Methodology:

All data were collected during the PS111-expedition to the southern Weddell Sea onboard the German research icebreaker RV Polarstern.

CTD

Hydrographic data were collected using a Seabird SBE-52 CTD that contains a ducted, pumped conductivity-temperature channel and samples at a rate of 1 Hz. The SBE-52 was mounted towards the front of ALR with the inlet and exhaust ducts attached to a pair of ports in the vehicle's hull.

ADCP

Velocity data were gathered using two Teledyne RDI 300 kHz Workhorse Acoustic Doppler Current Profilers (ADCPs). Both upward and downward looking ADCPs were configured in bottom track mode with 8 m bins and used for navigation as well as current measurements. Each ADCP was set to ping once every 2 seconds, with half-second ping separation between instruments to avoid interference, and the raw velocity data were processed using 5-ping (10 second) averaging. Current velocities in the vehicle frame were calculated by subtracting the bottom track velocity from the raw upwards and downwards-looking water track velocities and were then rotated into a geographic reference frame using the vehicle's heading.

Turbulence

Turbulence data were sampled using a front-mounted Rockland Scientific International (RSI) MicroRider turbulence package. The RSI MicroRider package had four microstructure probes sampling at a rate of 512 Hz: two orthogonally positioned shear probes and two thermistor probes. The turbulence data were processed using standard methods in the Rockland Scientific ODAS MATLAB Library.

Data collection:

Seabird SBE-52 Conductivity, Temperature and Depth sensor

Two Teledyne RDI 300 kHz Workhorse Acoustic Doppler Current Profilers

Rockland Scientific International (RSI) MicroRider turbulence package

Data quality:

From the Seabird SBE-52 Conductivity, Temperature and Depth sensor, the temperature data has an accuracy of ±0.002 °C and the conductivity data has an accuracy of ±0.0003 S/m. Post-deployment, the SBE-52 was calibrated against ship-based CTD casts taken from RV Polarstern, with small corrections made to both temperature (+0.0024°C) and conductivity (+0.0002 S/m). The stated accuracy of the Teledyne RDI 300 kHz Workhorse ADCPs is 0.5% of the water velocity relative to the ADCP ± 0.5 cm/s. The stated accuracy of the shear probes in the Rockland Scientific International MicroRider turbulence package is 5%. Missing values are indicated with a value of -9999.