Transports and budgets of total inorganic carbon in the subpolar and temperate North Atlantic

[1] Transports of Total Inorganic Carbon (TIC), Total Alkalinity (TA) and Anthropogenic Carbon (CANT) are calculated across a densely sampled World Ocean Circulation Experiment (WOCE) section at the southern boundary of the subpolar North Atlantic (WOCE A25, 4x cruise). The circulation pattern was approximated using an inverse model constrained with measured mass transports at specific sites, while conserving the mass and salt transports, and forcing the silicate flux to equal the river input north of the section. The mass and chemical fluxes are decomposed into their barotropic, baroclinic and horizontal components. The TA transport is negligible (transport ± maximum estimate of uncertainty, −135 ± 507 kmol s−1), while TIC is transported southwards (−1015 ± 490 kmol s−1) and CANT northwards (116 ± 125 kmol s−1). Combining our results with those from Roson et al. [2002] across 24.5°N (WOCE A5) we examine the contemporary and preindustrial TIC budgets in the subpolar and temperate North Atlantic based on two different approximations for the budget definitions. Initially, river input, biological production of TIC, along with sedimentation of calcium carbonate are ignored. Then, extended contemporary and preindustrial TIC budgets are discussed including rough estimates of the former processes, mainly based on values from the literature. Our findings point to the North Atlantic Ocean north of 24.5°N as a strong sink for atmospheric CO2 both today (2932 ± 2057 kmol s−1) and preindustrially (2439 ± 1721 kmol s−1). Only 17% of the contemporary CO2 air-sea uptake corresponds to CANT, which is mainly taken up in the temperate North Atlantic (between the 4x and 24.5°N sections). North of 24.5°N the Atlantic Ocean stores CANT at a rate of 1123 ± 200 kmol s−1. This CANT is mainly advected into the area in the upper limb of the overturning circulation, while 44% is directly introduced by air-sea uptake.

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