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Dissolved iron and iron isotopes in the southeastern Pacific Ocean
Author(s) -
Fitzsimmons Jessica N.,
Conway Tim M.,
Lee JongMi,
Kayser Richard,
Thyng Kristen M.,
John Seth G.,
Boyle Edward A.
Publication year - 2016
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1002/2015gb005357
Subject(s) - geotraces , hydrothermal circulation , ocean gyre , transect , plume , geology , oceanography , hydrothermal vent , seawater , deep sea , isotope , water column , environmental chemistry , geochemistry , chemistry , paleontology , subtropics , physics , quantum mechanics , fishery , biology , thermodynamics
The Southeast Pacific Ocean is a severely understudied yet dynamic region for trace metals such as iron, since it experiences steep redox and productivity gradients in upper waters and strong hydrothermal iron inputs to deep waters. In this study, we report the dissolved iron (dFe) distribution from seven stations and Fe isotope ratios (δ 56 Fe) from three of these stations across a near‐zonal transect from 20 to 27°S. We found elevated dFe concentrations associated with the oxygen‐deficient zone (ODZ), with light δ 56 Fe implicating porewater fluxes of reduced Fe. However, temporal dFe variability and rapid δ 56 Fe shifts with depth suggest gradients in ODZ Fe source and/or redox processes vary over short‐depth/spatial scales. The dFe concentrations decreased rapidly offshore, and in the upper ocean dFe was controlled by biological processes, resulting in an Fe:C ratio of 4.2 µmol/mol. Calculated vertical diffusive Fe fluxes were greater than published dust inputs to surface waters, but both were orders of magnitude lower than horizontal diffusive fluxes, which dominate dFe delivery to the gyre. The δ 56 Fe data in the deep sea showed evidence for a −0.2‰ Antarctic Intermediate Water end‐member and a heavy δ 56 Fe of +0.55‰ for distally transported hydrothermal dissolved Fe from the East Pacific Rise. These heavy δ 56 Fe values were contrasted with the near‐crustal δ 56 Fe recorded in the hydrothermal plume reaching Station ALOHA in the North Pacific. The heavy hydrothermal δ 56 Fe precludes a nanopyrite composition of hydrothermal dFe and instead suggests the presence of oxides or, more likely, binding of hydrothermal dFe by organic ligands in the distal plume.