28 april 2016

Global warming could deplete the oceans’ oxygen – with severe consequences

By Chris Mooney, Washington Post April 28

In the long list of troubling climate change scenarios, there’s one that gets relatively little attention, but definitely has enormous potential consequences.

It goes like this:

The oceans are getting warmer — they are, after all, where 90 percent of global warming actually ends up. And when they warm up they expand, because that’s what warm water does. This raises our sea levels, but it also has another effect — it reduces the amount of oxygen dissolved in the water. That’s simply physics: Warmer water contains less oxygen.

But it’s worse: If surface water is warmer, it doesn’t mix down as much into the ocean depths any longer. It’s less dense, and so less capable of doing that. That means that oxygen that enters the ocean in its upper layers — either through exchange with the atmosphere, or because it is generated by tiny photosynthesizing microorganisms, called phytoplankton, that hang out up there — won’t mix down into the deep as often.

“What’s happening is, there’s a physical mechanism that impedes the delivery of surface waters into the interior,” said Matthew Long, an oceanographer with the National Center for Atmospheric Research who is lead author of a troubling new study on what scientists call the “deoxygenation” of the oceans. The work appeared in Global Biogeochemical Cycles, co-authored with Curtis Deutsch of the University of Washington and Taka Ito of the Georgia Institute of Technology.


>>> Back to list