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Further Development of the Eddy Correlation Technique

PIs Peter Berg (UVA), Markus Huettel (FSU) and colleagues at MPI

berg_sensor

Image showing tip of the oxygen sensor and the ADV used for eddy correlation measurements.

The eddy correlation technique is a new promising technology for measuring sediment-water exchanges of dissolved constituents in the marine environment. It has until now been applied for oxygen. In short, the sediment-water exchange is derived from measured time series in the water column of the oxygen concentration and the vertical velocity. The technique has inherent advantages over other methods. For example, measurements are done under true in situ conditions, i.e. without any disturbances of the sediment and under natural light and hydrodynamic conditions.

Objectives addressed are to develop an eddy correlation instrument that can be built with off-the-shelf components; test a more rugged optode for long-term deployment, and employ the eddy correlation technique to study oxygen exchange dynamics and adapt the technology to study other processes. Two types of off-the-shelf optodes were compared with Clark-style electrodes to evaluate response times and signal/noise ratios. Data processing techniques are being improved to provide quantification of oxygen flux in day/night cycles. Diagenetic modeling using simulated oxygen uptake with both constant and variable diffusive boundary layer thicknesses showed good agreement of the mean values. In collaboration with J Crucius at USGS, eddy correlation has been successfully employed utilizing temperature sensors to measure groundwater outflow.

night deployment

Fluctuating oxygen concentration (red line, left axis) and fluctuating vertical velocity (blue line, right axis) measured at the same point 15 cm above a sediment surface at a frequency of 25 Hz and plotted vs time (sec). Positive velocities indicate a flow up and away from the sediment. The running mean values for the two variables are also shown, as are the smoothed oxygen concentration and the smoothed vertical velocity. Time series of 10 min or more are required to extract the vertical oxygen flux from such data.

last updated 31 July 2007



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