Increased Oxygen Levels Research Articles

The breath of life — did increased oxygen levels trigger the Cambrian explosion?

The breath of life — did increased oxygen levels trigger the Cambrian explosion?

Oxidation subscale of γ-titanium aluminide

The subscale formed during high temperature rapid oxidation of γ-titanium aluminum is revealed by transmission electron microscopy and microanalysis to consist of two phases: one hexagonal with unit cell dimensions a = 0.58nm, c = 0.47nm (±0.005nm), and a composition close to Ti 6Al 3O 4; the other simple cubic with a = 0.69nm (±0.005nm) and composition of Ti 3Al 2O 3, with oxygen concentration known to about 10% accuracy. The results strongly suggest that the hexagonal phase is a solid solution of O in Ti 3Al, while the cubic phase is a novel ternary compound with space group P4 232. These subscale phases exhibit some tendency for a crystallographic orientation relationship with (110) cubic//(01 1 0) hexagonal and [0 1 1] cubic//[ 2 112] hexagonal, and the hexagonal phase is less stable than the cubic phase as the distance to the sample surface decreases and oxygen level increases.

Pelagic and benthic ecology of the lower interface of the Eastern Tropical Pacific oxygen minimum zone

The distributions of pelagic and benthic fauna were examined in relation to the lower boundary of the oxygen minimum zone (OMZ) on and near Volcano 7, a seamount that penetrates this feature in the Eastern Tropical Pacific. Although the broad, pronounced OMZ in this region is an effective barrier for most zooplankton, zooplankton abundances, zooplankton feeding rates, and ambient suspended particulate organic carbon (POC) peaked sharply in the lower OMZ (about 740–800 m), in association with the minimum oxygen concentration and the increasing oxygen levels just below it. Zooplankton in the lower OMZ were also larger in size, and the pelagic community included some very abundant, possibly opportunistic, species. Elevated POC and scatter in the light transmission data suggested the existence of a thin, particle-rich, and carbon-rich pelagic layer at the base of the OMZ. Gut contents of planktonic detrifvores implied opportunistic ingestion of bacterial aggregates, possibly from this layer. Benthic megafaunal abundances on the seamount, which extended up to 730 m, peaked at about 800 m. There was a consistent vertical progression in the depth of first occurrence of different megafaunal taxa in this depth range, similar to intertidal zonation. Although the vertical gradients of temperature, salinity, and oxygen were gradual at the lower OMZ interface (in contrast to the upper OMZ interface at the thermocline), temporal variability in oxygen levels due to internal wave-induced vertical excursions of the OMZ may produce the distinct zonation in the benthic fauna. The characteristics of the lower OMZ interface result from biological interactions with the chemical and organic matter gradients of the OMZ. Most zooplankton are probably excluded physiologically from pronounced OMZs. The zooplankton abundance peak at the lower interface of the OMZ occurs where oxygen becomes sufficiently high to permit the zooplankton to utilize the high concentrations of organic particles that have descended through the OMZ relatively unaltered because of low metazoan abundance. A similar scenario applies to megabenthic distributions. Plankton layers and a potential short food chain (bacteria to zooplankton) at OMZ interfaces suggest intense utilization and modification of organic material, localized within a thin midwater depth zone. This could be a potentially significant filter for organic material sinking to the deep-sea floor.

Tectonic control on sedimentary evolution of three North Atlantic borderland Mesozoic basins1

AbstractMultiple episodes of extensional tectonism dominated the formation of Mesozoic fault‐bounded basins on the Grand Banks of Newfoundland, the Irish Continental Shelf and the central North Sea. A range of structural and stratigraphic responses in the Jeanne d'Arc, Porcupine and Moray Firth basins support widespread synchronous tectonic controls on sedimentation during one of these episodes, the Late Cimmerian.Rifting was preceded by a phase of related tectonism during which subsidence rates began to vary across broad areas but without significant fault block rotation. This Late Cimmerian ‘onset warp’ pattern of subsidence is considered to have been essential in the establishment of restricted anoxic basins from latest Oxfordian through Kimmeridgian (sensu gallico) time and the development of one prolific layer of organic‐rich source rocks.The most prominent and widely recognized structural/lithostratigraphic response to Late Cimmerian rifting was the deposition of sediment wedges. Tithonian to early Valanginian strata generally thicken‐ into northerly trending faults in the Jeanne d'Arc and Porcupine basins, indicating that extensional stress was orientated WNW‐ESE across a very broad area. The misalignment of this regional Late Cimmerian extensional stress with local inherited structural fabric may be responsible for transpressional uplift of individual fault blocks in the Outer Moray Firth basin.Sedimentological responses to Late Cimmerian rifting were varied, though a common lithofacies stacking pattern is recognized. Variably thick conglomerates and/or sandstones were widely deposited at the start of rift deformation, while palaeoenvironments ranged from alluvial and braid plain to submarine fan even within individual basins. The relatively coarse basal sediments fine upwards into a second layer of commonly organic‐rich shales and mark The widest variations in palaeoenvironments and sediment thicknesses occurred during the last phase of Late Cimmerian rift tectonism, though all three basins show evidence of decreasing water depths, increasing oxygen levels and increasing grain size. This lithofacies stacking pattern of relatively coarse to fine to coarse (reservoir/source/reservoir) and the development of bounding unconformities are largely attributable to progressive changes in rift‐controlled subsidence. Rift basin subsidence rates are interpreted to increase from a low at initiation of faulting to a mid‐rift peak, followed by slowing subsidence to the end of extension. A number of counteracting crustal mechanisms that may account for progressive variations in rift‐induced subsidence are considered.

Regulation of blue-light-induced proton pumping by Vicia faba L. guard-cell protoplasts: Energetic contributions by chloroplastic and mitochondrial activities

An initial response during signal transduction in guard cells, following absorption of blue light, is the extrusion of protons. Translocation of protons across the guard-cell plasmalemma is an energy-requiring activity. The present study has investigated the energetic contribution from guard-cell chloroplasts and mitochondria to blue-light-induced proton pumping by Vicia faba guard-cell protoplasts. The addition of 3(3,4-dichlorophenyl)-1,1-dimethylurea to the protoplast suspension had a minimal effect on rates of acidification when oxygen concentrations of the medium were maintained close to near-saturating levels. Under the same conditions, oligomycin reduced both the rates of blue-light-induced acidification and total proton efflux. Lowering the oxygen concentration of the suspending medium to approximately 20 μM resulted in complete inhibition of blue-light-induced acidification activity. Swelling of protoplasts induced by blue light was also inhibited by low oxygen levels. Levels of ATP from whole-protoplast extracts were reduced by about 64% when exposed to low levels of oxygen. Increasing oxygen levels to near-saturating levels restored both blue-light-induced acidification rates and swelling of the protoplasts within a 60-min recovery period. Levels of ATP also increased during the recovery period. Addition of 3(3,4-dichlorophenyl)-1,1-dimethylurea or oligomycin to the suspending medium prior to increasing the oxygen concentration caused a reduction in acidification rates after the recovery period by 40 and 80%, respectively. Levels of ATP in guard-cell protoplasts were also reduced by both inhibitors after a 60-min recovery period. The results demonstrate that both guard-cell chloroplasts and mitochondria contribute energetically to blue-light-induced proton pumping by guard-cell protoplasts. Furthermore, both energy sources are inhibited by low oxygen concentrations, suggesting coordinated metabolic regulation between photo- and oxidative phosphorylation in guard cells.

Thromboxane A2 analogue, U-46619, potentiates calcium-activated force in human umbilical artery

It has previously been shown that human umbilical artery (HUA) smooth muscle produces thromboxane A2 in response to increasing oxygen levels and that this thromboxane promotes contraction. To investigate the intracellular action of thromboxane A2, strips of HUA longitudinal smooth muscle were permeabilized using alpha-toxin from the bacterium Staphylococcus aureus. This treatment rendered the surface membrane permeable to low-molecular-weight substances but left functional thromboxane A2 receptors. Tension measurements were used to investigate the effect of the stable thromboxane A2 analogue, U-46619, on the Ca2+ sensitivity of smooth muscle contractile proteins. U-46619 (1 nM to 1 microM) potentiated submaximal Ca(2+)-activated force (generated by [Ca2+], 50 nM to 3 microM) but not maximal Ca(2+)-activated force (generated by [Ca2+], 10-100 microM). The specific thromboxane A2 receptor antagonist, GR-32191B (1 microM), inhibited the action of U-46619 (0.1 microM). The potentiation of submaximal Ca(2+)-activated force produced by the muscle in response to U-46619 (0.1 microM) was antagonized by guanosine 5'-O-(2-thiodiphosphate) (1 mM), the nonhydrolyzable analogue of GDP, and mimicked by guanosine 5'-O-(3-thiotriphosphate) (100 microM), the nonhydrolyzable analogue of GTP. These results suggest that U-46619 acts via the previously identified thromboxane A2 receptor to promote Ca2+ sensitivity of tension production in HUA smooth muscle. Furthermore, this effect appears to be mediated via a G protein.

Roles of Buffering Capacity and Pentose Phosphate Pathway Activity in the Gas Gland of the Gulf Toadfish Opsanus Beta

ABSTRACT The teleost gas gland is truly remarkable in its abilities to secrete gases into the swim bladder of physoclistous fish. The physiological and metabolic adaptations of this tissue have been elegantly summarized in a recent review article by Pelster and Scheid (1992). There are two key contributors to the function of the gland. First, a specialized metabolism of the swim bladder, involving copious and simultaneous production of lactate and CO2 from anaerobic glycolysis and the pentose phosphate pathway (also known as the hexose monophosphate shunt), respectively, contributes to gas exchange through pH and salting-out effects on the oxygen-carrying capacity of the blood. Second, a countercurrent multiplier system (i.e. a rete mirabile) enables gas tensions to be elevated further by back diffusion. Several features of metabolism and acid–base physiology remain unclear. First, despite the remarkable ability of this tissue to produce acid, it is not clear if or how intracellular pH (pHi) is regulated. Since ultimately the blood must be acidified, one would predict that the pHi of the tissue would be well regulated via high rates of membrane exchange of protons and/or high tissue buffering capacity. Second, although the functioning of the pentose phosphate pathway has been strongly inferred from measurements of enzyme activities (Boström et al. 1972; Pelster and Scheid, 1991), and from measurements of enhanced rates of CO2 excretion relative to the rates of oxygen uptake (Pelster et al. 1989), direct evidence for the existence of the shunt is lacking. Lastly, although the pentose phosphate pathway is expected to produce CO2, and thus contribute to the acidification of blood entering the gland, the pathway may have a different primary, or perhaps a dual, role, namely to maintain high tissue levels of NADPH for protection against oxygen radical damage to cells (Pelster and Scheid, 1992). The composition of the gas stored in the swim bladder can approach pure oxygen in some species, so it is not surprising that the teleost gas gland contains substantial levels of the enzymes catalase, superoxide dismutase and glutathione peroxidase, which scavenge deleterious radicals of oxygen and related harmful compounds (Morris and Albright, 1984). Noteworthy is glutathione peroxidase, which requires a constant supply of NADPH (presumably from the shunt) to maintain glutathione in a reduced state. Reduced glutathione is then used in a variety of oxygen radical detoxification mechanisms. If the pentose phosphate pathway has a role in oxygen detoxification, one would predict that flux rates through the pathway would increase with increased oxygen levels.

The Effect of Adventitious Oxygen on Nitrogen Inerted IR Reflow Soldering with Low Residue Pastes

The benefits of Nitraclean I nitrogen inerted reflow soldering are well documented. However, there has been some debate as to the maximum oxygen level that can be tolerated by different types of paste if those benefits are to be realised. It is demonstrated that, for all paste types, solder balls decrease and the spread factor increases with increasing oxygen level, but that it has little effect on either joint strength or microstructure. It is concluded that for RMApastes a maximum oxygen level of 1000 ppm is required and that for low residue pastes the level needs to be reduced to 200 ppm for optimum results.

Acute toxicity of ammonia to juvenile gilthead seabream Sparus aurata under reduced oxygen levels

The effect of dissolved oxygen concentration on the toxicity of ammonia to juvenile (0.4–3.2 g) gilthead seabream ( Sparus aurata) was studied. The mean 96-h LC50 value of ammonia was 23.7 mg/l total ammonia-N (19.3–28.7, 95% C.L.; equivalent to 1.27 mg/l NH 3-N). By comparison, S. aurata is somewhat less sensitive to ammonia than salmonids and similar in sensitivity to nonsalmonids. Increased toxicity of ammonia was observed with decreasing oxygen level. Our data suggest that below a threshold of approximately 40% D.O. saturation, the response of S. aurata to ammonia is no longer linear. Under reduced oxygen level most of the mortality occurs within a few hours, apparently as a consequence of an additive toxic effect. No evidence of pathological changes was found in the gills, liver and kidneys of fish with lost equilibrium in the presence of added ammonia. Acutely toxic conditions for S. aurata may prevail in medium-flow systems (2–6 kg fish/m 2 and 50% total daily water exchange) where oxygen and ammonia levels are influenced by microbial and algal activities. In such systems, ammonia toxicity may increase as a result of increasing ammonia levels and decreasing oxygen concentration following crashes of phytoplankton populations. In high-flow systems typical of most hatchery and nursery tanks as well as some grow-out ponds, it is likely that the chronic effects of ammonia toxicity will be more important than the acute ones. The data suggest that increasing oxygen level by aeration is sufficient to reduce acute ammonia toxicity under certain situations.

Gas Transfer Kinetics in Oxygen Activated Sludge

The validity of a dynamic model based on the two‐film theory is examined for predicting gas transfer in an oxygen system using surface mixers. Model predictions are compared to field measurements taken from a four stage, closed‐tank carbonaceous reactor at the City of Houston, Texas, 69th Street Complex. A liquid film limited model is found to be effective in predicting gas and liquid phase composition although direct interfacial transfer increased the overall oxygen transfer rate. DO predictions were best when using a linear relationship between the KLa for oxygen and the oxygen uptake rate. Carbon dioxide and nitrogen levels were adequately predicted using constant values for KLa, but the model was not sensitive to changes above 50% of the estimated KLa values. Leaks through cracks in the concrete tank cover had little effect on the gas phase composition in the first two stages, however, fourth stage leaks and intentional venting resulted in increased oxygen levels as nitrogen was displaced from the gas phase. Carbon dioxide levels were not appreciably affected by leaks or venting.

Regulation des mikrobiellen stickstoff-metabolismus durch Sauerstoff

Oxygen is one of the most important environmental factors for microorganisms. Many metabolic reactions of aerobic or facultative anaerobic bacteria are influenced by varying oxygen concentrations. A lot of enzyme reactions in respiration processes, catabolism, anabolism and gene expression depend upon oxygen. Other enzymes such as nitrogenase or hydrogenases can be inhibited by increasing oxygen levels. Also complex metabolic processes including anaerobic respiration and fermentations are regulated by oxygen. Finally toxic oxygen derivatives have to be eliminated by living cells to overcome damage of cell constituents. In this way also bacteria which are included into the nitrogen cycle in the nature are influenced by oxygen. The different strategies of microorganisms to protect their nitrogenases for oxygen inactivation and the regulation of dissimilative nitrate reduction by oxygen are demonstrated in detail.

Oxygen ingress into geothermal steam and its effect on corrosion of low carbon steel at Broadlands, New Zealand

Oxygen injected into high pressure (650 kPa) geothermal steam containing high H 2S levels drastically increased the corrosion rate of carbon steel. At increasing oxygen levels, formerly protective scales were replaced by semi-protective corrosion products identified as pyrrhotite, marcasite, pyrite and magnetite. Corrosometer probes were used to determine corrosion rates, but hydrogen probes and chemical analysis were also employed to diagnose corrosion mechanisms. Oxygen appeared to act as a cathodic depolarizer in addition to its oxidizing action on hydrogen sulphide to S, H 2O, SO 4 2− and polysulphides.

粗銅の陽極溶解活性に及ぼす含有酸素量の影響

A study was done by means of an electrochemical technique to determine how anode oxygen affects the dissolution activity during electrorefining of copper anodes.One particular anode material was remelted, and spiked with a wide range of oxygen levels. This set of copper anodes was used to investigate the dissolution characteristics by comparing pairameters such as critical anode current density, activation energy and i-t decay curve which were measured both at a fresh and aged surface.The results obtained have shown that, 1) Increasing oxygen level in the copper anodes initially results in an enhancement in the dissolution activity. This beneficial effect, however, is only so when the surface is fresh, and becomes counteracted soon by a layer of anode slimes which tends to grow thicker and denser with increasing oxygen level.2) When oxygen content increases in a copper anode which already contains a high nickel level, the tendency of this anode to passivate increases drastically. This is due to the formation of refractory NiO during anode casting making the slime layer denser and more restrictive to the mass transport of Cu2+ ions away from the surface of a corroding anode.

Field and Experimental Studies on the Effects of a power station effluent on tubificidae (Oligochaeta, Annelida)

1. Higher numbers of sexually mature worms of L. hoffmeisteri were found in the River Trent downstream from Drakelow Power Stations than upstream. 2. The condenser effluent from the power stations not only increased the temperature of the river but also produced a considerable increase in the concentration of dissolved oxygen. 3. Experiments were therefore carried out on the effects of these two variables on the reproductive rate of the worms. 4. In these experiments it was found that: (a) L. hoffmeisteri increased its rate of egg production with increase in temperature up to about 25°C while T. tubifex maintained a fairly steady rate of egg production over a range of temperatures from 10–25°C. (b) L. hoffmeisteri maintained a fairly steady rate of egg and cocoon production over a wide range of oxygen concentrations above 2 ppm. 5. Therefore it seems likely that the difference between the numbers of sexually mature L. hoffmeisteri upstream and downstream from the power station were influenced more by the increased temperature, than the increased oxygen levels of the power station effluent, though under extreme conditions of deoxygenation, aeration of the river by the cooling towers at the power stations could increase the abundance of this species.

Effect of Hypoxia and Hypercapnia Alone and in Combination upon the Circulating Red Cell Volume of Rats

SummaryThree groups of 50 rats each were exposed for periods of up to 24 days to either hypoxia (70 Torr PIO2), hypercapnia (140 Torr PIO2, 60 Torr PICO2), or a combination of this level of hypoxia and hypercapnia.The combined condition resulted in a much smaller rise in circulating red cell volume per body weight than in rats exposed to hypoxia alone. The increase that did occur could be mainly attributed to a release of stored red cells into the circulation. During hypercapnia, plasma volume increased with only small changes in numbers of circulating red cells. This resulted in a depression of hematocrit.It is still not clear whether concomitant hypercapnia increased oxygen levels in the hypoxic-hypercapnic rats sufficiently to remove the erythropoietic stimulus, or if CO2 actually inhibited erythropoiesis.

Composition of Some Plants Eaten by Deer in the Black Hills of South Dakota

two-fold increase in transparency of the water in addition to an increase in oxygen levels at cooler strata. The resulting clearer waters makes possible the capture of more energy, therefore increasing general lake productivity. The production of fish can thus be raised by increasing the volume of the trophogenic zone by a relatively inexpensive procedure. Specifications and method of application of the chemical are described.