HR: 0830h
AN: U11B-0006    [PDF]
TI: Exploring Cyclic Changes of the Ocean Carbon Reservoir in Deep-Sea Records from the South China Sea
AU: * Wang, P
EM: pxwang@online.sh.cn
AF: Tongji University, Department of Marine Geology, 1239 Siping Road, Shanghai, 200092 China
AU: Tian, J
EM:
AF: Tongji University, Department of Marine Geology, 1239 Siping Road, Shanghai, 200092 China
AU: Chen, X
EM:
AF: Tongji University, Department of Marine Geology, 1239 Siping Road, Shanghai, 200092 China
AU: Liu, Q
EM:
AF: Tongji University, Department of Marine Geology, 1239 Siping Road, Shanghai, 200092 China
AU: Xu, J
EM:
AF: Tongji University, Department of Marine Geology, 1239 Siping Road, Shanghai, 200092 China
AB: ODP Leg 184 drilled 17 holes at 6 deep water sites in the South China Sea (SCS), resulting in high-resolution long isotope sequences in the Western Pacific for the first time, such as a 5-myr record with 2-3 ka time resolution in the South (ODP Site 1143, 9$\deg$22'N, 113$\deg$17'E, water depth 2772 m), and a continuous 23-Ma isotope sequence with ~20 ka resolution in the North (ODP Site 1148, 18$\deg$50'N, 116$\deg$34' E, w.d.3294m). A distinguished feature in the 13C curves is the occurrence of long-term cycles of 400-500 ka superimposed on high- frequent fluctuations, and the 13C sequence is periodically punctuated by carbon isotope maximum events or 13Cmax, which are present in all long sequences over the global ocean. According to the Quaternary records from Site 1143 and elsewhere, major ice-sheet expansion and major transition in glacial cyclicity ( such as the Mid-Brunhes Event and the Mid-Pleistocene Revolution ) were all preceded by disturbance in the ocean carbon reservoir expressed as an episode of 13Cmax, implying the role of carbon cycling in modulating the glacial periodicity. This disturbance in carbon reservoirs might be attributed to changes in phytoplankton functional groups, the diatom/coccolith ratio, which determines `rain ratio' in oceanic carbon deposition. Because the diatom/coccolith ratio depends on the availability of silica mostly provided by tropical rivers, eventually the long-term variations of oceanic 13C are related to low-latitude processes such as monsoon. Judging from the records at Site 1148 and elsewhere,13C and 18O co-varied throughout the Miocene at the 400-ka eccentricity band, and the covariance persisted until at least 3 Ma ago. This is believed to be the characteristic of Antarctic glacial cycles. With the development of Arctic ice sheet, the relation between 13C and 18O in long-term cycles has been complicated: Over the last myr, the 100-ka periodicity turned predominant and the 400-ka vanishes in the 18O record but extended to ~ 500-ka in the13C record. Therefore, the carbon cycling has its own periodicity in reposing to orbital forcing. As the Earth is now passing through a new carbon isotope maximum, it is of vital importance to understand the cyclic variations in the ocean carbon reservoir and its climate impact.
DE: 3030 Micropaleontology
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 4806 Carbon cycling
DE: 9355 Pacific Ocean
SC: U
MN: 2003 Fall Meeting