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doi:10.2204/iodp.proc.303306.103.2006

Operations

Expedition 303 officially began with the first line ashore at St. John’s, Newfoundland, at 0628 h on 25 September 2004. The port call, which included an underwater hull inspection for the American Bureau of Shipping and extensive refueling, concluded when the last line was released at 1925 h on 30 September 2004. We completed the 276 nmi transit from St. John’s to Site U1302 at an average speed of 8.8 kt, traveling into a 20–25 kt headwind for most of the transit.

Site U1302

Hole U1302A

We arrived at Site U1302 at 0330 h on 2 October 2004 and spudded Hole U1302A at 1530 h. The recovery in the first core (only 50 cm) suggested a seafloor depth at 3568.6 meters below sea level (mbsl) (3579.4 meters below rig floor [mbrf]) or 5 m deeper than the corrected precision depth recorder depth (see “Hole U1302D” and “Hole U1302E” for more realistic seafloor depth estimates). Piston coring utilizing nonmagnetic core barrels advanced to 107.1 mbsf (Cores 1H through 13H) (Table T1), where detrital gravel caused problems with penetration and hole stability. An attempt was made to clean out the hole and continue coring, but hole stability problems persisted. Hole U1302A was terminated when the bit cleared the seafloor at 1245 h on 3 October. Additional operations included core orientation starting with Core 4H and two deployments of the advanced piston corer (APC) temperature tool at 76.1 mbsf (Core 9H) and 104.6 mbsf (Core 12H). The latter attempt was unsuccessful because the cutting shoe and associated electronics were damaged by hard debris. In Hole U1302A, we cored 107.1 m, recovering 91.7 m (85.6%); recovery may have been affected by heave as large as 3 m.

Hole U1302B

After offsetting the vessel 30 m to the northwest of Hole U1302A, Hole U1302B was spudded at 1340 h on 3 October 2004. With only 50 cm of recovery in Core 303-U1302A-1H, the bit was positioned 4.5 m above Core 303-U1302A-2H to achieve a good mudline core. A full core was obtained (Table T1) that did not establish the mudline. Piston coring advanced to 104.7 mbsf, recovering 102.82 m (98.2%). Hole U1302B was terminated when the APC partially stroked in the debris interval. The Tensor tool was run for core orientation beginning with Core 3H. The bit cleared the seafloor at 0200 h on 4 October, ending operations in Hole U1302B.

Hole U1302C

The vessel was offset 30 m to the northwest again, penetrating the seafloor at 0330 h on 4 October 2004, initiating Hole U1302C. Correlation of Hole 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 1H, suggesting that an additional section remained unsampled. Hole U1302C was advanced to 104.5 mbsf, recovering 97.06 m (92.9%) before refusal was experienced at Core 11H. Core orientation proceeded with Core 3H. Operations in Hole U1302C ended when the bit cleared the seafloor at 1540 h on 4 October.

Hole U1302D

The vessel was offset 30 m to the northwest and Hole U1302D was spudded at 1625 h. To attempt complete recovery of the upper section, the bit was positioned 9.5 m above the position of Hole U1302C. 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 13% (1.24 m) was recovered. With the poor recovery in Core 2H, we chose to move to Hole U1302E to ensure complete recovery of the upper section.

Hole U1302E

The ship was offset 30 m to the northwest, and the bit was positioned 4.5 m lower than in Hole U1302D. Hole U1302E was spudded at 1910 h on 4 October 2004, and a 5.6 m core was recovered, which was less than we anticipated based on bit position and recovery in Core 303-U1302D-1H. Sea state and vessel heave may have affected bit position during spudding. The seafloor depth based on recovery and bit position for this hole is 3558.1 mbsl (3568.9 mbrf). Core 2H (recovery = 94.6%) was taken to provide additional material for overlap with previous holes (see “Composite section”). The drill string was pulled to 2095 mbrf in preparation for transit in dynamic positioning (DP) mode, ending operations at Site U1302 at 2215 h on 4 October.

Site U1303

Hole U1303A

The 3 nmi transit from Site U1302 to Site U1303 was made in DP mode in 3.75 h. Hole U1303A was spudded at 0445 h, recovering 8.43 m, suggesting a seafloor depth of 3524.2 mbsl (3535 mbrf). The hole was advanced to 93.9 mbsf (Cores 1H through 10H) with 73.6% recovery (Table T1). 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 h, ending operations in Hole U1303A.

Hole U1303B

The ship was offset 40 m southeast and Hole U1303B was spudded at 1849 h on 5 October 2004. The bit was positioned 15 m shallower than in Hole U1303A because correlation to Site U1302 indicated that a substantial upper section was not recovered in Hole U1303A. This first attempt recovered no core, so the bit was positioned 9.5 m lower, recovering 9.62 m in Core 1H and indicating a seafloor depth of 3517.9 mbsl (3528.7 mbrf). The hole was cored to 85.7 mbsf (Cores 1H through 9H) with 83.5% recovery. Cores were oriented starting with Core 3H. The hole was terminated when the same difficult-to-core interval from Hole U1303A was encountered. With the combined recovery at Sites U1302 and U1303 sufficient to produce a composite record (see “Composite section”), we decided to end coring and proceed to the Eirik Drift sites. The drill string was retrieved to the rig floor and the ship was made ready for transit at 1315 h on 6 October, ending operations at Site U1303.