Specimens of the species Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus were sorted from Bongo net hauls during Polarstern cruise PS78 (ARK-XXVI/1) on a transect across Fram Strait. Their prosome length was measured onboard under a stereo-microscope (magnification: 16 – 32fold, error between 0.03 and 0.06 mm). Afterwards, each individual was transferred to a pre-weighted tin cap and stored at -20°C. The copepod samples were then dried at 60°C for at least 48 h and weighted to measure individual dry mass (mg). The analysis of carbon and nitrogen contents was carried out with the “EuroVector Elemental Analyzer EuroEA 300” (HEKAtech GmbH) and the software package “CallidusTM Software v.2E3”. As in preserved sample analyses, the three Calanus species were distinguished based on their prosome length (Unstad and Tande 1991).