Mechanism on the short-term variability of the Atlantic meridional overturning circulation in the subtropical and tropical regions

The continuous, moored observation revealed significant variability in the strength of the Atlantic Meridional Overturning Circulation (AMOC). Cause of such AMOC variability is an extensively studied subject. This study focuses on the short-term variability, which ranges up to seasonal and interannual timescales. A mechanism is proposed from the perspective of ocean water redistribution by layers. By offering explanations for four phenomena of AMOC variability in the subtropical and tropical oceans (seasonality, meridional coherence, layered-transport compensation as observed at 26.5°N, and the 2009/2010 downturn occurred at 26.5°N), this mechanism suggests that the short-term AMOC variabilities in the entire subtropical and tropical regions are governed by a basin-wide adiabatic water redistribution process or the so-called sloshing dynamics rather than diapycnal processes.