Indicators of recent environmental changes in a saline lacustrine sedimentary sequence recovered from Lake El Toro, Neuquén steppe, Argentina.

DAGA, R.; RIZZO, A.; RIBEIRO GUEVARA, S.; DUTRÚS, S.; ARRIBERE, M.A.

Miramar, Mar Chiquita, Córdoba

Conferencia; 11th International Conference on Salt Lake Research; 2011

International Society for Salt Lake Research y PROMAR Centro de Zoología Aplicada, Universidad Nacional de Córdoba

The analysis of lacustrine sedimentary sequences allows the reconstruction of past environmental conditions and processes through the study of materials derived from lake and catchment processes, or from catastrophic events that reach the bottom of the lake. A short sedimentary sequence was extracted with a messenger activated gravity type corer from Lake El Toro, a small saline and closed depression located in the steppe region, southeast of Neuquén province, Argentina. The sedimentation rate, estimated by means of 137Cs technique, was 0.111 g cm-2 y-1 (0.27 cm y-1). Organic matter contents (OM), biogenic silica (BSi), and major and trace elements, including rare earth (REE) were analyzed throughout the sequence, in sections of 1 cm. The deposition of volcanic ashes was clearly recorded by the parameters studied showing depletion of OM and BSi and increase in allochthonous elements contents (e.g. Al, Fe, Cr, Co, Sc). Besides, it was possible to observe an increasing tendency in allochthonous elements, including REE, in the upper 20 cm of the sequence, together with a shift to lower values in the OM content, which could be associated with increases in clastic input from the catchment in the last 60 years. On the other hand, BSi shows a strong increase in 9 to 6 cm depth layers. The increase in lake level water and the consequent decrease in total dissolved solids in the water would favor the precipitation of BSi, as it was observed in other saline lakes. At the same depth, Ca concentration undergoes a sharp decline, possibly associated to Ca compounds dilution. The biogeochemical indicators studied allowed to infer an increase in lake water level associated to the increase in the precipitations recorded in Northwest Patagonia during the cool-wet conditions in the seventies.