Showing papers on "Carbon dioxide in Earth's atmosphere published in 1994"

Effect of deep-sea sedimentary calcite preservation on atmospheric CO 2 concentration

Abstract: DURING the last glaciation, the atmospheric carbon dioxide concentration was about 30% less than the Holocene pre-industrial value1. Although this change is thought to originate in oceanic processes2, the mechanism is still unclear. On timescales of thousands of years, the pH of the ocean (and hence the atmospheric CO2 concentration) is determined by a steady-state balance between the supply rate of calcium carbonate to the ocean from terrestrial weathering, and the alteration and removal of carbonate by burial in sediments2–4. Degradation of organic carbon in sediments promotes the dissolution of calcium carbonate in sedimentary pore water5,6, so that a change in the relative rates at which organic carbon and calcium carbonate are deposited on the sea floor should drive a compensating change in ocean pH. Here we use a model that combines ocean circulation, carbon cycling and other sedimentary processes to explore the relationship between deep-sea-sediment chemistry and atmospheric CO2 concentration. When we include organic-carbon-driven dissolution in our model, a 40% decrease in the calcite deposition rate is enough to decrease the atmospheric CO2 concentration to the glacial value.

Stimulation of methane emission by carbon dioxide enrichment of marsh vegetation

Abstract: THERE is substantial evidence that many plants respond to increased concentrations of atmospheric carbon dioxide by increasing their productivity1–4. This observation has led to the suggestion that, by taking up CO2, the terrestrial biosphere might mitigate the potential greenhouse warming associated with anthro-pogenic CO2 emissions5. Whiting and Chanton6 have found, how-ever, that for wetlands of varying productivity around the world, higher net primary production is associated with higher emissions of methane—another important greenhouse gas. Here we present measurements of methane emissions from a marsh that has been exposed to twice the present ambient concentration of atmospheric CO2. We find that over a one-week period, the CO2-enriched sites had significantly higher emissions of methane than the control sites. Our results suggest that future increases in atmospheric CO2 concentration may lead to significant increases in methane emis-sions from wetlands.

Influence of atmospheric CO2 on the decline of C4 plants during the last deglaciation

Abstract: CHANGES in atmospheric carbon dioxide concentrations in the past may have caused changes in vegetation type1,2, and it has been suggested2 that the isotopic signature of such vegetation shifts, preserved in palaeosols3, might be used as a proxy for past CO2 variations. But the connection between palaeosol isotopic signatures and atmospheric CO2 concentrations has been difficult to establish, partly because of the unreliability of CO2 proxies and partly because of the difficulty in ruling out other potential causes of vegetation changes, such as climate4. Here we present palaeosol carbon isotope ratios that reveal a shift from C4-dominated grasses to C3-dominated shrubs about 7–9 kyr ago on an alluvial fan system in the Chihuahuan desert, New Mexico. This coincides with a rapid increase in atmospheric CO2 concentration recorded in Antarctic ice cores5–8 and increased aridity recorded by geo-morphic reconstructions9–11 and packrat remains12. Palaeosol oxygen isotope ratios, which depend on temperature and moisture, were relatively constant during the vegetation shift, suggesting that the CO2 change, rather than climate, was the dominant cause. We conclude that the carbon isotope ratios of ancient soils can indeed be used as a proxy for past CO2 changes.

Cooler estimates of Cretaceous temperatures

Abstract: THE Creataceous period is thought to have been warmer than the present1–3, with higher concentrations of atmospheric greenhouse gases such as carbon dioxide4. It has therefore been suggested5 that this time period could be used by modellers as an analogue for future climate change. But the Cretaceous Equator-to-Pole temperature gradient was flatter than today's, leading some to suggest that Cretaceous climate arose from a combination of factors, with higher atmospheric carbon dioxide concentrations leading to general warming, and other factors, such as increased ocean heat transport, leading to flattening of the latitudinal temperature gradient. Here we report new records of ocean palaeotemperature for Cenomanian sites in the Atlantic and Pacific oceans which, together with a re-evaluation of published data, cast doubt on the idea that the Cretaceous period was generally warmer. These data confirm that the latitudinal temperature gradient was flatter, but suggest that the global mean temperature was much cooler than previously believed, with minimum mean equatorial temperatures close to present values and polar temperatures close to 0 °C. In the light of these findings, the climatic role of atmospheric carbon dioxide in determining Cretaceous climate is unclear, suggesting that the Cretaceous cannot be used as an analogue for future climate change.

Trends in atmospheric carbon dioxide over the last ten to fifteen years

Abstract: This study looks at the relative importance of the factors which control the concentration of atmospheric carbon dioxide. EOF analyses are run for both the seasonal and non-seasonal variations for the ten years from 1981 to 1990. The first seasonal EOF represents the anthropogenic component as well as the breathing of the land biosphere. Representing 85% of the variation, it has a seasonal variation of almost 6. The second shows the component of just the land biosphere and has a seasonal variation of about 4. The third seasonal EOF is thought to portray the effect of upwelling in the Eastern Pacific on the tropical strip. The first non-seasonal EOF, accounting for 97% of the total variance, shows an increase of about 11.7 for the period; that of the Northern Hemisphere is about 1.5 times that of the Southern Hemisphere. A modification was made to the original anomalies to adjust for the long term trend in the carbon dioxide data. The rest of the procedure was the same. The first seasonal EOF, contributing to 65.8% of the variance, appears to represent changes in the NH terrestrial biosphere. The second seasonal EOF shows the variance between the long-term trend and the actual data. The third seasonal EOF, with a variance of 4, again depicts the oceanic variance due to upwelling off the coast of Peru. The first non-seasonal EOF matches the activity of the El Nifio, supporting the theory that upwelling increases atmospheric CO2 concentration. It represents over 50% of the total variation. Error in this study may stem from unreliable station data due to infrequent sampling, not a long enough time period for the analysis, and not enough stations to develop a good global result. A stronger, standardized network would greatly enhance the outcome of this analysis. Thesis Supervisor: Reginald Newell Title: Professor Acknowledgments I would like to thank Professor Reginald Newell for all his help and understanding as my advisor. He always managed to find that one piece of information I was looking for, and also helped me through some difficult times. To Wenjie Hu, I am forever indebted for her help with my attempts to program in a language which I knew nothing about, not to mention teaching me everything she new about eigenvector analysis. No matter how matter how many times I asked, she patiently explained everything until I finally understood it. I also want to thank my parents, Ronald and Arlene Strader, for their help and support of me in everything, no matter how small, that I have ever tried to do. They have always been there when I needed them. To my best friends Michelle Bakkila, John Hansen, Andrea Jensen, and Theresa Hutchings, I just want to say, I don't know how I could have gotten through and remained sane without you.

Model simulations of Cretaceous climates: the role of geography and carbon dioxide

Abstract: A general circulation model (GENESIS) with seasonally varying solar insolation and a mixed layer ocean is applied to assess the role of continental geometry and increased levels of carbon dioxide to explain the warmth of the Cretaceous period. Model experiments suggest that the role of geography is negligible, in contrast to early model studies with mean annual solar insolation and a simple energy balance ocean. Higher atmospheric carbon dioxide (4 times present) resulted in a 5.5°G globally averaged surface temperature increase, close to the lower limit required to explain the geologic record. Mid-Cretaceous carbon dioxide concentrations of 4–6 times the present day concentrations are a reasonable explanation of Cretaceous warmth if the GENESIS model provides an accurate estimate of climate sensitivity to geography and carbon dioxide.

Carbon export from continental shelves, denitrification and atmospheric carbon dioxide

Abstract: To investigate the long-term role of continental shelves, a global carbon ☐ model which included continental shelf waters and sediments, ocean surface waters, the deep-sea and the atmosphere was constructed. With nitrogen limiting oceanic primary production, the model included balanced nitrogen inputs (from the continents and atmosphere) and losses (primarily via denitrification). Carbon export to the deep-sea (without deposition or burial in sediments) affected the average conditions found in the shelves but did not influence atmospheric carbon dioxide content. Similarly, redistribution of nitrogen inputs to the surface oceans had no major effect on atmospheric pCO2. In contrast, atmospheric pCO2 changes were caused by redistribution of denitrification rates between the continental shelf sediments and the deep-sea. When denitrification in continental shelf sediments increased from 10% of the total oceanic rate to 95%, shelf denitrification removed more nitrogen from the surface ocean, supporting less of a flux of sinking particulate carbon (SPC) into the deep-sea. This increased atmospheric pCO2 by 11 ppm. When overall rates of nitrogen cycling were decreased by half to today's level, the atmospheric pCO2 content was increased by an additional 5 ppm. These effects may have influenced the ice-ages. As the glaciers expanded, shelf denitrification was lessened by the reduction in continental shelf area. Moving the site of denitrification from the shelves to the deep-sea would have increased both oceanic new production and the SPC flux into the deep-sea, thereby lowering atmospheric pCO2 levels during the initial periods of glaciation. Increased new production may have enhanced water column denitrification which in turn lowered the oceanic inorganic nitrogen content and restricted oceanic productivity. With less oceanic nitrogen, water column denitrification would have decreased resulting in a more equal proportioning of the total removal rate between the deep-sea and the continental shelves. Also, the total cycling rate of nitrogen would have lessened. In addition, inundation of the continental shelves during glacial retreat would have increased shelf denitrification. From the model, these trends would have released CO2 from the ocean, accentuating global warming and hastening the return to the interglacial climate.

Air-sea carbon dioxide exchange in the North Pacific subtropical Gyre: Implications for the global carbon budget

Abstract: The role of the ocean as a sink for anthropogenic carbon dioxide is a subject of intensive investigation and debate. Interest in this process is driven by the need to predict the rate of future increase of atmospheric carbon dioxide and subsequent global climatic change. Although estimates of the magnitude of the oceanic sink for carbon dioxide appear to be converging on a value of ∼2 (Gt) C yr−1 for the 1980s, a detailed understanding of the temporal and spatial variability in the rate of exchange of carbon dioxide between the ocean and the atmosphere is not available. For example, recent modeling work and direct measurements of air-sea carbon dioxide flux produce very different estimates of the air-sea flux in the northern hemisphere. As a consequence, it has been suggested that a large unidentified oceanic carbon dioxide sink may exist in the North Pacific. As a part of our time series observations in the North Pacific Subtropical Gyre, we have measured dissolved inorganic carbon and titration alkalinity over a four-year period. These measurements constitute the most extensive set of observations of carbon system parameters in the surface waters of the central Pacific Ocean. Our results show that the ocean in the vicinity of the time series site is a sink for atmospheric carbon dioxide. On the basis of these observations, we present a mechanism by which the North Pacific Subtropical Gyre can be a potential sink for ∼0.2 Gt C yr−1 of atmospheric carbon dioxide. Although our observations indicate that the North Pacific Subtropical Gyre is a sink for atmospheric carbon dioxide, the magnitude of this oceanic sink is relatively small. Our data and interpretations are therefore consistent with the argument for a relatively large sink during the 1980s in northern hemisphere terrestrial biomass. Another possibility is that the net release of carbon dioxide to the atmosphere owing to land use activities in tropical regions has been overestimated.

Roles of Nutrients in Controlling Growth of Epilithon in Oligotrophic Lakes of Low Alkalinity

Abstract: The ability of nutrients to control photosynthesis was compared in epilithon (the association on rock surfaces in the littoral zone) and phytoplankton of 13 low alkalinity lakes of the Experimental Lakes Area of northwestern Ontario. The study included (1) surveys of lakes varying in nutrient concentrations; (2) experimental additions to lakes of carbon and nitrogen (N), with or without phosphorus (P); and (3) experimental additions to lakes of sulfuric and nitric acids. Nutrient controls of planktonic and epilithic algal photosynthesis differed consistently. Phosphorus limited planktonic algal photosynthesis. In contrast, dissolved inorganic carbon (DIC) limited epilithic photosynthesis in both perturbed and unperturbed lakes because diffusive resistance kept the effective supply of DIC below the level needed for optimal growth. Epilithic photosynthesis was lowered when lake disturbances (e.g., acidification) reduced epilimnetic concentrations of DIC. Expected increases in atmospheric carbon dioxide can,...

Negotiating Climate Change: The Climate Change Negotiations

Abstract: Prologue Few issues have acquired priority in the international agenda in as short a time as global warming. Up to the early 1970s many scientists believed that the Earth might be moving towards a new ice age and that increasing levels of emissions of greenhouse gases (GHGs) from human activities would not alter this course and might even be helpful in slowing down this movement. It was only towards the close of the decade that scientific opinion tentatively endorsed the view that on average global temperatures might be rising. The first World Climate Conference, organized by the World Meteorological Organization (WMO) in Geneva in 1979, cautiously concluded that: It can be said with some confidence that the burning of fossil fuels, deforestation and changes of land use have increased the amount of carbon dioxide in the atmosphere by about 15 per cent during the last century and that it is at present increasing by about 0.4 per cent per year … it appears plausible that an increased amount of carbon dioxide in the atmosphere can contribute to a gradual warming of the lower atmosphere, especially at high latitudes. Despite continuing uncertainties in many of its aspects, this hypothesis made rapid headway in scientific circles in the 1980s. Workshops held in Villach (Austria) in October 1985 and in October 1987, and in Bellagio (Italy) in November 1987 gave impetus to this development.

Responses of respiration to increasing atmospheric carbon dioxide concentrations

Abstract: It has been recently recognized that increases in carbon dioxide concentration such as are anticipated for the earth's atmosphere in the next century often reduce plant respiration. There can be both a short-term reversible effect of unknown cause, and long-term acclimation, which may reflect the synthesis and maintenance of less metabolically expensive materials in plants grown at elevated carbon dioxide concentrations. Because respiration provides energy and carbon intermediates for growth and maintenance, reductions in respiration by increasing carbon dioxide concentrations may have effects on physiology beyond an improvement in plant carbon balance. As atmospheric carbon dioxide concentration increases, reduced respiration could be as important as increased photosynthesis in improving the ability of terrestrial vegetation to act as a sink for carbon, but it could also have other consequences.

Glacial-interglacial changes in continental weathering: possible implications for atmospheric CO2

Abstract: An eleven-box model of the ocean-atmosphere subsystem of the global carbon cycle is developed to study the potential contribution of continental rock weathering and oceanic sedimentation to variations of atmospheric CO2 pressure over glacial-interglacial timescales. The model is capable of reproducing the distribution of total dissolved inorganic carbon, total alkalinity, phosphate, δ13C, and Δ14C between the various ocean basins today, as well as the partial pressure of atmospheric CO2. A simple sedimentation scheme at 20 different depth levels drives carbonate deposition and dissolution as a function of the depths of carbonate and aragonite lysoclines in each ocean basins considered (Atlantic, Antarctic and Indo-Pacific). The coral-reef erosion-deposition cycle is also taken into account. Furthermore, a simple cycle of oceanic strontium isotopes has been added to this model to take advantage of the 87Sr/86Sr data recently published by Dia et al. (1992) for the last 300,000 years. These data emphasize the importance of weathering of continental silicate rocks at glacial-interglacial timescales. They are used to construct several scenarios of changes of continental weathering over the last glacial cycles. They suggest that the flux of alkalinity delivered to the ocean from continental silicate weathering may have been substantially larger during glacial times than today. We show that such variations of continental weathering may explain at least in part the observed changes of the partial pressure of atmospheric CO2 between glacial and interglacial periods.

Diurnal temperature range for a doubled carbon dioxide concentration experiment: Analysis of possible physical mechanisms

Abstract: An analysis of the results of a climate simulation for a doubling of atmospheric carbon dioxide concentration over the European region is reported. Physical mechanisms are sought which could explain possible changes in the diurnal temperature range (DTR) under conditions of increased atmospheric greenhouse gas content. We show that an important contribution to changes in DTR is given by soil moisture. In areas where soil moisture increases due to an increase in precipitation there is a positive change in latent heat flux and a decrease in sensible heat flux. As a result, in areas with increasing soil moisture, the increase in maximum daytime temperature will be smaller than that in minimum temperature, thereby causing a decrease in the DTR. The opposite occurs for areas which undergo soil drying. This process amplifies the effect of cloud changes on surface solar and infrared radiation and dominates the direct effect of downward infrared radiation associated with increasing greenhouse gas concentration. Because the soil water content is largely controlled by precipitation, our results are consistent with early observational findings of negative correlation between changes in precipitation and in diurnal temperature range.

Self-organization of the earth's biosphere-geochemical or geophysiological?

Abstract: We explore the implications of indicating the biosphere's self-organization by the trend over time of the net entropic flow from the Earth's surface, the actual physical boundary of virtually all biotic mass. This flow, derived from the radiative surface entropy budget, is approximately inversely related to the surface temperature when the solar incident flux remains constant. In the geophysiological ('gaian') interpretation, biospheric self-organization has increased with the progressive colonization of the continents and evolutionary developments in the land biota, as a result of surface cooling arising from biotic enhancement of weathering. The key site for this self-organization is at the interface between land and atmosphere, the soil, where carbon is sequestered by its reaction (as carbonic and organic acids) with calcium magnesium silicates. Along with disequilibrium (steady-state) levels of carbon dioxide in the atmosphere, the occurrence of differentiated soil is the critical material evidence for biospheric self-organization, whether it be geophysiological or geochemical (ie., purely result of inorganic reactions). The computed equilibrium levels of carbon dioxide and corresponding equilibrium temperatures in the past are dramatically different from the steady-state levels. With future solar luminosity increase, the biospheric capacity for climatic regulation will decrease, leading to the ending of self-organization some two billion years from now. The Earth's surface will then approach chemical equilibrium with respect to the carbonate-silicate cycle.

Carbon dioxide concentrations in surface water and the atmosphere : PMEL cruises 1986-1989

Abstract: 1

The Recent State of Carbon Cycling through the Atmosphere

Abstract: A summary of our knowledge about the recent carbon cycle is presented from the perspective of atmospheric observations. Particular emphasis is given to carbon isotopes as a tool to determine global carbon sources and sinks as well as their recent anthropogenic changes. In the case of atmospheric carbon dioxide, the yearly anthropogenic emissions are small if compared to the gross exchange between the most important reservoirs: biosphere and ocean. In order to derive net fluxes caused by climatic or anthropogenic perturbations, the gross fluxes have to be known as accurately as possible. One isotopic tool is to trace the penetration of bomb 14C into the ocean surface water so as to derive the atmosphere/ocean gas-exchange rate. Moreover, the distribution of δ13C in atmospheric CO2 can help to constrain the amount of excess CO2 taken up (or released) by the global biosphere. As for atmospheric methane, anthropogenic emissions today exceed natural release rates by nearly a factor of two. Although the total yearly methane emissions to the atmosphere are believed to be known to within 10–20%, large uncertainties still remain in the estimates for individual sources, in particular for natural ecosystems like wetlands and the oceans. Isotope observations provide strong constraints also for the global atmospheric methane budget because different source types (biogenic vs. thermogenic) produce their own characteristic isotopic fractionations during methane production. These isotopic signatures can be used further to predict the future development of atmospheric methane concentrations and to understand better the drastic changes observed in the past under different conditions.

The ocean as part of the global carbon cycle.

Abstract: The ocean plays a central role in the global carbon cycle being by far the largest active reservoir. Atmospheric CO2 level depends on the CO2concentration in the ocean surface layer, which is relatively low compared to mean oceanic values due to biological and physical carbon pumps. Although the ocean may take up much of the carbon released by the increased burning of fossil fuels, this capacity is limited because of the chemical buffering and a mismatch in time scales (oceanic mixing is much slower than anthropogenic perturbations).

Potential of controlled anaerobic wastewater treatment in order to reduce the global emissions of methane and carbon dioxide

Abstract: Based on literature an estimation is made of the potential global production and atmospheric emission of both methane and carbon dioxide from treatment of wastewaters from the Food & Beverage and Pulp & Paper Industry. Two main cases are considered: All wastewater is treated aerobically, and all wastewater is treated anaerobically. Methane production is estimated to be, respectively, 0.1–0.2 and 14–15 Tg/y, while atmospheric methane emission is estimated to be 0.1–0.2 and 0–2.2 Tg/y, respectively. Carbon dioxide production from fossil fuel use is estimated to be, respectively, 18 and 0 Tg/y, and atmospheric carbon dioxide emission is estimated to be 18 Tg/y and −30 Tg/y respectively. Calculations indicate that the potential of anaerobic treatment to reduce the global methane emission is limited (about 0.5% of the anthropogenic methane emission). The atmospheric emission of carbon dioxide from wastewater treatment, however, can be significantly reduced. Application of controlled anaerobic treatment systems, with a minimum of CH4 loss, consequently has a significant potential of reducing the total Global Warming Potential due to wastewater treatment.

Trace Gas Emissions to the Atmosphere by Biomass Burning in the West African Savannas

Abstract: Savanna fires and atmospheric carbon dioxide (CO2) detection and estimating burned area using Advanced Very High Resolution Radiometer_(AVHRR) reflectance data are investigated in this two part research project. The first part involves carbon dioxide flux estimates and a three-dimensional transport model to quantify the effect of north African savanna fires on atmospheric CO2 concentration, including CO2 spatial and temporal variability patterns and their significance to global emissions. The second article describes two methods used to determine burned area from AVHRR data. The article discusses the relationship between the percentage of burned area and AVHRR channel 2 reflectance (the linear method) and Normalized Difference Vegetation Index (NDVI) (the nonlinear method). A comparative performance analysis of each method is described.

Optical Remote Sensing of Marine Ecosystems: Bio-Geochemical Implications of Ocean Colour, Marine Productivity and Atmospheric Interactions

Abstract: Ocean colour data, derived from optical remote sensing of the water surface from space, have revealed for the first time the heterogeneity, from local to regional and global scales, in the concentration and distribution of various pigments present in water constituents, in particular those of phytoplankton. The assessment of the concentration of such water constituents allows the computation of plankton biomass indices, as well as visualisations of surface currents and of some deeper dynamic phenomena, such as upwelling; the determination of primary productivity, i.e. the rate at which photosynthesis proceeds; and the estimation of the rate at which the oceans sequester atmospheric carbon dioxide.