Sensitivity of terrestrial water and energy budgets to CO(2)-physiological forcing: an investigation using an offline land model

Increasing concentrations of atmospheric carbon dioxide (CO(2)) influence climate by suppressing canopy transpiration in addition to its well- known greenhouse gas effect. The decrease in plant transpiration is due to changes in plant physiology (reduced opening of plant stomata). Here, we quantify such changes in water flux for various levels of CO(2) concentrations using the National Center for Atmospheric Research's (NCAR) Community Land Model. We find that photosynthesis saturates after 800 ppmv (parts per million, by volume) in this model. However, unlike photosynthesis, canopy transpiration continues to decline at about 5.1% per 100 ppmv increase in CO(2) levels. We also find that the associated reduction in latent heat flux is primarily compensated by increased sensible heat flux. The continued decline in canopy transpiration and subsequent increase in sensible heat flux at elevated CO(2) levels implies that incremental warming associated with the physiological effect of CO(2) will not abate at higher CO(2) concentrations, indicating important consequences for the global water and carbon cycles from anthropogenic CO(2) emissions.

锡林河流域温带草地植物VOC释放及其对草地生态系统碳循环的贡献

植物源挥发性有机碳化合物（Volitale organic compounds, VOC）是大气VOC的主要来源，与对流层大气质量、大气化学密切相关。鉴于温带草地的分布范围很广，草地植物VOC释放潜力某种程度上影响植物源VOC的总释放量。另外，植物源VOC也是光合作用固定碳素的损失方式之一，可能在特定区域或生态系统中具有重要意义。基于上述想法，本文设计了四个方面的实验作为研究内容：1） 温带草地物种水平VOC释放潜力、及其与植物功能群的关系？2) 沙地植物物种水平VOC释放潜力、及其与植物功能群的关系？3) 沙地植物-草地植物VOC释放潜力存在显著性差异吗？4) 温带典型草地和退化草地的VOC释放速率如何？在生态系统水平，植物源VOC对温带草地碳循环的贡献多大？ 在所测定的175种温带草地植物中，不同植物间异戊二烯和单萜释放潜力差异很大;除少数物种外，大多数植物的异戊二烯和单萜释放潜力都较低，尤其是典型草地的优势物种。在此基础上，作者探讨了分类学赋值方法对温带草地植被的可行性，并初步建立了锡林河流域温带草地植物的VOC释放目录（共277种植物）。另外，温带草地植物的异戊二烯和单萜释放潜力与植物功能群（植物生活型和水分功能群）具有一定的联系，尤其是植物生活型。总的来说，温带草原的优势生活型（物种），即多年生根茎禾草（或多年生丛生禾草），具有较低的异戊二烯和单萜释放潜力。各水分功能群间差异不显著，但中旱生植物、旱中生植物 (温带草原的优势功能群)，具有较低的异戊二烯、单萜释放潜力。因此，温带草原退化过程中，那些具有较高VOC释放潜力的植物，重要性将会增加。 沙地植物种类组成非常丰富，不同物种间的异戊二烯和单萜释放潜力变异也很大。另外，沙地植物的异戊二烯和单萜释放潜力与其功能群间关系较密切，不同植物生活型间差异显著;其中也以多年生根茎禾草、多年生从生禾草的释放潜力最低，而乔木的释放潜力相对最高;该结论基本与草地的研究结论一致。然而，沙地植物的异戊二烯和单萜释放潜力与其水分功能群的关系比较模糊，中生植物具有更高的释放潜力，湿生植物的释放潜力较小。 通过对比沙地植物和草地植物的释放潜力，发现沙地植物的异戊二烯和单萜释放潜力比草地植物高，且这种差异整体上显著。另外，这种显著性差异，在不同植物生活型、水分功能群间也同样存在。沙地植物比对应的草地植物具有更高的异戊二烯和单萜释放潜力，最可能的原因：沙地正午的温度明显比草地温度高，前者实测温度可超过 45 ℃,这种经常性、周期性高温，促使沙地植物采用与草地植物不同的适应策略，即沙地植物通过释放更多的异戊二烯或单萜来减少其可能遭的热胁迫或热伤害，这种长期适应策略，使沙地植物具有更高的萜类化合物释放潜力。 本文还调查了温带典型草地生态系统和退化草地生态系统的异戊二烯和单萜释放速率，结果表明典型草地的标准异戊二烯和单萜释放速率分别为0.50 μgC g-1 h-1和0.69 μgC g-1 h-1;退化草地的标准异戊二烯和单萜释放潜力分别为0.32 μgC g-1 h-1和1.59 μgC g-1 h-1。总的来说，温带草地的异戊二烯和单萜释放速率都比较低，尤其是典型草地。整个生长季，典型草地释放的异戊二烯和单萜分别为31.6 mgC•m-2　和 70.4 mgC•m-2;退化草地的异戊二烯和单萜释放量分别为20.8 mgC•m-2 和 168.8 mgC•m-2。退化草地萜类化合物总释放速率远高于典型草地，尤其是单萜释放能力。过度放牧引起的草地退化，通过改变植被种类组成，对温带草地的异戊二烯和单萜释放速率产生显著影响;总体而言，温带草地退化将会使草地释放更多萜类化合物。 在温带草地生态系统中，Clost as VOC相对其NPP而言很小，在环境PAR和温度高时,它的贡献率相对较大;Clost as VOC约占典型草地生态系统NEP的5.32 %，退化草地生态系统NEP的0.23 %。植物源VOC释放所损失的碳素相对草地生态系统NPP而言几乎可以忽略不计;但是，相对其NEP，Clost as VOC还是具有一定的相关性。虽然，草地生态系统Clost as VOC对NPP或NEP的贡献率较小，但考虑到全球尺度植物源VOC的巨大释放速率，它在碳循环中的贡献率仍然不容忽视;在某些特殊的生态系统中，仍可能扮演重要角色。

末次盛冰期以来中国陆地生态系统碳储量变化研究

Carbon is an essential element for life, food and energy. It is also a key element in the greenhouse gases and therefore plays a vital role in climatic changes. The rapid increase in atmospheric concentration of CO_2 over the past 150 years, reaching current concentrations of about 370 ppmv, corresponds with combustion of fossii fuels since the beginning of the industrial age. Conversion of forested land to agricultural use has also redistributed carbon from plants and soils to the atmosphere. These human activities have significantly altered the global carbon cycle. Understanding the consequences of these activities in the coming decades is critical for formulating economic, energy, technology, trade, and security policies that will affect civilization for generations. Under the auspices of the International Geosphere-Biosphere Programme (IGBP), several large international scientific efforts are focused on elucidating the various aspects of the global carbon cycle of the past decade. It is only possible to balance the global carbon cycle for the 1990s if there is net carbon uptake by terrestrial ecosystems of around 2 Pg C/a. There are now some independent, direct evidences for the existence of such a sink. Policymarkers involved in the UN Framework Convention on Climate Change (UN-FCCC) are striving to reach consensuses on a 'safe path' for future emissions, the credible predictions on where and how long the terrestrial sink will either persist at its current level, or grow/decline in the future, are important to advice the policy process. The changes of terrestrial carbon storage depend not only on human activities, but also on biogeochemical and climatological processes and their interaction with the carbon cycles. In this thesis, the climate-induced changes and human-induced changes of carbon storage in China since the past 20,000 years are examined. Based on the data of the soil profiles investigated during China's Second National Soil Survey (1979-1989), the forest biomass measured during China's Fourth National Forest Resource Inventory (1989-1993), the grass biomass investigated during the First National Grassland Resource Survey (1980-1991), and the data collected from a collection of published literatures, the current terrestrial carbon storage in China is estimated to -144.1 Pg C, including -136.8 Pg C in soil and -7.3 Pg C in vegetation. The soil organic (SOC) and inorganic carbon (SIC) storage are -78.2 Pg C and -58.6 Pg C, respectively. In the vegetation reservoir, the forest carbon storage is -5.3 Pg C, and the other of-1.4 Pg C is in the grassland. Under the natural conditions, the SOC, SIC, forest and grassland carbon storage are -85.3 Pg C, -62.6 Pg C, -24.5 Pg C and -5.3 Pg C, respectively. Thus, -29.6 Pg C organic carbon has been lost due to land use with a decrease of -20.6%. At the same time, the SIC storage also has been decreased by -4.0 Pg C (-6.4%). These suggest that human activity has caused significant carbon loss in terrestrial carbon storage of China, especially in the forest ecosystem (-76% loss). Using the Paleocarbon Model (PCM) developed by Wu et al. in this paper, total terrestrial organic carbon storage in China in the Last Glacial Maximum (LGM) was -114.8 Pg C, including -23.1 Pg C in vegetation and -86.7 Pg C in soil. At the Middle Holocene (MH), the vegetation, soil and total carbon were -37.3 Pg C, -93.9 Pg C and -136.0 Pg C, respectively. This implies a gain of-21.2 Pg C in the terrestrial carbon storage from LGM to HM mainly due to the temperature increase. However, a loss of-14.4 Pg C of terrestrial organic carbon occurred in China under the current condition (before 1850) compared with the MH time, mainly due to the precipitation decrease associated with the weakening of the Asian summer monsoon. These results also suggest that the terrestrial ecosystem in China has a substantial potential in the restoration of carbon storage. This might be expected to provide an efficient way to mitigate the greenhouse warming through land management practices. Assuming that half of the carbon loss in the degraded terrestrial ecosystem in current forest and grass areas are restored during the next 50 years or so, the terrestrial ecosystem in China may sequestrate -12.0 Pg of organic carbon from the atmosphere, which represents a considerable offset to the industry's CO2 emission. If the ' Anthropocene' Era will be another climate optimum like MH due to the greenhouse effect, the sequestration would be increased again by -4.3 - 9.0 Pg C in China.

Coccolithophore bloom detection in the north east Atlantic using SeaWiFS: Algorithm description, application and sensitivity analysis

Coccolithophores are the largest source of calcium carbonate in the oceans and are considered to play an important role in oceanic carbon cycles. Current methods to detect the presence of coccolithophore blooms from Earth observation data often produce high numbers of false positives in shelf seas and coastal zones due to the spectral similarity between coccolithophores and other suspended particulates. Current methods are therefore unable to characterise the bloom events in shelf seas and coastal zones, despite the importance of these phytoplankton in the global carbon cycle. A novel approach to detect the presence of coccolithophore blooms from Earth observation data is presented. The method builds upon previous optical work and uses a statistical framework to combine spectral, spatial and temporal information to produce maps of coccolithophore bloom extent. Validation and verification results for an area of the north east Atlantic are presented using an in situ database (N = 432) and all available SeaWiFS data for 2003 and 2004. Verification results show that the approach produces a temporal seasonal signal consistent with biological studies of these phytoplankton. Validation using the in situ coccolithophore cell count database shows a high correct recognition rate of 80% and a low false-positive rate of 0.14 (in comparison to 63% and 0.34 respectively for the established, purely spectral approach). To guide its broader use, a full sensitivity analysis for the algorithm parameters is presented.

Electron transfer chains in sulfate reducing bacteria

Dissertação para a obtenção de grau de doutor em Bioquímica pelo Instituto de Tecnologia Química e Biológica. Universidade Nova de Lisboa.

Télédétection du carbone organique des lacs boréaux

Une estimation des quantités de carbone organique dissous dans les millions de lacs boréaux est nécessaire pour améliorer notre connaissance du cycle global du carbone. Les teneurs en carbone organique dissous sont corrélées avec les quantités de matière organique dissoute colorée qui est visible depuis l’espace. Cependant, les capteurs actuels offrent une radiométrie et une résolution spatiale qui sont limitées par rapport à la taille et l’opacité des lacs boréaux. Landsat 8, lancé en février 2013, offrira une radiométrie et une résolution spatiale améliorées, et produira une couverture à grande échelle des régions boréales. Les limnologistes ont accumulé des années de campagnes de terrain dans les régions boréales pour lesquelles une image Landsat 8 sera disponible. Pourtant, la possibilité de combiner des données de terrain existantes avec une image satellite récente n'a pas encore été évaluée. En outre, les différentes stratégies envisageables pour sélectionner et combiner des mesures répétées au cours du temps, sur le terrain et depuis le satellite, n'ont pas été évaluées. Cette étude présente les possibilités et les limites d’utiliser des données de terrain existantes avec des images satellites récentes pour développer des modèles de prédiction du carbone organique dissous. Les méthodes se basent sur des données de terrain recueillies au Québec dans 53 lacs boréaux et 10 images satellites acquises par le capteur prototype de Landsat 8. Les délais entre les campagnes de terrain et les images satellites varient de 1 mois à 6 ans. Le modèle de prédiction obtenu se compare favorablement avec un modèle basé sur des campagnes de terrain synchronisées avec les images satellite. L’ajout de mesures répétées sur le terrain, sur le satellite, et les corrections atmosphériques des images, n’améliorent pas la qualité du modèle de prédiction. Deux images d’application montrent des distributions différentes de teneurs en carbone organique dissous et de volumes, mais les quantités de carbone organique dissous par surface de paysage restent de même ordre pour les deux sites. Des travaux additionnels pour intégrer les sédiments dans l’estimation sont nécessaires pour améliorer le bilan du carbone des régions boréales.

Idealized model for changes in equilibrium temperature, mixed layer depth, and boundary layer cloud over land in a doubled CO2 climate

An idealized equilibrium model for the undisturbed partly cloudy boundary layer (BL) is used as a framework to explore the coupling of the energy, water, and carbon cycles over land in midlatitudes and show the sensitivity to the clear‐sky shortwave flux, the midtropospheric temperature, moisture, CO2, and subsidence. The changes in the surface fluxes, the BL equilibrium, and cloud cover are shown for a warmer, doubled CO2 climate. Reduced stomatal conductance in a simple vegetation model amplifies the background 2 K ocean temperature rise to an (unrealistically large) 6 K increase in near‐surface temperature over land, with a corresponding drop of near‐surface relative humidity of about 19%, and a rise of cloud base of about 70 hPa. Cloud changes depend strongly on changes of mean subsidence; but evaporative fraction (EF) decreases. EF is almost uniquely related to mixed layer (ML) depth, independent of background forcing climate. This suggests that it might be possible to infer EF for heterogeneous landscapes from ML depth. The asymmetry of increased evaporation over the oceans and reduced transpiration over land increases in a warmer doubled CO2 climate.

Cultivating C4 crops in a changing climate: sugarcane in Ghana

Over the next few decades, it is expected that increasing fossil fuel prices will lead to a proliferation of energy crop cultivation initiatives. The environmental sustainability of these activities is thus a pressing issue—particularly when they take place in vulnerable regions, such as West Africa. In more general terms, the effect of increased CO2 concentrations and higher temperatures on biomass production and evapotranspiration affects the evolution of the global hydrological and carbon cycles. Investigating these processes for a C4 crop, such as sugarcane, thus provides an opportunity both to extend our understanding of the impact of climate change, and to assess our capacity to model the underpinning processes. This paper applies a process-based crop model to sugarcane in Ghana (where cultivation is planned), and the São Paulo region of Brazil (which has a well-established sugarcane industry). We show that, in the Daka River region of Ghana, provided there is sufficient irrigation, it is possible to generate approximately 75% of the yield achieved in the São Paulo region. In the final part of the study, the production of sugarcane under an idealized temperature increase climate change scenario is explored. It is shown that doubling CO2 mitigates the degree of water stress associated with a 4 °C increase in temperature.

Plant Functional Type (PFT) map over Siberia derived from GlobCover 2005 dataset, link to dataset in NetCDF format

High-latitude ecosystems play an important role in the global carbon cycle and in regulating the climate system and are presently undergoing rapid environmental change. Accurate land cover data sets are required to both document these changes as well as to provide land-surface information for benchmarking and initializing Earth system models. Earth system models also require specific land cover classification systems based on plant functional types (PFTs), rather than species or ecosystems, and so post-processing of existing land cover data is often required. This study compares over Siberia, multiple land cover data sets against one another and with auxiliary data to identify key uncertainties that contribute to variability in PFT classifications that would introduce errors in Earth system modeling. Land cover classification systems from GLC 2000, GlobCover 2005 and 2009, and MODIS collections 5 and 5.1 are first aggregated to a common legend, and then compared to high-resolution land cover classification systems, vegetation continuous fields (MODIS VCFs) and satellite-derived tree heights (to discriminate against sparse, shrub, and forest vegetation). The GlobCover data set, with a lower threshold for tree cover and taller tree heights and a better spatial resolution, tends to have better distributions of tree cover compared to high-resolution data. It has therefore been chosen to build new PFT maps for the ORCHIDEE land surface model at 1 km scale. Compared to the original PFT data set, the new PFT maps based on GlobCover 2005 and an updated cross-walking approach mainly differ in the characterization of forests and degree of tree cover. The partition of grasslands and bare soils now appears more realistic compared with ground truth data. This new vegetation map provides a framework for further development of new PFTs in the ORCHIDEE model like shrubs, lichens and mosses, to represent the water and carbon cycles in northern latitudes better. Updated land cover data sets are critical for improving and maintaining the relevance of Earth system models for assessing climate and human impacts on biogeochemistry and biophysics.

Seawater chemistry, nutrients, chlorophyll a, and growth rate of Phaeocystis globosa during experiments

Phaeocystis globosa (Prymnesiophyceae) is an ecologically dominating phytoplankton species in many areas around the world. It plays an important role in both the global sulfur and carbon cycles, by the production of dimethylsulfide (DMS) and the drawdown of inorganic carbon. Phaeocystis globosa has a polymorphic life cycle and is considered to be a harmful algal bloom (HAB) forming species. All these aspects make this an interesting species to study the effects of increasing carbon dioxide (CO2) concentrations, due to anthropogenic carbon emissions. Here, the combined effects of three different dissolved carbon dioxide concentrations (CO2(aq)) (low: 4 µmol/kg, intermediate: 6-10 µmol/kg and high CO2(aq): 21-24 µmol/kg) and two different light intensities (low light, suboptimal: 80 µmol photons/m**2/s and high light, light saturated: 240 µmol photons/m**2/s) are reported. The experiments demonstrated that the specific growth rate of P. globosa in the high light cultures decreased with increasing CO2(aq) from 1.4 to 1.1 /d in the low and high CO2 cultures, respectively. Concurrently, the photosynthetic efficiency (Fv/Fm) increased with increasing CO2(aq) from 0.56 to 0.66. The different light conditions affected photosynthetic efficiency and cellular chlorophyll a concentrations, both of which were lower in the high light cultures as compared to the low light cultures. These results suggest that in future inorganic carbon enriched oceans, P. globosa will become less competitive and feedback mechanisms to global change may decrease in strength.

Pseudo-random single photon counting for space-borne atmospheric sensing applications

The ability to accurately observe the Earth's carbon cycles from space gives scientists an important tool to analyze climate change. Current space-borne Integrated-Path Differential Absorption (IPDA) Iidar concepts have the potential to meet this need. They are mainly based on the pulsed time-offlight principle, in which two high energy pulses of different wavelengths interrogate the atmosphere for its transmission properties and are backscattered by the ground. In this paper, feasibility study results of a Pseudo-Random Single Photon Counting (PRSPC) IPDA lidar are reported. The proposed approach replaces the high energy pulsed source (e.g. a solidstate laser), with a semiconductor laser in CW operation with a similar average power of a few Watts, benefiting from better efficiency and reliability. The auto-correlation property of Pseudo-Random Binary Sequence (PRBS) and temporal shifting of the codes can be utilized to transmit both wavelengths simultaneously, avoiding the beam misalignment problem experienced by pulsed techniques. The envelope signal to noise ratio has been analyzed, and various system parameters have been selected. By restricting the telescopes field-of-view, the dominant noise source of ambient light can be suppressed, and in addition with a low noise single photon counting detector, a retrieval precision of 1.5 ppm over 50 km along-track averaging could be attained. We also describe preliminary experimental results involving a negative feedback Indium Gallium Arsenide (InGaAs) single photon avalanche photodiode and a low power Distributed Feedback laser diode modulated with PRBS driven acoustic optical modulator. The results demonstrate that higher detector saturation count rates will be needed for use in future spacebourne missions but measurement linearity and precision should meet the stringent requirements set out by future Earthobserving missions.

Global compilation of benthic data sets I

Approaches to quantify the organic carbon accumulation on a global scale generally do not consider the small-scale variability of sedimentary and oceanographic boundary conditions along continental margins. In this study, we present a new approach to regionalize the total organic carbon (TOC) content in surface sediments (<5 cm sediment depth). It is based on a compilation of more than 5500 single measurements from various sources. Global TOC distribution was determined by the application of a combined qualitative and quantitative-geostatistical method. Overall, 33 benthic TOC-based provinces were defined and used to process the global distribution pattern of the TOC content in surface sediments in a 1°x1° grid resolution. Regional dependencies of data points within each single province are expressed by modeled semi-variograms. Measured and estimated TOC values show good correlation, emphasizing the reasonable applicability of the method. The accumulation of organic carbon in marine surface sediments is a key parameter in the control of mineralization processes and the material exchange between the sediment and the ocean water. Our approach will help to improve global budgets of nutrient and carbon cycles.

Avancement vers la synthèse du (+) et du (-)-hodgsonox

Ce mémoire décrit les travaux qui ont été réalisés sur la synthèse de l’hodgsonox, un sesquiterpène tricyclique comportant un éther diallylique dans un cycle tétrahydropyranique. Les approches envisagées sont la formation du cycle à cinq puis la formation du tétrahydropyrane et une autre plus convergente qui implique la synthèse des deux cycles en une seule étape. La première partie du mémoire discute de la synthèse d’un précurseur acyclique du cycle à cinq membres, afin de réaliser une réaction de métathèse de fermeture de cycle. Toutefois, les essais n’ont pas été concluants et cette voie a été abandonnée. Dans la deuxième partie, une nouvelle approche impliquant la synthèse d’un bicycle par une réaction de Pauson-Khand a été étudiée. Le précurseur de la réaction de Pauson- Khand a été préparé en 9 étapes (30% de rendement global) à partir du diéthyle tartrate. Le produit de cyclisation a été également obtenu mais il n’a pas été possible par la suite d’introduire le groupement isopropyle. Dans la dernière partie de ce mémoire, les travaux de Lise Brethous sur la synthèse de l’hodgsonox ont été repris. Celle-ci avait montré que le cycle à 5 membres pouvait être obtenu à partir de l’a-acétyl g-butyrolactone et que la formation du bicycle pouvait être réalisée par une réaction catalytique d’insertion d’un composé diazoïque dans un lien O-H. Certaines de ces étapes ont été optimisées et différents tests ont été effectués pour réaliser les dernières étapes de la synthèse de l’hodgosonox, mais sans succès.