Description: Geophysical processes cause a redistribution of masses within system Earth called mass transport. This mass transport induces variations in the observed gravity field of the Earth. A common scientific approach to draw conclusions about geophysical processes is to determine the imprint of individual geophysical processes in observed gravity field variations. For this purpose, modelers follow a sequence of specialized steps. From this sequence, we identified in close collaboration with Earth system modelers at the German Research Center for GeoSciences (GFZ) steps that can significantly benefit from Visual Analytics: (a) finding an applicable release of observed gravity field variations that exhibit the geophysical process of interest (b) separating individual geophysical processes in observed gravity field variations and (c) confirming the reduction of observed gravity field variations to the geophysical process of interest. We identified important analytical requirements for our Visual Analytics approach based on a user- and task-centered design. By providing tailored support for the identified requirements, our Visual Analytics approach provides a valuable expansion of the modeler’s toolbox.

Description: The West Antarctic Ice Sheet (WAIS) is assumed to be inherently unstable because it is grounded below sea level in a large part, where the bedrock deepens from today’s grounding line towards the interior of the ice sheet. Idealized simulations have shown that bedrock uplift due to isostatic adjustment of the solid Earth and the associated sealevel fall may stop the retreat of such a marine-based ice sheet (Gomez et al., 2012). Here, we employ a coupled model for ice-sheet dynamics and solid-Earth dynamics, including a gravitationally consistent description of sea level, to investigate the influence of the viscoelastic Earth structure on the WAIS’ future stability (Konrad et al. 2015). For this, we start from a steady-state condition for the Antarctic Ice Sheet close to present-day observations and apply atmospheric and oceanic forcing of different strength to initiate the retreat of the WAIS and investigate the effect of the viscoelastic deformation on the ice evolution for a range of solid-Earth rheologies. We find that the climate forcing is the primary control on the occurrence of the WAIS collapse. However, for moderate climate forcing and a weak solid-Earth rheology associated with the West Antarctic rift system (asthenosphere viscosities of 3x10ˆ19 Pa s or less), we find that the combined effect of bedrock uplift and gravitational sea-level fall limits the retreat to the Amundsen Sea embayment on millennial time scales. In contrast, a stiffer Earth rheology yields a collapse under these conditions. Under a stronger climate forcing, weak Earth structures do not prevent the WAIS collapse; however, they produce a delay of up to 5000 years in comparison to a stiffer solid-Earth rheology. In an additional experiment, we test the impact of sea-level rise from an assumed fast deglaciation of the Greenland Ice Sheet. In cases when the climatic forcing is too weak to force WAIS collapse by itself, the additional rise in sea-level leads to disintegration of the WAIS for asthenosphere viscosities of 3x10ˆ20 Pa s or higher. References Gomez, N., Pollard, D., Mitrovica, J. X., Huybers, P., & Clark, P. U. (2012). Evolution of a coupled marine ice sheet–sea level model. J. Geophys. Res. 117(F1). Konrad, H., Sasgen, I., Pollard, D. & Klemann, V. (2015). Potential of the solid-Earth response for limiting longterm West Antarctic Ice Sheet retreat in a warming climate. Earth Planet. Sci. Lett. 432, 2015.

Description: In den Geowissenschaften gehört es zum Standard, internationale Netzwerke aufzubauen, um Zugang zu bestimmten Regionen zu erhalten oder auf lokales Wissen zuzugreifen. Die DFG-Arbeitsgruppe „Geowissenschaftlicher Nachwuchs“ hat Netzwerkbildung und Internationalisierung im Rahmen eines Rundgespräches analysiert. Ein berufliches Netzwerk ist Grundbest andteil wissenschaftlichen Arbeitens. Es erleichtert Kenntnisse über den state of the art und erlaubt, Ergebnisse zu erzielen, die Einzelkämpfer nicht erreichen. Drittmittelgeber fordern häufig die Etablierung oder Nutzung internationaler Kooperationen. Aktiver wissenschaftlicher Austausch, Einladungen zu Vorträgen oder Fachbeiträgen können als Form des Netzwerkens die eigene Sichtbarkeit erhöhen und Chancen auf dem Bewerbungsmarkt verbessern.

Description: One task of the German National Climate Modeling Initiative PalMod will be to couple earth system models representing the atmospere, ocean and ice dynamics during the last glacial cycle with the dynamic loading response of a viscoelastic earth model. In preparation, we discuss in this study the influence of viscosity stratification and of lateral heterogeneities in the Earth structure on the solid-earth response to glacial loading. As discussed in literature, there is a controversy about the impact of lateral heterogeneity on the prediction of present and past GIA signals. The influence of the Earth structure on the far-field response is governed by the flexural behaviour of the regional lithosphere and upper-mantle structure in response to the varying ocean load. The influence at and around the glacial ice sheets is substantial with respect to the amplitudes and also with respect to the temporal evolution of the earth’s response. Depending on the region of interest, lithospheric variations are present over the extent of the glacial ice sheets varying between 40 and 200 km, and lateral variations in viscosity can vary by one or two orders of magnitude. The focus will be to what extent the behaviour of a laterally heterogeneous viscosity structure can be parameterised by an adjusted spherical earth model representation. Accordingly, we apply predefined ice-sheet histories (like ICE5G and ICE6G) and analyse ensemble runs representing the variability of relative sea-level and palaeotopography predictions. Spatial pattern of deformation fields will be discussed as the behaviour at specific sea-level curves. Furthermore, we compare the sensitivity on earth structure during the evolution of sea level and palaeo topography during the termination phase of the last glaciation to present-day rates of relative sea-level height and radial displacement.

Description: A major uncertainty in determining the mass balance of the Antarctic ice sheet from satellite gravimetry, and to a lesser extent altimetry, measurements is the poorly known correction for the glacial isostatic adjustment (GIA) of the solid Earth. Although much progress has been made in consistently modelling ice-sheet evolution and related bedrock deformation, predictions of GIA remain ambiguous due to the sparsity of geodetic and geological constraints. Here, we present an improved geodetic GIA estimate based on GRACE, Envisat/ICESat/CryoSat-2 and GPS measurements. Using viscoelastic response functions of the radial displacement and gravity field change to a disc load forcing, we estimate GIA based on multiple space-geodetic observations, making use of their different sensitivities to surface and solid Earth processes. The approach allows us to consider a laterally varying lithosphere thickness and mantle viscosity in Antarctica, and particularly investigate the effect of a low-viscosity asthenosphere and a ductile layer in the elastic lithosphere in West Antarctica. We compare our GIA estimate with published estimates and results from numerical modelling, and evaluate its impact on the determination of ice-mass balance in Antarctica from GRACE and CryoSat-2. The results presented are the final results of the Support To Science Element Project REGINA and its Supplementary Study of the European Space Agency, www.regina-science.eu.

Description: The GNSS Transpolar Earth Reflectometry exploriNg system (G-TERN) was proposed in response to ESA’s Earth Explorer 9 Revised Call by a team of 33 multi-disciplinary scientists. The primary objective of the mission is to quantify at high spatio-temporal resolution crucial characteristics, processes and interactions between sea ice and other Earth system components in order to advance the understanding and prediction of climate change and its impacts on the environment and society. The objective is articulated through three key questions: (1) In a rapidly changing Arctic regime and under the resilient Antarctic sea ice trend, how will highly dynamic forcings and couplings between the various components of the ocean, atmosphere and cryosphere modify or influence the processes governing the characteristics of the sea ice cover (ice production, growth, deformation and melt)? (2) What are the impacts of extreme events and feedback mechanisms on sea ice evolution? (3) What are the effects of the cryosphere behaviours, either rapidly changing or resiliently stable, on the global oceanic and atmospheric circulation and mid-latitude extreme events? To contribute answering these questions G-TERN will measure key parameters of the sea ice, the oceans and the atmosphere with frequent and dense coverage over polar areas, becoming a ’dynamic mapper’ of the ice conditions, ice production and loss in multiple time and space scales, and surrounding environment. Over polar areas, G-TERN will measure sea ice surface elevation (〈10 cm precision), roughness and polarimetry aspects at 30 km resolution and 3 days full coverage. G-TERN will implement the interferometric GNSS reflectometry concept, from a single satellite in near-polar orbit with capability for 12 simultaneous observations. Unlike currently orbiting GNSS reflectometry missions, G-TERN uses the full GNSS available bandwidth to improve its ranging measurements. The lifetime would be 2025- 2030 or optimally 2025-2035, covering key stages of the transition towards a nearly ice-free Arctic Ocean in Summer. This paper describes the mission objectives, it reviews its measurement techniques, summarizes the suggested implementation and finally it estimates the expected performance.