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 eighth blog post. 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 (February 26, 2009) -- We can't wait to get back to North Pond to start coring again, now that Frank is in safe hands. So in the meantime, here's a stab at describing some of the geophysics issues we're working on, although a warning: I can't tell you what they are in detail, as this is my real area of weakness.

When you look at geophysics, there are two types of data: the geophysical lines, which give cross-sectional maps of the rock, and the parasound maps, which tell us what the sediments look like. In theory, by combining these two you should be able to figure out how thick the sediments are in different places.

In practice, here at North Pond we are imaging the equivalent of the bottom of a soup bowl. When you get near the soup bowl rim, which is the area we're most interested in, the geophysics stop working. This is a problem.

We—the microbiologists and biogeochemical group—thought we had a clever solution to the problem. The geophysics group uses what looks like a 10-meter long, thick solid steel nail (it's kind of scary-looking to me) to probe thick sediments. But wait! That thing looks indestructible to us! Why not use it to probe the thin sediments near the edges of the pond?

The geophysicists (see a few of them in the photo to the left, working with their probe) got very alarmed when we asked them if they would mind using this device to figure out exactly where the rock is near the edges of the pond. It is not a device for finding rock, they state, with obvious distaste that the microbiologists and biogeochemists would even think of using this probe for such crude purposes. Ah well, at least we're all learning.

And that brings me to the very edge of my knowledge concerning geophysics.

Photo courtesy USC/Katrina Edwards