Biomarkers and Stable Isotopes in Loess Deposits Reveal Early Human-Environment Interactions in Central Asia

The loess-paleosol sequences of the Khovaling Loess Plateau in southern Tajikistan preserve a unique record of early hominin occupation and environmental changes during the Early Pleistocene (Marine Isotope Stages 11–15). Using a combination of biomarkers, stable isotopes, and magnetic susceptibility analyses, our research reconstructs paleoenvironmental and fire histories while investigating the impact of early humans on the landscape. Biomarker proxies, including straight-chain alkanes (n-alkanes) and polycyclic aromatic hydrocarbons (PAHs), reveal shifts between grass-dominated and forested ecosystems corresponding to glacial and interglacial cycles respectively. The enrichment of high molecular weight PAHs in stratigraphic layers with lithic artifacts suggests anthropogenic fire use during periods of wetter climates. The complementary stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes together with soil organic matter contents indicate intensive human activity in on-site contexts, with a reliance on C₃ vegetation under cooler, wetter conditions. Off-site and near-site locales exhibit isotopic signatures reflecting less intensive human use and more open landscapes dominated by grassier vegetation.

The integration of these geochemical and isotopic proxies highlights the potential of soils and sediments to offer insights into the interplay between environmental changes and human activity. By linking these molecular findings with lithic artifact distributions and magnetic susceptibility records, our study demonstrates how loess soils preserve evidence of early human adaptation, resource use, and ecological impacts, contributing to our understanding of co-evolutionary relationships between hominins and landscapes in Central Asia.