Canadian Lake Helps Scientists Refine Alien Life-Hunting Skills

"Forall intents and purposes," says Allyson Brady of the University of Calgary,Pavilion Lake, in British Columbia, "seems to be a pretty normal lake.There are fish in it; people have cottages around the lake, you can goswimming." It's a lovely place to bring the family for a summer vacation.

ButBrady, acting principal investigator of the Pavilion Lake Research Project(PLRP), and her colleagues won't be vacationing this week when they descendinto the depths of the lake, as they have for the past several summers.

Despiteits pastoral surface appearance, Pavilion Lakeis anything but normal. Carpeting the slopes of the lakebed is an underwaterforest of carbonate structures that, at first glance, might be mistaken forcoral. These carbonate formations — PLRP's researchers call them "microbialites"— range in size from small nodules the width of a quarter to massive moundsseveral meters across. Until they were discovered in Pavilion Lake, suchformations were relatively unknown in freshwater lakes.

Similarstructures are known to exist in a handful of other places in the world, inShark Bay, Australia, for example, "but these tend to be more extreme environments," Brady says. "Areas where you don't find much else living therebut bacteria," because it's too salty, too acidic or generally too extreme forother life forms to survive. No-one has been able to figure out yet what they'redoing in Pavilion Lake.

Thecentral question is what role biology has played in forming the microbialites. "We'retrying to figure out if we can identify, basically, abiotic versus bioticprocesses," Brady says. The structures are covered with a layer of livingbacteria, and there is evidence that these bacteria may be influencingcarbonate precipitation as a byproduct of their metabolism.

Soit's possible, indeed it's the leading theory, that Pavilion Lake bacteria areactively building the microbialite structures, and have been doing so forthousands of years. But it's also possible that some not-yet-understood processof chemical precipitation is at work: no biology required. Or even thatbacteria are the active builders at present, but may not have played that rolein the past.

Themicrobialites come in a wide variety of shapes as well as sizes, including somethat are similar in appearance to giant artichokes and cauliflower. Some havechimneys rising out of their midst. Their morphology, or shape, "seems tovary with the depth, but this isn't something that we've 100 percent proven andare working to identify trends throughout the lake," says Brady.

"Somethingthat we're going to try to explore is the relationship between the microbialcommunities and light levels." If carbonate precipitation, influenced byphotosynthetic bacteria, "is a main mechanism for forming themicrobialites, then changes in the light levels could be part of the reason whywe see the different morphologies" at different depths.

Understandingthe mechanics of what is going on in Pavilion Lake will help scientists makeprogress toward solving a broader problem, one central to astrobiology:identifying biosignatures. "A biosignature is an unambiguous signal of past life," says Brady.

"Ifwe can find biosignatures in these modern environments ? where you can samplethe living bacteria, you can sample the water chemistry, we can measure thelight levels ? and can do analyses to your heart's content, we might be able toapply that to either the geologic rock record," that is, signs of ancient life interrestrial rocks billions of years old, "or potentially toastrobiological environments as well," that is, signs of ancient life in Martian rocks billions of years old.

Biosignaturework is complicated by the fact that chemical signals that may make it possibleto identify present-day biological activity can degrade over time. In the caseof Pavilion Lake, even if scientists can clearly show that modern bacteria areresponsible for creating carbonate structures on the surface of themicrobialites, "once the biology is gone," that is, deeper within themicrobialites or in older structures, "the carbonate could dissolve andre-precipitate, and if that happens any sort of biological chemical signaturemight get wiped away," Brady says.

Researchersalso plan this year to take a closer look at "grazers": worms, snails andother small organisms that in most freshwater lakes consume bacteria at such aprodigious rate that the bacteria never get a chance to form any large-scalestructures. "At Pavilion, there are grazers, but we wonder if they'reactually having a significant impact on the microbialites ?. We are planningsome night-time investigations of the microbialites and looking to see ifgrazing activity, which we haven't really noticed in the daytime, actuallyincreases at night."

Apair of DeepWorkers, submersible vehicles, each large enough for a singleperson to squeeze inside, will play a pivotal role in these investigations.

?Forthe past two years, researchers have used the DeepWorkers to conduct acomprehensive survey of the lake and its microbialite structures. This year,Brady says, the DeepWorker activity will focus on studying particular areas ingreater detail, spending "a couple of hours going up and down a [single]slope," taking "the time to do really detailed imaging."

Andwhile they're busy helping to unlock the mystery of Pavilion Lake'smicrobialites, the DeepWorkers will be involved in another task as well:training astronauts to do good science. As they have in the past two years,astronauts from both NASA and the Canadian Space Agency (CSA) will take part inthis year's PLRP activities, including piloting the DeepWorker subs.

Astronautsare superbly well trained in the mechanics of space flight and proceduresrequired for survival in space, Brady says. But, she adds, "The question really comes down to:if you were an astronaut and you were on Mars," trying to find evidence oflife, "would you know what to look for, how to explore and adapt toin-field situations?"

Aspart of its ongoing activity, PLRP has "developed an astronaut trainingprogram where the astronauts come up? and they do everything: they get anintroduction to the history of the lake, the questions that frame the researchthat goes on at the lake? they help us with the [DeepWorker] flight planning,they drive the submersibles, they help with the data processing." They're "fullyintegrated into a real active field site" to help them develop the tools neededto become effective field scientists.

• Looking for Life on Mars — in aCanadian Lake
• The Ancient Past, Alive
• First (And Last) Voyage to Bottom ofthe Sea

Astrobiology Magazine will be reporting on the PLRP 2010 field season livefrom Lake Pavilion, posting regular blog entries. We will also give visitors toour website the opportunity to pose questions about PLRP directly to thescientists and astronauts involved.