We treat the ocean carbon cycle as a coupled physical-biogeochemical process. The interactions between mixed-layer dynamics and growth of phytoplankton in the layer are discussed, and the formal relationship between phytoplankton accumulation and new production is examined. A coupled biological-physical model is presented for studying the classical spring bloom in the N. Atlantic, and possible differences in the mechanisms that drive the seasonal phytoplankton blooms in the N. Atlantic and the Arabian Sea are discussed. Finally, recommendations are made for observational programs to improve our understanding of the biologically-mediated carbon cycle in the Arabian Sea.