Coupled Impacts of Ventilation of the North Pacific Intermediate Water and Biological Productivity on Late Quaternary sedimentary oxygenation in the Subtropical North Pacific

Abstract

    The North Pacific Ocean has been identified as an important region for studying the atmospheric carbon cycle on glacial-interglacial timescales. However, due to the lack of long-term records, the coupling relationship between ventilation of the North Pacific Intermediate Water, biological productivity and late Quaternary sedimentary oxygenation in the subtropical North Pacific, as well as their roles in regulating atmospheric CO2 are still unclear. In this study, we reconstructed the redox records in the subtropical North Pacific since Marine Isotope Stage (MIS) 6 based on geochemical parameters and productivity proxies in sediment from the Okinawa Trough. Sedimentary δ98/95Mo and other redox proxies show suboxic conditons during MIS5 and late MIS3. These suboxic environments were mainly driven by the increased productivity associated with the Kuroshio Current and East Asian Summer Monsoon (EASM). During interglacial periods, the enhanced induced upwelling carried nutrients and CO2 from the bottom water to the sea surface. We suggest that some CO2 outgassing from the subtropical Northwest Pacific helped to maintain high atmospheric CO2 concentrations during the interglacial period and contributed to the deglacial CO2 rise. The Okinawa Trough experienced a peak in anoxic or even sulfate reducing conditions during MIS4 and early MIS3. When enhanced deep water ventilation offset the impact of primary productivity in the Okinawa Trough during interglacial periods MIS1 and MIS5, the sedimentary environment was in a weakly oxic state. In contrast, NPIW produced strong downstream effects in the subtropical North Pacific during glacial periods (MIS6, MIS4 and MIS2), leading to suboxic and oxic conditions in the deep water Okinawa Trough. At those times, strengthened intermediate and deep-water stratification prevented the upwelling of deep-sea nutrients and CO2 transport to the surface. Overall, the sedimentary redox variation in the Okinawa Trough is tightly coupled with NPIW, upwelling, and biological productivity during glacial-interglacial cycles, indicating the important role that the subtropical North Pacific plays in regulating the atmospheric CO2 budget of the ocean.