The discovery in the 1970s of hydrothermal vents, where volcanoes in the sea produce hot liquid that exceeds 350 degrees Celsius, or 662 degrees Fahrenheit, radically changed the understanding of Earth and life. However, life in and under the sea is still very much a mystery today.
Acquiring a better understanding of these volcanic active areas is important, as the chemistry in the offshore branches generally affects ocean chemistry. Moreover, the unique marine environment supports biological and non-biological processes that provide data on how life first began on Earth, how it is provided over time, and the potential for life on other planetary bodies.
According to geochemist Jill McDermott, professor in the Department of Soil and Environmental Science at Lehigh University, past studies of hydrothermal fluid fluid chemistry have revealed reductions in certain gas species, such as molecular hydrogen. These depletions were thought to have been caused by microbial communities living in the shallow sea, collectively called the underwater biosphere.
However, the results of a new study by McDermott and colleagues contradict this assumption. The researchers analyzed samples of gas-tight hydrothermal fluid from the world-famous deepest deflation field, the Piccard hydrothermal field at the Mid-Cayman Rise, which is at a depth of 4,970 meters, or about 16,000 meters 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 decay) processes because fluid temperatures were beyond the limits that support life, understood to be 122 degrees Celsius, or about 250 degrees Fahrenheit, or lower.
The results were published online today in an article “Abiotic redox reactions in areas of hydrothermal mixing: reducing energy availability to the subsurface biosphere” in Proceedings 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 from the Woods Hole Oceanographic Institute; and Shuhei Ono, Associate Professor, Massachusetts Institute of Technology.
“Our study finds that these shifts in chemistry are driven by non-biological processes that deplete energy before microbial communities gain access to it,” says McDermott. “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: “It also means that the subsoil biosphere is likely to receive less energy than anyone has ever realized before. The extent to which abnormal consumption of hydrogen in the oceanic crust can reduce the impact of life at sea is an excellent target for future studies. “
Using chemical analysis of dissolved gases, inorganic compounds, and organic compounds, the team found that low-temperature liquid samples originated from the mixture between the sea and nearby Beebe Vents smokers, so named because the fluid expelled from the ducts resembles smoke. black from a chimney. In these mixed liquid samples, many chemical species are either abundant or abundant in abundance, according to McDermott. The sample with the largest changes in the amount of gas had a sea temperature of 149 degrees Celsius, or 300 degrees Fahrenheit, a very hot temperature for the life of the host. Thus, they concluded, the process responsible for geochemical changes cannot directly involve life.
The non-biological reactions they identified as responsible for these chemical shifts include sulfate reduction and biomass thermal degradation, and are supported by mass balance considerations, stable isotope measurements, and chemical energy calculations.
Samples were collected during two research expeditions using two remotely operated vehicles, the Jason II and the Nereus, both designed for deep-water exploration and to conduct a diverse range of scientific investigations into the world’s oceans.
“This was a really 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 can exist under the sea.”
Discovered in 2010, the Piccard Hydrothermal Basin is located just south of Grand Cayman in the Caribbean. The fluid samples that the researchers threw the study 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 interesting (hot) thing about this study is that we were able to find a group of blooms that flowed from where it was very hot for life, to where it was right,” says German. “This particularly delightful circumstance opened up the opportunity to gain new insights into what life may (and may not) be able to do, down under the sea.”
Changes in hydrothermal channel fluid temperature and chemical composition are known to serve as an important control over the structure and functioning of the community microbe in the oceanic crust throughout the world’s oceans.
“This relationship exists because hydrothermal fluids provide energy for specific microbial metabolic reactions,” says McDermott. “However, the opposite question of whether the chemistry of fluid flow is modified by life itself, or rather by inanimate processes, is an important one that is rarely addressed.”
Team discovery could serve to open a new path of exploration towards assessing whether non-biological processes serve as important controls for energy availability in addition to microbial processes.
Discovery of unknown hydrogen on the ocean ridge indicates hidden biosphere
Jill M. McDermott el al., “Redox Abiotic Reactions in Hydrothermal Mixing Areas: Reducing Energy Availability for the Surface Biosphere,” PNAS (2020). www.pnas.org/cgi/doi/10.1073/pnas.2003108117
Provided by Lehigh University
citation: Discovery transforms understanding of hydrogen loss in the high seas (2020, August 10) Retrieved August 10, 2020 from https://phys.org/news/2020-08-discovery-hydrogen-depletion-seafloor.html
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