Simulation of Southern Ocean Properties Across Model Generations and Future Changes under Continued 21st Century Warming in CMIP6.

Abstract:

The Southern Ocean (SO) is a vital component of the Earth system due to the dominant role this region plays in the air-sea exchange of heat and carbon. This a direct consequence of the physical ocean circulation that exists there. Despite its out sized role in the climate system, previous generations of climate models have struggled to accurately represent important properties and processes in the SO. This analysis assesses the performance of CMIP models from CMIP3 to CMIP6 in representing key observationally-based metrics related to the physical simulation of the SO. CMIP6 models show improved performance in representing the wind stress forcing at the ocean surface, the volume transport of the Antarctic Circumpolar Current (ACC), and the meridional density gradient across the ACC latitudinal band. However, in many models, the upper SO remains biased too warm and too fresh relative to that observed, and the Antarctic sea ice extent remains poorly represented in CMIP6. The future evolution of these metrics under continued 21^st century warming are analyzed and mean-state biases are considered when interpreting the projected trends.