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.

贫氧水域在热带东大洋的中层占据了很大的体积。贫氧条件对生态系统有着深远的影响，因为重要的移动性大型生物会避开缺氧区域，或者无法在其中生存。气候模型预测全球变暖会导致海洋溶解氧含量下降。我们通过将近期测量数据补充到历史数据库中，构建了选定热带海洋区域溶解氧浓度的50年时间序列。这些时间序列显示，在过去50年里，热带东大西洋和赤道太平洋中层深度的低氧区域在垂直方向上有所扩大。300米至700米层的氧气含量每年每千克减少0.09至0.34微摩尔。氧气含量的降低可能会对生态系统和沿海经济产生巨大影响。