The last 1000 years of natural and anthropogenic low-oxygen bottom-water on the Louisiana shelf, Gulf of Mexico

2008 ◽  
Vol 66 (3-4) ◽  
pp. 291-303 ◽  
Author(s):  
L.E. Osterman ◽  
R.Z. Poore ◽  
P.W. Swarzenski
Keyword(s):  
Gulf Of Mexico ◽  
Bottom Water ◽  
Low Oxygen ◽  
Louisiana Shelf

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 Live foraminiferal faunas (Rose Bengal stained) from the northern Arabian Sea: links with bottom-water oxygenation

2013 ◽  
Vol 10 (9) ◽  
pp. 15257-15304 ◽  
Author(s):  
C. Caulle ◽  
K. A. Koho ◽  
M. Mojtahid ◽  
G. J. Reichart ◽  
F. J. Jorissen
Keyword(s):  
Rose Bengal ◽  
Arabian Sea ◽  
Bottom Water ◽  
Principal Component ◽  
Environmental Parameters ◽  
Low Oxygen ◽  
The Core ◽  
Northern Arabian Sea ◽  
Transitional Group ◽  
Epistominella Exigua

Abstract. Live (Rose Bengal stained) benthic foraminifera from the Murray Ridge, within and below the northern Arabian Sea Oxygen Minimum Zone (OMZ), were studied in order to determine the relationship between faunal composition, bottom-water oxygenation (BWO), pore-water chemistry and organic matter (organic carbon and phytopigment) distribution. A series of multicores were recovered from a ten-station oxygen (BWO: 2–78 μM) and bathymetric (885–3010 m depth) transect during the winter monsoon in January 2009. Foraminifera were investigated from three different size fractions (63–125 μm, 125–150 μm and > 150 μm). The larger foraminifera (> 125 μm) were strongly dominated by agglutinated species (e.g. Reophax spp.). In contrast, in the 63–125 μm fraction, calcareous taxa were more abundant, especially in the core of the OMZ, suggesting an opportunistic behaviour. On the basis of a Principal Component Analysis, three foraminiferal groups were identified, reflecting the environmental parameters along the study transect. The faunas from the shallowest stations, in the core of the OMZ (BWO: 2 μM), were composed of "low oxygen" species, typical of the Arabian Sea OMZ (e.g., Rotaliatinopsis semiinvoluta, Praeglobobulimina spp. , Bulimina exilis, Uvigerina peregrina typeparva). These taxa are adapted to the very low BWO conditions and to high phytodetritus supplies. The transitional group, typical for the lower part of the OMZ (BWO: 5–16 μM), is composed of more cosmopolitan taxa tolerant to low-oxygen concentrations (Globocassidulina subglobosa, Ehrenbergina trigona). Below the OMZ (BWO: 26–78 μM), where food availability is more limited and becomes increasingly restricted to surficial sediments, more cosmopolitan calcareous taxa were present, such as Bulimina aculeata, Melonis barleeanus, Uvigerina peregrina and Epistominella exigua. Miliolids were uniquely observed in this last group, reflecting the higher BWO. At these deeper sites, the faunas exhibit a clear depth succession of superficial, intermediate and deep-infaunal microhabitats, because of the deeper oxygen and nitrate penetration into the sediment.

scholarly journals Correlation of <i>Virgulinella fragilis</i> Grindell & Collen (benthic foraminiferid) with near-anoxia in Aso-kai Lagoon, central Japan

2005 ◽  
Vol 24 (2) ◽  
pp. 159-167 ◽  
Author(s):  
Hiroyuki Takata ◽  
Koji Seto ◽  
Saburo Sakai ◽  
Satoshi Tanaka ◽  
Katsumi Takayasu
Keyword(s):  
Cluster Analysis ◽  
Pore Water ◽  
Coastal Lagoon ◽  
Bottom Water ◽  
Low Oxygen ◽  
Central Japan ◽  
Reactive Iron ◽  
Predominant Species ◽  
Oxygen Conditions ◽  
Cluster A

Abstract. The distribution of Virgulinella fragilis and the hydro-environment of Aso-kai Lagoon, central Japan, were studied to clarify the foraminifer’s adaptation to low-oxygen conditions. The hypolimnion of the lagoon is oxygen-poor during much of the year. Two faunas (A and B) are recognized, based on cluster analysis. Cluster A fauna consists of species common in brackish lagoons, such as the genera Trochammina and Ammonia, and occurs in seasonally oxygenated waters. Virgulinella fragilis, the predominant species of Cluster B fauna, dominates the central part of the lagoon. This species can tolerate more severe oxygen deficiencies than the typical brackish foraminifers (e.g. Trochammina spp.) and can adapt to long periods of oxygen-poor conditions in coastal lagoon environments, as well as in pelagic to hemi-pelagic settings. In order to survive in the near-anoxia of Aso-kai Lagoon, V. fragilis may have adapted to environments in which little reactive iron is available in the sediment, leaving pore-water and bottom-water sulphide available for symbionts, or may utilize sulphur denitrification processes.

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 A comparison of benthic foraminiferal Mn / Ca and sedimentary Mn / Al as proxies of relative bottom-water oxygenation in the low-latitude NE Atlantic upwelling system

2015 ◽  
Vol 12 (18) ◽  
pp. 5415-5428 ◽  
Author(s):  
C. L. McKay ◽  
J. Groeneveld ◽  
H. L. Filipsson ◽  
D. Gallego-Torres ◽  
M. J. Whitehouse ◽  
...  
Keyword(s):  
Inductively Coupled Plasma ◽  
Bottom Water ◽  
Secondary Ion Mass Spectrometry ◽  
Younger Dryas ◽  
Icp Oes ◽  
Low Oxygen ◽  
Ne Atlantic ◽  
Low Latitude ◽  
Upwelling System ◽  
Oxygen Conditions

Abstract. Trace element incorporation into foraminiferal shells (tests) is governed by physical and chemical conditions of the surrounding marine environment, and therefore foraminiferal geochemistry provides a means of palaeo-oceanographic reconstructions. With the availability of high-spatial-resolution instrumentation with high precision, foraminiferal geochemistry has become a major research topic over recent years. However, reconstructions of past bottom-water oxygenation using foraminiferal tests remain in their infancy. In this study we explore the potential of using Mn / Ca determined by secondary ion mass spectrometry (SIMS) as well as by flow-through inductively coupled plasma optical emission spectroscopy (FT-ICP-OES) in the benthic foraminiferal species Eubuliminella exilis as a proxy for recording changes in bottom-water oxygen conditions in the low-latitude NE Atlantic upwelling system. Furthermore, we compare the SIMS and FT-ICP-OES results with published Mn sediment bulk measurements from the same sediment core. This is the first time that benthic foraminiferal Mn / Ca is directly compared with Mn bulk measurements, which largely agree on the former oxygen conditions. Samples were selected to include different productivity regimes related to Marine Isotope Stage 3 (35–28 ka), the Last Glacial Maximum (28–19 ka), Heinrich Event 1 (18–15.5 ka), Bølling Allerød (15.5–13.5 ka) and the Younger Dryas (13.5–11.5 ka). Foraminiferal Mn / Ca determined by SIMS and FT-ICP-OES is comparable. Mn / Ca was higher during periods with high primary productivity, such as during the Younger Dryas, which indicates low-oxygen conditions. This is further supported by the benthic foraminiferal faunal composition. Our results highlight the proxy potential of Mn / Ca in benthic foraminifera from upwelling systems for reconstructing past variations in oxygen conditions of the sea floor environment as well as the need to use it in combination with other proxy records such as faunal assemblage data.

scholarly journals Parameterization of biogeochemical sediment–water fluxes using in situ measurements and a diagenetic model

2016 ◽  
Vol 13 (1) ◽  
pp. 77-94 ◽  
Author(s):  
A. Laurent ◽  
K. Fennel ◽  
R. Wilson ◽  
J. Lehrter ◽  
R. Devereux
Keyword(s):  
Water Column ◽  
Bottom Water ◽  
In Situ Measurements ◽  
Nutrient Loads ◽  
Water Fluxes ◽  
Overlying Water ◽  
Louisiana Shelf ◽  
Biogeochemical Models ◽  
Bottom Waters

Abstract. Diagenetic processes are important drivers of water column biogeochemistry in coastal areas. For example, sediment oxygen consumption can be a significant contributor to oxygen depletion in hypoxic systems, and sediment–water nutrient fluxes support primary productivity in the overlying water column. Moreover, nonlinearities develop between bottom water conditions and sediment–water fluxes due to loss of oxygen-dependent processes in the sediment as oxygen becomes depleted in bottom waters. Yet, sediment–water fluxes of chemical species are often parameterized crudely in coupled physical–biogeochemical models, using simple linear parameterizations that are only poorly constrained by observations. Diagenetic models that represent sediment biogeochemistry are available, but rarely are coupled to water column biogeochemical models because they are computationally expensive. Here, we apply a method that efficiently parameterizes sediment–water fluxes of oxygen, nitrate and ammonium by combining in situ measurements, a diagenetic model and a parameter optimization method. As a proof of concept, we apply this method to the Louisiana Shelf where high primary production, stimulated by excessive nutrient loads from the Mississippi–Atchafalaya River system, promotes the development of hypoxic bottom waters in summer. The parameterized sediment–water fluxes represent nonlinear feedbacks between water column and sediment processes at low bottom water oxygen concentrations, which may persist for long periods (weeks to months) in hypoxic systems such as the Louisiana Shelf. This method can be applied to other systems and is particularly relevant for shallow coastal and estuarine waters where the interaction between sediment and water column is strong and hypoxia is prone to occur due to land-based nutrient loads.

Mesozooplankton community in a seasonally hypoxic and highly eutrophic bay

2015 ◽  
Vol 66 (8) ◽  
pp. 719 ◽  
Author(s):  
Min-Chul Jang ◽  
Kyoungsoon Shin ◽  
Pung-Guk Jang ◽  
Woo-Jin Lee ◽  
Keun-Hyung Choi
Keyword(s):  
High Temperature ◽  
Bottom Water ◽  
Oxygen Solubility ◽  
Low Oxygen ◽  
Negative Effects ◽  
Mesozooplankton Community ◽  
Seawater Chemistry ◽  
Hypoxic Conditions ◽  
Bottom Waters ◽  
Major Factors

A 2-year survey of seawater chemistry and mesozooplankton abundance was carried out in Masan Bay, South Korea, one of the most eutrophic coastal ecosystems known. The study aimed to identify the major factors contributing to the seasonally persistent hypoxia in the bay, to characterise the Bay’s mesozooplankton community and to examine the effects of low oxygen on the distribution of mesozooplankton. Hypoxia (<2mgO2L–1) was present only in summer, with ultrahypoxia (<0.2mg O2 L–1) in the bottom waters of the inner bay in both years. Low summer oxygen can be attributed to high summer phytoplankton stocks, together with reduced oxygen solubility at high temperature and stratification of the water column that limits downward diffusion of oxygen. A seasonally and spatially distinct mesozooplankton community was identified in summer when there was greater influence of freshwater discharge in the inner bay. Marine cladocerans were very abundant, with a population outburst of Penilia avirostris in the inner bay (>4000 individuals m–3) during summer. During hypoxic events, the abundance of Penilia avirostris was positively related to oxygen levels in the bottom water, suggesting that hypoxic conditions may cause mortality or have sublethal negative effects on population growth of this filter-feeding cladoceran.

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

The effect of pressure on rock properties in the Gulf of Mexico: Comparison between compaction disequilibrium and unloading

2014 ◽  
Vol 2 (1) ◽  
pp. SB1-SB15 ◽  
Author(s):  
Hua Yu ◽  
Fred J. Hilterman
Keyword(s):  
Gulf Of Mexico ◽  
Rock Properties ◽  
Louisiana Shelf ◽  
Major Mechanism ◽  
Detailed Evaluation ◽  
Density Values ◽  
Pressure Regime ◽  
Relationship Of ◽  
The Relationship ◽  
Velocity Decrease

We used statistical methods on rock properties derived from more than 480 wells to catalog shale velocity and density trends in different pressure regimes in the Gulf of Mexico and evaluated the reasons for their variations. A detailed evaluation of the density and velocity trends revealed that in the northern part of the Louisiana shelf, unloading is the major mechanism of overpressure. The onset of overpressure occurs at depths around 3000 m where temperatures are normally greater than 70°C. The relationship of the temperature gradient increase and the velocity decrease to the smectite-illite transformation allowed us to believe that inelastic unloading may be the major mechanism for overpressure in this region. On the other hand, in the southern part of the Louisiana shelf, abnormal pore pressure is often caused by compaction disequilibrium where the sediment section has a low sand percentage. In this type of pressure regime, velocity and density values cease to change at the onset of overpressure and essentially remain at the same value below the onset.

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