Work

Future Warming of Circumpolar Deep Water Linked to Surface Buoyancy Forcing

Year: 2026

Type: article

Abstract: Circumpolar Deep Water (CDW) is a warm water mass in the deep Southern Ocean and its transport onto the Antarctic continental shelf is the main contributor of heat to the region. Observations suggest that CDW has warmed and shifted poleward recently, potentially contributing to increased poleward heat transport and the accelerated melting of Antarctic ice shelves. However, due to the sparsity of observations and the complex dependencies of CDW on changes in both the ocean interior and surface conditions, the processes driving its warming in the Southern Ocean remain unclear. In this study, we employ a high‐resolution global ocean‐sea ice model to investigate the mechanisms of CDW change, focusing on future change at the end of 21st century. We conduct separate perturbation experiments to isolate the effects of projected surface buoyancy forcing (from heat and salt fluxes) and wind stress. Our findings reveal a warming signal of CDW driven by surface buoyancy forcing, contrasted by a reduced warming signal when wind stress changes are also included. A heat budget analysis shows that the warming of CDW is due to reduced winter cooling from mixing with warmed waters above and below the thermocline. These changes in mixing processes include weaker convective mixing due to increased stratification, and less heat loss by vertical diffusion because of the warmer ocean surface. In addition to changes in the mixing processes, the warming of deeper CDW is partly driven by a reduced Antarctic Bottom Water formation, which causes isopycnal descent and thickening of CDW.

Source: Journal of Geophysical Research Oceans

DOI: 10.1029/2025jc023319

Authors: Hangyu Meng, Wilma G. C. Huneke, Wilton Aguiar, Andrew McC. Hogg, Adele K. Morrison, Hannah R. S. Dawson