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In an effort to better represent aerosol transport in mesoscale and global‐scale models, large eddy simulations (LES) from the National Center for Atmospheric Research (NCAR) Turbulence with Particles (NTLP) code are used to develop a Markov chain random walk model that predicts aerosol particle profiles in a cloud‐free marine atmospheric boundary layer (MABL). The evolution of vertical concentration profiles are simulated for a range of aerosol particle sizes and in a neutral and an unstable boundary layer. For the neutral boundary layer we find, based on the LES statistics and a specific model time step, that there exist significant correlation for particle positions, meaning that particles near the bottom of the boundary are more likely to remain near the bottom of the boundary layer than being abruptly transported to the top, and vice versa. For the unstable boundary layer, a similar time interval exhibits a weaker tendency for an aerosol particle to remain close to its current location compared to the neutral case due to the strong nonlocal convective motions. In the limit of a large time interval, particles have been mixed throughout the MABL and virtually no temporal correlation exists. We leverage this information to parameterize a Markov chain random walk model that accurately predicts the evolution of vertical concentration profiles. The new methodology has significant potential to be applied at the subgrid level for coarser‐scale weather and climate models, the utility of which is shown by comparison to airborne field data and global aerosol models.

Deposition of aerosolized desert dust can affect marine microbial community structure and function through pulsed addition of limiting micro‐ and macronutrients. However, few studies have captured responses to dust deposition in situ following trans‐oceanic transport. We conducted a 26‐d time series evaluating biogeochemical and microbial community response to Saharan dust deposition in surface waters in the subtropical western Atlantic (Florida Keys National Marine Sanctuary, U.S.A.). Following periods of elevated atmospheric dust concentrations, particulate and dissolved iron concentrations increased in surface waters. Autotrophic picoeukaryote abundance increased rapidly, followed by increases in the abundance of heterotrophic bacteria andSynechococcus. Concomitant to cell count changes, we observed successional shifts in bacterial community composition. The relative abundances ofProchlorococcusandPelagibacterdeclined with dust arrival, while relative abundance of heterotrophic bacteria increased, beginning with Vibrionales and followed sequentially by Chrysophyceae, Rhodobacteriaceae, and Flavobacteriaceae. Finally, a peak inSynechococcuscyanobacteria was observed. These results provide new insight into microbial community succession in response to Saharan dust deposition, their association with temporal dynamics in surface water dissolved and particulate iron concentrations, and a potential role for bioprocessing of dust particles in shaping marine microbial responses to deposition events.