Carbon distribution, fluxes, and budgets in the subtropical North Atlantic Ocean (24.5N)

Roson, G., Rios, A.F., Perez, F.F., Lavin, A. and Bryden, H.L. (2003) Carbon distribution, fluxes, and budgets in the subtropical North Atlantic Ocean (24.5N). Journal of Geophysical Research, 108 (C5), art. 3144. (doi:10.1029/1999JC000047).

Abstract

Hydrographic CO2 system data obtained from World Ocean Circulation Experiment (WOCE) transatlantic zonal section A5 across 24.5°N and Florida Straits are described. By combining CO2 measurements with hydrographic velocity calculations, the zonal and vertical variability of meridional fluxes of total alkalinity (TA), total dissolved inorganic carbon (TIC), and anthropogenic CO2 (C) are estimated. The resulting CO2 fluxes are examined in four geostrophic mid-ocean zones as well as in the Gulf Stream flow through Florida Straits and in the surface ageostrophic Ekman flow. This method allows an estimate of the net budgets of these chemical species in the system considering together the Arctic and Atlantic Oceans north of 24.5°N. Taking into account the net flux contribution through Bering Strait, total meridional transports of chemical properties across 24.5°N latitude are also estimated. The slightly divergent net TA budget (-460 ± 200 kmol s-1) suggests that the North Atlantic is a small alkalinity source. The divergent TIC budget (-2430 ± 200 kmol s-1 or -0.92 ± 0.08 GtC yr-1) suggests that the North Atlantic is a source of TIC and therefore a net sink for atmospheric CO2. This value is twice as large as a previous estimation made from a poorly sampled section. Surprisingly, the North Atlantic Ocean appears to act as a net sink of anthropogenic CO2 (+630 ± 200 kmol s-1 or +0.24 ± 0.08 GtC yr-1) and therefore a weak source of anthropogenic CO2 to the atmosphere. Its main contributor is the intense northward flux in the Florida Current (+1280 ± 100 kmol s-1). The calculations imply a divergent inorganic carbon budget of -3060 ± 200 kmol s-1 or -1.16 ± 0.08 GtC yr-1 in preindustrial times (TIC278, when the molar fraction of CO2 in the atmosphere was 278.2 ppm). This means that the North Atlantic would have had a 25% stronger divergence of TIC prior to the beginning of anthropogenic CO2 penetration.

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Contributors

Author: H.L. Bryden

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