Advective Controls on the North Atlantic Anthropogenic Carbon Sink
Sean Ridge, Galen A. McKinley
Abstract
Though it is clear that the North Atlantic is the site of the highest storage of anthropogenic carbon ( C a n t ) per area, it is uncertain whether the air‐sea C a n t fluxes contributing to North Atlantic C a n t storage occur in the subpolar gyre or upstream in the subtropical gyre. Using data and models, we show that air‐sea C a n t uptake capacity is advected into the subpolar gyre along the same subsurface pathway as nutrients. This pathway is known as the nutrient stream. On the A22 section between Woods Hole and Bermuda, nutrient stream waters are the oldest in the upper 2,000 m and contain low C a n t . These northward moving waters are sufficiently depleted in C a n t such that they could sustain a subpolar air‐sea C a n t flux of −0.19 Pg C a n t year −1 . The ocean hindcast model used here indicates that despite some subtropical re‐circulation, uptake capacity is transported into the subpolar gyre where it sustains subpolar air‐sea C a n t uptake. With this model, we show that high‐ and low‐end estimates of subpolar air‐sea C a n t flux are reconciled by accounting for a factor of two difference in their respective study areas. If half of the observed air‐sea C a n t uptake capacity transport at A22 is ventilated in the subpolar region, it can fully support high‐end estimates of the subpolar air‐sea C a n t sink (−0.09±0.01 Pg C a n t year −1 ).