163-G 1.4

Climatic, biotic and geomorphic drivers of the isotopic composition of terrestrial organic matter transported through fluvial systems draining the NW Argentinian Andes

The key question which this project aims to answer is how tectonic processes such as mountain-range uplift affect atmospheric circulation patterns and enforce subsequent hydrological changes. The NW Argentine Andes are an ideal location to study these processes, due to unique and characteristic circulations patterns associated with the South American Low Level Jet (SALLJ) as part of the SAMS, which were established as a consequence of the topographic growth of the Andean orogen. Based on our previous studies, the imprint of these circulation patterns on modern stable water-isotope ratios is reasonably well understood. Here, we plan to conduct catchment investigations to understand and provide a sound base to decipher the development of such tectonically forced hydrological patterns during the geological past. In particular, we will study terrestrial climate archives in the intermontane basins along and across the NW Argentine Andes representing different episodes of range uplift and orographic-barrier formation during the last 10 Ma. As a paleohydrological proxy, we will employ the hydrogen stable isotope composition of leaf wax lipids (δDwax), which has been shown to record the δD values of meteoric plant-source water as well as terrestrial evapotranspiration, to identify changes in moisture source area (i.e. before and after the establishment of the SALLJ), and to record the onset of aridity in the basins of the orogen interior. In addition, the stable carbon-isotope composition of these compounds (δ13Cwax) will be analyzed to assess changes in vegetation cover from C3 to aridity adapted C4 plants. By taking this approach into the spatial domain, i.e. using multiple terrestrial archives from different basins along (N-S) and across (E-W) the Andes, we will identify past dynamics of atmospheric processes and asses these changes in the context of mountain-range uplift. The PhD candidate will focus on understanding the isotopic characteristics of leaf waxes and their climatic and biotic (i.e. vegetation distribution) drivers in modern catchments. By studying the modern hydrological gradient across (E-W) and along (N-S) the orogen and its imprint on leaf-wax stable isotope ratios, we will develop a sound base to apply this proxy on a variety of terrestrial climate archives from the last 10 Ma.