Extended Data Fig. 5: Ocean-temperature observations.

We use 2,828 oceanographic temperature profiles collected by NASA’s Oceans Melting Greenland project. Each profile on the left is colour-scaled by a scalar local thermal anomaly value shown in the map on the right. The heavy black profile on the left represents the mean of all 2,828 profiles. By subtracting the mean profile from each individual profile and then calculating a mean anomaly value within the top 1,000 m of each profile, we obtain a measure of ocean temperature that reflects the spatial distribution of available heat energy, with minimal influence from the depth of the available observations. Map created with Arctic Mapping Tools for MATLAB⁵⁴ using geographic outlines developed in this work.