Quaternary climatic changes indicated by planktonic foraminifera of Northern Indian Ocean

Abstract

The relative abundances of planktonic foraminifera, the changes in their coiling and the isotopic record from deep sea cores of some crucial sites in Northern Indian Ocean indicate climatic fluctuations for the past 3.0 million years (Late Pliocene to Pleistocene). The abundance of temperate forms like Globigerina spp, together with sporadic occurrence of a polar species Neogloboquadrina pachyderm. during specific time intervals suggest cooling episodes. Warmer intervals are marked by the dominance of tropical assemblages including Globigerinoides spp., Globorotalia s.l., Pulleniatina and Globoquadrina. On the basis of the planktonic foraminiferal frequency changes, four intervals of major climatic cooling have been recognized- one in the Late Pliocene (2-3 m.y.), three in the Pleistocene immediately above the Pliocene/Pleistocene boundary (1.6 m.y.), at 0.6 m.y., and during the late Pleistocene. Marked shift in coiling directions within Pulleniatina populations and Globorotalia s.l., is observed to coincide with the frequency changes. There was marked increase of δ¹⁸O values in oxygen isotopic record of foraminiferal tests around 2-3 m.y. (Late Pliocene) and within the Pleistocene. Major faunal turnover accompanied by changes in coiling synchronous with the isotopic shilts, suggest these faunal changes to be climatically induced.