Around 90 % global warming occurs in the ocean but is insufficiently understood at the air–sea interface. Thermodynamics of the standard TEOS-10 is an improved tool for the description of heat exchange processes.

We study the Atlantic Meridional Overturning Circulation (AMOC) measured between Greenland and Portugal between 1993–2021. We identify changes in AMOC limb volume and velocity as two major drivers of AMOC variability at subpolar latitudes. Volume variations dominate on the seasonal timescale, while velocity variations are more important on the decadal timescale. This decomposition proves useful for understanding the origen of the differences between AMOC time series from different analyses.