Pollen analysts have long used a standardized methodology to extract the pollen from sediments (Faegri and Iversen, 1975). This has proven effective in concentrating the pollen from many different types of sediment and permits the comparison of pollen assemblages from different regions and various environments. Modifications to the method, such as sieving through 7-micon screens facilitated the application of pollen analysis in tundra regions (e.g., Cwynar et al., 1979; Gajewski, n.d.). For this reason, most Arctic pollen diagrams end up having a low temporal resolution, which limits the interpretations that can be drawn.

In the Laboratory for Paleoclimatology and Climatology at the University of Ottawa, we have been using a heavy-liquid separation technique to increase the number of pollen grains per slide, with a great deal of success. With this technique, the pollen floats and can be decanted off, whereas the heavier inorganic materials (such as quartz and clay) sink to the bottom. As a consequence, we can now concentrate the pollen from the clay-rich Arctic sediments more efficiently. Most previous pollen studies from the Canadian Arctic have, on average, around 20 levels counted (e.g., Gajewski, 1995; Gajewski and Frappier, 2001). With the application of this new technique, we have been able to generate pollen diagrams of 60 to 70 levels within the same time frame (Zabenskie, 2006; Peros and Gajewski, 2007), a significant improvement in both temporal resolution as well as the number of pollen grains counted at each level.

Traditionally, Bromoform has been used to concentrate the pollen material from the sediment matrix. However, Bromoform is highly toxic, and our goal was to find a material that would be safer to use. Sodium Polytungstate (SPT) is a noncorrosive material with a neutral pH. It is somewhat expensive (ca. $700 for 2 kg of crystals), but by filtering after the analysis of complete, SPT can be easily reclaimed, making it an ideal material for our purposes. Furthermore, because the SPT method separates heavy minerals from the lighter pollen grains, the use of HF can often be omitted from the procedure.

The use of heavy liquid separation in pollen processing is not new, yet the specific steps in its application are not widely known or advertised. In order to determine how to make the use of the SPT method most efficient for Arctic lake sediments, Zabenskie (2006) did a detailed literature survey, sought the advice of other palynologists, and undertook numerous laboratory trials. After months of testing, several modifications were made to some previously published heavy-liquid methods (Bolch, 1997; Munsterman and Kerstholt, 1995; Skipp and Brownfield, 1993; Takashi et al., 1998; Torresan, 1987), including the addition of an HCl step, several water washes, and agitation with a vortex mixer.

One of the most important tests undertaken was to determine whether the SPT method was comparable to traditional processing techniques using HF. Replicate samples were counted from sediment processed using both methods, and it was determined that the proportion of pollen types and the ratio of exotic marker to the overall number of pollen grains counted were statistically similar in sediment processed using both the SPT and HF methods. The only difference, of course, was that the samples processed using SPT had significantly higher concentrations of pollen.

The SPT method we use in the Laboratory for Paleoclimatology and Climatology works very well for Arctic lake sediments and we advocate is use. At present, we have not yet used this technique on sediments from non-Arctic regions, and we would be interested to know what experiences/opinions other researchers may have. please feel free to contact us at the address below.

For the full protocol, please visit out website: http://www.lpc.uottawa.ca/resources/pollen%20-%20heavy%20liquid.html

Extensive protocols for Quaternary paleoecology are found elsewhere on this website. We have purchased our SPT through: http://www.sometu.com/ This site has contact information as well as technical information about SPT.

Susan Zabenskie, Matthew Peros, and Konrad Gajewski
University of Ottawa Laboratory for Paleoclimatology and Climatology
University of Ottawa, Ottawa, Ontario, K1N, 6N5
E-mail: gajewski@uottawa.ca

Acknowledgements We thank Antonia López-Higuera (UMAN) for help in implementing the method and Brett O'Neill for extensive help in the lab.

References cited:

Bolch, C. J. S., 1997. The use of sodium polytungstate for the separation and concentration of living dinoflagellate cysts from marine sediments. Phycologia 36:472-478.

Cwynar, L. C., E. Burden, and J. H. McAndrews, 1979. An inexpensive method for concentrating pollen and spores from fine-grained sediments. Canadian Journal of Earth Sciences 16:1115-1120.

Faegri, K., and J. Iversen, 1975 Textbook of Pollen Analysis. 3rd edition. Hafner Press, New York. 295 pages.

Gajewski, K., n.d. Preparation of organic sediments for pollen analysis. http://www.lpc.uottawa.ca/resources/pollen.html

Gajewski, K., 1995. Modern and Holocene pollen accumulation in some small Arctic lakes from Somerset Island, N.W.T., Canada. Quaternary Research 44:228-236.

Gajewski, K., and M. Frappier, 2001. Postglacial environmental history from Prince of Wales Island, Nunavut, Canada. Boreas 30:485-489.

Gajewski, K., M. Garneau, and J. C. Bourgeois, 1995. Paleoenvironments of the Canadian High Arctic Derived from Pollen and Plant Macrofossils: Problems and Potentials. Quaternary Science Reviews 14:609-629.

Munsterman, D., and S. Kerstholt, 1995. Sodium polytungstate, a new non-toxic alternative to bromoform in heavy liquid separation. Elsevier 91:417-422.

Peros, M., and K. Gajewski, K. 2007. Holocene climate and vegetation change on Victoria Island, western Canadian Arctic. Quaternary Science Reviews ddoi:10.1016/ j.quascirev.2007.09.002.

Skipp, G. L., and I., Brownfield, 1993. Improved density gradient separation techniques using sodium polytungstate and a comparison to the use of other heavy liquids. U.S. Geological Survey Open-File Report 92-386.

Takeshi, N., E. Brugiapaglia, G. Digerfeldt, M. Reille, J. De Beaulieu, and Y. Yasuda, 1998. Dense-media separation as a more efficient pollen extraction method for use with organic sediment/deposit samples: comparison with the conventional method. Boreas 27:15-24.

Torresan, M., 1987. The use of sodium polytungstate in heavy mineral separations. U.S. Geological Survey Open-File Report 87-590.

Zabenskie, S., 2006. Postglacial Climatic Change on Boothia Peninsula, Nunavut, Canada. M.Sc. thesis, Department of Geography, University of Ottawa

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This article first appeared in CAP Newsletter 29(2):5-7, 2006. It is included here with permission of Konrad Gajewski; references have been updated.