Morphometric and stable isotopic evidence for subpopulations of Globorotalia truncatulinoides

Abstract

A detailed morphologic and stable isotopic study of the planktonic foraminiferal species Globorotalia truncatulinoides demonstrates for the first time the following: 1. the assumption of unimodality in population structure and the sole use of "mean shapes" may lead to misunderstandings regarding the paleoecology of foraminifera; 2. the population structure of G. truncatulinoides is bimodal to polymodal reflecting the existence of three subpopulations which have a particular shape and isotopic character in the southern Indian Ocean; 3. each morphotype occupies a distinct niche within the water column; 4. the predominance of each morphotype varies with latitude as the physiochemical parameters of the water column change with latitude; 5. the occurrence of significant 0.5 to 1.0.permill. differences in the .delta.18O and .delta.13C composition of the morphotypes may have important implications for paleoceanographic interpretations using the isotopic composition of planktonic foraminifera.