The dynamics of a changing arctic ocean

The Arctic Ocean is undergoing a period of rapid transition, and many different aspects of its environment (ocean, sea ice, and atmosphere) are changing faster than has ever previously been observed. Motivated by the role that the Arctic plays in the global climate and ocean circulation, the aim of this thesis is to investigate how the changing environment is affecting the dynamics and circulation of the Arctic Ocean. Observations show that freshwater accumulation in the Beaufort Gyre of the western Arctic Ocean has accelerated over the past decade. First, a simple process model and idealised perturbations to the annual cycle in ocean surface stress are used to show that the decline in Arctic sea ice cover and an increase in the annual mean momentum flux can explain this accelerated accumulation. The adjustment timescale and quantity of freshwater accumulated are determined by a balance between Ekman pumping and an eddy-induced volume flux, highlighting the importance of eddies in the changing Arctic. Sea ice decline may also drive periodic increases in vertical mixing. Using a 1D model of the Arctic Ocean water column, the competing effects of elevated vertical mixing and enhanced freshwater input on the stratification, the stability of the cold halocline, and the sea ice cover at the surface are explored. An elevated diffusive heat flux driven by stronger vertical mixing has little effect on the sea ice. Instead, the erosion of the cold halocline, which isolates the sea ice from the warm Atlantic water, represents the most important feedback for ongoing sea ice melt. The changing Arctic Ocean will further affect the freshwater export to either side of Greenland; however, local dynamics will also be important. In this chapter, the vertical structure of the tides in Nares Strait in the Canadian Arctic Archipelago are explored, as tidal turbulence may represent an important frictional constraint for the freshwater flow in this region. The tides propagate as either standing or progressive waves, and the vertical structure is set by the proximity of the semi-diurnal critical latitude, the requirement of no normal flow through the coast, and the strong stratification at the surface. There is little temporal variability in the vertical structure, and tidal dissipation is comparable in magnitude to that over the highly dissipative region of the northwest European Shelf.