Hydrothermal Vent Site Expands Estimates of Seabed Mineral Deposits – Astrobiology

When scientists discovered a hydrothermal vent site in the Arctic Ocean’s Aurora Hydrothermal System in 2014, they didn’t immediately realize how exciting their discovery was.

“Although the discovery of a vent in the Arctic Ocean was a first, we thought what we found was one of the least interesting types of vent sites that exist,” said Chris German. , senior scientist in the Department of Geology and Research at the Woods Hole Oceanographic Institution. Geophysics. “We came back from the expedition thinking, ‘Okay, we’ve found a site in the Arctic. It’s great, but if you take the ice cover off, it’s just another aeration site.”

However, after further analysis and a follow-up expedition in 2019 to the remote site, German and other researchers now believe it to be a very significant find. They believe this vent – and others yet to be found in the bottom of the Gakkel Ridge Rift Valley in the Arctic Ocean – could change our understanding of ultra-slow-spreading mid-ocean ridges, greatly expand estimates of precious marine mineral deposits rich in copper and gold and serve as natural laboratories to help inform the search for extraterrestrial life.

“Our findings have implications for ultra-slow ridge cooling, global marine mineral distributions, and the diversity of geologic settings that may harbor abiotic organic synthesis – relevant to the search for life beyond Earth,” according to the article, “Volcano-hosted venting with indications of ultramafic influence at the Aurora hydrothermal field on Gakkel Ridge,” published in Nature Communications.

“Most of what we may have discovered is a vent site under an ice-covered ocean that is also an ideal place to study organic synthesis relevant to the origin of life and to search for life beyond Earth,” said German, who is the paper’s lead author. “The combination of studying the geology of the seabed and the chemistry of the overlying water column is what gives us special insight into this vent site and reveals that it has these special qualities. “

The vent site could be a natural laboratory to prepare for exploring Saturn’s moon Enceladus, Jupiter’s moon Europa, and other solar system bodies with subterranean oceans that could provide habitable conditions for life. did he declare.

The advance in our understanding of subsurface minerals is also significant, according to German.

Findings at the vent site “suggest that hydrothermal mineral deposits that may be economically viable in the future – due, for example, to the high levels of copper and gold present in the deposits – may be much larger. abundant along half of all the ridges in the world that we have never appreciated before,” he said. “This is a class of vent sites that had previously been dismissed as incapable to support the growth of large hydrothermal mineral deposits Until now, scientists assumed that such small volcanic systems could not sustain hydrothermal circulation long enough to develop such large mineral deposits.

Regarding marine mining, German said: “As scientists, we believe that we should pass this information on to decision-makers, such as the International Seabed Authority, so that they can make informed decisions with better understanding of the natural world”.

The Aurora Hydrothermal System hosts active submarine venting with a large field of relict mineral deposits, associated with a neovolcanic mound located in the bottom of the Gakkel Ridge Rift Valley. However, depth camera and side-scan surveys the researchers conducted show that the site is more than 100 meters wide. This is unusually large for a volcanic vent hosted on a slow-spreading ridge and is more comparable to tectonically hosted systems that require large heat fluxes over a long period of time to form, according to the article. The Aurora hydrothermal plume exhibits much higher dissolved methane values, relative to manganese, than typical “black smokehouse” vents hosted in basalt. Instead, the plume closely resembles plumes from high-temperature ultramafic-influenced vents on slow-spreading ridges.

“We hypothesize that deep-penetrating fluid circulation may have supported the prolonged venting evident in the Aurora hydrothermal field with a hydrothermal convection cell that may access ultramafic lithologies underlying anomalously thin oceanic crust in this ultra-slow-spreading ridge frame,” the article notes. Pillow basalts observed in seabed outcrops “may only represent a relatively thin veneer of oceanic crust as the hydrothermal convection cell accesses the ultramafic lithologies below.”

Ultramafic rocks are primitive rocks from the Earth’s interior that are similar in bulk composition to meteorites. Ultra-slow-spreading ridges such as the Gakkel Ridge Rift Valley spread at 1 centimeter (cm; about half an inch) per year; in comparison, North America and Europe are spreading more than twice as fast at 2.5 cm (one inch) per year, while the Pacific Ocean seabed is spreading even faster at 10-20 cm (4-8 inches) per year.

For journal article co-author Eoghan Reeves, the significance of Aurora’s discovery is that it could soon add a crucial new data point to what is currently a very sparse chemical plot of these types of hot Springs.

“The vast majority of visually confirmed black smokers on the seafloor – numbering over 700 – primarily interact with basaltic or silica-richer rock types. Although the circulation of heated seawater in the ultramafic rock of the iron-rich mantle is a central topic in ocean-world astrobiology and origin-of-life research, we currently only have chemical compositions for less than a dozen hot springs influenced by such rocks on Earth’s seafloor, masking how chemically diverse — or similar — these fluids might be and what chemistries might still be lurking there,” said Reeves, an associate professor in the Department of Earth Sciences and the Center for Deep Sea Research at the University of Bergen “The few systems we currently know about emit fluids that differ widely from each other chemically, and i They have transformed our understanding of the microbiological and geochemical processes that occur in these types of systems. The Aurora plume shares some chemical similarity with another known hot spring, but we still have a lot to learn about the newly discovered site. It will be very exciting in the future to see if Aurora fits into or expands the chemical conspiracy we know of.

The paper’s co-author, Vera Schlindwein, said she was “intrigued by Aurora’s high-temperature ventilation.” The basalt mound “is in a strange place, right where the seabed drops to great depths in the magma-starved Lena Depression,” said Schlindwein, a professor at the Alfred-Wegener Center-Helmholtz Institute. for polar and marine research. Lena Trough is the southern extension of Gakkel Ridge. “Shallow ultramafic rocks appear natural in this location, but a sufficient source of heat and melt to build the Aurora basalt mound and maintain high-temperature ventilation is more of a surprise. With their very discontinuous melt supply, the ultra-slow spreading ridges could hold even more surprises in the geologic setting of the vent fields.

Reflecting on the findings, German said: “We continue to be amazed at the diversity and beauty of the seabed. Every time we go out and explore, we are surprised because we just don’t find the same thing. On the contrary, we keep finding completely new things, different from anything we’ve seen before.

This research was conducted with support from the National Oceanic and Atmospheric Administration, NASA; the German Research Council; the Max Planck Society, the European Research Council and the Research Council of Norway. Ship time support was provided by the Helmholtz Association (Germany) and the University of Tromso – Arctic University of Norway.

Astrobiology