NBP0505 sailed from Punta Arenas on June 23 with a diverse science
party that is collaborating to study the record of sedimentation from three
different glacial systems in Chile. On board are eight persons from Rice
University, two students from the University of Washington, five scientists
from University of Concepción (Chile), and one participant each from SHOA,
INACH, and University of Magallane (all Chile).
It took a few days for the Palmer
to reach the first study area. During that time everybody prepared
equipment, finalized plans, and enjoyed the spectacular scenery of Chile's
inner passage. Once in the study area, all aboard worked extremely long
hours.
The San Rafael study area consists of several small basins. The
outer fjords and middle basin are connected by a narrow and shallow pass that
the Palmer could cross only
during daylight hours. The middle basin and the inner basin are connected
by a six mile long river that can only be navigated by small vessels.
After completing a multibeam and 3.5 kHz survey of the outer and middle areas,
we began coring, seismic, and small boat operations. A total of 26 cores
were attempted and twelve kasten cores and five jumbo piston cores were
obtained. Of the nine failed core attempts, eight are attributed to a
hard sandy bottom. Seismic data was collected from the Palmer using two fifty cubic inch air
guns and then two fifteen cubic inch water guns for a higher resolution
survey. Each of these surveys shows laminated sediment packages onlapping
onto steep-sided bedrock walls. The final data to be collected at San
Rafael was a short sidescan sonar survey. Despite a rocky start, the
images from the sidescan system are of high quality and show what are most
likely sand waves formed by strong tidal currents.
Small boat operations had to be cancelled on the first day in the area
due to extremely high winds but were resumed on the second and fourth
days. A landing craft was used to deploy CTDs along the glacier front and
a zodiac was used to deploy personnel to retrieve data from a rain gauge set
earlier in the year. The Palmer's
work boat was used for the first time in science operations and collected
seismic data, using a boomer system, in the San Rafael Laguna along the glacier
terminus. The boomer data from the shallow water in the laguna is of very
high quality and, although of limited extent, promises to be very useful
in mapping the most recent deposits. The layered sediments of the laguna
lap out onto morainal ridges. Unfortunately, the work boat became stuck
in shallow water on the way back out of the river and the boat's rudder was
damaged. Although it has been successfully repaired, it was not available
for the final day at San Rafael.
All cores collected during this cruise are being split on board and
described, photographed, and sampled. This is not standard for cruises on
the Palmer but allows for
immediate analysis and therefore better selection of additional core sites as
well as person-to-person communication among the scientists from different
institutions. Surface sediments in the San Rafael area can be divided
into two basic types, clean sand or gravelly lags in shallow areas and sandy or
silty muds in the basins. Jumbo piston cores record the same basic
units. Many of the cores contain abundant bioturbation, fossils, and
living flora. Diatoms were observed in smear slide analysis from all
cores. Assemblages consist of a mixture of marine, brackish, and
freshwater species. Samples have been taken for 210Pb, 14C, foram,
additional diatom, protein, isotope, and opal analyses.
We are now in transit to the Penguin and Europa fjords. We
anticipate more ice in the work area but less difficulty with narrows and
shallows.