HR: 16:45h
AN: PP44A-04    [Abstracts]
TI: Sea-surface hydrographic variations during the past 170 thousand years in the southeastern South China Sea
AU: * Wei, K
EM: weiky@ntu.edu.tw
AF: Dept. of Geosciences, National Taiwan University, PO BOx 13-318, Taipei, 106 Taiwan
AU: Teh, E
EM: yuyucheng@ntu.edu.tw
AF: Dept. of Geosciences, National Taiwan University, PO BOx 13-318, Taipei, 106 Taiwan
AU: Shiao, L
AF: Inst. of Applied Geophysics, National Taiwan Ocean University, 2, Bei-Ning Rd., Keelung, 20224 Taiwan
AU: Chen, M
EM: mtchen@mail.ntou.edu.tw
AF: Inst. of Applied Geophysics, National Taiwan Ocean University, 2, Bei-Ning Rd., Keelung, 20224 Taiwan
AB: Using Mg/Ca ratios of planktonic foraminifer {\it Globigerinoides sacculifer} and alkenone unsaturation index of bulk sediments from the deep-sea core MD972142, we reconstructed sea-surface temperatures of the past 170 thousand years (kyrs) for the southeastern South China Sea (SCS) near the Palawan Island. The SSTs fluctuated between ~$24\deg$C and $29\deg$C through the past two glacial-interglacial cycles with the coldest temperature of $24\deg$C at the last glacial maximum. The SSTs during the late Holocene are comparable to the peak values of the marine oxygen isotope stage 5. The effects of temperature and ice-volume were subtracted from the $\delta$18O values of planktonic foraminifer {\it Globigerinoides sacculifer} to examine the past salinity and precipitation variations. The resultant residual $\delta$18O profiles indicate that the surface oceans have been fresher than today's for most of the time during the past 170 kyrs. In general, during the low sea-level periods, the ­ice-volume-corrected sea water $\delta$18O­" values tend to deviate from the current value, signifying various degrees of freshening of sea surface waters. Contrarily, during high sea-level stands, the surface waters tend to be as salty as it is today. A detailed examination of the hydrographic variation during the past 22 kyrs shows that the ice-volume-corrected $\delta$18O varied by 1 $\permil$. The relatively light values during the last glacial maximum and the Younger Dryas are ascribed to the low sea-level and thus a limited water exchange between the open ocean and the SCS. The Holocene values are virtually the same as today­Ýs except for two minor increases during 8-9 ka and ~ 3 ka. Notably, these two ­salty­" events are coincident with the ­8.2 ka­" event and the ­{\it Pulleniatina} Minimum Event­". A reduction of precipitation and thus a weakening of the summer monsoons might be the regional manifestation of these two events in the South China Sea.
DE: 9355 Pacific Ocean
DE: 4215 Climate and interannual variability (3309)
DE: 4267 Paleoceanography
DE: 1620 Climate dynamics (3309)
DE: 1655 Water cycles (1836)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting