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.

对植物组织和化合物的稳定同位素组成的分析在生物学、气候学、生态学和地质学/古生物学等领域有着广泛的应用。稳定同位素分析（如树木年轮）为探索过去的气候变率以及植物对环境变化的生理反应提供了有价值的工具。保存在陆相沉积体系中的花粉组合提供了一个档案，从中可以深入了解过去的环境变化和相关的植被动态，通常涵盖第四纪及以后。因此，花粉稳定同位素分析在古环境研究中的应用是一种较新的研究方法。原始和提取的花粉表面稳定同位素分析的初步结果表明，利用古花粉记录作为过去中长时间尺度陆地古环境变化的定量指标具有巨大的潜力。此外，通过将同位素分析与常规花粉组合相结合，可获得的信息大大增加，特别是关于植物群落对外部强迫（如气候）响应的相对时间。然而，稳定同位素比值在花粉中的适用性受到两个挑战的阻碍。首先，需要加大对花粉- d13c和花粉- d18o作为高质量气候或环境指标的校准和验证力度。其次，劳动密集的性质分离足够数量的谷物需要可靠的分析。为了应对这些挑战，我们希望建立一个花粉采样网络，包括7个生态条件不同的欧洲站点。目的是根据仪器气候数据（最初超过两年）评估季节内同位素变异。在两个地点，我们计划分析来自多种一年生和多年生植物分类群的花粉同位素比率，提供自然的种间和种内基线变异性，这将有可能更好地解释花粉同位素特征的气候或环境意义。通过比较在同一植被期开花的一年生植物和多年生植物的花粉同位素特征，我们打算评估多年生植物（即树木）花粉同位素特征的潜在时间滞后和携带效应。要想从湖泊沉积物中分离出特定的化石花粉，首先需要应用和测试用于快速连续颗粒分离（SPLITT）的分流横向输送薄分离池，以及MicroBeam紫外激光弹射器（ZEISS GmbH）。此外，我们将使用一种新型的专利闪蒸-高频感应装置，在线耦合到IRMS，通过在高达2400°C的温度下将微量有机样品转化为CO气体，实现d13C和d18O的高通量测量。

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.