[LINK] "New Type of Seafloor Vent Discovered, Dominated by Talc"

[rfmcdonald]

At Discover's The Extremo Files, Jeffrey Marlow draws from the Nature Communications paper "Talc-dominated seafloor deposits reveal a new class of hydrothermal system" to describe a new kind of life-supporting seafloor vent.

In December, however, a team of researchers from the National Oceanography Centre and the University of Southampton in Southampton, England, published a remarkable new finding: a new type of hydrothermal vent.*

At the Von Damm Vent Field (VDVF) in the Caribbean Sea, diverging plates move apart at a mere 15 milimeters per year – much slower than most mid-ocean ridges. This didn’t seem to bode well for rigorous venting activity: “It was originally thought that ultra-slow spreading ridges would not be able to support hydorthermal activity,” notes Matthew Hodgkinson, a PhD student at the University of Southampton who led the study. “As the spreading rates get slower, you generally have a lower magma supply and less heat to power hydrothermal vent fields.”

Which is why the 1997 discovery of hydrothermal venting at the ultra-slow spreading Southwest Indian Ridge came as a surprise. VDVF follows in this tradition, and is even more surprising given its slightly off-axis position. Electron-rich 200-degree (C) water was supporting a rich ecosystem comprised of many endemic species. “We’d expect there to be no magma whatsoever,” Hodgkinson explains, “so what’s powering this kind of activity? And what are the chemical consequences?”

During two different expeditions in 2010 and 2013 to the vents, the Southampton researchers tried to get answers, retrieving rock samples and developing high-resolution bathymetric maps of VDVF. When the remotely operated vehicle Isis returned to the ship after a day of sampling with a basket full of rocks, “the scientists would swarm around to get their samples,” Hodgkinson recalls, “bring them inside, take a photo, and do a quick description.” The more detailed analysis of mineralogy and rock precipitation history would be done back in the lab over the coming months and years.

Ultimately, the team found something remarkable: the dominant mineral was talc, a magnesium-rich silicate mineral perhaps best known for its softness and starring role in cosmetics products. It’s an unusual mineral to see at the seafloor, likely attributable the high pH values at VDVF (6) compared to those found at canonical black smokers (2-4). With a higher pH, the concentration of dissolved metals remains low, allowing silica to serve as a more prominent mineralogical player.