scholarly journals Fixed nitrogen loss from the eastern tropical North Pacific and Arabian Sea oxygen deficient zones determined from measurements of N 2 :Ar

2012 ◽  
Vol 26 (3) ◽  
Author(s):  
Bonnie X. Chang ◽  
Allan H. Devol ◽  
Steven R. Emerson
Keyword(s):  
North Pacific ◽  
Arabian Sea ◽  
Nitrogen Loss ◽  
Fixed Nitrogen

Expansion of the eastern North Pacific OMZ and the associated denitrification regime

2020 ◽  
Author(s):  
Allan Devol ◽  
Wendi Ruef
Keyword(s):  
Pacific Decadal Oscillation ◽  
North Pacific ◽  
Arabian Sea ◽  
Thermocline Depth ◽  
Fixed Nitrogen ◽  
Potential Density ◽  
Hurricane Intensity ◽  
Oxygen Minimum Zones ◽  
Marine Areas ◽  
Oxygen Minimum

<p> </p><p>At this point ocean deoxygenation is well documented, including in oxygen minimum zones (OMZs).  Within the large OMZs of the Arabian Sea and eastern Pacific are imbedded areas where oxygen concentrations are so low that they are undetectable by routine CTD sensors (oxygen deficient zones, ODZs).  How do we determine if these ODZ are losing O<sub>2</sub>?  Furthermore, denitrification occurs in oxygen minimum zones (OMZs) so one might hypothesize that denitrification is likewise expanding if oxygen is decreasing.  This is important because the ocean's fixed nitrogen inventory limits the productivity over large marine areas.</p><p>We have investigated these questions in the largest OMZ, the eastern tropical North Pacific (ETNP) through an analysis of  6 repeats of a 1000 km transect along 110<sup>o</sup> West in the heart of the ETNP ODZ between 1971-2019.  We use N*, a stoichiometric parameter calculated from nitrate and phosphate, as our indicator of denitrification. The more Negative N* the more denitrification has occurred. After secondary QC the values of O<sub>2</sub> concentration between potential density 24.75 and 1000m along with N* were integrated across the transect and over the depth of the ODZ.  </p><p>The results show a clear decrease in oxygen inventory along with an increase in N*, suggesting deoxygenation and intensification of denitrification over during the 50 year period. We discuss potential mechanisms for denitrification signal increase including ENSO, Pacific Decadal Oscillation, tropical hurricane intensity, and variations in thermocline depth.</p>

The effect of organic carbon on fixed nitrogen loss in the eastern tropical South Pacific and Arabian Sea oxygen deficient zones

2014 ◽  
Vol 59 (4) ◽  
pp. 1267-1274 ◽  
Author(s):  
Bonnie X. Chang ◽  
Jeremy R. Rich ◽  
Amal Jayakumar ◽  
Hema Naik ◽  
Anil K. Pratihary ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Arabian Sea ◽  
Nitrogen Loss ◽  
South Pacific ◽  
Fixed Nitrogen

scholarly journals Microbial niche differentiation explains nitrite oxidation in marine oxygen minimum zones

2021 ◽  
Author(s):  
Xin Sun ◽  
Claudia Frey ◽  
Emilio Garcia-Robledo ◽  
Amal Jayakumar ◽  
Bess B. Ward
Keyword(s):  
Nitrogen Loss ◽  
Niche Differentiation ◽  
Nitrite Reduction ◽  
Nitrite Oxidation ◽  
Fixed Nitrogen ◽  
Anoxic Waters ◽  
Biogeochemical Models ◽  
Nitrite Oxidizing Bacteria ◽  
Oxygen Addition ◽  
Oxygen Minimum

AbstractNitrite is a pivotal component of the marine nitrogen cycle. The fate of nitrite determines the loss or retention of fixed nitrogen, an essential nutrient for all organisms. Loss occurs via anaerobic nitrite reduction to gases during denitrification and anammox, while retention occurs via nitrite oxidation to nitrate. Nitrite oxidation is usually represented in biogeochemical models by one kinetic parameter and one oxygen threshold, below which nitrite oxidation is set to zero. Here we find that the responses of nitrite oxidation to nitrite and oxygen concentrations vary along a redox gradient in a Pacific Ocean oxygen minimum zone, indicating niche differentiation of nitrite-oxidizing assemblages. Notably, we observe the full inhibition of nitrite oxidation by oxygen addition and nitrite oxidation coupled with nitrogen loss in the absence of oxygen consumption in samples collected from anoxic waters. Nitrite-oxidizing bacteria, including novel clades with high relative abundance in anoxic depths, were also detected in the same samples. Mechanisms corresponding to niche differentiation of nitrite-oxidizing bacteria across the redox gradient are considered. Implementing these mechanisms in biogeochemical models has a significant effect on the estimated fixed nitrogen budget.

Denitrification as the dominant nitrogen loss process in the Arabian Sea

Nature ◽  
2009 ◽  
Vol 461 (7260) ◽  
pp. 78-81 ◽  
Author(s):  
B. B. Ward ◽  
A. H. Devol ◽  
J. J. Rich ◽  
B. X. Chang ◽  
S. E. Bulow ◽  
...  
Keyword(s):  
Arabian Sea ◽  
Nitrogen Loss ◽  
Loss Process

Denitrification exceeds anammox as a nitrogen loss pathway in the Arabian Sea oxygen minimum zone

2010 ◽  
Vol 57 (3) ◽  
pp. 384-393 ◽  
Author(s):  
Silvia E. Bulow ◽  
Jeremy J. Rich ◽  
Hema S. Naik ◽  
Anil K. Pratihary ◽  
Bess B. Ward
Keyword(s):  
Arabian Sea ◽  
Nitrogen Loss ◽  
Oxygen Minimum Zone ◽  
Minimum Zone ◽  
Oxygen Minimum

scholarly journals Metagenomic analysis of nitrogen and methane cycling in the Arabian Sea oxygen minimum zone

PeerJ ◽  
2016 ◽  
Vol 4 ◽  
pp. e1924 ◽  
Author(s):  
Claudia Lüke ◽  
Daan R. Speth ◽  
Martine A.R. Kox ◽  
Laura Villanueva ◽  
Mike S.M. Jetten
Keyword(s):  
Nitrogen Cycle ◽  
Arabian Sea ◽  
Nitrogen Loss ◽  
Global Ocean ◽  
Ammonium Oxidation ◽  
Active Nitrogen ◽  
Core Zone ◽  
Methane Cycling ◽  
Oxygen Minimum ◽  
Oxygen Concentrations

Oxygen minimum zones (OMZ) are areas in the global ocean where oxygen concentrations drop to below one percent. Low oxygen concentrations allow alternative respiration with nitrate and nitrite as electron acceptor to become prevalent in these areas, making them main contributors to oceanic nitrogen loss. The contribution of anammox and denitrification to nitrogen loss seems to vary in different OMZs. In the Arabian Sea, both processes were reported. Here, we performed a metagenomics study of the upper and core zone of the Arabian Sea OMZ, to provide a comprehensive overview of the genetic potential for nitrogen and methane cycling. We propose that aerobic ammonium oxidation is carried out by a diverse community ofThaumarchaeotain the upper zone of the OMZ, whereas a low diversity ofScalindua-like anammox bacteria contribute significantly to nitrogen loss in the core zone. Aerobic nitrite oxidation in the OMZ seems to be performed byNitrospina spp. and a novel lineage of nitrite oxidizing organisms that is present in roughly equal abundance asNitrospina. Dissimilatory nitrate reduction to ammonia (DNRA) can be carried out by yet unknown microorganisms harbouring a divergentnrfAgene. The metagenomes do not provide conclusive evidence for active methane cycling; however, a low abundance of novel alkane monooxygenase diversity was detected. Taken together, our approach confirmed the genomic potential for an active nitrogen cycle in the Arabian Sea and allowed detection of hitherto overlooked lineages of carbon and nitrogen cycle bacteria.

Isotopic composition of nitrate in the central Arabian Sea and eastern tropical North Pacific: A tracer for mixing and nitrogen cycles

1998 ◽  
Vol 43 (7) ◽  
pp. 1680-1689 ◽  
Author(s):  
Jay A. Brandes ◽  
Allan H. Devol ◽  
T. Yoshinari ◽  
D. A. Jayakumar ◽  
S. W. A. Naqvi
Keyword(s):  
Isotopic Composition ◽  
North Pacific ◽  
Arabian Sea ◽  
Nitrogen Cycles

scholarly journals Impact of deep-water renewal events on fixed nitrogen loss from seasonally-anoxic Saanich Inlet

2010 ◽  
Vol 122 (1-4) ◽  
pp. 1-10 ◽  
Author(s):  
Cara C. Manning ◽  
Roberta C. Hamme ◽  
Annie Bourbonnais
Keyword(s):  
Deep Water ◽  
Nitrogen Loss ◽  
Fixed Nitrogen ◽  
Water Renewal ◽  
Saanich Inlet ◽  
Renewal Events

scholarly journals Benthic Nitrogen Loss in the Arabian Sea Off Pakistan

2012 ◽  
Vol 3 ◽  
Author(s):  
Sarah Sokoll ◽  
Moritz Holtappels ◽  
Phyllis Lam ◽  
Gavin Collins ◽  
Michael Schlüter ◽  
...  
Keyword(s):  
Arabian Sea ◽  
Nitrogen Loss
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