Deep sea benthic foraminiferal response to the pliocene palaeoenvironmentsof the northen Indian Ocean

The benthic foraminiferal contents of two DSDP sites 219 (Arabian Sea) and 237 (Mascarene Plateau) have been analysed in order to understand paleocean ographic changes in the northern Indian Ocean during Pliocene. Uvigerina pr oboscidea is the most dominant taxon with intervals of marked fluctuations in its abundance at both the sites reflecting relatively higher surface wat er productivity with changing magnitudes during Pliocene. Earliest Pliocene (c. 5.6 to 5.0 Ma) is the interval of distinct increase in the surface wat er productivity in response to more SW Indian Ocean monsoonal upwelling. Th e faunal assemblage during c. 5.0 to 4.0 Ma suggests relatively warm, oxyge nated and more saline bottom waters and moderately low surface water produc tivity in the Arabian Sea region. This was also broadly the period of globa l warmth and higher eustatic sea Level. The surface water productivity duri ng c. 4.0 to 3.4 Ma at site 219 was moderately higher. However, site 237 is characterised by strong bottom currents and relatively lower surface produ ctivity. Further, the latest Pliocene (c. 2.5 Ma onwards) is characterised by significantly higher surface water productivity induced by higher rates of SW Indian Ocean monsoonal upwelling which corresponds with the onset of major Northern Hemisphere glaciation. These paleoenvironmental changes are suggested to be mainly responsible for several last occurrences of benthic foraminiferal taxa near the Pliocene/Pleistocene transition.