Response of northern Indian Ocean deep-sea benthic foraminifera to global climates during Pliocene-Pleistocene

Abstract

The Northern Indian Ocean (DSDP Site 214) benthic foraminifera have been examined quantitatively to understand their response to the global climatic events and to determine the history of bottom-water circulation in the Northern Indian Ocean during Pliocene-Pleistocene.Uvigerina spp.,Cibicides kullenbergi, C. wuellerstorfi, Globocassidulina pacifica, G. subglobosa, Oridorsalis umbonatus andBulimina alazanensis are the dominant members of the benthic assemblage and reveal significant changes in distribution patterns. Based on benthic foraminiferal frequency changes, four intervals of major faunal and climatic turnover have been recognized at 5.2-5.1 Ma, 3.9-3.2 Ma, 3.2-3.1 Ma and 3.1-0.6 Ma. The interval between 5.2-5.1 Ma is marked by widespread Antarctic glaciation, deep-sea hiatuses, bottom-water cooling, increased upwelling, high sedimentation rates, highestUvigerina abundances and intensified bottom-water circulation. During 3.9-3.2 Ma the bottom waters were warmer and bottom-water activity waned, with a sharp decline inUvigerina abundance and increase inCibicides. The interval between 3.2-3.1 Ma was a time of bottom-water cooling and coincides with a global benthic positive oxygen isotopic shift, Antarctic ice volume increase and possible initiation of Northern Hemisphere glaciation. The Late Pliocene and Pleistocene interval (3.1-Recent) is punctuated by major changes in benthic foraminiferal assemblages, warm/cold cycles, major glacial/interglacial intervals, increase in polar ice volume and intensification of upwelling. On the basis of cumulative percentages ofUvigerina andCibicides, nine intervals of major bottom-water cooling have been inferred in the Pliocene and two in the Pleistocene at Site 214 reflecting the major changes in bottom-water circulation.