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 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) high-latitude upwelling of DIC- and TA-rich deep waters. We find that temperature and upwelling are the two major drivers. 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). 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
2661-2681
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, Toby
6808411d-c9cf-47a3-88b6-c7c294f2d114
11 July 2019
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, Toby
6808411d-c9cf-47a3-88b6-c7c294f2d114
Wu, Yingxu, Hain, M.P., Humphreys, Matthew P, Hartman, Sue and Tyrrell, Toby
(2019)
What drives the latitudinal gradient in open ocean surface dissolved inorganic carbon concentration?
Biogeosciences, 16 (13), .
(doi:10.5194/bg-16-2661-2019).
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 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) high-latitude upwelling of DIC- and TA-rich deep waters. We find that temperature and upwelling are the two major drivers. 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). 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.
Text
DIC latitude gradient MS
- Accepted Manuscript
Text
bg-16-2661-2019
- Version of Record
More information
Accepted/In Press date: 20 June 2019
e-pub ahead of print date: 11 July 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: http://eprints.soton.ac.uk/id/eprint/432462
ISSN: 1726-4170
PURE UUID: d3115f36-88ab-4db3-b3c5-870d7c0a3ce4
Catalogue record
Date deposited: 16 Jul 2019 16:30
Last modified: 16 Mar 2024 02:52
Export record
Altmetrics
Contributors
Author:
Yingxu Wu
Author:
M.P. Hain
Author:
Matthew P Humphreys
Author:
Sue Hartman
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