Mineral dust, volcano ash and soot (black carbon) are among the major solid aerosol inputs to the world ocean. They deliver elements such as C, N, P, S and bioactive trace metals in significant amounts. However, in contrast to mineral dust, the impact of volcano ash and soot on microbial plankton is poorly studied, although total deposition rates are not much lower for volcano ash than for mineral dust in certain basins and soot delivers overall more P into the ocean than mineral dust. Aging processes in the atmosphere during horizontal transport, e.g. due to exposure to UV light and acidic conditions in clouds, increase the solubility and hence bioavailability of volcano ash and soot aerosols. Current findings suggest that volcano ash and soot are a source of nutrients and/or organic carbon, and influence aggregation processes. Volcano ash seems to stimulate phytoplankton, and soot bacterioplankton; both aerosols influence microbial diversity. We argue that volcano ash and soot have a significant, but comparatively less well-studied effects on microbial plankton that should, along with mineral dust, be better implemented into concepts and studies of microbial food webs to improve the mechanistic understanding of the role and performance of autotrophic and heterotrophic microorganisms in the ocean.
