Ice-Core Analysis on the Siple Coast of West Antarctica

Abstract

Pit and core studies at the Upstream Β camp (UpB) and ridge BC (BC) on the Siple Coast, West Antarctica, have revealed a number of interesting results. Both sites have 10 m temperatures near −26.5°C and accumulation rates near 0.09 m a−1 of ice. At both sites, the low densities of annual depth-hoar layers arise in the first year following snow deposition. Densification rates at UpB are accelerated compared to BC and to other sites, probably owing to stress enhancement of power-law-creep densification caused by the large longitudinal deviatoric stresses at UpB. The connectivity of firn, measured by the number of bonds per grain and by the fraction of total surface area per grain involved in bonds, correlates well with density and shows no significant dependence on grain-size. The longitudinal stresses at UpB cause the ice to develop a fabric of horizontally elongated bubbles and grains, interpenetrating grains, and strain shadows between about 30–70 m. Ice at BC below about 95 m shows rapid grain growth and development of a bimodal grain-size distribution, but no preferred orientation of grains or pores. The temperature-depth profile to 100 m at BC suggests a basal heat flux near 1.9 heat-flow units (HFU), typical of a region of active rifting. Surface-melt events occur about once every 50 years, and correlate well between UpB and BC.