The Beautiful and Intriguing Rocks of Lost City (Les magnifiques et interessantes roches de "la cite perdue")

Slideshow

Adelie Delacour

		April-May Sun Mon Tue Wed Thu Fri Sat 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Today's Question Q. How deep do submarines actually go? (Austin J., Homestead, Narrowsburg, New York) A. W. Bruce Strickrott answers: Well, the answer depends upon what submarine you're talking about. Alvin can go to 4500 meters, a little more than 14,500 feet. Normally we'll operate in the neighborhood of 2500 to 3000 meters but if need be we can go to the 4500 meter maximum. Other deep ocean research submarines, like the French Nautile and Japanese Shinkai, can go deeper, 6000 and 6500 meters respectively. In the past the deep submersible Trieste made the only manned trip to the deepest part of the ocean, the Marianas trench in the Pacific near Guam. Currently our institute, Woods Hole Oceanographic Institution, is looking into building a newer, deeper diving replacement for the current Alvin. Perhaps in a few years you'll be able to watch the new Alvin's operations via the Web.

Every morning, it's with real pleasure that I wake up to see the launch of Alvin, hoping that it will bring back a lot of samples, and every afternoon I’m waiting impatiently for its return to look at the collected samples from Lost City.

Alvin takes several kinds of samples: water samples, biologic samples, and rock samples. My interest is in the rock samples. My specialty on this cruise is the petrology and the geochemistry, and my “job” is to describe the rocks collected from the Lost City after each dive. I cut them, after a short description, in order to describe them in detail, and to learn about their history: where they come from, what were the conditions of formation, what kind of alteration do they display? However, the on-board description is succinct, and additional analyses will be performed in the laboratory on land (bulk, mineralogical, and isotopic compositions) and these analyses are essential to answer our questions and allow us to better understand the involved processes in the formation of the Lost City and how the alteration of the rocks controls the hydrothermal activity of the Lost City.

Huge carbonate vent sample

The samples collected at each dive amaze me. Imagine looking at and having in your hand rocks coming from the depth of the ocean: it’s magic!! And it’s even more surprising when I cut these samples. The carbonate vent structures display unbelievable textures that are very hard to describe; it’s kind of like a superposition of white crumpled papers or the inside of a wasp's nest.

View of a relatively fresh serpentinite. The chemical and mineral compositions will be analyzed later in laboratory.

The basement samples (peridotite, gabbro, serpentinites) are also amazing, because outside they look like the same thing—blocks covered by a black manganese crust. However, when they are cut in half, they display a large variety of textures, mineralogy and alteration.

Bruce and Tim remove the samples from the big slurp after a successful dive.

Today is our 10th Alvin dive, and Tim Shank wanted to take biology samples, so a strange machine, the 'hydraulic slurp', was mounted in front of Alvin. It's like a vacuum cleaner which sucks up life around Lost City. And when Alvin came up, the 'big slurp' seems to have worked very well. A lot of work is ahead of the biologists tonight!! I thought this morning that there would be no rock samples, however, Tim collected 3 vent carbonate samples, including a huge one that smells of H2S (it's like a rotten egg) and has a new interesting texture (to be continued)