Aquatic Eddy Correlation: Quantifying the Artificial Flux Caused by Stirring-Sensitive O2 Sensors
Figure 3
Characteristics of the electrochemical sensor and flow statistics.
A: The sensor response time was measured upon a step change in O2 saturation from 100 to 0%. Equation 9 was used to model the sensors response upon a step change. B: Several compiled and equation 2 was fitted to the compiled data set to determine the stirring sensitivity. Grey dots are individual data points, red dots are 2–20 bin averages. C+D: The response of the electrochemical sensor to changing flow velocities was measured after an abrupt increase of the velocity from 0 to 2.2 cm s-1 and for an oscillating velocity of 0.3 Hz. E depicts the mean velocities (20 s running average) of Exps. 1–4 underlaid with snap shots of instantaneous velocities. In the upper part the O2 concentrations of the electrochemical sensor show that the drift of the sensor is negligible over the course of the 5 min measurements. F shows the variance of the O2 concentration (blue line), the variance of the longitudinal velocity (black line) and the correlation coefficient of the u’ and c’ time series (red line) as a function of flow velocity for Exps 1–4. G shows the correlation coefficient of the w’ and c’ time series (red line) and the measured Reynolds stress (black line). The latter is compared to estimates from the Law of the Wall (LoW, grey dashed line) for the flow at 15 cm above the seafloor and assuming a roughness length scale of 2.8 cm.