Jurassic extinction may hold clues about our oceans’ future

Researchers have uncovered a significant clue in Italian limestone that helps explain a mass extinction of marine life millions of years ago during the Jurassic. The research may offer insights into the impact of oxygen depletion and climate change in today’s oceans. 

Michael A. Kipp, an assistant professor of earth and climate science at Duke University, co-authored a study measuring oxygen loss in oceans leading to marine species extinction 183 million years ago. 

“This event, and events like it, are the best analogs we have in Earth’s past for what is to come in the next decades and centuries,” he said.

Oxygen depletion during the Jurassic

During the Jurassic Period, extensive volcanic activity in what is now South Africa released approximately 20,500 gigatons of carbon dioxide (CO2) over 500,000 years, heating the oceans and causing significant oxygen depletion.

The result was a mass extinction of Jurassic marine species due to suffocation from the lack of oxygen.

“It’s an analog, but not a perfect one, to predict what will happen to future oxygen loss in oceans from human-made carbon emissions, and the impact that loss will have on marine ecosystems and biodiversity,” said co-author Mariano Remirez, an assistant research professor at George Mason University.

By examining limestone sediment that carries chemicals dating back to the time of the volcanic activity, researchers were able to estimate changes in ancient ocean oxygen levels. 

At one point, oxygen was completely depleted in up to 8% of the ancient global seafloor, an area roughly three times the size of the United States.

Unprecedented levels of atmospheric CO2

Since the Industrial Revolution, human activity has released CO2 emissions equivalent to 12% of what was released during the Jurassic volcanism. 

However, Kipp notes that today’s rapid rate of atmospheric CO2 release is unprecedented, making it difficult to predict when another mass extinction might occur or its severity.

“We just don’t have anything this severe,” Kipp said. “We go to the most rapid CO2-emitting events we can in history, and they’re still not rapid enough to be a perfect comparison to what we’re going through today. We’re perturbing the system faster than ever before.”

“We have at least quantified the marine oxygen loss during this event, which will help constrain our predictions of what will happen in the future,” he concluded.

Climate change and oxygen loss

In the ocean, climate change and oxygen loss are directly related. Warmer water holds less oxygen than cooler water, which means that dissolved oxygen levels are diminished as temperatures rise. 

On top of this, higher temperatures cause ocean stratification, where layers of water with different temperatures form. This prevents the mixing of oxygen-rich surface waters with deeper waters. 

Another contributing factor is the increased input of nutrients from agricultural runoff and other sources, which can lead to algal blooms. 

When these algae die and decompose, the process consumes large amounts of oxygen, creating hypoxic or “dead” zones where marine life cannot survive. 

Climate change can intensify these processes by altering rainfall patterns, increasing runoff, and thereby increasing the nutrient load entering the ocean.

Furthermore, the melting of polar ice caps and glaciers due to global warming can lead to changes in ocean circulation patterns. These changes affect the distribution of oxygen in the ocean, often leading to decreased oxygen levels in certain areas. 

Overall, the combination of warmer water temperatures, stratification, nutrient pollution, and changes in circulation patterns driven by climate change is causing significant oxygen loss in the ocean, which has serious implications for marine ecosystems and the organisms that depend on them.

How does oxygen loss impact marine species?

Oxygen loss in marine environments significantly impacts marine animals by reducing the availability of a critical element needed for their survival. 

As oxygen levels decrease, many marine species experience stress, which can lead to decreased growth rates, impaired reproductive success, and increased susceptibility to diseases. 

This hypoxic condition forces marine animals to either adapt, migrate to areas with higher oxygen levels, or face potential mortality. 

Additionally, oxygen depletion can disrupt food chains, as both predator and prey species are affected, leading to broader ecological consequences in marine ecosystems.

The study is published in the journal Proceedings of the National Academy of Sciences.

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