Investigating iron sources in the ocean
The rationale is that Fe availability in the ocean can affect biological productivity and the rate of carbon sequestration. However, the sources of dissolved Fe have not been fully explored, prompting initiation of the EU-funded 'Sources and biogeochemical cycling of iron isotopes in marine environments' (ISOMAR) project. The scientists aimed to determine if oceanic sources of Fe, like hydrothermal vents, display isotope signatures different to that of riverine or atmospheric Fe sources. Different isotope signatures may mean different chemical properties. Team members successfully achieved their first goal, which was to develop a new method to measure Fe isotopes in seawater. In fact, the precision of their novel approach is good enough to measure isotopes in deep seawater, hydrothermal plumes and coastal areas. Part of the project research also involved a cruise to the Loihi Seamount in Hawaii. The hydrothermal field there is an example of an environment where the biological and chemical oxidation of Fe can occur simultaneously. This makes it an ideal site to study metal sources and biogeochemical cycling. International collaborations were also initiated to measure Fe isotopes in the Gulf of Alaska and in the Indian River Lagoon in Florida, United States. Results so far suggest that Fe in coastal seawater does have a unique isotope signature in comparison with Fe from rivers. Initial ISOMAR research results point to Fe isotopes being valuable tracers for oceanic Fe sources. It is hoped that these efforts will help others to better assess the interplay between climate-driven changes and oceanic Fe availability.
