Glacial sediment-landform associations and paleoclimate during the last glaciation, Strait of Magellan, Chile

Glacial sediments and landforms preserved beside the Strait of Magellan rec ord repeated advances of an outlet of the Patagonian Icefield during and fo llowing the last glacial maximum (LGM; similar to 25,000-14,000 C-14 yr B.P ,). Ice-marginal landform assemblages consist of thrust moraine complexes, kame and kettle topography, and lateral meltwater channels, very similar to those found at the margins of modern subpolar glaciers. Taken together wit h other forms of paleoenvironmental evidence, the landform assemblages show that, during the LGM and late-glacial time, permafrost occurred near sea l ever in southernmost South America. This finding implies that mean annual t emperatures were similar to 7-8 degrees C lower than at present, somewhat l ower than those reconstructed by current glacier-climatic models. Compariso n,vith precipitation-temperature relationships for modern glaciers suggests , in addition, that precipitation levels were lower than today. Reduced gla cial-age precipitation may have resulted from a precipitation shadow induce d by the Patagonian Icefield, an equatorward migration of the average posit ion of westerly cyclonic storm tracks in the southern midlatitudes, or both these factors. (C) 2000 University of Washington.