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Explaining asymmetry between weakening and recovery of the AMOC in a coupled climate model

Haskins, Rosalind K., Oliver, Kevin I. C., Jackson, Laura C., Drijfhout, Sybren S., Wood, Richard A.
Climate dynamics 2019 v.53 no.1-2 pp. 67-79
asymmetry, climate, climate change, climate models, freshwater, salinity, temperature, Arctic region
The Atlantic meridional overturning circulation (AMOC) is projected to weaken in the coming century due to anthropogenic climate change. Various studies have considered AMOC weakening and collapse, with less research focusing on the processes and timescales of the recovery phase. This study uses a coupled climate model to explore the roles of salinity and temperature in AMOC recovery after a weakening. The North Atlantic and Arctic region was hosed with freshwater for 200 years. The mean Atlantic salinity increased strongly during recovery, and remained elevated for ~ 600 years post hosing. The behaviour of the AMOC was well reconstructed by applying “rotated geostrophy” to meridional density gradient profiles between 50°N and 30°S. This makes it possible to determine the role of overturning, gyre, and surface fluxes in the North and South Atlantic. Changes at 50°N dominate the weakening and early recovery. The magnitude of the overshoot to high AMOC transports in the recovery phase was related to density changes in the South Atlantic.