The Nature of Phosphorus Burial in Modern Marine Sediments

Abstract

Phosphorus is a key element in biogeochemical cycles because of its role as an essential nutrient. Because of the ability of certain marine organisms, such as cyanobacteria, to fix nitrogen, it has been normally assumed that the long term limiting factor in global oceanic productivity is phosphorus (e.g. Holland, 1978). Thus, a knowledge of phosphorus chemistry in the ocean is a key to a better understanding of the cycling of carbon, nitrogen, sulfur, and other bio-elements. Over shorter time scales, days to millenia, the cycle of phosphorus in the ocean is controlled by a combination of processes involving oceanic circulation, biosynthesis, sinking of particles, and bacterial regeneration of the particles at depth or on the sea floor (e.g. Berger et al., 1989). Consequently, concentrations of dissolved phosphorus in seawater vary from place to place as a result of the interaction of these processes. In this context sediments are important only as their surficial portions release additional dissolved phosphate to the overlying water. By contrast, sediments become much more important on longer time scales of tens of thousands to millions of years, because they are the ultimate repository for the removal of phosphate from the oceans. The overall level of phosphorus in the ocean, and therefore global biological productivity, is controlled by the long-term balance between input via rivers and output via burial in sediments.