| Over glacial cycles, ice masses and their geophysical impacts on surface topography
dramatically changed drainage patterns and river discharges. These changes impacted
meltwater discharge to the ocean, geomorphology, and climate. As the river systems—the
threads that tied the ice sheets to the sea—were stretched, severed, and rearranged during
deglaciation, they also shrank and swelled with the pulse of meltwater inputs and proglacial
lake dynamics. Here I present a general method to compute past river flow paths, drainage
basin geometries, and river discharges. I automate these calculations within GRASS GIS to
take advantage of rapid solution techniques for drainage networks in an open-source and
compute-cluster-ready environment. I combine modern topography and bathymetry with ice
sheet reconstructions from the last glacial cycle and a global glacial isostatic adjustment
model to build digital elevation models of the past Earth surface. I then sum ice sheet mass
balance with computed precipitation and evapotranspiration from a paleoclimate general
circulation model to produce grids of water input. I combine these topographic and
hydrologic inputs to compute past river networks and discharges through time. These
paleodrainage reconstructions connect ice sheets, sea level, and climate models to fluvial
systems, which in turn generate measurable terrace and sedimentary records as
they carry physical, compositional, and isotopic signatures of ice sheet melt and
landscape change through their channels and to the sea. Therefore, this work provides a
self-consistent paleogeographic framework within which models and geologic records
may be quantitatively compared to build new insights into past glacial systems. |