Advances in modelling subglacial lakes and their interaction with the Antarctic ice sheet

Subglacial lakes have long been considered hydraulically isolated water bodies underneath ice sheets. This view changed radically with the advent of repeat-pass satellite altimetry and the discovery of multiple lake discharges and water infill, associated with water transfer over distances of more than 200 km. The presence of subglacial lakes also influences ice dynamics, leading to glacier acceleration. Furthermore, subglacial melting under the Antarctic ice sheet is more widespread than previously thought, and subglacial melt rates may explain the availability for water storage in subglacial lakes and water transport. Modelling of subglacial water discharge in subglacial lakes essentially follows hydraulics of subglacial channels on a hard bed, where ice sheet surface slope is a major control on triggering subglacial lake discharge. Recent evidence also points to the development of channels in deformable sediment in West Antarctica, with significant water exchanges between till and ice. Most active lakes drain over short time scales and respond rapidly to upstream variations. Several Antarctic subglacial lakes exhibit complex interactions with the ice sheet due to water circulation. Subglacial lakes can therefore—from a modelling point of view—be seen as confined small oceans underneath an imbedded ice shelf.</jats:p

Ice core evidence for a 20th century increase in surface mass balance in coastal Dronning Maud Land, East Antarctica

Ice cores provide temporal records of surface mass balance (SMB). Coastal areas of Antarctica have relatively high and variable SMB, but are under-represented in records spanning more than 100 years. Here we present SMB reconstruction from a 120 m-long ice core drilled in 2012 on the Derwael Ice Rise, coastal Dronning Maud Land, East Antarctica. Water stable isotope (δ18O and δD) stratigraphy is supplemented by discontinuous major ion profiles and continuous electrical conductivity measurements. The base of the ice core is dated to AD 1759 ± 16, providing a climate proxy for the past  ∼ 250 years. The core's annual layer thickness history is combined with its gravimetric density profile to reconstruct the site's SMB history, corrected for the influence of ice deformation. The mean SMB for the core's entire history is 0.47 ± 0.02 m water equivalent (w.e.) a−1. The time series of reconstructed annual SMB shows high variability, but a general increase beginning in the 20th century. This increase is particularly marked during the last 50 years (1962–2011), which yields mean SMB of 0.61 ± 0.01 m w.e. a−1. This trend is compared with other reported SMB data in Antarctica, generally showing a high spatial variability. Output of the fully coupled Community Earth System Model (CESM) suggests that, although atmospheric circulation is the main factor influencing SMB, variability in sea surface temperatures and sea ice cover in the precipitation source region also explain part of the variability in SMB. Local snow redistribution can also influence interannual variability but is unlikely to influence long-term trends significantly. This is the first record from a coastal ice core in East Antarctica to show an increase in SMB beginning in the early 20th century and particularly marked during the last 50 years

Do citizens even want to hear the truth?: Public attitudes towards evidence- informed policy making

Evaluations-informed policy making is often glorified to be the true approach to introduce and evaluate public policies. Yet is this view also shared by the public? In this chapter, we consider the question which attitudes citizens have toward scientific evidence and how these differ across political systems and individual characteristics. We present the results of a cross-sectional survey among some 9000 citizens in six countries (Australia, Belgium, Canada, France, Switzerland and the United States) that has been conducted in the middle of the COVID-19 pandemic (2020/2021). The survey shows that public support for evidence substantially varies across countries and individuals. Post-truth countries show strong political polarization regarding the attitudes towards evidence-informed policy making. As we discuss, these findings might have import implications for evaluators and future research on evaluation, as they prompt the need for a paradigm shift toward more public participation in evaluations.The politics and administration of institutional chang

Trust, but verify? Understanding citizen attitudes toward evidence-informed policy making

In this article, we inquire to what extent different manifestations of trust are associated with public support for evidence informed policy making (EIPM). We present the results of a cross-sectional survey conducted in the peak of the second COVID-19 wave in six Western democracies: Australia, Belgium, Canada, France, Switzerland, and the United States (N = 8749). Our findings show that public trust in scientific experts is generally related to positive attitudes toward evidence-informed policy making, while the opposite is the case for trust in governments and fellow citizens. Interestingly, citizens' assessment of government responses to COVID-19 moderates the relationship between trust and attitudes toward EIPM. Respondents who do rather not trust their governments or their fellow citizens are more in favor of EIPM if they evaluate government responses negatively. These findings suggest that attitudes toward EIPM are not only related to trust, but also strongly depend on perceived government performance.The politics and administration of institutional chang

Actively evolving subglacial conduits and eskers initiate ice shelf channels at an Antarctic grounding line

Ice-shelf channels are long curvilinear tracts of thin ice found on Antarctic ice shelves. Many of them originate near the grounding line, but their formation mechanisms remain poorly understood. Here we use ice-penetrating radar data from Roi Baudouin Ice Shelf, East Antarctica, to infer that the morphology of several ice-shelf channels is seeded upstream of the grounding line by large basal obstacles indenting the ice from below. We interpret each obstacle as an esker ridge formed from sediments deposited by subglacial water conduits, and calculate that the eskers’ size grows towards the grounding line where deposition rates are maximum. Relict features on the shelf indicate that these linked systems of subglacial conduits and ice-shelf channels have been changing over the past few centuries. Because ice-shelf channels are loci where intense melting occurs to thin an ice shelf, these findings expose a novel link between subglacial drainage, sedimentation and ice-shelf stability

Beleidsevaluatie vandaag: Een voorzichtige balans

The politics and administration of institutional chang