Coordinated, High-Resolution Studies of Hydrated Sediments

Abstract

Abstract : The Naval Research Laboratory (NRL) has been conducting coordinated investigations of marine gas hydrates based on precise co-location of both direct sediment cores and data from a deep-tow multichannel seismic system. The seismic instrument (known as the Deep Towed Acoustics/Geophysics System (DTAGS)) was developed by NRL to support detailed studies of deep-ocean marine sediments by towing both the seismic source (220Hz - 1kHz, 200 dB //1 square Pa @ 1m ) and 48 channel hydrophone array 300 m above the seafloor in up to 6km deep water. This instrument has proven to ideal for studies of marine gas hydrates. Data from this system have been used to study the impact of hydrate dissociation on sediment properties on and near the Blake Ridge and on the Cascadia Margin. Investigations in the Gulf of Mexico are schedules for Spring 2005. Using bottom mounted acoustic transponders for long baseline (LBL) navigation, we have been able to co-locate the deep-tow seismic data with sediment cores, water samples, etc. to constrain models for processes that create and dissociate marine gas hydrates in much greater detail than previously possible. We show relationships between geologic features resolved with the seismic data and geochemical evidence for variability in methane flux through the seafloor. We also present preliminary results from lattice-gas numerical simulations of gas-fluid flow through complex sediments where parameters are predicated on results obtained with DTAGS and associated geochemical samples.