قالب وردپرس درنا توس
Home / Science / The discovery changed understanding of hydrogen depletion in the seabed

The discovery changed understanding of hydrogen depletion in the seabed



The discovery changed understanding of hydrogen depletion in the seabed

The Nereus remote operated hybrid vehicle was used to collect seabed samples, in addition to the Jason II remote-operated vehicle, at the Piccard vents in the Mid-Cayman Rise. Credit: Jill McDermott

The discovery of hydrothermal vents in the 1

970s, where undersea volcanoes produced hot liquids beyond 350 degrees C, or 662 degrees Fahrenheit, fundamentally changed understanding of Earth and how living. However, life in and on the seabed today is still very much a mystery.

A better understanding of these volcanic active areas is important, as the chemistry at seabed vents affects ocean chemistry in general. In addition, the seabed’s unique environment that supports biological and abiotic processes provides clues as to how life on Earth first started, how it sustains over time and the potential for life. live on other planets.

According to geochemist Jill McDermott, professor in the Department of Earth and Environmental Science at Lehigh University, previous studies on the chemistry of hydrothermal vent fluids have shown a reduction in some gases, such as molecular hydrogen. This decline is thought to be caused by microbial communities living on the shallow seabed, collectively known as the undersea biosphere.

However, the results of a new study by McDermott and colleagues contradict that assumption. The researchers analyzed samples of the world’s deepest vented magnetic field hydrothermal liquid known, the Piccard hydrothermal field in Mid-Cayman Rise, at a depth of 4970 meters, or about 16,000 feet below water level. sea. They observed that chemical changes in their samples, including large loss of molecular hydrogen, could only be the result of abiotic (abiotic) and thermogenic (fecal) processes. destruction), because the liquid temperature exceeds the life support limit. is 122 degrees C or about 250 degrees F or less.

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

The discovery changed understanding of hydrogen depletion in the seabed

Lead author Jill McDermott performed a chemical analysis called titration to analyze the hydrogen sulfide content of samples of vented liquids on board R / V Falkor in 2013. Photo Provider: Julie Huber

“Our study found that these changes in chemistry are due to abiotic processes that remove energy before microbial communities have access to it,” said McDermott. “This could have important implications for limiting the extent to which global geochemical cycles can sustain a deep biosphere and for the global hydrogen budget.”

“This also means that the subsurface biosphere is able to take in less energy than anyone has ever realized before. The level of abiotic hydrogen consumption in the ocean’s crust could be reduced,” she added. The impact of seabed life is a major target for future research. “

Using chemical analysis of dissolved gases, inorganic compounds, and organic compounds, the team discovered that low temperature liquid samples stem from a mix of seawater and smokers. nearby Beebe Vents black leaves, so named because the liquid coming out of the vents resembles black smoke from a chimney. In these mixed-liquid samples, many chemicals are either high or low, according to McDermott, according to McDermott. The sample with the largest change in gas had a undersea temperature of 149 degrees C, or 300 degrees F, a temperature too hot for host life. Therefore, they conclude, the process responsible for the geochemical changes cannot be directly related to life.

The abiotic reactions they identify as responsible for these chemical changes include sulfate reduction and thermal decomposition of biomass, and are supported by mass considerations, stable isotope measurements and Chemical energy calculation.

Samples were collected during two research expeditions using two remote controlled vehicles, Jason II and Nereus, both designed to probe deep water and perform a series of investigations. science in the oceans of the world.

The discovery changed understanding of hydrogen depletion in the seabed

Too hot for host life, Beebe Vents high-temperature black smokers act as a source of fluids to nearby mixing zones that stretch the thermal boundaries between the habitable environment and can’t be on the bottom of the sea. All vented liquids were collected using an airtight, titanium hydrothermal liquid sampler, which maintains a bottom pressure prior to sampling on board. Image Providers: Chris German, WHOI / NASA, NSF / ROV Jason / Woods Hole Oceanographic Institute

“This is a really interesting field program, offering a rare opportunity for us to explore the complex interactions between the chemistry of the natural environment and the life it supports,” Seewald said. “We are currently in a much better position to estimate the amount of microbial life that could exist below the seabed.”

Discovered in 2010, the Piccard hydrothermal field is located just south of Grand Cayman in the Caribbean. The liquid samples the researchers tested were ventilated at 44 to 149 degrees C (111 to 300 degrees F), providing the team with a rare opportunity to switch between life-support environments. and not life support.

“The interesting (hot) thing about this study is that we were able to find a set of vents that stretched from place too hot for life to moderately hot,” says German. “That set of particularly cute situations opens up the possibility of gaining new insights into what life can (and might not) do, on the sea floor.”

The change in temperature and chemical composition of hydrothermal vented fluids is known to be an important control measure for the structure and function of microbial communities in the oceanic crust throughout the oceans. positive in the world.

“This relationship exists because hydrothermal fluids power microbial specific metabolic reactions,” said McDermott. “However, the question of whether the liquid chemistry in the vents is altered by life itself, or rather non-living processes instead, is an important question that is rarely addressed. “

The team’s discovery could open up a new dimension of discovery to assess whether abiotic processes serve as important control measures for available energy, in addition to microbiological processes. or not.


The discovery of unknown hydrogen on the mid-ocean ridge points to the hidden biosphere


More information:
Jill M. McDermott el al., “Abiotic redox reactions in hydrothermal mixing zones: Reducing energy available to the subsurface biosphere,” PNAS (Year 2020). www.pnas.org/cgi/doi/10.1073/pnas.2003108117

Provided by Lehigh University



Quote: Discovery of understanding transformation of hydrogen depletion at seabed (2020, August 10) retrieved August 10, 2020 from https://phys.org/news/2020-08-discovery-hydrogen -depletion-seafloor.html

This material is the subject to have fake rights. Other than any fair dealings for academic or personal research purposes, no part may be reproduced without written permission. The content provided is for informational purposes only.




Source link