The vertical distribution of iron stable isotopes in the North Atlantic near Bermuda

• Published in: Global Biogeochemical Cycles
• Main Authors: John, Seth G., Adkins, Jess
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union 2012
• Subjects: North Atlantic
• Online Access: https://authors.library.caltech.edu/32361/; https://authors.library.caltech.edu/32361/1/John2012p18755Global_Biogeochem_Cy.pdf; https://resolver.caltech.edu/CaltechAUTHORS:20120711-132003222

Seawater dissolved iron isotope ratios (δ^(56)Fe) have been measured in the North Atlantic near Bermuda. In a full-depth profile, seawater dissolved δ^(56)Fe is isotopically heavy compared to crustal values throughout the water column (δ^(56)Fe_(IRMM-014) = +0.30‰ to +0.71‰). Iron isotope ratios are relatively homogenous in the upper water column (between +0.30‰ to +0.45‰ above 1500 m), and δ^(56)Fe increases below this to a maximum of +0.71‰ at 2500 m, decreasing again to +0.35‰ at 4200 m. The δ^(56)Fe profile is very different from the iron concentration profile; in the upper water column [Fe] is variable while δ^(56)Fe is relatively constant, and in the deeper water column δ^(56)Fe varies while [Fe] remains relatively constant. The δ^(56)Fe profile is also not well correlated with other hydrographic tracers in the North Atlantic such as temperature, salinity, or the concentrations of oxygen, phosphate, silica, and CFC-11. The dissimilarity between δ^(56)Fe profiles and profiles of [Fe] and other hydrographic tracers shows that Fe isotope ratios provide a unique sort of information about ocean chemistry, and they suggest that Fe isotopes may therefore be a valuable new tool for tracing the global sources, sinks, and biogeochemical cycling of Fe.