Radiocarbon of sediment trap samples from the Okinawa trough: lateral transport of C-14-poor sediment from the continental slope

Radiocarbon of carbonate (PIC) and of organic carbon (POC) in sediment trap samples from the Okinawa trough was measured by AMS. Concentrations of C-1 4 in PIC and POC (Delta(14)C-PIC and Delta(14)C-POC) ranged from approximat ely + 40 parts per thousand to -80 parts per thousand and average over the entire 2 years was approximately -32 parts per thousand. These values are m uch lower than Delta(14)C values of dissolved inorganic carbon (Delta(14)C- DIC) in the upper 200 m of the water column (+100 parts per thousand on ave rage), Delta(14)C-PIC and Delta(14)C-POC showed seasonal variability over 2 years with lower values in winter and higher values in summer. In the 1994 -1995 period, Delta(14)C-PIC was also low in spring. Variations in Delta(14 )C-PIC and Delta(14)C-POC were positively correlated with concentrations of inorganic and organic carbon, respectively, and negatively correlated with concentration of Al. This suggests that variability in Delta(14)C-PIC and Delta(14)C-POC were associated with the input of lithogenic materials. Assu ming Delta(14)C-PIC and Delta(14)C-POC for two end members (settling partic les produced in the overlying water column, and laterally transported mater ials produced outside of the overlying water column, which originated from the continental slope of the East China Sea). contributions of laterally tr ansported materials to the sediment trap samples were estimated for each co llecting period. The contribution of laterally transported materials ranged from approximately 50%-90% and the annual average of flux of old carbon wa s ca. 5 mg m(-2) day(-1) in 1993 and 10 mg m(-2) day(-1) in 1994-1995. (C) 2000 Elsevier Science B.V. All rights reserved.