New research suggests that subsurface microbes are crucial to storing substantial amounts of carbon underground between coastal trenches and inland chains of volcanoes.
Researchers from 27 institutions in six nations led by Rutgers University found that microbes are able to store carbon and keep it from entering the atmosphere as a greenhouse gas by helping to form a mineral comprised of calcium carbonate called calcite.
The international team discovered exactly how microbes alter the flow of volatile substances such as carbon, which can change from a solid or a liquid to a vapor in subduction zones, where two tectonic plates collide and the denser plate sinks, moving material from the surface into the Earth’s interior.
The subduction process produces deep-sea trenches and chains of volcanoes called volcanic arcs at the boundary of tectonic plates. Volcanic arcs, which can be found in South America, Central America and Japan, produce a significant amount of carbon dioxide emissions that re-enter the atmosphere from subducted material that often consists of marine sediment, oceanic crust and mantle rocks.
The study focused on the Nicoya Peninsula on the western coast of Costa Rica in the area between the trench and the volcanic arc called the forearc. The researchers found that the volcanic forearc is a deep sink for carbon dioxide.
The efficiency of the transfer of carbon and other volatile gases, fluids or mineral phases is vital for the nature and scale of geochemical heterogeneities in the Earth’s deep mantle and shallow crustal reservoirs, as well as the Earth’s oxidation state.
However, the proportions of volatiles released from the forearc and backarc are not well constrained compared to fluxes from the volcanic arc front, according to the study. The researchers used helium and carbon isotope data from deeply sourced springs along two cross-arc transects and found that about 91 percent of carbon released from the slab and mantle underneath the Costa Rican forearc is sequestered within the crust by calcite deposition.
“Around an additional 3 percent is incorporated into the biomass through microbial chemolithoautotrophy, whereby microbes assimilate inorganic carbon into biomass,” the researchers write. “We estimate that between 1.2 × 108 and 1.3 × 1010 moles of carbon dioxide per year are released from the slab beneath the forearc, and thus up to about 19 percent less carbon is being transferred into Earth’s deep mantle than previously estimated.”
The study could have lasting impacts, shedding light on the long-term impact volcanoes have on carbon dioxide and how it may be buffered by chemical and biological processes to evaluate the natural and human impacts on the climate. If scientists understand how carbon moves between the surface and the interior in the subduction zone, they can better understand one of the crucial processes that regulates the climate over tens of millions of years.
“Our study revealed a new way that tiny microorganisms can have an outsized impact on a large-scale geological process and the Earth’s climate,” co-author Donato Giovannelli, a visiting scientist from the University of Naples and former post-doc in the Department of Marine and Coastal Sciences at Rutgers University–New Brunswick, said in a statement.
The study was published in Nature.