Arctic Ocean in CMIP6 Models: Historical and projected temperature and
salinity in the deep basins
Abstract
We examine the historical and projected hydrography in the deep basin
of the Arctic Ocean in 23 climate models participating in the sixth
phase of the Coupled Model Intercomparison Project (CMIP6). The
comparison between historical simulations and observational climatology
shows that the simulated Atlantic Water (AW) layer is too deep and too
thick among the majority of the models and in the multi-model mean
(MMM). Moreover, the halocline is too fresh in the MMM. These issues
indicate that there is no visible improvement in the representation of
Arctic hydrography in the CMIP6 compared to the CMIP5. The climate
projections reveal that the sub-Arctic seas are outstanding warming
hotspots, supplying a strong warming trend in the Arctic AW layer. The
MMM temperature increase averaged in the upper 700 m till the end of the
21st century in the Arctic Ocean is about 40% and 60% higher than the
global mean in the SSP245 and SSP585 scenarios, respectively. Comparing
the AW temperature in the present day with its future change among the
models shows that the temperature climate change signals are not
sensitive to the model biases in the present-day simulations. The
upper-ocean salinity is projected to become fresher in the Arctic deep
basin in the MMM. However, the salinity spread is rather large and the
tendency toward stronger upper ocean stratification in the MMM is not
shared among all the models. The identified hydrography biases and
spread call for a collective effort for systematic improvements of
coupled model simulations.