Environmental context. Climate models are of considerable interest to scientists and the general public given the increasing awareness of global climate change. A large uncertainty in climate models is the influence of airborne particles on the amount of sunlight that clouds reflect back to space. Since oceans comprise 70% of the Earth’s surface, it is important that we gain an understanding of the factors that control the sources and nature of marine airborne particles. This work describes previously unexplored features of the marine aerosol at a clean site exposed to the Southern Ocean and its environmental importance, which will be of benefit to future climate models.

Abstract. Airborne particles (aerosol) collected at Cape Grim, Tasmania, in February 2006 in baseline conditions were examined by transmission electron microscopy. Particles recognised as marine exopolymer gels, and aggregates of insoluble organic particles that have diameters of ~40 nm, formed 9% of the particles larger than 200 nm. Once water-soluble compounds were removed by dialysis, the proportion rose to 30%. The gels and exopolymers were mainly of marine algal and bacterial origin. Their highly surface-active properties make them potentially environmentally important in the aerosol because of their ability to act as cloud condensation nuclei. The chemical constitution of particles in the 80–200-nm diameter size range is controversial, and widely varying estimates of the proportion of sea salt they contain have been published. Possible reasons for this are discussed. The present work supports the lowest estimate.