Microbial, inorganic, and photochemical reactions as well as particle adhesion are responsible for metal (Al, Cd, Cr, Cu, Fe, Mn, and Mo) sorption onto surface films that form on any solid phase exposed to seawater. The principal aim of the study was to investigate the relative extent of these various reactions as a function of time at a Sargasso Sea open ocean site to compare to previous studies at a coastal site. The metal/aluminum ratios for Cd, Cr, Cu, Fe, and Mn on surfaces exposed at a buoy 3 m deep in the Sargasso Sea largely correspond to leached Sargasso Sea atmospheric particulates indicating a primary atmospheric origin for these elements. However, in a series of incubation experiments, Cu, Fe, Mn, and Mo uptake was partially governed by oxidation/reduction processes (either bacterial or photochemical or both). The results suggest both a photochemical and bacterial reduction of insoluble Fe (III) oxides on the surfaces to soluble Fe (II). Mn/Al ratios suggested that a bacterial reduction of Mn (IV) oxides to Mn+2 was also taking place on the surface. Additional sorption of Cd, Cu and probably Mo onto surfaces seems to be governed by biological processes. The average ratios (Cd/Al, Cu/Al, and Mn/Al) reported for the surfaces of the incubation and buoy experiments tend to be relatively close to the average ratios for these trace metals in marine snow confirming their morphological similarities as revealed by scanning electron microscope.