Benthic foraminifera and Deep-Sea Water Masses in the Tropical Indian Ocean

The distribution patterns of important benthic foraminifera from surface sediment samples of 9 DSDP sites from the tropical Indian Ocean were examined. The faunal patterns reveal two major assemblages and one intermediate assemblage. The first assemblage is dominated by Uvigerina proboscidea and Globocassidulina pacifica and confined to a water depth ranging from 1800-2800m. This assemblage is associated with North Indian Deep Water (NIDW). The second assemblage, confined to waters deeper than 3800m, is dominated by Epislomineila umbonifera and is associated with Antarctic Bottom Water (AABW). The third assemblage occurs between 2800 and 3800m and is dominated by Uvigerina hispido-costata, Cibicides wuellerstorfi, Epistominella exigua, Pullenia bulloides, and Oridorsalis umbonatus. This assemblage is associated with a water mass intermediate between NIDW and AABW. A minor assemblage has also been observed at depths shallower than 1800m, dominated by Bulimina aculeata and Astrononion umbilicatulum. This assemblage appears to be associated with a water mass influenced by Antarctic Intermediate Water (AAIW).