The 620-km transit to Site 1138 was made in 30.5 hr at an average speed of 11.0 kt. We arrived at Site 1138 on 7 January 1999. Weather conditions upon arrival were moderate. At 2334 hr on 7 January 1999, we deployed a beacon on the precise Global Positioning System coordinates for Site 1138.
We spudded Hole 1138A at 0445 hr on 8 January 1999. It was difficult to establish the seafloor depth because the driller did not feel a hard "tag" that could be identified as bottom. Based on recovery in the first core, a seafloor depth adjusted to the rig floor was established at 1153.0 m below rig floor (mbrf), equivalent to 1141.4 m below sea level. The 3.5-kHz precision depth recorder had indicated an adjusted seafloor depth of 1158.4 mbrf.
Continuous wireline coring proceeded in diatom clay, nannofossil clay, and nannofossil ooze through Core 183-1138A-28R to a depth of 266 mbsf. No chert was encountered. The formation then graded into nannofossil chalk with occasional chert layers. A hydraulic hose supplying the Varco top drive burst after recovering Core 183-1138A-58R from 553.6 mbsf. The ruptured hose was isolated, and a spare hose was connected in 2.25 hr. Coring continued through chalk with thin interbeds of nannofossil claystone and into reddish brown glauconite-bearing sandy packstone and brown clayey siltstone. After recovering Core 183-1138A-72R from a depth of 688.5 mbsf, coring operations were halted to wait on weather. The sea state had been deteriorating most of the day, and eventually excessive heave caused us to suspend coring in a force 8 gale. During this period swell conditions reached 9-10 m, seas were 3 m, vessel heave was 4-7 m, and the wind speed was 42 kt, gusting to 46 kt. The drill string was hung off on knobby drilling joints with the bit ~20 m above the bottom of the hole.
After waiting on weather for 16 hr, conditions improved enough to resume operations. An additional hour was required to remove the knobbies and run the pipe back to bottom. Total time lost because of the weather was 17.25 hr. Sediment coring was resumed and continued until Core 183-1138A-75R was recovered with a single hard rock jammed in the core catcher. The driller reported elevated pump pressures with the core barrel removed from the string. After four successive deployments of the bit deplugger, the last two of which were stuck briefly upon attempted recovery, coring resumed with pump pressures still abnormally high. A half core was cut and retrieved with nearly full recovery indicating that the bit throat had been cleared. Coring then continued without any additional problems. Acoustic basement was eventually contacted at ~700 mbsf in Core 183-1138A-74R. Basaltic basement was finally reached at the base of Core 183-1138A-79R at ~745 mbsf. Recovery averaged 49.8%, and the rate of penetration averaged 7.2 m/hr (ranging from 3.6 to 18.8 m/hr). Coring was terminated with the recovery of Core 183-1138A-89R from a depth of 842.7 mbsf. This was ~98 m into basaltic basement or ~123 m into acoustic basement and satisfied the scientific depth objective for this site. A total of 411.98 m of core was recovered from Hole 1138A for an overall average of 48.9%. Summaries of core numbers, depths, and recovery are given in Tables T1 and T2.
Further coring was suspended in the interest of conserving time for the remaining three primary drill sites. A variance was requested and received from the Ocean Drilling Program/Texas A&M University to forego wireline logging at the site because logging at the remaining three primary sites was deemed more important to the scientific objectives of the leg. As a result of deteriorating weather conditions, it was unlikely that logging could have been conducted in the hole without waiting on weather until the sea state and vessel heave abated. A test of the Lamont-Doherty Earth Observatory wireline compensator confirmed this when it tripped the 5-m limit switch twice, once after operating for 5 min and again after operating for 9 min.