A link between the ice nucleation activity and the biogeochemistry of seawater

© 2020 BMJ Publishing Group. All rights reserved. Emissions of ice-nucleating particles (INPs) from sea spray can impact climate and precipitation by changing cloud formation, precipitation, and albedo. However, the relationship between seawater biogeochemistry and the ice nucleation activity of sea spray aerosols remains unclarified. Here, we demonstrate a link between the biological productivity in seawater and the ice nucleation activity of sea spray aerosol under conditions relevant to cirrus and mixed-phase cloud formation. We show for the first time that aerosol particles generated from both subsurface and microlayer seawater from the highly productive eastern tropical North Pacific Ocean are effective INPs in the deposition and immersion freezing modes. Seawater particles of composition similar to subsurface waters of highly productive regions may therefore be an unrealized source of effective INPs. In contrast, the subsurface water from the less productive Florida Straits produced less effective immersion mode INPs and ineffective depositional mode INPs. These results indicate that the regional biogeochemistry of seawater can strongly affect the ice nucleation activity of sea spray aeroso