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.

植物组织和化合物的稳定同位素组成分析在生物学、气候学、生态学和地质学/古生物学中有着广泛的应用。对树木年轮的稳定同位素分析为探索过去的气候变化以及植物对环境变化的生理反应提供了宝贵的工具。保存在陆地沉积系统中的花粉组合提供了一个档案，从中可以洞察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。在这方面，用于古环境应用的花粉稳定同位素分析是古生态研究中一种相当新的方法。对原始和提取的花粉外壁进行稳定同位素分析的初步结果的文献表明，利用古花粉记录作为过去中到长期时间尺度上陆地古环境变化的定量指标具有重要的潜力。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强，特别是关于植物群落对外部强迫的相对时间响应，例如气候。然而，稳定的同位素比率在花粉中的适用性受到两个挑战的阻碍。首先，在花粉-d13C和花粉-d18O作为优质气候或环境指标的校准和验证方面需要付出更多的努力。其次，分离足够数量的颗粒是可靠分析所需的劳动密集型。为了应对这些挑战，我们希望建立一个由7个生态条件不同的欧洲地点组成的花粉采样网络。其目的是对照仪器气候数据(最初超过两年)评估季节内的同位素变异性。在两个地点，我们计划分析各种一年生和多年生植物的花粉同位素比率，提供自然的种间和种内基线变异性，这将潜在地更好地解释花粉同位素特征的气候学或环境意义。通过比较在植被时期同一时间开花的一年生和多年生植物的花粉同位素特征，我们打算评估潜在的时间滞后和多年生植物，即树木的花粉同位素特征的影响。从湖泊沉积物中分离特定化石花粉的挑战将在第一步通过应用和测试用于快速和连续颗粒分离的分流横向传输薄分离器(Splitt)以及微束UV-激光弹射器(ZEISS GmbH)来解决。此外，我们将使用一种新型的、获得专利的闪速热解高频感应设备，与IRMS联机，通过将微量有机样品在高达2400°C的温度下转化为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.