Recent work shows that eddies can pull climate-warming carbon deep into the seas
URI Photo by Joe Giblin
Melissa Omand, 36
University of Rhode Island
As chief scientist for a voyage of the research vessel Endeavor, oceanographer Melissa Omand oversaw everything from the deployment of robotic submarines to crew-member bunk assignments. The November 2015 expedition 150 kilometers off Rhode Island’s coast was collecting data for Omand’s ongoing investigations of the fate of carbon dioxide soaked up by the ocean.
But Omand, an assistant professor at the University of Rhode Island’s campus in Narragansett, wasn’t on the ship. Instead of riding the waves with her crew, she was working, sometimes 16-hour days, inside a dark room at the university’s Inner Space Center — staring at computer monitors in a sort of NASA mission control for oceanographers. When she submitted the trip proposal a year earlier, she hadn’t foreseen that she’d be eight months pregnant with her first child when the ship set sail.
Still, missing the trip was unthinkable, she says. The Inner Space Center, she realized, offered a way to direct the mission from shore via satellite. After proposing the solution to her higher-ups, and a lot of meetings that followed, she got permission to be the first chief scientist to remotely lead an Endeavor cruise.
“She doesn’t let many obstacles get in her way,” says Colleen Durkin, an oceanographer at Moss Landing Marine Laboratories in California, who participated in the cruise. “That’s one of the fun things about working with her. She’s willing to try new things.”
Her commitment to her science and her drive to find creative solutions are helping Omand tackle a big problem in oceanography. For a decade, she has been studying the mechanisms — such as currents and the dining and dying of microorganisms — that move carbon and nutrients through the ocean. In a breakout paper, published last year in Science, she reported the discovery that eddies can pull carbon from phytoplankton deep into the ocean, a previously undescribed phenomenon. Studying the fate of that carbon isn’t just interesting, she says, it’s vital to predicting the fate of our climate. “The ocean has a huge capacity to absorb excess carbon dioxide in our atmosphere,” Omand says. But as the planet warms, atmosphere and ocean might interact differently. Scientists need all the information they can get to figure out how to adapt to those changing conditions and mitigate the effects of climate change.
Omand, 36, first got her feet wet on the rivers and lakes surrounding her hometown of Toronto. In her teens, she worked as a canoe guide, exploring the region’s waterways. “That was absolutely the root of my interest in earth science and environmental issues,” she says. “I’m essentially doing the same thing now, just on a much bigger boat.”
After starting off as a premed student at the University of Guelph in Canada, she was ultimately drawn to the university’s physics program. “I found it very satisfying that all these problems boiled down to a few underlying rules and equations,” she says. During her undergraduate studies, her focus was millions and millions of kilometers away from Earth’s oceans. She coded software used to help calibrate X-ray instruments on NASA’s Mars Exploration Rovers, which identified the makeup of Martian rocks.
Her work sets the table for the next decade in terms of understanding the interaction between the turbulence of the ocean and how carbon is injected down to depth.
— David Siegel
While considering areas of physics for her graduate studies, Omand received an email that altered her heading. Chris Garrett, a professor (now emeritus) at Canada’s University of Victoria, introduced her to physical oceanography. “He showed me demonstrations of what happens to dye in a rotating water tank,” she recalls. “I was hooked by that.” The churning of water appealed to Omand for the same reason the field of physics did: Whether in tanks or oceans, the water’s movements can be expressed by a set of specific equations, called the Navier-Stokes equations.
Omand has applied these equations in much of her work. During a Ph.D. at the Scripps Institution of Oceanography in La Jolla, Calif., she and colleagues studied the origins of a red tide off California’s coast. The team found that the red tide, fertilized by a layer of nutrients, had been festering under the ocean surface for a week before being drawn upward. Omand and her colleagues used a Jet Ski modified with a GPS system and scientific instruments to collect data. Later, as a postdoctoral researcher at Woods Hole Oceanographic Institution in Massachusetts, she and mentor Amala Mahadevan investigated mechanisms to explain how nitrogen, an important nutrient for phytoplankton, moves around below the sunlit layer of the sea.
During her time at Woods Hole, Omand also started tracking the journey of CO2 taken in by springtime algae blooms in the North Atlantic.
When the phytoplankton in these colossal blooms, which can stretch hundreds of kilometers across, die or are digested by other marine life, particles containing organic carbon are released into the water. The heavier of these particles sink, quarantining the carbon from the atmosphere. About 30 percent of all CO2 emitted by human activities has ended up in the oceans, thanks in part to these sinking particles.
Scientists had believed that smaller particles would remain near the surface. But with robotic submarines called gliders that cruised up and down the water column sensing light scattered by the particles, Omand and colleagues found a surprisingly large amount of small carbon particles. These particles were around 100 to 350 meters deep, in the ocean’s “twilight zone,” where phytoplankton rarely live.
Omand combined measurements such as temperature and salinity from several gliders to explain how the particles got pulled so far down. By analyzing those measurements alongside computer simulations and satellite data — an innovative mix of sources that provided finer details and the bigger picture — she showed that the carbon-rich particles were carried down by spiraling ocean currents called eddies. Water escaping these bowl-shaped depressions can become sandwiched between deeper ocean layers, remaining trapped along with any particles even once an eddy subsides.
The accompanying carbon drain cools the Earth, says Eric D’Asaro, an oceanographer at the University of Washington in Seattle who collaborated with Omand on the research. Though the finding doesn’t change the total amount of carbon known to be taken in, the study identifies a new mechanism that could account for as much as half of all carbon known to be pulled into the deep North Atlantic during spring. The mechanism could also play a role elsewhere in the world’s oceans, D’Asaro, Omand and colleagues reported in April 2015 in Science.
“Her work sets the table for the next decade in terms of understanding the interaction between the turbulence of the ocean and how carbon is injected down to depth,” says David Siegel, an oceanographer from the University of California, Santa Barbara. “She’s going to be one of the new leaders of this field.”
Now a mother — her daughter was born a few weeks after the cruise — and an assistant professor at the University of Rhode Island, Omand continues her creative problem-solving, often by calling on unexpected technology. On a research trip in June (she was on the ship this time), Omand used an iPhone in a waterproof case to automatically snap pictures every half hour of particles raining down from the ocean’s top layer. Scientists previously measured the rates of sinking particles with traps that provided no information about how the rates changed throughout the day. Omand got the idea to affix her old iPhone to the traps after being offered only $40 for the used phone. “There’s got to be something really amazing I can do with this,” she thought.
Next spring, Omand will harness the same telepresence software she used for the 2015 Endeavor trip to virtually take undergraduate students on board. Omand’s ability to harness technology to solve tricky scientific challenges is a big reason why she can identify new truths about our oceans, says Mahadevan. “Every problem she touches,” Mahadevan says, “something beautiful comes out.”
M.M. Omand et al. Eddy-driven subduction exports particulate organic carbon from the spring bloom. Science. Vol. 348, April 10, 2015, p. 222. doi: 10.1126/science.1260062.
M.M. Omand and A. Mahadevan. Large-scale alignment of oceanic nitrate and density. Journal of Geophysical Research: Oceans. Vol. 118, October 2013, p. 5322. doi: 10.1002/jgrc.20379.
M.M. Omand et al. Physical and biological processes underlying the sudden surface appearance of a red tide in the nearshore. Limnology and Oceanography. Vol. 56, May 2011, p. 787. doi: 10.4319/lo.2011.56.3.0787.
M. Omand, J.L. Campbell and J.A. Maxwell. Simulation of the relationship between element concentrations and X-ray yields in the Mars Exploration Rover’s X-ray spectrometer. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms. Vol. 229, February 2005, p. 123. doi: 10.1016/j.nimb.2004.11.014.
T. Sumner. Phytoplankton’s response to climate change has its ups and downs. Science News Online, July 8, 2016.
T. Sumner. Phytoplankton rapidly disappearing from the Indian Ocean. Science News. Vol. 189, March 5, 2016, p. 11.
G. Popkin. Ocean bacteria may have shut off ancient global warming. Science News. Vol. 185, May 31, 2014, p. 9.
D. Powell. Field test stashes climate-warming carbon in deep ocean. Science News Online, July 18, 2012.