HR: 1330h
AN: PP22A-1202    [PDF]
TI: Drastic change of the subtropical circulation in the super El Ni\~{n}o like condition during late Holocene; evidence from the fluctuation of the Kuroshio Current
AU: * Ujiie, Y
EM: yurika@uclink4.berkeley.edu
AF: Museum of Paleontology and Integrative biology, University of California-Berkeley, 1101 Valley Life Sciences Building #4780, Berkeley, CA 94720-4780 United States
AU: Watanabe, N
EM: naoko@nenv.k.u-tokyo.ac.jp
AF: Ocean Research Institute, University of Tokyo, Minamidai 1-15-1, Nakano-ku, Tokyo, 164-8639 Japan
AU: Ikehara, M
EM: ikehara@cc.kochi-u.ac.jp
AF: Center for Advanced Marine Core Research, Kochi University, B200 Monobe Nankoku, Kochi, 783-8502 Japan
AU: Ashi, J
EM: ashi@ori.u-tokyo.ac.jp
AF: Ocean Research Institute, University of Tokyo, Minamidai 1-15-1, Nakano-ku, Tokyo, 164-8639 Japan
AB: In the northwestern Pacific Ocean, the Kuroshio Current is a main component of subtropical circulation and heat transfer under the monsoon and ENSO system. The Ryukyu Arc region, especially the Okinawa Trough, is a key area for studying past variability of the Kuroshio since it is the area where the current becomes strong after diverging from the North Equatorial Current. In this area, Ujiie et al. (2003) reconstructed time-space changes in the surface water masses after 20 ka based on planktonic foraminiferal assemblage of 15 piston core samples. The fluctuations of the most characteristic species of the Kuroshio Water, which is the {\it Pulleniatina} group, represent that the effect of the Kuroshio Current diminished twice during the LGM and late Holocene, from 4.5 to 3 ka, respectively. Especially, the latter event ({\it Pulleniatina} minimum event; PME) has no cooling signal, although other water masses extended over the Ryukyu Arc region. This study focuses on the vertical fluctuations of the Kuroshio Current in the water column, comparing the fluctuations of $\delta$$^{18}$O and $\delta$$^{13}$C between surface and sub-surface habitual species in 5 piston core samples. During the PME, the $\delta$$^{18}$O curves of {\it Pulleniatina obliquiloculata} and {\it Neogloboquadrina dutertrei}, which are living in sub-surface water near the thermocline, indicate heavy values, although sea surface temperature estimated by $\delta$$^{18}$O of {\it Globigerinoides sacculifer} and planktonic foraminiferal assemblage has no change. At the same period, the differences of $\delta$$^{13}$C between {\it P. obliquiloculata} and {\it G. sacculifer} becomes small. According to the decrease of the abundance of the Kuroshio Water species during the PME, the transport of the Kuroshio Current tends to decrease and then the thermocline is shallower in the Okinawa Trough. At present, the transport of the Kuroshio Current decreases, when the North Equatorial Current bifurcate is at northernmost position prior to the El Ni\~{n}o. Impacts of the PME have been recognized outside of the Ryukyu Arc region including the South China Sea and probably within the equatorial Pacific Ocean. Therefore, the PME is likely a response to a broad scale oceanographic-climatic process of the subtropical and tropical circulation.
DE: 4267 Paleoceanography
DE: 4522 El Ni¤o
DE: 4855 Plankton
DE: 4870 Stable isotopes
DE: 9355 Pacific Ocean
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting