Simulated results from a twodimensional carbon cycle model of the Indian Ocean is used to analyze and discuss distributions of partial pressure of carbon dioxide at surface water and its control factors, influences of marine biology on the CO2 airsea exchange, and impacts of changes in nutrients and ocean circulation，which is also compared with GEOSECS observations. Ocean conditions related to partial pressure of carbon dioxide at surface water are studied. Some key factors and their influences for determining sources and sinks of surface carbon dioxide are further discussed. A few important conclusions are thus made that marine thermodynamics and ocean circulations have key impact on the chemical processes of carbon dioxide at surface water and the influence of marine biology on the CO2 airsea exchange is less important. In addition, several numerical experiments are carried out to study the potential influences for changes in marine physical and chemical processes on atmospheric CO2 by using the carbon cycle model.