A model of microenvironments in deep‐sea sediments: Formation and effects on porewater profiles1

The influence of suboxic microenvironments on the deep-ocean porewater nitrogen system is investigated via a porewater-sediment model in which respiration is confined exclusively to discrete sedimentary particles. The formation of suboxic zones within particles that are surrounded by oxygenated porewaters is favored by large particle size, rapid rates of oxygen consumption, and slow internal diffusivity. Of these parameters, the retardation of diffusion due to the presence of organic membranes and organism tests and the increase in respiration rates by the concentration of oxygen consumption into a small proportion of the total particles present represent the most likely mechanisms by which microenvironments form. Once present, however, the main influence of suboxic microzones is to decrease the magnitude of the nitrate maximum, shift the depth of the maximum to a shallower sediment horizon, and decrease the buildup of nitrogen gas in the porewaters. Surface sediments in the deep sea are ma