Thermocline variabilities at the southern margin of the western Pacific warm pool during the last 25,000 years

The temperature and depth of the thermocline are crucial features of the upper water column in the equatorial Pacific because they relate to heat transfer and intermediate water circulation between high- and low-latitudes. To infer changes in thermocline structure of the southwestern equatorial Pacific during the last 25,000 years, we analyzed geochemical proxies of Pulleniatina obiquiloculata (355-425 μm), a thermocline-dwelling planktic foraminifera, from the sediment core MD05-2925 (9°20'' S, 151°27'' E, water depth: 1642 m) in the Solomon Sea. Our results suggest that changes in magnitude and timing of the thermal gradient (ΔT) between surface and thermocline waters in western Pacific warm pool differed from that in the East Equatorial Pacific since the Last Glacial Maximim. The depth of thermocline in the Solomon Sea site has been shoaled continuously, probably relates to the increased tilt of thermocline across the equator. The presence of a δ13C minimum at the end of the deglaciation suggests that the thermocline in western equatorial Pacific might have played a role in “ocean tunneling” connecting the high- and low-latitude feedback loop during the Termination I. Our results collaborate with a previous hypothesis that during the deglaciation the 13C-depleted water has increased its production rate in the Southern Ocean and therefore expanded supplying more nutrients to the thermocline waters of the southwest Pacific warm pool