MORAINE CHRONOLOGIES COMBINED WITH LAKE RECORDS OF GLACIER ACTIVITY FROM THE PRE-LAST GLACIAL MAXIMUM TO THE LATE HOLOCENE IN CENTRAL PERU

Fluctuations in small tropical mountain glaciers serve as sensitive indicators of variations in past and present-day climate. Most of the world’s modern tropical glaciers are in the Peruvian Andes, where growing numbers of late Pleistocene to Holocene glacial records are emerging. Here we combine new and published ¹⁰Be moraine chronologies with high-resolution lacustrine records from the Huaguruncho massif (10°32’S, 75°56’W) and the Cordillera Blanca (9°49’S, 77°18’W) to reconstruct a multiproxy history of glacier activity in central Peru. Our composite regional record reveals the occurrence of multiple glacial episodes from the pre-Last Glacial Maximum to the Little Ice Age. At the Huaguruncho massif, ¹⁰Be exposure ages obtained from moraine sequences in a south-facing cirque indicate at least three major glacial stages spanning the Lateglacial to the Little Ice Age. Additional exposure ages are in development from moraines with stratigraphic positions that likely correspond to the Last Glacial Maximum and older glacial stages. Basal radiocarbon ages from lake sediments are consistent with ¹⁰Be exposure ages on outboard moraines enclosing the depositional basins when the ¹⁰Be ages are calculated using recently developed ¹⁰Be production rates in the high Andes. In general, the lake sediment records reveal that over that last 12,000 years the influx of glacigenic sediment (low organic carbon, high magnetic susceptibility and bulk density) 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 moraine ages and lake records at Huaguruncho are broadly correlative with those from the Cordillera Blanca, as well as moraine chronologies from the Cordillera Vilcabamba in southern Peru. The correspondence in age between moraine sequences and in lake sediment stratigraphy on opposite sides of the Andes suggests regional-scale coherency of multiple glacial fluctuations across the central Peruvian Andes from the late Pleistocene to the late Holocene, implying spatially uniform climate drivers in this region.