Site 1160 is 241 nmi east-northeast of Site 1159. Our average speed during the 20-hr transit was >12 kt. At 1600 hr on 21 December, we began a 7-nmi south-to-north single-channel seismic (SCS) and 3.5-kHz survey across the prospectus Global Positioning System (GPS) coordinates. Based on our survey, a positioning beacon was dropped ~0.7 nmi north of the prospectus GPS coordinates in order to avoid rubble that might have shed off a seamount that flanks the southern side of our operations area.
Water depth at Site 1160 was determined by the precision depth recorder (PDR) to be 4636.4 m below the rig floor. The nine-collar bottom-hole assembly used on earlier sites was rebuilt, and a new C-7 four-cone rotary bit was made up to a mechanical bit release. We began drilling Hole 1160A by washing down through the sediment column to 166.0 meters below seafloor (mbsf) at an average penetration of 66 m/hr. When the driller noted a sharp decrease in penetration rate, we retrieved the wash barrel and began coring into basement. We advanced Hole 1160A by rotary coring from 166.0 to 171.1 mbsf (Cores 187-1160A-2R and 3R; Table T1) before we decided to abandon the hole be-cause of poor drilling conditions and <10% recovery. A tracer of fluorescent microspheres was deployed on Core 187-1160-2R. The drill string was pulled free of the seafloor at 1045 hr on 22 December.
After we offset 200 m farther north, we washed down through sediment at a rate of 43 m/hr to 160.1 mbsf. We rotary cored from 160.1 to 205.2 mbsf, retrieving eight cores (Cores 187-1160B-2R through 9R) with nearly 30% recovery. A tracer of fluorescent microspheres was deployed on Core 187-1160B-2R. Drilling conditions deteriorated while coring the last interval. Since we had achieved our nominal penetration depth and recovered a significant amount of core, we decided to conclude operations at Site 1160. The drill bit cleared the seafloor at 2330 hr on 23 December and the rotary table at 0545 hr on 24 December.
During operations at Site 1160, one of the hoses attached to the new active heave compensation system ruptured, and hydraulic fluid began streaming out of the cover that protects the hoses. This resulted in an intermittent stream of hydraulic fluid that, at times, poured onto the rig floor. This fluid flow was most pronounced when the top drive was high in the derrick (i.e., adding a new length of drill pipe to the string). Because cores are handled on the rig floor immediately after a pipe connection and the core was extracted from the core barrel while a steady rain of hydraulic fluid blanketed the core handling area, some pieces of core may have come in contact with hydraulic fluid. Since all cores were pulled from the core barrel inside a plastic liner that was not split until it was on the catwalk, the bulk of the material we recovered was protected. The only exceptions are the few pieces of core that were in the core catcher, which was removed from the core barrel on the rig floor. These pieces were inspected for evidence of hydraulic fluid, and none was recognized. Nonetheless, samples from the last few centimeters recovered from each core barrel might have been contaminated. As soon as operations were concluded at Site 1160, the hoses were disconnected, so it is unlikely that any material recovered after Site 1160 was affected.