Dataset: Bottle-calibrated dissolved oxygen (DO) profiles from US Overturning in the Subpolar North Atlantic Program (OSNAP) cruises in 2020 and 2022 (AR45 and AR69-03)

These data were during cruises onboard the R/V Neil Armstrong to recover and redeploy mooring infrastructure of the international Overturning in the Subpolar North Atlantic Program (OSNAP) in 2020 (AR45) and 2022 (AR69-03). The mooring infrastructure maintained on these cruises is located in the eastern Labrador Sea (referred to as the LS line) and western Irminger Sea (referred to as the CF line). Beginning in 2020, the Gases in the Overturning and Horizontal circulation of the Subpolar North Atlantic Program (GOHSNAP) has added moored oxygen sensors to these sections of the OSNAP mooring array. During these cruises, Conductivity Temperature Depth (CTD) casts are conducted to provide data necessary to calibrate the moored sensors (Miller et al., in review), as well as hydrographic data that provide a valuable dataset in and of themselves.

This dataset uses CTD data collected by the OSNAP and GOHSNAP programs during AR45 (OSNAP 22) and AR69-03 (OSNAP 32) cruises, alongside discrete samples collected for this project during the cruises (Related Dataset: Palevsky et al. 2024) to produce calibrated, quality-controlled oxygen depth profiles. For further information on CTD-DO calibration and its role in the calibration of moored oxygen sensors, see Miller et al. (in review).

Data collection 

CTD casts were performed using a ship-provided SeaBird 911plus CTD and deck unit  (http://www.seabird.com//sbe911plus-ctd) configured to measure pressure, temperature, conductivity, oxygen current, and other variables. Rosettes were equipped with primary and secondary pumped CTD sensor packages to measure pressure, temperature, and conductivity in duplicate. A SBE43 dissolved oxygen sensor was integrated into the pumped flow path of the primary CTD sensor package. Sensor data were acquired by an SBE Deck Unit providing demodulated data to a personal computer running SEASAVE (http://www.seabird.com/software/seasavev7) acquisition software. Calibrations for CTD sensors were performed by the manufacturer before the cruise.  

SeaBird processing 

CTD data are processed using SeaBird data processing software. The raw 24 Hz CTD data are converted from HEX to ASCII, lag corrected, edited for large spikes, smoothed according to sensor, and pressure averaged into 2 db bins for final data quality control and analysis. Table 1 summarizes the order in which SeaBird Modules were processed and the inputs applied during each module. 

SeaBird (Version 7.26.7) data processing module inputs 

* DATCNV: Convert the raw data (.hex) to pressure, temperature, conductivity, and dissolved oxygen (V) to a file with a .cnv extension. Use default hysteresis correction
* BOTTLESUM: Writes out a summary of the bottle data to a file with a .btl extension
* ALIGNCTD: Advance Oxygen raw [V] by time determined by processing relative to pressure
* WILDEDIT: Checks for and marks ‘wild’ data points: first pass 2.0 standard deviations; second pass 20 standard deviations 
* CELLTM: Conductivity cell thermal mass correction; alpha = 0.03 and 1/beta = 7.0
* FILTER: Low pass filter pressure and depth (DO [V]) with a time constant of 0.15 seconds to increase pressure resolution for LOOPEDIT
* LOOPEDIT: Mark scans where the CTD is moving less than the minimum velocity (0.25 m/s) or traveling backward due to ship roll
* BINAVG: Average data into 2 db pressure bins to match bottle-calibrated salinity files 
* SPLIT (u or d): Split .cnv file into upcast and downcast files. Files are appended automatically with leading u or d