A new study, conducted by scientists from the University of Texas at Austin Jackson School of Geosciences, suggests the volcanic activity related to the plate-tectonic movements could have triggered climate changes in Earth's history. The research has investigated long-term changes in the planet's climate and discovered periods of heightened volcano activity along continental arcs coincide with warmer, greenhouse conditions over the last 720 million years.
The study had focused on resolving the question why our planet fluctuated between periods of ice and those when its polar region was free of ice cover. Results showed that periods of increased volcano activity along the continental arcs matched the warmer conditions while the times when the volcanoes were less active coincided with colder, icehouse conditions.
Continental volcanic arcs are systems created where the two tectonic plates meet, and the oceanic plates descend under the continental plate, forming subduction zones at active continental margins. During the subduction zones formation, magma mixes with carbon otherwise trapped inside the Earth's crust. Following the volcano eruptions, the carbon dioxide gas gets released into the atmosphere.
"Continental arc systems are plumbed through the Earth’s crust, and they tend to interact with carbon reservoir rock preserved beneath the surface," said Ryan McKenzie, a postdoctoral researcher at the Jackson School.
According to McKenzie, it was long known that the amount of carbon dioxide gas in the planet's atmosphere significantly impacts the climate. However, a question which needed answering was what exactly has caused the fluctuations of carbon dioxide observed in the geological records. The newest research puts into focus the amount of carbon dioxide released into the atmosphere, rather than the amount removed from it.
The scientists have used nearly 200 published studies and vast amounts of fieldwork and other data to create a global database from which the volcanic history of continental margins over the last 720 million years could be reconstructed.
"We studied sedimentary basins next to former volcanic arcs, which were eroded away over hundreds of millions of years. The distinguishing part of our study is that we looked at a very long geologic record – 720 million years – through multiple greenhouse-icehouse events," said co-author Brian Horton, a professor in the Jackson School’s Department of Geological Sciences.
The zircon mineral can be used to track continental arc volcanism, as it is less commonly found in other types of volcanic spots. The researchers have looked at data for about 120 000 zircon grains from thousands of samples.
"We’re looking at changes in zircon production on various continents throughout Earth’s history and seeing how the changes correspond to the various icehouse and greenhouse transitions. Ultimately, we find that during intervals of high zircon production we have greenhouse conditions, and as zircon production diminishes, we see a shift into our icehouse conditions," said McKenzie.
The research showed that periods of cooler, icehouse periods correlate with the assembly of the Earth's supercontinent while the warmer, greenhouse periods coincide with a time of enhanced continental volcanism and continental breakup.
- "Continental arc volcanism as the principal driver of icehouse-greenhouse variability" - N. Ryan McKenzie, Brian K. Horton, Shannon E. Loomis, Daniel F. Stockli, Noah J. Planavsky, Cin-Ty A. Lee - Science (2016) - DOI: 10.1126/science.aad5787
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