Leg 1 Logbook - Laser Raman Spectroscopy
Day 13 – Keith, you’re going to need a bigger dive bag!
July 19, 2009
On station at Barkley Canyon, 40 nautical miles southwest of Vancouver Island, Canada.
Latitude 48 degrees 18.6 minutes N
Longitude 126 degrees 3.9 minutes W
This is our last dive at Barkley Canyon. Most of the tasks that we set out to do have been completed, most of the measurements have been made, and only a few tasks remain so we looked forward to a short dive and an easy day. First on our list was a desire to get one or two more oil samples. With a short list for the day, we knew we could spend almost as much time on this task as we wanted. Arriving on the seafloor, we transited to the “Mount St. Helens” mound. As we set down on the edge of the mound the weight of the vehicle began forcing a steady stream of oil droplets out of the mud. It was all we could do to get the sampling funnel over the stream before it ran out. Much to our delight, within a few short minutes the sampling chamber was full and we collected the sample. Since that one went so easy we decided to try and get one more at the extreme southern mound, “Cliff Hanger.” Unfortunately, we had already found our “big gusher” for the day and try as we might, there was little oil to be found at the second site. Then, abruptly, the handle broke off the funnel as we attempted to use it to root around in the mud to find more oil. Obviously, we were now done with that task for the day, so we stowed what remained of the sampling funnel in one of the baskets on the toolsled tray and collected a push core instead. Perhaps there will be enough oil in that mud to make up for the lost sample.
Collecting our last push core at the “Cliff Hanger” mound where little oil was found. However, when we inserted the push core, a burst of droplets appeared.
At this point, we were way ahead of schedule, so we transited to the northernmost mound in search of solid hydrate. Along the way we stopped at “Cliff Hanger” and straightened up the stakes that had gotten inadvertently knocked over earlier in the day. Keith Hester had rigged a dive bag inside one of our sampling rings hoping to be able to maneuver a piece of hydrate about the size of a loaf of bread inside. Once inside, we could then use the manipulator arm to pull the string tight and trap the hydrate securely within. Approaching the mound we remembered seeing several slabs of hydrate sticking out along the rim the day before and hopefully we could break off one of these and catch it in the dive bag. As we set up for the procedure, one of the pilots got the idea that we could pry the hydrate loose using the benthic hoe. Sure enough, this worked, but then we got a big surprise: the slab of hydrate that we released was two-to-three times the size of the sampling ring, and no way would it fit inside the dive bag! Undaunted, we tried to capture it anyway, until it was very clear that we really did need a much larger bag to contain it!
Tidying-up the dive site, ROV Doc Ricketts sets the markers straight again after knocking them over earlier in the day. These markers will remain on site to give a visual reference point for all future visitors.
Using the benthic hoe, the ROV pilots pry a large slab of yellow gas hydrate loose from the seafloor. We immediately realize that we are going to need a bigger dive bag to collect this sample.
Fortunately, it was at this point that the hydrate slab broke into pieces. Several got away immediately, but the pilots did manage to capture one of the larger ones inside the bag. Realizing it was going to be a bit tricky to keep under control during the ascent, we abandoned the plan to tuck the sample in one of the sampling box and instead used one of the manipulator arms to pin the ring on top of the milk crate on the ROV's front porch. With our major find secure, we headed for the surface. Along the way, we heard from the bridge that several pieces of hydrate had popped-up at the sea surface just in front of the ship. They quickly maneuvered into position and Peter Walz scooped them up with a net. So, apparently, today one can loose their hydrate and get it back! Meanwhile, back on the ROV, we had a spectacular display of hydrate dissociation during the ascent to the surface.
Gas hydrates are only stable at the low temperature and high pressure conditions found on the seafloor. When the samples are brought unprotected to the surface, they decompose spontaneously releasing large volumes of methane gas.
Once on-board, we spirited the hydrate to the back deck where it was broken into small pieces and set it on fire: this ice really does burn!
When lit, this “ice” really burns. Methane gas is the primary component of these clathrate hydrate specimens along with ethane, propane, butane, and other low molecular weight hydrocarbons. As they decompose they release a flammable mixture of gases and fresh water.
A horde of happy hydrate hunters on the back deck of the R/V Western Flyer.