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Neodymium isotopic composition and concentration in the western North Atlantic Ocean: results from the GEOTRACES GA02 section

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Title: Neodymium isotopic composition and concentration in the western North Atlantic Ocean: results from the GEOTRACES GA02 section
Authors: Lambelet, M
Van de Flierdt, T
Crocket, K
Rehkamper, M
Kreissig, K
Coles, B
Rijkenberg, MJA
Gerringa, LJA
De Baar, HJW
Steinfeldt, R
Item Type: Journal Article
Abstract: The neodymium (Nd) isotopic composition of seawater is commonly used as a proxy to study past changes in the thermohaline circulation. The modern database for such reconstructions is however poor and the understanding of the underlying processes is incomplete. Here we present new observational data for Nd isotopes and concentrations from twelve seawater depth profiles, which follow the flow path of North Atlantic Deep Water (NADW) from its formation region in the North Atlantic to the northern equatorial Atlantic. Samples were collected during two cruises constituting the northern part of the Dutch GEOTRACES transect GA02 in 2010. The results show that the different water masses in the subpolar North Atlantic Ocean, which ultimately constitute NADW, have the following Nd isotope characteristics: Upper Labrador Sea Water (ULSW), εNd = -14.2 ± 0.3; Labrador Sea Water (LSW), εNd = -13.7 ± 0.9; Northeast Atlantic Deep Water (NEADW), εNd = -12.5 ± 0.6; Northwest Atlantic Bottom Water (NWABW), εNd = -11.8 ± 1.4. In the subtropics, where these source water masses have mixed to form NADW, which is exported to the global ocean, upper-NADW is characterised by εNd values of -13.2 ± 1.0 (2sd) and lower-NADW exhibits values of εNd = -12.4 ± 0.4 (2sd). While both signatures overlap within error, the signature for lower-NADW is significantly more radiogenic than the traditionally used value for NADW (εNd = -13.5) due to the dominance of source waters from the Nordic Seas (NWABW and NEADW). Comparison between the concentration profiles and the corresponding Nd isotope profiles with other water mass properties such as salinity, silicate concentrations, neutral densities and chlorofluorocarbon (CFC) concentration provides novel insights into the geochemical cycle of Nd and reveals that different processes are necessary to account for the observed Nd characteristics in the subpolar and subtropical gyres and throughout the vertical water column. While our data set provides additional insights into the contribution of boundary exchange in areas of sediment resuspension, the results for open ocean seawater demonstrate, at an unprecedented level, the suitability of Nd isotopes to trace modern water masses in the strongly advecting western Atlantic Ocean.
Issue Date: 15-Mar-2016
Date of Acceptance: 18-Dec-2015
URI: http://hdl.handle.net/10044/1/28815
DOI: 10.1016/j.gca.2015.12.019
ISSN: 0016-7037
Publisher: Meteoritical Society
Start Page: 1
End Page: 29
Journal / Book Title: Geochimica et Cosmochimica Acta
Volume: 177
Issue: 1
Copyright Statement: © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).
Sponsor/Funder: Natural Environment Research Council (NERC)
Natural Environment Research Council (NERC)
Natural Environment Research Council (NERC)
Funder's Grant Number: NE/J021636/1
Keywords: Science & Technology
Physical Sciences
Geochemistry & Geophysics
0402 Geochemistry
0403 Geology
0406 Physical Geography and Environmental Geoscience
Geochemistry & Geophysics
Publication Status: Published
Open Access location: http://www.sciencedirect.com/science/article/pii/S0016703715007139
Online Publication Date: 2015-12-23
Appears in Collections:Earth Science and Engineering
Faculty of Engineering