Origins of Southern Ocean warm SST bias in CMIP6 models

Abstract

Abstract The robust warm sea surface temperature (SST) bias in the Southern Ocean (SO) has persisted in several generations of Coupled Model Inter-comparison Project (CMIP) models, yet the origins of such bias remain controversial. Here by using the latest released CMIP6 multi-models, we find that the common warm SST bias in the SO features a zonally oriented non-uniform pattern mainly located between the north and south fronts of the Antarctic Circumpolar Current. Such bias is supposed to be not caused by the biases in the surface heat flux and the strength of the Atlantic meridional overturning circulation (AMOC) —the two sources of the SO warm SST bias that have been revealed based on CMIP5 models. Instead, it could be linked to the robust common warm bias in the Northern Atlantic deep ocean through the AMOC transportation in an adiabatic process, even though there is no systematic bias in the strength of AMOC. Our findings highlight that comprehensively considering physically-connected remote biases might help to improve the SO warm SST bias in CMIP models.