In the Weeds: Aquatic Plant Biomarker Sources to Arctic Lake Sediments

In reconstructing past changes in precipitation or evaporation from the geologic record, paleoclimatologists sometimes employ the dual-biomarker isotope method. This method requires that two co-occurring sedimentary lipids are derived from different biological sources, and that their compound-specific H-2/H-1 ratios record different aspects of the hydrologic cycle. Several studies have used this approach, typically by comparing the H-2/H-1 ratios of n-alkyl lipids (delta H-2(wax)) thought to be sourced from aquatic versus terrestrial plants that gain their hydrogen atoms from lake water and soil water, respectively. Yet confidently fingerprinting n-alkyl lipid sources continues to be a challenge because the wax inputs of different plant types vary across biomes, lake types, and time. New research in the Journal of Geophysical Research-Biogeosciences by Hollister et al. (2022, ) utilizes a combination of three independent metrics to demonstrate that for Arctic lakes, mid-chain n-alkanoic acids can be sourced principally from aquatic plants whereas long-chain n-alkanoic acids derive from a mixture of aquatic and terrestrial plants. By cataloging wax compound distributions and compound-specific H and C isotopes of many new plant species, their efforts will strengthen future biomarker paleoclimatology and reinforce previous applications of the dual-biomarker approach in high-latitude lakes. The identification of a lake system with a strong aquatic plant wax signal in the sediments should motivate future targeting of similar lakes for reconstructing past moisture with the dual-biomarker method. Plain Language Summary Lake sediments accumulate leaf wax molecules made by plants that climate scientists can use to reconstruct past changes in precipitation and evaporation, key climate variables in the Earth system. For scientists to leverage information from these chemical fossils, they need to understand which plants are producing the waxes, and whether those plants gain their water from soils, from lakes, or from another water source. While land plants using soil water can dominate sedimentary wax signals, a recently published study indicates that exceptions occur in Arctic lakes with abundant aquatic plant growth. These advances support paleoclimate research and demonstrate an approach for fingerprinting the source of plant waxes in Arctic lakes.

Automated summary

Paleoclimatologists use lake sediments to reconstruct past changes in precipitation and evaporation. Recent research in Arctic lakes shows that aquatic plants contribute significantly to the wax signals, providing a method for identifying the sources of plant waxes in these lakes.