You have full access to this open access article. Increased CO 2 triggers extensive Arctic warming, causing widespread melting of sea ice. The resulting freshwater spreads southward, first from the Labrador Sea and then the Nordic Seas, and proceeds along the eastern coast of North America. The freshwater enters the subpolar gyre north of the separated Gulf Stream, the North Atlantic Current. This decreases the density gradient across the current and the current weakens in response, reducing the inflow to the deepwater production regions.
This contrasts with the common perception that freshwater caps the convection regions, stifling deepwater production; rather, it is the inflow to the subpolar gyre that is suppressed. Changes in surface temperature have a much weaker effect, and there are no consistent changes in local or remote wind forcing among the models.
Thus an increase in freshwater discharge, primarily from the Labrador Sea, is the precursor to AMOC weakening in these simulations. The large-scale ocean circulation transports heat, nutrients, freshwater, and carbon around the globe.
In the Northern Hemisphere alone, 1. An essential part of this occurs in the Atlantic Ocean Trenberth et al. This is as is commonly done in the atmosphere; the three dimensional meridional circulation is made two dimensional following zonal integration of the velocities. But the integration obscures the 3D structure of the flow, with its western boundary currents and horizontal recirculations. The latter, for example, can extend the meridional pathways in both the upper and lower limbs of the AMOC, as fluid parcels may be delayed for years before moving northward.
This could greatly increase their net exposure to the atmosphere Bower et al. AMOC is not stationary, but varies on a range of time scales, from weekly to centennial Bryden et al. AMOC is predicted to weaken in the warming climate as well. Despite consistent indications from model simulations, there is a lack of consensus on the driving mechanisms for the weakening.
