Atmospheric Aerosols Versus Total Atmospheric Deposition in Guadeloupe (Lesser Antilles): Composition, Concentration, and Flux

Abstract

Atmospheric mineral dust deposition is an important source of nutrients for ocean and tropical island ecosystems. Direct deposition measurements are generally more reliable at local scale than dust deposition models, even those based on aerosol concentration measurements. Whatever the scale, relevant local observations are necessary for model evaluation. We present here the results obtained by direct measurement of atmospheric aerosols and total atmospheric deposition using a 14-month time series from the Caribbean region. Total deposition velocity, lifetime, and scavenging ratio of major and trace elements were determined. Comparing total deposition fluxes of aluminum (dust proxy) and sea-salt sodium (sea-salt proxy) with Community Atmosphere Model (CAM6) outputs shows that the modeled total deposition rate is underestimated by a factor of two for dust and by a factor of eight for sea salt, while model aerosol concentration is larger than concentration measured near ground level. This result is due to wet deposition being underestimated in the model. The scavenging ratio (w/w) of Saharan dust elements ranges from 95 to 1,390, with a median of 530, close to the geometric mean value of 513. Sea salt presents a greater range of scavenging ratio values, from 325 to 2,355, with a median of 1,180, close to the geometric mean value of 1,030. The lead isotope ratio ²⁰⁶Pb/²⁰⁷Pb clearly highlights differences in lead origin between aerosols and deposits, revealing that aerosol samples are enriched by anthropogenic sources.