Field of research: Experimentation

Institution: GEOMAR Helmholtz-Center for Ocean Research, KIMOCC, GEOMAR-Benthic Ecology
Contact: Dr. Claas Hiebenthal
Location: Düsternbrooker Weg 17 / Geomar-Pier


Instrument produced by Todd Martz laboratory at Scripps San Diego. It consist of a bundle of a Durafet pH sensor (Honeywell Process solutions, USA) an oxygen optode Aanderaa 3835 (Aanderaa Data Instruments AS, Norway) and a SBE 37 Ð SI CTD ( Sea-Bird electronic Inc., USA) The circulation of water between the SBE 37 Ð SI and the optode and Durafet is achieved by a SBE 5M pump (Sea.-Bird electronic Inc., USA). The coordination of pumping and recording by the SBE 37 and the optode is insured by a homemade data logger. To prevent from fouling on sensors, the SBE 37 Ð SI was equipped with tributyltin tablets and copper tubing linked the SBE 37 Ð SI and the flow cell to the pump. Calibration of the pH sensor is achieved by comparison with a reference seawater sample measured for pH by spectrophotometry.

Technical Data

See manufacturer for the Aanderaa O2 optode and Seabird pump and CTD. The technical data regarding the use of Durafet pH in seawater can be found in Martz et al., 2010; Testing the Honeywell Durafet for seawater pH applications; Limnology and Oceanography: Methods.


Accuracy in test tanks at varying salinity, temperature and pCO2 (bubbling in the tank of CO2 modified air): using as base Baltic Sea water.

Only the pH sensor was tested for performances. The sensor shown some difficulties to perform on the long term in a fluctuating environment within an acceptable precision pH, i.e. < 0.001. Discrepancy between pH calculated from discrete samples (pH=f(TA, DIC) at high pCO2 also appears to be a problem coming from the discrete samples analysis and / or calculations and not from the sensor. The sensor needs a monthly cleaning.


Long and short term measurement of pH, O2, temperature and salinity in seawater. Requires homemade battery packs 18V: 3x parallel 12 D-Cells in serie (36 in total).