The Pacific Ocean is the largest and deepest of Earth's oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean in the south and is bounded by Asia and Australia in the west and the Americas in the east. At 165,250,000 square kilometers in area, this largest division of the World Ocean—and, in turn, the hydrosphere—covers about 46% of Earth's water surface and about one-third of its total surface area, making it larger than all of Earth's land area combined; the centers of both the Water Hemisphere and the Western Hemisphere are in the Pacific Ocean. The equator subdivides it into the North Pacific Ocean and South Pacific Ocean, with two exceptions: the Galápagos and Gilbert Islands, while straddling the equator, are deemed wholly within the South Pacific, its mean depth is 4,000 meters. The Mariana Trench in the western North Pacific is the deepest point in the world, reaching a depth of 10,911 meters; the western Pacific has many peripheral seas. Though the peoples of Asia and Oceania have traveled the Pacific Ocean since prehistoric times, the eastern Pacific was first sighted by Europeans in the early 16th century when Spanish explorer Vasco Núñez de Balboa crossed the Isthmus of Panama in 1513 and discovered the great "southern sea" which he named Mar del Sur.
The ocean's current name was coined by Portuguese explorer Ferdinand Magellan during the Spanish circumnavigation of the world in 1521, as he encountered favorable winds on reaching the ocean. He called it Mar Pacífico, which in both Portuguese and Spanish means "peaceful sea". Important human migrations occurred in the Pacific in prehistoric times. About 3000 BC, the Austronesian peoples on the island of Taiwan mastered the art of long-distance canoe travel and spread themselves and their languages south to the Philippines and maritime Southeast Asia. Long-distance trade developed all along the coast from Mozambique to Japan. Trade, therefore knowledge, extended to the Indonesian islands but not Australia. By at least 878 when there was a significant Islamic settlement in Canton much of this trade was controlled by Arabs or Muslims. In 219 BC Xu Fu sailed out into the Pacific searching for the elixir of immortality. From 1404 to 1433 Zheng He led expeditions into the Indian Ocean; the first contact of European navigators with the western edge of the Pacific Ocean was made by the Portuguese expeditions of António de Abreu and Francisco Serrão, via the Lesser Sunda Islands, to the Maluku Islands, in 1512, with Jorge Álvares's expedition to southern China in 1513, both ordered by Afonso de Albuquerque from Malacca.
The east side of the ocean was discovered by Spanish explorer Vasco Núñez de Balboa in 1513 after his expedition crossed the Isthmus of Panama and reached a new ocean. He named it Mar del Sur because the ocean was to the south of the coast of the isthmus where he first observed the Pacific. In 1519, Portuguese explorer Ferdinand Magellan sailed the Pacific East to West on a Spanish expedition to the Spice Islands that would result in the first world circumnavigation. Magellan called the ocean Pacífico because, after sailing through the stormy seas off Cape Horn, the expedition found calm waters; the ocean was called the Sea of Magellan in his honor until the eighteenth century. Although Magellan himself died in the Philippines in 1521, Spanish Basque navigator Juan Sebastián Elcano led the remains of the expedition back to Spain across the Indian Ocean and round the Cape of Good Hope, completing the first world circumnavigation in a single expedition in 1522. Sailing around and east of the Moluccas, between 1525 and 1527, Portuguese expeditions discovered the Caroline Islands, the Aru Islands, Papua New Guinea.
In 1542–43 the Portuguese reached Japan. In 1564, five Spanish ships carrying 379 explorers crossed the ocean from Mexico led by Miguel López de Legazpi, sailed to the Philippines and Mariana Islands. For the remainder of the 16th century, Spanish influence was paramount, with ships sailing from Mexico and Peru across the Pacific Ocean to the Philippines via Guam, establishing the Spanish East Indies; the Manila galleons operated for two and a half centuries, linking Manila and Acapulco, in one of the longest trade routes in history. Spanish expeditions discovered Tuvalu, the Marquesas, the Cook Islands, the Solomon Islands, the Admiralty Islands in the South Pacific. In the quest for Terra Australis, Spanish explorations in the 17th century, such as the expedition led by the Portuguese navigator Pedro Fernandes de Queirós, discovered the Pitcairn and Vanuatu archipelagos, sailed the Torres Strait between Australia and New Guinea, named after navigator Luís Vaz de Torres. Dutch explorers, sailing around southern Africa engaged in discovery and trade.
In the 16th and 17th centuries Spain considered the Pacific Ocean a mare clausum—a sea closed to other naval powers. As the only known entrance from the Atlantic, the Strait of Magellan was at times patrolled by fleets sent to prevent entrance of non-Spanish ships. On the western side of the Pacific Ocean the Dutch threatened the Spanish Philippines; the 18th cen
Coral bleaching occurs when coral polyps expel algae that live inside their tissues. Coral polyps live in an endosymbiotic relationship with this algae crucial for the health of the coral and the reef; the algae provides up to 90% of the coral's energy. Bleached corals begin to starve after bleaching; some corals recover. Above-average sea water temperatures caused by global warming is the leading cause of coral bleaching. According to the United Nations Environment Programme, between 2014 and 2016 the longest recorded global bleaching events killed coral on an unprecedented scale. In 2016, bleaching of coral on the Great Barrier Reef killed between 29 and 50 percent of the reef's coral. In 2017, the bleaching extended into the central region of the reef; the average interval between bleaching events has halved between 1980 and 2016. The corals that form the great reef ecosystems of tropical seas depend upon a symbiotic relationship with algae-like single-celled flagellate protozoa called zooxanthellae that live within their tissues and give the coral its coloration.
The zooxanthellae provide the coral with nutrients through photosynthesis, a crucial factor in the clear and nutrient-poor tropical waters. In exchange, the coral provide the zooxanthellae with the carbon dioxide and ammonium needed for photosynthesis. Negative environmental conditions thwart the coral's ability to provide for the zooxanthellae's needs. To ensure short-term survival, the coral-polyp expels the zooxanthellae; this leads to a lighter or white appearance, hence the term "bleached". As the zooxanthellae provide up to 90% of the coral's energy needs through products of photosynthesis, after expelling, the coral may begin to starve. Coral can survive short-term disturbances, but if the conditions that lead to the expulsion of the zooxanthellae persist, the coral's chances of survival diminish. In order to recover from bleaching, the zooxanthellae have to re-enter the tissues of the coral polyps and restart photosynthesis to sustain the coral as a whole and the ecosystem that depends on it.
If the coral polyps die of starvation after bleaching, they will decay. The hard coral species will leave behind their calcium carbonate skeletons, which will be taken over by algae blocking coral re-growth; the coral skeletons will erode, causing the reef structure to collapse. Coral bleaching may be caused by a number of factors. While localized triggers lead to localized bleaching, the large scale coral bleaching events of the recent years have been triggered by global warming. Under increased carbon dioxide concentration expected in the 21st century, corals are expected to becoming rare on reef systems. Coral reefs located in warm, shallow water with low water flow have been more affected than reefs located in areas with higher water flow. Increased water temperature, or reduced water temperatures oxygen starvation caused by an increase in zooplankton levels as a result of overfishing increased solar irradiance increased sedimentation bacterial infections changes in salinity herbicides extreme low tide and exposure cyanide fishing elevated sea levels due to global warming mineral dust from African dust storms caused by drought pollutants such as oxybenzone, octyl methoxycinnamate, or enzacamene: four common sunscreen ingredients that are nonbiodegradable and can wash off of skin ocean acidification due to elevated levels of CO2 caused by air pollution being exposed to Oil or other chemical spills Elevated sea water temperatures are the main cause of mass bleaching events.
Sixty major episodes of coral bleaching have occurred between 1979 and 1990, with the associated coral mortality affecting reefs in every part of the world. In 2016, the longest coral bleaching event was recorded; the longest and most destructive coral bleaching event was because of the El Niño that occurred from 2014–2017. During this time, over 70% of the coral reefs around the world have become damaged. Factors that influence the outcome of a bleaching event include stress-resistance which reduces bleaching, tolerance to the absence of zooxanthellae, how new coral grows to replace the dead. Due to the patchy nature of bleaching, local climatic conditions such as shade or a stream of cooler water can reduce bleaching incidence. Coral and zooxanthellae health and genetics influence bleaching. Large coral colonies such as Porites are able to withstand extreme temperature shocks, while fragile branching corals such Acropora are far more susceptible to stress following a temperature change. Corals exposed to low stress levels may be more resistant to bleaching.
Scientists believe that the oldest known bleaching was that of the Late Devonian triggered by the rise of sea surface temperatures. It resulted in the demise of the largest coral reefs in the Earth's history. According to Clive Wilkinson of Global Coral Reef Monitoring Network of Townsville Australia,in 1998 the mass bleaching event occurred the indian ocean region worst affected by it due to rising of temperature of sea by 2℃ to normal temperature level coupled by strong El nino event in 1997-1998. In the 2012–2040 period, coral reefs are expected to experience more frequent bleaching events; the Intergovernmental Panel on Climate Change sees this as the greatest threat to the world's reef systems. Coral reefs worldwide were lost by 19%, 60% of the remaining reefs are at immediate risk of being lost. There are a few ways to tell the impacts of coral bleaching on reefs. First by the coral cover, the more coral, covering the ground the less of an impact bleaching had. Second, coral abundance, whic
The Portugal Current is a weak warm water current that flows south-easterly towards the coast of Portugal. The current results from the movement of water east caused by the North Atlantic Drift. Bischof, Barbie. "The Portugal Current System". Ocean Surface Currents. University of Miami Rosenstiel School of Marine and Atmospheric Science. Retrieved 2008-12-08
The Antilles Current is a variable surface ocean current of warm water that flows northeasterly past the island chain that separates the Caribbean Sea and the Atlantic Ocean. The current results from the flow of the Atlantic North Equatorial Current; this current completes the clockwise- cycle or convection, located in the Atlantic Ocean. It runs north of Puerto Rico and Cuba, but south to the Bahamas, facilitating maritime communication from across the Atlantic into these islands' northern coasts, connecting to the Gulf Stream at the intersection of the Florida Strait; because of its non-dominant pace and rich-nutrient waters, fishermen across the Caribbean Islands use it to fish. It moves parallel to the rich-nutrient Caribbean Current which flows south of Puerto Rico and Cuba, over Colombia and Venezuela. North Equatorial Current Ocean current Oceanic gyres
The Gulf Stream, together with its northern extension the North Atlantic Drift, is a warm and swift Atlantic ocean current that originates in the Gulf of Mexico and stretches to the tip of Florida, follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean. The process of western intensification causes the Gulf Stream to be a northward accelerating current off the east coast of North America. At about 40°0′N 30°0′W, it splits in two, with the northern stream, the North Atlantic Drift, crossing to Northern Europe and the southern stream, the Canary Current, recirculating off West Africa; the Gulf Stream influences the climate of the east coast of North America from Florida to Newfoundland, the west coast of Europe. Although there has been recent debate, there is consensus that the climate of Western Europe and Northern Europe is warmer than it would otherwise be due to the North Atlantic drift, the northeastern section of the Gulf Stream, it is part of the North Atlantic Gyre.
Its presence has led to the development of strong cyclones of all types, both within the atmosphere and within the ocean. The Gulf Stream is a significant potential source of renewable power generation; the Gulf Stream may be slowing down as a result of climate change. The Gulf Stream is 100 kilometres wide and 800 metres to 1,200 metres deep; the current velocity is fastest near the surface, with the maximum speed about 2.5 metres per second. European discovery of the Gulf Stream dates to the 1512 expedition of Juan Ponce de León, after which it became used by Spanish ships sailing from the Caribbean to Spain. A summary of Ponce de León's voyage log, on April 22, 1513, noted, "A current such that, although they had great wind, they could not proceed forward, but backward and it seems that they were proceeding well, its existence was known to Peter Martyr d'Anghiera. Benjamin Franklin became interested in the North Atlantic Ocean circulation patterns. In 1768, while in England, Franklin heard a curious complaint from the Colonial Board of Customs: Why did it take British packets several weeks longer to reach New York from England than it took an average American merchant ship to reach Newport, Rhode Island, despite the merchant ships leaving from London and having to sail down the River Thames and the length of the English Channel before they sailed across the Atlantic, while the packets left from Falmouth in Cornwall?
Franklin asked Timothy Folger, his cousin twice removed, a Nantucket Island whaling captain, for an answer. Folger explained that merchant ships crossed the then-unnamed Gulf Stream—identifying it by whale behavior, measurement of the water's temperature, changes in the water's color—while the mail packet captains ran against it. Franklin had Folger sketch the path of the Gulf Stream on an old chart of the Atlantic and add written notes on how to avoid the Stream when sailing from England to America. Franklin forwarded the chart to Anthony Todd, secretary of the British Post Office. Franklin's Gulf Stream chart was printed in 1769 in London, but it was ignored by British sea captains. A copy of the chart was printed in Paris circa 1770–1773, a third version was published by Franklin in Philadelphia in 1786; the inset in the upper left part of the 1786 chart is an illustration of the migration pattern of herring and not an ocean current. The Gulf Stream proper is a western-intensified current, driven by wind stress.
The North Atlantic Drift, in contrast, is thermohaline circulation–driven. In 1958 the oceanographer Henry Stommel noted that "very little water from the Gulf of Mexico is in the Stream". By carrying warm water northeast across the Atlantic, it makes Western and Northern Europe warmer than it otherwise would be. A river of sea water, called the Atlantic North Equatorial Current, flows westward off the coast of Central Africa; when this current interacts with the northeastern coast of South America, the current forks into two branches. One passes into the Caribbean Sea, while a second, the Antilles Current, flows north and east of the West Indies; these two branches rejoin north of the Straits of Florida. The trade winds blow westward in the tropics, the westerlies blow eastward at mid-latitudes; this wind pattern applies a stress to the subtropical ocean surface with negative curl across the north Atlantic Ocean. The resulting Sverdrup transport is equatorward; because of conservation of potential vorticity caused by the northward-moving winds on the subtropical ridge's western periphery and the increased relative vorticity of northward moving water, transport is balanced by a narrow, accelerating poleward current.
This flows along the western boundary of the ocean basin, outweighing the effects of friction with the western boundary current, is known as the Labrador current. The conservation of potential vorticity causes bends along the Gulf Stream, which break off due to a shift in the Gulf Stream's position, forming separate warm and cold eddies; this overall process, known as western intensification, causes currents on the western boundary of an ocean basin, such as the Gulf Stream, to be stronger than those on the eastern boundary. As a consequence, the resulting Gulf Stream is a strong ocean current, it transports water at a rate of 30 million cubic meters per second through the Florida Straits. As it passes south of Newfoundland, this rate increases to 150 million cubic metres per second; the volume of the Gulf Stream dwarfs all rivers that empty into the Atlantic combined, which total 0.6 million cubic metres per seco
The Humboldt Current called the Peru Current, is a cold, low-salinity ocean current that flows north along the western coast of South America. It is an eastern boundary current flowing in the direction of the equator, extends 500–1,000 km offshore; the Humboldt Current is named after the Prussian naturalist Alexander von Humboldt. In 1846, von Humboldt reported measurements of the cold-water current in his book Cosmos; the current extends from the southern Chile to northern Peru where cold, upwelled waters intersect warm tropical waters to form the Equatorial Front. Sea surface temperatures off the coast of Peru, around 5th parallel south, reach temperatures as low as 16 °C; this is uncharacteristic of tropical waters, as most other regions have temperatures measuring above 25 °C. Upwelling brings nutrients to the surface, which support phytoplankton and increase biological productivity; the Humboldt Current is a productive ecosystem. It is the most productive eastern boundary current system, it accounts for 18-20% of the total worldwide marine fish catch.
The species are pelagic: sardines and jack mackerel. The system's high productivity supports other important fishery resources as well as marine mammals and seabirds. Periodically, the upwelling that drives the system's productivity is disrupted by the El Niño-Southern Oscillation event with large social and economical impacts; the Humboldt has a considerable cooling influence on the climate of Chile and Ecuador. It is largely responsible for the aridity of Atacama Desert in northern Chile and coastal areas of Peru and of the aridity of southern Ecuador. Marine air is cooled by the current and thus; the trade winds are the primary drivers of the Humboldt Current circulation. Variability in this system is driven by latitudinal shifts between the Intertropical Convergent Zone and the trade winds in the north. Shifts within the South Pacific High at mid-latitudes, as well as cyclonic storms and movement of the Southern Westerlies southward contribute to system changes. Atmospheric variability off central Chile is enhanced by the aggravation of coastal low pressure systems trapped between the marine boundary layer and the coastal mountains.
This is prominent poleward from 27th parallel south to 42nd parallel south. The Humboldt current, occupying the upper ocean, flows equatorward carrying fresh, cold Sub-Antarctic surface water northward, along the outskirts of the subtropical gyre; the main flow of the current veers offshore in southern Peru, as a weaker limb continues to flow equatorward. Around 18th parallel south the fresh, cold waters begin to mix with the warm, high salinity Subtropical Surface waters; this collision causes partial subductions. Within this region, the equatorial undercurrent flows eastward along the equator, feeding the Peru-Chile undercurrent that moves poleward. Off the coast of central Chile, there is a coastal transition zone, characterized by high eddy kinetic energy; this energy forms mesoscale eddies. The CTZ has three distinct regions within its boundaries: high chlorophyll-a concentrations in wide regions off the coast of Peru, high chlorophyll-a concentrations in wide regions off the coast of Chile, high chlorophyll-a concentrations in narrow regions off the coast of northern Chile.
High chlorophyll-a concentrations are found within 50 km of the coast. The limb of the HCS that veers off the coast of Peru creates a decrease in ventilation within the system; this lack of ventilation is the primary driver of an intense oxygen minimum zone, formed in the sub-surface to intermediate depths. In the north, the EUC ventilates the OMZ, in the south the PCU advects low oxygen waters southward towards northern Chile; this OMZ is the fourth largest permeant hypoxic zone in the world's oceans. It occupies an area about 2.18 ± 0.66 × 106 km3. The core of this zone is centered off Peru, creating a shallow upper boundary that reaches from about 100 m down to 600 m. Another factor contributing to the OMZ is sinking and decay of primary productive resources; the OMZ forces many organisms to stay near the surface where nutrients and oxygen are obtainable. The presence of a shallow OMZ restricts the migration of zooplankton within the water column. Between 0 and 600 m, many species of zooplankton occupy this space within the OMZ.
This allows for a substantial exchange of carbon between the euphotic layer and the OMZ. 75% of the total zooplankton biomass move in and out of the OMZ. The OMZ serves as a refuge for organisms that can live in hypoxic conditions. Coastal upwelling is the main factor contributing to the high biological productivity of the Humboldt current. Upwelling within the current is not uniform across the entire system. Three notable upwelling subsystems are produced by this current: seasonal upwelling in Chile only during the spring and summer, because of the displacement of the subtropical center of high pressure during the period January–March, upwelling "shadow", less productive, but still large in northern Chile and Southern Peru, productive year-round upwelling in Peru; the upwelling shadow identified between 35°S and 15°S is caused by the oligotrophic subtropical gyre impinging on the coast. This creates a narrow, but productive, upwelling zone. Due to the upwelling zones within the Humboldt current, biological diversity is high.
The Humboldt Current is considered a Class I productive (>300 gC/
The Walker circulation known as the Walker cell, is a conceptual model of the air flow in the tropics in the lower atmosphere. According to this model, parcels of air follow a closed circulation in the zonal and vertical directions; this circulation, consistent with observations, is caused by differences in heat distribution between ocean and land. It was discovered by Gilbert Walker. In addition to motions in the zonal and vertical direction the tropical atmosphere has considerable motion in the meridional direction as part of, for example, the Hadley Circulation; the term "Walker circulation" was coined in 1969 by the Norwegian-American meteorologist Jacob Bjerknes. Gilbert Walker was an established applied mathematician at the University of Cambridge when he became director-general of observatories in India in 1904. While there, he studied the characteristics of the Indian Ocean monsoon, the failure of whose rains had brought severe famine to the country in 1899. Analyzing vast amounts of weather data from India and the rest of the world, over the next fifteen years he published the first descriptions of the great seesaw oscillation of atmospheric pressure between the Indian and Pacific Ocean, its correlation to temperature and rainfall patterns across much of the Earth's tropical regions, including India.
He worked with the Indian Meteorological Department in linking the monsoon with Southern Oscillation phenomenon. He was made a Companion of the Order of the Star of India in 1911. Walker determined that the time scale of a year was unsuitable because geospatial relationships could be different depending on the season. Thus, Walker broke his temporal analysis into December–February, March–May, June–August, September–November. Walker selected a number of "centers of action", which included areas such as the Indian Peninsula; the centers were in the hearts of regions with low pressures. He added points for regions where rainfall, wind or temperature was an important control, he examined the relationships of the summer and winter values of pressure and rainfall, first focusing on summer and winter values, extending his work to the spring and autumn. He concludes that variations in temperature are governed by variations in pressure and rainfall, it had been suggested that sunspots could be the cause of the temperature variations, but Walker argued against this conclusion by showing monthly correlations of sunspots with temperature, cloud cover, rain that were inconsistent.
Walker made it a point to publish all of his correlation findings, both of relationships found to be important as well as relationships that were found to be unimportant. He did this for the purpose of dissuading researchers from focusing on correlations that did not exist; the Walker Circulations of the tropical Indian and Atlantic basins result in westerly surface winds in Northern Summer in the first basin and easterly winds in the second and third basins. As a result, the temperature structure of the three oceans display dramatic asymmetries; the equatorial Pacific and Atlantic both have cool surface temperatures in Northern Summer in the east, while cooler surface temperatures prevail only in the western Indian Ocean. These changes in surface temperature reflect changes in the depth of the thermocline. Changes in the Walker Circulation with time occur in conjunction with changes in surface temperature; some of these changes are forced externally, such as the seasonal shift of the Sun into the Northern Hemisphere in summer.
Other changes appear to be the result of coupled ocean-atmosphere feedback in which, for example, easterly winds cause the sea surface temperature to fall in the east, enhancing the zonal heat contrast and hence intensifying easterly winds across the basin. These enhanced easterlies induce more equatorial upwelling and raise the thermocline in the east, amplifying the initial cooling by the southerlies; this coupled ocean-atmosphere feedback was proposed by Bjerknes. From an oceanographic point of view, the equatorial cold tongue is caused by easterly winds. Were the earth climate symmetric about the equator, cross-equatorial wind would vanish, the cold tongue would be much weaker and have a different zonal structure than is observed today; the Walker cell is indirectly related to upwelling off the coasts of Ecuador. This brings nutrient-rich cold water to increasing fishing stocks; the Walker circulation is caused by the pressure gradient force that results from a high pressure system over the eastern Pacific Ocean, a low pressure system over Indonesia.
When the Walker circulation weakens or reverses, an El Niño results, causing the ocean surface to be warmer than average, as upwelling of cold water occurs less or not at all. An strong Walker circulation causes a La Niña, resulting in cooler ocean temperatures due to increased upwelling. A scientific study published in May 2006 in the journal Nature indicates that the Walker circulation has been slowing since the mid-19th Century; the authors argue that global warming is a causative factor in the weakening of the wind pattern. However, a new study from The Twentieth Century Reanalysis Project shows that the Walker circulation has not been slowing from 1871–2008. Atmospheric circulation Earth's atmosphere Walker Institute, University of Reading, UK. http://www.walker-institute.ac.uk/about/sir_gilbert.htm Walker, JM. Pen Portrait of Sir Gilbert Walker, CSI, MA, ScD, FRS. Weather 1997 Walker, G. T. and Bliss, E. W. 1930. World Weather IV, Memoirs of the Royal Meteorological Society, 3, 81–95. Walker, G.