HR: 0830h
AN: PP11A-0212    [PDF]
TI: Paleo-SST and Seawater $\delta^{18}$O Reconstruction of the Kuroshio-Front Region since the Last Glacial Maximum
AU: * Sagawa, T
EM: sagawa@ees.hokudai.ac.jp
AF: Graduate School of Environmental Earth Sciecne, Hokkaido University, Kita-ku Kita10 Nishi5, Sapporo, 060-0810 Japan
AU: Toyoda, K
AF: Graduate School of Environmental Earth Sciecne, Hokkaido University, Kita-ku Kita10 Nishi5, Sapporo, 060-0810 Japan
AU: Oba, T
AF: Graduate School of Environmental Earth Sciecne, Hokkaido University, Kita-ku Kita10 Nishi5, Sapporo, 060-0810 Japan
AB: In the northwest Pacific, the Oyashio Current (low-temperature, low-salinity) and the Kuroshio Current (high-temperature, high-salinity) meet each other today at the east coast of Japan, and the Kuroshio-Front is located offshore Kashima in central Japan. Latitudinal gradient of SST is extremely steep in this region, and variations of SST and hydrological structure offshore Kashima are closely related to the north-south migration of the Kuroshio-Front. $\delta^{18}$O$_{calcite}$ ($\delta^{18}$O$_{c}$) and Mg/Ca ratios of {\it Globigerina bulloides} were analyzed from piston core MD012420 ($36\deg04$.05AŸƒ_›N, $141\deg48.92$AŸƒ_›E, 2101 m), recovered during the IMAGES-WEPAMA cruise to reconstruct water mass structures offshore Kashima. Both $\delta^{18}$O$_{c}$ and Mg/Ca ratios were measured from the same samples, then Mg/Ca-based SSTs were combined with $\delta^{18}$O$_{c}$ to estimate past seawater $\delta^{18}$O ($\delta^{18}$O$_{w}$) using a $\delta^{18}$O-temperature calibration. Estimated SSTs from the core-top and Last Glacial Maximum (LGM) are $15.8\deg$C and $6.4\deg$C, respectively. The calculated $\delta^{18}$O are $AŸ_0.10\permil$ for the Holocene average and $0.66\permil$ for the LGM average. The difference in calculated $\delta^{18}$O$_{w}$ between LGM and Holocene, $0.76\permil$, includes both global continental ice volume change and local $\delta^{18}$O$_{w}$ (salinity) changes. Assuming the amplitude of $\delta^{18}$O$_{w}$ variation due to glacial ice volume was $1.0\permil$, then the residual, $-0.24\permil$, must be due to local $\delta^{18}$O$_{w}$ (salinity) change. We suggest that the Kuroshio-Front was located further south and the influence of the Oyashio Current, constituting low salinity water, was dominant offshore Kashima during the LGM.
DE: 1050 Marine geochemistry (4835, 4850)
DE: 4267 Paleoceanography
DE: 9355 Pacific Ocean
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting