Basin‐wide particulate carbon flux in the Atlantic Ocean: Regional export patterns and potential for atmospheric CO2 sequestration

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Abstract
Particle flux data from 27 sites in the Atlantic Ocean have been compiled in order to determine regional variations in the strength and efficiency of the biological pump and to quantify carbon fluxes over the ocean basin, thus estimating the potential oceanic sequestration of atmospheric CO2. An algorithm is derived relating annual particulate organic carbon (POC) flux to primary production and depth that yields variations in the export ratio (ER = POC flux/primary production) at 125 m of between 0.08 and 0.38 over the range of production from 50 to 400 g C m−2 yr−1. Significant regional differences in changes of the export ratio with depth are related to the temporal stability of flux. Sites with more pulsed export have higher export ratios at 125 m but show more rapid decreases of POC flux with depth, resulting in little geographic variation in fluxes below ∼3000 m. The opposing effects of organic carbon production and calcification on ΔpCO2 of surface seawater are considered to calculate an “effective carbon flux” at the depth of the euphotic zone and at the base of the winter mixed layer. POC flux at the base of the euphotic zone integrated over the Atlantic Ocean between 65°N and 65°S amounts to 3.14 Gt C yr−1. Of this, 5.7% is remineralized above the winter mixed layer and thus does not contribute to CO2 sequestration on climatically relevant timescales. The effective carbon flux, termed Jeff, amounts to 2.47 Gt C yr−1 and is a measure of the potential sequestration of atmospheric CO2 for the area considered. A shift in the composition of sedimenting particles (seen in a decrease of the opal:carbonate ratio) is seen across the entire North Atlantic, indicating a basin‐wide phenomenon that may be related to large‐scale changes in climatic forcing.