Reconstruction of paleoceanographic changes in the central equatorial Pacific since the Last Glacial Maximum from the planktic foraminifera records

Abstract

We investigated paleoceanographic changes at a central equatorial Pacific site (6°40′N, 177°28′W) since the Last Glacial Maximum using planktic foraminifera assemblages, together with the oxygen isotope (δ18O) and Mg/Ca compositions of Globigerinoides sacculifer, Pulleniatina obliquiloculata, and Globorotalia tumida that dwell in the mixed layer, upper thermocline, and lower thermocline, respectively. The upper thermocline temperature increased by 3°C during the last deglaciation (18&#8211 12 ka) with a simultaneous decrease of δ18O while the mixed layer and lower thermocline temperatures varied within a narrow range from 18 ka onwards. Such changes can be explained by an enhanced mixing of the upper ocean and/or a reduced habitat depth separation between P. obliquiloculata and G. sacculifer during 18&#8211 12 ka, the last deglaciation. The faunal assemblage of planktic foraminifera during the last deglaciation resembles the modern assemblages at subtropical central Pacific sites. We suggest that the study site, presently under the strong influence of the Intertropical Convergence Zone (ITCZ)&#8211 North Equatorial Countercurrent, had been influenced by the northeasterly Trades and NEC during the 18&#8211 12 ka interval. This interpretation is consistent with previous documentation of a more southerly location of the ITCZ during two Northern Hemisphere cooling events the Heinrich Stadial 1 and the Younger Dry Globigerinoides sacculifer, Pulleniatina obliquiloculata, and Globorotalia tumida that dwell in the mixed layer, upper thermocline, and lower thermocline, respectively. The upper thermocline temperature increased by 3°C during the last deglaciation (18&#8211 12 ka) with a simultaneous decrease of δ18O while the mixed layer and lower thermocline temperatures varied within a narrow range from 18 ka onwards. Such changes can be explained by an enhanced mixing of the upper ocean and/or a reduced habitat depth separation between P. obliquiloculata and G. sacculifer during 18&#8211 12 ka, the last deglaciation. The faunal assemblage of planktic foraminifera during the last deglaciation resembles the modern assemblages at subtropical central Pacific sites. We suggest that the study site, presently under the strong influence of the Intertropical Convergence Zone (ITCZ)&#8211 North Equatorial Countercurrent, had been influenced by the northeasterly Trades and NEC during the 18&#8211 12 ka interval. This interpretation is consistent with previous documentation of a more southerly location of the ITCZ during two Northern Hemisphere cooling events the Heinrich Stadial 1 and the Younger Dry