4:45 PM - 5:00 PM
[HCG23-11] Characteristics of biomarker compositions in paleosol layers in the sediment core from Lake Suwa, central Japan
Keywords:paleosol, biomarker, Lake Suwa, paleoenvironment, the last glacier, lacustrine sediment
Soil profile reflects source materials, micro topography, and climatic and environmental conditions. Paleosols, which were formed and buried in the past are important paleoclimatic and environmental archives. Paleosols are identified by plant roots, stratigraphic positions and soil characteristics (Retallack et al., 2001). Organic matters in the sediments are also affected by soil formation and can be used to evaluate paleosols by biogeochemical analysis. Sediments collected from and around lake frequently record the change of various depositional environments such as floodplain and wetland depending on scaling of the lake areas. The sediment core from Lake Suwa contains various sedimentary facies and some paleosols in lacustrine sediments (Hatano et al., 2023). In this study, we analyzed biomarkers in the sediments from Lake Suwa (Nagtano prefecture) to reconstruct paleoenvironment and evaluate pedogenesis.
In our study, we used a sediment core (ST2020) collected from the shore of Lake Suwa. The ages were determined by AMS 14C dating, and the lowermost horizon was estimated to be about 27 cal yrs BP. The sediments (1-2 cm thick) were extracted by solvents and then separated into fractions by silicagel column. The apolar and polar fractions were analyzed by GC-MS. Sedimentary facies evaluated by sedimentary investigation indicated that the depositional environments changed from meandering fluvial, lacustrine, and delta in the ST2020 (Hatano et al., 2023).
In the ST2020 sediments, n-alkanes, anteiso-alkanes, and C30 hopanes were identified as major compounds. We analyzed carbon preference index (CPI) as the alkane proxy and ββ-hopane ratios as the hopane proxy. Especially, in paleosols and samples containing plant roots, CPI values were lower and ββ-hopane ratios were higher. This result might indicate influence of organic molecules from roots and microbes in rhizosphere. n-Alkane compositions from roots are reported to be weak odd number predominance (Gocke et al., 2013). The addition of n-alkanes from roots and fresh biological ββ-hopanes from abundant microbe in rhizosphere (Belin et al., 2018) might make CPI values lower and ββ-hopane ratios higher. Also, higher concentrations of anteiso-alkanes, which is considered to be derived from micro-organisms (Matsumoto et al., 1992), in these samples were likely to indicate high microbial activity.
In our study, we used a sediment core (ST2020) collected from the shore of Lake Suwa. The ages were determined by AMS 14C dating, and the lowermost horizon was estimated to be about 27 cal yrs BP. The sediments (1-2 cm thick) were extracted by solvents and then separated into fractions by silicagel column. The apolar and polar fractions were analyzed by GC-MS. Sedimentary facies evaluated by sedimentary investigation indicated that the depositional environments changed from meandering fluvial, lacustrine, and delta in the ST2020 (Hatano et al., 2023).
In the ST2020 sediments, n-alkanes, anteiso-alkanes, and C30 hopanes were identified as major compounds. We analyzed carbon preference index (CPI) as the alkane proxy and ββ-hopane ratios as the hopane proxy. Especially, in paleosols and samples containing plant roots, CPI values were lower and ββ-hopane ratios were higher. This result might indicate influence of organic molecules from roots and microbes in rhizosphere. n-Alkane compositions from roots are reported to be weak odd number predominance (Gocke et al., 2013). The addition of n-alkanes from roots and fresh biological ββ-hopanes from abundant microbe in rhizosphere (Belin et al., 2018) might make CPI values lower and ββ-hopane ratios higher. Also, higher concentrations of anteiso-alkanes, which is considered to be derived from micro-organisms (Matsumoto et al., 1992), in these samples were likely to indicate high microbial activity.