The Weakening and Poleward Migration of the Southeastern Front Associated With the South Indian Countercurrent From 1980 to 2023

Abstract

The Southeast Indian Subantarctic Mode Water (SEISAMW), a thick water layer located between the seasonal and permanent pycnoclines, is important for climate variability in the Southern Ocean. However, its impact on long-term changes of the Southeastern Front (SEF) associated with the South Indian Countercurrent has not been clearly revealed. By analyzing data from observations, objective products and an eddy resolving ocean general circulation model, the present study shows that the SEISAMW has shifted poleward (0.56° ± 0.12°) and weakened from 1980 to 2023, which causes the poleward migration (0.52° ± 0.12°) and weakening of the SEF in recent 44 years. The SEISAMW changes are associated with a significant shallowing and poleward shifting trend of the austral winter deep mixed layer in the Southeast Indian Ocean, as well as the poleward-shifted SEISAMW's outcrop lines, all of which are mainly driven by the poleward migrated westerlies in recent decades.