The Sea-Surface Microlayer: Fate and Residence Times of Atmospheric Metals

Deposition of atmospheric particles provides a major source of metals to the world's oceans. Before entering the water column these metals must pass through the sea-surface microlayer (upper $50 \mu m$)- a boundary with unique physical, chemical, and biological properties. A model, derived from laboratory microcosm studies, is used to predict the behavior of six metals under two conditions of biotic enrichment and wind mixing and three atmospheric deposition rates. Mean residence times of metals in the microlayer are 1.5-15 h. Maximum predicted enrichments (microlayer/water metals concentrations) are Pb > Cu > Zn > Ag > Ni > Mn. Predicted Pb enrichments with a $3.6 m s^-1$ wind are 130, 60, and 2 for urban, rural coastal, and oceanic environments. These predicted enrichments agree well with mean microlayer metal enrichments measured in the field.