Dive 2930 had several objectives, listed here in order of importance:
(1) Locate 14.5 permanent transponder and pull release pin.
(2) Move to Southern part of MEF, measure flange pool depth at Salut
for deployment of J hook.
(3) Do mesotech survey of Bastille complex.
(4) Locate marker "R" on Bastille, and sample.
(5) Additional sampling near Bastille, if possible.
The dive launched on time into slightly heavy seas for launching (I divined
from the grim expressions on deck) but improving weather with sunny skies. We
had a hard landing, which dislodged the manifold arm, as well as knocking some
bottles around in the rack. Our launch target was just north of our best
calculated location of the 14.5 transponder, (5591, 5120). Once below the
surface, the rocking and rolling abated, and we settled into steady flight
towards our target. On the descent Blee allowed me to try out the controls on
Alvin, steering a course towards our target. At about 9:20 we were approaching
the bottom, so we began to watch the range to the 14.5 transponder quite
carefully, driving in the direction of our calculated position and watching the
travel time get smaller and smaller. By 9:30 we had the transponder line in
sight. At (5160, 5154, 2138) the range to 10.0 transponder was 0.162 secs.
We then descended to the release pin, located ~15m north of where we first
sighted the line. My first view of the seafloor was of slightly sedimented
pillows, which dropped off out of my field of view. Our heading, from the
recorded navigation data, was ~250. Comments from the port side indicated that
the bottom dropped off quite sharply, indicating the transponder anchor was on
top of a small horst. A few minutes at the pin yielded a successful release at
1000L.
Next, we popped up into the water column (at about 100m above the seafloor)
and headed for Salut. During this transit we had the mesotech running
at it's maximum distance setting, and we began recording the first videotapes.
At a heading of ~311 deg, we could see horst-like features on the mesotech;
this seemed to correlate well with the ridge perpindicular grooves visible in
the AMS-120 images that John gave us to take along. Near to where we began our
descent Blee noticed a slight discrepancy between the altimeters (2 of them)
and the depth shown on the mesotech. This may be a significant problem when
dealing with the mesotech data, but needs to be looked into.
At ~1055L we descended and had the bottom in sight. We came down on some
sedimented basalt and were ~20m south of Salut, as reported by Blee. Thus, we
began to creep along the wall. At about 1101L I saw a sulfide structure off
to starboard...we were travelling up a ridge of basalt/talus that I would
presume was the fault scarp shown in Vero's map....we kept going north, but
realized that we had overshot to the north and circled back to the sulfides
that I had first seen off in the distance (?). At 1106L, with a heading of
160, we were looking at the "arrow" marker on Salut, (4863,5881). We then
proceeded to set up Alvin to measure the pool depth here at Salut. After an
unsuccessful first attempt to get oriented correctly, we pulled out and got
into a good position. The flange pool depths were deepest "just left of center"
at about 3 cm, and about 1-2 cm elsewhere in the pool. The flange seemed to be
quite fragile--if the measuring saw touched the top of the pool sulfides would
come cascading down in negative plume of glittering black smoke...almost as if
Blee was cleaning ashes out of a chimney!
Having sucessfully completed our first two dive goals, we moved on to the
mesotech survey. We popped up to height and flew to 4855,5969(?). There we
touched down and checked our depth control on the basalt flat just south
of the Bastille complex. We found that a depth of 2175 would put us above all
the known structures in the area. Our plan was to fly a box from 5950 to 6050 on
lines of constant x's. At this touch down site we sighted a smoker, which we
ended up coming back to sample (Blee mentioned that it looked easy to sample).
We then popped up into the water column and began the meso survey (end of tape
1). We completed all the lines but the 4890 line (we doubled on the 4860 line,
I think, because that's where we started) ... need to check this on the
navigation. Ended mesotech survey at 12:55, and moved on to our next dive
goal, which was to find marker "R". This is where the dive track/history begins
to get complicated.
We began south of Bastille, and proceeded north with the intent of ending
up right at marker "R" located on the south and middle of Bastille. After
passing the Tara (known from markers), I implored Blee to move to SW. At 1301L
we located marker "P"... at this point we were confused, since there was no
marker "P" on the map. At 1302L there were tubeworms visible out my porthole,
with a network of smokers and an active flange (?) on the port side of the
sub, while "P" was located on the starboard side. At 1305L we viewed a triple
spire, while a large spire was rising up to starboard...(4881,5995). One minute
later the sulfide was dropping off sharply to starboard, indicating that we
had probably drifted out over Bastille (actually had driven there due to hot
water under sub) All this time we were in contact with the surface trying to
make sense of the mysterious "P" marker. Two minutes later (1308) I first
spotted the camera basket, which is located in the tubeworm field north of
Peanut. At 1310L, heading 33 deg, we were looking head on at the basket...
(4870, 6012). Looking at the map in retrospect, it seems that this first
approach to "R" brought us up through the "Bastille" structure, centered
between the two southerly protruding lobes of Bastille, passing with "R"
(now P) to our starboard. After communicating with surface (K. Juniper, owner
of camera) we pinned our position. Now came the complexity of finding "P"
once more. It was decided the best route was to loop around to the west and
approach again from the south.
At this point, Russ attempted to guide Blee to the right location by looping
around Peanut...but the first turn was too much, and we ended back at the
camera basket after completing a loop around Peanut. The second attempt was
more successful, and we got on an easterly course before looping back to the
camera package. At 1328L we headed ran into sulfide, which Russ suggested we
circle to the right(south). This was not possible, though, since there was a
large sulfide spire rising up to the right. There was a small "pass", though,
which we went up and over. The sulfide spire that I saw was probably the small
southwestern lobe of Bastille, although at this point I was very disoriented,
so who knows. Three minutes later we spotted "P" again, with active smoker
very close to base of marker.
Here we sampled with the manifold, and deployed marker AM:
TEMP 360
PORT outer major
PORT inner major
PORT gas tight
STARBOARD gas tight
After completing sampling here, we moved on to the "easily sampleable" site
we had seen earlier before beginning the mesotech survey. This was an unsampled
(and unnamed) sulfide structure, which we named "Cannaport". On the way to
this site, we passed an uplifted block of pillows on the starboard side,
which was probably the break in the talus wall as shown on Vero's map.
We sampled here as well (4860, 5697) and deployed marker AP:
TEMP 349
BLUE 2 gas tight
RED 5 gas tight
BLUE 10 major
Out of power, so returned to surface (lift off at ~1505L). Slightly exciting
recovery (although not the worst of the dive series by far) due to winds and
chop.
Christian B. Parker, UW Oceanography, 6/13/95