A Potential Link Between the Southern Ocean Warming and the South Indian Ocean Heat Balance

Using a suite of reanalysis products, model output, and observational data, the Southern Ocean (SO) is demonstrated to be undergoing a significant warming during recent decades, and this SO warming influences the subsurface heat redistribution in the South Indian Ocean (SIO) via two pathways. First, the increasing surface heat flux over the SO induces a poleward shift of the westerlies and the entire subtropical gyre. Consequently, waters on the equatorial side of the potential density troughs become cooler and those on the poleward side become warmer. The specific outcome is that the subsurface SIO is dominated by an extensive cooling, with a prominent deep-reaching warming around 30 degrees S-20 degrees S. Second, the SO warming signals are transmitted northward along isopycnal surfaces from around 40 degrees S up to the tropical SIO through the meridional overturning circulation, modulating the decadal variability of the SIO. The present study highlights the role of the SO in regulating global ocean heat balance and facilitates a better understanding of the moderating effects of oceans on global climate.