Late Pleistocene zinc isotopic indices of paleoproductivity variations in the tropical West Pacific

The tropical western Pacific (TWP) plays a significant role in modulating the global climate, with solar radiation, sea surface temperature, and monsoon circulation. Marine prime productivity fluctuations in the TWP can change the global carbon cycle. However, isotopic geochemical evidence reconstructing the changes of pro-ductivity in the western Pacific warm pool (WPWP) is currently lacking. The forcing mechanism that changes productivity in the WPWP remains uncertain. Here, we used the Zinc isotope (delta 66Zn) composition in sediment carbonate with Ba/Ti ratios and differences in foraminiferal carbon isotopes between the surface, and thermo-cline obtained from the Ocean Drilling Program (ODP) Site 807A to reconstruct paleoproductivity and nutricline depth over the last 550 ka period. The Zn isotopic composition signal exhibited a generally fluctuating increase, which is similar in a trend found in the Ba/Ti records. In a periodogram of marine productivity tracing, delta 66Zn and Ba/Ti showed periodicities of 33 and 31 ka, respectively, suggesting the influence of long-term El Nin similar to o Southern Oscillation (ENSO)-like forcing. Good coherence between the paleoproductivity records and the nutricline suggests that nutricline changes could be the primary controlling factor in changes in paleoproductivity. During El Nin similar to o-like conditions, the shallow nutricline in the WPWP can result in high prime productivity accompanied by high delta 66Zn values. In addition, the higher productivity and shallower nutricline coeval with the occurrence of low CO2 concentrations in the Antarctic ice core might indicate that biological export production at low latitudes could act as a significant sink in the global carbon cycle and modify atmospheric CO2 concentrations. Our new datasets of sedimentary carbonates in the tropical ocean can provide better insight and constrain on marine Zn biogeochemical cycle and a strong potential tracer in paleoproductivity.