Stable carbon isotope analysis of Cedrus atlantica pollen as an indicator of moisture availability

Stable carbon isotope analysis of pollen provides potential for reconstruction of past moisture availability in the environment on longer time-scales compared to isotope analysis of plant tissue. Here we show that the carbon isotopic compositions (δ13C) of pollen, sporopollenin, leaf and stem tissues of Cedrus atlantica are strongly related. Untreated pollen δ13C has a significant linear relationship with sporopollenin δ13C (r2 = 0.97, p < 0.0001) which is relatively depleted in 13C by an average 1.5‰. Carbon isotope discrimination (Δ13C) by sporopollenin (derived from pollen δ13C values) is related to mean annual (r2 = 0.54, p < 0.001) and summer precipitation (r2 = 0.63, p < 0.0001). A 100 mm increase in mean annual precipitation results in sporopollenin Δ13C increasing by 0.52‰, or by 1.4‰ per 100 mm summer precipitation. There is a stronger relationship between sporopollenin Δ13C and long-term annual scPDSI (r2 = 0.86, p < 0.0001) and summer scPDSI (r2 = 0.86, p < 0.001) aridity indexes, with reduced Δ13C as aridity increases. These relationships suggest that stable carbon isotope analysis of C. atlantica fossil pollen could be used as a quantitative proxy for the reconstruction of summer moisture availability in Northwest Africa.