Controls on phosphorus concentration and accumulation in oceanic sediments

Abstract

Understanding phosphorus (P) sedimentation in the ocean is important both for quantifying outputs in the marine phosphorus cycle and for determining the controls on phosphogenesis (the authigenic formation of carbonate fluorapatite) and phosphorite deposition (large accumulations of P-rich sediments on continental margins). In this study I have compiled literature data on sedimentary P concentrations and sedimentation rates from continental margins, phosphogenic continental margins, and open ocean environments. I have also calculated P accumulation rates, the product of P concentration, sediment density, and sedimentation rate in these settings. Sedimentary P concentrations exhibit a similar range in a wide variety of oceanic environments and sedimentation rate conditions. For example, P concentrations in continental margin sediments range from 8 to 108 μmol P g −1, with sedimentation rates from 80 to 8,000 m my −1. In open ocean sediments, the P concentration range is similar (7–307 μmol P g −1), even though sedimentation rates are generally about 100 times lower (2–50 m my −1). The exception to this are phosphogenic environments, where P concentrations are exceptionally high (580–3,700 μmol P g −1) while sedimentation rates are relatively low (20–310 m my −1). Phosphorus accumulation rates appear to be controlled by sedimentation rate in ocean sediments. Although P concentrations generally exhibit similar ranges, the large difference in sedimentation rates between various environments results in P accumulation rates that are several orders of magnitude higher in continental margins (90–8,000 μmol P cm −2 kyr −1) compared to open ocean sediments (2–75 μmol P cm −2 kyr −1). In the case of phosphogenic environments, low sedimentation rates result in P accumulation rates (80–6,300 μmol P cm −2 kyr −1) that are surprisingly similar to those of non-phosphogenic continental margin sediments.