Observations of the Size Distribution of Frazil Ice in an Ice Shelf Water Plume

The size distribution of frazil ice is currently unconstrained in ice shelf cavity modeling. Here we observe the time-dependent behavior of the number and size of frazil ice particles in an Ice Shelf Water plume. A novel acoustic scattering inversion was used to infer frazil ice crystal diameters, assuming a log-normal distribution. Observation sites were on land-fast sea ice approximately 13 and 33 km from the front of the McMurdo Ice Shelf, Antarctica. The water column from the ice-water interface to 30 m below mean sea level was monitored over 3 weeks in November of 2016 and 2017. At 15 m below sea level the mean frazil crystal diameter was ∼1 mm. Fractional ice volume, derived from frazil crystal size and number density, correlates with in situ supercooling (up to 50 mK at 15 m below sea level). The data presented here provide valuable input for model initiation and evaluation.