First Antarctic Drilling 19721975

The period following World War II was marked by an expansion in both the scientific exploration of the oceans and the search for oil on the world's continental shelves. Echo-sounding techniques developed in war time were applied to marine seismic surveys for science and industry, and ship-based drilling for oil offshore attracted the attention of scientists for drilling through the Earth's crust. By the mid-1960s, the main features and gross chronology of most of the world's continental shelves were known by the oil industry, and the US marine science community persuaded its government to support the development of an international Deep Sea Drilling Project (DSDP) to drill the world's ocean floor, beginning in 1968. The main aims were to test and refine the new theory of Plate Tectonics as well as gain new knowledge from this unknown 70% of the Earth's surface that might improve our knowledge of Earth history.

DSDP was remarkably successful and in its first 4 years had drilled at over 200 sites around the world but not in the Antarctic region. The first venture south was Leg 28, designed to carry out the first drilling transect between Australia and Antarctica for dating the timing of continental separation from the age of sediment resting on basaltic ocean floor, and to core for climate and ocean history in the Southern Ocean and on the Ross continental shelf. The Ross Sea region had just been surveyed by the US research vessel USNS Eltanin during which several thousand kilometres of single channel seismic surveys were taken and used to define the three main shelf basins (Houtz and Meijer, 1970; Houtz and Davey, 1973). The Eastern Basin was most promising with dipping strata at the basin margin, allowing a drill ship with a subsea floor penetration limit of around 500 m, to core most of the sedimentary section in three well-chosen sites.

3.3.1. Ship-Based Drilling (1972-1973)

The Glomar Challenger sailed south on DSDP Leg 28 from Fremantle, Australia, in December 1972. In the 2 months that followed, it succeeded both to establish the history of continental separation south of Australia and to provide the first physical record of Antarctic glaciation extending back to Oligocene times (Hayes, Frakes et al., 1975). The three sites drilled in the eastern Ross Sea (Figs. 3.1 and 3.2) revealed large thicknesses of poorly sorted glacial marine debris ranging in age from late Oligocene (~25Ma) to Quaternary. The oldest glacial sediments were cored at DSDP Site 270, where they overlay a palaeosol developed on a calc-silicate gneiss basement.

DSDP Leg 29, which followed in March 1973, added a new and independent body of data with a significant bearing on Antarctic glacial history. The goal of Leg 29 was to sample the floor of the deep ocean south of Australia and New Zealand for as complete a record as possible of strata representing the whole Cenozoic Era to provide data on ocean history for the new field of palaeoceanography. This venture was also successful, both in recovering long and representative stratigraphic sequences and in finding

Figure 3.1: Map showing the Antarctic continent and ice drainage systems (based on Drewry, 1983), with sites of the first drill holes on the Antarctic continental shelf (DSDP Leg 28). Subsequent shelf sites in the McMurdo Sound region (box - see Fig. 3.3 for detail), Prydz Bay and the Antarctic Peninsula are also shown, each reflecting the history of the ice sheet in their respective regions. DSDP Leg 29 drilled lower latitude deep-sea sites south of New Zealand for the first Cenozoic isotopic record of ice volume and temperature (see text). Modified from Barrett (1999), with permission.

Figure 3.1: Map showing the Antarctic continent and ice drainage systems (based on Drewry, 1983), with sites of the first drill holes on the Antarctic continental shelf (DSDP Leg 28). Subsequent shelf sites in the McMurdo Sound region (box - see Fig. 3.3 for detail), Prydz Bay and the Antarctic Peninsula are also shown, each reflecting the history of the ice sheet in their respective regions. DSDP Leg 29 drilled lower latitude deep-sea sites south of New Zealand for the first Cenozoic isotopic record of ice volume and temperature (see text). Modified from Barrett (1999), with permission.

well-preserved calcareous microfossils for applying a new technique, stable isotope analysis, to these cores (Kennett, Houtz et al., 1975).

The result was the first record of warm early Cenozoic times followed by a decline in temperature from around early mid-Eocene times (~50Ma ago,

Figure 3.2: R/V Glomar Challenger at Site 270 (78°S) in January 1973. Seismic section shows how three holes sampled most of the sedimentary section (De Santis et al., 1999).

Shackleton and Kennett, 1975). Two features in the isotope record stand out and are still seen as significant today:

(i) An abrupt increase in 818O in earliest Oligocene times (now 34 Ma), interpreted as a consequence of global cooling, with extensive sea-ice formation around Antarctica. A major global climate event at this time had already been suspected from the change in terrestrial flora around the world.

(ii) Another increase in 818O at ~14Ma, and interpreted to be the result of development of a larger relatively stable Antarctic Ice Sheet like that of today.

Although deep ocean sediments were useful for their continuous record of past ocean chemistry, and in providing an ice volume-temperature signal from oxygen isotopes, they could not provide information on the extent of ice or regional climate in the high latitudes. This could only come out of sediment cores from the Antarctic margin, where the direct influence of ice advance and retreat (and perhaps also sea level fall and rise) could be obtained.

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