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Under the ice: the polar expedition to explore glacial lakes

Antarctica’s ice caps conceal a pristine and mysterious world. Recent expeditions have started to unveil the secrets of the glacial lakes that lie beneath, while carefully avoiding contamination.

It is no exaggeration to say that we know more about the surface of Mars than we do about Antarctica’s subglacial environments, but that is changing thanks to recent expeditions that have penetrated a lost world beneath the ice sheet.

Kilometres below the ice sheet that covers that Antarctic continent lies one of the planet’s largest wetlands that you’ve probably never heard of. Over 400 lakes, rivers and streams host ecosystems that exist in the sub-zero waters, in the darkness under the ice.

Even in the extreme cold of Antarctica this water remains liquid, heated by geothermal energy from the Earth’s crust, and insulated by a thick blanket of ice. The wetland’s waters could provide tantalising clues as to how life can exist off-planet in even more challenging conditions.

Exploration of the hydrology of this lost world is also informing climate change models to help us understand better how the vast ice sheet flows outwards to its edges and its likely impact on future sea levels when the ice breaks.

Andrei Kapitsa, an eminent Russian polar scientist, first postulated the existence of subglacial lakes in Antarctica in 1957 when he noted in his doctoral thesis that the area around the Soviet Vostok base was unusually flat and suggested that there might be a reservoir or lake below the surface.

In 1974, an airborne radio echo survey confirmed the existence of a giant lake with a surface area of 12,500km2 lying underneath 4km of ice. Its existence was further confirmed by satellite measurements of the ice surface in 1993. We now know that Lake Vostok is over 900m deep and is one of Earth’s largest bodies of fresh water.

An early goal was to sample the microbes that live in the lake, which could have been sealed off from the rest of the world for millennia. In December 2012, a Russian expedition drilled through 4,000m of ice to reach the surface waters of Lake Vostok, but the use of kerosene drilling fluid containing contaminated bacteria from the surface has produced contentious results and no definitively ancient life forms from the lake. The international community has not been able to persuade the Russians to apply an internationally agreed sterile protocol to continued ice drilling at Vostok that would protect any possible ancient microorganisms.

In the same season as the Russians drilled to Vostok in eastern Antarctica, a US-funded expedition to explore Lake Whillans successfully drilled through 800m of ice and penetrated the lake in January 2013 in west Antarctica.

Polar ecologist professor John Priscu of Montana State University was lead scientist on that expedition. He has been studying extremophiles – organisms capable of existing in environments once thought incapable of supporting life – for much of his career, which spans 35 Antarctic seasons.

He and his team deployed strict sterile protocols during hot water drilling to penetrate the ice (see box) and were the first scientists to study directly the microbes from deep under the ice. “The waters of the subglacial lakes are dark, and because of the pressure of the overlying ice, temperatures range from -0.5°C to -2°C,” he says. “Understanding how life evolved to live in such hostile conditions, developing creative metabolisms to cope, is guiding the search for extra-terrestrial life.”

A major group of microbes discovered living deep under the ice by Priscu and his team are chemolithoautotrophs – literally bacteria that eat rocks. They are present in the waters under the ice in similar quantities to microbial communities found in the deep open ocean. These life forms form the base of the ecosystem that lives in the subglacial lakes, producing a basic carbon source that other organisms can metabolise.

The microorganisms first found at Lake Whillans, and now in Lake Mercer, probably form part of a subglacial ecosystem living in the wetlands under the Antarctic ice sheet. They mobilise nutrients that are washed out into the Southern Ocean, fertilising the coastal waters, and are a significant, previously unrecognised source of carbon on Earth.

Logistics

Lake Mercer Expedition 2018/19

Planning and logistics in the polar regions are never simple. Planning to work only 400 miles from the South Pole on the ice above Lake Mercer was never going to be easy. It took many years of planning, and two years to deliver all the heavy drilling equipment, generators, fuel, science labs and some camp structures to the drilling site. Almost half a million tonnes of equipment had to be transported over the ice sheet. Three huge tractors, weatherised for the cold with battery heaters and oil that would work down to -10°C, dragged the material on to the ice above the long-buried Lake Mercer. The tractors traversed the 650 miles to the work site at an average speed of 7mph, taking over two weeks to complete the journey.

All of the equipment was pre-assembled in the USA and packed into shipping containers that could be sent by road, and then shipped by sea to the US Antarctic base at McMurdo. There, the containers were mounted on giant sleds with skis and towed very slowly to the work site. The lead tractor in the convoy had a ground-penetrating radar on the front to give an early warning of potentially dangerous crevasses that could sabotage the convoy.

The same operation was repeated a year later, in November 2018, assisted by multiple flights by both a turboprop DC3 and Twin Otters fitted with skis flying in the balance of the light cargo and the crew.

Dennis Duling, the lead ice-drilling engineer at Lake Mercer, explains the drilling process: “Everything we do follows the Antarctic Protocol to prevent contamination of the sub-surface ecosystems by surface organisms. We drill using hot water heated to 88°C, which will cut through ice at 0.25-0.5m a minute and use internationally agreed standards commonly used in food preparation and pharmaceutical manufacture to keep everything sterile. The drill water is filtered to 0.2 microns, and then subjected to ultraviolet light sterilisation. All equipment is washed with hydrogen peroxide.”

Describing the job, Duling says: “Precisely drilling through thousands of metres of ice is a challenging thing to do, you have clear goals, a budget, a timeline and a crew. Achieving all the goals is so rewarding, there’s not a better feeling on the planet.”

Building on the successes of the Whillans expedition, the team returned to the Antarctic during the 2018/2019 season to drill into subglacial Lake Mercer, 400 miles from the South Pole. In a modest understatement, the researchers describe their enterprise as logistically and technically challenging (see box for a description of how they got to the point of sampling the icy waters).

On 26 December 2018, a borehole melted through to the waters below. In an astonishingly unexpected discovery, when the sediment was sampled, the biologists found the remains of tiny animals. The organisms found included a single tardigrade, an eight-legged micro-animal that can withstand conditions in space and the most extreme environments on Earth. Also recovered from the mud were parts of crustacean shells with legs attached and what may be plant or fungal cells.

The tardigrade species found is similar to a moss-dwelling tardigrade and may have lived during one of the periods when the continent was last ice-free: 10,000 or 120,000 years ago. What is still not clear is whether these animals once lived in the lake, or whether their remains were washed into it by streams or rivers under the ice. Work is ongoing to confirm that these creatures were not the result of any surface contamination.

The team also sent down a slim remotely operated vehicle (ROV), dubbed Deep SCINI and designed at the University of Nebraska, Lincoln to fit into the narrow ice borehole. Deep SCINI was equipped with high-definition cameras to observe debris in the ice above the lake, and sensors to determine the depth of the lake and the nature of the sediments there. The cameras on the robot, along with other high-resolution cameras deployed down the borehole, produced the first exciting high-resolution images of the bottom of the lake.

Towards the end of their stay at Lake Mercer, the team sent their largest piece of kit down the borehole, the gravity corer. This uses the force of gravity to penetrate the lake’s sediments and bring back a sample to the surface. This was the first time a corer like this had been used in Antarctica.

The lake’s sediments record the life present at the time they were laid down, which in turn gives a great deal of information about the climate of that time. Once analysed, these sediments will extend our record of Antarctica’s climate, giving us clues as to how quickly the ice sheet has melted in the past, and an indication of how it could behave in the 21st century. 

Astrobiology

What can subglacial lakes tell us about life in space?

Astrobiologists believe that exploring the subglacial lakes of the Antarctic could help us in many ways when it comes to the search for extra-terrestrial life. Researchers currently believe that the most likely places to harbour alien life in our solar system lie beneath ice over 15km thick. Tough though it is to explore the deep buried Antarctic wetlands by using hot water drills to penetrate ice kilometres deep, translating that experience to an off-world location will be far harder.

John Priscu has been working with Nasa to help design missions to do just that, combining his decades of experience in studying microorganisms in the ice-encased lakes of the McMurdo dry valleys and subglacial lakes of Antarctica with field work with Nasa in Greenland on ice this summer, and in the lakes and glaciers of the Himalaya.

Some of the latest most-promising potential candidates for harbouring life in our solar system are the ice-covered moons of the gas giants Jupiter and Saturn, or below the southern ice cap of Mars. There is mounting evidence that underneath the icy exteriors of the gas giant moons Europa and Enceladus lie liquid oceans warmed by geothermal activity and tidal pulls that could be home to alien microorganisms.

Antarctic lakes are a good place to understand how to design missions to explore deep-space environments that may harbour liquid water and, potentially, life. By studying some of the Antarctic life forms, the extremophiles – so-called because they exist at the edge of conditions thought necessary to support life – in extremes of cold conditions or pressure, and in the absence of light found under the Antarctic ice, scientists can get a better idea of where to look for life and what form it might take.

“Searching these potential sub-surface bodies of liquid water is likely to be our best bet in the search for alien life off-planet in our solar system,” says Professor Priscu. “And, of course, our Antarctic work helps us to prototype technology to penetrate the oceans that we suspect lie below the ice on Europa or Enceladus.”

Gravity Core

Image credit: Kathy Kasic

Investigation

How to find Antarctic lakes

Exploring for Antarctic lakes sounds like fun. You fly over the frozen continent, bombarding it with radio waves to measure the bounce back of the signals, and use satellites with incredibly precise lasers to measure the top surface of the ice to reveal the tell-tale signs of a hidden lake. Once you have found one, you set off explosions to calculate the depth of the body of water. Martin Seigert, glaciologist, geophysicist and professor at Imperial College, London uses all of these techniques to discover new bodies of water under the ice.

The primary technique is radio echo sounding from an aircraft. Seigert uses a repurposed DC3. Radio waves emanating from instruments aboard the plane go straight through ice but will reflect where there is a change in the electrical properties of the substance they are travelling through, say where they meet bedrock or water.

“Water is a particularly strong reflector,” he says. “The radar image is bright and flat, and easily distinguishable from the ice-rock interface.

“Data from the Mars Express orbiter is producing strong radar profiles beneath the Red Planet’s frozen southern ice cap, similar to the ones we see from the Antarctic lakes – indirect evidence of liquid water on Mars.”

To track changes in the surface topography of the ice, satellite data is used. The team are currently using the European Space Agency’s Cryosat-2, the latest in a series of satellites that have been monitoring changes in the ice surface for the past 20 years. “Cryosat-2 uses laser altimetry to measure the changes in the thickness of the ice to a resolution of 1.3cm, making it easy to pick out the marked flattening of ice as it travels across the surface of a lake,” Seigert adds. Looking at these measurements over time allows the scientists to determine which lakes are static bodies of water, and which are active and dynamic.

Measuring the depth of water in any of the subglacial lakes means getting out on to the ice sheet and setting off controlled explosions, seismic charges which generate shockwaves that travel through the ice and into the water. Knowing the relative speed of sound wave transmission through ice and water allows the researchers to calculate the water depth in a lake.

Of the 400+ lakes discovered to date, about 180 are active, with water flowing from the centre of the ice sheet to the edges, where the ice meets the Southern Ocean. “Because water underlying the ice sheet has a fundamental impact on how that ice flows, we now have a better appreciation of ice-sheet dynamics, which in turn helps improve our models of how the ice sheet will react to climate changes,” explains Seigert.

 

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