Abstract:
Sea ice hosts a large community of algae which is released into the food chain when the ice melts. The sea ice algae grow rapidly in the Antarctic spring at a time that coincides with the ozone hole and when sea ice is most transparent to UVB. They are a good organism to study for the analysis of the effects of UVB on the Southern Ocean food chain. The changes in photosynthetic rate and the
... effects of UVB on the growth of sea ice algae was investigated at Cape Evans over several seasons by altering the UVB flux over four areas of sea ice providing plots of different UV treatment: 1) photosynthetically active radiation (PAR) only, 2) PAR + UVA, 3) PAR + UVA + UVB, and 4) PAR + UVA + enhanced UVB; in the second season, this plot was a control and was therefore ambient PAR + UVA + UVB. A light fitting with 6 UVB fluorescent tubes was set in a shallow trough cut in the ice to provide additional UVB radiance above ambient for plot 3 in season two as well. Samples from the bottom 100mm of ice cores were taken over two weeks, melted and analysed for changes in photosynthetic pigments, mycosporine like amino acids, total cell numbers, species composition and carbon, nitorgen and phosphorous content. A PUV500 submersible multichannel radiometer was used to measure UVB and visible radiation both above and beneath the ice. Oxygen microelectrodes were deployed under the ice. A CTD probe (conductivity, temperature and depth) was sent to the bottom of the bay (c. 35m) at 1pm each day. The probe records a profile of these physical parameters and also records chlorophyll levels of the phytoplankton in the water. Photosynthetic rates in situ were measured using PAM fluorescence techniques. It was used on small samples in the laboratory and was also deployed remotely under the ice. By taking measurements from early morning to midday, the adaptations the algae photosynthetic system made to the increasing radiation (photoacclimation) was observed and then as intensity passed through the maximum at solar noon, the delay in algal response to changing light intensity was measured. 
