Global Warming

Deoxygenation Due To Climate Change Threatens Marine Life

A drop in the amount of oxygen dissolved in the oceans due to climate change is already discernible in some parts of the world and should be evident across large parts of the ocean between 2030 and 2040, according to a new study.

Scientists know that a warming climate can be expected to gradually sap oceans of oxygen, leaving fish, crabs, squid, sea stars, and other marine life struggling to breathe. But it’s been difficult to determine whether this anticipated oxygen drain is already having a noticeable impact.

The entire ocean—from the depths to the shallows—gets its oxygen supply from the surface, either directly from the atmosphere or from phytoplankton, which release oxygen into the water through photosynthesis.

Warming surface waters, however, absorb less oxygen. And in a double whammy, the oxygen that is absorbed has a more difficult time traveling deeper into the ocean. That’s because as water heats up, it expands, becoming lighter than the water below it and less likely to sink.

Thanks to natural warming and cooling, oxygen concentrations at the sea surface are constantly changing—and those changes can linger for years or even decades deeper in the ocean.

For example, an exceptionally cold winter in the North Pacific would allow the ocean surface to soak up a large amount of oxygen. Thanks to the natural circulation pattern, that oxygen would then be carried deeper into the ocean interior, where it might still be detectable years later as it travels along its flow path. On the flip side, unusually hot weather could lead to natural “dead zones” in the ocean, where fish and other marine life cannot survive.