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Sensitivity of atmospheric CO2 to regional variability in particulate organic matter remineralization depths

Wilson, Jamie D., Barker, Stephen ORCID:, Edwards, Neil R., Holden, Philip B. and Ridgwell, Andy 2019. Sensitivity of atmospheric CO2 to regional variability in particulate organic matter remineralization depths. Biogeosciences 16 (14) , pp. 2923-2936. 10.5194/bg-16-2923-2019

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The concentration of CO2 in the atmosphere is sensitive to changes in the depth at which sinking particulate organic matter is remineralized: often described as a change in the exponent “b” of the Martin curve. Sediment trap observations from deep and intermediate depths suggest there is a spatially heterogeneous pattern of b, particularly varying with latitude, but disagree over the exact spatial patterns. Here we use a biogeochemical model of the phosphorus cycle coupled with a steady-state representation of ocean circulation to explore the sensitivity of preformed phosphate and atmospheric CO2 to spatial variability in remineralization depths. A Latin hypercube sampling method is used to simultaneously vary the Martin curve independently within 15 different regions, as a basis for a regression-based analysis used to derive a quantitative measure of sensitivity. Approximately 30 % of the sensitivity of atmospheric CO2 to changes in remineralization depths is driven by changes in the subantarctic region (36 to 60∘ S) similar in magnitude to the Pacific basin despite the much smaller area and lower export production. Overall, the absolute magnitude of sensitivity is controlled by export production, but the relative spatial patterns in sensitivity are predominantly constrained by ocean circulation pathways. The high sensitivity in the subantarctic regions is driven by a combination of high export production and the high connectivity of these regions to regions important for the export of preformed nutrients such as the Southern Ocean and North Atlantic. Overall, regionally varying remineralization depths contribute to variability in CO2 of between around 5 and 15 ppm, relative to a global mean change in remineralization depth. Future changes in the environmental and ecological drivers of remineralization, such as temperature and ocean acidification, are expected to be most significant in the high latitudes where CO2 sensitivity to remineralization is also highest. The importance of ocean circulation pathways to the high sensitivity in subantarctic regions also has significance for past climates given the importance of circulation changes in the Southern Ocean.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Environmental Sciences
Publisher: European Geosciences Union (EGU) / Copernicus Publications
ISSN: 1726-4170
Funders: UK NERC
Date of First Compliant Deposit: 29 August 2019
Date of Acceptance: 9 July 2019
Last Modified: 04 May 2023 22:01

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