Eos, Transactions American Geophysical Union

Indian Ocean Gas Study



In July 1984, a joint French-U.S. team of scientists embarked on the first in a series of research cruises in the southwest Indian Ocean aboard the research/supply vessel Marion Dufresne, which is operated by Terres Australes et Antarctiques Francaises (TAAF). This monthlong cruise marked the debut of a multiyear program aimed at delineating the distribution of anthropogenic CO2 in the Indian Ocean.

Deep waters from the Atlantic, Pacific, and Indian oceans move to the southern ocean and mix there. The resultant relatively homogeneous water becomes the major source of the Antarctic bottom water, which spreads back out into the deep world oceans. Consequently, the chemistry of southern ocean water is a baseline for the deep world oceans. Therefore the carbonate chemistry of the southern ocean water must be learned in order to understand the biogeochemical cycle of carbon from the global point of view. Unfortunately, only a few high-precision carbonate sampling programs have been conducted in the Indian Ocean section of the southern ocean (we know of only seven such stations south of 30°S). As a result, it is difficult to interpret variations in the carbonate chemistry or to calculate anthropogenic CO2 in the Indian Ocean because we do not know the characteristic properties of the water near its origin. Furthermore, the scant data in the southern Indian Ocean were all collected in the summer, and it is uncertain whether the summer data are representative of the mainly winter-formed deep waters.