Abstract

The bottom of most of the global oceans is filled with Antarctic Bottom Water, formed via complex processes on the Antarctic shelves. Long thought to take centuries to react to surface forcings, this water mass is actually already changing along with global warming, contributing to steric sea level rise. What about ocean models? Do they capture the observed trends? This talk will focus on the latest generation of coupled climate models which contributed to the IPCC Fifth Assessment Report (or CMIP5 models). I will first comment on the range of characteristics of present-day Southern Ocean bottom water in the models. I will show that the models which form their bottom waters via open ocean deep convection (instead of shelf processes) are the most similar to the observations. In a second part, we will see how bottom waters change globally under climate change scenarios, the link between these changes and abyssal volume transports, and the impact of these changes on sea level rise projections. Finally, I will present preliminary results from sensitivity experiments undertaken with the new HadGEM3 model in order to understand how open ocean deep convection can occur in climate models.