Then vs. now: Carbon release 10x faster

PENN STATE (US) — Carbon is being released into the atmosphere 10 times faster than during a period 55 million years ago. The rate may be too rapid for the environment to adjust, researchers suggest.

Scientists chose the Paleocene-Eocene Thermal Maximum (PETM) for comparison because “it is thought to be the best ancient analog for future climate change caused by fossil fuel burning,” says Lee R. Kump, professor of geosciences at Penn State, but the source of the carbon, the rate of emission, and the total amount of carbon involved during the PETM are poorly characterized.

The research is published in the journal Nature Geoscience.

Investigations of the PETM are usually done using core samples from areas that were deep sea bottom 55.9 million years ago that contain layers of calcium carbonate from marine animals that show whether the carbon in the carbonate came from organic or inorganic sources.

But when large amounts of greenhouse gases—carbon dioxide or methane—are in the atmosphere, oceans become more acidic, dissolving calcium carbonate.

“We were concerned with the fidelity of the deep sea records,” Kump says. “How do we determine the rate of change of atmospheric carbon if the record is incomplete? The incomplete record makes the warming appear more abrupt.”

A supply of rock cores at Spitsbergen, Norway, an area that was shallow arctic ocean bottom during the PETM, offered a more complete sample, making it easier to look at what happened through time, without the degradation caused by ocean acidification.

“Deep-sea cores usually have from 10 cm to a meter (about 4 inches to 3 feet) of core corresponding to the PETM,” Kump says. “The Spitsbergen cores have 150 meters (492 feet) of sediment for the PETM.”

The larger sediment section, made up of mud that came into the shallow ocean contains organic matter that can also supply the carbon isotope signature and provide the greenhouse gas profile of the atmosphere.

“We think the Spitsbergen core is relatively complete and shows an interval of about 20,000 years for the injection of carbon dioxide during the PETM,” Kump says.

Using the data collected from the cores, the researchers forced a computer model to in essence run backward. They set up the models to find the proper amounts of greenhouse gases and atmospheric temperature that would have resulted in the carbon isotope ratios observed in the cores.

The outcome was a warming of from 9 to 16 degrees Fahrenheit and an acidification event in the oceans.

“Rather than the 20,000 years of the PETM, which is long enough for ecological systems to adapt, carbon is now being released into the atmosphere at a rate 10 times faster,” said Kump. “It is possible that this is faster than ecosystems can adapt.”

Researchers from the University of Southampton and the University of Bristol contributed to the study, that was funded in part by the National Science Foundation and the Worldwide Universities Network.

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