skip to main content


The NSF Public Access Repository (NSF-PAR) system and access will be unavailable from 10:00 PM ET on Friday, December 8 until 2:00 AM ET on Saturday, December 9 due to maintenance. We apologize for the inconvenience.

Search for: All records

Award ID contains: 2153786

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Abstract

    Iron mineral transformations occurring in hydrocarbon‐contaminated sites are linked to the biodegradation of the hydrocarbons. At a hydrocarbon‐contaminated site near Bemidji, Minnesota, USA, measurements of magnetic susceptibility (MS) are useful for monitoring the natural attenuation of hydrocarbons related to iron cycling. However, a transient MS, previously observed at the site, remains poorly understood and the iron mineral phases acting as reactants and products associated with this MS perturbation remain largely unknown. To address these unknowns, we acquired mineral magnetism measurements, including hysteresis loops, backfield curves, and isothermal remanent magnetizations on sediment core samples retrieved from the site and magnetite‐filled mineral packets installed within the aquifer. Our data show that the core samples and magnetite packs display decreasing magnetization with time and that this loss in magnetization is accompanied by increasing bulk coercivity consistent with decreased average grain size and/or partial oxidation. Low‐temperature magnetometry on all samples displayed behavior consistent with magnetite, but samples within the plume also show evidence of maghemitization. This interpretation is supported by the occurrence of shrinkage cracks on the surface of the grains imaged via scanning electron microscopy. Magnetite transformation to maghemite typically occurs under oxic conditions, here, we propose that maghemitization occurs within the anoxic portions of the plume via microbially mediated anaerobic oxidation. Mineral dissolution also occurs within the plume. Microorganisms capable of such anaerobic oxidation have been identified within other areas at the Bemidji site, but additional microbiological studies are needed to link specific anaerobic iron oxidizers with this loss of magnetization.

    more » « less
  2. Free, publicly-accessible full text available March 1, 2024
  3. Free, publicly-accessible full text available March 1, 2024
  4. Free, publicly-accessible full text available February 15, 2024
  5. Free, publicly-accessible full text available February 1, 2024
  6. Free, publicly-accessible full text available February 1, 2024
  7. Abstract. Mineral specific surface area (SSA) increases as primaryminerals weather and restructure into secondary phyllosilicate, oxide, andoxyhydroxide minerals. SSA is a measurable property that captures cumulativeeffects of many physical and chemical weathering processes in a singlemeasurement and has meaningful implications for many soil processes,including water-holding capacity and nutrient availability. Here we reportour measurements of SSA and mineralogy of two 21 m deep SSA profiles attwo landscape positions, in which the emergence of a very small mass percent(<0.1 %) of secondary oxide generated 36 %–81 % of the total SSAin both drill cores. The SSA transition occurred near 3 m at bothlocations and did not coincide with the boundary of soil to weathered rock. The3 m boundary in each weathering profile coincides with the depth extentof secondary iron oxide minerals and secondary phyllosilicates. Althoughelemental depletions in both profiles extend to 7 and 10 m depth, themineralogical changes did not result in SSA increase until 3 m depth. Theemergence of secondary oxide minerals at 3 m suggests that this boundary may bethe depth extent of oxidation weathering reactions. Our results suggest thatoxidation weathering reactions may be the primary limitation in thecoevolution of both secondary silicate and secondary oxide minerals. Wevalue element depletion profiles to understand weathering, but our findingof nested weathering fronts driven by different chemical processes (e.g.,oxidation to 3 m and acid dissolution to 10 m) warrants the recognition thatelement depletion profiles are not able to identify the full set ofprocesses that occur in weathering profiles. 
    more » « less
    Free, publicly-accessible full text available January 1, 2024
  8. Abstract Particulate matter (PM) concentration levels in the London Underground (LU) are higher than London background levels and beyond World Health Organization (WHO) defined limits. Wheel, track, and brake abrasion are the primary sources of particulate matter, producing predominantly Fe-rich particles that make the LU microenvironment particularly well suited to study using environmental magnetism. Here we combine magnetic properties, high-resolution electron microscopy, and electron tomography to characterize the structure, chemistry, and morphometric properties of LU particles in three dimensions with nanoscale resolution. Our findings show that LU PM is dominated by 5–500 nm particles of maghemite, occurring as 0.1–2 μm aggregated clusters, skewing the size-fractioned concentration of PM artificially to larger sizes when measured with traditional monitors. Magnetic properties are largely independent of the PM filter size (PM 10 , PM 4 , and PM 2.5 ), and demonstrate the presence of superparamagnetic (< 30 nm), single-domain (30–70 nm), and vortex/pseudo-single domain (70–700 nm) signals only (i.e., no multi-domain particles > 1 µm). The oxidized nature of the particles suggests that PM exposure in the LU is dominated by resuspension of aged dust particles relative to freshly abraded, metallic particles from the wheel/track/brake system, suggesting that periodic removal of accumulated dust from underground tunnels might provide a cost-effective strategy for reducing exposure. The abundance of ultrafine particles identified here could have particularly adverse health impacts as their smaller size makes it possible to pass from lungs to the blood stream. Magnetic methods are shown to provide an accurate assessment of ultrafine PM characteristics, providing a robust route to monitoring, and potentially mitigating this hazard. 
    more » « less
  9. Magnetic elastomers with hard or permanent magnetic particulate are able to achieve complex motion not possible from soft magnetic elastomers. Magnetic annealing and fused deposition modeling (FDM) have been used to increase the performance of magnetic composites. This research explores how the magnetoactive properties of hard magnetic elastomers are influenced by magnetic annealing and the addition of the soft magnetic particulate. Three compositions of the thermoplastic magnetic elastomer composite are explored: 15 vol. % SrFe 12 O 19 , 10 vol. % SrFe 12 O 19 /5 vol. % carbonyl iron, and 5 vol. % SrFe 12 O 19 /10 vol. % carbonyl iron. The material is then extruded into FDM filaments. During the extrusion process, some filament is magnetically annealed in an axial applied field. Magnetic hysteresis loops show that the saturation magnetization and coercivity change based on the relative amount of hard and soft magnetic particulate. The presence of only one coercive field indicates magnetic coupling between the hard and soft components. Magnetoactive testing measures each sample’s mechanical deflection angle as a function of transverse applied magnetic field strength. Qualitative and quantitative results reveal that magnetic annealing is critical to the magnetoactive performance of the hard magnetic elastomers. The results also demonstrate that magnetic annealing and increased carbonyl iron both improve the magnetoactive deflection angle for a given applied field. Scanning electron microscopy shows a stratification effect in a range of the filaments. Understanding these hard magnetic elastomers provides insight into how performance can be controlled and optimized by magnetic annealing and combining hard and soft magnetic particulate. 
    more » « less
  10. Hart, John P. (Ed.)
    Amanzi Springs is a series of inactive thermal springs located near Kariega in the Eastern Cape of South Africa. Excavations in the 1960s exposed rare, stratified Acheulian-bearing deposits that were not further investigated over the next 50 years. Reanalysis of the site and its legacy collection has led to a redefined stratigraphic context for the archaeology, a confirmed direct association between Acheulian artefacts and wood, as well as the first reliable age estimates for the site. Thermally transferred optically stimulated luminescence and post-infrared infrared stimulated luminescence dating indicates that the Acheulian deposits from the Amanzi Springs Area 1 spring eye formed during Marine Isotope Stage (MIS) 11 at ~ 404–390 ka. At this time, higher sea levels of ~13-14m would have placed Amanzi Springs around 7 km from a ria that would have formed along what is today the Swartkops River, and which likely led to spring reactivation. This makes the Amanzi Springs Area 1 assemblage an unusual occurrence of a verified late occurring, seaward, open-air Acheulian occupation. The Acheulian levels do not contain any Middle Stone Age (MSA) elements such as blades and points that have been documented in the interior of South Africa at this time. However, a small number of stone tools from the upper layers of the artefact zone, and originally thought of as intrusive, have been dated to ~190 ka, at the transition between MIS 7 to 6, and represent the first potential MSA identified at the site. 
    more » « less