Seminar Details

Iron speciation as a redox proxy in the sediments of the Gulf of Aqaba




Valeria Boyko - Dept. of Geological and Environmental Sciences, Ben Gurion of the Negev


The iron speciation is one of the most accessible and effective inorganic paleoproxies utilized to identify depositional settings (oxic vs anoxic; ferruginous vs euxinic) in the ancient and modern marine systems and trace environmental changes throughout Earth’s evolution. This proxy is based on the distribution of iron among several fractions with different reactivity towards hydrogen sulfide. We have studied speciation of iron in the dust, dry creek sediments and sediments of the Gulf of Aqaba at various water depths in order to understand sources and transformations of iron minerals. Two sources of iron, dust and flash floods transported material, were found to possess distinct geochemical signatures: dust was found to be enriched in total and highly reactive iron relative to the sediments in creek beds. Superposition of these two sources leads to increase in content of highly reactive iron sediment with water depth. This increase, in turn, results in formation of lateral redox gradient with sulfidic pore-waters near the shore, and ferruginous-manganous pore-waters and cryptic sulfur cycling at the deeper water sites, despite increase in total organic carbon content with depth. Another result of dry aeolian deposition of desert dust to the sediments of the Gulf of Aqaba, overlaid by deep well-oxygenated waters, is anomalously high ratios of highly reactive to total iron, which are diagnostic for anoxic, iron-rich water columns.

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