High precision atmospheric oxygen (O 2 ) measurements are a relatively new and powerful tool for studying the global carbon cycle. Despite the development of several techniques for achieving these measurements over the past two decades, the quantification of small changes (ppm-level) in the background concentration of O 2 (21%) still remains very challenging. We have built a measuring system capable of detecting ppm-level changes in atmospheric O 2 that is suitable for continuous, automated, shipboard use. We tested this system under field conditions on a research cruise in the North Atlantic Ocean between Newfoundland and Iceland in summer 2006, collecting the first-ever atmospheric O 2 measurements over the Atlantic Ocean. We present these data, showing changes in atmospheric O 2 and CO 2 concentrations that are a result of changing air mass or water mass origins which incorporate influences from land/marine biospheric processes, ocean mixing, and temperature-induced solubility changes.