Understanding the fate of gas seeping from the seafloor is crucial for assessing the environmental impact of natural
and anthropogenic seep systems, such as CH4 cold seeps or leaks from gas wells or future carbon capture projects. We present a
comprehensive modelling framework that integrates physical, biological and chemical processes to estimate the 3-dimensional
dissolved concentration and total atmospheric flux of gas from seafloor seeps. The framework consists of two main steps:
1) A gas phase model that estimates free gas dissolution and direct atmospheric flux at the seep site, and 2) a concentration5
model that combines particle dispersion modelling, an adaptive-bandwidth kernel density estimator, and customizable process
modules. Using this framework, we successfully modeled the concentration field and atmospheric flux of CH4 between May
20 and June 20, 2018, from a natural seep site located at 200 meters depth offshore Northwestern Norway. Results show that
dissolved gas is primarily advected northeastward along the coast, spreading effectively across the shelves, and entering open
fjord systems. Within a few days, the CH4 concentration profile is near inverted, with peak concentrations close to the sea10
surface – facilitating atmospheric exchange. Diffusive emissions are spread out over large areas (>105km2) and exceeds the
local free gas flux by more than threefold (∼ 0.85%) during the modeling period while ∼40% of the CH4 remains in the
water column. Although high uncertainties remains regarding microbial oxidation rates, microbes represent the main sink of
CH4, converting ∼60% of dissolved CH4 to CO2 during the modeling period. These findings highlight the importance of
accounting for dissolved gas from seeps when evaluating their impact on atmospheric emissions and ecosystem interactions.15
Our framework provides a globally applicable tool that incorporates free and dissolved gas dynamics and flexible inclusion of
chemical and biological processes, supporting improved understanding and ability to quantify environmental impacts of seabed
gas seeps in the future |
