Abstract. Variations in Arctic sea ice are not only apparent in its extent and thickness but also in its internal properties under global warming. The microstructure of summer Arctic sea ice changes simultaneously due to varying external forcing, ice age, and extended melting seasons, which affect its optical properties. Sea ice cores sampled in the Pacific sector of the Arctic obtained by the Chinese National Arctic Research Expeditions (CHINARE) during the summers of 2008 to 2016 were used to

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... estimate the variations in the microstructures and inherent optical properties (IOPs) of ice and determine the radiation budget of sea ice based on a radiative transfer model. Compared with 2008, the volume fraction of gas bubbles in the top layer of sea ice in 2016 increased by 7.5 %, and decreased by 50.3 % in the interior layer. Meanwhile, the volume fraction of brine pockets increased clearly in the study years. The changing microstructure resulted in an increase in the scattering coefficient in the top ice layers by 9.3 % from 2008 to 2016, while an opposite situation occurred in the interior layer. These estimated ice IOPs fell within the range of other observations and their variations were related to increasing air temperature and decreasing ice ages. At the Arctic basin scale, the changing IOPs of ice greatly changed the amount of solar radiation transmitted to the upper ocean even when a constant ice thickness is assumed, especially in marginal ice zones, implying the presence of different sea ice bottom melt processes. These findings revealed the important role of the changing IOPs of ice in affecting the radiation transfer of Arctic sea ice.