Events

Speaker: Perianne Johnson, Distinguished Postdoctoral Fellow University of Texas Institute for Geophysics

Host: Krista Soderlund

Title: Seafloor Sediment Dynamics on Ocean Worlds

Abstract: Water-rock interactions occurring on the seafloor are of great interest for understanding the geochemistry and habitability of ocean worlds. Like Earth, Enceladus and Europa are expected to have ocean currents, due to buoyancy from temperature and salinity gradients, as well as possibly from tidal forcing and libration (e.g. Jansen, et al., 2023, Soderlund, et al., 2024). If these currents are fast enough, which we quantify in this presentation, they may transport loose sediment and lead to seafloor erosion. Ocean world seafloors may look very different from Earth’s, since they do not have river sediment nor any known biogenic sediment sources. Therefore, their seafloors could lack the protective alluvial layer that Earth has and the seafloor could be subject to bedrock incision, analogous to rivers on Earth.

We present the first model of seafloor erosion for ocean worlds, adapted from a model for subaerial rivers on Earth (Sklar and Dietrich, 2004). This model takes grain and flow properties (e.g. grain size and density, fluid density and viscosity, and flow dimensions) as inputs, and outputs the bedrock abrasion rate. The abrasion rate is calculated as the product of the volume of bedrock removed by a single grain impact, the rate of grain impacts, and the fraction of the bedrock which is exposed. This final factor is included because an existing layer of stationary sediment acts to protect the bedrock from erosion by absorbing the energy of grain impacts.

Gravity at the seafloor is the largest control on the erosion, with Europa (g = 1.41 m/s2) having an erosion rate about 10x smaller than Earth and Enceladus (g = 0.133 m/s2) about 100x smaller for equivalent grain and flow properties. In this presentation, we will quantify how the grain and flow properties affect the erosion rate. We will also discuss the current velocities needed for transport of sediment on ocean worlds and how that compares to predictions for currents from other analyses. We will speculate on what this means for the seafloor topography, both positive and negative, as well as the total volume of sediment produced over the lifetime of the moons.