A document by David Nicholas Wagner. Click on the document to view its contents.

We seek to calibrate the flow law for polythermal ice through shear strain analysis. In a warming climate, increased melting of glaciers and ice caps play a big role in sea level rise. Approximately 60% of the current contribution to sea level rise from ice loss is attributed to glaciers and ice caps, raising the urgency of sharpening mass balance change predictions in regions of streaming flow. Polythermal glaciers constitute a significant portion of these contributing glaciers, though our knowledge of their flow dynamics is incomplete. Thermally complex polythermal glaciers have both warm and cold ice which lead to weak wet-based beds, with significant amounts of basal sliding and deformable till. Consequently, polythermal glaciers experience significant shear strain as their lateral shear margins sustain the majority of the resisting stress. Most in-situ and in-lab studies of natural ice over recent years have focused on bodies of ice with frozen beds that experience minimal shear strain downglacier and across vertical planes (with depth) relative to the bed. The lack of studies on wet-based polythermal glaciers causes uncertainties in the flow law, as differences in flow law factors between polythermal ice and bodies of ice with frozen beds have the potential to induce more than an order of magnitude difference in ice velocity. To improve calibration of the flow law for polythermal ice, we seek to improve our understanding of their shear strain regimes. We developed and deployed tilt sensor systems on the polythermal Jarvis Glacier in Alaska, where we drilled multiple boreholes close to Jarvis’ shear margin and installed three boreholes with our tilt sensor systems. The tilt sensors measure gravity, magnetic and temperature data, and each system consists of multiple sensors connected along a cable and serially communicating along a common data bus with a datalogger. We have recently retrieved a year of Jarvis tilt sensor data and calculated the at-depth shear strain rates in the boreholes, allowing evaluation of the at-depth shear strain rate regimes of polythermal ice against theoretical models developed using Glen’s flow law. We present the development of our data collection methodology and the results of our shear strain analysis, with suggestions for potential calibrations of the flow law for polythermal ice.

The thermodynamic growth of sea ice is a critical factor in the mass balance of Arctic sea ice, which has important implications for Arctic communities and the global climate. However, the magnitude by which snow atop Arctic sea ice limits thermodynamic ice growth is still not fully understood. Prior work has shown that the wind-driven snow redistribution could significantly modify the heat conduction through the snow cover and hence the rate of thermodynamic ice growth. However, the effects of snow redistribution on sea ice growth have not been quantified and are not well represented in climate models. We use observations from the MOSAiC expedition to show how different facets of snow redistribution can enhance or reduce heat conduction through the snow cover for the same mean snow thickness. The net effect depends on ice topography and environmental conditions. For example, snow redistribution onto young ice in April at MOSAiC reduced heat conduction by approximately 5-15%. We quantify the impact winter and springtime snow redistribution events on the heat conduction on deformed, level, and young ice. We explore the implications of these snow redistribution processes in the Community Earth System Model and discuss priorities for improving climate models.