Absolute abundances of dinoflagellate cysts in surface sediment samples from four sites: Lycopodium marker-grain method

Absolute abundances (concentrations) of dinoflagellate cysts are often determined through the addition of Lycopodium clavatum marker-grains as a spike to a sample before palynological processing. An inter-laboratory calibration exercise was set up in order to test the comparability of results obtained in different laboratories, each using its own preparation method. Each of the 23 laboratories received the same amount of homogenized splits of four Quaternary sediment samples. The samples originate from different localities and consisted of a variety of lithologies. Dinoflagellate cysts were extracted and counted, and relative and absolute abundances were calculated. The relative abundances proved to be fairly reproducible, notwithstanding a need for taxonomic calibration. By contrast, excessive loss of Lycopodium spores during sample preparation resulted in non-reproducibility of absolute abundances. Use of oxidation, KOH, warm acids, acetolysis, mesh sizes larger than 15 µm and long ultrasonication (> 1 min) must be avoided to determine reproducible absolute abundances. The results of this work therefore indicate that the dinoflagellate cyst worker should make a choice between using the proposed standard method which circumvents critical steps, adding Lycopodium tablets at the end of the preparation and using an alternative method.

沟鞭藻囊孢（dinoflagellate cysts）的绝对丰度（浓度）通常通过在孢粉学处理前向样品中加入石松（Lycopodium clavatum）标记颗粒作为示踪剂来测定。为检验不同实验室采用各自前处理方法所得结果的可比性，本研究设立了一项实验室间校准实验。23家实验室均收到了四份均质分装的第四纪沉积物样品，样品来源各异且涵盖多种岩性。研究人员对样品中的沟鞭藻囊孢进行提取与计数，并计算其相对丰度与绝对丰度。结果显示，尽管仍需开展分类学校准，相对丰度具备较好的可重现性。与之相反，样品前处理过程中石松孢子的过度损失会导致绝对丰度无法重现。为获得可重现的绝对丰度结果，需避免使用氧化法、氢氧化钾（KOH）、热酸处理、乙酰解、筛孔尺寸大于15μm的筛网以及超声处理时长超过1分钟的操作。综上，本研究结果表明，沟鞭藻囊孢研究人员可在两种方案中择一使用：一是采用规避上述关键步骤的推荐标准方法，二是在前处理结束后加入石松示踪片并使用替代前处理方法。