Movement of the Intertropical Convergence Zone during the mid-pleistocene transition and the response of atmospheric and surface ocean circulations in the central equatorial Pacific

Abstract

This paper investigates the causes of a brief, but prominent, cooling episode (1.1-0.8 Ma) that occurred in the equatorial upwelling region of the Atlantic and Pacific during the mid-Pleistocene transition (MPT) using temporal changes in dust provenance, regional hydrology, and surface productivity recorded in a deep-sea sediment core from the central equatorial Pacific. The Sr-87/Sr-86 and epsilon Nd values of the inorganic silicate fraction indicate deposition of dust from Australia and Central/South America before 0.8 Ma, but a gradual increase in Asian dust deposition after 0.8 Ma. The change in dust provenance was accompanied by an increased dust flux and a decrease in surface productivity and salinity. These changes can be explained by the southward movement of the Intertropical Convergence Zone (ITCZ) and North Equatorial Counter Current (NECC) and the direct influence of these features on the site after 0.8 Ma. Our results, together with previously published Atlantic data, suggest the northward position of the ITCZ between 1.1 and 0.9 Ma, and the southward position thereafter. The meridional movement of the ITCZ is in phase with the cooling and warming trend in upwelling regions in the equatorial Pacific and Atlantic, which suggests strengthening of southeast trades relative to its northern counterpart between 1.1 and 0.9 Ma as a plausible cause of this brief cooling event. The southward movement of the ITCZ from 0.9 to 0.8 Ma indicates more significant cooling in the Northern Hemisphere (NH) than in the Southern Hemisphere, which is supportive of the interpretation that the NH ice sheet expanded significantly and stabilized after 0.9 Ma.