We explore the interconnection of phytoplankton community and function, and the interaction with the biogeochemical and climate system. We use a numerical model of the global ocean that resolves many phytoplankton types with a range of functionality, and many different combinations of nutrient, temperature and light requirements. A suite of integrations, along with simple ecological theory, are used to illustrate how the planktonic ecosystem exerts strong control on the biogeochemical environment and how this control may alter in a future warmer ocean. Temperature driven increase in biological rates promotes higher production, significant re-arrangement of species habitats, but little functional shifts in the community. In contract lower nutrient supplies due to a slower circulation and increased stratification leads to reduced production and sharp shifts in functionality. We examine how these two aspects of a changing ocean compete in different regions, leading to alterations in the ecosystem, biogeochemistry and ultimately the export of carbon to the deep ocean.