Infection Dynamics of a Bloom-Forming Alga and Its Virus Determine Airborne Coccolith Emission from Seawater

Abstract

Sea spray aerosols (SSA) are amongst the largest contributors to global aerosol mass, with a profound effect on climate through their radiative and microphysical properties. The contribution of oceanic microbial activity to SSA properties is yet to be fully established. We assessed the SSA emission of the calcite units (coccoliths) that compose the exoskeletons of the cosmopolitan bloom-forming coccolithophore, Emiliania huxleyi. We show that while emission of airborne coccoliths occurs in steady-state conditions, it increases by an order of magnitude during E. huxleyi infection by its specific E. huxleyi virus (EhV). The seawater to airborne coccolith ratio during viral infection was 1:108, from which we can estimate ambient airborne coccolith concentrations as a function of oceanic bloom properties. The unique aerodynamic structure of the emitted coccoliths yields a characteristic settling velocity ~25 times smaller compared to sea salt particles of the same size, resulting in an enrichment of the coccolith fraction in the air. The predicted enrichment is established in lab results, which show that coccoliths are key contributors to coarse mode SSA surface area, comparable with sea salt aerosols. This study demonstrates the coupling between key oceanic microbial interactions and fundamental atmospheric processes like SSA formation and emission.