Terra Nova Bay in Antarctica is a formation region for high-salinity shelf water (HSSW), which is a major source of Antarctic Bottom Water. Here, we analyze spatiotemporal salinity variability in Terra Nova Bay with implications for the local HSSW production. The salinity variations in the Drygalski Basin and eastern Terra Nova Bay near Crary Bank in the Ross Sea were investigated by analyzing hydrographic data from instrumented moorings, vessel-based profiles, and available wind and sea-ice products. Near-bed salinity in the eastern Terra Nova Bay ( ∼ 660 m) and Drygalski Basin (∼ 1200 m) increases each year beginning in September. Significant salinity increases (> 0.04) were observed in 2016 and 2017, which is likely related to active HSSW formation. According to velocity data at identical depths, the salinity increase from September was primarily due to advection of the HSSW originating from the coastal region of the Nansen Ice Shelf. In addition, we show that HSSW can also be formed locally in the upper water column (< 300 m) of the eastern Terra Nova Bay through convection supplied by brine from the surface, which is related to polynya development via winds and ice freezing. While the general consensus is that the salinity of the HSSW was decreasing from 1995 to the late 2000s in the region, the salinity has been increasing since 2016. In 2018, it returned to values comparable to those in the early 2000s.

The East Sea (Japan Sea), a small marginal sea in the northwestern Pacific, is ventilated deeply down to the bottom and sensitive to changing surface conditions. Addressing the response of this marginal sea to the hydrological cycle and atmospheric forcing would be helpful for better understanding present and future environmental changes in oceans at the global and regional scales. Here, we present an analysis of observations revealing a slowdown of the long-term deepening in water boundaries associated with changes of water formation rate. Our results indicate that bottom (central) water formation has been enhanced (reduced) with more (less) oxygen supply to the bottom (central) layer since the 2000s. This paper presents a new projection that allows a three-layered deep structure, which retains bottom water, at least until 2040, contrasting previous results. This projection considers recent increase of slope convections mainly due to the salt supply via air-sea freshwater exchange and sea ice formation and decrease of open-ocean convections evidenced by reduced mixed layer depth in the northern East Sea, resulting in more bottom water and less central water formations. Such vigorous changes in water formation and ventilation provide certain implications on future climate changes.

The intermediate water known as “East Sea Intermediate Water” found south of the Subpolar Front (SF) is known to be formed in the northern East/Japan Sea (EJS), and its physical properties are determined by wintertime air‐sea interaction north of the SF. Hydrographic data collected off the Korean coast show significant decadal oscillations in spiciness (π) following isopycnals of intermediate layer, which are explained by the Arctic Oscillation (AO) and consequent cold‐air outbreaks. During positive AO phases, the cold‐air outbreak and water formation are more active and the intermediate water having the same π reaches higher density (higher π following the same isopycnals). At interannual time scale, however, the π variability is well beyond the relationship with the AO. Especially, significantly lower π (both fresher and colder) intermediate water was observed in spring of 2010 than 2001 under the same surface net‐heat flux peaks in the northern EJS in the two winters. Such contrasting characteristics of intermediate water between 2001 and 2010 are consistent with the HYCOM reanalysis results which indicate widespread extension of low‐ (high‐) π intermediate water in the southwestern EJS in 2010 (2001). A clear contrast in circulation pattern is suggested to derive the distinctly different characteristics of the intermediate water. Northward penetration of the East Korea Warm Current (EKWC) inhibited the southward extension of the intermediate water in 2001 off the east coast of Korea. On the other hand, the EKWC that poorly developed in 2010 allowed low‐π intermediate water to prevail in the southwestern EJS.

Long‐term variability of nonseasonal ocean heat content (OHC) in the upper 500 m in the East/Japan Sea (EJS) exhibits a distinct east‐west contrast during the recent 30 years. The contrasting OHC variations are revisited and investigated more in detail by analyzing two observational data sets, the gridded data from 1976 to 2007 and in situ data from 1976 to 2011 in the southwestern EJS that covers the zone of western boundary current. The OHC variability shows in‐phase and predominant decadal variation in both east and west regions before 1995, but uncorrelated and predominant interannual variations after 1995. Heaving effects due to major branches of warm currents in the EJS, the East Korea Warm Current (EKWC) in the western part and other two branches in the eastern part, mainly contribute to the OHC variations. The heaving effect in the western EJS is shown to be associated with changes in winter wind‐stress curl field in the northern EJS. Weakening of the subpolar gyre due to weakening of positive wind‐stress curl in the Japan Basin related with wintertime Western Pacific teleconnection pattern and Siberian High appears to enhance the northward penetration of the EKWC resulting in an increase of OHC in the western EJS. The heaving effect in the eastern EJS is significantly correlated with the Siberian High, but the causative mechanism is inconclusive. This study also demonstrates the importance of using highly resolved data sets for areas affected by strong and narrow boundary currents in computing and understanding the OHC variability.