Leaf Wax δD and δ¹³C in Soils Record Hydrological and Environmental Information Across a Climatic Gradient in Israel

Abstract

The hydrogen (δDwax) and carbon (δ13Cwax) 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 δDwax and δ13Cwax 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 δ13Cwax and δDwax. This transect has three advantages: existence of long‐term precipitation isotopic composition (δDr) 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 δ13Cwax is constant (0.4‰, 1σ) across a 500‐ to 1,300‐mm/year rainfall gradient and appears insensitive to rainfall amount, unlike bulk plant δ13C. The absence of a rainfall effect suggests that δ13Cwax may be better suited to reconstructing C3/C4 plant ratios than bulk δ13C. Homologue average soil δDwax significantly correlate with δDr, and the offset between δDr and soil δDwax (εapp) correlates with growing season relative humidity. The seasonality of leaf production accounted for at most ~10% of total plant δDwax variability. Lastly, soil δDwax and δ13Cwax variability is reduced by ~80% relative to plant δDwax and δ13Cwax variability. Our results show that soil δDwax and δ13Cwax faithfully record δDr and landscape C3‐C4 plant contributions and thus support the utility of these proxy data in paleosols and archaeological sites.

Carbon reservoir perturbations induced by Deccan volcanism: Stable isotope and biomolecular perspectives from shallow marine environment in Eastern India

“…However, no such relations were observed between precipitation amount and δ 13 C alk values of both plants and modern soils along a climatic transect in Israel, although the δD alk values faithfully recorded changes in rainfall regime (Goldsmith et al, 2019). The δD alk and δ 13 C alk values in this study also show no correlation between each other (Figure 8e).…”

“…Numerical integration of globally available dataset suggest that impact of precipitation and evapotranspiration are far greater on the leaf wax δD alk values compared to the impact of change in plant taxonomy (Liu & An, 2018). Moreover, the variability in δD alk values commonly exhibited by individual plants within an area is reduced by ~80% in soils, allowing for a more meaningful reconstruction of past climatic changes from paleosol (Goldsmith et al, 2019). High δD alk values in Units 1-2 and Unit 8 suggest evaporative D-enrichment of source water during arid condition (Figure 8b), with lower δD alk values in Unit 6 suggesting an intermediate humid phase.…”

“…For instance, decrease of 3.3‰ in δ 13 C alk value in infra-trappean is not associated with change in the δD alk value. Also, the total low- shown to exert significant influence on the δ 13 C values of higher plants (Goldsmith et al, 2019;Schouten et al, 2007;Smith et al, 2007). Palynological studies conducted in infra-and inter-trappean beds from Central India have shown a considerable decrease in the gymnosperm pollen and a shift to pteridophyte and angiospermdominated palyno-assemblage in response to the main phase of volcanism (Samant & Mohabey, 2014).…”

Leaf Wax Hydrogen Isotopes as a Hydroclimate Proxy in the Tropical Pacific

“…Tropical Pacific n-C29-alkane δ 2 H values ranged from −177 to −139‰, while those of n-C28-acid ranged from −175 to −119‰ (Table 1; Figure 3). Adding these new measurements to an updated global compilation of δ 2 HWax values from all available surface sediment and soil data sets in non-marine settings (compilations from McFarlin et al, 2019, as well as data from Nelson, 2013;Bakkelund et al, 2018;Feng et al, 2019;Goldsmith et al, 2019;Li et al, 2019;Wu et al, 2019;Daniels et al, 2020;Lu et al, 2020;Struck et al, 2020;van der Veen et al, 2020) has minimal impact on the slope, y-intercept, or correlation coefficients for the global linear regression (Figure 3).…”

“…Regional calibrations are expected to have stronger than average correlations by constraining some variables that contribute to scatter in the global relationship between δ 2 HP and δ 2 HWax values (Garcin et al, 2012;Goldsmith et al, 2019;McFarlin et al, 2019). However, the new data from the tropical Pacific exceed a regional scale in many ways, spanning a distance of ~8500 km, larger than even continental-scale studies (e.g., Sachse et al, 2004) The scatter in the global relationship between δ 2 HP and δ 2 HWax (Figure 3) suggests that down-core changes as large as ~50‰ at any location could be driven by factors other than δ 2 HP values.…”