A Study on the Southern Ocean Upwelling Over the 21st Century Under a High-Emission Scenario

Abstract

The Southern Ocean upwelling, a crucial component of global upwelling systems, plays a key role in the global-scale redistribution of water, heat, salt, and carbon. This study aims to improve the understanding of this upwelling system by examining its climatology and future trend under a business-as-usual emission scenario, using 25 global climate model data sets. The ensemble mean of the simulated large-scale upwelling pattern in Southern Ocean follows Ekman dynamics, characterized by upwelling south of approximately 50°S and downwelling to the north. Upwelling is generally more pronounced at depths of 200 and 1,000 m (approximately 0.5 m/day) compared to 50 m (approximately 0.2 m/day). Under the high-emission scenario, both large-scale upwelling and downwelling in Southern Ocean are projected to intensify, with the net vertical volume flux expected to decrease by approximately 2 Sv (1 Sv ≡ 10⁶ m³/s) at both 50 and 200 m by the end of the 21st century. The projected changes in zonal wind stress and wind stress curl offer a reasonable mechanism for the projected changes in Southern Ocean upwelling and downwelling, while the enhanced vertical stratification (primarily due to warming) may partially counteract the upwelling and downwelling increase. These findings are essential for understanding the response of Southern Ocean circulations to global climate change.