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WAIS Divide Replicate Coring and Borehole Logging Science and Implementation Plan
Authors: Severinghaus J, Bay R, Brook E, Cole-Dai J, Pettit E and Sowers T
Year: 2008
Keywords: directional, replicate, deviation, wais, divide
Abstract: Replication of results is fundamental to experimental science, and replication of key findings in ice core science should be no less a requirement. The current practice of taking a single deep ice core from a given region makes replication and verification of the validity and spatial representativeness of key results difficult, and leaves the record vulnerable to missing intervals of ice (due to drilling problems, for example). The GISP2-GRIP experience highlights how important it is to have two cores in validating the stratigraphic integrity of the records. Furthermore, scientific demand for ice samples has been and will continue to be very unevenly distributed, with the ice core archive being completely depleted in depth intervals of high scientific interest (abrupt climate changes, volcanic sulfate horizons, meteor impact horizons, for example). In other intervals, however, nearly 90% of the ice remains, and space for storage at the National Ice Core Laboratory is becoming increasingly scarce. The lack of sample in key horizons hampers development and application of new techniques, and discourages entry of young investigators to the field.

The ability to obtain additional volume of ice sample in selected intervals would address these concerns and add value to the scientific return from ice coring. The US Ice Core Working Group recommended in 2003 that NSF pursue the means to accomplish taking of replicate samples, termed replicate coring. This recommendation was part of an agreement to reduce the diameter of the core to 12.2 cm to lighten logistics burdens, and the science community accepted the reduction in ice sample with the understanding that replicate coring would occur and provide extra sample volume in key intervals. The WAIS Divide effort would particularly benefit from replicate coring, because of the unique quality of the expected gas record and the large samples needed for gases and gas isotopes.

This Science and Implementation Plan discusses the scientific goals that may be attainable using replicate coring, and lays out a plan for achieving them. It does not make recommendations on the technological approach to obtaining extra sample, but does outline the scientific pros and cons of various approaches. In particular, it is of critical importance that the taking of replicate cores not compromise other scientific activities in a substantial way. Borehole logging is one such activity that may be impacted to varying degrees by the choice of technology for replicate coring. One technology under discussion is deviating the drill out of the borehole to take extra ice samples, using a device known as a whipstock to force the drill to one side. With input from the borehole logging community, it has become clear that leaving devices such as whipstocks in the hole would fundamentally compromise the science from borehole logging. Therefore we make the recommendation that 1) Replicate coring activities adopt a "leave no trace" ethic to the extent possible; and 2) that any whipstock or other device must be entirely removeable. We recognize that scarring of the borehole wall is unavoidable with deviation coring, but recommend that NSF study ways to minimize the potential for logging tools to become stuck on such scars. Furthermore, if deviation coring is the chosen method, we recommend that a full 2 year period is made available to logging activity, after reaching the bed, but before deviation coring commences. This will minimize adverse impacts on logging activity. We also recommend that NSF study the costs and benefits of other technological options, such as taking entirely separate second cores a few meters or kilometers away; these options need no such 2 year period.
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