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 simult aneously monitored on the TAG hydrothermal mound. Three 'Giant Kelps ( GKs)', vertical thermistor arrays of 50 m height, were moored on the p eriphery 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 sout h to west of CBC. Compilation of all data revealed semi-diurnal variat ions in water temperatures and current velocity, and allowed us to dis cuss the source of these anomalies. Temperature anomalies of GKs corre late well with current velocity, and are interpreted to be caused by t he main plume from CBC that was bent over by the tidal current. We ide ntified two types of asymmetric, periodic temperature variations at Da ibutsu 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 v ariation is located east to ESE of the probes, and the source of the o ther is located to the north. On Aug. 31, a new periodic anomaly emerg ed on Probe 2 with its amplitude up to 0.8 degrees C. The 6-h offset b etween the new anomaly and the previous one suggests that the source o f 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), wh ich is of the same order as direct estimates of diffuse flow at the TA G mound. It suggests that a significant amount of diffuse effluent is laterally advected by the prevailing current near the seafloor. (C) 19 98 Elsevier Science B.V. All rights reserved.