The Southern Ocean Carbon Cycle 1985–2018: Mean, seasonal cycle, trends, and storage

Hauck, Judith, Gregor, Luke, Nissen, Cara, Patara, Lavinia, Hague, Mark, Mongwe, Precious, Bushinsky, Seth, Doney, Scott C., Gruber, Nicolas, Le Quéré, Corinne ORCID: https://orcid.org/0000-0003-2319-0452, Manizza, Manfredi, Mazloff, Matthew, Monteiro, Pedro M. S. and Terhaar, Jens (2023) The Southern Ocean Carbon Cycle 1985–2018: Mean, seasonal cycle, trends, and storage. Global Biogeochemical Cycles, 37 (11). ISSN 0886-6236

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Abstract

We assess the Southern Ocean CO2 uptake (1985–2018) using data sets gathered in the REgional Carbon Cycle Assessment and Processes Project Phase 2. The Southern Ocean acted as a sink for CO2 with close agreement between simulation results from global ocean biogeochemistry models (GOBMs, 0.75 ± 0.28 PgC yr−1) and pCO2-observation-based products (0.73 ± 0.07 PgC yr−1). This sink is only half that reported by RECCAP1 for the same region and timeframe. The present-day net uptake is to first order a response to rising atmospheric CO2, driving large amounts of anthropogenic CO2 (Cant) into the ocean, thereby overcompensating the loss of natural CO2 to the atmosphere. An apparent knowledge gap is the increase of the sink since 2000, with pCO2-products suggesting a growth that is more than twice as strong and uncertain as that of GOBMs (0.26 ± 0.06 and 0.11 ± 0.03 Pg C yr−1 decade−1, respectively). This is despite nearly identical pCO2 trends in GOBMs and pCO2-products when both products are compared only at the locations where pCO2 was measured. Seasonal analyses revealed agreement in driving processes in winter with uncertainty in the magnitude of outgassing, whereas discrepancies are more fundamental in summer, when GOBMs exhibit difficulties in simulating the effects of the non-thermal processes of biology and mixing/circulation. Ocean interior accumulation of Cant points to an underestimate of Cant uptake and storage in GOBMs. Future work needs to link surface fluxes and interior ocean transport, build long overdue systematic observation networks and push toward better process understanding of drivers of the carbon cycle.

Item Type:	Article
Additional Information:	Data Availability Statement: All RECCAP2 data is available at Zenodo: Müller (2023; https://doi.org/10.5281/zenodo.7990823). The processed data for this study is available at Hauck et al. (2023a; https://zenodo.org/records/10074671). Code for each figure is in the GitHub repository: https://github.com/RECCAP2-ocean/Southern-Ocean, with a frozen version deposited at Hauck et al. (2023b; https://zenodo.org/records/10076121). Funding information: Initiative and Network Fund of the Helmholtz Association. Grant Number: VH-NG-1301; ERC-2022-StG. Grant Number: 101077209; European Unions Horizon 2020 research and innovation programme, project COMFORT. Grant Number: 820989; European Union's Horizon Europe research and innovation program, project OceanICU. Grant Number: 101083922; European Union's Horizon 2020 research and innovation programme SO-CHIC. Grant Number: 821001; European Union's Horizon 2020 research and innovation programme 4C. Grant Number: 821003; NASA Carbon Cycle Science. Grant Number: 80NSSC22K0156; NOAA Climate Program Office's Climate Observations and Monitoring, Climate Variability and Predictability, and Global Ocean Monitoring and Observation programs. Grant Number: NA21OAR4310260; NSF. Grant Number: OCE-2049631; Palmer LTER program National Science Foundation. Grant Number: OPP-2026045; Natural Environment Research Council SONATA grant. Grant Number: NE/P021417/1; UK Royal Society. Grant Number: RP\R1\191063; Woods Hole Oceanographic Institution Postdoctoral Scholar Program; Swiss National Science Foundation. Grant Number: 200020-20051; German Research Foundation. Grant Number: PA 3075/2-1 North German Supercomputing Alliance
Faculty \ School:	Faculty of Science > School of Environmental Sciences University of East Anglia Research Groups/Centres > Theme - ClimateUEA
UEA Research Groups:	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 Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences
Depositing User:	LivePure Connector
Date Deposited:	17 Jul 2024 10:31
Last Modified:	25 Sep 2024 17:56
URI:	https://ueaeprints.uea.ac.uk/id/eprint/95935
DOI:	10.1029/2023GB007848

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