On Sandström’s inferences from his tank experiments: a hundred years later

In 1908, J.W. Sandström conducted several tank experiments to illustrate oceanic circulations driven by the wind and by buoyancy fluxes. His main inference from them is: ‘A circulation can develop from thermal causes only if the level of the heat source lies below the level of the cold source’. This inference applies to buoyancy-driven overturning circulations that are steady and closed. The relevance of this inference, which is often quoted as ‘Sandström’s theorem’, has been under discussion ever since. It seems that Sandström was not careful enough in observing his experiments. He overlooked diffusively driven circulation patterns. At the same time, many of his pioneering ideas, together with his main inference, still appear qualitatively correct when applied to the observed Atlantic meridional overturning circulation. As a tribute to the centenary of Sandstr¨om’s publication some common misconceptions about what Sandstr¨om exactly said will be identified here. It is hoped that this clarification is substantiated by a translation of Sandström’s original 1908 paper into English.