Feedbacks upon feedbacks: Rock weathering and the climate

Since the early 1980s, Earth scientists have understood that erosion and weathering of rock slowly removes CO 2 from the atmosphere, regulating Earth’s climate on geological timescales. But recent studies have shown that erosion can also emit CO 2 by oxidizing organic carbon contained in eroding sediments. It hasn’t been clear how this competition between removal by rock weathering and emission by organic carbon weathering ends up affecting Earth’s climate.

A new study in the journal Nature Communications uses the geological past to test how these competing effects added up. Doctor Madeleine Stow of the University of Oxford, with colleagues from across the UK and France, examined a volcanically triggered episode of global warming that happened in the early part of the Jurassic period, 183 million years ago, known as the “Toarcian Ocean Anoxic Event.”

They found that eroding organic carbon amplified climate warming at the time, suggesting that the same process may apply to modern climate change. But the extent to which the past is prologue is uncertain.

Sampling the air using sediments from the seabed

The Toarcian warming event is one of a dozen or so periods of climate change in the geological past that were triggered by enormous volcanic phenomena known as large igneous provinces. Several are associated with mass extinctions, including the Great Dying at the end of the Permian period, which was caused by the Siberian Traps Large Igneous Province. The Toarcian event was triggered by massive volcanic eruptions across South Africa and Antarctica, which were joined together at the time. The resulting 6° to 7° C of global warming shuffled the makeup of plant and dinosaur species on land and caused a mass extinction of corals and other marine species.

“This event had been well studied before. We understand its drivers, we understand how it caused mass extinctions, and it’s driven by this Large Igneous Province release,” explained University of Oxford professor Bob Hilton, a coauthor and principal investigator in the study.