Estimation of sea-ice thickness and volume in the Sea of Okhotsk based on ICESat data.

Sea-ice thickness in the Sea of Okhotsk is estimated for 2004-2008 from ICESat derived freeboard under the assumption of hydrostatic balance. Total ice thickness including snow depth (h tot ) averaged over 2004-2008 is 95 cm. The interannual variability of h tot is large; from 77.5 cm (2008) to 110.4 cm (2005). The mode of h tot varies from 50-60 cm (2007 and 2008) to 70-80 cm (2005). Ice thickness derived from ICESat data is validated from a comparison with that observed by Electromagnetic Induction Instrument (EM) aboard the icebreaker Soya near Hokkaido, Japan. Annual maps of h tot reveal that the spatial distribution of h tot is similar every year. Ice volume of 6.3 × 1011 m3 is estimated from the ICESat derived h tot and AMSR-E derived ice concentration. A comparison with ice area demonstrates that the ice volume cannot always be represented by the area solely, despite the fact that the area has been used as a proxy of the volume in the Sea of Okhotsk. The ice volume roughly corresponds to that of annual ice production in the major coastal polynyas estimated based on heat budget calculations. This also supports the validity of the estimation of sea-ice thickness and volume using ICESat data.