EGI’s Stuart Simmons joins Alvin for undersea research
Descending through darkness to the sea floor, reaching bottom at about 200 m east of the East Pacific Rise ridge axis, researchers aboard the Alvin deep sea submersible dove over 2,500 m this past October, to study the geochemistry and extreme life forms surrounding hydrothermal vents called ‘black smokers.’ EGI Research Professor Stuart Simmons was on board the Alvin for a unique opportunity to study the geochemistry and undersea hydrothermal processes that help us understand the origins of life and evolution of oceans.
Hydrothermal vents & ‘black smokers’
Black smokers – so named for what appear to be plumes of black smoke emerging from delicate, pagoda-like chimneys far below sea level, these hydrothermal vents and their surrounding environments reveal the Earth at its newest. As superheated fluid (>350 °C) emerges from beneath the Earth’s crust, dissolved minerals contained in the fluid precipitate upon contact with the near-freezing (2 °C) water at the seafloor, depositing primarily metal sulfides around the vents.
Discovered in the late 1970s and found primarily at mid-ocean ridges, these vents emit jets of particle rich fluids that precipitate from the fluid and accumulate on the seafloor, forming delicate sulfide chimneys. The hydrothermal vents also support animal life (tubeworms, crustaceans, clams, fish) that depends on sulfur and bacteria that thrive in this extreme condition.
Geology & Geochemistry
The study site is located 9° north latitude on the East Pacific Rise (EPR 9N), about 500 miles south of Manzanillo Mexico. This is a well-known site, which since the late 1980s has been subject to a number of surveys and dives using Alvin and unmanned submersibles. During this latest survey, the RV Atlantis (the host ship) was positioned on site for almost 10 days, permitting nine dives in Alvin, with each dive lasting up to eight hours.
Simmons’ primary function as a member of the expedition was geochemical sampling of the hot water (370–380° C) emitted from vents. Not even in a geothermal well can one sample fluids this hot, so this is an excellent opportunity to understand how rock-forming elements and trace metals are mobilized by hydrothermal processes.
Inside the Alvin
Alvin only accommodates 3 people, a pilot and two scientists. The capsule is a perfect sphere, seven feet diameter, made of titanium with five portal windows. Alvin is untethered and moves under its own power for about 5–8 hours. It takes an hour to descend and an hour and a half to return to the surface, so one has plenty of time to reflect and observe the deep sea through the narrow portal windows.
As one who spends most of his time investigating terrestrial hydrothermal systems and geothermal resources, Simmons had a few notable comments about the experience: 1) the pillowed lava flows were very glassy, and the extent of the obsidian was striking; 2) the rift topography which forms the ridge axis is subtle comprising <100 m of relief; 3) visible marine life was absent except near the hydrothermal vents. It was easy to forget that on the seafloor, the outside pressure is 250 times that of sea level.
Alvin and RV Atlantis are research vessels that are operated by Woods Hole Oceanographic Institute (WHOI). Their website provides information about current and past research activities, the history of the Alvin vehicle, and scientific insights into the nature and future of the planet’s oceans.