GSTM2020-33
https://doi.org/10.5194/gstm2020-33
GRACE/GRACE-FO Science Team Meeting 2020
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

The Viscosity of the Top 700 km of the Lower Mantle estimated using GPS, GRACE, and Relative Sea Level measurements of Glacial Isostatic Adjustment

Donald Argus1, W. Richard Peltier2, Geoff Blewitt3, Corne Kreemer3, and Matteo Vacchi4
Donald Argus et al.
  • 1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, United States of America (Donald.F.Argus@jpl.nasa.gov)
  • 2Department of Physics, University of Toronto, Toronto, Ontario, Canada
  • 3Nevada Geodetic Laboratory, Nevada Bureau of Mines and Geology, University of Nevada, Reno, NV, USA
  • 4Dipartimento di Scienze della Terra, Università di Pisa, Via Santa Maria 53, 56126 Pisa

We distinguish between two models of solid Earth's viscous response to unloading of the Laurentide ice sheet over the past 26,000 years.  The upper mantle viscosity in both models is 0.5 x 1021 Pa s.  The viscosity of the top 700 km of the lower mantle (670 –1370 km) in model L17 is 13 x 1021 Pa s, eight times larger than the value of 1.6 x 1021 Pa s in ICE-6G_D (VM5a).  In ICE-6G_D (VM5a), viscous relaxation of solid Earth was rapid 8,000 years ago and is slow today, with present-day uplift at the Laurentide ice center being 12 mm/yr.  In L17, solid Earth relaxed more slowly 8,000 years ago but is faster today, with present uplift of the ice center at 20 mm/yr.  The significant difference is not due to different ice histories given that total ice loss in L17 is just 12% less than in ICE-6G_D.  We determine a comprehensive set of GPS uplift rates for North America that is more accurate than in prior studies due to (1) more sites and a longer data time history, (2) removal of elastic loading produced by increase in Great Lakes water, and (3) technical advances in GPS positioning that have significantly reduced the dispersion in position estimates.  We find uplift at the ice center to be about 12 mm/yr, supporting low value of the viscosity of the top 700 km of the lower mantle in ICE-6G_D (VM5a), but ruling out the high value in L17.

How to cite: Argus, D., Peltier, W. R., Blewitt, G., Kreemer, C., and Vacchi, M.: The Viscosity of the Top 700 km of the Lower Mantle estimated using GPS, GRACE, and Relative Sea Level measurements of Glacial Isostatic Adjustment, GRACE/GRACE-FO Science Team Meeting 2020, online, 27–29 Oct 2020, GSTM2020-33, https://doi.org/10.5194/gstm2020-33, 2020.