(2020) The Distribution of Long-Chain N-Alkan-2-Ones in Peat can be Used to Infer Past Changes in pH
Zhang Y, Huang X, Wang R & Naafs D
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10l: Room 3, Saturday 27th June 01:21 - 01:24
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This is a very interesting topic. When using the ketones to estimate the pH values, is it necessary to determine the sources of ketones first? And if there is any difference/correlation between the reconstructed pH values based on ketones and bGDGTs?
Dear Professor Wang, Thank you very much for your questions. I was unable to answer your questions in the video conference due to time constraints. I am very sorry about this. Yes, it is important to determine the source of ketones before use. Because the pH proxy is based on the conversion of ketones from n-alkanes and fatty acids. We can determine the source of ketones through similar molecular distribution, or the negative correlations between the content of ketones and n-alkanes and fatty acids. More importantly, some peat-forming plants can also synthesize ketones. Although the content is low, we need to exclude plants as the main source of ketones before using them as paleo-pH proxy. For example, we have evaluated the content of ketones in many plants from Chinese peatlands, and used the compound-specific carbon isotope composition to exclude plant sources. The second question is a very constructive one. We have been trying to compare different paleo pH proxies. We compared the estimated pH values of ketones with branched GDGTs in the Dajiuhu peat core. The two trends are consistent. The pH reconstructed by brGDGTs also shows relatively high values during the last glacial, and then decreased during the early Holocene. However, the absolute values are inconsistent. This may be because the pH calculation formula of branched GDGTs (CBT) is based on global soil and peat, while the pH formula of ketones is currently only a regional calculation. Differences in global and regional corrections may lead to inconsistent estimates of absolute pH values. We are further exploring the distribution of ketones in the surface peat of other peatlands to correct the pH calculation formula.
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