A 700,000 yr record of glacial flour flux to Lake Junín, Peru

Lake Junín (11.0°S, 76.2°W) is an intermontane lake at an elevation of 4085 masl in Junín, Peru. The lake spans ~300 km² and has a water depth of ~12m. It is dammed at its northern and southern ends by glacial alluvial fans that have been dated >250 ka, indicating that the lake is at least this old.  Lake Junín has never been overridden by ice in the past 1 million years making it one of the few lakes in the tropical Andes that predates the last maximum extent of glaciation and has a continuous record of waxing and waning of nearby Cordilleran glaciers. In July and August of 2015, piston cores were obtained from three sites in Lake Junin. These cores were overlapped to form a continuous record of ~7 glacial and interglacial cycles spanning the past ~700 ka. Siliciclastic flux, magnetic susceptibility (MS), mean grain size, and Ti/Ca of sediments from Lake Junín provide proxy records of glacial erosion and extent of ice in adjacent valleys. Comparison of these proxies with a local speleothem record of regional hydrologic balance reveals that during marine isotope stages 2 and 3 glacial erosion was strongly coupled to regional precipitation. However, beginning ~22 ka, proxies of glacial erosion began to decline in spite of sustained moist conditions. This indicates that the tropical Andes began to warm several millennia prior to the onset of the decline in global ice volume and increase in sea level.