Description: The Antarctic continental shelves and slopes occupy relatively small areas, but, nevertheless, are important for global climate, biogeochemical cycling and ecosystem functioning. Processes of water mass transformation through sea ice formation/melting and ocean–atmosphere interaction are key to the formation of deep and bottom waters as well as determining the heat flux beneath ice shelves. Climate models, however, struggle to capture these physical processes and are unable to reproduce water mass properties of the region. Dynamics at the continental slope are key for correctly modelling climate, yet their small spatial scale presents challenges both for ocean modelling and for observational studies. Cross-slope exchange processes are also vital for the flux of nutrients such as iron from the continental shelf into the mixed layer of the Southern Ocean. An iron-cycling model embedded in an eddy-permitting ocean model reveals the importance of sedimentary iron in fertilizing parts of the Southern Ocean. Ocean gliders play a key role in improving our ability to observe and understand these small-scale processes at the continental shelf break. The Gliders: Excellent New Tools for Observing the Ocean (GENTOO) project deployed three Seagliders for up to two months in early 2012 to sample the water to the east of the Antarctic Peninsula in unprecedented temporal and spatial detail. The glider data resolve small-scale exchange processes across the shelf-break front (the Antarctic Slope Front) and the front's biogeochemical signature. GENTOO demonstrated the capability of ocean gliders to play a key role in a future multi-disciplinary Southern Ocean observing system.

Description: With the Arctic rapidly changing, the needs to observe, understand, and model the changes are essential. To support these needs, an annual cycle of observations of atmospheric properties, processes, and interactions were made while drifting with the sea ice across the central Arctic during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition from October 2019 to September 2020. An international team designed and implemented the comprehensive program to document and characterize all aspects of the Arctic atmospheric system in unprecedented detail, using a variety of approaches, and across multiple scales. These measurements were coordinated with other observational teams to explore cross-cutting and coupled interactions with the Arctic Ocean, sea ice, and ecosystem through a variety of physical and biogeochemical processes. This overview outlines the breadth and complexity of the atmospheric research program, which was organized into 4 subgroups: atmospheric state, clouds and precipitation, gases and aerosols, and energy budgets. Atmospheric variability over the annual cycle revealed important influences from a persistent large-scale winter circulation pattern, leading to some storms with pressure and winds that were outside the interquartile range of past conditions suggested by long-term reanalysis. Similarly, the MOSAiC location was warmer and wetter in summer than the reanalysis climatology, in part due to its close proximity to the sea ice edge. The comprehensiveness of the observational program for characterizing and analyzing atmospheric phenomena is demonstrated via a winter case study examining air mass transitions and a summer case study examining vertical atmospheric evolution. Overall, the MOSAiC atmospheric program successfully met its objectives and was the most comprehensive atmospheric measurement program to date conducted over the Arctic sea ice. The obtained data will support a broad range of coupled-system scientific research and provide an important foundation for advancing multiscale modeling capabilities in the Arctic.

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.