Iron speciation in eutrophic and oligotrophic Mediterranean coastal waters; impact of phytoplankton and protozoan blooms on iron distribution

Speciation, distribution and temporal differences in iron chemistry are important for understanding the biological roles of iron in marine systems. This paper presents a study of iron species in different coastal systems of the northeastern Mediterranean and the observed consequences of enrichments of coastal water by major nutrients and iron. Iron species were detected by using a serial chromatographic column method in the eutrophic inner and middle, transient and oligotrophic outer section of zmir Bay, western Turkey. In order to understand the impact of biological activity on the distribution of Fe species in coastal systems, phytoplankton densities and POC were also measured along with other relevant biological, physical and chemical variables in surface waters at different stations and seasons in zmir Bay. A significant decrease in iron concentration was observed in the outer bay despite of a very high iron input particularly from the sediment in shallow waters of the inner and middle bay. Average colloidal iron (ColFe) was 14±7% of the total iron that could pass a filter (<0.4 μm) (TFFe) throughout the bay water, however, Chelex column-labile Fe (ClxLFe) was significantly higher (42±25% of TFFe) and reached up to 80% of TFFe, especially in the shallow inner and middle bay. A dramatic decrease in ClxLFe was observed during the phytoplankton bloom in early April in the inner and middle bay. Hydrophobic organically complexed iron (HpOFe) and ClxLFe increased with increasing protozoan activity and collapse of phytoplankton.