Nature of basal debris in the GISP2 and Byrd ice cores and its relevance to bed processes

Abstract

Successful core-drilling to bedrock of both the Greenland and Antarctic ice sheets offers unique opportunities for examining processes acting at the bed. At Byrd Station, Antarctica, penetration of the bed was accompanied by upwelling of glacial meltwater into the drillhole. The nature and disposition of sediment in the 4.83 m thick debris-rich basal ice, together with stable-isotope and gas analyses of the enclosing ice, confirm that incorporation of the debris occurred simultaneously with periodic “freeze-on” of basal meltwater. Currently, the presence of substantial meltwater at the ice/rock interface likely precludes any erosive activity at the bed. At GISP2, Greenland, basal silly ice, 13.1 m thick, is currently frozen to the bed at −9° C. Limited studies of the silty ice at GISP 2, together with results of more comprehensive investigations obtained by GRIP researchers on basal ice at a companion site at Summit indicate that the sediment-bearing basal ice likely formed in the absence of an ice sheet and was therefore unrelated to direct interaction of the present ice sheet with its bed. The fact that the basal ice at Summit is frozen to the bottom also precludes any likelihood of erosive activity at the bed.