Monsoon variability and deep oceanic circulation in the western equatorial Pacific over the last climatic cycle: Insights from sedimentary magnetic properties and sortable silt

Abstract

Magnetic and grain size properties of a sediment core located in the western equatorial Pacific, off the southeastern tip of the Philippine island of Mindanao, are presented in an effort to reconstruct past changes in the East Asian Monsoon and deep ocean circulation during the last 160 kyrs. The sedimentary concentration of magnetic particles, interpreted to reflect past changes in runoff from Mindanao, varies almost in antiphase with Northern Hemisphere insolation. This suggests that precipitation was lower in the western equatorial Pacific region during boreal insolation maxima and thus corroborates model results showing opposing trends in precipitation between land and the marine realm there. Variations in the grain size distribution of the inorganic sediment fraction, as recorded by both the sortable silt mean size and the magnetic grain size, provide a monitor of changes in sediment reworking by bottom currents. The close correlation of this proxy of bottom current strength and the benthic delta(18)O record from the same site implies a tight coupling between deep water flow, most likely Antarctic Intermediate Water (AAIW), and global climate.