The Southern Westerlies in Central Chile: Holocene precipitation estimates based on a water balance model for Laguna Aculeo (33°50'S)
Central Chile (32-35°S) lies at the northern border of strong influence of the Westerly circulation belt (Westerlies) and is therefore characterized by a steep precipitation gradient. In this region, quantitative reconstructions of Holocene precipitation are scarce. Hence, the present study estimates precipitation changes, based on lake level fluctuations of Laguna Aculeo (33°50'S, 70°54'W). The lake level curve has been reconstructed using a multi-proxy study of lake sediments. Lake level changes have been simulated using a simple water balance model. As a result, palaeo-precipitation could be estimated: uncertainties concerning the input parameters and past conditions have limitated the precision of precipitation estimates. The results suggest that during the beginning of the Holocene, when the lake level (<1.5 m) was low, precipitation was <200 mm/year. Before 8000 cal yr BP, the lake frequently dried out. Between 8000 and 6000 cal yr BP, precipitation appeared to be higher (150-300 mm/year) and after about 6000 cal yr BP, precipitation increased dramatically (350-450 mm/year). Around 3000 cal yr BP, modern lake level and precipitation (450-550 mm/year) were generally established. The dry conditions during the early and mid-Holocene are in good agreement with other records from Central Chile and northern Patagonia. The Westerlies were probably deflected southward by the southeast Pacific subtropical high-pressure cell during the mid- and early Holocene. Subsequently, the increase in moisture in Central Chile during the late Holocene appears to be strongly related to intensified Westerly activity and probably also to increased El Niño activity.