Calibration, Response, and Hysteresis in Deep-Sea Dissolved Oxygen Measurements

Accurately measuring the dissolved oxygen concentration in the ocean has been the subject of considerable research. Traditionally, the calibration and correction of profiling oxygen measurements has centered on static, steady-state errors, leaving dynamic or time-dependent errors in the sensor response largely untreated. This study evaluates a reengineered Sea-Bird Electronics dissolved-oxygen Clark electrode (SBE 43) and demonstrates the characterization of sensor time response over oceanographic temperatures and pressures as well as treating a time-dependent, pressure-induced effect observed as hysteresis, most notably in deep-ocean oxygen profiles. The effects of temperature and pressure on sensor response are measured separately and then combined into an expression for evaluating an in situ time constant. The physics of the pressure-induced hysteresis in oxygen sensors are discussed and modeled for many individual sensors in several locations throughout the world's oceans. This effort reduces the underlying uncertainty of Clark oxygen sensors to approximately 0.1% of the measured signal, which is equivalent to the accuracy of the chemical calibration standard.