Nitrogen often limits how much life the ocean can support, but a small group of microbes can pull nitrogen gas straight out of the water and convert it into a form other organisms can use. Most research has focused on the sunlight-dependent version of this process; we know far less about microbes that can do it in the dark.
I worked on a modeling study of the Gulf of Aqaba, in the northern Red Sea, to figure out how much these different nitrogen-fixing microbes — light-dependent and light-independent — matter to the local nutrient balance. We built simulations of the region’s chemistry and compared them against real measurements throughout the water column. A model without any nitrogen fixation matched near-surface chlorophyll but got the deeper nutrient chemistry wrong. Only a model including both light-dependent and light-independent nitrogen fixers reproduced the full pattern — evidence that nitrogen fixation happening in the dark is a real, necessary part of this ecosystem’s nutrient budget, not a minor detail.
Angela M. Kuhn 