Annual bands of Porites corals from the Cocos (Keeling) Islands (12ºS, 97ºE), eastern Indian Ocean, were analysed by radiocarbon for 1955-1985 AD. The results show a fast response of the site to bomb 14C with a maximum Delta 14C value of 132‰ in 1975. This value is much higher than those for the northwestern Indian Ocean, suggesting that surface waters reaching Cocos are not derived from the Arabian Sea. A good agreement is found between Delta 14C values for Cocos and those for Watamu (Kenya) over most of the study interval, suggesting that the South Equatorial Current carries 14C-elevated water rather than 14C-depleted water across the Indian Ocean. This implies that oceanic upwelling in the northwestern Indian Ocean is spatially confined and that it therefore cannot contribute significantly to the upper limb of the global thermohaline circulation. Variations in Cocos coral 14C, and their possible linkage to ENSO and Indian Ocean Dipole for the period 1955-1985 AD are also discussed.
This work was supported by AINSE (grants 01/207, 02/150P and 04/174).
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