Greetings all! It’s been a busy couple of days here on the Melville, so I apologize for the recent lack of blog posts. I’ll try to give you an idea of just how busy it’s been. Friday night I was sitting in the galley with the Seeps Team as we made our plan of attack for Saturday and at one point Yui (part of the Pelagic Environment Team) walked in to prepare not one, but two cups of coffee. It was already past 9 p..m and two cups of coffee at that hour seemed to indicate that someone wouldn’t be getting much sleep that night. When we asked what time he was going to bed he replied, “I’m not.” While pulling all-nighters might bring back memories of undergraduate life (not at all related to research) for some of us, on the Melville, it’s fairly common for oceanographers to be up throughout the night, ensuring that no ship time goes to waste. This was obviously the case for the Pelagic Environment Team, and yesterday when I woke up at 8 a.m. they were just finishing their CTD casts. At this point, it was our turn to take over.
The plan our team came up with was to start by revisiting some areas of interest we’d identified during previous surveys. These were areas where the seafloor sediments appeared disrupted. On the echosounder, these locations look like this:
You’ll notice the dark line running across the screen. That’s the ocean floor, and since it’s relatively hard, it sends a strong reflection of the sound waves back to the ship. You may also notice that at one point the ocean floor seems to disappear. This indicates a softer seafloor, which for our purposes we hope is caused by a mixture of sediment and methane gas. We spent about three hours resurveying the seafloor along a contour that looked interesting -- starting about three miles out from Mission Beach, heading north, and ending in 500 meters of water, three miles west of Point La Jolla. With the survey complete and the ROV out of commission, it was now time to explore the biology of the seafloor using the multicorer.
Although we had sites picked out where we were fairly certain there was some sort of gas seep, the odds of actually landing a multicorer on a seep community were very small. Imagine you’re in a helicopter hovering over San Diego. Your goal is to blindly drop a tennis ball and try to land it in a city park. Even though there are numerous parks in San Diego, I think we can agree that actually landing a tennis ball in one of those parks would be no easy task. Obviously out on the Melville we’re aiming for seep communities and not underwater city parks when we use the multicorer, but we encounter the same challenges. An entire seep area could be hundreds of meters across, but the bacterial mats, clam beds, or tubeworm beds that we typically look for to identify areas of active seepage might occur in patches of only a few meters.
Between 1 and 4 p.m. we dropped two multicorers at a site near La Jolla, and although we didn’t find any direct evidence of a seep, we did find Idas sp., a mussel that is often found near cold seeps and can potentially host symbiotic bacteria. And we had no shortage of mud to play with before dinner. Between 4 and 6 p.m. we transited to another point of interest where we did our third multicorer drop. We spent the rest of the evening sorting through mud looking for indications of seeps. Some of the organisms we found indicate a cold seep may be near by – pogonophoran worms, filamentous bacteria, ampharetids, and dorvilleids. By the time this was complete our team had spent 12 hours searching for seeps, and it was our turn to relax and go to sleep, leaving the other teams to take over and run plankton tows, trawls, and CTD casts through the night.
-- Rachel Marcuson, Scripps Graduate Student