Using WHOI’s deep-sea submersible vehicle Alvin, a drone called Sentry, an underwater video camera and other technologies, a team of scientists explore, and three-dimensionally map, a chain of volcanoes on the Pacific Ocean floor.
According to satellite data, there should have been a mountain at the specified coordinates, right between the Pacific Ocean’s Seamount Chain and an independent underwater volcano to the west.
But when a team of scientists on board the research vessel Atlantis arrived late last year, there, where the mountain should have been, was nothing. The sea floor was relatively flat. Nothing but ocean water and the odd sea creature to mark the spot.
“Things were not what we were expecting,” said Trish Gregg, a volcanologist at the University of Illinois at Urbana-Champaign (UIUC).
Late in 2016, Gregg led a five-week research expedition called OASIS (Off-Axis Seamount Investigations at Siqueiros) to explore, and three-dimensionally map, a never-before-visited underwater string of volcanoes called 8°20’N Seamount Chain.
The absence of an accurate chart was not a calamity for this group of scientists, as it was for the crew of the USS San Francisco, the nuclear sub that ran into an uncharted mountain in 2005.
However, with less than five percent of the ocean floor three-dimensionally mapped, such events underscore the need for exploration of this largely unknown frontier.
In addition to mapping the area, which encompasses thousands of square kilometers, Gregg and her team conducted scientific research on the unique geology of the volcano chain.
This included a voyage to the bottom of the sea, where a select few became the first humans ever to lay eyes on this particular piece of the planet.
“What I love about this work is that it’s about discovery,” said Gregg. “You’re getting to see things that nobody has ever seen before.”
15 Voyages to the Bottom of the Sea
With funding from the National Science Foundation, OASIS scientists set sea on Atlantis, a highly sophisticated research vessel owned by the U.S. Navy and operated by Woods Hole Oceanographic Institution (WHOI).
The team was granted access to all of the vessel’s high-tech tools, including Sentry, an autonomous underwater vehicle – essentially a deep-sea drone – which captured video and other data during the expedition.
Scientists reviewed Sentry data – as well as video from a Multidisciplinary Instrumentation in Support of Oceanography (MISO) TowCam, an underwater camera lowered and towed from the ship – to plan human expeditions aboard Alvin, the human-operated deep submergence vehicle that has gained fame over the years for its role in dives to the mid-ocean ridges and the Titanic shipwreck.
Those fortunate enough to take the plunge have found that Alvin isn’t exactly a comfy ride.
It’s damp and cold (roughly 40°F – inside – at low depths, where the ocean temp drops to 32°F), and there are no bathroom facilities, meaning passengers must forego privacy and use a portable urinal if nature calls during the up-to-10-hour voyage.
But for scientists keen on deep ocean exploration, these are small sacrifice for a front-row seat to scientific discovery.
Gregg described seeing “fireflies everywhere” on the way down, bioluminescent creatures large and small, some with glowing spines.
“Then you get down and the pilot flips on the external lights, and you see the volcanos and the lava flows and the critters. It’s amazing,” said Gregg.
“In my mind, I’d thought of the sea floor as something of a desert with maybe the occasional critter,” continued Gregg. “But it was this vast community – deep sea corals, tripod fish, Dumbo octopuses, crabs, sea stars, sea spiders – so many things I’d never seen before.”
In all, Alvin completed 15 dives during the expedition and collected hundreds of samples via its robotic arms and sample trays. It collected another two tons of rock using a dredge attached to the Atlantis.
From these caches, more than 400 samples were processed in a lab on board the Atlantis, where scientists worked in three shifts, 24/7, to complete as much research as possible while at sea.
Deep Ocean Discoveries
One of the goals of the expedition was to determine the age of the volcanoes and subsequent lava flows, in order to learn more about melt migration and the behavior of volcanoes wherever they occur, whether on Earth or other planets.
However, as science is wont to do, it raised more questions than answers.
“We have no idea how old the Seamounts are,” Gregg said. “The rocks look really old and there’s lots of sediment, sometimes up to a meter thick. Yet, at the same time, there are lava flows that appear to be very young, with extensive evidence of hydrothermal communities, indicating that these volcanoes were active in the not so distant past.”
Some of the strongest evidence for recent eruptions came in the form of hydrothermal chimney structures, which typically last only a couple of decades.
Even more surprising to Gregg and her colleagues, was the discovery of intact tube worm casings, which she said have never been found this far from the mid-ocean ridges. At these depths, tube worms require hydrothermal activity to exist, and their casings disintegrate rapidly, within just a few years.
Considering the geological timescale of hundreds of thousands of years, Gregg said that these findings are significant.
She hopes to see further research on the area – more geology studies, of course, because geologists are drawn to pillow basalt like others seek out diamonds.
But she also hopes to bring biologists on board to investigate whether the Seamounts, which stretch out perpendicularly from the mid-ocean ridge, may provide hydrothermal oases for organisms making their way from the ridge to other parts of the deep ocean.
As for that nonexistent mountain, previously thought to be a part of the Seamount Chain, the expedition confirmed that the westernmost volcano was a geologic feature on its own. As chief scientist of the expedition, Gregg – like other explorers discovering geologic features for the first time – got to name it. She christened it Liona Seamount, after her daughter.
“The first time we approached the volcano, it was so overwhelming I had to hold back tears,” Gregg said. “We were the first humans to see it, maybe be the only humans to ever see it, if nobody comes back to that spot. And the biology. All those sparkles of light and critters just everywhere.”
Gregg said it was mind blowing to discover this uncharted world beneath the ocean’s surface.
“It’s so otherworldly,” she said. “I think it’s the closest one can get to being an astronaut.”
Dive photos courtesy of P. Gregg (U. Illinois), D. Fornari (WHOI), and M. Perfit (U. Florida), co-chief scientists of OASIS cruise AT37-05 on RV Atlantis funded by the National Science Foundation. Photos and video taken from DSV Alvin using WHOI MISO Facility deep-sea camera systems and Alvin cameras. ©Copyright WHOI.