Discrete seawater samples in a Weddell Sea coastal polynya along the Ekström Ice Shelf were collected from two sets of repeat CTD casts, capturing tidal variability in the water column. One set was collected during RV POLARSTERN expedition PS89, between 8 and 11 January 2015. The second set was collected during RV POLARSTERN expedition PS117, between 11 and 12 January 2019. Dissolved inorganic carbon (DIC) and total alkalinity (TA) were measured using coulometric titration and potentiometric titration, respectively, on a VINDTA 3C system. DIC and TA have been normalised to salinity: nDIC and nTA. Nutrients were measured with UV-Vis spectrophotometry and a continuous gas-segmented flow auto-analyser.

A fraction of oceanographic profiles (from CTD casts), the temperature, salinity, oxygen, and nutrient data have already previously been published (https://doi.org/10.1594/PANGAEA.910673). We have included these to maintain consistency with the rest of the profiles in the dataset (for which these variables have not been published yet). In addition to the fact that exactly these data were used in the calculations for the marine carbonate system in Droste et al. (2022), it is also easier for users to work with this dataset in the future. The DOI of the already published data is included in the comment column of the dataset itself. Details on sample collection, analysis methods, and salinity-normalisation of DIC and TA can be found in Droste et al. (2022).