All sites have an alternate in case pack ice covers the primary sites (although this is most unlikely). In addition, lower priority sites (each with an alternate) have been selected in the mid-shelf basin where pre-collision sediments occur (APSHE-11A), and in the South Shetland trench where a high-resolution paleoclimate record is preserved within a trench turbidite succession (APSST 01A). Also, the Planning Committee (PCOM) recommended that an originally-specified Plio Pleistocene paleoclimate site in Bransfield Strait (APBRS-01A) be removed from the drilling plan because of a shortage of time. In fact, only the primary sites listed above will be drilled as planned if the leg proceeds without massive disruption by ice.

Drilling on the rise will involve double advanced hydraulic piston corer (APC) and extended core barrel (XCB) coring at the proximal site (to about 700 m), followed possibly by rotary core barrel (RCB) coring to 1450 mbsf, or most probably by offset to the distal APC/XCB site where the same full section is accessible within 600 m. The depth limit of drilling at Site APRIS-01A will depend on the effects of silica diagenesis on the biostratigraphy and on time constraints. These sites are in fine-grained alternating biosiliceous and barren muds and mudstones. The 50-m ultra high-resolution site (APSHE-13A), assumed to be essentially a diatom ooze, will be sampled by triple APC. The other shelf sites pose problems, in that the unsorted diamictons are unsuitable for APC/XCB sampling. Therefore, all five sites (that are between 500 and 800 m deep) will probably (in the absence of advice to the contrary) be rotary-drilled from the seabed down. Recovery will be reduced because of their lithology (with the possible exception of Site APSHE-05A), but we shall try for as complete a section as possible.


We plan to log shelf sites APSHE-01A to 05A and rise sites APRIS-01A and 02A with the following tool strings: the Triple Combination (litho-density, porosity, resistivity, and natural gamma tools); Formation MicroScanner (FMS)-Sonic (resistivity imaging, sonic velocity, and natural gamma tools); and Geological High-sensitivity Magnetometer (GHMT; magnetic field, susceptibility, and natural gamma tools). Also, we plan a vertical incidence vertical seismic profile (VSP) survey, using the well seismic tool (WST; downhole geophone), at one of the rise sites and at one or more of the shelf sites.

Thus, an extensive logging program is planned. Briefly, geophysical and geochemical logs will provide lithological information to complement core data and to help offset possible low recovery on the shelf; the FMS images can be used to investigate fine-scale bedding and fabric, including orientation; the GHMT will provide a magnetic stratigraphy; and the WST and synthetic seismograms will be used to correlate hole depths with travel times on the seismic section. The good quality logging results obtained on previous Antarctic Ocean Drilling Program (ODP) legs (113 and 119) in similar sediments, bode well for successful logging on this leg.


Standard ODP practice is to collect 3.5- and 12-kHz echo-sounder data on approach to each site. In addition, long magnetic and 3.5-kHz profiles will be acquired on the transits from Punta Arenas to the Antarctic Peninsula and from there to Cape Town.


For Leg 178, almost all sampling will probably be accomplished during the cruise; no postcruise sample party is currently planned. Most sites consist of a single hole, where fairly standard sampling is envisaged. At other sites, which will be double (Site APRIS-01A) and triple (Site APSHE-13A) cored, a composite section will be constructed for each site and then a sampling strategy will be developed. Nonstandard sampling at some of the sites might include high resolution whole-round sampling for physical properties and geochemical studies, U-channel sampling for paleomagnetism, and microbiological sampling.

All sampling to be conducted on Leg 178 must be approved by the sampling allocation committee (SAC), consisting of the Co-chiefs, Staff Scientist, and Curatorial Representative. Sampling plans are subject to modification depending upon the actual material recovered and collaborations that may evolve between scientists during the leg.

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