Environmental magnetic measurements of marine sediments from Antarctica: implications to paleoclimate changes during the past 15 ka

In this paper, authors report some results obtained from systematic rock magnetic measurements on Core NP95 1 and Core NG93 1 , which were collected from the Prydz Bay, Eastern Antarctica and Great Wall Bay (Maxwell Bay), Western Antarctica respectively during the 11th and 9th CHINARE and a sequence of paleoclimate variations is well established based on sediment rock magnetic properties. In Antarctica, the magnetic properties show a close linkage to paleoenvironmental variations. The Core NP95 1 well recorded several paleoclimatic events, such as Heinrich event 1, Bolling Allerod warm period and Younger Dryas cold event. The Heinrich event 1 occurred at about 14 2 ka B.P., Younger Dryas cold event occurred between 11 7 ka B.P. and 10 3 ka B.P., and the boundary of Pleistocene and Holocene in Antarctica is 10 3 ka B.P.. In Holocene, two warm periods were recorded at about 10 0 ka B.P. and 6 0 ka B.P. with a little cold period between them. After 6 0 ka B.P. , two cores both recorded a cold climatic oscillation. Paleoclimate described by two cores rock magnetic measurements was simultaneously changed in Eastern and Western Antarctica during the same period two cores commonly covered.

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

Soil magnetic characteristics are correlated with soil p H and organic matter content. Analyzing soil magnetic characteristics, organic matter content and p H can indirectly evaluate soil pollution caused by human activities. This study analyzed the soil magnetic characteristics, organic matter content and p H 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（χLF）, anhysteretic remanent magnetization susceptibility（χARM）, 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 χLF, χARM, 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 p H 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 χLF, 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 χARM, 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 χLF, χARM, SIRM and SOFT, but not significantly correlated with frequency-dependent susceptibility（χFD, 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.

Paleoclimatic and provenance implications of magnetic parameters from the Miocene sediments in the Subei Basin

Thick sediments from foreland basins usually provide valuable information for understanding the relationships between mountain building,rock denudation,and sediment deposition.In this paper,we report environmental magnetic measurements performed on the Miocene sediments in the Subei Basin,northeastern Tibetan Plateau.Our results show two different patterns.First,the bulk susceptibility and SIRM,ARM,and HIRM mainly reflect the absolute-concentration of magnetic minerals;all have increased remarkably since 13.7 Ma,related to provenance change rather than climate change.Second,the ratios of IRM100mT/SIRM,IRM100mT/IRM30mT,and IRM100mT/IRM60mT,together with the redness and S ratio,reflect the relative-concentration of hematite,being climate-dependent.Their vertical changes correlate in general with the long-term Miocene climatic records of marine oxygen isotope variations,marked by the existence of higher ratios between 17 and 14 Ma.This may imply that global climate change,rather than uplift of the Tibetan Plateau,played a dominant role in the long-term climatic evolution of the Subei area from the early to middle Miocene.

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.

Rock-magnetic characteristics and mechanisms of the Titel loess-paleosol sequence in northern Serbia since late Middle Pleistocene

The changing pattern of magnetic characteristics in eastern European loess deposits is the most similar across the world to that of the Chinese Loess Plateau,both of which are dominated by the strength of pedogenesis.Hence a systematical study to the rock magnetism of eastern European loess is not only helpful for understanding the paleoclimatic information preserved by themselves,but also beneficial for promoting the cognition of the pedogenic mechanism in loess records.In this study,a detailed rock-magnetic analysis of seventy loess/paleosol samples,taken from the Titel Loess Plateau in northern Serbia,is carried out for a better understanding of the magnetic records since late Middle Pleistocene.The results provide us some implications.First,the magnetic susceptibility values of the paleosols in the Titel loess-paleosol sequence are generally less than 100×10^(-8)m^(3)kg^(-1),significantly lower than those of the loess sections in the Chinese Loess Plateau,even though they are under similar climatic conditions.However,the behaviors of the parameters related to the distributions of magnetic particles in these two regions are similar.The difference in the contents of ferrimagnetic minerals is the leading reason that caused the difference in their magnetic characteristics,but the mechanism is still open to study.Second,based on the analysis of thermomagnetic curves,a gradually increasing trend of the relative contents of maghemite over the last four glacial-interglacial cycles is identified.The realization of thermally unstable maghemite from Chinese loess leads us to speculate that the long-term increasing trend of the relative contents of maghemite in Titel loess-paleosol sequence likely is a mineralogical response to the progressive enhancement of continental climate in the Pannonian Basin since the Middle Pleistocene.

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.

Magnetic characteristics of lake sediments in Qiangyong Co Lake,southern Tibetan Plateau and their application to the evaluation of mercury deposition

Heavy metals,one of the most toxic classes of pollutants,are resistant to degradation and harmful to the biological environment.The lakes that have developed on the Tibetan Plateau are ideal regions to investigate historic heavy metal pollution,particularly through the use of the reliable 210 Pb dating technique.Environmental magnetism has been successfully applied to estimate heavy metal pollution in different environmental systems due to its characteristics of simple processing steps,good sensitivity,and non-destructibility.However,it has not yet been applied to assess heavy metal pollution in lake sediments on the Tibetan Plateau.A series of environmental magnetic investigations of Qiangyong Co Lake sediments(southern Tibetan Plateau) was therefore conducted to explore the relationship between magnetic minerals and mercury(Hg) concentrations.The results showed that the magnetic mineral species in lake sediments remained stable,with similar levels of four different components from 1899 to 2011.However,the proportion of component 1(C1,hematite) increased continuously with the corresponding decrease in the proportion of C2(goethite),while the proportions of C3 and C4(magnetite) did not change significantly.As a result,the bulk magnetic signals(e.g.,SIRM and clf) were unsuitable for the evaluation of the Hg concentration;however,the proportion of hematite had a strong positive correlation with the Hg concentration.It is possible that the Qiangyong Glacier(the main water supply for Qiangyong Co Lake) has experienced faster melting with global and local warming,and the Hg trapped in cryoconite and ice was released.Hematite,with a large specific surface area,has a strong capacity for absorbing Hg,and both materials are ultimately transported to Qiangyong Co Lake.The proportion of hematite in a sample is therefore a suitable semi-quantitative proxy that can be used to evaluate the Hg concentration in Qiangyong Co Lake sediments.This study confirmed that the variation of magnetic minerals can provide a new method to estimate the variation of Hg concentrations and to study the process of Hg deposition in lakes in the southern Tibetan Plateau on the basis of a detailed environmental magnetic analysis.