Radiocarbon in the Arabian Sea water column: Temporal variations in bomb C-14 inventory since the GEOSECS and CO2 air-sea exchange rates

Results of measurements of C-14 in the upper 1500 m water column in 10 stat ions of the Arabian Sea are presented. The study carried out during 1994-19 45, which includes reoccupation of three Geochemical Ocean Sections Study ( GEOSECS) stations (1977-1978), provides an opportunity to assess the tempor al variations in the distribution and inventory of bomb radiocarbon over a period of similar to 2 decades. The Delta(14)C values of surface waters (5 m) range between 31 and 58 parts per thousand, similar to 20 parts per thou sand less than those measured during 1978 at-the three GEOSECS stations. Th e higher Delta(14)C values measured during the present (as well as GEOSECS) study occur in the southern Arabian Sea, which can be attributed to the in flux of low-salinity and high-Delta(14)C waters from the Bay of Bengal. The Delta(14)C in the Persian Gulf Water (PGW) and the Red Sea Water (RSW) are in the range of -34 to -59 parts per thousand and -89 to -113 parts per th ousand, respectively, and do not show any significant differences from thos e measured during the GEOSECS. The bomb C-14 inventories at the three GEOSE CS stations during 1977 and 1995 show that at station 417 in the central Ar abian Sea it has increased by similar to 30%, whereas at the other two stat ions, 416 and 418 in the north and south central Arabian Sea, it is nearly the same. In general, the bomb C-14 inventory in the region ranges between 3.5 and 7.7 x10(9) atoms cm(-2). The CO2 air-sea exchange rates, derived fr om the bomb C-14 inventory, yield values of 7 - 16 mol m(-2) yr(-1). These exchange rates coupled with reported pCO(2) measurements in surface Arabian Sea waters yield CO2 evasion rates in the range of 50-180 Tg-C yr(-1) for the Arabian Sea.