Tidally-driven effluent detected by long-term temperature monitoring at the TAG hydrothermal mound, Mid-Atlantic Ridge (vol 108, pg 143, 1998)

During August 13-21, 1994, temperatures and current velocity were simultane ously monitored on the TAG hydrothermal mound. Three 'Giant Kelps (GKs)', v ertical thermistor arrays of 50 m height, were moored on the periphery of t he 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. Compilatio n of all data revealed semi-diurnal variations in water temperatures and cu rrent velocity, and allowed us to discuss the source of these anomalies. Te mperature anomalies of GKs correlate well with current velocity, and are in terpreted 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. B y comparing temperatures and current velocity, they are attributed to non-b uoyant 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 othe r is located to the north. On August 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 anomal y 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 a s direct estimates of diffuse flow at the TAG mound. It suggests that a sig nificant amount of diffuse effluent is laterally advected by the prevailing current near the seafloor. (C) 1998 Elsevier Science B.V. All rights reser ved.