Climate change in southern South America during the last 51 ka based on geochemical analyses of Laguna Potrok Aike sediments

Abstract

The climate archive Laguna Potrok Aike is located in a scarcely studied yet key area of the southern hemisphere. Recent studies on the role of the Southern Hemispheric Westerlies and the Southern Ocean circulation patterns in the global climate system stress the importance of this area. The Laguna Potrok Aike lacustrine sediment record covers the past 51 ka of environmental change. In order to capture the high variability in the climate system, high resolution analysis is particularly important. Therefore, aside from conventional methods and X-ray fluorescence scanning, infrared spectrometry, a relatively new method for analyzing sediment biogeochemistry, was applied. The Diffuse Reflectance Fourier Transform Infrared Spectrometry technique has proven to provide the most reliable calibration models for the analysis of the organic and carbonaceous fraction of the Laguna Potrok Aike sediments. For glacial sediments, paleoenvironmental reconstructions for Laguna Potrok Aike rely on proxies recording variations in organic versus clastic input to the lacustrine system. Increases in organic productivity (mainly aquatic moss growth and diatom blooms) may have been caused by ameliorations of the climatic conditions in the Laguna Potrok Aike area. At the same time, sediment availability for erosional processes would have been limited by the development of soils and vegetation cover. Intervals with more organic sediment compositions are often associated with periods of Antarctic warming (Antarctic A-events, the postglacial warming and the Younger Dryas chronozone). During intervals of highly clastic, coarse grained sediment we assume that lacking vegetation and erosion related to high waves and flash flood events increased sediment availability in the catchment and on the lake shore. The transport of this material to the lake center would have been facilitated by strong winds. The sediment is especially clastic and coarse grained during the presumably cold, arid and windy Oxygen Isotope Stage 2. Despite these conditions, the lake level must have remained relatively high during glacial conditions as inorganic carbonate is not precipitated until the end of the Late Glacial. Glacial high lake levels may be attributed to increased runoff over permafrost grounds, reduced evaporation due to colder temperatures and lacking influence of the Southern Hemispheric Westerlies. The southward shift of the Southern Hemispheric Westerlies over the latitudes of Laguna Potrok Aike is not assumed to have occurred prior to ca. 9.4 cal. ka BP; the onset of continuous inorganic carbonate precipitation. Throughout the Holocene the variability in the total inorganic carbon record shows the frequent lake level fluctuation probably related to shifts in the position of the Southern Hemispheric Westerlies.