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During katabatic wind events in the Terra Nova Bay and Ross Sea polynyas, wind speeds exceeded 20 m s-1, air temperatures were below -25 °C, and the mixed layer extended as deep as 600 meters. Yet, temperature and salinity profiles were not perfectly vertical, as one would expect with vigorous convective heat loss. Instead, the profiles revealed bulges of warm and salty water starting at the ocean surface and extending to the top tens of meters. Considering both the colder air above and colder water below, we surmise that the increase in temperature and salinity reflects latent heat and salt release during unconsolidated frazil ice production throughout the upper water column. We use a simplified salt budget to analyze these anomalies to estimate in-situ frazil ice content 5.8 and 0.13 kg within the top 50 m of the water column. Estimates of vertical mixing by turbulent kinetic energy dissipation reveals rapid convection in these unstable density profiles, and mixing lifetimes from 2 to 30 minutes. The corresponding ice production rates yield an average ice thickness of 52 cm day-1, which compares well with previous empirical and model estimates. However, our individual estimates of production up to 358 cm day-1 reveal the intensity of short-term ice production in the windiest sections of the Terra Nova Bay Polynya.

Frazil ice growth and ice production during katabatic wind events in Ross Sea polynyas, Antarctica