AN APPARENT CONTRADICTION IN THE ROLE OF PHOSPHORUS IN CENOZOIC CHEMICAL MASS BALANCES FOR THE WORLD OCEAN

Little is known about the fluxes to and from the ocean during the Ceno zoic of phosphorus (P), a limiting nutrient for oceanic primary produc tivity and organic carbon burial on geologic timescales. Previous stud ies have concluded that dissolved river fluxes increased worldwide dur ing the Cenozoic and that organic carbon burial decreased relative to calcium carbonate burial and perhaps in absolute terms as well. To exa mine the apparent contradiction between increased river fluxes of P (a ssuming P fluxes behave like the others) expected to drive increased o rganic carbon burial and observations indicating decreased organic car bon burial, we determined P accumulation rates for equatorial Pacific sediments from Ocean Drilling Program leg 138 sites in the eastern equ atorial Pacific and leg 130 sites on the Ontong Java Plateau in the we stern equatorial Pacific. Although there are site specific and depth d ependent effects on P accumulation rates, there are important features common to the records at all sites. P accumulation rates declined fro m 50 to 20 Ma, showed some variability from 20 to 10 Ma, and had a sub stantial peak from 9 to 3 Ma centered at 5-6 Ma. These changes in P ac cumulation rates for the equatorial Pacific are equivalent to substant ial changes in the P mass balance. However, the pattern resembles neit her that of weathering flux indicators (Sr-87/Sr-86 and Ge/Si ratios) nor that of the carbon isotope record reflecting changes in organic ca rbon burial rates. Although these P accumulation rate patterns need co nfirmation from other regions with sediment burial significant in glob al mass balances (e.g., the North Pacific and Southern Ocean), it appe ars that P weathering inputs to the ocean are decoupled from those of other elements and that further exploration is needed of the relations hip between P burial and net organic carbon burial.