Late Quaternary foraminiferal distributions: problems related to size fraction

Planktonic foraminifera from marine sediment cores collected in different regions of the Mediterranean Sea were size-fractioned at 63, 125 and 150 µm in order to asses the effect of the sieve mesh size on the faunal composition. In most cases the fraction > 63 µm includes a notable minera- logical component and specimens that have not reached the adult stage of ontogeny, consequently many specimens are too small and difficult to identify. The census counts performed in the >125 and >150 µm fractions show a sensitive decrease of small species such as Turborotalita quinqueloba. This study documents that the choice of the sieve size may affect the results of the investigation, influencing the percentage composition of the assemblages and consequently the paleoceanographic interpretation based on the counts. We propose the use of the 125 µm mesh sieve size for quantitati- ve analysis in paleoclimatic and paleoceanographic reconstructions since it has allowed us to obtain, with the standard number of 300 individuals, a more realistic spectrum of the assemblage in the Mediterranean Sea.