Spatial variability of compound-specific δD at the field scale: A case study from miliacin in broomcorn millet (Panicum miliaceum).

Abstract : The hydrogen isotopic composition (δD) of individual compounds preserved in lake sediments has been proposed as a proxy of the hydrological conditions that prevailed at time of their synthesis. Numerous parameters are susceptible of influencing this parameter, the first of them being the δD of environmental waters. Then, the combination of environmental (aridity, soil properties...) and biological parameters alter the δD of leaf water that is finally used for the biosynthesis of organic molecules that fractionate hydrogen isotopes through enzymatic reactions. Lake sediments accumulate organic matter produced at catchment scale, thus produced by various organisms developed on soils of potentially different properties. The spatial variability of δD in plants at a catchment scale is rarely taken into account (Hou et al., 2007), although it might represent a serious source of uncertainty on the paleoclimatic interpretation of sedimentary lipids δD.