Polluted dust can impact ocean life thousands of miles away, study says

http://www.eurekalert.org/pub_releases/2016-05/giot-pdc051316.php

Public Release: 16-May-2016
Polluted dust can impact ocean life thousands of miles away, study says
Georgia Institute of Technology

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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."

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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.

But while the tropical phytoplankton may have released more oxygen into the atmosphere, their consumption of the excess nutrients had a negative effect on the dissolved oxygen levels deeper in the ocean.

"If you have more active photosynthesis at the surface, it produces more organic matter, and some of that sinks down," Ito said. "And as it sinks down, there's bacteria that consume that organic matter. Like us breathing in oxygen and exhaling CO2, the bacteria consume oxygen in the subsurface ocean, and there is a tendency to deplete more oxygen."

That process plays out in all across the Pacific, but the effects are most pronounced in tropical areas, where dissolved oxygen is already low.

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