Trace Element Geochemistry of Biogenic Sediments from the Western Equatorial Pacific

Twenty-seven surface samples ofbiogenic sediment, including radiolarian, nannofossil, and foraminiferal oozes from the Western Equatorial Pacific have been analyzed for potassium, magnesium, iron, rubidium, strontium, barium, chromium, cobalt, nickel, copper, and zinc by rapid instrumental techniques. Interelement associations have been evaluated with the use of a computer-compiled matrix of correlation coefficients. The variables considered include elemental determinations, water depth, and percentage of calcium carbonate. The associations calcium carbonate: strontium, potassium: rubidium, and barium: nickel: copper may all be explained with regard to their mode of entry into the sediment. The data indicate that organic fixation of metals is a significant process during the deposition of Pacific Equatorial sediments, whereas contributions from other sources, i.e., sorbed cations on the surfaces of clay~ and coprecipitation with iron or manganese oxides, are effectively masked in most cases by high rates of biogenous deposition. THE FLOOR of the Equatorial Pacific between the Line Islands (about 155 W) and the Ontong Java Plateau (about 155 E) is characterized by a thick sequence of biologically derived sediments. Foraminiferal and nannofossil oozes dominate areas above about 4,800 m, whereas radiolarian oozes are prevalent below this depth. Trace element data for biogenous sediments are scanty, particularly from this region. The majority of elemental data reported in the literature (Goldberg and Arrhenius 1958, el-Wakeel and Riley 1961 , Young 1968, and Cronan 1970) deal with samples from the eastern or northeastern Pacific. Twenty-seven biogenic sediment samples from the tops of cores taken by the research vessels of the Hawaii Institute of Geophysics have been used for this study. All samples except one were located within 10 of the equator (Figure 1). Locations, depth, and s~diment type are presented in Table 1. The purpose of this communication is threefold: (1) to report elemental abundances of the rare metals Rb, Sr, Ba, Cr, Co, Ni, Cu, and Zn in biogenous sediments from the Western Equatorial Pacific, (2) to evaluate interelement associations by linear regression techniques, and (3) to assess mechanisms that are operative in the fixation of trace elements into biogenic sediment. I would like to express thanks to the scientific party and crew of the research vessels of the Hawaii Institute of Geophysics for obtaining the samples used in this study. Drs. Robert M. Garrels, Pow-Foong Fan, Charles Fein, and James Andrews provided helpful comments on