Identifiant pérenne de la notice : 218859171
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Note publique d'information : Life on Earth emerged under anaerobic conditions. Many fundamental b- chemical and
metabolic pathways evolved before the atmosphere contained oxygen. Today, anaerobic
(anoxic) conditions in marine milieus are generally restricted to sediments and to
basins isolated from oxygenated deep-sea cir- lation. Oxygen-de?cientorhypoxicconditionsarede?nedinoperationalterms.
In speaking of the degree of O -de?ciency, the term hypoxic is usually de?ned 2 as
ranging between 22 and 64?MofO , while suboxic refers to a range below 2 10?M, and
anoxic is the complete absence of oxygen. Biologists commonly use the term hypoxia
to describe the point at which animals suffocate. But the papers presented in this
book deal with the whole range of oxygen-de?cient conditions, and the de?nitions some
authors have used here may vary. Enhanced oxygen consumption by decomposition of organic
matter and slow downward mixing and diffusion of dissolved oxygen from the surface
waters can lead to oxygen de?ciency in the water column in highly productive waters,
forming the Oxygen Minimum Zone (OMZ). Bottom waters of coastal upwelling regions
are frequently exposed to hypoxic (suboxic) or anaerobic conditions owing to extremely
high primary productivity. The development of these conditions represents an acute
perturbation to ecological dynamics and ?sheries. Inthepast,anoxicconditionsinthewatercolumnmayhavedeveloped
morereadily. Oceanicanoxicevents(OAE)wereepisodesofgloballyenhanced organic carbon
burial that signi?cantly affected global climate by reducing atmospheric CO . An excess
of nutrient loading leads to eutrophication of 2 coastal areas and enclosed seas,
a wide-spread global problem
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