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The copper isotope geochemistry of rivers and the oceans

The copper isotope geochemistry of rivers and the oceans
The copper isotope geochemistry of rivers and the oceans
We present the first extensive dataset for copper (Cu) isotopes in rivers, as well as preliminary data for estuaries and seawater. Rivers exhibit a range in dissolved ?65Cu (relative to NIST SRM 976) of + 0.02 to + 1.45 per mil (‰). The discharge-weighted average dissolved ?65Cu and Cu concentration for the studied rivers, representing around 25% of the global riverine water discharge, are + 0.68‰ and 18.8 nmol kg? 1, respectively. Isotopic data for the dissolved phase in two small estuaries in SE England exhibit relatively minor variation through the salinity gradient (+ 0.42 to + 0.94‰) and are close to both the data for the rivers upstream from the estuaries and a measurement of the coastal sea at their mouths. Analyses of the particulate phase in the estuaries reveal a complementary light pool (? 0.24 to ? 1.02‰). The isotopic composition of the total Cu inventory is, however, close to that of the crustal source. These data, along with published constraints, suggest that the isotopically heavy dissolved phase of all the rivers originates in an isotopic partitioning of the weathered pool of Cu between a light fraction adsorbed to particulates and a heavy dissolved fraction dominated by Cu bound to strong organic complexes. Open ocean seawater samples generally exhibit even heavier dissolved Cu isotopic compositions than the riverine input (?65Cu = + 0.9 to + 1.5‰). The heavy isotopic composition of seawater is inferred to originate from intra-oceanic processes. The small dataset presented here is most consistent with further isotopic partitioning between an isotopically light pool adsorbed to particulates and a heavy dissolved pool strongly bound to organic ligands. Scavenging appears to have greatest impact in the surface ocean and least in both the oxygen minimum zone and the ocean bottom, perhaps reflecting the relative importance of scavenging, and thus the sequestration of light Cu to particulate material, at different depths.

copper, isotope geochemistry, rivers, estuaries, seawater
0012-821X
204-213
Vance, D.
2cc02d9f-ca79-457f-b1fa-ca1e5e2a4d0e
Archer, C.
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Bermin, J.
a12c899d-e71c-475b-a9eb-11fde1865c5b
Perkins, J.
603c687a-7cde-4ca9-b6b0-c987141e3693
Statham, P.J.
51458f15-d6e2-4231-8bba-d0567f9e440c
Lohan, M.C.
6ca10597-2d0f-40e8-8e4f-7619dfac5088
Ellwood, M.J.
e996a92d-a268-4ce0-af42-793b225af8de
Mills, R.A.
a664f299-1a34-4b63-9988-1e599b756706
Vance, D.
2cc02d9f-ca79-457f-b1fa-ca1e5e2a4d0e
Archer, C.
0f61fde3-d0e0-4197-a63a-24858f8afdf5
Bermin, J.
a12c899d-e71c-475b-a9eb-11fde1865c5b
Perkins, J.
603c687a-7cde-4ca9-b6b0-c987141e3693
Statham, P.J.
51458f15-d6e2-4231-8bba-d0567f9e440c
Lohan, M.C.
6ca10597-2d0f-40e8-8e4f-7619dfac5088
Ellwood, M.J.
e996a92d-a268-4ce0-af42-793b225af8de
Mills, R.A.
a664f299-1a34-4b63-9988-1e599b756706

Vance, D., Archer, C., Bermin, J., Perkins, J., Statham, P.J., Lohan, M.C., Ellwood, M.J. and Mills, R.A. (2008) The copper isotope geochemistry of rivers and the oceans. Earth and Planetary Science Letters, 274 (1-2), 204-213. (doi:10.1016/j.epsl.2008.07.026).

Record type: Article

Abstract

We present the first extensive dataset for copper (Cu) isotopes in rivers, as well as preliminary data for estuaries and seawater. Rivers exhibit a range in dissolved ?65Cu (relative to NIST SRM 976) of + 0.02 to + 1.45 per mil (‰). The discharge-weighted average dissolved ?65Cu and Cu concentration for the studied rivers, representing around 25% of the global riverine water discharge, are + 0.68‰ and 18.8 nmol kg? 1, respectively. Isotopic data for the dissolved phase in two small estuaries in SE England exhibit relatively minor variation through the salinity gradient (+ 0.42 to + 0.94‰) and are close to both the data for the rivers upstream from the estuaries and a measurement of the coastal sea at their mouths. Analyses of the particulate phase in the estuaries reveal a complementary light pool (? 0.24 to ? 1.02‰). The isotopic composition of the total Cu inventory is, however, close to that of the crustal source. These data, along with published constraints, suggest that the isotopically heavy dissolved phase of all the rivers originates in an isotopic partitioning of the weathered pool of Cu between a light fraction adsorbed to particulates and a heavy dissolved fraction dominated by Cu bound to strong organic complexes. Open ocean seawater samples generally exhibit even heavier dissolved Cu isotopic compositions than the riverine input (?65Cu = + 0.9 to + 1.5‰). The heavy isotopic composition of seawater is inferred to originate from intra-oceanic processes. The small dataset presented here is most consistent with further isotopic partitioning between an isotopically light pool adsorbed to particulates and a heavy dissolved pool strongly bound to organic ligands. Scavenging appears to have greatest impact in the surface ocean and least in both the oxygen minimum zone and the ocean bottom, perhaps reflecting the relative importance of scavenging, and thus the sequestration of light Cu to particulate material, at different depths.

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More information

e-pub ahead of print date: 26 July 2008
Published date: 30 September 2008
Keywords: copper, isotope geochemistry, rivers, estuaries, seawater
Organisations: Geochemistry, Ocean and Earth Science, Marine Biogeochemistry

Identifiers

Local EPrints ID: 63319
URI: http://eprints.soton.ac.uk/id/eprint/63319
ISSN: 0012-821X
PURE UUID: 7f6a3a4a-52ef-4146-a76e-8d1d2ca850e6
ORCID for M.C. Lohan: ORCID iD orcid.org/0000-0002-5340-3108
ORCID for R.A. Mills: ORCID iD orcid.org/0000-0002-9811-246X

Catalogue record

Date deposited: 02 Oct 2008
Last modified: 16 May 2020 00:41

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Contributors

Author: D. Vance
Author: C. Archer
Author: J. Bermin
Author: J. Perkins
Author: P.J. Statham
Author: M.C. Lohan ORCID iD
Author: M.J. Ellwood
Author: R.A. Mills ORCID iD

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