Mass balance:
What is it?

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The Arctic ice pack is governed by two processes: thermodynamics and dynamics. The mass balance of sea ice is a straightforward thermodynamic concept. It is simply the balance of how much the ice grows in the winter and melts in the summer. For Arctic sea ice virtually all of the growth occurs on the bottom of the ice. Melting occurs on both the top and the bottom of the ice. In the vast majority of cases all of the snow melts during the summer, typically in just a couple of weeks. The mass balance is a powerful concept since is is the great integrator of the heat budget. If there is a net increase of heat, then the ice will thin. A net cooling will result in thicker ice.

 
 

 

The combined results of earlier sea ice mass balance studies (Untersteiner, 1961; Hanson, 1965; Koerner, 1973; Maykut and McPhee, 1995; Morison et al., 2002; Perovich et al., 2003) suggest that in addition to spatial differences, there is significant interannual variability in the ablation/accretion rate of the sea ice cover. Measurements of the ablation of unponded, level multiyear ice are presented in the bar chart below. Surface melt ranged from 20 to 70 cm, while bottom melt varied from 10 to 60 cm. Comparing data from similar locations indicates that the interannual variability at a particular location may be greater than the latitudinal variability in a single year.  

Comparison of summer melt from 7 sites in 7 years.

Location of mass balance study sites.