Detailed Report of Leg Two
August 23, 2000
Dive 4235
This dive was along Traverse 1 at GC 260/304. Depth ranged from 1414 to 1835 ft. A
carbonate hard ground was observed, which corresponded to an amplitude anomaly on the map.
The remainder of the dive was spent over a "soft sediment plain".
Dive 4236
Dive 4236 was along Traverse 2 on GC 260/304. Depth ranged from 1391 to 1507 ft.
Numerous small vents and a 3-m diameter brine pool were observed. The bottom then turned
to a mud bottom, and eventually a carbonate slab was collected. The carbonate slab was
part of a carbonate field observed toward the end of the traverse.
August 24, 2000
Dive 4237
This dive was along Traverse 1 in GC 354. Depth ranged from 1713 to 2434 ft. After
observing small mats of Beggiatoa bacteria, an area of large carbonate boulders,
sea fans, and numerous colonies of tube worms was discovered. After leaving the area of
carbonates and tube worms, and after an interval of muddy bottom, a mud flow with small
pockets of gas being released was observed. Another major mud flow with a very smooth,
non-burrowed, surface was observed in the vicinity.
Dive 4238
This dive was conducted along Traverse 2 in GC 354. Depth ranged from 1705 to
1909 ft. After observing a small colony of tube worms, the sub encountered an area of
carbonate rock with sea fans. Small patches of orange Beggiatoa bacterial mats
were observed, then a mud flow feature followed. An area of carbonate rocks with tube
worms followed. This area was comprised of numerous large tube worm bushes among the
carbonate features and could be considered a new high-density chemosynthetic community
site. Additional large carbonate rocks outcropped on the edge of the area. One of these
features was covered with a spectacular community of Lophelia coral, gorgonians,
numerous crabs and sponges. These features agreed very well with the amplitude maps.
August 25, 2000
Dive 4239
This dive was along Traverse 1 on Garden Banks 543. Depth ranged from 1771 to 1890 ft.
The first part of the transect was mud bottom with small rocks and boulders. A large area
of mud bottom with bacterial mats and small groups of tube worms followed. On top of a
small ridge, a small carbonate field with bacterial mats, tube worm bushes, and several
boulders were observed. On top of the ridge, a mud volcano with mud flows was observed; no
gas seeps were observed. A small chimney was observed and sampled; it appeared to be
composed of barite. A large area of exposed carbonate plates was observed containing
scattered rocks.
Dive 4240
This dive was along Traverse 1, GB 543. Depth ranged from 1990 to 2128 ft. After a
small ridge with bacterial mats was encountered, the traverse encountered an area of small
carbonate rocks. More limestone with small tube worms was encountered, then the transect
ended on a muddy bottom. A grab sample of mud was taken near the tubeworms, and another
was taken near the end of the transect.
August 26, 2000
Dive 4241
This dive took place along Traverse 1 on GB 535. Depth ranged from 1835 to 1964 ft.
After starting in a burrowed, hemipelagic mud bottom, the traverse progressed into an area
of scattered bacterial mats, with individual clam shells. A series of small ridges was
observed. An area of tubeworms was encountered, and tubeworm samples were collected.
Dive 4242
This dive took place along Traverse 2, GB 535. Depth ranged from 1872 to 1923 ft. From
the beginning of the transect, the sediment surface showed very little bioturbation and no
lumps or mounds. Bacterial mats were common throughout the transect until near the end.
Clam shells were also common throughout most of the transect. Many areas appeared to be
live clam communities showing short tracks or depressions made by living clams. Stalked
sea whips were numerous throughout the dive. As depth began to increase moving off the
amplitude feature, large mounds (1 m high) followed by substantial ridge structures ran
perpendicular to the track. A gorgonian field was observed at the end of the line.
August 27, 2000
Dive 4243
This dive took place along Traverse 2 on GB 460/461. This traverse crossed two large
mound features approximately one-half mile wide and over 300 ft. high. Depths ranged from
2295 ft to 2955 ft. Both mounds appeared to be dormant vent features, and were burrowed.
Grab samples were taken on the top of each mound. Preliminary analysis on the ship
indicates that both grab samples contained fine to medium grained sand, which was highly
rounded to very angular. The suite of minerals present, besides quartz, included both
igneous and metamorphic minerals, some of which suggests an Appalachian source. The nature
of the grain shape and composition suggests that this material was derived from several
sources. Initial hypothesis is that the material was derived from several sources. No
other indications of hardgrounds, hydrates or chemosynthetic organisms were observed.
Dive 4244
This dive took place along Traverse 1, GB 460/461. A large mound occurred on the NW end
of the traverse, and a large field of high amplitudes occurred on the eastern end of the
traverse. The entire traverse consisted of mostly hemipelagic, burrowed mud. A sediment
sample was taken on the crest of the mound. A few occasional clam (?) shells were
observed.
August 28, 2000
Dives 4245 and 4246
These two dives were made for the BBC at a hydrate mound in GC 234. Filming was done of
tube worms, mussels, polychaete worms, and hydrates.
August 29, 2000
Dives 4247
This dive was made for the BBC at a brine pool in GC 234.
August 30, 2000
Dive 4248
This dive covered Traverse 1 on EW 873. Depth ranged from 605 to 686 feet. Shortly
after arriving on bottom, a small vent site was located. In route to the major vent site
on the route, a hard ground area with sea fans and gorgonians was observed. A heading was
given for the crest of the first major vent, but due to poor visibility on the bottom
(less than 20 feet), the major vent was not observed. Several small vent fields were
observed, and grab samples were taken. The dive was aborted early due to worsening weather
conditions at the surface, and the afternoon dive was cancelled.
For more information, contact Keith Good.
