Sensitivity of North Atlantic subpolar gyre and overturning to stratification-dependent mixing: response to global warming

• Main Author: Juliette Mignot
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Nordic Seas; North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.596.5737; http://www.pik-potsdam.de/~anders/publications/marzeion_levermann10.pdf

Abstract We use a reduced complexity climate model with a three-dimensional ocean component and realistic topography to investigate the effect of stratification-dependent mixing on the sensitivity of the North Atlantic subpolar gyre (SPG), and the Atlantic meridional over-turning circulation (AMOC), to idealized CO2 increase and peaking scenarios. The vertical diffusivity of the ocean interior is parameterized as j * N-a, where N is the local buoyancy frequency. For all parameter values 0 B a B 3, we find the SPG, and subsequently the AMOC, to weaken in response to increasing CO2 concentrations. The weak-ening is significantly stronger for a C acr & 1.5. Depending on the value of a, two separate model states develop. These states remain different after the CO2 concentration is stabilized, and in some cases even after the CO2 concentration has been decreased again to the pre-industrial level. This behaviour is explained by a positive feedback between stratification and mixing anomalies in the Nordic Seas, causing a persistent weak-ening of the SPG.