Reconstruction of paleoproductivity in the central equatorial Pacific Ocean during the mid-Pleistocene transition using lipid biomarker approach

Abstract

The mid-Pleistocene climate transition (MPT) is a period of complex climatic change which brought about the Late Pleistocene ice age around 0.9Ma and a shift in the dominant periodicity of glacial- interglacial oscillations from 41 to 100kyr. The MPT also marks changes in the deep water circulation, caused by global cooling and the intensification of the Northern Hemisphere glaciation. We examine the changes in productivity in the central equatorial pacific during the MPT by applying a lipid biomarker approach. A sediment core from the central equatorial Pacific (5º 55 N, 177º 26 W, 557 cm long and 4136 m water depth) was studied for biomarkers on the time interval from 400 kyrs to ~1Ma, largely coinciding with the MPT. Contents of marine lipid biomarkers (alkenone, brassicasterol and dinosterol) showed different down-core variation. The concentration of brassicasterol and dinosterol increased during the MPT (0.7Ma) while alkenone concentration decreased. The shift in the phytoplankton marker concentrations likely reflects the changes in physical properties of the water column, as the relative contribution of alkenone to brassicasterol and dinosterol is greatest in well stratified oligotrophic water. Sea surface temperatures (SSTs) reconstructed showed ~ 2 ºC fall during the same time period.