25th International Meeting on Organic Geochemistry IMOG 2011

P-450
Proxies based on archaeal and bacterial GDGTs in surface
sediments of the Yangtze River Estuary, China: implications for
marine organic biogeochemistry
Peng Yao 1,2,3 , Brendan Keely 3 , Zhigang Yu 1,2 , Hongzhen Yin 1 , Meixun Zhao 1,2
1 Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, China, Qingdao, China,
2 Institute of Marine Organic Geochemistry, College of Chemistry and Chemical Engineering, Ocean
University of China, Qingdao, China, 3 Department of Chemistry, University of York, UK, York, United
Kingdom (corresponding author:yaopeng@ouc.edu.cn)
Glycerol dialkyl glycerol tetraethers (GDGTs) are
derived from archaeal and bacterial membrane lipids,
which occur ubiquitously in aquatic environments and
soils (Rueda et al., 2009). In recent years, proxies
based on GDGTs, such as TEX86, BIT, MBT/CBT
have been used successfully to reconstruct past sea
surface temperature (SST), continental mean annual
air temperature (MAT) and soil pH changes, and to
determine the relative inputs of fluvial soil organic
matter (OM) in marine environments [1] .
In China, similar studies are few, though the
importance of such studies has been recognized and
preliminary studies in lake sediments have been
conducted
[2] . The determinations of GDGTs in
China‘s estuaries and coastal environments, however,
have not been performed.
As the third largest river in the world (~6300 km in
length), the Yangtze River is of particular interest to
biogeochemists and organic geochemists because of
its high water runoff and sediment discharge. In
recent years, frequent harmful algal blooms and
increasing hypoxia area within the Yangtze River
Estuary (YRE) and its adjacent sea areas further
highlight the importance of studies in this estuary [3, 4] .
Therefore, comprehensive studies of marine organic
biogeochemistry in such an estuary are very
important and meaningful.
Here, we report GDGTs in surface sediments
collected from the upper YRE to the inner-shelf of the
East China Sea (ECS) in order to establish the
suitability of the use of the TEX86, BIT, MBT and CBT
proxies in this area. This is the first large scale test
case to validate the applicability of these novel
molecular proxies in China‘s seas and estuaries.
The high BIT values in upper estuary and river
mouth sediments, and further offshore, decrease
rapidly seaward, indicative of soil OM transport from
the upper estuarine regions.
Reconstructed SST values of samples from the
inner-shelf of the ECS, where marine OM dominates
relative to soil OM, compare well with multi-year
average SST obtained from historical records. By
contrast, the river mouth area, which has high BIT
values high sedimentary OM contents and high
deposition rate, is suitable for studies of historical
changes in river flow and soil OM contributions.
The distributions of branched GDGT-based MAT
and soil pH at the YRE are characterized by low
values at river mouth area, gradually increasing
seaward. The distribution differences of MAT and soil
pH could be caused by several factors, such as
differences in the deposition rates of sediments, in
situ production and selective degradation of GDGTs.
The high OM content and deposition rate of
sediments make the river mouth area a better place to
obtain a high resolution reconstructions of MAT and
soil pH for the Yangtze River drainage basin.
References
[1] Weijers et al., 2009. Geochimica et Cosmochimica Acta
73, 119–132.
[2] Yao et al., 2010. Advances in Earth Science 25, 474-483.
[3] Chen et al., 2007. Marine Environmental Research 64,
399–408.
[4] Li et al., 2010. Harmful Algae 9, 531–539.
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