Concentration variations of oxygen and carbon dioxide in air are linked by photosynthesis, respiration, and combustion. However, they are decoupled by air - sea exchange. Because oxygen is relatively insoluble in seawater, both anthropogenic carbon fluxes and oceanic carbon fluxes in the upper water column are rapidly and quantitatively imprinted on the oxygen concentration of air. In this project the distribution of oxygen in air will be studied in order to constrain (a) seasonal net production of organic carbon in the upper water column, (b) the rate of anthropogenic carbon dioxide dissolution in the oceans, and (c) the net rate of carbon dioxide production by conversion of the terrestrial biosphere. Variability in the atmospheric oxygen concentration is small, about 20 ppmV over the Earth's surface during the course of a year. This variability is measured to a precision of about + 1 ppmV using isotope ratio mass spectrometry to determine the oxygen/nitrogen ratio of dry air samples. The oxygen monitoring network will be expanded over the next three years, in order to monitor the seasonal and long term variability in the oxygen/nitrogen ratio of air. The measurements of seasonal variability will be interpreted in the context of ocean carbon cycle models and ocean color studies to give an integrated picture of spatial and temporal variability in net production and ocean ventilation on a global sale. The long term anthropogenic oxygen decrease will be used to constrain rates of biomass conversion and fossil carbon dioxide dissolution in the ocean.
