IODP Expedition 303:
North Atlantic Climate 1
Week 3 Report
PDF file is available for download.
October 13, 2004
Operations
Site U1302 (ORPH3A) (continued)
After offsetting the vessel 30 m
to the northwest of Hole U1302A, Hole U1302B was spudded at 1340 hr on 3
October 2004. With only 50 cm recovery in Core 1302A-1H, the bit was positioned
4.5 m above Core 1302A-2H to achieve a good mudline core. A full core was
obtained, which did not establish the mudline. Piston coring advanced to 104.7
mbsf, recovering 102.82 m (98.2%). Hole 1302B was terminated when the APC
partially stroked in the debris flow interval.
The vessel was offset 30 m to the northwest again,
penetrating the seafloor at 0330 hr on 4 October initiating Hole U1302C.
Correlation of Holes U1302A and U1302B records to a previous piston core from
Orphan Knoll (MD99-2237) suggested we had missed some of the upper section.
Therefore the bit was positioned 4.5 m higher than it was during spudding of
Hole U1302B. A full core was obtained for Core 1320C-1H suggesting additional
section remained unsampled. Hole 1302C was advanced to 104.5 mbsf, recovering
97.06 m (92.9%), before refusal was experienced at Core 1302C-11H.
The vessel was offset 30 m to the northwest and Hole U1302D was spudded at 1625 hr. A good 3.63 m mudline core was recovered, indicating a
seafloor depth of 3555.7 mbsl (3566.5 mbrf). A second core was taken to provide
overlap with core breaks from the previous holes; however, only 1.24 m (13%)
was recovered. With the poor recovery in Core 1302D-2H, to ensure complete recovery of the upper section, we choose to core a Hole 1302E.
Site U1303 (ORPH2A)
The 3 nm transit from Site 1302 to 1303 was made in
dynamic positioning mode in 3.75 hr. Hole U1303A was spudded at 0445 hr and
continuous coring advanced the hole to 93.9 mbsf (Cores 1H-10H) with 73.6%
recovery. Difficult coring (partial strokes of the APC) and poor recovery led
us to terminate the hole. The drill string was pulled clear of the seafloor at
1650 hr concluding operations at Hole 1303A.
The ship was offset 40 m southeast and Hole 1303B was
spudded at 1849 hr on 5 October. The bit was positioned 15 m shallower than at
Hole U1303A because correlation to Site 1302 indicated a substantial upper
section was not recovered in Hole U1303A. The hole was cored to 85.7 mbsf
(Cores 1303B-1H-9H) with 83.5% recovery. The hole was terminated when the same
difficult to core interval from Hole 1303A was encountered. With the combined
recovery at Sites U1302 and U1303 sufficient to produce a composite record for
the Orphan Knoll region, we decided to end coring and proceed to the Eirik
Drift area. The drill string was retrieved to the rig floor and ship was made
ready for transit at 1315 hr on 6 October, ending operations at Site U1303.
Transit: On the morning of 7 October, the
daily forecast for Eirik Drift area indicated that a
low pressure system over northwestern Canada was moving eastwards, and projected
to affect the LAB6A area by the afternoon of 9 October with the wind increasing
to 35-40 knots from the east-southeast. The wind was then expected to build
eventually reaching 40-50 knots with gusts to 65 knots from the northwest by 11
October. After considering the potential for 4-5 days of weather downtime
waiting for the storm to pass as well as the potential danger to the vessel
presented by this system, we decided to alter course to the closest alternate
primary site, GAR2A, at 0840 hr on 7 October.
Site U1304 (GAR2A)
We arrived at Site U1304 at 0630 hr on 9 October. After the drill string was deployed, we spudded Hole U1304A with the APC at 1345 hr. Piston
coring had advanced to 220 mbsf with 102% average recovery by the afternoon of
10 October.
Sites U1302/U1303 Preliminary Scientific Results
The
sediments recovered at Sites 1302 (ORPH3A) and 1303 (ORPH2A) are Pleistocene in
age (<1.16 Ma). One lithologic unit was recognized, which was subdivided
into two subunits. Subunit IA (~90 m thick) is composed of gray, greenish gray
and grayish brown silty clay, clay, and nannofossil ooze. Calcium carbonate
content ranges from 1 to 47 wt.% and total organic carbon content is low,
averaging 0.5 wt.%. Subunit IB (~17 m thick) is defined by a debris flow(s)
comprised of gray to dark gray silty clay to
nannofossil silty clay, and gray to dark gray silty sand. Calcareous
microfossils are abundant throughout the cored interval, whereas the abundance
and preservation of siliceous microfossils is variable. There is also variable
content of organic-walled microfossils with a terrigenous component that is
often dominant. Because of the proximity and similarity of core logging data
for Sites U1302 and U1303, a single splice was created for the combined sites.
The spliced section was constructed almost entirely from Site U1302 with one
core from Site U1303. Most of the succession is of normal polarity (Brunhes)
and is a good record of the geomagnetic field. A geomagnetic excursion, the
Iceland Basin Event (MIS Stages 6/7 boundary), is recorded at both sites.
High-resolution physical property measurements show a well defined pattern of
glacialinterglacial variability. Although penetration was stymied by a
presumed debris flow, Sites U1302 and U1303 provide an excellent proximal
record of the Laurentide Ice Sheet instability over the last ~1 Ma. This
record is manifested by numerous detrital layers that appear to have both an
Ice Rafted Debris (IRD) component, and a component deposited from suspension.
The latter may be related to turbiditic activity in the Northwest Atlantic
Mid-Ocean Channel, located ~200 km east of the sites.
Technical Support and HSE Activities
Week 3 of Expedition 303 saw the completion of Sites U1302 and U1303, a 3-day transit to Site U1304 and commencement of coring at this third site. At Sites
U1302 and U1303, 451.7 m of core was recovered and processed. A total of 535 samples have been taken at the first two sites. With the exception of organic geochemistry and porewater samples, personal sampling has been deferred to a postcruise sample party.
Laboratory Status: Initial lab activities during the first site presented
numerous problems with instrumentation and critical software. Instrument
problems included failure of the magnetic susceptibility loop and p-wave logger
on the whole-round multisensor track (WRMST), among other minor glitches.
Problematic software included programs designed to upload data from the
cryogenic magnetometer and magnetic susceptibility core logger (MSCL), and
download software to facilitate data access to Splicer, the stratigraphic
correlation software. The MSCL was
specially designed for Expeditions 303 and 306 to provide real-time feedback to
the driller for maximizing recovery of the stratigraphic section. As a result of these challenges,
shipboard technical and scientific personnel designed work arounds for data
access critical for drilling decisions. Shipboard technical staff repaired the
WRMST susceptibility loop within about one day. Shipboard and shorebased staff
have been troubleshooting data upload and download problems on a priority
basis. By the start of coring at
the third site, most of the major problems have been resolved while work on
additional problems is ongoing.
HSE: A fire and boat drill was held on 11 October 2004 for the entire ship's complement. An interactive DVD safety-training module covering Risk
Management has been received from Transocean and will be viewed by the IODP Expedition 303 staff.
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