Abstract
Abstract. The austral westerlies strongly influence precipitation and ocean circulation in the southern temperate zone, with important consequences for cultures and ecosystems. Global climate models anticipate poleward retreat of the austral westerlies with future warming, but the available paleoclimate records that might test these models have been limited to South America and New Zealand, are not fully consistent with each other and may be complicated by influences from other climatic factors. Here we present the first high-resolution diatom and sedimentological records from the winter rainfall region of South Africa, representing precipitation in the equatorward margin of the westerly wind belt during the last 1400 yr. Inferred rainfall was relatively high âŒ1400â1200 cal yr BP, decreased until âŒ950 cal yr BP, and rose notably through the Little Ice Age with pulses centred on âŒ600, 530, 470, 330, 200, 90, and 20 cal yr BP. Synchronous fluctuations in Antarctic ice core chemistry strongly suggest that these variations were linked to changes in the westerlies. Equatorward drift of the westerlies during the wet periods may have influenced Atlantic meridional overturning circulation by restricting marine flow around the tip of Africa. Apparent inconsistencies among some aspects of records from South America, New Zealand and South Africa warn against the simplistic application of single records to the Southern Hemisphere as a whole. Nonetheless, these findings in general do support model projections of increasing aridity in the austral winter rainfall zones with future warming.
Highlights
Winter storms borne on the austral westerlies are a major source of precipitation over the southernmost sectors of Africa, Australia-New Zealand and South America, and intensification and/or equatorward migration of the westerlies tends to increase rainfall in those regions on both seasonal and millennial time scales (Shulmeister et al, 2004; Reason and Roualt, 2005)
We present here the first high-resolution, continuous lacustrine diatom records from the South African winter rainfall zones (WRZ) (Fig. 1), representing decade-scale rainfall variability over the last 1400 yr that was associated with the equatorward margin of the westerlies
Climatic conditions in the South African WRZ, which we define as the near-coastal region spanning the area from Cape Agulhas northwest to the Orange River (Chase and Meadows, 2007), have exceptionally clear linkages to the austral westerlies because the dominant influences on precipitation there come from frontal storm systems borne on westerly winds that strike the Cape during winter and early spring
Summary
Winter storms borne on the austral westerlies are a major source of precipitation over the southernmost sectors of Africa, Australia-New Zealand and South America, and intensification and/or equatorward migration of the westerlies tends to increase rainfall in those regions on both seasonal (winter) and millennial time scales (Shulmeister et al, 2004; Reason and Roualt, 2005). Aridity is expected to increase in the austral winter rainfall zones (WRZ), with potentially serious consequences for centres of endemism, fire frequency, Published by Copernicus Publications on behalf of the European Geosciences Union. Stager et al.: Precipitation variability in the winter rainfall zone of South Africa agriculture and public water resources (Turpie et al, 2002; Thomas et al, 2004; Meadows, 2006)
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