Examining a stone is like reading a book. Rocks have a story to tell, says Frieder Klein, a research assistant professor in the Department of Marine Chemistry and Geochemistry at Woods Hole Oceanographic Institution (WHOI). Klein and his colleagues discovered St. Louis in the ocean about 500 km off the coast of Brazil. St. Paul Transform Fault. Peter and St. The rocks he analyzed from the submerged slopes of the St. Paul Archipelago tell a fascinating and previously unknown story about parts of the world. geological carbon cycle.

Transform faults, where tectonic plates cross each other, are one of the three major plate boundaries on Earth and are approximately 48,000 km long worldwide; the others are the global system of mid-ocean ridges (about 65,000 km) and subduction zones (about 55,000 km). ). kilometer).

The role of conversion errors in the carbon cycle

The carbon cycle at mid-ocean ridges and subduction zones has been studied for decades. In contrast, scientists have paid relatively little attention to CO.₂ On oceanic transform faults. Transform faults have long been considered “boring” places because of low magmatic activity, Klein says. “What we’re now piecing together is that the mantle rocks exposed along these ocean transform faults are potentially a large sink of CO2,” he says.

Partial melting of the mantle releases CO2₂The mantle captured by the hydrothermal fluid reacts with the mantle closer to the seafloor and becomes trapped there.

This is a previously unknown part of the geological carbon cycle,” said Klein, lead author of the new journal study published in Proceedings National Academy of Sciences (PNAS). Because transformation errors were not taken into account in previous estimates of global geological CO2 flux.₂magmatic CO mass transfer ₂ “Changing ocean mantle and seawater may be greater than previously thought.”

Geological emissions and climate

“Amount of CO₂It is negligible compared to the amount of anthropogenic or anthropogenic CO2 released through conversion errors.₂– says Klein. “But on geological time scales and before humans started emitting so much CO2₂“Geological emissions from the Earth’s mantle, including transform faults, were a major driver of Earth’s climate.”

As stated in the document, “global anthropogenic CO2 emissions₂ It is estimated at around 36 gigatonnes (Gt) per year, dwarfing the average geological emissions to the atmosphere and hydrosphere (0.26 Gt per year). With all this, CO emissions over geological timescales₂It plays an important role in regulating Earth’s climate and habitability, as well as C concentrations from the Earth’s mantle. [вуглецю] in surface reservoirs, including the oceans, atmosphere, and lithosphere.” Klein adds: “This was, of course, before the anthropogenic burning of fossil fuels.”

Understanding climate change through geological research

“To fully understand modern human-caused climate change, we need to understand natural climate fluctuations in Earth’s deep past that are linked to disruptions in the Earth’s natural carbon cycle,” said co-author Tim Schroeder, a professor at Bennington College in Vermont. “Large changes in such carbon flux over millions of years have caused Earth’s climate to be much warmer or colder than it is today.”

In the paper, to better understand the carbon cycle between Earth’s mantle and the ocean, Klein, Schroeder and their colleagues studied the St. It is stated that they examined the formation of soapstone “and other magnesite assemblages during mineral carbonation of mantle peridotite” in the Paul transform fault. . “Fueled by magmatism at or beneath the root zone of a transform fault and subsequent degassing, the fault is a conduit for CO-rich hydrothermal fluids.”₂Carbonation of peridotite is a potentially large sink for CO2 emissions₂“.

In the paper, the researchers note that it is “a combination of low melting rates that produce melts enriched in incompatible elements, volatiles, and particularly CO2.”₂and the presence of peridotite in oceanic transform faults creates conditions that lead to intense carbonation of minerals.”

The rocks were collected by vehicles carrying people during a trip to the region in 2017.

Finding and analyzing these stones “was a dream come true. “We predicted the presence of carbonate-altered rocks in the oceanic mantle 12 years ago, but we couldn’t find them anywhere,” says Klein. “We went to the archipelago to look for low-temperature hydrothermal activity and found no such activity there. It was incredible that we were able to find these rocks in a transform fault because we found them by chance while looking for something else.”