Abstract
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.
Highlights
1.1 The AMOC and its stabilityThe Atlantic meridional overturning circulation (AMOC) is an oceanic system of currents carrying warm buoyant waters to high northern latitudes, balanced by a cool deep return flow
We find that meridional density gradients explain the detailed temporal structure of the AMOC during both phases (Sect. 4), and that we are able to reduce the problem to a density analysis of the North and South Atlantic (Sect. 5)
Higher resolution models may have significant feedbacks that are absent from Fast Met Office/UK Universities Simulator (FAMOUS), such as altered net advection through the Bering Strait where a reduction of the freshwater flux may impact the response of the AMOC to freshwater forcing
Summary
The Atlantic meridional overturning circulation (AMOC) is an oceanic system of currents carrying warm buoyant waters to high northern latitudes, balanced by a cool deep return flow. The AMOC often recovers and sometimes with an overshoot, (Vellinga et al 2002; Stouffer et al 2006; Cao et al 2016) This may be due to the gradual warming of subsurface waters at low- and middle-latitudes (Stouffer and Manabe 1999) along with increased northward salinity advection (Thorpe et al 2001; Bitz et al 2007). Two of the simulations ended with AMOC strengths greater than that of the control run, as had been previously reported (Stouffer et al 2006) This was attributed to double-up resulting from ‘compensating’ deep-water formation in the GIN Seas continuing whilst the Atlantic deep-water formation recovered (Smith and Gregory 2009)
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