Monsoon forcing, hydrodynamics of the Kuroshio Current, and tectonic effects on sedimentary carbon and sulfur cycling in the Okinawa Trough since 90 ka

Monsoon forcing and hydrodynamic effects controlled carbon and sulfur biogeochemistry over the last 90 ka in a 43-m core from the Okinawa Trough (OT). Total organic carbon (TOC) contents co-vary with summer insolation at 30°N suggesting monsoon forcing of primary productivity and organic carbon burial. Before the last glacial maximum (LGM), total sulfur (TS) contents varied concomitantly with TOC. However, sea level rise and intensified Kuroshio inflow during the Holocene enhanced deepwater ventilation, which resulted in TS-depleted sediments with low degree of pyritization (DOP). By contrast, DOP values were high during the previous highstand (at ∼80 ka BP), when sea level was similar to that in the Holocene, as well as during the LGM when deepwater circulation was relatively weak. A topographic barrier is proposed to have sufficiently blocked the Kuroshio Current out of the OT during the previous sea level highstand, which weakened deepwater ventilation and led to reducing diagenetic conditions. Tectonic rifting in the southern OT at 60-30 ka BP enabled the major change in hydrodynamics and sediment biogeochemistry.