Comparative biogeochemical behaviors of iron-55 and stable iron in the marine environment

Abstract

Studies of atmospheric aerosols have demonstrated that much of the /sup 55/Fe associated with the aerosol input to the oceans is present as either an amorphous or hydrous iron oxide or as very small particulate species attached to the surfaces of the large aerosol particles. By comparison, nearly all of the stable iron is bound in the mineral phase of aerosol particles. This difference in the chemical and physical forms of the radioactive and stable iron isotopes results in the /sup 55/Fe being more biologically available than is the stable iron. This difference in availability is responsible for the transfer of a much higher specific activity /sup 55/Fe to certain ocean organisms and man relative to the specific activity of the total aerosol or of sea water. This differential biological uptake of the radioactive element and its stable element counterpart points out that natural levels of stable elements in the marine environment may not effectively dilute radioelements or other stable elements of anthropogenic sources. The effectiveness of dilution by natural sources depends on the chemical and physical forms of the materials in both the source terms and the receiving environments. The large difference in specific activities of /sup 55/Fe in aerosols and sea water relative to ocean organisms reflects the independent behaviors of /sup 55/Fe and stable iron.