Potential productivity and surface circulation in the northern Indian Ocean during the last glacial-to-interglacial transition: Application of a new paleoceanographic model
Abstract A new paleoceanographic model is presented which approximates concentrations of total PO 4 for the upper water column for the recent geologic past using the isotopes of carbon and oxygen from the tests of monospecific assemblages of planktic foraminifera. These calculated concentrations of total PO 4 are, in turn, used to estimate relative changes in potential productivity as well as changes in the position and intensity of surface currents for the recent geologic past. This new model is based uponthe statistical constancy of the Redfield Δ O 2 : Δ PO 4 ratio in the modern oceans and has been shown to be an accurate and reliable predictor of total PO 4 . The down core application of this model, thus far limited to five core sites in the northern Indian Ocean, has yielded results which are consistent with a number of other studies in characterizing the last glacial maximum in the northern Indian Ocean, as a time of reduced potential productivity and weak surface currents. In contrast, by 9 ky B.P., the potential productivity and the surface circulation had increased dramatically in the northern Indian Ocean. Conditions in the Holocene appear to be very similar to conditions which were in existence during the last glacial maximum. The observed general trends in surface circulation and potential productivity during the last 18,000 years in the northern Indian Ocean suggest a Milankovitch-type (astronomically induced changes in solar insolation) orbital forcing.