We investigated the transport of Arctic shelf water and its impacts on the downstream hydrographic structures in the Amerasian Basin by combining data collected in the summer of 2016 from two international cruises in the Pacific sector. The East Siberian Sea (ESS), in which cold shelf water with salinity of 31.0–32.8 is produced, was identified to be a major source of the near‐freezing temperature water for the Makarov Basin. This relatively low‐salinity shelf water was transported into the Chukchi Abyssal Plain and occupied the subsurface layer (30–60 m), which led to the formation of a subsurface oceanic front stretching along the Chukchi Plateau and northern side of the Mendeleev Ridge. The offshore transport of waters from the ESS caused an intrusion of the Atlantic Water onto the shelf and promoted the formation of the diapycnally mixed Lower Halocline Water (D‐LHW) at the bottom of the outer shelf. Our findings indicate that the source of the D‐LHW in the Arctic Pacific sector might extend from the Chukchi Plateau to as far as the Makarov Basin. We hypothesize that advection of waters from the ESS into the Makarov Basin promotes development of the subsurface halocline in the Makarov Basin. The volume transport of surface waters (salinity less than 30) on the ESS shelf was estimated to be about 0.6 Sv (10⁶ m³ s⁻¹) eastward to the Canada Basin in 2016, consistent with the cyclonic Arctic circulation regime in 2016.

Seasonal hypoxia in the bottom waters of the Peter the Great Bay (PGB) of the Japan/East Sea (JES) occurs in summer. Using the empirical relationship between dissolved oxygen (DO) and pH obtained for hypoxic conditions and available historical DO data, acidification rates were estimated. Carefully sampled time-series observations from the northwestern part of the JES, carried out from 1999 to 2014 along the 132°20′ E and 134°00′ E longitudes, were chosen to determine the interannual variability of the sea’s hydrochemical parameters (DO, pH, and TA—the total alkalinity phosphates, nitrate, and silicates). To limit the effects of seasonal and spatial variability, only data obtained in the warm period were used. Additionally, all data from depths shallower than 500 m were discarded because they are affected by high natural variability, mostly due to strong mesoscale dynamic structures. Our results demonstrated that the pH and DO concentrations measured in the Upper Japan Sea Proper Water (750 m), Lower Japan Sea Proper Water (1250, 1750, 2250 m), and Bottom Water (3000 m) have been decreasing in recent years. On the other hand, calculated normalized dissolved inorganic carbon (NDIC), CO₂ partial pressure (pCO₂), and measured nutrient concentrations have been increasing. Maximum rates of acidification and deoxygenation are occurring at around 750 m. The annual rate of increase of pCO₂ in the water exceeds the atmospheric rate more than 2-fold at a depth of 750 m. The observed variability of the hydrochemical properties can be explained by the combination of the slowdown ventilation of the vertical water column and eutrophication. However, the results obtained here are valid for the subpolar region of the JES, not for the whole sea. The synchronization of the deoxygenation of the open part of the JES and PGB has been found.

The variability of sea surface temperature (SST) in the Japan Sea is investigated using the complex EOF analysis of daily data produced at Tohoku University, Japan (New Generation SST; 2002–2006)....