On the Southern Ocean CO2 uptake and the role of the biological carbon pump in the 21st century

Hauck, J., Völker, C., Wolf-Gladrow, D. A., Laufkötter, C., Vogt, M., Aumont, O., Bopp, L., Buitenhuis, E. ORCID: https://orcid.org/0000-0001-6274-5583, Doney, S. C., Dunne, J., Gruber, N., Hashioka, T., John, J., Le Quéré, C. ORCID: https://orcid.org/0000-0003-2319-0452, Lima, I. D., Nakano, H., Séférian, R. and Totterdell, I. (2015) On the Southern Ocean CO2 uptake and the role of the biological carbon pump in the 21st century. Global Biogeochemical Cycles, 29 (9). 1451–1470. ISSN 0886-6236

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Abstract

We use a suite of eight ocean biogeochemical/ecological general circulation models from the Marine Ecosystem Model Intercomparison Project and Coupled Model Intercomparison Project Phase 5 archives to explore the relative roles of changes in winds (positive trend of Southern Annular Mode, SAM) and in warming‐ and freshening‐driven trends of upper ocean stratification in altering export production and CO2 uptake in the Southern Ocean at the end of the 21st century. The investigated models simulate a broad range of responses to climate change, with no agreement on a dominance of either the SAM or the warming signal south of 44°S. In the southernmost zone, i.e., south of 58°S, they concur on an increase of biological export production, while between 44 and 58°S the models lack consensus on the sign of change in export. Yet in both regions, the models show an enhanced CO2 uptake during spring and summer. This is due to a larger CO2(aq) drawdown by the same amount of summer export production at a higher Revelle factor at the end of the 21st century. This strongly increases the importance of the biological carbon pump in the entire Southern Ocean. In the temperate zone, between 30 and 44°S, all models show a predominance of the warming signal and a nutrient‐driven reduction of export production. As a consequence, the share of the regions south of 44°S to the total uptake of the Southern Ocean south of 30°S is projected to increase at the end of the 21st century from 47 to 66% with a commensurable decrease to the north. Despite this major reorganization of the meridional distribution of the major regions of uptake, the total uptake increases largely in line with the rising atmospheric CO2. Simulations with the MITgcm‐REcoM2 model show that this is mostly driven by the strong increase of atmospheric CO2, with the climate‐driven changes of natural CO2 exchange offsetting that trend only to a limited degree (∼10%) and with negligible impact of climate effects on anthropogenic CO2 uptake when integrated over a full annual cycle south of 30°S.

Item Type:	Article
Uncontrolled Keywords:	ocean carbon sink,export production,cmip5,southern annular mode,polar carbon cycle,ecosystem model intercomparison,sdg 13 - climate action,sdg 14 - life below water ,/dk/atira/pure/sustainabledevelopmentgoals/climate_action
Faculty \ School:	Faculty of Science > School of Environmental Sciences University of East Anglia Research Groups/Centres > Theme - ClimateUEA
UEA Research Groups:	Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences University of East Anglia Schools > Faculty of Science > Tyndall Centre for Climate Change Research Faculty of Science > Research Centres > Tyndall Centre for Climate Change Research
Depositing User:	Pure Connector
Date Deposited:	26 Aug 2015 14:14
Last Modified:	13 Apr 2023 13:48
URI:	https://ueaeprints.uea.ac.uk/id/eprint/54164
DOI:	10.1002/2015GB005140

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