Growing Ice in a Tank: Young Sea Ice Evolution and Turbulence in the Under Ice Boundary Layer

Thin sea ice and its modifications of the oceanic boundary layer are important in the context of the recent retreat of the Arctic sea ice cover. To study turbulence in the under ice boundary layer during thin sea ice growth, tank experiments in an ice laboratory were conducted under varying atmospheric and oceanographic conditions. Two main groups of experiments were investigated; circular current and stagnant water. Salinity data revealed that the ice releases brine both during freezing and melting conditions, before the solid ice starts melting. Four different methods were tested to quantify heat and salt fluxes. The covariance method underestimated the fluxes with up to two orders of magnitude, and hence did not resolve the fluxes present in the tank. The turbulent kinetic energy budget suggests non-uniform turbulence in the tank, leading to large differences in sources and sinks of turbulence over the relatively small surface area. The typical mixing length decreased downstream from 0.06 m to 0.03 m over a horizontal distance of 43 cm. Brine plumes leaving the ice were detected during all experiments, and enhanced the upper ocean mixing. The total importance of the large instantaneous salt and heat fluxes during brine plumes was less than 3 %, and did not considerably affect the heat and salt budgets in the tank.Master i Meteorologi og oseanografiMAMN-GEOFGEOF39