Ice microstructure (optical measurements) from Jarvis Glacier, Alaska, 2017-2020

Ice sheets and alpine glaciers discharge primarily though streaming flow, so the dynamics of that flow is central to the overall mass balance of the cryosphere. In glaciers and ice streams, the resistance to flow at the bed is important, but equally important is the internal viscous strength of the ice near the margins. In many cases, the lateral margins support greater than 50% of the resisting stress. At present, there is moderate to high uncertainty of the factors controlling the viscous strength of streaming ice under natural conditions. Although experiments suggest that variations in the intensity and orientation of the crystallographic fabric can result in up to a ten-fold difference in flow strength, in-situ observational studies of the microstructural architecture of streaming ice number in the low single digits. Most microstructural and in-situ rheological studies come from ice divides, near sites of paleoclimate coring. To complement that work and provide insight into the dynamic influence of streaming ice margins, our study documented both temperature and microstructure across a strain gradient at the lateral margin of Jarvis (Creek) Glacier and related those observations to modeled and observed 3D velocity structure. The dataset included here is one component of the larger project described above: crossed-polarized light images of thin-sections from three ice cores collected in spring 2017. Holes were drilled along a transect from less to more sheared ice, with the goal being to reach bed in at least two locations within the time constraints of the drilling season. We attempted six holes. Three were studied: JA, 63.4750˚N, 145.6753˚W, 1621 m elevation, 80 m long; JB, 63.4749˚N, 145.6759˚W, 1625 m, 30 m long; JE, 63.4743˚N, 145.6766˚W, 1625 m, 18 m long. JA and JE appear to have reached bed; other cores were limited by debris. We selected 12 samples from JA, 8 from JB, and 6 from JE to represent each ice core. For background, we also include a location map and core log.