Here we report the first in situ pH of hydrothermal vent fluids at mid-ocean ridges. Measurements were made during dives with DSV Alvin to the Main Endeavour Field (Juan de Fuca Ridge) and the East Pacific Rise at 21°N, and 9°-10°N using solid-state electrochemical sensors. Vent fluid temperature and pressure ranged from 180 to 384 °C and 220 to 250 bar, respectively. pH(in situ) of the highest temperature vent fluid is only slightly acidic (5.1-5.4), although sharply lower values occur at the seawater/vent-fluid interface. Knowledge of pH(in situ) is essential for unravelling the complex geochemical and biogeochemical processes controlling the evolution of seafloor hydrothermal systems.
Bibliographical noteFunding Information:
We thank Naibin Dong (UMN) and Ying Chen (ZJU) for assistance in development of the electronics package used with the pH sensor; Jeff Seewald (WHOI) and Michael E. Berndt (UMN) for assisting with acquisition of vent fluid chemistry during our 1999 cruise to the Main Endeavour Field (JDF). We also greatly acknowledge the pilots, officers and crewmembers of Atlantis/Alvin for their dedication and expertise, without which this study would not have been possible. The constructive reviews and suggestions provided by G. J. Massoth and I-Min Chou were particularly helpful and greatly appreciated. This work was supported by US National Science Foundation grants EAR-9614427 (K.D. and W.E.S.); OCE-9633132 (W.E.S., K.D. and M.K.T.); OCE-0117117 (W.E.S. and K.D.); OCE-9521436 and OCE-9633627 (M.K.T. and A.M.B.); and OCE-0002458 (K.L.V.D).
- Hydrothermal fluid
- In situ pH
- Mid-ocean ridges