People at Fort Hoofddijk

Lennart de Groot
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NWO VENI laureate
Dr. L.V. de Groot
Paleomagnetic Laboratory
Fort Hoofddijk
NOW home page
Department of Earth Sciences
Utrecht University 
Budapestlaan 17, 3584 CD Utrecht 
The Netherlands 

Phone +31 30 253 5418
E-mail l.v.degroot@uu.nl

Research
Publications

Personal webpage



Research of Lennart de Groot

A new approach for determining the absolute paleointensity of the Earth's magnetic field

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 behaviour is highly erratic – and poorly understood.

I am especially intrigued by very rapid and regional short-term fluctuations in the Earth’s magnetic field. For example, in some records we see its intensity double within 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.

Sampling a Hawaiian lava flow ..


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 impede 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%.

Drilling lavas on Gran Canaria
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.

publications Publications of Lennart de Groot
2016
  • De Groot, L.V., Pimentel, A.H.G., Di Chiara, A. (2016). The multi-method paleointensity approach applied to volcanics from Terceira: full-vector geomagnetic data for the past 50 kyr, Geophysical Journal International, 206, 590-604.    
  • Ertepinar, P. Langereis, C.G., Biggin, A.J., De Groot, L.V., Kulakoğlu, F., Omura, S. and Süel, A. (2016).  Full vector archaeomagnetic records from Anatolia between 2400 and 1350 BCE: implications for geomagnetic field models and the dating of fires in antiquity, Earth and Planetary Science Letters, 434, 171-186.   
  • Mullender, T.A.T., Frederichs, T., Hilgenfeldt, C., De Groot, L.V., Fabian, K., and Dekkers, M.J. (2016). Automated paleomagnetic and rock magnetic data acquisition with an in-line horizontal  '2G' system, Geochemistry, Geophysics, Geosystems, DOI: 10.1002/2016GC006436   
  • Pimentel, A., Zanon, V., De Groot,L.V., Hipólito, A., Di Chiara, A. and Self, S. (2016). Stress-induced comenditic trachyte effusion triggered by trachybasalt intrusion: multidisciplinary study of the AD 1761 eruption at Terceira Island (Azores), Bull. Volcanol. 78:22, DOI 10.1007/s00445-016-1015-6,  
2015
  • De Groot, L.V., Béguin, A., Kosters, M.E., van Rijsingen, E.M., Struijk, E.L.M., Biggin, A.J., Hurst, E.A., Langereis, C.G., and Dekkers, M.J. (2015). High paleointensities for the Canary Islands constrain the Levant geomagnetic high, Earth and Planetary Science Letters, 419, 154-167. 
  • Monster, M.W., de Groot, L.V. and Dekkers, M.J. (2015). MSP-Tool: a VBA-based software tool for the analysis of multispecimen paleointensity data. Front. Earth Sci. 3:86. doi: 10.3389/feart.2015.00086   
  • Monster, M.W.L., de Groot, L.V., Biggin, A.J. and Dekkers, M.J. (2015). The performance of various palaeointensity techniques as a function of rock-magnetic behaviour  - a case study for La Palma, Physics of the Earth and Planetary Interiors, 242, 36-49.
  • Van Hinsbergen, D.J.J., de Groot, L.V., van Schaik, S.J., Spakman, W., Bijl, P.K., Sluijs, A., Langereis, C.G., and Brinkhuis, H. (2015). A paleolatitude calculator for paleoclimate studies, PLoS ONE 10, e0126946. doi:10.1371/journal. pone.0126946  
2014
  • De Groot, L.V., Fabian, K., Bakelaar, I.A., Dekkers, M.J. (2014). Magnetic force microscopy reveals meta-stable magnetic domain states that prevent reliable absolute palaeointensity experiments. Nature Communications, 5, 4548   
  • De Groot, L. V., Dekkers, M.J., Visscher, M. and Ter Maat (2014), G.W. (2014). Magnetic properties and paleointensities as function of depth in a Hawaiian lava flow, Geochem. Geophys. Geosyst., 15, 1096–1112.    
2013
  • De Groot, L.V. (2013). High-resolution records of non-dipole variations in the intensity of the Earth's magnetic field, Utrecht Studies in Earth Sciences, Volume 37.   
  • De Groot, L.V., Biggin, A.J., Dekkers, M.J., Langereis, C.G. and Herrero-Bervera, E. (2013). Rapid regional perturbations to the recent global geomagnetic decay revealed by a new Hawaiian record, Nature Communications, 4, article number 2727, doi: 10.1038/ncomms3727  
  • De Groot, L.V., Mullender, T.A.T. and Dekkers, M.J. (2013). An evaluation of the influence of the experimental cooling rate along with other thermomagnetic effects to explain anomalously low paleointensities obtained for historic lavas of Mt. Etna  (Italy), Geophys. J. Int., doi: 10.1093/gji/ggt065   
2012
  • De Groot, L.V., Dekkers, M.J., Mullender, T.A.T. (2012). Exploring the potential of acquisition curves of the anhysteretic remanent magnetization as a tool to detect subtle magnetic alteration induced by heating, Phys. Earth Planet. Inter., 194-195, 71-84.