How Is Human Activity Choking off the Oxygen Supply to our Oceans?

There’s still time to fix the problem.

Carbon pollution is not the only man-made problem for Earth’s oceans. Coastal pollution from runoff, often containing fertilizers, pesticides and other waste products (sewage) are also hastening the collapse of Earth’s oceanic oxygen cycle. Oxygen-free “dead zones” in Earth’s oceans are appearing and expanding at an alarming rate. Disruptions in the oceans’ oxygen cycle are the single-most significant and direct consequence of global industrialization.

Humans and most other land and marine animals breathe oxygen, and complex life as we know it cannot survive without it. It look more than four billion years for oceanic photosynthesis to release sufficient quantities of oxygen for terrestrial life to evolve. Life on Earth depends upon a delicate balance between the atmosphere and oceans. Ocean water absorbs most of the heat Earth receives from the Sun, and the relationship between ocean currents and atmospheric chemistry shapes the global climate.

Prior to the Industrial Revolution of the 18th and 19th centuries, global oxygen levels had remained relatively stable for millions of years. As atmospheric carbon dioxide concentrations increase due to the burning of fossil fuels, excess heat from the Sun gets trapped, which in turn raises average ocean temperatures.

Because of its naturally volatile state, atomic oxygen doesn’t accumulate on Earth in large quantities; oxygen supplies in the ocean and atmosphere continuously regenerate so that fish, mammals and terrestrial life can flourish. In fact, 50-85 percent of Earth’s oxygen is generated by phytoplankton, tiny algae that release oxygen through photosynthesis.

oxygen, dead zones, oceanic anoxic event, ocean oxygen, ocean pollution
Phytoplankton. Source: National Oceanic and Atmospheric Administration

As temperatures in Earth’s oceans rise, natural processes like photosynthesis that release oxygen into the water cannot keep up with demand. Warm water does not hold onto atomic oxygen. Individual oxygen atoms are unstable (making it highly combustible, hence its use as rocket fuel) and bond with other oxygen atoms to form O2, which comprises 20 percent of Earth’s atmosphere. Molecules of O2 also bond with oxygen atoms to form O3 (ozone), the thin atmospheric layer that blocks ultraviolet light from the Sun. Furthermore, oxygen atoms bond with other elements, like carbon, to form compounds like carbon dioxide, leading to a feedback loop of more surface heating.

Climate change was also determined to be the cause of “the blob;” an enormous heatwave in 2016 that affected a quarter of the world’s oceans. Excess ocean heat decimated ecosystems throughout the oceans and led to the death of countless marine organisms. In a study in the Bulletin of the American Meteorological Society, lead researcher Dr. Eric Oliver and his team analyzed the effects “the blob” had on the seas off Australia’s northern coast, as well as the northern Pacific Ocean between Russia and Alaska. Heatwaves, like the blob in 2016, are responsible for killing thousands of marine animals, including birds and whales. Increases in oceanic heat also lead to the bleaching of coral reefs, such as the Great Barrier Reef in Australia.

“Scientists are inherently conservative about making grand claims, but we can say with 99 percent confidence that anthropogenic climate change made this marine heatwave several times more likely, and there’s an increasing probability of such extreme events in the future,” Dr. Oliver concluded. The series of heatwaves comprising the blob were the longest lasting and most intense ever recorded.

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