Multiproxy reconstruction of Holocene lake level variations in Laguna Huergo (Southern Patagonia, Argentina)

RAMÓN-MERCAU, M. J.; LAPRIDA, C.; ORGEIRA, M. J.; CIANFAGNA, F.; MARTIN, R.; MASSAFERRO, J.; QUINTANA, F. A.; MAIDANA, N. I.

General Roca

Congreso; Reunion anual de comunicaciones de la Asociacion Paleontologica Argentina; 2012

APA

In Southern Patagonia, the strong West-East precipitation gradient is a major determinant of lake hydrochemistry, rendering lacustrine sediments good archives of precipitation proxies. A short sediment core (41 cm) was obtained from Laguna Huergo (51º 45´ S / 72º 05´ W) for estimating past hydrological variations based on its fossil assemblages, grain-size sediment distribution and their magnetic properties. Variations in these parameters allow recognition of hydrometeorological changes occurring in the last 600 years as suggested by a preliminary Pb 210-based age model. The base of the core consists of fine to medium sand and it is interpreted as a relative low level stand. Towards the middle, a peak in magnetic susceptibility (к), the appearance of ostracod species indicative of oligohaline, bicarbonated waters and a decrease in grain size mark the onset of a lake level rise probably due to enhanced precipitations. The timing of this event would be broadly coincident with the ?Little Ice Age? as defined for Southern Patagonia. Thereafter, a shift from oligohaline to mesohaline conditions is inferred from variations in ostracod assemblage composition; together with an increase in grain size, this suggests a lowering in the lake level related to a less favourable hydrological balance. Towards the top of the core a second peak in к precedes a sandy-clay level which is interpreted as a lake level rise around 1850 AD. These results attest to the suitability of this record for tracking centennial scale dry/wet variations in the region.