Site summaries (continued)

Site GAT-3C (Gateway): upper Miocene

59°03.0′N, 179°12.2′W (WGS 84)
Water depth (m)
Target drilling depth (mbsf):
Approved maximum penetration (mbsf):
Previous drilling in area:
Relocated from GAT-3B to Shotpoint 2860 on Cruise KH99-3, 1999, Line Stk3-7 (EPSP December 2005)
Survey coverage (track map, seismic profile); sediment cores:
R/V Hakuhou-maru Cruise KH99-3 Leg 3 (1999):
• Track map (Figs. AF34, AF35)
• Seismic profiles: Line 3Stk3-7 (W–E); Crossing Line Stk3-5 (S–N) (Figs. AF36, AF37, AF38, AF39)
• 3.5 kHz: Line Stk3-7 (W–E) (Fig. AF40)
• Swath bathymetry: Lines Stk3-7 (W–E) and Stk3-5 (S–N) (Fig. AF41)
• Piston core (9.6 m)
USNS Bartlett Cruise 02, Leg 093 (1970):
• Deep penetration seismic reflection primary line: 256 Day, 1970, 04:56–20:15; begin 58.85100N, 179.94300W; finish 60.57400N, 173.20200W
Objective (see text for complete details):
Reconstruct and monitor evolution of the Arctic/Bering Strait Gateway and Pacific-Atlantic water mass exchange history from the upper Miocene through the Pleistocene.
Relatively deeper depth will provide alternate view to GAT-4C for comparison.
Drilling/coring program:
Triple APC to refusal and XCB to 400 mbsf:
• Holes A, B, and D: APC with core orientation to refusal (~200 mbsf)
• Hole D: XCB to ~400 mbsf
• Hole C: APC to 25 mbsf
Temperature measurements: 3 APCT-3, 2 DVTP if required
Downhole logging program:
Wireline logging: triple combo, FMS-sonic
Anticipated lithology:
Silty clay with siliceous microfossils

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