Real-time monitoring of the seafloor reveals unexpected links
Nicolle Rager Fuller
Gas bubbles effervesce from a mound of muck on the seafloor in a deep submarine canyon off the west coast of Canada. Microbes beneath the sediment belch the bubbles after feasting on the ancient remains of algae, sea critters and their poop: a primordial stew that’s been simmering since long before humans walked the Earth.
This gassy oasis attracts an odd collection of critters. Worms writhe in the goo, clams bask in the bacteria, herds of sea cucumbers dine on diatoms and sea stars scurry across the pitch black landscape. But the strangest inhabitant of all is a robot named Wally, whose every move is controlled by a human sea spy viewing the entire scene from a lab 8,000 kilometers away in Bremen, Germany.
Equipped with scientific instruments designed to explore this alien world, the deep-sea crawler is just one part of an unprecedented effort to check the ocean’s vital signs in real time. The NEPTUNE observatory — a ring of six underwater research stations connected to the Internet with fiber optic cables — is the first online observatory to brave the depths of the abyss. From their vantage points in labs and living rooms around the world, oceanic explorers now plug into an ever-changing world once cloaked in darkness, and tap into the pulse of the ocean as it lives and breathes.
Traditionally oceanographers have gleaned insight into the ocean through observations made on research cruises conducted for a few weeks a year at great cost. But these sparse samplings provide only snapshots of the sea’s shifting moods, says Kate Moran, NEPTUNE’s director. Add the emerging effects of climate change into the mix, and single-shot sampling can be woefully inadequate for scientific study, Moran says. “It can be almost anecdotal.”
Cycles that drive changes in the ocean’s chemistry and organisms take place over hours, days, seasons, years and even decades — timescales NEPTUNE can track. As global levels of carbon dioxide rise, changes in storm frequency, ocean temperature and acidity could have profound impacts on these delicate cycles. “We’re in a period where the oceans are changing very quickly,” says marine ecologist Kim Juniper of Canada’s University of Victoria, who oversees NEPTUNE’s scientific research. “We know that tomorrow’s oceans are not going to be the same oceans we’ve been studying for the last century.”
NEPTUNE researchers examine an astounding diversity of underwater worlds. Plunging into the ocean off the west coast of Vancouver Island, the more than 800 kilometers of fiber optic cables that connect the research stations stretch across the continental shelf, plummet down the slope and across an abyssal plain, and skirt hydrothermal vents near a mid-ocean ridge where the Earth gives birth to new ocean crust. Researchers endowed the observatory’s six nodes with instruments that measure the ocean’s changing temperature and chemistry, cameras that spy underwater creatures, hydrophones that listen to passing whales and seismometers and tsunami detectors that measure hazards as they happen.
From their vantage point on dry land, NEPTUNE’s deep-sea explorers have made connections between storms raging on the sea surface and plumes of gas bubbling out of the seafloor hundreds of meters below. They’ve picked up sounds of creatures not glimpsed in these waters for half a century, spotted marine mammals behaving in unexpected ways and measured the weight of tsunamis passing overhead. Some of the discoveries have even been made by intrepid citizen scientists scouring through NEPTUNE’s open online network from home.
“This in many ways has been an exploration, rather than a classic hypothesis testing experiment,” Juniper says. “You discover unexpected connections not just by seeing an event, but by seeing all parts of the puzzle.”
Dreaming of cables
Oceanographers started buzzing about the idea of cabled observatories more than two decades ago. At the time, scientists already had developed remotely operated vehicles that could roam the seafloor, and placed instruments on the ocean’s bottom that could record uninterrupted measurements for years. But they weren’t able to monitor the data in real time. Instead, they’d drag up their instruments once a year and download the data in nervous anticipation. When submarine cable technology for communications exploded in the mid-1990s to connect the world to the Internet, the possibility of a cabled ocean observatory ripened into reality.
John Delaney was among the first oceanographers to grasp the potential power of cabled observatories. Twenty-three years ago, the University of Washington scientist dreamed of a day when researchers would access the mysteries of the ocean on a continual basis. “The only way for us to fully understand the ocean is for us to be in it, and part of it,” says Delaney. “And humans aren’t well adapted to do that, but our robots and our sensors can be.”
At a meeting in San Francisco in 1991, exhausted after spending six months at sea on a research expedition, Delaney remembers sitting in a bar lamenting to a colleague about the difficulties of using human-occupied submersibles to study the ocean in a meaningful way. His colleague, oceanographer Alan Chave of the Woods Hole Oceanographic Institution in Massachusetts, told Delaney of “this thing called fiber optics” being developed at Bell Labs, where Chave worked at the time. “Maybe we could use that in the ocean,” Chave suggested.
Delaney ran wild with the idea, sharing it with everyone he knew in the world of oceanography, and found that others shared the same vision. “Some of them were whale watchers, some were fish trackers and some of them were earthquake checkers,” Delaney says. “Some of them were landslide folks, some of them were volcanologists and microbiologists, and it just went on and on and on.”
At a meeting in Canada in 2000, an international team drafted the initial plans for a cabled observatory that would encompass the Juan de Fuca tectonic plate, which stretches from the coast of British Columbia to Northern California. The Canadians set out to build an observatory on the northern third of the plate, while the Americans proposed an ambitious project covering the bottom two-thirds.
Delaney stood by as his Canadian colleagues at the University of Victoria secured the $200 million needed to launch NEPTUNE (Northeast Pacific Time-Series Undersea Networked Experiments). By the end of 2009, most nodes were up and running. Today, U.S. funding has caught up, and Delaney heads the Ocean Observatories Initiative’s Regional Scale Nodes — a cabled observatory just getting into the water off the Oregon coast. As the cables connecting that observatory unravel onto the seafloor, Canada’s NEPTUNE finishes its fourth year of operation. If all goes according to plan, NEPTUNE will collect data for a total of 25 years.
Wally the crawler has lived in NEPTUNE’s fizzy Barkley Canyon since 2009. The bubbles that comprise the robot’s seafloor oasis consist of methane — a greenhouse gas 20 to 25 times more potent than CO2. The fizz is a harbinger of the expansive deposit of frozen methane that lies below the seafloor. The cold temperature and high pressure of the deep-sea environment keeps most of the methane locked in a frozen crystalline form called methane hydrate. But as evidenced by the bubbles seeping out of the mud, portions of the deposit intermittently sublimate from their frozen cage.
Some scientists fear that an increase in temperature or drop in pressure could liberate large amounts of methane at once — an event that could destabilize the seafloor. That would pave the way for massive underwater landslides that could trigger tsunamis. Such a large-scale release could also fuel climate change. Despite the tenuous nature of the methane deposits, there is interest in mining them for fuel. Japan has already started extracting deep methane deposits, and South Korea has a plan in the works.
To understand the probability of future methane releases or the feasibility of harvesting the deposits, scientists need to better understand their dynamics and how they interact with the ocean environment. Getting a handle on this has been difficult without consistent monitoring: Mounds of methane have disappeared or shifted between research expeditions, for example. But now, through the ever watchful eyes of the robot Wally, scientists are starting to see connections missed during occasional visits.
Situated at 870 meters below the sea surface in Barkley Canyon, Wally uses a camera, methane detector and current flow meter to take stock of the release of methane bubbles from the seafloor. A 70-meter fiber optic cable connects the crawler back to a junction box that hooks into the rest of the NEPTUNE array. Viewing the streaming video from Wally in his lab at Jacobs University in Bremen,
Germany, oceanographer Laurenz Thomsen follows numbered signs protruding out of the sediment like bread crumbs to drive Wally back home after a day out in the field.
Thomsen and his colleagues have discovered that changes in ocean currents triggered by storms raging on the sea surface can
alter the release of gas from the hydrate mounds. The team reported last year in
Geophysical Research Letters that as currents scouring the seafloor increase in intensity, more methane seeps out of the mounds. So while it may take decades for warming at the sea surface to change deep-sea temperatures, alterations in wind-driven events may have more immediate effects. NEPTUNE’s continuous monitoring allowed Thomsen’s team to make the first connections between hydrate release and climate-induced changes hundreds of meters above.
While a cataclysmic event among the methane hydrate mounds could unfold sometime in the future, violent eruptions are the norm at Endeavour Ridge, the site of another NEPTUNE research node. Located on the opposite side of an expansive abyssal plain from Wally’s lair, the ridge hosts a hydrothermal hotbed of volcanic vents called black smokers. Through the process of seafloor spreading, new ocean crust continually comes into being here.
“Ocean ridges are the most dynamic places on our planet, and this is the first cabled observatory that goes out to one,” says oceanographer Peter Rona, who uses NEPTUNE to study the dynamics of the deep-sea volcanoes from his lab at Rutgers University in New Jersey. “This is really a revolutionary advance in oceanography, a total change in our understanding of the processes that we’re studying.”
Some scientists think deep-sea hydrothermal vents such as those at Endeavour Ridge may have given birth to life on Earth. The surrounding organisms live off chemicals from the vents, rather than light from the sun. Rona thinks the vents could be a model for life on other planets, or possibly even on moons in our own solar system like Jupiter’s Europa, which hosts a large sea locked under a thick layer of ice.“It’s real Star Trek–type stuff,” Rona says. “It’s a different basis for life, chemical energy instead of the light energy of the sun.”
The vents spew out substances from deep within the Earth’s crust, including iron, a metal known to seed plankton growth. Some engineers have even proposed dumping iron into the ocean to trigger phytoplankton blooms — a strategy that they speculate will slow global warming by removing carbon from the atmosphere (SN: 6/5/10, p. 16). The vents, Rona says, already help do this on their own. “They have a huge impact globally, as a major control on the composition of the ocean, and the distribution of life there,” Rona says.
Rona watches the vents cough up their metallic cargo, which heat the once-frigid ocean water to 400˚ Celsius. Rather than monitoring the vents with a camera, Rona uses sound. “Light would just illuminate a patch the size of a bed sheet at a range of maybe tens of feet at most,” says Rona. “But sound can illuminate a large volume of the ocean at almost any range.”
Situated at a relatively safe distance 30 meters away from the smokers, an acoustic device called COVIS (Cabled Observatory Vent Imaging Sonar) emits sound waves that bounce off of the particles belching from the vents. As Rona watches from Rutgers, the acoustic data get re-created into the constantly evolving shape of the plume in near-real time.
When the acoustic data are paired with wind measurements from buoys at the surface, Rona’s team can correlate changes in the plumes’ activity with events happening above. “The plumes bend and sway with the wind and tides,” Rona says. “Most people think of tides as something that rise and fall on the beach, but it actually affects the deepest ocean, and we’re watching it.”
Rona’s team reported in the July Geochemistry, Geophysics, Geosystems that wind-driven waves on the ocean’s surface take 13 days to propagate to the vents 2,000 meters below. Their wavelengths stretch as they travel to the bottom, a change the team calls a “blue-shift.” As changes in climate affect storms and ocean currents, Rona expects the activity of the plumes to change as well. These alterations could have an impact on the chemistry, and therefore life, in the ocean and on the rest of the planet.
Atmospheric events occurring at the ocean surface may sound the dinner bell for creatures living in the dark depths. Using an underwater camera and acoustic current profilers strategically placed along Barkley Canyon, researchers recently observed two food chains intersecting as bottom-feeders called squat lobsters reaped a windfall.
Winter storms raging overhead triggered ocean turbulence that propagated several hundred meters down to the middle of the water column, where shrimp normally hang out. “Because the shrimp aren’t very effective swimmers, they go to the seafloor to escape the turbulence,” Juniper says. There, the shrimp likely meet their demise in the eager claws of the squat lobsters. The team reported the shrimp shift in the Journal of Marine Systems in May.
“We saw a connection between organisms that live almost all of their lives in the water column and those that live on the seafloor,” Juniper says. “A storm brings two food chains together, in a way that was totally unexpected.”
As the timing and intensity of storms change with the climate, Juniper says connections like these could trigger unexpected changes in the ocean’s ecosystems. For instance, if storms start to occur during a vulnerable time in the shrimp life cycle — such as prior to mating — this could prevent the shrimp population from bouncing back after the annual fishing season.
The ocean’s creatures respond not only to storms and currents, but also to shifts in chemistry. For example, as global CO2 levels rise, increases in the acidity of the ocean are expected to have dramatic impacts on sea life. NEPTUNE researchers are in the midst of designing an efficient pH meter that, coupled with data from cameras and other sensors, will monitor ocean acidity and detect any effects.
Stretching the limits
The cables connecting NEPTUNE’s nodes and instruments traverse rugged, deep-water terrain and house delicate optical fibers. Surrounded by treacherous fields of sharp volcanic rocks, the violent hydrothermal vents of Endeavor Ridge are an inhospitable place to lay cable, says Juniper. “Most sensible submarine cable operators avoid places like that, but we don’t have a choice. That’s where we want to be.” Since NEPTUNE’s launch, several cable malfunctions have occurred along the ridge, and some are still down for unknown reasons, Juniper says.
The flat abyssal plains of soft silt haven’t managed to avoid cable troubles either. The abyss is the heart of NEPTUNE’s “tsunami meter,” an array of bottom pressure sensors that measure the weight of waves passing overhead. Like ultra-sensitive bathroom scales, the sensors can detect submillimeter changes in sea level, and NEPTUNE scientists hope to use them to understand the dynamics of tsunamis and alert people onshore.
But the most sensitive aspect of the array — a three-pronged “antenna” of sensors used to calculate the direction and speed of waves passing overhead — isn’t connected to the Internet. After the antenna successfully recorded the 2009 Samoan tsunami passing overhead, the team decided to push their luck by laying longer cables to enhance the antenna’s sensitivity. But the new cables — longer and thinner than others the team had tried — malfunctioned. “And now the meters are just sitting down there on the seafloor, recording internally,” says oceanographer Richard Thomson of the University of Victoria, the lead scientist for the tsunami array.
As the 2011 Tohoku tsunami passed overhead, the antenna detected the massive wave but kept its measurements to itself. The team is working on a new cable design and hopes to have the improved tsunami meter up and running within a year.
In the context of the 25 years of data the observatory is expected to record, the fumbles of the first few years may be a necessary, and expected, part of the adventure. Any journey into a new sphere of space or time carries with it the promise of unknown hazards, as well as unexpected discoveries, Juniper says. “We’re discovering things we never would’ve learned any other way.”
Note: To comment, Science News subscribing members must now establish a separate login relationship with Disqus. Click the Disqus icon below, enter your e-mail and click “forgot password” to reset your password. You may also log into Disqus using Facebook, Twitter or Google.