Mid Sweden University

During the years 2010-13, atmospheric eddy covariance measurement of oxygen was performed at the marine site Ostergarnsholm in the Baltic Sea. The fast response optode Microx TX3 was used with two different types of tapered sensors. In spite of the increased lifetime, the optical isolated sensor is limited by the slower response time and is unsuitable for ground-based eddy covariance measurements. The sensor without optical isolation shows a -2/3 slope within the inertial subrange and attains sufficient response time and precision to be used in air-sea applications during continuous periods of 1-4 days. Spectral and cospectral analysis shows oxygen measured with the nonoptical isolated sensor to follow the same shape as for CO2 and water vapor when normalized. The sampling rate of the Microx TX3 is 2Hz; however, the sensor was found to have a limited response and resolution, yielding a flux loss in the frequency range f > 0.3Hz. This can be corrected for by applying cospectral similarity simultaneously using measurements of latent heat as the reference signal. On average the magnitude of the cospectral correction added 20% to the uncorrected oxygen flux during neutral atmospheric stratification.