THERMAL FEEDBACKS TO BASAL WATER NETWORKS ALLOW PRESERVATION OF SUBGLACIAL MOUNTAIN TOPOGRAPHY

Over millions of years and multiple glacial cycles, mountain ranges serve as nucleation sites for continental ice sheets. Preservation of these mountains is essential for repeated glaciations, but it remains unclear why large, warm-based ice sheets with active subglacial water networks do not destroy high topography. Evidence from both large and small scales illustrates that subglacial water is critical to bedrock erosion. Here, we show how large subglacial mountains cause freezing and block water flow that would favor erosion using an extensive geophysical dataset across the Gamburtsev Subglacial Mountains in Antarctica. We demonstrate that the Gamburtsevs’ high relief resembles younger mid-latitude mountain landscapes with alpine-glacial signatures and determine that this relief has been preserved since the late Eocene (>34Myr ago). Preservation results from feedbacks among subglacial topography, the overlying ice sheet, and a coexisting large-scale basal drainage system that is identified through observations of extensive melt and basal water ponding along valleys. The ice sheet commonly drives subglacial water up steep topography where it freezes along high ridges. The freezing protects the peaks locally and creates thermal dams that pond water and prevent erosion. These thermodynamic feedbacks enable largely warm-based ice sheets to mantle subglacial mountain ranges for millions of years without significant bedrock erosion. Such mechanisms likely operated under prior ice sheets to preserve topography and promote ice sheet inception as carbon dioxide levels fluctuated.