Thirty-nine plankton samples were collected at the Drift Station "Arlis II" at the north of Greenland in the Arctic Ocean during the period from June to December, 1964. From the samples thirty-two species of copepods were identified, of which Calanus glacialis, C. hyperboreus, Microcalanus pygmaeus, Spinocalanus abyssalis, Metridia longa and Oithona similis were major components.

The maximum plankton biomass throughout the period was observed in July when C. hyperboreus was predominant. The plankton population during day season (light season from June to August) was characterized by abundance of C. hyperboreus, M. pygmaeus and O. similis, while the population during night season (dark season from September to December) was characterized by abundance of M. pygmaeus and O. similis.

Developmental stages of C. hyperboreus were collected in bulk in summer, suggesting that this species was breeding under the permanent ice floe.