Because of long-period swell (~3 m high) and the resulting heave, which averaged 1.5 m with excursions over 2.0 m, operations in water depths less than 300 m were precluded. Thus, we proceeded to alternate proposed site GAB-08A. The 46-nmi transit required 4.6 hr at an average speed of 10.0 kt. A beacon was launched at 1338 hr on 16 November, initiating Site 1131. A second beacon was deployed, as required for shallow-water operations.
The ship was stabilized on position, and an advanced hydraulic piston corer/extended core barrel (APC/XCB) bottom-hole assembly (BHA) was run to the seafloor. Hole 1131A was spudded at 1605 hr on 16 November. The bit was positioned at 339 meters below rig floor (mbrf), and Core 1H recovered 3.39 m, indicating a water depth of 333.4 meters below sea level (mbsl). Advanced hydraulic piston coring advanced to 60.4 meters below seafloor (mbsf) (Table T1). Cores 3H-7H were oriented, and an Adara tool heat-flow measurement was made during Core 4H. A nonmagnetic cutting shoe and a steel 10-finger core catcher were run on Cores 3H, 5H, and 7H (see "Appendix: Magnetics Experiment"). Recovery of Core 7H required 70 kips overpull; therefore, APC coring was terminated in favor of the XCB system. Hydrogen sulfide (H2S) (86 ppm; headspace analysis) was detected in Core 4H (26.9 mbsf). Hydrogen sulfide alert procedures were implemented, including use of breathing apparatus. Hydrogen sulfide concentrations reached a maximum of 156,600 ppm in a vacutainer sample (359.6 mbsf), but ambient air readings remained below 10 ppm. No H2S was detected below Core 56X (>511.3 mbsf)
Extended core barrel coring advanced from 60.4 to 616.9 mbsf with 56.3% recovery (Table T1). Recovery was minimal below 540.2 mbsf in presumed mixed chalk and chert, and five XCB hard-formation shoes were destroyed. Hydrocarbon gases up to C5 were detected beginning with Core 38X (338.3 mbsf), and the coring rate was controlled to allow proper gas monitoring. However, C2+ volumes were extremely low and subsequently diminished downhole; C1/C2 varied primarily as a function of methane fluctuation (see "Organic Geochemistry"). Coring was terminated near the depth objective because of poor recovery in cherts.
Hole conditions appeared to be excellent, and the bit was pulled to 102 mbsf without a conditioning trip for logging. Logging tools were run in the following order (depths of penetration are included): (1) triple combination logging tool (triple combo) from 578 mbsf, 39 m off bottom, to the mudline in two passes; (2) Formation MicroScanner (FMS)/sonic from 573 mbsf to the end of pipe; and (3) well seismic tool (WST) tool from 567 mbsf to the end of pipe, recording eight check-shot stations. With an improving forecast and diminishing long-period swell, continued operations at Site 1131 were postponed for a return to Site 1129. After plugging the hole with mud, the drill string was retrieved, both beacons were recovered, and the rig was secured for transit at 1800 hr on 19 November, ending Hole 1131A.
The ship was moved in dynamic positioning mode from Site 1129 back to Site 1131 to complete a second APC/XCB hole. The 2-nmi transit required 1 hr at 2 kt. A beacon was dropped at 0335 hr on 20 November, and the ship was positioned ~40 m north of Hole 1131A.
Hole 1131B was spudded at 0545 hr on 20 November. The bit was positioned at 342.0 mbrf, and Core 1H recovered 8.40 m, which indicated a water depth of 331.4 mbsl. Advanced hydraulic piston coring advanced to 65.4 mbsf with 94.0% recovery (Table T1). Cores 3H-7H were oriented and an Adara tool heat-flow measurement was taken on Core 6H. The nonmagnetic shoe and flapper core catcher with a steel 10-finger core catcher were deployed on Cores 3H, 5H, and 7H (see "Appendix: Magnetics Experiment"). Hydrogen sulfide was detected in Core 5H at 46 mbsf, and H2S alert procedures were implemented. Extended core barrel coring extended the hole from 65.4 to 105.8 mbsf with 83.3% recovery (Table T1). A Davis-Villinger temperature probe (DVTP) was deployed after Core 12X at 105.8 mbsf. We plugged the hole with mud, recovered the beacon, and secured the rig for transit; the vessel was under way for Site 1132 at 1730 hr, on 20 November.