Investigating Microbial Life at Hydrothermal Vents on Expedition Microverse

To the bottom of the ocean and back, investigating microbial life at hydrothermal vents on Expedition Microverse

Surrounded by miles of abyss, near the boundaries where two sea-floor plates meet, lie underwater oases akin to nothing else on Earth. At hydrothermal vents, where the sea meets the Earth’s crust, researchers are diving deeper into a hidden world vital to sustaining life on our blue planet. 

Seawater continuously moves and circulates throughout the ocean every day. In some places, water seeps into cracks in the Earth’s surface, is heated by underground magma, and gushes back out through deep-sea hydrothermal vents. As this slow and steady process continues, the entire ocean passes through the rocks beneath it, fueling a cycle that takes thousands of years to complete. 

“We can’t understand the health of the ocean without looking at the deep sea. These aren’t separate ecosystems – they’re one system. And hydrothermal vents lie at the center of it all,” said Damian Grundle, assistant professor at Arizona State University and the lead principal investigator of a recent project to investigate nitrogen cycling and the associated microbial processes.
  

Hydrothermal vents provide a route for chemically altered seawater to return to the ocean, discharging heated fluids enriched with minerals and nutrients critical to sustaining life in deep-sea ecosystems. Living in these harsh conditions, tiny microbial life turns this toxic fluid into energy. By cycling the nitrogen and carbon spewing out of hydrothermal vents, these microbes cultivate rich ecosystems in the deep sea and shape the ocean’s chemistry worldwide. 

To better understand these microbial communities, a team of researchers from ASU and Lehigh University embarked on an 18-day research cruise aboard R/V Atlantis, operated by Woods Hole Oceanographic Institution (WHOI), journeying to the Endeavour Hydrothermal Vent Field off the coast of Vancouver Island, Canada.

Dubbed Expedition Microverse, the project brought together microbiologists, chemists, geologists, and educators, all working to understand and share the role microorganisms play in cycling nitrogen and sustaining life at hydrothermal vents.
 

“Microbes are an integral part of determining the chemistry of the oceans,” said Sheryl Murdock, a post-doctoral researcher at ASU and co-chief scientist of the research cruise.

“We are interested in how they utilize nitrogen as an energy source or incorporate it into themselves to build their own molecules of life,” she said. “We want to study how microbes behave under their natural deep-sea pressures by bringing organisms up to the surface of the water, while maintaining seafloor conditions” 

The true novelty of the project lies in the fact that the team was able to do just that, showing greater detail and care than ever before. By preserving natural seafloor conditions, researchers can obtain more accurate measurements of nitrogen cycling at vent sites, as the collected samples retain gases that would normally escape under unpressurized sampling methods. 

The team utilized a specialized tool, the isobaric gastight sampler (IGT), which collects small amounts of fluid while maintaining the original pressure conditions. The tool was introduced by Lehigh collaborator and co-principal investigator on the project, Jill McDermott.

However, there was one more barrier to success: the answers to these questions lie over 2,000 meters below the ocean surface, in areas where sunlight does not penetrate, where oxygen levels are extremely low, and temperatures are close to freezing. 

To investigate these extreme environments, the team turned to the human-occupied vehicle (HOV) Alvin, a submersible that has been taking scientists to new depths for the past 60 years. 

Over the course of ten Alvin dives, researchers traveled to the bottom of the ocean to survey hydrothermal vent ecosystems, sample vent fluid, the surrounding seawater, sediment, and collect endemic tubeworm species. 

“HOV Alvin provides a unique perspective of being able to see the seafloor with your own eyes,” said Elizabeth Trembath-Reichert, assistant professor at ASU and senior project personnel. “Which is vital for understanding the interconnected nature of these little pockets of the seafloor.”

“HOV Alvin was especially important for this cruise, where we wanted to extensively sample a few locations to determine the full diversity of the types of fluids that emerge from cracks in the seafloor and the role biology plays in transforming them before they enter the larger ocean ecosystem,” she said.

Upon returning to port, the team will continue to uncover the roles these microorganisms play in transforming ocean chemistry worldwide, at the critical interface where the sea meets the Earth. Each discovery they make over the coming years will further our understanding of the full ocean ecosystem. 

“This was a dream cruise for me,” said Murdock, “It was a complete success as far as I’m concerned. I think we got everything we wanted on the cruise, and it was amazing to see this team work together. I can’t wait to do it again.”