Effects of water load on geophysical signals due to glacial rebound and implications for mantle viscosity

We investigate the effects of the ocean function on predictions of the sea-level changes and other geophysical signals due to glacial rebound. To precisely predict these signals, a realistic ocean function including the effects of the palaeotopography, the distribution of ice sheet and meltwater influx is required. The adoption of a precise ocean function is very important in simulating the observables in Hudson Bay for an earth model with a low lower mantle viscosity of ∼10²¹ Pa s. In this case, the contribution from water loads can be comparable to that from ice loads. In the Fennoscandian region, however, the predictions are less sensitive to the details of the ocean function, because the width of the Gulf of Bothnia is very small compared with that of Hudson Bay. With an assumption that the ice model is represented by ARC3+ANT4b, we have examined the viscosity structure using relative sea-levels, gravity anomaly and solid surface gravity changes in North America and northern Europe. This study suggests a lower mantle viscosity of greater than 10²² Pa s and a upper mantle viscosity of (4 ∼ 10) × 10²⁰ Pa s.