Ultraviolet Waters

Asteroids and meteor showers draw the most attention when it comes to dangers from the universe. Pat Neale deals with a silent assault: What if, instead of an asteroid, a dying star nearby exploded in a supernova? A beam of intense radiation called a gamma ray burst could endanger life by wiping out the ozone layer. The odds of such a thing happening are slim, but they highlight humanity’s dependence on ozone—a fragile molecule that still faces dangers from inside the Earth.

Supernova

Remnant of the supernova seen on Earth in 1054 A.D. A superdense neutron star (central white dot) now spews radiation into the surrounding Crab Nebula. © NASA/JPL-Caltech/ESA/CXC/Univ. of Ariz./ Univ. of Szeged

Ozone molecules (O3) shield us from the sun’s ultraviolet light. For humans, too much UV can cause sunburns and skin cancer. For microscopic creatures like phytoplankton, it can cause starvation.

The story of the ozone hole above the South Pole is well-known: Beginning in the 1930s, refrigerators, air conditioners and other newfangled technologies spewed out chemicals called chlorofluorocarbons (CFCs). Once in the atmosphere, the CFCs broke down and released ozone-destroying chlorine. Globally, it’s estimated CFCs raised the level of ultraviolet light reaching Earth’s surface by 5 percent. Fortunately the world woke up to the problem before it became too severe. In 1987 the United Nations created the Montreal Protocol to phase out CFCs and other ozone-depleting substances. Concentrations have since leveled off, though the ozone hole has not disappeared.

However, CFCs linger in the atmosphere for 50 or 60 years. Many of them add to global warming, with hundreds or thousands of times the power of CO2. And climate change brings new dangers of its own. CO2 traps the sun’s warmth in the lower layers of the atmosphere. As those layers simmer, the higher layers, cut off from sunbeams that used to bounce back, begin to cool. Ice crystals begin to form in the upper atmosphere, ice crystals that also can destroy precious ozone molecules.

Pat Neale works to understand what would happen if the ozone disappeared—whether via climate change or supernova—and what it would mean for life in the oceans. He is starting with some of its smallest organisms: microscopic phytoplankton.

Phytoplankton, or tiny marine algae, form the foundation of the ocean’s food web. Everything above, from tiny menhaden to giant blue whales, depends on them. They’re also critical for taking CO2 out of the atmosphere.  As plants, phytoplankton get their energy from photosynthesis, a process that transforms CO2 into biological carbon like sugars that plants use to grow.

Unlike visible light, high-frequency UV light can obstruct photosynthesis, a problem called photoinhibition. UV also makes it harder for them to reproduce. Loss of the ozone layer could destabilize the marine food web by chipping away at its base. While having too many phytoplankton can throw an ecosystem out of whack, having too few could do the same thing.

So far the story of the ozone hole has been one of hope: a story in which scientists discovered the planet was in danger and the global community listened. Pending a supernova, it offers an antidote to the despair that often plagues those who care for the environment. When an ecosystem is still on the edge, it is possible to pull it back.

Learn more about UV’s impact on the ocean in the Photobiology Lab.