| Summary: | In ice covered polar regions, the interaction between ocean, ice and atmosphere is an important component in the complex climate system. Exchange of heat, mass and momentum occurs across the boundary layers, both in the ocean and in the atmosphere, hence understanding the involved processes are crucial in order to determine future climate. In this thesis dynamics and thermodynamics of the under-ice boundary layer are investigated based on measurements of turbulent fluxes in close proximity to the ice/ocean interface and microstructure profiling of the upper ocean. The topic is addressed in four papers which focus on exchange processes at the ice/ocean interface as well as regional measurements of turbulence and turbulent fluxes in ice covered areas around Spitsbergen and in the Weddell Sea. High rates of melting are often encountered as sea ice drifts into water with temperatures well above freezing, which may be typical of the marginal ice zones. It has been shown in previous studies that these melting rates are limited by double diffusive effects in a thin layer close the ice/ocean interface. In this study, turbulent fluxes from the under-ice boundary layer are used to show that double diffusive effects are important for the melting rates and show that the strength of this double diffusion is close to the range suggested by previous studies. It is also shown that by not considering double diffusive effects at the boundary, melting rates are overestimated by up to several cm per day. By analyzing the conditional statistics of the Reynolds stress in the boundary layer it is found that the main fraction of the stress comes from high turbulence events, so called “sweeps” and “ejections”, which is consistent with boundary layer flows in other environments. Closest to the ice, the sweeps are found to be more intense than further away from the interface, which can be related to the observed increase in friction velocity with depth. The West Spitsbergen Current transports Atlantic Water, which is the main source of ...
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