ZOOPL.ANKTON STANDING CROP IN THE ARCTIC BASIN1

An estimate of zooplankton standing crop in the central Arctic Ocean was obtained from 118 closing-net samples collected from Ice Islands T-3 and ARLIS II. The T-3 samples were taken from the anticyclonic gyre in the Amerasia Basin north of Alaska; the ARLIS II samples were collected from the Eurasia Basin north of Greenland. Copepods were the most important group, constituting over 80 % of the biomass. The most important genus was Calanus, which averaged half the biomass in the upper 1,500 m. Below 1,500 m the relative importance of Calanus dcclincd. Copepods were also the most numerous (90 % ) metazoan plankters, though they were outnumbered by small radio-larians in the upper 100 m from July to early Septcmbcr. There was some cvidcncc of a summer (July-August) increase in biomass in 0-100-m samples from T-3 and an increase in ARLIS II 0-100-m samples from March to January as ARLIS II drifted towards Greenland. Average biomass concentrations for the three principal water masses of the Axtic Ocean were 0.62 mg clry wt/m ” for the Arctic surface layer (O-200 m), 0.14 mg/m ” for the Atlantic layer (200-900 m), and 0.04 mg/m ” for the Arctic deep-water mass (>900 m). Total zooplankton biomass in the central Arctic was estimated at l-2 x 10 ” metric tons (dry weight). Calculations basccl on available primary production data suggest that photosynthesis alone cannot meet the metabolic demands of the biomass of zooplankton in the central Arctic Basin. INTHODUCTION Plankton investigations in the Arctic Ocean have been primarily concerned with plankton systcmatics; we now have an extensive knowledge oE the species com-position of phytoplankton (Gran 1904