Colloids have been suggested to play critical roles in the marine geochemical cycling of elements which form hydrolysis products, including A1(III), Fe(III), and Th(IV). Complexation of metals by organic ligands in the colloidal size range may also be important for elements such as Cu(II) and Zn(II). Due to their function as required micro-nutrients, accurate information is needed on the speciation of Fe, Cu, and Zn (and other trace elements as well) in order to ultimately understand how this speciation is related to productivity and nutrition in the ocean. The very large surface/volume ratio of colloidal hydroxides may also affect the geochemistry of other particle-reactive elements. Colloids in the ocean could come from multiple sources, including river/estuarine transport, hydrolysis of Al and Fe released from aerosols, and production of high molecular weight organic ligands by marine microbes. This work involves an initial series of experiments designed to investigate these multiple sources of colloidal material and to determine whether, and under what conditions, colloidal trace metals are a significant fraction of the total "dissolved" pool of trace metals in the oceans. Samples from estuarine, coastal, and open-ocean waters will be collected using stringent anti-contamination methods and processed using cross-flow ultrafiltration (CFF).
