Exploring signatures of coastal erosion processes in the shoreline morphology of Titan’s seas

Abstract:

The shoreline morphology of Titan’s hydrocarbon seas may provide clues about the climatic and geologic history of this icy moon. However, the type and nature of the processes affecting shoreline evolution remain unknown. Observations from the Cassini spacecraft and calculations from wave modeling both suggest that waves can develop in Titan’s surface liquid; these waves could potentially drive coastline erosion. Processes not controlled by waves, such as dissolution, could also have a measurable effect on shoreline morphology. The record of coastal processes is further complicated by river incision and sea level change, which have clearly modified the north polar landscape where most of Titan’s active shorelines are located. We use a combination of landscape evolution models and measurements of shoreline shape to examine how shoreline morphology may reflect the relative influence of different coastal erosion mechanisms, an open question relevant to shorelines on both Earth and Titan. We develop a shoreline evolution model that erodes the coast in two different ways: (1) uniform retreat (representing dissolution or backwasting), in which the coast erodes at the same rate everywhere, and (2) erosion by waves, in which the erosion rate depends on local wave energy, which in turn depends on the fetch (the distance over which the wind blows to generate waves) and wind speed. We explore how these two end-member coastal erosion processes modify initial shorelines created by flooding either a randomly rough topographic surface or one that has been eroded by river networks. Erosion by waves causes embayed portions of coastlines to retreat more slowly than relatively exposed portions of coastlines, preferentially preserving shoreline roughness within embayments, whereas uniform erosion creates no such difference. We then use wavelets to quantify these differences by measuring the roughness at particular scales along the modeled shorelines. Applying the same measurement technique to shorelines on Earth with known coastal erosion mechanisms offers a useful comparison. Our results provide a framework for testing whether Titan’s coastlines bear a measurable signature of wave erosion or uniform retreat.