The new worldwide collapse caldera database (CCDB): A tool for studying and understanding caldera processes

Collapse calderas are one of the most important volcanic structures not only because of their hazard implications, but also because of their high geothermal energy potential and their association with mineral deposits of economic interest. The objective of this work is to describe a new general worldwide Collapse Caldera DataBase (CCDB), in order to provide a useful and accessible tool for studying and understanding caldera collapse processes. The principal aim of the CCDB is to update the current field based knowledge on calderas, merging together the existing databases and complementing them with new examples found in the bibliography, and leaving it open for the incorporation of new data from future studies. This database does not include all the calderas of the world, but it tries to be representative enough to promote further studies and analyses. We have performed a comprehensive compilation of published field studies of collapse calderas including more than 200 references, and their information has been summarized in a database linked to a Geographical Information System (GIS) application. Thus, it is possible to visualize the selected calderas on a world map and to filter them according to different features recorded in the database (e.g. age, structure). The information recorded in the CCDB can be grouped in seven main information classes: caldera features, properties of the caldera-forming deposits, magmatic system, geodynamic setting, pre-caldera volcanism, caldera-forming eruption sequence and post-caldera activity. Additionally, we have added two extra classes. The first records the references consulted for each caldera. The second allows users to introduce comments on the caldera sample such as possible controversies concerning the caldera origin. A further purpose of this work is to construct the CCDB web page. In this web page where registered users can acquire the current database version, as well as to propose corrections or updates and to exchange information with other registered members also involved in the study of caldera collapse processes. Additionally, the CCDB includes a formulary that will facilitate the incorporation of new calderas into the database.     

Reaktionen benthischer Tiefsee-Lebensgemeinschaften auf mechanische Störungen der Sedimente

Ocean Dynamics - Das Ökosystem der Tiefsee wird zunehmend durch industrielle Eingriffe beeinflusst. Über die Auswirkungen dieser Aktivitäten auf das Benthos wurden bisher nur...     

The Hoher List observations of the occultation of 28 Sagittarii by Titan

Observations of the occultation of 28 Sgr by Titan are presented. Apparently being located close to the central line of the occultation track, a double peaked central flash was observed. Some characteristic times of the phenomenon are given.     

Leaf-level gas exchange and scaling-up of forest understory carbon fixation rates with a “patch-scale” canopy model

Summary During the Hartheim experiment (HartX) 1992, conducted in the Upper Rhine Valley, Germany, we estimated water vapor flux from the understory by several methods as reported in Wedler et al. (this issue). We also examined the photosynthetic gas exchange of the dominant understory speciesBrachypodium pinnatum, Carex alba, andCarex flacca at the leaf level with an CO₂/H₂O porometer. A mechanisticallybased leaf gas exchange model was parameterized for these understory species and validated via the measured diurnal courses of carbon dioxide exchange. Leaf CO₂ gas exchange was scaled-up to patch- and then to stand-level utilizing the leaf gas exchange model as a component of the canopy light interception/energy balance model GAS-FLUX, and by further considering variation in vegetation patch-type distribution, patch-specific spatial structure, patch-type leaf area index, and microclimate beneath the tree canopy.At patch-level,C. alba exhibited the lowest net CO₂ uptake of ca. 75 mmol m^–2 d^–1 due to a low leaf-level photosynthetic capacity, whereas net CO₂ fixation ofB. pinnatum- andC. flacca-patches was approx. 178 and 184 mmol m^–2 d^–1, respectively. Highest CO₂ uptake was estimated for mixed patches whereB. pinnatum grew together with the sedge speciesC. alba orC. flacca. Scaling-up of leaf gas exchange to stand level resulted in an estimated average rate of total CO₂ fixation by the graminoid understory patches of approximately 93 mmol m^–2 d^–1 during the HartX period. The conservative gas exchange behavior ofC. alba at Hartheim and its apparent success in space capture seems to affect overall functioning of this pine forest ecosystem by limiting understory CO₂ uptake. The CO₂ uptake by the understory is approximately 20% of stand total CO₂ uptake. CO₂ uptake fluxes mirror the relative differences in water loss from the understory and crown layer during the HartX period. Comparative measurements indicate that understory vegetation in spruce and pine forests is not greatly different from that of other low-statured natural ecosystems such as tundra or marshes under high light conditions, although CO₂ capture by the understory at Hartheim is at the low extreme of the estimates, apparently due to the success ofC. alba. With 6 Figures     

Solar rotation and activity in the past and their possible influence upon the evolution of life

It is proposed that the rotational angular momentum of the lower Main Sequence stars determines the intensity of their magnetic spot activity. As a consequence of this feedback coupling, the stellar rotation and the activity decay exponentially by magnetic braking of the induced stellar flare- and wind-activity. Therefore, the Sun should have rotated much faster and must have shown a very enhanced activity in its early history. This strong solar activity in the past could have had influenced the evolution of terrestrial life, and may explain the stagnation of maritime life for about 2×10⁹ yr, the diversification of species during the Cambrian formation, and the land conquest by life in the upper Silurian system.Commemorating 120th anniversary of the first edition of Ch. Darwin's The Origin of Species.     

The heliometer principle and some modern applications

Beside some historical notes about the large Fraunhofer's heliometer used by Bessel and Argelander, some modern applications of the heliometer principle for the geometric and photometric autocalibration of detectors and the determination of absolute radial velocities with slitless field spectrographs are presented.Astronomy gains only by new results if these are unambiguously obtained. Not the premature guessing but the fundamental acquisition of data and knowledge must be the topic of the efforts.Communication presented at the International Conference on Astrometric Binaries, held on 13–15 June, 1984, at the Remeis-Sternwarte Bamberg, Germany, to commemorate the 200th anniversary of the birth of Friedrich Wilhelm Bessel (1784-1846).     

The Atmospheric Boundary Layer Over Baltic Sea Ice

A new parametrization for the surface energy balance of urban areas is presented. It is shown that this new method can represent some of the important urban phenomena, such as an urban heat island and the occurrence of a near-neutral nocturnal boundary layer with associated positive turbulent heat fluxes, unlike the traditional method for representing urban areas within operational numerical weather prediction (NWP) models. The basis of the new parametrization is simple and can be applied easily within an operational NWP model. Also, it has no additional computational expense compared to the traditional scheme and is hence applicable for operational forecasting requirements. The results show that the errors for London within the Met Office operational mesoscale model have been significantly reduced since the new scheme was introduced. The bias and root-mean-square (rms) errors have been approximately halved, with the rms error now similar to the model as a whole. The results also show that a seasonal cycle still exists in the model errors, but it is suggested that this may be caused by anthropogenic heat sources that are neglected in the urban scheme.The British Crowns right to retain a non-exclusive royalty-free license in and to any copyright is acknowledged.     

Reconstruction of palaeohydrological conditions in a lagoon during the 2nd Zechstein cycle through simultaneous use of δD values of individual n-alkanes and δ<Superscript>18</Superscript>O and δ<Superscript>13</Superscript>C values of carbonates

For the first time ¹⁸O and ¹³C values from carbonates and D values of individual n-alkanes were used to reconstruct palaeohydrological conditions in a lagoon at the southern margin of the Central European Zechstein Basin (CEZB). A 12-m core covering the complete Ca2 interval and adjacent anhydrites (A1 and A2) was analyzed for ¹⁸O and ¹³C values of dolomitized carbonates and D values of individual n-alkanes. ¹⁸O_carb values (+2 to +5 vs. VPDB) were strongly influenced by evaporation and temporal freshwater input into the lagoon. The ¹³C_carb values (–1 to +4 vs. VPDB) were controlled mainly by changes in primary production. Both isotopic ratios show an inverse relationship throughout most of the core, contradicting diagenetic alteration, since ¹³C_carb values are not altered significantly during dolomitization. Assuming a temperature range of 35–40 °C in the lagoon, ¹⁸O_carb values of +2.5 to +8 (vs. VSMOW) for the lagoonal water can be reconstructed. The lagoon may have desiccated twice during the Ca2 interval, as indicated by very high ¹⁸O_carb and low ¹³C_carb values, coinciding with increasing amount of anhydrite in the analyzed sample. These events seem to reflect not just local but a regional intra-Ca2 cyclicity. Measured D values of the short-chain n-alkanes, namely n-C₁₆ and n-C₁₈ which are widely used as indicators for photosynthetic bacterial and algal input, reflect the isotopic composition of the lagoonal water. Assuming constant fractionation during incorporation of hydrogen into lipids of –160, an average D value of +70 (vs. VSMOW) can be reconstructed for the lagoonal water, accounting for very arid conditions. The long-chain n-alkanes n-C₂₇, n-C₂₈, n-C₂₉ and n-C₃₀, thought to be derived from the leaf waxes of terrestrial higher plants, were shown to be depleted in D relative to the short-chain alkanes, therefore indicating a different hydrogen source. Terrestrial plants in arid areas mainly use water supplied by precipitation. By using a smaller fractionation of –120 due to evaporation processes in the leaves, reconstructed values vary between –74 and –9 (vs. VSMOW). These values are not indicating extremely arid conditions, implying that the long-chain n-alkanes were transported trough wind and/or rivers into the lagoon at the Zechstein Sea coast. D_water values, reconstructed using the n-C₁₆ alkane and ¹⁸O _water values, independently reconstructed on the same sample using the temperature dependant fractionation for dolomites are good agreement and suggest high amounts of evaporation affecting the coastal lagoon. Altogether, our results indicate that hydrogen isotopic ratios of n-alkanes give information on their origin and are a useful proxy for palaeoclimatic reconstruction.