Showing papers on "Atmospheric carbon cycle published in 1996"

Two Decades of Carbon Flux from Forests of the Pacific Northwest

Abstract: Earth`s climate is greatly influenced by carbon dioxide concentrations in the atmosphere. Besides combustion of fossil fuels, another important anthropogenic source of atmospheric carbon is associated with deforestation, especially in primary forests, which can store large amounts of carbon in the form of organic biomass. There are a number of problems with models of carbon flux previously developed. The authors are developing a strategy to estimate regional carbon fluxes designed to overcome many of them. This article describes the modeling strategy and the results of the carbon flux modeling in forest of the Pacific Northwest region of the USA using the following topic areas: C flux modeling strategy, demonstration of modeling strategy, significance to regional and global carbon cycle, and resource management implications. 53 refs., 7 figs., 1 tab.

Global carbon cycle and the optimal time path of a carbon tax

Abstract: The existing models of fossil fuel consumption with carbon accumulation imply that the optimal time path of carbon tax is either hump-shaped or monotonically decreasing. These models specify the decay of atmospheric carbon as a constant rate of total concentration. The authors extend this specification to more accurately reflect the global carbon cycle models of climatologists and show that this extension changes the basic economic properties of the optimal carbon tax. Their analysis reveals that the optimal carbon tax may as well be constant through time, increase monotonically, or have a U-shape. In addition, optimal resource extraction may have an open-close-open cycle. Copyright 1996 by Royal Economic Society.

Neogene growth of the sedimentary organic carbon reservoir

Abstract: We develop a recycling model using 13C/12C mass balance for net growth/loss of the sedimentary organic carbon (Corg) reservoir, and apply it to the Neogene bulk marine carbonate δ13C record. The model allows for variations in photosynthetic fractionation factors, carbon cycling rates, and the isotopic composition of riverine carbon inputs to the oceans. The sign of the net flux term is controlled by the difference between fractional Corg burial and fractional Corg weathering, independent of any variations in carbon cycling rate. These terms are in turn estimated from the carbon isotope mass balance of newly deposited and weathered sediments, respectively. The magnitude of the net flux is sensitive to the global carbon cycling (erosion/deposition) rate, which may be estimated by the use of the records of radiogenic isotopic variations (Nd, Sr) in paleoseawater. A key observation and input to the model is that photosynthetic carbon isotope fractionation by both marine algae and terrestrial plants has decreased during the Cenozoic. Incorporating time-dependent carbon isotope fractionation into the model shows that the sedimentary Corg reservoir has grown throughout most of the Neogene, even as marine δ13C values fell after 14 Ma. A similar result is obtained if the variation in the marine δ13C record is largely caused by changes in the carbon isotopic composition of river fluxes to the oceans, rather than changes in the organic/inorganic ratio of output to the burial sink. The growth of the sedimentary organic carbon reservoir requires that the Neogene sedimentary carbon cycle was a net source of O2 and a net sink of CO2 to the atmosphere, at least until the Plio-Pleistocene. As a consequence, Neogene CO2 consumption by silicate weathering cannot be balanced by oxidation of sedimentary Corg, placing a significant constraint on global carbon balance models. A related prediction of our model is that atmospheric O2 levels rose during the Neogene.

Coral reefs and carbon dioxide.

Abstract: This commentary argues the conclusion from a previous article, which investigates diurnal changes in carbon dioxide partial pressure and community metabolism on coral reefs, that coral `reefs might serve as a sink, not a source, for atmospheric carbon dioxide.` Commentaries from two groups are given along with the response by the original authors, Kayanne et al. 27 refs.

Significance of ocean carbonate budgets for the global carbon cycle

Abstract: Changes in the trace gas composition of the atmosphere over glacial–interglacial cycles are linked to changes in the oceanic carbon cycle. This paper examines the role of biologically driven fluxes of organic and inorganic carbon in modifying the carbon dioxide chemistry of the oceans, and the corresponding implications for the partitioning of CO2 between the atmosphere and ocean. Relevant details of the marine carbon system are presented together with an assessment of the significance of remineralization and dissolution processes. Recent estimates of the marine carbonate fluxes show significant uncertainties and inconsistencies which must be resolved in order to assess fully the role of the oceans' biota in the marine carbon system. Various types of ocean carbon cycle models have been developed in order to interpret the changes in past atmospheric carbon dioxide. Some take account of the role of the oceans' biota, focussing in the main on the cycling of organic matter. Relatively few have considered the role of the carbonate pump and the subtle interactions between organic and inorganic carbon cycling. The significance of carbonate formation and dissolution, and of the effects of global change on the marine carbonate system, for air–sea fluxes of CO2 are discussed. Finally some recommendations for future research are made in order to improve our understanding of how spatial and temporal variation in marine carbonate fluxes, in conjunction with processes determining the oxidation and burial of organic matter in the oceans, affect levels of CO2 in the atmosphere.

Environmental impact of biomethanogenesis.

Abstract: The environmental impact of biomethanogenesis is related to its ecological role, accumulation and effect as a greenhouse gas, and application in anaerobic digestion for conversion of biomass and wastes to methane and compost. Biological formation of methane is the process by which bacteria decompose organic matter using carbon dioxide as an electron acceptor in the absence of dioxygen or other electron acceptors. This microbial activity is responsible for carbon recycling in anaerobic environments, including wetlands, rice fields, intestines of animals sediments, and manures. The mixed consortium of microorganisms involved includes a unique group of bacteria, the methanogens, which may be considered to be in a separate kingdom based on genetic and phylogenetic variance from all other life forms. Because methane is a significant and increasing greenhouse gas, its source fluxes and their potential reduction are of concern. Biomethanogenesis may be harnessed for reduction of wastes and conversion of renewable resources to significant quantities of substitute natural gas which could mitigate carbon dioxide and other pollutants related to use of fossil fuels.

Regulation of atmospheric CO{sub 2} and O{sub 2} by photosynthetic carbon metabolism

Abstract: The objectives of this book are threefold: (1) discussion of the role of photosynthesis in regulating atmopsheric concentrtions of carbon dioxide and oxygen; (2) promotion of research and discussion about how the various carbons and CAM carbon cycles and algal carbon dioxide concentrating mechanisms could be integrated to help explain the regulation of atmospheric carbon dioxide; (3) increase of exchanges among biochemists concerned primarily with detailed reactions of photsynthetic carbon dioxide metabolism, and geologists and other concerned about increasing atmospheric carbon dioxide. Sections include those on background information on global carbon cycles and pools; the C3 cycle, photorespiration, and respiration, and the carbon dioxide concentration processes of C4 CAM and Algal pumps; discussion of plant metabolism might influence atmospheric carbon dioxide and oxygen concentrations.

Modeling soil organic carbon fluxes attributable to conversion of forest to corn cropping in a landscape of southwest France

Abstract: Recent concern about rising levels of atmospheric CO2 has directed attention to the stores of organic carbon in soils and to changes caused by human activities. In southwest France, thick, humic, loamy soils have developed from Quaternary silty alluvial deposits. Most forest lands on these soils have been converted to continuous intensive corn cropping. The spatial distribution of C stores under forest and the loss of C upon this conversion have been modeled in previous studies. The objective of this study was to determine if a spatial and temporal analysis of this conversion makes possible reliable estimates of the organic carbon fluxes attributable to this conversion. Forest clearing showed a sigmoid temporal progression. The analysis of changes in land use provided a useful tool to improve the prediction of soil organic carbon fluxes to the atmosphere. From 1948 to 1984, carbon release to the atmosphere was about 2.2 Tg, that is 6.35 kg.m -2 . Temperate soils may be an important source of atmospheric carbon when they are high in carbon content initially and then cultivated intensively.

The economics of increased carbon storage through plantations and forest management

Abstract: Forest plantations offer what appear to be one of the more attractive approaches to sequester atmospheric carbon (C). They are attractive because: (1) studies have indicated that forests have the potential to sequester large amounts of C; (2) the technology for establishing new forests exists; (3) forests have a number of environmental benefits aside from C sequestration; and (4) most studies indicate that the costs of C sequestration using forests are quite modest

Impact of climate change and atmospheric carbon dioxideconcentration on the growth of planted forests

Abstract: The impacts, if any, of climate change on planted forests will be apparent either as progressive change in the suitability or otherwise of particular areas for forestry, or through changes in the growth and yield of forests as a result of changing conditions. It is not possible to predict with any confidence the influence of climate change on the location of planted forests.

Integrated forestry and biofuel: land and labour allocations global modeling and european prospects

Abstract: The ECLAM (Energy Carbon Land Allocations Model) is used to simulate the potential of forestry and bio-fuels (fuels derived from biological raw material) in climate change response. The intuition for this approach is that, in the short and medium term, there is little flexibility in the energy supply system owing to the long lifetime of typical energy sector fixed assets, whereas there is substantial flexibility in the allocation of land at least until global population growth leads to greater demands for land, for food and fibre production. Furthermore, the utilisation of land for energy production and for a medium term ‘buffer stock’ of carbon results in a flow of rents to landowners which can provide the capital needed for the more intensive agriculture that will be needed in the next century. The carbon flows related to absorption by forestry and biofuel production, and to emissions from burning fuel, together with the effects of natural absorption, combine to yield a time profile for atmospheric carbon. Simulations run on a global scale demonstrate the medium term use of plantation forestry as a buffer stock of carbon, for eventual use partly as fibre, and partly as fuel. Results are shown for the variables associated with the scenario like rent of land, productivity of agriculture and effects on the labour market. An important decrease of atmospheric CO2 is diagnosed to be possible by the described integrated ‘biofuels and sequestration strategy1.

On the evidence for a lower 14C activity of the atmospheric carbon dioxide over the Arctic area than over Sweden

Abstract: On the evidence for a lower 14C activity of the atmospheric carbon dioxide over the Arctic area than over Sweden

Isotopic evidence for changes in the biogeochemical carbon cycle during the early-and mid-proterzoic eon: Implications for the biosphere and atmosphere

Abstract: The Archean fossil record reveals a biosphere whose biota were remarkably sophisticated. For example, bacteria were capable of photosynthesis, and they withstood the ultraviolet radiation and periodic desiccation which accompanied the intertidal environment. However, we can infer relatively little about evolutionary change between 3 and 1.1 billion years (Ga) ago. What biological events occurred, and how did changes in the environment influence the nature and timing of these events? The carbon biogeochemical cycle played a key role, and isotopic measurements of sedimented carbon can reveal long-term changes in this cycle. Additional information is contained in the original extended abstract.