Upwelling is an oceanographic phenomenon that involves the movement of dense, cooler, and usually nutrient-rich water to the surface of the ocean, replacing the warmer surface water, usually the nutrient deficiency. Nutrient-rich upwelled water stimulates the growth and reproduction of primary producers such as phytoplankton. Due to the biomass of phytoplankton and the presence of cold water in this region, the upwelling zone can be identified by cold sea surface temperature (SST) and high chlorophyll-a concentrations.
Increased availability of nutrients in upwelling areas produces high primary production rates and thus fisheries production. Approximately 25% of total global marine fish catch comes from five upwellings which occupy only 5% of the total ocean area. Upwelling is driven by coastal currents or diverging open ocean has the greatest impact on waters rich in nutrients and global fishery products.
Video Upwelling
Mekanisme
The three main drivers that work together to cause upwelling are wind, Coriolis effects, and Ekman transport. They operate differently for different types of upwelling, but the effects are generally the same. In the overall upwelling process, the wind blows across the sea surface in a certain direction, which causes a water-wind interaction. As a result of wind, water is transported clean from 90 degrees from the wind direction due to Coriolis forces and Ekman transport. Ekman's transport causes the surface layer to move about 45 degrees from the wind direction, and the friction between the layer and the layer below causes the successive layers to move in the same direction. This produces a spiral motion of water down the water column. Then, Coriolis forces dictate to where the water will move; in the Northern Hemisphere, water is transported to the right from the wind direction. In the southern hemisphere, water is transported to the left of the wind. If the net movement of this water is different, then upwelling the inner water occurs to replace the lost water.
Maps Upwelling
Type
The major marine environment is related to the difference in currents that carry deeper, colder, nutrient-rich waters to the surface. There are at least five types of upwelling: coastal upwelling, wind-driven large scale in the interior of the ocean, upwelling associated with vortex, upwelling associated with topography, and upwelling that diffuse widely in the interior of the ocean.
Coastal
The upwelling coast is the most recognizable upwelling type, and is most closely related to human activity as it supports some of the world's most productive fisheries. The wind-driven currents are diverted to the right wind in the northern hemisphere and to the left in the southern hemisphere due to the coriolis effect. The result is a clean movement of surface water at right angles to the wind, known as Ekman's transport (See also Ekman Spiral). When Ekman's transport takes place away from the shore, surface water moves away replaced by deeper, colder, and denser water. Typically, this upwelling process occurs at a rate of about 5-10 meters per day, but the level and proximity of upwelling to the coast may change due to the strength and distance of the wind.
Water is rich in nutrients, including nitrate, phosphate and silicic acid, itself the decomposition of drowning organic matter (dead/detrital plankton) from surface water. When brought to the surface, these nutrients are utilized by phytoplankton, along with dissolved CO 2 (carbon dioxide) and light energy from the sun, to produce organic compounds, through photosynthesis. Therefore, upwelling areas produce very high primary production rates (the amount of carbon assigned by phytoplankton) compared to other regions in the oceans. They account for about 50% of global marine productivity. High primary production spreads to the food chain because phytoplankton is at the base of the ocean food chain.
The food chain follows the path:
- Phytoplankton -> Zooplankton -> Zooplankton predator -> Filter feeders -> Fish predators -> Seabirds, marine mammals
Worldwide, there are five main coastal streams associated with upwelling areas: the Canary Stream (off Northwest Africa), the Benguela (off South Africa) Flows, the Flow of California (off California and Oregon), Humboldt Flows (Peru and Chile) and the Somali Current (off Somalia and Oman). All these currents support large fisheries. The four main eastern border currents where coastal upwelling occurs mainly are the Canary Flow, the Benguela Flow, the Flow of California, and the Humboldt Flow. The Benguela Current is the eastern boundary of the South Atlantic subtropical gyre and can be divided into northern and southern sub-systems with upwelling occurring in both areas. Subsystem is divided by the permanent upwelling area of ​​Luderitz, which is the strongest upwelling zone in the world. The California Current System (CCS) is the eastern border of the North Pacific which is also characterized by a split north and south. The split in this system takes place in Point Conception, California due to the weak upwelling in the South and strong upwelling in the north. The Canary Current is the eastern boundary of the North Atlantic and is also separated due to the presence of the Canary Islands. Finally, the Humboldt Flow or Peruvian Flow flows west along the coast of South America from Peru to Chile and extends up to 1,000 kilometers offshore. These four eastern border currents comprise the majority of coastal upwelling zones in the oceans.
Equatorial
Upwelling at the equator is related to the actual Intertropical Convergence Zone (ITCZ), and consequently, often located north or south of the equator. Easter (western) trade winds blowing from the Northeast and Southeast and gathered along the equator blowing west to form the ITCZ. Although no Coriolis forces are present along the equator, upwelling still occurs in the north and south of the equator. This results in a difference, with denser, nutrient-rich water being brought up from below, and yields the remarkable fact that the equatorial region of the Pacific can be detected from space as a broad line of high phytoplankton concentrations.
Southern Ocean
Large scale upwelling is also found in the Southern Ocean. Here, a strong western wind (toward the east) is blowing around Antarctica, prompting a significant flow of water to the north. This is actually a coastal upwelling type. Since there is no continent in the open latitudes between South America and the tip of the Antarctic Peninsula, some of this water is taken from a very deep depth. In many numerical models and observational syntheses, Southern Ocean upwelling is the primary means by which solid, deep water is brought to the surface. In some areas of Antarctica, the current-carrying wind near the coast draws relatively warm warm circumpolar water to the continental shelf, where it can increase the melting of the ice and affect the stability of the ice sheet. Shallower, wind-driven upwelling is also found off the west coast of North and South America, northwest and southwest Africa, and southwest and south Australia, all associated with a subtropical high-pressure ocean circulation (see upwelling beach above).
Some marine circulation models show that widespread upwelling occurs in the tropics, since the pressure-driven flow converges water toward the low latitudes where it diffuses hotly from above. The required diffusion coefficients, however, appear to be larger than those observed in the real ocean. Nonetheless, some diffusive upwelling may occur.
Other sources
- Local and interwelling upwellings can occur when offshore, mountain, or seawater islands cause deep current deflection, providing nutrient-rich areas in low-productivity marine areas. Examples include upwelling around the Galapagos Islands and the Seychelles Islands, which have large pelagic fisheries. Upwelling can also occur when a tropical cyclone crosses an area, usually when moving at a speed of less than 5 mph (8 km/h). The cyclone turns finally draws colder water from the underwater layer. This causes the cyclone to weaken.
- Artificial upwelling is produced by devices that use ocean wave energy or ocean thermal energy conversion to pump water to the surface. Marine wind turbines are also known to produce upwellings. Sea wave devices have been shown to produce plankton flowers.
Variations
The intensity of upwelling depends on the strength of the wind and the seasonal variability, as well as the vertical structure of the water, the variation of the lower bathymetry, and the instability in the currents.
In some areas, upwelling is a seasonal event that causes periodic productivity booms similar to spring blooms in coastal waters. Wind-induced upwelling is produced by a temperature difference between warm, mild air above ground and colder air that is denser over the ocean. In temperate latitudes, temperature contrasts vary widely, creating strong upwelling periods in spring and summer, to weak or no upwelling in winter. For example, off the Oregon coast, there are four or five powerful upwelling events that are separated by periods of little or no upwelling over six months of upwelling. In contrast, tropical latitudes have a more constant temperature contrast, creating a constant upwelling throughout the year. Peruvian floods, for example, occur throughout most of the year, producing one of the largest marine fisheries in the world for sardines and anchovies.
In years of anomalies when trade winds weakened or retreated, water liberated was much warmer and lower in nutrients, resulting in a sharp decline in biomass and phytoplankton productivity. This event is known as the El Nino-Southern Oscillation (ENSO) event. The upwelling system of Peru is highly vulnerable to ENSO events, and can cause extreme interannual variability in productivity.
Bathymetry changes can affect the strength of upwelling. For example, the back of a submarine that extends out of the coast will result in more favorable upwelling conditions than neighboring areas. Upwelling usually begins on the ridge and remains strong on the ridge even after expanding at other locations.
High productivity
Since upwelling areas are an important source of marine productivity, and they attract hundreds of species across trophic levels, the diversity of these systems has been a focal point of marine research. While studying the level and pattern of typical upwelling trophic areas, researchers have found that the upwelling system shows a waist-waist-wealth pattern. In this type of pattern, high and low trophic levels are well represented by high species diversity. However, intermediate trophic levels are represented only by one or two species. This trophic layer, which consists of small fish, pelagic fish is usually only about three to four percent of the species diversity of all existing fish species. The lower trophic layer is well represented with about 500 species of copepods, 2,500 types of gastropods, and 2,500 species of average crustaceans. At the peak and near-trophic levels, there are usually about 100 species of marine mammals and about 50 species of seabirds. However, important intermediary trophic species are small pelagic fish that usually eat phytoplankton. In most upwelling systems, the species is either anchovy or sardine, and usually only one is present, although two or three species may be present occasionally. This fish is an important food source for predators, such as large pelagic fish, marine mammals, and seabirds. Although they are not at the bottom of the trophic pyramid, they are a vital species that connects the entire marine ecosystem and keeps the productivity of the upwelling zones so high.
Threats to the towering ecosystem
A major threat to both these important secondary trophic levels and the entire upwelling tropical ecosystem is the problem of commercial fishing. Because the upwelling areas are the most productive and species rich regions in the world, they attract large numbers of commercial fishermen and fisheries. On the one hand, this is another benefit of the upwelling process as it serves as a source of food and income worthy of so many people and nations besides marine animals. However, just as in any ecosystem, the consequences of overfishing of a population can be detrimental to the population and the ecosystem as a whole. In upwelling ecosystems, each species plays an important role in the functioning of the ecosystem. If one species is significantly reduced, it will have an effect across the rest of the trophic level. For example, if a popular prey species is targeted by fisheries, fishermen can collect hundreds of thousands of individuals of this species simply by inserting their net into upwelling waters. When the fish is depleted, the food source for those who prey on the fish is depleted. Therefore, targeted fish predators will start to die, and there will not be many of them to feed predators above them. This system continues throughout the food chain, resulting in the possibility of ecosystem destruction. It is possible that ecosystems can be recovered from time to time, but not all species can recover from such events. Even if species can adapt, there may be a delay in this upwelling community reconstruction.
The possibility of such ecosystem collapse is the danger of fisheries in upwelling areas. Fisheries can target different species, and therefore they are a direct threat to many species in the ecosystem, but they pose the highest threat to medium pelagic fish. Because these fish form the core of the entire tropical process of upwelling ecosystems, they are highly represented throughout the ecosystem (even if there is only one species present). Unfortunately, these fish tend to be the most popular fishery targets because about 64 percent of all their catch consists of pelagic fish. Among them, the six major species that typically form the middle trophic layer represent more than half the catch.
In addition to directly causing ecosystem collapse due to the absence of ecosystems, this can create problems in ecosystems through various other methods as well. The higher animals at the trophic level may not completely starve to death and die, but the reduced food supply can still hurt the population. If animals do not get enough food, it will reduce their reproductive capacity which means that they will not reproduce as often or as easily as usual. This can lead to a decline in the population, especially in species that do not reproduce often under normal circumstances or mature reproductively in the elderly. Another problem is that the decline in a species' population due to fisheries can lead to a decrease in genetic diversity, resulting in a decrease in the biodiversity of a species. If species diversity declines significantly, this can cause problems for species in such varied and rapidly changing environments; they may not be able to adapt, which can lead to the collapse of the population or ecosystem.
Another threat to productivity and upwelling area ecosystems is the Southern El Nià ± ous Oscillation (ENSO) system, or more specifically the El Nià ± a event. During the normal period and La NiÃÆ' ± an event, the eastern trade wind is still strong, which continues to drive the upwelling process. However, during the El Nià ± o event, trade winds are weaker, causing a decrease in upwelling in the equatorial region as the north and south gates of the equator are not strong or prevalent. The coastal upwelling zone is also reduced because they are wind driven systems, and wind is no longer a very strong driving force in these areas. As a result, global upwelling has drastically declined, leading to a decrease in productivity as water no longer receives nutrient-rich water. Without these nutrients, the rest of the trophic pyramid can not be maintained, and rich upwelling ecosystems will collapse.
References
External links
- The Inverted Wind Winds: Upwelling and Downwelling
- Animation demonstrates the upwelling process.
- Upwelling Coastal
- About the influence of large wind farms in the upper ocean circulation. GÃÆ'¶ran BrostrÃÆ'¶m, Norwegian Meteorological Institute, Oslo, Norway
Source of the article : Wikipedia
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