Friday, July 17, 2015

4804: Part 2

I'm obviously going to have to split up this post into multiple entries. If you're confused about the Mumford and Sons reference, I know I never followed up on it in Part 1. It shows up here in a little bit; just keep reading.

Me inside Alvin. Photo by Adam Skarke.
Once we were all in place and the hatch was sealed, Alvin was hoisted by the ship's A-frame into the water. Deploying Alvin is a relatively streamlined process, but it involves a lot of people. Besides those on deck, there are two swimmers in the surface water that are responsible for unhooking Alvin from all its various cables and tethers to the ship. I had seen the swimmers do their thing from the surface before, but I didn't realize how much of their work was underwater. I watched through the porthole like a 5-year-old seeing reindeer land on her neighbor's roof, fascinated by the process before me. It took a few minutes, but then, we were off.

On the way down, our pilot, Chris, asked if it would be ok to turn on some music. I had no idea it was possible to play music in Alvin, but I guess for the pilots, it makes the dives more interesting. Chris's playlist was largely composed of indie folk artists, so it didn't take long for Mumford to come on. I'm telling you, those four Brits manage to be present on the best days of my life.

Before long, the water column had gotten dark, but I kept my face glued to the port hole. Tiny blue sparks flew through the water before me, the result of various bioluminescent organisms. Bioluminescence is a phenomenon by which organisms produce light. It's accomplished by various mechanisms and for various reasons. For example, if you hang out on the bow of a ship while transiting at night, you'll see bioluminescent diatoms glowing in the bow waves. It looks just like a blue sparkle on top of the waves. In our case, I don't know what the glowing organisms were, but they must have been small. I just saw tiny blue points passing my window, and all of them were headed up. Well, more accurately, we were headed down, which means we were disturbing the organisms on our way through the water column, and they responded to that disturbance by glowing temporarily. After a while, I started seeing glowing plumes of what appeared to be a viscous liquid. It could have been mucus or ink, but my eyes followed it every time, trying to discern the shape of an organism from its billowing form. It occurred to me then how effective bioluminescence can be as a technique to avoid predators. Emit a glowing fluid, and your predator will follow it instead of you. Heck, I had no interest in eating the things outside my window, and it worked well enough on me!

Unbeknownst to me, Adam took a picture of me gazing out
Alvin's port hole.
By the time we reached the bottom, I was thoroughly enchanted. We landed a little bit away from the site we were actually supposed to investigate, because it's better to approach benthic targets from the side than from the top. We could see soft sediment around us, very sparse organisms, and a few dead mussel shells. Mussel shells usually mean that a cold seep is close by, so we set a waypoint for the site of the suspected plume and started gliding towards it.

My notes from the dive reveal what happened next. Just a few minutes in, I noted the presence of a bacterial mat. A patch of fuzzy white carpet appeared on the soft sediment, the first indication of methanotrophic (methane-eating) biota. Ten minutes in, I noticed that the mussel shells were getting denser. Fifteen minutes in, we found our first live mussels. Adam, my dive buddy, spotted them first, but he turned to me for biological insight. He asked if I thought they were alive, and after a few seconds of assessment, I agreed. The mussels' valves were slightly ajar, and I could see their white tissues in the gap. Two orifices in the white tissue were the mussels' siphons, indicating they were actively filtering the water around them. Live mussels could only mean one thing: we had found a new cold seep habitat.

It was only a matter of time before we discovered the source of the gas, so we asked the pilot to fly over the mussel bed a little further. We eventually reached a jagged precipice covered in a dense population of mussels, and there it was: active bubbling. The pilot, Chris, has been on enough cold seep dives that he recognizes methane plumes quickly. As Alvin hovered in the water column just a few feet away from the precipice, we all scanned the seafloor in front of us. One, two, three streams of gas bubbles were right there, supplying methane and hydrogen sulfide to the bottom water.

We decided the precipice would be a good place to collect mussels, so Chris looked for a flat place to sit the sub down. A lot of the mussels were covered in the same white bacterial mat we had seen on the sediment before, and there were lots of crabs. Large, red brachyuran crabs, all flexing their claws in defense against Alvin, the bright alien invader from above. We collected several mussels and also grabbed some crabs. Chris was really curious to know whether the crabs would still be alive when we reached the surface, and for the record, they were.

I wish I could show you photos of what I saw, but the Alvin data isn't mine to share. I guess my words will have to do for now. Stay tuned for more in Parts 3 and 4, which I'll post tomorrow.

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