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The assessment of water balance components using global hydrological models is subject to climate forcing uncertainty as well as to an increasing intensity of human water use within the 20th century. The uncertainty of five state-of-the-art climate forcings and the resulting range of cell runoff that is simulated by the global hydrological model WaterGAP is presented. On the global land surface, about 62 % of precipitation evapotranspires, whereas 38 % discharges into oceans and inland sinks. During 1971–2000, evapotranspiration due to human water use amounted to almost 1 % of precipitation, while this anthropogenic water flow increased by a factor of approximately 5 between 1901 and 2010. Deviation of estimated global discharge from the ensemble mean due to climate forcing uncertainty is approximately 4 %. Precipitation uncertainty is the most important reason for the uncertainty of discharge and evapotranspiration, followed by shortwave downward radiation. At continental levels, deviations of water balance components due to uncertain climate forcing are higher, with the highest discharge deviations occurring for river discharge in Africa (−6 to 11 % from the ensemble mean). Uncertain climate forcings also affect the estimation of irrigation water use and thus the estimated human impact of river discharge. The uncertainty range of global irrigation water consumption amounts to approximately 50 % of the global sum of water consumption in the other water use sector.
Ecological networks are more sensitive to plant than to animal extinction under climate change
(2016)
Impacts of climate change on individual species are increasingly well documented, but we lack understanding of how these effects propagate through ecological communities. Here we combine species distribution models with ecological network analyses to test potential impacts of climate change on >700 plant and animal species in pollination and seed-dispersal networks from central Europe. We discover that animal species that interact with a low diversity of plant species have narrow climatic niches and are most vulnerable to climate change. In contrast, biotic specialization of plants is not related to climatic niche breadth and vulnerability. A simulation model incorporating different scenarios of species coextinction and capacities for partner switches shows that projected plant extinctions under climate change are more likely to trigger animal coextinctions than vice versa. This result demonstrates that impacts of climate change on biodiversity can be amplified via extinction cascades from plants to animals in ecological networks.
Evaluation of radiation components in a global freshwater model with station-based observations
(2016)
In many hydrological models, the amount of evapotranspired water is calculated using the potential evapotranspiration (PET) approach. The main driver of several PET approaches is net radiation, whose downward components are usually obtained from meteorological input data, whereas the upward components are calculated by the model itself. Thus, uncertainties can be large due to both the input data and model assumptions. In this study, we compare the radiation components of the WaterGAP Global Hydrology Model, driven by two meteorological input datasets and two radiation setups from ERA-Interim reanalysis. We assess the performance with respect to monthly observations provided by the Baseline Surface Radiation Network (BSRN) and the Global Energy Balance Archive (GEBA). The assessment is done for the global land area and specifically for energy/water limited regions. The results indicate that there is no optimal radiation input throughout the model variants, but standard meteorological input datasets perform better than those directly obtained by ERA-Interim reanalysis for the key variable net radiation. The low number of observations for some radiation components, as well as the scale mismatch between station observations and 0.5° × 0.5° grid cell size, limits the assessment.
Binary nucleation of sulphuric acid-water particles is expected to be an important process in the free troposphere at low temperatures. SAWNUC (Sulphuric Acid Water Nucleation) is a model of binary nucleation that is based on laboratory measurements of the binding energies of sulphuric acid and water in charged and neutral clusters. Predictions of SAWNUC are compared for the first time comprehensively with experimental binary nucleation data from the CLOUD chamber at European Organization for Nuclear Research. The experimental measurements span a temperature range of 208–292 K, sulphuric acid concentrations from 1·106 to 1·109 cm−3, and distinguish between ion-induced and neutral nucleation. Good agreement, within a factor of 5, is found between the experimental and modeled formation rates for ion-induced nucleation at 278 K and below and for neutral nucleation at 208 and 223 K. Differences at warm temperatures are attributed to ammonia contamination which was indicated by the presence of ammonia-sulphuric acid clusters, detected by an Atmospheric Pressure Interface Time of Flight (APi-TOF) mass spectrometer. APi-TOF measurements of the sulphuric acid ion cluster distributions (math formula with i = 0, 1, ..., 10) show qualitative agreement with the SAWNUC ion cluster distributions. Remaining differences between the measured and modeled distributions are most likely due to fragmentation in the APi-TOF. The CLOUD results are in good agreement with previously measured cluster binding energies and show the SAWNUC model to be a good representation of ion-induced and neutral binary nucleation of sulphuric acid-water clusters in the middle and upper troposphere.
Chemical reduction-oxidation mechanisms within mantle rocks link to the terrestrial carbon cycle by influencing the depth at which magmas can form, their composition, and ultimately the chemistry of gases released into the atmosphere. The oxidation state of the uppermost mantle has been widely accepted to be unchanged over the past 3800 m.y., based on the abundance of redox-sensitive elements in greenstone belt–associated samples of different ages. However, the redox signal in those rocks may have been obscured by their complex origins and emplacement on continental margins. In contrast, the source and processes occurring during decompression melting at spreading ridges are relatively well constrained. We retrieve primary redox conditions from metamorphosed mid-oceanic ridge basalts (MORBs) and picrites of various ages (ca. 3000–550 Ma), using V/Sc as a broad redox proxy. Average V/Sc values for Proterozoic suites (7.0 ± 1.4, 2σ, n = 6) are similar to those of modern MORB (6.8 ± 1.6), whereas Archean suites have lower V/Sc (5.2 ± 0.4, n = 5). The lower Archean V/Sc is interpreted to reflect both deeper melt extraction from the uppermost mantle, which becomes more reduced with depth, and an intrinsically lower redox state. The pressure-corrected oxygen fugacity (expressed relative to the fayalite-magnetite-quartz buffer, ΔFMQ, at 1 GPa) of Archean sample suites (ΔFMQ –1.19 ± 0.33, 2σ) is significantly lower than that of post-Archean sample suites, including MORB (ΔFMQ –0.26 ± 0.44). Our results imply that the reducing Archean atmosphere was in equilibrium with Earth’s mantle, and further suggest that magmatic gases crossed the threshold that allowed a build-up in atmospheric O2 levels ca. 3000 Ma, accompanied by the first “whiffs” of oxygen in sediments of that age.
Das Ziel dieser Arbeit ist die Untersuchung der stratosphärischen Meridionalzirkulation mit Hilfe von chemisch aktiven Spurengasen. Diese motiviert sich durch die Tatsache, dass der Klimawandel neben den viel erforschten Auswirkungen auf die Troposphäre, auch Reaktionen in der Stratosphäre zur Folge hat, welche bisher weit weniger tiefgehend untersucht wurden. Das macht die Stratosphäre zu einem aktuellen und frequentierten Forschungsgebiet der experimentellen und theoretischen Meteorologie. Neben vereinzelten hochaufgelösten in-situ Messungen und globalen Satellitendaten sind es hier vor allem globale numerische Klima-Chemiemodelle, die für Analysen genutzt werden. Für diese Arbeit wurden Daten des EMAC-Modells (engl.: ECHAM/MESSy Atmospheric Chemistry) ausgwertet, welche im Rahmen der ESCiMo (engl.: Earth System Chemistry integrated Modelling) Initiative vom MESSy-Konsortium (engl.: Modular Earth Submodel System) erstellt wurden. Die Zielsetzung dieser Arbeit war, ob sich etwaige Änderungen des stratosphärischen Transports anhand von modellierten, chemisch aktiven, idealisierten Spurengasen feststellen lassen. Idealisiert bedeutet hierbei, dass diese Gase ein konstantes Mischungsverhältnis am Erdboden aufweisen und den identischen chemischen Prozessen unterliegen wie die realistischen Tracer. Dies hat zur Folge, dass diese Spurengase somit nicht in das Strahlungsbudget des Modells rückkoppeln und ihre Verteilung nicht durch zeitliche troposphärische Trends beeinflusst wird. Zur Analyse des stratosphärischen Transports wurden die Differenzen der monatlich gemittelten Mischungsverhältnisse zweier Zeitpunkte der verschiedenen Substanzen im Vertikalprofil betrachtet und ausgewertet, wobei hier die photolytische Lebenszeit und die Zeitskala des Transports zu berücksichtigen war. Um die Saisonalität von Transport und Chemie zu berücksichtigen, wurden dazu die Monate März, Juni, September und Dezember analysiert.
Die Resultate zeigten, dass chemisch aktive Substanzen in der Tat geeignet sind Änderungen in der Dynamik festzustellen. So stellte sich heraus, dass mit einer allgemeinen Intensivierung der stratosphärischen Meridionalzirkulation im kommenden Jahrhundert gerechnet werden kann, wobei hiervon besonders die untere Stratosphäre betroffen ist. Eine Differenzierung welche Komponente der Zirkulation (Residualtransport oder bidirektionale quasi-horizontale Mischung) hierbei von übergeordneter Bedeutung ist, konnte nicht spezifiziert werden. Um abzuschätzen, ob sich die Änderung der Zirkulation durch Änderungen in den Mischungsverhältnissen von chemisch aktiven Substanzen mit Hilfe von direkten Messungen nachweisen lässt, wurde die atmosphärische Variabilität des Modells bestimmt und mit den Veränderungen dieser Mischungsverhältnisse verglichen. Es zeigte sich, dass diese modellierte atmosphärische Variabilität zum Teil deutlich größer war, als die Differenzen der Mischungsverhältnisse und so ohne eine Vielzahl von in-situ Messungen keine eindeutige Aussage zulassen. Um eine statistisch valide Aussage treffen zu können, müssen daher mehrere Messreihen innerhalb eines Monats durchgeführt werden. Zudem stellte sich heraus, dass der Monat Juni der bestmögliche Messzeitraum ist, da hier die natürliche Variabilität am geringsten ist. Zuletzt wurden die Spurengase mit vergleichsweise kleiner chemischer Lebenszeit auf normierten N2O-Isoplethen untersucht und die Verschiebung dieser Kurve zwischen den zwei Zeitpunkten analysiert. Die so gewonnenen Resultate ließen den Schluss zu, dass sich auf diese Weise die atmosphärische Variabilität reduzieren lässt und bei Nutzung mit experimentellen Daten eine zu den Tracer-Differenzen konsistente Aussage zulässt. So bestärkte diese Methode die These, dass sich der stratosphärische Transport innerhalb des 21. Jahrhunderts wahrscheinlich verstärken wird.
Background: Replicate population pairs that diverge in response to similar selective regimes allow for an investigation of (a) whether phenotypic traits diverge in a similar and predictable fashion, (b) whether there is gradual variation in phenotypic divergence reflecting variation in the strength of natural selection among populations, (c) whether the extent of this divergence is correlated between multiple character suites (i.e., concerted evolution), and (d) whether gradual variation in phenotypic divergence predicts the degree of reproductive isolation, pointing towards a role for adaptation as a driver of (ecological) speciation. Here, we use poeciliid fishes of the genera Gambusia and Poecilia that have repeatedly evolved extremophile lineages able to tolerate high and sustained levels of toxic hydrogen sulfide (H2S) to answer these questions.
Results: We investigated evolutionary divergence in response to H2S in Gambusia spp. (and to a lesser extent Poecilia spp.) using a multivariate approach considering the interplay of life history, body shape, and population genetics (nuclear miscrosatellites to infer population genetic differentiation as a proxy for reproductive isolation). We uncovered both shared and unique patterns of evolution: most extremophile Gambusia predictably evolved larger heads and offspring size, matching a priori predictions for adaptation to sulfidic waters, while variation in adult life histories was idiosyncratic. When investigating patterns for both genera (Gambusia and Poecilia), we found that divergence in offspring-related life histories and body shape were positively correlated across populations, but evidence for individual-level associations between the two character suites was limited, suggesting that genetic linkage, developmental interdependencies, or pleiotropic effects do not explain patterns of concerted evolution. We further found that phenotypic divergence was positively correlated with both environmental H2S-concentration and neutral genetic differentiation (a proxy for gene flow).
Conclusions: Our results suggest that higher toxicity exerts stronger selection, and that divergent selection appears to constrain gene flow, supporting a scenario of ecological speciation. Nonetheless, progress toward ecological speciation was variable, partially reflecting variation in the strength of divergent selection, highlighting the complexity of selective regimes even in natural systems that are seemingly governed by a single, strong selective agent.
When assessing global water resources with hydrological models, it is essential to know the methodological uncertainties in the water resources estimates. The study presented here quantifies effects of the uncertainty in the spatial and temporal patterns of meteorological variables on water balance components at the global, continental and grid cell scale by forcing the global hydrological model WaterGAP 2.2 (ISI-MIP 2.1) with five state-of-the-art climate forcing input data-sets. While global precipitation over land during 1971–2000 varies between 103 500 and 111 000 km3 yr−1, global river discharge varies between 39 200 and 42 200 km3 yr−1. Temporal trends of global wa- ter balance components are strongly affected by the uncertainty in the climate forcing (except human water abstractions), and there is a need for temporal homogenization of climate forcings (in particular WFD/WFDEI). On about 10–20 % of the global land area, change of river discharge between two consecutive 30 year periods was driven more strongly by changes of human water use including dam construction than by changes in precipitation. This number increases towards the end of the 20th century due to intensified human water use and dam construction. The calibration approach of WaterGAP against observed long-term average river discharge reduces the impact of climate forcing uncertainty on estimated river discharge significantly. Different homgeneous climate forcings lead to a variation of Q of only 1.6 % for the 54 % of global land area that are constrained by discharge observations, while estimated renewable water resources in the remaining uncalibrated regions vary by 18.5 %. Uncertainties are especially high in Southeast Asia where Global Runoff Data Centre (GRDC) data availability is very sparse. By sharing already available discharge data, or installing new streamflow gauging stations in such regions, water balance uncertainties could be reduced which would lead to an improved assessment of the world’s water resources.
Ice nucleating particles over the Eastern Mediterranean measured by unmanned aircraft systems
(2016)
During an intensive field campaign on aerosol, clouds and ice nucleation in the Eastern Mediterranean in April 2016, we have measured the abundance of ice nucleating particles (INP) in the lower troposphere from unmanned aircraft systems (UAS). Aerosol samples were collected by miniaturized electrostatic precipitators onboard the UAS at altitudes up to 2.5 km. The number of INP in these samples, which are active in the deposition and condensation modes at temperatures from −20 to −30 ◦C, were analyzed immediately after collection on site using the ice nucleus counter FRIDGE. During the one month campaign we encountered a series of Saharan dust plumes that traveled at several kilometers altitude. Here we present INP data from 42 individual flights, together with aerosol number concentrations, observations of lidar backscattering, dust concentrations derived by the dust transport model DREAM (Dust Regional Atmospheric Model), and results from scanning electron microscopy. The effect of the dust plumes is reflected by the coincidence of INP with the particulate mass (PM), the lidar signal and with the predicted dust mass of the model. This suggests that mineral dust or a constituent related to dust was a major contributor to the ice nucleating properties of the aerosol. Peak concentrations of above 100 INP std.l -1 were measured at −30 ◦C. The INP concentration in elevated plumes was on average a factor of 10 higher than at ground level. Since desert dust is transported for long distances over wide areas of the globe predominantly at several km altitude we conclude that INP measurements at ground level may be of limited significance for the situation at the level of cloud formation.
Recent analysis of long-term balloon-borne measurements of Antarctic stratospheric condensation nuclei (CN) and temperature combined with global model calculations showed the wide extent of a mid stratospheric layer of new particles. Here the nucleation model SAWNUC is used to derive Antarctic stratospheric gaseous sulfuric acid profiles and to investigate the nucleation process of this CN layer. The sulfuric acid profiles were derived for an altitude range of 18-32 km between July and October by simulating air parcel trajectories that descend inside the polar vortex and calculating the sulfuric acid amount that reproduces the observations. The derived sulfuric acid concentrations (volume mixing ratios) are of the order of magnitude of 104 cm-3 (10-14) in July. In the following months the concentrations increase to about 107 cm-3 (10 exp -11) in October. They depend strongly on the temperature because a given temperature leaves only a small sulfuric acid range to reproduce the observed magnitude of CN. Ion-induced nucleation occurs. However, while it dominates nucleation at higher temperatures it has no significant influence on the nucleation rates at lower temperatures. Preexisting particles significantly reduce nucleation at sulfuric acid mixing ratios below 1 ppt. First estimates of sulfuric acid production rates range from 0.5 to about 500 molecules cm-3 s-1. A production mechanism for gaseous sulfuric acid during the Antarctic winter seems to be necessary to fully explain the observations. The derived sulfuric acid profiles compare well with midlatitude and Arctic sulfuric acid concentrations.