Oceanographers are sounding the alarm that that our oceans are rapidly running out of oxygen, much faster than expected, because of man-made global warming.

"We were surprised by the intensity of the changes we saw, how rapidly oxygen is going down in the ocean and how large the effects on marine ecosystems are," said Andreas Oschlies, an oceanographer at the Helmholtz Center for Ocean Research Kiel in Germany, whose team tracks ocean oxygen levels worldwide.

Some areas have only lost a little, but Oxygen levels in some tropical regions have dropped by a startling 40 percent in the last 50 years.  The overall global average is a loss of two percent.

Warming and ocean acidification are stressing wildlife, but Oschlies says the loss of oxygen is the oceans' most-pressing problem for life in the sea.  After all, "they all have to breathe," he says.

Warm liquid is less able to hold gasses, which you might have noticed if you've ever left a soft drink in the sun.  Oxygen is depleted, leading to a more nitrogen-rich environment, which algae just loves.  Blooms occur, killing wildlife or chasing it away into cooler waters.  But that disrupts breeding cycles, resulting is less life in the ocean.

Even slight changes to oxygen levels in our oceans can lead to the decline of zooplankton, a range of tiny species at the bottom of the food chain that are a primary food source for many of fish and aquatic mammals.  If they disappear from an area, the amount of fish that can survive in those same zones will change.