Late Pleistocene Bioproductivity in the Eastern Equatorial Pacific: patterns and comparison of proxies

Export productivity at 6 core locations in the eastern equatorial Pacific (EEP) has been reconstructed based on a benthic foraminiferal transfer function. Two of the core sites lie along the equator, two lie below the influence of Peru margin upwelling water in the South Equatorial Current, and two lie outside the region of immediate equatorial upwelling influence. The core records show strong regionality, especially where affected by Peru margin upwelling of deeper Equatorial Undercurrent Water (EUC)(originally coming from the subantarctic). This Peru margin record differs from that seen along the equator where divergence leads to shallow upwelling, and it is generally inverse to that seen in cores outside the areas of equatorial upwelling. Principal components analysis shows that the main productivity pattern is one that correlates well to the global oxygen isotope record and has lowest values during isotope stages 2 and 4. In addition to this, equatorial cores show a higher frequency pattern of variation which becomes much more pronounced during MIS 3 and 2. The reconstructions based on benthic foraminifera were tested against those from non-accumulation rate based inorganic chemical proxies of export production. These were found to correlate very well in the region influenced by Peru upwelling; and to share notable similarities for sites along the equator. All the non-accumulation rate based paleotracers are consistent with one another and differ from those produced using accumulation rate derived proxies. The differences between the two classes of paleotracers may result from technical uncertainties in calculating actual biogenic fluxes, and from the different aspects of the EEP biogeochemical system that each class represents. Our results demonstrate regional patterns of productivity which indicate that variations in the properties of the EUC have had a primary influence on the biotic system of the EEP. Analysis of planktonic carbon isotope values for the EEP, and comparison of these to the record of the Pacific subantarctic indicate that the subantarctic contribution to the EUC was reduced during MIS 3 and 2. During this interval there were corresponding changes in productivity and plankton community properties.