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UTIG NewsRVIB Nathaniel B. Palmer
NBP-9507 Cruise Report
Week Three: November 10-16, 1995
During the third week of
NBP9507, we worked in Bransfield Strait and the southwest Scotia Sea. We acquired about
1,000 nautical miles of swath bathymetry, 67 miles of 48-channel seismic data, lowered the
ZAPS sled seven times, acquired three water sample rosettes, retrieved one sediment core,
took two dredge hauls, and made two camera lowerings.
Bransfield Basin
At the end of last week we had just rendezvoused with RV Polar Duke and started our
first ZAPS sled drift. After we finished the sled tow, we slalomed our way around the
central Bransfield Basin dodging icebergs, bergy bits, brash ice and some healthy pack
ice. Sometimes our course looked like a drunken sailor's meander back to his bunk. We then
approached the submarine volcano we had previously imaged (see the report from week 1) and lowered the ZAPS sled and a rosette into
the caldera.
On two previous Seabeam survey runs we passed very close to what should be a nearly
symmetrical volcano on the steep northern margin of central basin. Once again ice covered
the feature and we did not get near enough to image it. We then headed off to what is now
being called Fish Ridge for a ZAPS drift. The drift lasted eight hours and covered about
4.25 n.m. in a straight line along a sawtooth course created through deft adjustments by
the bridge officers to keep us atop the linear ridge.
Southwest Scotia Sea
After Sled Drift #20 we headed north into the Scotia Sea in hopes of collecting
multi-channel seismic data. We spent the next two days surveying the southwestern corner
of the Scotia Sea northwest of Elephant Island. On the second day, we crossed an east-west
trending ridge up to 600 m high with a steep (up to 45 degrees) south face. Lawver
interprets it to be the equivalent of the San Bernadino Mountains where the structure is
dominated by compressive forces resulting from a bend in the San Andreas fault. In this
area, the compressive stresses could be the result of a bend in the recently reorganized
Scotia-Antarctica plate boundary. We also found a linear fault trace along the east side
of the Shackleton Ridge with rotated fault blocks where the fault trend changes.
Seismic Work
On November 13th we
deployed the seismic streamer. It took about three hours to deploy the streamer and
airguns. Gun 5 was still leaking so it was shut off. We then headed north for about four
hours and recorded MCS data across the equivalent of the San Bernadino Mountains, turned
west for about an hour and then ran a parallel course to the south. As we crossed the
southwest Scotia Sea we saw a lot of structure in the sediments which ranged from 1 to 2
seconds thick. Basement was well-imaged but there was no sub- basement structure apparent
on the single channel monitor record. Toward the southern corner of the basin we detected
what may be a major normal fault. In all, we collected 13 hours of MCS data and
about 67 n.m. at the rate of just over 5 knots. The data look good.
Fish Ridge
We headed due south to take a ZAPS sled lowering along the ridge in the eastern Bransfield
Basin. The eastern Basin was now covered with a lot of pack ice where previously it had
been clear. We then returned to Fish Ridge, passing to the south of Bridgeman Island once
again. We did the second ZAPS drift in the Fish Ridge area. The survey was confined to a
small box less than 2 km by 1 km. In the process of dodging icebergs within this small
box, the sled detected an anomaly. Continued drifting was undertaken to try to determine
the extent of this plume. 
Dredge work
We next undertook Dredge #1.
The dredge team consisted of Carol Chin on the bridge advising the bridge of position, Jay
Simpkins on Simrad watch to relay depths to us, and Larry Lawver in aft control telling
the winch operator to lower and raise the winch. We laid the dredge on the bottom at about
1450 meters of wire out, got the ship underway, passed over the target area and then
pulled in the dredge. We got a series of four groups of significant pulls with the last
being the greatest at 5,000 lbs. of tension. The rocks weighed about 40 kg and included
two large pieces of unaltered vesicular basalt with many small attached organisms and
numerous smaller rocks including a few glacial erratics. We also collected three fish, one
slimey yucky worm-like creature, numerous brittle stars, and a small arthropod. 
The largest fish was a pouty-lipped
Scotia sea Gapehead (Chaenocephalus aceratus) about 47 cm long. Since the
fish were wedged into the dredge basket with the rocks we infer they were collected near
the bottom. The Gapehead is a bottom dweller although it has previously only been
collected in water depths of 5 to 439 m (Miller, 1993). This one was collected somewhere
around 1200 m.
Underwater Pictures!
Immediately after the first dredge we lowered the Benthos underwater camera loaded with
Polaroid black and white 35 mm film. We found this camera in the ASA warehouse in Punta
Arenas in 1993. During NBP9301, we pressure tested the housing and fired the camera in the
lab but did not get an opportunity to deploy it. The camera is triggered by bouncing a
dangling trip weight on the bottom. Thirty-five bounces over Fish Ridge produced about 20
successful photos. Most were of a flat muddy bottom with an abundance of brittle stars,
including over thirty in a field of view estimated to be only two meters across! A couple
of images showed basalt outcrops along with various other benthic creatures such as
seapens.
Side trip to slope volcano and a core
While giving the ZAPS crew time to recuperate, we made a short swath survey in which we
finally successfully surveyed the volcanic edifice perched on the northern slope of the
central basin. We recovered our second kastenlot core near where a German core contained
higher order hydrocarbons a number of years ago. We retrieved a full three meters of mud,
with more intriguing black- olive mud than in the first core. Additional surveying was
done in the northeast corner of central basin and we finally returned to Fish Ridge
(so-named for the Gapefish collected in the first dredge).
Return to Fish Ridge
A second ZAPS drift was
made along Fish Ridge in a similar sized box next to the original one. Again two very
large anomalies were found. A second dredge and a second camera run were made. The
proscribed dredge course into the wind resulted in dredging along a nearly flat bottom.
One very fresh looking basalt rock was recovered, again with an abundance of benthic flora
and fauna. The rock was about 25 cm by 15 cm by 15 cm and weighed about 6 kg. It appeared
to have been part of a pillow lava. The second camera run experienced initial difficulties
when the second pinger available on the ship turned out not to be an oceanographic pinger
but rather a location beacon. After worrying about what to do, it was decided we should
try to see if we could operate the camera without the use of a pinger utilizing the
tensionmeter. The total package including camera and pinger with about 1100 m of wire out
weighed 750 lbs. When the camera hit bottom the tensionmeter fell off to about 600 lbs.
So, we were able to control the camera along the bottom by observing the tensionmeter and
raising and lowering the camera about 5 to 10 meters between "hits". Twenty five
such lowerings get to be very boring. In the picture above, the bottom is muddy, with a pillow
basalt outcrop to the left (vent?) and a white brittle star and seapen nearby. After
the camera run we left the central Bransfield basin and headed for the eastern Bransfield
Basin where we began a ZAPS drift along the central of what we call the Three Sisters.
This ended what we considered to be a highly successful and satisfying week.
Next Week Tune in for more seismic, coring, and ZAPS, a trip to the Chilean Base
Frei, and Thanksgiving aboard the Palmer!
Reference
Miller, R.G., 1993, History and atlas of the fishes of the Antarctic Ocean, Foresta
Institute for Ocean and Mountain Studies, Carson City, Nevada, 795 p.
Lawver, Klinkhammer, and
the Shipboard Scientific Party