Degassing Of Carbon Dioxide Research Articles

Carbon dioxide degassing and lateral dissolved carbon export during the unprecedented 2019 Mississippi river mega flood – Implications for large river carbon transport under future climate

In 2019, the Mississippi River experienced the longest and largest flood that surpassed by far the 1927, 1973, and 2011 mega floods. This unprecedented event provided an unique opportunity to test the hypotheses that summer floods increase not only lateral dissolved carbon transport but also carbon dioxide (CO2) degassing, and that the increase in CO2 outgassing from river surface occurs mainly due to higher terrestrial carbon inputs and warmer temperatures. To test the hypotheses, we conducted intensive river sampling and in-situ measurements on partial pressure of CO2 (pCO2) and other water physical, chemical and biological parameters in 6-day intervals throughout the entire flood period (January 6th to August 5th, 2019). Water samples were analyzed for the concentration of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) and their carbon–13 isotopes. Compared to reported average pCO2 measured at the same place from the recent past (1500 μatm ± 743), we found significantly elevated pCO2 in the river water during the flood period (2217 μatm ± 805; max = 3359 μatm), which was positively correlated with water temperature (ρ = 0.83). During the flood with sustained high pCO2, the lower Mississippi River released 230 Gg C from its last 357-km river reach, which is 18 % greater than the annual CO2 emission (195 Gg C) reported for 2016–2018. A total of 3.73 Tg C DOC and 14.14 Tg C DIC was laterally transported into the Gulf of Mexico during the flood period, which were close to or greater than the previously reported annual averages. The findings support the initial hypotheses and strongly suggest that future climate change will intensify carbon cycling in world’s rivers. Our study adds firsthand results on land-sea carbon transport from by far the largest Mississippi River flood and helps constrain uncertainties in carbon budgeting of global rivers.

The influence of microbial mats on travertine precipitation in active hydrothermal systems (Central Italy)

AbstractThe study of hydrothermal travertines contributes to the understanding of the interaction between physico‐chemical processes and microbial mats in carbonate precipitation. Three active travertine sites were investigated in Central Italy to characterise the types of carbonate precipitates and the associated microbial mats at varying physico‐chemical parameters. Carbonate precipitated fabrics at the decimetre to millimetre‐scale and microbial mat composition vary with decreasing water temperature: (a) at relatively higher temperature (55–44°C) calcite and aragonite crystals precipitate on microbial mats of Chloroflexi and sulphur‐oxidizing microbes forming filamentous streamer fabrics with sparse cyanobacteria, (b) at intermediate temperature (44–40°C), rafts, coated gas bubbles and dendrites are associated with Spirulina cyanobacteria and other filamentous and rod‐shaped cyanobacteria, (c) low temperature (34–33°C) laminated crusts and oncoids forming in a terraced slope system are associated with diverse Oscillatoriales and Nostocales filamentous cyanobacteria, Spirulina and diatoms. At the microscale, carbonate precipitates are similar in the three sites consisting of prismatic calcite crystals organised in radial rosettes or fibrous aragonite spherulites (40–300 µm in diameter), overlying or embedded in Extracellular Polymeric Substances. Clotted peloidal micrite dominates at temperatures <40°C, also encrusting filamentous microbes. Carbonates are associated with gypsum crystals; extracellular polymeric substances are enriched in silicon, aluminium, magnesium, calcium, phosphorous and sulphur; authigenic aluminium‐silicates form aggregates on Extracellular Polymeric Substances. This study confirms that microbial communities in hydrothermal settings vary as a function of water temperature. Carbonate precipitates at the microscale are similar in the three settings, despite different microbial communities, suggesting that travertine precipitation, driven by carbon dioxide degassing, is influenced by biofilm extracellular polymeric substances acting as a substrate for crystal nucleation (Extracellular Polymeric Substances‐mediated mineralization) and affecting the resultant fabric types, independently from specific microbial community composition and metabolism.

Influence of tectonics on global scale distribution of geological methane emissions

Earth’s hydrocarbon degassing through gas-oil seeps, mud volcanoes and diffuse microseepage is a major natural source of methane (CH4) to the atmosphere. While carbon dioxide degassing is typically associated with extensional tectonics, volcanoes, and geothermal areas, CH4 seepage mostly occurs in petroleum-bearing sedimentary basins, but the role of tectonics in degassing is known only for some case studies at local scale. Here, we perform a global scale geospatial analysis to assess how the presence of hydrocarbon fields, basin geodynamics and the type of faults control CH4 seepage. Combining georeferenced data of global inventories of onshore seeps, faults, sedimentary basins, petroleum fields and heat flow, we find that hydrocarbon seeps prevail in petroleum fields within convergent basins with heat flow ≤ 98 mW m−2, and along any type of brittle tectonic structure, mostly in reverse fault settings. Areas potentially hosting additional seeps and microseepage are identified through a global seepage favourability model.

Crystallization pathways in the Great Artesian Basin (Australia) spring mound carbonates: Implications for life signatures on Earth and beyond

AbstractRecent studies of continental carbonates revealed that carbonates with similar fabrics can be formed either by biotic, biologically‐induced, biologically‐influenced or purely abiotic processes, or a combination of all. The aim of this research is to advance knowledge on the formation of carbonates precipitated (or diagenetically altered) in extreme, continental environments by studying biotic versus abiotic mechanisms of crystallization, and to contribute to the astrobiology debate around terrestrial analogues of Martian extreme environments. Both fossil (upper Pleistocene to Holocene) and active carbonate spring mounds from the Great Artesian Basin (South Australia) have been investigated. These carbonates consist of low‐Mg to high‐Mg calcite tufa. Four facies have been described: (i) carbonate mudstone/wackestone; (ii) phytohermal framestone/boundstone; (iii) micrite boundstone; and (iv) coarsely crystalline boundstone. The presence of filaments encrusted by micrite, rich in organic compounds, including ultraviolet‐protectants, in phytohermal framestone/boundstone and micrite boundstone is clear evidence of the existence of microbial mats at the time of deposition. In contrast, peloidal micrite, despite commonly being considered a microbial precipitate, is not directly associated with filaments in the Great Artesian Basin mounds. It has probably formed from nanocrystal aggregation on colloid particulate. Thus, where biofilms have been documented, it is likely that bacteria catalyzed the development of fabrics. It is less certain that microbes induced calcium carbonate precipitation elsewhere. Trace elements, including rare earth element distribution from laminated facies, highlight strongly evaporative settings (for example, high Li contents). Carbon dioxide degassing and evaporation are two of the main drivers for an increase in fluid alkalinity, resulting in precipitation of carbonates. Hence, although the growth of certain fabrics is fostered by the presence of microbial mats, the formation of carbonate crystals might be independent from it and mainly driven by extrinsic factors. More generally, biological processes may be responsible for fabric and facies development in micritic boundstone whilst micrite nucleation and growth are driven by abiotic factors. Non‐classical crystallization pathways (aggregation and fusion of nanoparticles from nucleation clusters) may be more common than previously thought in spring carbonate and this should be carefully considered to avoid misinterpretation of certain fabrics as by‐products of life. It is proposed here that the term ‘organic‐compound catalyzed mineralization’ should be used for crystal growth in the presence of organic compounds when dealing with astrobiological problems. This term would account for the possibility of multiple crystallization pathways (including non‐classical crystallization) that occurred directly from an aqueous solution without the direct influence of microbial mats.

A late Miocene methane-seep deposit bearing methane-trapping silica minerals at Joetsu, central Japan

The modern Japan Sea is characterized by active methane seeps associated with gas hydrates, but their ancient counterparts are not fully understood. This study describes a newly discovered methane-seep carbonate block, the ‘Nakanomata Seep Deposit’, from the upper Miocene Nodani Formation in Joetsu City, central Japan. The age of this deposit is constrained to 7.5–6.5Ma based on its fossil diatom assemblage. The deposit contains molluscan fossils typical of methane seeps, including vesicomyid and bathymodiolin bivalves, and provannid gastropods, and it retains an almost entirely aragonitic mineralogy, despite its Miocene age. It is composed of clotted microcrystalline aragonite containing nodules and intraclasts, and is crosscut by vein-like networks of voids and cavities rimmed with acicular aragonite. The δ13C values of the carbonate phases are as low as −41.1‰ and the presence of lipid biomarkers (pentamethylicosane and crocetane) suggests that the deposit originated from the anaerobic oxidation of methane. It is suggested that an initially diffuse methane seepage formed the micritic nodules, followed by a more rapid and intense methane seepage that led to the development of abundant voids in the sediment; finally, the sediment was cemented by microcrystalline aragonite and void-lining acicular aragonite. The seep deposit also contains peculiar globular silica minerals and authigenic quartz. During their precipitation, these globular silica minerals may have trapped methane gas bubbles, and the minerals may be pseudomorphs after silica clathrate. Sufficient increase in pH and supersaturation of silica, which led to the dissolution and subsequent precipitation of these silica minerals, could have resulted from the degassing of carbon dioxide, promoted by an effective supply of methane, and its supersaturation, thus forming gas bubbles.

Constraining silica diagenesis in methane-seep deposits

Silicified fossils and authigenic silica are common in ancient seep limestones. Silicification of calcareous fossils facilitates the preservation of even fine details and is therefore of great interest to paleontologists, permitting a reliable taxonomic identification of the chemosynthesis-based taxa that lived at hydrocarbon seeps. Four methane-seep limestones of Paleozoic, Mesozoic, and Cenozoic age with abundant silica phases are compared in this study; one, an Eocene seep deposit on the north shore of the Columbia River at Knappton, western Washington State, USA, is described for the first time. Its lithology and fabrics, negative δ13Ccarbonate values as low as −27.6‰, and 13C-depleted biomarkers of archaea involved in the anaerobic oxidation of methane (AOM) reveal that the carbonate rock formed at a methane seep. The background sediments of the studied Phanerozoic seep limestones contain abundant siliceous microfossils, radiolarian tests in case of the Carboniferous Dwyka Group deposits from Namibia and the Triassic Graylock Butte deposits from Oregon (USA), as well as diatom frustules in case of the Eocene Knappton limestone and an Oligocene seep deposit from the Lincoln Creek Formation (Washington State, USA). These microfossils are regarded as the source of dissolved silica, causing silicification and silica precipitation. Silica cements formed after AOM-derived cements ceased to precipitate but before equant calcite formed. Numerical experiments using the computer code PHREEQC confirmed that (1) AOM increases the pH of pore waters and that (2) this pH increase subsequently mobilizes biogenic silica, (3) followed by the re-precipitation of the dissolved silica in the periphery of the AOM hotspot. The experiments revealed that degassing of carbon dioxide has the potential to significantly increase the local pH of pore waters, exerting an even stronger control on the local pH and silica dissolution than the rate of AOM alone.

Petrologic characteristics and genesis of dolostone from the Campanian of the SK-I Well Core in the Songliao Basin, China

The well SK-I in the Songliao Basin is the first scientific borehole targeting the continental Cretaceous strata in China. Oval concretions, thin laminae and beds of dolostone are found intercalated within mudstone and organic-rich black shale in the Nenjiang Formation of Campanian age. Low ordered ferruginous dolomite is composed of euhedral–subhedral rhombs with cloudy nucleus and light rims formed during the diagenesis, which are typical features of replacement. The heavy carbon isotopes (δ13CPDB – 1.16–16.0) are results of both the fermentation of organic matter by microbes and degassing of carbon dioxide during the period of diagenesis, and the presence of light oxygen isotopes (δ18OPDB – 18.53∼−5.1) is a characteristic feature of fresh water influence which means the carbonate may have been altered by ground water or rainwater in the late diagenesis. Marine water incursions into the normally lacustrine basin have been proved by both the salinity of Z value and the occurrence of foraminifera in the same strata where dolomite occurs. Pyrite framboids observed by SEM are usually enclosed in the dolomite crystals or in the mudstones, supporting the sulfate reducing bacteria (SRB). The formation of both dolomite and pyrite are associated with marine water incursions, which not only supply magnesium ion for dolomite, but also result in limited carbonate precipitation in the basin. The presence of pyrite framboids indicates the development of an anoxic environment associated with salinity stratification in the lake. The dolomite in the Nenjiang Formation is the results of marine water incursions, diagenetic replacement of calcareous carbonate and sulfate reducing bacteria (SRB).

The geochemistry of cave calcite deposits as a record of past climate

Cave calcite deposits, and stalagmites specifically, are proving to be critical recorders of paleoclimate. Stalagmites develop from the slow accumulation of calcite deposited after the degassing of carbon dioxide from percolation water in caves. Stalagmites are therefore theoretically capable of recording the hydrochemistry of every drip of water that impacts their surface, but complications involving hydrology, cave air P CO2 variability, intra-aquifer processing, and petrography preclude straightforward interpretation. Nevertheless, stalagmite climate proxy records using stable isotopes, particularly of oxygen, are reconstructing the timing, structure, and in some cases magnitude of climate shifts worldwide.Trace element to calcium ratios in stalagmite are a promising new proxy for both independent reconstruction of climate and for supporting oxygen isotope ratios. Extensive monitoring of individual cave sites is required to most accurately interpret stalagmite proxy records.

Travertine terracing: patterns and mechanisms

Abstract Travertine terracing is one of the most eye-catching phenomena in limestone caves and around hydrothermal springs, but remains fairly poorly understood. The interactions between water chemistry, precipitation kinetics, topography, hydrodynamics, carbon dioxide degassing, biology, erosion and sedimentation constitute a complex, dynamic pattern formation process. The processes can be described and modeled at a range of abstraction levels. At the detailed level concerning the physical and chemical mechanisms responsible for precipitation localization at rims, a single explanation is probably insufficient. Instead, a multitude of effects are likely to contribute, of varying importance depending on scale, flux and other parameters.

Carbon dioxide degassing and thermal energy release in the Monte Amiata volcanic-geothermal area (Italy)

Abstract The quaternary volcanic complex of Mount Amiata is located in southern Tuscany (Italy) and represents the most recent manifestation of the Tuscan Magmatic Province. The region is characterised by a large thermal anomaly and by the presence of numerous CO2-rich gas emissions and geothermal features, mainly located at the periphery of the volcanic complex. Two geothermal systems are located, at increasing depths, in the carbonate and metamorphic formations beneath the volcanic complex. The shallow volcanic aquifer is separated from the deep geothermal systems by a low permeability unit (Ligurian Unit). A measured CO2 discharge through soils of 1.8 × 109 mol a−1 shows that large amounts of CO2 move from the deep reservoir to the surface. A large range in δ13CTDIC (−21.07 to +3.65) characterises the waters circulating in the aquifers of the region and the mass and isotopic balance of TDIC allows distinguishing a discharge of 0.3 × 109 mol a−1 of deeply sourced CO2 in spring waters. The total natural CO2 discharge (2.1 × 109 mol a−1) is slightly less than minimum CO2 output estimated by an indirect method (2.8 × 109 mol a−1), but present-day release of 5.8 × 109 mol a−1 CO2 from deep geothermal wells may have reduced natural CO2 discharge. The heat transported by groundwater, computed considering the increase in temperature from the infiltration area to the discharge from springs, is of the same order of magnitude, or higher, than the regional conductive heat flow (>200 mW m−2) and reaches extremely high values (up to 2700 mW m−2) in the north-eastern part of the study area. Heat transfer occurs mainly by conductive heating in the volcanic aquifer and by uprising gas and vapor along fault zones and in those areas where low permeability cover is lacking. The comparison of CO2 flux, heat flow and geological setting shows that near surface geology and hydrogeological setting play a central role in determining CO2 degassing and heat transfer patterns.

Induced Magnesium Ammonia Phosphate Precipitation to Prevent Incrustations and Measures for Phosphorus Recovery

In 1994 for the first time massive incrustations in the centrifuges treating the digested sludge were detected in some wastewater treatment plants (WWTP’s) of the Berliner Wasserbetriebe, which were, as was found out later, mainly due to the precipitation of white MAP (magnesium ammonium phosphate = struvite) deposits with small portions of different calcium phosphate compounds. The reason for this was the over saturation of the digested sludge and the process water (from the separated centrate of the digested sludge) with carbon dioxide, the spontaneous release of or degassing of carbon dioxide, causing the pH to increase, thus altering the solubility equilibrium, and facilitating crystallisation, resulting in deposits (incrustations) on the walls. Obviously, the wastewater purification process used, with enhanced biological phosphorus removal and concentrated streams of digesting sludge, favours the formation of incrustations during sludge treatment. These incrustations were the cause of a lot of operational problems. To prevent incrustations, modifications in the process engineering technology have been applied after several studies and trials. Deliberate extraction of the CO2, e.g. by air injection through a fine-bubble surface aeration system at the bottom of the digested sludge storage tank just before the centrifuges, causes the pH to rise to approx. 8 and thus to cause induced struvite precipitation. This technology enables a precipitation product suitable for recycling to be generated and separated from the anaerobic sludge using a hydro-cyclone. A subsequent second hydro-cyclone stage allowed a further increase in the P-concentration to approx. 40 kg/m3, giving a yield of phosphorus of 20 %. This corresponds with P-load of approx. 316 kg/day and amounts to 18 % of the P inlet load in the WWTP Waßmannsdorf. It was shown that this experimental process is in principle suitable for the separation of the MAP precipitation product in the anaerobic sludge. A complete washing process for the raw MAP is not yet installed, and furthermore, to find the best sizes of nozzles in the hydro-cyclones and most effective pressures tests will have to be carried out soon at pilot level. A comparison with the minimum nutrients content for different kinds of fertiliser (super-phosphate, dicalcium-phosphate with magnesium, NP-fertiliser) defined by the German Fertiliser Regulations, shows that the precipitated MAP is within the range of other legally certified fertilisers. The MAP showed contaminant levels 5 times or more below the limit values of the German Sewage Sludge Ordinance. The MAP precipitation product is very soluble in different solvents (from ammonium chloride to hydrochloric acid). This implies that the precipitation product can be used as a long term fertilizer. In two test soils having a pH value of 6.6 and 7.1, the MAP precipitation solid was tested using standard ryegrass and showed good phosphorus availability from this material leading to a good grass growth.

Evolution of fluid chemistry during travertine formation in the Troll thermal springs, Svalbard, Norway

AbstractArctic hydrothermal springs at Bockfjorden, Svalbard, have isotope and trace element signatures indicative of derivation from glacial melt waters with minor contribution from seawater. Downstream gradients in water chemistry, isotopic composition and carbonate precipitation rates have been documented for the Troll spring and travertine terrace system. The main controls on the downstream evolution of these parameters are carbon dioxide degassing, calcite precipitation, evaporation and biological activity. The carbonate precipitation rates not only show an approximately parabolic dependence on the calcite supersaturation levels, but depend also on local hydrodynamics. Downstream loss of light isotopes of oxygen and hydrogen can be explained as an effect of evaporation, as estimated using chloride as a conservative marker. Biological activity affects nitrate and bromide concentrations and influences the morphology of calcite precipitates.

Carbon dioxide degassing and inorganic carbon export from a marsh‐dominated estuary (the Duplin River): A marsh CO2 pump

We investigated the seasonal changes and the interactions of the CO2 system in a marsh‐dominated estuary, the Duplin River, on Sapelo Island, Georgia. Surface water pCO2, total alkalinity (TA), and total dissolved inorganic carbon (DIC) showed a pronounced seasonal progression in this system. The estuary released 256‐306 g C m‐2 (of water) yr‐1 of CO2 to the atmosphere and exported 109 g C m‐2 (of water) yr‐1 of DIC to adjacent coastal waters. There was a clear seasonal pattern in both fluxes with spring minima, and late summer and fall maxima. Release of inorganic carbon as a respiratory product from surrounding salt marshes is the primary process supporting these two carbon export terms. Concurrently, TA was exported from the Duplin River mainly in summer and fall as a result of anaerobic respiration in marshes. Based on data from the upper Duplin River, export of inorganic carbon from salt marshes was 156 g C m‐2 (of marsh) yr‐1. Extrapolation of this value to all southeastern U.S. salt marshes indicates that they cumulatively export 0.7 X 1012 g inorganic carbon annually to coastal waters. This export rivals that of riverine inorganic carbon flux. We propose that the CO2 fixation of marsh grasses and the subsequent export of inorganic and organic carbon is one major mechanism that causes the marsh‐influenced nearshore and offshore waters in the southeastern U.S. to be annual net sources of atmospheric CO2. We also suggest that this process provides an efficient and unique means for ocean carbon sequestration of atmospheric CO2.

Carbon dioxide degassing by advective flow from Usu volcano, Japan.

Magmatic carbon dioxide (CO2) degassing has been documented before the 31 March 2000 eruption of Usu volcano, Hokkaido, Japan. Six months before the eruption, an increase in CO2 flux was detected on the summit caldera, from 120 (September 1998) to 340 metric tons per day (September 1999), followed by a sudden decrease to 39 metric tons per day in June 2000, 3 months after the eruption. The change in CO2 flux and seismic observations suggests that before the eruption, advective processes controlled gas migration toward the surface. The decrease in flux after the eruption at the summit caldera could be due to a rapid release of CO2 during the eruption from ascending dacitic dikes spreading away from the magma chamber beneath the caldera.

Carbon dioxide in magmas and implications for hydrothermal systems

This review focuses on the solubility, origin, abundance, and degassing of carbon dioxide (CO2) in magma–hydrothermal systems, with applications for those workers interested in intrusion-related deposits of gold and other metals. The solubility of CO2 increases with pressure and magma alkalinity. Its solubility is low relative to that of H2O, so that fluids exsolved deep in the crust tend to have high CO2/H2O compared with fluids evolved closer to the surface. Similarly, CO2/H2O will typically decrease during progressive decompression- or crystallization-induced degassing. The temperature dependence of solubility is a function of the speciation of CO2, which dissolves in molecular form in rhyolites (retrograde temperature solubility), but exists as dissolved carbonate groups in basalts (prograde). Magnesite and dolomite are stable under a relatively wide range of mantle conditions, but melt just above the solidus, thereby contributing CO2 to mantle magmas. Graphite, diamond, and a free CO2-bearing fluid may be the primary carbon-bearing phases in other mantle source regions. Growing evidence suggests that most CO2 is contributed to arc magmas via recycling of subducted oceanic crust and its overlying sediment blanket. Additional carbon can be added to magmas during magma–wallrock interactions in the crust. Studies of fluid and melt inclusions from intrusive and extrusive igneous rocks yield ample evidence that many magmas are vapor saturated as deep as the mid crust (10–15 km) and that CO2 is an appreciable part of the exsolved vapor. Such is the case in both basaltic and some silicic magmas. Under most conditions, the presence of a CO2-bearing vapor does not hinder, and in fact may promote, the ascent and eruption of the host magma. Carbonic fluids are poorly miscible with aqueous fluids, particularly at high temperature and low pressure, so that the presence of CO2 can induce immiscibility both within the magmatic volatile phase and in hydrothermal systems. Because some metals, including gold, can be more volatile in vapor phases than coexisting liquids, the presence of CO2 may indirectly aid the process of metallogenesis by inducing phase separation.

Soil solution pH measurements using in-line chambers with tension lysimeters

During soil water extraction, pH can change as a result of atmospheric gas exchange. The pH change is important for monitoring soil acidification and determination of mineralogic controls on the solution composition. As part of a global change programme in Greenland for monitoring long-term changes in Arctic soil solutions we observed that the pH of extracted soil solutions increased in the order of a half pH unit during traditional sampling and handling of the soil solution. CO2 degassing is often considered the most important factor causing such a pH increase. Thus, traditional as well as in-line pH measurements were performed during the summers 1997 and 1998. The in-line method was designed to eliminate atmospheric contact with soil solutions prior to pH measurements. The time-dependent pH error was quantified based on laboratory experiments with soil solution under controlled temperatures and CO2 partial pressures. Equilibrium speciation modelling was used to predict pH values observed in the field and in the laboratory and the model was found to reproduce the observations well. We conclude that traditional pH measurements on extracted soil solutions in the pH range from 5 to 7 are not appropriate for detailed pH measurements due to errors associated with CO2 degassing. In-line measurements provide more accurate measurement necessary for detailed studies on soil acidification dynamics. Key words: pH, carbon dioxide degassing, soil solution, tension lysimeter, arctic soil

Stable isotope chemistry of gaylussite and nahcolite from the deposits of the crater lake at Malha, northern Sudan

Gaylussite (Na 2CO 3·CaCO 3·5H 2O) and nahcolite (NaHCO 3) in deposits of the crater lake at Malha are predictably characterized by a strong 18O enrichment that is typical of evaporitic environments. Both minerals also yield high δ 13C values, which, in the case of gaylussite, are covariant with the δ 18O values. The fact that the covariant trend, which is a feature that is commonly recognized for the deposits of closed basins, pertains both to the synsedimentary and pedogenic gaylussite deposits of the Malha basin demonstrates that 13C enrichment was mainly controlled by inorganic processes. An important biological control on the carbon isotope composition is also contradicted by the occurrence of a covariance for synsedimentary gaylussite that mainly formed by bottom growth in a well-mixed water mass. Degassing of carbon dioxide is the most likely cause of 13C enrichment, although this implies that CO 2 loss is a process that occurs concurrently with the evaporation of water, without, as could be expected, being driven by changes in the relative abundance of compounds within the CO 2–H 2O system. The lack of a covariance of δ 18O and δ 13C for nahcolite seems to be partly related to bacterial activity, which did play an important role during lake stages with nahcolite formation, and partly to the lack of a further increase of δ 18O with continued evaporation at advanced stages of the evaporitic concentration of brines.

Moss growth and travertine deposition: the significance of photosynthesis, evaporation and degassing of carbon dioxide

Abstract In situ measurements were performed on the travertine-encrusted mosses Cratoneuron commutatum var. commutatum and Eucladium verticillatum to obtain estimates of calcium carbonate deposition through photosynthesis, evaporation and carbon dioxide evasion. It was estimated that for both species, between 6 and 12% of the carbonate was deposited through photosynthesis, 10–20% through evaporation and the remaining 70–80% through gas evasion.

Degradation of naphthalene by Pseudomonas sp. strain KR3 investigated by flow calorimetry

Abstract Biotic degradation techniques are gaining importance in decontaminating soils and waste water from organic pollutants. One class of organic pollutants of much interest are polyaromatic hydrocarbons (PAH), ubiquitous substances some of which show a high carcinogenic and mutagenic potential and acute toxicity. Although they usually possess a high thermodynamic stability they can be degraded by microorganisms. In our investigations of PAH degradation we used naphthalene as a model substance because of its high solubility. The degradation of naphthalene at 25°C in liquid culture by Pseudomonas sp. strain KR3 was observed with a Thermometric microcalorimeter equipped with a flow cell. Bacterial cultures from a fermentor were pumped through this measuring cell via tubing. Parallel to the microcalorimetric investigations the amount of degraded naphthalene and the generation of metabolites were observed by HPLC analysis, and biomass production and oxygen consumption were measured. On degrading naphthalene, Pseudomonas sp. strain KR3 generated various metabolites at the same time. Only some of the metabolites had their maximum concentration synchronous to the maximum heat flow rate. Anabolic processes were delayed compared to the consumption of the substrate. A good correlation between calorimetric results and oxygen consumption was found. A relationship between a strong decrease in heat production after the main heat flow rate peak and inhibition of metabolic processes by lack of oxygen could be excluded. Decrease in the heat flow rate is assumed to be due to lowered gas exchange in the calorimeter tubes, i.e. the inhibited degassing of carbon dioxide. Calculation of an envelope for the heat flow rate is useful to improve experimental results.

Paleozoic Atmospheric CO 2 : Importance of Solar Radiation and Plant Evolution

Changes in solar radiation, as it affects the rate of weathering of silicates on the continents, and other changes involving weathering and the degassing of carbon dioxide (CO(2)) have been included in a long-term carbon-cycle model. These additions to the model show that the major controls on CO(2) concentrations during the Paleozoic era were solar and biological, and not tectonic, in origin. The model predictions agree with independent estimates of a large mid-Paleozoic (400 to 320 million years ago) drop in CO(2) concentrations, which led to large-scale glaciation. This agreement indicates that variations in the atmospheric greenhouse effect were important in global climate change during the distant geologic past.