Roles of thermal advection in setting the Southern Ocean warming pattern

Abstract

AbstractThe Southern Ocean is the major region of global ocean heat gain. Most of the heat gain is concentrated in the region of the Antarctic Circumpolar Current (ACC), but SST within the ACC only exhibits a slight increase. Ocean circulation plays a fundamental role in setting the pattern of temperature response to global warming. In this study, a 1/4° Southern Ocean eddy‐permitting model configured based on the Regional Ocean Modeling System is used to study the role of ocean in setting the warming pattern, by examining the response of ocean temperature and heat budget terms to a uniform air–sea heat flux (Qnet) increase. As Qnet increases by a constant value, the SST increases, but with a smaller value within the ACC region. Consequently, more heat flux in the ACC region is induced from the atmosphere to the ocean through thermal adjustment. Heat budget analyses suggest that the surface warming induced by vertical diffusion is largely offset by the cooling effect of heat advection, especially within the ACC region; however, in the subsurface, the effect of vertical diffusion becomes slight, and heat advection dominates the temperature change and induces warming in the ACC region. These results highlight the importance of heat advection in setting the temperature response pattern to air–sea heat flux increase: by transporting more heat from the surface to the deep ocean, the SST increase within the ACC region becomes smaller, and this induces more heat flux from the atmosphere to the ocean and thus makes the ACC region become a major region of heat gain.