Role of nitrification and denitrification on the nitrous oxide cycle in the eastern tropical North Pacific and Gulf of California

Abstract

[1] Nitrous oxide (N 2 O) is an important atmospheric greenhouse gas and is involved in stratospheric ozone depletion. Analysis of the isotopomer ratios of N 2 O (i.e., the intramolecular distribution of 15 N within the linear NNO molecule and the conventional N and O isotope ratios) can elucidate the mechanisms of N 2 O production and destruction. We analyzed the isotopomer ratios of dissolved N 2 O at a site in the eastern tropical North Pacific (ETNP) and a site in the Gulf of California (GOC). At these sites, the flux of N 2 O to the atmosphere is extremely high but denitrification activity in the oxygen minimum zone (OMZ) also reduces N 2 O to N 2 . We estimated the isotopomeric enrichment factors for N 2 O reduction by denitrification. The factor was À11.6 ± 1.0% for the bulk (average) N, À19.8 ± 2.3% for the center N (a-site nitrogen), À3.4 ± 0.3% for the end N (b-site nitrogen), and À30.5 ± 3.2% for the 18 O of N 2 O. Isotopomer analysis of N 2 O suggests that nitrifiers should contribute to N 2 O production more than denitrifiers at the oxycline above the OMZs in the ETNP (50-80 m) and in the GOC (80-300 m). In contrast, denitrifiers should largely contribute to the N 2 O production and consumption in the OMZs both in the ETNP (120-130 m) and in the GOC (600-800 m). The N 2 O isotopomer analysis will be a useful tool for resolving the distribution of water masses that carry a signal of N loss by denitrification.

Site selective real-time measurements of atmospheric N<sub>2</sub>O isotopomers by laser spectroscopy

“…6) for N 2 O emitted before fertiliser application with a slope of 1.18 ± 0.32 can be attributed to a partial consumption by N 2 O reductase activity of denitrifying bacteria (Koba et al, 2009;Yamagishi et al, 2007). Similar values between 1.0 and 1.2 for SP s / δ 15 N bulk s were reported by Ostrom et al (2007) for N 2 O reduction by two denitrifier species.…”

“…On the other hand, processspecific effects on δ 15 N bulk might be masked by shifts in the precursor signature (Well et al, 2008), and theoretical considerations indicate a major impact of the involved bacterial species (Schmidt et al, 2004). In contrast to δ 15 N bulk , the site preference is considered to be independent of the isotopic composition of the precursor and, thus, supplies clear process information even if the isotopic signature of the substrate for N 2 O production is lacking (Frame and Casciotti, 2010;Ostrom et al, 2007;Sutka et al, 2006;Toyoda et al, 2002;Yamagishi et al, 2007;Well and Flessa, 2009).…”

“…For N 2 O, up to date all process studies on N 2 O isotopic species had to rely on grab sampling followed by IRMS laboratory analysis because real-time analysis was not available with the required precision. Consequently, current research is based on short-term investigations with limited temporal and spatial averaging capabilities (Ostrom et al, 2010;Toyoda et al, 2011a;Yamagishi et al, 2007).…”

Molecular and biogeochemical evidence for ammonia oxidation by marine Crenarchaeota in the Gulf of California

“…Error bars denote one standard error of the triplicate quantitative PCR (qPCR) measurement and are not visible when less than the width of the data point. distribution of N isotopes in the N 2 O molecule) were indicative of N 2 O production by both denitrification and nitrification, while at 405 m, nitrification was the dominant process (no data are available from 450 m) (Yamagishi et al, 2007).…”

Recent advances in the biogeochemistry of nitrogen in the ocean

“…Naqvi et al: Advances in marine nitrogen biogeochemistry 1035 papers in each area. Some of the papers presented at the Workshop have already been published elsewhere (e.g., Devol et al, 2006;Johnson et al, 2006;Moisander et al, 2006;Paerl et al, 2006;Thamdrup et al, 2006;Westley et al, 2006;Brunelle et al, 2007;Casciotti and McIlvin, 2007;Deutsch et al, 2007;Hamersley et al, 2007;Yamagishi et al, 2007). The remaining papers, which deal with diverse aspects of the nitrogen cycle are included in this issue.…”