Climate change may shrink oxygen-deprived zones in oceans
Contrary to what one would expect, researchers have shown that climate change, as it weakens the trade winds, could shrink the size of the lowest-oxygen environment zones in the oceans.
"The tropics should actually get better oxygenated as the climate warms up," said Curtis Deutsch, an associate professor of oceanography at University of Washington.
Tropical regions are usually associated with an abundance of life, but they have some of the most inhospitable places for ocean dwellers.
The oxygen minimum zones off Mexico and Peru have oxygen levels already too low to support most animal life.
But when those levels drop even lower, a particular group of bacteria, which can use nitrogen instead of oxygen as a source of energy, thrives.
Nitrogen is an essential and very scarce nutrient for marine plants. When oxygen levels get low enough for that particular group of bacteria to take over, significant amounts of the ocean's fertiliser get deep-sixed to the bottom of the tropical ocean.
The research showed that water flowing into the tropics is indeed likely to get lower in oxygen, decreasing the initial oxygen supply.
"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.
Trade winds from the west cause deep water to percolate 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 comes up from the depths. Fewer plants grow at the surface. Finally, fewer oxygen-gobbling bacteria can survive.
The study appeared in the journal Science.
(Posted on 08-08-2014)