Hydrothermal Activity doesn't effect SST
Most of the Hydrothermal or volconic activity is observed at sea floor spreading regions (Mid oceanic ridges). The warm fluids ejects from the vents/volconic activity that mixes up with ambient cool waters at greater depths shows weak anomolies in temperature at the site itself. and the hot waters raises upto a neutrally bouyant level and starts mixing/flowing horizontally. so its effect cannot be noted on SST.
Senior Research Fellow,