Isotopic evidence of dissolved organic nitrogen production and consumption in ocean surface waters.

DON in Pacific and Atlantic surface waters shows δ15N-linked production and consumption, with minima in subtropical gyres and anomalously high DON δ15N indicating net transport and use there.

• Why it matters: Because dissolved inorganic nitrogen is scarce in much of the surface ocean, understanding whether DON is produced and consumed in situ is key to explaining nutrient recycling and productivity in low-latitude waters.
• What they did: The study measured DON concentration and δ15N (15N/14N ratios) in surface waters across the Pacific and Atlantic basins and tested for a δ15N correlation between surface DON and nitrate consumed.
• The result: A δ15N correlation indicates in situ DON production and consumption, while low-DON subtropical samples with high DON δ15N confirm net DON transport to and consumption in subtropical gyres; equatorial Atlantic data suggest net DON degradation.