Fast-flow signature in the stagnated Kamb Ice Stream, West Antarctica

Among the major ice streams that drain West Antarctica, Kamb Ice Stream (formerly called Ice Stream C) is unique in that it stagnated ∼150 yr ago, but its former fast-flow conditions are virtually unknown. Here we present surface-based radar profiles of the ice stream's undulating internal stratigraphy, which records these conditions. Our analysis of the profiles indicates that pre stagnation flow velocities, averaged over a period <740 yr, exceeded 350 m·yr−1 in the trunk of the ice stream. This velocity constraint would be lower if the ice had been thickening (higher if thinning), but suggests mass loss from the ice-stream catchment that is of sufficient magnitude to reverse the gain estimated for today's Siple Coast region. Analysis of other ice streams would allow comparison of velocities over millennial time scales with observations of present-day velocities, useful for evaluating how West Antarctic ice drainage has evolved

State of balance of the cryosphere

This is the published version, also available here: http://dx.doi.org/10.1029/91RG00784.The current state of balance of the terrestrial ice sheets and glaciers is poorly known. What little data are available suggest that, worldwide, mountain glaciers have receded since about the mid-nineteenth century, with occasional interruptions of the retreat. The interior part of the Greenland ice sheet appears to be thickening or in near equilibrium, but this ice sheet may be thinning in the coastal areas. Estimates of the mass balance of the Antarctic ice sheet suggest that it is positive, although the error limits allow for a slightly negative balance. There is an urgent need to greatly improve the current estimates and to monitor the ice sheets continuously for changes in volume and extent. A program based on satellite observation techniques, in cooperation with ground-based surveys repeated over long time periods (many years or decades), appears to be most opportune to achieve this

Radiocarbon constraint on relict organic carbon contributions to Ross Sea sediments

Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 7 (2006): Q04012, doi:10.1029/2005GC001097.We estimate the relative contribution of relict organic matter to the acid-insoluble organic carbon (AIOC) fraction of surface sediments from Ross Sea, Antarctica, on the basis of 14C abundance. The bulk isotopic characteristics of AIOC can largely be explained by simple two-source models of modern and relict organic carbon, when samples are grouped according to two geographical regions, namely, southwestern and south central Ross Sea. This spatial variability in relict organic carbon could be controlled by proximity to the edge of the Ross Ice Shelf and ice drainage areas. Radiocarbon abundance in the AIOC is potentially an excellent tool to estimate the contribution of relict organic carbon in the Antarctic margin sediments.This work was partly supported by a grant from Japan Society for the Promotion of Science to N.O

Anatomy of terminal moraine segments and implied lake stability on Ngozumpa Glacier, Nepal, from electrical resistivity tomography (ERT)

This research was supported financially by the European Commission FP7-MC-IEF (PIEF-GA-2012-330805), the University Centre in Svalbard (UNIS), National Geographic Society GRANT #W135-10.Moraine-dammed lakes at debris-covered glaciers are becoming increasingly common and pose significant outburst flood hazards if the dam is breached. While moraine subsurface structure and internal processes are likely to influence dam stability, only few sites have so far been investigated. We conducted electrical resistivity tomography (ERT) surveys at two sites on the terminal moraine complex of the Ngozumpa Glacier, Nepal, to aid assessment of future terminus stability. The resistivity signature of glacier ice at the site (100-15 kΩ m) is more consistent with values measured from cold glacier ice and while this may be feasible, uncertainties in the data inversion introduce ambiguity to this thermal interpretation. However, the ERT data does provide a significant improvement to our knowledge of the subsurface characteristics at these sites, clearly showing the presence (or absence) of glacier ice. Our interpretation is that of a highly complex latero-terminal moraine, resulting from interaction between previous glacier advance, recession and outburst flooding. If the base-level Spillway Lake continues to expand to a fully formed moraine-dammed glacial lake, the degradation of the ice core could have implications for glacial lake outburst risk.Publisher PDFPeer reviewe