Sediment Magnetic Susceptibility Research Articles

The usefulness of the magnetic susceptibility of loess paleosol sequences for paleoclimate and stratigraphic studies: The case of the Quaternary Palouse loess, northwestern United States

Worldwide, Quaternary loess-paleosol sequences archive terrestrial paleoenvironmental information. The Palouse loess in the northwestern USA is one such deposit representing at least a million years of sediment accumulation. Loess paleosol sequences are often studied via the magnetic susceptibility of sediments and the changes in susceptibility with depth. However, since variations in magnetic susceptibility can have different underlying causes, the interpretation of the magnetic susceptibility of loess depends on factors specific to each major loess region. We measured the magnetic susceptibility of sediments along depth profiles in a well-studied exposure of the Palouse loess in eastern Washington, USA (the “CLY-2 site,” 46.3131° N, 118.4874° W, WGS84). Our measurements show that the magnetic susceptibility of sediments in the Palouse loess varies systematically and predictably with depth and can be correlated with other magnetic susceptibility profiles at the outcrop scale and at the regional scale. We also measured changes in grain size, elemental abundance, mineralogy, and other magnetic properties to determine the most likely cause of the magnetic susceptibility signal. Based on these results, variations in magnetic susceptibility in the Palouse are likely driven mostly by changes in coarse sediment supply and accumulation of tephra rather than changes in weathering. Magnetic susceptibility is useful as an inexpensive, non-destructive tool for stratigraphic correlation of Quaternary loess deposits in the Palouse, especially in combination with paleosol stratigraphic markers and known tephra deposits.

Depositional environments and sequence stratigraphy of post-last glacial maximum incised valley-fill, Malay Basin, northern Sunda Shelf

The alternating submergence and subaerial exposure of the low-gradient, shallow Sunda Shelf of southeast Asia during Quaternary interglacial-glacial cycles played an important role in ocean circulation and monsoonal climate through the interchange of Indian Ocean and Pacific Ocean waters. The Quaternary stratigraphic development of this margin is, however, poorly understood. This study uses a multi-proxy approach (AMS radiocarbon, bulk sediment magnetic susceptibility, X-ray fluorescence spectrometry, and foraminiferal assemblage data) to characterize environmental change and late Pleistocene to Holocene sequence stratigraphic architecture in 16 cores from the northern Sunda Shelf off the east coast of Peninsular Malaysia.Five chronostratigraphic units are recognized. Unit 1 is an inner shelf deposit dating from a late Pleistocene sea-level highstand (the highstand systems tract of the pre-LGM base-level cycle). Units 2–4 represent different paleoenvironmenal components of the transgressive systems tract (TST) of the most recent base-level cycle. Unit 2 is a late Pleistocene shallow open embayment deposit that formed during the post-LGM inundation of the paleo-Chao Phraya River valley as sea level rose. Unit 3 is composed of late Pleistocene to early Holocene paralic peat and organic-rich mud and is capped by a transgressive ravinement surface. Unit 4 is a shallow shelf unit deposited during the early Holocene transgression on the Sunda Shelf prior to ca. 6500 cal yr BP (the onset of the regional Holocene sea-level highstand). Unit 5 represents the mid-Holocene to recent highstand systems tract (HST) deposited from ca. 6500 cal yr BP to present.The incised paleovalleys of the paleo-Chao Phraya River and its tributaries provide more accommodation space for sediment accumulation than the surrounding shelf. However, the thinness of the Holocene sedimentary record, 2–3 m in the incised valleys compared to <1 m over the adjacent shelf, indicates that the LGM incised valleys were almost filled by fluvial and coastal plain sediments before open marine conditions returned near the beginning of the Holocene. The multi-proxy approach of this study elucidates the geologic response of this shelf to sea-level rise and the sequence stratigraphic development of tropical, siliciclastic-dominated shallow shelf depositional sequences.

Palaeoseismic records in lacustrine sediments—A case study of the Daqingshan piedmont fault and Hasuhai Lake in Inner Mongolia, China

AbstractAs a traditional method for palaeoseismic studies, trenching can be combined with dating techniques to identify palaeoseismic events and the earthquake recurrence interval. However, when using trenches to study palaeoearthquakes, factors such as the active tectonic background of the earthquake‐caused structure, the lithology on both sides of the fault, the geomorphology location and type and the samples and methods for dating will affect the location of the trench. Thus, trenches should be carefully selected and used to identify the impact of ancient earthquakes. The results have substantial uncertainties and limitations. In recent years, scholars have made considerable progress in using other methods to reveal the palaeoseismic information of faults. Moreover, the history of fault activity may have been recorded in the lacustrine sediment adjacent to the fault. Hasuhai Lake is adjacent to the middle segment of the Daqingshan piedmont fault in Inner Mongolia. Since the Holocene, the region has experienced a temperate continental semi‐arid climate with little interference, and Hasuhai Lake and peripheral waters present weak hydrodynamic conditions that provide an ideal location for the study of palaeoseismic records in lacustrine sediments. Sediment samples and samples for dating were collected from three trenches excavated on the periphery of the Hasuhai Lake. Their variations in grain size and magnetic susceptibility revealed that wind and flowing water jointly produced the sedimentary conditions of Hasuhai sediments. The 14C dating results and variations in the grain size distribution, grain size components and magnetic susceptibility of sediments caused by seismic events obtained in this study were compared with those caused by a series of palaeoseismic events at the middle segment of the Daqingshan piedmont fault reported by previous studies using trenches, knickpoints and palaeosol records. The results identified seven palaeoseismic events recorded near Hasuhai Lake since 12,000 years. The combined use of lacustrine sediment variation characteristics and dating techniques is an effective method for studying palaeoseismic events.

Magnetic susceptibility parameters as proxies for desert sediment provenance

Magnetic susceptibility in sediments has been thoroughly studied as a paleoenvironmental proxy over the last decades. However, it is unknown to what extent magnetic susceptibility variation is also a diagnostic of different sediment sources. Here we investigate if multiple magnetic susceptibility-based parameters can effectively be used as sediment source indicators. New magnetic property data from the Mu Us and Tengger Deserts in China are compared to previously known sediment provenance based on other well-established proxies. To assess the magnetic properties of these deserts, magnetic susceptibility and its out-of-phase component, its dependence on frequency, temperature and low-field amplitude are analyzed. Our results indicate similar sources for the western Mu Us Desert and the Tengger Desert and a distinct source for the eastern Mu Us, in-line with previously hypothesized provenance patterns. However, magnetic properties within the Tengger Desert sediments are homogenous, which may suggest a uniform provenance for the entire Tengger Desert, that the sediments are greatly reworked, or similar magnetic properties in potential multiple source regions. Magnetite is the major magnetic mineral in the study area and the dominant causes for divergence in magnetic properties are the magnetic mineral concentration and domain state. The results here, in particular from the Mu Us, suggest considerable promise for using magnetic susceptibility parameters in desert sediment provenance research.

Recent cyanobacteria abundance in a large sub-tropical reservoir inferred from analysis of sediment cores

Salto Grande is a large South American reservoir on the border between Uruguay and Argentina that was impounded in 1979 and experiences recurrent, massive cyanobacteria blooms. A water-monitoring program was initiated 20 years after the dam was built, hence the causes and onset of cyanobacteria blooms remain poorly known. We collected two sediment cores from the old river channel in the reservoir (z = 17 m) and used physical, chemical and biological variables in the sediments, along with existing limnological data, to explore the history of cyanobacteria in the sub-tropical water body. Cyanobacteria fossil pigments were present at low concentrations during the first 24 years after impoundment, but more than doubled thereafter. Phytoplankton abundance tracked shifts in cyanobacteria pigment concentration, indicating an overall increase in all primary producers. Several sediment variables indicate a decline in water quality after 2003, such as increases in the number of photosynthetic sulfur bacteria and a reduction in sediment magnetic susceptibility. Akinetes (dormant cyanobacteria cells, Order Nostocales) in recent reservoir deposits were abundant and five species germinated under laboratory conditions, underscoring the ability of akinetes to initiate cyanobacteria blooms. The germinated assemblage reflected closely the composition of cyanobacteria blooms in the reservoir. Recorded increases in air temperature and decreases in wind speed, together with other variables (e.g. nutrients), can promote the large, recurrent cyanobacteria blooms. Invasion of the bivalve Limnoperna fortunei apparently promoted cyanobacteria blooms by preferential feeding on other phytoplankton taxa, and perhaps by altering nutrient concentrations and ratios. This work highlights the potential for using multiple variables in sediment cores from large reservoirs to better understand the responses of biota to multiple environmental stressors.

Exploring ground-penetrating radar and sediment magnetic susceptibility analyses in a sandstone rockshelter in northern Australia

Ground-penetrating radar (GPR) surveys offer several advantages for non-invasively assessing stratigraphy in archaeological rockshelters, including providing information about subsurface stratigraphy and the location of features such as roof fall and bedrock. Challenges to understanding the record of human impact and site formation processes in Australian rockshelter deposits include where to position archaeological excavations, how best to determine the onset of human occupation within sequences beyond the presence of stone artefacts (which can be limited at depth owing to sampling issues) and how to resolve issues relating to stratigraphic associations. This paper demonstrates how GPR can be used to gain a better understanding of buried deposits in a Pleistocene-aged rockshelter. When compared with results from sediment magnetic susceptibility studies, GPR verified the major stratigraphic units identified at the site, the depth of bedrock and the presence of roof fall, but it also provided information on the sediment volume within the stratigraphic units. This is a unique outcome for exploring rockshelter deposits and geophysical signatures overall, aiding in the interpretation of complex site sediments and offering a useful tool for future site investigations. Abbreviations: GPR: ground-penetrating radar; GS1: Gledswood Shelter 1; SU: stratigraphic unit; LOI: loss on ignition; MHz: mega hertz; ns: nanosecond; GSSI: Geophysical Survey Systems Inc.; Hz: hertz; P: phosphorus; Xfd: frequency dependence; PSA: particle size analysis; Tc: Curie temperature; YR: yellow red

The magnetic susceptibility analyzes of Motonuno lake sediment in Muna Regency, Southeast Sulawesi, Indonesia

Study on the magnetic susceptibility, magnetic mineral, and content of element contained in the sediment has been done at Motonuno Lake Sediment in Muna Regency, Southeast Sulawesi Indonesia. Sediment samples in the form of cores were taken from three different sites by using the gravity core tool. Measurement of the magnetic susceptibility values was carried out by using the MS2C susceptibilitymeter. Content of element in the sediment was measured by using the SEM-EDX tool. The results showed that the magnetic susceptibility of sediment is -1 x 10−5 SI to 3 x 10−5 SI (site 1) and -2 x 10−5 to 2 x 10−5 SI (site 2 and site 3). Based on the value of magnetic susceptibility, the dominant magnetic mineral in the three sediment cores is pyrite (FeS2) which is an authgenic magnetic mineral. All three sediment core samples show that magnetic susceptibility values tend to be higher at the bottom of core than the top of core. This means that the sediment deposition takes place on different climate conditions, namely dry climate and wet climate. The elements contained in the sediment consists of O, Ca, Si, S, Al, Na, Cl, Fe, Mg, Au, Ti, Co, Cu, and Ni. All magnetic informations obtained in this study are very important in the understanding of paleoclimate condition at Motonuno Lake and its surrounding areas.

Reconstructing human–landscape interactions in the context of ancient iron smelting on Elba Island, Italy, using sedimentological evidence

AbstractWe reconstruct human–landscape interactions in the context of ancient bloomery smelting on Elba Island, Tyrrhenian Sea, based on sedimentological evidence. Elba was, together with Populonia, the center of iron production in antiquity (mid‐6th century B.C.E. to 1st century C.E.). The sediment sequences obtained by vibracoring in the Campo plain reveal that the Holocene transgression triggered aggradation during the Early–Middle Holocene (&gt;5.4 ka cal BP). Nevertheless, wetland conditions prevailed in low‐lying areas during Roman times. Correspondingly, ancient smelting sites are found only on elevated areas along the edge of the plain. The palaeolandscape thus plays a key role in understanding location factors for smelting sites in antiquity. Our sediment sequences indicate that during Etrusco–Roman times (2.4–2.0 ka cal BP) morphodynamics on the island increased, as is evident from the alteration of slope deposits and slack water deposits in upstream positions, and the change from lacustrine to alluvial deposition in downstream areas. The charcoal record shows that fire dynamics increased simultaneously. The sediments that are synsedimentary to the ancient smelting period show significantly increased arsenic contents and high sediment magnetic susceptibility, whereas overall concentrations of heavy metals remain in the range of the geogenic background signal.

Statistical assessment to magnetic susceptibility and heavy metal data for characterizing the coastal sediment of East coast of Tamilnadu, India

A rapid urbanization and industrialization enhances the significant heavy metal pollution in the sediments of coastal area and introduced a serious threat to the human health. In the present study, concentration of heavy metals such as Al, Ti, Fe, V, Cr, Mn, Co, Zn, La, Pb, Mg, Ca, Ni, Cd and Ba are determined in sediments along Periyakalapet to Parangaipettai coastal area, Tamilnadu using energy dispersive X-ray fluorescence spectrometer (EDXRF).These metals have more affinity to establish metallic bond with ferrous material leading to enhancement of sediment magnetic susceptibility. Hence, a magnetic susceptibility (χLF, χHF, χFD) measurement was carried for sediments by using MS2B dual frequency susceptibility meter. Multivariate statistical analysis (Pearson correlation, factor and cluster analysis) was carried out between heavy metals and magnetic susceptibility to assess the anthropogenic impact in the sediments. The study revealed that a magnetic susceptibility measurement is an inexpensive, fast, non-destructive and suitable method to identify the heavy metal pollution sources.

Determination of grain-size characteristics from electromagnetic seabed mapping data: A NW Iberian shelf study

The electric conductivity and magnetic susceptibility of sediments are fundamental parameters in environmental geophysics. Both can be derived from marine electromagnetic profiling, a novel, fast and non-invasive seafloor mapping technique. Here we present statistical evidence that electric conductivity and magnetic susceptibility can help to determine physical grain-size characteristics (size, sorting and mud content) of marine surficial sediments. Electromagnetic data acquired with the bottom-towed electromagnetic profiler MARUM NERIDIS III were analysed and compared with grain size data from 33 samples across the NW Iberian continental shelf. A negative correlation between mean grain size and conductivity (R=−0.79) as well as mean grain size and susceptibility (R=−0.78) was found. Simple and multiple linear regression analyses were carried out to predict mean grain size, mud content and the standard deviation of the grain-size distribution from conductivity and susceptibility. The comparison of both methods showed that multiple linear regression models predict the grain-size distribution characteristics better than the simple models. This exemplary study demonstrates that electromagnetic benthic profiling is capable to estimate mean grain size, sorting and mud content of marine surficial sediments at a very high significance level. Transfer functions can be calibrated using grains-size data from a few reference samples and extrapolated along shelf-wide survey lines. This study suggests that electromagnetic benthic profiling should play a larger role for coastal zone management, seafloor contamination and sediment provenance studies in worldwide continental shelf systems.

Climatic periodicities recorded in lake sediment magnetic susceptibility data: Further evidence for solar forcing on Indian summer monsoon

The Indian summer monsoon exhibits considerable spatio-temporal variability. It is therefore important to understand its dynamics and the inherent periodicities. In this study, we have performed spectral and wavelet analyses of magnetic susceptibility data for sediments from Thimmannanayakanakere (TK)–a small lake in southern India. The main objective of this investigation is to identify and explain the possible origin of the prominent periodicities present in the magnetic susceptibility data. Significant periodicities in the TK χlf data are centered at 906, 232, 147, 128, 96, 61, 54 and 44 years, which might have a solar origin. The wavelet power spectrum of the raw and detrended χlf data confirms the findings of spectral analysis and also provides temporal variations of the significant cyclicities during the past 3700 cal. years B.P. Positive correlation is documented between sunspot activity and TK χlf data; cross-spectral analysis of the reconstructed sunspot data and TK χlf data suggest that there is a strong coherence between the two datasets as significant periodicities are documented in both. There is a good match between the TK χlf and the reconstructed total solar irradiance data for the past 1200 years. However, an out-of-phase relationship is documented at certain time-intervals, which may be attributed to uncertainties in the age-depth model. The results obtained from this study show that solar variations are the main controlling factor of the southwest monsoon and, like other archives from different regions in India, the TK lake sediments have also recorded these solar signatures.

A multi-proxy study of anthropogenic sedimentation and human occupation of Gledswood Shelter 1: exploring an interior sandstone rockshelter in Northern Australia

Rockshelters contain some of the most important archives of human activity in Australia but most research has focused on artifacts and cultural context. This study explores geomorphological and geoarchaeological approaches for understanding a sandstone rockshelter in interior northern Australia: Gledswood Shelter 1. At this site, magnetic susceptibility and micromorphology techniques were integrated with bulk sedimentology, soil chemistry and geochronology to better understand the record of human impact and site formation processes. The micromorphology studies indicate that primary depositional fabrics, such as graded bedding or laminations, are absent, and sediment structural development is low throughout the entire sequence, with most samples exhibiting a high degree of post-depositional mixing. The sediment magnetic susceptibility analysis reveals magnetic changes coinciding with human occupation, a result of anthropogenic burning. Specifically we highlight that combustion features are prevalent in this sandstone shelter and provide critical insights into the human usage of the shelter.

Biogenic silica in surface sediments of the South China Sea: Controlling factors and paleoenvironmental implications

We mapped the spatial distribution of biogenic silica (BSi) based on a total of 355 surface sediment samples from the South China Sea to provide a basin-wide BSi data set for paleoenvironmental reconstruction in the region. The results show that BSi relative abundance, calcium carbonate percentage, siliceous test total abundance, grain size and sediment magnetic susceptibility all show distinct spatial distribution patterns that are affected by environmental drivers. The gradual increase in BSi from the continental shelf to the abyssal plain suggests that decreased dilution of terrigenous sediments plays a greater role in BSi preservation than does increasing dilution by CaCO3, decreasing productivity or siliceous dissolution. The BSi correlation is weak for diatom abundance but relatively good for radiolarians, confirming that radiolarians are the primary contributor to BSi fluxes in the low-latitude South China Sea. In contrast, increased dissolution results in a decrease in CaCO3 with increasing water depth, reflecting the different preservation patterns of these two biogenic components. Correlation analysis also reveals a positive correlation between BSi and fine grain size, perhaps reflecting the ability of clay minerals to protect BSi from dissolution; volcanic ash and glass also can retard dissolution by increasing the pore-water saturation of SiO2 in abyssal basin sediments.

Vetygala Exposure: the problem of the lower boundary of Pleistocene

The presented results of palaeomagnetic and lithological investigations of the Vetygala Exposure are one more attempt to solve the problem of the lower boundary of the Pleistocene in Eastern Lithuania. Five lithological complexes distinguished in the deposit sequence of the Vetygala Exposure of up to 22 metres height were studied by means of lithology and palaeomagnetism. Carbonate analysis undertaken showed that the amount of carbonates is increasing only in the uppermost part of outcrop, but some carbonate content in the lower part suggests that the sediments in the Vetygala Exposure could have formed at the beginning of the Pleistocene. Results of measurements of the magnetic susceptibility of sediments and the determination of the anisotropy of magnetic susceptibility and remanent magnetisation for orientated samples from clayey silt interlayers demonstrate that changes of Earth’s magnetic field polarity were frequent during the sediments deposition and maintain about a relatively long period of sedimentation. The results of recent lithological and palaeomagnetic studies do not give a straight answer about the stratigraphical identity of investigated sediments. Thus, the stratigraphical subdivision of sediments in the Vetygala Exposure and their correlation with neighbouring geological sections are still open to variable interpretation.

Climate and environmental changes over the past 150 years inferred from the sediments of Chaiwopu Lake, central Tianshan Mountains, northwest China

We used a 55-cm sediment core from shallow Chaiwopu Lake in the central Tianshan Mountains of Xinjiang, northwest China, to investigate climate and environmental changes in this arid region over the past ~150 years. The core was dated using 137Cs. We compared temporal changes in several sediment variables with recent meteorological and tree-ring records. Organic matter had a positive correlation with the Palmer Drought Severity Index in the central Tianshan Mountains, and the δ13C of organic matter had a positive correlation with regional temperature. We applied constrained incremental sum-of-squares cluster analysis to element concentrations in the core and identified three distinct zones: (1) 55–46 cm, ~1860–1910, (2) 46–26 cm, ~1910–1952, and (3) 26–0 cm, 1952–present. Between 1880 and 1910 AD, following the Little Ice Age (LIA), the sediment environment was relatively stable, climate was cold and dry, and the lake water displayed high salinity, in contrast to conditions during the LIA. During the LIA, westerlies carried more water vapor into Central Asia when the North Atlantic Oscillation was in a negative phase, and encountered the enhanced Siberia High, which probably led to increased precipitation. In the period 1910–1950 AD, the lake was shallow and the regional climate was unstable, with high temperatures and humidity. In the last ~15–20 years, human activities caused an increase in sediment magnetic susceptibility, and heavy metal and total phosphorus concentrations in the sediment were substantially enriched. Mean annual temperature displays a warming trend over the past 50 years, and the lowest temperature was observed in the 1950s. There has been an increase in annual total precipitation since the 1990s. The combined influences of climate and human activity on the lake environment during this period were faithfully recorded in sediments of Chaiwopu Lake. This study provides a scientific basis for environmental management and protection.

Organic, elemental, and geochemical contributions to lake sediment deposits during severe spruce beetle (Dendroctonus rufipennis) disturbances

Recent outbreaks of native bark beetles are unprecedented during the historical period. The aim of this manuscript is to develop a proxy-based methodology to infer past bark beetle outbreaks using lake sediments to provide long-term context for recent outbreaks. We test three hypotheses to determine how the ecological impacts of severe spruce beetle (Dendroctonus rufipennis Kirby) disturbances are recorded in lake sediment deposits. The resulting mortality and defoliation of Engelmann spruce is hypothesized to: (1) decrease the ratio of spruce to fir pollen; (2) reduce canopy interception of precipitation leading to an increase in soil erosion and/or enhanced mobilization of terrestrial carbon; and (3) leach foliar nitrogen and enhance algal productivity resulting in increased nitrogen values in lake sediments. To test these hypotheses, we analyzed sediment cores from six spruce beetle-affected basins in Utah for spruce/fir pollen ratio (hypothesis 1), loss-on-ignition, magnetic susceptibility of sediments (hypothesis 2), and δ13CBOM, δ15NTN, elemental C and N, and the C/N ratio of bulk organic material (hypotheses 2 and 3). The dataset was statistically tested using general linear mixed models (GLMMs) to determine if the response variables differed significantly between outbreak and non-outbreak period. The spruce/fir pollen ratio responded significantly to outbreaks at all sites suggesting that this metric may be the most suitable for identifying past spruce beetle outbreaks. For our second hypothesis we found little support for an influx of terrestrial C due to strongly individualist responses of the basins. For our third hypotheses we found little support for increased sedimentary nitrogen, likely due to alterations to nutrient cycling from human activities. Therefore the host/non-host pollen ratio provides the most promising metric for detecting past outbreaks.

ГЕОДИНАМІКА

Magnetic susceptibility of sediments in the northern edge of the Dniepr-Donetsk depression was analyzed. Possibilities of c-metering implementation for vertical division and investigations of geological cross-section, also as correlations of defined elements were shown.

Near-surface electromagnetic, rock magnetic, and geochemical fingerprinting of submarine freshwater seepage at Eckernförde Bay (SW Baltic Sea)

Submarine groundwater discharge in coastal settings can massively modify the hydraulic and geochemical conditions of the seafloor. Resulting local anomalies in the morphology and physical properties of surface sediments are usually explored with seismo-acoustic imaging techniques. Controlled source electromagnetic imaging offers an innovative dual approach to seep characterization by its ability to detect pore-water electrical conductivity, hence salinity, as well as sediment magnetic susceptibility, hence preservation or diagenetic alteration of iron oxides. The newly developed electromagnetic (EM) profiler Neridis II successfully realized this concept for a first time with a high-resolution survey of freshwater seeps in Eckernforde Bay (SW Baltic Sea). We demonstrate that EM profiling, complemented and validated by acoustic as well as sample-based rock magnetic and geochemical methods, can create a crisp and revealing fingerprint image of freshwater seepage and related reductive alteration of near-surface sediments. Our findings imply that (1) freshwater penetrates the pore space of Holocene mud sediments by both diffuse and focused advection, (2) pockmarks are marked by focused freshwater seepage, underlying sand highs, reduced mud thickness, higher porosity, fining of grain size, and anoxic conditions, (3) depletion of Fe oxides, especially magnetite, is more pervasive within pockmarks due to higher concentrations of organic and sulfidic reaction partners, and (4) freshwater advection reduces sediment magnetic susceptibility by a combination of pore-water injection (dilution) and magnetite reduction (depletion). The conductivity vs. susceptibility biplot resolves subtle lateral litho- and hydrofacies variations.

Palaeoclimatological and palaeolimnological records from fossil midges and tree-rings: the role of the North Atlantic Oscillation in eastern Finland through the Medieval Climate Anomaly and Little Ice Age

Hydrological changes and air temperature variability are reconstructed from the sediments of Lake Pieni-Kauro, eastern Finland during the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA) using transfer functions derived from midge (Insecta: Nematocera)-based calibration models. The reconstructions are compared with a regional tree-ring chronology and sediment physical properties are determined to track depositional changes. An objective of the study is to examine the long-term relationship between the North Atlantic Oscillation (NAO) and climate (temperature, precipitation). Our results show that the MCA was characterized by warm and dry summer conditions, which were accompanied by changes in the sediment magnetic susceptibility values most likely representing major forest fires during the tree-ring indicated MCA megadrought. However, the midge-based stream flow reconstruction shows increased values during the MCA, thus implying enhanced spring floods after snowy winters. During the LIA, the tree-ring data indicate that a generally wetter climate prevailed during summers, but the stream flow reconstruction indicates less snowy winters. In the terms of long-term climatology, the present results show support to the concept that the NAO has a positive correlation between winter precipitation and annual temperature and a negative correlation between summer precipitation in eastern Finland. Thus, the results may serve as important background data for global change assessments.

Lithological and geochemical record of mining-induced changes in sediments from Macquarie Harbour, southwest Tasmania, Australia

Macquarie Harbour in southwest Tasmania, Australia, has been affected severely by the establishment of mines in nearby Queenstown in the 1890s. As well as heavy metal-laden acid rock drainage from the Mount Lyell mine area, over 100 Mt of mine tailings and slag were discharged into the Queen and Ring Rivers, with an estimated 10 Mt of mine tailings building a delta of ca. 2.5 km2 and ca. 10 Mt of fine tailings in the harbour beyond the delta. Coring of sediments throughout Macquarie Harbour indicated that mine tailings accreted most rapidly close to the King River delta source with a significant reduction in thickness of tailings and heavy metal contamination with increasing distance from the King River source. Close to the King River delta the mine tailings are readily discriminated from the background estuarine sediments on the basis of visual logging of the core (laminations, colour), sediment grain size, sediment magnetic susceptibility and elemental geochemistry, especially concentrations of the heavy metals Cu, Zn and Pb. The high heavy metal concentrations are demonstrated by the very high contamination factors (CF > 6) for Cu and Zn, with CF values mostly >50 for Cu for the mine-impacted sediments. Although the addition of mine waste into the King River catchment has ceased, the catchment continues to be a source of these heavy metals due to acid rock drainage and remobilisation of mine waste in storage in the river banks, river bed and delta. The addition of heavy metals to the harbour sourced from the Mount Lyell mines preceded the advent of direct tailings disposal into the Queen River in 1915 with the metals probably provided by acid rock drainage from the Mount Lyell mining area.