Is there direct evidence for late Quaternary collapse of the West Antarctic ice sheet?

By studying diatoms recovered from sediment taken from beneath the West Antarctic ice sheet (Ice Stream B), Scherer (1991) concluded that this feature must have collapsed at least once during the past 600 kyear and that the two likely candidates for time of collapse were oxygen-isotope stage 11 (362–423 kyear BP) and sub-stage 5e (110–128kyear BP). This conclusion does not stand up to critical examination of the data, however. Specifically, the diatom datum level, the last occurrence of Actinocyclus ingens, used to constrain the 600 kyear date is diachronous into higher latitudes and does not apply in sediments recovered from near Antarctica. Secondly, the additional diatoms used to constrain the time of collapse to the late Quaternary either range before the late Quaternary or have no published geological record. In spite of this, there are data to suggest that one or more late Quaternary interglacial intervals were as warm as, or warmer than, the present. As yet, however, no direct evidence exists to incorporate a West Antarctic ice sheet collapse into these scenarios. It is suggested that this debate is best resolved by study of deep-sea sediments of late Quaternary age recovered from around the Antarctic continent.