Increased methane emissions from deep osmotic and buoyant convection beneath submarine seeps as climate warms

TL;DR

This study reveals that osmotic effects, alongside buoyancy, significantly enhance methane seepage rates from seabed sediments, and climate warming could accelerate methane hydrate melting and release into oceans and atmosphere.

Contribution

The paper introduces a novel mechanism involving osmotic effects that, combined with buoyancy, explains high methane seepage velocities and their potential acceleration due to climate change.

Findings

Osmotic effects can generate large overpressures in sediments.

Deep seawater recirculation can occur at rates of hundreds of meters per year.

Climate warming may drastically increase methane release rates.

Abstract

High speeds have been measured at seep and mud-volcano sites expelling methane-rich fluids from the seabed. Thermal or solute-driven convection alone cannot explain such high velocities in low-permeability sediments. Here, we demonstrate that in addition to buoyancy, osmotic effects generated by the adsorption of methane onto the sediments can create large overpressures, capable of recirculating seawater from the seafloor to depth in the sediment layer, then expelling it upwards at rates of up to a few hundreds of metres per year. In the presence of global warming, such deep recirculation of seawater can accelerate the melting of methane hydrates at depth from timescales of millennia to just decades, and can drastically increase the rate of release of methane into the hydrosphere and perhaps the atmosphere.