EPISODIC THERMAL LOADING OF THE SEAFLOOR AND RELATED DISSOCIATION OF GAS HYDRATE - NORTHERN GULF OF MEXICO

The continental slope of the northern Gulf of Mexico is episodically impacted by thermal events related to direct Loop Current intrusions and eddies. Both qualitative observations from manned submersibles as well as in situ measurements indicate that the surface exposures and near-surface accumulations of gas hydrate decompose in response to Loop Current related thermal forcing. Instrumentation placed at an exposed gas hydrate site in Green Canyon Block 185 recorded the transit of a weak Loop Current eddy. Response of a newly exposed gas hydrate was recorded. A specially built doppler current meter measured gas emission from the hydrate. The z-component of the doppler tracked gas emission from the hydrate site. Pressure was also recorded by the doppler. A current meter mooring with two Aanderaa current meters recorded current speed and direction plus water temperature. A thermistor at the doppler site measured water temperature at the seafloor. All instruments recorded data for about one year. An elevated temperature record (max excursion ~ 3.1°C) occurred at the site for approximately two months. This temperature record is strongly coherent with pressure and the z-component of the doppler current meter record (a reflection of increased out-gassing). Satellite imagery confirmed that a weak Loop Current eddy moved across the site during the time of elevated temperatures, pressure, and out-gassing. The current (speed and direction), temperature, pressure, and out-gassing records exhibit variations at the tidal and 5-20 day frequencies. These data suggest a strong coherence between thermal loading by Loop Current events and out-gassing from surficial gas hydrates.