THE SURFACE OCEAN PRODUCTIVITY AND BOTTOM WATER OXYGEN SIGNALS IN DEEP-WATER BENTHIC FORAMINIFERAL ASSEMBLAGES

A previous study of the relative abundances of benthic foraminifera in the deep Pacific revealed that surface ocean productivity and bottom water oxygen signals were strongly imbedded in the foraminiferal data. The present report examines the nature of the species associations th at carry the productivity and bottom water oxygen concentration signal s. Principal components analysis is used to define species association s independently of the environmental variables. Principal components a nalysis of the correlation and the covariance matrices of species perc ents, and of taxon accumulation rate indices, was undertaken. The corr elation analysis gives equal weight to all taxa while the covariance a nalysis weights results to the more abundant species. The accumulation rate index analysis reduces the distorting effects of calculating per cents, and matrix closure, on the taxon abundance patterns. Deep water benthic foraminiferal assemblages from the Eastern Pacific Ocean show species distribution patterns dominated by a response to surface ocea n productivity. Principal components analysis of either relative abund ances or accumulation rate indices reveals a consistent set of species bearing the productivity signal. These include species normally found at depth (e.g. hispid Uvigerina) and taxa more commonly found on cont inental margins which are associated with infaunal microhabitats. The principal components analysis of both relative abundance and accumulat ion rate indices also shows that there are no taxa which are exclusive ly responsive to changing bottom water oxygen concentration. Rather, t his factor acts in concert with other environmental variables (product ivity in this study) to control benthic assemblage abundance patterns. Using relative abundance data convolves the oxygen concentration sign al with the productivity response of the benthic assemblage. However, experimentation with absolute abundance indices suggests that the oxyg en signal can be extracted from the assemblage data. This result is co nsistent with the previous analysis (Loubere, 1994) which yielded an r (2) of 0.96 for regression of assemblages against oxygen.