On the Reconstruction of Palaeo-Ice Sheets: Recent Advances and Future Challenges

Reconstructing the growth and decay of palaeo-ice sheets is critical to understanding mechanisms of global climate change and associated sea-level fluctuations in the past, present and future. The significance of palaeo-ice sheets is further underlined by the broad range of disciplines concerned with reconstructing their behaviour, many of which have undergone a rapid expansion since the 1980s. In particular, there has been a major increase in the size and qualitative diversity of empirical data used to reconstruct and date ice sheets, and major improvements in our ability to simulate their dynamics in numerical ice sheet models. These developments have made it increasingly necessary to forge interdisciplinary links between sub-disciplines and to link numerical modelling with observations and dating of proxy records. The aim of this paper is to evaluate recent developments in the methods used to reconstruct ice sheets and outline some key challenges that remain, with an emphasis on how future work might integrate terrestrial and marine evidence together with numerical modelling. Our focus is on pan-ice sheet reconstructions of the last deglaciation, but regional case studies are used to illustrate methodological achievements, challenges and opportunities. Whilst various disciplines have made important progress in our understanding of ice-sheet dynamics, it is clear that data-model integration remains under-used, and that uncertainties remain poorly quantified in both empirically-based and numerical ice-sheet reconstructions. The representation of past climate will continue to be the largest source of uncertainty for numerical modelling. As such, palaeo-observations are critical to constrain and validate modelling. State-of-the-art numerical models will continue to improve both in model resolution and in the breadth of inclusion of relevant processes, thereby enabling more accurate and more direct comparison with the increasing range of palaeo-observations. Thus, the capability is developing to use all relevant palaeo-records to more strongly constrain deglacial (and to a lesser extent pre-LGM) ice sheet evolution. In working towards that goal, the accurate representation of uncertainties is required for both constraint data and model outputs. Close cooperation between modelling and data-gathering communities is essential to ensure this capability is realised and continues to progress

Écoulements uniformes et graduellement variés en lit composé versus couches de mélanges libres

36th IAHR World Congress, La Haye, NLD, 28-/06/2015 - 03/07/2015International audienceMixing layers associated with uniform and gradually varied flows (GVF) in compound channel are experimentally investigated in two flumes, featuring a rectangular or a trapezoidal main channel (MC). These shear layers are compared with free mixing layers. Starting with uniform flow, the GVF are generated by an imbalance in the upstream discharge distribution between the floodplain (FP) and the MC. The GVF are longitudinally evolving under the influence of four external forcings: (i) a two-stage geometry, (ii) a varying vertical flow confinement (quantified by the relative flow depth, Dr = hf / hm, where hf and hm are the flow depths in the FP and MC); (iii) a variable lateral depth-averaged mean flow; (iv) a variable velocity ratio, l = Us/(2Uc), where Us = Ud2-Ud1 is the velocity difference, Uc = 0.5(Ud1+Ud2) is the mean velocity across the mixing layer, Ud1 and Ud2 are the depth-averaged velocities outside the mixing layer in the FP and MC, respectively. In the case of weakly or moderately sheared flows (l < 0.3 - 0.35), the peak values of scaled depth averaged Reynolds-stress, denoted Max (gd), are independent of l, but increase with a decrease in flow confinement, to reach the maximum values observed for free mixing layers. In the case of highly sheared flows (l > 0.3 - 0.35), the values of Max (gd) become independent of the flow confinement as l increases, reaching values that can be greater than the ones observed for free mixing layers. Despite the flow confinement, the high values of l trigger the development of 2D large coherent structures without interaction with the 3D bed-induced turbulence. Lastly, with nearly constant values of l and Dr, it was found that the scaled shear-layer turbulence was mainly dictated by the lateral flow. For both uniform flows and test cases with a lateral flow to the FP, the Rayleigh's inflection point criterion is fulfilled. This gives rise to large 2D structures and high values of Max (gd). By contrast, for test cases with a significant lateral flow to the MC, the convex velocity profiles without inflection-point are associated with low levels of Max (gd). Lastly, the trapezoidal MC was found to enhance the turbulent exchange compared with the rectangular one

Post-test analysis of the LOFT experiment L3-6 with the code RELAP4 MOD6

SIGLEAvailable from CEN Saclay, Service de Documentation, 91191 - Gif-sur-Yvette Cedex (France) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Brainhack: a collaborative workshop for the open neuroscience community

Brainhack events offer a novel workshop format with participant-generated content that caters to the rapidly growing open neuroscience community. Including components from hackathons and unconferences, as well as parallel educational sessions, Brainhack fosters novel collaborations around the interests of its attendees. Here we provide an overview of its structure, past events, and example projects. Additionally, we outline current innovations such as regional events and post-conference publications. Through introducing Brainhack to the wider neuroscience community, we hope to provide a unique conference format that promotes the features of collaborative, open science