"If we want to understand how biological and chemical aspects of the ocean will change in the future, we really have to pay a lot of attention to what happens with the winds," Deutsch said. "The winds can lead to conclusions that are exactly the opposite of what you'd expect."
Trade winds from the west cause deep water to percolate up along western coasts, bringing nutrients up from the deep sea. These nutrients feed marine plants, which feed marine animals, which decompose to feed bacteria that use up the remaining oxygen. As trade winds weaken, less nutrient-rich water percolates up from the deep. Fewer plants grow at the surface. Finally, fewer oxygen-gobbling bacteria can survive.
Deutsch is a climate modeler who studies tropical ocean circulation. He learned of sediment cores, collected off Mexico by co-authors William Berelson at the University of Southern California and Alexander van Geen at Columbia University, that showed a puzzling longer-term trend. The authors worked together to interpret the samples. Results show that for most of the time since 1850 the population of these nitrogen-eating bacteria has been going down, coincident with warming oceans and weakening trade winds. This implies that the local oxygen levels, for which few direct measurements exist, have been rising.
"I find it an interesting question for understanding the way the ocean functions on climatic or geologic timescales," Deutsch said.
Most climate models predict that trade winds will continue to weaken in the future, shrinking the oxygen-minimum zones in the Pacific Ocean off the coasts of Mexico, Chile and Peru, and in the Indian Ocean off western Australia.
Decreasing oxygen in the wider ocean is still a major concern, Deutsch said, as are overfishing, ocean acidification and warming water temperatures.
"This study shows that what happens to the winds, which is sometimes overlooked, is really important for predicting how the oceans will respond
|Contact: Hannah Hickey|
University of Washington