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Extreme environment

Scientists drill into frozen Lake Vida to explore its unusual biology, chemistry and history

 

Lake Vida isn’t a particularly accommodating place to live.

Consider that the Antarctic lake would hardly fall under the definition of “lake” for most people. It certainly wouldn’t be found on anyone’s top ten list of favorite fishing holes. In fact, neither fish nor much else could survive in the hypersaline lake, which appears to be frozen from the surface to nearly the bottom more than 20 meters down.

Oxygen is completely absent from Lake Vida, which is up to seven times saltier than seawater. Its chemistry is just weird, with the highest nitrous oxide levels of any natural water body on Earth. A briny liquid that courses through pockets and channels within this anaerobic environment exists at minus 13.5 degrees centigrade. Remember that the ocean never gets colder than a couple of degrees below zero.

“It’s so cold that we know very few liquid ecosystems on the planet where the constant temperature is that far below zero,” said Alison Murray, a molecular microbial ecologist at the Desert Research Institute in Reno, Nev., who studies how microorganisms interact with their environment.

“We don’t know much about cellular processes — what it takes to make a living — at that temperature,” added Murray, a principal investigator on a collaborative project to figure out how life has adapted for survival in Lake Vida.

Other members of the team, led by Peter Doran, a professor at the University of Illinois at Chicago, are interested in learning more about the history of the lake. For example, analyses of sediments from the lake bottom could provide clues as to what processes occur in bodies of water as the Earth moves into colder periods.

“The main goal is to get into that brine pocket and the sediment beneath it to both document and define the ecosystem that's there today, and the history of that ecosystem,” Doran said previously.

That’s exactly what Murray, Doran and their team attempted to do this past season: Probe deep into the lake to learn more about its biology, chemistry and history. And, as one might expect when exploring such an alien environment, they turned up the unexpected.

The first break

The 2010-11 expedition is the third visit to Lake Vida in about 15 years by U.S. scientists interested in its unique characteristics.

In October 1996, researchers extracted two ice cores from Lake Vida with an electromechanical drill, spending about two weeks at temperatures below 35 degrees Celsius to drill through 16 meters of ice.

A paper six years later in the journal Proceedings of the National Academy of Sciences, with Doran as the lead author, announced that Vida was not completely frozen and lifeless as previously assumed. Ground-penetrating radar, ice core analyses, and long-term temperature data, showed that Vida had a thick, light-blocking ice cover, a vast amount of ancient organic material and sediment, and a cold, super-salty, liquid layer below the ice.

Carbon dating placed the age of the microbes recovered and revived from the ice cores at some 2,800 years old.

Going deeper

Doran and colleagues returned to Lake Vida in 2005 with the intent of drilling through the ice cover into the liquid brew underneath. That’s when Murray got involved in the project, joined by DRI colleague Chris Fritsen, who was also on the 1996 team with Doran, John Priscu from Montana State University, and others.

The second attempt not only had the support of the National Science Foundation, which manages the U.S. Antarctic Program, but funding from the NASA Astrobiology Science and Technology for Exploring Planets (ASTEP) Program to test new drilling technology.

The conditions at Lake Vida could mimic those found on Mars or Jupiter’s moon Europa, destinations where the space agency hopes one day to search for life. A lightweight, functional drill might be needed aboard a future mission to probe into a similarly ice-covered environment.

Meanwhile, a second drill operated by a crew from the University of Wisconsin-Madison supported the science mission of reaching the liquid layer.

Keeping it clean

“One of the big things we developed for that project was to develop clean access procedures,” Murray said, explaining that the scientists wanted to keep the environment that was believed to exist about 20 meters under the ice as pristine as possible. Potentially, it hadn’t been in contact with the atmosphere for thousands of years.

Strong winds in Victoria Valley, the northernmost of the McMurdo Dry Valleys where Lake Vida sits, blow across sand dunes on one side of the 5-kilometer-long lake. The team didn’t want the sediments to end up in their hole.

So they set up stringent procedures to keep the drill site and equipment clean, working under a tent constructed on the lake’s surface. Everything that went down the hole was sterilized like a surgical tool. An ultraviolet light system under the floor of the tent gave the instruments a final dose of UV radiation for good measure.

“The cleaning part of this is quite a process,” Murray said.

The team even developed a way to clean the drill hole itself. After initially drilling a hole, they would widen it, and then clean the hole of all the water through a filtration process. They then would let the water in the hole refreeze, drilling through again into a clean ice “pipe” to sample the brine below the ice.

Running out of time

As the drill started to chew deep into the ice cover, a strange thing happened. Liquid brine began to fill up in the hole, well above where the GPR survey had identified the liquid water layer.

Brine channels that run through the lake started pouring into the borehole. The team pumped the brine out of the hole to analyze later and continued to bore down.

Unfortunately, time worked against them. A late start meant the researchers found themselves in the middle of the lake as the summer melt season began. The meltwater from nearby glaciers doesn’t flow into the frozen lake but pools on top.

“We were anticipating that we were going to get flooded out within a week, so we called it and closed the camp,” Murray said. The lake surface flooded about three days later.

Characterizing the brine

The researchers had to be satisfied with characterizing the brine, which was “quite unusual,” according to Murray.

The unusual chemistry somewhat resembles that found in the equally bizarre feature known as Blood Falls, where a subglacial pool of water under the Taylor Glacier in the Taylor Valley percolates to the surface of Lake Bonney. The iron oxide-enriched saltwater stains part of the face of the glacier red, as well as the ice-covered surface of the lake nearby.

And while Lake Vida isn’t the saltiest body of water in the Dry Valleys — that honor goes to Don Juan Pond, which also has high levels of the laughing gas called nitrous oxide — the salts are sodium chloride, probably residuals of marine-derived aerosols.

The brine also contained high levels of iron and manganese, probably derived from the nearby rocks. Bacteria cell counts were also surprisingly high, particularly of a small cell type that Murray said the team didn’t “know anything about.”

A weird day

Those enticing results brought them back in 2010-11 on a NSF-Supported project to take another shot at the liquid layer below the ice, intrigued by the clues found in the brine from the upper ice layers. “We’re really delving into the things that we found interesting last time,” Murray said.

Drillers with the Ice Drilling Design and Operations group from the University of Wisconsin-Madison again led the effort to reach the liquid layer and lake sediments below.

By mid-November, the drill breached the 20-meter-mark. Then 21 meters, 22 meters … Layers of ice mixed with layers of frozen sediments, which made the drilling difficult. Driller Jay Kyne, wearing a white Tyvek suit to avoid contaminating the equipment, kept stopping to sharpen the drill blades, eventually calling back to McMurdo Station for another set of cutters.

Twenty-three meters, 24 meters … Still no water even at 27 meters. The drill never dropped down as it should have if the drillers had penetrated a substantial water layer. “That was really quite a surprise,” Murray said of the lack of a brine pocket. “It was a weird day.”

Filtering away

A few weeks later, back at the Albert P. Crary Science and Engineering Center in McMurdo, team members spend long hours in the labs filtering brine water collected this season for various experiments that could reveal how the microbes in the lake produce energy in the absence of oxygen and light.

It could be that the organisms are chemotrophs, using the chemistry of their environment to obtain energy, explained Brian Glazer, a professor at the University of Hawaii who is one of several collaborators on the Lake Vida project.

“It’s better living through chemistry,” Glazer quipped. “They’re making sugars from the chemistry available to them.”

Some of the experiments take hours to complete, partly because of the difficulty of working with the brine. It has to be kept in an anoxic environment; otherwise, it forms particulates that clog filters used in different experiments. One method involves keeping a steady stream of nitrogen over the filter. A less appealing process involves working in an oxygen-free glove bag, a plastic bubble with built-in gloves.

“Even if we do manage to keep it anaerobic, there’s a large amount of dissolved organic matter in the brine, and it’s very sticky, and it also clogs the filters very rapidly,” Glazer said.

Some of the work takes place in a freezer with a constant temperature of minus 10 Celsius to keep the brine as close as possible to its original environmental conditions.

“It gives us as clear a picture as possible of what the brine really is” working in the freezer room, Glazer said.

Time will tell

Meanwhile, Hilary Dugan, wearing a big red parka, plays the role of team photographer in a different freezer room, with the temperature at a finger-numbing minus 20 degrees. A slushy, dirty-looking ice core sits on a light table. Dugan photographs each section of ice before it’s packed for shipment to the United States.

A PhD student with Doran, Dugan is interested in the physics and history of the lake system. The absence of a liquid layer could mean many different things. Perhaps the lake has frozen solid to the bedrock since the GPR survey 15 years ago. Maybe the spot where the team drilled was on a high point of the lake.

“We sort of have to readjust how [we think] the lake formed, which is neat because there’s no other lake in the world that has this much ice frozen right to the bottom with that amount of life, that amount of carbon in it,” Dugan said.

Dugan, with the help of the McMurdo Station Field Safety Training Program team, conducted a new GPR survey of the lake, hoping an updated view of the layers below the ice cover will tell the scientists something about that missing water pocket.

Speaking later via e-mail from the States, Doran said the team will meet soon to discuss the results of the latest radar survey to determine what the collaborators believe might be happening. 

“I think the leading candidate right now is that the lake is a sequence of dunes migrating over top of the lake, then more lake ice, then more dune migration, etc.,” he said. Additionally, there may be some muddy floodwaters mixed in the lake as well.

Laboratory work back in the States on the ice-sediment sequences in the core might provide some clues as to what happened in the past despite the mixed layering, according to Doran. 

“The problem with ice in this system is it comes and goes, and so we may not have a continuous sequence,” he said. “Sediments can tell you about the history and chemistry of the lake over time. So we’ll get our record, but it will be tricky and probably the timeline is going to be hard to nail down with as much accuracy.”

So close, so different

Each body of water in the Dry Valleys seems to possess its own unique history, making it difficult to compares lakes within the same valley, let alone the whole region. It seems surprising, given the whole region is only 4,800 square kilometers.

Doran explained that Lake Vida is unique because Victoria Valley is sheltered from winter katabatic winds that normally warm the valleys. That means it’s colder in Victoria Valley than farther south, allowing the lake’s ice cover to grow. The summer melt that later pools on top of the lake just adds to the thickness.

In fact, the lake ice cover has grown about a meter in the last decade, according to Dugan. “That’s a lot of hydrological input,” she said.

The Dry Valleys have always been a favorite analogue for scientists with a yearning to understand life beyond Earth. Vida may be the most alien of all.

“You can imagine you’re walking on Mars,” Dugan said, returning to the theme of planetary research that the Lake Vida project represents. “We might have a system that’s closer to life on other planets than other places in the Dry Valleys.”

Links to the past and future

Lake Vida is also an interesting model for those interested in studying ancient climate right here, when the planet was periodically in a deep freeze called Snowball Earth. Some scientists believe much of the planet, all the way to the equator in some models, was covered by ice hundreds of millions of years ago.

Murray said that it’s possible that Snowball Earth lakes could have resembled Lake Vida, with brine pockets that might have served as refuges for life on a planet turned extremely inhospitable.

“That’s a good link to past history on Earth,” she said.

A more tangible connection that Murray hopes to make as she gets into the genetic level of the study is how the Lake Vida microbial community compares to relatives of bacteria from other places on the planet. What adaptations do the lake extremophiles show compared to their cousins in less stressed environments?

“One of the biggest legacies I think we can get from this system is having a culture collection of diverse organisms that are from there and capable of life at minus 13.5. It could prove to be really useful models for studying cryobiology,” she said. “I’m quite interested in the diversity of those organisms.”

NSF-funded research in this story: Peter Doran and Fabien Kenig, University of Illinois at Chicago, Award No. 0739698; and Alison Murray, Chris Fritsen and Giles Marion, Award No. 0739681.

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Curator: Peter Rejcek, Antarctic Support Contract | NSF Official: Winifred Reuning, Division of Polar Programs