MITgcm study of AMOC multicentennial variability’s origin, mechanism, and oceanic climate impact

The Holocene climate has experienced multicentennial variability (MCV), which is suggested to be significantly influenced by the Atlantic Meridional Overturning Circulation (AMOC)’s MCV, as evidenced in proxy records. However, the AMOC MCV’s origin, mechanism, and climatic impact particularly on the ocean, remain not well studied. Utilizing the ocean-only MIT general circulation model (MITgcm), we conducted 40 experiments with varying setups of small-amplitude stochastic surface freshwater forcing, each exceeding 5000 years in duration. The simulated AMOCs generally exhibit MCV, primarily driven by salinity variability in the upper-ocean of the North Atlantic. This salinity variability is dominated by meridional salinity advection between the subtropical and subpolar North Atlantic, rather than processes related to the Arctic Ocean or South Atlantic. Consequently, this MITgcm study identifies a North Atlantic Ocean-originated AMOC MCV, largely attributed to meridional salinity advection.

In terms of climatic impact, the modeled AMOC MCV induces MCV in the magnitude of Antarctic Bottom Water formation and the northward Atlantic meridional oceanic heat transport. This suggests that in the context of global warming and potential change in AMOC variability, low-frequency oceanic climate variability may shift in magnitude, period, or both. Such changes could potentially influence the centennial-scale anthropogenic climate change, which can overlap with a certain phase of multicentennial natural variability.