March 3, 2009 | 1
Editor’s Note: University of Southern California geobiologist Katrina Edwards is taking part in a three-week drilling project at the Atlantic’s North Pond—a sediment-filled valley on the ocean floor—designed to locate and study what she calls the “intraterrestrials”: the myriad microbial life-forms living inside Earth’s crust. This post is a response to a question from a ScientificAmerican.com reader on the idea of a "10-year observatory" and what microbial life Edwards’ team hopes to find. To track her research ship’s current position, click here. To see all her posts, see "60 Seconds in North Pond."
STEAMING TOWARD THE NORTH POND—You’ve asked a question about my favorite subject: Observatories. Since scientists first came up with the idea of CORKs — devices that were made basically to plug the hole and provide data that would answer some really basic questions about what is going on in the ocean crust , scientists, mainly geophysicists, geochemists, and hydrogeologists, have been working with engineers to develop increasingly complex systems for understanding the subseafloor. What kind of chemistry happens where? How does this change over time? Where is water getting in and out of the crust, and how effective this water flow through the crust is at cooling it down? How good of a radiator is it in different places, to use that metaphor, and why?
As we progress to a system where we’re measuring and monitoring many things over time, that becomes an observatory—simply a station for long-term monitoring and study of a complex system. North Pond, site 395A, was one of the first sites where CORKs were used. It’s under about 4500 meters – about three miles –of water, and penetrates another 500 meters into the crust. Our plans for the observatory build directly from this foundation. We also are trying out some new approaches, building on what has already been tried elsewhere. For example, methods have been developed for CORKed holes that allow something like an internal inflatable gasket to be installed, in order to isolate off one part of a hole from another. At North Pond, we developed this a bit further, and plan to isolate different layers of the ocean crust to do experiments.
You can think of the superhighway of subseafloor ocean fluids like a real three-lane highway; in the left lane people are typically going like heck, in the middle, somewhat slower, and then, there is the slow lane. In the rocky crust, you have the same kind of thing, but the fast lane (in terms of microbial activity) is right next to the sediments, the middle lane a hundred or so meters down, and then the slow lane is from about 300 meters down. Just as you might generalize that certain type of people prefer to drive in the slow, middle, or fast lanes on the highways, we are guessing that intraterrestrial microbes will be layered as well.
So we want to isolate and study them specifically—who is in the fast lane, who is in the slow lane? We do this by sealing off the layers and then putting down containers for them to move into—our little tract houses for the subseafloor microbes. We just hope some of them will move in.
As to why we think of these as 10-year observatories, that’s really just an educated guess that will be informed by monitoring. These will be the first ground-up microbiological observatories in the ocean crust. Realistically, we are still going to be at version 1.0 when we start this. I’m willing to put my neck out there and say we’ll have new and better ideas five years into this project!
Here’s why: Not only do we put equipment right into the rock below the ocean floor, but we have a pumping system that will bring materials up that we can then study regularly by submersible vehicle, while leaving the equipment safe in the hole until the time is right. We’ll be sipping some of the subseafloor ocean water to monitor the chemistry and microbiology flowing through the rock.
We expect the system to feel the effects of the drilling, but we hope to be able to see it "rebound" after drilling, and be able to measure how many intraterrestrial microbes are riding on the superhighway of subseafloor ocean fluids. That won’t tell us how many we’ve trapped, or if they are growing, but it will give us some data on which we can base decisions about when to pull the experiments out.
What do we expect? It’s hard to say. We’ve made predictions about what might be going on in "normal" ocean crust ridge flanks such as those we are studying at North Pond, and some of our calculations predict that microbes that use abundant inorganic chemicals in the crust—such as iron and sulfur—may be favored. But we will just have to see. It is important to keep an open mind, and expect the unexpected when entering new territories of scientific exploration.
Photo of Katrina Edwards sampling basalt, courtesy Edwards/USC