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doi:10.2204/iodp.proc.341.105.2014 Site U14191J.M. Jaeger, S.P.S. Gulick, L.J. LeVay, H. Asahi, H. Bahlburg, C.L. Belanger, G.B.B. Berbel, L.B. Childress, E.A. Cowan, L. Drab, M. Forwick, A. Fukumura, S. Ge, S.M. Gupta, A. Kioka, S. Konno, C.E. März, K.M. Matsuzaki, E.L. McClymont, A.C. Mix, C.M. Moy, J. Müller, A. Nakamura, T. Ojima, K.D. Ridgway, F. Rodrigues Ribeiro, O.E. Romero, A.L. Slagle, J.S. Stoner, G. St-Onge, I. Suto, M.H. Walczak, and L.L. Worthington2Background and objectivesSite U1419 is located at 721 m water depth on a gently sloping bank on the continental slope above the Khitrov Ridge (Fig. F1). We informally refer to the feature as Khitrov bank. The site is within the influence of the surface Alaska Coastal Current (Stabeno et al., 2004; Weingartner et al., 2005) and at depths possibly influenced by deeply rooted surface eddies and the North Pacific Intermediate Water. Drilling objectives at the site exploited the preservation of carbonate microfossils and associated geochronologic methods that can be used to develop a high–temporal resolution, proximal sedimentary record of Late Pleistocene glacial dynamics and paleoceanography (Davies et al., 2011; Addison et al., 2012). A primary objective is to constrain the timing of multiple glacial events of the Pacific side of the northwestern Cordilleran ice sheet to test its relation to the dynamics of global ice sheets. An allied goal is to understand the role of North Pacific sea-surface temperatures as a control on the glacial system over the Late Pleistocene, potentially with decadal or century resolution in glaciated and laminated intervals. The proximity of the site to regions of seasonally high surface productivity (Ladd et al., 2007) allows us to address the dynamics of productivity and intermediate water circulation on hypoxia in the northeast Pacific and the role of these processes in the global carbon cycle. The probability for an independent and highly resolved radiocarbon and oxygen isotopic chronology (Davies et al., 2011) offers the potential to document the interrelationship between paleomagnetic intensity and secular variation in the Pacific in comparison with other global records. Coring results and high-resolution compressed high-intensity radar profiler (CHIRP) and multichannel seismic (MCS) reflection data reveal a complex depositional setting. This location is ~30 km west of the Bering Trough mouth, which may have been the terminus of the Bering Glacier at the Last Glacial Maximum (Carlson and Bruns, 1997; Berger et al., 2008) (Fig. F1). Site U1419 was surveyed during Cruise EW0408, resulting in a jumbo piston core (~11.5 m long) that contains a deglacial (~17.5 k.y.) to modern sedimentary record of hemipelagic and glacimarine sedimentation (Barron et al., 2009; Davies et al., 2011; Addison et al., 2012). Seismic reflection data (Fig. F2) reveal a range of seismic facies (Fig. F3) that likely reflect the time-varying input of glacigenic sediment interspersed with biogenic-rich hemipelagic facies. Processed CHIRP images (Fig. F3), coincident with the MCS profiles, reveal that an upper postglacial transparent layer on the profile corresponds to the upper ~8 m of the sediment in Core EW0408-85JC, which dates to younger than 14.7 ka (Davies et al., 2011). Higher amplitude reflections in the CHIRP line and from the sediment/water interface to ~0.03 s two-way traveltime (TWT) (~8–25 m) in MCS Line GOA3201 likely represent glacimarine sediments associated with the local Last Glacial Maximum (Fig. F3). It is hypothesized that the less reflective layered sediments in the MCS profile represent interstadial events, when the Bering Glacier terminus retreated relative to the shelf break and ice rafting of sediment was much reduced or absent. In contrast, the highly reflective intervals could indicate times when ice rafting was active, causing higher accumulation rates of coarser glacigenic sediment. Active faulting is imaged in high-resolution seismic Profile GOA3101, showing surface deformation indicative of significant amounts of extension or transtension (Fig. F3A) (Worthington et al., 2008). Seismic units for Site U1419 are discussed in detail in “Core-log-seismic integration.” They include seismic Units A–K (Fig. F4) and were selected based on seismic facies, possibly reflecting changes in glacial proximity. |
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