Enhanced marine productivity in the Kuroshio region off Shikoku during the last glacial period inferred from the accumulation and carbon isotopes of sedimentary organic matter

Abstract

AbstractWe obtained marine primary production records from cores MD01‐2422 and KH06‐3‐PC8 in the modern Kuroshio flow region in the western North Pacific for the last 35 ka. The organic carbon content of marine sediments is commonly used as a proxy for export production from the surface ocean. Most sedimentary organic carbon was derived from marine organisms, because carbon isotopes of organic matter (δ13Corg) in sediments were approximately −21‰, which is close to the typical marine δ13Corg value. The quantities of marine and terrestrial organic matter were reconstructed from the mass balance of δ13Corg in bulk total organic carbon. The accumulation of marine organic carbon, and presumably marine production, was enhanced during the latter half of the last glacial period in the subtropical gyre in the western North Pacific. Terrestrial organic matter varied synchronously with marine organic carbon changes, suggesting that both increased in late Marine Isotope Stage (MIS) 2. We conclude that in addition to aeolian dust supplied by the East Asia monsoon, the lateral transport of nutrients from the East China Sea to the subtropical gyre as a result of a sea‐level rise at the last deglaciation played an essential role in enhancing palaeoproductivity during the last glacial period. Copyright © 2009 John Wiley & Sons, Ltd.