Iron sources and dissolved-particulate interactions in the seawater of the Western Equatorial Pacific, iron isotope perspectives

Authors

M. Labatut, University of Toulouse
F. Lacan, University of Toulouse
C. Pradoux, University of Toulouse
J. Chmeleff, University of Toulouse
A. Radic, University of Toulouse
J. W. Murray, University of Washington
F. Poitrasson, University of Toulouse
Anne M. Johansen, Central Washington University
F. Thil, Laboratoire des Sciences du Climat et de l’Environnement, Gif-sur-Yvette, France

Document Type

Article

Department or Administrative Unit

Chemistry

Publication Date

10-10-2014

Abstract

This work presents iron isotope data in the western equatorial Pacific. Marine aerosols and top core margin sediments display a slightly heavy Fe isotopic composition (δ⁵⁶Fe) of 0.33 ± 0.11‰ (2SD) and 0.14 ± 0.07‰, respectively. Samples reflecting the influence of Papua New Guinea runoff (Sepik River and Rabaul volcano water) are characterized by crustal values. In seawater, Fe is mainly supplied in the particulate form and is found with a δ⁵⁶Fe between −0.49 and 0.34 ± 0.07‰. The particulate Fe seems to be brought mainly by runoff and transported across continental shelves and slopes. Aerosols are suspected to enrich the surface Vitiaz Strait waters, while hydrothermal activity likely enriched New Ireland waters. Dissolved Fe isotopic ratios are found between −0.03 and 0.53 ± 0.07‰. They are almost systematically heavier than the corresponding particulate Fe, and the difference between the signature of both phases is similar for most samples with Δ⁵⁶Fe_{DFe – PFe} = +0.27 ± 0.25‰ (2SD). This is interpreted as an equilibrium isotopic fractionation revealing exchange fluxes between both phases. The dissolved phase being heavier than the particles suggests that the exchanges result in a net nonreductive release of dissolved Fe. This process seems to be locally significantly more intense than Fe reductive dissolution documented along reducing margins. It may therefore constitute a very significant iron source to the ocean, thereby influencing the actual estimation of the iron residence time and sinks. The underlying processes could also apply to other elements.

Comments

This article was originally published in Global Biogeochemical Cycles. The full-text article from the publisher can be found here.

Recommended Citation

Labatut, M., F. Lacan, C. Pradoux, J. Chmeleff, A. Radic, J. W. Murray, F. Poitrasson, A. M. Johansen, and F. Thil (2014), Iron sources and dissolved particulate interactions in the seawater of the Western Equatorial Pacific, iron isotope perspectives, Global Biogeochem. Cycles, 28, 1044–1065, doi:10.1002/2014GB004928.

Journal

Global Biogeochemical Cycles

Rights

© 2014. American Geophysical Union. All Rights Reserved.