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Physical and biogeochemical controls on the variability in surface pH and calcium carbonate saturation states in the Atlantic sectors of the Arctic and Southern Oceans

Physical and biogeochemical controls on the variability in surface pH and calcium carbonate saturation states in the Atlantic sectors of the Arctic and Southern Oceans
Physical and biogeochemical controls on the variability in surface pH and calcium carbonate saturation states in the Atlantic sectors of the Arctic and Southern Oceans
Polar oceans are particularly vulnerable to ocean acidification due to their low temperatures and reduced buffering capacity, and are expected to experience extensive low pH conditions and reduced carbonate mineral saturations states (?) in the near future. However, the impact of anthropogenic CO2 on pH and ? will vary regionally between and across the Arctic and Southern Oceans. Here we investigate the carbonate chemistry in the Atlantic sector of two polar oceans, the Nordic Seas and Barents Sea in the Arctic Ocean, and the Scotia and Weddell Seas in the Southern Ocean, to determine the physical and biogeochemical processes that control surface pH and ?. High-resolution observations showed large gradients in surface pH (0.10–0.30) and aragonite saturation state (?ar) (0.2–1.0) over small spatial scales, and these were particularly strong in sea-ice covered areas (up to 0.45 in pH and 2.0 in ?ar). In the Arctic, sea-ice melt facilitated bloom initiation in light-limited and iron replete (dFe>0.2 nM) regions, such as the Fram Strait, resulting in high pH (8.45) and ?ar (3.0) along the sea-ice edge. In contrast, accumulation of dissolved inorganic carbon derived from organic carbon mineralisation under the ice resulted in low pH (8.05) and ?ar (1.1) in areas where thick ice persisted. In the Southern Ocean, sea-ice retreat resulted in bloom formation only where terrestrial inputs supplied sufficient iron (dFe>0.2 nM), such as in the vicinity of the South Sandwich Islands where enhanced pH (8.3) and ?ar (2.3) were primarily due to biological production. In contrast, in the adjacent Weddell Sea, weak biological uptake of CO2 due to low iron concentrations (dFe<0.2 nM) resulted in low pH (8.1) and ?ar (1.6). The large spatial variability in both polar oceans highlights the need for spatially resolved surface data of carbonate chemistry variables but also nutrients (including iron) in order to accurately elucidate the large gradients experienced by marine organisms and to understand their response to increased CO2 in the future.
Carbonate system, Ocean acidification, Arctic Ocean, Southern Ocean, Biogeochemistry
0967-0645
7-27
Tynan, Eithne
68dec99f-c067-4f3c-8bec-6a4f75547db6
Clarke, Jennifer S.
b52af005-821a-4b39-93b7-c0b66ce9d66c
Humphreys, Matthew P.
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Ribas-Ribas, Mariana
85a1f816-cfbd-4a9d-83ff-28611827edcd
Esposito, Mario
ec7184a9-d60e-4255-a8ea-5636d960d5df
Rérolle, Victoire M.C.
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Schlosser, C.
93df4206-5ae4-48a3-80b9-d6f4fc2d4b0a
Thorpe, Sally E.
7b1d7a35-346a-414a-83ae-9717d9176de5
Tyrrell, Toby
6808411d-c9cf-47a3-88b6-c7c294f2d114
Achterberg, Eric P.
685ce961-8c45-4503-9f03-50f6561202b9
Tynan, Eithne
68dec99f-c067-4f3c-8bec-6a4f75547db6
Clarke, Jennifer S.
b52af005-821a-4b39-93b7-c0b66ce9d66c
Humphreys, Matthew P.
40cb219a-c2dd-4581-94d0-52fb1c992498
Ribas-Ribas, Mariana
85a1f816-cfbd-4a9d-83ff-28611827edcd
Esposito, Mario
ec7184a9-d60e-4255-a8ea-5636d960d5df
Rérolle, Victoire M.C.
9b7aab63-4055-44f2-bbb4-8ba7b0ebc9bf
Schlosser, C.
93df4206-5ae4-48a3-80b9-d6f4fc2d4b0a
Thorpe, Sally E.
7b1d7a35-346a-414a-83ae-9717d9176de5
Tyrrell, Toby
6808411d-c9cf-47a3-88b6-c7c294f2d114
Achterberg, Eric P.
685ce961-8c45-4503-9f03-50f6561202b9

Tynan, Eithne, Clarke, Jennifer S., Humphreys, Matthew P., Ribas-Ribas, Mariana, Esposito, Mario, Rérolle, Victoire M.C., Schlosser, C., Thorpe, Sally E., Tyrrell, Toby and Achterberg, Eric P. (2016) Physical and biogeochemical controls on the variability in surface pH and calcium carbonate saturation states in the Atlantic sectors of the Arctic and Southern Oceans. Deep Sea Research Part II: Topical Studies in Oceanography, 127, 7-27. (doi:10.1016/j.dsr2.2016.01.001).

Record type: Article

Abstract

Polar oceans are particularly vulnerable to ocean acidification due to their low temperatures and reduced buffering capacity, and are expected to experience extensive low pH conditions and reduced carbonate mineral saturations states (?) in the near future. However, the impact of anthropogenic CO2 on pH and ? will vary regionally between and across the Arctic and Southern Oceans. Here we investigate the carbonate chemistry in the Atlantic sector of two polar oceans, the Nordic Seas and Barents Sea in the Arctic Ocean, and the Scotia and Weddell Seas in the Southern Ocean, to determine the physical and biogeochemical processes that control surface pH and ?. High-resolution observations showed large gradients in surface pH (0.10–0.30) and aragonite saturation state (?ar) (0.2–1.0) over small spatial scales, and these were particularly strong in sea-ice covered areas (up to 0.45 in pH and 2.0 in ?ar). In the Arctic, sea-ice melt facilitated bloom initiation in light-limited and iron replete (dFe>0.2 nM) regions, such as the Fram Strait, resulting in high pH (8.45) and ?ar (3.0) along the sea-ice edge. In contrast, accumulation of dissolved inorganic carbon derived from organic carbon mineralisation under the ice resulted in low pH (8.05) and ?ar (1.1) in areas where thick ice persisted. In the Southern Ocean, sea-ice retreat resulted in bloom formation only where terrestrial inputs supplied sufficient iron (dFe>0.2 nM), such as in the vicinity of the South Sandwich Islands where enhanced pH (8.3) and ?ar (2.3) were primarily due to biological production. In contrast, in the adjacent Weddell Sea, weak biological uptake of CO2 due to low iron concentrations (dFe<0.2 nM) resulted in low pH (8.1) and ?ar (1.6). The large spatial variability in both polar oceans highlights the need for spatially resolved surface data of carbonate chemistry variables but also nutrients (including iron) in order to accurately elucidate the large gradients experienced by marine organisms and to understand their response to increased CO2 in the future.

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e-pub ahead of print date: 29 January 2016
Published date: 1 May 2016
Keywords: Carbonate system, Ocean acidification, Arctic Ocean, Southern Ocean, Biogeochemistry
Organisations: Faculty of Natural and Environmental Sciences, Ocean and Earth Science, Marine Biogeochemistry

Identifiers

Local EPrints ID: 387274
URI: http://eprints.soton.ac.uk/id/eprint/387274
ISSN: 0967-0645
PURE UUID: 00887801-5c80-4468-b4cf-1ea9bd7daf41
ORCID for Matthew P. Humphreys: ORCID iD orcid.org/0000-0002-9371-7128
ORCID for Toby Tyrrell: ORCID iD orcid.org/0000-0002-1002-1716

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Date deposited: 17 Feb 2016 09:39
Last modified: 28 Apr 2022 02:11

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Contributors

Author: Eithne Tynan
Author: Jennifer S. Clarke
Author: Matthew P. Humphreys ORCID iD
Author: Mariana Ribas-Ribas
Author: Mario Esposito
Author: Victoire M.C. Rérolle
Author: C. Schlosser
Author: Sally E. Thorpe
Author: Toby Tyrrell ORCID iD

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