Transforming our understanding of the geodynamo: A new global synthesis and model of millennial-scale geomagnetic variability for late Pleistocene

Lead Research Organisation: University of Southampton
Department Name: School of Ocean and Earth Science

Abstract

Earth's magnetic field is essential to life on our planet and to electronic communication technologies upon which modern society depends because it provides protection from harmful cosmic rays and the solar wind that bombard the upper atmosphere. But this invisible protective field is far from constant. Its intensity and direction are always changing both temporally and spatially. On decadal timescales and longer these changes can be attributed to the interaction between Earth's rotation about its axis and convective motion in its molten interior- its geodynamo. Yet our understanding of the geodynamo and the mechanisms by which it drives changes in our magnetic field is primitive.

The main problem preventing progress is a lack of a robust data set recording past changes in magnetic field that extends back in time beyond the start of the Holocene geological epoch (~10,000 years ago, ka).

For the Holocene, we have a relatively well dated compilation of records, largely from archaeological and lake archives, showing changes in magnetic intensity and direction from a network of sites around the world. This allows us to develop computer models of global magnetic field variability through time, providing a way to transform our understanding of the geodynamo. But we must look beyond the Holocene because we need a longer perspective to study a fuller range of field variability. Earth's magnetic field has lost half its strength since Roman times but much larger changes in intensity occurred during the geological epoch that preceded the Holocene (the Pleistocene). Furthermore, there has not been an undisputed full (180 deg.) change in magnetic field direction or polarity excursion for ~40 kyrs and that event is just one of at least five well-documented excursions that took place during the last ~500 kyrs.

We propose to transform our understanding of the geodynamo and the cause of changes in Earth's magnetic field by turning to this Late Pleistocene record of changes in field intensity and direction. Marine sediment drillcores are well-suited to providing the long undisturbed records needed for this purpose but, until now, it has not been possible to date them sufficiently robustly to work globally at the resolution needed.

We will: (1) Build a new benchmark record of geomagnetic change for the last ~500 thousand years (kyr) using a suite of exceptional sediment archives recently drilled on the west Iberian Margin. (2) Undertake a comprehensive synthesis of existing high-resolution sedimentary palaeomagnetic records around the globe. (3) Take advantage of the unique chronological constraints of the Iberian Margin sediments, to precisely date the Exp. 339 records at the millennial scale. We will then export that chronology to the synthesized records using geochemical/physical property data sets available to develop a precisely dated global compilation of changes in magnetic field intensity and direction for the last ~500 kyr. This correlation method ensures that we make no assumption about synchronicity of palaeomagnetic change between sites (so that this issue can be studied). (4) Use these new high-resolution and well-dated datasets in collaboration with a leading geomagnetic field modeler to build the first computer models to reconstruct changes in Earth's geomagnetic field through time and space over the last few hundred kyr to overhaul our understanding of the dynamics and causes of geomagnetic variability.

Planned Impact

1. Who will benefit from this research?

The proposed project has significant economic and social impact and will benefit the following specific users: (1) 2G Enterprises, the world's leading manufacturer of superconducting rock magnetometers for rapid and accurate measurement of remanent magnetisations in various materials and geological and archaeological archives; (2) Bartington Instruments (a UK company), who supply instrumentation designed to perform magnetic susceptibility and environmental magnetic analyses for many industrial, medical, and research applications; (3) the general public who have a broad and established interest in global change research, particularly young people whom we seek to enthuse about science.

2. How will they benefit from this research?

The specific users group mentioned above will benefit from the results of the proposed research in the following ways.

(1) As one of 2G Enterprises' most successful products, superconducting rock magnetometers (SRM) are installed in research laboratories worldwide. 2G Enterprises is actively seeking numerical solutions and tools that significantly improve the efficiency and accuracy of SRM data collection and processing. The PI (Xuan) has a track record of working together with 2G Enterprises on developing such tools (see Case for Support, Part 1). Through the proposed project, Xuan will develop new algorithms, software packages, and tools that will directly benefit 2G Enterprises at new levels. Xuan has been in discussion with William Goodman and Lauren Keaton (Presidents, 2G Enterprises) to this end.

(2) Bartington Instruments (a UK company based in Oxfordshire) is a main provider of equipment designed for magnetic susceptibility and environmental magnetism analyses and actively seeking system improvements and new products that better-fit emerging scientific, medical and industrial demands. Results from our proposed research will provide valuable impact for future instrumentation needs and for high-resolution scientific data acquisition. Xuan has been in communication with Bartington Instruments on the need to build the next generation magnetic susceptibility track system that will significantly increase measurement precision through better background measurement and correction procedures, and deconvolution of raw data.

(3) The public have a broad and established interest in global change research and the UK public are particularly interested in the underlying nature of scientific research and endeavour. Results of our proposed research will benefit the general public by providing key information on Earth's magnetic field, relevant to everyday human activities. Our work will also benefit young people by raising curiosity and enthusiasm about scientific research.

Publications

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Description We have performed a substantial amount of palaeomagnetic analyses on the u-channel samples collected from IODP Expedition 339 drilled sediments since the start of this project. These results currently suggest that majority of the sediment sequences have favourable properties for the reconstruction of palaeomagnetic field information. In addition, we have started the design and construction of a database that will be used to store and organise research data produced by this project as well as data synthesised from published records.
Exploitation Route We are in the process of completing the proposed palaeomagnetic and other analyses on the project samples. Existing results are being analysed and discussed with project partners to build, exploit and publish reliable records of the geomagnetic field variabilities.
Sectors Education,Environment,Other