25th International Meeting on Organic Geochemistry IMOG 2011

P-487
Late Quaternary environmental change of Yellow River Basin: an
organic geochemical record in Bohai Sea (North China)
Yunping Xu 1,2 , Wenbing Tan 1 , Dongyan Sun 1
1 MOE Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Beijing,
China, 2 Center for Ocean Studies at Peking University, Beijing, China (corresponding
author:yunpingxu@pku.edu.cn)
Bulk geochemical characterization (total organic
carbon, grain size distribution, carbon isotope
composition) and molecular biomarkers (lignin
phenols, straight chain aliphatic hydrocarbons,
glycerol dialkyl glycerol tetraethers) were analyzed for
a 21 m deep core from the Bohai Sea (north China),
spanning ca 21 ka BP. These paleo-proxies
presented remarkable differences between the late
glacial period and the Holocene, reflecting continental
and coastal environments, respectively. Two peat
layers were deposited during the period of ca 9000–
8460 yr BP. Thereafter the core site has been
consistently covered by seawater until recent
reclamation of land from sea. The occurrence of a
total organic carbon maximum from ca 6000–3800 yr
BP was attributed to delivery of organic carbon
enriched sediments via the Yellow River, consistent
with increased vegetation density and higher
development of soil under warm and humid mid-
Holocene climate conditions. The distributions of
lignin phenol compositions and C31/C29 n-alkanes
suggested the largest expansion of woody plants
between ca 5300 and 4000 yr BP, corresponding to
the extremely favorable climatic conditions. Since ca
3800 yr BP, an abrupt increase in the C31/C29 nalkane
ratio suggested higher abundance of grasses,
consistent with a drying climate trend after the mid-
Holocene. Since our coastal sediments close to the
Yellow River outflow contain a catchment-integrated
environmental signal of the river basin, molecular
proxies demonstrate that the variability of vegetation
distributions in the Holocene is a widespread
phenomenon in those areas adjacent to Yellow River
basin.
Reference:
Shi, Y., Kong, Z., Wang, S., Tang, L., Wang, F., Yao,
T., Zhao, X., Zhang, P., Shi, S., 1993. Mid-Holocene
climates and environments in China. Global &
Planetary Change 7, 219–234
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