Constraining aerosol deposition over the global ocean

Aerosols significantly influence climate by modifying Earth’s radiative balance and marine biogeochemical cycles. However, accurate quantification of aerosol deposition onto ocean surfaces remains challenging, due to the limited direct observations over oceanic regions. Here, to address this observational gap, we use a newly developed method based on simultaneous measurements of the cosmogenic radiotracer beryllium-7 (7Be) in seawater and the atmosphere. 7Be is naturally produced in the atmosphere, rapidly attaches to submicron aerosol particles, and is deposited onto the ocean surface through wet and dry processes, making it a direct tracer for quantifying aerosol deposition. We combine previous measurements from cruises in the North Pacific, equatorial Pacific, North Atlantic, and Arctic Oceans with new measurements from the South Pacific, Indian, and Southern Oceans to derive a new aerosol deposition parameterization across the global ocean. Compared with current parameterizations used in the GEOS-Chem chemical transport model, we find aerosol deposition rates over the global ocean have been underestimated by 39 ± 23%, consequently overestimating aerosol lifetime over the oceans by an average of 69 ± 92%. Our observationally constrained results suggest that aerosol processes are more dynamic than previously estimated, with important implications on understanding aerosol-driven climate effects and marine biogeochemical processes globally.