Expanding Oxygen-Minimum Zones in the Tropical Oceans
Lothar Stramma,1* Gregory C. Johnson,2 Janet Sprintall,3 Volker Mohrholz4 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.
1 Institut für Meereswissenschaften an der Universität Kiel (IFM-GEOMAR), Düsternbrooker Weg 20, 24105 Kiel, Germany.
2 National Oceanic and Atmospheric Administration, Pacific Marine Environmental Laboratory, 7600 Sand Point Way NE, Seattle, WA 98115, USA.
3 Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, CA 92093, USA.
4 Baltic Sea Research Institute Warnemünde, Post Office Box 301161, 18112 Rostock, Germany.
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Globale Erwärmung 
One of the consequences of a warming climate, warmer oceans, is expected to cause a decrease in the oxygen concentration of the oceans. This prediction is based on the fact that the solubility of oxygen decreases as water temperature increases, as well as the modeled result of a slower rate of advection of water to the deep ocean while sinking organic matter continues to decay in a process that consumes oxygen. Stramma et al. (p.