Variations in hydrogen isotopic fractionation in higher plants and sediments across different latitudes: Implications for paleohydrological reconstruction

摘要

Sedimentary delta Dn-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 dDn-alkane values and precipitation delta D(delta D-p), defined as apparent fractionation (epsilon(app)). However, there is a critical concern about whether relatively constant epsilon(app) values exist across different latitudes. In this study, we systematically analyzed the variations of available epsilon(app) with latitudes based upon two compiled-new databases of higher plants and sediments over the world. We found that the total average eapp 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 eapp, i. e., -125 +/- 6% (n = 460), in sediments across the latitudes. The slightly lower average eapp in sediments relative to higher plants probably derived from the contribution of aquatic plants with isotopically D-depleted eapp in lake sediments. Interestingly, with consideration of plant types, average eapp increased in dicots but decreased inmonocots slightly from low to high latitudes. The counteraction of these competing trends generates relatively constant average eapp values in higher plants, and resultantly constant average eapp values occur in sediments at the global scale. It is important to elaborate relatively constant eapp values from higher plants and sediments across different latitudes when sedimentary delta Dn-alkane is utilized as a proxy for paleohydrological reconstruction. (C) 2018 Elsevier B.V. All rights reserved.