Amplification of Cretaceous warmth by biological cloud feedbacks

The extreme warmth of particular intervals of geologic history cannot be simulated with climate models, which are constrained by the geologic proxy record to relatively modest increases in atmospheric carbon dioxide levels. Recent recognition that biological productivity controls the abundance of cloud condensation nuclei (CCN) in the unpolluted atmosphere provides a solution to this problem. Our climate simulations show that reduced biological productivity (low CCN abundance) provides a substantial amplification of CO2-induced warming by reducing cloud lifetimes and reflectivity. If the stress of elevated temperatures did indeed suppress marine and terrestrial ecosystems during these times, this long-standing climate enigma may be solved.     

Rising atmospheric CO2 reduces sequestration of root-derived soil carbon

Forests have a key role as carbon sinks, which could potentially mitigate the continuing increase in atmospheric carbon dioxide concentration and associated climate change. We show that carbon dioxide enrichment, although causing short-term growth stimulation in a range of European tree species, also leads to an increase in soil microbial respiration and a marked decline in sequestration of root-derived carbon in the soil. These findings indicate that, should similar processes operate in forest ecosystems, the size of the annual terrestrial carbon sink may be substantially reduced, resulting in a positive feedback on the rate of increase in atmospheric carbon dioxide concentration.     

陆地生态系统碳·氮·水耦合机制研究进展

在大气CO2浓度升高和氮沉降增加等全球变化背景下,陆地生态系统碳、氮循环相互作用及功能耦合规律的研究是揭示这些不确定性的基础,也能反映森林生态系统生物产量与养分之间的作用规律,涉及到林地持久生产力的生态学机理问题。生态系统的碳循环和水循环以气孔行为为结点,耦联成有机的整体。因此,着重在生态系统尺度上,综述了碳、氮、水循环耦合作用研究的一些进展与存在的问题,并对今后研究方向进行了展望。     

Arctic lakes and streams as gas conduits to the atmosphere: implications for tundra carbon budgets

Arctic tundra has large amounts of stored carbon and is thought to be a sink for atmospheric carbon dioxide (CO(2)) (0.1 to 0.3 petagram of carbon per year) (1 petagram = 10(15) grams). But this estimate of carbon balance is only for terrestrial ecosystems. Measurements of the partial pressure of CO(2) in 29 aquatic ecosystems across arctic Alaska showed that in most cases (27 of 29) CO(2) was released to the atmosphere. This CO(2) probably originates in terrestrial environments; erosion of particulate carbon plus ground-water transport of dissolved carbon from tundra contribute to the CO(2) flux from surface waters to the atmosphere. If this mechanism is typical of that of other tundra areas, then current estimates of the arctic terrestrial sink for atmospheric CO(2) may be 20 percent too high.     

A terminal mesozoic "greenhouse": lessons from the past

The late Mesozoic rock and life records implicate short-term (up to 10(5) to 10(6) years) global warming resulting from carbon dioxide-induced "greenhouse" conditions in the late Maestrichtian extinctions that terminated the Mesozoic Era. Oxygen isotope data from marine microfossils suggest late Mesozoic climatic cooling into middle Maestrichtian, and warming thereafter into the Cenozoic. Animals adapting to climatic cooling could not adapt to sudden warming. Small calcareous marine organisms would have suffered solution effects of carbon dioxide-enriched waters; animals dependent upon them for food would also have been affected. The widespread terrestrial tropical floras would likely not have reflected effects of a slight climatic warming. In late Mesozoic, the deep oceanic waters may have been triggered into releasing vast amounts of carbon dioxide into the atmosphere in a chain reaction of climatic warming and carbon dioxide expulsion. These conditions may be duplicated by human combustion of the fossil fuels and by forest clearing.     

Europe's terrestrial biosphere absorbs 7 to 12% of European anthropogenic CO2 emissions

Most inverse atmospheric models report considerable uptake of carbon dioxide in Europe's terrestrial biosphere. In contrast, carbon stocks in terrestrial ecosystems increase at a much smaller rate, with carbon gains in forests and grassland soils almost being offset by carbon losses from cropland and peat soils. Accounting for non-carbon dioxide carbon transfers that are not detected by the atmospheric models and for carbon dioxide fluxes bypassing the ecosystem carbon stocks considerably reduces the gap between the small carbon-stock changes and the larger carbon dioxide uptake estimated by atmospheric models. The remaining difference could be because of missing components in the stock-change approach, as well as the large uncertainty in both methods. With the use of the corrected atmosphere- and land-based estimates as a dual constraint, we estimate a net carbon sink between 135 and 205 teragrams per year in Europe's terrestrial biosphere, the equivalent of 7 to 12% of the 1995 anthropogenic carbon emissions.     

Impacts of rising atmospheric carbon dioxide on model terrestrial ecosystems

In model terrestrial ecosystems maintained for three plant generations at elevated concentrations of atmospheric carbon dioxide, increases in photosynthetically fixed carbon were allocated below ground, raising concentrations of dissolved organic carbon in soil. These effects were then transmitted up the decomposer food chain. Soil microbial biomass was unaffected, but the composition of soil fungal species changed, with increases in rates of cellulose decomposition. There were also changes in the abundance and species composition of Collembola, fungal-feeding arthropods. These results have implications for long-term feedback processes in soil ecosystems that are subject to rising global atmospheric carbon dioxide concentrations.     

Exchange of materials between terrestrial ecosystems and the atmosphere

Many biogenic trace gases are increasing in concentration or flux or both in the atmosphere as a consequence of human activities. Most of these gases have demonstrated or potential effects on atmospheric chemistry, climate, and the functioning of terrestrial ecosystems. Focused studies of the interactions between the atmosphere and the biosphere that regulate trace gases can improve both our understanding of terrestrial ecosystems and our ability to predict regional-and global-scale canges in atmospheric chemistry.     

Stable-carbon isotope ratios as a measure of marine versus terrestrial protein in ancient diets

The stable-carbon isotope ratios for the flesh of marine and terrestrial animals from Canada's Pacific coast differ by 7.9 +/- 0.4 per mil, reflecting the approximately 7 per mil difference between oceanic and atmospheric carbon. This difference is passed on to human consumers. The carbon isotopic values (delta(13)C) for human collagen thus yield direct information on the relative amounts of marine and terrestrial foods in prehistoric diets.     

Regional changes in carbon dioxide fluxes of land and oceans since 1980

We have applied an inverse model to 20 years of atmospheric carbon dioxide measurements to infer yearly changes in the regional carbon balance of oceans and continents. The model indicates that global terrestrial carbon fluxes were approximately twice as variable as ocean fluxes between 1980 and 1998. Tropical land ecosystems contributed most of the interannual changes in Earth's carbon balance over the 1980s, whereas northern mid- and high-latitude land ecosystems dominated from 1990 to 1995. Strongly enhanced uptake of carbon was found over North America during the 1992-1993 period compared to 1989-1990.     

From anchovies to sardines and back: multidecadal change in the Pacific Ocean

In the Pacific Ocean, air and ocean temperatures, atmospheric carbon dioxide, landings of anchovies and sardines, and the productivity of coastal and open ocean ecosystems have varied over periods of about 50 years. In the mid-1970s, the Pacific changed from a cool "anchovy regime" to a warm "sardine regime." A shift back to an anchovy regime occurred in the middle to late 1990s. These large-scale, naturally occurring variations must be taken into account when considering human-induced climate change and the management of ocean living resources.     

Global biodiversity scenarios for the year 2100

Scenarios of changes in biodiversity for the year 2100 can now be developed based on scenarios of changes in atmospheric carbon dioxide, climate, vegetation, and land use and the known sensitivity of biodiversity to these changes. This study identified a ranking of the importance of drivers of change, a ranking of the biomes with respect to expected changes, and the major sources of uncertainties. For terrestrial ecosystems, land-use change probably will have the largest effect, followed by climate change, nitrogen deposition, biotic exchange, and elevated carbon dioxide concentration. For freshwater ecosystems, biotic exchange is much more important. Mediterranean climate and grassland ecosystems likely will experience the greatest proportional change in biodiversity because of the substantial influence of all drivers of biodiversity change. Northern temperate ecosystems are estimated to experience the least biodiversity change because major land-use change has already occurred. Plausible changes in biodiversity in other biomes depend on interactions among the causes of biodiversity change. These interactions represent one of the largest uncertainties in projections of future biodiversity change.     

Arbuscular mycorrhizal fungi increase organic carbon decomposition under elevated CO2

The extent to which terrestrial ecosystems can sequester carbon to mitigate climate change is a matter of debate. The stimulation of arbuscular mycorrhizal fungi (AMF) by elevated atmospheric carbon dioxide (CO(2)) has been assumed to be a major mechanism facilitating soil carbon sequestration by increasing carbon inputs to soil and by protecting organic carbon from decomposition via aggregation. We present evidence from four independent microcosm and field experiments demonstrating that CO(2) enhancement of AMF results in considerable soil carbon losses. Our findings challenge the assumption that AMF protect against degradation of organic carbon in soil and raise questions about the current prediction of terrestrial ecosystem carbon balance under future climate-change scenarios.     

Weak northern and strong tropical land carbon uptake from vertical profiles of atmospheric CO2

Measurements of midday vertical atmospheric CO2 distributions reveal annual-mean vertical CO2 gradients that are inconsistent with atmospheric models that estimate a large transfer of terrestrial carbon from tropical to northern latitudes. The three models that most closely reproduce the observed annual-mean vertical CO2 gradients estimate weaker northern uptake of -1.5 petagrams of carbon per year (Pg C year(-1)) and weaker tropical emission of +0.1 Pg C year(-1) compared with previous consensus estimates of -2.4 and +1.8 Pg C year(-1), respectively. This suggests that northern terrestrial uptake of industrial CO2 emissions plays a smaller role than previously thought and that, after subtracting land-use emissions, tropical ecosystems may currently be strong sinks for CO2.     

农田碳汇估算模型与应用研究述评

随着全球变化研究的不断深入,农田碳汇管理日益受到学术界与决策界的关注。农田作为陆地生态系统的重要组成部分,其固碳能力的发挥关系到能否降低大气CO2浓度和抑制全球变暖趋势。回顾近10多年来国内外农田碳汇估算模型与应用研究的主要进展,概述了4种代表性农田碳汇估算模型的原理、结构、参数及制备、应用案例和模型检验等技术环节,为区域、国家乃至全球尺度农田碳汇估算筛选了模型与方法。     

Foraminiferal calcification response to glacial-interglacial changes in atmospheric CO2

A record of foraminiferal shell weight across glacial-interglacial Termination I shows a response related to seawater carbonate ion concentration and allows reconstruction of a record of carbon dioxide in surface seawater that matches the atmospheric record. The results support suggestions that higher atmospheric carbon dioxide directly affects marine calcification, an effect that may be of global importance to past and future changes in atmospheric CO2. The process provides negative feedback to the influence of marine calcification on atmospheric carbon dioxide and is of practical importance to the application of paleoceanographic proxies.     

植物叶片水平δ13C与水分利用效率的研究进展

水分限制可能因全球气候变化加剧成为限制植物生产力的主要原因,因此,如何提高植物水分利用效率(WUE)是未来一个主要研究目标。WUE能够反映植物-土壤-大气之间的碳水循环的耦合状况,研究WUE有助于了解陆地生态系统碳水耦合机制。稳定性碳同位素技术已成为研究生态系统养分循环最有效的方法之一,也被利用到植物水分利用效率中。研究表明,植物叶片的稳定碳同位素比值(δ13C)是植物长期水分利用效率(WUE)的良好指标。本文综述了δ13C表征WUE的机制,植物δ13C和WUE的影响因子(包括:叶片结构性状、植物生理生态、气候因子、基因控制和遗传变异),分析了水分胁迫及酸沉降条件下植物的δ13C和WUE变化特征,并对全球气候变化下植物δ13C和WUE的研究进行了展望。指出气孔导度、比叶面积、叶片氮含量、细胞间CO₂浓度和大气CO₂浓度等因子可直接或间接作用植物的光合速率和蒸腾速率,从而引起WUE的变化。一般情况下,植物在干旱条件下具有更高的WUE和更低的δ13C,长期酸沉降下植物的气孔导度和光合作用均会下降,氮的输入可以通过改善水分利用效率来提高植物的生产力。建议为更清晰地认识全球气候变化,在利用稳定性同位素技术进行WUE研究过程中,需要突出数量性状基因座(QTL)、碳酸酐酶、水孔蛋白和光合羧化酶的大小亚基基因在遗传控制方面起到的关键作用,加强多时空尺度的关联研究,探索双重稳定同位素(δ13C、δ18O)概念模型的应用。      

The global carbon cycle: a test of our knowledge of earth as a system

Motivated by the rapid increase in atmospheric CO2 due to human activities since the Industrial Revolution, several international scientific research programs have analyzed the role of individual components of the Earth system in the global carbon cycle. Our knowledge of the carbon cycle within the oceans, terrestrial ecosystems, and the atmosphere is sufficiently extensive to permit us to conclude that although natural processes can potentially slow the rate of increase in atmospheric CO2, there is no natural "savior" waiting to assimilate all the anthropogenically produced CO2 in the coming century. Our knowledge is insufficient to describe the interactions between the components of the Earth system and the relationship between the carbon cycle and other biogeochemical and climatological processes. Overcoming this limitation requires a systems approach.     

Ice core records of atmospheric N2O covering the last 106,000 years

Paleoatmospheric records of trace-gas concentrations recovered from ice cores provide important sources of information on many biogeochemical cycles involving carbon, nitrogen, and oxygen. Here, we present a 106,000-year record of atmospheric nitrous oxide (N2O) along with corresponding isotopic records spanning the last 30,000 years, which together suggest minimal changes in the ratio of marine to terrestrial N2O production. During the last glacial termination, both marine and oceanic N2O emissions increased by 40 +/- 8%. We speculate that our records do not support those hypotheses that invoke enhanced export production to explain low carbon dioxide values during glacial periods.     

A Large Northern Hemisphere Terrestrial CO2 Sink Indicated by the 13C/12C Ratio of Atmospheric CO2

Measurements of the concentrations and carbon-13/carbon-12 isotope ratios of atmospheric carbon dioxide can be used to quantify the net removal of carbon dioxide from the atmosphere by the oceans and terrestrial plants. A study of weekly samples from a global network of 43 sites defined the latitudinal and temporal patterns of the two carbon sinks. A strong terrestrial biospheric sink was found in the temperate latitudes of the Northern Hemisphere in 1992 and 1993, the magnitude of which is roughly half that of the global fossil fuel burning emissions for those years. The challenge now is to identify those processes that would cause the terrestrial biosphere to absorb carbon dioxide in such large quantities.