Description: The waxy coating that protects the leaves and other soft tissues of plants includes n-alkane and n-alkanoic acid compounds that are commonly used as biomarkers to reconstruct past environment. Plant waxes have geological relevance given their persistence in soils and paleosols, as well as in lake and marine sediments, yet diagenesis may alter their molecular and isotopic signatures from synthesis to deposition. This study seeks to understand the fate of plant wax biomarkers in soils after leaf-fall as characterized by a series of tropical soil profiles. We investigate the changes in abundance, molecular distributions, and hydrogen (δD) and carbon isotopic compositions (δ13C) of plant waxes (n-alkanes and n-alkanoic acids) in six litter-to-soil profiles along a 2740 m elevation transect from the eastern flank of the Andes mountains down to the lowland Amazon floodplain in Peru. From litter to soil, we find acid/alkane ratios increase, while absolute abundances decrease. In contrast, within each soil, acid/alkane ratios are roughly constant and we find an equivalent exponential decline in concentration in both compound classes with depth; with molecular distributions indicating some new production. We observe a 4 - 6‰ 13C-enrichment from litter to deeper soils for both C29 n-alkanes and C30 n-alkanoic acids; of which the Suess effect accounts for ≤ 2‰. We infer that microbial degradation and production (or 'turnover') processes influence the δ13C of plant waxes that survive in soils; in contrast, no systematic change in δD values is observed. The plant wax signal in soils includes averaging of inputs and diagenetic effects, so this signature is particularly relevant for the interpretation of plant waxes archives in paleosols and the plant waxes eroded from soils and exported to downstream sedimentary archives. We show that soils represent the major stock of plant wax under living ecosystems, suggesting that soils may be a quantitatively-important source of plant waxes available for fluvial erosion, with implications for studies of carbon cycling and paleoenvironmental reconstructions from downstream geological archives.

Description: Geochemical data, brGDGT fractions and calculated indices for soils and river samples during the wet and dry season in the Madre de Dios catchment, Peru.

Description: The Central Asian Pamir Mountains (Pamirs) are a high-altitude region sensitive to climatic change, with only few paleoclimatic records available. To examine glacial-interglacial hydrological changes in the region, we analysed geochemical parameters of a 31-kyrs record from Lake Karakul and performed a set of experiments with climate models to interpret the results. δD values of terrestrial biomarkers showed distinct insolation driven trends reflecting major shifts of water vapor sources. For aquatic biomarkers, positive δD shifts driven by changes in precipitation seasonality, were observed at ca. 31-30, 28-26, and 17-14 kyrs BP. Multi-proxy paleoecological data and modelling results suggest that increased water availability, induced by decreased summer-evaporation, triggered higher lake levels during those episodes, possibly synchronous to Northern Hemispheric rapid climate events. We conclude that seasonal changes in precipitation-evaporation-balance significantly influenced the hydrological state of a large waterbody such as Lake Karakul, while annual precipitation amount and inflows remained fairly constant.