Evaluation of heavy-density separation techniques for pollen extraction in archaeological and paleoecological samples with high mineral content

Abstract

Heavy-density approaches can be useful for cleaning up samples, concentrating pollen, and speeding up sample counting. This study presents a new heavy-density processing procedure using sulfuric acid and compares it to existing methods in the literature, including zinc chloride and several tungstate solutions. Pollen has a density of 1.4 g/cm3, and concentrated sulfuric acid has a density of 1.8 g/cm3. Since most palynology labs have concentrated sulfuric acid readily available, and it is inexpensive and doesn’t have to be reused, it makes it a great alternative to other more expensive heavy-density methods.

We present the results of an experiment on different archaeological soil samples that have different sedimentological characteristics, from heavy sand to fine clay. Ten grams of soil was burned at 550 degrees Celsius to remove pollen from the samples and ~20,000 Lycopodium tracer spores were added to monitor the different processing techniques. A traditional suite of processing techniques was used including hydrochloric acid to dissolve carbonates, potassium hydroxide and acetolysis to remove humic acid and lignin, and hydrofluoric acid to remove silicates. After potassium hydroxide, a “swirl-and-pour” heavy-density method removed sand and large silicate particles. Heavy-density before hydrofluoric acid was not effective at removing fine silicates and clays, so the HF step could not be eliminated. Most samples needed to be sieved with a 10um mesh to remove clay particles. We hope to test our procedure using zinc chloride since it is also inexpensive and has been used with organic lake sediments, eliminating the need for acids.