A RECORD OF LATE HOLOCENE CLIMATE CHANGE FROM LAGUNA AMARGA, A SMALL SALINE LAKE IN SOUTHERN PATAGONIA

We investigated the geochemistry of Laguna Amarga (50° 58.5¢ S, 72° 45¢ W), a small, shallow (2.6 m mean depth), hydrologically closed saline lake, which borders Torres del Paine National Park in southernmost Chile. Significant changes in the lithology and geochemistry of sediments from a 1 m core suggest sharp fluctuations in the lake water balance which is strongly linked to the intensity of the westerly winds that carry moisture to the region. Results from our analysis of Mg/Ca and Sr/Ca ratios from ostracod calcite indicate fluctuations in the temperature and salinity of the lake over approximately the past 1000 years. A slight decreasing trend in these ratios towards the present suggests a transition to somewhat wetter and cooler conditions in the region of the lake. An analysis of the mineralogy and magnetic susceptibility of the sediments reveals changes in the input of authigenic carbonates versus clastic materials derived from the surrounding cordillera and lake margins. This includes two episodes of highly elevated clastic input as lake level dropped in response to arid conditions. We compare this new record to others from southern Patagonia and the broader region that is influenced by the Southern Hemisphere westerlies.