As climatologists closely monitor the impact of human activity on the world's oceans, researchers at the Georgia Institute of Technology have found yet another worrying trend impacting the health of the Pacific Ocean.A new modeling study conducted by researchers in Georgia Tech's School of Earth and Atmospheric Sciences shows that for decades, air pollution drifting from East Asia out over the world's largest ocean has kicked off a chain reaction that contributed to oxygen levels falling in tropical waters thousands of miles away."There's a growing awareness that oxygen levels in the ocean may be changing over time," said Taka Ito, an associate professor at Georgia Tech. "One reason for that is the warming environment — warm water holds less gas. But in the tropical Pacific, the oxygen level has been falling at a much faster rate than the temperature change can explain."The study, which was published May 16 in Nature Geoscience, was sponsored by the National Science Foundation, a Georgia Power Faculty Scholar Chair and a Cullen-Peck Faculty Fellowship.In the report, the researchers describe how air pollution from industrial activities had raised levels of iron and nitrogen — key nutrients for marine life — in the ocean off the coast of East Asia. Ocean currents then carried the nutrients to tropical regions, where they were consumed by photosynthesizing phytoplankton.