Characterizing oxygen isotope variability and host water relation of modern and subfossil aquatic mosses

A field survey in southern Patagonia has shown a highly significant linear correlation between delta O-18 values of cellulose extracted from modern submerged aquatic mosses and their respective host waters. The amount of aquatic moss remains preserved in lake sediments is, however, often not sufficient for cellulose extraction for oxygen isotope analysis. By comparison, the delta O-18 analysis of bulk organic matter of aquatic mosses requires much less material, but further pretreatment due to inorganic contamination is needed. In this study we extend the cellulose delta O-18 approach to aquatic moss organic matter and aquatic vascular plants in order to explore the relation between delta O-18 values of aquatic plants and host waters. Furthermore, we focus on a comparison between cellulose and pretreated organic matter of subfossil aquatic mosses and vascular plants with regard to their delta O-18 and delta C-13 values from Laguna Potrok Aike, a southern Patagonian maar lake. Subfossil remains of two representative submerged aquatic moss species and different moss parts (branches and leaves) are handpicked and an investigation on moss organic matter, moss cellulose and cellulose from coarse plant debris is performed in pairs within a moss-rich sediment section. Our results show that, similar to moss cellulose, a significant linear correlation exists between delta O-18 values of purified moss organic matter and their respective host waters. Past lake water delta O-18 values can thus be inferred from moss cellulose as well as from purified moss organic matter with comparable precision. Only a marginal O-18 enrichment (ca. 1 parts per thousand) is observed for delta O-18 values of cellulose from aquatic vascular plants compared to that of aquatic mosses, whereas delta C-13 values of aquatic vascular plant cellulose show a pronounced C-13 enrichment (ca. 20 parts per thousand) relative to aquatic mosses. Noticeable differences in delta O-18 values of organic matter from different moss species suggest a monospecific analysis for the reconstruction of lake water delta O-18 values based on moss organic matter. Separation of different submerged aquatic moss parts (branches and leaves) is, however, not necessary due to their indistinguishable delta O-18 values. The paired investigation demonstrates a consistent variation of lake water delta O-18 values inferred from moss organic matter, moss cellulose and, within limitations, cellulose from coarse plant debris. This offers the potential for combining results from different moss organic fractions (cellulose, purified OM) into a composite lake water delta O-18 record to achieve high-resolution paleoenvironmental reconstructions. Despite several open issues, the approach could be successfully applied to other lakes worldwide where aquatic moss remains are preserved. (c) 2014 Elsevier Ltd. All rights reserved.