Satellites Observe “Traffic Jams” in Antarctic Ice Stream Caused by Tides

News Writer: 
Robert Perkins

Glaciers

Research on Antarctic ice streams by Caltech's Brent Minchew and Mark Simons built on their previous work in Iceland, pictured here.
Credit: B. Minchew/Caltech

For the first time, researchers have closely observed how the ocean’s tides can speed up or slow down the speed of glacial movement in Antarctica. The new data will help modelers better predict how glaciers will respond to rising sea levels.

Caltech’s Brent Minchew (PhD ’16) and Mark Simons, along with their collaborators and in cooperation with the Italian Space Agency (ASI), exploited four COSMO-SkyMed radar-imaging satellites on the Rutford Ice Stream in Antarctica. The satellites gathered near-continuous data for nearly nine months from a variety of angles.

The Rutford Ice Stream is a fast-moving river of ice, approximately 300 kilometers long and 25 kilometers wide, in West Antarctica. It connects glaciers in the Ellsworth Mountains to the Filchner-Ronne Ice Shelf, a floating chunk of ice roughly the size of California. Driven by its own weight, the stream of solid ice flows downhill toward the sea at a rate of about one meter per day, though that speed varies by as much as 20 percent with the tides. 

The variability is driven by the ice’s interactions with the ocean. At low tide, the floating ice sinks far enough to ground out on the sea floor like a foundering ship, causing an ice traffic jam that can be detected up to 100 kilometers upstream. When the tide rises again, the ice lifts off of the sea floor and flows freely once more.

“A rising tide lifts all ships, and it also lifts all ice,” says Minchew, a PhD student at Caltech while conducting the research and now a postdoctoral researcher the British Antarctic Survey. Minchew is the lead author of a paper about the study that was published by the Journal of Geophysical Research on November 22.


Horizontal Motion of Ice Stream (12 seconds): As the tide falls, the floating Filchner-Ronne Ice Shelf grounds out, slowing down the progress of the Rutford Ice Stream. When the tide rises, the ice shelf floats again, allowing the flow of the ice stream to speed up. (B. Minchew/Caltech) [view full size on YouTube]

The ice stream was so sensitive to the change in tides that Simons and Minchew could detect the individual influences of solar and lunar tides.

The planet’s solar and lunar tides are caused by the tug of the sun and the moon, respectively, on the earth. High tide occurs simultaneously on the sides of the earth facing toward and away from the sun and the moon because their gravitational pulls create a bulge, or high tide, in the planet.

The lunar and solar tides are not perfectly in sync: the lunar tide cycles from high to low every 12-and-a-half hours, while the solar tide cycles every 12 hours. When those two cycles align perfectly, the sea experiences its strongest tides. When they are most misaligned, the sea experiences its weakest tides.

Previous efforts to explore the effect of the tide on glacial movement relied on placing a GPS device directly on the ice. This technique, however, provides information for only one point of movement.

The Caltech team instead collected pairs of images taken from the same location in space but at different times, thus showing movement not just of a single point but continuous tracking of every single square inch of the surface of the ice streams. (Ice does not move as one solid fixed mass, but rather it flows like an incredibly viscous syrup—its motion is often likened to that of cold honey. As such, the movement of one point provides only the most basic information about the entire glacier.) Further, the variety of viewing angles provided by the constellation of satellites offered three-dimensional information about the ice’s movement and revealed, for example, that the floating ice shelf moved more quickly, thus showing that the grounding effect was indeed responsible for changes in the ice’s speed. 

Studies on glacial movement could yield important data for scientists looking to model how glaciers will respond to the effects of climate change.

“The response of ice flow to changes in sea level and ocean temperature has a direct impact on contemporary sea-level rise,” says Simons, professor of geophysics at Caltech. “Quantifying this is critical for understanding how Antarctica will evolve over the next decades and centuries as the climate warms and the marine-terminating glaciers are exposed to warmer ocean water.”

With warmer water and high sea levels, glaciers will flow faster into the sea, melting more quickly once they reach the water.

Already, the study has yielded surprising information about the strength of ice and its ability to resist deforming due to glacial stress. As it turns out, ice is weaker along the margins of flowing glacial streams than previously suspected. The same technology and technique could be used to study the motion of glaciers worldwide, Minchew says.

Simons and Minchew collaborated with Caltech alumnus Bryan Riel (PhD ’14) and Pietro Milillo of the University of Basilicata in Italy, both of whom are now affiliated with JPL. Their paper is titled “Tidally induced variations in vertical and horizontal motion on Rutford Ice Stream, West Antarctica, inferred from remotely sensed observations.” This research was funded by NASA, the National Science Foundation, the Albert Parvin Foundation, and the Achievement Rewards for College Scientists (ARCS) Foundation.

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Lessons from Aliso Canyon

News Writer: 
Robert Perkins

Soil processing

Patricia Tavormina, associate research scientist at Caltech, removes a small amount of soil from the frozen samples, for DNA extraction. Even as little as a half gram of soil can provide information on thousands of different bacterial species. [VIEW THE SLIDESHOW]
Credit: Caltech

As the saying goes, every cloud has a silver lining. Even when that cloud is 109,000 metric tons of methane.

The Aliso Canyon leak, which began on October 23, 2015 at a SoCalGas natural gas storage facility and took nearly four months to plug, was one of the largest environmental disasters in U.S. history, triggering the evacuation of more than 6,800 nearby households.

The sudden flood of natural gas—a mixture of mostly methane and ethane—offers scientists a unique opportunity to study how the environment responds. Methane is the second-most prevalent greenhouse gas after carbon dioxide (CO2) and, like CO2, is rapidly increasing in concentration in the atmosphere globally. As such, scientists are interested in learning more about the mechanisms that nature already has in place to cope with fluctuations in methane levels—as well as the limitations of those mechanisms.

“The Aliso Canyon leak is disaster but it’s also an opportunity to study this unusual environmental perturbation experiment,” says Victoria Orphan, James Irvine Professor of Environmental Science and Geobiology at Caltech. Since December 2015, Orphan has been collaborating with Caltech associate research scientist Patricia Tavormina to study the growth and composition of microbial communities in the soil around the affected area.


John Eiler, the Robert P. Sharp Professor of Geology and Professor of Geochemistry, answers five critical questions about methane in our atmosphere.

Aliso Canyon has served as a natural gas storage facility for decades. In 1938, J. Paul Getty’s Tidewater Associated Oil Company discovered an oilfield north of the Porter Ranch neighborhood of Los Angeles in the northwestern San Fernando Valley. Oil production peaked in the 1950s with about 118 active wells, then tapered off. Some 32 wells still remain, but starting in the 1970s the bulk of the oilfield was converted into a natural gas storage facility.

Geologically, as a depleted oil field, Aliso Canyon is an ideal natural gas storage facility. With the oil pumped out, what remains is a region of porous rock about 9,000 feet below the surface through which gas can freely flow, topped by an impermeable capstone. It’s one of the largest such facilities in the U.S., reaching an average depth of 9,000 feet and capable of storing 86 billion cubic feet of natural gas. SoCalGas purchases natural gas from around the country and ships it to the site, where it is injected beneath the capstone and into the porous rock via 115 gas injection wells; when needed, the gas is pumped back out through those conduits. During the leak event, one of those wells, located about a mile north of homes in Porter Ranch, ruptured at a depth of about 300 feet, above the capstone.

SoCalGas tried several “top kills” to plug the leak—that is, injecting a slurry of mud and brine down the well in an attempt to plug it. The top kill failed, as high pressures inside the methane-packed porous rock repeatedly blew the plug back out again. The leak was finally plugged in February 2016, thanks to a newly constructed well that allowed SoCalGas to relieve the pressure on the damaged well and permanently plug the leak.

Previously, Orphan and Tavormina, in collaboration with Professor Samantha Joye at the University of Georgia, studied the effects of the 2010 Deepwater Horizon oil spill—which released nearly 5 million barrels of oil into the Gulf of Mexico near the Mississippi River Delta—on marine microbial communities.

Now they want to know if and how microbes in the soils of Aliso Canyon are able to survive and adapt to the sudden spike in local methane levels. To do so, they first collect soil samples both around the wellhead and within the nearby community.

The process of taking samples at Aliso Canyon starts out low tech. The researchers use a one-meter length of polyvinyl chloride (PVC) pipe that has been split lengthwise and then bound back together. They hammer this hollow cylinder into the ground as far as it will go (usually about half a meter) and then pull it up, separate the halves, and remove the soil inside. So far, they have taken 63 soil cores, about 16 of which are right by the wellhead. They anticipate that they will be collecting samples at least through February 2017.

The samples are brought back to Orphan’s Caltech lab, where they are processed and analyzed.

 

“The first thing we do is look for changes in the population of soil microorganisms. If I see changes throughout the overall population across space or time, that’s an indication that the population is responding to the gas—the population is being shaped, or structured, by the gas,” Tavormina says.

In addition to monitoring the changing demographics of the microbial population, the researchers physically count the most promising bacterial species—the ones that seem to be responding most to the natural gas. They enumerate how many of certain bacteria are in these samples and grow specific bacteria out of the soil and then ask what happens when the organisms are fed different components of natural gas, like methane.

It isn’t just as simple as saying that every change in the microbes is driven by methane, however. Depending on its source, natural gas contains a varying percentage of ethane, which could also be driving changes in microbial communities.

Further, the process that microbes use to break down methane contains several steps, each of which affects the environment of every other microbe in the immediate area. There are multiple pathways for breaking down methane and converting it into energy that microbes can consume. In general, the first step converts it to methanol, breaking down methanol yields formaldehyde, and so on. Microbes exist in complex heterogeneous communities that often work together to complete different steps of the process.

“Imagine two microorganisms talking to each other: ‘I can use your formaldehyde. You keep metabolizing the methane, and I’ll take care of this step.’ So it becomes like an assembly line,” Tavormina says.

Microbes that consume methane, known as methanotrophs, do so using an enzyme called particulate methane monooxygenase (pMMO). Measuring pMMO levels gives researchers a proxy by which they can estimate the number of methanotrophs in a sample. As such, when Orphan and Tavormina analyzed the soil samples from Aliso Canyon, they expected to find high levels of pMMO near the blowout.

“Most soils have some methanotrophic bacteria, but we were getting only a weak molecular signal for pMMO,” Orphan says. “You’d figure that the closer you get to the gas blowout, you’d see more evidence of methanotroph enrichment, but we didn’t, which was unexpected.”

Instead, they discovered increasing numbers of an uncommon bacterial species that had not been previously cultured in a lab. This as-yet-unnamed microbe uses a different version of the pMMO enzyme—one that is ferried around by the bacterium within a circular piece of DNA called a plasmid. Plasmids can reproduce independently of the rest of the bacterial genome, making them easier to share with other organisms—making it possible that this microbe is sharing the genes for processing methane with other species of microbes.

“We’re seeing whole new species and groups of microorganisms that we didn’t think consumed hydrocarbons, and finding that they are definitely involved in metabolizing it,” Tavormina says.

Down the line, understanding how microbes react to and process methane could help mitigate future disasters. Tavormina says it is not too far-fetched to imagine clean-up crews armed with soil mats filled with methanotrophic microbes responding to leaks.

For now, Orphan and Tavormina will continue to study nature’s response to the leak—and shine a light on microbes’ seemingly endless ability to survive and thrive under whatever circumstances they face.

This research is funded by the National Science Foundation.

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JPL News: From Monterey Bay to Europa

photo of Steve Chien with drones

JPL's Steve Chien with several of the underwater drones used in a research project earlier this year. Chien, along with his research collaborators, are developing artificial intelligence for these drones.
Credit: NASA/JPL-Caltech

If you think operating a robot in space is hard, try doing it in the ocean. Saltwater can corrode your robot and block its radio signals. Kelp forests can tangle it up, and you might not get it back. Sharks will even try to take bites out of its wings.

The ocean is basically a big obstacle course of robot death. Despite this, robotic submersibles have become critical tools for ocean research. While satellites can study the ocean surface, their signals can’t penetrate the water. A better way to study what’s below is to look beneath yourself — or send a robot in your place.

That’s why a team of researchers from NASA and other institutions recently visited choppy waters in Monterey Bay, California. Their ongoing research is developing artificial intelligence for submersibles, helping them track signs of life below the waves. Doing so won’t just benefit our understanding of Earth’s marine environments; the team hopes this artificial intelligence will someday be used to explore the icy oceans believed to exist on moons like Europa. If confirmed, these oceans are thought to be some of the most likely places to host life in the outer solar system.

If successful, this project could lead to submersibles that can plot their own course as they go, based on what they detect in the water around them. That could change how we collect data, while also developing the kind of autonomy needed for planetary exploration, said Andrew Thompson, assistant professor of environmental science and engineering at Caltech.

Read the full story from JPL News

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