Mechanical controls on methane bubble solute exchange within muddy aquatic sediments and its growth characteristics

Abstract

<p>Methane (CH<sub>4</sub>) bubbles in muddy aquatic sediments threaten climate sustainability and sediment mechanical stability. Mechanical response of muddy sediment to bubble growth is described by Linear Elastic Fracture Mechanics (LEFM). Minor roles of mechanical sediment characteristics in CH<sub>4</sub> bubble solute supply and growth rates were quantified compared to biogeochemical controls. We investigate them using a coupled single-bubble mechanical/reaction-transport numerical and analytical models. We demonstrate that inner pressure of the growing bubble at fracturing, concentration at its surface, bubble size and spatial location, are uniquely defined by Fracture Toughness. However, a temporal evolution of the bubble inner pressure at expansion between the fracturing events depends on Young’s modulus. Fracture Toughness and Young’s modulus thus play complementary, spatial and temporal, roles in bubble growth. Their proportionality suggested by LEFM manages the bubble growth rates.  Fracture Toughness controls development of longer flatter bubbles in the deeper sediments. A substantial role of mechanical muddy sediment characteristics in the CH<sub>4 </sub>bubble growth dynamics and solute exchange is demonstrated, comparable to the role of the biogeochemical controls. Their contribution to emergence of “no-growth” and competitive bubble growth conditions, affecting a macro-scale gas dynamics are discussed that encourages a proper experimental evaluation of muddy sediment mechanical characteristics.</p>