A mechanistic approach linking the population dynamics of plankton communities to the export of detrital material to the oceans interior, remains a largely unresolved component of global bio-geochemical models. We propose that the self-similarity of aggregation provides a tractable modelling framework for simulating the dynamics and sinking speed of natural marine particle aggregates. It provides a means to track both size and excess density of aggregates as they are formed and transformed by aggregation, degradation and fragmentation processes. A self-similarity parameter <em>a</em> in the range 1.8 to 2.1 is well supported by direct observations drawn from an extensive database of aggregate size and sinking speed. We provide a simple model, SISSOMA, that uses a 2 dimensional state-space representation of aggregate dynamics for which we conduct sensitivity analyses for the self-similarity parameter, stickiness, turbulent dissipation rate and the production rate of primary particles. The model provides size and density resolved estimates of the export flux of detrital material generated by a diverse community of primary producers. While open to improvement in several aspects, the model compares well with observations of aggregate size spectra covering the global ocean.