High-Fidelity Modeling of Turbulent Mixing and Basal Melting in Seawater Intrusion Under Grounded Ice

Abstract. Small-scale ice-ocean interactions near and within grounding zones play an important role in determining the current and future contribution of marine ice sheets to sea level rise. However, the processes mediating these interactions are represented inaccurately in large-scale coupled models and thus contribute to uncertainty in future projections. Due to limited observations and computational resources, grounding zone fluid dynamics in ice sheet models are simplified, omitting potential fluid exchange across the grounding zone. Previous modeling studies have demonstrated that seawater can interact with subglacial discharge upstream of the grounding zone and recent observations appear to support this possibility. In this study, we investigate turbulent mixing of intruded seawater and glacial meltwater under grounded ice using a high-fidelity computational fluid dynamics solver. In agreement with previous work, we demonstrate the strongest control on intrusion distance is the speed of subglacial discharge and the geometry of the subglacial environment. We show that, in some cases, turbulent mixing can reduce intrusion distance, but not prevent intrusion entirely. Basal melting from seawater intrusion produces buoyant meltwater which acts as an important negative feedback by reducing near-ice thermohaline gradients. Modeled basal melt rates from seawater intrusion exceed melt rates predicted by existing sub-ice shelf melt parameterizations, which make assumptions about the structure of the near-ice boundary layer that do not hold where seawater intrudes into fresh subglacial discharge. We conclude that, during periods of slow subglacial discharge, seawater intrusion can be an important mechanism of ocean-forced basal melting of marine ice sheets.