BREAKING THE ICE - LARGE-SCALE DISTRIBUTION OF MESOZOOPLANKTON AFTER A DECADE OF ARCTIC AND TRANSPOLAR CRUISES

Mesozooplankton collected during five summer expeditions to the Arctic Ocean between 1987 and 1991 was analysed for regional patterns in bio mass and species distribution, distinguishing between an epipelagic (0 -100 m) and a deeper (0-500 m) layer. A total of 58 stations was sampl ed mainly in the Nansen, Amundsen and Makarov Basins of the central Ar ctic Ocean and in areas of the Greenland Sea, West Spitsbergen Current and Barents Sea. Results from the different expeditions were combined to create a transect extending from the Fram Strait across the Eurasi an Basin into the Makarov Basin. Mesozooplankton dry mass in the upper 500 m decreased from 8.4 g m(-2) in the West Spitsbergen Current to l ess than 2 g m(-2) in the high-Arctic deep-sea basins. In the central Arctic Ocean, biomass was concentrated in the upper 100 m and was domi nated by the large copepods Calanus hyperboreus and C. glacialis. In c ontrast, the mesozooplankton in the West Spitsbergen Current was more evenly distributed throughout the upper 500 m, with C. finmarchicus as the prevailing species. The distribution of abundant mesopelagic spec ies reflected the hydrographic regime: the calanoid copepod Gaetanus t enuispinus and the hyperiid amphipod Themisto abyssorum were most abun dant in the Atlantic inflow, while Scaphocalanus magnus was a typical component of the high-Arctic fauna. The relatively high mesozooplankto n biomass and the occurrence of boreal-Atlantic species in the central Arctic Ocean are indicators for the import of organic material from a llochthonous sources, especially from the northern North Atlantic. Hen ce, in spite of its enclosure by land masses, the Arctic Ocean is char acterized by an exchange of water masses and organisms with the North Atlantic, and advection processes strongly influence the distribution of plankton species in this high-latitude ecosystem.