HR: 1340h
AN: B53A-0981    [Abstracts]
TI: Flow and Transport in Permeable Sediments Induced by Rising Gas Bubbles
AU: Stoehr, M
EM: mstoehr@mpi-bremen.de
AF: Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, Bremen, 28359 Germany
AU: * Boetius, A
AF: Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, Bremen, 28359 Germany
AU: * Boetius, A
AF: International University Bremen, Campusring 1, Bremen, 28759 Germany
AU: * Boetius, A
AF: Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, Bremerhaven, 27515 Germany
AU: Khalili, A
AF: Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, Bremen, 28359 Germany
AU: Khalili, A
AF: International University Bremen, Campusring 1, Bremen, 28759 Germany
AB: The transport of methane from marine sediments into the seawater and then into the atmosphere is important in the context of its role as a greenhouse gas. The amount of methane that escapes from the sediments can be significantly reduced due to microbial processes like anaerobic oxidation of methane (AOM). The efficiency of these processes is dominated by the local hydrodynamics of the seep. In the present work, we use an artificial laboratory setup in order to investigate the mechanisms of flow and transport induced by rising gas in a permeable sediment. A combination of the experimental techniques Particle Image Velocimetry (PIV), 3D Planar Laser-induced Fluorescence (3D PLIF) and refractive-index matching is employed for the visualization and quantification of different aspects of this multiphase flow phenomenon. We find that the gas, which is injected continuously into the sediment, forms a cone-shaped, vertical structure of trapped gas and leads to a spatially and temporally fluctuating escape of bubbles at the upper interface. The temporal variability of the total volume of trapped gas results in fluctuations of liquid velocities in the sediment pores and therefore leads to an enhanced mixing of solutes in the sediment. The area surrounding the seep is characterized by a reverse, i.e.\ downward directed flow of liquid into the sediment induced by the rising gas. From the analysis of a series of experiments with different sediment types and gas flow rates, we provide a quantitative description of the downward velocity as a function of the distance from the seep, the gas flow rate and the permeability of the sediment.
DE: 4832 Hydrothermal systems
DE: 4840 Microbiology
DE: 4894 Instruments and techniques
DE: 4211 Benthic boundary layers
DE: 4568 Turbulence, diffusion, and mixing processes
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting