DISTRIBUTION AND POTENTIAL SOURCES AND SINKS OF COPPER CHELATORS IN THE SARGASSO SEA

Copper speciation has been studied at an oligotrophic station in the southwestern Sargasso Sea to determine the distribution of Cu binding ligands and evaluate their potential sources and sinks. Speciation was studied using a ligand exchange/liquid-liquid partition procedure used in a previous study in Florida coastal waters [Moffet and Zika (1987a) Marine Chemistry, 21, 301-313]. Copper speciation was dominated by organic complexation at all depths studied (16-950 m). Complexation was greatest in the region of the chlorophyll maximum. In this region, speciation was dominated by two ligands or ligand classes; L1, with Kcond. = 1013.2, concentration = 2 nM, and a weaker but more abundant ligand class, L2 with Kincond. = 109.7, concentration = 80 nM. From 140 to 16 m, [Cu(II)]free/[Cu(II)]total increases by a factor of 20, due to a decrease in [L1] to a value below the ambient Cu concentration. Exposure of water from 140 m to sunlight indicated that photochemical decomposition of L1 may account for the decrease. Below the chlorophyll maximum there is a gradual increase in [Cu(II)]free/[Cu(II)]total suggesting that the ligands are of recent biological origin rather than derived from refractory materials. Cultures of a ubiquitous marine cyanobacterium, Synechococcus sp. produced a ligand with Kcond. comparable to L1, indicating that a biological source is plausible. © 1990.