Variations in hydrogen isotopic fractionation in higher plants and sediments across different latitudes: Implications...

Sedimentary δDn-alkane value is widely utilized as a reliable proxy for paleo-hydrological reconstruction. Applications of this proxy must be based upon a globally clear understanding of the relationship between leaf wax δDn-alkane values and precipitation δD (δDp), defined as apparent fractionation (εapp). However, there is a critical concern about whether relatively constant εapp values exist across different latitudes. In this study, we systematically analyzed the variations of available εapp with latitudes based upon two compiled-new databases of higher plants and sediments over the world. We found that the total average εapp was relatively constant, i.e., -116 ± 5‰ (n = 941), in higher plants across different latitudes without consideration of plant types (e.g., dicots, monocots, gymnosperms), and was still constant but slightly lower average εapp, i.e., -125 ± 6‰ (n = 460), in sediments across the latitudes. The slightly lower average εapp in sediments relative to higher plants probably derived from the contribution of aquatic plants with isotopically D-depleted εapp in lake sediments. Interestingly, with consideration of plant types, average εapp increased in dicots but decreased in monocots slightly from low to high latitudes. The counteraction of these competing trends generates relatively constant average εapp values in higher plants, and resultantly constant average εapp values occur in sediments at the global scale. It is important to elaborate relatively constant εapp values from higher plants and sediments across different latitudes when sedimentary δDn-alkane is utilized as a proxy for paleohydrological reconstruction.