Water Viscosity at High Pressure and Temperature

We have documented a two-fold increase in the viscosity of water from 0.1 MPa (1 bar) to 1 GPa at room temperature and a 1.3-fold increase at 1.5 GPa and 70 degrees Celcius using an externally-heated, rolling sphere diamond-cell viscometer. Given the importance of water in planetary geophysics, it is surprising that almost no measurements of viscosity are available above 1 GPa. This is at least in part due to the difficulty in reliably measuring the rapid fall times of spheres used to determine viscosities in fluids. This problem has been eliminated by using a strobed light-emitting diode, allowing us to calibrate to ambient-condition viscosities and obtain high pressure viscosities consistent with accurate values given in the literature for water. In principle, our approach can be extended to over 30 GPa and 1000 K, thereby providing significant tests of theoretical models of fluid transport properties at conditions existing deep inside planets.