi-year estimates of seasonal and annual SMB over the LCIS. There is high interannual variability in SMB as well as spatial variability: in the north, SMB is 0.40 ± 0.06 to 0.41 ± 0.04 m w.e. year−1, while farther south, SMB is up to 0.50 ± 0.05 m w.e. year−1. This difference between north and south is corroborated by winter snow accumulation derived from an airborne radar survey from 2009, which showed an average snow thickness of 0.34 m w.e. north of 66° S, and 0.40 m w.e. south of 68° S. Analysis of ground-penetrating radar from several field campaigns allows for a longer-term perspective of spatial variations in SMB: a particularly strong and coherent reflection horizon below 25–44 m of water-equivalent ice and firn is observed in radargrams collected across the shelf. We propose that this horizon was formed synchronously across the ice shelf. Combining snow height observations, ground and airborne radar, and SMB output from a regional climate model yields a gridded estimate of SMB over the LCIS. It confirms that SMB increases from north to south, overprinted by a gradient of increasing SMB to the west, modulated in the west by föhn-induced sublimation. Previous observations show a strong decrease in firn air content toward the west, which we attribute to spatial patterns of melt, refreezing, and densification rather than SMB.

  11. 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.

  12. The influence of the Amundsen Sea Low on the winds in the Ross Sea and surroundings: Insights from a synoptic climatology

    Science.gov (United States)

    Coggins, Jack H. J.; McDonald, Adrian J.

    2015-03-01

    The Amundsen Sea Low (ASL) is an area of climatologically low atmospheric pressure situated over the Southern Ocean. The depth and location of this feature have significant effects on winds, temperature, moisture transport, and sea ice in its vicinity. In this article, we quantify the modulating effect of this feature on winds over the Ross Sea and Ross Ice Shelf. We examine composites of surface winds sampled according to extrema in ASL depth, longitude, and latitude. We employ the output of a previously developed synoptic climatology to identify the explanatory synoptic-scale forcings. In autumn, winter, and spring (AWS) we find that the impact of the depth of the ASL is smaller than that of its location. The ASL moves eastward when it is deep, thereby reducing its influence on Ross Sea winds. When the ASL is northward, we find strongly enhanced southerly flows over the Ross Sea and Ice Shelf, forced by greater cyclonic activity in the north of the Ross Sea. In summer, we find increased cyclonic flow coinciding with a deeper ASL, despite the ASL being located in the Bellingshausen Sea at this time. The responses to the ASL longitude and latitude are profoundly different to those in AWS, suggesting that relationships are strongly dependent on the varying seasonal location of the low. We examine two metrics of the ASL depth and identify that the absolute mean sea level pressure (MSLP) has a more widespread response than that of the relative MSLP.

  13. 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

  14. Distribution of total alkalinity and pH in the Ross Sea (Antarctica waters during austral summer 2008

    Directory of Open Access Journals (Sweden)

    Paola Rivaro

    2014-10-01

    Full Text Available Measurements of total alkalinity (AT and pH were made in the Ross Sea in January–February 2008 in order to characterize the carbonate system in the Ross Sea and to evaluate the variability associated with different water masses. The main water masses of the Ross Sea, Antarctic Surface Water, High Salinity Shelf Water (HSSW, Deep Ice Shelf Water, Circumpolar Deep Water (CDW and Antarctic Bottom Water, were identified on the basis of the physical and chemical data. In particular, the AT ranged between 2275 and 2374 µmol kg−1 with the lowest values in the surface waters (2275–2346 µmol kg−1, where the influence of the sea-ice melting and of the variability of the physical properties was significant. In the deep layers of the water column, the AT maxima were measured in correspondence to the preferential pathways of the spreading HSSW. The pH had variable values in the surface layer (7.890–8.033 with the highest values in Terra Nova Bay and Ross Sea polynyas. A low pH (7.969±0.025 traced the intrusion of the CDW in the Ross Sea shelf area. All samples revealed waters that were oversaturated with respect to both calcite and aragonite, but near corrosive levels of aragonite saturation state (Ω ca. 1.1–1.2 were associated with the entrainment of CDW over the slope. Aragonite undersaturation is of particular concern for the zooplankton species comprising to calcifying organisms such as pteropods. The partial pressure of CO2 at the sea surface was undersaturated with respect to the atmospheric value, particularly in Terra Nova Bay and the Ross Sea polynyas, but a large variability in the sea–air CO2 fluxes was observed associated with different responses in the strength of the biological and physical processes.

  15. Tidal influences on a future evolution of the Filchner-Ronne Ice Shelf cavity in the Weddell Sea, Antarctica

    Science.gov (United States)

    Mueller, Rachael D.; Hattermann, Tore; Howard, Susan L.; Padman, Laurie

    2018-02-01

    Recent modeling studies of ocean circulation in the southern Weddell Sea, Antarctica, project an increase over this century of ocean heat into the cavity beneath Filchner-Ronne Ice Shelf (FRIS). This increase in ocean heat would lead to more basal melting and a modification of the FRIS ice draft. The corresponding change in cavity shape will affect advective pathways and the spatial distribution of tidal currents, which play important roles in basal melting under FRIS. These feedbacks between heat flux, basal melting, and tides will affect the evolution of FRIS under the influence of a changing climate. We explore these feedbacks with a three-dimensional ocean model of the southern Weddell Sea that is forced by thermodynamic exchange beneath the ice shelf and tides along the open boundaries. Our results show regionally dependent feedbacks that, in some areas, substantially modify the melt rates near the grounding lines of buttressed ice streams that flow into FRIS. These feedbacks are introduced by variations in meltwater production as well as the circulation of this meltwater within the FRIS cavity; they are influenced locally by sensitivity of tidal currents to water column thickness (wct) and non-locally by changes in circulation pathways that transport an integrated history of mixing and meltwater entrainment along flow paths. Our results highlight the importance of including explicit tidal forcing in models of future mass loss from FRIS and from the adjacent grounded ice sheet as individual ice-stream grounding zones experience different responses to warming of the ocean inflow.

  16. Marc Ross

    Indian Academy of Sciences (India)

    Marc Ross. Articles written in Pramana – Journal of Physics. Volume 69 Issue 6 December 2007 pp 1147-1150 Machine Detector Interface. A laser-wire system for the International Linear Collider · Nicolas Delerue Sudhir Dixit Fred Gannaway David Howell Myriam Qurshi Grahame Blair Stewart Boogert Gary Boorman ...

  17. Rossing update

    International Nuclear Information System (INIS)

    Griebel, E.G.

    2000-01-01

    Rossing Uranium, along with the rest of the industry, has been undergoing major changes to adjust to the increasingly competitive uranium market in the 1990's. This paper will outline the developments during the 1990's at the mine, as well as current projects. Rossing has successfully managed the transition through a phase of very low production in the first half of the 1990's, and is now operating at 70% of capacity. During this phase the mine was also able to implement tailings and water management strategies which have reduced fresh water requirements to historical lows, whilst preserving process performance despite cessation of iron oxide supplies. Capital investment in mining equipment, a pre-screening facility in the Fine Crushing plant, and currently an ore sorting pilot plant have been made to enhance Rossing's ability to lower costs further. Rossing is in the middle of a business improvement programme aimed at cutting unit costs in excess of 20%, whilst continuing to improve safety, health and environmental performance. Key focus areas of this programme are maintenance strategy, equipment and plant utilisation and people development. (author)

  18. 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.

  19. Optical-televiewer-based identification and characterization of material facies associated with an Antarctic ice-shelf rift

    OpenAIRE

    Hubbard, B.; Tison, J.-L.; Pattyn, F.; Dierckx, M.; Boereboom, T.; Samyn, D.

    2012-01-01

    We have drilled 13 boreholes within and around a through-cutting rift on the (unofficially named) Roi Baudouin Ice Shelf, East Antarctica. Logging by optical televiewer (OPTV) combined with core inspection has resulted in the identification and characterization of several material facies. Outside the rift, OPTV-imaged annual layering indicates ~150 years of accumulation over the 66m length of one of the boreholes. Luminosity analysis of this image also reveals the presence of numerous dark me...

  20. Circumpolar Deep Water transport and current structure at the Amundsen Sea shelf break

    Science.gov (United States)

    Assmann, Karen M.; Wåhlin, Anna K.; Heywood, Karen J.; Jenkins, Adrian; Kim, Tae Wan; Lee, Sang Hoon

    2017-04-01

    The West Antarctic Ice Sheet has been losing mass at an increasing rate over the past decades. Ocean heat transport to the ice-ocean interface has been identified as an important contributor to this mass loss and the role it plays in ice sheet stability makes it crucial to understand its drivers in order to make accurate future projections of global sea level. While processes closer to the ice-ocean interface modulate this heat transport, its ultimate source is located in the deep basin off the continental shelf as a core of relatively warm, salty water underlying a colder, fresher shallow surface layer. To reach the marine terminating glaciers and the base of floating ice shelves, this warm, salty water mass must cross the bathymetric obstacle of the shelf break. Glacial troughs that intersect the Amundsen shelf break and deepen southwards towards the ice shelf fronts have been shown to play an important role in transporting warm, salty Circumpolar Deep Water (CDW) towards the ice shelves. North of the shelf break, circulation in the Amundsen Sea occupies an intermediate regime between the eastward Antarctic Circumpolar Current that impinges on the shelf break in the Bellingshausen Sea and the westward southern limb of the Ross Gyre that follows the shelf break in the Ross Sea. Hydrographic and mooring observations and numerical model results at the mouth of the central shelf break trough leading to Pine Island and Thwaites Glaciers show a westward wind-driven shelf break current overlying an eastward undercurrent that turns onto the shelf in the trough. It is thought that the existence of the latter feature facilitates the on-shelf transport of CDW. A less clearly defined shelf break depression further west acts as the main pathway for CDW to Dotson and eastern Getz Ice shelves. Model results indicate that a similar eastward undercurrent exists here driving the on-shelf transport of CDW. Two moorings on the upper slope east of the trough entrance show a

  1. Sea Ice Formation Rate and Temporal Variation of Temperature and Salinity at the Vicinity of Wilkins Ice Shelf from Data Collected by Southern Elephant Seals in 2008

    Science.gov (United States)

    Santini, M. F.; Souza, R.; Wainer, I.; Muelbert, M.; Hindell, M.

    2013-05-01

    The use of marine mammals as autonomous platforms for collecting oceanographic data has revolutionized the understanding of physical properties of low or non-sampled regions of the polar oceans. The use of these animals became possible due to advancements in the development of electronic devices, sensors and batteries carried by them. Oceanographic data collected by two southern elephant seals (Mirounga leonina) during the Fall of 2008 were used to infer the sea-ice formation rate in the region adjacent to the Wilkins Ice Shelf, west of the Antarctic Peninsula at that period. The sea-ice formation rate was estimated from the salt balance equation for the upper (100 m) ocean at a daily frequency for the period between 13 February and 20 June 2008. The oceanographic data collected by the animals were also used to present the temporal variation of the water temperature and salinity from surface to 300 m depth in the study area. Sea ice formation rate ranged between 0,087 m/day in early April and 0,008 m/day in late June. Temperature and salinity ranged from -1.84°C to 1.60°C and 32.85 to 34.85, respectively, for the upper 300 m of the water column in the analyzed period. The sea-ice formation rate estimations do not consider water advection, only temporal changes of the vertical profile of salinity. This may cause underestimates of the real sea-ice formation rate. The intense reduction of sea ice rate formation from April to June 2008 may be related to the intrusion of the Circumpolar Depth Water (CDW) into the study region. As a consequence of that we believe that this process can be partly responsible for the disintegration of the Wilkins Ice Shelf during the winter of 2008. The data presented here are considered a new frontier in physical and biological oceanography, providing a new approach for monitoring sea ice changes and oceanographic conditions in polar oceans. This is especially valid for regions covered by sea ice where traditional instruments deployed by

  2. Environmental constraints on West Antarctic ice-sheet formation

    Energy Technology Data Exchange (ETDEWEB)

    Lindstrom, D R; MacAyeal, D R

    1987-01-01

    Small perturbations in Antarctic environmental conditions can culminate in the demise of the Antarctic ice sheet's western sector. This may have happened during the last interglacial period, and could recur within the next millennium due to atmospheric warming from trace gas and CO/sub 2/ increases. In this study, we investigate the importance of sea-level, accumulation rate, and ice influx from the East Antarctic ice sheet in the re-establishment of the West Antarctic ice sheet from a thin cover using a time-dependent numerical ice-shelf model. Our results show that a precursor to the West Antarctic ice sheet can form within 3000 years. Sea-level lowering caused by ice-sheet development in the Northern Hemisphere has the greatest environmental influence. Under favorable conditions, ice grounding occurs over all parts of the West Antarctic ice sheet except up-stream of Thwaites Glacier and in the Ross Sea region.

  3. Influence of submarine morphology on bottom water flow across the western Ross Sea continental margin

    Science.gov (United States)

    Davey, F.J.; Jacobs, S.S.

    2007-01-01

    Multibeam sonar bathymetry documents a lack of significant channels crossing outer continental shelf and slope of the western Ross Sea. This indicates that movement of bottom water across the shelf break into the deep ocean in this area is mainly by laminar or sheet flow. Subtle, ~20 m deep and up to 1000 m wide channels extend down the continental slope, into tributary drainage patterns on the upper rise, and then major erosional submarine canyons. These down-slope channels may have been formed by episodic pulses of rapid down slope water flow, some recorded on bottom current meters, or by sub-ice melt water erosion from an icesheet grounded at the margin. Narrow, mostly linear furrows on the continental shelf thought to be caused by iceberg scouring are randomly oriented, have widths generally less than 400 m and depths less than 30m, and extend to water depths in excess of 600 m.

  4. 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

  5. Ocean wave generation by collapsing ice shelves

    Science.gov (United States)

    Macayeal, D. R.; Bassis, J. N.; Okal, E. A.; Aster, R. C.; Cathles, L. M.

    2008-12-01

    The 28-29 February, 2008, break-up of the Wilkins Ice Shelf, Antarctica, exemplifies the now-familiar, yet largely unexplained pattern of explosive ice-shelf break-up. While environmental warming is a likely ultimate cause of explosive break-up, several key aspects of their short-term behavior need to be explained: (1) The abrupt, near-simultaneous onset of iceberg calving across long spans of the ice front margin; (2) High outward drift velocity (about 0.3 m/s) of a leading phalanx of tabular icebergs that originate from the seaward edge of the intact ice shelf prior to break-up; (3) Rapid coverage of the ocean surface in the wake of this leading phalanx by small, capsized and dismembered tabular icebergs; (4) Extremely large gravitational potential energy release rates, e.g., up to 3 × 1010 W; (5) Lack of proximal iceberg-calving triggers that control the timing of break-up onset and that maintain the high break-up calving rates through to the conclusion of the event. Motivated by seismic records obtained from icebergs and the Ross Ice Shelf that show hundreds of micro- tsunamis emanating from near the ice shelf front, we re-examine the basic dynamic features of ice- shelf/ocean-wave interaction and, in particular, examine the possibility that collapsing ice shelves themselves are a source of waves that stimulate the disintegration process. We propose that ice-shelf generated surface-gravity waves associated with initial calving at an arbitrary seed location produce stress perturbations capable of triggering the onset of calving on the entire ice front. Waves generated by parting detachment rifts, iceberg capsize and break-up act next to stimulate an inverted submarine landslide (ice- slide) process, where gravitational potential energy released by upward movement of buoyant ice is radiated as surface gravity waves in the wake of the advancing phalanx of tabular icebergs. We conclude by describing how field research and remote sensing can be used to test the

  6. Temperature under the Tongue: A paleotemperature record of the Drygalksi Ice Tongue with improved chronology of ice retreat

    Science.gov (United States)

    Subt, C.; Rosenheim, B. E.; Lee, J. I.; Yoo, K. C.; Browne, I. M.; Shevenell, A.

    2017-12-01

    The Ross Embayment is among the most well-studied regions in Antarctica. Despite the relative abundance of data, the style and forcing of deglaciation of the Ross Sea sector following the Last Glacial Maximum (LGM; 23-19 ka) is challenging due to the region's considerable size, complex geometry, and the difficulties in dating Antarctic glaciomarine sedimentary sequences. Ross Sea sediments indicate a dynamic glacial retreat in the western Ross Sea, whereas regional glacial systems may have retreated and advanced multiple times during the last deglaciation. Two marine sediment cores collected near the Drygalski Ice Tongue in the western Ross Sea during 2012 and 2015 Korea Polar Research Institute (KOPRI) expeditions reveal a sequence of alternating diatomaceous muds and oozes interbedded with diamict, which suggest dynamic post-LGM grounded ice retreat in the Ross Sea. Dynamic retreat is hypothesized to have been driven by rising sea levels and warmer ocean waters on the continental shelf, thus a record of upper ocean temperatures should reflect this. Here we present the first post-LGM upper ocean temperature record from the Ross Sea, developed using the TEX86 (tetraether index of lipids consisting of 86 carbons) paleothermometer. To overcome the difficulties of dating these sediments using traditional methods, we apply specialized Ramped PyrOx 14C dating for sediments with high proportions of relict carbon . This technique is particularly well-suited for the post-LGM retreat sedimentary sequences from Antarctic margins because it allows for separation of autochthonous and relict material for dating. By combining organic paleothermometry and state-of-the-art chronologic techniques, we gain a more thorough understanding of upper ocean temperatures in the Ross Sea during the last deglaciation, and their implications for ice retreat.

  7. Extensive Holocene ice sheet grounding line retreat and uplift-driven readvance in West Antarctica

    Science.gov (United States)

    Kingslake, J.; Scherer, R. P.; Albrecht, T.; Coenen, J. J.; Powell, R. D.; Reese, R.; Stansell, N.; Tulaczyk, S. M.; Whitehouse, P. L.

    2017-12-01

    The West Antarctic Ice Sheet (WAIS) reached its Last Glacial Maximum (LGM) extent 29-14 kyr before present. Numerical models used to project future ice-sheet contributions to sea-level rise exploit reconstructions of post-LGM ice mass loss to tune model parameterizations. Ice-sheet reconstructions are poorly constrained in areas where floating ice shelves or a lack of exposed geology obstruct conventional glacial-geological techniques. In the Weddell and Ross Sea sectors, ice-sheet reconstructions have traditionally assumed progressive grounding line (GL) retreat throughout the Holocene. Contrasting this view, using three distinct lines of evidence, we show that the GL retreated hundreds of kilometers inland of its present position, before glacial isostatic rebound during the Mid to Late Holocene caused the GL to readvance to its current position. Evidence for retreat and readvance during the last glacial termination includes (1) widespread radiocarbon in sediment cores recovered from beneath ice streams along the Siple and Gould Coasts, indicating marine exposure at least 200 km inland of the current GL, (2) ice-penetrating radar observations of relic crevasses and other englacial structures preserved in slow-moving grounded ice, indicating ice-shelf grounding and (3) an ensemble of new ice-sheet simulations showing widespread post-LGM retreat of the GL inland of its current location and later readvance. The model indicates that GL readvance across low slope ice-stream troughs requires uplift-driven grounding of the ice shelf on topographic highs (ice rises). Our findings highlight ice-shelf pinning points and lithospheric response to unloading as drivers of major ice-sheet fluctuations. Full WAIS collapse likely requires GL retreat well beyond its current position in the Ronne and Ross Sectors and linkage via Amundsen Sea sector glaciers.

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

    Science.gov (United States)

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

    2017-12-01

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

  9. Ross og demokratiet

    DEFF Research Database (Denmark)

    Svensson, Palle

    2006-01-01

    En kritisk analyse af Alf Ross' teori om demokrati på grundlag af Roberty A. Dahl's begrebsapparat.......En kritisk analyse af Alf Ross' teori om demokrati på grundlag af Roberty A. Dahl's begrebsapparat....

  10. Ross - for altid?

    DEFF Research Database (Denmark)

    Blume, Peter Erik

    2011-01-01

    Med baggrund i Jens Ewalds bog om Alf Ross omtaler artiklen en række de problemstillinger, som bogen behandler, samt vurderer den betydning, Ross har haft og måske fortsat har. Afslutningsvis betones den juridiske biografis betydning.......Med baggrund i Jens Ewalds bog om Alf Ross omtaler artiklen en række de problemstillinger, som bogen behandler, samt vurderer den betydning, Ross har haft og måske fortsat har. Afslutningsvis betones den juridiske biografis betydning....

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

    NARCIS (Netherlands)

    Lenaerts, JTM; Lhermitte, S.L.M.; Drews, R.; Ligtenberg, SRM; Berger, S.; Helm, V.; Smeets, C.J.P.P.; van den Broeke, MR; van de Berg, W.J.; van Meijgaard, E; Eijkelboom, M.; Eisen, O.; Pattyn, F.

    2017-01-01

    Surface melt and subsequent firn air depletion can ultimately lead to disintegration of Antarctic ice shelves1, 2 causing grounded glaciers to accelerate3 and sea level to rise. In the Antarctic Peninsula, foehn winds enhance melting near the grounding line4, which in the recent past has led to the

  12. New details about the LGM extent and subsequent retreat of the West Antarctic Ice Sheet from the easternmost Amundsen Sea Embayment shelf

    Science.gov (United States)

    Klages, J. P.; Hillenbrand, C. D.; Kuhn, G.; Smith, J. A.; Graham, A. G. C.; Nitsche, F. O.; Frederichs, T.; Arndt, J. E.; Gebhardt, C.; Robin, Z.; Uenzelmann-Neben, G.; Gohl, K.; Jernas, P.; Wacker, L.

    2017-12-01

    In recent years several previously undiscovered grounding-zone wedges (GZWs) have been described within the Abbot-Cosgrove palaeo-ice stream trough on the easternmost Amundsen Sea Embayment shelf. These GZWs document both the Last Glacial Maximum (LGM; 26.5-19 cal. ka BP) grounding-line extent and the subsequent episodic retreat within this trough that neighbors the larger Pine Island-Thwaites trough to the west. Here we combine bathymetric, seismic, and geologic data showing that 1) the grounding line in Abbot Trough did not reach the continental shelf break at any time during the last glacial period, and 2) a prominent stacked GZW constructed from six individual wedges lying upon another was deposited 100 km upstream from the LGM grounding-line position. The available data allow for calculating volumes for most of these individual GZWs and for the entire stack. Sediment cores were recovered seawards from the outermost GZW in the trough, and from the individual wedges of the stacked GZW in order to define the LGM grounding-line extent, and provide minimum grounding-line retreat ages for the respective positions on the stacked GZW. We present implications of a grounded-ice free outer shelf throughout the last glacial period. Furthermore, we assess the significance of the grounding-line stillstand period recorded by the stacked GZW in Abbot Trough for the timing of post-LGM retreat of the West Antarctic Ice Sheet from the Amundsen Sea Embayment shelf.

  13. Ice shelf melt rates in Greenland and Antarctica using time-tagged digital imagery from World View and TanDEM-X

    Science.gov (United States)

    Charolais, A.; Rignot, E. J.; Milillo, P.; Scheuchl, B.; Mouginot, J.

    2017-12-01

    The floating extensions of glaciers, or ice shelves, melt vigorously in contact with ocean waters. Melt is non uniform, with the highest melt taking place in the deepest part of the cavity, where thermal forcing is the greatest because of 1) the pressure dependence of the freezing point of the seawater/ice mixture and 2) subglacial water injects fresh, buoyant, cold melt water to fuel stronger ice-ocean interactions. Melt also forms along preferential channels, which are not stationary, and create lines of weakness in the shelf. Ice shelf melt rates have been successfully measured from space over the entire Antarctic continent and on the ice shelves in Greenland using an Eulerian approach that combines ice thickness, ice velocity vectors, surface mass balance data, and measurements of ice thinning rates. The Eulerian approach is limited by the precision of the thickness gradients, typically of a few km, and requires significant spatial averaging to remove advection effects. A Lagrangian approach has been shown to be robust to advection effects and provides higher resolution details. We implemented a Lagrangian methodology for time-tagged World View DEMs by the Polar Geoscience Center (PGS) at the University of Minnesota and time-tagged TanDEM-X DEMs separated by one year. We derive melt rates on a 300-m grid with a precision of a few m/yr. Melt is strongest along grounding lines and along preferred channels. Channels are non-stationary because melt is not the same on opposite sides of the channels. Examining time series of data and comparing with the time-dependent grounding line positions inferred from satellite radar interferometry, we evaluate the magnitude of melt near the grounding line and even within the grounding zone. A non-zero melt rate in the grounding zone has vast implications for ice sheet modeling. This work is funded by a grant from NASA Cryosphere Program.

  14. Dissolved rare earth elements in the central-western sector of the Ross Sea, Southern Ocean: Geochemical tracing of seawater masses.

    Science.gov (United States)

    Turetta, Clara; Barbaro, Elena; Capodaglio, Gabriele; Barbante, Carlo

    2017-09-01

    The present essay contributes to the existing literature on rare earth elements (REEs) in the southern hemisphere by presenting the first data, to our knowledge, on the vertical profiles of dissolved REEs in 71 samples collected in the central-western sector of the Ross Sea (Southern Ocean-SO). The REEs were measured in the water samples collected during the 2002-2003 and 2005-2006 austral summers. 4 samples were collected and analysed in the framework of a test experiment, as part of the WISSARD Project (Whillans Ice Stream Subglacial Access Research Drilling). Our results show significant differences between the REE patterns of the main water masses present in the SO: we could observe specific signature in the High Salinity Shelf Water (HSSW), Ice Shelf Water (ISW) and Low Salinity Shelf Water (LSSW). A significant increase in Terbium (Tb) concentration was observed in the HSSW and ISW, the two principal water masses contributing to the formation of Antarctic Bottom Water (AABW) in the Ross Sea area, and in LSSW. Some of the HSSW samples show enrichment in Neodymium (Nd). Dissolved REE could therefore be used as tracers to understand the deep circulation of the SO (Pacific sector). We hypothesize that: (I) the characteristic dissolved REE pattern may derive from the composition of source area and from the hydrothermal activity of the central-western area of the Ross Sea; (II) the Tb anomaly observed in the AABW on the South Australian platform could be partially explained by the contribution of AABW generated in the Ross Sea region. Copyright © 2017 Elsevier Ltd. All rights reserved.

  15. Characterisation of the nematode community of a low-activity cold seep in the recently ice-shelf free Larsen B area, Eastern Antarctic Peninsula.

    Directory of Open Access Journals (Sweden)

    Freija Hauquier

    Full Text Available BACKGROUND: Recent climate-induced ice-shelf disintegration in the Larsen A (1995 and B (2002 areas along the Eastern Antarctic Peninsula formed a unique opportunity to assess sub-ice-shelf benthic community structure and led to the discovery of unexplored habitats, including a low-activity methane seep beneath the former Larsen B ice shelf. Since both limited particle sedimentation under previously permanent ice coverage and reduced cold-seep activity are likely to influence benthic meiofauna communities, we characterised the nematode assemblage of this low-activity cold seep and compared it with other, now seasonally ice-free, Larsen A and B stations and other Antarctic shelf areas (Weddell Sea and Drake Passage, as well as cold-seep ecosystems world-wide. PRINCIPAL FINDINGS: The nematode community at the Larsen B seep site differed significantly from other Antarctic sites in terms of dominant genera, diversity and abundance. Densities in the seep samples were high (>2000 individuals per 10 cm(2 and showed below-surface maxima at a sediment depth of 2-3 cm in three out of four replicates. All samples were dominated by one species of the family Monhysteridae, which was identified as a Halomonhystera species that comprised between 80 and 86% of the total community. The combination of high densities, deeper density maxima and dominance of one species is shared by many cold-seep ecosystems world-wide and suggested a possible dependence upon a chemosynthetic food source. Yet stable (13C isotopic signals (ranging between -21.97±0.86‰ and -24.85±1.89‰ were indicative of a phytoplankton-derived food source. CONCLUSION: The recent ice-shelf collapse and enhanced food input from surface phytoplankton blooms were responsible for the shift from oligotrophic pre-collapse conditions to a phytodetritus-based community with high densities and low diversity. The parthenogenetic reproduction of the highly dominant Halomonhystera species is rather unusual

  16. Continent-Wide Estimates of Antarctic Strain Rates from Landsat 8-Derived Velocity Grids and Their Application to Ice Shelf Studies

    Science.gov (United States)

    Alley, K. E.; Scambos, T.; Anderson, R. S.; Rajaram, H.; Pope, A.; Haran, T.

    2017-12-01

    Strain rates are fundamental measures of ice flow used in a wide variety of glaciological applications including investigations of bed properties, calculations of basal mass balance on ice shelves, application to Glen's flow law, and many other studies. However, despite their extensive application, strain rates are calculated using widely varying methods and length scales, and the calculation details are often not specified. In this study, we compare the results of nominal and logarithmic strain-rate calculations based on a satellite-derived velocity field of the Antarctic ice sheet generated from Landsat 8 satellite data. Our comparison highlights the differences between the two commonly used approaches in the glaciological literature. We evaluate the errors introduced by each code and their impacts on the results. We also demonstrate the importance of choosing and specifying a length scale over which strain-rate calculations are made, which can have large local impacts on other derived quantities such as basal mass balance on ice shelves. We present strain-rate data products calculated using an approximate viscous length-scale with satellite observations of ice velocity for the Antarctic continent. Finally, we explore the applications of comprehensive strain-rate maps to future ice shelf studies, including investigations of ice fracture, calving patterns, and stability analyses.

  17. Ross og erkendelsesteorien

    DEFF Research Database (Denmark)

    Holtermann, Jakob von Holderstein

    2006-01-01

    Et argument for at den logiske positivismes notoriske problemer ikke - som almindeligt antaget - har gjort Alf Ross' retsfilosofi forældet. Mere konkret påvises det at Ross i virkeligheden passer bedre sammen med den empiriske erkendelsesteori der har rejst sig på den logiske positivismes ruiner....

  18. The Potsdam Parallel Ice Sheet Model (PISM-PIK – Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet

    Directory of Open Access Journals (Sweden)

    M. A. Martin

    2011-09-01

    Full Text Available We present a dynamic equilibrium simulation of the ice sheet-shelf system on Antarctica with the Potsdam Parallel Ice Sheet Model (PISM-PIK. The simulation is initialized with present-day conditions for bed topography and ice thickness and then run to steady state with constant present-day surface mass balance. Surface temperature and sub-shelf basal melt distribution are parameterized. Grounding lines and calving fronts are free to evolve, and their modeled equilibrium state is compared to observational data. A physically-motivated calving law based on horizontal spreading rates allows for realistic calving fronts for various types of shelves. Steady-state dynamics including surface velocity and ice flux are analyzed for whole Antarctica and the Ronne-Filchner and Ross ice shelf areas in particular. The results show that the different flow regimes in sheet and shelves, and the transition zone between them, are captured reasonably well, supporting the approach of superposition of SIA and SSA for the representation of fast motion of grounded ice. This approach also leads to a natural emergence of sliding-dominated flow in stream-like features in this new 3-D marine ice sheet model.

  19. The Potsdam Parallel Ice Sheet Model (PISM-PIK) - Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet

    Science.gov (United States)

    Martin, M. A.; Winkelmann, R.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.

    2011-09-01

    We present a dynamic equilibrium simulation of the ice sheet-shelf system on Antarctica with the Potsdam Parallel Ice Sheet Model (PISM-PIK). The simulation is initialized with present-day conditions for bed topography and ice thickness and then run to steady state with constant present-day surface mass balance. Surface temperature and sub-shelf basal melt distribution are parameterized. Grounding lines and calving fronts are free to evolve, and their modeled equilibrium state is compared to observational data. A physically-motivated calving law based on horizontal spreading rates allows for realistic calving fronts for various types of shelves. Steady-state dynamics including surface velocity and ice flux are analyzed for whole Antarctica and the Ronne-Filchner and Ross ice shelf areas in particular. The results show that the different flow regimes in sheet and shelves, and the transition zone between them, are captured reasonably well, supporting the approach of superposition of SIA and SSA for the representation of fast motion of grounded ice. This approach also leads to a natural emergence of sliding-dominated flow in stream-like features in this new 3-D marine ice sheet model.

  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. New constraints on the structure and dynamics of the East Antarctic Ice Sheet from the joint IPY/Ice Bridge ICECAP aerogeophysical project

    Science.gov (United States)

    Blankenship, D. D.; Young, D. A.; Siegert, M. J.; van Ommen, T. D.; Roberts, J. L.; Wright, A.; Warner, R. C.; Holt, J. W.; Young, N. W.; Le Meur, E.; Legresy, B.; Cavitte, M.; Icecap Team

    2010-12-01

    Ice within marine basins of East Antarctica, and their outlets, represent the ultimate limit on sea level change. The region of East Antarctica between the Ross Sea and Wilkes Land hosts a number of major basin, but has been poorly understood. Long range aerogeophysics from US, Australian and French stations, with significant British and IceBridge support, has, under the banner of the ICECAP project, greatly improved our knowledge of ice thickness, surface elevation, and crustal structure of the Wilkes and Aurora Subglacial Basins, as well as the Totten Glacier, Cook Ice Shelf, and Byrd Glacier. We will discuss the evolution of the Wilkes and Aurora Subglacial Basins, new constraints on the geometry of the major outlet glaciers, as well as our results from surface elevation change measurements over dynamic regions of the ice sheet. We will discuss the implications of our data for the presence of mid Pleistocene ice in central East Antarctica. Future directions for ICECAP will be discussed.

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

    Science.gov (United States)

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

    2017-12-01

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

  3. Sedimentary processes on the NW Iberian Continental Shelf since the Little Ice Age

    Science.gov (United States)

    Martins, Virgínia; Figueira, Rubens Cesar Lopes; França, Elvis Joacir; Ferreira, Paulo Alves de Lima; Martins, Paula; Santos, José Francisco; Dias, João Alveirinho; Laut, Lazaro L. M.; Monge Soares, António M.; Silva, Eduardo Ferreira da; Rocha, Fernando

    2012-05-01

    The OMEX core CD110 W90, retrieved from the Douro Mud Patch (DMP) off the River Douro in the north of Portugal, records the period since the beginning of Little Ice Age (LIA). The core chronology is based upon the data attributes for 210Pb, 137Cs and a 14C dating from a level near the core base. Geochemical, granulometric, microfaunal (benthic foraminifera) and compositional data suggest the occurrence of precipitation changes which may have been, at least partially, influenced by the North Atlantic Oscillation (NAO), that contributes to the regulation of the ocean-atmosphere dynamics in the North Atlantic. Southwesterly Atlantic storm track is associated with the negative phases of the NAO, when the Azores High is anomalously weak, higher oceanographic hydrodynamism, downwelling events and increased rainfall generally occurs. Prevalence of these characteristics during the LIA left a record that corresponds to phases of major floods. During these phases the DMP received a higher contribution of relatively coarse-grained terrigenous sediments, enriched in quartz particles, which diluted the contribution of other minerals, as indicated by reduced concentrations of several lithogenic chemical elements such as: Al, As, Ba, Ce, Co, Cu, Fe, K, La, Li, Mg, Mn, Mo, Na, Ni, P, Rb, Sc, Sn, Th, V and Y. The presence of biogenic carbonate particles also underwent dilution, as revealed by the smaller abundance of foraminifera and correlative lower concentrations of Ca and Sr. During this period, the DMP also received an increased contribution of organic matter, indicated by higher values of lignin remains and a benthic foraminifera high productivity index, or BFHP, which gave rise to early diagenetic changes with pyrite formation. Since the beginning of the 20th century this contribution diminished, probably due to several drier periods and the impact of human activities in the river basins, e.g. construction of dams, or, on the littoral areas, construction of hard

  4. Effect of vacuum-packaging and low dose gamma irradiation on the microbial, bio-chemical quality and shelf life of peeled shrimp (Litopenaeus vannamei) during ice storage

    International Nuclear Information System (INIS)

    Bojayanaik, Manjanaik; Naroth, Kavya; Prasad, Surjith; Shetty, Veena; Hiriyur, Somashekarappa; Patil, Rajashekar

    2015-01-01

    The present investigation was carried out to see the combined effect of vacuum packaging and low dose gamma irradiation (3kGy) on the shelf life of peeled and undeveined shrimp (Litopeanus vannamie) during ice storage. The fresh farm raised shrimps were peeled and un deveined, packed in high density polyethylene bags (aerobic and vacuum packaging) and were divided into four groups viz. control (C), Irradiated (I), Vacuum packed (V) and vacuum-packed with irradiation (VI). The two groups (I and VI) were irradiated at 3 kGy (Dose rate at the rate 6.043 kGy/hr) and aseptically stored in ice in an insulated polystyrene box. All the samples were periodically analysed for microbial (Total bacterial load, total Coliform, Faecal Coliforms, Staphylococcus, Salmonella, Vibrios and E. coli) and bio chemical (TVB-N, TMA, TBARS and pH) quality. The results revealed that the combination of low dose gamma irradiation and vacuum packaging had a significant effect on microbial load (p>0.05). The TVB-N, TMA-N, TBARS and pH were significantly lower in vacuum packed with irradiation when compare to non-irradiated and aerobically packed shrimp (p> 0.05), and shelf life of peeled shrimp extended up to 21 days in ice storage. (author)

  5. A comparison of basal reflectivity and ice velocity in East Antarctica

    Directory of Open Access Journals (Sweden)

    R. W. Jacobel

    2010-10-01

    Full Text Available Ground-based radio echo sounding data acquired along the 1700 km US-ITASE traverse have been used to determine ice attenuation and relative basal reflectivity across the major catchments funneling ice from East Antarctica to the Ross Ice Shelf. We find that basal reflectivity varies locally by up to 40 dB which we interpret as due to changes in the phase state at the bed. Some, though not all, areas of high local reflectivity are observed to have flat-lying bed reflections indicative of sub-glacial lakes. We compare basal reflectivity to ice balance velocity and find a general association of higher flow speeds with high radar reflection strength. This set of observations from two independent remotely sensed geophysical data sets extends the range of field observations to the interior of East Antarctica and confirms the importance of basal lubrication on modulating the ice dynamics of the largest ice sheet on the planet.

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

    Science.gov (United States)

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

    2015-04-01

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

  7. WHISPERS Project on the easternmost slope of the Ross Sea (Antarctica): preliminary results.

    Science.gov (United States)

    Olivo, E.; De Santis, L.; Bergamasco, A.; Colleoni, F.; Gales, J. A.; Florindo-Lopez, C.; Kim, S.; Kovacevic, V.; Rebesco, M.

    2017-12-01

    The advance and retreat of the West Antarctic Ice Sheet from the outer continental shelf and the oceanic circulation are the main causes of the depositional processes on the Ross Sea continental slope, at present time and during the most of the Cenozoic. Currently the Antarctic Bottom Water formation is directly linked to the relatively warm Circumpolar Deep Water that, encroaching the continental shelf, mixes with the colder Ross Sea Bottom Water. Detailed multibeam and geological surveys useful to locate and characterize peculiar morphological structures on the bottom are essential to study how the glacial and oceanographic processes interact with the seabed sediments. In the framework of the PNRA-WHISPERS project (XXXIIth Italian Antarctic expedition - January/March 2017), new multibeam bathymetric, sub-bottom chirp, were acquired from the easternmost margin of the Ross Sea, on the southeastern side of the Hayes Bank, usually covered by sea ice. We observed on the upper slope erosional features (incised gullies of likely glacial meltwater origin). A broad scar in the upper slope is characterized by an elongated SSW-NNE ridge (10 km long, 850-1200 m water depth, 2 km wide), that may be a remnants of previous glacial or debris flow deposits, eroded by meltwater outwash discharge at the beginning of grounding ice retreat and by RSBW cascading along the slope, as documented by Expandable Bathy-Thermograph and Acoustic Depth Current Profile data. Sub-bottom chirp profiles crossing this ridge show a very low amplitude reflective sea bed, supporting the hypothesis of its soft sediment nature, in good agreement with a very low acoustic velocity obtained by multichannel seismic data reprocessing. The occurrence of internal stratification on 2D multichannel seismic profiles would discount a gas-fluids related mud volcano origin. No sediment cores were collected, due to bad sea conditions and limited ship time, further data collection would be needed to fully understand

  8. Preserved Crevasse Casts in the Whales Deep Basin, eastern Ross Sea

    Science.gov (United States)

    Bart, P. J.; Tulaczyk, S. M.

    2017-12-01

    A recent seismic stratigraphic study showed that the large bathymetric saddle in the Whales Deep Basin in eastern Ross Sea is a compound grounding zone wedge (CGZW). The basin was occupied by the paleo Bindschadler Ice Stream when grounded ice advanced to the outer continental shelf during the last glacial maximum (LGM). The CGZW is composed of at least seven overlapping GZWs. The crest of the bathymetric saddle corresponds to the grounding zone of GZW7, i.e., the seventh GZW. The north face of the saddle is essentially equivalent to the GZW7 foreset and the south side of the saddle is the GZW7 topset, i.e., the seafloor surface to which the paleo Bindschadler Ice Stream was grounded. The GZW7 topset is mantled by a series of relatively small-amplitude, but very long, ridges with low sinuosity. These ridges were previously imaged by Mosola and Anderson (2006). Here we show a larger-area multibeam survey that was acquired in 2015 during expedition NBP1502B. The larger-area multibeam survey shows that the ridges have amplitudes ranging from 2 to 11 m above grade and have an overall northeast-southwest orientation over an area of at least 500 km2 on the central and western flank of Whales Deep Basin middle continental shelf in water depths ranging from 500 to 550 m. The ridges have spacing that mostly range between 1 and 2 km. The longest ridges are observed to be 40 km. The ridges in the center of the trough have flatter tops than those in the shallower water on the flank of Houtz Bank. In our ongoing investigation of these interesting features, we hypothesize that the ridges formed below a rapidly flowing ice stream as it thinned and was decoupling from the bed towards the end of GZW7 deposition. High ice deformation rates accompanying this process caused the development of large basal crevasses or ice shelf rifts that reached the seafloor. Subglacial till was scraped and collected into lower parts of these crevasses/rifts. Chronologic data indicates that these

  9. Glacial removal of late Cenozoic subglacially emplaced volcanic edifices by the West Antarctic ice sheet

    Science.gov (United States)

    Behrendt, John C.; Blankenship, D.D.; Damaske, D.; Cooper, A. K.

    1995-01-01

    Local maxima of the horizontal gradient of pseudogravity from closely spaced aeromagnetic surveys over the Ross Sea, northwestern Ross Ice Shelf, and the West Antarctic ice sheet, reveal a linear magnetic rift fabric and numerous subcircular, high-amplitude anomalies. Geophysical data indicate two or three youthful volcanic edifices at widely separated areas beneath the sea and ice cover in the West Antarctic rift system. In contrast, we suggest glacial removal of edifices of volcanic sources of many more anomalies. Magnetic models, controlled by marine seismic reflection and radar ice-sounding data, allow us to infer that glacial removal of the associated late Cenozoic volcanic edifices (probably debris, comprising pillow breccias, and hyaloclastites) has occurred essentially concomitantly with their subglacial eruption. "Removal' of unconsolidated volcanic debris erupted beneath the ice is probably a more appropriate term than "erosion', given its fragmented, ice-contact origin. The exposed volcanoes may have been protected from erosion by the surrounding ice sheet because of more competent rock or high elevation above the ice sheet. -from Authors

  10. Potential of oregano essential oil and MAP to extend the shelf life of fresh swordfish: a comparative study with ice storage.

    Science.gov (United States)

    Giatrakou, V; Kykkidou, S; Papavergou, A; Kontominas, M G; Savvaidis, I N

    2008-05-01

    The present study evaluated the effect of modified atmosphere packaging (MAP, 5% O(2)/50% CO(2)/45% N(2); treatment M), the addition of oregano oil (0.1%, v/w; treatment AO) as a natural preservative, as well as their combination (treatment MO) on the quality and shelf life extension of fresh Mediterranean swordfish fillets during a refrigerated storage (4 degrees C) period of 18 d. Simultaneously, swordfish fillets were stored under aerobic conditions (control treatment A, 4 degrees C) and on ice (usual commercial method of preservation, treatment I, 0 degrees C). Among the 5 treatments examined in the present study, the most effective one to inhibit the microbial and sensory spoilage proved to be the MO treatment, achieving a shelf life extension of 8 to 9 d. The dominant bacteria in the microflora of swordfish, irrespective of treatment, were the Pseudomonads and the H(2)S-producing bacteria, while both lactic acid bacteria (LAB) and the Enterobacteriaceae produced the lowest populations in swordfish samples kept on ice. Among the chemical indices examined, thiobarbituric acid (TBA) values showed no specific trend of lipid oxidation for swordfish, irrespective of treatment. Final trimethylamine nitrogen (TMA-N) and total volatile basic nitrogen (TVB-N) values for treatments, A, AO, M, and MO ranged between 1.33 and 14.29 mg N/100 g and 14.11 to 55.52 mg N/100 g, respectively, whereas for I samples they remained almost unchanged during storage. Sensory analysis (taste attribute) correlated well with microbiological analysis, indicating a shelf life of approximately 5 to 6 d for control, 10 to 11 d for AO, 12 d for I, 13 d for M, and 14 d for MO samples.

  11. The Rossing file

    International Nuclear Information System (INIS)

    Roberts, A.

    1980-01-01

    The subject is discussed under the headings: the issues; Rio Tinto-Zinc; Namibia; the United Nations Decree No. 1; enter RTZ; signing the contracts; Namibia's response -SWAPO; the Rossing Mine; workers' voice. It is argued that the uranium mining operations are illegal. The wages, working conditions and living standards of the workers are criticized. (U.K.)

  12. Rossing reaps training benefits

    Energy Technology Data Exchange (ETDEWEB)

    1982-06-17

    A training program for unskilled operators at the Rossing Uranium Mine provides on avenue for a number of Namibians to become skilled workers without doing an apprenticeship and despite a lack of basic education. The Patterson plan has worked well so far for the purpose. A cadet scheme for leadership and trust foundation for scholarship have also been implemented.

  13. Rossing uranium 1979

    International Nuclear Information System (INIS)

    Anon.

    1979-01-01

    This report describes the activities and organization of the Rossing uranium mine in South West Africa. The development of the mine during the last six years is described as well as the geology of the uranium deposits and aspects of the mining operations. The manpower structure and training possibilities for personnel are described

  14. Rossing reaps training benefits

    International Nuclear Information System (INIS)

    Anon.

    1982-01-01

    A training program for unskilled operators at the Rossing Uranium Mine provides on avenue for a number of Namibians to become skilled workers without doing an apprenticeship and despite a lack of basic education. The Patterson plan has worked well so far for the purpose. A cadet scheme for leadership and trust foundation for scholarship have also been implemented

  15. Detrital Carbonate Events on the Labrador Shelf, a 13 to 7 kyr Template for Freshwater Forcing From the Laurentide Ice Sheet

    Science.gov (United States)

    Jennings, A. E.; Andrews, J. T.

    2008-12-01

    A complex sequence of abrupt glacial advances and retreats punctuate the late phases of Laurentide Ice Sheet deglaciation. These episodes have been reconstructed from interpretation and mapping of glacial deposits on land and in marine basins proximal to the former ice margins in Hudson Strait, Hudson Bay, and the SE Baffin Island shelf. As these events likely produced pulses of freshwater discharge into the North Altantic, which may be responsible for rapid climate change, their timing and magnitude need to be understood. The timing of these events is well constrained by radiocarbon ages, but the ocean reservoir age in ice proximal areas is subject to very large uncertainties, making it difficult to determine calibrated ages for the glacial events so that they can be compared to other climate records. We suggest that the sequence of high detrital carbonate peaks in Holocene and Late Glacial sediments in the Cartwright Saddle of the Labrador shelf provides a template of the abrupt glacial events of the NE margin of the Laurentide Ice Sheet, particularly events that issued from Hudson Strait and Hudson Bay, but possibly including events in Baffin Bay. Once the Labrador Shelf was deglaciated and the local ice had retreated inland, the Cartwright Saddle was a distal trap for sediments released from Hudson Strait and other ice sheet outlets farther north as their sediments and meltwater were carried southwards by surface currents. Core MD99-2236 contains a sediment record beginning c. 13.9 cal ka. We assume a marine reservoir age for the Cartwright Saddle of 450 yrs, which is reasonable given the ice distal and oceanic position of the site. Carbonate was measured on average at a 30 yr time resolution. Carbonate values are elevated between 11.7 and 7 cal kyr BP, with six spikes exceeding 30 percent. Each spike corresponds to a light isotope spike in foraminifers, suggesting that each major spike is associated with a pulse of glacial meltwater. Elevated IRD counts

  16. Summer Distribution of Co2 Partial Pressure In The Ross Sea, Antarctica, and Relations With Biological Activity

    Science.gov (United States)

    Sandrini, S.; Tositti, L.; Tubertini, O.; Ceradini, S.; Palucci, A.; Barbini, R.; Fantoni, R.; Colao, F.; Ferrari, G. M.

    The oceans play a key role in the processes responsible for global climate changes, in fact the oceanic uptake of anthropogenic atmospheric carbon dioxide is estimated to be 17-39The Southern Ocean and Antarctic marginal seas are considered to absorb up to half of this fraction. The Ross Sea, during the summer pack-ice melting, expe- riences rapid seasonal outgrowths, giving rise to phytoplankton blooms, especially in polynya areas near the coast line. This has a direct influence on pCO2 concentration in surface water, and hence on CO2 fluxes between ocean and atmosphere. Both the Ross Sea and the Southern Ocean transect between New Zealand and Antarctica are sys- tematically investigated during Italian Antarctic oceanographic campaigns onboard of the R/V Italica. During the XVI expedition, which took place in January and Febru- ary 2001, simultaneous measurements of surface pCO2 and Chlorophyll-a by laser remote-sensing apparatus were collected. Chlorophyll-a and pCO2 showed a general anticorrelation along the cruise. The survey has revealed the presence of high produc- tive regions in the polynya and close to the ice edge. The linear regression analysis of the chl-a vs pCO2 values improved our knowledge of the time evolution of the phyto- planktonic growth, independently measured by means of the laser yield, thus allowing for discrimination between different initial and final blooms in the Antarctic Ross Sea. The results obtained are here presented and discussed. They confirm the importance of biological production in the net absorption of atmospheric CO2 in continental shelf zones.

  17. Phenolic compounds in Ross Sea water

    Science.gov (United States)

    Zangrando, Roberta; Barbaro, Elena; Gambaro, Andrea; Barbante, Carlo; Corami, Fabiana; Kehrwald, Natalie; Capodaglio, Gabriele

    2016-04-01

    Phenolic compounds are semi-volatile organic compounds produced during biomass burning and lignin degradation in water. In atmospheric and paleoclimatic ice cores studies, these compounds are used as biomarkers of wood combustion and supply information on the type of combusted biomass. Phenolic compounds are therefore indicators of paleoclimatic interest. Recent studies of Antarctic aerosols highlighted that phenolic compounds in Antarctica are not exclusively attributable to biomass burning but also derive from marine sources. In order to study the marine contribution to aerosols we developed an analytical method to determine the concentration of vanillic acid, vanillin, p-coumaric acid, syringic acid, isovanillic acid, homovanillic acid, syringaldehyde, acetosyringone and acetovanillone present in dissolved and particle phases in Sea Ross waters using HPLC-MS/MS. The analytical method was validated and used to quantify phenolic compounds in 28 sea water samples collected during a 2012 Ross Sea R/V cruise. The observed compounds were vanillic acid, vanillin, acetovanillone and p-coumaric acid with concentrations in the ng/L range. Higher concentrations of analytes were present in the dissolved phase than in the particle phase. Sample concentrations were greatest in the coastal, surficial and less saline Ross Sea waters near Victoria Land.

  18. 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.

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

    NARCIS (Netherlands)

    Blaschek, M.; Renssen, H.

    2013-01-01

    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

  20. Bandura, Ross, and Ross: Observational Learning and the Bobo Doll

    Science.gov (United States)

    Artino, Anthony R., Jr.

    2007-01-01

    Since the publication of their seminal article entitled, "Transmission of Aggression Through Imitation of Aggressive Models" (Bandura, Ross, & Ross, 1961), the work of Albert Bandura and his co-authors has had an immeasurable impact on the field of psychology, in general, and educational psychology, more specifically. The purpose of this report is…

  1. Uranium extraction at Rossing

    International Nuclear Information System (INIS)

    Kesler, S.B.; Fahrbach, D.O.E.

    1982-01-01

    Rossing Uranium Ltd. operates a large open pit uranium mine and extraction plant at a remote site in the Namib desert. Production started at the plant in 1978. A ferric leach process was introduced later, and the new leach plant began commissioning in October 1981. The process has proved to be reliable and easily controlled. Ferric iron is supplied through recovery from the acid plant calcine, and levels can be maintained above the design levels. Leach extractions were increased more than expected when this process was adopted, and the throughput has been considerably reduced, allowing cost savings in mining and milling

  2. 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.

  3. Rossing set for great future

    International Nuclear Information System (INIS)

    Anon.

    1978-01-01

    Rio Tinto's Rossing open pit operation - the world's largest uranium mine - has had difficult birth pangs. The teething troubles which beset the mine are examined, together with the mining and extraction methods employed. Rossing's enlightened ideas on the labour question are also covered

  4. Distribution and ventilation of water masses in the western Ross Sea inferred from CFC measurements

    Science.gov (United States)

    Rivaro, Paola; Ianni, Carmela; Magi, Emanuele; Massolo, Serena; Budillon, Giorgio; Smethie, William M.

    2015-03-01

    During the CLIMA Project (R.V. Italica cruise PNRA XVI, January-February 2001), hydrographic and chlorofluorocarbons (CFCs) observations were obtained, particularly in the western Ross Sea. Their distribution demonstrated water mass structure and ventilation processes in the investigated areas. In the surface waters (AASW) the CFC saturation levels varied spatially: CFCs were undersaturated in all the areas (range from 80 to 90%), with the exception of few stations sampled near Ross Island. In particular, the Terra Nova Bay polynya, where high salinity shelf water (HSSW) is produced, was a low-saturated surface area (74%) with respect to CFCs. Throughout most of the shelf area, the presence of modified circumpolar deep water (MCDW) was reflected in a mid-depth CFC concentration minima. Beneath the MCDW, CFC concentrations generally increased in the shelf waters towards the seafloor. We estimated that the corresponding CFCs saturation level in the source water region for HSSW was about 68-70%. Waters with high CFC concentrations were detected in the western Ross Sea on the down slope side of the Drygalski Trough, indicating that AABW was being supplied to the deep Antarctic Basin. Estimates of ventilation ages depend strongly on the saturation levels. We calculated ventilation ages using the saturation level calibrated tracer ratio, CFC11/CFC12. We deduced a mean residence time of the shelf waters of about 6-7 years between the western Ross Sea source and the shelf break.

  5. Antarctic Ice-Sheet Mass Balance from Satellite Altimetry 1992 to 2001

    Science.gov (United States)

    Zwally, H. Jay; Brenner, Anita C.; Cornejo, Helen; Giovinetto, Mario; Saba, Jack L.; Yi, Donghui

    2003-01-01

    A major uncertainty in understanding the causes of the current rate of sea level rise is the potential contributions from mass imbalances of the Greenland and Antarctic ice sheets. Estimates of the current mass balance of the Antarctic ice sheet are derived from surface- elevation changes obtained from 9 years of ERS - 1 & 2 radar altimeter data. Elevation time-series are created from altimeter crossovers among 90-day data periods on a 50 km grid to 81.5 S. The time series are fit with a multivariate linear/sinusoidal function to give the average rate of elevation change (dH/dt). On the major Rome-Filchner, Ross, and Amery ice shelves, the W d t are small or near zero. In contrast, the ice shelves of the Antarctic Peninsula and along the West Antarctic coast appear to be thinning significantly, with a 23 +/- 3 cm per year surface elevation decrease on the Larsen ice shelf and a 65 +/- 4 cm per year decrease on the Dotson ice shelf. On the grounded ice, significant elevation decreases are obtained over most of the drainage basins of the Pine Island and Thwaites glaciers in West Antarctica and inland of Law Dome in East Antarctica. Significant elevation increases are observed within about 200 km of the coast around much of the rest of the ice sheet. Farther inland, the changes are a mixed pattern of increases and decreases with increases of a few centimeters per year at the highest elevations of the East Antarctic plateau. The derived elevation changes are combined with estimates of the bedrock uplift from several models to provide maps of ice thickness change. The ice thickness changes enable estimates of the ice mass balances for the major drainage basins, the overall mass balance, and the current contribution of the ice sheet to global sea level change.

  6. Effect of some potentially synergistic treatments in combination with 100 Krad irradiation on the iced shelf life of cod fillets

    International Nuclear Information System (INIS)

    Licciardello, J.J.; Ravesi, E.M.; Tuhkunen, B.E.; Racicot, L.D.

    1984-01-01

    Irradiation of cod fillets with a maximum absorbed dose of 100 Krad extended iced storage life by about 9 days. Further extension of several days resulted when irradiation was combined concurrently with either 60% CO 2 packaging atmosphere or sorbate additive. Packaging at low oxygen tension did not provide any additional benefit for irradiated fish. No important difference in storage life of treated fish was observed due to one vs three day postmortem age. The 100 Krad treatment extended grade B quality market life as opposed to grade A (prime quality) market life. Certain physical/chemical tests were evaluated for their efficacy in estimating spoilage. Concentrations of TMA, DMA, hypoxanthine, APC and pH at spoilage were comparable in control and air-irradiated samples, but were less in sorbate-irradiated fillets. 48 references, 8 figures, 1 table

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

    International Nuclear Information System (INIS)

    Sorrell, Brian K; Safi, Karl; Hawes, Ian

    2013-01-01

    We compared planktonic primary and secondary production across twenty meltwater ponds on the surface of the McMurdo Ice Shelf in January 2007, including some ponds with basal brines created by meromictic stratification. Primary production ranged from 1.07 to 65.72 mgC m −3 h −1 in surface waters. In stratified ponds primary production was always more than ten times higher in basal brines than in the corresponding mixolimnion. Regression tree analysis (r 2 = 0.80) identified inorganic nitrogen (as NH 4 + ) as the main factor limiting planktonic primary production. However, there was also evidence of inorganic carbon co-limitation of photosynthesis in some of the more oligotrophic waters. Neither C nor N limited carbon fixation at [NH 4 –N] > 50 mg m −3 , with photoinhibition the factor most likely limiting photosynthesis under such conditions. Primary production was the only factor significantly correlated to bacterial production and the relationship (r 2 = 0.56) was non-linear. Nitrogen limitation and tight coupling of planktonic primary and bacterial production is surprising in these ponds, as all have large pools of dissolved organic carbon (1.2–260 g m −3 ) and organic nitrogen (all >130 mg m −3 ). The dissolved pools of organic carbon and nitrogen appear to be recalcitrant and bacterial production to be constrained by limited release of labile organics from phytoplankton. (letter)

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

    Science.gov (United States)

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

    2017-02-01

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

  9. Effect of incorporation of natural chemicals in water ice-glazing on freshness and shelf-life of Pacific saury (Cololabis saira) during -18 °C frozen storage.

    Science.gov (United States)

    Luo, Haibo; Wang, Weihua; Chen, Wei; Tang, Haiqing; Jiang, Li; Yu, Zhifang

    2017-12-14

    Microbial spoilage and lipid oxidation are two major factors causing freshness deterioration of Pacific saury (Cololabis saira) during frozen storage. To provide a remedy, the effects of several natural chemicals incorporated alone or in combination in traditional water ice-glazing on the freshness and shelf-life of Pacific saury during frozen storage at -18 °C were investigated. Pacific sauries were subjected to individual quick freezing followed immediately by dipping into cold tap water (control) or solutions containing nisin, chitosan, phytic acid (single-factor experiment) or their combinations ((L 9 (3 4 ) orthogonal experiment) for 10 s at 1 °C and then packaged in polypropylene bags before frozen storage at -18 °C. The storage duration tested was up to 12 months. All ice-glazing treatments with individual chemicals could significantly (P shelf-life of Pacific saury could be extended up to 12 months at -18 °C. The study indicated that the combination treatment with natural chemicals could be commercially utilized to maintain the freshness and prolong the shelf-life of Pacific saury. © 2017 Society of Chemical Industry. © 2017 Society of Chemical Industry.

  10. The late Cainozoic East Antarctic ice sheet

    International Nuclear Information System (INIS)

    Colhoun, E.A.

    1999-01-01

    Antarctic contribution to sea-level fall may have been much less than previously suggested by theoretical models. Most evidence points to the need to revise the maximum view of the model of Late Wisconsin glaciation in East Antarctica, derived from the maximum model of Ross Sea glaciation, towards a model of less extensive and thinner ice over the continental shelf

  11. A sensitivity analysis for a thermomechanical model of the Antarctic ice sheet and ice shelves

    Science.gov (United States)

    Baratelli, F.; Castellani, G.; Vassena, C.; Giudici, M.

    2012-04-01

    The outcomes of an ice sheet model depend on a number of parameters and physical quantities which are often estimated with large uncertainty, because of lack of sufficient experimental measurements in such remote environments. Therefore, the efforts to improve the accuracy of the predictions of ice sheet models by including more physical processes and interactions with atmosphere, hydrosphere and lithosphere can be affected by the inaccuracy of the fundamental input data. A sensitivity analysis can help to understand which are the input data that most affect the different predictions of the model. In this context, a finite difference thermomechanical ice sheet model based on the Shallow-Ice Approximation (SIA) and on the Shallow-Shelf Approximation (SSA) has been developed and applied for the simulation of the evolution of the Antarctic ice sheet and ice shelves for the last 200 000 years. The sensitivity analysis of the model outcomes (e.g., the volume of the ice sheet and of the ice shelves, the basal melt rate of the ice sheet, the mean velocity of the Ross and Ronne-Filchner ice shelves, the wet area at the base of the ice sheet) with respect to the model parameters (e.g., the basal sliding coefficient, the geothermal heat flux, the present-day surface accumulation and temperature, the mean ice shelves viscosity, the melt rate at the base of the ice shelves) has been performed by computing three synthetic numerical indices: two local sensitivity indices and a global sensitivity index. Local sensitivity indices imply a linearization of the model and neglect both non-linear and joint effects of the parameters. The global variance-based sensitivity index, instead, takes into account the complete variability of the input parameters but is usually conducted with a Monte Carlo approach which is computationally very demanding for non-linear complex models. Therefore, the global sensitivity index has been computed using a development of the model outputs in a

  12. MR diagnostics after Ross procedure

    International Nuclear Information System (INIS)

    Steffens, J.C.; Link, J.; Harringer, W.; Haverich, A.; Heller, M.

    1996-01-01

    Purpose: To determine the ability of MRI to diagnose morphological and functional changes in patients after Ross procedure. Material and methods: During one year, 5 patients after Ross procedure were studied by MRI. T 1 -weighted spin-echo sequences in different orientations as well as cine sequences and a VENC-sequence were used. Results: In all patients the morphology including the postoperative changes could be visualised by MRI. The cine sequences provided functional information on valvular and ventricular function. VENC-MR yielded an exact quantification of the regurgitant fraction. Conclusion: MRI is capable of providing all important diagnostic information in patients after Ross procedure such as valvular and ventricular function and valvular and outflow tract morphology in a single examination. (orig.) [de

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

    Science.gov (United States)

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

    2016-03-01

    Geological data indicate that there were major variations in Antarctic ice sheet volume and extent during the early to mid-Miocene. Simulating such large-scale changes is problematic because of a strong hysteresis effect, which results in stability once the ice sheets have reached continental size. A relatively narrow range of atmospheric CO2 concentrations indicated by proxy records exacerbates this problem. Here, we are able to simulate large-scale variability of the early to mid-Miocene Antarctic ice sheet because of three developments in our modeling approach. (i) We use a climate-ice sheet coupling method utilizing a high-resolution atmospheric component to account for ice sheet-climate feedbacks. (ii) The ice sheet model includes recently proposed mechanisms for retreat into deep subglacial basins caused by ice-cliff failure and ice-shelf hydrofracture. (iii) We account for changes in the oxygen isotopic composition of the ice sheet by using isotope-enabled climate and ice sheet models. We compare our modeling results with ice-proximal records emerging from a sedimentological drill core from the Ross Sea (Andrill-2A) that is presented in a companion article. The variability in Antarctic ice volume that we simulate is equivalent to a seawater oxygen isotope signal of 0.52-0.66‰, or a sea level equivalent change of 30-36 m, for a range of atmospheric CO2 between 280 and 500 ppm and a changing astronomical configuration. This result represents a substantial advance in resolving the long-standing model data conflict of Miocene Antarctic ice sheet and sea level variability.

  14. Consistent past half-century trends in the atmosphere, the sea ice and the ocean at high southern latitudes

    Energy Technology Data Exchange (ETDEWEB)

    Goosse, Hugues; Montety, Anne de; Crespin, Elisabeth [Universite Catholique de Louvain, Institut d' Astronomie et de Geophysique G. Lemaitre, Louvain-la-Neuve (Belgium); Lefebvre, Wouter [Universite Catholique de Louvain, Institut d' Astronomie et de Geophysique G. Lemaitre, Louvain-la-Neuve (Belgium); The Vlaams Instituut voor Technologisch Onderzoek (VITO), Mol (Belgium); Orsi, Alejandro H. [Texas A and M University, Department of Oceanography, College Station, TX (United States)

    2009-12-15

    Simulations performed with the climate model LOVECLIM, aided with a simple data assimilation technique that forces a close matching of simulated and observed surface temperature variations, are able to reasonably reproduce the observed changes in the lower atmosphere, sea ice and ocean during the second half of the twentieth century. Although the simulated ice area slightly increases over the period 1980-2000, in agreement with observations, it decreases by 0.5 x 10{sup 6} km{sup 2} between early 1960s and early 1980s. No direct and reliable sea ice observations are available to firmly confirm this simulated decrease, but it is consistent with the data used to constrain model evolution as well as with additional independent data in both the atmosphere and the ocean. The simulated reduction of the ice area between the early 1960s and early 1980s is similar to the one simulated over that period as a response to the increase in greenhouse gas concentrations in the atmosphere while the increase in ice area over the last decades of the twentieth century is likely due to changes in atmospheric circulation. However, the exact contribution of external forcing and internal variability in the recent changes cannot be precisely estimated from our results. Our simulations also reproduce the observed oceanic subsurface warming north of the continental shelf of the Ross Sea and the salinity decrease on the Ross Sea continental shelf. Parts of those changes are likely related to the response of the system to the external forcing. Modifications in the wind pattern, influencing the ice production/melting rates, also play a role in the simulated surface salinity decrease. (orig.)

  15. A Detailed Geophysical Investigation of the Grounding of Henry Ice Rise, with Implications for Holocene Ice-Sheet Extent.

    Science.gov (United States)

    Wearing, M.; Kingslake, J.

    2017-12-01

    It is generally assumed that since the Last Glacial Maximum the West Antarctic Ice Sheet (WAIS) has experienced monotonic retreat of the grounding line (GL). However, recent studies have cast doubt on this assumption, suggesting that the retreat of the WAIS grounding line may have been followed by a significant advance during the Holocene in the Weddell and Ross Sea sectors. Constraining this evolution is important as reconstructions of past ice-sheet extent are used to spin-up predictive ice-sheet models and correct mass-balance observations for glacial isostatic adjustment. Here we examine in detail the formation of the Henry Ice Rise (HIR), which ice-sheet model simulations suggest played a key role in Holocene ice-mass changes in the Weddell Sea sector. Observations from a high-resolution ground-based, ice-penetrating radar survey are best explained if the ice rise formed when the Ronne Ice Shelf grounded on a submarine high, underwent a period of ice-rumple flow, before the GL migrated outwards to form the present-day ice rise. We constrain the relative chronology of this evolution by comparing the alignment and intersection of isochronal internal layers, relic crevasses, surface features and investigating the dynamic processes leading to their complex structure. We also draw analogies between HIR and the neighbouring Doake Ice Rumples. The date of formation is estimated using vertical velocities derived with a phase-sensitive radio-echo sounder (pRES). Ice-sheet models suggest that the formation of the HIR and other ice rises may have halted and reversed large-scale GL retreat. Hence the small-scale dynamics of these crucial regions could have wide-reaching consequences for future ice-sheet mass changes and constraining their formation and evolution further would be beneficial. One stringent test of our geophysics-based conclusions would be to drill to the bed of HIR to sample the ice for isotopic analysis and the bed for radiocarbon analysis.

  16. Influence of Meteorological Regimes on Cloud Microphysics Over Ross Island, Antarctica

    Science.gov (United States)

    Glennon, C.; Wang, S. H.; Scott, R. C.; Bromwich, D. H.; Lubin, D.

    2017-12-01

    The Antarctic provides a sharp contrast in cloud microphysics from the high Arctic, due to orographic lifting and resulting strong vertical motions induced by mountain ranges and other varying terrain on several spatial scales. The Atmospheric Radiation Measurement (ARM) West Antarctic Radiation Experiment (AWARE) deployed advanced cloud remote sensing equipment to Ross Island, Antarctica, from December 2015 until January 2016. This equipment included scanning and zenith radars operating in the Ka and X bands, a high spectral resolution lidar (HSRL), and a polarized micropulse lidar (MPL). A major AWARE objective is to provide state-of-the-art data for improving cloud microphysical parameterizations in climate models. To further this objective we have organized and classified the local Ross Island meteorology into distinct regimes using k-means clustering on ERA-Interim reanalysis data. We identify synoptic categories producing unique regimes of cloud cover and cloud microphysical properties over Ross Island. Each day of observations can then be associated with a specific meteorological regime, thus assisting modelers with identifying case studies. High-resolution (1 km) weather forecasts from the Antarctic Mesoscale Prediction System (AMPS) are sorted into these categories. AMPS-simulated anomalies of cloud fraction, near-surface air temperature, and vertical velocity at 500-mb are composited and compared with ground-based radar and lidar-derived cloud properties to identify mesoscale meteorological processes driving Antarctic cloud formation. Synoptic lows over the Ross and Amundsen Seas drive anomalously warm conditions at Ross Island by injecting marine air masses inland over the West Antarctic Ice Sheet (WAIS). This results in ice and mixed-phase orographic cloud systems arriving at Ross Island from the south to southeast along the Transantarctic Mountains. In contrast, blocking over the Amundsen Sea region brings classical liquid-dominated mixed-phase and

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

    Science.gov (United States)

    Comiso, Josefino C.

    2012-01-01

    MODIS, AMSR-E and SSM/I data reveal that the sea ice production rate at the coastal polynyas along the Ross Ice Shelf has been increasing since 1992. This also means that the salinization rate and the formation of bottom water in the region are going up as well. Simulation studies indicate that the stronger production rate is likely associated with the ozone hole that has caused a deepening of the lows in the West Antarctic region and therefore stronger winds off the Ross Ice Shelf. Stronger winds causes larger coastal polynyas near the shelf and hence an enhanced ice production in the region during the autumn and winter period. Results of analysis of temperature data from MODIS and AMSR-E shows that the area and concentration of the sea ice cover are highly correlated with surface temperature for both the Arctic and Antarctic, especially in the seasonal regions where the correlation coefficients are about 0.9. Abnormally high sea surface temperatures (SSTs) and surface ice temperatures (SITs) were also observed in 2007 and 2011when drastic reductions in the summer ice cover occurred, This phenomenon is consistent with the expected warming of the upper layer of the Arctic Ocean on account of ice-albedo feedback. Changes in atmospheric circulation are also expected to have a strong influence on the sea ice cover but the results of direct correlation analyses of the sea ice cover with the Northern and the Southern Annular Mode indices show relatively weak correlations, This might be due in part to the complexity of the dynamics of the system that can be further altered by some phenomena like the Antarctic Circumpolar Wave and extra polar processes like the El Nino Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (POD),

  18. Measures Earth System Data Records (ESDR) of Ice Motion in Antarctica: Status, Impact and Future Products.

    Science.gov (United States)

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

    2014-12-01

    Spaceborne Synthetic Aperture Radar (SAR) data is an extremely useful tool for providing relevant information about the ice sheet ECV: ice vector velocity, grounding line position, and ice front location. Here, we provide an overview of the SAR Earth System Data Records (ESDR) for Antarctica part of MEaSUREs that includes: the first complete map of surface ice vector velocity in Antarctica, a map of grounding line positions around Antarctica, ice velocity time series for selected regions: Ross and Ronne-Filchner Ice Shelves and associated drainage basins, the Amundsen Sea Embayment of West Antarctica which is the largest contributor to sea level rise from Antarctica and the focus of rapid ice sheet retreat, and Larsen-B and -C ice shelves which is the second largest contribution to sea level rise from Antarctica. Other products include a database of ice shelf boundaries and drainage basins based on ice motion mapping and digital elevation models generated independently. Data continuity is a crucial aspect of this work and a fundamental challenge for the continuation of these products due to the lack of a dedicated interferometric mission on the cryosphere until the SAR mission under consideration between NASA and ISRO is approved. Four SAR missions ceased operations since IPY. CSA's RADARSAT-2 has provided important bridging data between these missions in Greenland and Antarctica. In 2014, ESA launched Sentinel-1a and JAXA launched ALOS-2 PALSAR, for which we will have limited data access. The Polar Space Task Group (PSTG) created by WMO has established a mandate to support cryospheric products from scientific research using international SARs which continues to play an active role in securing key data acquisitions over ice sheets. We will provide an overview of current efforts. This work was conducted at UC Irvine, Department of Earth System Science under a contract with NASA's MEaSUREs program.

  19. Dating glacimarine sediments from the continental shelf in the Amundsen Sea using a multi-tool box: Implications for West Antarctic ice-sheet extent and retreat during the last glacial cycle

    Science.gov (United States)

    Hillenbrand, C. D.; Smith, J.; Klages, J. P.; Kuhn, G.; Maher, B.; Moreton, S.; Wacker, L.; Frederichs, T.; Wiers, S.; Jernas, P.; Anderson, J. B.; Ehrmann, W. U.; Graham, A. G. C.; Gohl, K.; Larter, R. D.

    2016-02-01

    Satellite data and in-situ measurements show that today considerable mass loss is occurring from the Amundsen Sea sector of the West Antarctic Ice Sheet (WAIS). The observational record only spans the past four decades, and until recently the long-term context of the current deglaciation was poorly constrained. This information is, however, crucial for understanding WAIS dynamics, evaluating the role of forcing mechanisms for ice-sheet melting, and testing and calibrating ice-sheet models that attempt to predict future WAIS behavior and its impact on global sea level. Over the past decade several multinational marine expeditions and terrestrial fieldwork campaigns have targeted the Amundsen Sea shelf and its hinterland to reconstruct the WAIS configuration during the Last Glacial Maximum (LGM) and its subsequent deglacial history. The resulting studies succeeded in shedding light on the maximum WAIS extent at the LGM and the style, pattern and speed of its retreat and thinning thereafter. Despite this progress, however, significant uncertainties and discrepancies between marine and terrestrial reconstructions remain, which may arise from difficulties in dating sediment cores from the Antarctic shelf, especially their deglacial sections. Resolving these issues is crucial for understanding the WAIS' contribution to post-LGM sea-level rise, its sensitivity to different forcing mechanisms and its future evolution. Here we present chronological constraints on WAIS advance in the Amundsen Sea and its retreat from 20 ka BP into the Holocene that were obtained by various techniques, such as 14C dating of large ( 10 mg) and small (sample aliquots of calcareous microfossils, 14C dating of acid-insoluble organic matter combusted at low (300 °C) and high (800 °C) temperatures and dating of sediment cores by using geomagnetic paleointensity. We will compare the different age constraints and discuss their reliability, applicability and implications for WAIS history.

  20. Remote sensing of sea ice: advances during the DAMOCLES project

    Directory of Open Access Journals (Sweden)

    G. Heygster

    2012-12-01

    Full Text Available In the Arctic, global warming is particularly pronounced so that we need to monitor its development continuously. On the other hand, the vast and hostile conditions make in situ observation difficult, so that available satellite observations should be exploited in the best possible way to extract geophysical information. Here, we give a résumé of the sea ice remote sensing efforts of the European Union's (EU project DAMOCLES (Developing Arctic Modeling and Observing Capabilities for Long-term Environmental Studies. In order to better understand the seasonal variation of the microwave emission of sea ice observed from space, the monthly variations of the microwave emissivity of first-year and multi-year sea ice have been derived for the frequencies of the microwave imagers like AMSR-E (Advanced Microwave Scanning Radiometer on EOS and sounding frequencies of AMSU (Advanced Microwave Sounding Unit, and have been used to develop an optimal estimation method to retrieve sea ice and atmospheric parameters simultaneously. In addition, a sea ice microwave emissivity model has been used together with a thermodynamic model to establish relations between the emissivities from 6 GHz to 50 GHz. At the latter frequency, the emissivity is needed for assimilation into atmospheric circulation models, but is more difficult to observe directly. The size of the snow grains on top of the sea ice influences both its albedo and the microwave emission. A method to determine the effective size of the snow grains from observations in the visible range (MODIS is developed and demonstrated in an application on the Ross ice shelf. The bidirectional reflectivity distribution function (BRDF of snow, which is an essential input parameter to the retrieval, has been measured in situ on Svalbard during the DAMOCLES campaign, and a BRDF model assuming aspherical particles is developed. Sea ice drift and deformation is derived from satellite observations with the scatterometer

  1. 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,

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

    Science.gov (United States)

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

    2014-12-01

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

  3. Changing Roots : Remodelling after the Ross Operation

    NARCIS (Netherlands)

    A. Mookhoek (Aart)

    2016-01-01

    textabstractThe Ross operation is a surgical intervention in which a diseased aortic valve is replaced by the pulmonary valve of the same patient. A donor valve replaces the pulmonary valve. In this thesis, several key unanswered clinical questions are explored. Early mortality after the Ross

  4. A Range Correction for Icesat and Its Potential Impact on Ice-sheet Mass Balance Studies

    Science.gov (United States)

    Borsa, A. A.; Moholdt, G.; Fricker, H. A.; Brunt, Kelly M.

    2014-01-01

    We report on a previously undocumented range error in NASA's Ice, Cloud and land Elevation Satellite (ICESat) that degrades elevation precision and introduces a small but significant elevation trend over the ICESat mission period. This range error (the Gaussian-Centroid or 'G-C'offset) varies on a shot-to-shot basis and exhibits increasing scatter when laser transmit energies fall below 20 mJ. Although the G-C offset is uncorrelated over periods less than1 day, it evolves over the life of each of ICESat's three lasers in a series of ramps and jumps that give rise to spurious elevation trends of -0.92 to -1.90 cm yr(exp -1), depending on the time period considered. Using ICESat data over the Ross and Filchner-Ronne ice shelves we show that (1) the G-C offset introduces significant biases in ice-shelf mass balance estimates, and (2) the mass balance bias can vary between regions because of different temporal samplings of ICESat.We can reproduce the effect of the G-C offset over these two ice shelves by fitting trends to sample-weighted mean G-C offsets for each campaign, suggesting that it may not be necessary to fully repeat earlier ICESat studies to determine the impact of the G-C offset on ice-sheet mass balance estimates.

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

    Science.gov (United States)

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

    2014-07-01

    A new model of the deglaciation history of Antarctica over the past 25 kyr has been developed, which we refer to herein as ICE-6G_C (VM5a). This revision of its predecessor ICE-5G (VM2) has been constrained to fit all available geological and geodetic observations, consisting of: (1) the present day uplift rates at 42 sites estimated from GPS measurements, (2) ice thickness change at 62 locations estimated from exposure-age dating, (3) Holocene relative sea level histories from 12 locations estimated on the basis of radiocarbon dating and (4) age of the onset of marine sedimentation at nine locations along the Antarctic shelf also estimated on the basis of 14C dating. Our new model fits the totality of these data well. An additional nine GPS-determined site velocities are also estimated for locations known to be influenced by modern ice loss from the Pine Island Bay and Northern Antarctic Peninsula regions. At the 42 locations not influenced by modern ice loss, the quality of the fit of postglacial rebound model ICE-6G_C (VM5A) is characterized by a weighted root mean square residual of 0.9 mm yr-1. The Southern Antarctic Peninsula is inferred to be rising at 2 mm yr-1, requiring there to be less Holocene ice loss there than in the prior model ICE-5G (VM2). The East Antarctica coast is rising at approximately 1 mm yr-1, requiring ice loss from this region to have been small since Last Glacial Maximum. The Ellsworth Mountains, at the base of the Antarctic Peninsula, are inferred to be rising at 5-8 mm yr-1, indicating large ice loss from this area during deglaciation that is poorly sampled by geological data. Horizontal deformation of the Antarctic Plate is minor with two exceptions. First, O'Higgins, at the tip of the Antarctic Peninsula, is moving southeast at a significant 2 mm yr-1 relative to the Antarctic Plate. Secondly, the margins of the Ronne and Ross Ice Shelves are moving horizontally away from the shelf centres at an approximate rate of 0.8 mm yr-1, in

  6. Long-Endurance, Ice-capable Autonomous Seagliders

    Science.gov (United States)

    Lee, Craig; Gobat, Jason; Shilling, Geoff; Curry, Beth

    2013-04-01

    . The first successful section across the ice-covered Davis Strait occurred in 2006, while the first full mission took place September - February 2008. Mission duration was 25 weeks, with over 800 km of under-ice transit over 51 days. The glider was able to identify and surface through leads 10 times during under-ice operations. Most recently, a pair of successful missions collected continuous sections across Davis Strait from October 2010 through June 2011, including operations between January and June, when the strait was nearly entirely ice-covered and the glider rarely gained access to the surface. These missions provide the first year-round time series of high-resolution sections across Davis Strait. In the Antarctic, ice-capable Seagliders successfully transited beneath a 40-km ice bridge and self-extracted after being carried beneath the Ross ice shelf during missions conducted without the support of an acoustic navigation array. Ice-capable Seagliders can provide sustainable, continuous occupation of critical sections in ice-covered regions, including the marginal ice zone, with typical horizontal resolution of 3 km and routine sampling of the important, but hazardous, region near the ice-ocean interface. Future directions include development of basin-scale acoustic navigation ('underwater GPS' for the Arctic) and use of existing high-frequency acoustic communications for short-range data transfer.

  7. Death age, seasonality, taphonomy and colonization of seal carcasses from Ulu Peninsula, James Ross Island, Antarctic Peninsula

    Czech Academy of Sciences Publication Activity Database

    Nývlt, D.; Nývltová Fišáková, Miriam; Barták, M.; Stachoň, Z.; Pavel, V.; Mlčoch, B.; Láska, K.

    2016-01-01

    Roč. 28, č. 1 (2016), s. 3-16 ISSN 0954-1020 Institutional support: RVO:68081758 Keywords : James Ross Island * preservation state * Prince Gustav Channel * sea ice * seal behaviour Subject RIV: EH - Ecology, Behaviour Impact factor: 1.461, year: 2016

  8. Noncommutative Blackwell-Ross martingale inequality

    Science.gov (United States)

    Talebi, Ali; Moslehian, Mohammad Sal; Sadeghi, Ghadir

    We establish a noncommutative Blackwell-Ross inequality for supermartingales under a suitable condition which generalizes Khan’s work to the noncommutative setting. We then employ it to deduce an Azuma-type inequality.

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

    Science.gov (United States)

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

    2011-01-01

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

  10. Ice Motion and Topography Near Margin Areas of Kamb Ice Stream, Antarctica, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set includes ice motion and topography measurements that were taken by measuring movement and altitude of poles set in the West Antarctic Ice Shelf. The...

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

    Data.gov (United States)

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

  12. Spring–summer albedo variations of Antarctic sea ice from 1982 to 2009

    International Nuclear Information System (INIS)

    Shao, Zhu-De; Ke, Chang-Qing

    2015-01-01

    This study examined the spring–summer (November, December, January and February) albedo averages and trends using a dataset consisting of 28 years of homogenized satellite data for the entire Antarctic sea ice region and for five longitudinal sectors around Antarctica: the Weddell Sea (WS), the Indian Ocean sector (IO), the Pacific Ocean sector (PO), the Ross Sea (RS) and the Bellingshausen–Amundsen Sea (BS). Time series data of the sea ice concentrations and sea surface temperatures were used to analyse their relations to the albedo. The results indicated that the sea ice albedo increased slightly during the study period, at a rate of 0.314% per decade, over the Antarctic sea ice region. The sea ice albedos in the PO, the IO and the WS increased at rates of 2.599% per decade (confidence level 99.86%), 0.824% per decade and 0.413% per decade, respectively, and the steepest increase occurred in the PO. However, the sea ice albedo in the BS decreased at a rate of −1.617% per decade (confidence level 95.05%) and was near zero in the RS. The spring–summer average albedo over the Antarctic sea ice region was 50.24%. The highest albedo values were mainly found on the continental coast and in the WS; in contrast, the lowest albedo values were found on the outer edge of the sea ice, the RS and the Amery Ice Shelf. The average albedo in the western Antarctic sea ice region was distinctly higher than that in the east. The albedo was significantly positively correlated with sea ice concentration (SIC) and was significantly negatively correlated with sea surface temperature (SST); these scenarios held true for all five longitudinal sectors. Spatially, the higher surface albedos follow the higher SICs and lower SST patterns. The increasing albedo means that Antarctic sea ice region reflects more solar radiation and absorbs less, leading to a decrease in temperature and much snowfall on sea ice, and further resulted in an increase in albedo. Conversely, the decreasing

  13. The safety band of Antarctic ice shelves

    Science.gov (United States)

    Fürst, Johannes Jakob; Durand, Gaël; Gillet-Chaulet, Fabien; Tavard, Laure; Rankl, Melanie; Braun, Matthias; Gagliardini, Olivier

    2016-05-01

    The floating ice shelves along the seaboard of the Antarctic ice sheet restrain the outflow of upstream grounded ice. Removal of these ice shelves, as shown by past ice-shelf recession and break-up, accelerates the outflow, which adds to sea-level rise. A key question in predicting future outflow is to quantify the extent of calving that might precondition other dynamic consequences and lead to loss of ice-shelf restraint. Here we delineate frontal areas that we label as `passive shelf ice’ and that can be removed without major dynamic implications, with contrasting results across the continent. The ice shelves in the Amundsen and Bellingshausen seas have limited or almost no `passive’ portion, which implies that further retreat of current ice-shelf fronts will yield important dynamic consequences. This region is particularly vulnerable as ice shelves have been thinning at high rates for two decades and as upstream grounded ice rests on a backward sloping bed, a precondition to marine ice-sheet instability. In contrast to these ice shelves, Larsen C Ice Shelf, in the Weddell Sea, exhibits a large `passive’ frontal area, suggesting that the imminent calving of a vast tabular iceberg will be unlikely to instantly produce much dynamic change.

  14. Uncovering the glacial history of the Irish continental shelf (Invited)

    Science.gov (United States)

    Dunlop, P.; Benetti, S.; OCofaigh, C.

    2013-12-01

    In 1999 the Irish Government initiated a €32 million survey of its territorial waters known as the Irish National Seabed Survey (INSS). The INSS is amongst the largest marine mapping programmes ever undertaken anywhere in the world and provides high-resolution multibeam, backscatter and seismic data of the seabed around Ireland. These data have been used to provide the first clear evidence for extensive glaciation of the continental shelf west and northwest of Ireland. Streamlined drumlins on the mid to outer shelf record former offshore-directed ice flow towards the shelf edge and show that the ice sheet was grounded in a zone of confluence where ice flowing onto the shelf from northwest Ireland merged with ice flowing across the Malin Shelf from southwest Scotland. The major glacial features on the shelf are well developed nested arcuate moraine systems that mark the position of the ice sheet margin and confirm that the former British Irish Ice Sheet was grounded as far as the shelf edge around 100 km offshore of west Donegal at the last glacial maximum. Distal to the moraines, on the outermost shelf, prominent zones of iceberg plough marks give way to the Barra/Donegal fan and a well developed system of gullies and canyons which incise the continental slope. Since 2008 several scientific cruises have retrieved cores from the shelf and slope to help build a more detailed understanding of glacial events in this region. This presentation will provide an overview of the glacial history of the Irish shelf and will discuss ongoing research programmes that are building on the initial research findings to produce a better understanding of the nature and timing of ice sheet events in this region.

  15. Glacigenic landforms and sediments of the Western Irish Shelf

    Science.gov (United States)

    McCarron, Stephen; Monteys, Xavier; Toms, Lee

    2013-04-01

    Vibrocoring of possible glacigenic landforms identified from high resolution bathymetric coverage of the Irish Shelf by the Irish National Seabed Survey (INSS) has provided several clusters of short (<3m) cores that, due to a regional post-glacial erosional event, comprise last glacial age stratigraphies. In addition, new shallow seismic data and sedimentological information from across the Western Irish Shelf provide new insights into aspects of the nature, timing and pattern of shelf occupation by grounded lobate extensions of the last Irish Ice Sheet. Restricted chronological control of deglacial sequences in several cores indicates that northern parts of the western mid-shelf (south of a prominent outer Donegal Bay ridge) were ice free by ~24 ka B.P., and that ice had also probably retreated from outer shelf positions (as far west as the Porcupine Bank) at or before this time.

  16. STS-110 Crew Interview: Jerry Ross

    Science.gov (United States)

    2002-01-01

    STS-110 Mission Specialist Jerry Ross is seen during this preflight interview, where he gives a quick overview of the mission before answering questions about his inspiration to become an astronaut and his career path. Ross outlines his role in the mission in general, and specifically during the docking and extravehicular activities (EVAs). He describes the payload (S0 Truss and Mobile Transporter) and the dry run installation of the S0 truss that will take place the day before the EVA for the actual installation. Ross discusses the planned EVAs in detail and outlines what supplies will be left for the resident crew of the International Space Station (ISS). He ends with his thoughts on the most valuable aspect of the ISS.

  17. Bending the law: tidal bending and its effects on ice viscosity and flow

    Science.gov (United States)

    Rosier, S.; Gudmundsson, G. H.

    2017-12-01

    Many ice shelves are subject to strong ocean tides and, in order to accommodate this vertical motion, the ice must bend within the grounding zone. This tidal bending generates large stresses within the ice, changing its effective viscosity. For a confined ice shelf, this is particularly relevant because the tidal bending stresses occur along the sidewalls, which play an important role in the overall flow regime of the ice shelf. Hence, tidal bending stresses will affect both the mean and time-varying components of ice shelf flow. GPS measurements reveal strong variations in horizontal ice shelf velocities at a variety of tidal frequencies. We show, using full-Stokes viscoelastic modelling, that inclusion of tidal bending within the model accounts for much of the observed tidal modulation of horizontal ice shelf flow. Furthermore, our model shows that in the absence of a vertical tidal forcing, the mean flow of the ice shelf is reduced considerably.

  18. Full production approaching at Rossing Uranium

    International Nuclear Information System (INIS)

    Anon.

    1978-01-01

    The Rossing uranium mine, in South West Africa's Namib Desert, is an extraordinary operation by any standards. The open pit mining operation; the highly complex metallurgical plant that, unlike those at mines in South Africa extracts the uranium as far as the uranium oxide or yellowcake product; the back-up services; and the team of people who run Rossing were all seen in action on a recent visit by Coal Gold and Base Minerals. This article examines the geology, the initial exploration and the open pit

  19. Design of an Autonomous Underwater Vehicle to Calibrate the Europa Clipper Ice-Penetrating Radar

    Science.gov (United States)

    Stone, W.; Siegel, V.; Kimball, P.; Richmond, K.; Flesher, C.; Hogan, B.; Lelievre, S.

    2013-12-01

    Jupiter's moon Europa has been prioritized as the target for the Europa Clipper flyby mission. A key science objective for the mission is to remotely characterize the ice shell and any subsurface water, including their heterogeneity, and the nature of surface-ice-ocean exchange. This objective is a critical component of the mission's overarching goal of assessing the habitability of Europa. The instrument targeted for addressing key aspects of this goal is an ice-penetrating radar (IPR). As a primary goal of our work, we will tightly couple airborne IPR studies of the Ross Ice Shelf by the Europa Clipper radar team with ground-truth data to be obtained from sub-glacial sonar and bio-geochemical mapping of the corresponding ice-water and water-rock interfaces using an advanced autonomous underwater vehicle (AUV). The ARTEMIS vehicle - a heavily morphed long-range, low drag variant of the highly successful 4-degree-of-freedom hovering sub-ice ENDURANCE bot -- will be deployed from a sea-ice drill hole adjacent the McMurdo Ice Shelf (MIS) and will perform three classes of missions. The first includes original exploration and high definition mapping of both the ice-water interface and the benthic interface on a length scale (approximately 10 kilometers under-ice penetration radius) that will definitively tie it to the synchronous airborne IPR over-flights. These exploration and mapping missions will be conducted at up to 10 different locations along the MIS in order to capture varying ice thickness and seawater intrusion into the ice shelf. Following initial mapping characterization, the vehicle will conduct astrobiology-relevant proximity operations using bio-assay sensors (custom-designed UV fluorescence and machine-vision-processed optical imagery) followed by point-targeted studies at regions of interest. Sample returns from the ice-water interface will be triggered autonomously using real-time-processed instrument data and onboard decision-to-collect algorithms

  20. Glacial morphology and depositional sequences of the Antarctic Continental Shelf

    Science.gov (United States)

    ten Brink, Uri S.; Schneider, Christopher

    1995-01-01

    Proposes a simple model for the unusual depositional sequences and morphology of the Antarctic continental shelf. It considers the regional stratal geometry and the reversed morphology to be principally the results of time-integrated effects of glacial erosion and sedimentation related to the location of the ice grounding line. The model offers several guidelines for stratigraphic interpretation of the Antarctic shelf and a Northern Hemisphere shelf, both of which were subject to many glacial advances and retreats. -Authors

  1. 36 CFR 7.69 - Ross Lake National Recreation Area.

    Science.gov (United States)

    2010-07-01

    ... 36 Parks, Forests, and Public Property 1 2010-07-01 2010-07-01 false Ross Lake National Recreation... INTERIOR SPECIAL REGULATIONS, AREAS OF THE NATIONAL PARK SYSTEM § 7.69 Ross Lake National Recreation Area... snowmobiles the following locations within the Ross Lake National Recreation Area: (1) State Highway 20, that...

  2. Rapid Holocene thinning of outlet glaciers followed by readvance in the western Ross Embayment, Antarctica

    Science.gov (United States)

    Jones, R. S.; Whitmore, R.; Mackintosh, A.; Norton, K. P.; Eaves, S.; Stutz, J.

    2017-12-01

    Investigating Antarctic deglaciation following the LGM provides an opportunity to better understand patterns, mechanisms and drivers of ice sheet retreat. In the Ross Sea sector, geomorphic features preserved on the seafloor indicate that streaming East Antarctic outlet glaciers once extended >100 km offshore of South Victoria Land prior to back-stepping towards their modern configurations. In order to adequately interpret the style and causes of this retreat, the timing and magnitude of corresponding ice thickness change is required. We present new constraints on ice surface lowering from Mawson Glacier, an outlet of the East Antarctic Ice Sheet that flows into the western Ross Sea. Surface-exposure (10Be) ages from samples collected in elevation transects above the modern ice surface reveal that rapid thinning occurred at 5-8 ka, broadly coeval with new ages of grounding-line retreat at 6 ka and rapid thinning recorded at nearby Mackay Glacier at 7 ka. Our data also show that a moraine formed near to the modern ice margin of Mawson Glacier at 0.8 ka, which, together with historical observations, indicates that glaciers in this region readvanced during the last thousand years. We argue that 1) the accelerated thinning of outlet glaciers was driven by local grounding-line retreat through overdeepened basins during the early-mid Holocene, and 2) the glaciers subsequently readvanced, possibly linked to late Holocene sea-ice expansion, before retreating to their current positions. Our work demonstrates that these outlet glaciers were closely coupled to environmental and topography-induced perturbations near their termini throughout the Holocene.

  3. Sir Ronald Ross and the Malarial Parasite

    Indian Academy of Sciences (India)

    1997-08-20

    Aug 20, 1997 ... In 1857, a General in the Indian Army, Sir C C G Ross and his wife Matilda .... generally low-caste Indians who required a fee before drinking the water and ... nary demand being made upon their systems, as by fatigue, chill,.

  4. Sir Ronald Ross and the Malarial Parasite

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 11; Issue 7. Sir Ronald Ross and the Malarial Parasite - Discovery of its Route - From Man to Mosquito and Back. Shobhona Sharma. General Article Volume 11 Issue 7 July 2006 pp 4-13 ...

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

    Science.gov (United States)

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

    2017-12-01

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

  6. Comparison of the Ross/Ross-Konno aortic root in children before and after the age of 18 months.

    Science.gov (United States)

    Lo Rito, Mauro; Davies, Ben; Brawn, William J; Jones, Timothy J; Khan, Natasha; Stickley, John; Barron, David J

    2014-09-01

    Evaluation of long-term results after the Ross/Ross-Konno operation in patients Ross/Ross-Konno operation (1991-2011). Data were obtained from hospital records and follow-up was 100% complete. Between January 1991 and December 2011, 140 patients underwent the Ross/Ross-Konno operation and 22 patients were Ross operation and 8 patients a Ross-Konno operation. Presentation at surgery was aortic valve stenosis in 13, regurgitation in 7 and mixed disease in 2. Only 4 patients (18%) had no surgery prior to Ross/Ross-Konno, and among the others the previous most frequent operation was aortic valvotomy (55%). There were 3 early deaths, all in high-risk cases with poor preoperative left ventricular function. At discharge there was no neoaortic regurgitation in 10, trivial in 4 and mild in 5. The median follow-up is 10.8 years (range 0.96-21). There was 1 late death due to progressive ventricular dysfunction 2.4 years after Ross-Konno and mitral valve replacement. Survival for patients 18-months patients (P Ross/Ross-Konno can be invaluable in the younger age group but not without risk in the setting of ventricular dysfunction. Long-term performance of the neoaortic valve is significantly better than in older children, which is related to maintenance of normal root dimensions compared with progressive dilatation in patients undergoing Ross/Ross-Konno at older ages. © The Author 2014. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.

  7. Switch of flow direction in an Antarctic ice stream.

    Science.gov (United States)

    Conway, H; Catania, G; Raymond, C F; Gades, A M; Scambos, T A; Engelhardt, H

    2002-10-03

    Fast-flowing ice streams transport ice from the interior of West Antarctica to the ocean, and fluctuations in their activity control the mass balance of the ice sheet. The mass balance of the Ross Sea sector of the West Antarctic ice sheet is now positive--that is, it is growing--mainly because one of the ice streams (ice stream C) slowed down about 150 years ago. Here we present evidence from both surface measurements and remote sensing that demonstrates the highly dynamic nature of the Ross drainage system. We show that the flow in an area that once discharged into ice stream C has changed direction, now draining into the Whillans ice stream (formerly ice stream B). This switch in flow direction is a result of continuing thinning of the Whillans ice stream and recent thickening of ice stream C. Further abrupt reorganization of the activity and configuration of the ice streams over short timescales is to be expected in the future as the surface topography of the ice sheet responds to the combined effects of internal dynamics and long-term climate change. We suggest that caution is needed when using observations of short-term mass changes to draw conclusions about the large-scale mass balance of the ice sheet.

  8. Trends in the breeding population and driving factors of Adélie penguin in the Ross Sea

    Science.gov (United States)

    He, H.; Li, X.; Cheng, X.

    2017-12-01

    Ross Sea regions have been characterized by high penguin-chick-rearing habitat suitability in the recent past. Many studies have been done to study the Adélie penguins in the Ross Sea. However, the data they used both had advantages and drawbacks. Besides, little quantitative analysis were carried out to study the impact factors on the penguin population change. In this study, penguin population data from MAPPPD (Mapping application for penguin populations and projected dynamics) and IBA (Important bird areas in Antarctica) were integrated and analyzed to study the distribution and trends in the breeding population of Adélie penguin over time in the Ross Sea. In addition, linear fitting method for spatial data in time series were used to study the driving factors such as 2m-temperature, sea ice cover and chlorophyll-a concentration which can quantify phytoplankton blooms. Results indicated that there were 45 Adélie penguin colonies in the Ross Sea. Cape Adare and Cape Crozier were two biggest colonies on which current Adélie penguin abundance were 428516 and 280787 breeding pairs, respectively. Among these colonies, penguin population on 28 colonies increased, on 5 colonies decreased and on 5 colonies remained no change over time, and there were also 5 new colonies and one colony which were extinct. It was found that Adélie penguin population in most of colonies in the Ross Sea increased, which meant that Adélie penguins in the Ross Sea were "climate change winners". The main reasons for the increase in Adélie penguin population in the Ross Sea might be the rise in 2m-temperature and the increase in sea ice cover and phytoplankton. Higher temperatures have resulted in glacial retreat and snow melting, which leads to an increase in available habitat for penguins. The increased sea ice and phytoplankton might positively affect the abundance of Antarctic krill that was the major prey item for Adélie penguins in Antarctic.

  9. Investigation of land ice-ocean interaction with a fully coupled ice-ocean model: 1. Model description and behavior

    Science.gov (United States)

    Goldberg, D. N.; Little, C. M.; Sergienko, O. V.; Gnanadesikan, A.; Hallberg, R.; Oppenheimer, M.

    2012-06-01

    Antarctic ice shelves interact closely with the ocean cavities beneath them, with ice shelf geometry influencing ocean cavity circulation, and heat from the ocean driving changes in the ice shelves, as well as the grounded ice streams that feed them. We present a new coupled model of an ice stream-ice shelf-ocean system that is used to study this interaction. The model is capable of representing a moving grounding line and dynamically responding ocean circulation within the ice shelf cavity. Idealized experiments designed to investigate the response of the coupled system to instantaneous increases in ocean temperature show ice-ocean system responses on multiple timescales. Melt rates and ice shelf basal slopes near the grounding line adjust in 1-2 years, and downstream advection of the resulting ice shelf thinning takes place on decadal timescales. Retreat of the grounding line and adjustment of grounded ice takes place on a much longer timescale, and the system takes several centuries to reach a new steady state. During this slow retreat, and in the absence of either an upward-or downward-sloping bed or long-term trends in ocean heat content, the ice shelf and melt rates maintain a characteristic pattern relative to the grounding line.

  10. STS-88 Crew Interview: Jerry Ross

    Science.gov (United States)

    1998-01-01

    Jerry Ross discusses the seven-day mission that will be highlighted by the mating of the U.S.-built Node 1 station element to the Functional Energy Block (FGB) which will already be in orbit, and two spacewalks to connect power and data transmission cables between the Node and the FGB. Node 1 will be the first Space Station hardware delivered by the Space Shuttle. He also disscusses the assembly sequence. The crew will conduct a series of rendezvous maneuvers similar to those conducted on other Shuttle missions to reach the orbiting FGB. Once the two elements are docked, Ross and Newman will conduct two scheduled spacewalks to connect power and data cables between the Node, PMAs and the FGB. The day following the spacewalks, Endeavour will undock from the two components, completing the first Space Station assembly mission.

  11. Ross Versus Non-Ross Aortic Valve Replacement in Children: A 22-Year Single Institution Comparison of Outcomes.

    Science.gov (United States)

    Brown, John W; Patel, Parth M; Ivy Lin, Jiuann-Huey; Habib, Asma S; Rodefeld, Mark D; Turrentine, Mark W

    2016-05-01

    The Ross aortic valve replacement (AVR) has been the AVR of choice for children at our center since 1993. Absence or inadequate quality of the pulmonary valve or, less commonly, family or surgeon preference caused us to select an alternative AVR prosthesis for some children. This review compares the outcomes of 42 children who received a non-Ross AVR with 115 children undergoing Ross root replacement at our institution during the most recent 22 years. A retrospective chart review of the 42 pediatric non-Ross AVRs was compared with 115 Ross AVRs. The mean age at AVR was 11.0 ± 6.5 years (range, 1 month to 18 years) for the non-Ross and 11.4 ± 5.5 years (range, 6 weeks to 18 years) for the Ross groups. Follow-up was 7.8 ± 6.2 years for the Ross group and 8.7 ± 6.5 years for the non-Ross group. The Ross AVR technique was modified in 2000; these modifications were applied to 72 patients (63%) of the total Ross AVR group. All-cause early and late mortality of the non-Ross AVR group was 17% compared with 4% for the Ross cohort (p = 0.017). The actuarial survival rate at 20 years for the non-Ross AVR group was 81% compared with 94% for the Ross group (p = 0.018). Reintervention rate was 29% (12/38) in the non-Ross group and 28% (32/115) in the entire Ross group (60% [26/43] before 2000, and 8% [6/72] after 2000). Thromboemboli, bleeding, and endocarditis occurred in 2.4%, 1.4%, and 10% in the non-Ross group compared with 0.9%, 2.6%, and 1.7% in the Ross AVR group (p = 0.46, 0.01, and 0.02), respectively. Patients in the non-Ross group had a significantly higher recurrent or persistent aortic valve gradient (>20 mm Hg) than did patients in the Ross group at most recent follow-up (p Ross AVR than with other types of AVR prostheses. The Ross AVR remains the treatment of choice for children who have an adequate pulmonary valve. Reoperation for Ross root dilatation, regurgitation, or both (only 6% since our modifications in 2000) has markedly reduced the main drawbacks

  12. The Response of Ice Sheets to Climate Variability

    Science.gov (United States)

    Snow, K.; Goldberg, D. N.; Holland, P. R.; Jordan, J. R.; Arthern, R. J.; Jenkins, A.

    2017-12-01

    West Antarctic Ice Sheet loss is a significant contributor to sea level rise. While the ice loss is thought to be triggered by fluctuations in oceanic heat at the ice shelf bases, ice sheet response to ocean variability remains poorly understood. Using a synchronously coupled ice-ocean model permitting grounding line migration, this study evaluates the response of an ice sheet to periodic variations in ocean forcing. Resulting oscillations in grounded ice volume amplitude is shown to grow as a nonlinear function of ocean forcing period. This implies that slower oscillations in climatic forcing are disproportionately important to ice sheets. The ice shelf residence time offers a critical time scale, above which the ice response amplitude is a linear function of ocean forcing period and below which it is quadratic. These results highlight the sensitivity of West Antarctic ice streams to perturbations in heat fluxes occurring at decadal time scales.

  13. Antarctic Glaciological Data at NSIDC: field data, temperature, and ice velocity

    Science.gov (United States)

    Bauer, R.; Bohlander, J.; Scambos, T.; Berthier, E.; Raup, B.; Scharfen, G.

    2003-12-01

    velocity provides an upper limit for change in velocity for this glacier over the past decade. Two pairs of Landsat images were used to compare velocities from 2000-2001 to 1989-2000. No significant change in velocity is observed. A new ice discharge flux of 17.8 km3a-1 was determined, and basal melting at the grounding line was re-calculated at 11 m per year (Berthier et al., 2003, in press). Velocity data for the Institute Ice Stream was compiled at NSIDC using a Landsat images from 1986, 1989, and 1997. The data were recently used in a study outlining the velocity, mass balance, and morphology of the Institute ice stream and nearby Ronne ice shelf area. (Scambos et al., 2003, in review). The study indicates the Institute has regions with flow and morphology characteristics similar to the Ross Embayment ice streams. Ice velocity research contributes to understanding the mass balance and overall stability of the Antarctic Ice Sheet. The archiving of velocity data has proven to be a useful tool to the Antarctic science community, and VELMAP continues to grow as a valuable resource through PI contributions. If you have velocity data that you would like to contribute to the VELMAP archive please contact agdc@nsidc.org. The velocity data used in the two studies presented here can be accessed on the VELMAP web site at http://nsidc.org/data/velmap.

  14. Elisabeth Kubler-Ross as a Religious Leader.

    Science.gov (United States)

    Klass, Dennis; Hutch, Richard A.

    1986-01-01

    Considers Elisabeth Kubler-Ross as a charismatic religious leader and examines the feminine quality of her message and leadership style. An examination of the prospects for an enduring cultural innovation based on Kubler-Ross's work concludes that her leadership does not conform to conditions necessary for institutionalization of her charismatic…

  15. Success: Richard Dyer on Diana Ross [and Beyond

    NARCIS (Netherlands)

    Kooijman, J.

    2016-01-01

    In June 1982, film scholar Richard Dyer published a two-page essay on African-American star Diana Ross in the journal Marxism Today. Part of Dyer’s essay focuses on the American conception of success and specifically on how Ross is one of the few black artists who has been "allowed" to be such a

  16. Histomorphometry of the esophagus of adult ross broilers | Mobini ...

    African Journals Online (AJOL)

    The purpose of this study was to determine the histomorphometrical variations of esophagus at different regions in Ross broilers. Twenty four apparently healthy adult Ross broilers (12 females and 12 males), aged from 7 to 9 weeks, were used. Tissue samples were taken from middle parts of cervical and thoracic regions of ...

  17. The ICE-6G_C (VM5a) Global Model of the GIA Process: Antarctica at High Spatial Resolution

    Science.gov (United States)

    Peltier, W. R.; Drummond, R.; Argus, D. F.

    2016-12-01

    The ICE-6G_C (VM5a) global model of the glacial isostatic adjustment process (Argus et al., 2014 GJI 198, 537-563; Peltier et al. , 2015, JGR 119, doi:10.1002/2014JB011176) is the latest model in the ICE-nG (VMx) sequence. The model continues to be unique in that it is the only model whose properties are made freely available at each iterative step in its development. This latest version, which embodies detailed descriptions of the Laurentide , Fennoscandian/Barents Sea, Greenland and Antarctic ice sheets through the most recent glacial cycle, is a refinement based primarily upon the incorporation of the constraints being provided by GPS measurements of the vertical and horizontal motion of the crust as well as GRACE observations of the time dependent gravity field. The model has been shown to provide exceptionally accurate predictions of these space geodetic observations of the response to the most recent Late Quaternary glacial cycle. Particular attention has been paid to the Antarctic component as it is well known on the basis of analyses of the sedimentary stratigraphy off-shore and geomorphological characteristics of the continental shelf, that the Last Glacial Maximum state of the southern continent was one in which grounded ice extended out to the shelf break in most locations, including significant fractions of the Ross Sea and Weddell Sea embayments. In the latter regions especially, it is expected that grounded ice would have existed below sea level. In ICE-6G_C (VM5a) a grounding line tracking algorithm was employed (Stuhne and Peltier, 2015 JGR 120, 1841-1865) in order to describe the unloading of the solid surface by ice that was initially grounded below sea level, an apparently unique characteristic of this model. In the initially published version, in which the Sea Level Equation (SLE) was inverted on a basis of spherical harmonics truncated at degree and order 256, this led to "ringing" in the embayments when the Stokes coefficients of the model

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

    Science.gov (United States)

    Rignot, Eric

    2006-07-15

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

  19. Major adverse cardiac and cerebrovascular events after the ross procedure: A report from the german-dutch ross registry

    NARCIS (Netherlands)

    H. Sievers (Hans Hinrich); U. Stierle (Ulrich); E.I. Charitos (Efstratios); T. Hanke; M. Misfeld (Martin); J.F.M. Bechtel (Matthias); A. Gorski (Armin); U.F. Franke (Ulrich); B. Graf (Bernhard); D.R. Robinson (Derek); A.J.J.C. Bogers (Ad); A. Dodge-Khatami (Ali); J.O. Boehm (Juergen); J.G. Rein (Joachim); C.A. Botha (Cornelius); R. Lange (Rüdiger); J. Hoerer (Juergen); A. Moritz (Anton); T. Wahlers (Thorsten); M. Breuer (Martin); K. Ferrari-Kuehne (Katharina); R. Hetzer (Roland); M. Huebler (Michael); G. Ziemer (Gerhard); J.J.M. Takkenberg (Hanneke); W. Hemmer

    2010-01-01

    textabstractBackground-: The purpose of the study is to report major cardiac and cerebrovascular events after the Ross procedure in the large adult and pediatric population of the German-Dutch Ross registry. These data could provide an additional basis for discussions among physicians and a source

  20. Chemical evidence of the changes of the Antarctic Bottom Water ventilation in the western Ross Sea between 1997 and 2003

    Science.gov (United States)

    Rivaro, Paola; Massolo, Serena; Bergamasco, Andrea; Castagno, Pasquale; Budillon, Giorgio

    2010-05-01

    Data from three Italian CLIMA project cruises between 1997 and 2003 were used to obtain sections of the hydrographic and chemical properties of the main water masses across the shelf break off Cape Adare (western Ross Sea, Antarctica). Dissolved oxygen, nitrate and phosphate data were combined on the basis of the Redfield ratio to obtain the quasi-conservative tracers NO (9[NO 3]+[O 2]), PO (135[PO 4]+[O 2]) and phosphate star PO4* ( PO4*=[PO 4]+[O 2]/175-1.95). In 1997 and 2003 the presence of the High Salinity Shelf Water at the bottom depth near the sill was traced by both physical and chemical measurements. In 2001 the Modified Shelf Water, characterized by warmer temperature and by a lower dissolved oxygen content than High Salinity Shelf Water, was observed at the shelf edge. The distribution of the chemical tracers together with the hydrographic observations showed recently formed Antarctic Bottom Water on the continental slope during all of the cruises. These observations were confirmed by the extended optimum multiparameter analysis. The calculated thickness of the new Antarctic Bottom Water, as well as the tracer content, were variable in time and in space. The estimated volume of the new Antarctic Bottom Water and the export of dissolved oxygen and nutrient associated with the overflowing water were different over the examined period. In particular, a lower (˜55%) export was evidenced in 2001 compared to 1997.

  1. Company Reaserches Regarding Time and Insurance of Shelf-Life of Carcass, Cut Pieces and Chicken Organs

    Directory of Open Access Journals (Sweden)

    Carmen Viorica Radu

    2012-10-01

    Full Text Available The paper aims to study the shelf-life of the housing, cut up pieces and chicken organs in a company slaughterhouseduring the summer. The hybrid is Ross 308. Quality samples, taken randomly during the production process fromvarious parts, was studied by means of specific laboratory from microbiological point of view (determination ofSalmonella and E.coli, NTG, organoleptical and physico-chemical (easily hydrolyzable nitrogen and Kreissreaction during the eight days, until they exceeded the admited limits. Temperatures measured in depth of theproducts of the experiment exceeded the upper limit allowed by 3-4 degrees in the carcasse and 8-10 degrees inorgans. In terms of NTG in the liver they started to decrease in the third day of storage,in the gizzard and heart,there is a continuing increase in values during the entire experiment. This, like the gizzard increase in nitrogen value,although values range, may be a consequence of high temperatures packing and refrigeration products very slow.Storage conditions experienced cyclical deviations from the optimum temperature due to icing phenomenon ofevaporators. As a technical solution for evenly temperature during storage, it may be suggested purchasing a backuprefrigerating space. From the organoleptical point of view, all products undergo changes untill the sixth day, whichrecommends the establishment of shelf-life to this day. Microbiological and physico-chemical exceeding limitsoccurs on days seven and eight. The results, in addition to purely commercial usefulness can be considered abarometer of the correct application of technology to slaughter, hygienic production and the storage conditions ofgoods.

  2. Glacier History of the Northern Antarctic Peninsula Region Since the End of the Last Ice Age and Implications for Southern Hemisphere Westerly-Climate Changes

    Science.gov (United States)

    Kaplan, M. R.; Schaefer, J. M.; Strelin, J. A.; Peltier, C.; Southon, J. R.; Lepper, K. E.; Winckler, G.

    2017-12-01

    For the area around James Ross Island, we present new cosmogenic 10Be exposure ages on glacial deposits, and 14C ages on associated fossil materials. These data allow us to reconstruct in detail when and how the Antarctic Peninsula Ice Sheet retreated around the Island as the last Ice Age ended, and afterward when local land-based glaciers fluctuated. Similar to other studies, we found widespread deglaciation during the earliest Holocene, with fjords and bays becoming ice free between about 11,000 and 8,000 years ago. After 7,000 years ago, neoglacial type advances initiated. Then, both expansions and ice free periods occurred from the middle to late Holocene. We compare the new glacier record to those in southern Patagonia, which is on the other side of the Drake Passage, and published Southern Ocean marine records, in order to infer past middle to high latitude changes in the Southern Hemisphere Westerlies. Widespread warmth in the earliest Holocene, to the north and south of the Drake Passage, led to small glacier systems in Patagonia and wide-ranging glacier recession around the northern Antarctic Peninsula. We infer that this early Holocene period of overall glacier recession - from Patagonia to the northern Peninsula - was caused by a persistent far-southerly setting of the westerlies and accompanying warm climates. Subsequently, during the middle Holocene renewed glacier expansions occurred on both sides of the Drake Passage, which reflects that the Westerlies and associated colder climate systems were generally more equatorward. From the middle to late Holocene, glacier expansions and ice free periods (and likely related ice shelf behavior) document how the Westerlies and associated higher-latitude climate systems varied.

  3. The Myanmar continental shelf

    Digital Repository Service at National Institute of Oceanography (India)

    Ramaswamy, V.; Rao, P.S.

    reveal a minimum of 18 m thick strata of modern muds (Fig. 2g). At the outer boundary of the Gulf of Myanmar Continental Shelf 8 Martaban (15oN Latitude), brown muds overlie coarse sands indicating that modern deltaic sediments... on the Myeik Bank (Rodolfo, 1969a). Modern sediments on the Ayeyarwady shelf General composition, Texture and Grain-size: The distribution and sediment texture on the Ayeyarwady shelf shows fine-grained sediments comprising silty-clay and clayey...

  4. Climate change impacts on southern Ross Sea phytoplankton composition, productivity, and export

    Science.gov (United States)

    Kaufman, Daniel E.; Friedrichs, Marjorie A. M.; Smith, Walker O.; Hofmann, Eileen E.; Dinniman, Michael S.; Hemmings, John C. P.

    2017-03-01

    The Ross Sea, a highly productive region of the Southern Ocean, is expected to experience warming during the next century along with reduced summer sea ice concentrations and shallower mixed layers. This study investigates how these climatic changes may alter phytoplankton assemblage composition, primary productivity, and export. Glider measurements are used to force a one-dimensional biogeochemical model, which includes diatoms and both solitary and colonial forms of Phaeocystis antarctica. Model performance is evaluated with glider observations, and experiments are conducted using projections of physical drivers for mid-21st and late-21st century. These scenarios reveal a 5% increase in primary productivity by midcentury and 14% by late-century and a proportional increase in carbon export, which remains approximately 18% of primary production. In addition, scenario results indicate diatom biomass increases while P. antarctica biomass decreases in the first half of the 21st century. In the second half of the century, diatom biomass remains relatively constant and P. antarctica biomass increases. Additional scenarios examining the independent contributions of expected future changes (temperature, mixed layer depth, irradiance, and surface iron inputs from melting ice) demonstrate that earlier availability of low light due to reduction of sea ice early in the growing season is the primary driver of productivity increases over the next century; shallower mixed layer depths additionally contribute to changes of assemblage composition and export. This study further demonstrates how glider data can be effectively used to facilitate model development and simulation, and inform interpretation of biogeochemical observations in the context of climate change.Plain Language SummaryUnderstanding how the global ocean responds to climate change requires knowing the natural behavior of individual regions and anticipating how future changes will affect each region differently. It

  5. Investigation of land ice-ocean interaction with a fully coupled ice-ocean model: 2. Sensitivity to external forcings

    Science.gov (United States)

    Goldberg, D. N.; Little, C. M.; Sergienko, O. V.; Gnanadesikan, A.; Hallberg, R.; Oppenheimer, M.

    2012-06-01

    A coupled ice stream-ice shelf-ocean cavity model is used to assess the sensitivity of the coupled system to far-field ocean temperatures, varying from 0.0 to 1.8°C, as well as sensitivity to the parameters controlling grounded ice flow. A response to warming is seen in grounding line retreat and grounded ice loss that cannot be inferred from the response of integrated melt rates alone. This is due to concentrated thinning at the ice shelf lateral margin, and to processes that contribute to this thinning. Parameters controlling the flow of grounded ice have a strong influence on the response to sub-ice shelf melting, but this influence is not seen until several years after an initial perturbation in temperatures. The simulated melt rates are on the order of that observed for Pine Island Glacier in the 1990s. However, retreat rates are much slower, possibly due to unrepresented bedrock features.

  6. 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....... The first part concerns time series analysis of ice core data obtained from the Greenland Ice Sheet. We analyze parts of the time series where DO-events occur using the so-called transfer operator and compare the results with time series from a simple model capable of switching by either undergoing...

  7. The Paediatric Cardiology Hall of Fame – Donald Nixon Ross.

    Science.gov (United States)

    Somerville, Jane

    2015-10-01

    Donald Nixon Ross, FRCS (4 October 1922 to 7 July 2014) was a South African-born British cardiothoracic surgeon, who developed the pulmonary autograft, known as the Ross procedure, for the treatment of aortic valve disease, and also performed the first heart transplant in the United Kingdom in 1968. This paper, written by Jane Somerville, Professor of Cardiology [Retired], Imperial College London, London, United Kingdom, provides the personal recollections about Donald Ross from Jane Somerville, and thus provides a unique snapshot of cardiac surgical history.

  8. 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.

  9. 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.

  10. The Ross Procedure in Pediatric Patients: A 20-Year Experience of Ross Procedure in a Single Institution.

    Science.gov (United States)

    Yoon, Dong Woog; Yang, Ji-Hyuk; Jun, Tae-Gook; Park, Pyo Won

    2017-08-01

    The Ross/Ross-Konno procedure is considered a good option for irreparable aortic valve disease in pediatric patients because of its hemodynamic performance and potential for growth of the pulmonary autograft. This study is a review of the long-term results of our 20-year experience with the Ross and Ross-Konno operations in a single institution. Between June 1995 and January 2016, 16 consecutive patients (mean age, 6.0±5.9 years; range, 16 days to 17.4 years) underwent either a Ross operation (n=9) or a Ross-Konno operation (n=7). The study included 12 males and 4 females, with a median follow-up period of 47 months (range, 6 to 256 months). There were no cases of in-hospital or late mortality. Six reoperations were performed in 5 patients. Four patients underwent right ventricular-pulmonary artery (RV-PA) conduit replacement. Two patients underwent concomitant replacement of the pulmonary autograft and RV-PA conduit 10 years and 8 years after the Ross operation, respectively. The rate of freedom from adverse outcomes of the pulmonary autograft was 88% and 70% at 5 and 10 years, respectively. The rate of freedom from valve-related reoperations was 79% and 63% at 5 and 10 years, respectively. Pulmonary autografts demonstrated good durability with low mortality. The Ross/Ross-Konno procedure is a good option that can be performed safely in pediatric patients with aortic valve disease, even in a small-volume center.

  11. Ice, Ice, Baby!

    Science.gov (United States)

    Hamilton, C.

    2008-12-01

    The Center for Remote Sensing of Ice Sheets (CReSIS) has developed an outreach program based on hands-on activities called "Ice, Ice, Baby". These lessons are designed to teach the science principles of displacement, forces of motion, density, and states of matter. These properties are easily taught through the interesting topics of glaciers, icebergs, and sea level rise in K-8 classrooms. The activities are fun, engaging, and simple enough to be used at science fairs and family science nights. Students who have participated in "Ice, Ice, Baby" have successfully taught these to adults and students at informal events. The lessons are based on education standards which are available on our website www.cresis.ku.edu. This presentation will provide information on the activities, survey results from teachers who have used the material, and other suggested material that can be used before and after the activities.

  12. ROSS Skills, Knowledge, and Abilities Training Evaluation. Gaps and Recommendations

    Energy Technology Data Exchange (ETDEWEB)

    Ala, Maureen [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Gruidl, Jeremiah [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Buddemeier, Brooke [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2015-09-30

    This document describes the development of the ROSS SKAs, the cross-mapping of the SKAs to the available training, identifies gaps in the SKA and training, and provides recommendations to address those gaps.

  13. Minevikupärandit Häädemeestelt / Eevi Ross

    Index Scriptorium Estoniae

    Ross, Eevi, 1938-

    2012-01-01

    Raamatututvustus: Minevikupärandit Häädemeestelt : valimik korrespondentide murdetekste. VIII / Eesti Teaduste Akadeemia Emakeele Selts ; kogunud Marta Mäesalu ; koostanud ja toimetanud: Helju Kaal, Eevi Ross. Tallinn : Emakeele Selts, 2012

  14. DVD Review: "The Silver Fez" Directed by Lloyd Ross (2009 ...

    African Journals Online (AJOL)

    Abstract. Producer: Lloyd Ross, Joelle Chesselet. Sound design: Warrick Sony. Cast: Abubakar Davids, Mogamat Zain Benjamin. Approx. 87 min. Distributor: IRIS. ZAR 129.99. Journal of the Musical Arts in Africa, Volume 9 2012, 89–91 ...

  15. The Ross II procedure: pulmonary autograft in the mitral position.

    Science.gov (United States)

    Athanasiou, Thanos; Cherian, Ashok; Ross, Donald

    2004-10-01

    The surgical management of mitral valve disease in women of childbearing age, young patients, and children with congenital mitral valve defects is made difficult by the prospect of lifelong anticoagulation. We suggest the use of a pulmonary autograft in the mitral position (Ross II procedure) as an alternative surgical technique. We present a review of the literature, historical perspectives, indications, selection criteria, and surgical technique for the Ross II procedure. Our literature search identified 14 studies that reported results from the Ross II operation. Performed in 103 patients, the overall in-hospital mortality was 7 (6.7%), with a late mortality of 10 (9%). Although further research is needed, current evidence suggests the Ross II operation is a valuable alternative in low-risk young patients where valve durability and the complication rate from other procedures is unsatisfactory and anticoagulation not ideal.

  16. STS-74 M.S. Jerry L. Ross suits up

    Science.gov (United States)

    1995-01-01

    Spaceflight veteran Jerry L. Ross, Mission Specialist 2 on Shuttle Mission STS-74, is assisted by a suit technician as he finishes getting into his launch/entry suit in the Operations and Checkout Building. Ross and four fellow astronauts will depart shortly for Launch Pad 39A, where the Space Shuttle Atlantis awaits a second liftoff attempt during a seven-minute window scheduled to open at approximately 7:30 a.m. EST, Nov. 12.

  17. 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...

  18. The exchange of inorganic carbon on the Canadian Beaufort Shelf

    Science.gov (United States)

    Mol, Jacoba; Thomas, Helmuth; Hu, Xianmin; Myers, Paul G.

    2017-04-01

    The Mackenzie Shelf in the southeastern Beaufort Sea is an area that has experienced large changes in the past several decades as warming, sea-ice loss, and increased river discharge have altered carbon cycling. Upwelling and downwelling events are common on the shelf, caused by strong, fluctuating along-shore winds and resulting cross-shelf Ekman transport. Downwelling carries inorganic carbon and other remineralization products off the shelf and into the deep basin for possible long-term storage in the world oceans. Upwelling carries water high in dissolved inorganic carbon (DIC) and nutrients from the Pacific-origin upper halocline layer (UHL) onto the shelf. Profiles of DIC and total alkalinity (TA) taken in August and September of 2014 are used to investigate the cycling of inorganic carbon on the Mackenzie Shelf. The along-shore and cross-shelf transport of inorganic carbon is quantified using velocity field output from a simulation of the Arctic and Northern Hemisphere Atlantic (ANHA4) configuration of the Nucleus of European Modelling of the Ocean (NEMO) model. A strong upwelling event prior to sampling on the Mackenzie Shelf is analyzed and the resulting influence on the carbonate system, including the saturation state of aragonite and pH levels, is investigated. TA and δ18O are used to examine water mass distributions in the study area and analyze the influence of Pacific Water, Mackenzie River freshwater, and sea-ice melt on carbon dynamics and air-sea fluxes of CO2 in the surface mixed layer. Understanding carbon transfer in this seasonally dynamic environment is key in order to quantify the importance of Arctic shelf regions to the global carbon cycle and to provide a basis for understanding how its role will respond to the aforementioned changes in the regional marine system.

  19. Dynamics of the Ross-Stirling engine

    Energy Technology Data Exchange (ETDEWEB)

    Doige, A G; Walker, G

    1986-01-01

    A computer model has been developed for the simulation of the dynamic loading in a Stirling engine having a Ross linkage as the drive mechanism. The model is based on a complete theoretical formulation of the dynamics of the system. The masses and moments of inertia of all moving components have been included in the model. The computer program can be used for determining the effect of changes in many design parameters on the geometry, velocities, accelerations, dynamic loading and reactions at all pin connections and engine-mount locations. In this paper, emphasis is given to assessing the general characteristics of the reaction forces at the pin connections and to the reduction of overall engine shaking forces by simple balancing methods. The most heavily loaded element in the engine is the pin connecting the crank and the yoke. The force at that location is a combination of a static load produced by gas pressure in the cylinders and a combined inertia load for the whole engine which increases with the square of the rotational speed. 6 refs., 12 figs., 2 tabs.

  20. Iron Fertilization of the Southern Ocean: Regional Simulation and Analysis of C-Sequestration in the Ross Sea

    Energy Technology Data Exchange (ETDEWEB)

    Kevin Arrigo

    2012-03-13

    A modified version of the dynamic 3-dimensional mesoscale Coupled Ice, Atmosphere, and Ocean model (CIAO) of the Ross Sea ecosystem has been used to simulate the impact of environmental perturbations upon primary production and biogenic CO2 uptake. The Ross Sea supports two taxonomically, and spatially distinct phytoplankton populations; the haptophyte Phaeocystis antarctica and diatoms. Nutrient utilization ratios predict that P. antarctica and diatoms will be driven to nitrate and phosphate limitation, respectively. Model and field data have confirmed that the Ross Sea is iron limited with only two-thirds of the macronutrients consumed by the phytoplankton by the end of the growing season. In this study, the CIAO model was improved to simulate a third macronutrient (phosphate), dissolved organic carbon, air-sea gas exchange, and the carbonate system. This enabled us to effectively model pCO2 and subsequently oceanic CO2 uptake via gas exchange, allowing investigations into the affect of alleviating iron limitation on both pCO2 and nutrient drawdown.

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

    Science.gov (United States)

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

    2018-01-01

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

  2. Too Warm, Two Poles: Super Interglacial Teleconnections and Possible Dual Pole Ice Sheet Stability

    Science.gov (United States)

    Brigham-Grette, J.; Deconto, R. M.; Roychowdhury, R.; de Wet, G.; Keisling, B. A.; Melles, M.; Minyuk, P.

    2017-12-01

    Geologic records of the warm Pliocene and Pleistocene super interglacials from both the Arctic and the Antarctic show us that ice sheets are more vulnerable to subtle polar warming than once thought. The continuous 3.6 million-year old sediment record from Lake El'gygytgyn (Lake E), the largest, deepest unglaciated Arctic lake located in central Chukotka, Russia, contains evidence of the warm forested Pliocene and the transition to changing glacial/interglacial climate cycles including at least 9 super interglacials and numerous other strong interglacials. Most of these super interglacials especially MIS 11 and 31, record conditions warmer than MIS 5e and many occur when global cycles are dominated by apparent 41ka forcing during the transition from the warm Pliocene to stronger G/IG variability. Given community consensus on the reduction of the Greenland Ice sheet (GIS) during MIS5e, we suggest that previous interglacials likely forced even larger reductions in the GIS, perhaps consistent with cosmogenic isotope exposure histories. We can best match MIS 11 and 31 from the Antarctic ANDRILL records when diatomaceous ooze deposition in the past recovered from under the modern Ross Ice Shelf suggests collapse of the WAIS and open water conditions. It is possible that a large number of the other Lake E super interglacials correspond to other intervals of WAIS collapse, within the uncertainly of the ANDRILL chronology. The forcing of super interglacials was not necessarily the result of high atmospheric CO2 but the result of preconditioning during periods of extremely low eccentricity and high obliquity. The challenge is now to incorporate oceanographic models (as suggested in Melles et al. 2012) to gauge ice sheet and ocean circulation sensitivity and timescales to preconditioning. Yet confirmation of past warming driving frequent ice sheet collapse in both hemispheres is clear geologically-based evidence that informs our future. Today, anthropogenic CO2 emissions are

  3. Influence of Ross Sea Bottom Water changes on the warming and freshening of the Antarctic Bottom Water in the Australian-Antarctic Basin

    Directory of Open Access Journals (Sweden)

    K. Shimada

    2012-07-01

    Full Text Available Changes to the properties of Antarctic Bottom Water in the Australian-Antarctic Basin (AA-AABW between the 1990s and 2000s are documented using data from the WOCE Hydrographic Program (WHP and repeated hydrographic surveys. Strong cooling and freshening are observed on isopycnal layers denser than γn = 28.30 kg m−3. Changes in the average salinity and potential temperature below this isopycnal correspond to a basin-wide warming of 1300 ± 200 GW and freshening of 24 ± 3 Gt year−1. Recent changes to dense shelf water in the source regions in the Ross Sea and George V Land can explain the freshening of AA-AABW but not its extensive warming. An alternative mechanism for this warming is a decrease in the supply of AABW from the Ross Sea (RSBW. Hydrographic profiles between the western Ross Sea and George V Land (171–158° E were analyzed with a simple advective-diffusive model to assess the causes of the observed changes. The model suggests that the warming of RSBW observed between the 1970s and 2000s can be explained by a 21 ± 23% reduction in RSBW transport and the enhancement of the vertical diffusion of heat resulting from a 30 ± 7% weakening of the abyssal stratification. The documented freshening of Ross Sea dense shelf water leads to a reduction in both salinity and density stratification. Therefore the direct freshening of RSBW at its source also produces an indirect warming of the RSBW. A simple box model suggests that the changes in RSBW properties and volume transport (a decrease of 6.7% is assumed between the year 1995 and 2005 can explain 51 ± 6% of the warming and 84 ± 10% of the freshening observed in AA-AABW.

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

    Science.gov (United States)

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

    2018-01-01

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

  5. Design of the MISMIP+, ISOMIP+, and MISOMIP ice-sheet, ocean, and coupled ice sheet-ocean intercomparison projects

    Science.gov (United States)

    Asay-Davis, Xylar; Cornford, Stephen; Martin, Daniel; Gudmundsson, Hilmar; Holland, David; Holland, Denise

    2015-04-01

    The MISMIP and MISMIP3D marine ice sheet model intercomparison exercises have become popular benchmarks, and several modeling groups have used them to show how their models compare to both analytical results and other models. Similarly, the ISOMIP (Ice Shelf-Ocean Model Intercomparison Project) experiments have acted as a proving ground for ocean models with sub-ice-shelf cavities.As coupled ice sheet-ocean models become available, an updated set of benchmark experiments is needed. To this end, we propose sequel experiments, MISMIP+ and ISOMIP+, with an end goal of coupling the two in a third intercomparison exercise, MISOMIP (the Marine Ice Sheet-Ocean Model Intercomparison Project). Like MISMIP3D, the MISMIP+ experiments take place in an idealized, three-dimensional setting and compare full 3D (Stokes) and reduced, hydrostatic models. Unlike the earlier exercises, the primary focus will be the response of models to sub-shelf melting. The chosen configuration features an ice shelf that experiences substantial lateral shear and buttresses the upstream ice, and so is well suited to melting experiments. Differences between the steady states of each model are minor compared to the response to melt-rate perturbations, reflecting typical real-world applications where parameters are chosen so that the initial states of all models tend to match observations. The three ISOMIP+ experiments have been designed to to make use of the same bedrock topography as MISMIP+ and using ice-shelf geometries from MISMIP+ results produced by the BISICLES ice-sheet model. The first two experiments use static ice-shelf geometries to simulate the evolution of ocean dynamics and resulting melt rates to a quasi-steady state when far-field forcing changes in either from cold to warm or from warm to cold states. The third experiment prescribes 200 years of dynamic ice-shelf geometry (with both retreating and advancing ice) based on a BISICLES simulation along with similar flips between warm and

  6. Radiological Operations Support Specialist (ROSS) Pilot Course Summary and Recommendations

    Energy Technology Data Exchange (ETDEWEB)

    Alai, M. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Askin, A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Buddemeier, B. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Wogan, L. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Doshi, P. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Tai, L. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2016-09-30

    In support of the Department of Homeland Security / Science and Technology Directorate’s (DHS/S&T) creation of a new position called the Radiological Operations Support Specialist (ROSS), Lawrence Livermore National Laboratory (LLNL) in Sub-task 1.1 and 1.2 has assisted in the development of the ROSS skills, knowledge, and abilities (SKAs); identified potentially relevant training; cross-mapped the training to the SKAs; and identified gaps in the training related to the SKAs, as well as their respective level of training knowledge - current versus desired. In the follow on task, Sub-task 1.3, a 5 day ROSS Pilot Training course was developed to fill the priority gaps identified in Sub-Task 1.2. Additionally, in Sub-Task 1.5, LLNL has performed a gap analysis of electronic tools, handbooks, and job-aides currently available to the ROSS and developed recommendations for additional and next generation tools to ensure the operational effectiveness of the ROSS position. This document summarizes the feedback received from the instructors and pilot course observers on what worked in the course and what could be improved as well as an assessment of the Pre- and Post-Test administered to the students.

  7. Radiological Operations Support Specialist (ROSS) Pilot Course Summary and Recommendations

    International Nuclear Information System (INIS)

    Alai, M.; Askin, A.; Buddemeier, B.; Wogan, L.; Doshi, P.; Tai, L.

    2016-01-01

    In support of the Department of Homeland Security / Science and Technology Directorate's (DHS/S&T) creation of a new position called the Radiological Operations Support Specialist (ROSS), Lawrence Livermore National Laboratory (LLNL) in Sub-task 1.1 and 1.2 has assisted in the development of the ROSS skills, knowledge, and abilities (SKAs); identified potentially relevant training; cross-mapped the training to the SKAs; and identified gaps in the training related to the SKAs, as well as their respective level of training knowledge - current versus desired. In the follow on task, Sub-task 1.3, a 5 day ROSS Pilot Training course was developed to fill the priority gaps identified in Sub-Task 1.2. Additionally, in Sub-Task 1.5, LLNL has performed a gap analysis of electronic tools, handbooks, and job-aides currently available to the ROSS and developed recommendations for additional and next generation tools to ensure the operational effectiveness of the ROSS position. This document summarizes the feedback received from the instructors and pilot course observers on what worked in the course and what could be improved as well as an assessment of the Pre- and Post-Test administered to the students.

  8. Evidence for radionuclide transport by sea ice

    International Nuclear Information System (INIS)

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

    1997-01-01

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

  9. Cosmogenic 10Be ages from the Meirs and Garwood Valleys, Denton Hills, West Antarctica, suggest an absence in LGM Ice Sheet expansion.

    Science.gov (United States)

    Fink, David; Joy, Kurt; Storey, Bryan

    2014-05-01

    It has been hypothesised that during interglacials, thinning of the Ross Ice Shelf allowed a more open water environment with increased local precipitation. This resulted in outlet glaciers, which drain the Transantarctic Mountains and fed by the East Antarctic Ice Sheet, advancing during moist warmer periods, apparently out of phase with colder arid dry periods. Significantly the ice core record during these warm periods also shows increased accumulation continent wide The geomorphology of the Denton Hills in the Royal Society Range, West Antarctica, is a result of Miocene fluvial incision reworked by subsequent glacial advances throughout the Quaternary. The Garwood and Miers glacial valleys drain ice across the Denton Hills into the Shelf, and should thus show maximum extent during interstadials. To understand the chronology of late Quaternary glaciations, 15 granitic boulders from terminal moraines were sampled for 10Be and 26Al cosmogenic dating. Obtaining reliable exposure ages of erratics within moraines that represent timing of deposition (i.e. glacial advances) is problematic in polar regions, where glacial activity is principally controlled by ice sheet dynamics. Recycling of previously exposed debris, uncertainty in provenance of glacially transported boulders and a lack of a post-depositional hydrologic process to remove previously exposed material from a valley system, leads to ambiguities in multiple exposure ages from a single coeval glacial landform. More importantly, cold-based ice advance can leave a landform unmodified resulting in young erratics deposited on bedrock that shows weathering and/or inconsistent age-altitude relationships. Primarily, inheritance becomes a difficulty in qualifying exposure ages from polar regions. Preliminary results from the Garwood and Miers Valleys indicate that glaciers in the Denton Hills had begun to retreat from their last maximum positions no later than 23-37 ka, and thus the local last glacial maximum

  10. Does the Homograft for RVOT Reconstruction in Ross: Patients Fare Better than for Non-Ross Patients? A Single-Center Experience.

    Science.gov (United States)

    Ruzmetov, Mark; Geiss, Dale M; Shah, Jitendra J; Fortuna, Randall S; Welke, Karl F

    2015-07-01

    In patients undergoing the Ross procedure, the right ventricular outflow tract (RVOT) conduit is inserted in an orthotopic position rather than in the more heterotopic position used in the repair of complex congenital RVOT obstruction. The study aim was to compare the authors' institutional mid-term experience of large-sized homografts (>19 mm) in patients with Ross and non-Ross RVOT reconstructions. The outcome was reviewed of all homografts implanted for Ross (n = 72) or non-Ross (n = 64) RVOT reconstruction at a single center between 1993 and 2012. Echocardiographic data were reviewed to evaluate valve performance. Homograft dysfunction was defined as RVOT obstruction with peak echo-Doppler gradient >40 mmHg and/or grade >III/IV conduit valve regurgitation. Homograft failure was defined as the need for conduit replacement or catheter or surgical reintervention. The age, body weight, conduit diameter and previous surgery were significantly higher in patients with Ross compared to the non-Ross group (p = 0.002, 0.003 and Ross, n = 17; non-Ross, n = 18). The data acquired showed actuarial survival, freedom from conduit dysfunction and conduit failure to be similar in both cohorts. Freedom from any type of reoperation was worse for the Ross group (58%) than for the non-Ross group (72%) (p = 0.05). During the first 15 years after Ross or non-Ross pulmonary homograft implantation, the survival rate, freedom from failure and dysfunction, and RVOT gradient were statistically similar. Freedom from any type of reoperation was significantly higher in the non-Ross group, however.

  11. Rossing - uranium changes the face of the Namib

    International Nuclear Information System (INIS)

    Anon.

    1981-01-01

    Rossing is not only an important source of uranium for industrial countries, but a large revenue-earner. It is injecting money into the economy. For efficiency, personnel and equipment had to be comfortably established. The Rossing orebody is the largest known deposit of uranium occuring in granite. Over one million ton of ore and waste are removed weekly. By the use of scintillometer readings the ore is blended to give a constant feed to the mill. Modern developments are used to optimise the mining operation. Radioactivity will be always present and is therefore regulary measured. The best working environment are always ensured

  12. 75 FR 32802 - Certificate of Alternative Compliance for the Offshore Supply Vessel ROSS CANDIES

    Science.gov (United States)

    2010-06-09

    ... Compliance for the Offshore Supply Vessel ROSS CANDIES AGENCY: Coast Guard, DHS. ACTION: Notice. SUMMARY: The... vessel ROSS CANDIES as required by 33 U.S.C. 1605(c) and 33 CFR 81.18. DATES: The Certificate of... the offshore supply vessel ROSS CANDIES, O.N. 1222260. Full compliance with 72 COLREGS [[Page 32803...

  13. 77 FR 56859 - Federal Register Notification of Redesignation of Potential Wilderness as Wilderness, Ross Lake...

    Science.gov (United States)

    2012-09-14

    ... Register Notification of Redesignation of Potential Wilderness as Wilderness, Ross Lake National Recreation..., Ross Lake National Recreation Area, and Lake Chelan National Recreation Area as the Stephen Mather... acres of potential wilderness within Ross Lake National Recreation Area, including approximately 1,667...

  14. Outer Continental Shelf Lands Act

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This data represents geographic terms used within the Outer Continental Shelf Lands Act (OCSLA or Act). The Act defines the United States outer continental shelf...

  15. Setting the scientistic cat among the humanist pigeons Don Ross ...

    African Journals Online (AJOL)

    implications of cognitive science and economics for each other. Ross makes neoclassical economics central to the unification of the behavioural sciences, and defends its fundamental health against its critics. He locates the source of the empirical and conceptual problems besetting neoclassical economics in the mistaken ...

  16. R. E. van der Ross (1921–2017)

    African Journals Online (AJOL)

    19 Mrt. 2018 ... Sedert sy jeug het Richard Ernest van der Ross. (1921–2017) 'n belangrike rol in die breë Kaapse ge- meenskap gespeel. Hy het hom onderskei as 'n anti- apartheidsaktivis, 'n opvoedkundige, 'n geskied- skrywer en openbare intellektueel, 'n vakbondmens,. 'n gemeenskapsbouer, 'n maatskappydirekteur ...

  17. Grounding line transient response in marine ice sheet models

    Directory of Open Access Journals (Sweden)

    A. S. Drouet

    2013-03-01

    Full Text Available Marine ice-sheet stability is mostly controlled by the dynamics of the grounding line, i.e. the junction between the grounded ice sheet and the floating ice shelf. Grounding line migration has been investigated within the framework of MISMIP (Marine Ice Sheet Model Intercomparison Project, which mainly aimed at investigating steady state solutions. Here we focus on transient behaviour, executing short-term simulations (200 yr of a steady ice sheet perturbed by the release of the buttressing restraint exerted by the ice shelf on the grounded ice upstream. The transient grounding line behaviour of four different flowline ice-sheet models has been compared. The models differ in the physics implemented (full Stokes and shallow shelf approximation, the numerical approach, as well as the grounding line treatment. Their overall response to the loss of buttressing is found to be broadly consistent in terms of grounding line position, rate of surface elevation change and surface velocity. However, still small differences appear for these latter variables, and they can lead to large discrepancies (> 100% observed in terms of ice sheet contribution to sea level when cumulated over time. Despite the recent important improvements of marine ice-sheet models in their ability to compute steady state configurations, our results question the capacity of these models to compute short-term reliable sea-level rise projections.

  18. Channelization of plumes beneath ice shelves

    KAUST Repository

    Dallaston, M.  C.; Hewitt, I. J.; Wells, A. J.

    2015-01-01

    © 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.

  19. 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.

  20. Outcomes of Reintervention on the Autograft After Ross Procedure.

    Science.gov (United States)

    Kumar, S Ram; Bansal, Neeraj; Wells, Winfield J; Starnes, Vaughn A

    2016-11-01

    After a Ross procedure, a small subset of patients requires reintervention for autograft dilatation or valve insufficiency. We sought to determine the indications, nature, and outcomes of autograft reinterventions in the left ventricular outflow tract after a Ross procedure. We retrospectively reviewed the charts of 316 consecutive patients, age 4 days to 70 years, who underwent a Ross procedure at our institution. Of these, 47 patients (15%) required autograft reintervention during a median follow-up of 8.2 years. Forty-seven patients, median age 26 years (interquartile range [IQR], 14.4 to 44.8 years), 32 (68%) men, required autograft reintervention a median 5.5 years (IQR, 1.8 to 9.4 years) after a Ross procedure. In 47% (22 of 47 patients), the autograft valve could be salvaged (15 valve-sparing aortic replacements, 7 valve repairs). The remaining 53% underwent replacement of the root (10 mechanical, 5 homograft) or valve alone (7 mechanical, 3 bioprosthetic). Twenty patients presented without autograft root dilatation 1 year (IQR, 0.5 to 2.9 years) after Ross. Fifteen of them (75%) required valve replacement. The 27 patients who demonstrated root dilatation presented 6.9 years (IQR, 4.5 to 9.7 years; p Ross, and 17 (63%) of these valves could be spared (p = 0.01). There was no surgical mortality and 5 (11%) major morbidity events. Patients were followed up for 4.9 years (IQR, 2.1 to 7 years) after left ventricular outflow tract reintervention. For patients whose autograft valve could be spared, 3-, 5-, and 8-year freedom from valve replacement was 92%, 86%, and 86%, respectively. At last follow-up, only 1 patient had greater than mild aortic insufficiency, and all but 1 had normal ejection fraction. Autograft reintervention after a Ross appears to follow a bimodal distribution. Patients with primary autograft leaflet problems tend to present early without root dilatation and frequently require valve replacement. The autograft valve can be salvaged in the

  1. 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...

  2. Intra-seasonal variation in foraging behavior among Adélie penguins (Pygocelis adeliae) breeding at Cape Hallett, Ross Sea, Antarctica

    Science.gov (United States)

    Lyver, P.O.B.; MacLeod, C.J.; Ballard, G.; Karl, B.J.; Barton, K.J.; Adams, J.; Ainley, D.G.; Wilson, P.R.

    2011-01-01

    We investigated intra-seasonal variation in foraging behavior of chick-rearing Adélie penguins, Pygoscelis adeliae, during two consecutive summers at Cape Hallett, northwestern Ross Sea. Although foraging behavior of this species has been extensively studied throughout the broad continental shelf region of the Ross Sea, this is the first study to report foraging behaviors and habitat affiliations among birds occupying continental slope waters. Continental slope habitat supports the greatest abundances of this species throughout its range, but we lack information about how intra-specific competition for prey might affect foraging and at-sea distribution and how these attributes compare with previous Ross Sea studies. Foraging trips increased in both distance and duration as breeding advanced from guard to crèche stage, but foraging dive depth, dive rates, and vertical dive distances travelled per hour decreased. Consistent with previous studies within slope habitats elsewhere in Antarctic waters, Antarctic krill (Euphausia superba) dominated chick meal composition, but fish increased four-fold from guard to crèche stages. Foraging-, focal-, and core areas all doubled during the crèche stage as individuals shifted distribution in a southeasterly direction away from the coast while simultaneously becoming more widely dispersed (i.e., less spatial overlap among individuals). Intra-specific competition for prey among Adélie penguins appears to influence foraging behavior of this species, even in food webs dominated by Antarctic krill.

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

    DEFF Research Database (Denmark)

    Winter, Kate; Ross, Neil; Ferraccioli, Fausto

    2018-01-01

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

  4. Global ice sheet/RSL simulations using the higher-order Ice Sheet System Model.

    Science.gov (United States)

    Larour, E. Y.; Ivins, E. R.; Adhikari, S.; Schlegel, N.; Seroussi, H. L.; Morlighem, M.

    2017-12-01

    Relative sea-level rise is driven by processes that are intimately linked to the evolution ofglacial areas and ice sheets in particular. So far, most Earth System models capable of projecting theevolution of RSL on decadal to centennial time scales have relied on offline interactions between RSL andice sheets. In particular, grounding line and calving front dynamics have not been modeled in a way that istightly coupled with Elasto-Static Adjustment (ESA) and/or Glacial-Isostatic Adjustment (GIA). Here, we presenta new simulation of the entire Earth System in which both Greenland and Antarctica ice sheets are tightly coupledto an RSL model that includes both ESA and GIA at resolutions and time scales compatible with processes suchas grounding line dynamics for Antarctica ice shelves and calving front dynamics for Greenland marine-terminatingglaciers. The simulations rely on the Ice Sheet System Model (ISSM) and show the impact of higher-orderice flow dynamics and coupling feedbacks between ice flow and RSL. We quantify the exact impact of ESA andGIA inclusion on grounding line evolution for large ice shelves such as the Ronne and Ross ice shelves, as well asthe Agasea Embayment ice streams, and demonstate how offline vs online RSL simulations diverge in the long run,and the consequences for predictions of sea-level rise.This work was performed at the California Institute of Technology's Jet Propulsion Laboratory undera contract with the National Aeronautics and Space Administration's Cryosphere Science Program.

  5. 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.

  6. 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

  7. Ice targets

    International Nuclear Information System (INIS)

    Pacheco, C.; Stark, C.; Tanaka, N.; Hodgkins, D.; Barnhart, J.; Kosty, J.

    1979-12-01

    This report presents a description of ice targets that were constructed for research work at the High Resolution Spectrometer (HRS) and at the Energetic Pion Channel and Spectrometer (EPICS). Reasons for using these ice targets and the instructions for their construction are given. Results of research using ice targets will be published at a later date

  8. Towards a Universal Calving Law: Modeling Ice Shelves Using Damage Mechanics

    Science.gov (United States)

    Whitcomb, M.; Bassis, J. N.; Price, S. F.; Lipscomb, W. H.

    2017-12-01

    Modeling iceberg calving from ice shelves and ice tongues is a particularly difficult problem in glaciology because of the wide range of observed calving rates. Ice shelves naturally calve large tabular icebergs at infrequent intervals, but may instead calve smaller bergs regularly or disintegrate due to hydrofracturing in warmer conditions. Any complete theory of iceberg calving in ice shelves must be able to generate realistic calving rate values depending on the magnitudes of the external forcings. Here we show that a simple damage evolution law, which represents crevasse distributions as a continuum field, produces reasonable estimates of ice shelf calving rates when added to the Community Ice Sheet Model (CISM). Our damage formulation is based on a linear stability analysis and depends upon the bulk stress and strain rate in the ice shelf, as well as the surface and basal melt rates. The basal melt parameter in our model enhances crevasse growth near the ice shelf terminus, leading to an increased iceberg production rate. This implies that increasing ocean temperatures underneath ice shelves will drive ice shelf retreat, as has been observed in the Amundsen and Bellingshausen Seas. We show that our model predicts broadly correct calving rates for ice tongues ranging in length from 10 km (Erebus) to over 100 km (Drygalski), by matching the computed steady state lengths to observations. In addition, we apply the model to idealized Antarctic ice shelves and show that we can also predict realistic ice shelf extents. Our damage mechanics model provides a promising, computationally efficient way to compute calving fluxes and links ice shelf stability to climate forcing.

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

    Science.gov (United States)

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

    2017-12-01

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

  10. Early precursors to break-up of the Larsen Ice Shelves, Antarctica

    Science.gov (United States)

    Scambos, T. A.; Klinger, M.

    2017-12-01

    Ice flux into the embayments left behind by the collapse of the Larsen A and Larsen B ice shelves surged 2- to 6-fold after their disintegration events in 1995 and 2002. Glacier imbalance in the region since the events has been persistent, with elevation changes indicating a mass loss per year of approximately twice the rate of accumulation (Scambos et al., 2014, TCryo). The proximal cause of the disintegration events was a group of processes arising from the presence of extensive surface melt lakes and hydrofracture. However, precursor changes in the ice shelves beginning more than a decade before the disintegrations have been identified, and coincide with a trend towards reduced sea ice cover and increased foehn winds. Ice flow speeds in the Larsen A and B increased, even in the period prior to the loss of critical inboard areas of the ice shelf (which began in 1998 for the Larsen B), and elevation of the ice shelf surface decreased. Ice shelf surface lowering is interpreted as resulting from actual ice shelf thinning for this area, since field studies on both the Larsen A and B noted the upper firn of the shelf was almost completely converted to ice. Examination of satellite images spanning 1963 - 2014 shows that Larsen B shear margins and some suture zones evolved significantly prior to major ice shelf retreat. Overall, these changes suggest either increased ocean-driven basal melt or effects of increased surface meltwater on grounded glacier outflow are a cause of early shelf weakening that leads eventually to disintegration. Available ocean temperature data show that modified Weddell Deep Water, having a temperature 0.1-0.4°C above the surface freezing point, is present near the former ice fronts in some 1995-2012 profiles, but to date this has not been detected within the embayments or near the glacier grounding lines.

  11. Impact of environmental factors on the distribution of extreme scouring (gouging) event, Canadian Beaufort shelf

    Energy Technology Data Exchange (ETDEWEB)

    Blasco, Steve [Geological Survey of Canada, Dartmouth (Canada); Carr, Erin; Campbell, Patrick [Canadian Seabed Research Ltd., Porters Lake (Canada); Shearer, Jim [Shearer Consulting, Ottawa (Canada)

    2011-07-01

    A knowledge of the presence of scours, their dimensions and their return frequencies is highly important in the development of hydrocarbon offshore structures. Mapping surveys have identified 290 extreme scour events across the Canadian Beaufort shelf. This paper investigated the impact of environmental factors on the distribution of extreme scouring events in the Canadian Beaufort shelf. This study used the NEWBASE database of new ice scours to perform an analysis of the scours appearance mechanisms. The geotechnical zonation, the bathymetry and the shelf gradient were evaluated using these data. Estimation of the surficial sediment type, the surficial sediment thickness and sea ice regime were also made. It was found that the spatial distribution of extreme scour events is controlled by sea-ice regime, bathymetry and geotechnical zonation. The results obtained from mapping surveys suggested that the key controlling environmental factors may combine to limit the depth of extreme scour events to 5 meters.

  12. Morphology and stratal geometry of the Antarctic continental shelf: Insights from models

    Science.gov (United States)

    Cooper, Alan K.; Barker, Peter F.; Brancolini, Giuliano

    1997-01-01

    Reconstruction of past ice-sheet fluctuations from the stratigraphy of glaciated continental shelves requires understanding of the relationships among the stratal geometry, glacial and marine sedimentary processes, and ice dynamics. We investigate the formation of the morphology and the broad stratal geometry of topsets on the Antarctic continental shelf with numerical models. Our models assume that the stratal geometry and morphology are principally the results of time-integrated effects of glacial erosion and sedimentation related to the location of the seaward edge of the grounded ice. The location of the grounding line varies with time almost randomly across the shelf. With these simple assumptions, the models can successfully mimic salient features of the morphology and the stratal geometry. The models suggest that the current shelf has gradually evolved to its present geometry by many glacial advances and retreats of the grounding line to different locations across the shelf. The locations of the grounding line do not appear to be linearly correlated with either fluctuations in the 5 l s O record (which presumably represents changes in the global ice volume) or with the global sea-level curve, suggesting that either a more complex relationship exists or local effects dominate. The models suggest that erosion of preglacial sediments is confined to the inner shelf, and erosion decreases and deposition increases toward the shelf edge. Some of the deposited glacial sediments must be derived from continental erosion. The sediments probably undergo extensive transport and reworking obliterating much of the evidence for their original depositional environment. The flexural rigidity and the tectonic subsidence of the underlying lithosphere modify the bathymetry of the shelf, but probably have little effect on the stratal geometry. Our models provide several guidelines for the interpretation of unconformities, the nature of preserved topset deposits, and the

  13. Isad ja tütred, isad ja pojad / Jüri Ross, Kristine Ross, Fjodor Berman ...[jt.] ; üles kirjutanud Jaana Liigand

    Index Scriptorium Estoniae

    2011-01-01

    Büroomaailma juht Jüri Ross ja turundusdirektor Kristine Ross, BLRT Grupi omanik Fjodor Berman ja BLRT Grupi tütarfirma Refonda tegevdirektor Mark Berman, Saaremaa Laevakompanii ja paljude firmade omanik Vjatšeslav Leedo ja Mosaiigi kohviku omanik Katrin Leedo ärist, juhtimisest ja omavahelistest suhetest

  14. 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.

  15. The Potsdam Parallel Ice Sheet Model (PISM-PIK – Part 1: Model description

    Directory of Open Access Journals (Sweden)

    R. Winkelmann

    2011-09-01

    Full Text Available We present the Potsdam Parallel Ice Sheet Model (PISM-PIK, developed at the Potsdam Institute for Climate Impact Research to be used for simulations of large-scale ice sheet-shelf systems. It is derived from the Parallel Ice Sheet Model (Bueler and Brown, 2009. Velocities are calculated by superposition of two shallow stress balance approximations within the entire ice covered region: the shallow ice approximation (SIA is dominant in grounded regions and accounts for shear deformation parallel to the geoid. The plug-flow type shallow shelf approximation (SSA dominates the velocity field in ice shelf regions and serves as a basal sliding velocity in grounded regions. Ice streams can be identified diagnostically as regions with a significant contribution of membrane stresses to the local momentum balance. All lateral boundaries in PISM-PIK are free to evolve, including the grounding line and ice fronts. Ice shelf margins in particular are modeled using Neumann boundary conditions for the SSA equations, reflecting a hydrostatic stress imbalance along the vertical calving face. The ice front position is modeled using a subgrid-scale representation of calving front motion (Albrecht et al., 2011 and a physically-motivated calving law based on horizontal spreading rates. The model is tested in experiments from the Marine Ice Sheet Model Intercomparison Project (MISMIP. A dynamic equilibrium simulation of Antarctica under present-day conditions is presented in Martin et al. (2011.

  16. The Potsdam Parallel Ice Sheet Model (PISM-PIK) - Part 1: Model description

    Science.gov (United States)

    Winkelmann, R.; Martin, M. A.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.

    2011-09-01

    We present the Potsdam Parallel Ice Sheet Model (PISM-PIK), developed at the Potsdam Institute for Climate Impact Research to be used for simulations of large-scale ice sheet-shelf systems. It is derived from the Parallel Ice Sheet Model (Bueler and Brown, 2009). Velocities are calculated by superposition of two shallow stress balance approximations within the entire ice covered region: the shallow ice approximation (SIA) is dominant in grounded regions and accounts for shear deformation parallel to the geoid. The plug-flow type shallow shelf approximation (SSA) dominates the velocity field in ice shelf regions and serves as a basal sliding velocity in grounded regions. Ice streams can be identified diagnostically as regions with a significant contribution of membrane stresses to the local momentum balance. All lateral boundaries in PISM-PIK are free to evolve, including the grounding line and ice fronts. Ice shelf margins in particular are modeled using Neumann boundary conditions for the SSA equations, reflecting a hydrostatic stress imbalance along the vertical calving face. The ice front position is modeled using a subgrid-scale representation of calving front motion (Albrecht et al., 2011) and a physically-motivated calving law based on horizontal spreading rates. The model is tested in experiments from the Marine Ice Sheet Model Intercomparison Project (MISMIP). A dynamic equilibrium simulation of Antarctica under present-day conditions is presented in Martin et al. (2011).

  17. Validation of Robotic Surgery Simulator (RoSS).

    Science.gov (United States)

    Kesavadas, Thenkurussi; Stegemann, Andrew; Sathyaseelan, Gughan; Chowriappa, Ashirwad; Srimathveeravalli, Govindarajan; Seixas-Mikelus, Stéfanie; Chandrasekhar, Rameella; Wilding, Gregory; Guru, Khurshid

    2011-01-01

    Recent growth of daVinci Robotic Surgical System as a minimally invasive surgery tool has led to a call for better training of future surgeons. In this paper, a new virtual reality simulator, called RoSS is presented. Initial results from two studies - face and content validity, are very encouraging. 90% of the cohort of expert robotic surgeons felt that the simulator was excellent or somewhat close to the touch and feel of the daVinci console. Content validity of the simulator received 90% approval in some cases. These studies demonstrate that RoSS has the potential of becoming an important training tool for the daVinci surgical robot.

  18. The Externally Supported Ross Operation: Early Outcomes and Intermediate Follow-Up.

    Science.gov (United States)

    Jacobsen, Roni M; Earing, Michael G; Hill, Garick D; Barnes, Michael; Mitchell, Michael E; Woods, Ronald K; Tweddell, James S

    2015-08-01

    The externally supported Ross (supported Ross), consisting of a Dacron (DuPont, Wilmington, DE) graft to support the neoaortic root, has been used in adolescent and adult patients to prevent neoaortic dilatation. Outcomes after the supported Ross technique were compared with the Ross procedure using the standard aortic root replacement technique (standard Ross). This was a retrospective analysis of 36 adolescent and young adult patients who underwent the Ross procedure between 1992 and 2013. The outcomes of supported Ross procedures in 26 patients were compared with the Ross procedure in 10 patients. End points included survival, neoaortic root dilatation, development of neoaortic regurgitation, and the need for reintervention. The median age at operation was 14 years (range, 11 to 31 years), and indications for the operation were mixed lesions (47%), followed by aortic regurgitation (42%) and stenosis (11%). There were no early deaths. The mean follow-up was 2.2 years (range, 1 to 11 years). At the 1-year (p = 0.01) and 3-year (p Ross cohort had a smaller neoaortic root z-score. Neither cohort had a large number of patients with significant neoaortic regurgitation, with 1 patient in the supported cohort compared with 3 patients in the standard cohort. Overall, 4 patients (40%) in the standard Ross cohort had required reintervention, including 3 directed at the neoaortic root. One patient in the supported Ross cohort required early reintervention for revision of the right coronary artery. At intermediate follow-up, patients who underwent the supported Ross technique were less likely to have neoaortic root dilatation compared with patients who underwent a standard Ross procedure. Further studies are needed to evaluate the long-term durability of this technique, particularly in regards to the development of significant aortic regurgitation, the rate of reintervention, and application to younger and smaller patients. Copyright © 2015 The Society of Thoracic Surgeons

  19. Ross-Stirling engines: Variations on a theme

    Energy Technology Data Exchange (ETDEWEB)

    Walker, G; Fauvel, R

    1986-01-01

    A new mechanism called the Ross linkage offers the prospect for compact, lightweight, long-lived, relatively low-cost, Stirling engines with excellent prospects for early commercial developed for various applications. Ross-Stirling engines are unusually compact, with installation envelope about one-third of conventional engines, piston side forces are virtually eliminated facilitating the use of dry lubricated or close tolerance, gas lubricated seals and the linkage geometry automatically favors the large bore/short ratios preferred for Stirling engines. The linkage is simple to make with few moving parts so that cost is relatively low. Various potential or actual embodiments of Ross-Stirling engines are reviewed including Stirling-Stirling gas-fired heat pumps, multicylinder power systems and cryocoolers. The system has sufficient flexibility to readily accommodate widely disparate piston stroke and cylinder diameters. Most work has been done so far with two-piston Stirling engines but the same linkage may be adopted for piston-displacer Stirling engines. 6 refs., 10 figs.

  20. A global high-resolution data set of ice sheet topography, cavity geometry and ocean bathymetry

    DEFF Research Database (Denmark)

    Schaffer, Janin; Timmermann, Ralph; Arndt, Jan Erik

    2016-01-01

    of the Southern Ocean (IBCSO) version 1. While RTopo-1 primarily aimed at a good and consistent representation of the Antarctic ice sheet, ice shelves, and sub-ice cavities, RTopo-2now also contains ice topographies of the Greenland ice sheet and outlet glaciers. In particular, we aimed at agood representation....... For the continental shelf off Northeast Greenland and the floating ice tongue of Nioghalvfjerdsfjorden Glacier at about79 N, we incorporated a high-resolution digital bathymetry model considering original multibeam survey datafor the region. Radar data for surface topographies of the floating ice tongues...... for the geometry of Getz, Abbot, andFimbul ice shelf cavities. The data set is available in full and in regional subsets in NetCDF format from thePANGAEA database at doi:10.1594/PANGAEA.856844....

  1. 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.

  2. 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

  3. Modelling study of mesoscale cyclogenesis over Ross Sea, Antarctica, on February 18, 1988

    Energy Technology Data Exchange (ETDEWEB)

    Stortini, M.; Morelli, S.; Marchesi, S. [Modena e Reggio Emilia Univ., Modena (Italy). Dipt. di Scienze dell' Ingegneria, Sez. Osservatorio Geofisico

    2000-04-01

    This paper examines the development of a summer event of mesoscale cyclogenesis off the coast of Victoria Land in the presence of katabatic winds, by means of numerical simulations. These refer to the period from 00 UTC 17 February to 00 UTC 19 February 1988 and were performed using the hydrostatic ETA (1993 version) limited area model with resolution 55 km x 55 km x 17 levels. The ETA model reproduces katabatic winds from Terra Nova Bay and a trough on the southwestern Ross Sea. A cyclonic vortex is simulated in the trough, even though it is weaker than the one present in the analysis initialized by the European Center for Medium Range Weather Forecast (Reading, United Kingdom). Idealized simulations with varied surface conditions were also performed. In particular, an ice-covered ocean acts to weaken the atmospheric phenomena, while a no-mountain simulation emphasizes the influence of the orography and the cold winds from the coast of Victoria Land on the mesocyclonic activity.

  4. 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...

  5. New Jersey shallow shelf

    DEFF Research Database (Denmark)

    Expedition 313 Scientists; Bjerrum, Christian J.

    2009-01-01

    to key horizons in wells drilled into the adjacent coastal plain suggest the clinoform structures investigated during Expedition 313 were deposited during times of oscillations in global sea level; however, this needs to be determined with much greater certainty. The age, lithofacies, and core-log......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......) between 30 April and 17 July 2009, with additional support from the International Continental Scientific Drilling Program (ICDP). There were three objectives: (1) date late Paleogene–Neogene depositional sequences and compare ages of unconformable surfaces that divide these sequences with times of sea...

  6. Distribution of Ra-226 in the Ross Sea, Antarctica

    International Nuclear Information System (INIS)

    Bettoli, M.G.; Cantelli, L.; Queirazza, G.; Roveri, M.; Tositti, L.; Tubertini, O.; Valcher, S.

    1996-01-01

    An improved procedure for the determination of Rn-222 and Ra-226 in seawater developed for easier on-board operations is presented. Data on the radioactive disequilibrium between the mentioned radionuclides as directly determined in the field can be greatly helpful in the study of the gas-exchange processes at the air-sea interface, especially as far as the Antarctic Ocean is concerned. The method employed has been preliminary tested in laboratory on a set of seawater samples collected in the Ross Sea and Ra-226 data collected are discussed and compared to literature data. (UK)

  7. Application of ozonated dry ice (ALIGAL™ Blue Ice) for packaging and transport in the food industry.

    Science.gov (United States)

    Fratamico, Pina M; Juneja, Vijay; Annous, Bassam A; Rasanayagam, Vasuhi; Sundar, M; Braithwaite, David; Fisher, Steven

    2012-05-01

    Dry ice is used by meat and poultry processors for temperature reduction during processing and for temperature maintenance during transportation. ALIGAL™ Blue Ice (ABI), which combines the antimicrobial effect of ozone (O(3)) along with the high cooling capacity of dry ice, was investigated for its effect on bacterial reduction in air, in liquid, and on food and glass surfaces. Through proprietary means, O(3) was introduced to produce dry ice pellets to a concentration of 20 parts per million (ppm) by total weight. The ABI sublimation rate was similar to that of dry ice pellets under identical conditions, and ABI was able to hold the O(3) concentration throughout the normal shelf life of the product. Challenge studies were performed using different microorganisms, including E. coli, Campylobacter jejuni, Salmonella, and Listeria, that are critical to food safety. ABI showed significant (P Food Technologists®

  8. Ocean Tide Influences on the Antarctic and Greenland Ice Sheets

    Science.gov (United States)

    Padman, Laurie; Siegfried, Matthew R.; Fricker, Helen A.

    2018-03-01

    Ocean tides are the main source of high-frequency variability in the vertical and horizontal motion of ice sheets near their marine margins. Floating ice shelves, which occupy about three quarters of the perimeter of Antarctica and the termini of four outlet glaciers in northern Greenland, rise and fall in synchrony with the ocean tide. Lateral motion of floating and grounded portions of ice sheets near their marine margins can also include a tidal component. These tide-induced signals provide insight into the processes by which the oceans can affect ice sheet mass balance and dynamics. In this review, we summarize in situ and satellite-based measurements of the tidal response of ice shelves and grounded ice, and spatial variability of ocean tide heights and currents around the ice sheets. We review sensitivity of tide heights and currents as ocean geometry responds to variations in sea level, ice shelf thickness, and ice sheet mass and extent. We then describe coupled ice-ocean models and analytical glacier models that quantify the effect of ocean tides on lower-frequency ice sheet mass loss and motion. We suggest new observations and model developments to improve the representation of tides in coupled models that are used to predict future ice sheet mass loss and the associated contribution to sea level change. The most critical need is for new data to improve maps of bathymetry, ice shelf draft, spatial variability of the drag coefficient at the ice-ocean interface, and higher-resolution models with improved representation of tidal energy sinks.

  9. Evidence of calcium carbonates in coastal (Talos Dome and Ross Sea area) East Antarctica snow and firn: Environmental and climatic implications

    Science.gov (United States)

    Sala, M.; Delmonte, B.; Frezzotti, M.; Proposito, M.; Scarchilli, C.; Maggi, V.; Artioli, G.; Dapiaggi, M.; Marino, F.; Ricci, P. C.; De Giudici, G.

    2008-07-01

    Micrometre-sized aeolian dust particles stored in Antarctic firn and ice layers are a useful tool for reconstructing climate and environmental changes in the past. The mineral content, particle concentration and chemical composition of modern dust in firn cores from the peripherycal dome (Talos Dome) and coastal area of East Antarctica (Ross Sea sector) were investigated. During analyses there was a considerable decrease in microparticle concentrations within a few hours of ice sample melting, accompanied by a systematic increase in the concentration of calcium ions (Ca 2+) in solution. Based on mineralogical phase analyses, which reveal the presence of anhydrous and hydrous calcium carbonates such as calcite (CaCO 3), monohydrocalcite (CaCO 3·H 2O) and ikaite (CaCO 3·6H 2O, hexahydrate calcium carbonate), the observed variations in concentrations are ascribed to the partial dissolution of the carbonate content of samples. Soluble carbonate compounds are thus primary aerosols included into the samples along with insoluble aluminosilicate minerals. We hypothesize hydrous carbonates may derive from the sea ice surface, where ikaite typically forms at the early stages of sea ice formation. Back trajectory calculations show that favourable events for air mass advection from the sea ice surface to Talos Dome are rare but likely to occur.

  10. Seabed geology of the Canadian eastern continental shelf

    Science.gov (United States)

    Piper, David J. W.

    1991-08-01

    The physiography of the continental shelf off eastern Canada is irregular, developed by glacial erosion of a previously fluvially-dominated landscape. Northern shelves are deeper than southern shelves. Most surficial sediments on the shelf are relict or palimpsest. The principal modern source of sediment to the northern shelves is ice rafting and iceberg scour reworking of Quaternary sediments. Southern shelves receive sediment through erosion of Quaternary sediments; only small amounts of fine-grained sediment derived from coastal erosion and rivers escape from the coastal zone. Regional maps of sediment texture, carbonate content and heavy mineralogy consequently show differences between the northern and southern shelves. Large areas of the shelf show little net deposition. On the northern shelves, there is a surface veneer up to 0.5 m thick derived from ice rafting and iceberg turbation of underlying Quaternary sediment, modified by south-flowing currents [ WOODWORTH-LYNASet al. (this issue) Continental Shelf Research, 11, 939-961]. The overall effects of former iceberg turbation may extend to a depth of 10 m sub-bottom. On the southern shelves, bioturbation and perhaps storm-related currents rework exposed Quaternary sediments more slowly. Muds accumulate in deep basins on the shelves at rates of about 0.5 m per 1000 years; this accumulation is probably episodic and related to major storms reworking sediment from the surface sediment veneer in shallower areas of little net deposition. In water depths less than 110 m sand and gravel have formed as a result of reworking in the coastal zone during the post-glacial transgression. Over large areas of Georges Bank, the eastern Scotian Shelf and the Grand Banks of Newfoundland, such sands are mobilized during storms to form a wide suite of bedforms [ AMOS and JUDGE (this issue) Continental Shelf Research, 11, 1037-1068]. Elsewhere, particularly in deeper water, sandy surfaces appear moribund or inactive and large

  11. Jimmy, Sinclair, and Jim: on the biographical trail of James Sinclair Ross Jimmy, Sinclair, and Jim: on the biographical trail of James Sinclair Ross

    Directory of Open Access Journals (Sweden)

    John J. O'Connor

    2008-04-01

    Full Text Available The deaths of Earle Birney and Robertson Davies late in 1995 reminded readers of Canadian literature that the old order—those writers born before the First World War—was quickly passing. Of the major figures born in the early years of this century (Birney, Davies, Callaghan, MacLennan, Ross, only Ross was still living at the beginning of 1996, albeit in very poor health in a nursing home in Vancouver. The deaths of Earle Birney and Robertson Davies late in 1995 reminded readers of Canadian literature that the old order—those writers born before the First World War—was quickly passing. Of the major figures born in the early years of this century (Birney, Davies, Callaghan, MacLennan, Ross, only Ross was still living at the beginning of 1996, albeit in very poor health in a nursing home in Vancouver.

  12. Against Raising Hope of Raising the Dead: Contra Moody and Kubler-Ross.

    Science.gov (United States)

    Vicchio, Stephen J.; And Others

    1979-01-01

    Kubler-Ross and Moody have made assertions about survival after death. They argued that the subjects were not dead, but in the process of dying. An alternative explanation to this "glimpse of the afterlife" approach is offered. Other theological objections are raised to the Moody/Kubler-Ross approach. (Author)

  13. Does temperature structure phytoplankton community composition in the Ross Sea, Antarctica?

    Science.gov (United States)

    The Ross Sea polynya experiences one of the largest phytoplankton blooms in the Southern Ocean. Energy flow potential within the Ross Sea food web is primarily set by diatoms and prymnesiophytes, the latter dominated by Phaeocystis antarctica. We investigated physical, chemical,...

  14. Giving to Excellence: Generating Philanthropic Support for UK Higher Education. Ross-CASE Report 2016

    Science.gov (United States)

    Jain, Yashraj

    2016-01-01

    This report presents findings from the 2016 Ross-CASE Survey of Philanthropic Giving to Universities in UK. The project was conducted by CASE Europe and funded by HEFCE and the Ross-Group. This year's survey comes at a time of great change for the UK charity sector. The historical trend data of previous surveys will be invaluable in helping…

  15. Critiquing Research Methodology: Comments on Broader Concerns about Complex Statistical Studies. A Response to Ross

    Science.gov (United States)

    Stapleton, Paul

    2006-01-01

    Steven Ross's (2005) recent paper empirically measuring the efficacy of formative assessment compared to the summative variety found that the former produced positive effects on some aspects of language learning. In this critique, it is contended that Ross's study is flawed because his two groups of learners, one receiving summative assessment and…

  16. 75 FR 69432 - Ross Bachofer v. Calpine Corporation; Notice of Complaint

    Science.gov (United States)

    2010-11-12

    ... DEPARTMENT OF ENERGY Federal Energy Regulatory Commission [Docket No. EL11-3-000] Ross Bachofer v. Calpine Corporation; Notice of Complaint November 4, 2010. Take notice that on October 26, 2010, pursuant... Federal Power Act, 16 U.S.C. 2824c, Ross Bachofer (Complainant) filed a complaint against Calpine...

  17. Mortimer Hills pegmatite uranium prospect: a Rossing-type uranium deposit in the Gascoyne Province

    International Nuclear Information System (INIS)

    Carter, J.D.

    1984-01-01

    A uraninite-bearing pegmatite of large dimensions in the Gascoyne Province is described. The pegmatite is compared with the Rossing uranium ore body of South West Africa and the two are shown to have common characteristics. Exploration recommendations for Rossing-type uranium mineralization in the Gascoyne Province are made

  18. Production of organic matter in Antarctic ice shelf

    Digital Repository Service at National Institute of Oceanography (India)

    Dhargalkar, V.K.; Verlecar, X

    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 ...

  19. Cold shock treatment extends shelf life of naturally ripened or ethylene-ripened avocado fruits.

    Science.gov (United States)

    Chen, Jiao; Liu, Xixia; Li, Fenfang; Li, Yixing; Yuan, Debao

    2017-01-01

    Avocado is an important tropical fruit with high commercial value, but has a relatively short storage life. In this study, the effects of cold shock treatment (CST) on shelf life of naturally ripened and ethylene-ripened avocado fruits were investigated. Fruits were immersed in ice water for 30 min, then subjected to natural or ethylene-induced ripening. Fruit color; firmness; respiration rate; ethylene production; and the activities of polygalacturonase (PG), pectin methylesterase (PME), and endo-β-1,4-glucanase were measured. Immersion in ice water for 30 min effectively delayed ripening-associated processes, including peel discoloration, pulp softening, respiration rate, and ethylene production during shelf life. The delay in fruit softening by CST was associated with decreased PG and endo-β-1,4-glucanase activities, but not PME activity. This method could potentially be a useful postharvest technology to extend shelf life of avocado fruits.

  20. 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.

  1. STS-61B Astronaut Ross During ACCESS Extravehicular Activity

    Science.gov (United States)

    1985-01-01

    The crew assigned to the STS-61B mission included Bryan D. O'Conner, pilot; Brewster H. Shaw, commander; Charles D. Walker, payload specialist; mission specialists Jerry L. Ross, Mary L. Cleave, and Sherwood C. Spring; and Rodolpho Neri Vela, payload specialist. Launched aboard the Space Shuttle Atlantis November 28, 1985 at 7:29:00 pm (EST), the STS-61B mission's primary payload included three communications satellites: MORELOS-B (Mexico); AUSSAT-2 (Australia); and SATCOM KU-2 (RCA Americom). Two experiments were conducted to test assembling erectable structures in space: EASE (Experimental Assembly of Structures in Extravehicular Activity), and ACCESS (Assembly Concept for Construction of Erectable Space Structure). In a joint venture between NASA/Langley Research Center in Hampton, VA and the Marshall Space Flight Center (MSFC), ACCESS and EASE were developed and demonstrated at MSFC's Neutral Buoyancy Simulator (NBS). In this STS-61B onboard photo, astronaut Ross was working on the ACCESS experiment during an Extravehicular Activity (EVA). The primary objective of this experiment was to test the ACCESS structural assembly concept for suitability as the framework for larger space structures and to identify ways to improve the productivity of space construction.

  2. 78 FR 19330 - Supplemental Environmental Impact Statement for the Ross In-Situ Uranium Recovery Project in...

    Science.gov (United States)

    2013-03-29

    ... Ross In-Situ Uranium Recovery Project in Crook County, Wyoming AGENCY: Nuclear Regulatory Commission... Commission (NRC) for a new source materials license for the proposed Ross In-Situ Uranium Recovery (ISR) Project (Ross Project) proposed to be located in Crook County, Wyoming. The NRC is issuing for public...

  3. 76 FR 41308 - Strata Energy, Inc., Ross In Situ Recovery Uranium Project, Crook County, WY; Notice of Materials...

    Science.gov (United States)

    2011-07-13

    ..., Inc., Ross In Situ Recovery Uranium Project, Crook County, WY; Notice of Materials License Application...-4737, or by e-mail to [email protected] . The Ross In Situ Recovery Uranium Project License... source and byproduct materials license at its Ross In Situ Recovery Uranium Project site located in Crook...

  4. 78 FR 12357 - Brockway Mould, Inc., a Division of Ross International Ltd. Including Robert Lerch From BJR...

    Science.gov (United States)

    2013-02-22

    ... Division of Ross International Ltd. Including Robert Lerch From BJR Trucking, Brockport, PA; Amended..., applicable to workers and former workers of Brockway Mould, Inc., a division of Ross International Ltd... Brockway Mould, Inc., a division of Ross International Ltd., including Robert Lerch from BJR Trucking...

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

    Science.gov (United States)

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

    2018-05-01

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

  6. Short commentary on marine productivity at Arctic shelf breaks: upwelling, advection and vertical mixing

    Directory of Open Access Journals (Sweden)

    A. Randelhoff

    2018-04-01

    Full Text Available The future of Arctic marine ecosystems has received increasing attention in recent years as the extent of the sea ice cover is dwindling. Although the Pacific and Atlantic inflows both import huge quantities of nutrients and plankton, they feed into the Arctic Ocean in quite diverse regions. The strongly stratified Pacific sector has a historically heavy ice cover, a shallow shelf and dominant upwelling-favourable winds, while the Atlantic sector is weakly stratified, with a dynamic ice edge and a complex bathymetry. We argue that shelf break upwelling is likely not a universal but rather a regional, albeit recurring, feature of the new Arctic. It is the regional oceanography that decides its importance through a range of diverse factors such as stratification, bathymetry and wind forcing. Teasing apart their individual contributions in different regions can only be achieved by spatially resolved time series and dedicated modelling efforts. The Northern Barents Sea shelf is an example of a region where shelf break upwelling likely does not play a dominant role, in contrast to the shallower shelves north of Alaska where ample evidence for its importance has already accumulated. Still, other factors can contribute to marked future increases in biological productivity along the Arctic shelf break. A warming inflow of nutrient-rich Atlantic Water feeds plankton at the same time as it melts the sea ice, permitting increased photosynthesis. Concurrent changes in sea ice cover and zooplankton communities advected with the boundary currents make for a complex mosaic of regulating factors that do not allow for Arctic-wide generalizations.

  7. Short commentary on marine productivity at Arctic shelf breaks: upwelling, advection and vertical mixing

    Science.gov (United States)

    Randelhoff, Achim; Sundfjord, Arild

    2018-04-01

    The future of Arctic marine ecosystems has received increasing attention in recent years as the extent of the sea ice cover is dwindling. Although the Pacific and Atlantic inflows both import huge quantities of nutrients and plankton, they feed into the Arctic Ocean in quite diverse regions. The strongly stratified Pacific sector has a historically heavy ice cover, a shallow shelf and dominant upwelling-favourable winds, while the Atlantic sector is weakly stratified, with a dynamic ice edge and a complex bathymetry. We argue that shelf break upwelling is likely not a universal but rather a regional, albeit recurring, feature of the new Arctic. It is the regional oceanography that decides its importance through a range of diverse factors such as stratification, bathymetry and wind forcing. Teasing apart their individual contributions in different regions can only be achieved by spatially resolved time series and dedicated modelling efforts. The Northern Barents Sea shelf is an example of a region where shelf break upwelling likely does not play a dominant role, in contrast to the shallower shelves north of Alaska where ample evidence for its importance has already accumulated. Still, other factors can contribute to marked future increases in biological productivity along the Arctic shelf break. A warming inflow of nutrient-rich Atlantic Water feeds plankton at the same time as it melts the sea ice, permitting increased photosynthesis. Concurrent changes in sea ice cover and zooplankton communities advected with the boundary currents make for a complex mosaic of regulating factors that do not allow for Arctic-wide generalizations.

  8. 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; hide

    2013-01-01

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

  9. Inorganic carbon fluxes on the Mackenzie Shelf of the Beaufort Sea

    Science.gov (United States)

    Mol, Jacoba; Thomas, Helmuth; Myers, Paul G.; Hu, Xianmin; Mucci, Alfonso

    2018-02-01

    The Mackenzie Shelf in the southeastern Beaufort Sea is a region that has experienced large changes in the past several decades as warming, sea-ice loss, and increased river discharge have altered carbon cycling. Upwelling and downwelling events are common on the shelf, caused by strong, fluctuating along-shore winds, resulting in cross-shelf Ekman transport, and an alternating estuarine and anti-estuarine circulation. Downwelling carries dissolved inorganic carbon (DIC) and other remineralization products off the shelf and into the deep basin for possible long-term storage in the world's oceans. Upwelling carries DIC and nutrient-rich waters from the Pacific-origin upper halocline layer (UHL) onto the shelf. Profiles of DIC and total alkalinity (TA) taken in August and September of 2014 are used to investigate the cycling of carbon on the Mackenzie Shelf. The along-shore transport of water and the cross-shelf transport of DIC are quantified using velocity field output from a simulation of the Arctic and Northern Hemisphere Atlantic (ANHA4) configuration of the Nucleus of European Modelling of the Ocean (NEMO) framework. A strong upwelling event prior to sampling on the Mackenzie Shelf took place, bringing CO2-rich (elevated pCO2) water from the UHL onto the shelf bottom. The maximum on-shelf DIC flux was estimated at 16.9×103 mol C d-1 m-2 during the event. The maximum on-shelf transport of DIC through the upwelling event was found to be 65±15×10-3 Tg C d-1. TA and the oxygen isotope ratio of water (δ18O-H2O) are used to examine water-mass distributions in the study area and to investigate the influence of Pacific Water, Mackenzie River freshwater, and sea-ice melt on carbon dynamics and air-sea fluxes of carbon dioxide (CO2) in the surface mixed layer. Understanding carbon transfer in this seasonally dynamic environment is key to quantify the importance of Arctic shelf regions to the global carbon cycle and provide a basis for understanding how it will

  10. Inorganic carbon fluxes on the Mackenzie Shelf of the Beaufort Sea

    Directory of Open Access Journals (Sweden)

    J. Mol

    2018-02-01

    Full Text Available The Mackenzie Shelf in the southeastern Beaufort Sea is a region that has experienced large changes in the past several decades as warming, sea-ice loss, and increased river discharge have altered carbon cycling. Upwelling and downwelling events are common on the shelf, caused by strong, fluctuating along-shore winds, resulting in cross-shelf Ekman transport, and an alternating estuarine and anti-estuarine circulation. Downwelling carries dissolved inorganic carbon (DIC and other remineralization products off the shelf and into the deep basin for possible long-term storage in the world's oceans. Upwelling carries DIC and nutrient-rich waters from the Pacific-origin upper halocline layer (UHL onto the shelf. Profiles of DIC and total alkalinity (TA taken in August and September of 2014 are used to investigate the cycling of carbon on the Mackenzie Shelf. The along-shore transport of water and the cross-shelf transport of DIC are quantified using velocity field output from a simulation of the Arctic and Northern Hemisphere Atlantic (ANHA4 configuration of the Nucleus of European Modelling of the Ocean (NEMO framework. A strong upwelling event prior to sampling on the Mackenzie Shelf took place, bringing CO2-rich (elevated pCO2 water from the UHL onto the shelf bottom. The maximum on-shelf DIC flux was estimated at 16.9×103 mol C d−1 m−2 during the event. The maximum on-shelf transport of DIC through the upwelling event was found to be 65±15×10−3 Tg C d−1. TA and the oxygen isotope ratio of water (δ18O-H2O are used to examine water-mass distributions in the study area and to investigate the influence of Pacific Water, Mackenzie River freshwater, and sea-ice melt on carbon dynamics and air–sea fluxes of carbon dioxide (CO2 in the surface mixed layer. Understanding carbon transfer in this seasonally dynamic environment is key to quantify the importance of Arctic shelf regions to the global carbon cycle and provide a basis

  11. New marine geophysical and sediment record of the Northeast Greenland Ice Stream.

    Science.gov (United States)

    Callard, L.; Roberts, D. H.; O'Cofaigh, C.; Lloyd, J. M.; Smith, J. A.; Dorschel, B.

    2017-12-01

    The NE Greenland Ice Stream (NEGIS) drains 16% of the Greenland Ice Sheet (GrIS) and has a sea-level equivalent of 1.1-1.4 m. Stabilised by two floating ice shelves, 79N and Zachariae Isstrom, until recently it has shown little response to increased atmospheric and oceanic warming. However, since 2010 it has experienced an accelerated rate of grounding line retreat ( 4 km) and significant ice shelf loss that indicates that this sector of the GrIS is now responding to current oceanic and/or climatic change and has the potential to be a major contributor to future global sea-level rise. The project `NEGIS', a collaboration between Durham University and AWI, aims to reconstruct the history of the NE Greenland Ice Stream from the Last Glacial Maximum (LGM) to present using both onshore and offshore geological archives to better understand past ice stream response to a warming climate. This contribution presents results and interpretations from an offshore dataset collected on the RV Polarstern, cruises PS100 and PS109 in 2016 and 2017. Gravity and box cores, supplemented by swath bathymetric and sub-bottom profiler data, were acquired and initial core analysis including x-radiographs and MSCL data logging has been performed. Data collection focused principally in the Norske Trough and the area directly in front of the 79N ice shelf, a sub-ice shelf environment as recently as two years ago. On the outer shelf streamlined subglacial bedforms, grounding-zone wedges and moraines as well as overconsolidated subglacial tills, record an extensive ice sheet advance to the shelf edge. On the inner shelf and in front of the 79N ice shelf, deep, glacially-eroded bedrock basins are infilled with stratified sediment. The stratified muds represent deglacial and Holocene glacimarine sedimentation, and capture the recent transition from sub-ice shelf to shelf free conditions. Multiproxy palaeoenvironmental reconstructions, including foraminifera and diatom analysis, and radiocarbon

  12. [A reappraisal of the works of Elisabeth Kubler-Ross].

    Science.gov (United States)

    Afonso, Selene Beviláqua Chaves; Minayo, Maria Cecília de Souza

    2013-09-01

    This article presents a reappraisal of part of the works of Elizabeth Kubler-Ross, one of the most quoted authors addressing the end of life process, mourning and dying. Her work has contributed to a clearer understanding of these issues by health professionals, families, religious and lay people who handle and/or experience mourning. She has also been the subject of controversy related to ethical issues and the scientific rigor of her work. The books analyzed in this article are: On death and dying (1969); Questions and answers on death and dying (1971); Living with death and dying (1981); On children and death(1983); On life after death (1991) and Life lessons (2000).

  13. The Kubler-Ross model, physician distress, and performance reporting.

    Science.gov (United States)

    Smaldone, Marc C; Uzzo, Robert G

    2013-07-01

    Physician performance reporting has been proposed as an essential component of health-care reform, with the aim of improving quality by providing transparency and accountability. Despite strong evidence demonstrating regional variation in practice patterns and lack of evidence-based care, public outcomes reporting has been met with resistance from medical professionals. Application of the Kubler-Ross 'five stages of grief' model--a conceptual framework consisting of a series of emotional stages (denial, anger, bargaining, depression, and acceptance) inspired by work with terminally ill patients--could provide some insight into why physicians are reluctant to accept emerging quality-reporting mechanisms. Physician-led quality-improvement initiatives are vital to contemporary health-care reform efforts and applications in urology, as well as other medical disciplines, are currently being explored.

  14. Ross E. Baker, DC: A Canadian chiropractic survivor.

    Science.gov (United States)

    Brown, Douglas M

    2014-03-01

    This paper is an historical biography of a fortunate man. It begins with a glimpse of Ross E. Baker's origins in south-western Ontario, watches him going to school and working in Hamilton before joining the Canadian Army and shipping off to Europe to fight in the Second World War. At War's end, the article picks up Dr. Baker as he comes home, starts a family, becomes a chiropractor and sustains a viable practice. Now in the twilight of life, the good doctor is last seen content with his retirement, spending days at his cottage property, reviewing his memoirs and reflecting on the tumult, terror and eventual triumph of the D-Day landing at Normandy.

  15. Albert Ross Tilley: The legacy of a Canadian plastic surgeon.

    Science.gov (United States)

    Mowbrey, Kevin

    2013-01-01

    The present article chronicles the career of Dr Albert Ross Tilley, one of the most important Canadian plastic surgeons of the 20th century. Tilley is most well known for his innovations of burn management during World War II and his treatment of a group of burn patients known affectionately as the 'Guinea Pig Club'. In addition to the superb surgical skills he applied to the physical wounds of his patients, Tilley was also a pioneer of caring for the emotional and psychological afflictions suffered by many airmen of World War II. As one of the founding fathers of the Canadian Society of Plastic Surgeons, Tilley's work was instrumental in establishing the specialty and ensured its prosperity for years to come. Serving in the capacity of leader, educator and innovator, Tilley remains one of Canada's most decorated physicians, and his body of work encompasses contributions to the medical field that remain significant and beneficial to patient care to this day.

  16. Evolution of a Greenland Ice sheet Including Shelves and Regional Sea Level Variations

    Science.gov (United States)

    Bradley, Sarah; Reerink, Thomas; van de Wal, Roderik S. W.; Helsen, Michiel; Goelzer, Heiko

    2016-04-01

    Observational evidence, including offshore moraines and marine sediment cores infer that at the Last Glacial maximum (LGM) the Greenland ice sheet (GIS) grounded out across the Davis Strait into Baffin Bay, with fast flowing ice streams extending out to the continental shelf break along the NW margin. These observations lead to a number of questions as to weather the GIS and Laurentide ice sheet (LIS) coalesced during glacial maximums, and if so, did a significant ice shelf develop across Baffin Bay and how would such a configuration impact on the relative contribution of these ice sheets to eustatic sea level (ESL). Most previous paleo ice sheet modelling simulations of the GIS recreated an ice sheet that either did not extend out onto the continental shelf or utilised a simplified marine ice parameterisation to recreate an extended GIS, and therefore did not fully include ice shelf dynamics. In this study we simulate the evolution of the GIS from 220 kyr BP to present day using IMAU-ice; a 3D thermodynamical ice sheet model which fully accounts for grounded and floating ice, calculates grounding line migration and ice shelf dynamics. As there are few observational estimates of the long-term (yrs) sub marine basal melting rates (mbm) for the GIS, we developed a mbm parameterization within IMAU-ice controlled primarily by changes in paleo water depth. We also investigate the influence of the LIS on the GIS evolution by including relative sea level forcing's derived from a Glacial Isostatic Adjustment model. We will present results of how changes in the mbm directly impacts on the ice sheet dynamics, timing and spatial extent of the GIS at the glacial maximums, but also on the rate of retreat and spatial extent at the Last interglacial (LIG) minimum. Results indicate that with the inclusion of ice shelf dynamics, a larger GIS is generated which is grounded out into Davis strait, up to a water depth of -750 m, but significantly reduces the GIS contribution to Last

  17. Mechanisms of basal ice formation in polar glaciers: An evaluation of the apron entrainment model

    Science.gov (United States)

    Fitzsimons, Sean; Webb, Nicola; Mager, Sarah; MacDonell, Shelley; Lorrain, Regi; Samyn, Denis

    2008-06-01

    Previous studies of polar glaciers have argued that basal ice can form when these glaciers override and entrain ice marginal aprons that accumulate adjacent to steep ice cliffs. To test this idea, we have studied the morphology, structure, composition, and deformation of the apron and basal ice at the terminus of Victoria Upper Glacier in the McMurdo dry valleys, which are located on the western coast of the Ross Sea at 77°S in southern Victoria Land, Antarctica. Our results show that the apron has two structural elements: an inner element that consists of strongly foliated ice that has a steep up-glacier dip, and an outer element that lacks a consistent foliation and has a down-glacier, slope-parallel dip. Although strain measurements show that the entire apron is deforming, the inner element is characterized by high strain rates, whereas relatively low rates of strain characterize the outer part of the apron. Co-isotopic analyses of the ice, together with analysis of solute chemistry and sedimentary characteristics, show that the apron is compositionally different from the basal ice. Our observations show that aprons may become deformed and partially entrained by advancing glaciers. However, such an ice marginal process does not provide a satisfactory explanation for the origin of basal ice observed at the ice margin. Our interpretation of the origin of basal ice is that it is formed by subglacial processes, which are likely to include deformation and entrainment of subglacial permafrost.

  18. Oceanic hydraulic structures for developing a shelf. Issledovaniye morskikh gidrotekhnicheskikh sooruzheniy dlya osvoyenia sel'fa

    Energy Technology Data Exchange (ETDEWEB)

    Simakov, G.B.

    1980-01-01

    The anthology is devoted to practical problems of oceanic hydraulic engineering which arise during design and construction of specialized oceanic hydraulic structures to be erected and used in the shelf zones of seas and oceans. Most of the articles deal with studying the external effect of rough waters, impacts from ships and ice floes on floating and stationary hydraulic structures for developing a shelf. A great deal of attention is also given to the hydrodynamic and anchoring of floating hydraulic structures. The information reflects the current status of the problems of designing and building production facilities for developing a continental shelf.

  19. Reconstructing the last Irish Ice Sheet 2: a geomorphologically-driven model of ice sheet growth, retreat and dynamics

    Science.gov (United States)

    Greenwood, Sarah L.; Clark, Chris D.

    2009-12-01

    The ice sheet that once covered Ireland has a long history of investigation. Much prior work focussed on localised evidence-based reconstructions and ice-marginal dynamics and chronologies, with less attention paid to an ice sheet wide view of the first order properties of the ice sheet: centres of mass, ice divide structure, ice flow geometry and behaviour and changes thereof. In this paper we focus on the latter aspect and use our new, countrywide glacial geomorphological mapping of the Irish landscape (>39 000 landforms), and our analysis of the palaeo-glaciological significance of observed landform assemblages (article Part 1), to build an ice sheet reconstruction yielding these fundamental ice sheet properties. We present a seven stage model of ice sheet evolution, from initiation to demise, in the form of palaeo-geographic maps. An early incursion of ice from Scotland likely coalesced with local ice caps and spread in a south-westerly direction 200 km across Ireland. A semi-independent Irish Ice Sheet was then established during ice sheet growth, with a branching ice divide structure whose main axis migrated up to 140 km from the west coast towards the east. Ice stream systems converging on Donegal Bay in the west and funnelling through the North Channel and Irish Sea Basin in the east emerge as major flow components of the maximum stages of glaciation. Ice cover is reconstructed as extending to the continental shelf break. The Irish Ice Sheet became autonomous (i.e. separate from the British Ice Sheet) during deglaciation and fragmented into multiple ice masses, each decaying towards the west. Final sites of demise were likely over the mountains of Donegal, Leitrim and Connemara. Patterns of growth and decay of the ice sheet are shown to be radically different: asynchronous and asymmetric in both spatial and temporal domains. We implicate collapse of the ice stream system in the North Channel - Irish Sea Basin in driving such asymmetry, since rapid

  20. ASSESSMENT OF SEA ICE FREEBOARD AND THICKNESS IN MCMURDO SOUND, ANTARCTICA, DERIVED BY GROUND VALIDATED SATELLITE ALTIMETER DATA

    Directory of Open Access Journals (Sweden)

    D. Price

    2012-07-01

    Full Text Available This investigation employs the use of ICESat to derive freeboard measurements in McMurdo Sound in the western Ross Sea, Antarctica, for the time period 2003-2009. Methods closely follow those previously presented in the literature but are complemented by a good understanding of general sea ice characteristics in the study region from extensive temporal ground investigations but with limited spatial coverage. The aim of remote sensing applications in this area is to expand the good knowledge of sea ice characteristics within these limited areas to the wider McMurdo Sound and western Ross Sea region. The seven year Austral Spring (September, October, and November investigation is presented for sea ice freeboard alone. An interannual comparison of mean freeboard indicates an increase in multiyear sea ice freeboard from 1.08 m in 2003 to 1.15 m in 2009 with positive and negative variation in between. No significant trend was detected for first year sea ice freeboard. Further, an Envisat imagery investigation complements the freeboard assessment. The multiyear sea ice was observed to increase by 254 % of its original 2003 area, as firstyear sea ice persisted through the 2004 melt season into 2005. This maximum coverage then gradually diminished by 2009 to 20 % above the original 2003 value. The mid study period increase is likely attributed to the passage of iceberg B-15A minimising oceanic pressures and preventing sea ice breakout in the region.

  1. Estimating flexural rigidity and load magnitude required for formation of Ross Island flexure moat

    Science.gov (United States)

    Jha, S.; Harry, D. L.; Wenman, C. P.

    2017-12-01

    Lithospheric flexural subsidence around Ross Island in West Antarctica led to formation of the Ross Island flexure moat. This subsidence was caused by two major volcanic phases on Ross Island. The first phase saw the first surficial expression of Ross Island and volcanism at Mt. Bird to the north of Ross Island, which lasted from 5.2 - 2.9 Ma. The second phase lasted from 1.78 Ma to present and is comprised of eruptions from Mt. Terror to the east, Mt. Erebus to the west and Hut Point Peninsula (HPP) to the south of Ross Island. Flexural subsidence of the lithosphere due to volcanism on Ross Island led to formation of a sedimentary moat around the island, which is preserved in stratigraphy imaged on seismic reflection profiles. We identified 5 unconformities (from deepest upward Ri, RMU1, RMU2, RMU3, RMU4) in the seismic surveys which correspond to flexural subsidence episodes around Ross Island since early Pliocene. Ri (4.4 Ma) lies near the bottom of the flexural moat and RMU4 near the seafloor and top of the moat fill. These unconformities were used to make isopach maps to constrain flexure modeling of the area. Isopach maps show circular or semi-circular flexure basins around Ross Island which is approximated using a continuous plate, point load flexure model. We used Ri - sea floor isopach to constrain flexure models for 5 profiles centered on 4 volcanic centers and trending radially out of Ross Island. Flexure models along two profiles beginning on Mt. Bird and one profile off HPP show a flexural rigidity range of 1.47 - 6.44 x 1018 Nm with load center of mass on Mt. Bird and on HPP, respectively. A similar model along a profile initiating on Mt. Terror, passing through Mt Erebus and extending west of Ross Island across the moat, yielded a higher flexural rigidity estimate of 2.03 x 1019 Nm with load centered at Mt. Erebus. A flexure model to the north east of Ross Island along a profile beginning at Mt Terror and trending north, provide the highest flexural

  2. Turbulent heat exchange between water and ice at an evolving ice-water interface

    Science.gov (United States)

    Ramudu, Eshwan; Hirsh, Benjamin Henry; Olson, Peter; Gnanadesikan, Anand

    2016-07-01

    We conduct laboratory experiments on the time evolution of an ice layer cooled from below and subjected to a turbulent shear flow of warm water from above. Our study is motivated by observations of warm water intrusion into the ocean cavity under Antarctic ice shelves, accelerating the melting of their basal surfaces. The strength of the applied turbulent shear flow in our experiments is represented in terms of its Reynolds number $\\textit{Re}$, which is varied over the range $2.0\\times10^3 \\le \\textit{Re} \\le 1.0\\times10^4$. Depending on the water temperature, partial transient melting of the ice occurs at the lower end of this range of $\\textit{Re}$ and complete transient melting of the ice occurs at the higher end. Following these episodes of transient melting, the ice reforms at a rate that is independent of $\\textit{Re}$. We fit our experimental measurements of ice thickness and temperature to a one-dimensional model for the evolution of the ice thickness in which the turbulent heat transfer is parameterized in terms of the friction velocity of the shear flow. The melting mechanism we investigate in our experiments can easily account for the basal melting rate of Pine Island Glacier ice shelf inferred from observations.

  3. Ice Ages

    Indian Academy of Sciences (India)

    that the precession of the earth's orbit caused ice ages. The precession of the earth's orbit leads to changes in the time of the year at which ... than in the southern hemisphere. ..... small increase in ocean temperature implies a large increase in.

  4. Mixing processes at the subsurface layer in the Amundsen Sea shelf region

    Science.gov (United States)

    Mojica, J.; Djoumna, G.; Francis, D. K.; Holland, D.

    2017-12-01

    In the Amundsen Sea shelf region, mixing processes promote an upward transport of diapycnal fluxes of heat and salt from the subsurface to the surface mixing layer. Here we estimate the diapycnal mixing rates on the Amundsen shelf from a multi-year mooring cluster and five research cruises. By applying fine-scale parameterizations, the mixing rates obtained were higher near the southern end of Pine Island glacier front and exceeded 10-2 m2s-1. The eddy diffusivity increased near the critical latitude (74o 28' S) for semi-diurnal M2 tides, which coincided with near-critical topography on the shelf. This condition favored the generation of internal waves of M2 frequency. The semi-diurnal dynamic enhanced the mixing that potentially affected the heat budget and the circulation of the modified Circumpolar Deep Water. This can be observed in the characteristics of water exchange both below the ice shelves and between the continental shelf and the ice shelf cavities. The location of the critical latitude and critical topography provided favorable conditions for the generation of internal waves. KEYWORDS: Mixing processes, diapycnal fluxes, critical latitude, Circumpolar Deep Water.

  5. Multichannel Seismic Reflection Data - SCAR - Ross Sea - 1987, SDLS CD-ROM vol 13

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — These data are stacked multichannel marine seismic reflection data recorded during the 1987 field season in the Ross Sea, Antarctica, by SEVMORGEOLOGIA, RUSSIA. The...

  6. Elisabeth Kubler-Ross and the Tradition of the Private Sphere: An Analysis of Symbols.

    Science.gov (United States)

    Klass, Dennis

    1981-01-01

    Shows how Kubler-Ross' schema functions as a symbol system. Analyzes the symbol "acceptance." Shows how that symbol is part of a strong American tradition of symbols of the private sphere. (Author/JAC)

  7. Transcatheter Pulmonary Valve Replacement for Right Ventricular Outflow Tract Conduit Dysfunction After the Ross Procedure

    DEFF Research Database (Denmark)

    Gillespie, Matthew J; McElhinney, Doff B; Kreutzer, Jacqueline

    2015-01-01

    BACKGROUND: Right ventricular outflow tract (RVOT) conduit dysfunction is a limitation of the Ross procedure. Transcatheter pulmonary valve replacement (TPVR) could alter the impact of conduit dysfunction and the risk-benefit balance for the Ross procedure. METHODS: Retrospective review of databa......BACKGROUND: Right ventricular outflow tract (RVOT) conduit dysfunction is a limitation of the Ross procedure. Transcatheter pulmonary valve replacement (TPVR) could alter the impact of conduit dysfunction and the risk-benefit balance for the Ross procedure. METHODS: Retrospective review....... Of these, 56 (84%) received a Melody valve; in 5 of the 11 patients who did not, the implant was aborted due to concern for coronary artery compression, and 1 implanted patient required emergent surgery for left coronary compression. The RVOT gradient decreased from a median 38 mm Hg to 13.5 mm Hg (p

  8. 76 FR 81962 - Final Environmental Impact Statement for General Management Plan, Ross Lake National Recreation...

    Science.gov (United States)

    2011-12-29

    ... soundscapes, and scenery through traditional outdoor activities. The NPS would actively manage to reduce... Ross Lake NRA in order to protect and enhance soundscapes and wilderness character, experience, and...

  9. Multichannel Seismic Reflection Data - SCAR - Ross Sea - 1980, SDLS, CD-ROM vol 4

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — These data are stacked multichannel marine seismic reflection data from seven lines recorded during 1980 in the Ross Sea, Antarctica, by the Bundesanstalt fur...

  10. Multichannel Seismic Reflection Data - SCAR - Ross Sea - 1980, SDLS CD-ROM vol 3

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — These data are stacked multichannel marine seismic reflection data from four lines recorded during 1980 in the Ross Sea, Antarctica, by the Bundesanstalt fur...

  11. Multichannel Seismic Reflection Data - SCAR, Ross Sea - 1982-1983, CD-ROM vol 9

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — These data are stacked multichannel marine seismic reflection data from fourteen lines recorded during 1982 in the Ross Sea and Wilkes Island, Antarctica, by the...

  12. Multichannel Seismic Reflection Data - SCAR - Ross Sea - 1989, SDLS CD-ROM vol 14

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — These data are stacked multichannel marine seismic reflection data recorded during 1989 field season in the Ross Sea, Antarctica, by the SEVMORGEOLOGIA, RUSSIS. The...

  13. Multichannel Seismic Reflection Data - SCAR - Ross Sea 1980, SDLS, CD-ROM vol 5

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — These data are stacked multichannel marine seismic reflection data from eleven lines recorded during 1980 in the Ross Sea, Antarctica, by the Bundesanstalt fur...

  14. Multichannel Seismic Reflection Data - SCAR - Ross Sea 1982, SDLS CD-ROM vol 12

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — These data are stacked multichannel marine seismic reflection data from seven lines recorded during 1982 in the Ross Sea, Antarctica, by the Institut Francais du...

  15. Multichannel Seismic Reflection Data - SCAR - Ross Sea 1987-1988, SDLS CD-ROM vol 2

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — These data are stacked multichannel marine seismic reflection data from six lines recorded during 1988 in the Ross Sea, Antarctica, by the Bundesanstalt fur...

  16. Eulerian Method for Ice Crystal Icing

    NARCIS (Netherlands)

    Norde, Ellen; van der Weide, Edwin Theodorus Antonius; Hoeijmakers, Hendrik Willem Marie

    In this study, an ice accretion method aimed at ice crystal icing in turbofan engines is developed and demonstrated for glaciated as well as mixed-phase icing conditions. The particle trajectories are computed by an Eulerian trajectory method. The effects of heat transfer and phase change on the

  17. Long-term results of the Ross procedure in a population-based follow-up.

    Science.gov (United States)

    Kallio, Merja; Pihkala, Jaana; Sairanen, Heikki; Mattila, Ilkka

    2015-05-01

    The purpose of this study was to evaluate the long-term outcomes of the Ross procedure in a nationwide follow-up. This retrospective study involved all children treated with the Ross procedure in Finland between 1994 and 2009. The clinical records were reviewed for demographic and anatomical characteristics, Ross operation data, surgical history and status at the latest follow-up. The median follow-up time was 11.5 (range 2.4-19.2) years. Fifty-one patients underwent either the Ross (n = 37) or the Ross-Konno (n = 14) procedure at a median age of 4.8 (range 0.02-16.3) years, including 13 infants (Ross procedure was aortic valve stenosis, regurgitation or both, which was observed in 29, 24 and 47% of patients, respectively. The early mortality (before hospital discharge) rate was 10% (31% in infants) and the late mortality rate 6% (15% in infants). Higher mortality was discovered in patients treated with the Ross-Konno procedure (P = 0.001). The most common cause for reintervention was pulmonary homograft stenosis. The rate of freedom from right ventricular outflow tract reintervention was 98% at 5 years, 83% at 10 years and 59% at 15 years. The rate of freedom from autograft reintervention was 98% at 5 and 10 years, and 81% at 15 years. At the latest follow-up visit, mild-to-moderate aortic root dilatation was reported in 52% of patients, and 4 patients had undergone autograft-related reinterventions. Trivial autograft valve regurgitation was commonly seen, but only 1 patient developed severe autograft regurgitation requiring mechanical valve replacement 15.9 years after the Ross operation. The most common reason for reintervention after the Ross procedure in children is homograft stenosis. Aortic root dilatation and autograft valve regurgitation are relatively common but rarely lead to reinterventions before adulthood. Intraoperative complications and complex cardiac anatomy are associated with high mortality in infants undergoing the Ross-Konno procedure. In our

  18. An optimal ross filter system for soft X-ray spectra measurement

    International Nuclear Information System (INIS)

    Huang Tianxuan; Zheng Zhijian; Sun Kexu; Jiang Shaoen

    2000-01-01

    A broadband Ross filter spectrometer is described for measuring soft X-ray radiation (0.1∼1.5 keV) emitted from laser plasma. It consists of a number of channels, each representing a Ross filter pair in conjunction with Al cathode X-ray diodes. An optimal channel has flat response within the sensitivity band, and minimal response outside it. The effect of some uncertainties on the accuracy of measurements is calculated

  19. Sea ice - Multiyear cycles and white ice

    Science.gov (United States)

    Ledley, T. S.

    1985-01-01

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

  20. Improved Survival After the Ross Procedure Compared With Mechanical Aortic Valve Replacement.

    Science.gov (United States)

    Buratto, Edward; Shi, William Y; Wynne, Rochelle; Poh, Chin L; Larobina, Marco; O'Keefe, Michael; Goldblatt, John; Tatoulis, James; Skillington, Peter D

    2018-03-27

    It is unclear whether the Ross procedure offers superior survival compared with mechanical aortic valve replacement (AVR). This study evaluated experience and compared long-term survival between the Ross procedure and mechanical AVR. Between 1992 and 2016, a total of 392 Ross procedures were performed. These were compared with 1,928 isolated mechanical AVRs performed during the same time period as identified using the University of Melbourne and Australia and New Zealand Society of Cardiac and Thoracic Surgeons' Cardiac Surgery Databases. Only patients between 18 and 65 years of age were included. Propensity-score matching was performed for risk adjustment. Ross procedure patients were younger, and had fewer cardiovascular risk factors. The Ross procedure was associated with longer cardiopulmonary bypass and aortic cross-clamp times. Thirty-day mortality was similar (Ross, 0.3%; mechanical, 0.8%; p = 0.5). Ross procedure patients experienced superior unadjusted long-term survival at 20 years (Ross, 95%; mechanical, 68%; p mechanical, 84%; p = 0.018). In this Australian, propensity-score matched study, the Ross procedure was associated with better long-term survival compared with mechanical AVR. In younger patients, with a long life expectancy, the Ross procedure should be considered in centers with sufficient expertise. Crown Copyright © 2018. Published by Elsevier Inc. All rights reserved.

  1. A multivariate analysis of Antarctic sea ice since 1979

    Energy Technology Data Exchange (ETDEWEB)

    Magalhaes Neto, Newton de; Evangelista, Heitor [Universidade do Estado do Rio de Janeiro (Uerj), LARAMG - Laboratorio de Radioecologia e Mudancas Globais, Maracana, Rio de Janeiro, RJ (Brazil); Tanizaki-Fonseca, Kenny [Universidade do Estado do Rio de Janeiro (Uerj), LARAMG - Laboratorio de Radioecologia e Mudancas Globais, Maracana, Rio de Janeiro, RJ (Brazil); Universidade Federal Fluminense (UFF), Dept. Analise Geoambiental, Inst. de Geociencias, Niteroi, RJ (Brazil); Penello Meirelles, Margareth Simoes [Universidade do Estado do Rio de Janeiro (UERJ)/Geomatica, Maracana, Rio de Janeiro, RJ (Brazil); Garcia, Carlos Eiras [Universidade Federal do Rio Grande (FURG), Laboratorio de Oceanografia Fisica, Rio Grande, RS (Brazil)

    2012-03-15

    Recent satellite observations have shown an increase in the total extent of Antarctic sea ice, during periods when the atmosphere and oceans tend to be warmer surrounding a significant part of the continent. Despite an increase in total sea ice, regional analyses depict negative trends in the Bellingshausen-Amundsen Sea and positive trends in the Ross Sea. Although several climate parameters are believed to drive the formation of Antarctic sea ice and the local atmosphere, a descriptive mechanism that could trigger such differences in trends are still unknown. In this study we employed a multivariate analysis in order to identify the response of the Antarctic sea ice with respect to commonly utilized climate forcings/parameters, as follows: (1) The global air surface temperature, (2) The global sea surface temperature, (3) The atmospheric CO{sub 2} concentration, (4) The South Annular Mode, (5) The Nino 3, (6) The Nino (3 + 4, 7) The Nino 4, (8) The Southern Oscillation Index, (9) The Multivariate ENSO Index, (10) the Total Solar Irradiance, (11) The maximum O{sub 3} depletion area, and (12) The minimum O{sub 3} concentration over Antarctica. Our results indicate that western Antarctic sea ice is simultaneously impacted by several parameters; and that the minimum, mean, and maximum sea ice extent may respond to a separate set of climatic/geochemical parameters. (orig.)

  2. Water masses of Visakhapatnam shelf

    Digital Repository Service at National Institute of Oceanography (India)

    RamaRaju, V.S.; Sarma, V.V.; Rao, B.P.; Rao, V.S.

    The T-S relationships of shelf waters off Visakhapatnam in the Bay of Bengal are studied for the different seasons with the data collected during February 1979 to January 1981. The T-S relationships indicate distinct characteristics of the water...

  3. Quantifying fall migration of Ross's gulls (Rhodostethia rosea) past Point Barrow, Alaska

    Science.gov (United States)

    Uher-Koch, Brian D.; Davis, Shanti E.; Maftei, Mark; Gesmundo, Callie; Suydam, R.S.; Mallory, Mark L.

    2014-01-01

    The Ross's gull (Rhodostethia rosea) is a poorly known seabird of the circumpolar Arctic. The only place in the world where Ross's gulls are known to congregate is in the near-shore waters around Point Barrow, Alaska where they undertake an annual passage in late fall. Ross's gulls seen at Point Barrow are presumed to originate from nesting colonies in Siberia, but neither their origin nor their destination has been confirmed. Current estimates of the global population of Ross's gulls are based largely on expert opinion, and the only reliable population estimate is derived from extrapolations from previous counts conducted at Point Barrow, but these data are now over 25 years old. In order to update and clarify the status of this species in Alaska, our study quantified the timing, number, and flight direction of Ross's gulls passing Point Barrow in 2011. We recorded up to two-thirds of the estimated global population of Ross's gulls (≥ 27,000 individuals) over 39 days with numbers peaking on 16 October when we observed over 7,000 birds during a three-hour period.

  4. Ross, macdonald, and a theory for the dynamics and control of mosquito-transmitted pathogens.

    Science.gov (United States)

    Smith, David L; Battle, Katherine E; Hay, Simon I; Barker, Christopher M; Scott, Thomas W; McKenzie, F Ellis

    2012-01-01

    Ronald Ross and George Macdonald are credited with developing a mathematical model of mosquito-borne pathogen transmission. A systematic historical review suggests that several mathematicians and scientists contributed to development of the Ross-Macdonald model over a period of 70 years. Ross developed two different mathematical models, Macdonald a third, and various "Ross-Macdonald" mathematical models exist. Ross-Macdonald models are best defined by a consensus set of assumptions. The mathematical model is just one part of a theory for the dynamics and control of mosquito-transmitted pathogens that also includes epidemiological and entomological concepts and metrics for measuring transmission. All the basic elements of the theory had fallen into place by the end of the Global Malaria Eradication Programme (GMEP, 1955-1969) with the concept of vectorial capacity, methods for measuring key components of transmission by mosquitoes, and a quantitative theory of vector control. The Ross-Macdonald theory has since played a central role in development of research on mosquito-borne pathogen transmission and the development of strategies for mosquito-borne disease prevention.

  5. Evolution of ocean-induced ice melt beneath Zachariæ Isstrøm, Northeast Greenland combining observations and an ocean general circulation model from 1978 to present

    Science.gov (United States)

    Cai, C.; Rignot, E. J.; Menemenlis, D.; Millan, R.; Bjørk, A. A.; Khan, S. A.; Charolais, A.

    2017-12-01

    Zachariæ Isstrøm, a major ice stream in northeast Greenland, lost a large fraction of its ice shelf during the last decade. We study the evolution of subaqueous melting of its floating section from 1978 to present. The ice shelf melt rate depends on thermal forcing from warm, salty, subsurface ocean waters of Atlantic origin (AW), the mixing of AW with fresh, buoyant subglacial discharge at the calving margin, and the shape of the sub-ice-shelf cavity. Subglacial discharge doubled as a result of enhanced ice sheet runoff caused by warmer air temperatures. Ocean thermal forcing has increased due to enhanced advection of AW. Using an Eulerian method, MEaSUREs ice velocity, Operation IceBridge (OIB) ice thickness, and RACMO2.3 surface balance data, we evaluate the ice shelf melt rate in 1978, 1999 and 2010. The melt rate doubled from 1999 to 2010. Using a Lagrangian method with World View imagery, we map the melt rate in detail from 2011 to 2016. We compare the results with 2D simulations from the Massachusetts Institute of Technology general circulation model (MITgcm), at a high spatial resolution (20-m horizontal and 40-m vertical grid spacing), using OIB ice thickness and sub-ice-shelf cavity for years 1978, 1996, 2010 and 2011, combined with in-situ ocean temperature/salinity data from Ocean Melting Greenland (OMG) 2017. We find that winter melt rates are 2 3 times smaller than summer rates and melt rates increase by one order magnitude during the transition from ice shelf termination to near-vertical calving wall termination. As the last remaining bits of floating ice shelf disappear, ice-ocean interaction will therefore play an increasing role in driving the glacier retreat into its marine-based basin. This work was performed under a contract with NASA Cryosphere Program at UC Irvine and Caltech's Jet Propulsion Laboratory.

  6. Coordination: southeast continental shelf studies. Progress report

    Energy Technology Data Exchange (ETDEWEB)

    Menzel, D.W.

    1981-02-01

    The objectives are to identify important physical, chemical and biological processes which affect the transfer of materials on the southeast continental shelf, determine important parameters which govern observed temporal and spatial varibility on the continental shelf, determine the extent and modes of coupling between events at the shelf break and nearshore, and determine physical, chemical and biological exchange rates on the inner shelf. Progress in meeting these research objectives is presented. (ACR)

  7. Forecasting Turbine Icing Events

    DEFF Research Database (Denmark)

    Davis, Neil; Hahmann, Andrea N.; Clausen, Niels-Erik

    2012-01-01

    In this study, we present a method for forecasting icing events. The method is validated at two European wind farms in with known icing events. The icing model used was developed using current ice accretion methods, and newly developed ablation algorithms. The model is driven by inputs from the WRF...... mesoscale model, allowing for both climatological estimates of icing and short term icing forecasts. The current model was able to detect periods of icing reasonably well at the warmer site. However at the cold climate site, the model was not able to remove ice quickly enough leading to large ice...

  8. Uma releitura da obra de Elisabeth Kubler-Ross

    Directory of Open Access Journals (Sweden)

    Selene Beviláqua Chaves Afonso

    2013-09-01

    Full Text Available Este artigo apresenta uma releitura de parte da obra de Elizabeth Ross, uma das autoras mais citadas sobre a questão da terminalidade da vida, do luto e do morrer. Sua obra tem sido de grande contribuição tanto para os profissionais de saúde como para pais, mães, filhos, parentes, leigos e religiosos que vivenciam o luto. Também tem sido alvo de controvérsias relacionadas a questões éticas e quanto a seu rigor científico. Os livros aqui comentados são: On death and dying (Sobre A morte e o morrer, de 1969; Questions and answers on death and dying (Perguntas e respostas sobre a morte e o morrer, de 1971; Living with death and dying(Vivendo com a morte e os moribundos, de 1981; On children and death (Sobre as crianças e a morte, de 1983; On life after death (Sobre a vida depois da morte, de 1991 e Life lessons (Lições de vida, de 2000.

  9. Predictive modelling of Ross River virus notifications in southeastern Australia.

    Science.gov (United States)

    Cutcher, Z; Williamson, E; Lynch, S E; Rowe, S; Clothier, H J; Firestone, S M

    2017-02-01

    Ross River virus (RRV) is a mosquito-borne virus endemic to Australia. The disease, marked by arthritis, myalgia and rash, has a complex epidemiology involving several mosquito species and wildlife reservoirs. Outbreak years coincide with climatic conditions conducive to mosquito population growth. We developed regression models for human RRV notifications in the Mildura Local Government Area, Victoria, Australia with the objective of increasing understanding of the relationships in this complex system, providing trigger points for intervention and developing a forecast model. Surveillance, climatic, environmental and entomological data for the period July 2000-June 2011 were used for model training then forecasts were validated for July 2011-June 2015. Rainfall and vapour pressure were the key factors for forecasting RRV notifications. Validation of models showed they predicted RRV counts with an accuracy of 81%. Two major RRV mosquito vectors (Culex annulirostris and Aedes camptorhynchus) were important in the final estimation model at proximal lags. The findings of this analysis advance understanding of the drivers of RRV in temperate climatic zones and the models will inform public health agencies of periods of increased risk.

  10. Ghost Stories: Review of Ross Gibson's The Summer Exercises

    Directory of Open Access Journals (Sweden)

    Deane Williams

    2010-03-01

    Full Text Available Back 
in 
1986, 
Ross 
Gibson
 was 
interviewed 
in
 Filmnews 
by
 Adrian
 Martin 
and
Tina
 Kaufman
 about
 his
 experimental
 short
 essay
 film
 Camera
 Natura
 (1984. Accompanying
 that
 interview
 was
 a
 photo
 of
 Gibson
 ‘on
 location’
 for
 his
 film,
 wearing
 a
 hat
 not
 unlike
 the
 one
 that
 features
 on
 the
 cover
 of
 his
 new
 book
 The
 Summer 
Exercises.
 Back 
then
 I
 understood
 the 
hat
 to 
be
 an
explorer’s,
 someone 
like
 Charles
 Sturt,
 someone
 whose
 willingness
 to
 learn
 from
 his
 environment
 had
 impressed
 Gibson
 in
 fashioning
 his
 own
 history
 of
 Australian
 landscape
 imaging.
 Now
 the
 hat
 looks
 like
 a
 detective’s
 or,
 rather,
 Marcel
 Duchamp’s
 rendering
 of
 a
 detective’s
 hat: 
on 
display,
 ready 
for
 our
 re‐consideration.

  11. Permafrost oxygen isotope ratios and chronology of three cores from Antarctica

    International Nuclear Information System (INIS)

    Stuiver, M.; Yang, I.C.; Denton, G.H.

    1976-01-01

    It is stated that permafrost core sediments, associated with the last intrusion of the Ross Ice Shelf in the New Harbour region, were deposited in marine (0 - 85 m deep) as well as freshwater environments (100 - 125 m). Oxygen isotope ratio measurements on these cores provide palaeoclimatic information and show that the extension of the Ross Ice Shelf predates 150,000 yr BP, whereas the radiocarbon date of its retreat is about 5,800 yr b.p. (author)

  12. Methane-oxidizing seawater microbial communities from an Arctic shelf

    Science.gov (United States)

    Uhlig, Christiane; Kirkpatrick, John B.; D'Hondt, Steven; Loose, Brice

    2018-06-01

    Marine microbial communities can consume dissolved methane before it can escape to the atmosphere and contribute to global warming. Seawater over the shallow Arctic shelf is characterized by excess methane compared to atmospheric equilibrium. This methane originates in sediment, permafrost, and hydrate. Particularly high concentrations are found beneath sea ice. We studied the structure and methane oxidation potential of the microbial communities from seawater collected close to Utqiagvik, Alaska, in April 2016. The in situ methane concentrations were 16.3 ± 7.2 nmol L-1, approximately 4.8 times oversaturated relative to atmospheric equilibrium. The group of methane-oxidizing bacteria (MOB) in the natural seawater and incubated seawater was > 97 % dominated by Methylococcales (γ-Proteobacteria). Incubations of seawater under a range of methane concentrations led to loss of diversity in the bacterial community. The abundance of MOB was low with maximal fractions of 2.5 % at 200 times elevated methane concentration, while sequence reads of non-MOB methylotrophs were 4 times more abundant than MOB in most incubations. The abundances of MOB as well as non-MOB methylotroph sequences correlated tightly with the rate constant (kox) for methane oxidation, indicating that non-MOB methylotrophs might be coupled to MOB and involved in community methane oxidation. In sea ice, where methane concentrations of 82 ± 35.8 nmol kg-1 were found, Methylobacterium (α-Proteobacteria) was the dominant MOB with a relative abundance of 80 %. Total MOB abundances were very low in sea ice, with maximal fractions found at the ice-snow interface (0.1 %), while non-MOB methylotrophs were present in abundances similar to natural seawater communities. The dissimilarities in MOB taxa, methane concentrations, and stable isotope ratios between the sea ice and water column point toward different methane dynamics in the two environments.

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

    Science.gov (United States)

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

    2018-01-01

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

  14. Variable Basal Melt Rates of Antarctic Peninsula Ice Shelves, 1994-2016

    Science.gov (United States)

    Adusumilli, Susheel; Fricker, Helen Amanda; Siegfried, Matthew R.; Padman, Laurie; Paolo, Fernando S.; Ligtenberg, Stefan R. M.

    2018-05-01

    We have constructed 23-year (1994-2016) time series of Antarctic Peninsula (AP) ice-shelf height change using data from four satellite radar altimeters (ERS-1, ERS-2, Envisat, and CryoSat-2). Combining these time series with output from atmospheric and firn models, we partitioned the total height-change signal into contributions from varying surface mass balance, firn state, ice dynamics, and basal mass balance. On the Bellingshausen coast of the AP, ice shelves lost 84 ± 34 Gt a-1 to basal melting, compared to contributions of 50 ± 7 Gt a-1 from surface mass balance and ice dynamics. Net basal melting on the Weddell coast was 51 ± 71 Gt a-1. Recent changes in ice-shelf height include increases over major AP ice shelves driven by changes in firn state. Basal melt rates near Bawden Ice Rise, a major pinning point of Larsen C Ice Shelf, showed large increases, potentially leading to substantial loss of buttressing if sustained.

  15. Cryolithozone of Western Arctic shelf of Russia

    Science.gov (United States)

    Kholmyanskii, Mikhail; Vladimirov, Maksim; Snopova, Ekaterina; Kartashev, Aleksandr

    2017-04-01

    We propose a new original version of the structure of the cryolithozone of west Arctic seas of Russia. In contrast to variants of construction of sections and maps based on thermodynamic modeling, the authors have used electrometric, seismic, and thermal data including their own profile measurements by near-field transient electromagnetic technique and seismic profile observations by reflection method. As a result, we defined the spatial characteristics of cryolithozone and managed to differentiate it to several layers, different both in structure and formation time. We confirmed once again that the spatial boundary of cryolithozone, type and thickness of permafrost, chilled rocks and thawed ground are primarily determined by tectonic and oceanographic regimes of the Arctic Ocean and adjacent land in different geological epochs. Permafrost formed on the land in times of cold weather, turn to submarine during flooding and overlap, in the case of the sea transgression, by marine sediments accumulating in the period of warming. We have been able to establish a clear link between the permafrost thickness and the geomorphological structure of the area. This can be explained by the distribution of thermodynamic flows that change the temperature state of previously formed permafrost rocks. Formation in the outer parts of the shelf which took place at ancient conversion stage can be characterized by the structure: • permafrost table - consists of rocks, where the sea water with a temperature below 0 °C has replaced the melted ice; • middle horizon - composed of undisturbed rocks, and the rocks chilled through the lower sieving underlay; As a result of the interpretation and analysis of all the available data, the authors created a map of types of cryolithozone of the Western Arctic shelf of Russia. The following distribution areas are marked on the map: • single-layer cryolithozone (composed of sediments upper Pleistocene and Holocene); • monosyllabic relict

  16. Perennial water stratification and the role of freshwater in the mass balance of Arctic ice shelves and multiyear landfast sea ice

    International Nuclear Information System (INIS)

    Jeffries, M.O.

    1991-01-01

    A number of the ice shelves of northern Ellesmere Island in the Canadian High Arctic owe their origin to multiyear landfast sea ice (MLSI) growth during the post-Hypsithermal cooling ca. 3,000-4,000 BP. Since they grew in response to an arctic-wide climatic deterioration and contain evidence of occasional post-4,000 BP climatic ameliorations, they may be expected to be sensitive to future global climate changes manifested in the High Arctic. The purpose of this paper is to examine ice-ocean interactions and feedbacks, and the response of the ice shelves and the MLSI to the improved summer climate of the last ca. 100 years, and implications for the future. There is good evidence that there has been a negative surface mass balance since the turn of the century. Mass balance measurements on the Ward Hunt Ice Shelf between 1966 and 1985 indicate a total ice loss of 1.371 m at a mean annual rate of 68.5 mm. The interannual pattern of accumulation and ablation and the long-term losses on the ice shelf are similar to other Canadian High Arctic glacier mass balance records. It is evident from water and ice core records of salinity, δ 18 0 and tritium, that perennial water stratification is common below and behind the ice shelves and MLSI. The coastal waters are highly stratified, with anything from 0.5 m to 41.0 m of freshwater interposed between the overlying ice and underlying seawater. The primary source of the freshwater is summer run-off of snow-meltwater from the adjacent land and from the ice itself. There is minimal mixing between the influent freshwater and seawater, and the freshwater is either dammed behind the ice shelves and the MLSI, with subsequent under-ice freshwater outflows, or pooled in under-ice depressions

  17. Great Lakes Ice Charts

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Charts show ice extent and concentration three times weekly during the ice season, for all lakes except Ontario, from the 1973/74 ice season through the 2001/2002...

  18. Ice-sheet model sensitivities to environmental forcing and their use in projecting future sea level (the SeaRISE project)

    OpenAIRE

    Bindschadler, Robert A.; Nowicki, Sophie; Abe-Ouchi, Ayako; Aschwanden, Andy; Choi, Hyeungu; Fastook, Jim; Granzow, Glen; Greve, Ralf; Gutowski, Gail; Herzfeld, Ute; Jackson, Charles; Johnson, Jesse; Khroulev, Constantine; Levermann, Anders; Lipscomb, William H.

    2013-01-01

    Ten ice-sheet models are used to study sensitivity of the Greenland and Antarctic ice sheets to prescribed changes of surface mass balance, sub-ice-shelf melting and basal sliding. Results exhibit a large range in projected contributions to sea-level change. In most cases, the ice volume above flotation lost is linearly dependent on the strength of the forcing. Combinations of forcings can be closely approximated by linearly summing the contributions from single forcing experiments, suggestin...

  19. An improved bathymetry compilation for the Bellingshausen Sea, Antarctica, to inform ice-sheet and ocean models

    Directory of Open Access Journals (Sweden)

    A. G. C. Graham

    2011-02-01

    Full Text Available The southern Bellingshausen Sea (SBS is a rapidly-changing part of West Antarctica, where oceanic and atmospheric warming has led to the recent basal melting and break-up of the Wilkins ice shelf, the dynamic thinning of fringing glaciers, and sea-ice reduction. Accurate sea-floor morphology is vital for understanding the continued effects of each process upon changes within Antarctica's ice sheets. Here we present a new bathymetric grid for the SBS compiled from shipborne multibeam echo-sounder, spot-sounding and sub-ice measurements. The 1-km grid is the most detailed compilation for the SBS to-date, revealing large cross-shelf troughs, shallow banks, and deep inner-shelf basins that continue inland of coastal ice shelves. The troughs now serve as pathways which allow warm deep water to access the ice sheet in the SBS. Our dataset highlights areas still lacking bathymetric constraint, as well as regions for further investigation, including the likely routes of palaeo-ice streams. The new compilation is a major improvement upon previous grids and will be a key dataset for incorporating into simulations of ocean circulation, ice-sheet change and history. It will also serve forecasts of ice stability and future sea-level contributions from ice loss in West Antarctica, required for the next IPCC assessment report in 2013.

  20. A global, high-resolution data set of ice sheet topography, cavity geometry, and ocean bathymetry

    Science.gov (United States)

    Schaffer, Janin; Timmermann, Ralph; Arndt, Jan Erik; Savstrup Kristensen, Steen; Mayer, Christoph; Morlighem, Mathieu; Steinhage, Daniel

    2016-10-01

    The ocean plays an important role in modulating the mass balance of the polar ice sheets by interacting with the ice shelves in Antarctica and with the marine-terminating outlet glaciers in Greenland. Given that the flux of warm water onto the continental shelf and into the sub-ice cavities is steered by complex bathymetry, a detailed topography data set is an essential ingredient for models that address ice-ocean interaction. We followed the spirit of the global RTopo-1 data set and compiled consistent maps of global ocean bathymetry, upper and lower ice surface topographies, and global surface height on a spherical grid with now 30 arcsec grid spacing. For this new data set, called RTopo-2, we used the General Bathymetric Chart of the Oceans (GEBCO_2014) as the backbone and added the International Bathymetric Chart of the Arctic Ocean version 3 (IBCAOv3) and the International Bathymetric Chart of the Southern Ocean (IBCSO) version 1. While RTopo-1 primarily aimed at a good and consistent representation of the Antarctic ice sheet, ice shelves, and sub-ice cavities, RTopo-2 now also contains ice topographies of the Greenland ice sheet and outlet glaciers. In particular, we aimed at a good representation of the fjord and shelf bathymetry surrounding the Greenland continent. We modified data from earlier gridded products in the areas of Petermann Glacier, Hagen Bræ, and Sermilik Fjord, assuming that sub-ice and fjord bathymetries roughly follow plausible Last Glacial Maximum ice flow patterns. For the continental shelf off Northeast Greenland and the floating ice tongue of Nioghalvfjerdsfjorden Glacier at about 79° N, we incorporated a high-resolution digital bathymetry model considering original multibeam survey data for the region. Radar data for surface topographies of the floating ice tongues of Nioghalvfjerdsfjorden Glacier and Zachariæ Isstrøm have been obtained from the data centres of Technical University of Denmark (DTU), Operation Icebridge (NASA

  1. Antarctic sea ice increase consistent with intrinsic variability of the Amundsen Sea Low

    Science.gov (United States)

    Turner, John; Hosking, J. Scott; Marshall, Gareth J.; Phillips, Tony; Bracegirdle, Thomas J.

    2016-04-01

    We investigate the relationship between atmospheric circulation variability and the recent trends in Antarctic sea ice extent (SIE) using Coupled Model Intercomparison Project Phase 5 (CMIP5) atmospheric data, ECMWF Interim reanalysis fields and passive microwave satellite data processed with the Bootstrap version 2 algorithm. Over 1979-2013 the annual mean total Antarctic SIE increased at a rate of 195 × 103 km2 dec-1 (1.6 % dec-1), p 4.0 % dec-1) has been in the Ross Sea sector. Off West Antarctica there is a high correlation between trends in SIE and trends in the near-surface winds. The Ross Sea SIE seasonal trends are positive throughout the year, but largest in spring. The stronger meridional flow over the Ross Sea has been driven by a deepening of the Amundsen Sea Low (ASL). Pre-industrial control and historical simulations from CMIP5 indicate that the observed deepening of the ASL and stronger southerly flow over the Ross Sea are within the bounds of modeled intrinsic variability. The spring trend would need to continue for another 11 years for it to fall outside the 2 standard deviation range seen in 90 % of the simulations.

  2. Clinical Outcomes Following the Ross Procedure in Adults: A 25-Year Longitudinal Study.

    Science.gov (United States)

    Martin, Elisabeth; Mohammadi, Siamak; Jacques, Frederic; Kalavrouziotis, Dimitri; Voisine, Pierre; Doyle, Daniel; Perron, Jean

    2017-10-10

    Very few reports of long-term outcomes of patients who underwent the Ross procedure have been published. The authors reviewed their 25-year experience with the Ross procedure with the aim of defining very-long-term survival and factors associated with Ross-related failure. Between January 1990 and December 2014, the Ross procedure was performed in 310 adults (mean age 40.8 years) at a single institution. All patients were prospectively added to a dedicated cardiac surgery registry. Complete post-operative clinical examination and history were obtained, and transthoracic echocardiography was performed according to a standardized protocol. There was no loss to follow-up. Median follow-up was 15.1 years and up to 25 years. Bicuspid aortic valve was diagnosed in 227 patients (73.2%), and the most common indication for surgery was aortic stenosis (n = 225 [72.6%]). Freedom from any Ross-related reintervention was 92.9% and 70.1% at 10 and 20 years, respectively. Independent risk factors for pulmonary autograft degeneration were pre-operative large aortic annulus (hazard ratio: 1.1; p = 0.01), pre-operative aortic insufficiency (hazard ratio: 2.7; p = 0.002), and concomitant replacement of the ascending aorta (hazard ratio: 7.7; p = 0.0003). There were 4 hospital deaths (1.3%), and overall survival at 10 and 20 years was 94.1% and 83.6%, respectively. Long-term survival was not significantly different in patients who required Ross-related reintervention (log-rank p = 0.70). However, compared with the general population, survival was significantly lower in patients following the Ross procedure when matched on age and sex (p Ross procedure was associated with excellent long-term valvular outcomes and survival, regardless of the need for reintervention. Adults presenting with aortic insufficiency or a dilated aortic annulus or ascending aorta were at greater risk for reintervention. Unlike previous reports, long-term survival was lower in Ross

  3. Sediments in Arctic sea ice: Implications for entrainment, transport and release

    Science.gov (United States)

    Nurnberg, D.; Wollenburg, I.; Dethleff, D.; Eicken, H.; Kassens, H.; Letzig, T.; Reimnitz, E.; Thiede, Jorn

    1994-01-01

    Despite the Arctic sea ice cover's recognized sensitivity to environmental change, the role of sediment inclusions in lowering ice albedo and affecting ice ablation is poorly understood. Sea ice sediment inclusions were studied in the central Arctic Ocean during the Arctic 91 expedition and in the Laptev Sea (East Siberian Arctic Region Expedition 1992). Results from these investigations are here combined with previous studies performed in major areas of ice ablation and the southern central Arctic Ocean. This study documents the regional distribution and composition of particle-laden ice, investigates and evaluates processes by which sediment is incorporated into the ice cover, and identifies transport paths and probable depositional centers for the released sediment. In April 1992, sea ice in the Laptev Sea was relatively clean. The sediment occasionally observed was distributed diffusely over the entire ice column, forming turbid ice. Observations indicate that frazil and anchor ice formation occurring in a large coastal polynya provide a main mechanism for sediment entrainment. In the central Arctic Ocean sediments are concentrated in layers within or at the surface of ice floes due to melting and refreezing processes. The surface sediment accumulation in central Arctic multi-year sea ice exceeds by far the amounts observed in first-year ice from the Laptev Sea in April 1992. Sea ice sediments are generally fine grained, although coarse sediments and stones up to 5 cm in diameter are observed. Component analysis indicates that quartz and clay minerals are the main terrigenous sediment particles. The biogenous components, namely shells of pelecypods and benthic foraminiferal tests, point to a shallow, benthic, marine source area. Apparently, sediment inclusions were resuspended from shelf areas before and incorporated into the sea ice by suspension freezing. Clay mineralogy of ice-rafted sediments provides information on potential source areas. A smectite

  4. From cyclic ice streaming to Heinrich-like events: the grow-and-surge instability in the Parallel Ice Sheet Model

    Directory of Open Access Journals (Sweden)

    J. Feldmann

    2017-08-01

    Full Text Available >Here we report on a cyclic, physical ice-discharge instability in the Parallel Ice Sheet Model, simulating the flow of a three-dimensional, inherently buttressed ice-sheet-shelf system which periodically surges on a millennial timescale. The thermomechanically coupled model on 1 km horizontal resolution includes an enthalpy-based formulation of the thermodynamics, a nonlinear stress-balance-based sliding law and a very simple subglacial hydrology. The simulated unforced surging is characterized by rapid ice streaming through a bed trough, resulting in abrupt discharge of ice across the grounding line which is eventually calved into the ocean. We visualize the central feedbacks that dominate the subsequent phases of ice buildup, surge and stabilization which emerge from the interaction between ice dynamics, thermodynamics and the subglacial till layer. Results from the variation of surface mass balance and basal roughness suggest that ice sheets of medium thickness may be more susceptible to surging than relatively thin or thick ones for which the surge feedback loop is damped. We also investigate the influence of different basal sliding laws (ranging from purely plastic to nonlinear to linear on possible surging. The presented mechanisms underlying our simulations of self-maintained, periodic ice growth and destabilization may play a role in large-scale ice-sheet surging, such as the surging of the Laurentide Ice Sheet, which is associated with Heinrich events, and ice-stream shutdown and reactivation, such as observed in the Siple Coast region of West Antarctica.

  5. The weeding handbook a shelf-by-shelf guide

    CERN Document Server

    Vnuk, Rebecca

    2015-01-01

    "No! We can't rid of that!" Vnuk, author of the popular "Weeding Tips" column on Booklist Online, is here to show you that yes, you can. A library is an ever-changing organism; when done the right way, weeding helps a library thrive by focusing its resources on those parts of the collection that are the most useful to its users. Her handbook takes the guesswork out of this delicate but necessary process, giving public and school library staff the knowledge and the confidence to effectively weed any collection, of any size. Going through the proverbial stacks shelf by shelf, Vnuk: Explains why weeding is important for a healthy library, demonstrating that a vibrant collection leads to robust circulation, which in turn affects library budgets Walks readers through a library's shelves by Dewey area, with recommended weeding criteria and call-outs in each area for the different considerations of large collections and smaller collections Features a chapter addressing reference, media, magazines and newspapers, e-b...

  6. Dead-ice environments

    DEFF Research Database (Denmark)

    Krüger, Johannes; Kjær, Kurt H.; Schomacker, Anders

    2010-01-01

    glacier environment. The scientific challenges are to answer the key questions. What are the conditions for dead-ice formation? From which sources does the sediment cover originate? Which melting and reworking processes act in the ice-cored moraines? What is the rate of de-icing in the ice-cored moraines...

  7. On the shelf life of pharmaceutical products.

    Science.gov (United States)

    Capen, Robert; Christopher, David; Forenzo, Patrick; Ireland, Charles; Liu, Oscar; Lyapustina, Svetlana; O'Neill, John; Patterson, Nate; Quinlan, Michelle; Sandell, Dennis; Schwenke, James; Stroup, Walter; Tougas, Terrence

    2012-09-01

    This article proposes new terminology that distinguishes between different concepts involved in the discussion of the shelf life of pharmaceutical products. Such comprehensive and common language is currently lacking from various guidelines, which confuses implementation and impedes comparisons of different methodologies. The five new terms that are necessary for a coherent discussion of shelf life are: true shelf life, estimated shelf life, supported shelf life, maximum shelf life, and labeled shelf life. These concepts are already in use, but not named as such. The article discusses various levels of "product" on which different stakeholders tend to focus (e.g., a single-dosage unit, a batch, a production process, etc.). The article also highlights a key missing element in the discussion of shelf life-a Quality Statement, which defines the quality standard for all key stakeholders. Arguments are presented that for regulatory and statistical reasons the true product shelf life should be defined in terms of a suitably small quantile (e.g., fifth) of the distribution of batch shelf lives. The choice of quantile translates to an upper bound on the probability that a randomly selected batch will be nonconforming when tested at the storage time defined by the labeled shelf life. For this strategy, a random-batch model is required. This approach, unlike a fixed-batch model, allows estimation of both within- and between-batch variability, and allows inferences to be made about the entire production process. This work was conducted by the Stability Shelf Life Working Group of the Product Quality Research Institute.

  8. Swell propagation across a wide continental shelf

    OpenAIRE

    Hendrickson, Eric J.

    1996-01-01

    The effects of wave refraction and damping on swell propagation across a wide continental shelf were examined with data from a transect of bottom pressure recorders extending from the beach to the shelf break near Duck, North Carolina. The observations generally show weak variations in swell energy across the shelf during benign conditions, in qualitative agreement with predictions of a spectral refraction model. Although the predicted ray trajectories are quite sensitive to the irregular she...

  9. Future Antarctic Bed Topography and Its Implications for Ice Sheet Dynamics

    Science.gov (United States)

    Adhikari, Surendra; Ivins, Erik R.; Larour, Eric Y.; Seroussi, Helene L.; Morlighem, Mathieu; Nowicki, S.

    2014-01-01

    The Antarctic bedrock is evolving as the solid Earth responds to the past and ongoing evolution of the ice sheet. A recently improved ice loading history suggests that the Antarctic Ice Sheet (AIS) has generally been losing its mass since the Last Glacial Maximum. In a sustained warming climate, the AIS is predicted to retreat at a greater pace, primarily via melting beneath the ice shelves.We employ the glacial isostatic adjustment (GIA) capability of the Ice Sheet System Model (ISSM) to combine these past and future ice loadings and provide the new solid Earth computations for the AIS.We find that past loading is relatively less important than future loading for the evolution of the future bed topography. Our computations predict that the West Antarctic Ice Sheet (WAIS) may uplift by a few meters and a few tens of meters at years AD 2100 and 2500, respectively, and that the East Antarctic Ice Sheet is likely to remain unchanged or subside minimally except around the Amery Ice Shelf. The Amundsen Sea Sector in particular is predicted to rise at the greatest rate; one hundred years of ice evolution in this region, for example, predicts that the coastline of Pine Island Bay will approach roughly 45mmyr-1 in viscoelastic vertical motion. Of particular importance, we systematically demonstrate that the effect of a pervasive and large GIA uplift in the WAIS is generally associated with the flattening of reverse bed slope, reduction of local sea depth, and thus the extension of grounding line (GL) towards the continental shelf. Using the 3-D higher-order ice flow capability of ISSM, such a migration of GL is shown to inhibit the ice flow. This negative feedback between the ice sheet and the solid Earth may promote stability in marine portions of the ice sheet in the future.

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

    Science.gov (United States)

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

    2014-06-01

    The Antarctic bedrock is evolving as the solid Earth responds to the past and ongoing evolution of the ice sheet. A recently improved ice loading history suggests that the Antarctic Ice Sheet (AIS) has generally been losing its mass since the Last Glacial Maximum. In a sustained warming climate, the AIS is predicted to retreat at a greater pace, primarily via melting beneath the ice shelves. We employ the glacial isostatic adjustment (GIA) capability of the Ice Sheet System Model (ISSM) to combine these past and future ice loadings and provide the new solid Earth computations for the AIS. We find that past loading is relatively less important than future loading for the evolution of the future bed topography. Our computations predict that the West Antarctic Ice Sheet (WAIS) may uplift by a few meters and a few tens of meters at years AD 2100 and 2500, respectively, and that the East Antarctic Ice Sheet is likely to remain unchanged or subside minimally except around the Amery Ice Shelf. The Amundsen Sea Sector in particular is predicted to rise at the greatest rate; one hundred years of ice evolution in this region, for example, predicts that the coastline of Pine Island Bay will approach roughly 45 mm yr-1 in viscoelastic vertical motion. Of particular importance, we systematically demonstrate that the effect of a pervasive and large GIA uplift in the WAIS is generally associated with the flattening of reverse bed slope, reduction of local sea depth, and thus the extension of grounding line (GL) towards the continental shelf. Using the 3-D higher-order ice flow capability of ISSM, such a migration of GL is shown to inhibit the ice flow. This negative feedback between the ice sheet and the solid Earth may promote stability in marine portions of the ice sheet in the future.

  11. Whither the UK Continental Shelf?

    International Nuclear Information System (INIS)

    Kemp, A.G.

    1999-01-01

    The development of the oil and gas fields on the United Kingdom continental shelf has been carried out with remarkable success. However, low oil prices now threaten fresh investment and make it likely that both oil and gas output will start to fall in about 2001. The impact of a number of different price scenarios on further development is assessed. It is concluded that continuing technological improvements and the provision of adequate incentives by government should ensure a long productive future for the province. (UK)

  12. Rate of ice accumulation during ice storms

    Energy Technology Data Exchange (ETDEWEB)

    Feknous, N. [SNC-Lavalin, Montreal, PQ (Canada); Chouinard, L. [McGill Univ., Montreal, PQ (Canada); Sabourin, G. [Hydro-Quebec, Montreal, PQ (Canada)

    2005-07-01

    The rate of glaze ice accumulation is the result of a complex process dependent on numerous meteorological and physical factors. The aim of this paper was to estimate the distribution rate of glaze ice accumulation on conductors in southern Quebec for use in the design of mechanical and electrical de-icing devices. The analysis was based on direct observations of ice accumulation collected on passive ice meters. The historical database of Hydro-Quebec, which contains observations at over 140 stations over period of 25 years, was used to compute accumulation rates. Data was processed so that each glaze ice event was numbered in a chronological sequence. Each event consisted of the time series of ice accumulations on each of the 8 cylinders of the ice meters, as well as on 5 of its surfaces. Observed rates were converted to represent the average ice on a 30 mm diameter conductor at 30 m above ground with a span of 300 m. Observations were corrected to account for the water content of the glaze ice as evidenced by the presence of icicles. Results indicated that despite significant spatial variations in the expected severity of ice storms as a function of location, the distribution function for rates of accumulation were fairly similar and could be assumed to be independent of location. It was concluded that the observations from several sites could be combined in order to obtain better estimates of the distribution of hourly rates of ice accumulation. However, the rates were highly variable. For de-icing strategies, it was suggested that average accumulation rates over 12 hour periods were preferable, and that analyses should be performed for other time intervals to account for the variability in ice accumulation rates over time. In addition, accumulation rates did not appear to be highly correlated with average wind speed for maximum hourly accumulation rates. 3 refs., 2 tabs., 10 figs.

  13. Hemodynamic outcomes of the Ross procedure versus other aortic valve replacement: a systematic review and meta-analysis.

    Science.gov (United States)

    Um, Kevin J; McCLURE, Graham R; Belley-Cote, Emilie P; Gupta, Saurabh; Bouhout, Ismail; Lortie, Hugo; Alraddadi, Hatim; Alsagheir, Ali; Bossard, Matthias; McINTYRE, William F; Lengyel, Alexandra; Eikelboom, John W; Ouzounian, Maral; Chu, Michael W; Parry, Dominic; El-Hamamsy, Ismail; Whitlock, Richard P

    2018-01-09

    Life expectancy in young adults undergoing mechanical or bioprosthetic aortic valve replacement (AVR) may be reduced by up to 20 years compared to age matched controls. The Ross procedure is a durable, anticoagulation-sparing alternative. We performed a systematic review and meta-analysis to compare the valve hemodynamics of the Ross procedure versus other AVR. We searched Cochrane CENTRAL, MEDLINE and EMBASE from inception to February 2017 for randomized controlled trials (RCTs) and observational studies (n≥10 Ross). Independently and in duplicate, we performed title and abstract screening, full-text eligibility assessment, and data collection. We evaluated the risk of bias with the Cochrane and CLARITY tools, and the quality of evidence with the GRADE framework. We identified 2 RCTs and 13 observational studies that met eligibility criteria (n=1,412). In observational studies, the Ross procedure was associated with a lower mean aortic gradient at discharge (MD -9 mmHg, 95% CI [-13, -5], pRoss procedure was associated with a lower mean gradient at latest follow-up (MD -15 mmHg, 95% CI [-32, 2], p=0.08, I2=99%). The mean pulmonic gradient for the Ross procedure was 18.0 mmHg (95% CI [16, 20], pRoss procedure was associated with better aortic valve hemodynamics. Future studies should evaluate the impact of the Ross procedure on exercise capacity and quality of life.

  14. Shelf life of electronic/electrical devices

    International Nuclear Information System (INIS)

    Polanco, S.; Behera, A.K.

    1993-01-01

    This paper discusses inconsistencies which exist between various industry practices regarding the determination of shelf life for electrical and electronic components. New methodologies developed to evaluate the shelf life of electrical and electronic components are described and numerous tests performed at Commonwealth Edison Company's Central Receiving Inspection and Testing (CRIT) Facility are presented. Based upon testing and analysis using the Arrhenius methodology and typical materials used in the manufacturing of electrical and electronic components, shelf life of these devices was determined to be indefinite. Various recommendations to achieve an indefinite. Various recommendations to achieve an indefinite shelf life are presented to ultimately reduce inventory and operating costs at nuclear power plants

  15. Aortic Valve Replacement and the Ross Operation in Children and Young Adults.

    Science.gov (United States)

    Sharabiani, Mansour T A; Dorobantu, Dan M; Mahani, Alireza S; Turner, Mark; Peter Tometzki, Andrew J; Angelini, Gianni D; Parry, Andrew J; Caputo, Massimo; Stoica, Serban C

    2016-06-21

    There are several options available for aortic valve replacement (AVR), with few comparative reports in the literature. The optimal choice for AVR in each age group is not clear. The study sought to report and compare outcomes after AVR in the young using data from a national database. AVR procedures were compared after advanced matching, both in pairs and in a 3-way manner, using a Bayesian dynamic survival model. A total of 1,501 patients who underwent AVR in the United Kingdom between 2000 and 2012 were included. Of these, 47.8% had a Ross procedure, 37.8% a mechanical AVR, 10.9% a bioprosthesis AVR, and 3.5% a homograft AVR, with Ross patients being significantly younger when compared to the other groups. Overall survival at 12 years was 94.6%. In children, the Ross procedure had a 12.7% higher event-free probability (death or any reintervention) at 10 years when compared to mechanical AVR (p = 0.05). We also compared all procedures except the homograft in a matched population of young adults, where the bioprosthesis had the lowest event-free probability of 78.8%, followed by comparable results in mechanical AVR and Ross, with 86.3% and 89.6%, respectively. Younger age was associated with mortality and pulmonary reintervention in the Ross group and with aortic reintervention in the mechanical AVR. Of all 3 options, only the patients undergoing the Ross procedure approached the survival of the general population. AVR in the young achieves good results, with the Ross being overall better suited for this age group, especially in children. Although freedom from aortic valve reintervention is superior after the Ross procedure, the need for homograft reinterventions is an issue to take into account. All methods have advantages and limitations, with reinterventions being an issue in the long term for all, more crucially in smaller children. Copyright © 2016 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.

  16. Interannual variability of surface and bottom sediment transport on the Laptev Sea shelf during summer

    Directory of Open Access Journals (Sweden)

    C. Wegner

    2013-02-01

    Full Text Available Sediment transport dynamics were studied during ice-free conditions under different atmospheric circulation regimes on the Laptev Sea shelf (Siberian Arctic. To study the interannual variability of suspended particulate matter (SPM dynamics and their coupling with the variability in surface river water distribution on the Laptev Sea shelf, detailed oceanographic, optical (turbidity and Ocean Color satellite data, and hydrochemical (nutrients, SPM, stable oxygen isotopes process studies were carried out continuously during the summers of 2007 and 2008. Thus, for the first time SPM and nutrient variations on the Laptev Sea shelf under different atmospheric forcing and the implications for the turbidity and transparency of the water column can be presented.

    The data indicate a clear link between different surface distributions of riverine waters and the SPM transport dynamics within the entire water column. The summer of 2007 was dominated by shoreward winds and an eastward transport of riverine surface waters. The surface SPM concentration on the southeastern inner shelf was elevated, which led to decreased transmissivity and increased light absorption. Surface SPM concentrations in the central and northern Laptev Sea were comparatively low. However, the SPM transport and concentration within the bottom nepheloid layer increased considerably on the entire eastern shelf. The summer of 2008 was dominated by offshore winds and northward transport of the river plume. The surface SPM transport was enhanced and extended onto the mid-shelf, whereas the bottom SPM transport and concentration was diminished. This study suggests that the SPM concentration and transport, in both the surface and bottom nepheloid layers, are associated with the distribution of riverine surface waters which are linked to the atmospheric circulation patterns over the Laptev Sea and the adjacent Arctic Ocean during the open water season. A continuing trend toward

  17. Estimation of Antarctic Land-Fast Sea Ice Algal Biomass and Snow Thickness From Under-Ice Radiance Spectra in Two Contrasting Areas

    Science.gov (United States)

    Wongpan, P.; Meiners, K. M.; Langhorne, P. J.; Heil, P.; Smith, I. J.; Leonard, G. H.; Massom, R. A.; Clementson, L. A.; Haskell, T. G.

    2018-03-01

    Fast ice is an important component of Antarctic coastal marine ecosystems, providing a prolific habitat for ice algal communities. This work examines the relationships between normalized difference indices (NDI) calculated from under-ice radiance measurements and sea ice algal biomass and snow thickness for Antarctic fast ice. While this technique has been calibrated to assess biomass in Arctic fast ice and pack ice, as well as Antarctic pack ice, relationships are currently lacking for Antarctic fast ice characterized by bottom ice algae communities with high algal biomass. We analyze measurements along transects at two contrasting Antarctic fast ice sites in terms of platelet ice presence: near and distant from an ice shelf, i.e., in McMurdo Sound and off Davis Station, respectively. Snow and ice thickness, and ice salinity and temperature measurements support our paired in situ optical and biological measurements. Analyses show that NDI wavelength pairs near the first chlorophyll a (chl a) absorption peak (≈440 nm) explain up to 70% of the total variability in algal biomass. Eighty-eight percent of snow thickness variability is explained using an NDI with a wavelength pair of 648 and 567 nm. Accounting for pigment packaging effects by including the ratio of chl a-specific absorption coefficients improved the NDI-based algal biomass estimation only slightly. Our new observation-based algorithms can be used to estimate Antarctic fast ice algal biomass and snow thickness noninvasively, for example, by using moored sensors (time series) or mapping their spatial distributions using underwater vehicles.

  18. Dissolved and particulate trace metal micronutrients under the McMurdo Sound seasonal sea ice: basal sea ice communities as a capacitor for iron

    Science.gov (United States)

    Noble, Abigail E.; Moran, Dawn M.; Allen, Andrew E.; Saito, Mak A.

    2013-01-01

    Dissolved and particulate metal concentrations are reported from three sites beneath and at the base of the McMurdo Sound seasonal sea ice in the Ross Sea of Antarctica. This dataset provided insight into Co and Mn biogeochemistry, supporting a previous hypothesis for water column mixing occurring faster than scavenging. Three observations support this: first, Mn-containing particles with Mn/Al ratios in excess of the sediment were present in the water column, implying the presence of bacterial Mn-oxidation processes. Second, dissolved and labile Co were uniform with depth beneath the sea ice after the winter season. Third, dissolved Co:PO3−4 ratios were consistent with previously observed Ross Sea stoichiometry, implying that over-winter scavenging was slow relative to mixing. Abundant dissolved Fe and Mn were consistent with a winter reserve concept, and particulate Al, Fe, Mn, and Co covaried, implying that these metals behaved similarly. Elevated particulate metals were observed in proximity to the nearby Islands, with particulate Fe/Al ratios similar to that of nearby sediment, consistent with a sediment resuspension source. Dissolved and particulate metals were elevated at the shallowest depths (particularly Fe) with elevated particulate P/Al and Fe/Al ratios in excess of sediments, demonstrating a sea ice biomass source. The sea ice biomass was extremely dense (chl a >9500 μg/L) and contained high abundances of particulate metals with elevated metal/Al ratios. A hypothesis for seasonal accumulation of bioactive metals at the base of the McMurdo Sound sea ice by the basal algal community is presented, analogous to a capacitor that accumulates iron during the spring and early summer. The release and transport of particulate metals accumulated at the base of the sea ice by sloughing is discussed as a potentially important mechanism in providing iron nutrition during polynya phytoplankton bloom formation and could be examined in future oceanographic

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

    Science.gov (United States)

    Barnes, D K A

    2015-09-21

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

  20. Implementing an empirical scalar constitutive relation for ice with flow-induced polycrystalline anisotropy in large-scale ice sheet models

    Science.gov (United States)

    Graham, Felicity S.; Morlighem, Mathieu; Warner, Roland C.; Treverrow, Adam

    2018-03-01

    The microstructure of polycrystalline ice evolves under prolonged deformation, leading to anisotropic patterns of crystal orientations. The response of this material to applied stresses is not adequately described by the ice flow relation most commonly used in large-scale ice sheet models - the Glen flow relation. We present a preliminary assessment of the implementation in the Ice Sheet System Model (ISSM) of a computationally efficient, empirical, scalar, constitutive relation which addresses the influence of the dynamically steady-state flow-compatible induced anisotropic crystal orientation patterns that develop when ice is subjected to the same stress regime for a prolonged period - sometimes termed tertiary flow. We call this the ESTAR flow relation. The effect on ice flow dynamics is investigated by comparing idealised simulations using ESTAR and Glen flow relations, where we include in the latter an overall flow enhancement factor. For an idealised embayed ice shelf, the Glen flow relation overestimates velocities by up to 17 % when using an enhancement factor equivalent to the maximum value prescribed in the ESTAR relation. Importantly, no single Glen enhancement factor can accurately capture the spatial variations in flow across the ice shelf generated by the ESTAR flow relation. For flow line studies of idealised grounded flow over varying topography or variable basal friction - both scenarios dominated at depth by bed-parallel shear - the differences between simulated velocities using ESTAR and Glen flow relations depend on the value of the enhancement factor used to calibrate the Glen flow relation. These results demonstrate the importance of describing the deformation of anisotropic ice in a physically realistic manner, and have implications for simulations of ice sheet evolution used to reconstruct paleo-ice sheet extent and predict future ice sheet contributions to sea level.

  1. Long-Term Outcomes of the Ross Procedure Versus Mechanical Aortic Valve Replacement: Propensity-Matched Cohort Study.

    Science.gov (United States)

    Mazine, Amine; David, Tirone E; Rao, Vivek; Hickey, Edward J; Christie, Shakira; Manlhiot, Cedric; Ouzounian, Maral

    2016-08-23

    The ideal aortic valve substitute in young and middle-aged adults remains unknown. We sought to compare the long-term outcomes of patients undergoing the Ross procedure and those receiving a mechanical aortic valve replacement (AVR). From 1990 to 2014, 258 patients underwent a Ross procedure and 1444 had a mechanical AVR at a single institution. Patients were matched into 208 pairs through the use of a propensity score. Mean age was 37.2±10.2 years, and 63% were male. Mean follow-up was 14.2±6.5 years. Overall survival was equivalent (Ross versus AVR: hazard ratio, 0.91, 95% confidence interval, 0.38-2.16; P=0.83), although freedom from cardiac- and valve-related mortality was improved in the Ross group (Ross versus AVR: hazard ratio, 0.22; 95% confidence interval, 0.034-0.86; P=0.03). Freedom from reintervention was equivalent after both procedures (Ross versus AVR: hazard ratio, 1.86; 95% confidence interval, 0.76-4.94; P=0.18). Long-term freedom from stroke or major bleeding was superior after the Ross procedure (Ross versus AVR: hazard ratio, 0.09; 95% confidence interval, 0.02-0.31; PRoss procedure and mechanical AVR. However, the Ross procedure was associated with improved freedom from cardiac- and valve-related mortality and a significant reduction in the incidence of stroke and major bleeding. In specialized centers, the Ross procedure represents an excellent option and should be considered for young and middle-aged adults undergoing AVR. © 2016 American Heart Association, Inc.

  2. Cascading off the West Greenland Shelf: A numerical perspective

    Science.gov (United States)

    Marson, Juliana M.; Myers, Paul G.; Hu, Xianmin; Petrie, Brian; Azetsu-Scott, Kumiko; Lee, Craig M.

    2017-07-01

    Cascading of dense water from the shelf to deeper layers of the adjacent ocean basin has been observed in several locations around the world. The West Greenland Shelf (WGS), however, is a region where this process has never been documented. In this study, we use a numerical model with a 1/4° resolution to determine (i) if cascading could happen from the WGS; (ii) where and when it could take place; (iii) the forcings that induce or halt this process; and (iv) the path of the dense plume. Results show cascading happening off the WGS at Davis Strait. Dense waters form there due to brine rejection and slide down the slope during spring. Once the dense plume leaves the shelf, it gradually mixes with waters of similar density and moves northward into Baffin Bay. Our simulation showed events happening between 2003-2006 and during 2014; but no plume was observed in the simulation between 2007 and 2013. We suggest that the reason why cascading was halted in this period is related to: the increased freshwater transport from the Arctic Ocean through Fram Strait; the additional sea ice melting in the region; and the reduced presence of Irminger Water at Davis Strait during fall/early winter. Although observations at Davis Strait show that our simulation usually overestimates the seasonal range of temperature and salinity, they agree with the overall variability captured by the model. This suggests that cascades have the potential to develop on the WGS, albeit less dense than the ones estimated by the simulation.

  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. Salinity, temperature and density data for the Canadian Beaufort Sea shelf, March 1988

    Energy Technology Data Exchange (ETDEWEB)

    Hopky, G E; Chiperzak, D B; Lawrence, M J

    1988-01-01

    This report contains salinity, temperature and density (CTD) data collected in the waters of the Canadian Beaufort Sea Shelf during March 1988. Salinity and temperature profile data were measured using a Guildline Model 8870 probe deployed from the ice surface. Ice thickness was also measured. Density was calculated using salinity and temperature values. CTD profiles were measured at five stations. The maximum depths of profiles measured from the ice surface ranged from 31.2 to 16.8 dbar. Salinity and temperature measurements ranged from 0.35 to 34.83, and -1.87 to 1.08/sup 0/C, respectively. The data presented in this report will assist in the identification and delineation of potential habitat types, as part of the Critical Arctic Estuarine and Marine Habitat Project of the Northern Oil and Gas Program. 5 refs., 7 figs., 6 tabs.

  5. Sea-level response to abrupt ocean warming of Antarctic ice shelves

    Science.gov (United States)

    Pattyn, Frank

    2016-04-01

    Antarctica's contribution to global sea-level rise increases steadily. A fundamental question remains whether the ice discharge will lead to marine ice sheet instability (MISI) and collapse of certain sectors of the ice sheet or whether ice loss will increase linearly with the warming trends. Therefore, we employ a newly developed ice sheet model of the Antarctic ice sheet, called f.ETISh (fast Elementary Thermomechanical Ice Sheet model) to simulate ice sheet response to abrupt perturbations in ocean and atmospheric temperature. The f.ETISh model is a vertically integrated hybrid (SSA/SIA) ice sheet model including ice shelves. Although vertically integrated, thermomechanical coupling is ensured through a simplified representation of ice sheet thermodynamics based on an analytical solution of the vertical temperature profile, including strain heating and horizontal advection. The marine boundary is represented by a flux condition either coherent with power-law basal sliding (Pollard & Deconto (2012) based on Schoof (2007)) or according to Coulomb basal friction (Tsai et al., 2015), both taking into account ice-shelf buttressing. Model initialization is based on optimization of the basal friction field. Besides the traditional MISMIP tests, new tests with respect to MISI in plan-view models have been devised. The model is forced with stepwise ocean and atmosphere temperature perturbations. The former is based on a parametrised sub-shelf melt (limited to ice shelves), while the latter is based on present-day mass balance/surface temperature and corrected for elevation changes. Surface melting is introduced using a PDD model. Results show a general linear response in mass loss to ocean warming. Nonlinear response due to MISI occurs under specific conditions and is highly sensitive to the basal conditions near the grounding line, governed by both the initial conditions and the basal sliding/deformation model. The Coulomb friction model leads to significantly higher

  6. Stochastic ice stream dynamics.

    Science.gov (United States)

    Mantelli, Elisa; Bertagni, Matteo Bernard; Ridolfi, Luca

    2016-08-09

    Ice streams are narrow corridors of fast-flowing ice that constitute the arterial drainage network of ice sheets. Therefore, changes in ice stream flow are key to understanding paleoclimate, sea level changes, and rapid disintegration of ice sheets during deglaciation. The dynamics of ice flow are tightly coupled to the climate system through atmospheric temperature and snow recharge, which are known exhibit stochastic variability. Here we focus on the interplay between stochastic climate forcing and ice stream temporal dynamics. Our work demonstrates that realistic climate fluctuations are able to (i) induce the coexistence of dynamic behaviors that would be incompatible in a purely deterministic system and (ii) drive ice stream flow away from the regime expected in a steady climate. We conclude that environmental noise appears to be crucial to interpreting the past behavior of ice sheets, as well as to predicting their future evolution.

  7. Sea Ice Ecosystems

    Science.gov (United States)

    Arrigo, Kevin R.

    2014-01-01

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

  8. STS-37 Mission Specialist (MS) Ross during simulation in JSC's FB-SMS

    Science.gov (United States)

    1991-01-01

    STS-37 Mission Specialist (MS) Jerry L. Ross 'borrows' the pilots station to rehearse some of his scheduled duties for his upcoming mission. He is on the flight deck of the fixed-based (FB) shuttle mission simulator (SMS) during this unsuited simulation. The SMS is part of JSC's Mission Simulation and Training Facility Bldg 5.

  9. A Q-Methodological Study of the Kubler-Ross Stage Theory.

    Science.gov (United States)

    Metzger, Anne M.

    1979-01-01

    Investigated the correspondence between stage changes hypothesized by the Kubler-Ross theory and the perception of the course of illness by seriously ill patients and their spouses. Supported the use of Q-methodology as a research procedure for investigations of terminal illness. (Author)

  10. 76 FR 77684 - Establishment of the Fort Ross-Seaview Viticultural Area

    Science.gov (United States)

    2011-12-14

    ...; Treasury decision. SUMMARY: This Treasury decision establishes the 27,500-acre ``Fort Ross-Seaview... may purchase. DATES: Effective Date: January 13, 2012. FOR FURTHER INFORMATION CONTACT: Elisabeth C... may purchase. Establishment of a viticultural area is neither an approval nor an endorsement by TTB of...

  11. First stage of INTRAMAP: INtegrated Transantarctic Mountains and Ross Sea Area Magnetic Anomaly Project

    Directory of Open Access Journals (Sweden)

    D. Damaske

    1999-06-01

    Full Text Available INTRAMAP (INtegrated Transantarctic Mountains and Ross Sea Area Magnetic Anomaly Project is an international effort to merge the magnetic data acquired throughout the "Ross Sea Antarctic Sector" (south of 60°S between 135°-255°E including the Transantarctic Mountains (TAM, the Ross Sea, Marie Byrd Land, and the Pacific coast, and also to begin the compilation efforts for new data over the Wilkes Basin. This project is a component of the continental scale Antarctic Digital Magnetic Anomaly Project (ADMAP. The first stage of INTRAMAP addresses the analysis and merging of GITARA (1991-1994 and GANOVEX (1984 aeromagnetic surveys together with ground magnetic data (1984-1989. The combined data sets cover an area of approximately 30 km2 over Victoria Land and adjacent Ross Sea. Map and profile gridding were implemented to integrate the data sets. These approaches are studied for improving existing strategies to adopt for the whole magnetic compilation effort. The final microlevelled grid that we produce is a new tool for regional interpretation of the main tectonic and geologic features of this sector of Antarctica.

  12. Two Case Histories, Ishbel Ross and Emma Bugbee: Women Journalists Ride the Rail with the Suffragettes.

    Science.gov (United States)

    Merrick, Beverly G.

    The rise to prominence of the women's suffrage movement in the World War I years brought women reporters into U.S. newsrooms for the first time. In 1911 Emma Bugbee became the first woman hired as a "hard" news reporter for the "New York Tribune" (later the "Herald Tribune"). Ishbel Ross, author of "Ladies of the…

  13. Why can rossing uranium mine keep mining even in low price conditions of uranium market

    International Nuclear Information System (INIS)

    Tan Chenglong

    2004-01-01

    Rossing uranium mine is the only operating uranium mine in the world where the uranium occurs in intrusive alaskite. In the past 10 years, uranium market regressed in the world, uranium production weakened, expenditures of capital for uranium exploration were insufficient. Uranium spot market price rapidly decreased from $111.8/kg U in late 1970's to $22.1/kg U in mid-1990's. Why can Rossing uranium mine mined with traditional underground and open pit operation can keep running even in low price conditions of uranium market? Augumenting research on the deposit, mineral and technology, decreasing production cost and improving selling strategy can not only maintain Rossing's uranium production at present, but also ensure sustainable development in the coming 15 years. Exploration of low-costed uranium deposits is very important. However, obvious economic benefits can be obtained, as Rossing uranium mine does, by augumenting geological-economical research on the known uranium deposits of hard-rock type and by using new techniques to improve the conventional techniques in the uranium mine development. (authors)

  14. Assessing Competition with the Panzar-Rosse Model: The Role of Scale, Costs, and Equilibrium

    NARCIS (Netherlands)

    Bikker, J.A.|info:eu-repo/dai/nl/06912261X; Shaffer, S.; Spierdijk, L.

    2009-01-01

    The Panzar-Rosse test has been widely applied to assess competitive conduct, often in specifcations controlling for firm scale or using a price equation. We show that neither a price equation nor a scaled revenue function yields a valid measure for competitive conduct. Moreover, even an unscaled

  15. A Helping Hand in the Frederick Community—Ross Smith | Poster

    Science.gov (United States)

    By day, Ross Smith is the compliance and security officer for Data Management Services, Inc., assigned to the National Cancer Institute (NCI) at Frederick. His role is to ensure the secure operation of in-house computer systems, servers, and network connections. But in his spare time, Smith is also a volunteer firefighter and emergency medical technician (EMT).

  16. 76 FR 71082 - Strata Energy, Inc., Ross Uranium Recovery Project; New Source Material License Application...

    Science.gov (United States)

    2011-11-16

    ... NUCLEAR REGULATORY COMMISSION [Docket No. 40-9091; NRC-2011-0148] Strata Energy, Inc., Ross Uranium Recovery Project; New Source Material License Application; Notice of Intent To Prepare a... intent to prepare a supplemental environmental impact statement. SUMMARY: Strata Energy, Inc. (Strata...

  17. Photographer: Digital Telepresence: Dr Murial Ross's Virtual Reality Application for Neuroscience

    Science.gov (United States)

    1995-01-01

    Photographer: Digital Telepresence: Dr Murial Ross's Virtual Reality Application for Neuroscience Research Biocomputation. To study human disorders of balance and space motion sickness. Shown here is a 3D reconstruction of a nerve ending in inner ear, nature's wiring of balance organs.

  18. Märten Ross sõnastas majanduskriisi õppetunnid / Argo Ideon

    Index Scriptorium Estoniae

    Ideon, Argo, 1966-

    2011-01-01

    Ajutiselt peaministri majandus- ja rahandusnõunikuna töötanud endine Eesti Panga asepresident Märten Ross kirjutas loetelu õppetundidest, mida Eesti majanduspoliitika peaks arvestama 2008.-2009. aasta kriisi põhjal. Rossi 10 punkti lühidalt. Rahandusminister Jürgen Ligi ning Eesti Panga rahapoliitika ja majandusuuringute osakonna asejuhataja Martin Lindpere arvamus

  19. Ross In Situ Uranium Recovery Project NESHAP Subpart W Construction Approval

    Science.gov (United States)

    On May 5, 2015, EPA issued a Construction Approval under the National Emission Standards for Hazardous Air Pollutants (NESHAPs) at 40 CFR Part 61, subpart W, to Strata Energy, Inc., for their Ross In Situ Recovery (ISR) Uranium Project in Crook County, WY.

  20. The place of theology in the modern university | Ross | Journal of ...

    African Journals Online (AJOL)

    The place of theology in the modern university. Kenneth R. Ross. Abstract. No Abstract. Full Text: EMAIL FREE FULL TEXT EMAIL FREE FULL TEXT · DOWNLOAD FULL TEXT DOWNLOAD FULL TEXT · AJOL African Journals Online. HOW TO USE AJOL... for Researchers · for Librarians · for Authors · FAQ's · More about ...

  1. Sources of iron in the Ross Sea Polynya in early summer

    NARCIS (Netherlands)

    Gerringa, L. J. A.; Laan, P.; van Dijken, G. L.; van Haren, H.; De Baar, H. J. W.; Arrigo, K. R.; Alderkamp, A. -C.

    2015-01-01

    Dissolved Fe (DFe) was measured in the Ross Sea Polynya (RSP), Antarctica, during a GEOTRACES cruise between 20 December 2013 and 5 January 2014. DFe was measured over the full water column with special emphasis on samples near the seafloor. In the upper mixed layer, DFe was very low everywhere (

  2. Astronauts Ross and Helms at CAPCOM station during STS-61 simulations

    Science.gov (United States)

    1993-01-01

    Astronauts Jerry L. Ross and Susan J. Helms are pictured at the Spacecraft Communicators console during joint integrated simulations for the STS-61 mission. Astronauts assigned to extravehicular activity (EVA) tasks with the Hubble Space Telescope (HST) were simultaneously rehearsing in a neutral buoyancy tank at the Marshall Space Flight Center (MSFC) in Alabama.

  3. Transcatheter versus surgical valve replacement for a failed pulmonary homograft in the Ross population.

    Science.gov (United States)

    Alassas, Khadija; Mohty, Dania; Clavel, Marie Annick; Husain, Aysha; Hijji, Talal; Aljoufan, Mansour; Alhalees, Zohair; Fadel, Bahaa M

    2018-04-01

    Patients who undergo the Ross procedure are at increased risk of pulmonary valve (PV) homograft dysfunction. For those who require reintervention on the homograft, transcatheter PV replacement (tPVR) provides a less invasive therapeutic option than surgical PVR (sPVR). We examined the outcomes following tPVR versus sPVR in a cohort of patients who underwent the Ross procedure. We performed a retrospective analysis of Ross patients age ≥14 years who underwent tPVR (n = 47) or sPVR (n = 41) at our institution. The patients' clinical and echocardiographic data were reviewed. Baseline parameters, including demographic data and left ventricular and right ventricular (RV) systolic function, were similar in the 2 groups. The mean follow-up was 56 ± 24 months for the tPVR group and 89 ± 46 months for the sPVR group (P Ross patients who require reintervention on the PV homograft, both tPVR and sPVR provide low procedural mortality and comparable midterm outcome with no significant difference in mortality or PV reintervention. However, IE is more common following tPVR. A larger randomized study is needed to determine the role of each procedure in patient management. Copyright © 2017 The American Association for Thoracic Surgery. Published by Elsevier Inc. All rights reserved.

  4. Report of the Dutch experience with the Ross procedure in 343 patients

    NARCIS (Netherlands)

    Takkenberg, J. J. M.; Dossche, K. M. E.; Hazekamp, M. G.; Nijveld, A.; Jansen, E. W. L.; Waterbolk, T. W.; Bogers, A. J. J. C.

    2002-01-01

    Limited information is available on outcome after autograft aortic valve replacement, in particular with respect to the durability of the autograft and of the allograft used to reconstruct the right ventricular outflow tract. A retrospective follow-up study of all patients who underwent a Ross

  5. TEST OF THE CHEN-ROLL-ROSS MACROECONOMIC FACTOR MODEL: EVIDENCE FROM CROATIAN STOCK MARKET

    Directory of Open Access Journals (Sweden)

    Denis Dolinar

    2015-12-01

    Full Text Available This paper empirically examines the well-known Chen-Roll-Ross model on the Croatian stock market. Modifications of definitions of the Chen-Roll-Ross model variables showed as necessary because of doubtful availability and quality of input data needed. Namely, some macroeconomic and market variables are not available in the originally defined form or do not exist. In that sense this paper gives some alternative definitions for some model variables. Also, in order to improve statistical analysis, in this paper we have modified Fama-MacBeth technique in the way that second-pass regression was substituted with panel regression analysis. Based on the two-pass regression analysis of returns of 34 Croatian stocks on 4 macroeconomic variables during the seven-and-half-year observation period the following conclusion is made. In contrast to the results of Chen, Roll and Ross (1986 for the U.S. stock market, their model is not successful when describing a risk-return relation of Croatian stocks. Nevertheless, one observed version of the Chen-RollRoss model showed certain statistical significance. Namely, two risk factors in that version of the model were statistically significant: default premium, measured as risk premium for the corporate short-term bank loan financing, and term structure premium, measured on short-run basis.

  6. MR imaging of right ventricular function after the Ross procedure for aortic valve replacement: initial experience

    NARCIS (Netherlands)

    Grotenhuis, Heynric B.; de Roos, Albert; Ottenkamp, Jaap; Schoof, Paul H.; Vliegen, Hubert W.; Kroft, Lucia J. M.

    2008-01-01

    PURPOSE: To prospectively assess right ventricular (RV) function after the Ross procedure by using magnetic resonance (MR) imaging. MATERIALS AND METHODS: The local ethics committee approved the study and informed consent was obtained from all participants prior to enrollment in the study. Seventeen

  7. Unusual biogenic calcite structures in two shallow lakes, James Ross Island, Antarctica

    Czech Academy of Sciences Publication Activity Database

    Elster, Josef; Nedbalová, Linda; Vodrážka, R.; Láska, K.; Haloda, J.; Komárek, Jiří

    2016-01-01

    Roč. 13, č. 2 (2016), s. 535-549 ISSN 1726-4170 R&D Projects: GA MŠk ME 945 Institutional support: RVO:67985939 Keywords : James Ross Island * cyanobacteria * microalgae Subject RIV: EH - Ecology, Behaviour Impact factor: 3.851, year: 2016

  8. 76 FR 22338 - Proposed Fort Ross-Seaview Viticultural Area; Comment Period Reopening

    Science.gov (United States)

    2011-04-21

    ... May 9, 2005, from all interested persons. In response to a request from a local wine industry member... the Fort Ross-Seaview viticultural area. Two local wine industry members supported the petition without qualification; a third industry member supported the viticultural area's establishment while...

  9. Walrus areas of use in the Chukchi Sea during sparse sea ice cover

    Science.gov (United States)

    Jay, Chadwick V.; Fischbach, Anthony S.; Kochnev, Anatoly A.

    2012-01-01

    The Pacific walrus Odobenus rosmarus divergens feeds on benthic invertebrates on the continental shelf of the Chukchi and Bering Seas and rests on sea ice between foraging trips. With climate warming, ice-free periods in the Chukchi Sea have increased and are projected to increase further in frequency and duration. We radio-tracked walruses to estimate areas of walrus foraging and occupancy in the Chukchi Sea from June to November of 2008 to 2011, years when sea ice was sparse over the continental shelf in comparison to historical records. The earlier and more extensive sea ice retreat in June to September, and delayed freeze-up of sea ice in October to November, created conditions for walruses to arrive earlier and stay later in the Chukchi Sea than in the past. The lack of sea ice over the continental shelf from September to October caused walruses to forage in nearshore areas instead of offshore areas as in the past. Walruses did not frequent the deep waters of the Arctic Basin when sea ice retreated off the shelf. Walruses foraged in most areas they occupied, and areas of concentrated foraging generally corresponded to regions of high benthic biomass, such as in the northeastern (Hanna Shoal) and southwestern Chukchi Sea. A notable exception was the occurrence of concentrated foraging in a nearshore area of northwestern Alaska that is apparently depauperate in walrus prey. With increasing sea ice loss, it is likely that walruses will increase their use of coastal haul-outs and nearshore foraging areas, with consequences to the population that are yet to be understood.

  10. Submarine glacial landforms on the Bay of Fundy–northern Gulf of Maine continental shelf

    Science.gov (United States)

    Todd, B.J.; Shaw, J.; Valentine, Page C.

    2016-01-01

    The Bay of Fundy–northern Gulf of Maine region surrounds the southern part of Nova Scotia, encompassing, from west to east, the Bay of Fundy, Grand Manan Basin, German Bank, Browns Bank, Northeast Channel and northeastern Georges Bank (Fig. 1a, b). During the last glacial maximum (c. 24–20 14C ka BP), the SE margin of the Laurentide Ice Sheet (LIS) occupied the study area, the rest of the Gulf of Maine and the continental Scotian Shelf off Atlantic Canada (see Dyke et al. 2002, fig. 1; Shaw et al. 2006, fig. 8; Hundert & Piper 2008, fig. 16). Early mapping of the glaciated region on the Scotian Shelf using side-scan sonar imagery and seismic-reflection profiles revealed topographic features interpreted to be recessional moraines indicative of retreat of the LIS (King et al. 1972; King 1996). Subsequently, multibeam sonar seafloor mapping of local-scale glacial landforms on the inner Scotian Shelf off Halifax, Nova Scotia (Fig. 1b) provided further information on the dynamics of the advance and retreat of the ice sheet (Loncarevic et al.1994). Interpretation of seismic-reflection profiles across Georges Bank revealed that the surficial sediment is a veneer of glacial debris transported to Georges Bank by the LIS during the late Pleistocene from continental areas to the north (Shepard et al. 1934; Knott & Hoskins 1968; Schlee 1973; Twichell et al. 1987; Fader et al. 1988). Recent high-resolution multibeam sonar surveys of German Bank and the Bay of Fundy mapped a complex of ice-advance and ice-retreat features attributed to the activity of the LIS (Todd et al. 2007; Todd & Shaw 2012).

  11. Long-term Evaluation of the Ross Procedure in Acute Infective Endocarditis.

    Science.gov (United States)

    Ratschiller, Thomas; Sames-Dolzer, Eva; Paulus, Patrick; Schimetta, Wolfgang; Müller, Hannes; Zierer, Andreas F; Mair, Rudolf

    2017-10-05

    Optimal valve substitute for young patients with aortic valve endocarditis remains controversial. Given its better resistance to infection, the Ross procedure is an attractive alternative to prosthetic valve replacement or homograft implantation. The objective of this study was to assess long-term outcomes of the Ross procedure in this indication. From January 1991 to April 2017, 190 patients underwent a Ross procedure at our institution. Acute endocarditis was the indication for operation in 19 patients, including 6 patients with a bicuspid aortic valve. The pulmonary autograft was implanted as freestanding root replacement in all patients. The clinical follow-up is 100% complete, with a mean of 12.0 ± 5.7 years. The mean age of the study population was 35.9 ± 11.5 years. Moderate or severe aortic regurgitation was present in 84.2% of the patients. Systemic embolization had occurred in 36.8% of the patients. The mean aortic cross-clamp time was 126 ± 24 minutes. The median length of stay on the intensive care unit was 1 day. Mortality at 30 days was 5.3% (1 patient with gastrointestinal bleeding). Echocardiography at hospital discharge documented no or trivial aortic regurgitation in all patients. No case of recurrent endocarditis affecting the autograft occurred. One patient (0.4% per patient-year) was reoperated 1.8 years after the Ross procedure for homograft endocarditis. Three patients (15.8%) were reoperated for autograft aneurysm. The Ross procedure is a safe and effective alternative to prosthetic valve replacement or homograft implantation in selected young patients with acute endocarditis with a low rate of recurrent infection. Copyright © 2017 Elsevier Inc. All rights reserved.

  12. Valve-sparing root replacement for freestanding pulmonary autograft aneurysm after the Ross procedure.

    Science.gov (United States)

    Ratschiller, Thomas; Eva, Sames-Dolzer; Schimetta, Wolfgang; Paulus, Patrick; Müller, Hannes; Zierer, Andreas; Mair, Rudolf

    2018-02-20

    Autograft dilatation is the main long-term complication following the Ross procedure using the freestanding root replacement technique. We reviewed our 25-year experience with the Ross procedure with a special emphasis on valve-sparing reoperations. From 1991 to 2016, 153 patients (29.6 ± 16.6 years; 29.4% pediatric) underwent a Ross operation at our institution with implantation of the autograft as freestanding root replacement. The follow-up is 98.7% complete with a mean of 12.2 ± 5.5 years. Mortality at 30-days was 2.0%. Echocardiography documented no or trivial aortic regurgitation in 99.3% of the patients at discharge. Survival probability at 20 years was 85.4%. No case of autograft endocarditis occurred. Autograft deterioration rate was 2.01% per patient-year, and freedom from autograft reoperation was 75.3% at 15 years. A reoperation for autograft aneurysm was required in 35 patients (22.9%) at a mean interval of 11.1 ± 4.6 years after the Ross procedure. A valve-sparing root replacement was performed in 77% of patients, including 10 David and 17 Yacoub procedures with no early mortality. Three patients required prosthetic valve replacement within 2 years after a Yacoub operation. At latest follow-up, 92% of all surviving patients still carry the pulmonary autograft valve. Freedom from autograft valve replacement was 92.1% at 15 years. Using the David or Yacoub techniques, the autograft valve can be preserved in the majority of patients with root aneurysms after the Ross procedure. Reoperations can be performed with no early mortality, a good functional midterm result, and an acceptable reintervention rate. Copyright © 2018 The American Association for Thoracic Surgery. Published by Elsevier Inc. All rights reserved.

  13. A natural ice boom

    Energy Technology Data Exchange (ETDEWEB)

    Hopper, H.R. [Manitoba Hydro, Winnipeg, MB (Canada)

    1998-10-01

    Planning for ice jams and ice movements are critical on the Nelson River in northern Manitoba in designing cofferdams. Experience on the St. Lawrence River demonstrated the possibility of exercising some control over ice action by judicious placement of log booms or ice control structures. The success of experiments with man-made controls led to field tests in which an ice sheet of sufficient magnitude and competence was introduced into the open water stream of the Nelson River. The ice sheet was subsequently jammed in a narrow channel, thereby creating a natural ice bridge or boom upstream of a proposed hydro development. Under favourable conditions, this boom would initiate the progression of the ice cover from its location upstream, cutting off the downstream reach from the ice producing potential of the upstream reach. Although ice would still be generated downstream, the length of the reach between the ice boom and the development site would be short enough that ice jamming at the development site would never occur. Although problems in blasting prevented the introduction of a competent ice sheet into the main stream of the river at the location chosen, sufficient confidence in the theory was gained to warrant further consideration. 4 refs., 1 tab., 10 figs.

  14. The Ross Operation in Children and Young Adults: 12-Year Results and Trends From the UK National Database.

    Science.gov (United States)

    Zebele, Carlo; Chivasso, Pierpaolo; Sedmakov, Christo; Angelini, Gianni; Caputo, Massimo; Parry, Andrew; Stoica, Serban

    2014-07-01

    To determine UK national trends and results of the Ross operation in relation to all aortic valve interventions. Examination of the UK Congenital Central Cardiac Audit Database for all aortic valve procedures performed between 2000 and 2011 in children (0-16 years) and young adults (16-30 years). A total of 2,206 aortic valve procedures were performed in children and 1,824 in young adults, the proportions in the two groups being: Ross operation (19% vs 15%, respectively), surgical valvoplasty (9.5% vs 4%), surgical valvotomy (9.5% vs 1%), aortic valve replacement (AVR; 11% vs 55%), aortic root replacement (4% vs 18%), and balloon valvoplasty (47% vs 7%). The 30-day and 1-year survival after Ross is 99.3% and 98.7%, respectively, in the last four years achieving 100%. In children, the proportion of balloon valvoplasty increased from an average of 43% in 2000 to 2006 to 53% in 2007 to 2011, whereas the Ross operation decreased from 22% to 16% (P Ross (P Ross operations performed. The year-on-year changes show a significant decreasing trend locally and nationally. Despite an excellent track record, the Ross operation is performed less frequently in the United Kingdom. This report is a first step in comparing treatment modalities at national level. © The Author(s) 2014.

  15. The Ross procedure offers excellent survival compared with mechanical aortic valve replacement in a real-world setting.

    Science.gov (United States)

    Andreas, Martin; Wiedemann, Dominik; Seebacher, Gernot; Rath, Claus; Aref, Tandis; Rosenhek, Raphael; Heinze, Georg; Eigenbauer, Ernst; Simon, Paul; Ruetzler, Kurt; Hiesmayr, Joerg-Michael; Moritz, Anton; Laufer, Guenther; Kocher, Alfred

    2014-09-01

    The ideal prosthesis for young patients requiring aortic valve replacement has not been defined to date. Although the Ross procedure provides excellent survival, its application is still limited. We compared the long-term survival after the Ross procedure with mechanical aortic valve replacement. All consecutive Ross procedures and mechanical aortic valve replacements performed between 1991 and 2008 at a single centre were analysed. Only adult patients between 18 and 50 years of age were included in the study. Survival and valve-related complications were evaluated. Furthermore, survival was compared with the age- and sex-matched Austrian population. A total of 159 Ross patients and 173 mechanical valve patients were included. The cumulative survival for the Ross procedure was significantly better, with survival rates of 96, 94 and 93% at 5, 10 and 15 years, respectively, in comparison to 90, 84 and 75% (P Ross group but was significantly reduced in the mechanical valve group. In a real-world setting, the Ross procedure is associated with a long-term survival benefit in young adults in comparison to mechanical aortic valve replacement. © The Author 2014. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.

  16. Summer Epiphytic Diatoms from Terra Nova Bay and Cape Evans (Ross Sea, Antarctica) - A Synthesis and Final Conclusions

    Science.gov (United States)

    Majewska, Roksana; Convey, Peter; De Stefano, Mario

    2016-01-01

    Despite recent advances in polar marine biology and related fields, many aspects of the ecological interactions that are crucial for the functioning of Antarctic shallow water habitats remain poorly understood. Although epiphytic diatoms play an essential role in the Antarctic marine food web, basic information regarding their ecology, biodiversity and biogeography is largely unavailable. Here, we synthesise studies on Ross Sea epiphytic diatoms collected during 11 summer Antarctic expeditions between the years 1989/90 and 2011/12, presenting a full list of diatom taxa associated with three macroalgal species (Iridaea cordata, Phyllophora antarctica, and Plocamium cartilagineum) and their epiphytic sessile fauna. Diatom communities found during the three summer months at various depths and sampling stations differed significantly in terms of species composition, growth form structure and abundances. Densities ranged from 21 to >8000 cells mm-2, and were significantly higher on the surface of epiphytic micro-fauna than on any of the macroalgal species examined. Generally, host organisms characterized by higher morphological heterogeneity (sessile microfauna, ramified Plocamium) supported richer diatom communities than those with more uniform surfaces (Iridaea). Differences between epiphytic communities associated with different macroalgae were reflected better in species composition than in growth form structure. The latter changed significantly with season, which was related strongly to the changing ice conditions. A general trend towards an increasing number of erect forms in deeper waters and tube-dwelling diatoms in the shallowest sites (2–5 m) was also observed. This study explores further important and largely previously unknown aspects of relationships and interactions between Antarctic epiphytic diatoms and their micro- and macro-environments. PMID:27078637

  17. Forecast Icing Product

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Forecast Icing Product (FIP) is an automatically-generated index suitable for depicting areas of potentially hazardous airframe icing. The FIP algorithm uses...

  18. Current Icing Product

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Current Icing Product (CIP) is an automatically-generated index suitable for depicting areas of potentially hazardous airframe icing. The CIP algorithm combines...

  19. Green icebergs formed by freezing of organic-rich seawater to the base of Antarctic ice shelves

    Science.gov (United States)

    Warren, Stephen G.; Roesler, Collin S.; Morgan, Vincent I.; Brandt, Richard E.; Goodwin, Ian D.; Allison, Ian

    1993-01-01

    Although most icebergs are blue, green icebergs are seen occasionally in the Antarctic ocean. Chemical and isotopic analysis of samples from green icebergs indicate that the ice consists of desalinated frozen seawater, as does the basal ice from the Amery Ice Shelf. Spectral reflectance of a green iceberg measured near 67°S, 62°E, confirms that the color is inherent to the ice, not an artifact of the illumination. Pure ice appears blue owing to its absorption of red photons. Addition of a constituent that absorbs blue photons can shift the peak reflectance from blue to green. Such a constituent was identified by spectrophotometric analysis of core samples from this iceberg and from the Amery basal ice, and of seawater samples from Prydz Bay off the Amery Ice Shelf. Analysis of the samples by fluorescence spectroscopy indicates that the blue absorption, and hence the inherent green color, is due to the presence of marine-derived organic matter in the green iceberg, basal ice, and seawater. Thick accumulations of green ice, in icebergs and at the base of ice shelves, indicate that high concentrations of organic matter exist in seawater for centuries at the depth of basal freezing.

  20. Experiencia a largo plazo con la operación de Ross en pacientes pediátricos

    Directory of Open Access Journals (Sweden)

    José M. Caffarena Calvar

    2008-07-01

    Conclusions: The Ross and Ross-Konno operations have changed the prognosis of pediatric patients with complex disease of the valve and aortic root. There is growth of the neo-aortic root in young patients. Sinotubular dilatation of the autograft with neoaortic valve insufficiency has been detected in patients with previously dilated aortic root when root replacement technique was performed. The best results are obtained in the younger andlower weight patients with complex left ventricular outflow obstruction without root dilatation. A close follow-up of patients with aortic root dilatation is mandatory to definitely validate the Ross procedure over aortic prosthesis.

  1. Sputtering of water ice

    International Nuclear Information System (INIS)

    Baragiola, R.A.; Vidal, R.A.; Svendsen, W.; Schou, J.; Shi, M.; Bahr, D.A.; Atteberrry, C.L.

    2003-01-01

    We present results of a range of experiments of sputtering of water ice together with a guide to the literature. We studied how sputtering depends on the projectile energy and fluence, ice growth temperature, irradiation temperature and external electric fields. We observed luminescence from the decay of H(2p) atoms sputtered by heavy ion impact, but not bulk ice luminescence. Radiolyzed ice does not sputter under 3.7 eV laser irradiation

  2. The Northeast Greenland Shelf - Evidence of the existence of a pronounced salt-province

    Science.gov (United States)

    Schmitz, T.; Jokat, W.

    2003-04-01

    The Northeast Greenland shelf (NEGS) is the part of the continental margin of east Greenland located between the Jan Mayen Fracture Zone at about 72°N in the south and the Spitzbergen Fracture Zone at 81°N in the north. The eastern boundary, at the shelf edge, is the approximate position of the boundary between continental and oceanic crust and the western boundary is the coastline of Greenland. The shelf has a N-S orientation, is about 1000 km long, and between 125 km (southern part) and 380 km (at 78°N) wide. Based on present data the NEGS can be subdivided into a southern part influenced by Tertiary tectonism and volcanism (approx. 72°N to 75°N) and a northern, nonvolcanic, part (approx. 75°N to 81°N). Today the sedimentary history, stratigraphy, structure and origin of the basement below the sedimentary shelf south of 74°N are reasonable known, but only sparse information exists about the northern part of the shelf. Until 1990 there weren't any seismic lines north of 74°N, and all interpretations of stratigraphy and basin structures of the northern part of the NEGS were based on aeromagnetic data. During the last decade, the first seismic lines were shot over the northern part of the shelf to give more detailed information about sediment thickness, stratigraphy, and the structure of the sedimentary shelf. The area under investigation lies on the nonvolcanic northern part of the shelf between 78°30'N and 81°N. The sea floor topography indicates some submarine banks with water depth as shallow as 30 m, which are separated by valleys up to 500 m deep. These valleys were formed through erosion processes caused by cyclic movements of big grounded glacier tongues during the last ice-ages with a maximum expansion during the Wisconsin-Weichselian glaciation. During two scientific expeditions with the German research icebreaker Polarstern in 1997 and 1999, more than 1100 km of multichannel seismic data were collected. The cruise tracks during seismic

  3. A glimpse beneath Antarctic sea ice: observation of platelet-layer thickness and ice-volume fraction with multi-frequency EM

    Science.gov (United States)

    Hendricks, S.; Hoppmann, M.; Hunkeler, P. A.; Kalscheuer, T.; Gerdes, R.

    2015-12-01

    In Antarctica, ice crystals (platelets) form and grow in supercooled waters below ice shelves. These platelets rise and accumulate beneath nearby sea ice to form a several meter thick 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 for ice - ocean interactions. 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 sub-ice platelet-layer thickness and electrical conductivity, and calculated ice-volume fractions from platelet-layer conductivities using Archie's Law. The thickness results agreed well with drill-hole validation datasets within the uncertainty range, and the ice-volume fraction also yielded plausible results. Our findings imply that multi-frequency EM induction sounding is a suitable approach to efficiently map sea-ice and platelet-layer properties. However, we emphasize that the successful application of this technique requires a break with traditional EM sensor calibration strategies due to the need of absolute calibration with respect to a physical forward model.

  4. Physical, chemical, and biological data collected during two research cruises in the Ross Sea, Antarctica from December 2004 to January 2005 and October to November 2005 for Ross Sea Sulfur Dynamics study (NODC Accession 0117322)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This dataset contains transect data from two research cruises to the Ross Sea, Antarctica, aboard the RV Nathaniel B. Palmer (NBP) in December 2004 to January 2005...

  5. Representing grounding line migration in synchronous coupling between a marine ice sheet model and a z-coordinate ocean model

    Science.gov (United States)

    Goldberg, D. N.; Snow, K.; Holland, P.; Jordan, J. R.; Campin, J.-M.; Heimbach, P.; Arthern, R.; Jenkins, A.

    2018-05-01

    Synchronous coupling is developed between an ice sheet model and a z-coordinate ocean model (the MITgcm). A previously-developed scheme to allow continuous vertical movement of the ice-ocean interface of a floating ice shelf ("vertical coupling") is built upon to allow continuous movement of the grounding line, or point of floatation of the ice sheet ("horizontal coupling"). Horizontal coupling is implemented through the maintenance of a thin layer of ocean ( ∼ 1 m) under grounded ice, which is inflated into the real ocean as the ice ungrounds. This is accomplished through a modification of the ocean model's nonlinear free surface evolution in a manner akin to a hydrological model in the presence of steep bathymetry. The coupled model is applied to a number of idealized geometries and shown to successfully represent ocean-forced marine ice sheet retreat while maintaining a continuous ocean circulation.

  6. CLOUDS IN THE COLDEST BROWN DWARFS: FIRE SPECTROSCOPY OF ROSS 458C

    International Nuclear Information System (INIS)

    Burgasser, Adam J.; Simcoe, Robert A.; Bochanski, John J.; Saumon, Didier; Mamajek, Eric E.; McMurtry, Craig; Pipher, Judith L.; Forrest, William J.; Cushing, Michael C.; Marley, Mark S.

    2010-01-01

    Condensate clouds are a salient feature of L dwarf atmospheres, but have been assumed to play little role in shaping the spectra of the coldest T-type brown dwarfs. Here we report evidence of condensate opacity in the near-infrared spectrum of the brown dwarf candidate Ross 458C, obtained with the Folded-Port Infrared Echellette (FIRE) spectrograph at the Magellan Telescopes. These data verify the low-temperature nature of this source, indicating a T8 spectral classification, log 10 L bol /L sun = -5.62 ± 0.03, T eff = 650 ± 25 K, and a mass at or below the deuterium burning limit. The data also reveal enhanced emission at the K band associated with youth (low surface gravity) and supersolar metallicity, reflecting the properties of the Ross 458 system (age = 150-800 Myr, [Fe/H] = +0.2 to +0.3). We present fits of FIRE data for Ross 458C, the T9 dwarf ULAS J133553.45+113005.2, and the blue T7.5 dwarf SDSS J141624.08+134826.7B, to cloudless and cloudy spectral models from Saumon and Marley. For Ross 458C, we confirm a low surface gravity and supersolar metallicity, while the temperature differs depending on the presence (635 +25 -35 K) or absence (760 +70 -45 K) of cloud extinction. ULAS J1335+1130 and SDSS J1416+1348B have similar temperatures (595 +25 -45 K), but distinct surface gravities (log g = 4.0-4.5 cgs versus 5.0-5.5 cgs) and metallicities ([M/H] ∼ +0.2 versus -0.2). In all three cases, cloudy models provide better fits to the spectral data, significantly so for Ross 458C. These results indicate that clouds are an important opacity source in the spectra of young cold T dwarfs and should be considered when characterizing planetary-mass objects in young clusters and directly imaged exoplanets. The characteristics of Ross 458C suggest that it could itself be regarded as a planet, albeit one whose cosmogony does not conform with current planet formation theories.

  7. Helicopter Icing Review.

    Science.gov (United States)

    1980-09-01

    helicopter (i.e. in an icing tunnel or engine test cell ) and therefore can be subjected to controlled icing where spe- cific problems can be safely...evaluation. 69 2.2.5.2 Ice Protection Systems Demonstration Many of the systems noted in 2.2.5.1 can be evaluated in icing test cells or icing wind tunnels...Figure 2-32 illustrates a typical rotor deice system control arrangement. 104 (N >4 A.dO INaH -E- C4) uo U En 9 E-1 H m I ~z O 04 04iH U 0 El4 E-f C E

  8. Seasonal variation of air-sea CO2 fluxes in the Terra Nova Bay of the Ross Sea, Antarctica, based on year-round pCO2 observations

    Science.gov (United States)

    Zappa, C. J.; Rhee, T. S.; Kwon, Y. S.; Choi, T.; Yang, E. J.; Kim, J.

    2017-12-01

    The polar oceans are rapidly changing in response to climate variability. In particular, augmented inflow of glacial melt water and shrinking sea-ice extent impacts the polar coastal oceans, which may in turn shift the biogeochemistry into an unprecedented paradigm not experienced previously. Nonetheless, most research in the polar oceans is limited to the summer season. Here, we present the first direct observations of ocean and atmospheric pCO2 measured near the coast of Terra Nova Bay in the Ross Sea, Antarctica, ongoing since February, 2015 at Jang Bogo Station. The coastal area is covered by landfast sea-ice from spring to fall while continually exposed to the atmosphere during summer season only. The pCO2 in seawater swung from 120 matm in February to 425 matm in early October. Although sea-ice still covers the coastal area, pCO2 already started decreasing after reaching the peak in October. In November, the pCO2 suddenly dropped as much as 100 matm in a week. This decrease of pCO2 continued until late February when the sea-ice concentration was minimal. With growing sea ice, the pCO2 increased logarithmically reaching the atmospheric concentration in June/July, depending on the year, and continued to increase until October. Daily mean air-sea CO2 flux in the coastal area widely varied from -70 mmol m-2 d-1 to 20 mmol m-2 d-1. Based on these observations of pCO2 in Terra Nova Bay, the annual uptake of CO2 is 8 g C m-2, estimated using the fraction of sea-ice concentration estimated from AMSR2 microwave emission imagery. Extrapolating to all polynyas surrounding Antarctica, we expect the annual uptake of 8 Tg C in the atmosphere. This is comparable to the amount of CO2 degassed into the atmosphere south of the Antarctic Polar Front (62°S).

  9. Influence of estuaries on shelf foraminiferal species

    Digital Repository Service at National Institute of Oceanography (India)

    Nigam, R.

    Dabhol-bhatkal stretch of the west coast of India is marked by a number of estuaries. Cavarotalia annectens is selected to monitor the influence of these estuaries on the inner shelf foraminiferal fauna. The percentage distribution of this