Six primary and two alternate sites are proposed for drilling (Table 2). These fall into two groups: northeastern continental slope (Fig. 9) and southern slope (Fig. 10). A summary of the water depths for each site and the expected age/penetration is given in Figure 11.
Northeastern Continental Slope
Sites SCS-1 to 5 are located south of the Dongsha Islands in the northeast SCS (Fig. 9). The sites are designed to sample different water depths and to cover successive time intervals since the Oligocene (SCS-1: Pleistocene; SCS-2: middle Pliocene onward; SCS-3: Pliocene and Pleistocene; SCS-4: middle Miocene to Pliocene; SCS-5: Oligocene to Miocene). This suite of sites should provide the sections to identify and date the proposed stages of monsoon evolution in East Asia.
SCS-1 is targeted for 2050 m water depth, which is slightly above the sill depth of the Bashi Straits (2600 m). The location of Site SCS-1 is distinguished by extremely high sedimentation rates. The Holocene deposits in the nearby Core 17940 (20°07ŽN, 117°23ŽE, water depth 1727 m) reach almost 7 m in thickness, and Core MD 97.2.146 extends only to the oxygen stage 4/5 boundary at 38 m (C.Y. Huang, pers. comm., 1997). The summer monsoon cyclicity of 102 yr in the Holocene and the dry/humid cyclicity of 103 yr in the late Pleistocene found in Core 17940 (Wang et al., 1995a; Sun, 1996) indicate the great potential of this site in delivering high-resolution monsoon records for the Pleistocene. The target penetration of 450 m is anticipated to recover Quaternary sediments (~1 m.y.).
Proposed Site SCS-2 is downslope of SCS-1 at a water depth of 3190 m. This location has a lower sedimentation rate and is expected to provide a continuous record from the middle Pliocene to Pleistocene (Holocene). Because the sill depth of the Bashi Strait is located at ~2600 m, Sites SCS-1 and SCS-2 will also document the Quaternary changes in water mass characteristics across the sill, which is the only deep-water connection between the Pacific and the SCS. SCS-2 is targeted for 400 m penetration.
Site SCS-3C is on the upper slope (water depth ~1265 m) near the base of the modern oxygen minimum zone (State Oceanic Administration, 1988; Haupt et al., 1994). This site is expected to provide a sequence of Pliocene and Pleistocene sediments that record changes in the intermediate water characteristics well above the sill depth. The variables of most interest are temperature and oxygen content, as well as surface-water conditions. Site SCS-3C is targeted for 300 m penetration.
Site SCS-4 is downslope of Site SCS-3C at a water depth of 2093 m. On the basis of seismic records, the proposed site should recover a middle Miocene to Pliocene sequence, which underlies relatively thin Pleistocene deposits. This site also lies above the current sill depth of the Bashi Straits and, along with SCS-5C, offers a Mio-Pliocene history of sill-related water-mass changes. SCS-4 is targeted for 520 m penetration.
Site SCS-5C is located lower on the slope (3232 m) and is expected to recover an expanded Oligocene to Miocene section. On the basis of available seismic records and their correlation to Chinese reflector stratigraphy, SCS-5C is targeted for 700 m penetration. Given the expected accumulation rates and penetration depths, SCS-5C (and the alternate SCS-5D) are the only sites that will recover the Oligocene-Miocene history of the SCS, including the possible onset of the East Asian monsoon.
Sites SCS-5D and SCS-5E
Sites SCS-5D and SCS-5E are located about 65 and 20 km, respectively, northeast of Site SCS 5C. These alternate sites provide a somewhat expanded midsection compared to SCS-5C. They could be cored, if SCS-5C does not meet the expectations of a complete Oligocene-Miocene section.
A southern continental slope SCS site is proposed to reveal the history of tropical East Asia and the Western Pacific Warm Pool (Fig. 10). Although the terrigenous deposits of the paleo-Sunda and Mekong Rivers provide a number of attractive targets in the southern part of the SCS, and piston cores in the region have high sedimentation rates and display high frequency climate variations, especially since the last glaciation. Safety considerations have entailed moving the site farther downslope (to the north) and limiting penetration. This southern location will be the only site within the Western Pacific Warm Pool and will provide a thermal contrast to the northern sites.
Proposed Site SCS-9 is at a water depth of 2830 m. Penetration is limited to 400 m, reaching the upper part of the upper Miocene.
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