Ice nuclei in marine air: bioparticles or dust?

Ice nuclei can influence the properties of clouds and precipitation, but their sources and distribution in the atmosphere are still not well known. Particularly little attention has been paid to IN sources in marine environments, although anecdotal evidence suggests that IN populations in remote marine regions may be dominated by biological particles associated with sea spray. In this exploratory model study, we aim to bring attention to this long-neglected topic and identify promising target regions for future field campaigns. We assess the likely global distribution of marine biological ice nuclei using a combination of historical observations, satellite data and model output. By comparing simulated marine biological IN distributions and dust IN distributions, we predict strong regional differences in the importance of marine biological IN relative to dust IN. Our analysis suggests that marine biological IN are most likely to play a dominant role in determining IN concentrations over the Southern Ocean, so future field campaigns aimed at investigating marine biological IN should target that region. Climate-related changes in the abundance and emission of biological marine IN could affect marine cloud properties, thereby introducing previously unconsidered feedbacks that influence the hydrological cycle and the Earth's energy balance. Furthermore, marine biological IN may be an important aspect to consider in proposals for marine cloud brightening by artificial sea spray production.