Dissolved Iron and Iron Isotopes in the Southeastern Pacific Ocean

Jessica N. Fitzsimmons; Tim M. Conway; Jong-Mi Lee; Richard Kayser; Kristen M. Thyng; Seth G. John; Edward A. Boyle

doi:10.1002/2015GB005357

Dissolved Iron and Iron Isotopes in the Southeastern Pacific Ocean

Jessica N. Fitzsimmons, Tim M. Conway, Jong-Mi Lee, Richard Kayser, Kristen M. Thyng, Seth G. John, Edward A. Boyle

Research output: Contribution to journal › Article › peer-review

Abstract

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&hyphen;zonal transect from 20 to 27°S. We found elevated dFe concentrations associated with the oxygen&hyphen;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&hyphen;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&permil; Antarctic Intermediate Water end&hyphen;member and a heavy δ 56 Fe of +0.55&permil; for distally transported hydrothermal dissolved Fe from the East Pacific Rise. These heavy δ 56 Fe values were contrasted with the near&hyphen;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.

Original language	American English
Journal	Global Biogeochemical Cycles
Volume	30
DOIs	https://doi.org/10.1002/2015GB005357
State	Published - Oct 1 2016
Externally published	Yes

Keywords

iron isotopes
hydrothermal vents
oxygen‐deficient zone
Station ALOHA
South Pacific Ocean
trace metals

Disciplines

Marine Biology

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Dissolved Iron and Iron Isotopes in the Southeastern Pacific OceaFinal published version, 2.87 MBLicense: CC BY

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title = "Dissolved Iron and Iron Isotopes in the Southeastern Pacific Ocean",

abstract = " 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&hyphen;zonal transect from 20 to 27°S. We found elevated dFe concentrations associated with the oxygen&hyphen;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&hyphen;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&permil; Antarctic Intermediate Water end&hyphen;member and a heavy δ 56 Fe of +0.55&permil; for distally transported hydrothermal dissolved Fe from the East Pacific Rise. These heavy δ 56 Fe values were contrasted with the near&hyphen;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.",

keywords = "iron isotopes, hydrothermal vents, oxygen‐deficient zone, Station ALOHA, South Pacific Ocean, trace metals",

author = "Fitzsimmons, {Jessica N.} and Conway, {Tim M.} and Jong-Mi Lee and Richard Kayser and Thyng, {Kristen M.} and John, {Seth G.} and Boyle, {Edward A.}",

year = "2016",

month = oct,

day = "1",

doi = "10.1002/2015GB005357",

language = "American English",

volume = "30",

journal = "Global Biogeochemical Cycles",

}

TY - JOUR

T1 - Dissolved Iron and Iron Isotopes in the Southeastern Pacific Ocean

AU - Fitzsimmons, Jessica N.

AU - Conway, Tim M.

AU - Lee, Jong-Mi

AU - Kayser, Richard

AU - Thyng, Kristen M.

AU - John, Seth G.

AU - Boyle, Edward A.

PY - 2016/10/1

Y1 - 2016/10/1

N2 - 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&hyphen;zonal transect from 20 to 27°S. We found elevated dFe concentrations associated with the oxygen&hyphen;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&hyphen;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&permil; Antarctic Intermediate Water end&hyphen;member and a heavy δ 56 Fe of +0.55&permil; for distally transported hydrothermal dissolved Fe from the East Pacific Rise. These heavy δ 56 Fe values were contrasted with the near&hyphen;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.

AB - 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&hyphen;zonal transect from 20 to 27°S. We found elevated dFe concentrations associated with the oxygen&hyphen;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&hyphen;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&permil; Antarctic Intermediate Water end&hyphen;member and a heavy δ 56 Fe of +0.55&permil; for distally transported hydrothermal dissolved Fe from the East Pacific Rise. These heavy δ 56 Fe values were contrasted with the near&hyphen;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.

KW - iron isotopes

KW - hydrothermal vents

KW - oxygen‐deficient zone

KW - Station ALOHA

KW - South Pacific Ocean

KW - trace metals

UR - https://digitalcommons.usf.edu/msc_facpub/239

U2 - 10.1002/2015GB005357

DO - 10.1002/2015GB005357

M3 - Article

VL - 30

JO - Global Biogeochemical Cycles

JF - Global Biogeochemical Cycles

ER -

Dissolved Iron and Iron Isotopes in the Southeastern Pacific Ocean

Abstract

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