REPRODUCIBILITY IN THE RANDOM SETTLING METHOD FOR QUANTITATIVE DIATOM ANALYSIS

Seven lower Pliocene sediment samples from Ocean Drilling Program (ODP) Hole 642B on the outer Voring Plateau were analyzed in order to test the reproducibility of Moore's random settling method in quantitative diatom analysis. The results indicate that the absolute abundance of diatom valves per gram dry sediment are obtained within an error of +/- 5% at the 95% confidence level after a count of 400 valves. The results also indicate that relative abundance percentages for abundant species (approximately 20% of the total assemblage) are determined with a maximum error of +/- 3.5%, whereas relative abundance percentages for less abundant species are determined with a maximum error of +/- 1.5%. Species having relative abundances of approximately two percent or less may be overlooked. This study demonstrates that absolute abundance data are required in order to understand the cause of change in the relative abundance.