The , also known as the Black or or the is a north-flowing, warm

ocean current An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences. Depth contours ...

on the west side of the North

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contin ...

basin. It was named for the deep blue appearance of its waters. Similar to the Gulf Stream in the North Atlantic, the Kuroshio is a powerful

western boundary current Boundary currents are ocean currents with dynamics determined by the presence of a coastline, and fall into two distinct categories: western boundary currents and eastern boundary currents. Eastern boundary currents Eastern boundary currents are ...

that transports warm equatorial water poleward and forms the western limb of the

North Pacific Subtropical Gyre The North Pacific Gyre (NPG) or North Pacific Subtropical Gyre (NPSG), located in the northern Pacific Ocean, is one of the five major oceanic gyres. This gyre covers most of the northern Pacific Ocean. It is the largest ecosystem on Earth, locat ...

. Off the East Coast of Japan, it merges with the

Oyashio Current , also known as Oya Siwo, Okhotsk or the Kurile current, is a cold subarctic ocean current that flows south and circulates counterclockwise in the western North Pacific Ocean. The waters of the Oyashio Current originate in the Arctic Ocean an ...

to form the

North Pacific Current The North Pacific Current (sometimes referred to as the North Pacific Drift) is a slow warm water current that flows west-to-east between 30 and 50 degrees north in the Pacific Ocean. The current forms the southern part of the North Pacific Su ...

. The Kuroshio Current has significant effects on both physical and biological processes of the North Pacific Ocean, including nutrient and sediment transport, major pacific storm tracks and regional climate, and Pacific mode water formation.Terazaki, Makoto (1989) "Recent Large-Scale Changes in the Biomass of the Kuroshio Current Ecosystem" in Kenneth Sherman and Lewis M. Alexander (eds.), Biomass Yields and Geography of Large Marine Ecosystems (Boulder: Westview) AAAS Selected Symposium 111, pp. 37–65. Additionally, the current's significant nutrient transport results in a biologically rich

ecoregion An ecoregion (ecological region) or ecozone (ecological zone) is an ecologically and geographically defined area that is smaller than a bioregion, which in turn is smaller than a biogeographic realm. Ecoregions cover relatively large areas of ...

supporting an important fishing industry as well as diverse marine food webs. The South China Sea for example has relatively low nutrient concentrations in its upper waters, but experiences enhanced biological productivity due to the input from the

Kuroshio Current Intrusion The Kuroshio Current is a northward flowing Western Boundary Current (WBC) in the Pacific Ocean. It is a bifurcation arm of the North Equatorial Current and consists of northwestern Pacific Ocean water. The other arm is the southward flowing Mind ...

. Ongoing research centered around the Kuroshio Current's response to climate change predicts a strengthening in surface flows of this western boundary current which contrasts the predicted changes in the Atlantic Ocean's Gulf Stream.

Physical properties

The Kuroshio is a relatively warm ocean current with an annual average sea-surface temperature of about , is approximately wide, and produces frequent small to meso-scale eddies. The Kuroshio originates from the Pacific

North Equatorial Current The North Equatorial Current (NEC) is a westward wind-driven current mostly located near the equator, but the location varies from different oceans. The NEC in the Pacific and the Atlantic is about 5°-20°N, while the NEC in the Indian Ocean is v ...

, which splits in two at the east coast of

Luzon, Philippines Luzon (; ) is the largest and most populous island in the Philippines. Located in the northern portion of the Philippines archipelago, it is the economic and political center of the nation, being home to the country's capital city, Manila, as ...

, to form the southward-flowing

Mindanao Current The Mindanao Current (MC) is a southward current in the western Pacific Ocean that transports mass and freshwater between ocean basins. It is a low-latitude western boundary current that follows the eastern coast of the Philippine island group a ...

and the more significant northward-flowing Kuroshio Current. East of Taiwan, the Kuroshio enters the

Sea of Japan The Sea of Japan is the marginal sea between the Japanese archipelago, Sakhalin, the Korean Peninsula, and the mainland of the Russian Far East. The Japanese archipelago separates the sea from the Pacific Ocean. Like the Mediterranean Sea, i ...

through a deep break in the Ryukyu island chain known as the Yonaguni Depression. The Kuroshio then continues northwards and parallel to the Ryukyu islands, steered by the deepest part of the Sea of Japan, the

Okinawa Trough The (also called , literally China-Ryukyu Border Trough ) is a seabed feature of the East China Sea. It is an active, initial back-arc rifting basin which has formed behind the Ryukyu arc-trench system in the West Pacific. It developed where th ...

, before leaving the Sea of Japan and re-entering the Pacific through the Tokara Strait. It then flows along the southern margin of Japan but meanders significantly. At the

Bōsō Peninsula The is a peninsula that encompasses the entirety of Chiba Prefecture on Honshu, the largest island of Japan. It is part of the Greater Tokyo Area. It forms the eastern edge of Tokyo Bay, separating it from the Pacific Ocean. The peninsula covers ...

, the Kuroshio finally separates from the Japanese coast and travels eastward as the Kuroshio Extension. The Kuroshio Current is the Pacific analogue of the Gulf Stream in the

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

, transporting warm, tropical water northward toward the polar region. The Kuroshio's counterparts associated with the North Pacific Gyre are the: east flowing North Pacific Current to the north, the south flowing

California Current The California Current is a cold water Pacific Ocean current that moves southward along the western coast of North America, beginning off southern British Columbia and ending off southern Baja California Sur. It is considered an Eastern bound ...

to the east, and the west flowing

to the south. The warm waters of the Kuroshio Current sustain the

coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups. C ...

s of Japan, the northernmost coral reefs in the world. The part of the Kuroshio that branches into the

is called . Japan's_ocean_currents

Similar to the Atlantic Ocean's Gulf Stream, the Kuroshio Current creates warm ocean surface temperatures, and significant moisture in the atmosphere along the western Pacific basin, and thus produces and sustains

tropical cyclone A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depen ...

s. Tropical cyclones, also known as

typhoon A typhoon is a mature tropical cyclone that develops between 180° and 100°E in the Northern Hemisphere. This region is referred to as the Northwestern Pacific Basin, and is the most active tropical cyclone basin on Earth, accounting for a ...

s, are formed when

atmospheric instability Atmospheric instability is a condition where the Earth's atmosphere is generally considered to be unstable and as a result the weather is subjected to a high degree of variability through distance and time. Atmospheric stability is a measure of t ...

, warm ocean surface temperatures, and moist air are combined to fuel an atmospheric low-pressure system. The Western North Pacific Ocean experiences an average of 25 typhoons annually. The majority of typhoons occur from July through October during northern hemisphere summer, and typically form where the Kuroshio Current is the warmest near the equator. Typhoons tend to track along the current's warm water poleward until they dissipate in colder waters. The strength (

transport Transport (in British English), or transportation (in American English), is the intentional movement of humans, animals, and goods from one location to another. Modes of transport include air, land ( rail and road), water, cable, pipelin ...

) of the Kuroshio varies along its path and seasonally. Within the Sea of Japan, observations suggest that the Kuroshio transport is relatively steady at about 25 Sv (25 million cubic metres per second). The Kuroshio strengthens significantly when it rejoins the Pacific Ocean, reaching 65 Sv (65 million cubic metres per second) southeast of Japan, although this transport has significant seasonal variability. The Kuroshio Current splits into Kuroshio Current extension and the Tsushima Current, as the currents wrap around Japanese Island and reconnects, changes in flow will impact the flows of the other currents. The path of the Kuroshio may have been different in the geologic past based on historical sea level and bathymetry, however there is currently conflicting scientific evidence. It has been proposed that lower

sea-level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardised ...

and

tectonics Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents k ...

may have prevented the Kuroshio from entering the Sea of Japan during the last glacial period, approximately c. 115,000 – c. 11,700 years ago, and remained entirely within the Pacific basin. However, other proxies and ocean models have alternatively suggested that the Kuroshio path was relatively unaltered, possibly as far back as 700,000 years ago.

Sediment transport

The magnitude of the Kuroshio Current and seafloor bathymetry results in deep sea

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is dis ...

and sediment transport in multiple regions. Offshore of Southern Taiwan on the Kenting Plateau erosion is likely caused by the strong bottom currents which increase in velocity along the rise on this plateau. The bottom water accelerates as it travels from a depth of 3500 m to a depth around 400–700 m. The increase in current velocity exacerbates erosion revealing the Kuroshio Knoll, a 3 km × 7 km bean-shaped elevated flat area 60–70 m below surface levels in comparison to the rest of the Plateau which located at around 400–700 m. The Plateau is being uplifted and is balanced with erosion. The granulometry of the Kenting Plateau and surrounding area demonstrates the eroding qualities of the Kuroshio Current. The sediment grain size of the sand varies along the edge of the Plateau. The deeper down the edge, the larger the grains as smaller grains are swept away by the current. Some of these fine sand particles have settled into a dune field while the remaining sediment is transported and deposited throughout the region by the Kuroshio Current. The Kuroshio Current also transports

Yangtze River The Yangtze or Yangzi ( or ; ) is the longest list of rivers of Asia, river in Asia, the list of rivers by length, third-longest in the world, and the longest in the world to flow entirely within one country. It rises at Jari Hill in th ...

sediment. The amount of sediment transport is highly dependent on the relationship between the Kuroshio Current intrusion, the China Coastal Current, and the Taiwan Warm Current. The Yangtze River sediment is being deposited on the East China Sea inner shelf rather than the deep sea due to the interaction of the three currents. Western_Boundary_Currents_-_The_Kuroshio_Current

Western_Boundary_Currents_-_The_Kuroshio_Current

Distinct elemental characteristics of sediments from differing sources permits tracking sources of sediments within the Kuroshio. Taiwanese sediment notably contains

illite Illite is a group of closely related non-expanding clay minerals. Illite is a secondary mineral precipitate, and an example of a phyllosilicate, or layered alumino-silicate. Its structure is a 2:1 sandwich of silica tetrahedron (T) – alumina ...

and chlorite. These traceable compounds have been found all the way through the Kuroshio Current up into its branch through the Kuroshio Current Intrusion in the South China Sea. The South China Sea branch of the Kuroshio and the cyclonic eddy west of

Luzon Island Luzon (; ) is the largest and most populous island in the Philippines. Located in the northern portion of the Philippines archipelago, it is the economic and political center of the nation, being home to the country's capital city, Manila, ...

impact Luzon and

Pearl River The Pearl River, also known by its Chinese name Zhujiang or Zhu Jiang in Mandarin pinyin or Chu Kiang and formerly often known as the , is an extensive river system in southern China. The name "Pearl River" is also often used as a catch-a ...

sediments. The Luzon sediment containing high levels of

smectite A smectite (from ancient Greek ''σμηκτός'' smektos 'lubricated'; ''σμηκτρίς'' smektris 'walker's earth', 'fuller's earth'; rubbing earth; earth that has the property of cleaning) is a mineral mixtures of various swelling sheet sil ...

is unable to travel northwestward. The Pearl River sediments contains high levels of kaolinite and

titanium Titanium is a chemical element with the Symbol (chemistry), symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resista ...

(Ti) and is trapped above the abyssal basin between

Hainan Island Hainan (, ; ) is the smallest and southernmost province of the People's Republic of China (PRC), consisting of various islands in the South China Sea. , the largest and most populous island in China,The island of Taiwan, which is slightly ...

and the Pearl River mouth. These compounds allow scientists to track sediment transport throughout the Kuroshio Current.

Eddies

There are indications that

eddies In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid is in a turbulent flow regime. The moving fluid creates a space devoid of downstream-flowing fluid on the downstream side of the object. Fluid b ...

contribute to the preservation and survival of fish larvae transported by the Kuroshio.

Plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucia ...

biomass fluctuates yearly and is typically highest in the eddy area of the Kuroshio's edge. Warm-core rings are not known for having high productivity. However, there is evidence of equal distribution of biological productivity throughout the warm-core rings from the Kuroshio Current, supported by the upwelling at the periphery and the

convective mixing In fluid dynamics, convective mixing is the vertical transport of a fluid and its properties. In many important ocean and atmospheric phenomena, convection is driven by density differences in the fluid, e.g. the sinking of cold, dense water in p ...

caused by the cooling of surface water as the rings move north of the current. The thermostad is the deep

mixed layer The oceanic or limnological mixed layer is a layer in which active turbulence has homogenized some range of depths. The surface mixed layer is a layer where this turbulence is generated by winds, surface heat fluxes, or processes such as evaporat ...

that has discrete boundaries and uniform temperature. Within this layer, nutrient-rich water is brought to the surface, which generates a burst of primary production. Given that the water in the core of a ring has a different temperature regime than the shelf waters, there are times when a warm-core ring is undergoing its

spring bloom The spring bloom is a strong increase in phytoplankton abundance (i.e. stock) that typically occurs in the early spring and lasts until late spring or early summer. This seasonal event is characteristic of temperate North Atlantic, sub-polar, and ...

while the surrounding shelf waters are not. Pacific_typhoon_tracks_1980-2005

There are many complex interactions within warm-core rings and thus, lifetime productivity is not very different from the surrounding shelf water. A study from 1998 found that the primary productivity within a warm-core ring was almost the same as in the cold jet outside it, with evidence of upwelling of nutrients within the ring. In addition, there was discovery of dense populations of phytoplankton at the nutricline within a ring, presumably supported by the upward mixing of nutrients. Furthermore, there have been acoustic studies in the warm-core ring, which showed intense sound scattering from

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

and fish populations in the ring and very sparse acoustic signals outside of it.

Typhoons

Typhoon A typhoon is a mature tropical cyclone that develops between 180° and 100°E in the Northern Hemisphere. This region is referred to as the Northwestern Pacific Basin, and is the most active tropical cyclone basin on Earth, accounting for a ...

s can produce intense winds which push on the surface layer of the ocean for brief periods of time. These winds induce the warmer surface layer of the ocean to mix with the deeper cooler layer of water that is situated below the

pycnocline A pycnocline is the cline or layer where the density gradient () is greatest within a body of water. An ocean current is generated by the forces such as breaking waves, temperature and salinity differences, wind, Coriolis effect, and tides cause ...

. This mixing introduces nutrients from deeper cooler water to the warmer surface layer of the ocean. Organisms such as phytoplankton and algae use these newly introduced nutrients to grow. In 2003, two typhoons induced significant surface layer mixing as they passed through the region. This mixing directly produced two algal bloom events in the North Western Pacific Ocean that negatively affected Japan.

Nutrient transport

The Kuroshio Current is considered a nutrient stream because of high nutrient flux from surrounding oligotrophic waters with

primary production In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through ...

of 150 to 300 grams of carbon per square meter per year based on SeaWiFS global primary productivity estimates. The current transports significant amounts of nutrients to support this primary production from the East China Sea continental shelf to the subarctic Pacific Ocean. The maximum chlorophyll value is found around depth. Its importance in nutrient transport is demonstrated by the nutrient rich water in the Kuroshio Current is surrounded by ambient water of the same density with lower relative nutrient levels. The downstream of the Kuroshio Current receives large amounts of nutrients at rates of 100–280 kmol N*s-1. Nutrients are brought to the surface water from deeper layers where the Kuroshio Current flows over shallow areas and seamounts. This process occurs over the

and the Tokara Strait. The Tokara Strait also has high cyclonic activity where the Kuroshio Current passes through. This in combination with the

Coriolis effect In physics, the Coriolis force is an inertial or fictitious force that acts on objects in motion within a frame of reference that rotates with respect to an inertial frame. In a reference frame with clockwise rotation, the force acts to the ...

causes intense upwelling along the continental shelf. This upwelling and nutrient transport into surface layers is essential for primary production because these vital nutrients would otherwise be inaccessible to phytoplankton which need to remain in upper layers where sunlight is available for them to perform

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

. The constant transport of nutrient rich waters to regions with high levels of light therefore supports increased photosynthesis supporting the rest of the biologically diverse ecosystem associated with the Kuroshio current.

Marine life

Spring Bloom Colors the Pacific Near Hokkaido

The transportation of nutrients, heat and plankton by the Kuroshio Current and the current's transection of multiple different waterbodies gives way to high species richness in and adjacent to this current. In addition, the Kuroshio is classified as a

biodiversity hotspot A biodiversity hotspot is a biogeographic region with significant levels of biodiversity that is threatened by human habitation. Norman Myers wrote about the concept in two articles in ''The Environmentalist'' in 1988 and 1990, after which the c ...

, meaning the waters circulating through the region are host to many different species, yet many of its resident organisms are at risk of becoming endangered or are already at the brink of extinction as a result of local and/or global human activity. Overfishing and overharvest are the primary risks for many of the

threatened Threatened species are any species (including animals, plants and fungi) which are vulnerable to endangerment in the near future. Species that are threatened are sometimes characterised by the population dynamics measure of ''critical depensa ...

endangered An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and in ...

species here.Aldea, K. Q., Morales, M. I., Arajo, A. E., & Masagca, J. T. (2015). Biodiversity in the Kuroshio Region: Challenges and Trends in the Upstream.

Photoautotrophs

Phytoplankton

Phytoplankton are responsible for the aforementioned high rates of primary productivity within the current. Warm sea surface temperatures and low turbidity in the region lead to clearer waters which allows for deeper penetration of sunlight and an extension of the epipelagic zone. These particular characteristics, along with lower nutrient availability within the current, correspond well with the requirements of two specific cyanobacteria: ''

Prochlorococcus ''Prochlorococcus'' is a genus of very small (0.6 μm) marine cyanobacteria with an unusual pigmentation ( chlorophyll ''a2'' and ''b2''). These bacteria belong to the photosynthetic picoplankton and are probably the most abundant photosynth ...

and

Synechococcus ''Synechococcus'' (from the Greek ''synechos'', in succession, and the Greek ''kokkos'', granule) is a unicellular cyanobacterium that is very widespread in the marine environment. Its size varies from 0.8 to 1.5 µm. The photosynthetic c ...

''. ''Prochlorococcus'' is the dominate species of picophytoplankton within the Kuroshio Current and these two species may be responsible for as much as half of the fixation of in the entire Kuroshio Current photic zone. Further, there are substantial dust deposition events in this region due to Asian Dust Storms from the Gobi desert. During these events, dust clouds transport and deposit phosphate and trace metals which subsequently stimulate growth in both ''Prochlorococcus and Synechococcus'' as well as diatoms. Diatoms and

Trichodesmium ''Trichodesmium'', also called sea sawdust, is a genus of Filamentation, filamentous cyanobacteria. They are found in nutrient poor tropical and subtropical ocean waters (particularly around Australia and in the Red Sea, where they were first des ...

are speculated to play an important role in the redistribution of nitrogen and carbon in and out of the euphotic zone. Trichodesmium is an abundant

diazotroph Diazotrophs are bacteria and archaea that fix gaseous nitrogen in the atmosphere into a more usable form such as ammonia. A diazotroph is a microorganism that is able to grow without external sources of fixed nitrogen. Examples of organisms that ...

that directly correlates with overall nitrogen fixation within the current. This nitrogen fixation supplies a limiting nutrient (nitrate), to other photoautotrophs for growth and reproduction. Meanwhile, in areas influenced by upwelling with higher nutrient and carbon concentrations, diatoms are important contributors to carbon and nitrogen out of the euphotic zone due to the weight of their "glass houses" made of silica and their tendencies to sink.

Macro-flora

At least ten genera of seaweed reside in waters in and around the Kuroshio Current. ''

Caulerpa ''Caulerpa'' is a genus of seaweeds in the family Caulerpaceae (among the green algae). They are unusual because they consist of only one cell with many nuclei, making them among the biggest single cells in the world. A species in the Mediterran ...

'', is a green algae that grows densely near shore on the periphery of the Kuroshio Current while

brown Brown is a color. It can be considered a composite color, but it is mainly a darker shade of orange. In the CMYK color model used in printing or painting, brown is usually made by combining the colors orange and black. In the RGB color model us ...

and red algae also flourish adjacent the current, and like other photosynthesizing organisms, benefit from the nutrient transport and low turbidity of the region.

Invertebrates

Zooplankton

An increase in

biomass occurs in the significantly lower water temperatures of the upwelling sites within the Kuroshio Current due to high phytoplankton concentrations which are nourished by upwelling northeast of Taiwan. This upwelling event, the

Kuroshio Current intrusion The Kuroshio Current is a northward flowing Western Boundary Current (WBC) in the Pacific Ocean. It is a bifurcation arm of the North Equatorial Current and consists of northwestern Pacific Ocean water. The other arm is the southward flowing Mind ...

through the Luzon Strait and

South China Sea The South China Sea is a marginal sea of the Western Pacific Ocean. It is bounded in the north by the shores of South China (hence the name), in the west by the Indochinese Peninsula, in the east by the islands of Taiwan and northwestern Phi ...

, and summer monsoons, represent the convergence of a multitude of oceanic waters of different origin. These water convergence zones and subsequent circulation and mixing, have a major influence on the transport and distribution of many zooplankton species causing zooplankton communities to be more nutritious, unique and diverse. High diversity in copepods in waters adjacent the Kuroshio Current have also been reported. Two dominant copepod species of the current, ''C. sinicus'' and ''E. concinna'', are transported northward in high concentrations by the current from the East China Sea in winter. Like copepods and diatoms,

tunicate A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata (). It is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time ...

s, specifically

salp A salp (plural salps, also known colloquially as “sea grape”) or salpa (plural salpae or salpas) is a barrel-shaped, planktic tunicate. It moves by contracting, thereby pumping water through its gelatinous body, one of the most efficient ...

s and doliolids, also play an important role on the biogeochemical cycle as well as on the food web in the Kuroshio. Salps transport carbon to the region's bottom water with their carbon-rich, fast-sinking fecal pellets and carcasses. ''Thaliaceans'' (salps and doliolids) are known to feed a minimum of 202 marine species, however, these animal's blooms have been found to cause harmful feeding conditions for pelagic fishes in the region. Many species of fish larvae are also found in zooplankton communities transported by the current. Fish larvae are important contributor to the Kuroshio Current system food chain. Baleen whales for instance, make use of the current's transport of Japanese sardine and jack mackerel larvae to their feeding grounds in the north pacific. Climate change is reported to alter endemic fish larvae distribution. A fish species composition change analysis by Lu and Lee (2014) showed changes in fish larvae distribution have occurred during the region and suggest this altered clustering is associated with changes in the intensities and flow rates of the Kuroshio Current. These changes impacts the food chain below and above this trophic level. This can influence fish migration, fish population's at large and major fisheries. The Kuroshio Current has an influence of several species of

foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

, including species ''G. ruber'' and ''P. obliquiloculate''. ''G. ruber'' is normally a surface dweller and was found at depths of 1000 meters along the Kuroshio Current. ''P. obliquiloculate'' normally resides between 25 and 100 m, yet was found deep in the abyssal basin (>1000 m). The distribution of these species in comparison to their standard dwelling depths observed by Gallagher (2015) demonstrates the ability of this intrusion and the overall Kuroshio Current's to redistribute nutrients vertically making nutrients available many different species with differing requirements for prosperity.

Coral

The coral reefs within the Kuroshio Current reside at a higher latitude than any other tropical reef placement in the world (33.48°N). An important reef-building coral to this area, ''Heliopora coerulea'', has been listed as threatened due to anthropogenic stressors to its environment such as: warming sea surface temperatures from climate change, ocean acidification from anthropogenic greenhouse gas emissions and

dynamite fishing Blast fishing, fish bombing, dynamite fishing or grenade fishing is a destructive fishing practice using explosives to stun or kill schools of fish for easy collection. This often illegal practice is extremely destructive to the surrounding eco ...

. Studies confirming low genotypic diversity within the species further emphasizes this blue coral's threatened status. '' Acropora japonica'', ''

Acropora secale ''Acropora secale'' is a species of branching staghorn stony coral. It is found in shallow parts of the Indo-Pacific Ocean and the type locality is Sri Lanka. The oldest fossils found date back to the Pleistocene. Description ''Acropora secal ...

'', and ''

Acropora hyacinthus ''Acropora hyacinthus'' is a species of Acropora described from a specimen collected in Fiji by James Dwight Dana in 1846. It is thought to have a range that includes the Indian Ocean, the Indo-Pacific waters, southeast Asia, Japan, the East C ...

'' are 3 more reef-building corals in the region. These species utilize symbiotic relationships with zooxanthellae,

peridinin Peridinin is a light-harvesting apocarotenoid, a pigment associated with chlorophyll and found in the peridinin-chlorophyll-protein (PCP) light-harvesting complex in dinoflagellates, best studied in '' Amphidinium carterae''. Biological signif ...

and pyrrhoxanthin, as a source of carotenoids. In addition to anthropogenic, threats, these corals also have predators in the region such as the Crown-of-thorns starfish, ''Acanthaster planci'', and a regional sea snail, '' Drupella fragum''. The Crown-of-thorns starfish feeds on corals. When conditions are favorable, the population of this native starfish can explode, resulting in significant damage on entire coral communities, as well as the ecosystems these coral reefs support. A Crown-of-thorns starfish outbreak in conjunction with anthropogenic stressors can cause irreversible reef-system damage. The Kuroshio Current controls patterns of connectivity between coral reefs (as well as other marine organisms with a larval phase), transporting larvae from southerly coral reefs to downstream reefs along the Ryukyu Arc.

Squid

Western boundary currents are used by certain species of squid for rapid and easy transport, allowing mature squid to travel with minimum energy expenditure to exploit rich northern feeding grounds, while eggs and larvae develop in the warm current waters during winter. The

Japanese flying squid The Japanese flying squid, Japanese common squid or Pacific flying squid, scientific name ''Todarodes pacificus'', is a squid of the family Ommastrephidae. This animal lives in the northern Pacific Ocean, in the area surrounding Japan, along the ...

(''Todarodes pacificus''), for example, has three populations that breed in winter, summer, and autumn. The winter spawning group is associated with the Kuroshio Current, because following spawning events in January to April in the East China Sea the larvae and juveniles travel north with the Kuroshio Current. They are turned inshore and are caught between the islands of

Honshu , historically called , is the largest and most populous island of Japan. It is located south of Hokkaidō across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyūshū across the Kanmon Straits. The island se ...

and

Hokkaido is Japan's second largest island and comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaidō from Honshu; the two islands are connected by the undersea railway Seikan Tunnel. The lar ...

during the summer. The summer spawning is in another part of the East China Sea, from which the larvae are entrained into the

Tsushima current The , also known as the Black or or the is a north-flowing, warm ocean current on the west side of the North Pacific Ocean basin. It was named for the deep blue appearance of its waters. Similar to the Gulf Stream in the North Atlantic, the K ...

that flows north between the islands of Japan and the mainland. Afterward, the current meets a southward flowing cold coastal current, the Liman Current. The group of squid spawned in the summer are traditionally found around the boundary between the two currents, sustaining rich fisheries. In fact, studies have reported that annual catches in Japan have gradually increased since the late 1980s and it has been proposed that changing environmental conditions have caused the autumn and winter spawning areas in the Tsushima Strait and near the Goto Islands to overlap. In addition, winter spawning sites over the continental shelf and slope in the East China Sea are expanding.

Vertebrates

Fish

The Kuroshio Current is home to thousands of fish species occupying nutrient rich and diverse waters in this region. This expansive biomass is influenced by elevated rates of primary production leading to large biomass in the lower

trophic level The trophic level of an organism is the position it occupies in a food web. A food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the number of steps it ...

s, facilitated by warmer local oceanic and atmospheric conditions. Resident fish of this area include reef fish like rabbitfish and parrotfish, pelagic fishes such as

sardine "Sardine" and "pilchard" are common names for various species of small, oily forage fish in the herring family Clupeidae. The term "sardine" was first used in English during the early 15th century, a folk etymology says it comes from the It ...

anchovies An anchovy is a small, common forage fish of the family Engraulidae. Most species are found in marine waters, but several will enter brackish water, and some in South America are restricted to fresh water. More than 140 species are placed in 1 ...

, mackerel, and

sailfish The sailfish is one or two species of marine fish in the genus ''Istiophorus'', which belong to the family Istiophoridae ( marlins). They are predominantly blue to gray in colour and have a characteristically large dorsal fin known as the ...

, and higher trophic predators such as

shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachi ...

s. Fisheries have a strong presence in this area and depend strongly on the changing oceanic conditions, largely dependent on the Kuroshio Current. To the north, the

contains subarctic water that is much colder and fresher than the resident water east of Honshu, and the intersection of these two currents is called the Kuroshio-Oyashio region. Here, local oceanographic conditions vary through the year and determine the species assemblage and thus the success of fisheries. For example, when the Oyashio current is well developed and protrudes southward, the cold waters are favorable for capturing sardines. Additionally, when larger meandering flow develops in the Kuroshio Current, sardine availability elevates due to the proximity of the Kuroshio to the southern spawning grounds of sardine. Thus, intrusion and flow paths of these currents affect presence, biomass, and catch of species such as

pollock Pollock or pollack (pronounced ) is the common name used for either of the two species of North Atlantic marine fish in the genus ''Pollachius''. '' Pollachius pollachius'' is referred to as pollock in North America, Ireland and the United Kingd ...

, and

anchovy An anchovy is a small, common forage fish of the family Engraulidae. Most species are found in marine waters, but several will enter brackish water, and some in South America are restricted to fresh water. More than 140 species are placed in 1 ...

Marine Reptiles

Five out of the seven

sea turtle Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. The seven existing species of sea turtles are the flatback, green, hawksbill, leatherback, loggerhe ...

species on earth, loggerheads ( ''Caretta caretta''), green (''

Chelonia mydas The green sea turtle (''Chelonia mydas''), also known as the green turtle, black (sea) turtle or Pacific green turtle, is a species of large sea turtle of the family Cheloniidae. It is the only species in the genus ''Chelonia''. Its range exten ...

''), hawksbill (''

Eretmochelys imbricata The hawksbill sea turtle (''Eretmochelys imbricata'') is a critically endangered sea turtle belonging to the family Cheloniidae. It is the only extant species in the genus ''Eretmochelys''. The species has a global distribution, that is large ...

''), leatherbacks (''

Dermochelys coriacea The leatherback sea turtle (''Dermochelys coriacea''), sometimes called the lute turtle or leathery turtle or simply the luth, is the largest of all living turtles and the heaviest non-crocodilian reptile, reaching lengths of up to and weights ...

''), and Olive ridleys ( ''Lepidochelys olivacea''), utilize the Kuroshio Current to access warm waters. Female sea turtles utilize the transport potential of the current to access the warm nesting beaches of Japan's shores, and adolescent green and hawksbill turtles utilize the current transport to access waters surrounding Japan.

Marine Mammals

Marine mammals such as seals,

sea lion Sea lions are pinnipeds characterized by external ear flaps, long foreflippers, the ability to walk on all fours, short and thick hair, and a big chest and belly. Together with the fur seals, they make up the family Otariidae, eared seals. ...

s and cetaceans also make use of the high biodiversity within the Kuroshio Current. Charismatic megafauna odontocetes in this region include the

Spinner dolphin The spinner dolphin (''Stenella longirostris'') is a small dolphin found in off-shore tropical waters around the world. It is famous for its acrobatic displays in which it rotates around its longitudinal axis as it leaps through the air. It is a ...

(''Stenella longirostris''),

short-finned pilot whale The short-finned pilot whale (''Globicephala macrorhynchus'') is one of the two species of cetaceans in the genus '' Globicephala'', which it shares with the long-finned pilot whale (''G. melas''). It is part of the oceanic dolphin family (Del ...

(''Globicephala macrorhynchus''),

common bottlenose dolphin The common bottlenose dolphin or Atlantic bottlenose dolphin (''Tursiops truncatus'') is a wide-ranging marine mammal of the family Delphinidae. The common bottlenose dolphin is a very familiar dolphin due to the wide exposure it gets in captiv ...

(''Tursiops truncatus''),

Dall's porpoise Dall's porpoise (''Phocoenoides dalli'') is a species of porpoise endemic to the North Pacific. It is the largest of porpoises and the only member of the genus ''Phocoenoides''. The species is named after American naturalist W. H. Dall. Taxono ...

(''Phocoenoides dalli''),

Risso's dolphin Risso's dolphin (''Grampus griseus'') is a dolphin, the only species of the genus ''Grampus''. Some of the closest related species to these dolphins include: pilot whales (''Globicephala'' spp.), pygmy killer whales (''Feresa attenuata''), melon ...

(''Grampus griseus'') and the

Killer whale The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only extant species in the genus ''Orcinus'' and is recognizable by its black-and-white ...

(''Orcinus orca''). Three types of whales of the same genus (''Balaenoptera'') also use this rich area for feeding grounds, including the Common Minke (''Balaenoptera acutorostrata''), the Sei Whale (''Balaenoptera borealis'') and Bryde's Whale (''Balaenoptera edeni''). The availability of Japanese sardines and mackerel eggs, larvae, and juveniles are the baleen whales' primary food sources in these areas. Top-tier trophic predators can serve as units in developing conservation management in this region.

Carbonate chemistry

The ocean absorbs approximately one third of the CO₂ produced by fossil fuel combustion, cement production, and deforestation. One of the more significant oceanic sinks for atmospheric CO₂ is the Kuroshio Current. In its highly biologically productive regions, this uptake of CO₂ is Carbon burial is facilitated by a strong

biological pump The biological pump (or ocean carbon biological pump or marine biological carbon pump) is the ocean's biologically driven sequestration of carbon from the atmosphere and land runoff to the ocean interior and seafloor sediments.Sigman DM & GH ...

. In the less productive northern current transition, the Kuroshio remains an important CO₂ sink, through high CO₂ solubility. The Kuroshio Extension region is classified as the strongest sink for atmospheric CO₂ in the North Pacific. This is especially true in the winter when higher amounts of human-produced CO₂ are taken up in the Kuroshio Extension region when compared with the summer. This is likely explained by cooler temperatures facilitating the solubility of CO₂ in ocean water. As CO₂ levels continue to increase in the atmosphere, so does CO₂ uptake in the Kuroshio, making this seasonality more dramatic.

Climate implications

Western boundary currents are integrated parts in the world's climatic balance. The Kuroshio Current plays an important role in influencing regional climate and weather patterns mainly through the input of warm waters from lower latitudes northward into the western edge of the Pacific basin. Along with the other western boundary currents in the world, the Kuroshio Current is subject to seasonal changes that manifest in different flow rates, bifurcation latitudes, and water salinity. Circulation within the Pacific Ocean is largely influenced by this northerly transport of warm salty water north along the Western boundary, concurrently providing structure to the western edge of the

North Pacific Gyre The North Pacific Gyre (NPG) or North Pacific Subtropical Gyre (NPSG), located in the northern Pacific Ocean, is one of the five major oceanic gyres. This gyre covers most of the northern Pacific Ocean. It is the largest ecosystem on Earth, locate ...

. The resulting heat fluxes in this area represent some of the largest heat exchanges from ocean to atmosphere within the entire Pacific Basin, being more pronounced during the winter season. Heat transfer from the surface ocean to the atmosphere creates unstable atmospheric conditions, which is to say that air parcels and clouds derived or influenced by this process are warmer than the surrounding air, ultimately rising and enhancing chances of precipitation or shifting weather. In this way, monsoonal rain events and common through the summertime and typhoon storms are enhanced as they pass over the current. The climate of many Asian countries has been affected by the distribution of heat by these processes for millions of years, changing wind patterns, precipitation, and mixing warm tropical waters into the

Mode water formation

As the Kuroshio Current separates from the equatorial current and flows northward, warm water from the Western Pacific Warm Pool segues into the northwest Pacific Ocean Basin. Principal heat flux in the Kuroshio occurs via the Kuroshio Extension between 132°E and 160°E and 30°N to 35°N, depending on the latitude where the extension splits off from the Kuroshio Current along the coast of Japan. The process of warm water injection into the open ocean plays an important role in the formation of North Pacific Subtropical

Mode water Mode water is defined as a particular type of water mass, which is nearly vertically homogeneous. Its vertical homogeneity is caused by the deep vertical convection in winter. The first term to describe this phenomenon is ''18° water'', which wa ...

s and the regulation of sea surface temperatures, affecting moisture transport across the western Pacific Basin. North Pacific subtropical mode waters are created when Kuroshio Extension waters lose large amounts of heat and moisture to the cold and dry northerly winds during boreal wintertime months, creating dense salty surface waters prone to sink and cause convection. The temperature range of the sinking North Pacific Subtropical Mode Waters characteristically falls between 16 °C and 19 °C, however exact temperatures and depths to which these waters sink varies annually depending on the efficiency of water transportation by the extension, which is a function of atmospheric and mesoscale eddy conditions. The resulting homogeneous water mass typically separates the seasonal pycnocline from the surface waters in the mid to late summer months, remaining stratified below the warmer surface waters until shoaling back towards the surface with the mixed layer due to storm perturbation in the fall and winter. The contrast between the temperatures of these stratified vertical layers can be discernable such that the lateral advection of mode water can be traced for thousands of kilometers. Mode water formation is variable and largely dependent on the flow intensity of the Kuroshio Extension and atmospheric heat flux efficiencies. Heat flux processes sometimes experience feedbacks that enhance water temperature contrasts and can cause sea surface temperature features to last well past the end of the boreal winter. For example, with residually cooled surface waters in the late spring and early summer months, warm moist air from the south can cause low cloud formation and reflection of solar radiation, extending temporal sea surface cooling. The Kuroshio Extension is a dynamic but relatively unstable system, with variability in the associated bifurcation latitude occurring on interannual time scales. The cause of these variations and their effects on the surface flow and total transport of waters has been studied extensively, with recent advances in sea surface height satellite altimetry methods allowing for observational studies on larger timescales. Studies suggest that more northerly bifurcation latitudes have been historically correlated with greater surface water transport and mode water formation, associated with less meandering and more direct flow paths closer to the coasts of Japan and Taiwan during the wintertime months.

Climate change

Climate change, specifically with respect to increasing sea surface temperatures and decreasing salinity, has been predicted to strengthen the surface flow of the Kuroshio Current as well as other western boundary currents across the Pacific. The predicted effects of warming surface oceans may result in differing impacts between the Atlantic and Pacific oceans; the Atlantic is predicted to experience a slowing of the

Atlantic meridional overturning circulation The Atlantic meridional overturning circulation (AMOC) is part of a global thermohaline circulation in the oceans and is the zonally integrated component of surface and deep currents in the Atlantic Ocean. It is characterized by a northward fl ...

while the Pacific western boundary currents, including the Kuroshio Current, may strengthen. These changes are thought to come as a product of

wind stress In physical oceanography and fluid dynamics, the wind stress is the shear stress exerted by the wind on the surface of large bodies of water – such as oceans, seas, estuaries and lakes. Stress is the quantity that describes the magnitude of a f ...

and surface warming resulting from the increased

stratification Stratification may refer to: Mathematics * Stratification (mathematics), any consistent assignment of numbers to predicate symbols * Data stratification in statistics Earth sciences * Stable and unstable stratification * Stratification, or st ...

of the surface layers of future oceans. Specifically, predicted poleward shifting of westerly winds within the

Hadley Cell The Hadley cell, named after George Hadley, is a global-scale tropical atmospheric circulation that features air rising near the equator, flowing poleward at a height of 10 to 15 kilometers above the earth's surface, descending in the subtropics ...

is thought to create conditions in which the subtropical gyre wind stress curl would increase. This could cause an increased total geostrophic circulation and subsequently an intensification of the northern leg of the Kuroshio Current, in some predictions increasing flow velocities by almost double. The entire flow of the current is predicted to be strengthened however, from its point of bifurcation near the equator to the Kuroshio Extension. In addition, the general observed southward migration of both the NEC and SEC subcurrent bifurcation latitudes over the past thirty years has been consistent with a strengthening of western boundary currents. With shifting winds and increased gyre circulation in conjunction with a "business as usual" anthropogenic carbon input scenario, bifurcation latitudes are predicted to continue on poleward migrations into the future, contributing to the intensifying Kuroshio Current. Predictions are made using methods that combine historical data with oceanic modelling output, and one such study used the Coupled Model Intercomparison Project (CMIP5) to show the Kuroshio Current interacting with the northern extremity of the subtropical gyre, contrasting older predictions of simple gyre "spin up" forced acceleration. Modelling studies have also suggested that increasing stratification will occur with the strengthening of the surface layer current, creating conditions in which the opposite effect could occur in the deeper layer of the Kuroshio Current, which has been proposed to slow. The exact mechanisms causing this change are not well elucidated, however it is expected to be the result of wind stress changes within the gyre in addition to the increased stratification near the surface that may enhance surface and deep ocean layer separation and maintain different responses to warming oceans.

Economic considerations

The Kuroshio Current can be a useful as a shipping lane as the current can save time and fuel usage when underway with the current. However, ships that travel against the current will spend more time and fuel to compensate for the water flowing against the shipping vessel. The Kuroshio supports many important fisheries. Jack Mackerel populations are one of the most important fishery resources in Japan, Korea and Taiwan. As the Kuroshio flows northeastward from northeast of Taiwan along the shelf slope of the Eastern China Sea, it carries Jack Mackerel eggs and larvae to southern Japan and Honshu Island. These larvae are caught and then raised in aquaculture through adulthood and harvested. Other important fisheries include pollock, sardine, and anchovy.Belkin, I.
"Kuroshio Current: LME #49"
There are also many developing port cities along the Kuroshio Current. While the Kuroshio Current is historically known to support many fisheries where it meets with the Oyashio current, this region is still recovering from the Fukushima Daiichi Nuclear Power Plant accident. In 2011, a magnitude 9.0 earthquake triggered a devastating tsunami in 2011. This tsunami inundated more than 200 miles of Japan's coastline and drastically altered the sea level in some coastal areas by meters. It killed more than 18,500 people and set off a nuclear disaster at the

Fukushima may refer to: Japan * Fukushima Prefecture, Japanese prefecture ** Fukushima, Fukushima, capital city of Fukushima Prefecture, Japan ***Fukushima University, national university in Japan *** Fukushima Station (Fukushima) in Fukushima, Fukushim ...

nuclear plant, releasing radiocesium into the surrounding waters. While local water bodies were the most severely affected, this radiocesium was transported as far as the entire North Pacific Ocean by the North Pacific Current which is formed by the collision of the Kuroshio and the Oyashio current. Local fisheries lost over 90% of their fleets and were unable to resume operations for up to a year after the accident. The local economy has been working to return to pre-tsunami levels but, even now, fishery yields have not reached nearly the levels they were before the accident. No catches are made within a 10 km radius to the accident cite and even catches outside of that zone are subject to inspection for radioactive materials, costing fisheries both time and money. Minamisanriku had most of the town's port and aquaculture facilities restored by 2014 and as of 2018, reconstruction of Iwate and Miyagi, the

Japanese Prefectures Japan is divided into 47 prefectures (, ''todōfuken'', ), which rank immediately below the national government and form the country's first level of jurisdiction and administrative division. They include 43 prefectures proper (, ''ken''), two ...

, key infrastructure was near completion. Local Japanese fishing fleets hauled 5,928 tons of seafood product valued at over 2.21 billion yen (19.342 million U.S. dollars) in 2021. Changes in the Kuroshio Current and its warming conditions have impacted pilot whale migration. These animals are considered a delicacy but hunting is strictly regulated and transitions in migration timing is impacting those who depend on these animals as a source of income. Management practices must consider protecting these animals and recognizing the potential economic impacts on local hunters.

References

External links

Current map of the Kuroshio Current
{{Authority control Geography of Japan Currents of the Pacific Ocean