Aquatic and terrestrial plant contributions to sedimentary leaf waxes in a modern Arctic lake setting: Improving interpretations of Holocene climate change on Baffin Island

Abstract:

The Arctic is the fastest-warming region on Earth, causing vegetation to expand into areas previously dominated by snow and ice, exacerbating warming further. Aquatic and terrestrial plant leaf wax hydrogen isotope values are valuable proxies for past climate. However, it can be difficult to distinguish aquatic from terrestrial waxes in lake sediments, which can lead to uncertainty surrounding interpretations of past climate. We quantify the leaf wax n-alkanoic acid chain length distributions of soils, water filtrates, lake sediments, and 36 species of modern plants from Lake Qaupat on southern Baffin Island to track leaf wax production, transport, and deposition in a modern Arctic lake setting. We analyze leaf wax δ²H and δ¹³C in a subset of these samples as additional means to trace plant wax contributions to the sediments. We assess variability among modern plant chain length distributions using a principal component analysis (PCA), and plot the sediments, soils, and water filtrates as passive samples on the PCA. We find submerged aquatic plants (including four mosses and one sedge) and lake sediments group together in PCA, indicating submerged aquatic plants contribute large portions of leaf wax to lake sediments. Plant cover mapped in the Lake Qaupat catchment supports this finding: submerged aquatic plants cover 15% of the lake bed, and grow within the lake water, providing a straightforward path for aquatic waxes to lake sediments. In contrast, the most abundant terrestrial plant is Betula glandulosa, with 7.2% area cover within 50-meters of the lake shore.

We use the chain length distributions and isotopic compositions of modern to infer Holocene changes in plant communities from a downcore wax record. We compare our leaf wax-inferred Holocene record to a sedimentary ancient DNA (sedaDNA) record from the same cores, as they represent two methods to infer past plant communities. This study will strengthen interpretations of past vegetation changes, and thus enhance our understandings of vegetation response to climate change.