Sea surface temperatures vary over the course of decades through a climate pattern called the Pacific Decadal Oscillation, during which small changes in depth occur for existing low-oxygen regions, Deutsch said. Low-oxygen regions that rise to warmer, shallower waters expand as bacteria become more active; regions that sink to colder, deeper waters shrink as the bacteria become more sluggish, as if placed in a refrigerator.
"We have shown for the first time that these low-oxygen regions are intrinsically very sensitive to small changes in climate," Deutsch said. "That is what makes the growth and shrinkage of these low-oxygen regions so dramatic."
Molecular oxygen from the atmosphere dissolves in sea water at the surface and is transported to deeper levels by ocean circulation currents, where it is consumed by bacteria, Deutsch said.
"The oxygen consumed by bacteria within the deeper layers of the ocean is replaced by water circulating through the ocean," he said. "The water is constantly stirring itself up, allowing the deeper parts to occasionally take a breath from the atmosphere."
A lack of oxygen is not the only thing fish and other marine life must contend with, according to Deutsch. When oxygen is very low, the bacteria will begin to consume nitrogen, one of the most important nutrients that sustain marine life.
"Almost all algae, the very base of the food chain, use nitrogen to stay alive," Deutsch said. "As these low-oxygen regions expand and contract, the amount of nutrients available to keep the algae alive at the surface of the ocean goes up and down."
Understanding the causes of oxygen and nitrogen depletion in the ocean is important for determining the effect on fisheries and fish populations, he said.
Deutsch and his team used a computer model of ocean circulation and biological processes that produce or consume oxygen to predict how the ocean's oxyge
|Contact: Kim DeRose|
University of California - Los Angeles