title: Expanding oxygen-minimum zones in the tropical oceans.
abstract: 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.
authors.affiliation: Institut für Meereswissenschaften an der Universität Kiel (IFM-GEOMAR), Düsternbrooker Weg 20, 24105 Kiel, Germany. lstramma@ifm-geomar.de
authors.forename: Lothar
authors.initials: L
authors.lastname: Stramma
authors.forename: Gregory C
authors.initials: GC
authors.lastname: Johnson
authors.forename: Janet
authors.initials: J
authors.lastname: Sprintall
authors.forename: Volker
authors.initials: V
authors.lastname: Mohrholz