Changes in temperature and sulfide with depth in background and hydrothermal sediments. Relative to background sediment distal from venting (+), the (a) temperature increases with depth and toward the center of the vent features from gray sediments fringing the hydrothermal sites (▲), to the white patches (□) and orange/yellow precipitates (◆). The precipitates in Rocky Point and Spiegelei were both orange and those in Twinkie (symbol marked with ‘*’) were yellow in color. (b) Dissolved H2S concentrations also increase with depth in the gray and white sediments but are lowest in the yellow areas. Paired temperature and sulfide measurements in Twinkie and Spiegelei were made at 5 cm (the upper sediments) and 15 cm (lower sediments). Data from Rocky Point were measured at sediment depths of 10 cm and 20 cm.