National Cheng Kung University, Taiwan

Biogenic carbonate and organic carbon content of two deep sea cores (MD012404 and ODP site 1202) are measured to reconstruct surface ocean productivity variations in areas of the Okinawa Trough in the Western Pacific where the modern climate is highly sensitive to the East Asian monsoon and precipitation/river runoff. Based on foraminiferal isotope stratigraphy and AMS (super 14) C dating, the age models of the cores indicate that core MD012404 shows relatively low sedimentation rates with 50 cm ky (super -1) on average, and that the sedimentation rates in core ODP 1202 are extremely high with an average of 500 cm ky (super -1) . Total organic carbon (TOC) and carbonate contents in core ODP 1202 are 0.56% and 6.80% on average, respectively, and are 0.62% and 15.86%, respectively, in core MD012404. The relatively high carbonate contents in core MD012404 imply high carbonate productivity in the central Okinawa Trough. The sedimentary composition of core ODP 1202 is composed principally of terrestrial silt and clay, indicating enormous terrestrial flux from land and a carbonate dilution effect in the southern Okinawa Trough. The variations of TOC in core MD012404 reveal a dominant 23 kyr cycle, suggesting that the surface ocean productivity in the Okinawa Trough area appears to be driven by precession changes in the East Asian monsoon. High-frequency oscillations in the TOC records in core MD012404 also indicate that the surface ocean productivity changes share a similar structure with the climatic variability characteristic of northern high latitudes.