How iron isotopes offer a new window on the oceanic biogeochemical cycling of iron

Two process studies (2008 and 2012) designed to study temporal changes in the biogeochemical cycling of iron (Fe), provide in situ results for dissolved and particulate Fe (DFe and PFe) cycling during the annual spring bloom.

These field data have been complemented by a shipboard 700-L mesocosm incubation experiment. Later, a conceptual model helps figuring out the key chemical and biological processes involved in Fe isotope fractionation.

This works demonstrates that DFe is isotopically lighter than PFe at the beginning of the spring, likely reflecting the reduction of PFe by photochemistry and bacteria-mediated reduction processes. As the bloom develops, DFe within the surface mixed layer becomes isotopically heavier, consistent with the preferential uptake of light iron by phytoplankton while scavenging appears to play a minor role in fractionating Fe.

15 Ellwood l
Figure. This figure shows the increase in chlorophyll concentration across three different stages of the subtropical phytoplankton bloom (upper panels), along with depth profiles for dissolved iron and nitrate (middle panels), and the iron isotope composition of dissolved and particule iron (lower panels). Disssolved iron (DFe) is isotopically lighter (negative values) than particulate iron (PFe) at the beginning of the spring (stage I). As the bloom develops, DFe within the surface mixed layer becomes isotopically heavier (more positive values), consistent with the preferential uptake of light iron by phytoplankton. Click here to view the image larger.


Ellwood, M. J., Hutchins, D. A., Lohan, M. C., Milne, A., Nasemann, P., Nodder, S. D., Sander, S.G., Strzepek, R., Wilhelm, S.W., Boyd, P. W. (2014). Iron stable isotopes track pelagic iron cycling during a subtropical phytoplankton bloom. Proceedings of the National Academy of Sciences of the United States of America, 112(1), E15–20. doi:10.1073/pnas.1421576112. Click here to access the paper.

Latest highlights

Science Highlights

Spatial and temporal variability of bioactive trace metals, speciation and organic metal-binding ligands in the eastern Gulf of Mexico

Mellett and Buck present the concentrations of bioactive trace metals (Fe, Cu, Mn, Zn, Co, Ni, Cd, and Pb), Fe-and Cu-binding organic ligands, and electroactive Fe-binding humic substances in the eastern Gulf of Mexico.


Science Highlights

Thorium-Protactinium fate across the tropical Atlantic Ocean: what reveals the water column-sediment coupling

Twenty seawater profiles and twenty core-top 231-protactinium and 230-thorium analyses were realised by Ng and colleagues along five depth transects across the northern tropical Atlantic open ocean.


Science Highlights

Constraining Oceanic Copper Cycling through Artificial Intelligence and Ocean Circulation Inverse Model

Using available observations of dissolved copper, artificial neural networks, and an ocean circulation inverse model, authors calculated a global estimate of the 3-dimensional distribution and cycling of dissolved copper in the ocean.


Science Highlights

Particulate rare earth elements distributions, processes and characterisation of nepheloids in the North Atlantic

Lagarde et al. realised the first basin scale section of particulate rare earth elements concentrations across the North Atlantic Ocean.