Constraints on Cosmic Neutrino Fluxes from the ANITA Experiment

We report new limits on cosmic neutrino fluxes from the test flight of the Antarctic Impulsive Transient Antenna (ANITA) experiment, which completed an 18.4 day flight of a prototype long-duration balloon payload, called ANITA-lite, in early 2004. We search for impulsive events that could be associated with ultra-high energy neutrino interactions in the ice, and derive limits that constrain several models for ultra-high energy neutrino fluxes. We rule out the long-standing Z-burst model as the source for the ultra-high energy cosmic rays.Comment: 4 pages, 3 figures, accepted to PR

Is Vertical Shear in an Ice Shelf Negligible?

Vertical shear stress in ice shelves cannot be precisely zero, since the upper and lower surfaces are generally not parallel. By performing stress balance on a vertical column in an ice shelf we calculate what its magnitude must be. This is done for an unconfined glacier tongue and for a confined bay ice shelf; first, using the assumption of constant temperature and density with depth, and secondly, using realistic data and profiles for Erebus Glacier tongue and for the Amery ice shelf. Shear stresses increase almost linearly with depth and are proportional to surface slope. For Erebus Glacier tongue the shear stress is at most 5% of the magnitude of the direct stress deviators and its action through the ice shell should result in differential movement of 1.8 cm a−1 between the top and bottom of the ice shelf. For the Amery ice shelf, the shear stress is at most 0.4% of the magnitude of the direct stress deviators and this should lead to differential movement of 2.5 cm a−1 between the top and bottom of the ice shelf. Shear stresses are therefore generally negligible in comparison with direct stress deviators and can be ignored when considering the overall dynamics of ice shelves. Differential movement is unlikely to be detectable

Subglacial and Seabed Topography, Ice Thickness and Water Columm Thickness in the Vicinity of Filchner-Ronne-Schelfseis, Antarctica

The seabed morphology beneath the ice shelf is dominated by a slope down towards the interior of the continent. Deep troughs, possibly glacially deepened, run beneath the eastern and weatern sides of the ice shelf and cross the continental shelf. An area of small water column thickness to the north-west of Berkner Island suggests that extensive grounding could occur after a relatively small change in the ice shel

Melting of ice shelves and the mass balance of Antarctica

We calculate the present ice budget for Antarctica from measurements of accumulation minus iceberg calving, run-off and in situ melting beneath the floating ice shelves. The resulting negative mass balance of 469 Gt year−1 differs substantially from other recent estimates but some components are subject to high temporal variability and budget uncertainties of 20–50%. Annual accumulation from an earlier review is adjusted to include the Antarctic Peninsula for a total of 2144 Gt year−1. An iceberg production rate of 2016 Gt year−1 is obtained from the volume of large icebergs calculated from satellite images since 1978, and from the results of an international iceberg census project. Ice-shelf melting of 544 Gt year−1 is derived from physical and geochemical observations of meltwater outflow, glaciological field studies and modeling of the sub-ice ocean circulation. The highest melt rates occur near ice fronts and deep within sub-ice cavities. Run-off from the ice-sheet surface and from beneath the grounded ice is taken to be 53 Gt year−1. Less than half of the negative mass balance need come from the grounded ice to account for the unattributed 0.45 mm year−1 in the IPCC “best estimate” of the recent global sea-level rise

Flow lines on Antarctic ice shelves

Satellite images of Ronne and Filchner ice shelves show a variety of surface features many of which are believed to indicate flow lines in the ice. Sufficient imagery is now available from Landsat satellites to plot these features from mosaics. Although some of the features have been recognized from aircraft, it was not until an overall view was provided that the true extent of the features and their relationship to the major ice streams became apparent. Using this evidence together with published ice thickness data from radio echo and seismic sounding, flow patterns within the ice shelves and tributary glaciers can be inferred