Southern ocean mixing in an earth system context

This proposal aims to study the role of mixing processes in the circulation and biogeochemical cycles of the Southern Ocean. The project is motivated by the recent discovery of intense turbulent mixing in the Antarctic Circumpolar Current (ACC, the strongest current on Earth), an observation that defies present theories of the circulation based on the assumption of little turbulent mixing in the ocean interior. It is also inspired by the new recognition that Southern Ocean mixing processes may critically control global nutrient and carbon cycles. The proposed research is exciting because it will exploit innovative instrumentation and modelling techniques to explore many enigmatic facets of the Southern Ocean mixing environment, telling us how present theories of the circulation should be changed and how these changes will affect our view of global biogeochemical cycles. The project will consist of three work packages of increasingly wider scope. In work package 1 (WP1), I will test the hypothesis that turbulence plays a significant role in the circulation and dynamics of an important region of the ACC. I will achieve this by measuring and modelling turbulent processes in an ACC meander, studying how they relate to a range of aspects of the flow and the seabed. In work package 2 (WP2), I will combine new observations and analysis techniques to investigate the extent to which results from WP1 are representative of a much larger sector of the ACC. The same investigation will serve to unravel how the interaction between different mixing processes regulates exchanges between the upper-ocean and the deep ACC. In work package 3 (WP3) I will use the insight gained in WP1 and WP2 to probe the dependence of global biogeochemical cycles on the mixing processes and other essential variables (such as sea ice cover) of the Southern Ocean environment. I will accomplish this with a novel ocean circulation model simulating the spread of biogeochemical substances. A fundamental goal of WP3 will be to explore how a change in Southern Ocean circulation may have driven atmospheric CO2 variation between glacial and interglacial ages, as many scientists believe it did.