The model-based DLSD parameter—proposed in ref. 4 and using the EN4 reanalysis dataset—incorporates a larger area and greater depth range than do instrumental-data-only studies, such as ref. 5, which examines past variability in Labrador Sea convection and focuses on the central Labrador Sea and on depths less than 2,000 m, where most observational data are available. The comparison here of DLSD (purple line, three-year mean) from the EN4 dataset with instrumental data on density changes in the central Labrador Sea at 1,500–1,900 m depth (grey line, annual averages; black line, three-year mean) illustrates that the two parameters show very similar variability. Both are dominated by the density changes caused by deep convection in the Labrador Sea, which can reach down to around 2,000 m. Estimates of uncertainty are discussed in ref. 61.