Karl Fabian

Norwegian University of Science and Technology

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S. A. McEnroe

Norwegian University of Science and Technology

Clemens Reimann

Norwegian Geological Survey

Lennart V. de Groot

Utrecht University

Jochen Knies

Norwegian Geological Survey

Belinda Flem

Norwegian Geological Survey

R. J. Harrison

University of Cambridge

Roman Leonhardt

Central Institution for Meteorology and Geodynamics

Peter Robinson

University of Newcastle Australia

Valera P. Shcherbakov

Geophysical Survey

Manfred Birke

Federal Institute for Geosciences and Natural Resources

Cooperative Institutions

Norwegian Geological Survey

Gemalto (Israel)

Geological Survey of Sweden

University of Johannesburg

Departamento de Ciência e Tecnologia

TU Bergakademie Freiberg

Australian National University

Federal Institute for Geosciences and Natural Resources

Bureau de Recherches Géologiques et Minières

University of Bremen

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Statistical theory of weak field thermoremanent magnetization in multidomain particle ensembles

Geophysical Journal International (2003)

Karl Fabian

A non-equilibrium statistical theory of multidomain thermoremanent magnetization (TRM) is developed, which describes thermal magnetization changes as continuous inhomogeneous Markov processes.The proposed theory relies on three very general physical properties of TRM: (a) The probability that a magnetization state S j is transformed during an infinitesimal temperature change into state S i depends only on external conditions and on S j , but not on previously assumed states.(b) Due to time inversion symmetry of the Maxwell equations, the magnetic energies are invariant with respect to inversion of all spins in zero field.(c) The probability that an energy barrier between two magnetization states is overcome during a thermal process is governed by Boltzmann statistics.From these properties, the linearity of TRM with field is derived for generic multidomain particle ensembles.The general validity of Thellier's law of additivity of partial TRM's in weak fields is established and a method for proving a large class of similar additivity laws is developed.The theory allows consistent treatment of blocking and unblocking of remanence in multidomain particle ensembles and naturally explains apparent differences between blocking and unblocking temperatures.

Thermoremanent magnetization

Particle (ecology)

10.1046/j.1365-246x.2003.02057.x

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Citations (18)

Chemical and magnetic properties of rapidly cooled metastable ferri-ilmenite solid solutions: implications for magnetic self-reversal and exchange bias—III. Magnetic interactions in samples produced by Fe–Ti ordering

Geophysical Journal International (2012)

Peter Robinson R. J. Harrison Karl Fabian S. A. McEnroe

Paper II of this series described the chemical and microstructural evolution of ferri-ilmenite solid solutions during high-T quench and short-term annealing. Here we explore consequences of these Fe–Ti ordering-induced microstructures and show how they provide an explanation for both self-reversed thermoremanent magnetization and room-T magnetic exchange bias. The dominant antiferromagnetic interactions between (001) cation layers cause the net magnetic moments of ferrimagnetic ordered phases to be opposed across chemical antiphase domain boundaries. Magnetic consequences of these interactions are explored in conceptual models of four stages of microstructure evolution, all having in common that A-ordered and B-anti-ordered domains achieve different sizes, with smaller domains having higher Fe-content, lesser Fe–Ti order, and slightly higher Curie T than larger domains. Stage 1 contains small Fe-rich domains and larger Ti-rich domains separated by volumes of the disordered antiferromagnetic phase. Magnetic linkages in this conceptual model pass through disordered host, but self-reversed TRM could occur. In stage 2, ordered domains begin to impinge, but some disorder remains, creating complex magnetic interactions. In stages 3 and 4, all disordered phase is eliminated, with progressive shrinkage of Fe-rich domains, and growth of Ti-rich domains. Ordered and anti-ordered phases meet at chemical antiphase and synphase boundaries. Strong coupling across abundant antiphase boundaries provides the probable configuration for self-reversed thermoremanent magnetization. Taking the self-reversed state into strong positive fields provides a probable mechanism for room-temperature magnetic exchange bias.

Ferrimagnetism

Thermoremanent magnetization

Ilmenite

Exchange bias

Magnetism

10.1111/j.1365-246x.2012.05692.x

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Citations (11)

A Bayesian iterative geomagnetic model with universal data input: Self-consistent spherical harmonic evolution for the geomagnetic field over the last 4000 years

Physics of The Earth and Planetary Interiors (2019)

Patrick Arneitz Ramón Egli Roman Leonhardt Karl Fabian

Archaeomagnetic dating

Secular Variation

Geomagnetic secular variation

10.1016/j.pepi.2019.03.008

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Citations (43)

Comment on ‘Detecting uniaxial single domain grains with a modified IRM technique’ by R. Mitra, L. Tauxe and J. S. Gee

Geophysical Journal International (2012)

Karl Fabian

In a recent article, Mitra et al. (2011) propose a modified IRM technique to identify the symmetry of magnetic anisotropy in single domain particle ensembles. They apply this technique to support an earlier suggestion that single domain grains in young mid-ocean ridge basalts (MORB) exhibit multiaxial anisotropy. Here it is shown that the design of their measurement is flawed, in that they do not take into account that the outcome essentially depends on the initial demagnetization state of the sample before the experiment, and on the coercivity distribution of the sample. Because all MORB specimens measured by Mitra et al. (2011) carried their original NRM, which closely resembles a thermally demagnetized state, their measurements first of all reflect the coercivity distributions and domain states of the samples, and contain little or no information about the symmetry of the magnetic anisotropy. All arguments previously put forward in favour of a dominant uniaxial anisotropy in MORB are therefore still valid.

Single domain

10.1111/j.1365-246x.2012.05478.x

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Geosphere-biosphere circulation of chemical elements in soil and plant systems from a 100 km transect from southern central Norway

The Science of The Total Environment (2018)

Clemens Reimann Karl Fabian Belinda Flem Malin Andersson Peter Filzmoser

Soil horizon

Topsoil

10.1016/j.scitotenv.2018.05.070

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Citations (22)

Northern Hemisphere Glaciation during the Globally Warm Early Late Pliocene

PLoS ONE (2013)

Stijn De Schepper Jeroen Groeneveld B. David A. Naafs Cédéric Van Renterghem Jan A.I. Hennissen

The early Late Pliocene (3.6 to ∼3.0 million years ago) is the last extended interval in Earth's history when atmospheric CO2 concentrations were comparable to today's and global climate was warmer. Yet a severe global glaciation during marine isotope stage (MIS) M2 interrupted this phase of global warmth ∼3.30 million years ago, and is seen as a premature attempt of the climate system to establish an ice-age world. Here we propose a conceptual model for the glaciation and deglaciation of MIS M2 based on geochemical and palynological records from five marine sediment cores along a Caribbean to eastern North Atlantic transect. Our records show that increased Pacific-to-Atlantic flow via the Central American Seaway weakened the North Atlantic Current and attendant northward heat transport prior to MIS M2. The consequent cooling of the northern high latitude oceans permitted expansion of the continental ice sheets during MIS M2, despite near-modern atmospheric CO2 concentrations. Sea level drop during this glaciation halted the inflow of Pacific water to the Atlantic via the Central American Seaway, allowing the build-up of a Caribbean Warm Pool. Once this warm pool was large enough, the Gulf Stream–North Atlantic Current system was reinvigorated, leading to significant northward heat transport that terminated the glaciation. Before and after MIS M2, heat transport via the North Atlantic Current was crucial in maintaining warm climates comparable to those predicted for the end of this century.

Deglaciation

Marine isotope stage

Last Glacial Maximum

Gulf Stream

10.1371/journal.pone.0081508

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Citations (128)

Holocene climatic and palaeoenvironmental changes in the South-Eastern Barents Sea – new insights from palaeomagnetic and geochemical stratigraphy

Martin Klug Karl Fabian Jochen Knies Valérie K. Bellec Leif Rise

Holocene climate variability and environmental changes have been studied using a sediment record from the Barents Sea with focus on the spatio-temporal evolution of bio-productivity and terrestrial sediment deposition in response to changes of climate and regional oceanography. From a 3 m long sediment core recovered in the South-Eastern Barents Sea at 72.5&#176;N 32.5&#176;E u-channels were extracted and stepwise demagnetized and measured for their natural remanent magnetization (NRM) and anhysteretic remanent magnetization (ARM) at the cryogenic magnetometer facility at the Geological Survey of Norway. The u-channel measurements at 3 mm resolution allow the reconstruction of palaeoinclination, relative declination and relative palaeointensity. Comparison of these parameters to FENNOSTACK (Snowball et al., 2007) and EGLACOM-SVAIS (Sagnotti et al., 2011) establishes a robust age model for the sediment sequence which otherwise contains little datable material. We applied statistical factor analysis as centred logratio (clr) transformation to reduce dimensionality of the XRF data and compare changes in high-resolution magnetic susceptibility, wet bulk density and XRF elemental composition with changes of climate proxies in other North Atlantic sedimentary records.Based on the new chronostratigraphic framework changes of inorganic and organic proxies at long-term and sub-millennial scale resolve the temperature variability throughout the Holocene. Calcium content changes are related to regional bio-productivity changes in response to surface temperature changes with a pronounced deterioration at the beginning of the Neoglaciation and gradual enhancement during the late Holocene. Besides palaeoclimatic responses, the results offer the opportunity to study sediment transport and deposition during the regional deglaciation and mid-Holocene glacier growth in northwestern Fennoscandia. The temporal changes of the regional oceanography and the variability of marine palaeoproductivity in the South-Eastern Barents Sea indicate an active interplay between the North Atlantic Current (NAC) and the Norwegian Coastal Current (NCC) during the early Holocene, a predominance of the NCC during middle Holocene and a re-amplification of the NAC during the late Holocene. Comparison to other records from the Nordic Seas enables the reconstruction of responses and the vulnerability of this arctic marine ecosystem to past climate variations and may help to estimate upcoming responses to recent and future climate changes.&#160;References:Snowball, I., L. Zill&#233;n, A. Ojala, T. Saarinen, and P. Sandgren (2007), FENNOSTACK and FENNORPIS: Varve dated Holocene palaeomagnetic secular variation and relative palaeointensity stacks for Fennoscandia, Earth and Planetary Science Letters, 255, (1-2), 106&#8211;116Sagnotti, L., P. Macr&#236;, R. Lucchi, M. Rebesco, and A. Camerlenghi (2011), A Holocene paleosecular variation record from the northwestern Barents Sea continental margin, Geochemistry, Geophysics, Geosystems, 12, (11)

Biogenic silica

10.5194/egusphere-egu2020-7894

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Citations (0)

On the possibility of recovering palaeo-diurnal magnetic variations in transitional lava flows

Physics of The Earth and Planetary Interiors (2008)

Christian Vérard Roman Leonhardt Michael Winklhofer Karl Fabian

Thermoremanent magnetization

Deccan Traps

Magnetic mineralogy

10.1016/j.pepi.2008.07.018

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