Below is the final underway cruise report from the co-chief scientists on this cruise. It offers a summary of what we were looking for and what we found.

The R/V Melville returns to Papeete on Monday March 21, after a successful site survey for an IODP drilling program. The objectives of the cruise were to identify drill sites to study high latitude South Pacific oceanography during the period of Eocene extreme warmth. In addition, we collected sediments to study Quaternary frontal movement and biogeochemical cycles.

The site-survey cruise was conducted February 9 to March 21, 2005 aboard the R/V Melville, a cruise that described a southerly loop from Tahiti to the working areas along 50°S and back. The region thus surveyed covered the eastern half of the Southwest Pacific Basin, a very poorly known part of the world’s ocean. During the course of our two weeks of work along 50° south we experienced some of the weather the region is famous for but were able to complete all the surveys (one was slightly smaller in area because of the arrival of Cyclone Olaf) and raise the best new cores from the region in the past 30 years.

Highlights of the cruise include 7500 nautical miles (13,900 km) of swath-map trackline, resulting in a surveyed area of 167,000 sq km. For over half this trackline we also acquired seismic reflection to study sedimentation in the South Pacific. We surveyed 12 areas as potential sites for drilling. Of these, four between 31° and 39°S between 133 and 143° W had no discernable sediment. This discovery of at least a million square kilometers of Paleogene-aged bare sea floor is new and exciting, but not conducive to eventual scientific ocean drilling. Our best results occurred along the southern extent of the cruise, and will provide a foundation for our revised drilling proposal.

The piston cores we recovered from high southern latitudes indicate that we will be able to address three important scientific questions in addition to those posed in our drilling proposal. We are able to demonstrate that the modern CCD at 50°S is at about 4750 meters, so for much of its history the crust in the region has been above the CCD permitting paleoceanographic reconstructions based on both calcareous and siliceous microfossils. Two of our cores recovered calcareous sediment both above and below pelagic clay, suggesting that the CCD has changed dramatically, and the changes will be recorded in the sediments. At Site SP 1-A we raised a core of siliceous ooze and silt. As this site at 51.5°S is well south of the modern ice-berg limit, we assume the silt, and the basalt pebble found on the surface of sediment recovered at 46°S, represents ice rafting from Antarctica. Thus we anticipate a complete Antarctic ice rafting record might be available in these sediments. Since the more southerly sites backtrack to 59 to 66°S, the exact latitude of the Drake Passage, the issues concerning the development of this critical gateway should be approachable with the results of drilling at those locations.

Regards,
Mitch Lyle and Dave Rea
co-chief scientists