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, located between the equator and 50° N latitude, and comprising 20 million square kilometers.[1] The gyre has a clockwise circular pattern and is formed by four prevailing ocean currents: the North Pacific Current to the north, the California Current to the east, the North Equatorial Current to the south, and the Kuroshio Current to the west. It is the site of an unusually intense collection of man-made marine debris, known as the Great Pacific Garbage Patch.

The North Pacific Subtropical Gyre and the much smaller North Pacific Subpolar Gyre make up the two major gyre systems in the mid-latitudes of the Northern Pacific Ocean. This two-gyre circulation in the North Pacific is driven by the trade and westerly winds.[2] This is one of the best examples of all of Earth’s oceans where these winds drive a two-gyre circulation. Physical characteristics like weak thermohaline circulation in the North Pacific and it is mostly blocked by land in the north, also help facilitate this circulation. As depth increases, these gyres in the North Pacific grow smaller and weaker, and the high pressure at the center of the Subtropical Gyre will migrate poleward and westward.[2]

North Pacific Subtropical Convergence Zone
Significant ocean currents involved in the circulation of the North Pacific Subtropical and Subpolar gyres

Physical oceanography

Subtropical circulation in the North Pacific

Like all subtropical gyre systems, the North Pacific Subtropical Gyre is an anticyclone meaning the circulation is in a clockwise direction around its high pressure at the center because of its placement in the Northern Hemisphere. This circulation is also associated with equatorward Sverdrup transport and Ekman downwelling.[2] Ekman transport causes water to flow toward the center of the gyre, creating a sloped sea-surface, and initiating geostrophic flow. Harald Sverdrup applied Ekman transport while including pressure gradient forces to develop a theory for Sverdrup transport.[3]

The Kuroshio Current is the narrow, strong westward boundary current of the subtropical circulation. This current influences the water column all the way to the bottom. The Kuroshio current flows in a northerly direction, then eventually flows further from the westward boundary where it then takes an eastward direction into the North Pacific. This eastward flowing current is then called the Kuroshio Extension. The North Pacific Current is located just north of the Subtropical Gyre and flows in an easterly direction. Also, known as the West Wind Drift or the Subarctic Current, the North Pacific Current also includes the westward flow of the southern boundary of the North Pacific Subpolar Gyre.[4] The North Equatorial Current borders the North Pacific Subtropical Gyre on the south and flows in a westerly direction. The westward flow within the elongated tropical cyclonic circulation is also included in the North Equatorial current. The California Current System comprises the eastern boundary of the North Pacific Subtropical Gyre and flows south along the coast of California. Here coastal upwelling drives the eastern boundary current and an undercurrent that flows poleward.

In the western region of the North Pacific, the surface of the Subtropical Gyre generally has a "C-shape".[5][6] The Kuroshio current and Kuroshio Extension roughly from the outside of this "C-shape" where it then turns westwards into recirculation, where it then flows south parallel to the Kuroshio Current. From here the "C-shape" then flows eastward comprising the Subtropical Countercurrent at roughly 20 – 25⁰N, then finally the "C" wraps back towards the west forming the North Equatorial Current just south of 20⁰N. It is common for subtropical gyres to have this "C-shape" surface flow. The Subtropical Countercurrent is a shallow area of this "C"; at only about 250 dbar under the surface, circulation is a simpler closed, anticyclonic gyre.

Narrow east-west frontal zones that cross the Pacific are less than 100  km wide. The Subarctic Frontal Zone or Subarctic Boundary, about 42⁰N, is fixed in the North Pacific Current.[2] The Subarctic Frontal Zone, slightly south of the maximum westerly wind speeds, separates the North Pacific Subpolar Gyre from the Subtropical Gyre. In the central and eastern Pacific at roughly 32⁰N is the Subtropical Frontal Zone. Sometimes referred to as the Subtropical Convergence Zone, this frontal zone serves as the boundary between the west flowing North Equatorial Current from the North Pacific Current.[2] With increasing depth in the North Pacific Subtropical Gyre, it gets smaller in the western region near Japan and it also loses strength. The Subtropical Gyre does not exist below 1500 m below the surface with the exception of the Kuroshio Current and Extension regions.

Circulation dependence on depth

The North Pacific Subtropical Gyre diminishes spatially with increasing depth. Similar to all subtropical gyre systems, the North Pacific Subtropical Gyre shrinks towards its most energetic surface flows, in a northwestern direction between the Kuroshio Current and the Kuroshio Extension. This is drastic shrinkage from the surface to about 200 m below.[7] At the surface, the boundary that separates the westward and eastward flows from south of 20⁰N to about 25 – 30⁰N at 200 m. The "C-shape" in the western region of the Subtropical Gyre, including the Subtropical Countercurrent, generally does not exist below 200 m. At about 1000 – 1500 m, the Subtropical Gyre is located entirely in the western region of the North Pacific near the Kuroshio Current and Kuroshio Extension.[7] In the subtropical regions, flow is weak where influences from the Subtropical Gyre are minimal. Differences in steric heights over distances of 1000  km are on the order of 1  cm, rather than the differences of 10  cm within the area of the North Pacific Subtropical Gyre.

See also

References

  1. ^ Karl, David M. (1999). "A Sea of Change: Biogeochemical Variability in the North Pacific Subtropical Gyre". Ecosystems. Springer. 2: 181–214. doi:10.1007/s100219900068. JSTOR 3658829.
  2. ^ a b c d e Talley, Lynne D.; Pickard, George L.; Emery, William J.; Swift, James H. (2011). Descriptive Physical Oceanography: An Introduction. London, UK: Academic Press. ISBN 0750645520.
  3. ^ Pond, S.; Pickard, G. L. (1983). Introductory Dynamical Oceanography. Pergamon Press. ISBN 978-0-08-028728-7.
  4. ^ Sverdrup, H. U.; Johnson; Fleming, R. H. (1942). The Oceans: Their Physics, Chemistry, and General Biology. New York: Prentice-Hall. pp. M. W.
  5. ^ Wyrki, K. (1975). "Fluctuations of the Dynamic Topography of the Pacific Ocean". Journal of Physical Oceanography. 5 (3): 450–459. doi:10.1175/1520-0485(1975)005<0450:fotdti>2.0.co;2.
  6. ^ Hasunuma, K.; Yoshida, K. (1978). "Splitting of the subtropical gyre in the western North Pacific". Journal of Oceanography. 34 (4): 160–172. doi:10.1007/bf02108654.
  7. ^ a b Reid, J. L. (1997). "On the Total Geostrophic Circulation of the Pacific Ocean: Flow Patterns, Tracers, and Transports". Progress in Oceanography. 39 (4): 263–352. Bibcode:1997PrOce..39..263R. doi:10.1016/s0079-6611(97)00012-8.

External links

California Current

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 also one of five major coastal currents affiliated with strong upwelling zones, the others being the Humboldt Current, the Canary Current, the Benguela Current, and 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.

Charles J. Moore

Charles J. Moore is an oceanographer and boat captain known for articles that recently brought attention to the 'Great Pacific Garbage Patch', an area of the Pacific Ocean strewn with floating plastic debris which is three times the size of Texas.

Davidson Current

In oceanography, the Davidson Current is a coastal countercurrent of the Pacific Ocean running north along the western coast of the United States from Baja California, Mexico to northern Oregon, ending at about latitude 48°N.Its flow is adjacent to the California Current, but it flows north rather than south and hugs the coastline. The current is active year-round at 650 feet (200 meters) below sea level, but surfaces during the winter months, generally from mid-November through mid-February. In these months, northerly winds weaken and are replaced to some extent by southwesterly winds.

Ecosystem of the North Pacific Subtropical Gyre

The North Pacific Subtropical Gyre (NPSG) is the largest contiguous ecosystem on earth. In oceanography, a subtropical gyre is a ring-like system of ocean currents rotating clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere caused by the Coriolis Effect. They generally form in large open ocean areas that lie between land masses.

The NPSG is the largest of the gyres as well as the largest ecosystem on our planet. Like other subtropical gyres, it has a high-pressure zone in its center. Circulation around the center is clockwise around this high-pressure zone. Subtropical gyres make up 40% of the Earth’s surface and play critical roles in carbon fixation and nutrient cycling. This particular gyre covers most of the Pacific Ocean and comprises four prevailing ocean currents: the North Pacific Current to the north, the California Current to the east, the North Equatorial Current to the south, and the Kuroshio Current to the west. Its large size and distance from shore has caused the NPSG to be poorly sampled and thus poorly understood.

The life processes in open-ocean ecosystems are a sink for the atmosphere’s increasing CO2. Gyres make up a large proportion, approximately 75%, of what we refer to as the open ocean, or the area of the ocean that does not consist of coastal areas. They are considered oligotrophic, or nutrient poor because they are far from terrestrial runoff. These regions were once thought to be homogenous and static habitats. However, there is increasing evidence that the NPSG exhibits substantial physical, chemical, and biological variability on a variety of time scales. Specifically, the NPSG exhibits seasonal and interannual variations in primary productivity (simply defined as the production of new plant material), which is important for the uptake of CO2.

The NPSG is not only a sink for CO2 in the atmosphere, but also other pollutants. As a direct result of this circular pattern, gyres act like giant whirlpools and become traps for anthropogenic pollutants, such as marine debris. The NPSG has become recognized for the large quantity of plastic debris floating just below the surface in the center of the gyre. This area has recently received a lot of media attention and is commonly referred to as the Great Pacific Garbage Patch.

Great Pacific garbage patch

The Great Pacific garbage patch, also described as the Pacific trash vortex, is a gyre of marine debris particles in the north central Pacific Ocean. It is located roughly from 135°W to 155°W and 35°N to 42°N. The collection of plastic and floating trash originates from the Pacific Rim, including countries in Asia, North America, and South America. The patch is actually "two enormous masses of ever-growing garbage." What has been referred to as the "Eastern Garbage Patch" lies between Hawaii and California, while the "Western Garbage Patch" extends eastward from Japan to the Hawaiian Islands. An ocean current about 6,000 miles long, referred to as the Subtropical Convergence Zone, connects both of the patches, which extend over an indeterminate area of widely varying range, depending on the degree of plastic concentration used to define the affected area. The vortex is characterized by exceptionally high relative pelagic concentrations of plastic, chemical sludge, wood pulp, and other debris trapped by the currents of the North Pacific Gyre.Despite the common public perception of the patch existing as giant islands of floating rubbish, its low density (4 particles per cubic meter) prevents detection by satellite imagery, or even by casual boaters or divers in the area. This is because the patch is a widely dispersed area consisting primarily of suspended "fingernail-sized or smaller bits of plastic," often microscopic, particles in the upper water column. Researchers from The Ocean Cleanup project claimed that the patch covers 1.6 million square kilometers. The plastic concentration is estimated to be up to 100 kilograms per square kilometer in the center, going down to 10 kilograms per square kilometer in the outer parts of the patch. An estimated 80,000 metric tons of plastic inhabit the patch, totaling 1.8 trillion pieces. 92% of the mass in the patch comes from objects larger than 0.5 centimeters, while 94% of the total objects are represented by microplastics.Some of the plastic in the patch has been found to be over 50 years old, and includes fragments of and items such as "plastic lighters, toothbrushes, water bottles, pens, baby bottles, cell phones, plastic bags, and nurdles." It is estimated that approximately "100 million tons of plastic are generated [globally] each year," and about ten percent of that plastic ends up in the oceans. The United Nations Environmental Program recently estimated that "for every square mile of ocean," there are about "46,000 pieces of plastic." The small fibers of wood pulp found throughout the patch are "believed to originate from the thousands of tons of toilet paper flushed into the oceans daily." The patch is believed to have increased "10-fold each decade" since 1945.Research indicates that the patch is rapidly accumulating. A similar patch of floating plastic debris is found in the Atlantic Ocean, called the North Atlantic garbage patch.

Hansa Carrier

The Hansa Carrier is a container ship. On 27 May 1990, en route from Korea to the United States, the ship encountered a storm which caused the loss of 21 40-foot cargo containers south of the Alaska Peninsula, near 48°N 161°W. Five of these cargo containers contained 61,000 Nike shoes, each of which carried a unique serial number which later made it possible to clearly identify them as part of the spilled cargo.

Indian Ocean garbage patch

The Indian Ocean garbage patch, discovered in 2010, is a gyre of marine litter suspended in the upper water column of the central Indian Ocean, specifically the Indian Ocean Gyre, one of the five major oceanic gyres. The patch does not appear as a continuous debris field. As with other patches in each of the five oceanic gyres, the plastics in it break down to ever smaller particles, and to constituent polymers. As with the other patches, the field constitutes an elevated level of pelagic plastics, chemical sludge, and other debris; primarily particles that are invisible to the naked eye. The concentration of particle debris has been estimated to be approximately 10,000 particles per square kilometer.A similar patch of floating plastic debris in the Pacific Ocean, the Great Pacific garbage patch, was predicted in 1985, and discovered in 1997 by Charles J. Moore as he passed through the North Pacific Gyre on his return from the Transpacific Yacht Race. The North Atlantic garbage patch was discovered in 2010.

Junk raft

A junk raft is a type of home-built watercraft made of plastic bottles or other recycled materials constructed by artists and community-minded groups organizing recreational flotillas, or by environmentally concerned individuals seeking to draw attention to the problem of floating debris and the need for recycling. It can also be an improvised small, functional watercraft from readily available materials.

North Atlantic Gyre

The North Atlantic Gyre, located in the Atlantic Ocean, is one of the five major oceanic gyres. It is a circular system of ocean currents that stretches across the North Atlantic from near the equator almost to Iceland, and from the east coast of North America to the west coasts of Europe and Africa.

The currents that compose the North Atlantic Gyre include the Gulf Stream in the west, the North Atlantic Current in the north, the Canary Current in the east, and the Atlantic North Equatorial Current in the south. This gyre is particularly important for the central role it plays in the thermohaline circulation, bringing salty water west from the Mediterranean Sea and then north to form the North Atlantic Deep Water.

The North Atlantic Gyre traps man-made marine debris in the North Atlantic Garbage Patch, similar to how the North Pacific Gyre traps debris in the Great Pacific Garbage Patch.The North Atlantic Gyre forms the Sargasso Sea, noted for its still waters and dense seaweed accumulations.

North Pacific Oscillation

The North Pacific Oscillation (NPO) is a teleconnection pattern first described by Walker and Bliss and characterized by a north-south seesaw in sea level pressure over the North Pacific.

Rogers, using surface atmospheric temperature from St. Paul, Alaska, and Edmonton, identified two phases of the NPO, an Aleutian below (AB) phase that correspond to a deepened and eastward shifted Aleutian low and an Aleutian above (AA) phase that is the opposite.During the positive (AB) phase sea level pressure is enhanced over a large region in the subtropics that extend poleward to 40N° and reduced at higher latitudes, westerlies are enhanced over the central Pacific and winter temperature are mild along much of the North America west coast but cooler than usual over Eastern Siberia and the United States South-West, precipitations are higher than usual over Alaska and the Great Plains.

The NPGO is the oceanic expression of the NPO.

Ocean gyre

In oceanography, a gyre () is any large system of circulating ocean currents, particularly those involved with large wind movements. Gyres are caused by the Coriolis effect; planetary vorticity along with horizontal and vertical friction, determine the circulation patterns from the wind stress curl (torque).The term gyre can be used to refer to any type of vortex in the air or the sea, even one that is man-made, but it is most commonly used in oceanography to refer to the major ocean systems.

Pacific decadal oscillation

The Pacific Decadal Oscillation (PDO) is a robust, recurring pattern of ocean-atmosphere climate variability centered over the mid-latitude Pacific basin. The PDO is detected as warm or cool surface waters in the Pacific Ocean, north of 20°N. Over the past century, the amplitude of this climate pattern has varied irregularly at interannual-to-interdecadal time scales (meaning time periods of a few years to as much as time periods of multiple decades). There is evidence of reversals in the prevailing polarity (meaning changes in cool surface waters versus warm surface waters within the region) of the oscillation occurring around 1925, 1947, and 1977; the last two reversals corresponded with dramatic shifts in salmon production regimes in the North Pacific Ocean. This climate pattern also affects coastal sea and continental surface air temperatures from Alaska to California.

During a "warm", or "positive", phase, the west Pacific becomes cooler and part of the eastern ocean warms; during a "cool" or "negative" phase, the opposite pattern occurs. The Pacific Decadal Oscillation was named by Steven R. Hare, who noticed it while studying salmon production pattern results in 1997.The Pacific Decadal Oscillation index is the leading empirical orthogonal function (EOF) of monthly sea surface temperature anomalies (SST-A) over the North Pacific (poleward of 20°N) after the global average sea surface temperature has been removed. This PDO index is the standardized principal component time series. A PDO 'signal' has been reconstructed as far back as 1661 through tree-ring chronologies in the Baja California area.

Plastic soup

Plastic soup is a term referring to pollution of the sea by plastics in general, ranging from large pieces of fishing gear that can entrap marine animals to the microplastics and nanoplastics that result from the breakdown or photodegradation of plastic waste in surface waters, rivers or oceans.

The term was coined by Charles J. Moore in 1997, after he found patches of plastic pollution in the North Pacific Gyre between Hawaii and California. This Great Pacific Garbage Patch had previously been described in 1988 by scientists who used the term neuston plastic to describe "The size fraction of plastic debris caught in nets designed to catch surface plankton (hereafter referred to as neuston plastic)", and acknowledged that earlier studies in the 1970s had shown that "neuston plastic is widespread, is most abundant in the central and western North Pacific, and is distributed by currents and winds".The term is sometimes used to refer only to pollution by microplastics, pieces of plastic less than 5mm in size such as fibres shed from synthetic textiles in laundry: the British National Federation of Women's Institutes passed a resolution in 2017 headlined "End Plastic Soup" but concentrating on this aspect of pollution.The Amsterdam-based Plastic Soup Foundation is an advocacy group which aims to raise awareness of the problem, educate people, and support the development of solutions.As of January 2019 the Oxford English Dictionary did not include the terms plastic soup, neuston plastic or neustonic plastic, but it defined the term microplastic (or micro-plastic) as "Extremely small pieces of plastic, manufactured as such (in the form of nurdles or microbeads) or resulting from the disposal and breakdown of plastic products and waste" and its illustrative quotations all relate to marine pollution, the earliest being a 1990 reference in the South African Journal of Science: "The mean frequency of micro-plastic particles increased from 491 m-1 of beach in 1984 to 678 m-1 in 1989".

Project Kaisei

Project Kaisei (from 海星, kaisei, "ocean planet" in Japanese) is a scientific and commercial mission to study and clean up the Great Pacific Garbage Patch, a large body of floating debris trapped in the Pacific Ocean by the currents of the North Pacific Gyre. Discovered by NOAA, the patch is estimated to contain 20 times the density of floating debris compared to the global average. The project aims to study the extent and nature of the debris with a view to capturing, detoxifying, and recycling the material, and is organised by the Ocean Voyages Institute, a California-based 501c3 non-profit organisation dealing with marine preservation. The project is based in San Francisco and Hong Kong.

Take 3

Take 3 - A Clean Beach Initiative is a non-profit organisation based on the Central Coast of New South Wales, Australia. It was formed in 2009 by Tim Silverwood, a surfer, environmentalist and filmmaker, Amanda Marechal, and marine ecologist Roberta Dixon-Valk.Take 3 raises awareness of marine debris, especially plastic, and encourages individuals to take 3 pieces of rubbish before leaving the beach, places near waterways or coastal areas.In 2011, Take 3 won the Taronga Green Grant: $50,000 offered by the Taronga Foundation from Taronga Zoo.

In July 2011, co-founder Silverwood went on a research expedition to document the Great Pacific Garbage Patch, also known as North Pacific Gyre or Pacific Trash Vortex.

The Ocean Cleanup

The Ocean Cleanup is non-government engineering environmental organization based in Netherlands, that develops technology to extract plastic pollution from the oceans. After a couple of years of various tests they deployed their first full scale prototype. It ran into difficulty after two months and was towed to Hawaii for inspection and repair. In June 2019 their second prototype system was deployed.

The organization conducts scientific research into oceanic plastic pollution. It was founded in 2013 by Boyan Slat, a Dutch-born inventor-entrepreneur of Croatian origin who serves as its CEO. It has conducted two expeditions to the North Pacific Gyre, and published scientific papers. The clean-up approach uses barriers in ocean gyres to scoop up marine debris as the barrier is pushed by wind and current. The project aims to launch a total of 60 such systems in the patch by 2021. They predict this capability could clean up 50% of the debris in the Great Pacific Garbage Patch in five years.

Warming's lantern fish

Warming's lantern fish, Ceratoscopelus warmingii, is a lanternfish of the family Myctophidae, found circumglobally in both hemispheres, at depths of between 700 and 1,500 m (2,300 and 4,900 ft) during the day and between 20 and 200 m (70 and 660 ft) at night. Its length is about 8 cm (3.15 in).

Yellow Thing

The Yellow Thing is a double-hulled floating vessel (like a catamaran), used by Greenpeace to sample marine debris. As of 2006, its primary mission is to be used as a trawl for plastic samples in areas such as the Mediterranean Sea and the North Pacific Gyre. It is not self-powered, rather it is towed via a ship-attached boom (as of 3-2006, it was being used on the MV Esperanza). It is also considered to be relatively stable as a marine vehicle.

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