Tao Yuan (University of Colorado, USA) working with
Shijie Zhong, Glenn Milne, Donna dePolo

will present

Reconciling inferences of mantle viscosity and late Quaternary ice history – the importance of an asthenosphere and 3-D viscosity

Deglaciation history models from the last glacial maximum (LGM) and accompanying mantle viscosity structures have been jointly constrained by fitting the paleo-sea level data through glacial isostatic adjustment (GIA) modeling. However, some GIA-inferred 1-dimensional (1-D) viscosity models, including the widely used VM5a, contradict the mantle viscosity structure inferred using other approaches, such as seismic imaging, mineral physics and geodynamics. Here we show that GIA models with realistic 3-D mantle viscosity derived from seismic structures with an effective activation energy of 300-400 kJ/mol and a weak asthenosphere fit paleo-sea level data in North America better than several widely used 1-D GIA models. Our results also demonstrate that the inclusion of the asthenosphere and lateral viscosity variations permits a larger range of North American ice sheet reconstructions that produce quality fits to the sea-level data, including models with substantially greater volume at LGM, thus identifying a potential solution to balancing the sea level budget during this key climate event. To fit far-field sea level data, the ice volume at LGM in North America is required to be 10%-20% larger than that in ICE-6G, if ice models outside North America are unchanged.