Nitrogen (N2) fixation is an important component of the marine nitrogen (N) cycle, as it provides a major source of new N to the oligotrophic ocean, which often N limited. This input could increase global N inventories, leading to the sequestration of atmospheric CO2 via the biological pump. Any changes in N2 fixation can therefore theoretically change the carbon (C) sequestration capacity of the ocean. N2 fixing organisms, like the filamentous cyanobacterium Trichodesmium spp., are inherently not N limited. One would thus expect diazotrophs to thrive in the oligotrophic oceans