Under Pressure: Studying Life Below the Seafloor

Deep at the bottom of the ocean, below thousands of feet of seawater, below even the rocky ocean crust that composes the seafloor, lies something surprising: more water.

"It’s unintuitive, because most people think of rock as being solid. But it’s not; it has pores, and fractures, and cracks in it," said Jackie Goordial, a postdoctoral researcher at Bigelow Laboratory for Ocean Sciences.

In fact, water percolating into the crust forms the largest aquifer on earth. This sub-seafloor system contains a whopping two percent of the ocean’s volume, and scientists believe it may be home to large amounts of microbial life.

These tiny microbes are of global importance. Their activity in the sub-seafloor environment shapes the chemistry of the ocean and its influence on the atmosphere.

"Because the aquifer is so huge, it affects global environmental cycles," Goordial said. "Knowing what the microbes are doing and on what scale is important for understanding these environmental processes."

Little is known about the sub-seafloor environment or the hardy microbes who thrive there, under intense levels of pressure and far from the rays of the sun. More will be clear soon, however, as Bigelow Laboratory scientists analyze data from an October cruise to the Mid-Atlantic Ridge. Along this underwater mountain range in the Atlantic Ocean, the Earth’s tectonic plates are slowly spreading apart, providing scientists with easier access to the rock in the ocean crust.

Just reaching the research site, a valley between underwater peaks called "North Pond," was an adventure in itself. In Cape Cod, the researchers boarded the Woods Hole Oceanographic Institute research vessel Atlantis and sailed for nine days to North Pond, where they stayed for three weeks. Despite the remote location, the science team was in regular contact with the Girl Scouts of Maine as part of the outreach program Adopt A Microbe.

For Senior Research Scientist Beth Orcutt, the cruise was a long-awaited journey and a key part of a National Science Foundation-funded study. In 2011, she installed several sets of experiments and instruments that sit on the seafloor and reach down into the ocean crust. In October, she and three members of her lab group returned to pick up the experiments and sample water flowing through the crust. Each member came equipped with a different scientific approach to study the microbial life in this remote, enigmatic environment.

Who’s down there?

When Atlantis finally arrived at North Pond, it was time for another type of journey: straight down to the seafloor. Cue Jason, a remotely operated, deep-diving robot named for the mythical Greek ocean explorer.

Four and a half kilometers beneath the surface, Orcutt’s experiments sat nestled in the ocean crust. For six years, temperature and pressure sensors had logged continuous measurements and hundreds of meters of coiled tubing had collected a "time lapse" of water samples. Most excitingly, chips of different types of rock had been exposed to seawater and microbes in an innovative and unprecedented microbial colonization experiment.

"This was the first time such a long incubation had ever been done, so no one really knew what to expect," said Tim D’Angelo, a research associate in Orcutt’s lab.

Jason's primary task was to collect the experiments Orcutt had installed six years ago. Each time one completed the hours-long journey to the surface, a storm of activity followed. D’Angelo disassembled the experiment packages and collected water and rock samples, which he froze in preparation for analysis back at Bigelow Laboratory.

"We’re hoping to determine the role microbes play in rusting the crust," Orcutt said. "Volcanic rocks have iron and other dissolved metals that microbes might want to access. That activity can be important for changing the chemistry of the water moving through the rocks and iron, which is important for all forms of life."

Who’s active?

Towards this goal, Goordial is seeking to answer a fundamental question: in the microbial communities that live at different depths in the ocean crust, which microbes are actively growing and influencing the environment?

She starts by injecting a fake amino acid into her samples, which will cause microbes that are growing to fluoresce, visually highlighting the active microbes. Bigelow Laboratory’s Single Cell Genomics Center can then isolate and genetically sequence these individuals, providing a clear picture of the microbes that are active in this environment.

"This technique was just a gleam in somebody’s eye when the experiments were deployed six years ago," Goordial said. "Some of these single cell methodologies are going to push through differentiating between groups of active microbes and microbes that are perhaps dormant, or not doing much, and result in a better understanding of the ecology in this ecosystem."

What are they eating?

Postdoctoral researcher Rose Jones emphasized that this type of exploratory science is about getting covered in mud, rolling with the punches, and learning rather than perfectly executing pre-conceived plans.

"On this cruise, we had more in common with the old Victorian explorers going into the unknown than with the clinical white coat idea that most people have of scientists," Jones said.

Her part of the team’s research will help answer basic ecological questions about the mysterious subseafloor environment. There, microbes eat away at the crustal rock to gain energy by metabolizing its minerals. To learn what reactions a given microbe carries out, Jones "feeds" it voltages of electricity that simulate the chemistry of elements like iron or sulfur. Determining what chemical reactions the microbes are capable of will clarify the role different species play in the environment.

"It’s like how if you tried to plug in U.K. electronics in a U.S. power outlet, you’d get sparks," Jones said. "But if you get the right voltage, then it works perfectly. And it’s exactly the same with microbes."

Beyond the ocean

What the researchers learn as they analyze their samples may teach us not just about Earth’s seafloor, but about other planets as well. Mars used to have widespread oceans, and the moons Europa and Enceladus are covered by oceans topped with ice. Subsurface crustal environments on these planetary bodies may parallel those on earth. Learning about the microbial communities in Earth’s crust could help scientists understand the microbes that may be living in similar environments on other moons and planets.

"If we do find life on other planets, it will most likely be microbes," Jones said. "They have an amazing ability to make a living in environments too extreme for most other forms of life."

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