During the Polarstern cruise PS76 sea water samples (1 – 10 L) were collected from up to six different depths from the upper 100 m at CTD stations using a rosette equipped with a SEA-BIRD CTD system and 24 Niskin bottles (12 L). Seawater subsamples were filtered at low vacuum (<400 mbar) on board immediately after sampling onto GF/F filters and stored at −20°C until analysis. Prior to analysis, filters were soaked in 0.1N HCl to remove inorganic carbon and subsequently dried at 60°C. POC and PON concentrations were determined with a CHN elemental analyzer as described in detail in Nöthig et al. (2020).