Radiocarbon evidence for a smaller oceanic carbon dioxide sink than previously believed

Radiocarbon produced naturally in the upper atmosphere or artificially during nuclear weapons testing is the main tracer used to validate models of oceanic carbon cycling, in particular the exchange of carbon dioxide with the atmosphere and the mixing parameters within the ocean itself. Here we test the overall consistency of exchange fluxes between all relevant compartments in a simple model of the global carbon cycle, using measurements of the long-term tropospheric CO2 concentration and radiocarbon composition, the bomb 14C inventory in the stratosphere and a compilation of bomb detonation dates and strengths. We find that to balance the budget, we must invoke an extra source to account for 25% of the generally accepted uptake of bomb 14C by the oceans. The strength of this source decreases from 1970 onwards, with a characteristic timescale similar to that of the ocean uptake. Significant radiocarbon transport from the remote high stratosphere and significantly reduced uptake of bomb 14C by the biosphere can both be ruled out by observational constraints. We therefore conclude that the global oceanic bomb 14C inventory should be revised downwards. A smaller oceanic bomb 14C inventory also implies a smaller oceanic radiocarbon penetration depth, which in turn implies that the oceans take up 25% less anthropogenic CO2 than had previously been believed

Herstellung und Bewertung von elektrophoretisch abgeschiedenen keramischen 3D-Strukturen

Eine gesunde, ausgewogene Lebensweise und ein gutes soziales Standing sind bedingt durch funktionsfähigen, hochästhetischen Zahnersatz. Auch das steigende Bewusstsein für den eigenen Körper erhöht die Forderungen der Patienten nach hochästhetischem und metallfreiem Zahnersatz. Aktuell wird die vollkeramische Versorgung durch CAD/CAM basierte Fertigung von Monolithen und Gerüsten, die nachfolgend mit einer Verblendkeramik individualisiert werden müssen, erreicht. Es kommt immer noch zu Chipping und Gerüstfrakturen. Um dem entgegenzuwirken, hat sich diese Arbeit damit befasst, monolithische und hierarchisch geschichtete Käppchen unter Verwendung der Elektrophorese herzustellen und zu untersuchen. Es wurden verschiedene Setups mit individuellen Parametern erstellt, bei denen unterschiedliche Suspensionen zum Einsatz kamen. Es war dadurch möglich Monolithe, zu denen auch gesteuert poröse Käppchen zählen, aus verschiedenen Suspensionen zu produzieren. Anschließend wurden hierarchische Käppchen elektrophoretisch erzeugt, deren jeweilige Innen- bzw. Außenschicht auf die weitere strukturelle Funktion, wie zum Beispiel das adhäsive Befestigen zum Zahn oder ein verbesserter Haftverbund zur Verblendkeramik, abgestimmt wurde. Für die Suspensionen kamen nanoskalige Oxidkeramikpulver (Zirkoniumdioxid und Aluminiumoxid) zum Einsatz. Diese wurden mit absolutem Ethanol und Benzoesäure dispergiert. Teilweise wurden verschiedene Zusätze und Binder wie Butvar B 98, Tulopur 4000 oder Optapix PAF 46 hinzugefügt. Unter Anwendung der Nanoindentation konnte eine literaturbeschriebene Festigkeit des elektrophoretisch erzeugten Zirkongerüstes belegt werden. Es konnte ein druckknopfartiger Verbund von Zirkoniumdioxid und Aluminiumoxid nach dem Sintern im Rasterelektronenmikroskop beschrieben werden. Die einzelnen hierarchischen Schichten waren fest mit einander verbunden und es kam zu keinen strukturellen Trennungen bzw. Ablösungen der jeweiligen Schichten. Ein gesteigerter Haftverbund von 37,1 % von Zirkoniumdioxidgerüst und Verblendkeramik konnte unter Durchführung eines Druck-Scher-Versuches nachgewiesen werden. Der Test nach ISO 9693-2 belegt, dass unter Anwendung des neuentwickelten Bonders zuerst die Verblendkeramik nachgibt, während der Haftverbund noch intakt ist. Somit konnte gezeigt werden, dass eine hierarchische Strukturierung von dreidimensionalen Gerüstkeramiken möglich und umsetzbar ist. Modifizierte Schichten von Oxidkeramiken sind an ihrer Oberfläche ätzbar und sorgen somit für einen besseren Haftverbund zum Zahn und einer festeren Verbindung zur Verblendung. Auch die Einlagerung von Poren in die Gerüstkeramik konnte in Ansätzen gezeigt werden.A healthy, balanced way of life and well positioned social standing are both based on functional, high esthetic dental prosthesis. Even the raising awareness of the own body increases the patients request for high esthetic and crowns and bridges, which are free of alloys. The most popular possibility of all-ceramic dental care is the CAD/CAM-method. Monoliths and framework for dental covering are the products of this technology. Literature gives us a reference for the problem, called chipping and framework fracture. This work is based on the possibility of producing monolithic and hierachically structured frameworks, which were realized with Electrophoretic Deposition. Different setups were introduced with individual parameters and different suspensions. Caused on this, it was possible to produce monolithic dense and controlled porous frameworks. Afterwards 3D-frameworks with different hierarchical levels were investigated. The inner and outer layers were coordinated with their following function (for example the adhesiv cementation on a teeth or the increasing bond to the covering feldspar ceramic). Nanoscaled oxyd ceramic (circonia and aluminia) powder were used for the suspensions. They were dispersed in absolut ethanol and added with benzoic acid. Sometimes additives like Butvar B 98, Optapix PAF 46 and Tulopur 4000 were used. With the use of a nanoindenter it was documented, that the hardness of electrophoretic depositioned circonia is as high as it is mentioned in the literature. In the REM could be found a special bonding like a press button between circonia an aluminia after sintering. All hierarchically structures were straight bonded to each other. No cracks between the layers could be observed. With the results of pressure-shear-trials an increased bonding toughness of +37.1 % could be proved between the circonia framework and the added ceramic feldspar layer. The testing in the dependence on ISO 9693-2 had shown, that there is a delamination between the feldspar ceramic itself, while the bonding is still intact.So, it was demonstrated, that hierarchically structuring of dental frameworks with nanoscaled circonia and aluminia powder by using the epd technic is possible and realizable. Modified oxyd ceramic layers are on one hand etchable for a better framework-teeth-bonding and on the other hand for an increased toughness between framework and the feldspar ceramic layer. Even the inclusion of controlled pores in the framework could be shown

COCAP : a carbon dioxide analyser for small unmanned aircraft systems

Unmanned aircraft systems (UASs) could provide a cost-effective way to close gaps in the observation of the carbon cycle, provided that small yet accurate analysers are available. We have developed a COmpact Carbon dioxide analyser for Airborne Platforms (COCAP). The accuracy of COCAP's carbon dioxide (CO2) measurements is ensured by calibration in an environmental chamber, regular calibration in the field and by chemical drying of sampled air. In addition, the package contains a lightweight thermal stabilisation system that reduces the influence of ambient temperature changes on the CO2 sensor by 2 orders of magnitude. During validation of COCAP's CO2 measurements in simulated and real flights we found a measurement error of 1.2 mu mol mol(-1) or better with no indication of bias. COCAP is a self-contained package that has proven well suited for the operation on board small UASs. Besides carbon dioxide dry air mole fraction it also measures air temperature, humidity and pressure. We describe the measurement system and our calibration strategy in detail to support others in tapping the potential of UASs for atmospheric trace gas measurements.Peer reviewe

The climate benefit of carbon sequestration

Ecosystems play a fundamental role in climate change mitigation by photosynthetically fixing carbon from the atmosphere and storing it for a period of time in organic matter. Although climate impacts of carbon emissions by sources can be quantified by global warming potentials, the appropriate formal metrics to assess climate benefits of carbon removals by sinks are unclear. We introduce here the climate benefit of sequestration (CBS), a metric that quantifies the radiative effect of fixing carbon dioxide from the atmosphere and retaining it for a period of time in an ecosystem before releasing it back as the result of respiratory processes and disturbances. In order to quantify CBS, we present a formal definition of carbon sequestration (CS) as the integral of an amount of carbon removed from the atmosphere stored over the time horizon it remains within an ecosystem. Both metrics incorporate the separate effects of (i) inputs (amount of atmospheric carbon removal) and (ii) transit time (time of carbon retention) on carbon sinks, which can vary largely for different ecosystems or forms of management. These metrics can be useful for comparing the climate impacts of carbon removals by different sinks over specific time horizons, to assess the climate impacts of ecosystem management, and to obtain direct quantifications of climate impacts as the net effect of carbon emissions by sources versus removals by sinks.Peer reviewe

Continuous CO2 and CH4 Observations in the Coastal Arctic Atmosphere of the Western Taimyr Peninsula, Siberia : The First Results from a New Measurement Station in Dikson

Atmospheric observations of sources and sinks of carbon dioxide (CO2) and methane (CH4) in the pan-Arctic domain are highly sporadic, limiting our understanding of carbon turnover in this climatically sensitive environment and the fate of enormous carbon reservoirs buried in permafrost. Particular gaps apply to the Arctic latitudes of Siberia, covered by the vast tundra ecosystems underlain by permafrost, where only few atmospheric sites are available. The paper presents the first results of continuous observations of atmospheric CO2 and CH4 dry mole fractions at a newly operated station "DIAMIS" (73.506828 degrees N, 80.519869 degrees E) deployed on the edge of the Dikson settlement on the western coast of the Taimyr Peninsula. Atmospheric mole fractions of CO2, CH4, and H2O are measured by a CRDS analyzer Picarro G2301-f, which is regularly calibrated against WMO-traceable gases. Meteorological records permit screening of trace gas series. Here, we give the scientific rationale of the site, describe the instrumental setup, analyze the local environments, examine the seasonal footprint, and show CO2 and CH4 fluctuations for the daytime mixed atmospheric layer that is representative over a vast Arctic domain (-500-1000 km), capturing both terrestrial and oceanic signals.Peer reviewe