Session 1. Observations of present-day changes in glaciers, ice caps and ice sheets and the associated Earth deformation.

Conveners: Ingo Sasgen, Valentina  Barletta,  Bert Wouters

Mass variations in the polar regions are sensitive indicators of climate fluctuations and trends acting on various time scales. In recent years, much progress has been made in quantifying changes in the global ice regimes and attributing them to their causes. Yet, many challenges remain in understanding the complex dynamic interactions between the atmosphere, the ocean and the solid Earth. Geodetic observations, such as altimetry, gravimetry, and InSAR measurements, of increasing length and coverage offer unique constraints on the evolution of the cryosphere. With numerical modelling and data fusion, the spatial and temporal limits of the observations are overcome, and the time series can be interpreted in terms of the governing physical processes. Such data are essential to interpret crustal motion as observed by GNSS, and to separate the elastic and viscoelastic Earth response therein. We invite contributions on the recent and future evolution in the global ice regimes, from local to regional scales, and discussions of their impact on the crustal motion. We also welcome presentations highlighting potential contributions of upcoming satellite missions to solid Earth research in the cryosphere.

Session 2. Measurement and Models of Elastic Rebound.

Conveners: Jeff Freymueller, Mirko Scheinert, Tonievan Dam

Elastic loading theory can be used to model the deformation caused by changes in the hydrosphere and cryosphere whenever the timescales of deformation are short compared to the viscoelastic relaxation time of the mantle. In several regions, the Earth’s response to present-day cryospheric load changes can be safely assumed to be elastic; in these cases, the Glacial Isostatic Adjustment signal due to long-ago loading changes (e.g., LGM) and present-day changes can be cleanly separated using models of GIA. Models may not be sufficiently accurate in the case of the continental ice sheets in Greenland and Antarctica where the separation of GIA and elastic rebound is subject to ongoing investigations using both measurements and modelling. Elastic models are also used for most studies of sea level redistribution due to ongoing changes in the cryosphere (‘sea level fingerprint’ studies). In addition, elastic models can be used for seasonal deformation signals worldwide. In regions underlain by low mantle viscosity, elastic models are inadequate because the viscoelastic response to load changes over decadal timescales cannot be neglected; in these cases, fully viscoelastic models must be used. This session will include presentations with either a theoretical or observational focus on seasonal, interannual and present-day trends in surface loads that can be described well with elastic models, with implications for cryosphere, water cycle and sea level. We also welcome presentations that assess the limits of the elastic modeling approach.

Session 3. Glacial isostatic adjustment on a heterogeneous Earth.

Conveners: Wouter van der Wal , Natalya Gomez, Tom James

GIA is the ongoing response of the Earth to past ice-mass changes, and is sensitive to Earth rheology and glacier and ice sheet history. It generates crustal displacements and gravity changes that are important for interpreting bedrock geodetic measurements and satellite gravity observations, and that influence ice sheet formation, sedimentation, and volcanism. Most studies rely on GIA models in which mantle viscosity only varies in one dimension (radially) and the rheology is Maxwell viscoelastic. Viscosity in the real Earth can vary laterally as well as radially on a range of spatial scales, and laboratory experiments show transient and non-linear creep for mantle materials. Several models have been developed that can deal with three-dimensional (3D) Earth structure and non-Maxwell rheologies. This session is dedicated to recent developments and applications of 3D models. Possible topics may include the effect of 3D structure on GIA corrections to observations such as GPS and time-variable gravity, and the constraints offered through 3D GIA models on Earth’s structure and past glaciations. As well, observational studies that can constrain 3D structure through GIA modelling are welcomed, in particular for areas with potential low viscosity, such as West Antarctica, Alaska, Cascadia, Greenland, Iceland and Patagonia. Fundamental questions include: how can 3D structure and non-Maxwell rheologies be modeled? Under what circumstances are 3D models required to explain GIA observations?  Constraints from other Earth science disciplines are necessary for modelling a 3D Earth. Therefore we also encourage submissions from the fields of seismology, geodynamic modelling, rock and mineral physics, in order to contribute to a unified view of the Earth’s mantle for geodynamic modelling purposes.

Session 4. Reconciling models and observations of GIA.

Conveners: Pippa Whitehouse, Bas de Boer, Terry Wilson

Geodetic observations may be used to tune or validate models of glacial isostatic adjustment (GIA). In this session we welcome contributions from groups who are involved in GIA modelling, groups involved in the collection of geodetic data relating to GIA, and groups who are attempting to reconcile the two. In some cases, observations must first be corrected for the effects of present-day ice-mass change. This issue is explored in detail in other sessions of this Symposium, but we welcome further discussion on this subject in our session. In particular, we seek contributions that seek new methods of separating the signal of past and present ice mass change within the geodetic signal. We also invite contributions that seek to understand model-data misfits in the context of uncertainty associated with ice history throughout the last glacial cycle, viscoelastic deformation, Earth structure, or non-GIA processes.