Journal article
Obtaining High‐Resolution Magnetic Records From Speleothems Using Magnetic Microscopy
Geochemistry, geophysics, geosystems : G3, Vol.25(10), e2024GC011594
10/2024
DOI: 10.1029/2024GC011594
Abstract
Abstract Speleothems are mineral deposits capable of recording detrital and/or chemical remanent magnetization at annual timescales. They can offer high‐resolution paleomagnetic records of short‐term variations in Earth's magnetic field, crucial for understanding the evolution of the dynamo. Owing to limitations on the magnetic moment sensitivity of commercial cryogenic rock magnetometers (∼10 −11 Am 2 ), paleomagnetic studies of speleothems have been limited to samples with volumes of several hundreds of mm 3 , averaging tens to hundreds of years of magnetic variation. Nonetheless, smaller samples (∼1–10 mm 3 ) can be measured using superconducting quantum interference device (SQUID) microscopy, with a sensitivity better than ∼10 −15 Am 2 . To determine the application of SQUID microscopy for obtaining robust high‐resolution records from small‐volume speleothem samples, we analyzed three different stalagmites collected from Lapa dos Morcegos Cave (Portugal), Pau d'Alho Cave (Brazil), and Crevice Cave (United States). These stalagmites are representative of a range of magnetic properties and have been previously studied with conventional rock magnetometers. We show that by using SQUID microscopy we can achieve a five‐fold improvement in temporal resolution for samples with higher abundances of magnetic carriers (e.g., Pau d'Alho Cave and Lapa dos Morcegos Cave). In contrast, speleothems with low abundances of magnetic carriers (e.g., Crevice Cave) do not benefit from higher resolution analysis and are best analyzed using conventional rock magnetometers. Overall, by targeting speleothem samples with high concentrations of magnetic carriers we can increase the temporal resolution of magnetic records, setting the stage for resolving geomagnetic variations at short time scales.
Plain Language Summary Earth has a magnetic field that is generated in the outer core, and through paleomagnetism we can retrieve information about the evolution of the field from rocks. Different types of rocks have been used to determine how Earth's magnetic field has changed over time. In this study, we use magnetic microscopy to analyze the magnetic record of speleothems, which are rocks that form inside caves and that can record magnetic fields in annual scales. This allows us to obtain magnetic records with higher resolution than previous studies. This is important because Earth's magnetic field changes in timescales ranging from thousands of years to a few years, and obtaining records from speleothems using magnetic microscopy can help us track these variations. We provide data demonstrating how the technique can be used and showing its limitations, and we discuss how the geologic context of the cave influences the robustness of the magnetic record. We also provide protocols for future studies using magnetic microscopy in speleothems.
Key Points Magnetic microscopy can be used to produce a 5× improvement in temporal resolution of magnetic records from speleothems Variations in magnetic properties across speleothems can affect the temporal resolution of the magnetic record Protocols for conducting high‐resolution magnetic measurements of speleothems with magnetic microscopy are presented
Details
- Title: Subtitle
- Obtaining High‐Resolution Magnetic Records From Speleothems Using Magnetic Microscopy
- Creators
- Cauê S. Borlina - Purdue University West LafayetteEduardo A. Lima - Massachusetts Institute of TechnologyJoshua M. Feinberg - University of MinnesotaPlinio Jaqueto - University of MinnesotaIoan Lascu - National Museum of Natural HistoryRicardo I. F. Trindade - Universidade de São PauloEric Font - University of CoimbraElisa M. Sánchez-Moreno - Universidad de BurgosLuca Antonio Dimuccio - Centro de Estudos em Geografia e Ordenamento do TerritorioYusuke Yokoyama - The University of TokyoJosep M. Parés - National Research Center on Human EvolutionBenjamin P. Weiss - Massachusetts Institute of TechnologyJeffrey A. Dorale - University of Iowa
- Resource Type
- Journal article
- Publication Details
- Geochemistry, geophysics, geosystems : G3, Vol.25(10), e2024GC011594
- Publisher
- AMER GEOPHYSICAL UNION; WASHINGTON
- DOI
- 10.1029/2024GC011594
- ISSN
- 1525-2027
- eISSN
- 1525-2027
- Grant note
- NSF: EAR-2044806, EAR-2044535, EAR-2044506, PTDC/CTA-GEO/0125/2021, MIT-EXPL/ACC/0023/2021 MIT-Portugal Seed Fund: BU037P23 European Research and Development Fund: UIDP/GEO/04084/2020_UC
This work was partially supported by the National Science Foundation (NSF) Grants EAR-2044806, EAR-2044535, and EAR-2044506, Fundac & atilde;o para a Ciencia e a Tecnologia (FCT-Portugal, PTDC/CTA-GEO/0125/2021 and MIT-EXPL/ACC/0023/2021), and the MIT-Portugal Seed Fund. CSB thanks The Morton K. Blaustein Scholars Fund. EMSM acknowledges the project BU037P23 of the Junta de Castilla y Leon and the European Research and Development Fund. Fieldwork and speleothem sampling in Portugal were authorized by Instituto da Conservac & atilde;o da Natureza e das Florestas (ICNF I.P.), under the responsibility of LD and supported by CEGOT I&D Unit (FCT-Portugal, UIDP/GEO/04084/2020_UC). Fieldwork and speleothem collection in Brazil were authorized by the Instituto Brasileiro do Meio Ambiente e dos Recursos Renovaveis, and we thank the Centro Nacional de Pesquisa e Conservac & atilde;o de Cavernas (CECAV/ICMBio) for providing permission to collect stalagmite samples.
- Language
- English
- Date published
- 10/2024
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984722574602771
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