ICE-RAFTED DEBRIS ASSOCIATED WITH BINGE PURGE OSCILLATIONS OF THE LAURENTIDE ICE-SHEET

The North Atlantic sediment record suggests quasi-periodic (7000- to 1 2,000-year period) ice-rafted debris (IRD) depositions during at least the last glacial period. The cause of these Heinrich events, as they are commonly known, is not fully understood; however, they may point t o surges of the ice stream that drained the Hudson Bay/Hudson Strait r egion of the Laurentide Ice Sheet. We investigate a simple conceptual model of ice stream instability (the binge/purge model) to suggest way s in which the ice stream could have entrained sufficient debris to ac count for the estimated mass of IRD associated with a typical Heinrich IRD layer in the North Atlantic (1.0 +/- 0.3 x 10(15) kg). We find th at freezing of debris-laden ice at the bed of the ice stream during th e brief (almost-equal-to 750 years) surge phase of the ice stream's hy pothesized binge/purge cycle can incorporate up to 5.1 x 10(15) kg. Th is amount is sufficient to meet the constraints of the North Atlantic sediment record but by no means verifies the binge/purge model as the cause of Heinrich events.