Oelker, Julia; Spieß, Volkhard (2025): Continuous optical chlorophyll-a and turbidity data along RV SONNE cruise SO304 [dataset]. PANGAEA, https://doi.org/10.1594/PANGAEA.982743

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 12 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 and turbidity data during parallel operation of the sensors in the two boxes showed significant differences between the sensors. The sensors were aligned resulting in a consistent chlorophyll-a time series. For turbidity, a consistent time series could only be achieved until 16 Mar 2024 00:00 UTC. The sensors then start to deviate indicating biofouling despite regular cleaning intervals. The biofouling-affected turbidity data were flagged as potentially bad. The chlorophyll-a time series appears to be unaffected. A comparison for the corrected chlorophyll-a with satellite data using the GlobColour CHL1 product and additionally CHL2 product is provided. Turbidity data were also compared to the GlobColour SPM-OC5 product. Details on all quality control steps and the comparison with satellite data can be found in the data processing report. Note that the instruments are factory-calibrated, however, no post-calibration was performed due to missing reference data. Absolute values should be challenged. The resulting data set contains the original data and corresponding quality flags achieved by the quality control algorithm as well as the corrected chlorophyll-a and turbidity data with corresponding quality flags. 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.