Simulation of a fully coupled 3D glacial isostatic adjustment - ice sheet model for the Antarctic ice sheet over a glacial cycle

Glacial isostatic adjustment (GIA) has a stabilizing effect on the evolution of the Antarctic ice sheet by reducing the grounding line migration following ice melt. The timescale and strength of this feedback depends on the spatially varying viscosity of the Earth's mantle. Most studies assume a relatively long and laterally homogenous response time of the bedrock. However, the mantle viscosity is spatially variable, with a high mantle viscosity beneath East Antarctica and a low mantle viscosity beneath West Antarctica. For this study, we have developed a new method to couple a 3D GIA model and an ice sheet model to study the interaction between the solid Earth and the Antarctic ice sheet during the last glacial cycle. With this method, the ice sheet model and GIA model exchange ice thickness and bedrock elevation during a fully coupled transient experiment. The feedback effect is taken into account with a high temporal resolution, where the coupling time steps between the ice sheet and GIA model are 5000 years over the glaciation phase and vary between 500 and 1000 years over the deglaciation phase of the last glacial cycle. During each coupling time step, the bedrock elevation is adjusted at every ice sheet model time step, and the deformation is computed for a linearly changing ice load. We applied the method using the ice sheet model ANICE and a 3D GIA finite element model. We used results from a regional seismic model for Antarctica embedded in the global seismic model SMEAN2 to determine the patterns in the mantle viscosity. The results of simulations over the last glacial cycle show that differences in mantle viscosity of an order of magnitude can lead to differences in the grounding line position up to 700gkm and to differences in ice thickness of the order of 2gkm for the present day near the Ross Embayment. These results underline and quantify the importance of including local GIA feedback effects in ice sheet models when simulating the Antarctic ice sheet evolution over the last glacial cycle

A Formalisation of SysML State Machines in mCRL2

This paper reports on a formalisation of the semi-formal modelling language SysML in the formal language mCRL2, in order to unlock formal verification and model-based testing using the mCRL2 toolset for SysML models. The formalisation focuses on a fragment of SysML used in the railway standardisation project EULYNX. It comprises the semantics of state machines, communication between objects via ports, and an action language called ASAL. It turns out that the generic execution model of SysML state machines can be elegantly specified using the rich data and process languages of mCRL2. This is a big step towards an automated translation as the generic model can be configured with a formal description of a specific set of state machines in a straightforward manner

Inleiding op het themanummer ‘Dichtbij, Dialoog & Democratie’

‘Er is iets vreemds aan de hand met de democratie: iedereen lijkt ernaar te verlangen, maar niemand gelooft er nog in.’ Aldus typeert de Vlaamse cultuurhistoricus, archeoloog en auteur David Van Reybrouck (2013: 9) het hedendaagse debat over de democratie. Tegen deze achtergrond wordt alom gezocht naar manieren om – gezien het tanende geloof – het verlangen naar democratie op een eigentijdse, meer bevredigende wijze te vervullen. Zo verscheen recent, op initiatief van het Ministerie van Binnenlandse Zaken en Koninkrijksrelaties, de Agenda Lokale Democratie. Ook het VNG Jaarcongres, dat op 2 en 3 juni 2015 in de gemeente Apeldoorn wordt gehouden, staat in het teken van dit debat. Onder de titel Dichtbij, Dialoog & Democratie belichten David Van Reybrouck, Rob Wijnberg (filosoof en oprichter van het journalistieke platform De Correspondent) en Sheila Sitalsing (journaliste en columniste van de Volkskrant) dit thema

Shellfish reefs increase water storage capacity on intertidal flats over extensive spatial scales

Ecosystem engineering species can affect their environment at multiple spatial scales, from the local scale up to a significant distance, by indirectly affecting the surrounding habitats. Structural changes in the landscape can have important consequences for ecosystem functioning, for example, by increasing retention of limiting resources in the system. Yet, it remains poorly understood how extensive the footprint of ecosystem engineers on the landscape is. Using remote sensing techniques, we reveal that depression storage capacity on intertidal flats is greatly enhanced by engineering by shellfish resulting in intertidal pools. Many organisms use such pools to bridge low water events. This storage capacity was significantly higher both locally within the shellfish reef, but also at extensive spatial scales up to 115 m beyond the physical reef borders. Therefore, the footprint of these ecosystem engineers on the landscape was more than 5 times larger than their actual coverage; the shellfish cover approximately 2% of the total intertidal zone, whereas they influence up to approximately 11% of the area by enhancing water storage capacity. We postulate that increased residence time of water due to higher water storage capacity within engineered landscapes is an important determinant of ecosystem functioning that may extend well beyond the case of shellfish reefs provided here

A State-Dependent Quantification of Climate Sensitivity Based On Paleodata of the Last 2.1 Million Years

The evidence from both data and models indicates that specific equilibrium climate sensitivity S[X]—the global annual mean surface temperature change (ΔTg) as a response to a change in radiative forcing X (ΔR[X])—is state dependent. Such a state dependency implies that the best fit in the scatterplot of ΔTg versus ΔR[X] is not a linear regression but can be some nonlinear or even nonsmooth function. While for the conventional linear case the slope (gradient) of the regression is correctly interpreted as the specific equilibrium climate sensitivity S[X], the interpretation is not straightforward in the nonlinear case. We here explain how such a state-dependent scatterplot needs to be interpreted and provide a theoretical understanding—or generalization—how to quantify S[X] in the nonlinear case. Finally, from data covering the last 2.1 Myr we show that—due to state dependency—the specific equilibrium climate sensitivity which considers radiative forcing of CO2 and land ice sheet (LI) albedo, math formula, is larger during interglacial states than during glacial conditions by more than a factor 2