NOTE: THIS MS IS TO BE SUBMITTED FOLLOWING OUTCOME OF NATURE COMMUNICATIONS REVIEW OF A COMPANION MS.
ABSTRACT (246 words, 1,457 characters including spaces)
We measured the oxidation rates of N supplied as urea (UO) and ammonium (AO) in continental shelf and slope waters of the Southern Ocean west of the Antarctic Peninsula during the austral summer of 2018. The response of rates to substrate concentration varied by water mass. Rates increased moderately (up to 200%) with 440 vs 6 nM substrate amendments to samples from the Winter Water (WW, sampled at 35-100 m), but decreased (down to 7%) in samples from the Circumpolar Deep Water (CDW, 175-1000 m). AO rates decreased more than UO rates. This response suggests that CDW Thaumarchaeota are not well adapted to short-term variation in substrate concentrations and that even low amendments (we used 44 or 47 nM) may inhibit oxidation. Rates of AO and UO were not correlated; nor were they correlated with the abundance, or ratios of abundance, of marker genes; or with [NH4+]; or [urea]. UO and AO were distributed uniformly across the study area within a water mass; however, they displayed strong vertical gradients. Rates in most samples from Antarctic Surface Water (ASW, 10-15 m) were below the limit of detection. Highest rates of both processes were in samples from the WW (21.2 and 1.6 nmol L-1 d-1 for AO vs UO, respectively) and CDW (7.9 and 2.5 nmol L-1 d-1), comparable to rates from the study area reported previously. The contribution of UO to nitrite production was ~24% of that from AO alone, comparable to ratios measured at lower latitudes.
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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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- NSF-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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Abstract Marine oxygen deficient zones are dynamic areas of microbial nitrogen cycling. Nitrification, the microbial oxidation of ammonia to nitrate, plays multiple roles in the biogeochemistry of these regions, including production of the greenhouse gas nitrous oxide (N2O). We present here the results of two oceanographic cruises investigating nitrification, nitrifying microorganisms, and N2O production and distribution from the offshore waters of the Eastern Tropical South Pacific. On each cruise, high‐resolution measurements of ammonium ([NH4+]), nitrite ([NO2−]), and N2O were combined with15N tracer‐based determination of ammonia oxidation, nitrite oxidation, nitrate reduction, and N2O production rates. Depth‐integrated inventories of NH4+and NO2−were positively correlated with one another and with depth‐integrated primary production. Depth‐integrated ammonia oxidation rates were correlated with sinking particulate organic nitrogen flux but not with primary production; ammonia oxidation rates were undetectable in trap‐collected sinking particulate material. Nitrite oxidation rates exceeded ammonia oxidation rates at most mesopelagic depths. We found positive correlations between archaeal
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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.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/bg-17-2263-2020
