Sediments encountered at the seven primary sites will consist of periodically alternating layers of biopelagic carbonate and silica-rich sediment with varying amounts of fine-grained terrigenous detritus. Some terrigenous sand may be encountered. Because of the strong density and porosity variations associated with such lithologies, core and log physical property measurements are likely to be extremely important proxy indicators for reconstructing time series of sediment composition. Some sites may have high sediment accumulation rates, generating great potential for the achievement of very high-resolution records of paleoclimatic and paleoceanographic variability.
All proposed sites have penetration depths exceeding 300 m, and will be logged with the triple-combo and formation microscanner (FMS) tools. It is anticipated that most sites will also be logged using the geological high-resolution magnetometer (GHMT) tool string.
Most of the core material to be recovered during Leg 181 will be retrieved by APC and extended core barrel (XCB) coring, generally by triple coring for the first priority sites and by double coring for any secondary sites drilled. One half of one hole at each site will be the permanent archive half. Micropaleontology and sedimentology samples will be taken after a composite sampling splice is constructed from the two or more holes drilled at that site. High-resolution sampling is anticipated for most sites (2-5 cm interval), with 10 to 20 cm3 needed for each sample, depending on the abundance of fossils (especially benthic foraminifers). Sampling schedules will be worked out between the parties involved to optimize stratigraphic coverage and to minimize duplication. Geochemical sampling, which calls for larger volumes, will be done on material from the third hole if it would otherwise interfere with first-pass micropaleontology and sedimentology sampling. Whole-round samples may be available for pore-water studies from the third copy, as long as a sample's position is not crucial to filling gaps in the continuous stratigraphic record. If there is a need for a rapid decision on the location of a whole-round sample, but information is insufficient to identify critical intervals for continuous stratigraphy, only short whole-round sections (up to 15 cm long) will be permitted. Such sections should be separated by at least 1 m. Sampling for microbiological studies will also follow this strategy.
Sampling for physical properties will be undertaken so as not to interfere with stratigraphically sensitive sampling sequences and to take advantage of available continuous nondestructive measurements.
Should particularly thinly laminated sediments be encountered, or some other factor necessitate it, detailed very high-resolution sampling may be approved. The sampling allocation committee (SAC) will determine details of the sampling pattern in such instances.
Detailed sampling of cores from a given site will proceed only after a composite stratigraphy is constructed from cores from the two or more holes drilled at the site. The splice will be constructed, and the stratigraphic information will be distributed to the scientific party, in advance of postcruise sampling to facilitate planning and scientific collaboration. Requests to sample on board, for pilot studies or for projects requiring lower stratigraphic resolution, will be considered by the SAC.
Investigators should avoid sampling the center of core halves. Sample plugs should be taken as close to the edges of a split core as feasible, given the purpose of sampling. Samples may also be taken with the "scoop" tool, which includes material from the edges of the split core. Large samples taken with the "cookie-cutter" tool, for example for lamina-scale studies, will be shared among interested scientific party members.
The permanent archive will be the ODP-defined "minimum permanent archive." Once the working half of a core section is depleted, the temporary archives for that section will be accessible for sampling. Wherever possible, one quarter of such temporary archives should be preserved by sampling off-center.
The archive half-cores (permanent and temporary) for all holes will not be sampled aboard ship, and the permanent archive will be designated postcruise. Sampling for high-resolution isotopic, sedimentologic, and micropaleontologic studies will be conducted after construction of the spliced composite section. Most of the high-resolution sampling will, therefore, be deferred until after the cruise; however, the upper few cores in each hole that contain high-porosity sediments that may be disturbed during transport to the Texas A&M University (TAMU) repository will be sampled on board ship. High-resolution sampling is anticipated for most of the upper APC and XCB cores (2- to 5-cm intervals), depending on the abundance of microfossils (especially benthic foraminifers). U-channel sampling for high-resolution paleomagnetic and rock-magnetic studies will be conducted postcruise in the temporary archive half along the composite sampling splice, where appropriate.
Samples for organic geochemical analysis may need to be frozen, and therefore, must be taken on board. Facilities will be available for this.
All sampling for Leg 181, and the final sampling plan, will be approved by the SAC, consisting of the Co-chief Scientists (Carter, McCave), Staff Scientist (Richter), and Curatorial representative (McCarty). The initial sampling plan will be preliminary and may be modified during the cruise, depending upon actual material recovered and collaborations that may evolve between scientists.
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