Measurement of the isotopic composition of dissolved iron in the open ocean

F. Lacan (1) , Amandine Radic (2) , Catherine Jeandel (2) , Franck Poitrasson (3) , Géraldine Sarthou (4) , Catherine Pradoux (2) , Remi Freydier (3)

1 GEOMAR LEGOS
2 LEGOS - Laboratoire d'études en Géophysique et océanographie spatiales
3 LMTG - Laboratoire des Mécanismes et Transfert en Géologie
4 LEMAR - Laboratoire des Sciences de l'Environnement Marin (LEMAR)

This work demonstrates for the first time the feasibility of the measurement of the isotopic composition of dissolved iron in seawater for a typical open ocean Fe concentration range (0.1-1nM). It also presents the first data of this kind. Iron is preconcentrated using a Nitriloacetic Acid Superflow resin and purified using an AG1x4 anion exchange resin. The isotopic ratios are measured with a MC-ICPMS Neptune, coupled with a desolvator (Aridus II), using a 57Fe-58Fe double spike mass bias correction. Measurement precision (0.13‰, 2SD) allow resolving small iron isotopic composition variations within the water column, in the Atlantic sector of the Southern Ocean (from deltaFe=-0.19 to +0.32‰). Isotopically light iron found in the Upper Circumpolar Deep Water is hypothesized to result from organic matter remineralization. Shallow samples suggest that, if occurring, an iron isotopic fractionation during iron uptake by phytoplankton is characterized by a fractionation factor, such as: abs(deltaFe(plankton-seawater))< 0.48‰.

Domaines: Océan, Atmosphère

F. Lacan, Amandine Radic, Catherine Jeandel, Franck Poitrasson, Géraldine Sarthou, et al.. Measurement of the isotopic composition of dissolved iron in the open ocean. Geophysical Research Letters, 2008, pp.L24610. ⟨10.1029/2008GL035841⟩. ⟨hal-00399111⟩