The causes and consequences of geomagnetic excursions

Programme website: http://inspire-dtp.ac.uk

Project Rationale:
The Earth’s magnetic field is constantly changing. Palaeomagnetic records spanning the last few hundred of thousand years have revealed the frequent occurrence of geomagnetic excursions, during which the field intensity drops to a few percent of the present field level and direction of the field reverses for a short period of time (a few hundred to thousand years). Excursions have been observed in palaeomagnetic records from various archives including lava flows, marine and lake sediments, loess, and cave deposits, and in cosmogenic isotope records from ice cores and sediments. Understanding the detailed behaviour of the field during excursions is crucial to deciphering the causes and consequences of such events and the geodynamo that drives these changes. Yet our knowledge on even the most well-documented excursion (i.e. the Laschamp excursion, ~41 thousand years ago) is insufficient to reveal detailed field structure during an excursion and does not allow confident comparison of globally distributed records. Many outstanding questions remain. What happens to the geometry of the field during an excursion? Does it maintain a mainly dipolar structure or become rather complex? Do excursions start and end synchronously over the globe?

Methodology:
This project will take advantage of a new type of instrument called SQUID Microscopy (SSM) recently developed in Japan and will build upon existing collaborations between a team of UK and Japanese scientists. You will combine novel and traditional methods to make a step change in the resolution of palaeomagnetic records achievable from sediment archives to tackle fundamental questions on field behaviour. Using a selected set of sediment sequences from the North and South Atlantic and Japan that contain geomagnetic excursions, you will: (1) collect and assemble continuous paleomagnetic records at ultra-high resolution (e.g. every 100 micron) through analysis of continuous sediment thin section samples on a SSM; (2) compile and/or reconstruct high-resolution traditional palaeomagnetic directional and intensity records on superconducting rock magnetometers using both continuous and cut sediment samples; and (3) acquire high-resolution oxygen isotope records and x-ray fluorescence (XRF) core scan data. These data will be combined for the first time to reconstruct and exploit field behaviours at an unprecedented resolution for accurately dated/correlated records from different world locations, to overhaul our understanding of the structure and spatial variability of the Earth’s magnetic field over the geomagnetic excursions.

Training:
The INSPIRE DTP program provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted in Ocean and Earth Science at the National Oceanography Centre. Specific training will include:

● Sampling and core analysis at repositories in Europe and/or Japan and work in the laboratories of Japanese collaborators
● Stratigraphy and chronology construction of marine and lake sediments
● Sedimentological, geochemical, and core imaging studies
● Palaeomagnetic and environmental magnetic analysis of sedimentary archives
● managing and processing research data and advanced quantitative analysis techniques such as time-series analysis and field modelling
● Correlation, integration, and interpretation of multi-proxy datasets for geomagnetic and environmental reconstructions
● Participation of international scientific meetings to present project results