Drilling from Sea Ice 1975

The success of DSDP Leg 28 in the Ross Sea had shown the potential for offshore sediments around Antarctica providing a direct record of the glacial history on land. However, ice flow lines and lithologies of pebbles in cores from the sites in eastern Ross Sea indicated that sediments deposited there were derived from West Antarctica (Fig. 3.1; Barrett, 1975). To find a record of the much larger and possibly older East Antarctic Ice Sheet, sites were needed in the western Ross Sea adjacent to the Victoria Land coast.

Figure 3.3: Map and cross-section of McMurdo Sound (adapted from Naish et al., 2008a). (A) The map shows sites for the Dry Valley Drilling Project (1973-1975) and subsequent offshore drilling (MSSTS-1 in 1979, CIROS 2 and 1 in 1984 and 1986, respectively, CRP-1, -2 and -3 in 1997, 1998 and 1999, and ANDRILL MIS and SMS in 2006 and 2007 - details in Table 3.2). Contour interval 200 m. Transantarctic Mountains exposures in light brown, McMurdo Volcanics in dark brown. (B) The cross-section across McMurdo sound shows how a few key drill holes have sampled the entire Cenozoic record from this section of the basin. CRP sites provide an expanded and better dated record 70 km north of the Late Eocene-Early Miocene section cored by CIROS-1.

Figure 3.3: Map and cross-section of McMurdo Sound (adapted from Naish et al., 2008a). (A) The map shows sites for the Dry Valley Drilling Project (1973-1975) and subsequent offshore drilling (MSSTS-1 in 1979, CIROS 2 and 1 in 1984 and 1986, respectively, CRP-1, -2 and -3 in 1997, 1998 and 1999, and ANDRILL MIS and SMS in 2006 and 2007 - details in Table 3.2). Contour interval 200 m. Transantarctic Mountains exposures in light brown, McMurdo Volcanics in dark brown. (B) The cross-section across McMurdo sound shows how a few key drill holes have sampled the entire Cenozoic record from this section of the basin. CRP sites provide an expanded and better dated record 70 km north of the Late Eocene-Early Miocene section cored by CIROS-1.

A seismic survey in late 1974 showed that the thick sedimentary strata of the Victoria Land Basin did indeed extend close to the East Antarctic coast (Wong and Christoffel, 1981) and provided the justification for DVDP-15, the first Antarctic offshore hole to be drilled from the fast sea ice. Experience in moving equipment 70 km across the sea ice from McMurdo Station on Ross Island to the Marble Point airstrip on the Victoria Land coast had been gained from fuel train traverses, and the same logistics were employed in transporting the DVDP rig and related equipment from McMurdo Station to the site selected for DVDP-15 around 10 km off Marble Point. The rig was set up on 2 m of sea ice in 120 m of water and began drilling in early November 1975 (Fig. 3.4). Logistic delays and drilling problems reduced the time available for drilling, which was terminated at a depth of 62 m with over 52% recovery. The character of the sediments was surprising, for below 12 m of recent glacial debris lay 50 m of basaltic sand, presumed to have been erupted as volcanic ash and then wind-blown across the sea ice before settling (Barrett and Treves, 1981). Nevertheless, the experience had shown the feasibility of drilling from a sea-ice platform.

Figure 3.4: Development of sea-ice drilling systems from 1975 to 1999. (A) DVDP-15, 1975. Water depth 112m; depth Cored 62m bsf (below sea floor). (B) MSSTS-1, 1979. Water depth 195 m; Depth Cored 229 m bsf. (C) CIROS-1, 1986. Water depth 205m; depth Cored 702m bsf. (D) CRP-3, 1999. Water depth 305 m; depth Cored 942 m bsf.

Figure 3.4: Development of sea-ice drilling systems from 1975 to 1999. (A) DVDP-15, 1975. Water depth 112m; depth Cored 62m bsf (below sea floor). (B) MSSTS-1, 1979. Water depth 195 m; Depth Cored 229 m bsf. (C) CIROS-1, 1986. Water depth 205m; depth Cored 702m bsf. (D) CRP-3, 1999. Water depth 305 m; depth Cored 942 m bsf.

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