Stirring by mesoscale eddies, not trapping, is the dominant driver of global ocean meridional eddy heat transport
image: (a) Global distribution of S-EHF with positive and negative values denoting northward and southward directions, respectively. Black lines represent mean SST contours at 5°C intervals and the 23°C contour is highlighted using thick line. The subtropical frontal regions in North and South Pacific and South Indian Oceans are marked using black boxes. (b) Same with (a) but for the T-EHF.
Credit: ©Science China Press
This study is led by Yuan Qingguo, Dr. Zhang Zhiwei, Dr. Zhao Wei and Dr. Tian Jiwei from Physical Oceanography Laboratory at Ocean University of China and Dr. Liu Tongya from Second Institute of Oceanograph at Ministry of Natural Resources. The researchers have incorporated altimeter-based Eulerian and Lagrangian mesoscale eddy datasets, and more accurately quantified surface EHT induced by both the stirring and trapping effects. These results demonstrate that both stirring-induced surface EHT (S-EHT) and trapping-induced EHT (T-EHT) are predominantly poleward with elevated magnitudes in subtropical frontal regions. The magnitude of the S-EHT is about 1–2 orders of magnitude larger than that of T-EHT throughout most of the global ocean.
The S-EHF (eddy meridional heat flux) is predominantly poleward and down the temperature gradient in the global ocean (i.e. northward in the Northern Hemisphere and southward in the Southern Hemisphere). The magnitude of S-EHF is notably elevated in the subtropical frontal regions, the Antarctic Circumpolar Current (ACC), and the Western Boundary Currents (WBCs), including their extensions. In these areas, the magnitude of S-EHF can exceed 60 kW/m2. The T-EHF is also dominantly poleward across the global ocean, with elevated magnitudes in subtropical frontal regions. Different from the S-EHF, the T-EHF does not exhibit notably large values in the ACC or the WBCs and their extensions. Instead, its most prominent high-value regions are located in the ocean area southwest of Australia and the Mozambique Channel.
Overall, the magnitude of S-EHT is about 1–2 orders of magnitude larger than that of T-EHT throughout most of the global ocean. Therefore, the horizontal stirring effect of mesoscale eddies is the dominant mechanism of EHT. This finding clarifies the relative importance of the two mechanisms and enhances our understanding of meridional heat transport in the ocean.
See the article:
Yuan Q, Zhang Z, Liu T, Zhao W, Tian J. 2025. Stirring by mesoscale eddies dominates meridional eddy heat transport in global ocean. Science China Earth Sciences, 68(9): 2904–2912, https://doi.org/10.1007/s11430-024-1653-8