Organic Bioprocess Dominates Oceanic Nitrogen Loss

A new study clarifies and solidifies the dominant role of a critical pathway of nitrogen loss in the Arabian Sea-a difficult-to-study process that has weighty implications for oceanic influence on climate. An international team led by Princeton University's Bess B. Ward studied denitrification, the process by which microbes convert organic nitrogen-containing material to N₂ gas, which escapes from the ocean. Although denitrification had reigned as the major theory for oceanic N₂ loss, in recent years scientists have discovered another process known as anammox in which autotrophic microbes generate N₂ from inorganic materials. Some studies have suggested that anammox dominates, rather than denitrification. But the Princeton group examined samples from the Arabian Sea, an ocean where N₂ losses are particularly heavy, and found that denitrification is responsible for up to 99% of N₂ production, they report in Nature (2009, 461, 78). Understanding the details of the nitrogen cycle is essential for gauging how oceans respond to global-scale changes in temperature and CO₂, note nitrogen-fixation specialists Maren Voss and Joseph P. Montoya in an essay accompanying the paper.