Marine ecosystems are the largest of Earth's aquatic ecosystems and are distinguished by waters that have a high salt content. These systems contrast with freshwater ecosystems, which have a lower salt content. Marine waters cover more than 70% of the surface of the Earth and account for more than 97% of Earth's water supply and 90% of habitable space on Earth. Marine ecosystems include nearshore systems, such as the salt marshes, seagrass meadows, rocky intertidal systems and coral reefs, they extend outwards from the coast to include offshore systems, such as the surface ocean, pelagic ocean waters, the deep sea, oceanic hydrothermal vents, the sea floor. Marine ecosystems are characterized by the biological community of organisms that they are associated with and their physical environment. Salt marshes are a transition from the ocean to the land, where salt water mix; the soil in these marshes is made up of mud and a layer of organic material called peat. Peat is characterized as waterlogged and root-filled decomposing plant matter that causes low oxygen levels.
These hypoxic conditions are caused the growth of bacteria that give salt marshes the sulfurous smell they are known for. Salt marshes are needed for healthy ecosystems and a healthy economy, they are productive ecosystems and they provide essential services for more than 75 percent of fishery species and protect shorelines from erosion and flooding. Salt marshes can be divided into the high marsh, low marsh and the upland border; the low marsh is closer to the ocean, with it being flooded at nearly every tide except low tide. The high marsh is located between the low marsh and the upland border and it only flooded when higher than usual tides are present; the upland border is the freshwater edge of the marsh and is located at elevations higher than the high marsh. This region is only flooded under extreme weather conditions and experiences much less waterlogged conditions and salt stress than other areas of the marsh. Mangroves are trees or shrubs that grow in low-oxygen soil near coastlines in tropical or subtropical latitudes.
They are an productive and complex ecosystem that connects the land and sea. Mangroves consist of species that are not related to each other, are grouped together for the characteristics they share rather than genetic similarity; because of their proximity to the coast, they have all developed adaptions such as salt excretion and root aeration to live in salty, oxygen-depleted water. Mangroves can be recognized by their dense tangle of roots that act to protect the coast by reducing erosion from storm surges, currents and tides; the mangrove ecosystem is an important source of food for many species as well as excellent at sequestering carbon dioxide from the atmosphere with global mangrove carbon storage being estimated at 34 million metric tons per year. Intertidal zones are the areas that are visible and exposed to air during low tide and covered up by saltwater during high tide. There are four physical divisions of the intertidal zone with each one having its own distinct characteristics and wildlife.
These divisions are the Spray zone, High intertidal zone, Middle Intertidal zone and Low intertidal zone. The Spray zone is a damp area, only reached by ocean and submerged only under high tides or storms; the high intertidal zone is submerged at high tide but remains dry for long periods of time between high tides. Due to the large variance of conditions possible in this region, it is inhabited by resilient wildlife that can withstand these changes such as barnacles, marine snails and hermit crabs. Tides flow over the middle intertidal zone two times a day and this zone has a larger variety of wildlife; the low intertidal zone is submerged nearly all the time except during the lowest tides and life is more abundant here due to the protection that the water gives. Estuaries occur where there is a noticeable change in salinity between saltwater and freshwater sources; this is found where rivers meet the ocean or sea. The wildlife found within estuaries is quite unique as the water in these areas is brackish - a mix of freshwater flowing to the ocean and salty seawater.
Other types of estuaries exist and have similar characteristics as traditional brackish estuaries. The Great Lakes are prime example. There, river water creates freshwater estuaries. Estuaries are productive ecosystems that many humans and animal species rely on for various different activities; this can be seen as, of the 32 largest cities in the world, 22 are located on estuaries as they provide many environmental and economic benefits such as crucial habitat for many species, being economic hubs for many coastal communities. Estuaries provide essential ecosystem services such as water filtration, habitat protection, erosion control, gas regulation nutrient cycling, it gives education and tourism opportunities to people. Lagoons are areas that are separated from larger water by natural barriers such as coral reefs or sandbars. There are two types of lagoons and oceanic/atoll lagoons. A coastal lagoon is, as the definition above a body of water, separated from the ocean by a barrier. An atoll lagoon is a number of coral islands that surround a lagoon.
Atoll lagoons are much deeper than coastal lagoons. Most lagoons are shallow meaning that they are affected by changed in precipitation and wind; this means that salinity and temperature are varied in lagoons and that they can have water that ranges from fresh to hypersaline. Lagoons
The trophic level of an organism is the position it occupies in a food chain. 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. A food chain starts at trophic level 1 with primary producers such as plants, can move to herbivores at level 2, carnivores at level 3 or higher, finish with apex predators at level 4 or 5; the path along the chain can form either a one-way flow or a food "web". Ecological communities with higher biodiversity form more complex trophic paths; the word trophic derives from the Greek τροφή referring to nourishment. The concept of trophic level was developed by Raymond Lindeman, based on the terminology of August Thienemann: "producers", "consumers" and "reducers"; the three basic ways in which organisms get food are as producers and decomposers. Producers are plants or algae. Plants and algae do not eat other organisms, but pull nutrients from the soil or the ocean and manufacture their own food using photosynthesis.
For this reason, they are called primary producers. In this way, it is energy from the sun that powers the base of the food chain. An exception occurs in deep-sea hydrothermal ecosystems. Here primary producers manufacture food through a process called chemosynthesis. Consumers are species that can not need to consume other organisms. Animals that eat primary producers are called herbivores. Animals that eat other animals are called carnivores, animals that eat both plant and other animals are called omnivores. Decomposers break down dead plant and animal material and wastes and release it again as energy and nutrients into the ecosystem for recycling. Decomposers, such as bacteria and fungi, feed on waste and dead matter, converting it into inorganic chemicals that can be recycled as mineral nutrients for plants to use again. Trophic levels can be represented starting at level 1 with plants. Further trophic levels are numbered subsequently according to how far the organism is along the food chain.
Level 1: Plants and algae make their own food and are called producers. Level 2: Herbivores eat plants and are called primary consumers. Level 3: Carnivores that eat herbivores are called secondary consumers. Level 4: Carnivores that eat other carnivores are called tertiary consumers. Apex predators by definition are at the top of their food chains. In real world ecosystems, there is more than one food chain for most organisms, since most organisms eat more than one kind of food or are eaten by more than one type of predator. A diagram that sets out the intricate network of intersecting and overlapping food chains for an ecosystem is called its food web. Decomposers are left off food webs, but if included, they mark the end of a food chain, thus food chains start with primary producers and end with decay and decomposers. Since decomposers recycle nutrients, leaving them so they can be reused by primary producers, they are sometimes regarded as occupying their own trophic level; the trophic level of a species may vary.
All plants and phytoplankton are purely phototrophic and are at level 1.0. Many worms are at around 2.1. A 2013 study estimates the average trophic level of human beings at 2.21, similar to pigs or anchovies. This is only an average, plainly both modern and ancient human eating habits are complex and vary greatly. For example, a traditional Eskimo living on a diet consisting of seals would have a trophic level of nearly 5. In general, each trophic level relates to the one below it by absorbing some of the energy it consumes, in this way can be regarded as resting on, or supported by, the next lower trophic level. Food chains can be diagrammed to illustrate the amount of energy that moves from one feeding level to the next in a food chain; this is called an energy pyramid. The energy transferred between levels can be thought of as approximating to a transfer in biomass, so energy pyramids can be viewed as biomass pyramids, picturing the amount of biomass that results at higher levels from biomass consumed at lower levels.
However, when primary producers grow and are consumed the biomass at any one moment may be low. The efficiency with which energy or biomass is transferred from one trophic level to the next is called the ecological efficiency. Consumers at each level convert on average only about 10% of the chemical energy in their food to their own organic tissue. For this reason, food chains extend for more than 5 or 6 levels. At the lowest trophic level, plants convert about 1% of the sunlight they receive into chemical energy, it follows from this that the total energy present in the incident sunlight, embodied in a tertiary consumer is about 0.001% Both the number of trophic levels and the complexity of relationships between them evolve as life diversifies through time, the exception being intermittent mass extinction events. Food webs define ecosystems, the trophic levels define the position of organisms within the webs, but these trophic levels are not always simple integers, because organisms feed at more than one trophic level.
For example, some carnivores eat plants, some plants are carnivores. A large carnivore may eat both smaller car
In biology, a population is all the organisms of the same group or species, which live in a particular geographical area, have the capability of interbreeding. The area of a sexual population is the area where inter-breeding is possible between any pair within the area, where the probability of interbreeding is greater than the probability of cross-breeding with individuals from other areas. In sociology, population refers to a collection of humans. Demography is a social science. Population in simpler terms is the number of people in a city or town, country or world. In population genetics a sex population is a set of organisms in which any pair of members can breed together; this means that they can exchange gametes to produce normally-fertile offspring, such a breeding group is known therefore as a Gamo deme. This implies that all members belong to the same species. If the Gamo deme is large, all gene alleles are uniformly distributed by the gametes within it, the Gamo deme is said to be panmictic.
Under this state, allele frequencies can be converted to genotype frequencies by expanding an appropriate quadratic equation, as shown by Sir Ronald Fisher in his establishment of quantitative genetics. This occurs in Nature: localization of gamete exchange – through dispersal limitations, preferential mating, cataclysm, or other cause – may lead to small actual Gamo demes which exchange gametes reasonably uniformly within themselves but are separated from their neighboring Gamo demes. However, there may be low frequencies of exchange with these neighbors; this may be viewed as the breaking up of a large sexual population into smaller overlapping sexual populations. This failure of panmixia leads to two important changes in overall population structure: the component Gamo demos vary in their allele frequencies when compared with each other and with the theoretical panmictic original; the overall rise in homozygosity is quantified by the inbreeding coefficient. Note that all homozygotes are increased in frequency – both the deleterious and the desirable.
The mean phenotype of the Gamo demes collection is lower than that of the panmictic original –, known as inbreeding depression. It is most important to note, that some dispersion lines will be superior to the panmictic original, while some will be about the same, some will be inferior; the probabilities of each can be estimated from those binomial equations. In plant and animal breeding, procedures have been developed which deliberately utilize the effects of dispersion, it can be shown that dispersion-assisted selection leads to the greatest genetic advance, is much more powerful than selection acting without attendant dispersion. This is so for both autogamous Gamo demes. In ecology, the population of a certain species in a certain area can be estimated using the Lincoln Index. According to the United States Census Bureau the world's population was about 7.55 billion in 2019 and that the 7 billion number was surpassed on 12 March 2012. According to a separate estimate by the United Nations, Earth’s population exceeded seven billion in October 2011, a milestone that offers unprecedented challenges and opportunities to all of humanity, according to UNFPA, the United Nations Population Fund.
According to papers published by the United States Census Bureau, the world population hit 6.5 billion on 24 February 2006. The United Nations Population Fund designated 12 October 1999 as the approximate day on which world population reached 6 billion; this was about 12 years after world population reached 5 billion in 1987, 6 years after world population reached 5.5 billion in 1993. The population of countries such as Nigeria, is not known to the nearest million, so there is a considerable margin of error in such estimates. Researcher Carl Haub calculated that a total of over 100 billion people have been born in the last 2000 years. Population growth increased as the Industrial Revolution gathered pace from 1700 onwards; the last 50 years have seen a yet more rapid increase in the rate of population growth due to medical advances and substantial increases in agricultural productivity beginning in the 1960s, made by the Green Revolution. In 2017 the United Nations Population Division projected that the world's population will reach about 9.8 billion in 2050 and 11.2 billion in 2100.
In the future, the world's population is expected to peak, after which it will decline due to economic reasons, health concerns, land exhaustion and environmental hazards. According to one report, it is likely that the world's population will stop growing before the end of the 21st century. Further, there is some likelihood that population will decline before 2100. Population has declined in the last decade or two in Eastern Europe, the Baltics and in the Commonwealth of Independent States; the population pattern of less-developed regions of the world in recent years has been marked by increasing birth rates. These followed an earlier sharp reduction in death rates; this transition from high birth and death rates to low birth
The California Current is a Pacific Ocean current that moves southward along the western coast of North America, beginning off southern British Columbia and ending off southern Baja California Peninsula. It is considered an Eastern boundary current due to the influence of the North American coastline on its course, it is one of five major coastal currents affiliated with strong upwelling zones, the others being the Humboldt Current, the Canary Current, the Benguela Current, the Somali Current. The California Current is part of the North Pacific Gyre, a large swirling current that occupies the northern basin of the Pacific; the movement of Alaskan and northern ocean currents southward down the west coast results in much cooler ocean temperatures than at comparable latitudes on the east coast of the United States, where ocean currents come from the Caribbean and tropical Atlantic. The cooler ocean current along the west coast makes summer temperatures cooler on the west coast compared to the east coast.
For example, Half Moon Bay at 37 degrees latitude has no month with an average high above 67 °F and San Francisco stays below 70 °F in summer, while Virginia Beach, VA close to the same latitude has six months when high temperatures are above 70 °F. Additionally, extensive upwelling of colder sub-surface waters occurs, caused by the prevailing northwesterly winds acting through the Ekman Effect; the winds drive surface water to the right of the wind flow, offshore, which draws water up from below to replace it. The upwelling further cools the cool California Current; this is the mechanism that produces cool ocean waters. As a result, ocean surf temperatures are much colder along the Pacific coast than the Atlantic coast. For example, the average July SST at New York City at 40.7 degrees latitude is 73 °F, while at the same latitude in Eureka, CA is 57 °F. As such, ocean surf temperatures are above 66 °F during the summer along the California coast south to San Diego, while they are above 80 °F on the east coast from North Carolina southward.
The cold water is productive due to the upwelling, which brings to the surface nutrient-rich sediments, supporting large populations of whales and important fisheries. Winds of the appropriate direction and strength to induce upwelling are more prevalent in the presence of Eastern boundary currents, such as the California Current. Phytoplankton production is increased in these areas because the nutrient-rich water lying below the pycnocline is close to the surface and is thus upwelled. Scientists at Scripps Institution of Oceanography said in 2011 that the average surface temperature of the water at Scripps Pier has increased by 3 degrees since 1950; the "Bakun upwelling index" is based on a 20-year average of the monthly mean Ekman transport for different regions off the California coast. It ranges from 300 meters-cubed/second to −212 meters-cubed/second. There is year-round upwelling off Southern California's coast, but it is strongest in the summer months. Off the coast of Oregon and Washington, there is forceful downwelling in the winter months, upwelling in the region is restricted to the months of April through September.
Primary production is a topic of interest among those. In their study and Venrick found great variability in both biomass and the productivity of phytoplankton in the California Current; the differences observed by Hayward and Venrick in carbon-fixation rates show the heterogeneous nature of the California Current, with its combination of advected and upwelled water. Several studies have investigated the carbon flow from primary production to the pelagic fish stocks which depend on the California Current. Lasker described powerful "squirts" off northern and central California; these ` jets and squirts' move large quantities of nutrient rich water offshore. This water gets carried by the southward bound California Current and adds significant primary production to the sardine population. A narrower, weaker counter current, the Davidson Current moves somewhat warmer water northwards during the winter months. During El Niño events, the California Current is disrupted, leading to declines in phytoplankton, resulting in cascading effects up the food chain, such as declines in fisheries, seabird breeding failures and marine mammal mortality.
In 2005, a failure in the otherwise predictable upwelling events, unassociated with El Niño, caused a collapse in krill in the current, leading to similar effects. Within the Southern California Bight a sub-region of the California Current has unique physical properties. Upwelling is weak in the California Bight and Smith and Eppley stated that the 16-year average for primary production was 0.402 grams carbon/, or 150 grams carbon/. Further and Eppley found that the highest daily rates of temperature decrease were correlated with the maximum amount of upwelling. Digiacomo and Holt used satellite images to study the mesoscale and sub-mesoscale eddies in the Southern California Bight, their work showed that all eddies were less than 50 km in diameter and 70% of all eddies measured less than 10 km. The eddies appeared to be caused by topography and instabilities in the current; the location of these eddies was between the California Current (flowing toward the equa
Sea of Japan
The Sea of Japan is the marginal sea between the Japanese archipelago, the Korean Peninsula and Russia. The Japanese archipelago separates the sea from the Pacific Ocean, it is bordered by Japan and Russia. Like the Mediterranean Sea, it has no tides due to its nearly complete enclosure from the Pacific Ocean; this isolation reflects in the fauna species and in the water salinity, lower than in the ocean. The sea has bays or capes, its water balance is 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 has an 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 increasing as a result of the growth of East Asian economies. Sea of Japan is the dominant term used in English for the sea, the name in most European languages is equivalent, but it is sometimes called by different names in surrounding countries reflecting historical claims to hegemony over the sea.
The sea is called Rìběn hǎi or Jīng hǎi in China, Yaponskoye more in Russia, Chosŏn Tonghae in North Korea, Donghae in South Korea. A naming dispute exists about the sea name, with South Korea promoting the English translation of its native name as the East Sea; 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 instead of or in addition to "Sea of Japan; 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 while Korea was under Japanese rule, before 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 recognized the term "Sea of Japan" as the only title for the sea, stated they would will review the issue again in 2017.
For centuries, the sea had protected Japan from land invasions 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 named after him. In 1796, a British naval officer, William 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 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 documented the cyclonal character of the sea currents. Other notable expeditions of the 19th century include the American North Pacific Exploring and Surveying Expedition and British Challenger expedition; the aquatic life was described by V. K. Brazhnikov in P. Yu. Schmidt in 1903–1904; the Japanese scientific studies of the sea became systematic since the 1920s. American and French whaleships cruised for whales in the sea between 1848 and 1892. Most entered the sea via Korea Strait and left via La Pérouse Strait, but some entered and exited via Tsugaru Strait, they targeted right whales, but began catching humpbacks as right whale catches declined. They made attempts to catch blue and fin whales, but these species invariably sank after being killed. Right whales were caught from March with peak catches in May and June. During the peak years of 1848 and 1849 a total of nearly 160 vessels cruised in the Sea of Japan, with lesser numbers in following years; the Sea of Japan was a landlocked sea.
The onset of formation of the Japan Arc was in the Early Miocene. The Early Miocene period corresponds to the Japan Sea starting to open, the northern and southern parts of the Japanese archipelago separating from each other. During the Miocene, there was expansion of Sea of Japan; the north part of the Japanese archipelago was further fragmented until orogenesis of the northeastern Japanese archipelago began in the Late Miocene. The south part of the Japanese archipelago remained as a large landmass; the land area had expanded northward in the Late Miocene. The orogenesis of high mountain ranges in northeastern Japan started in Late Miocene and lasted in Pliocene also. Nowadays the Sea of Japan is bounded by the Russian mainland and Sakhalin island to the north, the Korean Peninsula to the west, 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 Asia
The Kuroshio known as the Black or Japan Current or the Black Stream, is a north-flowing ocean current on the west side of the North Pacific Ocean. It is part of the North Pacific ocean gyre. Like the Gulf stream, it is a strong western boundary current; the Kuroshio Current—named for the deep blue of its waters—begins off the east coast of Luzon, Philippines and flows northeastward past Japan, where it merges with the easterly drift of the North Pacific Current. It is analogous to the Gulf Stream in the Atlantic Ocean, transporting warm, tropical water northward toward the polar region; the path of Kuroshio south of Japan is reported every day. Its counterparts are the North Pacific Current to the north, the California Current to the east, the North Equatorial Current to the south; the warm waters of the Kuroshio Current sustain the coral reefs of Japan, the northernmost coral reefs in the world. The branch into the Sea of Japan is called Tsushima Current. Western boundary currents transport organisms long distances and a variety of commercially important marine organisms migrate in these currents in the course of completing their lives.
Subtropical gyres occupy a large fraction of the world's ocean and are more productive than thought. In addition, their fixation of carbon dioxide is an important factor in the global budget for carbon dioxide in the atmosphere. Satellite images of the Kuroshio Current illustrate how the current path meanders and forms isolated rings or eddies on the order of 100 to 300 kilometres. Eddies retain their unique form for several months and have their own biological characteristics that depend on where they form. If the eddies are formed between the current and coastline of Japan, they may impinge on the continental shelf; the eddies size and strength decline with distance from major ocean currents. The amount of energy decreases from the rings associated with the major currents and down to eddies remote from those currents. Cyclonic eddies have the potential to cause upwelling that would affect the global primary-production budget. Upwelling brings nutrient-rich water to the surface resulting in an increase in productivity.
The biological consequences for young fish populations that inhabit the shelf are quite large. The Kuroshio is a warm current—24 °C annual average sea-surface temperature—about 100 kilometres wide and produces frequent small to meso-scale eddies; the Kuroshio Current is ranked as a moderately high productivity ecosystem—with primary production of 150 to 300 grams —of carbon per square meter per year—based on SeaWiFS global primary productivity estimates. The coastal areas are productive and the maximum chlorophyll value is found around 100 metres depth. There are indications that eddies contribute to the preservation and survival of fish larvae transported by the Kuroshio. Plankton biomass fluctuates yearly and is highest in the eddy area of the Kuroshio’s edge. Warm-core rings are not known for having high productivity. However, the biology of the warm-core rings from the Kuroshio Current show results of productivity distributed throughout for a couple of reasons. One is upwelling at the periphery.
The thermostad is the deep mixed layer that has 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 while the surrounding shelf waters are not. There are many complex interactions with the warm-core ring and thus lifetime productivity is not different from the surrounding shelf water. A study in 1998 found that the primary productivity within a warm-core ring was 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 in a ring supported by upward mixing of nutrients. Furthermore, there have been acoustic studies in the warm-core ring, which showed intense sound scattering from zooplankton and fish populations in the ring and sparse acoustic signals outside of it.
Copepods have been used as indicator-species of water masses. It has been suggested that copepods have been transported from the Kuroshio Current into southwest Taiwan through the Luzon Strait; the Kuroshio intrusion through the Luzon Strait and further into the South China Sea may explain why copepods show a high diversity in adjacent waters of the intrusion areas. The Kuroshio Current intrusion has a major influence on C. sinicus and E. concinna, which are two copepod species with higher index values for winter and originate from the East China Sea. During the southwestern monsoon, the South China Sea Surface Current moves northward during the summer toward the Kuroshio Current; as a result of this water circulation, the zooplankton communities in the boundary waters are unique and diverse. The biomass of fish stocks depends on the biomass of lower trophic levels, primary production and on oceanic and atmospheric conditions. In the Kuroshio-Oyashio region, the fish catches depend on oceanographic conditions, such as the Oyashio’s southward intrusion and the Kuroshio’s large meander south of Honshu.
The Oyashio Current contains subarctic water, much colder and fr
The Barents Sea is a marginal sea of the Arctic Ocean, located off the northern coasts of Norway and Russia and is divided between Norwegian and Russian territorial waters. Known among Russians in the Middle Ages as the Murman Sea, the sea takes its current name from the Dutch navigator Willem Barentsz, it is a rather shallow shelf sea, with an average depth of 230 metres, is an important site for both fishing and hydrocarbon exploration. The Barents Sea is bordered by the Kola Peninsula to the south, the shelf edge towards the Norwegian Sea to the west, the archipelagos of Svalbard to the northwest, Franz Josef Land to the northeast and Novaya Zemlya to the east; the islands of Novaya Zemlya, an extension of the northern end of the Ural Mountains, separate the Barents Sea from the Kara Sea. Despite being part of the Arctic Ocean, the Barents Sea has been characterized as "turning into the Atlantic" because of its status as "the Arctic warming hot spot." Hydrologic changes due to global warming have led to a reduction in sea ice and in stratification of the water column, which could lead to major changes in weather in Eurasia.
The southern half of the Barents Sea, including the ports of Murmansk and Vardø remain ice-free year round due to the warm North Atlantic drift. In September, the entire Barents Sea is more or less ice-free; until the Winter War, Finland's territory reached to the Barents Sea, with the harbor at Petsamo being Finland's only ice-free winter harbor. There are three main types of water masses in the Barents Sea: Warm, salty Atlantic water from the North Atlantic drift, cold Arctic water from the north, warm, but not salty coastal water. Between the Atlantic and Polar waters, a front called. In the western parts of the sea, this front is determined by the bottom topography and is therefore sharp and stable from year to year, while in the east, it can be quite diffuse and its position can vary a lot between years; the lands of Novaya Zemlya attained most of their early Holocene coastal deglaciation 10,000 years before present. The International Hydrographic Organization defines the limits of the "Barentsz Sea" as follows: On the west: The northeastern limit of the Norwegian Sea.
On the northwest: The eastern shore of West Spitzbergen, Hinlopen Strait up to 80° latitude north. On the north: Cape Leigh Smith across the Islands Bolshoy Ostrov and Victoria. On the east: Cape Kohlsaat to Cape Zhelaniya. Through Vaigach Island to Cape Greben. On the south: The northern limit of the White Sea. Other islands in the Barents Sea include Timanets; the Barents Sea was formed from two major continental collisions: the Caledonian orogeny, in which the Baltica and Laurentia collided to form Laurasia, a subsequent collision between Laurasia and Western Siberia. Most of its geological history is dominated by extensional tectonics, caused by the collapse of the Caledonian and Uralian orogenic belts and the break-up of Pangaea; these events created the major rift basins that dominate the Barents Shelf, along with various platforms and structural highs. The geological history of the Barents Sea is dominated by Late Cenozoic uplift that caused by Quaternary glaciation, which has resulted in erosion and deposition of significant sediment.
Due to the North Atlantic drift, the Barents Sea has a high biological production compared to other oceans of similar latitude. The spring bloom of phytoplankton can start quite early close to the ice edge, because the fresh water from the melting ice makes up a stable water layer on top of the sea water; the phytoplankton bloom feeds zooplankton such as Calanus finmarchicus, Calanus glacialis, Calanus hyperboreus, Oithona spp. and krill. The zooplankton feeders include young cod, polar cod and little auk; the capelin is a key food for top predators such as the north-east Arctic cod, harp seals, seabirds such as common guillemot and Brunnich's guillemot. The fisheries of the Barents Sea, in particular the cod fisheries, are of great importance for both Norway and Russia. SIZEX-89 was an international winter experiment where the main objectives were to perform sensor signature studies of different ice types in order to develop SAR algorithms for ice variables such as ice types, ice concentrations and ice kinematics.
Although previous research suggested that predation by whales may be the cause of depleting fish stocks, more recent research suggests that marine mammal consumption has only a trivial influence on fisheries and a model examining the impact of fisheries and climate was far more accurate at describing trends in fish abundance. There is a genetically distinct polar bear population associated with the Barents Sea; the Barents Sea was known to Russians as Murmanskoye M