COMPARISON OF C-14 PRIMARY PRODUCTION DETERMINATIONS MADE BY DIFFERENT LABORATORIES

The results of an intercomparison exercise of primary production determinations made by different laboratories are reported here. The exercise was carried out by a Working Group of the International Council for Exploration of the Seas (ICES) in 1987 and was divided into 2 phases. In the first, different types of filters onto which C-14-containing algae had been filtered were distributed to 24 different laboratories from 15 countries. These laboratories counted the associated radioactivity using their usual methods. Significant differences were recorded in the results obtained by the different laboratories. Filter type and presence/absence of a quenching agent had a lesser but also significant effect on counting results. A data set describing C-14 incorporation as a function of photon flux density at different depths in the water column was also distributed to these laboratories and they were asked to calculate total daily primary production. Results from different laboratories varied by ca 15 %. The second phase was comprised of field studies where 12 laboratories representing 9 countries met and compared primary productivity measurements using 'own' and 'standard' methods on pooled and nonpooled samples. Very significant differences in results were recorded between laboratories even when using a 'standard method' on pooled samples. Incubator and filtering procedures have been identified as potential sources of error in C-14 incorporation studies.