The physico-chemical, morphological and biological characteristics of melt water ponds on Arctic sea ice as well as their seasonal development were investigated in the North East Greenland Current between 81 and 72 degrees N in 1993 and 1994. Parameters studied were water temperature, pH, salinity, conductivity, oxygen and nutrient concentrations, PAR, pond size, colour and depth, chlorophyll a and particulate organic carbon concentrations. The composition and abundance of the microbial plankton was examined microscopically. For comparison, other aquatic Arctic habitats (ponds and lakes at the North East Greenland coast; meltwater ponds on glaciers and icebergs; sea-water; sea ice) were investigated as well.

With a size range between <1 m^2 and about 21,000 m^2, the sea ice meltwater ponds were highly variable in size whereas their water depth did not exceed a few decimetres. In the study area, pure freshwater ponds (79 %) and oligomixohaline ponds with salinities not higher than 2 (15 %) dominated whereas brackish ponds with salinities between 8 and 22 were encountered very rarely. Low salinity and low ion levels as well as its ultraoligotrophic character and exposure to high levels of irradiance seem to act as limiting factors regarding the colonization of this extreme habitat. Algal biomass was low (median 0,04 micro-g chlorophyll a/l) and showed a slight, but statistically significant increase over summer. POC levels ranged from 18 to 313 g/l and were higher than to be expected from the chlorophyll data. POC showed a highly significant increase from end of June to mid of September. The pond plankton consisted of a microbial assemblage of bacteria and protists. Early in the melt pond cycle the assemblage was dominated by snow organisms, but soon turned into a "typical" freshwater sea ice pond assemblage with chlorophycean algae, chrysophytes, photo- and heterotrophic dinoflagellates, nanoflagellates and ciliates. Diatoms played a minor role. Heterotrophic dinoflagellates and haptorid ciliates seem to represent the highest trophic level within the planktonic food web of these ponds. The brackish pond assemblage contained additional taxa, mainly diatoms and prasinophytes as well as organisms characteristic of sea-water and the brine channel system.

It is concluded that the snow layer and freshwater meltwater ponds at the Arctic sea ice surface are very similar to the snow and glacial ecosystems found in polar regions and alpine environments. The sea ice surface is a mixing zone between the snow/glacial and the sea ice/marine environment represented by the brackish ponds.

Complete thesis with English abstract is published in Reports on Polar and Marine Research (Ber. Polarforsch.) 409, 2002. English table and figure legends are available from the author (carstens.pellnitz@t-online.de).