2014 AGU Fall Meeting

December 15 - 19, 2014

Fixed nitrogen (N) limits productivity across much of the low-latitude ocean. The magnitude of its inventory results from the balance of N input, mostly biotic N₂ fixation, and N loss, occurring in regionally well-defined low-oxygen waters and sediments (denitrification and anammox).

The simple view restricting N₂fixation to warm and iron-rich waters has been recently challenged by new evidence demonstrating a wider diversity of N₂ fixers and N₂ fixation strategies enabling new insights into the controls of this process. However, sources of fixed nitrogen are still unaccounted for, and the mechanisms regulating the response of N₂fixers to N deficits are not well understood.

In this tutorial I will discuss how the role of N in controlling ocean productivity has matured. I will review N₂ fixation estimates and their uncertainties from experimental, geochemical and modeling approaches. I will discuss the new insights gained into the controls on the marine N₂ fixation and the emerging questions on the N inventory regulatory mechanisms, which challenge our current paradigms and place important constraints on our efforts to represent the N cycle in models used for climate predictions. Finally, I will highlight the key challenges that need to be tackled over the coming years.

• NC - Nutrient Cycling
• OB - Ocean Biology and Biogeochemistry
• PC - Past, Present and Future Climate