Abstract: The Northwest Pacific is an important sink of global CO₂, which plays a key role in climate regulation. The carbon sequestration and storage processes of marine ecosystems in the Northwest Pacific are of great significance for the export and storage of primary productivity. The total organic carbon contents (TOC), stable carbon isotope (δ¹³C), and marine biomarkers (brassicasterol, dinosterol and C₃₇-alkenones) were measured in sediment cores of the Kuroshio-Oyashio Extension in the Northwest Pacific. The binary end-member mixing model was used to estimate the terrestrial and marine contributions of TOC, suggesting that sedimentary OC in this area is mainly from marine sources, with an average proportion more than 80%. In addition, carbon stock was calculated to evaluate the capacity of storing carbon in the study area. The results show that average carbon stock is 14 t/ha, 28 t/ha and 21 t/ha in Kuroshio Extension, mixed water region and Oyashio Extension (at 1 m), respectively. These values are much lower than the global average, but higher than the pelagic areas, e.g., central North Atlantic and central North Pacific. Therefore, understanding and emphasizing organic carbon burial in this area is of great significance for alleviating the greenhouse effect caused by the increasing CO₂ in the atmosphere.