Coupled large-eddy simulation and Lagrangian agent-based modelling of methane bubble dynamics in water column

We present a coupled modelling approach that integrates a three-dimensional large-eddy simulation (LES) hydrodynamic model with a Lagrangian agent-based representation of methane bubble dynamics in the water column. The fluid flow is resolved using Oceananigans, a non-hydrostatic, finite-volume ocean model that solves the Boussinesq equations on structured grids. Conceptually influenced by MITgcm, Oceananigans was developed from scratch by the Climate Modelling Alliance as an open-source model using the Julia programming language, and is particularly suited for high-resolution simulations of stratified and buoyancy-driven flows.

Methane bubbles are represented as discrete Lagrangian agents, whose trajectories and state variables evolve in response to the resolved flow field. The bubble dynamics model based on the multicomponent single-bubble model of McGinnis et al. (2006), which describes buoyant ascent and dissolution while accounting for pressure-dependent expansion and the diffusive exchange of methane along with four other dissolved gases. By coupling the bubble model with a three-dimensional LES hydrodynamic model, the framework describes how the resolved velocity field, temperature, and density stratification influence bubble rise and diffusive gas exchange across the bubble–water interface.

This coupled LES–agent-based approach allows simulation of methane transport from bottom sources through the water column in coastal zones and can be used to study methane bubble dynamics and estimate methane fluxes under variable environmental conditions.