A reconnaissance study of alkenone stratigraphy for the past 35 m.y. in the northern South China Sea (SCS) using sediments from Sites 1147 and 1148 of Ocean Drilling Program (ODP) Leg 184 has been completed. Alkenones were not detected in sediment samples older than ~31 Ma. However, C37:2 appeared in the sedimentary record between ~8 and 31 Ma and both C37:2 and C37:3 were present between 0 and 8 Ma. These changes in alkenone occurrences may signal a response to global-scale Neogene cooling as well as to monsoon intensification and sea level changes over time as a result of Himalayan uplift and the opening of the SCS. Alternatively, they may be related to an evolutionary record of the development of temperature control on alkenone production in coccolithophores. The Uk´37 index for 0–8 Ma produces sea-surface temperatures (SST) of 19°–26°C, which are in the range of previously determined glacial–interglacial values for the northern SCS. Before the late Pleistocene (~1.2 Ma), the SST range is between 23° and 26°C with less variation. This change in variability may signify the early stage of intensified winter monsoons where cold wind and waters from the north may not yet have had a significant effect on SST or it may be the evolutionary link between the early development of unsaturated alkenones in coccolithophores and modern temperature control of alkenone production. We believe a long-term alkenone record is useful for further understanding of global-scale neogene cooling, the development of the East Asian monsoon system, and the evolutionary development of temperature control on alkenone unsaturation. Our data indicate that a high-resolution Uk´37 record for at least the last ~8 Ma is feasible for the northern SCS.
1Mercer, J.L., and Zhao, M., 2004. Alkenone stratigraphy of the northern South China Sea for the last 35 m.y., Sites 1147 and 1148, ODP Leg 184. In Prell, W.L., Wang, P., Blum, P., Rea, D.K., and Clemens, S.C. (Eds.), Proc. ODP, Sci. Results, 184 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/184_SR/208/208.htm>. [Cited YYYY-MM-DD]
2Department of Earth Sciences, Dartmouth College, 6105 Fairchild Science Center, Hanover NH 03755, USA
3Department of Atmospheric Science, The University of Wyoming, Department 3038, 1000 East University Avenue, Laramie WY 82071, USA. mercer@uwyo.edu
Initial receipt: 10 August 2001
Acceptance: 4 March 2004
Web publication:
2 July 2004
Ms 184SR-208