Probing Pavilion Lake
But Brady, acting principal investigator of the Pavilion Lake Research Project (PLRP), and her colleagues won’t be vacationing this week when they descend into the depths of the lake, as they have for the past several summers. Despite its pastoral surface appearance, Pavilion Lake is anything but normal. Carpeting the slopes of the lakebed is an underwater forest of carbonate structures that, at first glance, might be mistaken for coral. These carbonate formations – PLRP’s researchers call them “microbialites” – range in size from small nodules the width of a quarter to massive mounds several meters across. Until they were discovered in Pavilion Lake, such formations were relatively unknown in freshwater lakes.
Similar structures are known to exist in a handful of other places in the world, in Shark Bay, Australia, for example, “but these tend to be more extreme environments,” Brady says. “Areas where you don’t find much else living there but bacteria,” because it’s too salty, too acidic or generally too extreme for other life forms to survive. No-one has been able to figure out yet what they’re doing in Pavilion Lake.
The central question is what role biology has played in forming the microbialites. “We’re trying to figure out if we can identify, basically, abiotic versus biotic processes,” Brady says. The structures are covered with a layer of living bacteria, and there is evidence that these bacteria may be influencing carbonate precipitation as a byproduct of their metabolism. So it’s possible, indeed it’s the leading theory, that Pavilion Lake bacteria are actively building the microbialite structures, and have been doing so for thousands of years. But it’s also possible that some not-yet-understood process of chemical precipitation is at work: no biology required. Or even that bacteria are the active builders at present, but may not have played that role in the past.
The microbialites come in a wide variety of shapes as well as sizes, including some that are similar in appearance to giant artichokes and cauliflower. Some have chimneys rising out of their midst. Their morphology, or shape, “seems to vary with the depth, but this isn’t something that we’ve 100 percent proven and are working to identify trends throughout the lake,” says Brady. “Something that we’re going to try to explore is the relationship between the microbial communities and light levels.” If carbonate precipitation, influenced by photosynthetic bacteria, “is a main mechanism for forming the microbialites, then changes in the light levels could be part of the reason why we see the different morphologies” at different depths.
Biosignature work is complicated by the fact that chemical signals that may make it possible to identify present-day biological activity can degrade over time. In the case of Pavilion Lake, even if scientists can clearly show that modern bacteria are responsible for creating carbonate structures on the surface of the microbialites, “once the biology is gone,” that is, deeper within the microbialites or in older structures, “the carbonate could dissolve and re-precipitate, and if that happens any sort of biological chemical signature might get wiped away,” Brady says.
Researchers also plan this year to take a closer look at “grazers”: worms, snails and other small organisms that in most freshwater lakes consume bacteria at such a prodigious rate that the bacteria never get a chance to form any large-scale structures. “At Pavilion, there are grazers, but we wonder if they’re actually having a significant impact on the microbialites…. We are planning some night-time investigations of the microbialites and looking to see if grazing activity, which we haven’t really noticed in the daytime, actually increases at night.”
A pair of DeepWorkers, submersible vehicles, each large enough for a single person to squeeze inside, will play a pivotal role in these investigations. For the past two years, researchers have used the DeepWorkers to conduct a comprehensive survey of the lake and its microbialite structures. This year, Brady says, the DeepWorker activity will focus on studying particular areas in greater detail, spending “a couple of hours going up and down a [single] slope,” taking “the time to do really detailed imaging.”
Astronauts are superbly well trained in the mechanics of space flight and procedures required 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 of life, “would you know what to look for, how to explore and adapt to in-field situations?”
As part of its ongoing activity, PLRP has “developed an astronaut training program where the astronauts come up… and they do everything: they get an introduction to the history of the lake, the questions that frame the research that 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 “fully integrated into a real active field site” to help them develop the tools needed to become effective field scientists.
Astrobiology Magazine will be reporting on the PLRP 2010 field season live from Lake Pavilion, posting regular blog entries. We will also give visitors to our website the opportunity to pose questions about PLRP directly to the scientists and astronauts involved. To submit a question, click the red Ask a Question button in this article or in any of the subsequent blog entries. We’ll get an answer back to you as quickly as we can.
PLRP is funded by the CSA CARN (Canadian Analogue Research Network) and NASA MMAMA (Moon and Mars Analog Mission Activities) programs. Additional funding is provided by the Natural Sciences and Engineering Research Council (NSERC) of Canada’s Discovery Grant program, NASA ESMD Analogs, NASA ASTEP and Nuytco Research.