Modern constraints on the sources and climate signals recorded by sedimentary plant waxes in west Greenland

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Dion-Kirschner, Hannah, McFarlin, Jamie M., Masterson, Andrew L., Axford, Yarrow, Osburn, Magdalena R.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2020
• Subjects: Compound-specific hydrogen isotopes; Compound-specific carbon isotopes; Leaf waxes; Paleohydrology; Paleoclimate; Arctic lakes; Greenland; Kangerlussuaq; Arctic
• Online Access: https://doi.org/10.1016/j.gca.2020.07.027

The hydrogen isotopic composition (δ²H values) of plant waxes preserved in the sedimentary record is a useful proxy for past hydroclimate, but a number of known biological and environmental factors can confound the climate signal this proxy records. High-latitude ecology and environmental conditions differ from those of the better-studied low latitudes, and the influence of arctic conditions on factors that affect δ²H records of climate is poorly constrained. Direct observations of arctic plant waxes and their δ²H values, particularly from aquatic plants, are very limited. Here we present a study of n-alkane and n-alkanoic acid homologue distributions, δ²H values, and δ¹³C values from west Greenland, including measurements of terrestrial and aquatic plants, algae, and Nostoc (colonial cyanobacteria). By examining samples collected from the same region and season, we focus on climate-independent factors that may affect the δ²H values of sedimentary plant waxes. We observe that the average abundance of leaf n-alkyl lipids (Câ‚‚â‚€-C₃â‚) in common terrestrial plants from this region exceeds that in aquatic sources by up to 30×. We also note weaker source specificity in n-alkanoic acids than in n-alkanes. A comparison of these data with surface sedimentary plant waxes from a lake within the study area, previously reported by McFarlin et al. (2019), indicates that at this site both mid-chain and long-chain sedimentary waxes are likely to derive from dominantly terrestrial sources, particularly biased towards the genus Salix. Abundance-weighted isotope data reveal that while terrestrial plants show taxonomic trends in δ²H values, the amplitude of these trends is unlikely to exceed the error of the proxy (the standard deviation on calculated ε_(app)). n-Alkane ε_(app) values are more variable in aquatic than in terrestrial sources, with median values ranging from −115‰ in n-C₃₠to −143‰ in n-Câ‚‚â‚. However, because sedimentary waxes at our study site are most similar to terrestrial ...