Flow cytometry method for purification of fossil pollen from Lake Van varved sediments for AMS radiocarbon dating – a new approach

为重建气候和环境变化而建立精确和可靠的地质年代学框架是一项挑战。在这方面，土耳其货车湖记录在2010年ICDP活动期间钻探，具有非凡的潜力，每年层压沉积物的保存，可用于与放射性碳测年相结合的纹层年代学。花粉粒可用于AMS放射性碳测量，特别是在湖泊沉积物中，那里很少或根本没有陆生植物宏体化石（如在货车湖）。因此，当获得的材料具有足够的纯度和浓度时，这是至关重要的。目前提取化石花粉的方法都有显着的缺点之间的权衡努力和丰富度以及纯度的化石花粉样品准备放射性碳测年。在这里提出的拟议研究项目中，我们将采用一种新颖的创新方法，能够快速纯化化石花粉，用于Tennant等人（2013）之后基于流式细胞术的AMS放射性碳测年。迄今为止，这种方法既没有用于建立沉积记录的系统时间框架，也没有用于改进连续纹层年代学。我们已经测试的方法作为初步工作的基础上湖货车样品。AMS技术的最新发展，降低了14 C分析和流式细胞术纯化花粉所需的样品量，导致测年结果在基于纹孔计数的预期范围内。基于纹管计数和14 C测量之间的交叉检查，我们将首次为货车湖记录产生一个强大的年份时间尺度，涵盖过去约14,000年。这是高分辨率花粉分析的先决条件，以确定在这段时间内突然和极端气候变化的显着时期。

Producing precise and robust geochronological frameworks for reconstructing climatic and environmental changes is a challenge. In this respect, the Lake Van record from Turkey drilled during an ICDP campaign in 2010 has an extraordinary potential caused by the preservation of annually laminated sediments which can be used for a varve chronology in combination with radiocarbon dating. Pollen grains can be used for AMS radiocarbon measurements especially in lake sediments, where little or no terrestrial plant macrofossils are present (such as in Lake Van). Therefore, it is essential when the obtained material is of sufficient purity and concentration. Current methods of extracting fossil pollen all have significant drawbacks regarding the trade-off between effort and abundance as well as purity of fossil pollen in the samples to be prepared for radiocarbon dating. In the proposed research project presented here, we will apply a novel and innovative method enabling rapid purification of fossil pollen for AMS radiocarbon dating based on flow cytometry after Tennant et al. (2013). This method has neither been used so far for establishing a systematic time frame of a sedimentary record nor for improving a continuous varve chronology. We have tested the method as preliminary work based on Lake Van samples. The successful combination of the recent development in AMS technique, i.e., downscaling of sample amount needed for 14C analysis and purification pollen by flow cytometry, led to a dating result within the range of expectation based on varve counting. Based on a cross check between varve counting and 14C measurements, we will produce for the first time a robust calendar-year time scale for the Lake Van record encompassing the last ca 14,000 years. This is a precondition for high-resolution pollen analyses to identify remarkable periods of abrupt and extreme climate change during this time interval.