Search

Coccolithophores are calcifying phytoplankton and major contributors to both the organic and inorganic oceanic carbon pumps. Their export fluxes, species composition, and seasonal patterns were determined in two sediment trap moorings (M4 at 12° N, 49° W and M2 at 14° N, 37° W) collecting settling particles synchronously from October 2012 to November 2013 at 1200 m of water depth in the open equatorial North Atlantic.The two trap locations showed a similar seasonal pattern in total coccolith export fluxes and a predominantly tropical coccolithophore settling assemblage. Species fluxes were dominated throughout the year by lower photic zone (LPZ) taxa (Florisphaera profunda, Gladiolithus flabellatus) but also included upper photic zone (UPZ) taxa (Umbellosphaera spp., Rhabdosphaera spp., Umbilicosphaera spp., Helicosphaera spp.). The LPZ flora was most abundant during fall 2012, whereas the UPZ flora was more important during summer. In spite of these similarities, the western part of the study area produced persistently higher fluxes, averaging 241×107 ± 76×107 coccoliths m−2 d−1 at station M4 compared to only 66×107 ± 31×107 coccoliths m−2 d−1 at station M2. Higher fluxes at M4 were mainly produced by the LPZ species, favoured by the westward deepening of the thermocline and nutricline. Still, most UPZ species also contributed to higher fluxes, reflecting enhanced productivity in the western equatorial North Atlantic. Such was the case of two marked flux peaks of the more opportunistic species Gephyrocapsa muellerae and Emiliania huxleyi in January and April 2013 at M4, indicating a fast response to the nutrient enrichment of the UPZ, probably by wind-forced mixing. Later, increased fluxes of G. oceanica and E. huxleyi in October–November 2013 coincided with the occurrence of Amazon-River-affected surface waters. Since the spring and fall events of 2013 were also accompanied by two dust flux peaks, we propose a scenario in which atmospheric dust also provided fertilizing nutrients to this area. Enhanced surface buoyancy associated with the river plume indicates that the Amazon acted not only as a nutrient source, but also as a surface density retainer for nutrients supplied from the atmosphere. Nevertheless, lower total coccolith fluxes during these events compared to the maxima recorded in November 2012 and July 2013 indicate that transient productivity by opportunistic species was less important than "background" tropical productivity in the equatorial North Atlantic. This study illustrates how two apparently similar sites in the tropical open ocean actually differ greatly in ecological and oceanographic terms. The results presented here provide valuable insights into the processes governing the ecological dynamics and the downward export of coccolithophores in the tropical North Atlantic.

We investigated changes in tropical climate and vegetation cover associated with abrupt climate change during Heinrich Event 1 (HE1, ca. 17.5 ka BP) using two different global climate models: the University of Victoria Earth System-Climate Model (UVic ESCM) and the Community Climate System Model version 3 (CCSM3). Tropical South American and African pollen records suggest that the cooling of the North Atlantic Ocean during HE1 influenced the tropics through a southward shift of the rain belt. In this study, we simulated the HE1 by applying a freshwater perturbation to the North Atlantic Ocean. The resulting slowdown of the Atlantic Meridional Overturning Circulation was followed by a temperature seesaw between the Northern and Southern Hemispheres, as well as a southward shift of the tropical rain belt. The shift and the response pattern of the tropical vegetation around the Atlantic Ocean were more pronounced in the CCSM3 than in the UVic ESCM simulation. For tropical South America, opposite changes in tree and grass cover were modeled around 10° S in the CCSM3 but not in the UVic ESCM. In tropical Africa, the grass cover increased and the tree cover decreased around 15° N in the UVic ESCM and around 10° N in the CCSM3. In the CCSM3 model, the tree and grass cover in tropical Southeast Asia responded to the abrupt climate change during the HE1, which could not be found in the UVic ESCM. The biome distributions derived from both models corroborate findings from pollen records in southwestern and equatorial western Africa as well as northeastern Brazil.

To understand the validity of δ18O proxy records as indicators of past temperature change, a series of experiments was conducted using an atmospheric general circulation model fitted with water isotope tracers (Community Atmosphere Model version 3.0, IsoCAM). A pre-industrial simulation was performed as the control experiment, as well as a simulation with all the boundary conditions set to Last Glacial Maximum (LGM) values. Results from the pre-industrial and LGM simulations were compared to experiments in which the influence of individual boundary conditions (greenhouse gases, ice sheet albedo and topography, sea surface temperature (SST), and orbital parameters) were changed each at a time to assess their individual impact. The experiments were designed in order to analyze the spatial variations of the oxygen isotopic composition of precipitation (δ18Oprecip) in response to individual climate factors. The change in topography (due to the change in land ice cover) played a significant role in reducing the surface temperature and δ18Oprecip over North America. Exposed shelf areas and the ice sheet albedo reduced the Northern Hemisphere surface temperature and δ18Oprecip further. A global mean cooling of 4.1 °C was simulated with combined LGM boundary conditions compared to the control simulation, which was in agreement with previous experiments using the fully coupled Community Climate System Model (CCSM3). Large reductions in δ18Oprecip over the LGM ice sheets were strongly linked to the temperature decrease over them. The SST and ice sheet topography changes were responsible for most of the changes in the climate and hence the δ18Oprecip distribution among the simulations.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1019-1021, In this work a highly productive deposition process for microcrystalline silicon thin-film solar cells is described. Therefore an outstanding high plasma excitation frequency of 140 MHz was used. A high efficiency of 9.6 % was achieved at 1.0 nm/s absorber layer deposition rate (8.6 % at 2.5 nm/s). In a first step the cell fabrication took place at a small scale electrode but later on the results can be transferred to a dynamic deposition system using linear VHF plasma sources. The concept of linear VHF plasma sources is also supported by plasma simulations using COMSOL multiphysics. This work summarizes the results achieved by TU-Dresden in work package 4 of the European project FAST TRACK.

29th European Photovoltaic Solar Energy Conference and Exhibition; 1917-1920, Microcrystalline silicon thin-film solar cells were deposited by VHF-PECVD at 140 MHz with absorber layer deposition rates up to 2.5 nm/s. High deposition rates are one possibility to reduce costs in the manufacturing process of thin-film photovoltaics. Here we achieve high deposition rates by a combination of very high plasma excitation frequencies (140 MHz) and high power high pressure deposition. The homogeneity of the deposition is ensured by the linear plasma source concept combined with a dynamic deposition process (moving substrates). High efficiencies of 9.3 % (9.6 % with AR coating) have been achieved at a deposition rate of 0.8 nm/s. At higher deposition rates (2.5 nm/s) the efficiency drops to 8.3 % (8.6 % with AR coating) although the absorber layer defect density is equal to the low rate material as was measured by PDS/FTPS. On the other hand the high rate material exhibits a pronounced crack formation in the absorber layer as was observed in SEM cross section images. This study investigates in how far the effect of cracks can be mitigated by different approaches, e.g. using μc-SiOx doped layers.

28th European Photovoltaic Solar Energy Conference and Exhibition; 2573-2579, The cost reduction of silicon based thin-film solar cells is of major importance in terms of the competitiveness of the technology. One major cost factor is the absorber layer deposition of the microcrystalline silicon (μc-Si:H) bottom cell of tandem devices. In this work results of the ultra fast μc-Si:H absorber layer deposition are described. To achieve the high deposition rates a plasma regime which combines high pressures and high power levels at an electrode distance of 10 mm and at a plasma excitation frequency of 140 MHz is used. At the beginning a μc-Si:H p-i-n reference process at moderate i-layer deposition rates (0.8 nm/s) was developed. After several optimization steps an efficiency of 8.3 % could be achieved (0.8 nm/s). In the next step the deposition rate of the absorber was increased up to 5 nm/s. Promising i-layer material with rates up to about 2.1 nm/s was incorporated into complete μc-Si:H p-i-n solar cells. A slight decrease of the solar cell parameters , FF, Uoc and Jsc was observed with increasing absorber deposition rate. Finally, an initial efficiency of 6.9 % could be achieved at an absorber layer deposition rate of 2.1 nm/s.

The diffusion barrier properties of PVD Ru and PECVD / PEALD Ru-C films, deposited by RuEtcp2 precursor and N2/H2 plasma, were compared on the basis of bias temperature stress measurements. An MIS test structure was used to distinguish between thermal diffusion induced by annealing and a Cu field drift due to applied electric fields. BTS-CV, TZDB and TDDB measurements revealed that the barrier performance is significantly better for PEALD and PECVD Ru-C films. This improvement is associated with carbon impurities in the Ru films with a concentration in the order of several percent according to ToF-SIMS and ERDA. The TDDB mean time to failure at 250 °C, +5 MV/cm was 7 s for PVD Ru samples, ~500 s for PECVD Ru-C, ~800 s for PEALD Ru-C and >3600 s for PVD TaN. Triangular voltage sweep measurements at 300 °C, 0.1 V/s confirmed the presence of Cu ions inside the SiO2 for degraded dots, in contrast to the Al reference sample and to PVD TaN, which performed best among all the Cu barriers under test. XRD data suggests that PEALD and PECVD Ru-C films are only weakly crystalline.

International audience; Assessing the response of interannual climate variability in the tropical Pacific Ocean to future greenhouse warming is of paramount importance. However, the dominant mode of Pacific atmosphere-ocean variability on interannual timescales, the El Niño-Southern Oscillation (ENSO), is poorly understood with respect to its behaviour under boundary conditions different from today. For last glacial conditions, model simulations and rare proxy records of interannual climate variability in the Pacific are contradictory. Here we present a monthly resolved reconstruction of tropical South Pacific climate from 15,000 years ago at the end of the last glacial. This period was characterised by substantial cooling in the North Atlantic Ocean and a reduction in the strength of the Atlantic Meridional Overturning Circulation (AMOC) in response to massive iceberg discharge associated with Heinrich stadial 1 (H1). Our Sr/Ca palaeotemperature record constructed from a fossil coral recovered by Integrated Ocean Drilling Program (IODP) Expedition 310 to Tahiti indicates pronounced interannual ENSO variability, even though the site is only weakly influenced by ENSO today. From our coral record and simulations with a comprehensive climate model (CCSM3) we conclude that interannual ENSO variability in the tropical Pacific was strong during H1. Our results suggest that enhanced interannual variability in tropical Pacific temperatures is the ENSO response to a reduced AMOC under glacial boundary conditions.

Das PC-River-Projekt stellt interessierten Anwendern Software zur probabilistischen Bemessung von Hochwasserschutzbauwerken zur Verfügung. Das niederländische Programm PC-Ring, entworfen für das Rheindelta, wurde auf die Verhältnisse im Tiefland und in den Mittelgebirgen angepasst und eine Anbindung an hydraulische Modelle erstellt. Als Ergebnis erhält der Anwender Versagenswahrscheinlichkeiten für einzelne Schutzbauwerke und gesamte Projektgebiete. Somit wird die Grundlage für risikobasierte Hochwasserschutzpläne bereitet und endlich eine echte Vergleichsmöglichkeit für die Zuverlässigkeit unterschiedlicher Bauwerkstypen und Varianten geschaffen. Anhand einer Fallstudie werden Arbeitsablauf und Erfolg diskutiert.

Objectives: The noradrenaline-selective antidepressant reboxetine in vitro is a weak inhibitor of both cytochrome P450 (CYP) 2D6 and CYP3A4. Thus, in this study the pharmacokinetics of reboxetine in relation to pharmacogenetics and the effects of reboxetine compared to paroxetine treatment on the CYP2D6 and CYP3A4 phenotype were analyzed in healthy control subjects. Methods: Healthy male volunteers were treated with either 6 mg reboxetine (n = 26) or 30 mg paroxetine (n = 25). On Days 10/11 of treatment, serum concentrations of the antidepressants were measured and pharmacokinetic parameters calculated. Volunteers were phenotyped at the end of treatment and after at least 3 weeks washout (true phenotype) using 30 mg dextromethorphan (DM) hydrobromide given orally and measuring DM and metabolites in serum 2 h after intake. CYP2D6 and CYP2C19 genotypes were determined in parallel. Results and conclusion: Reboxetine serum concentrations showed no correlation with the CYP2D6 genotype and the CYP2D6 phenotype, whereas paroxetine concentrations showed some dependence on CYP2D6. In contrast to in vitro investigations, indicating a major role of CYP3A4 in reboxetine metabolism, reboxetine concentrations in serum showed no correlation with the respective DM metabolic ratios. There was also no correlation between paroxetine concentrations and the CYP3A4 phenotype data. The CYP2C19 genotype (only heterozygosity) had no influence on reboxetine and paroxetine pharmacokinetics. There were only minor changes in the DM metabolite pattern on treatment with reboxetine and no evidence of enzyme inhibition was obtained. In contrast and as expected, paroxetine strongly inhibited CYP2D6. Thus, reboxetine treatment has no effect on the CYP2D6 genotype and no clinically relevant drug interactions involving CYP2D6 are anticipated.