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Abstract:
CTD data collected off the coast of Dronning Maud Land, Antarctica during the Troll Transect Cruise 2020-2021. This dataset contains pressure-gridded (1 dbar) CTD data (temperature, conductivity, salinity, chlorophyll, uncalibrated oxygen) from 14 profiles collected between 28.12.2020 and 07.01.2021. Data were collected using an SBE911+ unit (other CTD data were collected during the cruise - they are not included here).
Stations from 010_01 constitute a meridional (offshore) transect along approximately 6.1°E.
Data from an SBE 43 oxygen sensor are included (both as dissolved oxygen and raw sensor voltage) - please note that these data have not been calibrated or quality-controlled, and are provided as-is.
CTD Chlorophyll data were calibrated based on a linear fit of CTD fluorometer against bottle fluorescence measurements:
- First, the median value of dark counts at depth was determined based on measurements from 100 to 500 m depth.
- A visual inspection confirmed that there were no offsets between profiles.
- To calibrate the bottle Chl-a data to the bottle fluorescence measurements, we first only considered the bottle Chl-a value when the standard deviation of the bottle value divided by the fluorescence measurement was < 0.15, to avoid highly noisy parts of the fluorescence profile. Then we subtracted the offset value (1.0495) from the bottle fluorescence measurement, then we fit a linear regression with the bottle Chl-a measurement.
Salinity values have been compared with salinometer measurements from bottle samples from >1000 dbar (n=16). The average offset (CTD minus salinometer) was -0.0038. This was considered within the total margin of error, except for one notable outlier at station sta010_01, where a salinity difference of -0.0164 was found. Removing this offset from the profile brings the bottom temperature-salinity properties closer to the deep water masses further offshore along the same transect. Sta010_01 was also the first profile taken after the unloading operations, during which the CTD package was unsupervised inside a shipping container for several days, where e.g. accretion of salt crystals in the conductivity cell may have led to a time-depended bias when measurements were resumed. However, at this point, we cannot conclude whether the difference at this station is related to a sensor offset or an inaccurate salinometer sample, and no correction was applied to any of the profiles in this file, and with a greater uncertainty to be accounted for at sta010_01.
Versions
Version 1 (23.01.2024): First upload of data.