Changes in the Concentration of Soluble and Particulate Iron in Seawater Enclosed in Containers1

Seawater samples collected along the Washington coast (Puget Sound) were used as sources of naturally occurring iron fractions. Once the water was enclosed in a container, approximately half of the iron in the soluble fraction disappeared and could be quantitatively accounted for by an increase in the iron of the particulate fraction; when the particulate fraction was removed at zero time, soluble iron likewise disappeared, but most of it went onto the walls of the container. The changes were independent of temperature and soluble iron disappeared even when the particulate fraction (including organisms) was removed at zero time, ruling out biological activity. These changes were completed in 30–40 hr. Part of the soluble fraction was ferrous iron. Addition of Na2‐EDTA stabilized a portion of the soluble iron equivalent to the ferrous content and kept it from disappearing during the experiment. Ferrous iron may be present in a chelated form in the natural seawater.