An apparent contradiction in the role of phosphorus in Cenozoic chemical mass balances for the World Ocean
Tóm tắt
Little is known about the fluxes to and from the ocean during the Cenozoic of phosphorus (P), a limiting nutrient for oceanic primary productivity and organic carbon burial on geologic timescales. Previous studies have concluded that dissolved river fluxes increased worldwide during the Cenozoic and that organic carbon burial decreased relative to calcium carbonate burial and perhaps in absolute terms as well. To examine the apparent contradiction between increased river fluxes of P (assuming P fluxes behave like the others) expected to drive increased organic carbon burial and observations indicating decreased organic carbon burial, we determined P accumulation rates for equatorial Pacific sediments from Ocean Drilling Program leg 138 sites in the eastern equatorial Pacific and leg 130 sites on the Ontong Java Plateau in the western equatorial Pacific. Although there are site specific and depth dependent effects on P accumulation rates, there are important features common to the records at all sites. P accumulation rates declined from 50 to 20 Ma, showed some variability from 20 to 10 Ma, and had a substantial peak from 9 to 3 Ma centered at 5–6 Ma. These changes in P accumulation rates for the equatorial Pacific are equivalent to substantial changes in the P mass balance. However, the pattern resembles neither that of weathering flux indicators (87Sr/86Sr and Ge/Si ratios) nor that of the carbon isotope record reflecting changes in organic carbon burial rates. Although these P accumulation rate patterns need confirmation from other regions with sediment burial significant in global mass balances (e.g., the North Pacific and Southern Ocean), it appears that P weathering inputs to the ocean are decoupled from those of other elements and that further exploration is needed of the relationship between P burial and net organic carbon burial.
Từ khóa
Tài liệu tham khảo
Arthur M. A., 1991, Estimates of pCO2 for the last 120 Ma based on the δ13C of marine phytoplanktic organic matter, Eos Trans. AGU, 72, 166
Bentor Y. K., Marine Phosphorites — Geochemistry, Occurrence, Genesis SEPM Spec. Publ., 3
Berger W H., 1988, Biogeochemical Cycling and Fluxes Between the Deep Euphotic Zone and Other Oceanic Realms Res. Rep., 131
Berger W. H., 1991, Shipboard Scientific Party, Ontong Java Plateau, leg 130: Synopsis of major drilling results, Proc. Ocean Drill Program Initial Rep., 130, 497
Berger W. H., 1993, Neogene carbonate sedimentation on Ontong Java Plateau: Highlights and open questions, Proc. Ocean Drill Program Sci. Results, 130, 711
Broecker W. S., 1982, Tracers in the Sea
Codispoti L. A., 1989, Productivity of the Ocean: Present and Past, 377
Filippelli G. M., 1994, Phosphorus geochemistry and accumulation rates in the eastern equatorial Pacific: Results from leg 138, PrOC. Ocean Drill. Program Sci. Results
Fourni K. B., 1991, Controversies in Modern Geology, 56
Froelich P. N., The Interaction of Global Biogeochemical Cycles JPL Publ., 141
Garrison R. E., 1990, Phosphatic sediments and rocks recovered from the Peru margin during ODP leg 112, Proc. Ocean Drill Program Sci. Results, 112, 111
Herring J. R., 1988, North Pacific productivity as recorded by P/Al ratios over the past 55 Ma (abstract), Eos Trans. AGU, 69, 1254
Hodell D. A., 1990, Variation in the strontium isotopic composition of seawater (8 Ma to present): Implications for chemical weathering rates and dissolved fluxes to the oceans, Chem. Geol., 80, 291
Kroenke L. W. et al. Proc. Ocean Drill. Program Initial Rep. 130 1991.
Lindh T. B. Temporal variations in δ13C 34S global sedimentation during the Phanerozoic M.S. thesis 99 pp Univ. Miami Miami 1984.
Lyle M., 1992, Composition maps of surface sediments of the eastern tropical Pacific Ocean, Proc. Ocean Drill. Program Initial Rep, 138, 101
Mayer L., 1992, Proc. Ocean Drill. Program Initial Rep., 138
Miller K. G., 1987, Tertiary δ13C, abyssal circulation the P/C ratio (abstract), Eos Trans. AGU, 68, 330
Mortlock R. A., 1992, Silica and germanium in hydrothermal vents, plumes jets in the Pacific Ocean, Eos Trans. AGU, 73, 255
Resig J., 1976, Foraminiferal stratigraphy and depositional history of the Ontong Java Plateau, Deep Sea Res., 23, 441
Ruttenberg K. C. Diagenesis and burial of phosphorus in marine sediments: Implications for the marine phosphorus budget Ph.D. dissertation 375 pp. Yale Univ. New Haven 1990.
Schlesinger W. H., 1991, Biogeochemistry: An Analysis of Global Change
Shackleton N. J., 1994, Stable isotope records in bulk sediment, ODP leg 138, Proc. Ocean Drill. Program Sci. Results
Shackleton N. J., 1994, A new Late Neogene timescale: Application to leg 138 sites, Proc. Ocean Drill. Program Sci. Results
Sheldon R. P., 1980, Episodicity of phosphate deposition and deep ocean circulation, A hypothesis, SEPM Spec. Publ., 29, 239
Shipboard Scientific Party, 1991, Introduction, Proc. Ocean Drill. Program Initial Rep., 130, 5
Shipboard Scientific Party, 1992, Introduction, Proc. Ocean Drill. Program Initial Rep., 138, 5
Stax R., 1993, Long‐term changes in the accumulation of organic carbon in Neogene sediments, Ontong Java Plateau, Proc. Ocean Drill. Program Sci. Results, 130, 573
Yan C. Y., 1993, A plate tectonic reconstruction of the southwest Pacific, 0–100 Ma, Proc. Ocean Drill. Program Sci. Results, 130, 697