Anhysteretic Remanent Magnetization Susceptibility Research Articles

Within-city spatial variations in PM2.5 magnetite nanoparticles and brain cancer incidence in Toronto and Montreal, Canada.

Magnetite nanoparticles are small, strongly magnetic iron oxide particles which are produced during high-temperature combustion and friction processes and form part of the outdoor air pollution mixture. These particles can translocate to the brain and have been found in human brain tissue. In this study, we estimated associations between within-city spatial variations in concentrations of magnetite nanoparticles in outdoor fine particulate matter (PM2.5) and brain cancer incidence. We performed a cohort study of 1.29 million participants in four cycles of the Canadian Census Health and Environment Cohort in Montreal and Toronto, Canada who were followed for malignant brain tumour (glioma) incidence. As a proxy for magnetite nanoparticle content, we measured the susceptibility of anhysteretic remanent magnetization (χARM) in PM2.5 samples (N = 124 in Montreal, N = 110 in Toronto), and values were assigned to residential locations. Stratified Cox proportional hazards models were used to estimate hazard ratios (per IQR change in volume-normalized χARM). ARM was not associated with brain tumour incidence (HR = 0.998, 95% CI 0.988, 1.009) after adjusting for relevant potential confounders. Although we found no evidence of an important relationship between within-city spatial variations in airborne magnetite nanoparticles and brain tumour incidence, further research is needed to evaluate this understudied exposure, and other measures of exposure to magnetite nanoparticles should be considered.

Effect of land use conversion on heavy metals and magnetic minerals on water reservoir riparian soils

Spatial hydrological alterations seem to influence the variability of soil-bound magnetic particles and heavy metals in water reservoir riparian wetlands (RW). To date, applying geochemical analysis with magnetic techniques to assess heavy metal pollution is rarely practiced in RW soils. We studied the magnetic properties and heavy metals, including Cu, Cr, and Zn, of topsoils in RW and the adjacent upland regions (UR, as control) in the Three Gorges Reservoir, China. Potentially elevated low-frequency mass magnetic susceptibility (χLF), anhysteretic remanent magnetization susceptibility (χARM), isothermal remanent magnetism, and all selected heavy metals were found in RW. The grain size of the magnetic minerals was coarser in RW than that in UR. The pollution load index (PLI) of the studied samples was 1.18 ± 0.12 and 1.04 ± 0.21 in RW and UR, respectively. PLI and concentrations of Cu, Cr, and Zn were positively correlated with χLF, χARM, and isothermal remanent magnetism in RW, whereas no clear linkages were observed between PLI and isothermal remanent magnetism in UR. This finding reveals that hydrological alterations increased the magnetic enhancement and heavy metal enrichment in RW. We find that magnetic proxies of soils could trace the concentration of selected anthropogenic heavy metals and their pollution level in RW.

Abundance and characteristics of sediment-bound magnetic minerals and trace elements in karst ditch wetland: A case study from Guizhou Province, China

This study investigated sediment-bound magnetic properties and selected trace elements level in the karst ditch wetland, Caohai National Nature Reserve, Guizhou Province, China. Sediment-bound magnetic signals were quantified using low-frequency mass magnetic susceptibility (χLF), anhysteretic remanent magnetization susceptibility (χARM), saturation isothermal remanent magnetization (SIRM), and percentage frequency-dependent susceptibility (χfd%). Concentrations of Cd, Cr, Sb and Zn were determined using inductively coupled plasma mass spectrometry. Sediment χLF, χARM, SIRM, and χfd% were higher than those of bedrocks and mainly altered by the pedogenic processes. The estimated χfd% ranged from 6.15 % to 14.62 % and reflected the magnetic grain sizes were largely concentrated in the range of superparamagnetic particles. The elevated concentrations of sediment-bound Cd, Cr, Sb, and Zn supported the significant contribution of the anthropogenic sources in the karst ditch wetlands. The weak relationship between magnetic signals and selected trace elements (p < 0.05) suggested the occurrence of few sediment-bound iron-containing minerals associated with selected trace elements. These results indicated that a minor contribution of anthropogenic sources of selected trace elements to the elevated sediment magnetic signals in the karst ditch wetlands.

Influence of Magnetofossils on Paleointensity Estimations Inferred From Principal Component Analyses of First‐Order Reversal Curve Diagrams for Sediments From the Western Equatorial Pacific

AbstractRelative abundance of magnetite originated from magnetotactic bacteria (magnetofossils) in sediments may influence relative paleointensity (RPI) estimations of the geomagnetic field, as some studies reported an inverse correlation between RPI and the ratio of anhysteretic remanent magnetization susceptibility to saturation isothermal remanent magnetization (kARM/SIRM), a proxy of the proportion of biogenic to terrigenous magnetic minerals as well as magnetic grain size. This study aims to evaluate the influence of magnetofossils on RPI estimations more selectively using first‐order reversal curve (FORC) diagrams. We studied three cores (KR0515‐PC4, MD982187, and MR1402‐PC1) from the western equatorial Pacific, among which large differences exist in the average natural remanent magnetization intensity normalized by ARM and kARM/SIRM. Principal component analyses (PCAs) were applied to FORC diagrams measured on bulk specimens from the three cores and silicate‐hosted magnetic inclusions extracted from Core MD982187, and three endmembers (EMs) were revealed (EM1: silicate‐hosted magnetic inclusions, EM2: other terrigenous, EM3: biogenic). EM3 proportions vary widely among the three cores. The average RPI decreases with increasing EM3 proportion, which is probably caused by higher ARM acquisition efficiency of magnetofossils due to small magnetostatic interactions. EM3 proportion correlates with kARM/SIRM, which confirms that kARM/SIRM represents the proportion of biogenic to terrigenous magnetic components. Core MR1402‐PC1 has the highest EM3 proportion, and its within‐core variation is small. From FORC‐PCA applied solely to this core, we infer that the configurations of biogenic magnetite chains such as bending and collapse may also influence kARM/SIRM and RPI estimations.

Environmental magnetic properties of core sediments in the Yellow River subaqueous delta and their chronologicalapplications

The Yellow River has shifted frequently in the downstream region since 1885; it has flowed into the sea through the Qingshuigou channel from 1976 onward, thus forming the latest delta lobe (1976–present). During the past ~40 years, the sediment load of the Yellow River has been greatly reduced because of human and natural activities, such as reservoir construction, soil and water conservation, and river avulsion. Beginning in 2002, the water-sediment regulation scheme (WSRS) has also changed the sediment loading patterns of the Yellow River. Several studies have reported on the erosion and deposition characteristics of the latest lobe of the Yellow River Delta over the past several decades, based on remote sensing methods and water-depth measurements. However, continuous sedimentary records of delta erosion and deposition and their responses to natural and human activities in the watershed are lacking. Here, we obtained three sediments cores, YD01, YD02, and YD03, from the subaqueous delta of the latest lobe of the Yellow River Delta. These cores contain sediments deposited from 1976 to 2018. We analyzed the environmental magnetism and lithological characteristics of these cores, and investigated their responses to natural and human activities in the watershed of the Yellow River, as well as possible applications to sediment dating in the Yellow River Delta. The results show that frequency-dependent susceptibility ( χ fd%) and anhysteretic remanent magnetization susceptibility ( χ ARM) values were high in core sediments deposited from 1976 to 1996, indicating abundant contents of fine single-domain (SD) and superparamagnetic (SP) magnetic particles, and therefore a dominant sediment supply from the Chinese Loess Plateau. Small decreases in χ fd% and χ ARM in sediments deposited after 1986 revealed slight reduction of the sediment load from the Yellow River, which was likely caused by sediment retention related to the construction of the Longyangxia Reservoir. Rapid rises in χ fd% and χ ARM occurred in core YD01 sediments deposited during 2002 and ~2007, likely in response to the implementation of the WSRS, which resulted in an increase in sediment transportation. Increases in hard isothermal remanent magnetization (HIRM) values, an indicator of high-coercivity magnetic minerals such as goethite and hematite, in cores YD02 and YD03 from 2002 to ~2007 may also represent the start of the WSRS. This is because the downstream riverbed of the Xiaolangdi Reservoir underwent intense erosion during the implementation of the WSRS, leading to large-scale transportation of coarse sediments enriched in goethite and hematite, which were deposited on the riverbed before the implementation of the WSRS. The lack of increased contents of fine SD and SP magnetic minerals in cores YD02 and YD03 compared with YD01 in the interval deposited between 2002 and ~2007 was attributed to erosion and redeposition in the areas around cores YD02 and YD03. Large drops in SD and SP contents after ~2007 were detected in all three cores, revealing intense erosion near the river mouth likely caused by river channel shift and reduced capability of the WSRS to remove sediments. Contents of SD and SP particles increased again in sediments deposited after 2014 in cores YD02 and YD03, likely related to erosion of the present (after 1996) Yellow River mouth and transportation of fine particles to the region near cores YD02 and YD03. In summary, the magnetic parameters χ fd% and χ ARM and the lithological characteristics of cores YD01, YD02, and YD03 recorded sediment delivery changes caused by four events in the Yellow River watershed: The main river channel shift in 1976, construction of the Longyangxia Reservoir in 1986, the beginning of the WSRS in 2002, and weakened capability of the WSRS to remove sediments after ~2007. The notable changes of χ fd%, χ ARM, and lithology at the 1976, 1986, 2002, and ~2007 horizons may be used as dating points in future research of sediment cores from the Yellow River Mouth.

Tracing of traffic-related pollution using magnetic properties of topsoils in Daejeon, Korea

The present study was designed to explore the possibility of roadside pollution screening using magnetic properties of topsoil samples in Daejeon, South Korea. Low-field magnetic susceptibility, frequency dependence of magnetic susceptibility, susceptibility of anhysteretic remanent magnetization, isothermal remanent magnetization (IRM) acquisition and demagnetization, back-field IRM treatment, and thermal demagnetization of composite IRM were determined for roadside topsoil samples. Magnetic susceptibility measured on 238 samples from the upper 5 cm of the topsoils ranged from 8.6 to 82.5 × 10–5 SI with a mean of 28.3 ± 10.8 × 10–5 SI. The proximal zone, 55 m wide area situated on either side of the main street, exhibited an enhancement of magnetic susceptibility. In areas distant from the main street, low magnetic susceptibility (< 50 × 10–5 SI) was observed. The topsoil samples exhibited significant susceptibility contrasts, suggesting that two dimensional magnetic mapping was effective in identifying traffic-related pollution. A few magnetic hotspots with intensities of magnetic susceptibility near or over 50 × 10–5 SI might reflect the difference in topographic elevation and surface morphology. Among various IRM-related parameters, remanence of coercivity was most significant statistically. In most samples, IRM component analysis provided dual coercivity components. Thermal demagnetization of composite IRM and morphological observation of magnetic separates suggest angular magnetite produced by vehicle non-exhaust emissions spherical magnetite derived from exhaust emission to be the dominant contributors to the magnetic signal. It is likely that lower- and higher-coercivity components represent the presence of coarse-grained angular magnetite and fine-grained spherical magnetite, respectively.

Iron mineralogy and speciation of sediment iron-bearing minerals in mangrove forest: Case study of Zhangjiang estuary, China

Few investigations of iron speciation exist in intertidal conditions with little attention given to understanding the geochemical behavior of Fe3+–Fe2+ and its biogeochemical processes. Here, one sediment core was collected in Yunxiao mangrove forests, Zhangjiang estuary, China and iron mineralogy was determined by magnetic methods and Mössbauer spectroscopy. Changes in magnetic susceptibility, susceptibility of anhysteretic remanent magnetization, and saturation isothermal remanent magnetization were linked to changes of pseudo-single domain soft coercive components with minor antiferromagnetic fractions and the presence of minimal concentrations of superparamagnetic particles was confirmed by the no frequency dependent of AC magnetization. A positive correlation between L-ratio and hard isothermal remanent magnetization is congruent with the distribution of high-coercivity antiferromagnetic minerals. At 295 K, the Mössbauer spectrum of specimens was well fitted with a single magnetic sextet, hematite and two magnetic doublets, paramagnetic Fe2+ and paramagnetic Fe3+. The usefulness of magnetic data and Mössbauer spectroscopy could offer valuable analytical tools for tracking changes of iron speciation and phase in the intertidal conditions.

Association of black carbon with heavy metals and magnetic properties in soils adjacent to a cement plant, Xuzhou (China)

The Content of black carbon in soils close to a cement plant of Xuzhou, China, was determined to investigate its association with the concentration of heavy metals and the values of magnetic parameters. Black carbon content varied from 4. 4 to 25.2 mg/g, with an average value of 12.4 mg/g. The concentration of Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn was, on average, 0.8, 22.3, 235.8, 71.08, 1796.9, 88.4, 56.6 and 216.5 mg/kg, respectively. The average values of magnetic parameters such as the mass specific magnetic susceptibility, frequency susceptibility, susceptibility of anhysteretic remanent magnetization and saturation isothermal remanent magnetization were 83.5 × 10−8 m3/kg, 6.1%, 135.0 × 10−8 m3/kg and 1067.0 × 10−5 Am2/kg, respectively. Black carbon content showed significant positive correlation with the concentration of Cd, Co, Cu, Pb and Zn in soils, indicating that these metals were likely to be retained by black carbon. Significant correlations between black carbon content and magnetic parameters including magnetic susceptibility, susceptibility of anhysteretic remanent magnetization, saturation isothermal remanent magnetization together with interparametric ratios were also found. Cluster analysis and principal component analysis were used to further demonstrate the relationships between the above-mentioned variables, showing that cement plant emissions are the main source of black carbon in soils. These results provide the possibility for monitoring black carbon pollution with environmental magnetism methods.

A rock magnetic fingerprint of hydrothermal alteration in volcanic rocks - An example from the Los Azufres Geothermal Field, Mexico

Drill rock cuttings from different depths of two geothermal wells (Az-26 and Az-49) from the Los Azufres Geothermal Field (LAGF), Mexico, were analyzed for rock magnetic properties (magnetic susceptibility, χlf; frequency-dependent susceptibility, χfd; susceptibility of anhysteretic remanent magnetization, χARM; isothermal remanent magnetization, IRM; saturation isothermal remanent magnetization, SIRM; “hard” isothermal remanent magnetization, HIRM) and their inter-parametric ratios (SIRM/χlf, χARM/SIRM and S-ratio) to explore the relationship, if any, between these properties and hydrothermal alteration. In both the geothermal wells, the intensity of hydrothermal alteration increases with depth and temperature of the well. The samples exhibit hydrothermal alteration-induced changes in several rock magnetic properties: (1) a decreasing trend in the values of concentration-dependent rock magnetic parameters (χlf; χfd, χARM, IRM300mT, and SIRM); (2) a decrease in S-ratio (relative proportions of ferrimagnetic and anti-ferromagnetic minerals) values and an increase in HIRM (“hard” IRM; concentration of magnetically “hard” minerals, e.g., hematite) values; and (3) increasing SIRM/χlf and χARM/SIRM ratio values. Most of the rock cuttings in both the wells are characterized by coarse SSD grains and they exhibit χlf values between 1 × 10−6 m3kg−1 (acid igneous rocks) and 10 × 10−6 m3kg−1 (SSD/MD grain size).Our study also indicates that the initial (primary) mineralogy of reservoir rocks may have an influence on the type of hydrothermal minerals that would form at low reservoir temperatures and/or with low intensity of hydrothermal alteration; however, this may not have any significant influence at high reservoir temperatures and/or high intensity of hydrothermal alteration.Our study suggests that in a homogenous litho-unit (rocks of the same type and age) of a large area, a zone characterized by anomalously low values of concentration-dependent rock magnetic properties (χlf, χfd, χARM, IRM300mT and SIRM), high SIRM/χlf, χARM/SIRM and HIRM values and low S-ratio values may indicate intense hydrothermal alteration. Consequently, rock magnetic properties may be a simple, yet an important tool, to identify hydrothermally altered rocks and zones of hydrothermal alteration, particularly in the initial stages of geothermal exploration.

Gradual late stage deepening of Gega ice-dammed lake, Tsangpo gorge, southeastern Tibet, indicated by preliminary sedimentary rock magnetic properties

Gega lake, in southeastern Tibet, was formed by the blocking of Yarlung Tsangpo gorge by a glacier and is a well-known example of geomorphological damming. However, the evolution of the damming process at the site is still not understood in detail. Here, we use measurements of multiple magnetic parameters of the sediments from the Yusong (YS) 3 section, which is well-dated by optically stimulated luminescence, to provide a detailed history of the late stage of Gega dammed lake since 17.0 ka. Low-frequency field magnetic susceptibility (chi(lf)) increases upwards gradually from 25 to 79 x 10(-8) m(3)/kg above 5.5 m, but other magnetic properties, such as frequency-dependent magnetic susceptibility (chi(fd)% and (fd)), susceptibility of anhysteretic remanent magnetization (chi(ARM)), and saturation isothermal remanent magnetization (SIRM) did not show a similar degree of enhancement. The magnetic grain size indicators of chi(ARM)/chi(lf), chi(ARM)/SIRM, and chi(lf)/SIRM all indicate a trend of increasing magnetic grain size from the 5.5 m to the top of section; however, the bulk sediment grain size decreases gradually within the same interval. The total organic carbon is very low (0.2-0.7%), and thus, it is unlikely that the sedimentary environment is sufficiently strongly reducing to lead to the dissolution of magnetic minerals. Therefore, we infer that the coarsening-upwards of the magnetic grain size, and the increasing magnetic susceptibility from 5.5 m, reflect the gradual preferential preservation of magnetic minerals, caused by the deepening of the lake. Thus, we interpret the magnetic record of the section as reflecting the gradual deepening of the late stage of Gega ice-dammed lake. Last, the abrupt disappearance of the lake may have resulted in an outburst flood.

Magnetic characterization of distinct soil layers and its implications for environmental changes in the coastal soils from the Yellow River Delta

The soils in the Yellow River Delta (YRD) were formed through the deposition of the Yellow River sediments under complicated hydrodynamic conditions, resulting in large variability in soil properties. In this study, environmental magnetic analyses were conducted on four typical soil profiles and one high resolution soil profile with distinct soil layers to examine the soil formation process and to track the environmental changes. The results showed that the red clay layer (RCL) in the YRD soil profiles had unique magnetic properties, which could be clearly separated from the yellow silt layer (YSL) at frequency dependent susceptibility (χfd%)>6%, susceptibility of anhysteretic remanent magnetization (χARM)>250×10−8m3kg−1, χARM/magnetic susceptibility (χlf)>5, χARM/saturated isothermal remanent magnetization (SIRM)>45×10−5mA−1 and SIRM/χlf<12×103Am−1. The magnetic enhancement of the RCL could be attributed to the presence of fine superparamagnetic (SP)/single domain (SD) ferrimagentic grains sourcing from hydrodynamic sorting of old sediments (e.g., paleosol in the Chinese Loess Plateau). It was hard to discriminate the RCL and YSL in the <2μm fraction by magnetic bi-plots, suggesting that the abundance of clays with higher contents of secondary ferrimagnetic minerals contributed significantly to the magnetic variability of different soil layers in the YRD. Three units were identified in a high resolution soil profile based on the changes of magnetic curves, including a steady deposition process in the upper unit, a strong hydrodynamic process with varied provenance in the middle unit and a heterogeneous deposition process in the lower unit with the RCL. The three units were closely linked to the variation of nutrients (carbon and nitrogen) and metals (chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), zinc (Zn), titanium (Ti) and zirconium (Zr)) in the soil profile, indicating the influence of provenance and sorting during sediment transportation and deposition. The magnetic method is sensitive to characterize soil formation and environmental changes in the coastal zone.

The magnetic properties of sediment and sedimentary environment in the Huanghe Delta area after the last glacial maximum

On the basis of measuring the magnetic parameters of sediment in Core YDZ1, combined with a grain size analysis and Carbon-14 dating, the magnetic properties of sediment and sedimentary environment in the Huanghe (Yellow River) Delta area after the last glacial maximum have been studied. The results show that the ferrimagnetic minerals of a pseudo single domain and multi domain particles dominate the magnetic properties of sediment in Core YDZ1. The imperfect anti ferrimagnetic minerals have more contribution on sediment in a depth of 24.0–22.1 m, and more stable-single domain and pseudo single domain particles exist. The susceptibility of anhysteretic remanent magnetization and the ratio of the susceptibility of anhysteretic remanent magnetization to saturation isothermal remanent magnetization show a decrease trend below depth of 24 m, a marked increase trend in a depth of 24.0–13.5 m, and a rapid decrease at depth of 13.5 m, then a fluctuation trend upward. The above two magnetic parameters and the ratio of the susceptibility of anhysteretic remanent magnetization to the mass susceptibility can be regarded as the proxy indicators for the content of clay (<4 μm) and the fine-grained size (<32 μm). The sedimentary environment after the last glacial maximum in the Huanghe Delta area has experienced the fluvial facies, the tidal flat facies, the neritic facies, the pro delta facies, the delta front facies and the floodplain facies. Thickness of the Holocene transgression layer is 10.5 m and the depth of substrate is about 24 m according to the YDZ1 core. The sedimentary dynamic has a variation trend with strongweak- strong, which has been proved by the Flemming triangular schema.

Investigation of the pollution in the street dust at Xuzhou, China, using magnetic, micro-morphological and Mössbauer spectra analyses

This study reports a detailed examination of the magnetic mineralogy of street dust samples collected in Xuzhou, a heavily industrial city in China. Several different approaches have been utilized in the characterization, from standard mineral magnetic techniques such as magnetic hysteresis and microscopy to non-standard techniques such as Mossbauer spectroscopy. Magnetic properties and the concentrations of four metals including Cu, Zn, Ba and Pb were reported for each sample. The primary magnetic mineral was found to be multidomain magnetite-like material. Scanning electron microscope analyses of street dust revealed: spherule-shaped iron oxides and angular particles with complex chemical composition. The concentrations of Cu, Zn, Pb and Ba were 3, 4.8, 2.8 and 1.3 times higher, respectively, than the soil background values of this study area. Both Cu and Ba showed significant correlations with the magnetic concentration parameters χARM (susceptibility of anhysteretic remanent magnetization) and saturation isothermal remanent magnetization. The combination of the various methods offers a powerful analytical technique in the study of magnetic properties of street dust.

Environmental rock‐magnetism of Cenozoic red clay in the South Pacific Gyre

AbstractNonfossiliferous red clay can be used for elucidating long‐range environmental changes, although such studies were limited so far because of the difficulty in precise age estimation and extremely low sedimentation rates. We conducted an environmental rock‐magnetic study of Cenozoic red clay at the Integrated Ocean Drilling Program Site U1365 in the South Pacific Gyre. Magnetostratigraphy could be established only above ∼6 m below the seafloor (mbsf) (∼5 Ma). Below ∼6 mbsf, the ages of the cores were transferred from the published ages of nearby Deep Sea Drilling Project Site 596, which is based mainly on a constant Cobalt flux model, by intercore correlation using magnetic susceptibility and rare earth element content variation patterns. Rock‐magnetic analyses including first‐order reversal curve diagrams, the ratio of anhysteretic remanent magnetization susceptibility to saturation isothermal remanent magnetization (SIRM), and IRM component analyses revealed that magnetic minerals consist mainly of biogenic magnetite and terrigenous maghemite, and that the proportion of the terrigenous component increased since ∼23 Ma. We consider that the increase reflects a growth of eolian dust flux associated with a northward shift of Australia and the site to an arid region of the middle latitudes. The increase of the terrigenous component accelerated after ∼5 Ma, which may be associated with a further growth of the Antarctic glaciation at that time. This is coeval with the onset of the preservation of magnetostratigraphy, suggesting that the primary remanent magnetization is carried by the terrigenous component.

Identifying the influence of urbanization on soil organic matter content and pH from soil magnetic characteristics

Soil magnetic characteristics are correlated with soil pH and organic matter content. Analyzing soil magnetic characteristics, organic matter content and pH can indirectly evaluate soil pollution caused by human activities. This study analyzed the soil magnetic characteristics, organic matter content and pH in surface soil samples from different land use types in Shihezi city, a newly and rapidly developing oasis city in Xinjiang of China. The aims of this study were to explore the possible relationships among the soil magnetic parameters and thereby improve the understanding of influence of urbanization on soil properties. Eighty surface soil samples at the depth of 0–10 cm were collected from 29 July to 4 August 2013. The results showed that the magnetic minerals in surface soil were dominated by ferromagnetic minerals. Spatially, the magnetic susceptibility (χ LF), anhysteretic remanent magnetization susceptibility (χ ARM), saturation isothermal remanent magnetization (SIRM) and “soft” isothermal remanent magnetization (SOFT) were found to be most dominant in the new northern urban area B (N-B), followed by built-up areas (U), suburban agricultural land (F), and then the new northern urban area A (N-A). The values of χ LF, χ ARM, SIRM and SOFT were higher in the areas with high intensities of human activities and around the main roads. Meanwhile, the property “hard” isothermal remanent magnetization (HIRM) followed the order of U>N-B>F>N-A. Built-up areas had an average pH value of 7.93, which was much higher than that in the new northern urban areas as well as in suburban agricultural land, due to the increased urban pollutant emissions. The average value of soil organic matter content in the whole study area was 34.69 g/kg, and the values in the new northern urban areas were much higher than those in the suburban agricultural land and built-up areas. For suburban agricultural land, soil organic matter content was significantly negatively correlated with χ LF, and had no correlation with other magnetic parameters, since the soil was frequently ploughed. In the new northern urban areas (N-A and N-B), there were significant positive correlations of soil organic matter contents with χ ARM, SIRM, SOFT and HIRM, because natural grasslands were not frequently turned over. For the built-up areas, soil organic matter contents were significantly positively correlated with χ LF, χ ARM, SIRM and SOFT, but not significantly correlated with frequency-dependent susceptibility (χ FD, expressed as a percentage) and HIRM, because the soil was not frequently turned over or influenced by human activities. The results showed that soil magnetic characteristics are related to the soil turnover time.

Mineral magnetism of atmospheric dust over southwest coast of India: Impact of anthropogenic activities and implications to public health

Abstract We have used rock magnetic techniques in this study to assess atmospheric pollution at five stations in and around Mangalore city on the southwestern coast of India. Samples of dust were collected from two suburban areas (Thokkottu and Pumpwell located respectively ~ 10 km and 3 km from the city center), the city center itself (Milagres) and industrial/port areas (Panambur and Mangalore Refinery and Petrochemicals Limited (MRPL)). Low-frequency magnetic susceptibility (χ lf ), frequency-dependent susceptibility (χ fd ), susceptibility of anhysteretic remanent magnetization (χ ARM ) and isothermal remanent magnetization (IRM 20 to 1000 mT) were determined on 23 dust samples and inter-parametric ratios calculated. Results show that samples from suburban areas (particularly Thokkottu) are characterized by low χ lf ( − 8 m 3 kg − 1 ) and up to 6% χ fd , suggesting low levels of pollution and the presence of pedogenic magnetite possibly derived from soils by wind erosion. However, the average χ lf of Milagres, Panambur and MRPL dust samples is high by factors of 9.2, 3.3 and 2.6 compared to that of the Thokkottu sample. The Milagres sample contains magnetically “soft” minerals like magnetite, possibly indicating its derivation from motor vehicle exhaust. In contrast, the Panambur dust sample is characterized by magnetically “hard” minerals such as hematite and goethite as it has an 8-fold higher HIRM value compared to the Thokkottu sample. This magnetic signature is perhaps the result of dust particles derived from the grinding of hematite-rich iron ore by the Kudremukh Iron Ore Company Limited (KIOCL) at Panambur and its storage and export through the nearby New Mangalore Port. However, the dust sample from MRPL has magnetically “soft” minerals like magnetite. This magnetic mineral may have originated from petroleum refining processes at MRPL. Particulate pollution from industrial activities and motor vehicle exhaust is a threat to human health and is known to cause cardiovascular and respiratory ailments. Therefore, the pollution levels brought out by this study warrant a comprehensive epidemiological study in the area of study.

Sea‐ice conditions in the Okhotsk Sea during the last 550 kyr deduced from environmental magnetism

Reconstructing past sea‐ice conditions in the Okhotsk Sea is important because sea‐ice conditions vary in response to global climate changes, which in turn may affect global ocean circulation through intermediate water mass formation. We conducted an environmental magnetic study of six cores from three stations in the central Okhotsk Sea to better understand temporal and spatial sea‐ice variations. Intercore correlations and age estimations are based mainly on geomagnetic paleointensity; an oxygen‐isotope stratigraphy is available for one station. Magnetic susceptibility (MS) minima are accompanied by maxima in color b*, the ratio of the anhysteretic remanent magnetization susceptibility to saturation isothermal remanent magnetization (kARM/SIRM), and the S‐ratio, which indicates a higher proportion of biogenic to terrigenous magnetic components. This reflects enhanced ocean productivity. First‐order reversal curve diagrams and IRM component analyses support the dominance of biogenic magnetite at MS minima. In contrast, color b*, kARM/SIRM, and S‐ratio values are low when MS is high, which indicates an increased proportion of the terrigenous component that was probably transported as ice‐rafted debris (IRD). For the southern two stations, IRD accumulation increased in glacial and deglacial periods, which implies mobile sea‐ice conditions even in full glacials. This was succeeded by extremely enhanced ocean productivity in early interglacials, which suggests nearly ice‐free conditions. For the northernmost station, on the other hand, IRD accumulation was low in glacials and increased in early interglacials, which indicates perennial sea‐ice coverage with little mobility in glacials. Succeeding ocean‐productivity enhancement was delayed compared to the southern stations.

Magnetic properties and heavy metal pollution of soils in the vicinity of a cement plant, Xuzhou (China)

Abstract This study characterized the magnetic property and levels of heavy metals of the topsoils near a cement plant. The concentrations of five selected heavy metals (Pb, Cu, Zn and Cd) were measured on 32 topsoil samples (0–20 cm) collected near a cement plant via inductively coupled plasma/mass spectroscopy (ICP-MS). The orders of enrichment factors (EF), on average, were Cd (7.3) > Cu (3) > Zn (2.9) > Pb (2.1), respectively. A self-organizing map (SOM) was applied to the concentrations of heavy metals for “correlation hunting”. Mineral magnetic concentration parameters, such as the specific magnetic susceptibility (χ), susceptibility of anhysteretic remanent magnetization (χ ARM ), saturation isothermal remanent magnetization (SIRM), together with interparametric ratios (such as IRM − 100mT /SIRM, SIRM/χ, χ ARM /SIRM) show that ferrimagnetic, superparamagnetic (SP) and multi-domain (MD) minerals dominated the soils. The results of correlation analysis indicate that copper showed a significant correlation with χ, χ ARM and SIRM but such a relationship with χ, χ ARM and SIRM was only weakly identified for Zn, Cd and Pb.

Six million years of magnetic grain-size records reveal that temperature and precipitation were decoupled on the Chinese Loess Plateau during ~ 4.5–2.6 Ma

Magnetic grain-size variations have been used as sensitive paleoclimate proxies to investigate the evolution of the East Asian summer monsoon, but their relationship with temperature and precipitation is not entirely clear. Here we find that two magnetic grain-size proxy records (χARM/χLF and χARM/SIRM, where χARM, χLF and SIRM are anhysteretic remanent magnetization susceptibility, magnetic susceptibility measured at 470Hz and saturation isothermal remanent magnetization, respectively) of Chinese loess and red-clay sediments co-vary during the last 6Ma, except between ~4.5 and 2.6Ma, when these two records had opposite trends. We attribute this disparate behavior to the different responses of χARM/χLF and χARM/SIRM to temperature and precipitation during ~4.5–2.6Ma, when temperature and precipitation on the Chinese Loess Plateau were decoupled. A comparison of the loess and red-clay χARM/χLF and χARM/SIRM records with the global ice-volume proxy records reveals that χARM/χLF is more sensitive to temperature variations than χARM/SIRM. The results suggest that temperature on the Chinese Loess Plateau had a cooling trend from ~4.5 to ~2.6Ma, whereas rainfall tended to increase. Our studies demonstrate that joint analysis of loess χARM/χLF and χARM/SIRM records can reveal paleoclimatic information that cannot be revealed by a single parameter.

Magnetic evaluation of sediment provenance in the northern East China Sea using fuzzy c-means cluster analysis

Abstract To identify the provenance of fine-grained sediments in the northern East China Sea, various magnetic parameters indicating concentration (magnetic susceptibility, susceptibility of anhysteretic remanent magnetization (χ ARM ), and saturation of isothermal remanent magnetization (SIRM)), mineral composition (S 300 = − IRM − 300 mT / SIRM and HIRM (%) = 50 (SIRM − IRM 300 mT ) / SIRM), and grain size (frequency-dependent magnetic susceptibility (χ FD ), χ ARM / SIRM, and S 20 = IRM 20 mT / SIRM) were measured from surface sediments collected at 98 regularly spaced sites. As an unbiased analytic tool, fuzzy clustering analysis was performed on data from 97 sites except an outlier. Each dataset for each site comprised magnetic parameters representing ultrafine superparamagnetic (χ FD ), fine single-domain or pseudo-single-domain (χ ARM / SIRM), and coarse multidomain (S 20 ) fractions, and the relative dominance of low- and high-coercivity minerals (S 300 and HIRM (%), respectively). The statistical analysis yielded four clusters, indicating that the sediments in the study area can be differentiated magnetically. Of the magnetic properties of the cluster centers, the most distinctive feature of cluster 1 is a predominance of coarse-grained magnetic minerals (highest S 20 value), while the contribution of high-coercivity minerals is highest in cluster 2 (highest HIRM (%) value). Ultrafine- and fine-grained fractions are prominent in cluster 3 (highest χ FD and χ ARM / SIRM values), while cluster 4 has the highest ratio of low- to high-coercivity minerals (highest S 300 value). Related to sediment provenance, the sediments of cluster 1 are interpreted to have been derived from the Yangtze River in China. The old Yellow River deposits are the primary source of sediments in cluster 2. Sediments in cluster 3 were probably transported from Taiwan or the Northwest Pacific by the Taiwan Warm Current or the Kuroshio Current, respectively, while Korean river deposits are the most probable sources of sediments in cluster 4.