Rising levels of CO2 are making it hard for fish to breathe in addition to exacerbating global warming and ocean acidification.
Climate change has caused a drop in the amount of oxygen dissolved in the oceans in some parts of the world, and those effects should become evident across large parts of the ocean between 2030 and 2040, according to a new study led by researchers at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado.
The oceans receive their oxygen supply from the surface via the atmosphere or from phytoplankton, which release oxygen in the water by photosynthesis.
When the oceans are warmed they absorb less oxygen and marine life tend to move more slowly. The oxygen that is absorbed has a harder time reaching deeper into the ocean because when water heats up, it expands and becomes lighter than the water below it and is less likely to sink, according to the National Science Foundation report.
Curtis Deutsch, associate professor at the University of Washington’s School of Oceanography, studies how increasing global temperatures are altering the levels of dissolved oxygen in the world’s oceans.
Scientists have been warning that decreasing amounts of available oxygen will increase stress on a range of species, even as they also face the effects of rising temperatures and ocean acidification.
"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 effect from climate change to overwhelm the natural variability," said lead author Matthew Long of NCAR.
The researchers discovered that deoxygenation caused by climate change could already be detected in the southern Indian Ocean and parts of the eastern tropical Pacific and Atlantic basins.
However, the study shows that at least in some parts of the ocean—including areas off the east coasts of Africa, Australia, and Southeast Asia—deoxygenation from climate change may not be evident even by 2100.
The study is published in the American Geophysical Union journal Global Biogeochemical Cycles. The research was funded by the National Science Foundation (NSF).