Sources and transformations of iron in the sediments of the Gulf of Aqaba (Red Sea)

The Gulf of Aqaba is an oligotrophic marine system with an oxygen-rich water column. Aeolian dust from the Arabian, Sinai, and Sahara deserts is an important source of sedimentary material to the gulf, especially at 700 m water depth. The head of the gulf is affected by sediment transport from the Arava desert during winter flash floods. In this work, we have studied the 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. 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. Combination of these two sources leads to an increase of highly reactive iron in sediments with water depth. This increase, in turn, results in formation of a lateral redox gradient with sulfidic pore-waters near the shore, and ferruginous-manganous pore-waters and cryptic sulfur cycling at the deeper water sites. 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 have been proposed to be diagnostic for anoxic, iron-rich water columns, when applied as a paleoproxy.