Diversity and distribution of nitrogen fixation genes in the oxygen minimum zones of the world oceans

Abstract. Diversity and community composition of nitrogen (N) fixing microbes in the three main oxygen minimum zones (OMZs) of the world ocean were investigated using operational taxonomic unit (OTU) analysis of nifH clone libraries. Representatives of three of the four main clusters of nifH genes were detected. Cluster I sequences were most diverse in the surface waters, and the most abundant OTUs were affiliated with Alpha- and Gammaproteobacteria. Cluster II, III, and IV assemblages were most diverse at oxygen-depleted depths, and none of the sequences were closely related to sequences from cultivated organisms. The OTUs were biogeographically distinct for the most part – there was little overlap among regions, between depths, or between cDNA and DNA. In this study of all three OMZ regions, as well as from the few other published reports from individual OMZ sites, the dominance of a few OTUs was commonly observed. This pattern suggests the dynamic response of the components of the overall diverse assemblage to variable environmental conditions. Community composition in most samples was not clearly explained by environmental factors, but the most abundant OTUs were differentially correlated with the obvious variables, temperature, salinity, oxygen, and nitrite concentrations. Only a few cyanobacterial sequences were detected. The prevalence and diversity of microbes that harbor nifH genes in the OMZ regions, where low rates of N fixation are reported, remains an enigma.

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Diversity and distribution of Nitrogen Fixation Genes in the Oxygen Minimum Zones of the World Oceans

10.5194/bg-2019-445 ◽

2020 ◽

Cited By ~ 2

Author(s):

Amal Jayakumar ◽

Bess B. Ward

Keyword(s):

Nitrogen Fixation ◽

Surface Waters ◽

World Ocean ◽

Operational Taxonomic Unit ◽

N Fixation ◽

Oxygen Minimum Zones ◽

Abundant Otus ◽

The World ◽

Nifh Genes ◽

Oxygen Minimum

Abstract. Diversity and community composition of nitrogen fixing microbes in the three main oxygen minimum zones (OMZs) of the world ocean were investigated using operational taxonomic unit (OTU) analysis of nifH clone libraries. Representatives of the all four main clusters of nifH genes were detected. Cluster I sequences were most diverse in the surface waters and the most abundant OTUs were affiliated with Alpha- and Gammaproteobacteria. Cluster II, III, IV assemblages were most diverse at oxygen depleted depths and none of the sequences were closely related to sequences from cultivated organisms. The OTUs were biogeographically distinct for the most part – there was little overlap among regions, between depths or between cDNA and DNA. Only a few cyanobacterial sequences were detected. The prevalence and diversity of microbes that harbour nifH genes in the OMZ regions, where low rates of N fixation are reported, remains an enigma.

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Following the N<sub>2</sub>O consumption at the Oxygen Minimum Zone in the eastern South Pacific

Biogeosciences Discussions ◽

10.5194/bgd-9-2691-2012 ◽

2012 ◽

Vol 9 (3) ◽

pp. 2691-2707 ◽

Cited By ~ 1

Author(s):

M. Cornejo ◽

L. Farías

Keyword(s):

Primary Productivity ◽

High Reliability ◽

World Ocean ◽

South Pacific ◽

Future Scenarios ◽

N2o Production ◽

The World ◽

Minimum Zone ◽

Latitudinal Range ◽

Oxygen Minimum

Abstract. Oxygen deficient zones (OMZs), such as those found in the eastern South Pacific (ESP), are the most important N2O sources in the world ocean relative to their volume. N2O production is related to low O2 concentrations and high primary productivity. However, when O2 is sufficiently low, canonical denitrification takes place and N2O consumption can be expected. N2O distribution in the ESP was analyzed over a wide latitudinal range (from 5° to 30° S and 71°–76° to ~84° W) based on ~890 N2O measurements. The intense consumption of N2O appears to be related to secondary NO2− accumulation, the best indicator of very low O2 levels. Using relationships that depend on threshold levels of O2 (<8 μM) and nitrite (>0.75 μM), we reproduced the apparent N2O production (ΔN2O) with high reliability (r2=0.73 p=0.01). Our results contribute to quantify the ratio of N2O production/consumption that is being cycling in O2 deficient water of N2O and may improve the prediction of N2O behavior under future scenarios of the OMZ expansion.

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Contrasting biogeochemistry of nitrogen in the Atlantic and Pacific Oxygen Minimum Zones

Biogeosciences ◽

10.5194/bg-9-203-2012 ◽

2012 ◽

Vol 9 (1) ◽

pp. 203-215 ◽

Cited By ~ 52

Author(s):

E. Ryabenko ◽

A. Kock ◽

H. W. Bange ◽

M. A. Altabet ◽

D. W. R. Wallace

Keyword(s):

Surface Waters ◽

Inorganic Nitrogen ◽

Sharp Decrease ◽

Stable Isotope Ratio ◽

Saharan Dust ◽

N Loss ◽

Fractionation Factor ◽

Oxygen Minimum Zones ◽

Oxygen Minimum ◽

Oxygen Concentrations

Abstract. We present new data for the stable isotope ratio of inorganic nitrogen species from the contrasting oxygen minimum zones (OMZs) of the Eastern Tropical North Atlantic, south of Cape Verde, and the Eastern Tropical South Pacific off Peru. Differences in minimum oxygen concentration and corresponding N-cycle processes for the two OMZs are reflected in strongly contrasting δ15N distributions. Pacific surface waters are marked by strongly positive values for δ15N-NO3–) reflecting fractionation associated with subsurface N-loss and partial NO3– utilization. This contrasts with negative values in NO3– depleted surface waters of the Atlantic which are lower than can be explained by N supply via N2 fixation. We suggest the negative values reflect inputs of nitrate, possibly transient, associated with deposition of Saharan dust. Strong signals of N-loss processes in the subsurface Pacific OMZ are evident in the isotope and N2O data, both of which are compatible with a contribution of canonical denitrification to overall N-loss. However the apparent N isotope fractionation factor observed is relatively low (&varepsilon;d=11.4 ‰) suggesting an effect of influence from denitrification in sediments. Identical positive correlation of N2O vs. AOU for waters with oxygen concentrations ([O2] < 5 μmol l−1) in both regions reflect a nitrification source. Sharp decrease in N2O concentrations is observed in the Pacific OMZ due to denitrification under oxygen concentrations O2 < 5 μmol l−1.

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Supplementary material to "Diversity and distribution of Nitrogen Fixation Genes in the Oxygen Minimum Zones of the World Oceans"

10.5194/bg-2019-445-supplement ◽

2020 ◽

Author(s):

Amal Jayakumar ◽

Bess B. Ward

Keyword(s):

Nitrogen Fixation ◽

Oxygen Minimum Zones ◽

The World ◽

Supplementary Material ◽

Oxygen Minimum ◽

Nitrogen Fixation Genes

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Controls on redox-sensitive trace metals in the Mauritanian oxygen minimum zone

10.5194/bg-2018-472 ◽

2018 ◽

Cited By ~ 1

Author(s):

Insa Rapp ◽

Christian Schlosser ◽

Jan-Lukas Menzel Barraqueta ◽

Bernhard Wenzel ◽

Jan Lüdke ◽

...

Keyword(s):

Community Structure ◽

Trace Metals ◽

Surface Waters ◽

Oxygen Minimum Zones ◽

Carbon And Nitrogen ◽

Shelf Sediments ◽

Minimum Zone ◽

Ocean Carbon ◽

Shelf Region ◽

Oxygen Minimum

Abstract. The availability of the micronutrient iron (Fe) in surface waters determines primary production, N2 fixation and microbial community structure in large parts of the world's ocean, and thus plays an important role in ocean carbon and nitrogen cycles. Eastern boundary upwelling systems and the connected oxygen minimum zones (OMZs) are typically associated with elevated concentrations of redox-sensitive trace metals (e.g. Fe, manganese (Mn) and cobalt (Co)), with shelf sediments typically forming a key source. Over the last five decades, an expansion and intensification of OMZs has been observed and this trend is likely to proceed. However, it is unclear how trace metal (TM) distributions and transport are influenced by decreasing oxygen (O2) concentrations. Here we present dissolved (d; 0.2 μm) TM data collected at 7 stations along a 50 km transect in the Mauritanian shelf region. We observed enhanced concentrations of Fe, Co and Mn corresponding with low O2 concentrations (

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