Magnetic Data from Subglacial Clasts, West Antarctic Ice Sheet

The goal of this collaborative pilot project was to obtain the first petrological, geochemical, magnetic characterization of subglacial and basal sediments recovered from boreholes drilled to the base of the West Antarctic Ice Sheet (WAIS). Over the last two decades, samples of subglacial sediment (till) and basal debris were obtained from several locations across the WAIS (see map of locations, Vogel, 2004). Properties of the subglacial till layer were the specific target of hot water drilling at several Whillans, Kamb and Bindschadler Ice Stream (WIS, KIS and BIS) locations. At each site (UpB, newUpB, UpC, UpD, Siple Dome) piston cores up to 3 m long were recovered. Small amounts of subglacial till were recovered when drilling through Crary Ice Rise (CIR). Debris in basal ice (henceforth basal ice debris) was present in ice cores from Byrd Station, Unicorn, Siple Dome (H. Engelhardt and T. Gow personal communication) and the UpC Sticky Spot.

The goal of the magnetics part of our pilot project was to provide rock magnetic data that could help identify the provenance of bedrock clasts found in the ice cores. Of particular interest was the identification of basaltic clasts that could be from the Cenozoic volcanoes beneath the WAIS.

Grunow measured the intensity and susceptibility on more than 550 clasts found at the base of ice-cores in West Antarctica (see attached figure of magnetic data from granitic clasts). The work included rock density measurements necessary for volume correction of the magnetic data. Susceptiblity was measured on a KLY-3 kappabridge and intensity on a JR5A magnetometer for 550 clasts. Due to the irregular size of the pebbles,all of the data have been normalized to 1 cubic centimeter so that comparisons can be made with existing rock magnetic data found in the Antarctic Rock Magnetic Property database on the web.