9309765 Keeling The abundance of oxygen in the atmosphere is sensitive at the parts-per-million level to biological and anthropogenic activities over a wide range of space and time scales. Measurements of variations in atmospheric oxygen, detected through changes in the oxygen to nitrogen ratio, can address several important issues pertaining to the global carbon cycle: (1) the magnitude of new production of organic matter in surface waters over expanses of the ocean where direct, in situ, observations are lacking, (2) the magnitude of any terrestrial carbon sink at northern latitudes, and (3) the relative importance of terrestrial ecosystems versus the oceans as a sink for anthropogenic carbon dioxide. An improved understanding of these issues will be valuable for making more accurate forecasts of global climatic and biogeochemical changes in the decades ahead. The PIs have recently made measurements of the oxygen in air samples collected at several locations around the world. This project continues these measurements in order to carry out a systematic global survey of the variability in the oxygen to nitrogen ratio. Measurements will be carried out using a newly developed interferometric technique for oxygen to nitrogen analysis and using gas handling methods that obtain a precision of one part in 200,000 in the oxygen measurement. ***
