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The AlpArray seismic network
(2018)
The AlpArray programme is a multinational, European consortium to advance our understanding of orogenesis and its relationship to mantle dynamics, plate reorganizations, surface processes and seismic hazard in the Alps-Apennines-Carpathians-Dinarides orogenic system. The AlpArray Seismic Network has been deployed with contributions from 36 institutions from 11 countries to map physical properties of the lithosphere and asthenosphere in 3D and thus to obtain new, high-resolution geophysical images of structures from the surface down to the base of the mantle transition zone. With over 600 broadband stations operated for 2 years, this seismic experiment is one of the largest simultaneously operated seismological networks in the academic domain, employing hexagonal coverage with station spacing at less than 52 km. This dense and regularly spaced experiment is made possible by the coordinated coeval deployment of temporary stations from numerous national pools, including ocean-bottom seismometers, which were funded by different national agencies. They combine with permanent networks, which also required the cooperation of many different operators. Together these stations ultimately fill coverage gaps. Following a short overview of previous large-scale seismological experiments in the Alpine region, we here present the goals, construction, deployment, characteristics and data management of the AlpArray Seismic Network, which will provide data that is expected to be unprecedented in quality to image the complex Alpine mountains at depth.
Dumortierite was synthesized in piston-cylinder experiments at 2.5-4.0 GPa, 650-700 degrees C in the Al2O3 -B2O3-SiO2-H2O (ABSH) system. Electron-microprobe (EMP) analyses reveal significant boron-excess (up to 0.26 B-[4] per formula unit, pfu) and silicon-deficiency relative to the ideal anhydrous dumortierite stoichiometry Al7BSi3O18 . The EMP data in conjunction with results from single-crystal Raman spectroscopy and powder X-ray diffraction provide evidence that silicon at the tetrahedral site is replaced by excess boron via the substitution Si-[4] <--> B-[4] + H. The Raman spectrum of synthetic dumortierite in the frequency region 2000 4000 cm(-1) comprises eight bands, of which six are located at frequencies below 3400 cm(-1). This points to strong hydrogen bonding, most likely O2-H center dot center dot center dot O7 and O7-H center dot center dot center dot O2, arising from a high number of octahedral vacancies at the All site and substitution of trivalent Al3+ and B3+ for Si4+ at Si1 and Si2 sites, causing decreasing acceptor-donor distances and lower incident valence at the acceptor oxygen. Contrary to the synthetic high-pressure ABSH-dumortierite, magnesiodumortierite from the Dora-Maira Massif, which is assumed to have formed at similar conditions (2.5-3.0 GPa, 700 degrees C), does not show any B-excess. Tourmaline shows an analogous behaviour in that magnesium-rich (e.g., dravitic) tourmaline formed at high pressure shows no or only minor amounts of tetrahedral boron, whereas natural aluminum-rich tourmaline and synthetic olenitic tourmaline formed at high pressures can incorporate significant amounts of tetrahedral boron. Two mechanisms might account for this discrepancy: (i) Structural avoidance of Mg-[6]-(OR3+)-R-[4] configurations in magnesiodumortierite due to charge deficieny at the oxygens O2 and O7 and strong local distortion of M1 due to decreased O2-O7 bond length, and/or (ii) decreasing fluid mobility of boron in Al-rich systems at high pressures.
The intensification of Northern Hemisphere glaciations at the end of the Pliocene epoch marks one of the most substantial climatic shifts of the Cenozoic. Despite global cooling, sea surface temperatures in the high latitude North Atlantic Ocean rose between 2.9–2.7 million years ago. Here we present sedimentary geochemical proxy data from the Gulf of Cadiz to reconstruct the variability of Mediterranean Outflow Water, an important heat source to the North Atlantic. We find evidence for enhanced production of Mediterranean Outflow from the mid-Pliocene to the late Pliocene which we infer could have driven a sub-surface heat channel into the high-latitude North Atlantic. We then use Earth System Models to constrain the impact of enhanced Mediterranean Outflow production on the northward heat transport in the North Atlantic. In accord with the proxy data, the numerical model results support the formation of a sub-surface channel that pumped heat from the subtropics into the high latitude North Atlantic. We further suggest that this mechanism could have delayed ice sheet growth at the end of the Pliocene.
The intensification of Northern Hemisphere glaciations at the end of the Pliocene epoch marks one of the most substantial climatic shifts of the Cenozoic. Despite global cooling, sea surface temperatures in the high latitude North Atlantic Ocean rose between 2.9–2.7 million years ago. Here we present sedimentary geochemical proxy data from the Gulf of Cadiz to reconstruct the variability of Mediterranean Outflow Water, an important heat source to the North Atlantic. We find evidence for enhanced production of Mediterranean Outflow from the mid-Pliocene to the late Pliocene which we infer could have driven a sub-surface heat channel into the high-latitude North Atlantic. We then use Earth System Models to constrain the impact of enhanced Mediterranean Outflow production on the northward heat transport in the North Atlantic. In accord with the proxy data, the numerical model results support the formation of a sub-surface channel that pumped heat from the subtropics into the high latitude North Atlantic. We further suggest that this mechanism could have delayed ice sheet growth at the end of the Pliocene.
Improving our understanding of biodiversity and ecosystem functioning and our capacity to inform ecosystem management requires an integrated framework for functional biodiversity research (FBR). However, adequate integration among empirical approaches (monitoring and experimental) and modelling has rarely been achieved in FBR. We offer an appraisal of the issues involved and chart a course towards enhanced integration. A major element of this path is the joint orientation towards the continuous refinement of a theoretical framework for FBR that links theory testing and generalization with applied research oriented towards the conservation of biodiversity and ecosystem functioning. We further emphasize existing decision-making frameworks as suitable instruments to practically merge these different aims of FBR and bring them into application. This integrated framework requires joint research planning, and should improve communication and stimulate collaboration between modellers and empiricists, thereby overcoming existing reservations and prejudices. The implementation of this integrative research agenda for FBR requires an adaptation in most national and international funding schemes in order to accommodate such joint teams and their more complex structures and data needs.
GrassPlot is a collaborative vegetation-plot database organised by the Eurasian Dry Grassland Group (EDGG) and listed in the Global Index of Vegetation-Plot Databases (GIVD ID EU-00-003). GrassPlot collects plot records (releves) from grasslands and other open habitats of the Palaearctic biogeographic realm. It focuses on precisely delimited plots of eight standard grain sizes (0.0001; 0.001;... 1,000 m(2)) and on nested-plot series with at least four different grain sizes. The usage of GrassPlot is regulated through Bylaws that intend to balance the interests of data contributors and data users. The current version (v. 1.00) contains data for approximately 170,000 plots of different sizes and 2,800 nested-plot series. The key components are richness data and metadata. However, most included datasets also encompass compositional data. About 14,000 plots have near-complete records of terricolous bryophytes and lichens in addition to vascular plants. At present, GrassPlot contains data from 36 countries throughout the Palaearctic, spread across elevational gradients and major grassland types. GrassPlot with its multi-scale and multi-taxon focus complements the larger international vegetationplot databases, such as the European Vegetation Archive (EVA) and the global database " sPlot". Its main aim is to facilitate studies on the scale-and taxon-dependency of biodiversity patterns and drivers along macroecological gradients. GrassPlot is a dynamic database and will expand through new data collection coordinated by the elected Governing Board. We invite researchers with suitable data to join GrassPlot. Researchers with project ideas addressable with GrassPlot data are welcome to submit proposals to the Governing Board.
Fragmentation of landscapes creates a transition zone in between natural habitats or different kinds of land use. In forested and agricultural landscapes with transition zones, microclimate and matter cycling are markedly altered. This probably accelerates and is intensified by global warming. However, there is no consensus on defining transition zones and quantifying relevant variables for microclimate and matter cycling across disciplines. This article is an attempt to a) revise definitions and offer a framework for quantitative ecologists, b) review the literature on microclimate and matter cycling in transition zones and c) summarise this information using meta-analysis to better understand bio-geochemical and bio-geophysical processes and their spatial extent in transition zones. We expect altered conditions in soils of transition zones to be 10-20 m with a maximum of 50 m, and 25-50 m for above-ground space with a maximum of 125 m.
The depositional geometry and facies distribution of an Early Miocene (Burdigalian) carbonate system in the Perfugas Basin (NW Sardinia) comprise a well-exposed example of a transition from a ramp to a steep-flanked platform. The carbonate succession (Sedini Limestone Unit) is composed of two depositional sequences separated by a major erosional unconformity. The lower (sequence 1) records a ramp dominated by heterozoan producers and the upper (sequence 2) is dominated by photozoan producers and displays a gradual steepening of the depositional profile into a steep- flanked platform. This paper shows the process of creating a digital outcrop model including a facies model. This process consists of combining field data sets, including 17 sedimentary logs, and a spatial dataset consisting of differential global positioning system data points measured along key stratigraphic surfaces and sedimentary logs, with the goal of locking traditional field observations into a 3D spatial model. Establishing a precise geometrical framework and visualizing the overall change in the platform geometry and the related vertical and lateral facies variations of the Sedini carbonate platform, allows us to better understand the sedimentary processes leading to the geometrical turn- over of the platform. Furthermore, a detailed facies modeling helps us to gain insight into the detailed depositional dynamics. The final model reproduces faithfully the depositional geometries observed in the outcrops and helps in understanding the relationships between facies and architectural framework at the basin scale. Moreover, it provides the basis to characterize semiquantitatively regional sedimentological features and to make further reservoir and subsurface analogue studies.
The structure and alterations of subducted oceanic lithosphere ( e. g., thickness and seismic velocity of oceanic crust) can be obtained by analyzing guided seismic waves generated by earthquakes within the slab (Wadati- Benioff zone). In northern Chile prominent secondary phases from intermediate-depth seismicity, observed in the forearc region can be interpreted as guided waves. For the observation of guided waves it is usually required to have stations close to the wave guide, a fact which is not directly given for forearc stations in subduction zone environments. With the help of finite difference simulations we model the decoupling mechanism of guided waves at the contact between the descending oceanic plate and the upper plate crust where the wave guide is opened due to the equalization of seismic velocities. Provided that suited stations are available, this mechanism allows for the use of intermediate depth seismicity to study the shallow subduction zone structure ( <= 100 km depth)