As the climate continues to change in response to the increasing amount of carbon humans pump into the atmosphere, the oceans are being particularly hard hit from melting Arctic sea ice, acidification, and warming surface temperatures. Yet those are not the only difficulties that marine life has to deal with, as a new study reports that the oceans are also losing oxygen.

As the majority of marine life relies on the oxygen dissolved in the oceans, it is worrying that noticeable differences have been observed in the gas concentrations in the world's waters. The reduction in oxygen will have profound effects on ocean biodiversity, though as the study published in Global Biogeochemical Cycles shows, not all regions will be affected in the same way or over the same period of time.

“Loss of oxygen in the ocean is one of the serious side effects of a warming atmosphere, and a major threat to marine life,” explains lead author Matthew Long of the National Center for Atmospheric Research in a statement. “Since oxygen concentrations in the ocean naturally vary depending on variations in winds and temperature at the surface, it's been challenging to attribute any deoxygenation to climate change. This new study tells us when we can expect the impact from climate change to overwhelm the natural variability.”

The world's oceans are predicted to lose oxygen are different rates. Matthew Long/NCAR

Almost all oxygen found in the planet's oceans originates at the surface, be it by directly dissolving into the surface waters or from being produced by phytoplankton that rely on the Sun’s rays. Cold water is known to contain more dissolved oxygen than warm water, so as surface water temperatures increase around the globe, the ability of the oceans to take up oxygen is seriously hindered.

But the impact doesn’t stop there. As warm water expands, it becomes less dense than cold water, which means it is less able to mix with the deeper, colder water below. This reduces the amount of water circulation and impacts the levels of oxygen found in the ocean depths. Another study, published in Proceedings of the Royal Society B, researched the impact of climate change on the deep sea continental margins and found that these ecosystems and the diversity of marine life they contain are already under threat.

While the authors of the first study report that deoxygenation is already detectable in some parts of the Pacific Ocean, they expect this problem will become widepsread by 2030 or 2040, and that by 2100 most regions will have been impacted. The concern now is that the effects can last for decades, meaning that even if we do get our carbon emissions under control now, we may have already set the ball rolling in some areas.