David Dobson
The 2005 Outstanding Young Scientist Award is awarded to David Dobson for his internationally recognized work in developing high pressure techniques to measure the electrical conductivity of mantle minerals, the rheology of mantle minerals, and models of core composition.
David Dobson’s career has demonstrated that he is an outstanding young scientist, who leads the field internationally in many areas of high-pressure experimental petrology and geophysics. His work has addressed a remarkably wide range of problems in deep-Earth studies and demonstrates that, in addition to his exemplary experimental skills, he has the theoretical background and understanding of the really important problems to make him a really outstanding scientist.
David was instrumental in developing the high-pressure techniques with which he and others measured the electrical conductivity of mantle minerals under the appropriate mantle P-T conditions. Combining such laboratory data with geomagnetic field observations he was able to demonstrate that there is no thermal boundary layer in the middle mantle – a very important result in light of the still ongoing debate on large-scale convection styles.
Subsequent to this, David turned to transport properties of liquid iron alloys which are important parameters in constraining models of outer core convection and the generation of the geodynamo. David had developed an in situ technique to measure liquid viscosities of 10-3 PaS or lower (runnier than water) at multi-gigapascal pressures, and applied this technique to liquid iron alloy candidates to outer-core compositions. Combining these measurements with his measurements of self-diffusion in liquid alloys to over 20 GPa allowed him to test various a priori models of mass transport in liquid metals and demonstrate conclusively that the effect of pressure on the melting-temperature transport properties of liquid iron and its alloys was not significant. This was in marked contrast to previous experiments which had suggested an increase in viscosity between ambient and outer core conditions of between 7 and 21 orders of magnitude. Indeed the outer core viscosity values implied by David’s experimental results agreed with ab initio models to within a factor of 3 across the whole range of possible outer core conditions. Other experimental groups have subsequently revisited their earlier measurements and now agree with his results.
More recently, David has turned his attention to the geodynamics of the mantle. He has developed a technique to synthesize large, high-quality single crystals of magnesium silicate perovskite for use in crystallographical and EOS studies. He has used Na-doped silicate perovskites to investigate oxygen-ionic conductivity and oxygen diffusion with the conclusion that this is probably the main electrical conductivity mechanism in the deep lower mantle.
Finally, David is currently moving into high-pressure rheology techniques. He has developed an acoustic emission technique for the multi-anvil press by which he can detect dehydration reactions in situ and simulate “earthquakes” triggered by such reactions. So there is hope that the question of the enigmatic “deep focus earthquakes” which have puzzled scientists at least for the last 20 years, will eventually be resolved. In addition, he is developing new in situ techniques to measure the rheology of mantle minerals under very low strain-rates, using neutron-diffraction monitoring of elastic strain. These data will be vital in understanding the coupling mechanisms between crustal and mantle motions and underpinning numerical models of mantle convection.
David has published his scientific results in some 30 papers in internationally renowned journals with strict referee system, among them five papers in Science and Nature.