High-quality eddy covariance data through 17 hours measured over permeable sand in the Gulf of Mexico, Florida.
Water depth varied from 1 to 1.5 m, and sediment permeability was 1.3 10-11 m2.
Raw data were recorded in 15 min data segments that included a short pause at the end.
First panel: Three velocity components (x, y, z) and mean current velocity varying between 1 and 5 cm s-1. Most of the variation in velocity represents wave action.
Second panel: Oxygen concentration measured with a fast-responding micro-electrode and an oxygen meter. The latter was used for calibration.
Third panel: Cumulative oxygen fluxes with linear trends indicating a strong consistent flux signal in the data.
Fourth panel: Oxygen fluxes, one for each 15 min data segment, and light measured over the sand. Negative fluxes represent an uptake.
Note the clear day-night-day cycle (Fourth panel). The four last fluxes of extreme size were artificially induced by people wading upstream from the eddy covariance instrument.
Night time oxygen uptake averaged -368 ± 21 mmol m-2 day-1 (SE, n = 45) which is almost 4 times larger than the flux of -98 ± 21 mmol m-2 day-1 (SE, n = 5) measured concurrently in in situ chambers.
This difference was likely caused by extensive flushing of the permeable sediment by current flow, oscillating wave-generated flow, and oscillating pressure at the sediment surface. Existing chamber technology cannot fully reproduce these naturally occurring drivers of porewater exchange.
For further details on the data, see Berg and Huettel (2008) . The 16 Hz data (time, vx, vy, vz, O2) for this example can be downloaded here: BergData1