Here we focus on the changes of sea ice measured by Upward Looking Sonars (ULSs) at locations of our moorings (A, B, C, D, Figure 1). The Fresh Water Content (FWC) in sea ice (FWCI or solid) is formally given by equation (2)
Here, zice is the draft of the sea ice that we measured using Upward-Looking Sonars (ULSs); fb is the freeboard of the sea ice. The freeboard can be measured by satellites but here we calculate sea ice thickness (Hi, which is zice+fb) from the sea ice draft as Hi=zice(ρω/ρi), where ρi and ρω are ice and water densities, respectively. Assuming that sea ice salinity (Sice) is vertically uniform in the BGR, Sice=1.8 according to Perovich et al.,  the FWCI is calculated as
FWCI = 0.948Hi (3).
For snow FWC calculations we follow the recommendations of Sturm et al.  who analyzed the evolution and spatial distribution of the snow cover on the Arctic sea ice during the Surface Heat Budget of the Arctic Ocean (SHEBA) project. Specifically we assume that the snow has no salt and that the snow water equivalent, SWE = 0.343Hsn where Hsn is snow thickness.
The range of sea ice thickness changes (obtained from ULS records) varies among moorings. The seasonal magnitude of sea ice draft (Figure 2) is approximately 150 cm. The maximum ice draft/thickness in the BGR is observed between May and June and the minimum between late August and early November depending on the year and mooring location. The seasonal transformations of FWCI are discussed in section FWC seasonal transformations.
Hutchings, J. K., and I. G. Rigor (2009), Mechanisms explaining anomalous ice conditions in the Beaufort Sea during 2006 and 2007, Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abstract C51A-0525.
Perovich, D. K., J. A. Richter-Menge, K. F. Jones, and B. Light (2008), Sunlight, water, and ice: Extreme Arctic sea ice melt during the summer of 2007, Geophys. Res. Lett., 35, L11501, doi:10.1029/2008GL034007.
Perovich, D. K., T. C. Grenfell, B. Light, B. C. Elder, J. Harbeck, C. Polashenski, W. B. Tucker, and C. Stelmach, Transpolar observations of the morphological properties of Arctic sea ice J. Geophys. Res., 114, C00A04, doi:10.1029/2008JC004892 30 January 2009.
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