干旱区生态环境知识资源中心

Changes in the position and intensity of the Southern Westerly Winds (SWW) and related causal processes during the Quaternary are controversial and not well understood. Here, we present a record from continental Central Chile, based on coastal aeolian sand and dunes with intercalated palaeosols, reaching back 190 ka in time. Sixteen samples for luminescence dating and additional samples for geochemical procedures were analysed from three locations in the "Norte Chico" (La Serena, Los Vilos, Las Ventanas). Besides the recent Bw-horizons, four palaeosols (Btb1, Btb2, Btb3, Btb4) are identified. They formed in periods with stable surface conditions and a relatively dense vegetation cover, whereas sand accumulation reflects increased aeolian activity under dry conditions and, in parts, glacial sea level lowering. Three of these soils are well bracketed by luminescence data to <14 ka (Bw), 59-47 ka (Btb4) and 135-125 ka (Btb2). The formation of Btb1 and Btb3 tentatively occurred at 190-160 ka and 107-95 ka. Btb-horizons are interpreted to reflect wetter conditions than modern ones (Bw-horizons). Since the only way to bring wetter conditions to the coastal area of the Norte Chico are the SWW, the documented changes should reflect changes in paleo atmospheric circulation. The more humid periods appear to show a periodicity, dominated by the obliquity cycle. Increased Antarctic sea-ice during austral winter combined with a weak South Pacific Anticyclone at subtropical latitudes, seem to have favoured winter incursions of humid air masses from the Westerlies. (C) 2014 Elsevier B.V. All rights reserved.