Discovery changes concept of hydrogen output at sea

The discovery in the 1970s of hydrothermal vents, in which volcanoes on the ocean floor produce hot liquids of more than 350 degrees Celsius, or 662 degrees Fahrenheit, fundamentally changed the notion of Earth and life. Yet life on and under the seabed is still quite a mystery today.

Gaining a better understanding of these volcano active areas is important because the chemistry of sea urchins has a more general impact on ocean chemistry. In addition, the unique environment of the seabed supports biological and non-biological processes that provide clues as to how life on Earth first began, how it is formed over time, and its potential. for life on other planetary bodies.

According to geochemist Jill McDermott, a professor in the Department of Earth and Environmental Sciences at Lehigh University, past studies of the chemistry of hydrothermal vents have revealed reductions in certain gases, such as molecular hydrogen. These disturbances were thought to be caused by microbiological communities living in the shallow sea flower, collectively called the underfloor biosphere.

However, results of a new study by McDermott and colleagues oppose this assumption. The researchers analyzed gas-tight hydrothermal fluid samples from the deepest known ventilated field in the world, the Piccard hydrothermal field at the Mid-Cayman Rise, which lies at a depth of 4970 meters, or about 16,000 feet below sea level. They observed chemical shifts in their samples, including a large loss of molecular hydrogen, which could only be the result of abiotic (non-biological) and thermogenic (thermal decomposition) processes, because the flow temperatures were outside the limits it life support, understood to be 122 degrees Celsius, or around 250 degrees Fahrenheit, or lower.

The results were published online today in an article “Abiotic redox reactions in hydrothermal mixing zones: reduced energy availability for the subsurface biosphere” in the Procedures of the National Academy of Sciences. Additional authors include: Christopher German, Senior Scientist in Geology & Geophysics and Jeffrey Seewald, Senior Scientist in Marine Chemistry & Geochemistry and Sean Sylva, Research Associate III, in Marine Chemistry & Geochemistry of the Woods Hole Oceanographic Institution; and Shuhei Ono, Associate Professor, Massachusetts Institute of Technology.

“Our study finds that these shifts in chemistry are driven by non-biological processes that release energy before microbial communities can access it,” McDermott says. “This could have critical implications for limiting the extent to which global geochemical cycles can sustain a deep biosphere, and for the global hydrogen budget.”

She adds, “This also means that the biosphere under the ground is likely to receive less energy than previously thought. The extent to which non-biological hydrogen use in the oceanic crust can reduce the impact of life on sea buckthorn is a major goal. for future studies. “

Using chemical analysis of dissolved gases, inorganic compounds, and organic compounds, the team found that the low-temperature liquid samples arose from mixing between seawater and the nearby Beebe Vents black smokers, so named because the liquid that expelled from the valves resembles black smoke from a chimney. In these mixed liquid samples, many chemical species are high or low in abundance, according to McDermott. The sample with the largest shifts in the amount of gas had a sea air temperature of 149 degrees Celsius, or 300 degrees Fahrenheit, a temperature that is too hot to host life. Thus, they concluded, the process responsible for the geochemical changes could not directly involve life.

The non-biological reactions they identified as responsible for these chemical shifts include sulfate reduction and the thermal degradation of biomass, and are supported by considerations of mass balance, stable isotope measurements, and calculations of chemical energetics.

The samples were collected during two research expeditions using two remote-controlled cars, Jason II and Nereus, both designed to explore deep water and to conduct a diverse range of scientific research in the oceans of the world.

“This was a very exciting field program that provided a rare opportunity for us to explore the complex interaction between the chemistry of a natural environment and the life it supports,” Seewald said. “We are now in a much better position to estimate the amount of microbial life that exists beneath the sea urchin.”

Discovered in 2010, Piccard Hydrothermal Field is located just south of Grand Cayman in the Caribbean. The fluid samples the researchers examined fought at 44 to 149 degrees Celsius (111 to 300 degrees Fahrenheit), providing a rare opportunity for the team to study the transition between life-supporting and non-life-supporting environments.

“The cool (hot) thing about this study is that we were able to find a set of valves that ranged from where it was too hot for life, to where it was just right,” says German. “That particularly fun set of circumstances opened up the possibility of gaining new insights into what life might (and might not) do, under the seabed.”

Changes in hydrothermal vent fluid temperature and chemical composition are known to serve as an important control on microbial community structure and function in the oceanic crust in the world’s oceans.

“This relationship exists because hydrothermal fluids provide energy for specific microbial metabolic reactions,” McDermott says. “The inverse question of whether vent fluid chemistry is adapted by life itself, or rather by non-living processes, is an important one that is rarely addressed.”

The team’s discovery could serve to open up a new path of exploration after observing or non-biological processes as important controls for energy availability, in addition to microbial processes.