The relative amounts of visible, near and far UV radiation (Blue, Violet, UVA and UVB) falling onto sea ice in McMurdo Sound was measured at a site well cantered in the ice, i.e. not at the ice edge. Two instruments were used to measure the UV levels. One is a three channel motor, which measures the total downward radiation in the Blue, Violet and Ultraviolet regions. A shade can be used to ... separate the direct sun radiation from the background sky radiation and a filter provides a separation of the UV channel into UVA and UVB radiation. The second instrument consists of a monochromator attached to a small telescope and measures the spectral distribution of radiation from a 5 degree region of the sky. The incident light is separated into polarisation components and the instrument thus also measures the polarisation of the skylight. The weather during the recording period was overcast with snow and blizzards but the monitors were run throughout this period and accumulated data on UVA, UVB and UV radiation levels under overcast conditions. The amount of algae growing in the area around the ice was simultaneously quantified. A two wavelength detector measured the amount of light at different locations on a circle of about 1m radius. The detectors were sensitive to red and green wavelengths. Algae absorb radiation strongly in the green, so the relative intensity in these two bands should indicate the amount of algae present. The effect of various thicknesses of snowfall on the UV transmission through to the sea ice algae below the ice was measured using samples cut from snow drifts.