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The impact of interannual variations in sea ice area in the Okhotsk Sea was investigated through a composite analysis of years with extensive and limited sea ice areas (referred to as heavy and light ice years, respectively), using atmospheric and oceanic reanalysis data. The comparison of heavy and light ice-year composites in February revealed a substantial decrease in upward surface turbulent heat flux in the Okhotsk Sea (∼−250 W m−2) and a notable increase in a surprisingly extensive region in the western North Pacific (30–120 W m−2), spanning 2300 km from the ice edge. These differences were consistent with the decrease in surface air temperature and specific humidity, suggesting that during heavy ice years, cold and dry air blowing from Siberia to the North Pacific via the Okhotsk Sea undergoes less modification over larger sea ice areas, remaining colder and drier in the North Pacific and thereby enhancing the heat flux. Such advection can be associated with the Asian winter monsoon and migratory cyclones. Cloud cover and surface radiation flux altered consistently with these differences, although longwave and shortwave radiation largely counterbalanced each other. Additionally, the Pacific storm track exhibited variation. In accordance with the heat flux difference, sea surface temperature decreased, and the ocean mixed layer deepened around the subarctic during heavy ice years. These findings suggest that sea ice area in the Okhotsk Sea influences the lower atmosphere and surface ocean in the North Pacific. Such impacts could further affect ocean nutrient circulation, ecosystems, and atmospheric teleconnections.

Accelerated retreat of Arctic Ocean summertime sea ice has focused attention on the potential use of the Northern Sea Route (NSR), for which sea ice thickness (SIT) information is crucial for safe maritime navigation. This study evaluated the medium-range (lead time below 10 days) forecast of SIT distribution in the East Siberian Sea (ESS) in early summer (June-July) based on the TOPAZ4 ice-ocean data assimilation system. A comparison of the operational model SIT data with reliable SIT estimates (hindcast, satellite and in situ data) showed that the TOPAZ4 reanalysis qualitatively reproduces the tongue-like distribution of SIT in ESS in early summer and the seasonal variations. Pattern correlation analysis of the SIT forecast data over 3 years (2014-2016) reveals that the early summer SIT distribution is accurately predicted for a lead time of up to 3 days, but that the prediction accuracy drops abruptly after the fourth day, which is related to a dynamical process controlled by synoptic-scale atmospheric fluctuations. For longer lead times (> 4 days), the thermodynamic melting process takes over, which contributes to most of the remaining prediction accuracy. In July 2014, during which an ice-blocking incident occurred, relatively thick SIT (similar to 150 cm) was simulated over the ESS, which is consistent with the reduction in vessel speed. These results suggest that TOPAZ4 sea ice information has great potential for practical applications in summertime maritime navigation via the NSR.

The Sea of Okhotsk is a challenging environment for obtaining in situ data and satellite observation in winter due to sea ice cover. In this study, we evaluated the validity of hydrographic observations by marine mammals (e.g., seals and sea lions) equipped with oceanographic conductivity-temperaturedepth (CTD) sensors. During 4-yr operations from 2011 to 2014, we obtained total of 997 temperature-salinity profiles in and around the Soya Strait, Iony Island, and Urup Strait. The hydrographic data were mainly obtained from May to August and the maximum profile depth in shelf regions almost reaches to the seafloor, while valuable hydrographic data under sea ice cover were also obtained. In strong thermoclines, the seal-derived data sometimes showed positive biases in salinity with spikelike signal. For these salinity biases, we applied a new thermal mass inertia correction scheme, effectively reducing spurious salinity biases in the seasonal thermocline. In the Soya Strait and the adjacent region, the detailed structure of the Soya Warm Current including the cold-water belt was well identified. Dense water up to 27.0 sigma(theta), which can be a potential source of Okhotsk Sea Intermediate Water, has flowed from the Soya Strait into the Sea of Okhotsk in mid-winter (February). In summer, around the Iony Island and Urup Strait, remarkable cold and saline waters are localized in the surface layers. These regions are also characterized by weak stratification, suggesting the occurrence of tidally induced vertical mixing. Thus, CTD-tag observations have a great potential in monitoring data-sparse regions in the Sea of Okhotsk.

Iron (Fe) is an essential nutrient for marine phytoplankton and it constitutes an important element in the marine carbon cycle in the ocean. This study examined the mechanisms controlling seasonal variation of dissolved Fe (dFe) in the western subarctic North Pacific (WSNP), using an ocean general circulation model coupled with a simple biogeochemical model incorporating a dFe cycle fed by two major sources (atmospheric dust and continental shelf sediment). The model reproduced the seasonal cycle of observed concentrations of dFe and macronutrients at the surface in the Oyashio region with maxima in winter (February–March) and minima in summer (July–September), although the simulated seasonal amplitudes are a half of the observed values. Analysis of the mixed‐layer dFe budget indicated that both local vertical entrainment and lateral advection are primary contributors to the wintertime increase in dFe concentration. In early winter, strengthened northwesterly winds excite southward Ekman transport and Ekman upwelling over the western subarctic gyre, transporting dFe‐rich water southward. In mid to late winter, the southward western boundary current of the subarctic gyre and the outflow from the Sea of Okhotsk also bring dFe‐rich water to the Oyashio region. The contribution of atmospheric dust to the dFe budget is several times smaller than these ocean transport processes in winter. These results suggest that the westerly wind‐induced Ekman transport and gyre circulation systematically influence the seasonal cycle of WSNP surface dFe concentration.

Predictability of sea ice concentrations (SICs) in the Barents Sea in early winter (November–December) is studied using canonical correlation analysis with atmospheric and ocean anomalies from the NCEP Climate Forecast SystemReanalysis (CFSR) data. It is found that the highest prediction skill for a single-predictormodel is obtained from the 13-month lead subsurface temperature at 200-m depth (T200) and the in-phase meridional surface wind (Vsfc). T200 skillfully predicts SIC variability in 35% of the Barents Sea, mainly in the eastern side. The T200 for negative sea ice anomalies exhibits warm anomalies in the subsurface ocean temperature downstream of the Norwegian Atlantic Slope Current (NwASC) on a decadal time scale. The diagnostic analysis of NCEP CFSR data suggests that the subsurface temperature anomaly stored below the thermocline during summer reemerges in late autumn by atmospheric cooling and affects the sea ice. The subsurface temperature anomaly of the NwASC is advected from the North Atlantic subpolar gyre over ;3 years. Also, Vsfc skillfully predicts SIC variability in 32% of the Barents Sea, mainly in the western side. The Vsfc for the negative sea ice anomalies exhibits southerly wind anomalies; Vsfc is related to the large-scale atmospheric circulation patterns from the subtropical North Atlantic to the Eurasian continent. This study suggests that both atmospheric and oceanic remote effects have a potential impact on the forecasting accuracy of SIC.

Previous studies suggested that the interannual variability of the maximum sea ice extent (MSIE) in the Sea of Okhotsk is not explained only by atmospheric conditions. In this study, we examined the effect of the ocean thermal condition on the determination of the MSIE based on observational data. We found that the MSIE is highly correlated with the sea surface temperature (SST) and ocean temperature around the East Kamchatska Current (EKC) in the Pacific in late autumn (November–December). The significant relationship between the MSIE and the SST cannot be fully explained by prevailing atmospheric variabilities. Considering that the inflow of EKC water to the Okhotsk Sea is strengthened in winter, advection of anomalous ocean temperature likely influences the MSIE. A multiple regression model constructed as a function of SST in the EKC and the air temperature at 850 hPa over the upwind region of the Okhotsk Sea in late autumn, which is another determinant factor for the MSIE, significantly improves the prediction skill for the MSIE: 70% of the variance of MSIE can be predicted at the stage of 2 to 3 months before the MSIE season. The SST in the EKC and the upwind air temperature are likely to control the sea ice extent in the northeastern and center to southern parts of the Okhotsk Sea, respectively.

Three global monthly precipitation datasets, including gauge measurements, gauge/satellite merged analysis (CMAP), and NCEP/NCAR reanalysis, are analyzed with respect to Bi-Decadal Oscillation (BDO) in boreal winter during the 20th century. Correlation and coherency analyses between the precipitations and the strength of the Aleutian low, which is an action center of the BDO, reveal substantial impacts of the BDO on precipitations around the Pacific Ocean. The covariability of the precipitations is prominent for Hawaii, mid-latitude eastern North America, Florida and eastern-China/Southern-Japan, and at some other regions including the Southern Hemisphere. The most coherent BDO precipitation pattern common to the CMAP and reanalysis features significant anomalies over the tropical (10°–30°N), central (30°–50°N) and northern (50°–70°N) North Pacific with alternating polarities. The influence of the BDO on Hawaii winter droughts and salinity in the North Pacific is discussed.