Role of a simplified hydrological cycle and clouds in regulating the climate–biota system of Daisyworld

The role of a simplified hydrological cycle and a physical representation of clouds is investigated in the Daisyworld model, subject to constant and variable solar forcing and varying cloud albedo and height. Under constant forcing, properties of the cloudy hydrologic cycle control the long-term system dynamics to non-oscillatory, oscillatory, abiotic or biotic states. In case of oscillatory solutions, their amplitude and periodicity are controlled by the net cooling or warming effects from clouds. Two conditions are considered under variable forcing—active or neutral—depending on the existence or not of biota–environment feedbacks. Temperature, cloudiness and hydrological variables are self-regulated in the active condition, whereas non-regulated in the neutral condition. Self-regulation is quantified through two measurements (luminosity range and total life), both of which can be larger in our model than in several other variants of Daisyworld, depending on cloud characteristics. The hydrological cycle and clouds can make the planet more habitable for life, independent of the capacity of the system for biological adaptation. Two hypotheses are put forward: (1) beneficial effects for life emerge from biota–clouds interactions, enhancing the global amount of life and extending the life span; and (ii) the existence of a maximum self-regulation capacity principle.     

海南石碌铁矿独居石的成因类型、化学定年及地质意义

海南石碌铁矿是我国最大的富赤铁矿矿床,同时伴生有钴、铜等多金属矿产。轴向北西-南东向的复式向斜是石碌铁、钴铜矿体的主要控矿构造,富铁矿和钴铜矿的形成与该褶皱变形及伴随的韧性剪切和高温塑性流动有着密切的关系。为获得该构造变形的年代学信息和证实构造变形对成矿物质的富集影响,本文开展了石碌铁矿近矿围岩—石碌群第六层透辉石透闪石岩中独居石的显微结构观察和电子探针化学Th-U-Pb定年(CHIME法)。显微结构观察发现独居石往往沿岩石面理定向分布,且具典型的球冠结构,表现为围绕独居石核部向外依次出现磷灰石、褐帘石、绿帘石同心环。电子探针分析结果表明这些独居石为Ce-La-Nd磷酸盐[(Ce,La,Nd,Th)PO4],具富钍独居石端元组分。ThO 2含量范围(0.78%~4.61%)、稀土特征以及独居石的产出特征均暗示了其为同构造变质成因。电子探针CHIME化学定年结果表明独居石的年龄变化范围为614~397Ma,并具有两个峰值年龄:即主峰值ca.455Ma和次峰值ca.564Ma。低的ThO 2(0.78%~1.65%),PbO(0.02%~0.04%)和CaO(0.50%~0.97%)含量,以及高的Th/U比值(23.06~53.11)暗示了构成ca.564Ma的独居石是早期剪切变形事件的产物。而在随后剪切变形过程中独居石在低角闪岩相变质条件下以及碱性变质流体诱导下发生了溶解-再沉淀,形成了具ca.455Ma年龄的补丁状成分区。该过程引起了U-Pb体系的局部重置,形成的独居石具有变化较大的ThO 2(0.92%~4.61%)、PbO(0.01%~0.08%)和CaO(0.28%~1.58%)含量范围以及Th/U值(24.83~52.86)。在剪切变形之后,早期变质成因的独居石在绿片岩相退变质作用过程中及富Ca、Fe、Si、Al流体参与的条件下,经不平衡反应形成了磷灰石-褐帘石-绿帘石球冠物,反应机制以独居石和球冠矿物间的元素扩散动力学为主。该反应暗示了REE、Y、Th等元素发生了迁移,并可能引起边部独居石的部分Pb丢失。结合华南的构造演化,年龄谱主峰值455Ma代表了与华南加里东造山运动有关的区域变质和动力变质作用事件年龄,是加里东运动在海南岛的响应;次峰值年龄564Ma对应着冈瓦纳泛非事件,暗示了华南在晚新元古代-早古生代与冈瓦纳大陆具有亲缘性,华南加里东运动引起陆内造山过程可能与冈瓦纳大陆的聚合碰撞事件有关。因此,晚新元古代-早古生代造山事件对海南岛构造演化历史具重要影响。此外,该构造运动使石碌群发生褶皱变形,伴随产生的变质流体使铁、钴铜成矿元素进一步活化和富集,对石碌铁、钴铜矿的富集有着重要影响。     

Vertical profiles of biospheric and fossil fuel-derived CO2 and fossil fuel CO2 : CO ratios from airborne measurements of Δ14C, CO2 and CO above Colorado, USA

Measurements of  Δ¹⁴C  in atmospheric CO₂ are an effective method of separating CO₂ additions from fossil fuel and biospheric sources or sinks of CO₂. We illustrate this technique with vertical profiles of CO₂ and  Δ¹⁴C  analysed in whole air flask samples collected above Colorado, USA in May and July 2004. Comparison of lower tropospheric composition to cleaner air at higher altitudes (>5 km) revealed considerable additions from respiration in the morning in both urban and rural locations. Afternoon concentrations were mainly governed by fossil fuel emissions and boundary layer depth, also showing net biospheric CO₂ uptake in some cases. We estimate local industrial CO₂:CO emission ratios using in situ measurements of CO concentration. Ratios are found to vary by 100% and average 57 mole CO₂:1 mole CO, higher than expected from emissions inventories. Uncertainty in CO₂ from different sources was ±1.1 to ±4.1 ppm for addition or uptake of −4.6 to 55.8 ppm, limited by  Δ¹⁴C  measurement precision and uncertainty in background  Δ¹⁴C  and CO₂ levels.     

Contributions of carbon cycle uncertainty to future climate projection spread

We have characterized the relative contributions to uncertainty in predictions of global warming amount by year 2100 in the C4MIP model ensemble ( Friedlingstein et al., 2006 ) due to both carbon cycle process uncertainty and uncertainty in the physical climate properties of the Earth system. We find carbon cycle uncertainty to be important. On average the spread in transient climate response is around 40% of that due to the more frequently debated uncertainties in equilibrium climate sensitivity and global heat capacity.
This result is derived by characterizing the influence of different parameters in a global climate-carbon cycle 'box' model that has been calibrated against the 11 General Circulation models (GCMs) and Earth system Models of Intermediate Complexity (EMICs) in the C4MIP ensemble; a collection of current state-of-the-art climate models that include an explicit representation of the global carbon cycle.     

Assessment of the soil CO2 gradient method for soil CO2 efflux measurements: comparison of six models in the calculation of the relative gas diffusion coefficient

This paper uses a refined soil gradient method to estimate soil CO₂ efflux. Six different models are used to determine the relative gas diffusion coefficient (ξ). A weighted harmonic averaging is used to estimate the soil CO₂ diffusion coefficient, yielding a better estimate of soil CO₂ efflux. The resulting soil CO₂ efflux results are then compared to the soil CO₂ efflux measured with a soil chamber. Depending on the choice of ξ model used, the estimated soil CO₂ efflux using the gradient method reasonably approximates the efflux obtained using the soil chamber method. In addition, the estimated soil CO₂ efflux obtained by this improved method is well described by an exponential function of soil temperature at a depth of 0.05 m with the temperature sensitivity ( Q ₁₀) of 1.81 and a linear function of soil moisture at a depth of 0.12 m, in general agreement with previous findings. These results suggest that the gradient method is a practical cost-effective means to measure soil CO₂ emissions. Results from the present study suggest that the gradient method can be used successfully to measure soil CO₂ efflux provided that proper attention is paid to the judicious use of the proper diffusion coefficient.     

Is the recent build-up of atmospheric CO2 over Europe reproduced by models. Part 2: an overview with the atmospheric mesoscale transport model CHIMERE

In this issue, Ramonet et al. revealed a positive trend in European, atmospheric CO₂ concentrations relative to a marine, North Atlantic reference baseline, for the years 2001–2006. The observed build up mainly occurred during the cold season where it reaches a 0.8 ppm yr⁻¹ at low-altitude stations to a 0.3 ppm yr⁻¹ at mid-altitude stations. We explore the cause of this build-up using the mesoscale model CHIMERE. We first model the observed trends, using interannually varying fluxes and transport, then suppress the interannual variability in fluxes or aspects of transport to elucidate the cause. The run with no interannual variability in fluxes still matches observed trends suggesting that transport is the major cause. Separate runs varying either boundary layer height or winds show that changes in boundary layer height explain the trends at low-altitude stations within the continents while changes in wind regimes drive changes elsewhere.     

Measurements of desert dust optical characteristics at Porte au Sahara during SAMUM

Main optical characteristics of desert dust, such as phase function and single scattering albedo, have been derived from combinations of sun-/sky-radiometer and satellite measurements during the SAMUM experiment (10 May–10 June 2006) at the site Porte au Sahara (30.237°N, 5.607°W) in South Morocco. Scattering phase functions have been retrieved using combined data of spectral aerosol optical thickness (AOT) and spectral sky brightness in the almucantar, considering non-spherical light scattering. Intercomparisons of modelled top-of-atmosphere (TOA) reflectance with satellite observations of the Medium Resolution Imaging Spectrometer (MERIS) and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography () instrument have been used for the estimation of spectral single scattering albedo. For the radiative transfer calculations scattering phase functions and AOT from ground-based observations have been used. The spectral single scattering albedo ranges from 0.93 in the blue to 0.98 at 753 nm.     

Desert dust aerosol air mass mapping in the western Sahara, using particle properties derived from space-based multi-angle imaging

Coincident observations made over the Moroccan desert during the Sahara mineral dust experiment (SAMUM) 2006 field campaign are used both to validate aerosol amount and type retrieved from multi-angle imaging spectroradiometer (MISR) observations, and to place the suborbital aerosol measurements into the satellite's larger regional context. On three moderately dusty days during which coincident observations were made, MISR mid-visible aerosol optical thickness (AOT) agrees with field measurements point-by-point to within 0.05–0.1. This is about as well as can be expected given spatial sampling differences; the space-based observations capture AOT trends and variability over an extended region. The field data also validate MISR's ability to distinguish and to map aerosol air masses, from the combination of retrieved constraints on particle size, shape and single-scattering albedo. For the three study days, the satellite observations (1) highlight regional gradients in the mix of dust and background spherical particles, (2) identify a dust plume most likely part of a density flow and (3) show an aerosol air mass containing a higher proportion of small, spherical particles than the surroundings, that appears to be aerosol pollution transported from several thousand kilometres away.     

Costs and global impacts of black carbon abatement strategies

Abatement of particulate matter has traditionally been driven by health concerns rather than its role in global warming. Here we assess future abatement strategies in terms of how much they reduce the climate impact of black carbon (BC) and organic carbon (OC) from contained combustion. We develop global scenarios which take into account regional differences in climate impact, costs of abatement and ability to pay, as well as both the direct and indirect (snow-albedo) climate impact of BC and OC. To represent the climate impact, we estimate consistent region-specific values of direct and indirect global warming potential (GWP) and global temperature potential (GTP). The indirect GWP has been estimated using a physical approach and includes the effect of change in albedo from BC deposited on snow. The indirect GWP is highest in the Middle East followed by Russia, Europe and North America, while the total GWP is highest in the Middle East, Africa and South Asia. We conclude that prioritizing emission reductions in Asia represents the most cost-efficient global abatement strategy for BC because Asia is (1) responsible for a large share of total emissions, (2) has lower abatement costs compared to Europe and North America and (3) has large health cobenefits from reduced PM₁₀ emissions.     

The SAMUM-1 experiment over Southern Morocco: overview and introduction

In May/June 2006, the largest mineral dust experiment to date (Saharan Mineral Dust Experiment, SAMUM-1) was conducted in Southern Morocco. The aim was to characterize dust particles near the world's largest mineral dust source, and to quantify dust-related radiative effects. At one of the two ground-based measurement sites dust particle size distribution, optical, hygroscopic, chemical and structural particle characteristics were measured. One research aircraft mainly measured solar spectral irradiances and surface albedo. The other aircraft provided in situ physical aerosol measurements and samples and lidar profiles through the dust layers. Three ground-based lidars were operated at the second ground-based measurement site. They determined optical dust properties, particle shape and temporal development of dust layers. Columnar, ground-based sun photometer measurements complemented the lidar data. Additionally a station in Évora, Portugal monitored dust outbreaks from the North African source region to the Iberian Peninsula during SAMUM-1.
Volumetric and columnar closure exercises utilized these detailed measurements of dust characteristics together with optical and radiative transfer models. Concurrent developments of a mesoscale dust transport model were validated with the experimental data. The paper gives an overview over rationale and design of SAMUM-1, introduces and highlights the subsequent reports on experimental and modelling results.