Environmental Magnetism Approach Research Articles

Magnetic monitoring of anthropogenic pollution in Antarctic soils (Marambio Station) and the spatial-temporal changes over a decade

Marambio Station is one of the most important human settling in the Antarctic Peninsula, which has been polluted by human activities since the 1970s. Following the first magnetic monitoring in Antarctic soils (austral summer Antarctic campaign SAC 2006), a new soil survey was performed during the SAC 2014. We determined elemental contents, observed particles, and measured magnetic parameters of topsoil samples, as well as compared these results with previous ones in order to evaluate changes in pollution (from fuel combustion, solid waste disposal, etc.) over a decade after remediation practices. Magnetic results reveal the presence of magnetite minerals as main carriers with similar grain size and mineralogy-dependent magnetic parameters for both campaigns. In particular, we focus on the well-known proxy for pollution mass-specific magnetic susceptibility χ and geostatistical analysis for studying the spatial-temporal distribution of magnetic minerals for soil sites (n = 238 for SAC 2006; n = 185 for SAC 2014) around the station. The present environmental magnetism approach, combined with geostatistical techniques and the pollution index PLI, reveals a significant pollution decrease as consequence of a national remediation plan.

High-resolution late Middle Pleistocene paleoclimatic record from the Galería Complex, Atapuerca archaeological site, Spain - An environmental magnetic approach

The Galería Complex is a cave sediment succession at the Atapuerca paleoanthropological site (Burgos, Spain) that offers detailed environmental information about the late Middle Pleistocene, especially the period between marine oxygen isotope stages MIS10 and MIS7. Previous studies have reconstructed the chronology and detailed the environmental development of this key succession. We introduce rock magnetic climate proxies from the sedimentary units of the Galería succession that we correlate with the global climate record as represented by the marine oxygen isotope record. The cave sediment sequence consists of five infilling phases, four of which were sampled at high resolution across a 5 m thick composite profile. We propose a novel goethite climate proxy along with a frequently used ultrafine ferrimagnetic mineral proxy for paleoclimate reconstruction and detailed chronostratigraphic correlation with isotope stages and substages MIS10/MIS10-9, MIS9e-a and MIS8. The proxies reveal new paleoenvironmental information about paleoprecipitation and indicate that MIS9e was a humid (∼650 mm/year maximum annual precipitation) and intense interglacial in northern Spain that declined in steps into the globally weak glacial stage MIS8. MIS8 consisted of drier periods with 430–510 mm/year annual precipitation and at least one humid substage (600 mm/year).

Iron oxide mineralogy in Mollisols, Aridisols and Entisols from southwestern Pampean region (Argentina) by environmental magnetism approach

Ferromagnetic compounds of seven southwestern soils from Pampean region comprise iron oxides and oxyhydroxides that have an important role, because of their high surface reactivity, controlling soil adsorption and formation/conservation of soil structure among other properties. We detected minutes of iron oxides quantities by selective dissolution techniques: acid oxalate extraction (<12% of the total Fe) and dithionite-citrate-bicarbonate (<44% of the total Fe), moreover, we identified/quantified mixtures of magnetite, maghemite, goethite and hematite minerals by environmental magnetism approach. The magnetic particle size dependent parameters evidence a relationship with extractable Fe oxides, indicating that magnetic particle size distribution on these soils is a relevant property associated to poorly crystalline and free amorphous Fe oxides. In addition, the particle size and SP concentration of ferromagnetic iron oxides are associated with increments of cation exchange capacity and the specific surface area of soil samples. The estimated amounts of hematite are below 2.20 wt%, and lower contents of about 0.25 wt% correspond to magnetite components. Both magnetic iron oxides concentration, as well as the remanent coercivity, increase towards the western region, on the contrary, anhysteretic ratios decrease and hence relatively coarser magnetic particles are dominant in this western region. The present study provides valuable data to characterize Aridisols, Entisols and Mollisols in a region of high fertility that comprises ones of the world’s most productive agricultural soil region.

Coupled microbial bloom and oxygenation decline recorded by magnetofossils during the Palaeocene\u2013Eocene Thermal Maximum

Understanding marine environmental change and associated biological turnover across the Palaeocene–Eocene Thermal Maximum (PETM; ~56 Ma)—the most pronounced Cenozoic short-term global warming event—is important because of the potential role of the ocean in atmospheric CO2 drawdown, yet proxies for tracing marine productivity and oxygenation across the PETM are limited and results remain controversial. Here we show that a high-resolution record of South Atlantic Ocean bottom water oxygenation can be extracted from exceptionally preserved magnetofossils—the bioinorganic magnetite nanocrystals produced by magnetotactic bacteria (MTB) using a new multiscale environmental magnetic approach. Our results suggest that a transient MTB bloom occurred due to increased nutrient supply. Bottom water oxygenation decreased gradually from the onset to the peak PETM. These observations provide a record of microbial response to the PETM and establish the value of magnetofossils as palaeoenvironmental indicators.

An environmental magnetism approach to assess impacts of land-derived sediment disturbances on coral reef ecosystems (Cartagena, Colombia)

We used environmental magnetism methods to study recently deposited marine sediments from the estuarine ecosystems on the Caribbean coast of Colombia. Cartagena region has undergone an increasing sediment load during the last decades via sediment plumes from Magdalena River and its distributary man-made channel. Concentration dependent magnetic parameters show an increasing abundance of ferrimagnetic minerals on the uppermost sediments on sites located close to the continent (remanent magnetization SIRM = 5.4–9.5 × 10−3Am2 kg−1) as well as faraway sites (SIRM = 0.5–1.7 × 10−3Am2 kg−1 near Rosario Islands coral reef complex). The magnetic grain size and mineralogy along the cores are variable, showing the dominance of the magnetite-like minerals (remanent coercivity Hcr = 34.3–45.3 mT), with a minor contribution of high-coercivity minerals (Hcr = 472–588 mT). In addition, there is a moderate enrichment of elements Cu, Mo, and Zn (enrichment factor EF = 1.5–3.8) that indicates the additional land-derived contribution on sediments. The environmental magnetism approach, which shows significant signals of magnetic minerals and trace elements, is a reliable tool to prove the presence of continental sediment supply in coral reef ecosystems.

Holocene sedimentary records of the Katarraktes cave system (northern Greece): a stratigraphical and environmental magnetism approach

The Katarraktes cave system is located in northern Greece and is a complex of a rockshelter and a cave formed on the south river bank of Krousovitis River canyon (Serres, Macedonia region). The archaeological site area is well known as one of the most important archaeological sites in SE Europe since it hosts numerous archaeological findings dating back to the Early Bronze Age. Detailed stratigraphic analysis of three archaeological sections was performed in order to define the depositional conditions of the cave entrance facies sediments. Mineral magnetic properties were performed to enhance the paleoenvironmental interpretations and to detect sediment origins. Magnetic susceptibility (klf) obtained in high and low frequency as well as remanence parameters, such as saturation isothermal remanent magnetization (SIRM) and S-ratio, were measured in samples collected2from the archaeological sections. Results indicate a significant variability in the magnetic signal stored in the sedimentary record of Kataraktes cave system distinguishing between natural and anthropogenic sequences. The combination of the stratigraphic and magnetic results along with the archaeological data reveals that flood events of Krousovitis River and sediment accumulation from slackwater in the rockshelter area occurred around 3000 yr BC and were possibly the key factor for the abandonment of the prehistoric settlement.

Environmental response of a fragile, semiarid landscape (Bardenas Reales Natural Park, NE Spain) to Early Holocene climate variability: A paleo- and environmental-magnetic approach

Abstract The Bardenas Reales Natural Park (western Ebro Basin, NE Spain) constitutes a fragile landscape where the prevailing semiarid climate and erodability of the bedrock have resulted in high sensitivity to erosion/sedimentation oscillations during the Holocene. In this paper, we present new chronologic, sedimentologic, paleomagnetic and environmental magnetic results from the oldest unit (Qah1) of a system of nested cut-and-fill alluvial sequences, which is 18 m thick and crops out extensively in the central part of the natural park at the Bardena Blanca Depression. Radiocarbon dating indicates that Early Holocene unit Qah1 is younger than 9.38–8.89 cal kyr BP and gives ages of 8.92–8.42 and 7.59–7.37 cal kyr BP in the middle and uppermost parts of the unit, respectively. Sedimentologic data indicate that distal alluvial sediments of unit Qah1 accumulated in sandy mud flats and ephemeral playa lakes under arid conditions. The coincidence of enhanced magnetite content with moderate to intense root bioturbation in the lowermost and likely also uppermost sediments of unit Qah1 suggests that magnetite formed authigenically in response to relatively wetter conditions at the beginning and end of this dry period. These results indicate that onset and cessation of alluvial aggradation mark the passing of a geomorphologic threshold, most likely plant cover in the watershed, during a progressive drying–wetting event. The radiocarbon-based age model of unit Qah1 indicates that alluvial aggradation under arid conditions began at 9.13 cal kyr BP and ended at 7.16 cal kyr BP. This period is strikingly centered at around the 8.2 kyr cold event but spans a longer time period, supporting the notion of a global climatic deterioration as the underlying cause for this event. Paleomagnetic directions do not clearly display the characteristic patterns recognized in paleosecular variation curves derived from other European lacustrine sediments and cannot be used to refine the radiocarbon-based age model for unit Qah1. Our results demonstrate a quick and strong response of alluvial systems to Early Holocene climate variability in fragile Mediterranean landscapes such as those at the semiarid Bardenas Reales Natural Park.

Mid-Late Quaternary loess-paleosol sequence in Lantian’s Yushan, China: An environmental magnetism approach and its paleoclimatic significance

The application of rock magnetism methods to investigating the variations of magnetic minerals in the sediments is an important approach to the reestablishment of paleoclimate evolution. Thus we performed fine magnetic measurements on the loess-paleosol sequence (from L15 upwards to S5, in which L is short for Loess, S is short for Paleosol, the same hereinafter) of Yushan stratigraphic section, which is on the southeastern margin of Chinese Loess Plateau, in Lantian County of China’s Shaanxi Province, and the thickness of which is ca. 40 m. Our study shows that the primary magnetic carriers of loess and paleosol in this section are magnetite, maghemite, hematite and goethite. Thermomagnetic analyses on the samples of representative horizons show that the higher pedogenesis degree of the sediments, the smaller variations of magnetization there will be before and after heating, probably related to the pedogenic alteration of loess sediments. Analyses of several magnetic parameters show a significant discrepancy between the paleoclimatic conditions recorded in the strata from the loess unit L15 upward to the paleosol unit S5 in the study area and those recorded in the relative strata of other sections on the Chinese Loess Plateau, and those recorded in marine sediments, indicating the great impact of regional geological background. Similarly, the rapid and intensive change recorded in the segment from L15 to S9-1, and the significant difference between the paleoclimate evolutions of the two periods before and after the change (from L15 to S9-1, and from L9 to the base of S6) indicate the strong alteration of magnetic carriers in the study area as a result of the alternations of summer and winter monsoons in East Asia.

Assessment of suspended particulate pollution in the Bhadra River catchment, Southern India: an environmental magnetic approach

Open-cast mining generates sediment in river systems at globally significant scales. One of the challenges in attributing measured sediment loads to upstream mining activities is establishing the source of sediments that are a mixture of natural and mining-based materials. The environmental magnetic data (mass-specific magnetic susceptibility, anhysteretic remanent magnetisation, isothermal remanent magnetisation and inter-parametric ratios) on 57 samples of suspended sediment from the Bhadra River in the Sahyadri (the Western Ghat) of India have been used in this study. Samples were collected upstream, adjacent to and downstream of Kudremukh, a mountainous and high rainfall site where the largest mechanised open-cast mine in south Asia was located. Graphical and multivariate analyses and modelling of the data show that on average ~29% of the river suspended load downstream of the mine is derived from mining and allied activities at Kudremukh although the mine occupies less than 5% of the catchment. The contribution of primary ore is the maximum (18%), followed by transitional hard weathered ore (7%) and weathered ore (4%). The model has done a fairly good job of unmixing; the sum of errors is 71,000 for four samples. Modelling of samples with small mass seems to produce large errors. This investigation demonstrates the utility of environmental magnetic data, which can be obtained in a simple and rapid manner, and the unmixing of such data in identifying the contribution of mining activities to the total suspended sediment load.

The detection of roadside pollution of rapidly growing city in arid region using the magnetic proxies

This work is a complementary investigation to the earlier urban soil survey for a rapidly growing city of relatively high traffic density. Therefore, it aims to apply the environmental magnetism approach to assess the roadside pollution at a known polluted site. The used magnetic proxies are the initial magnetic susceptibility and saturation magnetization. The results prove the applicability of this method in detecting roadside pollution. The shape and magnitude of the magnetic signals was affected by the topography and prevailing wind direction that caused the magnetic peaks to be shifted accordingly. Particle size was found to affect the magnetic material content, where sand size (63–150 μm) bears the highest magnetic signals relative to smaller silt size (<63 μm). The magnetic anomalies coincided positively with heavy metal pollution in the studied site, which might indicate that the magnetic materials serve as an effective proxy for the metallic pollution (i.e., Fe, Ni, Pb, Cu, and Zn) originated mainly from vehicular sources.

Environmental magnetic approach towards the quantification of pollution in Kathmandu urban area, Nepal

The Kathmandu Valley is a bowl-shaped intermontane basin, which occupies an area of 583 km 2 in the heart of the Himalayas, with its floor at ≈1400 m and the surrounding mountains attaining a height of 2000–2800 m. It is inhabited by ≈1.5 million people, concentrated mostly in three cities, Kathmandu, Patan and Bhaktapur. Due to rapid but uncontrolled urbanisation and factors such as traffic movement, emissions from brick-kilns, cement factories, waste disposal and biomass burning, environmental pollution has been constantly increasing; adversely affecting land, water, air and biological systems. In order to quantify the degree of environmental pollution using magnetic methods, magnetic susceptibility of soils, sediments and roadside materials, in and outside the Kathmandu urban area has been measured. In areas far from roads or industry, median magnetic susceptibility is between 3 and 35 × 10 −5 SI, similar to that observed in the valley-filling clastic sediments and hence consistent with geologic or pedogenic origin. In traverses of in situ susceptibility across roads, a 5-m wide zone situated on either side of the asphalt-paved road exhibits an enhancement zone with maximum susceptibility of 240–850 × 10 −5 SI occurring 0.5–2.5 m from the road edge. In urban recreational areas, magnetic susceptibility varies within a broad range (3 to >100 × 10 −5 SI) with lowest values occurring ≈50 m from surrounding roads, in areas least disturbed by human activity. A systematic increase in susceptibility towards the roads or industrial sites is observed. Within urban areas, in the vicinity of heavy traffic or industrial sites, the upper 30–50 cm of soil profiles exhibit frequent enhancement in susceptibility, of one or two orders of magnitude, higher than those expected from geologic input. Such enhancement is attributed to input from anthropogenic or industrial sources. Magneto-mineralogical analyses and scanning electron microscopy on magnetic extracts, grain size fractions or bulk samples of road dust and soils, suggest lithogenic magnetite-like minerals and anthropogenic magnetic spherules to be the dominant contributors to the magnetic susceptibility signal. As the soils, sediments and roadside material exhibit significant susceptibility contrasts, which are most effective in identifying traffic-related pollution “hotspots”, it is highly desirable that the potential of susceptibility maps of the entire area affected by urbanisation, be fully explored to assess the status of environmental degradation.

Magnetic properties of marine sediment near the active Dead Dog Mound, Juan de Fuca Ridge, allow to refine hydrothermal alteration zones

We use environmental magnetic methodology to assess the effects of focused hydrothermal fluid discharge on Pleistocene marine sediment, that covers the Juan de Fuca Ridge in Middle Valley. Ocean Drilling Program Leg 169 Holes 1036A through C were drilled in the vicinity of one of the active mounds in the Dead Dog Vent Field (DDVF). Previous shipboard visual core description, geochemical, and smear slide analyses indicated that these three holes represent a transect from moderately to strongly hydrothermally altered sediment. The latter was best represented by the definition of lithological zones based on sediment-mineralogical criteria, for example, the first occurrence of anhydrite. The latter suggested that the 100–150 °C isotherm dips away from the active mound over a short lateral distance of about 100 m. The ubiquitous trace amount of the remanent magnetic minerals in marine sediment in Holes 1036 is highly sensitive to both temperature and fluid induced post-depositional alteration of the sediment and indicates that our environmental magnetic approach allows for a refined definition of the lithological alteration zones as well as the establishment of additional lateral hydrothermal fluid flow.

Fingerprinting of bed sediment in the Tay Estuary, Scotland: an environmental magnetism approach

Abstract. Sediment fingerprinting is commonly used for sediment provenance studies in lakes, rivers and reservoirs and on hillslopes and floodplains. This investigation explores the mixing of terrestrial and marine-derived sediment in the Tay Estuary, Scotland, using mineral magnetic attributes for fingerprinting. Samples representative of the estuary sediments and of four sources (end-members) were subjected to a suite of magnetic susceptibility and remanence measurements. Sediment samples from the beds of the Rivers Tay and Earn represented fluvial inputs while samples from the Angus and Fife coasts represented marine input. Multivariate discriminant and factor analysis showed that the sources could be separated on the basis of six magnetic parameters in a simple multivariate unmixing model to identify source contributions to estuarine bed sediments. Multi-domain magnetite signatures, characteristic of unweathered bedrock, dominate the magnetic measurements. Overall contributions of 3% from the River Earn, 17% from the River Tay, 29% from the Angus coast and 51% from the Fife coast source end-members, demonstrated the present-day regime of marine sediment derivation in the Tay Estuary. However, this conceals considerable spatial variability both along-estuary and in terms of sub-environments, with small-scale variations in sediment provenance reflecting local morphology, particularly areas of channel convergence. Keywords: bed sediment, environmental magnetism, fingerprinting, Tay Estuary, Scotland