IODP Proceedings    Volume contents     Search


Site U14261

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 U1426 is in the south central part of the marginal basin at 37°2.00′N, 134°48.00′E and 903 meters below sea level. The site is situated near the top of the Oki Ridge, which extends southwest–northeast and bounds the southern margin of the Yamato Basin. Site U1426 is at the same location as Ocean Drilling Program (ODP) Site 798 ~150 km to the north of Honshu Island (Fig. F1). The bathymetric setting of Site U1426 was chosen to minimize the influence of turbidites.

Site U1426 is under the influence of the second branch of the Tsushima Warm Current (TWC), which is a highly meandering current characterized by eddies (Hase et al., 1999). Previous results from Site 798 as well as from a piston core retrieved from almost the same location as Site U1426 during the site survey cruise suggest an average sedimentation rate of ~80 m/m.y. (Ingle, Suyehiro, von Breymann, et al., 1990). These rates are slightly higher than those found at previous IODP Sites U1423–U1425, but they are still low enough to detect the contribution of eolian dust from the Asian continent, considering the relatively large contribution of biogenic material at this site. Based on a moderate geothermal gradient of ~110°C/km (observed at Site 798), the opal-A/opal-CT boundary at Site U1426 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). We expected this to allow recovery of unconsolidated sediment back to at least 4 Ma, permitting reconstruction of eolian dust flux and provenance over this period in the southern part of the marginal basin. The relatively shallow depth of Site U1426 was also expected to provide better preservation of calcareous microfossils.

Located in the middle of the southern half of the IODP Expedition 346 latitudinal transect, Site U1426 lies at a relatively shallow depth in the expedition depth transect. Together with results from Sites U1423–U1425, Site U1426 will enable us to reconstruct changes in the position of the atmospheric Westerly Jet axis during the last ~5 m.y. and sea-surface temperature changes associated with the north–south movement of the Subpolar Front, as it is related to the strength of the TWC (Isoda, 2011). Finally, we will reconstruct changes in deepwater oxygenation and calcium carbonate compensation depth (CCD) during the last ~5 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 U1426. 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.346.107.2015

2Expedition 346 Scientists’ addresses.

Publication: 28 March 2015
MS 346-107