HOLOCENE PROXY RECORDS OF HYDROLOGIC VARIABILITY FROM TWO CARBONATE LAKES, CORDILLERA HUAYHUASH, PERU

Rising interest in tropical climate has led to increased research utilizing tropical lucustrine proxies. Holocene hydrologic variability proxies from Laguna Susucocha and Laguna Huarmicocha (both ~10°S, ~4700 masl) were used to reconstruct Holocene lake conditions in the Cordillera Huayhuash, Peru. Laguna Susucocha is on the western side of the Range, Laguna Huarmicocha is on the eastern. Both carbonate lakes lie on limestone bedrock and are accumulating authegenic marl. A ~7-meter-long core was obtained from both lakes with a square-rod corer, away from terriginous inflow. Each core was dated with ~8 accelerator mass spectrometry radiocarbon dates. Magnetic susceptibility throughout both cores is generally negative or null, because of the dominance of carbonate sediment and peat. Flux rates of organic and inorganic carbon were determined from sedimentation rates and carbon coulometery. Inorganic carbon content ranges from 0 weight % to 10% in Laguna Susucocha, and from 0% to 2% in Laguna Haurmicocha. The abundance of organic carbon in Laguna Susucocha ranges from 2% to 49%, and from 0% to 35% in Laguna Haurmicocha. The flux of inorganic carbon in Laguna Susucocha generally rose to a peak ~7,000 years before present (yrBP), and fell since, while inorganic carbon flux to Laguna Haurmicocha generally remained constant, with only short term variations. Fluxes of organic carbon to Laguna Susucocha generally decreased through time, yet remained high, with several troughs, in Laguna Haurmicocha. Overall, inorganic and organic carbon fluxes are inversely related in Laguna Susucocha, suggesting biologic respiration may limit marl preservation through dissolution. High inorganic carbon flux may indicate periods of increased aridity from 9900 to 9300 yrBP in Laguna Haurmicocha, and from 7400 to 6700 yrBP in Laguna Susucocha. These intervals are included within a widely recognized interval of aridity in the South American tropics during the early Holocene. Bulk density in Laguna Susucocha sediments increased with time, which paired with generally decreasing organic carbon content probably indicates an increase in clastic sedimentation through time. Isotopic analyses of oxygen and carbon stable isotopes are being conducted on the Laguna Susucocha core.