Transports and budgets of anthropogenic CO2 in the tropical North Atlantic in 1992-1993 and 2010-2011

Abstract

The meridional transport of anthropogenic CO2 (Cant) in the tropical North Atlantic (TNA) is investigated using data from transoceanic sections along 7.5°N and 24.5°N, carried out in the early 1990s and 2010s. The net Cant transport across both sections is northward. At 7.5°N, this transport increased from 315 ± 47 kmol s-1 in 1993 to 493 ± 51 kmol s-1 in 2010; similarly, across 24.5°N it grew from 530 ± 46 kmol s-1 in 1992 to 662 ± 49 kmol s-1 in 2011. These changes result from modifications in the intermediate and deep circulation patterns, as well as from Cant increase within the thermocline waters. In deep waters, lateral advection causes a net Cant input of 112 ± 60 kmol s-1 (234 ± 65 kmol s-1) in 1992-1993 (2010-2011); within these deep waters, the storage rate of Cant is not statistically different from the net Cant input, 139 ± 21 kmol s-1 (188 ± 21 kmol s-1) in 1992-1993 (2010-2011). The Cant increase in deep waters is due to the large injection of Cant across the 24.5°N by the Deep Western Boundary Current and the northward recirculation of North Atlantic Deep Water along 7.5°N. In contrast, a large net Cant output in the upper layer is caused by the Florida Current. Despite this net Cant output, the Cant accumulates at a rate of 215 ± 24 kmol s-1 (291 ± 24 kmol s-1) referenced to year 1993 (2010). From the two Cant budgets, we infer a Cant air-sea flux of 0.23 ± 0.02 Pg yr-1in the TNA, much larger than previous estimates. Key Points Transport of Cant at 7.5°N and 24.5°N Atlantic section from in situ data Cant storage rates in the tropical North Atlantic Cant air-sea fluxes in the tropical North Atlantic.