Showing papers on "Carbon dioxide in Earth's atmosphere published in 2006"

The carbon balance of north american wetlands

Abstract: We examine the carbon balance of North American wetlands by reviewing and synthesizing the published literature and soil databases. North American wetlands contain about 220 Pg C, most of which is in peat. They are a small to moderate carbon sink of about 49 Tg C yr−1, although the uncertainty around this estimate is greater than 100%, with the largest unknown being the role of carbon sequestration by sedimentation in freshwater mineral-soil wetlands. We estimate that North American wetlands emit 9 Tg methane (CH4) yr−1; however, the uncertainty of this estimate is also greater than 100%. With the exception of estuarine wetlands, CH4 emissions from wetlands may largely offset any positive benefits of carbon sequestration in soils and plants in terms of climate forcing. Historically, the destruction of wetlands through land-use changes has had the largest effects on the carbon fluxes and consequent radiative forcing of North American wetlands. The primary effects have been a reduction in their ability to sequester carbon (a small to moderate increase in radiative forcing), oxidation of their soil carbon reserves upon drainage (a small increase in radiative forcing), and reduction in CH4 emissions (a small to large decrease in radiative forcing). It is uncertain how global changes will affect the carbon pools and fluxes of North American wetlands. We will not be able to predict accurately the role of wetlands as potential positive or negative feedbacks to anthropogenic global change without knowing the integrative effects of changes in temperature, precipitation, atmospheric carbon dioxide concentrations, and atmospheric deposition of nitrogen and sulfur on the carbon balance of North American wetlands.

Mangroves, a major source of dissolved organic carbon to the oceans

Abstract: [1] Organic matter, which is dissolved in low concentrations in the vast waters of the oceans, contains a total amount of carbon similar to atmospheric carbon dioxide To understand global biogeochemical cycles, it is crucial to quantify the sources of marine dissolved organic carbon (DOC) We investigated the impact of mangroves, the dominant intertidal vegetation of the tropics, on marine DOC inventories Stable carbon isotopes and proton nuclear magnetic resonance spectroscopy showed that mangroves are the main source of terrigenous DOC in the open ocean off northern Brazil Sunlight efficiently destroyed aromatic molecules during transport offshore, removing about one third of mangrove-derived DOC The remainder was refractory and may thus be distributed over the oceans On a global scale, we estimate that mangroves account for >10% of the terrestrially derived, refractory DOC transported to the ocean, while they cover only <01% of the continents' surface

Carbon-Nitrogen Interactions in Terrestrial Ecosystems in Response to Rising Atmospheric Carbon Dioxide

Abstract: Interactions involving carbon (C) and nitrogen (N) likely modulate terrestrial ecosystem responses to elevated atmospheric carbon dioxide (CO2) levels at scales from the leaf to the globe and from the second to the century. In particular, response to elevated CO2 may generally be smaller at low relative to high soil N supply and, in turn, elevated CO2 may influence soil N processes that regulate N availability to plants. Such responses could constrain the capacity of terrestrial ecosystems to acquire and store C under rising elevated CO2 levels. This review highlights the theory and empirical evidence behind these potential interactions. We address effects on photosynthesis, primary production, biogeochemistry, trophic interactions, and interactions with other resources and environmental factors, focusing as much as possible on evidence from long-term field experiments.

The Southern Ocean biogeochemical divide

Abstract: The Southern Ocean has central roles in carbon dioxide exchange between the oceans and the atmosphere, and in nutrient supply to the rest of the world's oceans — but these are physically separated due to the nature of ocean circulation, creating a biogeochemical divide. The area south of the divide has the most important influence on carbon dioxide exchange with the atmosphere; while the area to the north has the most significant effect on global oceanic productivity. Modelling studies have demonstrated that the nutrient and carbon cycles in the Southern Ocean play a central role in setting the air–sea balance of CO2 and global biological production1,2,3,4,5,6,7,8. Box model studies1,2,3,4 first pointed out that an increase in nutrient utilization in the high latitudes results in a strong decrease in the atmospheric carbon dioxide partial pressure ( ). This early research led to two important ideas: high latitude regions are more important in determining atmospheric than low latitudes, despite their much smaller area, and nutrient utilization and atmospheric are tightly linked. Subsequent general circulation model simulations show that the Southern Ocean is the most important high latitude region in controlling pre-industrial atmospheric CO2 because it serves as a lid to a larger volume of the deep ocean5,6. Other studies point out the crucial role of the Southern Ocean in the uptake and storage of anthropogenic carbon dioxide7 and in controlling global biological production8. Here we probe the system to determine whether certain regions of the Southern Ocean are more critical than others for air–sea CO2 balance and the biological export production, by increasing surface nutrient drawdown in an ocean general circulation model. We demonstrate that atmospheric CO2 and global biological export production are controlled by different regions of the Southern Ocean. The air–sea balance of carbon dioxide is controlled mainly by the biological pump and circulation in the Antarctic deep-water formation region, whereas global export production is controlled mainly by the biological pump and circulation in the Subantarctic intermediate and mode water formation region. The existence of this biogeochemical divide separating the Antarctic from the Subantarctic suggests that it may be possible for climate change or human intervention to modify one of these without greatly altering the other.

A multiple proxy and model study of Cretaceous upper ocean temperatures and atmospheric CO2 concentrations

Abstract: foraminiferal d 18 O and Mg/Ca suggests that the ratio of magnesium to calcium in the Turonian-Coniacian ocean may have been lower than in the Albian-Cenomanian ocean, perhaps coincident with an ocean 87 Sr/ 86 Sr minimum. The carbon isotopic compositions of distinct marine algal biomarkers were measured in the same sediment samples. The d 13 C values of phytane, combined with foraminiferal d 13 C and inferred temperatures, were used to estimate atmospheric carbon dioxide concentrations through this interval. Estimates of atmospheric CO2 concentrations range between 600 and 2400 ppmv. Within the uncertainty in the various proxies, there is only a weak overall correspondence between higher (lower) tropical temperatures and more (less) atmospheric CO2. The GENESIS climate model underpredicts tropical Atlantic temperatures inferred from ODP Leg 207 foraminiferal d 18 O and Mg/Ca when we specify approximate CO2 concentrations estimated from the biomarker isotopes in the same samples. Possible errors in the temperature and CO2 estimates and possible deficiencies in the model are discussed. The potential for and effects of substantially higher atmospheric methane during Cretaceous anoxic events, perhaps derived from high fluxes from the oxygen minimum zone, are considered in light of recent work that shows a quadratic relation between increased methane flux and atmospheric CH4 concentrations. With 50 ppm CH4, GENESIS sea surface temperatures approximate the minimum upper ocean temperatures inferred from proxy data when CO2 concentrations specified to the model are near those inferred using the phytane d 13 C proxy. However, atmospheric CO2 concentrations of 3500 ppm or more are still required in the model in order to reproduce inferred maximum temperatures.

Negligible glacial–interglacial variation in continental chemical weathering rates

Abstract: Lead isotope records from rocks from the floor of the North Atlantic Ocean, combined with a simple quantitative model, are used to reconstruct chemical weathering rates in glaciated regions of North America over the past 550,000 years. This shows that chemical weathering rates in these regions were two to three times lower than today during glacial periods. Chemical weathering of the continents is central to the regulation of atmospheric carbon dioxide concentrations, and hence global climate1,2. On million-year timescales silicate weathering leads to the draw-down of carbon dioxide1, and on millennial timescales chemical weathering affects the calcium carbonate saturation state of the oceans and hence their uptake of carbon dioxide2. However, variations in chemical weathering rates over glacial–interglacial cycles remain uncertain. During glacial periods, cold and dry conditions reduce the rate of chemical weathering3, but intense physical weathering3,4 and the exposure of carbonates on continental shelves due to low sea levels5,6 may increase this rate. Here we present high-resolution records of the lead isotope composition of ferromanganese crusts from the North Atlantic Ocean that cover the past 550,000 years. Combining these records with a simple quantitative model of changes in the lead isotope composition of the deep North Atlantic Ocean in response to chemical weathering, we find that chemical weathering rates were two to three times lower in the glaciated interior of the North Atlantic Region during glacial periods than during the intervening interglacial periods. This decrease roughly balances the increase in chemical weathering caused by the exposure of continental shelves, indicating that chemical weathering rates remained relatively constant on glacial–interglacial timescales. On timescales of more than a million years, however, we suggest that enhanced weathering of silicate glacial sediments during interglacial periods results in a net draw-down of atmospheric carbon dioxide, creating a positive feedback on global climate that, once initiated, promotes cooling and further glaciation.

Technical Note: Long-term memory effect in the atmospheric CO 2 concentration at Mauna Loa

Abstract: The monthly mean values of the atmospheric carbon dioxide concentration derived from in-situ air samples collected at Mauna Loa Observatory, Hawaii, USA during 1958–2004 (the longest continuous record available in the world) are analyzed by employing the detrended fluctuation analysis to detect scaling behavior in this time series. The main result is that the fluctuations of carbon dioxide concentrations exhibit long-range power-law correlations (long memory) with lag times ranging from four months to eleven years, which correspond to 1/f noise. This result indicates that random perturbations in the carbon dioxide concentrations give rise to noise, characterized by a frequency spectrum following a power-law with exponent that approaches to one; the latter shows that the correlation times grow strongly. This feature is pointing out that a correctly rescaled subset of the original time series of the carbon dioxide concentrations resembles the original time series. Finally, the power-law relationship derived from the real measurements of the carbon dioxide concentrations could also serve as a tool to improve the confidence of the atmospheric chemistry-transport and global climate models.

Extensive phytoplankton blooms in the Atlantic sector of the glacial Southern Ocean

Abstract: [1] The sources and sinks of atmospheric carbon dioxide over glacial/interglacial cycles are under debate. Variation in productivity of the Antarctic Circumpolar Current (ACC) could potentially play a significant role, but current interpretations of sedimentary geochemical proxies suggest that glacial productivity was not higher than today. We present areal and down-core distribution patterns of previously overlooked diatom resting spores that indicate the occurrence of extensive phytoplankton blooms across the entire Atlantic sector of the ACC, particularly in the seasonal ice zone (SIZ), linked to higher iron input during the last glacial. Sea ice acts as an effective transporter of iron and enhances its bioavailability. The dominance of the deep living radiolarian Cyladophora davisiana in glacial SIZ sediments indicates that organic carbon export to mesopelagic depths was at least tenfold higher than today.

Establishing A Earth Observation Product Service For The Terrestrial Carbon Community: The Globcarbon Initiative

Abstract: 'Greenhouse gases', especially carbon dioxide, are intimately connected to climate change. To understand the future evolution of the climate system and find ways to manage the concentration of atmospheric carbon dioxide, the processes and feedbacks that drive the carbon cycle must first be understood. However, our current knowledge of spatial and temporal patterns is uncertain, particularly over land and in regions of potentially high sensitivity to change like the boreal zone. The European Space Agency (ESA) GLOBCARBON project aims to generate fully calibrated estimates of at-land products quasi-independent of the original Earth Observation source for use primarily in Dynamic Global Vegetation Models, but also as a contribution to the Global Carbon Project, a cooperation between the International Geosphere Biosphere Programme, International Human Dimensions Programme and the World Climate Research Programme to aid understanding of global carbon cycling. The service will feature estimation of global burned area, the fraction of absorbed photosynthetically active radiation (fAPAR), leaf area index (LAI) and Vegetation Growth Cycle. The demonstrator will focus on ten complete years, from 1998 to 2007 when overlap exists between ESA Earth Observation sensors and others that are synergistic. However, the system will be flexible so that it is not dependent on any single satellite sensor and therefore can be retrospectively applied to existing archives and used with future satellite sensors.

Atmospheric carbon dioxide in a less dusty world

Abstract: [1] The availability of iron exerts a significant control on primary production and the export of organic matter over large areas of the ocean, especially those far from land sources. We explore the regulation of the global soft tissue pump of carbon and atmospheric CO2 by the atmospheric delivery of iron in a three-dimensional ocean circulation and biogeochemistry model. There is only a small change in atmospheric CO2 when the aeolian iron source is increased several fold but a significant increase in response to a reduction in the aeolian iron source. This strong asymmetry suggests a positive feedback, amplifying an increase in atmospheric CO2 if a warmer world is also less dusty.

Carbon in the Geobiosphere: - Earth's Outer Shell -

Abstract: Chapter 1: Brief Overview of Carbon on Earth 1 An unusual look at Earth's shells 2 Global carbon cycle 3 Fundamental equation of a cycle and carbon flows 4 Carbon in Fossil Fuels 5 Feedbacks in the carbon cycle Chapter 2: Earth's Volatile Beginnings 1 The Major Volatiles 2 Primordial Atmosphere-Ocean System 3 Carbon Dioxide 4 Summary and Speculations 5 An Early Biosphere Chapter 3: Heat Balance of the Atmosphere and Carbon Dioxide 1 Heat Sources at the Earth's Surface 2 Solar Heating and Radiation Balance 3 Greenhouse Effect 4 Temperature of a Prebiotic Atmosphere 5 CO2 and Climate Change Chapter 4: Mineralogy, Chemistry, and Reaction Kinetics of the Major Carbonate Phases 1 Carbonate Minerals 2 Calcites 3 Dolomite 4 Aragonite 5 Carbonate Dissolution and Precipitation Kinetics 6 Carbonate Precipitation and Dissolution in Marine Ecosystems 7 Some Geological Considerations Chapter 5: Carbon Dioxide in Natural Waters 1 Dissolution and Dissociation of CO2 in Water 2 CO2 Transfer from Atmosphere to Water 3 Calcite and Aragonite in Natural Waters 4 Degree of Saturation With Respect to Carbonate Minerals 5 CO2 Phases: Gas, Liquid, Hydrate, Ice 6 Air-Sea CO2 Exchange due to Carbonate and Organic Carbon Formation Chapter 6: Isotopic Fractionation of Carbon: Inorganic and Biological Processes 1 Isotopic species and their abundance 2 Isotopic concentration units and mixing 3 Fractionation in inorganic systems 4 Photosynthesis and plant physiological responses to CO2 5 Biological fractionationand 13C cycle 6 Long-term trends Chapter 7: Sedimentary Rock Record and Oceanic and Atmospheric Carbon 1 Geologic Time Scale and Sedimentary Record 2 The Beginnings of Sedimentary Cycling 3 Broad Patterns of Sediment Lithologies 4 Differential Cycling of the Sedimentary Mass and Carbonates 5 Sedimentary Carbonate System 6 Evaporites and Fluid Inclusions 7 Isotopic Trends 8 Summary of the Phanerozoic Rock Record in Terms of Ocean Composition Chapter 8: Weathering and Consumption of CO2 1 Weathering Source: Sedimentary and Crystalline Lithosphere 2 Dissolution at the Earth's Surface 3 Mineral-CO2 Reactions in Weathering 4 CO2 Consumption from Mineral-Precipitation Model 5 CO2 Consumption from Mineral-Dissolution Model 6 Environmental Acid Forcing Chapter 9: Carbon in the Oceanic Coastal Margin 1 The Global Coastal Zone 2 Carbon Cycle in the Coastal Ocean 3 Inorganic and Organic Carbon 4 Marine Calcifying Organisms and Ecosystems 5 Present and Future of Coastal Carbon System Chapter 10: Natural Global Carbon Cycle through Time 1 The Hadean to Archaean 2 The Archaean to Proterozoic 3 The Phanerozoic 4 Pleistocene to Holocene Environmental Change Chapter 11: The Carbon Cycle in the Anthropocene 1 Characteristics of the Anthropocene 2 Major Perturbations in the Carbon Cycle: 1850 to the Early 21st Century 3 Partitioning of Carbon, Nitrogen and Phosphorus Fluxes 4 The Fundamental Carbon Problem of the Future

Soil respiration in northern forests exposed to elevated atmospheric carbon dioxide and ozone

Abstract: The aspen free-air CO2 and O3 enrichment (FACTS II-FACE) study in Rhinelander, Wisconsin, USA, is designed to understand the mechanisms by which young northern deciduous forest ecosystems respond to elevated atmospheric carbon dioxide (CO2) and elevated tropospheric ozone (O3) in a replicated, factorial, field experiment. Soil respiration is the second largest flux of carbon (C) in these ecosystems, and the objective of this study was to understand how soil respiration responded to the experimental treatments as these fast-growing stands of pure aspen and birch + aspen approached maximum leaf area. Rates of soil respiration were typically lowest in the elevated O3 treatment. Elevated CO2 significantly stimulated soil respiration (8-26%) compared to the control treatment in both community types over all three growing seasons. In years 6-7 of the experiment, the greatest rates of soil respiration occurred in the interaction treatment (CO2 + O3), and rates of soil respiration were 15-25% greater in this treatment than in the elevated CO2 treatment, depending on year and community type. Two of the treatments, elevated CO2 and elevated CO2 + O3, were fumigated with 13C-depleted CO2, and in these two treatments we used standard isotope mixing models to understand the proportions of new and old C in soil respiration. During the peak of the growing season, C fixed since the initiation of the experiment in 1998 (new C) accounted for 60-80% of total soil respiration. The isotope measurements independently confirmed that more new C was respired from the interaction treatment compared to the elevated CO2 treatment. A period of low soil moisture late in the 2003 growing season resulted in soil respiration with an isotopic signature 4-6 per thousand enriched in 13C compared to sample dates when the percentage soil moisture was higher. In 2004, an extended period of low soil moisture during August and early September, punctuated by a significant rainfall event, resulted in soil respiration that was temporarily 4-6 per thousand more depleted in 13C. Up to 50% of the Earth's forests will see elevated concentrations of both CO2 and O3 in the coming decades and these interacting atmospheric trace gases stimulated soil respiration in this study.

Carbon partitioning to mobile and structural fractions in poplar wood under elevated CO2 (EUROFACE) and N fertilization.

Abstract: To determine whether globally increasing atmospheric carbon dioxide (CO2) concentrations can affect carbon partitioning between nonstructural and structural carbon pools in agroforestry plantations, Populus nigra was grown in ambient air (about 370lmolmol � 1 CO2) and in air with elevated CO2 concentrations (about 550lmolmol � 1 CO2) using freeair CO2 enrichment (FACE) technology. FACE was maintained for 5 years. After three growing seasons, the plantation was coppiced and one half of each experimental plot was fertilized with nitrogen. Carbon concentrations and stocks were measured in secondary sprouts in seasons of active growth and dormancy during 2 years after coppicing. Although FACE, N fertilization and season had significant tissue-specific effects on carbon partitioning to the fractions of structural carbon, soluble sugars and starch as well as to residual soluble carbon, the overall magnitude of these shifts was small. The major effect of FACE and N fertilization was on cell wall biomass production, resulting in about 30% increased above ground stocks of both mobile and immobile carbon pools compared with fertilized trees under ambient CO2. Relative C partitioning between mobile and immobile C pools was not significantly affected by FACE or N fertilization. These data demonstrate high metabolic flexibility of P. nigra to maintain C-homeostasis under changing environmental conditions and illustrate that nonstructural carbon compounds can be utilized more rapidly for structural growth under elevated atmospheric [CO2] in fertilized agroforestry systems. Thus, structural biomass production on abandoned agricultural land may contribute to achieving the goals of the Kyoto protocol.

Health effects of increase in concentration of carbon dioxide in the atmosphere

Abstract: The toxic effects, to humans and other mammals, of concentrations of carbon dioxide in the atmosphere which are below the safe working level but above the present level are described. The likely physiological effects of the predicted increase in concentration of carbon dioxide in the atmosphere over the next 50 years are detailed.

Effects of Elevated Atmospheric Carbon Dioxide and Temperature on Soil Respiration in a Boreal Forest Using δ13C as a Labeling Tool

Abstract: Effects of elevated atmospheric carbon dioxide and temperature on soil respiration in a boreal forest using δ13C as a labeling tool

On the application and interpretation of Keeling plots in paleo climate research – deciphering δ 13 C of atmospheric CO 2 measured in ice cores

Abstract: . The Keeling plot analysis is an interpretation method widely used in terrestrial carbon cycle research to quantify exchange processes of carbon between terrestrial reservoirs and the atmosphere. Here, we analyse measured data sets and artificial time series of the partial pressure of atmospheric carbon dioxide (pCO2) and of δ13C of CO2 over industrial and glacial/interglacial time scales and investigate to what extent the Keeling plot methodology can be applied to longer time scales. The artificial time series are simulation results of the global carbon cycle box model BICYCLE. The signals recorded in ice cores caused by abrupt terrestrial carbon uptake or release loose information due to air mixing in the firn before bubble enclosure and limited sampling frequency. Carbon uptake by the ocean cannot longer be neglected for less abrupt changes as occurring during glacial cycles. We introduce an equation for the calculation of long-term changes in the isotopic signature of atmospheric CO2 caused by an injection of terrestrial carbon to the atmosphere, in which the ocean is introduced as third reservoir. This is a paleo extension of the two reservoir mass balance equations of the Keeling plot approach. It gives an explanation for the bias between the isotopic signature of the terrestrial release and the signature deduced with the Keeling plot approach for long-term processes, in which the oceanic reservoir cannot be neglected. These deduced isotopic signatures are similar (−8.6‰) for steady state analyses of long-term changes in the terrestrial and marine biosphere which both perturb the atmospheric carbon reservoir. They are more positive than the δ13C signals of the sources, e.g. the terrestrial carbon pools themselves (−25‰). A distinction of specific processes acting on the global carbon cycle from the Keeling plot approach is not straightforward. In general, processes related to biogenic fixation or release of carbon have lower y-intercepts in the Keeling plot than changes in physical processes, however in many case they are indistinguishable (e.g. ocean circulation from biogenic carbon fixation).

Atmospheric carbon dioxide enrichment effects on ecosystems — experiments and the real world

Abstract: The beneficial effect of atmospheric CO2 on the growth of plants has been known since 1804 (De Sassure 1804; cited in Kimball et al. 1993), and its role as a C source for vegetation was proven by Justus von Liebig 125 years ago. Atmospheric CO2 enrichment has been used to promote the growth of legumes in greenhouse cultures for >50 years. As early as 1961, greenhouses covering >1,600 ha were under enriched CO2 in the Netherlands alone. However, only after atmospheric CO2 concentrations had been recorded from continuous monitoring sites such as the Mauna Loa Observatory at Hawaii, where [CO2] has been recorded since 1958, was there a growing awareness that CO2 enrichment occurs on a global scale and that it affects ecosystems throughout the world. In 2005, the concentration of atmospheric CO2 will be around 380 μmol mol −1; thus already exceeding by ca. 35% the background concentration of ca. 280 μmol mol−1 before the beginning of industrialization. A further increase to at least 550 μmol mol−1 will have occurred by the end of this century (IPCC 2001). Consequently, numerous studies have been performed to test the response of vegetation and ecosystems to CO2 enrichment, and great progress has been made in developing experimental facilities and in our understanding of biosphere–atmosphere interactions with respect to CO2 by means of both experimentation and modelling. CO2 enrichment effects on crops were reviewed as early as the mid 1980s by Cure and Acock (1986) who reported an average increase in C3 crop yield due to CO2 doubling of approximately 41%. A mechanistic understanding of the physiological background for this CO2 fertilization effect in C3 plants that has been widely accepted was provided by von Caemmerer and Farquhar (1981). This CO2 gas exchange model for C3 plants was later extended and modified by Sage (1994) and other authors to explain photosynthetic acclimation to CO2 enrichment. Down-regulation of photosynthesis in C3 plants

Mauna Loa volcano is not a methane source: Implications for Mars

Abstract: [1] Thirteen years of continuous atmospheric carbon dioxide and methane measurements at the Mauna Loa Observatory in Hawaii are used to determine the methane emission rate from the summit of Mauna Loa volcano. We find no measurable methane emissions coming from the summit area, with a 95% confidence upper limit of 9 t CH4 yr−1. Recent studies have detected 10 ppb CH4 in the Martian atmosphere, requiring emissions of about 300 t CH4 yr−1. Volcanic activity has been suggested as a source of abiogenic CH4 on Mars, either by magmatic degassing or reactions in hydrothermal fluids heated by a magma intrusion. The most recent lava flows on Mars (2 My ago) are on the Tharsis shield volcanoes, which may still be active. If Mauna Loa is a valid terrestrial analog, our findings suggest that volcanic activity is not a significant source of methane to the Martian atmosphere.

Oceanography: Sick seas

Abstract: The rising level of carbon dioxide in the atmosphere is making the world's oceans more acidic. Jacqueline Ruttimann reports on the potentially catastrophic effect this could have on marine creatures.

Estimating carbon budgets for U.S. ecosystems

Abstract: On a global basis, plants and soils may hold more than twice the amount of carbon present in the atmosphere [Geider et al., 2001]. Under increasing atmospheric carbon dioxide (CO2) concentrations and subsequently warming temperatures, these large biogenic pools may change in size [Cox et al., 2000]. Due to a lack of long-term field studies, there is uncertainty as to whether vegetation and soils will act as a net sink or a source of atmospheric CO2 in coming years. It is certain, however, that no retrospective analysis of the U.S. carbon balance will be possible without a comprehensive historical baseline of the sizes of various ecosystem carbon pools and the variability in their net annual increments.

Snowball Earth on trial

Abstract: Many scientists have been considering the idea that the Earth may have completely frozen over sometime in the past. Kirschvink [1992] proposed that a runaway ice-albedo effect on continents amassed in low latitudes caused the descent into a global freeze. During a prolonged glacial period when oceans and atmosphere were isolated from each other, volcanic emissions would cause a buildup of atmospheric carbon dioxide (CO2), with no silicate weathering or photosynthesis to act as a sink. Eventually a reverse ice-albedo effect would cause a transient heat wave as the ice cover melted back rapidly.

Global change: the water cycle freshens up.

Abstract: Rivers are delivering increasing amounts of fresh water to the ocean. The cause seems to be the influence that higher concentrations of atmospheric carbon dioxide are having on water use by plants.

Vascular plant responses to elevated CO2 in a temperate lowland Sphagnum peatland

Abstract: Vascular plant responses to experimental enrichment with atmospheric carbon dioxide (CO2), using MINIFACE technology, were studied in a Dutch lowland peatland dominated by Sphagnum and Phragmites for 3 years. We hypothesized that vascular plant carbon would accumulate in this peatland in response to CO2 enrichment owing to increased productivity of the predominant species and poorer quality (higher C/N ratios) and consequently lower decomposability of the leaf litter of these species. Carbon isotope signatures demonstrated that the extra 180 ppmv CO2 in enriched plots had been incorporated into vegetation biomass accordingly. However, on the CO2 sequestration side of the ecosystem carbon budget, there were neither any significant responses of total aboveground abundance of vascular plants, nor of any of the individual species. On the CO2 release side of the carbon budget (decomposition pathway), litter quantity did not differ between ambient and CO2 treatments, while the changes in litter quality (N and P concentration, C/N and C/P ratio) were marginal and inconsistent. It appeared therefore that the afterlife effects of significant CO2-induced changes in green-leaf chemistry (lower N and P concentrations, higher C/N and C/P) were partly offset by greater resorption of mobile carbohydrates from green leaves during senescence in CO2-enriched plants. The decomposability of leaf litters of three predominant species from ambient and CO2-enriched plots, as measured in a laboratory litter respiration assay, showed no differences. The relatively short time period, environmental spatial heterogeneity and small plot sizes might explain part of the lack of CO2 response. When our results are combined with those from other Sphagnum peatland studies, the common pattern emerges that the vascular vegetation in these ecosystems is genuinely resistant to CO2-induced change. On decadal time-scales, water management and its effects on peatland hydrology, N deposition from anthropogenic sources and land management regimes that arrest the early successional phase (mowing, tree and shrub removal), may have a greater impact on the vascular plant species composition, carbon balance and functioning of lowland Sphagnum-Phragmites reedlands than increasing CO2 concentrations in the atmosphere.

Simulating Holocene carbon accumulation in a western Siberian watershed mire using a three‐dimensional dynamic modeling approach

Abstract: [1] The vast undisturbed mires in western Siberia formed a significant sink of atmospheric carbon dioxide during the Holocene However, the lack of spatially resolved simulation models hampers the quantification of Holocene carbon accumulation of the entire mire systems Here we developed a three-dimensional dynamic model, based on a hydrological approach We applied the model to a large mire complex in western Siberia to simulate its Holocene development and to quantify the long-term carbon accumulation rate (LORCA) Our model simulated a LORCA with a spatial variation of 10–85 g C m−2 yr−1 The average over the Holocene was 162 g C m−2 yr−1 Simulation scenarios for the 21st century show that the average LORCA dropped to 52 g C m−2 yr−1 because of oxidation and decomposition of peat following mire drainage after the 1950s Even in the undrained parts of the mire complex the LORCA is lowered substantially because of the dropped water table and resulting decrease in peat growth Our results show that carbon accumulation in western Siberian watershed mires will continue in the future Thus these mires might remain a significant sink of carbon

Impacts of urbanization on land-atmosphere carbon exchange within a metropolitan area in the USA

Abstract: Urbanization can cause changes in carbon fluxes, which, in turn, impacts atmospheric carbon dioxide (CO2) concentrations and possibly global surface temperatures. Using the Atlanta, Georgia, region as a case study, this paper explores the impact of urban expansion from 1973 to 2002 on land-atmosphere carbon exchange. The major objectives were to estimate net ecosystem pro- duction (NEP) values for multiple land-cover classes and to link urbanization-induced changes in land-cover to changes in NEP and overall carbon fluxes. The principal data were daily climatic data, year-specific land-cover data, annual net ecosystem exchange (NEE) values, and annual anthro- pogenic carbon emissions estimates. The principal methods were testing for climatic trends, deter- mining the composition of the land-cover classes, estimating annual NEP values for the land-cover classes, and estimating the overall carbon exchange. The major findings: (1) there were no significant trends for any of the climatic variables; (2) the region was only ~16% urbanized in 1973; however, by 2002, the region was ~38% urbanized; (3) the NEP in 1978-1980 of 443 g C m -2 yr -1 may have con- tinued until 1996-1998, despite the substantial loss of forest land; and (4) net carbon emissions increased from ~150 g in 1978-1980 to ~940 g C m -2 yr -1 in 1996-1998. Therefore, urban expansion greatly increased the carbon emissions of the Atlanta region; however, it is possible that, through increasing the growing-season length as well as increasing nitrogen and CO2 fertilization, urban expansion may not decrease the region-wide NEP.

Carbon dioxide exchange and early old‐field succession

Abstract: [1] Old-field succession is a widespread process active in shaping landscapes in the eastern United States, contributing significantly to the terrestrial sink of atmospheric carbon dioxide, particularly at midlatitudes. However, few studies document ecosystem-scale carbon dioxide exchange during the early years of old-field succession, particularly during the temporal transition from cultivation to abandonment. Rates of carbon dioxide exchange were measured for 20 months over a field in Virginia during the transition from an actively cultivated crop field to an unmanaged old field, including one season of crop growth and two seasons of successional growth. Ecosystem carbon respiration exceeded carbon assimilation during growing seasons and dormant periods, resulting in a net flux of carbon dioxide from the biosphere to the atmosphere of between 1.27 and 1.85 kg C m−2 for the entire 20-month period (an average loss to the atmosphere of 2.07 to 3.01 g C m−2 day −1). Crop growth (from 10 January 2001 to 6 June 2001) resulted in a net loss of between 0.22 and 0.32 kg C m−2 to the atmosphere (an average daily loss of 1.5 to 2.2 g C m−2), whereas the two seasons of successional growth combined contributed an additional 1.05 to 1.53 kg C m−2 to the atmosphere (an average daily loss of 2.2 to 3.3 g C m−2). Empirical modeling was used to demonstrate control of ecosystem carbon respiration by soil temperature, soil moisture status, and the status of vegetation growth activity. Tower-based estimates of carbon loss were compared at both short (half hourly) and long (seasonal) timescales to independent, ground-based measurements. Using estimates of carbon exchange from previously published studies, these results are placed in the context of a trajectory of old-field succession.

Impacts of large-scale climatic disturbances on the terrestrial carbon cycle

Abstract: The amount of carbon dioxide in the atmosphere steadily increases as a consequence of anthropogenic emissions but with large interannual variability caused by the terrestrial biosphere. These variations in the CO2 growth rate are caused by large-scale climate anomalies but the relative contributions of vegetation growth and soil decomposition is uncertain. We use a biogeochemical model of the terrestrial biosphere to differentiate the effects of temperature and precipitation on net primary production (NPP) and heterotrophic respiration (Rh) during the two largest anomalies in atmospheric CO2 increase during the last 25 years. One of these, the smallest atmospheric year-to-year increase (largest land carbon uptake) in that period, was caused by global cooling in 1992/93 after the Pinatubo volcanic eruption. The other, the largest atmospheric increase on record (largest land carbon release), was caused by the strong El Nino event of 1997/98. We find that the LPJ model correctly simulates the magnitude of terrestrial modulation of atmospheric carbon anomalies for these two extreme disturbances. The response of soil respiration to changes in temperature and precipitation explains most of the modelled anomalous CO2 flux. Observed and modelled NEE anomalies are in good agreement, therefore we suggest that the temporal variability of heterotrophic respiration produced by our model is reasonably realistic. We therefore conclude that during the last 25 years the two largest disturbances of the global carbon cycle were strongly controlled by soil processes rather then the response of vegetation to these large-scale climatic events.

Tropical forests and atmospheric carbon dioxide: current conditions and future scenarios

Abstract: This volume, first published in 2006, presents findings on climate change from leading international scientists, for researchers, policy-makers and engineers.

Carbon-dioxide emission measurements in a tillage experiment on chernozem soil

Abstract: Introductions The terrestrial ecosystems are the biggest carbon reservoirs on the earth and soils, as part of these ecosystems, play a very important role in the global carbon cycle. Globally, in the upper one meter of minerals soils 1300-1500 Gt carbon is stored, which is twice more than the amount stored in terrestrial vegetation (Neill et al. 1998). Therefore a considerable part of the atmospheric carbon pool came from the terrestrial ecosystems, especially from soils (Lai, R et al. 1998). The atmospheric carbon dioxide concentration was approximately 280 mg/kg in 1850 and 365mg/kg in 1996, so it has been increasing at a rate of 0.5 % per year. Now, this rate has reached the 1.5% per year, so if this trend does not change, the COj concentration of the atmosphere can be about 600mg/kg during the 21st century. (Lai R. et al. 1999) Globally, the agricultural originated carbon getting into the atmosphere is estimated at 2.5xlOlsg. This loss has an effect not only on the global warming, but plays an important role in the long-term quality of soils (Bloodworth and Uri, 2002). The balance must be found between the highly disturbed and the non-tillage cropping systems applied in agriculture to ensure the least possible carbon losses from soils. (Nemeth et al. 1998)