Consistency and Challenges in the Ocean Carbon Sink Estimate for the Global Carbon Budget

Type Article
Date 2020-10
Language English
Author(s) Hauck Judith1, Zeising Moritz1, Le Quere CorinneORCID2, 3, Gruber NicolasORCID4, Bakker Dorothee C. E.2, Bopp Laurent5, Chau Thi Tuyet Trang6, Guerses Oezguer1, Ilyina TatianaORCID7, Landschuetzer Peter7, Lenton Andrew8, 9, 10, Resplandy LaureORCID11, Roedenbeck Christian12, Schwinger Joerg13, Seferian Roland14
Affiliation(s) 1 : Helmholtz Zentrum Polar & Meeresforsch, Alfred Wegener Inst, Bremerhaven, Germany.
2 : Univ East Anglia, Sch Environm Sci, Norwich, Norfolk, England.
3 : Univ East Anglia, Tyndall Ctr Climate Change Res, Norwich, Norfolk, England.
4 : Swiss Fed Inst Technol, Eidgenoss Tech Hsch Zurich, Inst Biogeochem & Pollutant Dynam, Zurich, Switzerland.
5 : Univ PSL, Sorbonne Univ, Ecole Normale Super,CNRS, Lab Meteorol Dynam,Inst Pierre Simon Lapl,Ecole N, Paris, France.
6 : LSCE IPSL, Lab Sci Climat & Environm, Paris, France.
7 : Max Planck Inst Meteorol, Ocean Earth Syst, Hamburg, Germany.
8 : Commonwealth Sci & Ind Res Org CSIRO Oceans & Atm, Hobart, Tas, Australia.
9 : Univ Tasmania, Inst Marine & Antarctic Studies, Australian Antarct Program Partnership, Hobart, Tas, Australia.
10 : Ctr Southern Hemisphere Oceans Res, Hobart, Tas, Australia.
11 : Princeton Univ, Princeton Environm Inst, Dept Geosci, Princeton, NJ 08544 USA.
12 : Max Planck Inst Biogeochem, Biogeochem Signals, Jena, Germany.
13 : Bjerknes Ctr Climate Res, NORCE Norwegian Res Ctr, Bergen, Norway.
14 : Univ Toulouse, Meteofrance, CNRM, CNRS, Toulouse, France.
Source Frontiers In Marine Science (2296-7745) (Frontiers Media Sa), 2020-10 , Vol. 7 , P. 571720 (22p.)
DOI 10.3389/fmars.2020.571720
WOS© Times Cited 68
Keyword(s) ocean carbon uptake, anthropogenic CO2, ocean carbon cycle model evaluation, riverine carbon flux, variability of the ocean carbon sink, seasonal cycle

Based on the 2019 assessment of the Global Carbon Project, the ocean took up on average, 2.5 +/- 0.6 PgC yr(-1) or 23 +/- 5% of the total anthropogenic CO2 emissions over the decade 2009-2018. This sink estimate is based on simulation results from global ocean biogeochemicalmodels (GOBMs) and is compared to data-products based on observations of surface ocean pCO(2) (partial pressure of CO2) accounting for the outgassing of river-derived CO2. Here we evaluate the GOBM simulations by comparing the simulated surface ocean pCO(2) to observations. Based on this comparison, the simulations are well-suited for quantifying the global ocean carbon sink on the time-scale of the annual mean and its multi-decadal trend (RMSE <20 mu atm), as well as on the time-scale of multi-year variability (RMSE <10 mu atm), despite the large model-data mismatch on the seasonal time-scale (RMSE of 20-80 mu atm). Biases in GOBMs have a small effect on the global mean ocean sink (0.05 PgC yr(-1)), but need to be addressed to improve the regional budgets and model-data comparison. Accounting for non-mapped areas in the data-products reduces their spread as measured by the standard deviation by a third. There is growing evidence and consistency among methods with regard to the patterns of the multi-year variability of the ocean carbon sink, with a global stagnation in the 1990s and an extra-tropical strengthening in the 2000s. GOBMs and data-products point consistently to a shift from a tropical CO2 source to a CO2 sink in recent years. On average, the GOBMs reveal less variations in the sink than the data-based products. Despite the reasonable simulation of surface ocean pCO(2) by the GOBMs, there are discrepancies between the resulting sink estimate from GOBMs and data-products. These discrepancies are within the uncertainty of the river flux adjustment, increase over time, and largely stem from the Southern Ocean. Progress in our understanding of the global ocean carbon sink necessitates significant advancement in modeling and observing the Southern Ocean carbon sink including (i) a game-changing increase in high-quality pCO(2) observations, and (ii) a critical re-evaluation of the regional river flux adjustment.

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Hauck Judith, Zeising Moritz, Le Quere Corinne, Gruber Nicolas, Bakker Dorothee C. E., Bopp Laurent, Chau Thi Tuyet Trang, Guerses Oezguer, Ilyina Tatiana, Landschuetzer Peter, Lenton Andrew, Resplandy Laure, Roedenbeck Christian, Schwinger Joerg, Seferian Roland (2020). Consistency and Challenges in the Ocean Carbon Sink Estimate for the Global Carbon Budget. Frontiers In Marine Science, 7, 571720 (22p.). Publisher's official version : , Open Access version :