Picture: Beneath the waves. Credit: Emiliano Arano (Pexels)

The global ocean overturning circulation is the planetary-scale movement of waters in the vertical and north-south directions. It is the principal mechanism by which the oceans absorb, sink, and redistribute heat and carbon from the atmosphere, thereby regulating Earth’s climate.

Despite its importance, it is impossible to observe directly and must be inferred from sparse and infrequent proxy measurements.

The main upward branches of the overturning circulation are in the Southern Ocean, where strong westerly winds cause waters to well up from below. Thus, changes in these westerly winds will lead to changes in the overturning circulation, and, subsequently, Earth’s climate.

CLEX researchers and colleagues used a diagnostic tool, called the Ekman Streamfunction, to cast the change of the winds into a framework directly comparable with the overturning circulation. They used a state-of-the-art global ocean-sea-ice model to directly measure the overturning circulation, and through this to examine the relationship between the Ekman Streamfunction and the Southern Ocean overturning circulation.

The researchers found that throughout much of the Southern Ocean, the Ekman Streamfunction is a robust indicator of the strength and variability of the overturning circulation, with exceptionally high correlation.

  • Paper: Stewart, K. D., Hogg, A. M., England, M. H., Waugh, D. W., & Kiss, A. E. (2021). The Ekman streamfunction and the Eulerian and residual overturning circulations of the Southern Ocean. Geophysical Research Letters, 48, e2021GL093438. https://doi. org/10.1029/2021GL093438