Suffocating seas: how climate change is reducing ocean oxygen levels

Climate change’s stealthy advance alters our oceans in two well-known ways: acidification and sea level rise. But our planet’s subtle warming has had another, under-the-radar effect: oxygen depletion.

While oxygen depletion may not draw dramatic headlines or spark rallies, dipping oxygen levels pose a growing problem for marine life and fisheries. It works like this: first, as concentrations of greenhouse gases rise and the Earth warms, ocean temperatures rise. And since warmer water not only expands but also holds less oxygen than colder water, a rise in the mercury will leave fish and other marine life in certain areas without sufficient oxygen. Last July, global ocean surface temperature was the warmest on record: 1.06 degrees Fahrenheit above the 20th century average of 61.5 degrees.

Second, and more importantly, global warming stratifies the upper ocean, further limiting the oxygen supply to deeper waters. Scientists who study the ocean predict global ocean oxygen levels to drop anywhere from one to seven percent over the next century.

Expanding regions of low oxygen water have stressful and even deadly potential for marine life. In the most extreme situations, dead zones...

To view the rest of this article - you must be a paying subscriber and Login