This dataset was collected during the cruise MSM139 (GreenHab, 25.07 - 27.08.2025) with RV MARIA S MERIAN from Reykjavik, Iceland to Reykjavik, Iceland. The dataset contains chlorophyll a measurements [µg/L] from water samples collected from discrete sampling via CTD. In total, 33 stations have been sampled from various depth. 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 via 90% acetone. Concentrations were calculated from fluorescence measured with a pre-calibrated Turner Design TD7200-02 laboratory fluorometer (EPA445.0, Turner Manual). Chief Scientist of RV Maria S Merian cruise MSM139: Dr.Uwe John, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI).