This dataset contains calibrated chlorophyll concentrations for CTD profile data collected with the ship based CTD rosette during the cruise PS124 - COSMUS (Continental Shelf Multidisciplinary Flux Study) in the southern Weddell Sea between January and March 2021. Factory calibrated chlorophyll fluorescence sensor data was field calibrated using chlorophyll reference samples measured against chlorophyll a standard (see chlorophyll dataset for CTD bottles). Note the intense noise in fluorescence signals and resulting chlorophyll concentrations at station PS124_5-2 which was caused by optical interference. This effect might require noise reduction (convolving) methods in order to allow a reliable interpretation. Quality flags were given based on paragraph 6 Quality flags from SeaDataNet (2010).