Precession forcing of productivity in the Eastern Equatorial Pacific during the last glacial cycle

Abstract

We present a new multi-proxy reconstruction of sea-surface properties spanning the last 140 ka in the IMAGES Core MD02-2529 located in the eastern tropical Pacific Ocean off Costa Rica. Spectral analysis of the records allowed us to examine the ecological imprints of orbital changes on planktic foraminiferal and coccolithophore assemblages and on the pattern of primary production in the Eastern Equatorial Pacific, north of the Equatorial upwelling. Independent productivity reconstructions based on phyto- and zooplankton assemblages show a coherent pattern dominated by orbital precession, which appears to have control productivity changes recorded in the studied core over the last glacial–interglacial cycle. The proposed mechanism of this control invokes an atmospheric forcing associated with equatorial insolation maxima in spring and fall with a period of ∼20 ka. Faunal evidence for a stronger upper-ocean mixing with enhanced nutrient supply to the euphotic zone suggests a more vigorous local atmospheric circulation and associated enlargement of the Costa Rica Dome that influenced the core site at times of May insolation maxima. The last two terminations in the studied record are associated with conspicuous changes in planktic assemblages which require additional nutrient-delivery mechanisms to amplify the precession forcing. Our faunal and stable isotope data are in favour of the previously postulated nutrient advection via the Southern Ocean “tunnelling” operating during deglaciations.