Improved Constraints on Models of Glacial Isostatic Adjustment: A Review of the Contribution of Ground-based Geodetic Observations

The provision of accurate models of Glacial Isostatic Adjustment (GIA) is
presently a priority need in climate studies, largely due to the potential of the Gravity
Recovery and Climate Experiment (GRACE) data to be used to determine accurate and
continent-wide assessments of ice mass change and hydrology. However, modelled GIA isuncertain due to insufficient constraints on our knowledge of past glacial changes and to
large simplifications in the underlying Earth models. Consequently, we show differences
between models that exceed several mm/year in terms of surface displacement for the two
major ice sheets: Greenland and Antarctica. Geodetic measurements of surface displacement
offer the potential for new constraints to be made on GIA models, especially when
they are used to improve structural features of the Earth’s interior as to allow for a more
realistic reconstruction of the glaciation history. We present the distribution of presently
available campaign and continuous geodetic measurements in Greenland and Antarctica
and summarise surface velocities published to date, showing substantial disagreement
between techniques and GIA models alike. We review the current state-of-the-art in
ground-based geodesy (GPS, VLBI, DORIS, SLR) in determining accurate and precise
surface velocities. In particular, we focus on known areas of need in GPS observation level
models and the terrestrial reference frame in order to advance geodetic observation precision/
accuracy toward 0.1 mm/year and therefore further constrain models of GIA and
subsequent present-day ice mass change estimates.