Sources of bacterial 3-hydroxy fatty acids in Liangzihu Lake from central China: Implications for paleoclimate reconstruction

Abstract

Bacterial 3-hydroxy fatty acids (3-OH-FAs) derived proxies are new tools for paleoclimate reconstruction. However, their effectiveness in temperature reconstruction in lake environments remains unclear. We investigated the compositions of 3-OH-FA and bacterial community across a transect from nearshore soils to water column and surface sediments in the center of Liangzihu Lake (LZH), central China, to elucidate the origins of 3-OH-FA within the lake environments and to evaluate their potential as temperature proxies. The 3-OH-FA in lake center sediments was found to be produced in situ, which can be further supported by the 16S rRNA gene sequencing results. We quantified the input of soil organic matter (OM) in the lake using a δ¹³C_org based two-end member model. The contribution of soil OM ranged from above 50% in nearshore sediments to < 20% in the lake center, reflecting a decreased influence of soil contribution offshore. Moreover, 3-OH-FA based temperature proxies, RAN₁₃ (the ratio of anteiso to normal C₁₃) and RIN₁₇ (the ratio of iso to normal C₁₇) were examined. The temperature estimates derived from the RAN₁₃ were close to the meteorological temperature, whereas the temperature estimates based on RIN₁₇ are lower than the measured temperature. Therefore, our study not only elucidates the sources of 3-OH-FAs within LZH but also evaluates the reliability of associated temperature indices, which provides insights into temperature reconstruction in lake sediment cores.