SAMPLING STRATEGY
New sampling guidelines specify that a formal, leg-specific sampling strategy be prepared by the Sample Allocation Committee (SAC = co-chiefs, staff scientist, and ODP curator on shore or Curatorial Representative on board ship) for each prospectus. Modifications to the strategy during the leg must be approved by the SAC. The sampling strategy is here keyed to the new guidelines and will be refined as the sample requests are evaluated and considered by the entire shipboard party before reaching site.
Sampling Requests
Based on the Scientific Prospectus, each Leg 193 scientist (shipboard or shore based) should
prepare and submit to ODP/TAMU (Texas A&M University) a sampling request for his/her
postcruise research. These should be submitted to ODP at least three months before sailing. One
month before sailing, a complete sampling program should be completed, including resolution of
possible conflicts.
Dynamic Sampling Strategy and Critical Interval Definition
At the beginning of the leg, a meeting of the full shipboard scientific party will review the
sampling requests and define the procedures and a tentative schedule for sampling sessions. Given
the characteristics of the drilling targets and scientific objectives of Leg 193, it is foreseeable that
sampling may have to be carefully planned, with a permanent revision of the sampling strategy
according to findings. This will be particularly true at "critical intervals," such as veins, massive
sulfide intercalations, and other intervals of high scientific interest or low recovery. These may
require special consideration and special sampling procedures, such as a higher (or lower)
sampling density, reduced sample size, or sampling techniques not available on board ship. These
will be identified during the core description process and in the sampling protocol established by
the interested scientists and shipboard SAC. It will be the responsibility of SAC members to
identify and label critical intervals. Progress of the leg may justify reclassification of a former
critical interval into the unclassified status.
Minimum Permanent Archive
The minimum permanent archive will be the standard archive half of each core.
Sample Limit
Shipboard scientists may nominally expect to obtain as many as 100 samples up to 15 cm3 in size.
Additional samples may be obtained upon written request to ODP soon after the cores return to the
ODP Gulf Coast Repository. This guideline will be adjusted upward or downward by the
shipboard SAC, depending on penetration and recovery during Leg 193. All sample requests must
be justified in writing on the standard sample request form and approved by the SAC. Larger
samples can exceptionally be collected, subject to written justification and approval by the SAC.
Larger samples will be considered the equivalent of multiple samples in complete or partial
increments of 15 cm3.
Biological Sampling
Sampling for microbes and other living organisms and for biogenic molecules will take place
immediately after retrieval of core barrels, except if and when critical intervals may be destroyed or
rendered useless to other studies as a consequence of biological sampling. The overall number of
100 samples should be taken as a sampling rule. Exceptions (e.g., in the case of very small
samples) must be cleared with the SAC.
Redundancy of Studies
Some redundancy of measurement is unavoidable, but minimizing this redundancy among the
shipboard party and identified shore-based collaborators will be a factor in evaluating sample
requests. Requests for independent shore-based studies that substantially replicate the intent and
measurements of shipboard participants will require the approval of both those shipboard
investigators and the SAC.
Shipboard Samples and Data
Following core labeling, measurement of nondestructive properties, and splitting, samples will be
selected from core working halves by members of the shipboard party for routine measurement of
physical and magnetic properties, bulk chemical analyses by inductively coupled plasma-atomic
emission spectrophotometer (ICP-AES), carbon-hydrogen-nitrogen-sulphur (CHNS) analyzer,
and X-ray diffraction as necessary. Polished thin sections will be prepared for identification of
minerals, determination of mineral modes by point counting, and studies of texture and fabric.
We shall identify a suite of samples for full measurement characterization. At ~9.5-m intervals (once per full core), slabs measuring 10 cm x 6 cm x 1.5 cm, with a previously sampled central minicore, will be cut for all shipboard measurements then subdivided and split appropriately for further shore-based geochemical, mineralogical, and petrographic studies. Where necessary to avoid or include features like veins and alteration, full half-round slices or quarter slices may be taken instead of slabs.
Data from all shipboard studies, regardless of method or observer, including all core descriptions and measurements and the nondestructive measurements of physical and magnetic properties, are the property of the entire shipboard party and may be used exclusively by them in publication and preparation of manuscripts with proper citation to the Initial Reports volume until the publication of the Initial Reports volume or 12 months postcruise, whichever is later.
Shipboard Thin Sections
Shipboard thin sections will be selected from representative sections of the core and at some
critical intervals. These sections will remain the property of ODP. The thin-section chips from
which the sections are made will be retained by ODP and should normally be thick enough to
allow for the production of additional sections unless the sampling plan for a critical interval
precludes this. Members of the shipboard party can request the production of a thin section from
these chips for their personal use as part of their nominal 100 sample limit, but must arrange for
the prepaid manufacture of these thin sections with a third-party commercial service at their own
expense unless otherwise approved by the ODP Curator. The thin-section chip will then be sent
directly to the commercial service and returned directly to ODP by the service.
Sampling for Shore-Based Studies and Sampling Parties
To minimize the time and physical effort required for additional sampling for shore-based studies,
we shall organize sampling consortia among the principal scientific teams (igneous, metamorphic,
structural, physical, and magnetic properties) that will identify locations for similarly large (10 cm
x 6 cm x 1.5 cma minicore) or even larger samples, averaging approximately once per 9.5 m of
core. The actual size will depend on the number of investigators in the group, and it will be
subdivided among them, to count against the nominal 100-sample limit of each consortium
investigator. Follow-up sampling will be organized as short sample parties during reentries or
logging runs, for individuals using the second-look lab, or at the ODP Gulf Coast Repository, as
necessary.
Storage and Shipping Needs
The usual labeling, orientation, core placement, and storage procedures should be sufficient for
safe transportation to the ODP Gulf Coast Repository. Core handlers should wear back supports
while lifting and handling individual archive or working halves and especially when maneuvering
core storage boxes. Additionally, sulfide-bearing cores may require storage in special sealed bags
in an inert atmosphere.
Formation Water Sampling
Sampling and analysis of deep-seated hydrothermal fluids that enter the two outflow-zone
boreholes (Sites PCM-2A and PCM-3A) at permeable aquifers will greatly enhance our ability to
assess subsurface fluid-rock interactions and the chemical controls at the depth of sulfide mineral
deposition. Such fluids will also provide key information for modeling hydrothermal processes
deeper than the extent of coring, including additional pathways to assessing the sources of fluids
and metals, as well as the first comparisons with vent fluids previously collected at active
chimneys. Technologies used to collect high-temperature hydrothermal fluids from boreholes on
previous cruises have not been particularly successful, and an effort will be made prior to Leg 193
to design new sampling instruments. Our intention is to deploy these into the open hole at staged
intervals of drilling, or after completion of wireline logging, at depths where temperature
anomalies have been detected. With simpler forms of instrumentation, we do not expect the
samples to be pure end-member fluids from narrow formation intervals; rather, they will typically
be variably mixed within the borehole from several aquifers and will have been diluted by seawater
and drilling fluid. Procedures exist to resolve these effects of contamination. If suitable high
temperature packers can be developed, sampling of more concentrated hydrothermal fluids with
more specific sources will become an option. The exact strategies for collection of hydrothermal
fluids will depend on the nature and time requirements of the instrumentation adopted. At a
minimum, we will attempt one sample near the bottom of holes at Sites PCM-2A and PCM-3A,
and one near the collar of these or the adjacent logging-while-drilling holes.