Neodymium isotopic composition as a proxy of water mass provenance in the Atlantic Ocean: the modern ocean and the past 1200 kyr

• Main Author: Kazuyo, Tachikawa
• Other Authors: Centre européen de recherche et d'enseignement des géosciences de l'environnement (CEREGE), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2019
• Subjects: [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Greenland; Iceland
• Online Access: https://hal.science/hal-03544988

International audience Neodymium isotopic composition (143 Nd/ 144 Nd or e Nd) is one of the most widely used tracers to reconstruct ocean circulation and detrital inputs to the ocean. In this presentation, I will address the following topics by taking the Atlantic Ocean as an example: the distinction between conservative water mixing and local/regional Nd effects on seawater e Nd an assessment of sites where local/regional Nd inputs dominate; the combination of e Nd with foraminiferal d 13 C to investigate changes in oceanic circulation and the carbon cycle across the Mid-Pleistocene transition (MPT). Based on the present-day seawater database, the relationships between e Nd and other water mass tracers (d 13 C-DIC, nutrients, dissolved oxygen, 14 C, temperature and salinity) were determined for the Atlantic deep waters (≥ 1500m). Using multiple regression analysis, empirical equations were established to predict the large-scale deep-water e Nd trends from hydrographic parameters. The spatial distribution of significant local influence can be estimated as large offsets from the predicted values. The results indicate that deep waters in the northern subpolar Atlantic, close to Greenland and Iceland, are highly affected by local inputs. The authigenic e Nd values (foraminiferal oxides, fish teeth/debris, dispersive oxides) more frequently present an isotopic composition that deviates from expected values, often with a positive bias. This suggests a contribution of exchangeable radiogenic Nd from the detrital fraction to pore water and to authigenic fractions. To examine whether sites are suitable for using e Nd to evaluate water mass provenance, systematic comparison of core-top values with present-day seawater is recommended. Finally, two eastern Atlantic e Nd records were generated and combined with benthic foraminiferal d 13 C values to evaluate the role of deep-water circulation across the MPT. By comparing with existing data, the 900-ka event is suggested to be related to a reduced contribution of ...