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Uehara, H., Kruts, A.A., Mitsudera, H. Nakamura, T., and Volkov, Y.N. (26-Feb-14)

The dense shelf water (DSW) produced in the Okhotsk Sea causes the deepest ventilation and plays a key role in intermediate overturn in the North Pacific. The variability of the DSW salinity and its cause, however, has been unknown because of paucity of available data. We present the DSW salinity variability during the period 1950-2005 analyzing a new hydrographic dataset, expanded with Russian measurements. The DSW salinity shows a decreasing trend of -0.0024 ±0.0015 psu y-1 as well as decadal-scale variability. The DSW variability is controlled by surface salinity anomalies propagating along pathways associated with ocean currents from the Bering Sea to the Okhotsk Sea. The salt pathways can be traced upstream in the subarctic gyre. This pathway identifies the previously undefined upper branch of the North Pacific overturning cell. Our results indicate that long-term atmospheric variations and enhanced hydrological cycles over the North Pacific associated with climate changes are conducted to the intermediate layer through the salt pathways and subsequent DSW ventilation, leading to variability in material and biogeochemical cycles.