TDI-Brooks is providing Dr. Ian MacDonald at TAMU/GERG in late June ten (10) miniaturized self-contained temperature loggers for measuring time-temperature series at hydrate sites. These loggers will be inserted into the sediment using the submersible Johnson SEA-LINK’s robotic arm. These instruments are a new development of H. Villinger and Anteres Datensysteme GmbH, Stuhr, Germany. Each temperature logger is 185-mm long by 15-mm in diameter, weighing 120 g. Each has a titanium body to withstand the pressure to 6,000 meters water depth. The loggers each contain a 3 VDC Type DL1/3N battery and can log 65,000 temperature/time data points per deployment. The battery can operate for 500 days maximum. The logger’s measuring range is -20oC to +50oC with a resolution of 0.001oC. Its accuracy after calibration is better than �0.1oC. The time interval between measurements can be pre-programmed to be 1 second up to 4096 minutes (2.8 days). The data logging start time can be pre-programmed to be from immediate up to 30 days delay. Upon retrieval, data from the logger are uploaded to a laptop computer for processing. This design has undergone extensive field testing over the last year, and has proven extremely reliable.
The northern Gulf of Mexico is the site of many hydrate mounds that exist in water depths generally greater than 500 meters. Brooks and co-workers made the initial discoveries of both thermogenic and biogenic gas hydrates in these mounds and nearby deep ocean sediments in the mid-1980’s. Since that time the chemistry, biology and geology of these sites have been studied by the PIs and others. However, few heat flow measurements have been made around these mounds and none with the sophisticated state-of-the-art Heat Flow Probes that we can deploy.
The H. Villinger and Anteres Datensysteme GmbH thermistors will be deployed by Dr. Ian MacDonald with the submersible in July 2001 at the “Bush Hill” and GC-234 hydrate sites. The thermistors can be deployed in pairs to provide synoptic comparison of sediment/hydrate temperature with near-bottom water temperature. At two sites, GC-185 (Bush Hill) and GC-234, shallow deposits of gas hydrate are abundant at water depths of about 550 meters. At the most active vents, gas hydrate is exposed to the seawater and interacts with changing water temperatures [MacDonald et al., 1994]. Elsewhere, hydrate layers are buried beneath 10-20 cm of sediment. A recently developed hydrate drill will permit researchers to bore short, narrow holes (~25 x 3-cm) into the exposed hydrate from the submersible. For this program, we propose to place a pair of thermistors so that one probe is inserted into one of these holes and the other probe remains exposed to bottom water. A similar arrangement of probes will be deployed in the sediment-covered gas hydrate deposits. A control pair would be deployed in non-seep sediments off-axis at the “Bush Hill” site. The thermistors would be deployed, then recovered during the summer 2002 with the Johnson SEA-LINK submersible.
After deployment for one year, the five pairs of thermistors in the sediment and water column overlying the sediment will be recovered with the submersible. The temperature data will be useful in modeling the effect of sea bottom water and near-surface sediment fluctuations on gas hydrate stability at these two sites where hydrates exist as outcrops and as shallow hydrate burials. The magnitude of the temperature fluctuations from primarily loop-current intrusions will be able to be monitored over this long time series deployment as well as the extent of propagation into the associated sediments.
