The process of oxygen reduction in the oceans has been progressing as the climate gets warmer, the report of the International Union for Conservation of Nature (IUCN), presented on Saturday during the UN climate summit in Madrid COP25 showed. The report is based on data on ocean water quality collected since the late 1950s. The authors of the report indicated that in the years 1960-2010 there was a 2 percent decrease in oxygen content in ocean waters, mainly due to global warming.
Species groups such as tuna, marlin, and sharks are particularly sensitive to low oxygen because of their large size and energy demands. These species are starting to be driven into increasingly shallow surface layers of oxygen-rich water, making them more vulnerable to over-fishing, IUCN experts noted. The report showed that global warming leads to warming of the upper oceans and systematic deoxygenation.