Distribution and Transport of Water Masses in the East Siberian Sea and Their Impacts on the Arctic Halocline

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. Plain Language Summary The East Siberian Sea (ESS) is an important freshwater reservoir of the Arctic Ocean, but the water transport across the ESS remains poorly understood because there are few observations. In 2016, two hydrographic cruises were conducted in the ESS and nearby basins to reveal how water masses in the ESS affects ocean temperature and salinity downstream. We found that the ESS is the source of up to three different water masses that are found in the adjacent Makarov Basin. These water masses occupy a total thickness of about 100 m in the water column. We found that low‐salinity waters on the shelf of the ESS flowed toward the Chukchi Abyssal Plain, carrying a large amount of freshwater from the continental shelf of Russia into the Makarov Basin. We estimated that the volume of freshwater provided by the ESS is similar to the flow through the Bering Strait, indicating an important role of the ESS in the Arctic freshwater budget. Key Points Fresh and salty East Siberian shelf waters are identified using in situ hydrographic