Measurement of copper(I) in surface waters of the subtropical Atlantic and Gulf of Mexico

Cu(I) has been measured in the upper marine water column at various locations in the Atlantic Ocean and the Gulf of Mexico. Depth profiles characteristically display surface maxima, where Cu(I) comprises 5 to 10% of the total copper. Concentrations decline rapidly with depth to below the limit of detection (0.015 nM) at the base of the mixed layer and throughout the rest of the water column. Profiles show variability with depth and time of day consistent with photochemically mediated Cu(II) reduction. Cu(I) distribution appears to be controlled by a variety of factors including Cu(II) speciation, photochemically, or biologically produced Cu(II) reductants and possibly Cu(I) chelators which are significant only at subnanomolar Cu(I) levels. Hydrogen peroxide, which occurs in the photic zone and reduces Cu(II) to Cu(I) in seawater, accounts for a significant fraction of the Cu(I) observed, but other processes must also be involved. Cu(I) is analyzed by solvent extraction of its complex with 2,9-dimethyl 1, 10 phenanthroline, with ethylenediamine added simultaneously to mask Cu(II) interference. Details of the procedure are presented, along with an investigation of potential interferences.