Mapping Microbialites

Margarita Marinova, PLRP researcher and DeepWorker pilot, at a pilot’s planning meeting at Pavilion Lake. Credit: Henry Bortman

The Pavilion Lake Research Project (PLRP) is moving its base of operations. For the past several years, PLRP has used DeepWorker submersible vehicles to explore the unusual carbonate structures, known as microbialites, that line the bottom of Pavilion Lake in British Columbia, Canada. This year, instead, the project will be shifting its focus to nearby Kelly Lake, which also contains microbialite structures, although not to the same extent as Pavilion Lake.

As I did last year, I’ll be joining the PLRP team in the field at Kelly Lake, and reporting on their daily activities. And you’ll be able to submit questions directly to the PLRP scientists by clicking the red Ask a Scientist button that you’ll find on this page and on all the Astrobiology Magazine stories posted while the scientists are at work in the field.

In preparation for the upcoming work at Kelly Lake, I spoke with Margarita Marinova, a planetary scientist with the NASA Ames Research Center in Moffett Field, California. Marinova has been involved with PLRP for many years, both as DeepWorker pilot and as a research scientist. One of her primary areas of interest lies in understanding the distribution pattern of different types of microbialites in the lake, and the environmental factors that control that pattern.

But before I get into that, let me clear up one small point about terminology. “It’s a little bit of a misnomer to call them microbialites,” Marinova told me. “What we know for sure is that they’re carbonate structures. They’re made out of carbonate.” But as for the role that microbes play in forming them, well, “We’re pretty sure that microbes have something to do with it, and so that’s why calling them microbialites is generally fair.” But, she added, “We haven’t actually proven that the structures at Pavilion Lake are formed by microbes.”

Okay. But I’m going to keep calling them microbialites.

Which only served to raise a question that’s bugged me the whole time I’ve been writing about Pavilion Lake – and so I had to ask: Why is it so hard to figure out whether or not these structures are made by microbes?

“Figuring out causality is always difficult,” Marinova said. “If it’s pure chemistry,” all you need is a lot of carbonate in the water, “and then as soon as you have something start to precipitate carbonate, it becomes easier for other carbonate to precipitate onto it, and you start growing your carbonate structure.” She offered the example of the carbonate structures at Pyramid Lake, in Nevada. There, she said, “you can see these perfect crystalline structures, and so it’s pretty easy to understand that it was chemistry that was the driving force behind it all.”

But the process at Pavilion Lake isn’t quite so clear. At Pavilion, let’s say a little bit of carbonate precipitates. Then some microbes take up residence on the carbonate. A little more carbonate precipitates. Some of the organisms get encased in the carbonate. The process continues, and over time, complex structures form.

Years later, along come some scientists. They examine the present state of the structures in detail. But what they don’t get to see is the formation process in action. It’s still going on, but too slowly to observe in any meaningful way. So they scratch their heads and try to figure out what actually happened.

But after the fact, it’s hard to tell whether the microbes subtly changed the chemical environment, thereby encouraging the growth of the structures and affecting their shapes and textures, or if instead they were merely hanging out while a purely chemical process took place, and just happened to get buried by carbonate rain.

The carbonate structures at Pyramid Lake, Nevada, are formed by purely chemical processes.

“In both cases, you’re going to find organisms on the carbonate structure, and you’re going to find the little organisms encased in the carbonate.” Marinova explained. “How do you differentiate between the two?” Hmm. I thought I was the one asking the questions. But this is why I like hanging out with astrobiologists. They ask really interesting questions.

“We’re never going to be able to say, Here’s a recipe, and if you have exactly these characteristics it means that it was biologically precipitated, and if it’s exactly these other characteristics, then it was chemically precipitated. But I think the goal is to get to enough characteristics that” you can say, “Okay, well if you see these five things together, then it seems like biology was a central part of what happened.”

But to get back to Marinova’s research, I was curious about two things. First, what progress had been made on teasing out the patterns that describe which types of microbialites appear where in Pavilion Lake. And second, what did she hope the team would learn from the move to Kelly Lake?

One focus of Marinova’s work has been the implementation of a system for classifying and mapping the distribution of different microbialite morphologies (structural shapes). Some microbialites look like giant artichokes, others like cauliflower, some have chimneys, and so on; they come in various sizes; some have smooth surfaces, others rough, etc.

During every DeepWorker flight at Pavilion Lake, a camera mounted on the front of the submersible recorded continuous video images, and each video frame was tagged with its precise location and depth. To get the necessary morphology data into Marinova’s mapping system, PLRPers spent countless hours looking at these video frames – they classified the contents of a frame every six seconds– and encoded descriptions of what they saw into a database.

Although analyzing this data is work still in progress, some trends have emerged. For example, “From the surface to a depth of thirty meters, the microbialites are mostly rough.” About ninety percent of them. From “Thirty to forty-five meters,” some eighty to ninety percent of them are “more smooth. And then about forty-three meters to about fifty-two meters, where the bottom is, we see about equal amounts of both smooth and rough,” Marinova said.

I suggested that that seemed a bit odd. She agreed. “I have no idea what it means. But you see it and you think, This has to mean something. These are a lot of data points that have gone into this.” Tens of thousands of data points.

The role microbes play in forming the structures in Pavilion Lake, such as this “artichoke”-shaped microbialite, is still not fully understood. Credit: Donnie Reid

Other information about the lake, such as temperature, water chemistry, sedimentation rate and light level have also been entered into the data base, each bit of information linked to a precise latitude, longitude and depth. Over time Marinova hopes to be able to understand better the correlation between these various environmental factors and the distribution of microbialite morphologies in the lake.

And what is to be gained by studying Kelly Lake?

From studying Pavilion Lake, Marinova said, the PLRP team has developed some theories “about how these microbial structures form.” But “the real test of whether these ideas are true or not is seeing if they also apply to Kelly Lake. The systems are similar enough that you would expect that if a set of criteria apply to Pavilion Lake, the same criteria should apply to Kelly Lake.”

Using her own research as an example, she explained that she had light measurements from different depths at both Pavilion and Kelly Lakes. “If it is light level that actually sets the distribution of microbialites, then that should be very easy to compare between the two lakes.”

More generally, she added, “When you only have one system,” it can be difficult to be sure that what appears to be a causal relationship really is one. “You never really know if you’ve measured the right parameters.” It’s “being able to understand a number of similar systems” that ultimately tells you “whether you know what’s going on.”

DeepWorker dives are scheduled to begin at Kelly Lake on Monday, July 18. In the meantime, if you have questions of your own about Pavilion and Kelly Lakes, click the Ask a Scientist button and send it in. We’ll get you an answer as soon as we can.