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doi:10.2204/iodp.pr.310.2006

OPERATIONS

Mobilization of the Hunter

Mobilization of the drilling platform Hunter took place in two stages: the first stage was in Tampa, Florida (28 August–5 September 2005) and the second stage during the port call in Papeete, Tahiti (5–6 October 2005).

The first mobilization stage involved shipping of contractor drilling equipment and ESO laboratory and ancillary equipment to Tampa from Europe. After all the equipment had arrived and cleared customs, the vessel came on charter and was converted into a drilling vessel in just over 6 days. The Tampa Bay Shipyard Company provided port services, welders, and crane drivers. Seacore engineers carried out all engineering work, rig building, and certified the load testing of key structures. During the period of rig construction, ESO staff from the British Geological Survey (BGS) unloaded equipment from containers, set up a shipboard computer network, and connected power and water services to laboratories. They also made safe the walkways and core inspection areas on board with the drilling contractor. The ESO Operations Superintendent was also responsible for overseeing the entire load testing of key structural components of the rig. Verification of these milestone points was required to trigger contract stage payments. During this period of mobilization, we were pleased to receive a visit from Dr. Manik Talwani, President of IODP Management International Inc. (IODP-MI) and Dr. Jamie Allan of the U.S. National Science Foundation.

Mobilization work continued on passage to Panama (5–13 September 2005), where ESO personnel disembarked. Some Seacore personnel continued on the passage to Tahiti, completing mobilization activities en route (13 September–5 October).

The second stage of mobilization took place on 5–6 October 2005 during the port call in Papeete. Some air freight items for the expedition were taken on board during the port call; winches for logging and some equipment for the microbiology laboratory were loaded on deck. For this stage of mobilization, the complete ESO team was available. All laboratories and office spaces were networked with computers, the Drilling Information System (DIS) database system was set up, onboard equipment was laid out, and a satellite-based e-mail system was installed.

At 0900 h on 6 October, the Expedition 310 Scientists joined the Hunter. A visit to the Hunter was arranged for local schoolchildren and the press for 1 h in the morning. By 1830 h, mobilization was complete and the vessel commenced day rate operations. The Hunter departed for the first site at 1930 h on 6 October, after spending 36 h in port.

The Hunter arrived at Site M0005 at 2330 h on 6 October 2005 and immediately conducted dynamic positioning calibration tests ~250 m south of the first hole, M0005A. By 0250 h on 7 October, the vessel was positioned above Hole M0005A.

Hole M0005A

After overcoming problems with a hydraulic ram which caused the moonpool doors to fail to open, Seacore's Drilling and Reentry Template (DART) was deployed on American Petroleum Institute (API) drill string (used as conductor pipe for this expedition) to just above the seabed. From 1335 h on 6 October, a seabed survey around the position of the first site was conducted using the downpipe underwater camera. A suitable site was located ~2 m from the planned position, and the DART was placed on the seabed with 8 tonnes of weight. After removing the camera, the HQ (piggyback) drill string was run through the API conductor to the seabed, and coring operations in Hole M0005A commenced. The first core arrived on deck at 2000 h. Thereafter, coring continued with difficult barrel latching, and short core runs were used to avoid drilling rather than coring until the best coring parameters were established. The first cores displayed large cavities, and recovery was poor. Core barrel jams and problems with blocked bit–related mislatching led to slow progress in this hole. When reentering the hole after one particular drill string trip to remove a core blockage from the bit, coring appeared to recommence at 10.4 m. Good core was obtained, and it appeared that the borehole may have been restarted in a deviation or had avoided a previous deviation. This was taken as the start of a new hole, M0005B, at 1840 h on the 8 October.

At 0140 h on 9 October 2005 at 20 m depth, the core barrel failed to latch in. A replacement barrel also failed to latch. The hole was verified clear by the chisel tool. It was suspected that the HQ pipe was bent, and the string was tripped. On deck, the third and second pipe stands (four joints) of the HQ drill string were bent. The decision was made by all to terminate Hole M0005B, not to log, and make modifications to the DART before continuing with a new hole. The downpipe camera was prepared, and an environmental impact inspection of the coring area was carried out by raising the DART from the seabed and lowering the camera through the DART. There was difficulty in identifying the drilling area due to minimal impact of the DART on the seabed. The camera was recovered and the inspection was completed by 0615 h on 9 October.

Starting at 0615 h on 9 October, the API string was tripped and the DART was brought on deck and secured above moonpool. The vessel departed Site M0005 and headed for a nearby sheltered bay to carry out work on the DART. The DART feet were removed and a stinger was installed. The vessel departed the sheltered bay and was back at Site M0005 by 1330 h.

The Hunter took position above Hole M0005C, ~10 m east-southeast alongslope from Holes M0005A and M0005B, and was ready for operations by 1510 h on 9 October 2005. When lowering the DART on the API string, a burst hydraulic union on the rig hydraulics caused an operational shutdown until the oil spill on the deck was contained and repairs were made. At 1835 h, the downpipe underwater camera was deployed for a predrilling site check, and the stinger was engaged with the seabed under camera observation. The DART was drilled 1.3 m into seabed and stabilized ready for the coring string. The HQ coring string was run at 2000 h, and coring operations commenced in Hole M0005C. At 0545 h on 10 October, sand in the drill string caused the core barrel to jam and the string had to be tripped to free it. At 1110 h, the vessel requested a heading change, which was carried out with the HQ string off bottom but still in the hole. After the heading change, the core barrel was unable to be run into the HQ string and it was observed that the API pipe was not central in moonpool. The HQ string was tripped, and nine stands were removed with bends. A problem with the dynamic positioning system analyzed and resolved before resetting the DP to average the previous drilling position. At that position, the downpipe camera was run at 1515 h to see if the HQ hole was still in the stinger. No HQ hole was apparent, but the decision was made to trip the HQ string with an insert bit and drill down to the previous depth. Reentry into the earlier borehole was not confirmed, even though the template had not moved, so a new hole (Hole M0005D) was started.

Coring commenced in Hole M0005D at 2330 h on 10 October 2005. Coring was steady and recovery moderate to good throughout the day on 11 October. At 0510 h on 12 October, the decision was made to stop coring in Hole M0005D after reaching 102 mbsf and without reaching the basaltic basement. The HQ string was pulled and the logging tools were prepared.

At 0750 h on 12 October, the DIL45 (electrical resistivity) tool was lowered but got stuck just below the seabed. It was suspected that the top of the hole was unstable, within a zone of low recovery noted while drilling. The top 5 m of the hole was cased with HQ pipe. The DIL45 tool was lowered but was still unable to enter the hole from the pipe. The HQ pipe was run all the way to the base of the hole, a spectral gamma log was run inside the HQ pipe, and then, after ensuring that the pipe was free from obstruction, the HQ pipe was pulled back in 25 m increments and logging was conducted in the open hole below the pipe.

Logging operations in Hole M0005D continued with excellent logs being obtained until the hole finally collapsed after pulling back the HQ pipe to 17 m below the seabed. The logging tools were in danger of becoming stuck in the top-hole section and were retrieved. After a heading change, the remaining HQ pipe was pulled, the DART was lifted, and operations in Hole M0005D ceased at 1310 h on 13 October. A postdrilling seabed survey using the downpipe camera was conducted before leaving the hole.

Before departing Site M0005, four hammer samples were taken in Hole M0005E (~5 m alongslope from Hole M0005D in 61.34 m water depth). Four samples were taken to a depth of 2 m below seabed, with typically 80% recovery. After curation, these samples were handed to the microbiologists to sample at will, before the remainder was passed to the sedimentologists and coral specialists for description. Operations in Hole M0005E were concluded by 1635 h on 13 October 2005. Before progressing to the next site, the Hunter conducted a 360° maneuver to verify that positioning offsets at the drill string were zero.

A move to deeper water (~80 m) was undertaken, and the Hunter was repositioned above Hole M0006A in 81.58 m water depth. Another four hammer samples were collected, primarily for microbiology, before the drill string was lowered onto what appeared to be a very steep slope. Both the ship's transponder and tautwire indicated that they were sliding downslope and suggested that the bathymetric data were insufficient to allow a reasonable picture of the seabed. Any slope instability may have led to the DART sliding away downslope, and the decision was made to avoid the outer reef edge until either more seabed information was obtained or modifications were made to the DART to allow greater stability on steep slopes. Site M0006 was departed at 2300 h on 13 October 2005.

Hole M0007A

Hole M0007A was located farther back from the reef edge than Sites M0005 and M0006, in 44.45 m water depth. The seabed was surveyed using the downpipe camera, and at 0330 h on 14 October 2005, four hammer samples were taken. After hammer sampling, the HQ string was run and rotary coring commenced in the same hole. Coring continued with good recovery for the rest of the day. Total depth (TD; 44.4 m) was reached at 0120 h on 15 October.

Prior to tripping the HQ pipe, the gamma tool was run inside the pipe. Logging results from Hole M0005D indicated that the shape of the gamma trace through the pipe, when scaled accordingly, did not differ significantly when compared to the open hole trace, although statistically the results are less useful. After gamma logging, the HQ pipe was tripped, the core barrel removed, and the string rerun with a casing shoe to 7.5 m below seabed. Open hole logging commenced from TD to the casing shoe. After running the resistivity and hydrochemical tools in the open hole section, the acoustic imaging tool would not progress much beyond the casing shoe, despite being run with a sinker bar. Logging was terminated in Hole M0007A at 0700 h on 15 October.

After a postdrilling seabed survey using the downpipe camera, the Hunter moved 50 m alongslope to Hole M0007B. Two hammer samples were collected before rotary coring commenced in the same hole. Core recovery was poor in the top part of the hole, and the coring parameters were checked for any changes that may have been responsible. Zero bit weight and high rates of penetration confirmed that an open structure was being drilled. The formation became more compact with depth, and recovery improved accordingly. Coring continued until 0630 h on 16 October 2005.

The HQ pipe was tripped and a casing shoe fitted before the pipe was rerun to the base of the hole for in-pipe gamma logging. After gamma logging, the HQ pipe was pulled to 24.6 m below seabed, and resistivity, hydrochemical, acoustic imaging, and optical imaging tools were run. It was not possible to log the entire bottom-hole section due to hole blockage (below 30 m below seabed). Logging in Hole M0007B was completed by 1410 h on 16 October. The remainder of the HQ pipe was pulled, and a seabed survey using the downpipe camera was conducted. The survey showed that the DART had been drilled well into the seabed (1.5 m) and had left a shallow debris-filled depression. However, the surrounding seabed showed minimal disturbance from the drilling. The DART was then lifted onto the deck through the moonpool and secured.

At 1700 h on 16 October 2005, the vessel departed Site M0007 and headed for Site M0008, located on transect TAH-02A off the northeast coast of Tahiti, arriving at 2400 h.

Shortly after arrival at 2400 h, a seabed survey using the downpipe camera was conducted. At 0400 h on 17 October 2005, coring operations began in Hole M0008A. This hole was to serve as a reference hole for the other holes on the transect. However, the material recovered consisted of river deposits of unconsolidated basalt gravel and pebbles mixed with volcaniclastic sediments. As a result, recovery was poor throughout (24.5%). TD was reached at 40.2 m below seabed, and operations ended in Hole M0008A at 1720 h on 17 October.

Hole M0009A

An assessment was made of where to drill next, in light of the results obtained in Hole M0008A. It was decided to attempt to drill the pinnacle at proposed Site TAH-02A, #4 on seismic Profile SISM 079. Acknowledging that the feature imaged on the seismic line may be the result of sideswipe and may possibly be located off the seismic line, a localized search was made for a suitable drilling location using the ship's echo sounder and the tautwire to detect a shallower than expected water depth. No suitable position was located, and at 2100 h on 17 October 2005, the vessel was positioned above a flat terrace (Hole M0009A) nearby and drilling operations commenced and continued until 1915 h on 18 October. Recovery was moderate to poor (43.1%) to TD of 23.04 m below seabed. However, promising coral material was recovered and it was decided to attempt to recover the same section in a new hole nearby. By 2000 h, the HQ pipe had been recovered and the DART lifted off the seabed, and by 2015 h the vessel was positioned above Hole M0009B, ~5 m downslope from Hole M0009A. Coring operations commenced and continued until 1200 h on 19 October, with an improved recovery of 66.26%.

Prior to logging Hole M0009B, the hole was reamed. Logging began at 1530 h on 19 October 2005 with the resistivity and hydrochemical tools run in open hole over the interval 6–21 m below seabed. A hole blockage near the postglacial/Pleistocene boundary, which resisted attempts to clear with the chisel tool, prevented the tools from being run below ~21 m below seabed. Optical image logs were collected from 6 to 18.1 m below seabed, and acoustic image logs were collected between 6 and 13.8 m below seabed. Logging of Hole M0009B was concluded by 2320 h on 19 October.

Just before 0000 h on 20 October 2005, the Hunter moved to Hole M0009C, ~9 m west-northwest of Hole M0009B in 99.85 m water depth. Coring commenced and continued until 1935 h that day, reaching a TD of 25.66 m. Coring in Hole M0009C proved very difficult, with many bit blockages and crushed liners resulting from pieces of the formation breaking off and entering the core barrel, having not been properly cored. The lattice drilled was not strong enough to core and, in many cases, had to be crushed for progress to be made. Recovery improved toward the base of the hole, and the total core recovery was 51.86%. At 1935 h, the hole was completed and preparations made to move to Hole M0009D.

The Hunter was positioned above Hole M0009D, 5.5 m east of Hole M0009B in 103.18 m water depth, and coring began at 2210 h on 20 October 2005. Coring in Hole M0009D continued until 2230 h on 21 October to a TD of 44.59 m. Progress was steady, but core runs were short and bit blocking common. After TD was reached, preparations were made to log the hole.

Prior to logging the hole, the hole was reamed and flushed for 30 min. The HQ string was pulled and set with a casing shoe at 19 m below seabed to run the logging tools through the open hole section. Logging commenced at 2230 h on 21 October in very wet and windy conditions. This, combined with very poor hole conditions, led to a difficult logging period. Nevertheless, good logs were obtained in sections of open hole where it was possible to log. A hole blockage prevented the resistivity tool from reaching the base of the hole, and the chisel tool was used to clear the blockage. The resistivity, spectral gamma ray, and acoustic tools were run. However, large, meter-scale cavities in the formation created sticking points for some of the tools; thus, only some of the open bottom-hole interval was logged. The first optical image tool run was affected by power failures on the drill rig, possibly caused by very heavy rainfall. Logging was temporarily interrupted while the cause of the power failures was investigated. After these runs, the casing was pulled to 5 m below seabed. The top-hole section was logged with the resistivity and optical image tools, with cavities causing problems for the optical tool. While logging uphole, the optical image tool became stuck many times and needed to be pulled through obstructions by hand. Logging operations were completed by 1000 h on 22 October, and preparations were made to move to Hole M0010A.

The Hunter was positioned above Hole M0010A by 1400 h on 22 October 2005, ~140 m east-southeast of proposed Site TAH-02A, #4 in 89.53 m water depth. The DART was drilled into the seabed, and coring operations began at 1635 h. Coring continued until 1000 h on 23 October to a TD of 34.6 m below seabed. During the coring period, an HQ string trip was made to clear a continually blocking bit.

Hole M0011A was located ~140 m east of proposed Site TAH-02A, #4 in 101.34 m water depth. After running the API pipe, drilling the DART into the seabed, and running the HQ pipe, coring operations began at 1330 h on 23 October 2005. Coring commenced in very soft silts with poor recovery, but this improved when the river deposits gave way to a carbonate framework. At 0030 h on 24 October, coring operations were completed in Hole M0011A at a depth of 17.65 m below seabed.

Hole M0012A was the first of three holes to be located within the new EPSP-approved zone southeast of proposed Site TAH-02A, #4. Before the DART was lowered onto the seabed, a downpipe camera survey was run which showed a live coral colony at the first location. The ship was repositioned 25 m downslope in 77.05 m water depth, and the DART drilled in. Coring operations began om Hole M0012A at 0900 h on 24 October 2005. Recovery was generally poor, although it did improve in the more competent material at the base of the hole. Coring was completed at 2040 h on 24 October at a TD of 34.1 m.

Hole M0013A was located 30 m downslope from Hole M0012A, in 90.95 m water depth. The Hunter was positioned above the hole at 2300 h on 24 October 2005. After the API pipe and DART were lowered to the seabed, a seabed camera survey was conducted. Coring operations began at 0100 h on 25 October. At 0415 h, coring was abandoned due to the lack of suitable coral material. TD of the hole was 11.7 m.

Hole M0014A was spudded ~70 m north-northwest of Hole M0013A in 99.25 m water depth. Coring operations began at 0610 h on 25 October 2005 and were completed at 1615 h at a TD of 15.43 m. The HQ string, API pipe, and DART were lifted onto deck and secured for the transit to previous Site M0007 at the south end of the island.

Poor weather was forecast for north of the island, and so the decision was made to revisit promising sites in the south. The transit commenced at 1930 h, and Site M0007 reached at 0200 h on 26 October 2005.

Hole M0007C

Prior to coring Hole M0007C, a seabed camera survey was conducted which revealed a surprisingly barren sloping seabed in 43.35 m water depth. Coring operations began at 0315 h and continued until 2215 h. The hole progressed quickly, with core recovery generally poor and little formation resistance being evident on the bit. At ~30 m below seabed, the hole started to become sticky and then collapsed during a wireline trip, filling the outer core barrel with cuttings. The string was tripped, the barrel cleaned out (2 m of coral cuttings), and the HQ string rerun with an insert bit as the inner core barrel. The base of the hole was reached with difficulty, where rotation also became difficult. The string stuck a few times, and the hole was abandoned at a TD of 32.25 m.

After completing Hole M0007C, ~300 m to the northwest, the Hunter moved to Site M0015 in 72.15 m of water. After a short bathymetry traverse to locate a site for the hole, drilling operations began at 0030 h on 27 October 2005 and continued until 0325 h on 28 October. TD was 42.28 mbsf. There was generally good core recovery, with usually <1 m core runs between bit blocking and 72.71% average recovery for the hole.

Prior to logging, Hole M0015A was reamed and flushed for 1 h, after which the core barrel was removed and the drill string rerun with a casing shoe. Logging commenced at 0630 h on 28 October. Initially, the casing depth was set at 7 m but the logging tools would not pass downhole beyond 20 m, so they were removed and the casing run to the base of the hole then pulled back to 20 m. Logging then was possible in the bottom part of the borehole, but one tool was stuck for a while and had to be eased free with the downhole hammer. Thereafter, logging continued successfully, the casing was pulled back to 7 m, and the remainder of the hole logged with overlap. Logging operations in Hole M0015A were completed by 1930 h on 28 October. The string was then tripped to deck and the DART lifted off seabed.

Hole M0016A

After moving to new Site M0016, a tautwire bathymetry traverse was conducted to locate a site for Hole M0016A. By 2400 h on 28 October 2005, the Hunter was positioned above Hole M0016A in 80 m water depth. Shortly after midnight on 29 October, coring operations began. Throughout the day, coring continued with fairly poor recovery, and drilling indicated that the formation had many cavities. Coring in Hole M0016A was terminated at 0620 h on 30 October at a TD of 38.31 m. This was due to difficulty in overcoming bit blocking and, after a string trip to clean the whole core barrel system, the HQ inner barrel could not reenter the outer pipe because to the string was bending. It is most likely that the DART had moved on the seabed, possibly through subsidence.

Hole M0016B was located 5 m east of Hole M0016A. Initially, the noncoring insert bit was used to drill to 17 m below seabed and then coring continued with variable but generally good core recovery. Coring operations ended at 0230 h on 31 October 2005 at a TD of 44.62 m.

After moving to previous Site M0006, a tautwire site survey was conducted along a short transect. This survey was abandoned after the DART touched down on the seabed unexpectedly, indicating that the bathymetry for this area was not accurate. After running the downpipe camera to check for stinger damage and lifting the DART higher from the seabed, a new tautwire survey was conducted 10 m east of the previous transect. A suitable site was found, but when the DART was lowered it touched the seabed 2 m deeper than indicated by the tautwire. The topography of the seafloor was suspected to be very uneven at this survey location, so a new survey transect was initiated 10 m to the east. During this survey, the DART unexpectedly touched seabed again. The seabed depth at Site M0006 appeared to change rapidly, and the changes were not evident on the bathymetry data. Therefore the search for a new site was abandoned, the DART lifted into the moonpool, and the Hunter returned to previous Site M0015.

Hole M0015B

The Hunter moved back to previous Site M0015 to start new Hole M0015B in 71.53 m water depth. Coring operations began at 1330 h on 31 October 2005 and were completed by 1730 h on 1 November at a TD of 40.12 m. Because very short core runs were being achieved in the lower part of the hole and most liners were being crushed, the last four or five runs were made using the split chromed steel liners commonly used elsewhere for this type of coring. The immediate result was longer core runs before jamming, better core recovery, and improved preservation of delicate structures. Some horizons which would previously have been crushed were kept intact or kept in their correct cored position.

Hole M0017A was located ~60 m north of Hole M0015B in 56.5 m water depth. Before touching down with the DART, a seabed camera survey was run to check for living corals. None were observed, and so coring operations began at 2300 h on 1 November 2005. A faster penetration rate was achieved using the steel split liners, giving the drillers a much more sensitive indicator of bit blocking. As a consequence, they were able to detect bit blocking much quicker and were sometimes able to avoid it. This meant that the core runs were longer and the number of wireline trips reduced. Core recovery also improved. No problems were encountered with the subsequent curation or science through the use of steel split liners. Coring was completed by 1600 h on 2 November at a TD of 40.56 m.

Prior to logging Hole M0017A, the hole was flushed. There was some difficulty with a stuck HQ pipe while trying to trip the drill string, which could be rotated but not uplifted. The string eventually came free. A casing shoe was fitted for the logging operation. Logging commenced in Hole M0017A at 2130 h on 2 November and was completed by 0350 h on 3 November. Resistivity, acoustic imaging, optical imaging, hydrochemical, caliper, and sonic tools were run. The starting depth of the tools varied because the tools caught in cavities (between 31.55 and 23.23 mbsf) and the depth of the casing pipe was 13.35 mbsf. The core barrel fishing cable was used on one occasion to pull the sonic tool, which was stuck just below the casing, up to the surface. This process damaged a portion of the logging winch cable, which was cut at ~85 m. Reheading of the winch cable was completed well before the next logging operation.

A short echo sounder survey (30 m x 20 m grid) was conducted ~120 m south-southeast of proposed Site TAH-03A-1 to locate a suitable site for Hole M0018A. At 0915 h on 3 November 2005, the DART was lowered at the chosen site and touched the seabed 14 m deeper than suggested by the echo sounder survey. The specific site was resurveyed using the lead-line, and a new site chosen nearby. The DART was unable to be drilled-in at this site at first (a solid carbonate crust was evident on the camera survey) but was successfully drilled in on the second attempt (after the crust was broken by the stinger?). At 1640 h on 3 November, coring operations began in Hole M0018A and continued until 1200 h on 4 November. TD of the hole was 40.05 mbsf, with a total recovery of 61.50%. The nature and quality of the material collected indicated that most of the coreable material was being collected. A camera survey was conducted after withdrawing the drilling equipment from the hole. No undue disturbance was observed, although there was a significant mound where the DART was situated with a slight "tail" of (?)cuttings coming from it and going down the presumed slope.

Prior to departing the Maraa area, the tautwire was respooled and the DART lifted onto the deck of the Hunter and secured. Once on deck, the stinger below the DART was found to be missing, and a new stinger was fitted. The vessel departed the Maraa area at 1750 h on 4 November 2005 and arrived at the Faaa area at 2030 h.

On arrival at Faaa, the Hunter was positioned above Hole M0019A (~31 m south of proposed Site TAH-01A, #3) in 58 m water depth. All clearances with airport and seaport authorities were double-checked before occupying the new location, which was closest to the visible reef so far. A seabed camera survey was run, and no live corals were observed. The DART was lowered and drilled in, and coring operations in Hole M0019A began at 2320 h on 4 November 2005. Coring was completed at 2400 h on 5 November at a TD of 66.96 mbsf and with a total recovery of 41.12%. Penetration was rapid but recovery was poor. Checks of the Jean Lutz automatic drilling recorder data confirmed the driller's view that there were significant void spaces throughout. When penetration rate reduced to below 10 m/h, indicating more solid material, core was usually obtained.

Prior to coring Hole M0020A, the DART was retrieved and a short echo sounder survey was conducted 50 m north of Hole M0019A to locate a site for Hole M0020A. The chosen site was checked using the tautwire, and the DART and drill pipe were deployed in 83 m water depth. Coring operations began in Hole M0020A at 1200 h on 6 November 2005 and continued until 1220 h on 7 November to a TD of 42.16 m. Total recovery was 70.45%.

The vessel departed the Faaa area at 1320 h on 7 November 2005 and arrived in the Tiarei area at 1610 h.

An echo sounder survey (five profiles) was conducted over suspected drowned reefs near to the foreslope imaged on the bathymetry. The water depth was confirmed at two locations using the tautwire. After a seabed camera survey, the DART was drilled in at one of these locations, ~115 m southeast of proposed Site TAH-02A, #5 in 82 m water depth. Coring operations began in Hole M0021A at 2200 h on 7 November 2005 and continued until 1640 h on 8 November. TD was 34.23 mbsf and total recovery was 74.87%. Good core recovery confirmed that the submerged pinnacle is a drowned reef.

Hole M0009E

After coring in Hole M0021A was completed, the HQ pipe was lifted and the DART raised to 45 mbsl. The vessel moved 90 m northwest to previous Site M0009, where a site for Hole M0009E was chosen in a water depth of 93 m. The DART was lowered and drilled in, and coring operations in Hole M0009E began at 2030 h on 8 November 2005. Coring was completed at 0550 h on 9 November at a TD of 20.61 m and with a total recovery of 72.73%.

Prior to logging, the hole was flushed and the HQ pipe pulled and rerun with a casing shoe. From 0715 h on 9 November, Hole M0009E was logged between ~2 and 15 m below the seabed. The chisel tool was deployed once to clear a blockage at 6 mbsf. After logging was completed at 1440 h, the HQ pipe was tripped and the DART raised into mid-water.

The Hunter was positioned above Hole M0022A, ~175 m north-northwest of proposed Site TAH-02A-4 in 115 m water depth. After checking the depth with the tautwire, the DART was drilled in and coring commenced at 1750 h on 9 November 2005. It was hoped that the hole would penetrate a Pleistocene gulley which may been subsequently accreted by postglacial corals. Basalt gravel and volcaniclastic sand of Pleistocene affinity were recovered from a shallow depth, and so Hole M0022A was abandoned after 8.8 m penetration at 2310 h on 9 November. By midnight, preparations were being made to trip the API pipe and DART.

Hole M0023A

From 0000 h on 10 November 2005, the DART was raised to the moonpool after abandoning coring in Hole M0022A. The Hunter moved to a new area over a drowned reef to conduct an echo sounder survey, ~100 m southwest of proposed Site TAH-02A, #4. From 0200 h on 10 November, 9 m x ~110 m echo sounder traverses were made over the drowned reef pinnacle, from which a site for Hole M0023A was chosen in 67 m water depth. After a short camera survey, coring operations in Hole M0023A started at 0635 h on 10 November and ended at 2245 h that day after reaching a TD of 31.36 mbsf with a total recovery of 77.20%.

After raising the DART a short distance from the seabed, the Hunter was positioned above Hole M0023B, 5 m southwest of the previous hole in 67 m water depth. Coring operations in Hole M0023B began at 0120 h on 11 November 2005 and ended at 1540 h that day at a TD of 31.12 mbsf with a total recovery of 67.90%. The coring operation proceeded smoothly, with excellent core recovery in long core runs in often very porous formation.

Prior to logging, the drill pipe was pulled and the hole flushed to 30 min before the drill pipe was run-in with a casing shoe to ~6 mbsf. Logging commenced at 1700 h on 11 November. Initially, the tools would not pass below the casing shoe, even after the chisel tool was worked in the hole. The casing shoe was run to the base of the hole and back before the chisel tool was deployed to check that the casing shoe was clear. Logging operations restarted at 2000 h, with the tools reaching a maximum depth of 28.5 mbsf. A DP malfunction caused the vessel to move off location during logging, but the situation was recovered and the hole and equipment remained intact. The optical and acoustic log preview indicated that there were many cavities in the formation. Logging was completed in Hole M0023B at 0310 h on 12 November.

After clearing away the logging tools and lifting the DART back into the moonpool, the vessel moved to conduct an echo sounder survey in an area over a drowned reef pinnacle ~100 m east of proposed Site TAH-02A, #5. From 0515 h on 12 November 2005, 14 m x 50 m echo sounder traverses were made, from which a site for Hole M0024A was chosen in 90 m water depth. Coring operations in Hole M0024A began at 1010 h on 12 November and finished at 0400 h on 13 November at a TD of 32.3 mbsf. Total recovery was 83.74%.

Hole M0025A

A site for Hole M0025A was chosen from the echo sounder survey conducted on 12 November 2005, 25 m north-northwest of Hole M0024A. The DART touched down in a water depth of 105.4 m and coring began at 0530 h on 13 November and finished at 1645 h that day at a TD of 20.93 mbsf. Total recovery was 74.23%.

Following another echo sounder survey over a 50 m x 35 m area ~180 m east of proposed Site TAH-02A, #4 over a drowned reef pinnacle, a site for Hole M0026A was chosen. It proved difficult to interpret the results of the echo sounder survey (three strong seabed echoes and widely differing water depths over a few meters), and it took some time before identifying a suitable site in 105 m water depth. Coring operations in Hole M0026A started at 0920 h on 14 November 2005 and were completed by 1105 h that day at a TD of 12.4 mbsf. Total recovery was 58.45%.

Hole M0025B

After lifting the DART from Hole M0026A, the Hunter moved to previous Site M0025 to core Hole M0025B. After taking a tautwire depth of 95 m, the DART was lowered and coring began at 1215 h on 14 November 2005. Coring finished at 0100 h on 15 November at a TD of 20.5 mbsf with a total recovery of 71.19%.

Hole M0021B

After raising the DART to 50 m above seabed, the vessel was moved back to Site M0021 to core Hole M0021B. Once on position, the tautwire depth was taken as 80 m. The DART and drill pipe were lowered, and coring in Hole M0021B commenced at 0630 h on 15 November 2005 and continued until 2210 h that day. TD was 32.81 mbsf and the total recovery was 65.57%.

Prior to logging, the hole was flushed before the HQ pipe was run back into the hole with a casing shoe. Logging of Hole M0021B commenced at 0030 h on 16 November and was competed by 0645 h that day. All tools were run to 15 mbsf. Once logging was completed, the DART was lifted onto deck and secured for the transit back to the Port of Papeete.

The Hunter departed the last site at 0815 h on 16 November 2005 and arrived at the Port of Papeete at 1145 h. Demobilization of the vessel took place on 16–17 November 2005.

The cores collected offshore Tahiti were transported under refrigeration to the new IODP Bremen Core Repository and Laboratories in the MARUM building on the campus of Bremen University. Further analytical laboratories were accessed through the Department of Geosciences (geochemistry laboratories), the Research Center for Ocean Margins (RCOM) (physical property laboratories), and the Centre for Marine Environmental Research (MARUM) of Bremen University. During the Expedition 310 onshore science party (13 February–4 March 2006), the cores were described in detail ad minimum and some standard measurements were made (Table T2).

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