A Short and Somewhat Personal History of Yukon Glacier Studies in the Twentieth Century

Glaciological exploration of the Yukon for scientific purposes began in 1935, with the National Geographic Society’s Yukon Expedition led by Bradford Washburn and the Wood Yukon Expedition led by Walter Wood. However, Project “Snow Cornice,” launched by Wood in 1948, was the first expedition to have glacier science as its principal focus. Wood’s conception of the “Icefield Ranges Research Project” led the Arctic Institute of North America (AINA) to establish the Kluane Lake Research Station on the south shore of Kluane Lake in 1961. Virtually all subsequent field studies of Yukon glaciers were launched from this base. This short history attempts to document the trajectory of Yukon glacier studies from their beginnings in 1935 to the end of the 20th century. It describes glaciological programs conducted from AINA camps at the divide between Hubbard Glacier and the north arm of Kaskawulsh Glacier and at the confluence of the north and central arms of Kaskawulsh Glacier, as well as the galvanizing influence of the 1965 – 67 Steele Glacier surge and the inception and completion of the long-term Trapridge Glacier study. Excluded or minimized in this account are scientific studies that were conducted on or near glaciers, but did not have glaciers or glacier processes as their primary focus.L’exploration glaciologique du Yukon à des fins scientifiques remonte à 1935, à l’occasion de l’expédition du Yukon par la National Geographic Society dirigée par Bradford Washburn et de l’expédition Wood Yukon dirigée par Walter Wood. Cependant, le projet « Snow Cornice » mis en oeuvre par Walter Wood en 1948 a été la toute première expédition à être axée principalement sur la science des glaciers. En fait, le projet de recherche sur les chaînons des glaciers mis au point par Walter Wood a incité l’Institut arctique de l’Amérique du Nord (IAAN) à mettre sur pied la station de recherche du lac Kluane sur la rive sud du lac Kluane en 1961. Presque toutes les autres études sur le terrain relativement aux glaciers du Yukon ont eu cette base comme point de départ. Cette brève histoire tente de répertorier la trajectoire des études des glaciers du Yukon depuis leurs débuts en 1935 jusqu’à la fin du XXe siècle. On y décrit les programmes glaciologiques réalisés à partir des camps de l’IAAN à la ligne de partage entre le glacier Hubbard et le bras nord du glacier Kaskawulsh ainsi qu’à la confluence des bras nord et centre du glacier Kaskawulsh. On y décrit également l’influence de galvanisation de la crue du glacier Steele de 1965 à 1967 ainsi que la création et l’achèvement de l’étude à long terme du glacier Trapridge. Cette brève histoire aborde à peine, voire pas du tout, les études scientifiques réalisées sur les glaciers ou près de ceux-ci, études pour lesquelles les glaciers ou les processus des glaciers n’étaient pas le point de mire

History and Bathymetry of a Surge-dammed Lake

A survey was made in 1974 of the small lake which had formed as a result of the surge advance of Steele Glacier, Yukon Territory, in 1965-68. Maximum lake level is controlled by a drainage channel which passes over rock near the hydrologic left margin of Steele Glacier. Since the surge advance of 1965-68 the lake has twice drained subglacially, producing minor outburst floods on Steele Creek and increasing the discharge of the Donjek River which crosses the probable route of the Alaska Highway pipeline

Hydraulics of Subglacial Supercooling: Theory and Simulations for Clear Water Flows

Glaciohydraulic supercooling is a mechanism for accreting ice and sediment to the base of glaciers. We extend existing models by reworking the Spring‐Hutter model for subglacial water flow in tubular conduits to allow for distributed water sheets. Our goal is to determine diagnostic features of supercooling relative to controlling variables. Results focus on along‐path water flow under time‐varying conditions, with attention to ice accretion in and along subglacial overdeepenings. We contrast simulations with constant recharge to diurnally‐varying recharge and expose behavior that cannot be inferred from simple models. For example, locations of simulated ice accretion differ from those found for steady state models, even though total ice accretion remains comparable to field estimates. Downstream accretion influences upstream effective pressures that then modify the hydraulic gradient that drives water flow. This modified gradient tends to inhibit additional accretion by increasing velocity and heat production via viscous dissipation. During diurnal cycles, accretion varies considerably: in daytime, viscous dissipation dominates the heat balance and ice melts. In morning and evening, when flow is rising or falling, viscous dissipation is lower and accretion can proceed. Over nighttime, the largest temperature depressions occur in the subglacial system, but water flux is lowest and accretion rates are negligible. We conclude by inferring that overdeepened glaciers with only clear water flows evolve toward stronger supercooling regimes rather than toward a dynamic equilibrium. Stabilizing feedbacks are unlikely to occur through glacier hydrology alone, and other processes, such as erosion, sedimentation, and sliding, must play an important role

Evolution of Subglacial Overdeepenings in Response to Sediment Redistribution and Glaciohydraulic Supercooling

Glaciers erode bedrock rapidly, but evacuation of sediments requires efficient subglacial drainage networks. If glaciers erode more rapidly than evacuation proceeds, a protective subglacial till layer can form to armor the bed. Where glaciers cross overdeepenings, local closed depressions, the bed slope opposes the ice surface and lowers the hydraulic potential gradient that drives water flow. Here, we present results of a dynamic, distributed model of coupled basal water flow and sediment transport to show how overdeepenings evolve over the course of a melt season. We use steady-state calculations as well as numerical simulations to understand how alluvial bed erosion alters overdeepenings. Numerical results from a modified form of the Spring-Hutter equations show behaviors that cannot be inferred from either local or steady-state calculations. In general, opposition of surface and bed slopes lessens sediment transport regardless of ice accretion from glaciohydraulic supercooling. Drainage efficiency strongly affects erosion and deposition rates. Results show characteristic behaviors of flow through overdeepenings such as overpressured water systems and accretion rates compatible with field measurements. Simulations that start with overdeepened glacier configurations progress out of a freezing regime where glaciohydraulic supercooling occurs. This progression indicates that glacier hydrology is more strongly affected by erosion and deposition than by freezing from glaciohydraulic supercooling. We discuss how this outcome affects glacier erosion and sediment transport under modern and past ice sheets

Instruments and Methods: Direct measurement of sliding at the glacier bed

Sliding at the base of Trapridge Glacier, Yukon Territory, Canada, was measured using a “drag spool”. We describe this simple and inexpensive instrument as well as its installation and operation. From 1990 to 1992 seven sites were instrumented with drag spools. At six of the sites basal sliding, during the period of observation, accounted for 50-70% of the total flow observed at the glacier surface. The contribution from ice creep is known to be small, so most of the remaining surface motion must be attributed to subglacial sediment deformation. For the seventh site the observed sliding rate was ~ 90% of the total flow, an indication that the sliding contribution varies spatially across the bed. Diurnal variations in the response of one of our instruments appear to be correlated to subglacial water-pressure fluctuations and are interpreted in terms of changes in sliding velocity rather than the opening and closing of basal cavities

Printability of elastomer latex for additive manufacturing or 3D printing

Additive manufacturing, sometimes referred to as 3D printing is a new, rapidly developing technology which has the potential to revolutionize fabrication of certain high value, complex products. Until now conventional elastomers have not been widely used in the additive manufacturing process. The goal of our work was to determine the feasibility of additive manufacturing using ink jet printing of elastomeric latex materials. Particle size, viscosity, and surface tension were measured for five different latex materials—poly(2-chloro-1,3-butadiene), carboxylated styrene-butadiene rubber, carboxylated butadiene-acrylonitrile copolymer, natural rubber, and prevulcanized natural rubber. The XSBR latex was predicted as the one most likely to be printable. Printing trials carried out with the XSBR as the ink proved it to be printable, although technical problems of agglomeration and print head clogging need to be addressed and both the material and process need to be optimized for consistent printing to be achieved

Spring warming in Yukon mountains is not amplified by the snow albedo feedback

Decreasing spring snow cover may amplify Arctic warming through the snow albedo feedback. To examine the impact of snowmelt on increasing temperature we used a 5,000 m elevation gradient in Yukon, Canada, extending from valley-bottom conifer forests, through middle elevation tundra, to high elevation icefields, to compare validated downscaled reanalysis air temperature patterns across elevational bands characterized by different patterns of spring snowmelt. From 2000 to 2014 we observed surface warming of 0.01 °C/a·1,000 m in May (0.14 °C/a at 1,000 m to 0.19 °C/a at 5,000 m), and uniform cooling of 0.09 °C/a in June at all elevations. May temperature trends across elevationally dependent land cover types were highly correlated with each other despite large variations in albedo and snow cover trends. Furthermore, a clear dependency of infrared skin temperature on snow cover mediated albedo decline was observed in tundra, but this was insufficient to influence average diurnal air temperature. We observed negative June temperature trends which we attribute to increasing daytime cloud cover because albedo and snow cover trends were unchanging. We conclude that 8-day and monthly averaged Spring air temperature trends are responding to a synoptic external forcing that is much stronger than the snow albedo feedback in sub-Arctic mountains

Instruments and Methods: Direct measurement of sliding at the glacier bed

Sliding at the base of Trapridge Glacier, Yukon Territory, Canada, was measured using a “drag spool”. We describe this simple and inexpensive instrument as well as its installation and operation. From 1990 to 1992 seven sites were instrumented with drag spools. At six of the sites basal sliding, during the period of observation, accounted for 50-70% of the total flow observed at the glacier surface. The contribution from ice creep is known to be small, so most of the remaining surface motion must be attributed to subglacial sediment deformation. For the seventh site the observed sliding rate was ~ 90% of the total flow, an indication that the sliding contribution varies spatially across the bed. Diurnal variations in the response of one of our instruments appear to be correlated to subglacial water-pressure fluctuations and are interpreted in terms of changes in sliding velocity rather than the opening and closing of basal cavities

Airborne sampling of aerosol particles: Comparison between surface sampling at Christmas Island and P-3 sampling during PEM-Tropics B

Bulk aerosol sampling of soluble ionic compounds from the NASA Wallops Island P-3 aircraft and a tower on Christmas Island during PEM-Tropics B provides an opportunity to assess the magnitude of particle losses in the University of New Hampshire airborne bulk aerosol sampling system. We find that most aerosol-associated ions decrease strongly with height above the sea surface, making direct comparisons between mixing ratios at 30 m on the tower and the lowest flight level of the P-3 (150 m) open to interpretation. Theoretical considerations suggest that vertical gradients of sea-salt aerosol particles should show exponential decreases with height. Observed gradients of Na+ and Mg2+, combining the tower observations with P-3 samples collected below 1 km, are well described by exponential decreases (r values of 0.88 and 0.87, respectively), though the curve fit underestimates average mixing ratios at the surface by 25%. Cascade impactor samples collected on the tower show that \u3e99% of the Na+ and Mg2+mass is on supermicron particles, 65% is in the 1–6 micron range, and just 20% resides on particles with diameters larger than 9 microns. These results indicate that our airborne aerosol sampling probes must be passing particles up to at least 6 microns with high efficiency. We also observed that nss SO42− and NH4+, which are dominantly on accumulation mode particles, tended to decrease between 150 and 1000 m, but they were often considerably higher at the lowest P-3 sampling altitudes than at the tower. This finding is presently not well understood