Behaviour of chromium isotopes in the eastern sub-tropical Atlantic Oxygen Minimum Zone
Constraints on the variability of chromium (Cr) isotopic compositions in the modern ocean are required to validate the use of Cr isotopic signatures in ancient authigenic marine sediments for reconstructing past levels of atmospheric and ocean oxygenation. This study presents dissolved Cr concentrat...
Published in: | Geochimica et Cosmochimica Acta |
---|---|
Main Authors: | , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
2018
|
Subjects: | |
Online Access: | http://nora.nerc.ac.uk/id/eprint/519590/ https://nora.nerc.ac.uk/id/eprint/519590/7/1-s2.0-S0016703718301455-main.pdf https://doi.org/10.1016/j.gca.2018.03.004 |
id |
ftnerc:oai:nora.nerc.ac.uk:519590 |
---|---|
record_format |
openpolar |
spelling |
ftnerc:oai:nora.nerc.ac.uk:519590 2023-05-15T17:13:54+02:00 Behaviour of chromium isotopes in the eastern sub-tropical Atlantic Oxygen Minimum Zone Goring-Harford, Heather J. Klar, J.K. Pearce, Christopher R. Connelly, Douglas P. Achterberg, Eric P. James, Rachael H. 2018-09 text http://nora.nerc.ac.uk/id/eprint/519590/ https://nora.nerc.ac.uk/id/eprint/519590/7/1-s2.0-S0016703718301455-main.pdf https://doi.org/10.1016/j.gca.2018.03.004 en eng https://nora.nerc.ac.uk/id/eprint/519590/7/1-s2.0-S0016703718301455-main.pdf Goring-Harford, Heather J.; Klar, J.K.; Pearce, Christopher R. orcid:0000-0002-4382-2341 Connelly, Douglas P.; Achterberg, Eric P.; James, Rachael H. 2018 Behaviour of chromium isotopes in the eastern sub-tropical Atlantic Oxygen Minimum Zone. Geochimica et Cosmochimica Acta, 236. 41-59. https://doi.org/10.1016/j.gca.2018.03.004 <https://doi.org/10.1016/j.gca.2018.03.004> cc_by_4 CC-BY Publication - Article PeerReviewed 2018 ftnerc https://doi.org/10.1016/j.gca.2018.03.004 2023-02-04T19:46:17Z Constraints on the variability of chromium (Cr) isotopic compositions in the modern ocean are required to validate the use of Cr isotopic signatures in ancient authigenic marine sediments for reconstructing past levels of atmospheric and ocean oxygenation. This study presents dissolved Cr concentrations (CrT, where CrT = Cr(VI) + Cr(III)) and Cr isotope data (δ53Cr) for shelf, slope and open ocean waters within the oxygen minimum zone (OMZ) of the eastern sub-tropical Atlantic Ocean. Although dissolved oxygen concentrations were as low as 44–90 μmol kg−1 in the core of the OMZ, there was no evidence for removal of Cr(VI). Nonetheless, there was significant variability in seawater δ53Cr, with values ranging from 1.08 to 1.72‰. Shelf CrT concentrations were slightly lower (2.21 ± 0.07 nmol kg−1) than in open ocean waters at the same water depth (between 0 and 160 m, 2.48 ± 0.07 nmol kg−1). The shelf waters also had higher δ53Cr values (1.41 ± 0.14‰ compared to 1.18 ± 0.05‰ for open ocean waters shallower than 160 m). This is consistent with partial reduction of Cr(VI) to Cr(III), with subsequent removal of isotopically light Cr(III) onto biogenic particles. We also provide evidence for input of relatively isotopically heavy Cr from sediments on the shelf. Intermediate and deep water masses (AAIW and NADW) show a rather limited range of δ53Cr values (1.19 ± 0.09‰) and inputs of Cr from remineralisation of organic material or re-oxidation of Cr(III) appear to be minimal. Authigenic marine precipitates deposited in deep water in the open ocean therefore have the potential to faithfully record seawater δ53Cr, whereas archives of seawater δ53Cr derived from shelf sediments must be interpreted with caution. Article in Journal/Newspaper NADW Natural Environment Research Council: NERC Open Research Archive Geochimica et Cosmochimica Acta 236 41 59 |
institution |
Open Polar |
collection |
Natural Environment Research Council: NERC Open Research Archive |
op_collection_id |
ftnerc |
language |
English |
description |
Constraints on the variability of chromium (Cr) isotopic compositions in the modern ocean are required to validate the use of Cr isotopic signatures in ancient authigenic marine sediments for reconstructing past levels of atmospheric and ocean oxygenation. This study presents dissolved Cr concentrations (CrT, where CrT = Cr(VI) + Cr(III)) and Cr isotope data (δ53Cr) for shelf, slope and open ocean waters within the oxygen minimum zone (OMZ) of the eastern sub-tropical Atlantic Ocean. Although dissolved oxygen concentrations were as low as 44–90 μmol kg−1 in the core of the OMZ, there was no evidence for removal of Cr(VI). Nonetheless, there was significant variability in seawater δ53Cr, with values ranging from 1.08 to 1.72‰. Shelf CrT concentrations were slightly lower (2.21 ± 0.07 nmol kg−1) than in open ocean waters at the same water depth (between 0 and 160 m, 2.48 ± 0.07 nmol kg−1). The shelf waters also had higher δ53Cr values (1.41 ± 0.14‰ compared to 1.18 ± 0.05‰ for open ocean waters shallower than 160 m). This is consistent with partial reduction of Cr(VI) to Cr(III), with subsequent removal of isotopically light Cr(III) onto biogenic particles. We also provide evidence for input of relatively isotopically heavy Cr from sediments on the shelf. Intermediate and deep water masses (AAIW and NADW) show a rather limited range of δ53Cr values (1.19 ± 0.09‰) and inputs of Cr from remineralisation of organic material or re-oxidation of Cr(III) appear to be minimal. Authigenic marine precipitates deposited in deep water in the open ocean therefore have the potential to faithfully record seawater δ53Cr, whereas archives of seawater δ53Cr derived from shelf sediments must be interpreted with caution. |
format |
Article in Journal/Newspaper |
author |
Goring-Harford, Heather J. Klar, J.K. Pearce, Christopher R. Connelly, Douglas P. Achterberg, Eric P. James, Rachael H. |
spellingShingle |
Goring-Harford, Heather J. Klar, J.K. Pearce, Christopher R. Connelly, Douglas P. Achterberg, Eric P. James, Rachael H. Behaviour of chromium isotopes in the eastern sub-tropical Atlantic Oxygen Minimum Zone |
author_facet |
Goring-Harford, Heather J. Klar, J.K. Pearce, Christopher R. Connelly, Douglas P. Achterberg, Eric P. James, Rachael H. |
author_sort |
Goring-Harford, Heather J. |
title |
Behaviour of chromium isotopes in the eastern sub-tropical Atlantic Oxygen Minimum Zone |
title_short |
Behaviour of chromium isotopes in the eastern sub-tropical Atlantic Oxygen Minimum Zone |
title_full |
Behaviour of chromium isotopes in the eastern sub-tropical Atlantic Oxygen Minimum Zone |
title_fullStr |
Behaviour of chromium isotopes in the eastern sub-tropical Atlantic Oxygen Minimum Zone |
title_full_unstemmed |
Behaviour of chromium isotopes in the eastern sub-tropical Atlantic Oxygen Minimum Zone |
title_sort |
behaviour of chromium isotopes in the eastern sub-tropical atlantic oxygen minimum zone |
publishDate |
2018 |
url |
http://nora.nerc.ac.uk/id/eprint/519590/ https://nora.nerc.ac.uk/id/eprint/519590/7/1-s2.0-S0016703718301455-main.pdf https://doi.org/10.1016/j.gca.2018.03.004 |
genre |
NADW |
genre_facet |
NADW |
op_relation |
https://nora.nerc.ac.uk/id/eprint/519590/7/1-s2.0-S0016703718301455-main.pdf Goring-Harford, Heather J.; Klar, J.K.; Pearce, Christopher R. orcid:0000-0002-4382-2341 Connelly, Douglas P.; Achterberg, Eric P.; James, Rachael H. 2018 Behaviour of chromium isotopes in the eastern sub-tropical Atlantic Oxygen Minimum Zone. Geochimica et Cosmochimica Acta, 236. 41-59. https://doi.org/10.1016/j.gca.2018.03.004 <https://doi.org/10.1016/j.gca.2018.03.004> |
op_rights |
cc_by_4 |
op_rightsnorm |
CC-BY |
op_doi |
https://doi.org/10.1016/j.gca.2018.03.004 |
container_title |
Geochimica et Cosmochimica Acta |
container_volume |
236 |
container_start_page |
41 |
op_container_end_page |
59 |
_version_ |
1766071104292519936 |