Coupling of the Subpolar Gyre and the Overturning Circulation During Abrupt Glacial Climate Transitions

Abstract

We present a mechanism for self-sustained ocean circulation changes that cause abrupt temperature changes over Greenland in a multimillennial climate model simulation with glacial CO2 concentrations representative of Marine Isotope Stage 3. The Atlantic meridional overturning circulation (AMOC) and the subpolar gyre (SPG) oscillate on millennial time scales. When the AMOC is strong, the SPG is weak and contracted; when the AMOC is weak, the SPG is strong and extensive. The coupling between the two systems via wind-driven and density-driven feedbacks is key to maintaining the oscillations. The SPG controls the transport of heat and salt into the deep-water formation sites and thus controls the AMOC strength. The strength and location of the deep-water formation affect the density-driven part of the SPG and thus control the mean strength and extent of the SPG. This mechanism supports the hypothesis that coupled ocean-ice-atmosphere interactions could have triggered abrupt glacial climate change.