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On the basis of all available data, it is found that intermediate water temperature on the 26.8–27.4σθ isopycnals in the northwestern North Pacific has significantly increased during the past 50 years. The largest warming area exists in the western part of the Sea of Okhotsk with a 0.68°C/50‐yr temperature increase observed at 27.0σθ. The warming in the Pacific is found over the Oyashio and Subarctic Current regions, where the Okhotsk water extends along the subarctic gyre. This suggests that the warming originates from the Sea of Okhotsk. The warming trend is also accompanied by the significant decreasing trend of dissolved oxygen content, suggesting the weakening of overturning in the northwestern North Pacific. We propose that these trends of the water mass property are caused by a decrease in dense shelf water production in the northwestern shelf of the Sea of Okhotsk, which is a sensitive area to the current global warming.

Abstract. Using Defense Meteorological Satellite Program (DMSP) special sensor microwave imager (SSM/I) sea-ice data and meteorological data, we investigate processes controlling the advance and retreat of sea ice in the Sea of Okhotsk. For this investigation we apply a new algorithm to the SSM/I data, which is capable of calculating ice concentration and distinguishing sea-ice types; this algorithm is confirmed by comparison with National Oceanic and Atmospheric Administration (NOAA) advanced very high resolution radiometer (AVHRR) imagery. Our investigations show that there exists a locality for the areas of new-ice formation, and the ice formation near the ice edge always occurs as a recovery after sea ice has retreated suddenly. We also reveal that the speed of ice-edge advance fairly coincides with that predicted by 2% of the geostrophic wind. Furthermore, there exists a good correspondence between the times when the overall advance and retreat of ice cover begin and the decrease and increase of air temperature begin. We conclude that the advance of the ice cover in the Sea of Okhotsk occurs primarily through ice advection by wind and that the interannual variation in the maximum sea-ice extent can be interpreted by that in wind and air temperature conditions.

The volume of brine excluded from growing sea ice and its salinity were measured using a brine sampler. The measurements were made, in both laboratory and field, under various growth conditions of the sea ice. The salinity of the brine becomes higher, and the volume flux decreases as the sea ice growth rate decreases. Consequently, the salt flux of the brine decreases with decreasing growth rate. In the case of sea ice growth at a constant rate, as the sea ice becomes thicker, the salinity of the brine excluded increases while its volume flux decreases. However, the salt flux is nearly independent of the ice thickness increase, at least up to a thickness of 15 cm. For sea ice growth rates between 1.7×10−5 and 1.4×10−4 cm s−1, and for a seawater salinity of 33.0‰, the brine salinity ranged from 42.3‰ to 92.7‰, the volume flux ranged from 6.3×10−6 to 3.4×10−5 cc cm−2 s−1, and the salt flux ranged from 6.4× 0−7 to 1.5×10−6 g cm−2 s−1.