Orographic and convective precipitation control meteoric 10Be wet depositional fluxes at low latitude

Using meteoric 10Be (10Bem) as a tracer of Earth surface processes requires understanding the factors that control 10Bem depositional fluxes. How precipitation influences 10Bem depositional fluxes is still debated, especially at low latitudes where little empirical flux data exist. To investigate how precipitation amount and type (drizzle vs. intense rain) influence meteoric 10Be depositional patterns in equatorial regions, we measured 10Bem concentrations in rain across a 10-fold precipitation gradient on Santa Cruz Island in the Galápagos Archipelago (Ecuador) over one hydrological year. The island’s climate is characterized by a cool season, with aridity in the lowlands and persistent fog and drizzle in the highlands, and a warm season marked by localized, intense convective precipitation. Measured 10Bem concentrations during the warm season decrease with increasing precipitation. Conversely, during the cool season 10Bem concentrations increase with increasing precipitation. We attribute this behavior to dilution of 10Bem concentrations during intense precipitation events in the warm season and enhanced efficiency of scavenging of 10Bem bearing aerosols by fog droplets during the cool season. Overall, enhanced scavenging outweighs dilution, and annual fluxes show a greater-than-linear increase with precipitation. Our dataset demonstrates that 10Bem concentrations in rain near the equator vary spatially and temporally as a function of precipitation type. We recommend taking atmospheric processes leading to cloud and fog formation into account when assessing wet depositional fluxes of 10Bem, as these may enhance 10Bem scavenging from the atmosphere.