Description: The presentation will focus around the impact that major topographic features in the Southern Ocean have on the path of the Antarctic Circumpolar Current (ACC), and their relatively unknown role in the coupled ocean-atmosphere system. We investigate their influence by respectively flattening the bathymetry around the Kerguelen Plateau, Campbell Plateau, Mid-Atlantic Ridge, and Drake Passage in four simulations in a coupled climate model. The barriers lead to an increase in the ACC transport of between 3% and 14% in the four simulations. The removal of Kerguelen Plateau bathymetry increases convection south of the plateau and the removal of Drake Passage bathymetry reduces convection upstream in the Ross Sea, affecting the deep overturning cell. When the barriers are removed, zonal flattening of the currents leads to SST anomalies upstream and downstream of their locations. Interestingly, these SST anomalies strongly correlate to precipitation in the overlying atmosphere, with correlation coefficients ranging between r=0.92 and r=0.97 in the four experiments. Windspeed anomalies are also positively correlated to SST anomalies in some locations but other forcing factors obscure this correlation in general. Meridional variability in the wind stress curl contours over the Mid-Atlantic Ridge, the Kerguelen Plateau and the Campbell Plateau disappears when these barriers are removed, confirming the impact of bathymetry on overlying winds.

Description: The Arctic Ocean is a challenge to model accurately. Its exchanges with the rest of the global ocean occur through narrow gateways. Ventilation within the Arctic requires a realistic continental shelf hydrography and slope, interaction with the sea ice and atmosphere, and preservation of dense overflows. At all depth levels, an accurate bathymetry is needed to properly represent the circulation. The uppermost layers depend on both surface heat fluxes and freshwater fluxes from rivers, glaciers, sea ice, and the atmosphere, while the deepest layers are impacted by geothermal heating. Despite this, many parameterisations and tuning processes applied in the Arctic are not representative of the polar regions. In addition, observations used to constrain Arctic models are often limited to the summer season, ice-free regions, or upper ocean. Therefore, unsurprisingly, the coarse-resolution CMIP-type models are highly inaccurate in the Arctic Ocean. In this presentation, we review a non-exhaustive list of biases in Arctic Ocean water mass representation and circulation in CMIP6 models, with a specific focus on how these biases impact our ability to accurately project future Arctic Ocean and global changes. Key directions for improving the Arctic Ocean in climate models will be discussed. We will finish with promising examples of ongoing Arctic model development: regional high-resolution modelling to improve simulations of sea ice and the exchanges with the global ocean, including overflow representation; pan-Arctic modelling with an adaptative mesh to improve the representation of mesoscale eddies and mixing; and the nudging of an ultra-high-resolution model (250 m) against observations.