scholarly journals Interannual variation in summer N<sub>2</sub>O concentration in the hypoxic region of the northern Gulf of Mexico, 1985–2007

2013 ◽  
Vol 10 (11) ◽  
pp. 6783-6792 ◽  
Author(s):  
I.-N. Kim ◽  
K. Lee ◽  
H. W. Bange ◽  
A. M. Macdonald
Keyword(s):  
Nitrous Oxide ◽  
Gulf Of Mexico ◽  
Interannual Variation ◽  
Bottom Water ◽  
Areal Extent ◽  
Low Oxygen ◽  
N2o Production ◽  
Northern Gulf Of Mexico ◽  
The Mean ◽  
Stressed Region

Abstract. Microbial nitrous oxide (N2O) production in the ocean is enhanced under low-oxygen (O2) conditions. This is especially important in the context of increasing hypoxia (i.e., oceanic zones with extremely reduced O2 concentrations). Here, we present a study on the interannual variation in summertime nitrous oxide (N2O) concentrations in the bottom waters of the northern Gulf of Mexico (nGOM), which is well-known as the site of the second largest seasonally occurring hypoxic zone worldwide. To this end we developed a simple model that computes bottom-water N2O concentrations with a tri-linear ΔN2O/O2 relationship based on water-column O2 concentrations, derived from summer (July) Texas–Louisiana shelf-wide hydrographic data between 1985 and 2007. ΔN2O (i.e., excess N2O) was computed including nitrification and denitrification as the major microbial production and consumption pathways of N2O. The mean modeled bottom-water N2O concentration for July in the nGOM was 14.5 ± 2.3 nmol L−1 (min: 11.0 ± 4.5 nmol L−1 in 2000 and max: 20.6 ± 11.3 nmol L−1 in 2002). The mean bottom-water N2O concentrations were significantly correlated with the areal extent of hypoxia in the nGOM. Our modeling analysis indicates that the nGOM is a persistent summer source of N2O, and nitrification is dominating N2O production in this region. Based on the ongoing increase in the areal extent of hypoxia in the nGOM, we conclude that N2O production (and its subsequent emissions) from this environmentally stressed region will probably continue to increase into the future.

scholarly journals Interannual variation in summer N<sub>2</sub>O concentration in the hypoxic region of the northern Gulf of Mexico, 1985–2007

2013 ◽  
Vol 10 (4) ◽  
pp. 6315-6334
Author(s):  
I.-N. Kim ◽  
K. Lee ◽  
H. W. Bange ◽  
A. M. Macdonald
Keyword(s):  
Gulf Of Mexico ◽  
N2o Emission ◽  
Areal Extent ◽  
Northern Gulf Of Mexico ◽  
Hypoxic Zone ◽  
Modeling Analysis ◽  
Bottom Waters ◽  
The Mean ◽  
Global Increase ◽  
Stressed Region

Abstract. We present evidence of temporal variation in nitrous oxide (N2O) concentrations in the bottom waters of the northern Gulf of Mexico (nGOM) hypoxic zone. The analysis is based on a conceptual model simulating N2O biogeochemical processes in conjunction with water-column O2 levels, derived from summer Texas–Louisiana shelf-wide hydrographic data for twenty Julys between 1985 and 2007. The mean modeled nGOM N2O concentration was 7.7 &amp;pm; 6.7 nmol L−1, and was significantly correlated with the areal extent of hypoxia. Our modeling analysis indicates that the nGOM is a persistent summer source of N2O, and nitrification is a primary factor leading to its production in this region. Based on the ongoing increase in the areal extent of hypoxia in the nGOM, we conclude that N2O emission from this environmentally stressed region will continue to increase into the future contributing to the global increase in greenhouse gases.

Performance of an Ocean Buoyancy Glider in a Coastal Region: Application to the Gulf of Mexico Hypoxic Zone

2017 ◽  
Vol 51 (4) ◽  
pp. 41-51
Author(s):  
Elizabeth Ramey ◽  
Steven F. DiMarco ◽  
Karen Dreger ◽  
Heather M. Zimmerle
Keyword(s):  
Gulf Of Mexico ◽  
Action Plan ◽  
Coastal Region ◽  
Ocean Bottom ◽  
Low Oxygen ◽  
Northern Gulf Of Mexico ◽  
Hypoxic Zone ◽  
Horizontal Stratification ◽  
Oxygen Conditions ◽  
Oil Gas

AbstractThe Gulf of Mexico Coastal Hypoxia Glider Experiment was designed to assess the feasibility of using ocean glider technology in the coastal hypoxic zone of the northern Gulf of Mexico in Summer/Fall 2014. The objectives were (1) to coordinate and operate multiple autonomous buoyancy ocean gliders in depths less than 50 m and (2) to determine how close to the bottom gliders can reliably reach without making contact. Strong vertical and horizontal stratification gradients, strong coastal currents, and the low-oxygen conditions that occur within the lower water column characterize the coastal area of the northern Gulf of Mexico. These environmental conditions combine with the presence of more than 5,000 surface piercing oil/gas structures to make piloting and navigation in the region challenging. We quantify glider performance to assess the usefulness of buoyancy gliders to address the National Oceanic and Atmospheric Administration Action Plan goal to monitor the spatial extent, duration, and severity of the Gulf hypoxic zone. We find that the gliders, despite the operational challenges, were consistently able to travel from the surface to the oxygen-depleted depths of subpycnocline waters, that is, within 2 m of the ocean bottom. Our assessment is that gliders are able to provide real-time observations suitable to monitor coastal hypoxia.

scholarly journals Benthic Respiration in Hypoxic Waters Enhances Bottom Water Acidification in the Northern Gulf of Mexico

2020 ◽  
Vol 125 (10) ◽  
Author(s):  
Hongjie Wang ◽  
John Lehrter ◽  
Kanchan Maiti ◽  
Katja Fennel ◽  
Arnaud Laurent ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Bottom Water ◽  
Water Acidification ◽  
Northern Gulf Of Mexico ◽  
Benthic Respiration

Denitrification Dominates Sediment Nitrogen Removal and Is Enhanced by Bottom-Water Hypoxia in the Northern Gulf of Mexico

2015 ◽  
Vol 38 (6) ◽  
pp. 2279-2294 ◽  
Author(s):  
Mark J. McCarthy ◽  
Silvia E. Newell ◽  
Stephen A. Carini ◽  
Wayne S. Gardner
Keyword(s):  
Gulf Of Mexico ◽  
Nitrogen Removal ◽  
Bottom Water ◽  
Northern Gulf Of Mexico

scholarly journals Nitrous oxide dynamics in low oxygen regions of the Pacific: insights from the MEMENTO database

2012 ◽  
Vol 9 (12) ◽  
pp. 5007-5022 ◽  
Author(s):  
L. M. Zamora ◽  
A. Oschlies ◽  
H. W. Bange ◽  
K. B. Huebert ◽  
J. D. Craig ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
N2o Emissions ◽  
Low Oxygen ◽  
N2o Production ◽  
Oxygen Minimum Zones ◽  
A Value ◽  
The Pacific ◽  
Production And Consumption ◽  
The Relationship ◽  
Oxygen Minimum

Abstract. The eastern tropical Pacific (ETP) is believed to be one of the largest marine sources of the greenhouse gas nitrous oxide (N2O). Future N2O emissions from the ETP are highly uncertain because oxygen minimum zones are expected to expand, affecting both regional production and consumption of N2O. Here we assess three primary uncertainties in how N2O may respond to changing O2 levels: (1) the relationship between N2O production and O2 (is it linear or exponential at low O2 concentrations?), (2) the cutoff point at which net N2O production switches to net N2O consumption (uncertainties in this parameterisation can lead to differences in model ETP N2O concentrations of more than 20%), and (3) the rate of net N2O consumption at low O2. Based on the MEMENTO database, which is the largest N2O dataset currently available, we find that N2O production in the ETP increases linearly rather than exponentially with decreasing O2. Additionally, net N2O consumption switches to net N2O production at ~ 10 μM O2, a value in line with recent studies that suggest consumption occurs on a larger scale than previously thought. N2O consumption is on the order of 0.01–1 mmol N2O m−3 yr−1 in the Peru-Chile Undercurrent. Based on these findings, it appears that recent studies substantially overestimated N2O production in the ETP. In light of expected deoxygenation and the higher than previously expected point at which net N2O production switches to consumption, there is enough uncertainty in future N2O production that even the sign of future changes is still unclear.

scholarly journals Trends in summer bottom-water temperatures on the northern Gulf of Mexico continental shelf from 1985 to 2015

PLoS ONE ◽  
2017 ◽  
Vol 12 (9) ◽  
pp. e0184350 ◽  
Author(s):  
R. Eugene Turner ◽  
Nancy N. Rabalais ◽  
Dubravko Justić
Keyword(s):  
Gulf Of Mexico ◽  
Continental Shelf ◽  
Bottom Water ◽  
Northern Gulf Of Mexico

scholarly journals Year-round N<sub>2</sub>O production by benthic NO<sub>x</sub> reduction in a monomictic south-alpine lake

2013 ◽  
Vol 10 (12) ◽  
pp. 8373-8383 ◽  
Author(s):  
C. V. Freymond ◽  
C. B. Wenk ◽  
C. H. Frame ◽  
M. F. Lehmann
Keyword(s):  
Bottom Water ◽  
Significant Source ◽  
Ammonium Oxidation ◽  
Low Oxygen ◽  
Production Rates ◽  
Overlying Water ◽  
N2o Production ◽  
Water Column Stratification ◽  
Nitrifier Denitrification ◽  
N2o Fluxes

Abstract. Nitrous oxide (N2O) is a potent greenhouse gas, generated through microbial nitrogen (N) turnover processes, such as nitrification, nitrifier denitrification, and denitrification. Previous studies quantifying natural sources have mainly focused on soils and the ocean, but the potential role of terrestrial water bodies in the global N2O budget has been widely neglected. Furthermore, the biogeochemical controls on the production rates and the microbial pathways that produce benthic N2O in lakes are essentially unknown. In this study, benthic N2O fluxes and the contributions of the microbial pathways that produce N2O were assessed using 15N label flow-through sediment incubations in the eutrophic, monomictic south basin of Lake Lugano in Switzerland. The sediments were a significant source of N2O throughout the year, with production rates ranging between 140 and 2605 nmol N2O h−1 m−2, and the highest observed rates coinciding with periods of water column stratification and stably anoxic conditions in the overlying bottom water. Nitrate (NO3−) reduction via denitrification was found to be the major N2O production pathway in the sediments under both oxygen-depleted and oxygen-replete conditions in the overlying water, while ammonium oxidation did not contribute significantly to the benthic N2O flux. A marked portion (up to 15%) of the total NO3− consumed by denitrification was reduced only to N2O, without complete denitrification to N2. These fluxes were highest when the bottom water had stabilized to a low-oxygen state, in contrast with the notion that stable anoxia is particularly conducive to complete denitrification without accumulation of N2O. This study provides evidence that lake sediments are a significant source of N2O to the overlying water and may produce large N2O fluxes to the atmosphere during seasonal mixing events.

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