FUTURE INVESTIGATIONS

Drilling in the southwest Pacific Ocean remains in a state of reconnaissance. Even after the completion of Leg 181 there are still only 10 drill sites with significant sediment recovery in a region that extends from 35° to 60°S. This region is comparable in size to the North American Basin of the Atlantic, where there are >100 cored sites. Further drilling is essential for improving our state of knowledge of the history of the Southern Ocean water masses, fronts, and currents that are part of the planet's ocean circulation system. The completion of Leg 181 has made it much easier to recognize high-priority targets for future attention. We identify five such targets:

  1. Cores through the ~82- to 34-Ma-old postrift sediments of the circum-New Zealand sediment apron, especially at sites around the edges of the Campbell and Hikurangi Plateaus. Our knowledge of the oceanography of the southwestern proto-Pacific Ocean remains extremely limited and at present is essentially based on only three adventitious cores (Sites 1121, 1123, and 1124).
  2. The coring of complete, and preferably expanded, Oligocene-early Miocene successions (34-20 Ma). In most places, sediments of this age have been removed by erosion at the Marshall Paraconformity and the location of sections suitable for high-resolution coring studies will probably require new seismic surveys in areas of likely sediment accumulation. One suitable area is in the axis of the Great South Basin (Carter, R., 1988a, fig. 5), a now-filled tributary rift to the Bounty Trough, where an apparently continuous Oligocene biopelagic section was penetrated by petroleum exploration drilling. Related to drilling such Oligocene targets, the coring of more successions through the Marshall Paraconformity will provide important information regarding the nature of the global Eocene-Oligocene ocean reorganization.
  3. "Dipstick" coring through the DWBC drifts, especially the Chatham Drift, the record of which since 20.5 Ma has been so successfully deciphered at Site 1123. Shallower core sites may avoid the diagenesis problem encountered in the lower Miocene at Site 1123. A knowledge of the changing patterns of circulation and chemistry within the different CDW levels of the DWBC requires a depth transect of both shallower and deeper sites, which could be located on existing seismic profiles. In addition, coring the Hikurangi Fan-drift would provide a high-resolution century-scale record of sediment supply/DWBC interactions throughout the Pleistocene.
  4. Coring the main body of the large intermediate-water depth drifts along the Canterbury slope in the head of the Bounty Trough. Results from Site 1119 indicate that the deeper parts of these Canterbury Drifts will yield an outstanding record of the history of the STF and of the AAIW water mass and its predecessors, including the likelihood of penetrating the Marshall Paraconformity, which is known from seismic imagery to lie beneath the drifts.
  5. Coring "patch drifts" (Carter, L., and McCave, 1994) on the Hikurangi Plateau, close to the volcanic sources, will allow construction of the best available record of the pulsatory magmatic activity at the North Island convergent plate boundary.

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