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Encyclopedia > Anoxic sea water

Anoxic sea water refers to water depleted of oxygen. It is generally found in enclosed areas with restricted water exchange. In most cases, oxygen is prevented from reaching the deeper parts of the sea area by a physical barrier (sill) as well as a pronounced density stratification. Anoxic conditions will occur if the rate of oxidation of organic matter by bacteria is greater than the supply of oxygen. Anoxic waters are a natural phenomenon [1] [2], and anoxic waters have occurred during the geological history of the Baltic Sea [3] [4]. Recently, there have been some indications that eutrophication has increased the extent of the anoxic areas in, e.g., the Baltic Sea. General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless Atomic mass 15. ... Redox reactions include all chemical processes in which atoms have their oxidation number (oxidation state) changed. ... ‹ The template below has been proposed for deletion. ... The Baltic Sea is located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. ... Eutrophication is apparent as increased turbidity in the northern part of the Caspian Sea, imaged from orbit. ...

Anoxic conditions result from several factors; for example, stagnation conditions, density stratification[5], inputs of organic material, and strong thermoclines. The bacterial production of sulphide starts in the sediments, where the bacteria find suitable substrates, and then expands into the water column. The thermocline is a layer within a body of water where the temperature changes rapidly with depth. ... In chemistry, a sulfide (sulphide in British and Canadian English) is a combination of sulfur with an oxidation number of -2, with another chemical element or a radical thereof. ...

When oxygen is depleted in a basin, bacteria first turn to the second-best electron acceptor, which in sea water is nitrate. Denitrification occurs, and the nitrate will be consumed rather rapidly. After reducing some other minor elements, the bacteria will turn to reducing sulphate. If anoxic sea water becomes reoxygenized, sulphides will be oxidized to sulphate according to: Denitrification is the process of reducing nitrate, a form of nitrogen available for consumption by many groups of organisms, into gaseous nitrogen, which is far less accessible to life forms but makes up the bulk of our atmosphere. ... Redox reactions include all chemical processes in which atoms have their oxidation number (oxidation state) changed. ... Sulfate is the IUPAC name for the SO42- ion, consisting of a central sulfur atom single bonded to four tetrahedrally oriented oxygen atoms. ...

HS- + 2 O2 → HSO4-

Anoxic basins

Satellite image The Mediterranean Sea is a part of the Atlantic Ocean almost completely enclosed by land, on the north by Europe, on the south by Africa, and on the east by Asia. ... Map of the Black Sea. ... Caspian Sea viewed from orbit The Caspian Sea is a landlocked endorheic sea of Eurasia between Asia and Europe. ... Vancouver Island is separated from mainland British Columbia by the Strait of Georgia and the Queen Charlotte Strait, and from Washington by the Juan De Fuca Strait. ...


  1. ^ Richards, F.A. "Anoxic basins and fjords." Chemical Oceanography, 1965.
  2. ^ Sarmiento, J.A. et al. "Ocean Carbon-Cycle Dynamics and Atmospheric pCO2". Philosophical Transactions of the Royal Society of London, Series A, Mathematical and Physical Sciences, Vol. 325, No. 1583, Tracers in the Ocean (May 25, 1988), pp. 3-21.
  3. ^ Jerbo, 1972
  4. ^ Hallberg, 1974
  5. ^ Gerlach, 1994
  • Richards, F.A. (1965) "Anoxic basins and fjords", in Riley, J.P., and Skirrow, G. (eds) Chemical Oceanography, London, Academic Press, 611-643.
  • Zilli M., Guarino C., Daffonchio D., Borin S., Converti A. (2005) "The enigma of prokaryotic life in deep hypersaline anoxic basins". Science, 307:121-123.
  • Fenchel, Tom & Finlay, Bland J. (1995) Ecology and Evolution in Anoxic Worlds (Oxford Series in Ecology and Evolution) Oxford University Press. ISBN: 0198548389



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