The marine geochemistry of iron and iron isotopes


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dc.contributor.author Bergquist, Bridget A.
dc.coverage.spatial 30°N, 45°W
dc.coverage.spatial 10°N, 45°W
dc.coverage.spatial 24.5°S, 37°W
dc.date.accessioned 2007-11-30T16:14:57Z
dc.date.available 2007-11-30T16:14:57Z
dc.date.issued 2004-09
dc.identifier.uri http://hdl.handle.net/1912/1854
dc.description Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2004 en
dc.description.abstract This thesis addressed questions about the Fe cycle by measuring detailed profiles and transects of Fe species in the ocean and also by exploring the use of a new tracer of Fe, Fe isotopic fractionation. In the subtropical and tropical Atlantic Ocean, transects and profiles are presented for dissolved Fe (<0.4 μm), soluble Fe (<0.02 μm), and colloidal Fe (0.02 to 0.4 μm). Surface dissolved Fe distributions reflect atmospheric deposition trends with colloidal Fe following dust deposition more strongly than the soluble fraction of Fe. Observed surface maxima and shallow minima in dissolved Fe were always due to variations in the colloidal Fe fraction. Deep-water dissolved and colloidal Fe concentrations vary with water mass source, age, and transport path. Elevated dissolved Fe concentrations (>1 nmol/kg) were associated with an oxygen minimum zone in the tropical Atlantic at 10°N, 45°W. Fractionation of iron isotopes could be an effective tool to investigate the geochemistr of iron. Trace metal clean plankton tows, river samples, aerosol leachates, and porewater samples were measured for their iron isotopic composition using a GV Instruments IsoProbe Multi-collector ICPMS. The Fe isotopic composition of plankton tow samples vared by over 4% (in 56Fe/54Fe). North Pacific plankton tow samples had isotopically lighter Fe isotopic compositions than samples from the Atlantic. The overall isotopic range observed in the Amazon River system was 1.5%, with variability observed for different types of tributaries. The main channel river dissolved Fe samples and suspended loads were isotopically similar (≈ -0.2 to -0.45% relative to igneous rocks). The isotopically heaviest sample collected was dissolved Fe from an organic rich tributary, the Negro River (+0.16%). In contrast, the suspended load from the Negro River was isotopically light (-1 %). The isotopically lightest sample from the Amazon region was shelf porewater (-1.4%). In river water-seawater mixing experiments, the Fe isotopic signal of dissolved Fe of river water was modified by flocculation of isotopically heavy Fe. The observed range in the Fe isotopic composition of the natural samples including biological and aqueous samples demonstrates that significant and useful fractionation is associated with Fe biogeochemistry in the environment. en
dc.description.sponsorship This research was supported by NSF grants OCE-0002273 and OCE-99871442. The Amazon field trip was partially funded by the Houghton Fund at MIT. I was funded by the National Physical Science Foundation, Lawrence Livermore National Laboratory, and the Education Office of Woods Hole Oceanographic Institution. en
dc.format.mimetype application/pdf
dc.language.iso en_US en
dc.publisher Massachusetts Institute of Technology and Woods Hole Oceanographic Institution en
dc.relation.ispartofseries WHOI Theses en
dc.subject Seawater en_US
dc.subject Iron content en_US
dc.subject Isotopes en_US
dc.title The marine geochemistry of iron and iron isotopes en
dc.type Thesis en
dc.identifier.doi 10.1575/1912/1854

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