Observations and characteristics of the Ice-Ocean Boundary Layer in McMurdo Sound, Antarctica

Observation and analysis of Antarctic ice-ocean boundary layer formation is crucial to understanding paramount physical and biological interactions between sea-ice and ocean waters. Velocity measurements were made in November 2014 using Acoustic Doppler Current Profilers (ADCPs) moored in ~2m thick first year sea-ice in McMurdo Sound, Antarctica. Additionally, ADCPs mounted to an Autonomous Underwater Vehicle (AUV) were used to profile horizontal transects of up to 500m in length at 6-8m below the ice-ocean interface. A diurnal tidal cycle was observed with the stationary ADCP with maximum horizontal velocities in the range of 0.16-0.18ms-1. Laminar sub-layer thicknesses of up to 12m were identifiable from the stationary ADCP measurements over various stages of the tidal cycle, with the most pronounced velocity profiles corresponding to the flood tide events in McMurdo Sound. The first ever comparison under-ice of stationary ADCP and AUV mounted ADCP measurements yields a relatively good agreement of the under-ice velocity distribution during periods of maximum flow velocity; yet velocity variability of the AUV measurements (0.07-0.15ms-1) are considerably higher than those recorded by the stationary ADCP (0.01ms-1). Ultimately, this study provides a comparison of stationary ADCP and AUV mounted ADCP measurements, with the aim of fortifying the application of AUVs in under-ice environments. In particular, this is critical for measurements within the highly dynamic boundary layer region close to the under-ice surface, which have proven difficult to observe through conventional methods. The study focuses on velocity measurements within the first 25m beneath the ice, coinciding with physical measurements (temperature, salinity and density) to describe the observed boundary layer characteristics