Expedition Logbook: November

Sunset at Pano Papenoo

Day 41: The final Tahitian sunset
Drilling has finally finished at Papenoo (N Tahiti). After wire-line logging of the last hole, we will make the final transit tomorrow morning to Papeete to demobilize and disembark. At this point the scientists will spread to the four winds, returning to their home institutions all over the world before coming together again with our onshore colleagues in Bremen for the onshore science party February next year.

Well, this is my last expedition log entry for the Tahiti mission. I hope you have enjoyed the journey as much as I have enjoyed sharing it with you. We are all excited and confident that the scientific objectives of the mission have been met. There is still a very big job ahead in Bremen and beyond, but with the incredible material we have collected over the last 42 days we should all get ready for some very exciting science with far reaching implications for understanding global sea-level and climate change, and reef evolution.

Before signing off just a final word of thanks to the DP Hunter?s crew, SEACORE drillers, and ESO operators. They have done an outstanding job in often difficult conditions. The undoubted operational and scientific success of this mission is due in no small part to their tireless hard work and dedication. Well done to all.

Bon voyage from Tahiti.
Jody Webster

Day 34 : The science facilitators
By Jody Webster, Expedition Scientist

Drilling at Maraa (off Southern Tahiti) is finally complete. Over the last 2 days we have drilled two 40 metre (m) deep holes very close to the steep shelf edge in water depths of around 80 m. We are now confident that we have recovered a good portion of the post glacial (< 23000 years old) reef sequence at Maraa. For these holes, we modified our drilling technique and we are now drilling with steel splits (or two half tubes) inside the core barrel rather than a complete plastic liner tube. This has greatly improved core recovery, preservation and also reduced the drilling time. Yesterday, the Seacore drillers recovered a beautiful (and continuous) 3 metre section of fossil reef material. 100% recovery and truly a sight to behold.

We are now more than half way through the expedition. To review our progress and refine our future drilling plans, the ESO IODP Staff Scientist (David McInroy) and the Staff Scientist in training (Christian Wilson) convened a meeting with the co-chief scientists (Gilbert Camoin and Yasufumi Iryu) and the rest of the science party. The Staff Scientist wears several different "hats" on the expedition. He looks after the scientists, the scientific data collected and project manages the scientific aspects of the expedition, while working closely with the co-chief scientists to ensure that all work defined by the Scientific Prospectus is carried out and is consistent with IODP policy. Perhaps equally important, David and Christian are the main conduits between the scientists, the operator and IODP, ensuring smooth operations and seeing that good science can be done. Finally, they are responsible for collating the expedition scientific results, preparing the Preliminary Report and ultimately the Expedition Report (part of the Proceedings of the Integrated Ocean Drilling Program) to be finalised after the onshore workshop in Bremen.

With Maraa complete, we have now made the transit to Faaa and are on site just offshore Papeete Airport. After keeping a relatively low profile on the more remote sides of Tahiti, our big red ship will make quite the impression on the local sea and air traffic. Drilling will start in about 60 m of water and we expect to drill about 80 m of fossil reef material.

Day 29 : Coral reef drilling - more art than science.
By Jody Webster, Expedition Scientist
Drilling continues at Maraa (S Tahiti) in water depths between 75 and 85 m. After 2 days we have drilled two holes and are working on the third. The recovered material is fascinating with branching coral frameworks set in thick sequences of microbially derived laminated grey sediments. The geomicrobiologists were also jumping for joy as they identified a strange purple biofilm (or mucus) associated with tiny minerals in a cavity. Microscope work today confirmed the presence of lots microbes.

Yesterday we had two new visitors to the ship, a manta ray and a German TV crew. The manta just came by for a quick hello but the TV crew is here for a few days to film the drilling/science operations for a documentary to be screened early next year. Should be entertaining.

Today I was lucky enough to have a personally guided tour of the "rooster box" or platform. No, this not where we keep our poultry but rather where the SEACORE drillers work their magic. The platform is suspended about 40 m above the deck between the two heave compensation columns. From here the driller controls the drilling process. The journey to the "rooster box" is an adventure in itself. Picture this ? you have to scale a vertical ladder as the ship pitches and rolls in the swell. While you are doing this about 30 cm to your left and right the "rooster box" and heave compensators are going up and down. Now the all important dismount as you step off the ladder on to the moving platform. Once this delicate maneuver is achieved, with some dignity as the drillers are looking on with amusement, you are amazed that the "rooster box" and entire drill assembly are stable while it is the ship that is moving. This engineering marvel is made possible by high air pressures and a series of valve systems that increase or decrease the hydraulic oil pressure as needed to allow the ship to move up and down ?around? the drill rig. This system works entirely passively but also allows the driller to dial in the exact weight needed on the actual drill bit doing the coring. This is where the real art of drilling comes into play. How much weight? Which drill bit is best for which rock type? How much water pressure (the drilling lubricant in our case)? How much rotational speed and torque? How fast should the drill bit be advanced down the hole? A rather bewildering set of variables to balance, particularly given the notoriously difficult nature of coral reef drilling with large cavities, crumbly corals and loose sands. Despite these challenges the entire SEACORE drilling crew has done a great job with excellent core recovery. As far as shallow water carbonates are concerned we are confident that this drilling effort will rank among ODP/IODP's best.