Oxygen isotope records from Patagonian lakes as recorders of past hydroclimate and southern westerlies dynamics - calibration, present achievements and future perspectives

Abstract

The belt of the Southern Hemisphere Westerlies (SHW) is considered to have played an important role for global climate change by controlling, for instance, carbon dioxide release from the Southern Ocean. However, testing such a hypothesis is hampered by inconsistencies between both models and proxy records regarding intensity and latitudinal shifts of the SHW belt in the late Quaternary. Oxygen isotope proxies from lake sediments can be used to tackle questions related to past atmospheric dynamics and associated hydrological changes in Patagonia, presently located in the SHW core region. The modern database needed for the calibration of isotope proxies from this remote region, however, is extremely poor. To overcome this lack of data, samples of surface water and precipitation from Chile and Argentina between 37 °S and 55 °S were investigated. The isotope ratios of precipitation strongly reflect spatiotemporal patterns caused by orographic, latitudinal, and continental effects. The water balance has a strong influence on the isotopic composition of lake water. Bathymetry, exposition to wind, inflows, outflows, and climatic settings influence the water balances of Patagonian lakes. Thus, the choice of adequate sites and of reliable recorders of the oxygen isotopic composition of the lake water is important. Methodologically refined isotope proxies, such as oxygen isotope ratios of aquatic cellulose and chironomid head capsules, provided promising results in our calibration studies. Combined oxygen isotope records from aquatic mosses and authigenic carbonates, continuously covering the last 26,000 years at the ICDP site Laguna Potrok Aike in the Patagonian steppe, indicated an early gradual warming starting around 18,000 years ago and extreme drought conditions in the early to mid-Holocene in the Patagonian steppe region. Future investigations will concentrate on densifying the isotopic network and comparing isotope records from multiple proxies and archives.