The impact of atmospheric aerosols on trace metal chemistry in open ocean surface seawater: 2. Copper

Abstract

Atmospheric deposition contributes copper to the surface ocean. The biogeochemical importance and fate of this copper is poorly understood for open ocean regions. Atmospheric aerosols collected at Enewetak Atoll, in the tropical North Pacific, were exposed to seawater and artificial rainwater in laboratory experiments. Aerosol copper during the high‐dust season at Enewetak Atoll is made up of aluminosilicate, oceanic, and possibly soil organic matter components. During the low‐dust season, aerosol copper appears to be essentially all of oceanic origin. Virtually all nonaluminosilicate copper in marine aerosols collected at Enewetak is soluble in seawater. Dissolved organic matter and possibly cations in seawater increase the dissolution of aerosol copper. The net atmospheric flux of soluble copper to the tropical North Pacific near Enewetak is approximately 0.13 nmol cm⁻² yr⁻¹ out of a total net atmospheric copper flux of 0.14 nmol cm⁻² yr⁻¹. Atmospheric deposition supplies roughly the same quantity of soluble copper to tropical open North Pacific surface waters as does upwelling to eastern North Pacific surface waters. Atmospheric copper deposition, which appears to be primarily of natural origin, may be the most important input of copper to the surface waters of the central gyre of the North Pacific.