During Leg 1, the CTD (CTD RBR Maestro) was manually lowered in the water through an ice hole with a velocity of less than 0.3 ms-1 and an acquisition frequency of 6 Hz, yielding a vertical resolution of a few centimetres. During legs 2 to 4, the CTD (CTD RBR Concerto) was installed on a Seabird Scientific optical package frame, which was deployed with a velocity of 0.3 m s-1 and an acquisition frequency of 8 Hz. Only data from downcasts were used and poor quality profiles, that had been affected by ice-covered sensors, were removed. Atmospheric pressure observed at weather stations near the sampling locations (Aklavik, Inuvik, Shingle Point and Tuktoyaktuk) was used to tare the CTD pressure sensors. CTD profiles were smoothed and binned to a regular 0.01 m depth grid.

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