Investigating the impact of physical processes in the Southern Ocean on the carbon cycle during past, present and future climates

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The importance of the Southern Ocean for the global carbon cycle and atmospheric CO2 has been demonstrated by various recent data- and model-based studies. This includes present and potential future CO2 uptake, as well as the reduction in atmospheric pCO2 during the Last Glacial Maximum. Especially for the latter, various different mechanisms in the Southern Ocean have been proposed to explain some of the changes in pCO2, which are observed in ice cores, while a more convincing study which brings hypotheses into context with our physical knowledge based on ocean models and paleo reconstructions remains elusive so far. In this project we will explore the physical basis of various of these hypothesis on the (partial) explanation of glacial pCO2 values with a well established ocean general circulation model (MITgcm). We will analyse (a) if and how temporal and spatial changes in the wind field over the Southern Ocean lead to variations in water column stratification; (b) the impact of changing sea ice coverage (based on paleo-reconstructions or future predictions) on water properties and thus on stratification and ocean circulation; (c) interacting effects of both changes in wind and sea ice on Southern Ocean physics. Besides a physical understanding of these processes their impact on the Southern Ocean CO2 sink capacities, the global carbon cycle and on atmospheric pCO2 will be in focus. These topics are explored under preindustrial, present-day and glacial boundary conditions, but also for selected IPCC scenarios of future climate change.