Application of Neodymium isotopic ratio to reconstruct North-eastern Atlantic deepwater mass sources over the last 1Myr
Résumé
The oceanic circulation plays a significant role in climatic change. It is suggested to have contributed to the changes of the climatic cyclicity during the Mid Pleistocene Transition (1250 to 700 kyr) and to the variations of the magnitude between glacial and interglacial periods from the Mid Brunhes Event (430 kyr). Neodymium (Nd) isotopic ratio (143Nd/144Nd or eNd) recorded in authigenic oxides in foraminiferal tests has been successfully used to evaluate northern and southern sourced water mass contribution in relation to the variability in Atlantic meridional overturn circulation (AMOC). Previous studies conducted in deep Southern and North-western Atlantic Ocean showed more radiogenic values during glacial periods compared to interglacials, indicating a weakening of North Atlantic Deep Water formation at that time. However, Nd isotopic records covering the last 1 Myr are still scarce to describe long-term variability. We applied foraminiferal Nd isotopic composition to a marine sediment core MD03-2507 (3.1 km water depth) from the North-eastern Atlantic Ocean off the West Africa to trace the glacial/interglacial AMOC changes for the past 1 Myr. Core-top εNd value of -12.3 is in good agreement with the modern seawater value. The preliminary low-resolution record indicates εNd ranging from -12.5 to -10.8 over the whole study period with higher values during glacials. This glacial/interglacial εNd amplitude is consistent with a recent study focusing on the last 30,000 yrs from the same region and is smaller than for deep Southern and North-western Atlantic Ocean showing a shift of 3 e-units. Considering that the core location is under the Saharan dust plume, the results will be discussed as a deep-water circulation tracer by comparing with benthic stable isotopic records and by taking into account possible Nd contribution from detrital carbonates.