Thin and thinner: Sea ice mass balance measurements during SHEBA

Abstract

[1] As part of a large interdisciplinary study of the Surface Heat Budget of the Arctic Ocean (SHEBA), we installed more than 135 ice thickness gauges to determine the sea ice mass balance. While installing these gauges during the fall of 1997, we found that much of the multiyear ice cover was only 1 m thick, considerably thinner than expected. Over the course of the yearlong field experiment we monitored the mass balance for a wide variety of ice types, including first-year ice, ponded ice, unponded ice, multiyear ice, hummocks, new ridges, and old ridges. Initial ice thicknesses for these sites ranged from 0.3 to 8 m, and snow depths varied from a few centimeters to more than a meter. However, for all of their differences and variety, these thickness gauges sites shared a common trait: at every site, there was a net thinning of the ice during the SHEBA year. The thin ice found in October 1997 was even thinner in October 1998. The annual cycle of ice thickness was also similar at all sites. There was a steady increase in thickness through the winter that gradually tapered off in the spring. This was followed by a steep drop off in thickness during summer melt and another tapering in late summer and early fall as freeze-up began. Maximum surface melting was in July, while bottom ablation peaked in August. Combining results from the sites, we found an average winter growth of 0.51 m and a summer melt of 1.26 m, which consisted of 0.64 m of surface melt and 0.62 m of bottom melt. There was a weak trend for thicker ice to have less winter growth and greater net loss for the year; however, ice growth was also impacted by the snow depth. Considerable variability was observed between sites in both accretion and ablation. The total accretion during the 9-month growth season ranged from zero for thick ridged ice to more than a meter for young ice. Ponds tended to have a large amount of surface melting, while ridges had considerable bottom ablation.

Role of sea ice in global biogeochemical cycles: emerging views and challenges

“…In contrast, over the last two decades, the shares of basal and surface melt have been comparable. Thinner ice fosters the summer reduction in ice concentration, which in turn increases basal melt through to the ice-albedo feedback, as observed [Perovich et al, 2003;Perovich et al, 2007] and simulated [Vancoppenolle et al, 2009b]. Because the long-term ice retreat is more pronounced in summer than in winter [see, e.g., Deser and Teng, 2008], the amplitude of the seasonal cycle of Arctic sea ice extent has been increasing, which means that the total annual sea ice growth and melt has been increasing and should continue to increase in the future [e.g., Holland et al, 2006].…”

“…Because Antarctic air masses are relatively cold and dry [Andreas and Ackley, 1982], and because the ocean heat flux is much larger than in the Arctic [e.g., McPhee, 2008], basal ice melt largely overcomes surface melt in the Southern Ocean [Vancoppenolle et al, 2009b;Maksym et al, 2012]. Lateral melting is confined to the zones where ice floes are sufficiently small [Steele, 1992;Perovich et al, 2003] and has not been clearly evidenced as a significant large-scale mass balance contributor.…”

Seasonal evolution of melt ponds on Arctic sea ice

“…At SHEBA, melt onset was observed after a rain event on May 29. Air temperatures remained above freezing after 29 May, the snow cover completely melted by 5 June, and the first ponds appeared on 20 June [Perovich et al, 2002a[Perovich et al, , 2003. APLIS air temperatures cooled below 08C from 1 June to 12 June ( Figure 5), and melt pond fractions initially grew more slowly than those at SHEBA, taking eight additional days to reach 5% on 17 June (Figure 8).…”

Sea ice and snow thickness and physical properties of an ice floe in the western Weddell Sea and their changes during spring warming

“…6) and ice-core profiles presented by Hellmer et al (2006) and Tison et al (2008). As an alternative, we also have tried to use thickness gauges based on the use of heated wires (Perovich et al, 2003). However, as the holes for the heated wires had been drilled in late November and early December, they never froze solid again, and many of the wires could be pulled up without any significant resistance from the ice underside, making detection of the ice/water interface impossible.…”