A multi-modal approach to measuring particulate iron speciation in buoyant hydrothermal plumes

Brandy D. Stewart, Jeffry V. Sorensen, Kathleen A Wendt, Jason B. Sylvan, Christopher R. German, Karthik Anantharaman, Gregory J. Dick, John A. Breier, Brandy M. Toner

Research output: Contribution to journalArticlepeer-review

Abstract

Processes active within buoyant hydrothermal plumes are expected to modulate the flux of elements, such as Fe, to the deep ocean; however, they are yet to be described in a comprehensive manner through observations or models. In this study, we compare observed particulate Fe (pFe) speciation with thermodynamic (equilibrium) reaction path modeling for three vent fields in the Eastern Lau Spreading Center (ELSC). At each site, particles were collected from the buoyant rising portion of hydrothermal plumes using in situ filtration with a Remotely Operated Vehicle. Filter bound particles were analyzed by synchrotron micro-probe X-ray fluorescence mapping (XRF), X-ray diffraction (XRD), XRF spectroscopy, and X-ray absorption near edge structure (XANES) spectroscopy at the Fe 1 s edge, as well as XRF-based chemical speciation mapping for Fe. For buoyant plumes of the ELSC, diversity in solid-state chemistry was high, and poorly crystalline, meta-stable phases were common. We demonstrate that to fully describe the crystalline-to-noncrystalline character of plume pFe, a multi-modal XRD-XANES analytical approach is needed. We found that an equilibrium modeling approach worked well for pyrite but performed poorly for important families of meta-stable pFe, namely Fe (oxyhydr)oxides and monosulfides. Based on our findings, we recommend future field expeditions strategically explore sites representing a diversity of site-specific conditions to better capture the full range of processes active in plumes. We also recommend development of kinetic models, as well as expansion of thermodynamic databases to better reflect the solid-state composition of plumes. These steps should allow oceanographers to understand the processes controlling Fe speciation in plumes well enough to create realistic models of hydrothermal fluxes to the ocean.

Original languageEnglish (US)
Article number120018
JournalChemical Geology
Volume560
DOIs
StatePublished - Jan 20 2021

Bibliographical note

Funding Information:
We thank Chief Scientists Charles Fisher, Anna-Louise Reysenbach, George Luther, and Peter Girgus, the ROV Jason II team (dives J2-421 to J2-430, and J2-434 to J2-443), and the crews of the R/V Thompson (cruises TN235 and TN236). The research was supported by funds from the National Science Foundation's Ridge 2000 program ( BMT OCE-1037991 ; JAB OCE-1038055 ; GJD OCE-1038006 ; OCE-1851007 ). We thank Katrina Edwards and Sheri White for fieldwork support. We thank Matthew Marcus and Sirine Fakra for synchrotron support at the Advanced Light Source (BL 10.3.2 and 5.3.2), as well as Sarah Nicholas, Brandi Cron Kammermans, and Teng Zeng for assistance in synchrotron data collection. The Advanced Light Source is supported by the Director, Office of Science , Office of Basic Energy Sciences , of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 . We acknowledge and honor the indigenous communities native to the Twin Cities, Minnesota region where the University of Minnesota now resides on the ancestral land of the Wahpekute (Dakota), Anishinabewaki, and Očeti Šakówiŋ (Sioux) peoples. We wish to recognize the people of the Sioux tribe as the ongoing caretakers of this land.

Funding Information:
We thank Chief Scientists Charles Fisher, Anna-Louise Reysenbach, George Luther, and Peter Girgus, the ROV Jason II team (dives J2-421 to J2-430, and J2-434 to J2-443), and the crews of the R/V Thompson (cruises TN235 and TN236). The research was supported by funds from the National Science Foundation's Ridge 2000 program (BMT OCE-1037991; JAB OCE-1038055; GJD OCE-1038006; OCE-1851007). We thank Katrina Edwards and Sheri White for fieldwork support. We thank Matthew Marcus and Sirine Fakra for synchrotron support at the Advanced Light Source (BL 10.3.2 and 5.3.2), as well as Sarah Nicholas, Brandi Cron Kammermans, and Teng Zeng for assistance in synchrotron data collection. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. We acknowledge and honor the indigenous communities native to the Twin Cities, Minnesota region where the University of Minnesota now resides on the ancestral land of the Wahpekute (Dakota), Anishinabewaki, and O?eti ?ak?wi? (Sioux) peoples. We wish to recognize the people of the Sioux tribe as the ongoing caretakers of this land.

Publisher Copyright:
© 2020 Elsevier B.V.

Keywords

  • Fe
  • Fe speciation
  • Hydrothermal vents
  • Iron
  • Synchrotron microprobe XANES
  • Synchrotron microprobe XRD
  • Thermodynamic modeling

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