Controls on terminus change of marine terminating glaciers in Greenland over the last 40+ years
Since the 1980s, the Greenland ice sheet has been losing ice mass at an increased rate. Our current understanding of the complex physical processes that control dynamic mass loss is incomplete and, therefore, leads to a wide range of possible future contributions to sea level. Ice dynamics, or changes due to changes in ice flux, is dominated by the behavior of fast-moving outlet glaciers in Greenland. These glaciers are changing through melting of the terminus face and/or calving of icebergs; the combination of these processes and ice motion determines the position of a glacier terminus. In understanding how and why outlet glacier termini change over time compared to external forcing and internal glacier dynamics, we are able to move toward a better understanding of marine-terminating glaciers. In this dissertation, I use terminus traces to observe how and why marine-terminating glaciers change in order to better understand the mechanisms behind these complex heterogeneous changes in Greenland. I develop the largest database of manually-traced marine-terminating glacier terminus data for use in scientific and machine learning applications. These data have been collected, cleaned, assigned with appropriate metadata, including image scenes, and compiled so that they can be easily accessed by scientists. Then I use the location of the termini to identify features in the bed topography that inhibit the retreat of glaciers following the onset of ocean warming and widespread glacier retreat in the late 1990s. I find that the slope and lateral dimensions of bed features exhibit the strongest correlation to retreat and that the shape of the bed features allows different styles of terminus retreat, which may be indicative of how different ablation mechanisms are distributed across termini. Finally, I produce a time series of terminus morphological properties for four glaciers in western Greenland to identify the characteristics that are indicative of calving processes with the goal of categorizing glaciers by calving style. I find that a concave shape and low sinuosity are present at glaciers that calve via buoyant flexure, while the opposite is true at glaciers that are dominated by melt-induced calving via serac failure. I also find that glaciers do not persistently fit into single calving styles and may change over time. By studying how the terminus changes over time compared to external forcing and internal glacier dynamics, we are able to move toward a better understanding of marine-terminating glaciers.