Werner von Bloh

Causes of change in 20th century global river discharge

[1] A global vegetation and hydrology model (LPJmL) was applied to quantify the contributions of changing precipitation, temperature, atmospheric CO 2 content, land use and irrigation to worldwide trends in 20th century river discharge (Q). Consistently with observations, Q decreased in parts of Africa, central/southern Asia and south-eastern Europe, and increased especially in parts of North America and western Asia. Based on the CRU TS2.1 climatology, total global Q rose over 1901-2002 (trend, 30.8 km 3 a -2 , equaling 7.7%), due primarily to increasing precipitation (individual effect, +24.7 km 3 a -2 ). Global warming (-3.1), rising CO 2 (+4.4), land cover changes (+5.9) and irrigation (-1.1) also had discernible effects. However, sign and magnitude of trends exhibited pronounced decadal variability and differed among precipitation forcing datasets. Since recent trends in these and other drivers of Q are mainly anthropogenic, we conclude that humans exert an increasing influence on the global water cycle.

Determination of habitable zones in extrasolar planetary systems: Where are Gaia's sisters?

A general modeling scheme for assessing the suitability for life of extrasolar planets is presented. The scheme focuses on the identification of the “habitable zone” in main sequence star planetary systems accommodating Earth-like components. Our definition of habitability is based on the long-term possibility of photosynthetic biomass production under geodynamic conditions. Therefore all the pertinent astrophysical, climatological, biogeochemical, and geodynamic processes involved in the generation of photosynthesis-driven life conditions are taken into account. Implicitly, a cogenetic origin of the central star and the orbiting planet is assumed. A geostatic model version is developed and investigated in parallel for demonstration purposes. The numerical solution of the advanced geodynamic model yields realistic lookup diagrams for convenient habitability determination. As an illustration, the MACHO-98-BLG-35 event is scrutinized. It is shown that this event is definitely not tantamount to the discovery of one of Gaias sisters.

Biotic feedback extends the life span of the biosphere

The Sun is becoming more luminous with time and will eventually overheat the biosphere. However, life cools the Earth by amplifying the rate of silicate rock weathering and maintaining a low level of atmospheric CO2. Recent studies indicate a much stronger biotic weathering effect than in models used to estimate the life span of the biosphere. Here we show that the resulting feedback lengthens the survival of complex life by delaying the loss of CO2 from the atmosphere. The weathering biota can potentially maintain the Earth in a habitable state when otherwise it would be too hot for them. If so, catastrophic warming rather than gradual CO2 starvation will terminate complex life. Despite the possibility of an irreversible collapse, the current biosphere should remain resilient to carbon cycle perturbation or mass extinction events for at least 0.8 Gyr and may survive for up to 1.2 Gyr.

On the possibility of Earth-type habitable planets around 47 UMa

Abstract We investigate whether Earth-type habitable planets can in principle exist in the planetary system of 47 UMa. The system of 47 UMa consists of two Jupiter-size planets beyond the outer edge of the stellar habitable zone, and thus resembles our own Solar System most closely compared to all exosolar planetary systems discovered so far. Our study of habitability deliberately follows an Earth-based view according to the concept of Franck and colleagues, which assumes the long-term possibility of photosynthetic biomass production under geodynamic conditions. Consequently, a broad variety of climatological, biogeochemical, and geodynamical processes involved in the generation of photosynthesis-driven life conditions is taken into account. The stellar luminosity and the age of the star/planet system are of fundamental importance for planetary habitability. Our study considers different types of planetary continental growth models and takes into account a careful assessment of the stellar parameters. In the event of successful formation and orbital stability, two subjects of intense research, we find that Earth-type habitable planets around 47 UMa are in principle possible! The likelihood of those planets is increased if assumed that 47 UMa is relatively young (≲6 Gyr) and has a relatively small stellar luminosity as permitted by the observational range of those parameters.

Climate, vegetation, and global carbon cycle: the simplest zero-dimensional model

Abstract The mechanisms of interaction between climate and biosphere are studied for some hypothetical zero-dimensional (point) planet, where all parameters are globally averaged over the two-dimensional surface of the planet, which is without ocean. These mechanisms are formed by two causal loops: vegetation → albedo → temperature → vegetation and vegetation ⇔ atmospheric carbon → temperature → vegetation with a strong non-linear interaction. Using the conservation law for the total amount of carbon in the system and taking into account the assumption about quasi-stationary evolution of the system under anthropogenic CO2 emission, we reduce the dimension of the basic system of differential equations to two. The reduced system is then studied by qualitative methods. The system can have up to five equilibria, three of them can be stable. Here there are two bifurcation parameters: total amount of carbon (A) and product of maximal plant productivity and residence time of carbon in the biota. Considering the system evolution under increase of A, we can observe the change of the planet ‘status’ from ‘cold desert’ to ‘green cold planet’ (first bifurcation), then a ‘tropical planet’ arises (second bifurcation), and, as a result of further increase of carbon in the system, the planet transforms to a ‘hot desert’. In conclusion the model was calculated for ‘quasi-Earth’ values of parameters.

Cambrian explosion triggered by geosphere-biosphere feedbacks

[1] A new hypothesis for the cause of the Cambrian explosion is presented. For that the evolution of the planet Earth is described by the co-evolution of the geospherebiosphere system. Here we specify our previously published Earth system model for the long-term carbon cycle by introducing three different types of biosphere: procaryotes, eucaryotes, and complex multicellular life. They are characterized by different global temperature tolerance windows. The biotic enhancement of silicate weathering by complex multicellular life adds an additional feedback to the system and triggers the Cambrian explosion. The Cambrian explosion is characterized by a sudden increase of biomass and a rapid cooling, which amplified the spread of complex multicellular life. Cooling events in the Neoproterozoic, however, could force a premature appearance of complex multicellular life. INDEX TERMS: 0330 Atmospheric Composition and Structure: Geochemical cycles; 8125 Tectonophysics: Evolution of the Earth; 9699 Information Related to Geologic Time: General or miscellaneous; 3220 Mathematical Geophysics: Nonlinear dynamics; 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions. Citation: von Bloh, W., C. Bounama, and S. Franck, Cambrian explosion triggered by geosphere-biosphere feedbacks, Geophys. Res. Lett., 30(18), 1963, doi:10.1029/2003GL017928, 2003.

A zero-dimensional climate-vegetation model containing global carbon and hydrological cycle

A model of a hypothetical zero-dimensional planet containing a global carbon cycle, which describes the fundamental interaction between climate and biosphere, is used as a basis to formulate a new model incorporating a hydrological cycle. Using the conservation law for carbon and water in the system the number of differential equations is thereby reduced by two from five to three. The number and positions of the stable equilibria in the three-dimensional phase space is determined using numerical methods. This numbers is related to the value of the maximum productivity Pmax., the total amount of carbon A and water B in the system as bifurcation parameters of the system.

Multifractal characterization of microbially induced magnesian calcite formation in Recent tidal flat sediments

Abstract Structures resulting from biogenic carbonate cementation of microbial mats in Recent siliciclastic tidal flat sediments of the North Sea are analyzed quantitatively by a novel combination of scanning electron microscopy and energy-dispersive X-ray spectrometry (SEM/EDX) imaging and subsequent multifractal analysis. Evaluation of calcium distribution patterns and their links to sediment-intrinsic mineralization processes show that the applied geometrical technique is an efficient tool for detecting microscopic variations in elemental distributions and related minerals within sedimentary matrices. Two main conclusions can be drawn: (i) magnesian calcite is a rapidly formed product of the early diagenesis of organic matter in Recent bioactive marine sediments; and (ii) multifractal spectra are measures for the spatial inhomogeneity of authigenic calcification processes acting on the sedimentary structure. This implies that elemental distribution patterns in a sedimentary system are scale-independent phenomena. Processes causing such patterns have occurred over certain periods with varying rates and on different scales. The detection of multifractal measures also opens a way towards a systematic survey of dynamic processes occurring in sedimentary structures.

Drivers and patterns of land biosphere carbon balance reversal

The carbonbalance of the landbiosphere is the result of complex interactions between land, atmosphere andoceans, including climatic change, carbondioxide fertilization and land-use change.While the land biosphere currently absorbs carbondioxide from the atmosphere, this carbonbalancemight be reversed under climate and land-use change (‘carbonbalance reversal’). A carbonbalance reversalwould render climatemitigationmuchmoredifficult, as net negative emissionswould beneeded to even stabilize atmospheric carbondioxide concentrations.We investigate the robustness of the landbiosphere carbon sinkunderdifferent socio-economicpathwaysby systematically varying climate sensitivity, spatial patterns of climate change and resulting land-use changes. For this,we employ amodelling frameworkdesigned to account for all relevant feedbackmechanismsby coupling the integrated assessmentmodel IMAGEwith theprocess-baseddynamic vegetation, hydrology and crop growthmodel LPJmL.Wefind that carbon balance reversal can occurunder a broad range of forcings and is connected to changes in tree cover and soil carbonmainly innorthern latitudes. These changes are largely a consequence of vegetation responses to varying climate andonly partially of land-use change and the rate of climate change. Spatial patterns of climate change as deduced fromdifferent climatemodels, substantially determinehowmuchpressure in termsof globalwarming and land-use change the landbiospherewill tolerate before the carbonbalance is reversed.A reversal of the landbiosphere carbonbalance canoccur as early as 2030, although at very low probability, and shouldbe considered in thedesign of so-calledpeak-and-decline strategies. Introduction: the land biosphere carbon sink The land biosphere presently absorbs substantial amounts of carbon dioxide (CO2) from the atmosphere, partially compensating CO2 emissions from fossil fuel combustion and land use change and thus slowing anthropogenic climate change. Over the last three decades, land surfaces have absorbed about 2.3±0.8 Pg carbon (C) per year. Over the same period, land use change has led to average emissions of 1.0±0.5 Pg C yr, leaving a net carbon sink of 1.3 Pg C yr (Le Quéré et al 2014). This net carbon flux from the atmosphere to the land biosphere is a prominent negative (dampening) feedback mechanism in the Earth system (Friedlingstein et al 2006) that slows the rate of increase of atmospheric CO2. The interannual variability of the land–atmosphere carbon flux reflects its sensitivity to changes in precipitation in sensitive ecosystems (Schwalm et al 2012, Gatti et al 2014, Poulter et al 2014) as well as to variations in temperature (Lucht et al 2002). Land carbon uptake is projected to increase under climate change, mainly driven by the positive effects of CO2 fertilization of photosynthesis (Sitch et al 2008, Friend et al 2014), which are subject to large uncertainties (Schimel et al 2015). However, under high emission scenarios and severe climate change, some studies have found that the OPEN ACCESS

A minimal model of interaction between climate and vegetation: qualitative approach

Abstract A so-called “minimal model” is presented for the qualitative description of the interaction between climate and vegetation. Such conceptual simple models are important to give a better understanding of the fundamental feedback mechanisms acting between geo- and biosphere. This spatially one-dimensional model is analyzed in respect to the uniform biosphere and the existence of possible diffusive instabilities. It is proved that there do not exist any non-uniform equilibrium solutions, but the evolution of non-uniform initial perturbations is quite interesting: depending on the spatial form of the perturbations propagating non-linear waves are observed.