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Journal of Oceanography, Vol. 55, pp. 111 to 122. 1999

The Intermediate Water; Its Characteristics and Circulation

TOMOHARU SENJYU

Department of Fishery Science and Technology, National Fisheries University, 2-7-1, Nagata-honmachi, Shimonoseki, Yamaguchi 759-6595, Japan

(Received 18 September 1998; in revised form 2 November 1998; accepted 5 November 1998)

In the southern Japan Sea there is a minimum layer between the Tsushima Keywords: Current Water and the Japan Sea Proper Water. Since the salinity minimum corresponds ⋅ Japan Sea, to the North Pacific Intermediate Water, it is named the Japan Sea Intermediate Water ⋅ salinity minimum layer, (JIW). To examine the source and circulation of JIW, the basin-wide salinity minimum ⋅ distribution was investigated on the basis of hydrographic data obtained in 1969. The intermediate water, ⋅ mid-depth circula- young JIW, showing the highest oxygen concentration and the lowest salinity, is seen in ° tion, the southwestern Japan Sea west of 133 E, while another JIW with lower oxygen and ⋅ subduction area, higher salinity occupies the southeastern Japan Sea south of the subpolar front. Since the ⋅ isopycnal analysis. young JIW shows high oxygen concentrations, high temperatures and low densities, the source of the water is probably in the surface layer. It is inferred that the most probable of subduction is the subarctic front west of 132°E with the highest oxygen and the lowest salinity at shallow salinity minimum. In addition, property distributions suggest that JIW takes two flow paths: a eastward flow along the subarctic front and an southward flow toward the Ulleung Basin. On the other hand, a different salinity minimum from JIW occupies the northern Japan Sea north of the subarctic front, which shows an apparently higher salinity and high oxygen concentration than JIW. However, this salinity minimum is considered not to be a water mass but to be a boundary between overlying and underlying water masses.

1. Introduction 1994) revealed that the Proper Water consists of at least two The Japan Sea is one of the marginal on the water masses, the upper portion and the deep water, and the western North Pacific, but it has subtropical and subarctic former is produced by the wintertime deep convection south circulations bounded by the subarctic front, similar to the of . The deep convection occurring in the Japan open . The Tsushima Current flowing from the East Sea is the so-called open- convection (Senjyu and China Sea branches into two or three flows after passing the Sudo, 1993, 1994; Seung and Yoon, 1995; Choi, 1996); this (Fig. 1). The westernmost flow is called the type of convection has been observed in the Mediterranean, East Korean Warm Current, which flows northward along the , the , and the Antarctic the east coast of . This flow is considered to be the Ocean (Killworth, 1983; Gascard, 1991). western boundary current in the subtropical circulation in In addition, a vertical salinity minimum is found between the Japan Sea (Yoon, 1982). The counterpart in the subarctic the Tsushima Current Water and the Japan Sea Proper Water circulation is the Liman Current, which flows south to in the subtropical circulation, which seems to correspond to southwestward along the Russian and North Korean coasts. the North Pacific Intermediate Water in the North Pacific Both currents contact each other around 38°Ð40°N west of subtropical gyre (Sverdrup et al., 1942; Reid, 1965; Talley, 132°E and flow eastward along the subarctic front at about 1993). Miyazaki (1952, 1953) was the first to point out the 40°N. This situation is very similar to the Kuroshio-Oyashio existence of the salinity minimum, and named it the Inter- currents system in the North Pacific east of Japan (Kawai, mediate Water. This water is the same as “the forth water” 1974). referred to by Kajiura et al. (1958) and Moriyasu (1972). Another important feature of the Japan Sea similar to Since the salinity minimum is often accompanied by the the open oceans is deep water formation; the Japan Sea has dissolved oxygen maximum, Miyazaki (1952, 1953) and a peculiar deep water called the Japan Sea Proper Water Miyazaki and Abe (1960) speculated that the origin of the (Uda, 1934). Sudo (1986) and Senjyu and Sudo (1993, Intermediate Water is the sea surface water having sunk

111 Copyright  The Oceanographic Society of Japan. northeast, and the North Korean Cold Water flowing from the north along the Korean coast in summertime (Kim et al., 1991; Cho and Kim, 1994). Since the East Sea Intermediate Water east of Korea has a similar character to Miyazaki’s (1952, 1953) Inter- mediate Water, Kim and Chung (1984) thought that both are essentially the same. However, they could not clarify the relationship between the two waters because their work was limited to the southwestern Japan Sea. Recently, Seung (1997) suggested that there exists a cyclonic circulation of the Intermediate Water using a simple numerical model based on the ventilated thermocline theory developed by Luyten et al. (1983). His results are notable because shallow salinity minima are formed by the same mechanism in the North Pacific (Talley, 1985; Yuan and Talley, 1992). How- ever, to confirm his speculations, it is necessary to investigate the basin-wide structure of the salinity minimum layer. As the salinity minimum in the southern Japan Sea is considered to the counterpart of the North Pacific Interme- diate Water in the North Pacific, in this paper, we call the salinity minimum water the Japan Sea Intermediate Water (JIW). The Japan Sea can be regarded as a “miniature ocean” because of its open ocean like characteristics (Ichiye, 1984). Thus, the mechanism of JIW formation and circulation in the Japan Sea may be applied to other oceans. In this paper, JIW is defined and its formation and circulation are inferred based on the careful examination of Fig. 1. Bottom topography and main surface currents in the Japan salinity minimum structure in most of the Japan Sea. The Sea. Abbreviations for the main currents are as follows; TC: following basinwide maps of the salinity minimum will the Tsushima Current, LC: the Liman Current, EKWC: the provide useful information not only about the source and East Korean Warm Current, and NKCC: the North Korean modification of JIW but also about the mid-depth circula- Cold Current. tion in the Japan Sea.

2. Data Comprehensive hydrographic surveys in the Japan Sea around the subarctic front. have been carried out by the Japan Meteorological Agency On the other hand, Korean oceanographers have stud- (JMA), the Maizuru Marine Observatory, and the Hydro- ied the salinity minimum layer in the southwestern Japan graphic Department (HD) of the Japan Maritime Safety Sea in relation to the cold water appearing along the Korean Agency since 1965. Among them, surveys made by R/V coast. A low salinity and high dissolved oxygen water is Takuyo of HD in the period from July 1 to 22, 1969 and the found along the Korean coast at depths of 100Ð200 m (Kim multi-ship observation by JMA (Ryofu-Maru, Kofu-Maru, and Kim, 1983). They suggested that the water is brought to Chofu-Maru, and Seifu-Maru) during the period from Sep- the southwestern Japan Sea by the North Korean Cold tember 29 to October 18 are used for the present study, Current (Uda, 1934). Kim and Chung (1984) showed that because these surveys were carried out in almost all of the the salinity minimum coincides with the dissolved oxygen Japan Sea area, except for of north of 45°N and off maximum east of the Korean coast on the basis of the (Fig. 2). hydrographic data as far as 130°30′ E. They also showed that The hydrographic data used in this study were obtained the characteristics of salinity minimum and dissolved oxy- by serial observations with Nansen bottles, and thus tem- gen maximum near the Korean coast are emphasized com- perature, salinity and dissolved oxygen concentration were pared to Miyazaki’s (1952, 1953) Intermediate Water. They observed at standard depths. Temperature and salinity ac- called the water the East Sea Intermediate Water. Recent curacies are considered to be 0.02 deg and 0.01 psu, re- studies using CTD data suggested that the salinity minimum spectively. Dissolved oxygen concentrations were deter- water east of the Korean coast has two modes: the East Sea mined by Winkler’s method, and its error is considered to be Intermediate Water, which is warmer and flows from the 0.03 ml lÐ1.

112 T. Senjyu Fig. 2. Locations of traces and hydrographic stations used in the study. (a) R/V Takuyo survey carried out in the period of July 1Ð22, 1969 and (b) JMA multi-ship survey in September 29ÐOctober 18, 1969.

3. Classification of Salinity Minimum density and lower salinity modes in Figs. 3(a) and 3(b), To confirm the JIW distribution, first, all salinity mini- respectively. Since salinity in the shallow minimum shows mum depth data are extracted from the dataset. Then, the low values of up to about 32.20 psu in the southern Japan Sea depth data with more than 27.32 of potential density (σθ) are and increases with latitude (Fig. 3(b)), the shallow salinity excluded because the dense water above 27.31σθ is con- minimum is considered to be formed by evaporation at the sidered to be the upper portion of the Japan Sea Proper Water sea surface of the coastal water or the Water. (Senjyu and Sudo, 1994). On the other hand, the higher density mode corresponds to Meridional distributions of potential density and salinity the deeper salinity minimum lying in about 230 m. The for the salinity minimum are shown in Fig. 3. There are two deeper salinity minimum is found just below the main modes of potential density for the salinity minimum (Fig. thermocline, and between a salinity maximum of the 3(a)). The lower density mode lies in the range 22.0Ð26.0σθ Tsushima Current Water at about 70 m and relatively saline showing a density increase northward; the higher density water of the upper portion of the Japan Sea Proper Water mode lies at 27.0σθ or more, showing a slight density in- below. The salinity minimum layer corresponds to a dissolved crease northward. Both modes exist over the latitude range oxygen maximum layer; this is a general characteristic of from 36° to 45°N. Salinity also shows two modes (Fig. 3(b)): the Intermediate Water described by Miyazaki (1952, 1953). the lower salinity mode (less than 34.00 psu) showing an A similar salinity minimum is recognizable at most stations increase with latitude; the higher salinity mode has salinity in the southern Japan Sea. Thus, this study treats the salinity 34.00 psu or more. Figure 4 shows a typical example of minimum of the higher density mode. potential temperature (θ), salinity, dissolved oxygen and σθ The meridional distribution of the salinity minimum in profiles in the southern Japan Sea. The shallow salinity a density range of 27.00Ð27.32σθ is shown in Fig. 5. Most of minimum in the surface layer corresponds to the lower the salinity minimum north of 40°N shows more than 34.05

The Japan Sea Intermediate Water; Its Characteristics and Circulation 113 Fig. 3. Meridional distributions of (a) potential density (σθ) and (b) salinity for the salinity minimum.

Fig. 4. Typical profiles of potential temperature (θ), salinity (S), dissolved oxygen (O2), and potential density (σθ) in the southern Japan Sea (Sta. TA40, 36°49.0′ N 132°16.0′ E). Solid arrows indicate salinity minimum depths.

psu. By contrast, south of 40°N it is mostly less than 34.05 more (Group B; triangles), and a lower salinity group of less psu and seems to be subdivided into two groups by a than 34.025 psu south of 40°N (Group C; circles). Rela- discontinuity around 34.03 psu. Thus, three groups of the tionships between θ-S and O2-S for the salinity minimum are salinity minimum are formed: a group of more than 34.05 shown in Fig. 6. Group C shows higher temperatures (1.0Ð psu of salinity north of 40°N (Group A; squares in Fig. 5), 3.2°C) and a wider density range (mostly 27.15Ð27.25σθ) than a higher salinity group south of 40°N having 34.025 psu or the other two groups (Fig. 6(a)). Though Group A shows

114 T. Senjyu Fig. 5. Meridional distribution of the higher density mode (27.00Ð 27.32σθ) of salinity minimum. Three groups of salinity mini- mum are discernible: Group A (squares), Group B (triangles), and Group C (circles). Crosses denote salinity minima that do not belong to any of the groups.

somewhat higher than Group B, as mentioned above, its temperatures are mostly in the same range (0.3Ð 1.5°C) as those of Group B. However, dissolved oxygen concentrations of Group A are higher than those of Group B (6.1 ml lÐ1 or more with two exceptions, Fig. 6(b)); Group B shows a wider oxygen range of 5.1Ð6.6 ml lÐ1 but mostly in a range of 5.4Ð6.1 ml lÐ1. High oxygen concentrations of more than 6.1 ml lÐ1 are also found in Group C. This indi- cates that the waters of Groups A and C are younger than that of Group B, having left the sea surface later. Geographical distributions of salinity minimum clas- sified in three groups are shown in Fig. 7. Large symbols indicate stations of the salinity minimum accompanying the dissolved oxygen maximum. Small solid circles enclosed Fig. 6. Relationships of θ-S (a) and O2-S (b) for the salinity with dashed lines denote stations of no salinity minimum at minimum. Symbols denoting the group of salinity minimum which salinity shows a slight increase with depth or ho- are the same as in Fig. 5. Isopycnals of potential density (thin mogeneous values. A salinity minimum exists at all of the curved lines) and the typical θ-S range of the upper portion of stations south of 40°N, while no salinity minimum is observed the Japan Sea Proper Water (shaded area) are also shown in the in some regions north or northwest of 40°N. The three θ-S diagram. groups of salinity minimum are well organized in both July and SeptemberÐOctober. Group A occupies the northern Japan Sea north of 40°N; stations of Group C are seen only in the southwestern Japan Sea west of 133°E and south of many stations of Group C with the lowest salinity and the 40°N. The Yamato Basin, in the southeastern part of the highest oxygen concentration (Fig. 6(b)) show the dissolved Japan Sea, is occupied by the stations of Group B. Though oxygen maximum at the same depths as the salinity mini- Group C shows almost the same oxygen range as Group A mum east of the Korean coast. This agrees with Kim and (Fig. 6(b)), two group stations are separated geographically Chung’s (1984) description of the East Sea Intermediate by stations of no salinity minimum or Group B. Note that Water.

The Japan Sea Intermediate Water; Its Characteristics and Circulation 115 Fig. 7. Geographical distribution of salinity minimum classified in three groups: (a) in July and (b) in SeptemberÐOctober 1969. Large symbols indicate stations of the salinity minimum accompanying the dissolved oxygen maximum. Small solid circles enclosed with dashed lines denote stations of no salinity minimum. Crossed stations have a salinity minimum that does not belong to any of the three groups.

From the water characteristics and geographical distri- 4. Distribution of the Japan Sea Intermediate Water butions of three salinity minimum groups, the water of The core-layer method is a helpful technique to analyze Group B is considered to be the Intermediate Water de- horizontal variations of particular water masses; the core- scribed by Miyazaki (1952, 1953), and Group C is the East layer is defined as a depth of property extreme and property Sea Intermediate Water reported by Kim and Chung (1984). distributions are then traced along surfaces defined by JIW consists of two waters of Groups B and C. Group A extremes (Emery and Thomson, 1998). Lateral distributions shows the highest salinity and the highest oxygen concen- of depth and salinity at the salinity minimum are shown in tration and occupies the northern Japan Sea. Thus, the Fig. 8. In the northwestern Japan Sea north of 40°N core- salinity minimum of Group A must be a of different kind layer depths are shallow: less than 200 m in July (Fig. 8(a)) than JIW. and less than 100 m in SeptemberÐOctober (Fig. 8(b)). Groups A and C are considered to be younger water, Another shallow core-layer area (less than 200 m) is seen in having been at the sea surface later than Group B. However, the southwestern region west of 133°E and south of 40°N. Group A is not an early stage of Group B because it requires Note that a steep east-west salinity gradient is formed south much more fresh water to make the salinity of Group B. of 40°N; it is found at 132°Ð134°E in July (Fig. 8(c)) and There is no such fresh water around Group A. (Since Group 131°Ð133°E in SeptemberÐOctober 1969 (Fig. 8(d)). Low A is the water of salinity minimum, vertical mixing cannot salinities (less than 34.03 psu) are found west of the gradient, produce lower salinity water.) On the other hand, the water which coincide with shallow core-layers less than 200 m. On of Group C does seem to be an early stage of that of Group the other hand, east of the gradient, a vast area of 34.04Ð B because of its low salinity and high dissolved oxygen 34.05 psu extends eastward to the Japanese coast; this area concentration. corresponds to deep core-layers in the Yamato Basin (deeper

116 T. Senjyu Fig. 8. Depth and salinity distributions at the salinity minimum: depth (a) in July and (b) in SeptemberÐOctober, 1969; salinity (c) in July and (d) in SeptemberÐOctober, 1969. Symbols D, S, H and L denote deeper, shallower, higher and lower values, respectively. Dashed lines are the same as in Fig. 7.

The Japan Sea Intermediate Water; Its Characteristics and Circulation 117 Fig. 9. Dissolved oxygen distributions at salinity minimum depth: (a) in July and (b) in SeptemberÐOctober, 1969.

than 300 m). Another steep salinity gradient exists zonally The points of Group C on the θ-S diagram (Fig. 6(a)) at about 40°N, which corresponds to the subarctic front. are within a wide density range of 27.08Ð27.25σθ. This North of the subarctic front, relatively high salinities (34.06 suggests that the diapycnal mixing is dominant in the psu or more) are seen. Comparing Fig. 7 to Figs. 8(c) and southwestern Japan Sea. In contrast to this, the points of 8(d), one can see areas of three groups of salinity minimum, Groups A and B are not so scattered over a wide density and geographically separated by the subarctic front and the steep lie around 27.28σθ except for a few points. Thus, an isopycnal salinity gradient south of 40°N. for the 27.28σθ surface was selected to examine the circu- Figure 9 shows dissolved oxygen distributions at salin- lation path of JIW. Figure 10 shows maps of salinity and ity minimum depth. High oxygen areas of more than 6.5 depth on the 27.28σθ surface in SeptemberÐOctober 1969. ml lÐ1 are found sporadically in the northern and southwestern (Similar distributions are also seen in July 1969 (not shown).) Japan Sea. By contrast, the Yamato Basin corresponds to the A tongue-shaped area of 34.04Ð34.05 psu extends eastward lowest oxygen area in the Japan Sea (less than 6.0 ml lÐ1). The from 133° to 138°E along 39°N (Fig. 10(a)). This area oxygen distribution is similar to that in the upper portion of coincides with the area of 34.04Ð34.05 psu in Fig. 8(d); this the Japan Sea Proper Water, as shown in Senjyu and Sudo indicates that the salinity minimum lies on the 27.28σθ (1993); the formation region of the upper portion of the surface in this area. Low salinities of less than 34.04 psu are Japan Sea Proper Water was inferred in the northwestern seen west of the tongue-shaped area. The low salinity area Japan Sea from the dissolved oxygen distribution. However, coincides with the region of Group C (Fig. 7(b)), but the as previously stated, the salinity distribution indicates that salinity minimum lies at shallower depths. Nevertheless, the water north of the subarctic front cannot be a source of this salinity distribution strongly indicates that the south- JIW. In the southwestern Japan Sea south of the subarctic western Japan Sea is the upstream region for JIW. front, higher oxygen stations correspond to lower salinity, The flow pattern on the isopycnal surface can be while a close relationship between salinity and oxygen deduced from the depth distribution (Fig. 10(b)). Figure concentrations is not seen in the northern Japan Sea north of 10(b) suggests the subtropical and subarctic circulations in the subarctic front. the Japan Sea: a cyclonic subarctic circulation between 41°

118 T. Senjyu Fig. 10. Salinity and depth distributions on the 27.28σθ surface in SeptemberÐOctober, 1969.

and 43°N centered on a shallow region (less than 100 m) and Kajiura et al. (1958) and Moriyasu (1972). Since the oxygen an anticyclonic circulation in the southern Japan Sea centered maximum corresponds to the salinity maximum, it may be on a deep region (more than 300 m). Between both circu- a remnant of the Tsushima Current Water cooled in winter. lations, a strong eastward flow along the subarctic front can On the other hand, relatively high oxygen water is found just be deduced; this flow is considered to be the extension of the below the salinity minimum. This is the upper portion of the East Korean Warm Current. Note that the eastward flow is Japan Sea Proper Water which shows high oxygen concen- located slightly north of the tongue-shaped area of 34.04Ð trations of more than 6.0 ml lÐ1 in the northern Japan Sea 34.05 psu in Fig. 10(a). This suggests that the eastward flow (Senjyu and Sudo, 1993, 1994). This oxygen distribution transports a portion of JIW from east off the Korean coast suggests that the salinity minimum of Group A is not a water toward the Japanese coast. mass, but a boundary between these two water masses. This notion is supported by Fig. 6(a), which shows that about half 5. Discussion and Conclusion of Group A points on the θ-S diagram are within the typical JIW consists of two waters of Groups B and C, and temperature and salinity ranges of the upper portion of the occupies the subtropical region south of the subarctic front. Japan Sea Proper Water (shaded area). On the other hand, Group A is a salinity minimum newly From property distributions, it can be concluded that introduced in this study. What are the physical characteristics the southwestern Japan Sea west of 132°E is the upstream of Group A? Typical profiles in the northern Japan Sea are region of JIW. Since the younger JIW corresponding to the shown in Fig. 11. The deeper salinity minimum correspond- Group C water shows high dissolved oxygen concentra- ing to Group A is situated just below the main thermocline, tions, high temperatures, and low densities, the source of the as other groups, but it coincides with the dissolved oxygen water is probably in the surface layer. The subarctic front minimum, though its oxygen concentration is higher than west of 132°E is a highly probable subduction area. This is 6.0 ml lÐ1. Note that there is an oxygen maximum layer at supported by the salinity and dissolved oxygen distributions 30Ð50 m depths above the salinity minimum. This is the at the salinity minimum depth; the lowest salinity and the intermediate water in the cold-current region reported by highest oxygen concentration are found in the 38°Ð40°N

The Japan Sea Intermediate Water; Its Characteristics and Circulation 119 Fig. 11. Typical profiles of potential temperature (θ), salinity (S), dissolved oxygen (O2), and potential density (σθ) in the northern Japan Sea (Sta. 3581, 42°00.0′ N 137°00.0′ E). Solid arrows indicate salinity minimum depths.

Fig. 12. Potential temperature (a) and salinity (b) sections along 39°N in SeptemberÐOctober, 1969.

120 T. Senjyu areas west of 132°E (Figs. 8(d) and 9(b)). In addition, this Acknowledgements area is one of shallow salinity minimum core regions in the I wish to thank Profs. Hideo Sudo and Masaji Japan Sea (Fig. 8(b)). The potential temperature and salinity Matsuyama for their valuable comments and discussion. sections along 39°N in SeptemberÐOctober 1969 are shown Thanks are also due to Profs. Masaki Takematsu and Jong- in Fig. 12. Indeed, the low salinity water near the sea surface Hwan Yoon who gave me a chance to join the CREAMS (Stas. F10 and 09) seems to intrude into a sub-thermocline program. The data used in the study were provided from the layer west of 132°E forming an intermediate salinity mini- Japan Oceanographic Data Center. This study was pre- mum. sented in the third CREAMS Workshop at Seoul, Korea on The submerged low salinity water undergoes a diapycnal November 7Ð8, 1994. mixing with the upper portion of the Japan Sea Proper Water below. As a result, the younger JIW shows a fall of tem- References perature, increase of salinity and increase of density. Even- Cho, Y.-K. and K. Kim (1994): Two modes of the salinity- tually, the Group C water is modified to become the Group minimum layer water in the Ulleung Basin. La mer, 32, 271Ð B water. This mixing process is explained on the θ-S 278. diagram (Fig. 6(a)); the Group B water connects the Group Choi, Y.-K. (1996): Open-ocean convection in the Japan (East) Sea. La mer, 34, 259Ð272. C water with the upper portion of the Japan Sea Proper Emery, W. J. and R. E. Thomson (1998): Data Analysis Methods Water. This indicates that the water of Group B is a mixture in Physical Oceanography. Pergamon Press., Great Britain, of these two water masses. The temperature and salinity 634 pp. sections (Fig. 12) also imply the diapycnal aspect; the Gascard, J.-C. (1991): Open ocean convection and deep water salinity minimum layer west of 133°E shows a sinking formation revisited in the Mediterranean, Labrador, Greenland across the thermocline. and Weddell Seas. p. 157Ð181. In Deep Convection and Deep The property distributions suggest that JIW takes two Water Formation in the Oceans, ed. by P. C. Chu and J.-C. flow paths: an eastward flow along the subarctic front and a Gascard, Elsevier Oceanography Series, 57, Amsterdam. southward flow parallel with the Korean coast in the region Ichiye, T. (1984): Some problems of circulation and hydrography west of 132°E. The eastward flow seems to take an isopycnal of the Japan Sea and the Tsushima Current. p. 15Ð54. In Ocean process because the salinity minimum waters lie on the Hydrodynamics of the Japan and East China Seas, ed. by T. Ichiye, Elsevier Oceanography Series, 39, Amsterdam. isopycnal surface of 27.28σθ in the Yamato Basin. A part of Kajiura, K., M. Tsuchiya and K. Hidaka (1958): The analysis of JIW having sunk under the main thermocline is advected oceanographical condition in the Japan Sea. Rep. Develop. toward the Japanese coast on the isopycnal surface by the Fisher. Resour. in the Tsushima Warm Current, 1, 158Ð170 eastward flow along the subarctic front. In the course of the (in Japanese). circulation, JIW probably gradually loses the original char- Kawai, H. (1974): Transition of current images in the Japan Sea. acteristics through the mixing with the upper portion of the p. 7Ð26. In The Tsushima Warm Current—Ocean Structure Japan Sea Proper Water, and at the last stage it is entrained and Fishery, ed. by Fishery Soc. Japan, Koseisha-Kouseikaku, into overlying or underlying waters. Tokyo (in Japanese). The southward flow may correspond to the deep west- Killworth, P. D. (1983): Deep convection in the world ocean. Rev. ern boundary current of the cyclonic gyre suggested by Geophys. Space Phys., 21, 1Ð26. Seung (1997); he simulated the cyclonic circulation in the Kim, C. H. and K. Kim (1983): Characteristics and origin of the cold water mass along the east coast of Korea. J. Oceanol. Soc. subtropical intermediate layer by a simple numerical model Korea, 18, 73Ð83 (in Korean with English abstract). based on the ventilated theory (Luyten et al., 1983). Though Kim, C. H., H.-J. Lie and K.-S. Chu (1991): On the Intermediate such a strong southward flow cannot be deduced from the Water in the southwestern East Sea (Sea of Japan). p. 129Ð depth distribution on the 27.28σθ surface (Fig. 10(b)), it is 141. In Oceanography of Asian Marginal Seas, ed. by K. interesting that the lowest salinity (less than 34.03 psu) at the Takano, Elsevier Oceanography Series, 54, Amsterdam. southwestern corner (Fig. 10(a)) coincides with the deep Kim, K. and J. Y. Chung (1984): On the salinity-minimum and area of isopycnal depth (more than 300 m) which implies a dissolved oxygen-maximum layer in the East Sea (Sea of weak southward flow. The cyclonic circulation in the south- Japan). p. 55Ð65. In Ocean Hydrodynamics of the Japan and ern Japan Sea is also inferred in the upper portion of the East China Seas, ed. by T. Ichiye, Elsevier Oceanography Japan Sea Proper Water below (Senjyu and Sudo, 1993, Series, 39, Amsterdam. 1994). Luyten, J. R., J. Pedlosky and H. Stommel (1983): The ventilated thermocline. J. Phys. Oceanogr., 13, 292Ð309. The dataset used in the study is restricted in its vertical Miyazaki, M. (1952): The heat budget of the Japan Sea. Bull. resolution, as well as in its horizontal coverage. Besides, the Reg. Fisher. Res. Lab., 4, 1Ð54 (in Japanese with data were taken only in 1969; temporal variations are likely English abstract). to exist in both water characteristics and water mass distri- Miyazaki, M. (1953): On the water masses of the Japan Sea. Bull. butions. For further discussion of the JIW circulation, fur- Hokkaido Reg. Fisher. Res. Lab., 7, 1Ð65 (in Japanese with ther extensive observations in the Japan Sea are desired. English abstract).

The Japan Sea Intermediate Water; Its Characteristics and Circulation 121 Miyazaki, M. and S. Abe (1960): On the water masses in the Sudo, H. (1986): A note on the Japan Sea Proper Water. Prog. Tsushima Current area. J. Oceanogr. Soc. Japan, 16, 19Ð28 Oceanogr., 17, 313Ð336. (in Japanese with English abstract). Sverdrup, H. U., M. W. Johnson and R. H. Fleming (1942): The Moriyasu, S. (1972): The Tsushima Current. p. 353Ð369. In Oceans, Their Physics, Chemistry and General Biology. Kuroshio—Its Physical Aspects, ed. by H. Stommel and K. Prentice-Hall, New York, 1087 pp. Yoshida, Univ. of Tokyo Press, Tokyo. Talley, L. D. (1985): Ventilation of the subtropical North Pacific: Reid, J. L., Jr. (1965): Intermediate Waters of the . The shallow salinity minimum. J. Phys. Oceanogr., 15, 633Ð The Johns Hopkins Oceanographic Studies, 2, Johns Hopkins 649. Press, Baltimore, 85 pp. Talley, L. D. (1993): Distribution and formation of North Pacific Senjyu, T. and H. Sudo (1993): Water characteristics and circu- Intermediate Water. J. Phys. Oceanogr., 23, 517Ð537. lation of the upper portion of the Japan Sea Proper Water. J. Uda, M. (1934): The results of simultaneous oceanographical Mar. Sys., 4, 349Ð362. investigations in the Japan Sea and its adjacent waters in May Senjyu, T. and H. Sudo (1994): The upper portion of the Japan Sea and June, 1932. J. Imp. Fish. Exp. Sta., 5, 57Ð190 (in Japanese Proper Water; Its source and circulation as deduced from with English abstract). isopycnal analysis. J. Oceanogr., 50, 663Ð690. Yoon, J.-H. (1982): Numerical experiment on the circulation in Seung, Y.-H. (1997): Application of the ventilation theory to the the Japan Sea. Part I. Formation of the East Korean Warm East Sea. J. Korean Soc. Oceanogr., 32, 8Ð16. Current. J. Oceanogr. Soc. Japan, 38, 43Ð51. Seung, Y.-H. and J.-H. Yoon (1995): Some features of winter Yuan, X. and L. D. Talley (1992): Shallow salinity minima in the convection in the Japan Sea. J. Oceanogr., 51, 61Ð73. North Pacific. J. Phys. Oceanogr., 22, 1302Ð1316.

122 T. Senjyu