We know that climate change is having a drastic impact on the ice caps and glaciers, but it is also changing the chemical make-up of the oceans. While the levels of carbon dioxide are increasing, a new paper has documented how the concentration of oxygen in the oceans is decreasing.

The results have been published in Nature, and are an analysis of over 50 years’ worth of data looking at a range of parameters from ocean salinity to temperature. They calculated that over this period, the world’s oceans have lost an average 2 percent of their oxygen. This might not sound like much, but the researchers note that even such a small drop in oxygen concentration can be enough to completely alter some ecosystems, including the formation of dead zones.

The main process through which the oceans are losing their oxygen is simply the heating of the water. As the oceans warm, their ability to trap dissolved oxygen decreases, which is why colder waters on Earth contain a lower concentration of the gas. But this warming of the ocean has another effect: As the warming is generally contained to the upper reaches of the oceans, it decreases the density of the surface water, preventing it from dropping to the depths and taking the life-giving oxygen with it.

Combined with the myriad of other impacts climate change is having on the oceans, the results of this drop in oxygen could be catastrophic. As the polar ice caps melt, the increase in fresh water is expected to disrupt the ocean currents, something some argue has been driving the abnormal weather conditions seen in the past few winters over much of Northern Europe and America.

The increase in carbon dioxide levels in the seas, while beneficial for some organisms, is likely to be majorly harmful to many others. By increasing the acidity of the water, creatures with calcium carbonate shells will simply dissolve away, including the vast coral reefs in the tropics.

But it is not only the acidity that the reefs have to deal with, as the rising surface ocean temperatures also directly harm the organisms, and have been the driving force behind the worst bleaching event ever recorded on the Great Barrier Reef, the most biodiverse habitat on Earth. The rising temperature is also impacting the northern latitudes too, as the ranges of cold water fish, such as cod, are now thought to be shifting north as they follow the cooler waters.

It is estimated that over 3 billion people depend on the marine environment for their livelihoods. As climate change starts to radically impact these ecosystems, it will have a dramatic knock-on effect on the future of not only these people, but all of us.