Composition of particles in the global ocean

Abstract

A steady-state, ‘one and a half dimensional’ box model of the global ocean is used to generate the sinking fluxes of organic carbon, phosphorus, nitrogen, inorganic carbon and silica carried by ocean particles. The necessary input concentrations of dissolved components are derived from GEOSECS data averaged over ocean regions. The model particulate compositions are examined at three different depths (100, 1000 and 3500 m). The preferred Redfield compositions of the particles are, organic C:N:P:Si:inorganic C = 126:15.7:1:23.5:23.0 at 100 m, 125:15.8:1:94.4:56.0 at 1000 m and 144:16.3:1:119:71.5 at 3500 m. The model is compared with the results from sediment trap and large volume filtration experiments as well as with other theoretical work. There is broad agreement between theory and measurements, but there are some interesting discrepancies. In greement with Broecker et al. (1985, Journal of Geophysical Research, submitted), we find that the organic C:P ratio is higher than the accepted value of 106:1. Our values (125:1 increasing to 144:1 at 3500 m) are somewhat lower than sediment trap experiments have implied. The silica:carbonate ratio for the model particles is 1.8:1, significantly higher than has been observed. One-dimensional models of the ocean are inherently deficient, entailing a huge over-simplification of the complex, three-dimensional world ocean. Using a technique of multiple perturbations to the input parameters of the model, our conclusions are found to be relatively unaffected by large changes in the ocean circulation, except in so far as such changes affect the composition of water carrying ‘preformed’ nutrients to the deep sea.