Gulf of Mexico Hypoxia, A.K.A. "The Dead Zone"
The second largest zone of coastal hypoxia (oxygen-depleted waters) in the world is found on the northern Gulf of Mexico continental shelf adjacent to the outflows of the Mississippi and Atchafalaya Rivers. The combination of high freshwater discharge, wind mixing, regional circulation, and summer w...
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Published in | Annual review of ecology and systematics Vol. 33; no. 1; pp. 235 - 263 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
Palo Alto, CA 94303-0139
Annual Reviews
01.01.2002
4139 El Camino Way, P.O. Box 10139 USA |
Subjects | |
Online Access | Get full text |
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Summary: | The second largest zone of coastal hypoxia (oxygen-depleted waters) in the
world is found on the northern Gulf of Mexico continental shelf adjacent to the
outflows of the Mississippi and Atchafalaya Rivers. The combination of high
freshwater discharge, wind mixing, regional circulation, and summer warming
controls the strength of stratification that goes through a well-defined
seasonal cycle. The physical structure of the water column and high nutrient
loads that enhance primary production lead to an annual formation of the
hypoxic water mass that is dominant from spring through late summer.
Paleoindicators in dated sediment cores indicate that hypoxic conditions likely
began to appear around the turn of the last century and became more severe
since the 1950s as the nitrate flux from the Mississippi River to the Gulf of
Mexico tripled. Whereas increased nutrients enhance the production of some
organisms, others are eliminated from water masses (they either emigrate from
the area or die) where the oxygen level falls below 2 mg l
−1
or lower for a prolonged period. A hypoxia-stressed benthos is typified by
short-lived, smaller surface deposit-feeding polychaetes and the absence of
marine invertebrates such as pericaridean crustaceans, bivalves, gastropods,
and ophiuroids. The changes in benthic communities, along with the low
dissolved oxygen, result in altered sediment structure and sediment
biogeochemical cycles. Important fisheries are variably affected by increased
or decreased food supplies, mortality, forced migration, reduction in suitable
habitat, increased susceptibility to predation, and disruption of life
cycles. |
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Bibliography: | ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 ObjectType-Review-3 content type line 23 |
ISSN: | 0066-4162 2330-1902 |
DOI: | 10.1146/annurev.ecolsys.33.010802.150513 |