Diel cycle of sea spray aerosol concentration over vast areas of the tropical Pacific Ocean and the Caribbean Sea

Abstract Ocean-atmosphere interactions such as sea spray aerosol (SSA) formation have a major role in the climate system, but a global-scale assessment of this micro-scale process is highly challenging. We measured high-resolution temporal patterns of SSA number concentration over the Atlantic Ocean, Caribbean Sea, and the Pacific Ocean covering 42,000 km of open ocean waters. We discovered a ubiquitous 24-hour rhythm to the number concentration, clearly seen for particle diameters > ~ 0.58 µm, with spikes at dawn and drops at dusk throughout the Pacific Ocean and Caribbean Sea, showing more than doubling of the SSA number concentration during the day than at night. No correlation with surface winds, atmospheric radiation, pollution nor oceanic physical properties were found. Instead, parallel diel patterns in particle sizes detected in near-surface waters, attributed to variations in the size of particles smaller than ~ 1 µm, point to microbial day-to-night modulation of bubble-bursting dynamics as the cause of the SSA cycle.