Southern Ocean GLOBEC: Snow and Ice Studies

Don Perovich

During the July-September 2002 cruise of the Southern GLOBEC experiment, we sampled ice physical and optical properties in the Marguerite Bay area of the Palmer Peninsula. At 15 sites, ice thickness was measured every meter along 10- to 120-m-long survey lines. Excluding results from a single very thick floe, the combined mean ice thickness for these surveys was 119 cm, with a median of 77 cm and a maximum thickness of 565 cm. These values were much larger than the mean and median thicknesses of 62 cm and 44 cm measured during the 2001 cruise. Snow depths ranged from 0 cm to 140 cm, averaging 25 cm. At 21% of the thickness holes, a combination of deep snow and thin ice resulted in negative freeboard. At most sites the base of the snow cover was saline. The average ice salinity was 7.1 psu, with the largest salinities, of approximately 12 psu, found near the surface. Ice temperatures were warm resulting in large brine volumes. The thicker ice showed evidence of extensive rafting and ridging. Visible albedos were in the 0.9-0.95 range for snow-covered ice and 0.5-0.6 range for bare ice. Transmittance observations showed a strong biological signature, with peak values shifted to 565 nm. For 60-cm thick ice with 23 cm of snow, peak transmittances were only 2 to 3%. Removing the snow cover increased transmittance by an order of magnitude to almost 30%. The wavelength of peak transmittance was 565 nm indicating the presence of biology.