N2O production and consumption from stable isotopic and concentration data in the Peruvian coastal upwelling system. Issue 4 (18th April 2017)

• Record Type: Journal Article
• Authors: Bourbonnais, Annie; Letscher, Robert T.; Bange, Hermann W.; Échevin, Vincent; Larkum, Jennifer; Mohn, Joachim; Yoshida, Naohiro; Altabet, Mark A.
• Is Part Of: Global biogeochemical cycles. Volume 31:Issue 4(2017:Apr.)
• Page Start: 678
• Page End: 698
• Publication Date: 2017-04-18
• Subjects: nitrous oxide -- isotopomers -- stable isotopes -- oxygen deficient zone -- Eastern Tropical South Pacific -- coastal Peru; Biogeochemical cycles -- Periodicals; Electronic journals; 577.1405
• DOI: 10.1002/2016GB005567
• Languages: English
• ISSNs: 0886-6236

Abstract

Abstract: The ocean is an important source of nitrous oxide (N2 O) to the atmosphere, yet the factors controlling N2 O production and consumption in oceanic environments are still not understood nor constrained. We measured N2 O concentrations and isotopomer ratios, as well as O2, nutrient and biogenic N2 concentrations, and the isotopic compositions of nitrate and nitrite at several coastal stations during two cruises off the Peru coast (~5–16°S, 75–81°W) in December 2012 and January 2013. N2 O concentrations varied from below equilibrium values in the oxygen deficient zone (ODZ) to up to 190 nmol L −1 in surface waters. We used a 3‐D‐reaction‐advection‐diffusion model to evaluate the rates and modes of N2 O production in oxic waters and rates of N2 O consumption versus production by denitrification in the ODZ. Intramolecular site preference in N2 O isotopomer was relatively low in surface waters (generally −3 to 14‰) and together with modeling results, confirmed the dominance of nitrifier‐denitrification or incomplete denitrifier‐denitrification, corresponding to an efflux of up to 0.6 Tg N yr −1 off the Peru coast. Other evidence, e.g., the absence of a relationship between ΔN2 O and apparent O2 utilization and significant relationships between nitrate, a substrate during denitrification, and N2 O isotopes, suggest that N2 O production by incomplete denitrification or nitrifier‐denitrification decoupled from aerobic organic matter remineralization are likely pathways for extreme N2 O accumulation in newly upwelled surface waters. We observed imbalances between N2 O production and consumption in the ODZ, with the modeled proportion of N2 O consumption relative to production generally increasing with biogenic N2 . However, N2 O production appeared to occur even where there was high N loss at the shallowest stations. Key Points: High N2 O concentrations were observed in coastal waters off Peru Incomplete denitrifier‐denitrification was an important N2 O production pathway N2 O production occurred at high extent of N loss in the shallow ODZ