Faunal and solution patterns of planktonic foraminifera in surface sediments of the North Pacific

Abstract

Planktonic foraminifera in the sediments on the North Pacific sea floor follow the distribution patterns of their living counterparts. Left- and right-coiling N. pachyderma, G. bulloides, G. quinqueloba, G. ruber, and G. inflata are important in identifying four major faunal assemblages. These taxa dominate the faunas in various samples. Their distribution is closely related to either temperature or nutrient patterns of surface waters, or both. Multivariate statistical techniques, cluster, factor, and discriminant analysis, group samples from less than 3300 m into a variety of spatial patterns. The group separations generated by a discriminant analysis are readily interpreted in terms of the environment because samples were coded according to their respective zooplankton province, and because those provinces correspond to the major water masses of the North Pacific Ocean. Factor analysis created seven assemblages that map in overlapping patterns. Three of the seven assemblages show little relationship with surface water temperature. Dissolution obscures the record of faunal provinciality in core top samples from depths greater than 3300 m. The degree of dissolution affects percent similarity of samples measured relative to centroids, mean assemblages, for each faunal province. Plotted against depth, values of similarity indices follow trends much like those of percent carbonate. Groupings determined from sample to sample similarity matrices correspond to trends recorded by dissolution indices based on susceptibility rankings. Both measures illustrate a step-like response of foraminiferal assemblages to increasing dissolution. Dissolution can introduce systematic bias into temperature estimates derived from paleoecological transfer functions. The direction of the bias varies according to the temperature aspect of an assemblage. Temperature estimates based on dissolved samples are generally too low for central and equatorial regions and too high for transitional regions (winter conditions).