Abstract
Redox transformations of iron in the surface waters of the Gulf of Aqaba, Red Sea, were studied on recurrent cruises from September 2006 to May 2007. Fe(II) concentrations and oxidation kinetics were measured in situ using luminol chemiluminescence. High Fe(II) concentrations of 200-400 pM were recorded in the autumn, followed by low concentrations of 20- 130 pM in the winter-spring. A distinct diurnal pattern in Fe(II) concentrations was observed in the autumn with maximum values coinciding with maximum solar irradiance. In situ and in vitro Fe(II) oxidation rates showed temporal and spatial variability that was accounted for by changes in water temperature and pH. Dissolved oxygen was found to be the dominant oxidant in all but one cruise. In situ photoreduction rates (deduced from oxidation rates) were linearly correlated with solar irradiance during the autumn, suggesting that the reducible iron pool was not exhausted even at the strongest irradiances and that it was kept constant throughout the season. Phytoplankton had no discernible influence on Fe(II) production, consumption, or oxidation kinetics. Given the fast oxidation and photoreduction rates of up to 180 pM min-1, the turn-over rates of iron were estimated at 10-30 per day. Such a dynamic Fe redox cycle probably influences the chemical reactivity and bioavailability of iron and may enhance the solubility of the abundant aerosol dust.
| Original language | English |
|---|---|
| Pages (from-to) | 1540-1554 |
| Number of pages | 15 |
| Journal | Geochimica et Cosmochimica Acta |
| Volume | 72 |
| Issue number | 6 |
| DOIs | |
| State | Published - 15 Mar 2008 |
Bibliographical note
Funding Information:I acknowledge the help of many colleagues who made this research possible and enjoyable: Itzik Lerer, Asaph Rivlin, and Muriel Dray for help with field work; Boaz Lazar, Eric Roy, Tyler Goepfert, and Whitney King for assistance in operating the FeLume; the Israel National Monitoring Program (NMP) at the Northern Gulf of Aqaba (Amatzia Genin, Yonathan Shaked, Muriel Dray, Tanya Rivlin, Inbal Ayalon) for cruises and data; and Kathy Barbeau, Tina Voelker, Eric Roy, Micha Rijkenberg, Simon Ussher, Andrew Rose and two anonymous reviewers for providing valuable comments on the manuscript. This research was supported (in part) by the Israel Science Foundation (Grant No. 933/07) and the Hebrew University Moshe Shilo Minerva Center for Marine Biogeochemistry.