Can stable oxygen and hydrogen isotopes from Australian subfossil Chironomus head capsules be used as proxies for past temperature change?

Abstract

This paper presents the first systematic investigation of stable isotopes (δ18O and δ2H) from the subfossil chironomid head capsules (HCs) of a single taxon (Chironomus). The study focuses on sixteen south-eastern Australian lakes and investigates the potential of Chironomus spp. HC stable isotopes to reconstruct past temperature changes from these lakes. The relationship between δ18O values of Chironomus spp. HCs from Australian oligotrophic to mesotrophic lakes in humid areas and air temperature appears robust (r = 0.88) and in line with results from European lakes. Similar results were obtained for δ2H values and temperature (r = 0.94). For lakes that are located in semi-arid and sub-humid areas that have high evaporation compared to precipitation, and often long water residence time, the temperature relationship is not robust. This is due to the evaporative enrichment of δ18O values in lake water and the effect of salinity and higher nutrient status. Vital effects may also play a role. The overall findings of this study are that both Chironomus spp. HC δ18O and δ2H are potentially valuable tools for reconstructing temperature in cooler, low nutrient and low salinity lakes of Australia. In warmer, sub-humid to semi-arid regions, δ18O and δ2H may provide valuable information about past changes in hydrological conditions.