Seven years of conductivity-temperature-depth data enable direct computations of volume transport and a description of the temporal changes of water properties in the western subarctic Pacific. The cooling of the western subarctic surface layer is shown through the observation of the thermohaline transition, which occured in the western subarctic during 1990--1997. Its main consequences were changes of the Oyashio path and restratification of the western subarctic water. The example presented here uses data obtained during the Canada/Russia International North Pacific Ocean Climate Study, as well as the Russian project Subarctic to show that a warming and ventilation of the midlayers of the western subarctic (200--1000 dbar) occurred because of the influx of warm subtropical waters to the Oyashio and Sea of Okhotsk and to the weak coastal Oyashio before the transition. This influx appears to have reversed in the early 1990s; now subarctic intermediate waters displace the remnants of subtropical waters that penetrated to the Sea of Okhotsk through the Soya Strait and create strong stratification in the Oyashio area. This transition appears to have begun during the reinforcement in the coastal Oyashio. ¿ 2000 American Geophysical Union