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The development of pH and pCO2 microelectrodes for studying the carbonate chemistry of pore waters near the sediment‐water interface
Author(s) -
Cai WeiJun,
Reimers Clare E.
Publication year - 1993
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1993.38.8.1762
Subject(s) - microelectrode , chemistry , sediment , carbonate , environmental chemistry , seawater , analytical chemistry (journal) , mineralogy , electrode , geology , oceanography , paleontology , organic chemistry
We made stable and rapid‐responding pH and p CO 2 microelectrodes. The pH microelectrode has a ∼100‐ µ m‐diameter half‐sphere bulb tip of pH glass, and the p CO 2 sensor has a 200–300‐ µ m‐diameter silicone‐membrane covered tip. Because the pH microelectrodes have electrical resistances that are >10 10 ohms, all electrical connections arc kept scrupulously clean and dry to prevent current leakage during in situ measurements. Suspension effects are negligible when measuring pH in marine sediments. To demonstrate the performance of the pH and p CO 2 microelectrodes, we report in situ microprofiles of pH and p CO 2 and contiguous profiles of O 2 and the formation factor from coastal sediment in San Diego Bay, California. A sharp pH decrease from 7.90 to 7.15 (seawater scale) and a p CO 2 increase from 578 to 3,000 µ atm in the top 1 cm of sediment arc interpreted to be primarily the result of HS, Fe 2+ , and Mn 2+ oxidation by O 2 rather than metabolic CO 2 production. The O 2 , pH, and p CO 2 profiles also reveal that there was photosynthetic activity in the top 2 mm of sediment which caused an O 2 maximum and a total dissolved inorganic carbon minimum.