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A study of the variation in sea ice algal distribution and production was performed dur- ing June and early July 1999 in Young Sound, northeastern Greenland. Measurements were per- formed in situ by divers using an underwater pulse-amplitude-modulated (PAM) fluorometer, oxygen microelectrodes and 14 C incubations. In early June, Young Sound was covered by ~1.6 m of sea ice and ~30 cm of dry snow, which reflected ~75% of the incident light. These conditions resulted in low irradiance below the sea ice (<2 µmol photons m -2 s -1 ), low values of chlorophyll a (<1 µg l -1 sea ice) and low primary productivity (<0.05 µg C l -1 h -1 ) in the bottom ice (0 to 4 cm). The snow cover grad- ually disappeared during June, resulting in increased light penetration of up to 20 µmol photons m -2 s -1 , chl a concentrations of up to 15 µg l -1 (0.6 mg C m -2 ), and primary production rates of up to 0.2 µg C l -1 h -1 (0.2 mg C m -2 d -1 ) in the bottom ice. Light saturation curves of photosynthesis were obtained in situ on 3 occasions and showed adaptation of the sea ice algae to low irradiance; E k val- ues ranged from 12 to 35 µmol photons m -2 s -1 . Photosynthesis of sea ice algae resulted in supersatu- rated oxygen conditions (150 to 200%) at the sea ice-water interface as compared to ambient seawa- ter. In situ investigations of irradiance, algal biomass and photosynthetic activity on different metric scales showed a heterogeneous distribution of sea ice algae. Statistical treatment of the data obtained revealed that algal activity followed the light regime below the sea ice (radii of patches were 50 to 100 m), whereas algal biomass patches were smaller (radii of patches were 5 to 10 m). Sea ice algal production in Young Sound was 2 to 3 mg C m -2 during June and July 1999. Compared to other coastal fast-ice areas this rate is low. We suggest that the low biomass and productivity in Young Sound was caused by a combination of poor light conditions due to snow cover and freshwater drainage from melt ponds and river discharge removing and/or inhibiting the algae at the sea ice- water interface through physical disturbance and exposure to freshwater. The primary production of sea ice algae in Young Sound was <1% of the annual pelagic primary production.

Biomass, production and horizontal patchiness of sea ice algae in a high-Arctic fjord (Young Sound, NE Greenland)