The Influence of Surface Fluxes on Export of Southern Ocean Intermediate and Mode Water in Coupled Climate Models

Abstract

The Southern Ocean (SO) plays a crucial role in the process of sequestering heat and carbon dioxide from the atmosphere and transferring them to the deep ocean. This process is intricately linked to the formation of Antarctic Intermediate Water (AAIW) and Subantarctic Mode Water (SAMW), which are pivotal components of the Meridional Overturning Circulation (MOC) and have a substantial impact on the global climate balance. AAIW and SAMW take shape in specific regions of the Southern Ocean due to the influence of strong winds, buoyancy fluxes, and their effects, such as convection, the development of thick mixed layers, and wind-driven subduction. These water masses subsequently flow northward, contributing to the ventilation of the intermediate layers within the subtropical gyres. In this study, our focus lies on investigating the regional aspects of AAIW and SAMW transformation in CMIP6 models. We accomplish this by analyzing the relationship between the meridional transport of these water masses and air-sea fluxes, particularly Ekman pumping, freshwater fluxes, and heat fluxes. Our findings reveal that the highest transformation rates occur in the Indian sector of the Southern Ocean, with notable values also observed in the southeast Pacific and south of Africa. Additionally, we assess the potential changes in these formation regions under future scenarios projected for the end of the 21st century. Although the patterns of formation regions remain consistent, there is a significant decrease in the transformation process.