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We performed assays of chemoautotrophic carbon fixation and compared measured rates to rates predicted from oxidation of ammonia (AO), urea (UO) and nitrite (NO) N. Water samples used in this study were taken from aerobic shelf waters at stations on the continental shelf and slope west of the Antarctic Peninsula during January and February of 2018 (LMG1801). Chemoautotrophic carbon fixation rates averaged 1.8 and 1.7 nmol C L-1 d-1 in Winter Water (WW, 35-100 m) and Circumpolar Deep Water (CDW, 175-1000 m) water masses, respectively. Integrated over 1 year and a 440 m water column (excluding the Antarctic Surface Water mass, 0-34 m), chemoautotrophic production accounted for ~7 gC m2 yr-1, compared to an estimated mean annual photoautotrophic production of 180 gC m2 y-1. Chemoautotrophy in WW samples supported by AO, UO or NO was the equivalent of 0.91, 0.06, 0.13 nmol C L-1 d-1, while it was the equivalent of 0.37, 0.21 and 0.08 nmol C L-1 d-1 in samples from the CDW water mass. Chemoautotrophy coupled to AO+UO accounted for ~124% and ~55% of measured C fixation rates in these water masses, while chemoautotrophy coupled to complete nitrification (AO+UO+NO) accounted for ~128 and ~60% of measured C fixation rates. The mean turnover times for nitrite pools base on NO were 138 ± 35 d and 15 ± 3 d in WW and CDW samples, respectively. The rate of nitrite production from AO+UO in WW and CDW samples was 503 ± 233 and 24 ± 7 nmol L-1 d-1, respectively. The replacement time for the nitrite pool in the WW water mass by AO+UO calculated from these averages is 33 d while it is 9 d in the CDW. These calculations suggest the possibility of an additional sink for nitrite in the WW.
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Regulation of nitrous oxide production in low-oxygen waters off the coast of Peru
Abstract. Oxygen-deficient zones (ODZs) are major sites of net naturalnitrous oxide (N2O) production and emissions. In order to understandchanges in the magnitude of N2O production in response to globalchange, knowledge on the individual contributions of the major microbialpathways (nitrification and denitrification) to N2O production andtheir regulation is needed. In the ODZ in the coastal area off Peru, thesensitivity of N2O production to oxygen and organic matter wasinvestigated using 15N tracer experiments in combination with quantitative PCR (qPCR) andmicroarray analysis of total and active functional genes targeting archaeal amoAand nirS as marker genes for nitrification and denitrification, respectively.Denitrification was responsible for the highest N2O production with amean of 8.7 nmol L−1 d−1 but up to 118±27.8 nmol L−1 d−1 just below the oxic–anoxic interface. The highest N2O productionfrom ammonium oxidation (AO) of 0.16±0.003 nmol L−1 d−1occurred in the upper oxycline at O2 concentrations of 10–30 µmol L−1 which coincided with the highest archaeal amoA transcripts/genes.Hybrid N2O formation (i.e., N2O with one N atom from NH4+and the other from other substrates such as NO2-) was the dominantspecies, comprising 70 %–85 % of total produced N2O fromNH4+, regardless of the ammonium oxidation rate or O2concentrations. Oxygen responses of N2O production varied withsubstrate, but production and yields were generally highest below 10 µmol L−1 O2. Particulate organic matter additions increasedN2O production by denitrification up to 5-fold, suggesting increasedN2O production during times of high particulate organic matter export.High N2O yields of 2.1 % from AO were measured, but the overallcontribution by AO to N2O production was still an order of magnitudelower than that of denitrification. Hence, these findings show thatdenitrification is the most important N2O production process in low-oxygen conditions fueled by organic carbon supply, which implies a positivefeedback of the total oceanic N2O sources in response to increasingoceanic deoxygenation.
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- PAR ID:
- 10184777
- Date Published:
- Journal Name:
- Biogeosciences
- Volume:
- 17
- Issue:
- 8
- ISSN:
- 1726-4189
- Page Range / eLocation ID:
- 2263 to 2287
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/bg-17-2263-2020
