The Arctic Ocean CO2 Sink: Trends, Uncertainties, and the Impact of Sea Ice

The Arctic Ocean covers 3 % of the Earth's surface but is estimated to contribute 5–14 % to the global ocean carbon sink. Sparse and unevenly distributed observations complicate our understanding of the size and the controlling mechanisms of this carbon sink. We adopt and advance the two-step neural network approach of Landschützer et al. (2016, https://doi.org/10.1002/2015gb005359; Self Organizing Map—Feed Forward Network) to improve region-specific reconstructions of the surface ocean partial pressure of carbon dioxide ($p$(${\text{CO}}_2$)) in the Arctic Ocean and subsequently estimate the air-sea ${\text{CO}}_2$ flux. Our study shows that biogeochemical properties previously selected as predictor variables for $p$(${\text{CO}}_2$) at the global scale are not well suited to the Arctic Ocean and a sensitivity study reveals large differences in the size of the Arctic Ocean carbon sink depending on the choice of air-sea ${\text{CO}}_2$ flux parameterization. This is most acute for those relating to sea ice cover, leading to a difference of up to 25 % (9.2–13.3 Pg C) in the total size of the Arctic Ocean carbon sink over the 32-year duration of the study.