A sensitivity study of the dense shelf water formation in the Okhotsk Sea
[1] Sensitivity of Dense Shelf Water (DSW) formation to tidal mixing around the Kuril Straits, wind stress, and river runoff in the Okhotsk Sea is examined by an ice-ocean coupled model. Horizontal resolution of the model is set to 3–8 km in the northern Okhotsk Sea for well resolving the coastal polynyas which is believed to be the principal region of DSW formation. The model shows a good performance in terms of sea ice production and the consequent DSW formation. DSW is also found to be formed in the offshore region apart from the coastal polynya. DSW is defined independently for each experiment such that it identifies the water influenced by brine. By introducing such definition the sensitivity of the DSW formation is assessed separately for change of density and that of formation rate. The density of DSW exhibits high sensitivity to all the elements considered herein, while its formation rate is sensitive only to winds. Winds affect the DSW formation rate mainly by influencing that occurs in the offshore region.
Formation of 26.8-26.9 water in the Kuril Basin of the Sea of Okhotsk as a possible origin of North
By using all Japanese hydrographic data obtained south of 55°N in latitude in the Sea of Okhotsk, we compile a data set for this study. Our investigations with these data show that a large quantity of relatively cold, fresh, oxygen-rich homogeneous intermediate water with a density range of 26.8 to 26.9 σθ exists in the Kuril Basin; we name this intermediate water the Kuril Basin Intermediate Water (KBIW). Results of isosteric analyses show that a possible origin of KBIW is located in a region off the Hokkaido coast in the southwestern Sea of Okhotsk. We suggest that KBIW is produced by the isopycnal mixing of relatively dense Soya Warm Water, which appears only in early spring, with the colder, fresher water which originates from the northwestern Okhotsk. Finally, we demonstrate that KBIW may be a source water of the North Pacific Intermediate Water (NPIW) because it has the same density range and water properties.
Effects of sea ice formation and diapycnal mixing on the Okhotsk Sea intermediate water clarified with oxygen isotopes
Abstract Processes relating to the formation of dense shelf water and intermediate water in the Okhotsk Sea were studied by examining oxygen isotope ratios ( δ 18 O), salinity, and temperature. The salinity and δ 18 O of the cold dense shelf water on the northern continental shelf showed peculiar relationship. The relationship indicates that 3% of the mixed-layer water, having salinity of 32.6, froze and the remaining 97% became dense shelf water of salinities of more than 33.2 ( σ θ >26.7) during the sea ice formation. The salinity– δ 18 O relationship also shows that 20% of the Okhotsk Sea Intermediate Water at the σ θ =26.8 level was derived from the dense shelf water. The remaining 80% came from the Western Subarctic Pacific water modified by diapycnal mixing of water affected by the surface cooling and freshening within the Okhotsk Sea. The mixing with dense shelf water contributes to only 26% of the temperature difference or 8% of the salinity difference between the original Pacific water and the Okhotsk Sea Intermediate Water at σ θ =26.8. This result suggests that the cold and less saline properties of the Okhotsk Sea Intermediate Water are produced mainly by diapycnal mixing, rather than by mixing of the Pacific water with the dense shelf water.