Leg 3 Logbook - Gas Hydrates
Day 9 — Visiting old haunts and discovering new ones
August 10, 2009
Latitude 48 degrees 42.50 minutes N
Longitude 126 degrees 50.20 minutes W
Well, last night wasn’t exactly a gently rolling sea as I’d hoped, but I guess I’m starting to get used to the jerking motions and strange clunking noises the Western Flyer makes in a confused swell. It’s still a better ride than any other 35-meter (120-foot) boat I’ve been on. We had another long two-dive day today, but now the wind is dead calm, the seas are small, and best yet, we can actually see the sun as it’s setting!
This morning’s dive, like yesterday’s, was at Spinnaker Vent. We went back to do a little more systematic mapping of the various pits and mounds, and to collect some additional samples for chemical analysis and age dating. The place hadn’t changed much—it was still a bunch of shallow pits, surrounded by flat, muddy seafloor. Within each pit were methane-seep clams, maybe some tube worms, and a flatfish or a piece of kelp. The Neptunia snails were still perched on their egg towers, and the large red crabs were still skulking around the carbonate outcrops.
This colorful group of deep-sea animals (a deep-sea sole, a spiny sea star, and orange and white anemones) greeted us when we reached the seafloor during our first dive today. How large rocks like this one to be sitting out by itself in the middle of the muddy seafloor is one of the questions we’re trying to answer on this cruise.
We went from one pit to another collecting vibracores and rock samples. Charlie will be using some of these samples to try to figure out how old the various pits and outcrops are. We suspect that we’re seeing pits of various ages, with corresponding changes in their chemistry and biological communities. If we look back on all the methane-seep areas we’ve seen over the last week, it’s clear that some are currently active, while others haven’t been active for a long time—maybe tens of thousands of years. Figuring out the ages of these vents will also help Charlie figure out how they formed and evolved over time.
When we came out of the control room for lunch, blinking in the bright sunlight, we discovered that the neighborhood was becoming rather crowded. Within a kilometer of the Western Flyer were two much larger vessels. One was the research vessel Atlantis, from Woods Hole Oceanographic Institution. The other was a large ship used for laying trans-oceanic cables. The cable-laying ship was laying cables from Vancouver Island to a series of study sites on the deep seafloor. These cables will carry power and data for an automated undersea observatory called NEPTUNE Canada. Just last year, MBARI finished building a similar, but smaller, cabled observatory in Monterey Bay, the Monterey Accelerated Research System (MARS).
Bill, Mary, and Yirang look for tiny snails on a large piece of carbonate that we collected at Spinnaker Vent. We’ll bring these snails back to a researcher at MBARI, who will study their DNA to figure out how they’re related to similar snails that live all around the Pacific.
The Atlantis was using an ROV called ROPOS to install some of the undersea science nodes for the NEPTUNE Canada observatory. These nodes act like switches and junction boxes, to distribute power and data to different parts of the observatory and to individual science experiments on the seafloor. Once hooked up, such experiments will allow scientists to find out what’s happening in the deep sea 24 hours a day, without leaving the comfort of their offices on shore.
I found it amazing to look over at the Atlantis floating about a kilometer away from us, and realize that ROV Doc Ricketts was even farther away than this, but down on the seafloor below. We kept a careful distance from the other vessels. As one ROV pilot put it, “We’d tie the biggest knot in the Pacific if we got our tethers crossed.”
For our afternoon dive, we moved to an area picked by Michael Riedel, our geophysicist from the Geological Survey of Canada. This was another set of overlapping pits in the seafloor that Michael saw in our new AUV sonar data. These pits were located on a large, upraised block of seafloor, much like Hydrate Ridge to the south. However, unlike Hydrate Ridge and the other sites we looked at on this cruise, no one has ever studied this area before. Thus, we were excited to be breaking new ground (or seafloor, as the case may be).
As soon as we reached the seafloor, we saw methane-seep clams to the right, carbonate outcrops to the left, and several large cracks in the seafloor. Michael smiled. ”I can see this is going to be a great place!” He was right. It was a fascinating terrain of narrow, carbonate-covered ridges separated by deeper, sediment-filled swales. In some ways, it was the opposite of what we’d seen in the morning, with the carbonates and animal life on the ridges instead of in the low areas.
During our second dive we found fields of angular boulders sitting on the tops of undersea ridges. We’re still trying to figure out how they got there.
One of the strangest things we saw was that many of the ridges were covered with large, angular boulders. These boulder fields looked to me like miniature versions of the rocky talus slopes you’d see in avalanche chutes in the high Sierra. But what were they doing here along the tops of ridges on the bottom of the ocean? Where did the rubble come from?
We were also perplexed to find large, three-meter-wide boulders and carbonate outcrops perched on some of the ridges. On one of these boulders was growing a beautiful, hot pink “bubblegum coral.” At over two meters tall, it reminded me of the spectacular forests of deep-water corals we’ve seen on Davidson Seamount, off Monterey Bay. This large coral could easily have been over 100 years old, which suggests that these ridges are not very active right now.
This beautiful Paragorgia, or “bubblegum coral,” was over two meters high, and could be over 100 years old.
We only spent a couple of hours exploring this study area, which we called the “Ridge-Crest Crater Site.” But we can see that it has the potential to be just as scientifically exciting as Hydrate Ridge and the other well-known sites we’ve studied on this cruise.
Tomorrow, we’ll be doing a quick dive back on the fault east of Bullseye Ridge—our last ROV dive before we head south. We’re going to see if we can use our vibracoring system to create more methane geysers on the seafloor. If we succeed, it will be a fitting end for what has been a surprisingly exciting cruise.
After processing our sediment samples, we were treated to an hour or so of beautiful late-afternoon sunlight.