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Lina Garcia-Suarez

and 2 more

A solid understanding of the mechanisms behind the presently observed, rapid warming of the northwest North Atlantic Continental Shelf is lacking. We hypothesize that a weakening of the Labrador Current System (LCS), especially the shelfbreak jet along the Scotian Shelf, is contributing to these changes and that the future evolution of the LCS will be key to accurate projections. Here we analyze the response of a transient simulation of the high-resolution GFDL Climate Model 2.6 (CM2.6) which realistically simulates the regional circulation but includes only a highly simplified representation of ocean biogeochemistry. Then, we dynamically downscale CM2.6 using a medium-complexity regional biogeochemical ocean model to obtain projections of several ecosystem-relevant variables. In the simulation, the shelfbreak jet weakens throughout the century because of a reduction of the along-shelf pressure gradient caused by a buoyancy gain of the upper water column along the shelf edge. This buoyancy gain is the result of an increased presence of subtropical waters in the continental slope. Importantly, we find that the weakening of the shelfbreak jet is not in response to a northward shift of the Gulf Steam, as has been hypothesized by others, and that previous reports of a northward shift of the Gulf Stream North Wall (GSNW) are an artifact of the temperature-based GSNW criterion in common use. The projected weakening of the shelfbreak jet is likely to lead to a reduction in nutrient availability and a subsequent decline in productivity on the Scotian Shelf, Gulf of St. Lawrence, and Grand Banks.