『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.』
1. Introduction
2. Study area
3. Methods
3.1. Water sampling and trace metal clean protocols
3.2. Fe (II) determination
3.3. Total and filtered Fe determination
3.4.l Reagents
3.5. Other methods
4. Results and discussion
4.1. Seasonal and diurnal variations in surface Fe (II) concentrations
4.2. The role of photoreduction in Fe (II) formation
4.3. Fe (II) oxidation rates
4.4. The role of oxidation in determining autumn steady state
Fe (II) concentrations
4.5. The lack of biological influence on the iron redox cycle
in the Gulf of Aqaba
4.6. Implications for iron recycling and bioavailability
5. Conclusions
Acknowledgments
References