Exploring the potential of d18O and d13C in pollen for reconstruction of Quaternary palaeo-climate: Pilot study towards a comprehensive calibration of stable isotopes in modern pollen from selected European plant taxa.

• Applicants: Dr. Gerhard Helle; Professor Dr. Frank Riedel
• Subject Area: Palaeontology ; Mineralogy, Petrology and Geochemistry
• Term: from 2015 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 277812067

Analysis of the stable isotope compositions of plant-tissues and -compounds has myriads of applications spanning biology, climatology, ecology, and geology/palaeontology. Stable isotopic analysis of e.g. tree rings has provided a valuable tool to explore past climate variability as well as plant physiological responses to environmental change. Pollen assemblages that are preserved in terrestrial sedimentary systems offer an archive from which to gain insight into past environmental change and associated vegetation dynamics, typically covering the Quaternary and beyond. In this respect, stable isotopic analysis of pollen for palaeoenvironmental applications is a rather new approach in palaeoecological research. Literature on preliminary results from stable isotopic analyses of raw as well as extracted pollen exina suggest that significant potential exists to utilise palaeo-pollen records as quantitative indicators of past terrestrial palaeoenvironmental change over medium- to long-timescales. Moreover, by combining isotopic analyses with conventional pollen assemblages the information available is greatly enhanced, especially regarding the relative timing of plant community response to external forcing, e.g. climate. However, the applicability of stable isotope ratios in pollen is hampered by two challenges. Firstly, much more efforts need to be put in the calibration and verification of pollen-d13C and pollen-d18O as high quality climate or environmental proxies. Secondly, the labour intensive nature of the separation of sufficient numbers of grains required for reliable analyses. To tackle these challenges, we want to establish a pollen sampling network comprising 7 European sites differing in ecological conditions. The aim is to evaluate intra-seasonal isotope variability against instrumental climate data (initially over two years). At two sites we plan to analyse pollen isotope ratios from a large variety of annual and perennial plant taxa providing the natural inter- and intra-species baseline variability that will potentially allow a much better interpretation of the climatological or environmental significance of pollen isotope signatures. By comparing pollen isotope signatures of annual and perennial plants flowering at the same time of the vegetation period we intend to assess potential time lags and carry over effects in pollen isotope signatures of perennial plants, i.e. trees. The challenge of separating specific fossil pollen from lake sediments shall be approached in a first step by applying and testing split-flow lateral-transport thin separation cells for rapid and continuous particle fractionation (SPLITT), as well as a MicroBeam UV-laser catapult (ZEISS GmbH). Furthermore, we will use a novel, patented flash-pyrolysis-high-frequency-induction device coupled online to an IRMS that allows high throughput measurements of d13C and d18O by converting micro-amounts of organic samples to CO gas at temperatures of up to 2400°C.

• DFG Programme: Research Grants