Oxygen-deficient Environments Research Articles

Pseudoplankton: hitch-hikers through time or stuck in the mud?

Pseudoplanktic life modes have typically been invoked to explain the presence of abundant fossils belonging to normally low-oxygen intolerant taxa within oxygen-deficient black shales facies (e.g., bivalves, crinoids, barnacles, serpulid worms, brachiopods, gastropods, bryozoans, foraminifers, corals, hydrozoans, and sponges). The same explanation has been used for exceptional paleobiogeographic distribution of benthic species. However, detailed paleoecologic, population, and taphonomic analyses of numerous black-shale biotas in conjunction with recently published models for oxygen-deficient basins suggests that this hypothesis is no longer required to explain the distribution of these taxa in supposedly non-viable habitats. Actual examples that could be interpreted as evidence for pseudoplanktic life habit (i.e., colonization on both sides of ammonites) are very rare. For example, less than 2% of the encrusted ammonites (N = 1240) in the Jurassic Posidonienschiefer show pseudoplanktic colonization patterns. These could be interpreted as flipped specimens within the benthic zone. The remainder are stable “shell-island” substrates with ammonites (and large bivalve shells) colonized on one side only. Most logs believed to be colonized on the lower surface by bivalves and/or crinoids in floating position actually have evidence for benthic encrustation on the tops and sides of the logs, and have obvious current shadows of dead shells.The data show that: 1) the abundance of these taxa greatly exceeds the expectations of pseudoplanktic rain as well as the number of potential hosts; 2) they commonly occur as short-term event communities rather than as the normal populations expected of continuous pseudoplanktic rain; 3) specimens are commonly found in epibenthic life position; 4) their occurrence patterns show strong facies control usually reflecting benthic oxygen gradients; 5) many preserve a large prodissoconch or protoconch suggesting a long-term planktotrophic larval stage. Most of these “pseudoplanktic” groups appear to have had a benthic life habit.Moreover, most oxygen-deficient environments disappeared by the end of the Cretaceous along with some of the dominant pseudoplanktic taxa. Drifting logs and seaweeds are common today, but generally lack specific “pseudoplanktic” faunas, with the exception of boring bivalves, gooseneck barnacles, serpulid worms, and bryozoans. Epibenthic bivalves and crinoids are very rare to absent on potential “pseudoplanktic” hosts in modern seas, yet are the main groups of organisms designated as pseudoplankton in the fossil record.

Nitrous oxide in the Arabian Sea

Measurements of nitrous oxide (N 2O) at 16 stations in the Arabian Sea reveal high degrees of surface saturation (186 ± 37%) and consequently large atmospheric fluxes of N 2O (4.46 ± 2.60 μmol m −2 day −1). Unusually high for a non-upweling period, these values reflect the large vertical gradients of N 2O just below the mixed layer as the vertical exchange coefficients (0.55 ± 0.32 cm 2 s −1) required to sustain the observed fluxes are not very high. Vertical distribution of N 2O in the Arabian Sea conforms to the trends seen in other oxygen-deficient environments, with minimal values occurring within the secondary nitrite maximum and the maxima in the N 2O profiles located at the peripheries of this layer. Outside the denitrification zone, only one broad maximum is observed at mid-depth. The mechanisms proposed for the production of N 2O are re-evaluated in the light of recent data on the nitrogen isotopic composition of N 2O from the western North Pacific Ocean. It is proposed that a nitrification-denitrification couple represented by the pathway NH 4 + → NO → N 2O may be a potentially dominant mechanism for N 2O production in the ocean. This can explain the observed enrichment of 15N in N 2O as compared to NO 3 − while nitrification or denitrification alone cannot. Appreciable horizontal (east-west) gradients in N 2O concentrations are observed at intermediate depths close to the continental margin off the west coast of India suggesting a possible sink of N 2O within the marginal sediments. The diffusive losses of N 2O to the denitrifying waters and marginal sediments are estimated as >2 Tg N y −1. The Arabian Sea as a whole appears to be a net source of N 2O, suggesting that the gross production of oceanic N 2O h as been underestimated.

About this title

This volume is unique in its consideration of severe oxygen depletion in coastal shelf waters from the perspectives of both marine ecology and geology. Seasonal anoxia is a serious problem in the coastal waters of Europe, North America and Japan. Its drastic impact on environmental quality and on marine inshore fisheries has stimulated intensive research, in particular into the relative roles of biological and meteorological variables and of anthropogenic eutrophication. However, continental shelf anoxia is not a new phenomenon: at many times in the geological past vast areas of extensive shelf seas experienced episodes of severe oxygen depletion that lasted from thousands to millions of years, depositing most of the source beds for the world's hydrocarbon reserves. This fact stimulated intensive research into the sedimentology, palaeoecology and organic and inorganic geochemistry of these sediments. The editors' introductory review highlights the significance of the modern studies for an improved understanding of the ancient oxygen-deficient continental shelf environments. Accounts of modern anoxia are then presented, from areas as diverse as the Gulf of Mexico. New York Bight, Chesape.ake Bay, the Adriatic Sea, SW Africa and Peru-Chile. These are followed by Devonian to Tertiary examples of ancient anoxic facies from the USA, Greenland, Germany, UK, Brazil. France and Hungary. It is hoped that this book will inspire further research into this economically and environmentally important phenomenon.

Doomed pioneers: Gravity-flow deposition and bioturbation in marine oxygen-deficient environments

Isolated horizons of Thalassinoides and Gyrolithes burrows appear in exclusive association with gravity-flow deposits within sequences of nonbioturbated hernipelagic sedimentary rocks of the Miocene Monterey Formation of California and the Oligocene-Miocene San Gregorio Formation of Baja California. These burrowed levels are not associated with other ichnogenera such as Zoophycos and Chondrites . We infer a causal relation between gravity flow deposition and the presence of Thalassinoides and Gyrolithes and suggest that these gravity flows entrained thalassinidean crustacea. Upon deposition in oxygen-deficient environments, the surviving borrowers reworked substantial quantities of aminated, commonly organic-rich sediments in an environment from which they were previously excluded. The persistence of or the ecologically rapid return to oxygen-depleted conditions limited the survival time and ecological complexity of the transported infaunal dwellers and rendered them doomed pioneers. Ecological and physiological data support this hypothesis: thalassinidean crustacea have the capability to endure turbulent transport and survive up to 5-7 days of anoxia without being severely limited in their biological activities. The accurate recognition of doomed pioneer trace-fossil assemblages as ephemeral ecological phenomena in otherwise laminated successions may contribute to a better understanding and interpretation of paleo-oxygen levels and basin history.

Effect of fluctuating rhizosphere redox potential on carbon assimilation ofSpartina alterniflora

Spartina alterniflora Lois. plants from a Louisiana salt marsh were subjected to fluctuating levels of soil redox potential under controlled environmental conditions. The experiment was designed to examine the changes in carbon assimilation rates in response to the change in rhizosphere sediment redox condition representing a broad range of reduction normally associated with oxygen deficient environments. Variation in sediment redox potential is frequently encountered by this species in its natural environment in Louisiana's Gulf Coast marshes as a result of tidal patterns. Results indicated some adverse effects of extreme anoxic conditions on carbon assimilation ofS. alterniflora, a possible reflection of this species limited ability for maintaining root oxygenation under rapid, intense reduction in soil redox potential. It was also demonstrated that gas exchange limitations may be temporary and apparently may follow by some recovery. Carbon assimilation rates declined 15 to 21% when soil redox level decreased rapidly to below-200 mV which was followed by substantial recovery. A system for accurate control and measurement of rhizosphere redox potential and simultaneous measurement of plant photosynthetic activity is described.

Cobalt and copper distributions in the waters of Santa Monica Basin, California

The trace metals cobalt and copper are removed from the oceans interior by scavenging on to particle surfaces1, but the mechanisms for removal of these two metals are probably quite different. Cobalt appears to be scavenged by manganese oxide particles1,2, whereas organic compounds are the main carrier phase for copper3,4. Remobilization of these metals in marine sediments therefore proceeds by different pathways. The differences in the pathways of remobilization are accentuated in oxygen-deficient environments: manganese oxide reduction is accelerated at low oxygen levels5 and organic carbon is preserved6. Cobalt fluxes from sediments underlying oxygen-deficient waters should be enhanced and copper fluxes reduced. We report here measurements of the cobalt and copper distributions in the waters of an oxygen-deficient marine basin in the Southern California Bight. Cobalt concentrations near the bottom are raised four times above the background level, whereas copper concentrations show no increase. These measurements confirm features of existing models for the oceanic cycles of these metals.

Aspects of the biology of Ostertagia ostertagi in relation to the genesis of ostertagiasis

Adaptations such as the capacity of free-living stages to survive environmental stress, inhibition and density-dependent effects on population size and fecundity show O. ostertagi to be a consumate parasite of cattle in temperate environments. Knowledge of these adaptations, within an animal management context, provides the key to understanding the occurence of disease and a basis for control of parasite numbers. Substantial infections do arise from low egg contamination rates of pastures. Discontinuities in rates of infection are caused by poorly predicted seasonal events such as the effects on eggs of oxygen-deficient environments, fluctuating temperatures and the absence of sufficient moisture for migration of infective larvae from faeces to herbage. Time delays of several months between pasture contamination and availability of infection are therefore common. Ingestion of large numbers of larvae, over a short period early in the grazing season, gives rise to Type I disease or subclinical infections which decrease liveweight gains. In some ecotypes, environmentally induced inhibition leads to the accumulation of large populations of early 4th stage parasites within the host. These populations, under poorly defined conditions, can mature synchronously to produce severe diarrhoea, debility and even death in a proportion of mature cattle - the Type II disease.

Interpreting benthic oxygen levels in mudrocks: A new approach

Quantified paleoecology and gamma-ray spectrometry have been applied in the analysis of the Kimmeridge Clay, a highly organic-rich British Jurassic mudrock. Decreasing benthic oxygen trends are reflected in decreasing species richness and dominance-diversity values. Similarly, the degree of fragmentation of the benthos reflects the benthic energy levels and covaries with benthic oxygen. The calculation of authigenic uranium values from data gathered by gamma-ray spectrometry shows enrichment in more oxygen-deficient environments. The good correlation between the independently derived paleoecological and authigenic U data indicates the importance of these techniques in environmental analysis of marine petroleum source rocks.

Safety Precautions for Testing in Confined Spaces

This article discusses the hazards encountered while conducting tests in confined spaces. These hazards include insufficient natural ventilation, oxygen‐deficient environments, and the presence of toxic or flammable gases or vapors. Precautions are listed which will help water utility personnel detect and correct unsafe conditions in manholes and other confined spaces before the conditions become life‐threatening.

Formation of Barite Nodules in Dysaerobic and Anaerobic Zones of Stratified Basins: ABSTRACT

Barite nodules occur at numerous localities in black and gray shale sequences of Ordovician and Devonian age in the Appalachian basin. The nodules occur generally in rocks deposited in oxygen-deficient marine environments: (a) in stratigraphic positions recording dysaerobic bottom conditions and (b) in association with layers containing calcareous and pyritic nodules that formed in anaerobic to dysaerobic zones. The barite nodules do not generally occur in shales representing aerobic environments, and the nodules generally occur in anaerobic shales only in association with carbonate. The barite nodules are in units that probably represent sedimentation during a shallowing pulse following times of maximum transgression. Characteristics of the barite nodules and the surrounding rocks, such as the deformation of laminae in enclosing shales around nodules and the alternation of layers of calcite and barite in some nodules, suggest that the nodules formed during diagenesis when the surrounding rocks were still uncompacted and that they formed in response to fluctuations in chemical conditions. Sulfur and oxygen isotope values for barite nodules have a large range and are considerably heavier than values of coeval seawater. The enrichment of heavy isotopes may have occurred as the result of nodule formation at interfaces where rates of sedimentationmore » were slow relative to the rates of sulfate reduction. Although the amount of barium in normal seawater is very small, barium is soluble in anoxic seawater where sulfur is present mainly as hydrogen sulfide. Barite could be concentrated at interfaces having more oxygenated sulfate-bearing waters of the dysaerobic zones during early diagenesis, possibly with microbes serving as a catalyst. Barite could also be concentrated in areas of locally increased pH where calcium carbonate was forming in anaerobic environments.« less

Accumulation of organic matter in Cretaceous oxygen-deficient depositional environments in the central Pacific Ocean

Complete records of organic-carbon-rich Cretaceous strata were continuouslycored on the flanks of the Mid-Pacific Mountains and southern Hess Rise in the central North Pacific Ocean during DSDP Leg 62. Organic-carbon-rich laminated silicified limestones were deposited in the western Mid-Pacific Mountains during the early Aptian, a time when that region was south of the equator and considerably shallower than at present. Organic-carbon-rich, laminated limestone on southern Hess Rise overlies volcanic basement and includes 136 m of stratigraphic section of late Albian to early Cenomanian age. This limestone unit was deposited rapidly as Hess Rise was passing under the equatorial high-productivity zone and was subsiding from shallow to intermediate depths. The association of volcanogenic components with organic-carbon-rich strata on Hess Rise in the Mid-Pacific Mountains is striking and suggests that there was a coincidence of mid-plate volcanic activity and the production and accumulation of organic matter at intermediate water depths in the tropical Pacific Ocean during the middle Cretaceous. Pyrolysis assays and analyses of extractable hydrocarbons indicate that the organic matter in the limestone on Hess Rise is composed mainly of lipid-rich kerogen derived from aquatic marine organisms and bacteria. Limestones from the Mid-Pacific Mountains generally contain low ratios of pyrolytic hydrocarbons to organic carbon and low hydrogen indices, suggesting that the organic matter may contain a significant proportion of land-derived material, possibly derived from numerous volcanic islands that must have existed before the area subsided. The organic carbon in all samples analyzed is isotopically light ( δ 13C − 24 to − 29 per mil) relative to most modern rine organic carbon, and the lightest carbon is also the most lipid-rich. There is a positive linear correlation between sulfur and organic carbon in samples from Hess Rise and from the Mid-Pacific Mountains. The slopes and intercepts of C-S regression lines however, are different for each site and all are different from regression lines for samples from modern anoxic marine sediments and from Black Sea cores. The organic-carbon-rich limestones on Hess Rise, the Mid-Pacific Mountains, and other plateaus and seamounts in the Pacific Ocean are not synchronous but do occur within the same general middle Cretaceous time period as organic-carbon-rich lithofacies elsewhere in the world ocean, particularly in the Atlantic Ocean. Strata of equivalent age in the deep basins of the Pacific Ocean are not rich in organic carbon, and were deposited in oxygenated environments. This observation, together with the evidence that the plateau sites were considerably shallower and closse to the equator during the middle Creataceous suggests that local tectonic and hydrographic conditions may have resulted in high surface-water productivity and the preservation of organic matter in an oxygen-deficient environment where an expanded mid-water oxygen minimum developed and impinged on elevated platforms and seamounts.

Inhibition by silver ions of gas space (aerenchyma) formation in adventitious roots of Zea mays L. subjected to exogenous ethylene or to oxygen deficiency

We have studied the role of ethylene in accelerating the lytic formation of gas spaces (aerenchyma) in the cortex of adventitious roots of maize (Zea mays L.) growing in poorly aerated conditions. Such roots had previously been shown to contain increased concentrations of ethylene. Ten day-old maize plants bearing seminal roots and one whorl of emerging adventitious roots were grown in nutrient solution bubbled with air, ethylene in air (0.1 to 5.0 μl l(-1)), or allowed to become oxygen-deficient in nonaerated (but not completely anaerobic) solution. Additions of 0.1 μl l(-1) ethylene or more promoted the formation of aerenchyma, with lysis of up to 47% of the cortical cells. The effects of non-aeration were similar to those of exogenous ethylene. When silver ions, an ethylene antagonist, were present at low, non-toxic concentrations (circa 0.6 μM), aerenchyma formation was prevented in ethylene treated roots and in those exposed to oxygen deficiency. Silver ions also blocked the inhibiting effect of exogenous ethylene on root extension. By contrast, the suppression of aerenchyma formation by silver ions under oxygendeficient conditions was associated with a retardation of root extension, indicating the importance of aerenchyma for root growth in poorly aerated media. Rates of production of ethylene by excised roots were stimulated by a previous non-aeration treatment. The effectiveness of Ag(+) in inhibiting equally the action on cortical cells of exogenous ethylene and of non-aeration, supports the view that gas space (aerenchyma) formation in adventitious roots 'adpted' to oxygendeficient environments is mediated by increased concentrations of endogenous ethylene. The possibility that extra ethylene could arise from increased biosynthesis of a precursor in root tissues with a restricted oxygen supply is discussed.

Mitotic activity in rice seedlings germinating under oxygen deficiency.

Rice seedlings germinating in oxygen-deficient environments do not manifest visual evidence of seminal or adventitious root growth or normal leaf growth, the coleoptile being the only seedling structure to emerge under these environmental conditions. Microscopic evidence, however, shows that mitotic activity occurs in the different tissues comprising the shoots of the seedlings germinating under oxygen deficiency. Thus evidence is presented here which shows that mitotic activity in rice seedlings germinating in oxygen-deficient environments is not confined solely to the emerging coleoptiles of the germinating seedlings.

Erythrocyte Morphology and the Ecology of Species of Fundulus

Mature erythrocyte morphology was investigated in twenty species or subspecies and in one hybrid of the cyprinodont genus Fundulus. The findings suggest a relationship between the ecology of the fishes and red blood cell size. The tentative interpretation of the data is that the environment characteristically inhabited by species of Fundulus is reflected in erythrocyte size; small cells acting as a compensatory mechanism for oxygen deficient environments. While differences were observed between freshwater and brackish-water species, no marked effects of salinity on cell size were found in F. diaphanus or F. heteroclitus maintained in either

World's Energy Economy: ABSTRACT

The earth is a virtually closed material system composed of the 92 naturally occurring chemical elements, all but a minute radioactive fraction of which obey the laws of classical chemistry. Into and out of this system there occur a continuous flux and degradation of energy. As a consequence, the materials of the earth's surface undergo either continuous or intermittent circulation. The principal energy influxes into the earth's surface environment are three: solar energy 174,000 trillion thermal watts; geothermal energy, 32 trillion; and tidal energy 3 trillion. The outfluxes are low-temperature radiation into outer space. During more than 3 billion years of geologic history, a minute fraction of the materials of the earth's surface has been aggregated into the dynamical system of living organisms. By the process of photosynthesis, a small fraction of the incident solar radiation is captured by the green leaves of plants and is stored chemically in the organic molecules of carbohydrates and other more complex chemical compounds. This is the source of the physiological energy requirements for the entire plant and animal kingdoms. The rates of decay and of oxidation of organic materials are almost equal to their rate of formation, but a small fraction becomes buried in peat bogs or other oxygen-deficient environments of incomplete decay. Such accumulations during past geologic time have become buried unde thick accumulations of sedimentary strata and have become transformed into the earth's present supply of fossil fuels. By about 2 million years ago the ancestors of the present human species began to walk upright and to use stone tools. From that time to the present, this species has distinguished itself from all others in its cumulative inventiveness in means of capturing ever-larger quantities of the energy of its environment. A great increase in the consumption of energy per capita was not possible, however, until the exploitation of the large stores of energy of the fossil fuels was begun about 9 centuries ago. The rise of the world's present technological society, with its concurrent ecological disturbances, including that of the human species, has been an inexorable consequence. The length of time during which this has occurred is deceptive unless account is also taken of the exponential growth in the rates of consumption. During the 9 centuries since the beginning of coal mining, approximately 142 billion metric tons had been mined by the end of 1972. Of this, one half has been produced since about 1940. Eighty percent of the world's initial coal supply will be consumed within the next 2-3 centuries, and the middle 80 percent of the world's oil during the 65-year period from about 1967 to 2032. As to the future, the fossil fuels are short-lived; nuclear power is potentially large but also hazardous; water power is large but inadequate; and geothermal and tidal power are inadequate. On the other hand, the largest source of energy available to the earth is that of solar radiation. Because the earth itself cannot tolerate more than a few tens of doublings of any biological or technological activity--and most of these have occurred already--it is now becoming evident that the present episode of exponential industrial growth can be only a transitory epoch of about 3 centuries duration in the totality of human history. It represents a brief transitional period between two very much longer periods, each characterized by rates of change so slow as to be regarded essentially as a per od of nongrowth. Although the forthcoming period poses no insuperable physical or biological difficulties, it can hardly fail to force a major revision in those aspects of our current economic and social thinking which are based on the premise that the growth rates which have characterized this temporary period can somehow be sustained indefinitely. End_of_Article - Last_Page 1843------------