Central Chile (32–35°S) lies at the northern border of strong Westerly influence and thus exhibits a steep precipitation gradient. Therefore, the palaeoclimatic archives in the region are suitable for detecting past moisture changes. The study of Laguna Aculeo (33°50'S, 70°54'W) presents a multiproxy Holocene lake record including sedimentology, geochemistry, mineralogy, pollen, diatoms, and radiocarbon dating (17 dates). Results indicate an arid early to mid-Holocene period (about 9500–5700 cal yr B.P.). After 5700 cal yr B.P. effective moisture increased progressively and around 3200 cal yr B.P., modern humid conditions were established. Numerous intercalated clastic layers reflect flood deposition during rainy winters. A fluvial unit was deposited shortly before 9000 cal yr B.P. Subsequently, flood events were absent until 5700 but have become frequent since 3200 cal yr B.P. The frequency of flood layers possibly points to weak or no El Niño activity during the early and mid-Holocene, with a subsequent increase during the late Holocene. During the early and mid-Holocene, the Westerlies were probably blocked and hence deflected southward by the subtropical high-pressure cell. Higher precipitation during the last 3200 yr seems strongly related to a weakened subtropical high-pressure cell with intensified Westerlies and possibly increased El Niño activity.

No abstract

2005. Palaeohydrology of Laguna de Tagua Tagua (34 30 0 S) and moisture fluctuations in Central Chile for the last 46 000 yr.ABSTRACT: Central Chile (32-35 S) lies at the northern border of the strong influence of the westerly circulation belt and thus exhibits a steep rainfall gradient. A new core from Laguna de Tagua Tagua (34 30 0 S) provides a sedimentologic, geochemical and palynological record of regional hydrologic balance for the last 46 000 cal. yr BP. According to our age model, relatively humid conditions occurred during glacial times before 43 500 cal. yr BP and from 40 000 to 21 500 cal. yr BP. Reduced moisture conditions and likely lower temperatures occurred from 42 400-40 100 cal. yr BP. Higher lake levels, and pollen assemblages with Valdivian rainforest taxa, imply much higher precipitation during glacial times (40 100-21 000 cal. yr BP) compared to today and, therefore, enhanced westerly activity in northern Central Chile. Afterwards, the general decrease in moisture was punctuated by two abrupt arid periods at 21 000-19 500 cal. yr BP and 17 000-15 000 cal. yr BP, and two more humid intervals: 19 500-17 000 (almost coincident with the global Last Glacial Maximum, LGM) and 13 500-11 500 cal. yr BP. The early and mid-Holocene were the most arid periods in Central Chile for the studied time interval. Millennial-scale palaeohydrological reconstructions from Tagua Tagua are consistent with regional climatic records.

No abstract

We report multiproxy analyses of a sediment core obtained from Laguna Aculeo that spans the past 7500 years. Laguna Aculeo (33°50′S, 70°55′W) is one of the few natural inland lakes located in the Mediterranean zone of Central Chile, near the northern margin of the influence of the southern westerlies. The record shows elevated pollen counts of halophytes and seasonally drying of the lake basin prior to 5700 cal yr B.P., indicating severe aridity and warmer-than-present conditions. This was followed by the establishment of a fresh-water lake, along with an increase in arboreal and herbaceous plant diversity between 5700 and 3200 cal yr B.P. An intensification of this trend started at 3200 cal yr B.P., along with the abrupt decrease of halophytes until 100 cal yr B.P. Within this humid period, pollen accumulation rates show large-amplitude fluctuations, coeval with numerous turbidite layers, suggesting a highly variable and torrential rainfall pattern. This intense and variable precipitation regime is probably associated with the El Niño–Southern Oscillation (ENSO) phenomenon. We suggest that the modern Mediterranean climate of Central Chile was established at ∼3200 cal yr B.P. Paleovegetation and paleolimnological changes starting at 100 cal yr B.P. correlate with documented human activity surrounding the lake.