Glacial-interglacial variations in the neodymium isotope composition of seawater in the Bay of Bengal recorded by planktonic foraminifera

This study presents neodymium isotope and elemental data for cleaned plankt onic foraminifera from ODP site 758 in the southernmost reaches of the Bay of Bengal in the north-east Indian Ocean. Cleaning experiments using oxidat ive-reductive techniques suggest that diagenetic Fe-Mn oxyhydroxide coating s can be effectively removed, and that the measured Nd isotope composition reflects the composition of seawater from which the foraminiferal calcium c arbonate was precipitated. Modern core-top Pulleniatina obliquiloculata and Globorotalia menardii give epsilon(Nd) values of -10.12 +/- 0.16 and - 10. 28 +/- 0.16, respectively, indistinguishable from recent direct measurement s of surface seawater in this area. A high-resolution Nd isotope record obt ained from G. menardii for the past 150 kyr shows systematic variations (De lta epsilon(Nd)approximate to 3) on glacial-interglacial timescales. The ti ming of those variations shows a remarkable correspondence with the global oxygen isotope record, which suggests a process controlling the Nd isotope composition that responds in phase with global climate cycles. Palaeoclimat e reconstruction indicates that during the last glacial maximum changes in monsoon circulation resulted in a reduction in rainfall over the Indian sub continent, and a decrease in the flux of river water delivered to the Bay o f Bengal. Thus, changes in the riverine input of Nd, a change in either flu x or composition, most likely caused the isotope variations, although chang es in dust source or local ocean circulation may have also played a role. T hese results clearly establish a link between climate change and variations in radiogenic isotopes in the oceans, and illustrate the potential of Nd i sotopes in foraminifera for high-resolution palaeoceanographic reconstructi on. (C) 2000 Elsevier Science B.V. All rights reserved.