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IODP Expedition 323:
Bering Sea Paleoceanography
Week 2 Report (12-18 July 2009)
PDF file is available for download.
19 July 2009
After a 6.5 day transit from Victoria, BC, averaging 11.5
nmi/hr, we initiated dynamic positioning over Site U1339 (UMK-4D) at 1603 hr
(UTC-11h) on 16 July. The operations plan called for four holes to be drilled
at Site U1339. Hole U1339A was
spudded at 0430 hours on 17 July. The first core was shot with the bit at 1873 m DRF and recovered the mud line and 4.94 meters of core. The
hole was terminated after Core U1339A-4H with a suspected Bottom Hole Assembly
(BHA)/coring system problem resulting in almost 100,000 lbs of overpull on the
last core. The drill string was tripped out of the hole, the coring system components were inspected and several parts were changed. There
was no conclusive evidence found for the mechanical problem encountered. The
BHA was run and the coring system was tested successfully in the water
column. The vessel was offset 20
meters and the rest of the string was then tripped to the seafloor and Hole
U1339B was spudded at 2315 hours on 17 July. The first 4 cores (U1339B-1H to 4H) were dedicated to microbiology with both PFTs and whirl packs deployed. The remainder of Hole U1339B recovered the sedimentary
sequence from the total depth of Hole U1339A down to 196 mbsf with one short
core (U1339B-13H) when the APC fired into an unknown object, most likely a
glacial drop stone. Hole U1339B
ended at 2010 hours on 18 July when the bit cleared the seafloor. The vessel
was offset 28.3 meters and Hole U1339C was spudded at 2230 hours on 18 July.
The second week of IODP Expedition 323 to the Bering Sea
continued with daily science meetings and laboratory training aimed for
planning and preparing for coring and logging operations at out first site,
U1339 (UMK-4D), located off Bristol Bay on the Umnak Plateau. The main
scientific objectives at Site U1339 are to monitor the extent of glacial sea
ice in the Bering Sea, the exchange of North Pacific and Bering Sea waters and
evaluate microbial respiration, biomass and community composition in the subseafloor
sediments. The operations plan for Site U1339 consists of coring 3 holes to 200
m, one hole to ~35 m and logging the last hole. Coring was carried out using
non-magnetic core barrels and the Advanced Piston Coring (APC) system. The
shallower hole was dedicated for microbiological sampling. Two holes were
completed by the end of the week, including the microbiology dedicated cores
and one complete hole to 196 m DSF.
Only four cores (1H-4H, 0 to 33.5 m DSF; recovery 103%) were
recovered from Hole U1339A because of a mechanical problem with the coring
system that forced us to terminate the hole prematurely. Once the problem was
corrected, we cored Hole U1339B to a maximum depth of 196 m DSF (recovery
104%). The top four cores from Hole U1339B were dedicated for microbiological
sampling and the data from the rest of the cores were appended to the data
obtained from Hole U1339A cores. The sediments in Holes U1339A and U1339B are predominantly
silty to clayey diatomaceous ooze, with variable amounts of dispersed vitric
ash, occasional thin ice rafted debris (IRD) layers and isolated pebbles, and
numerous ash layers. The sediment color varies from different tones of dark green to gray, and the ash layers also show varying tones, suggesting a wide range of volcaniclastic sources.
All major microfossil groups have been found in the
sediments, however, siliceous microfossils greatly exceed calcareous forms and
provide a consistent and coherent biostratigraphic succession. The age interval
recovered in Holes U1339A and U1339B is at least 0.5-0.6 Ma at 167 m CSF according
to the diatom, radiolarian and silicoflagellate biostratigraphies. The
estimated ages are supported by correlation of physical properties with
previously recovered piston cores from the region.
The microbiology-dedicated cores (U1339B-1H to 4H) were
sampled at a very high resolution and samples are being prepared for shipboard
and post-expedition analyses.
Preliminary results from geochemical analyses suggest
elevated anaerobic oxidation of methane within the top 5 m and very high cell
activity in the sediments. Alkalinity increases with sediment depth reaching
maximum values (53 mM) at ~90 m CSF.
Technical Support and HSE Activities
HSE: Because of the cold temperatures and gas presence in
the recovered cores, all technical and scientific staff involved in core
processing in the catwalk are required to wear full face shields. All others on the catwalk are subject
to routine catwalk eye protection policy. Working with ODL staff to install
fall protection in science pallet area so that upper storage platform can be
safely accessed once installed. Additional protection is being designed for the
zero lift to prevent any hand pinch points.
Logistical activities: Work continues on the reorganization
of the Science Pallet Storage area and Logistics Shop. A new work shop has been
constructed on the raised platform in the Science Pallet Storage and equipment
mounts are being fabricated for the sander, grinder, and vise. The new -86¡C
Freezer is now operational in the Science Pallet Storage.
Laboratory activities: As of the date of this report we have
processed 26 out of the 69 cores recovered. Recovery has been near 100% with
our highest coring rate at ~11m/hr. Continuing to update track and data upload
programs for core flow efficiency.