How did volcanism trigger climate change before the eruptions started?

As the climate warms beyond historical ranges, there is an increasing need for scientists to study climates deeper into Earth’s past. Information about our futureOne of his research interests is a warming event known as the Miocene Climatic Optimum (MCO), which occurred about 17 to 15 million years ago. This period coincided with floods of basalt lava that covered a large area of ​​the northwestern United States, forming what is known as the “Columbia River Basalt.” Volcanic CO₂ The cause Of global warming.

These eruptions are the latest examples of “large igneous provinces,” a phenomenon that has repeatedly caused climatic upheaval and mass extinctions throughout Earth’s history. The Miocene eruptions were relatively mild, CO₂ level The earth’s temperature is rising, Ecosystem change and A large melting of Antarctic ice, But it did not cause a mass extinction.

paper Just published in the Geological Journalled by Jennifer Kasbaum Researchers at the Carnegie Institution for Science’s Earth and Planetary Institute have debunked the idea that the eruption caused the warming, but still blame it on the eruption. peak Warming climate.

This study is the first successful application of high-precision radiometric dating to climate records obtained by drilling marine sediments, paving the way for improved measurement of past climate changes. Furthermore, it validates mathematical models of our long-term orbit around the solar system.

Past climate and present CO₂ level

“Today, 420 ppm [of CO₂]”We’re essentially in the Miocene climatic optimum.” Thomas Westerhold Researchers at the University of Bremen peer-reviewed Kasbaum’s study. CO₂ Levels matchGlobal temperatures have yet to reach the maximum temperature of the MCO. 8°C “We are moving the Earth system in a completely opposite direction, away from what we call an ‘ice house world,'” Westerhold said.

When Kasbaum began looking into the link between basalts and the MCO warming in 2015, she found that there was a lot of uncertainty about the correlation. High-precision radiometric datingShe used the radioactive decay of uranium trapped in zircon crystals to date the basalts. She found that the new dates are no longer in the MCO warming range. “All these eruptions [are] “It’s all packed into a tiny fraction of the Miocene Climatic Optimum,” Kasbaum says.

But there were also large uncertainties in the age of the MCO, and the discrepancy could be due to those uncertainties. Kasbaum tried to apply the same high-precision dating methods to marine sediments that record the MCO.

A new approach to an old problem

“What’s really exciting is that this is the first time we’ve applied this technique to ocean drill core sediments,” Kasbaum said.

Typically, marine sediments drilled from the seafloor are dated using a combination of fossil changes, magnetic field reversals, and the alignment patterns of sediment layers due to orbital wobbles calculated by astronomers. Each of these methods has uncertainties, and further uncertainties are added by gaps in the sediments caused by the drilling process and natural pauses in the deposition of material. This makes it difficult to reconcile the different records with the precision needed to determine cause and effect.

These uncertainties made it unclear when the MCO would be implemented.

Radiometric dating avoids these uncertainties. But until about 15 years ago, such dates were subject to large errors that made them useless for resolving questions such as the timing of the MCO. And the technique typically requires several kilograms of sample to find zircon crystals with enough uranium, whereas ocean drill cores only produce a few grams.

But scientists have significantly reduced these limitations: “Overall, people have worked hard to track, quantify, and minimize every aspect of uncertainty in the measurements, which is why I can report these dates with such precision,” Kasbaum said.