IODP

doi:10.2204/iodp.sp.329.2010

Site summaries (continued)

Site SPG-4A

Priority: Primary
Position: 26°28.8932′S, 137°56.3625′W (WGS 84) (26.4816°S, 137.9394°W)
Water depth (m) 4284
Target drilling depth (mbsf): 120 m, including 100 into basement
Approved maximum penetration (mbsf): Up to 100 m basement penetration
Previous drilling in area: Closest drilling:
• DSDP Leg 92 Site 597, 640 nmi away
Comments: International waters; 250 nmi from Gambier Island, French Polynesia Preferred weather window: November–December
Survey coverage (track map, seismic profile): High-resolution seismics:
• Primary line(s): MCS Line 3 - Shotpoint 6896 (Fig. AF10)
• Crossing line(s): MCS Line 1 - Shotpoint 6125 (Fig. AF11)
• Subbottom profile, 3.5 kHz: Line 3 - JDay 364 at 04:29 GMT
• Detailed bathymetry and site location (swath bathymetry: collected with SIMRAD EM120) (Fig. AF12)
Sediment cores: Two piston cores, two trigger cores, one gravity core, and one eight-barrel multicore
Objectives (see text for complete details): • Document the habitats, metabolic activities, genetic composition, and biomass of microbial communities in subseafloor sediments with very low total activity.
• Test how oceanographic factors (such as surface ocean productivity) control variation in sedimentary habitats, activities, and communities from gyre center to gyre margin.
• Quantify the extent to which these sedimentary communities may be supplied with electron donors by water radiolysis, a process independent of the surface photosynthetic world.
• Determine how the basement habitats, potential activities, and communities vary with crust age and hydrologic regime (from ridge crest to abyssal plain).
Drilling/Coring program: • Quadruple APC to basement; RCB upper 100 m of basement
• Temperature measurements: APCT-3
Downhole logging program: Wireline logging: triple combo, FMS-sonic
Anticipated lithology: Homogeneous very dark brown clay with some mottling to very dark gray clay