Margaret L. Delaney2 and Linda D. Anderson2


We applied a sequential extraction technique that distinguishes five sedimentary phosphorus (P) components to sediments from three sites along a water depth transect on the Ceara Rise in the western equatorial Atlantic (Site 925, 3041 m water depth; Site 926, 3598 m; and Site 929, 4356 m). P concentrations in those components that serve to remove reactive P from the oceanic reservoir—adsorbed P, oxide-bound P, authigenic P, and organic P—account for the majority of sedimentary P in all sites. Detrital P typically accounts for a small fraction of total P, averaging 4%-5% of total P. Detrital P concentrations are similar at all three sites before about 10 Ma, and the two northernmost sites (925 and 929) show large increases (3-5 times) in detrital P concentrations over the past 10 m.y. Organic P, oxide-bound P, and adsorbed P concentrations account for minor fractions of total reactive P (typically 9%-12%, 8%-10%, and 7%-9%, respectively). P concentrations in these sedimentary components generally decrease with increasing sample age, with the largest changes in the past 10 m.y. The decreases in these components are offset by increases in authigenic P concentration, which constitutes a majority of reactive P burial. The reorganization of sedimentary P in the Ceara Rise sites with sediment age is similar to that observed in equatorial Pacific sediments. Neither calcium carbonate contents nor total reactive P concentrations in these sediments correlate with linear sedimentation rates. Reactive P concentrations do not appear to be directly affected by calcium carbonate dissolution.

1Shackleton, N.J., Curry, W.B., Richter, C., and Bralower, T.J., (Eds.), 1997. Proc. ODP, Sci. Results, 154: College Station, TX (Ocean Drilling Program).
2Institute of Marine Sciences, University of California, Santa Cruz, CA 95064, U.S.A. delaney@cats.ucsc.edu