Award: OCE-1334117

The main goal of this project was to develop improved aquatic eddy covariance instruments for the measurements of oxygen flux at the seafloor. Marine sediments cover approximately 70% of the Earth, they are sinks and sources for organic and inorganic carbon, and thereby play a central role in the global carbon cycle. Benthic oxygen fluxes, i.e. oxygen release or uptake by the seafloor, reflect the net effect of carbon production and mineralization of a sediment and also changes in the carbon cycling and ecosystem health. Oxygen fluxes thus are a good proxy for carbon cycling in marine sediments and they provide central input data for global carbon cycle and climate models. The aquatic eddy covariance technique is a powerful method to measure the oxygen fluxes because it does not disturb the flow and light fields at the seafloor and because it integrates flux over a large area thus taking the natural spatial patchiness of the seafloor into account. One of the main shortcomings of this method was the fragility and cost of the microelectrode oxygen sensor used. Malfunctioning and breakage of this sensor-type limited long-term deployment of the eddy covariance instruments and compromised the data it produced. This project was designed to solve this problem by developing robust eddy covariance oxygen sensors based on an optical measurement technology and accompanying software for oxygen flux extractions. The requirements for these new sensors were that they 1) can reliably measure oxygen concentrations over extended time periods in water with suspended particles and other matter, 2) can capture oxygen fluctuations caused by the eddies carrying the oxygen flux signal, and 3) do not distort these turbulent eddies.The project produced 4 new instrument-types: 1) Eddy covariance instrument with dual oxygen fiber optode sensors 2) Eddy covariance instrument with triple oxygen fiber optode sensors that can synchronously read up to 6 external sensors. 3) Eddy covariance instrument with a rugged fast micro-planar optode that can also be deployed in environments with very rough flow conditions. This sensor also has a fast temperature sensor for accompanying heat flux measurements. 4) Eddy covariance instrument with oxygen fiber technology developed specifically for aquatic eddy covariance measurements (final tests ongoing). The four instruments were tested in freshwater and marine environments, and demonstrated that the new optical fiber and planar oxygen sensors produce data that are of better quality than those produced with the oxygen electrode. The use of dual and triple oxygen sensor instruments allows generating extended continuous data series (e.g. one week length). Measuring simultaneously with more than one oxygen sensor allows an improved detection of compromised data, and the triple-sensor instrument permits new analysis of eddy flux extraction in environments with waves. The instrument with the rugged micro-planar optode produced data of unprecedented quality and now allows deployments in environments such a turbid rivers with strong turbulence and high particle load. With these new developments, reliable aquatic eddy covariance instruments now are available that can be deployed in shallow and deep environments under normal and rough flow conditions.Three graduate students were educated as part of the project in the use of the eddy covariance instrument and the data analysis. The new technologies were introduced in multiple journal articles and at international conferences. Direct consequences of such data are improved models for carbon cycling on the local, regional and global scale. In a time of rapid global environmental changes, the forecasting of these models provides information critical for environmental and human health, economy and decision makers. Last Modified: 05/07/2018 Submitted by: Markus H Huettel