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doi:10.2204/iodp.proc.346.103.2015

Operations

Port call

Expedition 346 began with the first line ashore at the Valdez Container Terminal in Valdez, Alaska (USA), at 1120 h on 29 July 2013. The first week of Expedition 346 consisted almost entirely of port call activities. This was the first port call in Valdez, and operations proceeded very smoothly. In spite of the remote location and logistical challenges, the vessel was resupplied and departed 1 day earlier than scheduled.

The IODP-United States Implementing Organization crew and the expedition Co-Chief Scientists arrived at the ship in Valdez on 29 July after an 8 h bus ride from Anchorage. The ship’s (Siem Offshore) crew arrived the following day. On day three of the port call, the Expedition 346 science party moved aboard, completing the sailing complement for the expedition.

Port call activities included routine resupply of consumables and offloading of the previous expedition’s (IODP Southern Alaska Margin Expedition 341) freight. All Expedition 341 core samples were offloaded to refrigerated containers and dispatched to the IODP Core Repository at Texas A&M University (College Station, TX, USA). All microbiological samples were offloaded and dispatched to the Expedition 341 scientists’ home institutions by courier. Three empty core liner boxes were also offloaded for disposal. In addition, 2441 sacks/122.1 short tons of barite, 3920 sacks/196.0 short tons of sea gel, and 1872 sacks/88.0 short tons of cement were loaded. Bunkering totals included loading 115,015 gal marine gas oil by trucks from a local Valdez refinery.

The ship’s crew’s activities included receipt and installation of a replacement standpipe valve, including the required X-ray certification of the high-pressure welds by a technician from Anchorage. In addition, a Schlumberger mechanic came to assist the logging engineer with repairs to the securing system holding the logging winch/transmission in place.

With port call activities completed, the R/V JOIDES Resolution departed for Site U1422 (proposed Site JB-3) with the last line away at 0718 h on 2 August. Departure was 28 h ahead of the scheduled departure time.

The 3556 nmi voyage to Site U1422 lasted 2 weeks at an average speed of ~10.2 kt. During the transit, we crossed two low-pressure cells with their associated strong winds and high seas, which impacted our cruising speed. Average speed over ground during those times was as slow as 7.5 kt. A total of eight time changes took place during the transit, with the clock being turned back 7 h and advanced 1 day to compensate for passage across the International Date Line. In effect, the day of 9 August was lost and the ship time jumped from 8 August directly to 10 August at 2400 h on 8 August. The last time change placed the ship at UTC + 9 h, which was the local time for all Expedition 346 sites as well as Japan and Busan, Korea.

The ship maintained good speed (11 kt) during the final days of the transit until entering the heavily trafficked Tsugaru Strait south of Hokkaido, Japan. A strong current on the bow reduced the vessel’s speed over ground through the strait to 6.0 kt. This lost time was made up once exiting the strait and turning to a more northerly course, during which an average speed of 11.7 kt was achieved during the last day of the transit.

Site U1422

We arrived at Site U1422 at 1448 h on 17 August 2013. Control of the ship was shifted from bridge cruise mode to dynamic positioning mode at 1528 h. A strong gale was blowing as the ship arrived on location, which complicated the vessel’s maneuvering over the location coordinates. However, the ship soon steadied over the site’s coordinates, and the rig crew began picking up drill collars and making up the advanced piston corer (APC)/extended core barrel (XCB) bottom-hole assembly (BHA). All tubular joints were measured and drifted (internal diameter clearance checked) as they were made up into the drill string. By ~0300 h on 18 August, the drill string had been deployed to the seafloor.

Five holes were cored at Site U1422 using the APC and nonmagnetic core barrels (Table T1; see also Fig. F2 in the “Expedition 346 summary” chapter [Tada et al., 2015a]). Two holes were cored to 9.5 m core depth below seafloor (CSF-A) (see the “Methods” chapter [Tada et al., 2015b]) (one core each), one hole to 205.2 m CSF-A, one hole to 141.8 m CSF-A, and one hole to 111.6 m CSF-A. A total of 63 cores were required to obtain 502.6 m of sediment (105.2% recovery). The advanced piston corer temperature tool (APCT-3) was deployed four times.

Hole U1422A

Operations continued at Site U1422 as the drill string was tripped to 3425.0 meters below rig floor (mbrf). The top drive was picked up, and the pipe was spaced out for spudding Hole U1422A. A precision depth recorder reading for the site established a projected seafloor depth of 3450.4 mbrf. This was 4.4 m deeper than the predicted depth of 3446.0 mbrf for operations at this site. The bit was placed at 3446.4 mbrf, and Hole U1422A was started at 0340 h on the morning of 18 August. When recovered, the core barrel was full (9.96 m), preventing the possibility of determining an accurate seafloor depth. This ended Hole U1422A.

Hole U1422B

The vessel was offset 15 m north of Hole U1422A, and Hole U1422B was spudded at 0515 h with the bit placed at 3441.4 mbrf. Once again, the barrel was recovered full (9.67 m), necessitating a third attempt to establish mudline.

Hole U1422C

The vessel was offset 30 m south of Hole U1422B, and Hole U1422C was spudded at 0640 h with the bit placed at 3435.4 mbrf. When recovered, the barrel contained 4.64 m of core, establishing a seafloor depth of 3440.3 mbrf. Coring operations continued in this hole using full-length APC core barrels to 125.3 m CSF-A. Core 346-U1422C-14H required 90,000 lb of overpull, indicating that we would need to either drill over future core barrels or switch to the half APC system. Because of the success of the half APC system during the previous expedition (341), this was the tool of choice. Very successful half APC coring continued to a total depth of 205.2 m CSF-A. The top drive was set back, and the drill string was pulled clear of the seafloor at 1950 h on 19 August, ending Hole U1422C and beginning Hole U1422D. Total recovery for this hole was 215.78 m (105.2%). A total of 17 half APC cores were recovered. A total of 79.90 m of penetration was achieved with this system, recovering 86.2 m (107.9%). Four successful temperature measurements were taken using the APCT-3 temperature shoe on Cores 4H, 7H, 10H, and 13H at depths of 33.1, 61.6, 87.3, and 115.8 m CSF-A, respectively.

Hole U1422D

The vessel was offset 15 m west of Hole U1422A, and Hole U1422D was spudded at 2120 h on 19 August. The bit was placed 3 m lower (3438.4 mbrf) than it was for Hole U1422C. The mudline core contained 8.14 m of core, establishing a seafloor depth of 3439.8 mbrf. APC operations continued in this hole to 141.8 m CSF-A. At that time, the Co-Chief Scientists decided that spending further time on the hole would not be fruitful because of the increasing amount of turbidites recovered from the section. The top drive was set back, and the drill string was pulled clear of the seafloor at 1235 h on 20 August, ending Hole U1422D and beginning Hole U1422E. A total of 141.8 m of penetration was achieved, recovering 152.83 m (107.8%).

Hole U1422E

The vessel was offset 15 m east of Hole U1422A, and Hole U1422E was spudded at 1320 h on 20 August, establishing a seafloor depth of 3440.0 mbrf. Coring operations continued in this hole, recovering 14 APC cores to 111.6 m CSF-A. Two of these cores (346-U1422E-9H and 10H) were half APC cores in an attempt to recover a turbidite section of the formation where recovery had been problematic. Incomplete stroke on Cores 13H and 14H led to curtailment of coring operations for the site. Total recovery for this hole was 114.34 m (102.5%). The top drive was set back, and the drill string was pulled clear of the seafloor at 0420 h on 21 August. The drill string was recovered back aboard the vessel, the BHA was set back in the derrick, and the vessel was secured for transit. At 1142 h that same day, the vessel got under way for IODP Site U1423. This ended operations at Site U1422.

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