Editing Sea of Japan (section)

==Hydrology==
[[File:Tategami-Rock6983.JPG|thumb|Tategami rock]]
[[File:Mitsukejima (Ishikawa) 1.jpg|thumb|[[Mitsukejima]], "Battleship Island"]]
The sea currents circulate in the counterclockwise direction. The Kuroshio (Japan Current), the Tsushima Current and the East Korea Warm Current bring warmer and more saline water to the north. There they merge into the Tsugaru Current and flow into the Pacific Ocean through the Tsugaru Strait. They also feed the Sōya Current and exit through the La Perouse Strait to the Sea of Okhotsk. The returning branch is composed of the Liman, North Korea and Central (or Mid-) Japan Sea currents which bring fresh and cold water along the Asian coast to the south.<ref name=brit/>

Water temperature is mostly affected by exchange with the atmosphere in the northern part of the sea and by the currents in the southern part. Winter temperatures are {{convert|0|C|F}} or below in the north and {{convert|10|-|14|C|F}} in the south. In this season, there is a significant temperature difference between the western and eastern parts owing to the circular currents. So at the latitude of Peter the Great Gulf, the water temperature is about {{convert|0|C|F}} in the west and {{convert|5|-|6|C|F}} in the east. This east-west difference drops to {{convert|1|–|2|C-change}} in summer, and the temperatures rise to {{convert|18|-|20|C|F}} in the north and {{convert|25|-|27|C|F}} in the south.<ref name=rev/>

Because the sea is enclosed, its waters form clearly separated layers which may show seasonal and spatial dependence. In winter, the temperature is almost constant with the depth in the northern part of the sea. However, in central-southern parts, it may be {{convert|8|-|10|C|F}} down to {{cvt|100|-|150|m|ft}}, {{convert|2|-|4|C|F}} at {{cvt|200|-|250|m|ft}}, {{convert|1.0|-|1.5|C|F}} at {{cvt|400|-|500|m|ft}} and then remain at about {{convert|0|C|F}} until the bottom. Heating by the sun and tropical monsoons increases the depth gradient in spring–summer.

In the north the surface layer (down to {{cvt|15|m|ft|disp=or}}) may heat up to {{convert|18|-|20|C|F}}. The temperature would drop sharply to {{convert|4|C|F}} at {{convert|50|m|ft|abbr=on}}, then slowly decrease to {{convert|1|C|F}} at {{convert|250|m|ft|abbr=on}} and remain so down to the seabed. On the contrary, the temperature in the south could gradually decrease to {{convert|6|C|F}} at {{convert|200|m|ft|abbr=on}}, then to {{convert|2|C|F}} at {{convert|260|m|abbr=on}} and to {{convert|0.04|-|0.14|C|F}} at {{convert|1000|-|1500|m|ft|abbr=on}}, but then it would rise to about {{convert|0.3|C|F}} near the bottom. This cold layer at about {{convert|1000|m|ft|abbr=on}} is formed by sinking of cold water in the northern part of the sea in winter and is brought south by the sea currents; it is rather stable and is observed all through the year.<ref name=brit/><ref name=rev/>

The hydrological isolation of the Sea of Japan also results in slightly lower average water salinity (34.09‰, where ‰ means parts per thousand) compared with the Pacific Ocean. In winter, the highest salinity at 34.5‰ is observed in the south where evaporation dominates over precipitation. It is the lowest at 33.8‰ in the south-east and south-west because of frequent rains, and remains at about 34.09‰ in most other parts.

Thawing of ice in spring reduces water salinity in the north, but it remains high at 34.60–34.70‰ in the south, partly because of the inflow of salty water through the [[Korea Strait]]. A typical variation of salinity across the sea in summer is 31.5‰ to 34.5‰ from north to south. The depth distribution of salinity is relatively constant. The surface layer tends to be more fresh in the sea parts which experience ice melting and rains.<ref name=rev/> The average water density is 1.0270&nbsp;g/cm<sup>3</sup> in the north and 1.0255&nbsp;g/cm<sup>3</sup> in the south in winter. It lowers in summer to 1.0253 and 1.0215&nbsp;g/cm<sup>3</sup>, respectively.<ref name=bse/>

[[File:国际客运列车在图们江铁路桥上行驶，离开朝鲜进入俄罗斯 - panoramio.jpg|thumb|The [[Tumen River]] flows into the Sea of Japan. The last 17&nbsp;km of the river form the [[North Korea–Russia border|border between North Korea and Russia]]. This picture is of the [[Korea Russia Friendship Bridge]] that crosses the Tumen River.]]
[[File:Sopka Sestra and Partizanskaya River.JPG|thumb|The mouth of [[Partizanskaya River]] near [[Nakhodka]]. View from {{ill|Sopka Sestra|ru|Сестра (гора)}}.]]

Few rivers flow into the Sea of Japan from mainland [[Asia]], the largest being [[Tumen River|Tumen]],<ref name=bse/> Rudnaya, Samarga, [[Partizanskaya River|Partizanskaya]] and Tumnin; all of them have a mountainous character. In contrast, numerous large rivers flow from Honshū and Hokkaidō into the sea, including Japan's four largest rivers: the [[Shinano River|Shinano]], [[Ishikari River|Ishikari]], [[Agano River|Agano]] and [[Mogami River|Mogami]]. The total annual river discharge into the sea is {{cvt|210|km3}} and is relatively constant through the year, except for a minor increase in July.<ref name=rev/> Most water (97% or {{cvt|52200|km3|disp=sqbr}}) flows into the sea through the Korea Strait and discharges through the Tsugaru (64% or {{cvt|34610|km3|disp=sqbr}}, La Pérouse {{cvt|10380|km3|disp=sqbr}}) and Korea straits. Rainfall, evaporation and riverine inflow make only 1% of the water balance. Between October and April, the outflow exceeds the inflow due to the lower income through the Korea Strait; this balance reverses between May and September.<ref name=rev/><ref name=bse/>

The sea has complex [[tide]]s, which are induced by the tidal wave of the Pacific Ocean penetrating through the [[Korea Strait]] and Tsugaru strait. The tides are semi-diurnal (rise twice a day) in the Korea Strait and in the northern part of the Strait of Tartary. They are diurnal at the eastern shore of Korea, [[Russian Far East]] and the Japanese islands of Honshū and Hokkaidō. Mixed tides occur in [[Peter the Great Gulf]] and Korea strait. The tidal waves have a speed of {{cvt|10|-|25|cm/s|0}} in the open sea. They accelerate in the Korea Strait ({{cvt|40|-|60|cm/s|disp=or}}), La Pérouse Strait ({{cvt|50|-|100|cm/s|disp=or|-1}}) and especially in the Tsugaru Strait ({{cvt|100|-|200|cm/s|disp=or|-1}}).

The amplitude of the tides is relatively low and varies strongly across the sea. It reaches 3 meters in the south near the [[Korea]] Strait, but quickly drops northwards to {{cvt|1.5|m|ft|0}} at the southern tip of Korean Peninsula and to {{cvt|0.5|m|ft}} at the North Korean shores. Similar low tides are observed in Hokkaidō, Honshū and south Sakhalin. The amplitude however increases to {{cvt|2.3|-|2.8|m|ft}} toward the north of the Strait of Tartary due to its funnel-like shape. Apart from tides, the water level also displays seasonal, monsoon-related variations across the entire sea with the highest levels observed in summer and lowest in winter. Wind may also locally change the water level by {{cvt|20|-|25|cm|in|0}}; for example, it is higher in summer at the Korean and lower at the Japanese coasts.<ref name=rev/>

The sea waters have blue to green-blue color and a transparency of about {{cvt|10|m|ft}}. They are rich in [[dissolved oxygen]], especially in the western and northern parts, which are colder and have more [[phytoplankton]] than the eastern and southern areas. The oxygen concentration is 95% of the saturation point near the surface; it decreases with the depth to about 70% at {{cvt|3000|m|ft}}.<ref name=rev/><ref name=bse/>