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Anoxic waters are areas of sea water, fresh water, or groundwater that are depleted of dissolved oxygen and are a more severe condition of hypoxia. The US Geological Survey defines anoxic groundwater as those with dissolved oxygen concentration of less than 0.5 milligrams per litre.[1] This condition is generally found in areas that have restricted water exchange.



Causes and effectsEdit





HS + 2 O2 → HSO4

or, more precisely:


Anoxia is quite common in muddy ocean bottoms where there are both high amounts of organic matter and low levels of inflow of oxygenated water through the sediment. Below a few centimeters from the surface the interstitial water (water between sediment) is oxygen free.



Human caused anoxic conditionsEdit


Gradual environmental changes through eutrophication or global warming can cause major oxic-anoxic regime shifts. Based on model studies this can occur abruptly, with a transition between an oxic state dominated by cyanobacteria, and an anoxic state with sulfate-reducing bacteria and phototrophic sulfur bacteria.[11]

Daily and seasonal cyclesEdit

The temperature of a body of water directly affects the amount of dissolved oxygen it can hold. Following Henry's law, as water becomes warmer, oxygen becomes less soluble in it. This property leads to daily anoxic cycles on small geographic scales and seasonal cycles of anoxia on larger scales. Thus, bodies of water are more vulnerable to anoxic conditions during the warmest period of the day and during summer months. This problem can be further exacerbated in the vicinity of industrial discharge where warm water used to cool machinery is less able to hold oxygen than the basin to which it is released.


Biological adaptationEdit


Anoxic basinsEdit

See alsoEdit


  3. ^ Richards, 1965; Sarmiento 1988-B
  4. ^ Jerbo, 1972;Hallberg, 1974
  6. ^ "Archived copy" (PDF). Archived from the original (PDF) on 2011-09-27. Retrieved 2013-03-05.CS1 maint: archived copy as title (link)
  7. ^ Gerlach, 1994
  8. ^ a b c Castro, Peter; Huber, Michael E. (2005). Marine Biology 5th ed. McGraw Hill. ISBN 978-0-07-250934-2.
  10. ^ Nudds, John; Selden, Paul (2008-07-01). "Fossil–Lagerstätten". Geology Today. 24 (4): 153–158. doi:10.1111/j.1365-2451.2008.00679.x. ISSN 1365-2451.
  11. ^ Bush; et al. (2017). "Oxic-anoxic regime shifts mediated by feedbacks between biogeochemical processes and microbial community dynamics". Nature Communications. 8 (1): 789. Bibcode:2017NatCo...8..789B. doi:10.1038/s41467-017-00912-x. PMC 5630580. PMID 28986518.
  • Gerlach, S. (1994). "Oxygen conditions improve when the salinity in the Baltic Sea decreases". Marine Pollution Bulletin. 28 (7): 413–416. doi:10.1016/0025-326X(94)90126-0.
  • Hallberg, R.O. (1974) "Paleoredox conditions in the Eastern Gotland Basin during the recent centuries". Merentutkimuslait. Julk./Havsforskningsinstitutets Skrift, 238: 3-16.
  • Jerbo, A (1972). "Är Östersjöbottnens syreunderskott en modern företeelse?". Vatten. 28: 404–408.
  • Richards, F.A. (1965) "Anoxic basins and fjords", in Riley, J.P., and Skirrow, G. (eds) Chemical Oceanography, London, Academic Press, 611-643.
  • Sarmiento, J.A. et al. (1988-B) "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.