Glacier-bed characteristics that are poorly known and modeled are important in projected sea-level rise from ice-sheet changes under strong warming, especially in the Thwaites Glacier drainage of West Antarctica. Ocean warming may induce ice-shelf thinning or loss, or thinning of ice in estuarine zones, reducing backstress on grounded ice. Models indicate that, in response, more-nearly-plastic beds favor faster ice loss by causing larger flow acceleration, but more-nearly-viscous beds favor localized near-coastal thinning that could speed grounding-zone retreat into interior basins where marine-ice-sheet instability or cliff instability could develop and cause very rapid ice loss. Interpretation of available data indicates that the bed is spatially mosaicked, with both viscous and plastic regions. Flow against bedrock topography removes plastic lubricating tills, exposing bedrock that is eroded on up-glacier sides of obstacles to form moats with exposed bedrock tails extending downglacier adjacent to lee-side soft-till bedforms. Flow against topography also generates high-ice-pressure zones that prevent inflow of lubricating water over distances that scale with the obstacle size. Extending existing observations to sufficiently large regions, and developing models assimilating such data at the appropriate scale, present large, important research challenges that must be met to reliably project future forced sea-level rise.

Glacier motion responds dynamically to changing meltwater inputs, but the multi-decadal response of basal sliding to climate remains poorly constrained due to its sensitivity across multiple timescales. Observational records of glacier motion provide critical benchmarks to decode processes influencing glacier dynamics, but multi-decadal records that precede satellite observation and modern warming are rare. Here we present a record of motion in the ablation zone of Saskatchewan Glacier that spans seven decades. We combine in situ and remote-sensing observations to inform a first-order glacier flow model used to estimate the relative contributions of sliding and internal deformation on dynamics. We find a significant increase in basal sliding rates between melt-seasons in the 1950s and those in the 1990s and 2010s and explore three process-based explanations for this anomalous behavior: (i) the glacier surface steepened over seven decades, maintaining flow-driving stresses despite sustained thinning; (ii) the formation of a proglacial lake after 1955 may support elevated basal water pressures; and (iii) subglacial topography may cause dynamic responses specific to Saskatchewan Glacier. Although further constraints are necessary to ascertain which processes are of greatest importance for Saskatchewan Glacier's dynamic evolution, this record provides a benchmark for studies of multi-decadal glacier dynamics.

The WAIS (West Antarctic Ice Sheet) Divide deep ice core was recently completed to a total depth of 3405 m, ending 50 m above the bed. Investigation of the visual stratigraphy and grain characteristics indicates that the ice column at the drilling location is undisturbed by any large-scale overturning or discontinuity. The climate record developed from this core is therefore likely to be continuous and robust. Measured grain-growth rates, recrystallization characteristics, and grain-size response at climate transitions fit within current understanding. Significant impurity control on grain size is indicated from correlation analysis between impurity loading and grain size. Bubble-number densities and bubble sizes and shapes are presented through the full extent of the bubbly ice. Where bubble elongation is observed, the direction of elongation is preferentially parallel to the trace of the basal (0001) plane. Preferred crystallographic orientation of grains is present in the shallowest samples measured, and increases with depth, progressing to a vertical-girdle pattern that tightens to a vertical single-maximum fabric. This single-maximum fabric switches into multiple maxima as the grain size increases rapidly in the deepest, warmest ice. A strong dependence of the fabric on the impurity-mediated grain size is apparent in the deepest samples.

The Rideau Canal in Canada was constructed in the 1800s to enable strategic military andcommercial transport in eastern Ontario between Lake Ontario and the Ottawa River. Today,the Rideau Canal is managed by Parks Canada and remains an engineered ecosystem,particularly in the urban Ottawa reach (7 km long) where it is largely channelized and ispartially drained during the winter to protect canal infrastructure (i.e., locks) andprovide recreational opportunities (i.e., skating). Interestingly, the Ottawa reach of theRideau Canal supports one of the few wild urban muskellunge (Esoxmasquinongy) fisheries in North America supported by natural reproduction.However, little is known about the spatial ecology, residency patterns or survival of thisapex freshwater predator in urban environments or canal systems. Radio-telemetry was usedto study adult (N = 10; total size range of 64 to 122 cm) muskellunge inthe Ottawa reach of the Rideau Canal over a multiple year period. The seasonal movementsand home range of muskellunge were greatest during spring corresponding with the periodwhen water levels in the canal were raised and muskellunge were presumably seeking outsuitable spawning habitats following ice-off. During the summer fish ranged throughout theentire 7 km urban reach of the canal and by early fall muskellunge moved to the deeperparts of the reach and became largely restricted to an embayment known as Dow’s Lake priorto the lowering of the canal where they stayed for the entire winter. The same pattern ofseasonal movements persisted across several years. None of the tagged muskellunge werestranded from the fall canal drainage. One fish emigrated from the urban reach of thecanal during the study period, moving upstream through a lock to an exurban reach. Inaddition, a single tagged fish died from a winterkill event. Environmental influences suchas seasonality and water depth (associated with canal operations) are believed to be theprimary mechanisms contributing to habitat selection and movement patterns of muskellungein this reach of the Rideau Canal. Data on the spatial ecology of muskellunge in the urbanreaches of the Rideau Canal will inform management of this unique population of fish toensure that the historic and ecological values are balanced to preserve this iconicCanadian natural heritage site and its biota.