Late Quaternary Variability of the Agulhas Thermohaline Valve from Nd Isotopes in Planktonic Foraminifera

Columbia University, New York NY

Investigators

Abstract

As a component of the shallow warm water return route of the "great ocean conveyor", and as the largest western boundary current in the world ocean, the Agulhas Current plans an important role in the transfer of heat and salt into the Atlantic Ocean. This "leakage" of Indian Ocean waters into the South Atlantic contributes to increased salinification of the thermocline. This preconditioning effect provides a positive feedback for North Atlantic Deep Water (NADW) formation, and thereby may play a critical role in driving the Meridional Overturning Circulation. This research investigates changes in the "Agulhas Leakage" (AL) over the last 30,000 years, seeking to better constrain the role that the oceanic water exchange via leakage had in past climate changes as an active player in major circulatory changes in the Atlantic. The neodymium isotopic composition of planktonic foraminifera will be used to reconstruct changes in the Agulhas Leakage intensity and position. The research centers around four hypotheses: 1) the AL is greater during warmer climate periods (and vice versa), 2) increases in AL contributed to increases in NADW export during the deglaciation, 3) decreases in AL contributed to decreased NADW export during the climate transition of the last glacial period, and 4) the position of the Agulhas retroflection was the same during the Holocene and LGM. Funding supports a postdoctoral researcher and application of a new paleoceanographic proxy.