Marine ice-cliff instability modeling shows mixed-mode ice-cliff failure and yields calving rate parameterization.

Marine ice-cliff instability could accelerate ice loss from Antarctica, and according to some model predictions could potentially contribute >1 m of global mean sea level rise by 2100 at current emission rates. Regions with over-deepening basins >1 km in depth (e.g., the West Antarctic Ice Sheet) are particularly susceptible to this instability, as retreat could expose increasingly tall cliffs that could exceed ice stability thresholds. Here, we use a suite of high-fidelity glacier models to improve understanding of the modes through which ice cliffs can structurally fail and derive a conservative ice-cliff failure retreat rate parameterization for ice-sheet models. Our results highlight the respective roles of viscous deformation, shear-band formation, and brittle-tensile failure within marine ice-cliff instability. Calving rates increase non-linearly with cliff height, but runaway ice-cliff retreat can be inhibited by viscous flow and back force from iceberg mélange.

Enhanced basal lubrication and the contribution of the Greenland ice sheet to future sea-level rise.

We assess the effect of enhanced basal sliding on the flow and mass budget of the Greenland ice sheet, using a newly developed parameterization of the relation between meltwater runoff and ice flow. A wide range of observations suggest that water generated by melt at the surface of the ice sheet reaches its bed by both fracture and drainage through moulins. Once at the bed, this water is likely to affect lubrication, although current observations are insufficient to determine whether changes in subglacial hydraulics will limit the potential for the speedup of flow. An uncertainty analysis based on our best-fit parameterization admits both possibilities: continuously increasing or bounded lubrication. We apply the parameterization to four higher-order ice-sheet models in a series of experiments forced by changes in both lubrication and surface mass budget and determine the additional mass loss brought about by lubrication in comparison with experiments forced only by changes in surface mass balance. We use forcing from a regional climate model, itself forced by output from the European Centre Hamburg Model (ECHAM5) global climate model run under scenario A1B. Although changes in lubrication generate widespread effects on the flow and form of the ice sheet, they do not affect substantial net mass loss; increase in the ice sheet's contribution to sea-level rise from basal lubrication is projected by all models to be no more than 5% of the contribution from surface mass budget forcing alone.

Fluid dynamics modeling for synchronizing surface plasmon resonance and quartz crystal microbalance as tools for biomolecular and targeted drug delivery studies.

We have used computational fluid dynamics modeling (CFD) to synchronize the flow conditions in the flow channels of two complementary surface-sensitive characterization techniques: surface plasmon resonance (SPR) and quartz crystal microbalance (QCM). Since the footprint of the flow channels of the two devices is specified by their function, the flow behavior can only be varied either by altering the height of the flow channel, or altering the volumetric rate of flow (flow rate) through the channel. The relevant quantity that must be calibrated is the shear strain on the measurement surface (center and bottom) of the flow channel. Our CFD modeling shows that the flow behavior is in the Stokes flow regime. We were thus able to generate a scaling expression with parameters for flow rate and flow channel height for each of the two devices: f(QCM)=2.64f(SPR)(h(QCM)/h(SPR)(2), where f(QCM) and f(SPR) are the flow rates in the SPR and QCM flow channels, respectively, and h(QCM)/h(SPR) is the ratio of the heights of the two channels. We demonstrate the success of our calibration procedure through the combined use of commercially available SPR and QCM flow channel devices on both a biomolecular interaction system of surface immobilized biotin and streptavidin and a targeted drug delivery model system of biotinylated liposomes interacting with a streptavidin functionalized surface.