Rapid decline of the CO₂ buffering capacity in the North Sea and implications for the North Atlantic Ocean

New observations from the North Sea, a NW European shelf sea, show that between 2001 and 2005 the CO 2 partial pressure ( p CO 2 ) in surface waters rose by 22 μ atm, thus faster than atmospheric p CO 2 , which in the same period rose approximately 11 μ atm. The surprisingly rapid decline in air‐sea partial pressure difference (Δ p CO 2 ) is primarily a response to an elevated water column inventory of dissolved inorganic carbon (DIC), which, in turn, reflects mostly anthropogenic CO 2 input rather than natural interannual variability. The resulting decline in the buffering capacity of the inorganic carbonate system (increasing Revelle factor) sets up a theoretically predicted feedback loop whereby the invasion of anthropogenic CO 2 reduces the ocean's ability to uptake additional CO 2 . Model simulations for the North Atlantic Ocean and thermodynamic principles reveal that this feedback should be stronger, at present, in colder midlatitude and subpolar waters because of the lower present‐day buffer capacity and elevated DIC levels driven either by northward advected surface water and/or excess local air‐sea CO 2 uptake. This buffer capacity feedback mechanism helps to explain at least part of the observed trend of decreasing air‐sea Δ p CO 2 over time as reported in several other recent North Atlantic studies.