A record of the lower Mammoth geomagnetic polarity reversal from a marine succession in the Boso Peninsula, central Japan

Summary Palaeomagnetic records from geological archives provide significant information about the nature of geomagnetic polarity reversals; however, there are few detailed palaeomagnetic records of pre-Pleistocene reversals. The lower Mammoth Subchron boundary (late Pliocene) is recorded in a 10-m interval of a marine succession deposited at high accumulation rates (9–66 cm/kyr) in the Boso Peninsula, central Japan. Here, we report a continuous palaeomagnetic record of the lower, normal to reverse boundary interval of the Mammoth Subchron, including the geomagnetic field direction and relative palaeointensity, with an average temporal resolution of ca 800 years. A hybrid method of thermal demagnetization at 200° C and progressive alternating field demagnetization were used to effectively extract the primary palaeomagnetic component, which is carried by magnetite. The lower Mammoth transition is characterized by palaeomagnetic direction of instability and decay of the relative palaeointensity, and occurred from late Marine Isotope Stage MG3 (3351 ka) to MG2 (3336 ka) or MG1 (3331 ka), spanning 15–20 kyr. Virtual geomagnetic poles (VGPs), calculated from primary palaeomagnetic directions, rapidly rebounded twice from southern latitudes to northern latitudes within the transition. In contrast to the complex lower Mammoth reversal behavior recorded in the Boso Peninsula succession, records from a lava sequence in O'ahu (Hawai'i) reveal a rebound following a 180° directional change, and those from a marl succession in Sicily (Italy) indicate a single rapid directional change. Diverse geomagnetic field evolution among these three sections is reflected resolution difference among the records likely in combination with an influence of non-axial dipole field.

Modified asymmetrical 13-level inverter topology with reduce power semiconductor devices

This paper introduces a modified multilevel inverter topology with asymmetrical dc sources combination. The significant features of the proposed circuit are the reduced number of switches and low total standing voltage (TSV). Proposed topology utilizes ten switches to produce 13 level output with per unit TSVp.u of 5.33. An additional feature of the proposed topology is the inherent negative level generation as there is no requirement of an H-bridge for the polarity reversals. Nearest level control (NLC) technique is used as the modulation strategy. Performance of the proposed topology is validated through extensive analysis using Simulink and PLECS software. Detailed circuit analysis and its power loss, as well as efficiency studies, have been carried out under constant and dynamic load conditions. Results obtained shows that the proposed topology is working well, producing an output of 13-level with total harmonic distortion of 6.36% and inverter efficiency of 98.8%. The topology is extended to n-level structure, and its generalized expressions for different parameters were formulated. The comparison of the generalized structure with other existing topology is carried out, and it is found that the proposed topology outperform other topologies on many parameters.

A coupled core-mantle evolution: review and future prospects

In this review, I provide the current status and future prospects for the coupled core-mantle evolution and specifically summarize the constraints arising from geomagnetism and paleomagnetism on the long-term secular variations of the geomagnetic field. The heat flow across the core-mantle boundary (CMB) is essential for determining the best-fit scenario that explains the observational data of geomagnetic secular variations (e.g., onset timing of the inner core growth, geomagnetic polarity reversals, and westward drift) and should include the various origins of the heterogeneous structures in the deep mantle that have affected the heat transfer across the core-mantle boundary for billions of years. The coupled core-mantle evolution model can potentially explain the onset timing of the inner core and its influence on the long-term geomagnetic secular variations, but it is still controversial among modeling approaches on the core energetics because the paleomagnetic data contains various uncertainties. Additionally, with the coupled core-mantle evolution model in geodynamo simulations, the frequency of the geomagnetic polarity reversals can be explained with the time variations of the heat flow across the CMB. Additionally, the effects of the stable region in the outermost outer core to the magnetic evolution are also crucial but there would be still uncertain for their feasibility. However, despite this progress in understanding the observational data for geomagnetic secular variations, there are several unresolved issues that should be addressed in future investigations: (1) initial conditions—starting with the solidification of the global magma ocean with the onset timing of plate tectonics and geodynamo actions and (2) planetary habitability—how the dynamics of the Earth’s deep interior affects the long-term surface environment change that has been maintained in the Earth’s multisphere coupled system.

Cataclysmic Geomagnetic Field Collapse: Global Security Concerns

In 2015, Tyler J. Williams authored “Cataclysmic Polarity Shift: Is U. S. National Security Prepared for the Next Geomagnetic Pole Reversal?” That document provides an extremely cogent and thorough description of some of the risks to national security and infrastructure expected to result from a geomagnetic polarity reversal. However, it describes geomagnetic field generation solely as currently promoted by the geophysics community which is based upon old ideas, circa 1940s-1960s, that are taken to be factual without any attempt to understand their limitations or to evaluate their validity in light of subsequent scientific developments. Moreover, the security concerns Williams described are relevant to humanity globally. Here I have reviewed the historical development of those old ideas, pointed out their problematic nature, and reviewed subsequent published advances that overcome their inherent problems and lead to a better understanding of the geophysics related to geomagnetic polarity reversals, geomagnetic excursions, and, at some yet unknown time, the permanent demise of the geomagnetic field. Mechanisms of rapid geomagnetic field collapse, both natural and potentially human-induced, are described. The present state of nuclear georeactor activity, whether geomagnetic field collapse leads to increased georeactor output, and whether it is likely to trigger earthquakes and volcano eruptions are yet unknown matters of seriously troubling human security concerns. Global security preparedness, even though addressed by sovereign nations, should be predicated upon the latest and most correct scientific understanding. In some areas that may be the case, but in the scientific areas described here there are clearly problems. The inherent problems, I submit, do not result from inadequate funding, but from inadequate methodologies, expectations and responsibilities of scientists, their national and parent institutions, publishers, and respective funding-agencies.

Geomagnetic Field Paleointensity during the Cretaceous Normal Superchron from Marine Magnetic Anomalies

<p>The knowledge of the geomagnetic field intensity during the Cretaceous Normal Superchron, a long term of forty million years without polarity reversals, may have a large impact on our understanding of the dynamo process occurring in Earth’s outer core. How, it is difficult to get the geomagnetic field behavior during the Cretaceous Normal Superchron resulting from the inadequate sampling or data of variable qualities from igneous rocks and sedimentary. Here we examine 20 magnetic anomaly profiles across the Cretaceous magnetic quiet zone of the Central Atlantic Ocean in the African flank extracted from the EMAG2v3, and calculate a synthetical magnetization profile based on the forward modeling method. We suggest that this profile records the high strength of geomagnetic field at the beginning of ~30 million years and low signal during the late period, which could be correlated with the low-resolution relative paleointensity record from the sediment samples at the Falkland Plateau, and which also could be found the VDMs/VADMs averaged by a 7-Ma sliding window from the absolute intensity records mostly from the MagIC database. Our results support the hypothesis that the distribution of heat flow along the core-mantle boundary is positively correlative to the intensity of the dipole field.</p>

Magnetostratigraphy and environmental magnetism of the Aptian-Albian boundary of sedimentary core from Sergipe-Alagoas Basin: preliminary results

<p>The Early Cretaceous was dominated by greenhouse conditions and increases in ocean crust production rate, with critical climate, geography and oceanography changes and abrupt shifts in redox conditions in the oceans. Prior to the Aptian, regarding the Earth’s magnetic field, a high rate of polarity reversals dominated. However, thereafter, a period of polarity stability, known as the Cretaceous Normal Polarity Superchron (CNPS), was established for 34 Myr. Although, there are debates on the causes and consequences of these extreme events. The exact behavior of the geomagnetic field in this period is still poorly understood, and data from volcanic and sedimentary rocks are conflicting. The biostratigraphy data from the sedimentary succession from the Aptian-Albian interval in the Sergipe-Alagoas Basin (Brazil) are rare and correlations are weak with Tethyan realm. Since some of the major reservoirs of the terrestrial portion of the Sergipe-Alagoas basin are from Aptian-Albian ages the lack of age models brings difficulties to the oil industry. Magnetic parameters such as magnetic susceptibility, ARM, IRM, and magnetostratigraphy data were obtained with a resolution of 25 cm in the Core SER-03 from Sergipe-Alagoas Basin. The entire section varies 4 Myr, including the Aptian-Albian boundary. Here, we present preliminary environmental magnetism and magnetostratigraphic interpretation for this core. Therefore, these data will aid to develop an age model framework in order to assist this uncovered region and for future comparisons with Tethyan realm.</p>