Microbes may be gatekeepers of Earth’s deep carbon

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New findings highlight the role of microbes in carbon moving from the Earth’s surface to interior.

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24 April 2019 | 0

A study finds that microbes affect the cycle of carbon moving from the Earth’s surface to the deep interior. Conducted in Costa Rica’s subduction zone two years ago, a team of scientists found that microbes consume and help to trap a small amount of sinking carbon. The study, published in science journal Nature, is hugely significant in understanding the Earth’s fundamental processes and revealing the ability of nature to alleviate climate change

Carbon sequestration

The Earth’s surface and interior can communication at a subduction zone. Two plates collide and the denser one sinks, thus moving material from the surface to the interior. The microbes near the surface play a crucial role in how elements including carbon are locked in the crust. The breakthrough gives new insight into the Earth’s processes and could aid researchers in anticipating its interiors developments.

Prof Chris Ballentine, co-author of the study and head of the department of earth sciences at the University of Oxford, says it shows that, “…in areas that are critically important for putting chemicals back down into the planet – these big subduction zones – life is sequestering carbon. On geological timescales life might be controlling the chemicals at the surface and storing elements like carbon in the crust.’

For the first time, there is evidence that subterranean life contributes to the removal of carbon from subduction zones. It is already established that microbes can take carbon dissolved in water and convert it into a mineral within the rocks. This process happens on a large scale across a subduction zone. The natural CO2 sequestration process can control the availability of carbon on the Earth’s surface.

Karen Lloyd, senior author and associate professor of microbiology at the University of Tennessee, says, “These microbes are literally sequestering carbon. Scientists are actively working on carbon sequestration to mitigate climate change and carbon capture and storage as a means to bury greenhouse gases over long time periods.” She notes that the study is a great example of this occurring naturally. “It was previously unrecognised. This study shows that this happens on a big, reservoir scale.”

Dr Peter Barry, lead author and fellow member of the Oxford earth science department, says, ‘We found that a substantial amount of carbon is being trapped in non-volcanic areas instead of escaping through volcanoes or sinking into Earth’s interior.

“Until this point scientists had assumed that life plays little to no role in whether this oceanic carbon is transported all the way into the mantle, but we found that life and chemical processes work together to be the gatekeepers of carbon delivery to the mantle.”

On a 12-day mission, the 25 strong team of researchers from multiple disciplines collected water samples from various thermal springs. It has long been predicted that Costa Rica’s thermal springs release ancient carbon molecules, subducted millions of years previous.

In comparing the relative amounts of two different kinds of carbon, those predictions rang true. Processes previously unrecognised were at play in the crust above the subduction zone, helping to trap substantial quantities of carbon. It is estimated that 94% of the carbon transforms into calcite minerals and microbial biomass.

Maarten de Moor, co-author and professor at the National University of Costa Rica’s Observatory of Volcanology and Seismology, marvels at the teams findings, saying, “It is amazing to consider that tiny microbes can potentially influence geological processes on similar scales as these powerful and visually impressive volcanoes, which are direct conduits to Earth’s interior.  The processes that we have identified in this study are less obvious, but they are important because they are operating over huge spatial areas in comparison to volcanoes.”

Interdisciplinary benefits

Acknowledging the benefits of taking an interdisciplinary approach, Dr Peter Barry, associate scientist at Woods Hole Oceanographic Institution, added, “We have people from three different fields working together and only with such an interdisciplinary approach can you make such breakthroughs. Moving forward, this will change how people look at these systems.”

Following on from this success, the researchers intend to investigate other subduction zones to establish whether the phenomenon is widespread. Proving that these processes occur worldwide would mean that there is 19% less carbon entering the deep mantle than previously estimated.

“There are likely even more ways that biology has had an outsized impact on geology…” says co-author Donato Giovannelli, assistant professor at the University of Naples Federico II, “…we just haven’t discovered them yet.”

The research is part of the Deep Carbon Observatory’s Biology Meets Subduction project. With 25 researchers from six nations belonging to each of Deep Carbon Observatory (DCO) Science Communities: Deep Life, Extreme Chemistry and Physics, Reservoirs and Fluxes, and Deep Energy.

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