Quaternary bottom water circulation and benthic foraminiferal changes in the Northern Indian Ocean

Abstract

The present study has been taken up to understand the history of bottom waler circulation in the Northern Indian Ocean during Quaternary, using quantitative analyses of benthic foraminifera. The main idea is to identify the phases and magnitude of cooling, and intensification of Northern Indian Ocean bottom waters and (heir impact on the distribution of benthic foraminiferal assemblages during Quaternary. The interpretations are based on frequency variation curves of some selected laxa showing significant changes, and species diversity, H(S}, and Equitability, E", trends. The base of the Quaternary is marked by a sharp decrease in abundance of Uvtgerina md Qtp-bocassidufina reflecting stable and warmer bottom waiter conditions as a result of waning Antarctic Bottom Water (AABW) circulation. This is Followed by a return of cool bottom waters as reflected by higher abundances of Neouvigerina proboscidea and Gtoho-cassidulina subghbosa and lower values of H[S) and E'. This interval represents a period of widespread global deep sea hiatuses, intensified bottom water circulation as a result of enhanced production of AAHW in response to increasing Antarctic glacialion and its effect in the Northern Indian Ocean bottom waters. In general, the Early Quaternary is characterized by less diverse benthic foraminiferal assemblages, unstable bottom water conditions, and coo/ing of bottom waters. The transition between Baily Quaternary and JLate Quaternary is marked by warming of boiu>m waters, and more equitable and more diverse assemblages, In Late Quaternary the bottom circulation was more uniform and less intensified and the benthic foraminiferal assemblages are more diverse, more equitable, and less abundant. This suggests (hat during Late Quaternary, the glacial activity was less Intensified in Antarctic region, thus causing decrease in intensity of AABW production. The modern assemblage at site 214 is dominated by Buiimina acukata and Textularia tythoslrota (both accounting for nearly 50% of the total assemblage), reflecting the influence of Circumpolar Deep Water (CDW) in the shallower sites of the Northern Indian ocean.