The Ocean Is Having Trouble Breathing

People who make their living catching fish on the open ocean first noticed the strange phenomenon a few decades ago. It occurred in the shadow zones, the spots between the great ocean currents where sea water doesn’t circulate, off the coasts of Peru, West Africa, and California. The fisher people shared the knowledge among them like a common secret, a bounty that had an even stranger explanation: Sometimes, when the conditions were right, fish would swim closer to the surface of the seas. This made them easier to catch, as the shimmering hordes pushed their way upward, where sunlight filtered through the waters and the oxygen was rich. For the fishing trawlers, this was a wild boon. For the fish, it was something else—the shadow zones, low in oxygen, were expanding, and wildlife habitats were shrinking. Swimming upward, the fish were trying to catch their breath.

It wasn’t until the late 2000s that scientists formally identified what was happening. Observing time-series data from a handful of research stations in Hawaii, Bermuda, and the North Pacific, researchers noticed that the world’s oceans had been losing oxygen, probably for half a century. The existence of