This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
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 is her first blog post. To track her research ship's current position, click here. To see all her posts, see "60 Seconds in North Pond."
POINT-À-PITRE, GUADELOUPE (February 14, 2009)—I'm sitting in a ship terminal with Jennifer Biddle, a postdoctoral researcher in Andreas Teske's lab at the University of North Carolina at Chapel Hill. We're waiting for someone to refuel the plane that will take us to Fort-de-France, Martinique, so we can board the Merian, the research ship that will take us to the North Pond. But there's a strike on, so the wait might be awhile.
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Might as well use the time to explain what we're up to: This expedition is the first in a series focused on a particular section of the bottom of the Atlantic known as "North Pond." The site, on the western flank of the Mid-Atlantic Ridge (an undersea mountain range), at latitude 22 degrees north, has quite a long history already of research and study, but never for our purposes: microbiology of the deep subsurface, or, intraterrestrial marine life—which happens to be entirely microbial—too small to see by eye without a microscope.
North Pond was first "surveyed" in 1974, to determine if it was a reasonable place to drill in order to recover a cross-section of ocean crust. This was early in the days of what was then the Deep Sea Drilling Project (DSDP), and marine geologists were interested in learning about the basic nature of igneous ocean crust—the portion that forms by eruptions of hot lava at the seafloor and right below the surface. Like the layers you can see in some rocks in road cuts made for highways, the ocean crust has a layered structure, too, but geologists were not able to see it without drilling holes.
During 1975 and 1976, the DSDP first drilled into North Pond, a tiny wedge of sediments that have collected in a valley ("pond") between mile-plus-high mountains of basalt. They picked this site because it was kind of average—so they hoped that what they found there would be pretty similar to what the crust was like most places in the ocean; that way they would not have to drill too many other holes all over the place. It turned out that North Pond was a good pick, and marine geologists learned a ton about what the crust is like from this site.
But there were some big surprises, too. When they poked one of these holes in the bottom of the ocean, the hole began sucking in seawater—a lot of seawater. The water rushed in at more than 250 gallons per hour. But what goes down, must come up, and so this means that a lot of ocean water is flowing into, out from, and within the ocean crust—a phenomenon that even today we don't understand too well.
That's the point of this trip. Heiner Villinger and Wolfgang Bach of the University of Bremen in Germany, and Geoff Wheat of the University of Alaska Fairbanks, and I will do geophysical site surveys and shallow microbiological and geochemical sedimentary surveys, supported by the German Research Council and the U.S.'s NSF (National Science Foundation), aboard the German R/V Merian. This is a precursor to a much bigger drilling program under the auspices of the Integrated Ocean Drilling Program proposal (IODP). Pre-IODP drilling, observatory engineering, fabrication, and experimental testing programs are ongoing, led by myself with support from the Gordon and Betty Moore Foundation since 2006. Post IODP, observatories will involve servicing and sampling from deep-sea submersibles such as ALVIN or JASON-II.
Once we get to the North Pond, we'll take samples of sediments lying on top of a previously discovered subterranean water flow path, take samples of the igneous rock that makes up the crust, and establish long-term (around 10-year) observatories under the seafloor to address two major scientific questions:
What is the nature of microbial communities living in young ridge flanks, and what is their role in ocean crust weathering? Laboratory studies and field experiments in the deep sea have shown that microbes are abundant and play active roles in the "tooth decay of the crust": the weathering of exposed rock on the seafloor. But what about microbes living inside the rock? We have some evidence for their activity, but solid microbiological and molecular data remains lacking. At North Pond, we will be using deep-sea laboratories to sample fluids in crustal rock for biological and chemical analysis, and to conduct on-site experiments to address the role of microbes in alteration of seafloor rock.
Where do deep-seated microbial communities come from? The biogeography of microbes is a hotly debated topic. Viable, diverse and distinct microbiological communities occur in deeply buried marine sediments. Where they come from is unknown. The isolated sediment pond at North Pond represents an ideal natural laboratory to address these questions.
These exciting discoveries led to some early fame for North Pond. But it didn't stop there, as I'll discuss later. Looks like it's finally time to board. Stay tuned.
Update (2/27/09): See Edwards's response to the question posed below.
photo of Katrina Edwards courtesy USC