Recent glacial history and rapid ice stream retreat in the Amundsen Sea

Abstract

Microfossil analyses of core top samples from 20 sites in the eastern and southern Amundsen Sea delimit three biotic provinces, which are related in part to the activity of a large ice stream and modern sea ice distribution. In Recent sediments on the Outer Shelf, planktonic and calcareous benthic foraminifera are abundant, but diatoms are rare. Here, low diatom abundances in sediments, despite high abundances in the overlying sea ice, are attributed to nondeposition caused by ocean currents. Pine Island Bay sediments are almost barren of microfossils, even though diatoms are abundant in overlying surface waters. We attribute this discrepancy to deposition of exclusively non‐organic sediments beneath a former extension of the floating terminus of Pine Island Glacier, which probably retreated from this area during the last century. The polynya which occupies this area during present‐day summers is probably so recent a feature that little or no biogenic sediment has accumulated. Recent sediments in the Eastern Margin Province, between Pine Island Bay and the Outer Shelf, contain abundant diatoms and arenaceous foraminifera. High diatom abundances here probably record the presence of the Amundsen Sea polynya during the last few millennia. The presence of a compact diamicton beneath Recent sediments on the Outer Shelf and in the Eastern Margin Province suggests that grounded ice formerly occupied the Amundsen Sea shelf with ice streams in deep, elongated troughs. These ice streams may have retreated up to 200 km during the Holocene.