Oxygen Consumption in Permeable and Cohesive Sediments of the Gulf of Aqaba
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Oxygen profiles were measured in the sediments of the Gulf of Aqaba (Red Sea), an oligotrophic marine system affected by episodic seasonal flash floods and intense aeolian dry deposition. Sediment cores were retrieved from shallow (15–45 m), intermediate (250–561 m) and deep (700 m) water sites of south–north and east–west transects. Dissolved oxygen concentrations were measured simultaneously by using microelectrodes and microoptodes immediately after sampling and after transportation. Oxygen penetration depths were found to increase from 2 to 5 mm at the shallow water sites with sandy permeable sediments to 10–21 mm at the deeper sites with cohesive muddy sediments. This increase corresponds to decrease in oxygen diffusive fluxes at the sediment–water interface and oxygen consumption rates with depth. Oxygen consumption rates exhibit local maxima at the oxic–anoxic sediment boundary, which may be attributed to oxygen reduction coupled to oxidation of dissolved Fe(II) and Mn(II) at deep and intermediate water sites and of hydrogen sulfide at shallow water sites. Microelectrodes and microoptodes measurements of cohesive sediments from deep and intermediate water sites yielded similar results. By comparison, the microoptodes displayed more robust measurements than microelectrodes in sandy near-shore sediments. This was attributed to their flexible fiber structure that is less likely to break or to abruptly displace sand particles. After transportation of sediment cores from Eilat to Beer Sheva followed by ≤ 24-h storage, no changes in oxygen fluxes and consumption rates were detected.
KeywordsGulf of Aqaba Sediment–water interface Oxygen consumption Oxygen penetration depth Diffusive boundary layer Microoptodes Microelectrodes
We would like to thank Shimon Feinstein (Ben-Gurion University of the Negev) and Viviana Bracha Farstey (IUI) for an opportunity to use their laboratory equipment. We are grateful to Asaph Rivlin, Sefi Baruch, Emanuel Sestieri, Shuki Isaacs, Ofir Hameiri, Yoav Lindeman, Shay Oron, Charlotte Wynn, Derya Akkaynak and Dmitri Churilov (IUI) for assistance with the field work and to Niva Levy, Hadar Cohen and Uriel Sinichkin for help with sample and data processing. Additionally, we would like to thank Peter Berg (University of Virginia) for sharing modeling software and helpful comments. This work was funded by Marie Curie Actions CIG PCIG10-GA-2011-303740 Grant.
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