| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | August 8, 2017 |
| Latest Amendment Date: | July 6, 2022 |
| Award Number: | 1645180 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Jonathan G Wynn
jwynn@nsf.gov (703)292-4725 EAR Division Of Earth Sciences GEO Directorate For Geosciences |
| Start Date: | August 15, 2017 |
| End Date: | March 31, 2023 (Estimated) |
| Total Intended Award Amount: | $400,000.00 |
| Total Awarded Amount to Date: | $419,950.00 |
| Funds Obligated to Date: |
FY 2021 = $19,950.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
302 BUCHTEL COMMON AKRON OH US 44325-0002 (330)972-2760 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
OH US 44325-0001 |
| Primary Place of Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): |
XC-Crosscutting Activities Pro, Geobiology & Low-Temp Geochem |
| Primary Program Source: |
01002122DB NSF RESEARCH & RELATED ACTIVIT |
| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
Traditionally, it was thought that caves formed only through the dissolution of rock by groundwater; however, the unusual chemistry of sulfuric acid caves suggested that microorganisms could also play an important role in cave formation. By studying this biogeochemistry, researchers discovered that caves could form through microbial oxidation of hydrogen sulfide gas, which accounted for as much as 25% of cave formation worldwide. They have hypothesized a new potential mechanism for microbially-driven cave formation, based on microbial respiration of iron(III) minerals in iron-rich rocks (known as banded iron formations; BIF). The identification of cave forming processes in BIF is significant as it dramatically expands the environments in which caves can form, which provide critical subterranean habitats for many rare and endangered animal species. There is also a strong correlation between the location of these BIF caves and the presence of iron ores of global economic significance, providing the source material for the production of steel. This correlation suggests that the cave forming processes may be linked to the creation of these important iron ore deposits. By gaining a better understanding of the microbial processes that form caves, it may be possible to selectively identify the processes that lead to ore formation. This may allow for more precisely targeted identification and mining of iron ore deposits, limiting the environmental impact that prospecting for such ores often generates.
Investigators' preliminary research has demonstrated the presence of active Fe(III) reducing microbial communities within BIF caves, abundant dissolved Fe(II) in pore fluids, and textural evidence of reductive dissolution of Fe(III) phases. Together, these observations suggest that microbial Fe(III) reduction may be responsible for driving mass separation, while groundwater flow may be responsible for Fe(II) removal to create the cave voids. Investigators will therefore test the hypothesis that the activities of Fe(III) reducing microorganisms are responsible for the formation of iron ore caves. To test this hypothesis they will use an approach that integrates biogeochemistry, environmental microbiology, laboratory microcosms, kinetic studies of Fe(III) bioreduction, and field-scale empirical data. Models of Fe(III) reduction rates and Fe(II) transport will be used to integrate this empirical data with potential cave forming processes across a range of scales, from microscopic to regional. Together these data should allow them to constrain the mechanisms and rates of iron cave formation and determine the role that microbes play in iron cave speleogenesis.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Banded iron formations (BIF) represent a critical resource for worldwide steel production. One of the world’s largest BIF deposits, called Itabirite, is found in Brazil. Itabilite is almost 70% iron by weight, making it remarkably resistant to erosion and dissolution. Yet Itabirite is also associated with an unusually high concentration of caves, which normally form through the dissolution of more soluble rocks. This project aimed to understand the processes that caused these caves to form. Our results indicate that microorganisms dissolve the iron by using it as an electron acceptor to make energy; much like humans use oxygen to burn our food to release energy. By studying the microorganisms behind the walls of the cave, we were able to demonstrate that rotting vegetation from the jungle above powers the process. Our data also indicated that periodic rainy seasons wash away accumulating iron, speeding up the process, while enriching for the microbial species that can carry out this activity and increasing their efficiency. We were also able to show that the microbes can survive the periodic exposure to oxygen that wall collapse causes, demonstrating that they are not killed in this process, and allowing cave enlargement to occur in cycles, which may be responsible for some of the large iron caves seen in this region.
Most caves form by water dissolving the rock as it flows through a central conduit, and this work demonstrated an entirely new way that caves form, which we called exothenic (from the inside-out) speleogenesis (cave forming). Such processes increase the porosity of the rock, which is responsible for creating the habitats used by the endangered animal species that reside within Itabirite. It also changes our understanding of the potential for large amounts of iron can move from the land and into the oceans, which has historically been difficult to explain. There are also real-world applications of this research. In particular, the iron dissolving processes of these microbes appeared to enrich for Rare Earth Elements (REEs). These metals are critically important for the manufacture of microchips and other electronics; however, there are no economically viable sources of REEs within the US – most US deposits are found at levels that are too costly to extract. The way in which our microorganisms mobilize iron appears to enrich for REEs and will be explored as a potential new technology to more effectively recover these critical minerals from domestic sources.
Last Modified: 10/30/2023
Modified by: Hazel A Barton
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