Intensity Of Earth's Magnetic Field Research Articles

New criteria for selecting reliable Thellier-type paleointensity results from the 1960 Kilauea lava flows, Hawaii

Thellier-type paleointensity experiments associated with partial thermal remanent magnetization checks have been widely used to determine paleointensity values from volcanic and archaeological media. However, previous studies have revealed that a substantial portion of paleointensity results with positive checks for historical lava samples largely fails to predict known Earth magnetic field intensity values. To determine the fidelity of paleointensity values, conventional Thellier-type paleointensity experiments were performed on Kilauea lava flows that erupted in 1960. The positive partial thermal remanent magnetization checks for our results range from 30.28 ± 1.38 µT to 52.94 ± 1.89 µT. This strongly indicates that conventional paleointensity checks cannot guarantee the fidelity of paleointensity results, especially when the unblocking temperatures for the newly formed magnetic particles are higher than the treatment temperature. Therefore, in this study, to check for thermal alteration during heating, the temperature dependence of the hysteresis parameter measured at room temperature for the thermally treated samples was also measured. Our new results show that nearly all biased paleointensity values correspond to a ratio of the coercivity of remanence to the magnetic coercivity of > 3 and a chemical alteration index > ~ 10%, which indicates the strong effect of the domain state and thermal alteration on the fidelity of the paleointensity results. Our study provides feasible criteria to further improve the fidelity of paleointensity estimations.

An inter-comparison exercise for the Mexican intensity secular variation curves: Case study of the Tingambato archaeological site (central-western Mexico)

Dating analysis of potsherds from three of the six units recently excavated in the Tingambato archaeological site, central-western Mexico, was carried out employing two regional intensity Paleosecular Variation Curves (PSVC) and the global model SHA.DIF.14k. A complete evaluation of the ceramic fragments' magnetic characteristics was done to determine the samples' magnetic carriers and their capacity to provide reliable archaeointensity data. The presence of two magnetization components in five analyzed potsherds provides two snapshots of the Earth's magnetic field intensity behavior at different temporalities. Intensity values were obtained following strict quality criteria, including cooling rate and anisotropy corrections. The principal causes of failure in archaeointensity experiments are associated with the alteration of the magnetic mineralogy during the heating of the specimens and with the presence of multidomain grains. Intensities within the established quality criteria were obtained for four out of the eleven ceramic fragments analyzed. The dating exercise shows a better correspondence of the intensity values with the regional curves than with the global model, especially for the temporal range between AD 400–1200, for which both regional curves are in good agreement. The obtained archaeomagnetic ages had a good correspondence with the radiocarbon ages reported in previous studies. By determining two archaeointensity values in one of the studied potsherds: one associated whit its fabrication and the other related to the fire (after which the site is supposed to be abandoned), archaeomagnetic ages of the probable end of Tingambato occupation were estimated. • Age comparison exercise favors the use of regional models over global models. • Two proposals for the end occupation of Tingambato are presented. • The period AD 400–1200 has the best dating results for the regional models.

The Growth and Sporulation of Bacillus subtilis in Nanotesla Magnetic Fields.

The order of magnitude of increased growth, multiplication rate, and decreased sporulation of Bacillus subtilis after exposure to nanotesla magnetic fields (MFs) relative to control samples were observed experimentally. Earth's total magnetic field intensity was reduced from 47.9 ± 0.4 μT to cover the range from 97.5 ± 1.7 nT to 1115 ± 158 nT in eight subsequent experiments by using three pairs of Helmholtz coils combined with Mu-metal shielding. The growth, multiplication rate, sporulation, and potassium content were measured in the probe and control containing B. subtilis cultures after 24 h of exposure to nanotesla and Earth's magnetic fields, respectively. The observed effect is discussed with regard to its possible repercussions on Earth's living species during geomagnetic reversals that occurred when the magnetic field was much weaker than the field that exists today. In addition, effects on future manned voyages into deep space, an environment with reduced magnetic field intensity, are considered.

Upgrade of the Argentine Islands INTERMAGNET observatory at Akademik Vernadsky station, Antarctica

The article describes the main features of upgrading the magnetometric complex based on the LEMI-025 variometer in January-April 2019 at the geomagnetic observatory (code AIA) of the Ukrainian Antarctic Akademik Vernadsky station. The observatory’s old magnetometric complex consisted of two LEMI-008 (No. 02 and No. 16) variometers and one POS-1 scalar magnetometer. The measurements of LEMI-008 and POS-1 were not mutually synchronized and this was one of the main problem. Every measuring instrument taken individually as a component of the whole magnetometric complex had good individual properties. However, in general, the complex as an entire system had reduced performance, mainly due to the lack of mutual synchronization of measurements. Some preliminary test results are also presented. Main objective. One of the main task of upgrading the AIA observatory was to install a new variometer that is compatible with the requirements of the 1-second INTERMAGNET data standard. For two decades, old LEMI-008 variometers at Akademik Vernadsky station have shown high baseline stability, which meets INTERMAGNET requirements. Unfortunately, the noise characteristics of old variometers, the accuracy of synchronization with UTC, and the resolution do not longer meet the current INTERMAGNET requirements for devices that produce 1-second data. Measurements of LEMI-008 variometers and POS-1 scalar magnetometer were not mutually  synchronized. Due to lack of reliable mutual synchronization, the differences between the field vector modules, calculated indirectly from the variometer measurements and measured directly with the scalar magnetometer, varied and could be unreliable. With strong geomagnetic disturbances, this reduced the overall accuracy of the magnetometric complex as an integral measuring system, although the complex consisted of high-precision instruments. Only one of LEMI-008 variometers was equipped with GPS synchronization. This made data processing difficult. Therefore, one of the crucial upgrading tasks was creation of a system for mutual synchronization of measurements provided by the variometer LEMI-025 and the scalar magnetometer POS-1 with an accuracy of approximately 0.1 s (but not worse than 1 s) using control computer. Methods. The problem of mutual synchronization of the measurements of the LEMI-025 variometer and the POS-1 scalar magnetometer (at the stage of upgrading the magnetometric complex as a whole system) was solved using a control computer by periodical adjusting the POS-1 clock and starting its measurement cycles with a given timing advance. New data arrays were obtained while the LEMI-025 magnetometer was operated in test mode. Using the Bartlett’s method and spectral harmonics averaging, the noise level of the magnetometers during a geomagnetically quiet day was estimated. The results of absolute measurements of the geomagnetic field components, regularly carried out in the observatory by two methods, were analyzed and the baselines values of the LEMI-025 magnetometer were estimated. The comparative analysis of the records of the Earth magnetic field intensity, obtained by direct measurements with a scalar magnetometer POS-1 and calculated from the baseline-adjusted components of the LEMI-025 variometer, was performed. Using the obtained baseline values and the total field difference signals the high calibration accuracy of the new variometer was confirmed and the orientation errors of its sensitivity axes in the geographical coordinate frame were estimated. Conclusions. Our preliminary results confirm that the characteristics of new LEMI-025 variometer meet the INTERMAGNET requirements. The orientation errors of LEMI-025 sensor do not exceed 5 arc minutes. The base line is quite stable. All its components have dispersion within ±2 nT, without pronounced temporal drift. The test results of LEMI-025 variometer showed that the characteristics of all magnetometric instruments in the measuring pavilion of the AIA observatory should be mutually agreed in terms of electromagnetic compatibility.

Refined 3600 years palaeointensity curve for Mexico

Our knowledge of the Earth's magnetic field intensity changes over the past few thousand years is still limited because of the uneven spatial and temporal distribution of data, which also includes the Americas. The present study reports 41 new palaeointensity data covering the past 3600 years which, together with 38 previously published data of similar quality, are used to construct a palaeointensity secular variation curve for Central Mexico. These new data are an important contribution to the global intensity database and will also improve the application of palaeomagnetic dating in Mexico, which is of interest because of the many Holocene monogenetic volcanoes within the Trans-Mexican Volcanic Belt, and of its archaeological heritage. The most conspicuous feature of the new intensity curve is the rapid increase between 400 and 250 BCE, from about 45 to 65 μT. Other relative intensity highs of ≈45–55 μT were found around 1600 BCE, 370 CE, and 1200 CE and relative intensity lows of ≈30–35 μT around 1350 BCE and 700 CE. Comparing the virtual axial dipole moment of our intensity curve with global VADM-VDM dipole estimates indicates that non-dipole components in Central Mexico have been observed at several times from 1600 BCE to 1000 CE while the dipole field was prevalent from 1000 to 1800 CE. A comparison of our results with selected data from southern USA shows a significant difference between the two regions which indicates an important nondipole feature of the magnetic field during the last few thousands of years, and/or undetected problems in the age/palaeointensity data accuracy.

Pedersen Ionic Contribution in Different Time Scales

AbstractPedersen conductivity is one of the main parameters in atmospheric electrodynamics, magnetosphere‐ionosphere‐thermosphere coupling, and several other geophysical processes. It is determined by the collision frequency between charged and neutral components and the Earth's magnetic field intensity through the gyrofrequency. This work analyzes the contribution of different ionic species to the variability of Pedersen conductance in time scales from hours to years within the period 1964–2008 based on the results of various atmospheric and ionospheric models. The main results are (1) there is a positive correlation between O+ density and Pedersen conductance, (2) Pedersen conductance of F layer has a larger increase with the solar activity than that of E layer, (3) Pedersen conductance has a long‐term trend that is determined by Earth's magnetic field intensity and electron density, and (4) at midlatitudes trends are mainly governed by the Earth's magnetic field and modulated by the electron density, while at high latitudes both are important.

Assessing the Influence of Personality on Sensitivity to Magnetic Fields in Zebrafish.

To orient themselves in their environment, animals integrate a wide array of external cues, which interact with several internal factors, such as personality. Here, we describe a behavioral protocol designed for the study of the influence of zebrafish personality on their orientation response to multiple external environmental cues, specifically water currents and magnetic fields. This protocol aims to understand whether proactive or reactive zebrafish display different rheotactic thresholds (i.e., the flow speed at which the fish start swimming upstream) when the surrounding magnetic field changes its direction. To identify zebrafish with the same personality, fish are introduced in the dark half of a tank connected with a narrow opening to a bright half. Only proactive fish explore the novel, bright environment. Reactive fish do not exit the dark half of the tank. A swimming tunnel with low flow rates is used to determine the rheotactic threshold. We describe two setups to control the magnetic field in the tunnel, in the range of the earth's magnetic field intensity: one that controls the magnetic field along the flow direction (one dimension) and one that allows a three-axial control of the magnetic field. Fish are filmed while experiencing a stepwise increase of the flow speed in the tunnel under different magnetic fields. Data on the orientation behavior are collected through a video-tracking procedure and applied to a logistic model to allow the determination of the rheotactic threshold. We report representative results collected from shoaling zebrafish. Specifically, these demonstrate that only reactive, prudent fish show variations of the rheotactic threshold when the magnetic field varies in its direction, while proactive fish do not respond to magnetic field changes. This methodology can be applied to the study of magnetic sensitivity and rheotactic behavior of many aquatic species, both displaying solitary or shoaling swimming strategies.

Variations of Earth Magnetic Field Intensity for the Past 5 Myr Derived From Marine Magnetic Anomalies in a Slow‐to‐Intermediate Spreading South Atlantic Ridge

AbstractWe investigated sea‐surface magnetic anomaly data for the past 5 Myr in the slow‐to‐intermediate spreading South Atlantic Ridge. After error analysis and signal processes, the sea surface magnetic anomaly profiles were downward continued to 1.5 km below sea level, and then the distance from spreading axis was converted to time by matching the observed anomalies with forward models of known polarity reversals. The stacked anomaly profiles from South Atlantic Ridge exhibit short‐wavelength wiggles superimposed on the first‐order variations of magnetic anomalies. The stacked anomaly profiles were first compared with commonly used geomagnetic palaeointensity data synthesized from sedimentary relative intensity records in the past and were further correlated with other available magnetic profiles derived from Central Indian Ridge, East Pacific Rise, and Pacific‐Antarctic Ridge. We found that short wavelength variations in the South Atlantic Ridge can be ascribed to geomagnetic intensity variations from excursions or short polarity events. Spectral analysis of marine magnetic anomalies records reveals that there is no obvious dominant periodicity for the geomagnetic field behavior during the past 5 Myr.

Continuous millennial decrease of the Earth’s magnetic axial dipole

Since the establishment of direct estimations of the Earth's magnetic field intensity in the first half of the nineteenth century, a continuous decay of the axial dipole component has been observed and variously speculated to be linked to an imminent reversal of the geomagnetic field. Furthermore, indirect estimations from anthropologically made materials and volcanic derivatives suggest that this decrease began significantly earlier than direct measurements have been available. Here, we carefully reassess the available archaeointensity dataset for the last two millennia, and show a good correspondence between direct (observatory/satellite) and indirect (archaeomagnetic) estimates of the axial dipole moment creating, in effect, a proxy to expand our analysis back in time. Our results suggest a continuous linear decay as the most parsimonious long-term description of the axial dipole variation for the last millennium. We thus suggest that a break in the symmetry of axial dipole moment advective sources occurred approximately 1100 years earlier than previously described. In addition, based on the observed dipole secular variation timescale, we speculate that the weakening of the axial dipole may end soon.

On-board algorithm for SamSat-218D nanosatellite orientation and stabilization system

Algorithms for determining the attitude and angular rate damping of the SamSat-218D nanosatellite developed at Samara State Aerospace University are described in the paper. The date of the prospective launching of the satellite into the Earth orbit from Vostochniy spaceport is April, 2016. A triaxial magnetometer and luminance sensors are used as sources of information in the orientation system. Three magnetic coils serve as actuators providing the angular rate damping onboard the nanosatellite. A known method of vector coordination with the original criterion of preliminary measurement rejection is used as the orientation determination algorithm since the vector coordination method is very sensitive to measurement errors. The traditional B-dot algorithm is used as the damping algorithm. The influence of the initial angular rates on the magnetic moment coefficient in the B-dot control algorithm is studied. Since the continuous mode of operation of magnetic coils on board the nanosatellite is unpractical due to the necessity of measuring variations in the Earth magnetic field intensity vector the damping process is analyzed in the discrete mode of operation at different values of angular rates of nanosatelite separation. The comparison of the algorithm processing speed in the continuous and discrete operating modes at various initial angular rates of separation is given.

Simulation of the process of angular rate damping of the SamSat-218D nanosatellite after separation from the launching-transporting container

The paper presents an algorithm of damping the initial angular rate of the SamSat-218D nanosatellite after its separation from the transporting-launching container. Three mutually orthogonal magnetic coils are used as actuators that provide damping of the initial angular rate on board the nanosatellite. The traditional B-dot algorithm is used as the damping algorithm. Two operating modes are possible for the B-dot algorithm: a continuous mode and a discrete one. As the continuous operating mode of the magnetic coils onboard the nanosatellite in orbital flight is inexpedient because of the necessity of measuring the Earth magnetic field intensity vector the discrete mode of operating of the algorithm of damping the initial angular velocities acquired by the nanosatellite after its separation from the transporting-launching container is analyzed. The results of the mathematical simulation during the analysis of choosing discretization intervals in the algorithm of damping the initial angular rate of the SamSat-218D nanosatellite are presented.

Holocene geomagnetic field intensity variations: Contribution from the low latitude Canary Islands site

New absolute paleomagnetic intensity (PI) are investigated from 37 lava flows located at Tenerife and Gran Canaria (Canary Islands). They complete previously published directional results from the same flows and therefore allow to examine the time variations of the full geomagnetic vector. Twenty-eight flows are radiocarbon dated between 1706 AD and about 13 200 BC and one is historical. Eight other flows are not dated but they have stratigraphic links with the dated flows and archeomagnetic ages had been attributed to them based on their paleomagnetic directions. Various mineralogical analyses were conducted, giving access to the nature of the magnetic minerals and to their grain size. We performed the original Thellier and Thellier paleointensity (PI) experiments with a success rate of about 65% coupling this experiment with the strict set of selection criteria PICRIT-03. The mean PIs at the flow level are based on 3 to 12 independent PI determinations except for one site in which only one reliable determination could be obtained. The data indicate some variability in the local field intensity with a prominent PI peak centered around 600 BC and reaching 80 μT (VADM 16×1022 Am2), documented for the first time in this region. Combined with the published data obtained from western Africa, Spain, Portugal, Morocco and the Azores within a 2000 km-radius around the Canary Islands, our data allow to construct a curve illustrating the Earth magnetic field intensity fluctuations for Southwestern Europe/Western Africa. This curve, compared to the one produced for the Middle East and one calculated for Central Asia shows that maximum intensity patches have a very large geographical extent. They do not yet appear clearly in the models of variations of the dipolar field intensity.

An integrated archeomagnetic and C14study on pre‐Columbian potsherds and associated charcoals intercalated between Holocene lacustrine sediments in Western Mexico: Geomagnetic implications

The firm relationship between archeomagnetic samples and their absolute ages, which is usually determined or estimated using a variety of methods (archaeological context, thermoluminiscense, C14, etc.), is crucial in any archaeomagnetic investigation. In this paper, we report 18 successful (from 65 analyzed) archaeointensity determinations of high technical quality performed on specimens obtained from three fragments of pre‐Columbian potsherds. These are unambiguously correlated with charcoal samples, as they were found together in three thin lacustrine sedimentary layers in western Mexico. Moreover, new radiometric results were obtained in this study from all charcoal samples (beta analytic) yielding ages of 1490 ± 40, 1510 ± 40, and 1580 ± 40 BP. In addition, detailed magnetic measurements were carried out on all studied ceramic fragments. These rock magnetic experiments, which included low field susceptibility versus temperature, hysteresis, and first‐order reversal curve measurements, indicate that the main magnetic carrier is Ti‐poor titanomagnetite. The average archeointensity values per ceramic fragments obtained in this study are very similar in all three cases: 35.2 ± 1.3 μT (N = 5), 36.8 ± 1.6 μT (N = 6), and 37.2 ± 3.4 μT (N = 7). This corresponds to an average intensity of 36.4 ± 1.1 μT and a virtual axial dipole moment value of 8.1 ± 0.2 × 1022Am2, which is slightly lower than the present field strength, corresponding at an age interval between 640 and 430 A.D. Although we detected some relationship between the Earth's magnetic field intensity and multidecadal climatic events, such observations can only be considered tentative at this stage.

A possible link between the geomagnetic field and catastrophic climate at the Paleocene-Eocene thermal maximum

Research Article| November 01, 2009 A possible link between the geomagnetic field and catastrophic climate at the Paleocene-Eocene thermal maximum Youn Soo Lee; Youn Soo Lee 1Geological Research Division, Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon 305-350, Korea Search for other works by this author on: GSW Google Scholar Kazuto Kodama Kazuto Kodama 2Kochi Core Center, Kochi University, Kochi 783-8502, Japan Search for other works by this author on: GSW Google Scholar Geology (2009) 37 (11): 1047–1050. https://doi.org/10.1130/G30190A.1 Article history received: 04 Mar 2009 rev-recd: 25 Jun 2009 accepted: 30 Jun 2009 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Youn Soo Lee, Kazuto Kodama; A possible link between the geomagnetic field and catastrophic climate at the Paleocene-Eocene thermal maximum. Geology 2009;; 37 (11): 1047–1050. doi: https://doi.org/10.1130/G30190A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract We report high-precision records of a magnetic reversal event at the Paleocene-Eocene thermal maximum (PETM), a cataclysmic global warming event initiated at 55.0 Ma. This event is confirmed by both an antipodal shift in direction and a reduction in magnetic intensity during the lower and upper transitions, and it is seen at additional sites, indicating that the characteristic remanent magnetization (ChRM) was primarily acquired by Earth's magnetic field during sedimentation. This major fluctuation of Earth's magnetic field intensity is interpreted to have been linked to the PETM and to have eventually facilitated the reversal. This Paleocene-Eocene magnetic reversal (PEMR) lasted for ~53 ka, from 54.964 to 54.911 Ma, but finally recovered to an original polarity. This suggests a possible coupling between Earth's core magnetofluid dynamo sphere and the atmosphere-hydrosphere during an abrupt catastrophic climate event. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Beryllium-10 in deep-sea sediments: a tracer for the Earth's magnetic field intensity during the last 200,000 years

We present a new approach for the reconstruction of the Earth's magnetic field intensity during the last 200,000 years based on 10Be in deep-sea sediments. A simple box model that is able to describe boundary scavenging of 10Be in the ocean is used to study the sensitivity of 10Be to changes of water circulation and/or varying particle rain rates. The model is applied to separate transport and production signal in single 10Be records. Vertical sediment accumulation rates are used as input values for the model calculations. The calculated scavenging factors are applied to correct the 10Be records for boundary scavenging. The model corrected 10Be based paleointensity record correlates well with other records from very different archives.

Grain‐size‐dependent paleointensity results from very recent mid‐oceanic ridge basalts

We report paleointensity analyses on a suite of four samples from two axial zero‐age mid‐oceanic ridge basalt flows from the East Pacific Rise. Paleointensity experiments have been performed on several profiles, each consisting of a batch of small (millimeter scale) subsamples going from the rapidly cooled glassy margin to the interior. The Coe version of the Thellier double‐heating procedure was used with back checks performed after every other heating step. Most of the samples show very good behavior, i.e., constant ratio between the lost and acquired magnetization through a large temperature range (quality factor usually above 10) and positive checks, which lead to unambiguous paleointensity determinations. Paleointensities obtained on glasses reported here and in a previously published study are very consistent and reproducible and in agreement with expected in situ values of Earth's magnetic field intensity. However, results found within the crystalline part of the samples show values that are considerably (up to 50%) higher than expected. These variations seem to be correlated with the cooling history of the samples and appear to be universal since all samples exhibit the same intriguing pattern. An extensive study of magnetic properties allows us to link this incongruent behavior to (1) the presence of multidomain effects and (2) the cooling rate difference between laboratory experiments and in situ cooling.

Uncontrollable Rotational Motion of the Mir Orbital Station

The results of determining the rotational motion of the Mir orbital station are presented for four long segments of its unmanned uncontrolled flight in 1999–2000. The determination was carried out using the data of onboard measurements of the Earth's magnetic field intensity. These data, taken for a time interval of several hours, were jointly processed by the least squares method with the help of integration of the equations of station motion relative to its center of mass. As a result of this processing, the initial conditions of motion and the parameters of the mathematical model used were evaluated. The technique of processing is verified using the telemetry data on angular velocity of the station and its attitude parameters. Two types of motion were applied on the investigated segments. One of them (three segments) presents a rotation around the axis of the minimum moment of inertia. This axis executes small oscillations with respect to a normal to the orbit plane. Such a motion was used for the first time on domestic manned orbital complexes. The second type of motion begins with a biaxial rotation which, in a few weeks, goes over into a motion very similar to the rotation around the normal to the orbit plane, but around the axis of the maximum moment of inertia.

Comparison of cosmogenic radionuclide production and geomagnetic field intensity over the last 200 000 years

The production rate of cosmogenic radionuclides such as 10Be or 14C is known to vary as a function of the geomagnetic field intensity. It should, therefore, be possible to extract a record of palaeofield intensity from the deposition record of these radionuclides in marine or terrestrial sediments and ice cores. Field intensity variations, however, are not the only factor that has influenced the cosmogenic radionuclide records. In the case of 14C, variations of the global carbon cycle, caused by reorganization of the ocean circulation patterns from the last glacial to the present interglacial, are superimposed. 10Be is not affected by these variations because it is not part of the carbon cycle, but its deposition rates in marine sediments vary as a function of lateral sediment redistribution and boundary scavenging intensity. A global stacked record of 10Be deposition rates, corrected for sediment redistribution by normalizing to 230Thex, was shown to remove most of the disturbances, and provides a record of 10Be production rate variations over the last 200 000 years, which translates into geomagnetic field intensity variations. This dataset is compared with palaeofield intensities reconstructed from marine sediments by palaeomagnetic methods, from variations in atmospheric 14C/12C derived from independent calibrations of 14C ages, such as U/Th dating and tree ring chronology, and from 36Cl and 10Be fluxes in polar ice cores. Potential influences of the Earth’s orbital parameters and insufficient correction for orbitally triggered climate variations on the palaeointensity reconstructions are assessed. It is argued that the palaeointensity records derived from marine sediments are not significantly affected by these factors.

Radiocarbon Levels in the Iceland Sea from 25–53 kyr and their Link to the Earth's Magnetic Field Intensity

By correlating the climate records and radiocarbon ages of the planktonic foraminifera N. pachyderma(s) of deep-sea core PS2644 from the Iceland Sea with the annual-layer chronology of the GISP2 ice core, we obtained 80 marine 14C calibration points for the interval 11.4-53.3 ka cal BP. Between 27 and 54 ka cal BP the continuous record of 14C/cal age differences reveals three intervals of highly increased 14C concentrations coincident with low values of paleomagnetic field intensity, two of which are attributed to the geomagnetic Mono Lake and Laschamp excursions (33.5-34.5 ka cal BP with maximum 550 marine δ14C, and 40.3-41.7 ka cal BP with maximum 1215 marine δ14C, respectively). A third maximum (marine δ14C: 755) is observed around 38 ka cal BP and attributed to the geomagnetic intensity minimum following the Laschamp excursion. During all three events the A14C values increase rapidly with maximum values occurring at the end of the respective geomagnetic intensity minimum. During the Mono Lake Event, however, our A14C values seem to underestimate the atmospheric level, if compared to the 36Cl flux measured in the GRIP ice core (Wagner et al. 2000) and other records. As this excursion coincides with a meltwater event in core PS2644, the underestimation is probably caused by an increased planktonic reservoir age. The same effect also occurs from 38.5 to 40 ka cal BP when the meltwater lid of Heinrich Event 4 affected the planktonic record.

Orbital modulation of the Earth's magnetic field intensity

More than 20 years ago, on the basis of data from a Pacific sediment core, it was suggested that geomagnetic field intensity may vary with the Earth's orbital obliquity (centred on a period of ∼41 kyr) as a result of the effect of obliquity on precessional forces in the Earth's core1. It had also been proposed that precession plays an important role in the energy budget of the Earth's geodynamo2. But subsequent analyses indicated that the energy available from precession is at least an order of magnitude less than that required to drive the geodynamo3. Here, however, we report a spectral analysis of sedimentary records of relative geomagnetic palaeointensity from two North Atlantic sites which shows significant power both at orbital eccentricity (∼100 kyr) and obliquity (41 kyr). The eccentricity power is also present in bulk magnetic properties (such as susceptibility) and is therefore attributable to lithological variations controlled by eccentricity-driven climate change. The obliquity power, however, is not apparent in bulk magnetic properties, and seems to be a property of the geomagnetic field itself, thus providing evidence for the orbital forcing of geomagnetic field intensity.