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Article ; Online: A Bootstrap Common Mean Direction Test

Heslop, David / Scealy, Janice L. / Wood, Andrew T. A. / Tauxe, Lisa / Roberts, Andrew P.

Journal of Geophysical Research: Solid Earth. 2023 Aug., v. 128, no. 8 p.e2023JB026983-

2023

Abstract: Paleomagnetic statistical inference is underpinned by a family of parametric null hypothesis tests. In many cases, however, paleomagnetic data do not meet the distributional assumptions of these tests, which can lead to spurious inferences. Earlier ... ...

Abstract	Paleomagnetic statistical inference is underpinned by a family of parametric null hypothesis tests. In many cases, however, paleomagnetic data do not meet the distributional assumptions of these tests, which can lead to spurious inferences. Earlier studies have proposed the bootstrap as a nonparametric alternative for paleomagnetic analysis, which can be applied even when the distributional form of the data is unknown. Key among these approaches is the bootstrap test for a common mean direction, which relies on assessment of the overlap of estimated confidence regions. In its current form, the bootstrap test for a common mean paleomagnetic direction does not consider a null hypothesis and can yield outcomes that cannot be interpreted in terms of a statistical significance level. To resolve these issues, we use recent advances to place such bootstrap tests within a null hypothesis significance testing framework, and unify them with the existing family of paleomagnetic statistical tests. Furthermore, using numerical experiments we demonstrate the applicability of such a nonparametric approach to moderately sized paleomagnetic data sets typical of modern and legacy studies. Finally, we demonstrate how a confidence region can be estimated for the common mean of two sets of directions and how known directions, such as the expected field produced by a geocentric axial dipole, can be compared to that mean.
Keywords	data collection ; fields ; geophysics ; journals ; solids ; statistical inference ; testing
Language	English
Dates of publication	2023-08
Publishing place	John Wiley & Sons, Ltd
Document type	Article ; Online
Note	JOURNAL ARTICLE
ISSN	2169-9313
DOI	10.1029/2023JB026983
Database	NAL-Catalogue (AGRICOLA)

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Article ; Online: Magnetotactic bacteria and magnetofossils: ecology, evolution and environmental implications.

Goswami, Pranami / He, Kuang / Li, Jinhua / Pan, Yongxin / Roberts, Andrew P / Lin, Wei

NPJ biofilms and microbiomes

2022 Volume 8, Issue 1, Page(s) 43

Abstract: Magnetotactic bacteria (MTB) are a group of phylogenetically diverse and morphologically varied microorganisms with a magnetoresponsive capability called magnetotaxis or microbial magnetoreception. MTB are a distinctive constituent of the microbiome of ... ...

Abstract	Magnetotactic bacteria (MTB) are a group of phylogenetically diverse and morphologically varied microorganisms with a magnetoresponsive capability called magnetotaxis or microbial magnetoreception. MTB are a distinctive constituent of the microbiome of aquatic ecosystems because they use Earth's magnetic field to align themselves in a north or south facing direction and efficiently navigate to their favored microenvironments. They have been identified worldwide from diverse aquatic and waterlogged microbiomes, including freshwater, saline, brackish and marine ecosystems, and some extreme environments. MTB play important roles in the biogeochemical cycling of iron, sulphur, phosphorus, carbon and nitrogen in nature and have been recognized from in vitro cultures to sequester heavy metals like selenium, cadmium, and tellurium, which makes them prospective candidate organisms for aquatic pollution bioremediation. The role of MTB in environmental systems is not limited to their lifespan; after death, fossil magnetosomal magnetic nanoparticles (known as magnetofossils) are a promising proxy for recording paleoenvironmental change and geomagnetic field history. Here, we summarize the ecology, evolution, and environmental function of MTB and the paleoenvironmental implications of magnetofossils in light of recent discoveries.
MeSH term(s)	Bacteria/genetics ; Ecosystem ; Fresh Water ; Prospective Studies
Language	English
Publishing date	2022-06-01
Publishing country	United States
Document type	Journal Article ; Review ; Research Support, Non-U.S. Gov't
ZDB-ID	2817021-0
ISSN	2055-5008 ; 2055-5008
ISSN (online)	2055-5008
ISSN	2055-5008
DOI	10.1038/s41522-022-00304-0
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article: A Bayesian Approach to the Paleomagnetic Conglomerate Test

Heslop, David / Roberts, Andrew P.

Journal of geophysical research. 2018 Feb., v. 123, no. 2

2018

Abstract: The conglomerate test has served the paleomagnetic community for over 60 years as a means to detect remagnetizations. The test states that if a suite of clasts within a bed have uniformly random paleomagnetic directions, then the conglomerate cannot have ...

Abstract	The conglomerate test has served the paleomagnetic community for over 60 years as a means to detect remagnetizations. The test states that if a suite of clasts within a bed have uniformly random paleomagnetic directions, then the conglomerate cannot have experienced a pervasive event that remagnetized the clasts in the same direction. The current form of the conglomerate test is based on null hypothesis testing, which results in a binary “pass” (uniformly random directions) or “fail” (nonrandom directions) outcome. We have recast the conglomerate test in a Bayesian framework with the aim of providing more information concerning the level of support a given data set provides for a hypothesis of uniformly random paleomagnetic directions. Using this approach, we place the conglomerate test in a fully probabilistic framework that allows for inconclusive results when insufficient information is available to draw firm conclusions concerning the randomness or nonrandomness of directions. With our method, sample sets larger than those typically employed in paleomagnetism may be required to achieve strong support for a hypothesis of random directions. Given the potentially detrimental effect of unrecognized remagnetizations on paleomagnetic reconstructions, it is important to provide a means to draw statistically robust data‐driven inferences. Our Bayesian analysis provides a means to do this for the conglomerate test.
Keywords	Bayesian theory ; data collection ; geophysics ; research
Language	English
Dates of publication	2018-02
Size	p. 1132-1142.
Publishing place	John Wiley & Sons, Ltd
Document type	Article
Note	JOURNAL ARTICLE
ISSN	2169-9313
DOI	10.1002/2017JB014526
Database	NAL-Catalogue (AGRICOLA)

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Article ; Online: Orbital- and millennial-scale Asian winter monsoon variability across the Pliocene-Pleistocene glacial intensification.

Ao, Hong / Liebrand, Diederik / Dekkers, Mark J / Roberts, Andrew P / Jonell, Tara N / Jin, Zhangdong / Song, Yougui / Liu, Qingsong / Sun, Qiang / Li, Xinxia / Huang, Chunju / Qiang, Xiaoke / Zhang, Peng

Nature communications

2024 Volume 15, Issue 1, Page(s) 3364

Abstract: Intensification of northern hemisphere glaciation (iNHG), ~2.7 million years ago (Ma), led to establishment of the Pleistocene to present-day bipolar icehouse state. Here we document evolution of orbital- and millennial-scale Asian winter monsoon (AWM) ... ...

Abstract	Intensification of northern hemisphere glaciation (iNHG), ~2.7 million years ago (Ma), led to establishment of the Pleistocene to present-day bipolar icehouse state. Here we document evolution of orbital- and millennial-scale Asian winter monsoon (AWM) variability across the iNHG using a palaeomagnetically dated centennial-resolution grain size record between 3.6 and 1.9 Ma from a previously undescribed loess-palaeosol/red clay section on the central Chinese Loess Plateau. We find that the late Pliocene-early Pleistocene AWM was characterized by combined 41-kyr and ~100-kyr cycles, in response to ice volume and atmospheric CO
Language	English
Publishing date	2024-04-19
Publishing country	England
Document type	Journal Article
ZDB-ID	2553671-0
ISSN	2041-1723 ; 2041-1723
ISSN (online)	2041-1723
ISSN	2041-1723
DOI	10.1038/s41467-024-47274-9
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article: Magnetic mineral diagenesis

Roberts, Andrew P

Earth-science reviews. 2015 Dec., v. 151

2015

Abstract: Reductionâoxidation (redox) reactions occur during burial because sediments contain reactive mixtures of oxidised and reduced components. Diagenetic chemical reactions represent the approach of all sedimentary components toward equilibrium, and control ...

Abstract	Reductionâoxidation (redox) reactions occur during burial because sediments contain reactive mixtures of oxidised and reduced components. Diagenetic chemical reactions represent the approach of all sedimentary components toward equilibrium, and control the long-term stability of sedimentary iron-bearing minerals. Magnetic minerals are sensitive indicators of sedimentary redox conditions and of changes in these conditions through time, with diagenetic effects ranging from subtle to pervasive. Despite the importance of magnetic mineral diagenesis in paleomagnetism, rock magnetism, and environmental magnetism, and the usefulness of these subjects in the Earth and environmental sciences, there is no systematic single published treatment of magnetic mineral diagenesis. This paper is an attempt to provide such a treatment for the full range of diagenetic environments. Magnetic mineral diagenesis during early burial is driven largely by chemical changes associated with organic matter degradation in a succession of environments that range from oxic to nitrogenous to manganiferous to ferruginous to sulphidic to methanic, where the free energy yielded by different oxidants decreases progressively in each environment. In oxic environments, the most important diagenetic processes involve surface oxidation of detrital minerals, and precipitation of Fe3+-bearing minerals from solution. In ferruginous environments, the most reactive detrital and authigenic iron oxides undergo dissolution, often mediated by dissimilatory iron-reducing bacteria, which releases Fe2+ that becomes available for other reactions. The Fe2+ in solution can diffuse upward where it is oxidised to form new authigenic iron (oxyhydr-)oxide minerals or it can become bioavailable to enable magnetotactic bacteria to biomineralise magnetite, generally at the base of the overlying nitrogenous zone. Alternatively, dissimilatory iron-reducing bacteria can produce extracellular magnetite within ferruginous environments. In sulphidic environments, iron-bearing detrital mineral assemblages undergo more radical alteration. Hydrogen sulphide, which is a byproduct of bacterial sulphate reduction or of anaerobic oxidation of methane, reacts with the Fe2+ released from iron mineral dissolution or directly with solid iron (oxyhydr-)oxide minerals to form iron sulphide minerals (mackinawite, greigite, and pyrite). Authigenic growth of ferrimagnetic greigite has important implications for paleomagnetic recording. Secondary iron sulphide formation can also occur as a result of anaerobic oxidation of methane. Methane migration through sediments in association with biogenic or thermogenic methane production or in association with gas hydrate dissociation can disrupt the diagenetic steady state and give rise to greigite and monoclinic pyrrhotite formation that remagnetises sediments. Most of the above-described diagenetic processes occur below 50Â°C. With continuing burial above 50Â°C, but at sub-metamorphic temperatures, magnetic minerals can undergo further thermally-induced chemical changes that give rise to a wide range of mineralogical transformations that affect the magnetic record of the host sediment. These changes include remagnetisations. Magnetic analysis can provide much valuable information concerning diagenesis in environmental processes. The range of processes discussed in this paper should assist researchers in analysing sediment magnetic properties for which the assessment of diagenetic effects has become a necessary component.
Keywords	bacteria ; byproducts ; dissociation ; environmental science ; gas hydrate ; Gibbs free energy ; hydrogen sulfide ; iron ; magnetic properties ; magnetism ; magnetite ; methane ; methane production ; organic matter ; oxidants ; oxidation ; pyrite ; researchers ; sediments ; sulfates ; temperature
Language	English
Dates of publication	2015-12
Size	p. 1-47.
Publishing place	Elsevier B.V.
Document type	Article
ZDB-ID	1792-9
ISSN	0012-8252
ISSN	0012-8252
DOI	10.1016/j.earscirev.2015.09.010
Database	NAL-Catalogue (AGRICOLA)

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Article ; Online: Sea level and deep-sea temperature reconstructions suggest quasi-stable states and critical transitions over the past 40 million years.

Rohling, Eelco J / Yu, Jimin / Heslop, David / Foster, Gavin L / Opdyke, Bradley / Roberts, Andrew P

Science advances

2021 Volume 7, Issue 26

Abstract: Sea level and deep-sea temperature variations are key indicators of global climate changes. For continuous records over millions of years, deep-sea carbonate microfossil-based ... ...

Abstract	Sea level and deep-sea temperature variations are key indicators of global climate changes. For continuous records over millions of years, deep-sea carbonate microfossil-based δ
Language	English
Publishing date	2021-06-25
Publishing country	United States
Document type	Journal Article
ZDB-ID	2810933-8
ISSN	2375-2548 ; 2375-2548
ISSN (online)	2375-2548
ISSN	2375-2548
DOI	10.1126/sciadv.abf5326
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article: Continental-scale magnetic properties of surficial Australian soils

Hu, Pengxiang / Heslop, David / Roberts, Andrew P / Viscarra Rossel, Raphael A / Zhao, Xiang

Earth-science reviews. 2020 Apr., v. 203

2020

Abstract: Soil magnetism reflects the physical properties of mainly iron oxide and oxyhydroxide minerals, which provides important information for deciphering soil environments. Establishing national scale soil magnetic databases can provide important reference ... ...

Abstract	Soil magnetism reflects the physical properties of mainly iron oxide and oxyhydroxide minerals, which provides important information for deciphering soil environments. Establishing national scale soil magnetic databases can provide important reference information that can assist mineral surveying and agricultural planning. Our aims are to provide visualizations and to describe multiple magnetic properties across Australia, to evaluate the relationship between soil magnetism and soil forming factors, and to interpret the mechanisms responsible for surface soil magnetism in Australia. We present the first surficial Australian soil magnetic database, which contains 471 topsoil samples of natural and unpolluted materials. The samples were characterized with detailed magnetic measurements, which show that the magnetic properties of Australian soils vary considerably, but most surficial soils have small concentrations of coarse-grained magnetic minerals. The vast central Australian interior is characterized by weak magnetism, with more hematite and goethite contribution. Strong magnetic hotspots occur in the northwestern plateau, Nullarbor Plain, and eastern highlands. Parent material acts as the dominant control on soil magnetic properties, influencing magnetic mineral concentration and grain size, and controlling the contribution and relative importance of hematite to goethite. Temperature and rainfall both have a weak negative influence on superfine ferrimagnetic particles, due to progressive transformation to hematite and particle migration driven by intensive rainfall in sandy soils. Biota and land use changes tend to have a more complex and integrated local influence on hematite and goethite formation and preservation.
Keywords	agricultural management ; databases ; goethite ; hematite ; highlands ; land use change ; magnetic properties ; magnetism ; mineral content ; rain ; sandy soils ; surveys ; temperature ; topsoil ; Australia
Language	English
Dates of publication	2020-04
Publishing place	Elsevier B.V.
Document type	Article
ZDB-ID	1792-9
ISSN	0012-8252
ISSN	0012-8252
DOI	10.1016/j.earscirev.2019.103028
Database	NAL-Catalogue (AGRICOLA)

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Article: Biomineralization and Magnetism of Uncultured Magnetotactic Coccus Strain THC‐1 With Non‐chained Magnetosomal Magnetite Nanoparticles

Li, Jinhua / Menguy, Nicolas / Leroy, Eric / Roberts, Andrew P. / Liu, Peiyu / Pan, Yongxin

Journal of geophysical research. 2020 Dec., v. 125, no. 12

2020

Abstract: Magnetotactic bacteria (MTB) have long fascinated geologists and biologists because they biomineralize intracellular single domain (SD) magnetite crystals within magnetosomes that are generally organized into single or multiple chains. MTB remains in the ...

Abstract	Magnetotactic bacteria (MTB) have long fascinated geologists and biologists because they biomineralize intracellular single domain (SD) magnetite crystals within magnetosomes that are generally organized into single or multiple chains. MTB remains in the geological record (magnetofossils) are ideal magnetic carriers and are used to reconstruct paleomagnetic and paleoenvironmental information. Here we studied the biomineralization and magnetic properties of magnetosomal magnetite produced by uncultured magnetotactic coccus strain THC‐1, isolated from the Tanghe River, China, by combining transmission electron microscope (TEM) and rock magnetic approaches. Our results reveal that THC‐1 produces hexagonal prismatic magnetite single crystals that are elongated along the [111] crystallographic direction. Most of the magnetite crystals within THC‐1 are dispersed without obvious chain assembly. A whole‐cell THC‐1 sample yields a normal SD hysteresis loop and a Verwey transition temperature of ~112 K. In contrast to MTB cells with magnetosome chain(s), THC‐1 cells have a teardrop first‐order reversal curve distribution that is indicative of moderate interparticle interactions. Due to the absence of a magnetosome chain, THC‐1 has relatively high values of the difference between the saturation isothermal remanent magnetization (SIRM) below and above the Verwey transition temperature for field‐cooled and zero field‐cooled SIRM curves (δFC, δZFC) and a low δFC/δZFC value. Together with previous studies, our results demonstrate that some MTB species/strains can form magnetosomal magnetite without linear chain configurations. Magnetite produced by MTB has diverse magnetic properties, which are distinctive but not necessarily unique compared to other magnetite types. Therefore, combining bulk magnetic measurements and TEM observations remains necessary for identifying magnetofossils in the geological record.
Keywords	Coccus ; biomineralization ; geophysics ; hysteresis ; magnetism ; magnetite ; nanoparticles ; paleoecology ; research ; rivers ; temperature ; transmission electron microscopes ; China
Language	English
Dates of publication	2020-12
Publishing place	John Wiley & Sons, Ltd
Document type	Article
Note	JOURNAL ARTICLE
ISSN	2169-9313
DOI	10.1029/2020JB020853
Database	NAL-Catalogue (AGRICOLA)

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Article: Unlocking information about fine magnetic particle assemblages from first-order reversal curve diagrams: Recent advances

Roberts, Andrew P. / Heslop, David / Zhao, Xiang / Oda, Hirokuni / Egli, Ramon / Harrison, Richard J. / Hu, Pengxiang / Muxworthy, Adrian R. / Sato, Tetsuro

Earth-science reviews. 2022 Jan. 25,

2022

Abstract: The magnetic domain state of a material determines its magnetic recording capability and magnetic properties. Constraining the domain state of magnetic components within complexly mixed natural magnetic mineral assemblages is challenging because other ... ...

Abstract	The magnetic domain state of a material determines its magnetic recording capability and magnetic properties. Constraining the domain state of magnetic components within complexly mixed natural magnetic mineral assemblages is challenging because other bulk magnetic methods do not enable component-specific domain state identification. First-order reversal curve (FORC) diagrams are the most diagnostic tool for this important endeavour. Over the last 20+ years, an extensive framework has been developed for FORC diagram interpretation. Recent years have been fertile and key developments are highlighted here. New FORC measurement types provide enhanced domain state diagnosis, including recognition of vortex state signatures and their importance in rock magnetism. FORC diagrams are also indicative of the dominant magnetic anisotropy type in a material, with multi-axial, in addition to uniaxial anisotropy, signatures recognised increasingly. A fundamental challenge in FORC data processing is to avoid emphasizing noise at the expense of signal or distorting a FORC distribution by excessive smoothing. Selection of an optimal FORC distribution that avoids over- or under-smoothing is now possible with machine learning approaches. A further new FORC measurement protocol enables identification of magnetically viscous particles and can assist in separating signals due to magnetic mineral mixtures. Furthermore, FORC unmixing for large sample sets now enables quantitative separation of magnetic mineral mixtures. Splitting of the FORC signal into remanent, induced, and transient magnetization components, each of which provides information about magnetic domain state fractions in a sample, holds potential for future single sample unmixing.
Keywords	anisotropy ; diagnostic techniques ; magnetism
Language	English
Dates of publication	2022-0125
Publishing place	Elsevier B.V.
Document type	Article
Note	Pre-press version
ZDB-ID	1792-9
ISSN	0012-8252
ISSN	0012-8252
DOI	10.1016/j.earscirev.2022.103950
Database	NAL-Catalogue (AGRICOLA)

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Article: Identification and characterization of magnetotactic Gammaproteobacteria from a salt evaporation pool, Bohai Bay, China

Liu, Peiyu / Tamaxia, Alima / Liu, Yan / Qiu, Hao / Pan, Juntong / Jin, Zhongke / Zhao, Xiang / Roberts, Andrew P. / Pan, Yongxin / Li, Jinhua

Environmental microbiology. 2022 Feb., v. 24, no. 2

2022

Abstract: Magnetotactic bacteria (MTB) are phylogenetically diverse prokaryotes that can produce intracellular chain‐assembled nanocrystals of magnetite (Fe₃O₄) or greigite (Fe₃S₄). Compared with their wide distribution in the Alpha‐, Eta‐ and Delta‐proteobacteria ...

Abstract	Magnetotactic bacteria (MTB) are phylogenetically diverse prokaryotes that can produce intracellular chain‐assembled nanocrystals of magnetite (Fe₃O₄) or greigite (Fe₃S₄). Compared with their wide distribution in the Alpha‐, Eta‐ and Delta‐proteobacteria classes, few MTB strains have been identified in the Gammaproteobacteria class, resulting in limited knowledge of bacterial diversity and magnetosome biomineralization within this phylogenetic branch. Here, we identify two magnetotactic Gammaproteobacteria strains (tentatively named FZSR‐1 and FZSR‐2 respectively) from a salt evaporation pool in Bohai Bay, at the Fuzhou saltern, Dalian City, eastern China. Phylogenetic analysis indicates that strain FZSR‐2 is the same species as strains SHHR‐1 and SS‐5, which were discovered previously from brackish and hypersaline environments respectively. Strain FZSR‐1 represents a novel species. Compared with strains FZSR‐2, SHHR‐1 and SS‐5 in which magnetite particles are assembled into a single chain, FZSR‐1 cells form relatively narrower magnetite nanoparticles that are often organized into double chains. We find a good relationship between magnetite morphology within strains FZSR‐2, SHHR‐1 and SS‐5 and the salinity of the environment in which they live. This study expands the bacterial diversity of magnetotactic Gammaproteobacteria and provides new insights into magnetosome biomineralization within magnetotactic Gammaproteobacteria.
Keywords	biomineralization ; evaporation ; gamma-Proteobacteria ; hypersalinity ; magnetite ; nanocrystals ; phylogeny ; prokaryotic cells ; China
Language	English
Dates of publication	2022-02
Size	p. 938-950.
Publishing place	John Wiley & Sons, Inc.
Document type	Article
Note	JOURNAL ARTICLE
ZDB-ID	2020213-1
ISSN	1462-2920 ; 1462-2912
ISSN (online)	1462-2920
ISSN	1462-2912
DOI	10.1111/1462-2920.15516
Database	NAL-Catalogue (AGRICOLA)

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