Variations In CO2 Concentration Research Articles

Eolian evidence from the Chinese Loess Plateau: the onset of the Late Cenozoic Great Glaciation in the Northern Hemisphere and Qinghai-Xizang Plateau uplift forcing

On the basis of a newly-constructed record of magnetic susceptibility (SUS) and the depositional rate change of eolian loess-red clay sequences in the last 7.2 Ma BP from the hea Plateau, together with a cornperison of a record of °18O values from the equatorial East Pacific Ocean and eolian Quartz flux variations fmm the North Pacific Ocean, the evolutiomuy process of the Late Cenozoic Great Glaciation in the Northern Hemisphere can be divided into three stages: the arrival stage around 7.2–3.4 Ma BP, the initial stage at about 3.4—2.6 Ma BP, and the Great Ice Age since 2.6 Ma BP. The evolution of the East Asian monsoon is characterized by paid winter and summer monsoons, and it is basically composed of the initial stage of weak winter and summer monsoons, the transitional stage of simultaneous increase in intensity of winter and summer monsoons, and the prevailing stage of strong winter and week summer monsoons, or weak winter and strong summer monsoons. The Late Cenowic global tectonic uplift, paaicdarly the Qinghai-Xizang Plateau uplift and the associated CO2 concentration variation, controls the dng processes of the onset of Great Glaciation and the long-term changes of East Asian monsoom climate in the Northern Hemisphere to a large extent. The accelerating uplift of the Qinghai-Xizang Plateau between 3.4 and 2.6 Ma BP provided an important driving force to global climiatic change.

Formulated Solvents: New Opportunities for Energy Efficient Separation of Acid Gases

Carbon dioxide (CO2) separation technology can be considered to be a mature technology. However, there remains ample room for process efficiency improvements in the existing plants. In addition to conventional gas processing, a number of other CO2 removal applications are emerging which may provide considerable opportunity to the gas processors. These new applications include enhanced oil recovery (EOR) gas processing separation of CO2 from power plant flue gases to minimize green house gas emissions, and so forth. They require newer technology or modification of existing technologies. Formulated amines can play a significant role in these areas. A formulated amine can be broadly defined as an amine that has been specifically formulated to perform specific task, for example, selective separation of H2S from light hydrocarbons in the presence of CO2, bulk separation of CO2, and so on. A formulated amine can consist of a single solvent such as methyl di ethanolamine (MDEA) or a solvent mixture such as a mixture of MDEA and diethanolamine (DEA) in aqueous solutions. Most of the proprietary solvents marketed by the major solvent manufacturers are based on formulated amines. By judicious choice of a formulated amine or amine mixture, process efficiency of the existing plants can be enhanced significantly compared to the use of traditional amines. Furthermore, some of the gas processing problems that can not be dealt with using the conventional technology in an economical manner can be easily handled with formulated amines. EOR gas processing is such an example. In the case of EOR gas processing, the concentration and volume of CO2 to be separated from the produced gas increases with time. This creates a major challenge for the design engineer in the design of a processing plant flexible enough to handle variations in CO2 concentrations ranging from 0 to 80 %. Formulated amines may be an answer to this problem. This article will describe the challenges and the opportunities formulated amines may provide to the gas processing industry.

A field fumigation system for elevated carbon dioxide exposure in chaparral shrubs

1. Modifications and improvements in the hardware and software of a free‐air CO2 enrichment (FACE) system are described. The modifications were undertaken to minimize the amount of structure required and to improve software control of CO2 set points. 2. A new low‐cost CO2 flow controller which provides increased reliability is described. 3. Analysis of system performance during a 79‐day evaluation period of operation (13 h day–1) showed that for 1 min averages, the system is capable of maintaining a 550 p.p.m. ± 10% CO2 set point during 78% of the operating time and a 550 p.p.m. ± 20% set point during 95% of the operating time. Ten‐minute averages were within ± 10% and 20% during 87% and 96% of the operating time, respectively. 4. Continuous measurements of the spatial variation in CO2 concentration inside the FACE ring over an 18‐day period showed that of the total 16‐m diameter treatment area, the central 11‐m diameter portion remains within the 550 p.p.m. ± 10% set point. 5. Daily course gas‐exchange measurements in matched individuals of the chaparral shrub Adenostoma fasciculatum just prior to and following a 6‐week fumigation period at 550 p.p.m. CO2 in the FACE treatment ring showed the FACE plants with reduced photosynthetic rates and higher (less stressful) water potentials compared with control A. fasciculatum plants measured at the same times and conditions, indicating the responsiveness of this species to elevated CO2 conditions.

Diurnal cycle of carbon isotope ratio in soil CO2 in various ecosystems

Our investigations of diurnal variations of the 13C/12C ratio and CO2 content in soil air were carried out in three environments during periods of high biosphere activity. It has been observed that diurnal variation of CO2 concentration is negatively correlated δ13. Particularly great variations occurred at shallow soil depths (10–30 cm) when the plant cover activity was high while the soil temperature was rather low. Under such conditions the δ13 variations had the magnitude of 4‰, while the CO2 concentration varied more than doubly. The maximum of the 13C/12C ratlo and the minimum of the CO2 concentration in a cultivated field with winter wheat took place in the afternoon, whereas in deciduous forest similar patterns were observed at dawn. In these cases soil temperatures at 10 cm depths varied less than 2°C. Hence, under wheat the variation in root respiration rate seem to be the main reason of the recorded varations. In an uncultivated grass-field during the hottest period in summer we did not measure any distinct variations of CO2 properties in spite of the fact that soil temperature varied up to 5°C. This might be due to dominant microbial respiration at the high soil temperature, which exceeded 20°C.

Whole plant respiration and photosynthesis of wheat under increased CO2 concentration and temperature: long‐term vs. short‐term distinctions for modelling

AbstractShort‐ and long‐term effects of elevated CO2 concentration and temperature on whole plant respiratory relationships are examined for wheat grown at four constant temperatures and at two CO2 concentrations. Whole plant CO2 exchange was measured on a 24 h basis and measurement conditions varied both to observe short‐term effects and to determine the growth respiration coefficient (rg), dry weight maintenance coefficient (rm), basal (i.e. dark acclimated) respiration coefficient (rg), and 24 h respiration:photosynthesis ratio (R:P). There was no response of rg to short‐term variation in CO2 concentration. For plants with adequate N supply, rg was unaffected by the growth‐CO2 despite a 10% reduction in the plant's N concentration (%N). However, rm was decreased 13%, and rb was decreased 20% by growth in elevated CO2 concentration relative to ambient. Nevertheless, R:P was not affected by growth in elevated CO2. Whole plant respiration responded to short‐term variation of ± 5 °C around the growth temperature with low sensitivity (Q10= 1.8 at 15 °C, 1.3 at 30 °C). The shape of the response of whole plant respiration to growth temperature was different from that of the short term response, being a slanted S‐shape declining between 25 and 30 °C. While rm, increased, rg decreased when growth temperature increased between 15 and 20 °C. Above 20 °C rm became temperature insensitive while rg increased with growth temperature. Despite these complex component responses, R:P increased only from 0.40 to 0.43 between 15° and 30 °C growth temperatures. Giving the plants a step increase in temperature caused a transient increase in R:P which recovered to the pre‐transient value in 3 days. It is concluded that use of a constant R:P with respect to average temperature and CO2 concentration may be a more simple and accurate way to model the responses of wheat crop respiration to ‘climate change’ than the more complex and mechanistically dubious functional analysis into growth and maintenance components.

Apoplastic pH of intact leaves ofVicia fabaas influenced by light

The fluorochrome FITC-dextran was used to measure the effect of light on the apoplastic pH of intact Vicia faba leaves with the ratio imaging technique. In darkadapted leaves the apoplastic pH varied depending on the leaf between 5.2 and 5.9. Red light (660 nm, 4–12 W m−2) leads to multiphasic responses: in the first seconds an alkalinization (˜0.3 pH units), and thereafter an acidification of the leaf apoplast (˜0.4 pH units) were observed. Both effects could be inhibited by DCMU. While variation of CO2 concentration revealed no effect on light-induced apoplastic pH changes, a decrease in O2 concentration decreased the effect. On the basis of our data it is suggested that the influence of photosynthesis on plasmalemma H+ ATPase is responsible for the observed effects, rather than altered CO2 uptake.

Refined estimation of marine and terrigenous contributions to sedimentary organic carbon

Molecular carbon isotopic (13C/12C) ratios of a selected marine organic biomarker compound (a C37 alkadienone) from the Pigmy Basin (Deep Sea Drilling Program Hole 619) in the northern Gulf of Mexico varied by 5.3‰ in sychrony with the last ∼100 ka glacial‐interglacial cycle. This carbon isotopic (δ13C) variation is likely due to the effect of climatically linked variations in concentrations of CO2(aq) on photosynthetic fractionation of carbon isotopes by phytoplankton. Measurement of the δ13C of the alkadienone (δ37:2) to reconstruct the carbon isotopic composition of total marine organic carbon permits improved estimates of the time‐varying δ13C of preserved marine organic carbon end members. With the time series record of marine end members, the concentrations and net accumulation rates of terrigenous Corg and marine Corg are calculated and their paleoceanographic significance is considered. Although this method may be improved by consideration of additional biomarkers representative of diverse marine and terrigenous inputs, it is the first application of molecular isotopic analysis to quantifying marine and terrigenous Corg concentrations. Further application of such techniques will be become valuable in reconstructing regional and global budgets of marine and terrigenous Corg accumulation.

The Impact of Atmospheric CO2 and Temperature Changes on Stomatal Density: Observation from Quercus robur Lammas Leaves

A comparative study of leaves formed on shoots during the spring and summer (lammas) of Quercus robur from three contrasting geographical locations (Cardiff, Durham and London) gives a measure of the effect of temperature on stomatal density. This is of value in attempting to distinguish the effects of CO2 and temperature on observed stomatal density changes under different CO2 and temperature conditions through the Quaternary. These leaves of normal and lammas shoots will have developed under similar CO2 levels but different environmental temperatures. Our results demonstrate that leaves formed under the warmer summer temperatures had reduced stomatal densities and indices from all sites, compared with their spring counterparts. This trend was also detected from measurements of spring and summer leaves made upon herbarium material collected from the same tree in 1840. The results suggest that for Q. robur temperature overrides the influence of irradiance intensity and small seasonal (⩽ 10 ppmv) variations of CO2 concentration in determining stomatal density. In accordance with previous work we have also documented a decline in stomatal density since 1840 by examining herbarium leaf material in response to the rising atmospheric CO2 concentration determined from ice core studies. In conclusion, if we are to understand changes in stomatal density as a response to CO2 linked temperature changes (the 'greenhouse effect') it is important to distinguish the effects of these two environmental parameters on plants.

CO2 environment, microclimate and photosynthetic characteristics of the moss Hylocomium splendens in a subarctic habitat.

In order to document the natural CO2 environment of the moss Hylocomium splendens, and ascertain whether or not the moss was adapted to this, and its interactions with other microenvironmental factors, two studies were carried out. Firstly, the seasonal variations of CO2 concentration, photosynthetically active radiation (PAR), tissue water content and temperature were measured in the natural microenvironment of H. splendens in a subarctic forest during the summer period (July-September). Secondly, the photosynthetic responses of the species to controlled CO2 concentrations, PAR, temperature, and hydration were measured in the laboratory. CO2 concentrations around the upper parts of the plant, when PAR was above the compensation point (30 μmol m-2 s-1), were mostly between 400 and 450 ppm. They occasionally increased up to 1143 ppm for short periods. PAR flux densities below saturating light levels for photosynthesis (100 μmol m-2 s-1), occurred during 65% (July), 76% (August) and 96% (September) of the hours of the summer period. The temperature optimum of photosynthesis was 20° C: this temperature coincided with PAR above the compensation point during 5%, 6% and 0% of the time in July, August and September, respectively. Optimal hydration of tissues was infrequent. Hence PAR, temperature and water limit CO2 uptake for most of the growing season. Our data suggest that the higher than normal ambient CO2 concentration in the immediate environment of the plant counteracts some of the limitations in PAR supply that it experiences in its habitat. This species already experiences concentrations of atmospheric CO2 predicted to occur over the next 50 years.

Challenges in Linking Atmospheric CO2 Concentrations to Fluxes at Local and Regional Scales

We describe relationships between atmospheric CO2 concentration variations and CO2 source-sink distributions, at two important scales between the single plant and the whole earth: the vegetation canopy and the atmospheric planetary boundary layer. For both these scales, it is shown how knowledge of turbulence and scalar dispersion can be applied to infer CO2 source-sink distributions or fluxes from concentration measurements. At the canopy scale, the turbulent transfer of CO2 and other scalars is non-diffusive close to any point source or sink in the canopy, but diffusive at greater distances. This distinction leads to a physically tenable description of turbulent transfer, and thence to an 'inverse method' for finding the vertical profiles of sources and sinks in the canopy from measured concentration profiles. The method is tested with data from a wheat crop. At the scale of the planetary boundary layer, we consider the daily CO2 concentration drawdown (the depression of the near-surface CO2 concentration below the free-atmosphere value) of typically 20-40 ppm. This is determined by both the regionally averaged CO2 uptake at the surface and the growth of the daytime convective boundary layer (CBL). It is shown that, for a column of air which fills the CBL and is moved across the landscape by the mean wind, the net cumulative surface CO2 flux (in mol m-2) is given to a good approximation by h(t)[Cm(t) - C+]/V, where h(t) is CBL depth, Cm(t) the CO2 concentration in the CBL column in mol mol-1, C+ the concentration above the CBL, V the molar volume and time t is measured from the time at which Cm = C+ in the morning, typically about 0800 hours local time. The resulting CO2 flux estimates are regionally averaged over the trajectory followed by the column. This 'CBL budget method' for inferring surface fluxes is compared with direct measurements of CO2 fluxes, with satisfactory results. The technique has application to scalars other than CO2.

Atmospheric CO_2 Concentrations Within a Mixed Forest: Implications for Seedling Growth

We studied carbon dioxide concentrations in a mixed deciduous forest in New England, USA by making continuous measurements at 0.05, 0.2, 3, and 12 m above the soil surface. The measurements began in early March and continued until the end of November 1985; therefore, they spanned the growing season and parts of the dormant seasons both before and afterwards. The data were compared with those from Mauna Loa, Hawaii, which represent global atmospheric CO2 levels in the Northern Hemisphere. The results show strong seasonal and daily variations in CO2 concentrations at all heights in the forest. On average, during the growing season, CO2 levels were generally higher in the forest than in bulk air at Mauna Loa. The highest level of CO2 was found near the forest floor and the lowest at the 12—m level. Daily levels of CO2 were constant throughout the day in the dormant season and were the same for all heights in the forest. However, during the growing season, the CO2 concentrations were lowest during the middle of the day, especially at the 12 m height. Thus, this study shows that the CO2 concentrations in the forest may be quite different than those in bulk air and that seedlings, saplings, and mature trees may experience different CO2 environments for which they may show different responses in photosynthesis, growth, and water use. Moreover, a tree may experience different CO2 environments as it grows towards the canopy, and different modules of an individual may also be growing in different CO2 atmospheres.

Stable isotopes of carbon dioxide in soil gas over massive sulfide mineralization at Crandon, Wisconsin

Alpers, C.N., Dettman, D.L., Lohmann, K.C. and Brabec, D., 1990. Stable isotopes of carbon dioxide in soil gas over massive sulfide mineralization at Crandon, Wisconsin. In: S.E. Kesler (Editor), Soil and Rock Gas Geochemistry. J. Geochem. Explor., 38: 69-86. Stable isotope ratios of oxygen and carbon were determined for CO2 in soil gas in the vicinity of the massive sulfide deposit at Crandon, Wisconsin with the objective of determining the source of anomalously high CO2 concentrations detected previously by McCarthy et al. (1986). Values of tSl3C in soil gas CO2 from depths between 0.5 and 1.0 m were found to range from - 12.68%0 to -20.03%0 (PDB). Organic carbon from the uppermost meter of soil has ~ t3C between -24.1 and -25.8%0 (PDB), indicating derivation from plant species with the Ca (Calvin) type of photosynthetic pathway. Microbial decomposition of the organic carbon and root respiration from C3 and C4 (HatchSlack) plants, together with atmospheric CO2 are the likely sources of carbon in soil gas CO2. Values of t~tsO in soil-gas CO2 range from 32 to 38%0 (SMOW). These ~sO values are intermediate between that calculated for CO2 gas in isotopic equilibrium with local groundwaters and that for atmospheric CO2. The 6IS o data indicate that atmospheric CO2 has been incorporated by mixing or diffusion. Any CO2 generated by microbial oxidation of organic matter has equilibrated its oxygen isotopes with the local groundwaters. The isotopic composition of soil-gas CO2 taken from directly above the massive sulfide deposit was not distinguishable from that of samples taken 1 to 2 km away. No enrichment of the t~3C value of soil-gas CO2 was observed, contrary to what would be expected if the anomalous CO2 were derived from the dissolution of Proterozoic marine limestone country rock or of Paleozoic limestone clasts in glacial till. Therefore, it is inferred that root respiration and decay of C3 plant material were responsible for most CO2 generation both in the vicinity of the massive sulfide and in the background area, on the occasion of our sampling. Interpretation of our data is complicated by the effects of rainfall, which significantly reduced the magnitude of the CO2 anomaly. Therefore, we cannot rule out the possible mechanism of carbonate dissolution driven by pyrite oxidation, as proposed by Lovell et al. ( 1983 ) and McCarthy et al. ( 1986 ). Further work is needed on seasonal and daily variations of CO2 concentrations and stable isotope ratios in various hydrogeologic and ecologic settings so that more effective sampling strategies can be developed for mineral exploration using soil gases.

The Effect of External Stimuli on Rat Middle Ear Epithelium in Culture

Serially cultivated rat middle ear epithelium was studied under exposure to various concentrations of carbon dioxide. Three experiments were performed exposing the epithelium to a gaseous environment containing 5 or 10% CO2 or to an atmosphere almost devoid of CO2. Oxygen was maintained constant at 20% and nitrogen was additionally supplied. Cells exposed at 0% CO2 showed a remarkably different morphology compared with the cultures at 5 and 10% CO2, cells could become extremely large at 0% CO2, also showing a great variation in shape and cell size within the culture. Proliferation was significantly impaired at 0% CO2 vis-à-vis the 5 and 10% experiments. Terminal differentiation, however, was not influenced by the different CO2 concentrations, indicating that in vitro, variation in CO2 concentration is of no importance regarding a possible differentiation of middle ear epithelium into a cornifying epithelium.

Development of an infrared laser long-path absorption system using a Raman shifter.

An infrared laser long path absorption experimental system has been developed using a dyelaser pumped by an Nd: YAG laser and a hydrogen Raman shifter. The accuracy of the measurement system was evaluated by CO2 absorption experiment using an open path in the laboratory and a long-path cell. The measurement error was estimated at less than 0.5 percent in a 10-minute measurement, indicating that the accuracy was high enough for observing diurnaland seasonal variations in CO2 concentration. From the systematic analysis of the measurement errors, the kind of error limiting the system performance was identified. A method for further improvement of the measurement accuracy was investigated.

A GLASSHOUSE CLIMATE MODEL AS PART OF A BIO-ECONOMIC MODEL.

Bio-economic models can be used as base for decision support systems. In protected cultivations, the glasshouse climate is of major importance on the financial result, both by costs and by yield. In this paper, a mechanistic climate model is described in detail. This glasshouse climate model is repartioned into four submodels: radiation- and lightintensity, heat- and daily ventilation need, mean day- and 24 hours temperature and a gas consumption submodel. Variation in CO2-concentration and low temperatures, especially at night had a large influence on the productivity.

The effects of illumination sequence, CO2 concentration, temperature and acclimation on the convexity of the photosynthetic light response curve

It was shown previously that the convexity (curvature or rate of bending) of the photosynthetic light response curve was strongly correlated with chlorophyll content in shade acclimated conifer needles (Leverenz 1987, Physiol. Plant. 71: 20–29), in agreement with an hypothesis that gradients of light within leaves affect the convexity. In the present study it is shown that the convexity at any given chlorophyll content can be altered when leaves of Pinus sylvestris L. Picea glauca (Muench), Picea mariana (M.II.) BS.P. and Picea abies (L.) Karst pre‐treated with less shade. This probably induced a differential acclimation of cells on the top and bottom sides of the leaves to their local light environment. Leaves were illuminated on i) their top surface, ii) their bottom surface, or iii) uniformly in a light integrating sphere during measurements of photosynthesis. After shoots had been transferred from their growth environment to a new measuring environment, the convexity increased from the first to the second day towards a maximum of 0.97. The rate of increase towards this maximum was 55 to 62% per day and probably is the result of re‐acclimation of cells within the leaves. The data shown that the act of measuring photosynthesis induces a significant alteration in the experimental material when measurements are made for more than one day.The convexity of the light response curve of photosynthesis, was independent of whether the steady state measurements were made beginning in the dark and sequentially increasing photon flux density or beginning at high light and sequentially lowering photon flux density. Neither variation of CO2 concentration from 35 to 200 Pa, nor of temperature from 5° to 32°C affected the convexity.

Relating Nimbus-7 37 GHz data to global land-surface evaporation, primary productivity and the atmospheric CO2concentration

Abstract Global observations at 37 GHz frequency by the scanning multichannel microwave radiometer (SMMR) on board the Nimbus-7 satellite are related to zonal variations of land surface evaporation and primary productivity, and to temporal variation of atmospheric CO2 concentration. The ground resolution of the 37 GHz data used in this study is 0·25° × 0·25° (latitude × longitude) and is composited monthly from January 1979 to December 1985. The annual actual evaporation and primary productivity data are extracted from the literature and correspond to averages for 5° latitude bands from 75° N to 55°S, while the CO2 data are monthly observations at 20 globally distributed monitoring stations from August 1981 to July 1983. The satellite sensor data have been averaged for 7 years and then averaged zonally in 5° latitude bands to relate to evaporation and primary productivity, while the monthly satellite sensor data have been averaged from 75° N to 55° S to relate to the CO2 data. The temporal variation of CO2 concentration and the zonal variations of evaporation and primary productivity are shown to be highly correlated with the satellite sensor data. Evaporation and primary productivity for latitude bands in the Sahel zone of Africa appear anamolous when compared with the satellite sensor data, perhaps because the estimated evaporation and primary productivity values do not represent the recent drought conditions over the Sahel zone. Potential usefulness of the 37 GHz data for global biospheric and climate studies are suggested.

Statistical Fluctuations of Temperature and Conversion at the Catalytic CO Oxidation in an Adiabatic Packed Bed Reactor

AbstractThe oxidation of CO with air at a Pt/γ‐Al2O3 supported catalyst employed in an adiabatic fixed‐bed reactor, is accompanied by nonperiodic variations of CO2 concentration and temperature at the reactor exit. The occurrence of these variations is confined to the region of bifurcation from monostable to bistable behaviour of the fixed‐bed reactor. The variations originate from small temporal and local fluctuations of the reaction rate—and hence the temperature—in the entrance cross‐section of the catalyst bed. In the bifurcation region the temperature humps of these fluctuations (ΔT ≈ 0.5 K) are strongly amplified and finally form reaction zones (ΔT ≈ 120 K) which move to the reactor exit with velocities of 3.5 to 11 mm/min. Measurements at a cluster of 10 catalyst pellets exposed to the CO/air gas stream showed that the fluctuations at the entrance of the fixed bed can be attributed to kinetic oscillations occurring in the regime of descending reaction rate with increasing CO feed. By periodic variations of the CO feed the reaction can be forced to show harmonic or subharmonic resonance. In the latter case, the quasiperiodic Fourier spectrum of the unperturbed reaction turns to a spectrum with a sextet at the subharmonic frequency.

Effects of incubation in an atmosphere of 20% CO2 in air on the syrian hamster embryo clonal transformation assay

An atmosphere containing 10% CO2 has been generally accepted as optimal for the growth of Syrian hamster embryo cells in a clonal transformation assay. Data presented in this paper show that 10% CO2 may not be the optimum environment for this assay. Using 10 or 20% (analytically measured) CO2 in air (1 atm pressure), hamster embryo cell pools were examined for clonal growth characteristics and transformability using five known carcinogens and a single noncarcinogenic compound. At 10% CO2, only 2 of 11 pools were transformed by the five carcinogens but not by the noncarcinogen. At 20% CO2, six of seven pools were transformed by the five carcinogens and not by the noncarcinogen. Further, the transformation frequencies were found to be greater in cultures incubated in an atmosphere consisting of 20% CO2 in air. The data also show that 20% CO2 increased the cloning efficiency of these cells. A comparison of the 10 and 20% CO2 data to results reported from other laboratories suggests that conflicting interlaboratory results with this assay system may be due, in part, to variations of CO2 concentrations. In some instances, the CO2 levels indicated by incubator flow meters vary considerably from analytically determined CO2 values. To prevent these CO2 discrepancies and their resultant effects on transformation and cloning efficiency, methods for monitoring the CO2 environment other than flow meters are recommended. The observation of increased cloning efficiencies and transformation rates strongly suggests that culture incubation at 20% CO2 is a preferred environment for the conduct of this assay.

Atmospheric CO2 Concentration During the Last Glaciation

Analyses of atmospheric air extracted from air bubbles in polar glacier ice provide a measure of past CO2 concentrations and their temporal variations. Earlier measurements have shown that the atmospheric CO2 concentration was significantly lower during the late Wisconsin stage and that the change from low to high CO2 concentration occurred in a relatively short time period.We measured the CO2 concentration of ice samples from the deep ice core recently drilled at Dye 3 (south Greenland). The core section investigated represents ice from about 40 to 30 ka BP. The air extracted from the ice samples shows large variations of CO2 concentration which are correlated with δ18O values of the ice samples. A probable explanation of the results is that corresponding changes of the atmospheric CO2 concentration occurred during that glacial period. These changes could have had a significant influence on the climate. Possible reasons for the variations of the atmospheric CO2 concentration are discussed.