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doi:10.2204/iodp.proc.303306.106.2006 Site U13061Expedition 303 Scientists2Background and objectivesIntegrated Ocean Drilling Program Site U1306 is located on the Eirik Drift in 2272 m water depth, 190.7 km (102.9 nmi) northeast of Site U1305 (Fig. F1). Site U1306 provides a shallower water depth site than Site U1305, which is located in 3459 m water depth. As discussed in “Background and objectives” in the “Site U1305” chapter, the difference in water depth between the two sites generates a contrasting sedimentation pattern largely because of the behavior of the Western Boundary Undercurrent (WBUC). The WBUC shallows and becomes less intense during glacial intervals, resulting in relatively expanded glacial intervals at Site U1306 and, in contrast, relatively expanded interglacial intervals at Site U1305. Core HU90-013-012, at 58.92°N, 47.12°W, is located 114.5 km (61.8 nmi) northwest of Site U1306 (Fig. F1). This 12.4 m core, retrieved in 2830 m water depth, was collected from the CCGS Hudson in 1991. Cores MD99-2228 and MD99-2242 were collected in 2900 m water depth at almost the same location (58.93°N, 47.14°W and 58.92°N, 47.13°W, respectively) during the 1999 Images cruise of the Marion-Dufresne (Turon et al., 1999). The susceptibility records from the two Marion-Dufresne cores can be correlated one to another and to Core HU90-013-012 (Fig. F2) and represent the best guide as to what to expect at Site U1306. Core HU90-013-012 extends into marine isotope Stage (MIS) 6, with Holocene and MIS 5e being largely absent and restricted to a few decimeters at most (Hillaire-Marcel et al., 1994; Stoner et al., 1995, 1998). The mean sedimentation rate between the base of the Holocene and the base of MIS 5d is ~9 cm/k.y. The contrasting sedimentation pattern between glacial and interglacial intervals is attributed to the location of the site at a water depth within the main axis of the WBUC (Fig. F1 in the “Site U1305” chapter). The axis of the WBUC was weaker and probably at a shallower water depth during glacial intervals, thereby facilitating deposition at the site (Hillaire-Marcel and Bilodeau, 2000). For the purpose of generating a high-resolution record of the uppermost Pliocene and Quaternary from the Eirik Drift in the 2000–2500 m water depth range, we targeted a location where the mid-Upper Pliocene seismic Reflector R1 was deepest at the desired water depth. Using the multichannel seismic network obtained over the Eirik Drift during Knorr Cruise KN166-14 in summer 2002, Site U1306 was placed at the crossing of seismic Line 19 and seismic Line 24c (Fig. F3 in the “Site 1305” chapter) at common depth point (CDP) 7435 on Line 24c and CDP 2550 on Line 19 (Fig. F3). The location is characterized by planar seismic reflectors, implying uncomplicated stratigraphy devoid of debris flows or mass transport deposits. At Site U1306, seismic Reflector R1 lies at an estimated depth of 420 meters below seafloor (mbsf) (0.27 s), indicating a mean sedimentation rate since mid-Late Pliocene of ~14 cm/k.y. The achieved penetration at Site U1306 (294.8 mbsf) is indicated in Figure F3, and the mean sedimentation rate for the recovered section was found to be ~15 cm/k.y. The 3.5 kHz data along seismic Line 19 are also shown (Fig. F4). As explained above and in the “Site U1305” chapter, the objectives at Site U1306 and Site U1305 are closely linked. The two sites are expected to exhibit contrasting sedimentation patterns. Glacial MISs at Site U1306 are expected to be relatively expanded and interglacial stages relatively condensed. The opposite pattern is expected at Site U1305. This alternating pattern provides a high-sedimentation-rate (high resolution) composite record at the two sites and will constrain the activity of the WBUC during the Quaternary. For Sites U1302, U1303, U1305, and U1306, the detrital layer stratigraphy, characterized by both detrital-carbonate layers and low-detrital-carbonate layers, provides a proxy for episodes of instability of the surrounding ice sheets, particularly the Laurentide and Greenland Ice Sheets. Detritus from the Greenland Ice Sheet was delivered to Site U1306 through slope gullies and then entrained in contour currents to the site (Cremer, 1989; Hiscott et al., 1989). Detritus derived from the Laurentide Ice Sheet was delivered as ice-rafted debris or as spillover turbidites from the Northwest Atlantic Mid-Ocean Channel, with the fine fraction deposited from suspension at Sites U1305 and U1306. The detrital layer stratigraphy at Site U1306 will be correlated with the detrital layer stratigraphies at Sites U1302, U1303, and U1305 and with the classic Heinrich-layer stratigraphy of the central Atlantic. The isotopic signature from both planktonic and benthic foraminifers and the microfossil assemblages will provide information on water mass structure, meltwater pulses, sea-surface temperatures, the activity of the West Greenland Current and WBUC, and, hence, the formation of North Atlantic Deep Water (Fig. F1 in the “Site 1305” chapter). The high mean sedimentation rate at Site U1306 (15 cm/k.y.), with more elevated sedimentation rates during glacial intervals, implies that this environmental record will have high resolution. In addition, the record has the attributes for excellent stratigraphic age control within the context of a paleointensity-assisted chronostratigraphy. |
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