HIGH-RESOLUTION MULTIPROXY RECORDS OF LATE QUATERNARY ENVIRONMENTAL CHANGE FROM ALPINE LAKES IN THE TROPICAL ANDES OF ECUADOR AND PERU

Downcore changes in sedimentologic and geochemical parameters provide continuous, high-resolution records of glacier extent, storm-induced sedimentation, and hydrologic balance. Here we review results of records spanning the last 12,000-25,000 cal years from 8 glacial lakes located from 2°45’-13°54’S and from 2500-4920 m asl. The first-order change in sedimentation seen in all lakes is an abrupt transition from inorganic (<1% TOC) sediment to organic-rich (>10% TOC) sediment, which reflects deglaciation of upvalley cirques. Accordingly, deglaciation from M.I.S. 2 ice limits commenced more than 18,520 cal yr B.P.; lakes located in catchments with cirque headwalls <5000 m asl record complete and final deglaciation between 16,330 and 11,400 cal yr B.P. Lakes in catchments with headwall elevations >5500 masl record the continuous presence ice throughout the late-Quaternary. Laguna Pacococha, adjacent to the Quelccaya Ice Cap (QIC; 4920 masl) in southeastern Peru, reveals complete disappearance of the QIC 12,000 cal yr B.P. and reappearance 5000 cal yr B.P. The concentration of glacier flour in alpine lakes in catchments that have been continuously occupied by glaciers reveals rapid deglaciation midway through the Younger Dryas, a minimum in glacial activity during the early Holocene, and an increase in glacial activity beginning ~8000 cal yr B.P. that culminated in maximum Holocene glacial activity ~1600 cal yr B.P. Superimposed on these overall trends of glacial flour production are oscillations at millennial-centennial time scales. Records of El Niño-induced sedimentation from southern Ecuador and a d¹⁸O record of hydrologic balance from Lake Junin, Peru reveal a progressive increase in moisture from both the tropical Pacific and tropical Atlantic beginning in the early-mid Holocene. Superimposed on this Holocene trend are oscillations at millennial-centennial scales, and these oscillations correspond closely with the aforementioned trends in glacial flour production suggesting a climatic linkage among ENSO activity, glacier mass balance, and regional hydrologic balance.