Stable isotope analyses of lacustrine chitinous invertebrate remains: analytical advances, challenges and potential.

This presentation examines recent developments in the application of oxygen stable isotope analyses to lacustrine invertebrate remains (e.g. chironomids) within palaeoenvironmental science. We explore improvements to instrumentation and measurement, and the opportunities that this presents for a more nuanced palaeoenvironmental approach. The improvements to the existing methodology of δ18Ochitin measurements now allow the possibility of taxon specific δ18Ochitin reconstructions and thus the potential to enhance our understanding of paleoclimate dynamics. Opportunities to reduce the sample size required have come from improvements to instrumentation, through more sensitive Thermal Conversion Elemental Analyser isotope ratio mass spectrometry (TC/EA-IRMS). We discuss the considerations needed to assess the sample size measured and avoid systematic bias. Is smallest always best or does this lead to a biased environmental reconstruction? Further, it is also unclear what between-taxa offsets exist for different chironomid morphotypes and whether δ18Ochitin offsets between taxa are stationary across large climate transitions, and the extent to which changing vital effects play a role. We present new data on taxon-specific trends from the robustly dated late-glacial sediment record from Lake Llangorse, UK. This will allow us to determine whether temperature is the main driver of the δ18Ochitin signal of each taxon, or if vital effects play a role.