German records from 1920s show long‐term ocean warming

Over past centuries the crews of ships regularly measured some basic properties of the waters through which they sailed, such as temperature and salinity. These historical observations have proven to be important for climate modelers who are trying to validate their work. In recent years the importance of the deep ocean as a sink for the extra energy trapped by anthropogenic climate change has come to the fore. Unfortunately, the vast majority of deep‐ocean observations do not start until the 1980s. From 1925 to 1927, however, the German research vessel Meteor crisscrossed the Atlantic Ocean on an expedition that collected a uniquely thorough record of oceanographic properties for the full depth of the ocean basin. The ship made 13 coast‐to‐coast sweeps from the Southern Ocean to the tropical North Atlantic, providing a set of observations that were largely unmatched until the 1990s.