The 1994-1996 Arabian Sea Expedition: An integrated, interdisciplinary investigation of the response of the northwestern Indian Ocean to monsoonal forcing

This issue summarizes the initial results of the US portion of the Arabian Sea Expedition that was conducted during 1994-1996. Despite the scientific interest that this unique portion of the ocean excites, practical matters such as distance from US shores had prevented a focused US scientific effort in this region for many years. At the time this expedition was organized, first-order issues such as whether or not the Arabian Sea was a sink or a source for atmospheric carbon dioxide were still unclear. Did high rates of primary productivity and large concentrations of sedimentary carbon make it a sink or were these processes overwhelmed by outgassing of carbon dioxide arising from the warming of deeper waters reaching the sea surface via upwelling and mixing? The principal unique feature of the Arabian Sea is the regular oscillation in monsoonal atmospheric conditions, which drive near-surface currents, affect mixed-layer development, and influence nutrient supply in a region experiencing relatively constant levels of illumination. The extremes in atmospheric forcing over the Arabian Sea lead to the greatest seasonal variability observed in any ocean basin. This atmospheric circulation is related to the fact that the Indian Ocean is bounded at relatively low latitudes in the northern hemisphere.