Chronology of a Wisconsin age proglacial lake in the Miers Valley, Antarctica

Mapping and oxygen isotopic, C‐14, and U/Th analyses of lacustrine sediments have shown that a lake (Glacial Lake Trowbridge) proglacial to the Ross Sea I Ice Sheet occupied Miers Valley from at least 23 000 years B.P. until 10 000 years B.P. This lake was at least 80 m deep and extended to more than 156 m above present sea level at its maximum extent 18 000–19 000 years ago. The lake was filled with waters with a similar isotopic composition to the modern Koettlitz Glacier. By 13 000–14 000 years B.P. evaporation had considerably reduced the size of the lake and resulted in the precipitation of calcite and gypsum evaporites. The isotopic composition of abundant sulphates within the evaporite sequences shows that although they were precipitated from isotopically depleted glacial meltwaters, the sulphates originated from seawater. Lake occupation of the Miers Valley was synchronous with proglacial lakes occupying other valleys in southern Victoria Land during the period of late Wisconsin glacial maximum. These appear to have been an indirect consequence of glacial eustatic sea level lowering, and a direct consequence of an altered meltwater budget in the valleys.