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  • 1
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    Intensity of the geomagnetic field in Europe for the last 3 ka: Influence of data quality on geomagnetic field modeling (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: One of the main challenges of paleomagnetic research is to obtain high-resolution geomagnetic field intensity reconstructions. For the last millennia, these reconstructions are mostly based on archeomagnetic data. However, the quality of the intensity data available in the databases is very variable, and the high scatter observed in the records clearly suggests that some of them might not be reliable. In this work we investigate how the geomagnetic field intensity reconstructions and, hence, our present knowledge of the geomagnetic field in the past, are affected by the quality of the data selected for modeling the Earth’s magnetic field. For this purpose we rank the European archeointensity data in four quality categories following widely accepted paleomagnetic criteria based on the methodology used during the laboratory treatment of the samples and on the number of specimens retained to calculate the mean intensities. Four geomagnetic field regional models have been implemented by applying the revised spherical cap harmonic analysis to these four groups of input data. Geomagnetic field models strongly depend on the used data set. The model built using all the available data (without any preselection) appears to be the less accurate, indicating some internal inconsistencies of the data set. In addition, some features of this model are clearly dominated by the less reliable archeointensity data, suggesting that such features might not reflect real variations of the past geomagnetic field. On the contrary, the regional model built on selected high-quality intensity data shows a very consistent intensity pattern at the European scale, confirming that the main intensity changes observed in Europe in the recent history of the geomagnetic field occurred at the continental scale.
    Description: Published
    Description: 2515–2530
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Description: open
    Keywords: Geomagnetism ; Paleomagnetism ; Archeomagnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.05. Geomagnetism::04.05.05. Main geomagnetic field ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    First directional European palaeosecular variation curve for the Neolithic based on archaeomagnetic data (2014)
    Elsevier Science Limited
    Details
    Publication Date: 2017-04-04
    Description: Neolithic, Chalcolithic and Bronze Age anthropogenic cave sediments from three caves from northern Spain have been palaeomagnetically investigated. 662 oriented specimens corresponding to 39 burning events (ash–carbonaceous couplets) from the three sites with an average of 16 samples per fire were collected. 26 new archaeomagnetic directions have been obtained for the time period ranging from 5500 to 2000 yr cal. BC. These results represent the oldest archaeomagnetic directions obtained from burnt archaeological materials throughout all Western Europe. Magnetisation is carried by pseudo-single domain low-coercivity ferromagnetic minerals (magnetite, magnetite with no significant isomorphous substitution and/or maghaemite). Rock-magnetic experiments indicate a thermoremanent origin of the magnetisation although a thermochemical magnetisation cannot be excluded. Combination of the new data presented here and the recent updated Bulgarian database allows us to propose the first European palaeosecular variation (PSV) curve for the Neolithic. A bootstrap method was applied for the curve construction using penalised cubic B-splines in time. The new palaeosecular variation curve is well constrained from 6000 BC to 3700 BC, the period with the highest density of data, showing a declination maximum around 4700 BC and a minimum in inclination at 4300 BC, which are not recorded by the recent global CALS10K.1b and regional SCHA.DIF.8K models due to the use of lake sediment data. Dating resolution by using the proposed PSV curve oscillates from approximately ±30 yr to ±200 yr for the period 6000 to 1000 yr BC, reaching similar resolution as radiocarbon dating. Considering the good preservation, age-control and widespread occurrence of burnt archaeological materials across Southern Europe, they represent a new source of data for geomagnetic field modelling, as well as for archaeomagnetic dating.
    Description: Published
    Description: 124-137
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: secular variation ; archaeomagnetism ; rock-magnetism ; thermoremanence ; Neolithic ; archaeology ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.05. Geomagnetism::04.05.05. Main geomagnetic field ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.07. Rock magnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.08. Instruments and techniques ; 04. Solid Earth::04.05. Geomagnetism::04.05.09. Environmental magnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    A geomagnetic field model fo the Holocene based on archaeomagnetic and lava flow data (2014)
    Elsevier Science Limited
    Details
    Publication Date: 2017-04-04
    Description: We propose a new geomagnetic field model for the Holocene period based on archaeomagnetic and lava flow data, avoiding the use of lake sediment data. The source of data comes from the GEOMAGIA50v2 database which has been updated with the new archaeomagnetic and volcanic studies published during the last 3 years. The model, called SHA.DIF.14k, allows us to analyse the behaviour of the geomagnetic field for the last 14000 years: from 12000 BC to 1900 AD. For the model construction we use the spherical harmonic analysis in space and the penalized cubic B-splines in time. Both spatial and temporal regularization norms are used to constrain the inversion problem and applied at the core-mantle boundary (CMB) to assure the convergence of the model. For the last 3ka, the model predictions agree with those given by the global model ARCH3k.1 and the European model SCHA.DIF.3k. For older epochs, the new model presents a clear improvement in field resolution with respect to other current models of the geomagnetic field for the Holocene. For the last 9ka, the time evolution of the dipolar moment obtained from the dipole field shows a clear minimum between 5500 BC and 3000 BC, and the well-known continuous decreasing trend of the geomagnetic field strength for the last millennium and half. A general view of the time-average evolution of the geomagnetic field flux lobes at the CMB for the northern hemisphere suggests a marked lobe of positive magnetic flux when the dipole moment was maximum. This lobe vanishes when the dipolar field is decreasing. The north polar wander paths of both north magnetic dip and geomagnetic poles were obtained showing an average rate of motion of 5.1 km/yr and 3.7 km/yr respectively. The model shows that the geomagnetic field can be averaged as axial dipolar in ~2000 years within an error of 5º, the typical uncertainty of the palaeomagnetic studies. Finally, and following the recent definition of archaeomagnetic jerks, we found 8 critical events in the time-evolution of the geomagnetic field for the last 8ka characterized by a maximum in the hemispheric asymmetry of the proposed model. The model is available in the Earth Ref Digital Archive at http://earthref.org/ERDA/1897/.
    Description: Published
    Description: 98-109
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: geomagnetism ; archaeomagnetism ; geomagnetic field model ; secular variation ; holocene ; 04. Solid Earth::04.05. Geomagnetism::04.05.01. Dynamo theory ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.05. Geomagnetism::04.05.03. Global and regional models ; 04. Solid Earth::04.05. Geomagnetism::04.05.05. Main geomagnetic field ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    First archaeomagnetic field intensity data from Ethiopia, Africa (1615 ± 12 AD) (2015)
    Elsevier Science Limited
    Details
    Publication Date: 2017-04-04
    Description: First archaeointensity determinations have been obtained from Ethiopia. Seven bricks (34 specimens) from the Däbsan archaeological remains were subjected to archaeointensity determination by means of classical Thellier–Thellier experiment including tests for magnetic anisotropy and magnetic cooling rate dependency. The age of the Däbsan Palace is well controlled by historical information: between 1603, when land grants were conceded to the Jesuits and the Catholicism was established as the official religion in Ethiopia, and the age of the Palace foundation in 1626–27. Successful archaeointensity determinations were obtained in 27 specimens from five individual bricks revealing an average field value of 33.5 ± 1.1 lT, which is 11–26% lower than expected values from global geomagnetic models based on historical and archaeomagnetic data. Global models for 1615 AD predict a low in central-southern Africa related to past location of the present Southern Atlantic Anomaly (SAA). Our results suggest that the field intensity in central Africa may have been slightly lower than global model predictions. This would indicate that the low could be probably more extended towards central-eastern Africa (or more intense) than previously considered. Further data from this region are especially welcome to delineate the evolution of the SAA.
    Description: Published
    Description: 24 - 35
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: Paleomagnetic secular variation ; Archeomagnetism ; Paleointensity ; Central Africa ; Geomagnetic models ; South Atlantic Anomaly ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 5
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    Recent developments in Archeomagnetism: the story of the Earth's past magnetic field (2015)
    Nova Science Publishers
    Details
    Publication Date: 2019-03-14
    Description: Since the pioneering studies in archeomagnetism in the second half of the 20th century, the number of archeomagnetic studies has increased exponentially. The huge density of archeomagnetic data collected during these years allows us to describe the past spatial and temporal evolution of the Earth’s magnetic field during the last millennia. Most of the data are located in the Northern Hemisphere, but currently, thanks to the strong effort of the paleomagnetic community, new collections of data are coming from the Southern Hemisphere, homogenizing the present database. Although the data distribution presents some epochs and locations where the data are still very scarce, they describe, to a greater or lesser degree of accuracy, the past behavior of the geomagnetic field. At regional scales, the use of archeomagnetic data permits the construction of paleosecular variation curves for the geomagnetic field elements: declination, inclination, and intensity. These curves describe the evolution of the elements at different times for the last millennia. During the last five years novel techniques, such as Bayesian statistics, bootstrap algorithms, or the Markov chain Monte Carlo method, have been applied to extract the most useful information from archeomagnetic data to build accurate and reliable curves. The accuracy of these curves can be exploited as a tool for archeomagnetic dating, assigning possible ages to archeological artifacts or volcanic lava flows with unknown age. At global scales, archeomagnetic data are jointly treated with other paleomagnetic data to generate continuous geomagnetic field models, reconstructing the past evolution of the geomagnetic field not only at the Earth’s surface, but also at the core-mantle boundary, shedding light on the past evolution of complex geodynamo processes.
    Description: Published
    Description: 99-158
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: restricted
    Keywords: Archeomagnetism ; Paleomagnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.05. Geomagnetism::04.05.03. Global and regional models ; 04. Solid Earth::04.05. Geomagnetism::04.05.05. Main geomagnetic field ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.07. Rock magnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.08. Instruments and techniques
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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  • 6
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    Non-Dipole and Regional Effects on the Geomagnetic Dipole Moment Estimation (2014)
    Springer Verlag
    Details
    Publication Date: 2019-03-14
    Description: The study of the temporal evolution of the dipole moment variations is a forefront research topic in Earth sciences. It constrains geodynamo simulations and is used to correct cosmogenic isotope production, which is evidence of past solar activity, and it is used to study possible correlations between the geomagnetic field and the climate. In this work, we have analysed the main error sources in the geomagnetic dipole moment computation from palaeomagnetic data: the influence of the non-dipole terms in the average approach, the inhomogeneous distribution of the current palaeomagnetic database, and the averaging procedure used to obtain the evolution of the dipole moment. To evaluate and quantify these effects, we have used synthetic data from a global model based on instrumental and satellite data, the International Geomagnetic Reference Field: 11th generation. Results indicate that the non-dipole terms contribute on a global scale of 〈6% in the averaged dipole moment, whereas the regional non-dipole contribution can show deviations of up to 35 % in some regions such as Oceania, and different temporal trends with respect to the global dipole moment evolution in other ones, such as Europe and Asia. A regional weighting scheme seems the best option to mitigate these effects in the dipole moment average approach. But when directional and intensity palaeomagnetic information is available on a global scale, and in spite of the inhomogeneity of the database, global modelling presents more reliable values of the geomagnetic dipole moment.
    Description: Published
    Description: 91-107
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: geomagnetism ; paleomagnetism ; archeomagnetism ; geomagnetic dipole moment ; geomagnetic field modelling ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.05. Geomagnetism::04.05.03. Global and regional models ; 04. Solid Earth::04.05. Geomagnetism::04.05.05. Main geomagnetic field ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 7
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    Statistical Analysis of Palaeomagnetic Data from the Last Four Centuries: Evidence of Systematic Inclination Shallowing in Lava Flow Records. (2014)
    Springer Verlag
    Details
    Publication Date: 2020-02-24
    Description: The main objective of this work is to compare directional (declination and inclination) volcanic and archaeomagnetic data for the last four centuries (1600–1990) with the historical geomagnetic predictions given by the GUFM1 model which spans from 1590 to 1990. The results show statistical agreement between archaeomagnetic data and directions given by the geomagnetic field model. However, when comparing the volcanic data with the model predictions, marked inclination shallowing is observed. This systematically lower inclination has already been observed in local palaeomagnetic studies (Italy, Mexico and Hawaii) for the 20th century, by comparing recent lava flows with the International Reference Geomagnetic Field (IGRF) model. Here, we show how this inclination shallowing is statistically present at worldwide scale for the last 400 years with mean inclination deviation around 3º lower than the historical geomagnetic field model predictions.
    Description: Published
    Description: 839–848
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: Inclination Shallowing ; Paleomagnetism ; Volcanic data ; Archeomagnetic data ; Geomagnetic field models ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.05. Geomagnetism::04.05.05. Main geomagnetic field ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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