Radiative and meteorological measurements were collected continuously during a cruise from Australia to Antarctica in austral summer 2000. On the average, the amount of fractional cloud cover was high (81%), reducing the incoming solar radiation. The albedo varied widely from over 80% for snow-covered undisturbed sea ice to below 10% for open water. In general, sea ice concentration was the strongest determining factor for the reflectivity. However, different ice types and snow cover also had a substantial influence on the reflectivity. When a highly reflecting surface was present (total snow-covered undisturbed ice pack with an albedo of 81%), the incoming global radiation under overcast conditions was 85% higher than for a water surface due to multiple reflections. The net radiation was found to be a strong function of both fractional cloud cover and surface albedo. For low albedo values, the net radiation increases with decreasing cloudiness, e.g., for a water surface (albedo 8%) the mean daily value increased from 88 Wm-2 for total cloud cover to 226 Wm-2 for clear skies. For highly reflecting surfaces, the net radiation decreases with decreasing cloud amount for most of the day. The mean daily value was slightly negative for clear skies (-7 Wm-2), but somewhat positive (23 Wm-2) for overcast conditions.