Abstract:The oceans are full of microorganisms, which play a significant role in global carbon cycle. Microbial carbon sequestration in the ocean, as a cutting-edge scientific issue, receives a great deal attention in the context of global climate change. Based on the microbial carbon pump conceptual framework, microbes are major producers of recalcitrant dissolved organic carbon (RDOC) that can stay in ocean water column for long time storage. Different microbial groups contribute to RDOC carbon pool in different ways. This paper addresses groups such as autotrophic and heterotrophic microorganisms, viruses and protozoa with respect to their various ecological characteristics and specific roles in RDOC formation.