The Martian North Polar Layered Deposits (NPLD) are composed of alternating water-ice and dust-rich layers resulting from atmospheric deposition and are key to understanding Mars’ climate cycles. Within these deposits are spiral troughs, whose migration affects deposition signals. To understand the relationship between NPLD stratigraphy and Martian climate, we must identify modern-day drivers of NPLD ice migration. Prevailing theory posits migration driven by upstream-migrating bed undulations bounded by hydraulic jumps, caused by katabatic winds flowing over trough walls with asymmetric cross-sectional relief. This is supported by trough-parallel clouds, whose formation has been attributed to hydraulic jumps. We present a cloud atlas across the Martian north pole using ~13,800 THEMIS images spanning ~18 Earth years. We find trough-parallel clouds in ~400 images, with regions nearer to the pole having higher cloud frequency. We compare spiral trough geometry to our cloud atlas and find regions with trough-parallel clouds often correlate with metrics associated with modern-day sublimation-deposition cycles (i.e., relief and asymmetry), but not always. In some regions, troughs with morphologies conducive to cloud formation have no clouds. Overall, trough geometry varies greatly across the deposits, both within and between troughs, suggesting localized differences in deposition relative to migration, varying katabatic wind intensities, differing past climatic states influencing the troughs, varying trough initiation properties, or the possibility of additional mechanisms for trough initiation and migration (e.g., in-situ trough erosion). Understanding what controls trough shape variability across the NPLD and how these controls change through time and space is key when interpreting Martian paleoclimate. Abstract content goes here

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.

We present a cost-efficient tilt sensor that was originally developed by our team at Dartmouth College to study ice deformation as part of the Jarvis Glacier Project, and we showcase our successful initial run that includes the development, deployment, and data collection processes. In this case study, we installed our tilt sensor system in two boreholes drilled close to the lateral shear margin of Jarvis Glacier in Alaska and successfully collected over 16 months of uninterrupted borehole deformation data in a harsh polythermal glacial environment. The data included gravity and magnetic data that we used to track the orientation of our sensors in the boreholes over time, and the resultant kinematic measurements enabled us to compute borehole deformation. While our sensors were applied under polythermal thermal regime conditions, we present use cases for our sensors in a variety of glacier thermal regimes including Athabasca glacier, a temperate glacier in Canada, and in Antarctic regions with similar polythermal regimes such as ice streams and outlet glaciers. Sensors embedded in our tilt sensors can be modified to suit different needs, and the tilt sensor can also be modified for different boreholes and glacier conditions. Our goal is to improve the accessibility of borehole geophysics research mainly through supporting production efforts of our sensor for various research needs. With an established sensor development plan, successful applications in the field, and years of experience, our team is open to potential research collaborations with researchers who are interested in using our tilt sensors. Our team is working with Polar Research Equipment, a Dartmouth alumni founded company that specializes in the development of polar research tools, that will serve as a commercial resource for researchers who may require support during the development process or mass-production of our cost-efficient (~20% the price of other commercial versions) yet effective tilt sensors.