Formation of turbid ice during autumn freeze-up in the Kara Sea

Abstract

A one-dimensional (vertical) model is used to estimate the mass of icerafted sediment in turbid sea ice on the shallow Kara Sea shelf during autumn freeze-up. Sediment is entrained into the ice through aggregation with frazil ice crystals that are diffused downwards by wind-generated turbulence. Data from local meteorological stations are used to force the model, while water stratifi cation and sediment concentrations from the area are used to initiate the model. Model results indicate a 0.2 m thick layer of slush ice created during 48 h with a mean wind of 6 m/s and an air temperature of –10 °C. This ice contains ca. 20 mg/l of sediment, or in total ca. 2 % of the annual sediment discharge by nearby rivers. In shallow areas (< 20 m depth) the process is very effective with winds of ca. 12 m/s, and the process can incorporate many years of sediment discharge. In the deeper areas (> 20 m depth), the strong salinity stratifi cation implies that winds above 18 m/s are needed for the process to be effective. For the rest of the winter months the same process may lead to additional sediment incorporated in a coastal polynya, but the freeze-up alone has the capacity to incorporate the total summer discharge of sediment into the surface ice. Calculated sediment concentrations in the surface ice cover are in the range 3 mg/l - 19 g/l, in good agreement with available fi eld data.