Observations of Sea Ice Properties in the Marguerite Bay Region during Spring

Bruce Elder, Sharon Stammerjohn, Keran Claffey, Donald Perovich, and Raymond Smith

During the spring 2001 cruise of the SO GLOBEC experiment, we sampled ice physical and optical properties in the Marguerite Bay area of the Palmer Peninsula. At 12 sites, ice thickness was measured every meter along 10- to 120-m-long survey lines. The combined mean ice thickness for these surveys was 62 cm, with a median of 43 cm and a maximum thickness of 280 cm. Snow depths ranged from 1 cm to 57 cm, averaging 16 cm. At 45% of the thickness holes, a combination of deep snow and thin ice resulted in negative freeboard. A stratigraphic analysis of ice thin sections showed that more than half of the ice cover was granular and that virtually all of the upper 20 cm of the ice was granular. There are indications that snow-ice formation at the surface contributed significantly to ice formation. At most sites the base of the snow cover was wet and saline. The average ice salinity was 7 psu, with the largest salinities, of approximately 10 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. Maximum transmittances were between 400 and 500 nm. For 30-cm thick ice with 7 cm of snow, peak transmittances were only 2 to 3%. Removing the snowcover increased transmittance by an order of magnitude to almost 30%.