Sea of Japan
|Sea of Japan|
|English: Japan Sea|
|North Korean name|
|English: Korea East Sea|
|South Korean name|
|English: East Sea|
|English: Japanese Sea|
The Sea of Japan is a marginal sea of the western Pacific Ocean, between the Asian mainland, the Japanese archipelago and Sakhalin. It is bordered by Japan, North Korea, Russia and South Korea. Like the Mediterranean Sea, it has almost no tides due to its nearly complete enclosure from the Pacific Ocean. This isolation also reflects in the fauna species and in the water salinity, which is lower than in the ocean. The sea has no large islands, bays or capes. Its water balance is mostly determined by the inflow and outflow through the straits connecting it to the neighboring seas and Pacific Ocean. Few rivers discharge into the sea and their total contribution to the water exchange is within 1%.
The seawater is characterized by the elevated concentration of dissolved oxygen that results in high biological productivity. Therefore, fishing is the dominant economic activity in the region. The intensity of shipments across the sea has been moderate owing to political issues, but it is steadily increasing as a result of the growth of East Asian economies. A controversy exists about the sea name, with South Korea promoting the appellation East Sea.
- On the Southwest. The Northeastern limit of the Eastern China Sea [From Nomo Saki (32°35'N) in Kyusyu to the South point of Hukae Sima (Goto Retto) and on through this island to Ose Saki (Cape Goto) and to Hunan Kan, the South point of Saisyu To (Quelpart), through this island to its Western extreme and thence along the parallel of 33°17' North to the mainland] and the Western limit of the Inland Sea [defined circuitously as "The Southeastern limit of the Japan Sea"].
- On the East. In the Tsugaru Kaikô. From the extremity of Siriya Saki (141°28'E) to the extremity of Esan Saki (41°48'N).
- On the North. From Cape Tuik (51°45'N) to Cape Sushcheva.
Geography and geology
The Sea of Japan was once a landlocked sea when the land bridge of East Asia existed. The onset of formation of the Japan Arc was in Early Miocene. The Early Miocene period also corresponds to incipient opening of the Japan Sea, and the northern and southern parts of the Japanese archipelago that were separated from each other. During the Miocene, there was expansion of Sea of Japan. The northern part of the Japanese archipelago was further fragmented at later periods until the orogenesis of the northeastern Japanese archipelago began in the later Late Miocene. The southern part of the Japanese archipelago remained as a relatively large landmass. The land area had expanded northward in the Late Miocene. The orogenesis of high mountain ranges in the northeastern Japan started in Late Miocene and it lasts in Pliocene also.
Nowadays it is bound by the Russian mainland and Sakhalin island to the north, the Korean Peninsula to the west, and the Japanese islands of Hokkaidō, Honshū and Kyūshū to the east and south. It is connected to other seas by five straits: the Strait of Tartary between the Asian mainland and Sakhalin; La Pérouse Strait between the islands of Sakhalin and Hokkaidō; the Tsugaru Strait between the islands of Hokkaidō and Honshū; the Kanmon Straits between the islands of Honshū and Kyūshū; and the Korea Strait between the Korean Peninsula and the island of Kyūshū. The Korea Strait is composed of the Western Channel and the Tsushima Strait, on either side of Tsushima Island. The straits were formed in recent geologic periods. The oldest of them are the Tsugaru and Tsushima straits. Their formation had interrupted the migration of elephants into the Japanese islands at the end of the Neogene Period (about 2.6 million years ago). The most recent is La Perouse Strait. Its formation about 60,000 to 11,000 years ago had closed the path used by the mammoths which had earlier moved to the northern Hokkaidō. All the straits are rather shallow with a minimal depth of the order of 100 meters or less. This hinders water exchange thereby isolating the water and aquatic life of the Sea of Japan from the neighboring seas and oceans. The sea has a surface area of about 978,000 km² (377,600 sq mi), a mean depth of 1,752 m (5,748 ft) and a maximum depth of 3,742 m (12,276 ft). It has a carrot-like shape, with the major axis extending from southwest to northeast and a wide southern part narrowing toward the north. The coastal length is about 7,600 km with the largest part (3,240 km) belonging to Russia. The sea extends from north to south for more than 2,255 km and has a maximum width of about 1,070 km. It has three major basins: the Yamato Basin in the southeast, the Japan Basin in the north and the Tsushima Basin (Ulleung Basin) in the southwest. The Japan Basin is of oceanic origin and is the deepest part of the sea, whereas the Tsushima Basin is the shallowest with the depths below 2,300 meters. On the eastern shores, the continental shelves of the sea are wide, but on the western shores, particularly along the Korean coast, they are narrow, averaging about 30 kilometers.
There are three distinct continental shelves in the northern part (above 44°N). They form a staircase-like structure with the steps slightly inclined southwards and submerged to the depths of 900–1400, 1700–2000 and 2300–2600 meters. The last step sharply drops to the depths of about 3,500 meters toward the central (deepest) part of the sea. The bottom of this part is relatively flat, but has a few plateaus. In addition, an underwater ridge rising up to 2,300 meters runs from north to south through the middle of the central part.
The Japanese coastal area of the sea consists of Okujiri Ridge, Sado Ridge, Hakusan Banks, Wakasa Ridge and Oki Ridge. Yamato Ridge is of continental origin and is composed of granite, rhyolite, andesite and basalt. It has uneven bottom covered with boulders of volcanic rock. Most other areas of the sea are of oceanic origin. Seabed down to 300 meters (1,000 ft) is of continental nature and is covered with a mixture of mud, sand, gravel and fragments of rock. The depths between 300 and 800 meters (1,000–2,600 ft) are covered in hemipelagic sediments (i.e., of semi-oceanic origin); these sediments are composed of blue mud rich in organic matter. Pelagic sediments of red mud dominate the deeper regions.
There are no large islands in the sea. Most of the smaller ones are located near the eastern coast, except for Ulleungdo (South Korea). The most significant islands are Moneron, Rebun, Rishiri, Okushiri, Ōshima, Sado, Okinoshima, Ulleungdo, Askold, Russky and Putyatin. The shorelines are relatively straight and are lacking large bays or capes; the coastal shapes are simplest for Sakhalin and are more winding in the Japanese islands. The largest bays are Peter the Great Gulf, Sovetskaya Gavan, Vladimira, Olga, Posyet in Russia, East Korea Bay in North Korea and Ishikari (Hokkaidō), Toyama and Wakasa (Honshū) in Japan. Prominent capes include Lazareva, Peschanyi (sandy), Povorotny, Gromova, Pogibi, Tyk, Korsakova, Crillon, Sōya, Nosappu, Tappi, Nyuda, Rebun, Rishiri, Okushiri, Daso and Oki.
The sea climate is characterized by warm waters and monsoons. This combination results in strong evaporation, which is especially noticeable between October and March when the strong (12–15 m/s or higher) northwestern monsoon wind brings cold and dry continental air. The evaporation is blown further south causing snowfall in the mountainous western coasts of Japan. This winter monsoon brings typhoons and storms with the waves reaching 8–10 meters which erode the western coasts of Japan. Tsunami waves were also recorded in the sea. In addition, the monsoon enhances the surface water convection, down to the depths of 30 meters. The coldest months are January and February with the average air temperature of −20 °C in the north and 5 °C in the south. The northern one-quarter of the sea, particularly the Siberian coast and the Strait of Tartary, freezes for about 4–5 months. The timing and extent of freezing vary from year to year, so ice may start forming in the bays as early as in October and its remains may be seen even in June. Ice cover is continuous only in the bays and forms floating patches in the open sea. Ice melting in spring results in cold currents in the northern areas.
In summer the wind weakens to 2–7 m/s and reverses its direction, blowing warm and humid air from the North Pacific onto the Asian mainland. The warmest month is August with the average air temperature of 15 °C in the north and 25 °C in the south. Annual precipitation increases from 310–500 mm in the north-west to 1,500–2,000 mm in the south-east.
A peculiar turbulent cloud pattern, named Von Karman vortices, is sometimes observed over the Sea of Japan. It requires a stable field of low clouds driven by the wind over a small (isolated) and tall obstacle, and usually forms over small mountainous islands. The Sea of Japan meets these conditions as it has frequent winds and cloudy skies, as well as compact, tall islands such as Rishiri (1,721 m), Ulleungdo (984 m) and Ōshima (732 m).
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.
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 0 °C or below in the north and 10–14 °C 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 0 °C in the west and 5–6 °C in the east. This east-west difference drops to 1–2 °C in summer, and the temperatures rise to 18–20 °C in the north and 25–27 °C in the south.
As a result of the enclosed nature of the sea, 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 8–10 °C down to 100–150 m, 2–4 °C at 200–250 m, 1.0–1.5 °C at 400–500 m and then remain at about 0 °C until the bottom. Heating by the sun and tropical monsoons increases the depth gradient in spring–summer. So in the north the surface layer (down to 15 m) may heat up to 18–20 °C. The temperature would sharply drop to 4 °C at 50 m, then slowly decrease to 1 °C at 250 m and remain so down to the seabed. On the contrary, the temperature in the south could gradually decrease to 6 °C at 200 m, then to 2 °C at 260 m and to 0.04–0.14 °C at 1000–1500 m, but then it would rise to about 0.3 °C near the bottom. This cold layer at about 1000 m 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.
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. The average water density is 1.0270 g/cm3 in the north and 1.0255 g/cm3 in the south in winter. It lowers in summer to 1.0253 and 1.0215 g/cm3, respectively.
Few rivers flow into the Sea of Japan from mainland Asia, the largest being Tumen, Rudnaya, Samarga, Partizanskaya and Tumnin; all of them have mountainous character. In contrast, numerous large rivers flow from Honshū and Hokkaidō into the sea, including Japan’s four largest rivers in the Shinano, Ishikari, Agano and Mogami. The total annual river discharge into the sea is 210 km3 and is relatively constant through the year, except for a minor increase in July. Most water (97% or 52,200 km3) flows into the sea through the Korea Strait and discharges through the Tsugaru (64% or 34,610 km3), La Pérouse (10,380 km3) 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.
The sea has complex tides, 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 10–25 cm/s in the open sea. They accelerate in the Korea Strait (40–60 cm/s), La Pérouse Strait (50–100 cm/s) and especially in the Tsugaru Strait (100–200 cm/s). The amplitude of the tides is relatively low and strongly varies across the sea. It reaches 3 meters in the south near the Korea Strait, but quickly drops northwards to 1.5 meters at the southern tip of Korean Peninsula and to 0.5 meters at the North Korean shores. Similar low tides are observed in Hokkaidō, Honshū and south Sakhalin. The amplitude however increases to 2.3–2.8 meters toward the north of the Strait of Tartary due to its funnel-like shape. Apart from tides, the water level also experiences 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 20–25 cm; for example, it is higher in summer at the Korean and lower at the Japanese coasts.
The sea waters have blue to green-blue color and a transparency of about 10 meters. 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 3,000 meters.
Flora and fauna
The high concentration of dissolved oxygen results in the rich aquatic life of the Sea of Japan – there are more than 800 species of aquatic plants and more than 3,500 animal species, including more than 900 species of crustaceans, about 1000 of fish and 26 of mammals. The coastal areas contain several kg/m2 of biomass. Pelagic (oceanic) fishes include saury, mackerel, Jack mackerels, sardines, anchovies, herring, sea bream, squid and various species of salmon and trout. The demersal (sea-bottom) fishes include cod, pollock and Atka mackerel. Mammals are represented by seals and whales, and the crustaceans by shrimps and crabs. Because of the shallow straits connecting the sea with Pacific Ocean, the sea of Japan has no characteristic oceanic deep-water fauna. Flora and fauna unique to the region near the Sea of Japan are known as "Japan Sea elements".
Fishery had long been the main economic activity on the Sea of Japan. It is mainly carried out on and near the continental shelves and focuses on herring, sardines and bluefin tuna. These species are however depleted from after World War II. Squid is mostly caught near the sea center and salmon near the northern and southwestern shores. There is also a well-developed seaweed production. The importance of the fishery in the sea is illustrated by the territorial disputes between Japan and South Korea over Liancourt Rocks and between Japan and Russia over the Kuril Islands. It is also reflected in various legends, such as the legend of the Heishi rock, which says that once when herring vanished, an old fairy threw a bottle with a magic water into the sea, and the herring returned. The bottle got stuck to the seabed and turned into a rock, which became a representation of the God of the Sea of Japan.
Vladivostok is a base for the Russian whaling fleet. Although it operates in the northern seas, its production is processed and partly distributed in the Vladivostok area. Vladivostok is also a terminal point of the Trans-Siberian Railway which brings much goods to and from this major port. There is a regular ferry service across the Strait of Tartary between the Russian continental port of Vanino and Kholmsk in Sakhalin.
The sea has magnetite sands as well as natural gas and petroleum fields near the northern part of Japan and Sakhalin Island. The intensity of shipments across the sea is moderate, owing to the cold relations between many bordering countries. As a result, the largest Japanese ports are located on the Pacific coast, and the significant ports on the Sea of Japan are Niigata, Tsuruta and Maizuru. Major South Korean ports are Busan, Ulsan, and Pohang situated on the southeastern coast of the Korean Peninsula, but they also mainly target countries not bordering the Sea of Japan. The major Russian port of Vladivostok mainly serves inland cargos, whereas Nakhodka and Vostochny are more international and have a busy exchange with Japan and South Korea. Other prominent Russian ports are Sovetskaya Gavan, Alexandrovsk-Sakhalinsky and Kholmsk, and the major ports of North Korea are Wonsan, Hamhung and Chongjin. The intensity of shipments across the Sea of Japan is steadily increasing as a result of the growth of East Asian economies.
History and exploration
For centuries, the sea had protected Japan from land invasions, particularly by the Mongols. It had long been navigated by Asian and, from the 18th century, by European ships. Russian expeditions of 1733–1743 mapped Sakhalin and the Japanese islands. In the 1780s, the Frenchman Jean-François de Galaup, comte de Lapérouse, traveled northward across the sea through the strait that was named after him. In 1796, another Frenchman Robert Broughton explored the Strait of Tartary, the eastern coast of the Russian Far East and the Korean Peninsula. In 1803–1806, the Russian navigator Adam Johann von Krusenstern while sailing across the globe in the ship Nadezhda also explored, in passing, the Sea of Japan and the eastern shores of Japanese islands. In 1849, another Russian explorer Gennady Nevelskoy discovered the strait between the continent and Sakhalin and mapped the northern part of the Strait of Tartary. Russian expeditions were made in 1853–1854 and 1886–1889 to measure the surface temperatures and record the tides. They also documented the cyclonal character of the sea currents. Other notable expeditions of the 19th century include the American North Pacific Exploring and Surveying Expedition (1853–1856) and British Challenger expedition (1872–1876). The aquatic life was described by V. K. Brazhnikov in 1899–1902 and P. Yu. Schmidt in 1903–1904. The Japanese scientific studies of the sea began only in 1915 and became systematic since the 1920s.
The use of the term "Sea of Japan" as the dominant name is a point of contention. South Korea wants the name "East Sea" to be used, either instead of or in addition to "Sea of Japan;" while North Korea prefers the name "East Sea of Korea".
The primary issue in the dispute revolves around a disagreement about when the name "Sea of Japan" became the international standard. Japan claims the term has been the international standard since at least the early 19th century, while the Koreas claim that the term "Sea of Japan" arose later while Korea was under Japanese rule, and prior to that occupation other names such as "Sea of Korea" or "East Sea" were used in English. The International Hydrographic Organization, the international governing body for the naming bodies of water around the world, in 2012 rejected the use of "East Sea" and recognized the term "Sea of Japan" as the only title for the sea.
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