Abstract
We analyse the interaction between the North Atlantic subpolar gyre (SPG) and the Atlantic Meridional Over-turning Circulation (AMOC) during DO-like AMOC oscillations. The oscillations occur in a simulation with thecoupled climate model MPI-ESM under constant forcing with a CO2concentration of 206 ppm and prescribedmodern continental ice sheets. The AMOC oscillates between a strong and a weak state on timescales between700 and 1500 years, which is comparable to the timescales of DO-events.The strong AMOC state is characterised by high temperatures over Greenland, a warm and salty North At-lantic, a weak SPG, and partially ice free Nordic Seas with active deep convection. The weak AMOC state ischaracterised by low Greenland temperatures, a cold and fresh North Atlantic, a strong SPG, extensive sea-icecover and sporadic deep convection south of Iceland. The transition between the two states is driven by aredistribution of salt between the tropical and the subpolar North Atlantic which is controlled by the strength andextent of the SPG. The SPG oscillates between a strong and extensive state and a weak and contracted state. TheAMOC and SPG are anti-correlated and coupled via a feedback loop between the northward salt transport, thelocation of deepwater formation and the resulting density structure in the subpolar North Atlantic. Changes in thewind-driven component of the SPG seem to play a key role in triggering the transition from the weak to the strongAMOC state.Even though the simulated AMOC/SPG oscillations occur with modern ice sheets, the presented mecha-nism supports the hypothesis that DO-events could have been the result of unforced changes in the North Atlanticcirculation system.
