Comparison of oxygen isotope records from lakes and tree-rings in southern Patagonia (OXICLIM)

MAYR,C; DUBOIS, NATHALIE; LUCKE, A; MAUAD,MELINA; MASSAFERRO, JULIETA

Zaragoza

Congreso; 5th PAGES open science meeting; 2017

Past Global Changes

The project ?Synthesis of oxygen isotope proxies for climate reconstruction in southern Patagonia? (OXICLIM) is a recently launched Argentinean-German scientific initiative intended to combine regional continental climate archives by means of oxygen isotope records. The long-term aim of our study is to provide the foundation for quantitative climate reconstructions using statistical methods and mechanistic models. The study area, close to Los Glaciares National Park in southern Patagonia, exhibits a distinct humidity gradient evident as a transition from humid Andean Nothofagus forest to Patagonian steppe. Two sites represent the humid (Laguna Verde; 49.20°S; 72.98°W) and dry (Laguna Las Gemelas Este; 49.39°S; 72.90°W) ends of this gradient. For Laguna Verde we have found weak but significant negative correlations (r2=-0.28 and r2=-0.26) between tree-ring width and temperature variability and the SAM index, respectively. For both sites, we have extracted cellulose from tree-ring records from the lakes? catchments and analysed the 18O/16O ratios of single years. Concurrently, chironomid head capsules and aquatic cellulose were extracted from the lake sediments and their oxygen isotope ratios were analysed. Radiometric dating (210Pb, 137Cs) and tephrochronology provide a robust chronology for the sediment cores, whereas tree-rings are annually dated from present-day backwards. The oxygen isotope composition of tree-rings cellulose (?) from Nothofagus pumilio reflects the source water isotopic composition overprinted by plant physiology and air humidity changes. The lacustrine oxygen isotope records reflect the isotopic composition of lake water, which is determined by hydrological constrains such as the lake water balance and the origin of rainfall controlled by orography and trajectories of air masses. Combining both oxygen isotope archives - tree-rings and lake sediment - is a novel and challenging approach. The best test of its applicability is possible in areas with a strong hydrological gradient, such as along the eastern flanks of the Patagonian Andes