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Four adjacent lakes (Arco, Budd, Deming, and Josephine) within Itasca State Park in Minnesota, USA are reported to be meromictic in the scientific literature. However, seasonally persistent chemoclines have never been documented. We collected seasonal profiles of temperature and specific conductance and placed temperature sensor chains in two lakes for ~ 1 year to explore whether these lakes remain stratified through seasonal mixing events, and what factors contribute to their stability. The results indicate that all lakes are predominantly thermally stratified and are prone to mixing in isothermal periods during spring and fall. Despite brief, semi-annual erosion of thermal stratification, Deming Lake showed no signs of complete mixing from 2006 to 2009 and 2019-2022. Geochemical data indicate that water in Budd Lake, the most dilute lake, is predominantly sourced from precipitation. The water in the other three lakes is calcium-magnesium bicarbonate type, reflecting a source of water that has interacted with the landscape. δ18OH2O and δ2HH2O measurements indicate the lakes are supplied by precipitation modified by evaporation. The water residence time in meromictic Deming Lake is short (100 days), yet it maintains a large reservoir of dissolved iron. Josephine, Arco, and Deming lakes sit in a valley with likely permeable sediments and may be hydrologically connected through wetlands, and recharged with shallow groundwater, as no streams are present. All four lakes develop subsurface chlorophyll maxima layers during the summer. All lakes also develop subsurface oxygen maxima that may results from oxygen trapping in the spring by rapidly developed thermoclines.

Reputed to be the driest desert in the world, the Atacama Desert in the Central Andes of Northern Chile is an extreme environment with high UV radiation, wide temperature variation, and minimum precipitation. Scarce lagoons associated with salt flats (salars) in this desert are the surface expression of shallow groundwater; these ponds serve as refugia for life and often host microbial communities associated with evaporitic mineral deposition. Results based on multidisciplinary field campaigns and associated laboratory examination of samples collected from the Puquios of the Salar de Llamara in the Atacama Desert during austral summer provide unprecedented detail regarding the spatial heterogeneity of physical, chemical, and biological characteristics of these salar environments. Four main lagoons (‘Puquios’) and more than 400 smaller ponds occur within an area less than 5 km2, and are characterized by high variability in electrical conductivity, benthic and planktonic biota, microbiota, lagoon bottom type, and style of mineral deposition. Results suggest that electrical conductivity is a driving force of system heterogeneity. Such spatial heterogeneity within the Puquios is likely to be expanded with temporal observations incorporating expected seasonal changes in electrical conductivity. The complexity of these Andean ecosystems may be key to their ability to persist in extreme environments at the edge of habitability.

Despite the harsh environmental conditions in the world's oldest and driest desert, some salt flat or 'salar' environments in the Atacama Desert host standing bodies of water known as saline lakes. Evaporite minerals deposited within saline lakes result from the equilibrium of environmental, sedimentological, and biogeochemical processes that occur in the salar; consequently, these minerals are sensitive records of human activities and ecological, evolutionary, and geological changes. The objective of this study was to evaluate feedbacks between physical, chemical, and microbial processes that culminate in distinct trends in brine chemistry, saline lake morphology, and associated evaporite sediments. Using samples from the Puquios of the Salar de Llamara, Atacama Desert, northern Chile, an analysis of spatial gradients and vertical stratification of lake elemental chemistry and mineral saturation indices were integrated with a comprehensive analysis of lake morphology, including depth, slope gradient, substrate type, and mineralogy. Lake waters ranged from saline to hypersaline, and exhibited normal, well mixed and inverse stratification patterns, and results suggest a correlation with lake morphology in the Salar de Llamara. Saline to hypersaline lakes (150 mS/cm) with stratified brines tended to have crystalline substrate and deep (35 cm) and steep-sided lake morphologies, while unstratified lakes with lower electrical conductivity (90 mS/cm and microbial substrates had gentle slopes and characteristically shallow depths (30 cm). Differences in minor element chemistry (Mn and Sr) between saline lakes were observed on scales of meters to kilometers, and result in different accessory mineral assemblages. Quantification of the physical, chemical, and microbial feedbacks that produce the observed heterogeneity in these ecosystems provides key insight into the geochemical composition and lake morphology of saline lakes in extreme environments around the world.

Geosphere-biosphere interactions are ubiquitous features of the Earth surface, yet the development of interactions between newly exposed lithologic surfaces and colonizing plants during primary succession after glaciation are lacking temporal detail. To assess the nature, rate, and magnitude of vegetation influence on parent material and sediment delivery, we analyzed ecosystem and geochemical proxies from lacustrine sediment cores at a grassland site and a forested site in the northern United States. Over time, terrigenous inputs declined at both sites, with increasing amounts of organic inputs toward present. The similarities between sites were striking given that the grassland sequence began in the Early Holocene, and the forested sequence began after the last glacial maximum. Multiple mechanisms of chemical weathering, hydrologic transport, and changes in source material potentially contribute to this pattern. Although there were strong links between vegetation composition and nitrogen cycling at each site, it appears that changes in forest type, or from oak woodland to grassland, did not exert a large influence on elemental (K, Ti, Si, Ca, Fe, Mn, and S) abundance in the sedimentary sequences. Rather, other factors in the catchment-lake system determined the temporal sequence of elemental abundance.

The Atacama Desert, Central Andes of Northern Chile, is an extreme environment characterized by high UV radiation, wide temperature variation, minimum precipitation and is reputed as the driest desert in the world. Scarce lagoons associated with salt flats (salars) in this desert are the surface expression of shallow groundwater which serve as refugia for life, and often host microbial communities associated with evaporitic mineral deposition. Recent investigations of the Puquios of the Salar de Llamara in the Atacama Desert based on multidisciplinary field studies provide unprecedented detail regarding the spatial heterogeneity of physical, chemical, and biological characteristics of such saline lake environments. Four main lagoons (‘Puquios’) and more than 400 smaller ponds, occur in an area less than 5 km2, are characterized by high variability in electrical conductivity, benthic and planktonic biota and microbiota, lagoon bottom type, and style of mineral deposition. The heterogeneity of system parameters as observed spatially in the Puquios is likely to be expanded with temporal observations incorporating seasonality. Results provide new insight into the complexity of these Andean ecosystems, which may be key to resilience in extreme environments at the edge of habitability.

Near-shore marine sediments deposited during the Paleocene-Eocene Thermal Maximum at Wilson Lake, NJ, contain abundant conventional and giant magnetofossils. We find that giant, needle-shaped magnetofossils from Wilson Lake produce distinct magnetic signatures in low-noise, high-resolution first-order reversal curve (FORC) measurements. These magnetic measurements on bulk sediment samples identify the presence of giant, needle-shaped magnetofossils. Our results are supported by micromagnetic simulations of giant needle morphologies measured from transmission electron micrographs of magnetic extracts from Wilson Lake sediments. These simulations underscore the single-domain characteristics and the large magnetic coercivity associated with the extreme crystal elongation of giant needles. Giant magnetofossils have so far only been identified in sediments deposited during global hyperthermal events and therefore may serve as magnetic biomarkers of environmental disturbances. Our results show that FORC measurements are a nondestructive method for identifying giant magnetofossil assemblages in bulk sediments, which will help test their ecology and significance with respect to environmental change.

A wide variety of Earth and planetary materials are very good recorders of paleomagnetic information. However, most magnetic grains in these materials are not in the stable single domain grain size range but are larger and in nonuniform vortex magnetization states. We provide a detailed account of vortex phenomena in geologic materials by simulating first‐order reversal curves (FORCs) via finite‐element micromagnetic modeling of magnetite nanoparticles with realistic morphologies. The particles have been reconstructed from focused ion beam nanotomography of magnetite‐bearing obsidian and accommodate single and multiple vortex structures. Single vortex (SV) grains have fingerprints with contributions to both the transient and transient‐free zones of FORC diagrams. A fundamental feature of the SV fingerprint is a central ridge, representing a distribution of negative saturation vortex annihilation fields. SV irreversible events at multiple field values along different FORC branches determine the asymmetry in the upper and lower lobes of generic bulk FORC diagrams of natural materials with grains predominantly in the vortex state. Multivortex (MV) FORC signatures are modeled here for the first time. MV grains contribute mostly to the transient‐free zone of a FORC diagram, averaging out to create a broad central peak. The intensity of the central peak is higher than that of the lobes, implying that MV particles are more abundant than SV particles in geologic materials with vortex state fingerprints. The abundance of MV particles, as well as their single domain‐like properties point to MV grains being the main natural remanent magnetization carriers in geologic materials.

First‐order reversal curve (FORC) diagrams of synthetic binary mixtures with single‐domain, vortex state, and multi‐domain end members (EMs) were analyzed using principal component analysis (FORC‐PCA). Mixing proportions derived from FORC‐PCA are shown to deviate systematically from the known weight percent of EMs, which is caused by the lack of reversible magnetization contributions to the FORC distribution. The error in the mixing proportions can be corrected by applying PCA to the raw FORCs, rather than to the processed FORC diagram, thereby capturing both reversible and irreversible contributions to the signal. Here we develop a new practical implementation of the FORC‐PCA method that enables quantitative unmixing to be performed routinely on suites of FORC diagrams with up to four distinct EMs. The method provides access not only to the processed FORC diagram of each EM, but also to reconstructed FORCs, which enables objective criteria to be defined that aid identification of physically realistic EMs. We illustrate FORC‐PCA with examples of quantitative unmixing of magnetic components that will have widespread applicability in paleomagnetism and environmental magnetism.

For two days, together with friends across the country, Craiova celebrated Ion D. Sîrbu. Only those who deliberately ignore him do not understand the spiritual force of this creator who left a undenieble fingerprint upon the place where he lived his life. His books, but also his existence full of tribulations and restrictions have been subject of reflection in the events that took place in several places that have been close to the great writer and moralist.

Bax is a major player in the apoptotic process, being at the core of the mitochondria permeabilization events. In spite of the major recent advances in the knowledge of Bax organization within the membrane, the precise behavior of the C-terminal helix α9 remains elusive, since it was absent from the resolved structure of active Bax. The Proline 168 (P168) residue, located in the short loop between α8 and α9, has been the target of site-directed mutagenesis experiments, with conflicting results. We have produced and purified a recombinant mutant Bax-P168A, and we have compared its behavior with that of wild-type Bax in a series of tests on Large Unilamellar Vesicles (LUVs) and isolated mitochondria. We conclude that Bax-P168A had a greater ability to oligomerize and bind to membranes. Bax-P168A was not more efficient than wild-type Bax to permeabilize liposomes to small molecules but was more prone to release cytochrome c from mitochondria.

The special issue of Earth, Planets and Space “Recent Advances in Geo-, Paleo- and Rock-Magnetism” was motivated by presentations given in Session S-EM18 “General Contributions in Geomagnetism, Paleomagnetism, and Rock magnetism” held during the Japan Geoscience Union–American Geophysical Union (JpGU–AGU) 2017 Joint Meeting (20–25 May in Chiba, Japan). Contributions span the broad range of topical developments in Earth magnetism including the disciplines of archeomagnetism, paleomagnetism, paleointensity, rock magnetism, crustal magnetism and biogeomagnetism. In addition, several contributions present advances in methods of analysis. These areas are briefly introduced below with an emphasis on the advances represented, current community debates and the motivation the new results provide for further study.

Modern magnetic microscopy (MM) provides high-resolution, ultra-high-sensitivity moment magnetometry, with the ability to measure at spatial resolutions better than 10−4 m and to detect magnetic moments weaker than 10−15 Am2. These characteristics make modern MM devices capable of particularly high-resolution analysis of the magnetic properties of materials, but generate extremely large data sets. Many studies utilizing MM attempt to solve an inverse problem to determine the magnitude of the magnetic moments that produce the measured component of the magnetic field. Fast Fourier techniques in the frequency domain and non-negative least-squares (NNLS) methods in the spatial domain are the two most frequently used methods to solve this inverse problem. Although extremely fast, Fourier techniques can produce solutions that violate the non-negativity of moments constraint. Inversions in the spatial domain do not violate non-negativity constraints, but the execution times of standard NNLS solvers (the Lawson and Hanson method and Matlab’s lsqlin) prohibit spatial domain inversions from operating at the full spatial resolution of an MM. In this paper, we present the applicability of the TNT-NN algorithm, a newly developed NNLS active set method, as a means to directly address the NNLS routine hindering existing spatial domain inversion methods. The TNT-NN algorithm enhances the performance of spatial domain inversions by accelerating the core NNLS routine. Using a conventional computing system, we show that the TNT-NN algorithm produces solutions with residuals comparable to conventional methods while reducing execution time of spatial domain inversions from months to hours or less. Using isothermal remanent magnetization measurements of multiple synthetic and natural samples, we show that the capabilities of the TNT-NN algorithm allow scans with sizes that made them previously inaccesible to NNLS techniques to be inverted. Ultimately, the TNT-NN algorithm enables spatial domain inversions of MM data on an accelerated timescale that renders spatial domain analyses for modern MM studies practical. In particular, this new technique enables MM experiments that would have required an impractical amount of inversion time such as high-resolution stepwise magnetization and demagnetization and 3-dimensional inversions., Earth, Planets and Space, 71, ISSN:1343-8832, ISSN:1880-5981

Research supported by US NSF grants 0850413 and 1014506, and the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement No. 320750. The UK NERC and BGS funded the recovery of Core MD04-2822.

Flooding events are major natural hazards that present significant risk to communities worldwide. Calculations of flood recurrence rate through time are important tools for regulating land use, determining insurance rates, and for the design and construction of levees and dams. Typically, flood recurrence rates are based on limited historical data or on evidence preserved in the geologic record as overbank deposits, tree ring scars, or high water scour marks. However, these approaches are either limited in their ability to produce continuous time series of flooding events or do not consider the effects of regional land use change. Here we use scanning superconducting quantum interference device (SQUID) microscopy to rapidly image the magnetization associated with flood layers in a polished surface of an annually laminated stalagmite from Spring Valley Caverns (SVC) in southeastern Minnesota. A time series of magnetization peaks, each of which corresponds to a flooding event, yields an average flood recurrence rate of ≤5 events per century for the last 500 years. This rate increases to ∼7 events per century since 1900, coincident with historical timber and agricultural land-use changes in Minnesota. This approach produces a continuous record of well-dated, extreme-precipitation events that can be examined within the context of land use change.

Lake sediments from the Magherus, Valley in the lowlands of northern Transylvania provide new evidence of paleoenvironmental development in Romania during the Late Glacial. The studied sediments were deposited as a result of the damming of a small river valley following a series of mass wasting events that occurred during the deglaciation period. A continuous sedimentary sequence belonging to the former lake is preserved in the banks of the stream, and contains evidence of paleoenvironmental changes associated with the Late Glacial Interstadial (Bolling-Allerod or Greenland Interstadial 1, GI-1) and the Late Glacial Stadial (Younger Dryas or Greenland Stadial 1, GS-1), implying that the hallmark climatic episodes of northwestern Europe are also expressed in Eastern Europe. We employ a multiproxy approach based on the analysis of sediment composition and texture, mineral magnetism, organic macrofossils, and radiocarbon dating. The reconstructed paleoenvironmental evolution at the site captures the warm and humid conditions associated with GI-1, as well as the subsequent cooling concomitant with the onset of GS-1. These climatic events are paralleled by vegetation shifts in the region, as deduced from comparisons with pollen sequences from Magherus, and neighboring locations in Transylvania and the Carpathians. The Late Glacial Interstadial was warmer and wetter, as evidenced by increased organic matter content in the lake, decreased erosion in the catchment, development of palustrine plant communities in the proximity of the lake, and expansion of spruce during the Allerod (GI-1c-a). The Late Glacial Stadial was colder and dryer, as indicated by low sedimentary organic matter content, an increase in erosion markers, and the decline of spruce and its replacement by birch. The landscape was more open, as herbs and grasses also expanded during this time. These fluctuations imply that Late Glacial climatic events are well expressed not only in upland areas of Romania, but also in lowland regions such as the Transylvanian Basin, where climatic effects are expected to be more muted. (C) 2014 Elsevier Ltd and INQUA. All rights reserved.

Processes and rates of ecosystem development can be reconstructed using lacustrine sedimentary sequences, but this approach often requires records that contain the start of primary succession. Most lakes in the upper Midwestern U.S. were formed by glaciers at the end of the last Ice Age approximately 11,700 cal yr BP. Devils Lake, Wisconsin is a rare example of a lake from this region whose sediments extend into the Pleistocene and may include the Last Glacial Maximum. Sediment magnetic, geochemical, pollen, and charcoal records were generated from a 10 m core whose basal sediments may be 28,000 years old. Together with a previously published pollen record, these proxies combine to reveal a history of long-term climatic, vegetative and geologic change during the late Pleistocene to Holocene. We identify six sedimentary units that indicate a series of consecutive events rather than a predictable trajectory of ecosystem development at the site. Productivity in the lake was low during the late Pleistocene and increased during the Holocene, as reflected by the sediment lithology, which shows a sudden shift from glacial vivianite-rich and organic-poor clastic-dominated sediments to Holocene diatomaceous sapropels. Several important processes initiated around 17,000 cal yr BP, including the onset of organic matter accumulation and fire in the terrestrial ecosystem. However, the post-glacial landscape was not devoid of vegetation because pollen assemblages indicate that terrestrial vegetation, likely a spruce tundra, survived near the site. A switch to a hardwood forest period during the Holocene also led to a change in the fire regime, with increased frequency of burning. Aquatic ecosystem productivity lagged terrestrial ecosystem productivity throughout the record. Nutrient cycling (as recorded by sedimentary δ15N) was variable but not directional, and appeared to be correlated with climate conditions early in the record, and terrestrial ecosystem processes later in the record. Throughout the Holocene magnetic mineral concentration decreased as productivity increased, and the source of magnetic material shifted from almost exclusively lithogenic to approximately 50% derived from soil or biogenic sources. Magnetic grain size, Ambrosia pollen percentages, and charcoal concentration increased and δ15N decreased in the most recent part of the record, due to anthropogenic influence in the region including agricultural activities.

We describe a quantitative magnetic unmixing method based on principal component analysis (PCA) of first-order reversal curve (FORC) diagrams. For PCA we resample FORC distributions on grids that capture diagnostic signatures of single-domain (SD), pseudo-single-domain (PSD), and multi-domain (MD) magnetite, as well as of minerals such as hematite. Individual FORC diagrams are recast as linear combinations of end-member (EM) FORC diagrams, located at user-defined positions in PCA space. The EM selection is guided by constraints derived from physical modeling and imposed by data scatter. We investigate temporal variations of two EMs in bulk North Atlantic sediment cores collected from the Rockall Trough and the Iberian Continental Margin. Sediments from each site contain a mixture of magnetosomes and granulometrically distinct detrital magnetite. We also quantify the spatial variation of three EM components (a coarse silt-sized MD component, a fine silt-sized PSD component, and a mixed clay-sized component containing both SD magnetite and hematite) in surficial sediments along the flow path of the North Atlantic Deep Water (NADW). These samples were separated into granulometric fractions, which helped constrain EM definition. PCA-based unmixing reveals systematic variations in EM relative abundance as a function of distance along NADW flow. Finally, we apply PCA to the combined dataset of Rockall Trough and NADW sediments, which can be recast as a four-EM mixture, providing enhanced discrimination between components. Our method forms the foundation of a general solution to the problem of unmixing multi-component magnetic mixtures, a fundamental task of rock magnetic studies. This article is protected by copyright. All rights reserved.

[1] Speleothems, especially stalagmites, hold great potential as recorders of the Earth's ancient magnetic field. However, our understanding of the magnetic mineral assemblages within speleothems is not well developed. We present tandem rock magnetic characterization of bulk samples and electron microscopy of magnetic extracts from five North American stalagmites. Magnetite and goethite are present in all samples, albeit in varying abundances and morphologies. Magnetite grains are likely detrital, showing evidence of transport and weathering, including plumose markings and etch pits. These grains are unlikely to have precipitated abiotically in the cave environment. Titanomagnetite and exsolved intergrowths of Fe-Ti oxides indicate that a significant portion of the magnetic mineral assemblage is allochthonous and was transported into the caves. These Ti-rich grains display a range of morphologies from euhedral to well rounded, indicating that earlier morphological models for speleothem magnetization do not apply in all geologic settings. Goethite was observed in three morphologies: isolated needles, needle aggregates, and polycrystalline aggregates of randomly oriented nanoscale grains. The magnetite and titanomagnetite, as well as their partially oxidized equivalents, likely hold a depositional remanent magnetization (DRM), whereas if goethite grains were precipitated in situ on the stalagmite drip surface, they are more likely to hold a chemical remanent magnetization (CRM) because of their small size and low saturation magnetization. Until the remanence of goethite can be shown to be paleomagnetically meaningful, we propose that paleomagnetic studies of speleothems include a 150°C thermal demagnetization step to remove any goethite remanence.

We have investigated the variability of the magnetic properties of surface sediments across eight Minnesota lake basins. The measured magnetic properties are controlled by the competing fluxes of allochthonous and autochthonous magnetic particles, and differ according to location in the basin. Shoreline sediments are dominated by detrital magnetic particles, whereas littoral and profundal sediments are characterized by a combination of bacterial magnetosomes and detrital particles. The position of the oxic–anoxic interface, which may occur in the water or within the sediment column, controls the depth at which living magnetotactic bacteria occur, and determines the degree of preservation of their magnetosome chains in the surface sediment. The preservation potential of undisturbed chains is higher for bacterial magnetite formed at the top of the sediment column in the littoral area than for magnetosomes originating in the water column in the profundal area. Bacterial magnetite in the profundal facies will contain a higher proportion of chains collapsed during settlement through the water column to the lake bottom. This process increases the fraction of interacting magnetosomes, which in turn artificially lowers the ARM ratio (χ ARM /IRM), which ceases to be a reliable grain size indicator in the profundal environment. Our results indicate that a holistic approach to interpreting limnologically-derived paleoecological data should be employed. Specifically, a thorough understanding of evolving and interrelated factors such as basin morphology and limnologic conditions is crucial for a more confident interpretation of the sedimentary record in terms of environmental conditions at the time of sediment deposition.

Both terrestrial and aquatic ecosystems should respond to abrupt climate changes such as those that affected the midcontinent of North America during the Holocene. A variety of paleorecords indicate that the onset of prolonged dry conditions in this region occurred as rapidly as 300 yr during the early Holocene, with a subsequent increase in moisture occurring rapidly in the late Holocene. Here, we report a 9500 yr multiproxy sediment record from Deming Lake, Minnesota, USA, that demonstrates only subtle dynamics during rapid climate changes that caused vegetation in the catchment to shift among pine forest, open grassland, and deciduous forest. The most substantial changes in ecosystem properties immediately followed deglaciation of the landscape, formation of the lake, and initial development of pine forests. In contrast, there were only muted responses to pronounced mid-Holocene climate changes that caused vegetation in the catchment to switch from pine forest to open grassland (ca. 8000 yr B.P.), and then deciduous forest (ca. 5400 yr B.P.). The flux of organic and inorganic terrigenous material, the processing of carbon, and catchment erosion changed rapidly during the most recent shift at 3300 yr B.P. to the modern pine forest. These changes coincided with the onset of meromictic conditions that influenced internal lake dynamics. However, the terrestrial influence on the lake sedimentary record gradually diminished over time, indicating a trajectory of increasing catchment stabilization that was relatively impervious to dramatic regional climate changes. The relative complacency of the Deming Lake record during the late Holocene indicates relative resistance to abrupt climate change at later stages of ecosystem development.

The present work was supported by Grant No. EP/I036079/1 from the Engineering and Physical Sciences Research Council. Elastic and anelastic properties of ceramic samples of multiferroic perovskites with nominal compositions across the binary join PbZr0.53Ti0.47O3–PbFe0.5Ta0.5O3 (PZT–PFT) have been assembled to create a binary phase diagram and to address the role of strain relaxation associated with their phase transitions. Structural relationships are similar to those observed previously for PbZr0.53Ti0.47O3–PbFe0.5Nb0.5O3 (PZT–PFN), but the magnitude of the tetragonal shear strain associated with the ferroelectric order parameter appears to be much smaller. This leads to relaxor character for the development of ferroelectric properties in the end member PbFe0.5Ta0.5O3. As for PZT–PFN, there appear to be two discrete instabilities rather than simply a reorientation of the electric dipole in the transition sequence cubic–tetragonal–monoclinic, and the second transition has characteristics typical of an improper ferroelastic. At intermediate compositions, the ferroelastic microstructure has strain heterogeneities on a mesoscopic length scale and, probably, also on a microscopic scale. This results in a wide anelastic freezing interval for strain-related defects rather than the freezing of discrete twin walls that would occur in a conventional ferroelastic material. In PFT, however, the acoustic loss behaviour more nearly resembles that due to freezing of conventional ferroelastic twin walls. Precursor softening of the shear modulus in both PFT and PFN does not fit with a Vogel–Fulcher description, but in PFT there is a temperature interval where the softening conforms to a power law suggestive of the role of fluctuations of the order parameter with dispersion along one branch of the Brillouin zone. Magnetic ordering appears to be coupled only weakly with a volume strain and not with shear strain but, as with multiferroic PZT–PFN perovskites, takes place within crystals which have significant strain heterogeneities on different length scales. Publisher PDF

Short-lived events such as geomagnetic excursions are global events that are used for dating purposes across scientific disciplines. A critical ingredient for characterizing such geomagnetic instabilities are tightly constrained age models that enable high-resolution magnetostratigraphies. The focus of this study is a speleothem geomagnetic record of the Laschamp excursion, which was the first geomagnetic excursion recognized and described in the paleomagnetic record, and remains the most studied event of its kind

The Laschamp geomagnetic excursion was the first short-lived polarity event recognized and described in the paleomagnetic record, and to date remains the most studied geomagnetic event of its kind. In addition to its geophysical significance, the Laschamp is an important global geochronologic marker. The Laschamp excursion occurred around the time of the demise of Homo neanderthalensis, in conjunction with high-amplitude, rapid climatic oscillations leading into the Last Glacial Maximum, and coeval with a major supervolcano eruption in the Mediterranean. Thus, precise determination of the timing and duration of the Laschamp excursion would help in elucidating major scientific questions situated at the intersection of geology, paleoclimatology, and anthropology. Here we present a North American speleothem geomagnetic record of the Laschamp excursion that is directly dated using a combination of high-precision 230Th dates and annual layer counting using confocal microscopy. We have determined a maximum excursion duration that spans the interval 42,250-39,700 yr BP, and an age of 41,100 ± 350 yr BP for the main phase of the excursion, during which the virtual geomagnetic pole was situated at the southernmost latitude in the record. Our chronology provides the first age bracketing of the Laschamp excursion using radioisotopic dating, and improves on previous age determinations based on 40Ar/39Ar dating of lava flows, and orbitally-tuned sedimentary and ice-core records.

Droughts are recurrent features in sedimentary records at the prairie–forest ecotone of northern U.S.A. It is therefore important to understand the duration of such events, as well as their severity and consequences beyond the century-scale instrumental record. The existing drought records can be complemented with additional proxies that clearly document the interactions between external factors and the depositional environment. Here we attempt to reconstruct the last millennium drought history of Deming Lake, a small lake at Minnesota's prairie–forest ecotone, using sediment magnetism. In particular, this approach allowed us to explore the interactions between lake and catchment, and test the hypothesis that periods of moderate aridity result in decreased hydrologic sediment transport from the catchment to the lake, as a consequence of reduced erosion and overland flow. Concordantly, during dry episodes we find that the mass fractions of in-lake produced organic matter and biogenic magnetic particles increase relative to allochthonous component fractions. We identify several episodes of aridity at Deming Lake consistent with existing regional drought reconstructions. The most prolonged dry event occurred at the end of the Little Ice Age, suggesting that the second half of this cold interval was drier in the region than previously thought.

The human nucleoside diphosphate (NDP) kinase A, product of the NME1 gene also named NM23-H1, is known as a metastasis suppressor protein. A naturally occurring variant, S120G, identified in neuroblastomas, possesses native three-dimensional structure and enzymatic activity but displays reduced conformational stability and a folding defect with the accumulation of a "molten globule" folding intermediate during refolding in vitro. As such intermediate has been postulated to be involved in amyloid formation, NDP kinase A may serve as a model protein for studying the relationship between folding intermediates and amyloid fibrils. The NDP kinase A S120G was heated in phosphate buffer (pH 7.0). The protein precipitated as amyloid fibrils, as demonstrated by electron microscopy, Congo red, and thioflavin T binding and FTIR spectroscopy. The NDP kinase A S120G, at neutral pH and at moderate temperature experiences a transition towards amyloid fibrils. The aggregation process was faster if seeded by preformed fibrils. The fibrils presented a large proteinase K-resistant core not including residue Gly 120, as shown by mass spectrometry. This suggests that the aggregation process is triggered by the reduced stability of the S120G variant and not by a specific increase in the kinase domain intrinsic aggregation propensity at the place of mutation. This constitutes one of the few reports on a protein involved in cancer biology able to aggregate into amyloid structures under mild conditions.

Amyloid fibrils are ordered beta-sheet protein or peptide polymers. The benzothiazole dye Thioflavin-T (ThT) shows a strong increase in fluorescence upon binding to amyloid fibrils and has hence become the most commonly used amyloid-specific dye. In spite of this widespread use, the mechanism underlying specific binding and fluorescence enhancement upon interaction with amyloid fibrils remains largely unknown. Recent contradictory reports have proposed radically different modes of binding. We have studied the interaction of ThT with fibrils of the prion forming domain of the fungal HET-s prion protein assembled at pH 2 in order to try to gain some insight into the general mechanism of ThT-binding and fluorescence. We found that ThT does not bind to HET-s(218-289) fibrils as a micelle as previously proposed in the case of insulin fibrils. We have measured binding kinetics, affinity and stoichiometry at pH values above and below the pI of the HET-s(218-289) fibrils and found that binding is dramatically affected by pH and ionic strength. Binding is poor at acidic pH, presumably as a result of repulsive electrostatic interaction between the positively charged ThT molecule and the fibril surface. Finally, we found that ThT acquires chiral properties when it is fibril-bound. These results are discussed in relation to the different ThT-binding modes that have been proposed.

A major challenge in groundwater and petroleum modeling is how to represent the diagenesis effect "sensu lato" and its associated features (e.g., karst cavities, porosity and permeability characteristics). Both geometrical descriptions and genesis are necessary for modeling diagenetic features, because they allow the restitution of phenomenon in subsurface settings where they cannot be fully observed. This study focuses on flank-margin caves developed on carbonate islands (as in the case of the Bahamian islands). Over the last twenty years numerous measurements and observations have been carried out on Quaternary carbonate islands. These, together with reasonable hypotheses of genesis (fresh-water lens dissolution), make island karst an appropriate subject for developing concepts and modeling methods which can be then applied to other diagenetic features, such as reflux dolomitization and hydrothermal fluid effects. The speleogenesis of flank-margin caves was modeled following deterministic and stochastic methods to achieve a description of dissolution genesis. A fresh-water lens surface was built based on the topography of Long Island, Bahamas, and was then used to simulate virtual development of flank-margin caves at several formation phases, including uncertainty coefficients applied to both fresh-water-lens location and stability time by using 3D probability cubes. The cave simulations were compared with over sixty Bahamian cave surveys, in order to substantiate our modeling processes and results. Finally, the model was exposed to a cave collapse situation. The likelihood of preservation and the extent of the area affected were measured to provide an evaluation of the spatial distribution of associated petrophysical characteristics (e.g., porosity and permeability). The results reveal close resemblance and coherence between modeled and field data (including collapse features). Therefore the optimum method for restituting diagenetic features is by stochastic modeling actively driven by process concepts and most up-to-date methods.

Human nucleoside diphosphate (NDP) kinase A is a ‘house-keeping’ enzyme essential for the synthesis of nonadenine nucleoside (and deoxynucleoside) 5′-triphosphate. It is involved in complex cellular regulatory functions including the control of metastatic tumour dissemination. The mutation S120G has been identified in high-grade neuroblastomas. We have shown previously that this mutant has a folding defect: the urea-denatured protein could not refold in vitro. A molten globule folding intermediate accumulated, whereas the wild-type protein folded and associated into active hexamers. In the present study, we report that autophosphorylation of the protein corrected the folding defect. The phosphorylated S120G mutant NDP kinase, either autophosphorylated with ATP as donor, or chemically prosphorylated by phosphoramidate, refolded and associated quickly with high yield. Nucleotide binding had only a small effect. ADP and the non-hydrolysable ATP analogue 5′-adenyly-limido-diphosphate did not promote refolding. ATP-promoted refolding was strongly inhibited by ADP, indicating protein dephosphorylation. Our findings explain why the mutant enzyme is produced in mammalian cells and in Escherichia coli in a soluble form and is active, despite the folding defect of the S120G mutant observed in vitro. We generated an inactive mutant kinase by replacing the essential active-site histidine residue at position 118 with an asparagine residue, which abrogates the autophosphorylation. The double mutant H118N/S120G was expressed in inclusion bodies in E. coli. Its renaturation stops at a folding intermediate and cannot be reactivated by ATP in vitro. The transfection of cells with this double mutant might be a good model to study the cellular effects of folding intermediates.

The Nm23-H1/nucleoside diphosphate (NDP) kinase A is a metastasis suppressor, besides its enzymatic activity. The mutant S120G has been found in high-grade neuroblastomas. The mutant protein, once denatured in urea, is unable to refold in vitro. A size-exclusion chromatography analysis of the folding/association pathway showed that recombinant wild-type and S120G mutant human Nm23-H1/NDP kinase A unfold and refold passing through a molten globule state while typical hexameric NDP kinases unfold without dissociated species and refold through a native monomeric intermediate. A survey of the recent literature showed that several proteins involved in cancer, and their mutants, are marginally stable, like the wild-type Nm23-H1/NDP kinase A, or are misfolded, like its S120G mutant. We therefore suggest that the low thermodynamic stability and the folding intermediate of the Nm23-H1/NDP kinase A may be necessary for its regulatory properties.

We isolated and analyzed by chromatin immunoprecipitation (ChIP) in viable M14 cells DNA sequences bound to the antimetastatic protein nucleoside diphosphate kinase (NM23/NDPK) to shed some light on the nuclear functions of this protein and on the mechanism by which it acts in development and cancer. We assessed the presence of selected sequences from promoters of platelet-derived growth factor A (PDGF-A), c-myc, myeloperoxidase (MPO), CD11b, p53, WT1, CCR5, ING1, and NM23-H1 genes in the cross-linked complexes. Quantitative PCR (Q-PCR) showed a substantial enrichment of the correlated oncosuppressor genes p53, WT1, ING1, and NM23-H1 in the immunoprecipitated (IP) DNA. This suggests that NM23/NDPK binding is involved in the transcription regulation of these genes. These results reveal new interactions that should help us to disclose the antimetastatic mechanism of NM23. J. Cell. Biochem. 98: 421–428, 2006. © 2006 Wiley-Liss, Inc.

Background: The metastasis-suppressing role of the NM23 gene in the metastatic spread of solid tumors is still debated. We examined the role of NM23 in tumor development and metastatic dissemination by using transgenic mice that lack mouse NM23 (NM23-M1) in two mouse models of hepatocellular carcinoma (HCC) that recapitulate all steps of tumor progression. Methods: We induced HCC in mice that contained (NM23-M1 +/+ ) or lacked (NM23-M1 − / − ) NM23-M1 by diethylnitrosamine injection or by a crossing scheme that transferred a transgene that leads to liver expression of simian virus 40 large T antigen (ASV mice). We used microscopic examination and immunohistochemistry to analyze tumor progression. Expression of Nm23 protein isoforms (Nm23-M1 and Nm23-M2) and several tumor markers was analyzed in the primary tumor and in metastases by Western blotting. The statistical signifi cance of differences in the incidence of Nm23-M2 overexpression in null mice relative to that in wild-type mice was tested by a one-sided Fisher’s exact test. The statistical signifi cance of differences in the incidence of metastases was examined using one-sided chisquare tests. All other statistical tests were two-sided. Results: In both models, Nm23-M1 and/or Nm23-M2 were overexpressed in the primary liver tumors compared with nontumor liver tissue; however, the lack of the NM23-M1 gene had no effect on primary tumor formation in either model. ASV mice developed pulmonary metastases that were positive for the Hep-Par 1 antibody, which recognizes a specifi c hepatocyte antigen, whereas the few pulmonary nodules that developed in diethylnitrosamine-injected mice were negative for this antigen. Statistically signifi cantly more ASV/NM23-M1 − / − mice than ASV/NM23-M1 +/+ mice developed lung metastases (69.2% versus 37.5%; difference = 31.7%, 95% confi dence interval = 13.1% to 50.3%; P