Dinitrogen Fixation Within and Adjacent to Oxygen Deficient Waters of the Eastern Tropical South Pacific Ocean
Margaret R Mulholland1, Brittany Widner1, Peter W Bernhardt2, Bonnie X Chang3 and Amal Jayakumar4, (1)Old Dominion University, Ocean, Earth and Atmospheric Sciences, Norfolk, VA, United States, (2)Old Dominion University, Department of Ocean, Earth and Atmospheric Sciences, Norfolk, VA, United States, (3)Univ Washington, Seattle, WA, United States, (4)Princeton University, Princeton, NJ, United States
Abstract:
Recent work suggests that planktonic diazotrophs are geographically more widely distributed than previously thought including relatively warm (14-23oC) aphotic oxygenated pelagic waters and in aphotic waters within oxygen deficient zones. Because the volume of aphotic water in the ocean is large and may increase in the future, if dinitrogen (N2) fixation is widely occurring at sub-euphotic depths, this could result in a dramatic upward revision of global nitrogen (N) inputs via this process. N2 fixation rates were measured during a cruise in the Eastern Tropical South Pacific using stable isotope tracer techniques that account for slow gas dissolution. Results are compared with light, nutrient, and oxygen gradients (and necessarily temperature gradients). In addition, rates of N2 fixation made in vertical profiles within and above oxygen deficient waters are compared with those measured in vertical profiles adjacent to oxygen deficient waters. Results suggest that while rates of N2 fixation were measurable in deeper anoxic waters, volumetric N2 fixation rates were higher in surface waters.
