The Development and Testing of a New Technique for the Estimation of Profiles of Epsilon using an Acoustic Doppler Current Profiler (ADCP)

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Although Continental shelf seas make up a relatively small fraction (~7%) of the world ocean's surface they are thought to make a major contribution (accounting for between 20 and 50% of the total) to the open ocean storage of CO2. The drawdown of CO2 from the atmosphere is driven by a biological pump which is only effective in seasonally stratified zones of the shelf seas. A limiting component of this pump is the vertical mixing which supplies nutrients across the seasonal thermocline to the euphotic zone, thus supporting new primary production. Whilst profiler techniques have been successfully used to estimate the vertical mixing rate through measurement of profiles of epsilon (the rate of dissipation of turbulent kinetic energy) these techniques are costly and time consuming and so measurements limited to short (12-24 hours) periods of time. Our proposal is to develop a new technique, based on a technique already used in Radar Meteorology, which uses a convensional off the shelf ADCP, to measure long time series of the vertical structure of epsilon in the thermocline. The technique will initially be applied to data we have already collected, and the results will be validated against simultaneously collected profiler measurements of epsilon. We also propose to test the technique at a more fundamental level - using spectral techniques - on data which we propose to collect in the Menai Strait.