SWIM-IRMS: METHODS IN EXPLORING ISOTOPE COMPOSITION IN MICROFOSSILS, AND ITS APPLICATION IN PALEOECOLOGY (Invited Presentation)

The limitation of available substrate for analyses is a major hurdle in the use of stable carbon isotopes in micropaleontology. Traditional techniques (e.g., EA-IRMS) can be time consuming and require substantial fossil material that is often unavailable. To combat these issues, we developed techniques using a spooling wire microcombustion device (SWiM) were interfaced with IRMS to explore paleoecological questions that were previously difficult to answer. One example is the evolution and expansion of C₄ grasses. Using SWiM-IRMS, single pollen isotope AnaLysis (SPIRAL) was developed to measure nanomolar amounts of carbon in single pollen grains and estimate the abundance and probability of occurrence of C₄ grasses. We were able to show with SPIRAL the lack of C₄ grasses in the Eocene of southeastern North America, the earliest presence of C₄ grasses in the Oligocene of western Europe, and that C₄ grasses were relatively abundant in the Middle Miocene of Spain. Quaternary applications of SPIRAL have focused on identifying the environmental drivers of C₄ grass abundance in tropical East Africa and temperate southeastern Australia over the last 25,000 years. Beyond pollen, SWiM-IRMS is being used to measure the carbon isotopes in individual dissolved chironomid head capsules from Alaskan lakes to quantify the effects of environmental change on lake methane production. The SWiM-IRMS can potentially capture differences in δ¹³C within and among species that were previously masked by the large sample sizes needed for traditional methods. This also can be used in different microfossils to assess further paleoecological questions integrating several proxies captured from the same organism, such as taxonomy and geochemistry. The potential of SWiM-IRMS in paleoecological studies has likely yet to be fully explored.