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      Thresholds of hypoxia for marine biodiversity

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      Proceedings of the National Academy of Sciences

      Proceedings of the National Academy of Sciences

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          Abstract

          Hypoxia is a mounting problem affecting the world's coastal waters, with severe consequences for marine life, including death and catastrophic changes. Hypoxia is forecast to increase owing to the combined effects of the continued spread of coastal eutrophication and global warming. A broad comparative analysis across a range of contrasting marine benthic organisms showed that hypoxia thresholds vary greatly across marine benthic organisms and that the conventional definition of 2 mg O 2/liter to designate waters as hypoxic is below the empirical sublethal and lethal O 2 thresholds for half of the species tested. These results imply that the number and area of coastal ecosystems affected by hypoxia and the future extent of hypoxia impacts on marine life have been generally underestimated.

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          Most cited references 43

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          Expanding oxygen-minimum zones in the tropical oceans.

          Oxygen-poor waters occupy large volumes of the intermediate-depth eastern tropical oceans. Oxygen-poor conditions have far-reaching impacts on ecosystems because important mobile macroorganisms avoid or cannot survive in hypoxic zones. Climate models predict declines in oceanic dissolved oxygen produced by global warming. We constructed 50-year time series of dissolved-oxygen concentration for select tropical oceanic regions by augmenting a historical database with recent measurements. These time series reveal vertical expansion of the intermediate-depth low-oxygen zones in the eastern tropical Atlantic and the equatorial Pacific during the past 50 years. The oxygen decrease in the 300- to 700-m layer is 0.09 to 0.34 micromoles per kilogram per year. Reduced oxygen levels may have dramatic consequences for ecosystems and coastal economies.
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            Gulf of Mexico Hypoxia, A.K.A. “The Dead Zone”

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              Emergence of anoxia in the California current large marine ecosystem.

               H Weeks,  Robin Chan,  J Barth (2008)
              Eastern boundary current systems are among the world's most productive large marine ecosystems. Because upwelling currents transport nutrient-rich but oxygen-depleted water onto shallow seas, large expanses of productive continental shelves can be vulnerable to the risk of extreme low-oxygen events. Here, we report the novel rise of water-column shelf anoxia in the northern California Current system, a large marine ecosystem with no previous record of such extreme oxygen deficits. The expansion of anoxia highlights the potential for rapid and discontinuous ecosystem change in productive coastal systems that sustain a major portion of the world's fisheries.
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                Author and article information

                Journal
                Proceedings of the National Academy of Sciences
                PNAS
                Proceedings of the National Academy of Sciences
                0027-8424
                1091-6490
                October 07 2008
                October 07 2008
                October 07 2008
                September 29 2008
                : 105
                : 40
                : 15452-15457
                Article
                10.1073/pnas.0803833105
                2556360
                18824689
                © 2008

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