科研之友
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摘要
The analysis of delta C-13 in speleothem calcite is established as a palaeoenvironmental proxy, but records can often be complex to interpret due to multiple controls on the signal. Here we present a novel palaeoenvironmental application of non-purgeable organic carbon (NPOC) delta C-13 analysis and compound-specific isotope analysis (CSIA) to speleothems, and compare the resultant signals to a conventional calcite delta C-13 record. By accessing the carbon pool held in molecular organic matter, we are able for the first time to produce stable isotope records complementary to the CO2-derived signal from the speleothem calcite, and begin to identify separate ecological and climatic controls. In this sample from north-west Scotland, the calcite delta C-13 record and the NPOC delta C-13 both show fluctuations at a period of increasing wetness and change from birch woodland to more open peatland, the NPOC signal having a strong correlation with biomarkers for vegetation change. We interpret an inverse correlation between the NPOC and CO2 delta C-13 signals as primarily driven by changes in soil conditions impacting upon microbial activity, with decreased activity leading to a reduction in C-13 enrichment of the residual organic matter (the NPOC fraction), and an increase in delta C-13 in the CO2 pool (calcite) due to a decrease in respired C-12. This opens the way for the application of parallel analyses to distinguish between soil conditions and vegetation parameters as the primary control on a record, and highlights the advantage of combining both inorganic and organic geochemical techniques in the palaeoenvironmental interpretation of stable carbon isotopic records.
- 出版日期2013-9-1
