Fourier analysis of the planktonic foraminifer Neogloboquadrina pachyderma (Ehrenberg) from the Pleistocene Santa Barbara Formation, California

Abstract. A Fourier analysis was performed on three hundred and fifty two specimens of Neogloboquadrina pachyderma. obtained from eleven sedimentary rock samples of the Pleistocene Santa Barbara Formation. Statistical analytical methods, including Chi square values, Q-mode cluster analysis, O-mode factor analysis and discriminant function classification, were also carried out on these specimens.

Two natural groups are recognized which can be correlated with the assemblages previously defined as warm and cool Neogloboquadrina pachyderma phenotypes, as recognized by microscope. The amplitude values of the second, third, fourth, and seventh harmonics of the warm phenotype specimens are greater than those of the cool phenotype specimens. On the other hand, the amplitude values of the fifth harmonic of the warm phenotype specimens are less than those of the cool phenotype specimens. Only the second harmonic is statistically significant in describing the shape differences between the warm and cool phenotypes. Increased compaction of the cool phenotype tends to decrease elongation, resulting in low amplitude values for the second harmonic. An intergradational form between the warm and cool water phenotypes comprises 9.4 percent of the specimens.

This intergradation, albeit narrow, identified by Fourier analysis and the discriminant function indicates that the controlling factors in the shape variation of the test are local, and are caused by variation in seasonal surface circulation patterns. The warm and cool water phenotypes of Neogloboquadrina pachyderma are therefore ecophenotypic varients within a single species.