Size fraction effects on planktonic foraminifera assemblages: a compositional contribution to the golden sieve rush

A comparative study of Last Glacial to Holocene planktonic foraminiferal assemblages obtained from >150 to >106 μm size fractions of a Tyrrhenian sea core was carried out by means of compositional data analysis methods. The results show a major loss of small-sized species in the>150μmsize fraction, resulting in underdetection limit values for several Holocene samples. Statistical tests, performed by means of contrast and bootstrap, indicate that the assemblages obtained differ statistically. Nevertheless, despite the drawbacks of the analysis based on the >150 μm fraction, these differences do not imply, in the compositional data analysis approach, a significant change in covariance structure. Under compositional data analysis, covariancebased analysis should give similar results regardless of the size fraction adopted, while distance-based ones may give partly different results. The >106 μm size fraction, in which both large and small-sized species are sufficiently represented, is proposed for adoption in future studies focussing on palaeoclimatic reconstruction.