Saturation Isothermal Remanent Magnetization Research Articles

Magnetic properties of muddy sediments on the northeastern continental shelves of China: Implication for provenance and transportation

Mud deposits are widespread in estuaries and on continental shelves, and contain important information regarding interactions between terrestrial and coastal processes. Magnetic properties of muddy sediments from the northeastern continental shelves of China, including shelves close to Korean coasts, were analyzed using bulk and size-fractionated samples to elucidate muddy sediment sources and transport. Types, concentration, and granulometry of magnetic minerals were determined and all samples were found to be dominated by magnetite. Muddy sediments from the Zhemin coast (off the Zhejiang and Fujian coasts) have the highest magnetic susceptibility ( χ) and saturation isothermal remanent magnetization ( SIRM) values, while those from the central and southeastern South Yellow Sea and the western Korea Strait have lower values reflecting lower magnetic mineral concentrations. Single domain ferrimagnetic grains dominate the magnetic particles in the central South Yellow Sea, while superparamagnetic (SP) grains contribute significantly to the magnetic grains in the Bohai Sea. SP and coarse multi-domain (MD) grains dominate magnetic grain assemblages in the North Yellow Sea and along the Zhemin Coast. Rock sediment particle size is not a major factor affecting the magnetic properties of the mud deposits in the study area. Rather, terrigenous inputs and hydrodynamic transport processes primarily control the magnetic properties, and sediments from the Changjiang and Huanghe rivers make the most significant contribution. This observation applies to the whole study area, although terrigeneous magnetic mineral concentrations decrease with increasing distance from the river mouths due to both sorting and mixing with other sediments with weak magnetic signatures. Bacterial magnetosomes also play a role in the central South Yellow Sea.

Toward a new < 250 °C pyrrhotite–magnetite geothermometer for claystones

We investigate the effects of burial and moderate experimental heating on claystones from three regions with different degrees of maturation: immature (burial temperature ∼ 40 °C) of Bure Callovo–Oxfordian claystones in the Basin of Paris (France); early mature (burial temperature ∼ 85 °C) of Opalinus Lower Dogger claystones from the Mont Terri anticline in front of the Jura fold belt (Switzerland); and mature to overmature (burial temperature < 170 °C) of Chartreuse Callovian–Oxfordian claystones from Chartreuse Sub-Alpine chains. To have information about the nature of the magnetic assemblage, we perform low-temperature (10 K–300 K) investigation of an isothermal remanent magnetization. In a first set of laboratory heating experiments, we aim to impart a chemical remanent magnetization (CRM) at 95 °C for several weeks in Bure and Opalinus claystones. Thermal demagnetization of the CRM reveals that magnetite is formed by heating the Opalinus claystones while an assemblage of magnetite and iron sulphide is formed in Bure claystones. Further, we document the appearance of a magnetic transition at ∼ 35 K in Bure claystones after heating. We name this transition the P-transition and we propose that it is related to the formation of fine-grained pyrrhotite (Fe 7S 8). The P-transition is also detected in early mature to mature Opalinus and Chartreuse claystones. We conduct additional experimental heating of natural Opalinus claystones. One set of experiments is referred to as short-term heating (1 h) from 100 °C to 200 °C. It is dedicated to an investigation of the effect of short-lived heating processes in geology. A second set of heating experiments is designed to approach burial conditions using a gold capsule. In burial-like experiments, we heated Opalinus claystones from 150 °C to 250 °C for several weeks under a pressure of 100 MPa. In both experiments, we observe a correlative diminution of the pyrrhotite signature at 35 K with increasing temperature. We interpret this trend as the appearance of magnetite. We derive a parameter PM from the warming curve of a saturated isothermal remanent magnetization acquired at 10 K (ZFC). We report on a consistent evolution of PM with temperature in the range of 40 °C to 250 °C, including natural samples, heated samples at 95 °C, and burial-like heated samples. PM first increases between ∼ 40 °C up to ∼ 85 °C, implying that pyrrhotite gradually dominates the magnetic assemblage at low temperature. For temperatures above 85 °C, PM decreases up to 250 °C, implying that the formation of magnetite gradually overshadows the magnetic input of pyrrhotite. PM values obtained from mature to overmature claystones from the Chartreuse are lower than the PM values obtained from the burial-like heated Opalinus claystones, suggesting that the formation of magnetite is driven by kinetics. The continuous trend of the PM parameter suggests that the magnetic properties of pyrrhotite–magnetite claystones can be used to infer paleo-temperatures and we propose to name this geothermometer MagEval.

Geomagnetic relative paleointensity chronostratigraphy of sediment cores from the Okhotsk Sea

We conducted a paleomagnetic study of three piston cores from the central Okhotsk Sea to enable inter-core correlation and age estimation using relative paleointensity of the geomagnetic field, which can provide the basis for paleoceanographic studies in this area. The cores are composed of diatom-bearing dark olive gray silty clay. Magnetic overprints were generally removed by alternating-field demagnetization of up to 10 mT. Magnetic properties reveal no evidence of reductive diagenesis or magnetite dissolution. The anhysteretic remanent magnetization (ARM) was used as a normalizer for relative paleointensity estimations, because there is a smaller coherence between normalized intensity and the ARM than with saturation isothermal remanent magnetization (SIRM). Depths of the three cores were converted to ages by correlating relative paleointensity variations with those from Ocean Drilling Program Site 983, which was selected as a target curve because of its higher resolution than the widely-used Sint-800 paleointensity stack. The age at the bottom of the cores is estimated to be between 360 and 540 ka. Inter-core correlation using relative paleointensity variations reveals that changes in magnetic properties such as magnetic susceptibility and magnetic mineral grain size are not synchronous between the northernmost site and the southern two sites despite their close proximity, which indicates regional differences in paleoenvironmental variations associated with glacial–interglacial changes. Nevertheless, relative paleointensity variations among the three cores are mutually consistent, and agree with other published paleointensity curves, which indicates that our paleointensity records are not influenced significantly by lithological changes.

3H]AL-5848 ([3H]9beta-(+)-Fluprostenol). Carboxylic acid of travoprost (AL-6221), a novel FP prostaglandin to study the pharmacology and autoradiographic localization of the FP receptor.

AL-5848 (5Z,13E)-(9 S,11R,15S)-9,11,15-trihydroxy-5,13-prostadienoic acid) is the carboxylic acid of travoprost (AL-6221), a single (+)-isomer of (+/-)-fluprostenol, an FP-class prostaglandin agonist which lowers intraocular pressure. We have prepared a radioligand from this selective prostaglandin and demonstrated its utility for studying the pharmacology and autoradiographic location of the FP-receptor. Specific [3H]AL-5848 binding (84% of total) was linearly related to bovine corpus luteum tissue concentration and reached equilibrium within 275 min at 23 degrees C. Scatchard analysis of saturation isotherms indicated interaction of [3H]AL-5848 with a single class of high-affinity (dissociation constant, Kd, = 33.8+/-2.9 nM, n = 4) and saturable (Bmax = 37.3+/-3.0 pmol (g wet weight tissue)(-1)) FP receptor-binding sites in bovine corpus luteum. Specific [3H]AL-5848 binding was potently inhibited by the FP-receptor ligands 16-phenoxyPGF2alpha (inhibition constant Ki = 17.3 nM); cloprostenol (Ki = 56.8 nM); 17-phenyl PGF2alpha (Ki = 87.0 nM); AL-5848 (Ki = 52.1 nM); PGF2alpha (Ki = 195 nM); PHXA85 (Ki = 223 nM); (n = 3-11) but very weakly by PGD2, ZK118182, BW245C, PGE2, PGI2 and U-46619. The pharmacology of specific [3H]AL-5848 binding correlated well with the pharmacology of [3H]PGF2alpha binding in the bovine corpus luteum preparation (r = 0.98, n = 14, P<0.0001) and also with functional responses in Swiss 3T3 and rat vascular smooth muscle cells (A7r5) (r = 0.96) expressing FP receptors. Autoradiographic studies revealed high levels of specific FP-receptor binding with [3H]AL-5848 on granulosa cells in the bovine corpus luteum sections, and on longitudinal ciliary muscle, the ciliary process, the iris sphincter and the retina in eye sections from man. These studies show [3H]AL-5848 to be a high-affinity agonist radioligand capable of selectively labelling the FP prostaglandin receptor.

Hallmarks of maghemitization in low‐temperature remanence cycling of partially oxidized magnetite nanoparticles

In environmental, soil, and sediment magnetism, it is important to be able to estimate the degree of oxidation of magnetite grains. We report a new method for finding the oxidation parameter z semiquantitatively from cooling‐warming cycles of room temperature remanences. We measured magnetization M continuously for stoichiometric and partially oxidized magnetites with average grain sizes of 37 and 220 nm during zero‐field cycling of 2.5 T saturation isothermal remanent magnetization (SIRM) from 300 K to 20 K and back to 300 K. Oxidized magnetites were obtained by heating stoichiometric magnetite in air at 100°C, 150°C, and 200°C. In other experiments, SIRM was given at 10 K, and M was monitored during zero‐field warming to 300 K. In the oxidized magnetites, SIRM at first increases in cooling from 300 K and then decreases in approaching the Verwey transition. The hump‐like form is even more pronounced in the warming curves above TV. For maghemite, the fully oxidized end member, we found reversible cooling‐warming curves with no Verwey transition. In partially oxidized grains, consisting of a maghemite surface layer and a largely unoxidized core, a Verwey transition is resolvable up to high degrees of oxidation. Hallmarks of maghemitization include (1) a smeared‐out Verwey transition shifted to lower temperatures when warming 20 K SIRM, (2) a shifted and broadened transition region in both cooling and warming of 300 K SIRM, and (3) humped cooling and warming curves of 300 K SIRM between 300 K and TV. Property 3 has excellent diagnostic value. It results from the combination of a slowly increasing M of maghemite and the rapid and nonlinear decrease in M of magnetite during cooling and is seen even for the slight initial oxidation of the reduced 37 nm magnetite. Certain properties, such as the change in M in warming from 20 K to TV and the change in initial and final M values in a complete cooling‐warming cycle, are roughly proportional to the oxidation parameter z. However, the proportionality factors also depend on grain size d, which would have to be known independently in order to estimate z.

Application and evaluation of biomagnetic and biochemical monitoring of the dispersion and deposition of volcanically-derived particles at Mt. Etna, Italy

article i nfo Article history: Received 6 August 2009 Accepted 4 January 2010 Available online xxxx Biomagnetic monitoring, using tree leaves as passive surfaces for particle collection, has been shown to be a promising technique for assessing the dispersion and deposition of particles in the context of anthropogenic pollution. By comparing leaves' magnetic properties with trace metal levels measured in the leaves, we here assess the utility of the biomagnetic technique as a sensitive, fast and inexpensive method for assessment of volcanic plume deposition. Samples of sweet chestnut leaves (Castanea sativa) were collected from the area surrounding Mt. Etna volcano in Sicily during the 2008 growing season when the volcano was displaying mild eruptive activity. Previous work has shown that the trace metal concentrations of these leaves show promise as a bio-indicator of volcanic gas, aerosol and ash deposition on the flanks of Mt. Etna. For 2008, ICP- MS analysis of the elemental abundances within the leaves showed that As, Cd, Cu, Mo, Tl, K, B, Al and Co displayed elevated concentrations downwind of the volcanic source, to the E-ESE, but with overall reduced concentrations relative to 2007. Less explosive activity than 2007 and a broader, more easterly wind field may have distributed the volcanic plume over a wider area, both of which would account for reduced trace element concentrations in 2008. Correspondence of elevated concentrations in both years (2007 and 2008) with their respective wind fields suggests that plume deposition is the controlling factor rather than variability in the soils and that these leaves do indeed have potential as bio-indicators of the plume's dispersion. Magnetic analysis of the leaves shows that the spatial distribution of saturation isothermal remanent magnetisation (SIRM) and magnetic susceptibility (χlf) values display a strong correlation with the wind-influenced plume transport direction for 2008, with elevated concentrations of magnetic minerals on the eastern flanks, in broad agreement with the ICP-MS data. This spatial distribution provides further evidence of plume variability as the main control on the concentrations of magnetic particles on the leaf surfaces and on elemental uptake by the tree and suggests that biomagnetic monitoring may also hold promise as a method of assessing the dispersion and impacts of volcanic plumes. The dominant magnetic mineral on the leaf surfaces is a magnetite-like mineral (contributing >90% of the SIRM), of coarse, multi- domain (MD) grain size (∼ 5t o 15 μm). A volcanogenic source is most likely, as magnetites from anthropogenic sources are typically an order of magnitude smaller in grain size (∼0.1-1 μm). These new results from the use of environmental magnetism on leaves, in a volcanically-affected region, suggest that biomagnetic monitoring offers a new, sensitive and rapid means for the assessment of volcanic plume deposition over wide areas.

Demagnetization of terrestrial and extraterrestrial rocks under hydrostatic pressure up to 1.2 GPa

We carried out hydrostatic pressure demagnetization experiments up to 1.24 GPa on samples of terrestrial and extraterrestrial rocks and minerals of different lithologies as well as on synthetic samples. The magnetic remanence of samples was measured directly under pressure using a non-magnetic high-pressure cell of piston-cylinder type that was inserted into a high sensitivity SQUID magnetometer. In order to bring light on the pressure demagnetization effect, we investigated 50 samples with different magnetic mineralogies, remanent coercivities ( B cr) and hysteresis parameters. The samples consisted of pyrrhotite-, magnetite- and titanomagnetite-bearing Martian meteorites, taenite-, tetrataenite- and kamacite-bearing ordinary chondrites and pyrrhotite-bearing Rumuruti chondrite; magnetite- and titanomagnetite-bearing basalts, andesites, ignimbrites, obsidians and granites; a variety of pyrrhotite- and hematite-bearing rocks and minerals (jasper, schist, rhyolite, radiolarite); samples of goethite and greigite as well as synthetic samples of dispersed powders of magnetite, hematite, pyrrhotite and native iron set into epoxy resin. Under hydrostatic pressure of 1.24 GPa, applied in a low magnetic field (<5 μT), the samples lost up to 84% of their initial saturation isothermal remanent magnetization (SIRM) without any changes in their intrinsic magnetic properties. We found that the efficiency of the pressure demagnetization is not exclusively controlled by the magnetic hardness of the samples ( B cr), but that it is strongly dependent on their magnetic mineralogy. For a given magnetic mineralogy the resistance to hydrostatic pressure is roughly proportional to ln( B cr). It was shown that there is no simple equivalence between pressure demagnetization and alternating field demagnetization effects. The pressure demagnetization was shown to be time-independent but repeated application of the same pressure level resulted in further demagnetization.

Anthropogenic magnetic particles and heavy metals in the road dust: Magnetic identification and its implications

Magnetic properties of road dusts in the East Lake area in Wuhan, China, were measured and compared with the results of heavy metal analyses in order to delineate the sources of pollutants. A total of ninety-seven dust samples were collected spatially from four segments with different traffic density and field settings from the roads encircling the lake. Thermomagnetic and hysteresis measurements revealed that the dominant magnetic carrier is coarse-grained magnetite. Correlations between magnetic parameters and element concentrations with traffic density and distances to the industrial region revealed that elements Cu, Ni and Fe mainly originate from vehicle traffic, which is also the major source of coarser magnetic particles (e.g., pseudo-single-domain/multi-domain (PSD/MD) grains), while element Pb and the smaller grains such as single-domain (SD) magnetic particles mainly originate from industrial emissions. The ratio between anhysteretic remanent magnetization and low-field magnetic susceptibility (ARM/ χ lf) can be employed as an indirect indicator for Cu, Fe and Ni emissions resulting from vehicle traffic. Due to the intermixture of elements from different sources, the element concentrations are not conclusive about the pollution source. A linear correlation between magnetic concentration-related parameters (e.g., ARM and saturation isothermal remanent magnetization, SIRM) and the concentrations of major elements (e.g., Cu, Co, Fe, Mn, Ni and V) suggests that they can be used as a proxy for heavy metal pollution. Road dusts in four segments show different magnetic characteristics, indicating various influxes of anthropogenic magnetic materials from vehicle traffic and industrial plants due to the different traffic loads and field settings. These results suggest that magnetic measurements can serve as an efficient complementary tool for the routinely employed geochemical methods to map the heavy metal pollution and trace the sources of pollutants in the road dust.

Magnetic Properties of Street Dust: A Case in Xi'an City, Shaanxi Province, China

AbstractSystematic analysis of magnetic characteristics of the street dust from Xi'an city indicates high concentration of magnetic minerals corresponding to the high values of magnetic susceptibility (χ), anhysteretic susceptibility (χARM) and saturation isothermal remanent magnetization (SIRM). The value of χ is positively correlated to the intensity of human activity and the value of χARM and SIRM is determined by the intensity and the magnetic mineralogy. The к‐T curve and the IRM acquisition curve indicated that the samples were dominated by ferromagnetic minerals, such as magnetite and maghemite, as well as some iron, the relative concentration of the iron might be related to the variety of the human activity: the iron pollution is mainly due to the human flow rather than pure traffic pollution and metallurgical industry. From the King‐plot and the Dearing‐plot we can conclude that the most magnetic domains of the magnetic minerals are pseudo‐single domain and multidomain. Our results suggested that magnetic measurements could be used to identify the varieties and sources of pollutants in street dust, and as the potential tools for monitoring and classifying the pollution.

Relationship between magnetic parameters and heavy element contents of arable soil around a steel company, Nanjing

Magnetic parameters and element contents were determined in core NJ008 collected from the uppermost ca. 40 cm in a steel company in southwest Nanjing. The results showed that magnetic susceptibility (χ), saturation isothermal remanent magnetization (SIRM) and anhysteretic remanent magnetization (ARM) were enhanced in the uppermost 20 cm, with a mean magnetic susceptibility value of 112.5×10−8 m3 kg−1. Below 20 cm, χ decreased sharply with a mean value of 27.8×10−8m3 kg−1. Low-coercivity minerals such as magnetite dominate in arable soils, while the relative content of antiferromagnetic minerals increases below 20 cm. Heavy metals (Ni, Cu, Fe, Pb, V, and Zn) have similar vertical trends as χ. Principal component analysis reveals common high loadings of the same factor for magnetic concentration parameters ( χ, ARM, and SIRM) and elements (Ni, Cu, Fe, Pb, V, and Zn) with an excellent linear correlation (0.69⩽R⩽0.98) between them. Magnetic susceptibility of paddy soil core NJ013, which had the same parent material as NJ008 but was far from pollution sources, showed stable values of magnetic concentration parameters along the whole core. Absolute values correspond to the so-called magnetic background value (below 20 cm) of NJ008. This indicates that pesticide and fertilizer had little effect on magnetic signals of the upper part of core NJ008 and the extremely enhanced magnetic concentration parameters originate from the steel company emission. Although, the arable soil does not reveal the pollution history and transportation due to annual ploughing, the significant linear relationship between magnetic concentration parameters and heavy metal contents suggests that magnetic parameters can serve as a proxy for quickly detecting soil metallic pollution and estimating the extent of contamination.

Hysteretic Gas Sorption in a Microporous Metal–Organic Framework with Nonintersecting 3D Channels

AbstractA permanently porous metal–organic framework (MOF) based on infinite chains of metal ions and angular dicarboxylate ligands was synthesized, and its unusual gas sorption properties were characterized. Zn2+ ions react with 2,7‐ndcH2 (2,7‐naphthalenedicarboxylic acid) to produce a double‐walled framework, [Zn(2,7‐ndc)]. The porous MOF possesses narrow channels in three perpendicular directions. Gas sorption studies using Ar, CO2, H2, N2, and O2 at various temperatures reveal that saturation isotherms show a stepwise adsorption and hysteresis loops that are highly unusual features for microporous materials. The unexpected gas sorption behavior of the microporous MOF is due to the unique arrangement of the pore channels and their narrow passages comparable to the critical dimensions of adsorptive gases. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2010)

Magnetic properties of street dust from Chibi City, Hubei Province, China: Its implications for urban environment

Magnetic measurements and heavy metal analyses were performed on street dusts from the main urban area of Chibi (赤壁) City, Hubei (湖北) Province, China. Results revealed that a PSD/MD (pseudo-single-domain/multi-domain) magnetite-like phase dominates the magnetic phases of the street dust. Concentration-related magnetic parameters, such as magnetic susceptibility (χ), anhysteretic remanent magnetization (ARM), and saturation isothermal remanent magnetization (SIRM) of samples increased in the main roads but appeared lower in the landscape area of the Lushui (陆水) Lake and closely correlated with the concentration of heavy metal Fe, Cu, and Co, and the correlation coefficients are 0.786 for Fe-χ, 0.548 for Cu-χ, and 0.580 for Co-χ, respectively. However, much strong correlations between SIRM and the concentrations of heavy metal suggest that SIRM is a better indicator for heavy metal pollution in the street dust in the study area. The magnetic particles in the street dust are mainly derived from anthropogenic activities, such as vehicle emissions, abrasion of tires, coal combustion, cement works, and building materials. These results make it possible to use magnetic techniques as simple, rapid, and nondestructive tools for assessing the heavy metal pollutions in urbanization process.

Environmental magnetic responses of urbanization processes: evidence from lake sediments in East Lake, Wuhan, China

SUMMARY We present a study on the environmental magnetic response to urbanization processes from nine sediment cores from East Lake in Wuhan, China. The concentration of magnetic particles, heavy metals and organic matter in the upper 2–18 cm of the sediment cores have been significantly elevated due to the input of coarse magnetite grains from industrial (e.g. power generation and steelmaking) and other anthropogenic activities (e.g. vehicle emissions). Concentration-related magnetic parameters, such as magnetic susceptibility (χ), saturation isothermal remanent magnetization and anhysteretic remanent magnetization, are significantly correlated with concentration of heavy metals and organic matter, for example, Pearson's correlation coefficients are 0.921 for χ-Cu, 0.660 for χ-Pb and 0.848 for χ-loss-on-ignition, respectively. The magnetic properties of the lake sediments document the pollution history caused by human impact on the lake catchment during urbanization. The environmental quality of the lake was fairly good before the 1960s. Magnetic, heavy metal and organic matter contents of the sediments were low and relatively constant, which indicates relatively stable natural inputs from the lake catchment. Pollution trends since the 1960s are reflected in downcore magnetic property variations of the lake sediment. The concentration of magnetic particles in the lake sediments started to increase since 1957, when the Wuhan Iron and Steel Company and the Qingshan Thermal Power Plant, which are located upwind of the lake, were built and put into production. Lake pollution was further aggravated since the acceleration of industrialization and urbanization in East Lake area in the 1980s, which is verified by the elevated concentration of heavy metals and organic matter in the sediments. The magnetic mineral concentration in the lake sediment increased continuously until it peaked in the 1990s and has remained a high level since then. These results suggest that magnetic properties respond sensitively to environmental status, and that the magnetic properties of sediments can provide an excellent record of the industrial and anthropogenic history in an urban lake catchment.

Geochemical identification of impactor for Lonar crater, India

Abstract— The only well‐known terrestrial analogue of impact craters in basaltic crusts of the rocky planets is the Lonar crater, India. For the first time, evidence of the impactor that formed the crater has been identified within the impact spherules, which are ?0.3 to 1 mm in size and of different aerodynamic shapes including spheres, teardrops, cylinders, dumbbells and spindles. They were found in ejecta on the rim of the crater. The spherules have high magnetic susceptibility (from 0.31 to 0.02 SI‐mass) and natural remanent magnetization (NRM) intensity. Both NRM and saturation isothermal remanent magnetization (SIRM) intensity are ?2 Am2/Kg. Demagnetization response by the NRM suggests a complicated history of remanence acquisition. The spherules show schlieren structure described by chains of tiny dendritic and octahedral‐shaped magnetite crystals indicating their quenching from liquid droplets. Microprobe analyses show that, relative to the target basalt compositions, the spherules have relatively high average Fe2O3 (by ?1.5 wt%), MgO (?1 wt%), Mn (?200 ppm), Cr (?200 ppm), Co (?50 ppm), Ni (?1000 ppm) and Zn (?70 ppm), and low Na2O (?1 wt%) and P2O5 (?0.2 wt%). Very high Ni contents, up to 14 times the average content of Lonar basalt, require the presence of a meteoritic component in these spherules. We interpret the high Ni, Cr, and Co abundances in these spherules to indicate that the impactor of the Lonar crater was a chondrite, which is present in abundances of 12 to 20 percent by weight in these impact spherules. Relatively high Zn yet low Na2O and P2O5 contents of these spherules indicate exchange of volatiles between the quenching spherule droplets and the impact plume.

Environmental magnetism of Pleistocene sediments in the North Pacific and Ontong‐Java Plateau: Temporal variations of detrital and biogenic components

An environmental magnetic study was conducted to investigate temporal variations of the sources of magnetic minerals in the Pacific Ocean using sediment cores of Pleistocene age. The proportion of interacting (I) to noninteracting (N‐I) single‐domain components was estimated from first‐order reversal curve diagrams, and the proportion of middle‐ (M) to low‐ (L) coercivity components was determined from decomposition of isothermal remanent magnetization (IRM) acquisition curves. The I and M components are interpreted to be carried by terrigenous maghemite, while the N‐I and L components represent biogenic magnetite. An inverse correlation between the ratio of anhysteretic remanent magnetization susceptibility (χARM) to saturation IRM (SIRM) and the I/N‐I ratio was confirmed for sediments across wide expanses in the Pacific Ocean. This implies that χARM/SIRM can be used to estimate the relative abundances of biogenic and terrigenous components in sediments. In the North Pacific, the relative abundance of the I and M components increases in glacial periods. Variations of χARM/SIRM and S ratio (S−0.1T) resemble each other and decrease in the same time intervals. These variations reflect increases of terrigenous input in glacial periods as eolian dust. On the Ontong‐Java Plateau in the western equatorial Pacific, on the other hand, minima in χARM/SIRM and S−0.1T occur at glacial‐to‐interglacial transitions, and the relative abundance of the I and M components increases in these periods. Terrigenous material in this region is considered to be transported mainly from the New Guinea and Solomon Islands by the Equatorial Undercurrent. The higher proportion of the terrigenous component at glacial‐to‐interglacial transitions is coeval with carbonate preservation maxima reported from the Ontong‐Java Plateau, suggesting a linkage between the two.

On the statistical analysis of the rock magnetic S-ratio

The S-ratio is a rock magnetic parameter employed to provide a relative measure of the contributions of low and high coercivity material to a sample's saturation isothermal remanent magnetization (SIRM). The current form of expressing the S-ratio involves reporting a single value that represents the relative contribution of the low coercivity material, such as magnetite, to the overall SIRM. Expressing the S-ratio in this form is somewhat misleading, suggesting that the derived values are real numbers held in a Euclidian sample space. In fact, S-ratio data are constrained to a 1-D unit-simplex, meaning that many of the descriptive statistics reported for collections of data, for example, means and standard deviations, are in error because the employed statistical methods are designed for unconstrained data only. A simple example of this problem will be given, followed by a demonstration of how meaningful statistics for the S-ratio can be obtained using the additive-log-ratio transform of Aitchison.

Magnetic properties of micrometeorites

Most micrometeorites are strongly magnetic: the signal of a single micrometeorite may exceed the signal of a weakly magnetized standard sediment sample. Micrometeorites contain abundant magnetite, mostly produced by high‐temperature oxidation during atmospheric entry. In this study, we carried out measurements on 520 micrometeorites (505 melted cosmic spherules, 6 partially melted scoriaceous micrometeorites, and 9 unmelted micrometeorites). The natural remanent magnetization and the saturation isothermal remanent magnetization have been measured, followed by alternating field or thermal stepwise demagnetization. The natural remanent magnetization is in the range of 0.4–300 A/m for cosmic spherules; it is a stable thermal remanent magnetization acquired by quenching in the Earth's magnetic field. The range is 3.8–16 A/m for scoriaceous micrometeorites and 78–525 A/m for unmelted micrometeorites, which may have preserved a preatmospheric magnetization. The magnetic susceptibility is in the range of 0.005–2.9 SI for cosmic spherules and is in the range of 0.06–0.12 SI for scoriaceous and unmelted micrometeorites. Temperature‐dependent susceptibility analyses and thermal demagnetization indicate that magnetite is cation substituted in cosmic spherules. Different populations of magnetite grains may have different degrees of cation substitution within a single micrometeorite. Anisotropy of magnetic susceptibility measurements indicates that micrometeorites are strongly anisotropic (anisotropy degree &gt;15%) and that most have oblate fabrics consistent with the parallel habit of magnetite in barred olivine cosmic spherules.

Persistent inflammatory pain decreases the antinociceptive effects of the mu opioid receptor agonist DAMGO in the locus coeruleus of male rats

Persistent inflammatory nociception increases levels of endogenous opioids with affinity for delta opioid receptors in the ventromedial medulla and enhances the antinociceptive effects of the mu opioid receptor (MOPr) agonist [D-Ala 2, N-Me-Phe 4, Gly 5-ol]enkephalin (DAMGO) [Hurley, R.W., Hammond, D.L., 2001. Contribution of endogenous enkephalins to the enhanced analgesic effects of supraspinal μ opioid receptor agonists after inflammatory injury. J. Neurosci. 21, 2536–2545]. It also increases levels of endogenous opioids that act at MOPr elsewhere in the CNS [Zangen, A., Herzberg, U., Vogel, Z., Yadid, G., 1998. Nociceptive stimulus induces release of endogenous β-endorphin in the rat brain. Neuroscience 85, 659–662]. This study tested the hypothesis that a sustained release of endogenous opioids leads to a downregulation of MOPr in the locus coeruleus (LC) and induces a state of endogenous opioid tolerance. Four days after injection of complete Freund's adjuvant (CFA) in the left hindpaw of the rat, both the magnitude and duration of the antinociception produced by microinjection of DAMGO in the right LC were reduced. Saturation isotherms demonstrated a 50% decrease in MOPr B max in homogenates of the LC from CFA-treated rats; K d was unchanged. Receptor autoradiography revealed that this decrease was bilateral. The decreased efficacy of DAMGO in CFA-treated rats most likely results from a decreased number of MOPr in the LC. Microinjection of the MOPr antagonist D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH 2 (CTAP) in the LC did not exacerbate hyperalgesia in the ipsilateral hindpaw or produce hyperalgesia in the contralateral hindpaw of CFA-treated rats. The downregulation in MOPr is therefore unlikely to result from the induction of endogenous opioid tolerance in the LC. These results indicate that persistent inflammatory nociception alters the antinociceptive actions of MOPr agonists in the CNS by diverse mechanisms that are nucleus specific and likely to have different physiological implications.

East Asian summer monsoon intensity inferred from iron oxide mineralogy in the Xiashu Loess in southern China

The Xiashu Loess, in comparison to the well-studied loess sequences in the Chinese Loess Plateau (CLP), provides a good opportunity for studying East Asian monsoon variations from a southern China perspective. Here we present a study of the iron oxide mineralogy of the Xiashu Loess using integrated geochemical and diffuse reflectance spectroscopy (DRS) measurements as well as magnetic data. Our results show that the free iron oxide (Fe d) to total iron (Fe t) ratio (Fe d/Fe t), hematite (Hm) to goethite (Gt) ratio (Hm/Gt) and saturation isothermal remanent magnetization (SIRM) to magnetic susceptibility ( χ) ratio (SIRM/ χ) all indicate particularly strong summer monsoons during the formation of paleosols PS5 and PS4 (equivalent to Marine Isotope Stage 13 and 11, respectively). However, magnetic susceptibility and Fe d/Fe t are not consistently reliable indicators of summer monsoon intensity for the whole section. Our results indicate that a multi-proxy approach can give a more reliable summer monsoon intensity reconstruction. The summer monsoon shows a cooling trend and a declining of precipitation from 0.5 to ∼0.3 Ma, after which it becomes warmer and wetter towards the top of paleosol PS1 (equivalent to MIS 5). However, PS1 was formed under a relatively cooler temperature and wetter soil conditions in comparison to PS5 and PS4. Such supra-orbital variations in the East Asian summer monsoon superimposed on the effects of glacial–interglacial cycles in southern China are also reflected in the 0.4–0.5 Ma cycle of marine carbon isotopes in the global ocean, possibly indicating a strong link between terrestrial weathering and the global carbon cycle.

Grain size dependence of low-temperature remanent magnetization in natural and synthetic magnetite: Experimental study

Abstract Magnetic measurements at cryogenic temperatures (&lt;300 K) proved to be useful in paleomagnetic and rock magnetic research, stimulating continuous interest to low-temperature properties of magnetite and other magnetic minerals. Here I report new experimental results on a grain size dependence of the ratio (R LT) between a low-temperature (20 K) saturation isothermal remanent magnetization (SIRM) imparted in magnetite after cooling in a 2.5 T field (field cooling, FC) and in a zero field environment (zero field cooling, ZFC). Synthetic magnetite samples ranged in mean grain size from 0.15 to 100 μm, representing nearly single-domain (SD), pseudosingle-domain (PSD), and multidomain (MD) magnetic states. The R LT ratio monotonically increases from 0.58 to 1.12 with the decreasing mean grain size, being close to unity for PSD grains (0.15-5 μm) and smaller than unity for MD magnetite (12-100 μm). The R LT ratio of 1.27 is observed for acicular magnetite characterized by nearly SD behavior. These observations indicate that within the range of ~0.15 to ~5 μm, the low-temperature SIRM may be higher than that expected from “normal” magnetic domain wall displacement. Such a behavior can be caused by the presence of a SD-like component in the magnetization of these grains, which origin, however, is uncertain. The natural rocks containing nearly stoichiometric magnetite manifest a dependence of the R LT ratio on magnetic domain state identical to that observed from synthetic magnetites. Therefore, the comparison of FC SIRM and ZFC SIRM at very low temperatures may allow a crude estimate of magnetic domain state in some magnetite-bearing rocks, such as shallow mafic intrusions or some marine sediments.