The sub-ice fauna of the Laptev Sea and the adjacent Arctic Ocean in summer 1995

The sub-ice habitat and fauna in the Laptev Sea and the adjacent Arctic Oce an were investigated during the "Polarstern" cruise ARK XI/1 in summer 1995 . At the ice-water interface a thin thermo- and halocline developed at many stations due to melting processes. In the lower centito decimetres of the ice, an accumulation of organic matter was found (particulate organic carbo n: 1.9 mg l(-1), chi a: 3.3 mu g l(-1)) that may have provided a food sourc e for the fauna. The water layer directly beneath the ice was inhabited by high numbers of various nauplii (130-23911 ind. m(-3)), and two ecological groups, the pelagic sub-ice fauna that originates from the surface water pl ankton, and the sympagic sub-ice fauna that migrates into this boundary lay er from the ice interior. The pelagic fauna dominated the sub-ice community both in terms of species number and abundance. Both groups mainly comprise d small copepods (e.g. Oithona similis, Oncaea borealis, Pseudocalanus spp. , Halectinosoma spp., Tisbe spp.), but foraminifers and pteropods, for exam ple, also occurred regularly. Diversity was generally low. Factors influenc ing the composition and abundance of the sub-ice fauna were most likely wat er depth, salinity and sea-ice sediments.