GP31C-0803
Determination of Anthropogenic Boundary Depth in Industrially Polluted Soil Profiles and Semi-Quantification of Heavy Metal Loads Using Magnetic Susceptibility
Magnetic susceptibility processing and analysis provides new opportunities towards fast and cost-efficient discrimination and semi-quantification of anthropogenic heavy metal loads in forest soil. Rapid magnetic susceptibility measurements on vertical soil profiles generate a solid data base for optimized magnetic site characterization, allowing for reduction of heavy metal analyses to a minimum of two analyses per site. The quality of the method is ensured by a sufficiently large number of vertical magnetic susceptibility curves, providing reliable mean values of the investigated area. Test sites of ~10 m2 represent "site scale" dimensions, forming the smallest units in semi-quantitative magnetic soil pollution mapping. Spatial variability of magnetic susceptibility in soil core sets from "site scale" sized locations enables for statistical determination of a boundary depth, indicating the transition from the "polluted" upper soil layers to the "unpolluted" lower zone. The boundary depth separates the soil profile into two distinct magnetic layers and is crucial for standardized and site-independent magnetic susceptibility data processing. Introduction of a block master curve simplifies the complex variations of individual magnetic susceptibility curves, representing mean values for the "polluted" and "unpolluted" soil zones. Magnetic susceptibility data of a selected individual soil core are transformed into a block individual curve and linked to the block master curve by a correction factor. Heavy metal contents are only determined on two sub-samples of the selected individual soil core, one from the "polluted" and one from the "unpolluted" part. Determination of the anthropogenic heavy metal content which is representative for the site is performed using the correction factor obtained from block curve processing. With this integrated magnetic susceptibility and heavy metal data processing scheme conventional time-intensive steps are performed cost and time efficiently using magnetic methods and data processing, while heavy metal analyses are reduced to a minimum. This provides an applicable tool for semi-quantification of anthropogenic heavy metal loads in soil.
GP31C-0804
Delineation of Hydrocarbon Contamination of Soils and Sediments With Environmental Magnetic Methods: Laboratory and Field Studies
Hydrocarbon contamination of soils and sediments is a worldwide environmental problem. The present research focuses on the study of magnetic properties of hydrocarbon contaminated soils and sediments using environmental magnetic methods both on field sites as well as in laboratory batch experiments. The main objectives of this research are i) to determine a possible application of magnetic proxies for the delineation of organic contamination in soils and sediments and ii) to examine the role of bacteria in changing soil magnetic properties after hydrocarbon contamination. A former oil field and a former military site which are heavily contaminated with hydrocarbons were studied. Additionally, three different types of natural clean soils were investigated in laboratory experiments by simulating hydrocarbon contamination in sterile and microbial active setups. Magnetic properties, soil properties, iron bioavailability, iron redox state and hydrocarbon content of samples were measured. Additionally, magnetic susceptibility (MS) was monitored weekly in laboratory batch set-ups during several months. Results from the field sites showed that there is an increase of MS and a good correlation between MS and hydrocarbon content. A weekly monitored MS result from the laboratory study clearly indicated~~10% change (increase as well as decrease) of initial MS of respective soils only in microbial active set-ups with saturation after a few weeks of experimental period. This depicts that there is a change of MS caused by microbial iron mineral transformation in presence of hydrocarbon contamination in soils. The results from the field study demonstrate that magnetic proxies can be used to localize hydrocarbon contamination. However, more field sites with hydrocarbon contaminated soils and sediments need to be investigated by using environmental magnetic methods for better understanding the factors driving such changes in magnetic properties.
GP31C-0805
Accumulation of vehicle derived pollutants and its relation with road types in traffic controlled urban area
Mineral magnetic properties and heavy metal concentration of roadside dusts in Metropolitan Seoul, Korea, were measured to investigate the accumulation of vehicle derived particulates. Electron microscopic analyses were carried out to verify magnetic components in dust. A total of 308 dust samples were collected monthly at twelve traffic controlled sites (nine from > 100,000 traffics/day and three from < 50,000 traffics/day) and at two park areas as for comparison. In order to minimize the washout effect, samples were collected in dry seasons from October 2005 – April 2006 when precipitation was < 20 mm/month. The magnetic concentration parameters (e.g., ARM, SIRM and χ) showed a significant correlation with selective metal elements including Cr, Cu, Fe and Zn, suggesting that magnetic parameters can faithfully reflect heavy metal pollutions. In particular, relatively higher magnetic concentrations were observed in some traffic sites where buildings with minimum four-story were aligned along the roadside. As anticipated, a site with notorious frequent traffic jams revealed the heaviest magnetic concentration and the heaviest concentration of the analyzed metal elements (Cd, Cr, Cu, Fe, Mn, Pb and Zn). In summary, our observations indicate that the vehicle derived pollutants can be highly accumulated where winds were less circulated.
GP31C-0806
Characterization of anthropogenic pollutants in Asian dust
It has well known that the Asian dust storm (ADS) carried anthropogenic pollutants produced in the industrial areas in China to the adjacent East Asian nations including Korea, Japan and Taiwan. In order to characterize such anthropogenic pollutants forced by ADS, detailed electron microscopic observations were carried out on ADS samples collected from the 12 ADS events occurred for the past three years (2004-2006) in Seoul, Korea. In addition, their temporal accumulations were traced using magnetic proxy parameters. As a comparison, companion samples were also collected before- and after- ADS events. We found that anthropogenic signatures in the ADS samples were C, Cr, Pb, S and Zn. Most of these elements were tied with Fe. Therefore the magnetic proxy is highly applicable to trace the quantitative variations in anthropogenic pollutants in ADS. Slightly increasing magnetic concentration parameters reflect increasing amount of anthropogenic pollutants carried by the ADS for the past three years. Connecting with the air- mass trajectories of ADS, the highest magnetic concentration (highest pollution) was observed on the ADS samples from Central China which travelled nearby highly industrialized major cities where foreign multinational enterprises were concentrated.
GP31C-0807
Evaluation of Magnetic Biomonitoring as a Robust Proxy for Traffic-Derived Pollution.
Inhalation of particulate pollutants below 10 micrometers in size (PM10) is associated with adverse health effects. Here we examine the utility of magnetic remanence measurements of roadside tree leaves as a quantitative proxy for vehicle-derived PM, by comparing leaf magnetic remanences with the magnetic properties, particulate mass and particulate concentration of co-located pumped air samples (around Lancaster, UK). Leaf samples were collected in early autumn 2007 from sites in close proximity to a major ring road, with a few additionally from background and suburban areas. Leaves were collected from lime trees (Tilia platyphyllos) only, to avoid possible species-dependent differences in PM collection. Magnetic susceptibility values were small and negative, reflecting the diamagnetic nature of the leaves. Low- temperature remanence curves show significant falls in remanence between 114 and 127 K in all of the leaf samples. ÷ARM/SIRM ratios indicate that the dominant size of the leaf magnetic particles is between c. 0.1-2 micrometers. Analysis of leaf particles by SEM confirms that their dominant grain size is < 2 micrometers, with a significant number of iron-rich spherules < 1 micrometer in diameter. Particle loading is concentrated around ridges in the leaf surface; significant numbers of the finer particles (< 500 nm) are frequently agglomerated, most likely due to magnetic interactions between particles. Larger particles exhibit an irregular morphology, with high silica and aluminum content. Particle composition is consistent with exhaust outputs collected on a filter. Critically, leaf saturation remanence (SIRM) values exhibit strong correlation with the particulate mass and SIRM of co-located, pumped air samples, indicating they are an effective proxy for ambient particulate concentrations. Biomagnetic monitoring using tree leaves can thus potentially provide high spatial resolution data sets for assessment of particulate pollution loadings at pedestrian-relevant heights. Not only do leaf SIRM values increase with proximity to roads with higher traffic volumes, leaf SIRM values are c. 100 % higher at 0.3 m than at c. 1.5 to 2 m height.
GP31C-0808
A Magnetic Record of Aeolian Dust Transport to the Scotia Sea Through the Quaternary?
Artificial iron fertilization experiments in the Southern Ocean – a high nutrient, low chlorophyll (HNLC) region of the world oceans – indicate that productivity and subsequent drawdown of carbon dioxide from the atmosphere can be enhanced with increases in bioavailable iron supply. The past record of terrestrial dust flux to the Southern Ocean thus carries potential significance in the context of whether this region was a significant glacial sink for CO2 due to enhanced biological productivity (through iron fertilisation by increased glacial dust fluxes) and lock-up of CO2 in the deep Southern Ocean. Debate exists regarding the presence of dust in Southern Ocean sediments. The supply of detrital minerals to the Southern Ocean has so far been attributed dominantly to glacigenic processes, with glacial erosion of mafic magmatic rocks in distinct source areas, seaward transport of the glacigenic debris by glaciers and ice streams, and offshore transport by current and turbidite activity and ice-rafting. Prompted by the strong resemblance between the downcore magnetic susceptibility of Scotia Sea sediments and the dust flux record in Antarctic ice cores, this study examines if there is a glacial/interglacial signal of changes in terrestrial dust flux in sediment cores from the Southern Ocean, based not only on analyses of sediment magnetic mineralogy and magnetic grain size but also on particle size, iceberg-rafted debris content and the magnetic properties of potential source materials from the S. American continent.
GP31C-0809
Environmental Magnetism of Late Quaternary Sediments From the Southern Okinawa Trough: Paleoceanographic Implications and History of the Kuroshio Current
The objective of this study is to advance our understanding of the late Cenozoic environmental and paleoceanographic history of the Southern Okinawa Trough and the Kuroshio Current. Our investigation is based on the environmental magnetic record of a suite of u-channel samples that span the upper 140 m (0.42 m.y.) of ODP Site 1202. This site was drilled in the southernmost Okinawa Trough off the northeast coast of Taiwan and provides, with sedimentation rates of up to 9 m/k.y., one of the highest-resolution records of environmental and paleoceanographic change ever recovered. Variations in the concentration of fine-grained magnetite (anhysteretic remanent magnetization, ARM), magnetic grain size (ARM/k), magnetic hardness (ARM(30)/ARM(0)), and overall mineralogy (susceptibility, k) reflect fluctuations in climate, sea level, source material, and depositional environment. Eleven AMS C-14 dates of planktonic foraminifers and scaphopod samples combined with oxygen isotope stratigraphy (Wei et al., 2005) provide a relatively low- resolution, but well-defined age model. Based on the magnetic characteristics we distinguished five distinctive intervals with boundaries at 11.3, 14.3, 18.6, and 27.4 ka. From the beginning of the record at about 40 ka to 27.4 ka (MIS-3) all magnetic parameters remain remarkably constant indicating very little variation in sediment source and processes. Sea level during this time interval fluctuated at around -80 m. At 27.4 ka a significant decrease in magnetic grain size is accompanied by an increase in the amount of magnetic material. This change coincides with a drop in sea level below -80 m in the buildup to the sea level lowstand of the Last Glacial Maximum (LGM). Sediment source during this time interval was predominantly the East China Sea (Wei, 2006; Diekmann et al., in press). MIS-2 is characterized by constantly increasing magnetic grain size and a decreasing amount of magnetic material. At 14.3 ka after melt water pulse (MWP) 1A, which is expressed as a short spike in all magnetic parameters, the magnetic signature changes significantly, shows very little variability and remains constant until MWP-1B at 11.3 ka. An effect of the Younger Dryas is possibly preserved in the magnetic susceptibility signal. Associated with a significant sea level rise at the onset of the Holocene, a change in sediment source to Taiwan (Wei, 2006; Diekmann et al., in press) and the onset of the Kuroshio Current as sea level rose above -50 m, magnetic parameters shift and remain relatively constant throughout the Holocene. This allowed for the extraction of a high-resolution relative paleointensity record from 0-9.4 ka. MWP-1C is associated with a short and sudden increase in magnetic grain size.
GP31C-0810
Evolution of the Li-Yu Lake at Eastern Taiwan: Evidences from Magnetic Proxies and Pollen Analysis
The Li-Yu Lake located at Hua-Lien County of eastern Taiwan seems to be originally a river and was trapped by a landslide to form a lake after. To investigate the truth, a lacustrine sediment core of about 8 meters was raised from the lake and magnetic proxies and pollen analysis were employed to analyze it. Based on the C- 14 dating, this core provides the information for the last 7000 years Magnetic proxies point out that the records could be clearly distinguished into two parts from the depth of about 2.6 meters : the deeper part dominates very coarse grained with higher oxidized magnetic minerals and vice versa at the shallower part. This boundary corresponds an ages of about 2300 yrB.P. Pollen analysis reveals that no pollen could be found at the depths below 2.8 meters; only aquatic plant pollens, such as Poaceae, Cyperaceae and Mynophyllum, were found at the depth between 2.8-2.5 meters; tree and shrub pollens began to appear at about 2.5 m in depth. These results proposed that sediments below 2.8 m (before 2400 yrBP) might be a river deposit; the river was blocked at its northern end to form a lake between 2300-2400 yrBP in consideration of the topography, and regular lake deposits occurred after 2300 yrBP. Furthermore, magnetic proxies were found to have a clear change during the age interval of about 900-600 yrBP. Pollen patterns also support this point. It is proposed that the river piracy might have happened at the southern area of the lake at this time. The literatures recording the human activity in this area seem to support this point of view.
GP31C-0811
Environmental Magnetism Record of Holocene From Tropical Lake Sediments on Western México: Tacambaro Lake
Lacustrine records of late Pleistocene- Holocene in central Mexico have presented a number of difficulties in documenting environmental and climatic change, as often sedimentary sequences are discontinuous or affected by volcanic activity, and some critical knowledge of past conditions remain unclear. A 8.4 m core of laminated sediments collected in Lake Tacambaro (Michoacán, central Mexico), is of particular interest for the region, as it will provide a high resolution record of the Holocene environmental conditions and new data for the history of pre-Hispanic settlement. Rock magnetism, diatom, pollen, geochemical and total organic and inorganic carbon content analysis are in progress. The combined multiproxy analyses provide the basis of reconstruction of erosion, redoximorphic iron mineral diagenesis and biogenic productivity.
GP31C-0812
Using Magnetic Remanence Parameters to Reconstruct Past Precipitation From Buried Soils.
Magnetic measurements that rely on the comparisons between magnetically enhanced paleosols and their unaltered parent materials have long been used to quantify magnetic enhancement and to reconstruct past climatic conditions. We present measurements of magnetic remanence parameters (ARM/IRM, magnetic coercivity distributions) which, for many sites, allow for the direct quantification of pedogenically produced magnetite and estimates of past climatic conditions. Since our method does not rely on comparisons between magnetically enhanced soil horizons and their presumably unaltered parent material, this method might be especially suited for the analysis of thin loess-paleosol sequences, where pedogenically unaltered loess is absent. To test our method we analyzed the Brady soil in several locations in eastern Colorado, southwestern Nebraska and northwestern Kansas. Our analyses yielded mean annual precipitation values of 450 mm/a (Wauneta, 40.4983 ° N, -101.404 ° W), 550 mm/a (Devil's Den, 41.4561 ° N, -100.192 ° W) and 575 mm/a (Harlan County Lake, 40.0709 ° N, -99.2737 ° W), which is slightly lower than present-day precipitation at these sites and correlates well with isotope-derived reconstructions of paleoprecipitation. These quantitative reconstructions should be considered minimum estimates of paleoprecipitation as the method assumes a relatively rapid formation of the magnetic signal and no significant alteration of the magnetic phase after burial.
GP31C-0813
The Effects of Wildfires on the Magnetic Properties of Soils in the Everglades
As part of an effort to better understand the role of wildfire in the Everglades ecosystem, we are studying the effects of fires on the magnetic properties of Everglades soils. We present results from a suite of soil samples collected at vegetation survey sites within the Cape Sable seaside sparrow (CSSS) habitat in southern Everglades, for which vegetation data, hydrologic data, organic carbon content, iron concentration and the fire history of the sites (burn frequency and time since the most recent burn) are available. We conducted a series of rock magnetic experiments (initial susceptibility, frequency dependent susceptibility, anhysteretic remanence acquisition and isothermal remanence acquisition) designed to identify the magnetic minerals present in these soils. Each of the samples is characterized by contributions from both low and very high-coercivity magnetic components. We interpret these components as magnetite-maghemite and goethite respectively. Following a major fire in the late Spring of 2008, we collected 20 soil cores (10 cm) from within the fire boundary, and 10 cores from nearby unburned sites. Each core was sub-sampled from the surface, and from 2 and 7 cm depths. The sites burned in 2008 showed a consistent pattern defined by a major decrease to complete removal of the very high-coercivity phase iron oxyhydroxides (goethite) in the surface and shallow samples, while greater concentrations of this phase persist at depth. The iron oxyhydroxides appeared to be nearly completely replaced by the more reduced, low-coercivity phase (magnetite/maghemite) in the surface/shallow samples as a result of the fire. Because phosphorous is strongly adsorbed onto iron oxyhydroxides (such as goethite), these results may have important implications for phosphorous cycling in fire-prone environments.
GP31C-0814
Hemo-Ilmenite as Proxy to Deduce Landscape Development
The use of magnetic particles in soils as proxy to deduce landscape development is tested. Precondition to
use such particles is their lithogenic origin, high weathering resistance, and unique mineral-chemical and
magnetic properties. Hemo-ilmenite is a potential candidate fulfilling these requirements.
We investigated an
alluvial soil in a flat lying flood plain of the Bafini river in the savannah woodland of southern Mali. The soil is
characterized by a water regime governed by regularly occurring wet and dry seasons. The soil was
subdivided into four horizons Ap, A2, A3, and Ag with a redox-cline indicated by the minimum concentration of
Mn in the A3 horizon.
Hemo-ilmenite as dominant magnetic constituent is distributed throughout the soil
profile.Chemical analysis of single particles showed that the hemo-ilmenite can be described as solid solution
((1-y)Fe2O3 - yFeTiO3) with y = 0.83. X-ray diffraction of separated particles revealed
single crystal properties with an ilmenite-like structure. The solid solution is homogeneous with respect to the
resolution of the transmission electron microscope. Inhomogeneity on a molecular level is documented by
electron paramagnetic resonance (EPR) and ferromagnetic resonance (FMR) spectroscopy as well as ac
and dc magnetization analyses. The zero-field and field-cooled magnetizations and ac susceptibility
measurements indicate magnetic inhomogeneity of the solid solution at low temperature, as manifested by
spin glass-like properties below 40 K. FMR spectroscopy gives clues that the generation of spin glass-like
properties starts at about 100 K followed by the freezing of a spin glass configuration at 40 K. At lower
temperature, EPR spectra reveal the occurrence of screened Ti(IV)-enriched Fe(III) clusters
supporting the spin-glass properties at low temperature.
Since all hemo-ilmenite particles in the soil profile
exhibit the same unique magnetic properties, it can be postulated that the source area during the formation
of the alluvial deposit was constant. Moreover, based on the magnetic information, a Permian dolerite
outcropping in the catchment area of the Bafini river in western Burkina Faso in a distance of about 50 km
from the sampling location can be deduced as source area.
This proto-typical study demonstrates that
lithogenic particles carrying unique mineral-chemical and magnetic properties that are characteristic for a
specific origin can have the potential as proxy to deduce landscape development.
GP31C-0815
A new AC susceptibility instrument for detecting frequency dependence over a wide range of frequencies
A unique equipment was developed for measuring low-field AC susceptibility over a frequency spectrum ranging from 10 Hz to 4 kHz. The coil system consists of a primary coil for applying an excitation field, and a set of pickup coils linked in series and wound oppositely for compensation. The number of turns for the primary coil is 6,000 and that for the pickup coils is 4,400, using 0.1 mm thick copper wire, wound around a quartz-glass tube of 36 mm in diameter, allowing to measure conventional 10cc samples. The excitation field is produced by a commercial function generator with two independent outputs, capable of generating sinusoidal current with frequencies of 0 to 10 MHz. A mutual inductor coil is connected in series, to which the wave generator supplies, through the second output, a small current that can be adjusted in phase and magnitude to compensate the out-of-balance of the pickup coils. The resulting signal output voltage is fed to a digital rock-in amplifier. The AC frequency spans practically from 10 Hz to 4 kHz due to the limitation of the lock-in amplifier, but can be swept over the entire range with a constant amplitude of the applied field, which is changeable from 0.4 to 1.0 Oe. The outputs from the lock-in amplifier, in both magnitude and phase, are transferred to a PC to obtain the frequency dependence spectrum of both real and imaginary parts of AC susceptibility. The system calibration was made using a paramagnetic Gd2O3 powder as well as several natural samples that have ever been used for inter-laboratory calibrations.