Leaf Wax δD and δ 13 C in Soils Record Hydrological and Environmental Information Across a Climatic Gradient in Israel

The hydrogen (δD wax ) and carbon (δ 13 C wax ) isotope compositions of long‐chain alkanes derived from plant waxes record hydrological and environmental conditions. However, the integration of plant n ‐alkanes into the sedimentary cycle, the variability of δD wax and δ 13 C wax in soils, and the paleoclimate applicability in paleosols and archaeological sediments are poorly constrained. We sampled plants and soils across a steep climate transect in Israel to understand how plant type and environmental parameters shape δ 13 C wax and δD wax . This transect has three advantages: existence of long‐term precipitation isotopic composition (δD r ) records, a single wet season potentially reduces variability due to seasonality, and abandoned Byzantine period (~300–600 AD) agricultural terraces that reduce modern and ancient soil mixing and provide age constraints. We find that soil δ 13 C wax is constant (0.4‰, 1 σ ) across a 500‐ to 1,300‐mm/year rainfall gradient and appears insensitive to rainfall amount, unlike bulk plant δ 13 C. The absence of a rainfall effect suggests that δ 13 C wax may be better suited to reconstructing C 3 /C 4 plant ratios than bulk δ 13 C. Homologue average soil δD wax significantly correlate with δD r , and the offset between δD r and soil δD wax ( ε app ) correlates with growing season relative humidity. The seasonality of leaf production accounted for at most ~10% of total plant δD wax variability. Lastly, soil δD wax and δ 13 C wax variability is reduced by ~80% relative to plant δD wax and δ 13 C wax variability. Our results show that soil δD wax and δ 13 C wax faithfully record δD r and landscape C 3 ‐C 4 plant contributions and thus support the utility of these proxy data in paleosols and archaeological sites.