Leg 3 Logbook - Gas Hydrates
Day 7 — Just the same old stuff (whale bones and underwater gas eruptions)
August 8, 2009
Latitude 48 degrees 40.26 minutes N
Longitude 128 degrees 50.20 minutes W
We had so much fun exploring the slope east of Bullseye Vent yesterday
that we decided to try it again today. So it was like déjà vu all over
again (to quote Yogi Berra), except that we found even more cool stuff!
As I mentioned in Thursday’s blog, despite its name, Bullseye Vent is a
long, narrow, rectangular pit in the seafloor, oriented northeast to
southwest. Data from our mapping AUV suggests that the hole is elongated
because it runs along a fault. Charlie’s goal today was to try and look
at an underwater slope east of the Bullseye Vent where we might find
evidence of this fault on the seafloor.
As we searched the seafloor for methane vents, we
found many “gardens” of sea pens, each with its own brittle star.
At first we seemed to have no luck—all we saw were broad expanses of
muddy seafloor dotted with sea pens. These relatives of corals look like
half-meter-long sticks embedded in the seafloor, with lots of little
purple flowers all along the length of the stick (the flowers are
polyps—individual animals in a colony). At the top of each sea pen was a
brittle star, its snake-like arms waving in the current, like Medusa’s
hair. We don’t know for sure, but we think the brittle stars climb up
the sea pens so that they can catch tiny animals and bits of debris
drifting by on the currents.
Anyhow, after meandering among the sea pens for an hour or so, we
decided to head back to the whale skeleton that we discovered
yesterday. We spent an hour or two at the whalefall today,
photographing the bones, and collecting one small piece of bone to take
back to Bob Vrijenhoek’s lab at MBARI. We also collected several push
cores full of the black, smelly ooze from underneath the whale bones. We
also looked for the cool bone-eating worms that Bob first discovered a
few years ago, but didn’t see any, at least in the ROV’s video.
Taking a closer look at the whale skull
we found yesterday, we discovered tubeworms growing up from underneath
One thing we did see, however, was vestimentiferan tubeworms growing up
from underneath one of the whale’s jawbones. In Monterey Bay, these
tubeworms are usually found at methane seeps, but not at whalefalls.
These worms can live for over 100 years, and may take decades to form a
colony. From the size of the worm colony and the decay of the whale
bones, it’s possible that this whale skeleton could have been lying on
the seafloor for 50 years or more!
Bob’s research group gives names to all of the whalefalls that they have
studied in Monterey Bay. We decided to name this whalefall “Shannon”
after Shannon Johnson, a research technician in Bob’s lab who works on a lot of
the whalefalls in the bay. Shannon has not only led a dozen whalefall
dives on the research vessel Point Lobos, but has had the unenviable
task of cutting up dead whale bones with a chain saw. She's an incredibly dedicated scientist—and it's a bit of a smelly job to work with dead whales.
After bidding farewell to “Shannon,” we went looking for more methane
seeps and for evidence for the fault that appears to cut through the
Bullseye Vent. Not far from the whalefall we found a beautiful little
mound in the seafloor, perhaps three meters across. With its star-shaped
cracks, it looked just like the active methane vent we
found yesterday. This mound wasn’t emitting bubbles, but we thought we’d
collect a vibracore to find out what was beneath the surface.
I should explain that we collect vibracores in thin-walled aluminum
tubes about 6 centimeters in diameter and up to two meters long. To collect a
core, we mount one of these tubes on a vertical stand on the ROV. A
motor containing a heavy weight is then attached to the aluminum tube.
When we run the motor, the tube vibrates. This liquefies the surrounding
sediment and (in theory) allows us to push the core into the seafloor.
After pushing the tube in as far as possible, we pull the tube out and
hope the layers of sediment will stay inside the tube until we bring it
back to the surface.
In any case, as we were pushing the vibracore tube into the seafloor at
this one mound, a few bubbles came trickling out the side of
the tube. We were excited to see evidence of methane this close to the
seafloor. Then the tube stopped moving, apparently because it had hit a
layer of harder sediment. Somewhat disappointed, we started to pull the
core out. As we did so, more and more bubbles came out, until they
formed a spectacular plume of bubbles that rose up into the water
column. In taking the vibracore, we had inadvertently created our own
After collecting one vibracore, we inadvertently
created an underwater “geyser” of methane bubbles.
Even after we removed the vibracore, the geyser of bubbles kept growing.
Seeing how pressurized the gas was, we were a little afraid it would
cause damage to the ROV, or that the seafloor itself would start
buckling underneath us. Charlie exclaimed, “It’s almost as if we had a
blow-out on a gas well.”
We could only guess that the gas had been trapped underneath a layer of
hard sediment, which we had breached or weakened with our vibracore.
Fortunately, the stream of bubbles peaked after 10 or 20 minutes, and
then began to slow down, which allowed us to collect water samples and
additional sediment cores around our newly created vent. The pilots even
managed the neat trick of landing the ROV right on top of the vent, so
that our heat-flow probe could be directed into the bubbling borehole.
After that excitement, we flew around the area looking for other mounds
covered with cracks. They were easy to see because the cracks were often
filled with white mats of bacteria. We found quite a few mounds, and
collected cores at several of them. Although we created one or two new
methane vents in the process, none were quite as dramatic as the first
one we came to. When we returned to our original site several hours later,
it was still burping intermittently.
It was a little hard to tell for sure, but most of the mounds seemed to
lie right along the fault line Charlie had been looking for. Thus we had
apparently managed to both find the fault zone and locate a collection
of methane seeps of various ages. And in the process, we’d had a little
adventure, as well! We also saw rocks over 10 centimeters across that looked
as if they’d been lifted up out of cracks in the seafloor by recent gas
eruptions. These could provide circumstantial evidence for some of
Charlie’s theories on how Bullseye Vent formed.
Chief Scientist Charlie Paull inspects an
elaborate array of syringes we used to extract fluids from the sediment
at different levels within a vibracore that we collected today at a
Ironically, we spent the last two or three hours of the dive searching
unsuccessfully for additional mounds and seeps. At some point in the
afternoon, the ship’s captain came into the control room holding an
official-looking piece of paper. He informed us that he had received a
fax from the NEPTUNE Canada cable-laying ship. They informed us that
they were going to begin operations around the southern Bullesye Vent in
about 12 hours, and requested us politely to leave the area. So tonight
we’ll be heading a few kilometers north to another area called
“Spinnaker Vent”. This site was apparently named after a local brand of
beer. After all the excitement of the last couple of days, I can’t wait
to see what’s brewing down there.