Trace metal enrichment in the sea-surface microlayer

Abstract

Sea-surface microlayer samples have been analyzed for the trace metals aluminum, copper, iron, manganese, nickel, lead, and vanadium by atomic absorption and neutron activation. Samples were collected with polyethylene screens in the estuarine waters of Narragansett Bay, Rhode Island, the coastal waters of the New York Bight, and open ocean regions between Iceland and Nova Scotia. Metal enrichment in the ‘particulate’ and ‘chloroform-extractable’ fraction of the surface microlayer compared to water 20 cm below the surface varied from virtually none up to approximately 50 for copper, iron, and nickel and up to 20 for lead in the Narragansett Bay samples. There was no enrichment in the soluble, ‘inorganic’ fraction of the surface microlayer for those metals in Narragansett Bay. The degree of surface enrichment was correlated with the presence of observable slicks on the water surface. None of the New York Bight or open ocean samples were collected while observable slicks were present. Significant enrichments in particulate and chloroform-extractable phases in the surface microlayer still occurred in the majority of cases in both areas. The variability of its occurrence and magnitude may be due to several factors, including the presence of coherent slicks, biological activity, and local pollution sources, both atmospheric and water. On the open ocean, atmospheric input of some trace metals to the surface microlayer may be quite significant. Where surface microlayer enrichment of trace metals does occur, enrichment of these metals on sea-salt aerosols formed at the sea surface may also occur.