Chlorophyll a and phaeophytin a measurements from discrete water samples during RV MARIA S. MERIAN cruise MSM139

This dataset was collected during the cruise MSM139 (GreenHab, 25.07 - 27.08.2025) with RV MARIA S. MERIAN from Reykjavic, Iceland to Reykjavik, Iceland. The dataset contains chlorophyll-a measurements [µg/l] from water samples directly collected from the seawater supply (Reinseewassersystem, RSWS) of the ship to calibrate the fluorometers of the RSWS system. To obtain chl-a concentrations, water samples were filtered onboard through 0.7 μm pore size, glass fiber filters (Whatmann GF/F) under low vacuum. Filters were frozen immediately at -80 °C until extraction in laboratory by 90% acetone method. Concentrations were calculated from fluorescence measured with a pre-calibrated Turner Design TD 7200-02 laboratory fluorometer (EPA445.0, Turner Manual).