The University of Southampton
University of Southampton Institutional Repository

Separating biogeochemical cycling of neodymium from water mass mixing in the Eastern North Atlantic

Separating biogeochemical cycling of neodymium from water mass mixing in the Eastern North Atlantic
Separating biogeochemical cycling of neodymium from water mass mixing in the Eastern North Atlantic
The radiogenic neodymium (Nd) isotope ratio 143Nd/144Nd (expressed in ?Nd?Nd) is being used as a tracer in paleo and modern ocean circulation. However, the mechanisms controlling input, distribution, and internal cycling are far from understood. For example, globally, Nd concentration ([Nd]) commonly follows patterns of nutrient tracers, generally increasing with depth below the thermocline, while ?Nd?Nd, tends to reflect the water masses, which has often been referred to as the ‘Nd-paradox’. Here we present dissolved Nd isotopes and concentrations at unprecedented vertical and spatial resolution from the eastern part of the US GEOTRACES North Atlantic Zonal Transect (Gulf of Cadiz – Mauritanian Shelf – Cape Verde Islands).

The [Nd] of all samples ranges from 12.3 to 36.7 pmol/kg, with lowest [Nd] usually found within the layer of highest chlorophyll-a levels (chl-max), suggesting removal through scavenging. The Nd isotope compositions range between ?Nd=?13.4?Nd=?13.4 and ?9.9, with lower values at the surface within the extension of the Saharan dust plume and a benthic nepheloid layer (BNL). Less negative values are found in oligotrophic surface waters, Mediterranean Outflow Water (MOW), and near the Cape Verde Islands. Overall, water mass mixing derived from ?Nd?Nd is best visible at the Strait of Gibraltar, where MOW enters the Atlantic Ocean. Most of the sub-thermocline ?Nd?Nd varies within a small range with poor water mass distinction due to the dominance of North Atlantic Deep Water. High surface [Nd] associated with more negative ?Nd?Nd is interpreted to be the result of dust deposition and dissolution. Local [Nd] maxima with no apparent change in ?Nd?Nd compared to ambient seawater, observed within a zone of minimum oxygen concentration (OMZ) at ?500 m depth off Mauritania, suggest minor input of lithogenic Nd but a rather high contribution through desorption of previously scavenged Nd. That is, Saharan dust in this area has only a minor influence on the isotope composition of water below the uppermost surface layer. The low ?Nd?Nd values and elevated [Nd] within the BNL on the other hand indicate release from detrital material. Our new high-resolution dataset gives valuable insights into the Nd distribution near continental margins, influenced by high atmospheric inputs and changing oxygen conditions. We show how vertical and lateral processes overlap to produce the observed Nd distribution, bringing us forward in understanding the Nd-paradox.
GEOTRACES, OMZ, Nd isotopes, seawater, dust, Nd paradox
0012-821X
245-260
Stichel, Torben
c04e16ca-782d-47af-b955-7bbdd9e7f91d
Hartman, Alison E.
93d2f63e-7b2d-4a50-bcff-b29c867d2e31
Duggan, Brian
7c2ff0ac-8bc2-4438-9858-11e7ae263d3a
Goldstein, Steven L.
5f6ecae9-7c9f-44a8-bba1-28b007e61361
Scher, Howie
4390f56e-2f72-45af-8ddf-170920e99ead
Pahnke, Katharina
7745025d-b534-4731-bfa6-d4d45300d0ff
Stichel, Torben
c04e16ca-782d-47af-b955-7bbdd9e7f91d
Hartman, Alison E.
93d2f63e-7b2d-4a50-bcff-b29c867d2e31
Duggan, Brian
7c2ff0ac-8bc2-4438-9858-11e7ae263d3a
Goldstein, Steven L.
5f6ecae9-7c9f-44a8-bba1-28b007e61361
Scher, Howie
4390f56e-2f72-45af-8ddf-170920e99ead
Pahnke, Katharina
7745025d-b534-4731-bfa6-d4d45300d0ff

Stichel, Torben, Hartman, Alison E., Duggan, Brian, Goldstein, Steven L., Scher, Howie and Pahnke, Katharina (2015) Separating biogeochemical cycling of neodymium from water mass mixing in the Eastern North Atlantic. Earth and Planetary Science Letters, 412, 245-260. (doi:10.1016/j.epsl.2014.12.008).

Record type: Article

Abstract

The radiogenic neodymium (Nd) isotope ratio 143Nd/144Nd (expressed in ?Nd?Nd) is being used as a tracer in paleo and modern ocean circulation. However, the mechanisms controlling input, distribution, and internal cycling are far from understood. For example, globally, Nd concentration ([Nd]) commonly follows patterns of nutrient tracers, generally increasing with depth below the thermocline, while ?Nd?Nd, tends to reflect the water masses, which has often been referred to as the ‘Nd-paradox’. Here we present dissolved Nd isotopes and concentrations at unprecedented vertical and spatial resolution from the eastern part of the US GEOTRACES North Atlantic Zonal Transect (Gulf of Cadiz – Mauritanian Shelf – Cape Verde Islands).

The [Nd] of all samples ranges from 12.3 to 36.7 pmol/kg, with lowest [Nd] usually found within the layer of highest chlorophyll-a levels (chl-max), suggesting removal through scavenging. The Nd isotope compositions range between ?Nd=?13.4?Nd=?13.4 and ?9.9, with lower values at the surface within the extension of the Saharan dust plume and a benthic nepheloid layer (BNL). Less negative values are found in oligotrophic surface waters, Mediterranean Outflow Water (MOW), and near the Cape Verde Islands. Overall, water mass mixing derived from ?Nd?Nd is best visible at the Strait of Gibraltar, where MOW enters the Atlantic Ocean. Most of the sub-thermocline ?Nd?Nd varies within a small range with poor water mass distinction due to the dominance of North Atlantic Deep Water. High surface [Nd] associated with more negative ?Nd?Nd is interpreted to be the result of dust deposition and dissolution. Local [Nd] maxima with no apparent change in ?Nd?Nd compared to ambient seawater, observed within a zone of minimum oxygen concentration (OMZ) at ?500 m depth off Mauritania, suggest minor input of lithogenic Nd but a rather high contribution through desorption of previously scavenged Nd. That is, Saharan dust in this area has only a minor influence on the isotope composition of water below the uppermost surface layer. The low ?Nd?Nd values and elevated [Nd] within the BNL on the other hand indicate release from detrital material. Our new high-resolution dataset gives valuable insights into the Nd distribution near continental margins, influenced by high atmospheric inputs and changing oxygen conditions. We show how vertical and lateral processes overlap to produce the observed Nd distribution, bringing us forward in understanding the Nd-paradox.

Full text not available from this repository.

More information

Published date: 15 February 2015
Keywords: GEOTRACES, OMZ, Nd isotopes, seawater, dust, Nd paradox
Organisations: Geochemistry

Identifiers

Local EPrints ID: 373417
URI: http://eprints.soton.ac.uk/id/eprint/373417
ISSN: 0012-821X
PURE UUID: 83d4abbb-9a34-4da8-8bc9-7fff4f2d3f29

Catalogue record

Date deposited: 21 Jan 2015 14:29
Last modified: 15 Jul 2019 21:33

Export record

Altmetrics

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×