The marine phosphorus cycle

TLDR

Phosphorus entering the ocean must ultimately be removed to maintain a steady state, with rivers dominating input while aeolian and hydrothermal contributions are negligible, and removal processes such as sorption and authigenic phase formation remain poorly quantified. Natural pre‑industrial phosphorus input is estimated at ~10⁻⁸ mol P cm⁻² yr⁻¹, with ~90 % of sediment flux from biogenic debris, negligible fish debris burial and basalt reactions, and overall sources and sinks balancing to give an ocean residence time of ~10⁵ years.

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.