Abstract

Studying past changes in the eastern equatorial Pacific Ocean dynamics and their impact on precipitation on land gives us insight into how the Intertropical Convergence Zone (ITCZ) movements and the El Nino-Southern Oscillation modulate regional and global climate. In this study we present a multiproxy record of terrigenous input from marine sediments collected off the Ecuadorian coast spanning the last 500 kyr. In parallel we estimate sea surface temperatures (SST) derived from alkenone paleothermometry for the sediments off the Ecuadorian coast and complement them with alkenone-based SST data from the Panama Basin to the north in order to investigate SST gradients across the equatorial front. Near the equator, today's river runoff is tightly linked to SST, reaching its maximum either during the austral summer when the ITCZ migrates southward or during El Nino events. Our multiproxy reconstruction of riverine runoff indicates that interglacial periods experienced more humid conditions than the glacial periods. The north-south SST gradient is systematically steeper during glacial times, suggesting a mean background climatic state with a vigorous oceanic cold tongue, resembling modern La Nina conditions. This enhanced north-south SST gradient would also imply a glacial northward shift of the Intertropical Convergence Zone at least in vicinity of the cold tongue: a pattern that has not yet been reproduced in climate models.