Tide-influenced acidic hydrothermal system offshore NE Taiwan

Abstract

Elemental sulfur and hydrogen sulfide emitted offshore of northeastern Taiwan known to local fishermen for generations, but never studied until recently, are found to have originated from a cluster of shallow (< 30 m depth) hydrothermal vents. Among the mounds is a massive 6 m high chimney with a diameter of 4 m at the base composed of almost pure sulfur and discharging hydrothermal fluid containing sulfur particles. The sulfur in the chimney has a δ 34S = 1.1‰ that is isotopically lighter than seawater. A yellow smoker at shallow depths with such characteristics has never been reported on anywhere else in the world. Gas discharges from these vents are dominated by CO 2 (> 92%) with small amounts of H 2S. Helium isotopic ratios 7.5 times that of air indicate that these gases originate from the mantle. High temperature hydrothermal fluids have measured temperatures of 78–116 °C and pH (25 °C) values as low as 1.52, likely the lowest to be found in world records. Low temperature vents (30–65 °C) have higher pH values. Continuous temperature records from one vent show a close correlation with diurnal tides, suggesting rapid circulation of the hydrothermal fluids.