Time-series observation of POC fluxes estimated from 234 Th in the northwestern North Pacific

Time-series measurements of Th-234 activities and particulate organic carbon (POC) concentrations were made at time-series stations (K1, K2, K3, and KNOT) in the northwestern North Pacific from October 2002 to August 2004. Seasonal changes in POC export fluxes from the surface layer (similar to 100 m) were estimated using Th-234 as a tracer. POC fluxes varied seasonally front approximately 0 to 180 mg Cm-2 d(-1) and were higher in spring-summer than in autumn-winter. The export ratio (e-ratio) ranged from 6% to 55% and was also higher in spring-summer. Annual POC fluxes were estimated to be 31 g C m(-2)y(-1) in the subarctic region (station K2) and 23 g C m(-2)y(-1) in the region between the subarctic and subtropical gyres (station K3). POC fluxes and e-ratios in the northwestern North Pacific were much higher than those in most other oceans. The annual POC flux corresponded to 69% of annual new production estimated from the seasonal difference of the nutrient in the Western Subarctic Gyre (45 g C m(-2) y(-1)). These results indicate that much of the organic carbon assimilated in the surface layer of the northwestern North Pacific is transferred to the deep ocean in particulate form. Our conclusions support previous reports that diatoms play an important role in the biological pump. (c) 2007 Elsevier Ltd. All rights reserved.