The deep Arctic Ocean and Fram Strait in CMIP6 models

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Céline Heuzé , Hannah Zanowski, Salar Karam, Morven Muilwijk


Arctic sea ice loss has become a symbol of ongoing climate change, yet climate models still struggle to reproduce it accurately, let alone predict it. A reason for this is the increasingly clear role of the ocean, especially that of the "Atlantic layer", on sea ice processes. We here quantify biases in that Atlantic layer and the Arctic Ocean deeper layers in 14 representative models that participated in the Climate Model Intercomparison Project phase 6. Compared to observational climatologies and hydrographic profiles, the modelled Atlantic layer core is too cold by on average -0.4°C and too deep by 400 m in the Nansen basin. The Atlantic layer is too thick, extending to the seafloor in some models. Deep and bottom waters are in contrast too warm by 1.1 and 1.2°C. Furthermore, the modelled properties hardly change throughout the Arctic. We attribute these biases to an inaccurate representation of shelf processes: only three models seem to produce dense water overflows, at too few locations, and these do not sink deep enough. No model compensates with open ocean deep convection. Therefore, the properties are set by the inaccurate fluxes through Fram Strait, biased low by up to 6 Sv, but coupled to a too-warm Fram Strait, resulting in a somewhat accurate heat inflow. These fluxes are related to biases in the Nordic Seas, themselves previously attributed to inaccurate sea ice extent and atmospheric modes of variability, thus highlighting the need for overall improvements in the different model components and their coupling.



Earth Sciences, Oceanography and Atmospheric Sciences and Meteorology


Arctic, climate models, ocean circulation


Published: 2022-04-04 15:32

Last Updated: 2022-09-14 06:35

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CC BY Attribution 4.0 International

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Conflict of interest statement:

Data Availability (Reason not available):
All CMIP6 data are freely available via the Earth Grid System Federation. For this paper, we used the German Climate Computing Centre (DKRZ) node: and the Geophysical Fluid Dynamics Laboratory (GFDL) node: The Unified Database for Arctic and Subarctic Hydrography is freely available via All versions of the World Ocean Atlas climatology are freely available via All versions of the Polar science center Hydrographic Climatology are freely available via The EN4 climatology is freely available via The gridded bathymetry GEBCO is freely available via The volume, heat, and salt flux time series will be submitted to PANGAEA during the peer-review process; we will add their DOI here latest during copy-editing.

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