Easter Microplate Expedition
March 25, 2005 Day 14
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Alvin dive# 4091, 38°S:
Shana and Nicole were the observers, and Gavin was the pilot. Today's dive was to a new part of the ridge, about 8 miles north of the vents we've visited on the last four dives. It is a highly fractured part of the ridge with a cleft zone (a down-dropped valley bounded by walls 50-100m higher) on the ridge axis and grabens some 200m deeper on either side. The dive began at 2222m at the southern end of the cleft, on a series of large fractures and a young sheet flow. Shimmering water from diffuse venting was all over. Some inactive sulfide structures were observed, but no active hydrothermal chimneys were found. Serpulid worms, crabs, galatheids, patches of mussels, sea cucumbers, crinoids, and barnacles were plentiful. The serpulids were far more abundant than Shana had ever seen, and they named the area "Serpulid City." Otherwise there was not much difference in the faunal assemblage from the more southern site along this ridge segment; there were no clams or tubeworms for Bob.
Poking down on an inactive chimney surrounded by mussels (brown clusters), serpulids (thin white strands), and crabs (larger white critters with claws).
After sampling mussels and a rock, they zig-zagged northward along fractures to the east wall of the cleft, then the west wall, then the east wall again. On the way, young lobate flows surrounded older pillows, and farther on, there were only the older pillow lavas. The topography was very rugged: steep walls, down-faulted steps that they ascended only to find another beyond, and tectonic fractures cutting through the lava flows. This area was more interesting geologically than the southern site, Nicole said, it exhibited active rift faulting, whereas the other site was more gently sloping terrain. The maps and camera tow photos that Nicole had seen of the region indicated that there was a cleft but did not capture the rugged, stair-stepped nature of the site, and she said it was hard to figure out where they were until they located the walls of the cleft.
Highly vesicular lava from last night's dredge at about 2250m, just off the main axis of the mid-ocean ridge. The scale bar is in centimeters and inches.
The dive was terminated early because the weather was deteriorating. It is predicted to continue, so rather than risk a dive day being cancelled, we have decided to run north to the 32°S site. It will take about 36 hours at 12 knots. We'll be operating the multibeam sonar to map segments of the Juan Fernandez Microplate system that have never been mapped before. Satellite altimetry data have given us a rough view of the seafloor's topography, which helped guide my selection of the track for the ship to take.
Left: Raul (Ordinary Seaman) was the lucky swimmer to ride and roll with the Alvin as the ship motored to it. right: Jerry (Able-Bodied Seaman) guiding the chase-boat into its cradle on deck after Alvin's recovery.
Major Life Experience!
Yesterday I had one of the most incredible experiences of my life—my first Alvin dive! Dive number 4090 for the more seasoned Alvin. I dove to a depth of 2230m at the 38°S site. I still can’t believe it happened… when I first learned about Alvin years ago, I thought about how amazing it would be to dive, but that it was very unlikely that it would EVER happen to me. How wrong I was!
The night before my dive felt a lot like Christmas Eve: I couldn’t sleep because I was SO excited about what the next day would hold for me. Ridiculously excited, really. I did everything I could do to get ready, like studying my dive plan and packing my little pillowcase with things I would need on the dive. I also reviewed the videos from the previous day’s dive so I would know exactly what to expect. Again, how wrong I was…
Well, I had some idea what to expect, but actually BEING there on the seafloor was even better than I thought it would be. The space in the sub is tiny, but slightly more comfortable for the 3 of us (pilot Pat Hickey, Victoria Orphan, and me) than I expected. I also was surprisingly comfortable in the freezing cold sphere—my 4 layers, ski socks, scarf, mittens, and Alvin’s resident wool blankets kept me nice and toasty (impressive in a titanium ice cube!)
The descent was beautiful. The water outside of my viewport changed from that gorgeous south Pacific blue to pitch black as we sunk, but as soon as it was dark enough the underwater fireworks begin. Bioluminescence in many forms passed by my window as the sub disturbed the water by passing through. Sometimes it was a mix of tiny independent dots, but occasionally I could see groups of dots or lines moving in such a way that I could only imagine what kind of unseen creature was really there.
As we neared the bottom, Pat hit the lights and the seafloor appeared outside our viewports. No boring expanses of mud here, but instead the strangest place I have ever seen: glassy rocks and basalt "pillows" that cover the seafloor as far as the sub’s lights could illuminate. Scattered among the pillows was an assortment of deep-sea life forms like sea dandelions, sea pens, purple sea urchins, and soft fluffy white sponges. There also were several white fish—they didn’t scatter and try to escape, but rather went about their slow swimming movements as if we weren’t even there. Of course my thoughts tend toward wondering what on EARTH these fish are thinking when they see us (these fish DO have eyes, unlike many other deep-sea creatures!). We’re just not that exciting to them, apparently.
Left image: Microscope image of Saxipendium, commonly known as the spaghetti worm. They lie draped over rocks in the vicinity of vents. Saxipendium coronatum was described in 1985 from the Galápagos Rift and belongs to a group know as acorn worms or Hemichordata. The field of view is 2cm. Right image: Image of a gorgonian found on a rock away from any vents. Little is known about this colonial animal that is closely related to sea pens and other coral-like animals. Field of view is 1cm. Photo by Greg Rouse, South Australian Museum
We then went about searching for the hydrothermal vents that we knew were nearby from the previous days’ dives. We succeeded in finding the markers placed on the seafloor by our comrades, and collected some of the animals around them. These weren’t the huge spectacular vents that can be found in other areas, but to me they were still incredible—shimmering hot fluid coming out of the tall structures on the seafloor with very specialized animals crowding all around. It is a good thing that we had specific dive objectives, because I definitely could have gone about collecting LOTS of interesting things that no one on the ship is studying! Maybe next time.
After cruising around for a few hours, it sadly was time to leave. I could have stayed indefinitely, exploring along the ridge seeing what I could see, but we were on a tight schedule. We began our ascent to the surface, and then had about 90 minutes to talk about how awesome it was to dive in Alvin and to listen to some Buffett (Pat let me DJ!) I also had to give the science report to the surface over the "phone" (my job as port observer—very cool!). The natural light returned to our viewports and we were hoisted out of the sea by Atlantis (a fascinating process in itself!) Our arrival was met with cheers (Victoria and I are both first-timers!) and then the inevitable official New Diver Greeting on the deck: LOTS of water. Ours was in the form of a surprise hose dousing followed by the usual buckets of ice water to the head. It was freezing, but somehow it still felt GREAT to be the one getting doused, after hearing about it from my labmates for years. What a GREAT day!
Gavin (today's pilot) and Bob (Chief Scientist) discussing the dive. Kazumi (Shipboard Science Support Group), Victor (science party) and Ed (Ordinary Seaman).
All underwater photos were taken with the submersible Alvin, and are courtesy of Woods Hole Oceanographic Institution.