Abstract
The role of methane as a green-house gas is widely recognized and has sparked considerable efforts to quantify the contribution from natural methane sources including submarine seeps. A variety of techniques and approaches have been directed at quantifying methane fluxes from seeps from just below the sediment water interface all the way to the ocean atmosphere interface. However, there have been no systematic efforts to characterize the amount and distribution of dissolved methane around seeps. This is critical to understanding the fate of methane released from seeps and its role in the submarine environment. Here we summarize the findings of two field studies of the Bush Hill mud volcano (540 m water depth) located in the Gulf of Mexico. The studies were carried out using buoyancy driven gliders equipped with methane sensors for near real time in situ detection. One glider was equipped with an Acoustic Doppler Current Profiler (ADCP) for simultaneous measurement of currents and methane concentrations. Elevated methane concentrations in the water column were measured as far away as 2 km from the seep source and to a height of about 100 m above the seep. Maximum observed concentrations were ∼400 nM near the seep source and decreased away steadily in all directions from the source. Weak and variable currents result in nearly radially symmetric dispersal of methane from the source. The persistent presence of significant methane concentrations in the water column points to a persistent methane seepage at the seafloor, that has implications for helping stabilize exposed methane hydrates. Elevated methane concentrations in the water column, at considerable distances away from seeps potentially support a much larger methane-promoted biological system than is widely appreciated.
Highlights
The importance of methane, leaked from the seafloor at seeps, as a food source in the deep oceans supporting complex biological communities is well documented (e.g., Kennicutt et al, 1988a; MacDonald et al, 1989; Sibuet and Olu, 1998; Sibuet and Roy, 2002; Cordes et al, 2005; Levin, 2005; Girard et al, 2020)
We present the findings of two in situ characterization studies of methane concentrations around the Bush Hill mud volcano conducted in the spring and fall of 2018
High spatial resolution (∼5 m) mapping of methane concentrations as close as ∼5–90 m above the seafloor allowed a 3D understanding of the methane plume
Summary
The importance of methane, leaked from the seafloor at seeps, as a food source in the deep oceans supporting complex biological communities is well documented (e.g., Kennicutt et al, 1988a; MacDonald et al, 1989; Sibuet and Olu, 1998; Sibuet and Roy, 2002; Cordes et al, 2005; Levin, 2005; Girard et al, 2020). Studies of these seep communities typically focus on megafaunal communities and microbial mats found close to release points on the seafloor. The release point on the seafloor can shift location on time scales of days (Razaz et al, 2020)
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