Displays

Rocks have complicated histories and form under various conditions. However, all rocks, terrestrial and extraterrestrial, have been subjected to some form of pressure during their genesis. The effect of pressure (strain) on the magnetic remanence is a largely unexplored problem, with most of the work being focused on the study of meteorites. 

In the absence of a magnetic field, subjecting a rock to pressure can demagnetize the natural remanent magnetization (NRM). This loss of magnetic remanence can lead to an underestimation of paleointensities. On the other hand, in the presence of a magnetic field, magnetic minerals can record a pressure remanent magnetization (PRM). The superposition of the remaining NRM and a newly acquired PRM can influence the remanence direction as well as the paleointensity. Since the reconstruction of the temporal changes of Earths’ magnetic relies on robust estimations of direction and intensity, the effects of pressure on the remanence should be taken into account.

Here we present a series of experiments that aim to explore the acquisition process of PRMs and their net contribution with respect to the rock’s original magnetization. Stoichiometric magnetites of four different grain sizes (65 nm, 440 nm, 16.9 µm, and 18.3 µm) and magnetic domain states were subjected to crustal pressures (226, 301, and 376 MPa) in the presence of a magnetic field. Surprisingly, the PRM intensity showed no detectable dependence on grain size. However, because the acquisition of a thermal remanence (TRM) is strongly dependent on particle size,  populations of large multidomain particles can acquire a PRM, which may represent up to 30% of a TRM acquired in the same field.

Finally, we will show how the influence of pressure on the magnetic remanence can be visualized by modern magnetic imaging techniques like the quantum diamond microscope (QDM). The QDM has a  ~1 µm maximum spatial resolution that is able to resolve the magnetic fields of individual mineral assemblages with ~10 µm diameter. The high spatial resolution and sensitivity enables us to visualize the changes in magnetic remanence due to pressure cycling and can help to better understand the possible implications for paleomagnetism.

How to cite: Volk, M., Fu, R., and Feinberg, J.: Under pressure: How pressure affects magnetic remanence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-915, https://doi.org/10.5194/egusphere-egu2020-915, 2020.

Slice-and-view nanotomography uses a dual beam SEM-FIB to reconstruct the 3D volume of a mineralogical sample using a sequential series of nanoscale slices created with a focussed beam of Ga ions. This method reveals the true shapes and forms of naturally occurring magnetic inclusions hosted by the silicate minerals feldspar and pyroxene. High-resolution 3D morphological data for the magnetic minerals is extracted, converted to tetrahedral meshes, and micromagnetically modelled using the MERRILL software.

This study optimises the step-by-step process of extracting and processing micromagnetic data from polished thin-sections to generate a full rock magnetic classification of the remanence carriers in silicates. Slice-and-view nanotomography follows known preparation methods with a protective platinum layer, carbon rod guides and trenches, but also introduces a carbon slab along the Z-direction for e-beam alignment. This method reduces the need for auto focus, as the e-beam alignment will have a constant imaging distance and generates a good reference point for stack alignment. Image processing is limited to 3D a gaussian blur and 3D mean filters. Paraview is used to set the correct voxel dimensions and to generate the surface mesh. Freeware software Meshmixer and Meshlab are used for their powerful smoothing, mesh interaction tools and geometric calculations. The tetrahedral volume mesh is produced with iso2mesh in Matlab.

Micromagnetic hysteresis and back-field simulations of >400 inclusions with a broad range of morphologies have been performed using MERRILL using 20 different field directions, enabling average magnetic properties to be calculated for a random ensemble. The results give a detailed and direct description of the micromagnetic structure of naturally formed magnetic minerals that compliments macroscopic approaches, such as FORC analysis.

How to cite: Nikolaisen, E. S., Harrison, R. J., McEnroe, S. A., and Fabian, K.: Micromagnetic modeling of silicate-hosted magnetic inclusions using SEM-FIB slice-and-view nanotomography, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20552, https://doi.org/10.5194/egusphere-egu2020-20552, 2020.

Our understanding of the behavior of the geomagnetic field arises from magnetic signals stored in geological materials, e.g. lavas. Almost all experiments to determine the past state of the Earth’s magnetic field use bulk samples (typically 1 - 10 cc) and measure their magnetic moment after series of laboratory treatments. Lavas, however, consist of mixtures of different iron-oxide grains that vary in size, shape, and chemistry. Some of these grains are good recorders of the Earth’s magnetic field; others are not. Only a small amount of adverse behaved magnetic grains in a sample already hampers all classical experiments to obtain paleointensities; success rates as low as 10-20% are common, i.e. for 80-90% of all lavas vital information on paleointensities is lost before it can be uncovered.

Recently, we showed that it is possible to determine the magnetization of individual grains inside a synthetic sample using a new technique: Micromagnetic Tomography. The individual magnetizations of grains are determined by inverting scanning magnetometry data from the surface on the sample onto the known locations, sizes and shapes of the magnetic grains that are obtained from a microCT scan of the sample. The synthetic sample used for our proof-of-concept, however, was optimized for success: the dispersion of magnetic markers was low, and the magnetite grains had a well-defined grain size range. Furthermore, the scanning SQUID microscope used requires the sample to be at 4 K, below the Verweij transition of the magnetite grains.

Here we present the first Micromagnetic Tomography results from natural samples. We used two magnetic scanning techniques that operate at room temperature, a Magnetic Tunneling Junction set-up and a Quantum Diamond Magnetometer, to acquire the magnetic surface scans from a Hawaiian lava and calculated magnetic moments of individual grains present. We show that it is possible to acquire rock magnetic information as function of grain size from these natural samples and reveal the first results of interpreting a paleomagnetic direction from selected subsets of grains in our samples. These are the first steps towards deriving rock magnetic and paleomagnetic information from subsets of known good recorders inside lava samples, a technique that will revolutionize our field of research.

How to cite: de Groot, L., Fabian, K., Béguin, A., Kosters, M., Fu, R., Harrison, R., Barnhoorn, A., and van Leeuwen, T.: First steps towards deriving rock magnetic and paleomagnetic data from subsets of magnetic grains in lavas using Micromagnetic Tomography, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18114, https://doi.org/10.5194/egusphere-egu2020-18114, 2020.

Development in instrumentation and technology now allows for mapping of magnetic anomalies, caused by spatial variations in magnetization in the source materials, over a wide range of scales, from the millimeter mineral scale to the km crustal scale.

Traditional rock magnetic methods, used to investigate the magnetization in natural rock samples, are bulk measurements, which cannot be directly correlated to the individual mineral phases, or particles.  Scanning magnetic microscopy is a high-resolution mapping technique that allows for detailed investigation of the magnetization in natural rock samples. The technique generates a map of the magnetic field distribution over a planar surface of a rock sample with sub-millimeter resolution that can be used to correlate specific magnetic signals to the underlying mineralogy. This information is vital for an understanding of the origin of rock bulk behavior measured in both the laboratory, and in magnetic surveys.

Here we use 3D magnetic modeling to investigate the sources of the magnetic anomalies mapped over a sample thin section. The oxide grains in the thin sections are modeled using information from optical and electron microscopy (SEM and TEM) to constrain the source geometry, and with magnetic property data. The internal geometry of the oxide mineral phases (exsolution lamellae, intergrowths, symplectites) and compositions are constrained by EMP and TEM. 

Magnetic scans aid in locating the magnetic sources, and resolving the different magnetic components contributing to the bulk rock properties.  By modeling the small-scale variations in the oxides the direction and intensity of the magnetic grains are determined.  Aeromagnetic and ground magnetic data from the sample locations are used in conjunction with thin section magnetic mapping. Thin section results can be up-scaled to compare with ground and aeromagnetic data.

How to cite: McEnroe, S., Pastore, Z., Church, N., Langenhorst, F., and Oda, H.: Mineral sources of magnetic anomalies: Insights from scanning magnetic microscopy , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19911, https://doi.org/10.5194/egusphere-egu2020-19911, 2020.

The NRM of the ocean floor is carried by titanomagnetite grains that undergo low-temperature oxidation after initial cooling. Progressing oxidation is known to generate shrinkage cracks in   grains larger than approximately 5 mkm, and is suspected to   control the long wavelength variation of NRM-intensity across the ocean floor. Here we develop a quantitative theory of single-phase oxidation and crack formation by solving the vacancy-diffusion equation that describes the oxidation process for spherical titanomagnetite particles, where the diffusion coefficient strongly decreases with vacancy concentration. The latter dependence has been experimentally demonstrated and is essential to explain the peculiarities of the observed variations of oxidation-degree with ocean-floor age. The calculated diffusion profiles provide the exact stress distributions inside oxidized titanomagnetite spheres, and  predict a size limit for shrinkage-crack formation that agrees   with   microscopic observations of crack appearance in ocean-floor basalt samples. The new diffusion model provides a unified explanation of long-known experimental facts that 1) temperatures for the onset of low-temperature oxidation during laboratory heating are theoretically estimated as 200-400 °C, depending on grain size, and 2) that heating to 400-500 °C is required to obtain a sufficiently high degree of oxidation z about 0.8  for the development of  high-temperature exsolution lamellae. Calculations for ocean-floor conditions    quantitatively suggest that a rapid decrease of NRM intensity during the first 40 ka  results from  a deflection of magnetization by strong stresses that emerge in titanomagnetite grains of sub-critical sizes, and randomization of domain-state by crack formation in larger grains. This work was supported by Russian Science Foundation grant 19-47-04110401 (VS)

How to cite: Shcherbakov, V. and Fabian, K.: Theory of low-temperature deuteric oxidation with application to time evolution of ocean magnetic anomalies, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3733, https://doi.org/10.5194/egusphere-egu2020-3733, 2020.

Interpretation of palaeointensity measurements is difficult since natural samples are made up of magnetic grains of different size, shape and chemical composition. Néels single-domain (SD) model is the main theoretical tool used to understand paleomagnetic measurements, but it is limited since it only applies to uniformly magnetized grain assemblies.

Recent work has shown that the single-vortex (SV) state is not only significantly more common than SD as it occupies a much larger range of grain sizes but is also surprisingly thermally stable [1]. As these grains likely account for the majority of the signal measured in the laboratory, they must also be responsible for the range of observations that lead to large inaccuracies in measurement, for example, pTRM tails. Additionally, if we have a clear understanding of the SV state, can we account for the true cooling rate dependence of grain assemblies, and also find a physical link between magnetic coercivity and blocking temperature.

We present a framework of tools for paleomagnetists to interpret measurements in the light of advances in numerical modelling and the increase in speed of modern computers. We hope that these tools will advance our understanding of the basic mechanisms by which samples record and preserve the Earth’s magnetic field and so will allow for the quantification of errors observed in real samples.

[1] L.  Nagy,  W.  Williams,  A.  R.  Muxworthy,  K.  Fabian,  T.  P.  Almeida, P. Ó Conbhuí, and V. P. Shcherbakov. Stability of equidimensional pseudo–single-domain magnetite over billion-year timescales. PNAS 114(39):10356–10360, 2017

How to cite: Nagy, L., Williams, W., Tauxe, L., Muxworthy, A., and Fabian, K.: Beyond single model and single domain : Using big data to answer fundamental questions in rock magnetism, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9355, https://doi.org/10.5194/egusphere-egu2020-9355, 2020.

The common theory of paleomagnetic recording is based on the acquisition of thermoremanent magnetization in  single-domain (SD) particles (Neel, 1955). The physical consequences of this theory  agree  well enough  with observations as to be of utmost use in understanding and assessing the quality of paleomagnetic data in almost all practical applications in paleomagnetism. This is to a large extent due to the statistical nature of the interpretations based on SD theory, which apparently is sufficiently robust to make up for minor descrepancies between the real remanence carriers and their physical description on which the statistical interpretation is founded. Exceptions to this rule are becoming more important as increasingly sophisticated technical methods for paleomagnetic measurements are developed and used, that involve fewer and fewer individual magnetic particles to contribute to the measured signal. Examples are the determination of paleointensity from individual mineral grains, and the development of scanning magnetometers that average over relatively small numbers of magnetic grains in a sample. The statistical uncertainties of paleomagnetic quantities resulting from using small sample sizes have been studied for SD particle ensembles for example by Berndt et al. (2016).  First experimental data indicate that in case of PSD particles the statistical sample size required to  reconstruct paleomagnetic field direction may be smaller than for SD particles. Here, a theoretical study is presented that describes the micromagnetic background of this hypothesis and allows to test  it for a simplified mathematical model of TRM acquisition in PSD particles.

How to cite: Fabian, K. and de Groot, L. V.: A pseudo-single domain theory of paleomagnetic recording, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11247, https://doi.org/10.5194/egusphere-egu2020-11247, 2020.

Speciation analysis of Fe in single plagioclase crystals separated from two different gabbros was performed to understand the crystallization mechanisms of magnetite exsolution. Iron species in single crystals were measured using Fe K- and L_III-edge X-ray absorption fine structure (XAFS) analysis. The K-edge pre-edge analysis showed variation in the averaged valence state of Fe in plagioclase crystals even if they had been separated from the same gabbro that was further confirmed by the L_III-edge analysis. The K-edge pre-edge analysis also suggests the various degrees of contribution from tetrahedral Fe. The mixing of tetrahedral and octahedral Fe leads to an underestimation of the averaged valence state of Fe for the K-edge pre-edge analysis; thus, we adopted the L_III-edge result for the valence state of Fe in plagioclase crystals. Iron K-edge extended XAFS (EXAFS) analysis of two plagioclase crystals separated from the same gabbro clearly showed different coordination environments. A weakening of EXAFS oscillation was recognized in one sample, because two Fe‒O bonds (Fe³⁺‒O₁ and Fe²⁺‒O2) cancelled out the oscillations of each other. The EXAFS spectrum of the other plagioclase crystal suggested a homogeneous distribution of Fe. The content of exsolved magnetite in these crystals is nearly identical, indicating that the exsolution of magnetite in plagioclase crystal had been completed before the temperature decrease that stopped the ordering of Fe ions in tetrahedral sites.

Reference: Nakada et al. (2019) G-Cubed, vol. 20 (11), 5319-5333.

How to cite: Nakada, R., Sato, M., Ushioda, M., Tamura, Y., and Yamamoto, S.: Determination on iron species in plagioclase crystals toward the understanding on the magnetite exsolution, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12040, https://doi.org/10.5194/egusphere-egu2020-12040, 2020.

Smythite (Fe₉S₁₁) is an occasionally reported magnetic iron sulphide mineral that occurs in varied geological settings and co-occurs commonly with other magnetic iron sulphide minerals. Determining the magnetic properties of smythite is important to understand its geological distribution and paleomagnetic and environmental magnetic significance. We have identified sedimentary smythite from three locations in Taiwan (one terrestrial and two marine), which suggest that smythite forms in methanic diagenetic environments into which sulfide has been reintroduced. We report the magnetic properties of our purest smythite sample and compare them with those of other magnetic iron sulfide minerals. The magnetization of smythite is controlled by multi-axial anisotropy, with magnetic easy axes that lie within the crystallographic basal plane. Smythite has stable magnetic properties with no low-temperature magnetic transition. The magnetic properties of smythite at elevated temperatures are dominated by thermal alteration, which precludes Curie temperature determination. Hysteresis and coercivity properties of stable single domain smythite are similar to those of greigite at, and below, room temperature. In contrast to greigite, and similar to pyrrhotite polytypes, smythite crystals occur as hexagonal plates. This morphological contrast facilitates discrimination of smythite from greigite in electron microscope observations, but it does not assist discrimination from pyrrhotite. Similar magnetic and morphological properties between smythite and other magnetic iron sulfides means that diagnostic mineralogical analyses (e.g., X-ray diffraction) are needed to identify these minerals. Further work is needed to obtain pure samples to develop a comprehensive domain state dependent magnetic property framework for smythite.

How to cite: Roberts, A. and Horng, C.-S.: Magnetic properties of sedimentary smythite (Fe9S11), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12922, https://doi.org/10.5194/egusphere-egu2020-12922, 2020.

How to cite: Nowaczyk, N.: Re-sedimentation experiments with mud from the Southeastern Black Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4399, https://doi.org/10.5194/egusphere-egu2020-4399, 2020.

Patterns of variability in Pleistocene magnetic susceptibility (k) from deep-sea sediment cores from the Scotia Sea show a striking similarity to patterns of dust flux recorded in the EPICA Dronning Maud Land (EDML) ice core.  Antarctic marine k records broadly reflect the interplay of lithogenic sediment provenance, biological productivity, sediment transport processes, and post-depositional diagenesis. Here we explore the origin of the Scotia Sea k record via a detailed rock magnetic study across the transition from MIS 6 to MIS 5. We analyzed bulk sediment and grain size separates in order to construct magnetic signatures of iceberg rafted debris (IBRD), sortable silt, and eolian input. The MIS 6-MIS 5 transition consists of three lithologies, a high k silty-clay-rich diatomaceous mud deposited during the glacial interval, an IBRD-rich but low k silty clay that marks the onset of deglaciation, and a low k diatomaceous ooze in which IBRD decreases forward through time. The high k glacial sediment is characterized by multi-domain hysteresis parameters, low χ_ARM/χ values, S ratios near 1, and thermomagnetic curves indicative of low-Ti titanomagnetite. The absence of k peaks in the IBRD-rich silty-clay and IBRD rich diatomaceous ooze likely reflects the weakly magnetic lithogenic detritus supplied by Weddell Sea Embayment (WSE) ice streams, such as sandstone, quartzite, metasedimentary lithologies, phyllite and schist observed in lateral moraines adjacent to ice streams of the eastern WSE. The deglacial interval is characterized by elevated M_R/M_S, χ_ARM/χ, and HIRM values, and decreased S-ratios in the bulk sediment, suggesting a greater proportion of high coercivity minerals such as hematite or goethite in the iron oxide assemblage. Preliminary data from grain size separates indicates that the clay mass fraction is > 0.5 in all three lithologies. Clay is also the dominant size fraction in the EDML ice core dust, with particle sizes generally < 5 μm. The Scotia Sea clay fraction k values are a factor 1.5 to 5 weaker than the silt fraction k values, and therefore are not the main carrier of the bulk k signal. The rock magnetic signatures of Scotia Sea sediment will be compared to those of terrestrial till and bedrock from the WSE, and to those of potential dust sources in South America to identify the sediment sources and environmental processes responsible for the k signal.

How to cite: Brachfeld, S., Reilly, B., Tauxe, L., Lee, B., Weber, M., Raymo, M., Williams, T., Bailey, I., Garcia, M., Guitard, M., Hemming, S., Martos, Y., OConnell, S., Perez, L. F., Ronge, T., Zheng, X., and Licht, K. and the Expedition 382 Scientists: Origin of the Scotia Sea Magnetic Susceptibility Signal Across the MIS6-MIS5 Transition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12027, https://doi.org/10.5194/egusphere-egu2020-12027, 2020.

Obtaining reliable global and regional records of the past climatic changes during the glacial Pleistocene is of prime importance for building up consistent climate models of the near and far future. Magnetic signature along sequences of alternating loess and (paleo)soil units from the terrestrial environments is considered as semi-continuous record of climate change in the geological past. However, soil formation in aeolian landscapes may occur under different and changing conditions of dust sedimentation. Viewing from this standpoint the depth variations of several rock magnetic characteristics along profiles of Holocene soils from low Danube area allowed us to establish a set of criteria for identification of the past regimes of aeolian sedimentation persisted during the soil forming periods. A conceptual model for the time evolution of the grain size of the pedogenic magnetic fraction  with soil depth is proposed,  which is build upon  the mechanism of soil formation – accretional or  stable land surfaces,  or a combination of the two. According to the proposed conceptual model, discrimination between accretional soils and soils developed without dust additions during soil forming period can be done. Accretional soils are characterized by parallel changes in grain size sensitive magnetic proxies. Soils, developed at stable landscape conditions show gradation of the depths at which maximum enhancement of various proxies occurs with deepest occurrence of the maximum in frequency dependent magnetic susceptibility, followed by depth of maximum anhysteretic susceptibility and the normalized anhysteretic to isothermal remanence acquired at 100mT field. It is shown that the mean coercivity of the pedogenic component of accretional soils is higher than that of soils developed without eolian input at equal temperature conditions because of the soils’ thermal gradient and different depths, at which pedogenic minerals form in the two settings.

How to cite: Jordanova, D. and Jordanova, N.: Deducing the role of eolian dust sedimentation during soil forming periods on mineral magnetic records and its implications for paleoclimate reconstructions , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4523, https://doi.org/10.5194/egusphere-egu2020-4523, 2020.

There are longstanding and ongoing controversies about the abiogenic or biogenic origin of magnetite in banded iron formations (BIFs). The trace element composition of magnetite was proposed as a promising tracer for distinguishing biogenic from abiogenic magnetite, which, however, remains to be explored quantitatively. Here, we compared the partitioning of trace elements Zinc (Zn) and Nickel (Ni) in both abiogenic and biogenic magnetite produced either by an abiotic reaction of ferrihydrite with by Fe²⁺_aq or by Fe(III)-reducing bacteria Shewanella oneidensis MR-1. We compared the transformation of three different ferrihydrite (Fh) starting materials: 1) Control Fh without added trace elements, 2) ferrihydrite with co-precipitated Zn (ZnFh) and 3) ferrihydrite with co-precipitated Ni (NiFh) – both in either NaHCO₃ or HEPES buffer. We monitored Fe concentration and speciation in both aqueous and solid phases over time using the spectrophotometric ferrozine assay, analyzed Fh transformation products by Mössbauer spectroscopy as well as X-ray diffraction and quantified Zn and Ni in solution and in the minerals by iCAP-Qc quadrupole mass spectrometer after acidic dissolution of the minerals. In summary our results revealed that both Zn and Ni are much more depleted in abiogenic magnetite than those in biogenic magnetite, independent of whether magnetite was precipitated in NaHCO₃ or HEPES buffer. Although further analyses are needed, this suggests that the trace element distribution could be a chemical signature to distinguish biogenic from abiogenic magnetite in BIFs.

How to cite: Han, X., Tomaszewski, E., Schönberg, R., Pan, Y., Byrne, J., and Kappler, A.: Zinc and Nickel signature for abiogenic and biogenic magnetite: implications for the origin of magnetite in banded iron formations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21076, https://doi.org/10.5194/egusphere-egu2020-21076, 2020.

    All organisms survive and multiply under the geomagnetic magnetic field (GMF) ^[1]. With the launch of the Moon and Mars space program, during long-distance space mission, astronauts will inevitably be exposed to an environment with a hypomagnetic field (HyMF), which several thousand times weaker than GMF^[2]. Spatial hypomagnetic field exists on the surface of the moon or in the deep space of the solar system, and its magnetic intensity is less than 5 μT^[3]. At present, the research on the effects of HyMF on the health of astronauts is mainly focused on the conditions of ground simulation experiments, including the central nervous system, blood system and brain cognition ^[4,5]. However, relevant safety of the skeletal system studies about HyMF are deficient. Our recent research indicated that the effects of HyMF on bone cannot be overlooked. In vivo, our study found that HyMF aggravated bone loss induced by hindlimb unloading (HLU) in rats and mice, which related to the changes in iron metabolism^[6,7]. In addition, HyMF also inhibited the recovery of simulated microgravity-induced osteoporosis of mice, probably by restraining elevated iron return to normal levels^[8]. Meanwhile, we found that HyMF can inhibit osteoblast differentiation and mineralization^[9], promote osteoclast formation and bone resorption in vitro^[10]. The research results have significant academic values in the field of magneto-biology and the potential application values in space activities for the manned moon landing exploration.

Key words: 

Hypomagnetic field, geomagnetic field, safety management, iron storage.

References

[1]Dubrov A P. The Geomagnetic Field and Life: Geomagnetobiology. Bioscience. 1978. 978-1-4757-1610-8.

[2]Belyavskaya N. Biological effects due to weak magnetic field on plants. Advances in space Research, 2004, 34(7): 1566-1574.

[3]Mo W C, Ying L & He R Q. Hypomagnetic field, an ignorable environmental factor in space? Science China -Life Sciences, 2014. 57(7): 726-728.

[4]Mo WC, Liu Y & He RQ. A biological perspective of the hypomagnetic field: from definition towards mechanism. Prog Biochem Biophys, 2012, 39: 835–842 

[5]Jia B, Zhang WJ, Xie L, Zheng  Q, Tian ZC & Shang P. Effects of hypomagnetic field environment on hematopoietic system in mice. Space Medicine &Medical Engineering, 2011.24(5): 318-322.

[6] Jia B, Xie L, Zheng Q, Yang P F, Zhang W J & Shang P. A hypomagnetic field aggravates bone loss induced by hindlimb unloading in rat femurs. PloS one, 2014, 9(8): e105604.

[7] Yang J, Meng X, Dong D, Xue Y, Chen X & Shang P. Iron overload involved in the enhancement of unloading-induced bone loss by hypomagnetic field. Bone, 2018 Sep;114:235-245.

[8]Xue YR, Yang JC, Luo J, Ren L, Shen Y & Shang P, Disorder of iron metabolism inhibits the recovery of unloading-induced bone loss in hypomagnetic field. Journal of bone and mineral research.2020. DOI: 10.1111/JBMR.3949.

[9]Yang J, Zhang J, Ding C, Dong D & Shang P. Regulation of Osteoblast Differentiation and Iron Content in MC3T3-E1 Cells by Static Magnetic Field with Different Intensities. Biological trace element research, 2017, 184(7): 1-12.

[10]Zhang J, Meng X, Ding C, Xie L, Yang P & Shang P. Regulation of osteoclast differentiation by static magnetic fields. Electromagnetic biology and medicine, 2017, 36(1): 8-19.

How to cite: Shang, P. and Xue, Y.: Safety of hypomagnetic field and its effects on the skeletal system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2510, https://doi.org/10.5194/egusphere-egu2020-2510, 2020.

Paleomagnetic measurements provide very important methods to study the evolution of and variations in the Earth’s magnetic field throughout time. A vital tool used in paleomagnetism are natural magnetic minerals, such as the titanomagnetite (TM) solid solution series (Fe_3-xTi_xO₄, 0 ≤ x ≤ 1). The main source of magnetic information in TMs is the thermal remanent magnetisation (TRM) they retain whilst being cooled below their Curie temperature (T_C) during their formation.

The key factor determining the T_C  is the composition. However, recent studies on natural and synthetic TM powders [1,2,3] have shown that their T_C  is also heavily influenced by their thermal history. Annealing various natural and synthetic TM powders at temperatures between 300°C and 425°C for timescales of hours to months resulted in changes in their T_C  of up to 150°C.

The accuracy of many paleomagnetic measuring techniques, such as geomagnetic paleointensity estimates and paleomagnetic paleothermometry, depends on the exact knowledge of the Curie temperature. Changes in T_C  of such a considerable extend could deeply impact those techniques or even render them doubtable. So far, vacancy-mediated chemical clustering at the octahedral site of the TM structure has been postulated as the mechanism causing this phenomenon [2,3]. To further investigate the underlying processes, we synthesised a large (~6.5 mm diameter;  ~27 mm length) TM single crystal using an optical floating zone furnace. Via SEM-EDX techniques it was established that the crystal was homogenous over its whole length with a composition of  Fe_2.64Ti_0.36O₄. Using a Physical Properties Measurement System (PPMS) the Curie temperatures of several pieces of the crystal were determined after different annealing treatments. For the first time it has been possible to detect systematic changes in T_C  with annealing in a TM single crystal.

Additionally within the scope of this project it was possible to determine the relationship between the extend of change in T_C  and the microstructure for polycrystalline samples.

[1] Bowles, J. A., Jackson, M. J., Berquó, T. S., Solheid, P. A. and Gee, J. S. (2013), Nature Communications, 4, 1916. https://doi:10.1038/ncomms2938

[2] Jackson, M. J., and Bowles, J. A. (2018), J. Geophys. Res., 123, 1-20. https://doi:10.1002/2017JB015193

[3] Bowles, J. A., Lappe, S.‐C. L. L., Jackson, M. J., Arenholz, E., & van der Laan, G. (2019). Geochem. Geophy. Geosy. 20. https://doi.org/10.1029/2019GC008217

How to cite: Lappe, S.-C., Winkens, G., Persson, J., Nandi, S., and Petracic, O.: Curie temperature variations in synthetic titanomagnetite single crystals, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8865, https://doi.org/10.5194/egusphere-egu2020-8865, 2020.

Greigite (Fe₃S₄) is a ferrimagnetic mineral widespread in sedimentary environments, commonly found in lacustrine and marine sediments that records ancient geomagnetic field variations and environmental processes. However, its magnetic properties are not yet well understood due to the lack of a single crystal greigite suitable for magnetic measurements. In particular, the dependency of its magnetic properties with respect to structural and morphological properties remains uncertain.

In the present study, we analyzed the structural and magnetic properties of synthetic, polycrystalline greigite formed by controlled colloidal synthesis [Rhodes et al. 2017]. X-ray diffractometry and transition electron microscopy reveal that greigite forms flakes of about 100 nm that consist of epitaxial intergrown nanoparticles with a mean coherence length of 19 nm. Therefore, our synthetic greigite can be considered as polycrystalline flakes with a nanotexture.

The saturation magnetization (M_s) of the nanotextured greigite is 32.7 Am²kg^-1 and the coercivity is B_c = 41 mT. The M_s is about 45% below the value for relatively large, synthetic crystal and this in turn is probably caused by the nanotexture, e.g., interfaces between nanocrystallites. The ratios M_r./M_S = 0.54 and B_ar/B_Sc = 1.33 indicate single-domain (SD) particles with pre-dominant uniaxial anisotropy [Roberts 1995]. The FORC diagram at room temperature shows an oval contour plot supporting that the flakes are nanotextured with interacting SD particles. The hysteresis parameters B_c and M_S continuously increase upon cooling to 10 K.

Low-temperature cycling of the magnetization between 300 and 10 K in fields between 10 mT and 1000 mT shows the expected behavior for ferrimagnets with the superposition of the cooling and warming curves at fields B ³ 500 mT. At weaker fields a slight magnetic induction upon warming is found and the relative increase in magnetization is field dependent. This irreversibility most likely stems from the magnetization of the nanoparticle interfaces and their interactions in the flakes.

Ferromagnetic resonance spectroscopy (FMR) at room temperature shows a resonance field B_res= 213 mT and linewidth DB = 160 mT. Upon cooling the B_res decreases continuously down to 50 K followed by a pronounced shift to lower values down to 10 K. The shift goes along with markedly linewidth broadening. The discontinuity of the spectral parameters at T < 50 K points to a change in the effective anisotropy of the flakes most likely due to changes of the magnetocrystalline and the interaction anisotropies in the nanotexture, because the shape anisotropy of the polycrystalline flakes undergoes no significant change. 

In summary, the magnetic properties of greigite can be critically affected by the nanotexture. The response of the nanotexture to the magnetization and anisotropy properties can be taken to identify and characterize greigite nanoparticles in natural environments and to critically evaluate their use for paleomagnetic studies.

Rhodes, Jordan M., et al. "Phase-controlled colloidal syntheses of iron sulfide nanocrystals via sulfur precursor reactivity and direct pyrite precipitation." Chemistry of Materials 29.19 (2017): 8521-8530.

Roberts, Andrew P. "Magnetic properties of sedimentary greigite (Fe3S4)." Earth and Planetary Science Letters 134.3-4 (1995): 227-236.

How to cite: Lesniak, B., Charilaou, M., and Gehring, A.: Magnetic properties of nanotextured greigite., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13170, https://doi.org/10.5194/egusphere-egu2020-13170, 2020.

The occurrence and nature of primary magnetic phases in ultramafic rocks is a subject of debate. Studies of ultramafic rocks originating in the deep crust commonly report secondary magnetic phases due to later metamorphism, serpentinization, or alteration as sources for long-wavelength anomalies. To assess the potential magnetic contribution from primary magnetic minerals occurring ‘in situ’ in deep-seated ultramafic rocks, the stability of these phases at lower crustal pressure and temperature conditions must be addressed. However, to study the magnetization of deep-crustal rocks, we are limited to exposures of unaltered uplifted rocks. Studying the petrophysical and rock magnetic properties of these ultramafic rocks can aid in predicting magnetic behavior deeper in the crust. 

Here, we present the results of a petrophysical and rock magnetic study on the ultramafic rocks of the Reinfjord Ultramafic Complex (RUC). These rocks are part of the Seiland Igneous Province, a magmatic plumbing system that formed in the deep crust (25-35 km depth). The dunites and wehrlites are minimally serpentinized, which indicates that the magnetic oxides in these rocks may be representative of those at depth. The primary magnetic carriers in these rocks were characterized using optical and electron microscopy, hysteresis and FORC measurements, backfield unmixing curves, and scanning magnetic microscopy. The primary magnetic carriers in the RUC are Cr-magnetite blebs exsolved from Al-chromite, and exsolved magnetite lamellae within clinopyroxene. The magnetic carriers have a range of domain states from SD to MD. 

The ultramafic rocks from the RUC are remarkably pristine and therefore provide insight into the magnetization of the lower crust. Due to the presence of SD magnetic carriers, these rocks may hold a stable remanence at lower crustal conditions and therefore be a potential source for long-wavelength anomalies.

How to cite: ter Maat, G., McEnroe, S., Church, N., and Oda, H.: Magnetization of lower crustal rocks - potential sources of long wavelength anomalies, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19223, https://doi.org/10.5194/egusphere-egu2020-19223, 2020.

Marginal areas off southwestern Taiwan have been widely considered a high potential reservoir of gas hydrates based on several geophysical, geological, and geochemical investigations since the past decades. First gas hydrate sample has been collected on 21 June 2018 during the cruise MD214 at the core site MD18-3542 on the South Yung-An East Ridge. In the study, we focus on magnetic properties of this MD core. The most attractive feature in the magnetic susceptibility is an abrupt drop recorded at about 4 meters core depth. To clarify and identify the dominant magnetic mineral in the core, hysteresis loop parameters were first measured and then presented on the Day Plot, and further the X-ray diffraction analysis was applied to the selected core samples. Based on the magnetic results, the clear drop in the magnetic susceptibility is related to the change of dominant magnetic minerals in core sediments. Before about 4 meters core depth, the dominant magnetic mineral remains detrital magnetite. Below the depth, however, core sediments should have been infected by methane released by gas hydrate dissociation. Authigenic greigite and pyrite have become dominant, and therefore low magnetic susceptibility appears below 4 meters core depth.

How to cite: Huang, Y.-S., Horng, C.-S., Su, C.-C., Hsu, S.-K., and Lin, J.-Y.: Rock magnetic signature as a result of gas hydrate dissociation off southwestern Taiwan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8095, https://doi.org/10.5194/egusphere-egu2020-8095, 2020.

The Nankai Trough is an accretionary complex which extends over several thousands of kilometers along the Japanese Pacific coast. Many ocean scientific drilling expeditions have taken place in this zone to better understand the mechanisms of big earthquakes and generation of devastating tsunamis. Offshore Cape Muroto, Shikoku Island, is one of investigated zones. A recent International Ocean Discovery Program (IODP) expedition (IODP Expedition 370) in the area has focused on the temperature limit of life in deep subseafloor sediments. Here we present paleomagnetic and rock magnetic preliminary results on two neighboring sites in this zone drilled during two former Ocean Drilling Program (ODP) legs: Site 808 of ODP Leg 131 and Site 1174 of ODP Leg 190. At all sites, shipboard magnetostratigraphy was challenging because of a strong diagenetic alteration of the magnetic mineral assemblages. Four main downcore magnetic zones, characterized by specific magnetic properties and mineralogy, are identified. At Site 808, catagenesis of the organic matter has been proposed to explain the downcore rock magnetic properties. This explanation however could not stand for Site 1174. We present here a first attempt of a comparative paleomagnetic and rock magnetic study in high temperature marine sediments, off Cape Muroto.

How to cite: Kars, M., Fukuta, T., and Becker, C.: Paleomagnetic and rock magnetic investigation in marine sediments, Nankai Trough, offshore Cape Muroto , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12655, https://doi.org/10.5194/egusphere-egu2020-12655, 2020.

Ocean sediment records from the West Iberian margin can be correlated to both Antarctic and Greenland ice cores as well as to European terrestrial pollen data. Previous studies have focussed on comparatively short sediment cores collected from relatively deep-water sites (i.e. >~2500mbsl). Here we present magnetic mineralogy and grain size from Integrated Ocean Drilling Programme Sites U1385 (2585mbsl) and U1391 (1085mbsl) to further understand magnetic sediment provenance and palaeocurrent evolution on the west Iberian margin dating back to ~416 ka. The gradient of IRM acquisition curves, shape of hysteresis loops, and marked decrease in magnetic susceptibility at ~580°C indicate that magnetite is the dominant magnetic phase at Site U1391. At depth, increased contributions of a higher coercivity component are seen at intervals where the concentration of magnetic material is low. FORC diagrams indicate the presence of a narrow ridge elongated along the Bc axis consistent with a higher coercivity component observed in IRM acquisition data. Magnetic grain size proxy (k_ARM/k) records from Site U1391 also show a significant difference in pattern of variability at depth. After ~130 ka k_ARM/k closely follows relative sea level, however prior to ~130 ka there is higher frequency variability with apparent coarser magnetic grain size, suggesting the higher coercivity component could have resulted from diagenetic processes. This is particularly apparent during warm intervals where magnetic material concentration is low (MIS 7, 9 and 11). This behaviour differs from that observed at either Site U1385, or in the younger portion of the record at Site U1391. We infer that the intervals of diagenetically effected sediments at U1391 could have resulted from increased productivity, vertical migration of the Mediterranean outflow water and associated changes in bottom water ventilation. Further understanding of sediment composition, redox conditions, transport and provenance through the last few glacial cycles underpins much of the other palaeoclimatic investigation at these sites. Results from our analysis of rock magnetism will be used to guide the reconstruction of reliable relative palaeointensity records from the Iberian Margin sediments to assess past geomagnetic changes in the region.

How to cite: Nichols, M., Xuan, C., Hodell, D. A., Richter, C., Acton, G. D., and Wilson, P. A.: Environmental and rock magnetic investigations into provenance and processes of west Iberian margin sediments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18890, https://doi.org/10.5194/egusphere-egu2020-18890, 2020.

Magnetotactic bacteria (MTB) represent a group of microorganisms with the ability to orient and swim along geomagnetic field lines. They can synthesize magnetosomes through the biomineralization processes. Previously studies have reported that some species of protozoa can graze MTB and accumulate magnetosomes in the cells. Here, we characterize a slightly magnetically responsive MTB-grazing ciliate from the intertidal sediment of Huiquan Bay. According to molecular biological information, the ciliate is tentatively identified as Uronemella parafilificum. Using transmission electron microscopy, we observed that two to four different shapes of magnetosomes were randomly distributed within this ciliate. Energy-dispersive X-ray spectroscopy and high-resolution transmission electron microscopy images of them were consistent with magnetite. Although the same shapes and components of magnetosomes were also detected in MTB occurred in the same environment, the size of them was larger than that in ciliates. The results suggest that this ciliate species is capable of grazing and ingesting different types of MTB. These data reveal broad diversity and wide distribution of magnetically responsive protozoa and provide us more possibilities for researching the origin of magnetoreception in eukaryotes.

Keywords: ciliate, magnetotactic bacteria, magnetosome, graze, ingest.

How to cite: Si, C., Hongmiao, P., Kaixuan, C., Wenyan, Z., Yicong, Z., and Tian, X.: Characterization of a magnetotactic bacteria-grazing ciliate in sediment from the intertidal zone of Huiquan Bay, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6234, https://doi.org/10.5194/egusphere-egu2020-6234, 2020.

Paleoenvironmental reconstructions from three mountaineous lakes located in northern Iberia are compared and completed with classical magnetic analyses in order to detect the influence of different processes on the record and preservation of magnetic properties. The lakes are located in the Cantabrian Mountains, Enol Lake, and in the Pyrenees, the Marboré Lake and Basa de la Mora Lake and share a similar composition of their catchment areas, dominated by limestones. They present other different characteristics, such as in the organic matter content, being Enol the one with the highest organic carbon values. Redox indicator (Mn/Fe) is higher and more variable in Basa de la Mora Lake, whereas in Enol and Marboré Lakes steadily increases towards the top of the sequences. New and revisited results from sedimentary cores unravel the significance of the magnetic changes respect to the geochemical and sedimentological variations found in the geological record.

The magnetic mineralogy present after analyses done in discrete samples (less than 500 mg) is magnetite in all samples, due to a sharp decrease at 120 K (Verwey crystallographic transition) and 580ºC (Curie temperature of magnetite) in the thermomagnetic curves performed in the MPMS and the Curie balance respectively. No indication of neither pyrrhotite (phase transition at 35 K) nor siderite is observed. The high temperature thermomagnetic analyses show the presence and creation of magnetite during heating, see an increasing of induced magnetization forming a broad peak above 450ºC in the heating curve. In addition, a subtle change in the induced magnetization is observed at around 300ºC. All analyses related with coercivity indicate the predominance of low coercitive minerals (“soft”) as magnetite is.

The combination of geochemical, sedimentological and magnetic proxies suggest that in Enol Lake the magnetic signal may be dominated by the formation of new minerals in relation to redox processes favored by the higher presence of organic matter (6%organic content), whereas in Marboré Lake, the increase of the magnetic signal toward the top of the sequence seems related to the oxic environment and the preservation of magnetite, since this lake is ultra-oligotrophic. In Basa de la Mora Lake, the source rock seems to play a role in the magnetic signal of the sequence.

These results indicate that diagenesis and changes in the redox conditions alter the concentration of magnetic minerals during the Late Pleistocene and Holocene and underlines their value as environmental and paleoclimate archives.

Acknowledgements

Funding for this research was provided by the Spanish Inter-Ministry Commission of Science and Technology through MEDLANT (CGL2016-76215-R) and DINAMO 3 (Ref CGL2015-69160-R) projects and by the European Commission (EFA056/15 REPLIM). The Institute for Rock Magnetism (IRM), the Instrumentation and Facilities program of the National Science Foundation of the Earth Science Division and the University of Minnesota are acknowledged for supporting visits and the free use of the facilities at the IRM, together with the both easy-going and expert guidance from the IRM staff.

How to cite: Oliva-Urcia, B., Moreno, A., and Valero-Garcés, B.: Standard magnetic properties in three mountain lakes of northern Iberia, ¿what is the influence of the major environmental processes?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8417, https://doi.org/10.5194/egusphere-egu2020-8417, 2020.

Soil contamination by heavy metals has become a severe problem in many parts of the world, affecting people and other living organisms. The anisotropy of magnetic susceptibility (AMS) was successfully used to track deformation and flow directions in rocks and unconsolidated sediment, however, it has been very rarely applied to soils. In this study, magnetic susceptibility, electromagnetic (EM) methods and AMS of soils around three historical mining areas at the Sudetes Mountains (Poland) were studied. These sites are diversified in terms of exploitation time and type of ore (Zloty Stok – gold and arsenic, Janowa Gora – iron and Szklary - nickel). They were selected in order to examine the spatial spread of contamination from mine tailings, their potential sources and to test the potential use of the AMS to study migration pathways.

Magnetic susceptibility (к), GCM (ground Conductivity Electromagnetic Method) and magnetometric measurements were carried out in situ to get a spatial resolution of the magnetic data. Bartington MS2 magnetic susceptibility meter was used for mapping of к, whereas GCM measurements were made to obtain conductivity distribution from 6 different depth ranges. Magnetometric measurements were conducted with GEM GSM-19T Overhauser Magnetometer integrated with GPS, allowing for measurement of the total magnetic field and its vertical gradient. Moreover, soils samples were taken for further analyses in the laboratory. For AMS measurements, all samples were oriented northward and carefully placed into 8 ccm plastic, non-magnetic cubic boxes to prevent artificial modification of in situ magnetic fabrics. Then, these samples were measured in three mutually perpendicular positions using KLY-5 Kappabridge (Agico).

The highest values of magnetic susceptibility (1-5x10^-3 SI) are observed around nickel tailings, whereas the lowest values (60-120x10^-6 SI) characterise iron mining area. Preliminary results of GCM and magnetometry indicate the occurrence of overlapping anomalies in the studied area. Mapping of in situ magnetic susceptibility shows variability within particular sites. For Szklary, all three methods indicate the presence of the elongated anomaly roughly NE-SW oriented. Although AMS axes of in-phase susceptibility are randomly distributed for all sites, the magnetic fabric created by ferromagnetic minerals (out-of-phase, opAMS) indicate well grouped maximum susceptibility axes mainly oriented NE-SW. There is a clear correlation between mapped anomaly around nickel tailings (Szklary) and opAMS lineation. Outside the anomaly, opAMS directions are oriented SE-NW. For other sites, opAMS is also in line with the results of EM methods. Taking into account these results, as well as landforms and hydrological conditions, it could be concluded that magnetic minerals accompanied with heavy metals, most likely, migrate with subsurface runoff and opAMS is capable of detecting changes in the direction of the pollution spread. However, more study is necessary to fully explain this mechanism.

How to cite: Dudzisz, K., Oryński, S., Górka-Kostrubiec, B., and Klityński, W.: Anisotropy of out-of-phase magnetic susceptibility as a tool for tracking heavy metals pollution: a new approach to environmental magnetism study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-804, https://doi.org/10.5194/egusphere-egu2020-804, 2020.

We studied the magnetic properties and trace element concentrations (Cr, Cu, Fe, Mn, Pb, Ti, V, Zn) of urban topsoils from 111 urban sites in a large REE-Nb-Fe mining and smelting city, Baotou, Inner Mongolia, China. The results show that pseudo-single domain and multi-domain magnetite dominates the magnetic properties of the soil samples, and the magnetic concentration parameters show a large positive anomaly near the Baotou iron and steel works. The average contents of all trace metals exceeded their background level in soils in Inner Mongolia, except for Pb. The spatial distribution and correlation analysis show that magnetic parameters related to the magnetite concentration and Cr, Fe, Mn, Ti, V and Zn show similar trends of variation. In addition, the results of PCA show that Fe, Ti, and V are highly correlated with the magnetic particles derived from the Baotou iron and steel works, tailing dam, chromium plant, and cement plant. In contrast, Cr, Mn, Pb and Zn are derived from both the steel plant and traffic pollution. Using a PMF model, three potential pollution sources are identified: industrial pollution, including the steel works, tailing dam, cement plant and chromium plant, are reflected by χ_lf, χ_ARM, SIRM and SOFT, and they account for 71.2%; traffic pollution is reflected by Pb and Zn and accounts for 9.0%; and natural sources, reflected by χ_fd%, χ_ARM/χ, χ_ARM/SIRM, HARD%, S_-300, S_-100 and Ti, contribute 19.8%. The results are potentially useful for developing control measures for reducing trace metal contamination in soils in Baotou city, and in addition we conclude that a combined magnetic approach and geochemical approach is an effective means for qualitative and quantitative sources apportionment of urban surface soil pollution.

How to cite: Wang, B., Xia, D., and Jia, J.: Source apportionment of soil-contamination in Baotou City (Northwestern China) based on a combined magnetic and geochemical approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3879, https://doi.org/10.5194/egusphere-egu2020-3879, 2020.

The Kupa River basin occupies the west-central part of Croatia and is shared by two neighboring countries (Slovenia, Bosnia and Herzegovina). It is the tributary of the Sava River and meets the latter at Sisak after traversing a distance of 294 km. The Sava River belongs to the Danube River watershed and enters the Danube River at Belgrade (Serbia).      

An extreme barium anomaly in sediments of Kupica and Kupa rivers was discovered during 2003 (Frančišković-Bilinski, 2006). It is result of un-careful mine waste disposal. Therefore this river has a big potential to be used as a “natural laboratory” in the future to study sediment transport processes in rivers, so we repeated sampling on most important locations in 2018, to see which processes happened during that time frame. In the current study, we aim to investigate correlations between magnetic susceptibility (MS) and elemental content of 26 studied elements in the fine sediment fraction (<63 µm) of samples from 2018. MS method is a fast and cheap method, which can give indication of contamination with some metals, so we aimed to test its suitability on Kupa River sediments. Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) was used to determine the concentration of the studied elements, after sequential extraction procedure (Sakan et al., 2016). Total concentrations of each element were determined as the sum of concentrations determined in each fraction. The same method was applied recently for determination of Ba concentrations in Kupa River sediments by Frančišković-Bilinski et al. (2019).

Correlation analysis was performed to reveal statistical correlations between MS and 26 elements analyzed by ICP-OES. Ten of them showed negative correlation (As, B, Ba, Fe, K, Li, Mg, Na, P, S), while other elements showed positive. Chromium showed excellent correlation with MS (0.91) and is element with the highest correlation to MS. All other elements show much weaker correlation with MS. Element with strongest correlation to MS after Cr is vanadium (0.62), followed by Mn (0.52), Al (0.52) and Cd (0.50). All other elements have rather weak correlation with MS, among which highest are those of Sr (0.45), Zn (0.35), Be (0.28), Co (0.27), Pb (0.27) and Ti (0.26). Rest of elements has very low correlation.

Our research confirmed that MS is not suitable to study barium contamination in sediments, as they have low negative correlation (-0.18). Low negative correlation of MS with Fe (-0.12) indicates that MS is not caused by iron minerals in Kupa River sediments. MS values show extreme value at the same location as does Cr, which is bound to residual fraction of yet not known mineral composition.

Earlier data of Frančišković-Bilinski (2007) show that SiO₂ group of minerals predominate in Kupa sediment at Pokupsko, where MS and Cr have highest values.

Rererences:

Frančišković-Bilinski, S. (2006). J.Geochem.Explor. 88, 1-3, 106-109.

Frančišković-Bilinski, S. (2007). Fresenius Env.Bull. 16, 5, 561-575.

Frančišković-Bilinski S., Bilinski, H., Sakan, S., Đorđević, D., Popović, A. (2019). SGEM Conference proceedings, 19, 3.1., 73-80.

Sakan, S., Popović, A., Anđelković, I., Ðorđević, D. (2016). Env.Geochem.Health 38, 855–867.

How to cite: Frančišković-Bilinski, S., Sakan, S., Đorđević, D., Popović, A., Škrivanj, S., and Bilinski, H.: Investigation of correlations between magnetic susceptibility and elemental content in the Kupa River sediments (Croatia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3602, https://doi.org/10.5194/egusphere-egu2020-3602, 2020.

The Sterkfontein caves system in the Cradle of Humankind (South Africa) is a karstic environment resulting from a ghost-rock karstification process that developed in the Malmani dolomite formation presenting interlayered more resistant chert layers (Bruxelles, 2017). This process of karstification occurs under low hydrodynamic conditions leaving in place a residual highly porous altered rock, which preserves the structure of the initial bedrock, and which is called “ghost rock”. Due to its high porosity and in the presence of water, ghost-rocks can represent a potential habitat for microorganisms, ubiquitous on and in Earth, with metabolisms mainly relying on dissolution or precipitation processes of minerals. Thus some secondary mineralizations of manganese and iron oxides, found associated to microorganisms in cave systems, could have a biological origin (Banerjee and Joshi, 2012). To better characterize the alteration phases and understand the process of karstification and the potential role of microorganisms and biofilms, samples including dolomitic bedrock, cherts and ghost-rocks were collected at the Sterkfontein cave system. We report here magnetic properties of powdered samples (low-field susceptibility, hysteresis parameters, saturation magnetization and MPMS measurements). In parallel to these magnetic measurements, XRD analyses, FTIR spectroscopic analyses and microscopic observations (SEM) have been realized in order to better characterize the mineralogy of bedrock and secondary phases and to better constrain the alteration processes. We observe that the ghost-rock is mostly composed of quartz and oxides. The magnetic phases detected are mainly hematite and goethite, precipitated on the quartz grain boundaries. These first observations could be explained by a total dissolution of the main bedrock (dolomite) and a partial chemical alteration and mechanical erosion of cherts. To go further, an additional microbial ecology study in the cave system is needed to better constrain the role of microorganisms in the precipitation of oxides detected.

Banerjee, S., Joshi, S.R., 2013. Insights into Cave Architecture and the Role of Bacterial Biofilm. PNAS, India Section B: Biological Sciences 83, 277–290.

Bruxelles L., 2017. Des fantômes et des hommes. Le rôle de la fantômisation dans la formation des karsts à homininés d’Afrique du Sud. Karstologia 69, 1–8.

How to cite: Isambert, A., Watkinson, M., Pisapia, C., Gérard, E., Menez, B., Maire, R., and Bruxelles, L.: Magnetic characterization of ghost rocks from the Sterkfontein cave (South Africa): are iron oxides linked to biological activity? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7344, https://doi.org/10.5194/egusphere-egu2020-7344, 2020.

Multicellular magnetotactic prokaryotes (MMPs) are a group of aggregates composed of 10-100 gram-negative cells synthesizing intracellular magnetic crystals. Two morphotypes of MMPs have been identified, including several species of globally distributed spherical mulberry-like MMPs (sMMPs), and ellipsoidal pineapple-like MMPs (eMMPs). We recently collected MMPs from the intertidal zone of Huiquan Bay, Qingdao. Optical microscopy showed that there were two types of MMPs in the area, including sMMPs and eMMPs. We observed the size of eMMPs was 9.25 ± 0.79 × 7.48 ± 0.79 μm (n = 24), and the average diameter of sMMPs was 5 ± 0.66 μm (n = 24). Transmission electron microscopy showed that these MMPs contained three sizes of bullet-shaped crystals in parallel chains or clusters. The length and width ratios of the sizes of these magnetosomes were 4.16±0.64, 3.07±0.29 and 2.51±0.36 (n=44). The 16S rRNA gene of micromanipulation-purified sMMPs and eMMPs were cloned and sequenced. Phylogenetic analysis based on the 16S rRNA gene sequence revealed that 565 sequences of MMPs belonged to 16 OTUs, affiliated with Deltaproteobacteria. Four OTUs displayed >3.48% sequence divergence and two OTUs displayed >7.26% sequence divergence with respect to previously reported MMPs. This result suggested that they represented six new species and two novel genera. These results indicated that the intertidal zone of Huiquan Bay has a high diversity of MMPs that bio-mineralize iron crystals and play an important role in iron cycling in such a complex environment. These observations provide a new perspective of the diversity of MMPs in general and expand knowledge of the occurrence of MMPs in the Huiquan Bay.

Keywords: Intertidal zone, Diversity, Multicellular magnetotactic prokaryotes (MMPs),  16S rRNA gene, Magnetosomes

How to cite: Yicong, Z., Wenyan, Z., Hongmiao, P., Kaixuan, C., Si, C., and Tian, X.: Diversity of multicellular magnetotactic prokaryotes in the intertidal zone of Huiquan Bay, Qingdao, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6208, https://doi.org/10.5194/egusphere-egu2020-6208, 2020.

Magnetotactic bacteria (MTB) biomineralize intracellular magnetic nanocrystals and can use the geomagnetic field to navigate towards specific microenvironments in water columns and sediments. MTB are a model system to study the mechanisms of microbial magnetoreception and biomineralization. The majority of MTB identified so far are from environments with pH values near neutral and at the normal range of temperature. MTB from extreme environments, such as hot springs, has not been observed and described until recently. However, our knowledge on extremophilic MTB is still very limited. Here we report the identification and characterization of various MTB in Tengchong hot springs, China, with a temperature range of 41.3-69.5 °C and a pH range of 7.1-8.6. Although MTB are diverse in cell morphology, they all form bullet-shaped magnetite magnetosomes organized into either one chain or multiple bundles of chains. Through genome-resolved metagenomics, we have reconstructed five genome bins of hot spring MTB that are all affiliated within the Nitrspirae phylum. Genomic analyses and metabolic reconstructions are now in progress. These results will help to better understand the extremophilic MTB and may shed new lights on the origin and evolution of microbial magnetoreception and biomineralization.

How to cite: Liu, J., Zhang, W., Yuan, F., Pan, Y., and Lin, W.: Magnetotactic bacteria in Tengchong hot springs, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12310, https://doi.org/10.5194/egusphere-egu2020-12310, 2020.

With the goal to provide the new magnetostratigraphic investigations of the Miocene marine deposits of the Black Sea Basin the forty-four oriented hand blocks of the Cop-Takyl section (45°N, 36°E, Kerch peninsula, Crimea) were collected during summer 2019 field work. The section is composed mainly of clays, has a total thickness of ~ 53 m and covered the Tarhanian stratigraphic interval. Standard paleomagnetic measurements have been performed to establish a new magnetostratigraphic record for the Cop-Takyl section. The composition of the ferromagnetic fraction was examined using dependences of magnetic susceptibility on temperature and saturation magnetic moment on temperature. These thermo magnetic analyzes showed that the low concentration of magnetite is the main carrier of the natural remanent magnetization NRM. Coercivity of remanence Bcr values, determined from backfield demagnetization measurements, range between ~34 and 91 mT. The structure of the magnetite grains is mainly pseudo-single domain. In order to determine true NRM directions, we studied the anisotropy of magnetic susceptibility. The rock sample possesses a planar anisotropy, which is a characteristic of the normal sedimentary rocks. The alternating field demagnetization of the samples (three duplicates from each level) was used for obtaining NRM vector angle elements. Demagnetization results were analyzed using orthogonal plots and stereographic projections. Polarity components were isolated in most samples between 15-60 mT. The values of the declination D and inclination I of the NRM satisfactory agree for all three duplicates from each level. This allows to average angle elements and construct curves of I and D variations over the thickness of the section. New paleomagnetic data of the Cop-Takyl section will used for assessing the effect of astronomical cyclicity on sedimentation processes. This work was supported by Russian Science Foundation, project № 19-77-10075.

How to cite: Filina, E., Pilipenko, O., and Rostovtseva, Y.: Paleomagnetic investigation of the Tarhanian deposits of Cop-Takyl section (Kerch peninsula, Crimea), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8524, https://doi.org/10.5194/egusphere-egu2020-8524, 2020.

We present the combining results of 6-year comprehensive studies, which have been done on fifteen key sections the Permian-Triassic red beds located within the Russian Basin (East European platform). In our presentation we discuss some aspects of paleomagnetism and rock magnetism of sediments, such as inclination shallowing, anisotropy of magnetic susceptibility and so on. The main achievement of our work is getting the new mean Permian-Triassic paleomagnetic pole for the East European platform as well as calculation of its Late Permian and Early Triassic poles. We also present new version of the magnetostratigraphic correlation of studied sections within the Russian Basin and with Global Geomagnetic Polarity Time Scale, taking into account obtained results of U-Pb LA-ICPMS dating of detrital zircons and paleontological constraints. One of the most intriguing conclusions of our work is a suggestion about the existing of quite long-lasting time interval of non-GAD (Geocentric Axial Dipole) configuration of the Earth's magnetic field close to the Permian-Triassic boundary, evidences of which we have found in some of studied P-Tr sections. This study is supported by the grant of the RFBR (18-05-00593).

How to cite: Fetisova, A., Veselovskiy, R., Golubev, V., Chistyakova, A., Arefiev, M., and Bagdasaryan, T.: Paleomagnetism and magnetostratigraphy of the Permian-Triassic red beds, East European Platform, Russia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17434, https://doi.org/10.5194/egusphere-egu2020-17434, 2020.

The Early Cretaceous was dominated by greenhouse conditions and increases in ocean crust production rate, with critical climate, geography and oceanography changes and abrupt shifts in redox conditions in the oceans. Prior to the Aptian, regarding the Earth’s magnetic field, a high rate of polarity reversals dominated. However, thereafter, a period of polarity stability, known as the Cretaceous Normal Polarity Superchron (CNPS), was established for 34 Myr. Although, there are debates on the causes and consequences of these extreme events. The exact behavior of the geomagnetic field in this period is still poorly understood, and data from volcanic and sedimentary rocks are conflicting. The biostratigraphy data from the sedimentary succession from the Aptian-Albian interval in the Sergipe-Alagoas Basin (Brazil) are rare and correlations are weak with Tethyan realm. Since some of the major reservoirs of the terrestrial portion of the Sergipe-Alagoas basin are from Aptian-Albian ages the lack of age models brings difficulties to the oil industry. Magnetic parameters such as magnetic susceptibility, ARM, IRM, and magnetostratigraphy data were obtained with a resolution of 25 cm in the Core SER-03 from Sergipe-Alagoas Basin. The entire section varies 4 Myr, including the Aptian-Albian boundary. Here, we present preliminary environmental magnetism and magnetostratigraphic interpretation for this core. Therefore, these data will aid to develop an age model framework in order to assist this uncovered region and for future comparisons with Tethyan realm.

How to cite: Gewehr de Mello, R., Fauth, G., Guilherme Diemer Kochhann, K., Gonsalves Leandro, C., Daniel Rodrigues Bruno, M., Krahl, G., Marcanth Lopes, F., and Francisco Savian, J.: Magnetostratigraphy and environmental magnetism of the Aptian-Albian boundary of sedimentary core from Sergipe-Alagoas Basin: preliminary results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17533, https://doi.org/10.5194/egusphere-egu2020-17533, 2020.

The Ediacaran Period (635-542 Ma) witnessed a series of extraordinary events. It arises with the end of the Marinoan Glaciation and deposition of worldwide enigmatic cap carbonate deposits. This abrupt shift in paleoclimatic conditions coincides with major fluctuations in the  isotope ratios of carbon and sulfur, and with significant changes in the concentration of redox-sensitive elements in marine sediments. The Ediacaran is also a period marked by rapid changes in geomagnetic polarity. Magnetostratigraphy may therefore provide high-resolution correlation between Ediacaran successions worldwide. Here, we combine stratigraphy logs, carbon isotopes and magnetostratigraphy on the Avellaneda Formation (590-560 Ma) which at the Rio La Plata Craton, eastern Argentina. We investigated two drill cores (TSE-34 and TSE-7) with a 0.3-0.7 m resolution covering the entire Avellaneda Formation, corresponding to 98 standard specimens (25 mm in diameter). The basal contact of the Avellaneda Formation with the underlying mudstone rocks from Loma Negra Formation (~ 590 Ma) is present in both cores. The upper contact with the Alicia Formation, only observed in TSE-34 core, is transitional. The TSE-7 displays an erosional contact between Avellenda and Cerro Negro Formations (~ 560 Ma). After stepwise thermal demagnetization up to 600°C, almost all samples provided a characteristic magnetization between 350°C and 600°C, therefore Ti-poor magnetite or titanohematite is likely the main carrier of the stable remanence in these rocks. A high-temperature, dual-polarity component is persistent and coherent in the two drill cores. The base of the unit is marked by normal polarity, followed by a reverse interval, followed by persistent normal polarity across to the upper part of the Avellaneda Formation. This magnetostratigraphic framework, together with the carbon isotope signal, will be compared with results recently obtained for potentially coeval successions in China, Canada and United States.

How to cite: Afonso, J., Trindade, R., Franceschinis, P., and Rapalini, A.: Magnetostratigraphy and Carbon isotopes of Ediacaran Avellaneda Formation, Rio de La Plata Craton, Argentina, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1162, https://doi.org/10.5194/egusphere-egu2020-1162, 2020.

Presentation of magnetic hysteresis data has long been a standard component of paleomagnetic, rock magnetic, and environmental magnetic publications. It has become standard practice to correct the high-field slope of hysteresis loops using a line fit through data points between 70 and 100% of the maximum applied field. Implicit to this approach is that the magnetization is considered saturated if the loop is closed at the point at which 70% of the maximum applied field is reached. This approach treats hysteresis overly simplistically because it assumes that the irreversible magnetization, which is what gives rise to hysteresis, is the only relevant part of the magnetization. The reversible component of magnetization is also important; this component approaches saturation non-linearly following the so-called law of approach to saturation, where the magnetization continues to increase due to rotation of magnetic moments parallel to the applied field, which is resisted by the anisotropy of the material. Various mathematical formulations exist for the law of approach to saturation. Use of this law is not straightforward for geological materials because terms in the respective equations depend on the material analysed and must be approximated, which becomes problematical for samples with mixed magnetic components. Alternatively, hysteresis loops can be fitted and extrapolated to high fields to estimate the approach to saturation using hyperbolic functions. We illustrate issues associated with linear slope correction at 70–100% of the maximum applied field by comparing hysteresis parameters estimated using approach to saturation fitting with various maximum applied fields. In all cases, for maximum fields used typically in mineral magnetic studies (e.g., 1 T), conventional slope correction underestimates the saturation magnetization M_s and overestimates the ratio of the saturation remanent magnetization M_rs to M_s. Hysteresis loop undersaturation is likely to be widespread in mineral magnetic studies with inadequate slope correction probably causing a large uncertainty in published hysteresis parameters. We recommend routine application of approach to saturation fitting of hysteresis loops, which can help to better estimate M_s and M_rs/M_s, as well as help to indicate whether a maximum applied field is sufficient to achieve magnetic saturation.

How to cite: Zhao, X., Roberts, A., and Heslop, D.: High-field slope correction of hysteresis loops: are we doing it correctly?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13109, https://doi.org/10.5194/egusphere-egu2020-13109, 2020.

Thermal demagnetization furnaces are routine facilities for paleomagnetic studies. The ideal thermal demagnetizer should maintain “zero” magnetic field during thermal treatments. However, magnetic field noises, including residual magnetic fields of material and induced fields caused by the heating current in the furnace are always present. The key to making high-performance demagnetization furnace is to reduce the magnetic field noises. By combining efficient demagnetization of shielding and a new structure of heating wire, we have developed a new demagnetization furnace with low magnetic field noises. Repeated progressive thermal demagnetization experiments using specimens that were previously completely thermal demagnetized above their Curie temperature were carry out to explore the effects of field within various types of furnace during demagnetization. These experiment confirm that magnetic field noises in the furnace can have an observable and detrimental impact on demagnetization behavior. Comparison between commercial furnaces and our new design show a notable reduction in the impacts of on thermal demagnetization behavior. The new heating element design and procedure for reducing magnetic field noises represent a significant improvement in the design of thermal demagnetizers and allows for extremely weak specimens to be successfully measured.

How to cite: Qin, H., Zhao, X., Liu, S., Paterson, G., Jiang, Z., Cai, S., Liu, Q., and Zhu, R.: A new furnace for improving thermal demagnetization in paleomagnetism, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6879, https://doi.org/10.5194/egusphere-egu2020-6879, 2020.

Elimination of the geomagnetic field impairs adult hippocampal neurogenesis and cognition

Bingfang Zhang^1,2,4, Lei Wang^3,4, Aisheng Zhan^1,2,4, Min Wang³, Lanxiang Tian^1,2,*, Weixiang Guo^3,4,*, Yongxin Pan^1,2,4,

¹Biogeomagnetism group, Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

²Innovation Academy for Earth Science, Chinese Academy of Sciences, Beijing 100029, China

³State Key Laboratory for Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China

⁴University of Chinese Academy of Sciences, Beijing 100049, China

The geomagnetic field (present-day intensity 25-65 μT, GMF) plays a fundamental role in the survival and evolution of organisms, but organisms including human beings could be exposed to hypomagnetic field (HMF, intensity < 5 μT), e.g., during geomagnetic polarity reversals, some artificial environments without GMF such as magnetic shielded room, and the prolonged periods in deep-space travelling. Previous studies have shown that HMF exposure could trigger central nervous system (CNS) dysfunction-like behavioral effects and influence the cognitive processes of various animals, from insects to human beings. However, the underlying mechanism is still an enigma. In general, adult hippocampus continuously generates new-born neurons throughout animals’ life which are functionally integrated into hippocampal circuits and contribute to memory and learning, and the process of adult neurogenesis has been shown to be strongly influenced by a variety of environment stimuli. Here, we show that long-term HMF exposure markedly attenuates cell proliferation, influences multiple stages of neurogenesis of adult hippocampus, resulting in the impairments of hippocampal neurogenesis and hippocampus-dependent cognition of mice. This study provides new insights into the potential risk of long-term HMF exposure on adult hippocampus in deep space missions.

How to cite: Zhang, B., Wang, L., Zhan, A., Tian, L., Wang, M., Guo, W., and Pan, Y.: Elimination of the geomagnetic field impairs adult hippocampal neurogenesis and cognition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18667, https://doi.org/10.5194/egusphere-egu2020-18667, 2020.