Methodology:

A total of 13 successful CTD casts were undertaken using the NERC Arctic Station CTD frame. The unit consists of a SeaBird SBE 19+ V2 CTD (a pumped system), and additional sensors for chlorophyll fluorescence, particle scattering, and photosynthetically active radiation (PAR).

The CTD casts were carried out either from the UK station Polarcirkel workboat or the King's Bay R/V Teisten. The frame was lowered and raised either using a hand-winch system (Polarcirkel) at approximately 0.5m/s, or via an electric winch system (Teisten) at approximately 1m/s. The CTD was lowered in a continuous movement, but rate of recovery likely varied, especially with the hand-winching system.

An initial soak of 3 minutes at 5m water depth was carried out, before winching the frame to the surface and lowering to within approximately 10m of the seafloor, with depth recorded from the onboard echosounder.

Between casts the CTD frame and sensors were washed in freshwater; the conductivity cell flushed through three times and then stored kept in clean tap water.

The deepest cast was 320m, and the shallowest cast was 45m.

The data were downloaded and processed using SeaBird software. The processing order used was:

Data Conversion

Filter 0.15s on conductivity and pressure

Thermal Mass Correction

Loop edit

Derive depth (latitude 79 degrees N), salinity, and density (sigma-theta)

Remove surface soak

Bin Average in depth down cast only 1m bins

Save .csv file

Data collection:

SeaBird SBE 19+ V2 CTD and SeaBird software (Seasoft V2.4.0 and SeatermV2 2.8.0)

Data quality:

The instrument was calibrated by SeaBird scientific in August 2021 and November 2024 with no drift in data. These final data were processed using the calibration constants from November 2024. CTD casts were replicated on different days from the same location.