[A-CG43] Science in the Arctic Region

[ACG43-05] Spring ocean salinity profiles teach us decreasing trend of sea ice thickness in the southern Okhotsk Sea

*Mariko Honda¹, Kay I. Ohshima¹, Vigan Mensah¹, Jun Nishioka¹, Stephen Riser² (1.Hokkaido Univ., 2.University of Washington)

Keywords:Okhotsk sea, sea ice, sea ice melt, global warming, profiling float, salinity profile

Sea-ice extent of the Okhotsk Sea has decreased by about 25% for the past four decades, which indicates that the Okhotsk Sea is sensitive to global warming. On the other hand, information of sea-ice thickness has been very limited in this sea. Its average, spatial distribution and interannual variations have not been understood except for the observation by ICESat (Nihashi et al., 2018). When sea ice melts in spring, the ocean surface is considerably freshened. Vertical integration of this salinity decrease provides estimation of the amount of sea-ice melt, giving the inference of the sea-ice thickness. Evolution of the surface freshening observed by the profiling floats confirms the validity of the estimation method of ice-melt amount. Spatial distribution and interannual variations of ice-melt amount in the Okhotsk Sea are estimated from all the available salinity profiles by the hydrographic and float observations. The estimated ice-melt amount is relatively large in the western and southern parts, and this spatial distribution is consistent with the ice thickness distribution observed by the ICESat. From the analysis of the interannual variations of ice-melt amount south of 53° N, where the data number is relatively large, the averaged ice thickness likely exhibits the decreasing trend, from 72 cm during 1960’s to 51cm during 2000’s, with the decreasing rate of 30% per 40 years.