Oelker, Julia; Urlaub, Morelia; Voß, Daniela; Wollschläger, Jochen (2025): Continuous optical chlorophyll-a and turbidity data along R/V SONNE cruise SO299/2 [dataset]. PANGAEA, https://doi.org/10.1594/PANGAEA.974880

Underway optical chlorophyll-a and turbidity data were collected along the cruise track with Sea-Bird Scientific ECO FLNTU sensors installed within two autonomous measurement systems, called self-cleaning monitoring boxes (SMBs). The SMBs measure alternatingly. While one box is measuring, the other one is being cleaned. The boxes switched generally every 6 hours. The water inlet for the SMBs is at about 4 m below sea surface. Observed chlorophyll-a and turbidity data were both quality controlled. Analysis of the chlorophyll-a data during parallel operation of the sensors in the two boxes showed a significant offset between the sensors. The sensors were aligned resulting in a consistent chlorophyll-a time series. A comparison for the corrected chlorophyll-a with satellite data using the GlobColour CHL1 showed significantly higher SMB Chla compared to satellite Chla. Satellite matchups during night-time and unaffected by non-photochemical quenching (20:00-24:00 local time) were used to calibrate the time series. We note that a calibration with satellite data is not as accurate due to temporal and spatial mismatch between the underway and satellite data and due to uncertainty of the satellite product. The chlorophyll-a time series shows effects of non-photochemical quenching which was not corrected (out of the scope of the quality control). The user may only want to use night-time data unaffected by non-photochemical quenching. Details on all quality control steps and the comparison and calibration with satellite data can be found in the data processing report. The resulting data set contains the original data and corresponding quality flags achieved by the quality control algorithm, and, in case of chlorophyll-a, also the calibrated data with corresponding quality flag. The data source is given through the name of the active SMB. The data set contains data during transit time and station work. We recommend to use ship's speed to filter for only transit data.