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What drives the latitudinal gradient in open ocean surface dissolved inorganic carbon concentration?

What drives the latitudinal gradient in open ocean surface dissolved inorganic carbon concentration?
What drives the latitudinal gradient in open ocean surface dissolved inorganic carbon concentration?
Previous work has not led to a clear understanding of the causes of spatial pattern in global surface ocean dissolved inorganic carbon (DIC), which generally increases polewards. Here, we revisit this question by investigating the drivers of observed latitudinal gradients in surface salinity-normalized DIC (nDIC) using the Global Ocean Data Analysis Project version 2 (GLODAPv2) database. We used the database to test three different hypotheses for the driver producing the observed increase in surface nDIC from 10 low to high latitudes. These are (1) sea surface temperature, through its effect on the CO2 system equilibrium constants, (2) salinity-related total alkalinity (TA), and (3) highlatitude upwelling of DIC- and TA-rich deep waters.We find that temperature and upwelling are the two major drivers. 15 TA effects generally oppose the observed gradient, except where higher values are introduced in upwelled waters. Temperature-driven effects explain the majority of the surface nDIC latitudinal gradient (182 of the 223 μmol kg􀀀1 increase from the tropics to the high-latitude Southern Ocean). 20 Upwelling, which has not previously been considered as a major driver, additionally drives a substantial latitudinal gradient. Its immediate impact, prior to any induced air–sea CO2 exchange, is to raise Southern Ocean nDIC by 220 μmol kg-1 above the average low-latitude value. However, this immediate effect is transitory. The long-term impact of upwelling (brought about by increasing TA), which would persist even if gas exchange were to return the surface ocean to the same CO2 as without upwelling, is to increase nDIC by 74 μmol kg-1 above the low-latitude average.
DIC, dissolved inorganic carbon, ocean carbon, latitudinal gradient, surface distribution, upwelling, entrainment, CO2 solubility
1726-4170
2261-2681
Wu, Yingxu
a16b5b90-529a-453d-a43b-6471c416007e
Hain, M.P.
72efed7b-e866-4af9-8be9-a11312d84dd0
Humphreys, Matthew P
40cb219a-c2dd-4581-94d0-52fb1c992498
Hartman, Sue
4666254f-5f64-4f34-97ea-72bc56725b4f
Tyrrell, Luke
6808411d-c9cf-47a3-88b6-c7c294f2d114
Wu, Yingxu
a16b5b90-529a-453d-a43b-6471c416007e
Hain, M.P.
72efed7b-e866-4af9-8be9-a11312d84dd0
Humphreys, Matthew P
40cb219a-c2dd-4581-94d0-52fb1c992498
Hartman, Sue
4666254f-5f64-4f34-97ea-72bc56725b4f
Tyrrell, Luke
6808411d-c9cf-47a3-88b6-c7c294f2d114

Wu, Yingxu, Hain, M.P., Humphreys, Matthew P, Hartman, Sue and Tyrrell, Luke (2019) What drives the latitudinal gradient in open ocean surface dissolved inorganic carbon concentration? Biogeosciences, 16 (13), 2261-2681. (doi:10.5194/bg-16-2661-2019).

Record type: Article

Abstract

Previous work has not led to a clear understanding of the causes of spatial pattern in global surface ocean dissolved inorganic carbon (DIC), which generally increases polewards. Here, we revisit this question by investigating the drivers of observed latitudinal gradients in surface salinity-normalized DIC (nDIC) using the Global Ocean Data Analysis Project version 2 (GLODAPv2) database. We used the database to test three different hypotheses for the driver producing the observed increase in surface nDIC from 10 low to high latitudes. These are (1) sea surface temperature, through its effect on the CO2 system equilibrium constants, (2) salinity-related total alkalinity (TA), and (3) highlatitude upwelling of DIC- and TA-rich deep waters.We find that temperature and upwelling are the two major drivers. 15 TA effects generally oppose the observed gradient, except where higher values are introduced in upwelled waters. Temperature-driven effects explain the majority of the surface nDIC latitudinal gradient (182 of the 223 μmol kg􀀀1 increase from the tropics to the high-latitude Southern Ocean). 20 Upwelling, which has not previously been considered as a major driver, additionally drives a substantial latitudinal gradient. Its immediate impact, prior to any induced air–sea CO2 exchange, is to raise Southern Ocean nDIC by 220 μmol kg-1 above the average low-latitude value. However, this immediate effect is transitory. The long-term impact of upwelling (brought about by increasing TA), which would persist even if gas exchange were to return the surface ocean to the same CO2 as without upwelling, is to increase nDIC by 74 μmol kg-1 above the low-latitude average.

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DIC latitude gradient MS - Accepted Manuscript
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Accepted/In Press date: 20 June 2019
Published date: 11 July 2019
Keywords: DIC, dissolved inorganic carbon, ocean carbon, latitudinal gradient, surface distribution, upwelling, entrainment, CO2 solubility

Identifiers

Local EPrints ID: 432462
URI: https://eprints.soton.ac.uk/id/eprint/432462
ISSN: 1726-4170
PURE UUID: d3115f36-88ab-4db3-b3c5-870d7c0a3ce4
ORCID for Yingxu Wu: ORCID iD orcid.org/0000-0002-7847-6215
ORCID for Luke Tyrrell: ORCID iD orcid.org/0000-0002-1002-1716

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Date deposited: 16 Jul 2019 16:30
Last modified: 15 Oct 2019 00:52

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Contributors

Author: Yingxu Wu ORCID iD
Author: M.P. Hain
Author: Matthew P Humphreys
Author: Sue Hartman
Author: Luke Tyrrell ORCID iD

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