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

• Main Authors: Pace, Lisa, Smith, Madison, Thomson, Jim, Stammerjohn, Sharon, Ackley, Steve, Loose, Brice
• Format: Text
• Language: English
• Published: 2019
• Subjects: Ross Sea; Terra Nova Bay; Antarc*; Antarctica
• Online Access: https://doi.org/10.5194/tc-2019-213; https://tc.copernicus.org/preprints/tc-2019-213/

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 ℃, and the mixed layer extended as deep as 600 meters. Yet, upper ocean temperature and salinity profiles were not perfectly homogeneous, as would be expected with vigorous convective heat loss. Instead, the profiles revealed bulges of warm and salty water directly beneath the ocean surface and extending downwards tens of meters. Considering both the colder air above and colder water below, we suggest the increase in temperature and salinity reflects latent heat and salt release during unconsolidated frazil ice production within the upper water column. We use a simplified salt budget to analyze these anomalies to estimate in-situ frazil ice concentration between 332 × 10 −3 and 24.4 × 10 −3 kg m −3 . Contemporaneous estimates of vertical mixing by turbulent kinetic energy dissipation reveal rapid convection in these unstable density profiles, and mixing lifetimes from 2 to 12 minutes. The corresponding median rate of ice production is 26 cm day −1 and compares well with previous empirical and model estimates. Our individual estimates of ice production up to 378 cm day −1 reveal the intensity of short-term ice production events during the windiest episodes of our occupation of Terra Nova Bay Polynya.