Displays

Soil is a hyper-heterogeneous environment, and how plants respond to changes in belowground variations in microclimate, soil properties and biota is extremely difficult to disentangle. Environmental gradients have been proposed as useful to help understand how root traits mediate plant responses to soil hyper-heterogeneity, and if in turn, there is a feedback mechanism that then impacts soil processes.

We present data from studies of forests and prairies situated along temperate elevational gradients. We measured functional traits from individual plant species and also in species mixtures at the community level. Distinct patterns in aboveground traits were found with increasing altitude. However, even though there were changes in soil biota, physical and chemical properties along gradients, we show that at the species level, several plant root traits were more sensitive to variations in local soil properties, compared to global variations along the elevation gradient. At the community level however, patterns of trait variation in individual species were often masked. Earthworm populations were also mostly driven by local soil properties, and elevation and plant species composition had only an indirect effect on population size. We also demonstrate that increased diversity in soil microbial communities was linked to the species composition of vegetation at a local level, rather than broad scale soil or climate characteristics.

Results will be discussed with regard to their impact on shaping soil processes such as carbon stockage, aggregation and hydraulic conductivity. Integrating these data into conceptual models of mountain ecosystem functioning is a challenging next step.

How to cite: Stokes, A. and the Co-authors: Thinking globally or acting locally? Belowground biotic responses to local- and broad- scale variations in mountain soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13922, https://doi.org/10.5194/egusphere-egu2020-13922, 2020.

The Poaceae (the grass family) includes over 11000 species and covers large part of the Earth land surfaces. Their history is rooted in the Cretaceous, but this group only expanded fully over the globe during the late Miocene. In the Amazon drainage basin (ADB) grasses were at the core of a heated debate, in which it was hypothesized that during the Pleistocene glacial periods grasses replaced vast extents of the Amazon rainforest. Although this hypothesis is now rejected, the history of grasses in the ADB still remains to be resolved. In this paper we propose a 3-staged model for grass development in the ADB: (1) from c. 23 to 9 Ma western Amazonia was dominated by a megawetland (the ‘Pebas system’) that harboured large amounts of (aquatic?) grasses; (2) from c. 9 Ma Andean uplift prompted megafan and fluvial environments on the Andean slopes and in the Amazon lowlands respectively, these environments created new settings for grass colonization; (3) from c. 5 Ma grasses were firmly established in the tropical alpine vegetation (páramo), the tropical lowland floodplains (várzeas), and savannas (cerrado). To test these scenarios we analysed Neogene and extant Andes-Amazonian grasses by means of Fourier Transform Infrared spectroscopy, we performed a Light- and Scanning Electron Microscopy analysis, and compared the results with existing biomarker data from the Neogene sediments. Here we report on the preliminary results that, among others, suggest that in the middle Miocene aquatic (C3) taxa were comon in the Amazon lowlands. Although further study will have to confirm the precise nature of the ADB grass history, we anticipate that abiotic processes during the Neogene and Quaternary left a strong imprint in the grass phytogeography of northern South America.

How to cite: Hoorn, C., Kirschner, J., Beer, M., Wei, C., Kukla, T., and Jardine, P.: Grass development in the Amazon drainage basin, evidence from the fossil and phytochemical record, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13822, https://doi.org/10.5194/egusphere-egu2020-13822, 2020.

Physical and chemical weathering processes fulfil a crucial function in the biogeochemistry of terrestrial ecosystems. Rock‐derived weathering products provide essential plant nutrients, and regulate the chemical composition of soil, surface, and groundwater. The rate and extent of chemical weathering are influenced by the combined effects of climate, parent material, topography, and vegetation, and ultimately determine the mineral composition and element ratios of soil material. Understanding the spatial variation of rock‐derived weathering products across heterogeneous landscapes not only relies on knowledge of the environmental controls but also of their interactions.

High Andean tropical ecosystems provide a good opportunity to study the association between chemical weathering, local topography and vegetation patterns: the climate, parent material and soil age can be held constant at the landscape scale, while the vegetation and slope morphology can vary greatly from the hilltops to the valley bottoms. In this study, we selected 10 soil toposequences on andesitic flows: 5 under tussock grasses, 3 under cushion forming plants and 2 under native forest. A marginally significant increase in base cation depletion is observed along topographic gradients that can be associated with physical transport of weathered soil particles downslope or subsurface water fluxes. Beyond the hillslope-scale topographic control on chemical weathering extent, we observed highly significant differences in chemical weathering extent between vegetation communities with total mass losses in forest soils being respectively 19% and 22% higher than in grasslands and cushion forming plants. Although biotic factors can play a role in creating the observed patterns in soil development, the vegetation communities can also hint to the existence of hillslope micro-topography and subsurface hydrological patterns that are challenging to map in the field.

How to cite: Vanacker, V., Molina, A., Zhiminaicela, S., Corre, M., and Veldkamp, E.: High Andean Soil Landscapes Shaped by Interactions between Geomorphology, Vegetation, and Hydrology, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17996, https://doi.org/10.5194/egusphere-egu2020-17996, 2020.

Hillslope processes in terrestrial ecosystems are significantly modified by changes in climate and land use. At the same time they strongly influence ecosystem retention capacity, pedocomplexity and biodiversity. This undoubtedly makes hillslope processes one of the crucial components of terrestrial ecosystem dynamics. In this study we focus on the long overlooked biogeomorphological impact of tree death in forested landscapes. Tree uprooting caused by strong storms affects soil and regolith formation and movement quite differently from the decomposition of intact root systems of standing trees that died due to e.g. fire or bark beetle infestation. We quantify the biogeomorphic processes associated with tree death in various terrestrial forest ecosystems and specifically assess (i) the significance of these processes in hillslope dynamics (e.g. slope denudation) of forested landscapes and (ii) the extent to which infrequent severe disturbances can shape these dynamics.

We used data from repeated tree censuses carried out in ten permanent forest plots (13–74 ha in area) located in Central Europe and North America, differing in a range of characteristics such as tree species composition, climate and disturbance regime. In total, life history of more than 134,000 trees was recorded over periods of up to 47 years, during which about one third of these trees died. Using this information together with empirical models and allometric equations we were able to quantify the average areas and volumes of soil annually affected by dying trees. These quantities differed markedly between sites with different disturbance regimes. Tree uprooting-related volumes accounted annually for 0.01–13.5 m³ha⁻¹ reaching maximum values on sites with occurrence of infrequent strong windstorms (Zofin and Boubin primeval forests, Czech Republic). Volumes related to trees that died standing ranged anually between 0.17 and 20.7 m³ha⁻¹ and were highest in the presence of stand-replacing fires (Yosemite National Park, U.S.). Comparison of these quantities with long-term erosion rates derived using cosmogenic nuclides (¹⁰Be) suggests that on certain sites, over the last few millennia, tree uprooting can be the main driver of soil erosion.

How to cite: Šamonil, P., Daněk, P., Lutz, J. A., Jaroš, J., Rousová, A., Anderson-Teixeira, K. J., and Adam, D.: Tree death as a crucial geomorphic agent in temperate forests: effects of weak and severe disturbances from local to continental scale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15999, https://doi.org/10.5194/egusphere-egu2020-15999, 2020.

The connections between the Earth’s interior and its surface are manifold, and defined by processes of material transfer: from the deep Earth to lithosphere, through the crust and into the interconnected systems of the atmosphere-hydrosphere-biosphere, and back again. One of the most spectacular surface expressions of such a process, with origins extending into the deep mantle, is the emplacement of large igneous provinces (LIPs), which have led to rapid climate changes and mass extinctions, but also to moments of transformation with respect to Earth’s evolving paleogeography. But equally critical are those process which involve material fluxes going the other way—as best exemplified by subduction, a key driving force behind plate tectonics, but also a key driver for long-term climate evolution through arc volcanism and degassing of CO_2.

Most hotspots, kimberlites, LIPs are sourced by plumes that rise from the margins of two large low shear-wave velocity provinces in the lowermost mantle. These thermochemical provinces have likely been quasi-stable for hundreds of millions, perhaps billions of years, and plume heads rise through the mantle in about 30 Myr or less. LIPs provide a direct link between the deep Earth and the atmosphere but environmental consequences depend on both their volumes and the composition of the crustal rocks they are emplaced through. LIP activity can alter the plate tectonic setting by creating and modifying plate boundaries and hence changing the paleogeography and its long-term forcing on climate. Extensive blankets of LIP-lava on the Earth’s surface can also enhance silicate weathering and potentially lead to CO₂ drawdown (cooling), but we find no clear relationship between LIPs and post-emplacement variation in atmospheric CO₂ proxies on very long (>10 Myrs) time-scales. Hotspot and kimberlite volcanoes generally have relatively small climate effects compared with that of LIPs (because of volumetric and flux differences), but the eruption of large kimberlite clusters, notably in the Cretaceous, could be capable of delivering enough CO₂ to the atmosphere to trigger sudden global warming events.

Subduction is a key driving force behind plate tectonics but also a key driver for the long-term climate evolution through arc volcanism and degassing of CO₂. Subduction fluxes derived from full-plate models provide a powerful way of estimating plate tectonic CO₂ degassing (sourcing). These correlate well with zircon age frequency distributions and zircon age peaks clearly correspond to intervals of high subduction flux associated with greenhouse conditions. Lows in zircon age frequency are more variable with links to both icehouse and greenhouse conditions, and only the Permo-Carboniferous (~330-275 Ma) icehouse is clearly related to the zircon and subduction flux record. A key challenge is to develop reliable full-plate models before the Devonian in order to consider the subduction flux during the end-Ordovician Hirnantian (~445 Ma) glaciations, but we also expect refinements in subduction fluxes for Mesozoic-Cenozoic times as more advanced ocean-basin models with intra-oceanic subduction are being developed and implemented in full-plate models.

How to cite: Torsvik, T. H., Svensen, H. H., Steinberger, B., Royer, D. L., Jerram, D. A., Jones, M. T., and Domeier, M.: Connecting the Deep Earth and the Atmosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9952, https://doi.org/10.5194/egusphere-egu2020-9952, 2020.

In the EARS orographic forcing of rainfall, pronounced relief contrasts between shoulder areas and the axial rift sectors results in steep environmental and surface-process gradients, severed fluvial networks, and diverse vegetation types. Due to sustained Quaternary tectono-volcanic activity and the effects of a superposed, highly variable climate these basins have been further differentiated into distinct environments that are either isolated or fluvially connected on time scales of several 10³ to 10⁶ years. The EARS thus comprises important physical corridors, but also barriers with spatially varying topographic conditions and resource distribution. Varying paleo-environmental settings and the present-day distribution of some mammal groups in the EARS' Kenya Rift highlight the importance of rift corridors for the migration of species and the interchange of now geographically isolated lineages.

For example, the presently disjunct distribution of the Bat-eared fox (Otocyon megalotis), the Black-backed jackal (Canis mesomelas) and the Oryx sister taxa (Oryx beisa and O. gazella) in northeastern vs. southern Africa, or of various rainforest antelopes such as Bongo (Tragelaphus euryceros) in the Congo basin and beyond the EARS in central Kenya, suggests that variability in connectivity along and across the rift has influenced species dispersal. Protracted rifting dictates the overall geomorphic character of the migration corridors, but fluvial connectivity varies significantly as a response to orbitally driven climatic conditions. These factors were responsible for lateral change in vegetation cover, such as the distribution of wet forests that enabled dispersal in the equatorial sectors of the rift. Such conditions ultimately determined whether the meridionally oriented rift segments acted as gateways or barriers.

How to cite: Strecker, M. R., Dommain, R., Garcin, Y., Olaka, L. A., Potts, R., and Riedl, S.: Rift-basin compartmentalization and changing environments: tectono-climatic forcing of environmental conditions and species dispersal in the East African Rift System (EARS), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8675, https://doi.org/10.5194/egusphere-egu2020-8675, 2020.

Explaining the origin of large-scale biodiversity gradients has been a key aspiration of early naturalists such as Wegener, Darwin and Humboldt; who looked at natural processes in an integrated way. Early on, these naturalists acknowledged the role of plate tectonics and climate variations in shaping modern day biodiversity patterns. 

As science advanced, the complexity of ecological, evolutionary, geological and climatological processes became evident while research became increasingly fragmented across different disciplines. Nevertheless, recent development in mechanistic modeling approaches now enable bringing disciplines back together, opening a new interdisciplinary scientific pathway.

Here, we present GEN3SIS, the GENeral Engine for Eco-Evolutionary SImulationS. It is the first spatially explicit eco-evolutionary model that incorporates deep-time Earth history, including plate tectonics, as well as climate variations in a modular way. The modular design allows exploring the consequences of user-defined biological processes that act across “real world” spatio-temporal landscapes. Emerging from the model are specie’s ranges, alpha and beta diversity patterns, ecological traits as well as phylogenies. Subsequently, these patterns can be compared to empirical data. Furthermore, GEN3SIS allows assessing paleoclimatic and paleogeographic hypotheses by using different Earth history scenarios and comparing simulation outputs with empirical biological data.

As a case study, we explore the cold-adapted plant biodiversity dynamics throughout the Earth’s Cenozoic history, based on a deep-time tectonic and climate reconstruction. The Cenozoic India-Asia collision formed the Himalayan mountain range. In this highly elevated region, the first cold niches of the Cenozoic appeared, demanding adaptation from the local living flora. We hindcast diversification of cold-adapted species with GEN3SIS, for which we use a topo-climatic reconstruction for the last 55 Myr. The model predicts the emergence of current cold-species richness patterns. Moreover, simulations indicate that cold-adapted flora emerged in the Oligocene, first in the Himalayas, followed by a spread to the Arctic. This agrees with observed low species richness and high nestedness of Arctic assemblages compared to those of the Himalayan mountain ranges. Under ongoing climate change a major loss of cold-adapted plant diversity is expected by the end of the century, particularly in lower latitude mountain ranges. Hindcasting and forecasting dynamics of cold-adapted lineages highlights the transient fate of cold organisms in a warming world.

GEN3SIS is made available as an R package, which allows customizing (i) the simulated landscape including environmental variables and (ii) all the processes interacting under different spatial and temporal scales. Consequently, GEN3SIS fosters collaborations between different natural disciplines and therefore contributes to an interdisciplinary understanding of the processes that shaped Earth’s history.

How to cite: Hagen, O., E. Onstein, R., Flück, B., Fopp, F., Hartig, F., Pontarp, M., Albouy, C., Luo, A., Boschman, L., S. Cabral, J., Xing, Y., Wang, Z., F. Rangel, T., Scotese, C., and Pellissier, L.: GEN3SIS: An engine for simulating eco-evolutionary processes in the context of plate tectonics and deep-time climate variations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20627, https://doi.org/10.5194/egusphere-egu2020-20627, 2020.

Erosion and sediment transport in river catchments depend significantly on tectonics, climate and associated vegetation-cover. In this study, we used a numerical modelling approach to quantify the effects of temporal variations in precipitation rates and vegetation-cover over different uplift rates (0.05 mm a^-1, 0.1 mm a^-1, 0.2 mm a^-1) and periodicities (23 kyr, 41 kyr and 100 kyr) of climate and associated vegetation-cover oscillations on erosion, sediment transport and deposition at catchment scale. Landlab, a landscape evolution modelling toolkit was modified to incorporate surface vegetation-cover dependent hillslope and coupled detachment-transport limited fluvial processes, weathering and soil production. The model was applied to (two) sites in the Coastal Chilean Cordillera namely Pan de Acuzar (~26), and La Campana (~33). These sites show a steep gradient in climate and vegetation density from arid climate and sparse vegetation density in northern latitudes to wetter temperate climate and abundant vegetation in the south, with granitic bedrock. The model simulations were run for 15 Myr to create steady-state topographies for both model domains. The sensitivity of these landscapes to changing climate and surface vegetation-cover was analyzed for 3 Myr for five transient model scenarios: (1) oscillating precipitation and constant vegetation cover, (2) constant precipitation and oscillating vegetation cover, (3) coupled oscillations in precipitation and vegetation cover, (4) coupled oscillations in precipitation and vegetation cover with variable periodicities, (5) coupled oscillations in precipitation and vegetation cover with variable rock uplift rates. The results suggest that erosion and sediment transport in densely vegetated landscapes are dominated by changes in precipitation, rather than vegetation-cover change in the southern study area (La Campana), as a result of higher amplitude of precipitation change i.e., 460 mm. Arid (northern) and sparsely vegetated landscapes are dominated by changes in vegetation density rather than precipitation, explained by higher erosion rates in periods with no surface vegetation-cover. Coupled oscillations in climate and vegetation cover suggested dampened influence of transient forcing on climate or vegetation-cover. The influence of periodicity of climate oscillations is significantly pronounced for shorter period (23 kyr oscillations) in terms of erosion rates. Results from different uplift rates suggested a positive linear relationship of topographic elevation and slope, erosion and sediment transport. However, sediment thickness decreases with increasing uplift rates, attributed to higher sediment flux on hillslopes due to linear dependence of slope on rock uplift rates.  These results broadly demonstrate the implications of long term climate change with associated vegetation density on geomorphic processes shaping the topography.

How to cite: Sharma, H., Ehlers, T. A., and Schmid, M.: Influence of oscillating vegetation cover, precipitation, and sediment transport on topography: Insights from a landscape evolution model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3412, https://doi.org/10.5194/egusphere-egu2020-3412, 2020.

Chemical weathering and physical erosion are important processes shaping topography, producing soils, and providing nutrients for life.  The rates of these processes are influenced not only by tectonics, but also by climate and biota.  The Chilean Coastal Cordillera from 26° to 38°S is a natural laboratory to investigate chemical weathering and physical erosion rates over different climatic settings.  From North to South, climate changes from arid (Pan de Azúcar), semi-arid (Santa Gracia), Mediterranean (La Campana) to temperate humid (Nahuelbuta).  Here we present chemical weathering and physical erosion rates based on published and new in situ-produced cosmogenic nuclides and immobile elements published from soil pedon depth profiles in the four study areas.

Calculated chemical weathering rates range from zero in Pan de Azúcar to an high value of 211 t/(km² yr) in La Campana.  Chemical weathering rates are comparable in Santa Gracia and Nahuelbuta (~20 t/(km² yr).  Physical erosion rates are low in Pan de Azúcar (~11 t/(km² yr)) and increase towards the South (~ 40 t/(km² yr)).  Combined chemical weathering and physical erosion rates indicate that denudation rates are lowest in Pan de Azúcar and highest in La Campana.  The contribution of chemical weathering to total denudation rates is increasing and then decreasing with increasing mean annual precipitation from North to South.  The observation that the calculated chemical weathering rates in the southernmost location with the highest mean annual precipitation and the highest chemical index of alteration are not the highest of all four study areas is evaluated and discussed.   We investigate possible influence of precipitation and vegetation on chemical weathering and physical erosion rates.

How to cite: Schaller, M. and Ehlers, T. A.: Chemical weathering and physical erosion rates along a vegetation and climate gradient, Chilean Coastal Cordillera (26° – 38°S), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3442, https://doi.org/10.5194/egusphere-egu2020-3442, 2020.

The Cretaceous angiosperm radiation was a major event for terrestrial plant evolution, and flowering plants represent more than 94 % of present-day plant diversity. The fossil record shows that angiosperm leaf vein densities reached particularly high values (> 12 mm/mm²) between the Albian and the Cenomanian (108–94 Ma) compared to gymnosperms (~ 2.5 mm/mm²). Empirical models also suggest that stomatal conductance to water vapour increases as a response to higher leaf vein densities. How much do this shift to higher values of stomatal conductance have modified the continental transpiration budget, and ultimately global hydrological cycle ? To address this question we used the IPSL coupled atmosphere-vegetation model forced by Cretaceous boundary conditions, and built plant functional types including stomatal conductance values consistent with the fossil record. We quantify the transpiration fluxes through different sensitivity experiments and explore the vegetation-atmosphere feedbacks and their impact on the Cretaceous climate.

How to cite: Bres, J., Sepulchre, P., Vuichard, N., and Viovy, N.: Did the rise of highly-transpiring angiosperms influenced Cretaceous climate ? A modelling approach with the IPSL atmosphere-land surface model., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9293, https://doi.org/10.5194/egusphere-egu2020-9293, 2020.

How to cite: Husson, L., Boucher, F., Sarr, A.-C., Sepulchre, P., and Cahyarini, S. Y.: Sundaland's subsidence requires revisiting its biogeography, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3575, https://doi.org/10.5194/egusphere-egu2020-3575, 2020.

Soil erosion is one of the main problems in soil degradation nowadays and is widely distributed in many landscapes worldwide. Particularly water erosion is widespread and determined by rain erosivity, soil erodibility, topographic factors and the management carried out to mitigate this phenomenon. Although this process is mostly known as a consequence of human management such as agriculture or forestry, it is a process that also occurs naturally, being one of the factors that regulate the shape of the landscape.

One of the main agents that stabilize the soil surface is biota and its activity, either in the form of plants, microorganisms or as an assemblage in the form of a biological soil crust (biocrusts). However, there are limited studies about how and what extent biota drives soil-stabilizing processes. With particular view on the impact of biocrusts on soil erosion, most studies have been carried out in arid and semi-arid regions, so its influence under other climates is largely unknown.

This study focuses on the influence of biota on soil erosion in a temperature and rainfall gradient, covering four climate zones (arid, semi-arid, mediterranean and humid) with very limited human intervention. Other variables such as the origin of the geological formation, geographical longitude and glacial influence were kept constant for all study sites. The effect of vegetation (biocrusts) and its abundance, microbiology and terrain parameters are investigated using rainfall simulation experiments under controlled conditions and by a physico-chemical evaluation of the soil, surface runoff, percolation and sediment discharge, in order to determine the different environmental filtering effects that the soil develops under different climatic conditions.

It is expected that as vegetation vigor and cover increase, soil erodibility will decrease. The biocrust is the protagonist of this stabilization in conditions of low pedological development and will become secondary as edaphoclimatic conditions favor the colonization of plants.

The results of this study will help to achieve a better understanding of the role of biota in soil erosion control and will clarify its influence on soil losses under different climate and slope conditions. Analyses are currently ongoing and first results of our work will be presented at the EGU 2020.

How to cite: Riveras, N., Witzgall, K., Rodríguez, V., Kühn, P., Mueller, C. W., Oses, R., Seguel, O., Seitz, S., Tapia, Y., Salazar, O., Wagner, D., and Scholten, T.: Soil erosion controlled by biota along a climate gradient in Chile, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10817, https://doi.org/10.5194/egusphere-egu2020-10817, 2020.

Antarctica with its unique conditions for soil development offers the opportunity to disclose basic soil biogeochemical processes in an environment with a low degree of ecosystem interactions. The region’s climate is divided by the mountain ridge of the Antarctic Peninsula: on the South Shetland Islands (King George Island (KGI)) in the west a maritime cold climate prevails, while James Ross Island (JRI) in the east faces the continental cold climate of a polar desert with less precipitation and distinctly more pronounced temperature variations throughout the year. In addition, the autochthonous vegetation differs; while it solely consists of cryptogams on JRI, on KGI two vascular plants (Dechampsia antarctica, Colobanthus quitensis) are endemic. This scarce vegetation patterns together with land surfaces ice-free for several millenia allows studying the complex interaction between soil organic matter (SOM) sequestration and soil structure development with respect to the varying presence and growth of vegetation.  

The main aim of our study is to decode the mechanisms determining the fate of SOM in maritime Antarctica and to understand how the scarce vegetation drives the chemical composition and distribution of SOM within specific physical SOM fractions. Therefore, we sampled transects ranging from vegetated patches to plant-free soil surfaces. The distance to these vegetation patches was reflected in clear variations in the distribution of carbon and nitrogen and in a decrease in labile SOM constituents as revealed by ¹³C-CPMAS NMR spectroscopy, while clay-sized mineral-associated SOM dominated the carbon storage throughout all sites. The ongoing climate change is assumed to significantly alter the vegetation distribution and thus drive the storage and composition of SOM. In the future, this will also strongly affect soil microbial activity and land-ocean transitions in Antarctica.

How to cite: Prater, I., Hrbacek, F., Meier, L. A., Braun, C., Nyvlt, D., and Mueller, C. W.: How vegetation drives initial soil development together with soil organic matter accrual in maritime Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17376, https://doi.org/10.5194/egusphere-egu2020-17376, 2020.

Over the last decades, a progressive glacier melting has been detected induced by climate change which cause a rapid enlargement of ice-free areas in glacier forelands in Arctic, Antarctic and Alpine regions. These recently deglaciated areas represent highly dynamic environments in terms of vegetation development and soil formation. Tundra plant communities of glacier forelands mainly consist of cryptogamic species forming biological soil crusts (BSCs) on the surface. These BSCs are known to promote the accumulation of aeolian particles and organic material being relevant to soil formation. It is important to understand both BSC development and soil formation in glacier forelands as fundamental to future development of mature tundra which contributes to an increase in soil organic carbon (SOC) and nitrogen (N) stocks in soil. The heterogeneous terrain of glacier forelands affects the spatial variation in both soil and vegetation characteristics which are additionally influenced by the distance to the glacier terminus. This study focuses on the spatial variation in soil and BSC characteristics in Arctic glacier forelands of Svalbard using multi-scale contextual soil mapping (CSM) and Euclidean distance fields (EDF). The data set comprises of soil (SOC, N, texture) and BSC characteristics (species composition, percent cover) from 168 sampling locations as well as terrain covariates (elevation, slope, aspect, curvature) at several scales using CSM and spatial covariates (EDF). Random forests (RF) are used to analyse the relationships between the covariates and soil and BSC characteristics, respectively.

Preliminary results show a good quality of the RF models (R²/RMSE) which is similar for SOC (0.41/6.19) and N (0.44/0.22). Elevation, curvature and slope at large scales are the most important covariates to explain the spatial variation in SOC and N. On large scales, these covariates represent the distance to the glacier terminus and generally explain the increase in SOC and N with increasing distance from the glacier terminus.  Additionally, elevation at small scales represents relevant issues of predominant geomorphologic features signature (e.g. moraine topography) to soil formation and BSC development. Analyses of the spatial variation and interrelationships of soil and BSC characteristics are still ongoing and further results will be presented at EGU 2020.

How to cite: Gries, P., Schmidt, K., Kühn, P., Eberle, J., Seitz, S., Scholten, T., Węgrzyn, M., and Wietrzyk-Pełka, P.: Soil formation and biological soil crust development in glacier forelands of Svalbard (High Arctic), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8213, https://doi.org/10.5194/egusphere-egu2020-8213, 2020.

The Atacama Desert is the driest non-polar desert on Earth, presenting precarious conditions for biological activity. In the arid coastal belt, life is restricted to areas with fog events that cause almost daily wet-dry cycles. In such an area, we discovered a hitherto unknown and unique ground covering biocoenosis dominated by lichens, fungi and algae attached to grit-sized quartz- and granitoid stones (grit crust). In contrast to previously known CGC from arid environments to which frequent cyclic wetting events are lethal, here every fog event is answered by photosynthetic activity of the soil community and thus considered as the desert’s breath. Photosynthesis of the new CGC-type is activated by the lowest amount of water known for such a community worldwide thus enabling the unique biocoenosis to fulfill a variety of ecosystem services such as protection against soil erosion and contributions to accumulation of soil carbon and nitrogen and soil formation through bio-weathering. Using state-of-the-art remote sensing technology, we estimate the total cover of the grit crust and show that the newly discovered organisms cover large areas along the coastal belt of the Atacama Desert.

How to cite: Jung, P., Lehnert, L., Lakatos, M., Schermer, M., Baumann, K., Wraase, L., Eckhardt, K.-U., Bader, M., Leinweber, P., Bendix, J., and Büdel, B.: How the recently discovered grit crust shapes the Atacama Desert – Combining environmental studies on cryptogams and remote sensing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19107, https://doi.org/10.5194/egusphere-egu2020-19107, 2020.

In high mountain environments with harsh weather conditions, soil development and its limitations strongly depend on topography and morphodynamics, both leading to heterogeneous landscape patterns of different geological substrate, vegetation, (micro)relief, and (micro)climate. In addition, as glaciers currently are retreating disproportionately strong, a large area is exposed to initial soil development, enabling to study time related issues of soil formation.

These mosaic-like patterns are particularly intensified within the high-alpine and nival zone, due to the dominating influence of cryospheric elements, such as ice (e.g. retreating glaciers), snow (e.g. snowbeds; shallow self-deepening sinks with snow accumulation at altitudes above 2500 m a.s.l.), and frost (e.g. causing solifluction, controlling physical weathering, changing permafrost dynamics, increasing the probability mass movements and sediment transport). The high-alpine environment with its site diversity therefore represents a perfect study area to analyze soil-vegetation-interactions at various microsites within a single catchment.

To study the influence of time, the glacier foreland of Zufall- and Fürkeleferner (Martelltal, South Tyrol) was found to be excellent for an interdisciplinary chronosequence study. Large amounts of historical maps, aerial orthophotos, and remote sensing data are available, enabling reconstructed glacier retreat with a high spatial and temporal accuracy. Study sites of different soil age were chosen for the analysis of various soil and vegetation parameters. The influence of temperature and soil water availability were determined by installing temperature and soil matric potential data loggers.

Furthermore, to study soil development as a function of geological substrate, microrelief, altitude, slope, and microclimate, an additional transect along an altitudinal gradient (Martelltal, South Tyrol, within the maximum extent of Egesen) was sampled and analyzed regarding central soil properties, vegetation, and microclimate. Directly bordering to those sites, heterogeneous and morphodynamically active microsites were investigated. These special sites were characterized by different morphological features, in particularly: soil sinks of different genesis, hilltops, and scree-dominated sites with initial soil development after primary plant succession.

As expected, we found clear trends of soil development with changing altitude and/or time. However, the small-scaled special sites differed distinctly from the reference sites regarding basic soil properties such as soil pH or soil organic matter content, and also remarkably in plant-available NH4-N, microbial activity, and microbial biomass. This was especially true where the water regime was strongly affected by the microrelief.

The observed distinct changes in soil properties within small scales of sometimes only several meters help to better understand and predict soil formation and diversity as well as soil-plant-interactions in high alpine environments of the European Alps.

How to cite: Müller, S., Ramskogler, K., Knoflach, B., Stötter, J., Erschbamer, B., Illmer, P., and Geitner, C.: Development of soil in heterogeneous landscapes of a high alpine catchment in the Central European Alps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18826, https://doi.org/10.5194/egusphere-egu2020-18826, 2020.

The impact of soil dwelling animals on the terrain shaping is assumed to be largely coupled with vegetation and soil characteristics, particularly in arid and semi-arid regions. The vegetation determines the habitat availability by providing necessary resources such as food and shelter while the burrowing activities of soil dwelling animals impacts at the same time soil properties and nutrient fluxes needed for plant growth. This important relationship and feedbacks between bioturbators, vegetation, climate, soil conditions and landscape shaping is to date completely understudied, particularly the dependencies between soil animals and the vegetation cover. Thus, comprehensive studies to gain a detailed understanding are urgently required. Here, we modeled the presence of all signs of bioturbation (burrows, holes and mounds) within a study area of 1 km² with an elevation gradient of 100m height difference in a semi-arid (Santa Gracia, Chile) and Mediterranean (NP La Campana, Chile) zone of coastal Chile using UAV (unmanned aerial vehicle) images. We then compared their relationship between the two climate zones in regard to the vegetation, elevation and soil characteristics. The images were obtained at a flight altitude of 15-60 meters above one study area per each climate zone by means of a Solo quadropter drone equipped with a RGB GoPro camera. Ancillary in-situ data were measured within 10 plots per study area with a size of 10m x 10m. Within the plots, the amount and size of the burrows and mounds as well as the vegetation cover was quantified. In addition, the GPS coordinates of several holes and mounds with a diameter of 10cm and above were measured. Twenty representative soil samples in regard to the land cover, vegetation type and presence of bioturbation activity were taken along the elevation gradient and analyzed for skeleton fraction, soil texture, bulk density and water content. The RGB images obtained by the drone system were firstly used for a supervised land-use classification and to calculate the vegetation density across the study area. The surface roughness was estimated by creating the point cloud of the area and calculating the standard deviation of the point cloud and original images using moving window of 5x5 pixels/points. The presence of soil animal activity was modeled using random forest where drone images, digital elevation model, surface roughness and land cover characteristics (land use, vegetation density and type) were used as predictors. The results showed modeled spatial distribution of burrows and mounds within the study areas, and a dependence of the predicted bioturbation activity on vegetation density and type as well as on elevation and soil conditions along the elevation gradient at both sites. The dependencies are finally compared between the two climate zones.

How to cite: Grigusova, P., Kraus, D., Larsen, A., Klug, A., Fischer, R., Achilles, S., Chifflard, P., Farwig, N., and Bendix, J.: Area-wide detection and spatial modeling of signs of bioturbation activity along a climate and elevation gradient in Chile using UAV and their dependence on vegetation and soil characteristics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10618, https://doi.org/10.5194/egusphere-egu2020-10618, 2020.

Earthworms are ecosystem engineers, capable of modifying the soil environment they inhabit. Recent evidence indicates that they increase the mobility and availability of potentially toxic elements in soils, but the systematic synthesis of the evidence required to understand mechanisms and identify soils most susceptible to earthworm-induced potentially toxic element mobilisation is lacking. We undertook a meta-analysis of 43 peer reviewed journal articles, comprising 1185 pairwise comparisons to quantify the impact of earthworms on potentially toxic element mobility in bulk earthworm-inhabited soil and earthworm casts and on plant uptake and concentration. We find that earthworms mobilise potentially toxic elements primarily due to the passage of soil through the earthworm gut and that this results in an increase in the concentration and uptake by plants. Earthworms mobilise potentially toxic elements in uncontaminated soils to a greater extent than contaminated soils. Soils with either very low (<2%) or very high (>10%) soil organic matter content are most susceptible to earthworm-induced potentially toxic element mobilisation. These findings have important implications for exotic earthworms burdening plants with toxic metals, but also offer a promising phenomenon that, if harnessed, may help to alleviate micronutrient deficiencies in degraded soils.

How to cite: Sizmur, T. and Richardson, J.: Earthworms accelerate the biogeochemical cycling of potentially toxic elements: Results of a meta-analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1873, https://doi.org/10.5194/egusphere-egu2020-1873, 2020.

Besides nitrogen, phosphorus (P) is the major limiting nutrient of terrestrial primary productivity, with major P stocks being bound in soils. Stocks, speciation, and bioavailability of soil P differ among ecosystem types and with rock weathering status, which are both driven by climatic conditions. Microorganisms and plants have developed a range of strategies to mobilize P from organic and inorganic sources, e.g. expression of extracellular phosphatases and excretion of low-molecular-weight organic acids (LMWOA). However, the impact of precipitation, vegetation type, and soil P speciation on plant P acquisition strategies is not well understood, yet.

A semi-desert-to-humid-temperate-rainforest ecosystem sequence was investigated. Soil samples were taken from three sampling sites, all developed on granodiorite, comprising a precipitation gradient (66 mm a^-1 to 1469 mm a^-1) along the Chilean Coastal Cordillera. Small-scale gradients (mm) from single roots to bulk soil in three depths were sampled to examine changes in P speciation, enabling the identification of local P depletion by plant roots and differences in P-speciation between rhizosphere and non-rhizosphere soil. Phosphorus speciation was examined by X-ray absorption near edge structure analysis. LMWOA as biotic weathering agents, and acid phosphatase kinetics as proxy for organic P recycling, were quantified. The aim was to disentangle the impact and functions of roots and associated microorganisms on driving agents of P-cycling.

Rhizosphere P speciation in soil changed considerably along the precipitation gradient from mainly primary P minerals in the semi-desert ecosystem to a dominance of organic P species in the humid-temperate rainforest. Contents of organically bound P were higher in root proximity compared to bulk soil in the humid-temperate rainforest soils (320 mg kg^-1 and 70 mg kg^-1, respectively) and in the topsoil of the Mediterranean woodland ecosystem (134 mg kg^-1  and 62 mg kg^-1, respectively).  In contrast, the rhizosphere soil was depleted in sesquioxide-adsorbed P in comparison to root-free bulk soil.

The content of LMWOA was correlated with inorganic P in soils of the semi-desert ecosystem, indicating intensive LMWOA exudation for biogenic P weathering of primary and secondary minerals. Under temperate rainforest LMWOA content, phosphatase activity, and microbial biomass carbon exhibited a negative correlation with secondary inorganic P forms but were positively linked to organic P species. We therefore conclude that P nutrition in this ecosystem relies less on weathering of P bearing minerals by LMWOA but is mainly based on organic P sources.

In terms of process understanding, these findings clearly show that LMWOA fundamentally change their role in the rhizosphere depending on the nutrient acquisition strategy of the respective ecosystem, which is affected by mean annual precipitation. While LMWOA facilitate biogenic weathering of P bearing minerals in the semi-desert, they mainly contribute to P recycling in the humid-temperate rainforest by preventing its precipitation and sorption. We conclude that P acquisition and cycling depends on the nutritional constrains of the given ecosystem: from biological weathering of inorganic P forms in the semi-desert driven by LMWOA and plant uptake to intensive P recycling from organic forms in the humid-temperate rainforest.

How to cite: Spielvogel, S., Köster, M., Stock, S., Nájera, F., Abdallah, K., Gorbushina, A., Prietzel, J., Matus, F., Klysubun, W., Boy, J., Kuzyakov, Y., and Dippold, M.: From rock-eating to vegetarian ecosystems — plant phosphorus acquisition strategies along a Chilean precipitation gradient, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4084, https://doi.org/10.5194/egusphere-egu2020-4084, 2020.

Water flow as well as the presence and growth rate of land plants are commonly thought to present drivers of rock weathering. While plants are indeed key players in weathering, the quantitative evaluation of biota on total abiotic and biotic weathering processes remains vague.

Here, we report on weathering rates and nutrient uptake along the “EarthShape” climate and vegetation gradient in the Chilean Coastal Cordillera. The hypothesis we evaluated is whether weathering rate and degree does increase from north to south along the EarthShape climate gradient and whether the increase in biomass growth rate along this gradient is accommodated by additional nutrient-supply induced through weathering. We quantified the bio-available fraction of nutritive elements in regolith and we measured ⁸⁷Sr/⁸⁶Sr isotope ratios in the different compartments of the Earth’s Critical Zone (bedrock, regolith, bio-available fraction in saprolite and soil, and vegetation) to identify the sources of mineral nutrients to plants. We were thus quantified gains and losses of nutritive elements in and out of these ecosystems and to quantify nutrient recycling.

We find that despite the increase in biomass growth the weathering rate is relatively uniform along the gradient. Instead of accelerating biogenic weathering ecosystems with high productivity rely on efficient recycling between plants and soil to sustain their nutrition. Thus, the organic nutrient pathway (between plants and litter on the foerst floor) intensifies, whereas the geogenic nutrient pathway (from minerals to plant) remains steady despite increasing precipitation and primary productivity. We further speculate that the presence of plants might compensate weathering downward by regulating the hydrological cycle, fostering secondary-mineral formation, and a microbial community specializing on nutrient-recycling rather than nutrient-acquisition through weathering.

How to cite: Oeser, R. and von Blanckenburg, F.: Decoupling primary productivity from silicate weathering – how ecosystems regulate nutrient uptake along a climate and vegetation gradient, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8801, https://doi.org/10.5194/egusphere-egu2020-8801, 2020.

Christopher Schwerdhelm¹, Ferdinand Hampl², Carolina Merino^3,4, Francisco Matus^4,5, Thomas Neumann², Andreas Kappler¹, Casey Bryce¹

¹ Geomicrobiology, Center for Applied Geoscience (ZAG), Eberhard-Karls-University Tuebingen, Sigwartstrasse 10, 72076 Tuebingen, Germany

² Technische Universität Berlin, Institute of Applied Geosciences, Department of Applied Geochemistry, Office BH 9-3, Ernst-Reuter-Platz 1, 10587 Berlin, Germany

³ Center of Plant, Soil Interaction and Natural Resources Biotechnology Scientific and Technological Bioresource Nucleus (BIOREN), Temuco, Chile

⁴ Network for Extreme Environmental Research, Universidad de la Frontera, Temuco, Chile

⁵ Department of Chemical Sciences and Natural Resources, Universidad de La Frontera, Avenida Francisco Salazar, 01145 Temuco, Chile

Mineral weathering shapes Earth’s surface by transforming bedrock to soil in the ‘critical zone’. Among these transformation processes, microbial weathering plays an important role, as it contributes to all stages of rock-soil transformation such as primary rock colonization, rock breakdown, saprolite formation, and element cycling. Fe-metabolizing microorganisms, i.e. Fe(II)-oxidizing and Fe(III)-reducing microorganisms, are key players in weathering as they can directly attack minerals via their metabolism. However, most direct evidence for the role of these microbes in critical zone processes comes from shallow and humid tropical soils and saprolite, or from transects across corestones. Much less is understood about the direct role of these microorganisms in critical zone processes in more arid climates.  

In this study we have obtained drill cores from the critical zone of a semi-arid region of the Chilean Coastal Cordillera (Santa Gracia Reserve). Despite receiving only 66 mm of rain per year, the weathering profile is very deep (>80 m). The rock material of the drill core is a Cretaceous quartz monzodiorite rich in hornblende, biotite and chlorite with ca. 1-2 wt.-% Fe(III) oxyhydroxides and very low TOC content. Using cultivation-based methods we found microaerophilic Fe(II)-oxidizing bacteria in zones of weathered saprolite (up to ca. 25 m depth) and at the weathering front (70-76 m), while Fe(III)-reducing bacteria, grown either with dihydrogen or organic carbon, were successfully enriched from samples across the whole 87 m profile. A robust contamination control confirmed that cultivated microbes were from the in-situ community and not related to drill fluid contamination.  

These findings suggest there is potential for Fe-metabolizing microbes to contribute to mineral-weathering processes even in deep weathering profiles in semi-arid environments. The occurrence of cultivatable Fe(II)-oxidizing bacteria is controlled by the presence of highly fractured zones functioning as fluid and oxygen transport pathways. It is notable that despite the fact that much of the silicate minerals contain Fe(II), Fe(III)-reducing bacteria are more common. The co-occurrence of Fe(II)-oxidizing and Fe(III)-reducing bacteria in some isolated parts of the profile could represent a self-sustaining cycle of iron redox reactions.

How to cite: Schwerdhelm, C.: Could Fe-metabolizing microbes weather sub-surface minerals in a semi-arid climate?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6037, https://doi.org/10.5194/egusphere-egu2020-6037, 2020.

Studies of paleoclimatology, paleoceanography, paleobiology, and other studies of paleoenvironment require paleogeographic reconstructions that display the past distribution of land and sea, and of bathymetry and altimetry. Quantitative reconstructions of past positions of continents and oceans have been available for decades, and have become easy to access and develop with the advance of GPlates software. Quantitative estimates of bathymetry and especially altimetry and topography, however, are considerably more challenging to develop. First attempts towards a global, quantitative approach towards paleotopography reconstruction were made in recent years. However these models are largely based on present day topography and require extensive manual adjustment for local modification that is subjective and precludes reproducibility. In this project, we attempt to overcome this subjectivity, and develop a quantitative methodology to calculate paleogeography based on kinematic input parameters.

Our aim is to develop ‘Paleogeography.org’, a free, online paleogeography calculator. This project calculates oceanic bathymetry and continental altitude and topography from plate tectonic reconstructions for various geodynamic settings. The algorithms are based on simple and straightforward dynamic principles: bathymetry of the ocean floor is at first order inferred from its age, and altimetry is based on computing crustal thickness based on shortening or extension reconstructions, assuming isostacy. Distinctions are made between undisturbed ocean floor, oceanic plateaus, trenches, continental rifts and back-arc basins, oceanic and continental volcanic arcs, upper plate orogens (e.g., Andes, Tibet) vs accretionary orogens (Zagros, Himalaya, Apennines, Alps), etc. This allows to calculate a global geography for any given time slice for which underlying kinematic reconstructions are available. These reconstructions are subsequently tested against independent quantitative estimates of e.g., altimetry and bathymetry and iterated where necessary. This approach provides a reproducible, global estimate of paleogeography without input from paleobiological or paleoclimatic indicators, enabling an independent platform for paleo-environmental study. The iteration between prediction and observation, moreover, will provide novel constraints on 4D geodynamic processes.

Code is written mainly in Python, especially using pyGPlates. The calculator will be available as open source code for scientists and other professionals. They can use it to make reproducible paleogeographic reconstructions based on their own plate tectonic reconstructions or on specific moments in time. In addition the output makes appealing pictures of plate tectonic reconstructions for both scientists and a wider audience.

How to cite: van der Linden, T., Dupont-Nivet, G., and van Hinsbergen, D.: Towards a quantitative paleogeography calculator, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2402, https://doi.org/10.5194/egusphere-egu2020-2402, 2020.

Tufas are continental freshwater carbonates common in epi-karst zones. They are composed of micrite and microsparitic crystals of calcite with variable primary moldic and fenestral porosity and with the frequent presence of biogenic content. By definition, tufa petrogenesis depends on climate processes and usually has precipitation induced by biological activity. Our examples include two morphotypes resulting from weathering of limestone of the Crato Formation, Araripe Basin, NE Brazil, and precipitated along vugular fractures. To understand how the climate and the biological activity act on precipitation of these rocks, we integrate structural data, petrography, and δ¹⁸O and δ¹³C values. Tufas are always associated with joints and faults in the northern boundary of the basin. The block where tufas occur has a dip angle between 5º and 30º, which differs from the regional average of 0° to 3º. The tufas fill vugular steep fractures with preferential planes oriented N50E and N30W and have a pipe-shaped growth pattern with top-down and center-out growth direction. The presence of organic filaments and mollusk shells are recurrent in all samples. Isotopic values measured on 32 samples indicate δ¹⁸O VPDB between -11,4‰ and -1,7‰ and δ¹³C VPDB between -12,1‰ and -5,1‰. The enrichment of ¹⁶O reveals the composition of meteoric water, responsible by the limestone dissolution and tufa precipitation. Organic fractioning induced by photosynthesis of the C4 plants result in ¹²C enrichment in the tufas. Macro and microscopic analysis revealed bryophyte filaments. Moreover, the porosity pattern strongly evidences the presence of these plants in tufa diagenesis. The close association of these rocks with the boundary faults suggests a relationship with climate denudation processes. The Araripe Basin is part of a set of continental rift basins in the Brazilian Northeast affected by uplifting. Thus, there are two stages recognized; the first one corresponds to the exhumation and reworking of the basement, probably in the early Cenozoic; and in the second stage a more intense weathering under semi-arid climate during Oligocene, or later.

How to cite: Lopes Diniz, J., Wohnrath Tognoli, F. M., Siqueira de Miranda, T., Nóbrega Sial, A., Vieira de Souza, L., Campos Inocêncio, L., Bonato, J., Modica Custódio, C., and Spaniol, A. F.: Interaction among biogenic, climate and tectonic processes influences tufa precipitation, Araripe Basin, Brazil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11908, https://doi.org/10.5194/egusphere-egu2020-11908, 2020.

The iron biogeochemical cycle is redox-sensitive and, therefore, can be linked to the major variations on the atmospheric and ocean compositions over the Earth’s evolution. Regarding the two main increases in the oxygen levels during the Precambrian, the Great and the Neoproterozoic Oxidation Events, both are related to paleogeographic, paleoenvironmetal and biochemical changes, linked also to global glaciations. These paleoclimatic variations caused disturbances in the iron cycle, which reacted by depositing paleoclimatic archives as banded iron formations (BIF). Investigations on the iron cycle can shed a light on the responses of the ocean redox state and the iron reservoir through these atmospheric variations. Thus, the analyses of the iron isotopic composition in the BIFs are a fundamental tool for these studies. It is essential to considerate the associated isotopic fractionation processes and uncertainties during the interpretation of these data. To this extend, many authors address the possibility of the impact of post-depositional processes in the primary signature of iron isotopic values, such as diagenesis, metamorphism and weathering. In all these scenarios and along the depositional process, the metabolic activity of planktonic bacteria must be considered as an active mechanism of isotopic fractioning. Therefore, the biologic enrolment in Fe (II) oxidation in a poor-O₂ atmosphere environment can help the understanding of BIF genesis during the major paleoclimatic events and its connection to life evolutionary leaps. In this study, we have performed a statistic evaluation of a bulk iron isotopic compilation from BIFs of different localities through the Precambrian, highlighting the Archean, the Paleoproterozoic and the Neoproterozoic. This evaluation was applied to ensure an iron isotopic anomaly, pointing towards an intense fractionation, found in the Neoproterozoic BIF of Banda Alta Formation (Jacadigo Group), located at Urucum district, West Brazil, bordering Bolivia. This formation is mainly composed of banded iron formations, interbedded with manganese facies, granular iron formation, diamictite and pelitic siliciclastic units. Its age constrains is in current debate, often linked to the Marinoan glaciation, whereas a recent biostratigraphic study indicates connection to the Sturtian glaciation. One of the main goals of this research is the evaluation of the uncertainty of primary isotopic signature regarding the impacts of post-depositional processes. To this extent, we have performed a detailed diagenetic characterization using clay mineralogy on stratigraphic cores establishing the diagenetic-low metamorphic stage in which these BIFs where submitted to. Moreover, in order to interpret the iron isotopic anomalous values, this research aimed the recognition of biogenic contribution in the BIF genesis. For this purpose, magnetic measures, such as low temperature magnetic measurements and standard bulk rock magnetism analyses, were performed to understand the minerology of the iron oxide phases and their genesis, in particular the attempt to identify biogenic magnetite proxies. In conclusion, a multiproxy approach was used targeting the understanding of the observed iron isotopic anomaly in the BIF of Urucum district.

How to cite: Fazio, G., Yokoyama, E., Cruz, L., and Trigilio, G.: Conundrum of the iron isotopic fractionation: banded iron formation from Urucum district, West Brazil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6020, https://doi.org/10.5194/egusphere-egu2020-6020, 2020.

The Andes are the longest continental mountain range on Earth, stretching from tropical Colombia and Venezuela in the north to temperate to sub-polar Patagonia in the south along the western margin of the South American continent. Biological diversity is extraordinarily high, especially in the northern tropical Andes, which are considered to be the richest biodiversity hotspot in the world. The Andes are relatively young; a large part of the modern topography is the result of surface uplift that occurred during and since the Miocene. However, large differences exist in the timing of shortening, exhumation, and surface uplift between the northern, central, and southern Andes, as well as between the various parallel Cordilleras. Mountain building directly links to climate dynamics, the development of drainage patterns, and the evolution of biomes and biodiversity. Therefore, determining the timing of surface uplift for each of the different Andean regions is of crucial importance for our understanding of continental-scale moisture transport and atmospheric circulation, the origin and evolution of the Amazon River and Rainforest, and ultimately, the origin and evolution of species in South America.

Determining surface elevations through geological time is not straightforward because the geological record does not contain a direct measure of topography. Commonly used methods to indirectly estimate paleo-elevation include low temperature thermochronology, palynology/paleobotany, the identification and dating of paleosurfaces, and analyzing the stratigraphic record of foreland basins that quantitatively record the topographic and erosional history of an adjacent mountain range. Additionally, paleo-elevation can be estimated more directly by stable isotope paleo-altimetry: atmospheric δ¹⁸O and δD vary with elevation as precipitation from ascending air parcels along an orographic barrier removes the heavy isotopes. The δ¹⁸O and δD values in authigenic/pedogenic materials (paleosols or lakes), biogenic archives (e.g. fossil teeth), volcanic glass, or organic biomarkers (e.g. leaf-wax n-alkanes preserved in soils or sediments) may thus record paleo-elevation.

In this study, we present a compilation of (direct and indirect) estimates of paleo-elevation of the Andes. We generate a reconstruction of surface uplift, per latitudinal sector of the Andes and per Cordillera or range, containing elevation values per 1x1 degree cell and per Myr. We discuss the areas and/or times where this reconstruction is uncertain as a result of either a lack of data, or a discrepancy between different data sets. Next, we present a compilation of low temperature thermochronology data, and compare the paleo-elevation history of the Andes with its exhumation history. We analyze spatial and temporal variations in erosion rates during Andean mountain building. Last, we use the paleo-elevation reconstruction to analyze the role of Andean mountain building in the rates of species diversification for hummingbirds (clade of Brilliants and Coquettes), iguanians (Liolaemus), tree frogs (two families), and flowering plants (centropogonids and orchids). We use a model‐testing approach that compares various diversification scenarios including a series of biologically realistic models to estimate speciation and extinction rates using a phylogeny, while assessing the relationship between diversification and environmental variables.

How to cite: Boschman, L., Bermúdez, M., and Condamine, F.: Mountain building and species radiations in the Andes: a reconstruction of surface uplift and species diversification since the Late Cretaceous from a compilation of paleo-elevation estimates, thermochronology, and phylogenetic data., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7941, https://doi.org/10.5194/egusphere-egu2020-7941, 2020.

The greater McArthur Basin is a regionally extensive Palaeo-to-Mesoproterozic, intra-cratonic, super basin system overlying the North Australian craton. Deposition initiated after the Pine Creek Orogeny whereby the basin extends from Western Australia to northwestern Queensland. Lithostratigraphic units are divided into five coherent packages of similar age, stratigraphic position and facies association. Successions of the basin system are dominated by an assemblage of sedimentary siliciclastics, evaporitic carbonates and organic-rich mudstones with minor intersections of volcanic rocks and records nearly a billion years of Earth’s history from ca. 1.82 Ga to the Tonian. This period has generally been considered a time of stability within the Earth system and is therefore unfortunately titled ‘the boring billion’. However, compilation of new and existing water chemistry proxies shown in this study reflected the contrary. Notably, shales and carbonates from the greater McArthur Basin chronicled a critical time in Earth’s history; where the oxygenation of the ocean and atmosphere began and multi-cellular eukaryotes started to thrive within the ecosystem, demonstrating that this interval in the geological record is anything but boring.

This study applied a multi-proxy approach based on observations of isotopic tracers and elemental variations from an extensive archive of carbonate-rich units throughout the greater McArthur Basin to reconstruct its palaeoenvironment, determine the tectonic setting and establish regional or global correlations. Elucidating the evolution of the basin is essential for understanding the controls of its petroleum and mineral resources as well as how Earth system processes developed during the Proterozoic. Radiogenic and stable isotopes are used to infer palaeo-depositional constraints such as biological productivity, weathering fluxes and provenance sources. Redox-sensitive elemental concentrations can also be used to reflect the changes in water-column chemistry between oxic, anoxic and euxinic conditions.

Consequently, results from this study illustrate the relationship between the precipitation of metal compounds, production of organic matter and preservation of both systems with large-scale biogeochemical processes. Furthermore, this study also highlights the spatial and temporal variations of water chemistry within the basin. Enrichment in Mo concentrations in the Wollogorang Formation within the Tawallah Group indicated spells of widespread euxinia. Base metal concentrations within the unit showed lithogeochemical, halo-like distribution that is strongly correlated with changes in water column redox conditions. A shift to more radiogenic ⁸⁷Sr/⁸⁶Sr values up to ∼0.722 in the Fraynes Formation of the Limbunya Group reflected an increase in relative contribution of strontium from old continental crust in contrast to hydrothermal input which is consistent with a transient basin restriction from the open ocean. Rare earth and yttrium (REY) plots of the Dook Creek Formation inferred parts of the basin may have been lacustrine at ca. 1.5 Ga. Further up stratigraphy, the Middle Velkerri showed a shift towards more positive ε_Nd(t) values, representing a change to more juvenile source regions. These mafic provenances are richer in essential nutrients for biological activity such as phosphorus. More juvenile ε_Nd(t) data within the Velkerri Formation coincide with an increase in P concentrations and total organic carbon content (>8 wt. %).

How to cite: Subarkah, D., Blades, M., Collins, A., Farkas, J., Yang, B., Cox, G., Jarrett, A., Cassidy, E., Shannon, A., Liebelt, S., McFazdean, G., and Munson, T.: Shale and carbonate geochemistry of the Proterozoic greater McArthur Basin, Australia., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12458, https://doi.org/10.5194/egusphere-egu2020-12458, 2020.

As a result of sustained tectonic and magmatic processes throughout the latter half of the Cenozoic, the eastern branch of the EARS exhibits an extensional tectonic system with pronounced relief contrasts, constituting both corridors and barriers for species dispersal. The tectono-magmatic history has generated a region of highly variable topography that results in widely varying amounts of rainfall and vegetation cover. Today, the generally dry eastern branch of the EARS hosts numerous sub-basins and adjacent local high-relief areas that are hydrologically isolated, with unique microclimates, vegetation types, faunas and superposed surface processes. However, during episodes of climate change with a trend toward more humid conditions, many of these basins hosted freshwater lakes that were hydrologically connected. These areas have repeatedly exhibited freshwater conditions and likely served as gateways and migration corridors mainly for aquatic organisms, in particular fish, facilitating population expansion, dispersal and gene flow.

Here, we analyze the manifold manifestations of the AHP in Kenya and adjacent sectors of the EARS to establish the timing and spatial extent of a paleo-drainage system documented by lake shorelines, deltas, overflow channels and sediments. These vestiges of fluvial connectivity in the rift have emerged as analogs for recurrent Pleistocene episodes with high lake levels and inter-basin linkage that repeatedly connected equatorial basins with regions to the north and south, respectively. For example, fossil evidence for the Pleistocene occurrence of the Nile crocodile (Crocodylus niloticus) as far south as equatorial Lake Bogoria (Kenya) and its present occurrence in the now closed Lake Baringo basin indicate fluvial connectivity over several degrees of latitude during more humid episodes in the past. Similarly, the occurrence of more than a dozen of the same fish species in the presently unconnected Lakes Albert and Turkana is likely due to a mutual connection during the AHP when Lake Turkana was overflowing into the White Nile.

Taken together, the divergent fossil and modern faunal evidence and geomorphic and sedimentological evidence of contrasting hydrological conditions between the wet AHP and the present, suggest that the conditions during the AHP provides a template of fluvial connectivity and potential dispersal patterns for earlier humid phases during the Plio-Pleistocene.

How to cite: Dommain, R., Riedl, S., Olaka, L., deMenocal, P., Deino, A., Potts, R., and Strecker, M.: Hydrological basin connectivity in a low-latitude rift: the impact of the Holocene African Humid Period (AHP) on fluvial activity and species dispersal in the Kenya Rift, East African Rift System (EARS), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9323, https://doi.org/10.5194/egusphere-egu2020-9323, 2020.

The southwestward propagation of the East African Rift System inside the southern African plateau generated the Okavango basin in a strike-slip context. This setup generates one of the largest endoreic ecosystem in Africa: the Okavango Delta alluvial fan. The sedimentary and topography dynamics of that system are driven by both annual flooding and strike-slip geodynamics. To evaluate the impact of ground deformation on the long-term evolution of the Okavango ecosystem, we estimated the 3D strain field from the deformation of a geodetic network composed of 7 dual-frequency GPS semi-permanent stations measured during 4 years. The Okavango basin is a half-graben: its SE edge being limited by a set of normal faults, while the NW limit is bounded by a right-lateral fault. This fault pattern generates strain partitioning with a stretching direction that changes from oblique to parallel to the graben trend and with the highest dilation to the NE and shortening to the SW. Integrating geophysical data, we propose a crustal model describing a strike-slip basin with a normal detachment zone connected to a steep strike-slip shear zone in the lower crust. We show that strain partitioning lead to dilating and shortening domains, which favors water flow toward the NE and progressively restricts water discharge into Lake Ngami, SW of the Delta.

At regional scale, the vertical component of the ground deformation recorded over 10 years reveals annual variations generated by the cyclic flooding, this process acting in addition to the ground deformation induced by the regional geodynamics. A preliminary numerical modeling of the ground flexure induced by the floods constrains the rheological properties of the crust. It highlights two domains with high subsidence limiting a domain with lower subsidence allowing differential water storage.

We conclude that the geodynamic deformation linked to the propagation of the East African Rift into the Okavango half-graben is a key factor controlling the hydrodynamics and ecosystem evolution of the Okavango Delta fan. This control is super-imposed to the effects of variations in sediment and water supply linked to regional climate change. More generally, we show that intra-continental endoreic systems can be highly sensible to low amplitude tectonic deformation.

How to cite: Dauteuil, O., Jolivet, M., Murray-Hudson, M., Barrier, L., Audran, A., and Radenac, A.: The interplay between geodynamics and flooding drives the dynamics of the inner Okavango Delta (North Botswana), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20291, https://doi.org/10.5194/egusphere-egu2020-20291, 2020.

What forms the landscapes of the Earth with their mountains, rivers, soils - the places we live in? Earth’s surface is shaped when rocks are uplifted by geologic forces, and are then destroyed by rain, ice, and wind that carve landscapes by erosion and weathering. But there is the green layer of life between rocks below and climate above. Do plants with their roots, animals that dig into soil, and the vast number of microorganisms shape the landscapes? Or do minerals, soil, and water provide the environment for life? Or are they both interdependent? Can they together resist the massive climate change imposed by humans today?

Showcasing these complex interactions in an audiovisual format provides a fantastic opportunity for science dissemination, but making a movie is a formidable challenge that scientists are not experienced in. Based on the the German National Science Foundation (DFG)- funded research network “EarthShape – Earth Surface Shaping by Biota”, we produced a movie intended as public outreach for scientists as well as classrooms and a general public audience.

Watch the scientists of the German-Chilean “EarthShape” project study the shaping of the Earth along a climate gradient in Chile, in the National Parks Pan de Azúcar, La Campana, and Nahuelbuta. Take a tour through fascinating landscapes and see the young scientists study the interactions between geology and biology, from the dry Atacama desert to dense forests, and in their sophisticated home laboratories. See how feedbacks control Earths’ climate. The movie is available online in Youtube, including separate process animations, and as Open-Access MP4 resource.

Playlist on Youtube: https://go.daf.li/EarthShape; DOI of the English movie version: https://doi.org/10.2312/gfz.3.3.2019.005

How to cite: Übernickel, K., von Blanckenburg, F., and Ehlers, T. A.: “The Skin of the Earth – Where Life meets Rocks” – A Science Movie, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7321, https://doi.org/10.5194/egusphere-egu2020-7321, 2020.