Hidden carbon layer may have sparked ancient bout of global warming

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https://www.science.org/content/article/hidden-carbon-layer-may-have-sparked-ancient-bout-global-warming

By Paul Voosen, Science Magazine. 

Excerpt: There is no perfect parallel in Earth’s past for present-day climate change—human-driven warming is simply happening too fast and furiously. The closest analog came 56 million years ago, when over the course of 3000 to 5000 years, greenhouse gases soared in the atmosphere, causing at least 5°C of warming and pushing tropical species to the poles. The cause of the Paleocene-Eocene Thermal Maximum (PETM) has long been debated, with researchers invoking exotic mechanisms such as catastrophic releases of methane from the sea floor or even asteroid strikes. But over the past few years, evidence has mounted for a more prosaic culprit: carbon-spewing volcanoes that emerged underneath Greenland as it tore away from Europe. Now, researchers have found signs of an effect that would have supercharged the warming effect of the volcanoes, making them a stronger suspect. The underside of Greenland is thought to be encrusted with carbon-rich rocks, like barnacles on the keel of a ship. During the rifting, they might have liberated a gusher of carbon dioxide (CO2), says Thomas Gernon, a geologist at the University of Southampton and leader of the new study. “It’s a perfect storm of conditions.” Mudrocks on the sea floor also contain carbon that originated in living things, and magma from submarine eruptions could have heated the rocks and liberated the carbon. But in 2017, researchers analyzed plankton fossils from an ocean core and found the carbon released during the PETM was heavier than previously thought. For some, that indicated the carbon wasn’t from living sources. “Given the current state of knowledge, it seems likely to be volcanism,” says Marcus Gutjahr, a geochemist at GEOMAR Helmholtz Centre for Ocean Research Kiel, who led the 2017 study. ...CO2 and other gases can bubble out of tectonic plates as they dive into the mantle, percolating up into the underside of thick crusts like Greenland’s, and forming carbonate formations that can be stable for millions or even billions of years.…

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