LATE GLACIAL-HOLOCENE CLIMATE CHANGE RECORDED IN PROGLACIAL LAKE SEDIMENT CORES FROM THE HUAGURUNCHO MASSIF, EASTERN PERUVIAN ANDES

Alpine glaciers respond rapidly to changes in climate and this is recorded in lakes downvalley from former glaciers. These lakes provide continuous archives of glaciation and climate change that complement the inherently discontinuous records of glaciation preserved by moraines. The aim of this study is to generate a continuous record of glaciation from lake sediment cores on the southeastern side of the Huaguruncho Massif (5789 masl) in the eastern Peruvian Andes. The lakes studied are Laguna Jaico (10.56° S, 75.92° W; 4271 masl) and Laguna Yanacocha (10.56° S, 75.93° W; 4357 masl). The records generated will be combined with the record of glaciation preserved in upvalley moraines that are dated by the cosmogenic radionuclide ¹⁰Be. Lake cores were obtained using a Livingstone square-rod piston corer and a modified Nesje percussion corer from an inflatable raft. Cores were analyzed for total carbon (TC), total inorganic carbon (TIC), bulk density (BD), magnetic susceptibility (MS), stable isotopes of C and O, and major element composition (by scanning XRF). Age control was achieved by radiocarbon dating detrital charcoal fragments (>250 µm) isolated by sieving. Records of glacigenic sediment input from both lakes reveal similar patterns; here we describe the record from Laguna Jaico. Glacial flour dominates the core, with little to no organic material (TC<0.5%) and high MS (~100-200 SI) from the base of the core (363 cm depth) upcore to ~225 cm (>8260 cal yr BP); thereafter, the sediment record transitions into a brecciated, high TC (3-9%), low MS (~0 SI) section from ~225 – 90 cm depth (8260 –1430 cal yr BP). Extending upcore to the core top (<1426 cal yr BP), the record reveals a section of intermediate TC (0.1-3%) and low MS (0-1 SI). These results combined with those from Laguna Yanacocha show that over that last 12,000 years the influx of glacigenic sediment (low TC, high MS and BD) was low from ~13,000 –11,500 and from ~8500 – 1500 cal yr BP. In contrast, from ~11,500 – 8500 cal yr BP and since 1500 cal yr BP, glacigenic sediment input increased significantly. The intervals of increased glacigenic sediment input correlate well with the age of upvalley moraines, and with a recent summary of glacigenic sediment records from the western cordillera of central Peru (Stansell et al., 2013).