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Holmzaden ichthyosaurs died off at the beginning of the Cretaceous-Paleogene extinction pulse. Image: Utah Museum

Holmzaden ichthyosaurs died off at the beginning of the Cretaceous-Paleogene extinction pulse. At the time, oceanic dead zones were similar to today’s. Image: Utah Museum

The Inertia

Somewhere around 94 million years ago, a huge chunk of the ocean’s creatures died off. You probably learned about in school, scribbled a few answers on a test about it, then promptly forgot that it ever happened because 94 million years is a pretty long time and who gives a shit about the Cretaceous Period? It’s called the Oceanic Anoxic Event-2 (OAE-2 from now on, because I don’t want to type that over and over again), and it happened because the levels of oxygen in the ocean dropped relatively dramatically over the course of 50,000 years. In the end, nearly 30 percent of marine invertebrates went extinct. According to a research paper published in Science Advances, the current rates of deoxygenation are strikingly similar to those of the OEA-2, and it’s likely that’s we’re headed down the same path.

“Increased ocean deoxygenation is already apparent in the modern ocean,” the authors of the paper wrote, “because marine dioxygen has decreased by two percent over roughly the last half century, and recent models predict a continued loss of 0.5 to 3.5 per cent over the next half century, which would result in huge expansions of ocean anoxia within the next few thousand years.”

There have been five mass extinction events on earth. They’ve occurred at the end of the Ordovician, Devonian, Permian, Triassic, and Cretaceous periods, and wouldn’t you know it? At the rate we’re going, some researchers think we could be living through one right now. As an interesting aside, the Cretaceous Period one–widely accepted to have been caused by a meteor–was relatively small. During the Permian Period, about 252 million years ago, a staggering 9 out of 10 species dropped dead. It’s known as The Great Dying, which would be a good name for a metal band.

Of course, OEA-2 occurred from natural causes. Here’s what happens, in the most basic of explanations: it’s theorized that the extremely high levels of volcanism at the time released vast amounts of carbon dioxide into the atmosphere. That–if you believe in facts and science and all that hocus-pocus–warmed the planet warmed up. Then, the ocean’s acidity skyrocketed and the ocean’s excess CO2 resulted in giant algal blooms which were then fed upon by aerobic bacteria, whose populations exploded, who then died and decomposed, which produced oceanic anoxia, which killed everything. Basically, exactly what’s happening right now in places like the Gulf of Mexico, with the exception of the volcanoes.

Those expansive, oxygen-starved areas of ocean are known as dead zones, and if you’ve been following the news you know that this year’s dead zones are far larger than they’ve ever been. It’s not caused by volcanism, though–it’s caused by us and our unquenchable thirst for more of everything. In our effort to feed a sweaty, fat population 72-ounce steaks for breakfast, lunch, and dinner, we vomit out vast amounts of sewage and nitrogen-rich fertilizers. And like Ecclesiastes said, all streams run to the sea, where alga thrives on nitrogen and human shit. It’s happening right now in the Gulf of Mexico and the Baltic Sea. During the OEA-2, the dead zone process happened over a long time. But since we’re gluttonous humans, we’ve jacked the scale right up. “Our results show that marine deoxygenation rates prior to the ancient event were likely occurring over tens of thousands of years, and surprisingly similar to the two per cent oxygen depletion trend we’re seeing induced by anthropogenic activity over the last 50 years, said Dr. Sune Nielson of the Woods Hole Oceanographic Institution. “We don’t know if the ocean is headed toward another global anoxic event, but the trend is, of course, worrying.”

So if we are headed for another OEA-2 as the numbers seem to suggest, what kind of time frame are we looking at? Well, good news for the selfish ones out there–we’ll probably be dead… but pretty freshly dead.

“Localized oxygen loss is already apparent in the modern ocean, and the ability to observe more widespread perturbation seems realistic under currently projected carbon emissions,” researchers wrote. “Should anthropogenically induced oxygen loss occur at similar rates as in the period leading up to OAE-2, then the current area of seafloor hypoxia would double in about the next 102 to 344 years. Without positive human intervention, ancient OAE studies are destined to become uncomfortably applicable in the not-so-distant future.”


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