Seamounts Cruise
April 29, 2004, Day 3
Today was an adventure in deep-sea clam hunting. With the skill of the
ROV pilots, we collected a few of the many clams we saw with the suction
sampler. We were after these elusive clams on San Juan Seamount for two
main reasons. First, seamount clam samples collected from previous
seamount cruises at President Jackson, Davidson, Pioneer, and Rodriguez
Seamounts have been analyzed
in our molecular ecology lab. Until today's dive (T662), the Rodriguez seamount was the most
southern population of deep-sea seamount clams we have analyzed. By
adding additional collections of seamount clams, we can get a more
thorough picture of the evolutionary processes that may influence the
distribution and genetic composition of these unique animals. Second, we
wanted to collect some seamount clam specimens for a colleague who will
analyze the reproductive state of the seamount clams. By looking at
the
reproductive organs of the clam, we will be able to estimate the
contribution that a seamount clam can make to the next generation of
seamount clams. This clam attaches to rocks like a brachiopod. It is about to be collected with gentle suction and
put into a biojar for safe transport to the surface. With a dive planned for the Northeast Bank tomorrow, we
are hoping to find additional populations of seamount clams to add to
our collection and further our knowledge of seamount clams and the
seamounts on which they live.
--Joe Jones
Joe holding a jar containing some of the tiny animals we found attached to the rocks.
Seamount clams in a dish of seawater prior to being frozen for later study. These clams have an extremely thin, fragile, nearly transparent shell and a pink body.
We steamed from Rodriguez Seamount to San Juan Seamount overnight and
arrived for a normal dive schedule with ROV preparation at 6 am and
launch at 6:30 am. The dive was a great success and covered a long
distance up the axis of the volcano from the southwest and heading
towards the summit. Tiburon was on bottom about 8 am and we started
right in collecting rocks and animals. The ridge line actually consists
of a series of small volcanic cones and we wanted to collect samples
from as many as possible, since each probably formed during a different
eruption and is likely to have a slightly different composition. We are
always trying to find dense lava samples, which are the best samples to
obtain radiometric age dates from and to analyze for full chemical
compositions. We also try to find volcaniclastic rocks (sedimentary
rocks consisting of fragments of lava ranging from basketball-sized
clasts to sand and silt sized grains). The particles in these rocks
commonly erupted explosively and the magma was quenched in water to form
volcanic glass. The glass is easy to analyze and also contains the gases
that were dissolved in the magma, which otherwise escapes as lava flows
cool and crystallize. Nearly all these rocks are also coated with crusts
of Fe-Mn-oxides that precipitate out of seawater slowly over millions of
years. Jim and Brandie study these deposits to understand how they form.
As the dive progressed, we crossed over pillow lavas, then
volcaniclastic deposits, then talus (broken rock fragments on steep
slopes), again and again. By the end of the dive we had collected 33
rocks, mostly lava samples since the volcaniclastic rocks are more
difficult to 
sample.
Angular basalt rock just collected from an outcrop of lava with the vehicle's manipulator arm and the same rock in the lab after the dive, scrubbed and described
Along the way we also collected many samples for the biologists who have accompanied us, as well as colleagues who could not come along. Biologic specimens collected included bamboo corals for climate study (by Tessa), specimens of a deep sea clam for genetic study (by Joe), small branches of Paragorgia (bubble-gum coral) for genetic study, several stalked crinoids for comparison with specimens collected last year on Rodriguez Seamount, a tunicate we had not seen previously, and various sponges, anemones, sea stars, brittle stars, a squat lobster, and several chitons that came up with the rock samples. The science party is close to wrapping up the sample labeling, bagging, dissecting, preserving, describing, and photographing at 9:30 pm.
--Dave Clague
A
Stauroteuthis octopus swims by for a peek at the ROV Tiburon.
Brisingid and basket stars, white trumpet and frilled sponges, and a bamboo coral (in the background) are living attached to a lava flow.
Kathie holds a styrofoam head that was shrunk on our dive today. These
are popular souvenirs of deep dives: the air trapped in the foam is
compressed by the tremendous pressure of the overlying water, leading to
entertaining shrunken, misshapen forms. Kathie has decorated hers with a
celebration of seamounts.