Observational evidence indicates an increasing trend in the amplitude of the seasonal cycle of atmospheric CO2 over the last several decades. Here, the influence of nitrogen deposition on the seasonal cycle of atmospheric CO2 is investigated using a global carbon cycle model embedded in a 3-D general circulation model. We employ a recently published estimate of the enhancement of carbon dioxide uptake induced by the atmospheric deposition of NOy and NHx. We partition the carbon sink related to nitrogen deposition over the seasonal cycle of CO2 uptake. The modeled increase in the amplitude of the seasonal cycle of CO2 in the Northern Hemisphere related to the simulated nitrogen deposition alone is 25%--50% of observed. At Mauna Loa the increased amplitude in the CO2 seasonal cycle due to nitrogen deposition 50--90% of that observed. The subtle interaction between 3-D atmospheric transport, atmospheric nitrogen deposition, and seasonal CO2 uptake results in significant changes in the amplitude of the seasonal cycle of atmospheric CO2. The magnitude of these nitrogen deposition-induced changes in the atmospheric behavior of CO2 is comparable to other processes that are thought to influence global carbon cycle dynamics. ¿ 1999 American Geophysical Union