A team of scientists from the Woods Hole Oceanographic Institution (WHOI), University of Hawaii, Whitman College and international colleagues will conduct the first systematic study of life in the deepest marine habitat on Earth—ocean trenches, which are regions of the sea floor ranging from 19,685 to 36,089 feet (6,000 to 11,000 meters).
Due to the extreme pressures and the technical challenges involved in reaching this depth, known as the hadal zone, trenches are among the least studied environments on the planet. Filmmaker James Cameron's dive on March 26, 2012, to the Challenger Deep—the world's deepest region—in the Mariana Trench marked only the second time in 52 years that a human occupied vehicle has reached that area of the seafloor.
"Over the years, we've made large leaps in understanding life at deep-sea hydrothermal vents, seeps and seamounts, but we know relatively little about life in our ocean trenches," said Tim Shank, a deep-sea biologist at WHOI and lead investigator on the Hadal Ecosystem Studies (HADES) program.
Shank and his colleagues were awarded a $1.4 million collaborative grant from the National Science Foundation for a three-year program of studies in the deepest parts of the world's ocean. The program includes international collaborators at the University of Aberdeen (UA) in Scotland, National Institute of Water and Atmospheric Research (NIWA) in New Zealand, and The National Oceanography Centre (NOC) at the University of Southampton.
"The program is global in scope. The goal is to conduct detailed studies of the composition, diversity, and adaptations of life in the major deep ocean trenches and then compare these findings between the trenches around the world," said Shank.
The work of the HADES program is made possible by recent advances in imaging technology, as well as the sampling and exploration capabilities of Nereus, a deep-diving Hybrid Remotely Operated Vehicle developed at WHOI. Conceived in 2000, it took nearly a decade to design and build. On its maiden voyage in 2009, Nereus successfully dove to the Challenger Deep, an area nearly 36,000 feet below the surface, providing new and unprecedented access to the deepest parts of the ocean floor.
"With a robot like Nereus, we can now explore virtually anywhere in the ocean," said Andy Bowen, the project manager and principal developer of the vehicle. "It marks the start of a new era in ocean exploration and research."
The unmanned vehicle can operate either as an autonomous, free-swimming robot for wide-area surveys, or as a tethered vehicle for close-up investigation and sampling. It will allow researchers to gather high definition video along the trench axis, as well as recover organisms and sediment samples.
The HADES program will begin its work in 2013 at the Kermadec Trench, an area roughly 750 miles long and 32,963 feet (10,047 meters) deep located off the northeastern tip of New Zealand. It will later conduct expeditions to the Mariana Trench near the island of Guam in the west Pacific.
This expedition will build on studies of the Kermadec Trench by HADES program collaborator Alan Jamieson at UA's Oceanlab and colleagues at NIWA and the University of Tokyo. Using a state of the art, free-falling autonomous baited camera system, the research team documented many new species of animals in the Kermadec and other trenches around the Pacific Rim in the past few years.
"To date, this method has been successful in observing the deepest fish ever seen alive," Jamieson said. "By combining WHOI's HROV Nereus with Oceanlab's Hadal-Lander technology, the team have the best available technology at their disposal."
Despite the harsh conditions in ocean trenches—icy temperatures, intense pressure, no sunlight—some species are able to thrive there. For one reason, food is plentiful, as organic material in the ocean is moved by currents and pulled down into the abyss.
"We know there's an excess food supply in the trenches, which means it can support more and potentially highly-diverse life forms," Shank said. In addition to sampling these species and imaging the terrain they live in, the HADES team plans to analyze their DNA to begin to unravel how they have evolved the ability to survive in such an extreme environment.
The team plans to examine the food supplies, energetic demands, and metabolic rates of trench organisms to determine the role they play in biological structure of trench ecosystems. Jeffrey Drazen from the University of Hawaii will lead the program's efforts in this area.
"The energy requirements of hadal animals have never been measured before," said Drazen. "Some deep-sea animal groups have 10-fold lower metabolic rates than shallow living species. Metabolic data will help us understand how food supply regulates the distribution and density of hadal animals, which can help us put together a picture of the flow of energy throughout the food web."
Since pressure in the hadal zone can reach more than 16,000 pounds per square inch, the team will also examine the mechanisms that trench species have evolved to cope with the extreme force.
Exactly how these animals withstand intense pressures is not completely known, but scientists are putting together pieces of the evolutionary puzzle. Paul Yancey, HADES program collaborator from Whitman College, noted that although extreme hydrostatic pressure can inhibit the activity of proteins, small molecules called piezolytes may be able to protect proteins from the pressure. Yancey plans to investigate the role that piezolytes play in the adaptation of trench animals.
"Pressure might very well be the primary factor determining what species can live in Hadal zones," Yancey said. "High hydrostatic pressure in essence inhibits and distorts biomolecules like enzymes and other proteins. One way this happens is that pressure traps dense layers of water molecules around proteins, making it harder for them to bind to other molecules which they must do as part of their function."
At more moderate depths, Yancey said, there is evidence of life adapting to pressure in two ways: by evolutionary changes in protein structures that make those molecules more resistant to pressure effects, and with piezolytes, which seem to help remove the dense layers of water trapped around proteins.
"We don't know if either or both mechanisms work at the greatest ocean depths, and whether they work in all kinds of organisms or only some," he added. "These are questions we hope to answer."
In addition to deep-sea life with novel adaptations, there is also evidence to suggest that trenches act as carbon sinks, making the HADES program's research relevant to climate change studies. The V-shaped topography along trench axes funnels resources, including surface-derived organic carbon, downwards.
Hadal zones, Shank said, may be the final location of carbon and other chemicals sequestered in our oceans. Understanding how that sequestration process plays out could reveal clues to ocean trenches' role in regulating the global carbon budget, and ultimately, climate.
"Trenches are the largest unexplored biome on Earth." Shank said. "That's what makes this project so exciting. There will be major impacts on our understanding about life on Earth as a result of doing this work."
The Woods Hole Oceanographic Institution is a private, non-profit organization on Cape Cod, in Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the oceans and their interaction with the Earth as a whole, and to communicate a basic understanding of the oceans' role in the changing global environment.
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