Under Antarctic ice, microbes gobble up greenhouse gas | Science News for Students

Under Antarctic ice, microbes gobble up greenhouse gas

Bacteria break down the powerful methane before it can reach the atmosphere
Sep 1, 2017 — 7:00 am EST
Antarctic ice sheet

In a lake beneath an Antarctic ice sheet like this one, scientists have found bacteria that eat methane, a powerful greenhouse gas.

Elaine Hood, National Science Foundation

Trapped beneath blankets of ice in Antarctica are huge amounts of methane, a powerful greenhouse gas. Scientists have long feared that climate change will melt these ice sheets and release the climate-altering gas. But a new study suggests the threat might not be as bad as it seemed. That’s thanks to some microscopic helpers: bacteria.

“In nature, one bug’s poison is another bug’s food,” says study coauthor John Priscu. He’s a polar ecologist at the Montana State University in Bozeman. He specializes in microbes in ice. He and his team have now turned up bacteria eating methane deep beneath the ice there, at the bottom of the world. And he suspects they’re hungry enough to gobble all of it up before it can escape into the air.

Millions of years ago, sea levels were higher. This left an ocean covering Antarctica. When sea levels dropped and the ocean retreated, it left behind a layer of debris from plant and animal life. As global temperatures cooled, a thick sheet of ice gradually formed. Years went by. Eventually, bacteria under the ice broke down the organic material. And they exhaled methane.

That’s what scientists believed, anyway. “No one ever measured it. It’s very difficult to get to the bottom of the Antarctic ice sheet,” Priscu explains. So his group set out to do just that.

Four years ago, they drilled down more than 800 meters (about half a mile) through the ice. Then they scooped up samples of water and sediment from the lake below. This Lake Whillans is known as a subglacial lake, or a body of water that sits far below some ancient blanket of ice. That’s what scientists believed, anyway. “No one ever measured it. It’s very difficult to get to the bottom of the Antarctic ice sheet,” Priscu points out. 

Analyses of those lake samples now confirm for the first time what scientists had long suspected. “Yep, there is methane,” Priscu says. And the methane’s chemical makeup confirmed that it came from bacteria eating ancient organic material.

But the scientists also found something they hadn’t expected. “There’s another group of organisms, and it is eating the methane,” Priscu reports. These bacteria digest methane and release carbon dioxide (CO2). Yes, CO2 is also a greenhouse gas. But it’s a far weaker one (methane is around 30 times more powerful than CO2) — and plants can soak up the CO2.

The team published its findings online July 31 in Nature Geoscience.

Methane munchers on Earth and beyond

David Karl says the new findings are important. A microbiologist, he works at the University of Hawaii at Manoa. Karl says the new data offer the first direct evidence that there’s life in these subglacial lakes.

Antarctic water sampling
Here's the 1,000 meter hose used for sampling water from Lake Whillans. It’s seen mostly spooled up, awaiting its first test use in Antarctica.
Janet Raloff/SNS

The scientists showed that methane is forming in sediment at the bottom of the lake. “But, voila, when they go and look for [methane in the water] it’s not there,” Karl says. The team used genetics, modeling, geochemistry and other sciences to show that the methane disappears because microbes are eating it. The methane eaters seem to be totally canceling out the methane producers — at least in this lake.

These data are good news for climate scientists. Some have feared that methane released by melting ice could make climate change much worse. But this suggests that bacteria could eat the methane before it ever enters the air. Sites similar to Lake Whillans exist across Antarctica. So Priscu thinks it’s likely that these methane-eating bugs are widespread.

The new findings also could prove of great interest to scientists who look for life on other planets. Conditions in Antarctica are similar to those on icy worlds in our solar system, such as Jupiter’s moon Europa. Studying how microbes grow in extreme habitats such as subglacial lakes gives scientists an idea of what life might look like on these other planets. It’s also a chance to develop tools that could come in handy on future space missions.

To get through the ice covering Lake Whillans, the scientists had to invent a new hot-water drill. “Think of a giant garden hose with a 12-foot-long nozzle at the end that blasts out almost-boiling water,” Priscu says.

Scientists used melted glacier water to drill through the ice. But first they sterilized the water. They needed to make sure that no surface germs could infect their samples or the delicate ecosystem under the ice.

It took 12 tractors to haul more than 450,000 kilograms (a million pounds) of gear on sleds 1,000 kilometers (600 miles) to the research site. Fifty-two scientists, engineers, and other crew members camped in tents on the glacier for two weeks. They worked around the clock to drill through the ice and collect the samples. But Priscu says it was worth it.

“We know more about the surface of the moon than we know about the Antarctic continent,” he says. “Every time I go down there, I’m overwhelmed by questions.”

Power Words

(for more about Power Words, click here)

Antarctica     A continent mostly covered in ice, which sits in the southernmost part of the world.

atmosphere     The envelope of gases surrounding Earth or another planet.

bacteria     ( singular: bacterium ) Single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals).

biology     The study of living things. The scientists who study them are known as biologists.

bug     The slang term for an insect. Sometimes it’s even used to refer to a germ.

carbon     The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.

carbon dioxide (or CO2)    A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter burns (including fossil fuels like oil or gas). Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

climate     The weather conditions that typically exist in one area, in general, or over a long period.

climate change     Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.

coauthor     One of a group (two or more people) who together had prepared a written work, such as a book, report or research paper. Not all coauthors may have contributed equally.

colleague     Someone who works with another; a co-worker or team member.

continent     (in geology) The huge land masses that sit upon tectonic plates. In modern times, there are six established geologic continents: North America, South America, Eurasia, Africa, Australia and Antarctica. In 2017, scientists also made the case for yet another: Zealandia.

debris     Scattered fragments, typically of trash or of something that has been destroyed. Space debris, for instance, includes the wreckage of defunct satellites and spacecraft.

digest     (noun: digestion) To break down food into simple compounds that the body can absorb and use for growth. Some sewage-treatment plants harness microbes to digest — or degrade — wastes so that the breakdown products can be recycled for use elsewhere in the environment.

ecology     A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

ecosystem     A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra.

engineer     A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.

Europa     One of the moons of Jupiter and the sixth-closest satellite to the planet. Europa, 1,951 miles across, has a network of dark lines on a bright, icy surface.

genetic     Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.

geochemistry     A science that deals with the chemical composition of and chemical changes in the solid material of Earth or of another celestial body (such as the moon or Mars). Scientists who study geochemistry are known as geochemists.

geoscience     Any of a number of sciences, like geology or atmospheric science, concerned with better understanding Earth. People who work in this field are known as geoscientists.

greenhouse gas     A gas that contributes to the greenhouse effect by absorbing heat. Carbon dioxide is one example of a greenhouse gas.

habitat     The area or natural environment in which an animal or plant normally lives, such as a desert, coral reef or freshwater lake. A habitat can be home to thousands of different species.

ice sheet     A broad blanket of ice, often kilometers deep. Ice sheets currently cover most of Antarctica. An ice sheet also blankets most of Greenland. During the last glaciation, ice sheets also covered much of North America and Europe.

Jupiter     (in astronomy) The solar system’s largest planet, it has the shortest day length (10 hours). A gas giant, its low density indicates that this planet is composed of light elements, such as hydrogen and helium. This planet also releases more heat than it receives from the sun as gravity compresses its mass (and slowly shrinks the planet).

methane     A hydrocarbon with the chemical formula CH4 (meaning there are four hydrogen atoms bound to one carbon atom). It’s a natural constituent of what’s known as natural gas. It’s also emitted by decomposing plant material in wetlands and is belched out by cows and other ruminant livestock. From a climate perspective, methane is 20 times more potent than carbon dioxide is in trapping heat in Earth’s atmosphere, making it a very important greenhouse gas.

microbe     Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

microbiology     The study of microorganisms, principally bacteria, fungi and viruses. Scientists who study microbes and the infections they can cause or ways that they can interact with their environment are known as microbiologists.

nozzle     A round spout or slot at the end of a pipe, hose or tube. Nozzles are typically used to control the flow of a jet of some high-pressure liquid or gas.

organic     (in chemistry) An adjective that indicates something is carbon-containing; a term that relates to the chemicals that make up living organisms. 

sea     An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.

sea level     The overall level of the ocean over the entire globe when all tides and other short-term changes are averaged out.

sediment     Material (such as stones and sand) deposited by water, wind or glaciers.

solar system     The eight major planets and their moons in orbit around our sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.

Citation

Journal: A.B. Michaud et al. Microbial oxidation as a methane sink beneath the West Antarctic Ice Sheet. Nature Geoscience. Vol. 10, published online July 31, 2017. doi: 10.1038/ngeo2992.