SWERVE, Canada-Sweden Arctic Ocean 2025 Expedition (AO25), IB Oden, 9 August 2025 - 19 September 2025 From August 9 - September 19, 2025, the Swedish icebreaker Oden carried out an expedition with the Canadian icebreaker CCGS Louis S. St-Laurent to map the seabed in the Arctic Ocean, which took place within the framework of the UNCLOS program (United Nations Convention on the Law of the Sea). In symbiosis with this, an extensive Early Career Scientist program also took place on board Oden, consisting of the course "The Arctic Ocean Climate System". Expedition webpage: https://www.polar.se/en/expeditions/canada-sweden-arctic-ocean-2025/ Area: Central Arctic Ocean, Alpha Ridge and Mendeleev Rise Expedition Coordinator: Katarina Gårdfeldt, Katarina.Gardfeldt@polar.seECS-program Coordinator: Michael Tjernström, michael.tjernstrom@polar.seCTD data curator: Julia Muchowski, julia.muchowski@polar.se Other meteorological, oceanographic and ship data collected from IB Oden during this expedition are published on SND: Canada-Sweden Arctic Ocean 2025 - Meteorological, Oceanographic and Ship data, collected onboard the icebreaker Oden, DOI: https://doi.org/10.48515/w8yg-ez41 This data set includes raw and processed Conductivity, Temperature and Depth (CTD) data collected during the Canada-Sweden Arctic Ocean 2025 Expedition with the Swedish Icebreaker Oden between August and September 2025. The data include high resolution (0.2 m) vertical profiles of the water column properties in terms of salinity, temperature, dissolved oxygen, turbidity, fluorescence, and CDOM (colored dissolved organic matter) over a total of 12 casts. The dataset has a total size of 194 MB and includes the following types of files: raw, metadata, processed_profiles, and processed_bottle_files. processed_profiles Processed profiles contain the processed and quality-controlled CTD data from the downcast in csv files with data from each CTD cast. Data were processed with the SBE Data Processing software and a python wrapper (Tunatools) around the SBE software. Tunatools is openly available on Github. Tunatools enables processing of single files or entire folders with raw files as output by the Sea-Bird Seasave software when collecting the data. Each file contains a header that provides metadata to the cast, the used sensors, and their calibration data. All files follow the naming convention AO25-Oden-CTD-[Date:YYMMDD]-[Time:HH:MM]-Station-[Station nb]-Cast-[Cast nb].csv Each file contains the following parameters: time NMEA time in UTC in the format yyyy-mm-dd HH:MM:SS.SSS lat Latitude (°N) lon Longitude (°E) pressure pressure (dbar) pump Pump status (on/off) T1, T2 In situ Temperature (°C) for first/second sensor pack S1, S2 Practical Salinity (PSU) from first/second sensor pack OXY1_SAT,OXY2_SAT Oxygen Saturation (%) from second sensor pack OXY1_ML, OXY2_ML Oxygen Concentration (ml/l) from second sensor pack FLUOR Fluorescence, WET Labs ECO-AFL/FL (mg/m³) TURB Turbidity, WET Labs ECO (NTU) CDOM Colored dissolved organic matter (ppb) DESC Descent rate (m/s) ALTIM Altimeter reading of distance above the seafloor (m) CNT Scan count T1_quality_flag, T2_quality_flag Quality flags for temperature sensors S1_quality_flag,S2_quality_flag Quality flags for salinity sensors OXY1_quality_flag, OXY2_quality_flag Quality flag for oxygen sensors Note that there were dual temperature, conductivity, and oxygen sensor packs installed on the CTD. Definition of quality flags: 0 good data 1 sketchy data 2 bad data Data were flagged bad when: out of range, difference between the dual sensors, significant outliers — especially at the top and bottom of profiles. In addition, salinity and oxygen data were flagged bad if the pump status was off. Data were flagged as sketchy when abrupt changes occured (spikes, outliers) or unexplainable differences between the dual sensors occured. All other data are flagged as good. All collected temperature, salinity and oxygen sensor data were quality controlled. In some casts NMEA positioning was not available, therefore the fields lat and lon are empty in the data files. processed_bottle_files Processed bottle files contain processed data for each water sample that was taken, in a text file with the ending _Upcast.btl. _Upcast indicates that the data were collected during the upcast. Each file contains a header that provides metadata to the cast, the used sensors, and their calibration data. For each bottle that was sampled, the following parameters are included as average only: Bottle Position Date Time Date and time in the format mmm-dd-yyyy HH:MM:SS Potemp090C and Potemp190C Potential temperature (°C) derived from in situ temperatures in first and second sensor pack using the TEOS10 toolbox Sbeox0ML/L, Sbeox1ML/L Oxygen (ml/l) from the first and second sensor pack Sbeox0PS, Sbeox1PS Oxygen saturation (%) from the first and second sensor pack SvCM Soundvelocity (m/s) DepSM Depth (salt water, m) (if calculated) DepFM Depth (fresh water, m) (if calculated) Sal00, Sal11 Practical salinity (psu) from the first and second sensor pack Density00, Density11 Density (kg/m³) from the two temperature and salinity sensor packs Sigma00, Sigma11 Density with reference pressure of 0 dbar (kg/m³) from the two temperature and salinity sensor packs The following parameters are included as average and, in addition, the standard deviation (sdev), their minimum value (min) and maximum value (max) while the bottle was fired are provided: Dz/dtM Descent rate (m/s) Latitude Latitude (°N) Longitude Longitude (°E) TimeS Elapsed seconds since the beginning of the CTD cast (s) T090C, T190C In situ temperature (°C) from the two sensor packs Sbeox0V, Sbeox1V Oxygen sensor raw data (V) from the two sensor packs PrDM Pressure, Digiquartz, Strain Gauge (db) AltM Altimeter reading of distance to seafloor (m). This value starts to be reliable when approaching the last 100m above the seafloor C0S/m, C1S/m Conductivity (S/m) Processing of the data was done in the same manner as for the processed profiles, using Tunatools, a Python wrapper around the SBEDataProcessing software. raw Raw CTD data, as collected with a Sea-Bird SBE 911plus CTD and as output by the Sea-Bird Seasave software. Each CTD cast includes four files, named as AO25-Oden-CTD-[Date:YYMMDD]-[Time:HH:MM]-Station-[Station nb]-Cast-[Cast nb].*. The files have the following file endings and content. bl Bottle files with information of water samples taken hdr Header files hex Raw data files XMLCON Configuration files Configuration files with ending .XMLCON include calibration coefficients and dates of the applied calibrations for all sensors. The configuration files can be opened in a text editor or with the SBE software DisplayConFile, which is part of the above mentioned SBEDataProcessing software. metadata Metadata files, using the same naming convention as the raw files plus the file ending _Metadata.txt. Metadata include weather and ice conditions. additional information A logbook file named AO25-Oden-CTD_logsheet.csvand a README.txt file are inlcuded in the data set. Providing an overview of all collected CTD casts and general information about the expedition, respectively.