Lennart de Groot
Paleomagnetic laboratory Fort Hoofddijk - Utrecht University
I work as an assistant professor/NWO-VENI laureate at paleomagnetic laboratory Fort Hoofddijk, Utrecht Univerisity, the Netherlands.
Dr. Lennart V. de Groot
Paleomagnetic laboratory Fort Hoofddijk
3584 CD Utrecht
The Earth’s magnetic field is generated in the liquid outer core of the Earth and is driven by both the rotation of the Earth and its slow but everlasting cooling. Since turbulent processes in a liquid drive the geomagnetic field its behavior is highly erratic – and poorly understood. I am especially intrigued by very rapid and regional short-term fluctuations in the Earth’s magnetic field; e.g. in some records we see its intensity double within a couple of decades and decline at least as fast. The origin and cause of these non-dipole phenomena are still highly enigmatic. To understand these features of the Earth’s magnetic field high-resolution (both in space and time) descriptions of its behavior through the recent geological history are indispensable.
During my PhD defense
Sampling at Gran Canaria
The only recorders to derive such full vector records (records comprising both variations in direction AND intensity) of the Earth’s magnetic field from are well-dated volcanic edifices. Lavas record and store this vital information in a specific suite of minerals (‘titanomagnetites’). It is therefore straightforward to obtain directional information from oriented samples, but the physical properties of those grains often hamper a reliable reconstruction of the intensity of the Earth’s magnetic field. In my PhD thesis I compared the veracity of various protocols to estimate the intensity of the paleofield from volcanic samples, and added a new technique to the paleointensity toolbox. With this ‘multi-method paleointensity approach’ I was able to obtain a reliable estimate of 65-70% of all cooling units sampled, in contrast to a traditional success rate of ~20%.
Nevertheless, it is intriguing why samples from some cooling units yield correct estimates of the intensity of the paleofield and others fail in paleointensity experiments. By applying advanced techniques from material sciences, such as magnetic force microscopy, changes in magnetic domains (nano-scale magnetic features that actually define the magnetization of a material) can be visualized. These techniques were not systematically applied in paleo- and rockmagnetic research before. We therefore just scratched the problem of non-ideal behaved volcanics, but the potential of this line of research is very extensive.