A MECHANISM FOR EMPLACEMENT AND CONCENTRATION OF DIATOMS IN GLACIGENIC DEPOSITS

The occurrence of diatoms (both marine and freshwater) in sediments be neath the West Antarctic Ice Sheet (WAIS) is suggestive of past ice-sh eet collapse. However, it is not the only model explaining such occurr ences. We propose another mechanism for introducing diatoms beneath ic e sheets by considering the fate of a diatom placed (by eolian process es) on top of an ice sheet. Mathematical modeling indicates that the r oute the diatom will take through the ice sheet is dictated by the bas al melting rate. If no basal melting takes place, flowlines will crop out at the ice-sheet margin. However, if basal melting is as low as 0. 01 m/yr the trajectories of all flowlines except for those nearest the margin will intersect the bed, with those diatoms deposited near the dome reaching the bed about halfway down the flowband. Larger values o f basal melting lead to the diatoms reaching the bed even faster and c loser to the point of origin. Tn light of these results, the presence of diatoms in sediments beneath the WAIS does not lead to a unique sol ution; it is not necessary to invoke past ice-sheet collapse to accoun t for their presence.