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| Titel |
Bulk organic δ13C and C/N as an indicator for the palaeomonsoonal variability during the mid Holocene - A case study from the Pearl River estuary, China |
| VerfasserIn |
F. Yu, Y. Zong, J. M. Lloyd, G. Huang, M. J. Leng, A. L. Lamb, W. W.-S. Yim |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250019802
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| Zusammenfassung |
| This study aims to examine the applicability of organic carbon isotopes as a palaeo-monsoon
proxy for summer monsoon freshwater discharge, using a case study in the Pearl River
estuary, China. This research is based on the assumption that different sources of organic
carbon possess different isotopic signatures and these differences are bigger than changes in
the response to climate variability. Specifically, sources of organic matters within an estuary
including terrestrial plants and soil, saltmarshes and mangroves, and in-situ productivity
of algae. We assume that organic carbon materials of freshwater environment are
chemically different from those of marine environment. Thus, δ13C and C/N values of
organic matters from estuarine sediments can help differentiate sources of organic
carbon.
Samples collected range from terrestrial areas including plants and soil samples, to the
estuarine area including seasonal estuarine particulate organic carbon (POC) and
surface sediment. Results suggest variation of δ13C and C/N ratios in the Pearl
River delta and estuarine area is highly related to sources of the organic matter. For
example, surface sediment samples from the marine environment exhibit more positive
δ13C values (–23.1 to –21.1), whilst samples from the freshwater environment
possess more negative δ13C values (–26.8 to –24.6). This relationship is supported by
isotope ratios of suspended organic matter taken from different sites across the
estuary. Thus, in the Pearl Estuary, more negative δ13C values reflect greater level
of contribution of freshwater organic carbon, i.e. stronger monsoonal freshwater
discharge.
We then applied this technique to a sediment core obtained from the mouth of the estuary.
The results show that freshwater discharge from the Pearl River catchment gradually declined
from c. 6500 to 2300 cal. years BP, suggesting a gradual weakening of summer
monsoon precipitation. The results are comparable to stalagmite records from caves
and records from pollen analyses from southern China. We conclude that organic
carbon isotopes are a good environmental proxy for palaeo-monsoon variability. |
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