WASHINGTON -- Two new studies show global warming is making oceans sicker, depleting them of oxygen and harming delicate coral reefs more often.

The researchers say the lower oxygen levels are making marine life far more vulnerable. They say the problem is worsening and more complex than previously thought.

Oxygen is crucial for nearly all life in the oceans, except for a few microbes

A second study finds that severe bleaching outbreaks are hitting coral reefs four times more often than before as waters warm.

Both studies are in Thursday's edition of the journal Science.