Samples of the bottom ice algae and brine algae (within 30cm of the top of the ice) were subjected to temperature, salinity, light and UVB experiments and analysed with PAM rapid light curves to determine the response of the algae to changes they will encounter during the processes of ice formation at the start of winter and ice melting in summer. Brine algae are likely to be adapted to high light ... and high UVB conditions near the surface of the ice and may have produced higher levels of protective pigments, MAA's, therefore the content of MAA's was analysed. Imaging PAM fluorometry was also used to gain a 3D image of photosynthetic stressors during the process of ice freeze and thaw on both algae and bacterial cells. The difference in thylakoid structure with increase in temperature was also analysed. Bacterial cells were collected at the end of exposure and a CTC assay was performed on them to determine the effect of UVB radiation. Bottom ice algae exposed to different light levels and UV exposure was analysed for cell counts, antioxidants and MAAs. Bacterial response to changes in light and salinity was examined by adding a fluorescent stain (CTC) to a melted entire sea ice core, a brine sample and a bottom ice sample and exposing the samples to various combinations of light and salinity. Samples were examined for cells that fluoresce due to metabolized CTC. The bacterial response to light and the presence/absence/inhibition of microalgae was examined using the vital stain and probe technique after exposing melted ice core samples to a range of irradiances for 4 hours. Samples of the brine community were collected and incubated for 5 days to determine the longer term response to light. Tritiated leucine was used calibrate the use of the CTC method.