HOLOCENE CLIMATE AND GLACIER VARIABILITY RECORDED IN LAKE AND BOG SEDIMENTS FROM THE SOUTHERN PERUVIAN ANDES

Lake and bog sediments preserve high-resolution records of environmental change that significantly improve our knowledge of the timing and extent of glaciation. Tropical glacier fluctuations are among the most valuable indicators of regional climatic forcings because these glaciers respond sensitively to small climate shifts, but continuous sediment records of past glacier activity remain relatively scarce. Here we present results from two alpine valleys in the Cordillera Vilcabamba (13°20’S latitude) of southern Peru that contain continuous records of clastic sediment deposition for the last ~12,000 years. The study location fills a major geographic gap in available climate proxy data and offers opportunities to combine intercalated lake and bog sediments with precisely-dated moraine sequences. Our regional glacial and climate record is developed using lake and bog deposits characterized by alternating inorganic and organic-rich laminae. Analyses include AMS radiocarbon dating, sedimentological studies, clastic flux, and magnetic susceptibility on seven sediment cores recovered from three bogs enclosed immediately upvalley from ¹⁰Be-dated moraines. Trends in clastic flux and magnetic susceptibility indicate that glaciers began to retreat by ~9,500 cal yr BP, and are consistent with a readvance during the late Holocene. A prominent peak in magnetic susceptibility at 1650 cal yr BP is present in four out of seven sediment cores and serves as a chronostratigraphic marker. Ongoing efforts are focused on developing detailed records of biogenic silica and clastic sediment flux, and further augmenting the ¹⁰Be moraine chronology with precise limiting radiocarbon ages.