Summer stratification of Andean lakes of Patagonia and Tierra del Fuego.

Global warming or ENSO effects?

Abstract

Lakes are traps of water and sediment. As such, they can record past times climate changes. High-latitude Andean piedmont lakes only give information of the interglacial periods - ice-free periods. Climatic studies should be based on analogies with current lakes. In this sense, we must corroborate if varves respond to annual changes (summer-winter seasonality) or if they represent cycles in a longer temporal scale (interannual). Sedimentary records can stand for trends (glacial advances, retreats or captures), local effects (vulcanism, gravity-dominated phenomena) or episodes jokulhaups, scablands). Depending on their dynamics, glacial lakes stratified differently during summer time (monomic, dimictic or polimictic lakes). According to some models, global warming is supposed to give rise to significant changes in the vertical structure of lakes. There are some experiments that indicate these variations (Lydersen et al. 2007). We found that Patagonian and Fueguian lakes stratified at depths between 10 and 22 m during summertime between 2001 and 2007. These thermoclines’ depths were shallower tan those recorded in summer 1984. On the other side, the lakes from the volcanic district (Neuquén in Argentina and Chilean IX- Region) are recording increases in their temperature with depth. In some lakes, turbidity plumes were recognized as conditioning sedimentation rates and therefore the sedimentary record.