Responses of sedimentary δ2Halk values to environmental changes as revealed by different plant responses to altitude and altitude-related temperatures

Abstract

Single species-based altitudinal transects may provide a new understanding of the variabilities in sedimentary wax-derived n-alkane hydrogen isotope (δ²H_alk) values caused by altitude and complex climatic change linked with the growth of mountains. We investigated Kobresia pygmaea (Kobresia), Quercus aquifolioides (Quercus) and Berberis thunbergii DC (Berberis) along three altitudinal transects on the Tibetan Plateau (TP), i.e., the southern TP, the Longmen Mountains (LM; eastern TP) and the Qilian Mountains (QL; northeastern TP). Here we present 47 plant δ²H_alk values: these include 14 Kobresia, 27 Berberis and 6 Quercus samples, which are accompanied by comparisons with nine new soil δ²H_alk values from the QL, and 105 previously-published δ²H_alk values for surface soils along the first two transects. Our data show that altitude is the dominant factor in determining three plant δ²H_alk values. However, we observed substantial differences in the δ²H_alk values and their ε_wax-p ratios for Kobresia, Quercus and Berberis for different climatic regimes and along these three transects. Significantly, for Kobresia along the LM and QL transects, ∆δ²H_alk = -84.3‰/km (r² = 0.94; p < 0.05; n = 4) and - 65.5‰/km (r² = 0.74; p < 0.01; n = 10), and ∆ε_wax-p = -80.4‰/km (r² = 0.93; p < 0.05) and -56.7‰/km (r² = 0.66; p < 0.01), respectively, were three or four times as large as for the soil δ²H_alk values observed along these altitudinal gradients. Overall, the altitudinal lapse rate (ALR) of δ²H_alk values and their ε_wax-p ratios varies between species, with Kobresia being the most negative and Berberis the least negative, potentially resulting from the strong response of monocotyledoneae Kobresia δ²H_alk values to cooling with increasing altitude, and the relative influence of cryosphere meltwater at higher altitudes. Thus, impact of climate change on the sedimentary δ²H_alk values should therefore be fully taken into account during reconstructions of paleoaltitudes.

Keywords: Altitude-related temperatures; Berberis thunbergii DC; Kobresia pygmaea; Quercus aquifolioides; The apparent hydrogen isotope fractionation (ε(wax-p)); Wax-derived n-alkane hydrogen isotope values (δ(2)H(alk)).