Contribution of upwelling filaments to offshore carbon export in the subtropical Northeast Atlantic Ocean

Revisiting previously published data we show that upwelling filaments off Iberia and NW Africa export to the offshore system, largely as dissolved organic matter (DOM), from 35% to 58% of the net community production generated in the coastal upwelling systems. Transport by filaments accounts for 2.5 to 4.5 times the offshore carbon export driven by Ekman transport. The fate of this carbon is unknown, although conservative mass balance analysis in the subtropical Northeast Atlantic region suggests that < 16% of the exported carbon may be respired in the coastal transition zone (CTZ). Thus, DOM exported by the filaments cannot fully account for the previously reported metabolic imbalance (i.e., net heterotrophy) of the surface waters of the CTZ. The remainder of exported organic matter is transported to and accumulated in the subtropical gyre, where high surface DOM concentrations have been reported. Since filaments are ubiquitous features in all coastal transition zone systems, they must represent a significant flux of carbon to the open ocean, which should be considered in global biogeochemical models.