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doi:10.2204/iodp.sp.318.2008

Risks and contingency strategy

The planned Wilkes Land and Adélie Basin drill sites are situated in an area of pronounced latitudinal gradients in wind because of the effects of the off-the-continent katabatic winds as well as the location of the frontal zone between polar easterlies and westerlies. Average January–March wind speeds can be from 6.4 to 7.7 m/s, but may reach up to 23 m/s at the shelf sites. The sea ice conditions, based on analysis on satellites, ships, continental stations, and synoptic modeling, may vary strongly from year to year. While the most offshore sites may be presumed to be ice free in the Austral summer, the shelf sites may not. The open-water period at the Adélie site begins about 29 January and extends through 7 March, on average. However, the late summer return of sea ice can begin as early as 20 February or as late as 16 March at this site. The open-water period at proposed shelf sites begins in mid-January and extends through 3 March, on average. However, the late summer return of sea ice can begin as early as 22 February or as late as 16 March at this site. The shelf sites may likely have <10%–0% ice cover between the end of January until the beginning of March.

Based on this information we have developed the following contingency strategies to help us maximize our possibilities of achieving the scientific objectives listed above:

  1. If the shelf is covered with ice at the beginning of our drilling operations, we envision two possibilities, both starting with coring and logging the continental rise deposits at proposed Site WLRIS-02A.

    • Proposed Site WLRIS-02A to WLSHE-09B to WLSHE-08A to ADEL-01A to WLRIS-04A. This scenario considers that by the time drilling at proposed Site WLRIS-02A is concluded, the shelf is free of ice. In this case we would move to the shelf to core and log shelf proposed Sites WLSHE-09B, WLSHE-08A, and ADEL-01B (or alternates) and conclude our drilling operations at proposed Site WLRIS-04A (or alternate).

    • Proposed Site WLRIS-02A to WLRIS-04A to WLSHE-09B to WLSHE-08A to ADEL-01B to WLRIS-04A. This scenario considers that at the end of drilling proposed Site WLRIS-02A the shelf is not free of ice. We would then core and log proposed Site WLRIS-04A until shelf drilling is possible. We would move to drill proposed Sites WLSHE-09B, WLSHE-08A, and ADEL-01B. After completion of drilling the shelf sites we would transit to reoccupy proposed Site WLRIS-04A and core until the end of time allotted for this expedition.

      • To account for the possibility that some sectors of the shelf may open while others may remain inaccessible, additional alternate sites with objectives similar to proposed Sites WLSHE-09 and WLRIS-08 on the shelf have been identified (proposed Sites WLSHE-10A, WLSHE-11A, and WLSHE-12A) and submitted for approval.

  2. If the shelf is free of ice upon beginning of drilling operations, our strategy would be to start coring and logging the shelf proposed Sites WLSHE-09B, WLSHE-08A, and ADEL-01A then move to the abyssal plain to drill proposed Site WLRIS-02A and finalize with drilling operations at proposed Site WLRIS-04A.

  3. If the coast and shelf remains ice covered, we will concentrate our drilling operation on the continental abyssal plain by drilling a third hole at proposed Site WLRIS-02A before proceeding to proposed Site WLRIS-04A. Because the drilling will rely only on these two sites, an alternate site for proposed Site WLRIS-02A will be submitted for approval.

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