Southern Illinois University Carbondale geology researcher Daniel Hummer holds a mineral sample taken in Costa Rica while doing research on the Earth’s carbon-cycling process. The team recently published an article in the scientific journal Nature that showed almost all the carbon found in subduction zones is turned into minerals or consumed by microbes before returning to the surface via volcanoes. (Photo provided)
May 07, 2019
Earth’s carbon-cycling process examined by team including SIU geologist
A Southern Illinois University Carbondale geology researcher is part of team that recently found microbes consume and help trap carbon in one of the most geologically dynamic places on Earth: subduction zones on the ocean floor.
The study, which began two years ago, looked at an area in Costa Rica’s subduction zone where the ocean floor is slowly sinking beneath the continent. The volcanic area is a place where the Earth moves materials from its surface into its interior through massive geological forces.
Nature recycling Earth’s carbon
Researchers wanted to know if microbes might affect the carbon cycling inherent in this process, which involves the denser of two plates moving beneath the other as they collide. The team found that microbes do indeed have an impact, both by consuming and more importantly trapping a small amount of the carbon in the area.
The study, published recently in the scientific journal Nature, could have important implications for understanding one of the planet’s basic processes, as well as demonstrating how nature might mitigate the amount of carbon released into the atmosphere, and thereby impact climate change.
Playing key role on the team
Daniel Hummer, assistant professor in the geology degree program, was one of seven career scientists who organized the project, wrote the proposal to the Sloan Foundation, and arranged the expedition to Costa Rica to collect samples. Eventually the team would number more than 20.
“Each of the seven leaders of the project was in charge of a different aspect of sampling, and my role was to organize sampling of rocks and minerals, since my field of expertise is mineralogy,” Hummer said.
SIU Undergraduates participate
Along with Hummer, SIU undergraduate geology students Corey Swiger, Nathan Shelton, Desiree Baker-Wright and Thomas Corcoran also assisted on the project.
“Each worked on samples from this project in my lab,” Hummer said. “They've looked at different sets of samples and characterized what's in them and what they say about the geochemistry happening in the volcanic region of Costa Rica.”
Confirming a theory, making discoveries
Scientists for some time have understood that much of the carbon in a subduction zone comes back to the surface through the volcanoes above, Hummer said. During a 12-day expedition, the team of scientists collected water samples from thermal springs throughout Costa Rica.
By comparing the relative amounts of two different kinds of carbon they found in the samples, they confirmed a long-standing theory that such waters contain carbon molecules that were subducted millions of years previously.
Importantly, the study found a substantial portion of that carbon – about 94 percent – doesn't even make it to the volcanic region at the edge the upper plate. It instead forms minerals before reaching the surface or it is eaten by microbes on the way up.
“It's an amazing revelation that life plays a role not only in the carbon cycle here on Earth's surface, but also affects the way that carbon cycles through the deep Earth,” Hummer said. “The more we investigate, the more we find that life plays a much larger role in geologic processes than we've imagined.”
The study provides the first evidence that subterranean life plays a role in removing carbon from subduction zones. Such an understanding might help researchers understand how the planet’s interior might change over time.
The research team next plans to investigate other subduction zones to test whether this a local or widespread phenomenon.