This dataset contains calibrated chlorophyll concentrations for CTD bottle 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. Pigment extraction from 1L water samples filtered onto GFF filters was performed with 90 % acetone including cell disruption with glass beads. Linear regression between sample chlorophyll concentration (n=62) and chlorophyll fluorescence sensor data from CTD bottle measurements was accomplished with a Robust Linear Model and Andrew's Wave weight function using the python package statsmodels v0.14.0. Coefficient of determination (R²) of the resulting regression was 0.95 while excluding 3 outliers. The resulting coefficient was 0.4118 and the constant 0.004. 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).