Reconstructing the Preindustrial Coastal Carbon Cycle Through a Global Ocean Circulation Model: Was the Global Continental Shelf Already Both Autotrophic and a CO2 Sink?. Issue 2 (24th February 2021)

• Record Type: Journal Article
• Authors: Lacroix, Fabrice; Ilyina, Tatiana; Laruelle, Goulven G.; Regnier, Pierre
• Is Part Of: Global biogeochemical cycles. Volume 35:Issue 2(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-02-24
• Subjects: anthropogenic perturbation -- biogeochemistry -- carbon fluxes -- coastal ocean -- global continental shelf -- residence time; Biogeochemical cycles -- Periodicals; Electronic journals; 577.1405
• DOI: 10.1029/2020GB006603
• Languages: English
• ISSNs: 0886-6236

Abstract

Abstract: The contribution of continental shelves to the marine carbon cycle is still poorly understood. Their preindustrial state is, for one, essentially unknown, which strongly limits the quantitative assessment of their anthropogenic perturbation. To date, approaches developed to investigate and quantify carbon fluxes on continental shelves have strongly simplified their physical and biogeochemical features. In this study, we enhance the global ocean biogeochemistry model HAMburg Ocean Carbon Cycle by explicitly representing riverine loads of carbon and nutrients, as well as improving the representation of organic matter dynamics in the coastal ocean. Our simulations, at a resolution of ∼0.4°, reveal a globally averaged shelf water residence time (RT) of 12–17 months, which is much shorter than the global RTs previously assumed in benchmark studies (>4 years). This shorter global RT, induced primarily through outer shelf regions with large oceanic inflows, promotes an efficient offshore transport of terrestrial and marine organic carbon (0.44 PgCyr −1 ) and a dissolved inorganic carbon sink from the organic cycling of carbon on the global shelf (net ecosystem productivity [NEP] equal to +0.20 PgCyr −1 ). In turn, this autotrophic state of continental shelves contributes to a weak global preindustrial sink of atmospheric CO2 (0.04 PgCyr −1 ), dominated by extensive regions with large oceanic inflows and positive NEPs, such as the Patagonian shelf, the East China Sea and the outer North Sea. The contemporary global shelf CO2 uptake of 0.15 PgCyr −1 furthermoresuggests that the anthropogenic CO2 uptake (0.11 PgCyr −1 ) on the global continental shelf is less efficient with respect to the open ocean. Key Points: In a Global Ocean Biogeochemical Model, we simulate short continental shelf water residence times driven by dominant open ocean inflows These hydrodynamical features lead to net autotrophy and a slight sink of atmospheric CO2 over the preindustrial global shelf The results also suggest that the global continental shelf is a less efficient sink of anthropogenic CO2 than the open ocean