Signature of ocean warming at the mixed layer base

The warming climate influences the ocean by changing its wind‐driven dynamics and by inputting extra heat. This study analyzes the warming where temperature anomalies penetrate the ocean interior, i.e. by focusing on the winter mixed layer (WML) base. This allows to distinguish regions where ocean circulation contribute to warm anomalies from locations where density‐compensated temperature anomalies locally enter the ocean along isopycnals. Multidecadal (1980‐2018) local temperature trends from a hydrographic dataset are examined at the WML base, and partitioned into components relating to isopycnal movement (heave) and change along isopycnals (spice). Subtropical gyres and western boundary currents show warming larger than the global average that mostly projects onto heave. This is the result of the strengthening of the circulation in the Southern Hemisphere subtropical gyres, and is related to both wind‐driven changes and Southern Ocean warming. Subtropical regions of surface salinity maxima are influenced by warm anomalies along isopycnals.