The marine phosphorus cycle

Abstract

Phosphorus introduced to the ocean must ultimately be removed if a steady state is to be maintained over geologic time. Aeolian input is insignificant, and there is evidently no hydrothermal contribution. Rivers dominate P-input to the ocean. The fluvial P-flux is poorly quantified due to the interactions of two factors: (1) man's influence on river-nutrient fluxes; and (2) inherent complexities in understanding the biological and inorganic associations of P in estuarine and coastal waters. Our best estimate of the natural or pre-man P-input flux is about 10 x 10/sup -9/ moles - P/cm/sup 2/-ocean surface/year. Of the identified flux of phosphorus to the sediments, about 90 percent is in the form of biogenic debris or its regeneration products. The burial of phosphatic fish debris is negligible. P-removal by direct reaction of phosphate in seawater with sea-floor basalts during mid-ocean ridge hydrothermal circulation is insignificant. P-removal by processes such as sorption on clay surfaces or formation of authigenic Fe and Al phosphate phases is presently unquantified and remains a serious uncertainty in the phosphorus cycle. The identified sources and sinks approximately balance, yielding a residence time for P in the oceans of about 10/sup 5/ yrs.