Climate Change in the Baltic Sea Region: A Summary

Based on the Baltic Earth Assessment Reports of this thematic issue in Earth System Dynamics and recent peer-reviewed literature, current knowledge about the effects of global warming on past and future changes in climate of the Baltic Sea region is summarized and assessed. The study is an update of the Second Assessment of Climate Change (BACC II) published in 2015 and focusses on the atmosphere, land, cryosphere, ocean, sediments and the terrestrial and marine biosphere. Based on the summaries of the recent knowledge gained in paleo-, historical and future regional climate research, we find that the main conclusions from earlier assessments remain still valid. However, new long-term, homogenous observational records, e.g. for Scandinavian glacier inventories, sea-level driven saltwater inflows, so-called Major Baltic Inflows, and phytoplankton species distribution and new scenario simulations with improved models, e.g. for glaciers, lake ice and marine food web, have become available. In many cases, uncertainties can now be better estimated than before, because more models can be included in the ensembles, especially for the Baltic Sea. With the help of coupled models, feedbacks between several components of the Earth System have been studied and multiple driver studies were performed, e.g. projections of the food web that include fisheries, eutrophication and climate change. New data sets and projections have led to a revised understanding of changes in some variables such as salinity. Furthermore, it has become evident that natural variability, in particular for the ocean on multidecadal time scales, is greater than previously estimated, challenging our ability to detect observed and projected changes in climate. In this context, the first paleoclimate simulations regionalized for the Baltic Sea region are instructive. Hence, estimated uncertainties for the projections of many variables increased. In addition to the well-known influence of the North Atlantic Oscillation, it was found that also other low-frequency modes of internal variability, such as the Atlantic Multidecadal Variability, have profound effects on the climate of the Baltic Sea region. Challenges were also identified, such as the systematic discrepancy between future cloudiness trends in global and regional models and the difficulty of confidently attributing large observed changes in marine ecosystems to climate change. Finally, we compare our results with other coastal sea assessments, such as the North Sea Region Climate Change Assessment (NOSCCA) and find that the effects of climate change on the Baltic Sea differ from those on the North Sea, since Baltic Sea oceanography and ecosystems are very different from other coastal seas such as the North Sea. While the North Sea dynamics is dominated by tides, the Baltic Sea is characterized by brackish water, a perennial vertical stratification in the southern sub-basins and a seasonal sea ice cover in the northern sub-basins</p

Climate change in the Baltic Sea region: a summary

Based on the Baltic Earth Assessment Reports of this thematic issue in Earth System Dynamics and recent peer-reviewed literature, current knowledge of the effects of global warming on past and future changes in climate of the Baltic Sea region is summarised and assessed. The study is an update of the Second Assessment of Climate Change (BACC II) published in 2015 and focuses on the atmosphere, land, cryosphere, ocean, sediments, and the terrestrial and marine biosphere. Based on the summaries of the recent knowledge gained in palaeo-, historical, and future regional climate research, we find that the main conclusions from earlier assessments still remain valid. However, new long-term, homogenous observational records, for example, for Scandinavian glacier inventories, sea-level-driven saltwater inflows, so-called Major Baltic Inflows, and phytoplankton species distribution, and new scenario simulations with improved models, for example, for glaciers, lake ice, and marine food web, have become available. In many cases, uncertainties can now be better estimated than before because more models were included in the ensembles, especially for the Baltic Sea. With the help of coupled models, feedbacks between several components of the Earth system have been studied, and multiple driver studies were performed, e.g. projections of the food web that include fisheries, eutrophication, and climate change. New datasets and projections have led to a revised understanding of changes in some variables such as salinity. Furthermore, it has become evident that natural variability, in particular for the ocean on multidecadal timescales, is greater than previously estimated, challenging our ability to detect observed and projected changes in climate. In this context, the first palaeoclimate simulations regionalised for the Baltic Sea region are instructive. Hence, estimated uncertainties for the projections of many variables increased. In addition to the well-known influence of the North Atlantic Oscillation, it was found that also other low-frequency modes of internal variability, such as the Atlantic Multidecadal Variability, have profound effects on the climate of the Baltic Sea region. Challenges were also identified, such as the systematic discrepancy between future cloudiness trends in global and regional models and the difficulty of confidently attributing large observed changes in marine ecosystems to climate change. Finally, we compare our results with other coastal sea assessments, such as the North Sea Region Climate Change Assessment (NOSCCA), and find that the effects of climate change on the Baltic Sea differ from those on the North Sea, since Baltic Sea oceanography and ecosystems are very different from other coastal seas such as the North Sea. While the North Sea dynamics are dominated by tides, the Baltic Sea is characterised by brackish water, a perennial vertical stratification in the southern subbasins, and a seasonal sea ice cover in the northern subbasins

Low power reactor for remote applications

A compact, low power reactor is being designed to provide electric power for remote, unattended applications. Because of the high fuel and maintenance costs for conventional power sources such as diesel generators, a reactor power supply appears especially attractive for remote and inaccessible locations. Operating at a thermal power level of 135 kWt, the power supply achieves a gross electrical output of 25 kWe from an organic Rankine cycle (ORC) engine. By intentional selection of design features stressing inherent safety, operation in an unattended mode is possible with minimal risk to the environment. Reliability is achieved through the use of components representing existing, proven technology. Low enrichment uranium particle fuel, in graphite core blocks, cooled by heat pipes coupled to an ORC converter insures long-term, virtually maintenance free, operation of this reactor for remote applications. 10 refs., 7 figs., 3 tabs

Electron Doping of the Iron-Arsenide Superconductor CeFeAsO Controlled by Hydrostatic Pressure

In the iron-pnictide material CeFeAsO not only the Fe moments, but also the local 4f moments of the Ce order antiferromagnetically at low temperatures. We elucidate on the peculiar role of the Ce on the emergence of superconductivity. While application of pressure suppresses the iron SDW ordering temperature monotonously up to 4 GPa, the Ce-4f magnetism is stabilized, until both types of magnetic orders disappear abruptly and a narrow SC dome develops. With further increasing pressure characteristics of a Kondo-lattice system become more and more apparent in the electrical resistivity. This suggests a connection of the emergence of superconductivity with the extinction of the magnetic order and the onset of Kondo-screening of the Ce-4f moments.Comment: 6 pages, 3 figures + supplemental materia

Gadolinium trisilicide - a paramagnetic representative of the YbSi₃ type series

Binary gadolinium trisilicide GdSi3 was prepared by high-pressure high-temperature synthesis at typically 9.5(5) GPa and 870 K before quenching to ambient conditions. At ambient pressure, GdSi3 exhibits an exothermic decomposition at 647(10) K into the thermodynamically stable phases GdSi2-x and Si, indicating its metastable character. Powder X-ray diffraction data is consistent with the YbSi3-type crystal structure comprising slabs of condensed Si-2 dumbbells, which enclose layered arrangements of gadolinium cations. Quantum chemical analysis of the chemical bonding shows, that the framework is formed by silicon dumbbells with homopolar bonds. The magnetic moment of 8.13(8) mu(B) is consistent with Gd4f(7) (Gd3+ state) and antiferromagnetic ordering is observed below 64(1) K

Nanostructuring of Ba8Ga16Ge30 clathrates by sol-gel-calcination/chemical-reduction route

Nanoparticles (NPs) of Ba8Ga16Ge30 clathrate-I were synthetized via sol-gel-calcination/chemical-reduction route. A solution of the metallic cations was used to prepare an acryl-amid-based gel. The gel is dried and calcined to obtain nanocrystalline powders of precursor oxides. The oxides are reduced by reacting with CaH2 to produce the clathrate, which is embedded in a CaO matrix. CaO is removed by a washing step to obtain the clathrate NPs. The shape and size of the precursor oxide NPs can be modified by addition of complexing agents, surfactants or by varying the pH or the metal and surfactant concentration in the gel. Powder X-ray diffraction and SAED patterns confirm the clathrate-I-type crystal structure of the products. SEM/TEM investigations show that the size and morphology of the oxides are retained in the clathrate NPs after the reduction. The clathrate NPs exhibit morphology of thin plates similar to 300 x similar to 300 nm(2) and thickness of similar to 50 nm, or sphere-like morphology with similar to 200 nm diameter, depending on the sol gel synthesis conditions. The clathrate NPs were compacted via spark plasma sintering (SPS) to pellets with 53-93 % of crystallographic density. The total thermal conductivity (kappa) of the pellet with 93 % density shows a reduction of 25 % in comparison to the reported K in bulk clathrate. Preliminary characterization of the Seebeck (S) and electrical resistivity (R) of the low density sample (53 %) indicates n-type conduction and semiconductor behavior of the Ba8Ga16Ge30 clathrate-I. The transport properties of Ba8Ga16Ge30 clathrate-I with 3-, 4- or 5-layer slabs and [100] surface termination as well as of the bulk material were calculated by using the semi-classical Boltzmann transport theory within the constant scattering approximation. Our results show an increase in S for the geometries with reduced dimensions in agreement with the experimental observations

Thermoelectric characterization of the clathrate-I solid solution Ba_8-δAu_xGe_46-x

Clathrate-I-based materials are promising for waste-heat recovering applications via thermoelectric (TE) effects. However, the lack of highly efficient p-type materials hampers the development of clathrate-based TE devices. In this work, the synthesis of the p-type semiconductor Ba7.8Au5.33Ge40.67 with clathrate-I structure is up-scaled by steel-quenching and spark plasma sintering treatment at 1073 K. A thermoelectric figure of merit ZT approximate to 0.9 at 670 K is reproducibly obtained, and 40 chemically homogeneous module legs of 5 x 5 x 7 mm(3) are fabricated. By using a carbon layer as a diffusion barrier, electrical contacts are sustainable at elevated application temperatures. Eight couples with the clathrate-I compounds Ba7.8Au5.33Ge40.67 as p-type and Ba8Ga16Ge30 as n-type materials are integrated into a TE module with an output power of 0.2 W achieved under a temperature difference Delta T = 380 K (T-1 = 673 K and T-2 = 293 K). The thermoelectric performance of Ba7.8Au5.33Ge40.67 demonstrates the potential of type-I clathrates for waste heat recycling