Our chief scientist, Dr. David Valentine, is a professor of Geochemistry at University of California Santa Barbara. We managed to tear him away from his work long enough to ask him a few questions.
How did you get involved in subsurface monitoring?
It started shortly after the Deepwater Horizon sank. I do a lot of work on the geochemistry of methane, of gas hydrates and of oil. Fairly soon after it was realized there was a significant leak, I started getting phone calls, largely from the media, asking questions about what was going to happen. Soon thereafter, John Kessler (the chief scientist on the Pisces’ last mission) and I started talking about what was going on with methane. We studied the area around the wellhead for about two weeks in June, looking at methane and other gases. Then, John got a call to serve as chief scientist on the Pisces on the last leg, and since we’ve been collaborating on this for many years he gave me a call and we marshaled resources to man that project, and then they asked me to serve as chief scientist on this leg. Six weeks of ship time later, here I am!
You mentioned methane hydrate. Can you explain what exactly methane hydrate is?
Methane is normally a gas. Under very high pressures and cold temperatures, its preferred state is in a trapped structure with water. It forms a water-ice structure where the water molecules will entrap the methane. It’s technically called a methane clathrate, where clathrate is a word that means “cage.” It’s methane that’s caged in water-ice. Clathrates are stable in conditions like the deep water in the Gulf of Mexico. At about 600m of water depth, you only need to be down to about 5 degrees Celsius for methane clathrates to be stable. Therefore, it’s typical when you have gas emanating into the deep ocean waters for it to form immediately into that structure.
So is this the form in which they’re coming out of these seeps that we’re mapping?
There’s definitely methane hydrate forming at the seeps. The bubbles that we see are probably bypassing methane hydrate formation in the subsurface. Normally when they come into contact with water they form hydrate but what often happens is that as you have gases migrating up through the sediment in the ocean floor, they will form methane hydrate and will do so until there is no water left, so you have a gas pathway that’s going through that’s basically coated with solid methane hydrate. It then comes out at the seafloor and begins to bubble up, and if you were to look closely at those bubbles, you would see that they actually form a skin of methane hydrate around the outside. As they rise it will decompose, but the methane hydrate will actually prevent the gas from dissolving rapidly into the water.
What do you think of the results you’ve seen so far on this project?
With the coring, I don’t think we got enough cores to say too much. We haven’t seen oil in the ones we have gotten, by way of the analyses that have been run so far on the ship. So that’s good. If we’d been hitting oil everywhere it would be really disconcerting. The fact that we’re not doesn’t mean it’s not there, it just means it’s not everywhere, which is a good thing. We’ve been doing a lot of CTD casts looking at oxygen anomalies and fluorescence peaks. Most of the more severe fluorescence anomalies and oxygen sags are not in the area of the wellhead. They’ve moved largely off to the southwest, which is what we saw on the last trip. The last day and a half we’ve been sampling extensively for oil in the water. These samples are being stored to be analyzed as soon as we get back. We’re collecting about 18 samples for oil analysis on every CTD cast. At a rate of 12 casts a day, it’s adding up in a hurry. Somebody’s going to be doing a lot of oil analysis when these water samples arrive.
What are some of the challenges you face in this research?
Doing things on a very short fuse. We had about six days of advance notice for this particular mission. Bringing together everything that you need for one of these projects is a big challenge. You really have to pack for everything. You’re on a boat. No magic wand is going to make something appear that you need, so you have to bring it, you have to plan for it.
How do you feel about the work you are doing here?
I feel fortunate in that my area of expertise has become an area of importance in responding to this disaster. At the same time, there was a lot of environmental damage that occurred. I wish the oil spill had never happened, but I feel fortunate that I have been able to use my expertise to help out in some way.