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Density separation in pollen preparation: How low can you go?

Abstract

In palynology and other laboratory-based disciplines, methodological literature often lags the development and adoption of new practices. Here we highlight the lack of literature on the application of heavy liquid density separation for pollen preparations, a technique that has become common practice in recent years. In a study of Holocene-age sediments from Lake Pupuke, northern New Zealand, we found that the density of the heavy liquid used to separate pollen from the minerogenic fraction, within the range of reported practice, affected pollen counts. When a relatively low density was used (2.0 g/cm3), buoyant pollen grains such as Prumnopitys taxifolia and Dacrydium cupressinum were overrepresented, whereas small, compact pollen grains such as Libocedrus and Metrosideros were underrepresented. This result raises wider concerns, as heavy liquid densities reported in the literature range from 1.88 to 2.40 g/cm3. We draw attention to this problem and recommend steps that palynologists can take to ensure that their enumerated pollen assemblages are representative and do not lead to spurious interpretations.

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Acknowledgements

We thank Drs. Xun Li and Marcus Vandergoes for their recommendations regarding appropriate heavy liquid density; without their advice, the problematic effects of using a low-density liquid may never have been discovered. We also thank two anonymous reviewers for their helpful comments, and the editors for giving us the opportunity to improve our manuscript during the review process. Vandergoes and Li, along with authors Newnham and Rees are key investigators of the Lakes380 Research Programme, funded by New Zealand’s Ministry for Business, Innovation and Employment Endeavour Fund. This paper benefited from and is a contribution to the Lakes380 Programme. Postgraduate study of VB was funded through Marsden Fund Project 14-UOA-040.

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Correspondence to Valerie van den Bos.

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van den Bos, V., Newnham, R., Rees, A. et al. Density separation in pollen preparation: How low can you go?. J Paleolimnol 63, 225–234 (2020). https://doi.org/10.1007/s10933-020-00112-6

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Keywords

  • Palynology
  • Density separation
  • Sodium polytungstate
  • Saccate pollen