University Of Texas Researchers Examine Volcanoes' Role In Historic Climactic Shifts

AUSTIN, TX --- There are ambitious research studies, and then there's really ambitious research studies. A new one from University of Texas at Austin researchers is in the latter category, exploring ancient volcanic activity might have played a role in historical climate shifts.

Details of the study are outlined in the April 22 edition of Science magazine. Findings by researchers at the university's Jackson School of Geosciences center on plate-tectonic movement of continents that could be the reason for climate shift from hot to cold over tens and hundreds of millions of years throughout the history of the Earth, officials explained.

The scientists's study addresses why the Earth has fluctuated from periods when the planet was covered in ice to times when even the polar regions were ice-free. It explores very long-term shifts in Earth’s baseline climate, researchers note -- not short-term or man-made climate change.

Lead researcher Ryan McKenzie said findings indicate that periods when volcanoes along continental arcs were more active coincided with warmer (or greenhouse) conditions over the past 720 million years. Conversely, periods when continental arc volcanoes were less active coincided with colder (or icehouse) conditions.

"Continental volcanic arc systems such as the Andes Mountains are created at active continental margins where two tectonic plates meet and the oceanic plate descends under the continental plate, forming a subduction zone," university officials explained. "When this happens, magma mixes with carbon trapped in the Earth’s crust and releases carbon dioxide (CO2) gas into the atmosphere when volcanoes in the system erupt."

McKenzie said interplay between layers of rock also figured prominently: “Continental arc systems are plumbed through the Earth’s crust and they tend to interact with carbon reservoir rock preserved beneath the surface,” said McKenzie, who began the work as a postdoctoral researcher at the Jackson School and finished the study at Yale University.

While scientists have long known the amount of carbon dioxide in the atmosphere influences the planet's climate, the cause of CO2 fluctuations observed in the geologic record has remained a mystery. A departure in the prevailing thinking on the issue is central to the University of Texas study.

Past theories have suggested geological forces (mountain building, for instance) have introduced large amounts of new material to the Earth's surface at various times in the planet's history. Central to that idea is theory is the pulling of CO2 out of the atmosphere as that new material weathers.

The UT study points to the amount of CO2 being released into the atmosphere, rather than the amount removed from it, as the primary driver of Earth's climate, researchers explained.

Did we mention the study is ambitious? Researchers used nearly 200 published studies along with their own field work and data to create a global database in reconstructing volcanic history over the past 720 million years.

That's what we call a longitudinal study.

“We studied sedimentary basins next to former volcanic arcs, which were eroded away over hundreds of millions of years,” said co-author Brian Horton, a professor in the Jackson School’s Department of Geological Sciences. “The distinguishing part of our study is that we looked at a very long geologic record – 720 million years – through multiple greenhouse-icehouse events.”

Specifically, researchers looked at the uranium-lead crystallization ages of the mineral zircon, which is largely created during continental volcanic arc activity, officials said. Zircon is less common in other types of volcanic settings -- Hawaii or island arc volcanoes such as the Marianas, for example -- so the mineral can be used to track continental arc volcanism.

As part of the study, researchers examined data for some 120,000 zircon grains from thousands of samples across the globe.

“We’re looking at changes in zircon production on various continents throughout Earth’s history and seeing how the changes correspond with the various icehouse and greenhouse transitions,” McKenzie said. “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.”

Horton noted the cooler so-called icehouse periods tended to correlate with the assembly of the Earth’s supercontinents, during a time of diminished continental volcanism. Conversely, the warmer greenhouse periods correlated with continental breakup, during times of enhanced continental volcanism.

Jackson School researchers Shannon Loomis and Daniel Stockli, Yale University’s Noah Planavsky, and Rice University’s Cin-Ty Lee also worked on the study. The research was funded by the National Science Foundation.

>>> First image via WikiMedia Commons; second image courtesy of Brian Horton, who writes: "Volcano Licancabur, an active volcano in the Andean continental volcanic arc on the Chile-Bolivia border, looms above flamingos in a nearby lake."