Net Community Production from O2 measurements on Argo Floats

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The flux of biologically-produced organic matter out of the upper, sun-lit waters to the deep ocean is known as the "biological pump". The geographic distribution and temporal variability of the marine biological pump influences atmospheric carbon dioxide levels, and maintains the oxygen distribution in the ocean below the sun-lit zone. Determining this flux is essential for understanding the marine carbon cycle feedback related to climate change. Shipboard oxygen measurements, the currently-used method, are accurate and can resolve small changes, but they cannot provide the areal and temporal oxygen distribution necessary to resolve global geographic variability in primary productivity. The goal of this project is to attain the necessary geographic diversity of experimental results by measuring accurate annual cycles of oxygen using sensors on autonomous platforms along three ocean transects with strong gradients in carbon export. Results from this study will broaden the geographic distribution of experimentally-determined marine biological pump observations. The project will involve training for a postdoctoral researcher and will develop an educational module on carbon cycle science for high school teachers.The oxygen mass balance method has been used to determine net annual biological oxygen production at marine time-series sites using shipboard oxygen measurements and mooring-based oxygen sensors that are calibrated by Winkler titrations. It has thus far been difficult to use this method on profiling floats because the oxygen sensors have not been accurate. Recent studies have shown improved accuracies in oxygen concentration measurements using Optodes on Argo floats compared with the Winkler titrations. In this project, a researcher will deploy Argo floats with calibrated and specially mounted Aanderaa Optode oxygen sensors along three transects in the Atlantic and Pacific Oceans that cross regions of stark contrasts in biological carbon export. The data will be used along with an upper ocean model to determine annual net biological oxygen production, which is stoichiometrically related to annual net community production (ANCP) and annual organic carbon export. The goal of this work is to determine the geographic distribution of ANCP, and compare it with carbon export values determined from satellite-based methods. In addition, the researcher will also develop an oxygen-Argo system capable of monitoring small changes in the oxygen concentration of the oxygen minimum zone.