18 Oct 2022
18 Oct 2022
Status: this preprint is open for discussion.

Underestimation of oceanic carbon uptake in the Arctic Ocean: Ice melt as predictor of the sea ice carbon pump

Benjamin Richaud1, Katja Fennel1, Eric C. J. Oliver1, Michael D. DeGrandpre2, Timothée Bourgeois1,3, Xianmin Hu1,4, and Youyu Lu4 Benjamin Richaud et al.
  • 1Department of Oceanography, Dalhousie University, Halifax, NS, Canada
  • 2Department of Chemistry and Biochemistry, University of Montana, Missoula, MT, USA
  • 3NORCE Norwegian Research Centre, Bjerknes Centre for Climate Research, Bergen, Norway
  • 4Bedford Institute of Oceanography, Department of Fisheries and Oceans, Dartmouth, NS, Canada

Abstract. The Arctic Ocean is generally undersaturated in CO2 and acts as a net sink of atmospheric CO2. This oceanic uptake is strongly modulated by sea ice, which can prevent air-sea gas exchange and has major impacts on stratification and primary production. Moreover, carbon is stored in sea ice with a ratio of alkalinity to dissolved inorganic carbon that is larger than in seawater. It has been suggested that this storage amplifies the seasonal cycle of seawater pCO2 and leads to an increase in oceanic carbon uptake in seasonally ice-covered regions compared to those that are ice-free. Given the rapidly changing ice-scape in the Arctic Ocean, a better understanding of the link between the seasonal cycle of sea ice and oceanic uptake of CO2 is needed. Here, we investigate how the storage of carbon in sea ice affects the air-sea CO2 flux and quantify its dependence on the ratio of alkalinity to inorganic carbon in ice. To this end, we present two independent approaches: a theoretical framework that provides an analytical expression of the amplification of carbon uptake in seasonally ice-covered oceans, and a simple parameterization of carbon storage in sea ice implemented in a 1D physical-biogeochemical ocean model. Sensitivity simulations show a linear relation between ice melt and the amplification of seasonal carbon uptake. A 30 % increase in carbon uptake in the Arctic Ocean is estimated compared to ice melt without amplification. Applying this relationship to different future scenarios from an Earth System Model that does not account for the effect of carbon storage in sea ice suggests that Arctic Ocean carbon uptake is underestimated by 5 to 15 % in these simulations.

Benjamin Richaud et al.

Status: open (until 13 Dec 2022)

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  • RC1: 'Comment on egusphere-2022-861', Anonymous Referee #1, 08 Nov 2022 reply

Benjamin Richaud et al.

Data sets

Data set of 1D model runs, CTRL and ICE runs, associated with "Underestimation of oceanic carbon uptake in the Arctic Ocean: Ice melt as predictor of the sea ice carbon pump" Richaud, Benjamin, Fennel, Katja, Oliver, Eric C. J., DeGrandpre, Michael D., Bourgeois, Timothée, Hu, Xianmin, and Lu, Youyu

Benjamin Richaud et al.


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Short summary
Sea ice is a dynamic carbon reservoir. Its seasonal growth and melt modify the carbonate chemistry in the upper ocean, with consequences on the Arctic Ocean carbon sink. Yet, the importance of this process is poorly quantified. Using two independent approaches, this study provides new methods to evaluate the error on air-sea carbon flux estimates due to the lack of biogeochemistry in ice in Earth System Models. Those errors range from 5 to 30 %, depending on the model and climate projection.