Abstract <p>Using GLORYS12 ocean reanalysis and ERA5 atmosphere reanalysis, we quantitatively and qualitatively analyze ocean–atmosphere interactions on a synoptic timescale through water mass transformation rate and buoyancy flux in the Labrador Sea. Calculated for the entire World Ocean over 31 years, from 1993 to 2023, the buoyancy flux dataset is used to derive average climatological values for the North Atlantic. Based on buoyancy flux data, water mass transformation rates in the Labrador Sea are calculated and the mean long-term distribution of transformation at different water densities and long-term transformation dynamics are considered. Bandpass filtering highlights the importance of synoptic timescale in water mass transformation in the Labrador Sea. Cases with large increases in water mass transformation rates, which are related to synoptic atmospheric dynamics, are considered in detail, using January–March 1993 as an example.</p>