Organic carbon, nitrogen, and iron (total-Fe, reactive-Fe) in sediments and iron in pore water were determined, using 23 sediment samples collected at the Harima-Nada, Seto Inland Sea, Japan. Vertical profiles of organic-C and reactive-Fe were similar and a high correlation coefficient (r=0.86) was detected between organic-C and reactive-Fe. A relatively high correlation coefficient (r=0.66) was also obtained between reactive-Fe in sediments and total-Fe in pore water. These results suggest

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... when a reductive condition is achieved in marine sediments, some parts of iron conjugated with organic matter are eluted to the pore water and subsequently returned to the overlying sea water. Organic iron in pore water of the sediments was separated with Sephdex G-10 chromatography. The growth-promoting activities to Chattonella aniqua with separated iron fractions in pore water were estimated. Considerable activites were found in the two iron fractions which eluted before the NaC1 fraction. Fig. 2. Distribution of total-Fe and reactive-Fe in sediment samples in the Harima-Nada.