1. Introduction -- 2. From inorganic carbon to organic carbon -- 3. The return from organic to inorganic carbon -- 4. Carbon processing at the seafloor -- 5. Biogeochemical processes and inorganic carbon dynamics -- 6. Organic matter is more than CH2O. .Open AccessThis open access book discusses biogeochemical processes relevant to carbon and aims to provide readers, graduate students and researchers, with insight into the functioning of marine ecosystems. A carbon centric approach has been adopted, but other elements are included where relevant or needed. The book focuses on concepts and quantitative understanding of primary production, organic matter mineralization and sediment biogeochemistry. The impact of biogeochemical processes on inorganic carbon dynamics and organic matter transformation are also discussed.