HR: 1330h
AN: PP22A-1204    [PDF]
TI: Evidence of Arid to Semi-arid Climate Near Western Pacific Warm Pool During Sea-Level Lowstands: Caliche Surfaces in Late Cenozoic Carbonates of Nansha Islands, South China Sea
AU: * Gong, S
EM: gng@mail.nmns.edu.tw
AF: Department of Geology, National Museum of Natural Science, 1 Kuan Chien Road, Taichung, 404 Taiwan
AU: Mii, H
AF: Department of Earth Science, The National Taiwan Normal University, 88 Sec. 4 Tingjou Rd, Taipei, 116 Taiwan
AU: Horng, C
AF: Institute of Earth Science, Academia Sinica, NanKang P.O.Box 1-55, Taipei, 115 Taiwan
AU: Huang, F
AF: Exploration & Development Research Institute, Chinese Petroleum Corporation, 1 Da Yuan, Wen Shan, Miaoli, 360 Taiwan
AU: Chi, W
AF: Exploration & Development Research Institute, Chinese Petroleum Corporation, 1 Da Yuan, Wen Shan, Miaoli, 360 Taiwan
AU: Yui, T
AF: Institute of Earth Science, Academia Sinica, NanKang P.O.Box 1-55, Taipei, 115 Taiwan
AU: Torng, P
AF: Exploration & Development Research Institute, Chinese Petroleum Corporation, 1 Da Yuan, Wen Shan, Miaoli, 360 Taiwan
AU: Huang, S
AF: Exploration & Development Research Institute, Chinese Petroleum Corporation, 1 Da Yuan, Wen Shan, Miaoli, 360 Taiwan
AU: Wang, S
AF: Department of Geology, National Museum of Natural Science, 1 Kuan Chien Road, Taichung, 404 Taiwan
AU: Wu, J
AF: Exploration & Development Research Institute, Chinese Petroleum Corporation, 1 Da Yuan, Wen Shan, Miaoli, 360 Taiwan
AU: Yang, K
AF: Exploration & Development Research Institute, Chinese Petroleum Corporation, 1 Da Yuan, Wen Shan, Miaoli, 360 Taiwan
AB: Whether the climate of tropical seas during glacial periods became cold and dry has been an open debate. Models by different authors proposed the tropical sea-surface temperature (SST) during the Last Glacial Maximum (LGM) to be about 2\deg lower, or 5-6\deg lower than present. The controversy partly arise from disparate reconstructions of temperature from stable oxygen isotope archives of marine sediments. In this paper, we provide field evidence of semi-arid or arid climate during late Cenozoic sea-level lowstands from an atoll located in central South China Sea near the Western Pacific Warm Pool (WPWP). Lower rainfall and higher evaporation associated with the dry conditions might have resulted in less meteoric water component in the surface sea-water, and this factor should be taken into considerations in deciphering temperature from isotopic records. Taiping Islet (Itu Aba), located at N10\deg 23' and E114\deg 22' is part of the Nansha (Spratly) Islands near the northwestern margin of the Western Pacific Warm Pool. Rock cores of a borehole at Taiping became accessible to the authors in the recent years. We identified at least four subaerial exposure surfaces (SES) in the late Cenozoic carbonates. Caliche deposits are recognized on each of the four surfaces on the basis of alveolar texture, micro-rhizolith, caliche glaebules and corroded limestone nodules in reddish matrix (terra-rossa). Caliche developed on limestones typically forms in semi-arid to arid areas with annual precipitation from about 500 to 1000mm, while the modern annual rainfall of Nansha Island is 1800-2100mm. The occurrence of the Nansha caliche suggests the climate was much drier than present during the sea-level lowstands represented by the four SES. During the sea-level falls, reduced surface area of South China Sea with continental shelves exposed might have resulted in less moistures in the atmosphere and therefore less precipitation and higher evaporation rates. As a result, the reduced amount of meteoric fresh water in the surface sea-water may yield heavier oxygen isotopic compositions. We suggest that paleo-SST interpretations based on oxygen isotope archives in or near South Chine Sea should take the precipitation factor into consideration. Previous studies in Southeast Asian land regions and offshore northern Australia have proposed a scenario of a drier WPWP during LGM. Our data suggest such dry condition may not only occur in LGM but also in the previous glacial periods or sea-level lowstands; may not only in lands, but also in the central South China Sea.
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting