Lower levels of oxygen in the Earth's oceans could be another sign of fundamental changes related with global climate change, McClatchy Newspapers reported on Sunday quoting scientists of different disciplines.

Areas of low oxygen have long existed in the deep ocean. However, these areas -- in the Pacific, Atlantic and Indian oceans -- appear to be spreading, covering more square miles, the papers said.

"The depletion of oxygen levels in all three oceans is striking," said Gregory Johnson, an oceanographer with the National Oceanic and Atmospheric Administration in Seattle .

In some spots, such as off the Southern California coast, oxygen levels have dropped roughly 20 percent over the past 25 years. Elsewhere, scientists said, oxygen levels might have declined by one-third over 50 years.

Barth, an oceanography professor at Oregon State University and others said the changes are consistent with current climate-change models.

"If the Earth continues to warm, the expectation is we will have lower and lower oxygen levels," said Francis Chan, a marine researcher at Oregon State.