Antarctic bedrock topography uncertainty and ice sheet stability

All Rights Reserved. Antarctic bedrock elevation estimates have uncertainties exceeding 1km in certain regions. Bedrock elevation, particularly where the bedrock is below sea level and bordering the ocean, can have a large impact on ice sheet stability. We investigate how present-day bedrock elevation uncertainty affects ice sheet model simulations for a generic past warm period based on the mid-Pliocene, although these uncertainties are also relevant to present-day and future ice sheet stability. We perform an ensemble of simulations with random topographic noise added with various length scales and with amplitudes tuned to the uncertainty of the Bedmap2 data set. Total Antarctic ice sheet retreat in these simulations varies between 12.6 and 17.9m equivalent sea level rise after 3kyrs of warm climate forcing. This study highlights the sensitivity of ice sheet models to existing uncertainties in bedrock elevation and the ongoing need for new data acquisition. Key Points Quantify how Antarctic bed elevation uncertainty affects ice sheet simulations Simulate retreat of the Antarctic ice sheet for a warm Pliocene climate Identify key areas for future improvements to bed elevation data

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A Single-Level Tunnel Model To Account For Electrical Transport Through Single Molecule-And Self-Assembled Monolayer-Based Junctions

We present a theoretical analysis aimed at understanding electrical conduction in molecular tunnel junctions. We focus on discussing the validity of coherent versus incoherent theoretical formulations for single-level tunneling to explain experimental results obtained under a wide range of experimental conditions, including measurements in individual molecules connecting the leads of electromigrated single-electron transistors and junctions of self-assembled monolayers (SAM) of molecules sandwiched between two macroscopic contacts. We show that the restriction of transport through a single level in solid state junctions (no solvent) makes coherent and incoherent tunneling formalisms indistinguishable when only one level participates in transport. Similar to Marcus relaxation processes in wet electrochemistry, the thermal broadening of the Fermi distribution describing the electronic occupation energies in the electrodes accounts for the exponential dependence of the tunneling current on temperature. We demonstrate that a single-level tunnel model satisfactorily explains experimental results obtained in three different molecular junctions (both single-molecule and SAM-based) formed by ferrocene-based molecules. Among other things, we use the model to map the electrostatic potential profile in EGaIn-based SAM junctions in which the ferrocene unit is placed at different positions within the molecule, and we find that electrical screening gives rise to a strongly non-linear profile across the junction