Remotely propagating salinity anomaly varies the source of North Pacific ventilation

• A new hydrographic dataset revealed the variability of dense shelf water (DSW) in the Sea of Okhotsk.
• The DSW salinity showed the decreasing trend and decadal variations.
• A salt pathway from the subarctic gyre to the DSW formation region via the Bering Sea were discussed.
• Surface salinity anomalies propagating along the salt pathway likely impact the DSW variations.
• The DSW variations subsequently affect ventilation in the intermediate layer of the Sea of Okhotsk.

The dense shelf water (DSW) produced in the Sea of Okhotsk causes the deepest ventilation in the North Pacific and plays a key role in overturning to the depth of intermediate layers. Salinity determines the density of DSW in cold seas such as this. However, the variability of DSW salinity has yet to be quantified and its causes remain unknown because of the paucity of available observation data. Here, we describe the variability of DSW salinity in the period from 1950 to 2005 through the analysis of a newly compiled hydrographic dataset, expanded with Russian measurements in the Sea of Okhotsk and the Bering Sea. DSW salinity exhibits a decreasing trend of −0.0024 ± 0.0015 y−1 over 1950–2005, in addition to decadal-scale variability with a typical magnitude of ∼0.1. We have found that DSW variability is controlled largely by surface salinity anomalies that propagate along pathways associated with ocean currents from the Bering Sea to the Sea of Okhotsk. These salt pathways can be traced farther upstream to the Alaskan Stream and western subarctic gyre. We suggest that this is a possible pathway which consists of a previously undefined upper branch of the North Pacific overturning cell. Along this pathway, the effects of the nodal tide that has an 18.6-year period may also propagate from the Kuril Straits and the Aleutian Passes. Our results indicate that long-term atmospheric variations and enhanced hydrological cycles over the North Pacific, which are associated with global climate changes, are conducted to the intermediate layer through surface salt pathways and subsequent DSW ventilation and lead to variability in material circulation and biogeochemical cycles.