Decoupling of particles and dissolved iron downstream of Greenlandic glacier outflows

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C. M. van Genuchten
Rosing, Minik Thorleif
M. J. Hopwood
T. Liu
J. Krause
L. Meire

Glaciers can be a significant and locally dominant source of iron (Fe), a biologically essential micronutrient, in high latitude coastal seas. The vast majority of this glacial Fe delivery is associated with particles, yet the speciation of the solid-phase Fe and specifically the relationships that govern exchange between particulate and dissolved Fe phases in these environments are poorly described. In this work, we performed measurements of in situ dissolved Fe (dFe) along meltwater and particle plumes in three transects around Disko Bay and Ameralik Fjord (West Greenland). Measurements of dFe were combined with Fe K-edge X-ray absorption spectroscopy analysis of ∼40 suspended sediment samples obtained from the same transects and from select depth profiles down to 300 m. We observed relatively constant dFe levels (4 to 10 nM for nearly all dFe measurements) across fjords with widely varying particulate Fe(II) contents (from 20 to 90% Fe(II)), indicating that dFe concentrations had little dependence on the oxidation state of Fe in the suspended sediment. Particulate Fe data were grouped by underlying bedrock geology, with suspended sediment consisting of 80-90% biotite-like Fe(II) in fjords with Precambrian shield geology and poorly-ordered Fe(III) particles (<20-30% Fe(II)) in one fjord with suspended sediments derived from tertiary basalts. Our characterization data indicated no significant change in the average Fe oxidation state and bonding environment of particles along the fjord transects, implying that Fe(II) in biotite-like coordination is not a readily labile Fe form on this spatial scale. Our results suggest that dFe in these glacially-modified coastal waters is buffered at a relatively constant low nM concentration due to factors other than particle Fe mineralogy and that glacier-derived Fe phases are relatively inert on this spatial scale.

Originalsprog	Engelsk
Artikelnummer	117234
Tidsskrift	Earth and Planetary Science Letters
Vol/bind	576
Antal sider	14
ISSN	0012-821X
DOI	https://doi.org/10.1016/j.epsl.2021.117234
Status	Udgivet - 2021

Bibliografisk note

Funding Information:
We gratefully acknowledge beam line assistance from Ryan Davis at SSRL and Kajsa Sigfridsson Clauss at MAX IV who locally facilitated XAS data collection during virtual synchrotron experiments caused by COVID-19 travel restrictions. Changxun Yu and Elizabeth Shoenfelt are acknowledged for providing Fe reference mineral spectra directly or via online databases. Use of SSRL, SLAC National Accelerator Laboratory, was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Contract No. DE-AC02-76SF00515. We acknowledge MAX IV Laboratory for time on Beamline Balder under Proposal 20190671. Research conducted at MAX IV, a Swedish national user facility, is supported by the Swedish Research Council under contract 2018-07152, the Swedish Governmental Agency for Innovation Systems under contract 2018-04969, and Formas under contract 2019-02496. Moreover, the research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. This study formed part of project MarineGreen; Novo Nordic Foundation grant NNF17SH0028142. Mark Hopwood was financed by the DFG (award number HO 6321/1-1) and by the GLACE project, organised by the Swiss Polar Institute and supported by the Swiss Polar Foundation. L.M. was funded by research programme VENI with project number 016.Veni.192.150, which is financed by the Dutch Research Council (NWO). We gratefully acknowledge the contributions from the Danish Centre for Marine Research (DCH), Greenland Institute of Natural Resources and the crew of RV Sanna for excellent field assistance.

Funding Information:
We gratefully acknowledge beam line assistance from Ryan Davis at SSRL and Kajsa Sigfridsson Clauss at MAX IV who locally facilitated XAS data collection during virtual synchrotron experiments caused by COVID-19 travel restrictions. Changxun Yu and Elizabeth Shoenfelt are acknowledged for providing Fe reference mineral spectra directly or via online databases. Use of SSRL, SLAC National Accelerator Laboratory, was supported by the U.S. Department of Energy , Office of Science, Basic Energy Sciences, under Contract No. DE-AC02-76SF00515 . We acknowledge MAX IV Laboratory for time on Beamline Balder under Proposal 20190671. Research conducted at MAX IV, a Swedish national user facility, is supported by the Swedish Research Council under contract 2018-07152 , the Swedish Governmental Agency for Innovation Systems under contract 2018-04969 , and Formas under contract 2019-02496 . Moreover, the research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. This study formed part of project MarineGreen; Novo Nordic Foundation grant NNF17SH0028142 . Mark Hopwood was financed by the DFG (award number HO 6321/1-1) and by the GLACE project, organised by the Swiss Polar Institute and supported by the Swiss Polar Foundation . L.M. was funded by research programme VENI with project number 016.Veni.192.150 , which is financed by the Dutch Research Council (NWO). We gratefully acknowledge the contributions from the Danish Centre for Marine Research (DCH), Greenland Institute of Natural Resources and the crew of RV Sanna for excellent field assistance.

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© 2021 Elsevier B.V.

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