GLACIER READVANCES IN THE ANDES AT 12500-10000 YR BP - IMPLICATIONS FOR MECHANISM OF LATE-GLACIAL CLIMATIC-CHANGE

Radiocarbon dates from two sites in the Andes (Ecuador and Peru) confirm that glaciers culminated a readvance after 11 000 yr BP. A moraine stage, equivalent in altitude and position relative to existing glaciers, is present in most glacierized ranges, but its age is equivocal. Broadly limiting dates from Colombia and Peru suggest that the stage may be Late-glacial, as it is younger than 12 100 yr BP, but formed before the early Holocene; in southern Chile a comparable moraine stage is older than ca. 91 00 yr B P. Andean glaciers appear to have advanced at least twice during the Late-glacial interval. Glacier reconstruction from these moraine limits suggests depression of the equilibrium line altitude by at least 300-400 m in the northern and north-central Andes, and possibly less than this farther south. Late-glacial climatic change occurred globally and possibly reflects North Atlantic temperature and circulation changes forced by deglaciation of the northern ice sheets, migrations north and south of the Atlantic Polar Front, and the switching off and on of a 'dust pump' in low mid-latitudes.