Tidally-driven effluent detected by long-term temperature monitoring at the TAG hydrothermal mound, Mid-Atlantic Ridge

During Aug. 13-21, 1994, temperatures and current velocity were simultaneously monitored on the TAG hydrothermal mound. Three 'Giant Kelps (GKs)', vertical thermistor arrays of 50 m height, were moored on the periphery of the central black smoker complex (CBC). A 'Manatee', multi-monitoring system including current velocity, was deployed 50 m east of CBC. Four 'Daibutsu' geothermal probes penetrated the sediment south to west of CBC. Compilation of all data revealed semi-diurnal variations in water temperatures and current velocity, and allowed us to discuss the source of these anomalies. Temperature anomalies of GKs correlate well with current velocity, and are interpreted to be caused by the main plume from CBC that was bent over by the tidal current. We identified two types of asymmetric, periodic temperature variations at Daibutsu Probes 2 and 8, located 20 m to the south of CBC. By comparing temperatures and current velocity, they are attributed to non-buoyant effluents laterally advected by the tidal current. The source of one variation is located east to ESE of the probes, and the source of the other is located to the north. On Aug. 31, a new periodic anomaly emerged on Probe 2 with its amplitude up to 0.8 degrees C. The 6-h offset between the new anomaly and the previous one suggests that the source of the new anomaly lies to the west of Probe 2. The heat flux of these non-buoyant effluents is estimated to range from 30 to 100 kW/m(2), which is of the same order as direct estimates of diffuse flow at the TAG mound. It suggests that a significant amount of diffuse effluent is laterally advected by the prevailing current near the seafloor. (C) 1998 Elsevier Science B.V. All rights reserved.