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

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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.