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Site U14251

R. Tada, R.W. Murray, C.A. Alvarez Zarikian, W.T. Anderson Jr., M.-A. Bassetti, B.J. Brace, S.C. Clemens, M.H. da Costa Gurgel, G.R. Dickens, A.G. Dunlea, S.J. Gallagher, L. Giosan, A.C.G. Henderson, A.E. Holbourn, K. Ikehara, T. Irino, T. Itaki, A. Karasuda, C.W. Kinsley, Y. Kubota, G.S. Lee, K.E. Lee, J. Lofi, C.I.C.D. Lopes, L.C. Peterson, M. Saavedra-Pellitero, T. Sagawa, R.K. Singh, S. Sugisaki, S. Toucanne, S. Wan, C. Xuan, H. Zheng, and M. Ziegler2

Background and objectives

Integrated Ocean Drilling Program (IODP) Site U1425 is in the central part of the marginal sea surrounded by the Japanese Islands, the Korean Peninsula, and the Eurasian continent at 39°29.44′N, 134°26.55′E and 1909 meters below sea level (mbsl). The site is situated in the central part of a northeast-southwest–oriented graben in the middle of the Yamato Bank. Site U1425 is ~60 km southwest of Ocean Drilling Program (ODP) Site 799, which also sits within the graben (Fig. F1). A major difference between these two sites is that Site 799 is located in the deepest part of the graben and Site U1425 is situated on a terrace that is one step higher than the bottom of the graben (Fig. F2). The higher topographic setting of Site U1425 was chosen to minimize the influence of turbidites, which were numerous at Site 799.

Site U1425 is the northernmost site of the southern half of the latitudinal transect targeted by IODP Expedition 346 and the middepth site of the depth transect. Preliminary site survey results suggested that Site U1425 was characterized by very slow yet continuous sedimentation (4 cm/k.y.) during the last 600 k.y., which is ideal for detecting the contribution of eolian dust from the Asian continent. Based on the relatively low geothermal gradient of ~100°C/km (observed at nearby Site 799), the opal-A/opal-CT boundary at Site U1425 was predicted to be at ~400 m core depth below seafloor (CSF-A) (see the “Methods” chapter [Tada et al., 2015b]) (Ingle, Suyehiro, von Breymann, et al., 1990). At this site, we expected to recover unconsolidated sediment back to 10 Ma or older, permitting reconstruction of eolian dust flux and provenance changes over this period. In combination with other sites in the marginal sea, it will be possible to reconstruct changes in the position of the atmospheric Westerly Jet stream axis during the last ~5 m.y.

Site U1425 is located on the Subpolar Front in the marginal sea and is under the influence of the first branch of the Tsushima Warm Current (TWC) during summer. Sediment from Site U1425 will be used to reconstruct sea-surface temperature changes associated with the north–south movement of the Subpolar Front, which is considered to be influenced by the strength of the TWC (Isoda, 2011). In addition, the sea ice margin may have reached the site location during glacial periods, and the sedimentary record at this site will help constrain the southern limit of ice-rafted debris events. Together with results from IODP Sites U1422–U1424, Site U1425 will enable us to reconstruct temporal changes in the southern limit of sea ice in the marginal sea during the last 4 m.y. Lastly, we will reconstruct changes in deepwater oxygenation and calcium carbonate compensation depth (CCD) during the last 4 m.y. by combining results from the Expedition 346 depth transect sites.

1 Tada, R., Murray, R.W., Alvarez Zarikian, C.A., Anderson, W.T., Jr., Bassetti, M.-A., Brace, B.J., Clemens, S.C., da Costa Gurgel, M.H., Dickens, G.R., Dunlea, A.G., Gallagher, S.J., Giosan, L., Henderson, A.C.G., Holbourn, A.E., Ikehara, K., Irino, T., Itaki, T., Karasuda, A., Kinsley, C.W., Kubota, Y., Lee, G.S., Lee, K.E., Lofi, J., Lopes, C.I.C.D., Peterson, L.C., Saavedra-Pellitero, M., Sagawa, T., Singh, R.K., Sugisaki, S., Toucanne, S., Wan, S., Xuan, C., Zheng, H., and Ziegler, M., 2015. Site U1425. In Tada, R., Murray, R.W., Alvarez Zarikian, C.A., and the Expedition 346 Scientists, Proc. IODP, 346: College Station, TX (Integrated Ocean Drilling Program). doi:10.2204/iodp.proc.346.106.2015

2Expedition 346 Scientists’ addresses.

Publication: 28 March 2015
MS 346-106