Realistic appraisal of paleoclimatic information obtained from a particular location requires accurate knowledge of its paleolatitude defined relative to the Earth's spin-axis. This is crucial to, ...among others, correctly assess the amount of solar energy received at a location at the moment of sediment deposition. The paleolatitude of an arbitrary location can in principle be reconstructed from tectonic plate reconstructions that (1) restore the relative motions between plates based on (marine) magnetic anomalies, and (2) reconstruct all plates relative to the spin axis using a paleomagnetic reference frame based on a global apparent polar wander path. Whereas many studies do employ high-quality relative plate reconstructions, the necessity of using a paleomagnetic reference frame for climate studies rather than a mantle reference frame appears under-appreciated. In this paper, we briefly summarize the theory of plate tectonic reconstructions and their reference frames tailored towards applications of paleoclimate reconstruction, and show that using a mantle reference frame, which defines plate positions relative to the mantle, instead of a paleomagnetic reference frame may introduce errors in paleolatitude of more than 15° (>1500 km). This is because mantle reference frames cannot constrain, or are specifically corrected for the effects of true polar wander. We used the latest, state-of-the-art plate reconstructions to build a global plate circuit, and developed an online, user-friendly paleolatitude calculator for the last 200 million years by placing this plate circuit in three widely used global apparent polar wander paths. As a novelty, this calculator adds error bars to paleolatitude estimates that can be incorporated in climate modeling. The calculator is available at www.paleolatitude.org. We illustrate the use of the paleolatitude calculator by showing how an apparent wide spread in Eocene sea surface temperatures of southern high latitudes may be in part explained by a much wider paleolatitudinal distribution of sites than previously assumed.
Volcanic rocks are considered reliable recorders of past changes in the Earth's magnetic field. Recent flows, however, sometimes fail to produce the known magnetic field at the time of cooling. ...Previous research on Mt. Etna suggests paleomagnetic data might not be accurately recorded. Here we test the accuracy of paleomagnetic data obtained from Mt. Etna lavas by comparing paleomagnetic data from historical flows to direct measurements of the magnetic field above the current topography. The inclinations and intensities in both data sets are biased toward lower values, while there is no such trend for the declination. Inclinations are on average 2.9° lower than expected; intensities are on average 8.8 µT lower. The deviations from the expected values depend on the height above the flow. Moreover, the inclinations and intensities vary as a function of topography. Both are higher above ridges and lower in gullies; the variations within a site are up to 14.1° in inclination and 12.9 µT for intensity. To suppress this paleomagnetic data bias it is important to take samples several meters apart and from different parts of the flow whenever possible. While this leads to a higher degree of scatter in paleodirections, the results better represent the Earth's magnetic field at the time of cooling. This emphasizes the importance of reporting paleomagnetic sampling strategies in detail.
Plain Language Summary
Paleomagnetic data from lavas is routinely used in the Earth Sciences to for example, reconstruct the past behavior of the Earth's magnetic field, or make models of past plate motions. Very young flows for which the ambient magnetic field at the time of cooling is known, however, sometimes fail to produce the known reference values. Lava flows from Mt. Etna are extensively studied in the past and the paleomagnetic data obtained does often not agree with the known magnetic field value in which the lavas cooled. Here we show that the topography of volcanic terrain may influence the magnetic signal of new, overlying, flows, and we make recommendations for sampling strategies that suppress these terrain effects as much as possible.
Key Points
Paleomagnetic data from Mt. Etna does often not reproduce the known geomagnetic field well
Local magnetic anomalies explain bias in paleomagnetic data as function of topography
Optimizing the paleomagnetic sampling strategy may suppress this bias in paleomagnetic data
Tidal wetlands, such as tidal marshes and mangroves, are hotspots for carbon sequestration. The preservation of organic matter (OM) is a critical process by which tidal wetlands exert influence over ...the global carbon cycle and at the same time gain elevation to keep pace with sea-level rise (SLR). The present study assessed the effects of temperature and relative sea level on the decomposition rate and stabilization of OM in tidal wetlands worldwide, utilizing commercially available standardized litter. While effects on decomposition rate per se were minor, we show strong negative effects of temperature and relative sea level on stabilization, as based on the fraction of labile, rapidly hydrolyzable OM that becomes stabilized during deployment. Across study sites, OM stabilization was 29 % lower in low, more frequently flooded vs. high, less frequently flooded zones. Stabilization declined by ∼ 75 % over the studied temperature gradient from 10.9 to 28.5 ∘C. Additionally, data from the Plum Island long-term ecological research site in Massachusetts, USA, show a pronounced reduction in OM stabilization by > 70 % in response to simulated coastal eutrophication, confirming the potentially high sensitivity of OM stabilization to global change. We therefore provide evidence that rising temperature, accelerated SLR, and coastal eutrophication may decrease the future capacity of tidal wetlands to sequester carbon by affecting the initial transformations of recent OM inputs to soil OM.
Background:
Clinical measures in multiple sclerosis (MS) face limitations that may be overcome by utilising smartphone keyboard interactions acquired continuously and remotely during regular typing.
...Objective:
The aim of this study was to determine the reliability and validity of keystroke dynamics to assess clinical aspects of MS.
Methods:
In total, 102 MS patients and 24 controls were included in this observational study. Keyboard interactions were obtained with the Neurokeys keyboard app. Eight timing-related keystroke features were assessed for reliability with intraclass correlation coefficients (ICCs); construct validity by analysing group differences (in fatigue, gadolinium-enhancing lesions on magnetic resonance imaging (MRI), and patients vs controls); and concurrent validity by correlating with disability measures.
Results:
Reliability was moderate in two (ICC = 0.601 and 0.742) and good to excellent in the remaining six features (ICC = 0.760–0.965). Patients had significantly higher keystroke latencies than controls. Latency between key presses correlated the highest with Expanded Disability Status Scale (r = 0.407) and latency between key releases with Nine-Hole Peg Test and Symbol Digit Modalities Test (ρ = 0.503 and r = −0.553, respectively), ps < 0.001.
Conclusion:
Keystroke dynamics were reliable, distinguished patients and controls, and were associated with clinical disability measures. Consequently, keystroke dynamics are a promising valid surrogate marker for clinical disability in MS.
Background:
Early detection and monitoring of cognitive dysfunction in multiple sclerosis (MS) may be enabled with smartphone-adapted tests that allow frequent measurements in the everyday ...environment.
Objectives:
The aim of this study was to determine the reliability, construct and concurrent validity of a smartphone-adapted Symbol Digit Modalities Test (sSDMT).
Methods:
During a 28-day follow-up, 102 patients with MS and 24 healthy controls (HC) used the MS sherpa® app to perform the sSDMT every 3 days on their own smartphone. Patients performed the Brief International Cognitive Assessment for MS at baseline. Test–retest reliability (intraclass correlation coefficients, ICC), construct validity (group analyses between cognitively impaired (CI), cognitively preserved (CP) and HC for differences) and concurrent validity (correlation coefficients) were assessed.
Results:
Patients with MS and HC completed an average of 23.2 (SD = 10.0) and 18.3 (SD = 10.2) sSDMT, respectively. sSDMT demonstrated high test–retest reliability (ICCs > 0.8) with a smallest detectable change of 7 points. sSDMT scores were different between CI patients, CP patients and HC (all ps < 0.05). sSDMT correlated modestly with the clinical SDMT (highest r = 0.690), verbal (highest r = 0.516) and visuospatial memory (highest r = 0.599).
Conclusion:
Self-administered smartphone-adapted SDMT scores were reliable and different between patients who were CI, CP and HC and demonstrated concurrent validity in assessing information processing speed.
Magnetic signals in igneous rocks arise from assemblages of iron‐oxide bearing minerals that differ in for example, size, shape, and chemistry. Paleomagnetic measurements on bulk samples measure ...millions of such grains simultaneously, producing a statistical ensemble of the magnetic moments of the individual grains. Scanning magnetometry techniques such as the Quantum Diamond Microscope (QDM) measure magnetic signals on micrometer scales, allowing the identification of magnetic moments of individual grains in a sample using for example, Micromagnetic Tomography (MMT). Here we produce a grain‐size distribution of iron‐oxides in a typical Hawaiian basalt from the superparamagnetic threshold (∼40 nm) to grains with a diameter of 10 µm. This grain‐size distribution is obtained by combining FIB‐SEM and MicroCT data from sister specimens, and normalizing them to the mineral surface area of non‐magnetic minerals. Then we use this grain‐size distribution to determine the contributions of individual magnetic carriers to bulk magnetic measurements and surface magnetometry. We found that measurements on bulk samples are sensitive to relatively small grain sizes in the realm of single domain or vortex states (<200 nm), while signals in surface magnetometry arise mainly from larger grains with diameters >1 µm. This implies that bulk measurements cannot be compared straightforwardly to signals from surface magnetometry from the same sample. Moreover, our observations explain why MMT results are insensitive to the presence of many small grains in a sample that intuitively should hamper their outcome.
Plain Language Summary
Magnetic grains in lavas acquire a magnetic signal while cooling in presence of Earth's magnetic field. However, not all grains preserve the signal well, meaning that both good and bad recorders are present. Classical paleomagnetic techniques measure the magnetic signal of all recorders together, that is, the bulk signal. New scanning magnetometry techniques such as Micromagnetic Tomography acquire the signal from individual recorders in the lava, enabling the selection of potentially good recorders and the rejection of signals from bad recorders. Here we found that these two types of magnetic measurements do not measure the same grains that are present in the sample: classical techniques emphasize small grains (<200 nm), while signals in surface magnetometry arise mainly from larger grains with diameters >1 μm. This means that measurements from both techniques performed on the same sample material cannot be compared straightforwardly. Furthermore, our results explain why Micromagnetic Tomography results often are successful, even when many small magnetic grains that intuitively should hamper this technique are present in a sample.
Key Points
We determine contributions of individual magnetic carriers to bulk magnetic measurements and surface magnetometry
Measurements on bulk samples are sensitive to small grains (<200 nm); surface magnetometry emphasizes signals from larger grains (>1 μm)
Our observations explain why undetected ghost grains in MMT experiments have an unintuitively low impact on the accuracy of MMT results
Obtaining reliable information from even the most challenging paleomagnetic recorders, such as the oldest igneous rocks and meteorites, is paramount to open new windows into Earth's history. ...Currently, such information is acquired by simultaneously sensing millions of particles in small samples or single crystals using superconducting quantum interference device magnetometers. The obtained rock‐magnetic signal is a statistical ensemble of grains potentially differing in reliability as paleomagnetic recorder due to variations in physical dimensions, chemistry, and magnetic behavior. Here we go beyond bulk magnetic measurements and combine computed tomography and scanning magnetometry to uniquely invert for the magnetic moments of individual grains. This enables us to select and consider contributions of subsets of grains as a function of particle‐specific selection criteria and avoid contributions that arise from particles that are altered or contain unreliable magnetic carriers. This new, nondestructive, method unlocks information from complex paleomagnetic recorders that until now goes obscured.
Plain Language Summary
Information about the past state of the Earth's magnetic field is obtained from igneous rocks that take a snapshot of the ambient magnetic field as they cool. Igneous rocks, however, contain a broad range of different grains that have their specific magnetic properties, and many are known to be incapable of storing a magnetization reliably over time. The signal obtained from traditional bulk samples that contain many millions of grains is a statistical ensemble of all these grains—the good and the bad. To improve the quality of the magnetic signal from these rocks, we go beyond bulk samples and identify magnetizations of individual grains in a sample using an X‐ray tomography‐assisted magnetic inversion. We show that it is possible to uniquely and nondestructively obtain magnetizations for a limited number of grains. Isolating the individual magnetizations of grains enables selecting only the known good recorders and rejecting the adverse recorders present in the sample. This would make it possible to obtain information from even the most complex paleomagnetic recorders, including igneous rocks, meteorites, and extraterrestrial material that until now goes obscured.
Key Points
Individual magnetic moments are isolated for a suite of grains while embedded in a nonmagnetic medium using micromagnetic tomography
The traditional nonuniqueness of this inversion problem is tackled by adding spatial information using microCT scanning
Our new technique is nondestructive; hence, grains can be analyzed multiple times and in different magnetic states
Paleointensity.org is an online, open source, application to analyze paleointensity data produced by the most common paleointensity techniques. Our application currently supports four different ...methods: thermal Thellier (all variations), microwave Thellier, pseudo‐Thellier, and the multispecimen protocol. Data can be imported using a variety of input file formats such as ThellierTool files, the generic PmagPy file format, and a number of lab‐specific formats. The data for the individual paleointensity methods are visualized by the relevant graphs and parameters, which are updated dynamically while interpreting the data. Beyond manual interpretation, Paleointensity.org features an autointerpreter for specimen level Thellier‐type data. Interpretations and data can be exported to csv and MagIC files. Moreover, it is possible to export the local storage containing all data, saved interpretations, and settings. This file can be shared among researchers or attached to a paper as supporting information. Because of its many features and ease of use, Paleointensity.org is a major step forward in enhancing an open paleomagnetic community in which data can be shared, checked, and reused in line with the findable, accessible, interoperable, and reusable data principles.
Plain Language Summary
Obtaining reliable estimates of the past strength of Earth's magnetic field is very challenging. Over the past decades, different techniques were developed to obtain information on the paleointensity of Earth's magnetic field. Here we present a new online, open source application to ease and standardize the interpretation of the most commonly used paleointensity techniques. Paleointensity.org supports the import and export of multiple file formats, including the format used by the global paleomagnetic database MagIC. This promotes and supports the findable, accessible, interoperable, and reusable use of data by the paleointensity community worldwide.
Key Points
We present a new online, open source, application for the interpretation of the most commonly used paleointensity techniques
Paleointensity.org currently supports Thermal Thellier, Microwave Thellier, pseudo‐Thellier, and Multispecimen data
Data can be imported and exported in several formats, including MagIC files, to promote the FAIR use of data
Micromagnetic tomography aims at reconstructing large numbers of individual magnetizations of magnetic particles from combining high‐resolution magnetic scanning techniques with micro X‐ray computed ...tomography (microCT). Previous work demonstrated that dipole moments can be robustly inferred, and mathematical analysis showed that the potential field of each particle is uniquely determined. Here, we describe a mathematical procedure to recover higher orders of the magnetic potential of the individual magnetic particles in terms of their spherical harmonic expansions (SHE). We test this approach on data from scanning superconducting quantum interference device microscopy and microCT of a reference sample. For particles with high signal‐to‐noise ratio of the magnetic scan we demonstrate that SHE up to order n = 3 can be robustly recovered. This additional level of detail restricts the possible internal magnetization structures of the particles and provides valuable rock magnetic information with respect to their stability and reliability as paleomagnetic remanence carriers. Micromagnetic tomography therefore enables a new approach for detailed rock magnetic studies on large ensembles of individual particles.
Key Points
Micromagnetic Tomography uniquely recovers higher‐order multipole terms for several individual grains in a sample
Higher order multipole moments are an expression of the internal domain structure of magnetic grains
Ultimately, this enables to select individual grains for rock‐ and paleomagnetic studies based on domain configuration
The recently developed Micromagnetic Tomography (MMT) technique combines advances in high resolution scanning magnetometry and micro X‐ray computed tomography. This allows precise recovery of ...magnetic moments of individual magnetic grains in a sample using a least squares inversion approach. Here we investigate five factors, which are governing the mathematical validity of MMT solutions: grain concentration, thickness of the sample, size of the sample's surface, noise level in the magnetic scan, and sampling interval of the magnetic scan. To compute the influence of these parameters, we set up series of numerical models in which we assign dipole magnetizations to randomly placed grains. Then we assess how well their magnetizations are resolved as function of these parameters. We expanded the MMT inversion to also produce the covariance and standard deviations of the solutions, and use these to define a statistical uncertainty ratio and signal strength ratio (SSR) for each solution. We show that the magnetic moments of a majority of grains under the inspected conditions are solved with very small uncertainties. However, increasing the grain density and sample thickness carry major challenges for the MMT inversions, demonstrated by uncertainties larger than 100% for some grains. Fortunately, we can use the SSR to extract grains with the most accurate solutions, even from these challenging models. Hereby we have developed a quick and objective routine to individually select the most reliable grains from MMT results. This will ultimately enable determining paleodirections and paleointensities from large subsets of grains in a sample using MMT.
Plain Language Summary
Iron‐bearing rocks have the ability to capture and store the direction and strength of Earth's magnetic field. This information is used to unravel the behavior of the magnetic field that protects us from harmful solar radiation. However, obtaining a reliable signal from these rocks is difficult using existing methods because many iron‐oxide grains exhibit complex magnetic behavior and obscure the magnetic information in them. To determine magnetic moments from individual grains, a new method known as Micromagnetic Tomography (MMT) has been developed. This method works similarly to imaging techniques in hospitals, but now a thin slice of rock containing magnetic grains is scanned. By using computer models we discovered that MMT is able to reliably extract magnetic signals from a majority of grains in many rock samples. Additionally, we have developed two new parameters that help us to easily select the magnetic moments of the most reliable grains in a sample. In this way, the signal of those grains can be effectively used to provide accurate information on the present and past state of Earth's magnetic field.
Key Points
The mathematical performance of Micromagnetic Tomography (MMT) is tested against the sample's geometry, instrumental noise and sampling interval
Sample thickness and grain density are the prime factors controlling the theoretical uncertainty of magnetic moments of individual grains
The mathematical accuracy of MMT results can be assessed using the signal strength ratio and uncertainty ratio
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