anoxic afrin

8/4/2019 Anoxic AFRIN

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Anoxic waters

Anoxic waters are areas of sea water or fresh water that are depleted ofdissolvedoxygen. This condition is generally found in areas that have restricted waterexchange.

In most cases, oxygen is prevented from reaching the deeper levels by a physicalbarrier (silt) as well as by a pronounced density stratification, in which, forinstance, heavierhypersaline waters rest at the bottom of a basin. Anoxicconditions will occur if the rate ofoxidation of organic matter by bacteria is

greater than the supply ofdissolved oxygen.

Anoxic waters are a natural phenomenon,[1] and have occurred throghoutgeological history. Anoxic basins exist at present, for example, in theBaltic Sea,[2]

and elsewhere (see below). Recently, there have been some indications that

eutrophication has increased the extent of the anoxic areas in areas including theBaltic Sea, and the Gulf of Mexico.[3]

Causes and e f fec tsAnoxic conditions result from severalfactors; for example,stagnation conditions,

density stratification,[4] inputs of organic material, and strongthermoclines. Thebacterial production ofsulfide starts in the sediments, where the bacteria find

suitable substrates, and then expands into the water column.
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When oxygen is depleted in a basin, bacteria first turn to the second-best electronacceptor, which in sea water is nitrate.Denitrification occurs, and the nitrate willbe consumed rather rapidly. After reducing some other minor elements, thebacteria will turn to reducingsulfate. If anoxic sea water becomes reoxygenized,

sulfides will be oxidized to sulfate according to the chemical equation:

HS + 2 O2 HSO4

In the Baltic Sea the slowed rate of decomposition under anoxic conditions hasleft remarkably preservedfossils retaining impressions of soft body parts, in

Lagersttten.

Anox ic event

As early as 1911, major oceanic currents were well mapped and understood, albeitwithout today's understanding of how they affect regional and globalclimatologicalconditions.
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This world perspective on oceanic currents demonstrates the interdependencies oftransnational regions on circulating currents.

Oceanic anoxic events oranoxic events occur when theEarth's oceans becomecompletely depleted ofoxygen (O2) below the surface levels. Although anoxic

events have not happened for millions of years, the geological record shows thatthey happened many times in the past. Anoxic events may have causedmassextinctions.[citation needed] These mass extinctions were so characteristic they include

some of those whichgeobiologists employ to serve as a time markerinbiostratigraphic dating. It is believed[by whom?] oceanic anoxic events are stronglylinked to lapses in key oceanic current circulations, to climate warming and

greenhouse gases.

Occur renceOceanic anoxic events most commonly occurred during periods of very warmclimate characterized by high levels ofcarbon dioxide (CO2) and mean surfacetemperatures probably in excess of 25 C (77 F). The Quaternary levels, ourcurrentperiod, are just 13 C (55 F) in comparison. Such rises in carbon dioxidemay have been in response to a great outgassing of the highly flammablenatural

gas (methane) some have christened an "oceanic burp".[2][4] Vast quantities ofmethane are normally locked into the Earth's crust on the continental plateaus inone of the many deposits consisting of compounds ofmethane hydrate, a solid

precipitated combination of methane and water much like ice. Because the

methane hydrates are unstable, save at cool temperatures and high (deep)pressures, scientists have observed smaller "burps" due to tectonic events. Studiessuggest the huge release of natural gas[4] could be a major climatological trigger,methane itself being agreenhouse gas many times more powerful than carbondioxide. However, anoxia was also rife during theHirnantian (late Ordovician)ice age.

Oceanic anoxic events have been recognized primarily from the already warmCretaceous andJurassicPeriods, when numerous examples have beendocumented,[6][7] but earlier examples have been suggested to have occurred in thelate Triassic,Permian,Devonian (Kellwasser event/s), Ordovician andCambrian.

ThePaleoceneEocene Thermal Maximum (PETM), which was characterized by aglobal rise in temperature and deposition of organic-rich shales in some shelfseas, shows many similarities to oceanic anoxic events.

Typically, oceanic anoxic events last for under half a million years, before a fullrecovery.
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ConsequencesOceanic anoxic events have had many important consequences. It is believed thatthey have been responsible for mass extinctions of marine organisms both in the

Paleozoic andMesozoic.[8] The early Toarcian andCenomanian-Turonian anoxicevents correlate with the Toarcian andCenomanian-Turonian extinction events ofmostly marine life forms. Apart from possible atmospheric effects, many deeper-dwelling marine organisms could not adapt to an ocean where oxygen penetratedonly the surface layers.

Another, economically significant consequence of oceanic anoxic events is the fact

that the prevailing conditions in so many Mesozoic oceans has helped producemost of the world'spetroleum andnatural gas reserves. During an oceanic anoxicevent, the accumulation and preservation of organic matter was much greater thannormal, allowing the generation of potential petroleumsource rocks in manyenvironments across the globe. Consequently some 70 percent of oil source rocksare Mesozoic in age, and another 15 percent date from the warm Paleogene: onlyrarely in colder periods were conditions favorable for the production of sourcerocks on anything other than a local scale.

Majo r ocean ic anox ic even ts
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Jurassic and Cretaceous

The timeline data of the Jurassic and Cretaceous

The concept of the oceanic anoxic event (OAE) was first proposed in 1976 bySeymour Schlanger (19271990) and geologist Hugh Jenkyns[9] and arose fromdiscoveries made by theDeep Sea Drilling Project(DSDP) in the Pacific Ocean. Itwas the finding of black carbon-rich shales in Cretaceous sediments that hadaccumulated on submarine volcanic plateaus (Shatsky Rise, Manihiki Plateau),coupled with the fact that they were identical in age with similar deposits cored

from the Atlantic Ocean and known from outcrops in Europe - particularly in thegeological record of the otherwise limestone-dominatedApennines[9] chain in Italy- that led to the realization that these widespread intervals of similarstratarecorded highly unusual oxygen-depleted conditions in the world ocean during

several distinct discrete periods ofgeological time.

Sedimentological investigations of these organic-rich sediments, which havecontinued to this day, typically reveal the presence of fine laminations undisturbedby bottom-dwelling fauna, indicating anoxic conditions on the sea floor, believedto be coincident with a low lying poisonous layer of hydrogen sulfide.[1]

Furthermore, detailed organic geochemical studies have recently revealed thepresence of molecules (so-called biomarkers) that derive from bothpurple sulfurbacteria[1] andgreen sulfur bacteria: organisms that required both light and freehydrogen sulfide (H2S), illustrating that anoxic conditions extended high into theilluminated upper water column.

Such sulfidic (or euxinic) conditions, which exist today in many water bodies fromponds to various land-surroundedmediterranean seas[10] such as theBlack Sea oftoday, were particularly prevalent in theCretaceous Atlantic but alsocharacterized other parts of the world ocean. In an ice-free sea of these supposed

super-greenhouse worlds, oceanic waters were as much as 200 meters higher, insome eras. During the time spans in question, the continental plates are believedto have been well separated, and the mountains we know today were (mostly)
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future tectonic eventsmeaning the overall landscapes were generally much lower and even the half super-greenhouse climates would have been eras of highlyexpedited water erosion[1] carrying massive amounts of nutrients into the worldoceans fueling an overall explosive population of microorganisms and their

predator species in the oxygenated upper layers.

Detailed stratigraphic studies of Cretaceous black shales from many parts of theworld have indicated that two oceanic anoxic events were particularly significantin terms of their impact on the chemistry of the oceans, one in the earlyAptian(~120 Ma), sometimes called the Selli Event(or OAE 1a) after the Italian

geologist, Raimondo Selli (19161983), and another at the CenomanianTuronianboundary (~93 Ma), sometimes called the Bonarelli Event(or OAE 2) after the

Italian geologist, Guido Bonarelli (18711951).

Insofar as the Cretaceous OAEs can be represented by type localities, it is thestriking outcrops of laminated black shales within the vari-colored claystones

and pink and white limestones near the town of Gubbio in the ItalianApennines that are the best candidates.

The 1-meter thick black shale at the CenomanianTuronian boundary thatcrops out near Gubbio is termed the Livello Bonarelli after the man who firstdescribed it in 1891.

More minor oceanic anoxic events have been proposed for other intervals in theCretaceous (in the Valanginian,Hauterivian,Albian andConiacianSantonian

stages), but their sedimentary record, as represented by organic-rich black shales,appears more parochial, being dominantly represented in the Atlantic and

neighboring areas, and some researchers relate them to particular localconditions rather than being forced by global change.

The only oceanic anoxic event documented from the Jurassic took place during theearly Toarcian (~183 Ma).[6][7] Because no DSDP or ODP (Ocean Drilling

Program) cores have recovered black shales of this age there being little or noToarcian ocean crust remaining in the world ocean the samples of black shale

primarily come from outcrops on land. These outcrops, together with materialfrom some commercial oil wells, are found on all major continents and this eventseems similar in kind to the two major Cretaceous examples.

Atm ospher ic e f fec tsA model put forward by Lee Kump, Alexander Pavlov and Michael Arthur in 2005suggests that oceanic anoxic events may have been characterized by upwelling ofwater rich in highly toxic hydrogen sulfide gas which was then injected into theatmosphere. This phenomenon would likely have poisoned plants and animals andcaused mass extinctions. Furthermore, it has been proposed that the hydrogen

sulfide rose to the upper atmosphere and attacked the ozone layer, which normally
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blocks the deadly ultraviolet radiation of the Sun. The increased UV radiationcaused by this ozone depletion would have amplified the destruction of plant andanimal life. Fossil spores from strata recording thePermian extinction showdeformities consistent with UV radiation. This evidence, combined with fossilbiomarkers ofgreen sulfur bacteria, indicates that this process could have played

a role in thatmass extinction event, and possibly other extinction events. Thetrigger for these mass extinctions appears to be a warming of the ocean caused bya rise of carbon dioxide levels to about 1000 parts per million.[15]

Hypox ia (env ironm enta l )Hypoxia, oroxygen depletion, is a phenomenon that occurs in aquaticenvironments as dissolved oxygen (DO; molecular oxygen dissolved in the water)becomes reduced in concentration to a point where it becomes detrimental toaquatic organisms living in the system. Dissolved oxygen is typically expressed asa percentage of the oxygen that would dissolve in the water at the prevailingtemperature and salinity (both of which affect the solubility of oxygen in water; seeoxygen saturation andunderwater). An aquatic system lacking dissolved oxygen(0% saturation) is termed anaerobic,reducing, oranoxic; a system with lowconcentrationin the range between 1 and 30% saturationis calledhypoxic ordysoxic. Most fish cannot live below 30% saturation. A "healthy" aquaticenvironment should seldom experience less than 80%. The exaerobic zone is foundat the boundary of anoxic and hypoxic

W here hypox ia occurs

Hypoxia can occur throughout the water column and also at high altitudes as wellas near sediments on the bottom. It usually extends throughout 20-50% of thewater column, but depending on the water depth and location of pycnoclines
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(rapid changes in water density with depth)[1] it can occur in 10-80% of the watercolumn. For example, in a 10-meter water column, it can reach up to 2 metersbelow the surface. In a 20-meter water column, it can extend up to 8 meters belowthe surface.[2]

Hypoxia can also occur outside of an aquatic environment, in conditions where theoxygen content of the air is reduced. This is common, for example, in the sealedburrows of some subterranean animals, such as blesmols.[3]

Causes o f hypox ia

Decline of oxygen saturation to anoxia, measured during the night inKiel Fjord,Germany. Depth = 5 m

Oxygen depletion can result from a number of natural factors, but is most often aconcern as a consequence ofpollution andeutrophication in whichplant nutrientsenter a river, lake, or ocean, andphytoplankton blooms are encouraged. While

phytoplankton, throughphotosynthesis, will raise DO saturation during daylighthours, the dense population of a bloom reduces DO saturation during the night byrespiration. When phytoplankton cells die, they sink towards the bottom and aredecomposed by bacteria, a process that further reduces DO in the water column. If

oxygen depletion progresses to hypoxia,fish kills can occur and invertebrates likeworms andclams on the bottom may be killed as well.
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Still frame from an underwater video of the sea floor. The floor is covered withcrabs, fish, and clams apparently dead or dying from oxygen depletion.

Hypoxia may also occur in the absence of pollutants. In estuaries, for example,because freshwater flowing from a river into the sea is less dense than salt water,

stratification in the water column can result. Vertical mixing between the waterbodies is therefore reduced, restricting the supply of oxygen from the surfacewaters to the more saline bottom waters. The oxygen concentration in the bottomlayer may then become low enough for hypoxia to occur. Areas particularly proneto this include shallow waters of semi-enclosed water bodies such as theWaddenzee or the Gulf of Mexico, where land run-off is substantial. In these areas

a so-called "dead zone" can be created. The World Resources Institute hasidentified 375 hypoxic coastal zones around the world, concentrated in coastalareas in Western Europe, the Eastern and Southern coasts of the US, and East

Asia, particularly in Japan.[4]
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Jubilee photo from Mobile Bay

Hypoxia may also be the explanation for periodic phenomena such as the MobileBay jubilee, where aquatic life suddenly rushes to the shallows, perhaps trying toescape oxygen-depleted water. Recent widespread shellfish kills near the coasts ofOregon and Washington are also blamed on cyclicdead zone ecology.[5]

Solut ionsTo combat hypoxia, it is essential to reduce the amount of land-derived nutrientsreaching rivers in runoff. Defensively this can be done by improving sewagetreatment and by reducing the amount of fertilizers leaching into the rivers.Offensively this can be done by restoring natural environments along a river;marshes are particularly effective in reducing the amount of phosphorus andnitrogen (nutrients) in water.

Technological solutions are also possible, such as that used in the redevelopedSalford Docks area of the Manchester Ship Canalin England, where years ofrunoff from sewers and roads had accumulated in the slow running waters. In2001 a compressed air injection system was introduced, which raised the oxygen

levels in the water by up to 300%. The resulting improvement in water quality ledto an increase in the number of invertebrate species, such as freshwatershrimp, tomore than 30. Spawningand growth rates of fish species such as roach andperchalso increased to such an extent that they are now amongst the highest in England.[6]
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Graphs of oxygen and salinity levels at Kiel Fjord in September 1998.

In a very short time the oxygen saturation can drop to zero when offshore blowingwinds drive surface water out and anoxic depthwater rises up. At the same time adecline in temperature and a rise in salinity is observed (from the longtermecological observatory in theseas at Kiel Fjord, Germany). New approaches oflong-term monitoring of oxygen regime in the ocean observe online the behaviorof

fish andzooplankton, which changes drastically under reducedoxygen saturations(ecoSCOPE) and already at very low levels ofwater pollution.

Bog chem is tryIn certain northern Europeansphagnum acidic bogs, a condition of hypoxia arisesthat prevents tissue decay by impeding micro-organisms in the soil and

groundwater. Remarkable preservation of human mummies has occurred in somecases such as the discovery of Haraldskr WomanandTollund Man inJutland,

Denmarkand Lindow manin Cheshire,England.

Ocean deoxygenation

Ocean deoxygenation is a term that has been suggested to describe the expansion

ofoxygen minimum zones in the world's oceans as a consequence ofanthropogenicemissions ofcarbon dioxide[1].

Oceanographers and others have discussed what phrase best describes thephenomenon to non-specialists. Among the options considered have been 'oceansuffocation' (which was used in a news report from May 2008[2]), 'ocean oxygen
http://en.wikipedia.org/wiki/Oxygen_saturationhttp://en.wikipedia.org/wiki/Longterm_ecological_observatoryhttp://en.wikipedia.org/wiki/Longterm_ecological_observatoryhttp://en.wikipedia.org/wiki/Seahttp://en.wikipedia.org/wiki/Behaviorhttp://en.wikipedia.org/wiki/Fishhttp://en.wikipedia.org/wiki/Zooplanktonhttp://en.wikipedia.org/wiki/Oxygen_saturationhttp://en.wikipedia.org/wiki/EcoSCOPEhttp://en.wikipedia.org/wiki/Water_pollutionhttp://en.wikipedia.org/wiki/Sphagnumhttp://en.wikipedia.org/wiki/Haraldsk%C3%A6r_Womanhttp://en.wikipedia.org/wiki/Tollund_Manhttp://en.wikipedia.org/wiki/Jutlandhttp://en.wikipedia.org/wiki/Denmarkhttp://en.wikipedia.org/wiki/Lindow_manhttp://en.wikipedia.org/wiki/Cheshirehttp://en.wikipedia.org/wiki/Englandhttp://en.wikipedia.org/wiki/Oxygen_minimum_zonehttp://en.wikipedia.org/wiki/Oceanshttp://en.wikipedia.org/wiki/Human_impact_on_the_environmenthttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/File:Anoxie_allemagne2.pnghttp://en.wikipedia.org/wiki/File:Anoxie_allemagne2.pnghttp://en.wikipedia.org/wiki/Oxygen_saturationhttp://en.wikipedia.org/wiki/Longterm_ecological_observatoryhttp://en.wikipedia.org/wiki/Longterm_ecological_observatoryhttp://en.wikipedia.org/wiki/Seahttp://en.wikipedia.org/wiki/Behaviorhttp://en.wikipedia.org/wiki/Fishhttp://en.wikipedia.org/wiki/Zooplanktonhttp://en.wikipedia.org/wiki/Oxygen_saturationhttp://en.wikipedia.org/wiki/EcoSCOPEhttp://en.wikipedia.org/wiki/Water_pollutionhttp://en.wikipedia.org/wiki/Sphagnumhttp://en.wikipedia.org/wiki/Haraldsk%C3%A6r_Womanhttp://en.wikipedia.org/wiki/Tollund_Manhttp://en.wikipedia.org/wiki/Jutlandhttp://en.wikipedia.org/wiki/Denmarkhttp://en.wikipedia.org/wiki/Lindow_manhttp://en.wikipedia.org/wiki/Cheshirehttp://en.wikipedia.org/wiki/Englandhttp://en.wikipedia.org/wiki/Oxygen_minimum_zonehttp://en.wikipedia.org/wiki/Oceanshttp://en.wikipedia.org/wiki/Human_impact_on_the_environmenthttp://en.wikipedia.org/wiki/Carbon_dioxide


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deprivation'[3], 'decline in ocean oxygen', 'marine deoxygenation', 'ocean oxygendepletion' and 'ocean hypoxia'

Dead zone (eco logy ) .

Red circles show the location and size of many dead zones.Black dots show dead zones of unknown size.

The size and number of marine dead zonesareas where the deep water is so lowin dissolved oxygen that sea creatures cant survivehave grown explosively in

the past half-century. NASA Earth Observatory[1]

Dead zones are hypoxic (low-oxygen) areas in the world's oceans, the observedincidences of which have been increasing since oceanographers began noting

them in the 1970s. These occur near inhabitedcoastlines, where aquatic life ismost concentrated. (The vast middle portions of the oceans which naturally havelittle life are not considered "dead zones".) The term can also be applied to theidentical phenomenon in large lakes.

In March 2004, when the recently establishedUN Environment Programmepublished its firstGlobal Environment Outlook Year Book(GEO Year Book 2003)it reported 146 dead zones in the world's oceans wheremarine life could not be

supported due to depleted oxygen levels. Some of these were as small as a squarekilometre (0.4 mi), but the largest dead zone covered 70,000 square kilometres(27,000 mi). A 2008 study counted 405 dead zones worldwide.[2][3]

C a u s e s
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Dead zones are often caused by the decay ofalgae duringalgal blooms, like thisone off the coast ofLa Jolla, San Diego, California.

Climate has a significant impact on the growth and decline of ecological deadzones. During Spring months, as rainfall increases, more nutrient rich water flowsdown the mouth of the Mississippi River. At the same time, as sunlight increasesduring the Spring, algal growth in the dead zones increases dramatically. In Fallmonths, tropical storms begin to enter the Gulf of Mexico and break up the dead

zones and the cycle repeats again in the spring.

Aquatic and marine dead zones can be caused by an increase in chemical nutrients(particularly nitrogen and phosphorus) in the water, known as eutrophication.These chemicals are the fundamental building blocks of single-celled, plant-likeorganisms that live in the water column, and whose growth is limited in part by the

availability of these materials. Eutrophication can lead to rapid increases in thedensity of certain types of these phytoplankton, a phenomenon known as an algalbloom. Although these algae produce oxygen in the daytime viaphotosynthesis,during the night hours they continue to undergo cellular respiration and cantherefore deplete the water column of available oxygen.[citation needed] In addition,when algal blooms die off, oxygen is used up further during bacterialdecomposition of the dead algal cells. Both of these processes can result in a
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significant depletion of dissolved oxygen in the water, creating hypoxic conditions.Dead zones can be caused by natural and by anthropogenic factors. Use ofchemicalfertilizers is considered the major human-related cause of dead zonesaround the world. Natural causes include coastal upwelling and changes in windand water circulation patterns. Runoff from sewage, urban land use, and fertilizers

can also contribute to eutrophication.[4]

Notable dead zones in the United States include the northern Gulf of Mexicoregion, surrounding the outfall of the Mississippi River, and the coastal regions ofthe Pacific Northwest, and the Elizabeth River in Virginia Beach, all of which havebeen shown to be recurring events over the last several years.

Additionally, natural oceanographic phenomena can cause deoxygenation of partsof the water column. For example, enclosed bodies of water such asfjords or the

Black Sea have shallow sills at their entrances causing water to be stagnant therefor a long time. The eastern tropical Pacific Ocean and Northern Indian Ocean

have lowered oxygen concentrations which are thought to be in regions wherethere is minimal circulation to replace the oxygen that is consumed (e.g. Pickard& Emery 1982, p 47).[5] These areas are also known as Oxygen Minimum Zones(OMZ). In many cases OMZ's are permanent or semi-permanent areas.

Remains of organisms found withinsedimentlayers near the mouth of theMississippi Riverindicate four hypoxic events before the advent of artificial

fertilizer. In these sediment layers, anoxia-tolerant species are the most prevalentremains found. The periods indicated by the sediment record correspond tohistoric records of high river flow recorded by instruments atVicksburg,

Mississippi.Ef fects
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Underwater video frame of the sea floor in the WesternBaltic covered with deador dying crabs, fish and clams killed by oxygen depletion

Low oxygen levels recorded along the Gulf CoastofNorth America have led toreproductive problems in fish involving decreased size of reproductive organs, low

egg counts and lack of spawning.In a study of the Gulfkillifish by the Southeastern Louisiana University done inthree bays along the Gulf Coast, fish living in bays where the oxygen levels in thewater dropped to 1 to 2 parts per million (ppm) for 3 or more hours per day were

found to have smallerreproductive organs. The male gonads were 34% to 50% aslarge as males of similar size in bays where the oxygen levels were normal (6 to 8

ppm). Females were found to have ovaries that were half as large as those innormal oxygen levels. The number of eggs in females living in hypoxic waters wereonly one-seventh the number of eggs in fish living in normal oxygen levels.(Landry, et al., 2004)

Fish raised in laboratory-created hypoxic conditions showed extremely lowsex-hormone concentrations and increased elevation of activity in twogenes triggeredby the hypoxia-inductile factor (HIF)protein. Under hypoxic conditions, HIF pairswith another protein, ARNT. The two then bind to DNA in cells, activating genes inthose cells.

Under normal oxygen conditions, ARNT combines with estrogen to activate genes.Hypoxic cells in a test tube didn't react to estrogen placed in the tube. HIFappears to render ARNT unavailable to interact with estrogen, providing amechanism by which hypoxic conditions alter reproduction in fish. (Johanning, et

al., 2004)It might be expected that fish would flee this potential suffocation, but they areoften quickly rendered unconscious and doomed. Slow moving bottom-dwellingcreatures like clams, lobsters and oysters are unable to escape. All colonialanimals are extinguished. The normal re-mineralization and recycling that occursamongbenthic life-forms is stifled.

Locat ions
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DRAINAGE SYSTEM OF ANOXIC WATER
http://www.google.co.in/imgres?q=anoxic+water&um=1&hl=en&sa=N&biw=1366&bih=650&tbm=isch&tbnid=OzWKxG63r1ZxEM:&imgrefurl=http://www.in.gov/dnr/reclamation/3507.htm&docid=tmVeg-Jq7FXn2M&w=750&h=494&ei=WSg4TtjABoTWrQfshtTnDw&zoom=1http://en.wikipedia.org/wiki/File:Dead_Zone_NASA_NOAA.jpg

anoxic afrin

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