The reconstruction of low-latitude ocean-atmosphere interactions is one of the major issues of paleo-environmental studies. The trade winds, extending over 20° to 30° of latitude in both hemispheres, between the subtropical highs and the intertropical convergence zone (ITCZ), are dominant factors of atmospheric circulation and little is known about their long-term variability on geological time-scales, in particular in the Pacific sector. Our work focuses on Plio-Pleistocene variations in southeast trade wind strength and its dust transport in the Southeast Pacific as missing links for a comprehensive understanding of changes in regional oceanography, El Niño behavior and associated changes in upwelling. To assess trade wind intensities, we investigate changes in grain size distribution of the wind-blown sediment fraction over time. We here present the modern spatial pattern of siliciclastic grain size variability in eastern equatorial and subtropical Pacific (10°N to 25°S) surface sediments as a reference data set for currently performed downcore studies on ODP sites 1237 and 1239, ~150km off the coasts of Peru and Ecuador, respectively. The surface samples were analyzed for grain size (Beckmann-Coulter laser particle sizer) and clay mineral (XRD) distributions in order to identify sediment dispersal patterns of terrigenous input, i.e., eolian signals and possible fluvial overprints.In general, the fine silt fraction dominates the siliciclastic component of surface sediments west of the South American deep-sea trench, with modes ranging from 4.5 to 8µm. First results confirm a decrease in grain-size in the prevalent wind direction away from the source regions in the Atacama Desert. Dust input thus is a valuable indicator for changes in atmospheric circulation patterns in the SE Pacific and for South American continental aridity. Additionally, grain-size distributions in the Panama Basin appear to reflect the pattern of prominent bottom water currents.
Helmholtz Research Programs > MARCOPOLI (2004-2008) > POL6-Earth climate variability since the Pliocene