Description: The horizontal position of the remotely operated vehicle (ROV) during the ARTofMELT2023 expedition in May and June 2023 was measured using an acoustic Long Base Line (LBL) positioning system (LinkQuest Pinpoint) with an operating frequency of 26.77-44.62kHz. It consists of a transceiver onboard the ROV and 3 transponders which were deployed on 5 m long chains through the drifting ice cover at different horizontal distances from the ROV ice access hole. Due to the high latitude and glitches in the Pinpoint software's coordinate conversions, the surveys were virtually moved and 'fake' geographic positions centered around 1°N/1°E were used. The survey track was smoothed using a Kalman filter from initial acoustic fixes and cleaned for most obvious outliers. This calibration result in a floe-fixed, relative coordinate system (distance, relative, X and distance, relative, Y) with the origin (X=0 m, Y=0 m) at the ROV hole. The final position was recorded in the SPOT.ON survey systems software (OceanModulesTM). A quality flag for the position is introduced based on the time to the closest fix with "1" indicating good positon (fix reached 〈= 3s), "2" medium position (fix reached 〉 3s & 〈= 5s), and "3" bad position (fix reached 〉 5s). Depending on the scientific aim, a position with quality flag "3" can still be useful. The ROV depth was measured by an integrated pressure sensor (Keller A-21Y, Keller AG) included in the main electronics housing of the ROV and calibrated to 0 during pre-survey procedures, when the top side of the ROV was at the same level as the water surface. The accuracy of the sensor is 0.10 m. ROV attitude (roll, pitch, heading) was measured with an onboard inertial measuring unit (Microstrain) with three axis accelerometer, magnetometer, and gyroscope.

Description: Fluorometric data on chlorophyll a concentration, Fluorescent Dissolved Organic Matter (FDOM) concentration, and optical backscatter were measured by a triplet fluorometer (ECO-Puck BBFL2SSC, Wetlabs) attached to a remotely operated vehicle (ROV) during the ARTofMELT2023 expedition in May and June 2023. Data use manufacturer calibration.

Description: Nitrate and UV-absorbance spectra were measured by a SUNA V2 UV-spectrometer (Satlantic) mounted in the sensor skid of a remotely operated vehicle (ROV) during the ARTofMELT2023 expedition in May and June 2023. The instrument header is SATSLS0847. Data use manufacturer calibration.

Description: Attention points as logged by the operators in the recording software Spot.On for remotely operated vehicle (ROV) surveys during the ARTofMELT2023 expedition in May and June 2023.

Description: Videos as recorded by two HD-zoom cameras attached to a remotely operated vehicle (ROV) during the ARTofMELT2023 expedition in May and June 2023: An Insite Pacific Inc. Mini Zeus Mark III until June 5 and a Bowtech Surveyor WAHD with a 10:1 optical zoom since June 6.

Description: Quicklook plots for all data collected using a remotely operated vehicle (ROV) during the ARTofMELT2023 expedition in May and June 2023.

Description: The distance between a remotely operated vehicle (ROV) and the sea-ice underside was measured by a single-beam upward-looking acoustic sonar altimeter (Tritech PA500) attached to the ROV during the ARTofMELT2023 expedition in May and June 2023. Sea-ice draft was derived by subtracting the distance to the sea-ice underside from the ROV depth, uncorrected for ROV attitude (pitch, roll). An offset between the depth reference (ROV bumper bars) and the altimeter of 0.105 m is accounted for in the presented data.

Description: pH values were obtained using a SBE18 pH sensor (Seabird) mounted on the remotely operated vehicle (ROV) during the ARTofMELT2023 expedition in May and June 2023. The values were derived from the sensor voltages using the same calibration during the entire expedition.

Description: Conductivity, temperature, and pressure were measured by a Glider Payload CTD (SBE GPCTD, Seabird). Oxygen frequency was measured by an oxygen optode (SBE 43F DO, Seabird). Both instruments were mounted in the sensor skid of a remotely operated vehicle (ROV) during the ARTofMELT2023 expedition in May and June 2023. Data use manufacturer calibration. The Gibbs SeaWater (GSW) Oceanographic Toolbox of TEOS-10 was used to derive other hydrographic data. The conversion from oxygen frequency to dissolved oxygen concentration was performed using the OOI L2 data product DOCONCF (Vardaro, 2014).