Title

Inter-molecular variations of fatty acid δD in algae and submerged plants from the north-eastern Tibetan Plateau

Authors

Hu Liu, Chinese Academy of SciencesFollow
Hong Yang, Bryant UniversityFollow
Yunning Cao, Chinese Academy of Sciences
Qin Leng, Bryant UniversityFollow
Weiguo Liu, Chinese Academy of SciencesFollow

Document Type

Conference Proceeding

Comments

Abstract to conference proceeding

Identifier Data

https://agu.confex.com/agu/fm18/meetingapp.cgi/Paper/349837

Publisher

American Geophysical Union Meeting

Abstract

Hydrogen isotopic ratios (δD) of fatty acids (FAs) in lake sediments have been widely used in palaeoclimatic reconstruction, however, there are limited investigations on FA δD values in algae and submerged plants from natural lakes, greatly hampering the application and interpretation of their δD values in lacustrine environments. In this study, we systematically investigated δD values of short-chain (C₁₄-C₁₈), mid-chain (C₂₀-C₂₄), and long-chain (C₂₆-C₃₀) FAs in four algae and submerged macrophytes, including two algal genera Chara and Cladophora and two angiospermous genera Potamogeton and Ruppia, which commonly occur in six lakes on the north-eastern Tibetan Plateau. Our results are as below: (i) In C₄-like taxa (Potamogeton, Ruppia, and Chara), the C₁₆ and C₂₆ FAs have minor differences in their δD values, while in the C₃-like Cladophora, δD values of C₁₆ FAs are significantly more negative (avg. -48 ± 7‰) than those of the C₂₆ FAs. We propose that different photosynthetic mechanisms in these algae and submerged plants account for the different inter-molecular δD variations between C₁₆ and C₂₆ FAs. (ii) δD values of C₂₆ FAs in the carbonate coated alga Chara are significantly correlated with the δ¹⁸O values of carbonate encrustations; such a co-variance suggests that in addition to lake water, other factors may also affect both lipid synthesis and carbonate encrustation building up in Chara, leading to a significantly positive apparent hydrogen isotope fractionation factors (ε_FA-W) between C₂₆ FAs of Chara and lake water. (iii) δD values of C₂₆ FAs from Potamogeton, Ruppia, and Cladophora are correlated well with lake water δD values (R² = 0.84, p < 0.001, n = 19), suggesting that their δD values of long-chain FAs potentially record δD variations of lake water with the apparent hydrogen isotope fractionation factors (ε_FA-W) of C₂₆ FAs ranging from -153 to -134‰. Our results highlight the impact of different photosynthetic pathways on the inter-molecular difference of FA δD values in algae and submerged plants and illustrate both the potential and the challenge of applying their FA δD values as a palaeo-hydrology proxy.