Understanding the Arctic continental shelf mixing regimes and their impact on shelf sea-circulation and upper ocean stratification

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Rapid climate change is indisputable in the Arctic, where the record minimum sea-ice extent of September 2007 has been followed by the fastest recorded rate of sea-ice loss in August 2008 leading to near-minimum record levels again this year. A serious concern is that global climate models consistently underpredict the observed rate of Arctic climate change. A key environment in the Arctic are the continental shelf seas that account for 53% of the area covered by the Arctic Ocean and are the critical link between terrestrial and oceanic components of the earth system. There is much we still do not understand about how the energy from tides, wind, winter cooling and summertime heating can interact to mix fresh light river water with saltier sea water on the Arctic continental shelves. This gap in understanding has led to poorly parameterised shelf-sea physics in the global numerical computer models used to predict future climate. What happens in the Arctic shelf seas is tremendously important to the Arctic Ocean environment as lighter fresher shelf waters spread out into the layers of the interior basins, while denser shelf waters cascade down the continental slopes, penetrating to deeper levels where they encounter dense, warm, salty water from the Atlantic that has come from Fram Strait. The lighter cold, fresh shelf waters are thought to replenish the Arctic halocline layer that acts as critical barrier to heat fluxes from the deep warm Atlantic waters that may undermine Arctic sea-ice cover. The denser shelf waters mix with the Atlantic water at depth as it circumnavigates the Arctic Ocean, before exiting as a denser cooler fresher overflow current through the Nordic Seas. This dense Nordic Sea overflow is critical component of the global oceanic 'conveyor belt' of heat and freshwater know as the global overturning circulation that helps regulate global climate. Therefore, the Arctic shelf water production mechanisms are not just important for regional climate but also global climate. In the research proposed here, I aim to characterize mixing processes on Arctic continental shelfs, taking the important first step towards a comprehensive understanding of the Arctic earth-ocean system and improving predictions of future change and the consequences for global climate. I am interested in specific questions about how tidal energy can be used to mix water masses either by generating turbulence or by straining a vertically well-mixed but laterally differentiated water column and causing convection. Another key question I will address is how energy from the wind can be used to generate inertial oscillations that may also interact with the tide and cause mixing. These processes have been shown to be important in temperate shelf seas, but have yet to be investigated in an environment subjected to the extreme seasonal fluctuations, large riverine freshwater discharges and ice-formation-melt-cycle experienced on the Arctic continental shelves. My strategy is to use all the available data to gain an understanding of the shelf sea state and its seasonal heating and cooling cycles and then map out the different mixing regimes on the shelves, so that we can determine how, where and what kind of shelf water is being produced. These ideas will then be incorporated into a shelf-sea numerical computer model to test the sensitivity of the shelf seas system to scenarios of increasing river discharge and sea-ice loss which are resulting from climate change. This will enable us to diagnose feedbacks in the continental shelf -ocean circulation and climate system and help us improve the representation of the important shelf processes in global climate models, and ultimately, the predictions of our future climate.