Effect of eolian Fe-supply change on the phytoplankton productivity and community in central equatorial Pacific Ocean during the Pleistocene: A lipid biomarker approach

Abstract

The effect of iron (Fe) fertilization on biological productivity and community structure in the equatorial Pacific, a region with high nutrient and low chlorophyll concentrations, has been debated for many years. Here we present lipid biomarker and geochemical proxy records in a sediment core from the central equatorial Pacific spanning from 1100 to 600ka to investigate the response of marine phytoplankton communities to eolian Fe supply and to assess links to environmental fluctuations during the Pleistocene. We found a strong link between change in eolian Fe input and phytoplankton community structure. Our data demonstrate that an increase in eolian Fe supply across the 800ka boundary resulted in a shift in the major primary producer from coccolithophores (alkenones) to diatoms (epi-brassicasterol) and dinoflagellates (dinosterol) at the study site. This strong link between changes in eolian Fe supply and the community structure of plankton during 800–600ka may have been associated with a change in atmospheric and ocean conditions due to southward migration of the Intertropical Convergence Zone (ITCZ). The lipid biomarker results show that such a high supply of eolian Fe might have led to a change in the dominant phytoplankton group. However, the opal record, which is often used asa primary productivity indicator, was not consistent with the biomarker results. Therefore, the results indicate that multi-proxy approaches should be used in paleoenvironmental studies because different proxies can reveal different aspects of environmental conditions, thus contributing to a better understanding of paleoceanographic conditions.