A LACUSTRINE RECORD OF LATE PLEISTOCENE CLIMATIC-CHANGE IN THE SUBTROPICAL ANDES

Significant changes in moisture have occurred in the subtropical Andes over the last 20,000 years as evidenced by shorelines of high lake st ands and extensive glacial moraines. Lakes with sediment records that reflect these moisture changes are present in some valleys where headw alls are below the snowline elevation reached during the latest Pleist ocene glacial culmination (14,000 - 12,000 BP). One such lake, Laguna Kollpa Kkota, which is located on the western slope of the eastem cord illera in Bolivia, has basal radiocarbon dates of about 20,000 BP. The snowline reconstruction for this site confirms earlier work in the re gion that suggests late Pleistocene snowline depression was less than 500 m, or half the amount generally considered for low-latitude region s during the last glacial maximum. The sediment stratigraphy from Lagu na Kollpa Kkota indicates that sediment accumulation and organic carbo n deposition increased significantly from 14,000 to 12,600 BP. This in crease in sedimentation may have resulted from greater inwash to the l ake and higher productivity in the lake itself as a result of higher l ake levels. These changes could reflect the postulated late Pleistocen e increase in precipitation that led to the formation of Lago Tauca on the Altiplano and to glacial advances in the surrounding cordillera.